I believe that many readers are familiar with the two terms drum brake and disc brake, but tracing back to the origin, what are the differences between them and what are their respective advantages? Today, the editor will help you analyze it.
Disc brakes and drum brakes, the debate over the advantages and disadvantages of braking effects has been going on for a long time. Many people say that the main performance of disc brakes is better than traditional drum brakes. In fact, this is not absolute and needs to be viewed rationally.
Drum brake
Working principle animation
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Development history
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In 1916, Americans invented drum brakes, which rely on the brake shoes installed on the axle to cooperate with the wheel brake drum to complete the braking effect. This brake has greater braking force than the early bicycle brakes (including tire type, rim type, pulley type, clamp type, etc.), and the braking is smoother and more reliable. At that time, almost all American motorcycles used this brake. The drum brake used in modern motorcycles was developed on this basis.
Braking principle
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When the drum brake is applied, the external force exerts a force on the two half-moon-shaped brake shoes, pressing the inner wall of the drum chamber, and the friction force prevents the brake drum from rotating to achieve the braking effect.
The working principle can be vividly described by a cup. The brake drum is like a cup. When you put five fingers into the rotating cup, the fingers are the brake pads. As long as you spread your five fingers outward and rub the inner wall of the cup, the cup will stop rotating.
Disc brake
Working principle animation
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Development history
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Although drum brakes were promoted and used earlier, disc brakes appeared 3 years earlier than drum brakes.
In 1913, a British-made "Douglas" motorcycle participating in the French Grand Prix was eye-catchingly equipped with a set of mechanically operated disc brakes. This is the world's first motorcycle to use disc brakes.
In 1969, Honda of Japan took the lead in using hydraulically operated disc brakes on Honda 750 motorcycles. Since then, all road motorcycle manufacturers around the world have used this advanced hydraulic disc brake.
Braking principle
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Disc brake, the brake disc is made of cast iron or alloy steel and fixed on the wheel, rotating with the wheel. The caliper is fixed on the front shock absorber or rear swing arm, and the two friction plates on the brake caliper are installed on both sides of the brake disc. The hydraulic pressure pushes the friction plate to rub against the brake disc, just like clamping the rotating plate with pliers, achieving the effect of deceleration and braking.
Working principle of automobile disc brake
Part I: caliper and brake disc
Part II: brake master cylinder and vacuum booster
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Pros and cons comparison
1
Braking force
In terms of braking force, the brake force of drum brake is much greater than that of disc brake, not because the drum brake technology is more advanced, but because of its inherent structural characteristics.
In the drum brake system, there is a metal object that looks like a drum. This is the core component of the drum brake, and the drum brake is named after it.
Two sets of brake shoes are set in the brake drum. When we step on the brake pedal, the driver's force will be transmitted to the brake shoes, pushing the semi-circular U-shaped brake shoes on both sides, making them expand and squeeze outward, and pressing the brake shoes tightly against the brake drum. At this time, there will be strong friction between the brake drum and the brake shoes, thus achieving a braking effect.
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Disc brakes are different from drum brakes, which are wrapped inside. We can see the brake parts of disc brakes intuitively from the appearance. They will move with the movement of the wheels and keep synchronization with the wheels, which is equivalent to the brake drum in the drum brake.
When we squeeze the brake, the hydraulic device transmits this force to the brake caliper, and makes the brake caliper tightly clamp the brake disc, and the friction force generated by the friction between the brake disc and the brake caliper is used to achieve the purpose of braking.
This brake device cannot generate amplification force by itself, so relying on human strength alone is not enough to obtain effective braking force. It must be assisted by hydraulic devices to generate sufficient braking force.
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2
Heat dissipation performance
However, disc brakes are superior to drum brakes in many aspects, otherwise they would not be used in a large number of new models at present, but these benefits are not reflected in braking force, but in other aspects.
Drum brakes are in a closed space, so their heat dissipation is not very good, and a lot of heat will accumulate during braking.
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Brake shoes and wheel drums are more likely to undergo extremely complex deformation under the influence of high temperature, which is prone to brake decay and tremor, causing a decrease in braking efficiency.
3
Drainage performance
Drainage is another feature that disc brakes are superior to drum brakes. When water enters the brake system, the impact on braking performance is obvious. If the water cannot be discharged in time, the braking performance will be greatly reduced.
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From the structure, it can be seen that the closed design of drum brakes is obviously not as conducive to drainage as disc brakes.
4
Economic cost
Drum brakes were first used in brake systems, and the manufacturing technology is relatively more mature, so the cost is due to disc brakes.
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The quality of the brake disc of disc brake needs to be improved. The cost of the brake caliper, piston, brake pad and other components cannot be compared with that of drum brake.
5
Others
In rural areas with many muddy roads, high-speed driving is not common. The braking force of drum brake is more suitable. At the same time, the advantage of drum brake, a brake system with better sealing, in dealing with harsh environments is reflected, and muddy roads are extremely lethal to disc brake pads.
The braking response speed of drum brake is not linear and accurate enough, so it is difficult to equip the ABS system based on drum brake. Disc brake can be equipped with ABS to achieve uniform, fast and effective ABS braking.
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Comparison between drum brake and disc brake
Drum brake
Disc brake
Advantages:
1. When obtaining the same braking torque, the diameter of the brake drum of the drum brake device can be much smaller than that of the brake disc of the disc brake
2. Low manufacturing cost
Advantages: 1. Disc brake has better heat dissipation than drum brake, and it is less likely to cause brake failure due to brake decay when the brake is stepped on continuously.
2. The change in the size of the brake disc after heating does not increase the travel of the brake pedal.
3. The disc brake system responds quickly and can perform high-frequency braking actions, so it is more in line with the needs of the ABS system.
4. Disc brakes do not have the automatic braking function of drum brakes, so the braking force of the left and right wheels is relatively even.
5. Because the brake disc has better drainage, it can reduce the situation of poor braking caused by water or mud.
6. Compared with drum brakes, disc brakes have a simple structure and are easy to repair.
Disadvantages:
1. The diameter of the drum brake drum will increase after heating, causing the travel of the brake pedal to increase, which is prone to the situation where the brake response is not as expected. Therefore, when driving a vehicle with drum brakes, try to avoid continuous braking to cause the brake pads to produce thermal decay due to high temperature.
2. The brake system responds slowly, and the braking force is difficult to control, which is not conducive to high-frequency braking actions.
Disadvantages: 1. Because there is no automatic braking effect of drum brakes, the braking force of disc brakes is lower than that of drum brakes.
2. The friction area between the brake pads and brake discs of disc brakes is smaller than that of drum brakes, so the braking force is also relatively small.
3. In order to improve the above-mentioned disadvantages of disc brakes, a larger pedal force or oil pressure is required. Therefore, a brake disc with a larger diameter must be used, or the oil pressure of the brake system must be increased to increase the braking force.
4. The handbrake device is not easy to install. Some models with disc brakes on the rear wheels have a set of drum brake handbrake mechanisms for this purpose.
5. The brake pads are more worn and the replacement frequency may be higher
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Conclusion
Vehicles on the market generally use disc brakes on the front wheels and drum brakes on the rear wheels, which is the so-called "front disc and rear drum" configuration. The reason why disc brakes are not used on the rear wheels is because of cost issues. Many large-displacement motorcycles have front and rear disc brakes.
Generally speaking, when braking, the center of gravity will shift forward, and the weight on the rear wheels will become less and less. The braking force of the vehicle comes more from the front wheels. Even if it is a front and rear disc brake, the front wheel disc brake is obviously thicker than the rear wheel because it has to bear more braking force.
So on a car with a low mass, there is nothing wrong with the rear wheel drum brake, as long as you pay attention to the braking technique, control the speed and excessive use of the brakes.
Front and rear disc brakes are not omnipotent, and drum brakes are not useless. No matter how powerful the brakes are, they are not as safe as careful driving.
