GB2317928A - Advance arrangement for a fuel injection pump - Google Patents

Abstract

An advance arrangement for adjusting the timing of a fuel injection pump comprises a cam ring having lobes 18a and located within a housing 46. The cam ring has spaced projections 40 and the housing 46 spaced abutment members 42, the projections and abutments together defining a plurality of control chambers to which fuel under pressure can be supplied to apply a torque to the cam ring. The torque acts against the action of a plurality of springs 52, each spring being located over a respective pin 50 extending through a drilling 48 provided in a respective projection 40. Each spring 52 engages the head 50a of its pin 50 and a respective abutment member.

Description

ADVANCE ARRANGEMENT This invention relates to an advance arrangement for use in controlling the timing of fuel delivery by a fuel pump.

A known type of fuel pump comprises a plunger reciprocable within a bore under the influence of a cam arrangement including an angularly adjustable cam ring. Suitable passages and porting arrangements are provided whereby fuel is supplied to the bore, subsequent movement of the plunger pumping fuel from the bore to a delivery port. The cam arrangement is angularly adjustable in order to adjust the timing at which inward movement of the plunger occurs to pump fuel from the bore. In order to adjust the position of the cam arrangement, an advance arrangement including an advance piston is provided. The advance piston is slidable within a bore and is biased towards one end of the bore by a spring. Fuel is applied at an appropriate pressure to the end of the piston remote from the spring, thus the axial position of the piston is dependent upon the pressure applied thereto.

The cam arrangement includes an outwardly extending peg which cooperates with the piston so that axial movement of the piston causes the angular position of the cam arrangement to be adjusted.

The fuel pressure applied to the advance piston may be controlled by an advance actuator, or may be directly related to the speed of the associated engine.

Such an advance arrangement has the disadvantages that, in use, the high torque applied to the cam arrangement as the plunger rides over the cam surface thereof results in the fuel pressure in the bore of the advance piston rising excessively resulting in fuel leakage. Further, as the peg often does not lie on the centre-line of the advance piston, the high torque results in a torque being applied to the advance piston causing increased wear and leakage. A further disadvantage is that the advance arrangement is relatively bulky which may lead to difficulties in installing the pump.

In an alternative arrangement, a plunger is reciprocable within a bore under the influence of a cam arrangement including an angularly adjustable roller cage, the rollers of which cooperate with a cam surface provided on an end of the plunger. Adjustment of the angular position of the roller cage adjusts the timing of delivery by the pump, thus the roller cage, in effect, replaces the cam lobes of the ring 18.

It is an object of the invention to provide a fuel pump in which these disadvantages are reduced.

According to the present invention there is provided an advance arrangement comprising a cam arrangement angularly adjustable within a housing, at least one spring arranged to bias the cam arrangement towards a first angular position with respect to the housing, and means for applying fuel under pressure to a plurality of chambers defined between the cam arrangement and abutment members associated with the housing to move the cam arrangement against the action of the spring(s).

The chambers are preferably located so that the torque applied to the cam arrangement by the application of fuel to the chambers is in the same plane as and coaxial with the torque applied to the cam arrangement by a plunger of an associated pump, in use, in order to avoid the application of an undesirable offset force to the cam arrangement.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a sectional view of a pump including an advance arrangement in accordance with an embodiment of the invention; Figure 2 is a sectional view along the line 2-2 of Figure 1; Figure 3 is a diagrammatic sectional view illustrating the advance arrangement; and Figures 4 and 5 are views similar to Figures 2 and 3 of an alternative arrangement.

The pump illustrated in Figure 1 comprises a distributor member 10 rotatable within a sleeve 12. The distributor member 10 includes a diametrically extending through bore within which plungers 14 are reciprocable, the outer end of each plunger carrying a shoe and roller arrangement 16, the roller of which engages the cam surface of a cam ring 18, the cam surface of which includes a plurality of cam lobes 18a.

The distributor member 10 is provided with an axially extending passage 20 which communicates with the diametrically extending through bore, the passage 20 further communicating with a plurality of axially aligned, radially extending flow passages 22 and a radially extending outlet passage 24. The flow passages 22 are arranged so as to register, in turn, with an inlet port 26 provided in the sleeve 12, whilst the outlet passage 24 is arranged to register, in turn, with axially aligned outlet ports 28 which communicate with respective outlets of the pump which, in use, are connected to respective injectors arranged to deliver fuel to the cylinders of an associated engine. The number of cam lobes, flow passages, and outlet ports are conveniently equal to one another and to the number of cylinders of the associated engine.

A rotary vane pump 30 is mounted upon an end of the distributor member 10 so as to be rotatable therewith, a valve arrangement 32 being connected between the inlet 30a, and an outlet 30k of the vane pump 30 in order to control the pressure of fuel at the outlet 30k thereof. The end of the distributor member 10 remote from the vane pump 30 is keyed to a drive shaft 34 which is arranged to rotate at a speed related to the speed of an associated engine.

In the illustrated embodiment, the outlet 30k communicates via an annulus provided in the distributor member 10 with a metering valve 36 which controls communication with the inlet port 26. It will be appreciated that in other types of pump, the metering valve may be omitted and instead the quantity of fuel delivered may be controlled, for example, using a spill valve. The outlet 30k further communicates through a passage 38 with an advance arrangement illustrated in greater detail in Figures 2 and 3.

As illustrated in Figures 2 and 3, the cam ring 18 includes four equiangularly spaced, outwardly extending projections 40, and in between each of the projections 40, an abutment member 42 is located, the abutment members 42 being mounted upon the sleeve 12 by bolts 44 or other suitable means. In an alternative arrangement, the abutment members 42 may be integral with the sleeve 12. As illustrated in Figure 2, the outer periphery of each projection 40 is shaped so as to conform with the inner surface of a housing 46 within which the cam arrangement is located, the shaping of the projections 40 together with the engagement between the abutment members 42 and the cam ring 18, guiding the cam ring 18 for angular movement within the housing 46.

Each of the projections 40 is provided with a drilling 48 within which a pin 50 extends, a spring 52 being located over the pin 50 and being engaged between the head 50a of each pin 50 and a respective abutment member 42. It will be appreciated that the springs 52 bias the cam ring 18 towards the position shown in Figure 2. The head 50a of each pin 50 is of part-spherical form and is able to articulate within a cylindrical or other suitably shaped recess formed in the respective drilling 48 in order to allow for angular movement of the cam ring 18.

Each projection 40 is further provided with a slot 54 located in and extending across a surface of the projection opposite the surface from which the drilling 48 extends, the surface of the projection provided with the slot 54 defining, with an associated abutment member 42, a control chamber which is arranged to be supplied with fuel under pressure through an associated check valve 56 (see Figure 3).

In the illustrated embodiment, each check valve 56 comprises a drilling provided in the sleeve 12, the drilling being shaped so as to define a seating with which a spherical valve element is engageable, a cruciform insert being located within the drilling in order to limit movement of the spherical valve element away from its seating whilst permitting fuel to flow along the drilling. It will be appreciated that other types of check valve could be used. In use, the check valves 56 are arranged to receive fuel from the vane pump 30 through the passage 38. An advance actuator 58 is arranged to control the pressure of fuel applied to the check valves 56 and hence to the control chambers of the advance arrangement. It will be appreciated that in other types of pump to which the advance arrangement may be applied, the advance actuator may be omitted, the fuel pressure applied to the control chambers being directly related to engine speed.

The advance actuator 58 conveniently comprises a solenoid controlled valve arranged to control fuel flow from the outlet of the vane pump 30 to each of the check valves 56, and hence control the fuel pressure in each of the control chambers. A position sensor is conveniently arranged to determine the position of the cam ring, the output from the sensor being used to control the solenoid controlled valve to move the cam ring towards a desired position.

In use, starting from the position illustrated in Figure 1, fuel is supplied to the inlet port 26 which is in register with one of the flow passages 22, hence fuel is supplied to the axially extending passage 20 and to the through bore within which the plungers 14 are located. The application of fuel to the through bore pushes the plungers 14 outwardly.

Subsequent rotation of the drive shaft 34 and the distributor member 10 results in the engagement between the flow passage 22 and inlet port 26 being broken, further rotation resulting in the outlet passage 24 registering with one of the outlet ports 28. Further rotation results in the shoes of the shoe and roller arrangements 16 engaging the leading flanks of respective cam lobes 1 8a provided on the cam ring 18. Such engagement results in the plungers 14 commencing inward movement causing the fuel in the through bore to be pressurized and causing fuel to be delivered through the outlet passage 24 to the outlet port 28 registered with the outlet passage 24, subsequently resulting in injection commencing from the injector connected to that outlet port 28.

Further rotation of the drive shaft 34 results in the shoe and roller arrangements 16 riding over the crests of the cam lobes 18a, thus inward movement of the plungers 14 is terminated. The communication between the outlet passage 24 and associated outlet ports 28 is broken, and subsequently another of the flow passages 22 registers with the inlet port 26, such registration permitting fuel to be delivered to the through bore resulting in outward movement of the plungers 14 as described hereinbefore. The pumping cycle described hereinbefore is then repeated.

In order to control the timing at which inward movement of the plungers 14 commences, the angular position of the cam ring 18 is adjustable as described hereinbefore, the angular position of the cam ring 20 being dependent upon the pressure of fuel applied to the control chambers. At high engine speeds, the pressure of the fuel applied to the control chambers by the advance actuator 58 may be relatively high causing a relatively large angular movement of the cam ring 18 against the action of the springs 52 to advance the timing of fuel injection. If the pressure of fuel applied to the control chambers is reduced, the springs 52 return the cam ring 18 towards the position shown in Figure 2 thus retarding the timing of commencement of injection.

It will be appreciated that the engagement of the rollers with the cam lobes 18a applies a torque to the cam ring 18 tending to move the cam ring 18 to pressurize the fuel within the control chambers. The presence of the check valves 56 restricts the flow of fuel from the control chambers, thus minimising angular movement of the cam ring 18 when such engagement occurs. In order to permit angular movement of the cam ring 18 in this direction, it will be appreciated that a restricted flow of fuel past the check valves 56 is permitted, the check valves 56 being arranged to permit substantially unrestricted flow of fuel to the control chambers in order to permit movement of the cam ring 18 against the action of the springs 52.

In order to minimise leakage, the cam ring 18 and abutment members 42 are of equal axial length, and an annular member 60 is secured to the sleeve 12 by the bolts 44. The springs 52 and recesses 54 are positioned such that the torque applied to the cam ring 18 due to the application of fuel to the control chambers is in substantially the same plane as the torque applied to the cam ring, in use, due to engagement with the rollers associated with the plungers 14 in order to minimise tilting of the cam ring 18 in use.

The provision of four separate control chambers permits the provision of an arrangement in which the effective area over which the pressurized fuel acts in the control chambers is significantly greater than that available under the conventional arrangement described hereinbefore, thus the pressure generated in each control chamber due to the engagement of the rollers with the cam lobes of the cam ring 18 can be reduced even though the distance of the control chamber from the cam ring is less than the separation of a conventional advance piston from its cam ring, the reduction in pressure resulting in an improvement in the level of leakage. Depending upon the spring characteristics, the pressure of fuel which must be applied to the control chambers in order to advance the timing of injection may be reduced.

If desired, the abutment members 42 may form part of a sleeve, conveniently a steel outer sleeve reducing the effects of differential thermal expansion and wear, and such a sleeve may be secured directly to the housing 46 by means of radially extending bolts thereby avoiding transmitting the torque applied to the cam ring to the sleeve 12.

In order to reduce the pressurization of the fuel within the control chambers due to the engagement of the rollers with the cam lobes, the control chambers may unevenly spaced around the cam ring. Such uneven spacing results in the cam arrangement not being pressure balanced thus when the rollers engage the cam lobes, a force is exerted on the cam ring in a direction perpendicular to the axis thereof leading to an increase in the frictional forces between the cam ring 18 and housing 46 acting against angular movement of the cam ring.

Alternatively, one or more of the abutment members 42 may be of reduced angular extent, thus a greater surface area of the cam ring 18 is exposed to the fuel pressure within the associated control chamber(s).

Such an arrangement results in the cam ring not being pressure balanced as described hereinbefore.

The arrangement illustrated in Figures 4 and 5 is similar to that of Figures 1 to 3, but in this arrangement, the abutment members 42 are of dimensions such that a radial clearance exists between the abutment members 42 and the cam ring 18. In order to minimise leakage between the abutment members 42 and the cam ring 18, grooves 42a are provided in the abutment members 42, rollers 42b being mounted in the grooves 42a. Similar grooves 42a and rollers 42k are provided in the surfaces of the projections 40 which engage the housing 46. The provision of this arrangement reduces leakage whilst providing greater tolerance to machining inaccuracies.

The grooves 42a are shaped so as to act, with the rollers 42k, as a sprag clutch. When the pressure of fuel within the control chambers is relatively high, the fuel urges the rollers 42k into positions in which they restrict movement of the cam ring 18 in the direction which retards injection timing thus reducing cam ring movement when the shoe and roller arrangements cooperate with the cam lobes to commence inward movement of the plungers. Movement of the cam ring to advance injection timing is not significantly restricted. When lower pressures are applied to the control chambers, the fuel pressure acting on the rollers is not sufficient to restrict movement of the cam ring to retard injection timing.

It will be appreciated that if the position of the groove and roller provided in one or more of the abutment members is adjusted, the area of the cam ring exposed to the fuel pressure within the associated control chamber can be adjusted to achieve an arrangement in which the cam ring is not pressure balanced with the advantages described hereinbefore.

In an alternative arrangement, a rotatable plunger is reciprocable within a bore under the influence of a roller cage arrangement which cooperates with a cam surface provided on an end face of the plunger. In order to adjust the timing of fuel delivery, the roller cage is angularly adjustable, the cage including a plurality of projections which, together with abutment members provided in a housing within which the cage is located, define control chambers to which appropriately pressurized fuel is applied to adjust the angular position of the cage, the fuel pressure within the control chambers acting against appropriate springs.

Claims (3)

1. An advance arrangement comprising a cam arrangement angularly adjustable within a housing, at least one spring arranged to bias the cam arrangement towards a first angular position with respect to the housing, and means for applying fuel under pressure to a plurality of chambers defined between the cam arrangement and abutment members associated with the housing to move the cam arrangement against the action of the spring(s).

2. An advance arrangement as claimed in Claim 1, wherein the chambers are located to ensure that the torque applied to the cam arrangement due to the application of fuel under pressure to the chambers acts in the same plane and is coaxial with a torque applied to the cam arrangement by a plunger of an associated pump, in use.

3. An advance arrangement substantially as hereinbefore described with reference to Figures 1 to 3 or Figures 4 and 5 of the accompanying drawings.