Patent Publication Number: US-7909414-B2

Title: Hydraulic circuit for spring applied-hydraulically released brake and hydraulic motor

Description:
BACKGROUND OF THE INVENTION 
     When a hydraulic system failure occurs or when the engine of the prime mover is not running to drive the pump for a brake system having spring applied-pressure released brakes, the brakes are spring applied by the loss of hydraulic pressure. When such a loss of pressure occurs, a vehicle of this type cannot be towed to a suitable repair station until the brakes are again pressurized, thus releasing the brakes. 
     Manual pumps are used to pressurize and release the brakes. These known manual pumps typically include at least three ports: a pressure port, a brake port, and a tank port. In these known manual pumps, when one is manually pumping to pressurize the brakes, the pressure port is typically blocked and hydraulic fluid is drawn from the tank to pressurize the brake. One known manual pump includes more than one rod, i.e. a first rod that acts as a piston for the manual pump and a second rod that acts as spool of a valve to block flow from the pressure port to the brake port. Another known manual pump includes valves in combination with rods. The valves require the operator to turn or adjust the valves to block flow from the pressure port to the brake port. Both of these known manual pumps require a complex manifold structure to provide the proper fluid communication between the ports in different operating modes and also require operator training to know which rods to push or which valves to turn. 
     Many vehicles that employ spring applied-pressure released brakes also employ hydraulic motors to drive the vehicle. When the engine is not running to drive the pump for the hydraulic motors, typically a shut-off valve is disposed in the hydraulic circuit to block the flow of hydraulic fluid through the hydraulic motors thus prohibiting rotation of the hydraulic motor and thus the vehicle. These hydraulic motors can also be used to perform dynamic braking to stop the vehicle. Dynamic braking is also performed by blocking flow through the motors so that the motors cannot rotate. Release valves or counter-balance valves can be disposed in the circuit to dump the flow of hydraulic fluid during dynamic braking so that the hydraulic motors do not come to an abrupt halt. 
     As stated above, when the engine is not running or a hydraulic system failure has occurred the flow of hydraulic fluid through the motors stops and, therefore, blocks, or greatly inhibits, rotation of the hydraulic motors. When the vehicle that includes these hydraulic motors needs to be moved, the shut-off valve can be short circuited to allow for the movement of fluid through the hydraulic motors. Typically, a needle valve is located in the hydraulic circuit remote from the aforementioned manual pump used to pressurize the brakes. Accordingly, to move a vehicle that includes spring applied-pressure released brakes and hydraulic motors that are blocked upon loss of pressure, one must pressurize the brakes using a manual pump and move to another location on the vehicle to open a needle valve to short circuit the shut-off valve that blocks flow through the motors. 
     SUMMARY OF THE INVENTION 
     According to one embodiment, a hydraulic circuit includes a spring applied-pressure release brake, a hydraulic motor, and a control in fluid communication with the brake and the motor. The control is operative between a first position and second position. When the control is in the first position and in response to a pressure loss upstream of the motor, movement of the fluid through the motor is inhibited such that rotation of an output shaft of the motor is also inhibited. When the control is in the first position and in response to a pressure loss upstream of the brake, the brake is spring applied. When the control is in the second position the brake communicates with an auxiliary pressure source for selectively supplying pressure to the brake. When the control is in the second position and in response to pressure being applied upstream of the control, the control is automatically reset to the first position. 
     In another embodiment, a hydraulic circuit includes a spring applied-pressure released brake, a hydraulic motor, and a control in fluid communication with the brake and the motor. The control includes a valve operative between a first position and a second position. When in the first position, the brake receives pressure from a first brake pressure source. When in the second position the brake receives pressure from a second pressure source and the motor is short circuited in relation to a motor pressure source. In response. to a pressure loss in the circuit while in the first position, the brake is in communication with the motor. 
     A prime mover including a hydraulic motor, a bypass conduit in communication with the motor, a spring applied-pressure released brake, a first pressure source, a second pressure source and a control in fluid communication with the bypass conduit, the brake, the first pressure source and the second pressure source is disclosed. The control operates between a first position and a second position. When the control is in the first position the control couples the brake to the first pressure source and the bypass conduit is blocked in the control. When in the second position the control couples the brake to the second pressure source and the second pressure source draws fluid from upstream the first pressure source. Also when in the second position, the bypass conduit communicates with a bypass outlet of the control. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a schematic drawing of a hydraulic circuit for spring applied-pressure released brakes and hydraulic motors. 
         FIG. 2  is a cross-sectional view of a control for use in the hydraulic circuit depicted in  FIG. 1  with portions of the hydraulic circuit schematically depicted. The control is shown in a first operating position. 
         FIG. 3  is cross-sectional view of the control of  FIG. 2  shown in a second operating position. 
         FIG. 4  is a cross-sectional view taken 90° from the cross-sectional view shown in  FIG. 3  where the control is shown in the second operating position and an inner rod of the control is extended to depict a pumping action. 
         FIG. 5  is a perspective view of the control depicted in  FIGS. 2-4 . 
         FIG. 6  is an alternative embodiment of a hydraulic circuit for a spring applied-pressure released brake and a hydraulic motor. 
         FIG. 7  is another alternative embodiment of a hydraulic circuit for a spring applied-pressure released brake and a hydraulic motor. 
         FIG. 8  is a perspective view of a control for use with the hydraulic circuit depicted in  FIG. 7 . 
         FIG. 9  is a cross-sectional view of the control depicted in  FIG. 8 , the control being shown in a first operating position. 
         FIG. 10  is a cross-sectional view taken  900  from the cross-sectional view shown in  FIG. 9  where the control was shown in the first operating position. 
         FIG. 11  is a cross-sectional view similar to that depicted in  FIG. 9  where the control is shown in the second operating position. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 1 , a hydraulic circuit is shown including first and second hydraulic motors  10  and  12 , respectively, first and second spring applied-pressure released brakes  14  and  16 , respectively and a control  20  to release the brakes  14  and  16  and the motors  10  and  12  so that a prime mover that includes the hydraulic circuit can be moved without power. Each motor  10  and  12  drives a wheel (not shown) in a manner that is known. Each brake  14  and  16  stops rotation of an output shaft of the respective motor, and thus the respective wheel, in a manner that is known. As will be explained below, use of the control  20  allows a simple release of both brakes  14  and  16  and a short circuit of the hydraulic motors  10  and  12 . This circuit also allows for the automatic reset of the control  20  with the application of hydraulic pressure to either the first motor  10  or the second motor  12  or upon manual actuation, which will be described in more detail below. In this circuit, the brakes  14  and  16  can apply when both wheel circuits have no pressure and release when either wheel circuit  26  and/or  28  has pressure. Also, this hydraulic circuit allows the operator of the prime mover to dismount the prime mover while it remains running. The hydraulic circuit is described as including two motors and two hydraulic brakes; however, a fewer or greater number of motors and/or brakes can be provided without departing from the scope of the invention. 
     With continued reference to  FIG. 1 , a first adjustable flow rate reversible pump  22  delivers pressure to drive the first motor  10 . Similarly, a second adjustable flow rate reversible pump  24  delivers pressure to the second motor  12 . The first motor  10  and the first pump  22  can be described as operating within a first wheel circuit  26  and the second motor  12  and the second pump  24  can be described as working in a second wheel circuit  28 . In the depicted embodiment, the wheel circuits  26  and  28  have the same configuration. 
     In the first wheel circuit  26 , a first shuttle valve  32  communicates with the first motor  10  and the first pump  22 . The position of the first shuttle valve  32 , e.g. the position of a check ball disposed in the shuttle valve, is dependent upon the direction of flow through the first motor  10 . Similarly, a second shuttle valve  34  is disposed in the second wheel circuit  28  and communicates with the second motor  12  and the second pump  24  in a manner similar to the first shuttle valve  32 . A first passage  36 , which can be referred to as part of a bypass conduit, connects the first shuttle valve  32  to a third shuttle valve  38 . Similarly, a second passage  42 , which can also be referred to as part of the bypass conduit, connects the second shuttle valve  32  to the third shuttle valve  38 . The third shuttle valve  38  precludes direct communication between the first wheel circuit  26  and the second wheel circuit  28  so that a short circuit does not develop between the first motor  10  and the second motor  12 . The operating position of the shuttle valve  38  is a function of the pressure differential between the first wheel circuit  26  and the second wheel circuit  28 , which can be a function of the operating pressure of the function to the shuttle valves can be used instead of the shuttle valves that are disclosed. 
     The first wheel circuit  26  and the second wheel circuit  28  each communicate with the control  20  through the shuttle valve  38  and a conduit  44 . The control  20  includes a valve  50  that operates between a first operating position  50   a  and a second operating position  50   b . In the first operating position, the pumps  22  and  24 , depending on which pump is operating at a higher pressure in its respective wheel circuit, delivers fluid pressure to each of the brakes  14  and  16  through the valve  50 . If the hydraulic circuit were to experience a pressure loss, for example when the engine of the prime mover is not running to drive either pump  22  or  24  or when one of the lines or components in the hydraulic circuit have lost pressure, the springs located in the brakes  14  and  16  would overcome any hydraulic fluid located in the pressurized chamber of the brake. Accordingly, upon pressure loss fluid would move through the system from the brakes  14  and  16  through the control  20 , which contains the valve  50 , and towards one of the hydraulic motors  10  and  12  (dependent upon the position of the shuttle valve  38 ) where the hydraulic fluid may leak from the motor into the ambient or into a reservoir, such as a tank  52 . 
     While the valve  50  is in the first position and there has been a loss of pressure in the circuit, the motors  10  and  12  will be inhibited from rotating, not only by the actuation of the brakes  14  and  16 , but also by the design of the circuit. Any rotation of the motor, either motor  10  or motor  12 , by towing of the vehicle in which the circuit is disposed would result in the motor acting as a pump. Accordingly, when the wheel that is attached to the motor is rotated fluid would want to travel through the motor as its output shaft is rotated. When there is a loss of pressure, fluid is precluded from moving through the pumps  22  and  24  due to the design of these pumps. Accordingly, fluid would travel towards the first shuttle valve  32  from the first motor  10  and towards the second shuttle valve  34  from the second motor  12 . With respect to the first wheel circuit  26  fluid would be precluded from traveling towards the tank  52  by check valves  60  and  62 . Likewise, for the second wheel circuit  28  fluid would be precluded from traveling into the tank  52  by check valves  64  and  66 . Accordingly, fluid would travel from the first motor  10  through the first shuttle valve  32  and toward the third shuttle valve  38  and thus towards the control  20  through conduit  44 . Similarly, fluid would travel through the second shuttle valve  34  in the second motor  28  towards the third shuttle valve  38  and towards the control  20  through the conduit  44 . While the valve  50  is in the first position  50   a , communication between the first and second wheel circuits  26  and  28  and the tank  52  is blocked. Accordingly, fluid is precluded from traveling through this path. Upon rotation of the motors  10  and  12 , fluid can also pass through the valve  50  towards the brakes  14  and  16 ; however, at that time the spring is actuated and the hydraulic fluid pressure that is provided via the motors rotating does not overcome the pressure of the spring and therefore the flow of fluid through the motors  10  and  12  is inhibited. 
     The control  50  can be moved from the first operating position  50   a  to the second operating position  50   b  when there has been a loss in pressure in the circuit. When in the second operating position  50   b , hydraulic motors  10  and  12  are in fluid communication with the tank  52  through the valve  50 . Accordingly, fluid can easily move through both of the motors  10  and  12  into the tank  52  upon rotation of the output shaft. 
     While in the second operating position  50   b , the pumps  22  and  24  are isolated from the brakes  14  and  16  through the valve  50 . An auxiliary pressure source  70 , e.g. a hand pump, is provided to pressurize the brakes  14  and  16 . Instead of communicating with the tank  52 , the pump  70  draws fluid from upstream the main pumps  22  and  24  through a filter  72  and a check valve  74 . The auxiliary pump  70  pushes the fluid through another check valve  76  and towards the brakes  14  and  16  since the line leading back to the valve  50  is blocked when the valve is in the second operating position  50   b.    
     With reference to  FIG. 2 , the control  20  for a hydraulic circuit generally includes a-manifold housing  112  and a movable member  114 , which will also be referred to as a pump rod subassembly. The control  20  is not limited to only the configuration that is disclosed. 
     The control  20  is movable between a first mode of operation (depicted in  FIG. 2  and equivalent to first operating position  50   a  in  FIG. 1 ) and a second mode of operation (depicted in  FIGS. 3 and 4  and equivalent to the second operating position  50   b  in  FIG. 1 ). The first mode, or position, allows for fluid communication between a pressure source, e.g. pumps  22  and  24 , and spring applied-pressure released brakes  14  and  16 . While in the first mode of operation, the hydraulic motors  10  and  12  are isolated from the tank  52 . 
     With continued reference to  FIG. 2 , the manifold housing  112  includes a central bore, or cavity,  132  that receives a portion of the pump rod subassembly  114 . In the depicted embodiment, the central bore  132  is substantially cylindrical and axially symmetric about a longitudinal axis  134  of the manifold housing  112 . In the depicted embodiment, the central bore  132  does not extend entirely through the manifold housing  112 , but instead ends near a lower portion of the housing (as depicted in  FIG. 2 ). 
     The manifold housing  112  also includes a plurality of ports and passages that are in communication with the central cavity  132 . The ports and passages will be described as having certain configurations. The invention is not limited to only the configurations that are described below and depicted in the figures. To the contrary, the invention is defined by the appended claims. 
     A pressure port  136  communicates with a lower portion of the cavity  132 . A pressure port fitting  138  is received inside the pressure port  136  to allow for a hose, which will be described in more detail below, to connect the pumps  22  and  24  ( FIG. 1 ) to the pressure port  136 . A first brake port  142  and a second brake port  144  also communicate with the cavity  132 . As more clearly seen in  FIG. 5 , first and second brake port fittings  146  and  148  are received in the respective brake ports. The brake port fittings allow for hydraulic hoses, or other device for carrying hydraulic fluid which will be described below, to connect the brakes  14  and  16  to the control  20 . An annular groove  152 , which will be referred to as the lower annular groove, is machined out of the manifold housing  112 , or formed in another manner, to allow for fluid communication between the brake ports  142  and  144  and the cavity  132 . 
     With continued reference to  FIG. 2 , the control  20  also includes a first motor port  160  that is in fluid communication with the bore  132  and a second motor port  162  that is also in communication with the bore  132 . In the depicted embodiment, the first motor port  160  is spaced from the second motor port  162  along the central axis  134 . A second annular groove  164 , which will be referred to as the intermediate annular groove, is machined in the manifold housing  112  to allow for fluid communication between the first motor port  160  and the internal bore  132 . Similarly, a third annular groove  166 , which will be referred to as the upper annular groove, is also machined into the manifold housing  112  to provide fluid communication between the second motor port  162  and the internal bore  132 . The upper annular groove  166  is spaced from the intermediate annular groove  164  along the central axis  134  of the manifold housing  112 . As more clearly seen in  FIG. 5 , a first motor port fitting  168  allows for a fluid hose, or other device, to connect to the first motor port  160  ( FIG. 2 ). Similarly, a second motor port fitting  172  allows for the connection of a hydraulic hose, or similar fluid carrying device, to the manifold housing  112  to allow for fluid communication with the second motor port  162  ( FIG. 2 ). 
     The invention is not limited to the exact locations of the ports and fittings as shown in the figures. To the contrary, the location of the ports and fittings can be elsewhere. 
     A pin  180  is received in a transverse, e.g. radial, bore  182  of the manifold housing  112 . The transverse bore  182  intersects the upper annular groove  166 . The pin  180  limits the linear movement of the pump rod assembly  114  in the manifold housing  112  in a manner that will be described in more detail below. Other means of retaining the movable member may also be used. 
     With continued reference to  FIG. 2 , the pump rod assembly  114  includes an outer rod, or spindle,  200  and an inner rod  202  that is received inside the outer rod. The push rod assembly  114 , and more specifically the spindle  200 , is moveable between a first operating position, as shown in  FIG. 2 , and a second operating position as shown in  FIGS. 3 and 4 . 
     The outer rod  200  includes a first, i.e. upper, counterbore  204  and a second, i.e. lower, coaxial counterbore  206  that has a smaller diameter and extends further into the outer rod  200  as compared to the first counterbore  204 . The upper counterbore  204  receives a bushing  208 . The bushing  208  receives the inner rod  202  and protects the inner rod from wear and also retains the inner rod. A snap ring  212  contains the bushing  208  inside the upper counterbore  204 . The lower counterbore  206  receives the inner rod  202  to define a pump chamber of the pump  70  (depicted schematically in  FIG. 1 ). The dimensions of the inner rod  202  and the lower counterbore  206  can change, for example, where it is desirable to provide a larger pump chamber. 
     The outer rod  200  also includes a plurality of annular grooves. Each groove is configured to receive a seal. The seals are spaced from one another along the axis  134 . The seals isolate the annular grooves that are formed in the manifold housing  112 , i.e. lower annular groove  152 , intermediate annular groove  164  and upper annular groove  166 , from one another. In the depicted embodiment, there are four seals: a first (upper) seal  220 , a second (upper intermediate) seal  222 , a third (lower intermediate) seal  224 , and a fourth (lower) seal  226 . Each seal contacts an inner surface of the internal bore  132  of the manifold housing  112 . 
     The outer rod  200  also includes an elongated annular notch  232  machined into the outer rod. The elongated notch  232  cooperates with the pin  180  to limit upward movement of the outer rod  200  when pressure is applied to the pressure port  136 . The pin  180  also limits downward movement of the outer rod  200 . In the depicted embodiment, the pin  180  limits downward movement of the outer rod  200 , as opposed to the bottom of the cavity  132  limiting the downward movement. In the depicted embodiment, the elongated notch  232  has a dimension that is parallel with the axis  134 , i.e. axial dimension, that is about equal to the distance between the lower planar surface of the outer rod  200  and the bottom of the central bore  132  of the manifold housing  112 , although such a configuration is not required. 
     With reference to  FIGS. 1 and 2 , the first valve  74 , which in the depicted embodiment is a one-way check valve, is inserted into an axial passage  242  of the outer rod  200 . The filter  72  can also be disposed adjacent the one-way check valve  74 . The passage  242  communicates with the lower counterbore, i.e. pump chamber  206 , of the outer rod  200 . With reference to  FIG. 4 , the second one-way check valve  76  is disposed in a radial passage  248  in the outer rod  200 . The passage  248  communicates with the pump chamber  206 . The flow of hydraulic fluid through these check valves will be described in more detail below. 
     As explained above and with reference back to  FIG. 2 , the inner rod  202  is received in the second bore  206  of the outer rod  200 . The inner rod  202  includes annular grooves that are spaced from one another along the central axis  134 . A lower annular groove receives a first (lower) seal  250  and an upper groove receives a second (upper) seal  252 . Two seals are provided to encourage the generation of a vacuum during manual pumping, which will be described in more detail below. 
     A biasing member, e.g. a spring,  254  biases the inner rod  202  out of the second counterbore  206  of the outer rod  200 . The biasing member contacts the bushing  208  and a handle  256  disposed at an end of the inner rod  202  opposite the seals  250  and  252 . A bellows  258  surrounds the inner rod  200  and the spring  254  between the handle  256  and the manifold housing  112 . An alternative biasing member, e.g. a bellows spring, can bias the inner rod  202  out of the second counterbore  206  of the outer rod  200 . Use of the bellows spring can obviate use of the spring  256 ; however, the bellows springs can be used in addition to the spring. 
     As explained above, the control  20  operates between a first operating position ( FIG. 2 ) and a second operating position ( FIG. 3 ). In the first operating position the primary pressure source, i.e. pumps  22  and  24  ( FIG. 1 ), communicate with the brakes  14  and  16  ( FIG. 1 ) via the pressure port  136  and the brake ports  142  and  144 . As more clearly seen in  FIG. 2 , when in the first operating position the lower seal  226  resides in the lower annular groove  152 . Alternatively, the lower seal  226  can contact the outer rod  200  above the lower annular groove  152  and the manifold housing  112  to isolate the hydraulic fluid from the remainder of the ports. Also while in the first operating position, the first motor port  160  is isolated from the second motor port  166  by the upper intermediate seal  222 . Furthermore, the lower intermediate seal  224  further isolates the first motor port  160  from the brake ports  142  and  144 . Accordingly, pressure is delivered from the pumps  22  and  24  through the motors  10  and  12  through lines  36  and  42  ( FIG. 1 ) toward the third shuttle valve  38  ( FIG. 1 ). With reference back to  FIG. 1 , from the third shuttle valve  38  fluid passes through line  44  and splits at a fitting  270  into a pressure brake line  272  and a pressure motor line  274 . The pressure brake line  272  connects to the pressure port fitting  138 . The pressure motor line  274  connects to the first motor port fitting  168 . With continued reference to the first operating position, fluid that enters the control  20  through the first motor port fitting  138  is blocked from traveling to the second motor port  162  ( FIG. 2 ) and thus out a motor/ tank line  276 , which is connected to the tank  52  and the second motor port fitting  172 . While in the first operating position, pressurized fluid can travel from the brake pressure line  272  through the control  20  and out brake port fittings  146  and  148 . A first brake line  280  connects to the first brake fitting  146  and a second brake line  282  connects to the second brake fitting  148 . The first and second brake lines connect at a fitting  284  to a main brake line  286 . Another brake line  288  branches off to connect to the second brake  16  and the main brake line continues to the first brake  14 . If desired, only one brake port may be provided to provide pressure to both brakes  14  and  16  or two separate brake lines may be used. 
     When pressure is not being applied to the brakes  14  and  16  via either pump  22  or  24 , the springs in the brake actuate. With reference to  FIG. 3 , when pressure is not being supplied to the pressure port  136 , the push rod assembly  114  can be moved into the second operating position that is shown in  FIG. 3 . In this operating position, the brake ports  142  and  144  are isolated from the pressure port  136  by the lower seal  226  being disposed below the lower annular groove  152 . The first one-way check valve  74  allows for fluid to be drawn upstream from the pumps  22  and  24  into the second bore  206  of the outer rod  200  upon upward movement (as per the orientation shown in  FIG. 4 ) of the inner rod  202 . With reference to  FIG. 4 , downward movement of the inner rod  202  results in fluid passing through the second one-way check valve  76  into the lower annular groove  152  and thus into the brake ports  142  and  144 . Accordingly, by pumping the inner rod  202  while the outer rod  200  is in the second operating position, pressure can be applied to the brakes  14  and  16  thus releasing the springs. In other words, fluid is allowed to travel from upstream of the pump  70  ( FIG. 1 ) and through the first check valve  72 ; however, the first check valve prohibits flow from the auxiliary pump  70  towards the primary pumps  22  and  24 . Also, fluid is allowed to travel from the auxiliary pump  70  towards the brakes  14  and  16  through the second check valve  76 ; however, the second check valve prohibits fluid from traveling from the brakes  14  and  16  toward the pump  70 . In the depicted embodiment, while the control  20  is in the first position fluid can enter the pump chamber  206  through the first valve  74  and leak into the lower annular groove  152  through the second valve  76  ( FIG. 4 ). 
     While no pressure is being applied by the pumps  22  and  24 , the motors  10  and  12  in the depicted configuration will not turn while the control  20  is in the first operating position ( FIG. 2 ). This is because line  274  ( FIG. 1 ) is blocked from line  276  and the motors  10  and  12  can no longer communicate with the tank  52 . Accordingly, fluid does not travel through the motors and the motors do not rotate. With reference to  FIG. 3 , when the outer rod  200  is pushed into the second operating position, the upper intermediate seal  222  moves below and/or into the intermediate annular groove  164  so that the first motor port  160  can communicate with the second motor port  168 . Thus, while in the second operating position, the pumps  22  and  24 , which are configured to block flow when not running, are short circuited and the motors  10  and  12  can communicate with the tank  52  via the control  20  so that they can rotate. As seen in  FIG. 4 , the upper seal  220  is maintained above the second motor port  166  so that communication is allowed between the first motor port  160  and the second motor  166  while fluid does not escape internal bore  132  of the manifold housing  112 . 
     The control  20  is automatically reset upon pressurization of the pressure port  136 . Pressurization of the pressure port  136  results in the outer rod  200  moving upward so that the pumps  22  and  24  can communicate with the brakes  14  and  16  via the brake ports  142  and  144 . The pin  180  cooperates with a lower portion of the annular notch  232  formed in the outer rod  200  to limit further movement of the outer rod so that it does not travel out of the manifold housing  112  upon pressurization by the pumps  22  and  24 . 
     As seen in  FIG. 1 , the control unit  20  can be a stand alone unit that allows for the connection of pressure hoses. Nevertheless, the pump rod assembly  114  can be dropped into an existing manifold (some ports and passages in the manifold may need to be machined) such that the pump rod assembly  114  acts as a sort of cartridge valve. In other words, the housing for the control is not limited to the housing as shown in  FIG. 5 . Instead, the housing can be an existing manifold or it can take some other configuration. 
     The control allows the operator of a prime mover to manually pressurize spring actuated-pressure released brakes by moving a single movable member. Accordingly, the control can be housed in a compact housing as compared to known manual pumps that are used to manually pressurize brakes. Furthermore, this single shaft control unit can draw fluid downstream from the pump, as opposed to from the tank, to pressurize the brakes thus simplifying the construction as compared to known pumping devices. Adequate fluid is located in the circuit between the pump and the control to pressurize the brakes. Additionally, downward movement of the shaft also allows the hydraulic motors to rotate freely; therefore, the operator of the prime mover need not turn an additional needle valve to allow for free rotation of the hydraulic motors. 
     With reference to  FIG. 5 , a name plate  290  attaches to the manifold housing  112  using fasteners  292 . The name plate can carry indicia regarding the source of the control, as well as other information. 
     With reference to  FIG. 6 , an alternative embodiment of a hydraulic circuit that allows for the release of spring applied hydraulically released brakes and the hydraulic motors is disclosed. The configuration of the wheel circuits for the hydraulic circuit depicted in  FIG. 6  is the same as for the hydraulic circuit depicted in  FIG. 1  and therefore the same reference numerals will be used. In the circuit depicted in  FIG. 6 , a control  300  is used to release the brakes  14  and  16  and short circuit the motors  10  and  12  with respect to their respective pumps  22  and  24 . 
     The control  300  includes a two position valve  302  having a first operating position  302   a  and a second operating position  302   b . In the first operating position, the brakes  14  and  16  receive pressure from primary pressure sources, e.g. pumps  22  and  24 , in much the same manner as was described with reference to the circuit disclosed in  FIG. 1 . Fluid travels from the motors  10  and  12  through lines  36  and  42  and into the shuttle valve  38 . Whichever wheel circuit is operating at a greater pressure delivers fluid to line  44  which connects to a brake pressure port  304  that is in communication with the valve  302 . With the valve  302  in the first operating position  302   a , fluid travels through the pressure port  304 , through the valve  302  and into respective brake ports  306  and  308  towards the brakes  14  and  16  in a manner similar to the hydraulic circuit described with reference to  FIG. 1 . 
     When pressure is lost in the circuit, the springs in the brakes  14  and  16  apply thus inhibiting rotation of the output shafts of the respective motors  10  and  12 . When the valve  302  is in the first operating position  302   a  and fluid pressure is lost in the circuit, fluid travel through the motors  10  and  12  is also inhibited. A first short circuit line  312  connects to the first wheel circuit  26  on a first side the pump  22  and a second short circuit line  314  connects to the wheel circuit  26  on an opposite side (either upstream or downstream depending on the direction of flow through the motor  22 ). Similarly, a third short circuit line  316  connects to the second wheel circuit  28  on a first side of the pump  24  and a fourth short circuit line  318  connects to the second wheel circuit  28  on an opposite side of the second pump  24 . When the valve  302  is in the first operating position  302   a  the first short circuit line  312  is blocked from the second short circuit line  314 . Likewise, when the valve  302  is in the first operating position  302   a  the third short circuit line  316  is blocked from the fourth short circuit line  318 . Since the short circuit lines are blocked from one another, the motors  10  and  12  are isolated from one another so that when a loss of pressure occurs the motors are inhibited from rotating. 
     When the valve  302  is in the second operating position  302   b  the first short circuit line  312  is allowed to communicate with the second short circuit line  314 . Likewise, when the valve  302  is in the second operating position  302   b , the third short circuit line  316  is allowed to communicate with the fourth short circuit line  318 . Accordingly, fluid can travel from an outlet of the motor  10  through the first short circuit line  312  and through the valve  302  into the second short circuit line  314  and into the inlet of the motor. Similarly, fluid can exit the second motor  12  into the third short circuit line  316  and travel through the valve  302  into the fourth short circuit line  318  and back through the motor  12 . Accordingly, while in the second operating position  302   b  both motors  10  and  12  can rotate as the prime mover is towed. 
     In the hydraulic circuit depicted in  FIG. 6 , the brakes  14  and  16  can be pressurized using an auxiliary pressure source  322 , which can be a hand pump, that acts similarly to the auxiliary pressure source  70  depicted in  FIG. 1 . The auxiliary pressure source  322  draws fluid from downstream the primary pressure sources  22  and  24  through a filter  324  and a check valve  326 . The auxiliary pressure source  322  pushes fluid through a second check valve  328  towards the brake ports  306  and  308  to pressurize the brakes  14  and  16 . 
     The control  300  can take a similar configuration to the control  20  depicted in  FIGS. 1-5 ; however, instead of having only two motor ports, which is the configuration depicted in  FIG. 5 , the control can include two additional motor ports to provide the connections for short circuiting both motors  10  and  12  without returning fluid to the tank  52 . The motor port connections can be axially spaced from one another, similar to the configuration depicted in  FIGS. 2-5 . The rod assembly disclosed in  FIGS. 2-5  would isolate the motor ports from one another in a manner that is depicted schematically in  FIG. 6 . 
     With reference to  FIG. 7 , an alternative embodiment of a hydraulic circuit that allows for the release of spring applied-hydraulically released brakes and the hydraulic motors is disclosed. The circuit disclosed in  FIG. 7  can be particularly useful in providing a high pressure bypass for the hydraulic motors; however, the circuit is not limited to such configurations. The configuration of the wheel circuits for the hydraulic circuit depicted in  FIG. 7  is the same as for the hydraulic circuit depicted in  FIGS. 1 and 6 . Therefore, the same reference numerals for the wheel circuits will be used. In the circuit depicted in  FIG. 7 , a control  350  is used to release the brakes  14  and  16  and short circuit the motors  10  and  12  with respect to their respective pumps  22  and  24 . In this circuit, the motor bypass, i.e. the short circuit aspect of the hydraulic circuit, is a high-pressure motor bypass in that the control  350  does not reset until a predetermined pressure has been reached upstream of the control. 
     The control  350  includes a two position valve  352  having a first operating position  352   a  and second operating position  352   b . In the first operating position, the brakes  14  and  16  receive pressure from primary pressure sources, e.g. pumps  22  and  24 . Fluid travels from the motors  10  and  12  through lines  36  and  42  and into a shuttle valve  38 , which in the embodiment depicted in  FIG. 7  is disposed in the same housing (e.g. manifold) as the valve  352 , as well as other components of the control  350 . Because of this configuration, a first motor shuttle port  354  and a second motor shuttle port  356 , each being in communication with opposite sides of the shuttle valve  38 , are provided on the control  350 . The first wheel circuit  26  communicates with the shuttle valve  38  through line  36  which is connected to the first motor shuttle port  354 . Similarly, the second wheel circuit  28  communicates with the shuttle valve  38  through line  42  which is connected to the second motor shuttle port  356 . 
     With the valve  352  in the first operating position  352   a , fluid travels through a first check valve  366  and through the valve  352  into respective brake ports  358  and  360  to which brake lines  362  and  364  are attached in a known manner. The first check valve  366  operates at a predetermined pressure, typically the check valve opens at between about 2 psi to about 300 psi. Pumps, for example pumps  22  and  24 , can maintain residual hydraulic pressure even when the pump is disposed in a neutral position. Accordingly, the first check valve  366  can preclude communication between the valve  352  and the wheel circuits  26  and  28  when the engine of the prime mover that drives the pumps  22  and  24  is idling and the pumps are not delivering fluid to the motors other than the residual pressure described. When the valve  352  is in the second position  352   b , the first check valve  366  can also preclude communication with the valve  352  so that the valve  352  is not automatically reset when the prime mover is being towed and fluid is flowing through the system which may result in pressure spikes somewhere in the hydraulic circuit. 
     When the valve  352  is in the second operating position  352   b , the shuttle valve  38  and thus the motors  10  and  12  communicate with the tank  52  via a tank port  368 . Accordingly, fluid travels from the motors  10  and  12  into the shuttle valve  38  through the valve  352  in the second operating position  352   b  and towards the tank  52  out the tank port  368 . While in the second operating position  352   b , both motors  10  and  12  can rotate as the prime mover is towed. 
     In the hydraulic circuit depicted in  FIG. 7 , when the control is in the second operating position  352   b  the brakes  14  and  16  are pressurized using an auxiliary pressure source  370 , which can be a hand pump. In the hydraulic circuit depicted in  FIG. 7 , the auxiliary pressure source  370  draws fluid from the tank  52  through a second check valve  372 , a filter  374  and a third check valve  376 . The first check valve  366  will not open in response to the vacuum being drawn by the pump  370  since the predetermined pressure at which the first valve  366  opens is higher than the vacuum pressure generated by the pump  370 . The auxiliary pressure source  370  pushes fluid through a fourth check valve  378  towards the brake ports  360  and  362  to pressurize the brakes  14  and  16 . The second check valve  372  provides for communication with the tank  352  for suction only. No return to the tank is provided through a second tank port  380 . A fifth check valve  382 , which is parallel to the first check valve  366 , lets pressure out of the valve  352  while the first check valve  366  lets pressure into the valve  352 . 
     The control  350  can take a number of configurations, many of which would be similar to the control depicted in  FIGS. 1-5 . With reference to  FIGS. 8-11  an embodiment of the control  352  is disclosed. Nevertheless, the control is not limited to only the embodiment depicted in  FIGS. 8-11 . Instead, the control can take a number of configurations that are functionally equivalent to the schematic control depicted in  FIG. 7 . The control  350  includes a manifold housing  412  and a pump rod subassembly  114 , that is identical to the pump rod subassembly described with reference to  FIGS. 2-5 , and therefore for the sake of brevity will not be described in further detail. The manifold housing  412  can take a number of configurations, only one is disclosed in detail. 
     The manifold housing  412  takes a very similar configuration to the manifold housing  112  described with reference to  FIGS. 2-5  and therefore much of it will not be described in detail. 
     With reference to  FIG. 9 , while the control is in the first operating position lines  42  and  36  connect to motor shuttle ports  354  and  356  respectively. With reference to  FIG. 10 , the motor shuttle ports  354  and  356  each communicate with a passage  414  formed in a manifold housing  412 . A ball  416  is disposed in the passage  414  such that the ball  416  and passage  414  operate as a shuttle valve  38  (depicted schematically in  FIG. 7 ). Also a cartridge or press in type shuttle valve may be used. With continued reference to  FIG. 10 , pressurized fluid is delivered from the transverse bore  414  into an axial bore  418  that is in communication with an annular bore  422  that while the control is in the first operating position is isolated from other ports by an upper intermediate seal  424  and a lower intermediate seal  426 . With reference back to  FIG. 9 , while the control is in the first operating position fluid passes from the transverse bore  414  ( FIG. 10 ) through the first check valve  366  and into a central bore of the manifold  412  so that pressure is delivered to the brake lines  362  and  364  via brake ports  360  and  358  ( FIG. 8 ). When the control  350  is in the first operating position, the shuttle valve  38  precludes direct communication between the motors  10  and  12  and the shuttle motor ports  354  and  356  are isolated from the tank  352  by the intermediate seals  424  and  426 . 
     With reference to  FIG. 11 , with the control in the second operating position the intermediate seal  424  is disposed in the annular bore  422  such that the annular bore  422  can now communicate with the tank  52 , as seen in  FIG. 11 . This allows for a direct short from the motors  10  and  12  to the tank  52 . Also, while the control is in the second operating position fluid can be drawn from the tank  52  through the check valve  372  and into a pump chamber  432  through another check valve  376 . When in the second position, the fourth check valve  378  ( FIG. 10 ) aligns with a lower annular bore  434  that is in communication with the brake ports  360  and  358  so that fluid is pushed through the fourth check valve  378  towards the brakes  14  and  16  ( FIG. 7 ). 
     Various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. Even though embodiments of the invention are disclosed above, the invention is not to be limited to only the embodiment disclosed. For example, the controls described above can take different configurations than what is disclosed in  FIGS. 2-5  and  8 - 11  that are functionally equivalent to the configurations disclosed in  FIGS. 1 ,  6  and  7 . The invention is defined by the appended claims and the equivalents thereof.