= = = Launch Control vs. Traction Control = = =
#1
07-08-2012, 06:11 AM
= = = Launch Control vs. Traction Control = = =
Hi Member's, below is a interesting article from Motor Trend that I thought you would enjoy or be enlighten.
Launch Control vs. Traction Control
Charting the Differences Between the Two Systems
July 06, 2012
By Angus McGyver
Just when it seems like the internal combustion engine has reached a performance peak, another automaker pushes the power and torque bar even higher. Thanks to sophisticated computerized sensing and control systems, fuel injection, and intake boosting, today's powerplants have higher outputs and cleaner emissions than ever -- all while consuming less fuel.
Of course, fat power and torque curves are only useful if all that power can be transmitted from the crankshaft to the pavement. Thankfully, just as closed-loop control systems have enabled powertrain engineers to extract more work from every drop of fuel, they're also helping vehicle integration engineers do the same when it comes to enabling cars to get a better grip of the road by using launch and traction control.
Closed-loop control
Closed-loop systems continuously manage the behavior of a controlled variable by monitoring that variable with sensors and then adjusting actuators to achieve the desired behavior. Closed-loop control of the wheels and tires began in the late1970s with the debut of anti-lock brake systems (ABS). ABS consists of sensors that measure the rotational speed of each wheel and a hydraulic control unit (HCU) that can independently adjust the brake pressure applied to each corner of the car to maximize braking power while retaining stability and steerability.
Over the past three decades, engineers have increased the capability of those HCUs and added more sensors and actuators to enable the traction (TCS) and stability (ESC) control systems that are now becoming standard equipment in all new cars and trucks. While ABS could only modulate the pressure that the driver was applying through the brake pedal, TCS/ESC can apply the brakes to individual wheels without input from the driver as well as modulate engine torque output.
What is a mu-slip curve?
Whether you have 60 or 600 horsepower under the hood, getting a vehicle moving requires some friction between the tires and the road surface to generate tractive force. If you can think back to high-school or college physics, you may recall some lessons that referred to coefficient of friction, or mu, as it's usually defined in equations. The friction force that can be generated between any two objects is equal to the perpendicular force pushing the objects together, multiplied by the coefficient.
In physics class, we were generally told to assume that the objects were non-deformable, so there were two constant coefficients of friction: a static value when neither object was moving, and a lower dynamic value once they were sliding against each other. Making these assumptions allows the calculations be fairly straightforward.
Cut to the real world, where objects like tires actually deform when you apply a force to them. Instead of a constant coefficient of static friction that drops to a dynamic value once it moves, tires follow a curve where mu varies as the tires deform and their slip increases.
Tire slip is defined as the ratio between the tangential speed of the tire (VT) at the contact patch and the speed of the vehicle (VV).
Slip = (VT / VV) * 100%
A car that is not moving (VV = 0) while the wheels are spinning (VT> 0) would have 100% slip. If the tires are rolling at the same speed as the vehicle, slip is zero. When slip is at zero, so is the coefficient of friction. As the tire begins to slip, mu rapidly climbs to a peak and then tapers off. How high the peak gets and how rapidly it drops off depends on the road surface and the tire construction and compound.
For most road legal tires, the peak mu is usually somewhere between 0.85 and 1.0 and it peaks in the 5-20-percent slip range. Maximum traction is achieved at the peak of the mu-slip curve and the engineers that calibrate ABS/TCS systems generally try to control their systems to keep the tires slipping somewhere around that peak to achieve top performance.
How much slip is enough or too much?
In general, traction control tries to manage the slip on the drive wheels near the peak of the mu-slip curve in order to preserve stability and keep the car from sliding around. It does this by monitoring parameters like engine torque, gear and throttle position, and the driven and undriven wheel speeds to determine when the drive wheels are starting to spin up and break away.
The undriven wheel speeds are used as the vehicle speed for the slip calculation. The combination of slip, wheel acceleration, throttle, and torque can be a very accurate indicator of the amount of grip available and whether you're driving on ice, snow, gravel, or pavement.
TCS cuts the engine torque and applies some brake force to the drive wheels to keep things under control. Under most circumstances, this control strategy works fine and lets drivers make the most of the available grip while preventing the driven axle from trying to slide out from under the car.
Unfortunately, this strategy typically leaves the engine spinning well below its peak torque rpm, which is fine on snow or ice where you don't want all the torque anyway. However, when you are trying to get a quick launch without bogging that torque monster in the engine bay, turning the engine at a speed where you only have half or less of your peak torque can seriously hamper your acceleration.
Enter Launch control
Traction control is optimized for vehicle stability and the system can't always determine the driver's intent. Adding a launch control mode lets the driver make his or her intent explicitly obvious and tells the slip control system they want maximum acceleration on the next launch.
Instead of doing closed-loop control around wheel slip as traction control does, launch control closes the loop around engine speed. Launch control systems generally try to maintain a constant engine speed somewhere near the torque peak by adjusting the electronically controlled throttle, ignition, and brakes as the tires gradually hook up during a launch.
With launch control enabled (a cumbersome process on many cars), the driver simply pushes the accelerator to the floor and holds it there while releasing the left-most pedal (the brake for auto-shifting gearboxes, or the clutch on three-pedal cars).
Depending on how the automaker has implemented launch control, it may use a combination of engine and brake management or just engine alone. In some cases, like the 2013 Shelby GT500, the driver can actually select from either mode depending on their driving style or skill level. The GT500 and the no-longer-available-in-America Lotus Exige 260S also give drivers the ability to adjust to various traction conditions by dialing in the desired engine speed.
The beauty of a well-executed launch control system like the Corvette ZR1 or the new GT500 is that even novice drag racers can reel off incredibly consistent launches timeaftertime, making them the terror of the Friday night bracket races at the local dragstrip. An expert driver may well be able to cover the quarter-mile a couple of tenths of a second quicker with the launch control off.
However, only the best drivers will be able to achieve the run-to-run consistency available from the electronics. Drivers who want to work on their technique and challenge themselves to achieve smooth, quick starts can always turn off launch control. Weekend racers who want to avoid tire-shredding wheel spin that doesn't lead to actual motion will probably leave the launch control enabled.
What would you do ?
Launch Control vs. Traction Control
Charting the Differences Between the Two Systems
July 06, 2012
By Angus McGyver
Just when it seems like the internal combustion engine has reached a performance peak, another automaker pushes the power and torque bar even higher. Thanks to sophisticated computerized sensing and control systems, fuel injection, and intake boosting, today's powerplants have higher outputs and cleaner emissions than ever -- all while consuming less fuel.
Of course, fat power and torque curves are only useful if all that power can be transmitted from the crankshaft to the pavement. Thankfully, just as closed-loop control systems have enabled powertrain engineers to extract more work from every drop of fuel, they're also helping vehicle integration engineers do the same when it comes to enabling cars to get a better grip of the road by using launch and traction control.
Closed-loop control
Closed-loop systems continuously manage the behavior of a controlled variable by monitoring that variable with sensors and then adjusting actuators to achieve the desired behavior. Closed-loop control of the wheels and tires began in the late1970s with the debut of anti-lock brake systems (ABS). ABS consists of sensors that measure the rotational speed of each wheel and a hydraulic control unit (HCU) that can independently adjust the brake pressure applied to each corner of the car to maximize braking power while retaining stability and steerability.
Over the past three decades, engineers have increased the capability of those HCUs and added more sensors and actuators to enable the traction (TCS) and stability (ESC) control systems that are now becoming standard equipment in all new cars and trucks. While ABS could only modulate the pressure that the driver was applying through the brake pedal, TCS/ESC can apply the brakes to individual wheels without input from the driver as well as modulate engine torque output.
What is a mu-slip curve?
Whether you have 60 or 600 horsepower under the hood, getting a vehicle moving requires some friction between the tires and the road surface to generate tractive force. If you can think back to high-school or college physics, you may recall some lessons that referred to coefficient of friction, or mu, as it's usually defined in equations. The friction force that can be generated between any two objects is equal to the perpendicular force pushing the objects together, multiplied by the coefficient.
In physics class, we were generally told to assume that the objects were non-deformable, so there were two constant coefficients of friction: a static value when neither object was moving, and a lower dynamic value once they were sliding against each other. Making these assumptions allows the calculations be fairly straightforward.
Cut to the real world, where objects like tires actually deform when you apply a force to them. Instead of a constant coefficient of static friction that drops to a dynamic value once it moves, tires follow a curve where mu varies as the tires deform and their slip increases.
Tire slip is defined as the ratio between the tangential speed of the tire (VT) at the contact patch and the speed of the vehicle (VV).
Slip = (VT / VV) * 100%
A car that is not moving (VV = 0) while the wheels are spinning (VT> 0) would have 100% slip. If the tires are rolling at the same speed as the vehicle, slip is zero. When slip is at zero, so is the coefficient of friction. As the tire begins to slip, mu rapidly climbs to a peak and then tapers off. How high the peak gets and how rapidly it drops off depends on the road surface and the tire construction and compound.
For most road legal tires, the peak mu is usually somewhere between 0.85 and 1.0 and it peaks in the 5-20-percent slip range. Maximum traction is achieved at the peak of the mu-slip curve and the engineers that calibrate ABS/TCS systems generally try to control their systems to keep the tires slipping somewhere around that peak to achieve top performance.
How much slip is enough or too much?
In general, traction control tries to manage the slip on the drive wheels near the peak of the mu-slip curve in order to preserve stability and keep the car from sliding around. It does this by monitoring parameters like engine torque, gear and throttle position, and the driven and undriven wheel speeds to determine when the drive wheels are starting to spin up and break away.
The undriven wheel speeds are used as the vehicle speed for the slip calculation. The combination of slip, wheel acceleration, throttle, and torque can be a very accurate indicator of the amount of grip available and whether you're driving on ice, snow, gravel, or pavement.
TCS cuts the engine torque and applies some brake force to the drive wheels to keep things under control. Under most circumstances, this control strategy works fine and lets drivers make the most of the available grip while preventing the driven axle from trying to slide out from under the car.
Unfortunately, this strategy typically leaves the engine spinning well below its peak torque rpm, which is fine on snow or ice where you don't want all the torque anyway. However, when you are trying to get a quick launch without bogging that torque monster in the engine bay, turning the engine at a speed where you only have half or less of your peak torque can seriously hamper your acceleration.
Enter Launch control
Traction control is optimized for vehicle stability and the system can't always determine the driver's intent. Adding a launch control mode lets the driver make his or her intent explicitly obvious and tells the slip control system they want maximum acceleration on the next launch.
Instead of doing closed-loop control around wheel slip as traction control does, launch control closes the loop around engine speed. Launch control systems generally try to maintain a constant engine speed somewhere near the torque peak by adjusting the electronically controlled throttle, ignition, and brakes as the tires gradually hook up during a launch.
With launch control enabled (a cumbersome process on many cars), the driver simply pushes the accelerator to the floor and holds it there while releasing the left-most pedal (the brake for auto-shifting gearboxes, or the clutch on three-pedal cars).
Depending on how the automaker has implemented launch control, it may use a combination of engine and brake management or just engine alone. In some cases, like the 2013 Shelby GT500, the driver can actually select from either mode depending on their driving style or skill level. The GT500 and the no-longer-available-in-America Lotus Exige 260S also give drivers the ability to adjust to various traction conditions by dialing in the desired engine speed.
The beauty of a well-executed launch control system like the Corvette ZR1 or the new GT500 is that even novice drag racers can reel off incredibly consistent launches timeaftertime, making them the terror of the Friday night bracket races at the local dragstrip. An expert driver may well be able to cover the quarter-mile a couple of tenths of a second quicker with the launch control off.
However, only the best drivers will be able to achieve the run-to-run consistency available from the electronics. Drivers who want to work on their technique and challenge themselves to achieve smooth, quick starts can always turn off launch control. Weekend racers who want to avoid tire-shredding wheel spin that doesn't lead to actual motion will probably leave the launch control enabled.
What would you do ?
#3
07-08-2012, 06:27 AM
Thanks StumpMi (LOL) that's a good way to put it 4-Sure.
I think these electronic devices are good, but I still prefer to `be be the driver & not have a computer drive my ride..
Now, you just push button's....Aim & hit the gas pedal...
Pretty soon a owner can just remotely drive his car to the line with a joy stick, push a button & watch his car go through the 1/4 mile...LOL Not my kinda fun
I prefer to control my own power
and go sideways `off the line or around a corner LOL...spin `Out
If I lose the Race, I want to take the blame, and not say it was my computer's fault (LOL)...Yes, I would have beat you `if I had a faster computer...Just wait till next week when I get that new computer chip that's coming out... LOL
I think these electronic devices are good, but I still prefer to `be be the driver & not have a computer drive my ride..
Now, you just push button's....Aim & hit the gas pedal...
Pretty soon a owner can just remotely drive his car to the line with a joy stick, push a button & watch his car go through the 1/4 mile...LOL Not my kinda fun
I prefer to control my own power
and go sideways `off the line or around a corner LOL...spin `Out If I lose the Race, I want to take the blame, and not say it was my computer's fault (LOL)...Yes, I would have beat you `if I had a faster computer...Just wait till next week when I get that new computer chip that's coming out... LOL
Last edited by Space; 07-08-2012 at 06:34 AM.
#4
07-08-2012, 06:31 AM
Thanks StumpMi (LOL) that's a good way to put it 4-Sure.
I think these electronic devices are good, but I still prefer to `be be the driver & not have a computer drive my ride..
Now, you just push button's....Aim & hit the gas pedal...
Pretty soon a owner can just remotely drive his car to the line with a joy stick, push a button & watch his car go through the 1/4 mile...LOL Not my kinda fun
I think these electronic devices are good, but I still prefer to `be be the driver & not have a computer drive my ride..
Now, you just push button's....Aim & hit the gas pedal...
Pretty soon a owner can just remotely drive his car to the line with a joy stick, push a button & watch his car go through the 1/4 mile...LOL Not my kinda fun
I too preferr the "real Deal"
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