Control system for a hybrid vehicle

A control system for a hybrid vehicle having an auxiliary power unit, at least one electrochemical battery and at least one electric drive motor for traction, the vehicle having a high load driving condition, a low load driving condition, and a regenerative braking condition, the control system comprising:

• a voltage control to set system voltage to charging voltage of the electrochemical battery in the low load driving condition and the regenerative braking condition, and to set the system voltage to output voltage from the electrochemical battery for the high load driving condition;
• a current control to set output from the auxiliary power unit to a charging level for the electrochemical battery in the low load driving condition and the regenerative braking condition, and to set the power level from the auxiliary power unit based on vehicle speed, motor load and state of charge of the electrochemical battery for the high load driving condition;
• control means to switch on the auxiliary power unit when the state of charge of the electrochemical battery is below a predetermined level and switch off the auxiliary power unit when the electrochemical battery is fully charged;
• and
• a battery temperature control system with a battery cooling system, the battery temperature control system maintaining the battery temperature within a predetermined range by activating the battery cooling system.

A method of controlling a hybrid vehicle having an auxiliary power unit, at least one energy storage device and at least one electric drive motor for traction, the vehicle having a high load driving condition when the motor is powered by the auxiliary power unit and the energy storage device, a low load driving condition when the auxiliary power unit provides power to the motor and to charge the energy storage device, and a regenerative braking condition when the auxiliary power unit and the motor provide power to charge the energy storage device, comprising the steps of:

• controlling system voltage to a charging voltage of the energy storage device in the low load driving condition and the regenerative braking condition;
• controlling the system voltage to an output voltage from the energy storage device for the high load driving condition;
• controlling the output power from the auxiliary power unit to a charging level for the energy storage device in the low load driving condition and the regenerative braking condition;
• controlling the output power from the auxiliary power unit to a level determined from statistical analysis of vehicle speed, motor load and state of charge of the energy storage device for the high load driving condition, and
• controlling the operation of the auxiliary power unit to provide power to charge the energy storage device when the state of charge of the energy storage device is below a predetermined level.