7/1/2003 | 1 MINUTE READ

Braking By Wire (Almost)

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What Is It?
Electro-hydraulic braking unit (EHB) from TRW Automotive (Warren, MI). It’s the first step toward brake-by-wire systems that replace the mechanical connection between the brake pedal and foundation brakes. In effect it is a by-wire unit with hydraulic redundancy.

How Does It Work?
The so-called Brake Pedal Unit (BPU) contains the hydraulic fluid reservoir, pedal damping and hydrostatic fail-safe unit. It measure the pedal’s position, and calculates the amount of braking needed at the wheels. The Electro-Hydraulic Control Unit (EHCU) contains a high-pressure accumulator that stores the energy generated by the EHCU, and distributes it to the wheels individually, based on demand.

Why Is It An Advantage?
TRW says the EHB combines the ability to provide the optimum brake pressure at each wheel with the capacity to supply this pressure more quickly than a conventional hydraulic braking system. This results in reduced stopping distances. Pedal effort no longer affects brake performance–that is, pushing harder doesn’t get you more braking force. That’s because the sensors in the BPU determine the severity of the stop by how quickly the brakes are applied, not by how far the pedal is pushed. This allows the OEM to easily tailor pedal feel to the vehicle type and driver demographic through software changes. And packaging is enhanced by the integrated design.

What Else Is Unique?
TRW claims EHB can easily be blended with regenerative braking systems, like Hydraulic Launch Assist, to give the driver a consistent pedal feel independent of the type or amount of braking (HLA torque or friction) being used. It also can be integrated with ABS and traction control, vehicle stability systems, panic brake assistance, and Adaptive Cruise Control in whole or in part.

Will It Be Used?
TRW expects EHB will be the centerpiece for high-line European manufacturers as they introduce collision avoidance systems on their flagship cars. The units will be integrated with the Active Cruise Control unit’s forward-looking sensors and active restraint system, like TRW’s Active Control Retractor for seatbelts to provide even greater occupant safety. As OEMs become even more concerned about packaging more stuff into the same space–and costs continue to drop–TRW says the units will move into mid-size vehicles, and platforms used to produce multiple vehicle types.


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