Saving weight and space are just two of the advantages.
Beneath their often wildly futuristic bodies, today’s cars host technology that hasn’t changed much since the very early days – but manufacturers are seeking to change that with brake-by-wire systems.
Braking systems are an example of technology that has stayed largely the same for years: although not widely adopted until a little later, hydraulic brakes have been around since the turn of the 20th century. So: what is a brake-by-wire system?
What is a brake-by-wire system?
A brake-by-wire system controls the brakes of their car through the use of electricity, rather than a traditional hydraulic system. There is no mechanical connection between the driver and the car.
The idea was that electric calipers would do the braking and electric steering racks would enable fancy features such as enabling the car to take major avoiding action in emergency situations without ripping the driver’s thumbs off on the steering wheel spokes.
Ditching hydraulics and cleaning up and simplifying brake systems by moving to electronic actuation (so-called brake-by-wire) has been discussed for years, and there have been plenty of prototypes.
The first step towards it happening for real was Continental’s MKC1 system, which made its debut in 2018 on the Alfa Romeo Giulia and Alfa Romeo Stelvio, but that was just the beginning of the company’s plans for what it calls Future Brake Systems (FBS), which will lead to complete brake-by-wire systems.
The MKC1 system goes part of the way to full brake-by-wire but stops short of electric brake calipers. What it does do is integrate the tandem master brake cylinder (which generates the hydraulic pressure to apply the brakes), the brake booster, the ABS unit and the ESC unit, saving about 4kg.
Brake-by-wire systems for parking brakes
Electronic parking brakes have used a developed version of brake-by-wire, which removed the need for a traditional cable-operated system and a handbrake lever.
Alfa Romeo and the Giulia name is back, and returned in the shape of a saloon that is determined to disrupt the top order – watch out BMW, Jaguar, Mercedes-Benz and Audi
Modern cars are now fitted with electronic systems that can automatically release when moving off, or assist a car when temporarily stopped on an incline, called ‘hold assist’.
How does a brake-by-wire system work?
Brake-by-wire systems control the brakes using electricity, employing a sensor to monitor how forcefully a driver has pushed down on the brake pedal.
The system’s control unit then sends a message to an electric pump to produce the desired amount of pressure to slow down the car, or bring it to a complete stop.
Continental’s plan has four levels, with ‘FBS 0-3’ the long-term objective. The firm has already developed its MKC1 system into MKC2, which sits at level FBS 0. This combines the brake master cylinder, ABS and ESC into one unit, rather than the driver’s foot being linked directly to a hydraulic cylinder.
It combines the brake master cylinder, ABS and ESC into one unit, and rather than the driver’s foot being linked directly to a hydraulic cylinder via the brake pedal, it’s working a sensor instead. Hydraulics are still involved, but a pump generates the pressure to apply the brakes.
FBS 1 will get rid of the sizeable unit mounted near the driver’s feet on the car’s firewall and replace it with an electronic pedal, freeing up space, but beyond that the brakes will still be ‘wet’.
FBS 2 will be ‘semi-dry’ or ‘dry on one axle’, meaning the front brake calipers will still be actuated by hydraulics while the rears become electromechanical. Continental says its customers are interested in this as a first step.
The full monty will be FBS 3, where hydraulics are gone, with a fully ‘dry’ system being electronically controlled and electrically actuated. Continental says that will decentralise the braking system, enabling vehicle architectures to use space more effectively.
FBS 2 is already a reality. It will enter production with an American maker in 2025.
Advantages of brake-by-wire
Brake-by-wire systems are intuitive and there are several benefits over a mechanical braking system.
Aside from the packaging and weight, pedal feel can be tuned by engineers using driving simulators to give a more aggressive response on track and a more relaxed response in traffic.
Another advantage is that pedal travel doesn’t increase when the brakes take a beating and get hot. What the driver actually feels is a simulator built into the MKC1 that generates the sensation normally fed back through the hydraulics, only it remains consistent however hard the brakes are working.
Full drive-by-wire wire brakes would also allow manufacturers to dispense with that nasty, inflammable, corrosive material that is hydraulic brake fluid, giving them dry chassis and production lines that have no need for the messy liquid.
Complete corners consisting of suspension, wheel hubs, discs and brakes could be preassembled ready to bolt on the car. A further advantage of doing away with hydraulic brake fluid is that it’s hygroscopic (it absorbs atmospheric moisture) so needs changing at intervals.
It will also mean that brake systems, like the modern vehicle architectures to which they are fitted, can become modular and distributed throughout the car.
Steer-by-wire systems
Steer-by-wire is one of those technologies that has remained on the fringes for a couple of decades, but as these systems become increasingly sophisticated, they can be used to engineer driver involvement into a car’s handling and performance capabilities.
Steer-by-wire systems retain the familiar steering rack, driven by an electric motor like a conventional electric power steering system (EPAS), but with no steering column or other mechanical connection to the driver.
The latest steer-by-wire electric systems give engineers the opportunity to get exactly the characteristics they need for a particular car, from dawdling around town to a brisk drive on B-roads or a motorway cruise.
Steer-by-wire also fits the bill for utilitarian applications, such as commercial and autonomous vehicles.
It is due in the Toyota bZ4X this year, and will be in the Lexus RZ 450e in 2024. Infiniti introduced it in the Q50 almost 10 years ago but the ‘redundancy’ was mechanical, with a steering column remaining in place, just in case.
True steer-by-wire has no mechanical connection between the steering wheel and steering rack, just an electronic link, and that’s what the Toyota and Lexus One Motion Grip system will have.
Although it may seem like a dodgy idea, there are many benefits, both for manufacturers and drivers. Steer-by-wire comes under the broader category of drive-by-wire elements, such as electronic throttle control, which have been in production for years. One advantage for manufacturers of by-wire systems is the potential to produce a ‘dry’ chassis, with no hydraulic fluid involved.
The idea is for each suspension corner of the car to be pre-assembled and bolted on to the car on a production line and literally plugged in, doing away with messy hydraulic fluid and all that entails. The ratio is reduced as the car gathers speed, slowing the response right down at motorway speeds to avoid the car becoming twitchy.
UK firm Titan, which started life in the 1960s developing racing cars, is now a specialist in advanced steering systems. It has recently developed a precision steer-by-wire system aimed at lower-volume manufacturers that not only work with smaller numbers but also may need a bespoke system tailored for, say, a sports car or an autonomous delivery van.
Autonomous vehicles need autonomous steering, but there are advantages for human drivers too. An example is a variable steering ratio and variable weight. With no mechanical connection, the ratio can be lowered when cruising in the straight-ahead, making the steering less sensitive to unwanted inputs.
A full steer-by-wire system is also quite mechanically simple. The steering wheel directly works a control unit like a gaming machine and motors on the steering rack actually move the wheels.
Linking the two, a computer brain takes the signals from the driver’s steering input and relays them to the steering rack. The caveat is that the computer decides what the wheels will do and not necessarily the driver, but the benefit is that steering lock can be almost infinitely variable, reducing turns in the case of the Toyota and Lexus to a mere 150deg in either direction at parking speeds.
That last aspect is true of more conventional variable-ratio steering, but steer-by-wire also opens up the possibilities for semi-autonomous safety systems like accident avoidance, where a car can literally steer out of trouble if the driver isn’t quick enough.
Titan’s technical director, Paul Wilkinson, thinks a big benefit is the ease of tuning that steer-by-wire gives. An algorithm that can differentiate between a thrash around the lanes or a drive in the city can adapt the feedback to suit.
Alternatively, drivers can choose modes as they might now between, say, Sport and Comfort for suspension, or Normal, Sport and Eco for a powertrain.
EPAS once had drawbacks compared with hydraulic systems when it first emerged, lacking feel and feedback. Since then, advances in electronics have enabled engineers to compensate for internal friction and even changes in ambient temperature.
Wilkinson says one of the biggest problems with providing feedback from the road to the steering wheel was the inertia of the electric motor working the steering rack, in effect blocking it so little if any reached the driver.
Titan solves that problem by creating a digital model of the motor’s inertia, and compensating for that in the control software. The motor then reacts in a way that the feedback can travel back from the road wheels to the driver’s hands.
It also means that for less able drivers, cars could be steered by a mini wheel or a joystick. Like some aeroplanes, which have relied on fly-by-wire systems for years in both civilian and military aviation, the systems are fully redundant, which means that if any critical hardware or software parts fail, there’s a back-up ready to take over