Abstract: In order to shorten considerable time lag, which allows racing of an engine and lowers the transmission output torque peak, an accumulator back-up pressure acting on an accumulator for a start-up friction element is increased momentarily to quickly move a servo piston after a manual selector valve has been shifted from N range position to D range, for example, until the friction element is brought into the intial engagement stage. Subsequently, the accumulated back-up pressure is lowered to soften the frictional engagement.

Abstract: A device for controlling an automatic motor vehicle clutch is arranged between a driving enging and a transmission. This clutch operates primarily as a starting clutch and the engine torque TM and the rotational speeds before and after the clutch nM, nGE are detected or measured. A control device transforms an electric signal coming from an electronic control unit into a control value for the regulating device for the opening and closing of the clutch from the frequency and the amplitude of the engine speed and/or the transmission input speed, unacceptable vibrations (S) in the drive train betweeen the engine, clutch and transmission are detected and eliminated through a predetermined opening of the clutch. This opening takes place up to a path mark which is derived from a characteristic curve stored in an electronic control unit.

Abstract: A system for controlling a friction clutch of a motor vehicle having a continuously variable transmission. The system has an actuator for shifting a clutch plate of the clutch. Vehicle start intention is detected in accordance with a first depression of an accelerator pedal. In response to the vehicle start intention, the actuator operates to shift the clutch plate to a partial engagement position at a maximum speed. The clutch plate is kept at the position and then the clutch plate is shifted from the partial engagement position to an entire engagement position, when the transmission is upshifted.

Abstract: A device for automatic actuation of a friction clutch in the transmission line of a motor vehicle between an internal combustion engine and a change-speed gear, including a setting drive system for positioning a clutch releaser of the friction clutch in dependence upon an ideal-position signal, an engine rotation rate sensor which generates an engine rotation rate signal corresponding to the rotation rate of the internal combustion engine, a sensor device generating a gear rotation rate signal corresponding to the input rotation rate of the change-speed gear, and a control system responding to the engine rotation rate sensor and controlling the setting drive system for the engagement and disengagement of the clutch, the control system, for the engagement of the clutch in the starting of the motor vehicle, generates the ideal position signal according to a predetermined characteristic in dependence upon the engine rotation rate signal, and increases the ideal-position signal, in dependence upon the engine rota

Abstract: Disclosed is a control method and controller for a magnetic powder clutch system including a magnetic powder clutch having an input shaft connected to an engine and an output shaft. In the method, the magnetic powder clutch is energized by an energizing strength which is determined based on a target transmitting torque. The energizing strength is compensated with a predetermined correction factor to realize high accuracy control. Moreover, the correction factor is always updated in response to an error between the target transmitting torque and the detected actual transmitting torque.

Abstract: A method of adaptively idling a transmission in an electronic automatic transmission system putting the transmission to "neutral" when the engine is idling and the brakes are applied.

Abstract: A control system for a vehicle drive train includes a controller which is responsive to a throttle signal from a throttle position sensor and which controls a clutch unit to control speed and acceleration and to obtain optimum driver "feel". The system is responsive to advancing movement of a throttle to a more open position to efficiently utilize rotating energy of engine parts for more rapid vehicle acceleration.

Abstract: A shaft-turning device includes a driving element in the form of a hydraulic motor having a first pressure fluid inflow line, and an element for connection with a shaft to be turned in the form of a clutch having a second pressure fluid inflow line communicating with the first pressure fluid inflow line. The clutch includes locking elements being hydraulically forced counter to a spring force.

Abstract: The clutch comprises at least one weight (11), and preferably two weights, disposed in a bell element (3) radially of the output shaft (2) of the motor (1), subjected to the action of an elastic element (21) for biasing the weight to a de-clutched position at rest, and capable of being driven by centrifugal force developed by the rotation of the shaft (2) of the motor (1) to a clutching position in which the weight engages the bell element (3). The bell element (3) is provided internally with a stressed spring (24) which frictionally bears against the inner wall of the bell element and is provided with at least one clutch dog (24a), and preferably two clutch dogs, cooperative with the weight or weights (11). The spring (24) limits the torque and permits avoiding rebounds in the event of a sudden stoppage of the bell element (3) at the end of the travel of the actuator.

Abstract: A brake arrangement is disclosed which includes a wheel support, a wheel borne by the wheel support, a brake drum, at least one brake guide saddle arranged in the brake drum so as to bear against the wheel support, a fluid drive piston arranged in a bore in the guide saddle, the guide saddle having guide lugs extending in a direction parallel to the direction of the bore, the guide lugs delimiting a channel in the peripheral direction, and a brake element placed in the channel so that it may be driven by the piston. In order to improve serviceability and to ensure a long useful life, the at least one brake guide saddle is separate from the wheel support. Retainer elements are provided, which are accessible from the inner side of the wheel, and are detachably connecting the guide saddle with the wheel support; and at their longitudinal sides, the guide lugs, each delimiting such guide channel are bridged over at their longitudinal sides by ribs delimiting the guide channel at the end.

Abstract: A system for controlling clutch current of an electromagnetic clutch at acceleration of a vehicle on a downhill. The clutch is engaged when vehicle speed is higher than a first reference speed. When the vehicle is accelerated on a downhill at a speed higher than a second reference speed which is lower than the first reference speed, the clutch is engaged to provide an engine braking effect.

Abstract: A control system for an electromagnetic clutch for a vehicle has an engine speed sensor, a clutch driven member speed sensor and a throttle position sensor. The system has a memory storing first torque capacities increasing with increase of engine speed and storing second torque capacities at clutch engagement rate 100% in accordance with engine speed and throttle position. The actual clutch engagement rate is calculated based on output signals of the engine speed sensor and the clutch driven member speed sensor. A first torque capacity and a second capacity are derived from the memory in accordance with output signals of the sensors. A torque capacity Tc for engaging the clutch is calculated as follows,Tc=Re.multidot.TcL+(1-Re).multidot.Tcswhere Re is the clutch engagement rate, Tcs is the first torque capacity and TcL is the second torque capacity.

Abstract: In order to accurately detect an engine or prime mover entering an idling state the position and rate of movement of a control element (such as an engine throttle valve) which varies with the load or torque produced is monitored. If the rate of movement is found to be sequentially within two ranges, the second of which is narrower than the first, and the control element is close to its minimum torque indicative position, a control signal is issued to release a transmission lock-up clutch or the like device which is associated with the engine.

Abstract: A system for controlling an electromagnetic clutch for a motor vehicle at transient state of driving condition of the motor vehicle. An actual engagement ratio is obtained in dependence on speeds of a drive member land a driven member of the clutch. A desired engagement ratio of the clutch is obtained in accordance with the speeds of the drive member and driven member. Clutch current is controlled so as to converge the actual engagement ratio on the desired engagement ratio. The transition of the change of the actual engagement ratio is observed and a correction signal is generated when the actual engagement ratio does not change in a converging direction. The clutch current is corrected by the correction signal.

Abstract: An adaptive clutch torque capacity control for an automotive vehicle clutch utilizing a dual area apply piston for engagement of the clutch plate for accurate control over a larger than normal torque range. The use of two piston areas allows one area to be controlled in a "coarse" fashion, while the other piston area, which is generally a small area, provides a "vernier" or fine adjustment control. The small area piston is controlled by an electronic closed loop for fine adjustment of any errors occurring in the "coarse" control.

Abstract: A method for controlling an AMT system (10) is provided including sensing vehicle start from stop operation, determining a target engine speed value (A) based upon the operator setting of the throttle pedal (THL) and modulating the fuel supplied to the engine (FC) to cause the engine speed (N) to rapidly equal and then be maintained at said target engine speed value. The clutch (16) is engaged at a relatively slow first rate (106), or a relatively rapid second rate (126) depending upon the value of engine speed (N) relative to the target value (A) and upon the value of the amount (FC) and/or the rate of change of the amount (dFC/dt) of fuel supplied to the engine. The first rate of engagement is a function of, and varies directly with, the value of operator setting of the throttle (THL).

Abstract: A clutch control method for a fluid torque converter of a vehiclar transmission which has a clutch for mechanically connecting the input and output sides of the fluid torque converter within a predetermined vehicular speed range by such a relatively low engaging force as to allow slippage of said clutch. The control method includes a step of determining that the throttle opening of the engine has been decreased at a rate higher than a predetermined value and to a value lower than a predetermined reference throttle opening, even if the vehicular speed is within said predetermined range for allowing clutch slippage, and then increasing the engaging force of said clutch to a value higher than that for said reference opening to provide vehicle braking by the engine.

Abstract: Disclosed is a control method for a magnetic powder clutch system including a magnetic powder clutch having an input shaft connected to an engine and an output shaft. In the method, the magnetic powder clutch is energized by an energizing strength which is determined based on a transmitting torque. The energizing strength is compensated with a predetermined correction factor to realize the control in high accuracy. Moreover, the correction factor is always updated in response to an error between the target engagement revolution speed and the detected actual engagement revolution speed. By correcting the energizing strength to diminish the error, the magnetic powder clutch is correctly engaged at the target engagement revolution speed.

Abstract: A clutch control apparatus and method for a vehicle. The apparatus includes two sensors for detecting an engine speed Ne and a speed Nin of a clutch at an input side of a transmission and a conroller, respectively. The controller stores in advance a transmission coefficient C (referring to a speed ratio Nin/Ne) of the clutch and determines an output torque of the clutch using the transmission coefficient C and the engine speed Ne.In the method, an engine speed Ne and an input shaft speed Nin of a transmission are detected, then a speed ratio Nin/Ne is calculated. On the other hand, a transmission coefficient C is determined from a predetermined relation of the transmission coefficient C and the speed ratio Nin/Ne. Finally, the output torque of the clutch is determined using the transmission coefficient C and the engine speed Ne, for instance, by a formula which is C.multidot.(N.sub.e).sup.2.

Abstract: A clutch target position control system of an engine includes a clutch actuator for controlling a clutch stroke, a sensor for detecting a parameter corresponding to an accelerator pedal depression amount, an engine revolution sensor for detecting a revolution speed of the engine and an input shaft revolution sensor for detecting a revolution speed of the input shaft. The disclosed system utilizes the steps of: reading clutch engagement amounts from map tables of registered data corresponding to each of the sensors, the detected signals from each sensor being converted into and used as address signals; calculating a total of three read clutch engagement amounts; and controlling the clutch actuator to control the actual clutch engagement amount on the basis of the calculated total amount.

Abstract: For the automatic actuation of a friction clutch arranged in the torque transmission path between an engine and a change-speed gearbox of a motor vehicle an actuating element of the clutch is coupled to a controllable drive device which moves the actuating element between a clutch-release position, in which the clutch is completely released, and a clutch engagement position in which the clutch is completely engaged. The position of the actuating element in the slipping range between a position of commencing torque transmission and the engaged position is adjusted by a program control, which responds to the engine rotation rate and controls the clutch engagement operation of the drive device, according to a position characteristic provided by means of a first function generator, in starting, as a function of the engine rotation rate. The program control comprises a second function generator controlling the position of the actuating element independently of the first function generator.

Abstract: A power door lock actuator includes a one piece molded and centrifugally expandable brake ring that is held on a drive ring to a motor shaft within a lock lift arm driving cup that is freely pivoted to the shaft. A camming member on the drive ring fits within the brake ring so as to retain it to the shaft, to maintain it in a ready position spaced from the cup when stationary, and so as to jam it into the wall of the cup when turning.

Abstract: A system for controlling a drag torque of an electromagnetic clutch at releasing of an accelerator pedal of a motor vehicle with a continuously variable belt drive transmission. A detector is provided for detecting whether vehicle speed is lower than a predetermined low speed. At the low vehicle speed, the drag current is gradually reduced as the vehicle speed increases.

Abstract: A system for controlling a drag torque of an electromagnetic clutch at idling operation of an engine for a motor vehicle with a continuously variable belt drive transmission. A detector is provided for detecting whether engine speed is higher or lower than a predetermined minimum idling speed. When the engine speed is at a higher engine speed, a standard current is passed in a coil of the clutch. At a lower idling speed, the drag current is gradually reduced until the engine speed increases to the predetermined minimum idling speed.

Abstract: In an automatic transmission system in which a gear transmission and a clutch are electronically controlled so as to shift the transmission to the optimum gear position, the system comprises a first generator for generating a set of initial map data corresponding to the position of a selector, the initial map data being for determining an initial target gear position to which the gear should be initially shifted after the position of the selector is changed, and a second generator for generating a set of normal map data corresponding to the position of the selector, the normal map data being for determining a normal target gear position to which the gear should be shifted after the gear is shifted to the determined initial target position. One of the outputs of the first and second generators is selected and applied to a calculator in which the target gear position is calculated in accordance with the selected map data. The gear transmission is automatically shifted to the calculated gear position.

Abstract: A system for controlling an electromagnetic clutch for a motor vehicle at starting of the motor vehicle. An actual engagement rate is obtained in dependency on speeds of a drive member and a driven member of the clutch. A desired output-input speed ratio of the clutch is obtained in accordance with load on the engine and the speed of the driven member, the output-input speed ratio representing a decreasing function of the engine load and an increasing function of the speed of the driven member. Clutch current is controlled so as to converge the actual output-input speed ratio to the desired engagement rate, thereby smoothly engaging the clutch at the start of the vehicle.

Abstract: A system for controlling a drag torque of an electromagnetic clutch at releasing of an accelerator pedal of a motor vehicle. A detector is provided for detecting whether vehicle speed is lower than a predetermined low speed. At the low vehicle speed, drag current is corrected in dependency on engine speed so as to provide a constant drag torque.

Abstract: A system for controlling an electromagnetic clutch for a motor vehicle at a transient state of a driving condition of the motor vehicle. An actual engagement rate (actual engagement ratio is obtained in dependency on speeds of a drive member and a driven member of the clutch. A desired engagement rate (desired engagement ratio) of the clutch is provided in accordance with conditions of the transient state and driving conditions. Clutch current is controlled so as to converge the actual engagement rate to the desired engagement rate, allowing the clutch to slip in dependency on the transient state conditions.

Abstract: A system for controlling clutch current of an electromagnetic clutch at release of an accelerator pedal of a vehicle in a low vehicle speed range. The clutch is disengaged when the accelerator pedal is released in the low vehicle speed range. The disengagement of the clutch and reduction of an engine are delayed so s to prevent oscillaiton of the speed of a power transmission system.

Abstract: A centrifugal clutch for use especially in a motor-driven chain saw. The clutch includes a carrier which is provided for attachment to a drive shaft and on which radially moveable centrifugal weights are mounted. The weights can move radially outwardly under centrifugal force and counter to spring force and come into contact engagement with the drum which is the output end of the clutch. A restraining device is provided between each centrifugal weight 2 and carrier 1 so that the engagement of the clutch does not occur until after an elevated speed has been reached. Disengagement of the clutch occurs as in known clutches somewhat above the idling speed. The restraining device is configured so that it does not clear the outward path of the centrifugal weight until a certain minimum centrifugal force has been exceeded. This has the effect that the clutch engages suddenly at mid range speeds and can transmit a very high initial torque to the output tool driven through the clutch.

Abstract: Disclosed is a starting control apparatus for an automatic transmission system, in which an accelerator pseudo signal voltage determined on the basis of a target engine rotation speed and the present engine rotation speed detected by an operating condition detecting device is applied to an engine control device to increase the present engine rotation speed to the target engine rotation speed, and, when the engine rotation speed has attained its peak, whether or not the engine rotation speed is synchronous with the rotation speed of a clutch is judged by a synchronous rotation judging device. A clutch engagement judging device decides that the clutch is to be completely engaged when the synchronous rotation judging device judges that the engine and the clutch are under synchronous rotation, but decides that the clutch is to be operated in a semi-engaged state when the synchronous rotation judging device judges that the engine and the clutch are under asynchronous rotation.

Abstract: A housing having a telescopingly extendible and retractable leg is carried by the frame of a motorcycle. A camming mechanism which drives the leg is secured to a reversible motor through a limited torque coupling whereby the extension of the leg is automatically terminated upon firm contact with the ground. Switching circuitry provides that the motor is manually actuated by the operator of the vehicle.

Abstract: A lock-up clutch of an automatic transmission is controlled by an electronic control unit using a gear shift diagram and a lock-up clutch changeover diagram each having vehicle velocity plotted along identical abscissa and throttle opening plotted along identical ordinate. Changeover of the lock-up clutch is controlled upon setting a changeover line in the changeover diagram in accordance with which the lock-up clutch is changed over from OFF to ON state, and changeover of transmission gear ranges is controlled upon setting a transmission gear range changeover point in the gear shift diagram. The changeover line is set in such a manner that it will not intersect a region in the gear shift diagram where the shift position is 2nd gear range or less and the throttle opening is less than a predetermined value. Thus, the lock-up clutch is not engaged in a case where the transmission is in 2nd gear range or less and, moreover, the throttle opening is less than a predetermined value.

Abstract: In an apparatus for controlling an internal combustion engine for a vehicle provided with an electronically controlled automatic transmission system including a friction-type clutch and a gear-type transmission, the speed of the engine is controlled in accordance with a target speed determined by whether the clutch is engaged or not, and at the moment the clutch becomes engaged, the target engine speed gradually changes from the target speed for the disengaged condition of the clutch to that for the fully engaged condition of the clutch, whereby the mechanical shock occurring at the time of the engagement of the clutch is remarkably reduced.

Abstract: Disclosed is an electronic shaft synchronization system. The system employs a proportional integral controller for controlling the speed offset between two shafts approaching synchronization. The speed offset is determined by calculating an error signal representative of the shaft speed differences. Means for measuring the quality of the error signal is provided to allow the integrator to be initialized once the error signal reaches a first threshold. By initializing the integrator in this manner, the typical delay problem experienced with such integration is alleviated to allow a substantially faster synchronization between the shafts.

Abstract: A system has a start mode in which clutch torque of the clutch increases with increase of speed of an engine of the motor vehicle, a lock-up engagement mode in which the clutch torque is increased, and a drag mode in which the clutch torque is reduced to produce a drag torque, one of the modes being selected in accordance with depression of the accelerator pedal and speed of the vehicle. When a vehicle speed detector does not produce a vehicle speed signal for a predetermined period in the start mode at engine speed higher than a predetermined speed, a fail-safe signal is produced. In response to the fail-safe signal, the system operates to keep clutch torque.

Abstract: An apparatus and method for controlling an electro-magnetic particle clutch is provided. The apparatus includes first through third sensors, a memory, first through fourth calculating devices, first through third determining devices and a controller. The first sensor detects a throttle opening and outputs a first detected signal. The second sensor detects an actual engine revolution speed and outputs a second detected signal. The first calculating device calculates an engine torque in accordance with a first relationship and outputs a first calculated signal. The second calculating device calculates a tentative desired revolution speed and outputs a second calculated signal. The third sensor detects at least one of a plurality conditions in which the vehicle begins moving and outputs at least one of a plurality of detected signals. The first determining device determines a total compensation value in accordance with a third relationship and outputs a first determined signal.

Abstract: A device for automizing a vehicle clutch having at least one single-action hydraulic jack includes two solenoid valves or an equivalent assembly, two pulse sensors for respectively detecting the speed of the wheels and the engine speed of the vehicle, an actuating contact and an electronic cirucit connected to the solenoid valves, the sensor and the contact. The electronic circuit controls declutching and clutching to provide gradual controlled engaging of the clutch according to data relating to the engine speed and vehicle acceleration.

Abstract: For the control of the drive slip of a motor vehicle a first rotation rate sensor produces a first rotation rate signal corresponding to the rotation rate of the driven wheel or the output rotation rate of the change-speed gear. A second rotation rate sensor generates a second rotation rate signal corresponding to the rotation rate of a non-driven wheel. The friction clutch of the motor vehicle is engageable and disengageable through a controllable servo drive, and a control system controls the clutch in the release direction when the first rotation rate signal represents a rotation rate higher by at least a pre-determined difference value than the second rotation rate signal. The control system controls the clutch in the engagement direction when the rotation rates represented by the first and the second rotation rate signals differ by less than the pre-determined difference value.

Abstract: A controlled system for the clutch in a torque converter of an automatic transmission wherein the clutch is normally engaged in a predetermined range of vehicle and engine operating conditions for efficient operation. An atmospheric pressure sensor is used in the control system to disengage the clutch in that predetermined range at higher altitudes to allow the torque converter to function to increase the torque being transmitted thereby compensating for the reduced engine performance at higher altitudes.

Abstract: A control device for a hyudraulic friction clutch for a motor vehicle, wherein a piston is moved by a pressurized fluid supplied to a pressure chamber, to effect frictional engagement between driving and driven rotary members, and a proximity shut-off valve is disposed in the piston, for permitting the fluid to be discharged from the pressure chamber through a discharge passage when the piston has reached a ready-to-operate position from which the piston is moved to start the frictional engagement.

Abstract: An arrangement for the control of the force-transmission of a four-wheel drive vehicle in which a main driving axle is driven directly by an internal combustion engine by way of a clutch transmission unit and an auxiliary driving axle is driven by the internal combustion engine by way of a continuously controllable longitudinal clutch. A desired traction force of all wheels is determined from a desired power output and from a velocity of the vehicle, from which a control magnitude for the control of the longitudinal clutch is obtained by a distribution factor dependent on operating or driving parameters. The longitudinal clutch can additionally be controlled either alone or advantageously also in combination with this control magnitude by a further control magnitude which is determined by a square of a rotational speed difference at the longitudinal clutch, having a weighting dependent on operating or driving parameters.

Abstract: A system for controlling an electromagnetic clutch for a motor vehicle at starting of the motor vehicle. When the clutch slips and engine speed does not change, a stall signal representing a stall condition is produced. A reference clutch current is provided in accordance with opening degree of a throttle valve of the engine at the stall condition. Clutch current in the stall condition is controlled so as to coincide with the reference clutch current.

Abstract: A power transmitting system for a four-wheel drive vehicle having an automatic transmission has a central differential operatively connected to an output member of the automatic transmission for providing a full time four-wheel drive vehicle. A fluid operated multi-disk friction clutch is provided for locking the central differential. A hydraulic control circuit is provided for applying line pressure in the automatic transmission to the friction clutch so as to engage it to lock the central differential.

Abstract: A system for slipping an electromagnetic clutch when a motor vehicle is driven at a low speed in a closed choke valve condition. The system is provided with a choke switch for producing a choke signal, accelerator pedal position switch for producing a release signal and a vehicle speed signal detector in order to reduce current passing in the clutch to cause the clutch to slip at the release of an accelerator pedal in a low vehicle speed range. The slipping is controlled to keep the vehicle speed constant.

Abstract: An automatic transmission apparatus comprising a friction clutch (31) coupled to an output shaft of an engine (30), a clutch actuator (42) for operating the friction clutch, a parallel shaft type gear transmission (32), the input shaft of which is coupled to the friction clutch, a gear position changer (51) for changing the speed ratio of the transmission, and a rack actuator (38) for operating the control rack (35) of a fuel injection pump. A signal from a drive state-detector is used to determine a change in the speed ratio of the transmission (32). The rack actuator (38) gradually moves the control rack to an idling speed position, after which the clutch actuator disengages the friction clutch (31). The gear position changer (51) is operated in accordance with the disengagement of the friction clutch (31), so that the speed ratio of the transmission is changed accordingly.

Abstract: A vehicular transmission having a fluid torque converter of the type in which a clutch is provided for mechanically connecting the input and output sides of a fluid torque converter above certain vehicle speeds for improved operation and economy and in which the clutch is operated within a predetermined vehicular speed range by such a relatively low engaging force as to allow slippage of said clutch for minimizing vibration. A control system causes the engaging force of the clutch to be increased more than that which is normally established below a reference value of small throttle valve opening for providing a braking effect by the engine. The control system also may provide for stopping the increase in engaging force at small throttle valve openings when the r.p.m. of the output side of the fluid torque converter falls below the r.p.m.

Abstract: In an apparatus for controlling a vehicle clutch which is located between an internal combustion engine and a transmission device whose gear shift position is determined in accordance with the operating position selected by a selector, the apparatus comprises a control signal generator which determines the operating pattern for engaging the clutch in response to at least a position signal showing an operating position selected by the selector and produces a control signal for operating the clutch according to the determined operating pattern in response to the output of a command signal for commanding the beginning of the starting of the vehicle. Thus, the clutch is engaged in accordance with an engaging pattern corresponding to the selected operating position of the selector at that time in response to the output of the command signal.

Abstract: In a transmission for an automotive vehicle, a control system is provided for controlling a direct-coupling mechanism for mechanically engaging input and output members of a hydraulic power transmission mechanism of the transmission. The control system includes a first sensor for detecting the value of a first parameter indicative of the engine load, and a control mechanism adapted to compare the value of the first parameter detected by the first sensor with a predetermined reference value for selectively engaging and disengaging the input and output members with and from each other through the direct-coupling mechanism. A second sensor detects the value of a second parameter indicative of the vehicle speed, and a reference value setting device sets the predetermined reference value to a value dependent on the value of the second parameter detected by the second sensor.

Abstract: A tractor power take-off drive line which includes a friction clutch (12) which is engaged by a fluid pressure operated actuator (12a) via a solenoid-operated valve (14). The engagement of the clutch is controlled by a system which includes a pulse width modulation function for providing a series of electrical pulses to the solenoid (14a) of the valve in successive predetermined time intervals during engagement of the clutch. Each pulse has an "on" period during which the valve connects the actuator to a source of pressurized fluid and an "off" period during which the valve connects the actuator to a dump line. Sensors (18,19) provide signals indicative of the input and output speeds of the clutch, and a micro processor control circuit (25) establish for successive time intervals the ratio between the intput and output speeds of the clutch and the change in this ratio by comparison with the ratio for a previous time interval.