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Giáo trình chế tạo ôtô - Phần 25

Tham khảo tài liệu 'giáo trình chế tạo ôtô - phần 25', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | CONTENTS c H A p T E R 25 Brakes 1. Introduction. 2. Energy Absorbed by a Brake. 3. Heat to be Dissipated during Braking. 4. Materials for Brake Lining. 5. Types of Brakes. 6. Single Block or Shoe Brake. 7. Pivoted Block or Shoe Brake. 8. Double Block or Shoe Brake. 9. Simple Band Brake. 10. Differential Band Brake. 11. Band and Block Brake. 12. Internal Expanding Brake. 25.1 Introduction A brake is a device by means of which artificial frictional resistance is applied to a moving machine member in order to retard or stop the motion of a machine. In the process of performing this function the brake absorbs either kinetic energy of the moving member or potential energy given up by objects being lowered by hoists elevators etc. The energy absorbed by brakes is dissipated in the form of heat. This heat is dissipated in the surrounding air or water which is circulated through the passages in the brake drum so that excessive heating of the brake lining does not take place. The design or capacity of a brake depends upon the following factors 1. The unit pressure between the braking surfaces 2. The coefficient of friction between the braking surfaces 3. The peripheral velocity of the brake drum 917 CONTENTS 918 A Textbook of Machine Design 4. The projected area of the friction surfaces and 5. The ability of the brake to dissipate heat equivalent to the energy being absorbed. The major functional difference between a clutch and a brake is that a clutch is used to keep the driving and driven member moving together whereas brakes are used to stop a moving member or to control its speed. 25.2 Energy Absorbed by a Brake The energy absorbed by a brake depends upon the type of motion of the moving body. The motion of a body may be either pure translation or pure rotation or a combination of both translation and rotation. The energy corresponding to these motions is kinetic energy. Let us consider these motions as follows 1. When the motion of the body is pure translation. .