System and method for controlling working hydraulic pressure for automatic transmission with fluid transmission device

A method for controlling a working fluid hydraulic pressure of a mechanical power transmission of a power transmission applicable to an automotive vehicle, the power transmission having a fluid power transmitting device, an input axle of the mechanical power transmission being linked to an output axle of the fluid power transmitting device, comprising the steps of:

• a) detecting an input revolutional speed (N.sub.E) of the fluid power transmitting device;
• b) detecting an output revolutional speed (N.sub.T) of an output axle of the fluid power transmitting device;
• c) detecting an output revolutional speed (N.sub.M) of an output axle of the mechanical power transmission;
• d) determining whether a shifting operation of the mechanical power transmission occurs;
• e) measuring a duration of time (Ts) of the shifting operation upon determination that a shifting operation occurs;
• f) retrieving a target duration of time (To) during which the shifting operation occurs from a table map according to a speed ratio (e) between the input axle revolutional speed (N.sub.E) of the fluid power transmitting device and output axle revolutional speed (N.sub.T) thereof and input axle revolutional speed (N.sub.E);
• g) comparing the measured duration of time (Ts) with the target duration of time (To);
• h) retrieving a characteristic value of the mechanical power transmission from a memory according to a result of comparison;
• i) correcting the characteristic value according to the result of comparison;
• j) estimating an input torque of the mechanical power transmission on the basis of the corrected characteristic value and input axle revolutional speed of the fluid power transmitting device;
• and
• g) setting a value of the working fluid pressure on the basis of the estimated input torque and speed ratio between the output axle revolutional speed of the fluid power transmitting device and output axle revolutional speed of the mechanical power transmission.

In an automatic power transmission having fluid power transmitting means connected to an output shaft of an internal combustion engine, mechanical gear shifting means hydraulically controlled, and an electromagnetic valve which controls the operation of hydraulic actuators provided in the mechanical gear shifting means in response to a duty ratio signal from control means,

• said control means comprising:
• a) first means for detecting an input revolution speed of said fluid power transmitting means and outputting a first signal indicative thereof;
• b) second means for detecting an output revolution speed of said fluid power transmitting means and outputting a second signal indicative thereof;
• c) third means for rewritably storing a characteristic value of said fluid power transmitting means with respect to a speed ratio between the input and output revolution speeds detected by said first and second means;
• d) fourth means for detecting an actual duration of time during which a shifting operation occurs;
• e) fifth means for storing a target duration of time during which the shifting operation occurs, according to an operating state of said fluid power transmitting means;
• f) sixth means for comparing the target duration of time retrieved from said fifth means with the actual duration of time detected by the fourth means and correcting and rewriting the characteristic value retrieved from said third means on the basis of the comparison result thereof;
• g) seventh means for estimating an input torque of the mechanical gear shifting means on the basis of the first and second signals and on the basis of the learned characteristic value of said fluid power transmitting means;
• and
• h) eighth means for controlling the duty ratio of the signal transmitted to the electromagnetic valve according to the estimated input torque of said mechanical gear shifting means so that the hydraulic pressure supplied to said hydraulic controlled actuators including the clutch means, frictional elements, and actuator valves of the mechanical gear shifting means is adjusted and set.