Compact Radial Piston Hydraulic Machine Having a Cylinder Block with Deforming Regions

Abstract

A hydraulic machine has a cylinder body with first and second ports and a plurality of cylinder bores disposed radially with openings through a side surface. Deformation regions, formed around each cylinder bore opening, expand and contract in response to pressure changes in the cylinder bores. A continuous band extends around the cylinder body closing the cylinder bore openings and applying a pre-stress compressive force to each deformation region. A plurality of pistons are slideably received in the plurality of cylinder bores and a plurality of valve arrangement couple the cylinder bores to the first and second ports. A shaft with an eccentric cam drives the pistons to slide within the cylinder bores. Each deformation region distorts in response to pressure in the associated cylinder bore wherein the circumference of that cylinder bore becomes more circular as the cylinder pressure increases.

Description

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to hydraulic machines, such as pumps and hydraulic motors, and more specifically to such machines that have pistons which move in cylinder bores that are arranged radially around an eccentric drive shaft.

2. Description of the Related Art

A common type of radial piston pump comprises a body with a plurality of cylinder bores radially disposed around a drive shaft. A piston is slideably received within each cylinder bore and a plug closes the exterior end of the cylinder bore, thereby defining a chamber between the piston and the plug. The drive shaft has an eccentric cam against which the pistons ride due to bias forces provided by springs. An inlet port supplies fluid to an inlet passage that is coupled through a separate inlet check valve to each cylinder chamber. A set of outlet check valves couples the cylinder chambers to an outlet passage that leads to an outlet port of the pump.

As the drive shaft rotates, the eccentric cam causes each piston to slide cyclically in and out of the respective cylinder bore, thereby reducing and expanding the volume of the associated cylinder chamber. During an intake phase of the piston cycle, when a given cylinder chamber volume is expanding, the inlet check valve opens allowing fluid to be drawn from the inlet passage into the cylinder chamber. During the subsequent exhaust phase of each piston cycle, when the volume of the cylinder chamber is reducing, fluid is expelled under pressure through the outlet check valve to the outlet port. The fluid intake and exhaust phases occur repeatedly during every rotation of the eccentric cam. At any point in time, some of the radially disposed cylinder bores are in the intake phase and other cylinder bores are in the exhaust phase.

Conventional radial piston pumps typically are relatively large in diameter in order to accommodate the biasing springs and plugs that close the outer ends of the cylinder bores. In many installations, the amount of space for the pump is restricted, thus it is desirable to reduce the size of the pump. Often the pump is mounted along side an engine or transmission and the radial space is limited restricting installation of conventional radial piston pumps.

SUMMARY OF THE INVENTION

A novel hydraulic machine includes a cylinder body that has two end surfaces with a curved side surface there between. A first port and a second port provided for making hydraulic connections to the cylinder body. A plurality of cylinder bores is disposed radially in the cylinder body and each cylinder bore has an opening through the side surface. A deformation regions is formed around each opening and deforms in response to pressure changes in the adjacent cylinder bore. A separate piston assembly is slideably received in each cylinder bore. A drive shaft is rotatably located in the cylinder block and has an eccentric cam for driving the plurality of pistons reciprocally within the plurality of cylinder bores. A valve arrangement couples the cylinder bores to the first and second ports and allow fluid to enter and exit the bores at appropriate times during each piston cycle.

A closing band engages the curved side surface and extends over the openings of the plurality of cylinder bores. The closing band applies force to each deformation region thereby applying a compressive force to the cylinder body

In one aspect of the present hydraulic machine, each deformation region comprises a rim extending around each cylinder bore opening and proud of the side surface.

In another aspect of the present hydraulic machine, pressure within each cylinder bore during a compression stage of a piston cycle reduces the compressive force that the closing band exerts on the deformation region associated with that cylinder bore. For example, as pressure within each cylinder bore increases, the cross sectional shape of the cylinder bore becomes more circular, i.e., the circumference changes from a pronounced oval toward a circle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a hydraulic system that incorporates a radial piston, hydraulic machine according to the present invention;

FIG. 2 is a radial cross section showing the arrangement of cylinder bores and pistons in the hydraulic machine;

FIG. 3 is an axial cross section through the hydraulic machine along line 3-3 in FIG. 2;

FIG. 4 is a perspective view of the cylinder block hydraulic machine;

FIG. 5 is a cut-away enlargement a section of FIG. 3 at the top of one cylinder bore; and

FIG. 6 is a graph depicting the inner circumference of a cylinder bore at different pressure levels.

DETAILED DESCRIPTION OF THE INVENTION

With initial reference to FIG. 1, a hydraulic system 10 has a prime mover 12, such as an internal combustion engine or an electric motor, that is coupled by a shaft to drive a hydraulic machine 14 to function as a pump. The hydraulic machine 14 can be configured as a fixed or variable displacement pump to draw fluid in from the first conduit 15 and force the fluid under pressure into the second conduit 16, thereby driving a hydraulic motor 18 in one direction. The hydraulic motor 18 rotates a component, such as one or more wheels 19 of a vehicle, for example.

The same design of the hydraulic machine also can be used as a hydraulic motor, such as hydraulic motor 18. Here the hydraulic machine receives pressurized fluid at one port and converts that fluid power into mechanical energy that is applied to a shaft connected to the wheel 19.

Therefore, the apparatus described herein is generically referred to as a “hydraulic machine” because it can be configured to function as either a pump or a hydraulic motor depending upon how and where it is used in a hydraulic system. In some situations, the same hydraulic machine may operate as both a pump and a motor at different times depending upon whether the machine is driving the load, such as wheels 19, or is being driven by fluid received from the load, such as when the vehicle coasts to a stop.

With reference to FIGS. 2, 3 and 4, the hydraulic machine 14 has a cylinder block 20 with first and second flat, circular end surfaces 21 and 22 between which a cylindrically curved side surface 38 extends. The cylinder block 20 has a plurality of cylinder bores 36 extending radially inward from side surface 38 to a central shaft bore 41. The exemplary hydraulic machine 14 has nine cylinder bores 36 spaced at 40 degree increments around the central shaft bore 41, however other hydraulic machines may have a greater or lesser number of cylinder bores.

A plurality of first bores 24 extends into the first end surface 21 of the cylinder block 20 with each of those bores communicating with a different one of the cylinder bores 36 through an curved cavity 43 that extends in an annular manner around and opens into that one cylinder bore. An end plate 23 is bolted against the first end surface 21 and a plurality of apertures 27 extend through that plate aligned with the plurality of first bores 24. Each pair of a first bore 24 and an aperture 27 form an intake passage for one of the cylinder bores 36. An inlet manifold 26 abuts an exposed surface of the end plate 23 and has an annular inlet passage 31 connecting all of the end plate apertures 27 to an inlet port 32 of the hydraulic machine 14. Fluid entering the hydraulic machine though the inlet port 32 flows via the inlet passage 31, apertures 27, and first bores 24 to each of the cylinder bores 36, as will be described.

A plurality of second bores 25 extends into the second end surface 22 of the cylinder block with each of the second bores communicating with a different one of the cylinder bores 36 through the respective curved cavity 43. An exhaust manifold 28 abuts the second end surface 22 and has an annular outlet passage 29 connecting all the second bores 25 to an outlet port 35 of the hydraulic machine 14. The annular inlet passage 31 and the annular outlet passage 29 encircle the shaft bore 41 that extends through center of the cylinder block 20. The cylinder block 20, the end plate 23, the inlet manifold 26 and the exhaust manifold 28 combine to form a body 30 of the hydraulic machine 14.

A separate inlet check valve 33 is located in each of the first bores 24. The inlet check valve 33 opens when the pressure within the inlet passage 31 is greater than the pressure within the associated cylinder chamber 37, as occurs during the intake phase of the piston cycle. A separate outlet check valve 34 is located each of the second bores 25. The outlet check valve 34 opens when pressure within the associated cylinder chamber 37 is greater than the pressure within the outlet passage 29, as typically occurs during the exhaust phase of the piston cycle. Each of the inlet and outlet check valves 33 and 34 is passive meaning that it operates in response to pressure exerted thereon and is not electrically operated.

Referring specifically to FIGS. 2 and 3, a drive shaft 40 extends through the shaft bore 41 and is rotatable therein being supported by separate bearings 42 at each end of the cylinder block 20. The central section of the drive shaft 40, that is within the cylinder block 20, has an eccentric cam 44. The cam 44 has a circular outer surface, the center line of which is offset from the axis 45 of the remainder of the drive shaft 40. As a consequence, as the drive shaft 40 rotates within the cylinder block 20, the cam 44 rotates in an eccentric manner about the axis 45. A cam bearing 46 extends around the drive shaft cam 44. The cam bearing 46 may have an optional inner race that is pressed onto the outer circumferential surface of the drive shaft cam. A plurality of rollers 49 are located between the inner race and an outer race 48. The inner race may be eliminated by heat treating and machining the surface of the eccentric cam 44 to function as that race. Although a cam bearing 46 with cylindrical rollers is depicted, a bearing with other types rolling elements or a journal type bearing with or without lubrication may be used.

A piston assembly 50 is slideably received within each of the cylinder bores 36, thereby defining a chamber 37 within the cylinder bore. Each piston assembly 50 comprises a piston 54 and a piston rod 52. The piston rod 52 extends between the piston 54 and the cam bearing 46. The piston rod 52 has a curved shoe 56 that abuts the outer race 48 of the cam bearing 46 and which is wider than the shaft of the piston rod creating a flange portion. A pair of annular retaining rings 58 extend around the cam 44 engaging the flange portion of each piston rod shoe 56, thereby holding the piston rods 52 against the cam bearing 46, which is particularly beneficial during the intake phase of a piston cycle. The curved piston rod shoe 56 evenly distributes the piston load onto the outer race 48 of the cam bearing 46 and also distributes local load forces onto the rollers 49 of that bearing. As the drive shaft 40 and cam 44 rotate within the cylinder block 20, the outer race 48 of the cam bearing 46 rotates at a very slow rate as compared to the rotational speed of the drive shaft. Therefore, there is little relative motion between each piston rod shoe 56 and the cam bearing's outer race 48.

The piston 54 is cup-shaped having an interior cavity that opens toward the drive shaft 40. An end of the piston rod 52 is received within that interior cavity and has a spherical head that engages a mating partially spherical depression in the piston 54. The piston rod 52 is held against the piston 54 by a bushing 57 and a snap ring 59 that rests in an interior groove in the piston's interior cavity (see FIG. 5). As the piston rod 52 follows the eccentric motion of the cam 44 and the piston 54 in turn follows by sliding within the cylinder bore 36, the bushing and snap ring arrangement allows the spherical head of the piston rod to pivot with respect to the piston 54 when a rotational moment is imposed onto the piston rod 52 by rotation of the cam 44. Because of that pivoting, the rotational moment is not transferred into the piston 54, thereby minimizing lateral forces between the piston and the wall of the cylinder bore 36.

With particular reference to FIG. 3, the drive shaft 40 includes an internal lubrication passage 60 extending from one end to the outer surface at the center of the eccentric apex of the cam 44 to feed lubricating fluid into the cam bearing 46. The lubrication passage 60 at the end of the drive shaft opens into a supply chamber 62 that receives lubricating fluid that is fed into a lubrication port 64. As the drive shaft 40 rotates, centrifugal force expels fluid from the lubrication passage 60 into the cam bearing 46. This action draws additional fluid into the lubrication passage 60 from the supply chamber 62, thereby providing a pumping action for fluid that lubricates the cam bearing 46. The outer race 48 has apertures through which the fluid flows to lubricate the piston rod shoes 56. If the cam bearing 46 has an inner race, that inner race has apertures to convey the lubricating fluid to the rollers 49.

Each cylinder bore 36 has an opening 39 through the curved side surface 38 of the cylinder block 20. With specific reference to FIG. 4, a separate raised annular rim 66 projects proud of the side surface 38 around each cylinder bore opening As seen in FIGS. 2 and 3, a continuous closing band 68 is shrunk fitted to extend circumferentially around the cylinder block 20 tightly abutting each of the cylinder rims 66, thereby sealing every cylinder bore opening To achieve that sealing, the annular surface of each rim 66 that contacts the closing band 68 is curved to conform to the inner circumferential surface of the closing band. The continuous closing band 68 eliminates the plugs previously inserted into the outer end of each cylinder bore, which required longer bores in which to receive those plugs. Thus using the closing band 68 reduces the overall diameter of the cylinder block 20 and the size of the hydraulic machine 14.

The closing band 68 compressively pre-stresses the cylinder block 20, which has a greater material strength in compression than in tension. The compressive force from the closing band 68 is concentrated through each annular rim 66. Although bands had been used previously around a cylindrical cylinder block, the curved side surface of such cylinder blocks was smooth and did not have the annular rims 66 extending proud of that side surface. As a consequence, the compressive force from the prior band was evenly distributed over a relatively large surface area of the cylinder block. In contrast, the compressive force from the present closing band 68 is concentrated at each annular rim 66. As a result, the present closing band may apply a force of 76,000 psi (5,343 kgf/cm²) to the cylinder block, for example, which force is more than ten times the force applied by previous bands. As a result, previous bands tended to move away from the cylinder bore opening as the cylinder chamber pressure increased during normal operation. That movement allowed fluid from the cylinder chamber to leak between the band and the cylinder block. In fact, it was common practice to provide channels in the side surface of the cylinder block to direct such leakage toward the drain port or the low pressure outlet port of the previous hydraulic machine

As indicated in FIG. 5, the annular rim 66 and a portion of the cylinder block 20 between the rim and the annularly curved cavity 43 form a deformation region 70, that flexes or distorts resiliently as pressure within the associated cylinder chamber 37 changes. The deformation region 70 is portion of the cylinder block that extends in a cantilevered manner over the curved cavity 43 beneath the rim 66. With reference to FIG. 6, before the closing band 68 is placed around the cylinder block 20, the circumference of the cylinder bore 36 is circular, being equidistant along a longitudinal axis L that is parallel to the axis 45 of the drive shaft 40 and along a radial axis R in a radial plane through the cylinder block. Upon being shrunk fitted around the cylinder block 20, the closing band applies a radially compressive force onto each of the cylinder rims 66 which distorts the associated deformation region 70 and the cross sectional shape of the respective cylinder bore 36. Specifically, the deformation region 70 is pressed inward, wherein the dimension of the cylinder bore circumference along the radial axis R decreases, while the dimension along the longitudinal axis L increases as denoted by the dotted line in FIG. 6. That deformation results in the cylinder bore circumference having a pronounced non-circular shape, such as a oval. It is engagement of the closing band with the annular rim 66 around the opening of each cylinder bore 36 which concentrates exertion of the compressive forces into the deformation region 70 of the cylinder block 20. The contracted first position of the deformation region 70 in this unpressurized or low pressurized state of the associated cylinder chamber 37 is depicted by solid lines in FIG. 5. The curved cavity 43 beneath the rim 66 limits the degree to which forces from the closing band 68 deform the section of the cylinder bore 36 within which the piston 54 slides.

Such low pressure conditions exists during the intake phase of a given piston cycle. The intake phase begins after the piston 54 has passed top dead center, the outlet check valve 34 has closed and the piston chamber pressure has decompressed as the piston moves in the respective cylinder bore 36 toward the center axis 45 and the cylinder chamber 37 is expanding. Due to that expansion, pressure within cylinder chamber 37 is less than pressure in the inlet passage 31, which causes the inlet check valve 33 for that cylinder bore to open. Thus fluid flows from the inlet passage 31 through the associated aperture 27 and first bore 24 into the expanding cylinder chamber. That cylinder chamber pressure is less than the pressure in the outlet passage 29, thereby holding the associated outlet check valve 34 closed.

After the volume of the cylinder chamber 37 is filled, the compression or exhaust phase of the piston cycle begins. In the exhaust phase, the piston slides away from the center axis 45 decreasing the volume of the cylinder chamber 37 and causing pressure within the cylinder chamber to increase. As that pressure rises, the inlet check valve 33 closes preventing flow from the cylinder chamber 37 outward through the respective first bore 24.

The higher pressure acting on the inside surface of the closing band 68 pushes the band radially outward, thereby reducing the compressive forces that the band exerts on the curved side surface 38 of the cylinder block 20. In response, the deformation region 70 around the respective cylinder bore 36 also expands outward, i.e., the annular surface of the rim 66 moves radially outward maintaining contact and a seal with the closing band 68, ultimately reaching a second position shown by the dashed lines in FIG. 5. Deflection of the deformation regions 70 follows motion of the closing band 68 which tends to prevent leakage from the piston chamber as the pressure increases. The amount of cylinder block movement has been exaggerated in FIG. 5 for illustration purposes. Stresses within the cylinder block 20 decrease due to the distortion of the compression regions as the pressure within the cylinder chambers 37 increase. By the closing band 68 pre-stressing the cylinder block 20 in compression, the tensile stresses resulting from increased pressure in the cylinder chamber 37 are mitigated which enables higher pressure and power density operation of the hydraulic machine Movement of the deformation region 70 changes the shape of the circumference of the cylinder bore 36 toward a circular shape, as depicted by the dashed line in FIG. 6. In other words the difference between the dimensions of the cylinder bore along the radial and longitudinal axis becomes smaller. Thus, as a piston moves through the exhaust phase, the cylinder bore becomes more circular mitigating power loss due to fluid leakage past the piston and mitigating interference with the sliding piston, thereby improving machine efficiency.

The increasing pressure within the cylinder chamber 37 eventually exceeds the pressure within the outlet passage 29 by an amount that causes the outlet check valve 34 to open. At that time, fluid flows from the cylinder chamber 37 through the outlet passage 29 to the outlet port 35 of the hydraulic machine 14. The inlet check valve 33 remains closed until pressure in the cylinder chamber 37 once again become less than pressure in the inlet passage 31 during another intake phase of the piston cycle.

When the pressure within the cylinder chamber 37 decreases during the subsequent intake phase, the deformation region 70 contracts back to the first position shown in FIG. 5 in response to the compressive force from the closing band 68. Thus, the deformation region 70 of the cylinder block 20 resiliently flexes or distorts back and forth between the first and second positions depicted in FIGS. 5 and 6 as pressure in the cylinder chamber 37 repeatedly increases and decreases during a series of piston cycles.

The foregoing description was primarily directed to a preferred embodiment of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.

Claims

1. A hydraulic machine comprising: a cylinder body with a first port, a second port and a side surface, and having a plurality of cylinder bores disposed radially about an axis with each cylinder bore having an opening through the side surface, the cylinder body further having deformation regions formed around each opening, wherein the deformation regions expand and contract radially with respect to the axis in response to pressure changes in the cylinder bores;a closing band extending around the cylinder body and closing the openings of the plurality of cylinder bores, wherein the closing band applies force to each deformation region that compresses the cylinder body;a plurality of piston assemblies each slideably received in a different one of the plurality of cylinder bores;a plurality of valve arrangements the plurality of cylinder bores to the first and second ports; anda drive shaft rotatably received in the cylinder block for driving the plurality of piston assemblies within the plurality of cylinder bores.

2. The hydraulic machine as recited in claim 1 wherein the cylinder body further comprises: a cylinder block that has the plurality of cylinder bores and the side surface;an inlet manifold having the first port; andan exhaust manifold having the second port.

3. The hydraulic machine as recited in claim 1 wherein the side surface of the cylinder block is cylindrical and the closing band is circular.

4. The hydraulic machine as recited in claim 1 wherein the closing band extends in a continuous circle.

5. The hydraulic machine as recited in claim 1 wherein each deformation region comprises a rim extending around each cylinder bore opening and proud of the side surface.

6. The hydraulic machine as recited in claim 1 wherein each deformation region comprises a cantilevered portion of the cylinder body extending as least partially around the associated cylinder bore.

7. The hydraulic machine as recited in claim 1 wherein each deformation region expands as pressure in the adjacent cylinder bore increases and contracts as pressure in the adjacent cylinder bore decreases.

8. The hydraulic machine as recited in claim 1 wherein pressure within a given cylinder bore during a compression stage of an operating cycle reduces compressive forces that the closing band exerts on the deformation region associated with that cylinder bore.

9. The hydraulic machine as recited in claim 1 wherein as pressure within each cylinder bore increases, the adjacent deformation region flexes thereby changing a circumference of the cylinder bore from non-circular towards becoming circular.

10. The hydraulic machine as recited in claim 1 wherein each of the plurality of piston assemblies comprises a piston and a piston rod, wherein the piston rod comprises a stem with a curved shoe through which force is transferred to the drive shaft.

11. The hydraulic machine as recited in claim 10 wherein: the drive shaft has an eccentric cam; andfurther comprising a cam bearing extending around the eccentric cam and having an outer race and a plurality of rollers between the outer race and the eccentric cam, wherein the shoe of each piston rod abuts the outer race.

12. The hydraulic machine as recited in claim 11 further comprising a retaining ring extending around the drive shaft and engaging the curved shoe of every piston rod, thereby constraining the curved shoe from moving away from the eccentric cam.

13. The hydraulic machine as recited in claim 1 wherein each of the plurality of piston assemblies comprises a piston and a piston rod, wherein the piston rod has an end with a partially spherical head that engages a partially spherical depression in the piston.

14. The hydraulic machine as recited in claim 1 wherein: the cylinder block comprises a plurality of first bores, each extending between the first port and one of the plurality of cylinder bores, and a plurality of second bores, each extending between the second port and one of the plurality of cylinder bores; andthe valve arrangement comprises a plurality of first valves, each located in one of the first bores, and a plurality of second valves, each located in one of the second bores.

15. The hydraulic machine as recited in claim 14 wherein each of the plurality of first valves and the plurality of second valves is a check valve.

16. A hydraulic machine comprising: a cylinder body with a first port, a second port and a curved side surface, and including a plurality of cylinder bores disposed radially in the cylinder block with openings through the side surface and passages connecting the plurality of cylinder bores to the first and second ports, the cylinder body having a plurality of deformation regions each comprising a rim projecting outwardly from the side surface and around one of the openings, wherein the deformation regions repeatedly deform in response to pressure changes in the cylinder bores;a closing band extending around the cylinder body and closing the openings of the plurality of cylinder bores, wherein the closing band applies compressive force to the cylinder body through the rim of each deformation region;a plurality of piston assemblies each slideably received in a different one of the plurality of cylinder bores; anda drive shaft rotatably received in the cylinder block and having an eccentric cam for driving the plurality of piston assemblies within the plurality of cylinder bores.

17. The hydraulic machine as recited in claim 16 further comprising a plurality of valves located in the passages of the cylinder body.

18. The hydraulic machine as recited in claim 16 wherein the cylinder body further comprises: a cylinder block that has the plurality of cylinder bores and the side surface;an inlet manifold having the first port; andan exhaust manifold having the second port.

19. The hydraulic machine as recited in claim 16 wherein each deformation region comprises a cantilevered portion of the cylinder body extending as least partially around the associated cylinder bore.

20. The hydraulic machine as recited in claim 19 wherein the cantilevered portion is defined by a curved cavity within the cylinder body and opening into the cylinder bore.

21. The hydraulic machine as recited in claim 16 wherein each deformation region expands as pressure in the adjacent cylinder bore increases and contracts as pressure in the adjacent cylinder bore decreases.

22. The hydraulic machine as recited in claim 16 wherein pressure within a given cylinder bore during a compression stage of an operating cycle reduces compressive forces that the closing band exerts on the deformation region associated with that cylinder bore.

23. The hydraulic machine as recited in claim 16 wherein as pressure within each cylinder bore increases, the adjacent deformation region flexes thereby changing a circumference of the cylinder bore from non-circular towards becoming circular.