Brake-By-Wire, AEB Is The Way Forward For Braking Tech

Written by  Sameer Kumar | 10 February 2017 | Published in February 2017 ( Technology )

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With relentless advances in automotive technology, cars are now more powerful and faster than ever before. In this scenario, braking technology is also being advanced to keep up with upgrades in power and performance. OEMs and suppliers are working on a host of braking hardware, electronics/ software systems, which ensure that cars stop as hard as they go. Here, we will take a look at some of the most important developments in the area of automotive braking technology and understand future directions for this critical area in automotive R&D.

ON-GOING DEVELOPMENTS

Up until the time when the braking function in cars was purely mechanical, with no electronics/ software anywhere in the equation, the move from drum brakes to disc brakes was possibly the biggest advancement in automotive braking technology. Of course, while many budget cars still use drum brakes (especially for the rear wheels), these definitely can't match the power, feel and precision of a well-sorted disc brake set-up. High-end cars feature large metal discs, gripped by four- or even six-piston callipers, while supercars are often offered with optional carbon/ ceramic discs that offer even more stopping power.

With the advent of electronic anti-lock braking systems (ABS) in the early-1970s, a technology that prevented wheels from 'locking up' under hard braking, stopping was never the same again. The 1971 Chrysler Imperial was the first production car with electronic ABS (which was developed by Bendix), and Mercedes-Benz started offering ABS on some of their cars from 1978 onwards, using a system produced by Bosch. The widespread adoption of ABS by automotive OEMs has been one of the most significant steps towards improved safety.

Going forward, ABS has been supplemented with various other electronic safety aids like electronic brake force distribution (EBD), electronic stability control (ESC) and traction control, all of which work in tandem towards improving vehicle stability under hard acceleration and/ or braking, even on wet and slippery surfaces.

The next step forward in this area will be brake-by-wire systems, which will eliminate the physical linkage between the brake pedal and the actual braking hardware (discs and callipers, etc.) With brake-by-wire, stopping will become entirely computer controlled, with the system taking inputs from various sensors on the vehicle (including throttle position, gear position, suspension data, engine rpm, wheel speeds and many other factors) and applying braking force accordingly, to each individual wheel.

EXACTING DEMANDS

With increasingly stringent requirements and more demanding customers, OEMs are now asking vendors for braking hardware that's smaller and lighter (to help reduce unsprung weight, which also improves suspension performance), more durable and cost effective, and also more effective at the same time. That's a tall order, yes, but suppliers like ZF TRW, Continental and Bosch are already working on systems that offer unprecedented performance, at relatively reasonable prices.

To quote one example, ZF TRW's all-new Integrated Brake Control (IBC) is much lighter than other similar modules and works without the need for a vacuum pump or a conventional booster pump, for faster and more accurate brake actuation. It's also scalable, which allows OEMs to use it on smaller cars as well as much bigger SUVs, leading to improved efficiencies and, possibly, lower costs of repair and maintenance.

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BRAKE-BY-WIRE

Going forward, while developments in braking hardware will continue to be extremely important, software developments will also be a critical area for OEMs and suppliers. The average mid- to high-end car already has dozens of microprocessors and ECUs, many kilometres of electric wiring and millions of lines of code. The sheer speed and efficiency with which software systems allow data (pertaining to a car's driving dynamics) to travel across a car in real time, simply cannot be matched by old world physical linkages. Hence, suppliers are working on brake-by-wire systems, which do away with the physical link between the brake pedal and the braking hardware, replacing it with an ECU.

Already in use in F1 since 2014, where it's used alongside an energy-recovery system, brake-by-wire is expected to come to mainstream production cars in the near future, whereby when the driver hits the brake pedal, the system doesn't directly operate the brake callipers via the master brake cylinder, but simply sends a signal to the car's braking ECU. It's the braking ECU that reads the signal, interprets the intensity – as per pressure applied on the brake pedal, but also taking into account other factors like individual wheel speeds, engine rpm, gear position, steering wheel modulation and suspension movement – and works the actual braking hardware in a way that maximises braking power and efficiency, slowing the vehicle down in the shortest possible time.

While brake-by-wire is a promising technology and is likely to see widespread adoption in the near future, it's been through troubling times in the past. Mercedes-Benz was already offering a Bosch-developed 'Sensotronic Brake Control' (SBC) brake-by-wire system on the SL, CLS and E-Class models from 2001, but had to withdraw this system from the E-Class from 2006 onwards, due to problems with the software. All cars with SBC also had a back-up circuit with conventional hydraulics, so SBC failure never caused any mishaps, but customers simply felt more comfortable with conventional hydraulic brakes. Also, at that time, Mercedes-Benz said that SBC was withdrawn because of the high cost factor and the fact that with advancements in conventional hydraulic braking technology, they were able to offer almost all the benefits of SBC with regular braking hardware, at a lower price point.

Despite the above, brake-by-wire systems are the future of braking technology, especially because hybrid and electric vehicles, as well as autonomous, self-driving vehicles that might still be 5-10 years away from going into production, will simply not be able to function without by-wire operation for all functions, including acceleration, navigation and braking. Drive-by-wire (where the throttle is entirely computer controlled) and shift-by-wire (fully computer controlled transmission) is already commonplace on regular cars – not just high-end vehicles, so it's only natural that brake-by-wire should also follow soon.

Many suppliers are already working on brake-by-wire systems for mainstream cars and, to quote just one example, Continental's 'MK C1' brake-by-wire system (which made its debut last year, fitted as standard on the Alfa Romeo Giulia) is expected to become more widely available next year, for the company's customers in Europe and North America, followed by other parts of the world. The company's stated intent is to move beyond brake-by-wire usage on hybrids and EVs, and move to adoption of these braking systems on a wide range of regular IC-engined cars as well. By eliminating the vacuum pump and other mechanical parts from the equation, Continental – as well as other suppliers working on similar systems – hopes to produce lighter, more efficient braking systems that also help with improving fuel economy.

Apart from Continental, there are manufacturers like Bosch, which is working on its iBooster braking system (not a full brake-by-wire set-up, but a sort of midway solution that makes use of the best of both worlds), and Brembo, which is working on a full brake-by-wire system that uses an electro-mechanical pedal sensor, ECU and electric motor that provides hydraulic output to a vehicle's brake callipers. Given the critical nature of the braking function, Brembo's brake-by-wire system, which is expected to be ready for mainstream use by the year 2020, features multiple system redundancies for fail-safe operation. An added benefit is the system's response time, which is a particularly impressive 90 ms (as compared to around 300 ms for most conventional systems), thereby further shortening stopping time and distance, especially in the event of an emergency braking manoeuvre.

There's also Delphi, which is currently working on an advanced electro-mechanical braking (EMB) system, which uses electrically driven actuators in place of conventional hydraulically operated components. Doing away with the physical link between the brake pedal and the actual braking hardware, Delphi's EMB system features a pedal module, an electrical power system, ECU, four intelligent braking actuators (a separate unit for each wheel), and software interfaces to other onboard vehicle systems. Claimed benefits include elimination of residual torque between brake pads and brake discs, more accurate response and easier integration with traction control and stability assist systems. Plus, given the fact that the system is based on a safety-critical fault-tolerant architecture, risk of failure is entirely minimised.

Indeed, given that brake-by-wire systems offer unmatched system integration with the vehicle's other electronics systems and sub-systems, eliminate power-consuming mechanical pumps, help reduce weight and improve stopping efficiency by a big margin, their widespread adoption on mainstream cars in the coming years looks inevitable.

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AUTOMATIC EMERGENCY BRAKING

In addition to developments in hardware and software that make driver-initiated braking more effective, the next frontier in braking technology development is automatic braking in emergency scenarios. Expected to become a mandatory requirement in some parts of the world by the year 2022, automatic emergency braking (AEB) systems may require OEMs to work with a common electronic architecture for simplified development and deployment.

The aim with AEB systems is to trigger a car's braking function automatically, even when the driver fails to take action, using an array of sensors to detect obstacles in the path of the vehicle's intended trajectory. AEB is designed to work at a range of speeds and while current braking systems might struggle to meet the response times required for AEB activation, it's a challenge that OEMs and suppliers hope to meet by increased collaboration, and the development of more advanced software algorithms, which in turn would speed up the working of various sensors, controllers and actuators.

Is AEB worth the cost and the effort? Well, according to the results of research conducted by Euro NCAP and its associated bodies, it certainly is. According to their research, use of AEB showed an up to 38 % reduction in rear-end collisions in the real world, while noting that the technology requires widespread adoption for maximum benefit. Research reports also advocate the adoption of pedestrian protection AEB technology, which is designed to further reduce the risk of crash-related injuries to road users. This also became a part of the Euro NCAP test procedure at the beginning of 2016, encouraging more OEMs to go for standard fitment of AEB. While this technology has seen very limited deployment in India, European markets already see a fair rate of AEB adoption, with about a fifth of all new cars featuring this as standard, and a roughly similar percentage of new cars featuring AEB as an option.

CONCLUSION

Going forward, it seems to be clear that in the future, braking hardware will evolve hand in hand with software and electronic driver assistance systems. As computers take over all critical functions in a car (including throttle management, steering, transmission and, finally, braking), brake-by-wire will ultimately see widespread adoption in the near future, followed by AEB systems, which will make driving safer for everyone.

TEXT: Sameer Kumar

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