Fuel pump

Abstract

 A rotary distributor fuel pump has a cam ring (17) which is angularly adjustable in the pump body (10) to enable the timing of fuel delivery to be varied. The angular setting of the cam ring in the pump body is sensed by an optical sensor (30) mounted in the pump body and positioned to observe a reflective band (29) on the cam ring. The reflectivity of the band varies along its length.

Description

[0001] This invention relates to a rotary distributor type fuel pump for supplying fuel to an internal combustion engine and of the kind comprising a pump body in which the distributor member is mounted, a drive shaft extending from the body and coupled to the distributor member, a bore formed in the distributor member and a pumping plunger therein, an annular cam ring defining cam lobes which impart inward movement to the plunger as the distributor member rotates, passage means through which fuel can be supplied to the bore to effect outward movement of the plunger, a delivery passage communicating with the bore and opening onto the periphery of the distributor member for registration in turn and during successive inward movements of the plunger, with a plurality of outlet ports in the pump body, the outlets in use communicating with injection nozzles of the engine, and means for moving the cam ring angularly about the axis of rotation of the distributor member in order to vary the timing of commencement of inward movement of the pumping plunger.

[0002] Such pumps are well known in the art and the purpose of effecting angular movement of the cam ring is to adjust the timing of fuel delivery to the associated engine. In the past the setting of the cam ring has been responsive to a fuel pressure which varies in accordance with the speed of the associated engine, the fuel pressure being the output pressure of a low pressure fuel pump utilised to supply fuel to the bore containing the plunger. With the more stringent exhaust emission regulations more precise control of the timing of fuel delivery is required and the need therefore to be able to provide an indication of the actual angular setting of the cam ring.

[0003] The cam ring is located in the pump body and is likely to be immersed in fuel furthermore, since the pump is mounted on the structure of the engine it will be subject to vibration at levels attaining 100g. Moreover, the total movement of the cam ring between its extreme positions may be no more than 15° and during the use of the pump the temperature change may be as much as 100°C.

[0004] GB-A-2086491 describes a pump of the type set out above which also includes a pair of transducers one of which is secured in the pump body and the other of which is mounted on the cam ring so as to move therewith. Both transducers observe a series of "marks" on a rotary member which is coupled to the drive shaft and the interval between the pulses produced by the transducers as a mark on the rotary member passes the transducers, can be used to provide an indication of the angular setting of the cam ring within the body. Apart from the transducers there is associated with the pump a complex circuit for processing the signals produced by the transducers and as a result the cost of the installation is considerable.

[0005] The object of the present invention is to provide a pump of the aforesaid kind in a simple and convenient form.

[0006] According to the invention a pump of the kind specified comprises an optical sensor mounted in the body adjacent a face of the cam ring and a reflective band formed on or secured to the cam ring at a position to be observed by the sensor, the reflective band having a reflectivity which varies progressively along the length of the band, whereby the output signal provided by the sensor varies in accordance with the angular setting of the cam ring.

[0007] An example of a pump in accordance with the invention will now be described with reference to the accompanying drawings in which:-

Figure 1 is a sectional side elevation of the pump, and

Figure 2 is a perspective view of part of the pump seen in Figure 1.

[0008] Referring to the drawings the pump comprises a pump body 10 in which is journalled a rotary cylindrical distributor member 11. The distributor member is coupled to a drive shaft 12 and formed in the distributor member is a transversely extending bore 13 in which is located a pair of pumping plungers 14. The pumping plungers at their outer ends are engaged by cam followers comprising shoes 15 and associated rollers 16 which engage the internal surface of an annular cam ring 17. The cam followers are located within slots formed in an enlarged portion 18 of the drive shaft.

[0009] Formed in the distributor member is a longitudinal drilling 19 which at one end communicates with the portion of the bore 13 lying intermediate the plungers and at its other end communicates with a radially disposed delivery passage 20 which is adapted to register in turn and as the distributor member rotates, with outlet ports 21 which in use, are connected to the injection nozzles respectively of an associated engine.

[0010] The passage 19 also communicates with a radially disposed inlet passage 22 which can communicate with a plurality of inlet ports 23 only one of which is shown. Flow of fuel through the inlet port 23 is controlled by an electrically operable valve 24, the fuel being derived from a low pressure pump 25 the rotary part of which is conveniently coupled to the distributor member or to the drive shaft.

[0011] The cam ring 17 is angularly adjustable within the body, the adjustment being effected by a fluid pressure operable piston 27 which is coupled to the cam ring and which is housed in a cylinder. Flow of fuel to the cylinder to urge the piston against the action of a spring, is conveniently effected by means of an electrically operable valve 26, the fuel again being derived from the low pressure pump 25.

[0012] On the internal peripheral surface of the cam ring there is formed a plurality of cam lobes 28. The cam lobes are arranged in pairs so that as the drive shaft and the distributor member are rotated inward movement will be imparted to the plungers 14. During such inward movement fuel is delivered through the delivery passage 20 to one of the outlets 21. During continued rotation of the distributor member the passage 20 will move out of register with an outlet 21 and the passage 22 will move into register with an inlet port 23. When the valve 24 is opened a volume of fuel flows to the bore to effect outward movement of the plungers, the actual volume of fuel depending on the time during which the valve 24 is open. During continued rotation of the distributor member the passage 22 moves out of register with the inlet 23 and the passage 20 is brought into register with the next outlet so that fuel is supplied to the combustion spaces of the engine in turn.

[0013] The timing of fuel delivery will depend upon the quantity of fuel which is supplied to the bore 13 and it will also depend upon the angular setting of the cam ring 17. Opening the valve 26 will result in movement of the cam ring in the direction opposite to the direction of rotation of the distributor member and the timing of fuel delivery will be advanced. A further valve may be provided to allow fuel to escape from the cylinder containing the piston or there may be a controlled leak so that the piston can move under the influence of the spring to retard the delivery of fuel.

[0014] The valves 24 and 26 will be controlled by an electronic control system which also carries out an engine speed governing function. In order to ensure that the timing of fuel delivery is correct it is necessary to know the angular position of the cam ring 17 within the body of the pump and with reference to Figure 2 the periphery of the cam ring is provided with a reflective band 29 on its outer peripheral surface. The circumferential length of the band is sufficient to cope with the range of angular adjustment of the cam ring. The reflective band is observed by an optical sensor 30 which will include a light source and also a light responsive device which provides an output signal responsive to the light reflected by the band. The reflectivity of the band varies along its length so that from the signal provided by the light responsive device, it is possible to determine the angular setting of the cam ring.

[0015] The outer peripheral surface of the cam ring is a close fit within the body 10 of the pump and a small aperture is provided in the body to accommodate the sensor. In view of the close fit of the cam ring within the body the likelihood of bubbles of air interfering with the optical sensor is minimised.

[0016] The reflective band 29 can be formed by ruling or etching lines on the surface of the cam ring the closeness of the lines varying along the length of the band so that the reflectivity of the band varies along its length. The signals provided by the sensor as the lines move past the sensor will enable the direction of cam ring movement to be determined. In order to calibrate the sensor there is at one end of the band a patch 31 of known reflectivity and the cam ring can be placed in a position such that the sensor observes this patch.

[0017] Although ruling or etching the band directly onto the surface of the cam ring is the preferred arrangement, the band may be in the form of a label which is secured to the cam ring and be formed from a suitable reflective material. Moreover, the band can be formed on a side wall of the cam ring if so desired.

[0018] The pump described above is of the type in which the quantity of fuel supplied to the bore is controlled so that the instant of delivery of fuel to the associated engine varies in accordance with the amount of fuel supplied to the bore. The pump can be of the type in which fuel is spilled from the bore after the start of fuel delivery has taken place. In this case the bore is completely filled with fuel prior to inward movement of the plungers and so it is only the setting of the cam ring which determines the timing of fuel delivery.

Claims

1. A rotary distributor type fuel pumping apparatus comprising a pump body (10) in which the distributor member (11) is rotatably mounted, a drive shaft (12) coupled to the distributor member, a bore (13) in the distributor member and a pumping plunger (14) therein, an annular cam ring (17) defining cam lobes (28) which input inward movement to the plunger as the distributor member rotates, passage means (22, .23) through which fuel can be supplied to the bore, a delivery passage (20) in the distributor member and in communication with the bore, the delivery passage registering with the outlet ports (21) in turn during successive inward movements of the plunger, and means (27) for moving the cam ring (18) angularly about the axis of rotation of the distributor member in order to vary the timing of commencement of inward movement of the pumping plunger (14) characterised by an optical sensor (30) mounted in the body (10) adjacent a face of the cam ring (17) and a reflective band (29) formed on or secured to the cam ring at a position to be observed by the sensor (30), the reflective band having a reflectivity which varies progressively along the length of the band whereby the output signal provided by the sensor (30) varies in accordance with the angular setting of the cam ring.

2. An apparatus according to Claim 1, characterised by a patch (31) of known reflectivity at one end of the band (29).

3. An apparatus according to Claim 1 or Claim 2, characterised in that the band (29) comprises a series of lines the closeness of which varies along the length of the band.

4. An apparatus according to Claim 3, characterised in that said lines are ruled or etched on the surface of the cam ring.

5. An apparatus according to any one of Claims 1, 2 or 3, characterised in that the band is in the form of a label which is secured to the cam ring.

Drawing