CAN in a hybrid drive car

Source: CAN Newsletter September 2007

The Ford Research Center Aachen, Germany, develops operating strategies and energy management concepts for hybrid drive structures. They use a Ford Fiesta as the experimental vehicle for testing and optimizing a micro hybrid drive, focusing on control strategies for hybrid-drive-specific functions such as stop/start and regenerative braking.
The bandwidth of hybrid drives ranges from what are called micro hybrid drives to mild, medium, and even full hybrid concepts. Micro hybrid drives are considerably less expensive than full hybrid drives. The ratio of additional costs to achievable fuel consumption reduction means they can compete with other vehicle-related CO₂ reduction measures and are therefore an alternative for the mass market. As well as the stop/start and regenerative braking functions, they also have a function known as stall recovery. This restarts the engine automatically if it stalls. The stop/start function switches the engine off when it is idle. This avoids CO₂ and other emissions, and also saves fuel, for example, while the vehicle is waiting at traffic lights. The engine is then automatically restarted by the B-ISG machine. It is not possible, or desirable, to switch off the engine in every case, so the state of the vehicle and its subsystems is monitored and analyzed. This is done by a control unit, which receives its data from various sensors distributed throughout the vehicle, and from the CAN networks in the vehicle. The control unit is also the bus master in a LIN installation, serving a battery monitoring system with computing power. The operating strategy that was implemented prevents the combustion engine from being switched off, for example, during the warm-up phase of engine and catalytic converter, or if the battery is low.
Another potential fuel saving with the micro hybrid drive is when the vehicle decelerates. During deceleration, part of the vehicle’s kinetic energy is converted into electrical energy by means of the B-ISG machine. The controller controls the B-ISG power electronics via a CAN network. The generated energy is stored in the battery and made available whenever generating electrical energy is fuel-intensive or even impossible, for example, during acceleration phases or engine shutdown. When a vehicle is used mainly in city traffic, these functions cut fuel consumption by up to 15 %.