汽车设计第四版吉林大学8〔Automobile design fourth edition, Jilin University, 8〕Automobile designFourth EditionMain contents of this chapter:* overview;* analysis of brake system structure;* determination of the main parameters of the brake;* design and calculation of brakes;* design and calculation of brake actuating mechanism;* braking force regulating mechanism;* the main structural elements of the brake.The first section is an overviewFirst, the basic functions of the brake system:To make the car drop speed until the parking in the appropriate deceleration;In the downhill, the vehicle speed to maintain the stability of the appropriate;To make reliable cars parked in situ or ramp.Two. Brake assembly: brake and brake drive.Three the design of the brake system shall meet the following main requirements:1) have enough braking efficiency.2) reliable work.3) when braking at any speed, the car should not lose control and direction stability.The first section is over!Analysis of structural scheme of second brakeDrum brakeMajor difference:The number and position of the fulcrum are different.The form and quantity of the opening device are different.When braking, is there any interaction between two pieces of hoof?.Brake force: the force or torque that a brake produces at the input pressure or force of a unit.Brake efficiency factor: the ratio of the friction force (M / R) to the input force F0 at the action radius R of the brake drum or brake disc2. one way, two collar, hoof typeStructure features: two pieces of shoes each have their own fixed fulcrum, and two fixed fulcrum at two different ends of the hoof.Advantages and disadvantages: this system is used when the car is moving forward and brakingThe brake efficiency of the actuator is quite high; two can be used separatelyThe independent circuit drives two shoe pieces separately; easy to adjustThe clearance between the entire shoe and the brake drum, on the two shoeThe unit pressure is equal, so that the degree of wear is close,Same life. Unidirectional double collar brake systemThe stability of dynamic performance is stronger than that of force increasing brake.When reversing brake, the braking efficiency drops obviously. Compared with the leading shoe brake, the structure is slightly complicated due to the addition of a wheel cylinder.Application: suitable for forward braking, front axle, axle load and adhesion greater than the rear axle, while reversing brake, the reverse of the front wheel of the car. It is not used in the rear wheel, but also because of the two central cylinder wheels that are mutually symmetrical, it is difficult to attach the parking brake drive mechanism.3. two-way, double collar, hoof typeConstruction features: two shoe floats, with each of the two pistons with two rounds of cylinder to expand the hoof.Advantages and disadvantages: whether forward or backward braking,The two pieces of the brake shoe are always on the hoof, soThe braking efficiency is quite high and remains unchanged. Because of the brakeThere are two wheel cylinders, so it is suitable for double circuit driveInstitution. When a pipe fails, the brake changes toCollar brake. In addition, the two-way double collar hoofThe two brake shoes of the type brake have equal unit pressure, so the wearing degree is similar and the service life is the same. Because of two wheel cylinders, the two way twin collar brake structure is complex, and the gap between the brake shoe and the brake drum is difficult to adjust.Application: this kind of brake is widely used. For rear wheels, a central parking brake is required.4. pairs from hoof typeStructure features: two shoes each have a fixed fulcrum, andThe two fixed pivot points are arranged at different ends of the two hoof plates, and each of them is provided with one endThe two cylinder of the piston opens the hoof piece.Advantages and disadvantages: the brake performance is the best, but the brakeLowest efficiency.Applications: rarely used.5. one-way reinforcement typeConstruction features: two hoof pads have only one fixed fulcrum, two hoofThe lower end is connected with each other by a push rod,The brake has only one wheelThe cylinder is used to produce thrust and expand the hoof.Advantages and disadvantages: the car forward, braking, brake performance is very high.Compared with the bidirectional force brake, the structure is simple. But the brake performance stability is quite poor. Reversing the brake, the two hoof is from the hoof, so that the brake performance is very low. Because of the unequal unit pressure between the two pieces of shoes, the uneven wear and tear of the hoof and the different life span. This brake has only one wheel cylinder, so it is not suitable for the dual loop drive me。