In the car brake drum, generally only one wheel cylinder, in the brake wheel cylinder from the total pump after the hydraulic force, both ends of the wheel cylinder will be at the same time to the left and right brake shoe hoof end,the force is the same. But because the wheel is rotating, the brake drum acts on the brake shoe pressure asymmetry, resulting in self-force or the role of self-restraint. Therefore, the industry will increase their own side of the brake hoof known as the collar hoof, self-restraint side of the brake shoe is called from the hoof, collar hoof friction torque is from the hoof of 2 to 2.5 times, two brake hoof The degree of wear of the friction lining is not the same.
In order to maintain good braking efficiency, there is an optimum clearance between the brake shoe and the brake drum. As the friction lining wears, the gap between the brake shoe and the brake drum increases, requiring a mechanism to adjust the gap. The past drum brake gap needs to be manually adjusted to adjust the gap with a stopper. After the improvement of the car drum brakes are used automatically adjust the way, friction linings will automatically adjust the gap with the brake drum. When the clearance increases, when the amount of brake shoe is out of a certain range, the adjustment gap mechanism pulls the adjusting lever (pawl) to the position where the next tooth is engaged with the adjustment tooth, thereby increasing the length of the connecting rod so that the brake shoe Position displacement, return to normal clearance.
Car drum brakes are generally used for rear wheels (front wheel disc brakes). In addition to the relatively low cost of the drum brakes, there is a benefit that it is easy to combine with the parking (parking) brake, all cars with a rear wheel as a drum brake, the parking brake is also combined on the rear wheel brake The This is a mechanical system that is completely separate from the car brake hydraulic system: the use of hand-operated joystick or parking pedal (American car) to tighten the steel cable, control the drum brakes to expand the brake shoe To the parking brake effect, making the car will not slip; release the steel cable, the return spring so that the brake shoe to restore the original position, the braking force disappears.