GB2296111A

GB2296111A - Timing of fuel delivery in a distributor-type fuel injection pump

Info

Publication number: GB2296111A
Application number: GB9425423A
Authority: GB
Inventors: Mark David Duncan
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1994-12-16
Filing date: 1994-12-16
Publication date: 1996-06-19
Also published as: GB9425423D0

Abstract

In a pump, such as a rotary VE-type pump, where the timing device comprises a cam follower 4 arranged against a rotatable cam plate 2 having cams 6 thereon, timing is effected by movement of the cam follower 4 relative to the cam plate 2 either in or opposite to the direction of rotation. Movement of the cam follower 4 is effected by means of a hydraulic cylinder 9 which is regulated electronically by a solenoid valve 12. The method of controlling fluid pumping cycle timing comprises the steps of modulating the valve to cause oscillation of the cam follower 4 to control initiation of pumping during each pumping cycle and ensuring that the frequency of modulation of the valve 12 is not equal to pumping frequency of the pump 1 or a harmonic thereof. <IMAGE>

Description

A METHOD OF TIMING OF FUEL DELIVERY IN A DISTRIBUTOR-TYPE FUEL INJECTION PUMP The invention relates to a method of controlling timing of fuel delivery in a distributor-type fuel injection pump and particularly to, although not exclusively limited to, a method of controlling such timing in a Rotary VP pump of a diesel engine.

A typical rotary pump known as a VE pump, used on certain diesel engines, is illustrated in cross-section in Fig 1.

Fuel is pumped to the injection nozzle of each cylinder via a pumping element in the form of a reciprocable and rotary plunger 1 which delivers the fuel to each cylinder in turn.

Reciprocating motion of the plunger 1 is effected by means of a cam 2 fixed to one end of the plunger 1. The cam is rotated by the engine crankshaft and moves over a projecting roller 3 on a cam follower 4 causing the plunger 1 to be reciprocated and rotated within a distributor 5 thereby delivering fuel through ports Sa in the distributor 5. The cam 2 is normally biased against the roller 3 by a spring 2a and plate 2b.

Each pumping stroke is initiated by a lobe 6 of the cam 2 contacting the cam follower to cause an axial movement of the plunger 1. It can be seen that moving the cam follower in the direction of rotation of the cam plate 2 will cause the start of the pumping stroke to be delayed while movement of the cam follower in the opposite direction will cause the pumping stroke to begin earlier.

In the pump of Fig 1 fuel delivery timing is controlled by a timing device 7. The timing device 7 is a mechanical control device employing bob weights (not shown) to vary timing as a function of engine speed. Later pumps, known as VP pumps use a hydraulic chamber regulated electronically by an electrical solenoid valve to move the cam follower 4.

Such a pump is illustrated in Fig 2 which shows a schematic representation of timing control in a VP pump.

In Fig 2 a cam 2 is shown in both side and end elevations. The cam follower 4 is located so as to contact the surface of the cam 2. As the cam 2 rotates the lobes 6 on the cam 2 contact the cam follower and cause the cam 2 to reciprocate axially.

The cam follower 4 is attached to a piston 8 slidable in a bore 9 formed in the pump. A spring 10 acts between one end of the bore 9 and an adjacent end of the piston 8. A chamber 11 is defined between the opposite end of the bore 9 and the other end of the piston 8. The chamber 11 receives hydraulic fluid fed via a solenoid valve 12 which is controlled by an electronic control unit 13. The electronic control unit 13 receives engine data such as speed, driver input etc and determines the required timing. The control unit 13 then operates the solenoid valve 12 to regulate the admission of hydraulic fluid to the chamber 11 causing the piston 9 to move against or under the action of the spring 10. In that way the cam follower 4 can be shifted under the control of the electronic control unit 13 to determine fuel delivery timing.

Pumps having the arrangement described with respect to Fig 2 to determine fuel delivery timing can meet problems when the solenoid valve is modulate at a frequency which is the same as the reciprocating frequency of the plunger 1 or a harmonic thereof. In such a case, pressure shock waves occurring in the pump can cause the cam follower 4 to move more or less than expected and in an erratic manner giving rise to instabilities in fuel delivery timing. It has been proposed to modulate the valve at two alternating fixed frequencies for fixed periods of time but instabilities still occur.

It is an object of the invention to provide an improved method of controlling fluid pumping cycle timing.

According to the invention there is provided a method of controlling timing of fuel delivery in a distributor type fuel injection pump having a reciprocable rotary cam cooperable with a follower for operating a pumping element, an actuator being provided for moving the follower relative to the cam to vary fuel delivery timing, the method comprising sensing operational frequencies of the pumping element and applying modulation frequencies to the actuator such that, at any given time, the modulation frequency applied to the actuator is not the same as the operational frequency of the pumping element or a harmonic thereof.

In a preferred embodiment, the frequency of modulation of the valve may be selected from a predetermined list of values, selection of which may be dependent upon an operating parameter such as engine speed.

The invention also includes a pump which operates according to the method as set out in any of the two immediately preceding paragraphs. The pump may be a Rotary VP-type pump, preferably arranged for use in an internal combustion engine.

The valve is preferably a solenoid-operated valve.

Embodiments of the invention will now be described in detail by way of example and with reference to Fig 3 of the accompanying drawings in which parts corresponding to parts in Fig 2 carry the same reference numerals.

Engine crankshaft speed will determine the operational frequency of the plunger 1 and a crankshaft speed sensor 15 provides a signal to the engine control unit 13. The engine control unit 13 selects a modulation frequency of the solenoid valve 12 from a "look-upl table 16 stored in its memory so that the selected frequency is not the same as the operational frequency of the plunger 1 or a harmonic thereof. If desired the " look-up table can be adaptive, that is, the values in the table can be updated on the basis of engine operating data. In an alternative embodiment the electronic control unit 13 monitors the solenoid valve modulation frequency and the frequency of plunger 1 and alters the modulation frequency of the solenoid valve 12 when it approaches the pumping frequency or a harmonic thereof. In such a case, the frequency of modulation is effectively infinitely variable as opposed to being selected from a predetermined list.

Where the invention is applied to a fuel pump in an engine, the problem of instability in the timing of the start of injection is substantially reduced.

Claims

1. A method of controlling timing of fuel delivery in a distributor type fuel injection pump having a reciprocable rotary cam co-operable with a follower for operating a pumping element, an actuator being provided for moving the follower relative to the cam to vary fuel delivery timing, the method comprising sensing operational frequencies of the pumping element and applying modulation frequencies to the actuator such that, at any given time, the modulation frequency applied to the actuator is not the same as the simultaneous operational frequency of the pumping element or a harmonic thereof.

2. A method according to Claim 1 including providing a list of predetermined frequencies and selecting the frequency of modulation of the actuator from the list.

3. A method according to Claim 2 including selecting the frequency of modulation from the list in response to an operating parameter of an engine to which the pump supplies fuel.

4. A method according to Claim 2 or 3 including altering the predetermined frequencies on the list during running of the pump.

5. A method of controlling timing of fuel delivery in distributor type fuel injection pump substantially as described herein with reference to the accompanying drawings.

6. A pump which operates according to the method of any preceding Claim.

7. A pump according to Claim 6 in the form of a rotary VE type pump.

8. A pump according to Claim 6 or 7 in which the pump is arranged to supply fuel to an internal combustion engine.

9. A pump according to Claim 6, 7 or 8 in which the actuator is a solenoid-operated valve.

10. A pump constructed and arranged substantially as described herein with reference to Fig 3.