Service Advisor Customer Service Skills SERVICE ADVISOR

INDUCTION

Technical for Non-technical - Transmissions

Objectives of this session O

bje

ctives This section aims to deal with the whole idea of getting the power from your engine to the wheels in order to move your car forward.

During this session we will discuss some aspects of basic vehicle technology. In order to fully understand some of the latest technologies and features, it is important to understand where some of these features may have originated from. In addition, some technologies are just as current today as they were decades ago. It is important for you to be able to visualise the feature or component you are talking about with a customer.

Objectives O

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ctives

Once you have completed this section, you will be able to:

•Describe transmissions.

•Explain how a clutch and torque convertor works.

•Understand how a manual gearbox, automatic gearbox and CVT transmission works.

Why a Gearbox? D

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In a nutshell - why a gearbox?

From the section on engines you know that the pistons drive the main crank in the engine so that it spins. Idling, it spins around 900rpm. At speed it can be anything up to 7,500rpm. You can't simply connect a set of wheels to the end of the crank because if the speed is too high and too variable, you'd need to stall the engine every time you wanted to stand still.

Instead you need to reduce the RPM of the crank down to a usable value. This is known as gearing down - the mechanical process of using interlocking gears to reduce the number of revolutions of something that is spinning.

Visual of a Manual Gearbox

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In the next pages we will discuss a manual gearbox and the sections of the gearbox illustrated below.

Manual Gearbox

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x Having looked at the image below, you'll see the internals of a generic gearbox. You can see the helical gears meshing with each other. The lower shaft in this image is called the layshaft - it's the one connected to the clutch - the one driven directly by the engine. The output shaft is the upper shaft in this image. Once you are done with this section, you'll be able to look at this image and say with some authority,

"Ah yes, that's a 5-speed manual gearbox!".

Manual Gearbox

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So how can you tell? Well look at the output shaft. You can see 5 helical gears and 3 sets of selector forks. At the most basic level, that tells you this is a 5-speed box (note the example has no reverse gear). In the next two pages we describe how this gearbox works.

Manual Gearbox

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How does it work?

With the clutch engaged (we will discuss how a clutch works in the section on clutches after this section), the layshaft is always turning. All the helical gears on the layshaft are permanently attached to it so they all turn at the same rate. They mesh with a series of gears on the output shaft that are mounted on slip rings so they actually spin around the output shaft without turning it.

Manual Gearbox

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Look closely at the selector forks; you'll see they are slipped around a series of collars with teeth on the inside. Those are the dog gears and the teeth are the dog teeth. The dog gears are mounted to the output shaft on a splined section which allows them to slide back and forth. When you move the gear stick, a series of mechanical pushrod connections move the various selector forks, sliding the dog gears back and forth.

Manual Gearbox

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How do we engage gears?

When the gearstick is moved to select fourth gear, the selector fork slides backwards. This slides the dog gear backwards on the splined shaft and the dog teeth engage with the teeth on the front of the helical fourth gear. This locks it to the dog gear which itself is locked to the output shaft with the splines. When the clutch is let out and the engine drives the layshaft, all the gears turn as before but now the second helical gear is locked to the output shaft and voila - fourth gear!

The Clutch Th

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Before the gearbox - the clutch:

So now you have a basic idea of how gearing works there's a second item in your transmission that you need to understand - the clutch.

The Clutch Th

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Before the gearbox - the clutch:

The clutch is what enables you to change gears, and sit at traffic lights without stopping the engine. You need a clutch to disengage the engine from the crank, which is spinning all the time. You need some way to disconnect this constantly-spinning crank from the gearbox, both to allow you to stand still as well as to allow you to change gears.

The Clutch Th

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Before the gearbox - the clutch:

The clutch is composed of three basic elements; the flywheel, the pressure plate and the clutch plate(s). The flywheel is attached to the end of the main crank and the clutch plates are attached to the gearbox layshaft using a spline.

The Clutch Th

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So how does all of this work?

So as the engine turns, the flywheel, clutch cover, diaphragm springs and pressure plate are all spinning together.

The clutch pedal is connected either mechanically or hydraulically to a fork mechanism which loops around the throw-out bearing. When you press on the clutch, the fork pushes on the throw-out bearing and it slides along the layshaft putting pressure on the innermost edges of the diaphragm springs. These in turn pivot on their pivot points against the inside of the clutch cover, pulling the pressure plate away from the back of the clutch plates.

The Clutch Th

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So how does all of this work?

This release of pressure allows the clutch plates to disengage from the flywheel. The flywheel keeps spinning on the end of the engine crank but it no longer drives the gearbox because the clutch plates aren't pressed up against it.

As you start to release the clutch pedal, pressure is released on the throw-out bearing and the diaphragm springs begin to push the pressure plate back against the back of the clutch plates, in turn pushing them against the flywheel again.

Visual of a Automatic Gearbox

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ox Cars with automatic transmissions are very popular for both

new and experienced drivers, as they are generally simpler to operate than manual transmissions and can be more comfortable for short trips.

In the next pages we will discuss automatic gearboxes, how it works and an explanation on the following types of automatic gearboxes.

Fully Automatic gearboxes

Semi-Automatic

Intelligent Automatics

CVT gearboxes

Automatic Gearbox

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ox Decoupling an Automatic Gearbox

Just like a manual gearbox, an automatic gearbox needs a method of decoupling the constantly-spinning engine from the gearbox components. To do this it uses a torque converter which is a viscous fluid coupling (because it's full of hydraulic fluid). A torque converter consists of three basic elements. The impeller, the turbine and the stator. The impeller is attached to the torque converter housing which itself is attached to the engine flywheel. The impeller is basically a centrifugal pump. As the flywheel spins, so does the impeller and the vanes take the fluid from the central part of the torque converter and fling it to the outside creating a pumping action.

Automatic Gearbox

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Fully Automatic gearboxes

Traditional fully automatic gearboxes use torque converters as opposed to clutches on manual gearboxes. The layout of the gearbox is not the same as a manual, with traditional automatics using a planetary gear arrangement as opposed to lay shafts.

Automatic Gearbox

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Fully Automatic gearboxes

When you take apart and look inside an automatic transmission, you find a huge assortment of parts in a fairly small space. Among other things, you see:

•An ingenious planetary gearset

•A set of bands to lock parts of a gearset

•A set of three wet-plate clutches to lock other parts of the gearset

•An incredibly odd hydraulic system that controls the clutches and bands

•A large gear pump to move transmission fluid around

Automatic Gearbox

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ox The center of attention is the planetary gearset.

About the size of a cantaloupe, this one part creates all of the different gear ratios that the transmission can produce. Everything else in the transmission is there to help the planetary gearset do its thing. An automatic transmission contains two complete planetary gear sets folded together into one component. Any planetary gearset has three main components:

•The sun gear

•The planet gears and the planet gears' carrier

•The ring gear

Each of these three components can be the input, the output or can be held stationary. Choosing which piece plays which role determines the gear ratio for the gearset.

Automatic Gearbox

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x Intelligent Automatics

Due the myriad of designs that various manufacturers came out with, there is no real clear-cut name for intelligent automatic gearboxes.

However, they all to varying degrees upped the performance and driving experience by some margin. Examples of intelligent automatics include:

• Button or paddle shift.

• Performance shift – which only changes gear when the ‘red-line’ is reached.

• Sports shift – which locks the selected gear – even when the red-line is achieved.

• Semi-automatic technology.

Automatic Gearbox

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Semi-Automatic

The transition from intelligent to semi-automatic is grey, but strictly speaking we could classify semi-automatics as gearboxes with ‘manual’ clutches that change gears automatically.

Some manufacturers have adopted multi-clutch devices which replace the torque convertor. The gearboxes can change gears at lightning speeds of as little as 100 milliseconds.

Dual Clutch

One of the most popular gearboxes are the Dual Clutch gearbox. Not to be confused with multi-clutch gearboxes, DCT boxes are currently the best performing gearboxes – manual or otherwise. Combining the dynamics of a manual gearbox, with the lightening speed of a sports automatic, these gearboxes select two gears simultaneously. The control unit can accurately anticipate which the next gear will be and select it. Gear shifts occur at between 8 and 50 milliseconds.

Automatic Gearbox

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As noted on the previous page, one of the most popular gearboxes are the Dual Clutch gearbox.

So how does this work? Well, a DCT gearbox has one layshaft like a normal gearbox, but two output shafts that mesh to a third shaft which goes to the differential. One output shaft has 1st, 3rd and 5th gears on it whilst the other has 2nd, 4th and 6th.

Automatic Gearbox

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x Dual Clutch Gearbox – how does it work continuous….

The layshaft is actually two shafts one inside the other connected to two concentric 4-plate basket-type clutches at the end. In first gear, one clutch is engaged and the central layshaft is connected to the engine. Selector forks have the first dog-gear engaged with the first helical gear and the car is moving forwards. At the same time though, on the second output shaft, the second dog gear is already engaged with the second helical gear.

Automatic Gearbox

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Dual Clutch Gearbox – how does it work continuous….

Because the outer clutch on the layshaft is disengaged though, there is nothing driving this second gear and the outer layshaft is simply spinning freely. At the point when the gearbox needs to shift up, it simply engages the second clutch at the same moment it disengages the first and the outer layshaft is now being driven from the engine.

Because second gear was already engaged there is literally no delay in shifting so the gear change is near instantaneous. Once in second gear, the inner layshaft is now freewheeling as the selector forks engage third gear on the first output shaft and so on and so forth.

Automatic Gearbox

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CVT Gearbox - Constantly Variable Transmission

Traditional transmissions use a gearset that provides a given number of ratios (or speeds). The transmission (or the driver) shifts gears to provide the most appropriate ratio for a given situation: Lowest gears for starting out, middle gears for acceleration and passing, and higher gears for fuel-efficient cruising.

Though there are several types of CVTs, most cars use a pair of variable-diameter pulleys, with a metal belt or chain running between them. One pulley is connected to the engine (input shaft), the other to the drive wheels (output shaft).

Automatic Gearbox

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CVT Gearbox – How does it work?

The halves of each pulley are moveable (known as variators); as the pulley halves come closer together the belt is forced to ride higher on the pulley, effectively making the pulley's diameter larger. Changing the diameter of the pulleys varies the transmission's ratio (the number of times the output shaft revolves for each revolution of the engine), in the same way that a 10-speed bike routes the chain over larger or smaller gears to change the ratio.

Automatic Gearbox

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CVT Gearbox – How does it work continues…

Making the input pulley smaller and the output pulley larger gives a low ratio (a large number of engine revolutions producing a small number of output revolutions) for better low-speed acceleration. As the car accelerates, the pulleys vary their diameter to lower the engine speed as car speed rises. This is the same thing a conventional automatic or manual transmission does, but while a conventional transmission changes the ratio in stages by shifting gears, the CVT continuously varies the ratio -- hence its name.

Automatic Gearbox

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CVT Gearbox

Some customers are not aware of how the CVT gearbox works and this could raise some questions. We will discuss the advantages as well as the perceived disadvantages of the CVT gearbox.

Advantages

Engines do not develop constant power at all speeds; they have specific speeds where torque , horsepower or fuel efficiency are at their optimum levels. Because there are no gears to tie a given road speed directly to a given engine speed, the CVT can vary the engine speed as needed to access maximum power as well as maximum fuel efficiency. This allows the CVT to provide quicker acceleration than a conventional automatic or manual transmission while delivering superior fuel economy.

Automatic Gearbox

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CVT Gearbox – Perceived Disadvantages

The CVT's biggest problem has been user acceptance. Because the CVT allows the engine to rev at any speed, the noises coming from the engine bay sound odd to ears accustomed to conventional manual and automatic transmissions.

The gradual changes in engine note sound like a sliding transmission or a slipping clutch -- signs of trouble with a conventional transmission, but perfectly normal for a CVT. Flooring an automatic car brings a lurch and a sudden burst of power, whereas CVTs provide a smooth, rapid increase to maximum power. To some drivers this makes the car feel slower, when in fact a CVT will generally out-accelerate an automatic.

Automatic Gearbox

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CVT Gearbox

In Conclusion

Designers have gone to great lengths to make the CVT feel more like a conventional transmission. Most CVTs are set up to creep forward when the driver takes his or her foot off the brake. This provides a similar feel to a conventional automatic, and serves as an indicator that the car is in gear. Other CVTs offer a "manual" mode that simulates manual gear changes.

Transmissions Tran

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Now that you have completed this section, you will be able to describe transmissions, explain how a clutch and torque convertor works and understand how a manual gearbox, automatic gearbox and a CVT transmission work.

End

End

This concludes the e-learning module on the Technical for non-technical transmissions section

Thank you for your participation!