General Motors has developed various versions of vehicle stability enhancement systems. Most commonly, the systems are marketed as StabiliTrak and Active Handling. A stability enhancement system automatically assists when the vehicle senses loss of control during acceleration, braking, or turning maneuvers. The system responds by comparing how much the driver is turning the steering wheel with how well the vehicle is responding. To improve control the system precisely applies force to the appropriate brake to slow the vehicle and help bring it back to the driver's intended path. Applying the proper brake force at just the right time helps steer the car as you may steer a canoe by dragging an oar in the water.
Like traction control, the system is dependent on several components of the antilock braking system. In addition to gathering information from wheel speed sensors and the powertrain control module, the system monitors steering wheel position and yaw. Yaw is a measurement of the vehicle’s rotation around its center point.
The system is complex, expensive and very effective. In tests, average drivers on a closed track were able to attain better lap times with active handling than without it. More important than lap times, stability enhancement systems help keep vehicles from swerving, spinning and skidding off the road under low traction conditions.
For information on all three systems see http://www.chevrolet.com/safety/before/stabilitrak/
Wednesday, February 27, 2008
Monday, February 18, 2008
Traction Control Systems
Vehicles equipped with Antilock Brakes often have the added feature of traction control. The traction control system operates from the antilock brake control module, utilizing the wheel speed sensor signals and other components. It also works with the powertrain control module and, if equipped, the transmission control module.
The intent of traction control is the exact opposite of antilock braking. Whereas antilock brakes assist in offering controlled braking under low traction conditions, traction control helps the driver experience controlled acceleration in low traction conditions. It is not designed to keep a vehicle from spinning or skidding on a turn – that’s a different system.
While accelerating, if the wheel speed sensors indicate that one wheel is spinning faster than the others, the control module recognizes that traction was lost by that wheel. At this point there are various actions that can be taken. Typically, the control unit will first reduce engine power. If the condition persists it may then command the transmission to shift to a higher gear, or apply brake pressure to the wheel that has lost traction. The result of braking the wheel is that power will then be diverted to the opposite wheel through the compensating gears in the differential.
Tests have proven that under low traction conditions, a traction control system consistently allows for a vehicle to accelerate quicker. This is a valuable safety feature; just ask anyone who has had to merge onto or cross a major road under snowy, icy, or otherwise hazardous conditions. One consequence of traction control is that it works very discretely with little feedback of its operation to the driver. Therefore, to ensure the driver’s awareness of the potentially hazardous driving condition, a “low traction” indicator lamp is usually incorporated into the instrument panel. Remember that this light does not indicate a problem with the system, but instead shows that it’s working.
There are occasions when traction control can work against you. Most notably, when the vehicle is stuck in snow, sand, etc., traction control will prevent the driver from “rocking the car” to get it in motion and out of the situation. To help with this, all systems have an override switch somewhere on the dashboard. They are typically labeled T/C Off or something similar. Unless stuck, always leave the system on (active) while driving. Also, since the antilock brakes and traction control systems work together, a failure in in one system will often affect the other. Address any ABS or T/C system problem immediately – your safety is at stake. Consult your owner’s manual for more specific information, and locations of the indicators and the override switch.
The intent of traction control is the exact opposite of antilock braking. Whereas antilock brakes assist in offering controlled braking under low traction conditions, traction control helps the driver experience controlled acceleration in low traction conditions. It is not designed to keep a vehicle from spinning or skidding on a turn – that’s a different system.
While accelerating, if the wheel speed sensors indicate that one wheel is spinning faster than the others, the control module recognizes that traction was lost by that wheel. At this point there are various actions that can be taken. Typically, the control unit will first reduce engine power. If the condition persists it may then command the transmission to shift to a higher gear, or apply brake pressure to the wheel that has lost traction. The result of braking the wheel is that power will then be diverted to the opposite wheel through the compensating gears in the differential.
Tests have proven that under low traction conditions, a traction control system consistently allows for a vehicle to accelerate quicker. This is a valuable safety feature; just ask anyone who has had to merge onto or cross a major road under snowy, icy, or otherwise hazardous conditions. One consequence of traction control is that it works very discretely with little feedback of its operation to the driver. Therefore, to ensure the driver’s awareness of the potentially hazardous driving condition, a “low traction” indicator lamp is usually incorporated into the instrument panel. Remember that this light does not indicate a problem with the system, but instead shows that it’s working.
There are occasions when traction control can work against you. Most notably, when the vehicle is stuck in snow, sand, etc., traction control will prevent the driver from “rocking the car” to get it in motion and out of the situation. To help with this, all systems have an override switch somewhere on the dashboard. They are typically labeled T/C Off or something similar. Unless stuck, always leave the system on (active) while driving. Also, since the antilock brakes and traction control systems work together, a failure in in one system will often affect the other. Address any ABS or T/C system problem immediately – your safety is at stake. Consult your owner’s manual for more specific information, and locations of the indicators and the override switch.
Saturday, February 9, 2008
Anti-lock Braking Systems
I can still remember my driver’s ed. teacher, Mr. Pollizotto saying “Pump the brakes!” while the 1977 sedan slid sideways down a snow covered street.
The idea behind the action was that once the tires locked, they lost direct contact with the road and the vehicle became uncontrollable. When a tire skids, slides, hydoplanes, etc. the vehicle is no longer firmly connected to our home planet – by pumping the brakes, the wheels would alternately lock and then release. This allowed you to maintain directional control while slowing the car.
Antilock braking systems offer the advantage of keeping the driver in control of the vehicle under moderate to hard braking and while on low traction surfaces. They do not necessarily provide a shorter stopping distance, but instead allow for a controlled stop instead of an uncontrolled skid. As anyone who has driven on a snow or ice covered road (in a car not equipped with ABS) will attest, once the tires start to slide, turning the wheels has little to no effect.
How an ABS system works involves a tremendous amount of electronics and engineering. In layman’s terms, the heart of the system is a controller that regulates how much pressure is applied to each wheel when you step on the brake pedal. There is a speed sensor attached to each wheel that constantly feeds information back to the controller. When braking, if one of those sensors goes to zero, that indicates the tire is skidding (or locked). At that point the controller activates a valve that releases the pressure from that wheel. Once the wheel unlocks and again sends back a speed reading, the controller reapplies the brake pressure. It’s alot like the old “pump the brakes” process except much more efficient and effective. The controller can cycle the pressure on and off ten to fifteen times per second and only on the wheels that are locked so that the wheels with good traction can continue working to stop the vehicle.
If you have ever experienced an ABS assisted stop you likely heard a buzzing/ fluttering noise from under the hood and felt a vibration in the brake pedal. When starting the vehicle, the ABS light may flash for three seconds and you may a buzzing noise from under the hood as it goes through a self-diagnostic test. Both conditions are completely normal. If the light stays on or continuously flashes, have the system checked ASAP. The hydraulic portion of the braking system may be working properly, but you jeopardize getting yourself into a difficult situation that may require ABS, and while the light is on, the system is typically inactivated.
ABS systems require little maintenance; check your owner’s manual for recommended service intervals. What does require diligence is the condition of you tires. Even with ABS, your vehicle can only stop as well as it is connected to the road. If your tires are mismatched, or low on air, the antilock system will not be able to function properly. If you have a small space-saver spare and have occasion to drive with it on the vehicle, the ABS lamp will probably come on since the smaller tire will be spinning much faster than the three normal size tires and therefore confuse the controller. Check the owner’s manual before scheduling a service appointment.
Anti-lock brakes are a valuable safety feature worthy of the additional cost, if any, when purchasing a new vehicle. As an added feature, opting for ABS may include a Traction Control System or TCS. We’ll discuss that system next week.
For more information check out http://www.acdelco.com/service/systems-guide/brake.htm
The idea behind the action was that once the tires locked, they lost direct contact with the road and the vehicle became uncontrollable. When a tire skids, slides, hydoplanes, etc. the vehicle is no longer firmly connected to our home planet – by pumping the brakes, the wheels would alternately lock and then release. This allowed you to maintain directional control while slowing the car.
Antilock braking systems offer the advantage of keeping the driver in control of the vehicle under moderate to hard braking and while on low traction surfaces. They do not necessarily provide a shorter stopping distance, but instead allow for a controlled stop instead of an uncontrolled skid. As anyone who has driven on a snow or ice covered road (in a car not equipped with ABS) will attest, once the tires start to slide, turning the wheels has little to no effect.
How an ABS system works involves a tremendous amount of electronics and engineering. In layman’s terms, the heart of the system is a controller that regulates how much pressure is applied to each wheel when you step on the brake pedal. There is a speed sensor attached to each wheel that constantly feeds information back to the controller. When braking, if one of those sensors goes to zero, that indicates the tire is skidding (or locked). At that point the controller activates a valve that releases the pressure from that wheel. Once the wheel unlocks and again sends back a speed reading, the controller reapplies the brake pressure. It’s alot like the old “pump the brakes” process except much more efficient and effective. The controller can cycle the pressure on and off ten to fifteen times per second and only on the wheels that are locked so that the wheels with good traction can continue working to stop the vehicle.
If you have ever experienced an ABS assisted stop you likely heard a buzzing/ fluttering noise from under the hood and felt a vibration in the brake pedal. When starting the vehicle, the ABS light may flash for three seconds and you may a buzzing noise from under the hood as it goes through a self-diagnostic test. Both conditions are completely normal. If the light stays on or continuously flashes, have the system checked ASAP. The hydraulic portion of the braking system may be working properly, but you jeopardize getting yourself into a difficult situation that may require ABS, and while the light is on, the system is typically inactivated.
ABS systems require little maintenance; check your owner’s manual for recommended service intervals. What does require diligence is the condition of you tires. Even with ABS, your vehicle can only stop as well as it is connected to the road. If your tires are mismatched, or low on air, the antilock system will not be able to function properly. If you have a small space-saver spare and have occasion to drive with it on the vehicle, the ABS lamp will probably come on since the smaller tire will be spinning much faster than the three normal size tires and therefore confuse the controller. Check the owner’s manual before scheduling a service appointment.
Anti-lock brakes are a valuable safety feature worthy of the additional cost, if any, when purchasing a new vehicle. As an added feature, opting for ABS may include a Traction Control System or TCS. We’ll discuss that system next week.
For more information check out http://www.acdelco.com/service/systems-guide/brake.htm
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