Here again the picture of an ABS system, this time with the symbols of hydraulics. The best thing to do first is look at the brake circuit 1. Start at the top left of the master cylinder, turn left and take the first branch down. If you follow this line all the way down, you have already detected at least the operation of a wheel brake.

For the other side in front you have to take at the top the first branch to the left. And then all the way down to the wheel brake cylinder. The brake circuit 2 is arranged in mirror image. Taking that into account, the paths are the same. You do not need anymore for normal braking.

Typically, only one valve has appeared on your way to the wheel brake cylinder. So when ABS intervenes, this valve first stops the direct connection. Prerequisite, of course, the system is one hundred percent okay. One speaks here of redundancy, a certain multiple interpretation and mutual checking. As a fallback, the brake simply works as it has always done.

And only when the direct path through the system has been closed, the lower branch becomes interesting. Before that, one should briefly look at the non-return valve connected to the parallel connected shut-off valve. It opens when the pressure on the wheel brake cylinder is greater than that coming from the master cylinder. So if the brake pedal is pulled back, the whole regulation is over. The brake releases immediately.

But if the brake pressure in front of the valve remains high or even rises, then the wheel brake cylinder is in any case isolated from now on. The controller can decide if it should be lowered. If so, it opens the corresponding valve 4 and the brake fluid flows into the room 5 with the spring-loaded piston. The wheel brake cylinder is relieved, the wheel brake is released.

The entire cycle on a wheel is finished when the valve 4 is closed again and the valve 3 opened. If the pressure from the wheel brake cylinder still proves to be too high, the whole regulation circuit starts from the beginning, up to 10 times a second (!). At the same time, the recirculation pump runs on each cycle and empties the room 5. Here may an excessively high pressure develop under no circumstances, because then the relief of the wheel brake cylinder would no longer be possible.

Finally, allow a consideration that concerns the limits of the system. After all, yes here occurs a pump against the foot force of the driver. Let's assume a man this time and a particularly strong one. Workshop people know about extreme foot forces with partly bent pedals. What happens when such a muscleman meets an ABS system in extreme cases? We can only state that somewhere between 180 and 200 bar, a limit has to be reached.

After all, the control unit gets the measurements of the pressure transmitter 7 and also notices that the pressure at the sensor 6 is not lower. To suspect it would switch to normal brake and go into the emergency mode, but we could not try it yet. We simply lacked the muscleman.