US3255638A - Fluid motor - Google Patents

Description

C. B. LIVERS June 14, 1966 FLUID MOTOR Filed Jan. 22, 1963 QQLOS B. Ln/Ezs NVENTOR ATTOQN EVS United States Patent O 3,255,638 FLUID MOTOR Carlos B. Livers, North Hollywood, Calif., assignor to Sprague Engineering Corporation, Gardena, Calif., a corporation of California Filed Jan. 22, 1963, Ser. No. 253,130 2 Claims. (Cl. 74-60) This invention relates to uid motors of the wobble plate type such as shown in United States Letters Patent 2,994,306 and the present invention has to do with improvements upon such motors.

In some servo mechanism applications it is common to have substantially equal pressures simultaneously applied to both the inlet-and outlet ports of the motor. Under such conditions most piston-type fluid motors tend to lock and, even under conditions of no load, require a very substantial differential pressure between the inlet and outlet ports in order to cause the motor to operate. Even then the motor is apt to run rough and this renders it unacceptable for use with delicate mechanisms, The cause of this locking is the fact that all the pistons are under pressure and the heavy loads that result are additive to the side loads, bearing loads and general friction.

An object of the invention is to provide a novel construction in a uid motor of the piston-and-wobble plate type which overcomes the above noted disadvantage of other fluid motors of this type and which enables the motor to operate easily and elfectively on only slight differential of pressure between the inlet and outlet ports, irrespective of the fact that both ports may be subjected to'high pressure. v

To accomplish this it is an object of the invention to provide means for maintaining pressure in the motor casing which is approximately equal to the lowest pressure applied to the two ports of the motor. When this is accomplished all the forces which are ordinarily applied to one-half the pistons during their return strokes are canceled, and the forces which are ordinarily applied to the other half of the pistons during their power strokes are reduced to that amount represented by the differential pressure. Thus this greatly reduces the total forces customarily encountered and permits the motor to operate smoothly and with low differential pressure and good sensitivity.

More specifically it is an object to provide novel means for pressurizing the interior of the casing beyond the cylinders and the pistons by utilizing the pistons as a means of carrying fluid pressure thereto. It is therefore an object to provide a novel piston construction which permits bleeding pressure uid through the pistons.

Another object is to provide a novel piston and slipper construction embodying fluid passage means for pressurizing the interior of the casing.

Still another object is to provide a novel shaft seal arrangement which permits return of leakage uid to the system.

A further object is to provide a novel wobble plate assembly and a novel piston and slipper assembly in combination therewith.

These and other objects will be apparent from the drawing and the following description. Referring to the drawing:

FIG. l is a central longitudinal section through a motor embodying the invention; v

FIGS. 2, 3 and 4 are cross-sectional views on lines 2 2, 3 3 and 4 4, respectively, of FIG. l;

FIG. 5 is an enlarged sectional view of a slipper and the adjacent end of one of the pistons; and

FIG. 6 is an elevational view of the end face of the slipper on line 6 6 of FIG. 5.

More particularly describing the invention, the motor including a shell or casing 11 having radial ports 12 and 3,255,638 Patented June 14, 1966 ice together with the cylinder block provide uid passages to the cylinders from an annular space 23. Each cylinder also has a port 24 leading to the annular space 25 communicating with port 13. In each cylinder 17 is -a piston 26 having a radially reduced center portion 27. Each piston acts as a valve to control flow of iluid to one of the other cylinders in the manner described in U.S. Patent 2,994,306. Also, the cylinder block 16, inner body 20 and shell 17 are joined as by brazing into an integral unit.

The pistons 26 operate against a thrust plate 30 of a wobble plate assembly 31. The latter is mounted on a tubular shaft 33 joumaled in bearings 34 and 35 in the body 20 and mounting plate 15, respectively. An inner,

having an angularly disposed outer cylindrical surface 41,

the bushing being ixed to shaft 33 by pin 42. Mounted on the bushing are two thrust plates, designated 30 and 44, a spacer 45 and a bearing 46. The thrust plate 30 provides a surface 30 against which the pistons can operate and, by virtue of bearing 46 between the two thrust plates, plate 30 can rotate independently as required. Behind plate 44 is a wobble plate 50 having an inclined forward surface 51 and a rear surface 52 which is normal to the axis of the shaft 33 upon which the wobble plate is mounted and secured by pins 53. Axial thrust is taken by a bearing 54 which is supported on a radially reduced section 55 provided on the inner end of the mounting plate 15. A bearing thrust plate 57 is located behind the bearing.

Each piston is fitted with a slipper 60 and this comprises a body 61 having a working face 62 adapted to abut the Athrust surface 30' of thrust plate 30. Each slipper has a spherical-Shaped recess 63 receiving the lball head 64 at the end of an associated piston, the lip portion 65 Ibeing swaged over the head to retain it. The several slippers are retained in relatively close contact with the thrust surface 30 during conditions when there is no hydraulic pressure available to do this by a spider comprising a plate 66 having apertures 67 receiving the slippers anda ball section 68 adapted to bear against a concave spherical bearing surface 69 of a bearing 70.

`In order to pressurize the space or chamber 72 beyond the cylinders, each piston is provided with a uid passage 73 therethrough and in like manner each slipper has a fluid passage 74 therethrough which communicates with the passage in the piston. The y'working face 62 of each slipperl is provided with an inner groove 76 which is connected to the passage -74 .by a radial groove 77. -An ou-tergroove 78 is connected to the space around the slipper by a radial groove 79.

y It will be apparent that, in the operation of the motor, pressure fluid will pass through the pistons and slippers into chamber 72 which is sealed and pressure will then build up in this chamber. Fluid under pressure may move through the pistons and slippers and occupy areas under the slippers which are determined .by the areas of the grooves in the working faces 62 thereof. The areas of such grooves are smaller than the diameter of the piston in orderthat the forces tending to separate the iFurther it will be apparent that since the casing isV closed or sealed the pressure inside the casing willl rise until it reaches a pressure slightly greater than the return pressure. Consequently a small force exists which tends to lift the slippers olf the face 30 of the thrust plate 30. The amountby which the force can lift the slippers is controlled by the longitudinal clearance in the bearings of the motor. This clearance should be suicient to permit adequate drainage of the case liuid back through the returning pistons and into the return system. There results a casing pressure slightly higher than the return pressure.

In view of the high pressure in the casing a two-stage shaft seal is used. The first stage consists of a sleeve 80 which lits the shaft closely and which carries a resilient seal ring 81 in a peripheral groove 82. Beyond this is a second seal 83 which may be a flexible member of any suitable conventional construction. Such fluid as leaks past the first seal 80 is returned to the system through a passage 85 and return port 86.

Although I have shown and described preferred forms of my invention, I contemplate that various changes and modifications can be made therein Without departing from the invention, the scope of which is indicated by the following claims. Also, it should be understood that while the invention is primarily designed for yuse as a fluid motor, it is also operable as a pump when the shaft is turned by an external prime mover, and, consequently the word motor in the claims should be interpreted as inclusive of a pump.

I claim:

I1. In awobble plate type motor, a casing, a cylinder block in said casing having a plurality of cylinders disposed equidistantly around and parallel to a common axis, a shaft journalled in said casing on said axis, a wobble plate fixed to said shaft and having an inner surface disposed angularly transverse to the shaft, a bushing fixed to the shaft inwardly of and adjacent to the thrust plate and having a cylindrical outer surface whose axis is normal to the plane of the inner surface of the wobble plate, `a thrust plate assembly including a pair of annular thrust plates and bearing means therebetween, said assembly being mounted on said bushing against the inner face of said wobble plate, and piston means in each cylinder .bearing against said thrust plate assembly.

2. The wobble plate type lm-otor set yforth in claim -1 in which said shaft comprises a hollow outer mem-ber journalled in said casing and an inner member extending from the region of said wobble plate to and beyond the outer end of said outer member, said inner member being of less diameter than the inner diameter of the outer memlber lwhere it traverses .the same except at its inner end, and means tixedly securing the inner end of said inner member to said outer member.

References Cited by the Examiner UNITED STATES PATENTS 1,958,221 5/19'34 Wilcox 277-59 2,273,129 2/ 1942 Messinger 277-59 2,498,679 2/1950 Hall 74-60 2,733,619 2/1956 Smith 74--569 2,776,628 l/ 1957 Keel 74--60 X 2,944,430 7/1960 Huber 74-60 2,979,037 4/1961 Budzich 1211-119 2,997,956 7/ 1961 Stewart 74-60 X 3,049,940 8/ 1962 yNeff et al. 74--569 3,056,387 10/ 1962 Budzich 12-1-119 BROUGHTON G. DURHAM, Primary Examiner.

JOSEPH H. BRANSON, JR., Examiner.

W. L. FREEH, F. E. BAKER, Assistant Examiners.

Claims (1)

1. IN A WOBBLE PLATE TYPE MOTOR, A CASING, A CYLINDER BLOCK IN SAID CASING HAVING A PLURALITY OF CYLINDERS DISPOSED EQUIDISTANTLY AROUND AND PARALLEL TO A COMMON AXIS, A SHAFT JOURNALLED IN SAID CASING ON SAID AXIS, A WOBBLE PLATE FIXED TO SAID SHAFT AND HAVING AN INNER SURFACE DISPOSED ANGULARLY TRANSVERSE TO THE SHAFT, A BUSHING FIXED TO THE SHAFT INWARDLY OF AND ADJACENT TO THE THRUST PLATE AND HAVING A CYLINDRICAL OUTER SURFACE WHOSE AXIS IS NORMAL TO THE PLANE OF THE INNER SURFACE OF THE WOBBLE PLATE, A THRUST PLATE ASSEMBLY INCLUDING A PAIR OF ANNULAR THRUST PLATES AND BEARING MEANS THEREBETWEEN, SAID ASSEMBLY BEING MOUNTED ON SAID BUSHING AGAINST THE INNER FACE OF SAID WOBBLE PLATE, SAID PISTON MEANS IN EACH CYLINDER BEARING AGAINST SAID THRUST PLATE ASSEMBLY.

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