One of the major drivers for brake systems today are NCAP requirements for pedestrian and vehicle automatic emergency braking (AEB). Higher performance brake systems are critical to driver assist systems; autonomous braking will also be required for future autonomous driving functions such as electronically controlled deceleration for adaptive cruise control (ACC) up to AEB and Auto Hold electric park brakes.
AEB requirements are driving ZF TRW’s work on brake and sensor systems – especially in terms of stopping time and object recognition. “We’re having discussions with customers about improved braking systems that can automatically bring a car to stop in less than 300-400 milliseconds,” says Manfred Meyer, vice president of ZF TRW Braking Engineering.
“The speed of the brake system’s response determines how much time the sensors have to analyze a potential emergency situation. Everything has to be optimized, from the brake control unit to the calipers to the system’s fluid dynamics. We have very clear development plans in place to achieve very fast pressure-apply with conventional electronic stability control (ESC).”
Emission reduction targets are playing an important role in the uptake of fuel efficient technologies and systems which allow recuperation of energy during braking.
“With brakes, automakers are looking for solutions that are smaller, lighter, faster, safer, more durable – and more affordable every year,” says Meyer. “The reduction of residual drag and the growth of start-stop functionalities are driving ZF TRW’s braking development work.”
In the last few years, fitment of start-stop has reached 30-40% of new cars. In the near future, this will rise to more than 50% globally.
“When vehicles with the start-stop feature halt at a traffic light, sometimes the engine stops, sometimes it doesn’t,” Meyer says. “That’s because the decision to switch off the engine is safety related. The vehicle must have the power to stop and restart safely. For that, there needs to be enough pressure in the brake system, enough vacuum in the brake booster and enough electrical power on board. The longer the vacuum lasts, the longer it is before the pump and engine need to restart. This translates into direct fuel and CO2 savings.”
ZF TRW’s cooperation of hydraulic hold (also out of Auto Hold) and electric park brake is important. The company is also working to reduce residual drag without compromising other brake functionalities. Reducing residual drag by just 0.5Nm per caliper, 2Nm at vehicle level, can save up to 0.1 liters per 100km of fuel. Advances are possible even in ZF TRW’s standard cast iron Colette design. But when the company’s next generation product enters production later this year, it will have an improved guiding system, pad abutment and spring arrangement to achieve the lowest possible drag.
Finally, ZF TRW’s Integrated Brake Control (IBC) remains a key advanced technology. It replaces the ESC system, vacuum booster, pumps and cabling with a single integrated unit. The system’s light weight and pressure dynamics are perfect for AEB and its suitability for driver assist functions will be compelling. IBC is ideally suited for regenerative braking and full brake blending. ZF TRW’s core architecture that enables high levels of component re-use, so the technology can be scaled from entry-level vehicles to high-end requirements.
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