IL32948A - Low friction radial piston pump or motor - Google Patents

Description

LOW FBICTIQN BADIA L PISTON FJMP OB MOT 05 TIPS nam η¾7κ»·η ni3¾a 7ga map W nasatp Title: LOW FRICTION RADIAL PISTON PUMP OR MOTOR Abstract of the Disclosure: A radial piston pump or motor including a cylinder block rotatable about a pintle shaft, a reaction ring assembly rotatable about an axis parallel to and displaced from the axis of said pintle shaft, pistons eciprocable in the bores cf said cylinders and link means comprising at least one pair of parallelogram links connecting the pistons to the reaction ring, for transmitting forces between said assembly and pistons. The connection between the link means and piston is effected along a line perpendicular to the piston axis, the assembly thus being characterized by a force transmission between pistons and reaction ring which precludes the application to the pistons of forces which tend to cock or tilt the pistons relative to the cylinder bores.

This application is a continuation-in-part of my copending application Serial No. :31,.i84j., filedN0v.-"~ 28:, 1968, entitled RADIAL PISTON PUMP AND MOTOR DEVICE.

Background of the Invention: Field of the Invention.

This invention is in the field of radial piston pumps and motors.

The Prior Art.

It is well known to provide a radial piston pump or motor in which a block having radially directed cylinders rotates about a pintle shaft. The pintle shaft includes outwardly directed high and low pressure distribution chambers sequentially communicated to the cylinders as they rotate about the shaft by fluid passages extending radially from the cylinders and opening ring surrounds the pistons and the outermost ends of the pstons, ^ either directly or through an interposed piston shoe, are pressed against the reaction ring. The axis of the reaction ring is displaced from the axis of the pintle shaft in normal operation and thus, in the course of rotation of the cylinder block, pressure is exerted by the pistons against reaction ring portions which are not precisely perpendicular to the axes of the cylinder bores.

As a result of the application of such pressures against non-perpendicular portions of the reaction ring, it will be observed that cocking or tilting force vectors are applied against the piston members during substantially the entire rotation of the cylinder block, the forces being ax: 11 of the piston only when a projection of the cylinder axis simultaneously intersects the axes of the reaction ring and pintle shaft, i.e. at the innermost and outermost limits of movement of the pistons within the cylinders. As a result of the cocking or tilting forces applied to the piston which tend to tilt the piston in a plane extending through the axes of the cylinders, wear of the piston and cylinder components is tremendously accelerated under load.

Various attempts have been made to counteract the effects of wear. Specifically, it has been proposed to elongate the pistons to thus reduce the deleterious effects of non-axially plied forces. However, piston elongation introduces other problems which materially detract from the efficiency and compactness of the pump or notor.

For example, where lengthwisely extended piston areas engage the cylinder bores, lubrication of the large, relatively snoving surfaces is difficult and expedients such as by-pass large overlaps between the pistons and cylinder bores nrnsr^be retained.

It will be observed that an increased piston stroke in hydraulic devices of this sort is achieved by increasing the distance between the pintle axis and the reaction ring axis and that the side components of forces exerted increase with such displacement. Accordingly, wear of the parts is increased drastically with attempts to increase the piston stroke.

Other expedients have been employed to counteract the effects of piston cocking. In United States Patent No. 3255,706, for instance, a complex arrangement is provided whereby fluid from the pressure chamber is diverted through the pistons and expelled into a chamber disposed between the cylinder wall and a side portion of the piston, the forces thus developed tending to counteract the tilting tendencies of the piston. Such solution provides, at best, an inexact compensation since the correcting forces can only roughly approximate the tilting forces. Also, the corrective effects can be achieved only with pistons traversing the pressure distribution chamber.

Further such apparatus must reduce the efficiency of the device by drawing away significant quantities of the fluid under pressure.

Summary of the Invention.

The present invention relates to a radial piston pump or motor wherein the forces exerted between the pistone and the reaction ring are channeled through a parallelogram link connector assembly comprising a pair of relatively movable arms or links pivotally connected at spaced points to the piston assembly, The parallel links assure that at all positions of the block relative to the reaction ring, the piston axis is maintained 4 parallel with the axi.". of the cylinder and, thus, there is no cocking or tilting forces exerted on the piston.

The device above described may be, but is not necessarily, combined with a further refinement incorporating a piston stabilizer which functions to prevent Lhe piston axis, although maintained parallel with the cylinder axis by the link assembly, from tending to be displaced transversely with respect to the cylinder axis.

More specifically, the parallel link assembly prevents any cocking of the piston and the stabilizer assembly maintains the parallel oriented piston centralized within the cylinder bore.

From the foregoing it will readily appreciated that • numerous advantages flow fronr the use of the parallel link assembly per se or in combination with the above described refinements. Specifically, it is possible to use a piston head which is shorter than heretofore practicable, with resultant savings in mass, reduction in size, and elimination of lubrication problems.

Secondly, since no side forces in any significant amounts are exerted by the piston against the cylinder, problems of wear between the piston and cylinder components are virtually eli in ted.

The linkage also permits a far greater piston travel than heretofore practicable, with little increase in overall size.

A further advantage lies in the fact that, since the engagement of the piston within the cylinder is not relied on as the means for stabilizing the piston, it is possible, for the first time in a hydraulic device of this type, to make effective use of piston rings, thus greatly reducing the cost of fabrication An additional advantage lies in the fa t that no sliding or slipping movement between the pistons and/or piston shoes ^ relative to the reaction ring is experienced, all relative movements being effected through bearing linkages between the link arms and the piston and reaction ring.

As will be more fully appreciated in connection with the detailed description of the device, the radial movement of the pistons is a double harmonic function, resulting from the super- imposition of the movement imparted to the piston by the pivoting of the links about the reaction ring on the harmonic (sine) function generated by the rotation όΓ the reaction ring. As a result, the initial movements of the pistons away from the minimum displacement position and the final return movements of the pistons to the minimum displacement positions are more gradually accomplished than would be the case if the pistons were controlled solely by a conventional reaction ring. This phenomenon results from the fact that the pivotal movement of the parallel links exerts a subtractive influence as respects the direction of movement imparted to the p i s"ton by the reaction ring assembly as the pistons leave and approach the minimum displacement positions.

Accordingly, it is an object of the invention to provide an improved radial piston pump or motor.

A further object of the invention is to provide a device of the type described in which there is no tendency for the piston to cock relative to the cylinder bores.

Still a further object of the invention is the provision of a radial piston pump or motor wherein the connection between the pistons and the reaction ring is effected through a paralello-gram linkage connector means which maintijins the piston axis paral- tween pist on and reaction ring in such parallel directions. ' Still a further object of the invention is- the provision of a device of the class described and including an auxiliary piston stabilizer which absorbs, externally of the piston and cylinder, any side thrust forces exerted against the pistons.

Still a further object of the invention is to provide, in a device of the class described, a piston head which employs piston rings.

To obtain these objects and such further objects as may appear herein or be hereinafter pointed out, reference is made to the accompanying drawings, forming a part hereof, in which: Figure 1 is a vertical sectional view through a radial piston pump or motor in accordance with the invention; Figure 2 is a magnified section taken on the line 2—2 of Figure 1 ; Figure 3 is a magnified vertical section through an embodiment of the invention; Figure 4 is a section taken on the line 4—4 of Figure 3 Figure 5 is a magnified section taken on the line 5—5 3 of Figure -4.

Referring now to the drawings, there is shown in Fig- es I and 2 a radial piston hydraulic pump-motor which comprises the usual pintle shaft 10 carrying a rotatable cylinder block assembly II in driving connection with an outpu; or drive shaft 12. The apparatus carries, in addition, a reaction ring chassis 13 which can, in the usual manner, be shifted from side to side relative to the pintle shaft, namely, from left to right as viewed in It will be appreciated that, as in the usual radial . hydraulic pump or motor, some mechanical linkage (not shown) is connected to the reaction ring chassis 13 through a manual or servo mechanism, to control its position and, hence, the degree and sense of eccentricity of the reaction ring relative to the pintle shaft.

Typically, the reaction ring chassis position may be varied to locate the axis of the reaction ring to either side or coaxial of the axis of the pintle shaft selectively, in accordance with the desired operation of the apparatus. The reaction ring chassis includes spaced support disks 14 , 15 , providing laterally elongated clearance spaces 16 , 17 , respectively, for effecting the desired eccentricity. The disks 14 , 15 are joined by the usual yoke or like assembly (not shown), forming a part of the mechanical linkage, to permit their simultaneous lateral movement to effect the reaction ring eccentricity referred to above.

The peripheries 18 , 19 of the disks 14, 15 form bearing races for the support of cylindrical bearing members 20 , 21 , or like bearing assemblies, the opposite races for the bearings being formed in the reaction rings 22 , 23 , respectively.

In the usual manner, the block 11 includes a central bearing portion 24 which is rotatably mounted about the pintle shaft 10. The pintle shaft incorporates high and low pressure conduits 25 , 26 , terminating in pressure distribution chambers 27 , 28 . It will be appreciated that the d istribution -chambers 27 , 28 are outwardly open, the chambers being separated by divider lands 29 , 30 .

The cylinder block includes a multiplicity of radially internal bores 32, the radial innermost ends of the bores incorporating fluid distribution passages 33.

Optionally but preferably, the passages are shaped in the manner shown in my United States Pnt nt No. 3345,916 of October .10, 1967, being axially elongated in the direction of the pintle shaft and angularly reduced in size in the areas adjacent said shaft, the passages progressively becoming wider and shorter as they merge with the cylinder bores 32. It will be understood that the inner terminal ends of the fluid passages are sequentially connected to the radially open high and low pressure distribution chambers 27, 28 of the pintle shaft as the block rotates, the land areas 29, 30 being of a sufficient angular extent completely to seal with a minimum of overlap each of the passages as they scan the land areas.

Within each of the bores there is mounted for reciprocation a piston assembly including a piston head portion 34 in sealing relation of the bore and a piston rod 35 extending radially outwardly from the piston head. Adjacent their outermost encs 36, the piston rods 35 are formed with a pair of bosses 37, 38, carrying cross rods 39, 40. The axes of the cross rods 39, ^fO are equi-distant from the radius R of the pindle shaft when the pistons are in axial alignment within the bores 32 of the cylinders. The c"istal ends of the rods 39, 40 are provided with bearing structures, such as roller bearings 41.

The outer race or component of each of the bearings 41 is affixed to the outermost end of a connector link 42a, 42b. In the illustrated device, four connector links are secured to each piston rod in view of the fact that the reaction rings proper are pair of link arms may be used to control the action of the piston.^ such an arrangement being appropriate where the reaction ring is disposed in outward surrounding relation of the pistons.

The links 42a, 42b will hereafter be referred to as a pair of links, the two links on the opposite side of the block 11 and connected to the opposite reaction ring 22 also comprising a pair.

The opposite ends of the links are connected to bearing members 43 supported on stub shafts 44 extending inwardly from the reaction rings 22, 23. It is important that each pair of links 42a, 42b be mounted so that the axis of the upper ends of the links and the pivot axis of the lower ends of the links of each pair in all positions remain parallel to each other and thus act in the manner of a parallelogram linkage.

From the foregoing description it will be apparent that by reason of the parallelogram linkages effected between the link pairs and the pistons, all forces transmitted by the pistons to the reaction ring or by the reac .ion ring to the pistons must be exerted against the pistons in a direction which is precisely in alignment with the longitudinal axes of the pistons and, hence, with the longitudinal axes of the cylinder bores.

By way of illustration, assuming the reaction ring chassis 13 to have been displaced to one side or another of the central position, thus to offset the axis of rotation of the reaction rings 22, 23 from the radius R of the pintle shaft, as shown in Figure 1, if a torque is applied to the block through the drive shaft 12, (thus using the apparatus as a pump) , the block will rotate, carrying with it the reaction rings 22, 23. As the block rotates, the pistons during one half of a rotation, and being refilled with hydraulic . # fluid from the low pressure distribution conduit 28 during the outward movement of the pistons. In the course of the rotary movement, since all forces communicated from the reaction ring to the pistons are communicated through the parallelogram linkages, it is clear that the piston axes are at all times maintained parallel with the axes of the cylinders. Therefore, any tendency of the pistons to cock or tilt within the cylinders is eliminated witnout the requirement of employing spherical or elongated pistons or similar disadvantageous expedients.

It will be observed that while moderate lateral forces between the sides of the piston heads and the cylinder bores will be deveiped in the course of force transmission, such forces are nowhere near as destructive as cocking forces which tend to tilt tie pistons within the cylinders. The destructive nature of the cocking forces results from bringing relatively small areas of the pistons into contact with small areas of the cylinders, the destructive effect being accelerated by reason of the fact that in conventional radial piston pumps and motors such forces are exerted through an extended moment arm by reason of the spacing j of the pistons from the reaction ring. j As previously alluded to, many design and functional % benefits may be derived from elimination of cocking or tilting forces to the piston. Specifically, since the piston head is not relied upon as the primary means for stabilizing the piston within the cylinder, pistons with shorter heads may be effectively employed, without fear of scoring or instability. The use of shorter head pistons brings secondary benefits by way of facilitating lubrication, enabling increased displacement per over-all and permitting the use of sealing mechanisms, such as p ston rings, between the piston head and the piston wall.

It will be further appreciated that, unlike conventional radial piston pumps end motors in which a relative sliding action occurs between the piston and/or piston shoe and the reaction ring, all of the thrust between these parts is effected between the rotary bearing assemblies, such as the bearings 41 and 43.

In Figures 3 and 4 there is shown a further embodiment of the invention which is calculated primarily to further reduce friction, being provided with mechanism which relieves the piston head from the application of lateral forces exerted between the piston head and the cylinder bore. In this embodiment, wherein like parts have been given like reference numerals, piston rod 35' is rigidly connected to a cross bar assembly 50, the cross bar or arm assembly being perpendicular to the axis of cylinder bore 32. While the cross bar and piston rod may be integrally formed, the connection is preferably effected through a threaded or otherwise secured inter-engaging stud 51 on the piston, received within threaded aperture 52 on the assembly 50.

The pairs of connector arms 42a, 42b, with interposed bearing members, secure the cross bar assembly 50 to the reaction rings in the manner previously set forth, to assure the absence of any cocking forces.

Tne cylinder members 53 of this embodiment are formed with external guide surfaces 54, 55 which parallel the cylinder axis. The cross arm 50 is internally threaded, as at 56, and receives a guide cup 57, the upper end 58 of which is externally threaded and received within the portion 56. The guide cup is threaded into the cross bar assembly 50, the cup including ver parallel spaced relation to the surfaces 55, 54, respectively, on the cylinders. Sets of needle bearings 61, 62, diagramma ically illustrated, or other suitable anti-friction guides, are interposed between the respective surfaces 55, 59 and 54, 60, to provide a low friction guiding function between the cup 57 and the cylinder 53.

It will be observed that by reason of the parallel links connection between the cross arm 50 and the reaction ring, there is no tilting moment applied to the guide cup 57. Thus, the bearing assemblies 61, 62 are required to resist only lateral forces, which forces are divided essentially equally among the bearing rollers of each race. In contrast, if the parallelogram linkage were not employed, it is evident that the considerable forces developed would be applied against an upper roller of one bearing set and a lower roller of another.

Formed at the lower end of piston rod 35* is a piston head 65 which, as shown in Figure 3, provides substantial clearances with respect to the cylinder walls. The piston head is provided with a series of spaced annular grooves 66, within which are mounted piston rings 67. The rings provide the requisite seals with respect to the cylinder bore 32'. It will be noted that, as in all devices incorporating piston rings, the rings 67 permit a degree of lateral movement of the pistons in the cylinders, by reason of the clearances of the rings in grooves 66. The permitted lateral movement does not interfere with the proper operation of the illustrated device, however, since the piston head is not relied on as a stabilizing element.

As best seen in Figures 4 and 5, the land area 29' i se aratin the hi h and low ressure areas of the ntle s t depth of which need not exceed a few thousandths of an inch.

These grooves function to reduce leakage across the outer surface of the lands between the lands and the rotating block, despite the existence of normal operating clearances. Without limitation, it is believed that the reduction in leakage is a result of an interruption of laminar flow across the face of the lands, the grooves tending to induce a turbulence in any such laminar movement and thereby reducing leakage losses.

From the foregoing it will be appreciated that there is provided a radial piston pump and motor in which all forces exerted by or against the piston members are constrained to act in a direction which maintains the piston axis parallel with the cylinder axis. By this construction numerous advantages by way of reduced wear, greater design flexibility, increased stroke and reduced over-all size per given displacement are achieved. Additionally, there are no relatively movable sliding surfaces, all bearings being of the low friction ball or roller bearing types .

Where the device is employed in connection with the external piston s.tabilizer or guide, substantially all lateral forces are eliminated between the piston head and the cylinder bore. Since the piston need no longer function as a stabilizing mechanism, it is now possible to use piston rings or like sealing mechanism, with their attendant economies.

No attempt has been made herein exhaustively to describe and explain all of the various design advantages and economies which may flow from the improved construction hereof.

For instance, a variation or modification of the design, ' extending the stub shafts 44 parallel to the axis of the pintle ( shaft and utilizing each said stub shaft as the bearing or pivot support for the radial innermost end of link 42a of one piston assembly and the link 42b of the adjacent piston assembly. In other words, in accordance with such modification each stub shaft 44 of each of the reaction rings 22 and 23 will thus pivot- ally carry the innermost end of two links, namely, the trailing link of one piston assembly and the leading link of the adjacent piston assembly.

In such construction the links will be further elongated as contrasted with the illustrated embodiments, and only half the number of stub shafts 44 will be required, the shafts being equally angularly spaced from each other about the rings 22 and 23 Obviously, the links supported on any stub shaft must be offset from each other in the direction of the pintle shaft axis so as not to interfere with each other in the course of their independent pivotal movement about the stub shafts, the extension of the stub shafts 44 noted above being for the purpose of providing such clearance.

The invention is to be broadly construed within the scope of the appended claims.

Claims (2)

P.A. 32948/2 WHAT IS CLAIMED ISi

1. A radial piston pump or motor comprising a IP pintle shaft, a cylinder block mounted on said shaft and including a plurality of radially extending 3Ί cylinder members having internal cylinder bores and external guide surfaces, said guide surfaces being disposed in a plane parallel with said bores, a reaction ring assembly mounted for rotation about an axis parallel with and displaced from the axis of said pintle shaft, a piston member mounted for reciprocation in each said bore, each said member including a head ' portion carrying piston rings in sealing relation with said bore and a radially directed piston rod extending outwardly beyond the end of said cylinders, a cross arm assembly rigidly affixed to the outer end of each said piston rod including a spaced pair of bearing members having their axes disposed in a common plane normal to the axis of said cylinder bore, a pair of parallel links having first end portions pivotally connected to said bearing members, the other ends of said links being pivotally connected to said reaction ring assembly whereby said cross arm assemblies are maintained normal to said axes of said bores at all rotated positions of said block and reaction ring assembly, guide means extending radially inwardly from said cross arm assemblies in outwardly lapping, sliding engagement with said guide surfaces of said cylinders, said links maintaining said cross arms at all times P.A. 32948/2

2. A radial piston pump or motor substantially as described with reference to and as illustrated in the accompanying drawings* COHEN ZEDEK & SPISBACH P.O. Box 33116, Tel Aviv Attorneys for Applicants*