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Electronic Stability Control

Last Update:

09/06/2016

Introduction

When a driver applies brakes to his speeding vehicles the wheels can get locked and if the surface is slippery, the car can skid. Under these circumstances it is electronic stability control (ESC) that comes to a driver’s rescue by selectively applying brakes to each wheel to bring the vehicle back under control. By incorporating this technology into modern braking systems there are fewer fatal accidents and loss of lives.

History

Faster vehicles, higher traffic on roads and development of ABS and EBD gave an impetus to further control a vehicle’s braking capability. Studies showed that while ABS and EBD were effective, they were not intelligent enough to provide stability a vehicle during the braking process, especially on wet surfaces or when the driver was turning the vehicle.

  • Traction control systems were first developed around 1983 and were used in the Crown models from Toyota. These units applied selective braking to each individual wheel besides controlling the throttle to improve stability but it did not help in steering.
  • Mitsubishi was, perhaps, the first auto manufacturer to introduce a traction control system in 1990, the unit helped a driver steer even while brakes were being applied such as when cornering. The onboard computer senses the speed while turning and regulates the throttle even as it applies brakes to maintain traction.
  • Other car manufacturers such as BMW and general Motors worked on various versions employing the same basic principles that enabled better stability control in their cars such as the i3 BMW and Opel of GM.
  • Ford developed its own version in 2000 incorporating roll stability control, fitted to the Volvo XC90 in 2003.
  • Full-fledged system was first seen in the Mercedes Benz S600 coupe in 1995 followed by BMW in their 7 Series.
  • Audi’s A8 and A6 gained ESP sometime around 1997.
  • Volvo S80 was fitted with a dynamic stability and traction control unit with similar functions sometime in 1998.
  • Extensive on road tests showed that ESC significantly improved safety and this system became standard on most modern cars.

 

Evolution

Auto manufacturers pursued their own program of developing systems that controlled throttle and braking of individual wheels.

  • The simplest earliest systems had a simple throttle control and individual wheel braking in order to maintain braking.
  • Later evolutions included skid and traction control, enabling the driver to safely negotiate bends and corners with the use of intelligent computerized algorithms that matched database with the car’s actual on road performance to adjust traction and braking. These early units did incorporate control of steering angle, individual wheel braking and throttle position but did not factor in yaw, the sideways movement of a vehicle during turning.
  • Advanced units fitted on the Cadillac Eldorado featured steering, traction control, engine control and variable road sensing suspension.
  • Another variation from Ford included these features in addition to roll stability control.

 

Main Parts

The ESC unit is integrated with the car’s computer and braking unit. Its main parts comprise of:

  • Wheel speed sensors fitted to each wheel
  • Steering angle sensor
  • Yaw rate sensor
  • Lateral acceleration sensor
  • Control modules
  • Pressure generator
  • Hydraulic unit
  • Hydraulic Pump
  • Master cylinder
  • Brakes

All these work in conjunction with the ABS and EBD units through the central computer. Sophisticated units may have electronic differential lock, engine drag torque control, over boost hydraulic booster, hydraulic brake assist and brake disc wiper unit.

 

How It Works

  • The ESC system is always up and running in the background, monitoring the wheels and the vehicle’s movement. It kicks in when sensors feed data that match with a set of predefined parameters.
  • A driver may take evasive steering action that affects traction. The result is either spinning out or over-steering of the rear of the vehicle, or plowing out of the front also known as under-steering, both of them dangerous.
  • The system detects that the car is changing direction at a faster rate and kicks in by applying front brakes to prevent vehicle going off the road or crashing into buildings or into other vehicles.
  • In the latter situation, the computer detects that the car is not changing direction quickly enough and applies rear brakes to compensate for under-steering and keeps the vehicle on the road in its path.
  • The steering angle sensor and the yaw sensor are responsible for detecting these changes in direction and momentum that cause over-steer or under-steer as well as deceleration.
  • The steering sensor delivers output to the ABS control module, which also takes inputs from the wheel speed sensors, senses the difference and applies brakes at the front or rear.
  • The yaw rate sensor delivers information about the direction in which the car is headed and the steering angle sensor delivers information about the direction of the front wheel.  
  • The ABS unit is responsible for detecting the difference in the rotational speeds between left and right wheels during a turn and also checks traction.
  • The car’s computer factors in all these discrepancies while issuing commands to take suitable action.
  • While applying brakes, the central control unit also reduces throttle to reduce engine output. It is not just errors made while turning that are sensed; the unit also senses the road surface on which the vehicle is being driven in order to implement corrective action.
  • The main outcomes are that over-steering and under-steering are prevented; car is stabilized during evasive action taken by driver, traction improves as does handling.

The action is extremely fast and response is quicker within split-second, than most human drivers are capable of, resulting in prevention of accidents.

 

Effectiveness

  • Today’s ESC systems are sophisticated and respond much faster than a normal driver can. Studies have shown that ESC systems in cars reduce chances of fatal accidents by 25%.
  • ESC is quite effective at preventing skidding and overturning that cause crashes and result in serious accidents and works effectively even in wet conditions or where roads are far from perfect. In the USA alone over 7000 lives are saved as a result of the cars having ESC systems.
  • Most major manufacturers have their own proprietary versions of the ESC system.
  • However, the ESC system can add additional cost of the vehicle, something not all car owners may not be willing to invest in.
  • The system is also quite complex to which a driver may take some time getting used to it.

 

Maintain

  • Today’s ESC systems have in-built fault diagnosis systems that alert the drivers of a failure. Diagnostics are usually carried out in well equipped service stations using scan tools used by trained technicians.
  • Normal drivers will hardly be able to repair the unit. At best, they can check that sensors are clean and free of dust and that the hydraulic lines are without leaks. Mechanical checks are possible on the pump and the brake shoes.

In some countries use of ESC is mandatory on all vehicles. ESC makes the difference between safety and accidents, completing the line up of ABS and EBD.

 

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