Auto Service Professional

OCT 2017

Magazine for the auto service professional

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Page 31 of 77

30 | ASP October 2017 Technical controller (ABS module e.g.) linked via the CAN system for continuously comparing the information from the SAS input, WSSs and accelerometer sensors to determine if the vehicle is reacting the way the driver wants or expects it to. If the vehicle isn't reacting that way (side-skid condition) the ESC will make the needed corrections to get the vehicle back to the direction the driver intended if it isn't. Using WSS data the ESC controller is looking to see if the vehicle is under-steering (the front wheels will be turning slower than the rear wheels) or over-steering (the front wheels turn faster than the rear wheels) compared to the inputs from the driver. When this WSS data is combined with the yaw sensor data and SAS inputs, the ESC will make calculations and start applying wheel brakes to correct the situation. is brake application could be a single wheel or multiple wheels, depending on what the ESC module feels is the best response using the available data. If the vehicle is under-steering on a right turn, it may only apply the right-side brakes to assist in a right rotation. e opposite happens if the vehicle is over steering or fish-tailing on a right-hand turn. It will only apply the left or outside brakes to compen- sate and allow the driver to regain control. If the situation cannot be corrected using the brakes alone, the ESC may also cut the throttle, retard ignition timing, shut off injec- tors and even change transmission settings to intervene, all attempting to allow the driver to regain control. When this skid condition is happening, the driver may be alerted with a flashing ESC light. e driver may also hear the ABS func- tioning, and may notice a decrease in power until the ESC has decided to return control. Other features can be added to the base ESC programs to improve other stability issues that normal drivers can experience. GM's StabiliTrak and Ford's AdvancTrac can control trailer sway by detecting the yaw induced into the pulling vehicle by the trailer. Both systems will automatically apply the needed individual brakes on the tow vehicle to get the trailer and tow vehicle back in line. Corner braking can be incorporated into the ESC system, to improve the vehicle's stability if the driver brakes during a slippery turn or where traction is different from right to left. Because an uneven braking force will result at the wheels due to a weight shift to the outside of the turn, the ESC unit will observe the front WSS speed differences and can pulsate the braking on the outside wheels to create an equal braking force on all four wheels. Stopping on a road surface that has a fric- tion difference between left and right sides of the vehicle may need some ABS activation to provide balanced braking, but the driver will usually need to provide some form of steering input to keep the vehicle going straight. In this situation, the ESC unit may The steering angle sensor was built into this steering column on a Kia. Repair for this vehicle meant replacement and recalibration.

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