US20080060594A1

US20080060594A1 - Engine tubular camshaft assembly with multi-lift cam sets and method

Info

Publication number: US20080060594A1
Application number: US11/531,490
Authority: US
Inventors: Michael R. Cline; Daniel L. O'Neil
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2006-09-13
Filing date: 2006-09-13
Publication date: 2008-03-13
Also published as: DE102007043169A1; CN101153549A

Abstract

An engine camshaft assembly includes a hollow tubular shaft mounting a plurality of separate cam sets, each including multiple camps. Each cam includes an outer cam surface bounded by opposite parallel sides and including an axial opening extending through said sides. Each cam set includes at least two associated cams positioned in side-by-side relation with their openings axially aligned. A shoulder protruding from a side of one of the cam engages an adjacent side of another associated cam, thus maintaining the sides of the associated cams in fixed parallel relation. The tubular shaft extends through the cam openings and supports the cam sets on a common rotational axis. During assembly, the shaft is expanded into engagement with the openings so that the cam sets are retained in fixed axial and angular relation on the shaft.

Description

TECHNICAL FIELD

This invention relates to assembled camshafts for internal combustion engines, particularly those which are assembled by expansion of a central tube within associated cams and other components. In preferred embodiments, the invention relates to camshafts for use with two-step valve lifters capable of opening the engine valves with selectable low or high valve lift settings or full lift and zero lift selectable settings for differing conditions of engine operation

BACKGROUND OF THE INVENTION

It is known in the art to manufacture engine camshaft assemblies by the expansion of tubular shafts into prelocated cams, journals and other elements to be included in the assembly. Current engine designs including two intake and two exhaust valves per cylinder have required space for many valve actuation components within an engine cylinder head. Current plans for varying the lift of intake or exhaust valves require the use of cams of differing geometries which may interact with other hydraulically switched components to control which geometry effects movement of the valve functions. Two or three cams per valve are required to execute that control. The added cams and other component complexities limit space availability and require minimum size and extremely precise control at locations of the camshaft features.

SUMMARY OF THE INVENTION

The present invention provides features that improve the control of lateral spacing and perpendicularity of dissimilar components such as cams, spacers and other elements as they are assembled and fixed to an expandable tubular shaft. Through the addition of spacer sleeves and cam shoulders, very tight dimensional control may be obtained of these characteristics. Such control is necessitated by a two-step camshaft design that does not permit high tolerances for lateral spacing and perpendicularity characteristics. Proposed cam follower designs require three actuating mechanisms to contact the three cams that control the lift events for each valve. Two sliding followers contact the outside cams while a rolling follower unit makes contact with the steel center cam. These precise mechanisms must be located accurately, as must be the cam contact points, for the system to perform properly at high speeds.
The present invention provides cam sets for each valve that may include a steel central cam associated with two cast iron end cams. The cam sides are accurately spaced from one another and maintained perpendicular by the use of shoulders on the central cam, which extend into engagement with the end cams to maintain close tolerances for their lateral spacing. Spacers, which may act as bearing sleeves, are provided for accurately spacing the cam sets laterally from one another. The design of the assembly allows the use of differing cam materials, or materials for other components applied to a camshaft, to be assembled with a high degree of accuracy for lateral spacing and with a minimum of manufacturing difficulty for the individual components utilized in the cam sets and other elements. The use of hardened steel cams with spacing shoulders, and bearing sleeves precision cut to a length and perpendicularity, afford the accurate dimensional characteristics required for assembled camshafts capable of operating in the current limited space available in some new engine designs.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a portion of an assembled camshaft having a pair of spaced three element cam sets separated by a bearing sleeve spacer and secured by expansion of a hollow tube within the components by mechanically passing a steel ball or similar member through the hollow center of the tube to expand its outer periphery into engagement with the components attached.

FIG. 2 is an exploded view of the camshaft of FIG. 1 illustrating the cams of the cam sets, the spacer sleeve and the tubular shaft making up the camshaft assembly illustrated in FIG. 1.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT

Referring to the drawings in detail, numeral 10 generally indicates an assembled camshaft formed in accordance with an exemplary embodiment of the invention and having a rotation axis 11. The assembly includes an axially extending hollow tubular shaft 12, a plurality of cam sets 14 each including one inside or center cam 16 and two end or outside cams 18, and a tubular spacer or bearing sleeve 20 laterally separating the cam sets 14 along the axis 11 for rotation with the shaft 12.
Each of the cams 16, 18 includes an axial opening 22 extending through opposite parallel sides 24 of the cam. A similar axial opening 26 extends through the bearing sleeve 20. The central or inner cam 16 includes annular shoulders 28 extending from the opposite sides 24 of the cam with accurately machined end surfaces 30 of the shoulders engaging inner sides 24 of the associated end cams 18. In assembly, the parallel sides 24 of the end cams and the end surfaces 30 of the center cam shoulders coact to maintain parallelism of the cams 16, 18 making up each cam set 14. Parallel end surfaces 32 of the bearing sleeves 20 similarly engage outer sides 24 of the adjacent cam sets to maintain parallel relations of the cams in the associated cam sets.
The cam sets and bearing sleeves are fixed in position on the tubular shaft 12 by insertion of the shaft through the openings 22, 26 of the cam sets and bearing sleeve respectively and maintaining the assembled components in longitudinal engagement while mechanically expanding the tubular shaft 12 by passing of an oversized ball through the hollow center 34 of the shaft. This process expands the exterior of the tube into engagement with the openings of the various components to lock the cam sets and bearing sleeve into position on the tubular shaft 12 so that the cams 16, 18 and the bearing sleeve 20 are maintained in predetermined lateral and angular relation established prior to the mechanical expansion step. The sides of the cams are also maintained in parallel relation with predetermined accurate dimensional spacing between the sides of the associated cams in each cam set 14.
As illustrated, outer surfaces 38 of the end cams 18 have maximum eccentricities for actuation of the associated engine valves to high or maximum lift. Outer surfaces 36 of the center cams 16 have reduced eccentricities for actuation of the associated engine valves to a low lift setting.
In an exemplary embodiment, the center cams 16 may be made from hardened steel while the end cams 18 may be formed of gray cast iron or other suitable material for use with sliding contact cam followers. Similarly, in the center cams, hardened steel material is suitable for use with conventional roller follower lifters. The bearing sleeve or spacer 20 may be formed of gray cast iron or steel depending on its use as a bearing and other requirements of the application. The tubular shaft 12 may be formed of a mild steel suitable for use in the ball expansion process. In order to maintain accurate dimensioning of the outer surface 36, 38 of the center and end cams, respectively, these surfaces are ground to final dimensions after the expansion step that forms the elements of the camshaft into an assembly.
In addition to the ball expansion process, other forms of tube expansion could be used in practice of the present invention. These could include mechanical forms of expansion, other than balls, as well as tube expansion by hydraulic or other forces.
It should be understood that other materials and processes could be utilized, for the various components and steps embodied in assemblies of the present invention, in addition to those specifically mentioned in regard to the illustrated embodiment. The various features of the invention including the parallel sides and shoulders of the cam set elements and the bearing sleeves or spacers and the premachined axial spacing provided by the shoulders and bearing sleeves, together with the final grinding of the cam surfaces 36, 38 of the cam sets after assembly of the elements on the shaft, all combine to provide an accurately formed camshaft assembly with minimum tolerance variations and capable of actuating the closely spaced followers of two-step or switching valve lifters while occupying a minimum amount of space within the cylinder head or other camshaft mounting location in an engine.
While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.

Claims

1. An engine camshaft assembly rotatable on a rotational axis and comprising:

a hollow tubular shaft and a plurality of separate cam sets each including multiple cams;

each cam including an outer cam surface bounded by opposite parallel sides and an axial opening extending through the sides;

each cam set including at least two associated cams positioned in side by side relation with their openings axially aligned and a shoulder protruding from a side of one of the cams and engaging an adjacent side of an other associated cam, thus maintaining the sides of the associated cams in fixed parallel relation;

the tubular shaft extending through the cam openings and supporting the cam sets on a common axis, the shaft being expanded into engagement with the openings so that the cam sets are retained in fixed axial and angular relation on the shaft.

2. An assembly as in claim 1, wherein the outer cam surfaces are finished by grinding after assembly of the cam sets to the shaft.

3. An assembly as in claim 1, including camshaft bearing journals formed between at least selected pairs of cam sets and having bearing surfaces formed by grinding after assembly of the camshaft.

4. An assembly as in claim 3, wherein the bearing journals are formed on steel bearing sleeves fixed by expansion of the tubular shaft within the sleeves.

5. An assembly as in claim 4, wherein the bearing sleeves include ground parallel ends engaging the sides of adjacent cams in the cam sets and assisting in maintaining the parallel relation of the cams in the cam sets of the camshaft assembly.

6. An assembly as in claim 1, wherein at least some of the cam sets include cams having differing eccentricities for actuation of two-step valve lifters.

7. An assembly as in claim 1, including cam sets for actuation of two-step valve lifters, each such cam set including a low lift central cam positioned between two high lifter end cams.

8. An assembly as in claim 7, wherein the central cams are formed of hardened steel for actuation of roller followers and the end cams are formed of cast iron for actuation of sliding cam followers.

9. An assembly as in claim 8, wherein the central cams have shoulders extending from both sides and engaging the sides of the associated end cams to provide a predetermined spacing of the outer cam surfaces from one another.