by Jim Kerr
When it comes time to stop a vehicle, most drivers slowly press on the brake pedal. Even during an emergency situation, studies have shown that almost all drivers will press only partially on the brake pedal for the first few milliseconds until their brain has time to analyse the situation and then the brake pedal is pressed firmly. This slight delay in braking enables the vehicle to travel several metres further and can mean the difference between a controlled stop and a fender bender. There are several other factors that delay the vehicle’s response to a braking situation. Mercedes-Benz is trying to reduce or eliminate as much as possible these factors with their new brake systems. They call it Sensotronic Brake Control. I call it Smart Braking.
Mercedes-Benz first introduced the Sensotronic brake system on their SL-Class sports car. Now this technology has been introduced to the E-Class sedans and wagons. The brake system is integrated into the car’s stability control and traction control systems to predict the amount of braking force required at each wheel of the car. Rather than simply reacting to the slip of a tire on the road, the brake controller anticipates the maximum potential braking force all the time the car is rolling down the road. This ensures optimum braking performance at each wheel when needed.
Actual brake application begins long before the driver pushes on the brake pedal. By monitoring the accelerator pedal position, the brake computer can measure the rate at which a driver releases the pedal. If a driver is removing their foot quickly, then it could be in response to an emergency situation. The brake controller reacts by applying slight hydraulic pressure to each brake calliper to move the brake pads toward the brake rotor, eliminating any delay in applying braking force.
By now, the driver has started to step on the brake pedal but probably not firm enough for an emergency stop. The computer measures the rate of brake pedal application by the driver and if the response is rapid, the computer will apply the brakes fully, even before the driver realizes that maximum braking effort is required. The computer can vary the amount of hydraulic pressure at each wheel to provide maximum deceleration even when the vehicle is on a turn or in a rapid evasive manoeuvre. If a tire should happen to lock up because of changes in road surface traction, the ABS system will work to get the tire rolling again so that maximum brake pressure can be applied. In conjunction with the stability control and ABS systems, the Sensotronic brake system can keep the car stable even during the most severe brake applications on differing road surfaces.
Rain poses another problem for braking. Water coats the surface of the brake rotors and acts as a low friction surface between the brake pad and rotor. The Sensotronic system overcomes this by slightly applying the brake pads against the rotors for a short time every few minutes so that the water film is squeezed off the brake rotor and the rotor is heated by the friction to keep it dry. How does the computer know the brakes are wet? It uses the windshield wiper input. If you have the wipers on, the road surface must be wet.
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The Mercedes-Benz Sensotronic brake system is a good example of how technology can make our cars safer. Here is a system that anticipates rather than reacts. It controls the pressure at each wheel independently for maximum stopping power and it does all this without changing the way we operate our vehicles. I like to think of the system as a great equaliser. Even inexperienced drivers can have braking control approaching that of the world’s best race-car drivers. Now that is ‘smart braking’!