Reversible Motor Hydraulic Control System

Abstract

A hydraulic control system is provided comprising essentially a reversible electric motor-pump which drives a hydraulic actuator. The hydraulic system includes a compensator shuttle valve coupled to a reservoir for compensating for the unequal displacements in the actuator and feeding the pump. A starting switch is provided for operating the motor in one direction, and the hydraulic system functions to store and impart a starting torque of opposite rotational sense each time the motor is brought to a momentary stall condition under load, thereby reversing the motor and the pump driven thereby. In one embodiment, on the return stroke the cylinder is allowed to touch bottom in the actuator, which again provides a torque reversal for reversing the direction of motor rotation. The cycle is repeated as long as power is applied to the motor, with no manual, electrical or hydraulic switching. In another embodiment, a single stroke return-and-stop operation is provided, utilizing a limit switch to remove power on the motor at the termination of the return stroke of the cylinder.

Description

BACKGROUND OF THE INVENTION

This invention relates to a hydraulic control system, and more particularly to a reversible motor hydraulic control system for automatically and rapidly reversing the flow of hydraulic fluid and cylinder action in such a system.

Many hydraulic systems have been provided for controlling the operation of a cylinder in a hydraulic actuator by means of a reversible pump which provides a reversible fluid supply acting through some form of control valve. The usual method of reversing flow in such a system is to use a pump and motor and to divert the fluid flow from one side of an actuator to another by means of a four-way valve which is actuated either electrically or mechanically. Such systems are complex and generally require a variety of components, e.g. check valves, relief valves, pressure switches, etc., which make the systems difficult to operate and maintain. The reversal operation usually requires a manual operation of an operator or a switch and four-way directional valve to accomplish the desired result.

Accordingly, it is an object of the present invention to provide a new and improved hydraulic control system which automatically reverses the flow of fluid in such a system with a minimum of components and operator effort.

SUMMARY OF THE INVENTION

In carrying out this invention in one illustrative embodiment thereof, the hydraulic control system is provided having a reversible motor and an electrical circuit for the operation of the motor, and a hydraulic system having a reversible pump for driving a hydraulic actuator. In the hydraulic system, a compensator shuttle valve is coupled to a reservoir and to the reversible pump and hydraulic actuator for equalizing forward and return cylinder displacements in the actuator. Fluid reversal in the system is accomplished by reversing the rotation of the motor pump assembly, which is accomplished by the matched dynamics of the hydraulic load. The hydraulic system stores enough energy to impart an initial starting torque of opposite rotational sense each time the motor is brought to a stall condition under load, thereby reversing the motor and pump. In one embodiment, on the return stroke of the cylinder, the cylinder is allowed to touch bottom in the actuator, which again provides a torque reversal for reversing the direction of motor rotation. The cycle is repeated as long as power is supplied to the motor, with no manual electrical or hydraulic switching.

In another embodiment, a single stroke return-and-stop operation is provided, utilizing a limit switch to remove power on the motor at the termination of the return stroke of the cylinder in the hydraulic actuator .

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of one form of electrical control circuit, together with the driven hydraulic system shown in one operating position.

FIG. 2 is a schematic of the hydraulic system shown in FIG. 1, operating in a reverse direction from that shown in FIG. 1.

FIG. 3 is an electrical schematic diagram of another embodiment of an electrical control circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, a hydraulic system in accordance with this invention is illustrated in one operative position on the right side of the figure, while one form of electric control circuit is shown on the left side of the figure. Since the electrical control circuits may be varied, and two embodiments thereof are shown in FIGS. 1 and 3, the hydraulic portion of the system will be described first, and like elements will be designated with the same reference numerals throughout the drawings.

The hydraulic control system illustrated on the right side of FIG. 1 is comprised basically of a reversible pump 10, a compensator shuttle valve 12, a reservoir 20 containing a supply of hydraulic fluid 25, a hydraulic actuator 35 for driving a work ram 40, and suitable interconnecting hydraulic lines. The reversible pump 10 is coupled by a line 28 to the blind end 33 of the hydraulic actuator 35 and by a line 30 to the rod end 37 of hydraulic actuator 35. The compensator shuttle valve 12 is comprised of two opposing poppet valves 14 and 16, mechanically linked together by a rod 18. The compensator shuttle valve 12 incorporates three ports, one of which is connected by a line 22 to the reservoir 20, and the other ports are connected by a line 24 to line 28 and by a line 26 to line 30, and are alternately opened, depending on the direction of fluid flow, and accordingly the direction of the rotation of the reversible pump 10. The compensator shuttle valve 12 replaces the normal use of four check valves to accomplish the same result. The hydraulic actuator 35 has a piston 36 and a rod 38 which is connected to and used for driving a work ram 40. The system utilizes the inertia of the motor coming to a stall against a load in order to obtain the desired force to perform the work without requiring a much larger electric motor. Thus in a typical example, a 1/3 hp. motor can be employed where normally a 3 hp. motor would be required for one type of garbage compactor. The flexibility and energy-storing capacity of the hydraulic system is referred to as an accumulator. Depending on the application of the system and the stored energy requirements, additional accumulators 32, coupled to line 28, and/or 34 coupled to line 30, may be provided in the form of a bellows, a spring with piston arrangements, longer or larger diameter hydraulic lines, or any other suitable means for applying any additional energy storing ability required.

One form of electric control circuit is shown on the left side of FIG. 1, which primarily functions to start and control a reversible electric motor 70 which drives the reversible pump 10. Any single phase reversible motor may be employed utilizing the required voltage for that type of motor, for example 110, 220, or 440, and the selection of the motor will depend upon the application of the hydraulic control system. The type of motor illustrated in FIG. 1 is a capacitor start type, with the motor 70 having a rotor 72, a field operating winding 74, and a start or auxiliary winding 76 in series with a capacitor 78. Power for the motor 70 is derived from an electrical plug 50 which is connected to a suitable electric outlet with the desired source of power. The power line is provided with a fuse 52 and a bidirectional semiconductor switch 54, called a triac, which is connected to the operating winding 74 of the motor 70, and through a resistance 58 to contacts of a start switch 60. The start switch 60 is a momentary-on type having contact pairs 65 and 67. The closure of the momentary on-switch 60 closes contacts 65 which operate a latching relay 64, and closes its contact 66 in latching engagement until deactivated by a stop-switch 62. A manual reversal switch 56 having contacts 57, 59, 61 and 63 is connected across the starting winding 76, capacitor 78, and a bidirectional switch 84. Also connected across the starter winding are a centrifugal switch 80 and a resistor 82. The manual reversal switch 56 functions merely to reverse the starting winding to drive the motor 70 in a reverse direction when actuated, and will be used when the work ram is stuck or in any situation when a motor reversal is manually desired.

In the operation of the electric circuit shown in FIG. 1, when the start switch 60 is depressed, closing the contacts 65 and 67, power is applied through the closed contacts 57 and 61 of the manual reversal switch 56 to the starter winding 76. Also, the closing of contacts 65 activates the latching relay 64 and closes its contact 66, which switches on the triac switch 54 to put power on the operating winding 74 of the motor 70. The triac 54 carries the motor load current, limiting the amount of current handled by the remaining circuit switches. Similarly, the triac 84 in the motor start circuit carries the motor starting quadrature current, and the centrifugal switch 80 in the motor, which is normally open until the motor starts, must make and break only 1/50 of the start winding's current. This feature will normally extend motor life to the limit resulting from bearing fatigue. To utilize the manual reversal switch 56, both the start switch 60 and 56 must be actuated together to accomplish the desired reversal, and then the stop switch 62 is depressed when it is desired to manually stop the operation.

In the operation of FIG. 1, fluid reversal is accomplished by reversing the rotation of the motor 70, and accordingly the pump 10. Normal reversal is accomplished by the matched dynamics of the hydraulic load in which the accumulator action of the system stores enough energy to impart an initial starting torque of opposite rotational sense each time the motor 70 is brought to a stall condition under load. A normal work-producing stroke of the ram 40 consists of the application of power to the motor 70 with its starting winding 76 phased to produce high pressure on the blind side 33 of the hydraulic actuator 35, providing stored energy in the accumulator 32. To start the operation, the momentary start switch 60 is depressed, which closes the latching relay 64 and associated contacts 66 to actuate the starting winding 76 and switch on the triac switch 54 to put power on the operating winding 74 of the motor 70. This action drives the pump 10 in the direction indicated by the arrows on FIG. 1. The blind end 33 of the hydraulic actuator 35 has a higher volumetric displacement than the rod end 37 because of rod volume. The difference in flow due to rod volume is not sufficient to maintain the desired output flow, and accordingly it is necessary for the pump 10 to draw fluid 25 from the reservoir 20 through the shuttle valve 12 to make up the difference. The shuttle valve 12 is driven by pressure differential which opens the port associated with the poppet 16 to provide fluid in the direction shown from the reservoir, which creates an automatic replenishing system. Fluid is also drawn from the rod end 37 of the actuator 35. As fluid is supplied by the pump 10 from the rod end 37 and the reservoir 20 through the open port of poppet valve 16 to the blind end 33, the piston 36 and its connected rod 38 move downward, driving the work ram 40 downward. This forward stroke is terminated by force, or fluid pressure limit. This peak force, or pressure limit, is made equal to the motor torque, pump pressure stall limit. In producing the work stroke, the pump 10 has charged the accumulator 32 to peak pressure P.sub.1. Under isothermal conditions, the work done in charging the accumulator 32 is

W = p.sub.1 v.sub.1 1n (V.sub.2 /V.sub.1)

which states that the work available from the accumulator 32 is proportional to the product of the accumulator volume by the natural log of the compressed air volume ratio. At hydraulic pressures normally used, thus 500 - 3,000 psi, energy to produce a starting torque sufficient for reliable reversal can easily be achieved.

Accordingly, when the stalled condition is reached, with the full extension of work ram 40, the direction of the motor 70 is reversed, and the pump 10 now supplies fluid to the rod end 37 of the hydraulic actuator 35, as is shown by the direction of the arrows in FIG. 2. The fluid discharge from the blind end 33 is now greater than the pump 10 output into the rod end, so the excess must be diverted to the reservoir 25. This is accomplished by the compensator shuttle valve 12, which now senses the hydraulic pressure on the rod end 37, closing poppet valve 16 and the port associated therewith to maintain pressure, and opening poppet valve 14 and its associated port to the reservoir 20. Accordingly, the pump 10 moves fluid from the blind end 33 to the rod end 37, with the excess being diverted through the open poppet valve 14 to the reservoir 20. The compensator shuttle valve 12 thus functions to control the flow of fluid from and to the reservoir 20 automatically regardless of fluid direction or direction of the work ram 40. The diameter of the rod 38 or the piston 36 has no effect on the operation of the compensator valve 12, since the compensator shuttle valve position is controlled by the pressure lines to the hydraulic actuator 35.

For the continuous cyclic operation of the system shown in FIG. 1, the piston 36 is allowed to touch bottom at the end of the return stroke, recharging the back side accumulator 32 and again reversing the motor 70. This cycle is repeated as long as power is applied to the motor 70 with no electrical or hydraulic switching. As has been previously pointed out, the accumulators and their action depend on the flexibility of the system, and additional accumulator action may be provided by providing longer or larger diameter hoses or lines, or various other bellows or spring/piston arrangements connected to the hydraulic lines. The system may be stopped by depressing the momentary stop switch 62 to remove power on the motor 70. A timer or other control means may be provided and connected to the stop switch 62 to control the cyclical operation of the hydraulic system. As previously stated, once the system has been stopped, manual reversal may be achieved by pressing the manual reversal switch 76 along with start switch 60, which reverses the connections to the starting winding 76 of the motor 70.

The work ram 40 may perform a plurality of functions. The hydraulic actuator 35 provides a means of amplifying or increasing the force applied to the work ram 40. The work ram may be used for cutting when a die is attached thereto, log splitting, pressure for extraction of juice, metal forming and cutting, or other pressing operations, such as garbage compaction.

The hydraulic system described in FIGS. 1 and 2 may by utilized for a variety of applications, and the electrical control circuits for the system may vary in accordance with such applications. FIG. 3 provides an illustrative embodiment of another electric control circuit for a single stroke return-and-stop operation. In this embodiment, a start switch 92 is provided having contacts 93, 95, 97, 98 and 99 which, on activation, provide power to the starting winding 76 and the operating winding 74, but at the same time provide an automatic reversal of the starting winding 76 when the start switch is released. The circuit in FIG. 3 also includes a limit switch 90 which is shown in phantom on FIG. 2, merely to show its positioning for actuation by the ram 40. The operation of the hydraulic system is the same as that shown in FIGS. 1 and 2. In the embodiment shown in FIG. 3, the motor 70 is started by momentarily depressing the switch 92, which places starting current on the starting winding 76 and power onto the operating winding 74 of the motor 70. At the instant the momentary starting switch 92 is released, the rotor 72 of the motor 70 is up to speed, and the reversing connection on the starting winding 76 is made, with the reverse connection having no effect on direction of motor rotation or the power producing output. Again the motor size is selected which has the stall torque equivalent to the power required to produce maximum hydraulic pressure, or the ram force desired. The motor 70 is already connected for reverse direction rotation, and a reverse torque is produced from a stalled or locked position. When the hydraulic ram 40 pressure reaches the stalled torque value, the motor rotor 72 is instantly at rest, producing starting torque in the reverse direction. This stall condition occurs for a fraction of a second, and almost immediately the motor 70 reverses and runs again until the ram 40 triggers the limit switch 90, which interrupts power to the motor 70, and the motor 70 shuts down. The start switch 92 is a momentary-on type because an operator is required only to energize the system to initiate the forward stroke of the piston 36. The operator can release the switch 92 anytime after the limit switch 90 is cleared (approximately one second), and before the motor reaches the stall condition. Since the work stroke of the ram 40 is predominantly the longer time period of the cycle, the deactivation of the limit switch 90 is negligible. This operation minimizes operator error, and to actually damage the motor the operator must deliberately hold the switch 92 while the motor is in a stalled condition. The limit switch is used to automatically shut down the system after the cycle is completed. In this application, the back side accumulator 32 is not needed. The switch 92, enabling the operator to start the motor in one direction and reverse the connections of the initial direction of the motor, makes it easier to match the dynamics of the system to the load and makes it easier to provide the automatic reversal feature with a variety of different types of motors and pumps.

The hydraulic control system of this invention offers a number of advantages relating to the reduction of parts, such as relief valves, directional valves, pressure switches, and the setting of central pressures. Smaller size motors may be used, depending on the application, which will usually be one third of the size normally required, which also provides a saving in power. A flywheel may also be used with the motor to provide additional inertia to operate larger work loads when required. With the reduced parts, maintenance problems are minimized due to component failure and breakdowns due to fluid contamination. The smaller, compact package has greater application with reduced wire and plumbing lines, and the smaller system permits the use of a smaller reservoir. The smaller size is also more economical than other equivalent type systems.

Since other modifications and changes, varied to fit particular operating requirements and environments, will be apparent to those skilled in the art, the invention is not considered limited to the examples chosen for purposes of disclosure, and covers all modifications and changes which do not constitute departures from the true spirit and scope of this invention.

Claims

I claim:

1. A reversible motor-driven hydraulic control system comprising

a. a reversible pump,

b. a reservoir containing a source of fluid,

c. an actuator cylinder having a hydraulic piston movable in two directions therein coupled to said reversible pump,

d. a compensator means coupled to said reservoir and between said pump and said actuator cylinder for equalizing fluid displacement in said actuator cylinder on the movement of said piston therein and replenishment of fluid to the system,

e. a reversible motor coupled to said reversible pump having a stalled torque value substantially equivalent to the torque required to produce a predetermined hydraulic pressure under load conditions on the piston in said actuator cylinder, and

f. momentary switch means actuating said motor for rotation in one direction until the hydraulic pressure reaches the stalled torque value thereby producing a starting torque in the reversed direction and reversing the direction of rotation of said motor and the reversible pump driven thereby.

2. The reversible motor-driven hydraulic control system set forth in claim 1 wherein said compensator means comprises two opposing poppet valves which are mechanically linked and three ports, one of which is coupled to said reservoir and the other two associated with said opposed poppet valves and coupled to opposite sides of said pump and said piston in said actuator cylinder, said poppet valves being opened in accordance with the hydraulic pressure in said system.

3. The reversible motor-driven hydraulic control system set forth in claim 1 wherein said momentary switch means includes a latching relay and associated contacts across a source of power which applies starting current to the start winding and power to an operating winding of said motor.

4. The reversible motor-driven hydraulic control system set forth in claim 2 having a manual reversal switch means connected to the start winding of said motor for reversing the connections to said start winding whereby said motor may be reversed in direction of rotation by actuating said reversal switch means.

5. The reversible motor-driven hydraulic control system set forth in claim 1 having a stop switch means in circuit with the contacts of said latching relay for releasing said latching relay and stopping said motor.

6. The reversible motor-driven hydraulic control system set forth in claim 1 wherein said momentary switch means comprises a reversal switch for reversing the connections to the start winding of said motor, limit switch means connected to said motor and actuated under control of said movable piston of said actuator cylinder for removing power from said motor after a single stroke and return of said movable piston of said actuator cylinder.

7. The reversible motor-driven hydraulic control system set forth in claim 1 including accumulator means connected between said reversible pump and actuator cylinder.