Abstract: A hydraulic transmission apparatus with a lockup clutch has a pump impeller, a turbine runner, a side cover, a lockup clutch, a clutch piston, a lockup control unit, a frictional engagement unit and a resilient member, a backward movement stopping unit, wherein a transmission capacity of the lockup clutch by virtue of a biasing force of the resilient member is set smaller than a torque absorption capacity of the pump impeller when the engine is in an idle state so that the clutch piston is held at the predetermined backward position by virtue of the pressure difference when the engine is in the idle state.

Abstract: A tightening force of a lockup clutch (2) exerted between a pump impeller (1a) connected to an engine (21) and a turbine runner (1b) connected to an automatic transmission (23) is controlled by a controller (5). The controller (5) determines a target relative rotation speed of the pump impeller (1a) and the turbine runner (1b), and performs feedback control of the tightening force such that the difference between the target relative rotation speed and the real relative rotation speed is decreased. The controller (5) also performs feedforward control of the tightening force. When the variation of the relative rotation speed due to the feedforward control has exceeded the predetermined value, the controller (5) corrects the feedback control amount to moderate the effect of the variation, thereby suppressing sudden change in the tightening force.

Abstract: In a drive train for a working machine, in particular, a wheel loader, the driving speed is preselected via a driving pedal (11) and the working hydraulic system is actuated via a selector lever (8), whose signals are fed to an electronic control unit (10) which regulates a drive engine (1) and a clutch (2) arranged between the drive engine (1) and a pump impeller (3) of a hydrodynamic torque converter in such a manner that an auxiliary drive (6) for a pump (7) of the working hydraulic system is operated at a sufficient speed, while the preselected driving speed is not exceeded.

Abstract: A clutch is operated by an actuating pressure pressure during an engaging process of the clutch. The actuating pressure is controlled over time such that predetermined characteristics for an engagement of said clutch are approximated by starting a process for changing a rotational speed of an output shaft of the torque converter for an adaptation of the rotational speed to an actual velocity of the vehicle during engagement of the clutch. An ideal signal for the rotational speed is determined which corresponds to an estimate for an engagement of the clutch with the predetermined characteristics. An actual signal of the rotational speed of the output shaft over time is measured during said process. Deviations are determined between the actual signal and the ideal signal. Finally the signal of the actuating pressure over time is automatically changed in order to reduce the deviations between the actual signal and the ideal signal if the deviations exceed a threshold.

Abstract: An engaging force of a pump impeller (1a) connected to an engine (21) and a turbine runner (1b) connected to an automatic transmission (23) is controlled by a controller (5). The controller (5) determines a target relative rotation speed of the pump impeller (1a) and the turbine runner (1b), and performs feedback control of the engaging force such that the difference between the target relative rotation speed and the real relative rotation speed is decreased. The controller (5) also performs feedforward control of the engaging force in a increasing direction. When the engine (21) is in a predetermined engine-stall prevention condition, the controller (5) prohibits the feedforward control so as to prevent an interference between feedback control and feedforward control.

Abstract: A drive control apparatus for a vehicle including an engine which generates power using combustion of fuel; a hydrodynamic power transmission device which transmits an output of the engine via fluid, includes an input side and an output side which can be directly coupled; a lock-up engagement device which engages the lock-up clutch when a predetermined lock-up engagement condition is satisfied; and a lock-up restriction device which stops engagement control performed by the lock-up engagement device so as to disengage the lock-up clutch if there is a possibility that knocking will occur in the engine when the lock-up clutch is engaged by the lock-up engagement device. A shock at the time of tip-in acceleration is suppressed irrespective of knocking prevention control so as to improve riding comfort. In addition, occurrence of a droning noise is suppressed.

Abstract: In a differential limiting torque control section, a target differential rotation speed between front and rear drive shafts is established according to a dial position inputted by a driver of a variable dial. Further, an actual differential rotation speed between front and rear drive shafts is calculated and a deviation between the target differential rotation speed and the actual differential rotation speed is calculated. Based on the deviation, a first differential limiting torque and based on a dial position of a variable dial a second differential limiting torque are calculated. Further, a third differential limiting torque is calculated based on the dial position and a throttle opening angle. A final differential limiting torque between front and rear drive shafts is obtained by summing up these first, second and third differential limiting torques.

Abstract: A center differential limiting control unit calculates and sets a vehicle speed, a target difference in a rotational speed between front and rear axle shafts, a control start difference in the rotational speed, and an actual difference in the rotational speed, respectively. Then, when the actual difference is large than the control start difference, it is determined that a front and rear axle shaft control start condition is established, and front and rear axle shaft differential limiting torque is calculated according to the actual difference and the target difference. In contrast, when the actual difference is smaller than the control start difference, it is determined that the front and rear axle shaft control start condition is not established, and an integral term in the front and rear axle shaft limiting torque and control is set to 0.

Abstract: A mobile vehicle is to be operated at constant speed, during which the speed of the drive engine, which drives a step-down transmission (5) via a hydrodynamic torque converter, varies. To do this, a clutch (2) arranged, between the drive engine and the pump impeller (3), is regulated in such manner that the actual speed of the vehicle corresponds to the specified speed.

Abstract: In a lockup control system of an automatic transmission with a lockup torque converter, a controller pre-stores a predetermined lockup control map including at least a predetermined coast slip lockup area, within which the system executes a slip lockup control mode under the vehicle's coasting condition, so that a speed difference between input and output speeds of the torque converter is brought closer to a predetermined value. The controller determines whether a first transition from the vehicle's driving condition to the predetermined coast slip lockup area occurs in a release mode of the lockup clutch or a second transition from the vehicle's coasting condition to the predetermined coast slip lockup area occurs in the release mode. When the first transition occurs, the lockup clutch is conditioned in the slip lockup control mode. When the second transition occurs, the lockup clutch is conditioned in the release mode.

Abstract: A vehicle speed control system is adapted to a vehicle equipped with an automatic transmission with a torque converter. The vehicle speed control system detects whether the automatic transmission is put in a lock-up condition, and corrects a command drive torque according to the lock-up condition of the automatic transmission. Particularly, the vehicle speed control system decreases a correction quantity of the command drive torque when the automatic transmission is put in the un-lockup condition. Therefore, the vehicle speed control system can adapt its response characteristic to a controlled system response characteristic which varies according to the lock-up condition of the transmission.

Abstract: In a method for determining evaluation data for transmissions in vehicles, data is measured in the vehicle via sensors, the measured data is used to form intermediate data specific to the vehicle and then, from the measured data and the intermediate data, evaluation data is determined which is shown, stored or transmitted to a data collecting station.

Abstract: A control apparatus for feedback-controlling an engaging action of a clutch disposed between an engine and a transmission of an automotive vehicle, wherein an engaging force control device is operated upon an engaging action of the clutch, for determining a control amount and feedback-controlling the engaging action on the basis of the determined control amount such that the clutch is placed in a desired state of engagement, and a control amount limiting device is operated to limit the determined control amount when the determined control amount has changed to cause an engaging force of the clutch to be reduced.

Abstract: A method for controlling a damper clutch release control system which performs duty control in releasing a damper clutch for down-shifting in a sports mode decreasing gear-shift shock, is provided. The method requires determining whether a down-shift signal is inputted in a state when a gear shift mode is a sports mode and a throttle valve opening angle is within a predetermined range, and performing duty control until a transmission control outputs a down-shift start signal to a transmission when it is determined that the down-shift signal is inputted.

Abstract: In a method for controlling a drive line of a vehicle, in which a power-shift clutch is engaged for torque transmission while driving, the point of engagement of a power-shift clutch that is disengaged in parallel is determined by a nonsteady-state engagement operation.

Abstract: An initial command oil pressure of a lock-up control of coasting lock-up region is set by using a lock-up learning correction amount calculated by a learning control in a lockup control of the other of the plurality of lock-up regions such as slip lock-up region and complete lock-up region when one of the lock-up control of these other lock-up regions is performed before the lock-up control of the coasting lock-up region. Thus, a lock-up learning correction amount can be commonly used among three kinds of lock-up regions, and a lock-up as set is early realized in each lock-up region.

Abstract: A damper clutch control method comprising the steps of detecting a throttle opening, an engine rpm and an turbine rpm; performing lift-foot-up shifting if throttle opening is abruptly decreased; determining if a difference in engine rpm and turbine rpm is below a predetermined value; and duty controlling a damper clutch if the difference in engine rpm and turbine rpm is below the predetermined value.

Abstract: In an apparatus for controlling an automatic transmission which is provided with a torque converter having a fluid coupling unit for coupling driving force to a transmission through fluid coupling and a direct coupling unit for coupling the driving force to the transmission through mechanical coupling and being operative to take a fluid coupling state, a direct coupling state or an intermediate state between the fluid and direct coupling states in accordance with a working pressure applied to the direct coupling unit, a control signal is generated for changing the initial value of the working pressure in accordance with the driving force during the period of transition between the fluid coupling state and the direct coupling state.

Abstract: In an apparatus for controlling an automatic transmission which is provided with a torque converter having a fluid coupling unit for coupling driving force to a transmission through fluid coupling and a direct coupling unit for coupling the driving force to the transmission through mechanical coupling and being operative to take a fluid coupling state, a direct coupling state or an intermediate state between the fluid and direct coupling states in accordance with a working pressure applied to the direct coupling unit, a control signal is generated for changing the initial value of the working pressure in accordance with the driving force during the period of transition between the fluid coupling state and the direct coupling state.

Abstract: An apparatus and method determine a state of a power train that includes a power transmission apparatus that is configured to transmit power of a first driving power source to an input side of a second driving power source via a clutch and a transmission, and is capable of changing a torque capacity of the clutch and a gear ratio of the transmission. The apparatus and method determine a state of the clutch or the transmission based on a revolution speed of the first driving power source and information indicating a state of the second driving power source, e.g., a revolution speed of the input side of the second driving power source.

Abstract: In an apparatus for controlling an automatic transmission which is provided with a torque converter having a fluid coupling unit for coupling driving force to a transmission through fluid coupling and a direct coupling unit for coupling the driving force to the transmission through mechanical coupling and being operative to take a fluid coupling state, a direct coupling state or an intermediate state between the fluid and direct coupling states in accordance with a working pressure applied to the direct coupling unit, a control signal is generated for changing the initial value of the working pressure in accordance with the driving force during the period of transition between the fluid coupling state and the direct coupling state.

Abstract: A method and system for controlling the switching in of ancillary equipment driven by an engine of a vehicle, the ancillary equipment being arranged to be driven by the engine until at least a minimum operating level relating to the status of the ancillary equipment is attained.

Abstract: A slip control system for a torque converter with a lockup clutch comprises a controller that outputs a slip control signal to a slip control actuator of the lockup clutch to adjust an actual slip rotation speed of the torque converter at a target slip rotation speed. The controller is coupled to sensors for detecting information indicative of a condition of a drive system including the torque converter. The controller decides an operating state of the torque converter at time when the slip control is started, and selects one of initial valves for a slip command signal corresponding to the slip control signal according to the decided operating state of the torque converter at the start of the slip control. This arrangement functions to prevent troubles including shocks due to shortage of slippage in the torque converter and generation of radial slippage of the torque convert from generating at a time staring the slip control.

Abstract: A lockup control system controls a lockup state of the automatic transmission employing a torque converter with a lockup clutch. The lockup control system executes a lockup clutch engagement pressure control for decreasing an engagement differential pressure of the lockup clutch at a predetermined differential pressure for a predetermined time period under a coast lockup state. Further, the lockup control system executes a learning control for obtaining the predetermined differential pressure by adding a differential pressure correction value to a differential pressure learning value by which the torque converter generates a slight slip under the coast lockup state. Therefore, even during the coast lockup state, both of suppressing vibrations by a lowering of a lockup capacity and maintaining a responsibility for re-increasing the differential pressure are ensured.

Abstract: A torque converter lock-up clutch controlling system for a vehicle drive train inputs a vehicle speed signal and an engine load signal. The vehicle drive train includes an automatic transmission operable in a manual ("M") ratio change mode when an operator selects a "M" range position. The system enables the automatic transmission to behave like a manual transmission upon selection of the "M" range position. A memory includes a "M" range lock-up shift point map for storing data which relates the lock-up application and release to the vehicle speed and engine load signals. The "M" range lock-up shift point map includes lock-up application values, which correspond to the magnitudes of the vehicle speed signal at which lock-up clutch applications are to occur. The magnitudes of the vehicle speed signal at which lock-up clutch applications are to occur are determined in a manner as a function of the magnitudes of the engine load signal.

Abstract: The power train of a motor vehicle employs a torque transmitting apparatus having a hydrokinetic torque converter with a lockup clutch and a torsional damper between the output member of the clutch and the hub of the turbine in the cover of the torque converter. The torque capacity of the damper is less than the nominal torque of the engine whose output element drives the cover of the torque converter. The lockup clutch is designed in such a way that the transmission of torque from the cover to the damper can be regulated in several stages, one of which involves the transmission of torque within a range of between about 10% and 60% of the maximum torque transmitted by the engine and another of which involves the transmission of torque corresponding to not less than 60% of the maximum torque transmitted by the engine.

Abstract: A slip control apparatus for a torque converter with a lockup clutch controls a slip rotation speed between input and output elements of the torque converter so as to be set at a slip rotation speed command value through the control of an engagement condition of the lockup clutch. The slip control apparatus comprises a target converter torque calculating section which calculates a target converter torque for achieving the slip rotation speed command value on the basis of a characteristic of the torque converter. A target engagement capacity calculating section calculates a target engagement capacity of the lockup clutch by subtracting the target converter torque from an output torque of the engine. The lockup clutch engagement force controlling section controls an engagement force of the lockup clutch so as to adjust a lockup clutch engagement capacity of the lockup clutch at the target lockup clutch engagement capacity.

Abstract: A gear shift failure of an automatic transmission to a wrong gear other than an indented gear is made by estimating slippage theoretically caused in a torque converter on the basis of an engine speed and a turbine speed theoretically determined for an intended gear according to the vehicle speed and comparing the estimating slippage with predetermined reference slippage. When the estimated slippage exceeds the predetermined threshold slippage, it is decided that there has occurred a wrong shift to a gear other than the intended gear.

Abstract: A releasable coupling control system in combination with an electronic engine control unit executable a fuel cutoff mode during vehicle deceleration and re-startable a fuel-supply recovery mode as soon as an engine speed drops below a predetermined threshold value, for controlling engaging and disengaging operations of a releasable coupling device placed in an automotive power train between an engine and drive wheels, comprises a wheel-speed sensor for detecting a drive-wheel speed to generate a drive-wheel speed indicative signal, and a controller being configured to be responsive to the drive-wheel speed indicative signal for moderately releasing the releasable coupling device at a moderate turn-off mode when the drive-wheel speed indicative signal value drops below a first predetermined value, and for quickly releasing the releasable coupling device at a quick turn-off mode when the drive-wheel speed indicative signal value drops below a second predetermined value.

Abstract: The lock-up clutch control apparatus is provided with reference values for operating variations of the accelerator pedal predetermined for respective gear positions. The lock-up clutch control apparatus comprises a tightening permission judgement device 25 for judging whether it is appropriate to permit or prohibit tightening of the lock-up clutch, based on comparison between a reference value and an operating variation at present car conditions. Thereby, the lock-up clutch control apparatus is capable of reflecting the driver's intention to accelerate or reduce the car speed and is capable of enhancing drivability as well.

Abstract: A fuzzy control method of a damper clutch and, more particularly, a fuzzy control method enhances engine brake effect by directly connecting a pump to a turbine by engaging the damper when a shift control unit identifies an engine brake state. The fuzzy control method of a damper clutch includes receiving or checking input signals relating to a damper clutch; controlling shift timing by a fuzzy control; determining if an engine brake should be used or not; checking an amount of driver's engine brake will if the engine brake should be used; determining if an emergency brake should be used or not; engaging the damper clutch when an emergency brake should be used; and controlling the damper clutch through a normal control when both the engine brake and emergency brake are not used.

Abstract: In a fluid pressure control system for a continuously variable transmission, a valve for regulating a torque converter pressure is a pilot actuated valve having a pressure increasing side pilot port for receiving a control pilot pressure for controlling a line pressure and a pressure decreasing side pilot port for receiving a second pilot pressure. A selector valve is switched between a first state for allowing the supply of the second pilot pressure to decrease the torque converter pressure supplied to the torque converter and a second state for draining the second pilot pressure to increase the torque converter pressure. By controlling the selector valve, a control unit increases the torque converter pressure in a wide throttle high speed vehicle operation with the torque converter in a lockup state to ensure the lockup engagement and in a wide throttle starting operation with the torque converter in a non-lockup state to prevent an engine stall.

Abstract: According to a torque converter lockup control, a lockup actuator, including a lockup solenoid, is operative responsive to an output command signal issued by a controller to adjust lockup clutch engagement force to a commanded value. The lockup clutch engagement force is a force with which the lockup clutch is engaged. The controller determines the commanded value as a function of a deviation between a current value of slip speed within the torque converter and a desired value thereof. For preventing the lockup clutch from shifting deeply into its converter position when the deviation persists to stay in the neighborhood of zero, the controller sets a limit to the determined commanded value during operation of the lockup clutch in the slip lockup mode.

Abstract: Vehicle control apparatus including a running stability controller for performing a predetermined operation for improving stability of running of the vehicle by reducing engine output, braking the vehicle, holding automatic transmission in a predetermined position or shifting up the transmission, for example, and a device for preventing an interference between the operation of the running stability controller and an operation of a device, such as the automatic transmission, a torque converter lock-up clutch and a differential limiting clutch, which device is provided in a power transmitting system and which is controlled by an appropriate controller.

Abstract: An engine-transmission drivetrain includes a torque converter situated between the engine output shaft and the transmission. The torque converter includes a lock-up clutch. A speed sensor, which measures the rotational speed of an output shaft of the transmission, generates a pulse signal. A transmission controller includes a deceleration dependent lock-up release command generator and a torque converter speed dependent lock-up release command generator. The pulse signal from the speed sensor is used as inputs to both of the lock-up release generators. In the deceleration dependent lock-up release command generator, the pulse signal is processed to derive information as to the magnitude of deceleration which the transmission output shaft is subject to. In the torque converter speed dependent lock-up release generator, the pulse signal is processed to derive information as to rotational speed of an output element of the torque converter.

Abstract: A control system of a lockup clutch of a torque converter of a vehicle automatic transmission. A basic manipulated variable is determined in response to the vehicle operating condition in accordance with a predetermined characteristic, and the lockup clutch engaging force is controlled in response to the variable. In the system, fuzzy reasoning is carried out using the detected vehicle operating parameters to correct the basic manipulated variable, and the engaging force is controlled in response to the corrected manipulated variable, when the control condition is met. The corrected manipulated variable is gradually decreased with respect to time when the vehicle driving state has shifted from a region in which the engaging force is controlled in response to the corrected manipulated variable to a region in which the lockup clutch is disengaged.

Abstract: A control device for an automatic transmission having a hydraulic power transmission with a lock-up clutch includes a device for setting a predetermined pressure that is less than a pressure at which a target value convergence control is started. The predetermined pressure is set as the hydraulic pressure applied to the lock-up clutch by a predetermined pressure setting device for a predetermined time. The predetermined time is a time from a satisfaction of conditions for the slip control start until an input rotation speed is stabilized, as set by a time setting device.

Abstract: A lockup control apparatus for use with an automotive vehicle including an engine, an automatic transmission and a torque converter having a lockup clutch operable on a variable engagement force to provide a controlled degree of mechanical connection between the engine and the automatic transmission during deceleration. The lockup engagement force is set at a target value substantially equal to a first value calculated based on vehicle operating conditions plus a second value calculated based on engine output at a first stage of lockup control operation when the engine output remains positive after the driver's operation is detected and it is decreased at a predetermined rate to the first value at a second stage of lockup control operation after the engine output becomes negative.

Abstract: A slip control system for a torque converter with a lockup clutch comprises a controller from which a slip control signal is outputted to a slip control actuator of the torque converter. The controller is arranged to calculate a reference value of a lockup clutch engagement pressure on the basis of a characteristic of the torque converter, to calculate a difference canceling lockup clutch engagement pressure for adjusting an actual slip rotation speed to the target slip rotation speed, to obtain the sum of the lockup clutch engagement pressure reference value and the difference canceling lockup clutch engagement pressure as a lockup clutch engagement pressure command value, and to output the control signal indicative of the lockup clutch engagement pressure command value to the actuator.

Abstract: A lock-up control device controls an engaging force of a lock-up clutch, which shares engine output with a torque converter to transmit it toward an input shaft of a transmission of a car. First, target driving force is produced based on accelerator pedal opening and car velocity. Then, required torque is produced based on a gear ratio and the target driving force. Target engine speed is produced based on the required torque, wherein the target engine speed is set to avoid occurrence of abnormal sounds and abnormal vibrations. Thus, the lock-up clutch is controlled in such a way that real engine speed does not become less than the target engine speed in case of a gear change corresponding to a shift-up operation, for example. Basically, the lock-up clutch is controlled to have engaging force, which is made as maximal as possible to improve fuel efficiency. In other words, the lock-up clutch is controlled to be as tightly as possible.

Abstract: A transmission assembly and method for controlling a torque converter of a transmission assembly in which an electronic controller monitors the load on the vehicle power train in addition to a number of other vehicle dynamics, including the currently engaged gear ratio and the temperature of the transmission fluid. The electronic controller is operable for causing the activation of the converter clutch in response to a number of predetermined operating conditions, one of which includes the operation of the vehicle when the fluid in the torque converter exceeds a predetermined temperature and the vehicle power train is operated under a heavy load for a period of time which exceeds a predetermined time interval. Engagement of the converter clutch during such times inhibits relative rotation between the torque converter turbine and impeller, improving fuel economy and preventing the torque converter from generating a substantial amount of heat.

Abstract: A control apparatus of the present invention can realize stable and good follow-up slip control of a plant, such as a lock-up clutch, irrespective of a characteristic perturbation of the plant, for example, deterioration of frictional members or operating oil of the clutch. The apparatus of the present invention also has an improved convergence of transient response. The control apparatus approximates a characteristic perturbation by a high-order function in a frequency domain and gives requisites for the stable and good follow-up control as a sensitivity function S and a complementary sensitivity function T of a feedback control system. Design of the feedback control system is considered as an issue of mixed sensitivity of H.infin. control. A controller is accordingly designed with a function of predetermined order, which is substantially equal to the order of the high-order function approximating the characteristic perturbation.

Abstract: A lock-up clutch slip control system for controlling a lock-up clutch, which is arranged in parallel with a hydraulic power transmission for connecting a prime mover and a speed change unit, selectively into a slip state. It is decided whether or not a slip control of changing the lock-up clutch from a complete apply state to a slip state is to be executed according to the operation of lowering the output of the prime mover. The output of said prime mover is changed to suppress the output fluctuation of the prime mover when it is decided that the slip control of the lock-up clutch is to be executed.

Abstract: A control system for controlling a lock-up clutch of a torque converter employed in an automatic transmission of a vehicle, the lock-up clutch being controllable by a pressure differential between apply and release pressures comprises a detector for detecting a demand of change (decrease/increase) in the pressure differential, a pressure-differential setting circuit for setting a target pressure differential in response to the demand of change in the pressure differential, and a pressure-differential filter having a desired dynamic characteristic and being responsive to the target pressure differential for outputting a filtered pressure-differential command value via a filtering process based on the desired dynamic characteristic.

Abstract: A lockup control apparatus of a torque converter for a vehicle comprises a coast condition detecting section for detecting coast running of a vehicle, a lockup clutch slip detecting section for detecting a target slip generated between the input and output elements of the torque converter and a slip start capacity storing section, and a coast lockup control section for detecting a lockup capacity. The slip start capacity storing section detects a slip start capacity by once decreasing the lockup capacity to the sum of a last stored slip start capacity and a preset capacity and stores the slip start capacity while updating it. During the coast running a coast lockup control section controls the lockup capacity at a minimum lockup engagement capacity which is the sum of the newest slip start capacity and a predetermined capacity.

Abstract: A method is provided for adaptively determining a torque-related (K-factor) value for a torque converter in a vehicle and providing adaptive torque management to an automatic transmission. The torque-related K-factor value is computed for a given torque converter as a function of engine speed and difference in torque measured with the vehicle operating in idle neutral and drive. The vehicle dynamically learns the K-factor value and manages torque applied to the transmission by limiting the engine output speed as a function of the learned torque-related K-factor and vehicle speed.

Abstract: A lockup control apparatus for use with an automotive vehicle having an engine, an automatic transmission and a torque converter operable in a coast lockup mode having a lockup capacity to provide a controlled degree of mechanical connection between the engine and the automatic transmission when the vehicle is coasting. The apparatus employs a memory having a desired value for the lockup capacity stored therein. A first signal is produced when a slip rotation occurs in the torque converter and a second signal is produced when the coast lockup mode is released. The desired lockup capacity value is updated with a greater value in response to the first signal. A frequency at which either of the first and second signals occurs is measured. The desired lockup capacity value is updated with a smaller value when the measured frequency exceeds a reference value.

Abstract: A hydraulic pressure control system for an automatic transmission is capable of reducing the size and simplifying the structure of a lockup controlling hydraulic circuit. An oil pressure output from a solenoid valve acts on an oil pressure chamber. The internal pressure of another oil pressure chamber becomes high only in a forward low-speed range and becomes low in all of the other gear shift ranges. The internal pressure of another oil pressure chamber becomes high only in forward ranges and becomes low in neutral and reverse ranges. The valve member moves in accordance with oil pressures applied to the oil pressure chambers to change over oil paths connected to a clutch control oil chamber and a torque converter oil chamber, whereby a lockup clutch assumes one of engaged, slip, and released states.

Abstract: A facing surface of a clutch piston is previously moved to a position just before it abuts against an inner surface of a torque converter cover, or a position in which it extremely slightly abuts against the inner surface of the torque converter cover by outputting an initial engage pressure YMIN set in accordance with a vehicle speed and the like only for a predetermined time TMPS prior to the start of engagement of a lockup clutch. When the engagement of the lockup clutch is started, the engage pressure is gradually increased. When the engage pressure approaches a target pressure set in accordance with the target speed ratio, a feedback control of the engage pressure is carried out such that the actual speed ratio of the torque converter is converged to the target speed ratio. Thus, when the lockup clutch of the torque converter is brought into an engaged state, the responsiveness can be enhanced while preventing the generation of a shock.

Abstract: A control system for controlling an automatic transmission equipped with a torque converter which is locked and unlocked through a lockup clutch has a lockup release control device which releases locking of the torque converter at different release rates between a downshift resulting from an increase in engine load and a downshift resulting not from an increase in engine load.