ROTARY HYDRAULIC MACHINE

Abstract: An axial piston pump (10) or the like rotary hydraulic machine, which includes a rotational cylinder block (28) and a valve plate (44) affixed within the housing (12) and including arcuate slots (46, 48) corresponding to the radius of rotation of the cylinders (30). The slots (46, 48) respectively connect cylinders (30) to the machine inlet and outlet ports (50, 52) as the cylinders register with the slots. The valve plate (44) also includes first and second pressure valves (72, 74) adjacent to leading edges (73, 75) of the arcuate slots (46, 48) (with respect to the direction of cylinder rotation) and responsive to fluid pressure for porting the cylinders (30) to the adjacent slots (46, 48) and thereby, in effect, extending the arcuate dimension of the slots (46, 48) and altering machine timing as a function of fluid pressure.

Description: The present invention is directed to rotary hydraulic machines, as described in the preamble to claim 1. For purposes of convenience, the invention will be described in conjunction with a presently preferred implementation thereof embodied in an inline variable displacement piston pump. It will be understood, however, that the principles of the invention apply equally as well to so-called bent axis piston pumps, as well as to hydraulic motors of analogous structure. Conventional inline variable displacement piston pumps of the subject type comprise a case or housing within which a cylinder block is coupled to a rotatable drive shaft. The cylinder block contains a plurality of cylinder cavities disposed in a circumferential array surrounding the shaft axis. A corresponding plurality of pistons are slidably positioned within the respective cylinders. The pistons engage a yoke cam which is variably positionable within the pump housing for collectively adjusting stroke or displacement of the pistons within the cylinders. The cylinder block rotates against a valve plate having arcuate inlet and outlet kidney-shaped slots which serve in a well-known manner to provide properly phased or timed communication between the end ports of the cylinder bores within which the pistons reciprocate and inlet and outlet passages and ports in the pump housing. Timing of the hydraulic pump by circumferential positioning of the slot ends in the valve plate involves matching pump cylinder pressures to inlet and outlet passage pressures at the angular position at which the cylinder begins to communicate through the slot with the inlet and outlet ports. Thus, pump timing is conventionally optimized for only one set of operating conditions, i. e. one design combination of inlet and outlet pressures, pump speed, fluid flow, fluid temperature and fluid type. Deviation from these optimum or design conditions creates under compression or over compression of fluid in the cylinder block, causing high fluid velocities at edges of the timing slots, noise, fluid cavitation, pump wear and flow oscillations resulting in pressure ripple. All of these effects are undesirable in controlled hydraulic circuits. In a hydrostatic transmission containing a hydraulic pump and a hydraulic motor separate noise reducing valve assemblies for the inlet and outlet pressure ports are provided (US-A-3,956,969). The high pressure port is connected to an intermediate port through a passage including a restrictor and, parallel thereto, a valve having a control chamber which is connected to high pressure through an orifice or restrictor, and a spring acting against the pressure in the control chamber, the spring chamber being connected to tank. As is known in the art, restrictive orifices can be blocked by mud. In such a case, the high pressure will not enter into the control chamber of the spool, and therefore the spool will not move, making the arrangement ineffective. Furthermore, it is to be noted that a similar restrictor-valve-arrangement is provided symmetrically at the low pressure port of the pump, where the passages are connected to the intermediate port and the low pressure port. Therefore, only one of these arrangements is responsive to the pressure in the high pressure slot. It has been normal practice to operate a pump at constant pressure condictions by varying pump displacement. However, microprocessor-based control systems provide facility for enhanced control in a plurality of otherwise desirable pump operating modes, such as constant flow and constant power modes. However, pump timing is not optimum for conditions which depart from the pump design conditions, resulting in the various problems noted above. A general object of the present invention is to provide a rotary hydraulic machine, such as an inline variable displacement piston pump, in which pump port timing varies with operating conditions. A more specific object of the invention is to provide a machine of the described character in which timing is optimized for two sets of operating conditions, specifically high and low output pressure conditions. Thus, a yet more specific object of the invention is to provide dual pressure timing for axial-piston rotary hydraulic machines such as variable displacement piston pumps. In accordance with the present invention, a rotary hydraulic machine includes a housing having a shaft mounted for rotation about a shaft axis within the housing. A cylinder block is coupled to the shaft for corotation with the shaft within the housing and includes at least one cylinder, and preferably a plurality of cylinders, disposed in a circumferential array parallel to and surrounding the shaft axis. A piston is disposed to reciprocate within each of the cylinders and is coupled to a yoke for determining displacement of the pistons within the cylinders. A valve plate is affixed within the housing for facing engagement with the rotating cylinder block. The valve plate includes arcuate slots at a radius from the axis of rotation corresponding to that of the cylinders and respectively connecting cylinders to the machine inlet and outlet ports as the cylinders register with the slots. In accordance with a distinguishing feature which characterizes one aspect of the present invention, the valve plate includes first and second pressure valves respectively mounted on the plate adjacent to the arcuate slots and responsive to fluid pressure for porting the cylinders to the adjacent slots and thereby, in effect, extending the arcuate dimension of the slots and altering machine timing as a function of fluid pressure. As applied specifically to dual-pressure timing of an inline variable displacement piston pump, the pressure valves may be mounted within the valve plate and are situated adjacent to respective leading edges of the first and second slots with respect to a predetermined direction of shaft and cylinder block rotation so as to effectively advance and retard timing of the pump as a function of pump output pressure. Each pressure valve comprises a valve spool positioned within an associated radial bore and having a spool waist for selectively connection valve passages extending from the bore to the cylinder-engaging face of the valve plate and to the adjacent plate slot. A pilot passage extends from the inner end of each bore to the plate slot associated with the pump fluid outlet port, and a coil spring is captured in compression between the plate and the outer end of each valve spool. The valve plate is mounted within the pump housing in a cavity containing fluid at case pressure, and the valve springs are captured within the plate by a keeper having a damping orifice through which fluid may flow at case pressure to and from the spring cavity. In accordance with another important aspect of the present invention, the rotary machine housing includes first and second housing sections affixed to each other to form the internal cavity at case fluid pressure within which the cylinder block and yoke are disposed. At least one fluid passage extends through the interface between the housing sections. In particular, in the preferred embodiment which comprises a variable displacement pump, yoke position is controlled by an actuator piston which receives fluid at controlled pressure through a passage which extends across the housing section interface. At the interface, such passage takes the form of a cylinder cavity composed of opposed half-cavity recesses in the respective housing sections connected by fluid passages to receive fluid at case pressure. Inwardly oriented annular channels are formed in each housing section and open into the associated cavity half-section midway between the housing section interface and the cavity base. The metered fluid passages to the actuator piston terminate in the respective channels. A hollow sleeve is captured within the cylindrical cavity and has outwardly facing annular channels in registry with the inwardly facing channels of the housing sections, and a passage which connects the outwardly facing channels and thereby feeds fluid at metered pressure to the yoke actuator piston. Sealing rings are carried by the sleeve. The invention, together with additional objects, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which: Figs. 1A and 1B together comprise a sectional view in side elevation of an inline variable displacement piston pump embodying the present invention; Fig. 2 is an elevational view of the valve plate assembly in Fig. 1B and is taken substantially along the line 2-2 in Fig. 1B; Figs. 3 and 4 are fragmentary sectional views taken substantially along the lines 3-3 and 4-4 in Fig. 2; Figs. 5 and 6 are fragmentary sectional views taken substantially along the lines 5-5 and 6-6 in Figs. 3 and 4 respectively, and Fig. 7 is a fragmentary sectional view of a portion of the pump illustrated in Figs. 1A and 1B and showing a modification thereto in accordance with another aspect of the invention. Figs. 1A and 1B illustrate an inline variable displacement piston pump 10 as comprising a housing 12 including a first housing section 14 having a mounting flange 16 and an adapter block or second housing section 18 affixed to opposed ends thereof so as to form an open internal cavity 20. A pump drive shaft 22 is mounted by a bearing 24 for rotation within housing 12 in a predetermined direction 26. A cylinder block 28 is affixed to shaft 22 for corotation therewith within cavity 20 and includes a plurality of cylinders 30 which extend in a circumferential array around and parallel to the axis of rotation of shaft 22 and comprise a respective port 31. A plurality of pistons 32 are respectively slidably disposed within corresponding cylinders 30 and have piston shoes 34 which slidably engage the opposing face of a yoke 36. Yoke 36 is variably positionable about a shaft 38 by a yoke actuator 40 acting against the force of a yoke-biasing spring 42. Valve plate means 44 (Fig. 1B) is affixed to second housing section 18 and includes slots 46, 48 (Fig. 2) for selectively connection the cylinders 30 of block 28 to pump inlet or low pressure port 50 and pump outlet or high pressure port 52 as a function of cylinder block rotation. A valve block 54 (Fig. 1A) is mounted to adapter block 18 and carries a blocking valve 56 adjacent to outlet 52 and a solenoid valve 58 adjacent to a compensator valve 60 on adapter block 18. Solenoid valve 58 is controlled by external electronics (not shown) for connection pump outlet 52 to yoke actuator 40, and thereby selectively demanding the minimum position of yoke 36 and pump displacement and also to actuate the blocking valve 56 to isolate the hydraulic circuit and pump. Valve plate means 44 in accordance with the present invention comprises an assembly illustrated in greater detail in Figs. 2 through and includes - as the valve plate - a flat annular disc 64 of generally uniform thickness having a central opening 66 which surrounds the shaft 22. Arcuate slots 46, 48 extend around the axis of disc 64 and shaft 22 at a diameter which corresponds to the diameter of motion of the ports 31 of cylinder 30 (shown in phantom in Fig. 2) which engage the opposing flat face 68 of disc 64. Arcuate slot 48 is on high pressure and coupled to pump output port 52 (Fig. 1A) and may include integral strengthening ribs 70 (Fig. 2). First and second pressure valves 72, 74 are carried in the valve plate 64 adjacent to the leading edges 73, 75 of the respective slots 46, 48 above which the ports 31 rotate as indicated by the arrow 26 in Fig. 2. The valve 74 (Figs. 3 and 5) comprises a spool 76 slidably carried within a cylindrical bore 78 which may extend radially outwardly of valve plate 64. An O-ring 80 is captured within a recess adjacent to the outer end of spool 76 for slidable sealing engagement with surrounding bore 78. A pair of coil springs 82, 84 are coaxially captured in compression between a stepped keeper skirt 86 carried by and engaging the outer end of the spool 76, and a flat keeper disc 88 captured by a retaining ring 90 within an enlarged spring cavity 92 in valve plate 64. The ends of outer spring 82 are captured between the surrounding wall of the spring cavity 92 and an opposing shoulder 94 on keeper skirt 86 and a rib 96 on keeper disc 88. Inner spring 84 is captured within rib 96 and surrounds a central guide post 98 which integrally projects from keeper 86. A central orifice 91 in keeper disc 88 vents spring cavity 92 to case cavity 20 (Fig. 1B). The inner end of bore 78 is enlarged to form a control cavity 100 which is connected by a control duct 102 (Fig. 5) to the adjacent edge 75 of the high-pressure slot 48. The end of spool 76 within the control cavity 100 is tapered to admit fluid therebeneath. A pair of openings 104 form a row of spaced parallel fluid passages (Figs. 2 and 3) which extend from the bore 78 to the cylinder-engaging face 68 of the valve plate 64. The row of the openings 104 has a predetermined distance to the edge 75 of the slot 48. An associated pair of spaced parallel fluid passages 106 (Fig. 5) extend from bore 78 to slot 48. Valve spool 76 has a pair of waist 108 separated by a land 110 and spaced from each other by the same distance as the separations between openings 104 and passages 106. Waists 108 thus interconnect openings 104 and passages 106 when the spool 76 is urged by the springs 82, 84 against the inner end or base of bore 78 and waists 108 register with the openings 104 and the passages 106 as shown in the drawings. On the other hand, land 110 between waists 108 and a land 111 at the inner end of the spool 76 are positioned on spool 76 so as to block fluid passage between each opening 104 and its associated passage 106 as spool 76 is moved (upwardly in Figs. 3 and 5) against springs 82, 84. Valve 72 is similar in construction to valve 74 hereinabove described in detail. Control duct 102 (Fig. 6) which extends from the control cavity 100 to the high-pressure slot 48, has to pass a substantial distance across the valve plate 64, whereas passages 106 extend to the adjacent low-pressure slot 46. Other elements of valve 72 are identical in structure and function to corresponding elements of valve 74 and are indicated by correspondingly identical reference numerals in Figs. 4 and 6. In operation, spools 76 of valves 74, 72 are initially urged by springs 82, 84 to the positions shown in the drawings at which the spools open openings 104 to passages 106. The combination of openings 104 and passages 106 in valve 74 thus effectively extends the arcuate dimension of the high-pressure slot 48 against or in opposition to the direction of motion 26. Thus, openings 104 effectively advance timing of fluid output from the pump cylinders 30. States differently, as cylinder ports 31 rotate in the direction 26 from the bottom dead center or BDC position (Fig. 2) with respect to valve plate 64, fluid within the cylinder is precompressed. However, such precompression is limited by registry of the cylinder port 31 with openings 104 and fluid flow from the cylinder 30 through openings 104 and passages 106 into the slot 48. Likewise, openings 104 in valve 72 effectively enlarge the arcute dimension of low-pressure slot 46 in the direction opposed to cylinder motion, and thereby effectively advance timing of porting the cylinders 30 to slot 46 which is the low-pressure input port. That is, negative pressure increase within the cylinders 30 prior to registry with slot 46 is limited by valve 72 and associated openings 104. Thus, under low output pressure conditions, high fluid velocities at the leading ends of slots 46, 48 are avoided by effective extension thereof through valves 72, 74. As fluid pressure at pump output port 52 increases and fluid pressure within valve plate slot 48 correspondingly increases, increasing pressures within control cavities 100 through control ducts 102 urge spools 76 against the spring forces. It will be noted that transient output pressure variations are effectively damped by limited fluid flow at case pressure through orifices 91 in keeper discs 88. However, as steady-state output pressure increases, valve spools 76 are moved against the opposing springs until lands 110, 111 effectively block flow between the openings 104 and the passages 106 in each valve 72, 74. Thus, when fluid output pressure exceeds the threshold set by the valve springs 82, 84, which threshold is preferably identical at each valve 72, 74, pump timing is effectively retarded to timing corresponding to the dimensions of the slots 46, 48 per se. Dual pressure timing is thus provided in accordance with the invention. It will be noted that gradual closure of valves 72, 74 between low and high pressure conditions (and corresponding gradual opening as output pressure declines) effects gradual rather than abrupt changes in pump timing. Thus, although the valve plate means 44 as described is designed specifically for timing at high and low sets of pressure conditions, intermediate conditions are also more readily accomodated than in fixed timing pumps of the prior art. Moreover, several rows of openings 104 connected to separate valves 72, 74 - those set pressure (Ansprechdruck) is on separate values -may be provided instead of each a single row, such rows having stepped distances to the leading edges 73 and 74, respectively, of the slots 46, 48, so that port timing is more proportional function of pressure. Thus, pump 10 is optimally timed for two (or several) pump outlet pressures (all other parameters remaining unchanged), which can be particularly beneficial on a pressure-scheduled or dual-range pressure-compensated pump. Recompression at lower operating pressure is reduced, thereby reducing pump wear, noise, pressure ripple, input power and cavitation. Such wear and cavitation reduction enhances pump life. Lower pressure ripple increases fatigue life in the complete hydraulic system. Reduced input power yields higher efficiency and lower heat rejection. As noted above, the invention is not limited to variable-displacement in-line pumps, but applies equally as well to bent-axis and fixed displacement pumps, as well as analogous motion structures. The invention may be implemented at low costs. It will also be appreciated that the spool valves of the preferred embodiment respond to low frequency changes in outlet pressure, but not to differences between cylinder and port pressures. This reduces required bandwidth of the spool valves, and thereby diametrically reduces wear and fatigue problems. Fig. 7 illustrates a modified pump 10a, which is otherwise identical to the pump 10 of Figs. 1 through 6, wherein a flow transfer assembly 120 is positioned within control duct 62 between compensator valve 60 (shown schematically) and yoke actuator 40, at the interface between housing section 14 and 18, for reducing leakage due to high-pressure conditions within the control duct. In particular, a cylindrical cavity 122 is formed perpendicularly of the planar interface between housing section 14 and 18 by opposed cylindrical half-cavities 124, 126 in the respective case sections. A fluid passage 128 within housing section 14 connects cavity 122 to cavity 20 (Fig. 1B) at pump case pressure. An annular channel 130 is formed in housing section 18 and opens into cavity section 126 approximately midway between the case section interface and the cavity section base. Likewise, an annular channel 132 is formed in housing section 14 and opens into cavity section 124 midway between the interface and cavity base. Control duct 62 in housing sections 18 and 14 terminate within channels 130, 132, respectively. A hollow tubular sleeve 134 is captured within cavity 122 and has axially spaced channels 136, 138 formed in the outer surface thereof at positions to register with channels 130, 132 in housing sections 14 and 18, respectively. An internal passage 140 within sleeve 134 provides fluid flow at case pressure to compensator valve 60. An angulated passage 142 formed in sleeve 134 couples channels 136, 138 to each other. O-rings 144 are captured within corresponding channels surrounding sleeve 134 on each side of channel 136, and again on each side of channel 138, and sealingly engage the opposing surfaces of channel sections 124, 126 in housing section 14 and 18. Thus, fluid at control pressure is fed from compensator valve 60 through channels 130, 136, through passage 142 to channels 132, 138, and then through duct 62 in housing section 14 to actuator 40. However, the forces applied by the control fluid against housing sections 18 and 14 are substantially radial adjacent to the housing sections interface. Axial forces at the interface are at case pressure which remains substantially constant. Thus, the tendency of the housing sections to separate at the interface is substantially reduced.

Claims: A rotary hydraulic machine (10, 10a) comprising a housing (12), a shaft (22) mounted within said housing (12) for rotation in a predetermined direction (26) cylinder means (28) coupled with said shaft (22) for corotation therewith within said housing (12) and including one or more cylinder cavities (30) with respective inlet and outlet cylinder ports (31) on a porting radius, piston means including one or more pistons (32) respectively disposed in said one of said cylinder cavities (30), low and high pressure fluid ports (50, 52) in said housing (12), and valve plate means (44) having first low pressure and second high pressure diametrically opposed arcuate slots (46, 48) in a face (68) engaged by said cylinder means (28), arranged at a radius from the shaft axis corresponding to said porting radius of said cylinder ports (31) from said axis and having ends at positions which limit porting of said cylinder ports (31) to said fluid ports (50, 52) and are constructed for preselected pressure conditions, said respective slots (46, 48) being hydraulically connected to said respective fluid ports (50, 52), and means for altering port timing as a function of pressure at said high pressure port (52) comprising: first and second valves (72, 74) mounted on said valve plate means (44) adjacent to respective leading edges (73, 75) of said first and second slots (46, 48) with respect to said predetermined direction of rotation (26), each said valve (72, 74) Including a valve element (76), a cylindrical bore (78), a control duct (102), valve ports (104, 106), and spring means (82, 84) captured in compression against a radial outer end of said valve element (76), said control duct (102) extending through said valve plate means (44) to a control space (100) of said bore (78), said valve ports (104, 106) extending from said respective bore (78) to the adjacent said slot (46, 48) and to said face (68) of said valve plate means (44), said valve element (76) comprising a valve spool having a land (110, 111) for selectively interconnecting or disconnecting said valve ports (104, 106) as a function of spool position, characterized in that said valve plate means (44) comprise a valve plate (64) affixed within said housing (12) in a cavity (20) containing hydraulic fluid at case pressure, each said cylindrical bore (78) of said first and second valves (72, 74) opens radially outwardly of said plate (64) and contains said control space (100) at its radial inner end, said control ducts (102) of both said first and second valves (72, 74) are connected to said high pressure slot (48) so that both said valve elements (76) are responsive to pressure in said high pressure slot (48), and, by opening or closing said valve ports (104, 106), alter the port timing of said cylinder ports (31), and each said spring means (82, 84) being disposed within a valve cavity (92) connected through a damping orifice (91) to case pressure. The machine set forth in claim 1 including keeper means (86, 88, 90) secured adjacent to a radially outer end of said bore (78), said spring means (82, 84) being captured in compression between said keeper means (86, 88, 90) and a radially outer end of said spool (76), said orifice (91) being positioned in said keeper means (88) for venting that portion (92) of said bore (78) surrounding said spring means (82, 84) to case pressure. The machine set forth in claim 2 wherein each said keeper means (86, 88, 90) comprises a keeper disc (88) and means (90) removably securing said disc (88) adjacent to said radially outer end of the associated said bore (78). The machine set forth in claim 3 wherein each said valve (72, 74) further comprises a stepped keeper skirt (86) engaging an associated said valve spool (76), each said spring means (82, 84) comprising a first coil spring (82) captured between said keeper disc (88) and a peripheral shoulder on said keeper skirt (86), and a second coil spring (84) coaxial with said first spring (82) captured between said keeper disc (88) and said keeper skirt (86), each said keeper skirt (86) including a central guide post (98) extending into the associated said second coil spring (84). The machine set forth in claim 3 or 4 wherein each said keeper disc (88) includes an annular rib (96) positioned between the associated said springs (82, 84). The machine set forth in any preceeding claim characterized in that said housing (12) comprising first and second housing sections (14, 18) sealingly affixed to each other, at least one fluid passage (62) extending between said sections (14, 18), said machine (10, 10a) further comprising a cylindrical cavity (122) formed by opposed cavity half-sections (124, 126) in said housing sections (14, 18), means (128) connecting said cylindrical cavity (122) to fluid at case pressure, an annular channel (130, 132) in each said housing section (14, 18) surrounding and opening into the associated said cavity half-sections (124, 126), at least one fluid passage (62) in each said housing section (14, 18) terminating in the associated said channel (130, 132), and a hollow tubular sleeve (134) captured within said cylindrical cavity (122), said sleeve (134) having outwardly facing annular channels (136, 138) opposite to said channels (130, 132) in said housing sections (14, 18), means (142) coupling said outwardly facing channels (136, 138) to each other and means (144) sealingly engaging opposed wall sections to said cylindrical cavity (122).

Inventors: TOVEY, PETER
Applicants: VICKERS INCORPORATED
Application year: 1988
Main classification: F04B1
IPC codes: F01B3, F04B27, F04B1