DE4118236A1 - Cyclic-delivery fuel injection system for combustion engine - employs two control valves in low-pressure system supplying nozzle with fuel also during pre-injection period - Google Patents

Abstract

A pumping piston (2) is driven by a plunger (3) from e.g. the camshaft against the opposition of a spring (4), to expel fuel from a cylindrical chamber (21) through a control valve (14) into the tank (18) when another valve (13) controlling admission to the low-pressure system is closed. During this preinjection phase the pressure in the injection line (23) is maintained and the nozzle (6) injects fuel into the combustion chamber. The main injection phase sees both valves (13, 14) closed. ADVANTAGE - Exhaust and noise emissions are reduced significantly by preinjection with exact setting of the fuel pressure.

Description

The invention relates to an injection system for internal combustion engines seem that a pre-injection and a subsequent Main injection allows, with a combined Pump nozzle that has a pump piston that is mechanical is preferably actuated via a cam, with the Control of the start of spraying a control valve is provided.

An injection system is known from EP-A 3 15 564, in which a piston is operated via a cam. Furthermore is a Control valve provided, which in its open position Injection line connects to the drain port, which the Injection end can be set exactly. For an advance To allow spraying, a compensation chamber is provided hen that take up fuel over a certain period of time can. In this way, the injection pressure is reduced and thus enables a pre-injection.

However, it is not possible with this known injection nozzle Lich, the injection pressure of the pre-injection and in particular determine and influence the duration of the pre-injection.

Injection systems are also known in which pumping piston is operated via a cam. At the beginning of the one to be able to control spraying depending on the engine condition, a control valve is provided which is open in its position the injection line with the drain port binds. The cam is designed so that the pumps piston before the earliest possible injection is moved down. Until the scheduled start of the on spraying, the control valve is open, so that the pump piston overflow displaced fuel into the leak oil system can. By closing the control valve builds up in the Injection line a pressure that will eventually open the Needle leads.

It is also possible to a certain extent with such systems perform a pre-injection. First of all, the Control valve closed for a short period of time, so that one  small amount of fuel under a relatively low pressure is injected. The pilot injection is done by opening of the control valve ended. The new closing of the tax erventiles does the main injection.

It has been found that with such a system a pre-injection is feasible, but that Pollutant emission and noise emission with this one engines equipped with a spray system can be further improved can.

The object of the invention is to provide an injection system a clearer reduction by means of a pre-injection enables exhaust and noise emissions from engines.

According to the invention is a device for exact adjustment a predetermined fuel pressure in the pre-injection and to control the duration of the pilot injection. It has been recognized by the inventors that one of the disadvantages of the known injection systems on the between pre and Main incision pressure drop taking place and the right resulting interruption in the needle stroke. This print case is caused by the fact that the control valve at be knew injection system for the pre-injection only very briefly closes and opens again. The device according to the invention to adjust the fuel pressure allows it initially the predetermined pilot injection pressure via a steep flank reach and over another steep flank without one there intermediate pressure drop to the main injection pressure to ge long. In this way, you can inject both Amounts of fuel as well as the exact start of pre-fuel Determine the injection and main injection.

There is to every engine condition, i. that is, to any combination of Speed and load, a certain course of the Optimalein injection rate with the optimal we for this engine condition efficiency of the engine and a low pollutant and Ge noise emission is achieved. The course of such an spray rate can be shown in a diagram in which the injected fuel volume over the crank angle is wearing. The key determinants are the time the start of spraying, the time of the start of the main injection  tion, duration of the injection and that during the pre-injection force and force injected during the main injection fabric volume. The present invention now enables to specify these parameters largely independently of each other. Thus, depending on the Engine state sets the optimal parameters for each operating state of the internal combustion engine optimal Ver keep being achieved.

The device for the exact setting is preferably a predetermined fuel pressure verbun with the control valve the one that is designed as a valve with three switching positions. The three switch positions of the valve correspond to the Ru helage, the pre-injection and the main injection.

It is favorable if a further control valve is provided is that controls the start of the main injection. The for high-speed engines required switching times on Easiest achieved by vorese two control valves hen are.

Such fast switching times can be done in a particularly simple manner ten can be achieved if the control valves are used as solenoid valves are trained.

According to a particularly preferred embodiment of the Er Invention is provided that the device for adjustment of the fuel pressure as a pressure valve or as a throttle is formed that in connection with the injection line stands and opens when a predetermined pressure is applied. The pre-injection pressure in ex be determined on a current basis. Even with a simple Dros sel is such a definition of the pre-injection pressure in the we considerably possible.

In a further development of this embodiment variant is provided hen that the cylinder space of the pump piston over a first Control line is connected to the first control valve and with a second control line via the pressure valve the further control valve is connected. It is by the Closing the first control valve turned on the pilot injection directs and by closing the second control valve Main injection started.  

A particularly inexpensive and simple variant is given when the control valves are connected to the drain oil system are.

According to another preferred embodiment of the Erfin It is provided that the device for setting the Fuel pressure in the pre-injection as a pressure accumulator is formed, which is connected to the control valve. The Pre-injection takes place with the ready from the memory put pressure. The pump piston needs to start Pre-injection does not necessarily have to move.

Subsequently, it can be provided that the nozzle needle with a piston is connected, the cylinder space in a Stel tion of the control valve is connected to the pressure accumulator, whereas in the other position of the control valve with the Leakage oil connection is connected. It stops in the rest position the accumulator pressure acting on the piston in the nozzle needle their closed position. Only when through the connection of the cylinder chamber with the drain port this force on the If the needle drops, the pressure on the nozzle needle can be reduced acting memory pressure open this.

The cylinder chamber of the piston is preferably the spring chamber of the the spring loading the nozzle needle.

A particularly simple design results when a white teres control valve is provided via a control line is connected to the cylinder space of the pump piston.

To bring about a quick closing of the nozzle needle and a To prevent dripping effectively, it can be provided that the cylinder space of the pump piston over an equal Room relief valve with the pressure chamber of the nozzle needle in Connection is established. This equalization relief valve acts in the type of a check valve that controls the flow of force material from the cylinder space of the pump piston into the injection line enables. The pressure drops in this cylinder space by opening the control valve to the leakage oil pressure, so closes this equalization relief valve. Through its spe zial construction is a ge in this closing operation rings fuel quantity sucked out of the injection line, so  that the pressure in the injection line immediately drops sharply falls.

The invention is illustrated below with reference to the figures presented embodiments explained in more detail. The picture genes show schematically:

Fig. 1 shows a first embodiment of the injection system according to fiction, including the respective fuel supply,

Fig. 2, the injection system of Fig. 1 in the rest position,

Fig. 3 shows the system of FIG. 1 with pre-injection and

Fig. 4 the system of Fig. 1 during the main injection.

Fig. 5 is a diagram indicating the opening of the solenoid valves, the needle stroke and the injection pressure over the time axis for the injection system shown in Figs. 1 to 4.

Fig. 6 shows a second embodiment of he inventive injection system including impaired supplied fuel supply,

Fig. 7, the injection system of Fig. 6 in the rest position,

Fig. 8 shows the system of FIG. 6 with pre-injection and

Fig. 9 the system of Fig. 6 during the main injection.

Fig. 10 is a diagram indicating the opening of the solenoid valves, the Na delhub and the injection pressure over the time axis for the injection system shown in FIGS . 6 to 10.

Fig. 11 shows schematically a variant embodiment with a three-way valve.

The embodiment of FIGS. 1 to 4 consists of a pump body 1 , which is firmly connected to an injection nozzle 5 via a union nut 10 . A pump piston 2 is axially displaceably mounted in the pump body 1 and can be actuated by a camshaft (not shown) via a tappet 3 . A spring 4 exerts an upward force on the plunger 3 . The nozzle needle 6 is loaded by a spring 8 acting on the pressure piece 7 in the direction of its closed position. For manufacturing reasons, the components 9 a and 9 b are provided between the injection nozzle 5 and the pump body 1 .

Laterally on the pump body 1 , the control valves 13 and 14 formed as solenoid valves are arranged. These Steuererven tiles 13 and 14 are switched via a control device, not shown, via current pulses. The control points t ₁ , t ₂ and t ₃ are determined depending on the state of the engine in a predetermined manner.

The injection system is supplied with fuel in a manner known per se via a low-pressure system. This consists of a backing pump 15 , a pressure valve 16 and a throttle 17 , whereby a defined pressure and a defined flow in the low pressure system is guaranteed. The fuel is removed from a reservoir 18 . The control valves 13 and 14 have connections 13 a and 14 a for the admission pressure and leak oil connections 13 b and 14 b. The fuel delivered via the connections 13 a and 14 a serves in addition to the filling of the injection pump for cooling the control valves 13 and 14 .

The piston 39 of the first control valve 13 allows in the open position to connect the line 22 to the circuit 13 a for the form. In the closed position of the control valve 13 , the line 22 is separated from the connection 13 a ge.

The piston 40 of the second control valve 14 in its open position connects the pressure valve 11 to the drain port 14 b of the second control valve 14 . In the closed position of the control valve 14 , this connection is interrupted.

The cylinder chamber 21 of the pump piston 2 is connected to the first control valve 13 via a first line 22 . A pressure relief valve 12 provided in the area of this line 22 prevents the occurrence of impermissibly high pressures. In normal operation of the injection system, this valve 12 is always closed. Furthermore, the injection chamber 23 starts from the cylinder chamber 21 , which opens into the pressure chamber 19 of the nozzle needle 6 . A branch 24 of the injection line 23 is connected via a pressure valve 11 to the second control valve 14 . The Fe derraum 20 of the spring 8 is connected via a further line 25 with the leak oil system.

In Fig. 2 the rest position of the injection system is Darge. In this state, the valve needle 6 is closed and the cylinder space 21 may be filled with fuel. The control valves 13 and 14 are both in the open state. In FIG. 2, the lines and cavities, which are filled with the low-pressure fuel highlighted. This fuel is supplied via the connections 13 a and 14 a and can essentially circulate throughout the injection system. If following an injection of the pump piston 2 moves upward, the cylinder space 21 is filled with this fuel. The excess fuel leaves the leakage oil connections 13 b and 14 b of the injection system.

In Fig. 3, the state of the injection system is shown during the pilot injection. The first control valve 13 is closed ge. The pump piston 2 moving downward can no longer discharge the fuel displaced from the cylinder chamber 21 into the low-pressure system via the line 22 . The pressure in the cylinder chamber 21 and thus in the injection line 23 increases until the pre-injection pressure is reached and the pressure valve 11 opens. About the pressure valve 11 so much fuel is emitted via the second control valve 14 in the leak oil system that the pre-injection pressure in the cylinder space 21 and the injection line 23 is maintained. The nozzle needle 6 opens and the fuel is injected into the combustion chamber of the internal combustion engine. In FIG. 3, the under Voreinspritzdruck lines and cavities are shown hervorge lifted.

In FIG. 4, the state is shown of the injection system during the main injection. Both control valves 13 and 14 are closed. The fuel displaced by the pump piston 2 can no longer escape via the pressure valve 11 into the leakage oil system. Therefore, the entire, from the cylinder space 21 displaced fuel is injected at high pressure via the injection line 23 and the spray openings in the combustion chamber of the internal combustion engine. In FIG. 4, which is under injection pressure lines and cavities are highlighted.

In Fig. 5, the timing of the injection process is plotted in a diagram. The start of the injection process is determined at time t ₁ by closing the first control valve 13 . At this point it must be ensured that the pump piston 2 is already pressed down by the cam via the tappet 3 . The injection pressure p _e rises up to the pre-injection pressure p _before . This pre-injection pressure p _before is only dependent on the pressure valve 11 . The steepness of the increase _{1 of} the injection pressure p _e depends, among other things, on the respective engine speed n. In accordance with the increase F _{1 in} the injection pressure p _e , the needle stroke h reaches its maximum value limited by a stop.

At time t ₂ , the control valve 14 closes, so that the injection pressure p _{e can} continue to rise. The maximum pressure p _max that can be reached depends, among other things, on the engine speed n. The needle stroke h does not change during the transition from the pre-injection to the main injection. The injection process is ended at time t ₃ by opening the first control valve 13 . The fuel from the cylinder chamber 21 and the injection line 23 can now freely escape into the leakage oil system. The nozzle needle 6 closes immediately after the action of the spring 8 . The second control valve 14 opens at any time after opening the first control valve 13th

In FIG. 6, a further variant embodiment of a OF INVENTION to the invention injection system. The same parts are designated with the same reference numerals. The fuel supply has in addition to the low pressure system, which is designed analogously to the embodiment of FIGS. 1 to 4, a medium pressure system. This medium pressure system consists of a high pressure pump 26 , a fuel accumulator 27 and a pressure control valve 28 . The fuel accumulator 27 does not necessarily have to consist of a separate component. It can also be designed as a fuel line with a corresponding inner diameter. The pressure control valve 28 is set to the desired pilot injection pressure.

On the pump body 1 , the control valves 13 and 34 are attached to the side, the control valve 34 being formed as a 2/3 way valve. The piston 29 of the control valve 34 connects the central annular space 31 with the upper annular space 30 in one position and the central annular space 31 with the lower annular space 32 in the other position of the control valve 34 . The lower annular space 32 is on the one hand with the connection 34 c in connec tion, at which the storage pressure is present and on the other hand via a check valve 33 and a connecting line 35 with the injection line 23 in connection. The middle annular space 31 is connected with a line 36 to the spring chamber 20 of the spring 8 connected. The upper annular space 30 is connected to the leakage oil system. The cylinder chamber 21 of the pump piston 2 is connected to the injection line 23 via a constant-space relief valve 37 .

In Fig. 7, this embodiment is shown in the rest development. The control valve 13 is open and the control valve 34 is in the lower position. The fuel under storage pressure passes through the fuel accumulator 27 and the connection 34 c into the lower annular space 32nd This fuel flows further via the check valve 33 , the connecting line 35 and the injection line 23 into the pressure chamber 19 of the valve needle 6 . The Ventilna del 6 can not open, however, because the spring chamber 20 of the Fe 8 on the top of the valve needle 6 is acted upon via the line 36 and the central annular space 31 with the same storage pressure. This storage pressure acts on the back of the valve needle 6 , which is designed as a piston and the Na del 6 holds in its closed position. The cavities and lines under storage pressure are highlighted in FIG. 7. The remaining cavities and lines are under leakage oil pressure.

In FIG. 8, the injection system is shown during the pilot injection. The control valve 34 is switched to its upper position by a current pulse. The control valve 13 is still open. The spring chamber 20 is connected in this state via the line 36 and the central annular space 31 with the obe ren annular space 30 . This is connected through the terminal b 34 to the leakage system. Thus, there is also 20 leakage oil pressure in the spring chamber. Since the valve needle 6 is now relieved of pressure, the storage pressure still present in the pressure chamber 19 can open the nozzle needle 6 and the fuel is injected into the combustion chamber. The equal space relief valve 37 prevents fuel from flowing out of the injection line 23 into the cylinder space 21 of the pump piston 2nd In Fig. 8, the cavities and lines standing under storage pressure are highlighted Darge provides.

In Fig. 9, the state of the injection system is shown during the main injection. The control valve 13 is closed and the control valve 34 is in its upper position. At the beginning of the main injection, it must be ensured that the pump piston 2 has already started its downward movement. This downward movement of the fuel is compressed in the cylinder chamber 21 . Since an overflow into the leakage oil system through the closed control valve 13 is not possible, the constant-space relief valve 37 is opened and the fuel enters the injection line 23 . The check valve 33 prevents the fuel from escaping via the connecting line 35 . The end of the main injection is sufficient by opening the control valve 13 . The fuel can flow out of the cylinder chamber 21 into the leak oil system via the first line 22 . As a result, the pressure in the cylinder chamber 21 drops very quickly to the leakage oil pressure. The ste in the injection line 23 at injection pressure rising fuel includes, in cooperation with the spring 38 of the constant-volume-relief valve 37 of this, this constant volume relief valve 37, a small amount of fuel from the injection line 23 to be drawn through the piston-like construction. This ensures that the fuel pressure drops very quickly in the injection line 23 and thus in the pressure chamber 19 and that the nozzle 6 is quickly closed without dripping.

In Fig. 10, the timing of the injection process is plotted in a diagram. The start of the injection process is determined at time t ₁ by switching the control valve 34 . The injection pressure p _e rises up to the pre-injection pressure, p _before . This pre-injection pressure p _before speaks to the accumulator pressure. The steepness of the increase s _{1 of} the injection pressure is independent of the engine speed n. In accordance with the increase F _{1 of} the injection pressure p _e , the needle stroke h reaches its maximum value limited by a stop.

At time t ₂ , the control valve 13 closes, so that the injection pressure p _{e can} continue to rise. The achievable maximum value p _max depends, among other _things, on the engine speed n. The needle stroke h does not change during the transition from the pre-injection to the main injection. At any time during the main injection, the Steuererven valve 34 is switched back to its original position. If at the time t ₃ the injection process is ended by opening the control valve 13 , the storage pressure in the spring space 20 supports the closing of the nozzle needle 6 . In this way, the closing process is accelerated and dripping is effectively prevented.

From Fig. 11 it can be seen in a schematic manner that the control valve 41 , which is designed as a three-way valve, has two inputs which are connected via the connections 42 and 43 with the cylinder chamber 21 and with the pressure valve 11 . The output of the control valve 41 is connected to the leakage oil system via the connection 44 . The symbols 45 a, 45 b and 45 c indicate the rest position, the position in the case of pre-injection and the position in the case of main injection. In the rest position (symbol 45 a), both the cylinder chamber 21 and the pressure valve 11 are connected to the leakage oil system. In the pre-injection (symbol 45 b), the pressure valve 11 remains connected to the leakage oil system, whereas the connection 42 is interrupted. For the main injection (symbol 45 c) both the connection 42 and the connection 43 are interrupted. With 46 a and 46 b springs are schematically indicated, which enable the function of the control valve 41 . This control valve 41 can be constructed so that a switch from the rest position to the position of the pre-injection against the opposing state of the spring 46 b is effected by a rela tively weak pulse. The main injection position can be achieved by a stronger electrical impulse against the common resistance of the springs 46 a and 46 b.

Claims (11)

1. Injection system for internal combustion engines, which enables a pre-injection and a subsequent main injection, with a combined pump nozzle that has a pump piston, which can preferably be actuated mechanically via a cam, a control valve being provided to control the start of the injection, characterized in that a device for the exact setting egg nes predetermined fuel pressure in the pre-injection and for controlling the duration of the pre-injection is provided. 2. Injection system according to claim 1, characterized in that the device for the exact setting of a pre-determined fuel pressure with the control valve ( 41 ) is connected, which is guided as a valve with three switching positions. 3. Injection system according to claim 1, characterized in that a further control valve ( 13 , 14 ) is provided which controls the start of the main injection. 4. Injection system according to one of claims 1 to 3, characterized in that the control valves ( 13 , 14 ) are designed as solenoid valves. 5. Injection system according to one of claims 1 to 4, characterized in that the device for adjusting the fuel pressure is designed as a pressure valve ( 11 ) or as a throttle valve, which is connected to the injection line ( 23 ) and opens when a predetermined pressure is present . 6. Injection system according to claim 5, characterized in that the cylinder chamber ( 21 ) of the pump piston ( 2 ) via a first control line ( 22 ) with the first control valve ( 13 ) is connected and via a second control line ( 24 ) via the pressure valve ( 11 ) or the throttle element is connected to the further control valve ( 14 ). 7. Injection system according to claim 5 or 6, characterized in that the control valves ( 13 , 14 ) are connected to the Leckölsy stem. 8. Injection system according to one of claims 1 to 4, characterized in that the device for adjusting the fuel pressure in the pre-injection is designed as a Druckspei cher ( 27 ) which is connected to the control valve ( 34 ). 9. Injection system according to claim 8, characterized in that the nozzle needle ( 6 ) is connected to a piston, the cylinder chamber in one position of the control valve les ( 34 ) is connected to the pressure accumulator ( 27 ), whereas it is in the other position of the control valve ( 34 ) is connected to the drain port ( 34 b). 10. Injection system according to claim 8 or 9, characterized in that a further control valve ( 13 ) is provided which is connected via a control line ( 21 ) to the cylinder space of the pump piston ( 2 ). 11. Injection system according to one of claims 8 to 10, characterized in that the cylinder chamber of the pump piston ( 2 ) via a constant space relief valve ( 37 ) with the pressure chamber ( 19 ) of the nozzle needle ( 6 ) is in communication.