TRW Chassis Systems has announced production contracts with two major European vehicle manufacturers for its Electro-Hydraulic Braking (EHB)system due for launch in 2003.
Additionally, the company has a development contract with a leading North American vehicle manufacturer to develop regenerative braking based on an EHB system.
‘Brake-by-wire technologies improve stopping distances by up to 5% and deliver significant improvements in the comfort of pedal feel,’ said Thomas Straub, Technical Director of Advanced Vehicle Controls at TRW Chassis Systems.
‘Beyond EHB, the introduction of Electro-Mechanical Braking (EMB)will deliver additional environmental benefits due to the elimination of brake fluid,’ he added.
In its first generation, brake-by-wire will complement today’s hydraulic braking systems. In an EHB system, the conventional brake booster is replaced with a Brake Pedal Unit (BPU) simulator and the engine compartment contains an Electro-Hydraulic Control Unit, which generates the required braking energy.
The pedal simulator communicates the driver’s braking demand to the modulator, and a closed loop pressure control measures the pressure at the wheels every millisecond. All brake applications are carried out by the system and not by the energy of the driver’s foot on the pedal. In case of electrical failure, the system is equipped with a secondary hydraulic braking mode that functions in the same manner as today’s conventional systems.
‘Looking further ahead, the final generation of brake-by-wire, in the form of EMB, sees the end of hydraulic connections,’ Straub added.
‘These hydraulic connections are replaced by a central, fault-tolerant control unitconnected to actuators on each wheel that are controlled by the BPU. Driver pedal effort no longer affects brake performance. The BPU measures the pedal position, calculates brake demand, and applies it to each wheel actuator.’
TRW anticipate that production of an EMB system would not be before 2005.