US3915064A - Fluid drive means - Google Patents

Abstract

A fluid drive device for high torque, low speed applications.

Description

US. Patent Oct. 28, 1975 Sheet 1 of3 3,915,064

FLUID DRIVE MEANS In the art of rotating apparatus fluid powered drive mechanisms have been used to drive large rotating equipment such as large diameter thickeners and settlers and like equipment which must receive power at extremely high torque values for rotation at very low speeds. one such fluid drive mechanism comprises a plurality of hydraulically actuated driving arms disposed generally tangentially to a driven ring or wheel portion of the apparatus to be rotated thereby and intermittently engageable therewith in the manner of a ratchet and pawl mechanism. In practice selected ones of such driving arms engage the ratchet wheel for a power stroke to incrementally rotate the driven apparatus while other selected driving arms simultaneously end a previous power stroke thereof, disengage from the ratchet wheel and are repositioned to reengage the ratchet wheel for a subsequent power stroke. The alternating incremental rotations thus produced rotate the driven apparatus in a smooth, continuous manner. Such a drive system may be constructed so as to provide very low rotational speeds on the order of 0.01 to 10 revolutions per hour at very high torque capacities, for example up to and well in excess of one million foot pounds.

The present invention is an improved fluid drive of the type specified having such advantages over similar known mechanisms as for example a simplified elastomeric mounting which affixes a driving arm assembly in the operational position thereof and renders such assembly laterally movable with respect to the driven ratchet wheel. The improved mounting is operable without recourse to other conventional supports such as pin connections, ball and socket joints, springs and like elements customarily used in the prior art. Additionally, the improved mounting is highly wear resistant andrequires no lubrication.

The present invention additionally includes an improved'driving arm having cam means adjacent respective inner and outer sides thereof which are cooperable with the driven ratchet wheel and with a control valve means to control operation of the drive device.

These and other objects and advantages of the present invention are more completely specified in the following description and illustrations in which:

FIG. 1 is a top plan view, partly in section and partly schematic of a fluid powered drive mechanism constructed in accordance with the principles of the present invention;

FIG. 2 is a side view, partly in section, of the fluid drive of FIG. I substantially as seen from line 2-2 of FIG. 1;

FIG. 3 is an enlarged fragmentary portion of FIG. 1, partly in section, illustrating an actuating cylinder and driving arm assembly and a mounting therefor constructed in accordance with the principles of the present invention;

FIG. 4 is a side view of the driving arm of FIG. 2 substantially as seen fromline 4--4 of FIG. 3; and

FIG. 5 is an enlarged fragmentary portion of FIG. 1 illustrating a driving arm and a control valve assembly of the present invention including selected operational positions thereof illustrated diagrammatically.

There is generally indicated at in FIGS. 1 and 2 a fluid powered drive mechanism constructed in accordance with the principles of the present invention and presumed for purposes of illustration to be of a type utilized to power such large rotating apparatus as a large diameter thickener or clarifier. Such apparatus is well known to those versed in the art and therefore is not shown as exhaustively described herein inasmuch as such description is not necessary for an understanding of the present invention. Sufiice it to note in this regard that in practice thedrive 10 is disposed atop a thickener tank (not shown) and adapted to drivingly engage one end of a rotatable shaft 8 extending vertically therewithin and having rake arms or the like (not shown) affixed adjacent its opposing end within such a thickener tank whereby drive 10 powers the rake arms in rotation in a well known manner and for such customary purposes as for example the separation of solid components from a liquid mixture. It is of course to be understood that thedrive 10 of the present invention may be utilized to rotate various other types of rotating equipment about vertically or horizontally disposed axes, for example a center pier type thickener or clarifier or a large horizontally disposed rotating drum type diffuser, and therefore should not be construed as being limited to the illustrative application described herein.

Drive 10 comprises: a generallyrectangular housing 20 rigidly carried by a well known truss or bridge 11 spanning the diameter of the thickener tank and rigidly affixed thereto; aratchet wheel 30 rotatably carried within thehousing 20 and drivingly engaging the shaft 8; cooperabledriving assembly pairs 40 and 40a which include drivingarms 42 rigidly affixed adjacent the forward ends thereof, thearms 42 extending substantially tangentally to thewheel 30 and adapted to intermittently engage selected peripheral portions thereof; and valve means orcontrol assemblies 50 and 50a rigidly disposed withinhousing 20 and cooperable with se lected ones ofarms 42 to control theassemblies 40 and 40a through a suitable hydraulic actuatingcircuit 60.

Thehousing 20 is a rigid structure shown as comprising a pair of generally rectangular plate-like upper and lower members and 72, respectively, disposed in vertically spaced parallel relation as illustrated in FIG. 2 and retained thereat by a plurality ofwall portions 74 extending verticallyintermediate members 70 and 72 and rigidly affixed thereto adjacent outer peripheral portions thereof. Thewall portions 74 are rigidly affixed together at respective corners ofmembers 70 and 72 so as to form an outer peripheral portion of thehousing 20.Housing 20 additionally includes a circular innerperipheral portion 76 encompassed by awall portion 24 extending vertically intermediate and rigidly affixed tomembers 70 and 72 and adapted to receivewheel 30 therewithin, and a plurality of drivingassembly mounting portions 82 rigidly affixed outwardlyadjacent wall portions 74 and adjacent respective comers ofhousing 20, and adapted. to receive respective mountings 80 (FIG. 3) ofassemblies 40 and 40a.

In FIGS. 1 and 2wheel 30 is shown as comprising a pair of circular plate-like upper andlower members 32 and 34 rigidly retained in vertically spaced parallel relation such as by awall portion 38 extendingintermediate members 32 and 34 adjacent an inner peripheral portion thereof. A plurality of circumferentially spacedcylindrical pins 36 extends axiallyintermediate members 32 and 34 and are rigidly afiixed therebetween adjacent an outer peripheral portion thereof.

Thewheel 30 is rotatably carried withinportion 76 ofhousing 20 by suitable bearing means (not shown) such as a well known turntable bearing or the like and suitably adapted such as by splines (not shown) to drivingly engage an upper end portion of the shaft 8. Therespective arms 42 ofassemblies 40 and 40a intermittently and drivingly engagepins 36 in a ratchet-like manner such that thewheel 30 is powered in rotation thereby.

Referring now to FIG. 3 there is depicted one ofdriving assemblies 40 shown as comprising a hydraulically actuatedcylinder assembly 41 including a piston (not shown) slideably carried therewithin to which is affixed one end of apiston rod 44. One ofarms 42 is suitably rigidly affixed as bymating threads 46 adjacent the opposing end ofrod 44. Eachassembly 40 is retained by a respective mounting 80 adjacent one ofassembly mounting portions 82 ofhousing 20. It is to be understood thatassemblies 40a are identical in every respect toassemblies 40. Accordingly, the description hereinabove and hereinbelow regarding structure and operation of theassemblies 40 also applied toassemblies 40a.

Eachmounting portion 82 includes anannular flange 94 spaced outwardly fromwall portion 74 and rigidly affixed thereto as byportions 70 and 72 ofmembers 70 and 72 (FIG. 2) extending therebetween and bysupport members 75a and 75b also extending therebetween and further extending inwardly ofwall portion 74intermediate members 70 and 72 and rigidly affixed thereto (FIGS. 1 and 3). Aspace 92 to receive thedriving assembly 40 into mountingportion 82 is formed intermediateadjacent support members 75a and 75b.

Flange 94 carries a generally frustoconical assembly mount retaining member 90 comprising: a transverseannular flange portion 91 which is adapted to be rigidly afiixedadjacent flange 94 such as bybolts 96 or by weldments (not shown); a transverse assembly mounting retaining portion 98 spaced rearwardly fromflange 91; and a taperingintermediate portion 100 extendingintermediate portions 91 and 98 which receives adjacent a taperinginner surface 97 thereof themounting 80.

Eachmounting 80 includes a generallyfrustoconical body member 86 formed from a suitably resilient elastomer such as rubber and having forward andrearward faces 81 and 83, respectively. Thefaces 81 and 83 are bonded to respective forward and rearwardrigid mounting plates 84 and 88 to form the substantiallyunitary mounting 80.

In assembly, themounting 80 extends intermediate member 90 ofportion 82 and the rearward end ofhydraulic cylinder 41, theforward plate 84 thereof being rigidly and releasably affixed adjacent the rearward end ofcylinder 41 as for example by asuitable adaptor plate 43 rigidly secured therebetween such as bybolts 45a and 45b or the like, and therearward plate 88 thereof being rigidly and releasably affixed adjacent portion 98 of member 90 as byscrews 99. In this con- 7figurationi configuration body 86 is captively retained 1 within member 90 adjacent the mating tapered surface through arespective opening 78 inwall portion 24 and substantially tangentally to thewheel 30. By virtue of the inherent resiliency ofbody 86assembly 40 is laterally movable with respect to the axis XX for purposes to be described hereinbelow.

By reference to FIGS. 3 and 4 it is seen that thearm 42 comprises: a rigid forward end orjaw portion 47; a rigid elongated support portion49 spaced rearwardly therefrom; and'a relatively flexibleintermediate portion 48 extending longitudinally betweenportions 47 and 49 and rigidly affixed thereto. Thearm portions 47, 48 and 49 have inward andoutward side surfaces 62 and 64, respectively, extending longitudinally thereon intermediate the longitudinal ends ofarm 42.

Jaw portion 47 includes: ajaw 51 adjacent the forward end thereof suitably formed to be engageable withpins 36 and having alip 73 formed adjacent inwardside 62; a bifurcatedend portion 57 which extends forwardly ofjaw 51 adjacentoutward side 64; a bifurcated guiding orcam portion 52 rigidly affixed intermediate the longitudinal ends ofportion 47 adjacent outwardside 64 and extending outwardly therefrom; and a camming or guidingroller 53 rotatably carried intermediate the legs ofportion 52.Jaw portion 47 additionally includes a bearing orsupport surface portion 17 disposed intermediate the longitudinal ends ofportion 47 adjacent a lower side thereof and adapted to support the forwardmost end of theassembly 40 by bearing in sliding engagement upon a peripheral portion ofwheel member 34 outwardly adjacent pins 36 (FIG. 2).

Support portion 49 includes: an outward offset orbend 66 intermediate the longitudinal ends thereof; anotch 54 formed ininward side portion 62 inwardlyadjacent offset 66; and an inwardly slanting portion 71 ofinward side 62 extendingintermediate notch 54 and apoint 68 spaced forwardly therefrom.

Intermediate portion 48 as shown includes alongitudinal web portion 50 disposed substantially in a horizontal plane, andtransverse flanges 59 rigidly affixed to the longitudinal ends ofweb 50 and suitably secured to respective adjacent ends ofportions 47 and 49 such as byscrews 61 andlockwires 63 or the like. Theportion 48 is designed to be relatively more flexible thanarm portions 47 and 49, it being formed from any suitable high strength material having a relatively low modulus of elasticity, for example aluminum. Additionally, the relatively thin section presented byweb 50 provides a degree of vertical bending capacity not oflered by comparativelyrigid arm portions 47 and 49 whereby excessive vertical bending moments and side loads resulting for example from angular misalignment betweenjaw 51 and apin 36 will be absorbed by transverse bending ofweb 50 and will not be transmitted viaportion 49 androd 44 to bushings and seals within thecylinder 41. It is of course to be understood thatportion 48 is designed to bend only in response to side loads or bending moments applied thereto, the design thereof being sufficient to sustain the maximum anticipated axial loads to be imposed uponarm 42 without bending or buckling.

Awear plate 55 is rigidly affixed toinward side 62 ofportion 49 forwardly adjacent surface 71 and extends longitudinally forwardly therefrom adjacentinward side 62 to terminate rearwardly adjacent astep 56 formed rearwardly adjacent thelip 73. The inwardly exposed side ofplate 55 and adjacent surface 71 form a continuous cam or guidingsurface 67 having anantifriction surface 69 bonded thereto to minimize friction withpins 36 during engagement therebetween which occurs as described hereinbelow. It is to be noted thatplate 55 extends adjacent theinward side 62 ofarm portions 47, 48 and 49 but is rigidly affixed only toportion 49 and thus does not interfere with the hereinabove described bending ofportion 48.

As noted hereinabove the drive includescontrol assemblies 50 and 50a which are cooperable with selected ones ofarms 42 to actuaterespective assemblies 40 and 40a.Control assembly 50, which it is to be understood is identical toassembly 500, is shown in FIG. 5 as including a flat plate-like base 102 rigidly affixed within housing and carrying thereupon a well knownpilot valve 106 and a generally angularcontrol arm assembly 108 pivoted thereto as at 114.Control arm assembly 108 has oneend portion 110 thereof pivotally affixed as at 116 to an actuatingstem 118 ofvalve 106 and anopposing end portion 120 engageable withpins 36 and with one of thearms 42 carried byassemblies 40. A biasing force onarm assembly 108 is provided by a suitablehelical spring mechanism 122 affixed tobase 102 and pivoted toarm portion 110 as at 111intermediate pivots 114 and 116 to continuously urge thearm 108 in a clockwise direction about pivot 1 14 (as viewed in FIG. 5) toward a neutral position thereof which is adjustable as by an adjustingscrew 124 carried byarm portion 120 and cooperable withadjacent wall portion 24.

Arm portion 120 includes anend portion 126 which is rigidly secured toarm portion 110 adjacent pivot 1 14 and an elongatedcam follower portion 130 which in practice is disposed intermediate the legs of bifurcatedcam portion 52 ofarm 42 and intermittently engageable bycam roller 53. Acam roller 128 is disposedintermediate arm portions 126 and 130 and spaced inwardly therefrom as by abracket 134 whereby inpractice roller 128 is intermittently engageable bypins 36. The hereinabove mentioned interactions ofcooperable pins 36, drivingarm 42 andcontrol arm assembly 108 serve to control operation of thedrive 10 through actuation of thecircuit 60 as follows.

In FIG. 1 thecircuit 60 is shown as comprising: a suitable flow source such as apump 134;fluid flow conduits 138 and 140 which communicate between thepump 134 and respective rear and front portions ofcylinder assemblies 41; and amain valve 136 which is cooperable withpilot valve 106 to direct fluid flow frompump 134 to the rear or front portion ofcylinders 41 throughrespective conduits 138 or 140 for advancing and retracting ofrods 44.Circuit 60 additionally includes a well known regenerative orfeedback conduit 142 communicating betweenconduit 140 andpump 134 and having a suitable oneway check valve 144 therein; apressure relief valve 146 in communication withconduit 140; and a suitable flow source such as apump 39 which supplies fluid flow to thepilot valve 106.

It is to be understood that inasmuch as theconduits 138 and 140 communicate with bothcylinders 41 ofassemblies 40, theassemblies 40 are operable in unison at all times. Thecylinders 41 ofassemblies 40a are likewise operable in unison at all times by an actuating circuit (not shown) which is functionally equivalent to thecircuit 60 described hereinabove. It is to be further understood that thepins 36 are so spaced and thecontrol assemblies 50 and 50a so positioned with respect thereto that theassemblies 40 and 40a alternately engage selectedpins 36 of thewheel 30 to provide a sequence of incremental rotations thereof.

As illustrated in FIG. 1 thecircuit 60 is supplying 5 fluid flow frompump 134 throughvalve 136 andconduit 138 to the rearward portion ofcylinders 41 for a power stroke whereby thearms 42 are being driven forward to incrementally rotatewheel 30. In the course of such a power stroke thearms 42 andwheel 30 will ultimately reach a position near the end of the power stroke as shown by the solid lines in FIG. 5, at which position thepin 36 is about to disengage thejaw 51 and substantially simultaneously engagecam roller 128 which is disposed adjacent thepin 36 intermediate the legs ofarm portion 57 and apin 36a spaced circumferentially clockwise frompin 36 has advanced into the clearance provided by thenotch 54adjacent cam surface 67. At this point theassemblies 40a engage selectedpins 36 to begin a power stroke thereof. For a short ensuing period all ofassemblies 40 and 40a are engagingpins 36 androtating wheel 30 in what is known as an overlap stroke.

As the power stroke ofassemblies 40 ends the overlap stroke ends andwheel 30 continues rotating under the impetus of the power stroke ofassemblies 40a. Aswheel 30 continues rotating thepin 36 disengages fromjaw 51 and advances to the position indicated at 36' whereat it is engagingcam roller 128 at 128', andpin 36a concurrently advances to the position indicated at 36a whereat it is engaging thecam surface 67. It is seen that by engaging cam roller 128',pin 36 has displacedarm 108 counterclockwise about pivot 114 to the position 108' against the biasing force ofspring 122 wherebypilot valve 106 has been actuated in response thereto to shiftmain valve 136 in a well known manner and thus direct fluid flow frompump 134 throughconduit 140 to the front of the affectedcylinders 41 for the powered retraction ofrespective arms 42. It will be understood that such powered retraction of thearms 42 is completed in substantially less time than the power stroke ofassemblies 40a inasmuch as thepump 134 is supplying fluid to a considerably reduced volume including only that portion of the volume ofcylinder 41 in front of the piston and not occupied byrod 44.

Under the continuing impetus of theassemblies 40a pin 36a advances to aposition 36a" and cams the retractingarm 42 laterally outwardly by engagement withsurface 67, and pin 36 concurrently advances to theposition 36". In response to the outward displacement ofarm 42roller 53 engages thefollower portion 130 tocam arm 108 outwardly thereby maintainingcircuit 60 in the retract mode of operation.

During the outward displacement ofarm 42 theentire assembly 40 is pivoted outwardly aboutmount body 86, for example from an axis XX (FIG. 5) to an outwardly displaced axis XX', thereby deforming themount body 86. The inherent resiliency ofbody 86 thereupon exerts an inwardly directed restoring force upon theassembly 40 wherebyassembly 40 is maintained in forceful engagement withpin 36a throughout the retract portion of the cycle. It is of course to be understood thatbody 86 provides the capability for deflection ofassemblies 40 in any plane containing the axis XX in the manner of a universal pivot.

Whenarm 42 has been completely retracted to the position 42' it is retained thereat during the dwell portion of the cycle aspump 134 maintains a nominal pressure in theconduit 140 and dumps excess flow to a suitable reservoir throughrelief valve 146. It is to be noted that during dwell the arm at 42 maintainscircuit 60 in the retract mode by means of roller 53' engagingcam portion 130 ofarm 108 as at 130.

The continuing power stroke ofassemblies 40a further advancespin 36a to a position (not shown) forwardly adjacent thelip 73 ofjaw 51 whereat the inward bias provided by mountingbody 36 urgesarm 42 inwardly such thatpin 36a engaged thejaw end portion 57 forwardly ofjaw 51 and thecam roller 53 disengagescam follower portion 130 thereby permittingspring 122 to pivotarm 108 in a clockwise direction to the neutral position thereof. In response theretocircuit 60 shifts to the power stroke mode illustrated in FIG. 1.

During the initial stages of the power stroke mode thearm 42 advances at a relatively rapid rate in an overtake stroke thereof by virtue of the additional fluid supplied toconduit 138 from the front portion ofcylinder 41 throughconduits 140 and 142, andvalve 144.Arm 42 thus quickly overtakes and engages thepin 36a just prior to the end of the power stroke byassemblies 40a whereupon an overlap stroke is begun. Subsequently,assemblies 40 begin a new power stroke asassemblies 40a disengagerespective pins 36 and are actuated through sequential retract, dwell and overtake strokes as hereinabove described, and a full cycle of operation ofdrive 10 is thus completed.

By virtue of the structure defined hereinabove a greatly simplified and streamlined drive mechanism is provided. The drive mechanism of the present invention provides a plurality of driving assemblies each supported by an elastomeric mounting affixed adjacent one longitudinal end thereof and captively retained within a socket-like member, and by a support portion disposed adjacent the other longitudinal end thereof and adapted to engage the driven member. Such driving assemblies are thus supported solely from their respective axial extremities with sufficient axial stiffness to withstand maximum anticipated axial loads and in the manner of a universal pivot which permits angular deflection of the driving assembly. The simplified mounting additionally provide an inherent restoring bias to oppose all such angular deflections whereby the driving assembly mounting scheme is operable without recourse to customary universal or pivot joints or spring biasing means.

Furthermore, the driving arms hereof are greatly streamlined by the use of camming means carried only by such arms to control all phases of the operating cycle except the beginning of the retract stroke which is controlled by the ratchet pins. It is to be noted that the drive hereof is operational in response to the relative positions of ratchet pins and driving assemblies; therefore, a retract stroke cannot begin until a pin has been advanced to a predetermined position and a power stroke cannot begin until the driving arm has assumed a predetermined position behind the pin to be engaged.

Finally, it is to be noted that wear on driving cylinder seals and bushings is greatly alleviated by the flexible driving arm portion which bends in response to bending moments and side loads applied thereto.

Inasmuch as the present invention comprises a fluid drive system having a plurality of driving assemblies affixed by elastomeric mountings to a housing member and including pusher arms therefor adapted to engage a driven member and further adapted to control the operational cycle thereof, various modifications thereto are possible without departing from the broad spirit and scope thereof. Forexample mounting body 86 may take any of numerous forms consistent with the requirements of axial shock absorbing capacity and lateral motion such as a frustrum of a pyramid or a rectangular solid, camming means carried byarms 42 could take various forms,flexible arm portion 48 could be of a cylindrical or other suitable cross section to allow for bending in various planes and the like.

These and other modifications having been envisioned and anticipated it is requested that this invention be interpreted broadly and limited only by the scope of the claims appended hereto.

What is claimed is:

1. A hydraulic driving system for imparting a rotary motion to a rotary load comprising: a body member; a driving ring adapted to be drivingly connected to such a rotary load; said driving ring including a plurality of circumferentially spaced driving portions thereon; a plurality of elongated intermittently acting hydraulically actuated piston assemblies carried by said body member and each having reciprocable extensible portions which are drivingly engageable with selective ones of said driving portions throughout at least a portion of the extension thereof; valve means adapted to communicate with a hydraulic fluid pressure source and operative to control the flow of fluid from such a source to said piston assemblies to provide sequential extension and retraction of said extensible portions; and at least one of said piston assemblies including camming means thereon which are cooperable with selective ones of said driving portions to control the operation of said valve means.

2. A hydraulic driving system as specified in claim 1 wherein said camming means are carried solely by said extensible portion.

3. A hydraulic driving system as specified in claim 1 wherein each of said piston assemblies is pivotally mounted to said body member adjacent one end thereof opposite said extensible portions and said extensible portions extend generally tangentially with respect to the periphery of said driving ring.

4. A hydraulic driving system as specified in claim 3 wherein during at least a major portion of the retraction stroke of said extensible portion of said at least one of said piston assemblies said selective ones of said driving portions engages a portion of said camming means on the inner longitudinal side of said extensible portion to cause said at least one of said piston assemblies to pivot outwardly from the periphery of said driving ring about said one end thereof.

5. A hydraulic driving system as specified inclaim 4 wherein during at least a major portion of the retraction of said extensible portion of said at least one of said piston assemblies a portion of said camming means on the other longitudinal side of said extensible portion engages said valve means to cause said valve means to maintain pressure fluid flowing to the retract side of said piston assemblies.

6. A hydraulic driving system as specified in claim 1 wherein at the end of the extension stroke of said extensible portion of said at least one of said piston assemblies, the driving portion being driven by said extensible portion operatively engages said valve means to cause said valve means to channel pressure fluid to the retract side of said piston assemblies and initiate a retraction stroke of said extensible portion.

7. A hydraulic driving system as specified in claim 3 wherein said piston assemblies are pivotally connected to said body member by respective pivot assemblies each comprising: an elastomeric member rigidly secured to said one end; a cup-shaped retaining member rigidly secured to said body member and said elastomeric member; and the inner periphery of said retaining member conforms to the outer periphery of said elastomeric member in a manner that at least the major portion of said outer periphery engages said inner periphery when said elastomeric member is rigidly secured to said body member.

8. A method of operating a piston assembly which has a reciprocable extensible portion thereof selectively drivingly engaging circumferentially spaced engageable portions of a driving ring which is drivingly connected to a rotary load to apply a rotary motion thereto comprising the steps of: extending said extensible portion by supplying a hydraulic pressure fluid to the extension side of said piston assembly; simultaneously with said extending, drivingly engaging a selective one of said engageable portions with the free end of said extensible portion throughout at least the major portion of said extending; at the termination of said extending, said extensible portion engaging a valve means in cooperation with said selective one of said engageable portions to cause the supply of hydraulic pressure fluid to be supplied to the retraction side of said piston assembly to retract said extensible portion.

9. A method of operating a piston assembly as specified in claim 8 including the additional step of: retracting said extensible portion from the extended position thereof by supplying hydraulic pressure fluid to the retraction side of said piston assembly.

10. A method of operating a piston assembly as specified in claim 9 including the additional step of: simultaneously with said retracting engaging said valve means with said extensible portion to maintain the flow of hydraulic fluid to said retract side throughout said retracting.

11. A method of operating a piston assembly as specified inclaim 10 wherein said last mentioned engaging is maintained by biasing said extensible portion outwardly with respect to the periphery of said driving ring.

Claims (11)

1. A hydraulic driving system for imparting a rotary motion to a rotary load comprising: a body member; a driving ring adapted to be drivingly connected to such a rotary load; said driving ring including a plurality of circumferentially spaced driving portions thereon; a plurality of elongated intermittently acting hydraulically actuated piston assemblies carried by said body member and each having reciprocable extensible portions which are drivingly engageable with selective ones of said driving portions throughout at least a portion of the extension thereof; valve means adapted to communicate with a hydraulic fluid pressure source and operative to control the flow of fluid from such a source to said piston assemblies to provide sequential extension and retraction of said extensible portions; and at least one of said piston assemblies including camming means thereon which are cooperable with selective ones of said driving portions to control the operation of said valve means.

2. A hydraulic driving system as specified in claim 1 wherein said camming means are carried solely by said extensible portion.

3. A hydraulic driving system as specified in claim 1 wherein each of said piston assemblies is pivotally mounted to said body member adjacent one end thereof opposite said extensible portions and said extensible portions extend generally tangentially with respect to the periphery of said driving ring.

4. A hydraulic driving system as specified in claim 3 wherein during at least a major portion of the retraction stroke of said extensible portion of said at least one of said piston assemblies said selective ones of said driving portions engages a portion of said camming means on the inner longitudinal side of said extensible portion to cause said at least one of said piston assemblies to pivot outwardly from the periphery of said driving ring about said one end thereof.

5. A hydraulic driving system as specified in claim 4 wherein during at least a major portion of the retraction of said extensible portion of said at least one of said piston assemblies a portion of said camming means on the other longitudinal side of said extensible portion engages said valve means to cause said valve means to maintain pressure fluid flowing to the retract side of said piston assemblies.

6. A hydraulic driving system as specified in claim 1 wherein at the end of the extension stroke of said extensible portion of said at least one of said piston assemblies, the driving portion being driven by said extensible portion operatively engages said valve means to cause said valve means to channel pressure fluid to the retract side of said piston assemblies and initiate a retraction stroke of said extensible portion.

7. A hydraulic driving system as specified in claim 3 wherein said piston assemblies are pivotally connected to said body member by respective pivot assemblies each comprising: an elastomeric member rigidly secured to said one end; a cup-shaped retaining member rigidly secured to said body member and said elastomeric member; and the inner periphery of said retaining member conforms to the outer periphery of said elastomeric member in a manner that at least the major portion of said outer periphery engages said inner periphery when said elastomeric member is rigidly secured to said body member.

8. A method of operating a piston assembly which has a reciprocable extensible portion thereof selectively drivingly engaging circumferentially spaced engageable portions of a driving ring which is drivingly connected to a rotary load to apply a rotary motion thereto comprising the steps of: extending said extensible portion by supplying a hydraulic pressure fluid to the extension side of said piston assembly; simultaneously with said extending, drivingly engaging a selective one of said engageable portions with the free end of said extensible portion throughout at least the major portion of said extending; at the termination of said extending, said extensible portion engaging a valve means in cooperation with said selective one of said engageable portions to cause the supply of hydraulic pressure fluid to be supplied to the retraction side of said piston assembly to retract said extensible portion.

9. A method of operating a piston assembly as specified in claim 8 including the additional step of: retracting said extensible portion from the extended position thereof by supplying hydraulic pressure fluid to the retraction side of said piston assembly.

10. A method of operating a piston assembly as specified in claim 9 including the additional step of: simultaneously with said retracting engaging said valve means with said extensible portion to maintain the flow of hydraulic fluid to said retract side throughout said retracting.

11. A method of operating a piston assembly as specified in claim 10 wherein said last mentioned engaging is maintained by biasing said extensible portion outwardly with respect to the periphery of said driving ring.

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