Abstract:
This disclosure provides for pressure limiting a hydraulic system to a desired pressure value by a particular circuit by controlling and closing the compensator when the desired pressure setting is achieved. Closing the compensator will reduced the pressure head and flow in the circuit resulting in improved efficiency. One illustrated embodiment of the disclosure provides a relief valve in the pilot signal for a compensator. The method relates to limiting the pressure on an open side of the compensator, such that the pressure on the other side closes the compensator thereby limiting the pressure and also flow in the hydraulic circuit. In other words, the pressure on the open side is limited by the relief valve. Thus, the pressure on the other side increases thereby regulating the flow and pressure through the compensator. 
     In another embodiment of the disclosure, instead of reducing the pressure on the open side, the pressure on the closed side is increased, thereby controlling the flow and pressure of the hydraulic circuit. The pressure can be increased by a pump or any other suitable mode.

Description:
TECHNICAL FIELD 
     The present disclosure relates to pressure limiting the hydraulic circuits, and more particularly to controlling the pilot signal pressure of the compensator. 
     BACKGROUND 
     This disclosure relates generally to hydraulic systems, and more particularly, but not exclusively, this disclosure relates to a method and system to control the flow and pressure in a hydraulic system. 
     With the advancement in the field of hydraulics, there has been an interest in development of a hydraulic system capable of performing a plurality of functions efficiently. One of the basic functions is too regulate the pressure and flow of the fluid passing through the hydraulic system. It is relatively common requirement, for hydraulic post compensated implement systems, to limit work port pressure to a value below the maximum system pressure. This requirement is typically met by adding work port relief valves, however the work port relief valves result in high flow losses and therefore reduces the efficiency. In another method, pre-pressure compensated circuits can also be used in a similar method to limit pressure. While various hydraulic compensators have been developed, there is still room for improvement. Thus, a need persists for further contributions in this area of technology. 
     SUMMARY 
     This disclosure provides for removing the work port relief valves used in the prior art to control the pressure. The pressure is limited in a particular circuit by controlling and closing the compensator when the desired pressure setting is achieved. As the compensator closes flow will be reduced in the circuit resulting in improved efficiency. One illustrated embodiment of the disclosure provides a relief valve in the pilot signal for a compensator. The method relates to limiting the pressure on the open side of the compensator, such that the pressure on the other side closes the compensator thereby limiting the pressure and also flow in the hydraulic circuit. In other words, the pressure on the open side is limited by the relief valve. Thus, the pressure on the other side increases thereby regulating the flow and pressure through the compensator. In another embodiment of the disclosure, instead of reducing the pressure on the open side, the pressure on the closed side is increased, thereby controlling the flow and pressure of the hydraulic circuit. The pressure can be increased by a pump or any other suitable source of external pressure. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a schematic illustration of a first embodiment of the present invention; and 
         FIG. 2  is a schematic illustration of a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     A compensated hydraulic system  100  according to one illustrative embodiment of the current disclosure is shown in  FIG. 1 . The hydraulic system  100 , can be used for example in machines such as track type tractors, wheel loader or similar equipment (not shown), for bucket or blade lifting systems, includes a source of hydraulic fluid such as a pump  12 , an operational valve  14  and a pressure compensator  16  or a compensator valve  16 , and a hydraulic actuator assembly  18 . The pump  12  is configured to provide hydraulic fluid at a pressure head. The pressurized fluid from the pump  12  is pumped through the hydraulic system  100  to a load or to perform various functions by using the hydraulic actuator assembly  18 . In this embodiment the hydraulic actuator assembly  18  is a piston cylinder arrangement  18 . Further, in this embodiment the operational valve  14  is a control spool  14 . The control spool  14  is configured to control the direction of the piston cylinder arrangement  18 . In other words the, the control spool  14  directs the hydraulic fluid to the piston cylinder arrangement  18  to expand or retract the pistons. It should be appreciated that the hydraulic system  100  includes only one control spool  14  according to an embodiment of the disclosure. However, plurality of operational valves or control spools can be provided in a circuit as per the requirement in the circuit. Further, the system  100  is shown to include the compensator  16 . The compensator  16  is arranged on the top of the control spool  14 . The compensator  16  is provided to maintain a constant pressure drop across the control spool  14 . The compensator  16  has two inlets, first inlet  16   a  and a second inlet  16   b . The first inlet  16   a  is located on the open end of the compensator  16 . The first inlet  16   a  is subjected to pressure tending to open the compensator and thereby allow the flow of hydraulic pressure. The second inlet  16   b  is located at the closed end of the compensator  16 . The second inlet  16   b  is subjected to a spring force and additional pressure sources (if any) to close the opening of the compensator, thereby limiting the flow of hydraulic fluid. The term first inlet  16   a  and open end  16   a  have been used interchangeably in the description and refer to the same inlet/same end of the compensator  16 . The term second inlet  16   b  and closed end  16   b  have been used interchangeably in the description and refer to the same inlet/same end of the compensator  16 . 
     The control spool  14  can control the direction of the fluid to direct the hydraulic fluid to expand or retract the cylinder piston arrangement  18 . Further, the compensator  16  is provided to maintain a constant pressure drop across the control spool  14 . 
     Further, the hydraulic system  100  can include a supply line  20  connecting the control spool  14  with an inlet  16   c  of the pressure compensator  16  through a load drop check valve  22 . The load drop check valve  22  prevents the backflow of fluid to the control spool  14  when the pump  12  is not functioning. The inlet  16   c  is connected to the supply line  20  from the pump  12 . 
     The hydraulic system  100  further includes a first signal line  24  and a second signal line  26 . The first signal line  24  is located upstream of control spool  14 . The first signal line  24  provides the fluid pressure head, and allows the hydraulic fluid to bias the spool member (not shown) of the control spool  14  through the closed end  16   b  of compensator  16 . The first signal line  24  on the closed side  16   b  tends to close the compensator  16 . The first signal  24  act in the same direction of the compensator spring  28  tending to close the compensator  16 . 
     The second signal line  26  is connected with the open end  16   a  of the compensator  16  and allows flow of fluid, to bias the pressure compensator  16  in the opposite direction of compensator spring  28  and the first signal line  24 . The second signal line  26  is located on the open side  16   a  of the compensator and tends to open the compensator  16 . The second signal line  26  works opposite to the force of the first signal line  24  on the closed end  16   b  and the compensator spring  28 . 
     Further, the hydraulic system  100  includes a regulating valve  30 . In this embodiment, the regulating valve  30  is essentially a pressure relief valve. The pressure relief valve  30  is arranged at the open side  16   a  of the compensator  16  in the second signal line  26 . Thus, the relief valve  30  is arranged on the pilot passage  26  which is tending to open the compensator. 
     Accordingly, an increase in the pressure in the second signal line  26 , in the open side  16   a  of the compensator  16 , is limited to pressure value set by relief valve  30 . Consequently, the pressure tending to open the compensator  16  is limited to a desired pressure value set through the relief valve  30 . Thus limiting the pressure on the open side  16   a , relatively causes the pressure from the first signal line  24  and the compensator spring  28  to increase and close the compensator  16 . This leads to controlling of both the pressure and the flow of the hydraulic fluid in the circuit  100  when the pressure in the signal line  26  increases beyond the set threshold value of the relief valve  30 . 
     To provide a better understanding, consider the scenario, where the pump  12  is provided with a pump inlet line  32  leading to the control spool  14 . The pressure from the pump  12  is passed to the compensator  16  from the control spool  14 , and the supply line  20 . Further, the system is shown to include a check valve  34  which is connected to the actuator  18 . The check valve  34  acts as a sensor for determining the load condition of the actuator  18  during expansion or retraction. 
     Downstream the control spool  14 , the supply line  20  is subjected to the relief valve  30  through the second signal line  26 . Pressure in the supply line  20  tends to open the compensator thereby allowing flow of hydraulic fluid through the control spool  14 . The pressure line  20  is subjected to the relief valve  30 , which operates beyond a set pressure threshold. Thus, when the pressure exceeds the desired pressure value or the set pressure threshold of the relief valve  30 , the relief valve  30  opens and drains the hydraulic fluid to a reservoir/tank. This results in decrease in the pressure of the hydraulic fluid on the open side  16   a  of the compensator  16 . Thereby, relatively increasing the pressure from the first signal line  24  and the compensator spring  28  and allowing the combined force of the spring  28  and the pressure from the first signal line  24  on the closed side  16   b  to close the compensator  16 . 
     Therefore, such arrangement results in pressure limiting and leads to control of pressure head and the flow of the hydraulic fluid without affecting the other function of the hydraulic system  100 . In other words, the system is more efficient as it provides the pre-compensated control of the pressure and the flow to the cylinder piston arrangement  18 . 
       FIG. 2  is a schematic illustration of a hydraulic system  200  in a second embodiment of the present invention. The hydraulic system  200  is similar to the hydraulic system  100  as described in  FIG. 1 . However, the hydraulic system  200  does not include the relief valve  30 . Instead, the hydraulic system  200  includes a pressure controlling means. In this embodiment, the pressure controlling means includes a control valve  202  and external pressure source  204 . In an embodiment, the pressure control valve  202  can be electronically controlled or mechanically controlled, as shown. 
     The control valve  202  has an open side  202   a  and closed side  202   b . The open side  202   a  is subjected to a pressure tending to open the flow through the control valve  202  from pressure source  204 , whereas the closed side  202   b  is subjected to a spring pressure tending to close the flow from pressure source  204  through the control valve  202 . The control valve  202  is connected to direct the fluid from the external source  204  towards the closed end  16   d  of the compensator  16 . In other words, the control valve  202  causes the pressure from the pressure source  204  to act in the same direction of the compensator spring  28 . Further, the control valve  202  includes a control spring  206 , which is tending to close the control valve  202 . It is to be noted that the external pump can be any suitable pressure source  204 . 
     Furthermore, the control valve  202  is operated based on the signal from the signal line  208  and  210 . The signal line  208  and  210  are connected to the opens side  202   a  of the control valve  202 . The signal lines  208  and  210  are connected through a check valve arrangement  212 . The signal line  208  and  210  senses the fluid pressure in the piston cylinder arrangement  18  during expansion and retraction, respectively. The signal line  208  and  210  signals the increase in pressure on the work side of the piston cylinder arrangement  18  to the open side  202   a  of the control valve  202 , through the check valve  212 . 
     In the current arrangement, the signal from the signal line  208  or  210  during expansion or retraction is passed to the open side  202   a  of the control valve  202 . The pressure signal from the signal line  208  or  210  tends to open the control valve  202  against the force of the control spring  206 . Thereby, connecting the pressure from the pressure source  204  with the closed side  16   d  of the compensator  16 . The increase in pressure on the closed side  16   d  leads to closing of the compensator thereby controlling the pressure and flow of hydraulic fluid through the control spool  14 . Consequently, the pressure in the cylinder piston arrangement  18  is reduced and controlled. Vice-versa, any decrease in the pressure in the pressure signal line  208  or  210  causes the closing of the control valve  202 , thereby disconnecting the pressure source  204  with the closed side  16   d  of the compensator  16 . This leads to relative decrease in pressure on the closed side  16   d  of the compensator and hence the pressure on the open side  16   a  of the compensator opens the compensator and increase the flow through the control spool  14 . 
     Thus as compared to  FIG. 1 , the embodiment described in  FIG. 2 , increases the pressure on the closed side  16   d  of the compensator  16  to control the pressure and flow in the hydraulic fluid. 
     To summarize, first embodiment as described in  FIG. 1  is configured to reduce the pressure on the open side  16   a  of the compensator  16 , whereas the second embodiment as described in  FIG. 2 , senses the pressure in the piston cylinder arrangement  18  and accordingly, controls the compensator by providing an additional pressure on the closed side  16   b  of the compensator  16 . 
     It is to be noted the hydraulic system  100  or hydraulic system  200  as described above can be used in any hydraulic circuit, such as circuits in hydraulic machine, loader, tractors, backhoe loaders, wheel loader, mine trucks, and the like. 
     Industrial Applicability 
     The hydraulic system  100  described above provides for improvement in capability of pressure limiting a hydraulic circuit without significant losses. The system  100  provides for utilizing the compensator  16  to pressure limit and at the same time minimizing the flow losses. The disclosed hydraulic system  100  includes a regulating valve  30 . The regulating valve  30  is configured to pressure limit the hydraulic system  100  by controlling the pilot signal which is tending to open the compensator  16 . For a better understanding, consider a scenario, where the system  100  is supplied with high pressure hydraulic fluid from the pump  12 . High hydraulic pressure, beyond the safety limits, can cause damage to the hydraulic machinery, such as it may cause damage to the seals and piston rings in the actuators  18 . Thus, it is mandatory to limit the maximum hydraulic pressure in the system  100 . The disclosed system  100  provides for controlling the opening aperture of the compensator  16  as compared to releasing the extra pressure through a relief valve. Thus, in any hydraulic system, the energy generated from the pump  12  is not wasted by releasing the pressure through the relief valve, but the energy is controlled by controlling the compensator  16 . 
     As described above, a relief valve  30  is hydraulically connected to the pilot signal line  20  of the compensator  16 . The pilot signal which is tending to open the compensator is subjected to the regulating valve  30 . The regulating valve  30  is configured to relieve the additional pressure beyond a set limit. Thus, the regulating valve  30  regulates the pressure in the pilot signal line  20 . Therefore, when the pressure in the hydraulic circuit increases beyond a safety limit, the regulating valve  30  opens and reduces the pressure on signal line tending to open the compensator  16 , which in turn allows the pressure  24  and the spring force  28  tending to close the compensator to close the compensatory. Hence, the flow rate and the pressure through the compensator is controlled and the pressure in the hydraulic system  100  is controlled. Such system provides for controlling the pressure from the pump instead of wasting the work done by the pump  12  through a safety release valve. 
     In an alternate embodiment, to achieve the same objective, instead of reducing the pressure on the side tending to open the compensator, the pressure on the side tending to close the compensator is boosted. As described above, it is required to maintain a safety limit of the pressure in the hydraulic circuit. In this embodiment, an additional pressure source  204  is provided in the system  200 . The pressure source can be any suitable source already present in the system  200 . The pressure source  204  is connected through a control valve  202 . The control valve on one side is connected with the pressure line for expanding and contracting the actuators  18 . On the other side the control valve  202  is biased by the spring  206 . Any increase in pressure beyond a set limit on the side of pressure line is sensed and is transmitted to the control valve  202 . Thus the control valve  202  connects the pressure source  204  to the side  16   d  of the compensator  16 . The pressure from the pressure source  204  together with the spring force  28  closes the compensator, thereby reducing the flow rate and pressure of hydraulic fluid through the spool  14 . In an alternate embodiment, the control valve  202  can be controlled electronically by using strain gauges and other suitable pressure sensors. 
     In summary, the hydraulic system  100  is disclosed for automatically pressure limiting any hydraulic circuit without energy loss from the pump and minimal flow losses. The system  100  is configured to control both the flow rate and pressure through the compensator  16  by controlling the opening and closing of the compensator  16  by sensing the pressure in the actuation line. 
     Aspects of this disclosure may be applied to any hydraulic circuit, specifically in hydraulically circuits drawing power driven by engines, as increase in engine speed can speed the pump thereby resulting in continuous fluctuation in the pressure. Aspects of this disclosure may also be applied to hydraulic system in machines such as excavators, track type tractors, backhoe loaders, wheel loaders, pipe layers, compactors, and trucks. Although the embodiments of this disclosure as described herein may be incorporated without departing from the scope of the following claims, it will be apparent to those skilled in the art that various modifications and variations can be made. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.