GB2141787A - Fuel injection pumping apparatus - Google Patents

Abstract

A fuel injection pumping apparatus includes a constant stroke plunger pump, a valve 38 operable to allow fuel to flow to a drain during a pumping stroke of the pump thereby to control the flow of fuel through a delivery passage 34. The fuel which flows past the valve enters one end of a cylinder 39 which contains a spring loaded piston 40. The piston is displaced by the fuel and an indication of the extent of its displacement is provided by a transducer 42. <IMAGE>

Description

SPECIFICATION Fuel injection pumping apparatus This invention relates to a fuel injection pumping apparatus for supplying fuel to an internal combustion engine and of the kind comprising a high pressure pump including a constant stroke plunger reciprocable in a bore defining a pumping chamber, an outlet from the pumping chamber, a low pressure supply pump for supplying fuel to the high pressure pump to completely fill the pumping chamber and valve means operable to connect the pumping chamber to a drain, said valve means being operable during a pumping stroke of the plunger to control the amount of fuel flowing through said outlet.

Such apparatus is well known in the art and several forms of valve means are known. In one form the valve means is an electromagnetically operated valve the supply of electric current to which is controlled by an electronic control system. The control system is responsive to a number of actual and desired engine operating parameters. For precise control of the associated engine it is necessary for the control system to be supplied with a signal representing the amount of fuel which is being supplied to the engine.

The object of the present invention is to provide an apparatus of the kind specified in a form in which this desideratum is achieved.

According to the invention a fuel injection pumping apparatus of the kind specified comprises a piston slidable within a cylinder, means for urging the piston towards one end of said cylinder, and said one end of the cylinder forming said drain and a transducer for providing a signal representing the displacement of said piston.

An example of an apparatus in accordance with the invention will now be described with reference to the accompanying sectional drawing and referring to the drawing there is provided a two part housing 10 the first part 11 of which defines a generally cylindrical cavity 12 the open end of which is closed by the second part 13 of the housing, the two parts being secured together in any convenient manner.

The first part 11 of the housing is provided with a mounting flange 14wherebythe apparatus can be mounted on an associated engine.

The first part 11 of the housing mounts a rotary drive shaft 15 which extends to the exterior of the housing and is adapted to have a drive wheel mounted thereon. The drive wheel in use is coupled to a rotary part of the engine so that the shaft is driven in timed relationship therewith. The shaft 15 extends into the cavity 12 and has an enlarged cup-shaped portion 16 which is located about an enlarged end portion 17 of a rotary cylindrical distributor member 18 which is carried by a sleeve 18A secured in the second part 13 of the housing.

The enlarged end portion 17 of the distributor member has a reduced extension which extends into the enlarged end of a cylinder 19 formed in the drive shaft. Carried by the enlarged portion of the cylinder is a seal memberwhich engages with the periphery of the extension of the distributor member.

Formed in the enlarged end portion 17 of the distributor member is a diametrically disposed bore 20 in which is mounted a pair of pumping plungers 21. The plungers 21 engage at their outer ends, with cam followers 22 respectively the cam followers including rollers which engage with the internal peripheral surface of an annular cam ring 23 which is secured against rotation by attachment to the second part 13 of the housing by axial bolts. The cam followers 22 are accommodated within slots formed in the cup-shaped portion 16 of the drive shaft and the distributor member is coupled to the drive shaft so as to rotate therewith.

The drive shaft has a cup-shaped member 44 secured thereto, the rim portion of the member 44 having a running fit with the periphery of the cam ring 23. The drive shaft 15 is therefore supported about the cam ring and also by a bearing 45 carried in the housing part 11.

In addition, the distributor member carries a drive plate 46 which has a pair of tongues which locate in the slots respectively in the enlarged portion 16 of the drive shaft and a tang which is located within a recess in the distributor member. The distributor member is thus driven from the drive shaft. The aforesaid tongues are provided with indents which locate the cam followers for assembly purposes.

The bore 20 constitutes the pumping chamber of a high pressure pump and it communicates with the cylinder 19 by way of a non-return valve 24 which is carried in a mounting 25 which is secured within the extension of the distributor member. The cylinder 19 contains a spring-loaded piston 26 the extent of movement of which within the cylinder is limited by a stop in the form of a spring clip 27 located within a groove in the cylinder. Fuel under pressure is supplied to the cylinder to move the piston against the action of its spring, by means of a low pressure supply pump 28 conveniently of the vane type and which has its rotary part secured to the drive shaft and its stationary part located within a recess in the housing part 11.A diaphragm 29 is fixed within the cavity 12 and closes the recess and also defines a channel with connects a circumferential groove on the drive shaft which the outlet of the pump. The aforesaid groove is connected by way of a drilling 30, to the cylinder 19. The inlet of the pump is connected to a fuel inlet 31 in the housing part 11 and the piston 26 in conjunction with a port 32 acts to control the pressure within the cylinder 19.

The non-return valve 24 permits fuel from the cylinder 19 to pass into the bore 20 and to effect outward movement of the plungers 21 when permitted by the lobes on the internal peripheral surface of the cam ring 23. There are as many lobes on the cam ring as there are cylinders of the associated engine and the lobes are disposed in pairs.

The bore 20 communicates with an axially extending passage 33 in the distributor member and this communicates at one point with a radially disposed delivery passage 34 which can communicate in turn and during the whole time the plungers are moved inwardly, with outlets 35 only one of which is shown, opening onto the periphery of the distributor member and communicating with fuel outlets 36 carried by the housing part 13. The outlets 36 are connected in use, to the injection nozzles of the associated engine.

The plungers 21 have a constant stroke so that each time the plungers are actuated by the cam lobes, the same quantity of fuel will be displaced along the passage 33. In order to control the quantity of fuel which is supplied through the outlets, valve means is provided which can be operated to permit fuel to escape from the passge 33 and thereby prevent its delivery to an outlet. For this purpose the passage 33 is in constant communication with a spill passage 37 formed in the aforesaid sleeve and which communicates with one end of a bore which contains an axially movable spill valve member 38 the bore communicates with one end of a cylinder 39 which contains a spring-loaded piston 40, the piston being biased towards the aforesaid one end of the cylinder.The valve member 38 is movable by an electromagnetic device generally indicated at 41 and it is arranged that when the device 41 is energised, the valve is closed. In other words, in order that fuel shall be delivered through an outlet 36 it is necessary to energise the device 41. When the device 41 is de-energised the valve member 38 will move under the action of a spring, to place the spill passage 37 in communication with the end of the cylinder 39. As fuel is displaced by the pumping plungers the piston 40 will move against the action of its spring and this movement is detected by a transducer element 42.

The signal provided by the transducer element represents the amount of fuel which is spilled and hence it is possible knowing the displacement of the plungers 21, to determine how much fuel has been delivered to the associated engine.

In the particular example the piston 40 is springloaded and the fuel pressure in the one end of the cylinder 39 is arranged to be higher than the pressure in the cylinder 19. At the end of delivery of fuel therefore when the plungers move over the crests of the cam lobes, the valve member 38 is retained in the open position and the piston 40 displaces the fuel from the cylinder 39 towards the bore 20. When the piston 40 engages the one end of the bore 39, the valve 24 opens to permit fuel to flow from the cylinder 19 to move the plungers outwardly their maximum extent. The cycle of operation can then be repeated with the valve member 38 being moved to the closed position as and when delivery of fuel to the associated engine is required.

As shown, the valve member 38 is provided with an axial passage the purpose of which is to provide pressure balancing of the valve member. In addition the end of the cylinder 39 which contains the spring, is vented to the cavity 12 which is at a low pressure.

An outlet 43 is provided which is connected in use, to a drain.

As described the spring force is utilised to return the piston 40 to the one end of the cylinder and the fuel displaced during this movement is returned to the high pressure pump. It may be desirable howeverto provide a separate venting arrangement for the one end of the cylinder 39 to be absolutely certain that the piston 40 reaches the one end of the cylinder before inward movement of the plungers 21 takes place. The separate venting arrangement may include a rotary valve constituted by the distributor member. It will also be appreciated that the total displacement of the piston 40 must be at least equal to the maximum displacement of the plungers 21.

Claims (7)

1. Afuel injection pumping apparatusforsupplying fuel to an internal combustion engine comprising a high pressure pump including a constant stroke plunger reciprocable in a bore defining a pumping chamber, an outlet from the pumping chamber, a low pressure supply pump for supplying fuel to the high pressure pump to completely fill the pumping chamber and valve means operable to connect the pumping chamber to a drain, said valve means being operable during a pumping stroke of the plunger to control the amount of fuel flowing through said outlet, a piston slidable within a cylinder, means for urging the piston towards one end of said cylinder, said one end of the cylinder forming said drain and a transducer for providing a signal representing the displacement of said piston.

2. An apparatus according to Claim 1 including a non-return valve through which said pumping chamber is connected to the low pressure pump.

3. An apparatus according to Claim 2 in which said piston is resiliently biased towards said one end of the cylinder.

4. An apparatus according to Claim 3 in which the pressure of fuel in the one end of the cylinder at the end of the pumping stroke of the plunger is greater than the pressure of fuel required to open the non-return valve whereby the fuel contained within the one end of the cylinder will be displaced back to the bore.

5. An apparatus according to Claim 3 including a venting arrangement for venting said one end of the cylinder to allow return movement of the piston.

6. An apparatus according to any one of the preceding claims including a spring loaded piston mounted in a cylinder, the cylinder being connected to the outlet of the low pressure pump.

7. Afuel injection pumping apparatusforsupplying fuel to an internal combustion engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawing.