Continuously variable transmissions ("CVTs"), generally utilize a pair of adjustable pulleys, typically defined as a primary pulley and a secondary pulley. The primary pulley is connected to an engine and the secondary pulley is connected to the drive train of the vehicle, typically through a clutch. One example of such a CVT is shown in Smirl, U.S. Pat. No. 4,433,594 entitled "Variable Pulley Transmission" and incorporated herein by reference.
Interconnecting the pulleys is a drive belt. Specifically the drive belt transfers power from the primary pulley to the secondary pulley, i.e., from the engine to the drive train, by means of frictional contact between the side faces of the drive belt and the contact faces of the pulleys. The side faces of the drive belt are shaped to correspond to the contact faces of the pulleys.
Each pulley is constructed from two flanges, each flange having a conical side surface which thereby defines a V-shaped gap between the flanges. At least one of the flanges is movable along the axis of the respective pulley shaft allowing the gap between the flanges to be varied. In such a fashion the transmission ratio of the CVT can be varied, i.e., changing the effective gap width between the flanges of the two pulleys varies the radial position of the drive belt in each pulley. This allows for a continuous adjustment of the drive ratio between the shafts.
Movement of the flanges is achieved through a hydraulic servo which moves the flange through a fluid constraining chamber. Increasing fluid pressure in the chamber axially moves the flange and thus increases the effective diameter of the pulley. As fluid pressure is exhausted from the chamber the flange moves along the shaft in the opposite direction, thus decreasing the effective diameter of the pulley. Generally the effective diameter of the primary pulley is moved in one direction as the effective diameter of the secondary pulley is moved in the other. A further and more detailed description of the movement of the flange may be found in Neuman et al. U.S. Pat. No. 5,006,092 entitled "Continuously Variable Transmission Power Train Configuration" and incorporated herein by reference.
The connection between the movable flange and the drive shaft allows the flange to move axially while being fixed radially. The prior art details several ways to accomplish such a connection. For example, an internal keyway may be provided in the respective shaft to receive a key fitting. The keyways, however, must be machined into the shaft and flange, an expensive procedure. During loading of the pulley, moreover, high forces are required to slide the movable flange axially along the keyway. Loading on the key, under these circumstances, can become excessive and may lead to premature failure of the transmission.
Another way to connect the movable flange to the shaft is through a ball-spline connection. In such a design a plurality of balls are used with mating grooves, the balls functioning as both anti-friction elements and to provide a drive connection between the flange and shaft. This type of connection is expensive to construct as it requires machining close tolerances between the balls and mating grooves of the shaft and the flange.
Instead of the above-described movable flange-shaft connections, Bessette, U.S. Pat. No. 3,868,862 entitled "Expansible Pulley With Speed And Torque Responsive Means" teaches the use of a pivotally connected link or links between the movable flange and the drive member. In one embodiment a single link is circumferentially arranged with respect to the flange and drive member, and in another embodiment, three spaced links are angularly arranged with respect to the flange and drive member. In both embodiments, the links must be rigid and must be provided with pivoting joints which, in the case of the second embodiment, are universal joints. To operate properly, these joints must be constantly lubricated. The link or links exert a force component to the pulley flange which either adds to or subtracts from the force applied by other means to the flange.
A support between a movable flange and a shaft is disclosed in d'Herripon, U.S. Pat. No. 5,013,283. This reference teaches the use of pin members carried by the movable flange and fixed between the movable flange and an inwardly bent edge of a cylinder mounted to the flange. The pin members extend through and are supported by a piston mounted on the shaft. This structure provides that the pin members take up the forces exerted by the belt close to their point of application so that the moveable sheave may be constructed less rigid and with smaller mass.
The known pulley designs heretofore used are believed to perform satisfactorily but nevertheless improvements are desirable. The flange-shaft drive connection should be accomplished in a low cost manner, e.g., requiring a minimum of machining of the shaft or flange or utilizing low cost, high volume methods.
Accordingly it is an object of the present invention to provide a drive connection to a movable flange which will fix the flange radially to a shaft while allowing the flange to move axially without the use of ball splines or other joining methods which require costly machining.
It is another object of the present invention to provide increased structural rigidity to the servo mechanism used to axially move the flange along the shaft.
Other objects, advantages and features of this invention will become apparent on reading the following description and appended claims, and upon reference to the accompanying drawings.