Patent ID: 6257082
Filing Date: 2001-07-10
Classification: B60W,F16H,Y10T

Abstract:
A method for controlling range section shifting in a manually shifted, vehicular compound transmission having a manually shifted main section connected in series with a range section having a high range ratio and a low range ratio, said transmission having an input shaft for connection to an engine having a highest (ES.sub.MAX) and a lowest (ES.sub.MIN) allowable engine speed, said main transmission section having a plurality of main section ratio positions (1/5, 2/6, 3/7, 4/8) available in both high and low range, a sensor for sensing a current position of a shift selector (72) manually movable in a shift pattern to selectively engage and disengage main section ratios, a range section actuator for shifting the range section in response to command signals, a manually operated range ratio selection means for selecting engagement of one of the high and low range ratios, a speed sensor for sensing vehicle speed and providing a signal indicative thereof, and a controller for receiving input signals, including said signals indicative of the current position of the shift selector and of vehicle speed, and processing same according to predetermined logic rules to issue command output signals to system actuators, including said range section actuator, said method including the steps of:(i) determining vehicle speed, position of the range ratio selection means, position of the shift selector, and target ratio (GR.sub.T);(ii) determining if said target ratio is acceptable under existing vehicle operating conditions;(iii) if said target ratio is acceptable under existing vehicle operating conditions, allowing the range section to be engaged in the range ratio indicated by the range ratio selection means; and(iv) if said target ratio is not acceptable under existing vehicle operating conditions, (a) determining an alternative overall transmission ratio (GR.sub.ALT) obtained by engaging the main section in the operator-selected main section ratio position thereof and engaging the range section in the ratio not indicated by the range ratio selection means, (b) determining if the alternate overall ratio is more acceptable than the target ratio under existing vehicle operating conditions, and (c) if the alternate overall ratio is more acceptable than the target ratio under existing vehicle operating conditions, causing the range section to be engaged in said ratio not indicated by the range ratio selection means.