GB2304385A - Distributor pump for fuel - Google Patents

Abstract

A rotary distributor pump for delivering fuel to an internal combustion engine includes an accumulator (50) and a distributor member (40) which delivers fuel from the accumulator, in turn, to injectors (70) feeding the engine combustion spaces. The accumulator is charged by a plurality of pumping plungers (32) which are actuated by a face cam having cam lobes (28). The face cam and the distributor member are driven by a drive shaft (20). Three-way valves (56,58) are located between the accumulator and the distributor. Each valve is associated with a group of four injectors and controls the delivery of fuel to each of its injectors. During the period when fuel is passing from the accumulator to an injector via the distributor, the associated valve is switched to break the communication between the accumulator and the injector, and instead connect the injector to low pressure so terminating the delivery.

Description

DISTRIBUTOR PUMP This invention relates to a distributor pump for use in delivering fuel under pressure to the cylinders of an associated engine, in turn.

In a known type of distributor arrangement, a distributor member having a plurality of radially extending reciprocable pumping plungers is rotatable within a body including a cam surface, the pumping plungers being reciprocable under the influence of cam lobes of the cam surface.

The pumping plungers are used to charge an accumulator from which the pressurized fuel is delivered to the cylinders of an associated engine through a delivery valve and a distributor arrangement. As the plungers are arranged radially, only a relatively small number of plungers can be provided otherwise the pumping capacity of each plunger is significantly reduced.

It is desirable for the accumulator to be charged to substantially the same pressure between each delivery which in pradice requires the same number of pumping strokes to occur between each delivery. For an eight cylinder engine this requires eight or a multiple of eight pumping strokes per revolution of the distributor member. Such arrangements are generally impractical.

According to the present invention there is provided a distributor pump comprising at least one pumping plunger reciprocable under the influence of a cam surface provided on a face cam, the or each plunger being arranged to charge an accumulator, and a distributor arrangement arranged to distribute pressurized fuel from the accumulator to the cylinders of an associated engine in turn, in use.

The face cam is preferably arranged to be driven by a drive shaft, the drive shaft conveniently being arranged to rotate a distributor member of the distributor arrangement.

Preferably, the distributor pump includes a plurality of pumping plungers arranged to generate a plurality of pumping strokes per revolution of the drive shaft, the number of pumping strokes being a multiple of the number of cylinders of the associated engine.

The pumping plungers are preferably reciprocable within bores which extend generally parallel to the axis of rotation of the drive shaft.

One embodiment of the invention will be described, by way of example, with reference to the accompanying drawing which is a diagrammatic cross-sectional view of a distributor pump.

The distributor pump illustrated in the accompanying drawing comprises a generally cylindrical housing 10 consisting of a first part 12 comprising a generally cylindrical wall having one end thereof closed by an end wall 14, a second part 16 closing the other end of the cylindrical wall of the first part 12, and a third part 18 which surrounds the cylindrical wall of the first part 12.

The end wall 14 of the first part 12 is provided with an opening through which a drive shaft 20 extends, bearings 22, 24 being provided between the drive shaft 20 and the first part 12 in order to permit rotation of the drive shaft 20 with respect thereto. The part of the drive shaft 20 extending within the first part 12 includes an enlarged region 26, the surface thereof facing away from the end wall 14 of the first part 12 being provided with three equiangularly spaced cam lobes 28 defining a cam surface.

The second part 16 is provided with eight equiangularly spaced plunger bores 30 which face the cam surface, a plunger 32 being reciprocable within each of the bores 30. Each of the plungers 32 is provided with a shoe 34 carrying a roller 36 which is arranged to engage the cam surface. A tubular member 16a is secured to the second part 16, the member 16a including transverse slots which house the shoes 34 in order to maintain the correct positioning of the shoes 34 with respect to the bores 30.

A cylindrical sleeve 38 is provided within an opening provided in the second part 16 aligned with the axis of rotation of the drive shaft 20.

The sleeve 38 includes a central passage within which a distributor member 40 is rotatable, the distributor member 40 being keyed to the drive shaft 20 such that rotation of the drive shaft 20 with respect to the housing 10 results in rotation of the distributor member 40 within the sleeve 38. A transfer pump arrangement 42 is provided on the second part 16 and arranged to be driven by the drive shaft 20 through the distributor member 40. The transfer pump arrangement 42 includes an annular outlet 42a to which a metering arrangement 44 is connected.

The metering arrangement is illustrated as being provided outside of the housing 10, but it will be understood that it could be provided within, for example, the second part 16.

The metering arrangement 44 communicates with the bores 30 through inlet non-return valves 46 illustrated schematically in the drawing, the inlet non-return valves 46 being arranged so as to permit the flow of fuel from the metering arrangement 44 towards the bores 30, but to substantially prevent the reverse flow of fuel.

Each of the bores 30 also communicates with an outlet non-return valve 48 illustrated schematically in the drawing, the outlet non-return valves 48 communicating with respective accumulator chambers provided in the third part 18 of the housing 10, the accumulator chambers being connected to one another by means of an annular passage provided in the second part 16 to define an accumulator 50. The inlet and outlet non-return valves 46, 48 may take the form of ball valves or alternatively may comprise poppet arrangements.

The accumulator 50 communicates through passages 52, 54 with two three-way valves 56, 58. The first three-way valve 56 communicates through a passage 60 with a pair of feed ports 62 provided in the sleeve 38 spaced apart by 1800 from one another. The second threeway valve 58 communicates with a second similar pair of feed ports 64 through a passage 66.

The second part 16 is provided with eight equiangularly spaced outlet ports 68 each of which communicates with the injector 70 of a respective cylinder of an associated engine. Each of the outlet ports 68 communicates through a passage 72 to a respective delivery port 74 provided in the sleeve 38. The delivery ports 74 are arranged in two groups, one group of four delivery ports 74 being associated with the feed ports 62 associated with the first three-way valve 56, the second group of four delivery ports 74 being associated with the feed ports 64 associated with the second three-way valve 58.

The distributor member 40 is provided with first and second delivery passages 76 each of which is arranged to provide communication between one of the pairs of feed ports 62, 64 and the associated group of delivery ports 74. Each of the delivery passages 76 comprises a leg having an outlet arranged to align with the respective group of delivery ports 74 upon rotation of the drive shaft 20, and a pair of legs arranged to align with the feed ports 62, 64 upon rotation of the drive shaft 20, the pair of legs having outlets arranged at 900 from each other.

In use, the inlet to the transfer pump arrangement 42 is connected to a suitable source of fuel, and the drive shaft 20 is arranged to be rotated at a speed related to engine speed. Upon rotation of the drive shaft 20, fuel is delivered by the transfer pump arrangement 42 to the inlet nonreturn valves 46, the quantity of fuel being delivered thereto being controlled by the metering arrangement 44. Starting from the position illustrated in the drawing, the pumping plunger 32 illustrated in the top part of the drawing is in its innermost position, thus movement away from this position results in the pumping plunger being pushed outwardly due to the pressure of fuel supplied by the transfer pump arrangement 42 through the inlet non-return valve 46. It will be recognised that fuel does not enter the bore 30 from the accumulator 50 due to the presence of the outlet non-return valve 48 which substantially prevents such flow of fuel. Meanwhile, the pumping plunger illustrated in the lower part of the drawing is being pushed inwardly due to the engagement of the roller 36 thereof with one of the cam lobes 28 of the drive shaft 20. Such inward movement of the pumping plunger 32 results in fuel being pumped from the bore 30 through the outlet nonreturn valve 48 to the accumulator 50, thus charging the accumulator 50.

It will be recognised that fuel is substantially prevented from flowing from the bore 30 towards the transfer pump 42 by the presence of the inlet non-return valve 46.

Since the distributor pump is provided with three equiangularly spaced cam lobes 28 and eight equiangularly spaced pumping plungers 32, it will be recognised that for each revolution of the drive shaft 20, twenty four separate pulses of fuel are delivered to the accumulator 50.

At the same time as the accumulator 50 is being charged with fuel, the drive shaft 20 rotates the distributor member 40 to permit the delivery of fuel to the injectors 70 of the cylinders of the associated engine. Starting from the position illustrated in the drawing, fuel from the accumulator 50 communicates through the passage 52, the first three-way valve 56 and the passage 60 with the first pair of feed ports 62. From the first pair of feed ports 62, the fuel is carried through the first delivery passage 76 to one of the delivery ports 74 of the group associated with the feed ports 62 and from there through the respective passage 72 and through the respective outlet port 68 to the injector 70 associated therewith.When delivery is to be terminated, the first three-way valve 56 is switched so as to break the communication between the accumulator 50 and the outlet port 68, and instead the outlet port 68 is permitted to communicate through the first three-way valve 56 to a volume at a relatively low pressure. The application of the relatively low pressure to the outlet port 68, and hence to the injector 70 results in the injector 70 closing and hence in the termination of delivery.

Continued rotation of the drive shaft 20 results in the first delivery passage 76 moving out of alignment with the feed port 62 and delivery port 74, further rotation of the drive shaft 20 resulting in the second delivery passage 76 aligning with one of the feed ports 64 and one of the delivery ports 74 associated therewith. Once such alignment has occurred, the second three-way valve 58 is switched so as to permit communication between the accumulator 50 and the feed ports 64 thus permitting high pressure fuel to be delivered through the outlet port 68 associated with the respective one of the delivery ports 74. In order to terminate delivery, the second three-way valve 58 is switched so as to break the communication with the accumulator 50 and instead to connect the outlet port 68 to a volume at a relatively low pressure as described above.

It will be recognised that by providing an arrangement in which for each revolution of the drive shaft 20, the accumulator 50 is charged with twenty four separate pulses of fuel, the torque load on the drive shaft 20 is substantially uniform, and since twenty four pulses of fuel are applied to the accumulator 50 at regular intervals, it will be recognised that three pulses are applied between each delivery of fuel from the outlet port 68.

The pressure of fuel within the accumulator 50 is therefore likely to be substantially uniform for each delivery of fuel from the outlet ports 68.

Although in the illustrated embodiment a metering arrangement 44 is provided in order to control the flow of fuel to the plungers and hence to control the quantity of fuel supplied to the accumulator 50, instead, a fuel regulator could be provided which is arranged to control the pressure of fuel within the accumulators directly, and to relieve the pressure therein when the pressure exceeds a predetermined level.

A single annular accumulator chamber could be provided instead of the eight separate accumulator chambers linked by an annular passage as in the illustrated embodiment. In order to reduce the weight of the distributor pump, the first part 12 of the housing 10 may be constructed of aluminium, the third part being constructed of steel in order to provide sufficient strength to accommodate the accumulator or accumulator chambers.

The pair of three-way valves 58, 60 may be replaced by a single threeway valve provided that the valve is capable of switching sufficiently quickly to control the delivery of fuel to eight separate injectors 70, and to be able to deliver a sufficiently large quantity of fuel therethrough.

The delivery passages 76 provided in the distributor member 40 are shaped so as to permit the use of a first pair of feed ports 62 and a second pair of feed ports 64, but the pairs of feed ports 62, 64 could be replaced by a pair of annular chambers which would permit the use of a pair of rectilinear delivery passages 76 instead of a pair of bifurcated passages as illustrated.

Claims (3)

1. A distributor pump for delivering fuel under pressure to the combustion spaces of an associated engine in turn comprising at least one pumping plunger movable under the influence of a cam surface provided on a face cam, an accumulator which is charged with fuel by the or each plunger and a distributor arrangement arranged to distribute pressurized fuel from the accumulator to the combustion spaces of the engine in turn.

2. A pump according to Claim 1, in which the face cam and a distributor member forming part of the distributor arrangement are driven by a drive shaft.

3. A pump according to Claim 1, including a plurality of pumping plungers arranged to generate a plurality of pumping strokes per revolution of the drive shaft, the member of pumping strokes being a multiple of the number of cylinders of the associated engine.