Electric shift transfer case system for an automobile

In an electric shift transfer case system (10) or an automobile having first and second electronically selectable drive modes, said electric shift transfer case system having a transfer case (14) and an electronic control circuit (16),

• said transfer case (14) having a rotatable input shaft (40), first and second rotatable output shafts (22,30), and a selectively engagable coupling (38) between said input shaft and said second output shaft to permit drive torque to be transferred from said input shaft to said second output shaft,
• said transfer case (14) further including a direct current electric shift motor (58) having first and second terminals (58a,58b) electrically connected to said electronic control circuit (16), with said electric shift motor being mechanically connected to said coupling (38) to shift the vehicle from the first drive mode to the second drive mode when rotating in a first direction and to shift the vehicle from the second drive mode to the first drive mode when rotating in a second direction,
• said electronic control circuit (16) having a microprocessor (73) and a motor drive circuit (70) with said motor drive circuit connected to said electric shift motor (58) and operable under control of said microprocessor to drive current through said electric shift motor in either of two directions to thereby rotate said electric shift motor an either of said first and second directions,
• said motor drive circuit (70) having a plurality of switching elements (74-77) connected in circuit to selectively connect each of said terminals (58a,58b) of said electric shift motor (58) to a power source and to a return path for the power source, said motor drive circuit further including a command input for each of said switching elements with said switching elements being electronically switchable by its associated command input between an electrically conductive state and an electrically non-conductive state, whereby certain combinations of voltage levels on said command inputs result in desirable combinations of conductive and non-conductive states of said switching elements and certain other combinations of voltage levels on said command inputs result in undesirable combinations of conductive and non-conductive states of said switching elements,
• said electronic control circuit (16) having an interface circuit (72) coupled to data outputs of said microprocessor (73) and said command inputs of said motor drive circuit (70), said interface circuit being responsive to any combination of voltage levels on said data outputs to provide a combination of voltage levels on said command inputs that results in one of said desirable combinations of conductive and non-conductive states of said switching elements (74-77), whereby said undesirable combinations of conductive and non-conductive states of said a switching elements are prevented;
• wherein said electric shift transfer case system (10) is characterized by:
• said interface circuit (72) being connected to said microprocessor to receive n commands from said microprocessor (73), wherein said motor drive circuit (70) has 2.sup.n -m desirable combinations of conductive and non-conductive states of said switching elements (74-77), where m is an integer and 0<m<2.sup.n-1.

In an electronic control circuit (16) for a direct current electric shift motor (58) of a vehicle transfer case system (10), said electronic control circuit having a microprocessor (73) and a motor drive circuit (70);

• said motor drive circuit (70) having first and second output terminals for connection to the electric shift motor (58) and including first, second, third, and fourth switching elements (74-77), with said first switching element (74) coupled between said first output terminal and a supply voltage node, said second switching element (75) coupled between said first output terminal and a ground node, said third switching element (76) coupled between said second output terminal and said supply voltage node, and said fourth switching element (77) coupled between said second output terminal and said ground node, said first, second, third, and fourth switching elements each having conductive and non-conductive states selectable by respective first, second, third, and fourth command inputs;
• whereby certain combinations of voltage levels on said command inputs result in desirable combinations of conductive and non-conductive states of said switching elements (74-77) and certain other combinations of voltage levels on said command inputs result in undesirable combinations of conductive and non-conductive states of said switching elements;
• and
• said microprocessor (73) having a plurality of data outputs coupled to said command inputs;
• said electronic control circuit (16) having an interface circuit (72) connected between said microprocessor (73) and said motor drive circuit (70), said interface circuit being responsive to any combination of voltage levels on said data outputs to provide a combination of voltage levels on said command inputs that results in one of said desirable combinations of conductive and non-conductive states of said switching elements (74-77), whereby said undesirable combinations of conductive and non-conductive states of said switching elements are prevented;
• wherein said electronic control circuit (16) is characterized by:
• said data outputs of said microprocessor (73) including a clockwise output and a counterclockwise output, said interface circuit (72) generating an inhibit signal as a logical combination of said clockwise and counterclockwise outputs.