Patent Publication Number: US-11644028-B2

Title: Control arrangement for variable displacement pump

Description:
TECHNICAL FIELD 
     The present disclosure relates to control arrangements for variable displacement pumps. 
     BACKGROUND 
     Variable displacement pumps typically include controllers that control pump displacement through one or more of pressure compensation, load sensing, electric displacement control, mechanical torque control, and/or electric torque control. The electric displacement control, mechanical torque control, and/or electric torque control systems are typically included within a servo bore of the pump housing designed specifically for the pump frame size. 
     SUMMARY 
     The present disclosure provides control arrangement for a variable displacement pump that overcome the deficiencies of the known pumps discussed above. 
     According to the present disclosure, a control arrangement for a variable displacement pump comprises a pressure control unit providing at least one of pressure compensation control or load sensing control, and a mechanical control unit providing at least one of mechanical torque control, electronic torque control, or electronic displacement control. The pressure control unit attaches to the variable displacement pump at a first interface and the mechanical control unit attaches to the variable displacement pump at a second interface that is different than the first interface. 
     According to the present disclosure, the mechanical control unit may comprise a housing including a pump mating surface configured to interface with the variable displacement pump at the second interface. The mechanical control unit includes a cam shaft disposed within the housing that has a distal end extending outward from the housing at the pump mating surface. The distal end of the cam shaft may be configured to engage a servo piston controlling displacement of the variable displacement pump when the mechanical control assembly is mounted to the variable displacement pump. 
     According to the present disclosure, the control arrangement may further comprise a sensor assembly configured to detect an angle of the cam shaft to determine pump displacement. 
     According to the present disclosure, the mechanical control unit comprises a rotary feedback assembly configured to monitor actuation of the servo piston controlling displacement of the variable displacement pump. The rotary feedback assembly controls actuation of the servo piston based at least on the monitored actuation. According to the present disclosure, the rotary feedback assembly comprises the cam shaft configured to engage the servo piston. A control spool controlling actuation of the servo piston is actuated at least in part due to rotary motion of the cam shaft. The rotary feedback assembly may further comprise a pressure setpoint adjuster the control spool may control actuation of the servo piston based at least in part on rotary motion of the cam shaft and a pressure setpoint defined by the pressure setpoint adjuster. 
     According to the present disclosure, a control arrangement for a variable displacement pump comprises a pressure control unit providing at least one of pressure compensation control or load sensing control, and a mechanical control unit providing at least one of mechanical torque control, electronic torque control, or electronic displacement control. The pressure control unit is configured to attach to the variable displacement pump at a first mounting surface and the mechanical control unit is configured to attach to the variable displacement pump at a second mounting surface formed on an opposite side of the variable displacement pump from the first mounting surface. 
     According to the present disclosure, the mechanical control unit may comprise a housing including a pump mating surface configured to interface with the variable displacement pump at the second mounting surface, and a cam shaft disposed within the housing and having a distal end extending outward from the housing at the pump mating surface. The distal end of the cam shaft is configured to engage a servo piston controlling displacement of the variable displacement pump when the mechanical control assembly is mounted to the variable displacement pump. 
     According to the present disclosure, the control arrangement may further comprise a sensor assembly configured to detect an angle of the cam shaft to determine pump displacement. 
     According to the present disclosure, the mechanical control unit may comprise a rotary feedback assembly configured to monitor actuation of a servo piston controlling displacement of the variable displacement pump and to control actuation of the servo piston based at least on the monitored actuation. According to the present disclosure, the rotary feedback assembly comprises the cam shaft configured to engage the servo piston. A control spool controlling actuation of the servo piston is actuated at least in part due to rotary motion of the cam shaft. The rotary feedback assembly may further comprise a pressure setpoint adjuster the control spool may control actuation of the servo piston based at least in part on rotary motion of the cam shaft and a pressure setpoint defined by the pressure setpoint adjuster. 
     According to the present disclosure, the rotary feedback assembly may further comprise a rocker arm rotatably driven by the cam shaft, and a feedback pin carried by the cam shaft and in contact with the rocker arm, the feedback pin being biased against the rocker arm by a working pressure of the variable displacement pump. The control spool may control actuation of the servo piston based at least in part on rotary motion of the cam shaft, a moment on the rocker arm due to the feedback pin, and a pressure setpoint defined by the pressure setpoint adjuster. 
     According to the present disclosure, a control arrangement for a variable displacement pump comprises a mechanical control unit providing at least one of mechanical torque control, electronic torque control, or electronic displacement control. The mechanical control unit comprises a housing including a pump mating surface configured to interface with the variable displacement pump, and a cam shaft disposed within the housing and having a distal end extending outward from the housing at the pump mating surface. The distal end of the cam shaft is configured to engage a servo piston controlling displacement of the variable displacement pump when the mechanical control assembly is mounted to the variable displacement pump. 
     According to the present disclosure, the control arrangement may further comprise a sensor assembly configured to detect an angle of the cam shaft to determine pump displacement. 
     According to the present disclosure, the mechanical control unit comprises a rotary feedback assembly configured to monitor actuation of a servo piston through the cam shaft and to control displacement of the variable displacement pump through actuation of the servo piston based at least on rotary motion of the cam shaft. The rotary feedback assembly may control movement of a control spool based at least in part on rotary motion of the cam shaft, the control spool controlling actuation of the servo piston. The rotary feedback assembly may further comprise a pressure setpoint adjuster controlling movement of the control spool and the control spool may control actuation of the servo piston based at least in part on rotary motion of the cam shaft and a pressure setpoint defined by the pressure setpoint adjuster. According to the present disclosure, the rotary feedback assembly may further comprise a rocker arm rotatably driven by the cam shaft, and a feedback pin carried by the cam shaft and in contact with the rocker arm, the feedback pin being biased against the rocker arm by a working pressure of the variable displacement pump. The control spool may control actuation of the servo piston based at least in part on rotary motion of the cam shaft, a moment on the rocker arm due to the feedback pin, and a pressure setpoint defined by the pressure setpoint adjuster. 
     These and other objects, features and advantages of the present disclosure will become apparent in light of the detailed description of embodiments thereof, as illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a top, rear, right-hand side perspective view of a variable displacement pump including a control arrangement according to the present disclosure; 
         FIG.  2    is a partially exploded top, front, right-hand side perspective view of the variable displacement pump and control arrangement of  FIG.  1   ; 
         FIG.  3    a schematic diagram of the control arrangement of  FIG.  1    in a first configuration; 
         FIG.  4    is an internal perspective view of a mechanical control unit of the control arrangement of  FIG.  1    in the first configuration; 
         FIG.  5    a schematic diagram of the control arrangement of  FIG.  1    in a second configuration; 
         FIG.  6    a schematic diagram of the control arrangement of  FIG.  1    in a third configuration; 
         FIG.  7    is an internal perspective view of a mechanical control unit of the control arrangement of  FIG.  1    in the third configuration; 
         FIG.  8    is a partial cross sectional view of the mechanical control unit of  FIG.  7   ; 
         FIG.  9    a schematic diagram of the control arrangement of  FIG.  1    in a fourth configuration; 
         FIG.  10    is a partial cross sectional view of the mechanical control unit of  FIG.  9   ; and 
         FIG.  11    is a partially exploded top, front, right-hand side perspective view of a mechanical control unit of the control arrangement of  FIG.  1    with a sensor assembly. 
     
    
    
     DETAILED DESCRIPTION 
     Before the various embodiments are described in further detail, it is to be understood that the invention is not limited to the particular embodiments described. It will be understood by one of ordinary skill in the art that the control arrangements and systems described herein may be adapted and modified as is appropriate for the application being addressed and that the control arrangements and systems described herein may be employed in other suitable applications, and that such other additions and modifications will not depart from the scope thereof. 
     In the drawings, like reference numerals refer to like features of the systems of the present application. Accordingly, although certain descriptions may refer only to certain figures and reference numerals, it should be understood that such descriptions might be equally applicable to like reference numerals in other figures. 
     Referring to  FIG.  1   , a control arrangement  10  for a variable displacement pump  12  according to the present disclosure is shown. The control arrangement  10  includes a pressure control unit  14  and a mechanical control unit  16 , each mounted separately on a housing  18  of the variable displacement pump  12  by bolts  17  or the like. The variable displacement pump  12  is an open circuit variable displacement pump that includes a cylinder block having plurality of pistons and a swashplate controlling displacement of the plurality of pistons, with an angle of the swashplate, and therefore the displacement of the pump, being controlled by the control arrangement  10 . The pressure control unit  14  provides pressure control for the variable displacement pump  12 , for example, through a pressure compensator, load sensing, an electric pressure compensator, or combinations thereof. The mechanical control unit  16  provides rotary feedback control for the variable displacement pump  12 , for example, through Electric Displacement Control (EDC), Mechanical Torque Control (MTC), or Electric Torque Control (ETC). 
     Referring to  FIG.  2   , the pressure control unit  14  includes a pressure control unit housing  19  with a pump mating surface  20  that includes pressure ports  22  formed therethrough forming pressure inlets and/or outlets to the pressure control unit  14 . The pump mating surface  20  is configured to engage a corresponding pressure control mounting surface  24  formed on the housing  18  of the variable displacement pump  12 . The pressure control mounting surface  24  includes pressure ports corresponding to the pressure ports  22  of the pump mating surface  20 , which interact with the pressure ports  22  of the pump mating surface  20  when the pressure control unit  14  is mounted to the housing  18 . A seal carrier  26  may be provided between the pump mating surface  20  and the pressure control mounting surface  24  to provide sealing around the pressure ports  22 . As discussed above, the pressure control unit  14  may provide pressure control for the variable displacement pump  12  through a pressure compensator, load sensing, an electric pressure compensator, or combinations thereof and pump mating surface  20  has the same configuration regardless of which control is implemented. 
     The mechanical control unit  16  includes a mechanical control unit housing  28  with a pump mating surface  30  configured to engage a corresponding mechanical control mounting surface  32  formed on the housing  18  of the variable displacement pump  12 . The mechanical control unit  16  comprises a transverse bore  33  extending through the mechanical control unit housing  28  and opening at one end at the pump mating surface  30 . A cam shaft  34  is positioned within the transverse bore  33  and has a distal end portion  36  extending outward from the mechanical control unit housing  28  through the opening at the pump mating surface  30 . The other end of the transverse bore  33  opposite the pump mating surface  30  may be closed by a removable cover  37 . In addition to the opening of the transverse bore  33  for the distal end portion  36  of cam shaft  34 , the pump mating surface  30  also includes pressure ports formed therethrough forming pressure inlets and/or outlets to the mechanical control unit  16 . 
     The mechanical control mounting surface  32  of the housing  18  includes a cam shaft opening  38  configured to receive the distal end portion  36  of the cam shaft  34  when the mechanical control unit  16  is mounted to the housing  18 . The mechanical control mounting surface  32  also includes pressure ports  40  corresponding to the pressure ports of the pump mating surface  30 , which interact with the pressure ports of the pump mating surface  30  when the mechanical control unit  16  is mounted to the housing  18 . A seal carrier  42  may be provided between the pump mating surface  30  and the mechanical control mounting surface  32  to provide sealing around the pressure ports. While the seal carrier  42  may have a different seal layout than the seal carrier  26 , the pressure ports of the pressure control unit  14  and the pressure ports of the mechanical control unit  16  may also be provided on the respective pump mating surfaces in the same layout to allow for the use of a common seal carrier for both the seal carrier  26  and the seal carrier  42 . As discussed above, the mechanical control unit  16  may provide rotary feedback control for the variable displacement pump  12  EDC, MTC, or ETC control techniques and pump mating surface  30  and distal end  36  of cam shaft  34  have the same configuration regardless of which control is implemented. 
     Referring to  FIG.  3   , a schematic view of a first configuration of the control arrangement  10  for controlling variable displacement pump  12  through a servo piston  43  is shown. As shown, the servo piston  43  is a single acting hydraulic cylinder, where the supply of hydraulic fluid to chamber  44  controls movement of the servo piston  43  in one direction and a spring  45  controls movement of the servo piston  43  in the opposite direction. The servo piston  43  controls the angle of the swashplate of the variable displacement pump  12  and, therefore, the displacement of the pump. As shown, the mechanical control unit  16  is in an MTC configuration and the pressure control unit  14  includes a pressure compensator control portion  46  and a load sensing control portion  48 . 
     The pressure compensator portion  46  operates in the same manner as other known pressure compensation controllers by using pump outlet pressure to control the position of the servo piston  43 . Specifically, the pressure compensator portion  46  receives pump outlet pressure from the variable displacement pump  12  via pressure input  50 , which is provided through one of the pressure ports  22 , shown in  FIG.  2   , of the pressure control unit  14 . When the pump outlet pressure exceeds a predetermined maximum working pressure, a control spool  52  of the pressure compensator portion  46  actuates to a servo pressure-increasing position, thereby providing hydraulic fluid to increase the pressure in chamber  44 , which moves the servo piston  43  to increase the displacement of the variable displacement pump  12 . 
     The load sensing portion  48  also operates in the same manner as other known load sensing controllers by using pump outlet pressure and a load feedback pressure to control the position of the servo piston  43 . Specifically, the load sensing portion  48  receives pump outlet pressure from the variable displacement pump  12  via pressure input  54  and load feedback pressure via pressure input  56 , which are provided through pressure ports  22 , shown in  FIG.  2   , of the pressure control unit  14 . The load sensing portion  48  monitors and compares pressure values for the pump outlet pressure and load feedback pressure. When the pump outlet pressure is not equal to a sum of the load sensing feedback pressure and a load sensing set value, a control spool  58  of the load sensing portion  48  moves to increase or decrease the pressure in chamber  44 , which moves the servo piston  43  to alter the displacement of the variable displacement pump  12  until the pump outlet pressure is equal to the sum of the load feedback pressure and the load sensing set value. 
     The mechanical control unit  16  includes a rotary feedback assembly  60  controlling actuation of a control spool  62  using rotary input from cam shaft  34  and pump outlet pressure provided via pressure input  64 , which is provided through one of the pressure ports of the mechanical control unit  16 . Actuation of the control spool  62  increases or decreases the pressure in chamber  44 , which moves the servo piston  43  to alter the displacement of the variable displacement pump  12  until a torque control setpoint is reached. 
     Referring to  FIG.  4   , the rotary feedback assembly  60  includes the cam shaft  34 , a feedback pin  65  disposed within a bore  66  formed in a head  67  of the cam shaft  34 , and a rocker arm  68  that pivots about a pivot point  69 . The cam shaft  34  is rotatable in the transverse bore  33  and cam shaft opening  38  of pump housing  18 , shown in  FIG.  2   . The cam shaft opening  38  of the pump housing  18 , shown in  FIG.  2   , intersects a servo piston bore for servo piston  43 . The servo piston  43  includes a tapered portion  70  at the intersection between the servo piston bore and the cam shaft opening  38 . The cam shaft  34  includes an eccentric shoulder  71  that slides on the tapered portion  70  of the servo piston  43 , such that the cam shaft  34  is driven in rotary motion in response to movement of the servo piston  43 . A plunger  72  biased by a spring  73  engages the cam shaft  34  to maintain contact between the cam shaft  34  and servo piston  43 . 
     The feedback pin  65  in the head  67  of cam shaft  34  acts against the rocker arm  68  in response to system pressure, i.e., pump outlet pressure provided via pressure input  64 , shown in  FIG.  3   . Specifically, the system pressure acts on the feedback pin  65  against rocker arm  68 . As the servo piston  43  strokes and pump displacement gets smaller, cam shaft  34  rotates due to movement of the tapered portion  70  and a moment arm between feedback pin  65  and the pivot point  69  of rocker arm  68  gets smaller. Conversely, pump displacement at maximum will make the moment arm between feedback pin  65  and pivot point  69  of rocker arm  68  the largest. The moveable control spool  62  is balanced between the rocker arm  68  on one end and an adjustable spring  74  on the other end, which is adjustable via a mechanical adjuster  76 . The control spool  62  and adjustable spring  74  are concentrically located at a constant distance from pivot point  69  of rocker arm  68 . When the moment of the feedback pin  65  on the rocker arm  68  becomes larger than a moment from adjustable spring  74 , the control spool  62  moves to communicate hydraulic oil at system pressure to chamber  44  of servo piston  43 , shown in  FIG.  3   . When the moment of the feedback pin  65  the on rocker arm  68  is smaller than the moment from adjustable spring  74  on the rocker arm  68 , the control spool  62  moves to vent servo pressure oil in chamber  44  of the servo piston  43  to pump case  18 , shown in  FIG.  2   . The MTC pressure set point is reached when the moment of the feedback pin  65  on the rocker arm  68  and the moment of the adjustable spring  74  on the rocker arm  68  are balanced and control spool  62  is centered in a metering position. 
     Referring to  FIG.  5   , wherein like numerals represent like elements, a schematic view of a second configuration of the control arrangement  10  for controlling variable displacement pump  12  through servo piston  43  is shown. In the second configuration, the mechanical control unit  16  is in an ETC configuration rather than an MTC configuration. The control arrangement  10  is, otherwise, identical to the control arrangement  10  shown in  FIG.  3    and, therefore, the details of the pressure control unit  14  including pressure compensator control portion  46  and load sensing control portion  48  will not be discussed again in detail. The mechanical control unit  16  includes a rotary feedback assembly  160  controlling actuation of control spool  62  using rotary input from cam shaft  34  and pump outlet pressure provided via pressure input  64 , which is provided through one of the pressure ports of the mechanical control unit  16 . The only difference between the rotary feedback assembly  160  and the rotary feedback assembly  60  shown in  FIGS.  3  and  4    is that the rotary feedback assembly  160  includes an electronic adjuster in place of the mechanical adjuster  76 , shown in  FIG.  4   , for adjusting the adjustable spring  74 . The rotary feedback assembly  160  is, otherwise, identical in structure and operation to the rotary feedback assembly  60  shown in  FIGS.  3  and  4    for controlling actuation of control spool  62  to increase and decrease pressure in chamber  44  to move servo piston  43  until the torque control setpoint is reached and, therefore, the details of the rotary feedback assembly  160  will not be discussed again in detail. 
     Referring to  FIG.  6   , wherein like numerals represent like elements, a schematic view of a third configuration of the control arrangement  10  for controlling variable displacement pump  12  through servo piston  43  is shown. In the third configuration, the mechanical control unit  16  is in a first EDC configuration rather than an MTC or ETC configuration. The pressure control unit  14 , including pressure compensator control portion  46  and load sensing control portion  48 , of the control arrangement  10  is identical to the pressure control unit  14  shown in  FIG.  3    and, therefore, the details of the pressure control unit  14  will not be discussed again in detail. The mechanical control unit  16  includes a rotary feedback assembly  260  controlling actuation of control spool  62  using rotary input from cam shaft  34  and an electronically set control setpoint. 
     Referring to  FIG.  7   , the rotary feedback assembly  260  includes the cam shaft  34 , a feedback pin  265  disposed within a bore  266  formed in a head  267  of the cam shaft  34 , and a rocker arm  268  that pivots about a pivot point  269 . The rotary feedback assembly  260  also includes a spring  278  disposed within bore  266  adjacent the feedback pin  265  and providing a constant load on the feedback pin  265  against the rocker arm  268 . The rotary feedback assembly  260  includes a solenoid actuator  280  driving an actuator rod  282  positioned between the solenoid actuator  280  and the rocker arm  268 . 
     The cam shaft  34  is rotatable in the transverse bore  33  and cam shaft opening  38  of pump housing  18 , shown in  FIG.  2   . The cam shaft opening  38  of the pump housing  18 , shown in  FIG.  2   , intersects a servo piston bore for servo piston  43 . The servo piston  43  includes tapered portion  70  at the intersection between the servo piston bore and the cam shaft opening  38 . The cam shaft  34  includes eccentric shoulder  71  that slides on the tapered portion  70  of the servo piston  43 , such that the cam shaft  34  is driven in rotary motion in response to movement of the servo piston  43 . Plunger  72  biased by spring  73  engages the cam shaft  34  to maintain contact between the cam shaft  34  and servo piston  43 . Force from the solenoid actuator  280  is exerted on rocker arm  268  via the actuator rod  282  to shift a control set point maintained by adjustable spring  74 . 
     Referring to  FIG.  8   , if a moment generated by the solenoid actuator  280  on rocker arm  268  acts in the same direction as a moment on the rocker arm  268  from the feedback pin  265 , the control set point, which is the desired outlet flow at a given shaft speed, decreases in response to actuation of the solenoid actuator  280 . The control set point is reached when the moment from the feedback pin  265  on rocker arm  268 , the moment from adjustable spring  74  on rocker arm  268 , and the moment from solenoid actuator  280  on rocker arm  268  are balanced and control spool  62  is centered in metering position. 
     Referring to  FIG.  9   , wherein like numerals represent like elements, a schematic view of a fourth configuration of the control arrangement  10  for controlling variable displacement pump  12  through servo piston  43  is shown. In the fourth configuration, the mechanical control unit  16  is in a second EDC configuration similar to the first EDC configuration, rather than an MTC or ETC configuration. The pressure control unit  14 , including pressure compensator control portion  46  and load sensing control portion  48 , of the control arrangement  10  is identical to the pressure control unit  14  shown in  FIG.  3    and, therefore, the details of the pressure control unit  14  will not be discussed again in detail. The mechanical control unit  16  includes a rotary feedback assembly  360  controlling actuation of control spool  62  using rotary input from cam shaft  34  and an electronically set control setpoint. 
     With reference back to  FIG.  7   , the rotary feedback assembly  360  includes the same cam shaft  34 , feedback pin  265  and spring  278  disposed within bore  266  formed in head  267  of the cam shaft  34 , and rocker arm  268  that pivots about pivot point  269 . The spring  278  disposed within bore  266  adjacent the feedback pin  265  provides the constant load on the feedback pin  265  against the rocker arm  268 . The cam shaft  34  is rotatable in the transverse bore  33  and cam shaft opening  38  of pump housing  18 , shown in  FIG.  2   . The cam shaft opening  38  of the pump housing  18 , shown in  FIG.  2   , intersects a servo piston bore for servo piston  43 . The servo piston  43  includes tapered portion  70  at the intersection between the servo piston bore and the cam shaft opening  38 . The cam shaft  34  includes eccentric shoulder  71  that slides on the tapered portion  70  of the servo piston  43 , such that the cam shaft  34  is driven in rotary motion in response to movement of the servo piston  43 . Plunger  72  biased by spring  73  engages the cam shaft  34  to maintain contact between the cam shaft  34  and servo piston  43 . 
     Referring to  FIG.  10   , the rotary feedback assembly  360  includes a solenoid actuator  380  driving an actuator rod  382  positioned between the solenoid actuator  380  and the rocker arm  268  and force from the solenoid actuator  380  is exerted on rocker arm  268  via the actuator rod  282  to shift a control set point maintained by adjustable spring  74 . However, in the configuration shown in  FIG.  10   , the moment generated by the solenoid actuator  380  on rocker arm  268  acts in the same direction as the moment on the rocker arm  268  from the adjustable spring  74 , rather than the same direction as the moment from the feedback pin  265  as in  FIG.  8   . In this configuration, the control set point, which is the desired outlet flow at a given shaft speed, increases in response to actuation of the solenoid actuator  380 . The control set point is again reached when the moment from the feedback pin  265  on rocker arm  268 , the moment from adjustable spring  74  on rocker arm  268 , and the moment from solenoid actuator  380  on rocker arm  268  are balanced and control spool  62  is centered in metering position. 
     Referring to  FIG.  11   , the mechanical control unit  14  may include a sensor assembly  84  that is bolted on to the mechanical control unit housing  28  in place of the removable cover  37 , shown in  FIG.  2   . The sensor assembly  84  includes an angle sensor  86  disposed within a cover  87  that bolts to the housing  28 . The angle sensor  86  detects an angle of the cam shaft  34  to determine pump displacement. For instance, the angle sensor  86  may be a magnetic sensor, such as Hall effect sensor or the like, that detects movement of a magnet carrier  88  disposed on an end of the cam shaft  34 . While the angle sensor  86  is described in connection with the mechanical control unit  14 , a variable displacement pump that does not include MTC, ETC or EDC control may still include the angle sensor  86  by providing an adapter cover with the cam shaft  34  solely for the purpose of providing the cam shaft angle for determining pump displacement. 
     The control arrangement  10  of the present disclosure advantageously provides a control-to-pump interface between the pressure control unit  14  and the pump  12  that requires only ports for hydraulic connections and advantageously provides a control-to-pump interface between the mechanical control unit  16  and the pump  12  that requires only ports for hydraulic connections and a single bore for cam shaft  34  of the rotary feedback assembly. Additionally, the distal end portion  36  of the cam shaft  34  that interfaces with servo piston  43  of the variable displacement pump  12  is advantageously the same for EDC, MTC, and ETC control. 
     Thus, the control arrangement  10  of the present disclosure may advantageously be used on multiple frame sizes of open circuit variable displacement pumps and product families by providing identical control-to-pump interfaces on each frame size for both the pressure control unit  14  and the mechanical control unit  16 . This advantageously reduces the cost for the pumps by reducing variation of the pump controls as well as significantly reducing the total number of components. 
     The mechanical control unit  14  also advantageously implements the same concept of a rotary feedback system form EDC, MTC, and ETC control, thereby allowing a majority of the components (e.g. control housing, control spool, adjustable spring, and rocker arm) to be interchangeable regardless of the control type. This substantially reduces variation of large and more expensive components such as pump housings and swashplates across product families of variable displacement pumps. Furthermore, many other smaller components, such as the sensor assembly  84  and removable cover  37 , may also advantageously be common for all frame sizes. 
     Additionally, separation of pressure controls in the pressure control unit  14  from the EDC, MTC, or ETC controls in the mechanical control unit  16  advantageously allows for significantly lower total number of components &amp; control sub-assemblies for entire a product family, thereby reducing cost and making the product more attractive to customers. 
     While the principles of the present disclosure have been described herein, it is to be understood by those skilled in the art that this description is made only by way of example and not as a limitation as to the scope of the disclosure. Other embodiments are contemplated within the scope of the present disclosure in addition to the exemplary embodiments shown and described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present disclosure.