Coasting downshift control for automatic transmissions
First Claim
1. A method for controlling a powertrain that includes an engine, automatic transmission having an offgoing friction element to be disengaged during a gear ratio change, and a torque converter having a turbine, the method comprising the steps of:
- initiating a gear ratio change from a current gear ratio to a next gear ratio;
determining a value representing a desired engine speed until disengagement of the offgoing friction element is detected;
determining a predicted current gear synchronous speed, and an offset to the current gear synchronous speed;
setting the desired engine speed equal to the predicted current gear synchronous speed plus an offset to the current gear synchronous speed;
using the desired engine speed value to control engine speed until disengagement of the offgoing friction element is detected during the gear ratio change;
determining a rate of increase of desired engine speed during a period following detection of the disengagement of the offgoing friction element;
increasing the desired engine speed value at the start of the period by said determined rate of increase of desired engine speed during the period; and
using the desired engine speed value to control engine speed during the gear ratio change.
1 Assignment
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Accused Products
Abstract
An automatic transmission ratio shift control system and method for a powertrain having an engine and multiple-ratio gearing controlled by friction elements actuated by hydraulic pressure, an electronic controller for establishing torque transitions among the friction elements as the gear ratio changes, the engine speed being controlled by an electronic throttle control. The strategy employs an electronic throttle and closed loop engine speed control and uses fuel and air as an energy source to increase engine speed during a power-off downshift. The engine speed is boosted to a level close to the synchronous speed in conjunction with release of the off-going friction element. The on-coming friction element is then applied as the engine speed approaches a desired speed. The engine speed increase is timed to lead an increase in torque converter speed.
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Citations
7 Claims
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1. A method for controlling a powertrain that includes an engine, automatic transmission having an offgoing friction element to be disengaged during a gear ratio change, and a torque converter having a turbine, the method comprising the steps of:
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initiating a gear ratio change from a current gear ratio to a next gear ratio; determining a value representing a desired engine speed until disengagement of the offgoing friction element is detected; determining a predicted current gear synchronous speed, and an offset to the current gear synchronous speed; setting the desired engine speed equal to the predicted current gear synchronous speed plus an offset to the current gear synchronous speed; using the desired engine speed value to control engine speed until disengagement of the offgoing friction element is detected during the gear ratio change; determining a rate of increase of desired engine speed during a period following detection of the disengagement of the offgoing friction element; increasing the desired engine speed value at the start of the period by said determined rate of increase of desired engine speed during the period; and using the desired engine speed value to control engine speed during the gear ratio change. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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Specification