Pulley

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 trans­ mission ratio of the transmission. The movable disc (1; 2) being mounted on a shaft (3), by means of support means (5; 7; 16, 18; 20, 21) possibly formed eccentrically relative to the shaft (3). The support 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.

Description: The invention relates to a pulley as outlined in the preamble of claim 1. Such a pulley is known from GB-A-907,405, 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 effective gap width of the two pulleys can be varied by means of the pressure applying device, which width is adjusted by axial movement of the axially movable disc in order to exert a force on the discs which is dependent upon the transmitted torque. The object of the invention is to further develop the known pulley and to make it suited for a continuously variable transmission. Thereto the pulley of the kind mentioned in the preamble has according to the invention features as outlined in the characterizing portion of claim 1. 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 when applying the pulley according to the invention in a continuously variable transmission, as well as in a reduced cost price and/or a simplified construction. Forming of the pressure applying device as a cylinder-piston assembly provides an effective way of varying the transmission ratio continuously when applying the pulley according to the invention in a transmission system for e.g. automobiles, wherein transmission ratios vary continuously and in a wide range. According to a further eleboration of the invention the hydrostatic support is provided eccentrically with respect to the pulley shaft. The driving belt only makes contact with the discs of the pulleys along a certain segment of a circle, causing an eccentric load of the discs and resulting in an asymmetric deformation of the discs, an unbalanced contact pressure on the driving belt and a reduced transmission efficiency. By providing said hydrostatic support eccentrically outwardly of the shaft, as proposed, all this can be overcome in an optimal manner. According to a further elaboration of the invention the radially outward hydrostatic support is provided with means for the transmission of forces towards a medium not being the pulley shaft. Because of the measure the forces exerted on the discs are no longer transmitted by the pulley shaft but by another part, e.g. the housing of a continuously variable transmission, whose construction is already rigid by nature. The pulley shaft may be less rigid and less complicated in that case, which benefits the efficiency, the mass inertia of the pulley as well as the cost price of the pulley. 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 diagrammatic elevational view of a first embodiment according to the invention; and Figure 3 shows a diagrammatic elevational view of a second embodiment of the invention provided with a fluid support with one (a) or more (c - d) non-eccentrically (b) or eccentrically loaded compartments; 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 represents 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. In the embodiment of figure 2 bearing supports 17 and 18 respectively are provided near the two pulley discs 1, 2, whereby bearings 16 are provided between the bearing support 17, 18 and the pulley discs 1 and 2 respectively, which bearings 16 support the pulley discs radially outwardly. The bearing support 17 may thereby be fixed with respect to the transmission housing, e.g. in a manner not shown. The bearing support 18 is axially movably accommodated, as a piston unit, in a cylinder 19', which in its turn may be connected with e.g. a part 19 of the transmission housing or another external medium, so that the forces need not be taken up by the pulley shaft 3. Said part 19 of the transmission housing, the cylinder 19' and the bearing support 18 thereby enclose a cylinder chamber 30, in which the pressure or the delivery flow can be varied, so that the axial position of the bearing support 18, as well as the pulley disc 2 and the transmission ratio of the continuously variable transmission are adjustable. Figure 3a illustrates an embodiment wherein bearing supports 20, 21 are provided adjacent to the two pulley discs 1,2, said bearing supports 20, 21 having compartments 22 in which a fluid, such as e.g. oil or air can be introduced. Said fluid will move out of the compartment radially inwardly and outward via the gaps 23 and 24 respectively, whereby a pressure is built up between the bearring support 20, 21 and the pulley discs 1 and 2 respectively, and the pulley discs 1 and 2 respectively are radially outwardly hydrostatically supported. The bearing support 21 is in its turn axially movable in a cylinder 19' mounted on the transmission housing 19, enclosing a cylinder chamber 30. Said hydrostatic support may moreover eccentrically act on the pulley in an advantageous manner, in order to compensate for the likewise eccentric load by the driving belt 12, by providing the compartment 22 eccentrically in the support 20, 21. Said bearing support will thereby be fixed against rotation. Instead of the single annular compartment 22 also more compartments may be provided, e.g. the compartments 22' - 22'''' according to the figures 3c and 3d. In order to build up an eccentric hydrostatic bearing thereby the compartments can be put under different pressures, e.g. by varying the pre-resistance in the fluid supply to the compartments, and/or by varying the leakage gaps 23, 24 of the various compartments. Thus the pulley according to prior art, as illustrated in figure lb, 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 adaptation 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 whereby at least one of the discs (1, 2) is provided with a pressure applying device for axially moving said one disc (1;2) with respect to the shaft (3), said pulley comprises a bearing support (17, 18; 20, 21), radially outward of the shaft (3), for at least one of the discs (1, 2), for supporting a bearing (16,22) located between said bearing support (17,18;20,21) and said disc (1;2) characterized in that the pressure applying device is formed as a cylinder-piston assembly (2, 19') enclosing a cylinder chamber (30), and that the bearing support (18;21) is a piston, which piston is axially movable in the cylinder chamber (30). Pulley according to claim 1, characterized in that one or more bearings (16) are provided between the disc (1, 2) and the bearing support (17, 18; 20, 21). Pulley according to claims 1 or 2, characterized in that the bearing support (17,18;20,21) is provided eccentrically with respect to the shaft (3). Pulley according to one of the claims 1-3, characterized in that the bearing support is constructed as a hydrostatic support (18, 20, 21). Pulley according to claim 4, characterized in that the hydrostatic support (18, 21) is axially movable in the cylinder chamber (30), and that a fluid can be provided between the disc (1, 2) and the hydrostatic support (18, 21). Pulley according to claim 4 or 5, characterized in that the hydrostatic support (18, 21) comprises one or more compartments (22, 22'-22''''). Pulley according to claim 6, characterized in that different fluid pressures can be adjusted in the compartments (22, 22'-22''''), in such a manner that any eccentric load applied to the disc (2) by a driving belt (12) is at least partly compensated by a corresponding eccentric pressure assembly. Pulley according to one of the claims 1-7, characterized in that the cylinder-piston assembly has a radially extending closing part (19), closing the cylinder chamber (30) in axial direction, which part (19) is connected with the shaft (3) or with a housing of the pulley. Pulley according to one of the claims 1-8, characterized in that both discs (1, 2) are supported, radially outward of the shaft (3). 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, F16H9, F16H55