Engine braking control system for automotive automatic transmissions

An engine braking control system for an automotive automatic transmission, comprising:

• shift solenoids activated for executing a down-shift operation by selectively engaging or releasing frictional elements for a gear train, in response to an engine braking requirement;
• sensor means for monitoring a vehicle speed, an opening angle of a throttle valuve, and a depression amount of a brake-pedal, said sensor means generating signals respectively representative of the vehicle speed, the throttle valve opening angle and the brake-pedal depression amount;
• and
• engine braking control means for controlling said down-shift operation on the basis of the signals from said sensor means such that said control means activates said shift solenoids so as to shift to lower gear ratio for said engine braking requirement only when the throttle valve opening angle, the brake-pedal depression amount, and the vehicle speed satisfy their respective conditions, namely a first predetermined condition wherein the throttle opening angle is equal to or less than a predetermined threshold throttle opening angle, a second predetermined condition wherein the brake-pedal depression amount exceeds a predetermined threshold depression amount, and a third predetermined condition wherein the vehicle speed becomes less than a predetermined threshold vehicle speed;
• means for deriving a depression speed of the brake-pedal on the basis of the signals representative of at least two brake-pedal depression amounts, said control means deactivating said shift solenoids when the throttle opening angle is equal to or less than the predetermined threshold throttle opening angle and the brake-pedal depression speed exceeds a predetermined threshold depression speed;
• whereby a braking force which includes engine braking is applied after application of a foot-brake and said down-shift operation is inhibited during a quick braking operation.

A method for controlling engine braking for an automotive automatic transmission including shift solenoids activated for executing a down-shift operation by selectively engaging or releasing frictional elements for a gear train, in response to an engine braking requirement, comprising the steps of:

• (a) deriving a vehicle speed, an opening angle of a throttle valve, and a depression amount of a brake-pedal, from signals output from sensor means for monitoring the vehicle speed, the throttle opening angle, and the brake-pedal depression amount;
• (b) calculating a depression speed of the brake-pedal on the basis of the signals representative of at least two brake-pedal depression amounts;
• (c) comparing the throttle opening angle with a predetermined threshold throttle opening angle;
• (d) comparing the brake-pedal depression speed with a predetermined threshold depression speed;
• (e) comparing the brake-pedal depression amount with a predetermined threshold depression amount;
• (f) comparing the vehicle speed with a predetermined threshold vehicle speed;
• (g) outputting a command signal to the shift solenoids for executing the down-shift operation, when the throttle opening angle is equal to or less than the predetermined threshold throttle opening angle, the brake-pedal depression speed is equal to or less than the predetermined threshold brake-pedal depression speed, the brake-pedal depression amount exceeds the predetermined threshold brake-pedal depression amount, and the vehicle speed is less than the predetermined threshold vehicle speed;
• and
• (h) outputting a command signal to the shift solenoids for deactivating said shift solenoids when the throttle opening angle is equal to or less than the predetermined threshold throttle opening angle and the brake-pedal depression speed exceeds the predetermined threshold depression speed.