Contents: Concerns ↓ Disable the undisableable ↓ How to brake? ↓ Surprises of coverage ↓ Don't be afraid to turn the steering…↓
The wheel speed sensor is located in the hub.
The purpose of ABS is simple to formulate – it prevents the wheels from locking when braking. Is the brake pedal pressed too hard? No problem – the electronics, comparing the signals from the speed sensors on each wheel, determine the moment of sudden wheel stop and, opening the electromagnetic valve, releases excess pressure from the brake line into a special hydraulic accumulator. The brake pads are released, the wheel rotation is restored, the valve again connects the line to the pressure that the driver's right foot creates with the help of the brake booster. And if this pressure is still too high, the cycle is repeated again and again. In the cabin, the activation of ABS is manifested by a crackling sound when the actuator unit is operating and by jolts on the brake pedal, more or less noticeable depending on the design of the system. In fact, ABS imitates the actions of an experienced driver who, on a slippery road, avoids wheel locking by using intermittent braking. But ABS does this with a frequency and accuracy that is inaccessible to humans – up to 15 times per second. As a result, ABS should not only provide the car with a minimum braking distance, but also make it obey the steering wheel – after all, the wheels roll and perceive lateral force as much as the tires' grip on the surface allows. And this is the main advantage of ABS. After all, if the wheels lock, the car slides uncontrollably straight, even when the steering wheel is turned all the way.
Concerns
It would seem that everything is already clear. Anti-lock braking systems are recognized by the entire civilized automotive world and have already become standard equipment on cars, starting with the middle class. But often there are voices of dissatisfaction.
"No electronics can compare with an experienced driver," some say. "Give me the same car without ABS, and I'll stop sooner!"
Others do not like the fact that ABS, interfering with the braking process, completely excludes human participation. No matter how hard you press the pedal, it will be pushed back with an unpleasant vibration. The car brakes itself, there is no way to influence the deceleration process, and with ABS it is very difficult to calculate the braking distance and predict where the car will stop. All you can do is wait... Unbearable for a driver accustomed to being in control of the situation!
And others point to rally drivers. They say, it's not for nothing that they fear ABS like the plague! And they, the athletes, know better...
Disable the undisableable
In order to put everything in its place, we committed a technological crime. We found a plug under the hood that fits the ABS actuator unit and pulled it out of its socket, causing the yellow ABS indicator light to light up and the red brake light in the instrument cluster to blink alarmingly. This is how we deactivated the non-disconnectable anti-lock braking system. The tests were conducted according to the following scheme. We selected four main exercises: braking on a straight line - on a uniform and mixed surface (mixed), on a turn and while going around an obstacle (that is, when performing a rearrangement maneuver). The Passat was equipped with recording equipment that accurately measured speed and braking distance. And our expert testers were behind the wheel. However, some of the exercises were also offered to ordinary drivers of various qualifications - from a novice car enthusiast to an experienced professional. Everyone could practice before the test runs, get used to the car and "zero in" for the next maneuver.
Each exercise was performed in two series. First, they did more than ten runs with the ABS working, then they switched off the system, and the car again hurried to the track marked with bright markers for the next maneuver.
How to brake?
With an anti-lock braking system, everything is simple: if you want to get the maximum possible deceleration, then press the pedal to the floor without thinking twice. But how do you brake without ABS?
At first we tried to do everything "according to theory" - brake on the verge of wheel locking. It doesn't work! The overly sensitive Volkswagen pedal doesn't allow us to accurately dose the braking force - and we make mistakes, both in one direction and the other. And this is in a calm environment. But try to do this in an extreme situation, when an accident is imminent!
Then we used a tried and tested method – intermittent braking.
And for comparison, we tried, without further ado, to brake "to the floor", with the wheels locked. What is the difference? On a straight line, the main difference is in directional stability. This was especially evident when braking on a mixed road. There was wet asphalt under the left wheels, and a snowy shoulder under the right ones.
With ABS on, the car initially starts to pull towards the road with better grip, but the electronics work properly: the Passat instantly levels out and then brakes straight ahead, requiring virtually no steering adjustments. During intermittent braking without ABS, the driver had to steer a little, and the braking distance turned out to be longer.
But with the wheels fully locked, the car braked almost as effectively as with ABS. But at the same time, it turned sharply to the left at a dangerous angle - up to 40°! The advantage of ABS here is obvious.
Surprises of coverage
Ice can be smooth as a mirror or rough like the surface of sandpaper. Snow can be dense, rolled out, loose, stuck together, frozen...
What are we getting at? Well, each surface has its own specifics, and after our tests we cannot give a clear answer to the question that interests everyone - under what conditions will the braking distance with ABS be shorter than without it!
There are many options. For example, when, during repeated stops on the same straight line, the wheels of our car rolled a track of rough ice crushed by spikes, the braking distance with ABS and without it with locked wheels turned out to be almost the same. It is not for nothing that our athletes say that the most "sticky" surface is not asphalt, but an ice track striped with "nails". And on the snow - what a surprise! - the car with ABS stopped a little later. The thing is that on the snow surface the coefficient of adhesion turned out to be lower than on rough ice - the spikes do not work so effectively here. For ABS, apparently, this turned out to be disadvantageous. But during "normal" intermittent braking (press-release-press) during the period of wheel locking a snow roller is formed in front of them, which helps the car slow down more intensively. The operation of ABS prevents the wheel from locking - and the roller does not form.
Don't be afraid to turn the steering wheel!
Imagine a very real situation: a truck in front of you suddenly skids on a slippery turn and turns across the road. Or another: a car jumps out of a side drive onto a narrow street right in front of your nose and blocks your lane, leaving only the oncoming traffic free.
On the wave of adrenaline rushing into the blood, the driver will panic, reflexively, and with all his might press the brake. The wheels will lock. And with locked wheels, the car will fly out of the turn in the first situation, and in the second, it will crash into an obstacle. Because without ABS, only intermittent braking will help avoid an accident, and here the driver is required not only to have outstanding composure and endurance, but also extraordinary skill.
And here is our example. The most experienced expert had to call upon all his skills to repeat and even slightly surpass the results of the same maneuvers with ABS, alternating strictly dosed pushes on the brake pedal and precise steering wheel work.
But so what? Even the tester needed to make more than ten sighting runs for this, and in a real situation there will be only one chance! And the electronics will work reliably and for the good.
When braking on a turn, the driver's task was generally very simple: press the brake, turn the steering wheel - and the car, clearly tracking the specified trajectory, slows down intensively. This is available to anyone. It is only important to remember that during braking with ABS, the car can and should be controlled. Do not numbly grip the steering wheel, but boldly use it!
When going around an obstacle (we braked while performing a rearrangement maneuver familiar to our readers) the situation was like this. When the speed of the maneuver approached the maximum, after going around the obstacle, the rear axle began to skid. This happened both with and without ABS. But using ABS, it was possible to reduce the speed so much that the skid was not so sharp and deep. And the braking distance after going around was 15 meters shorter. Significantly!
True, in order to stay on the road, when correcting a skid, it was necessary to release the brake pedal even with the anti-lock system working. Why? We do not argue, ABS leaves the ability to change the trajectory during emergency braking, and not slide in a straight line with locked wheels. But when fighting a skid, the operation of ABS greatly reduces the effectiveness of corrective actions with the steering wheel. And even those drivers whose cars are equipped with ABS, in such situations need to be ready to release the brake pedal for a moment, consciously refusing the services of electronics.
The material is reprinted from an online resource www.ToyotaMan.ru