ELECTRONIC STABILISATION OF AN AUTOMOBILE

Sidhartha Pattnaik

B.Tech(Mechanical Engineering)

College Of Engineering and Technology, Bhubaneswar
sidharthapattnaik28@gmail.com

Where airbags are not even compulsory in India, Europe has made Electronic Stability Control (ESC) of Vehicles mandatory.

Now what is Electronic Stability Control? Let’s take a close look at it.

Electronic Stability Control is a computerised system used in automobiles that detects loss of traction (skidding) in a vehicle and improves stability.

Basically, ESC improves stability of a vehicle when there is a loss of steering. It automatically detects this. ESC works in complement with Anti-Lock Braking System (ABS) and Traction Control System (TCS). In layman’s term ESC uses high-tech sensors, car’s central computer and mechanical action/devices to implement better control and stability of the vehicle.

Electronic Stability Control (ESC) is also known as Electronic Stability Program (ESP) or Dynamic Stability Control (DSC). Different auto-makers have different names for it. Ford calls it Advance Trac , GM has a name StabiliTrac , Porsche calls it Porsche Stability Management.

The ESC was first developed by Bosch in the year 1995. Mercedes Benz S-Class and BMW 7-series were the first to introduce it as a safety feature.

Electronic Stability Control Explained

So what does ESC do?

ESC uses a number of intelligent sensors that detect any loss of control and automatically apply brake on intended wheel, putting the car back on track. Additionally it reduces engine power temporarily to bring the vehicle back on track.

ESC is of assistance to the driver in:

·         correcting impending over steering or under steering;

·         stabilising the car during sudden evasive manoeuvres;

·         enhancing handling on gravel patches, such as road shoulders; and

·         Improving traction on slippery or icy roads.

During normal driving, ESC works in the background and continuously monitors steering and vehicle direction. It compares the driver's intended direction (determined through the measured steering wheel angle) to the vehicle's actual direction (determined through measured lateral acceleration, vehicle rotation (yaw), and individual road wheel speeds).

ECS intervenes when there is a probable loss of steering i.e the vehicle is not going in its intended path. This is technically called correcting over steering and under steering.

Under steer happens when the front wheels don't have enough traction and the car continues moving forward rather than turning. Over Steer is just the opposite, the car turns farther than the driver intended causing the rear wheels to slide and the car to spin. This can be properly understood by the following diagram.

 ESC estimates the direction of the skid, and then applies the brakes to individual wheels asymmetrically in order to create torque about the vehicle's vertical axis, opposing the skid and bringing the vehicle back in line with the driver's commanded direction. Additionally, the system may reduce engine power or operate the transmission to slow the vehicle down.

Components of ESC:

Electronic Stability Control (ESC) system incorporates other vehicle safety features like ABS, Traction Control System and Yaw control system.

A vehicle having ABS, Traction control etc. need not have electronic stability system but an ESC compulsorily has these systems. Now let’s see how these systems help in vehicle safety.

ABS refers to Anti-Lock braking system. Before the 1990s, drivers were taught to pump the brake pedal to keep the brakes from locking up and causing a slide. With the invention of anti-lock brakes, driving safely became much easier. ABS electronically pumped the brakes faster than the driver could, which kept them from locking and causing under steer or over steer. ESC uses this system to correct the problem almost before it can start by activating the ABS for as many wheels as needed, from one individual wheel to all four. The nature of ABS keeps the over- or under steer from getting worse while slowing the car to a controllable speed.

Traction control senses wheel slip (the drive wheels breaking loose and spinning) and reduces engine power or applies the brakes to stop it. Traction control can prevent some types of skids, but it does not provide the same level of protection as ESC. ESC programs have a traction control function, so while ESC can do the same job as traction control, traction control cannot do the same job as ESC.  If the traction control system is detecting wheel slippage, the electronic stability control sensor will pick up on the direction of the slide. If there's a difference between the angle of the steering wheel and the direction the car is sliding, the ESC will work with the traction control system to engage the ABS at the proper wheel (or wheels) and control the throttle to reduce the speed of the vehicle, too.

Now coming to Yaw Control, yawing is a gyroscopic effect on both ships as well as cars. Yawing means spinning or movement of the body about vertical axis or Z-axis. The ESC detects if the vehicle is spinning too far and springs into action and stabilises it.

The above image shows two cases one with ESC and other without.

There are various sensors used in ESC. The most important ones are-

1. Steering Wheel angle sensor- It measures the direction of rotation of the car i.e the direction in which the driver intends to aim the car. If it’s different than the direction that the car is actually travelling, ESC system activates.

2. Wheel Speed sensor- It measures the speed of the wheels. This sensor is attached to each wheel.

3. Yaw Rate sensor or Rotational speed sensor- This sensor determines how much the car is turning. It measures the actual state of the vehicle.

ESC uses a hydraulic modulator, so that all the brakes receive correct brake pressure.

The controlling centre of Electronic Stability Control System is the Electronic Control unit (ECU). Various control units are embedded in it.