GB2090329A

GB2090329A - I.C. engine fuel pump maximum delivery control

Info

Publication number: GB2090329A
Application number: GB8134999A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1980-12-31
Filing date: 1981-11-20
Publication date: 1982-07-07
Also published as: GB2090329B

Abstract

The maximum permitted delivery of a fuel pump 13 is reduced when the temperature of the combustion chamber or the exhaust manifold is below the normal operating temperature, the maximum permitted delivery increasing with increasing temperature. The signal from a temperature sensor 18 is fed to an electronic control circuit 15 operating the pump actuator 14 dependent upon operator demand, engine speed and air intake pressure. Exhaust gas recirculation, injection timing and spark ignition timing may be adjusted in response to the fuel supply limitation. The circuit 15 may include idling speed and maximum engine speed governing components. <IMAGE>

Description

SPECIFICATION Internal combustion engines This invention relates to internal combustion engines of the kind comprising a combustion chamber in which fuel is burned, a piston against which the fluid pressure created by the combustion of the fuel can act, and a fuel system for supplying fuel to the engine.

Engines produced at the present time have fuel systems which are designed to ensure that the exhaust of the engine contains no more than the allowed levels of noxious substances. In steady state conditions the engine operating parameters are stable however, when the engine operating conditions change the operating parameters in particular the combustion chamber temperature, alter. If the fuel system anticipates the final operating parameters then during the period when the parameters are changing the engine will operate in an unsatisfactory manner.

The problem outlined is particularly important when the power demand on the engine is increased after the engine has been operating for a period of time at low power. When the engine is operating a low power the energy input to the engine is relatively low and the operating temperature of the engine in particular of the combustion chamber, is also low. If the power demand on the engine is suddenly increased and large quantities of fuel are suddenly supplied to the combustion chamber the combustion process operates at low efficiency and excessive smoke is produced this gradually diminishing as the new operating temperature is attained.

The object of the invention is to provide an engine of the kind specified in a simple and improved form.

According to the invention an engine of the kind specified includes a sensor mounted on the engine to provide a signal representative of the temperature of the combustion chamber, the fuel system including means responsive to said signal and arranged so that a limit is imposed on the maximum amount of fuel, said limit varying as the temperature of the combustion chamber changes.

According to a further feature of the invention the ignition timing in the case of a spark-ignition engine is responsive to said signal as also is the timing of delivery of fuel in the case of a compression ignition engine.

According to a still further feature of the invention said signal is utilized to effect a control of an exhaust gas recirculation system forming part of the engine.

An example of an engine in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a block diagram of the engine and fuel system; and Figure 2 is a block diagram of part of the system shown in Figure 1.

In the drawings an engine cylinder is shown at 10 together with a piston 11. Fuel is supplied in timed relationship to the combustion chamber defined by the cylinder, by a fuel injection nozzle 1 2. Fuel is supplied to the nozzle by means of Q fuel pump 13 and the amount of fuel is determined by an actuator 14 which controls the setting of the quantity control member of the pump.

The actuator 1 4 is of the electromagnetic type and power is supplied to it by a control circuit 1 5 which performs an engine governing function. For this purpose the circuit is supplied with an engine speed signal from a sensor 1 6 associated with the engine and in addition, is supplied with a demand signal supplied to a transducer 17 forming part of the throttle control of the vehicle driven by the engine. The circuit 1 5 in response to a change in the demand signal alters the amount of fuel which is supplied to the engine.In conventional systems of this type if the demand is increased and the circuit is operating in the manner of an "all-speed" governor, the amount of fuel supplied is increased to a maximum value which is dependent upon the engine speed and in some cases the pressure of air supplied to the combustion chamber. With an increased flow of fuel to the engine more power is produced and the engine speed will increase.

As previously explained if the quantity of fuel supplied is suddenly increased then poor combustion of fuel can occur in the combustion chamber because the temperature of the combustion chamber is too low. As the combustion chamber temperature increases the combustion efficiency will be restored. In order to minimise the period of poor combustion a sensor 18 is provided which senses the temperature of the combustion chamber and this provides a signal which is supplied to an additional circuit 1 9 which in turn provides a control signal to the circuit 1 5. The signal provided by the circuit 1 9 acts to limit the actual increase of fuel supplied to the engine, the fuel supplied to the engine being allowed to increase to the aforesaid maximum value as the combustion chamber temperature increases.In this manner the combustion efficiency will be maintained at an acceptable level. In a practical situation the rate of increase of fuel cannot be made too low since this would reduce the rate of increase of power from the engine.

It may also be desirable to control the timing of delivery of fuel to the engine so that it changes more slowly than in the case of the conventional system, although in most cases the timing control will be responsive to the amount of fuel which is being supplied to the engine and hence the variation of engine timing will take place automatically. The timing can however be separately adjusted if required.

The signal provided by the circuit 1 9 can also be used to effect a further control over the amount of exhaust gas recirculation which takes place in an engine which incorporates this feature. As with the timing variation the amount of exhaust gas recirculated in an engine will normally be responsive to the amount of fuel being supplied to the engine and hence the variation will take place automatically.

As described the engine is a direct injection engine that is to say the fuel is delivered directly into the engine cylinder. The concept is equally applicable to an engine of the so-called indirect injection type in which the fuel is delivered into a combustion chamber which is connected to the engine cylinder through a small passage. In this case the sensor is mounted in the wall of the combustion chamber and may for example be incorporated in a heater plug secured in the wall of the combustion chamber.

The concept can also be applied where the circuit 1 5 is operating in the manner of a "twospeed" governor. In this case the control of the amount of fuel supplied to the engine in the intermediate speed range i.e. between idling and maximum speed, is effected by the operator of the engine.

An example of the control circuit 1 5 which operates as a two speed governor is shown in Figure 2 and with reference to Figure 2 the circuit includes a lowest wins circuit 20 the output of which constitutes the fuel demand signal and is applied to the actuator 14. The circuit 20 has three inputs the lowest of which is selected by the circuit for supply as the fuel demand signal.

One input of the circuit 20 is connected to the output of a high gain amplifier 21 provided with feedback. One input of the amplifier is provided with a reference signal representative of the maximum allowed engine speed whilst the other input is supplied with the actual engine speed signal from the transducer 16 by way of a decoding circuit 22.

The second input of the circuit 20 is connected to a circuit 23 which also receives the speed signal and provides a signal representing the maximum fuel signal throughout the speed range of the engine.

The third input of the circuit 20 is connected to the output of a high wins circuit 24 which has two inputs. The first input is connected to the output of a high gain amplifier 25 provided with feedback and having two inputs one of which receives a reference signal representing the desired engine idling speed and the other of which receives the engine speed signal. The second input of the circuit 24 is connected to the output of a shaping circuit 26 which receives the engine speed signal and also a signal from a decoding circuit 27 which in turn receives a signal from the transducer 1 7.

In operation at engine idling speeds the amplifier 25 is operative to determine the demanded fuel signal at the output of the circuit 20 since with no demand on the part of the operator, the output from the amplifier will be larger than the output from the shaping circuit 26 but smaller than the output of the circuit 23 and the amplifier 21. When the operator places a demand on the engine by depressing the throttle pedal, the output of the shaping circuit becomes higher than the output of the amplifier. If only a small demand is made then the signal from the circuit 24 will still be lower than those provided by the circuit 23 and the amplifier 21. Hence the driver will control directly the amount of fuel supplied to the engine and with an increased flow of fuel the engine will accelerate.If the operator makes a large demand on the engine then it is likely that the output of the circuit 24 will be greater than the output of the circuit 23 in which case the rate of fuel supply will be controlled by the circuit 23 until the output of the circuit 24 becomes smaller thereby restoring the control of the fuel supply to the operator. If the maximum allowed engine speed is attained then the output of the amplifier 21 becomes less and the fuel supply to the engine will be reduced to control the speed of the engine. The shaping circuit 26 is arranged to modify the apparent demanded fuel in accordance with increases in the engine speed to provide feedback to the operator of the engine.

Furthermore, the idling speed may be modified in accordance with variation in low fuel demand on the part of the operator. This provides a smooth transition from the control by the amplifier 25 to the control by the circuit 26 and eliminates "lost motion" in the operator adjustable control.

The signal provided by the circuit 1 9 can be used to control the rate of increase of fuel in the intermediate speed range by applying the signal to the circuit 23 so that if for example the demand is suddenly increased to the maximum, the actual amount of fuel delivered to the engine will gradually increase to the maximum value.

The invention may also be applied to a spark ignition engine and in this case the ignition timing can also be varied.

As described the sensor 1 7 is mounted in the wall of the combustion chamber. it may however be located at some other position for example, the exhaust manifold providing the signal which it provides is representative of the temperature of the combustion chamber.

Claims

1. An internal combustion engine comprising a combustion chamber in which fuel is burned, a piston against which the fluid pressure created by the combustion of fuel can act, a fuel system for supplying fuel to the engine, a sensor mounted on the engine to provide a signal representative of the temperature of the combustion chamber, the fuel system including means responsive to said signal and arranged so that a limit is imposed on the maximum amount of fuel, said limit varying as the temperature of the combustion chamber alters.

2. An engine according to Claim 1 in which said fuel system includes a fuel pump operable in timed relationship with the engine, an electronic control system including circuit means for controlling the maximum amount of fuel which can be supplied to the engine and an electromagnetic actuator operable to determine the setting of fuel control member of the pump, the supply of current to said actuator being controlled by said electronic control system.

3. An engine according to Claim 1 in which the ignition timing in the case of a spark ignition engine is responsive to said signal as also is the timing of delivery of fuel in the case of a compression ignition engine.

4. An engine according to Claim 1 in which said signal is utilized to control an exhaust gas recirculation system of the engine.

5. An internal combustion engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying diagrams.