Patent Publication Number: US-2021171325-A1

Title: Hydraulic control system for on-vehicle winch

Description:
TECHNICAL FIELD 
     The present disclosure relates to hydraulic winch systems mounted on a vehicle, and more particularly to hydraulic control systems for such winches. 
     BACKGROUND 
     It is common to mount a hydraulic winch system onto a vehicle where the vehicle includes an onboard hydraulic system. For example on a light armored vehicle (LAV) intended for use in military or law enforcement applications may be provided with a hydraulically driven winch. It is desirable to integrate such a hydraulic winch with the onboard hydraulic system of the vehicle. 
     SUMMARY 
     In one aspect, the present disclosure is directed to a hydraulic control circuit for a hydraulic on-vehicle winch. The hydraulic control circuit comprises a main circuit pressure inlet connectible in fluid communication with a source of pressurized hydraulic fluid, a reel-out port connectible in fluid communication with a reel-out connector of the winch, a reel-in port connectible in fluid communication with a reel-in connector of the winch, and a winch control circuit. The winch control circuit is hydraulically interposed between the main circuit pressure inlet and the reel-out port and between the main circuit pressure inlet and the reel-in port and operable to selectively supply pressurized hydraulic fluid from the main circuit pressure inlet to one of the reel-out port and the reel-in port. The winch control circuit is governed by a pilot-operated directional valve in fluid communication with a reel-out pilot valve, a reel-in pilot valve and the main circuit pressure inlet. When the reel-out pilot valve supplies hydraulic pressure to the pilot-operated directional valve, hydraulic fluid flow from the main circuit pressure inlet to the reel-out port is permitted while hydraulic fluid flow from the main circuit pressure inlet to the reel-in port is obstructed. When the reel-in pilot valve supplies hydraulic pressure to the pilot-operated directional valve, hydraulic fluid flow from the main circuit pressure inlet to the reel-in port is permitted while hydraulic fluid flow from the main circuit pressure inlet to the reel-out port is obstructed. An enabling circuit is hydraulically interposed between the main circuit pressure inlet and the winch control circuit and selectively configurable between an enabling configuration and a disabling configuration. In the enabling configuration, hydraulic fluid flow from the main circuit pressure inlet to the pilot-operated directional valve, the reel-out pilot valve and to the reel-in pilot valve is permitted, and in the disabling configuration hydraulic fluid flow from the main circuit pressure inlet to the pilot-operated directional valve is obstructed. 
     The hydraulic control circuit may further comprise a tank return outlet connectible in fluid communication with a hydraulic fluid return tank coupling. In such an embodiment, the winch control circuit is further coupled in fluid communication with the tank return outlet, and the winch control circuit is configured so that when the reel-out pilot valve supplies hydraulic pressure to the pilot-operated directional valve, hydraulic fluid flow from the winch into the reel-in port is directed to the hydraulic fluid return tank coupling, and when the reel-in pilot valve supplies hydraulic pressure to the pilot-operated directional valve, hydraulic fluid flow from the winch into the reel-out port is directed to the hydraulic fluid return tank coupling. 
     The hydraulic control circuit may further comprise a case drain outlet connectible in fluid communication with a hydraulic fluid tank and a case drain inlet connectible in fluid communication with a winch case drain connector, with the case drain inlet in fluid communication with the case drain outlet. 
     The hydraulic control circuit may further comprise a load sense port connectible in fluid communication with a load sense inlet on the vehicle. The enabling circuit is configured to supply pressurized hydraulic fluid to the load sense port, with the pressurized hydraulic fluid supplied to the load sense port being at a pressure representative of a load-induced pressure at an inlet of the winch control circuit. 
     The enabling circuit may comprise an enabling circuit pressure inlet in fluid communication with the main circuit pressure inlet, a pilot valve outlet in fluid communication with the reel-out pilot valve and the reel-in pilot valve, a directional valve outlet in fluid communication with the pilot-operated directional valve, a drain outlet, a vented logic element, an enable valve, and a pressure relief valve. The enabling circuit pressure inlet is in fluid communication with the pilot valve outlet, and the vented logic element is hydraulically interposed, downstream of a fluid communication coupling between the enabling circuit pressure inlet and the pilot valve outlet, between the enabling circuit pressure inlet and the directional valve outlet and also between the enabling circuit pressure inlet and a sink. The enable valve is interposed between the vented logic element and the drain and the pressure relief valve is interposed between the enable valve and the drain. When the enable valve is in an open configuration, the enabling circuit is in the enabling configuration and the vented logic element can vent through the enable valve and then through the relief valve to the sink, whereby pressurized hydraulic fluid can flow through the vented logic element to the directional valve outlet. When the enable valve is in a closed configuration, the enabling circuit is in the disabling configuration and venting of the vented logic element is obstructed, whereby pressurized hydraulic fluid flow through the vented logic element to the directional valve outlet is obstructed. 
     The vented logic element may be, for example, a spool-type logic element. 
     The sink may be, for example, a case drain outlet of the hydraulic circuit and the case drain outlet is connectible in fluid communication with the hydraulic fluid return coupling. 
     The hydraulic control circuit may further comprise a free spool port in fluid communication with the case drain outlet and connectable in fluid communication with a free spool connector on the winch and a free spool pilot valve hydraulically interposed between the free spool port and the case drain outlet and selectively configurable between a winding configuration and a free spooling configuration. In the winding configuration, flow of hydraulic fluid from the free spool port to the case drain outlet is permitted, and in the free spooling configuration, hydraulic fluid is supplied to the free spool port and flow of hydraulic fluid from the free spool port to the case drain outlet is obstructed. 
     The hydraulic control circuit may further comprise a brake release port in fluid communication with the case drain outlet and connectible in fluid communication with a brake release connector on the winch. The reel-out pilot valve may be hydraulically interposed between the brake release port and the case drain outlet. In such an arrangement, when the reel-out pilot valve supplies hydraulic pressure to the pilot-operated directional valve, hydraulic fluid flow from the brake release port to the case drain outlet is obstructed and hydraulic fluid flow to the brake release port from the main circuit pressure inlet is permitted, and when the reel-out pilot valve obstructs hydraulic pressure to the pilot-operated directional valve, hydraulic fluid flow from the brake release port to the case drain outlet is permitted and hydraulic fluid flow to the brake release port from the main circuit pressure inlet is obstructed. 
     A pilot operated pressure-reducing valve assembly may be hydraulically interposed between a main inlet of the winch control circuit inlet and a primary inlet of the pilot-operated directional valve. A fluid line may connect from between the pilot operated pressure-reducing valve assembly and the pilot-operated directional valve in valve-governed fluid communication with the tank return outlet. 
     A pressure-limiting valve may be hydraulically interposed between the pilot valve outlet and the reel-out pilot valve and between the pilot valve outlet and the reel-in pilot valve. The pressure-limiting valve may also be hydraulically interposed between the pilot valve outlet and the free spool pilot valve. 
     A counterbalance valve may be hydraulically interposed between the pilot-operated directional valve and the reel-in port, with the counterbalance valve having a reel-in port fluid aperture connected in fluid communication with the reel-in port, a pilot-operated directional valve fluid aperture connected in fluid communication with the pilot-operated directional valve, and a pilot pressure inlet connected in fluid communication with the reel-out port. The counterbalance valve may be configured so that when pressure exceeding a counterbalance valve threshold is supplied to the pilot pressure inlet from the reel-out port, hydraulic fluid flow from the reel-in port through the counterbalance valve to the pilot-operated directional valve is permitted, and when pressure supplied from the reel-out port to the pilot pressure inlet is below the counterbalance valve threshold, hydraulic fluid flow from the reel-in port through the counterbalance valve to the pilot-operated directional valve is obstructed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features will become more apparent from the following description in which reference is made to the appended drawing wherein: 
         FIG. 1  is a schematic diagram of a first illustrative embodiment of a hydraulic control system according to an aspect of the present disclosure; 
         FIG. 1A  is a schematic diagram of a second illustrative embodiment of a hydraulic control system according to an aspect of the present disclosure; 
         FIG. 2  shows an illustrative handheld, cabled pendant containing toggle switches for controlling the hydraulic control system of  FIG. 1 ; 
         FIG. 3  is a perspective view showing an illustrative enabling manifold for housing components of an enabling circuit; 
         FIG. 4  is a perspective view showing an illustrative control manifold for housing components of a winch control circuit according to the first illustrative embodiment; 
         FIG. 4A  is a perspective view showing an illustrative control manifold for housing components of a winch control circuit according to the second illustrative embodiment; and 
         FIG. 5  is a perspective view showing the enabling manifold of  FIG. 3  and the control manifold of  FIG. 4  in their mounted positions relative to a hydraulic winch assembly. 
     
    
    
     DETAILED DESCRIPTION 
     Throughout the specification, references to specific model numbers of valves and other components, unless otherwise specified, refer to those offered by HydraForce, Inc., having an address at 500 Barclay Blvd., Lincolnshire, Ill. 60069 USA, and are merely examples for purposes of illustration and are not intended to be limiting. The illustrated embodiment is intended to operate with an input hydraulic flow rate of about 12-40 GPM, with a tank line pressure of about 50-800 PSI depending on the flow rate (higher flow rates result in higher pressure); again these are merely illustrative example values and are not intended to be limiting. 
     Reference is now made to  FIG. 1 , which is a schematic diagram of a first illustrative hydraulic control circuit  100  for a hydraulic on-vehicle winch. In  FIG. 1 , port size and thread type are designated at the indicated connections as follows:
         4T=−4 SAE O-ring Boss (SAE J1926/1)   10T=−10 SAE O-ring Boss (SAE J1926/1)
 
These are merely examples, and are not intended to be limiting.
       

     The winch is illustrated schematically by the rectangular box  102  at the upper portion of  FIG. 1 . The illustrated winch  102  includes a brake release connector  104 , a reel-out connector of  106 , a reel-in connector  108 , a free spool connector  110  and a case drain connector  112 . This is merely an illustrative embodiment of a winch, and hydraulic control circuits according to aspects of the present disclosure may be used with other winches. For example, some winches may not include a brake release connector and/or free spool connector. The winch  102  is described and illustrated solely for the purpose of explaining operation of the hydraulic control circuit  100 , and does not form part of the invention as claimed. 
     The hydraulic control circuit  100  integrates the winch  102  with the on-board hydraulic system of a vehicle, illustrated schematically by the rectangular box  114  at the lower portion of  FIG. 1 . The on-board hydraulic system of the vehicle  114  includes a load sense inlet  116 , a source of pressurized hydraulic fluid  118 , a case drain coupling  120  and a hydraulic fluid return tank coupling  122  that communicates with a hydraulic fluid tank on the vehicle. Typically, hydraulic fluid received at the case drain coupling  120  is recycled to the hydraulic fluid tank. The on-board hydraulic system of the vehicle  114  is described and illustrated solely for the purpose of explaining operation of the hydraulic control circuit  100 , and does not form part of the invention as claimed. Again, the illustrated on-board hydraulic system of the vehicle  114  is merely an illustrative embodiment, and hydraulic control circuits according to aspects of the present disclosure may be used with other hydraulic systems. For example, some hydraulic systems may not include a load sense inlet. 
     The hydraulic control circuit  100  comprises a main circuit pressure inlet P 1  connectible in fluid communication with the source of pressurized hydraulic fluid  118 , a reel-out port RO connectible in fluid communication with the reel-out connector  106  of the winch  102  and a reel-in port RI connectible in fluid communication with the reel-in connector  108  of the winch  102 . 
     The hydraulic control circuit  100  comprises a winch control circuit, denoted by upper dashed box  130 . The winch control circuit  130  is hydraulically interposed between the main circuit pressure inlet P 1  and the reel-out port RO and between the main circuit pressure inlet P 1  and the reel-in port RI. The winch control circuit  130  is operable to selectively supply pressurized hydraulic fluid from the main circuit pressure inlet P 1  to one of the reel-out port RO and the reel-in port RI and thereby control operation of the winch  102 . 
     The winch control circuit  130  is governed by a pilot-operated directional valve PD 1 , which is in fluid communication with a reel-out pilot valve SV 2  and a reel-in pilot valve SV 3  and with the main circuit pressure inlet P 1  (as described further below). The reel-out pilot valve SV 2  controls the reel-out function of the winch  102  and, the reel-in pilot valve SV 3  controls the reel-in function of the winch  102 . Where a brake/brake release function is present, the reel-out pilot valve SV 2  may control this function as well, as described further below. In the illustrated embodiment, the pilot-operated directional valve PD 1  is a pilot-operated, spool-type hydraulic directional valve, for example model HPD42-S67D-0-U-170 and the reel-out pilot valve SV 2  and the reel-in pilot valve SV 3  are both solenoid-operated, 3-way, direct-acting, spool-type directional valves, for example model SV58-30-0-P-24ER/Z. These are merely illustrative examples and are not intended to be limiting. 
     When the reel-out pilot valve SV 2  supplies hydraulic pressure to the pilot-operated directional valve PD 1 , hydraulic fluid flow from the main circuit pressure inlet P 1  to the reel-out port RO is permitted, via the pilot-operated directional valve PD 1 , while hydraulic fluid flow from the main circuit pressure inlet P 1  to the reel-in port RI is obstructed. Conversely, when the reel-in pilot valve SV 3  supplies hydraulic pressure to the pilot-operated directional valve PD 1 , hydraulic fluid flow from the main circuit pressure inlet P 1  to the reel-in port RI is permitted through the pilot-operated directional valve PD 1 , while hydraulic fluid flow from the main circuit pressure inlet P 1  to the reel-out port RO is obstructed. 
     The hydraulic control circuit  100  also comprises an enabling circuit, denoted by lower dashed box  132 . The enabling circuit  132  is hydraulically interposed between the main circuit pressure inlet P 1  and the winch control circuit  130 . The enabling circuit  132  is selectively configurable between an enabling configuration and a disabling configuration. When the enabling circuit  132  is in the enabling configuration, hydraulic fluid flow from the main circuit pressure inlet P 1  to the pilot-operated directional valve PD 1 , to the reel-out pilot valve SV 2  and to the reel-in pilot valve SV 3  is permitted. When the enabling circuit  132  is in the disabling configuration, hydraulic fluid flow from the main circuit pressure inlet P 1  to the pilot-operated directional valve PD 1  is obstructed, although hydraulic fluid flow from the main circuit pressure inlet P 1  to the reel-out pilot valve SV 2  and to the reel-in pilot valve SV 3  may be permitted. 
     In the illustrated embodiment, the hydraulic control circuit  100  further comprises a tank return outlet T connectible in fluid communication with the hydraulic fluid return tank coupling  122 , and the winch control circuit  130  is further coupled in fluid communication with the tank return outlet T. The winch control circuit  130  is configured to return the pressurized hydraulic fluid supplied to the winch  102  to drive rotation of the winch drum (i.e. reel-in and reel-out operation) back to the tank return outlet T. In this regard, it is contemplated that pressurized hydraulic fluid supplied to the reel-out connector  106  will, after driving rotation of the winch drum, be directed to flow out of from the reel-in connector  108 . Likewise, it is contemplated that that pressurized hydraulic fluid supplied to the reel-in connector  108  will, after driving rotation of the winch drum, be directed to flow out of the reel-out connector  106 . 
     When the reel-out pilot valve SV 2  supplies hydraulic pressure to the pilot-operated directional valve PD 1 , hydraulic fluid flows through the reel-out port RO into the reel out connector  106 , through the winch  102  and then the reel-in connector  108  into the reel-in port RI. This fluid is then directed through the pilot-operated directional valve PD 1  to the tank return outlet T and then to the hydraulic fluid return tank coupling  122 . Similarly, when the reel-in pilot valve SV 3  supplies hydraulic pressure to the pilot-operated directional valve PD 1 , hydraulic fluid flows through the reel-in port RI into the reel-in connector  108 , through the winch  102  and then the reel-out connector  106  into the reel-out port RO, and is then is directed through the pilot-operated directional valve PD 1  to the tank return outlet T and then to the hydraulic fluid return tank coupling  122 . 
     In the illustrated embodiment, the hydraulic control circuit  100  further comprises a case drain outlet  140  connectible in fluid communication with the hydraulic fluid tank. For example, where the on-board hydraulic system of the vehicle provides for hydraulic fluid received at the case drain coupling  120  to be recycled to the hydraulic fluid tank, the case drain outlet  140  may be connectible in fluid communication with the case drain coupling  120 . The illustrated hydraulic control circuit  100  further comprises a case drain inlet  142  connectible in fluid communication with the winch case drain connector  112 , and the case drain inlet  142  is in fluid communication with the case drain outlet  140 . 
     The illustrated hydraulic control circuit  100  further comprises a free spool port FS connectible in fluid communication with the free spool connector  110  and also in fluid communication with a sink. In the illustrated embodiment, the sink is the case drain outlet  140  and connection is by way of a winch control circuit drain outlet  144 . A free spool pilot valve SV 4  is hydraulically interposed between the free spool port FS and the case drain outlet  140  and selectively configurable between a winding configuration and a free spooling configuration. In the winding configuration, flow of hydraulic fluid from the free spool port FS to the case drain outlet  140  is permitted. It is contemplated that when no hydraulic fluid is supplied to the free spool connector  110 , a free spool actuator in the winch  102  is biased into a configuration in which pressurized hydraulic fluid supplied to the reel-out connector  106  or the reel-in connector  108  will drive rotation of the drum. In the free spooling configuration, hydraulic fluid is supplied to the free spool port FS through the free spool pilot valve SV 4  and flow of hydraulic fluid from the free spool port FS to the case drain outlet  140  is obstructed. This leaves the winch  102  in a default condition where the winch drum can be driven by hydraulic flow but does not rotate freely. When hydraulic fluid is supplied to the free spool connector  110 , the free spool actuator in the winch  102  will be moved into a configuration in which the drum can freely rotate. The free spool pilot valve SV 4  may be, for example, a solenoid-operated, 3-way, direct-acting, spool-type directional valve, for example model SV58-30-0-P-24ER/Z. This is merely an illustrative example and is not intended to be limiting. Where the winch does not include a free spool feature, the corresponding aspects of the hydraulic control circuit  100  may be omitted. 
     In the illustrated embodiment, the hydraulic control circuit  100  further comprises a brake release port BR in fluid communication with the sink and connectible in fluid communication with the brake release connector  104  on the winch  102 . As noted above, in the illustrated embodiment the sink is the case drain outlet  140 , with connection via the winch control circuit drain outlet  144 , although other configurations are also contemplated. The reel-out pilot valve SV 2  is hydraulically interposed between the brake release port BR and the case drain outlet  140 . It is contemplated that when no hydraulic fluid is supplied to the brake release connector  104 , a on the winch  102 , for example a sprag clutch, will be engaged, and when hydraulic fluid is supplied to the brake release connector  104 , the brake will be disengaged. The sprag clutch is merely one example of a brake, and is not intended to be limiting. When the reel-out pilot valve SV 2  supplies hydraulic pressure to the pilot-operated directional valve PD 1 , hydraulic fluid flow from the brake release port BR to the case drain outlet is obstructed and hydraulic fluid also flows into the brake release connector  104  to disengage the brake. When the reel-out pilot valve SV 2  obstructs hydraulic pressure to the pilot-operated directional valve PD 1 , hydraulic fluid flow from the brake release port BR to the case drain outlet  140  is also obstructed, and the ratchet-brake will engage. Where the winch does not include a brake, the corresponding aspects of the hydraulic control circuit  100  may be omitted. 
     In the illustrated hydraulic control circuit  100 , the enabling circuit  132  comprises an enabling circuit pressure inlet  162 , a pilot valve outlet  164 , a directional valve outlet  166 , an enabling circuit drain outlet  168 , a load sense port  170 , a vented logic element EV 1 , an enable valve SV 1  and a pressure relief valve RV 1 . The directional valve outlet  166  is in fluid communication with the main inlet  150  of the winch control circuit  130 , and thereby in fluid communication, through an on-demand pressure compensator valve EC 1  (described further below) with the pilot-operated directional valve PD 1 . The enabling circuit drain outlet  168  is in fluid communication with the case drain outlet  140 . 
     The load sense port  170  is connectible in fluid communication with the load sense inlet  116  on the vehicle. The enabling circuit  132  is configured to supply pressurized hydraulic fluid to the load sense port  170 . The pressurized hydraulic fluid supplied to the load sense port  170  is at a pressure representative of a load-induced pressure at the main inlet  150  of the winch control circuit  130 . The main inlet  150  is the inlet that receives the pressurized hydraulic fluid to be supplied to the reel-out connector  106  and reel-in connector  108  on the winch  102 , as distinguished from the pilot valve inlet  152 . The pilot valve inlet  152  receives the pressurized hydraulic fluid that will be supplied to the pilot valves SV 2 , SV 3  and SV 4 , and is coupled in fluid communication with the pilot valve outlet  164  to receive pressurized hydraulic fluid therefrom. 
     The enabling circuit pressure inlet  162  is in fluid communication with the pilot valve outlet  164 , and the vented logic element EV 1  is disposed downstream of a fluid communication coupling between the enabling circuit pressure inlet  162  and the pilot valve outlet  164 . The vented logic element EV 1  is hydraulically interposed between the enabling circuit pressure inlet  162  and the directional valve outlet  166 . The pressurized hydraulic fluid supplied to the directional valve outlet  166  is also fed, through a check valve CV 1  to prevent back flow, to the load sense port  170 . The vented logic element EV 1  is further hydraulically interposed between the enabling circuit pressure inlet  162  and the sink, in this instance the case drain outlet  140  via the enabling circuit drain outlet  168 . The enable valve SV 1  is interposed between the vented logic element EV 1  and the case drain outlet  140 , and the pressure relief valve RV 1  is interposed between the enable valve SV 1  and the case drain outlet  140 . As can be seen, in the illustrated embodiment the enable valve SV 1  is interposed between the vented logic element EV 1  and the enabling circuit drain outlet  168 , and the pressure relief valve RV 1  is interposed between the enable valve SV 1  and the enabling circuit drain outlet  168 . The enabling circuit drain outlet  168  then feeds to the case drain outlet  140 . 
     In the illustrated embodiment, the vented logic element EV 1  is a spool-type logic element in the form of a high flow pilot operated valve and the enable valve SV 1  is a solenoid operated, 2-way, normally closed, direct-acting spool-type directional valve. The vented logic element EV 1  cooperates with the enable valve SV 1  to move the enabling circuit  132  between the enabling configuration and the disabling configuration and the pressure relief valve RV 1  sets the minimum pressure for the winch control circuit  130 . 
     When the enable valve SV 1  is in an open configuration, the enabling circuit  132  is in the enabling configuration. When the enabling circuit  132  is in the enabling configuration, the vented logic element EV 1  can vent through the enable valve SV 1  and then through the relief valve RV 1  to the case drain outlet  140 . This enables pressurized hydraulic fluid to flow through the vented logic element EV 1  to the directional valve outlet  166  and then to the main inlet  150  of the winch control circuit  130 . 
     When the enable valve SV 1  is in a closed configuration, the enabling circuit  132  is in the disabling configuration. When the enabling circuit  132  is in the disabling configuration, venting of the vented logic element EV 1  is obstructed by the closed enable valve SV 1 , with the result that pressurized hydraulic fluid flow to the directional valve outlet  166  is obstructed by the vented logic element EV 1 . 
     Thus, when the enabling circuit  132  is in the enabling configuration, hydraulic fluid flow from the main circuit pressure inlet P 1  to the main inlet  150  of the winch control circuit  130 , and thereby to the pilot-operated directional valve PD 1 , is permitted. At least in the enabling configuration, hydraulic fluid flow from the main circuit pressure inlet P 1  to the pilot valve inlet  152  and thereby to the reel-out pilot valve SV 2  and to the reel-in pilot valve SV 1  is also permitted. Conversely, when the enabling circuit  132  is in the disabling configuration, hydraulic fluid flow from the main circuit pressure inlet P 1  to the main inlet  150  of the winch control circuit  130 , and hence to the pilot-operated directional valve PD 1 , is obstructed. 
     In the illustrated embodiment, the vented logic element EV 1  may be, for example, model EV12-S34-0-N-100. Other types of vented logic elements may be used in alternate embodiments; for example, a poppet-type valve may be used with suitable modification of the hydraulic control circuit. The enable valve SV 1  may be, for example, model SV58-24-0-P-24ER and the pressure relief valve RV 1  may be, for example, model RV50-22H-0-P-50/5.0. The check valve CV 1  may be, for example, model HCV06-20-U-05. These are merely examples and are not intended to be limiting. 
     Pressurized hydraulic fluid received at the pilot valve inlet  152  from the pilot valve outlet  164  passes through a pressure-reducing valve PR 2 , which sets the maximum pressure in the pilot circuit portion of the winch control circuit  130 . The pressure-reducing valve PR 2  is hydraulically interposed between the pilot valve inlet  152  and the pilot valves, that is, the reel-out pilot valve SV 2 , the reel-in pilot valve SV 3  and the free spool pilot valve SV 4 . Thus, a pressure-limiting valve (pressure-reducing valve PR 2 ) is hydraulically interposed between the pilot valve outlet  164  and the reel-out pilot valve SV 2 , between the pilot valve outlet  164  and the reel-in pilot valve SV 3 , and between the pilot valve outlet  164  and the free spool pilot valve SV 4 . Since the spring chamber of the pressure-reducing valve PR 2  is referencing the case drain outlet  140 , the tank pressures have no effect on its setting and the pressure-reducing valve PR 2  will provide stable pressure throughout the operating flow range. The pressure-reducing valve PR 2  may be, for example, model PR58-38H-0-P-20/7.0, and in the illustrated embodiment, the pressure-reducing valve PR 2  steps down the pressure to about 700 PSI; these are merely examples and are not intended to be limiting. 
     Pressurized hydraulic fluid received at the main inlet  150  from the directional valve outlet  166  passes through an on-demand pressure compensator valve EC 1 , which serves as a high flow pilot operated pressure-reducing valve. The on-demand pressure compensator valve EC 1  is hydraulically interposed between the main inlet  150  and the pilot-operated directional valve PD 1 , and may be, for example, model HEC16-32-0-U-80. This is merely an example and is not intended to be limiting. A pressure relief valve RV 2  is hydraulically interposed between the on-demand pressure compensator valve EC 1  and the case drain outlet  140 , in this case between the on-demand pressure compensator valve EC 1  and the winch control circuit drain outlet  144 . The pressure relief valve RV 2  sets the pressure for the on-demand pressure compensator valve EC 1 , and may be, for example, model RV58-20H-0-P46/34.0. This is merely an example and is not intended to be limiting. An orifice ORF 1  enables fluid communication from a position between the on-demand pressure compensator valve EC 1  and the pilot-operated directional valve PD 1  to a position between the on-demand pressure compensator valve EC 1  and the pressure relief valve RV 2 , and may be, for example, a 0.025 inch diameter orifice. This is merely an example and is not intended to be limiting. Thus, in the illustrated embodiment a pilot operated pressure-reducing valve assembly (on-demand pressure compensator valve EC 1 , pressure relief valve RV 2  and orifice ORF 1 ) is interposed between the main inlet  150  of the winch control circuit  130  and the primary inlet of the pilot-operated directional valve PD 1 . This sets the pressure for the pilot-operated directional valve PD 1 . In the illustrated embodiment, this pressure is set to about 3400 PSI although this is merely one example and is not intended to be limiting. 
     Fluid communication from a position between the on-demand pressure compensator valve EC 1  and the pilot-operated directional valve PD 1 , downstream of the orifice ORF 1 , to the tank return outlet T is governed by a pressure relief valve RV 3 . This is to obviate pressure spikes. Thus, in the illustrated embodiment an overpressure valve governs a fluid line which connects between the pilot operated pressure-reducing valve assembly (on-demand pressure compensator valve EC 1 , pressure relief valve RV 2  and orifice ORF 1 ) and the pilot-operated directional valve PD 1 , in valve-governed fluid communication with the tank return outlet T. 
     The solenoid valves SV 1 , SV 2 , SV 3  and SV 4  and hence the hydraulic control circuit  100 , may controlled by suitable actuators in a control interface. Once such control interface is a handheld, cabled pendant containing toggle switches, an illustrative implementation of which is shown in  FIG. 2  and indicated generally at reference  200 . The pendant  200  includes an enable switch  202 , a reel control switch  204  and a free spool switch  208 . The enable switch  202  is in electrical communication with the enable valve SV 1 , the reel control switch  204  is in electrical communication with the reel-out pilot valve SV 2  and the reel-in pilot valve SV 3 , and the free spool switch  208  is in electrical communication with the free spool pilot valve SV 4 . 
     When the enable switch  202  is in the “disable” position, no voltage flows to the coil on the enable valve SV 1 , which remains closed. This leaves the enabling circuit  132  in the disabling configuration, in which hydraulic fluid flow from the main circuit pressure inlet P 1  to the main inlet  150  of the winch control circuit  130 , and hence to the pilot-operated directional valve PD 1 , is obstructed by the enabling circuit  132 . 
     When the enable switch  202  is flipped to the “enable” position, voltage is sent to the coil on the enable valve SV 1 . This opens the enable valve SV 1 , allowing hydraulic fluid from the vented logic element EV 1  to vent and placing the enabling circuit  132  in the enabling configuration. With the enabling circuit  132  in the enabling configuration, hydraulic fluid flow from the main circuit pressure inlet P 1  through the enabling circuit  132  to the main inlet  150  of the winch control circuit  130 , and thereby to the pilot-operated directional valve PD 1 , is permitted. The pressure setting on the relief valve RV 1  and the spring bias in the vented logic element EV 1  set the minimum system pressure. In the illustrated embodiment, target pressure is about 600 PSI although this is merely an example and is not intended to be limiting. 
     When the enable switch  202  is flipped to the “enable” position, placing the enabling circuit  132  in the enabling configuration, and the reel control switch  204  is moved to the “reel-out” position, voltage is applied to the solenoid on the reel-out pilot valve SV 2 . This opens the reel-out pilot valve SV 2 , which causes hydraulic fluid to flow through the brake release port BR to the brake release connector  104 . The open reel-out pilot valve SV 2  also supplies hydraulic fluid to the reel-out port  180  of the pilot-operated directional valve PD 1 , which shifts to deliver pressurized hydraulic fluid to the reel-out port RO and thereby to the reel-out connector  106  on the winch  102  to drive the winch motor. The pressurized hydraulic fluid can be supplied to the brake release connector  104  and the reel-out port  180  of the pilot-operated directional valve PD 1  at, for example, about 700 PSI, although this is merely an example and not limiting. The pilot operated pressure-reducing valve assembly (on-demand pressure compensator valve EC 1 , pressure relief valve RV 2  and orifice ORF 1  in cooperation) limit the maximum pressure to the value of (a) the setting of the pressure relief valve RV 2  added to (b) the spring rate of the on-demand pressure compensator valve EC 1 . This will be a restrictive pressure control and is referencing the case drain to make the setting immune to the tank pressure. The pressure is further controlled by the pressure relief valve RV 3 . 
     When the enable switch  202  is flipped to the “enable” position to place the enabling circuit  132  in the enabling configuration, and the reel control switch  204  is moved to the “reel-in” position, voltage is applied to the solenoid on the reel-in pilot valve SV 3 , opening the reel-in pilot valve SV 3 . The open reel-out pilot valve SV 3  then allows hydraulic fluid to flow to the reel-in port  182  of the pilot-operated directional valve PD 1 , for example at about 700 PSI. This causes the pilot-operated directional valve PD 1  to shift to deliver pressurized hydraulic fluid to the reel-in port RI and thereby to the reel-in connector  108  on the winch  102 , driving the winch motor. As with the reel-out mode, the pilot operated pressure-reducing valve assembly (on-demand pressure compensator valve EC 1 , pressure relief valve RV 2  and orifice ORF 1  in cooperation) limits the maximum pressure, and the pressure is further controlled by the pressure relief valve RV 3 . 
     When the enable switch  202  is flipped to the “enable” position, placing the enabling circuit  132  in the enabling configuration, and the free spool switch  208  is activated, voltage is applied to the solenoid on the free spool pilot valve SV 4 . This opens the free spool pilot valve SV 4  to deliver hydraulic fluid to the free spool port FS, for example at about 700 PSI, and thereby to the free spool connector  110  on the winch. 
       FIG. 1A  shows an alternate embodiment of a hydraulic control circuit according to the present disclosure. The hydraulic control circuit shown in  FIG. 1A  is identical to that shown in  FIG. 1 , save for the addition of a counterbalance valve CBV 1 , which is hydraulically interposed between the pilot-operated directional valve PD 1  and the reel-in port RI. Thus, like references denote like features in  FIGS. 1 and 1A . 
     The counterbalance valve CBV 1  has a reel-in port fluid aperture  184 , a pilot-operated directional valve fluid aperture  186  and a pilot pressure inlet  188 . The reel-in port fluid aperture  184  is connected in fluid communication with the reel-in port RI, the pilot-operated directional valve fluid aperture  186  is connected in fluid communication with the pilot-operated directional valve PD 1  and the pilot pressure inlet  188  is connected in fluid communication with the reel-out port RO. The counterbalance valve CBV 1  is configured so that when pressure exceeding a counterbalance valve threshold is supplied to the pilot pressure inlet  188  thereof from the reel-out port RO, hydraulic fluid flow from the reel-in port RI through the counterbalance valve CBV 1  to the pilot-operated directional valve PD 1  is permitted. The counterbalance valve CBV 1  is further configured so that when pressure supplied from the reel-out port RO to the pilot pressure inlet  188  is below the counterbalance valve threshold, hydraulic fluid flow from the reel-in port RI through the counterbalance valve CBV 1  to the pilot-operated directional valve PD 1  is obstructed. The counterbalance valve may be, for example, a model CBGALHN valve offered by Sun Hydraulics LLC, having an address at 1500 West University Parkway, Sarasota, Fla. 34243, USA. This is merely an illustrative example and is not intended to be limiting. 
     With certain types of winch cables and anchoring arrangements, heavy loads can induce an elastic tension into the winch cable during reel-in operations. Without a counterbalance valve, during the transition to reel-out operations, the sudden release of tension can lead to over-rotation of the winch drum in the reel-out direction, which can damage mechanical components. Without promising any particular utility, it is believed that in some applications the counterbalance valve CBV 1  may enhance control during reel-out operations and protect the winch components when under heavy loads. Where the winch cable and anchoring is not susceptible of excessive elastic tension under anticipated loads, the counterbalance valve CBV 1  may be omitted; however the counterbalance valve CBV 1  may also limit acceleration during reel-out operation by imposing valve-controlled dynamic braking, which may be desirable in some applications (independent of winch cable tension issues). 
       FIG. 3  shows an illustrative enabling manifold, indicated generally at reference  300 , for housing the components of the enabling circuit  132 , including the enable valve SV 1 , the vented logic element EV 1 , the check valve CV 1  and the relief valve RV 1 . 
       FIG. 4  shows an illustrative control manifold, indicated generally at reference  400 , for housing the components of the first illustrative winch control circuit  130  shown in  FIG. 1 , including the on-demand pressure compensator valve EC 1 , pilot-operated directional valve PD 1 , pressure-reducing valve PR 2 , pressure relief valve RV 2 , pressure relief valve RV 3 , reel-out pilot valve SV 2 , reel-in pilot valve SV 3  and free spool pilot valve SV 4 .  FIG. 4A  shows the control manifold for housing the winch control circuit  130  shown in  FIG. 1A , further including the counterbalance valve CBV 1 .  FIG. 4A  shows an illustrative control manifold for housing the components of the second illustrative winch control circuit  130  shown in  FIG. 1A , with like references denoting like features. The control manifold  400  shown in  FIG. 4A  further houses the counterbalance valve CBV 1 . 
       FIG. 5  shows the enabling manifold  300  and the control manifold  400  in their mounted positions relative to a hydraulic winch assembly, indicated generally at  500 . The winch  102  may be, for example, a model PRD30B winch offered by Paccar Inc., having an address at 800 East Dallas Street, Broken Arrow, Okla. 74012 U.S.A. This is merely an example and is not intended to be limiting. 
     One or more currently preferred embodiments have been described by way of example. It will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the claims.