Lifesavers

The ABC of ABS, ebd and other high-tech safety features

Words: Marcus Dowling

Traction control systems have been around for a decade and a half in sports-oriented performance vehicles. But it's only in the past few years that these systems have been added to 4WDs.

Historically speaking, some would say necessity was the mother of invention when traction control was adapted for 4WD vehicles in place of a lowrange transfer case.

The basic principles behind traction control are relatively simple. Wheel speed sensors are connected to the wheels: these measure speed and any variance in speed. When a difference is detected, the system applies the brakes to the fastest spinning wheel or wheels and forces torque (driving force) to the slower turning wheel or wheels that provide the greatest resistance (grip).

To give you a better understanding, let's look at each individual D‑MAX component in isolation:

Anti-lock braking system (ABS)

ABS is a computer-controlled system that measures and monitors wheel speed information sent individually from each wheel. The ABS computer receives the information and calculates an average; the system has preset nominated values and uses these as reference points.

When a difference has been determined, the ABS is activated by controlling (regulating) the brake fluid pressure, therefore activating the brakes.

The primary function of ABS is to make the vehicle manoeuvrable in an emergency situation. ABS is not designed to stop the vehicle in a shorter distance.

In the Isuzu D‑MAX, a calibration occurs while in low-range 4WD incorporating information from the G-force sensors.

Electronic Breakforce Distribution (EBD)

The ABS computer controls the braking force between the front and the rear wheels according to vehicle load. When a brake application is detected, the EBD system compares the difference between front and rear wheel speeds. When the nominated set value is different from what is detected, the brake fluid pressure is regulated (activating the brakes) by supplying more pressure to the rear when loaded and less when not loaded.

Electronic Stability Control (ESC)

The ABS computer measures and monitors the vehicle's angular rotation by receiving direct information from the yaw rate sensor and also the steering wheel angle sensor.

ESC is activated when a loss of steering control is detected. Braking is applied to each wheel individually, thereby helping ‘steer' the vehicle in the intended direction of travel. Activation of this system means the vehicle's computers have the ability to apply braking force to the opposite side of the vehicle, depending on the direction of rotation. This can be explained in understeer and oversteering driving situations when the inner or outer wheels have the brakes automatically applied to keep the vehicle in a straight line.

Traction Control System (TCS)

Excessive opening of the throttle on start-up or acceleration on a slippery surface may cause the driving wheels to spin due to excessive engine torque. TCS suppresses the driving wheel slippage by controlling brake fluid pressure and also engine torque.

The ABS computer calculates the drive wheels' average speed and the vehicle speed based on the wheel speed sensor signal sent from each wheel. The engine computer continually sends the macerator pedal position information to the ABS computer.

When the drive wheel starts to slip and the difference between the average speed of the drive wheel and the vehicle speed exceeds the nominated set value, the ABS computer sends a request to the engine computer to reduce the accelerator pedal position percentage. In doing so, the engine fuel injection volume is reduced, thus reducing the engine torque momentarily.

TCS offers improved driver and passenger safety by giving the vehicle greater control over the road or terrain. An additional feature of TCS is that it replaces the need for a Limited Slip Differential (LSD). This is all achieved through the advanced ABS computer, which calculates precise wheel speed and divides power (drive) to the wheels that have traction (grip) by regulating brake pressure.

The LSD only runs through the rear wheels, limiting control to only the rear, whereas TCS extends the control to the front wheels, offering all-round traction control. In short, LSD is old technology that limits the vehicle's capability through manual components. TCS, however, functions by means of a computer system.

Though its main purpose is often considered to improve safety, TCS also reduces the D‑MAX's overall weight and the number of mechanical components in the differential, therefore reducing wear on vehicle parts and giving greater fuel economy as a result of reduced rolling resistance.

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