Hydraulic pressure control system for hydraulically operated vehicle transmission

A system for controlling hydraulic pressure of a hydraulically operated vehicle transmission, comprising:

• vehicle operating condition detecting means for detecting parameters indicative of operating conditions of the vehicle;
• gearshift command output means for determining a gear ratio to be shifted to based on the detected parameters, to output a gearshift command;
• a plurality of frictional engaging elements for selectively establishing one gear stage in the transmission;
• speed detecting means for detecting a rotational speed of at least one of a plurality of rotational members of the transmission which changes at a time of gearshift;
• desired rotational speed change rate determining means for determining a desired rotational speed change rate of the one rotational member based on at least one of the detected parameters;
• and
• hydraulic pressure control means for controlling a supply of hydraulic pressure to at least one of the frictional engaging elements in response to the gearshift command such that the determined gear ratio is established to transmit engine power to a vehicle wheel, said hydraulic pressure control means operating to control the supply of hydraulic pressure to the frictional engaging element such that a change of the rotational speed of the one rotational member concurs with the desired rotational speed change rate,
• wherein said hydraulic pressure control means includes:
• parameter fluctuation discriminating means for discriminating whether the at least one of the parameters fluctuates,
• wherein said hydraulic pressure control means discontinues the operation when said parameter fluctuation discriminating means discriminates that the parameter fluctuates,
• wherein said parameter fluctuation discriminating means includes:
• difference calculating means for calculating a difference of the at least one of the parameters between those obtained at a different timing, and
• comparing means for comparing the difference with a reference value, and
• wherein said parameter fluctuation discriminating means discriminates that the at least one of the parameters fluctuates when the difference exceeds the reference value.