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Transmission System

 Introduction

The transmission helps to transmit power from the engine to the wheels. It consists of gears, shafts, and other electrical connections. It is composed of systems shown in Figure 2.1:

Figure shows arrangement of components like engine, clutch, transmission, drive shaft, and rear axle drive with dirrerential.
Figure 2.1 Arrangement of components.

2.2 Clutch

This part is used to engage and disengage the engine from drive. It allows the driver to control the power flow between the engine and transmission or transaxle operating by the friction principle.

Figure shows six motor vehicles with different engine arrangements; wherein two diagrams have engine arrangements labelled.
Figure 2.2 Engine arrangements.
Figure, which exhibits principle of clutch, shows a clutch, a driving shaft, and a driven shaft.
Figure 2.3 Principle of clutch.

Need for Clutch

  • Allows gradual engagement of two rotating plates
  • Provides positive linkage capable of transmitting maximum engine torque
  • Rapidly separates engine from drive train and reengages engine to drive train
  • Provides force between pressure plate and flywheel to load clutch disk

Transmission of torque depends on:

  • Size
  • Engagement time
  • Free pedal play
  • Rate of Heat loss
  • Easy in operation
  • Balancing of mass
  • Lightness

Power flow from one unit to another can be controlled with a drive disc and a driven disc.

Thus, the clutch can transmit twice as much torque

For multi-disk clutch T = (n–1)µWR

Where,

W – Spring force (N)

Figure shows a clutch assembly, from engine to transmission transaxle, consisting of a flywheel, a clutch disc, a spring, a pressure plate and its cover.
Figure 2.4 Clutch assembly.
Figure shows clutch analysis which identifies a flywheel, a driven-plate, a thrust spring, a pressure-plate and a gearbox primary shaft.
Figure 2.5 Clutch analysis.
Figure shows a model of a clutch identifying external radius, internal radius, and mean radius.
Figure 2.6 Model of clutch.

r2 – External radius (m)
r1 – Internal radius of (m)
n – Number of contacting pairs
µ – Coefficient of friction

Mean radius is given as:

Tangential force is given by F = µW

Friction torque is given as T = F × R = ½ µW (r1 + r2)

Since there are n pairs so:

If N is speed of the clutch then the power transmitted is given as:

Example 4.5

A single-plate clutch of 0.15 m effective diameter is lined with material of coefficient of friction 0.35. If the total spring force is 2.5 kN, Calculate:

  1. the torque transmitted
  2. the power transmitted at 3000 rev/min.

Solution

Total spring force, W             = 2.5 kN = 2500 N

Effective radius, R                 = 0.075 m

Pairs of contact surfaces, n   = 2

Coefficient of friction µ          = 0.35

Rotational speed, N               = 3000 rev/min

  1. Torque transmitted,
                                              
  2. Power transmitted
                                             

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