The present invention relates generally to lubrication systems for power transmission devices, and more particularly, to an improved centrifugal shaft lubrication system for power transmission devices
As is known, motor vehicles are equipped with power transfer devices, such as manual and automatic transmissions or four-wheel drive transfer cases, for transmitting driving torque from a power source to the ground engaging wheels. Conventional power transfer devices include a number of drive elements (i.e., clutches, drive gears, bearings and the like) that are journally supported upon shafts for relative rotation with respect thereto. While such drive elements are typically illustrated in part prints to be in metal-to-metal contact with the shaft, they are actually supported upon on a thin film of lubrication. If the drive elements were actually in metal-to-metal contact with the shaft, they would quickly generated heat and, in some instances, become welded or seized to the shafts. In other cases, excessive amounts of wear can occur resulting in the premature failure of the power transfer device. Thus, in order to increase the reliability and service life of these devices, it is important to provided ample amounts of lubrication to these areas such that the lubrication film is maintained between the drive elements and the power transfer shaft.
In this regard, it is well known that oil or other viscous lubrication can be communicated to the drive elements via radial passages connecting to an axial bore formed within the rotating shaft. Such an arrangement for lubricating elements of a manual transmission is disclosed and discussed in U.S. Pat. No. 4,222,283. Thus, lubrication can be delivered to the drive elements within a power transfer device by first forming an axial bore within the shaft and then forming radial passage which communicate with the axial bore such that lubrication within the axial bore is delivered to the circumference of the shaft where the drive elements are supported.
When several drive elements are support along the shaft the axial bore must be extended and a number of radial passages are required to supply lubrication to each of the drive elements. Unfortunately, there is a tendency for an uneven discharge of lubrication through these radial passages as the lubricant flows along the axial bore. As a result, a lubrication "starvation" condition may be generated which can reduce the durability and reliability of the drive elements. Also, when the shaft is angled with respect to the earth, gravity tends to counteract the flow causing a further reduction in the amount of lubrication which is drawn along the axial bore. Such conditions may occur due to the design of the power transfer device or where a vehicle in which the power transfer device is incorporated operates at an angle, such as when driving up or along a hill.
Accordingly, the present invention is directed to an improved lubrication system for power transfer devices which greatly improves the flow of lubrication along an axial bore formed within a rotating shaft. In the present invention, a rotor is disposed within the bore of a rotating shaft and secured to rotate with the shaft. The rotor acts to draw substantially more lubrication along the bore than would normally flow thereby improving the supply of lubrication to the drive elements disposed along a rotating power transmission shaft.
Another advantage of the present invention is that the improved lubrication system counteracts the above-noted gravitational effects such that the flow and distribution of lubrication flow along the axial bore of a rotating shaft disposed at an angle with respect to the earth is greatly enhanced.
Yet another advantage of the present invention is to provide a lubrication system which is inexpensive and adaptable to any power transfer device incorporating a centrifugal lubrication system.