The Hindu Business Line : What is electronic stability system?

By interfering in the braking process, electronic stability control, with the help of sensors, ensures that the driver does not lose control of the car in the event of wheel slippage or loss of traction in any one of the wheels.

Electronic stability-control systems are among the more recent active safety features that automobile manufacturers have incorporated into their passenger vehicles. At work every time the car is taken out, ESC or ESP (electronic stability programme) revolves around the car's various braking systems.

By interfering in the braking process, with the help of sensors, ESC ensures that the driver does not lose control of the car in the event of wheel slippage or loss of traction in any one of the wheels. Most accidents are caused by inability to control the vehicle during wheel slippage or loss of traction at high-speeds and in off-road conditions.

High-speed travel and the advent of high-ground-clearance vehicles, such as sports utility vehicles were originally the reasons for developing the electronics enabling the performance of ESC systems. As a system that integrates a number of active safety add-ons that are built around the vehicle's brakes, ESC enables far greater reliable braking performance.

Many of the features are on stand-by and get automatically activated based on inputs from electronic sensors in the car. ESC works discreetly and performs its job, many a time even without the knowledge of the driver. Some of the safety features that ESC or ESP systems use in tandem and that are built around the car's brakes include anti-lock braking systems (ABS), electronic brake force distribution (EBD) and the brake assist system (BAS).

ABS with EBD and BAS

Anti-lock brakes are the most common of the new generation braking systems that is now also available in many cars in India, either as standard fitment or as an optional add-on. ABS is different from conventional disc brakes in its ability to prevent wheel lock-up and the consequent skidding of the vehicle.

Automakers design and manufacture their vehicles with an eye on ensuring an equitable distribution of weight. This affects the vehicle's on-road driving dynamics and has a bearing on its stability. However, the centre-of-gravity of the car can be affected, either because of the seating pattern of passengers or due to the positioning of heavy luggage.

To keep the vehicle stable at all times, EBD employs electronic sensors that detect the distribution of weight inside the car and uses the information to send signals to the car's brakes to increase or decrease the intensity of braking at each wheel.

Brake assist systems, as the name suggests, enable quicker and firmer braking during emergencies or when the driver indicates the need to stop quickly. Many of these additional features are offered only in high-end, luxury cars due to the high price of these technologies.

When ESC comes into play

One of the most effective systems that work to keep a car stable under slippery conditions is ESC.

Electronic stability control collaborates and activates all or any of the following — the braking systems, the engine management system and in some cases the four-wheel drive system in order to prevent the vehicle from sliding away from the direction of intended travel. Unlike racing, where the demands on the car are for different reasons, in real world conditions, most of the times that the ESC or ESP system needs to be activated will invariably be during potentially severe cornering or while travelling in very slippery road conditions.

Being an active safety feature that can dramatically improve the safety of the car's occupants, to know exactly when to interfere, the ESC system relies on electronic sensors and related components that are embedded in the car's brakes and control module.

The ESP is also activated when the system detects that the driver's steering response is in excess or inadequate to perform the turning or cornering manoeuvre that is being attempted. In the absence of ESP, this usually leads to under steer or over steer and eventually will lead to the driver losing control of the vehicle.

ESC at work

The ESC typically reacts to correct the potential slippage problem by automatically applying the brakes at the relevant wheel to correct the slippage and keep the vehicle on course. For example, during under-steer, the brake force in the inner front wheel is increased and during over-steer, the brake force in the outer rear wheel is increased.

To implement the ESP's function, additional sensors are added to the car's braking system. A steering wheel angle sensor is also used to detect driver input with a yaw rate sensor and a low-G sensor that measure the vehicle response.

Some ESP systems include a connection to the engine or the powertrain controller of the vehicle to enable a reduction in engine torque when required. To integrate the various systems and detect potential loss of control, yaw and low-G sensors are also employed and are usually located in a separate cluster near the vehicle's centre of gravity.

Different vehicle manufacturers have their own versions of ESC that may have been co-developed with component manufacturers. For example, GM calls its system StabiliTrak and Toyota's latest ESC version (offered in the all-new Highlander Hybrid) is called the Vehicle Dynamics Integrated Management (VDIM) System.

ESP is, as yet, one of the most expensive safety features and is found only in luxury cars and high-end sports utility vehicles.

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