Know your vehicle’s safety electronics
Ever wondered what the difference is between ABS, ESP, VDC, VSC and ETC? Let 4x4 Professor explain which one does what and how it keeps you safe.
Vehicles, even most bakkies, are full of electronics to make its handling safer and better. But what do all the abbreviations on the buttons stand for and how do these electronics work exactly? Vehicles generally have three types of electronics that help with its handling: anti-lock braking system or ABS brakes, stability control, and traction control. Let’s see how it works.
ABS brakes
Not everyone know this but locked tyres during hard braking take longer to bring a vehicle to a standstill than turning tyres. It’s even worse when the road is wet or slippery. Also, a vehicle can’t turn if the tyres are locked. So if you had to brake hard and simultaneously had to swerve, the vehicle would merely plough along with screeching tyres. The first anti-lock or ABS brakes were commonly used in the 1950s in airplanes – where it helped to prevent the airplanes’ brakes from locking during landings. In the 1970s a few vehicle manufacturers started experimenting with ABS brakes, but it was Mercedes-Benz that in 1978 launched the first production vehicle with anti-lock brakes. The system’s electronics were developed by Bosch. An ABS system uses four wheel sensors (one for each wheel), an hydraulic pump, four hydraulic valves, and an electronic control unit. The control unit constantly monitors each wheel’s rotational speed, and when it detects that one or more wheels turn at a speed that doesn’t correspond with the vehicle’s speed, it activates a hydraulic valve for that wheel’s brake line so that braking power is reduced. So that individual
wheel can start turning again. As soon as that happens, brake power is restored to the wheel – until it detects the wheel locking again, after which the process is simply repeated until the vehicle comes to a standstill or you release the brake pedal. The electronic control unit monitors this process up to 15 times per second! Note: In off-road conditions, where you drive slower, ABS is not a good thing and consequently a vehicle’s ABS braking is automatically deactivated when you choose low range. Vehicles like the VW Amarok 8-speed automatic, which doesn’t have low range, has an Off Road setting during which the ABS makes special provision for off-road conditions.
Stability control
Stability control has various names, depending on the manufacturer. It ranges from ESP (Electronic Stability Programme), ESC (Electronic Stability Control), VSC (Vehicle Stability Control) to VDC (Vehicle Dynamic Control). It also makes use of your ABS system’s sensors and was introduced in the 1990s, also by Mercedes-Benz. According to the Insurance Institute for Highway Safety in the USA, it can prevent up to one third of all fatal accidents. Stability control uses six main components: wheel speed sensors, a control unit, a steering angle sensor, a yaw-rate sensor, an accelerometer, and a hydraulic control unit. The latter is the same unit that forms part of a vehicle’s ABS brakes, therefore a vehicle with stability control only needs three extra components – which makes you wonder why manufacturers don’t fit this to all vehicles. But how does stability control work in practise? Well, imagine you’re driving at 100km/h and a pedestrian walks into the road. You quickly swerve to the right to avoid him. Suddenly a range of things happen in your vehicle’s “brain”. Your vehicle angle sensor determines in which direction your vehicle is pointing. The steering angle sensor determines in which direction your front wheels are pointing. The accelerometer determines whether your vehicle has started slipping, and the wheel speed sensors determine how fast the wheels are turning. Because you swerved to the right, your vehicle will initially understeer because there isn’t enough weight on your front wheels. Your vehicle will therefore not turn as sharply as it should. The control module will notice the difference between your steering inputs and the vehicle’s position and then send a signal to the hydraulic control unit to brake the right-hand rear wheel. That will help the vehicle turn sharper to the right. If necessary, the control unit will also cut engine power to help get the vehicle under control. If a vehicle oversteers, the control unit will ensure that the outside front wheel is braked – and it will probably also cut engine power – to get the vehicle under control.
Traction control
Traction control works the same as stability control, and some vehicles use this technology to make up for the absence of a diff lock. When your vehicle encounters mud or uneven terrain, it sometimes happens that one tyre starts to spin while the other one stands still because a diff lock always sends power to the wheel with the least amount of resistance. It’s here where the traction control takes charge by braking the spinning wheel. Not only does it help to again get a foothold, but power is also sent to the non-spinning wheel. Note: If you have an off-road vehicle with traction control instead of diff locks, it’s important that you don’t modulate the accelerator to regain traction once the wheels start spinning, like you would with a conventional 4x4. If you start modulating the accelerator you will only confuse the onboard computer and it’ll take longer for the system to figure out exactly how much which tyres need to be slowed down. So keep your accelerator at a steady position and see how the traction control starts doing its thing after a second or three – it’s different from vehicle to vehicle and situation to situation – and sorts out spinning wheels to help you overcome an obstacle.