Assembled camshafts.

Abstract: Camshaft assemblies, methods and apparatus are provided for making camshafts (10) by the expansion of tubular shafts (11) into pre-located cams (12), journals (14) and other elements, if desired. Features of the camshafts (10) include tri-lobe or poly-lobe element openings (15), preferably splined or serrated for low-energy filling and high torque-capacity, and high-strength low-alloy mild steel tubular shaft material. The method emphasizes loading the shaft (11) to prevent axial lengthening thereof during expansion thereof by a technique such as mechanical "ballizing". The apparatus (27) includes adjustable thrust blocks (38) and locating plungers (39) with incorporated flush pin gauges (40,42) together with hydraulic or other loading means (51), all for use in carrying out the assembly method with various benefits from the incorporated features.

Description: Technical Field This invention relates to camshaft assemblies for intenal combustion engines and similar engines. In particular, the invention relates to an assembled camshaft as specified in the preamble of claim 1. Background United States patent 4,597,365 discloses a camshaft assembly and method involving retention of cam and journal elements on a hollow shaft by expansion of the shaft into engagment with pre-shaped openings of the elements. Various other camshaft assemblies and methods are also shown by the prior art. While certain of these arrangements provide benefits in economy and structure, further economies are desirable for making the most efficient use of this technology. Summary of the Invention The present invention provides improved camshaft assemblies, which yield benefits in structural soundness for assembled camshafts, particularly of the type described in the afore-mentioned U.S. patent 4,597,365, the disclosure of which is incorporated herein by reference. A camshaft assembly for an internal combustion engine according to the present invention is characterised by the features specified in the characterising portion of claim 1. An improved camshaft according to the invention includes the use of non-round element openings comprising so-called curved polygons of preferably uniform diameter and having odd numbers of slightly eccentric lobes. These configurations minimize the energy required for their filling by expansion of an associated hollow shaft whilst providing a joint of high torque capacity. The addition of one or more small grooves or splines on the ends of the lobes further improves the torque capacity. By use of preferred materials for the shaft, the torsional strength relative to the expansion energy required may be further improved. These and other advantages of the invention will be more fully understood from the following description of certain embodiments of the invention taken together with the accompanying drawings. Brief Drawing Description In the drawings: Figure 1 is a pictorial view of a portion of an internal combustion engine camshaft assembly formed in accordance with the invention; Figure 2 is a transverse cross-sectional view of a portion of the camshaft assembly from the plane indicated by the line 2-2 of Figure 1; Figure 3 is a longitudinal cross-sectional view of a portion of the camshaft assembly from the plane indicated by the line 3-3 of Figure 2; Figure 4 is a pictorial view of a separate cam element prior to assembly and having a tri-lobe opening according to the invention with inwardly-splined lobes; and Figure 5 is a graphical presentation of the development of a tri-lobe configuration having uniform diameters according to the invention. Detailed Description Referring now to the drawings in detail, numeral 10 generally indicates part of a finished camshaft assembly formed in accordance with the invention. Camshaft 10 includes a hollow supporting tubular shaft 11 which has been expanded in a manner to be subsequently described. While the shaft may be made of ordinary low carbon steel as noted in US-A-4,597,365, it is preferable to make the shaft 11 of a mild steel of High Strength Low Alloy specification such as SAE 1022 HSLA. The steel tubing used to make the shaft may be of a type which is electric resistance-welded and drawn over a mandrel, having a yield strength of 310264.2379211.8 kPa (45,000-55,000 psi). Fixedly positioned on the tube 11 are a plurality of cam elements 12 and journal elements 14. Additional elements such as gears, eccentrics or sprockets could also be included if desired. The elements 12, 14 are longitudinally spaced and the cam elements 12 are angularly oriented in predetermined positions for actuating valve gear in an internal combustion engine. The cam elements 12 are preferably forged and hardened, either fully or on the wearing surfaces thereof, and the journal elements 14 may be similarly formed or, if desired and their operation permits, may be formed of non-hardened material. The forged, or otherwise formed, cam and journal elements are provided with shaft-receiving openings 15, which are preferably non-circular to positively lock the elements onto the shaft when it is expanded into the openings. It has been found that a preferred shape or configuration for the openings is that of a so-called curved polygon of preferably uniform, or essentially uniform, diameter. Such curved polygons may be made with any odd number of lobes, however it is preferable to obtain good results using a configuration, which is termed a tri-lobe, having three eccentric lobes 16 (see Figure 2). Minimal eccentricity of the opening is required and preferred for achieving high torque capacity with a minimum of expansion energy exerted on deforming the shaft. An eccentricity of only 0.000127 m (five thousandths of an inch) (0.000127 m difference in radial height between the lobes and adjacent valleys) gives good results although greater eccentricities can be used if desired. Preferably the periphery of said openings 15 has an eccentricity of from 0.4 to 1.5 percent of the uniform diameter of the openings. To further increase the torque capacity, the addition of one or more small serrations or splines 17, preferably at the ends of the lobes, is also desirable. The addition of nine inwardly-protruding and longitudinally-extending splines 17 has been found effective. These splines are preferably arranged in closely spaced groups of three at the end of each of the lobes 16 of the openings 15. The splines protrude inwardly only about 0.000127 m (0.005 inches), or approximately equal to the preferred tri-lobe eccentricity. The addition of these splines was found to increase the breakaway torque for the shaft-mounted tri-lobe elements by about 20-25 percent. Figure 4 illustrates a cam element 12 prior to assembly and having the preferred nine-splined tri-lobe opening previously described. Obviously, in this and the previous views, the eccentricity of the opening is grossly exaggerated for clarity of illustration as it would be almost unnoticeable if drawn in its true configuration. In Figure 5, a graphical illustration of the development of a tri-lobe figure is presented having an eccentricity 18 measured from a circle 19 defining the minimum radius of the tri-lobe perimeter 20. The developed perimeter 20 is made up of blended tangent swing radii in the form of a series of alternating long arcs 22 and short arcs 23 which are drawn from three equally spaced centres 24 spaced about the true centre 25 of the figure. The result is that the perimeter has an overall uniform height or width 26 in any direction. For simplicity, this is generally referred to as a uniform diameter 26 although it should be understood that this uniform diameter dimension passes sequentially through each of the three centres 24 and only passes through the true centre 25 when the diameter is at the midpoints of two opposing long and short arcs 22, 23. Assembly Method The manufacture of a camshaft assembly in accordance with the invention is in many ways similar to that described in US-A-4,597,365, although including significant differences in the following preferred steps: 1) The elements, such as cams and journals, a gear, eccentric or sprocket, are made with, or provided with, the pre-formed shaft openings 15 and are formed to relatively close, but normally unfinished, dimensions. In accordance with the invention, the openings are preferably non-round curved polygons of minimal eccentricity, preferably tri-lobes having one or more inwardly-projecting splines 17 at the lobe ends. Additionally, grooves or serrations extending outwardly from or into the tri-lobe surface, or other variations, may be used. The tri-lobe or other odd-lobed curved polygon shape requires lower energy for filling by tube expansion while giving high breakaway torques for the completed assembly. Displacement of material from the valleys into the adjacent lobes with a minimum of expansion due to the preferred constant diameter, or height, of the polygon eccentric perimeter is believed to be an advantage of this configuration that leads to the lower energy requirement. 2) A tubular shaft 11 is provided, preferably made of high-strength low-alloy mild steel such as SAE 1022 HSLA. The tubular shaft may be of the resistance-welded type, sized by drawing over a mandrel and having a yield strength of 310264.2-379211.8 kPa (45,000-55,000 psi). This low yield strength combines with significant work-hardening after yielding to provide low expansion energy with significantly higher breakaway torques after assembly than other materials. The shaft outer diameter is circular and sized to fit closely but freely within the eccentric shaft openings 15 of the elements 12 and 14. The dashed line 53 in Figures 2 and 4 represents the shaft outer diameter before expansion. Camshafts have been made with shafts of 19.1 mm, 22.22 mm and 25.4 mm (3/4, 7/8 and 1 inch) outer diameters but other sizes including larger and smaller diameters could be utilized if desired. 3) The cam, journal and other elements, if any, are positioned in a fixture with their openings 15 aligned on a common axis. The fixture may be similar to, but preferably differs from, that described in US-A-4,597,365 in various ways, including the construction of the locators and spacers and the addition of locating and gauging means and shaft end-loading means described in our co-pending divisional European patent application referred to hereinafter. 4) The fixture is closed, holding the elements in position and the shaft is inserted into the openings 15 in a predetermined longitudinal position. The shaft ends are then loaded by hydraulic, mechanical or other force-applying means with a force sufficient to prevent substantial longitudinal growth of the shaft during the subsequent steps. 5) The shaft is expanded in any suitable manner. Mechanical expansion by a ball forced through the tubular shaft 11 from one end to the other end is the preferred process. With this process, sometimes known as "ballizing", a uniformly-sized smooth interior 54 is formed within the tubular shaft. The ball is preferably large enough to expand the tubular shaft into full engagement with the element openings 15 and radially beyond the openings between the elements, as is shown clearly in Figure 3, so that the elements are permanently fixed in their established positions, both angularly and longitudinally. Preferably the ball has an outer diameter which is greater than the initial diameter of the tubular shaft by an amount greater than the sum of (1) the eccentricity of the cam element opening and (2) the initial diametral clearance between the tubular shaft, prior to the expansion thereof, and the least radial dimension of the cam element opening, but which is less than three times that sum. In an embodiment wherein the initial clearance between the tri-lobe openings 15 and the shaft 11 before expansion was 0.000203 m (0.008 inches) on the diameter and the tri-lobe eccentricity was the preferred 0.000127 m (0.005 inches), the use of a ball 48, oversize by 0.000889 m (0.035 inches) relative to the initial inner diameter of the shaft 11, provided the desired results with a minimum amount of expansion energy required relative to the high level of breakaway torque obtained for the assembled cam elements. However, in some cases greater tri-lobe eccentricities may be desirable as, for example, when wide journal or cam elements are used and more volume for displacement of the expanded shaft material is required to avoid excessive longitudinal carryover of the displaced material. Tri-lobe openings with from 0.000127 m-0.000508 m (0.005 to 0.020 inch) eccentricity have been tested but other dimensions could also be used as desired. 6) After expansion of the shaft, the end loading of the shaft is released by backing-off the force-applying means. The assembled camshaft is then removed from the fixture for other finishing steps, if any, which may be required, such as hardening of the cams if they are not pre-hardened, or grinding of the cams and journals. The force of the end-loading of the shaft should be sufficient to prevent significant longitudinal growth of the shaft 11 during "ballizing". This causes all the growth to be radial and provides the preferred complete filling of the tri-lobe openings 15 and the further expansion of the shaft material radially beyond the openings 15 in the spaces located longitudinally between the elements 12 and 14. In addition, the end-loading prevents the elements from being locked against the spacers by lengthwise growth of the shaft during "ballizing" and, thus, after release of the end-loading, allows easy removal of the assembled camshaft 10 from the fixture. Bending and other damage which might otherwise result from forced removal are thereby avoided. Advantages From the foregoing description of certain preferred embodiments of an improved camshaft assembly it is seen that the various features of the invention provide numerous advantages including: more accurate axial location of cam, journal and other elements on the shaft; higher breakaway torques by reason of improved splined tri-lobe or other curved polygon-shaped openings, and improved shaft material selection. A method of manufacture of a camshaft assembly in accordance with the present invention, and an assembly apparatus therefor, is disclosed and claimed in our co-pending divisional European patent application No.90201407.5 (0389070).

Claims: 1. A camshaft assembly (10) for an internal combustion engine, said assembly comprising a plurality of cam (12) and journal (14) elements, each including a non-round axial opening (15) therethrough and each being secured in predetermined fixed orientation and spacing, with said openings (15) axially aligned, on a hollow tubular shaft (11) expanded into interference engagement with all of the element openings (15), characterised in that each of said non-round axial opening (15) has an odd number of regularly spaced lobes (16), said odd number being at least three, the periphery (20) of said opening (15) being primarily defined by joined outwardly-convex arcs (22, 23) of varying radii, and having an eccentricity of from 0.4 to 0.508/19.1 (about 2.67) percent of the uniform diameter (26) of the opening (15). 2. A camshaft assembly according to claim 1, in which each of said axial openings (15) has a periphery (20) having an eccentricity of from 0.4 to 1.5 percent of the uniform diameter (26) of the opening (15). 3. A camshaft assembly according to claim 1, in which each of said lobes (16) includes at the end thereof at least one longitudinal serration (17) of radial extent approximately equal to the eccentricity of the opening (15), said tubular shaft (11) being expanded into intimate contact with said at least one serration (17). 4. A camshaft assembly according to claim 3, in which said serration (17) extends radially inwards from the periphery of the corresponding lobe (16). 5. A camshaft assembly according to claim 1, in which said openings (15) are formed with a substantially constant uniform diameter dimension at all angular positions. 6. A camshaft assembly according to any one of the preceding claims, in which said tubular shaft (11) is made from a high-strength, low-alloy mild steel having a relatively low yield point but which is subject to substantial work-hardening after yielding. 7. A camshaft assembly according to claim 1, in which said openings (15) are tri-lobed openings formed with a substantially constant uniform diameter dimension at all angular positions. 8. A camshaft assembly according to claim 7, in which each of the lobes (16) of the tri-lobed openings (15) includes at the end thereof at least one longitudinal serration (17) of radial extent approximately equal to the eccentricity of the tri-lobed opening, said tubular shaft (11) being expanded into intimate contact with said at least one serration (17). 9. A camshaft assembly according to any one of the preceding claims, in which the tubular shaft (11) has a uniform smooth-sided interior configuration (54), and portions of the exterior of the tubular shaft (11) between the elements (12, 14) are expanded diametrically beyond the element openings (15) to secure the elements (12, 14) permanently on to the tubular shaft (11) in said predetermined orientation.

Inventors: ARNOLD, PHILIP DALE, KAYWOOD, ROY G.
Applicants: GENERAL MOTORS CORPORATION
Application year: 1988
Main classification: F01L1
IPC codes: B23P21, F01L1, B21D39, F16H53, B21D26, B23P19