Axle shaft and assembly

An axle shaft has radially outwardly extending drive fingers which drivingly engage drive slots in a wheel hub cover. The hub cover is rigidly secured to a wheel hub and maintains the axial position of the axle shaft. A shock absorber may be positioned between the drive fingers and the drive slots. The axle shaft may be formed from a hollow tube or a solid shaft by cutting an end portion of the shaft and deforming a cut section radially outwardly to form a drive finger.

BACKGROUND OF THE INVENTION

This invention relates in general to vehicle axles and more particularly to wheel drive axles.

Axle shafts are used to connect a driving and a driven member, such as the differential of an automotive vehicle and a driven wheel. Axle shafts, particularly for automotive vehicles, typically are formed of solid metal shafts with their opposite ends formed for connecting to the drive and driven members of the vehicle. For example, a flange may be forged or welded onto one end of the shaft for connection to a wheel hub, while the opposite end of the shaft may be provided with a spline for connection to a differential gear. Because such shafts must transmit considerable torque and are subjected to rapid starts and stops of power transmission, they must be rigid and strong enough to perform under both normal and overload conditions. Typically, axle shafts are formed from solid steel bar or rod to provide the required strength and rigidity.

In an effort to reduce cost and weight, hollow axle shafts have been used in the past with a wheel driving flange friction welded to the outer or wheel end of the shaft and a spline provided on the opposite end by a cutting, broaching or similar process. Unfortunately, much of the cost benefit of using a hollow shaft is lost using a typical friction welding process to attach a wheel driving flange. Wheel driving flanges have been connected to hollow shafts through splines, but these designs have been complicated and not viable due to the structural problems in strength and rigidity and maintaining the axial position of the wheel driving flange.

It would be desirable to provide a simple lightweight shaft with a wheel drive flange which can be cost effectively manufactured and which provides sufficient rigidity and torque carrying capacity.

SUMMARY OF THE INVENTION

This invention relates an axle shaft having a radially outwardly extending drive finger or fingers which are configured to drivingly engage a wheel hub. Preferably, the wheel hub includes a rigidly secured hub cover having drive slots which drivingly engage the drive fingers. A shock absorber may be positioned between the drive fingers and the drive slots. The hub cover may also maintain the axial position of the shaft.

The axle shaft may be formed from a hollow tube or a solid shaft by cutting an end and bending a cut section radially outwardly to form a drive finger. In a preferred embodiment, four equally circumferentially spaced drive fingers are formed.

Various aspects of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring toFIG. 1, a typical prior art vehicle axle shaft10is formed from a solid steel bar or rod12. The shaft12has a spline end portion22. Splines24typically are formed through a cutting or rolling process. The splines drivingly engage a differential gear of a vehicle. An annular groove23is provided to accept a clip for axial retention of the shaft12within a differential gear. A wheel drive flange14is provided on the opposite end portion of the shaft12. The flange12may be forged onto the end of the shaft or attached through a process such as friction welding. The flange14includes bolt holes16to facilitate attachment of the shaft to a wheel hub.

FIG. 2shows a wheel end assembly30utilizing the present invention. The assembly30includes a wheel hub32. An axle shaft60extends along a longitudinal or rotational axis A through the hub32. The hub32includes a wheel mounting plate34having threaded bolt holes36for attaching a vehicle wheel. A hub housing38contains bearings and lubricant, as is well known in the art. The hub housing38has an open end39which is sealed by a hub cover50. The hub cover50drivingly engages drive fingers70on the axle shaft as will be explained in detail below. The housing38has eight axially extending threaded holes42. Eight bolts41extend through eight bolt holes52in the cover50and are threaded into the eight threaded bolt holes42to secure the cover50to the housing38. Of course, the number of bolts41may vary according to the vehicle and axle designs.

Referring toFIGS. 3 and 4, the hub cover50has an axially inner surface53which sealingly engages the hub housing38near the outer periphery of the hub. The inner surface53defines four radially extending drive slots54. The drive slots54may be forged or cut into the hub cover50. The drive slots54are equally circumferentially spaced about the inner surface53. Each drive slot54has a bottom surface56for engagement with an outer surface of a drive finger70and two opposed and radially extending drive surfaces58for engagement with corresponding drive surfaces of the drive finger as will be explained below. The slots54extend from a radially inner wall59near the center of the hub cover50to the outer periphery55.

Referring toFIGS. 3A and 4A, for some applications, it may be desirable to have the drive slots54′ extend radially outwardly a length short of the outer periphery55′ of the hub cover50′. Such a design may in some applications allow the hub housing38to be more readily sealed by the hub cover50′. Referring toFIG. 3B, for easier fabrication, it may be desirable to eliminate the inner walls59by extending diametrically opposed or coaxial slots into each other. In other words, slots54″ extend completely across the inner surface of the hub cover50″, creating two intersecting slots54″, each of which would engage two drive fingers70. A gasket or O-ring may be provided between the hub cover and the hub for sealing.

Referring toFIG. 5, an unhardened hollow shaft or tube60has a longitudinal or rotational axis A. The shaft60preferably is formed from AISI 1541 or similar steel, but may be formed from any suitable material, such as ionconel, for example. One end portion of the tube60is provided with a spline (not shown) for connection to a differential gear. The spline may be formed in any conventional manner. The opposite end portion of the tube60has four equally circumferentially spaced slots62. The slots may be cut into the tube60in any conventional manner, such as with a cutting tool, a laser, etc. The slots62define cut segments69which will form the drive fingers70. After cutting the tube60, the cut segments69are bent radially outwardly approximately 90 degrees into an upright position relative to the shaft axis A. The bending may be done by any suitable process, such as rolling, as will be apparent to those skilled in the art. The disclosed embodiment has four cut segments69and drive fingers70, but any number of fingers may be used, depending on the vehicle application, torque, speed, shock load requirements, etc.

Referring toFIG. 6, the bending process will result in each drive finger70having a radially extending and axially facing inner surface72which has the curvature of the outer surface of the tube60, and a radially extending and axially facing outer surface74which has the curvature of the inner surface of the tube60. Each drive finger70will have opposed radially extending and generally circumferentially facing drive surfaces76. The drive surfaces76are the surfaces of the tube where the cuts were made. Drive surfaces76are planar or flat but are oriented at an oblique angle transverse to the shaft axis A. The drive surfaces76of each drive finger70could be further deformed or cut to be parallel with each other if desired for any particular application. Hardening may or may not be required or desirable after the fingers70are formed into a near final shape. If required or desired, hardening may be accomplished by any known process such as induction hardening or carburization . A final machining step may be required to give the fingers70a final shape.

Referring toFIG. 7, each drive finger70is positioned in a corresponding drive slot54of the hub cover50. An optional shock absorber80is provided between each drive finger drive surface76and the corresponding hub cover slot drive surface58. The shock absorber80is an elastomeric member molded to or adhered to the drive finger drive surface76. Of course, the shock absorber80may also be molded into or adhered to the hub cover drive surface58. The shock absorber80may have any size or shape as required for any particular application. For example, the shock absorber80may extend completely around the finger70and extend the complete length of the finger70. Similarly, the shock absorber may completely line the hub cover slot54. Of course, other types of shock absorbers may be used, such as a spring.

When the hub cover50is assembled onto the hub32, the outer surface74of each drive finger70is in contact with the bottom surface56of the corresponding drive slot54and the inner surface72of each drive finger70is in contact with the outer surface39of the hub housing38. The drive fingers70, and therefore the axle shaft60, thereby are held in an axial position by the hub cover50and hub housing38. The drive fingers70are not directly bolted to the hub cover or hub housing and therefore have no bolt apertures.

FIG. 8shows an alternative axle shaft60′ formed form a hollow shaft. The initial rolling process used to bend the drive fingers70′ radially outwardly leaves each drive finger in a curved configuration. A secondary straightening process is utilized to form the radially outward tips71′ of each drive finger into the cross-sectional shape of the drive fingers70shown inFIG. 7, with flat axially facing inner72′ and outer74′ surfaces. Drive surfaces76′ may extend at an oblique angle relative to the shaft axial A, or may be deformed or machined to be parallel to each other. It may not be necessary to straighten the entire drive finger70′, leaving a curved intermediate section78′ positioned readily inwardly of the drive finger tips71′. Of course, the hub cover slots would have to accommodate the additional axial depth of the intermediate curved portion78′.

FIG. 9shows an alternative embodiment of the present invention in which an axle shaft100is formed from an unhardened bar or rod of AISI 1541 steel or any other suitable material. One end portion of the shaft100is provided with a spline91for connection to a differential gear. The spline may be formed in any conventional manner. The opposite end portion of the shaft100is provided with four radially extending and equally circumferentially spaced drive fingers90. The drive fingers90are formed utilizing a forging process in which the solid rod or bar is forged into a near net configuration with integral drive fingers90at one end. A machining operation may be required to give the fingers90a desired final shape. Optionally, the shaft may be hardened using any known process. A final machining step may be required after hardening to give the fingers90a final shape after hardening. It is preferred for this embodiment that the radially extending drive surfaces96are parallel to each other and perpendicular to the shaft axis A′.

FIG. 9Ashows an alternative embodiment of the hub cover150′ in which the drive slots do not extend to the periphery radially outer periphery. This allows for better hub cover contact with the gasket151. Of course, an O-ring or other sealing device may be used.

The hub cover150has drive slots154for drivingly engaging the drive fingers90. Because the drive fingers90have been forged, the drive slots154are essentially joined into a single channel in the hub cover surface153, the channel having four radially extending grooves to match the configuration of the drive fingers90. The hub cover50′ has a scalloped outer periphery to match the scalloped shape of the hub housing and to reduce weight and material.

FIG. 10shows an enlarged view of the shaft100with the drive fingers90drivingly engaged with the hub cover150. A shock absorber110in the form of an elastomeric bushing is positioned between the drive fingers90and the drive surfaces of the hub cover slots154. The bushing110is a one-piece molded unit which is inserted into the slots154prior to insertion of the drive fingers90. Alternatively, the bushing110can be molded or adhered to the drive fingers90or to the hub cover slots154. Of course, alternative shock absorbers may be used as well, such as springs.

FIG. 11shows an alternative method of making an axle shaft of the present invention. Axle shaft120is formed from an unhardened bar of rod of AISI 1541 or similar steel. An end of the shaft has four equally circumferentially spaced slots122. The slots may be cut in any conventional manner, such as with a cutting tool, a laser, etc. The slots122define four drive fingers124. After cutting, the fingers124are bent radially outwardly into an upright position 90 degrees from the shaft axis A. Bending may be done by any suitable process, such as rolling, as will be apparent to those skilled in the art. The fingers124are then deformed into a desired cross-sectional shape, such as a rectangular shape or a trapezoidal shape similar to that of the drive finger70ofFIG. 7. After the fingers124are formed into their final shape, the shaft is hardening through a carburizing and quenching process as is well known in the art. A final machining step may be required after hardening to give the fingers124a final shape.

The present invention may be particularly useful for on-highway heavy duty trucks. A conventional solid axle for such an application has an outer diameter of about 1.87 inches and a length of about 40 inches. A typical hub has an outer diameter of about 8.5 inches. A hollow axle60having an outer diameter of about 1.95 and an inner diameter of about 1.14 inches would provide comparable strength and rigidity. The axial thickness of each drive finger70would be approximately 0.40 inches, with a hub cover thickness of about 0.8 inches. A solid shaft axle100,120of the present invention having comparable strength and rigidity could be made having the same approximately 1.87 inch outer diameter. With either a hollow or solid shaft, the hub cover diameter would be about 8.5 inches, with the drive fingers extending radially outwardly approximately 3 inches from the outer surface of the shaft. Of course, the dimensions would change for lighter or heavier applications such as a golf cart or construction equipment. In any event, the radial length of the drive fingers is at least 10% of the maximum outer surface diameter of the shaft from which it extends.

The principle and mode of operation of this invention have been explained and illustrated in the preferred embodiments. However, this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.