GB2316716A - Fuel pump for an internal combustion engine - Google Patents

Abstract

A fuel pump includes a pumping chamber and a spill valve 52 controlling fuel flow from the pumping chamber through a spill passage 54 to a reservoir, the spill valve 52 being controlled by a trigger valve 62 which supplies pressurised fuel through passages 56 to open the valve. A valve arrangement in the form of a plate valve member (66, Fig.2) closes the spill passage 54 during the subsequent filling of the pump working chamber to ensure that spilt fuel from the reservoir returns to the pumping chamber only via the trigger valve 62. This has the advantage that the spilt fuel and fresh fuel admitted to a passage 42, flow together into the working chamber through the same passage 40. In known pumps the two flows are in opposite direction which has a detrimental effect upon filling of the pump.

Description

FUEL PUMP This invention relates to a fuel pump for use in supplying fuel at high pressure to the cylinders of an internal combustion engine.

In order to control the quantity of fuel delivered during each pumping stroke of a fuel pump, it is known to provide a spill valve arranged to be opened after delivery of the desired quantity of fuel so that any further fuel displaced by the pump during that pumping stroke passes through the spill valve to a suitable accumulator or to a low pressure reservoir rather than being delivered to the engine, the fuel pressure at the outlet falling to an extent sufficient to terminate fuel injection. Where the spilt fuel is supplied to an accumulator, it is known to return fuel from the accumulator to the pump prior to the next pumping stroke, further fuel being supplied to the pump from a low pressure reservoir by a low pressure pump, if required.

In a known fuel pump of the type described hereinbefore, the flow of fuel from the accumulator flows in a direction opposite to the direction of fuel flow from the low pressure reservoir. It is thought that these flows of fuel interfere with one another, the interference having a detrimental effect upon filling of the pump.

It is an object of the invention to provide a fuel pump in which this disadvantage is reduced.

According to the present invention there is provided a fuel pump comprising a plunger reciprocable within a bore under the influence of a cam arrangement, a spill valve arranged to communicate through a spill passage with the bore and arranged to return a quantity of spilt fuel to the bore during filling of the bore, a supply arrangement arranged to supply additional fuel to the bore, a trigger valve arranged to control movement of the spill valve, and a valve arrangement associated with the spill valve and arranged to close the spill passage during filling of the bore so that spilt fuel is returned to the bore through the trigger valve.

By locating the trigger valve appropriately, the fuel pump can be arranged so that the spilt fuel returned through the trigger valve flows in the same direction as the fuel from the supply arrangement thus reducing the disadvantageous effects referred to hereinbefore.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a fuel pump in accordance with an embodiment of the invention; Figure 2 is a cross-sectional view of part of the pump of Figure 1; and Figure 3 is a diagrammatic view of part of the pump.

The fuel pump illustrated in Figure 1 comprises a distributor member 10 which is rotatable within a sleeve 12, the distributor member 10 being driven by a drive shaft 14 which is arranged to rotate at a speed related to the speed of rotation of an associated engine. A rotary vane pump 16 is mounted upon the end of the distributor member 10 remote from the drive shaft 14. A valve arrangement 18 is connected between the inlet and outlet of the rotary vane pump 16 and is arranged to control the pressure at the outlet 16a of the vane pump 16 such that the pressure at the outlet 16a is related to the speed of rotation of the drive shaft 14.

Fuel from the outlet 1 6a is supplied through an inlet valve 20 to a plurality of inlet ports22 provided in the sleeve 12. The number of inlet ports is conveniently equal to the number of cylinders of the associated engine, and in the illustrated embodiments six inlet ports 22 are provided. The sleeve 12 is further provided with six equiangularly spaced, axially aligned outlet ports 24 which communicate with respective outlets provided in a housing 26 of the pump.

The distributor member 10 includes a region 28 of enlarged diameter provided with three equiangularly spaced, diametrically extending through bores within which plungers 30 are reciprocable, the outer end of each plunger carrying a respective shoe and roller arrangement 32, the roller of which is arranged to cooperate with the cam surface of a cam ring 34. The cam ring 34 is angularly adjustable with respect to the housing 26 in order to adjust the timing of fuel delivery, the angular position of the cam ring 34 being adjusted using a conventional advance piston arrangement 36 which is arranged to be supplied with fuel by the vane pump 16.

The through bores provided in the distributor member 10 are arranged to communicate with an axially extending passage 38 which in turn communicates with six equiangularly spaced, and axially aligned flow passage 40 which are arranged to be registrable with the inlet port 22, and an outlet passage 42 which is registrable, in turn, with the outlet ports 24, upon rotation of the distributor member 10.

A cap 46 is in screw-threaded engagement with the end of the distributor member 10 remote from the vane pump 16, the distributor member 10 defining a cylinder within which a piston 48 is slidable, a spring 50 being engaged between the cap 46 and the piston 48 in order to bias a spill valve member 52 provided on the surface of the piston 48 remote from the spring 50 into engagement with a seating defined around an end of a spill passage 54 which communicates with the through bores.

The piston 48 and distributor member 10 define a chamber which communicates through six equiangularly spaced passages 56 provided in the distributor member 10 with respective ports 58 provided in the distributor member 10, the ports 58 in turn being registrable with a port 60 which communicates with an electromagnetically operable trigger valve 62. The trigger valve 62 controis communication between the port 60 and a ports 64 which is registrable upon rotation of the distributor member 10 with the flow passages 42 provided therein. As illustrated in Figure 3, the ports 60 and 64 extend over a relatively large angle, the ports 60, 64 being symmetrical to one another about the vertical plane of the pump, but axially offset from one another as shown in Figure 2.

The chamber defined by the piston 48 and distributor member 10 further houses a plate valve member 66 which surrounds and is slidable on the spill valve member 52 and is biased into sealing engagement with the distributor member 10 by a spring 68 which is engaged between the plate valve member 66 and the piston 48.

Starting from the position shown in the accompanying drawings, the through bores are full of fuel, the plungers 30 occupying their outermost positions in which the rollers associated therewith engage the cam surface of the cam ring 34. The spill valve member 52 is in engagement with its seating, and the plate valve member 66 engages the end of the distributor member 10. The trigger valve 62 is closed thus communication between the port 64 and the port 60 is prevented.

Rotation of the distributor member 10 results in the communication between the flow passages 42 and inlet ports 22 being broken and similarly in the communication between one of the flow passages 42 and the port 64 being broken. Further rotation results in the delivery passage 44 aligning with one of the delivery ports 24, and subsequently the rollers associated with the plungers 30 come into engagement with the leading flanks of the cam lobes provided on the cam ring 34 thus inward movement of the plungers 30 commences resulting in fuel being displaced from the through bores through the axially extending passage 40 to the outlet port 24 which is registered with the outlet passage 44, and subsequently in fuel being delivered from the injector associated with that delivery port 24. Such rotation of the distributor member 10 also results in one of the flow passages 42 registering with the port 64, but not in communication occurring between any other of the flow passages 42 and the inlet ports 22.

When it is determined that sufficient fuel has been delivered, the trigger valve 62 is actuated so as to permit communication between the port 64 and the port 60. The communication between the port 64 and the port 60 results in fuel being supplied at high pressure through the passages 56 to the chamber defined by the piston 48 and distributor member 10, the application of high pressure fuel to this chamber being sufficient to move the piston 48 against the action of the spring 50 thus lifting the valve member 52 from its seating. Such movement of the spill valve member 52 results in high pressure fuel fiowing through the spill passage 54. The pressure of this fuel is sufficient to push the spill valve member 52 further against the action of the spring 50 and to lift the plate valve member 66 against the action of the spring 68.

The volume of the chamber defined by the piston 48 and distributor member 10 is sufficient that the increased volume available for the fuel to occupy results in a rapid fall in the pressure of the fuel, and is sufficient for continued inward movement of the plungers 30 to displace fuel to the chamber. If very little fuel is delivered, the pressure of fuel within the chamber defined between the piston 48 and distributor member 10 may be sufficient to move the piston 48 to such an extent that outlet ports 70 provided in the distributor member 10 are uncovered thus permitting fuel to escape to the housing of the pump which is maintained at relatively low pressure.

After inward movement of the plungers 30 has been completed, the spring 68 returns the plate valve member 66 to the position illustrated in Figure 2. The plate valve member 66 is relatively small and light, so such movement occurs quickly. The spring 50 causes the piston 48 to commence movement towards the position shown in Figure 2. Such movement of the piston 48 results in fuel being displaced through the passages 56 and through the trigger valve 62 to return to the through bores, the return flow of fuel through the spill passage 54 being prevented by the engagement of the plate valve member 66 with the distributor member 10. Subsequent rotation of the distributor member 10 results in the communication between the outlet passage 44 and the delivery port 24 being broken and in the flow passages 42 communicating with the inlet ports 22. Such communication between the flow passages 42 and inlet ports 22 permits further fuel to the supplied to the through bores, if necessary, by the vane pump 16.

In the illustrated embodiment, only five of the inlet ports 22 are shown.

The sixth inlet port 22 may be located so that registration of that part with one of the flow passages 42 after communication of that flow passage 42 with the port 64 has been broken.

It will be appreciated that the flow of fuel through the distributor member 10 during the filling part of the pumping cycle all occurs in the same direction along the axially extending passage 40, thus the disadvantages associated with the conventional arrangements in which the momentum of the fuel flowing from the spill arrangement interferes with the flow of fuel from the inlet port are reduced.

Claims (3)

1. A fuel pump comprising a plunger reciprocable within a bore under the influence of a cam arrangement, a spill valve arranged to communicate through a spill passage with the bore and arranged to return a quantity of spilt fuel to the bore during filling of the bore, a supply arrangement arranged to supply additional fuel to the bore, a trigger valve arranged to control movement of the spill valve, and a valve arrangement associated with the spill valve and arranged to close the spill passage during filling of the bore so that spilt fuel is returned to the bore through the trigger valve.

2. A fuel pump as claimed in Claim 1, wherein the valve arrangement comprises a plate valve member which surrounds and is slidable upon a spill valve member forming part of the spill valve, the plate valve member being biased into sealing engagement with a seating surrounding the spill passage.

3. A fuel pump substantially as hereinbefore described with reference to the accompanying drawings.