1 General [Gen_FD_0528_1]
1.1 Scope [Gen_FD_0528_2]
This document is valid for the functionality Cooperative Regenerative Braking(CRB). It is used within brake systems for vehicles with an electric generator. The generator must be able to recuperate electrical brake torque.
1.2 Abstract [Gen_FD_0528_4]
The main intention of the CRB function is to distribute brake requests by any other
functions of the vehicle brake systems towards the two brake actuators consisting of
the hydraulic brake system and the recuperative generator brake. Thereby the main goal is to optimize the recuperation efficiency of the vehicle. The performance of the
brake system, pump noise, pedal vibrations and feedback are taken into account by
the CRB function. A main goal is the avoidance of noticeable unintended
deceleration changes caused by the switching between the two brake actuators.
Therefore the CRB function considers different boundary conditions:
● Capability of the current regenerative power of the generator
● Information from the vehicle stability controllers
● Hydraulic brake pressure actuator influences such as pump run noises, pedal
vibrations
● Possibility of blending the brake fluid volume and the brake pedal force
1.2.1 CRB as part of the vehicle's brake system [Gen_FD_0528_2803]
CRB receives requested brake force, e.g. by driver applying the brake pedal. Out
from this request CRB calculates the target brake force for the friction brake and the
regenerative brake considering all boundary conditions.
The residual brake force that brakes the wheels is the sum of the friction brake force
and the regenerative brake force, as the following graph illustrates:
Figure 1 Closed loop force distribution generator and friction brake
As CRB is no closed loop controller, CRB does not check if the vehicle decelerates
as desired. But the brake force requester, in this example the driver, gets this
feedback and can adapt his brake request.
1.2.2 Capability of the current regenerative power of the generator
The available potential of regenerative braking depends on the velocity and is
limited by the state of charge of the battery. Therefore the distribution of the brake
torque has to be adapted dependent on the current available regenerative torque.
