GB2072261A

GB2072261A - A fuel injection system for internal-combustion engines

Info

Publication number: GB2072261A
Application number: GB8104869A
Authority: GB
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1980-02-29
Filing date: 1981-02-17
Publication date: 1981-09-30
Also published as: FR2477227B1; FR2477227A1; DE3007637A1; IT8147870A0; IT1142325B; GB2072261B

Abstract

The fuel injection system has an injection pump 3 and a reservoir 4 from which fuel is supplied via feed lines 16 to injection nozzles 5 in each of the cylinders of the engine 1. Each feed line 16 also constitutes the input 15 of a logistor 25 which also has a control input 19. The control input 19 is connected to an electronic unit 6 so as to be responsive to various parameters such as engine speed 7, throttle opening 8, air temperature or pressure 10, 9 or road speed 11. The unit 6 gives a square-wave output voltage, whose frequency is dependent of the parameters, which controls the individual logistors 25 to give an intermittent flow of fuel through the logistor 25 and hence the injector nozzle 5. A mechanical/hydraulic system replacing the unit 6 is also disclosed. <IMAGE>

Description

SPECIFICATION Fuel-injection system for internal-combustion engines The invention relates to a fuel-injection system for internal combustion engines with a fuel feed line from which fuel is supplied to an injection nozzle during an injection phase. In fuel-injection systems of this kind which are generally known, fuel injection is effected continuously through the injection nozzle, the injection phase being determined by the pressure rise in the fuel feed line.

The object of the invention is to improve the combustion of the injected fuel in the internalcombustion engine by effecting fuel injection discontinuously during an injection phase.

According to the present invention there is provided a fuel-injection system for internalcombustion engines with a fuel feed line from which fuel is supplied to an injection nozzle during an injection phase, wherein the fuel feed line constitutes the main flow input of a logistor and pressure changes imposed from outside in the input or in a control input of the logistor generate an intermittent flow of fuel through the logistor due to its being opened and closed several times during an injection phase.

In the fuel-injection system designed according to the invention, the intermittent flow of fuel through the logistor brings about a discontinuous injection of the fuel into the combustion chamber of the internal-combustion engine. The intermittent injections of fuel during each cycle which are thereby obtained result in a very fine distribution of the injected fuel, thus ensuring a smooth combustion which can be clearly defined.

The opening times of the logistor may have different lengths, during an injection phase due to pressure changes of different levels and/or periods of time, which enables the individual partial injected quantities to be varied during an injection phase and, consequently, enables the progress in time of the injected quantity to be adapted to the requirements of optimum combustion. For example, in this way, preliminary and main injections which are separated in time and have precisely fixed injected quantities can be achieved with simple means.

One advantageous and simple way of imposing pressure may be provided if the control input is connected to a return line which can be closed by means of a control element the control element opening and closing the connection between the control input and the return line several times during an injection phase. Operating parameters of the internal-combustion engine, such as load and speed or air pressure and air temperature, can be supplied electrically, in a simple way, to the control member actuating the control element.

Preferred embodiments of the fuel-injection system have a mechanical/hydraulic form of imposing pressure which can be varied continuously, so that the advantages arises that the logistor, with its very high possible vibration frequency, is the only vibrating system in the injection system.

One such embodiment includes a reservoir which is connected to the main input of the logistor and in which a pressure which varies with time and lies above the pressure in the fuel feed line can be generated during the injection phase.

In this case, the system may also include a restrictor and a non-return valve opening towards the logistor in the fuel feed line between the connecting points of the reservoir and of the control input.

In another embodiment, a second logistor, is connected in the open position, to the input of the first logistor, and the output and control input of which are connected to a reservoir in which a pressure which varies with time and lies below the pressure in the fuel feed line can be generated during the injection phase.

The embodiments incorporating a reservoir may include a piston which is adapted to vary the volume of the reservoir and which in operation, is driven by a cam. The cam may be a threedimensional cam which is adapted to be adjusted in dependence on the load of the internal combustion engine. A regulating element may be located in the fluid connection between the reservoir and the logistor this regulating element changing the level of the imposed pressure in dependence on the load of the internalcombustion engine.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 shows a diagrammatic representation of an internal-combustion engine with a fuelinjection system having an eiectro-hydraulic imposition of pressure, Figure 2 shows on a larger scale, a part of the injection system of Figure 1, and Figures 3 and 4 show parts of injection systems with mechanical/hydraulic imposition of pressure.

Referring now to Figure 1 the internalcombustion engine depicted schematically is designated by reference 1. Fuel is supplied to it from a tank 2 via an injection pump 3, a reservoir 4 and injection nozzles 5. As illustrated in more detail in Figure 2, integrated into each of the injection nozzles 5 is a logistor which can, however, also be separated in space from the associated injection nozzle. The individual logistors and, consequently, the course of the injection process are controlled by an electronic unit 6 which can also contain a VCO part (voltage controlled oscillator) for generating an electrical square-wave signal, the frequency of which is dependent on the electrical input control.The input parameters for the electronic unit 6, are in particular, the speed of the internal-combustion engine 1 which is detected via a sensor 7, the position of the accelerator pedal 8, the air pressure (sensor 9), the ambient air temperature (sensor 10) and/or a preselected roadspeed (lever 11).

The injection nozzle 5 illustrated in Figure 2, with integrated logistor, contains an outwardly opening injection valve 12 whose basic mode of operation is known. When the pressure exceeds a given value in the nozzle chamber 13 located in front of the injection valve 12, the injection valve 12 opens and fuel is injected into the combustion chamber (not shown in more detail) of the internal combustion engine. The nozzle chamber 13, is, at the same time, the logistor output which can be closed by means of the logistor ball 14.

A fuel feed line 1 6 from the reservoir 4 (Figure 1) opens into the input 1 5 of the logistor.

The input 1 5 is connected to a control input 19 of the logistor via a by-pass 1 8 which is provided with a restrictor 1 7. Connected to the control input 19 is a return line 20 which can be closed by means of a spherical control element 21. This is actuated by an electromagnetic control member 22. The control member 22 contains an electromagnet 23 to which the electrical squarewave signals generated in the electronic unit 6 are supplied via electrical leads 24.

When the internal-combustion engine 1 is in operation, fuel is supplied, via the fuel feed line 16, to the injection nozzle 5 at a constant pressure. With the control element 21 closed, the logistor ball 14 closes the nozzle chamber 13, and no fuel is injected. When the control member 22 is excited by an electrical square-wave signal, the electromagnet 23 attracts a control slide 24a, the control element 21 opens the connection between the return line 20 and the control input 19, and the pressure drops so far in the latter that the pressure prevailing in the input 1 5 can lift the logistor ball 14. Fuel now flows from the input 1 5 into the nozzle chamber 13, the injection valve 12 opens and fuel is injected.If the control member 22 receives an electrical zero signal from the electronic unit 6, the control element 21 closes, the pressure prevailing in the fuel feed line 1 6 builds up in the control input 1 9 via the by-pass 1 8 and the logistor ball 14 closes the nozzle chamber 13. Injection is interrupted. The length of the individual partial injections and, consequently, the partial injected quantities can therefore be controlled precisely from outside and can be adapted in an optimum way to the requirements of good combustion.

In the injection system illustrated in Figure 3, fuel is supplied to the input 1 5 of a logistor 25 via a fuel feed line 1 6. A restrictor 26 and a non return valve 27 which opens towards the logistor 25 are located in the fuel feed line 1 6 shortly upstream of the logistor 25. Furthermore, the fuel feed line 1 6 is connected, upstream of the restrictor 26 and the non-return valve 27, to the control input 1 9 of the logistor 25 via a by-pass 18. In a similar way to that shown in Figure 2, the output 28 leads to the injection valve, not shown here.

The input 1 5 is connected via a line 29 to a reservoir 30 which is shut off by a piston 32 loaded by a spring 31. The piston 32 can be moved in the reservoir 30 by means of the cam 33 of a cam-shaft which rotates at half the speed of the internal-combustion engine, and this piston determines the volume of the reservoir 30 in dependence on the position of the cam 33.

In the initial position, with the output 28 of the logistor 25 being closed by the logistor ball 14, the same pressure prevails in the input 5, in the control input 19 and in the reservoir 30 as in the fuel feed line 1 6. If the piston 32 is pushed into the reservoir 30 by the cam projection 34, fuel is forced out of said reservoir into the input 1 5, the pressure rise which occurs here as a result lifts the 1 logistor ball 14 and fuel flows via the output 28 to the injection valve. Consequently, with a constant pressure in the control input 19, the pressure in the input 1 5 drops and the logistor ball 14 again closes the output 28 and fuel injection is interrupted. This cycle is repeated several times, as long as the piston 32 is pushed into the reservoir 30 by the leading edge of the cam projection 34.Subsequently, fuel is drawn into the reservoir 30 by means of the piston 32, via the non-return valve 26 and the restrictor 27, until the initial position is reached again.

The number of partial injections per injection phase and the individual partial injected quantities can be fixed precisely by means of the adjustment between the piston 32 and the logistor 25 and, in particular, by the path of the leading edge of the cam projection 34. The influence of the load and of other operational parameters of the internalcombustion engine can be taken into account by means of a regulating element 35, which is fitted in the line 29 and which varies the excess pressure in the input 1 5 in accordance with these operating parameters. However, it is also possible to design the cam 33 as a three-dimensional cam, so that leading edges of the cam projection 34, which are of varying shape in dependence on the operating parameters of the internal-combustion engine, engage on the piston 32.

In the injection system illustrated in Figure 4, the fuel feed line 1 6 is connected to the input 36 of a second, pilot logistor 37 and via the latter to the input 1 5 of a first logistor 25 (corresponding to logistors described in the previous embodiments) whose output 28 leads to the injection valve. The output 38 and the control input 39 of the pilot logistor 37 and the control input 1 9 of the first logistor 25 are connected to one another and to a reservoir 30 which, in the same manner as the embodiment of Figure 3, is shut off by a spring-loaded piston 32. The piston 32 can be moved in the reservoir 30 by means of a cam 33, with a cam depression 40, of a camshaft which rotates at half the speed of the internal-combustion engine.

In the initial position, the same pressure prevails in the two logistors 25 and 37 and in the reservoir 30 as in the fuel feed line 1 6. When the leading edge of the cam depression 40 reaches the piston engagement point 41 on the cam 33, the piston 32 is moved by the spring 31 and the volume of the reservoir 30 is enlarged. As a result fuel is drawn into the reservoir 30, the pressure in the control input 1 9 of the logistor 25 diminishes, the logistor ball 14 opens the output 28 and fuel is injected. Simultaneously, the pressure in the control input 39 of the pilot logistor 37 also diminishes, so that the logistor ball 42 of the latter opens the output 38 and fuel flows from the fuel feed line 16 into the reservoir 30 and to the two control inputs 1 9 and 39.The two logistor balls 14 and 42 then close the outputs 28 and 38 again. This cycle is repeated several times, as long as the piston engagement point 41 lies on the cam depression 40, the number and lengths of the individual partial injections being determined by the shape of the profile of the cam depression 40 and the adjustment between the two logistors 25 and 37 and the piston 32.

Furthermore, a third logistor 43 is provided, and input 44 of which is connected to the reservoir 30 and the output 45 of which is connected to a fuel return line 46. Via this logistor 43, fuel can be conveyed out of the reservoir 30 when the piston 32 is pushed into the reservoir 30, as long as the piston engagement point 41 slides along the trailing edge of the cam depression 40.

As in the embodiment according to Figure 3, the influence of the operating parameters of the internal-combustion engine can be taken into account by means of a regulating element 35 in the line 47 to the reservoir 30 or by designing the cam 33 as a three-dimensional cam.

Claims

1. A fuel-injection system for internalcombustion engines with a fuel feed line from which fuel is supplied to an injection nozzle during an injection phase, wherein the fuel feed line constitutes the main flow input of a logistor and pressure changes imposed from outside in the main input or in a control input of the logistor generate an intermittent flow of fuel through the logistor due to its being opened and closed several times during an injection phase.

2. A system according to claim 1 , wherein the opening times of the logistor have different lengths, during an injection, phase, due to pressure changes of different levels and/or periods of time.

3. A system according to claim 1 or 2, wherein the control input is connected to a return line which can be closed by means of a control element, the control element opening and closing the connection between the control input and the return line several times during an injection phase.

4. A system according to claim 3, wherein an electromagnetic control member which is dependent on at least one operating parameter of the internal-combustion engine actuates the control element.

5. A system according to claim 1 or 2, including a reservoir which is connected to the main input of the logistor and in which a pressure which varies with time and lies above the pressure in the fuel feed line can be generated during the injection phase.

6. A system according to claim 5, further including a restrictor and a non-return valve opening towards the iogistor in the fuel feed line between the connecting points of the reservoir and of the control input.

7. A system according to claim 1 or 2, wherein a second logistor is connected, in the open position, to the input of the first logistor, and the output and control input of which are connected to a reservoir in which a pressure which varies with time and lies below the pressure in the fuel feed line can be generated during the injection phase.

8. A system according to claim 5, 6 or 7, including a piston which is adapted to vary the volume of the reservoir and which is driven, in operation, by a cam.

9. A system according to claim 8, wherein the cam is a three-dimensional cam, which is adapted to be adjusted in dependence on the load of the internal-combustion engine.

10. A system according to any one of claims 5 to 8, wherein a regulating element is located in the fluid connection between the reservoir and the logistor, this regulating element changing the level of the imposed pressure in dependence on the load of the internal-combustion engine.

11. A fuel injection system for internalcombustion engines substantially as described herein with reference to and as illustrated in Figures 1 and 2 or Figures 1 and 2 as modified by Figures 3 and 4 of the accompanying drawings.