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:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 13/266,378, that is the national stage of International Application No. PCT/US2010/036072 filed on May 25, 2010. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    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. 
         [0005]    2. Description of the Related Art 
         [0006]    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. 
         [0007]    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. 
         [0008]    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 
       [0009]    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. 
         [0010]    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 
         [0011]    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. 
         [0012]    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 
         [0013]      FIG. 1  is a schematic diagram of a hydraulic system that incorporates a radial piston, hydraulic machine according to the present invention; 
           [0014]      FIG. 2  is a radial cross section showing the arrangement of cylinder bores and pistons in the hydraulic machine; 
           [0015]      FIG. 3  is an axial cross section through the hydraulic machine along line  3 - 3  in  FIG. 2 ; 
           [0016]      FIG. 4  is a perspective view of the cylinder block hydraulic machine; 
           [0017]      FIG. 5  is a cut-away enlargement a section of  FIG. 3  at the top of one cylinder bore; and 
           [0018]      FIG. 6  is a graph depicting the inner circumference of a cylinder bore at different pressure levels. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    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. 
         [0020]    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 . 
         [0021]    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. 
         [0022]    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. 
         [0023]    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. 
         [0024]    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 . 
         [0025]    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. 
         [0026]    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. 
         [0027]    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&#39;s outer race  48 . 
         [0028]    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&#39;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 . 
         [0029]    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 . 
         [0030]    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 . 
         [0031]    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/cm 2 ) 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 
         [0032]    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. 
         [0033]    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. 
         [0034]    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 . 
         [0035]    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. 
         [0036]    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. 
         [0037]    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. 
         [0038]    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.