Calibration method for transmission control clutches

In a control system for a vehicle powershift transmission in a power train having an engine for driving the transmission, a disconnect device for connecting and disconnecting an output shaft of the transmission from a drive shaft and a plurality of hydraulic pressure operated control elements for shifting the transmission, at least one of which is operated by an electrohydraulic proportional control valve, a method of determining the pressure required to initially engage the control element controlled by the proportional control valve, comprising the following steps:

• controlling engagement of certain ones of the plurality of the control elements other than the control element being calibrated in order to cause relative rotation between parts of the control element being calibrated;
• operating the engine at a predetermined speed range;
• modifying a signal applied to the proportional control valve to gradually increase the pressure applied to the control element being calibrated while monitoring engine speed;
• when the monitored engine speed droops by predetermined amount, saving a value of the signal applied to the proportional control valve as the element calibration pressure;
• and
• automatically shifting the transmission to neutral if vehicle motion is sensed.

In a control system for a vehicle powershift transmission in a power train having an engine for driving the transmission, a disconnect device for connecting and disconnecting an output shaft of the transmission from a drive shaft and a plurality of hydraulic pressure operated control elements for shifting the transmission, at least one of which is operated by an electrohydraulic proportional control valve, a method of determining the pressure required to initially engage the control element controlled by the proportional control valve, comprising the following steps:

• disengaging the disconnect device so that the transmission output shaft is free to rotate;
• operating the engine in a predetermined speed range;
• modifying a signal applied to the proportional control valve to gradually increase the pressure applied to the control element being calibrated while monitoring engine speed;
• and
• when the monitored engine speed droops by predetermined amount, saving a value of the signal applied to the proportional control valve as the element calibration pressure.

In a control system for a vehicle powershift transmission in a power train having an engine for driving the transmission, a disconnect device for connecting and disconnecting an output shaft of the transmission from a drive shaft and a plurality of hydraulic pressure operated control elements for shifting the transmission, at least one of which is operated by an electrohydraulic proportional control valve, a method of determining the time required to initially engage the control element controlled by the proportional control valve, comprising the following steps:

• disengaging the disconnect device so that the transmission output shaft is free to rotate;
• operating the engine in a predetermined speed range;
• sensing and storing an initial engine speed;
• applying a predetermined pressure to the control element to be calibrated for a predetermined time period;
• sensing the current engine speed;
• increasing the predetermined time period by an increment and repeating the applying and sensing steps until the sensed engine speed droops by a predetermined amount when compared to the initial engine speed;
• and
• when the sensed engine speed has drooped by a predetermined amount indicating that the control element is being loaded, storing a time value.