US 3698287 A
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United States Patent Martin 1451 0a. 17, 1972  AXIAL PISTON DEVICE 72 Inventor: Robert J. Mart H t h' K Primary Exammer paul Maslousky u c mson ans Attorney-Gregory J. Nelson,'.lames W. McFarland  Assignee: The Cessna Aircraft Company, and Miller& Brown Wichita, Kans. 22 Filed: Dec.9, 1970  ABSTRACT An improved manner of supporting the cylinder barrel [2H Appl' 96451 against side or transverse loads utilizing a flat, un-
crowned spline driving connection between the drive  US. Cl ..91/507 Shaft and ylin rrel- Th un is constructed so 51 1m. 01.; ..F0lb 3/00,F01b 13/04 that the Side load imposed on the Cylinder barrel and 5s Fieldof Search ..91/499, 500-507 Shaft acts at h Outer edge of the cylinder y controlling design parameters such as shaft selection  References Cited and bearing location, the point of maximum shaft deflection is maintained at a location within the axial UNITED STATES PATENTS length of the cylinder barrel to maintain alignment of the side load and its support during shaft deflection to Wtlght ..9 t f ld b 1 3,007,420 11/1961 Budzich ..91/499 prev 1 mg 0 6 cy m er 3,468,263 9/1969 Niemiec ..91/499 8 Claims, 6 Drawing Figures 20 w a 40 3o 27 2| 29 I7 fl ZFT 3| I l w y 1-- "7am 34 I6 15 37 35 l m s9 142 Tea-"31 PATENTEDncmmn SHEET 1 UF' 3 ROBERT J. MARTIN INVENTOR 5%TORNEY PATENTEUUU 111912 SHEET 3 0F 3 ROBERT J. MARTIN I INVENTOR I, I
/l/ ////.VVVLV 1 AXIAL PISTON DEVICE BACKGROUND OF THE INVENTION This invention relates generally to axial piston fluid pumps and motors, and more particularly to improved means for supporting the rotating cylinder barrel of such units against transverse side loads experienced during operation.
Axial piston units of this class include a rotary cylinder barrel having a flat face in abutment with a stationary valve face, and a plurality of axial bores adapted to receive reciprocating pistons that engage an adjacent inclined cam surface. By sliding on the inclined cam, the pistons transmit transverse side load and driving torque between the cylinder barrel and pistons. The cylinder barrel mounts upon a drive .shaft for transverse support and for rotation therewith. It is important that support for the cylinder barrel against this side load be so arranged that no tilting moments are induced upon the barrel, as the barrel must remain in flat engagement with the valve face for proper unit operation. If the cylinder barrel tilts or cocks slightly, the fluid bearing between the valve face and barrel may lift the barrel completely off the valve face to cause galling or possibly destruction of the entire unit.
Rather than attempting to constrain the cylinder barrel against tilting through resistive design strength, which method has not been consistent with high production techniques, prior art devices permit the cylinder barrel to move slightly in response to the heavy transverse loads. The barrel is supported upon the drive shaft which is subject to slight deflection, and the barrel, though maintaining flat contact with the valve face, slips transversely as the shaft deflects to find its own position on the valve face. The most important aspect to proper operation of such an arrangement is to assure that the drive shaft support for the barrel transverse side force precisely aligns with such force. In this manner, the barrel experiences no tilting couple from the side load and does not cock upon the valve face. For example, U.S. Pat. No. 2,642,810, typical of the prior art, assures alignment of the side load and its support by use of a crowned spline driving connection and support between the barrel and shaft. The spline connection is somewhat loose and crowned or rounded to permit, to a limited degree, universal movement of the barrel relative to the shaft. The cylinder barrel support is at the crest of the crown, and the unit is designed to position the crest in line with the transverse side load.
SUMMARY OF THE INVENTION The present invention provides an alternate structure and solution to the side load and support alignment problem that eliminates the need for expensive crowned spline connections, generally reduces critical tolerances to provide a more economical unit, and provides longer unit life with more efficient operation than heretofore possible. According to this invention, a flat, straight and uncrowned driving connection between the cylinder barrel and drive shaft supports the barrel against its side loads. The driving connection extends inwardly toward the valving from the edge of the cylinder barrel adjacent the cam surface. The driving connection supports the barrel at this outer edge at a plane aligned with the transverse side loads imposed on the cylinder barrel during operation. The shaft is supported so that upon deflection the point of maximum deflection is between the face of the cylinder barrel engaging the valve face and the axial midpoint of the driving connection. The support location remains at the barrel outer edge aligned with the side load even as the shaft deflects.
Accordingly, it is a primary object of the present invention to provide an axial piston unit with improved supportmeans for the cylinder barrel to resist side loads imposed on the unit.
More particularly, it is an object of the invention to provide a non-universal driving connection between the cylinder barrel and shaft which continually sup ports the barrel at a predetermined position aligned with the cylinder barrel side load.
Yet another object in accordance with thepreceding objective is to provide a structure whereby the cylinder barrel is supported on an axial driving connection on the shaft at its end opposite that which engages the valve face, and wherein the location of maximum shaft deflection is between the axial midpoint of the driving connection and the valve engaging end of the cylinder barrel.
A further object is to provide a flat tooth, uncrowned spline connection between the cylinder barrel and drive shaft in accordance with the preceding objectives.
These and other more specific objectives and advantages of the present invention are specifically set forth or will become apparent from the following description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:
FIG. 1 is an offset transverse section of an axial piston unit incorporating the present invention;
FIG. 2 is a section view taken along line 2-2 of FIG.
FIG. 3 is a diagram and partial section similar to FIG. 1 showing in exaggeration the present invention under load,
FIG. 4 is a partial section taken along line 4-4 of FIG. 3;
FIG. 5A is a flat projection of a circular section taken along line 5-5 of FIG. 4; and
FIG. 5B is a view similar to FIG. 5A of a device not using the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT The axial piston unit of FIG. 1, utilizable either as a pump or motor, is generally designated by the numeral 10. The unit has a two-piece outer housing, a hollowed casing 11 firmly secured to fluid porting backplate 12 Drive shaft 13 extends axially into the housing, being supported at bearings 14 and 15 in the casing and backplate respectively, with one end 16 projecting outwardly for rotary driving connection with a prime mover in the case of pump operation or with a work performing device if the unit operates as a motor. A tiltable cam plate 17 has trunnions (not shown) journalled to the casing 11 in a plane at right angles to the drive shaft axis.
Cylinder barrel 18 mounts for driving connection and radial support upon shaft 13 at spline 19. The
spline comprises inter-engaging, axially flat, straight teeth of involute form on both the barrel and shaft. The left face of cylinder block 18, extending perpendicularly to the shaft axis, abuts face 21 of backplate 12. Face 21 has a pair of arcuate valve slots 22 and 23, FIG. 2, communicating with fluid inlet and outlet ports 24, 25 in the stationary backplate. A'fluid bearing is maintained between the faces 20, 21 to lubricate same and provide barrel axial support. Upon rotation of the cylinder barrel, ports 26 alternately register with valve slots 22, 23 to deliver and receive fluid therefrom. Each barrel port 26 opens into an axial bore 27, which bores 27 are symmetrically disposed about the shaft axis. Bores 27 reciprocally carry working pistons 28 whose spherically formed ends 29 protrude outwardly of the barrel toward cam plate 17.
Swaged for pivotal movement on piston sphere ends 29 are slipper shoes 30 which directly abut the inclined cam surface. The piston shoes 30 extend through openings in a unitary retainer or spider plate 33 which has a central spherical socket accepting the spherical outer surface of a pivot 34. Thrust force, indicated by arrow 31, directed through the center of ball end 29 and perpendicular to the cam surface, urges piston 28 inwardly upon cylinder barrel rotation. This thrust can be resolved into an axial component acting along the piston axis and a transverse component 32 perpendicular to the piston axis. This latter component is the side load imposed on the unit and constitutes the driving torque transmitted between the pistons and cylinder barrel.
Spring in the central bore of the cylinder barrel acts through a plurality of pins 36, symmetrically disposed about the shaft axis, to bias the pivot 34 and spider plate 33 rightwardly. The spring force is transmitted through shoes 30 and to urge pistons 28 outwardly toward the inclined cam surface. Spring 35 is oppositely grounded to the shaft by snap ring 37. Pins 36 are located radially inwardly of the cylinder barrel, passing axially through the driving connection at the spline area. Each pin 36 (two are shown in FIG. 4) is located in an opening formed by the absence of a spline tooth on the cylinder barrel, or alternately, in a space formed by deleting a shaft spline tooth. The straight spline configuration as contrasted to usual crowned splines, permits easy insertion of the force transmitting pins into their respective openings. Strength of the forwardly extending neck portion of the barrel is greatly increased by situating pins 36 in the spline area rather than through the neck portion proper.
During operation, several piston chambers 27 will simultaneously experience the high pressure in one of valve slots 22, 23 and accordingly, each corresponding piston exerts a side load thrust 32 on the cylinder barrel. These forces 32, acting through the center of spherical ends 29, have a transversely directed sum acting in a plane 38 crossing the drive shaft axis approximately at the point 39 where the plane 40 containing the centers of spherical ends 29 also intercepts the shaft axis. Such operation is illustrated in FIG. 3 which shows four pistons under pressure and their four transverse thrusts 32. Their resultant, shown by arrow 41, is in a plane 38 that intersects both the piston sphere end plane 40 and the shaft axis at the location 39. The location of resultant side load 41 varies slightly during unit operation as the number of pistons on pressure varies as when one piston chamber leaves pressure stroke and another comes on pressure; however, averaged over a full revolution of the cylinder barrel, the resultant of side force 41 will be as shown.
To assure that the shaft transverse support for the cylinder barrel is in line with side load 41 so as not to induce tilting couples upon the barrel, as will be explained in greater detail hereafter, the outer edge 42 of the barrel is positioned in plane 38 in direct alignment with side force 41. Plane 38 thus becomes the rightward end of the axial extent of driving connection 19, the leftward end being at the end 43 of the shaft spline teeth. The driving connection is defined in axial extent as that distance over which the spline teeth of the shaft and cylinder barrel inter-engage.
The shaft 13 deflects or bends downwardly under the action of transverse thrust 41 as shown in greatly exaggerated proportions in FIG. 3. The supports for shaft 13, bearings 14 and15, the location of the spline and diameter of the shift, or diameters in the case of a stepped shaft, are so selected that maximum shaft bending occurs at the plane denoted 44. Maximum deflection plane 44 is inside or to the left of the inner driving connection end 43, between end 43 and cylinder block end 20. To the right of plane 44, therefore, the shaft continuously curves upwardly, keeping the cylinder barrel support located at the right edge 42 and plane 38. Cylinder barrel 18 slides transversely downwardly, from its original position shown by the dashed lines, but does not tilt since its support remains in alignment with transverse force 41. It will be noted that the spline connection 19 provides sufficient diametral clearance to permit the slight relative movement between cylinder barrel and shaft, the difference between the perpendicular cylinder barrel movement and the angular bending of shaft 13 about plane 44.
The effective length of the shaft spline, that is the length extending inward from the outer edge of the barrel, should be held to the minimum within good design practice to accommodate the imposed torque loading. In this way, the necessary diametral clearance permitting relative movement can also be held to a minimum inasmuch as increased spline length requires increased clearance for barrel movement.
FIGS. 4 and 5A clearly illustrate the manner in which the support point remains aligned with the transverse load at edge 42. Assuming right valve slot 23 of FIG. 2 to be under high pressure and rotation of the shaft and barrel to be counterclockwise in FIGS. 2 and 4, the barrel side load is supported primarily by the right side of the spline, whose teeth engage as shown at plane 38. FIG. 5A is a flat projection axial view of the mating teeth 45 and 46 of the drive shaft and cylinder barrel. During shaft deflection, the uncrowned shaft teeth 45 curve upwardly from maximum deflection plane 44, and they engage the cylinder barrel and support same only at the outer edge 42. Thus, though the shaft spline teeth cock slightly relative to the cylinder barrel under load 41, they remain in supporting engagement only at edge 42.
FIG. 5B illustrates operation of a device in which the maximum deflection plane 44' is not properly located intermediate the driving connection midpoint and cylinder block valving end in accordance with the present invention. Maximum deflection plane instead is located to the right of the axial center of the spline driving connection. The shaft and its straight teeth 45 curve upwardly in both directions from plane 44 such that, dependent upon the form of the bending curve, engagement between teeth 45, 46 occurs at either or both ends of the driving connection or somewhere intermediate. Accordingly, transverse support for the barrel noted by arrow 47 shifts, for instance, to end 43. The misalignment of support 47 and load 41 induces a couple upon the cylinder barrel cocking barrel end relative to valve face 21. It will be apparent that if the plane 44 of maximum deflection is to the right side of barrel end 42 in FIG. 5A, barrel support shifts to the opposite end 43 of the driving connection and produces a moment on the cylinder block.
Assuming that the deflection profile curve of shaft 13 is symmetric about plane 44, the support point properly remains at edge 42 as long as plane 44 is situated to the left. of the axial midpoint of the driving connection. That is, maximum shaft deflection must occur between the center of the axial extent of spline teeth inter-engagement and the valve face 20 of the cylinder barrel. Though shaft deflection is, in general, symmetric about its maximum deflection, such may not be the case, and location of the plane 44 could then more reliably be located between spline end 43 and face 20. Location of plane 44 to the left of end 43 in FIG. 5A will most assure proper support of the barrel during shaft deflection.
Contact between the teeth 45, 46 and cylinder block end 42 causes material wear which forms the teeth to the configuration best suited to absorb the load therebetween. The use of a flat-tooth spline as taught by this invention provides a greater predictability of the form of such wear during unit life, such wear still tending to maintain the load support at edge 42. In contrast, wear between the crowned spline teeth inherently is less predictable, tending to shift the load support position as the crest of the crown moves with wear. The present invention thus improves the life of the device and prevents deterioration of its efficiency and performance after long use.
It is many times advantageous in various unit designs to alter the position of the valve slots 22, 23 of FIG. 2 from their symmetric disposition shown. For instance, it may be desirable to skew or rotate the pressure slot, for instance slot 23, slightly counterclockwise so that there is greater area above than below center line 48. This also alters the location of transverse load 41, shifting plane 38 to intercept the shaft axis slightly left of point 39 where piston sphere end plane 40 intercepts the shaft axis. Itwill be readily apparent that skewing slot 23 clockwise will move load 41 and its plane 38 rightwardly of point 39. By taking into consideration the valve slot position, the unit may be properly designed such that cylinder block end 42 is properly aligned with transverse load 41, whether or not same is in line with the point 39 defined by the piston sphere end plane. The location of transverse load 41 may also alter slightly dependent upon rotational speed and operating pressure of the unit. Designing the unit to locate the cylinder block edge 42 at the position of transverse load 41 when the unit is operating under its normal or most average conditions will provide consistent, reliable and longer unit operation. Though perfect alignment of load 41 and barrel edge 42 cannot be maintained under all conditions, the above outlined approach to determining the usual transverse load location and locating the barrel to same will attain optimum results.
Having described my invention with sufficient clarity such that those skilled in the art may practice and use it, I claim:
1. In an axial piston device having a housing provided with valve means and fluid inlet and outlet ports at one end, an inclined or inclinable cam plate at the opposite end of the housing; a drive shaft extending axially in the housing; a cylinder barrel mounted intermediate the housing ends in driving relation with the shaft and positioned having an inner end face in flat surface contact with said valve means, said barrel having a plurality of axial bores; pistons reciprocally mounted in said bores having spherical outer ends in driving relation with the cam plate so as to transmit transverse thrust to said cylinder barrel upon rotation of said barrel; improved means for supporting said barrel against said transverse thrust, comprising:
an axially extending flat driving connection on said shaft;
an axially extending flat driving connection on said barrel mating with said shaft connection, said barrel positioned with its outer end along the axial length of said shaft connection and with said outer end coincident with the plane in which said transverse thrust acts whereby said driving connection supports the barrel at the outer end at said transverse thrust plane; and
said shaft being supported within the housing such that the point of maximum transverse shaft deflection is intermediate said barrel end face and the axial midpoint of the mating portions of said driving connections, whereby upon deflection of said shaft, said barrel remains supported on the shaft at said barrel outer end and said transverse thrust plane, and said end face remains in flat surface contact with the valve means.
2. The device of claim 1 wherein said point of maximum transverse shaft deflection is intermediate said barrel end face and said mating portions of the driving connections.
3. The device of claim 1 wherein the plane containing the centers of said piston spherical ends and said transverse thrust plane intersect the drive shaft axis at a common point.
4. The device of claim 1 wherein the plane containing the centers of said piston spherical ends intersects the drive shaft axis at a first point and said transverse thrust plane intersects said shaft axis at a second point spaced from said first point.
5. The device of claim 1 wherein said driving connections on said shaft and barrel comprise a spline connection of inter-engaging flat teeth.
6. The device of claim 5 further comprising biasing means located in a central bore of said barrel intermediate said barrel transverse end face and said spline connection; pivot means positioned forwardly of said barrel in a direction toward said cam plate and having an outer spherical surface, force transmitting means extending from said spring means freely through said 7 8 spline to contact said pivot, a piston retainer plate slipper shoes pivotally attached to said piston sphere pivotal on said pivot spherical surface, and a force ends engaging said inclined cam surface whereby transmitting connection between said retainer plate upon rotation of said barrel thrust is transmitted to and pistons whereby said spring biases said pistons said barrel in a direction perpendicular to said toward said cam plate. inclined cam surface and having a thrust com- 7. The device of claim 6 wherein said force transponent transverse to said shaft; mitting connection comprises a plurality of pins a flat tooth spline connection between said barrel disposed about the drive shaft axis extending through and Sald Shaft at a S c PPOS IZC end of the baropenings formed between teeth of said spline connecfel, Sald splme y Supporting Sald barrel i 10 against the transverse component of said thrust;
8. An axial piston devi p i i said barrel positioned between said valve means and a housing having transversely flat valve means at one Sald Cam Surface P X the Puter edge of Sald end; barrel second end aligns with said thrust transverse an inclined or inclinable cam plate at the opposite component; f
d f Said housing; bearings supporting said shaft to the housing ends so a drive shaft extending axially through the housing; f the PQ F of maxllnum tfansverse deflectlon of a cylinder barre] drivingly having a first end in flat said shaft is intermediate said barrel first end and surface contact with said valve means and further 531d SPlme Yonnectlon, whereby upon deflecFlon of having a plurality f axial bores; the shaft said barrel remains supported at said barpistons reciprocally mounted in said bores having edge and moves only Fransversely to mamtam spherically Shaped ends extending outwardly of said flat surface contact with the valve means. said barrel toward the cam plate;