Mechanism

What is the ESP system in cars

What does ESP stand for in a car?

ESP in cars stands for Electronic Stability Program, which is considered one of the most important safety systems which exists in cars.It is alternatively known as Electronic Stability Control (or ESC for short). Other alternative terms sometimes used include Electronic Stabilisation Program, Vehicle Dynamic Control (VDC), Vehicle Stability Assist (VSA) and Dynamic Stability Control (DSC).

How ESP works.

ESP is basically a term that refers to a collection of driving safety systems which all work towards keeping a car on the road in a controlled manner. These systems include traction control (TCS) and anti-lock brakes (ABS).

When you’re driving a car, your control inputs, which includes use of the wheel and pedals, is monitored by sensors which send data to a central computer. This computer compares what you’re doing with how the car is responding.

So if, for example, you are steering right but the car is continuing to move straight ahead, the computer can instruct the onboard safety systems to assist with this issue. If your braking hard and there’s a risk of locking up the wheels due to low grip on the road, the computer can instruct the anti-lock braking system to kick in.

Another way it can help is if you accelerate hard on a wet or icy road and your driven wheels begin to spin. ESP can instruct the traction control to control acceleration in a way that will keep the car moving without any spinning of the wheels.

The whole process of the ESP detecting trouble with your car and using other safety systems to assist with driving happens in mere fractions of a second.

Cars with ESP.

Because of legal reasons, ESP is a standard safety feature of every single vehicle you can find within the new car market.

Having ESP in cars has been a mandatory requirement under EU law since 2014. Older road cars which do not have ESP are still allowed on the road. However, past research has shown that having ESP on a car can reduce the chance of being in a fatal crash by 25 per cent.

Electronic stability control vs traction control.

Some motorists incorrectly believe that the stability control system is either exactly the same as traction control or you can only have one or the other in a car. In reality, the vast majority of cars around include both electronic stability control and traction control.

Because of their respective roles, traction control is nowadays usually considered a secondary function of stability control. While traction control focuses on one specific goal, ESP manages numerous systems at once to help keep drivers safe behind the wheel during trickier driving situations.

ESP warning light.

ESP has a dedicated dashboard warning light, which is a yellow car with two skid marks beneath it, as pictured above. This warning light will flash if the car is at the edge of grip and the system activates, which is particularly likely if you drive on a slippery surface. If, however, the light comes on and stays on, it either indicates that the ESP system has a fault or has been turned off, so you’ll need to get the system checked at a garage or simply turn it back on via the button usually found in your centre console.

Technical specifications.

Components of the Electronic Stability Program ESP.

1. Hydraulic unit with attached control unit.

The hydraulic unit executes the commands from the control unit and regulates, via solenoid valves, the pressure in the wheel brakes. The hydraulic modulator is the hydraulic connection between the master cylinder and the wheel cylinders. It is located in the engine compartment. The control unit takes over the electrical and electronic tasks as well as all control functions of the system.

2. Wheel-speed sensor.

The control unit uses the signals from the wheel-speed sensors to compute the speed of the wheels. Two different operating principles are used: passive and active wheel-speed sensors (Inductive and Hall-effect sensors). Both measure the wheel speed in a contact-free way via magnetic fields. Nowadays active sensors are mostly employed. They can identify both the direction of rotation and the standstill of a wheel.

3. Steering-angle sensor.

The task of the steering-angle sensor is to measure the position of the steering wheel by determining the steering angle. From the steering angle, the vehicle speed and the desired braking pressure or the position of the accelerator pedal, the driving intention of the driver is calculated (desired state).

4. Yaw-rate and lateral-acceleration sensor.

A yaw-rate sensor registers all the movements of the vehicle around its vertical axis. In combination with the integrated lateral-acceleration sensor, the status of the vehicle (actual state) can be determined and compared with the driver’s intention.

5. Communication with engine management.

Via the data bus, the ESP control unit is able to communicate with the engine control unit. In this way, the engine torque can be reduced if the driver accelerates too much in certain driving situations. Similarly, it can compensate for excessive slip of the driven wheels provoked by the engine drag torque.

ESP® value-added functions.

The fundamental task of ESP® is to prevent skidding. The possibilities offered by the ESP®, however, go beyond this. As ESP® can build up braking pressure independently of the brake-pedal position, a series of so-called value-added functions can be realized with ESP®. These provide additional driving safety and allow the driver to experience enhanced driving comfort and driving agility.

A range of these value-added functions are already available on the market today. Others will follow to meet the growing demand for safety and comfort. Depending on the vehicle manufacturer and the vehicle type, the ESP® value-added functions are available either as optional or as standard features to the already fitted ESP.

1.Hill Hold Control.

Hill starts are not always easy, particularly when the vehicle is heavily loaded. The driver has to operate brake, accelerator and clutch pedals very fast in order to prevent the vehicle from accidentally rolling backwards. The ESP® Hill Hold Control facilitates a hill start by keeping the brakes applied for about two more seconds after the driver has already released the brake pedal. The driver has enough time for changing from brake to accelerator pedal without using the handbrake. The vehicle drives off comfortably and without rolling backwards.

2. Hydraulic Brake Assist.

In critical driving situations, drivers often brake too hesitantly. The Hydraulic Brake Assist identifies an imminent emergency braking situation by monitoring the pressure on the brake pedal as well as the pressure gradient. If the driver does not brake strongly enough, the Hydraulic Brake Assist increases the brake force to a maximum. The stopping distance is then reduced.

3. Load Adaptive Control.

The volume and position of a commercial vehicle’s load can vary considerably from trip to trip. The load has an important impact on the braking, the traction, the cornering ability and the roll-over tendency. The ESP® Load Adaptive Control identifies changes in the vehicle mass and center of gravity along the longitudinal axis of the vehicle and adapts the interventions of the safety systems ABS, TCS and ESP® to the vehicle load. In this way, Load Adaptive Control optimizes braking effectiveness, traction and stability. In addition, it reduces the risk of roll over via the improved utilization of Roll Over Mitigation and minimizes brake-pad wear by optimizing the distribution of braking forces.

4. Roll Over Mitigation.

The loading and the higher center of gravity of light commercial vehicles make them reach a critical lateral acceleration faster than passenger cars. The risk of roll over is thus considerably higher. The Roll Over Mitigation function constantly monitors the vehicle behavior with the help of the ESP® sensors and intervenes when the vehicle threatens to roll over. Roll Over Mitigation brakes individual wheels and reduces the driving torque to prevent roll over and to stabilize the vehicle.

5. Tire Pressure Monitoring System.

A loss of tire pressure leads to a deviant rotation speed of the wheel concerned. By comparing the wheel speeds a potential tire deflation is detected. This value-added function permits tire pressure monitoring without the use of pressure sensors in the tires.

6. Trailer Sway Mitigation.

Trailers sway easily. A minor steering error, a gust of wind or a bump on the road surface can cause a critical increase in the swaying movement. The counter steering and the acceleration of the towing vehicle make the critical situation even worse. With the help of the ESP® sensors, Trailer Sway Mitigation identifies these swaying movements of the trailer and intervenes by braking individual wheels of the towing vehicle. The vehicle and trailer are slowed down to an uncritical speed and stabilized.

Reference:

Stephen Goldasz (17-2-2017), “WHAT IS ESP IN CARS?”، www.carkeys.co.uk

Hugo Griffiths. Andy Goodwin (27-9-2017), “What is ESP on a car?”، www.carbuyer.co.uk

Charlie Constant (15-12-2012), “ESP: Electronic Stability Program”، www.car-engineer.com

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