Patent Application
20070117640
The present invention relates to torque transferring devices used within vehicle transmissions, and, more particularly, to a composite clutch shaft assembly.
Clutch shafts for use in vehicle transmissions are well known in the art. Generally, a shaft extends from a clutch hub and supports a gear. A clutch selectively engages teeth formed within the clutch hub to selectively transfer torque between the clutch and the gear. The vehicle transmission may experience an audible noise or “squawk” when the clutch is applied or released at elevated temperatures. This “squawk” may be a result of instability of the clutch hub and shaft system. The spring rate and inertia of the system may be such that the shaft behaves as a one degree of freedom system, with the clutch hub and clutch plates acting as the inertia and the output end of the shaft acting as the ground.
The hub is subject to the friction force of the slipping clutch, which can exhibit a negative coefficient of friction versus slip speed characteristic when the clutch becomes hot, aged, or subject to high unit loading. This negative friction slope emulates negative damping, which may cause the one degree of freedom system to become unstable if the negative slope and the positive internal damping of the shaft sum to a negative value. In such situations, the oscillation of the hub (inertia) across the shaft (spring) will increase exponentially until a non-linearity is encountered. Such non-linearities may be that the clutch plate splines no longer contact the hub or that the rotational velocity of the clutch moves the friction characteristics out of the negative slip zone. Engineers have improved “squawk” characteristics in the past by increasing the diameter of the shaft, increasing the inertia of the hub, increasing heat extraction from the clutch pack, increasing clutch surface area, and/or the addition of a damper. The damper may be either a coulomb type or a tuned mass damper.
Provided is a composite clutch shaft having a hub and a shaft extending from the hub. The shaft has a core portion disposed within a generally tubular outer portion. The core portion has a higher internal damping characteristic than the outer portion. The core portion may be either solid or hollow. Additionally the core portion may be formed from grey iron and press fit into the outer portion which may be formed from steel. The core portion may extend substantially the entire length of the shaft.
Also provided is a composite clutch shaft including a hub having a shaft extending therefrom. The shaft is formed from a heat treatable material and the shaft has a heat treated outer portion and a non-heat treated core portion. The non-heat treated core portion has a higher internal damping characteristic than the heat treated outer portion.
The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.
a is a schematic cross sectional view of one embodiment of the shaft portion of the composite clutch shaft assembly taken along line A-A of
b is a schematic cross sectional view of a second embodiment of the shaft portion of the composite clutch shaft assembly also taken along line A-A of
a is a schematic cross sectional view of a third embodiment of the shaft portion of the composite clutch shaft assembly also taken along line A-A of
b is a schematic cross sectional view of a fourth embodiment of the shaft portion of the composite clutch shaft assembly also taken along line A-A of
Referring to
The hub 12 includes a circumferential wall 16 having a plurality of teeth 18 protruding radially therefrom. The plurality of teeth 18 preferably extend about the entire perimeter of the circumferential wall 16. Lubricant openings 20 extend through at least some of the plurality of teeth 18 to allow lubricant to flow into and out of the composite clutch shaft 10. The hub 12 is preferably configured to engage the clutch within the vehicle transmission. When the clutch is applied, splined clutch plates transfer torque from the clutch to the hub 12 for substantially unitary rotation therewith.
The shaft 14 extends from the hub 12 to a splined end portion 22. Splines 24 are formed on an outer surface 26 of the shaft 14 at the splined end portion 22. In the preferred embodiment, the splines 24 extend around the entire outer surface 26 of the shaft 14. The splines 24 are preferably configured to support a gear. Preferably, the splines 24 are induction hardened following formation, thereby reducing spline degradation caused by the gear.
With reference to
An exemplary embodiment of the shaft 14 in
A third and fourth embodiment of the present invention is shown respectively in
Exemplary of the embodiments shown in
Those skilled in the art will recognize that the relative radial thicknesses of the outer portions 28, 28′ and the core portions 30, 30′, 30″, and 30′″ will be dictated by engineering constraints such as torsional loading on the shaft 14, 14′. The composite clutch shaft 10 of the present invention may reduce unwanted noise and vibration within the power transmission by increasing the damping effectiveness of the shaft 14 and 14′.
While the best modes for carrying out the invention have been described in detail, it is to be understood that the terminology used is intended to be in the nature of words and description rather than of limitation. Those familiar with the art to which this invention relates will recognize that many modifications of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced in a substantially equivalent way other than as specifically described herein.
