A B C D E F G H I J K L M N O P Q R S T U V W X Y Z|
|Rear axle load in kg||Front Brake pressure in bar||Rear brake pressure in bar||Air suspension pressure in bar|
A truck differs from a motor car not only in that it can carry large loads. In trucks, the weight difference between a full and an empty vehicle is also distinctly higher. If one disregards the tipping equipment and other special truck constructions, the maximum pay load can be about as high as the tare weight. Whereas in trailers, the pay load can amount to double, the motor car can carry not more than about half. This requires special precautions as far as the braking system is concerned.If the rear axle is, during partial braking in an unloaded state, also braked with the same pressure as the front axle, the rear wheels could lock and break out, making the vehicle uncontrollable. The load dependent brake power control provides for decreased pressure depending on the amount of load. On the other hand, the pressure on the front axle can, under certain loading conditions, exceed that of the rear axle.
In the above chart the brake pressures of the front- and rear axle are shown depending on the rear-axle load. In addition, the pressures rising proportionately to the rear-axle load are transferred to the rear air-suspension bellows. When checking the brake assembly, with the engine running, or when filling with external air, there is always enough pressure in the system. Manometers are connected to the respective operational brake circuits of both front- and rear axle. By means of long flexible tubes, their reading is possible in the driver's cab while pressing the brake pedal. The column second from the left, shows the pressures which must be reached on the front axle by purposefully pressing the brake pedal. The third column now shows the pressures which must be reached in each case on the rear axle. A cautious tolerance of ± 0.2 bar can be shown, however, manufacturer's data varying from this, must of course, be rigidly adhered to.
So, what it's all about is, a specific inspection of the automatic, dependent on load, brake pressure control valve (ALB). Should leaf-spring-suspension exist instead of air suspension, the last column should actually contain the spring compression in millimetres. The above figure shows the pivot point down to the axle. The sleeve with spring, below on the right allows the top of the bar, directly on the regulator, to be turned in both directions by using simple tools, for example, cable ties. On the centre of rotation of the bar it is indicated by which amount this is to be turned and thus, simulating a greater load. The length from the centre of rotation of this bar is checked exactly before each inspection of the brake pressure allocation. The position, in an unloaded state, can be adjusted on the grommet on the left. After that, the further relationships, between front- and rear-axle pressure under various loading conditions, can be determined.