2020 High quality Tow Axle - How to adjust the brake of automatic adjusting arm – MBP

The automatic adjusting arm will be designed according to the different models of the axle, and different brake clearance values will be preset. If the clearance exceeds the limit value during normal use, the brake adjusting arm will adjust the clearance value to a gear when the brake action is returned. The one-way clutch mechanism inside the drive will adjust the clearance value to a gear, so that the brake clearance can be kept within the correct range.

In the process of truck driving, frequent braking will lead to constant wear of brake shoes and brake drums, resulting in the gap between them gradually becoming larger; eventually, the stroke of brake chamber push rod will become longer, the thrust will drop, resulting in brake lag and brake force reduction. In order to ensure the safety of driving, it is necessary to ensure that there is a proper fit clearance between the brake shoe and the brake drum. The automatic adjusting arm is used to adjust and control the clearance between the two.

Brake clearance automatic adjusting arm is also called “automatic clearance adjusting arm” or “automatic adjusting arm”. In recent years, the manufacturers of trucks, buses and trailers in Europe, America and other regions have taken it as the standard configuration of the whole vehicle. Let’s introduce how to loosen the auto adjusting arm.

With the use of the auto adjustment arm, the vehicle is driven with the following characteristics:
1. Ensure that the wheels have constant brake clearance, and the brake is safe and reliable;
2. The stroke of push rod of brake pump is short, and the brake is quick and reliable;
3. Before braking, the push rod of the wheel cylinder is always in the initial position to ensure the best braking torque;
4. The braking effect of all wheels is consistent and stable;
5. The consumption of compressed air is reduced and the service life of air compressor, brake cylinder and other parts in compressed air system is prolonged;
6. The material consumption is reduced and the service life of brake components is prolonged;
7. It is easy to install and use, reduces the number of manual maintenance, and improves the economic benefit;
8. The adjusting mechanism is enclosed in the shell and well protected, so as to avoid damp, dirt and collision.

The important parts of the automatic adjusting arm are as follows:
1. Shell
2. Worm gear and worm
3. One way clutch assembly (composed of gear, square steel spring and inner gear sleeve)
4. Rack, control ring, helical compression spring

Design idea
The function of the automatic adjusting arm should be to accurately record the increase of the clearance caused by the wear of the friction lining, and accurately adjust the brake clearance to the normal working range.

Angular travel during braking
When braking, the angular stroke of the adjusting arm can be divided into three parts
1. Clearance angle, corresponding to the normal clearance between brake drum and friction lining;
2. The excessive clearance angle corresponds to the increased clearance due to the wear of friction lining;
3. The elastic angle corresponds to the elasticity caused by the brake drum, friction lining, brake cylinder and brake system power transmission.

When the clearance is adjusted automatically, the elastic angle in the angular stroke should be avoided as far as possible. If we do not distinguish between the excessive clearance angle and the elastic angle, we should compensate them at any time, which will lead to over adjustment, resulting in “dragging” or even “locking”.

Working process of automatic adjusting arm
At the beginning of braking, the adjusting arm drives the camshaft to rotate the clearance angle and excess clearance angle, and accurately records the wear. At this time, the cam angular stroke is in the clearance area, which is characterized by little change of braking torque.
When the brake continues, the cam angular travel enters the elastic deformation zone, and the braking torque rises sharply until the car stops. Release the pedal, brake return, brake torque drop, cam angular travel back to the clearance area. According to the excessive clearance recorded during braking, the internal adjustment mechanism drives the camshaft to rotate through a certain angle through the worm gear, so as to complete an adjustment.

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