Abstract: The spline-ended connecting shaft of an engine-accessory disconnect device has a radially outwardly projecting drive flange coaxially secured to an intermediate portion thereof. A housing captively retains the flange, permitting axial translation and rotation of the flange and shaft relative to the housing. A burst of compressed air injected into the housing is caused to exert sequentially opposite forces on the flange to rapidly initiate and terminate axial uncoupling motion of the shaft without imposing appreciable rigid impact force on the disconnect components. The shaft extends through openings in end walls of the housing so that it is freely rotatable and axially translatable relative to the housing without touching the surfaces of the housing openings.

Abstract: A control system for a power shifted transmission includes an electrical signal processing system, incorporating a digital processor, which provides output signals to regulate operation of the directional clutch and the range clutches through a plurality of spool valves. A hydraulic stabilizer is connected to a common line supplying the directional clutch, to provide a predetermined amount of fluid with each change in direction, with the remainder of the fluid being provided through a forward-reverse modulating valve. A neutral bleed valve is connected to reduce the measured amount of fluid in the stabilizer when the clutch is being shifted from the neutral position, instead of a full directional change. To improve range shifts, the directional clutch is slipped while the range change is made, and the directional clutch is then re-applied. A horsepower indicator provides the vehicle operator with an instantaneous indication of the vehicle operating efficiency.

Abstract: A viscous coupling adapted to be positioned within the housing of a torque converter automatic transmission for use as a bypass of the torque converter and including an annular clutch lining secured to a side face of the outer peripheral portion of the coupling and a control valve assembly positioned in the outer peripheral portion to cushion the impact of engagement of the annular clutch lining with the confronting surface of the torque converter housing. The control valve assembly includes a rolling diaphragm which extends across the open end of an axially extending bore in the outer peripheral portion and is arranged to rollingly traverse the bore to successively cover or uncover a series of axially spaced leakage holes communicating with the main chamber of the torque converter and the bore.

Abstract: A pressure control system for a transmission having a series of fluid-operated clutches which are engaged and disengaged through a selector valve to change drive ratios, has a valve for modulating the fluid pressures applied to the clutches to effect smooth shock free shifting. Basic control of the pressure at any of the clutches is effected by a modulation valve upstream of the selector valve. The modulation valve has an auxiliary chamber formed at one end thereof, a piston mounted therein and an auxiliary port connected to one of the clutches having a maximum filling time thereby shortening the filling time thereof without changing filling times of other clutches.

Abstract: Fluid pressure for engagement of a clutch is controlled by a valve alternating between supply and drain conditions in response to a high frequency electrical square wave signal. The valve produces a low flow pilot pressure signal which controls clutch engagement pressure through a valve incorporating a piston which allows clutch engagement pressure to drain whenever that pressure exceeds pilot pressure.

Abstract: The present invention discloses a hydraulic clutch comprising friction plates; a hydraulic piston for pressing the friction plates; a pair of annular protrusions respectively formed at radially outer portion and relatively inner portion of the piston with an annular space therebetween, said protrusions being designed to press the adjacent friction plate; an oil passage formed in the piston through which the annular space is connected to a pressure chamber at the back of the piston; a check valve arranged in the oil passage, said valve including a ball forced to close toward the friction plates and partially projecting beyond the protrusions toward the friction plates; an accumulation chamber formed in the piston and connected to the annular space; and a drain means connected to a space in which the friction plates are arranged.

Abstract: A power shift transmission control system includes a modulation control valve connected for regulating the pressure engagement of forward and reverse direction-friction devices and including a pressure-regulating spring which is adjusted by means of a pressure boost piston. A feedback conduit conveys fluid pressure from the forward or reverse direction-friction device to the chamber, and the rate at which this pressure is conveyed to the chamber is controlled by an orifice-selector valve which is operative to selectively place various sized orifices in the feedback conduit in response to the speed-selector valve being placed in the various speed positions.

Abstract: In an agricultural vehicle in which a power takeoff modulating valve is shifted in response to a control lever so as to pass pressurized hydraulic fluid through a groove in the outer surface thereof between recesses in an adjacent bore wall for application to a power takeoff clutch to cause engagement of the clutch, application of the hydraulic fluid pressure to the clutch is modulated by an arrangement which selectively diverts the pressurized hydraulic fluid away from the clutch and to a sump in accordance with the rate of pressure increase of the hydraulic fluid to prevent excessively rapid engagement of the clutch. The hydraulic fluid is sumped by a trimmer valve having a first end which immediately responds to high fluid pressures by sliding into a position which sumps the conduit supplying hydraulic fluid to the clutch by an amount directly related to the pressure.

Abstract: A multi-functioning hydraulic transmission control circuit in which a shifting power is provided by hydraulic pressure.

Abstract: A push rod assembly for a clutch master cylinder having a rod in abutment with a piston of the clutch master cylinder, a clevis operatively connected to a clutch pedal, and a rubber vibration isolator interposed between the rod and the clevis wherein the rod is formed by stamp forging, the clevis is formed by press working and the rubber vibration isolator is secured to the rod and the clevis during forming thereof, thereby decreasing the resulting cost and increasing the intensity of adhesion thereof.

Abstract: The device comprises a cylinder-piston unit B, the chambers B1 and B2 whereof are connected with the delivery of control pump A and with the control member K2 of utilizer K1. The movable part 14 of the said cylinder-piston unit B is subjected to the influence of spring means 16 and presents a calibrated opening D, said opening being co-axial with the said cylinder-piston unit, while means 20 and 22 sensitive to the pressure building up in chamber B2 of the cylinder-piston unit B control the communication between the said chamber B2 and discharge A1. Said means 20 and 22 are combined with adjustable members 24, 28, 36 which counteract the action of the pressure building up in chamber B2 of the cylinder-piston unit B. It is thus possible to fill the actuating group K2 within a pre-determined period of time.

Abstract: A clutch pedal operated rod to the brake lever in a transmission brake system for tractors and the like is formed of two spaced longitudinally aligned rod lengths connected by a coupling for transmitting force therebetween through a fluid medium. The coupling is secured to the end of one length and slidable receives a spring loaded piston head on the aligned end of the other length. The piston head is in fluid seal engagement with the coupling and separates such coupling into an upper and lower chamber with a fluid supply disposed in the upper chamber in non-operating position. A fluid conduit exteriorly of the coupling communicates with both chambers. Depression of the clutch pedal effects relative movement of the piston head against the fluid supply in the upper chamber where the fluid acts as a solid member under pressure to transmit force to the brake operating rod for stopping the transmission.

Abstract: An antivibration device for a clutch pedal in a clutch operating mechanism wherein upon depressing the clutch pedal a hydraulic pressure is caused in a master cylinder, which in turn actuates an operating cylinder to operate a withdrawal lever, the device having an oil damper provided in a hydraulic passage communicating between the master and operating cylinders, thereby absorbing fluctuations in hydraulic pressure in the operating cylinder caused by engine vibrations to prevent vibration of the clutch pedal.

Abstract: A control system for use with dependent hydraulic clutches in which an accumulator valve (22) is used to provide improved engagement characteristics for the hydraulic clutch assembly (10). The accumulator valve includes back-to-back pistons (96, 100) separated by an outer spring (102) and an inner spring (104). Movement of the pistons provides an initial fast fill of the clutches, followed by a period of cushioned engagement, and then complete engagement. The dual spring arrangement provides two distinct periods of cushioned engagement.

Abstract: A hydraulically actuated friction clutch, especially a lamellae clutch for automatic transmissions of motor vehicles, with a cylinder-piston unit whose interior space is subdivided into chambers by means of a ring-shaped extension provided at the cylinder bottom; the extension thereby projects into an annular channel provided in the piston and at least one further chamber is formed by way of interconnected sealing elements.

Abstract: A control valve system for controlling the capacity of a hydraulic clutch in a power transmission mechanism wherein the clutch torque established by the hydraulic clutch will be nearly equal to the engine torque for the engine with which the transmission is used, thereby resulting in a smooth clutch engagement as a torque transmitting path is established from the engine to a driven member.

Abstract: Two cooperatively arranged pistons and a spring interposed therebetween are arranged within the clutch, one of the pistons is formed as a simple and compact annular plate with flat parallel surfaces and the other formed with an annular recess for receiving the plate.

Abstract: A fluid pressure operated clutch which transmits torque from an engine output shaft to a transmission input shaft, including a rotatable flywheel connected to the output shaft, an adapter connected to the flywheel for rotation with the flywheel, the adapter having a first annular plate with a fluid passage near the inner periphery of the plate, and a centrifugal piston which defines with the adapter a fluid chamber supporting a rotatable torus of hydraulic fluid. The piston has a second annular plate, slideable with respect to the first plate, and a second fluid passage near the outer periphery of the second plate. The first and second plates, at their inner peripheries, provide a controlled clearance to vary the rate of hydraulic fluid into the first fluid chamber as the second plate slides.

Abstract: The spool of the inching valve has first and second lands, a first portion connected to the first land and tapered or suitably formed in such a manner as to gradually increase the flow resistance of the inlet port in accordance with the axial movement of the spool into a position in which the first land fully closes the inlet port, and a second portion connected to the second land and having a reduced uniform diameter or a suitable form which initially temporarily abruptly reduces the flow resistance of the drain port and subsequently gradually reduces the flow resistance thereof in accordance with the axial movement of the spool from a position in which the second land opens the drain port.

Abstract: An oil pressure control means for an automatic transmission having a gear mechanism, low and high speed friction engaging means and high and low speed accumulators, wherein in downshifting the operating pressure of the high speed accumulator is reduced abruptly to a level which causes slippage of the high speed friction engaging means in accordance with the rise of the oil pressure in the low speed friction engaging means up to a predetermined level and the operating pressure of the low speed accumulator is increased abruptly to a level which causes substantial engagement of the low friction engaging means in accordance with the reduction of the oil pressure in the high speed friction engaging means to a predetermined level.

Abstract: A modulatable power transmission clutch has a rotatable driving member, a rotatable driven member, and slippingly engagable clutch plates between said members which are movable into engagement by a fluid-applied spring-released movable piston having two separate fluid application areas thereon, with one area being larger than the other. Fluid is supplied directly to the smaller piston area by an operator-controlled proportional solenoid valve to regulate clutch modulation. Fluid flow to the larger piston area is controlled by a spring-biased trigger valve which pops open when fluid pressure to the smaller piston area reaches a predetermined level, to thereby effect maximum clutch engagement. The trigger valve operates a dump valve which opens to relieve fluid pressure on the larger piston area when the trigger valve recloses in response to reduction of fluid pressure from the solenoid valve.

Abstract: An hydraulic control system for automatic transmissions includes at least first and second engaging members, a transmission for establishing at least two change gear ratios due to the selective engagement of said first and second engaging members, a first servo-mechanism for controlling the engagement of the first engaging member for shifting to a high speed, and a second servo-mechanism for controlling the engagement of the second engaging member for shifting to a low speed. Shifting to a high speed is established due to engagement of the first engaging member and release of the second engaging member, and shifting to a low speed is established due to release of the first engaging member and engagement of the second engagement member. A shift timing valve controls the communication of the second servo-mechanism with an accumulator for use with the second servo-mechanism, in response to the build-up of a pressure to a given level in the first servo-mechanism.

Abstract: A hydraulic control system for a hydraulic clutch for a transmission is provided with means for temporarily reducing a line or control pressure fed to the clutch only during disengagement of the clutch.

Abstract: An annular disc spring interposed between inner and outer pistons and located in the inner piston, in a direction parallel with a clutch disk, in series with a wall surface through which the inner and outer pistons are in slidably fitted relationship to each other. The outer piston has a central circular aperture to cut off a central portion of the outer piston, and an inner portion of each of clutch housing, clutch hub and the inner piston which is offset in the direction of the axis of the clutch and away from the outer piston to form a cavity on the inner portion of the inner piston for accommodating an inner portion of a converter cover and an end of an output shaft of an engine.

Abstract: In a control apparatus, for a vehicle having a transmission and brake means wherein hydraulic passage means connects a source of fluid pressure to a fluid actuated clutch, an improved inching valve interposed in said passage means for selectively reducing the hydraulic pressure supplied to the clutch in proportion to the degree of actuation of the brake means in two successive stages wherein there is no direct initial mechanical connection between the inching valve spool and its actuating means whereby in the first stage of operation the solely hydraulical connection between the actuating means and the spool member positively restricts the operation of the improved inching valve to pressures below the maximum desired clutch slip pressure and wherein during the second stage of operation, the clutch pressure is further reduced to a minimum slip pressure.

Abstract: A vehicle power transmission for tractors and the like having a fluid operated speed-change mechanism which comprises a plurality of rotatably mounted speed-change gears arranged on a lay shaft and a plurality of fluid actuated clutches associated with the respective speed-change gears for selectively connecting each of the gears to the lay shaft. A brake is provided which selectively brakes the lay shaft at the non-operation state of the fluid operated speed-change mechanism. The brake prevents unexpected transmission of power through the speed-change mechanism at the non-operation state of the mechanism, thereby preventing problems such as an unexpected start of the vehicle.

Abstract: In this device, two stacks of discs form at least two sub-assemblies separated by an axially movable intermediate pressure disc, the first of these sub-assemblies being located between the intermediate pressure disc and a stop integral with one of the bodies, whereas the second is located between the intermediate pressure disc and an end pressure disc also axially movable, the control means exerting their action in the direction of the stop, first of all on the two pressure discs so as to cancel out the clearances between the discs of the first sub-assembly, then on the end pressure disc so as to cancel out the clearances between the discs of the second sub-assembly and finally on the whole of the discs of both sub-assemblies so as to compress them.

Abstract: A hydraulic pressure control device for use, for example, in an automatic transmission, in which a line pressure to be supplied from a hydraulic pressure source to a hydraulic pressure servo-device is controlled in three stages by means of a main spool which is displaced in a bleed-off valve of the line pressure by a subsidiary spool under a varying hydraulic control pressure. The subsidiary spool has at least one land forming a piston slidingly fitted in a movable sleeve having a closed end, the movable sleeve also forming a piston by being in turn slidingly fitted for limited movement in a stationary sleeve having a closed end. A first space between the outer wall of the closed end of the movable sleeve and the inner wall of the closed end of the stationary sleeve, and a second space within the piston chamber of the movable sleeve have ports for the introduction of hydraulic control pressure.

Abstract: Hydraulic controls in a transmission for engaging a clutch for the F-R, or forward or reverse, direction before a clutch for first, second, or third speed. Flow of hydraulic fluid to each direction clutch and to each speed clutch is by way of a reducing valve which modulates fluid pressure in controlled way by throttling the flow. After the power unit for the clutch for the F-R clutches and the power unit for the clutch for first, second or third speed are filled with fluid by the reducing valve, pressure in the power units is then slowly raised by the valve linearly toward its maximum; for this purpose the hydraulic controls are supplied by a single source of hydraulic fluid and operate therefrom to provide a pair of modulated pressure outputs which are maintained with varying differences throughout their range of operation, and which operate the selected one of the F-R clutches and the selected one of the first second or third clutches.

Abstract: A multi-functioning hydraulic transmission control circuit including interacting valve mechanism parts which, in response to a shift being called for in a clutch-cylinder-controlled multi-speed transmission, inaugurate a fill pressure flow to the clutch cylinders concerned, prior to the subsequent fluid pressure rise effected therein; thereafter, upon completion of the fill, the parts modulate pressure rise of the hydraulic clutch fluid from and at approximately actual clutch fill pressure up to, and remaining at, the final pressure of engagement.

Abstract: A multi-functioning hydraulic transmission control circuit including interacting valve mechanism parts which, in response to a shift being called for in a clutch-cylinder-controlled multi-speed transmission, inaugurate a fill pressure flow to the clutch cylinders concerned, prior to the subsequent fluid pressure rise effected therein; thereafter, upon completion of the fill, the parts modulate pressure rise of the hydraulic clutch fluid from and at approximately actual clutch fill pressure up to, and remaining at, the final pressure of engagement.

Abstract: Modulated hydraulic clutch pack engagement is provided in a single valve body which includes a drive direction selector spool, a dump valve, a pressure modulating spool, a downstream system pressure regulator and a provision for continuous flow to a downstream torque converter. The modulator spool interrupts communication between a first and second chamber. Fluid pressure develops in the first chamber in response to selector spool initiation of clutch pack fill line pressure. A pressure differential is generated between the first and second chambers resulting in modulator spool displacement allowing equalization of chamber pressures. Metered flow to the back side of the modulator spool generates pressure that reseats the spool with the aid of spring pressure. Pressure then builds in the first chamber. The modulation is repeated rapidly resulting in the clutch pack being fully pressurized, however, the modulator will continue to regulate fluid to be supplied to the torque converter.

Abstract: A two-stage, four-way valve has fluid input and output connections, and passes a fluid under controlled pressure to an actuator to operate any component. Such operation is sensed and, after comparison with a reference signal, a control signal regulates the duty cycle of a pulse-width modulation (PWM) circuit. The output square-wave signal from the PWM circuit regulates a solenoid incorporated in the valve, to modify its operation and regulate the pressure of the controlled fluid. The valve has a spool which effectively integrates the PWM signal and provides a type 1 servo system when connected in a closed loop system.

Abstract: A hydraulic transmission control circuit for modulating the controls of a loader includes an accumulator connected to the reverse speed clutch. The accumulator, which has a free sliding piston, has one end communicating with the reverse speed clutch, while the other end of the accumulator has an inlet communicating with the discharge port of a torque converter for charging the accumulator and an outlet communicating with a fluid reservoir through a check valve. A directional control valve may be utilized to selectively connect the accumulator with the reverse speed clutch or a forward speed clutch for respective loader or bulldozer applications.

Abstract: A control valve having a rotor for communicating outlet port or ports selectively to fluid drain port or to inlet port so as to change flow direction of fluid to be supplied to fluid operated apparatus. The control valve comprises first and second pistons inserted in a hollow space of the rotor and a compression spring arranged between the pistons. At the operation position(s) of the rotor or the valve, the first piston which is biased by the compression spring oscillatingly blocks and reopens fluid passage formed within the rotor outside the first piston for communicating the inlet port to the outlet port(s) under the influence of the compression spring and fluid pressure of the outlet port(s) from which fluid is constantly drained with a small rate through the valve. Fluid pressure of the outlet port may be varied by varying the force of the compression spring by an advance of the second piston.

Abstract: A hydraulic control system including a plurality of individual clutch valves for selective operation for controlling clutches in a power shift transmission. A modulating valve and a clutch valve release mechanism are included for modulating the clutch engaging pressure and the clutch disengaging pressure automatically. A single source of pressurized fluid provides pressurized fluid for operating the hydraulic actuators through the clutch valves and pressurized fluid to lubricate the power shift transmission having wet clutches which operate in hydraulic fluid.

Abstract: This invention relates to a fluid pressure supplying method for fluidically actuating a frictional engaging apparatus in a vehicle transmission, including the steps of supplying high pressure to actuate the frictional engaging apparatus, reducing the high pressure to a lower pressure when the frictional engaging apparatus is initially engaged, and increasing the fluid pressure to line pressure in the frictional engaging apparatus after the frictional engaging apparatus is fully engaged, thereby smoothly engaging the frictional engaging apparatus without giving a shock to the apparatus and reducing the engaging time of the frictional engaging apparatus.

Abstract: A valve assembly for a power shift transmission with a valve body and valve cover integrally mounted on the transmission housing. The valve body includes flow control valves while the valve cover includes pressure control valves for regulating and modulating fluid pressure supplied through the valve assembly to hydraulic fluid clutch actuators in the power shift transmission.

Abstract: A hydraulic control system for automatic transmissions of motor vehicles without resorting to a one-way clutch wherein the fluid pressure to act on a piston member is controlled to effect a shift from a higher speed position to a lower speed position. The fluid pressure is controlled in accordance with the direction of rotation of multi-plate friction elements which are provided within the transmissions.

Abstract: A towing winch system with fluid pressure actuated power input and winch input clutches disposed serially between the power take-off and cable drum. A controlled but variable reduced fluid pressure from a source is applied to the winch input clutches and full fluid pressure is applied to the power input clutch through a valve which opens in response to and when the pressure applied to the winch input clutches exceeds a manually selectable low or high value for inching or non-inching operation, respectively.

Abstract: A power transmission system for swinging the upper section of a mobile crane in opposite directions comprises a prime mover, a torque converter, a modulatable torque converter clutch connected between the prime mover and the torque converter, and a transmission connected to be driven by the torque converter and including a pair of alternately actuatable modulatable transmission clutches therein. The torque converter clutch is modulatable between disengaged and engaged positions. Each transmission clutch is modulatable between a minimum engaged position and a fully engaged position. Selectively operable control means are provided for modulating the torque converter clutch and a selected one of the transmission clutches to swing the crane upper in a desired direction. The control means effect full engagement of the selected transmission clutch prior to full engagement of the torque converter clutch.

Abstract: A hydraulic control device for use in an automatic transmission includes an accumulator which moderates the increased fluid pressure supplied to a hydraulically actuated frictional engagement device when a gear shift is made to a forward drive condition. The hydraulic control device has an orifice and a check valve disposed in parallel to each other in a passage supplying the fluid pressure to the frictional engagement device so that the check valve is closed and the orifice reduces the increased fluid pressure supplied to the frictional engagement device as the frictional engagement device is actuated.

Abstract: Hydraulic controls in a transmission for engaging a clutch for the F-R, or forward or reverse, direction before a clutch for first, second, or third speed. Flow of hydraulic fluid to each direction clutch and to each speed clutch is by way of a reducing valve which modulates fluid pressure in controlled way by throttling the flow. After the power unit for the clutch for the F-R clutches and the power unit for the clutch for first, second or third speed are filled with fluid by the reducing valve, pressure in the power units is then slowly raised by the valve linearly toward is maximum; for this purpose the hydraulic controls are supplied by a single source of hydraulic fluid and operate therefrom to provide a pair of modulated pressure outputs which are maintained with varying differences throughout their range of operation, and which operate the selected one of the F-R clutches and the selected one of the first second or third clutches.

Abstract: A modulation control valve includes a modulating valve coupled by springs to an accumulator piston with both fluidly connected to a reservoir valve. The modulating valve is moved by pressurized fluid in an inlet port connected thereto when a predetermined fill pressure is reached. The fluid in the outlet port pressurizes the accumulator piston to move it to urge the modulating valve to pressure modulate fluid flow between the inlet and an outlet ports. Pressurized fluid in the outlet port acts on a return spring end of the reservoir valve to prevent the accumulator piston and on the other end of the reservoir valve from being relieved to a fluid reservoir. When the accumulator piston abuts the modulating valve, the inlet and outlet ports will be placed in full fluid communication to end modulation.

Abstract: Electro-hydraulic apparatus for actuating a friction clutch has a hydraulic actuating motor and electrical or electronic means to control the hydraulic motor through a control valve system, which includes at least one viscosity independent flow regulator to control flow of hydraulic fluid to or from the motor during operation of the clutch.

Abstract: A pressure limiting arrangement is disclosed for automatically reestablishing full clutch engagement pressure to a hydraulic pressure actuated clutch of a vehicle whenever the operator, by the manipulation of an inching valve, attempts to slip the clutch above a predetermined partial engagement pressure and includes a mechanical biasing device connected to the inching valve and effective in overriding the manual control thereof to shift the valve to its full clutch engaging position, an actuator connected for effecting the disengagement of the biasing device to allow normal operation of the valve, and a control system to effect the selective operation of the actuator and including a first device responsive to a predetermined application of the manual control member of the valve to effect the initial disengagement of the biasing device and a second device responsive to the predetermined partial clutch engagement pressure to effect the reengagement of the mechanical biasing device.

Abstract: An oil pressure control system for an automatic transmission system which includes a fluid torque converter, a transmission gear and friction engaging means adapted to be selectively supplied with line pressure for establishing a selected transmission engagement in said transmission gear, said friction engaging means being provided with a buffering accumulator which buffers its operating pressure, said accumulator comprising a fluid displacing element which is supplied with a torque converter pressure as a back pressure.

Abstract: A control apparatus of a steering clutch for a tractor with distinctive features including a pair of yokes which release and control, under pressure, the lefthand and righthand steering clutches and which are connected with a pair of operating pistons respectively, with individual pressure receiving chambers of the said individual operating pistons being connected with a liquid pressure source, respectively by way of a control valve, and a pair of spools controlling the supply of the liquid delivered from the liquid pressure source to one of the pressure receiving chambers by the control valve in response to the action of the lefthand and righthand steering clutch control units so constructed as to have a progressive working valve increasing progressively the pressure of the said liquid supplying unit in response to the degree of control of the steering clutch control unit.

Abstract: A control for a hydraulically operable clutch of a winch applied to a grapple-skidder includes a pressure-reducing valve which is selectively operable to permit the clutch to slip in those instances when a cable connected between a drum of the winch and a load or grapple structure is being wound in and the load or grapple structure comes into engagement with an immovable object such as a tree or framework at the rear of the grapple-skidder. The clutch is of a disc type adapted for operating in a lubricating fluid and the pressure-reducing valve is operative to effect an increase in the flow of lubricating fluid to the clutch when the valve is operated to permit the clutch to slip.

Abstract: A pressure control circuit for use in connection with an automatic transmission of a vehicle is disclosed which comprises a pressure regulating valve for regulating a hydraulic pressure discharged from a pressure source and for actuating frictional engaging means, said pressure regulating valve including an accumulator, a valve spool and a spring urging said valve spool in one direction, said accumulator including a hydraulic chamber, into which is supplied the hydraulic pressure which will mechanically impart an additional force to said spring at a given value of the hydraulic pressure.