Implementation of serial braking strategy
Once the brake pedal is pressed and depending on the level of depression, a brake torque
is sent. Now this brake torque passes into the brake control strategy block. Here, firstly it
is checked if battery state-of-charge is below 80% which is set as the maximum permissible
3-2 Brake strategy subsystem 13
level of charge. If that condition is satisfied, then the battery is recharged. The brake torque
requested is compared to the maximum regenerative torque limit of the motor-generator. If
the overall brake torque requested is less than or equal to the maximum regenerative torque,
then the vehicle brakes purely on regenerative torque and the battery is charged. The amount
of charge ultimately put in depends also on the motor-generator operation efficiency and the
battery charging efficiency. If the overall brake torque requested is greater than what the
motor-generator can provide, then the friction brakes kick-in. Now since the vehicle is front
driven, it is checked if the total brake torque requested from front is less than or equal to
maximum regenerative torque capability of motor-generator. If yes, then front braking is
provided purely by regeneration and rear (non-driven axle) by friction. Once the total brake
torque request increases further, then front friction brakes (driven axle) comes into play in
combination with rear friction brakes and front regenerative braking, to satisfy the overall
brake torque demand. This has been represented in a flow chart manner in the figure