GB2145779A - A face cam drive, particularly for fuel injection pumps - Google Patents

Abstract

A face cam (3) for reciprocating a piston (1) of an injection pump runs over rollers (7) mounted on pins (9). The ends of the pins (9) are received in radially extending recesses (10) in a roller support ring (15) mounted in a housing (20). Thrust plates (18) are shrink-fitted or force-fitted onto the pins (9), whereby radially outward forces received by the pins (9) are transmitted to the support ring (15) and not to the housing wall (16). <IMAGE>

Description

SPECIFICATION "A face cam drive, particularly fuel injection pumps" The invention relates to a face cam drive of the type in which a face cam plate cooperates with rollers journalled in a roller support body.

A face cam drive of this kind for a fuel injection pump is described in U.S.A. Patent Specification No. 3 374 685, in which there is provided a roller support ring which is angularly displaceably fitted in a circular cylindrical housing and has an inner circular wall and an outer circular wall which define a recess for receiving the rollers. Each of the two ends of each pin on which the rollers are mounted is journalled in a respective wall, such that the pins terminate flush with the circular-cylindrical wall surface of the housing of the injection pump. A radially outwardly directed thrust ring is provided on each pin, as well as a floating bush on which the respective roller is mounted.The roller and bush abut in a radially outward direction against the thrust ring whose radially outwardly located end face is adapted to the circular configuration of the outer wall of the roller support ring. In order to ensure a contact surface of constant size between the roller and the cam track of the face cam plate which runs over the rollers, the outer circumference of the floating bush is of spherical construction, so that the roller is tiltable. Cam drives designed in such a manner, partiuclarly those having a cylindrical floating bush, have the disadvantage that the pins are moved radially outwardly when the face cam plate is subjected to a high load, so that the pins dig into the wall of the circular cylindrical housing which accommodates the roller support ring.In an extreme case, the housing wall can be pierced, or, alternatively, the angular displaceability of the roller support ring is obstructed in the event that the fuel injection pump is operated for a long time with the roller support ring in a given angular position. This is particularly the case when the face cam plate is driven for the purpose of running over the rollers, and the roller support ring is subatantially stationary. With such a design, corrective adjustment of the roller support ring is only necessary in order to time the commencement of injection. Damage to the circular cylindrical housing wall can prevent angular displacement of the roller support ring in an unfavourable case, if the pin or pins project into these damaged portions of the housing wall during the adjusting movement.

The present invention resides in a face cam drive having a circular face cam plate whose circular cam track co-operates with at least one roller which is mounted on a pin which is directed radially of the axis of the face cam plate and whose ends are mounted in a support body, the latter being located radially in a housing and having a recess for receiving the roller, and a thrust disc being disposed on the pin between the radially outwardly directed end face of the roller and the adjacent wall of the recess in the support body, the pin located relatively to the support body in a radially outward direction.

This has the advantage that he radial outward force components acting upon the pins are absorbed by the support body, so that no force component is transmitted to the wall of the housing.

If the thrust disc is connected to the pin by means of friction, it is possible to transmit the radial force component to the roller support body over a large area, so that wear can be minimised.

By rigidly connecting the thrust disc to the pin, a simple solution is obtained which is advantageous with respect to machining and in which there is no need to modify the geometrical shape of the pins and the thrust disc relative to the construction known hitherto.

If an intermediate bush, by which the roller is journalled, is axially connected to the pin, a large-area contact under friction with the pin is obtained, the intermediate sleeve advantageously being shrunk onto the pin.

If a retaining ring is disposed on the pin between the thrust ring and the roller, simple assembly is enabled and secure connection with only a slight loss of bearing surface between the roller and the pin is ensured, the dimensions otherwise being the same as those in the known constructions.

The roller is advantageously mounted on a floating intermediate bush which in turn abuts as a force transmission member against the retaining ring.

Instead of the expense of assembly involved in rigidly connecting an intermediate bush to the pin, the pin may have a bearing portion on which the roller is journalled and which is of a larger diameter than at least a portion of the pin mounted in the support body. Reliable force transmission between the pin and the thrust disc is thereby ensured.

The invention is further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a fragmentary cross section through the parts, material to the invention, of a fuel injection pump having a pump piston which is reciprocated and rotated by a face cam drive in accordance with one embodiment of the invention, Figure 2 shows a detail of a second embodiment of the pin having a pressed-on intermediate ring which carries the roller provided for supporting the face cam plate, Figure 3 shows a third embodiment having a retaining ring which is fitted into an annular groove in the pin and whose portion project ing beyond the pin extends into an annular recess of the floating bush which is mounted on the piston. and which carries the roller, Figure 4 shows a fourth embodiment modified relative to the embodiment of Fig. 3, the floating bush being shortened by the width of the retaining ring, Figure 5 shows a pin which is welded to the support body, and Figure 6 is a fragmentary cross section through the support body with the pin, thrust disc, floating bush and roller ring, and a portion of the housing wall which is radially adjacent to the support body, a thrust ring made from wear-resistant material being let into the housing wall.

Referring to the fragmentary cross section through a distributor-type fuel injection pump shown in Fig. 1, only that portion of a pump piston 1 is shown whose foot 2 is mounted on a face cam plate 3 to which the pump piston is non-relatively-rotatably connected by way of a pin 4. The pump piston is pressed against the face cam plate by means of a compression spring 5 which abuts against a support (not further illustrated) secured relative to the housing and which is seated on the foot 2 of the pump piston. The face cam plate is circular and the peripheral portion of its face remote from the pump piston 1 has a cam track 6 by means of which the face cam plate rests on rollers 7. The rollers 7 are mounted on pins 9 by way of floating bushes 8. The pins 9 project at each end beyond the floating bushes 8, and their free ends are mounted in U-shaped recesses 10.The recesses 10 are located in the end face of an inner wail 1 2 and the end face of an outer wall 1 4 of a roller support ring 1 5. The roller support ring 1 5 is also of circular configuration and is fitted into a cylinder 1 6 of the housing of the fuel injection pump, such that it is possible to anguiarly displace the roller support ring by means of an actuating device (not illustrated). This angular displacement is effected for the generally known purpose of timing the commencement of injection and need not be further described here. The pins 9 are located in a radial plane parallel to the face cam plate and are radially directed and distributed such that the cam plate is loaded preferably symmetrically by the support forces exerted by the rollers 7.A respective thrust disc 1 8 is mounted on each pin 9 radially outwardly between the end faces of the rollers 7 and of the floating bushes 8 and the inner end face of the outer wall 14 of the roller support ring 15, the thrust disc being connected by friction to the pin by, for example, shrinking-on or pressing-on.

The thrust discs 18 and the rollers 7 together with the floating bushes 8 extend into an annular recess 1 9 which is formed by the inner annular wall 1 2 and the outer annular wall 14 of the roller support ring 1 5.

While the roller support ring 1 5, as described above, is only turned for the purpose of correction, and is substantially stationary and is supported on the bottom of the housing in the axial direction of the pump piston by a support ring 20, the face cam plate is rotated by a drive shaft 22 by way of an interposed coupling 23 The cam lobes provided on the face cam plate determine the number of strokes of the pump piston per revolution.When the face cam plate is moved upwardly against the force of the return spring, impact-like forces act upon the rollers 7 and, in conjunction with the rotary movement, seek to displace the pins 9 outwardly By virtue of the fact that. in the advantageous design in accordance with the invention, the thrust disc 1 8 is connected to the pin by friction, the pin 9 comes into abutment against the outer wall 1 4 of the roller support ring by way of the disc 1 8, hence avoiding stress on the cylindrical housing wall 1 6. The outer face of the thrust ring 1 8 is shaped such that it is adapted to the internal radius of the outer wall 1 4 and comes into abutment thereagainst.

Only a cross section through the roller support ring 1 5 is shown in Fig. 2 in order to illustrate a second embodiment of the pin and roller, Here also. the pin 9 is located in Ushaped recesses 10 in the roller support ring 1 5 in the same manner. However, in this embodiment, the floating bush 8' is an intermediate sleeve which is shrunk onto the pin and on which the roller 7 runs. In the same manner as in the embodiment of Fig. 1, the thrust disc 1 8 is provided between the end face of the intermediate sleeve 8' and the inner end face of the outer race 14, and, when subjected to radial stress, the pin 9, together with the intermediate sleeve 8', come into abutment against the thrust disc 18.Hence, in this embodiment, the pin 9 abuts against the roller support ring by way uf the intermediate sleeve 8' and the thrust disc 1 8. Large area contact with the pin 9 is provided by shrinking the sleeve 8' onto the pin 9, so that a reliable connection can be made. In an alternative design, the pin 9 can have a collar at this location instead of the shrunk-on intermediate sleeve 8', this having advantages with regard to manufacture and assembly. This embodiment is also advantageous in that the pin 9 can be of symmetrical construction, so that there is no risk of confusion during assembly.

As above, the embodiment of Fig. 3 is shown only in the form of fragmentary cross section. In the present embodiment, a pin 9' is provided which has an annular recess 24 into which a retaining ring 25 is fitted. The retaining ring 25 projects beyond the external diameter of the pin 9' and extends into a recess 26 at the outermost end of the internal diameter of the floating bush 8" which has already been described with reference to Fig.

1. Advantageously, the recess 26 can be in the form of a chamfer in the internal bore.

The roller 7 is mounted on the floating bush 8" in the same manner as in Fig. 1. The roller 7 and the bush 8" abut radially against the thrust disc 18 which is also provided in the present instance and which is rotatably mounted on the pin 9' at the other side of the retaining ring 25. In this embodiment, either the pin 9' and the retaining ring 25 can abut against the thrust disc 18, or the floating bush 8' can abut against the retaining ring 25. In both cases, the pin 9' is secured outwardly in an axial direction.

It is disadvantageous that the floating bush 8" is asymmetrical at one end, and hence there is the risk of confusion during assembly.

However, a bush which is of symmetrical construction in order to avoid this disadvantage again has the disadvantage that its bearing surface is considerably red,uced relative to the installation space available.

This disadvantage is avoided by the embodiment of Fig. 4 in which the floating bush 8"' is again of symmetrical construction and does not have a recess 26, and is shortened only by width of the retaining ring 25. Hence, although the bearing surface is also slightly decreased compared with the construction of the roller ring without securing the pin, there is more bearing surface available than in the case of the embodiment of Fig. 3. The spatial requirement at the supporting end of the pin can be further reduced by providing the thrust disc 1 8 with a chamfer adjacent to the retaining ring 25. The width of the bush is then only decreased by approximately half the width of the retaining ring.

In an alternative embodiment (not shown), the pin has a bearing portion of larger diameter on which the intermediate bush is received and a portion of smaller diameter on which the thrust disc is received and which is supported by the outer annular wall of the roller support body. The step between the larger and small diameter portions thus axially abuts the thrust disc.

A solution having the maximum !oad-bearing capacity is shown in Fig. 5 in which the thrust disc 18, the floating bush 8 and the roller 7 are freely rotatable on the pin 9, but in which the pin 9 is welded by its supporting surfaces to the U-shaped recesses 10 of the roller support ring 1 5 to prevent axial displacement. Preferably, this can be effected by electron-beam welding, a method by which extremely accurate welds can be made without any considerable and detrimental development of heat.

The embodiment of Fig. 6 shows a further possibility of axially securing the pin 9. The present embodiment is modified relative to Fig. 5 in that, instead of welding the pin 9, a ring 28 made from wear-resistant material is let into the adjacent cylindrical housing wall, so that damage to, or a change in, the cylindrical wall does not occur in the region of the pin 9, or only occurs after the fuel injection pump has been in operation over a considerable period of time.

Claims (11)

1. A face cam drive having a circular face cam plate whose circular camtrack co-operates with at least one roller which is mounted on a pin which is directed radially of the axis of the face cam plate and whose ends are mounted in a support body, the latter being located radially in a housing and having a recess for receiving the roller, and a thrust disc being disposed on the pin between the radially outwardly directed end face of the roller and the adjacent wall of the recess in the support body, the pin located relatively to the support body in a radially outward direction.

2. A face cam drive as claimed in claim 1, in which the pin is connected by friction to the thrust disc which abuts the said recess wall.

3. A face cam drive as claimed in claim 2, in which the thrust disc is rigidly connected to the pin.

4. A face cam drive as claimed in claim 2, in which an intermediate bush on which the roller is mounted is rigidly connected to the pin.

5. A face cam drive as claimed in claim 2, in which a retaining ring is disposed on the pin and between the thrust disc and the roller.

6. A face cam drive as claimed in claim 5, in which an intermediate bush serving as a bearing for the roller is mounted on the pin.

7. A face cam drive as claimed in claim 1, in which the pin is welded to at least one support point on the support body.

8. A face cam drive as claimed in claim 2, in which the pin has a portion which has a larger diameter than at least a portion of the pin mounted in the support body and which serves as a bearing for the roller.

9. A face cam drive as claimed in claim 1, in which a ring of wear-resistant material is let into the wall of the housing so as to be abutted by the outer end of the pin and thereby receive the radially outward forces from the pin, instead of such forces being received by the support body.

10. A face cam drive as claimed in any preceding claim, in which the face of the thrust disc abutting the said recess wall is adapted to the radius of the inner surface of such wall.

11. A face cam drive constructed substantially as herein described with reference to and as illustrated in the accompanying drawings.