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Control strategy and method for independently controlling friction element actuators for an automatic transmission

  • US 6,385,520 B1
  • Filed: 08/10/2000
  • Issued: 05/07/2002
  • Est. Priority Date: 08/10/2000
  • Status: Expired due to Term
First Claim
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1. A method and strategy for controlling engagement and release of friction elements of a multiple ratio automatic transmission in an automotive vehicle powertrain with a throttle-controlled internal combustion engine, the transmission having pressure-operated friction clutch and brake elements, an electronic controller having signal input portions and output driver portions, a pressure control circuit including solenoid valve actuators communicating with the friction elements and with the output driver portions, and gearing controlled by the friction clutch and brake elements to establish plural torque flow paths from the engine to vehicle traction wheels, the signal input portions of the electronic controller being in communication with sensors for measuring powertrain variables including engine speed, output shaft speed, engine throttle position and transmission speed ratio range selection, the method and strategy comprising the steps of:

  • determining input variables for the electronic controller by reading and processing signals from the sensors;

    computing a friction element capacity reduction for the offgoing friction element on a ratio upshift during a shift start mode;

    maintaining a pressure on the oncoming friction element sufficient to initiate engagement of the oncoming friction element;

    increasing the oncoming clutch pressure during a torque transfer phase as a function of torque ratio of friction element torque to input torque and clutch gain;

    controlling the oncoming and offgoing clutch pressures to effect a calibrated speed ratio rate of change from the previous ratio to the next ratio as a function of throttle position during a ratio change mode; and

    controlling the oncoming friction element using a closed loop control to obtain a speed ratio change rate of a calibrated value during the ratio change mode.

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