Electro-hydraulic control system for speed-changing mechanism switchable under load

In a speed-changing mechanism with at least three stages comprising each a hydraulic coupling element individually activable to the exclusion of the coupling elements of the other stages for establishing respective speed ratios between an engine and a load capable of developing either positive or negative reaction torques, said engine being provided with a controller for varying the supply of fuel thereto, said stages being provided with electrical valve-operating means responsive to control signals for activating said coupling elements, the mechanism further comprising circuit means for generating said control signals in response to upshifting and downshifting commands for successively activating the coupling elements of adjoining stages in sequences of increasing and decreasing speed ratios, respectively, the combination therewith of:

• selection-responsive discriminating means including a first two-position switch for distinguishing between said upshifting and downshifting commands by alternately occupying an up position and down position;
• load-responsive discriminating means including a second two-position switch coupled with said controller for distinguishing between positive and negative torques by alternately occupying a load position and a pull position;
• and
• switch means in said circuit means jointly controlled by said selection-responsive discriminating means for establishing a first changeover condition in response to a concurrence of said up position with said pull position, indicative of a coincidence of upshifting commands with negative reaction torques, and in response to the concurrence of said down position with said load position, indicative of a coincidence of downshifting commands with positive reaction torques, and for establishing a second changeover condition in response to a concurrence of said up position with said load position, indicative of a coincidence of upshifting commands with positive reaction torques, and in response to a concurrence of said down position with said load position, indicative of the coincidence of downshifting commands with negative reaction torques, said first changeover condition introducing a predetermined delay period between deactivation of a previously activated coupling element of an adjoining stage and activation of a coupling element of a selected stage, said second changeover condition causing activation of a coupling element of a selected stage substantially concurrently with deactivation of a previously activated coupling element of an adjoining stage.