WO1990008900A1

WO1990008900A1 - Split vane for vane pumps or motors

Info

Publication number: WO1990008900A1
Application number: PCT/US1990/000282
Authority: WO
Inventors: John L. Acheson
Original assignee: Racine Fluid Power, Inc.
Priority date: 1989-02-03
Filing date: 1990-01-10
Publication date: 1990-08-09

Abstract

A hydraulic pump or motor having a casing defining a chamber for receiving a rotor having a plurality of radially extending slots therein, a pair of independent vane sections in each slot, and a cam ring surrounding the rotor in a position to engage the tip of the vane sections, the cam ring being movable between concentric and eccentric positions with respect to the rotor to define the extent of travel of the vane sections, vane sections splitting the tip load on the cam ring so that the tip load of each vane section approximates the design load of the surface of the cam ring.

Description

SPLIT VANE FOR VANE PUMPS OR MOTORS

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to hydraulic pumps and motors of the type having system pressure actuated control pistons for regulating cam ring eccentricity and in particular to a rotor having split vane assemblies operatively engaging the cam ring to produce the pumping action.

Description of the Prior Art

Variable volume vane pumps of the type contem¬ plated herein are shown and described in U.S. Letters Patent Number 4,340,338 entitled "Hydraulic Pressure Biased Linear Motion Thrust Block for Hydraulic Pumps and Motors^/ issued on July 20, 1982, and assigned to the same assignee. This type of pump is provided with radially directed, diametrically opposed, pressure actuated pistons for regulating the position of a movable cam ring in response to pump pressure requirements. The cam ring position is also controlled by the action of a thrust block assembly which maintains the cam ring position with respect to the pressure actuated pistons as the cam ring is moved to the high pressure position. A net unbalanced force is applied radially to the cam ring as a result of the asymmetry of the pump pressure distribution .within the pump chamber. This force is ■balanced on the ring by the thrust block assembly that applies an oppositely directed radial reaction to the outer periphery of the ring.

The requisite ring motion is cyclic in nature. Pump pressure continually varies in response to load. As the pump pressure increases, the vanes are subjected to hydraulic forces which cause the vane to move into contact with the cam ring. The tip load of the vanes on the cam ring is calculated and, based on those calculations, the design load of the cam ring is determined. In order to meet the design loads, the vanes have to be specially heat treated and the cam ring surface treated.

. It has been determined that at high fluid pressures the vanes tend to deflect and deform at the tip taking on a curved shape that results in a short length of the tip being in contact with the inside surface of the cam ring. The hydraulic force acting on the underside of the vane produces a tip load on the cam ring in excess of the design load of the cam ring since full tip contact is not possible. The under vane force is a function of the area of the vane and the pressure on the under side of the vane. As "the effective contact length of the vane tip is reduced, the tip load will increase to a level that causes excessive burnishing and wear on the inside surface of the cam ring. Heavy burnishing is indicative of high unit loads and a precursor to spalling or galling of the cam ring.

Past analysis attributed the heavy burnishing to straightness problems; crowning of the vanes as a result of grinding errors or humping of the ring surface due to ring deflection. Past attempts to eliminate ring-vane spalling and galling problems have been directed at improving dimensional control, surface finish, straightness and wear surface heat treatment plus the addition of anfci-friction coatings to the wear surfaces.

SUMMARY OF THE INVENTION The invention herein disclosed and claimed achieves a number of specific objects and advantages which eliminate or minimize current problems present in hydraulic pump and motor technology by a simple modification of the vane configuration. It has been found that the problems relating to cam ring wear and efficiency can be corrected by changing the deflection characteristic of the vane and particularly where and how the vane tip contacts the interior surface of the cam ring.

In this regard, it has been determined that vane bending can result in a change in vane tip profile that approximates a crowned vane. This deflection of the vane tip is increased by the chamfers provided on the rotors. The magnitude of the arc and the amount of vane deflection will determine the effective or actual tip contact length. As the effective contact length is reduced from the theoretical, the tip load will increase accordingly. Vane tip loading can then be much greater ^"than the calculated loads. It has been determined that burnishing of the cam ring can be minimized by splitting the vane into two separate vane sections resulting in a reduced area at the bottom of each vane section which is exposed to under vane pressure thereby reducing the resultant unit force of each vane section bearing on the cam ring to a level approximating the calculated design load.

The primary object of the invention is the reduction of the load of the vane tips on the cam ring. This has been achieved by using two vane sections in each rotor slot in order to split the vane tip load between the two vane sections. One of the primary advantages of the invention is the decrease of the vane tip load with a corresponding reduction in cost of parts by the elimination of costly secondary heat treatments of the vanes and the elimination of the complicated surface treatment of the cam ring.

Another advantage of the invention is the provision of uniform support across the back of the vanes by using a scalloped rotor in place of the chamfered rotors.

Other objects and advantages will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an elevation view in section of a variable volume vane pump taken normal to the shaft axis and through the cam ring.

Figure 2 is an elevation view of the pump taken on line 2-2 of Figure 1.

Figure 3 is a perspective view of a prior art vane construction. Figure 4 is a perspective view of a prior art vane under hydraulic conditions.

Figure 5 is a perspective view of one of the vane assemblies according to the present invention.

Figure 6 is a perspective view of the vane assembly under load.

Before describing one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details as set forth in the following description, or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Variable volume vane pumps, as shown in Figures 1 and 2 are generally constructed with a two-part casing 10A and 10B. A cylindrical chamber 12 is machined into casing 10A for receiving the pumping elements, the other casing 10B serving to close off the chamber 12.

The pumping elements generally include a rotor .14, whose direction of rotation is as indicated throughout by the vector A, having a series of outwardly extending slots 16 each of which receives an outwardly movable vane assembly 18. Each vane assembly is capable of radial movement within the slot 16 outwardly under the action of centrifugal force. The extent of outward movement of the vane assemblies 18 being controlled by a movable cam ring 20. The radial movement of the vane assemblies 18 on the high pressure side of the ' pump being enhanced by the hydraulic pressure on the high pressure side which acts through a passage 31 which is connected to slots 16 and to the discharge port 25.

The rotor 14 includes scallops or recesses 13 between the slots 16 to provide access to the discharge ports 25 and inlet ports 27. The scallops 13 also define ridges 11 across the front and back of the vane assemblies 18 which provide support across the full width of the vane section 18A and 18B. The rotor 14 is mounted on a shaft 15 for rotation in chamber 12. The shaft 15 is suitably fit at its ends in bearings 17 which are received in openings 19 in the casing parts 10A and 10B.

In order to form closed pumping spaces between adjacent vane assemblies 18 and the cam ring 20, the sides of the spaces are closed off by means of a pair of pressure plates 22 and 23 positioned in the chamber 12 at opposite sides of the rotor 14. Leakage at this interface is reduced by the use of seals and the preloaded contact produced by pump pressure tending to urge the plates 22 and 23 inwardly toward the rotor 14. A spacer ring 24 can be positioned between the pressure plates 22 and 23 surrounding the cam ring 20 to limit the pressure of the plates 22 and 23 against the rotor 14 and cam ring 20.

The movable cam ring 20 is regulated in its positioning relative to the rotor axis to control the pump output by hydraulic or mechanical means which may include a pair of diametrically opposed hydraulic pistons 26 and 28 engaging the outer surface of the cam ring 20. A net unbalanced radial force is developed in the pumping chamber defined by vane assemblies 18, the rotor 14, the pressure plates 22, 23 and the cam ring 20. This radial force, a product of the pump chamber pressures and the area on which it acts as applied to the cam ring, is outwardly directed and aligned with the axis of a thrust block assembly 50 as shown and described in the above identified U.S. patent serial number 4,340,338.

The piston 26 is movable in a bore 32 in the casing part 10A and has an operative end 34 extending through an opening 36 in the spacer ring 24 to engage the outer surface of the cam ring 20. The piston 26 is continually subjected to the pump output pressure and will urge the cam ring 20 away from the eccentric position shown in Figure 1 and toward a concentric position relative to the rotor 14 to thereby reduce the volume of the pump output.

Cam ring positioning is further determined by the action of piston 28 acting in opposition to piston 26. Piston 28 is movable in a bore 38 formed in the casing and has a reduced end 40 extending through an opening 42 in the spacer ring 24 to engage the outer surface of the cam ring 20. The piston chamber 38 is generally exposed to a pressure compensating servo valve which may be operative or not depending on actual pump operating conditions and a predetermined threshold at which compensation initiates. When the servo is not pressure compensating, chambers 32, 38 and piston 26 and 28 are subjected to outlet fluid pressure in which case piston 28 urges the ring 20 to the right since its area, and consequently the force applied, are about twice that of piston 26. As pressure increases and compensation initiates, fluid is drained from piston 28 and chamber 38. Cam ring 20 is then controlled solely by the action of piston 26 and assumes a position concentric with the rotor axis.

The extremities of cam ring motion are, at the low volume end, fully concentric with the rotor 14 and at the high volume end, at the maximum eccentricity permitted as when the cam ring 20 abuts the spacer ring 24. Between these extremes, as outlet pressure varies in excess of and short of the compensating pressure at which piston 26 predominates to influence cam ring positioning, the cam ring 20 will cycle eccentically of the pump axis and generally along the line defined by the axis of piston 26 and 28.

Referring to Figures 3 and 4, perspective views of portions of the prior art vane pumps disclosed in U.S. Letters Patent 4,340,338 are shown. The rotor 20" includes slots 16' for supporting vanes IS'. The rotor 20' includes chamfers 21' to provide access to the inlet and discharge ports thus leaving the vane IS' unsupported at the edges.

Referring to Figure 4, the vane 18 is shown under hydraulic pressure. The response of the vane IS', as pressure increases, is to deflect rearward and deform at the ends of the tip of the vane. The tip of the vane 18' takes on a curved shape or arc that results in a short length -" " of the tip contacting the inside surface of the cam ring 20 . The hydraulic force of the fluid in the slot 16' acts on the inner edge of the vane 18" to force the vane IB ' into contact with the cam ring 20' resulting in a unit load " ," , that is concentrated in the contact area, of the tip which exceeds the design load of the cam ring since full tip contact is not possible. The under vane load is a function of the area of the inner edge of the vane, width and length, and the pressure of the fluid in slot

16'.

Referring to Figures 5 and 6_r the split vane assembly 18, according to the present invention, is shown. Each vane section 18A and 18B in slot 16 is supported across its full length by means of the ridge

11 thereby reducing the deflection of the outer edges of the vane sections. Under full load pressure, both ends of each vane section are deflected and deformed reducing the vane tip contact area to the length L and

A L . However, as a result of the split of the vane

B assembly 18 into two sections 18A and 18B, the tip load on the vane assembly 18 is split between the vane sections; the resultant force and tip load on the cam - ring is also split resulting in a load at each vane section approximating the design load of the cam ring.

Thus, it is apparent that there has been provided, in accordance with the invention, a split vane assembly for a vane pump that fully satisfies the aims and advantages set forth above. While the invention has been fully described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and scope of the appended claims.

Claims

CLAIMSThe embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows?

1. A hydraulic pump or motor having a casing defining a chamber for receiving a rotor and a cam ring surrounding said rotor, said cam ring being movable relative to the axis of said rotor in response to pressures generated within said pump or motor, the improvement comprising a plurality of radially extending vane assemblies slidably disposed in said rotor, each of said vane assemblies including a pair of vane sections of equal width and length and being urged radially outwardly into sliding engagement with said cam ring whereby the tip load acting on said cam ring is split between each of said vane sections.

2. A vane pump comprising: a casing having a chamber, a rotor mounted for rotary motion in said chamber, a cam ring positioned in said chamber and surrounding said rotor, a plurality of vane assemblies mounted in said rotor for radial movement into engagement with said cam ring, and means for moving said cam ring within said chamber between concentric and eccentric positions with respect to said rotor, each of said vane assemblies including two vane section of equal length and width whereby the force of engagement of the vane assemblies with the cam ring is equally split between said vane sections.

3. The pump according to claim 2 wherein said rotor is scalloped between said vane assemblies to form a ridge on each side of each vane assembly to minimize deformation of the outer edges of said vane section .

4. The pump according to claim 1 wherein said rotor includes a plurality of axial slots extending radially outwardly from said rotor, said vane assemblies being positioned in said slots for movement into engagement with said cam ring and define pressure chambers between said vane assemblies.

5. The pump according to claim 4 including means for connecting said slots to the high pressure side of said pump for moving said vane sections into engagement with said cam ring.