Abstract:
A pump enable system includes a variable-displacement piston pump having a displacement control device. The displacement control device controls displacement of pistons in the pump based on a position thereof, and a position control system in the pump controls a position of the displacement control device based on a load on the pump. An over-ride system selectively over-rides the position control system such that the displacement control device assumes a position which reduces displacement of the pistons in the pump.

Description:
This application claims priority on provisional application Serial No. 60/074,336 filed on Feb. 6, 1998, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a pump enable system and method; and more particularly, a pump enable system and method for variable-displacement piston pumps. 
     2. Description of Related Art 
     FIG. 1 schematically illustrates a well-known variable-displacement piston pump  10  such as Vickers Incorporated&#39;s Model No. PVE19R930CVPC. The piston pump  10  includes a pump  12  having a plurality of pistons (not shown). The pump  12  is connected between a suction line  14  and a pressure line  16 , and is driven by an engine  18 . Oil leaking in the pump  12  is drained via a drain line  20 . 
     As is well-known, a swash plate  22  (also known as a wobble plate), connected to the pistons in the pump  12 , controls the displacement of the pistons; and thus, the flow rate of the pump  12 . More specifically, the position of the swash plate  22  determines the displacement of the pistons in the pump  12 . A servo piston  24  controls the movement of the swash plate  22  based on hydraulic pressure (i.e., fluid) supplied thereto. 
     As shown in FIG. 1, a pressure compensation valve  26  and a flow compensation valve  28  cooperatively regulate the supply of hydraulic pressure generated by the pump  12  to the servo piston  24  based on the hydraulic pressure in a load sense line  30 . The load sense line  30 , for instance, is connected to a directional control valve (not shown), which when placed in a state requiring hydraulic pressure supplies hydraulic pressure to the load sense line  30 . Both the pressure and flow compensation valves  26  and  28  are two-state valves. 
     When a load is placed on the pump  12 , the pressure compensation valve  26  and the flow compensation valve  28  are both placed in a first state as shown in FIG.  1 . In this first state, the hydraulic pressure generated by the pump  12  is not supplied to the servo piston  24 , and the servo piston  24  is connected with the drain line  20  to remove hydraulic pressure therefrom. As a result, the servo piston  24  retracts and the swash plate  22  moves to an inclined position, which increases the displacement of the pistons in the pump  12  and increases the flow rate of the pump  12 . 
     When no load is placed on the pump  12 , the pressure compensation valve  26  and the flow compensation valve  28  both attain a second state. While not shown as being in the second state, FIG. 1 does illustrate the second states of the pressure and flow compensation valves  26  and  28 . In this second state, the hydraulic pressure generated by the pump  12  is supplied to the servo piston  24 . As a result, the servo piston  24  extends and moves the swash plate  22  to a more vertical position, which reduces the piston displacement in the pump  12  and decreases the flow rate of the piston pump  12 . When fully stroked, the servo piston  24  moves the swash plate  22  to a position which reduces the hydraulic pressure generated by the pump  12  to a stand-by pressure. 
     Whether the pressure and flow compensation valves  26  and  28  are placed in the first or second state depends on the hydraulic pressure in the load sense line  30  and the pressure line  16 . Namely, the hydraulic pressure generated by pump  12  is supplied to first control inputs  40  and  44  of the pressure compensation valve  26  and the flow compensation valve  28 , respectively, and the hydraulic pressure in the load sense line  30  is supplied to a second control input  42  of the pressure compensation valve  26 . First and second springs  45  and  46  bias the pressure and flow compensation valves  26  and  28 , respectively, to the right in FIG.  1 . 
     When no load is placed on the load sense line  30 , the hydraulic pressure generated by the pump  12  causes the pressure and flow compensation valves  26  and  28  to move to the left in FIG. 1 (i.e., the second state). However, when a load is placed on the load sense line  30 , the hydraulic pressure applied to the second control input  42  of the pressure compensation valve  26  causes the pressure compensation valve  26  to move to the right (i.e., the first state). As a result, the hydraulic pressure applied to the first control input  44  of the flow compensation valve  28  is exhausted to the drain line  20  via the pressure compensation valve  26 , and the flow compensation valve  28  moves to the right (i.e., the first state). 
     The hydraulic pressure generated by the pump  12  and supplied via the pressure line  16  typically powers hydraulically operated machinery. As discussed above, the variable-displacement piston pumps  10  can be connected to a directional control valve. The directional control valve applies hydraulic pressure to the load sense line  30  depending on the need for hydraulic pressure from the variable-displacement piston pump  10 . Unfortunately, if the directional control valve sticks in an open state for operating machinery connected thereto when an operator wants the directional control valve closed, the variable-displacement piston pump  10  continues to supply hydraulic pressure. 
     As such, it is desirable, such as in emergency conditions, to immediately stop operation of that machinery. Often this is accomplished by removing the supply of hydraulic pressure necessary to operate the machinery. FIG. 1 illustrates a conventional dump system for removing the supply of hydraulic pressure. 
     As shown in FIG. 1, a dump valve  32  is connected between the pressure line  16  and a reservoir  34 . In a closed state, the dump valve  32  prevents hydraulic pressure from flowing to the reservoir  34  from the pressure line  16 . However, in an open state, as shown in FIG. 1, the dump valve  32  permits hydraulic pressure to flow to the reservoir  34 , which substantially eliminates hydraulic pressure in the pressure line  16 . By placing the dump valve  32  in the open state, operation of machinery utilizing the hydraulic pressure in the pressure line  16  can be brought to a halt. 
     FIG. 2 schematically illustrates another well-known variable-displacement piston pump  110  such as Parker Hannifin Corporations Model No. PAVC65X29948. The piston pump  110  includes a pump  112  having a plurality of pistons (not shown). The pump  112  is connected between a suction line  114  and a pressure line  116 , and is driven by an engine  118 . Oil leaking in the pump  112  is drained via a drain line  120 . 
     As is well-known, a swash plate  122 , connected to the pistons in the pump  112 , controls the displacement of the pistons; and thus, the flow rate of the pump  112 . More specifically, the position of the swash plate  122  determines the displacement of the pistons in the pump  112 . A servo piston  124  controls the movement of the swash plate  122  based on hydraulic pressure (i.e., fluid) supplied thereto. 
     As shown in FIG. 2, a differential adjustment valve  126  regulates the supply of hydraulic pressure generated by the pump  112  to the servo piston  124  based on the hydraulic pressure in a load sense line  130 . The load sense line  130 , for instance, is connected to a directional control valve (not shown), which when placed in a state requiring hydraulic pressure supplies hydraulic pressure to the load sense line  130 . 
     The differential adjustment valve  126  is a two-state valve. When no load is placed on the pump  110 , the differential adjustment valve  126  is placed in a first state. While FIG. 2 does not illustrate the differential adjustment valve  126  in the first state, FIG. 2 does illustrate the first state. Specifically, because no hydraulic pressure is supplied to the control input  140  of the differential adjustment valve  126  by the load sense line  130 , a spring  142  biases the differential adjustment valve  126  down in FIG. 2 (i.e., biases the differential adjustment valve  126  towards the first state). This connects the servo piston  124  to the drain line  120 , and hydraulic pressure at the servo piston  124  exhausts via the drain line  120 . As a result, the servo piston  124  retracts and moves the swash plate  122  to a more vertical position, which reduces the piston displacement in the pump  112  and decreases the flow rate of the pump  112 . When fully retracted, the servo piston  124  moves the swash plate  122  to a position which reduces the hydraulic pressure generated by the pump  112  to a stand-by pressure. 
     When a load is placed on the pump  110 , the differential adjustment valve  126  is placed in a second state as shown in FIG.  2 . Namely, when a load is placed on the pump  110 , hydraulic pressure is applied to the control input  142  of the differential adjustment valve  126  by the load sense line  130 . This hydraulic pressure causes the differential adjustment valve  126  to move up in FIG. 2 (i.e., move towards the second state). In this second state, the pressure line  116  is connected to the servo piston  124 , and hydraulic pressure is supplied to the servo piston  124 . As a result, the servo piston  124  extends and the swash plate  122  moves to an inclined position, which increases the displacement of the pistons in the pump  112  and increases the flow rate of the pump  112 . 
     The hydraulic pressure generated by the pump  112  and supplied via the pressure line  116  typically powers hydraulically operated machinery in the same manner discussed above with respect to the variable-displacement piston pump  10  of FIG.  1 . As such it is desirable, such as in emergency conditions, to immediately stop operation of that machinery 
     As shown in FIG. 2, a dump valve  132  is connected between the pressure line  116  and a reservoir  134 . In a closed state, the dump valve  132  prevents hydraulic pressure from flowing to the reservoir  134  from the pressure line  116 . However, in an open state, as shown in FIG. 2, the dump valve  132  permits hydraulic pressure to flow to the reservoir  134 , which substantially eliminates hydraulic pressure in the pressure line  116 . By placing the dump valve  132  in the open state, operation of machinery utilizing the hydraulic pressure in the pressure line  116  can be brought to a halt. 
     In the dump systems of FIGS. 1 and 2, the immediate elimination of hydraulic pressure in the pressure line  116  causes a significant shock or jolt. Furthermore, this immediate elimination of hydraulic pressure defeats the benefits provided by systems incorporating a ramp down feature. Systems incorporating a ramp down feature include hydraulic elements which gradually reduce their demand for hydraulic pressure such that the hydraulic pressure supplied by the variable-displacement piston pump  10  or  110 , in response to this demand, gradually decreases. Consequently, machinery operating based on the hydraulic pressure supplied by the variable-displacement piston pump  10  or  110  gradually comes to a halt. 
     SUMMARY OF THE INVENTION 
     The pump enable system according to the present invention comprises: a variable-displacement piston pump having a displacement control device, said displacement control device controlling displacement of pistons in said pump based on a position thereof, and position control system for controlling a position of said displacement control device based on a load on said pump; and an over-ride system for selectively over-riding said position control system such that said displacement control device assumes a position which reduces displacement of said pistons in said pump. 
     The method of enabling a variable-displacement piston pump according to the present invention, in which said pump includes a displacement control device controlling displacement of pistons in said pump based on a position thereof and position control system for controlling a position of said displacement control device based on a load on said pump, comprises: selectively over-riding said position control system such that said displacement control device assumes a position which reduces displacement of said pistons in said pump. 
     By controlling the displacement control device, as opposed to exhausting hydraulic pressure supplied by the pump, the pump enable system and method according to the present invention significantly reduces the pressure supplied by the variable-displacement pump without causing a shock or jolt. 
     In at least one embodiment of the pump enable system and method according to the present invention, over-riding the position control system is delayed to prevent defeating the ramp down feature. 
     Other objects, features, and characteristics of the present invention; methods, operation, and functions of the related elements of the structure; combination of parts; and economies of manufacture will become apparent from the following detailed description of the preferred embodiments and accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
     FIG. 1 schematically illustrates a prior art variable-displacement piston pump with a dump system; 
     FIG. 2 schematically illustrates another prior art variable-displacement piston pump with a dump system; 
     FIG. 3 schematically illustrates a first embodiment of the pump enable system according to the present invention in a first state; 
     FIG. 4 schematically illustrates a first embodiment of the pump enable system according to the present invention in a second state; 
     FIG. 5 schematically illustrates a second embodiment of the pump enables system according to the present invention in a first state; 
     FIG. 6 schematically illustrates a second embodiment of the pump enable system according to the present invention in a second state; and 
     FIG. 7 illustrates a control circuit for the solenoid valve in the pump enable system according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 3 schematically illustrates a first embodiment of the pump enable system according to the present invention in a first state. As shown in FIG. 3, the pump enable system according to the first embodiment includes the variable-displacement piston pump  10  discussed in detail above with respect to FIG.  1 . Accordingly, the description of this variable-displacement piston pump will not be repeated. 
     As further shown in FIG. 3, the housing  50  of the variable-displacement piston pump  10  has been modified to include a solenoid valve  52 . The solenoid valve  52  is connected between the first control input  40  of the pressure compensation valve  26  and the servo piston  24 . The solenoid valve  52  has a closed state which prevents hydraulic pressure from flowing to the servo piston  24  from the first control input  40 , and an open state which allows hydraulic pressure to flow from the first control input  40  to the servo piston  24 . The solenoid valve  52  assumes either the open or closed state based on a received control signal. 
     When the solenoid valve  52  is placed in the closed state as shown in FIG. 3, the variable-displacement piston pump  10  operates in the conventional manner. When, however, the solenoid valve  52  is placed in the open state as shown in FIG. 4, the hydraulic pressure at the first control input  40  of the pressure compensation valve  26  (i.e., the hydraulic pressure generated by the pump  12 ) flows to the servo piston  24  via the solenoid valve  52 . 
     Even if the servo piston  24  is connected with the drain line  20  via the pressure and flow compensation valves  26  and  28  as shown in FIG. 2, this connection to the drain line  20  can not sufficiently exhaust the hydraulic pressure being supplied via the solenoid valve  52  to prevent the servo piston  24  from extending. As a result, the servo piston  52  extends and the swash plate  22  moves and reduces the displacement of the pistons in the pump  12 . This causes a reduction in the flow rate of the pump  12 . Specifically, the swash plate  22  reduces the displacement of the pistons in the pump  12  such that the pump  12  can not generate hydraulic pressure above 150 PSI. Hydraulic pressure below 150 PSI is insufficient to operate machinery, but the shock or jolt experienced in prior art pump enable systems is substantially eliminated. 
     Furthermore, when de-energized, the solenoid valve  52  is in the open state. Unless the solenoid valve  52  is energized, the variable-displacement piston pump  10  does not generate a hydraulic pressure above 150 PSI. Accordingly, even if, for example, the directional control valve to which the variable-displacement piston pump  10  is connected sticks in the open state, undesired operation of machinery does not occur. 
     As an alternative embodiment, the solenoid valve  52  is connected externally to the variable-displacement piston pump  10 . 
     FIG. 5 schematically illustrates another embodiment of the pump enable system according to the present invention in a first state. As shown in FIG. 5, the pump enable system according to this embodiment includes the variable-displacement piston pump  110  discussed in detail above with respect to FIG.  2 . Accordingly, the description of this variable-displacement piston pump  110  will not be repeated. 
     As further shown in FIG. 5, a solenoid valve  152 , external to the housing  150  of the variable-displacement piston pump  110 , is connected to the variable-displacement piston pump  110 . Specifically, the solenoid valve  152  is connected between the servo piston  124  and the drain line  120 . The solenoid valve  152  has a closed state which prevents hydraulic pressure from flowing to the drain line  120  from the servo piston  124 , and an open state which allows hydraulic pressure to flow from the servo piston  124  to the drain line  120 . The solenoid valve  152  assumes either the open or closed state based on a received control signal. 
     When the solenoid valve  152  is placed in the closed state as shown in FIG. 5, the variable-displacement piston pump  110  operates in the conventional manner. When, however, the solenoid valve  152  is placed in the open state as shown in FIG. 6, the hydraulic pressure at the servo piston  124  flows to the drain line  120  via the solenoid valve  152 . 
     The hydraulic pressure at the servo piston  124  exhausts to the drain line  120  via the solenoid valve  152  regardless of the state of the differential adjustment valve  126 . For instance, as shown in FIG. 6, even if the differential adjustment valve  126  is in the second state for supplying hydraulic pressure to the servo piston  124 , when the solenoid valve  152  is in the open state, hydraulic pressure exhausts from the servo piston  124  to the drain line  120 . 
     As a result, the servo piston  124  retracts and the swash plate  122  moves to reduce the displacement of the pistons in the pump  112 . This causes a reduction in the flow rate of the pump  112 . Specifically, the swash plate  122  reduces the displacement of the pistons in the pump  112  such that the pump  112  can not generate hydraulic pressure above 150 PSI. Hydraulic pressure below 150 PSI is insufficient to operate machinery, but the shock or jolt experienced in prior art pump enable systems is substantially eliminated. 
     Furthermore, when de-energized, the solenoid valve  152  is in the open state. Unless the solenoid valve  152  is energized, the variable-displacement piston pump  110  does not generate a hydraulic pressure above 150 PSI. Accordingly, even if, for example, the directional control valve to which the variable-displacement piston pump  110  is connected sticks in the open state, undesired operation of machinery does not occur. 
     As an alternative embodiment, the housing  150  of the variable-displacement piston pump  110  is modified to include the solenoid valve  152 . 
     FIG. 7 illustrates a control circuit for the solenoid valve  52  or  152  in the pump enable system according to the present invention. As shown, a motion signal from a function controller or switch is supplied to both a motion alarm  200  and delay timer  202 . The delay timer  202  also receives a  12  volt power supply, and outputs the control signal to the solenoid valve  52  or  152 . 
     The delay timer  202  includes an internal timer circuit  204  and a switching relay  206 . The switching relay  206  includes a coil  208  and a switch  210 . The coil  208  receives an output signal from the internal timer circuit  204 . The switch  210  is connected between the 12 volt power supply and the solenoid valve  52  or  152 . When the coil  208  is de-energized, the switch  210  is open, and when the coil  208  is energized, the switch  210  closes and provides a control signal to energize the solenoid valve  52  or  152 . 
     When the motion alarm  200  receives a motion signal, the motion alarm  200  outputs an alarm. When the internal timer circuit  204  receives the motion signal, the internal timer circuit  204  counts to a predetermined period of time, and then energizes the coil  208 . Accordingly, the switch  210  closes and energizes the solenoid valve  52  or  152 . 
     When the motion signal is discontinued, the motion alarm  200  stops issuing the alarm and the internal timer circuit  204  de-energizes the coil  208  a predetermined period of time after the motion signal is discontinued. Once the coil is de-energized, the switch  210  opens and the solenoid valve  52  or  152  is de-energized. 
     Because of the delay timer  202 , the solenoid valve  52  or  152  is energized or de-energized a predetermined period of time after the motion signal is issued or discontinued. This delay allows systems incorporating a ramp down feature and the pump enable system according to the present invention to enjoy the features of the ramp down system. Namely, the ramp down begins when the motion signal is discontinued, but the solenoid valve  52  or  152  is not de-energized until a predetermined period of time thereafter. Consequently, machinery operating based on the hydraulic pressure supplied by the variable-displacement piston pump  10  or  110  gradually comes to a halt. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.