GB2174515A - Fuel injection pump - Google Patents

Abstract

A fuel injection pump of the rotary distributor type has a piston 35 for adjusting the timing of fuel delivery, a valve member 28 adjustable to determine fuel quantity and a low pressure pump which supplies fuel at a pressure varying with speed. Fixed orifices 60, 74 are connected in series between the outlet of the low pressure pump and a variable orifice 53, 76 defined by the member 28, the variable orifice allowing fuel flow to a drain. The piston is subject to the pressure intermediate the fixed orifices. A first valve means 45 is responsive to the pressure drop across the orifice 60 and acts to maintain the pressure drop constant on reaching a predetermined value and a second valve means 46 is responsive to the pressure between the orifices and when this attains a predetermined value it opens a flow path from downstream of the orifice 74 to a drain at 54. <IMAGE>

Description

SPECIFICATION Fuel injection pump This invention relates to fuel injection pumps for supplying fuel to compression ignition engines and of the kind including a low pressure pump which supplies fuel to a high pressure pump at a pressure which varies in accordance with the speed at which the pump is driven, and a fluid pressure operable device forming part of the high pressure pump for varying the timing of fuel delivery by the high pressure pump and means for controlling the quantity of fuel which is supplied by the high pressure pump.

It is known that the timing of the delivery of fuel to a compression ignition engine needs to be carefully controlled in order to avoid damage to the engine and in order to avoid the emission of noxious exhaust gases.

The object of the invention is to provide such an injection pump in a simple and convenient form.

According to the invention a fuel injection pump of the kind specified comprises an adjustable orifice through which fuel can flow to a drain, said adjustable orifice being controlled in accordance with the setting of said means whereby as said means is adjusted to increase the amount of fuel supplied to the associated engine the degree of restriction offered by said adjustable orifice will be decreased, first and second fixed orifices connected in series with said adjustable orifice with the first orifice being positioned immediately downstream of the outlet of the low pressure pump, said fluid pressure operable device being responsive to the pressure intermediate said first and second fixed orifices, first valve means responsive to the pressure drop across said first orifice and arranged to maintain the pressure drop substantially constant when a predetermined pressure drop has been attained, and second valve means responsive to the pressure intermediate said first and second orifices and arranged when said pressure exceeds a further predetermined value to open a flow path from downstream of said second orifice to a drain.

In the accompanying drawings: Figure lisa diagrammatic view of a number of components of the pump according to the invention with the components in the position as when maximum fuel is being supplied by the pump, Figure 2 is a view of the components of Figure 1 in the positions they adopt when the minimum fuel is being supplied by the pump, Figure 3 is a diagram showing the variation of various pressures in the pump as the speed varies, Figure 4 is a diagram showing the variation of the advance of fuel delivery in accordance with speed at different engine loads, Figure 5 is a sectional side elevation of a pump in accordance with the invention, Figure 6 is a cross section on the line VI-VI of Figure 5, and Figures 7 and 8 are cross sections to an enlarged scale of two valves forming part of the pump.

Referring to Figure 5 of the drawings the pump comprises a two part housing 9, 10 to the housing part 9 being provided with an open end in which is located the part 10 of the housing. The part 10 of the housing has a sleeve 10A defining a bore in which is mounted a rotary cylindrical distributor member 11.

The distributor member 11 is coupled to an input shaft 12 which is located in the part 9 of the housing and which is adapted to be driven in timed relationship with an engine with which the pump is associated. Formed in the distributor member is a transverse bore 14 in which is mounted a pair of reciprocable plungers 15 and which are arranged to be moved inwardly as the distributor member rotates, through the intermediary of a pair of rollers 16 respectively, by cam lobes not shown formed on an annular cam ring 17 mounted for angular movement within the part 9 of the housing.

Also formed in the distributor member 11 is a longitudinally extending passage 18 which at one end is in communication with the transverse bore and at its other end is in communication with a radially disposed delivery passage 19. The delivery passage is arranged to register in turn with a plurality of equiangularly spaced delivery ports constituted by passages 20 which in use are connected by pipe lines respectively to injection nozzles mounted on the associated engine. The aforesaid registration of the passage 19 with one of the delivery ports takes place during the whole time the plungers 15 are being moved inwardly so that liquid fuel contained within the transverse bore 14 will be displaced to a combustion space of the engine.

At another point the longitudinal passage 18 is in communication with a plurality of equiangularly spaced and radially disposed inlet passages 22 which are arranged to register in turn with an inlet port 23 formed in the sleeve 1 OA and which is in communication with a control port 25 by way of a passage 24. The control port 25 has variable communication with the outlet 26 of a low pressure feed pump 27 by way of an axial groove formed on an angularly movable valve member 28. The arrangement is such that when an inlet passage 22 registers with the inlet port 23 fuel will flow from the outlet of the feed pump to the transverse bore 14to move the plungers 15 outwardly. This registration takes place only during the time when the delivery passage 19 is out of register with a passage 20.By adjusting the angular setting of the valve member 28 the rate at which fuel can flow to the bore can be controlled and hence also the amount of fuel delivered to the engine.

The feed pump 27 is provided with an inlet which is in communication with an inlet port 30 formed in a hollow part 37 which is secured to the part 10 of the housing. The inlet communicates with the inlet ports 30 by way of a passage 29 also formed in the part 37 and the latter mounts a tubular filter element 32 and a relief valve which includes a spring loaded element 33. One end of the element 33 is exposed to the pressure of fuel delivered by the low pressure pump 27 and it controls the size of a spill port 34. The arrangement is such that the low pressure pump always pumps more fuel than is delivered to the engine with the result that its output pressure is controlled in a manner which is dependent upon the speed of the engine and which increases as the engine speed increases.

As previously mentioned the cam 17 is angularly adjustable so that the timing of delivery of fuel to the engine can be varied. This adjustment is achieved by a spring loaded piston 35 which is mounted in a cylinder 36. The piston is connected to the cam ring by means of a pin or peg 37 which is in screw thread engagement with the cam ring. Fuel is supplied to one end of the cylinder 36 to move the piston, the fuel being supplied by the low pressure pump with its pressure further modified as will be described.

The fit of the piston 35 within the cylinder 36 is slack so that leakage occurs therebetween. Moreover, a check valve 38 is incorporated in the supply passage 51 to the cylinder and this closes to prevent fuel passing from the cylinder to the supply passage due to the interaction of the roller 16 with the cam lobes.

The angular setting of the valve member 28 is conveniently controlled by a mechanical governor which includes weights 39 which are accommodated in a cage driven by the shaft 12. The weights and cage are accommodated in the first housing part 9 and the weights act upon an axially movable flanged collar 40 mounted about the drive shaft 12. The axial movement of the collar is resisted by a governor spring 41 which is mounted between one of a pivotal lever 42 and an operator adjustable member 43. The other end of the lever 42 bears upon the collar.

Furthermore, said one end of the lever 42 is connected by a tie rod 44 to the valve member 28 and the arrangement is such that as the speed of rotation of the engine rises, the collar 40 will be moved axially by the weights against the action of the governor spring and during this movement the member 28 will be moved angularly to reduce the quantity of fuel delivered to the engine.

Referring now to Figure 6, the derivation of the pressure which is applied to the piston 35 is effected by a pair of valves 45,46 the detailed construction of which will be described with reference to Figures 7 and 8. The valves are screwed into apertures formed in the housing parts 9 and 10. The inner end of the valve 45 is exposed to the pressure at the outlet 26 of the low pressure pump by way of a passage 47 and a groove 48 defined between the sleeve 1 0A and the body 10. Moreover, the valve 45 intermediate its ends has a pressure tapping which communicates with a recess 49 defined about the body of the valve and communicating by way of a passage shown in dotted outline at 50, with the passage 51. The passage 51 is also in communication by way of a further groove 52 formed in the periphery of the sleeve, with the inner end of the valve 46.This valve has a first pressure tapping which communicates with a passage 53 which opens into the bore containing the valve member 28 art a position to have variable communication as the valve member is moved angularly, with a helical groove on the throttle member. The helical groove communicates with the interior of the housing of the apparatus and the extent of communication of the passage 53 with the interior of the housing depends upon the angular setting of the valve member 28. The valve 46 has an additional pressure tapping which is connected directly to the interior of the housing of the apparatus by way of a passage 54.

Referring now to Figure 7 which illustrates the valve 45, this comprises a body 55 in which is formed a stepped bore 56. The narrower portion of the bore is open to the inner end of the body 55 and communicates, in use, with the groove 48. Slidable in the narrower portion of the bore is a valve member 57 in which is formed a longitudinal passage 58 which is in communication with a chamber 59 defined by the wider portion of the bore by way of a restricted orifice 60. The portion of the valve member within the chamber 59 is provided with a flange to limit the extent of movement of the valve member under the action of a coiled compression spring 61 which is located in the chamber and which engages at its end remote from the valve member with an adjustable abutment 62.The valve includes a closure 63 which is in screw thread engagement with the wider portion of the bore and which defines a threaded bore in which the abutment 62 is located. A locking member 64 is provided to secure the abutment once adjustment has been affected.

Extending into the narrower portion of the bore is a port 65 which communicates in use with the passage 50 and also communicating with this passage is a further port 66 which by way of an annular clearance defined between the narrower portion of the bore and a reduced portion of the valve member communicates with the chamber 59 by way of apertures formed in the flanged portion of the valve member. In addition, the valve member is provided with a circumferential groove 67 which as the valve member is moved against the action of the spring 61, can communicate with the port 65.

The construction of the valve 46 is somewhat similar, the valve having a flanged valve member 68 which is biased by a spring 69, the force exerted by which can be adjusted by means of an adjustable abutment 70. The valve member is slidable within a bore 71 the inner end of which communicates with the groove 52. The aforesaid passage 53 communicates with a port 72 which is in constant communication with a groove 73 formed on the valve member and this groove communicates byway of restricted orifice 74, with the inner end of the bore. The groove 73 can also communicate as the valve member is moved against the action of its spring, with a port 75 which in use, is connected to the passage 54. The extent of movement of the valve member 68 is determined by the abutment of the flange on the valve member with a stop surface 76 defined on a closure 77.

Both valves 45 and 46 mount sealing members to provide sealing between the various pressure tappings.

The groove on the metering valve 28 is illustrated diagrammatically in Figure 1 being provided with the reference number 76. At all times the groove is in communication with the interior of the housing but as mentioned above it has variable communication with the port constituted by the end of the passage 53.

Considering now the operation of the device and referring to Figure 1 which shows the metering valve 28 set to a position to allow the maximum amount of fuel to be delivered to the associated engine, the engine therefore working at full load. In this position the groove 76 is in full communication with the port defined by the end of the passage 53. At low speed the valve members of the valves 45 and 46 assume the positions shown in the drawings and fuel from the low pressure pump flows through the orifices 60 and 74 which are connected in series from the outlet 26 of the low pressure pump to the interior of the housing. The pressure which is supplied to the cylinder 36 is therefore the transfer pressure minus the pressure drop across the orifice 60.As the speed continues to increase the output pressure of the low pressure pump will also increase and an increasing pressure will be applied to the piston 35. This pressure is also effective on the valve member 68 and can move this valve member against the action of the spring 69. Such movememt however will have no effect upon the pressure applied to the timing piston since the passage 53 is already in communication with the interior of the housing and the fact that the port 75 is uncovered is immaterial. However, as the output pressure of the low pressure pump increases there will be an increasing pressure drop across the orifice 60 and eventually the pressure drop will become sufficiently large to cause movement of the valve member 57 against the action of the spring 61.A point will be reached at which the groove 67 is uncovered to the port 65 and the valve 45 then acts as a constant pressure drop valve so that the pressure which is applied to the piston 35 corresponds to the output pressure of the low pressure pump minus a constant value determined by the valve 45.

Turning now to Figure 2, this corresponds to the light load operation of the engine with the valve member 28 at a position such that minimum fuel is supplied to the engine. It will be noted that in this position the groove 76 no longer communicates with the end of the passage 53. At low speeds the valve members of the two valves will have moved their maximum extent under the action of their springs.

Since the port at the end of the passage 53 is closed no flow of fuel can take place and therefore at low speeds the pressure which is applied to the piston 35 corresponds to the pressure at the outlet of the low pressure pump. As the pressure increases the valve member 68 will move against the action of its spring and after a predetermined movement the groove 73 will startto uncover the port 75. When this occurs fuel can start to flow through the orifice 74 and the valve 46 acts to maintain the pressure which is applied to the piston 35 substantially constant. It will be understood however that there is a flow of fuel through the orifice 60 of the valve member 45 and that the valve member 57 is subject to the pressure drop across this orifice.With the valve member 68 of the valve 46 in contact with its stop, it can no longer act to maintain the fuel pressure acting on the piston substantially constant. As the output pressure of the low pressure pump continues to increase the pressure applied to the piston 35 will also increase. The increasing pressure drop across the orifice 60 will eventually cause movement of the valve member 57 to allow the groove 67 to move into register with port 65. The valve 45 will then act as described with reference to Figure las a constant pressure drop valve.

The two extreme positions for the valve member 28 have been described above and it will be appreciated that when the valve member 28 is set to cause an intermediate quantity of fuel there will be a degree of registration between the helical groove and the end of the passage 53. In this case therefore there will always be a small flow of fuel through the orifice 73 and hence a pressure drop across this orifice. At low speeds therefore the pressure which will be applied to the piston 35 will be lower than in the case when the metering valve is set to provide the minimum fuel flow to the associated engine.

The diagram in Figure 3 shows the variation of pressures for different rotational speeds either of the engine or of the rotary injection pumps, according to the scale selected. The directrix lines have been drawn as solid lines, Pe being the line relating to the output pressure of the low pressure pump, Pl the pressure controlled by the orifices 60 and 74, with the metering valve 28 in the fully open position, and F1 the pressure controlled by the orifice 60 and the passage restricted at the port 75 of the valve 46 by adjustment of the abutment 70, with the metering valve 28 almost closed.In accordance with the operation described for the engine under load, the actuating pressure applied to the piston 35 is controlled by the orifices 60 and 74 until the difference in relation to the outlet pressure Pe of the low pressure pump reaches a value "c" which makes it possible to compress the spring 61 of the control valve 45. Because of the characteristics of the control valve 45, the difference between the pressure Pe and the actuating pressure Pc applies to the piston, under load is kept constant. so that the pressure Pc will follow a path parallel to the pressure Pe.

The pressure lines Pvl and Pv2 correspond respec timely to no load operation of the engine with and without operation of the stop surface 76 for the valve member 68 of the control valve 46. In accordance with the description given, for engine operation under no load the pressures are equal to the pressure Pe in a first stage. When a value "a" is reached, the control valve 46 opens the port 75 and the pressure Pvl and Pv2 are kept constant.

In the event of the operation of the stop surface 76, when the maximum opening of the port 75 is reached, the no-load piston actuating pressure Fv1 will follow the path P II of the pressure controlled by the orifice 60 and the stop 76 until a difference equal to "c" relative to the pressure Pe is reached, at which point the spring 61 of the control valve 45 will yield and the no-load piston actuating pressure Pvl will follow a path parallel to the pressure Pe. When the stop surface 76 is not effective the no-load piston actuating pressure Pv2 will remain constant and equal to "a" as far as the point where it reaches the straight line corresponding to the piston actuating pressure under load, thereon its difference relative to the pressure Pe will be equal to "c", this path being followed as this difference is kept constant.

The diagram in Figure 4 shows the variation of timing in degrees, corresponding to various engine loads plotted against the rotational speeds of the rotary injection pump in revolutions per minute. As can be seen from the dashed lines, which correspond to the operation of the engine at full load, the timing is advanced. The top curve represents the timing obtained under no-load conditions with the stop surface 76 of the control valve 46 in operation.

The timings corresponding to the operation of the engine with increasing loads are similarly shown, this diagram complying with the aim of the invention.

Claims (5)

1. Afuel injection pump of the kind specified comprising an adjustable orifice through which fuel can flow to a drain, said adjustable orifice being controlled in accordance with the setting of said means whereby as said means is adjusted to increase the amount of fuel supplied to the associated engine the degree of restriction offered by said adjustable orifice will be decreased, first and second fixed orifices connected in series with said adjustable orifice with the first orifice being positioned immediately downstream of the outlet of the low pressure pump, said fluid pressure operable device being responsive to the pressure intermediate said first and second fixed orifices, first valve means responsive to the pressure drop across said first orifice and arranged to maintain the pressure drop substantially constant when a predetermined pressure drop has been attained, and second valve means responsive to the pressure intermediate said first and second orifices and arranged when said pressure exceeds a further predetermined value to open a flow path from downstream of said second orifice to a drain.

2. A pump according to Claim 1 in which said second valve means includes a valve member which is subjected to the pressure intermediate said orifices and is movable by said pressure against the action of resilient means to progressively open said flow path.

3. A pump according to Claim 2 in which when said adjustable orifice is closed, said second valve is operative to maintain the pressure intermediate said fixed orifices substantially constant until said first valve operates when said predetermined pressure drop across the first orifice has been attained.

4. A pump according to Claim 2 including a stop surface to limit the movement of said valve member.

5. A fuel injection pump for supplying fuel to a compression ignition engine substantially as hereinbefore described with reference to the accompanying drawings.