Pulley

Abstract: Pulley, in particular for a continuously variable transmission. The pulley is provided with two discs (31,32) on a pulley shaft (30), at least one disc (32) being axially movable relative to the other disc (36) by means of control means. The movable disc (32) is connected to the pulley shaft (30) by means of a key/groove connection. A radially inward profile (37) of the key/groove connection is connected to the disc (32), and a radially outward profile (38) of the key/groove connection is connected to the shaft (30).

Description: The invention is related to a pulley, in particular for a continuously variable transmission, provided with two discs on a pulley shaft, at least one disc being axially movable by means of control means comprising a piston/cylinder assembly, said movable disc being connected non-rotatably to the pulley shaft by means of a key/groove connection and being immovably connected to a radially inward profile of the key-groove connection, said shaft being immovably connected to a radially outward profile of the key/groove connection. Such a pulley is known from US-A-4 552 545, and is used in particular in continuously variable transmissions, which are used in, for example, motor cars. In a continuously variable transmission two pulleys, with a drive belt between them, are used. The transmission ratio of the transmission can be set by varying the radial position of the drive belt between the discs of the two pulleys. The radial position of the drive belt between the discs of the pulley can be altered by altering the mutual position of the discs of the pulley. For this purpose, at least one disc must be fixed non-rotatably, but in such a way that it is axially movable, on the pulley shaft. This can be achieved by, for example, using a key/groove connection. The control means generally comprise a piston/cylinder assembly. In the case of the known pulley, the key/groove connection is a radially outward directed key/groove profile which is connected to the pulley shaft and interacts with a radially inward directed key/groove profile which is connected to the disc. The key/groove connection is in open communication with the cylinder chamber, so that the key/groove connection is always sufficiently lubricated. The known pulley has a number of disadvantages. First, complex parts are necessary, and these make the pulley expensive. Moreover, the transfer of the driving couple between the disc and the pulley shaft takes place at a relatively small radius. This leads to the generation of relatively high internal forces in the key/groove/connection. The object of the invention is to overcome the abovementioned disadvantages. This object is achieved in that the piston of the piston cylinder assembly is connected to the shaft and the cylinder of the piston cylinder assembly is provided with an axially extending piston sleeve, whereby the flange is provided with said radially inward profile and the sleeve is provided with said radially outward profile. The cylinder can be connected to a wall of a compensating chamber. The flange is preferably situated between the cylinder and the compensating chamber. The piston sleeve can run into a radially inward directed part of the piston, which part is fixed on the pulley shaft. By providing the disc with an axially extending disc sleeve which is situated fully inside the cylinder sealed off by the piston, optimum use is made of the available area to exert sufficient pressure on the disc, and the pulley can be of a compact design. According to the invention, a spring can be fitted between the pulley shaft and the movable disc, which spring presses the movable disc in the direction of the other disc. A basic pressure on the movable disc is consequently guaranteed. In particular, radially outwards the spring can be confined by the piston sleeve, and radially inwards by the disc sleeve. The spring can rest against the radially inward directed part of the piston. This means that the spring requires only a limited fitting space. The invention will be illustrated with reference to a drawing, in which: Fig. 1 shows diagrammatically a continuously variable transmission with a pulley according to the prior art; and Fig. 2 shows diagrammatically an embodiment of the pulley according to the invention. The continuously variable transmission of Figure 1 is provided with two pulleys according to the prior art. Fitted on the pulley shafts 1 and 7 are a fixed disc 2 and 8 respectively and an axially movable disc 3 and 9 respectively. A drive belt 14 is fitted between the discs 2, 3, 8 and 9. The movable discs 3 and 9 are provided with control means, in this case piston/cylinder assemblies 6, 5 and 11, 10 respectively, which enclose a cylinder chamber 4 and 12 respectively. When fluid is fed in and/or discharged in a suitable manner through the pipes 15 and 13, the quantity of fluid is varied in the cylinder chambers 4 and 12 respectively, in such a way that the movable discs 3 and 9 respectively assume the desired axial position. Said axial position in this case determines the radial position of the drive belt 14 between the discs 2, 3 and 8, 9 respectively, and consequently the transmission ratio of the transmission. Although the discs 3 and 9 must be fitted so that they are axially movable, they must also be fixed non-rotatably on the pulley shaft 1 and 7 respectively. In the case of the movable disc 3, the movement is achieved, as in EPO.145.462, by using a key/groove connection. The cylinder 5 is immovably connected to the pulley shaft 1 by means of a flange 16 and is provided with a radially inward key/groove connection 18. The piston 6 is immovably connected to the disc 3. Said disc 3 is further connected to the sleeve 17 which provides for guidance of the disc 3 over the pulley shaft 1. The sleeve 17 is in turn provided with a radially outward directed key/groove profile 19. The key/groove connection 18, 19 is lubricated by leakage losses of fluid from cylinder chamber 4 to chamber 20. The construction is rather complex and expensive. Moreover, the sleeve 17 extends into chamber 20, so that the pressure of the cylinder chamber 4 is not exerted on the face 21 of the sleeve 17, and optimum use therefore cannot be made of the disc surface to press the disc by means of the fluid pressure in cylinder chamber 4 in the direction of the fixed disc 2. This can be overcome only by making the disc radially large, which is a disadvantage in terms of fitting space. It is also not uncommon to use compensating chambers for pulleys. The fact is that, in addition to the preset pressure, pressure which builds up in the rapidly rotating cylinder chamber through the centrifugal effect occurs in the cylinder chamber 4. This centrifugal pressure upsets the preset pressure, so that a compensating chamber is commonly used to compensate for the centrifugal pressure. A spring is often used to press the disc with a certain basic force in the direction of the fixed disc 2. However, in the case of the illustrated pulley according to the prior art, the use of a compensating chamber and/or of a spring is very difficult or impossible, for example because it takes up considerable fitting space. Figure 2 shows an embodiment of the pulley according to the invention. The pulley comprises a fixed disc 31 which is fitted on the pulley shaft 30, and a disc 32 which is movable axially over the pulley shaft 30. The pulley shaft 30 is also provided with two sliding rings 46 and 47 for the contact with the movable disc 32 and the disc sleeve 43 connected thereto. The movable disc 32 is provided with a cylinder 33. The piston 34 is fixed on the pulley shaft 30 by means of an axially extending piston sleeve 39 and a radially inward directed piston part 42. The cylinder 33 and the piston 34 enclose a cylinder chamber 35. The cylinder chamber 35 can be fed with fluid by way of bore 48 in the shaft 30. The cylinder 33 is provided with a radially inward key/groove profile 37 at the position of the axially extending flange 36. The piston 34 is provided with a radially outward profile 38 at the position of the piston sleeve 39. The radially inward key/groove profile 37 which is in engagement with the radially outward key/groove profile 38 allows an axial movement of the disc 32 relative to the pulley shaft 30, while the disc 32 is still non-rotatably connected to the pulley shaft 30. This construction is simple and relatively cheap, because the key/groove connection is fitted in the piston/cylinder combination already present, without expensive constructional measures and/or additional parts being necessary. Moreover, the two profiles can also be fitted in separate rings, which are in turn connected to the disc and the shaft respectively. The disc sleeve 43 is situated fully inside the cylinder chamber 35, so that the pressure of the fluid in the cylinder chamber 35 is also exerted on the faces 49 of the disc sleeve 43. The faces 49 thus form an effective surface for increasing the force on the disc 32 in the direction of the fixed disc 31. This means that the radial size of the disc 32, and consequently the fitting space, can remain limited. The spring 44 is confined radially inwards by the disc sleeve 43 and radially outwards by the piston sleeve 39. The spring 44 rests against the radially inward directed piston part 42. The spring 44 consequently presses the disc 32 with a certain initial tension in the direction of the fixed disc 31, with the result that a certain force on the drive belt is always ensured, and the disc also constantly seeks to keep the smallest possible distance between the two discs 31 and 32. The use of the spring 44 is possible through the measure of the invention, and the spring 44 is fitted in a very compact way, and is also adequately confined and supported. The cylinder 33 is connected to the wall 40 of the compensating chamber 41. Fluid at a relatively low pressure is introduced into compensating chamber 41 by way of bore 45 in the pulley shaft 30. Through the key/groove connection, fluid also leaks into and out of the compensating chamber 50. The key/groove connection is also lubricated in this way, so that it is guaranteed to function. Rotation of the pulley produces a centrifugal pressure in the chambers 41 and 50. The same centrifugal pressure also occurs in the cylinder chamber 35. However, the unwanted centrifugal pressure in cylinder chamber 35, which presses the disc 32 in the direction of the fixed disc 31, is compensated for by the centrifugal pressure in the compensating chambers 40 and 50, which is exerted on cylinder wall 51 and the wall 40 in the direction facing away from the fixed disc 31. The use of the compensating chamber is possible through the measures according to the invention, and a very compact assembly is also produced. For the rest, the term key/groove connection in the context of the invention should be understood as meaning any positive connection by means of corresponding shapes which permits an axial movement and is non-rotatable.

Claims: Pulley, in particular for a continuously variable transmission, provided with two discs (31,32) on a pulley shaft (30), at least one disc (32) being axially movable relative to the other disc by means of control means comprising a piston/cylinder assembly (33,34) with a cylinder (33) and a piston (34), said movable disc (32) being connected to the pulley shaft so as to rotate therewith, characterized in that said piston (34) is connected to said shaft (30) so as to rotate therewith and is provided with an axially extending piston sleeve (39) on which is provided a radially outward profile (38), and said cylinder (33) is fixed to said movable disc (32) and is provided with an axially extending flange (36) on which is provided a radially inward profile (37) which cooperates with said radially outward profile (38) so as to form a key/groove connection there between. Pulley according to Claim 1, characterized in that the cylinder (33) is connected to a wall (40) of one or more compensating chambers (41). Pulley according to one of Claims 1 or 2, characterized in that the piston sleeve (39) of said piston (34) runs into a radially inward directed part (42), which part is fixed on the pulley shaft (30) so as to rotate therewith. Pulley according to one of Claims 1 to 3, characterized in that said movable disc (32) is provided with an axially extending disc sleeve (43), which is situated fully inside the cylinder (33) sealed off by the piston (34). Pulley according to one of the preceding claims, characterized in that a spring (44) is fitted between a piston part and the movable disc (32), which spring presses the movable disc in the direction of the other disc. Pulley according to Claim 5, characterized in that radially outwards the spring is at least partially confined by the piston sleeve (39). Pulley according to Claim 5, characterized in that radially inwards the spring is partially confined by the disc sleeve (43). Pulley according to one of the preceding claims, characterised in that the radially inward profile (37) and the radially outward profile (38) is fitted in separate rings.

Inventors: BONGERS SEBASTIAAN PIETER HENR, SCHELLEKENS ANTONIUS LAMBERTUS, BONGERS, SEBASTIAAN PIETER HENRICUS JOZEF, SCHELLEKENS, ANTONIUS LAMBERTUS
Applicants: DOORNES TRANSMISSIE BV, VAN DOORNE'S TRANSMISSIE B.V.
Application year: 1996
Main classification: F16H55
IPC codes: F16H55, F16H9