Transmission and transmission control device for providing downshifting

摘要

A method is described for controlling a vehicle transmission mechanism which incorporates several selectively engagable power transmission systems each being selectively individually connectable between a first member and a second member for transmitting rotational power between them, with each such power transmission system including a clutching mechanism which can be selectively controlled either to freewheel in both rotational directions or to provide direct transmission of rotational power in one rotational direction only and to freewheel in the other rotational direction. While a first one of the power transmission systems which is for providing a certain speed stage is connected between the first member and the second member for transmitting rotational power between them at a gearing ratio appropriate to that speed stage, a second one of the power transmission systems which is for providing the speed stage one lower than that certain speed stage is also individually connected in parallel with the first power transmission system, with the particular clutching mechanism associated with the second power transmission system being controlled to be able to provide direct transmission of rotational power in one rotational direction only and to freewheel in the other rotational direction. Thus, the clutching mechanism of the second power transmission system freewheels. When a downshift is required, the clutching mechanism of the first power transmission system is disengaged, and the second power transmission system takes over the power transmission. A device for practicing this method is also described.