This document discusses the components and layout of light vehicle drivelines. It describes the basic components of drivelines including the clutch, transmission, propeller shaft, differentials and drive axles. It also outlines common driveline configurations such as front-wheel drive, rear-wheel drive and four-wheel drive and how power is transferred from the engine to the wheels in each case. Finally, it discusses how universal joints and constant velocity joints are used to allow for angular movement between the rotating driveline components.
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Aim: To show the function and operation of light vehicle driveline and transmission system units and components.
Objective: At the end of this presentation, learners will be able to describe the purpose and operation of light vehicle driveline and transmission units and components.
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Begin with an overview of a standard transmission layout, showing how each component is linked to the other and transmits drive from the engine to the road wheels.
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Show the components of a friction clutch.
Ask learners to name each component of the friction clutch.
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Explain the operating mechanisms of friction clutch systems.
Describe the advantages and disadvantages of cable operated systems. If appropriate take learners into the workshop and show the operating mechanism in action.
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Explain the operating mechanisms of friction clutch systems.
Describe the advantages and disadvantages of hydraulically operated systems. If appropriate take learners into the workshop and show the operating mechanism in action.
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Describe the construction of the clutch friction/drive plate. Show the friction material, cushion springs, torsional springs and centre hub. If possible hand a friction plate around the class so that the different sections can be seen.
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Ask learners the meaning of the word ‘hydraulics’.
Answer – the science of movements of liquids. As liquids are virtually incompressible they can be used to operate mechanisms.
Explain the function of the components found inside a torque converter. Describe how fluid is taken into the impeller, and thrown outwards into the blades of the turbine by centrifugal force. Upon leaving the turbine, fluid strikes the blades of the stator then turns the impeller at speed multiplying torque.
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Ask learners why a car needs a gearbox.
Answer – to multiply the torque or turning effort produced by the engine, so that it is usable under many different driving conditions.
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Show how torque and leverage can be multiplied by using gears.
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Explain the principle of gear ratios – when a small drive gear operates a large driven gear, speed is reduced and torque is multiplied. When a large drive gear operates a small driven gear, speed is increased and torque is reduced.
Ask learners to calculate gear ratios from simple given values.
Describe the function and operation of an idler gear. Explain that this gear has no effect on overall gear ratio, but merely serves to change the direction of rotation and this is how reverse gear is achieved.
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Describe the differences between spur and helical gears and the advantages and disadvantages of each.
Spur gears act directly and create low amounts of drag, which helps improve overall performance, but can make them noisy in operation. A spur-cut gear can be slid in and out of mesh with another spur-cut gear making them useful as a reverse gear idler.
A helical-cut gear has teeth on an angle as shown in the illustration. This means the teeth are not just cut on a diagonal; If they were extended around a cylinder they would actually be shaped like that of a coil spring. Helical-cut gear teeth provide a large surface area making them very strong, less prone to wear and quiet in operation. Unfortunately due to the design and shape of a helical-cut gear they cannot be slid in and out of mesh. This means they have to be used in a gearbox known as a ‘constant-mesh’.
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Explain that when a gearbox is in operation, thrust from the gear teeth is trying to disengage them. Describe how a detent mechanism operates and helps to keep a selected gear in position.
Use a ratchet and socket attachment to show how a detent works (it is similar to how a socket is kept on the end of a ratchet).
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Gears within a gearbox are turning at different speeds; ask learners what would happen if two different gears were selected at the same time.
Answer – the gearbox would lock up and be unable to turn.
Describe the process of using an interlock mechanism to prevent two gears being selected at the same time.
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Describe the operation of a selector hub.
Describe the operation of the synchroniser and why a baulk ring mechanism needs to be added to improve gear selection. State how the grooves on the inside of the baulk ring are designed to cut through the surface tension of the lubrication oil to provide grip in the form of a friction clutch.
If possible, hand a dismantled synchromesh mechanism around the class, so learners are able to see the different parts.
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Describe front-wheel drive layout.
Ask learners to sketch the drive layout and investigate vehicle manufacturers and types of vehicle which use this drive system.
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Describe rear-wheel drive layout.
Ask learners to sketch this drive layout and investigate vehicle manufacturers and types of vehicle which use this drive system.
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Describe four-wheel drive system.
Ask learners to sketch this drive layout and investigate vehicle manufacturers and types of vehicle which use this drive system.
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Explain why universal joints (see next slide) are required when used with prop shafts. Describe the process of cyclic variation (speeding up and slowing down of the prop shaft), if the universal joints at either end of the prop shaft are not synchronised.
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Connect a universal joint from a socket set to a ratchet and socket.
Ask learners to undo a bolt at an angle so they can feel the speeding up and slowing down.
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Explain to learners why constant velocity joints are required on front-wheel drive vehicles, i.e. due to the nature of front suspension movement and steering operation, universal joints would be unsuitable due to the speed variation created.
Ask learners what would happen if the constant velocity drive shaft gaiter becomes split.
Answer – lubrication grease would leak from the constant velocity joint, leading to rapid wear and noise.
Explain the process of checking for noise on a constant velocity joint.
