Abstract: A hydraulic control apparatus for an automatic transmission having a mechanical parking mechanism includes a manual valve disposed in the hydraulic control apparatus and having a parking (P) position, reverse (R) position, neutral (N) position and at least one forward speed position. The manual valve is provided with a drain port for releasing, in the parking position, the hydraulic pressure of a hydraulic circuit which establishes the reverse range, and the drain port is provided with an orifice which limits the discharge rate of hydraulic pressure.

Abstract: A power transmission device for four wheel drive vehicle includes a differential motion limiting device, for limiting differential motion of a center differential device, which is made up by a wet-type frictional clutch and a hydraulic actuator. Under running condition, the frictional clutch is engaged by certain engaging force, and considering frictional coefficient of roads, the clutch is engaged with some slips so that torque distribution to front and rear wheels becomes even (50:50), then torque is distributed from the center differential device to front and rear wheels. The line pressure is applied to the hydraulic actuator through a regulator valve. In normal running condition, the regulator valve reduces the line pressure pre certain ratio, the reduced pressure is applied to the hydraulic actuator. In the case the manual valve being shifted to R range or low speed position, the regulator valve is switched to apply the line pressure directly to the hydraulic actuator.

Abstract: In an automatic transmission having a torque converter, a planetary gear mechanism receiving an output from the torque converter and including brakes and clutches, and a hydraulic pressure circuit for actuating the brakes and clutches. An arrangement is provided for varying servo hydraulic pressure, which is for achieving low gear, in dependence upon vehicle velocity.

Abstract: In an upshift timing system which provides a drain passage at higher flow resistance for a first friction engaging device to be disengaged when a hydraulic fluid pressure of a second friction engaging device to be engaged supplied as an actuating pressure to a control port of an upshift timing control valve is less than a certain value and at lower flow resistance when the actuating pressure is greater than the certain value, the control port is supplied with the actuating pressure directly from a pressure chamber of the second friction engaging device via a passage which is separate from a passage which supplies actuating pressure from a pressure source to the pressure chamber of the second friction engaging device.

Abstract: An exhaust brake control system includes an input switch for commanding actuation of an exhaust brake, a throttle sensor for sensing that an accelerator pedal has been depressed in excess of a predetermined angle, a control unit for outputting a control signal in dependence upon output signals from the input switch and throttle sensor, and a valve means for opening and closing an exhaust passageway in dependence upon a control signal produced by the control unit. The control unit includes a shift sensor for sensing at least an L-range shift of an automatic transmission, and a servo hydraulic pressure sensor for sensing servo hydraulic pressure that actuates a servo piston for establishing 1st speed range.

Abstract: An automatic transmission has first and second pressure actuated friction engaging devices to provide a lower speed stage when the first friction engaging device is engaged and the second friction engaging device is disengaged, or vice versa; a speed shift valve which changes over supplying and exhausting hydraulic fluid pressure to and from the first and second friction engaging devices; a downshift timing system which provides lower flow resistance at lower road speed and higher flow resistance at higher road speed in a passage for supplying hydraulic fluid pressure to the first friction engaging device; an upshift timing system which provides higher flow resistance to a passage for exhausting hydraulic fluid pressure from the first friction engaging device before the hydraulic fluid pressure in the second friction engaging device increases to a predetermined value and lower flow resistance to the same drain passage when the hydraulic fluid pressure in the second friction engaging device has increased to th

Abstract: A parking device for an automatic transmission system in automotive vehicles includes a parking gear connected to the engine output shaft, a pawl having one end pivotally mounted to the transmission housing and the other end pivotable towards and away from the parking gear, and a parking cam operatively associated with the pawl and movable axially of the gear for bringing the pawl into and out of engagement with the parking gear. A cam guide and a reaction supporting bracket are retained by a plurality of bolts and by at least one boss having a flat surface and affixed to the transmission housing so as to be situated on the side of the pawl opposite the parking cam.

Abstract: A pressure regulating device for use in a hydraulic control system for an automatic transmission having a torque convertor, a gear transmission and an hydraulic control system provides a first pressure regulating valve for regulating the pressurized fluid output from a pump to a line pressure level, and applying the line pressure to the hydraulic control system. A second pressure regulating valve regulates the pressure of an excess portion of fluid supplied to the hydraulic control system from the first pressure regulating valve, and supplies the excess fluid to the torque convertor and regions requiring lubrication. Overheating of fluid in the torque convertor is prevented at low pressures by a bypass passage which assures at least a minimum fluid flow through the torque convertor at all times.

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.