Hydraulic system, manifold and volumetric compensator

A hydraulic system manifold having a body, a counterbalancer in the body and a flow controller in the body is disclosed. The body has first and second pump ports, first and second cylinder ports, first and second compensator ports and first and second supply conduits in communication with the first and second pump ports, the counterbalancer and the flow controller. The counterbalancer is in communication with the first and second supply conduits and the cylinder ports, to communicate hydraulic fluid between the first and second supply conduits and the first and second cylinder ports while counterbalancing hydraulic fluid pressure in the first and second supply conduits. The flow controller is in communication with the first and second supply conduits and the compensator ports, to control the flow of hydraulic fluid between the compensator ports and the first and second supply conduits to supply and store hydraulic fluid in a volumetric compensator in communication with the compensator ports.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to hydraulic systems and more particularly to a hydraulic system manifold and a volumetric compensator.

2. Description of Related Art

Hydraulic linear actuators are well known and widely used in industry. In contrast to electromechanical actuators, they are more practical and reliable in applications requiring a large, controllable force. A double-acting hydraulic linear actuator applies such force both in extension and in retraction.

Conventionally, a hydraulic linear actuator is connected to a remote supply of pressurized hydraulic fluid through a closed network of pipes and control valves. However, those are applications where it is desirable for a hydraulic linear actuator to be freestanding and mobile, having a prime mover, a pump, and a closed hydraulic fluid control system all integrated with and located proximate to the linear actuator. Such freestanding actuators are particularly suitable for vehicular applications, such as on automobiles and aircraft.

Prior art freestanding hydraulic actuators are disclosed in U.S. Pat. No. 2,640,323 and 2,640,426 to Stewart B. McLeod and U.S. Pat. No. 5,144,801 to Dino Scanderbeg et al.

It appears that the devices disclosed in each of these references use a reservoir to supply a pump with hydraulic fluid and, where unbalanced cylinders (single rod cylinders) are used, the reservoir absorbs excess hydraulic fluid ejected from the cylinder during rod retraction. Disadvantageously, fluid in a reservoir flows in response to gravitational force, and thus the orientation of the reservoir and the actuator at large may be constrained. If a reservoir-type actuator is improperly oriented, the pump may not be properly supplied with fluid and cavitation may result. Furthermore, generally, a reservoir-type actuator requires more hydraulic fluid to reduce the risk of cavitation.

Conventional freestanding hydraulic linear actuators do not provide for load locking, except through operation of the prime mover. Locking the actuator in position to support a load requires that sufficient fluid pressure be maintained in the actuator cylinder to support the rod. Convention al freestanding hydraulic linear actuators do not normally have the necessary valve configuration to accomplish this task, and thus depend on the prime mover to maintain fluid pressure for load locking.

Thus, there is a need for a way to provide a reservoir-less, freestanding, hydraulic linear actuator that can be operated in any orientation, independent of gravitational forces and which provides for load locking without the operation of a prime mover.

SUMMARY OF THE INVENTION

The above problems in the prior art are addressed by providing a hydraulic system manifold comprising a body, a counterbalancer in the body and a flow controller in the body. The body has first and second pump ports, first and second cylinder ports, first and second compensator ports and first and second supply conduits in communication with the first and second pump ports, the counterbalancer and the flow controller. The counterbalancer is in communication with the first and second supply conduits and the cylinder ports, to communicate hydraulic fluid between the first and second supply conduits and the first and second cylinder ports while counterbalancing hydraulic fluid pressure in the first and second supply conduits. The flow controller is in communication with the first and second supply conduits and the compensator ports, to control the flow of hydraulic fluid between the compensator ports and the first and second supply conduits to supply and store hydraulic fluid in a volumetric compensator in communication with the compensator ports.

The counterbalancer may comprise first and second cross piloted counterbalance valves. The first cross piloted counterbalance valve may be connected between the first supply conduit and the first cylinder port and the second cross piloted counterbalance valve may be connected between the second supply conduit and the second cylinder port such that a fraction of hydraulic pressure in the first supply conduit is operable to actuate the second cross piloted counterbalance valve to permit fluid to flow from the second cylinder port to the second supply conduit and such that a fraction of hydraulic pressure in the second supply conduit actuates the first cross piloted counterbalance valve to permit fluid to flow from the first cylinder port to the first supply conduit.

Preferably, the first and second cross piloted counterbalance valves are independently thermally actuated to permit hydraulic fluid flow from the first and second cylinder ports to the first and second supply conduits respectively, when the temperature of hydraulic fluid at a corresponding one of the cylinder ports exceeds a value.

The flow controller may include first and second cross piloted check valves. The first cross piloted check valve may be in communication with the first supply conduit and the first compensator port and the second cross piloted check valve may be in communication with the second supply conduit and the second compensator port. The first cross piloted check valve may be actuated by a fraction of hydraulic pressure in the second supply conduit to permit fluid to flow from the first supply conduit to the first compensator port and the second cross piloted check valve may be actuated by a fraction of hydraulic pressure in the first supply conduit to permit fluid to flow from the second supply conduit to the second compensator port.

Preferably, first and second pressure relief valves are connected in opposite directions between the first and second supply conduits respectively.

The body may have a pump mount for removably mounting a hydraulic fluid circulating pump to the body for communication with the first and second pump ports. The body may also have a cylinder mount for removably mounting a hydraulic cylinder in communication with the first and second cylinder ports. The body may also have a volumetric compensator mount for removably mounting the volumetric compensator in communication with the first and second compensator ports.

A hydraulic system may be formed by a hydraulic cylinder mounted to the body in communication with the first and second cylinder ports, a hydraulic circulating pump mounted to the body in communication with the first and second pump ports, and a volumetric compensator mounted to the body in communication with the first and second volumetric compensator ports.

The volumetric compensator may have a housing having an opening for communicating with the first and second compensator ports to receive and expel hydraulic fluid, a flexible diaphragm member defining an expandable volume within the housing and in communication with the openings to receive hydraulic fluid therein, and a counterforce provider, for providing a counterforce on the flexible diaphragm member, tending to reduce the expandable volume.

The counterforce provider may comprise a spring acting between the housing and the flexible diaphragm member.

Preferably the volumetric compensator has a mount for removably mounting the housing to the hydraulic system manifold such that the opening is in communication with first and second compensator ports of the manifold.

Other aspects and features of the present invention will become apparent to those ordinary skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

DETAILED DESCRIPTION

Referring toFIG. 1, a hydraulic system according to a first embodiment of the invention is shown generally at10. In this embodiment, the hydraulic system is a linear actuator system. The system includes a manifold12to which is removably mounted a hydraulic pump14, and a prime mover16, which in this embodiment is an electric motor. Also mounted to the manifold12is a hydraulic cylinder18, a volumetric compensator20and a mounting lug21. Effectively, the manifold12serves to conduct and control the flow of hydraulic fluid between the pump14, the compensator20, and the hydraulic cylinder18.

Referring toFIG. 2, the manifold12is comprised of a body22having a pump interface shown generally at24, a cylinder interface shown generally at26and a compensator interface shown generally at28. The pump interface24has a pump mounting surface23having first and second pump ports30and32in communication with first and second supply conduits34and36respectively, formed in the body22. The pump mounting surface23facilitates mounting of the pump14onto the body22such that corresponding ports35and37of the pump14are in communication with the first and second pump ports30and32respectively such that hydraulic fluid is communicated between the pump ports30and32and the supply conduits34and36respectively.

Referring back toFIG. 1, in this embodiment the hydraulic pump14is a bi-directional rotary pump. Those skilled in the art will recognize that other types of pump could also be used to implement aspects of the invention, such pumps including gear pumps, axial piston pumps, radial piston pumps, gerotor pumps, and geroler pumps.

The pump14may have a mechanical coupling39for receiving torque from a prime mover41, which in this embodiment is an electric motor. Other types of prime mover could also be used, including internal combustion engines, for example.

When the prime mover41applies torque in a first direction, the pump14draws hydraulic fluid from the first pump port30and forces hydraulic fluid into the second pump port32. When the prime mover41applies torque in a second direction opposite to the first direction, the pump14draws hydraulic fluid from the second pump port32and forces the hydraulic fluid into the first pump port30.

The first supply conduit34has a first portion38and a second portion40, while the second supply conduit has a first portion42and a second portion44.

Preferably first and second pressure relief valves74and76are connected in opposite directions between the first and second supply conduits34and36, respectively, to prevent excess hydraulic fluid pressure from building and exceeding a value.

The first portions38and42of the first and second supply conduits34and36respectively are in communication with a counterbalancer shown generally at46. The counterbalancer46is further in communication with first and second cylinder ports48and50of the cylinder interface26, and communicate hydraulic fluid to the hydraulic cylinder18. The counterbalancer46communicates hydraulic fluid between the first and second supply conduits34and36and the first and second cylinder ports48and50respectively, and isolates hydraulic fluid pressure in the first and second supply conduits34and36from hydraulic fluid pressure in the cylinder18.

Normal flow of hydraulic fluid from the first portions38and42of the first and second supply conduits34and36to the first and second cylinder ports48and50respectively is provided through first and second cartridge style check valves51and53. Pressure isolation between the first and second supply conduits34and36and the first and second cylinder ports48and50is achieved through the use of first and second cross piloted counterbalance valves52and54respectively, which are in communication with the first and second check valves51and53respectively, such that they permit fluid to flow in directions opposite to that of the first and second check valves respectively. The first cross piloted counterbalance valve52is connected between the first portion38of the first supply conduit34and the first cylinder port48. The second cross piloted counterbalance valve54is connected between the first portion42of the second supply conduit36and the second cylinder port50. First and second pilot conduits55and57are formed in the manifold12such that a fraction of hydraulic pressure in the first portion38of the first supply conduit34is operable to actuate the second cross piloted counterbalance valve54to permit fluid to flow from the second5cylinder port50to the second supply conduit36and such that a fraction of hydraulic pressure in the first portion42of the second supply conduit36is operable to actuate the first cross piloted counterbalance valve52to permit fluid to flow from the first cylinder port48to the first supply conduit34. It has been found that a 3:1 cross piloting ratio provides suitable results.

Preferably the first and second cross piloted counterbalance valves52and54are independently thermally actuated to permit hydraulic fluid flow from the first and second cylinder ports48and50to the first and second supply conduits34and36respectively, when the temperature of hydraulic fluid at a corresponding one of the cylinder ports48and50exceeds a value.

Referring back toFIG. 1, the hydraulic cylinder18has a cylinder barrel100having a blind end102and a rod end104. The blind end102is sealingly mounted to the body22and is in communication with the first cylinder port48. In contrast, the rod end104is terminated in an annular cylinder head106.

The cylinder barrel100houses an annular piston108that supports a tubular piston rod110having an internal bore112. The cylinder barrel100, cylinder head106, piston108and piston rod110are coaxial. The annular cylinder head106defines an opening114sized to sealingly accept the piston rod110for reciprocating motion therethrough. In this embodiment the cylinder18is unbalanced, however, aspects of the invention would also apply to balanced cylinder embodiments.

The cylinder18further includes an elongated transfer tube116, concentric with the piston rod110and sized to fit sealingly within its internal bore112such that the piston rod110may reciprocate axially along the transfer tube116. The transfer tube116has a blind end118proximate the body22and in communication with the second cylinder port50and has an open rod end120proximate the cylinder head106, for communicating with the internal bore112of the piston rod110, seen best in FIG.3.

Ducts122perforate the piston108and the piston rod110. The ducts122provide a fluid path between the piston108the bore112in the piston rod110to an interior volume enclosed between the piston108and the cylinder head106.

Flow Controller

The second portion40and44of the first and second supply conduits34and36respectively are in communication with a flow controller shown generally at58. The flow controller58is further in communication with first and second compensator ports60and62respectively. The flow controller58controls the flow of hydraulic fluid between the first and second compensator ports60and62and the second portions40and44of the first and second supply conduits34and36to supply and store hydraulic fluid in the volumetric compensator20which is in communication with the compensator ports60and62.

In this embodiment, the flow controller58includes first and second cartridge style cross piloted check valves64and66. Third and fourth pilot conduits68and70are formed in the manifold12such that the first cross piloted check valve64is actuated by a fraction of hydraulic pressure in the second supply conduit36to permit fluid to flow from the first supply conduit34to the first compensator port60and such that the second cross piloted check valve66is actuated by a fraction of hydraulic pressure in the first supply conduit34to permit fluid to flow from the second supply conduit36to the second compensator port62. Again, a 3:1 cross piloting ratio has been found to provide suitable results.

In this embodiment, the volumetric compensator20has a housing80having a large opening shown generally at82for communicating with the first and second compensator ports to receive and expel hydraulic fluid therefrom. A flexible diaphragm member84is secured between the housing80and the manifold and is dimensioned to define an expandable volume86within the housing80, between the flexible diaphragm member84and a mounting surface88of the compensator interface28. The flexible diaphragm member84is sealingly seated to the housing80and circumscribes the first and second compensator ports60and62. This expandable volume86is in communication with the first and second compensator ports60and62to receive hydraulic fluid therein.

The volumetric compensator20further includes a piston89positioned inside the housing80adjacent the flexible diaphragm member84, and a counterforce provider90, which in this embodiment is a spring acting between the housing80and the piston89, for providing a counterforce on the flexible diaphragm member84, tending to urge the piston89toward the flexible diaphragm member84, to reduce the expandable volume, and expel hydraulic fluid into either of the first and second compensator ports60and62.

The piston89is sized and shaped to be enveloped by the flexible diaphragm member84as it collapses, as shown in FIG.1. The piston89and the spring90are selected merely to aid the flexible diaphragm member84to roll and unroll, however, low pressure at either compensator port60or62may accomplish this without such aid. Those skilled in the art will appreciate that the flexible diaphragm member84could be replaced by other components having similar functionality, including a piston accumulator having a low gas charge, for example.

Operation

An important aspect of the invention is the way in which the differential volume of hydraulic fluid created by the piston rod retracting into the cylinder barrel is stored.

When the pump14is rotated in a direction to retract the piston rod112, the second pump port37expels hydraulic fluid under pressure into the second supply conduit36. The second supply conduit36distributes this hydraulic fluid into the first and second portions42and44thereof, which conduct hydraulic fluid to the second check valve53and to the second cross piloted checkvaluevalve66respectively. The second checkvaluevalve53opens, permitting fluid to flow from the second cylinder port50into the transfer tube116, to retract the piston rod110, while the second cross piloted check valve66is held closed by pressure in the second portion44of the second supply conduit36. Closure of the second cross piloted check valve66prevents pressurized fluid from exiting the second compensator port62and entering the expandable chamber of the volume compensator20.

When the piston rod110is fully retracted continued pressure from the pump14causes a pressure signal to communicate from the second portion44of the second supply conduit36, by the third pilot conduit68to the first cross piloted check valve64causing it to open so that the difference between the volume of hydraulic fluid required to fill the rod end104of the cylinder18and the volume of hydraulic fluid expelling from the, blind end of the cylinder into the first cylinder port48can be communicated to the compensator20. Hydraulic fluid flows through the first portion38of the first supply conduit34to the second portion40thereof to pass through the first cross piloted checkvaluevalve64to exit the first compensator port60into the expandable volume86. The volumetric compensator20, thus stores a volume of hydraulic fluid approximately equal to the volume occupied by the piston rod110in the cylinder18, when the piston rod112is fully retracted.

Conversely, when the pump14rotates in a direction to extend the piston rod110, hydraulic fluid from the first pump port35flows into the first pump port30, and into the first and second portions38and40of the first supply conduit34. Fluid in the first portion38is communicated to the first check valve51, which opens to permit fluid to flow from the first cylinder port48, into the blind end102of the cylinder18. At the same, time fluid in the second portion40of the first supply conduit34is received at the first cross piloted check valve64, closing it and preventing pressurized fluid from entering the expandable volume86of the volume compensator20. A pressure signal from the second portion40of the first supply conduit34is communicated to the second cross piloted check valve66by the fourth pilot conduit70, which opens the second cross piloted check valve66to permit hydraulic fluid to flow from the expandable volume into the second compensator port62, through the second piloted check valve66and into the second portion44of the second supply conduit36. This additional fluid from the volumetric compensator20is provided into the second supply conduit to compensate for the limited amount of fluid which can be supplied by the fluid expelling from the lesser volume of the rod end104.

When thermal expansion takes place in the cylinder18, an increase in hydraulic fluid pressure may be seen in either the rod end104or the blind end102of the cylinder18, depending on which side is under pressure at the time. The increase in pressure will cause one of the thermal relief counterbalance valves74or76to open to relieve the increase in hydraulic fluid volume in the cylinder, by bleeding some hydraulic fluid into the first and/or second supply conduits34and/or36which conduct such hydraulic fluid to the first or second pilot operated check valves64and66, which increases the pressure in one of the pilot conduits68or70. The pilot conduit68or70that receives the greatest pressure, will open its corresponding pilot operated check valve66or64to permit hydraulic fluid to enter into the expandable volume86of the volumetric compensator20. Thus, thermal expansion of hydraulic fluid in the system is compensated by the volumetric compensator20and has little or no effect on the function of the self-contained hydraulic actuator.

In the event that the pump14stops, fluid flow in the first and second supply conduits34,36stops, causing the first and second check valves51and53to close, whereby fluid flow to and from the cylinder18is prevented, thereby locking the piston rod112in position.

During extension, retraction, or locking, if fluid pressure should become too great in either the first or the second conduit34or36, then either the first or the second pressure relief valve74or76will open to reduce the pressure by transferring fluid to the other supply conduit34or36.

The above described manifold is thus reservoir-less and enables the implementation of a free standing hydraulic linear actuator that provides for load locking without the operation of a prime mover, while providing the volumetric compensation of the difference in volume required on opposite sides of the hydraulic cylinder.

While a specific embodiment has been described, those skilled in the art will recognize many alterations that could be made within the spirit of the invention, which is defined solely according to the following claims.