Method for controlling a vehicle brake system

A control unit for controlling a vehicle brake system of a heavy duty vehicle, the brake system comprising a service brake system and an electrical machine brake system, wherein a service brake wheel end module is arranged to control wheel braking by a service brake actuator, an electrical machine wheel end module is arranged to control an electrical machine, and a vehicle control unit is arranged to control operations by the two wheel end modules by sending torque request and slip limits, the control unit comprising applying wheel-specific slip control strategies by configuring a service brake wheel slip limit above a electrical machine wheel slip limit, processing circuitry and an interface, wherein the processing circuitry is configured to determine a total brake torque request for braking a wheel of the vehicle, to obtain a brake torque capability of the electrical machine via the interface, and to determine if the total brake torque request exceeds the brake torque capability of the electrical machine, wherein the control unit is configured to apply a baseline brake torque by the service brake system if the total brake torque request exceeds the brake torque capability of the electrical machine but is below a predetermined threshold level, and controlling braking according to the total brake torque request while keeping wheel slip magnitude below a wheel slip magnitude limit, wherein the baseline brake torque is configured to compensate for a difference between total brake torque request and brake torque capability of the electrical machine, and wherein the control unit is configured to brake the vehicle solely by the service brake system and to control wheel slip solely by the service brake system in case the total brake torque request is above the predetermined threshold level, while the control unit is configured to control wheel slip by the electrical machine brake system, while a system slip controller of the service brake system is not active, if the total brake torque request is below the predetermined threshold level, wherein the electrical machine wheel end module modifies the torque request into an applied torque in dependence on current wheel slip and updates the brake torque capability of the electrical machine, wherein the electrical machine reacts to a wheel slip before the service brake wheel slip control, wherein the vehicle control unit sends wheel speed requests to the electrical machine wheel end module when the electrical machine wheel slip limit is breached, and wherein service brake wheel slip control is triggered when the service brake wheel slip limit is breached.