Pulley with bellows

Abstract: In a continuously variable transmission with a pulley having discs (1, 2) wherebetween a driving belt (12) runs, at least one of the discs is movable for influencing the transmission ratio of the transmission. The movable disc (1; 2) being mounted on a shaft (3), by means of a bellow means (7;8) possibly formed eccentrically relative to the shaft (3). The bellow means take up the forces exerted by the driving belt (12) close to the point of application of the forces, so that in particular the movable pulley disc may be constructed less rigid, with a smaller mass and at a reduced cost price. Further the bellow construction provides torque transmission with the shaft and axial guide of the disc.

Description: The invention relates to a pulley having at least two discs which are provided on a pulley shaft and which are fixed against relative rotation, and whereby at least one of the discs is provided axially movably with respect to the shaft. Such a pulley is known from European patent application EP-A-0 128 611 and is often used in a continuously variable transmission, wherein a driving belt is provided between a pair of pulleys. By means of frictional contact between the side faces of the driving belt on the one hand and the contact faces of the pulleys on the other hand, to which end the side faces of the driving belt are usually conical and the discs of the pulley enclose a V-shaped gap for accommodating the driving belt therein, power can be transferred from the one shaft to the other shaft. The transmission ratio of the continuously variable transmission can be varied by changing the effective gap width of the two pulleys, which width is adjustable by axial movement of the axially movable disc. The known pulley works satisfactorily but nevertheless has a number of drawbacks. The known pulley is rigid in order to be able to take up the forces exerted on said pulley under all circumstances. This makes the pulley relatively costly, heavy and complicated, and besides its mass inertia is large, which is not conductive to the efficiency and the dynamic behaviour of the pulley in particular and of the continuously variable transmission in general. The object of the invention is i.a. to overcome said drawbacks. The pulley of the kind mentioned in the preamble is according to the invention characterized in that for at least one of the discs the pulley comprises a support radially outward of the shaft, which support is formed by a bellows construction extending parallel to the shaft. Because of this measure the forces exerted on the discs are taken up and transmitted closer to the point of application, as a result of which an undesired build-up of forces in the construction is prevented and the pulley and accordingly the shaft may be less rigid, which results in an improved efficiency and dynamic behaviour, as well as in a reduced cost price and/or a simplified construction. Advantageously a continuation is obtained of a fixation of the pulley disc against relative motion with respect to the shaft and the axial guiding of the disc, while the disc is radially outward supported. The invention will be further explained with reference to a drawing and a few embodiments of the invention. In the drawing: Figure 1a, b shows a diagrammatic elevational view of a driving belt on a pulley according to prior art; Figure 2 shows a diagrammtic elevational view of an embodiment provided with a bellows construction; and Figure 3 shows a diagrammatic elevational view of a further embodiment provided with a double bellows construction. Figure 1 diagrammatically illustrates a driving belt 12 applied on a known pulley having pulley discs 1, 2. The pulley disc 1 is fixed to the pulley shaft 3, whilst the pulley disc 2 is fixed against rotation, but is provided axially movably on the pulley shaft 3. Both pulley discs 1, 2 are directly supported by the shaft 3, therefore, said shaft 3 thus directly having to take up all forces exerted on the pulley discs. The pulley disc 2 is provided, in an otherwise known manner, with a cylinder wall 4 in which there is present a piston 6 mounted on the shaft 3, thus forming a cylinder-piston assembly. By changing the pressure in or the delivery flow through the cylinder chamber 30 in a known manner the axial position of the pulley disc 2 with respect to the pulley shaft 3 can be adjusted. The driving belt 12 is located at a distance R from the center of the pulley shaft 3. Said distance R is dependent on the momentaneous transmission ratio of e.g. a continuously variable transmission in which the pulley-driving belt assembly is provided. It is obvious however, that the driving belt is constantly located radially outwardly of the pulley shaft 3. This means that when the pulley is only supported by the shaft 3, e.g. in this case by means of the ball tracks 40, which are costly and complicated because of the required accuracy, a substantial bending/twisting torque is transmitted by the driving belt, by means of the force F, to the shaft via the pulley. The pulley and the shaft must be able to take up said bending/twisting torque and accordingly are designed rigidly. As a result the pulley shaft/pulley assembly is relatively complicated and costly, whilst it reprents a large mass inertia, which is not conductive to the dynamic behaviour. Figure 1 furthermore shows that the driving belt has only contact with the pulley along a segment of a cirle ψ , as a result of which an eccentric load is applied to the pulley, the pulley discs 1, 2 are asymmetrically deformed and the driving belt is pressed down on the pulley discs in an unbalanced manner. Figure 2 shows an embodiment of the invention, wherein the pulley disc 2 is provided with a bellows construction 7 provided radially outwardly of the shaft and extending parallel thereto. Said bellows construction 7 is provided with a radially inward part 8 which is fixed to the shaft 3. Also in this manner it is ensured that there is a radially outward support of the pulley, closer to the point at which the driving belt 12 makes contact. The bellows construction may thereby effect an axial movement of the pulley disc 2, by a certain deformation as a result of an increase or a reduction of the pressure or the delivery in the cylinder chamber 30, thus changing the adjustment of the transmission ratio. Said bellows construction 7 is moreover very advantageous, since it combines two functions which are normally carried out separately, viz. fixation of the pulley disc against relative rotation with respect to the shaft 3, and axial guiding. Figure 3 illustrates a corresponding bellows construction 7, 8, in this embodiment both pulley discs 1, 2 are provided with such a bellows construction, however. In this framework it is noted that according to the invention in general, but also for other embodiments in which only one pulley disc is provided with means and /or measures according to the invention, one of the two pulley disc as well as both pulley discs may be provided with means and/or measures according to the invention. In case both pulley halves or pulley discs are provided axially movably an optimum alignment (the error in alignment equals 0) of the belt can be ensured at all times, which is beneficial to the life of the belt. The pulley according to prior art, as illustrated in figure 1b, may e.g. be adapted to the standards of the invention by providing teeth on the circumference of the radial end of the piston unit 6, which extend into slots to be provided in the interior of the cylinder 4. As a result of this adaption according to the invention the piston/cylinder assembly will serve as a power-connected, radially outward support of the pulley.

Claims: Pulley having at least two discs (1, 2) which are provided on a pulley shaft (3) and which are fixed against relative rotation, and wherein at least one of the discs (2) is provided axially movably with respect to the shaft (3), characterized in that said pulley comprises a support, radially outward of the shaft, for at least one of the discs, which support is formed by a bellows construction (7) extending parallel to the shaft (3). Pulley according to claim 1, characterized in that said bellows construction (7) is also provided with radially extending means (8) for fixing the bellows construction (7) to the pulley shaft (3). Pulley according to claim 1 or 2, characterized in that said bellows construction (7) is connected with the transmission housing. Pulley according to claim 1, characterized in that said bellows construction (7) mutually connects the two pulley discs (1,2). Continuously variable transmission provided with one or more pulleys according to any one or more of the preceding claims.

Inventors: D HERRIPON BASTIAAN ANDREAS, D'HERRIPON, BASTIAAN ANDREAS
Applicants: DOORNES TRANSMISSIE BV, VAN DOORNE'S TRANSMISSIE B.V.
Application year: 1990
Main classification: F16H55
IPC codes: F16H61, F16H55