GB2289114A

GB2289114A - Manufacture of camshafts

Info

Publication number: GB2289114A
Application number: GB9408667A
Authority: GB
Inventors: Roger Harvey Slee
Original assignee: T&N Technology Ltd
Current assignee: Federal Mogul Technology Ltd
Priority date: 1994-04-30
Filing date: 1994-04-30
Publication date: 1995-11-08
Also published as: GB9408667D0; WO1995030079A1

Abstract

A camshaft (10) is manufactured by forming a plurality of individual cams (12) and mounting them on a shaft (20). Each cam has a groove (16) formed in a bounding surface of a shaft-receiving hole (14) thereof and the cam is held in position by means of a key (30) which is received in the groove (16) and engages a flat (22) formed on the exterior surface of the shaft (20). The flats (22) ensure the correct positioning of the cams. The key (30) may be held in place by its resilience, by adhesive or it can receive a tapered screw in a tapered bore to expand it (Figs. 5 and 6). <IMAGE>

Description

MANUPACTURE OF CAMSHAFTS This invention is concerned with the manufacture of camshafts, for example camshafts of the type used for operating the valves of an internal combustion engine.

Conventionally, camshafts are cast in one piece, ie a plurality of cams and the shaft on which they are mounted are formed at an integral casting. This method, however, requires complex casting and hardening processes and the cast camshaft has to be finished by protracted grinding operations.

There have been numerous proposals for manufacturing camshafts by forming the cams and the shafts separately, assembling the cams on the shaft, and securing the cams to the shaft. For example, the cams may be brazed to the shaft or the shaft may be formed as a tube which is caused to expand into gripping contact with the cams by hydraulic expansion or by passing a ball through the tube. Such methods, however, introduce complex assembling and joining operations to ensure that the cams project from the camshaft in the correct orientations and are securely mounted on the camshaft to prevent relative movement.

Assembled camshafts have hitherto not utilised chill cast cams, ie cams whose surfaces are chilled as they solidify to harden them, because existing attachment methods involve heating which damages the hardened surfaces or, in the case of expansion, tends to split the cams.

It is an object of the present invention to provide a method of manufacturing a camshaft in which the cams and the shaft can be formed separately and assembled to form the completed camshaft, the method being suitable for use with chill cast cams.

The invention provides a method of manufacturing a camshaft by assembling a plurality of individual pre-formed cams on a generally-cylindrical shaft which fits into shaft-receiving holes which pass through the cams, the method comprising forming a key-receiving groove in each cam, the key-receiving groove having an entrance in the bounding surface of the shaft-receiving hole of the cam, the key-receiving groove being positioned at a predetermined orientation relative to the cam, the method also comprising forming flats on the external surface of the shaft at positions along the shaft where cams are required and at orientations such that, when one of the flats is positioned so that it closes the entrance of a key-receiving groove of a cam on the shaft with said flat centralised relative to said entrance, the cam is at the required orientation therefor, the method also comprising positioning said cams on the shaft at their required positions along the shaft and with the entrance of each key-receiving groove closed by a flat, and inserting a key into each key-receiving groove so that the key engages the flat and the cam and locks the cam into its required orientation and position.

In a method in accordance with the invention, the cams can be simply manufactured by chill casting to ensure a relatively soft core and a hard surface. The manufacture of the cams can be completed by drilling the hole and machining the groove. Casting the cams individually and avoiding the need to maintain an accurate angular relationship between different cams during casting allows improved accuracy of the cam profile and consequently a reduction in the finish grinding requirement and hence lower cost. The shaft can also be easily manufactured.

Assembly of the cams on to the shaft is simple and inserting the keys ensures that the cams remain correctly orientated. Furthermore, any orientation error is corrected as the key is inserted since the key centres the cam relative to the flat.

Preferably, the keys each have a flat surface arranged to engage a flat on the shaft. Furthermore, the keys may be arranged to resiliently contract as they are inserted to make insertion easier. For example, the keys may be provided with longitudinally-extending slots therein so that they are deformed as they are inserted and spring back to grip the shaft and the cam. The keys may also be tapered to enable them to be more easily inserted.

In order to lock the cams more firmly in position, the keys may be arranged to be expanded after insertion. For example, each key may have a tapered threaded bore therein into which a tapered threaded expansion member can be inserted to expand the key.

The key-receiving grooves may have a cross-section which is in the shape of a circle with a section bounded by a chord of the circle cut off. This arrangement enables the grooves to be formed by simple machining operations such as slot drilling. Because there is more metal available in that area, the key-receiving groove of each cam may be positioned between the shaft-receiving hole and a crest of the cam surface, eg with a line bisecting the cross-section of the key-receiving groove also passing through the crest.

In order to ensure that the cams do not move on the shaft they may also be secured to the shaft by adhesive, eg Loctite (Registered Trade Mark). The keys may also be secured in the grooves by similar adhesive.

The flats may be formed by machining a maximum of between lmm and 3mm off a cylindrical surface.

The invention also provides a camshaft manufactured by a method according to the invention.

There now follow detailed descriptions, to be read with reference to the accompanying drawings, of two methods of manufacturing a camshaft which are illustrative of the invention.

In the drawings: Figure 1 is a perspective view of a portion of a camshaft, of a cam, and of a key used to secure the cam to the shaft; Figure 2 is a side elevational view of the cam and the portion of the shaft shown in Figure 1 but showing the key in a different relative position; Figure 3 shows an elevational and an end view of the key shown in Figures 1 and 2; Figure 4 is a perspective view of a smaller scale, of the shaft a portion of which is shown in Figures 1 and 2; Figure 5 is an elevational view of an alternative form of key to that shown in Figure 3; and Figure 6 is an elevational view showing the use of the key shown in Figure 5.

The first illustrative method is for manufacturing a camshaft 10, a portion of which is shown in Figures 1 and 2. The method comprises assembling a plurality of individual pre-formed cams 12 on a generally-cylindrical shaft 20. Each of the cams 12 has a cam surface 12a extending around the periphery thereof. The cams 12 are formed by casting and are chilled to harden the surface 12a. Each cam 12 has a shaft-receiving hole 14 passing through the cam in a direction parallel to the cam surface 12a. The holes 14 are cylindrical and are formed by drilling. The shaft 20, which is tubular, fits into the holes 14 and is a close fit therein.

The first illustrative method comprises forming a keyreceiving groove 16 in each cam 12, the groove 16 having an entrance 16a in the bounding surface of the hole 14. The key-receiving groove 16 is formed by slot drilling a smaller cylindrical hole parallel to the hole 14 with the holes 14 and 16 partially overlapping. Thus, the keyreceiving groove 16 can be considered to have a crosssection which is in the shape of a circle with a section bounded by a chord (at the interception points of the holes 14 and 16) cut off.

The key-receiving groove 16 is positioned at a predetermined orientation relative to the cam surface 12a.

Specifically, the key-receiving groove 16 is positioned between the shaft-receiving hole 14 and a crest 12b of the surface 12a with a line bisecting the groove 16 passing through the crest 12b and a central axis 18 of the hole 14.

The first illustrative method also comprises forming flats 22 on the generally-cylindrical external surface of the shaft 20. As illustrated by Figure 4, the shaft 20 is provided with the flats 22 by machining off a portion of the cylindrical external surface of the shaft 20 to leave a flat surface with a maximum of between lmm and 3mm being machined off from the cylindrical surface. The flats 22 are formed at positions along the shaft 20 where cams 12 are required and at orientations such that, when one of the flats 22 is positioned so that it closes the entrance 16a of a key-receiving groove 16 of a cam 12 on the shaft 20 with said flat 22 centralised relative to said entrance 16a, the cam 12 is at the required orientation therefor. In other words, when the cam 12 is in the required position and orientation, a line normal to the flat 22 at the centre thereof bisects the groove 16.

The first illustrative method also comprises positioning the cams 12 on the shaft 20 at their required positions along the shaft 20 and with the entrance 16a of each key-receiving groove 16 closed by a flat 22, and inserting a key 30 into each key-receiving groove 16 so that the key 30 engages the flat 22 and the cam 12 and locks the cam 12 into its required position and orientation. If the orientation of a cam 12 is slightly incorrect, the action of inserting the key 30 serves to correct this.

The form of the keys 30 can be seen from Figure 3.

Each key 30 is generally cylindrical except that it has a flat surface 32 arranged to engage the flat 22 on the shaft 20. In a cross-sectional view, the surface 32 appears as a chord of the circle formed by the key 30. At one end thereof, the key 30 is tapered inwardly as shown at 34 to assist in insertion of the key into the groove 16. The tapered end 34 also has a bore centrally formed therein so that the interior of the key is hollow and the key is split longitudinally by four equally-spaced slots 36 which each extend from the external surface of the key 30 to the bore 35. This arrangement enables the key 30 to resiliently contract as it is inserted into the groove 16 and to expand once in the groove 16 to grip the cam 12 and the shaft 20 firmly.

In order to enhance the firmness of the joints, the cams 12 are also secured to the external surface of the shaft 20 by adhesive and the keys 30 are secured in the grooves 16 by adhesive.

As shown in Figure 2, the flats 22 are sufficiently long to receive both the cam 12 and the key 30 which can be aligned with the groove 16 so that axial movement of the key 30 inserts it into the groove 16. In order to assist this process, a tool 40 can be inserted so that it engages a shoulder 22a at the end of a flat 22 and also engages one side of a cam 12. This tool 40 braces the cam 12 against movement towards the shoulder 22a so that the key 30 can be inserted, eg by use of a hammer, without moving the cam 12 along the shaft 20.

The second illustrative method is generally similar to the first illustrative method described above and like reference numerals are used to refer to like parts. The second illustrative method only differs from the first illustrative method in two respects, viz. in the form of the entrances to the key-receiving grooves 16 and in the form of the keys inserted in said grooves 16.

In the second illustrative method, the keys 40 shown in Figures 5 and 6 are used instead of the keys 30. Each key 40 is generally-cylindrical except for a flat surface 42 arranged to engage a flat 22. A threaded bore 44 extends longitudinally through each key 40 and this bore is tapered at an inclination of one in sixteen. A longitudinal slot 46 extends from the bore 44 to a cylindrical portion of the external surface of the key 40.

This slot 46 enables the key 40 to be expanded after insertion in one of the grooves 16 by insertion of an expansion member 48 into the bore 46. The expansion member 48 has a tapered and threaded external surface and can be screwed into the bore 46 using a hexagonal recess in an end of the member 48. The expansion of the key 40 locks the cam 12 more firmly in position and allows the adhesive mentioned above to be dispensed with.

In the second illustrative method, the entrances 16a to the grooves 16 are enlarged relative to those used in the first illustrative method to allow more centralising movement as the key 40 is inserted.

Claims

1A method of manufacturing a camshaft by assembling a plurality of individual pre-formed cams on a generally-cylindrical shaft which fits into shaft receiving holes which pass through the cams, the method comprising forming a key-receiving groove in each cam, the key-receiving groove having an entrance in the bounding surface of the shaft-receiving hole of the cam, the key-receiving groove being positioned at a predetermined orientation relative to the cam, the method also comprising forming flats on the external surface of the shaft at positions along the shaft where cams are required and at orientations such that, when one of the flats is positioned so that it closes the entrance of a key-receiving groove of a cam on the shaft with said flat centralised relative to said entrance, the cam is at the required orientation therefor, the method also comprising positioning said cams on the shaft at their required positions along the shaft and with the entrance of each key-receiving groove closed by a flat, and inserting a key into each key-receiving groove so that the key engages the flat and the cam and locks the cam into its required orientation and position.

2 A method according to claim 1, wherein the keys each have a flat surface arranged to engage the flat on the shaft.

3 A method according to either one of claims 1 and 2, wherein the keys are arranged to resiliently contract as they are inserted.

4 A method according to claim 3, wherein the keys are provided with longitudinally-extending slots to enable them to resiliently contract as they are inserted.

5 A method according to any one of claims 1 to 4, wherein the keys are arranged to be expanded after insertion.

6 A method according to claim 5, wherein each key has a tapered threaded bore therein into which a tapered threaded expansion member can be inserted to expand the key.

7 A method according to any one of claims 1 to 6, wherein the key-receiving grooves have a cross-section which is in the shape of a circle with a section bounded by a chord of the circle cut off.

8 A method according to any one of claims 1 to 7, wherein a line bisecting the cross-section of the key receiving groove of a cam also passes through a crest of a cam surface of the cam.

9 A method according to any one of claims 1 to 8, wherein the cams are also secured to the shaft by adhesive.

10 A method according to any one of claims 1 to 9, wherein the keys are also secured in the grooves by adhesive.

11 A method according to any one of claims 1 to 10, wherein said flats are formed by machining a maximum of between 1 and 3mm off a cylindrical surface of the shaft.

12 A method of manufacturing a camshaft substantially as hereinbefore described with reference to the accompanying drawings.

13 A camshaft manufactured by a method according to any one of claims 1 to 12.