Enhanced performance through brake-by-wire

By Christopher A. Sawyer
The Virtual Driver

(August 13, 2018) “Brake-by-wire.” Let those words sink in for a moment as you think of the last time your smartphone, tablet or personal computer threw a wobbly and left you scratching your head. Better yet, remember the punch line to the joke about the car filled with engineers that suddenly stops at the side of the road. After the mechanical, chemical, and electrical engineers each give a diagnosis and plan of action, all eyes turn to the computer engineer who says plaintively: “I was thinking that we could turn it off, get out of the car, get back in, and restart it.” Fills you with confidence, doesn’t it?

“Actually,” says Bastien Russery, Customer Line Organization Manager — NAFTA at Chassis Brakes International, “today’s dual-circuit brake systems have less redundancy than our Smart Brake brake-by-wire concept.”

The man saying these words, a youthful Frenchman with a ready smile, seems completely sane, though the words coming from his mouth appear to be heretical, if not downright crazy. How could a braking system that relies on a pedal simulator, electric motor/gearbox units on each brake, and a bunch of wires be safer than one that uses physical connections?


“If you have four autonomous brakes,” Russery explains, “you have natural redundancy. Should you have a defect with one, the other three are still available to stop the vehicle, and can be individually modulated to keep the vehicle under control. You might not, except for the light on the instrument panel telling you there is a fault, ever realize that there is a problem.” It’s a logical answer, except perhaps to those few who believe that, when computers are involved, you’re dealing with the Wizard of Odds.

Smart Brake clamps and releases the brake disc via an electric motor/gearbox unit mounted to the caliper body. A true plug-and-play system, it is drag-free when not activated, and can be used to increase the dynamic envelope of the vehicle, especially in emergency situations.

“For our Smart Brake, we are looking at 2030,” says Russery, “which is about three generations from today, when it is predicted that electric vehicles will be a significant percentage of vehicle production.”

It’s expected that by then dedicated EVs will be built around a “skateboard” platform where the battery pack forms a large percentage of the floor. To this, assembly workers will bolt on subframes containing plug-and-play modules for the electric motors, steering system, suspension, and brakes.

A concept like the Smart Brake would eliminate the vacuum booster, hoses, clamps and hydraulic fluid, as well as the “evacuate and fill” process where the brakes are filled and bled. This would improve both packaging and crashworthiness, and eliminate a potential environmental hazard. In addition, brake performance and feel would be set via software, and parts could be shared across an automaker’s lineup or between OEMs.

“An EV has stringent regenerative braking, which is used for most of the braking events,” Russery intones. “So you can project that on an EV, or even a hybrid vehicle, the percentage of regenerative braking will increase, leaving the foundation brakes to fill in the gaps while having the capacity for emergency braking.” In addition, the electric braking units can be plumbed into a chassis-wide control unit that shares information to increase the vehicle’s dynamic bandwidth.

“There are a few things we are thinking about that will add new capabilities,” says Russery, “like being able to steer by braking individual wheels.” Thus, in an emergency situation, a vehicle with advanced driver assist systems would be able to scan the road ahead, determine a course of action, look at the inputs from the driver, and modulate them by braking individual wheels to increase or decrease the effective steering angle and vehicle response.

The technology behind the Smart Brake is similar to that seen on electrically actuated parking brakes. In addition to capabilities like hill hold assist and drive-off release, these units can supply emergency braking in the event of a braking system failure.

Using information gained from the tires, the vehicle dynamics controller would be able to fill each tire’s available friction circle using the most effective and energy efficient means available, balancing input though the steering rack with that from the brakes to increase agility without unsettling the vehicle. Or, on a more prosaic level, the same information could be used to squeeze into tight parking spaces, and provide drivers with one more variable whose response can be individualized.

“There are other capabilities that are possible with the Smart Brake,” says Russery, “and we have put together a group to develop the technology based on our customers’ needs and ideas.” Part of that discussion, he imparts, includes how much power will be required from the brake motor. “We not only have to have the right source of energy, but our solution has to be adapted to the energy that is going to be available in the vehicle.”

This wouldn’t seem to be much of a hurdle in an electric vehicle, but Russery is quick to add that the Smart Brake concept is not limited to electric, or even electrified, vehicles, though that is where the bulk of the development currently is taking place. “It can be used with conventional powertrains, though they would need a battery backup for redundancy. That would be the only major difference between it and the hybrid or EV version,” he says. That and a 48-volt power source, of course.

After years of speculation and expectation, however, vehicles powered by an internal combustion engine soon will be shifting to a 48-volt electrical system, eliminating this hurdle. Russery expects that, as the Smart Brake concept is refined for production, the power density of the electric motors will increase, its power draw will decrease, and the electronics will become cheaper, smaller and more powerful. He does not, however, see it replacing electro-hydraulic systems overnight.

“Inevitably, the initial cost for Smart Brake will be higher, but it is uniquely suited for the modular architecture and efficiency needs of a dedicated electric vehicle,” he says, “and that is where we expect it to debut.”

However, as the time and effort spent developing brake-by-wire is amortized over more vehicles and platforms, the cost per unit will drop, aided by a reduction in assembly time, removal of mechanical systems, and elimination of the costs associated with handling hydraulic fluid.

“As the cost of electronics and electrical systems inevitably declines,” he says, “we believe this technology will make its way onto internal combustion vehicles as they move to new platforms.”

It’s a statement with which even the Wizard of Odds might agree.

The Virtual Driver