Automotive design fourth edition Jilin University 8Car design The fourth edition The main content of this chapter: * overview; The analysis of the structure of the brake system; The determination of the main parameters of the brake; The design and calculation of the brakes; The design and calculation of the brake driving mechanism; * power regulating mechanism; * the main structural elements of a brake. Section 1 overview The basic functions of the brake system: To drive the car at a reasonable speed and slow down until it stops. To keep the car in the right speed while it is moving downhill. The car is reliably parked in place or on the ramp. The composition of brake gear: brake and brake actuator. Design brake system should meet the following main requirements: 1) sufficient braking effect. 2) work is reliable. 3) when braking at any speed, the car should not lose its maneuverability and directional stability. The first section ends! Section 2 structural plan analysis of brakes A drum brake Major differences: The number and position of the fixed branch of the shoe plate are different. The form of an open device is different from the quantity. There is no interaction between the two pieces of hooves when brake. Brake efficiency: the force or torque that the brake forces on the unit input pressure or force. Brake efficiency factor: the ratio of friction (M/R) to the input force F0 on the radius R of the brake drum or brake disc Single to double hoofed Structural features: two pieces of hooves each have their own fixed pivot points, and the two fixed branches are located at different ends of the two hoofs. Pros and cons: when the car moves forward, the system is made The actuators braking efficiency is quite high; You can use two Separate circuits that drive two hoofs. Easy to adjust Between the whole shoe and the brake drum, the two hoofs The unit pressure is equal, the degree of wear is similar, Life expectancy is the same. The system of a single double leading shoe brake Dynamic performance stability, only better than the strength brake. When the reverse brake, the braking effect is obviously decreased. Compared with the leading shoe brake, the structure is slightly more complicated due to the extra cylinder. Application: it is applicable to the front axle and the attached force of the front shaft when the forward braking is greater than the rear axle, while the reverse braking is the opposite of the front wheel. It is not used for the rear wheel, but also because of the two intercentric cylinder, which is difficult to attach to the brake drive. Two-way double hooves Structural features: two hoofs float and two cylinders with two pistons to open their hoofs. Pros and cons: whether forward or backward, The two pieces of the brake are always the hoof, so The braking efficiency is quite high and constant. Because of the brake There are two cylinders in the inside, so it is suitable for the double loop drive Institutions. When a casing circuit fails, the brake changes to Take the shoe brake. In addition, two-way double hoofs The unit pressure on the two pieces of the brake is equal, so the degree of wear is similar and the life is the same. It is the fault of the double leading shoe brake, which is complicated in structure, and the gap adjustment between the hoof and brake drum. Application: this brake is widely used. For the rear wheels, the central stationary brake is required. 4. Double from hoof type Structural features: two hoofs each have a fixed fulcrum, and Two fixed branches are located at different ends of the two hoofs, and each has one The pistons two cylinders open the hoofs. Pros and cons: brake efficiency is best, but brake Effectiveness of the lowest. Application: rarely used. Unit 5 Structural features: two hoofs have only one fixed branch and two hoofs The lower ends are connected to each other,The brake has only one wheel The cylinder is used to generate thrust and open hoofs. Pros and cons: the brakes are very efficient when the car is moving forward. Compared with the bidirectional force brake, the structure is simple. But the brake efficiency is quite poor. In reverse braking, both hoofs are from the hoof, making the brake less effective. Because of the pressure of the unit on the two hoofs, it causes the pieces of the hoof to wear out uneven and the life span is different. This brake has only one cylinder, so it is not suitable for the dual circuit driving mechanism, and it is difficult to adjust the gap between the hoofs because of the linkage between the two parts of the shoe. Application: a small minority of commercial vehicles use it as a front wheel brake. Two ways of increasing force Structure features: two to have a brake shoe end without using Shared protection at the same time, a wheel cylinder below the fulcrum, built-in two piston to drive at the same time open two shoe, the push rod under the two shoe connected into one. After the advantages and disadvantage