Roller vane pump

Abstract: The invention relates to a roller vane pump for operating an automatic transmission for motor vehicles. The pump is provided with a pump housing (12), a rotor (4), a cam ring (2) and roller elements (7), which define a number of pump chambers (13). Fluid is communicated between a hydraulic channel (24) and a pump chamber (13) through suction ports (11 and 16) and discharge ports (17 and 18). According to the invention a front part of a circumference (32) of a slot (6) seen in a direction of rotation of the rotor (4) is at least partly curved such that the curvature of a curved part (32a) substantially matches the curvature of a roller element (7) accommodated in said slot (6).

Description: The invention relates to a roller vane pump used for operating an automatic transmission for motor vehicles and in particular for pumping automatic transmission fluid in a continuously variable transmission. The pump is provided with a pump housing, a rotor located in the pump housing and rotatable by means of a drive shaft, a cam ring located around said rotor and roller elements slideably accommodated with some tolerance in slots on the periphery of the rotor. On rotation of the rotor the roller elements interact in a sealing manner with the surface of the cam ring. The cam ring, the rotor, the roller elements and the pump housing define a number of pump chambers, which may arrive in communication with hydraulic channels in the pump housing for allowing flow of fluid to and from the pump chambers. Fluid is communicated between a hydraulic channel and a pump chamber either through one or more suction ports for allowing a predominantly axial flow of fluid to a pump chamber, or through one or more discharge ports for allowing a predominantly axial flow of fluid from a pump chamber. Such a roller vane pump is known from the British patent specification no. 1.291.720. From this document it is further known to provide the front part of a circumference of the slots as seen in a direction of rotation of the rotor with a roller supporting surface between the outer rotor circumference and the inner extremity of the slot, which supporting surface limits the radial inward movement of the roller accommodated in such slot during its travel. The depth of the slot from the outer rotor circumference to the supporting surface thereby being substantially equal to the diameter of the roller. A similar type of roller vane pump is known from the European patent 0.555.909, which is in particular adapted for pumping of large volumes of fluid particularly automatic transmission fluid, while maintaining a high pressure in a hydraulically controlled and operated continuously variable transmission for motor vehicles. In a continuously variable transmission of the belt-and-pulley type a large amount of fluid at a high pressure is needed to control the transmission ratio and the belt pinching force, even at a low engine speed. Since the pump is driven by a shaft drivingly connected to the engine shaft, the pump is designed to be able to provide a desired pump yield even at the lowest rotational speed of the engine. When the pump is operated, the rotor rotates and a low pressure or suction pressure is effected in a pump chamber. Due to the suction pressure fluid is drawn from a hydraulic channel through a suction port or ports into a pump chamber. The flow of the fluid is dependent of said suction pressure and of the surface area of the suction port or ports. Inside a pump chamber, fluid is compressed and subsequently discharged through a discharge port to a hydraulic channel. Although the known pump functions satisfactory per se, it possesses certain drawbacks. Both the amount of wear of pump parts and the level of noise generated by the pump are not optimal. The aim of the invention is to optimise the known pump by reducing at least one of wear of pump parts and noise generated by the pump. This aim is, according to the insight underlying the present invention, achieved in the pump having a slot circumference design according to claim 1. The claimed slot circumference being such as to effect a reduction of the pressure gradient. When a roller element, located in a slot on the periphery of the rotor, has just passed a discharge port, the fluid pressure in a pump chamber in front of that roller element has changed from a high discharge pressure to a much lower suction pressure. The difference between the two pressures is relatively large, as is the pressure gradient associated with said pressure change. Due to said pressure difference and since a roller element is fitted with some tolerance inside a slot, the roller element moves towards the front of the slot as seen in rotational direction of the rotor, where it collides with the rotor generating noise and resulting in wear of the element and of the rotor. Furthermore, inside the known pump the suction pressure becomes low enough for cavitation to occur even at generally occurring pump parameters. Cavitation amounts both to wear of pump parts and to noise generated by the pump, as is commonly known. A pump according to the invention has an improved functionality, since its functional life is prolonged and less noise is generated by the pump during operation. In an embodiment of the solution according to the invention, the circumference of a slot as seen in axial direction is at least partly curved such, that the curvature of the curved part substantially matches the curvature of the roller element that is located in said slot. In this manner, a surface contact instead of a line contact between roller element and rotor can be effected. If said curved part is part of the front part of the circumference of a slot as seen in rotational direction of the rotor, said rapid movement of a roller element towards said front of the slot is dampened, because fluid is to be squeezed from in between the roller element and the rotor. Therefore, the force of the collision between roller element and rotor is reduced. For optimal results, said curved part substantially starts at the instantaneous radial position of the axial centre line of the roller element, at the instance the roller element starts to interacts with the front of the slot, and continues in a radially inward direction. Said instance occurs immediately after the fluid pressure in the pump chamber in front of the roller element has dropped from the discharge pressure to the suction pressure. Taking into account both functional and manufacturing aspects, the curvature of the curved part preferably extends over a 30 to 90 degree angle. A value over 90 degrees presents manufacturing problems and hinders the radial and or tangential movement of a roller element, whereas a value under 30 degrees results in a negligible damping. According to a further development of this solution, said front part of said circumference consists at least of said curved part and one or more straight parts adjacent to said curved part, to provide support for the roller element and/or to increase the volume of a pump chamber and the surface area through which fluid can be supplied to and discharged from a pump chamber. This effect is enhanced even further if the back part of said circumference extends over a substantially equal radial distance as said front part. Preferably said back part is substantially parallel to a straight part of said front part. A rotor with slots according to the invention reduces the pressure gradient during pumping and the noise generated by the pump is reduced. The invention will now be explained in greater detail with reference to the non-restricting examples of embodiment shown in the figures. Figure 1 shows an axial view of the inner pump parts of a rotary pump according to the state of the art. Figure 2 shows the cross-section II-II of the pump according to figure 1. Figure 3 shows a partial view in axial direction of the inner pump parts with a rotor with slots according to the invention. Figure 4 shows the preferred embodiment of the inner pump parts with a rotor with slots according to the invention. The rotary pump according to figures 1 and 2 is provided with a pump housing 12 composed of three pump housing parts 1, 8 and 9. The central pump housing part 1 contains a cam ring 2 with a cam surface 2a and a rotor 4 with slots 6, each of which accommodates a roller elements 7 such, that the roller element can slide in a radial direction. The cam ring 2, the rotor 4 and the roller elements 7 define a number of pump chambers 13 in axial direction bounded by the inner surfaces 14 and 23 of the outer pump housing parts 9 and 8 respectively, and which may arrive in communication with hydraulic channels 24 in the pump housing for allowing flow of fluid to and from the pump chambers. The pump is provided with a number of suction ports 11 and 16 and/or discharge ports 17 and 18 for allowing a predominantly axial flow of fluid between a pump chamber 13 and a hydraulic channel 24 in the outer pump housing part 9. The rotor 4 mounted rotatably inside the pump housing 12 is connected to a drive shaft 5 by means of a wedge 3. On rotation of the rotor 4, the volume of a pump chamber 13 varies between a minimum and a maximum value. The three pump housing parts 1, 8 and 9 can be secured to each other by means of bolts that are inserted in holes in the pump housing, e.g. hole 10. With a suitable manufacturing method pump parts can be constructed as a single piece. Figure 3 shows a partial view in axial direction of the inner pump parts with a rotor 4 with slots 6 according to the present invention. The circumference 32 of a slot as seen in axial direction is partly curved such, that the curvature of the curved part 32a substantially matches the curvature of a roller elements 7. From figure 3 it is apparent, that a surface contact is effected between roller element 7 and rotor 4. Therefore, a certain amount of fluid is to be expelled from in between a roller element 7 and the rotor 4 during said movement of a roller element 7 towards the front part of said circumference 32 as seen in rotational direction 34. This dampens said movement and decreases the force of the collision of a roller element 7 with the front of a slot 6. Therefore, the pressure gradient in the fluid inside a pump chamber 13 is reduced. Wear of the roller elements 7 and the rotor 4 as well as noise generated by the pump during operation is reduced significantly. In figure 4 the preferred embodiment of a rotor 4 with slots 6 according to the invention is shown. The front part of said circumference 32 consists of a curved part 32a and two substantially straight parts 32b and 32c adjacent to said curved part 32a. Said curved part 32a is located in said front part substantially starting at the instantaneous radial position of the axial centre line 35 of a roller element 7, at the instance said roller element 7 starts to interact with said front part, and continuing in a radially inward direction. Said curved part 32a extends over a 90 degree angle. The back part of 32d of said circumference 32 extends over the same radial distance as the front part. In this development of the solution, the roller element 7 is provided with sufficient support by the rotor 4 and the volume of a pump chamber 13 is increased. Preferably said back part 32d is oriented substantially parallel to one or more of said straight parts 32b and/or 32c of said front part.

Claims: Roller vane pump for operating an automatic transmission for motor vehicles provided with a pump housing (12), a drivably rotatable rotor (4), a cam ring (2) located around said rotor (4) and roller elements (7) accommodated in slots (6) on the periphery of the rotor (4), wherein the cam ring (2), the rotor (4), the roller elements (7) and the pump housing (12) define a number of pump chambers (13), characterised in that a front part (32a, 32b, 32c) of a circumference (32) of a slot (6) seen in a direction of rotation (34) of the rotor (4) is at least partly curved such that the curvature of a curved part (32a) substantially matches the curvature of a roller element (7) accommodated in said slot (6), whereby said curved part (32a) substantially starts form the instantaneous radial position of the axial centre line (33) of a roller element (7), at the instance said roller element (7) starts to interact with the front part (32a, 32b, 32c) of said circumference (32) during operation, and continues in a radially inward direction. Roller vane pump according to claim 1, characterised in that , said curved part (32a) extends over an angle in between 30 and 90 degrees. Roller vane pump according to claims 1 or 2, characterised in that the front part (32a, 32b, 32c) of said circumference (32) consists at least of said curved part (32a) and two predominantly radially oriented straight parts (32b and/or 32c) provided adjacent to said curved part (32a). Roller vane pump according to claim 3, characterised in that one of the predominantly radially oriented straight parts (32b) has a radial dimension which substantially corresponds to that of the curved part (32a). Roller vane pump according to claim 3 or 4, characterised in that , a back part (32d) of the circumference (32) of the slot (6) seen in the direction of rotation of the rotor (4) is oriented substantially parallel to one or more of said straight parts (32b and/or 32c). Roller vane pump according to claim 5, characterised in that , said back part (32d) extends over substantially the same radial distance as the front part (32a, 32b, 32c) of said circumference (32). Automatic transmission for motor vehicles provided with a roller vane pump according to any of the preceding claims.

Inventors: VAN SPIJK JOHANNES GERARDUS LU, VAN WIJK ELIAS, VAN SPIJK, JOHANNES GERARDUS LUDOVICUS MARIA, VAN WIJK, ELIAS
Applicants: DOORNES TRANSMISSIE BV, VAN DOORNE'S TRANSMISSIE B.V.
Application year: 1997
Main classification: F04C2
IPC codes: F04C2, F16H61, F04C15