Traction control systems are essential to maneuvering a vehicle, limiting wheel spin while preventing excessive acceleration on low friction surfaces. These systems interact closely with the vehicle’s differential and other systems such as ABS and ESC. Prior to the modern electronic system, a limited slip rear differential was generally used as the primary method of traction control. Most current vehicles feature these systems in conjunction with Electronic Stability Control, which enhances steering control and tracking.

Traction control systems prevent wheel spin upon acceleration, while ABS (anti-lock brakes) perform a similar function when braking on slippery surfaces. The current systems employ multiple sensors that monitor each wheel’s rotational speed. Hydraulic brake modulators communicate with the ECU to equalize the wheels’ speed, reducing slippage.

Here we will demystify the various types of traction control and examine how integral they are to vehicle dynamics.

What Is Traction Control?

Car Driving In Snow Winter Traction Control System
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Traction control is necessary for the elimination of wheel slip.  The most basic form of the system, called "MaxTrac", was used on the 1971 Buick Riviera. The advent of modern systems began in the late 1980s. On the dash, the traction control system is often indicated by a pictogram of a car leaving behind wavy tracks. This system performs the key function of reducing wheel spin and slippage on soft, uneven, or slippery surfaces. An example of this would be driving on snow, mud, or gravel.

Each wheel is equipped with its own sensor that sends data to the ECU regarding its rotational speed. If one wheel is spinning faster than the others, it can be modified to match the conditions in question and create the optimal equilibrium of wheel speed.

Although the traction control system cannot add traction to a slippery surface, it can enhance the driver's ability to control the vehicle and accelerate in low friction conditions.  The system can also be deactivated if desired, typically by pressing the "TCS" button or pulling the corresponding fuse.

Traction Enhancement

Traction Control Nissan System Electronic Vehicle Active Safety Feature
via autoexpress.co.uk

In order to provide the correct power and braking force, the traction control system works closely with ABS (anti-lock brakes) and ESC (electronic stability control).

ABS applies braking force to govern wheel spin when braking in low friction conditions.  Anti-lock brake systems were invented in 1929 to enhance braking control on aircraft. In 1958, it was tested in motorcycles as a safety feature. The first automotive iteration made its debut on the 1971 editions of the Chrysler Imperial and GM Cadillac.

This system activates solenoid valves within a hydraulic modulator to prevent tire lock when rapid deceleration is sensed. In situations where you might have to slam on the brakes, this can enhance maneuverability and reduce skidding.

The differential can be considered the mechanical component of the system and was the original form of traction control. The locking differential provides a variable distribution of torque to the wheels. This can be useful in off-road conditions to apply power to the wheel with more traction. Its downside is the possibility of binding due to an excess of accumulated torque. The common open differential allows the wheels to have independent rotation. This can put the car at a disadvantage, as a wheel with little to no traction will be receiving power.

The limited slip differential allows for the application of torque where necessary without the requirement of equal distribution. This differential, also referred to as positraction, allows a difference of wheel power within a certain margin, reducing slip. Torsen (torque sensing) differentials, common on performance vehicles, are gear-driven limited slip differentials that are highly responsive to varying conditions.

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Traction Control VS Stability Control

Traction Control Wheel Spin Car
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In contrast to traction control, Electronic Stability Control (ESC) works to limit the possibility of rollover or an unintended trajectory that can quickly become uncontrollable and dangerous. The ESC includes additional sensors that monitor the path, rotation, and acceleration of the vehicle.  The system, invented by Bosch, made its first appearance on the 1995 Mercedes S-Class.  In 2011, the NHTSA made ESC systems mandatory in all vehicles with a GVWR of under 10,000lbs.

An accelerometer monitors components of the car’s acceleration and a yaw sensor measures angular velocity around the car’s vertical axis. Sensors in the steering wheel take the intended motions and path into account. The system has the ability to apply brakes to each wheel independently.

The balanced combination of traction and stability control systems can contribute significantly to vehicle safety.  According to SAE International, the implementation of ESC systems has resulted in a reduced rollover incidence of 50.6%.  It can be especially useful for trucks and SUVs, which can face a high probability of rollover due to their higher center of gravity.  Starting in 2017, the NHTSA began implementing requirements for anti-rollover systems in trucks and buses surpassing a GVWR of 26,000lbs.

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