Gear ratio shift control system for automatic vehicle transmission

A method of controlling gear ratio shifting in an automatic transmission mounted on a vehicle, including:

• a plurality of gears each of which transmit engine torque to a drive shaft;
• a plurality of frictional engaging elements which operate to selectively establish one gear ratio from among the gear ratios;
• and
• shift solenoid valves provided in an oil pressure control circuit connected to a source of pressurized oil;
• and including the step of:
• generating a shift command to upshift from one gear ratio currently established to a next gear ratio by determining a command to the solenoid valves to discharge the pressurized oil from the frictional engaging elements that establish the current gear ratio so as to slip-control the frictional engaging elements, and to charge the pressurized oil to the frictional engaging elements that establish the next gear ratio to be shifted to;
• wherein the method comprises the steps of:
• determining the command such that an actual slip rate of the frictional engaging elements that establish the current gear ratio converges to a first desired slip rate;
• determining the command such that the actual slip rate of the frictional engaging elements that establish the current gear ratio converges to a second desired slip rate;
• detecting means for detecting a maximum actual slip rate;
• calculating a difference between the detected maximum actual slip rate and the second desired slip rate;
• correcting the command in response to the calculated difference ;
• and
• storing the corrected command to be used as the command in the first step in controlling a next upshift.

A computer program embodied on a computer-readable medium for controlling gear ratio shifting in an automatic transmission mounted on a vehicle, including:

• a plurality of gear trains each of which transmits engine torque to a drive shaft;
• a plurality of frictional engaging elements which operate to selectively establish one gear ratio from among the gear ratios;
• and
• shift solenoid valves provided in an oil pressure control circuit connected to a source of pressurized oil;
• and including the step of:
• generating a shift command to upshift from one gear ratio currently established to a next gear ratio by determining a command to the solenoid valves to discharge the pressurized oil from the frictional engaging elements that establish the current gear ratio so as to slip-control the frictional engaging elements, and to charge the pressurized oil to the frictional engaging elements that establish the next gear ratio to be shifted to;
• wherein the method comprises the steps of:
• determining the command such that an actual slip rate of the frictional engaging elements that establish the current gear ratio converges to a first desired slip rate;
• determining the command such that the actual slip rate of the frictional engaging elements that establish the current gear ratio converges to a second desired slip rate;
• detecting means for detecting a maximum actual slip rate;
• calculating a difference between the detected maximum actual slip rate and the second desired slip rate;
• correcting the command in response to the calculated difference;
• and
• storing the corrected command to be used as the command in the first step in controlling a next upshift.