Patent ID: 6068576
Filing Date: 2000-05-30
Classification: F16H,Y10T

Abstract:
A hydraulic control system for an automatic transmission having an input shaft for receiving power from an engine output shaft; an output shaft which is connected to vehicle wheels; and a plurality of selectively engageable and disengageable friction elements that determine a ratio of power transmission between the input shaft and the output shaft, said hydraulic control system comprising:a plurality of hydraulic servos, corresponding to the friction elements, that engage and disengage the corresponding friction elements;a hydraulic controller which controls hydraulic pressures applied to the hydraulic servos; anda control unit, which receives input signals from sensors indicating a vehicle driving state, comprising:a disengagement side controller which outputs signals to said hydraulic controller to control a hydraulic pressure applied to one of the hydraulic servos for a first friction element of said plurality of friction elements, the first friction element being disengaged in a down shift to a predetermined gear ratio,an engagement side controller which outputs signals to said hydraulic controller to control a hydraulic pressure applied to another of the hydraulic servos for a second friction element of said plurality of friction elements, the second friction element being engaged in the down shift to the predetermined gear ratio,a shift progress detector which detects a shift parameter indicative of actual progress of the down shift,a shift action detector which detects a changing control parameter of the down shift control by the disengagement side controller, anda change determiner which determines if the detected shift parameter indicates progress of the down shift to an extent of fulfilling a predetermined condition of the down shift in response to said shift action detector detecting a predetermined state of the control parameter and which chances primary control of the down shift from the disengagement side controller to the engagement side controller upon determining that the predetermined condition of the downshift is not fulfilled.