GB2291136A - Cam ring-advance mechanism linkage - Google Patents

Abstract

A rotary distributor type fuel pumping apparatus includes a cam ring (12) which is angularly adjustable about the axis of rotation of the distributor member to vary the timing of fuel delivery. A fluid pressure operable piston (14) is provided to vary the angular setting of the cam ring and this is coupled to the cam ring by a linkage including a peg (18) on the cam ring and an element (22) interposed between a surface of the peg and the piston. The interengaging surfaces of the peg, the element and the piston are shaped to allow relative movement as the piston moves the cam ring. A number of other embodiments each having a different form of linkage are described. <IMAGE>

Description

CAM RING - ADVANCE MECHANISM LINKAGE This invention relates to a linkage for transmitting movement of a distributor pump advance mechanism to the cam ring thereof.

In distributor pumps for use in supplying fuel to diesel engines, it is common for the cam ring of the pump to be angularly adjustable about the axis of the distributor member, angular movement of the cam ring being used to adjust the timing at which fuel is supplied to an associated engine. In order to adjust the position of the cam ring, an advance mechanism, commonly in the form of a piston arranged to be driven by pressurised fuel from a pump, is used. A peg engages in a screw threaded bore provided in the outer periphery of the cam ring, the piston being arranged to engage with the head of the peg so that actuation of the piston results in the angular position of the cam ring being adjusted to adjust the timing of the engine. A helical spring is provided in order to return the cam ring to its original position.

Where such a peg is used, there is generally line contact between the head of the peg and the piston. Such contact is undesirable, area contact being preferred in order to reduce wear.

According to the present invention there is provided a linkage for interconnecting the cam ring and advance mechanism of a distributor pump.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross sectional view of a distributor pump including a linkage according to a first embodiment; Figures 2, 3 and 4 are cross-sectional views similar to Figure 1 of second, third and fourth embodiments; Figure 5 is a cross-sectional view along the line X-X in Figure 4; Figure 6 is a cross-sectional view along the line Y-Y in Figure 4; Figure 7 is a cross-sectional view of a pump including a linkage according to a fifth embodiment; Figure 8 is a cross-sectional view along the line Z-Z of Figure 7; Figure 9 is a cross-sectional view of a pump including a linkage according to a sixth embodiment; Figure 10 is a cross-sectional view of a pump including a linkage according to a seventh embodiment; Figure 11 is a cross-sectional view along the line W-W of Figure 10; and Figure 12 is a cross-sectional view of a distributor pump with which the linkages of each of the first to seventh embodiments are suitable for use.

The distributor pump illustrated in Figure 12 comprises a housing 10 within which is provided a sleeve 100, a distributor member 102 being rotatable within the sleeve 100. The distributor member 102 includes an end region 104 provided with, for example, four equally spaced bores 106 each of which houses a plunger which is reciprocable therein. The outer end of each plunger is provided with a shoe 108 housing a roller which is arranged, in use, to engage with the inner surface of a cam ring 12 provided with a plurality of cam lobes (Figure 1). The distributor member 102 includes passages 110, 111, 112 arranged to communicate with inlet and delivery passages 114, 116 provided in the sleeve 100 to deliver fuel to and from the bores 106.

At the opposite end of the distributor member to the bores which accommodate the plungers, is mounted the rotor 116 of a vane type feed pump having an inlet 118 and an outlet 120 in the body part. The inlet 118 of the feed pump in use is connected to a source of liquid fuel and the inlet 118 and outlet 120 are interconnected by way of a valve which controls the output pressure of the feed pump in such a manner that it varies in accordance with the speed at which the apparatus is driven.

Since the distributor member is driven by the engine the output pressure of the feed pump is also dependent upon the speed of the engine.

In use, the distributor member 102 is arranged to rotate in timed relation with an associated engine, the plungers moving outwardly as fuel is delivered to the bores 106 through an inlet port or ports, and being pushed inwardly when the rollers engage with the cam lobes, pumping the fuel to a cylinder of the associated engine through one of the delivery passages 114.

In order to adjust the time at which fuel is delivered, the mounting of the cam ring 12 is arranged to permit limited angular adjustment, and the pump is provided with an advance piston 14 arranged to drive the cam ring 12 through a linkage 16.

The linkage 16 illustrated in Figure 1 comprises a peg 18 provided on the outer periphery of the cam ring 12, the peg 18 being integral with the cam ring 12 and extending outwardly of the cam ring 12 in a generally radial direction. One face of the peg 18 is provided with a part spherical recess. The advance piston 14 of the embodiment of Figure 1 includes a generally planar end face 20. A part spherical element 22 is provided between the peg 18 and the end face 20 of the advance piston 14, the element 22 being seated in the recess of the peg 18 and including a generally planar surface arranged to engage with the generally planar end face 20 of the advance piston 14.

A helical spring 24 is provided within the housing 10 and is arranged to bias the peg 18 towards the advance piston 14 in order to retain the part spherical element 22 in position between the peg 18 and the advance piston 14, and in order to return the cam ring 12 to its original position on removal of high pressure fuel from the advance piston 14.

Conveniently the spring at one end is located within a cup shaped end closure and at its other end in a cup shaped plunger slidable in the pump housing and having a spherical surface in engagement with the peg.

In use, the angular position of the cam ring 12 varies in accordance with the output pressure of the feed pump. As the pressure increases, the advance piston 14 moves the peg 18 and the cam ring 12 in a clockwise direction as viewed in Figure 1 thereby advancing the timing of fuel delivery to the engine. As the piston 14 extends, the generally planar face of the element 22 remains in contact with the end face 20 of the piston 14, the orientation of the element 22 with respect to the peg 18 adjusting to maintain such contact. The angular movement of the cam ring 12 results in the element 22 moving upwardly as shown in Figure 1.

If the engine speed falls, the fuel pressure is reduced and the piston moves under the action of the spring to retard the timing of fuel delivery.

It will be understood that the area of contact between the part spherical element 22 and the end face of the piston 14, and the area of contact between the part spherical element 22 and the peg 18 is relatively large compared to that where a piston engages directly with the head of a peg, and hence wear of the components is reduced.

The linkage 16 illustrated in Figure 2 comprises a radially extending integral peg 28 provided on the cam ring 12, the peg 28 including a pair of generally parallel planar faces, a part spherical element 30 including a generally planar face arranged to engage with one of the faces of the peg 28, the part spherical element 30 being seated within a part spherical recess provided in the end face of the advance piston 14.

In use, the angular position of the cam ring 12 varies in accordance with the output pressure of the feed pump 116. As the pressure increases, the advance piston 14 moves the peg 28 to the left as shown in Figure 2, moving the cam ring 12 in a clockwise direction. As the cam ring 12 moves, the planar faces of the peg 28 move away from the generally vertical position as shown in Figure 2, the part sphericai eiement 30 moving angularly in the recess of the piston end face so that the planar face thereof remains in contact with, but slides along, the face of the peg 28. On reduction of the engine speed, the pressure applied to the piston is reduced, the helical spring 24 pushing the peg 28 and hence the piston 14 to the right as shown in Figure 2 retarding the timing of fuel delivery to the engine.

As with the embodiment of Figure 1, the area of contact of the part spherical element 30 and the end face of the piston 14 and with the peg 28 is larger than if the piston 14 engaged directly with the head of a peg, thus reducing wear. By providing the part spherical element 30 in a part spherical seat in the end of the piston 14, vertical movement of the part spherical element 30 does not occur, the force moving the cam ring 12 always being directed along the centre line of the piston 14.

The embodiment illustrated in Figure 3 comprises a cam ring 12 provided with an integral peg 34 which extends asymmetrically outwardly from the periphery of the cam ring 12. One surface of the peg 34 is provided with a part spherical recess within which a part spherical element 36 engages. The part spherical element 36 includes a generally planar face which is arranged to engage with a planar end face 38 of the piston 14.

The position of the cam ring 12 is adjusted by applying high pressure fuel to the piston 14 to move the piston 14 which occurs when the engine operates at relatively high speed. As the piston 14 moves, the part spherical element 36 rotates by a small amount with respect to the peg 36, the planar surface thereof remaining in contact with the end face 38 of the piston 14. It will be recognised that the cam ring 12 moves clockwise on such movement of the piston 14, the movement resulting in the part spherical element 36 sliding on the end face 38 of the piston 14. When movement first commences, the sliding movement is in a downward direction as shown in Figure 3, downward movement continuing until the centre of the part spherical element 36 aligns with the centre of the cam ring 12.Further movement of the piston 14 results in the part spherical element 36 sliding on the end face 38 of the piston 14 in an upward direction.

The provision of the asymmetric peg 34 reduces the total sliding movement of the part spherical element 36, and hence reduces the deviation of the centre of the part spherical element 36 from the centre line of the piston 14. Since the element 36 contacts both the peg 34 and the piston end face 38 over a relatively large area, wear of the parts is reduced.

In the embodiment illustrated in Figures 4, 5 and 6, the cam ring 12 is provided with a curved peg 40 provided with a part spherical recess.

The advance piston 14 is provided with an opening 46 arranged to receive part of the peg 40, the face of the advance piston 14 within the opening 46 which faces the recess of the peg 40 is provided with a part spherical recess. Between the peg 40 and the face of the advance piston 14 is provided an element 42 having a cylindrical centre portion and hemispherical end faces. The hemispherical ends are seated within the recesses of the peg 40 and the advance piston 14. The end of the piston 14 is provided with a cylindrical recess 44 within which a helical spring 24 is provided to bias the advance piston 14 to the right as shown in Figure 4.

In use, the fuel pressure applied to the piston is dependent upon engine speed. At high engine speeds, the applied pressure is large moving the piston to the left, the cam ring 12 being moved to advance the timing of fuel delivery to the engine. The relative positions of the peg 40 and the advance piston 14 change due to the angular movement of the cam ring 12 and the linear movement of the advance piston 14 resulting in the angle of the element 42 changing with respect to both the peg 40 and the advance piston 14.

As contact between the element 42 and both the peg 40 and the advance piston 14 is over a relatively large area, wear of the moving components is reduced. Since the recess is provided on the centre line of the piston 14, the force applied to the element 42 is also applied along the centre line of the piston 14.

When the application of high pressure fuel to the piston 14 ceases due to a reduction in engine speed, the spring 24 acts against the advance piston 14 to move the piston 14 to the right as shown in Figure 6. As the peg 40 is provided in the opening 46 of the piston 14, such return movement of the piston 14 results in the peg 40 bearing against the surface of the opening opposite that provided with the recess and element 42, hence resulting in the cam ring 12 being moved in an anticlockwise direction.

Figures 7 and 8 show a linkage 16 in use with a cam ring 12 provided with a radially extending peg 50 of square cross-section, although the peg may be of other cross-sectional shapes, for example circular or rectangular. The peg 50 is slidable within a bore provided in a trunnion 52, the bore being of similar shape and size cross-section as the peg 50.

The bore may be a blind bore, but in the illustrated embodiment the bore is a through bore. The trunnion 52 comprises a cylindrical member having its axis arranged parallel to the axis of the cam ring 12 and the distributor member of the pump, the bore extending diametrically across the trunnion 52.

The trunnion 52 is seated in a part cylindrical recess provided in the end face of the advance piston 14, and a similarly shaped recess provided in a spring biased piston 54 arranged opposite the advance piston 14 to return the advance piston 14 and the cam ring 12 to their original positions.

In order to achieve a change in the timing of the associated engine, the cam ring 12 is angularly moved by applying high pressure fuel from the feed pump to the advance piston 14 resulting in the advance piston 14 moving to the left, pushing the trunnion 52 and hence the peg 50 of the cam ring 12 towards the left as shown in Figure 7. Such movement results in the trunnion 52 moving angularly about its axis slightly, and in the peg 50 sliding within the bore. The movement of the advance piston 14 also has the effect of compressing the spring biased piston 54.

On reducing the pressure applied to the piston 14 resulting from a reduction in engine speed, the spring biased piston 54 pushes the trunnion 52 and advance piston 14 to the right, moving the peg 50 and hence the cam ring 12 in an anticlockwise direction retarding the timing of fuel delivery to the engine.

Due to the relatively large area of contact between the trunnion 52 and the advance piston 14 and between the trunnion 52 and the peg 50, wear of the various parts is reduced. Since the trunnion 52 is seated in a part cylindrical recess provided in the centre of the end face of the advance piston 14, the force applied to the trunnion 52 is always along the centre line of the piston 14.

It will be recognised that a spherical trunnion could be used instead of the cylindrical trunnion described and illustrated, such a trunnion being seated in part spherical recesses.

Figure 9 shows a cam ring 12 provided with a short radially extending cylindrical peg 56 slidably received within a diametrically extending bore provided in a cylindrical trunnion 58.

The trunnion 58 is received within a cylindrical bore provided in the advance piston 14, the bore provided in the piston 14 extending parallel to the axis of the cam ring 12 and distributor member of the pump. The end of the advance piston 14 is provided with a cylindrical recess 60 arranged to house an end of a helical spring 24 which also engages with a screw threaded element mounted on the housing 10 in order to bias the advance piston 14 to a retracted position.

On applying high pressure fuel from the feed pump to the advance piston 14 due to the engine operating at relatively high speeds, the piston 14 moves, pushing the trunnion 58 towards the left as shown in Figure 9. Such movement of the trunnion 58 results in the peg 56 being moved towards the left, moving the cam ring 12 in a clockwise direction.

As the cam ring 12, and hence the peg 56, are arranged to move angularly, and the piston 14 and hence the trunnion 58 move linearly, the movement results in the trunnion 58 rotating slightly within the bore of the advance piston 14, and in the peg 56 sliding within the bore of the trunnion 58.

When the pressure of the fuel applied to the advance piston 14 is reduced due to a reduction in engine speed, the helical spring 24 acts to return the advance piston 14, trunnion 58, cam ring 12 and peg 56 retarding the timing of delivery of fuel to the engine.

The area of contact between the advance piston 14, trunnion 58 and peg 56 are relatively large, so the force transmitted to the cam ring 12 is transmitted over a relatively large area reducing the wear of the linkage 16.

Figure 10 and 11 show an embodiment in which the cam ring 12 is provided with a transverse cylindrical peg 62, the axis of the peg 62 extending parallel to the axis of the cam ring 12. The peg 62 is angularly movable within a cylindrical slot provided in an end face of a cylindrical trunnion 64, the slot extending diametrically across the trunnion 64.

The trunnion 64 is slidable within a cylindrical bore 68 provided in the advance piston 14 approximately mid way along the length of the piston 14, the bore 68 extending diametrically across the piston 14 and being of depth great enough to accept the trunnion when the peg is at its lowermost point. An end of the piston 14 is provided with a cylindrical recess 66 housing a helical spring 24 arranged to engage with a screw threaded element mounted on the housing 10, the spring 24 biasing the advance piston 14 the right as shown in Figure 10. The piston 14 is provided with a transverse U-shaped slot adjacent the bore 68 which receives the edges of the peg, in use.

On applying high pressure fuel from the feed pump to the advance piston 14 due to relatively high engine speeds, the piston 14 moves towards the left as shown in Figure 10, moving the trunnion 64, peg 62 and cam ring 12 to the left. Due to the angular movement of the cam ring 12 and peg 62 and the linear movement of the advance piston 14, the angle of the peg 62 with respect to the trunnion 64 changes during extension of the piston 14, the trunnion 64 sliding in an upwards direction as shown in Figure 10.

When the high pressure fuel is no longer applied to the advance piston 14 due to a reduction in engine speed, the piston 14, trunnion 64, peg 62 and cam ring 12 return under the action of the spring 24 retarding the timing of delivery of fuel to the engine.

The areas of contact between the advance piston 14, trunnion 64 and peg 62 are relatively large, wear of these part therefore being small.

The advance piston 14 of the embodiments of Figures 7 to 11 may comprise an aluminium piston, for example and anodised aluminium piston, such a material being suitable due to the relatively low contact stress occurring in these linkages. The use of aluminium has the advantage that since the housing is also of aluminium construction, the piston and housing have the same coefficient of thermal expansion, hence the clearance between the piston and the housing remains substantially constant for varying temperatures. Leakage of fuel can therefore be minimised. Such an aluminium piston could also be used in the embodiment of Figures 4 to 6 instead of the composite steel piston in an aluminium "bucket" as shown.

Claims (2)

1. A rotary distributor type fuel injection pump comprising a cam ring which is angularly adjustable about the axis of rotation of the distributor member to vary the timing of delivery of fuel by the pump, a timing control mechanism and a linkage interconnecting the timing control mechanism with the cam ring.

2. A pump according to Claim 1, in which said timing control mechanism includes a fluid pressure operable piston housed in a cylinder, and the linkage comprising a peg extending outwardly of the cam ring and an element interposed between the peg and the piston, the engaging surfaces of said peg, element and piston being shaped so as to allow relative movement as the cam ring is moved angularly by movement of the piston.