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With the Electronic Wedge Brake (EWB), which electronics and mechatronics developer Siemens VDO unveiled at last fall's Frankfurt auto show, it is now possible to realize a 12V brake-by-wire system.
Compared to the traditional hydraulic brake, the modern "wedge" brake design offers substantial advantages in areas such as safety and comfort. Start of production is planned for the end of the decade.
Future advanced driver assistance systems will not only monitor the ongoing traffic situation but provide active support to the driver in an emergency. By autonomously intervening, these systems will increasingly contribute to the vehicle remaining under control in difficult situations. One enabler for this is a fast and intelligent brake system. Siemens VDO sees brake-by-wire technology, in the form of the EWB, as the answer to future vehicle chassis safety, weight, reliability, and installation space demands.
Faster and more effective
Siemens VDO’s EWB is the continuation of a development begun by eStop, a company which Siemens VDO acquired in early 2005. And the control technology for the new brake has its roots in the German Aerospace Center (DLR).
When the EWB is actuated, a brake pad connected to a wedge is pushed between the brake caliper and the brake rotor. The wedge effect is automatically amplified as the result of the wheel's rotation allowing varying degrees of braking force to be generated with little effort.
The intelligently controlled wedge converts the kinetic energy of the vehicle directly into braking energy. As a result of its self-reinforcing action, the EWB is faster than today’s hydraulic brake and requires only one-tenth the energy to operate.
A vehicle with EWB has a separate intelligent brake module at each wheel. The module consists of a brake pad, the wedge and wedge bearings, the mechanical power transmission between the two electric motors and a sensor system to detect motion and force. The sensors measure the speed of each wheel about one hundred times per second and, at even greater resolution, the forces and wedge positions acting on the brake.
Electronic Wedge Brake anatomy: The brake rotor (1) is engaged by the pad (2), which is moved by electric motors (3, 4) using several roller screws (5) along wedge-shaped angled surfaces (6).
When the driver depresses the brake pedal, the system transmits an electronic brake signal to the system's networked modules. Depending on the sensor readings and the intensity of the received brake signal, the electric motors move the brake wedge to the required position. This movement is actuated through wedge thrust bearings consisting of several roller screws, which press the brake pad against the rotor. (View a video of EWB operation
The braking effect is "self-energizing" and builds up very rapidly. The intelligent controls eliminate any risk of the wedge unintentionally locking up the brakes. The principle of “fuzzy” control logic was adopted from critical aerospace safety systems and adapted for automotive use.
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