 Brake testing 2
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Why does this brake tester have six small rollers on the one side? Because it not only allows him to test vehicles with four-wheel drive quite unrestrictedly, but also very little preparation is required. If you only have one roller
for the front and rear axle, you obviously have to align them depending on the wheelbase.
If you test such a vehicle on a test bench for single-axle powered cars, the vehicle's own electronics can interfere. In the best case scenario, you can simply switch off the all-wheel drive. However, if it is permanent or
switches on automatically, it becomes problematic.
In the previous chapter we showed a plate brake tester. Of course, there are at least two input variables that cannot be reproduced exactly: the speed and the moment or strength of the pedal pressure. Some newer parking
brakes are also harder to check or cannot be checked at all.
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| Danger threatens with all-wheel drive. |
So let's stick with the cases in which the connection between the front and rear axle cannot be separated exactly. Certain Torsen differentials can be excluded from these because they have a type of freewheel that breaks the
connection when the drive torque is initiated via the drive wheels. However, with the switchable ones, the connection may have to be disconnected via the diagnostic interface.
It also pays off that the manufacturers already have made connections that are too strong and cannot be separated a taboo because of the ESP regulations. After all, rigid connections can usually always be detached. What
remains are the friction clutches with, in extreme cases, up to 75 percent locking effect.
The risk is that a defect occurs both on the test bench and in the vehicle's own drive system. Imagine that the TÜV or a workshop could be held responsible for this. Therefore, information about the testing options is
necessary for each individual vehicle, which should then be updated regularly.
One method if you only have a single-axle test bench available for an all-wheel drive test is to have the wheels on the one axle rotate in exactly the opposite direction to each other. Of course, only the forward rotating wheel
should be measured, so the test should be carried out twice.
The effect to be achieved is that the two directions of rotation in the differential work in such a way that no rotational movement is transmitted to the drive train. Of course, no limited-slip differential is allowed to have any effect
here. Everything outside of one axis 'doesn't notice' that it is being tested.
Sometimes you can even change the speed of the two wheels relative to each other in such a way that there is as little influence as possible from the differential gear, so to speak that it runs in the middle of its clearance. It's
unbelievable what's possible between 0 and 5 km/h.
Unfortunately for the workshops, there will probably still be an adjustment to the test benches, namely to be able to measure the degree of recuperation. However, this often only starts at speeds of more than 5 km/h, so
extensive changes will be necessary here, and not just in terms of limit values.
The rolls above show how broad the area of application for such test benches is. We have already shown such a test bench for two-wheelers. Below you can see an even more specific task area. The wheels also have
different coatings that ensure that the wheels do not lock too early and you cannot test the full braking effect.
| This largely covers the mechanical-hydraulic part of the hydraulic brake. |
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