WO2012089378A1 - Pump of a fuel injection system - Google Patents

Abstract

A pump of a fuel injection system is equipped with a compressible pressure chamber (54) for the delivery of fuel under pressure into a pressure region of the fuel injection system (10). The compressible pressure chamber (54) is directly connected in fluid-conducting fashion to an expandable storage chamber (60) and serves for the autonomous regulation of the pressure generated by means of the pump.

Description

 Description title

 Pump of a Kraftstoffeinspritzsvstems prior art

The invention relates to a pump, in particular a high-pressure pump, a fuel injection system, with a compressible pressure chamber for conveying fuel under pressure in a pressure range of the fuel injection system.

Today's fuel injection systems of internal combustion engines or internal combustion engines, in particular gasoline engines, operate as so-called direct injection (DI) with injection pressures of up to 200 bar. The pressure is generated by means of a pump, in particular a high-pressure pump, which is mechanically driven by the internal combustion engine or engine in known fuel injection systems. The pump has a pressure chamber, which is generally compressible by means of a piston in order to convey fuel from the pressure chamber into a pressure region, in particular a high-pressure region, from where the fuel is injected. An electromechanical, in particular electromagnetic, quantity control valve controls the quantity of fuel delivered by the high-pressure pump per unit time into the high-pressure region, a so-called rail. Together with a high pressure signal measured by a high-pressure sensor, an engine control unit thus regulates the pressure in the pressure range to the desired level by means of the quantity control valve.

Disclosure of the invention

According to the invention, a pump of a fuel injection system is provided with a compressible pressure space for conveying fuel under pressure in a pressure range of the fuel injection system, wherein the

Compressible pressure chamber directly fluid-conducting with an expandable Memory space is connected. In this context, "direct fluid-conducting connection" means a connection in which there are no further components, in particular no components separating the connection, between the pressure chamber and the storage space. In particular, a direct contiguity of pressure space and storage space is understood.

The pressure space of the pump is compressible as described to expel fuel into the pressure range under pressure. The pressure chamber has a direct fluid-conducting connection to the storage space. A property of the memory space is that its volume is also variable or variable. The volume of the storage space changes depending on the pressure prevailing in it. At high pressure, the storage space is comparatively large, at low pressure comparatively small. Thus, the storage space from the pressure in the pressure chamber can be enlarged or expanded.

In the design of this type, pressure is built up in the pressure chamber in a compression phase of the pump, thereby expelling fuel under pressure into the pressure region or high-pressure region of the fuel injection system. At the outlet of the pump is located in a known manner an outlet valve. If a predefined pressure is exceeded during this compression of the pressure chamber, the storage space begins to expand or increase in a targeted manner. The still remaining in the pressure chamber residual flow of fuel is then no longer completely promoted by the exhaust valve in the pressure range, but in the increasing volume of the storage space. The pressure in the pressure range now increases much less.

This allows a purely mechanical regulation of the pressure in the pressure range. There are no electrical and electronic components required for control. A dependence on a control unit and electrical power amplifiers for the control is eliminated. It is thus created a stand-alone pump including regulation. Furthermore, eliminates an electromagnetic quantity control valve and its electrical control, thereby amplifiers can be omitted in the control unit and optionally a pressure sensor and less wiring is required. This allows a cost effective system for

Direct injection. It is also advantageous that a demand-based flow rate of the pump is achieved. This results in a lower power loss than pure pressure control or pressure limitation via a pressure control valve and a fully pump. The construction can be made more compact, since the forces acting on the parts due to the structure of the invention are lower.

In addition, during the suction phase, the pressure in the pressure chamber of the pump is kept at approximately pre-pressure level from the low-pressure range. This can ensure that the fuel is always in liquid form. There are no cavitation effects, such as blistering, to be expected.

In the subsequent suction phase of the pump, the storage space initially returns to its original size, even before via an inlet valve of the pump in a known manner fuel in the pressure chamber nachgefördert. This allows a particularly fast filling of the pressure chamber. There is no drop in pressure in the pressure chamber significantly below the pressure level in the low pressure range.

The compressible pressure space and the expandable storage space are preferably formed by means of a cylinder. The cylinder assumes a double function. Pressure chamber and storage space are housed in a single component in the form of a cylinder or a housing. This is a cost effective solution. The cylinder forms an outer overall seal of the hydraulic system. It is an integral construction, in which the pressure chamber and the storage space are combined in one unit.

The expandable storage space is preferably limited by a piston. The piston is in particular displaceably mounted in the cylinder. By such an embodiment, the volume of the storage space is due to the

Displacement of the piston variable. The piston which delimits the storage space is preferably an evasive pressure regulating piston. The piston is preferably arranged directly on the pressure chamber inside the pump or its cylinder. Alternatively, the storage space may be delimited by means of a membrane.

The piston is preferably sealed in its rest position by means of a seat seal. The piston stroke is limited by a stop. At this stop is a seal on which the piston is tight, in particular rests. Preferably, a so-called seat seal is used here. For a particularly good sealing of the piston is achieved in its rest position. In this way, the pressure in the pressure chamber does not drop or only very slowly below the pressure level in the low pressure range.

The expandable storage space is preferably expandable against a spring element. The spring preload is adjusted so that it corresponds to the hydraulic force of the regulated high pressure in the storage space. As long as the pump generates a desired pressure, the piston remains tensioned by the spring against its stop. However, if the pump generates too high a pressure, the piston will be pushed back accordingly and the spring will be compressed. The high pressure or overpressure is regulated by the now increasing storage space. The expandable storage space is preferably expandable against a spring element with a very low spring rate. Such a low spring rate arrangement means that the spring is relatively easy to compress. This allows the piston to be moved accordingly easier on this spring. Due to the slight backpressure, the pressure in the pressure chamber only increases very slightly or there is only a slight increase in pressure in the pump when a predefined desired control pressure is reached. In this way, a particularly needs-based fuel delivery is achieved.

At the same time, the pressure in the pressure range is adjusted, preferably to a pressure of between 40 bar and 60 bar, particularly preferably to a pressure of 50 bar.

Furthermore, the expandable storage space is preferably delimited by means of a piston with respect to a spring chamber, and a leakage line is provided on the spring chamber. The leakage line is used for the discharge of

Leakage, which is between the piston and the cylinder and there in the

Usually formed sliding seal inevitably results. The room at the of Storage space facing away from the piston may be filled with fluid under admission pressure of the inlet.

The expandable storage space is preferably delimited by means of a piston with respect to a spring chamber and a line is provided on the spring chamber. The line establishes a fluid-conducting connection from the spring chamber to the suction side of the pump. The line is thus coupled to the low pressure port of the pump. A leakage from, or in the spring chamber is discharged to the low pressure area. Advantageously, such a design also results in a damping effect with respect to the piston movement on the storage space. In this way, a leakage line, as mentioned above, can be saved.

In the line a check valve is optionally provided. The check valve is preferably arranged such that the leakage can flow away from the spring chamber, but not back into the spring chamber. As a result, vapor pressure is advantageously established in the spring chamber.

According to a further advantageous embodiment of the pump according to the invention, a throttle is provided in the line. The throttle leads to the least possible impact on the storage space and thus the pressure chamber from the low pressure side of the pump and the resulting there

Pressure pulsations.

Optionally, a bypass line is also provided from the high-pressure region to the low-pressure region with a pressure relief valve arranged therein. Instead of the pressure relief valve, a check valve, a rupture disc or a simple ball valve is preferably arranged in the bypass line. A rupture disc allows a higher temporary overpressure in the pressure range. By designing with such a Bypassieitung an impermissible pressure increase with a stationary engine and thus standing pump is prevented in case of failure or in the so-called hot-soak.

An exemplary embodiment of the solution according to the invention will be explained in more detail below with reference to the attached schematic drawings. It shows: Fig. 1 is a fuel injection system with a pump according to the prior art and

 Fig. 2 is a fuel injection system with a pump according to the invention. In Fig. 1, a fuel injection system 10 is shown with a pump 12. In the case of the fuel injection systems 10, the region on the suction side of the pump 12 is referred to as the low-pressure region and the region on the pressure-side of the pump 12 as the pressure region or high-pressure region.

In the low-pressure region, fuel is pumped from a tank 14 through an electric fuel pump 16 at a pressure of about 5 bar through a fuel filter 18 to a line 20. A pressure relief valve 22 may direct fuel from the fuel pump 16 back into the tank 14. On line 16, a low pressure damper 24 is arranged.

In the line 20, the fuel delivery rate of the pump 12 is regulated by a quantity control valve 26. The pump 12 increases the pressure of this fuel up to about 200 bar, wherein the fuel is conveyed through a Raildrossel 44 in a rail 28. This high pressure defines the already mentioned high-pressure region on the pressure side of the pump 12. The fuel can pass from the rail 28

Injectors 30 are injected into an internal combustion engine 32.

The pressure generated by the pump 12 is too high, for example, in the event of a fault or in hot soak. Therefore, that overpressure of the pump 12 is discharged from the high-pressure region into the pump 12. For this purpose, on the pressure side of the pump 12 branches off from the high-pressure region from a return line 34, which leads back into the delivery chamber of the pump 12. A check valve 36 mounted on the pressure side of the pump 12 forms the outlet valve of the pump 12. The check valve 36 only opens at a certain pressure level and prevents fuel from flowing in the opposite direction to its delivery direction. Another, arranged in the return line 34 check valve 38 ensures that only fuel is returned under pressure in the pump 12. Also, this check valve 38 opens only from a certain higher pressure level in the flow direction to the low pressure area. In addition, as mentioned, in the low-pressure region, the amount of fuel delivered by the pump 12 can be influenced by the quantity control valve 26, so that ideally the pump 12 does not generate too much excess pressure at all. Regulated is the funded amount of fuel over

comparatively complex electromechanical system. On rail 28, a high pressure sensor 40 measures the pressure applied there. A controller 42 receives the information regarding the rail pressure from the high pressure sensor 40 and processes it. According to the programming of the controller 42 is the

Quantity control valve 26 adjusted. Thus, the quantity control valve 26 regulates the amount of fuel delivered by the pump 12 per unit time due to the fuel pressure occurring and measured in the rail 24.

2 shows a fuel injection system 10 according to the invention, in which the fuel is first pumped into the line 20 of the low-pressure region. On the line 20 may optionally be arranged a low pressure damper 24. In contrast to FIG. 1, here a quantity control valve 26 is omitted and the fuel flows through a check valve 72 into the pump 12.

On the pressure side of the pump 12, in the pressure range or high pressure region, a check valve 36 is arranged. The check valve 36 opens only in the delivery phase of the pump 12 and prevents fuel then can flow opposite to the conveying direction. Subsequently, the fuel is due to the pump pressure of the pump 12, promoted by the Raildrossel 44, in the rail 28. From there, the fuel reaches the injection valves 30 and is injected into the engine 32.

Since the pump 12, as already mentioned, can temporarily generate overpressure, the high-pressure side of the pump 12, the return line 34 is provided, which leads to a valve 46. The valve 46 in Fig. 2, as in Fig. 1 the

Check valve 38, also designed as a check valve. It opens at a certain preset overpressure in the return line 34. In the flow direction behind the valve 46, the fuel flowing through initially comes back into the low-pressure region. The pump 12 in FIG. 2 comprises a housing or a cylinder

48, in which the various components of the pump 12 are arranged. Shown are a pump piston 50 which is displaceable by a drive 52 in the cylinder 48. The area in which the pump piston 50 moves is the pressure chamber 54. Opposite to the pump piston 50, a storage piston or a piston 56 is arranged, which can move in the region of a storage space 60. The storage space 60 is limited in the cylinder 48 by a seat seal 58. In rest position, the piston 56 is biased against the seat seal 58 by means of a spring element 62, or a spring. Between the piston 56, or its lateral edges and the cylinder 48 is a minimum gap 64. In a spring chamber 66 at the rear of the piston 56, the spring element 62 is arranged. The piston 56 can be moved in the region of the spring chamber 66. In this case, the distance between the piston 56 and the seat seal 58, which forms the stop when the piston 56 is at rest, becomes larger. The space that is released with the thus increasing distance is referred to as storage space 60. In addition, the spring chamber 66 is connected by means of a line 68 to the suction-side region of the pump 12 or the low-pressure region. On the line 68, a throttle 70 is arranged.

As in Fig. 1, the fuel from the fuel pump 16 is pumped to the pump 12 in Fig. 2. The pump 12 compresses the fuel and directs it under high pressure to the rail 28. So that the pump 12 does not generate too high pressure, the storage space 60 is provided in the cylinder 48 of the pump 12. In the case of an overpressure during pump delivery, the spring element 62 is designed such that the piston 56 pushes the spring element 62 back, thus increasing the volume of the storage space 60. The fuel can thus also in addition to the pressure chamber 54 in the storage space 60 spread and thus reduces the pressure generated by the pump 12. The choice of a suitable spring element 62 or its design ensures that the fuel leaves the pump 12 on the pressure side with a certain minimum necessary pressure. Necessarily, the piston 56 also exerts a pressure on the storage space 60 and the fluidically coupled thereto pressure chamber 54 in order to ensure a stable outlet pressure to the rail 28 out. Usually, the pressure at the pump 12, the so-called desired control pressure, the pressure side between about 40 bar and about 60 bar. Particularly preferred is a spring with a for the desired control pressure, in particular a pressure of about 50 bar, corresponding or adapted spring force used as a spring element 62 in order to regulate the pressure in the specified range with the smallest possible bandwidth.

As soon as the pump 12 completes the next intake stroke, the pressure in both the pressure chamber 54 and in the storage chamber 60 decreases and the piston 56 moves back to its starting position on the seat seal 58.

Between the piston 56 and the cylinder 48, leakage occurs due to a sliding seal formed there. The leakage is discharged into the spring chamber 66. The spring chamber 66 is coupled by means of the line 68 to the low pressure region. On the line 68 is the throttle 70. Such a throttle 70 may be designed for example with a diaphragm.

The spring chamber 66 is completely filled with fuel, in particular by the spring chamber 66 is connected directly hydraulically to the low pressure input of the pump 12. To achieve the least possible interference between piston movement and pressure pulsations, the throttle 70 between the spring chamber 66 and suction-side low-pressure inlet of the pump 12 can advantageously be dimensioned accordingly.

The function of this line and throttle arrangement formed by the throttle 70 comprises that the fuel which passes through the gap 64 into the spring chamber 66, can be discharged from this again in the direction of the low pressure region. The line 68 serves for leakage compensation in the direction

Low pressure area.

The passage cross section of the throttle 70 is preferably dimensioned so that the piston 56 on the one hand reciprocate to a sufficient, desired extent, but on the other unwanted overshoot of the piston 56 can be prevented. With the throttle 70 is achieved that occurring in the spring chamber 66 pressure pulsations can not or only significantly attenuated in the line 20, ie in the low pressure range, can spread. Likewise, with the throttle 70 is achieved, if necessary, by the fuel pump 16 generated pressure pulsations can not or only significantly attenuated in the spring chamber 66 can spread.

As a further securing mechanism with respect to an overpressure on the pressure side of the pump 12 is a return line 34 from the pressure range to

Low pressure area arranged. On the return line 34 is a valve 46, preferably a check valve attached. The function of the valve 46 is to allow fuel to flow from the pressure range to the low pressure range as soon as this fuel exceeds a certain pressure level at the valve 46.

In other words, the inventive embodiment of FIG. 2 can be described as follows: In the pump 12, a piston 56 is integrated in addition to the pump piston 50, which is biased by a spring element 62 and tightly rests on a piston stop in the form of a seat seal 58. The spring preload is adjusted to match the hydraulic force of the high pressure regulator.

In the compression phase of the pump 12, the fuel is conveyed into the pressure range or high-pressure range and thereby compressed. If, during compression, the desired control pressure, in particular of e.g. 50 bar exceeded, then lifts off the piston 56, so that the remaining for the piston stroke residual flow is not promoted to the rail 28, but in the liberated volume or in the storage space 60 of the evasive piston 56. The pressure in the high pressure region increases only slightly depending on the spring stiffness of the spring element 62. As a result, an on-demand fuel delivery is achieved while adjusting the pressure. Preferably, the spring element 62 is designed with such a small spring rate that during the entire pressure stroke of the pump piston 50 only the smallest possible increase in pressure results.

In the subsequent suction phase of the pump 12, the piston 56 first returns to its initial position to the seat seal 58, before the suction side of the pump 12 nachgefördert new fuel. The opposite spring chamber 66, in which the spring element 62 is located, can, with sufficient tightness between the piston 56 and cylinder 48, be filled with air at ambient pressure. In this modified, not shown embodiment, an opening may be provided, via which a pressure equalization between the spring chamber 66 and the ambient air can take place. In this modified, not shown embodiment, the line 68 can be saved.

In a further, not shown, modified embodiment, a check valve is provided. The non-illustrated check valve is installed so that the possibly between the piston 56 and the cylinder 48 in the spring chamber 66 leaking fuel from the spring chamber 66 in the

 Low pressure range, more precisely in the line 20, is discharged. With the check valve, not shown, no fuel from the line 20 can get into the spring chamber 66. Because the spring element 62 is so strong that it pushes the piston 56 in the direction of reducing the storage space 60 during a suction stroke of the pump piston 50, this is not shown in this

Variant during the suction stroke, the pressure in the spring chamber 66 down to the vapor pressure.

The embodiment can also be modified so that a non-illustrated check valve is installed so that the possibly between the

Piston 56 and the cylinder 48 in the spring chamber 66 leaking fuel from the spring chamber 66 downstream behind the suction-side check valve 72 into the pressure chamber 54 is passed. The non-illustrated check valve is installed so that no fuel from the pressure chamber 54 enters the spring chamber 66 in the reverse direction. Also in this embodiment, not shown, falls during the suction stroke of the pump 12, the pressure in the spring chamber 66 down to the vapor pressure.

To prevent an increase in pressure in the hot soak, a fuel heating when the internal combustion engine and thus standing pump 12, optionally a pressure relief valve, for example a simple ball valve,

or if the system components withstand a higher temporary overpressure, and a rupture disc at the high pressure region of the fuel injection system 10, in particular be provided as a replacement for the valve 46.

Claims

claims 1. Pump of a fuel injection system with a compressible  Pressure chamber (54) for conveying fuel under pressure in one  Pressure range of the fuel injection system (10),  characterized in that the compressible pressure chamber (54) is directly fluid-conductively connected to an expandable storage space (60). 2. Pump according to claim 1,  characterized in that the compressible pressure space (54) is formed by means of a cylinder (48) and the expandable storage space (60) is also formed by the cylinder (48). 3. Pump according to claim 1 or 2,  characterized in that the expandable storage space (60) by a piston (56) is limited, which is in particular displaceably mounted in the cylinder (48). 4. Pump according to claim 3,  characterized in that the piston (56) is sealed in its rest position by means of a seat seal (58). 5. Pump according to one of claims 1 to 4,  characterized in that the expandable storage space (60) is expandable against a spring element (62) whose spring rate is selected such that the pressure required for expansion corresponds to the pressure to be produced in the pressure chamber (54). 6. Pump according to one of claims 1 to 5, characterized in that the expandable storage space (60) is expandable against a spring element (62) with a low spring rate. 7. Pump according to one of claims 1 to 6,  characterized in that the expandable storage space (60) by means of a piston (56) with respect to a spring chamber (66) is delimited and on the spring chamber (66) a leakage line (68) is provided. 8. Pump according to one of claims 1 to 6,  characterized in that the expandable storage space (60) by means of a piston (56) opposite a spring chamber (66) is delimited and on the spring chamber (66) a conduit (68) is provided by means of a fluid-conducting connection from the spring chamber (66) Suction side of the pump (12) is made. 9. Pump according to claim 8,  characterized in that in one of the spring chamber (66) to the pressure chamber (54) leading line, in particular in the conduit (68), a  Check valve is provided. 10. Pump according to claim 8 or 9,  characterized in that in the conduit (68) has a throttle (70) is provided.