Leading wedge technology

Siemens

has unveiled a prototype automotive braking system based on the same principle used to slow down horse-drawn carriages a century ago.

The Electronic Wedge Brake (EWB) uses a wedge-shaped braking mechanism to bring a wheel to a standstill. The brake-by-wire system relies on advanced sensor technology and electronics to control the process and prevent the brakes from locking.

Siemens VDO Automotive claimed the EWB system — which emerged from technology developed in the aerospace sector — is more efficient, responds faster and requires 90 per cent less energy than conventional hydraulics.

Its improved efficiency means the unit can be smaller, cutting the vehicle’s weight and saving space while removing the need for brake lines, a servo-unit and a brake fluid reservoir. This will give car designers an extra 22 litres of space in the engine compartment, according to the German engineering giant.

Each wheel has its own control unit consisting of a brake pad, a mechanical transmission and two electric motors that allow precision control. There are also sensors to monitor movement and the forces produced during operation.

A further four sensors measure the wheel rotation about 100 times per second to gauge the vehicle’s speed, the braking force applied and the position of the wedge.

Wedges were once used to stop horse-drawn carriages, but the Siemens system takes the concept into the realms of brake-by-wire.

When the driver pushes the brake pedal, the force is transmitted electromechanically to the wheels. Taking the readings from the movement sensors and braking signals from the driver into account, the two electric motors move the brake pad over a series of rollers and along a slanted surface to create a wedge shape. The position of the rollers determines where the pad is applied to the brake disc. As friction increases the electric motors either hold the brake pad in place or move it to a better position.

All this takes place in milliseconds and is powered by the car’s normal 12-volt power system.

Siemens plans to develop algorithms that would allow the EWB system to respond faster than ABS. While ABS can respond within 140 and 170 milliseconds, Siemens believes EWB could reduce this to 100 milliseconds, shortening the vehicle’s braking distance and giving the driver improved control in difficult conditions.

The EWB system could be rolled out to trucks and trailers. It could also have applications in slowing the spinning parts of lifts, high- speed trains and industrial motors.

The company aims to produce a working prototype for installation on a test car by the end of this year.

Electric motors, guided by sensors monitoring the wheel's rotation, move the wedge-shaped brake pads into place