Traction Control

THE ECU AND TRACTION CONTROL.

Some of the biggest advances in automotive technology in the past 10 years have come in the area of safety. Spurred by improvements in microprocessor speed, miniaturization, and software development, the automobile continues to evolve. In addition to telemetric based services like OnStar, digital satellite radio and in-car e-mail, recent advances in braking technology have led to shorter stopping distances and increased control while driving in inclement conditions. All these developments have been possible because a certain device, the ECU, was integrated into the automobiles.

An Electronic Control Unit or ECU (also known as an "engine management system") is an electronic device, basically a computer, in an internal combustion engine that reads several sensors in the engine and uses the information to control the fuel injection and ignition systems of the engine. This approach allows an engine's operation to be controlled in great detail, allowing greater fuel efficiency, better power and responsiveness, and much lower pollution levels than earlier generations of engines. Because the ECU is dealing with actual measured engine performance from millisecond to millisecond, it can compensate for many variables that traditional systems cannot.

Modern ECUs use a microprocessor which can process the inputs from the engine sensors in real time. An electronic control unit comprises both hardware and software. The hardware consists of electronic components on a printed circuit board (PCB). The main component on this circuit board is a micro-controller chip (CPU). The software is stored in the microcontroller or other similar chips on the PCB, typically in Flash-Memory or EPROM’s so that the CPU can be re-programmed by uploading updated code. This is also referred to as an ‘electronic’ Engine Management System (EMS).

Sophisticated management systems receive inputs from other sources apart from the engine hence controlling other parts of the car as well. Moreover by interfacing them with other electronically-controlled systems like automatic transmissions, traction control systems, and the like the vehicle of today are offering drivers the benefit of ‘space-age’ electronics that not only improve a car's safety but also its drivability!

Traction control is one of the main safety developments and enhancements that have embedded themselves in the automobile during this period and hence will be the focus of this article.

But what is traction control, and how does it work? The word traction refers, in general, to the car's ability to maintain adhesive friction between the tires and the pavement, and hence deals with the lateral (front-to-back) loss of friction during acceleration. Maximum acceleration is achieved by limiting the slip between the tire and the road and this is the point at which a tire is just beginning to slip against the road resulting in the maximum coefficient of friction value.

In other words, when your car accelerates from a dead stop, or speeds up while passing another vehicle, traction control works to ensure that there is maximum contact between the road surface and your tires, even under less-than-ideal road conditions.

INSERT THE GRAPH HERE

From the graph above it can be seen the maximum coefficient of friction (µ) occurs at a slip between tire and road of 10% when dry, and around 5% when wet.

Maintaining this level of slip is inherently difficult as the grip levels drop off significantly above these levels, meaning the balance between too much wheel spin and not enough power is very fine. But with the advent of fast reacting electronics on cars, this problem has been successfully tackled with Traction Control systems.

Traction Control systems have two fundamental functions: to maintain the precise level of slip that will give close to 100% of the available grip, and to maintain