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 the pump is provided with a suction port (26) for allowing a predominantly radial flow of fluid to a pump chamber (13) and/or with a rotor (4) with slots (6) with a circumference (32) which is partly curved with a curvature substantially matching the curvature of the roller elements (7) and/or with a rotor (4) with a circumference segment (30) deviating at least partly from a circle, in order to decrease the amount of wear of pump parts as well as the noise level generated during pumping.

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, as disclosed in the preamble of claim 1, is known from the European patent 0.555.909 and 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 providing for a modified cam ring, the modification being such as to effect an increase of the suction pressure and 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 a first embodiment of the solution according to the invention, the cam ring is provided with a recess constituting a suction port for allowing a predominantly radial flow of fluid to a pump chamber. The recess may be in communication with a hydraulic channel through a state of the art suction port for allowing a predominantly axial flow of fluid. In this case said state of the art suction port is extended radially outward. According to a further development of the solution, the recess is in communication with a hydraulic channel through an additional suction port. Said additional suction port may allow either a predominantly axial or a predominantly radial flow of fluid to the recess. In the latter case fluid is allowed to the recess through the additional suction port from a hydraulic channel located in radial direction outside the cam ring. Since the roller elements are supported by the cam ring, the depth of a recess as seen in axial direction is limited. A suction port for allowing a predominantly radial flow of fluid to a pump chamber increases the surface area through which fluid is drawn to that pump chamber, thereby increasing the suction pressure. Therefore, the occurrence of cavitation is shifted towards a higher pump yield and/or operating temperature and the pressure gradient during pumping is reduced. Wear of pump parts and noise generated by the pump is reduced. It is remarked that a fuel pump with a suction port for providing a predominantly radial flow of fluid to a pump chamber, however with a different constitution, is known from the German patent application 3.014.147-A. As opposed to the field of the present invention, a fuel pump is especially adapted for the pumping of fuel. This type of usage requires less flow of a less viscous medium while maintaining a lower pressure. Furthermore, the fuel pump is usually electrically driven, so it can be operated at a constant and freely adjustable rotational speed of the rotor depending on the desired flow. Moreover, the suction port disclosed in DE3.014.147-A is constituted by a hole in the cam ring. This type of port increases the cost of the manufacturing process of the cam ring, because said hole is introduced into the cam ring either by drilling or by a core during the casting or sintering of the cam ring, which increases the complexity and the cost of the process. A suction port according to the invention may be introduced simply by the shape of the cam ring mould. 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 3a shows a detail of the cross-section II-II given in figure 2, however, with a cam ring and an outer pump housing part according to the invention. Figure 3b shows another embodiment of a cam ring and an outer pump housing part according to the invention. Figure 3c shows a cam ring and a central pump housing part 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 3a shows a detail of the cross-section II-II, however, with a cam ring 2 and an outer pump housing part 9 according to the invention. The cam ring 2 is provided with a recess 25 constituting a suction port 26, for allowing a predominantly radial flow of fluid from a hydraulic channel 24 to a pump chamber 13. Thereto a state of the art axial suction port 11 and hydraulic channel 24 are extended radially outward to arrive into open connection with recess 25 for allowing a predominantly axial flow of fluid to said recess 25. The effective surface area (11, 16 and 26) through which fluid is allowed to flow to a pump chamber 13 is increased. It is known from fluid mechanics, that this effects a reduction of the suction pressure. Because of the decreased suction pressure at otherwise constant pump parameters, the undesired cavitation effect will occur only at a higher pump yield and/or temperature. Furthermore, said pressure gradient is reduced. In figure 3b another embodiment of a cam ring 2 and an outer pump housing part 9 according to the invention is shown. The recess 25 is in communication with a hydraulic channel 24, provided in an outer pump housing part, through an additional suction port 27 for allowing a predominantly axial flow of fluid. In figure 3c yet another embodiment of a cam ring 2 according to the invention is shown. Recesses 25 are introduced in axial direction on opposite sides of the cam ring 2 over the entire radial width of the cam ring 2. Furthermore, at the location of recess 25 the edges of the radially outer surface of the cam ring 2 are rounded, so as to promote the flow of fluid to a pump chamber 13. The cam ring 2 shown in figure 3c directs the flow of fluid into the desired direction with a minimal disturbance of said flow. The recesses 25 are in communication with a hydraulic channel 24 through an additional suction port 28 in radial direction outside the cam ring 2.

Claims: Roller vane pump for pumping automatic transmission fluid in a continuously variable transmission for motor vehicles, provided with a pump housing (12), a drivingly rotatable rotor (4) adapted for drivingly connection to a main drive shaft of the motor vehicle, 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), which chambers (13) may arrive in communication with one or more hydraulic channels (24) provided in the pump housing (12) through at least two suction ports (11 and 16) for allowing a predominantly axial flow of fluid to a pump chamber (13), characterised in that , the cam ring (2) is provided with a recess (25) constituting a suction port (26) for allowing a predominantly radial flow of fluid to a pump chamber (13), whereby at least one of said suction ports (16) for allowing a predominantly axial flow of fluid to a pump chamber (13) and the suction port (26) for allowing a predominantly radial flow of fluid to a pump chamber (13) adjoin one another. Roller vane pump according to claim 1, characterised in that , a suction port (11) for allowing a predominantly axial flow of fluid is extended radially outward for allowing a flow of fluid from a hydraulic channel (24) to said recess (25). Roller vane pump according to claim 1, characterised in that , an additional suction port (27) for allowing a predominantly axial flow of fluid is provided for allowing a flow of fluid from a hydraulic channel (24) to said recess (25). Roller vane pump according to claim 1, characterised in that , a suction port (28) for allowing a predominantly radial flow of fluid is provided in radial direction outside the cam ring (2) for allowing a flow of fluid from a hydraulic channel (24) to said recess (25). Roller vane pump according to claim 1, characterised in that , the cam ring (2) is provided with two recesses (25), in axial direction on opposite sides of the cam ring (2). Roller vane pump according to claim 5, characterised in that , the radially outer part of the cam ring (2) is at least partly rounded. 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: F04C15
IPC codes: F16H61, F04C15, F04C2