GB2136884A

GB2136884A - Fuel-injection device for an internal-combustion engine

Info

Publication number: GB2136884A
Application number: GB08404724A
Authority: GB
Inventors: Wilfried Hofken
Original assignee: LOrange GmbH
Current assignee: LOrange GmbH
Priority date: 1983-03-19
Filing date: 1984-02-23
Publication date: 1984-09-26
Also published as: FR2542815A1; GB2136884B; DE3310030A1; GB8404724D0; DE3310030C2; JPS59176463A; FR2542815B1

Abstract

A fuel-injection device for an internal-combustion engine comprises a pump (6, 7), an accumulator (11, 48) and a solenoid valve (16) in a fuel- injection line (17, 22) leading to an injection nozzle (19). The solenoid valve (16) is operated by a control device (31), such that while the valve is closed the pump (6, 7) pressurises fuel in a pump chamber (8) and thereby adjusts a pressure- loaded plunger (12), of the accumulator (11) whereas when the valve is opened fuel is delivered by the plunger (12) to the injection nozzle (19). The delivery stroke of the plunger (12) is detected by a measuring device (30) and the output signal of this measuring device (30) is conducted to the control device (31). The solenoid valve (16) is closed by a switching signal of the control device (31) when a required delivery stroke is reached. Thus the volume of the fuel injected can be exactly metered at any time. <IMAGE>

Description

SPECIFICATION Fuel injection device for an internal-combustion engine This invention relates to a fuel-injection device for an internal-combustion engine in which the injection is effected by the discharge of an accumulator controlled by the opening or closing of a solenoid valve.

By comparison with conventional injection systems comprising an injection pump with spill port metering, solenoid controlled accumulator systems have the advantage that the injection pressure is substantially constant even with changing rotational speed and that the injection start is variable within wide limits in dependence on the rotational speed. In known systems, for the generation of high injection pressures, expensive hydraulic accumulators are needed which have to be fed by a pressure generator, which is also expensive, namely a high-pressure pump.

Furthermore, in systems of this kind it is also disadvantageous that, upon changes of the flow resistance for example on the nozzle openings, the quantity of injected fuel varies and thus the internal-combustion engine is not operated under optimal conditions.

The present invention seeks to provide an improved and simplified fuel-injection device of the type which includes an accumulator.

According to the invention there is provided a fuel-injection device for an internal-combustion engine comprising a pump, an accumulator and a solenoid valve in a fuel-injection line leading to an injection nozzle, which solenoid valve is operated by a control device, wherein the pump delivers fuel into a pump chamber and thereby adjusts a pressure-loaded plunger, which, when the pump has stopped the delivery of fuel, delivers the fuel via the open solenoid valve to an injection nozzle, characterised in that the delivery stroke of the plunger is detected by a measuring device, in that the signal of this measuring device is conducted to the control device and that the solenoid valve is closed by a switching signal of the control device, when a required delivery stroke is reached.

The invention is thereby based on the idea that by a control of the opening time of the injection valve in dependence on the delivery stroke of a pressure-loaded plunger the volume of the fuel injected each time can be exactly metered.

The plunger of the accumulator could be loaded by the pressure of a spring, however in order to generate high injection pressures of more than 1000 bar a relatively big steei spring would have to be used. Moreover, a steel spring of this kind would have the disadvantage that the discharge of the accumulator would be too slow. According to an advantageous development of the invention the plunger is therefore loaded by a volume of pressurised fluid e.g. a liquid subject to a given pressure. Thus the elasticity of a volume of liquid is used for the discharge. In order to support the pressure loading of the plunger a fluid spring accumulator e.g. a gas spring accumulator can be used, particularly when the volume of the working substance is relatively small.

In a particularly advantageous embodiment of the invention the plunger is formed as a differential plunger whereby the area of the pressure plunger limiting the pump chamber is smaller than the area of the accumulator plunger loaded by the pressure of the volume of liquid or by the gas spring accumulator. Thus the high necessary injection pressure can be realised by means of a relatively small cpunterpressure and a pressure generator of a relatively small effect is sufficient, because only the leakage losses of this working substance have to be balanced.

According to a further refinement of the invention in a multi-cylinder engine a common highpressure delivery line is provided for all plungers assigned to the various cylinders. In such an arrangement, a large volume of working substance and thus an advantageous flat spring characteristic is created without considerable extra expense.

As a result of the invention an injection system has been created in which a high, constant injection pressure can be realised with simple means and in which the injection may be controlled with regard to injection start and quantity of fuel injected with sufficient accuracy.

In order that the invention and its various other preferred features may be understood more easily, two embodiments thereof will now be described, by way of example only, with reference to the drawings, in which: Figure 1 is a diagrammatic view of an injection device constructed in accordance with the invention and Figure 2 is a diagrammatic view of an injection arrangement in accordance with the invention for a multi-cylinder engine.

Referring now to Fig. 1, a cam 1 of a camshaft moves a plunger 6 of a pump via a roller 2 and a tappet 3 upon which a spring 4 acts. This plunger is lapped in a guide body 7 indicated by hatching and limits the pump chamber 8. The plunger 6 is equipped with a suction valve 9, via which the fuel flows into a pump chamber 8 from a fuel supply line 10 during a suction stroke of the plunger 6.

An accumulator has a differential plunger 11 comprising an accumulator plunger 1 3 and a pressure plunger 12. The plunger area of the pressure plunger 12 limits the pump chamber 8.

The accumulator plunger 1 3 is loaded by a volume of fluid e.g. a liquid or gas subject to a given pressure in a high-pressure delivery line 14. The plunger area of this accumulator plunger 13 is larger than the plunger area of the pressure plunger 12.

During a suction stroke of the pump plunger 6., fuel flows into the pump chamber 8. During the following delivery stroke of the plunger 6 the pressure plunger 1 2 and the differential plunger 11 respectively are adjusted by the fuel contained in the pump chamber 8. The cam 1 is formed in a way that its radius, which determines the maximal delivery stroke, is constant in a sector of angle a. Consequently the plunger 6 is stationary after termination of the delivery stroke, while cam 1 continues to turn through the angle a. During this period of time the liquid contained in the pump chamber 8 is subject to the pressure.

plunger area of the accumulator plunger 1 3 P1 = P2 x plunger area of the pressure plunger 12 whereby P2 is the pressure in the high-pressure delivery line 14. It can be seen that, when a differential plunger is used, the pressure in the pump chamber 8 can be much higher than the pressure in the high-pressure delivery line 14 and is held constant at this value as long as the plunger 6 is at rest, whilst the cam 1 turns through the angle a.

From the pump chamber 8 extends a fuel-injection line which first comprises a pressure channel 17 controllable by a solenoid valve 16. When the solenoid valve 16 is open the fuel subject to high pressure flows out of the pump chamber 8 passing a valve cone 18 8 into a line 22 and to an injection valve 19 comprising an injection nozzle (not designated). When the solenoid valve is closed, that means when the pressure channel 1 7 is closed, the fuel in -the line 22 is relieved via a return line 23 and a constant-pressure valve 24. The constant-pressure valve 24 is adjusted to a particular opening pressure which is chosen such that the pressure between two injections does not decrease too much in the return line 23.Furthermore a line 26 is branched off the line 22 to a safety valve 27, which prevents an inadmissable increase of pressure in the pump chamber 8, for example when the solenoid valve fails or when the differential plunger 11 seizes. Moreover several lines for the return of surplus fuel to a fuel reservoir are to be seen, from which reservoir the fuel is supplied into the fuel-inlet line 10 via a pre-supply pump MV.

A measuring device 30 with an electrically operated displacement sensor is included in the electric part of the injection device. The signal of this sensor is conducted to a control device 31 via a measured-value amplifier 32. This control device 31 provides switching signals for the control of the solenoid valve 16, which switching signals are conducted to the solenoid valve via a power amplifier 33. To the control device 31, further input signals are conducted in a known manner, for example the signal of an accelerator pedal 34 for adjustment of the engine power and, via a lead 35, the signal of a rotational-speed sensor coupled with the camshaft and not shown in detail. The control device computes the injection start from these input signals and with a particular angular positionof the cam shaft releases a switching signal for opening the solenoid valve 16.Furthermore the control device 31 compares the delivery stroke of the differential plunger 11 indicated by the measuring device 30 with a given value and provides a switching signal for closing the solenoid valve 16, when a given delivery stroke is reached. In this manner it is ensured that the fuel delivery exactly meets the optimal value in all conditions of engine load.

The sector of angle a having constant radius of cam 1 is chosen in such a way that during normal operating conditions the plunger 6 is at rest until injection is terminated. When the turning of the cam is continued the suction stroke of the pump begins again, because the plunger 6 is moved downwards by the force of the spring 4. The differential plunger 11 follows this downward movement until the accumulator plunger 1 3 abuts a stop 25. In the further downward movement of the plunger 6 the suction valve 9 opens and a new fuel flows into the pump chamber 8. Thereafter the injection described above is repeated.

Fig. 1 shows that the high-pressure delivery line 14 is protected by an accumulator safety valve 40. Leakage losses which can occur on the differential plunger 11 are balanced by a small pump 29 aggregate MA, so that the pressure in this high-pressure delivery line 14 is constantly held at a given value. Accordingly a fluid spring accumulator 48 e.g. a gas pressure accumulator is disclosed which is needed, when the volume of fluid contained in the highpressure delivery line 14 is relatively small and thus of insufficient volume to provide required spring properties. The spring properties in these circumstances are substantially realised by the fluid spring accumulator 48. The pressure in the high-pressure delivery line 14 can be adjusted to different values, so that also different, but constant injection pressures can be used. The fluid contained in the high-pressure delivery line 14 can advantageously be fuel.

Fig. 2 shows a diagrammatic view of an injection device for an internal-comnustion engine with n cylinders. In this case to each of these cylinders a differential plunger 11 is assigned. All of these differential plungers are loaded by the pressure of a fluid in a common high-pressure delivery line 14. In this way the technique becomes less complicated in comparison with known systems, because an operative accumulator is not needed for each cylinder. The high-pressure delivery line 14 which all the differential plungers have in common is filled by a single pump aggregate MA. Because in this embodiment the volume of fluid in the high-pressure delivery line 14 is relatively big, the additional fluid spring accumulator 48 can be omitted under certain circumstances, when the volume of liquid already has the necessary spring properties.In such circumstances the delivery line 14 itself constitutes a fluid spring.

Further advantageous features and developments of the fuel-injection device shown in the drawing are as follows: The supply pump is driven via a cam 1, on which the roller 2 supports. Because short supply times are not necessary in an injection system comprising an accumulator, the surface pressure between cam and roller and thus also the wear is relatively small. Due to the use of a suctionvalve pump whose suction valve is arranged in the pump plunger, no spill ports are necessary in the area of the plunger guide, where the high pressures come into existence.

On the whole this fuel-injection device has the advantages of a long service life and a simple manufacture. In particular the injection start is adjustable within wide limits and also with a high, constant injection pressure of more than 1000 bar the injection quantity is exactly adapted to required operational conditions.

Finally it is pointed out that the electronic control device 31 of multi-cylinder engines can be developed in such a way that it compares the strokes of the differential plungers 11 and, when these strokes deviate from one another, the respective solenoid valve or the valves are controlled in time in a way that all differential plungers carry out the same stroke. This results in an injection of the same volume into all cylinders.

Claims

1. A fuel-injection device for an internal-combustion engine comprising a pump, an accumulator and a solenoid valve in a fuel-injection line leading to an injection nozzle, which solenoid valve is operated by a control device, wherein the pump delivers fuel into a pump chamber and thereby adjusts a pressure-loaded plunger, which, when the pump has stopped the delivery of fuel, delivers the fuel via the open soleniod valve to an injection nozzle, characterised in that the delivery stroke of the plunger (12) is detected by a measuring device (30), in that the signal of this measuring device (30) is conducted to the control device (31) and that the solenoid valve (16) is closed by a switching signal of the control device (31), when a required delivery stroke is reached.

2. A fuel-injection device for an internal-combustion engine as claimed in claim 1, characterised in that the pressure plunger (12) is loaded by a volume of pressurised fluid.

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3. A fuel-injection device as claimed in claim 2, characterised in that the pressurised fluid is fuel.

4. A fuel-injection device for an internal-combustion engine as claimed in any one of the preceding claims characterised in that the pressure acting upon the plunger (12) is provided by a fluid spring accumulator (48).

5. A fuel-injection device for an internal-combustion engine as claimed in claim 2, 3 or 4, characterised in that the pressure plunger (1 2) together with an accumulator plunger (1 3) forms a differential plunger (11), whereby the area of the pressure plunger (12) limiting the pump chamber (8) is smaller than the area of the accumulator plunger (13) loaded by the pressure of the volume of liquid or by the gas spring accumulator (48).

6. A fuel-injection device for an internal-combustion engine as claimed in any one of the preceding claims characterised in that the pressure loading the accumulator plunger (13) is adjustable.

7. A fuel-injection device for an internal-combustion engine as claimed in any one of the preceding claims, characterised in that in an internal-combustion engine with several cylinders (a, b...n) a common high-pressure delivery line (14) receiving the liquid is provided for all accumulator plungers (13) assigned to the various cylinders.

8. A fuel-injection device for an internal-combustion engine as claimed in any one of claims 2 to 7, characterised in that leakage losses of the liquid loading the accumulator plunger (13) are balanced by a pressure generator (MA).

9. A fuel-injection device for an internal-combustion engine as claimed in any one of the preceding claims, characterised in that the pump delivering fuel into the pump chamber (8) is a suction valve pump comprising a suction valve (9) in the pump plunger (6).

10. A fuel-injection device for an internal-combustion engine as claimed in any one of the preceding claims, characterised in that the pump plunger (6) is driven via a cam (1) and that the radius of the cam (1) determining the maximal delivery stroke of the plunger (6) is constant during the injection in a given sector of dial (a).

11. A fuel-injection device as claimed in any one of the preceding claims, characterised in that in an internal-combustion engine with several cylinders (a, b...n) the delivery strokes of the various differential plungers (11) are compared and by a control of the various solenoid valves (16) in dependence thereon the same volume of fuel is injected into all cylinders.

1 2. A fuel injection device for an internal-combustion engine substantially as described herein with reference to the drawings.