ROTARY VALVE PLATE

Abstract: A rotary valve plate (27) of an internal gear machine (11), which rotary valve plate (27) is provided between a commutator (25) and a gear set comprising an inner gear (17) and an outer gear (29), has an imbalance thereacross due to high pressure fluid on the commutator side of the valve plate (27) being opposite low pressure fluid in variable displacement chambers (21) on the gear side of the valve plate. This imbalance is corrected by a recess (39) which extends around the periphery of the valve plate (27) and receives fluid from the gear side of the valve plate to urge the valve plate (27) toward the commutator (25). Preferably, the internal gear machine is of a kind having an orbiting outer rotor (19) orbiting in an annulus (20) with intermediate pressure fluid in the annulus (20). The recess (39) on the gear side of the valve plate (27) is disposed to receive intermediate pressure fluid from the annulus.

Description: The invention relates generally to hydraulic internal gear machines and particularly to rotary valve plates for such machines. Machines of this kind are often referred to as gerotor machines and can be used as pumps or motors. Many types of prior art hydraulic devices have utilized internal gear sets often called gerotors or rotors. Such devices can be used as pumps where shaft work is converted to hydraulic work and as motors where hydraulic work is converted to shaft work. Examples of gerotor pumps and motors are shown in Patent Specifications US-A-3 572 983; 4 411 607; 4 545 748 and 4 586 885. In an internal gear pump or motor, an inner gear having outwardly directed teeth co-operates with an external gear having inwardly directed teeth so that fluid chambers there between increase and decrease in volume as the inner and outer gears rotate in a housing. By connecting the inlet and outlet of the device to the proper location along the sides of the gear set, the variable displacement chambers receive and discharge hydraulic fluid so that the device can function as a pump or motor. A shaft or other mechanical device can be connected to either the inner or outer gear depending upon the type of device. Many of the internal gear pumps and motors of the prior art utilize a housing having a fixed inlet and outlet. In other gerotor pumps or motors, a rotary valve plate or disc is used. Examples of gear devices with a rotary valve plate are shown in Patent Specifications US-A-4 411 607; is 545 748; 4 586 885 and EP-A-0 261 757. As described in these specifications the internal gear devices with rotary valves have a control plate or commutator with a plurality of inlet and outlet openings or windows on an axial face thereof. A valve plate with a plurality of openings extending axially there through is disposed between the gear set and the commutator selectively to communicate the inlet and outlet openings with the variable displacement chambers in the gear set. The valve plate is connected to rotate with the gear set such that the closing variable displacement chambers in the gear set are connected with the outlet openings of the commutator while the opening variable displacement chambers of the gear set are connected with the inlet. A well known problem which occurs in devices with rotary valve plates is that the valve plate is subject to a tilting moment caused by high pressure fluid acting against one radial half of the valve plate, while low pressure fluid acts against the other radial half of the valve plate. In addition, there is a relatively larger area of pressure acting on the gear set side of the valve plate than on the commutator side of the valve plate. The combination of this pressure imbalance reduces the efficiency and operational life of the device by increasing friction and wear on the moving components. A partial solution to the imbalance is shown in Patent Specification US-A-4 411 607 wherein recesses and grooves are provided on the rotary valve face on the commutator side of the rotary valve plate. These recesses provide a greater fluid pressure area on the commutator side of the valve plate to counterbalance the normally greater area of fluid pressure on the gear set side of the valve plate. However, the imbalance of high pressure from the commutator ports on one radial half (commutator side) of the valve plate versus low pressure on the same radial half (gear set side) partially remains. Patent Specification EP-A-0 261 757 shows a further means of balancing the imbalance comprising ports which extend through the valve plate to communicate high pressure fluid on the commutator side of the valve plate to a peripheral groove on the low pressure gear set side of the valve plate. These ports are selectively communicated with the high pressure in the commutator openings by the rotation of the valve. Thus, the radial half of the control plate which is not balanced due to high pressure commutator ports being opposite low pressure displacement chambers in the gear set are balanced by an area of high pressure fluid on the gear set side communicated through the special ports. However, some leakage of this high pressure fluid into the low pressure variable displacement chambers in the gear set occurs causing a reduction in efficiency of the motor or pump which would not occur if the leakage were not present. Further, this solution is not possible on machines where the outer rotor orbits as opposed to the inner rotor orbiting. Patent Specification DE-A-3 342 131 shows an arrangement wherein a valve disc is formed as a stepped piston with an inner part fitted in a corresponding cylindrical bore in a surrounding casing and sealed with a circumferential joint and an outer annular surface of the valve disc is loaded with working pressure to assist with pressing the valve disc into abutment with a rotor with which it co-operates so that the spring pressure which would otherwise be requied can be reduced. Patent Specification GB-A-1 386 796 shows a gear pump with twin gears between which fluid passes with the shafts of the gears supported in bushes with D-shaped end profiles. So called 'speed slots' are provided at the peripheral edges of the bushes on the sides thereof facing the gears for part of the circumference 150° to balance the areas over which high and low pressures are applied. According to one aspect of the invention there is provided a rotary valve plate for an internal gear machine of the kind having a gear set including an inner gear and an outer gear disposed for rotation in a housing such that a plurality of variable displacement chambers are defined between the inner gear and the outer gear as they rotate; a commutator through which fluid is conveyed to and from the variable displacement chambers and disposed axially with respect to the gear set with a plurality of commutator openings therein with some of the commutator openings connected to an inlet in the housing and some of the commutator openings connected to an outlet in the housing; the valve plate being connected for rotation with the gear set and disposed axially between the gear set and the commutator, so as to have a commutator side and a gear set side, and having a plurality of valve plate openings therein selectively to communicate the commutator openings with the variable displacement chambers of the gear set; characterised in that the valve plate has a periphery and a gear set side recess formed in the gear set side thereof, the gear set side recess being disposed to receive pressurized fluid therein from the gear set side of the valve plate; extending continuously around the gear set side of the valve plate adjacent the periphery of the valve plate; and being sized to provide an axially balanced pressure on the valve plate which compensates for imbalance resulting from high pressure fluid in the commutator opening being opposite low pressure fluid in the variable displacement chambers; the gear set side recess being sealingly isolated from fluid on the commutator side of the valve plate. According to another aspect of the invention there is provided an internal gear machine of the kind having a gear set defining variable displacement chambers as the gear set rotates in a housing with an outer gear orbiting in an annulus having intermediate pressure therein, a commutator disposed axially with respect to the gear set and having inlet and outlet openings therein for conveying fluid to and from the variable displacement chambers, and a rotatable valve plate connected for rotation with the inner gear and disposed sealingly between the gear set and the commutator selectively to convey inlet and outlet fluid there between by means of a plurality of valve plate openings extending axially through the valve plate; characterised in that the valve plate has a periphery and a gear set side with a recess formed in the valve plate and extending continuously about the gear set side of the valve plate adjacent the periphery so that intermediate pressure fluid from the annulus is communicated to the recess and urges the valve plate towards the commutator to balance the forces of high pressure fluid in the commutator openings opposing low pressure fluid in the variable displacement chambers across the valve plate. Such a valve plate, while of simple construction, can prevent or reduce leakage from the commutator side of the valve plate to the gear set side of the valve plate. Such a valve plate can be operative for an internal gear machine of the kind having an orbiting outer gerotor. Thus, to compensate for the tilting moments acting on the valve plate while preventing substantial leakage of fluid from high pressure to low pressure location in the machine, the valve plate has the recess around the periphery of the valve plate which provides a uniform axial pressure to aid the balance provided by the recesses on the commutator side of the valve plate. The recess on the gear set side of the valve plate does not communicate with the commutator side of the valve plate so that no fluid pressure is lost across the valve plate by means of these recesses. The valve plate works best in the kind of internal gear machine with an orbiting outer rotor which orbits in an annulus having a fluid pressure which is intermediate the fluid pressure in the inlet and outlet. The recess on the gear side of the valve plate communicates directly with the annulus in which the orbiting outer gerotor orbits so that pressure from the intermediate pressure fluid therein urges the valve plate toward the commutator. The size of the recess is adjusted to balance the unbalanced tilting moment on the valve plate resulting from the high pressure fluid in high pressure openings in the commutator bearing against the valve plate opposite low pressure fluid bearing against the gear set side of the valve plate. The invention is diagrammatically illustrated by way of example in the accompanying drawings, in which:- Figure 1 is a cross sectional view of an internal gear machine having a rotary valve plate according to the invention, taken on line I-I of Figure 5; Figure 2 is a front view of the valve plate illustrated in Figure 1; Figure 3 is a cross sectional view of the valve plate shown in Figure 2 taken on line 3-3 of Figure 2; Figure 4 is a rear view of the valve plate illustrated in Figure 2 rotated 180° from the view of Figure 2; Figure 5 is a cross sectional view of the internal gear machine of Figure 1 taken on line 5-5 of Figure 1; and Figure 6 is a cross sectional view of the internal gear machine of Figure 1 taken on line 6-6 of Figure 1. The invention provides an improved internal gear motor or pump of the kind shown in EP-A-0 261 757 and in US-A-4 586 885. The operation of the internal gears and other parts of the machine are well known in the art and are described in these documents. The general description of the operation of these parts contained in these documents is not described herein, but for the purpose of these details, descriptions therein are hereby incorporated by reference. Referring now to Figure 1 and Figures 5 and 6, an internal gear machine 11 includes a housing 13 which contains a rotatable shaft 15. Connected for rotation with the shaft 15 is an inner gear or gerotor 17. The inner gear 17 has rolls 18 extending around its periphery to form the teeth of the gear 17. An outer gear or rotor 19 meshes with the inner gear 17 such that variable displacement chambers 21 are formed there between. As seen best in Figure 5, the outer gear or rotor 19 orbits as the inner gear 17 rotates with the shaft 15. As the inner gear 17 rotates and the outer gear 19 orbits, the variable displacement chambers 21 increase and decrease in volume and this increase and decrease is utilized to translate the shaft power of the shaft 15 into hydraulic power of fluid conveyed to and from the chambers 21 (or vice versa in a motor as opposed to a pump). The outer peripheral face of the gear 19 has semi-cylindrical recesses therein to receive rollers 23 extending about the space in the housing 13 which receives the gear set 17, 19. The space in housing 13 which receives the gear set 17, 19 has a larger diameter than the outer diameter of the outer gear 19 so that the outer gear 19 is free to move in an orbiting motion as the inner gear 17 rotates and the outer gear 19 remains meshed therewith as it moves. The space between the outer gear 19 and the housing 13 is an annulus 20. The annulus 20 contains fluid with a pressure intermediate the high and low pressure fluid in the inlet and outlet of the housing and gears. The intermediate pressure results from leak paths between the high and low pressure areas of the pump which communicate with the annulus 20. As the gear set 17, 19 rotates and orbits, hydraulic fluid must be conveyed to and from the variable displacement chambers 21 there between. This is achieved by means of a commutator plate 25 and a valve plate 27. The commutator plate 25 is fixed with respect to the housing 13, while the valve plate 27 is rotatable with the inner gear 17. The valve plate 27 has a spline connection to the shaft 15 to rotate with the shaft 15 and the gear 17. The commutator plate 25 has a plurality of openings 29 extending in a circular array about the shaft 15. These openings 29 are connected to inlet and outlet openings in the housing 11 to convey hydraulic fluid to and from the variable displacement chambers 21 in the gear set 17, 19. So as selectively to connect the commutator openings 29 with the variable displacement chambers 21 at the proper time in the rotation and orbiting of the gear set 17, 19, the valve plate 27 has a plurality of valve plate openings 31 extending axially there through in a circular array as depicted in Figures 2 to 4. As the gear set 17 rotates together with the valve plate 27, the valve plate openings 31 open and close with respect to the commutator openings 29 selectively to communicate the inlet and outlet fluid to the opening and closing variable displacement chambers 21. This is best seen in Figure 6 where the openings 29 in the commutator 25 are shown in dotted lines beneath the valve plate 27 and its openings 31. Each alternate opening 29 is connected to the inlet of the housing and the other openings 29 are connected to the outlet of the housing. Thus, the rotating valve plate 27 sealingly separates the gear set 17, 19 from the commutator 25 except for the proper conveyance of fluid to and from the selected set of openings 29 through the openings 31. The valve plate 27 achieves this sealing separation by the close fit of the surfaces between the gear set 17, 19, the commutator 25, the housing 13, the shaft 15 and the exterior surfaces of the valve plate 27. The valve plate 27 has a commutator front side 33 shown in Figure 2 and a gear set rear side 35 shown in Figure 4. A well known problem with valve plates is that the valve plate is subjected to a tilting moment caused by one radial half of the valve plate being subjected to high pressure, while the other radial half of the valve plate is subjected to low pressure. This occurs on the gear set side 35 of the valve plate 27 since one radial half of the variable displacement chambers 21 are decreasing in volume (high pressure) while the other radial half are increasing in volume (low pressure). As described in US-A-4 411 607, a partial solution to this problem is to provide arcuate recesses 37 in the commutator side of the valve plate 27. These recesses 37 provide a partial counterbalance to the high pressure on the gear set side 35 of the valve plate 27. No compensation is provided on the gear set side 35 to correct the tilting moment due to high pressure ports covered on the commutator side 33. This problem is described in EP-A-0 261 757. The invention can provide a solution to this further tilting moment without requiring fluid from the commutator side of the valve plate to be conveyed to the gear set side of the valve plate through special ports. It also provides a solution for the orbiting outer rotor kind of machine where the special ports cannot function. To provide this balance, a continuous recess 39 is provided in the gear set side 35 of the valve plate 27. The inner radial extent of the recess 39 is a shoulder 40. The recess 39 extends continuously around the valve plate 27 adjacent the periphery 41 of the valve plate 27 so as to form a step which can receive fluid from the gear set side 35 of the valve plate 27. The positions of the shoulder 40 and the periphery 41 are shown in dotted lines in Figure 5. The fluid received in the recess 39 provides a uniform axial pressure opposing that provided by the high pressure openings in the commutator side of the valve plate 27 opposite the low pressure displacement chambers in the gear set. In this way the tilting moment resulting from the imbalance is corrected. By means of this uniform axial pressure, the recess 39 balances the tilting moment which would otherwise be present due to the unbalanced high pressure and low pressure forces acting on the opposite sides of valve plate 27. This can be achieved while sealingly separating the fluid which fills the recess 39 from the openings 29 in the commutator 25. The sealing is provided by the exterior surfaces of the valve plate 27 which fit closely within the housing 13 and the commutator 25 and the gear set 17, 19. The size of the recess 39 required to balance the unbalanced forces depends on the sizes of the commutator and valve plate openings, the area of the variable displacement chambers, the inlet pressure, the outlet pressure, the intermediate pressure, and the area of the recesses on the valve plate side. In most instances the size of the recess 39 to balance the imbalance is sufficiently small so that a sealing area between the intermediate pressure annulus and the displacement chambers is maintained as shown in Figure 5.

Claims: A rotary valve plate (27) for an internal gear machine (11) of the kind having a gear set including an inner gear (17) and an outer gear (19) disposed for rotation in a housing (13) such that a plurality of variable displacement chambers (21) are defined between the inner gear (17) and the outer gear (19) as they rotate; a commutator (25) through which fluid is conveyed to and from the variable displacement chambers (21) and disposed axially with respect to the gear set (17, 19) with a plurality of commutator openings (29) therein with some of the commutator openings (29) connected to an inlet in the housing (11) and some of the commutator openings (29) connected to an outlet in the housing (11); the valve plate (27) being connected for rotation with the gear set (17, 19) and disposed axially between the gear set (17, 19) and the commutator (25), so as to have a commutator side (33) and a gear set side (35), and having a plurality of valve plate openings (31) therein selectively to communicate the commutator openings (29) with the variable displacement chambers (21) of the gear set (17, 19); characterised in that the valve plate (27) has a periphery (41) and a gear set side recess (39) formed in the gear set side (35) thereof, the gear set side recess (39) being disposed to receive pressurized fluid therein from the gear set side of the valve plate; extending continuously around the gear set side (35) of the valve plate (27) adjacent the periphery (41) of the valve plate; and being sized to provide an axially balanced pressure on the valve plate which compensates for imbalance resulting from high pressure fluid in the commutator opening (29) being opposite low pressure fluid in the variable displacement chambers (21); the gear set side recess (39) being sealingly isolated from fluid on the commutator side (33) of the valve plate (27). An internal gear machine (11) of the kind having a gear set (17, 19) defining variable displacement chambers (21) as the gear set rotates in a housing (13) with an outer gear (19) orbiting in an annulus (20) having intermediate pressure therein, a commutator (25) disposed axially with respect to the gear set (17, 19) and having inlet and outlet openings (29) therein for conveying fluid to and from the variable displacement chambers (21), and a rotatable valve plate (27) connected for rotation with the inner gear (17) and disposed sealingly between the gear set (17, 19) and the commutator (25) selectively to convey inlet and outlet fluid there between by means of a plurality of valve plate openings (31) extending axially through the valve plate (27); characterised in that the valve plate (27) has a periphery (41) and a gear set side (35) with a recess (39) formed in the valve plate and extending continuously about the gear set side (35) of the valve plate (27) adjacent the periphery (41) so that intermediate pressure fluid from the annulus (20) is communicated to the recess (39) and urges the valve plate (27) towards the commutator (25) to balance the forces of high pressure fluid in the commutator openings (29) opposing low pressure fluid in the variable displacement chambers (21) across the valve plate (27).

Inventors: DLUGOKECKI, ANDREW N.
Applicants: PARKER HANNIFIN CORPORATION
Application year: 1988
Main classification: F04C2
IPC codes: F04C2, F04C15, F04C18