Multiple Speed Hydraulic Gear Motor Driven Gear Unit

Abstract

A multiple-speed hydraulic drive transmission for power winches or the like which incorporates a pair of unequal, fixed displacement hydraulic motors for tandemly driving the winch at different speeds in response to delivery of motive fluid to either one or both of the motors. A single, pressure responsive fluid flow control valve in the discharge duct associated with the larger motor normally prevents exhaust flow therefrom, and is responsive to the pressure of motive fluid presented to either or both of the hydraulic drive motors to move to a position permitting exhaust flow as long as winch speed is not excessive, so that the single control valve limits winch speed in all operational stages of the transmission.

Description

This invention relates to hydraulic power transmissions and relates more particularly to changeable-speed type transmissions and means associated therewith for preventing uncontrolled rotation of the transmission by the load imposed thereupon.

Power machinery such as winches or other devices are many times used in applications for lifting and lowering heavy loads. Utilization of a hydraulic power transmission for driving the winch permits desirable variation of the winch speed in order to produce the torque necessary to lift the load under widely varying conditions. A heavy inertial load, when being lowered, will tend to overdrive the winch, and it is important to brake or otherwise restrain the winch during lowering to limit speed thereof and prevent overrunning of the hydraulic drive motor. Otherwise, such excessive speed and high momentum will be imparted to the load that unnecessary damage or destruction to the winch and transmission may result. Also, highly undesirable cavitation conditions may be created in the hydraulic drive motors when they are overrun.

Certain types of winch transmissions such as those incorporating worm gear drive units are not faced with the problem of high speed, inertial load driving of the winch. Such transmissions are so highly inefficient that they offer resistance to winch operation so great that even a very heavy load cannot drive or unwind the winch at any speed of substantial value. Obviously, such an arrangement has highly undesirable characteristics such as high fuel consumption, greater internal heat, excessive wear and generally short life.

More efficient power winch transmissions, such as those incorporating a planetary, spur gear reduction unit for driving the winch in the speed range normally contemplated, are more sensitive to the inertial load overdrive problem, due simply to their greater efficiency. It is conventional practice in these types of winch transmissions to include a mechanical brake which operates to hinder and/or prohibit rotation of the winch in a direction in which it is subject to heavy inertial loads. Such a brake in itself is not particularly well-suited for continuously controlling winch speed, as the brake would need by applied essentially continuously during the winch unwinding operation. Excessively high friction and consequent short life of the brake would accordingly result.

It has also been conventional practice to effect hydraulic locking (and consequent braking of the winch) of the hydraulic drive motor of the transmission. By simply blocking or restricting exhaust flow from the drive motor, winch speed operation can be conveniently controlled regardless of the magnitude of the load attached thereto. Utilization of the hydraulic locking technique has, however, been limited to such power transmissions that incorporate only one hydraulic drive motor in combination with an exhaust control valve that limits rotational speed of that one motor to a predetermined level.

It is useful, on the other hand, to utilize a plurality of hydraulic motors to provide selection of different winch speeds. Inexpensive and reliable fixed-displacement motors can then be used to effect speed selection simply by operating the motors individually or in combination. The primary drawback to use of hydraulic braking in conjunction with a plurality of drive motors is the requirement of incorporation of identical exhaust flow control valves for each of the motors in order to create acceptable, smooth and reliable winch operation, particularly when the motors are being driven in combination. These exhaust flow control valves need to be perfectly matched in operating characteristics to such a fine degree that this arrangement has heretofore been found impractical in application. Use of a plurality of such valve also, of course, adds to the complexity and expense of the system.

Yet, it would be highly desirable to provide a power transmission capable of utilizing a plurality of hydraulic drive motors which can be operated individually or in combination in order to drive the winch at different selective speeds to provide the torque necessary to lift loads under widely varying conditions, and to utilize hydraulic locking and braking for controlling and limiting winch operational speed. In this manner, an acceptable hydraulic power transmission could be provided which incorporates inexpensive fixed displacement hydraulic motors and pumps.

Transmissions such as those utilized in conjunction with power winches or the like are quite compact in overall construction, presenting, for instance, a final drive gear reduction unit, brakes and clutches, along with the winding spool and other appurtenances of the winch, all this as a single, compact and versatile winch unit capable of being mounted at locations sometimes remote from the primary power engine. To complement this compactness, it is desirable to utilize hydraulic drive motors which can be coupled adjacent the winch unit and proximal to the work station thereof. Such arrangement accentuates the versatility of the winch as no direct, mechanical drive train extending from the primary engine to the winch is required. Instead, only motive fluid supply lines connect with the drive motors, reducing the criticality of the relative locations of the winch and the engine and permitting winch-operating controls to be located as desired at positions remote from the winch.

It is an important object of the present invention to provide a hydraulic drive for devices that may be subject to heavy loads when operating in at least one direction, which drive is capable of operating the device in different modes at selectively different speeds, the drive also including means for hydraulically braking the winch in its load-imposed direction to limit the speed thereof to different maximum speeds in the different operating modes to assure safe, reliable winch operation under all conditions.

It is another important object of the invention to provide a multi-motor hydraulic drive of the class described wherein a single exhaust flow control means associated with and controlling exhaust flow from but one motor is operable to control winch speed during all modes of operation to prevent inertial load overdrive of the winch, regardless of whether or not that one motor is being positively driven, so that matched, duplicate exhaust flow control valves need not be provided.

It is another object of the invention to provide a single control means of the class described which is operable in response to the pressure of motive inlet flow that may be delivered to any of the motors, in order to function in all operational modes.

It is another object of the present invention to provide a hydraulic drive system for power winches which includes a plurality of commonly rotating, fixed displacement hydraulic motors, control means for directing motive fluid to individual ones or combinations of the motors in order to present a multi-speed transmission, and a pressure responsive fluid control valve for selectively blocking and permitting discharge flow from one of the motors to control speed and prevent motor cavitation and unrestrained high speed dropping of the load, said flow control valve being connected with the inlet sides of all the motors so as to be operable in all operational modes and precludes the need for duplicate, perfectly matched and synchronously operating pressure control means.

It is yet another object of the invention to provide pressure feed means for directing the pressure of motive inlet fluid flow to the flow control valve to operate same, which pressure feed is operatively connected with all of said motor inlet sides across separate flow restricting orifices so as to conduct motive inlet pressure to the flow control valve in all operational modes while preventing leakage cross-flow between said motor inlet sides to minimize efficiency losses in this hydraulic system and permit existence of different pressures in said inlet sides to provide different transmission operating speeds.

It is yet another object of the invention to provide a hydraulic transmission of the class described in combination with power winch means driven thereby, said winch means including a mechanical brake engageable with the output shaft to prevent rotation thereof, which brake is hydraulically released and is controlled by said pressure feed means associated with the flow control valve to preclude inclusion of a separate pressure supply for releasing the mechanical brake.

It is yet another object of the invention to provide a hydraulic drive transmission capable of driving a winch in opposite directions at different speeds, which includes a pair of reversible, unequal displacement, hydraulic motors, operatively coupled to drive the winch in opposite inhaul and downhaul directions; control means for selectively directing motive fluid to either side of one or both of said motors so as to present different winch operating speeds in both directions; speed control means at one side of one of the motors for controlling discharge flow therefrom and limiting winch speed when the latter is downhauling, and bypass means for permitting reverse inlet flow to said one motor side in a manner bypassing the speed control to present maximum power for driving the winch in the opposite inhaul direction.

Another object of the invention is to provide an inlet pressure responsive, exhaust flow control valve in a system of the class described, which valve variably restricts exhaust flow of one motor in response to the magnitude of the motive inlet pressure in different operational modes of the transmission so as to control and limit operating speed while the transmission is being driven by the inertial load imposed thereon.

It is another object of the invention to provide a multi-speed transmission for power winches or the like which presents a compact, unitary motor housing for at least two hydraulic gear motor sections, said motor housing being positionable adjacent and proximal the working station of the winch so as to be suitable for use with compact winch units such as those of the planetary type in a manner complementing the versatility and compactness of such a winch unit.

These and other objects and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of a preferred embodiment of the invention and the accompanying drawing wherein:

The single FIGURE is a schematic and partially perspective representation of the hydraulic drive transmission and a winch system being operated by the hydraulic drive.

Referring now more particularly to the drawing, a power lifting winch spool 10 has a winding cord or rope 12 fastened upon a load (not shown) to be lifted and lowered upon opposite rotation of the winch spool. The winch spool 10 has a central rotating drive shaft 14 to which is secured an overrunning clutch plate 16 for rotation therewith. The clutch illustrated has a plurality of indentures at its outer surface and cooperating rollers 18 housed therein. A cylindrical brake drum 20 surrounds the clutch plate 16 for rotation therewith in one direction of the drive shaft. The brake drum 20 has a spring-biased shoe 22 which is secured to a nonrotating housing (not shown), and a reciprocating plunger 24 is biased downwardly by spring 26 to exert braking action between shoe 22 and drum 20. Upon rotating counterclockwise in the direction depicted by arrows in the drawing to cause lowering of rope 12, the drive shaft 14 rotates clutch plate 16 in a direction causing its rollers 18 to back away from the deepest notched ends 28 of the plate and roll sufficiently outwardly to engage brake drum 20 in a wedging manner. The brake drum 20 will consequently be driven to rotate with clutch plate 16. Upon opposite, clockwise rotation of drive shaft 14, the rollers 18 remain at the deep end 28 of their notches to roll upon and relative to drum 20 and thus permit free rotation of clutch plate 16 and drive shaft 14 while brake drum 20 remains stationary.

The illustrated form of the brake and clutch mechanism may be replaced by any one of numerous similar devices. For instance, many conventional planetary, spur gear winches include a speed reducing final drive, wet disc type brakes, and one-way clutches in combination with the winch winding spool. For the sake of clarity and ease of explanation, the drawing depicts a simplified form of winches of the class described, not showing the final drive or other appurtenances which may be conventionally included with the winch or similar devices. The present invention, while retaining its numerous advantageous features and characteristics, may be utilized in conjunction with planetary gear winches or a variety of other devices and transmissions.

The hydraulic power drive circuitry includes a fixed displacement, gear-type hydraulic pump 30 which draws fluid from a reservoir 32 and delivers same to a discharge duct 34. Operatively coupled to drive shaft 14 are a pair of fixed displacement hydraulic gear motors 36 and 38 which have their lower gears commonly affixed upon drive shaft 14. The gear motors rotate in tandem with the drive shaft, and winch operation may be effected by operating either one or both of motors 36 and 38. Whenever shaft 14 rotates, both motors 36 and 38 rotate therewith.

Each motor 36, 38 comprises a complementary set of intermeshing gears which, preferably, may be enclosed within a single motor housing, depicted schematically by the double line 40, as separate gear motor sections, such arrangement being conventionally referred to as a double-gear motor. The upper gears of each set are journaled in housing 40 for synchronous, idling rotation with their respective lower gears. The drive shaft 14 journals within the motor housing 40 which may be disposed proximal to the winding spool working station of the winch. The double motor is quite compact in construction, lending itself suitably for use in conjunction with compact winch units. The motor 36 is substantially smaller in displacement than its companion motor 38, as the gears of motor 38 are substantially wider, while the gears of each motor are equal in radial size to permit simple mounting of each motor on the same shaft 14 at adjacent locations. Instead of gear type motors, various equivalent arrangements of unequal displacement, rotary hydraulic motors, such as vane or piston motors, may be mounted in driving relationship upon a single drive shaft 14 as shown, or upon operably equivalent, common power transmitting means coupled to the winch spool 10.

Inlet and discharge ducts 42 and 44 lead from the opposite sides of motor section 36 for selective, reversible interconnection with pump supply conduit 34 and reservoir 32. Similarly, the larger motor 38 has inlet and discharge ducts 46 and 48 at its opposite sides. The ducts 42, 44, 46 and 48 are provided in isolated relationship to one another in the motor housing 40. Conventional four-way, three-position directional flow control valves 49 and 50, identical in structure and operation, are interposed between the supply and discharge ducts respectively associated with motors 36 and 38. Control valve 49, for instance, is manually shiftable rightwardly to a position directing motive pressure flow from conduit 34 to motor inlet duct 44, while directing fluid discharged through conduit 42 into conduit 51 which leads to the low pressure reservoir 32. Conversely, leftward movement of control valve 49 interconnects the pressure supply conduit 34 with motor duct 42 and connects the other motor duct 44 with return conduit 51. The other control valve 50 operates similarly upon leftward and rightward movement thereof to direct motive inlet flow respectively to ducts 46 and 48.

The control valves 49 and 50, pump 30 and other hydraulic circuitry may be disposed at a location remote from motor housing 40, interconnected therewith only by the fluid ducts and conduits 42, 44, 46 and 48. Thus, the winch manual control valves 49 and 50 are capable of being positioned near the operator whereas the drive motors are located proximal to the working station of the winch.

Each inlet duct 60, 62 of valves 49, 50 is connected in parallel with pump outlet conduit 34 to provide separate fluid supplies to each motor 36 and 38 so that the motors may be operated individually. Control valves 49 and 50 are open-center in design, and are illustrated in their neutral positions wherein they direct pressure fluid flow from inlet conduit 34 through parallel bypass conduit 54 and conduit 56 to an outlet conduit 58 which leads back to low pressure reservoir 32. This conventional, open-center, bypass flow arrangement continually directs fluid displaced from pump 30 back to reservoir 32 until one of the control valves 49 or 50 shifts away from its neutral position. The shifted control valve thereupon interrupts flow from conduit 34 to discharge conduit 58, and pressure fluid from pump 34 is available at either or both of inlet ducts 60 and 62 for subsequent flow to either side of motors 36 and 38.

A flow control valve 64 of the so-called counter-balance or lockout type is interposed in the motor duct 48 associated with the larger motor 38 and is biased by a gradient-force spring 66 to its normal flow-blocking position preventing exhaust flow from motor 38 through duct 48. Valve 64 is pressure responsive and has a fluid pressure operator 68 coupled with a pilot pressure feed line 70, the latter being shown in dashed lines for clarity. A predetermined pressure in feed line 70 will overcome the bias of spring 66 and urge counterbalance valve 64 to its open position permitting exhaust flow from motor 38 through duct 48.

Connected in parallel with counterbalance valve 64 in duct 48 is a bypass conduit 72 which has a one-way check valve 74 interposed therein. Check valve 74 permits motive fluid flow from duct 34 through duct 48 to motor 38 upon rightward movement of control valve 50, while preventing reverse discharge flow from motor 38 through bypass conduit 72 when valve 50 is shifted leftwardly from neutral. All fluid exhausting from motor 38 into duct 48 must, therefore, pass through the counterbalance valve 64, while inlet flow through duct 48 completely bypasses the counterbalance valve.

Pilot pressure feed line 70 interconnects with the fluid ducts 42 and 46 by a pair of conduits 76 and 78 that are illustrated by dashed lines. Appropriate flow restrictions 80 and 82 are disposed in conduits 76, 78 to severely restrict flow from the motor ducts 42, 46 associated with pressure pilot feed line 70. The restrictions 80, 82 illustrated are in fixed size type, but other forms of flow restrictions may be utilized in place of those illustrated. Pilot pressure feed line 70 is also interconnected with the hydraulic brake actuator 24 through pressure feed conduit 86.

Conduits 76 and 78 interconnect with ducts 42 and 46 at locations proximal to the respective motors 36 and 38, and counterbalance valve 64 is also located adjacent the side of motor 38 associated with duct 48. Such arrangement assures sensitivity of counterbalance valve 64 in response to pressure fluctuations at the sides of the motors associated with ducts 46 and 48. Due to the lag in response time as well as added complexity to the circuitry associated with interconnecting pilot pressure feed line 70 with pump outlet duct 34, it has been found distinctly superior to interconnect pressure line 70 with the motors at locations near the latter, rather than with pump 30 which is advantageously disposed at a location quite remote from motor housing 40 as discussed above. Further in this respect, the counterbalance valve 64, along with conduits 70, 76 and 78, may be incorporated within the motor housing 40 to further conserve installation space.

In operation, the fastest raise operation is selected by shifting control valve 49 rightwardly to its straightthrough position while control valve 50 remains in its central, neutral position. All flow from fixed displacement pump 30 is directed to the side of smaller displacement motor 36 associated with duct 44 to rotate the shaft 14 at a speed related to the displacement of motor 36 in a clockwise direction to wind up rope 12 and raise or inhaul the load attached thereto. Fluid displaced from motor 36 into duct 42 is returned to control valve 49 to be directed to duct 51 and reservoir 32. Motor 38, of course, due to its firm securement on the rotating output shaft 14, rotates synchronously with motor 36 in a direction displacing fluid therefrom into duct 46. Valve 50 is in its neutral position short-circuiting or interconnecting motor ducts 46 and 48, so that fluid displaced from motor 38 into duct 46 returns through duct 48 and bypass conduit 72 directly back to the other side of motor 38. It will be noted that in the neutral position, both ducts 46 and 48 are interconnected with discharge duct 52 and low pressure reservoir 32, with leakage makeup and cooling fluid flow from reservoir 32 keeping motor 38 full. This arrangement prevents cavitation or fluid starvation of motor 38 and permits freewheeling operation of motor 38. Motor 38, therefore, rotates in a manner neither hindering nor helping the other pressure driven motor 36 in rotating drive shaft 14. Alternately, the opposite sides of motor 36 may each be directly connected with the reservoir to induce the freewheeling action in neutral.

Medium speed raising by the winch can be selected by positioning control valve 49 in its neutral position while shifting the other control valve 50 rightwardly to its straightthrough, raise position so that all fluid from pump 30 is directed to the larger displacement hydraulic motor 38 via duct 48, bypass conduit 72 and across one-way check valve 74. Fluid displaced from motor 38 through duct 46 is returned to reservoir 32 by conduit 52, while fluid displaced from motor 36 into its associated duct 42 is short-circuited back to duct 44 or to interconnected reservoir 32 so that motor 36 now freewheels. The shaft and winch again rotate clockwise, with raising speed of winch 10 now being proportional to the displacement of motor 38. In this operational mode, winch speed will be somewhat slower for a given rate of flow from pump 30 than when motor 36 is driving the winch in accordance with the larger displacement and therefore, slower rotating speed of motor 38.

Still slower raising speed can be selected by shifting both valves 49 and 50 rightwardly to their raise positions so that fluid displaced from pump 30 into inlet conduit 34 splits and flows through both ducts 44 and 48 to both motors 36 and 38. Pressure in both of ducts 44 and 48 will, of course, be equal, and the transmission will effectively rotate drive shaft 14 clockwise as though pump 30 were supplying fluid to a single motor whose displacement were equal to the total displacement of both motors 36 and 38. Accordingly, rotation of drive shaft 14 will be substantially slower than during either of the operational modes described above.

During all of these raising operations, the pilot pressure feed line 70 and brake pressure feed control line 86 will remain at a relatively low pressure due to ultimate interconnection of one or both ducts 42 and 46 with reservoir 32. Accordingly, the brake hydraulic operator 24 will maintain firm engagement of shoe 22 with drum 20 to positively prevent rotation of the latter. However, the shaft is rotating in a clockwise direction, and the clutch plate 16 freewheels with respect to the stationary brake drum 20 to permit clockwise shaft rotation in a manner unrestrained by the mechanical brake.

The present invention also permits lowering operation by the winch at the same three different speeds at which raising may occur. Fast lowering is selected by shifting control valve 49 leftwardly to its crisscross position, while the other control valve 50 remains in its central, neutral position. All flow from the pump 30 is directed to the smaller motor 36 with pressure developing at the side of motor 36 associated with duct 42 to a sufficiently high level so as to force the counterbalance valve 64 to an open position permitting exhaust flow from the other motor 38. Until moved to an open position, counterbalance valve 64 hydraulically locks motor 38 against rotation. Valve 64 thereby also locks the shaft 14 and motor 36 that are affixed for common rotation with motor 38. Once pressure in inlet duct 42 of motor 36 exceeds the predetermined level at which the bias force of counterbalance spring 66 is overcome, valve 64 will open, motor 38 will be released, and lowering rotation of the shaft and motors may proceed. The larger motor 38 is again short-circuited during delivery of motive flow to motor 36 to permit freewheeling of the nondriven motor 38 once valve 64 opens.

Whenever rotating to lower a heavy load, the winch is subject to forces tending to drive it at excessive and dangerous speeds. When the winch lowering speed exceeds a certain velocity, the driven motor 36 will begin to outrun the rate of motive fluid flow being supplied by pump 30. As a result, the inlet pressure in conduit 42 and in pilot pressure feed line 70, will drop substantially. In response to sensing the excessive speed of the winch by the drop in motive inlet pressure in conduit 42, the counterbalance valve 64 will be urged by spring 66 to its closed, flow-blocking position to prohibit or severely restrict exhaust flow from the larger motor 38 and thereby brake and slow down the overrunning winch. It is important to note that valve 64 is now controlling winch lowering speed by controlling exhaust flow from a motor 38 that is not even being driven by the motive inlet pressure fluid flow, but that is instead, simply freewheeling.

The counterbalance valve 64 may be a variable restricter type, being incrementally positionable in response to the balance of opposing forces exerted by the gradient force of spring 66 and the motive inlet pressure in pilot line 70 so as to variably meter and control the rate of exhaust flow from motor 38. As the winch speed tends to become excessive, the inlet pressure in duct 42 will decrease, permitting spring 66 to move the counterbalance valve 64 to a position more severely restricting discharge flow to slow down the winch and permit pressure in inlet duct 42 to build. With increase in inlet pressure, the valve will open to a greater degree in opposition to greater force thereupon exerted by gradient spring 66 to speed up the winch. Transmission speed will thereby be controlled to a level at which pump flow keeps up with motor 36, a speed proportional to the displacement of driven motor 36. For a given rate of motive flow from the pump, the "fast" lower-ing which speed will be equal to the "fast" raising winch speed.

During this fast lowering mode, a certain amount of pressure fluid fed from conduit 76 to pilot pressure feed line 70 will leak across orifice 82 to the other conduit 78 interconnected with motor duct 46. The orifices 80 and 82 severely restrict the flow through the pilot pressure feed line to limit such leakage cross-flow between ducts 42 and 46 to a minimal, acceptable level. Pressure line 70 is essentially deadheaded by hydraulic operator 68, and little flow is required therethrough to deliver the motive pressure from duct 42 to valve 64. The actual pressure maintained within pilot feed line 70 may be slightly lower than the actual pressure existing in duct 42 due to the cross-flow between conduits 76 and 78. The pressure in pilot feed line 70 will, however, be directly proportional to, and therefore indicative of, motive inlet pressure existing in duct 42. The severe restrictions afforded by orifices 80 and 82 act to dampen movement of counterbalance valve 64 to make it less sensitive to minor fluctuations in motive inlet pressure, and the minor leakage cross-flow between conduits 76 and 78 tends to stabilize the operation of counterbalance valve 64.

While rotating in a counterclockwise direction to effect downhaul, the shaft and clutch plate 16 force the brake drum 20 to rotate therewith. Accordingly, the brake shoe 22 must be released from drum 20 before winch lowering can proceed. To this end, the brake pressure operating conduit 86 interconnects with pilot pressure feed line 70 downstream of orifices 80 and 82 to present the motive inlet pressure of motor duct 42 to brake hydraulic operator 24. Operator 24 is responsive to move to a brake-release position whenever pressure in interconnected conduits 70 and 86 exceeds a certain level and overcomes the bias of spring 26. The brake will release at a substantially lower pressure than the pressure required to open valve 64. Thus, as pressure builds within motor duct 42, brake operator 24 will first release brake shoe 22; but counterbalance valve 64 will remain in its flow-blocking position to hydraulically lock the shaft against rotation until pressure in duct 42 reaches a predetermined level sufficiently high to overcome the bias of counterbalance valve spring 66. During winch operation, therefore, counterbalance valve 64 normally controls winch speed. The brake 22 acts primarily as a safety holding device when the winch is inactive.

A medium lowering speed may be selected by shifting valve 50 leftwardly to its crisscross position to deliver motive fluid from pump 30 to motor duct 46, while the other control valve 49 remains in its neutral position. The preselected rate of flow from pump 30 will drive the output shaft 14 at a substantially slower speed equal to the medium speed range provided for raising operations, this speed being proportional to the larger displacement capabilities of motor 38. The smaller motor 36 will now be in a freewheeling condition with its fluid ducts 42 and 44 interconnected with reservoir 32 by control valve 49, and leakage cross-flow will proceed in the opposite direction from conduit 78 to conduit 76. Pilot feed lines 70 and brake pressure feed conduit 86 will again sense motive inlet pressure, this time from duct 46, and in response, counterbalance valve 64 acts to limit rotational velocity of output shaft 14 to the medium speed that is proportional to the displacement of motor 38.

Accordingly, whether motive inlet fluid is directed to motor 36 or motor 38 in the "fast" and "medium" lowering speed modes, motive inlet pressure will be presented to pressure operator 68 of valve 64. The counterbalance valve, in turn, will prevent winch lowering operation in both modes until the motive inlet pressure reaches the predetermined level.

The slowest lowering speed is selected by shifting both control valves 49 and 50 leftwardly from their neutral positions to split motive fluid inlet flow between ducts 42, 46 and both motors 36, 38. Leakage cross-flow between conduits 76 and 78 is now immaterial as both ducts 42 and 46 are maintained at equal pressure, and this equal, motive inlet pressure is again directed through pilot feed line 70 to operate counterbalance valve 64. Valve 64 again acts to control lowering speed of the winch and, in this mode limits same in proportion to the sum of the displacement of both the motors, i.e., a speed at which the combined flow rate from both motors 36 and 38 is the same as the pump flow rate.

By delivering the same rate of flow during both raising and lowering, the hydraulic drive will present three different downhaul speeds that are equal to the three different inhaul speeds available for selection. During downhaul, the pilot pressure feed line 70 delivers the motive inlet pressure, regardless of whether motive inlet flow is directed to either one or both of the motors, so that a single counterbalance valve may be utilized in the exhaust conduit 48 to control winch-lowering operation, regardless of which motor or motors are being positively driven by motive fluid from the pump. A simple, reliable, automatic hydraulic brake feature for multimotor transmissions is thereby presented by the present invention.

Counterbalance valve 64 is preferably interposed in the duct 48 associated with the largest motor 38, and this motor is affixed upon shaft 14 at a location nearer the winch spool and load than is the smaller motor 36. This arrangement minimizes required hydraulic braking torque due to the proximity of brake motor 38 to the load, and requires minimal braking pressure when counterbalance valve 64 is in its closed, flowblocking position due to the larger displacement capabilities of motor 38.

The hydraulic system of the present invention is illustrated in conjunction with a winch device which is subject to loads in only one direction of rotation. It will be apparent to those skilled in the art, however, that the present arrangement is equally useful in driving devices that may be subject to heavy external loads in both directions of rotation of the hydraulic drive motors. In this latter case a second counterbalance valve 64 and motive inlet pressure feed conduit arrangement may be included in conjunction with the other discharge duct 46 associated with motor 38. Operating characteristics of this arrangement of a second counterbalance 64 are in no way critical relative to the other counterbalance valve, as the two valves would never operate together, but operate separately, depending on the direction of motor rotation.

These and other alterations and variations to the invention will be apparent to those skilled in the art. Accordingly, the foregoing detailed description of the preferred embodiment of the invention is to be considered exemplary in nature and not as limiting to the scope and spirit of the invention as set forth in the appended claims.

Claims

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In a hydraulic power transmission system having a rotary output shaft subject to external loads tending to rotate the shaft in at least one direction:

at least first and second rotary, fixed displacement fluid drive motors of unequal displacement coupled to the shaft for common rotation therewith, said first and second motors each being responsive to delivery of motive inlet fluid flow to respective one sides thereof to rotate said shaft in said one direction and to effect consequent displacement of exhaust fluid from both of said first and second motors at respective sides thereof opposite said one sides;

means operatively coupled with said one sides of both said first and second motors for selectively directing said motive inlet fluid flow to said one side of the first motor and to said one side of the second motor in different operational modes; and

flow control means disposed in the path of exhaust flow from said opposite side of the first motor and operatively coupled with said one sides of both the first and second motors to be responsive to pressure of said motive inlet fluid flow in both of said different operational modes, said flow control means being in a position for blocking exhaust flow from said one side of the first motor to prevent shaft rotation in said one direction in both of said different operational modes whenever said motive inlet pressure is below a predetermined level, and said flow control means being shiftable to a position for permitting exhaust flow from said one side of the first motor to allow shaft rotation in said one direction in response to a rise in said motive inlet pressure above said predetermined level.

2. A system as set forth in claim 1, wherein said flow control means includes: a pressure responsive control member disposed in the path of exhaust flow from said one side of the first motor to control exhaust flow therefrom; and pressure conducting means for interconnecting said control member with both said one sides of the first and second motors so that said control member is responsive to said motive inlet pressure to shift between said flow-blocking and flow-permitting positions in both of said different operational modes.

3. A system as set forth in claim 2, wherein is provided first and second flow restrictors interposed in said pressure-conducting means at positions between said control member and said one sides of the first and second motors respectively, said restrictors being operable to restrict fluid communication between said one sides of the first and second motors through said pressure-conducting means.

4. A system as set forth in claim 3, wherein said pressure-conducting means includes: a feed conduit communicating with said control member; and first and second pilot conduits respectively interconnecting said one sides of the first and second motors with said feed conduit, said first and second flow restrictors being respectively interposed in said first and second pilot conduits.

5. A system as set forth in claim 2, wherein is provided biasing means operatively engaging said control member for urging the latter to its flow-blocking position in opposition to the urgings of said motive inlet pressure, said biasing means being operable to normally hold said control member in said flow-blocking position whenever said motive inlet pressure is below said predetermined level.

6. A system as set forth in claim 2, wherein said control member is variably positionable in response to the magnitude of said motive inlet pressure to effect correspondingly variable restriction of exhaust flow from said one side of the first motor in both of said different operational modes.

7. A system as set forth in claim 1, wherein said flow-directing means are selectively operable in a combined operational mode to direct said motive inlet fluid flow simultaneously to said one sides of both the first and second motors, said flow control means being operable in said different and said combined operational modes to prevent shaft rotation in said one direction whenever said motive inlet pressure is below said predetermined level.

8. A system as set forth in claim 1, wherein said flow-directing means are operatively coupled with said one and said opposite sides of both the first and second motors, said flow-directing means being operable in a first operational mode to direct said motive inlet flow to said one side of the first motor while operatively interconnecting said one side and said opposite side of the second motor, and being operable in a second operational mode to direct said motive inlet flow to said one side of the second motor while operatively interconnecting said one side and said opposite side of the first motor downstream of said flow control means.

9. A system as set forth in claim 1, wherein said flow-directing means are operatively coupled with said one and said opposite sides of both the first and second motors, said flow-directing means being selectively operable to direct said motive inlet fluid flow to said opposite side of said first motor and to said opposite side of the second motor in different reverse modes to effect rotation of said motors in the shaft in a direction opposite said one direction at different speeds in said different reverse modes.

10. A system as set forth in claim 9 wherein is provided: a bypass conduit communicating with said opposite side of the first motor in parallel relationship with said flow control means for carrying fluid flow into said opposite side of the first motor upon rotation of the shaft in said opposite direction; and an unidirectional check valve interposed in said bypass conduit for preventing passage of exhaust flow from said opposite side of the first motor through said bypass conduit upon rotation of the shaft in said one direction.

11. A system as set forth in claim 1 wherein said first and second motors respectively include first and second sets of intermeshing gears, said gear sets being of unequal width; and wherein is provided a unitary motor housing for enclosing and hydraulically separating said first and second gear sets, said shaft being rotatably mounted within said motor housing and being operatively secured to said first and second gear sets.

12. A system as set forth in claim 11 wherein is provided a power winch coupled to said shaft for rotation therewith, said winch including a winding spool secured upon said shaft at a working station proximal to said unitary motor housing.

13. A system as set forth in claim 12 wherein said first gear set of said first motor is wider than said second gear set and is operatively secured upon said shaft at a location nearer said working station than is said second gear set.

14. A hydraulic system as set forth in claim 12 wherein is provided: mechanical brake means for normally operatively engaging said shaft to prevent rotation thereof in said one direction when said brake means is applied; and brakeoperating means operatively coupled with said brake means and said flow control means for releasing said brake means to permit rotation of said shaft in said one direction in response to said motive inlet pressure whenever the latter exceeds a preselected level which is substantially lower than said predetermined level at which said flow control means shifts to said flow-permitting position.

15. A system as set forth in claim 14 wherein is provided an overrunning clutch interposed between and operatively coupled with said shaft and said brake means for permitting free rotation of said shaft in a direction opposite said one direction even while said brake means is applied.

16. In a multiple speed drive for planetary winches:

a rotary power drive shaft;

a winch winding spool secured to the shaft at a working station and adapted to effect movement of a load in opposite directions upon opposite rotation of the shaft;

a stationary hydraulic drive motor housing positioned at a location proximal to said working station, said shaft being journalled within said motor housing;

first and second rotary hydraulic gear motor sections of unequal width carried in said housing, each section being operatively secured to the shaft for common rotation therewith in said one direction;

supply means operatively coupled with said motor housing for delivering motive inlet fluid flow thereto;

means interposed between said supply means and said first and second motor sections for selectively directing motive inlet fluid flow in a first operational mode to one side of said first motor section to effect shaft rotation in said one direction at one speed, and for directing said motive inlet fluid flow in a second operational mode to one side of said second motor section to effect shaft rotation in said one direction at a different speed, each of said motors being operable in both of said first and second operational modes to displace fluid from respective sides thereof opposite said one sides; and

pressure operated control means operatively coupled with said one sides of both of the first and second motors and disposed in the path of exhaust flow from said opposite side of the first motor, said control means being operable for blocking exhaust flow from said opposite side of the first motor to prevent shaft rotation in said one direction in both of said first and second operational modes whenever pressure of said motive inlet pressure fluid is below a predetermined level.