Patent Publication Number: US-7594802-B2

Title: Large angle sliding valve plate pump/motor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present application relates in general to hydraulic machines, and in particular to a yokeless pump/motor with a sliding valve plate. 
     2. Description of the Related Art 
     Pump/motors having sliding valve plates are well known in the industry. An advantage that such motors have over pump/motors employing a yoke and trunnion for displacement control is fewer moving parts. However, for reasons that will be explained below, sliding valve plate pump/motors are generally limited as to the maximum stroke angle possible. Inasmuch as maximum available efficiency and energy transfer are directly related to maximum stroke angle, a long-sought goal has been the development of sliding valve plate pump/motors capable of displacement angles greater than around 20 degrees. 
     Referring to  FIG. 1 , the back plate  100  of a known pump/motor is shown. The sliding surface  102  may be seen, whereon a valve plate is configured to ride. The lateral position of the valve plate  108 , as shown in  FIG. 2 , is controlled by the rocking pin  106 . Fluid feed apertures  104  provide high and low pressure fluid to the valve plate  108 . 
     The back side  108   b  of the valve plate  108  may be seen in  FIG. 2 . The valve plate  108  includes fluid feed channels  112  configured to receive fluid from the fluid feed apertures  104  of the back plate  100 , and to transmit that fluid to the piston barrel of the pump, via the kidney slots, or valve slots  116 , visible through the fluid feed channels  112 , and more easily visible in  FIG. 3 . Sealing lands  110  provide a seal between the sliding surface  102  of the back plate and the valve plate  108 . 
       FIG. 3  shows the top surface  108   a  of valve plate  108 . The top surface  108   a  includes the valve slots  116 , the annular sealing land  118 , and the barrel pin  103 . A cylinder barrel is configured to sit on the top surface  108   a  of the valve plate  108  and engage the barrel pin  103 . When operating in motor mode, cylinder ports in a bottom surface of the barrel receive high-pressure fluid from one of the valve slots  116  and, as the barrel rotates, discharge the fluid into the opposite side valve slot  116 , in a known manner. 
     The displacement of the pump/motor, and hence the degree of energy transfer, is determined by the angle of an axis of the barrel relative to an axis of a thrust plate and output shaft of the pump/motor. This is sometimes referred to as the stroke angle of the machine. The rocking pin  106 , shown in  FIG. 1 , is configured to engage the rocking bore  114  of  FIG. 2  for the purpose of adjusting the angle of the barrel. 
     By comparing the bottom surface  108   b  of the valve plate  108  with the back plate  100 , it may be seen that the travel of the valve plate  108  over the back plate  100  is limited by the length of the fluid feed channels  112 , and the length of the sliding surface  102 . It will be understood that in order for the pump/motor to function properly, the sliding surface  102  must be sufficiently broad such that when the valve plate is at either extreme end of its travel, the entire length of each of the sealing lands  110  is in contact with the sliding surface  102 . Additionally, when the valve plate  108  is at either extreme, the fluid feed apertures  104  must have access to the fluid feed channels  112 . Thus, it would seem a simple matter, in order to produce a pump/motor capable of greater displacement angles, to manufacture a valve plate having longer fluid feed channels  112 , and correspondingly broader sliding surfaces  102 . However, significant design problems arise when such modifications are attempted. 
     Reference is made to  FIGS. 4 and 5  to facilitate an explanation of the problems associated with changing the dimensions of the fluid feed channel  112 . 
     Where the value n is used in the figures and descriptive text to indicate an undefined quantity, it will be understood that any number of the indicated feature may be appropriate. For example, in the case of drive cylinders and pistons, as described below, an odd number, such as seven or nine, is generally employed, though machines utilizing other quantities are also known. 
       FIGS. 4 and 5  show diagrammatical cross-sections of a sliding valve plate pump/motor  133  of a type similar to that illustrated in  FIGS. 1-3 . More particularly,  FIG. 4  shows a cross-section taken in a plane X, indicated in  FIG. 5  at lines  4 - 4 , while  FIG. 5  is taken in a plane Y.  FIGS. 4 and 5  are diagrammatical in nature, and do not represent a functional machine. In particular, the cylindrical barrel  107  and semicircular kidney port  117  of  FIG. 5  are depicted as being flat or planar for the purpose of describing forces acting on the various components of the pump/motor. 
     The pump/motor  133  of  FIGS. 4 and 5  includes a back plate  101 , a valve plate  109 , and a barrel  107 . Pistons  111   a - 111   n  are positioned within respective cylinders  115   a - 115   n . Pressurized fluid is provided to the pump/motor  133  via fluid feed passage  121  and fluid feed aperture  105 . The pressurized fluid passes into the valve plate  109  via the fluid feed channel  113 , and from the valve plate  109  to the barrel  107  via the valve slot  117 . The fluid enters each of the cylinders  115  via cylinder ports  123   a - 123   n.    
     Pascal&#39;s law teaches that a pressurized fluid in an enclosed space exerts equal pressure on all surfaces of that space. Accordingly, with reference to  FIG. 4 , fluid entering cylinder  115   b  via cylinder port  123   b  will exert equal pressure on all surfaces within the cylinder  115   b . Assuming that the pump/motor  133  is functioning as a motor, and that the fluid entering the fluid feed passage  121  is at a drive pressure, the pressure of the fluid will drive the piston  111   b  in an upward direction. Since force acting on the piston  111   b  in an upward direction is not transmitted to the barrel  107 , there is substantially no upward force exerted on the barrel  107 , by fluid inside the cylinder  115   b . However, the pressurized fluid is also acting on the cylinder&#39;s shoulders  119  in a downward direction, pushing the barrel downward onto the valve plate  109 , and the valve plate  109  downward onto the back plate  101 . Inasmuch as  FIG. 4  shows no surfaces of the valve plate  109  on which the fluid is acting, there is a net downward force from the barrel  107 , through the valve plate  109 , to the back plate  101 , with respect to the surfaces shown in  FIG. 4 . This is sometimes referred to as the clamping force, and, in most known sliding valve plate systems, is the major force holding the barrel  107  and valve plate  109  against the back plate  101 . 
     Referring now to  FIG. 5 , it may be seen that, in the Y plane, there are several surfaces upon which pressurized fluid may act to generate upward force. For example, the barrel  107  has a surface  125  that is in contact with pressurized fluid, which affects the net clamping force of the cylinder barrel  107 . Additionally, valve plate  109  has interior surfaces  131  upon which pressurized fluid will exert upward pressure. Finally, there is a pressure gradient across the sealing lands  110  (see  FIG. 2 ) that imposes a net upward force on the valve plate  109 . 
     It will be understood that, in order for the pump/motor  133  to function properly, the total downward force acting on the valve plate  109  must exceed the total upward force, to prevent the valve plate  109  from lifting from its position. The sum of these forces can be referred to as the net lifting force. The net lifting force F acting on the valve plate  109  of the pump/motor  133  may be approximated as follows: 
     
       
         
           
             
               
                 
                   F 
                   = 
                   
                     
                       
                         ( 
                         
                           C 
                           + 
                           G 
                         
                         ) 
                       
                       ⁢ 
                       
                         in 
                         2 
                       
                       × 
                       
                         
                           lb 
                           . 
                         
                         
                           in 
                           2 
                         
                       
                     
                     - 
                     B 
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
             
           
         
       
     
     Where C is equal to the total area of the fluid feed channel  113  minus the total area of the valve slot  117 , G is equal to half the total area of the sealing lands  110 , B represents the net clamping force of the cylinder barrel  107 , and the pounds per square inch represents the fluid pressure in psi. 
     As long as the resulting value of F is a negative value, the pump/motor  133  will function properly. However, if the resulting figure is a positive value, the barrel  107  and the valve plate  109  will not remain properly seated, and pressurized fluid will escape from the system, preventing the pump/motor  133  from functioning. In simple terms, the net clamping force of the barrel  107  must be greater than the sum of forces acting on the sealing lands  110  and the horizontal component of the surfaces  131  of the valve plate. 
     Returning now to the question of lengthening the fluid feed channel in order to improve the maximum displacement capability of the pump/motor  133 , it may be seen that, as the dimension C Y , representing the length of the fluid feed channel  113 , increases, so too will the surface area  131  of the valve plate  109 . As the surface area  131  increases, the upward forces acting on that surface area will very quickly overcome the downward forces acting on surface areas  119  to cause the valve plate  109  to separate from the back plate  101 . A common response to this problem has been to increase the surface area of the shoulders  119  of the cylinders  115   a - 115   n . To do this, the cylinder ports  123  are narrowed in the dimension indicated at P x  of  FIG. 4 , thus broadening the shoulders  119 . However, when the dimension P x  is reduced, the width of the valve slot  117 , the fluid feed channel  113 , and the fluid feed aperture  105 , indicated in  FIG. 4  as dimensions S x , C x , and B x , respectively, must each be reduced in turn. This results in narrowing the fluid passages, especially the fluid passing through the fluid feed aperture  105 , and entering the cylinder ports  123 . As a result, the rate of fluid transfer into the cylinders  115   a - 115   n  is reduced, or choked, reducing the efficiency with which the motor transfers energy. Thus, in order to increase the maximum displacement angle of the pump/motor  133 , efficiency is sacrificed. 
     BRIEF SUMMARY OF THE INVENTION 
     According to an embodiment of the invention, a pump/motor is provided, including a back plate having first and second fluid ports configured to be differentially pressurized, a plurality of reaction plates rigidly coupled to the back plate, a valve plate slideably coupled to the back plate and having first and second fluid feed channels configured to receive fluid from the first and second fluid ports, and a plurality of hold-down pistons positioned in respective hold-down cylinders formed in the valve plate, each of the hold-down pistons configured to be biased, by pressurized fluid in the respective hold-down cylinder, against a surface of one of the reaction plates. 
     The pump/motor also includes a barrel, rotatably coupled to the valve plate and having a plurality of drive cylinders formed therein, a plurality of drive pistons, each having a first end positioned in a respective one of the plurality of drive cylinders, and a thrust plate having a surface configured to receive second ends of each of the plurality of drive pistons, the thrust plate coupled to an output shaft of the pump/motor. 
     According to another embodiment of the invention, a hydraulic machine is provided, including a back plate having a concave surface configured to slideably receive a valve plate thereon, first and second fluid ports formed in the concave surface and configured to transmit differentially pressurized fluid to the valve plate, and first and second reaction plates coupled to the back plate, each having a convex reaction surface substantially facing, and spaced a selected distance from, the concave surface of the back plate. 
     According to an embodiment of the invention, a method is provided, including the steps of coupling a first pressurized fluid source to a rotatable barrel via a first fluid feed channel in a valve plate and a first fluid port in a back plate, coupling a second pressurized fluid source to the rotatable barrel via a second fluid feed channel in the valve plate and a second fluid port in the back plate, biasing a first plurality of hold-down pistons against a first reaction plate coupled to the back plate, and biasing a second plurality of hold-down pistons against a second reaction plate coupled to the back plate. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         FIG. 1  shows a back plate of a pump/motor, according to known art. 
         FIG. 2  shows a back side of a valve plate of the pump/motor of  FIG. 1 . 
         FIG. 3  shows a front side of the valve plate of  FIG. 2 . 
         FIG. 4  is a diagrammatic representation of a portion of a pump/motor according to known art, in a first plane. 
         FIG. 5  is a diagrammatic representation of the portion of a pump/motor of  FIG. 4 , in a second plane, perpendicular to the plane of  FIG. 4 . 
         FIG. 6A  is an orthographic view of a portion of a pump/motor according to an embodiment of the invention. 
         FIG. 6B  is a sectional view of the portion of the pump/motor of  FIG. 6A . 
         FIG. 6C  is a sectional view of the portion of the pump/motor of  FIG. 6A . 
         FIG. 7A  is a top view of a valve plate of a pump/motor according to an embodiment of the invention. 
         FIG. 7B  is a bottom view of the valve plate of  FIG. 7A . 
         FIG. 8  shows a valve plate according to an embodiment of the invention, with internal fluid channels in phantom lines. 
         FIG. 9  is an orthographic view of a valve plate according to another embodiment of the invention. 
         FIG. 10  shows a sectional view of a portion of the valve plate of  FIG. 9 , a hold-down piston, and a reaction plate. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to the principles of the invention, means are provided for exerting a downward force on the valve plate, external to the fluid passages between the fluid feed and the cylinders of the barrel. 
     Features of an embodiment of the invention are illustrated with reference to  FIGS. 6A-8 . 
       FIG. 6A  shows a portion of a pump/motor  120 , with a segment cutaway to reveal pertinent details. The pump/motor  120  includes a back plate  122 , a valve plate  124 , a barrel  160  having a plurality of drive cylinders  169  and drive pistons  170 , of which only two are depicted, a thrust plate  168 , a main bearing  172 , and a drive bearing  174 . A drive shaft  176  is coupled to the thrust plate  168 . 
     The pump/motor  120  also includes reaction plates  130 , rigidly coupled to the back plate  122 . The valve plate  124  is provided with hold-down pistons  132 , shown generally in hidden lines, along two sides thereof, and configured to bear upward against reaction plates  130 . The reaction plates  130  include a convex reaction surface  153  substantially facing the concave surface  155  of the back plate  122 , and spaced a distance therefrom, the distance being selected to accommodate the valve plate  124  and hold-down pistons  132 . 
     An actuator and linkage  135  is provided to control the stroke angle of the valve plate  124  and barrel  160 . As the actuator piston extends, the valve plate  124  is compelled to slide along the surface of the back plate  122 , while the hold-down pistons  132  maintain a biasing force against the reaction plates, thereby holding the valve plate  124  firmly against the back plate. 
       FIGS. 6B and 6C  show the pump/motor  120  in a cross-section taken through the hold-down pistons  132  on one side of the valve plate  124 .  FIG. 6B  shows the pump/motor  120  with a stroke angle of zero, while  FIG. 6C  shows the pump/motor with a maximum stroke angle. With reference to  FIGS. 6A-6C , it can be seen that the reaction surfaces  153  of the reaction plates  130  and the convex surface  155  of the back plate  122  are in the form of sections of concentric cylinders. 
     It may be seen that the hold-down pistons  132  are each positioned in a respective hold-down cylinder  126 . Each of the hold-down cylinders  126  is in fluid communication with a fluid feed channel  134 , as will be described in more detail with reference to  FIGS. 7A-8 . 
     In operation, pressurized fluid is provided to selected hold-down cylinders  126  to act upon a bottom surface of each of the hold-down pistons  132 , driving them outward against the reaction plates  130 , and biasing the valve plate  124  firmly against the back plate  122 . The hold-down pistons are configured to slide along the stationary reaction plate, maintaining biasing pressure thereon. 
       FIGS. 7A and 7B  show front and back views, respectively, of the valve plate  124 . 
     The front surface  141  of the valve plate  124  includes valve plate apertures  127  and hold-down cylinders  126 . The back surface  143  of the valve plate  124  includes sealing lands  129  and fluid feed channels  134 . As most clearly shown in  FIG. 7A , the central axis of each of the hold-down cylinders  126  lies in a plane that is substantially perpendicular to a surface  151  configured to receive a rotatable cylinder barrel. In the embodiment of  FIG. 7A , the axes of three hold-down cylinders  126  on a left side of the valve plate  124  lie in a first plane, and the axes of three hold-down cylinders  126  on a right side of the valve plate  124  lie in a second plane, parallel to the first plane. 
     In a pump/motor according to known art, such a valve plate would separate from the back plate as soon as pressurized fluid was applied. However, the sum of the areas of the selected hold-down cylinders  126  is selected to compensate for the additional lifting force created by the added surface area  139 . Accordingly, the length of the fluid feed channels is not limited by the dimensions of shoulders within the cylinders of the barrel  160 , and thus, the maximum stroke angle is no longer limited by these constraints. 
     A new formula for approximating the net lifting force F acting to lift the valve plate and cylinder barrel may be expressed as follows: 
     
       
         
           
             
               
                 
                   F 
                   = 
                   
                     
                       
                         ( 
                         
                           C 
                           + 
                           G 
                           - 
                           H 
                         
                         ) 
                       
                       ⁢ 
                       
                         in 
                         2 
                       
                       × 
                       
                         
                           lb 
                           . 
                         
                         
                           in 
                           2 
                         
                       
                     
                     - 
                     B 
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
               
             
           
         
       
     
     Where H represents the total transverse sectional area of the selected hold-down cylinders  126 . 
       FIG. 8  shows porting channels for providing pressurized fluid to hold-down cylinders  126   a - 126   f , according to an embodiment of the invention. Cylinders  126   a  and  126   c  are coupled to the fluid feed channel  134   a  by hold-down feed lines  148 . Hold-down cylinder  126   b  is coupled to the fluid feed channel  134   b  by opposite side hold-down feed line  150 . Hold-down cylinders  126   d  and  126   f  are coupled to the right side fluid feed channel  134   b  by hold-down feed lines  152 , while cylinder  126   e  is coupled to the fluid feed channel  134   a  by opposite side hold-down feed line  154 . 
     It will be understood that, during operation of the pump/motor  120 , one of the fluid feed channels  134  will be coupled to a high-pressure fluid source, while the other will be coupled to a low-pressure fluid source. By providing the fluid coupling to the hold-down cylinders  126   a - 126   f  as previously described, high-pressure fluid is provided to two of the hold-down cylinders  126  adjacent to the fluid feed channel receiving high-pressure fluid, while one of the hold-down cylinders on the opposite side of the valve plate also receives high-pressure fluid. By the same token, low-pressure fluid is provided to two of the hold-down cylinders  126  adjacent to the fluid feed channel  134  receiving low-pressure fluid, while one of the hold-down cylinders  126  on the opposite side of the valve plate  124  also receives low-pressure fluid. In this way, balanced forces are maintained in the valve plate  124 . 
     According to another embodiment of the invention (not shown), hold-down cylinders  126   a - 126   c  are coupled to the fluid feed channel  134   a , while hold-down cylinders  126   d - 126   f  are coupled to the fluid feed channel  134   b.    
       FIGS. 9 and 10  illustrate an alternative embodiment of the invention. Valve plate  136  includes a plurality of hold-down pistons  138 ,  149 . Each of the hold-down pistons  138  is positioned in a respective hold-down cylinder  145 , while each of the hold down pistons  149  is positioned in a respective hold-down cylinder  147 . The hold down cylinders  145 ,  147  are formed in the valve plate  136  in a manner similar to that described with reference to  FIG. 6 . Each cylinder  145 ,  147  is in fluid communication with a fluid feed channel of the valve plate  136  in a manner similar to previously described embodiments. 
     Each of the hold-down pistons  138 ,  149  includes a fluid passage  142 , as shown in the hold-down piston  138  of  FIG. 10 . The fluid passage  142  is configured to permit fluid to pass from a cylinder end of the hold-down piston to a face  140  thereof. As can be seen in  FIGS. 9 and 10 , an outer surface of the face  140  of each of the hold-down pistons  138 ,  149  conforms to the convex surface  153  of the reaction plates  130 . 
     In operation, fluid passing through the fluid passage  142  of the hold-down pistons  138 , provides lubrication between the face  140  of the hold-down piston and the reaction plate  130 . 
     Referring to  FIG. 9 , it may be seen that the surface  151 , on which a barrel is configured to rotate, is off-center, with respect to the length of the valve plate. Inasmuch as the barrel contributes to the downward forces holding the valve plate  136  against a back plate, it will be recognized that the downward forces will be uneven across the length of the valve plate  136 . To compensate for this imbalance, hold-down cylinders  145  are larger in diameter than hold-down cylinders  147 , and hold-down pistons  138  are likewise larger in diameter than hold-down pistons  149 . Accordingly, the hold-down pistons  138  each exert more force against the reaction plates  130  than the hold-down pistons  149 , thereby balancing the downward forces across the valve plate  136 . 
     A sliding valve plate pump/motor manufactured according to the principals of the present invention is capable of a significantly higher maximum displacement angle than conventional pump/motors, without sacrificing efficiency of the motor due to excessive fluid choking. For example, according to an embodiment of the invention, a maximum stroke angle exceeding 25° is provided. According to another embodiment, a maximum stroke angle exceeding 40° is provided. 
     Referring to  FIG. 6B , the displacement, or stroke angle of the pump/motor  120  is shown to be at zero. Namely, the barrel, relative to the drive plate, is coaxial. In contrast,  FIG. 6C  shows the pump/motor  120  at a maximum stroke angle. According to the embodiment of  FIGS. 6A-6C , a maximum stroke angle is around 45° degrees. 
     A significant increase in efficiency is realized by increasing the maximum possible stroke angle beyond the nominal 20° available in previously known machines. In a machine with a high stroke angle, the angle of the drive pistons against the thrust plate is increased, which results in more of the force from the piston being directed in the direction of rotation, while less is directed normal to the thrust plate (compare  FIGS. 6B and 6C , noting the angles of the pistons  170 , relative to the thrust plate  168 ). 
     Additionally, because the cylinder barrel is not the only source of clamping force holding the valve plate against the back plate, the shoulders of the cylinders may have a smaller surface area, which in turn means that the cylinder ports may be larger. This results in a machine that can run at high efficiency at higher rpm&#39;s than previously known machines, because fluid is less restricted as it passes at high rates into and out of each cylinder. 
     Tests performed comparing a commercially available pump/motor similar to those described in the background section with a pump/motor having a maximum stroke angle exceeding 40° indicate that the prior art pump/motor achieved a 90% efficiency in a narrow range around 1000 rpm&#39;s, and only at stroke angles above about 60% of the maximum stroke angle. In contrast, the large angle pump/motor achieved a 90% efficiency in a range between around 500 and 2500 rpm&#39;s, and at stroke angles above about 40%-45% of the maximum stroke angle. 
     All of the above U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, are incorporated herein by reference, in their entirety. 
     From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.