The National Highway Traffic Safety Administration has mandated that Electronic Stability Control (ESC) systems be progressively phased in as standard equipment on all passenger vehicles with a gross vehicle weight rating of 4,536 kg (10,000 lbs) or less, starting with the 2009 model year. All such vehicles must have the system installed by the 2012 model year. Consequently, for those of us not too familiar with these systems it might benefit us to learn something about their operation.
Overview
In its most basic form, ESC uses an electronic sensor to detect the rotation of the car around its vertical axis, also known as yaw. This sensor (called a yaw sensor) can detect whether the car is turning left or right, and how fast it is doing so. The other major input to ESC is a steering angle sensor that senses the degree and direction of the steering lock applied by the driver. The system compares the degree of steering angle with the amount of yaw to determine if the car is turning in the right direction, and at the right rate, to match the steering input.
If the system detects that the car is not following the path dictated by the steering input, it knows that the car is sliding. If the car is not turning as much as the steering angle sensor indicates it should be, the car must be understeering. If, on the other hand, the car is turning more than the steering angle sensor indicates, it must be oversteering. If either of these conditions is detected, ESC brakes individual wheels and/or reduces engine power to return the car's path to that being requested (via the steering input) by the driver.
Obviously, an anti-lock braking system (ABS) is also necessary for the operation of ESC. As in the case of ABS, a hydraulic modulator is used to apply the correct braking force to each wheel. However, while ABS only needs to reduce pressure during braking, ESC additionally needs to increase pressure, sometimes to the point of actually stopping wheel rotation, in certain situations. Traction control systems (TCS) are often incorporated into ESC. These have sensors which monitor drive-wheel slip under acceleration and individually brake the slipping wheel, or wheels, and/or reduce engine power until control is regained. Keep in mind, however, ESC acieves a different purpose than either ABS or TCS, alone or in combination. Whereas ABS and TCS ensure straight line stability, ESC maintains stability in turns.
Currently, many ESC systems have an overide switch to disable its operation, which may be desirable in certain situations such as when using an undersized spare tire which could interfere with sensor input. The sensitivity of the ESC, and how much oversteer or understeer it permits before it intervenes is entirely up to the car manufacturers policies and its engineers. Some makers program the ESC software to allow the car to be near the point of no return before the system intervenes, while others apply brakes and reduce engine power before the driver can detect any sliding at all. Some cars even have switchable levels of ESC where the driver can determine at what point he wants it to intervene.
Whether or not a more uniform standard will be devised as ESC proceeds to full implementation in 2012 is not known at this point, at least by this writer.
References
For a graphic and dramatic view of the overwhelmingly positive benefits of ESC systems, look at the following two videos:
http://www.youtube.com/watch?v=K3m24bjkfg0
http://www.youtube.com/watch?v=pQq-4KYBxsI&NR=1
For a brief explanatory article on ESC with diagrams, go to:
http://www.iihs.org/ratings/esc/esc_explained.html
For a technical analysis and a description of how ESC is implemented in a variety of cars, go to:
http://www.roadandtrack.com/article....rticle_id=6826
Happy Motoring!
Overview
In its most basic form, ESC uses an electronic sensor to detect the rotation of the car around its vertical axis, also known as yaw. This sensor (called a yaw sensor) can detect whether the car is turning left or right, and how fast it is doing so. The other major input to ESC is a steering angle sensor that senses the degree and direction of the steering lock applied by the driver. The system compares the degree of steering angle with the amount of yaw to determine if the car is turning in the right direction, and at the right rate, to match the steering input.
If the system detects that the car is not following the path dictated by the steering input, it knows that the car is sliding. If the car is not turning as much as the steering angle sensor indicates it should be, the car must be understeering. If, on the other hand, the car is turning more than the steering angle sensor indicates, it must be oversteering. If either of these conditions is detected, ESC brakes individual wheels and/or reduces engine power to return the car's path to that being requested (via the steering input) by the driver.
Obviously, an anti-lock braking system (ABS) is also necessary for the operation of ESC. As in the case of ABS, a hydraulic modulator is used to apply the correct braking force to each wheel. However, while ABS only needs to reduce pressure during braking, ESC additionally needs to increase pressure, sometimes to the point of actually stopping wheel rotation, in certain situations. Traction control systems (TCS) are often incorporated into ESC. These have sensors which monitor drive-wheel slip under acceleration and individually brake the slipping wheel, or wheels, and/or reduce engine power until control is regained. Keep in mind, however, ESC acieves a different purpose than either ABS or TCS, alone or in combination. Whereas ABS and TCS ensure straight line stability, ESC maintains stability in turns.
Currently, many ESC systems have an overide switch to disable its operation, which may be desirable in certain situations such as when using an undersized spare tire which could interfere with sensor input. The sensitivity of the ESC, and how much oversteer or understeer it permits before it intervenes is entirely up to the car manufacturers policies and its engineers. Some makers program the ESC software to allow the car to be near the point of no return before the system intervenes, while others apply brakes and reduce engine power before the driver can detect any sliding at all. Some cars even have switchable levels of ESC where the driver can determine at what point he wants it to intervene.
Whether or not a more uniform standard will be devised as ESC proceeds to full implementation in 2012 is not known at this point, at least by this writer.
References
For a graphic and dramatic view of the overwhelmingly positive benefits of ESC systems, look at the following two videos:
http://www.youtube.com/watch?v=K3m24bjkfg0
http://www.youtube.com/watch?v=pQq-4KYBxsI&NR=1
For a brief explanatory article on ESC with diagrams, go to:
http://www.iihs.org/ratings/esc/esc_explained.html
For a technical analysis and a description of how ESC is implemented in a variety of cars, go to:
http://www.roadandtrack.com/article....rticle_id=6826
Happy Motoring!
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