Are drum brakes really outdated?

  Recently, there has been an uproar in the rights protection of female car owners in Shanghai, China. Experts from all walks of life have become extremely interested in Tesla’s braking system, trying to find out the cause of the "brake failure". Many of them are from Tsinghua University. The doctoral supervisor stood up and expressed his views.

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  In order to find out the problem of Tesla's "brake failure", Gang brother also began to research and analyze the data published by Tesla and the views of various great gods. In this process, Chong Ge discovered an interesting phenomenon: Most electric cars on the market currently use disc brakes instead of drum brakes. Is the braking performance of disc brakes really better than that of drum brakes? If Tesla uses drum brakes, will the result be different?


  # Combining the characteristics of drum brakes and disc brakes, Cungge believes that the effect of drum brakes on electric vehicles will be better than disc brakes:


  1. Drum brakes have a better braking effect than disc brakes. Drum brakes are mainly composed of a brake oil pump, pistons, brake pads and drum chambers. When the driver steps on the brake pedal, the high-pressure brake fluid of the brake cylinder will push the brake fluid to push the piston, and the two half-moon-shaped brake shoes The sheet exerts a force to press against the inner wall of the drum, and the brake drum is prevented from rotating by friction to achieve a braking effect.

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  Because the drum brake is designed with a rotating structure, it has an internal self-increasing effect. This part of the pressure will be transmitted to the brake pads as the wheels rotate, and greater pressure will be generated between the brake pads and the brake disc. The larger contact area can achieve a higher braking effect than disc brakes. This is why most large commercial vehicles still use drum brakes instead of disc brakes.


  Second, the drum brake has a closed structure and has a good anti-rust ability. However, due to the closed structure of the drum brake, the heat formed during the braking process is difficult to release into the atmosphere, causing the heat to accumulate inside, causing the friction material/brake pad performance to decline significantly, resulting in a decrease in braking force. Therefore, many cars are produced The business began to gradually abandon drum brakes and began to turn to disc brakes. However, this shortcoming is perfectly solved by the kinetic energy recovery function of electric vehicles.


  Since the kinetic energy recovery application of electric vehicles can greatly reduce the braking temperature, the thermal decay problem of drum brakes can be fundamentally solved. It is worth mentioning that the closed structure of drum brakes makes them have better anti-corrosion capabilities than disc brakes. For example, in a rainy day with high humidity, after a disc brake is parked outside for one night, obvious rust spots will appear on the surface of the brake disc, which is prone to problems such as insufficient braking force.

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  Through the above comparison, the braking effect of drum brakes is better than that of disc brakes. It is worth mentioning that, in addition to better braking effect than disc brakes, drum brakes are also more in line with the current concept of energy saving and emission reduction. Compared with disc brakes, drum brakes can collect 80% of the suspended particulate emissions (PM10) generated during braking in the brakes, reducing dust emissions. Many people will ask, since the braking effect of drum brakes is better than that of disc brakes, why do most manufacturers prefer disc brakes rather than drum brakes?


  The reason is actually very simple, because with the reform of automobile electrification, in addition to the addition of new concepts such as batteries and electronic architecture, the functional requirements of traditional hardware are also quietly changing. Many hardware like drum brakes have been formed in the hearts of consumers. The inherent impression is that disc brakes are better than drum brakes.


  Although from a technical point of view, the use of drum brakes in electric vehicles is completely okay, but it does not mean that it is feasible in the market. If you want to make drum brakes with better parking effect widely used in the market again, it is indispensable to break the inherent impression of drum brakes at this stage.


  #What are the classifications of brakes?


  The following is the classification of brakes:


  1. Drum brake. Two semi-circular brake pads are installed in the wheel hub. The brake pads are pushed by the "lever principle" to make the brake pads contact the inner surface of the wheel drum and cause friction. Many people call it "brake pot";

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  2. The drum brake can use lower oil pressure and has the function of automatic braking. It has low technical difficulty and low cost; but the disadvantages are also obvious. The dongfeng truck diameter of the brake drum becomes larger after heating, the brake heat attenuation effect is obvious, and the structure is complicated. Brake clearance requires higher maintenance level;


  3. Disc brake, two brake pads are controlled by brake calipers to clamp the brake disc on the wheel, the working principle is simple and direct;

  4. The disc brake has excellent heat dissipation effect, less heat decay, and rapid braking response. It can meet the needs of high-frequency braking such as ABS and ESP. Its structure is simple and convenient for maintenance; the contact area of the disc brake pad and the brake disc is small, in order to achieve A certain braking effect intelligently increases the oil pressure or increases the diameter of the brake pads.


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