Patent ID: 7559876
Filing Date: 2009-07-14
Classification: F16H,Y10T

Abstract:
1. A method of detecting and preventing tie-up during a double transition shift of an automatically shiftable transmission operatively connected with an engine, wherein the double transition shift includes shifting from an initial speed ratio to a final speed ratio through an intermediate speed ratio, the method comprising: shifting the automatically shiftable transmission from the initial speed ratio to the intermediate speed ratio; commanding the automatically shiftable transmission to shift from the intermediate speed ratio to the final speed ratio; determining if the automatically shiftable transmission has been operating in the intermediate speed ratio for greater than a predetermined amount of time after commanding the automatically shiftable transmission to shift from the intermediate speed ratio to the final speed ratio; preventing shifting from the intermediate speed ratio to the final speed ratio to avoid tie-up if it is determined that the automatically shiftable transmission has been operating in the intermediate speed ratio for greater than the predetermined amount of time; and wherein the intermediate speed ratio is lower than the final speed ratio and wherein the final speed ratio is lower than the initial speed ratio.