Abstract: A hydraulic control circuit for an automatic transmission which has a plurality of hydraulic type frictional engagement elements for switching gear stages and a lockup clutch juxtaposed to a hydraulic power transmission device for transmitting engine power to the gearing. The hydraulic control circuit includes a lockup relay valve for switching oil pressure between an application side oil chamber and a release side oil chamber of the lockup clutch to apply and release the lockup clutch and a lockup switching valve for switching the lockup relay valve. A lockup control valve functions to increase the pressure difference between the application side oil chamber and the release side oil chamber at the time of application of the lockup clutch, as a signal pressure rises. A transient pressure control valve controls the transient pressure of a hydraulic frictional engagement element in accordance with the signal pressure.

Abstract: An automatic transmission of a vehicle including a speed change gear mechanism including rotary members such as gears and gear carriers and hydraulically operated friction engaging means and adapted to provide various speed stages according to selective engagement and disengagement of the friction engaging means is controlled by such steps as detecting rotation speed of at least one of the rotary members during a shifting between the speed stages, changing hydraulic pressure of at least one of the friction engaging means during a first phase of the speed stage shifting so as to make the rotation speed of the one rotary member follow a first change performance curve calculated according to a first feedback control program, and changing the hydraulic pressure of the one friction engaging means during a second phase of the speed stage shifting so as to make the rotation speed of the one rotary member follow a second change performance curve calculated according to a second feedback control program in continuity

Abstract: In a certain speed stage shifting of an automatic transmission of a vehicle including a speed change gear mechanism including rotary members such as gears and gear carriers and hydraulically operated friction engaging brakes and clutches adapted to provide various speed stages according to selective engagement and disengagement of the friction engaging brakes and clutches, the servo oil pressure of a first friction engaging brake is immediately lowered down to a stand-by pressure marginally higher than a threshold pressure bordering non sliding and sliding of the first friction engaging brake at the start of a change-over of a second friction engaging brake is and then, when a substantial change-over of the second friction engaging means started, the servo oil pressure is further lowered across the threshold pressure and thereafter periodically lowered by a decrement the magnitude of which may desirably be increased along with a lapse of time.

Abstract: In controlling an automatic transmission in a vehicle by a combination of an electronic computer system and a hydraulic actuation system according to a principle of feedback control so that the electronic computer system computes a target control state for the hydraulic actuation system and the hydraulic actuation system is operated according to a difference between the target control state and a current control state thereof, the difference is modified by an amount which is decreased along with lapse of time so that the delay in the operation of the hydraulic actuation system is compensated for by a simulation that at the start of control the difference is beforehand increased for an amount which is gradually cancelled by a delay function of the difference itself as the delay in the operation of the hydraulic actuation system disappears. The difference may further be modified so that the modification is started with a time lag. The difference may further be modified by the rate of change of itself.

Abstract: In an automatic transmission in a vehicle having a tandem connection of a first gear unit such as lower and upper gear stages and a second gear unit such as having three gear stages so that selective engagement and disengagement of clutches and brakes in each gear unit selectively provide six gear states, a certain clutch or brake of the first gear unit is controlled in reference to a difference between certain target engaged/disengaged condition and actual engaged/disengaged condition of itself in setting up a certain gear stage in the first gear unit as well as to difference between certain target engaged/disengaged condition and actual engaged/disengaged condition of (and further, though optionally, a signal for controlling) a certain clutch or brake of the second gear unit in setting up a certain gear stage in the second gear unit.

Abstract: A linear solenoid valve apparatus for discharging foreign matter collected at the exhaust port by engaging the electromagnet of the linear solenoid valve. The apparatus includes a linear solenoid valve having a valve sleeve, a spool, a spring, and an electromagnet, and a modulator valve including an exhaust port in which foreign matter is collected. The electromagnet is energized by foreign matter discharging control, responsive to detection of lack of need for output pressure from the solenoid valve, so that the foreign matter is discharged from the exhaust port.