Drum brakes are acting friction brakes at the brake pads on a cylindrical surface ( the drum). Upon actuation of the brake, the brake pad is usually pressed against the inside of the rotating drum. In automobiles, drum brakes are increasingly being replaced by the disc brake. For less powerful cars they are still used on the rear axle; heavy-duty trucks and trailers, the drum brake is still state of the art.
In the rotating brake drum, the two on the brake anchor plate movably supported by the brake shoes are pressed against a corresponding device from the inside. The pressing of the brake shoes can be directly mechanically via a camshaft, a spreading wedge or a wheel cylinder.
The first internal shoe drum brake was installed in 1900 in the 35 hp Mercedes automobile. The drum brakes were fitted by Wilhelm Maybach to the rear wheels, the brake pads were water-cooled.
" Maybach was apparently patented neither the drum brakes and the water cooling so that the drum brakes traversed in the shortest time in the automotive industry. "
Louis Renault in 1902 applied for patents on various types of internal shoe brakes, and eventually took over the simplex brake into series production. On a motorcycle, the internal shoe brake was only in the 1920s with the prior art.
- Due to the internal reinforcement only relatively low actuation forces are required. The measure of the internal reinforcement of the brake characteristic value C *. He is depending on the version between 2.0 and 5.0. This eliminates the need for light vehicles, to a brake booster.
- The brake shoes are well protected against corrosion (water, salts, dust ) and from dust by the closed case. For SUVs and construction truck drum brakes are used mostly still.
- Due to the closed design means less wear settles on the rim.
- Drum brakes are more durable than disc brakes.
- With drum brakes, the brake pad change compared with the disc brake is more complex.
- Drum brakes are compared to disc brakes more sensitive to the coefficient of friction. This resulted in the usual until the 1970s cars with drum brakes on the front axle, often at a slant stall or even prevent the vehicle during braking.
- With the same braking power is - in truck - a drum brake harder than a corresponding disc brake.
- The heat dissipation in high performance brakes is comparatively poor.
The simplex brake is the simplest and most widely used type of the drum brake. They are found from bicycles to heavy trucks. She has a leading brake shoe and a trailing brake shoe. This means that both in forward and in reverse, the brake effect is the same. The spread of the brake shoes is effected by a central wheel cylinder, while the brake shoes are mounted to a pivot point on the other side. For heavy trucks and trailers, the operation via an S - cam done. In smaller version, the simplex brake can be found as a parking brake in many cars. The brake coefficient C * is 2.0.
→ Main article: Duplex brake
In duplex brake each brake shoe has its own actuating means on one side. Thus both jaws are accrued and thus self-reinforcing. The brake coefficient C * is when driving forward 3.0 and is significantly lower when reversing. The advantage over the simplex brake is an approximately 50% higher braking effect at the same actuation force. Their disadvantage is the larger manufacturing and maintenance costs and the fact that the braking effect is substantially lower when reversing. Duplex brakes were used mainly before the general introduction of disc brakes on the front axle heavy cars and light commercial vehicles as well as motorcycles.
Duo - duplex brake
The duo - duplex brake, in contrast to duplex two brake wheel cylinder, working in both directions, ie two accumulating ( self-reinforcing ) brake shoes in forward and reverse. She looks so equally in both forward and reverse. Due to the high internal gain, it is easy to operate but not sensitive to dose. This elaborate design is rarely used since the 1960s. The brake coefficient C * is in forward and in reverse direction 3.0.
The highest internal gain, the servo brake. It has like the simplex brake on a wheel cylinder, however, are at the lower pivot point, the brake shoes mounted floating. With a pushpin the supporting force of the primary jaw ( flooding ) is transferred to the secondary shoe ( drip) and caused a self-amplification of both brake shoes in a direction of travel. When reversing the self-boosting is not ensured.
This results in a very large difference in the braking effect between forward and reverse. Due to the high internal gain of the servo - brake, it requires the lowest operating forces, but is hard to dose and very sensitive to Reibwertschankungen the brake pads. The brake coefficient C * is when driving forward 5.0 and is significantly lower when reversing.
The duo-servo brake is initially identical to the Servo brake. The disadvantage of the lack of braking during reverse travel is compensated for in that the pressure bolt can be supported, depending on the direction of movement on a bearing. This two accumulating ( self-reinforcing ) brake shoes arise in both directions.
They are used for light and medium duty trucks as well as a parking brake ( cup wheel ) for cars with four brake discs ( on the wheel flange together with the disc brakes on the rear axle ). The brake coefficient C * is in forward and in reverse direction 5.0. This is the highest possible self- reinforcing.
Drum brakes is also available in the reverse order: the grind brake shoes from the outside on a drum. This drum brakes can be found nowadays in engineering, especially in conveyor systems for braking carriers, for example, in mining and in the elevator, and are usually attached to the input or output shaft of gear. This type of drum brake was also in the 1920s, the automobile familiar as a brake on the gearbox or on the propeller shaft, and thus indirectly on the axis drive the rear axle and decelerate without then specially wheel brakes were installed. This system has also been used for a long time as a parking brake.