Hydraulic control system and method with electro-proportional pressure valve and integral check

A hydraulic control assembly includes means for holding pressure in a cylinder to inhibit boom or arm drop of a machine in the event that a hose between the cylinder and a main control valve (MCV) ruptures. The pressure holding means of the hydraulic control assembly include a hydraulic valve and a parts-in-body check assembly both configured for insertion into a valve cavity defined by a valve body. The hydraulic valve comprises a proportional piloted valve that controls pressure.

TECHNICAL FIELD

This patent disclosure relates generally to a hydraulic valve and, more particularly, to a hydraulic control assembly with an electro-proportional pressure valve and an integral check safety feature in the event of a loss in hydraulic fluid, such as when a hose ruptures or bursts.

BACKGROUND

Machines such, as excavators and backhoe loaders, typically include a lifting linkage comprising an assembly of parts (e.g., a combination of a boom and an arm) used for raising and lowering a lift point for use in an object handling process. The machine can include a linkage control system comprising a hydraulic circuit having a plurality of hydraulic control components used for raising and lowering the lift point in object handling applications.

When such machines are used for object handling, a failure or rupture in the hydraulic circuit could endanger persons under raised loads and could damage the lifting linkage. These risks can be reduced by applying a lowering control device for controlled lowering of the load in the case of a hydraulic line failure or rupture.

Conventional solutions use a pilot-operated proportional poppet that controls the flow between the boom and the main control valve. The proportional poppet is controlled via remote pilot pressure that can come from either a pilot-operated joystick or an electro-proportional pressure reducing/relieving valve. In some cases, the electro-proportional valve is integrated with the proportional poppet into one casting or manifold, but a separate component within the assembly.

There is a continued need in the art to provide additional solutions to enhance the use and safety of hydraulic circuits over a range of conditions. For example, there is a continued need for techniques for maintaining a load in position and/or for controlled lowering of the load in the event that there is a loss of hydraulic fluid in the circuit, such as, in the case of a hydraulic line failure or rupture.

It will be appreciated that this background description has been created by the inventors to aid the reader, and is not to be taken as an indication that any of the indicated problems were themselves appreciated in the art. While the described principles can, in some aspects and embodiments, alleviate the problems inherent in other systems, it will be appreciated that the scope of the protected innovation is defined by the attached claims, and not by the ability of any disclosed feature to solve any specific problem noted herein.

SUMMARY

The present disclosure, in one aspect, is directed to embodiments of a hydraulic control assembly. In embodiments, a hydraulic control assembly includes means for holding pressure in a cylinder to inhibit boom or arm drop of a machine in the event that a hose between the cylinder and a main control valve (MCV) ruptures.

In one embodiment, a hydraulic control assembly includes a body, a hydraulic valve, and a check assembly. The body defines a valve cavity, a first port, a second port, and a third port. Each of the first port, the second port, and the third port are in fluid communication with the valve cavity. The first port is adapted to be fluidly connected to a cylinder of a hydraulic circuit, the second port is adapted to be fluidly connected to a main control valve (MCV) of the hydraulic circuit through which the second port is fluidly connected to a source of hydraulic fluid, and the third port is adapted to be fluidly connected to a tank of the hydraulic circuit. The hydraulic valve is mounted to the body such that the hydraulic valve is at least partially disposed within the valve cavity. The hydraulic valve comprises an electro-proportional pressure valve and has a nose. The check assembly is disposed within the valve cavity and in abutting relationship with the hydraulic valve such that the check assembly is seated against the nose of the hydraulic valve.

The check assembly is configured to permit a flow of hydraulic fluid from the second port to the first port through the check assembly and to prevent the flow of hydraulic fluid from the first port to the second port through the check assembly. The hydraulic valve is configured to permit the flow of hydraulic fluid from the first port to the second port through the hydraulic valve once a load pressure at the first port exceeds a threshold pressure and to block the flow of hydraulic fluid from the first port to the second port when the load pressure is below the threshold pressure.

In still another aspect, embodiments of a method of controlling a hydraulic circuit are disclosed. In one embodiment, a method of controlling a hydraulic circuit can be used to control a hydraulic circuit including a pump, a main control valve (MCV), a body, a hydraulic valve, a check assembly, a cylinder, and a tank. The body defines a valve cavity, a first port, a second port, and a third port. Each of the first port, the second port, and the third port are in fluid communication with the valve cavity. The first port is fluidly connected to the cylinder, the second port is fluidly connected to the MCV through which the second port is fluidly connected to a source of hydraulic fluid from the pump, and the third port is fluidly connected to the tank. The hydraulic valve is mounted to the body such that the hydraulic valve is at least partially disposed within the valve cavity. The hydraulic valve comprises an electro-proportional pressure valve and has a nose. The check assembly is disposed within the valve cavity and is in abutting relationship with the hydraulic valve such that the check assembly is seated against the nose of the hydraulic valve. The method includes performing a lifting operation in which a flow of pressurized hydraulic fluid is conveyed from the second port to the first port through the check assembly. A coil of the hydraulic valve is maintained in a de-energized condition during the lifting operation.

Further and alternative aspects and features of the disclosed principles will be appreciated from the following detailed description and the accompanying drawings. As will be appreciated, the hydraulic control assemblies, the hydraulic circuits, and methods disclosed herein are capable of being carried out in other and different embodiments, and capable of being modified in various respects. Accordingly, it is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and do not restrict the scope of the appended claims.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In embodiments, a hydraulic control assembly includes means for holding pressure in a cylinder to inhibit boom or arm drop of a machine in the event that a hose between the cylinder and a main control valve (MCV) ruptures. In embodiments, the pressure holding means includes an embodiment of a hydraulic valve and of a check assembly constructed according to principles of the present disclosure.

Embodiments of a hydraulic control assembly constructed according to principles of the present disclosure include a means for electro-proportionally holding pressure in the cylinder. In embodiments, the electro-proportional pressure holding means includes an embodiment of a hydraulic valve and of a check assembly constructed according to principles of the present disclosure.

Embodiments of a hydraulic control assembly constructed according to principles of the present disclosure include an electro-proportional pressure valve with an integral check safety feature in the event of a loss in hydraulic fluid, such as when a hose ruptures or bursts. The hydraulic control assembly can be configured to hold the load of the boom or arm in the event of a hose rupture between the actuator and the MCV by means of pressure control while having free reverse flow.

Embodiments of a hydraulic control assembly constructed according to principles of the present disclosure can include a hydraulic valve and a check assembly both configured for insertion into a valve cavity defined by a body. In embodiments, the hydraulic valve comprises a proportional piloted valve that controls pressure. In embodiments, the hydraulic valve comprises an electro-proportional pressure valve including a coil assembly with a coil wherein the threshold pressure is inversely proportional to an electrical current input to the coil. In embodiments, the hydraulic control assembly includes a “parts-in-body” check valve that is disposed within the valve cavity of the body. In embodiments, the parts-in-body check valve is engaged with the nose of the hydraulic valve, which acts as its seat. In embodiments, the parts-in-body check valve is less expensive and more compact than using an integral check within a cartridge valve.

Embodiments of a hydraulic control system and of a method of controlling a hydraulic system following principles of the present disclosure are adapted to control the operation of one or more hydraulic cylinders and to maintain a load of the cylinder in position and/or to controllably lower the load in the event that there is a loss of hydraulic fluid in the circuit, such as, in the case of a hydraulic line failure or rupture. Techniques and principles of the present disclosure can be used for operating a lifting linkage of a machine, such as an excavator or loader, or other systems requiring additional load-holding/load-controlling safety in the event of a loss of hydraulic fluid.

Embodiments of a hydraulic valve in the form of a screw-in or threaded cartridge valve constructed according to principles of the present disclosure can be easily serviceable. For example, a threaded hydraulic cartridge valve constructed according to principles of the present disclosure can be easily removed and replaced as part of an efficient service program.

Embodiments of a hydraulic control assembly constructed according to principles of the present disclosure can be configured to provide two functions in one cavity: pressure control and free reverse flow check. Embodiments of a hydraulic control assembly constructed according to principles of the present disclosure can include a proportional hydraulic valve that is internally piloted with no need for an additional pilot line or pilot source.

Turning now to the Figures, an embodiment of a hydraulic control assembly10constructed according to principles of the present disclosure is shown inFIGS.1and2. The illustrated hydraulic system10includes a body12defining a valve cavity14, an embodiment of a hydraulic valve15constructed according to principles of the present disclosure, and a check assembly17. The hydraulic valve15and the check assembly17are both configured for insertion into the valve cavity14defined by the body12. In the illustrated embodiment, the hydraulic valve15comprises a proportional piloted valve that controls pressure. In the illustrated embodiment, the check assembly17comprises a parts-in-body check valve that is disposed within the valve cavity14of the body12. In the illustrated embodiment, the parts-in-body check valve17is engaged with a nose20of the hydraulic valve15, which acts as the seat of the check valve17.

Referring toFIG.2, the body12defines the valve cavity14, a first port1, a second port2, and a third port3which are each in fluid communication with the valve cavity14. Each of the first port1, the second port2, and the third port3are in fluid communication with the valve cavity14. The hydraulic valve15is mounted to the body12such that the hydraulic valve15is at least partially disposed within the valve cavity14. In embodiments, the hydraulic valve15comprises an electro-proportional pressure valve. The check assembly17is disposed within the valve cavity14and is in abutting relationship with the hydraulic valve15such that the check assembly17is seated against the nose20of the hydraulic valve15.

In the illustrated embodiment, the check assembly17is configured to permit a flow of hydraulic fluid from the second port2to the first port1through the check assembly17and to prevent a flow of hydraulic fluid from the first port1to the second port2through the check assembly17. In the illustrated embodiment, the hydraulic valve15is configured to selectively permit a flow of hydraulic fluid from the first port1to the second port2through the hydraulic valve15once a load pressure at the first port1exceeds a threshold pressure and to block the flow of hydraulic fluid from the first port1to the second port2when the load pressure is below the threshold pressure.

Referring toFIGS.2and3, the first port1of the body12is adapted to be fluidly connected to a cylinder22of a hydraulic circuit21of a lifting linkage system of a machine. The second port2is adapted to be fluidly connected to a main control valve (MCV)23of the hydraulic circuit21of the lifting linkage system and through which it is fluidly connected to a source of hydraulic fluid supplied by a pump25. The third port3is adapted to be fluidly connected to a tank27of the hydraulic circuit21. The tank27is in fluid communication with the pump25so that the pump25can selectively draw hydraulic fluid from the tank27to provide the source of pressurized hydraulic fluid.

In the illustrated embodiment, the hydraulic control assembly10is adapted to permit a flow of hydraulic fluid from the second port2to the first port1so that the MCV23can selectively control the cylinder22of the lifting linkage system to perform a lifting operation. The hydraulic control assembly10is adapted to permit a flow of hydraulic fluid from the first port1to the second port2so that the MCV23can selectively control the cylinder22of the lifting linkage system to perform a lowering operation. The hydraulic control assembly10is adapted to permit a flow of hydraulic fluid from the first port1to the third port3to perform a pressure relief operation.

Referring toFIG.2, the illustrated check assembly17includes a check poppet31, a poppet guide32, and a check spring34. The check poppet31and the poppet guide34are each hollow and cylindrical. The check poppet31is in abutting relationship to the nose20of the hydraulic valve15. The poppet guide32is disposed remotely from the hydraulic valve15(relative to the check poppet31) and is in engaged relationship with the body12. The check spring34is disposed around the poppet guide32and within a counterbore defined by the check poppet31such that the check spring34is interposed between the check poppet31and the poppet guide32. The check spring34is adapted to generate a check spring force to urge an exterior surface35of the check poppet31into engaging relationship with the nose20of the hydraulic valve15to fluidly prevent the flow of hydraulic fluid from the first port1to the second port2through the check assembly17. The check spring34acts to urge the check poppet31into occluding relationship with the second port2relative to the first port1.

In the illustrated embodiment, the check assembly17is configured such that the flow of hydraulic fluid from the second port2to the first port1sufficient to overcome the check spring force of the check spring34moves the check poppet31away from the nose20of the hydraulic valve15toward the poppet guide32into an open position in which the flow of hydraulic fluid from the second port2to the first port1is permitted. A flow of hydraulic fluid hydraulic fluid from the first port1to the third port3is permissible through the interior of the hollow components of the check assembly17and the hydraulic valve15provided the pressure is sufficient to open the hydraulic valve15.

Referring toFIG.1, in the illustrated embodiment, the hydraulic valve15includes a cage40defining a plurality of cross holes41and an axial bore43. The cross holes41are in fluid communication with the axial bore43. The cross holes41are in fluid communication with the second port2of the body12, and the axial bore43is in fluid communication with the first port1of the body12.

The hydraulic valve15includes a movable member45in the form of a spool which is configured to selectively occlude the cross holes41defined in the cage40of the hydraulic valve15to fluidly isolate the first port1and the second port2from each other. The spool45is disposed within the axial bore43of the cage40and is axially movable over a range of travel with respect to the cage40between a closed position in which the spool45occludes the cross holes41to fluidly isolate the first port1and the second port2from each other and an open position in which the first port1and the second port2are in fluid communication with each other through the cage40. In the illustrated embodiment, a spool spring47is arranged with the spool45to generate a spring force against the spool45to bias the spool45to the closed position such that the flow of hydraulic fluid from the first port1to the second port2is blocked until the load pressure at the first port1is sufficient to overcome the spring force of the spool spring47to move the spool45to the open position.

In embodiments, the hydraulic valve15comprises an electro-proportional pressure valve including a coil assembly50with a coil51wherein the threshold pressure is inversely proportional to an electrical current input to the coil51. When the coil assembly50of the hydraulic valve15is de-energized, the spool45is in a normally-closed position in which the first port1and the second port2are fluidly isolated from each other through the hydraulic valve15. When the coil assembly50of the hydraulic valve15is energized, the spool45can be moved to one of a range of open positions in which a flow of hydraulic fluid is permitted from the first port1to the second port2through the cross holes41of the cage40of the hydraulic valve15.

In embodiments, at least one component of the check assembly17is seated against the nose20of the hydraulic valve15. In embodiments, the nose20of the hydraulic valve15comprises any portion of a distal end53of the hydraulic valve15which is inserted in the body12. In embodiments, the nose20of the hydraulic valve15against which the check assembly17is seated comprises at least one of the cage40and the movable member45. In the illustrated embodiment, the nose20of the hydraulic valve15against which the check assembly17is seated comprises the spool45. The check poppet31can include a chamfer surface54configured to facilitate the engagement of the check poppet31with the nose20of the hydraulic valve15. In embodiments, the nose20of the hydraulic valve against which the check assembly17is seated can include either only the cage40or the cage40and the spool45. In embodiments, the spool45is seated against the cage40, and the check assembly17is seated against the cage40.

In embodiments, the hydraulic valve15is configured such that the flow of hydraulic fluid from the first port1to the second port2is pressure relieved to the third port3through the hydraulic valve15. In the illustrated embodiment, when permitted, the flow of hydraulic fluid from the first port1to the second port2can be pressure relieved to the third port3through the hydraulic valve15wherein the main poppet mimics the small poppet.

In the illustrated embodiment, the check assembly17is arranged such that the load pressure at the first port1acts upon the movable member45of the hydraulic valve15through the hollow interior of the check poppet31, the poppet guide32, and the check spring34. The check assembly17and the hydraulic valve15are configured such that a flow of hydraulic fluid from the first port1to the third port3is permissible through the hollow interior of the check assembly17and the hydraulic valve15provided the flow of hydraulic fluid generates a pressure sufficient to open a pilot poppet55of the hydraulic valve15.

Referring toFIG.3, the hydraulic control assembly10can be used to perform a lifting operation in which a flow of pressurized hydraulic fluid is conveyed from the second port2to the first port1through the check assembly17. In embodiments, the hraulic control assembly is configured to act as an electro-hydraulic boom lock (EHBL). During the lift operation, the coil51of the hydraulic valve15is de-energized. In the event that there is a loss of hydraulic fluid in the hydraulic circuit21, such as, in the case of a hydraulic line failure or rupture, for example, the check assembly17is configured to block the flow of hydraulic fluid from the cylinder22(i.e., from the first port1to the second port2) to maintain the load in position. Should the pressure in the cylinder22exceed a predetermined limit, the main spring47of the hydraulic valve15can be overcome to provide a pressure relief function in which fluid is conveyed from the first port1to the third port3through the valve15.

The hydraulic control assembly10can be used to perform a lowering operation in which a flow of pressurized hydraulic fluid is conveyed from the first port1to the second port2through the hydraulic valve15. The coil51of the hydraulic valve15is energized to proportionally reduce the effective force exerted by the main spring47of the hydraulic valve15to resist movement of the spool45to the open position to help perform a controlled lowering operation. During the lowering operation, pressurized fluid in the cylinder22can flow from the first port1to the second port2via the cross-holes41of the cage40of the hydraulic valve15.

It will be understood that, in other embodiments, the hydraulic control assembly10can be configured to selectively and independently operate a plurality of hydraulic valves and associated check assemblies constructed according to principles of the present disclosure. It will be understood that, in embodiments, the hydraulic control assembly10can include other and different components. In other embodiments, it will be understood that a hydraulic control assembly constructed according to principles of the present disclosure can be used in an application other than a lifting linkage system.

Referring toFIG.4, the hydraulic valve15is suitable for use in embodiments of a hydraulic control assembly constructed according to principles of the present disclosure is shown in a closed position. The hydraulic valve15comprises a screw-in, cartridge-style, pilot-operated, hydraulic pressure relief valve, which can be adjusted across a prescribed range using a variable electric input to the coil51of its coil assembly50. The hydraulic valve15comprises a two-stage valve in which a main element45is controlled by a pilot element70via a smaller flow, called a pilot flow.

Pressure output is inversely proportional to the current input to the coil51of the coil assembly50. The hydraulic valve15is configured to block hydraulic flow from the first port1to the second port2until sufficient pressure is present at the first port1to move the spool45to an open position by overcoming the preset induced spring force. With no current applied to the coil51, the valve15will relieve within a predetermined range of the spring maximum. Applying current to the coil51of the coil assembly50reduces the induced spring force, thereby reducing the valve setting. The regulated pressure is inversely proportional to the input electrical current to the coil51of the coil assembly50.

The hydraulic valve15includes a valve body71connected to the cage40and defining an internal cavity72that is fluidly connectable with the bore43of the cage40. A pilot-operated valve70is disposed intermediately with respect to the cage40and the valve body71to fluidly isolate the internal cavity72of the valve body71from the bore43of the cage40. The pilot-operated valve70is subjected to a hydraulic opening force of pilot fluid that is present in the bore43of the cage40. A pilot spring73is disposed within the internal cavity72of the valve body71and is arranged to subject the pilot-operated valve70to a closing spring force. An adjustable plug74is disposed within the valve body71and is adapted to adjust the closing spring force applied by the pilot spring73.

The pilot-operated valve includes a housing75fixedly disposed within the cavity72of the valve body71. The housing75includes a longitudinal passageway77having an interior opening78and an external opening79. The longitudinal passageway77is in communication with a transverse pilot passageway80and a longitudinal bore81. The housing75includes a pilot seat82circumscribing the interior opening78of the longitudinal passageway77. The housing75can define a damping orifice83that communicates with the longitudinal passageway77so that the housing defines a restricted axial passageway with a pilot hole disposed adjacent the poppet55, a radial passageway or pilot tank connection via the transverse pilot passageway, and an axial poppet bore within which the pilot poppet55is disposed.

The pilot poppet55is moveably disposed within the axial poppet bore portion of the longitudinal bore77of the housing75. The pilot poppet55is adapted to sealingly engage the pilot seat82. When the pilot poppet55is unseated from the pilot seat82, the first port1is placed in fluid communication with the third port3via the transverse pilot passageway80.

The coil assembly50is mounted to the valve body71. The hydraulic valve15is configured such that, when the coil assembly50of the hydraulic valve15is de-energized, the movable member45is in a normally-closed position in which the first port1and the second port2are fluidly isolated from each other through the hydraulic valve15, and, when the coil assembly50of the hydraulic valve15is energized, the movable member45can be moved to one of a range of open positions in which a flow of hydraulic fluid is permitted from the first port1to the second port2through the cross holes41of the cage40.

The coil assembly50includes the coil51, an armature84, and a pole piece85. The coil51is disposed around the armature84. The pole piece85and the armature84are disposed within the internal cavity72of the valve body71. The pilot spring73is disposed between the pole piece85and the armature84. The armature84is disposed between the pilot spring73and the pilot-operated valve70. An electric current applied to the coil51provides a magnetic force acting on the armature84that causes motion of the armature84toward the pole piece85such that the closing spring force can be selectively adjusted, thereby adjusting the threshold pressure of the hydraulic valve15.

A retainer nut87is mounted to an actuator tube88which comprises a part of the valve body71and which has a generally cylindrical bore forming part of the internal valve cavity72. The retainer nut87is mounted to the actuator tube88, a portion of which is threadedly engaged within the central bore of the retainer nut87. The retainer nut87is configured to secure the coil51of the coil assembly50to the actuator tube88. The coil assembly50of the hydraulic valve15can include a coil frame containing the coil51circumferentially mounted on the actuator tube88.

The housing75is fixed within the bore of the actuator tube88. The pole piece85is fixed within the bore of the actuator tube88and has a generally cylindrical axial bore and a downwardly facing surface. The adjustable plug74acts as a pilot spring adjuster and is seated within the bore of the pole piece85.

The armature84is slidably disposed within the bore of the actuator tube88adjacent the spring adjuster74. The armature84has a generally cylindrical axial bore and an upwardly facing surface. The pilot spring73is disposed within the axial bore of the pole piece85and the axial bore of the armature84. The pilot spring73abuts the spring adjuster74and the armature84to provide a biasing force against the armature84to resists its movement toward the pole piece85when an electrical current is applied to the coil51.

In embodiments, a gap89is defined by the downwardly facing surface of the pole piece85and the upwardly facing surface of the armature84. The gap89can have a generally frustoconical shape and extend around the perimeter of the pilot spring73. In embodiments, a flexible, non-magnetic washer can be disposed within the gap89to help prevent the buildup of residual magnetism between the pole piece85and the armature84. While the gap89may have a variety of useful configurations, preferably the proximate surfaces of the pole piece85and the armature84have a slope of approximately six to nine degrees with the tip of the frustoconical gap oriented toward the retainer87and the base oriented toward the housing75. The non-magnetic washer is preferably brass, but may be bronze, plastic, stainless steel, or any other suitable non-magnetic material with spring-like characteristics. The washer can be similar in other respects to a washer as shown and described in U.S. Pat. No. 6,267,350, which is incorporated herein in its entirety by this reference.

A spacer90is disposed within the armature84. The control member or pilot poppet55is slidably disposed in the axial poppet bore of the housing75and abuts the spacer90. The pilot poppet55has a head with a circumference that is smaller than that of the poppet bore of the housing75. The head of the pilot poppet55has a tip91that is seated in the restricted axial passageway83of the housing75when the movable member45of the valve15is in a closed position.

The cage40of the hydraulic valve15defining the generally cylindrical axial bore43which comprises the first ports, the row of cross holes41comprising the second port2, and a spring chamber92. The spool45is slidably arranged in the axial bore43of the cage40. The spool45has a generally cylindrical axial bore93and a spring chamber94. A filter orifice95can be disposed in the bore93of the spool45and threadedly engaged therewith to retain the filter orifice95in fixed relation to the spool45. The spool spring47is disposed in the spring chamber92of the cage40and the spring chamber94of the spool45with its upper end abutting the housing75and its lower end contacting a stepped portion in the axial bore93of the spool45.

The filter orifice95can include an inlet96disposed in an inlet end of the insert, an outlet97disposed in an outlet end thereof, and an orifice98therebetween such that communication is established between the inlet96and the outlet97via the orifice98. The filter orifice98can cooperate with the axial bore93of the spool45to define a filtered fluid passage therebetween. The filtered fluid passage is in communication with cross holes of the filter orifice which lead to the orifice98defined by the filter orifice95. The filter orifice95can be similar in operation to the filter40and the orifice146described in U.S. Pat. No. 7,137,406, which is incorporated herein by reference.

When the valve15is in the closed position, as shown inFIG.4, the spool45and the cage40are in overlapping relationship with each other along the longitudinal axis of the valve and are disposed in such proximity to each other along the transverse axis to provide a seal which substantially prevents the flow from the main passage to the cross holes defining the second port2.

The valve15is shown inFIG.4in the closed position with no current applied to the coil51. The first port1is adapted to be connected to the cylinder22of a lifting linkage system, which can comprise a source of pressurized fluid. The pressurized fluid in the cylinder22acts upon the first port1. The fluid travels through the filter orifice95and into the spring chambers94,92of the spool45and the cage40. The fluid travels through the restricted axial passage77of the housing75. The fluid acts against the tip91of the pilot poppet55that is seated in the restricted axial passage77of the housing75, causing the pilot poppet55to move upward when force exerted by the pressurized fluid flowing from the first port1exceeds the spring force exerted by the pilot spring73. At that point, the pilot poppet55moves upward, which in turn causes the spacer90and the armature84to move up as well, thereby allowing the fluid to move from the pilot orifice83through the transverse passageway80of the housing75and out of the hydraulic valve15via the third port3which is adapted to be a pilot tank connection. The upward movement of the armature84compresses the pilot spring73. The pilot poppet55moves upward until the forces exerted by the pressurized fluid and the compressed pilot spring73reach equilibrium. As the force exerted by the pressurized fluid increases, the pilot poppet55moves up further and allows a greater volume of fluid to exit the hydraulic valve15via the third port3to the pilot tank connection. This flow, also referred to as the “pilot flow,” causes the fluid pressure in the restricted axial passage77of the housing75and the spring chambers92,94of the cage40and the spool45to drop below the fluid pressure at the first port1. The resulting differential pressure across the spool45produces an upward force on the spool45. When this upward force is sufficient to overcome the resiliency of the main spring47, the spool45moves upward until fluid communication is established between the first port1and the second port2.

When a current is applied to the coil51of the valve15, a magnetic field is created that magnetizes the pole piece85. If the current is sufficient, the resulting magnetic force causes the armature84to overcome the biasing force of the pilot spring73so that the armature84moves toward the pole piece85. The upward motion of the armature84causes the spacer90to move up as well, thereby allowing pressure from fluid entering in the pilot orifice83of the housing75to push the pilot poppet55upward and allow the fluid to move from the pilot orifice83through the restricted axial passageway77of the housing75and out of the hydraulic valve15via the pilot tank connection established through the third port3. As the upward magnetic force increases, the armature84moves up further and allows a greater volume of fluid to exit from the spring chambers92,94of the cage40and the spool45via the pilot tank connection of the housing75. In embodiments, a current can be applied to the coil51of the valve15such that force of the main spring47is balanced.

Embodiments of a hydraulic control system constructed according to principles of the present disclosure can be used to carry out a method of controlling a hydraulic system as described above. In embodiments, a method of controlling a hydraulic system following principles of the present disclosure can be used with any embodiment of a hydraulic valve according to principles discussed herein.

In one embodiment, a method of controlling a hydraulic circuit can be used to control a hydraulic circuit including a pump, a main control valve (MCV), a body, a hydraulic valve, a check assembly, a cylinder, and a tank. The body defines a valve cavity, a first port, a second port, and a third port. Each of the first port, the second port, and the third port are in fluid communication with the valve cavity. The first port is fluidly connected to the cylinder, the second port is fluidly connected to the MCV through which the second port is fluidly connected to a source of hydraulic fluid from the pump, and the third port is fluidly connected to the tank. The hydraulic valve is mounted to the body such that the hydraulic valve is at least partially disposed within the valve cavity. The hydraulic valve comprises an electro-proportional pressure valve and has a nose. The check assembly is disposed within the valve cavity and is in abutting relationship with the hydraulic valve such that the check assembly is seated against the nose of the hydraulic valve. The method includes performing a lifting operation in which a flow of pressurized hydraulic fluid is conveyed from the second port to the first port through the check assembly. A coil of the hydraulic valve is maintained in a de-energized condition during the lifting operation.

In embodiments, a lowering operation can be performed in which a flow of hydraulic fluid is conveyed from the first port to the second port through the hydraulic control valve. The coil of the hydraulic valve is energized during the lowering operation to proportionally reduce the effective force exerted by a main spring of the hydraulic cartridge valve.

In embodiments, if a loss of hydraulic fluid in the hydraulic circuit occurs, the flow of hydraulic fluid from the cylinder can be blocked to maintain the load in position by preventing the flow of hydraulic fluid from the first port to the second port through the check assembly. In embodiments, if the pressure in the cylinder exceed a predetermined limit, a pressure relieving operation can be performed in which hydraulic fluid is conveyed from the cylinder via the first port to the third port through the hydraulic valve by moving a movable member of the hydraulic valve by overcoming a force of a main spring of the hydraulic valve.