Collision Repair Training | United States
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Current Events/News: Advantage Online: 2002 Archives
BRAKING THE MERCEDES-BENZ SL500 October 7, 2002 -Engineers are always looking for ways to apply state of the art technology to improve vehicle performance and safety. Often this has consequences for repair technicians. Mechatronics is a new term being used to describe a new application in the industry which combines electronics and mechanics to do more than either technology could alone. The speed and decision making ability of electronic sensors and microcomputers, combined with reliable mechanical systems, can produce significant improvements in a system’s performance. The electronic control of such systems also means that service work must follow very specific procedures and may require special scan tools.Sensotronic Brake Control
SBC allows engineers to do many things with the braking system not possible with conventional systems. Steering angle, vehicle speed range, wheel speed, and driver actions such as quickly releasing pressure on the accelerator pedal are all used to calculate the exact commands sent to the pressure regulators at each wheel. Emergency stopping is anticipated when the driver suddenly releases pressure on the accelerator. The system increases pressure to the calipers, pushing the brake pads out to the rotors. When the driver hits the brake pedal, braking starts very quickly. This pre-filling has resulted in about a 3% decrease in stopping distance in tests by Mercedes-Benz. Standard anti-lock brake systems (ABS) interrupt the pressure applied to the wheels. SBC is able to regulate pressure at each wheel in real time. As vehicle weight shifts, or surface friction varies, the system is able to apply maximum braking at each corner. Much like a motorcycle rider controls each brake separately for maximum effect, SBC controls each wheel separately. This is more effective and doesn’t result in the pulsing felt in the pedal in standard ABS. DaimlerChrysler’s Berlin research facility has tested drivers in a driving simulator and found that that almost two thirds of all drivers are startled when ABS pulsation sets in. This startle response resulted in not increasing pressure further or momentarily releasing pressure. Instead of the need to select brake bias from front to rear, this system can vary the braking done by the front and rear, as well as left and right, wheels depending on conditions. At higher speeds, the bias is shifted to the front wheels to avoid rear wheel lockup. In slow speed driving, the rear brakes get a higher percentage of the braking loads to increase brake response and even out wear to the pads. When braking during cornering, the outer wheels receive greater pressure as they have greater traction. The yaw sensor monitors whether the rear of the vehicle is swinging out. Should this happen, slight braking force on the inside rear wheel stabilizes the vehicle. SBC works with the Electronic Stability Program (ESP) to keep the vehicle stable. ESP will reduce throttle while the SBC applies selective braking. The Soft-Stop function of the SBC software ensures particularly gentle and smooth stopping because of the precise control available. Pressure can be gradually built up and reduced. During wet weather, when the wipers are turned on, SBC moves the brake pads out to lightly touch the rotors at regular intervals, drying the brake surfaces to ensure maximum braking is available at all times. The system is so precise that the driver doesn’t feel anything. The SBC on some SL500 models also includes two other functions: Traffic Jam Assist and Brake Control Drive-Away Assist. Traffic Jam Assist, when activated by using the cruise control switch while the vehicle is stationary, the driver only needs to release pressure on the accelerator pedal and SBC slows the car to a standstill at a steady rate of deceleration. The Traffic Jam Assist can remain operational up to 60 km/h (37 mph) and switches off automatically at higher speeds. Brake Control Drive-Away Assist prevents the car from rolling backwards or forwards. This is useful on steep driveways or hills. Stepping on the brake pedal quickly and hard activates the function. Releasing the brake and pushing the accelerator allows the car to drive off smoothly. Because the system is constantly pressurized, working on brake parts requires specific procedures that can only be done by a Mercedes-Benz dealership. This is because before the caliper is removed or any lines opened, the system must be disabled, and this is only possible using a Mercedes-Benz scan tool. Bleeding the braking system also requires the Mercedes-Benz tool. Keyless Go Keyless Go is an option on the SL500. This system uses a credit card-sized access chip that doesn’t even have to leave the driver’s wallet. When the driver gets close to the car, Keyless Go turns ON, allowing the driver to open the doors and trunk and start the vehicle all without a key. The car starts with the push of a button. Body Innovations There are some innovations on the SL500 body. Rocker panels extend in front of the hinge pillar to allow the front suspension to impact on it. This is designed to direct collision energy away from the passenger compartment. The front crush zones and frame crossmember are both modular and bolted in place. Specific sectioning procedures must be followed for all pillars and rocker panels. These procedures currently are only available to Mercedes-Benz dealership technicians. Conclusion It is usually the case that new technologies are introduced in luxury class vehicles, and then start appearing in other makes and models if the systems are well received. That could well be the situation with the SBC braking system and other technology found on the Mercedes-Benz SL500. |
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