Abstract:
The invention concerns a variable pump or hydraulic motor with a drive shaft with a first axis of rotation and first plungers connected to the drive shaft and rotatable around the first axis of rotation. A port plate mounted in the housing can rotate around an axis intersecting the first axis, for adjusting the stroke volume. The port plate positioning drive comprises two counter-acting hydraulic actuators acting on the port plate in the direction of the first plungers.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of pending International patent application PCT/EP2006/060543, filed Mar. 8, 2006, which designates the United States and claims priority from European patent application no. 05101934.7, filed Mar. 11, 2005, the content of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention concerns a pump or hydraulic motor comprising 
     a drive shaft with a first axis of rotation rotatably mounted in a housing, first plungers connected to the shaft and rotatable around the first axis of rotation, 
     a port plate mounted in the housing and provided with a port plate surface with a high-pressure port at the first radius and a low-pressure port at a first radius each connected to a respective pressure line, 
     a second axis of rotation which intersects the first axis of rotation in a centre plane, 
     first cylinders rotatable around a second axis of rotation, and sealingly fitted around the first plungers for forming chambers with the first plungers, each chamber having a volume that in a full rotation of the first cylinders and first plungers changes according to a stroke volume, 
     a plurality of cylinder channels each cylinder channel rotatable with a respective first cylinder and connected to a respective chamber and ending in a valve surface wherein the valve surface abuts and is rotatable relative to the port plate surface for connecting the chambers through respective cylinder channels with the high-pressure port or the low-pressure port, 
     whereby a bearing supports each port plate in the housing and by rotating the port plate in the housing around a third axis of rotation which is perpendicular to the centre plane and intersects the first axis of rotation and the second axis of rotation, the stroke volume can be changed using a port plate positioning drive located in the centre plane exerting a force on the port plate. 
     BACKGROUND OF THE INVENTION 
     Such pumps or hydraulic motors are known as bent axis pumps or motors. The plungers of the known pumps or motors are swivable connected to a flange and are movable in cylinders, which are at one end of a rotor. At the other end of the rotor a port plate is positioned; this end of the rotor forms the valve surface. The port plate is located between the valve surface of the rotor and the housing. In the known pumps or motors, the port plate positioning drive comprises hydraulic actuators, which move a coupling pin in a slot in the housing. The coupling pin is positioned in a hole in the centre of the port plate so coupling the port plate to the hydraulic actuators. 
     This known construction has the disadvantage that in the centre plane at the location of the slot the housing does not support the port plate sufficiently so that the port plate can deform under influence of the high pressure between the port plate surface and the valve surface. Also between the pressure ports, which is in the area of the centre plane, the pressure between the port plate surface and the valve surface fluctuates with the passage of the cylinder channels and thereby causes fluctuations in the deformations. It is not possible to compensate for these fluctuations in the design of the parts. These fluctuating deformations create gaps, which cause leakage of oil. If the deformations are limited, for instance to a maximum of 3 to 5 micro millimeters, the leakage between the port plate surface and the valve surface remains acceptable. A higher value reduces the efficiency of the pump or motor in an undesirable way. This requirement limits the first radius, as a larger radius reduces the stiffness of the port plate and increases the deformations. 
     A further disadvantage of the known construction is that it is not possible to extend the drive shaft through an opening in the port plate. Such an extension would make it possible to connect several pumps or motors inline. An opening in the port plate with a diameter suitable for letting the drive axis pass through would further reduce the stiffness of the port plate and would interfere with the hydraulic actuators. 
     SUMMARY OF THE INVENTION 
     In order to overcome these disadvantages the pump or hydraulic motor further includes a port plate characterized in that the port plate positioning drive comprises a first hydraulic actuator and a second hydraulic actuator acting on the port plate in the direction parallel to the second axis of rotation and counteracting each other. Supporting the port plate in the centre plane using the hydraulic actuators reduces the deformations caused by the fluctuating high-pressure between the valve surface and the port plate surface, making it possible to overcome the disadvantages of the known design and to reduce leakage. 
     In accordance with an aspect of the instant invention, the pump or hydraulic motor further includes a first hydraulic actuator and a second hydraulic actuator which act on the port plate at a radius equal or larger than the first radius. In this way the hydraulic actuators directly support the area with the fluctuating pressure thereby further reducing the fluctuating deformations. 
     In accordance with an aspect of the instant invention, the pump or hydraulic motor further includes a first hydraulic actuator connected to a control unit and the second hydraulic actuator to the high-pressure port. By connecting the second actuator with the high-pressure port, it is necessary that the control unit keeps the first actuator under pressure as well. In this way it is ensured that both actuators support the port plate. 
     In accordance with an aspect of the instant invention, the pump or hydraulic motor further includes a port plate positioning drive which comprises a third hydraulic actuator which is connected to the first hydraulic actuator and which is placed opposite and counteracting the second hydraulic actuator. The first hydraulic actuator and the third hydraulic actuator work together, whereby the third hydraulic actuator directly compensates the force that the second hydraulic actuator exerts on the port plate. This leads to lower forces on the port plate and reduces deformations. 
     In accordance with an aspect of the instant invention, the pump or hydraulic motor further includes a port plate which comprises a first canal that connects the first hydraulic actuator and the third hydraulic actuator. In accordance with another aspect the port plate comprises a second canal that connects the second hydraulic actuator with the high-pressure port. This reduces the number of separate parts. 
     In accordance with an aspect of the instant invention, in the pump or hydraulic motor the forces exerted by the third hydraulic actuator on the port plate are parallel to the second axis of rotation. This way the torque for positioning or rotating the port plate is more or less independent of the rotational position of the port plate, so making positioning the port plate easier. 
     In accordance with an embodiment, the pump or hydraulic motor further includes hydraulic actuators which each comprise a second plunger mounted in the housing and a cup shaped second cylinder fitted around the second plunger sealing in a plane perpendicular to the second axis. In this way, the hydraulic actuators have a simple and cost effective design. 
     In accordance with an aspect of the instant invention, the pump or hydraulic motor further includes second cylinders which are slidable and/or sealingly supported on the port plate. This ensures that the second cylinders do not exert a sideways force on the port plate and that the design can be more compact by having canals in the port plate for supplying oil to the various cylinders. 
     In accordance with an aspect of the instant invention, the pump or hydraulic motor further includes a second cylinder and/or a port plate having spring and/or locking means for preventing a large gap between the second cylinder and the port plate. This ensures that during starting pressure build-up can take place in the high-pressure port and in the connected cylinders by pre-venting leakage through various gaps. After starting, the high pressure ensures that the gaps remain closed. 
     In accordance with an aspect of the instant invention, the variable pump or hydraulic motor further includes first plungers and first cylinders that are identical respectively with second plungers and second cylinders. This reduces the number of different parts in the device and eases production or maintenance of the pump or motor. 
     In accordance with an aspect of the instant invention, the variable pump or hydraulic motor further includes a port plate comprising first and second cylindrical bearing surfaces on a side of the port plate opposite from a side with the port plate surface for supporting the port plate in the housing, the first and second cylindrical bearing surfaces having the third axis of rotation as the centre line, wherein one of the first and second cylindrical bearing surfaces is provided with a first opening connected to the high-pressure port and the other of the first and second cylindrical bearing surfaces is provided with a second opening connected to the low-pressure port. By providing the bearing surfaces with openings connected to the pressure ports, there is a simple and direct connection between the pressure lines and the chambers. 
     In accordance with an aspect of the instant invention, the variable pump or hydraulic motor further includes a drive shaft comprising a flange with a set of first plungers on each side of the flange extending in opposite directions. On each side of the flange there is a ring shaped port plate through which the drive shaft extends. In this way a compact high capacity pump or motor is made. 
     In one advantageous embodiment a pump or hydraulic motor which includes a first axis of rotation rotatable mounted in a housing, first plungers connected to the shaft and rotatable around the first axis of rotation, a port plate mounted in the housing and provided with a port plate surface with a high-pressure port at a first radius and a low-pressure port at the first radius each connected to a respective pressure line, first cylinders rotatable around a second axis of rotation, which intersects the first axis in a centre plane, and sealingly fitted around the first plungers for forming chambers with the first plungers with a volume that in a full rotation changes a stroke volume, cylinder channels each rotatable with and connected to a chamber and ending in a valve surface which is rotatable along the port plate surface for connecting the chamber with the high-pressure port or the low pressure port, whereby by rotating the port plate around a third axis which is perpendicular to the centre plane and intersects the first axis and the second axis, the stroke volume can be changed using a port plate positioning drive located in the centre plane exerting a force on the port plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained below with reference to an embodiment and with the aid of a drawing, in which: 
         FIG. 1  shows a cross section and the interior of a hydraulic device such as a pump; 
         FIG. 2  shows a perspective view of the interior of the hydraulic device of  FIG. 1 ; 
         FIG. 3  shows a perspective view of the port plates and the port plate drives of the hydraulic device of  FIG. 1 ; 
         FIG. 4  shows a side view of a port plate of the hydraulic device of  FIG. 1 ; and 
         FIG. 5  show a frontal view of the port plate of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The hydraulic device shown in  FIG. 1  is described below as a pump  12 . A motor (not shown) drives the pump  12  via a splined shaft end  24 . The pump  12  is connected with pressure lines (not shown) and compresses oil of low-pressure to oil of high-pressure. Using more or less the same components the hydraulic device can be used as a hydraulic motor as well. In that case, oil of high-pressure feeds into the motor and the splined shaft end  24  drives equipment. The document WO 03/058035 describes the various components used in the embodiment in more detail and this description is included herein if required for further explanation of the invention. 
     The pump  12  comprises a housing  22  on which a first cover  10  and a second cover  23  are fastened with bolts  11 , the first cover  10  and the second cover  23  have bearings  2  in which a shaft  3  can rotate around a first axis L. The shaft  3  sealingly extends through the second cover  23  and ends as the splined shaft end  24 . The shaft  3  has a flange  29  in the centre of the housing  22  and pump plungers  28  extend on both sides of the flange  29 , in this embodiment on both sides twelve pump plungers  28 . Pump cylinders  26  enclose the pump plungers  28  and rest against a channel plate  25 . The pump plungers  28  have a spherical sealing surface that seals against the inside surface of the pump cylinder  26 , so that the inside of the pump cylinder  26  forms a pump chamber with the pump plunger  28 . During use, the pump cylinders  26  seal against the channel plate  25  under influence of the pressure in the pump chamber. In order to prevent that leakage occurs in situations where the pressure in the pump chamber is too low a spring  27  is provided, this spring  27  presses the pump cylinders  26  against the channel plate  25 . In other embodiments instead or in addition to the spring  27 , other locking means hold the pump cylinder  26  against the channel plate  25 , thereby maintaining the possibility of a sliding movement of the pump cylinder  26  over the channel plate  25 . 
     An opening in the bottom of the pump cylinder  26  connects with a channel  31 , which ends at a valve surface  6  of the channel plate  25 . The valve surface  6  rotates over a port plate surface  7  of a port plate  8 . The channel plate  25  rotates with the shaft  3  and is coupled with the shaft  3  by a sphere shaped coupling  4 , so that it can swivel over the coupling  4  and rotate around a second axis M, which intersects the first axis L. The port plate  8  determines the tilt angle of the second axis M. The direction of centre lines M′ of the pump cylinders  26  is parallel to the second axis M, so that the sealing surface between a pump plunger  28  and a pump cylinder  26  is perpendicular to the second axis M. The first cover  10  and the second cover  23  and the housing  22  have canals (not shown) that connect the pressure lines with the port plates  8  and so with the pump chambers. Due to the angle between the first axis L and the second axis M in a full rotation of the shaft  3  the volume of the pump chamber changes according to a stroke volume between a maximum value and a minimum value. The stroke volume determines the pump capacity. By rotating the port plate  8  around a third axis N (see  FIGS. 4 and 5 ), which is perpendicular to a centre plane through the first axis L and second axis M and intersects these axis L and M, the angle between the first axis L and the second axis M is changed and with this also the stroke volume and capacity of the pump  12 . A first actuator  33  and a third actuator  19  rotate the port plate  8  in a first direction. The first actuator  33  comprises a plunger  1  mounted in the first cover  10 . A cylinder  14  is mounted around the plunger  1 . To follow the rotation of the port plate  8  the underside of the cylinder  14  can slide over a slide surface  35  which is the bottom of a slot  34  in the port plate  8 . An actuator chamber of the first actuator  33 , formed by the plunger  1  and the cylinder  14 , is open at the bottom and connects with an interconnecting channel  17  in the port plate  8  to a similar actuator chamber of the third actuator  19 . The third actuator  19  has a hollow plunger  18  mounted in a support  21  attached to the house  22 . A canal through this hollow plunger  18  is part of a control channel  20  that is connected to a control unit (not shown). By increasing oil pressure in the control channel  20 , the first actuator  33  and the third actuator  19  rotate the port plate  8  towards a position with a reduced stroke volume. The second actuator  13  comprises a plunger  1  mounted in the first cover  10  and a cylinder  14  slidable over the slide surface  35 . The actuator chamber is connected through the opening in the bottom of the cylinder  14  with a high pressure channel  16  in the port plate  8  that connects the actuator chamber with a high-pressure port  39  (see  FIGS. 4 and 5 ). The high-pressure port  39  is connected to the pressure line with oil of high pressure and the second actuator  13  counter acts the torque that is acted by the first actuator  33  and the third actuator  19  on the port plate  8  and the second actuator  13  moves the port plate  8  to a position with an increased stroke volume. 
     When starting the pump  12  a spring  30  presses the port plates  8  in a tilted position, a spring support  32  positions the spring  30  on the port plate  8 . In the tilted position, the stroke volume is maximal during starting. In order to prevent leakage between the cylinders  14  and the port plate  8  the cylinders are pressed by a spring (not shown) against the port plate  8 . In another embodiment, there are (additional to or instead of the spring) locking means that hold the cylinders  14  slidingly against the port plate  8 . After the pump  12  has started the pressure in the actuator chamber presses the cylinders  14  against the port plate  8 . The  FIGS. 2 ,  3 ,  4  and  5  show the interior of the pump  12  and the port plates  8 . Each port plate  8  has in the port plate surface  7  a high-pressure port  39  and a low-pressure port  40 , between these ports there is a crossover area  41 . The other side of the port plate  8  has a cylindrical bearing surface  37  that rests in a cylindrical support surface (not shown) of the first cover  10  or the second cover  23 . The port plate  8  can rotate in this cylindrical support surface around the third axis N. The cylindrical bearing surface  37  that lies opposite the high-pressure port  39  has a high-pressure canal  38  that connects in the port plate  8  with the high-pressure port  39 . In the first cover  10  or the second cover  23  the high-pressure canal  38  continues to the high-pressure pressure line. In the same way, the cylindrical bearing surface  37  that lies opposite the low-pressure port  40  has a low-pressure canal  36  that connects to the low-pressure pressure line in the first cover  10  or the second cover  23 . 
     During operation the high-pressure port  39  produces a high oil pressure between the port plate surface  7  and the valve surface  6  at the location of the high-pressure port  39  and a diminishing pressure in the surrounding seal land, that is the surrounding area of the high-pressure port  39  that works as a seal between the high pressure and the pressure-less inside of the pump  12 . The high oil-pressure causes a force on the port plate  8  that is more or less completely counteracted by force in the direction of the port plate surface  7  caused by the high pressure in the high-pressure canal  38  in the cylindrical bearing surface  37  and the surrounding seal land. This requirement determines the area of the high-pressure canal  38  in the cylindrical bearing surface  37 . The rotating pump cylinders  26  and the rotating channels  31  cause a fluctuating pressure in the crossover area  41  as the pressure changes when a channel  31  changes from the connection with the high-pressure port  39  to the low-pressure port  40  or vice versa. This fluctuating pressure causes a fluctuating force on the port plate  8  and causes fluctuating gaps between the port plate surface  7  and the valve surface  6 , which leads to oil leakage that must be as little as possible as it reduces the efficiency of the pump  12 . In order to reduce these gaps the first actuator  33  and the second actuator  13  work on the port plate  8  in the direction of the port plate surface  7  and have a direction perpendicular on this surface. In this way, the forces of the first actuator  33  and the second actuator  13  help to close the possible gaps and reduce the deformations of the port plate  8 . The first actuator  33  and the second actuator  13  work at a distance from the third axis on the port plate  8 , which is equal or larger than the radius of crossover area  41 , which also reduces deformations of the port plate  8 . Preferably, the positions of the first actuator  33  and the second actuator  13  are such that the stroke of the plungers  1  and  18  in the cylinders  14  is equal or less than the stroke of the pump plungers  28  in the pump cylinders  26 , so that the same parts can be used. This means that at a maximum the distance of the first actuator  33  and the second actuator  13  to the first axis L can be twice the radius of the pump plungers  28  around the first axis L. 
     Placing the actuators at a distance from the third axis N that is greater than the radius of the pressure ports  39  and  40  has the additional advantage that the shaft  3  can extend through a hole in the port plate  8 . It is then possible to place several pumps in line with each other whereby the shafts  3  are connected. 
     The disclosed embodiment shows two sets of pump plungers  28  each working with a port plate  8 . This design has the advantage that a small angle between the first axis L and the second axis M obtains a pump of high capacity. It will be clear that the various measures taken to obtain a simple and efficient design are independent from this advantage. In addition, the design of the port plate  8  and the actuators is for instance also suitable for bent axis pumps that have a rotor with cylindrical holes whereby a port plate supports this rotor directly.