Abstract:
An electrohydraulic control system that includes a bidirectional electric motor responsive to application of electrical power for rotation in either of two directions, and a hydraulic pump coupled to the motor and having ports for supplying hydraulic fluid in either of two flow directions as a function of direction of rotation of the electric motor. A hydraulic actuator is coupled to the pump for receiving fluid in either of two flow directions and performing work as a function thereof. An electronic controller applies electrical power to the electric motor so as to obtain a desired level of work at the actuator. The electronic controller includes one or more sensors operatively coupled to the actuator for applying electrical power to the motor as a function of motion at the actuator. The bidirectional electric motor in the preferred embodiments of the invention comprises a fluid-cooled motor, and the system includes valves for routing hydraulic fluid through the motor housing between the pump and the actuator.

Description:
The present invention is directed to electrohydraulic systems for controlling operation at a bidirectional actuator, and more particularly to a bidirectional electric-motor/hydraulic-pump unit for use in such a system. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Electrohydraulic systems for controlling operation at a bidirectional actuator coupled to a load conventionally include electronic circuitry for applying electrical power to the motor, and solenoid-operated valves, such as servo valves or proportional valves, for controlling flow of fluid from the pump to the actuator and thereby controlling motion at the actuator. One or more sensors may be connected to the actuator, and/or the load coupled to the actuator, for feeding information indicative of motion at the actuator or load to control electronics and providing closed-loop control of position, velocity and/or acceleration at the actuator and load. Excess fluid flow from the pump is returned by the control valve(s), and represents power loss converted to heat. Attempts have been made to reduce such power loss by controlling pump displacement, which renders the pump mechanism undesirably expensive and complex. Furthermore, hydraulic controls are subject to variations in fluid viscosity, fluid temperature and system resonance stability. 
     It is therefore a general object of the present invention to provide an electrohydraulic control system having enhanced electronic control of operation at a bidirectional hydraulic actuator while eliminating one or more of the aforementioned deficiencies in the prior art. Specifically, it is an object of the present invention to provide an electrohydraulic control system in which electric control of directional hydraulic control valves is eliminated, and in which both direction and quantity of fluid flow to the actuator is controlled by variable operation at the motor and pump. Another object of the present invention is to provide a system of the described character in which electronic control is implemented by controlling application of electrical power to a bidirectional electric motor coupled to a bidirectional hydraulic pump. Another and related object of the present invention is to provide an integrated electric-motor/hydraulic-pump unit that includes a bidirectional electric motor, and one or more pumps mounted on and coupled to the motor for providing bidirectional fluid flow as a function of electrical power applied to the motor. 
     An electrohydraulic control system in accordance with the present invention includes a bidirectional electric motor (i.e., a reversible motor) responsive to application of electrical power for rotation in either of two directions, and a hydraulic pump coupled to the motor and having ports for supplying hydraulic fluid in either of two flow directions as a function of direction of rotation of the electric motor. A hydraulic actuator is coupled to the pump for receiving fluid in either of two flow directions and performing work as a function thereof. An electronic controller applies electrical power to the electric motor so as to obtain a desired level of work at the actuator. The electronic controller in the preferred embodiments of the invention includes one or more sensors operatively coupled to the actuator for applying electrical power to the motor as a function of motion at the actuator. The bidirectional electric motor in the preferred embodiments of the invention comprises a fluid-cooled motor, and the system includes hydraulic valves for routing hydraulic fluid through the motor housing between the pump and the actuator. 
     Valves are preferably operatively coupled to the pump and the actuator for controlling flow of fluid between the pump and the actuator. Such valves preferably comprise passive hydraulic valves responsive to direction and/or pressure of hydraulic fluid flow for controlling fluid flow between the pump and the actuator. The valves may comprise a pilot-operated check valve controlling the vent port of a two-stage pressure relief valve, a pilot-operated sequencing valve or a pilot-operated unloading valve for controlling direction of fluid flow through the actuator, and/or check valves for controlling direction of fluid flow between fluid ports on the pump and the actuator. 
     The bidirectional electric motor in the preferred embodiments of the invention has a motor output shaft that is coupled to the bidirectional hydraulic pump. The motor has one or more endplates into which the shaft extends. In some embodiments of the invention, the hydraulic pump comprises a bidirectional pump mounted on one motor endplate and directly coupled to the shaft. In other embodiments of the invention, the hydraulic pump comprises a pair of unidirectional hydraulic pumps, preferably mounted on opposed motor endplates and coupled to the motor shaft by a pair of directional couplers such that the pumps are alternately coupled to the shaft as a function of direction of rotation of the shaft. The pump (or pumps) have ports that function as inlet and outlet ports, and the system further includes valves responsive to direction and/or pressure of hydraulic fluid flow for controlling fluid flow between the actuator and the pump ports. The actuator likewise has a pair of ports, and the valves are responsive to direction and/or pressure of hydraulic fluid flow for controlling fluid flow to the actuator ports. 
     In accordance with a second aspect of the present invention an electric-motor/hydraulic-pump unit is provided as an integrated assembly that includes a bidirectional electric motor having a motor output shaft and at least one endplate into which the shaft extends, a hydraulic pump mounted on the motor endplate, and a coupler connecting the shaft to the pump. The pump may comprise a bidirectional pump directly coupled to the motor output shaft. Alternatively, the pump may comprise a pair of unidirectional pumps mounted on opposed endplates of the motor housing and coupled to the motor output shaft by a pair of unidirectional couplers that alternately connect the pumps to the shaft as a function of direction of rotation of the shaft. Most preferably, the electric motor is a fluid-cooled motor having a housing with ports for feeding fluid through the housing, and the motor housing is connected to the pump so that hydraulic fluid is routed between the motor housing and the pump. In the most preferred embodiments of the invention, the integrated motor/pump unit is surrounded by a sound-deadening enclosure through which fluid inlet and outlet ports extend. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with additional objects, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which: 
     FIG. 1 is a functional block diagram of an electrohydraulic control system in accordance with one presently preferred embodiment of the invention; 
     FIG. 2 is a schematic diagram of the fluid-cooled bidirectional electric-motor/hydraulic-pump unit in the system of FIG. 1; and 
     FIGS. 3-7 are functional block diagrams of respective alternative embodiments to the control system illustrated in FIG. 1. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an electrohydraulic control system 10 in accordance with one presently preferred embodiment of the invention as comprising a fluid-cooled bidirectional integrated electric-motor/hydraulic-pump unit 12 having a pair of fluid ports 50, 52 connected through corresponding check valves 14, 16 to respective ports 18a, 18b of a bidirectional rotary fluid actuator 18. Actuator 18 has an output shaft 20 for connection to a suitable load (not shown). A pair of pilot-operated sequencing or unloading valves 22, 24 have inlet ports respectively connected to inlet ports 18a, 18b of actuator 18, and control ports connected to the opposing actuator inlet port. The fluid outlet ports of valves 22, 24 are connected to a fluid inlet port 26 on the motor housing 28 of integrated motor/pump unit 12. Housing 28 also receives make-up fluid through an inlet port 29 from a sump 30. An electronic controller 32 receives an input command signal from an external source (not shown), and provides an output control signal as a function of a difference between such command signal(s) and feedback signals from one or more sensors 34 connected to actuator 18 and/or the associated load. The output of controller 32 controls operation of motor drive electronics 36 so as to apply electrical power from a suitable source to the motor of integrated unit 12. 
     FIG. 2 illustrates integrated motor/pump unit 12 in greater detail. Motor housing 28 has a housing spacer or endplate unit 40 into which motor output shaft 42 extends. A bidirectional hydraulic pump 44 is mounted on endplate 40, and has an input shaft 46 directly coupled to motor output shaft 42 by a coupler 48. Pump 44 has a pair of fluid ports 50, 52 that alternately function as fluid inlet and outlet ports depending upon the direction of rotation of the pump. Endplate 40 has a hollow interior into which shafts 42, 46 extend, and within which coupler 48 is disposed. Cooling fluid flows into and through motor housing 28 into the hollow interior of endplate 40, and out of a pair of endplate outlet ports 54, 56. Port 54 is connected through a check valve 58 to pump port 50, and port 56 is connected through a check valve 60 to pump port 52. Endplate 40 is mounted to motor housing 28 and pump 44 so as to form an integrated unitary assembly with fluid-tight seals between the motor, pump and endplate components. Most preferably, motor control electronics 32 and motor drive electronics 36 (FIG. 1) are mounted within an electronic enclosure 61 on a heat sink 63 for heat transfer with motor housing 28 and cooling by the fluid that passes through motor housing 28. Electronics 32, 36 receive electrical power and are connected to sensor 34 (FIG. 1) by means of a connector 65. Also most preferably, integrated motor/pump unit 12 with on-board electronics 32, 36 is disposed within and enclosed by a sound-deadening enclosure 62 (FIG. 1) made possible by fluid-cooling of the motor, as illustrated in U.S. Pat. No. 5,354,182. 
     In operation, assume first that motor/pump unit 12 is rotating in a direction such that pump port 52 is an inlet port. Fluid is drawn into port 52 through check valve 60 from port 56 (FIG. 2) of endplate 40. Fluid is fed under pressure from pump port 50 through check valve 14 to port 18a of actuator 18. When pressure at port 18a is such as to open valve 24, fluid is fed from actuator port 18b through valve 24 to housing inlet port 26 (FIGS. 1 and 2), and thence into the motor of motor/pump unit 12 to cool the motor windings. When actuator 18 has reached the desired position, as indicated by sensor 34 in a position control mode of operation, operation of motor/pump unit 12 is terminated by control electronics 32 and drive electronics 36, valve 24 closes and actuator 18 is hydraulically locked in position. To reverse operation, the motor/pump unit is operated in the reverse direction, such that port 50 becomes the pump inlet port so as to draw fluid from endplate port 54 through check valve 58. Fluid is fed under pressure from pump port 52 through check valve 16 to port 18b of actuator 18. When the pressure of such fluid reaches the control setting of sequencing or unloading valve 22, valve 22 opens so that fluid is fed from actuator port 18a through valve 22 and port 26 into the motor housing. There is thus formed, in either direction of motor/pump rotation, a closed fluid path through the motor housing to the pump. Any make-up fluid that is necessary is drawn from sump 30. 
     FIGS. 3-7 illustrate various modifications to the system of FIG. 1. In each of FIGS. 1-7 identical reference numerals indicate identical components, and reference numerals followed by a letter suffix indicate related components. 
     FIG. 3 illustrates a modified control system 70, in which motor/pump unit 12 of FIG. 1 is replaced by an integrated fluid-cooled electric-motor/hydraulic-pump unit 72. In unit 72, a pair of unidirectional pumps 74, 76 are mounted on the axially spaced endplates 78, 80 of the motor housing. The motor within housing 72 is connected to the respective pumps by associated unidirectional couplers 82, 84, such that one or the other of the pumps 74, 76 is operatively coupled to the motor shaft during rotation in each direction, while the other pump unit is idle. Each pump 74, 76 has an associated inlet port that receives fluid from within the motor housing, and an outlet port connected through an associated check valve 14, 16 to an associated side of a single-rod linear actuator 86. Sequencing or unloading valves 22, 24 are connected as in the embodiment of FIG. 1 for selectively returning fluid from one or the other side of actuator 86 to inlet port 26 of motor/pump unit 72. Inlet port 26 also receives make-up fluid from sump 30. A pressure sensor 34a is connected to one cavity of actuator 86 for feeding a corresponding fluid pressure signal to controller 32. A position, velocity and/or acceleration sensor 34b is connected to the rod of actuator 86, or to the load coupled thereto, for feeding corresponding motion-indicating signals to controller 32. Thus, when the motor of motor/pump unit 72 is driven by controller 32 and amplifier 36 in one direction, in which pump 74 is coupled to the motor by coupler 82 and pump 76 is idle for example, fluid is fed through check valve 14 to one side of actuator 86. When the fluid pressure exceeds the setting of valve 24, fluid is fed from the opposing side of actuator 86 through valve 24 to motor housing inlet port 26. When the motor is actuated in the opposite direction, pump 76 is operative through check valve 16 and valve 22 to move actuator 86 in the opposite direction. 
     FIG. 4 illustrates a control system 90 for operating a double-rod linear actuator 92 from an air-cooled motor/pump unit 94. Port 50 of pump 44 is connected directly to one side of actuator 92, while the opposing side of actuator 92 is connected directly to pump port 52. The rod of actuator 92 is connected to a position, velocity and/or acceleration sensor 34b for feeding corresponding motion signals to controller 32. When motor/pump unit 94 is operated such that port 50 is an outlet port and port 52 is the inlet port, fluid is supplied under pressure to one side of actuator 92 and withdrawn from the opposite side. Make-up fluid is available from a sump 30a through a check valve 96. When motor/pump unit 94 operated in the reverse direction, fluid is fed under pressure from pump port 52 to the second side of actuator 92, and withdrawn from the first side of actuator 92 into pump inlet 50, again with make-up fluid being available from a sump 30b through a check valve 98. 
     FIG. 5 illustrates a system 100 that features the combination of single-rod linear actuator 86 with associated sensors 34a, 34b, sequencing or unloading valves 22, 24 and check valves 14, 16 as in FIG. 3, with air-cooled bidirectional integrated electric-motor/hydraulic-pump unit 94 as in FIG. 4. Operation of system 100 in FIG. 5 will be self-evident from previous discussion. 
     FIG. 6 illustrates a system 102 that features a single-rod linear actuator 86 with associated sensors 34a, 34b, check valves 14, 16 and sequencing or unloading valves 22, 24 as in FIG. 3, in combination with an air-cooled bidirectional motor/pump unit 104 having unidirectional pumps 74, 76 mounted on the endplates 78, 80 thereof, again as illustrated in FIG. 3. The primary difference between system 102 in FIG. 6 and system 70 in FIG. 3 is that the fluid is returned by valves 22, 24 to sump 30 connected to the inlet sides of unidirectional pumps 74, 76 in FIG. 6, rather than to the motor housing fluid inlet 26 in FIG. 3. 
     FIG. 7 illustrates a system 106 that features flow control to and from actuator 86 by means of a pair of pilot-operated check valves 108, 110 that control the vent ports of a pair of two-stage pressure relief valves 112, 114. Pilot-operated check valves 108, 110 will open and permit fluid flow at lower pressure than sequencing or unloading valves 22, 24. Relief valves 112, 114 provide a relatively large cross section to fluid flow to the pump inlet or fluid sump. This large passage opening is accomplished at low pressure, as contracted with sequencing valves that provide an opening proportional to applied pressure. Relief valves 112, 114 also provide protection against over-pressurizing the input circuit to the actuator. 
     There has thus been provided an electrohydraulic control system, and an integrated bidirectional electric-motor/hydraulic-pump unit for use therein, which fully satisfy all of the aims previously set forth. In each disclosed embodiment, control of motion at the actuator is obtained by means of electronic control of electrical power applied to the pump, both in terms of magnitude and direction of electrical power. In each embodiment, the motor of the integrated motor/pump unit is controlled to provide only the hydraulic flow required to satisfy the requirements for motion at the load. The rate of fluid flow is controlled as a function of motor speed, which in turn may be controlled by means of any suitable electronic method, such as by controlling frequency applied if the motor is an ac motor. Direction of rotation at the motor is controlled in order to control direction of motion at the actuator and load. Fluid pressure is controlled by controlling amplitude of current applied to the motor. Control electronics 32 may operate in any suitable conventional mode, such as position, velocity and/or acceleration control modes. The motor drive electronics 36 may be likewise be operated in any suitable conventional mode, such as a variable frequency control mode or power vector control mode. The pump motor may comprise an ac asynchronous brushless servo motor, an ac synchronous motor or a dc synchronous brushless servo motor, and the motor controller may correspondingly comprise an ac adjustable-speed drive, an ac servo drive or a dc brushless servo drive. The hydraulic pumps may be of any suitable conventional type, such as fixed displacement piston pumps, fixed displacement vane pumps or fixed displacement gear pumps.