Electromechanical braking systems are those which rely entirely on electronic actuators, sensors and control systems to operate the brakes. They are true 'brake-by-wire' systems. This makes them distinct from existing electro-hydraulic set-ups, which - although having no direct connection between the pedal and hydraulic system - still rely on hydraulics to operate the brakes themselves.
Electromechanical brakes are not the only 'X-by-wire' system to be considered for use or employed in cars; Infiniti has deployed a steer-by-wire system, while other manufacturers are considering clutch-by-wire set-ups. All are predominately employed to enable quicker responses, easy adjustment of their behaviour, a wide range of automation features and new safety-related systems.
What are the benefits of EMB systems?
There are several advantages to EMBs. Firstly, they require no hydraulic fluid. They are therefore easier to assemble and maintain and less harmful to the environment. Also, because they are electrically operated, installing EMBs on a production line is far quicker and less complex than fitting, checking and bleeding conventional hydraulic brakes.
They do not require a master cylinder or brake servo, either, meaning less space is required in the engine bay - aiding designers battling packaging requirements and safety concerns. There are benefits for the driver, too; because there is no physical connection between the brake pedal and the EMB units, no vibrations are transmitted back into the cabin. EMBs are also reportedly quieter in operation, due to the lack of a servo and fewer moving parts.
EMBs can also be quicker to respond than a conventional hydraulic system. Continental, for example, states that its electrically boosted MK C1 master cylinder can produce enough power to lock the brakes within 150ms - which is reputedly twice as quick as conventional vacuum-operated systems. Some EMBs, though, have achieved similar in just 50ms during trials.
On a similar note, because EMBs are entirely electronically controlled, a wide range of features can be easily integrated or enabled - such as anti-lock braking, emulation of torque vectoring, brake-based traction control for off-roading, regenerative braking, automatic emergency braking, a parking brake and auto-hill hold assist.
EMBs can also apply continuously varying pressures, granting potentially improved anti-lock performance compared to pulsed anti-lock braking systems. The ease of fitment and the lack of hydraulics also means that EMBs could be ideal for use in electric wheel hub motors; this would mean, on a production line, that a hub motor and brake assembly could simply be bolted together and plugged in.
What are the disadvantages of EMBs?
The key issue is safety. While a hydraulic system is not devoid of issues, complete and unexpected failures are relatively uncommon. An electromechanical system, on the other hand, is far more complicated and the potential for issues far higher as a result.
Consequently, the use of redundant communication and actuation systems is essential to ensure safety and customer confidence. For example, an electromechanical caliper could be equipped with an integral battery to deliver braking power if the primary power circuit is damaged or fails.
Infiniti faced similar issues when developing its steer-by-wire system, which resulted in it having to adopt a mechanical failsafe - negating some of the weight and simplicity benefits of using the by-wire system in the first place. Manufacturers also have to carefully calibrate the system and pedal response to deliver a satisfactory experience for the driver.
Are there any examples of such a system in the automotive world?
Several companies, including Siemens VDO, have previously demonstrated complete prototype brake-by-wire systems - not just electronic parking brakes which, while similar in concept, only have a fraction of the capability of full EMB systems.
Reportedly, most investigating EMBs ceased development due to the lack of the high-voltage electrical vehicle architecture required to support the peak power demands of the braking system itself. That said, in 2005 Siemens VDO showcased a set-up that utilised a 'wedge brake' - pictured throughout - which could operate on 12V. When triggered, electric motors drive a wedge which pushes the pad into contact with the disk; the rotation of the wheel amplifies the wedging effect, which causes a larger braking force to be generated.
According to Siemens VDO, the stopping distance from 62mph was two metres shorter than a conventional hydraulic brake-equipped car. Stopping distances were also found to be 15 per cent shorter in icy conditions, due to the quick and precise control on offer and the self-energising action - like the self-servoing action utilised by drum brakes.
Siemens VDO had planned for its system to go into production in 2010 but, perhaps due to the takeover by Continental AG in 2007 - a company which was developing similar technology - the concept was seemingly shelved.
Other prototype systems exist, though, but many use linear actuators which press the pad directly into the disc. In any case, as safety and automation demands increase, brake-by-wire systems could once again become the focus of many a manufacturer - particularly given the increase in 48V systems, which could easily permit the operation of more power-intensive EHB set-ups.
There is, however, one example of a car with electrically actuated brakes: the fabled GM EV1. The all-electric car, which was available to lease from 1996-1999, used many innovative technologies - including electro-hydraulic braking for the front axle.
Its rear drum brakes, however, were entirely electrically operated. There were no hydraulics and no cables for the parking brake operation, either; instead, an electrically operated latch would simply hold the shoes in contact with the drum when parked.