Automatic transmission controls with multiple downshift off-highway mode

An improved automatic transmission system for vehicles having a throttle-controlled engine, an operator actuated throttling control means and a transmission having a plurality of gear ratio combinations selectively engageable between a transmission input shaft and a transmission output shaft, said transmission input shaft being operatively connected to said engine, said transmission system including an information processing unit having means for receiving a plurality of input signals including (1) an input signal indicative of the position of said throttle controlling means, (2) an input signal indicative of the rotational speed of said engine, and (3) an input signal indicative of the speed of said vehicle, said processing unit including means for processing said input signals in accordance with a program to select a desirable gear ratio for a given combination of input signals and for generating output signals whereby said transmission system is operated in accordance with said program, and means associated with said transmission effective to actuate said transmission to effect engagement of one of said gear ratio combinations in response to said output signals from said processing unit, the improvement characterized by:

• said processing unit including means for processing said input signals to provide a calculated expected engine speed value indicative of the expected rotational speed of the engine at a selected vehicle speed in various selectable gear ratio combinations;
• said program having a first mode of operation wherein upon sensing an engine speed equal to or less than the engine speed at which downshifts to a lower gear ratio are required is effective to:
• (a) first compute a first expected engine speed value at the current vehicle speed and in the Nth lower gear ratio where N is an integer greater than 1;
• (b) then to command initiation of a downshift into a gear ratio intermediate the currently engaged gear ratio and the Nth lower than the currently engaged gear ratio if the first computed expected engine speed value is equal to or greater than the magnitude thereof at the maximum allowable speed of the engine and to command initiation of a downshift into the Nth lower gear ratio if the first computed expected engine speed value is less than the maximum allowable engine speed magnitude.