System and method for controlling an automatic engine stop-start based on transmission conditions

A method for controlling a powertrain in a motor vehicle, the powertrain having an engine and a transmission with an accumulator, the method comprising:

• determining a pressure of a fluid in the accumulator;
• comparing the pressure to a first threshold;
• inhibiting the engine from shutting off if the pressure is less than the first threshold;
• comparing the pressure to the first threshold plus a hysteresis value, wherein the hysteresis value is a negative value;
• inhibiting the engine from shutting off if the pressure is less than the first threshold plus the hysteresis value;
• determining the operating time of the engine;
• calculating an engine operating time threshold based on a speed of the engine and a temperature of the engine;
• comparing the operating time of the engine to the engine operating time threshold;
• and
• inhibiting the engine from shutting off if the operating time of the engine is less than the engine operating time threshold.

A method for controlling a powertrain in a motor vehicle when the motor vehicle is in a stop state and an ignition is on, the powertrain having a transmission with an accumulator and an engine, the method comprising:

• comparing a commanded line pressure in communication with the accumulator to a threshold;
• calculating a time value that the commanded line pressure in communication with the accumulator has been larger than the threshold if the commanded line pressure is larger than the threshold;
• increasing the commanded line pressure to a higher commanded line pressure that is greater than the threshold if the commanded line pressure is less than the threshold;
• calculating a time value for the actual line pressure in communication with the accumulator to reach the higher commanded line pressure if the commanded line pressure is less than the threshold;
• calculating a time value for the accumulator to reach a full charge based on the commanded line pressure and a temperature of the hydraulic fluid;
• comparing the time value that the commanded line pressure in communication with the accumulator has been larger than the threshold;
• and
• inhibiting the engine from shutting off if the time value that the commanded line pressure has been larger than the threshold is less than the time value for the accumulator to reach the full charge;
• determining how long the engine has been running;
• calculating an engine run time threshold based on a speed of the engine and a temperature of the engine;
• comparing the time that the engine has been running to the engine run time threshold;
• inhibiting the engine from shutting off if the time that the engine has been running is less than the engine run time threshold.