In utility vehicles, a braking pressure controller that limits the braking pressure (electronic brake force limiter, EBL) is used in particular to distribute the desired braking effect of a brake system or a driver to the vehicle axles in a suitable manner, so that the vehicle is decelerated according to a driver's wishes or a target vehicle deceleration specified by a driver and at the same time remains stable depending on the driving situation. This is because in the event of hard braking, i.e. in the case of a high target vehicle deceleration, the weight of the vehicle is displaced to the front axle, so that the rear wheels on the rear axle are pressed less strongly onto the ground, whereby locking of the rear wheels is assisted.
By limiting the braking pressure on wheel brakes of the rear wheels, premature locking of the rear wheels during braking can be avoided. The limiting of the braking pressure can be carried out depending on an axle loading, because in the case of vehicles that are heavily loaded more braking force can be applied to the road by means of the rear axle than with unladen vehicles, in which excessive braking of the rear wheels amplifies the effect described above still further; the tendency to locking of the rear wheels increases.
For measuring the load in the case of spring suspension vehicles, a mechanical displacement sensor can be provided that is deflected to a greater or lesser extent depending on the load. In the case of pneumatic suspension vehicles, a pressure sensor that measures the pressure in a supporting bellows can be used for this. Depending on the load-dependent measurement signal, the weight can be concluded and limiting of the braking pressure can be carried out depending thereon.
In vehicles without such a mechanical displacement sensor or pressure sensor, in which no direct measurement of the load is provided, electronic braking pressure limiting can be provided. In this case, control of the braking pressure on the wheel brakes of the rear wheels is carried out depending on a difference between a wheel revolution rate of the front wheels and the wheel revolution rate of the rear wheels, or depending on the difference between a brake slip of the front wheels and the brake slip of the rear wheels. Because the difference in the wheel revolution rates or the brake slips is load-dependent, the braking pressure is distributed accordingly to the vehicle axles to prevent the wheels of the rear axle from prematurely showing a tendency to lock and in order to decelerate the vehicle as desired.
DE 10 2008 009 948 B3 discloses an electronic braking pressure controller, with which the braking pressure on the wheel brakes is controlled depending on an axle load sensor and the target vehicle deceleration. In the event of a failure of the axle load sensor, control of the braking pressure is carried out depending on the difference of the brake slips on the vehicle axles, i.e. depending on a measured actual differential slip.
DE 10 2011 118 130 B4 also discloses an electronic braking pressure controller, with which the braking forces are distributed depending on a determined actual differential slip or a determined speed difference of the wheels on the vehicle axles in order to decelerate the vehicle as desired. During this, the braking pressure on the wheel brakes of the rear wheels is limited if the actual differential slip exceeds a target differential slip. In this case, the target differential slip is a function of the target vehicle deceleration, wherein the target differential slip increases at higher target vehicle decelerations in order to guarantee a more sensitive transition to ABS control, which is more likely to intervene in this case rather than in the case of a constant target brake slip. It is disadvantageous in this case that an increase in the target differential slip in the case of a high target vehicle deceleration causes early actuation of the ABS controller, whereby the braking behavior is less smooth and less safe, because ABS control must intervene sooner.
In DE 10 2006 045 317 A1, an electronic braking force distribution is disclosed, with which the braking forces are distributed to the vehicle axles as a function of the vehicle deceleration instead of as a function of the differential slip. For this purpose, it is provided to measure an actual vehicle deceleration and to control the braking pressure on the rear axle on reaching a maximum deceleration, i.e. a defined threshold value for the actual vehicle deceleration. In this case, the maximum deceleration is defined in such a way that from said value the rear wheels tend to lock more than the front wheels. Thus, a tendency to locking of the rear wheels is matched to the tendency to locking of the front wheels. After exceeding the maximum deceleration, it is provided to build up the braking pressure on the wheel brakes of the rear wheels in a controlled manner, wherein the gradient is smaller than the gradient of the braking pressure that is building up on the wheel brakes of the front wheels. As a result, the braking pressure on the wheel brakes of the rear axle tracks the braking pressure on the wheel brakes of the front wheels, i.e. in order to remain lower by a defined value. It is disadvantageous in this case that above the maximum deceleration the braking behavior acts in an unsettled manner overall owing to the adjustment and is perceived as unpleasant.