GB2119133A

GB2119133A - Fuel pumping apparatus

Info

Publication number: GB2119133A
Application number: GB08306304A
Authority: GB
Inventors: Colin Peter Brotherston; Ian Roy Thorhthwaite; Kevin John Mooney
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1982-04-17
Filing date: 1983-03-08
Publication date: 1983-11-09
Also published as: GB2119133B; GB8306304D0

Abstract

A fuel pumping apparatus for supplying fuel to an internal combustion engine includes a fuel pump 10 including a component 11 movable to vary the amount of fuel supplied by the pump. The pressure applied to the component is varied by an electromagnetic valve 19 which is controlled by an electronic control circuit 26 in response to various desired and actual operating parameters. In the event of a fault in the circuit 26a valve 21 is closed and a mechanical valve means 27 takes over to control the pressure. The timing piston 40 normally controlled by solenoid valve 42A is similarly controlled in the event of a fault. <IMAGE>

Description

SPECIFICATION Fuel pumping apparatus This invention relates to a fuel pumping apparatus for supplying fuel to an internal combustion engine, the apparatus comprising a high pressure pump which in use delivers fuel at high pressure to injection nozzles respectively of the associated engine, a low pressure pump for supplying fuel to the high pressure pump, the high pressure pump including a component responsive to a varying fluid pressure to determine the quantity of fuel supplied by the high pressure pump to the engine in use, a first electromagnetically operable valve for varying said fluid pressure and an electronic control system for controlling the electric current flow in said valve in response to various input signals.

One form of such an apparatus is described in British Published Application 2037365A although there is no description of the electronic control system. Various forms of electronic control system are known in the pumping apparatus art and they have advantages over mechanical systems in that they can be designed to take into account many more engine operating parameters and as a result, are able to control the amount of fuel supplied to an engine much more closely than is the case with a mechanical system. In general modern electronic systems are very reliable even so, they can on occasions fail. With a mechanical system it might be possible to continue to run the engine but in general with an electronic system steps are taken to ensure that the engine is prevented from operating. It is therefore possible for a vehicle powered by the engine to be stranded.

The object of the present invention is to provide an apparatus of the kind specified in a form in which it is possible for continued operation of the engine in the event of failure of the electronic control system.

According to the invention in a fuel pumping apparatus of the kind specified the apparatus includes a second electromagnetically operable valve through which said first valve is connected to a source of fluid under pressure, said second valve when said control system is operative, being maintained in one position but reverting to another position upon failure of said control system, the apparatus further including mechanical valve means operable to determine the pressure applied to said component when said second valve is in said other position.

Two example of fuel pumping apparatus in accordance with the invention will now be described with reference to the accompanying drawings in which Figures 1 and 2 show diagrammatic representations of the hydraulic circuits of two exampies of the apparatus, and Figure 3 shows a block diagram of the electrical portion of the apparatus.

As shown in Figure 1 the apparatus includes a high pressure fuel injection pump which is generally indicated at 10 and which includes a component in the form of a rotary cylindrical distributor member 11, which has an end surface forming part of a chamber 12 to which can be supplied a varying fluid pressure. Axial movement of the distributor member 11 against the action of a coiled spring 13 will effect a reduction in the quantity of fuel supplied by the apparatus to an associated engine.

Also provided is a low pressure pump 14the output pressure of which is controlled by a valve 15.

The inlet of the pump 14 is connected to a reservoir 16 and the outlet of the pump is connected by way of an on/off valve 17 to an inlet port formed in the portion of the apparatus which supports the distributor member 11. A more comprehensive description of the portion of the apparatus so far described is contained in British Published Specification 2037365A but sufficient to say that as the pressure in the chamber 12 is increased, the distributor member 11 will move against the action of a spring to cause a reduction in the amount of fuel supplied to the associated engine. The valve 17 is an electromagnetically operated valve and the supply of current to the valve is controlled by a switch 18 which conveniently is the driver operable key switch of the associated vehicle.The switch 18 therefore will be closed when the driver requires to start the engine and maintain the engine in operation.

In order to control the pressure in the chamber 12 a first electromagnetically operable valve 19 is provided and this includes a valve member 20 slidable within a cylinder one end of which is connected by way of a second electromagnetically operable valve 21, to the outlet of a further low pressure pump 22. The output pressure of the low pressure pump 22 is controlled by a valve 23 so that it varies in accordance with the speed at which the apparatus is driven. If desired, the pumps 14 and 22 together with the valves 15 and 23 can be replaced by a single pump and valve assembly.

When the valve 21 is open the output pressure of the pump 22 will be applied to the valve member 20 which is so constructed that the valve member will tend to move to an open position. The valve member is moved towards the closed position by the force exerted by the solenoid forming part of the valve and by varying the current in the solenoid, so the pressure in the chamber 12 can be varied. A passage 24 connected to the chamber includes a restricted orifice 25, the orifice 25 together with the restriction offered by the valve 19, providing a fluid potentiometer. The passage 24 communicates with a drain conveniently the reservoir 16.

The flow of current in the valve 19 is controlled by an electronic control system which is indicated generally at 26 and which is described later in the specification. The control system includes a fail safe system whereby when the system 26 is functioning correctly, the valve 21 is maintained in the open position. In the event of failure of the control system however the valves 19 and 21 are de-energised. The valve member 20 moves to the open position and a coiled compression spring forming part of the valve 21, breaks the direct communication between the valve 19 and the outlet of the pump 22 and places in circuit a mechanical valve means generally indicated at 27.

The mechanical valve means when the valve 21 is closed, acts to control the pressure of fuel in the chamber 12. The valve means comprises a cylinder 28 having a closed end which is connected to the outlet of the pump 22. Slidable within the cylinder is a valve member 29 which is biased by a spring 30 towards the closed end of the cylinder. The end of the spring remote from the valve member is located in an adjustable abutment 31 the position of which is controlled by a cam 32 coupled to a lever 33. The lever 33 is mechanically coupled to the throttle control of the vehicle and also associated with the throttle control is a transducer which provides a signal to the control system 26. Formed in the wall of the cylinder 28 is a port the effective size of which is controlled by the valve member 29.The port is connected to a point intermediate the valve 19 and 21 and in operation, when the valve 21 is closed and the valve 19 is open, the pressure in the chamber 12 will depend upon the output pressure of the pump 22 and the setting of the lever 33. If the setting of the lever 33 is maintained constant, then as the engine speed increases so also will the output pressure in the chamber 12 increase. As a result of the increase in pressure in the chamber 12 the distributor member 11 will move to reduce the amount of fuel supplied to the engine. A speed governing effect is therefore obtained.If the lever 33 is moved to increase the force exerted by the spring 30 the port in the wall of the cylinder will have a reduced effective size and the pressure in the chamber 12 will decrease thereby allowing the distributor memberto move under the action of its spring 13 to increase the amount of fuel supplied to the engine.

The mechanical valve means also includes a maximum fuel valve which is generally indicated at 34 and which includes a cylinder 35 having a closed end which is connected to the port in the wall of the cylinder 28. The opposite end of the cylinder is closed by an adjustable screw 36 and this end of the cylinder is connected to a drain as also is the portion of the cylinder 28 which contains the spring 30.

Slidable within the cylinder 35 is a valve member 37 which is biased by means of a spring 38 the opposite end of which engages the screw 36. The valve 34 acts to control the minimum pressure in the chamber 12 and it does this by means of a circumferential groove on the valve member 37 which is in constant communication with the one end of the cylinder 35.

Formed in the wall of the cylinder 35 is a port 39 which is connected to the outlet of the pump 22. In operation, assuming that the valve member 29 has moved to fully cover the port in the wall of the cylinder 28, the pressure in the closed end of the cylinder 35 will fall to allow the groove to move into register with the port 39 thereby allowing fuel to flow into the closed end of the cylinder 35 and increase the pressure therein. The pressure in the closed end of the cylinder 35 is transmitted to the chamber 12 and by adjustment of the screw 36 it is possible to determine the minimum pressure in the chamber 12 and hence the maximum amount of fuel which can be supplied to the associated engine. The valve 34 also functions to allow an excess of fuel for starting purposes.At rest the valve member 37 moves to cover the port 39 and if the valve member 29 also covers the port in the wall of the cylinder 28, no pressure will exist in the chamber 12 until the valve member 29 is moved to again open the port in the cylinder 28. Pressure is then applied to the distributor member 11 and also the valve member 37 which can then function as described.

As is conventional practice, the high pressure pump 10 includes a cam ring the angular setting of which about the axis of rotation of the distributor member 11, can be controlled to vary the timing of delivery of fuel to the engine. The setting of the cam ring is controlled by a fluid pressure operable piston which is shown at 40, the piston being loaded by a spring 41. The end of the piston 40 remote from the spring, is connected by way of an anti-shock valve 42 to the outlet of the pump 22 and the pressure of the fuel in the chamber containing the spring 41 can be controlled in a manner similar to the control of the pressure in the chamber 12. For this purpose a further electromagnetically operable valve similar in construction to the valve 19 is provided and this is indicated at 42A.The outlet of the valve 42A is connected to the spring chamber and the latter is connected to a drain by way of a restrictor 43 so that the valve and the restriction form a fluid potentiometer. The flow of current in the solenoid of the valve 42A is controlled by the control system 26. In the event of failure of the control system the valve 21 closes and the valve 42A opens. In this situation the inlet of the valve 42A is connected to the outlet of the pump 22 by way of a restrictor 44.

The pessure in the chamber accommodating the spring 41 will due to the potentiometer effect of the restrictors 43 and 44, be less than the pressure directly applied to the piston from the outlet of the pump 22. The piston 40 will therefore tend to move to advance the timing of delivery of fuel as the output pressure of the pump 22 increases. The restrictor 43 may be replaced by a spring loaded valve 43A itself incorporating the restrictor. The valve modifies the timing characteristic which is obtained.

Turning now to the apparatus shown in Figure 2, like reference numerals are used whenever possible.

In this form of the apparatus the second electromagnetically operable valve referenced 46, has a different construction and the dispositions of the valve 19 and the valves 27 and 34are different. In the construction of Figure 1 the valve 19 is in series with the valves 27 and 34 with the valve 21 acting to by-pass the valves 27 and 34 for normal operation. In the construction of Figure 2 the valve 19 is in parallel with the valves 27 and 34 and the valve 46 has a changeover function.

The valve 46 includes a valve member 47 which is operatively connected to the armature of the associated electromagnetic device 48. The valve member is spring loaded towards one end of the cylinder in which it is located. The valve member has a central passage which communicates with the outlet of the pump 22 by way of a filter 49 and the passage communicates with a groove 49A on the valve member. In one position of the valve, when the eiectromagnetic device is energised and when the control system is functioning correctly, the groove 49A communicates with a pair of ports which lead to the valves 19 and 42A. These valves are therefore operative to control the pressures in the chamber 12 and the chamber containing the spring 41.

In the event of failure of the control system the valve member is moved by the spring to another position in which the aforesaid ports are closed but two further ports are brought into register with the groove 49A. One of these ports communicates with the valves 27 and 34 which therefore operate in the manner described to control the pressure in the chamber 12 and the other port communicates with the chamber containing the spring 41 by way of a restrictor 50 which corresponds to the restrictor 44 of Figure 1. The pressure in the chamber containing the spring 41 is therefore determined by the potentiometer effect of the restrictors 50 and 43.

The apparatus of Figure 2 includes additional restrictors 51 positioned upstream and downstream of the valve 19 and downstream of the valve 42A.

The purpose of these restrictors is to protect the valves 19 and 42Afrom pressure pulses which may be generated in the chamber 12 and in the chamber containing the spring 41.

The apparatus of Figure 2 also includes a bleed valve 52 which is connected in series with a restrictor 53 to the downstream side of the shut-off valve 17.

The purpose of the bleed valve and associated restrictor is to facilitate purging of air which may be drawn into the apparatus.

The control circuit 26 and the associated electrical connections thereto are shown in more detail in Figure 3. Those items which have already been mentioned are provided with the same reference numerals. In order to provide proper control, the control circuit which may be for example, a microprocessor, is supplied with an operator demand signal by a transducer 53 which is associated with the throttle pedal of the vehicle. In addition the control circuit is provided with an engine speed signal by a speed transducer 54, an engine position signal by means of a transducer 55, an engine temperature signal by means of a temperature sensor 56 and depending upon the type of engine, an inlet manifold pressure signal by a sensor 57.The control circuit on the basis of the stored program and stored data concerning desired fuel levels etc., controls the operation of the valves 19 and 42A to adjust the fuel supplied to the engine and the instant of fuel delivery. Information regarding the actual fuel delivery and the actual timing of fuel delivery is provided by transducers 58 and 59 which sense the positions of the distributor member 11 and the piston 40 respectively. Other inputs may be applied to the control circuit if desired.

In operation, it is arranged that the control circuit 26 does not function during engine starting so that valves 21 or 48 are de-energised and valve 34 enables an excess of fuel to be supplied. Upon starting of the engine the control system starts to function by first making a number of checks to ensure that the signals provided by various of the sensors and transducers are present and sensible.

For example, following starting of the engine the transducer 54 should provide a signal indicating rotation of the engine at a relatively low speed. If such a signal is not present then the control circuit will not energise the valves 21 or 48 and the engine will remain under the control of the valves 27 and 34.

The valves 19 and 42A will be controlled by power transistors operating in the switching mode and faults in the power transistors can be detected by ensuring that they are always switching. If it is detected that the switching action is not taking place due to some failure then the valves 21 or 46 can be de-energised to restore control to the valves 27 and 34. In similar fashion the valves 21 or 46 may be controlled by a power transistor operating in the switching mode and the switching action periodically checked. If the power transistor associated with this valve should fail in the closed circuit condition, the fuel supply to the engine can be halted by opening the valve 19 fully to move the distributor member to the zero fuel position. In this situation the engine will stop and cannot be restarted.

Claims

1. A fuel pumping apparatus for supplying fuel to an internal combustion engine comprising a high pressure pump which in use delivers fuel at high pressure to injection nozzles respectively of the associated engine, a low pressure pump for supplying fuel to the high pressure pump, the high pressure pump including a component responsive to a varying fluid pressure and movable in response to the varying fluid pressure to determine the quantity of fuel supplied by the high pressure pump to the engine in use, a first electromagnetically operable valve for varying said fluid pressure, an electronic control system for controlling the electric current flow in said valve in response to various input signals, a second electromagnetically operable valve through which said first valve is connected to a source of fluid under pressure, said second valve when said control system is operative, being maintained in one position but reverting to another position upon failure of said control system, the apparatus further including mechanical valve means operable to determine the pressure applied to said component when said second valve is in said other position.

2. An apparatus according to Claim 1 in which said mechanical valve means includes a spring loaded piston slidable within a cylinder, operator adjustable means for varying the force exerted by said spring, said piston being moved against the action of said spring by the action of fuel under pressure at the outlet of the low pressure pump, said pump including valve means operable to ensure that the outlet pressure of the pump varies in accordance with the speed of the associated engine, said mechanical valve means including a port controlled by said piston whereby when said second electromagnetically operable valve is in said another position, an increase in the speed of the associated engine will cause a reduction in the amount of fuel supplied to the engine.

3. An apparatus according to Claim 2 in which said port is progressively opened with increasing speed to increase the pressure applied to said component.

4. An apparatus according to Claim 2 in which said mechanical valve means includes a further valve operable to control the fluid pressure applied to said component so that when said second electromagnetically operable valve is in said another position the normal maximum supply of fuel to the engine is not exceeded during engine running conditions.

5. An apparatus according to Claim 4 in which said further valve acts to control the minimum pressure applied to said component when said port is closed by the piston.

6. An apparatus according to Claim 5 in which said further valve when the associated engine is being started is inoperative to control the minimum pressure thereby allowing said component to assume a position such that an excess of fuel is supplied to the engine.

7. An apparatus according to any one of the preceding claims in which said second electromagnetically operable valve comprises an on/off valve and is connected in parallel with said mechanical valve means between the source of fluid under pressure and said first electromagnetically operable valve means.

8. An apparatus according to any one of Claims 1-6 in which said second electromagnetically operable valve means comprises a changeover valve in which in said one position it places said first electromagnetically operable valve in communication with said source of fluid under pressure and in said other position places said mechanical valve means in communication with said source.

9. An apparatus according to Claim 7 or Claim 8 in which the high pressure pump includes a further component responsive to fluid pressure for varying in response to a varying fluid pressure applied thereto, the timing of fuel delivery by the pump, the apparatus including a third electromagnetically operable valve for varying the fluid pressure applied to the second component when said second electromagnetically operable valve is in said one position, the fluid pressure applied to said second component when said second electromagnetically operable valve is in said another position being determined by a fixed restrictor.

10. A fuel pumping apparatus for supplying fuel to an internal combustion engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

11. Afuel pumping apparatus for supplying fuel to an internal combustion engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to Figure 2 of the acompanying drawings.