Wheel-s-pun

What is traction?
Traction refers to the friction between a drive member and the surface it moves upon, where the friction is used to provide motion.

For the purposes of driving a wheeled vehicle, high friction is generally desired, as it provides a more positive connection between the driving and driven members. In contrast, motion in a geared mechanism is provided by interference, and friction is usually detrimental because the gear mechanism has intrinsic sliding, and sliding under friction causes heating losses.

In the case of a wheeled vehicle, when the motor and/or transmission turns the axles, a reaction torque on the axles is created by the traction of each wheel on the ground. Without traction, there would be no torque (other than that required to overcome the friction and inertia of the transmission and wheels themselves), and hence no movement of the vehicle.

Traction between two surfaces usually depends on several factors including

• Material properties of each surface.
• Macroscopic and microscopic shape or "roughness".
• Force of contact.
• Area of contact.
• Contaminants at the material boundary including lubricants and adhesives.

A traction control system (TCS), on current production vehicles, are typically (but not necessarily) electro-hydraulic systems to prevent loss of traction (and therefore the control of the vehicle) when excessive throttle or steering is applied by the driver. Although similar to electronic stability control systems, traction control systems do not have the same goal.

The intervention can consist of any, or all, of the following:

• Retard or suppress the spark to one or more cylinders
• Reduce fuel supply to one or more cylinders
• Brake one or more wheels
• Close the throttle, if the vehicle is fitted with drive by wire throttle.
• In turbo-charged vehicles, the boost control solenoid can be actuated to reduce boost and therefore engine power.

Typically, the traction control system shares the brake actuator and the wheel speed sensors with the anti-locking braking system.

Traction control helps limit tyre slip in acceleration on slippery surfaces. In the past, drivers had to feather the gas pedal to prevent the drive wheels from spinning wildly on slippery pavement. Many of today's vehicles employ electronic controls to limit power delivery for the driver, eliminating wheel slip and helping the driver accelerate under control.

Early Traction Control

Powerful rear-drive cars from the sixties often had a primitive form of traction control called a limited slip rear differential. Sometimes referred to as Positraction, a limited-slip rear axle will mechanically transfer power to the rear wheel with the most traction, helping to reduce, but not eliminate wheel spin. While limited-slip rear axles are still in use in many front- and rear-drive vehicles today, the device can't completely eliminate wheel slip. Hence, a more sophisticated system was needed.

Enter electronic traction control. In modern vehicles, traction-control systems utilize the same wheel-speed sensors employed by the antilock braking system. These sensors measure differences in rotational speed to determine if the wheels that are receiving power have lost traction. When the traction-control system determines that one wheel is spinning more quickly than the others, it automatically "pumps" the brake to that wheel to reduce its speed and lessen wheel slip. In most cases, individual wheel braking is enough to control wheel slip. However, some traction-control systems also reduce engine power to the slipping wheels. On a few of these vehicles, drivers may sense pulsations of the gas pedal when the system is reducing engine power much like a brake pedal pulsates when the antilock braking system is working.

Many people mistakenly believe that traction control will prevent their vehicle from getting stuck in the snow. This couldn't be further from the truth. Traction control does not have the ability to increase traction; it just attempts to prevent a vehicle's wheels from spinning. For drivers who routinely drive in snowy and icy conditions, traction control, antilock brakes, and snow tires are must-have safety features.