What Brake Pads For Active Cruise Control

Countering a market perception that OEM replacement pads must be fitted to vehicles equipped with Active Cruise Control (ACC), Bendix Brakes Application Engineer, Tim Paton, sets out the facts.

Active Cruise Control (ACC) is a driving aid fitted to some new cars, operating the accelerator and the brakes to maintain a distance from the car in front, whereas a conventional cruise control system only operates the accelerator to maintain a pre-set speed.

Tim Paton states that Active Cruise Control places no more demands on the brake system than a conventional driver-operated brake, and so it does not require any special consideration when selecting a replacement brake pad. “If we compare it with other driver aids, such as traction control, electronic stability control (ESC) and anti-lock braking systems (ABS) which also perform computer-controlled brake applications, these systems are all more sensitive to brake pad properties than ACC”, said Tim. “Extensive testing and years of field experience have shown that all of these systems function properly when the vehicle is fitted with quality non-genuine replacement brake pads”, he said.

Active Cruise Control systems may actuate the brakes to maintain a pre-set distance from the car in front. They apply the brakes gently, and with much faster feedback adjustment than any human operator could ever do. If the brakes are more or less effective than what the system assumes, the system will detect that the car is decelerating more or less than expected, and will compensate by adjusting brake pressure - within milliseconds.

By comparison ABS, ESC, traction control etc. function in the same way, but under much more demanding conditions. ABS systems have to compensate and re-calculate for differences in traction between tyre and road, far more than they have to compensate for differences in pad performance. ABS systems are very adaptable - they function with new tyres on dry hotmix , worn tyres on wet clay and even with one wheel on tarmac and one on ice and the differences in pad friction are trivial in that context.

When ABS is activated, the computer determines what brake effect is required, then calculates and commands a brake pressure that would give that effect if the car was in the same perfect factory condition as the vehicles used to calibrate the computer. The system then monitors what actual brake effect it's getting, re-calculates what pressure should be delivered, and commands it. Then it monitors what actual brake effect it's getting, re-calculates etc. - it's iterative, and adjusts very quickly. The first calculation is based on the system's calibration values taking the brake pad properties into account and from then on, it adjusts as required.

Exactly the same applies to ACC. If the brake pads are non-standard, then the first pressure command will need to be corrected slightly when the feedback kicks in. The effect of fitting aftermarket pads to an ACC-equipped car is insignificant.

As Tim Paton succinctly puts it - using a quality aftermarket pad such as Bendix is quite irrelevant in vehicles fitted with ACC and to suggest that only OEM pads must be fitted is a red herring.

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