Patent ID: 7841455

Claim:
A hydraulic control unit for an automatic transmission, comprising: a plurality of friction engagement elements that switch power transmission paths between an input shaft and an output shaft, the plurality of friction engagement elements comprise a first friction engagement element and a second friction engagement element, the second friction engagement element being released at the same time as the first friction engagement element is engaged so as to accomplish an upshift to a predetermined shift speed; hydraulic servos that engage and disengage the friction engagement elements; hydraulic control means that controls hydraulic pressure of the hydraulic servos for the first friction engagement element and the second friction engagement element; at least one sensor for outputting signals representing a vehicle drive condition; and a control unit that receives signals from each sensor based on the vehicle driving condition and outputs a hydraulic pressure control signal to the hydraulic control means, wherein, the control unit comprises engaging-side hydraulic control means that calculates a change in hydraulic pressure to the hydraulic servo for the first friction engagement element and outputs the hydraulic pressure to the hydraulic control means, and releasing-side hydraulic control means that calculates a change in hydraulic pressure to the hydraulic servo for the second friction engagement element and outputs the hydraulic pressure to the hydraulic control means; and the releasing-side hydraulic control means comprises an initial control that involves sweeping down in a torque phase to a predetermined releasing-side hydraulic pressure that is calculated depending on an engaging-side hydraulic pressure by the engaging-side hydraulic control means and at which the second friction engagement element has a minute torque capacity, and a hold control that controls to substantially hold the predetermined releasing-side hydraulic pressure after the initial control and until a start of an inertia phase following the torque phase is detected, wherein the engaging-side hydraulic control means comprises a first sweep control involving sweeping up with a first gradient toward a target hydraulic pressure immediately before the inertia phase starts, and a second sweep control involving sweeping up with a second gradient lower than the first gradient until rotation change in an input rotational speed is detected from the target hydraulic pressure, and wherein the initial control of the releasing-side hydraulic control means is calculated depending on an engaging-side hydraulic pressure of the first sweep control.