DE10157886A1 - Fuel injection unit for especially diesel engine has control valve to increase and reduce pressure in control chamber, whereby jet needle is opened if pressure in control chamber drops - Google Patents

Abstract

The unit has a control valve (5) to increase and reduce the pressure in the control chamber (4), whereby the jet needle (12) is opened if the pressure in the control chamber drops. The fuel injection unit additionally has a control section in order to control the lift position of the jet needle at a predetermined position which is lower than a full stroke position during a period of fuel injection while the pressure in the control chamber is held at a high value which is higher than the full stroke pressure of the jet needle if the control valve is controlled so that it opens and closes.

Description

The present invention relates to a Fuel injection unit of an internal combustion engine such as for example a diesel engine. More specifically, refers the present invention to a Fuel injector where the stroke of the nozzle needle can be variably controlled. In addition, the present invention to a fuel injection unit, the Injection rate can be changed.

To like fuel under high pressure in an engine for example, to inject a diesel engine conventionally a common fuel injection unit Rail art applied. With this fuel injection unit the fuel from one common rail to one Fuel injector supplied by each cylinder and it becomes a solenoid drive type fuel injection valve largely used as this fuel injector. In the past was a fuel injector Piezoelectric drive proposed in which a piezoelectric actuator is used, which in Consistency with an applied voltage expands and contracts. In this fuel injector piezoelectric drive type will shift the piezoelectric actuator directly or hydraulically transferred to a nozzle needle. Therefore this is Piezoelectric drive type fuel injector advantageous in terms of its high Kraftstoffeinspritzansprecheigenschaften.

In these conventional fuel injection units, the Amount of fuel injected through the valve opening time the nozzle needle controlled. However, it is a predetermined one  Period of time for opening and closing the valve Nozzle needle required. Therefore the nozzle needle behaves unstable when the amount of fuel injected is low is, that is when the period of fuel injection is small. As a result, it is difficult to Control fuel injection quantity reliably. To the To solve the problems set out above, the inventors of present invention studies relating to a method performed by which the stroke of the nozzle needle is variable is controlled with a small amount of fuel a high controllability can be injected. What the Fuel injection unit relates to a variable Control by the stroke of the nozzle needle Piezoelectric drive type fuel injector is an example in U.S. Patent No. 5,803,370 disclosed. According to this patent, if one on one piezoelectric actuator applied voltage controlled is the stroke of the one with the piezoelectric Drive member one-piece rod driven nozzle needle like this changed that the nozzle needle at an intermediate position (half Stroke position) between a contact position of the nozzle needle the valve seat and a full lift position can be held.

However, according to that in U.S. Patent No. 5,803,370 disclosed the fuel injection unit described above the rod attached to the piezoelectric actuator is formed in one piece, directly the nozzle needle on. Therefore, it is required that the piezoelectric Actuator according to the displacement of the nozzle needle is shifted and that also the piezoelectric Actuator a force corresponding to the displacement of the Nozzle needle generated. For the reasons set out above the size of the piezoelectric actuator is forced with that for driving the piezoelectric actuator required intensity of energy too. Furthermore, it is for stopping the nozzle needle at a predetermined one  Half stroke position required to provide a damper element. More specifically, a damper piston is slidable around the rod arranged around to drive the nozzle needle, and one Damper chamber is located at the upper position. Of another is connected to the damper chamber Fuel chamber at a lower position of the damper piston arranged to prevent the rod and the nozzle needle while contracting the piezoelectric Actuator are hindered. Like this above is that described in U.S. Patent No. 5,803,370 disclosed structure of the fuel injection unit complicated.

On the other hand, a fuel injection unit is created been in which a back pressure of a nozzle needle through a Hydraulic control valve is controlled by a piezoelectric actuator is driven. At this Fuel injection unit is the hydraulic control valve built up that it's between a control chamber for application a back pressure on the nozzle needle and a drain channel can open and close. If the pressure in the control chamber is in Agreement with the opening and closing process of the Drain channel increases and decreases, the nozzle needle is raised and lowered. With this fuel injection unit, it is sufficient that the piezoelectric actuator one to Driving the hydraulic control valve required displacement generated. It is therefore possible to size this Reduce fuel injection unit. However so far no investigations regarding the half stroke control Have been carried out.

It is an object of the present invention To create fuel injection unit at which the back pressure the nozzle needle is controlled by a hydraulic control valve, characterized by the following: a Half stroke control of the nozzle needle can be carried out; the  The size of the fuel injection unit is small and the The controllability of the fuel injection unit is high.

The fuel injection unit of an internal combustion engine is included an injector to deliver a fuel to the Form a mixture to inject into each cylinder. The Injector can be between the injection of Fuel where fuel is injected from a nozzle hole and stopping the fuel by the action of a Switch the needle that is moved in a straight line freely. On Drive state of the needle is driven between the first one State in which the needle is pushed in one direction is that the displacement of the needle is 0, and the second Drive state selected in which the drive direction is opposite to that of the first drive state and the needle is pushed in a direction such that the Maximum displacement of the needle. If the drive state of the Needle is switched in this way, the injection of fuel can be changed between start and stop.

A typical setup for switching the drive state of the Needle is described below.

A pushing force in the valve opening direction is always on the Needle exerted by the pressurized fuel. At the same time, there is one on the rear end face side of the needle Back pressure chamber for generating a back pressure in the Provided fuel through which the needle in the Valve closing direction is pressed so that a back pressure between a high state and a low state can be changed. Is the back pressure by the pressure of the Fuel increases from the high pressure source in the Back pressure chamber is introduced, and the needle is in the Pressed towards the seat in which a shift of the Needle becomes 0. In the second drive state, the Back pressure decreases when the fuel is in the  Back pressure chamber is delivered to a low pressure source, and the needle is pushed in the stroke direction in which the Maximum displacement of the needle.

Injecting and dispensing fuel Fuel from the back pressure chamber can be drawn through a 2-way valve or a 3-way valve can be changed between the Back pressure chamber and the low pressure source is arranged. The Opening and closing movement is carried out by one on the Injector mounted actuator executed.

In this context, there have been renewed ones in the past Attempts have been made to purify the exhaust gas or the Increase performance of an internal combustion engine by the Injection rate or atomization state in accordance is changed with the drive state of the internal combustion engine, for example by the injection rate or the Atomization state between a low speed range and a high speed range is changed or alternatively by the injection rate or atomization state between one Light load area and a heavy load area is changed, so that the best combustion state can be realized, that is suitable for the drive state. For the establishment of the Change the injection rate or the atomization state applied the following procedures. The cross-sectional area of a Flow channel for determining the flow rate of the Injection is essentially through the opening area of the Nozzle hole determined. However, at an initial state, at which has an end portion of the needle lifting from one Reference state begins at which an end portion of the needle is on seated to determine the cross-sectional area of the channel the flow rate of the injection through the space determined between the end portion of the needle and the seat is trained. This cross-sectional area of the channel will increases as the stroke increases. However, after the hub becomes a has reached a predetermined value, this cross-sectional area of the  Channel determined by the opening area of the nozzle hole. Therefore the needle is in an intermediate state (half stroke) in which the needle does not reach the total stroke, controlled so that the Fuel injection in accordance with the opening area that is determined by the space that formed between the end portion of the needle and the seat is.

As a specific facility for realizing one State of a half stroke, it is possible, for example Facility to be considered by a back pressure of the Needle is changed between two steps by the Flow rate of the discharged from the back pressure chamber Fuel is set. However, this facility does a disadvantage in that the structure compared to a simple injector structure becomes complicated, where the drive state of the needle is simply between two Values is changed.

The present invention is in view of the above outlined circumstances and their job is to to create a fuel injection unit that will change the fuel injection rate by means of a simple construction in able.

A fuel injection unit of the first embodiment of the present invention comprises: a Control chamber for exerting pressure in a Valve closing direction on a nozzle needle for opening and Closing a nozzle hole; and an increase control valve and reducing the pressure in the control chamber if that Control valve is opened and closed, the nozzle needle is opened when the pressure in the control chamber decreases.

The fuel injection unit also has one Control section on to a stroke position of the nozzle needle  a predetermined position lower than one Total stroke position is in a period of Control fuel injection while the pressure in the Tax chamber is held at a value higher than that Pressure of the total stroke of the nozzle needle is when the control valve is controlled so that it opens and closes.

In the fuel injection unit with the above set-up, in which the pressure of the control chamber to Exerting a counter pressure on the nozzle needle through the Control valve is controlled, for example, when the control valve is opened and closed repeatedly, possible to set the pressure in the control chamber in a predetermined Keep area. Accordingly, it is possible to add the nozzle needle to control any position before the total stroke position, and it is possible, for example, the nozzle needle at a Half stroke position to control by the pressure in the control chamber is controlled. Consequently, it is possible to control the Improve fuel injector without reducing the size of the Increase unit and even without building complicated shape. Therefore, it is possible to use a fuel injection unit to realize, their size is small and their controllability is high.

More specifically, according to the second embodiment, FIG present invention the control valve opens when power is delivered to him so that the tax chamber with a Drain channel is connected, and the control section controls the pressure in the control chamber when the control section is a Opening and closing movement of the control valve repeated. More specifically, the control valve is in a normal state closed so that the control chamber at a high pressure is held. When the control valve through the control section is opened, the pressure in the control chamber is reduced. If the opening and closing movement is repeated, the Pressure in the control chamber increases and decreases so that the  Nozzle needle can be controlled and at a desired Stroke position can be maintained.

In the third embodiment of the following invention the control section supplies power to the control valve so that the control valve repeats at a predetermined period for can be opened for a predetermined time. If to this Timing the control valve a constant valve opening and Repeated valve closing movement, the pressure in the Control unit repeatedly increased and in a constant range reduced. It is therefore possible to control the nozzle needle in such a way that a stroke position of the nozzle needle in a constant range can be held.

In the fourth embodiment of the present invention the control section repeatedly performs an opening and Closing movement of the control valve such that a Valve opening time longer the first time than after the first Can be. In the case where the nozzle needle is raised high force is required when the nozzle needle of the nozzle seat is first raised. Hence the Valve opening movement of the control valve the first time extended, so the pressure in the control chamber is extraordinary to reduce.

In the fifth embodiment of the present invention a fuel injector further includes one Stroke detection device to a stroke of a nozzle needle directly or indirectly. The control section opens and closes the control valve in accordance with Detection signal sent by the stroke detector becomes. For example, if a stroke of the nozzle needle exceeds the predetermined value, the control valve closed and the pressure in the control chamber is increased. in the Conversely, if a stroke of the nozzle needle is less than is a predetermined value, the control valve is opened so that  the pressure in the control chamber decreases. Like this above it is possible to use the nozzle needle in one predetermined stroke range with a high controllability hold.

In the sixth embodiment of the present invention the control section executes a half stroke control in which the Nozzle needle controlled at a predetermined half stroke position when a target fuel injection amount or a Target fuel injection period less than a predetermined one Is worth. If a stroke is on a smaller stroke than in the case of an overall stroke is reduced, it is possible to To reduce the opening area around the nozzle needle so that the injection rate (the injection quantity per unit of time) can be reduced. Since it is possible to open and Closing the nozzle needle to reduce the time required the half stroke control of the present invention is effective if the fuel injection amount is small or Fuel injection period is short. Therefore, the Fuel injection quantity can be controlled extremely precisely.

In the seventh embodiment of the present invention the control section performs a half stroke control to control the Nozzle needle at a predetermined half stroke position when a fuel injection period of an internal combustion engine itself extraordinarily from a compression top dead center different. As for a different time than the one above Injection carried out dead center of compression, at that the pressure in a cylinder is not sufficiently high, so it is necessary to reduce the injection rate so that a deterioration in the lubricity of the cylinder wall is prevented when fuel adheres to the cylinder wall. As in the case where a pilot injection (Pre-injection) before performing a main injection is executed, it is required Run fuel injection at a slight  Amount of fuel is injected. In this case it is Half stroke control of the present invention feasible and the Controllability of fuel injection can be extraordinary be improved.

In the eighth embodiment of the present invention the total opening area of the nozzle hole changes to Agreement with the stroke position of the nozzle needle. If for example, a plurality of injection holes is provided and the number of injection holes to open between one Case where the nozzle needle is set at an overall stroke position is, and a case in which the nozzle needle at a Half stroke position is set, the amount can be changed injected fuel can be adjusted with ease by changing the stroke position. Therefore, the Controllability of the fuel injector be further improved.

In the ninth embodiment of the present invention the control valve is replaced by a piezoelectric Actuator driven and the control section controls the Nozzle needle at a predetermined half stroke position repeatedly applying a predetermined high voltage and a lower voltage on the piezoelectric Actuator. Preferably a piezoelectric Actuator applied, the response property is high is because the control valve opens with a high controllability and can be closed. If at this time the Control section alternately a predetermined high voltage is required to open the control valve, and a applies lower voltage to close the control valve or for essentially closing the control valve is required, the control valve is repeatedly opened and closed so that a half-stroke control can be carried out can.  

In the tenth embodiment of the present invention the control section controls the nozzle needle at one predetermined half stroke position by repeated opening and The control valve closes and the control valve becomes such controlled that it was not exactly on the valve seat at the Valve closing time sits. In the case where the control valve, which is in the open state, is closed even if the control valve is not fully on the Valve seat sits slightly from the valve seat is raised, a pressure change in the control chamber in the Essentially the same as in the case where the Control valve is fully seated on the valve seat. If the further the control valve slightly from the valve seat is raised to slightly raise the Control valve required energy much less than that for completely placing the control valve on the valve seat is required. Therefore, it is possible to meet the need for energy greatly reduce that to close the Control valve is required without the injection power too change.

In the eleventh embodiment of the present invention, there is provided a fuel injector in which starting and stopping fuel injection can be freely changed by a linearly moving needle that is constructed such that the larger the shift from a reference state of stopping the fuel injection , the more the cross-sectional area of a flow channel for determining the flow rate of the injection is expanded, the fuel injection unit having the following:
an injector having a drive means capable of changing between the first drive state in which the needle is pushed in a direction such that the displacement of the needle is zero and the second drive state in which the needle is in a close the driving direction is pushed in the reverse driving direction in the first driving state, and the needle is pushed in such a direction that the displacement of the needle is maximum; and
a control device for changing a drive state of the needle by controlling the drive device,
wherein the controller can be switched between a high injection rate mode in which the drive state is set to the second drive state and the needle remains at the maximum displacement and a low injection rate mode in which the first and second drive states are repeated in such a manner that the drive state can return to the first drive state after the drive state is set to the second the second drive state and before the stroke of the needle reaches a stroke at which the cross-sectional area of the flow channel becomes maximum.

In the low injection rate mode, the Drive state back to the first drive state before the Cross-sectional area of the flow channel becomes maximum. thats why it only if the drive state of the needle is between two Values is switched, possible, optionally an injection at a lower injection rate than the maximum injection rate execute by the maximum area (e.g. the Opening area of the nozzle hole) is determined, which is the maximum Value of the cross-sectional area of the flow channel. This is it is possible to realize a switchover of the injection rate, without complicating the structure of the injection device.

In the twelfth embodiment of the present invention is a fuel injector according to the eleventh Embodiment of the present invention provided, wherein the injector is a nozzle of a first type which is opened when the needle makes a first shift passes, and has a nozzle of a second kind that opens  if the needle exceeds a second displacement, the is greater than the first shift.

If the needle exceeds the first shift, the Nozzle of the first kind opened. After that, when the needle is the second displacement exceeds the nozzle of the second type opened in addition to the nozzle of the first kind. Accordingly in the low injection rate mode, the fuel from that Injected nozzle hole of the first type and in the mode of high injection rate, the fuel is injected from the nozzle hole first type and the second type injected. Because in this case even if the needle stroke position is slightly fluctuates, the injection rate through the opening area of the Nozzle hole is limited, a desired injection rate with ease with every mode of the Fuel injection rate can be realized.

In the thirteenth embodiment of the present Invention is a fuel injection unit according to the twelfth Embodiment of the present invention provided, wherein the injector has two types of holes that are in one Nozzle body are formed in which a needle is slidable is held and pilot hole for supplying fuel is formed with one end of each hole forming a surface the nozzle body is open and the other end of each hole communicates with the pilot hole, with each hole passing through the needle can be closed, taking the two types Holes at an interval in one direction Needle displacement are formed, the hole being opened when a needle shift is the first shift exceeds, is the first nozzle hole, and the hole that is opened when the needle moves the second Displacement exceeds, the second nozzle hole is.

In this way, two types of nozzles can be easily done be formed.  

In the fourteenth embodiment of the present Invention is a fuel injection unit according to the eleventh to thirteenth embodiment of the present invention created, the time of changing from the first Drive state in the second drive state in the mode a low injection rate is used at a point in time, before the stroke of the needle reaches a displacement at which the Cross-sectional area of the flow channel becomes zero.

When the movement of the needle is in a half-stroke condition is stopped, it is possible to use a fuel injection unit to realize that to run a continuous Fuel injection in the same way as the unit with the low injection rate.

The present invention is set forth in the following Description of the preferred embodiments together with the accompanying drawings easier to understand.

Fig. 1 is a cross-sectional view showing the overall structure of a fuel injector according to the present invention.

Fig. 2 shows a fragmentary cross-sectional view of a fuel injection unit from another example of the profile of a nozzle hole.

Fig. 3 is a timing chart for explaining the operation shown by the fuel injection unit according to the present invention.

Fig. 4 is a graph showing a relationship between a generated force and the displacement in the opening-closing control of a three-way valve.

Figure 5 shows a fragmentary cross-sectional side view of an injector that is part of the fuel injector of the present invention.

FIG. 6 shows an enlarged view of a main portion of FIG. 5.

Fig. 7 is a view showing a structure of a fuel injection unit.

Fig. 8 is a timing chart showing the operation of the fuel injection unit.

An embodiment to which the present invention is applied will be explained with reference to the accompanying drawings. Fig. 1 shows an overall structure of a fuel injection valve which has a main portion of a fuel injection unit of the present invention. For example, this fuel injection valve is preferably used in an injection system of the common rail type of a diesel engine. A piezoelectric drive portion 1 is provided in the upper end portion of the fuel injection valve. An injector portion 10 is provided at the lower end portion of the fuel injection valve. Provided between the piezoelectric drive section 1 and the injector section 10 are a three-way valve 5 , which is a control valve driven by the piezoelectric drive section 1 , and a control chamber 4 , the pressure of which is increased and decreased when the three-way valve 5 is driven. The nozzle needle 12 provided on the injector section 10 is moved up and down so that the nozzle hole 11 is opened and closed at one end of the nozzle body B1 so that the fuel injection is started or stopped. When the nozzle needle 12 is at the upper end position, the nozzle hole 11 is fully opened and the fuel is supplied to the nozzle hole 11 from the fuel reserve space 31 , which is connected to the high pressure passage 3 through a space formed around the nozzle needle 12 , On the other hand, when the nozzle needle 12 is at a lower end position, the nozzle hole 11 is completely closed, so that a connection of the nozzle hole 11 to the fuel reserve space 31 is closed and the fuel supply is stopped. The lower end position of the nozzle needle 12 is determined by the nozzle seat 13 on which the nozzle needle 12 is seated, and the upper end position is determined by the orifice plate P1, which is arranged on an upper section of the nozzle body B1.

For the injector section 10 , as shown in FIG. 1, the general type injector is used, and further the variable injector type injector section 10 shown in FIG. 2 may be used. In the injection nozzle section 10 shown in FIG. 2, a plurality of nozzle holes 11 a, 11 b are provided, which are arranged parallel to one another at an end section of the nozzle body B1, the height of the nozzle holes 11 a and that of the nozzle holes 11 b in the axial direction is different from each other. The nozzle needle 12 is hollow and the cavity within the nozzle needle 12 is formed into a high-pressure channel 34 which is in communication with the fuel reserve space 31 . Therefore, when the nozzle needle 12 is raised, fuel is supplied to the nozzle holes 11 a and 11 b via the high pressure passage 34 . Due to the above construction, the number of the nozzle holes to be opened, that is, the total opening area of the nozzle holes to be opened can be changed in accordance with the stroke position of the nozzle needle 12 . Therefore, the half-stroke control which is characteristic of the present invention can be carried out effectively. This half-stroke control is explained in detail below.

The nozzle body B1 is arranged at a lower end of the housing H of the piezoelectric drive section 1 via the diaphragm plates P1 and P2 and is fixed oil-tight on the cylindrical nozzle holder B2. The high-pressure duct 3 extends upward from the fuel reserve space 31 and is connected to an external common rail (not shown) via the diaphragm plates P1 and P2 and the interior of the housing H. A drain channel 2 for returning the fuel is provided in the housing H, the drain channel 2 being connected to an external fuel tank (not shown). The control chamber 4 is formed between the upper end portion of the nozzle needle 12 and the orifice plate P1. The nozzle needle 12 is always pressed in the closing direction (downward) by a spring force of the spring 41 , which is arranged in the control chamber 4 , and also by the hydraulic pressure in the control chamber 4 .

The hydraulic pressure in the control chamber 4 is controlled by the three-way valve 5 , which acts as a control valve. The three-way valve 5 consists of a substantially conical valve chamber 51 , which is formed at a lower end of the housing H, and a substantially spherical valve body 52 . The valve chamber 51 is always connected to the control chamber 4 via a channel which penetrates the orifice plates P1 and P2 and via the main orifice 42 which is arranged at the lower end of the orifice plates. The valve chamber 51 is provided with two openings, one outlet opening 21 and the other a high-pressure opening 32 . When the valve body 52 is moved up or down in the valve chamber 51 and one of the two openings is closed, the other opening is open and communicates with the control chamber 4 . The drain opening 21 is connected to the drain channel 2 via the overflow chamber 22 , which is arranged on an upper section of the valve chamber 51 . The high pressure opening 32 perpendicularly penetrates the orifice plate P2 and communicates with the high pressure passage 3 through the groove 33 which is provided on a lower end side of the orifice plate P2 in the radial direction.

Due to the structure described above, when the valve chamber 51 communicates with the drain port 21 , the pressure in the control chamber 4 decreases, and the nozzle needle 12 is separated from the nozzle seat 13 and raised. On the other hand, when the valve chamber 51 communicates with the high pressure port 32 , the pressure in the control chamber 4 increases, and the nozzle needle 12 is lowered and placed on the nozzle seat 13 . In this case, the control chamber 4 is always in communication with the high-pressure passage 3 through the sub-orifice 43 which is arranged on the orifice plate P1 which communicates with a lower end of the high-pressure opening 32 without passing through the three-way valve 5 , This sub-aperture 43 acts as follows. When fuel is brought to flow from the high pressure passage 3 into the control chamber 4 via the sub-orifice 43 , a pressure decrease in the control chamber 4 is facilitated when the fuel injection starts, so that the nozzle needle 7 can be opened gradually. When the fuel injection is stopped, the pressure rise is relieved so that the nozzle needle 7 can be closed quickly.

In this connection, an opening portion of the drain opening 21 to the valve chamber 51 forms a drain seat 53 , which is a conical valve seat, and an opening portion of the high pressure opening 32 to the valve chamber 51 forms a flat high pressure seat 54 . One of them is made flat because the axis of the valve body 52 can be deviated. When the valve body 52 is seated on either the seat 53 or 54 , the corresponding opening is closed. However, the pressure in the valve chamber 51 is always higher than the pressure in the drain opening 21 . Therefore, the valve body 52 is usually placed on the drain seat 53 . The force required for placing the valve body 52 on the high-pressure seat 54 is exerted by the piston 18 with the small diameter of the piezoelectric drive section 1 . The piezoelectric drive section 1 is explained in detail below.

The piezoelectric drive section 1 has the following:
A piezoelectric actuator 14 housed in an upper end portion of the housing H; and a piezoelectric piston that comes into contact with a lower end of the piezoelectric actuator 14 such that the piezoelectric piston 15 is slid integrally with the piezoelectric actuator 14 . Displacement of the piezoelectric actuator 14 is transmitted to the small-diameter piston 18 via the large-diameter piston 17 and the displacement expansion chamber 6 . The piezoelectric actuator 14 is assembled in a manner known from the prior art. The piezoelectric actuator 14 is composed of piezoelectric bodies stacked on top of each other, and the piezoelectric actuator field 14 is lengthened by applying an electric charge and contracted by releasing an electric charge. The piezoelectric actuator 14 is lengthened and contracted in accordance with an applied voltage so that the piezoelectric piston 15 is driven. The application of the voltage to the piezoelectric actuator 14 is controlled by an ECU 9 , which is a control device. The piezoelectric piston 15 is slidably disposed in the piezoelectric cylinder H1 and connected to the large diameter piston 17 through the small diameter rod 16 . The large diameter piston 17 and the small diameter piston 18 are slidably disposed in the large diameter cylinder H3 and the small diameter cylinder H4, respectively, which are coaxially formed in the cylinder forming member H2. The rod 16 extends from an upper surface of the large diameter piston 17 and is fixed to a lower surface of the piezoelectric piston 15 by insertion.

The space defined in a lower section of the piezoelectric piston 14 around the rod 16 is a fuel reserve space 7 , which is connected to the drain channel 2 . The spring 71 is accommodated in this space in such a way that the piezoelectric piston 15 is pressed upwards. At the same time, the large diameter piston 17 , which is connected in one piece to the piezoelectric piston 15 , is pressed upwards by the spring 71 . Due to the structure described above, the piezoelectric piston 15 and the large-diameter piston 17 are moved integrally according to the extension and contraction of the piezoelectric actuator 14 up and down. On the outer circumference of the piezoelectric piston 15 , an O-ring 73 is provided, through which the piezoelectric actuator 14 can be prevented from being contaminated with the hydraulic oil located in the reserve space chamber 62 . A channel for connecting the reserve room chamber 7 to the drain channel 2 is formed in such a manner that a through hole is formed in the reserve room chamber 7 in the radial direction from the side wall of the housing H, the through hole being closed by the raw cover 74 .

The cylinder forming member H2 has a smaller diameter portion at an upper portion of the small diameter piston 18 . Therefore, a shoulder 61 is formed on the cylinder forming element H, which limits an upward movement of the piston 18 with the small diameter. The large cylinder and the small cylinder H3 and H4 communicate with each other through this reduced diameter section. Therefore, a displacement expansion chamber 6 is formed by the hydraulic chamber formed between the reduced diameter portion and the small diameter piston 18 and the hydraulic chamber formed between the reduced diameter portion and the large diameter piston 17 is. The displacement expansion chamber 6 hydraulically converts a displacement of the piezoelectric actuator 14 . Therefore, the displacement of the piezoelectric actuator 14 is increased in accordance with a difference between the diameter of the large piston 17 and the diameter of the small piston 18 . For example, the displacement of the piezoelectric actuator 14 is amplified by two or three times the displacement of the piston 17 with the large diameter and transmitted to the piston 18 with the small diameter. A lower end portion of the piston 18 with the small diameter is located in the overflow chamber 22 , which is formed on a lower portion of the cylinder formation member H2. An end portion of the piston 18 with the small diameter comes into contact with the valve body 52 which is inserted into the drain port 21 .

In the piston 17 having the large diameter, a channel 72 is provided which is formed in the axial direction of the piston 17 with the large diameter. An upper end of the channel 72 extends to the base end portion of the rod 16 and branches into a T-shape and is open to the reserve room chamber 7 . A lower end of the passage 72 is open to the lower end side of the large-diameter piston 17 and communicates with the displacement expansion chamber 6 through the check valve 8 attached to the lower end of the large-diameter piston 17 . The check valve 8 is provided so that the fuel is supplied from the reserve space chamber 7 into the displacement expansion chamber 6 when the fuel in the displacement expansion chamber 6 decreases due to a leak. The check valve 8 consists of a flat valve 81 for closing the lower end opening of the channel 72 and a disc spring 82 for pushing the flat valve 81 upwards. The flat valve 81 consists of a disc-shaped sheet, the thickness of which is 0.1 to 0.2 mm. At the center of the flat valve 81 , a needle hole 84 is formed, the diameter of which is 0.002 to 0.5 mm.

The profile of the disc spring 82 is a very thin ring, the thickness of which is 0.01 to 0.05 mm. Therefore, the intensity of the pressing force of the disk spring 82 is low, that is, the pressing force of the disk spring 82 is set at 0.5 to 2 N. The profile of the holder 83 for accommodating and holding the flat valve 81 and the disc spring 82 is a cylinder with a bottom, and the holder 83 is fixed to an outer periphery of the lower end portion of the piston 17 with the large diameter. When the pressure in the displacement expansion chamber 6 decreases due to fuel leakage, the flat valve 81 is lowered while the valve 81 resists the pressing force of the disc spring so that the fuel flows into the displacement expansion chamber 6 from the passage 72 . The holder 83 has a through hole 85 , the area of which is substantially larger than that of the pin hole 84 , and the fuel can freely circulate between the space in the holder 83 and the displacement expansion chamber 6 . Therefore, the fuel can be quickly supplied into the displacement expansion chamber 6 .

The pinhole 84 of the flat valve 81 allows the fuel to return from the displacement expansion chamber to the reserve chamber. For example, even if an electric charge cannot be released from the piezoelectric actuator 14 due to an abnormality in the fuel injection process, it is possible for the fuel to return through the pinhole 84 . Therefore, the fuel injection is stopped when the pressure in the displacement expansion chamber 6 decreases. Furthermore, the pinhole 84 has the advantages discussed below. When the fuel is supplied into the displacement expansion chamber 6 after the fuel injection unit is assembled, the suction by the negative pressure for supplying the fuel is made easy. Therefore, the fuel can be delivered quickly and no problems arise because there is no air left in the unit. In the case where the engine has been stopped for a long period of time, there is a possibility that the small diameter piston 18 sinks due to its own weight and the fuel is supplied to the displacement expansion chamber 6 again through the check valve 8 . However, it is possible that the fuel is discharged from the needle hole 84 into the drain passage 2 . Therefore, the small diameter piston 18 and the valve body 52 are ready for upward movement so that the fuel injection unit is ready to start the engine. The size of the pinhole 84 is determined so that the above-described operations can be performed without the fuel properties of the fuel injection unit being affected by the size of the pinhole 84 .

A method for controlling the fuel injection valve described above by the ECU 9 will be explained with reference to the flowchart shown in FIG. 3. The dotted lines in FIG. 3 show the behavior of the sections in the case of a normal control in which the nozzle needle 12 is fully raised. With the overall stroke control, the process is carried out as follows. First, when the fuel injection is started (time t1), a predetermined high voltage (for example, 100 volts) is applied to the piezoelectric actuator 14 in accordance with an injection signal sent from the ECU 9 . The piezoelectric actuator 14 produces a displacement that is proportional to the applied voltage (a). Therefore, the piezoelectric piston 15 and the large diameter piston 17 are moved down by the same displacement, so that the hydraulic pressure in the displacement expansion chamber 6 increases.

As the hydraulic pressure in the displacement expansion chamber 6 increases , the small diameter piston 18 is lowered and the valve body 52 is pressed down by the drain sheet 53 . The stroke (b) of the valve body 52 is increased along with the increase in the applied voltage (a). In this case, a movement to that under section in Fig. 1 is defined as positive. The valve body 52 is then placed on the high pressure seat 54 . At this time, the stroke (b) of the valve body 52 with respect to the displacement of the piezoelectric actuator 14 is increased by the ratio of the area (for example, twice) of the large diameter piston 17 to the small diameter piston 18 .

According to the stroke (b) of the valve body 52 , the valve chamber 51 and the drain port 21 communicate with each other, and then the connection with the high pressure port 32 is released . Therefore, the pressure in the valve chamber 51 decreases and the hydraulic pressure (c) of the control chamber 4 , which communicates with the valve chamber 51 , decreases. When the hydraulic pressure (c) in the control chamber 4 has decreased and the hydraulic pressure in the fuel reserve space 31 , which acts on the nozzle needle 12 so that it can be moved upward, the hydraulic force of the control chamber 4 and the spring force of the spring 41 overcomes, the stroke (d) of the nozzle needle 12 is started from the nozzle seat 13 and the fuel injection from the nozzle hole is started (time t2). Even after the time t2 has passed, the hydraulic pressure (c) in the control chamber 4 decreases and the stroke (b) of the nozzle needle 12 is raised to the full stroke position. This state is maintained until a predetermined injection stop timing.

In the case of stopping fuel injection, the applied voltage (a) is reduced to zero by discharging the electric charge of the piezoelectric actuator 14 (time t4). During this time, the piezoelectric actuator 14 contracts by a displacement that occurs at the time the voltage is applied and returns to its original length, and the piezoelectric piston 15 is raised by being pressed by the spring 71 . The large diameter piston 17 connected to the piezoelectric piston 15 through the rod 16 is raised together with the piezoelectric piston 15 , so that the hydraulic pressure in the displacement expansion chamber 6 is reduced. When the hydraulic pressure in the displacement expansion chamber 6 decreases, the force of the small diameter piston 18 , by which the valve body 52 is pressed against the high pressure seat 54, which resists the pressure of the high pressure opening 32 , is derived. Therefore, the piston 18 with the small diameter is raised together with the valve body 52 .

When the valve body 52 is seated on the drain seat 53 again and its stroke position (b) returns to the original state, the valve chamber 51 communicates with the high pressure port 32 and the connection with the drain port 21 is disconnected. Therefore, the hydraulic pressure (c) in the valve chamber 51 and in the control chamber 4 is restored. When the hydraulic pressure (b) in the control chamber 4 is increased and the force acting down on the nozzle needle 12 overcomes the hydraulic force in the fuel reserve space 31 , the nozzle needle is lowered from the full stroke position and placed on the nozzle seat 13 again and the fuel injection will take place stopped (time t6).

In the full-stroke control described above, the ECU 9 controls the voltage application start time and the start time of discharge of the electric charge of the piezoelectric actuator 14 in accordance with a target amount of fuel injection. In general, the fuel injection amount is increased in proportion to the valve opening period (fuel injection time) of the nozzle needle 12 . However, since a predetermined period of time is required for the nozzle needle 12 to be fully raised and also for the nozzle needle 12 to be seated on the nozzle seat 13 from the full lift position, it is necessary that the nozzle needle be small in the case where the target amount of fuel injection is small 12 starts lowering. For the reason set out above, a fluctuation between the fuel injection shots can occur, making it difficult to control the fuel injection amount accurately.

Therefore, the process in the present invention is carried out as follows. The stroke position of the nozzle needle 12 at the time of valve opening is controlled at any position, its stroke being less than the full stroke and, for example, the stroke position of the nozzle needle 12 at the time of valve opening is controlled at a predetermined half stroke position. A solid line in Fig. 3 shows an example (half-stroke control ( 1 )) of a half-stroke control. The fuel injection is started in the same manner as in the full stroke control described above, and a predetermined high voltage, which is the same as a requested voltage at the time of the full stroke, is applied to the piezoelectric actuator 14 by the ECU 9 (time t1). As a result, the piezoelectric actuator 14 generates a displacement corresponding to the applied voltage (a) and drives the valve body 52 via the piezoelectric piston 15 , the large-diameter piston 17 , the displacement expansion chamber 6, and the small-diameter piston 18 . When the hydraulic pressure (c) in the control chamber 4 is reduced to a predetermined pressure in accordance with the stroke (b) of the valve body 52 , the stroke (b) of the nozzle needle 12 is started (time t2).

At the time of full stroke control, the applied voltage (a) is kept constant even after time t2 up to time t4. However, in this case, in order to perform the half-stroke control, a high voltage is applied to the piezoelectric actuator 14 in such a manner that a predetermined high positive voltage (e.g. 100 volts) and an electric potential of zero are alternately supplied. More specifically, immediately after the time t2 at which the nozzle needle 12 starts lifting, the electric charge of the piezoelectric actuator 14 is released so that the applied voltage (a) is zero (time t3). Since the applied voltage (a) is kept at a predetermined high voltage at the time of full stroke control, the hydraulic pressure (c) in the control chamber 4 communicating with the drain port 21 is reduced until the nozzle needle 12 is fully raised. However, when the applied voltage (a) becomes zero in the half stroke control, the valve body 12 is put back on the drain seat 53 , and the hydraulic pressure (c) in the control chamber 4 is raised again without failing the minimum pressure (dotted Line) reached at the time of the full stroke. Thereafter, the lifting of the nozzle needle 12 continues for a while. However, the lifting speed is slow and the nozzle needle 12 starts lowering again without reaching the full stroke.

Then, when the application of a predetermined high voltage and the discharge of the electric charge are repeatedly performed, a state in which the stroke (b) of the valve body 52 is set on the valve seat 53 and a state in which the stroke occurs alternately occur (b) the valve body 52 is placed on the high pressure seat 54 . Accordingly, the hydraulic pressure (c) in the control chamber 4 is increased and decreased and the nozzle needle 12 fluctuates in a constant range, which includes the half-stroke position. In this case, the application of the high voltage is performed 4 times ((2) to (5)) repeatedly at constant intervals from the time t2 to the time t4. When the electric potential according to (5) becomes zero, the nozzle needle 12 lowers to a position where the nozzle needle 12 is seated on the nozzle seat 13 , and the fuel injection is completed (time t5). At this time, the nozzle needle 12 lowers from the half-stroke position. Therefore, the fuel injection completion timing t5 occurs earlier than the fuel injection completion timing t6 at the full stroke timing.

In the case of the half-stroke control, as shown in FIG. 2, the time period of applying the high voltage at the first time (1) to the piezoelectric actuator 14 is longer than that at the second time (2) and as that (3) to (5). The reason for this is that when the nozzle needle 12 is raised, it is necessary, due to the output of a pressure balance, to substantially reduce the pressure in the control chamber 4 in the case where the nozzle needle 12 is seated on the nozzle seat 13 than in that Case in which the nozzle needle 12 has already been raised from the nozzle seat 13 . At the time (2) to the time (5), the period of applying a high voltage and the interval can be set each time so that the hydraulic pressure (c) in the control chamber 4 can be changed significantly in a range that corresponds to the lower limit value and the upper limit value of the nozzle needle 12 , which have previously been set.

In order to keep the nozzle needle 12 at a predetermined half-stroke position, it is possible to provide a device that detects the stroke of the nozzle needle 12 directly or indirectly, and according to the result of the detection, the three-way valve 5 can be controlled so that it opens and closes so that the stroke of the nozzle needle 12 can be in a predetermined range. For example, a known gap sensor of the capacitive type or of the eddy current type is arranged near the nozzle needle 12 in such a way that the stroke of the nozzle needle 12 is detected directly. Alternatively, a known pressure sensor for detecting the pressure in the control chamber 4 is arranged such that it indirectly detects the stroke of the nozzle needle 12 by means of the pressure in the control chamber 4 . Then, the applied voltage (a) is controlled so that the stroke position of the nozzle needle 12 can be in a constant range, that is, the applied voltage (a) is controlled so that the stroke of the nozzle needle 12 is not lower than the lower limit or not is higher than the upper limit.

In this way, it is possible to keep the nozzle needle 12 at a predetermined half stroke position with high controllability. In the half-stroke control, the opening area around the nozzle needle 12 is smaller than at the time of the full stroke and the injection rate (fuel injection length per unit time) is lower than in the half-stroke control, and furthermore, the time period required for opening and closing is shorter in the half-stroke control. Therefore, it is possible to stably perform injection of a small amount of fuel. Thus, when a target amount of fuel injection or a target time of fuel injection is less than a predetermined value, it is possible to control the fuel injection amount with high accuracy by executing this half-stroke control. Specifically, when the injection nozzle portion shown in Fig. 2 10, the number can be changed to holes is used, and only the nozzle holes 11 are opened at the under side at the time of Halbhubs a, so that the total opening area of the nozzle holes at the time of Halbhubs less than at the time of the full stroke, the desired fuel injection amount can be easily realized in a safe manner. For example, to reduce the noise generated by a diesel engine, it is advantageous to perform pilot fuel injection in which a small amount of fuel is injected before main fuel injection is performed. However, it is difficult to accurately adjust the small amount of fuel. Furthermore, when the fuel injection time differs greatly from the compression top dead center, fuel injected at a high injection rate adheres to a cylinder wall and the lubricant in the engine is diluted by the fuel thus injected. In this case, half stroke control of the present invention is applicable. If the fuel injection control is carried out stably, the combustion performance of an internal combustion engine can be greatly improved. Furthermore, if the injection ratio is decreased, the fuel can be prevented from adhering to the cylinder wall.

A two-dot chain line in FIG. 3 shows another example of the control of an applied voltage (a) applied to the piezoelectric actuator 14 in the case of half-stroke control (half-stroke control ( 2 )). After a high voltage (for example, 100 volts) is applied the first time (1), the applied voltage (a) is not lowered to an electric potential of zero, and a predetermined low positive voltage is held and then the high voltage is reapplied. This process is repeated. In this case, the predetermined positive voltage is a minimum voltage (e.g., 60 volts) at which the valve body 52 is kept open with respect to the drain hole 21 , that is, the predetermined positive voltage is set to a low value so that the valve body 52 cannot be placed on the drain seat 53 . Because of this, the stroke (b) of the valve body 52 is alternately repeated between a state in which the valve body 52 is seated on the high-pressure seat 54 and a state in which the valve body 52 is not fully seated on the drain seat 53 but is slightly raised. In this connection, an increase phase of the hydraulic pressure in the control chamber 4 is rarely changed because a flow of the high pressure fuel from the high pressure port 32 is dominant in this area even when the valve body 52 is seated on the drain seat 53 , as in 1 , or even when the valve body 52 is slightly raised from the drain seat 53 , as shown in this embodiment.

Accordingly, the stroke (d) of the nozzle needle 12 is substantially the same as in the case of the half-stroke control ( 1 ) described above, and the same half-stroke control can be carried out. The control described above can be realized because when the excited voltage is reduced from the applied voltage (voltage required for full stroke) of the piezoelectric actuator to set the valve body 52 of the three-way valve 5 on the high pressure seat 54 , the valve body 52 can essentially sit on the drain seat 53 (the valve body 52 is not fully seated but is slightly raised) even if the voltage is not reduced to zero.

In Fig. 4, point A shows the displacement and force generated by the piezoelectric actuator 14 and required for the valve body 52 to begin lifting from the drain seat 53 . Since the high pressure in the valve chamber 51 acts on the valve body 52 in the valve closing direction, the strongest possible generation force of the piezoelectric actuator is required at this point A and a voltage of 90 volts is required. Once the valve body 52 is raised from the drain seat 53 , the hydraulic pressure prevailing in the valve chamber 51 acts in the valve opening direction. As a result, the piezoelectric actuator 14 is not required to generate a strong force. At point B, where the valve body 52 is fully raised and placed on the high pressure seat 54 , a voltage of 100 volts is required, which is slightly higher than at point A. When valve body 52 is lowered from point B, the voltage is reduced to 60 volts, and then valve body 53 reaches point C, where valve body 52 is substantially seated on drain seat 53 , and the hydraulic pressure in control chamber 4 becomes raised in substantially the same manner as in the case where the valve body 52 is fully seated.

Accordingly, when movements in which the stroke decreases from point B and the valve body 52 is placed on the drain seat 53 and then fully raised, it is not necessary that the valve body 52 is fully seated on the drain seat 53 but it is sufficient that the valve body 52 is moved between points C and B. That is, if the applied voltage is changed from 100 volts to 60 volts and from 60 volts to 100 volts, it is possible to implement the same half-stroke control. If the control described above is carried out, it is possible to reduce the amount of energy required by 60% compared to the case of 100 volts → 0 volts → 100 volts. Accordingly, it is possible to perform the half stroke control by means of a lower energy level.

In the embodiment described above, this is Three-way valve used as the control valve. However it is possible to assemble the unit in such a way that a two-way valve is used instead of the three-way valve. In which The embodiment described above is Control chamber set up to have an upper end side the nozzle needle is facing. However, a structure is possible at which a piston element moves together with the nozzle needle and a back pressure of the control chamber acts on this element.

FIGS. 5 and 6 show views of the structure of an injection device of a diesel engine is mounted in a fuel injection unit of the common rail type in which the present invention is applied. Fig. 7 is a view showing a structure of the fuel injection unit.

Injectors 1011 , the number of which is the same as the number of cylinders of the diesel engine, are arranged corresponding to the cylinders. In the example shown in the drawing, only one injection device 1011 is shown. Each injector 1011 is supplied with fuel from the common rail 1015 , which is connected to the injector 1011 via the delivery line 1016 . The injector 1011 injects fuel into the combustion chamber of each cylinder at substantially the same injection pressure as the fuel pressure in the common rail 1015 . This pressure is referred to below as the common rail pressure in this description. The fuel is supplied under pressure from the fuel tank 1012 to the common rail 1015 by the high pressure delivery pump 1014 , so that the fuel is stored in the common rail 1015 at a high pressure.

The fuel supplied from the common rail 1015 to the injector 1011 is used not only for injecting into the combustion chamber, but also for the hydraulic pressure for controlling the injector 1011 . The fuel circulates from the injector 1011 to the fuel tank 1012 , which is a low pressure source, via the drain line 1017 .

The ECU 1071 mainly consists of a general microcomputer and calculates the time and the amount of fuel injection in accordance with a detection signal such as a crank angle signal. A control signal corresponding to the calculation is output from the ECU 1071 into an EDU 1072 to drive the piezoelectric actuator 1006 (shown in FIG. 5) mounted on each injector 1011 . As a result, the fuel is injected from the injector 1011 for a predetermined period of time. The EDU 1072 includes a DC-DC converter whose power supply is a battery, not shown, and electrically charges the piezoelectric stack 1061 of the piezoelectric actuator 1006 such that the piezoelectric stack 1061 can be charged with a predetermined amount of electricity. In other words, the piezoelectric stack 1061 can be charged with electricity until it reaches a predetermined charging voltage. According to the control signal, the EDU 1072 alternates between charging and discharging.

The ECU 1071 controls the fuel pressure to be an appropriate fuel injection pressure in accordance with the operating state detected by other sensors. Pressure sensor 1073 is provided in common rail 1015 to control fuel injection pressure. Based on the pressure in the common rail, the ECU 1071 controls the flow control valve 1013 and adjusts the amount of fuel under pressure supplied to the common rail 1015 .

The injector 1011 is a rod-shaped body, and the lower portion of the injector 1011 penetrates a combustion chamber wall (not shown) of an engine and protrudes into the combustion chamber. The housing 1002 of the injector 1011 is composed of the following. A multiplicity of housing elements 1021 , 1022 , 1023 and 1024 which are essentially column-shaped or disk-shaped are stacked in the axial direction and are formed in one piece by the sleeve-shaped holding device 1025 . Spaces are formed within the housing 1002 , in which the fuel channel 1101 is formed and the needle 1031 is accommodated.

A guide hole 1201 is formed in the long and slender housing element 1021 , which is a nozzle body on the lowermost end side of the housing 2 , the upper end of which is closed by the housing element 1022 , which is located directly above the housing element 1021 . The rod-shaped needle 1031 is slidably held in the guide hole 1201 . The needle 1031 can be moved over a range determined by a difference between the length of the needle 1031 and the length of the guide hole 1201 . An elongated hole 1301 is provided in the needle 1031 , which is formed along the axis of the needle 1031 and is open to a lower end side. At an upper end portion of the needle 1031, there is a side hole 1301 that crosses the elongated hole 1301 . Both ends of the side hole 1302 are open to the sides of the needle 1031 . On the outer periphery of the needle 1031 , at the opening position of the side hole 1302, a ring-like fuel reserve space 1103 is provided, which is in communication with the high pressure passage 1101 via the high pressure branch passage 1102 . Pressurized fuel is introduced from common rail 1015 into high pressure duct 1101 . The size of the fuel reserve space 1103 in the vertical direction is determined so that the side hole 1302 and the fuel reserve space 1103 can communicate with each other when the needle 1031 is offset in the above-mentioned range. Accordingly, pressurized fuel is continuously supplied from the common rail 1015 to the elongated hole 1301 of the needle 1031 . The needle 1031 sits on a seat on the bottom side 1201 a of the guide hole 1201 . When the needle 1031 on the bottom side 1201 of the guide hole sits a 1201 the long hole 1301 is closed.

At a lower end portion of the case member 1021 , nozzle holes 1104 and 1105 are provided for fuel injection. The nozzle holes 1104 and 1105 are side holes that cross the guide hole 1201 and are open to the side 1021 a, which is a surface of the housing member 1021 . There are two types of nozzle holes 1104 and 1105 ; one is lower side nozzle hole 1104 and the other is upper side nozzle hole 1105 . The lower side nozzle holes 1104 and the upper side nozzle holes 1105 each form groups. In this connection, the injection directions of the nozzle holes 1104 and 1105 are designed so that they are most optimal with regard to the combustion state of the injected fuel.

As described above, the nozzle holes 1104 and 1105 cross the guide hole 1201 and are open to the side 1201b of the guide hole 1201 . The opening positions of the nozzle holes 1104 and 1105 are determined such that the opening positions and are located higher than the bottom side 1201 a of the guide hole 1201 is lower than the position which is as high as the range in which the needle can be moved 1031st

Accordingly, when the needle 1031 is at the lowermost position, the lower side nozzle holes 1104 referred to as the first type nozzle holes and the upper side nozzle holes 1105 referred to as the second type nozzle holes are made through needle 1031 closed. When the needle 1031 is moved upwards in this closed state, the nozzle holes 1104 of the first type on the lower side are first opened. When the needle 1031 is further pushed up, the nozzle holes 1105 of the second type on the upper side are also opened. The definitions of the first shift and the second shift are set out as follows. When the needle 1031 is at the lowest position, the displacement is zero. The shift at which the nozzle holes 1104 of the first type are opened is defined as the first shift, and the shift at which the nozzle holes 1105 of the second type are opened is defined as the second shift.

The high pressure fuel flowing out of the elongated hole 1301 of the needle is supplied to a bottom portion of the guide hole 1201 that is lower than the needle 1031 . Therefore, when the needle 1031 exceeds the first displacement, fuel is injected from the nozzle holes 1104 of the first type. When the needle 1031 exceeds the second displacement, fuel is injected from the nozzle holes 1105 of the second type in addition to the nozzle holes 1104 of the first type.

Since the fuel under high pressure is constantly supplied from the common rail 1015 to the elongated hole 1301 of the needle 1031 , the needle 1031 is constantly pushed up by the fuel present in the elongated hole 1301 and in the bottom portion of the guide hole 1201 .

In the guide hole 1201 , a coil spring 1051 is provided at an upper position of the needle 1031 so that the needle 1031 is pressed down by the coil spring 1051 . The guide hole 1201 on an upper section of the needle 1031 is designed as a counter pressure chamber 1106 , into which fuel under high pressure is constantly introduced from the high pressure channel 1101 via the inlet orifice 1107 . The pressure of the fuel in the back pressure chamber 1106 acts on an upper end side of the needle 1031 and pushes the needle 1031 down.

The pressure of the fuel in the back pressure chamber 1106 can be freely changed by the drive device 1111 a. If the drive device 1111 a between a state in which a downward force acting on the needle 1031 is greater than an upward pushing force and a state in which a downward pushing force on the needle 1031 is less than one after pushing force directed upward changes, the driving direction of the needle 1031 can be changed.

The drive device 1011 a is explained below. The back pressure chamber 1106 communicates with the valve chamber 1109 via the outlet orifice 1108 and the low pressure opening 1110 communicating with the low pressure chamber 1111 is open to the uppermost portion of a cup-shaped cover side of the valve chamber 1109 . The low-pressure chamber 1111 is connected to the drain line 1017 via a low-pressure channel (not shown) formed in the injector 1011 . A high pressure port 1112 communicating with the high pressure passage 1101 is open at a position located on a bottom side of the valve chamber 1109 and directly below the low pressure port 1110 .

A control valve 1032 is provided in the valve chamber 1109 . The control valve 1032 is cup-shaped, with its lower side being separated horizontally. When the control valve 1032 is shifted upward, it sits on the ring-like seat 1109 a, hereinafter referred to as a low pressure seat, on the opening outer peripheral portion of the low pressure port 1110 so that the low pressure port 1110 is closed. When the control valve 1032 is shifted downward, it sits on the ring-like seat 1109b , hereinafter referred to as a high pressure seat, on the opening outer peripheral portion of the high pressure opening 1112 so that the high pressure opening 1112 is closed. Accordingly, when the control valve 1032 closes the low pressure port 1110 , fuel is prevented from being discharged from the back pressure chamber 1106 and the pressure in the back pressure chamber 1106 rises to a high level. In this case, when the coil spring 1051 or the like is set so that the downward pushing force acting on the needle 1031 is higher than the upward pushing force, the needle 1031 can be driven down to the lowest position.

In this state, if the control valve 1032 is raised from the low-pressure seat 1109 a and the high-pressure opening 1112 closes, the fuel is returned from the counter-pressure chamber 1106 into the fuel tank 1012 via the low-pressure opening 1110 . Due to this, the pressure of the fuel in the back pressure chamber 1106 is reduced to a value which is determined by the cross section of the channel of the inlet orifice 1107 or the outlet orifice 1108 . In this case, if the cross section of the channel or the like is set so that the downward pushing force acting on the needle 1031 is less than the upward pushing force acting on the needle 1031 , the driving direction of the needle 1031 is directed upward and the Needle 1031 is moved up. If this condition is maintained, the needle 1031 is raised by the maximum displacement and reaches the highest position at which the needle 1031 comes into contact with the cover side of the back pressure chamber 1106 .

On the other hand, when the control valve 1032 is raised again from the high pressure seat 1112 and the low pressure port 1110 closes in the state where the needle 1031 is raised, the fuel is prevented from being discharged from the back pressure chamber 1106 and the fuel flows from the high pressure passage 1101 into the back pressure chamber 1106 via the high pressure opening 1112 , the valve chamber 1109 and the outlet orifice 1108 . As a result, the pressure of the fuel in the back pressure chamber 1106 returns to the original high pressure level. Because of this, the drive direction of the needle valve 1031 is changed downward, so that the needle 1031 begins the downward displacement. If this state is maintained, 1031 reaches the needle, the lowest position at which the needle 1031 a of the guide hole 1201 is located on the bottom side 1,201th

In this connection, when the needle 1031 is pushed up, the nozzle holes 1104 and 1105 are opened and fuel is injected. This process is explained in detail below.

The control valve 1032 is driven as follows. Elongated holes 1202 and 1203 are formed above the low pressure chamber 1111 and are connected to the low pressure chamber 1111 . The small diameter elongated hole 1202 on the low pressure chamber 1111 side serves as a small diameter cylinder 1202 for slidably holding the small diameter piston 1041 . The large diameter elongated hole 1203 serves as a large diameter cylinder 1203 for slidably holding the large diameter piston 1042 . The fuel is loaded into the spaces in both cylinders 1202 and 1203 , which are defined by both pistons 1041 and 1042 , and the hydraulic chamber 1113 is defined by the space. When the large-diameter piston 1042 is shifted downward, the fuel in the hydraulic chamber 1113 is compressed, and the small-diameter piston 1041 is pushed and pushed down by the pressure of the fuel. At this time, the displacement of the piston 1041 with the small diameter, a value obtained when the displacement of the piston is extended in 1042 with the large diameter due to the difference in diameter of the piston 1041 relative to the piston 1042nd

The thin lower end portion 1411 of the small diameter piston 1041 protrudes from the low pressure chamber 1111 into the valve chamber 1109 via the low pressure port 1110 . As a result, it is possible that the thin lower end portion 1411 of the small-diameter piston 1041 comes into contact with the control valve 1032 . Due to the structure described above, the control valve 1032 is shifted downward by a pressing force of the piston 1041 with the small diameter.

The pressing force of the small-diameter piston 1041 is generated as follows. A chamber 1204 for accommodating the piezoelectric actuator 1006 is provided above the large diameter cylinder 1203 . The piezoelectric actuator 1006 is provided with a piezoelectric stack 1061 in which a piezoelectric ceramic layer such as PZT and an electrode layer are alternately stacked on top of one another. The layer direction of the piezoelectric stack 1061 is vertical and the piezoelectric stack 1061 is housed in the uppermost portion of the chamber 1204 for housing the piezoelectric actuator 1006 . When charging or discharging is performed on the piezoelectric stack 1061 by the EDU 1072 , the piezoelectric stack 1061 lengthens or contracts. A lower section of the cylinder housing 1062 of the piezoelectric stack 1061 consists of a bellows 1621 , the lower end section of which is closed by a plate element 1063 . A rod 1064 is provided between the piezoelectric stack 1061 and the plate element 1063 , which is inserted into the bellows 1621 . The rod 1064 comes into contact with the piezoelectric stack 1061 and the plate member 1063 .

On the other hand, in the chamber for housing the actuator, the small-diameter shaft portion 1422 , which is a half portion on the upper side of the large-diameter piston 1042 whose diameter is smaller than that of the sliding portion 1421 , protrudes and the plate member 1063 across from. Between the spring retainer 1043 , which is fixed to an upper end portion of the large diameter piston shaft portion 1422 , and the bottom side of the chamber 1204 for accommodating the actuator, there is provided a coil spring 1052 which constantly pushes the large diameter piston 1042 upward, so that the large diameter piston 1042 and the plate member 1063 are always in contact with each other. Due to the structure described above, the amount of expansion and contraction of the piezoelectric rod 1061 is converted into a displacement of the piezoelectric rod 1061 as such.

Accordingly, when the piezoelectric rod 1061 is expanded by the electric charge and the large-diameter piston 1042 is pushed down, the small-diameter piston 1041 is also pressed down over the hydraulic chamber 1013 . Accordingly, the control valve 1032 is raised from the low pressure seat 1109 a and is placed on the high pressure seat 1109 b. Due to this, the driving direction of the needle 1031 is directed upward as described above. On the other hand, when the piezoelectric rod 1061 is electrically discharged and contracts and the large-diameter piston 1042 is pushed up, the downward pushing force acting on the small-diameter piston 1041 is released, and the control valve 1032 is released from it High pressure seat 1109 b raised by an upward force generated by the pressure of the fuel from the high pressure port 1112 . Therefore, the control valve 1032 is placed on the low pressure seat 1109 a. Because of this, the needle 1031 is driven downward as described above.

The ECU 1071 , which is a control device, determines the type of fuel injection 14013 00070 552 001000280000000200012000285911390200040 0002010157886 00004 13894zung in accordance with the engine speed, the accelerator opening degree and the pressure in the common rail. Based on the type of fuel injection, the ECU 1071 outputs a control signal to the EDU 1072 . The type of fuel injection includes the fuel injection amount and the fuel injection time in the same manner as in the conventional fuel injection. Furthermore, the type of fuel injection includes the mode and frequency of the fuel injection, which are special features in relation to the present fuel injection unit. There are two types of injection modes. One mode is a low rate injection and the other mode is a high rate injection. The low injection rate mode is selected when it is judged from the engine speed and the accelerator opening degree that the engine operation is performed in a light load range, and the high injection rate engine is selected in other cases. Whether or not the engine operation is carried out in a light load range is judged in accordance with a table previously stored in a ROM by inputting the engine speed and the accelerator opening degree.

Fig. 8 is a timing chart showing a relationship between the control signal outputted from the ECU to the EDU 1071 1072, and the stroke of the needle 1031st The first half shows a case in which the low injection rate mode has been selected, and the second half shows a case in which the high injection rate mode has been selected. When the EDU 1072 receives a control signal, the piezoelectric stack 1061 is charged when the electricity increases and the piezoelectric stack 1061 is discharged when the electricity decreases. Accordingly, the fuel is injected in accordance with the period of the output from this control signal, that is, the period of the output corresponds to a fuel injection amount.

In the low injection rate mode, a pulse on the control signal is output once or frequently. The ECU 1071 calculates the required injection amount in accordance with the engine speed and the accelerator opening degree. At the same time, the ECU 1071 calculates a frequency N of the injection, which is a frequency of the output of the control signal.

As the level of the control signal increases, the piezoelectric stack 1061 is charged with electricity as described above and the needle 1031 is driven upward. Thus, the needle 1031 is raised from the seat 1201 a and the nozzle holes 1104 of the first type are opened. The fuel injection is started by the above-described operation.

In this case, the time period of the control signal is set at a value at which the control signal drops before the displacement of the needle 1031 reaches the second displacement that opens the nozzle holes 1105 of the second type. Because of this, the drive direction of the needle 1031 is reversed, that is, the needle 1031 is driven downward. Therefore, the nozzle holes 1105 of the second type are not opened. Since the nozzle holes 1105 of the second type are not opened, the opening area is relatively smaller than the opening area in the case where both the nozzle holes of the first and the second type 1105 are opened. Therefore, compared to a case where the fuel is injected from both the nozzle holes 1104 of the first type and the nozzle holes 1105 of the second type, atomization of the fuel is facilitated.

In this connection, when the period of the control signal is adjusted, the inertia of the needle 1031 and the delay in the response of each component with respect to the fall of the control signal are naturally taken into account. The time period of the control signal per unit time can be designed to a fixed value. However, it is possible to design this variable in accordance with the operating condition, such as the pressure in the common rail.

As described above, in the mode of low injection rate such fuel injection stated that the fuel injection rate is low and the Fuel is atomized finely.

Then, according to the required injection quantity Q, the second control signal, the third control signal,. , , is output so that the required injection quantity Q is ensured. Accordingly, in the ECU 1071, the injection frequency N is determined when the required injection amount Q is divided by the injection amount q, which is the amount of fuel injected per unit time according to the control signal.

The time period in which the fuel injection is carried out only through the nozzle holes 1104 of the first type in accordance with the control of a signal for one time depends on the time period from the first shift in which the nozzle holes 1104 of the first type are opened to the second Displacement from which the nozzle holes 1105 of the second type are opened. This time period is determined by the interval between the opening position of the nozzle holes 1104 of the first type on the side 1205 b of the guide holes and the opening position of the nozzle holes 1105 of the second type on the side 1205 b of the guide holes, and also determined by the speed of the displacement of the needle 1031 , Therefore, the distance between the nozzle hole 1104 and the nozzle hole 1105 is determined so that the required amount of fuel q that is injected per time according to the control signal is ensured.

When the control signal drops, the drive direction is changed downward with respect to the needle 1031 . If the output time of the next control signal, by which the drive direction is reversed, is set to a point in time before which the needle 1031 reaches a position under the first shift, that is, if the output time of the next control signal, by which the drive direction is reversed, is set at a point in time before the needle 1031 returns to a fully closed state, even if the control signal is output as a pulse, the fuel injection itself can be carried out continuously in the same manner as in a fuel injection unit in which one low injection rate is realized by holding the needle in a half stroke state. Of course, an interrupted fuel injection can be carried out according to a pulse-like output of the control signal.

On the other hand, when the low injection rate mode is selected, the control signal is output for a sufficiently long period of time in accordance with the required fuel injection amount, and the needle 1031 reaches the maximum displacement. Because of this, both the first-type nozzle holes 1104 and the second-type nozzle holes 1105 are opened, and the cross-sectional area of the flow channel for determining the injection flow rate is a value obtained by adding the opening area of the first-type nozzle holes 1104 to the opening area of the nozzle holes 1105 of the second type is obtained. Therefore, fuel injection is obtained by using a larger opening area than that in the case of the low injection rate mode.

As described above, in the present fuel injection unit, the driving direction is alternately changed so that after the driving direction of the needle 1031 has been set up, the driving direction returns to the downward direction before the area at the opening area of the nozzle holes 1104 and those of the nozzle holes 1105 that determine the flow rate of the fuel injection are maximally added to each other. Therefore, like a fuel injection unit in which the needle 1031 is made stationary in a half-stroke state, it is possible to realize a fuel injection unit that can achieve fuel atomization at a low injection rate without a complicated structure of the injector 1011 .

As for the nozzle holes, there are provided nozzle holes 1104 of the first type that open when the needle 1031 exceeds the first displacement, and nozzle holes 1105 of the second type that open when the needle 1031 exceeds the second displacement that is greater than the first Shift is. Therefore, the fuel injection unit of the present invention provides the following advantages compared to a conventional fuel injection unit in which the fuel injection is carried out at a low injection rate when the needle is made to be stationary in a half-stroke state by the flow rate of the back pressure chamber delivered fuel is set. In the conventional fuel injection unit, in the case of a full stroke, the stroke can be accurately determined by an interval between the needle and the cover side of the back pressure chamber that receives the needle. Therefore, the needle can be made to be stationary at the stroke. However, in the case of a half stroke, it is difficult to precisely control the back pressure of the needle, and the controllability of the fuel injection rate is not necessarily high, and the same applies to the fuel injection amount. On the other hand, in the present fuel injection unit, the cross-sectional area of a flow passage for determining the fuel injection amount is changed in two steps by two types of nozzle holes 1104 and 1105 , which are opened with different displacements. Therefore, the injection rate can be kept stable and the fuel injection amount can be adjusted with high accuracy.

Since the holes 1104 and 1105 are side holes that are open to the side 1201b of the guide hole 1201 of the needle 1031 , the fuel injection unit can be manufactured with ease, and further, the period from when the nozzle holes 1104 of the first one Can be easily set by setting an interval between both nozzle holes 1104 and 1105 in the shifting direction until the time when the nozzle holes 1105 of the second type are opened. In this connection, the present invention is not necessarily limited to the construction with two types of nozzle holes 1104 and 1105 , the needle displacement of which are different from each other when the nozzle holes are opened, in which the opening area of the nozzle holes 1104 and the opening area of the nozzle holes 1105 are different. It is possible to adopt the structure described below. In the case of the nozzle holes of a single construction, before the stroke of the needle reaches a value determined by the maximum area that is the opening area of the nozzle holes, the driving direction of the needle is changed in the direction of setting the needle valve. Because of this, the opening area of the nozzle holes can be set substantially at a value determined by the distance between the needle and the seat. The fuel injection is carried out in accordance with this value. In this case, fuel injection can be realized using the structure of the injector realized, and the piezoelectric stack is controlled while being charged and discharged.

While the present invention with reference to specific embodiments have been described, which for For purposes of illustration, should have been chosen for Professionals will be obvious that many variations can be made without departing from the scope of the invention departing.

It is a control chamber for creating a back pressure created, which acts on a nozzle needle, the one Nozzle hole opens and closes. A three-way valve to open and closing between the control chamber and a drain channel is controlled by an ECU. The ECU adjusts the voltage which is applied to a piezoelectric actuator to to drive the three-way valve such that the three-way Valve is opened and closed repeatedly, and the pressure  in the control chamber is held at a value higher than is the pressure by which the nozzle needle is raised completely becomes. Because of this, the stroke of the nozzle needle at the Fuel injection period at a half-stroke position held.

Claims (14)

1.Fuel injection unit with:
a control chamber for generating pressure in a valve closing direction, which acts on a nozzle needle that opens and closes a nozzle hole; and
a control valve for increasing and decreasing pressure in the control chamber when the control valve is opened and closed, the nozzle needle being opened when the pressure in the control chamber decreases,
wherein the fuel injection unit further includes a control section for controlling a stroke position of the nozzle needle at a predetermined position that is lower than a full stroke position at a period of fuel injection while maintaining the pressure in the control chamber at a high value that is higher than that Full stroke pressure of the nozzle needle is when the control valve is controlled to open and close. 2. The fuel injection unit according to claim 1, wherein the control valve is opened when there is power to this is supplied so that the control chamber with a drain channel communicates, and the control section the pressure in the Control chamber controls when the control section has an opening and closing movement of the control valve repeated.   3. The fuel injection unit according to claim 2, wherein the control section supplies energy to the control valve, so that the control valve repeats at a predetermined Period can be opened for a predetermined time. 4. Fuel injection unit according to one of claims 2 or 3, in which the control section repeats an opening and Closing movement of the control valve so that a Valve opening time the first time longer than after the first time can be. 5. Fuel injection unit according to one of claims 1 to 4, which further comprises a stroke detection device which detects a stroke of the nozzle needle directly or indirectly, wherein the control section the control valve in accordance with one sent by the stroke detection device Detection signal opens and closes. 6. Fuel injection unit according to one of claims 1 to 5, where the control section executes half-stroke control at the nozzle needle at a predetermined half stroke position is controlled when a target fuel injection amount or a target fuel injection period less than one is a predetermined value. 7. Fuel injection unit according to one of claims 1 to 5, where the control section executes half-stroke control to the To control the nozzle needle at a predetermined half-stroke position, when an internal combustion engine fuel injection time essentially from a top dead center of compression different.   8. Fuel injection unit according to one of claims 1 to 7, where a total opening area of the nozzle hole Changes in accordance with a stroke position of the nozzle needle. 9. The fuel injection unit according to one of claims 1 to 8, wherein
the control valve is driven by a piezoelectric actuator and
the control section controls the nozzle needle at a predetermined half-stroke position by repeatedly applying a predetermined high voltage and a lower voltage than that to the piezoelectric actuator. 10. The fuel injection unit according to one of claims 1 to 9, wherein
the control section controls the nozzle needle at a predetermined half-stroke position by repeatedly opening and closing the control valve, and
the control valve is controlled such that it cannot be placed exactly on a valve seat at the valve closing time. 11. A fuel injection unit in which starting and stopping of fuel injection can be freely changed by a linearly moving needle that is constructed such that the larger the shift from a reference state of stopping the fuel injection, the more the cross sectional area of a flow passage to Determining the flow rate of the injection is expanded, the fuel injection unit having the following:
an injector having a drive means capable of changing between the first drive state in which the needle is pushed in a direction such that the displacement of the needle is zero and the second drive state in which the needle is in a close the driving direction is pushed in the reverse driving direction in the first driving state, and the needle is pushed in such a direction that the displacement of the needle is maximum; and
a control device for changing a drive state of the needle by controlling the drive device,
wherein the controller can be switched between a high injection rate mode in which the drive state is set to the second drive state and the needle remains at the maximum displacement and a low injection rate mode in which the first and second drive states are repeated in such a manner that the drive state can return to the first drive state after the drive state is set to the second the second drive state and before the stroke of the needle reaches a stroke at which the cross-sectional area of the flow channel becomes maximum. 12. The fuel injection unit according to claim 1, wherein the injection device a nozzle hole of a first type, that opens when the needle makes a first shift exceeds, and has a nozzle hole of a second type, that opens when the needle moves a second time that is greater than the first shift. 13. The fuel injection unit according to claim 12, wherein the injector has two types of holes that are in a nozzle body are formed, in which a needle is slidable and guide hole for delivering Fuel is formed with one end of each hole closed one surface of the nozzle body is open and the other end of each hole communicates with the pilot hole, where each hole can be closed by the needle, the both types of holes at an interval in one direction the needle displacement are formed, the hole that is opened when the needle moves first Displacement exceeds that is the first nozzle hole, and that  Hole that opens when the needle moves second displacement exceeds, the second nozzle hole is. 14. Fuel injection unit according to one of claims 11 to 13, where the time of changing from the first drive state in the second drive state in a low mode Injection rate is used at a time before the stroke the needle reaches a displacement at which the Cross-sectional area of the flow channel becomes zero.