Question

1. Make a search to introduce the design view point for the subject of brakes and friction clutches.

Answer 1

Solution:

Since brakes and friction clutches are a complete subject in themselves, I will try to give you a Design View Point of the primitive brake and clutches.

Design View Point: It is the design considerations and the necessary equation required to design a system completely. Let us start with Brakes.

Design View Point of Brakes:

Def: A brake is defined as a mechanical device, which is used to absorb the energy possessed by a moving system or mechanism by means of friction. The primary purpose of the brake is to slow down or completely stop the motion of a moving system, such as a rotating drum, machine or vehicle.

Brakes are classified into the following three groups:

(i) Mechanical brakes,

(ii) Hydraulic and pneumatic brakes,

(iii)Electrical brakes,

Brake capacity depends upon the following three factors:

• (i) The unit pressure between braking surfaces
• (ii) The contacting area of braking surface
• (iii) The radius of the brake drum
• (iv) The coefficient of friction
• (v) The ability of the brake to dissipate heat that is equivalent to the energy being absorbed

Design Methodology:

The first step in the design of a mechanical brake is to determine the braking-torque capacity for the given application. The braking-torque depends upon the amount of energy absorbed by the brake. When a mechanical system of mass m moving with a velocity v1 is slowed down to the velocity v2 during the period of braking, the kinetic energy absorbed by the brake is given by

In certain applications like hoists, the brake absorbs the potential energy released by the moving weight during the braking period. When a body of mass m falls through a distance h, the potential energy absorbed by the brake during the braking period is given by

PE = mgh

Depending upon the type of application, the total energy absorbed by the brake is determined by adding the respective quantities. This energy is equated to the work done by the brake.

Therefore,

E = Mtq

where

• · E = total energy absorbed by the brake (J)
• · Mt = braking-torque (N-m)
• · q = angle through which the brake drum rotates during the braking period (rad)

Design View Point of Friction Clutches:

The clutch is a mechanical device, which is used to connect or disconnect the source of power from the remaining parts of the power transmission system at the will of the operator. An automotive clutch can permit the engine to run without driving the car.

Clutches are classified into the following fourgroups:

(i) Positive contact Clutches

(ii) Friction Clutches

(iii) Electromagnetic Clutches

(iv) Fluid Clutches and Couplings

A single plate friction clutch consisting of two flanges is shown in Fig. One flange is rigidly keyed to the driving shaft, while the other is connected to the driven shaft by means of splines

Fig. : Single Plate Clutch

TORQUE TRANSMITTING CAPACITY:

• D = outer diameter of friction disk (mm)
• d = inner diameter of friction disk (mm)
• p = intensity of pressure at radius r (N/mm2)
• P = total operating force (N)
• Mt = torque transmitted by the clutch (N-mm)

The intensity of pressure p at radius r may be constant or may be variable.

Consider an elemental ring of radius r and radial thickness dr For this ring, elemental area = (2pr dr)

• elemental axial force = p(2pr dr) = 2p(pr dr)
• elemental friction force = mp(2pr dr)
• elemental friction torque = mp(2pr dr) r = 2pm (pr2 dr)

Integrating the expression, we get

Comments:

• Two theories are used to obtain the torque capacity of the clutch. They are called uniform pressure theory and uniform wear theory.
• Feel free to ask for any help in the comment section.
• Please rate and up-vote my work.

All the best!