Fig. 8 is a diagram of the control system. The hybrid control unit controls the hybrid system so that it functions properly receiving the control signal from the individual system controller of the vehicle. The individual controller is connected to a network for optimum control.

When the engine experiences a heavy load during start and acceleration, the electric motor will generate power to assist the engine. Torque assist is controlled so that the optimum balance of exhaust emissions and fuel efficiency is achieved. An early up shift is possible because of the torque assist from the motor, which also improves fuel economy (Fig. 9(1)).

When running at constant speed, the vehicle is driven solely by the diesel engine, without the torque assist of the motor generator, with the optimum gear selected to save fuel consumption depending on road and driving conditions. When running at high speed, losses due to the friction of the motor and field weakening become large, and the motor generator is disconnected by the dog clutch of the PTO (Fig. 9(2)).

During deceleration, the wet multiple disc clutch of the Smoother-E Autoshift system disconnects the engine so that the motor generator can effectively absorb the kinetic energy of the vehicle. Because the engine is disconnected, energy recovery is possible at low speed immediately before stopping completely and at relatively low deceleration comparable to engine braking. If the driver wants a greater braking force and downshifts the transmission or engages the exhaust brake switch, the wet multiple-plate clutch is engaged and engine and exhaust braking are activated for a greater deceleration force (Fig. 9(3)).

When the vehicle is stopping, the engine shuts down automatically if the shift lever is moved to the "N" position and fuel consumption can be saved. When the shift lever moves to the "D" from "N", the engine starts automatically (Fig. 9(4)).