In this education piece, you will learn about the following:
Gear Selection – Pulling off
Gear Selection – Driving
To check and update your knowledge of gearbox use with regards to fuel efficiency and introduce new gearbox related technology.
By the end of this session you will be able to discuss how to use a gearbox in a safe and economical manner, and will be able to identify the various techniques used for gear changing with both a manual and an automatic gearbox.
What is the purpose of the gearbox?
Your initial thought may well be ‘to allow the vehicle to
change between different speeds’, however, controlling
speed is only one element of what a gearbox does.
- Controls the torque being transmitted by the engine
- Provides a means of reversing the vehicle
- Disconnects the engine from the drive wheels
- Provides power to ancillary equipment
- Maximises the fuel efficiency of the vehicle
There are many varieties of manual gearbox. Common variants used on
larger vehicles include those shown below.
Manual Gearboxes: Terminology
Four over four: a common configuration featuring a ‘low-high’ range selector. This allows selections of the four low ratio gears while in ‘low range’ and the four high ratio gears in ‘high range’
Three over three: similar to four over four but consisting of just three low range gears and three high range gears.
4 by 4 – this configuration consists of four low gear ratios on the left side of the gearbox and four higher gear ratios on the right, accessed by pushing across and through a gate.
‘Crawler’ gear: low forward gear, only used in demanding situations or when conducting very fine manoeuvres.
What precautions should be taken when using a crawler gear?
- Vehicle may quickly reach its maximum
RPM, so take care not to damage the
- Road speed will be minimal; when the
clutch is dipped the vehicle will slow
- Increased torque transmitted throughout
the drive train. The high levels of friction
created by the load weight and between
the tyre and the road mean drive shafts
or prop shafts may simply twist and
break under the torque.
What factors should you consider when selecting a gear for moving off?
Selecting a Gear for Moving off
Selecting a Gear for Driving
- Selection and use of the correct gear whilst driving is equally
as important as any other driver-orientated input
- The art of efficient gear changing depends upon the driver’s
ability to match the gear to the road speed and skilfully using
the clutch and accelerator
- Selecting the correct gear whilst driving is a major factor to
- Knowing where the engine manufacturer’s peak performance
point is assists you in knowing when you should be changing
Peak performance points are commonly indicated by a green coloured section on the rev counter; however, other coloured sections may also be evident.
Do you know what the colours represent on the rev counter in your own vehicle?
Colours may vary but a general guide is as follows:
Standard use, adequate power and optimum fuel efficiency
Occasional use when accelerating firmly
Optimum use for engine braking
Driving at this rate of revs could cause damage to the engine.
What are some of the effects of using too low a gear?
What are some of the effects of using too high a gear?
Too high a gear will cause the engine to labour, creating stress and forcing the engine to operate out of the most economical power ranges. This will affect acceleration and reduce engine braking.
What is Block Gear Changing?
- Fuel efficient way to drive
- Reduces the number of gears selected
- Reduces the number of times the clutch is operated
- Increases the longevity of the components
- Can minimise wear and tear on the driver’s body
This approach cannot be applied to every situation:
- Not all vehicles will necessarily be suited to the
- Traffic conditions should always be taken into account.
Care should always be taken when using the gearbox to slow the vehicle down.
Slowing down can be conducted by use of the brakes; however, changing down gear will compliment and aid reduction of speed.
You may have heard following traditional phrase:
In fact, modern engines use little fuel when the accelerator pedal is not in use.
Hence, it could be more efficient to use a mix of the exhaust brake and gears to reduce the speed of the vehicle and only use brakes to stop.
Whichever system you use, please follow manufacturer guidelines. Care should always be taken when using the gearbox to slow the vehicle down.
How many types of automatic gearbox are there?
There may be slight variations in naming and operation, but each system works on the same basic principles.
- Automated Manual Transmissions – this is the most common variety of automatic gearbox used in the logistics sector. This operates differently from a traditional automatic transmission. Automated manual transmissions employ a manual gearbox, with the clutch and gearshifts controlled by an electronic system.
- Semi-automated Manual Transmission – these are predominantly found on Scania vehicles and work in a very similar way to the AMT but with a clutch pedal used only when moving off or bringing the vehicle to a stop.
- Automatic Gearbox – this is the type of auto gearbox generally used in vehicles such as refuse vehicles, road sweepers, etc. This is a hydraulic system that uses planetary gearing and torque converters.
Automatic gearboxes are simple to operate and effective to use.
What are the big differences when using an automatic gearbox?
No clutch pedal, so no requirement for you to ‘control’ the bite point of the clutch.
- Variety of methods used for engaging drive
- You may find other switch positions available. These might, for example, hold the vehicle in a certain gear, or allow for slow manoeuvring applications.
- The general principles of operation are similar for all automatic gearboxes
- Manufacturers all develop their own systems of activation and gear selection
- You must always familiarise yourself with the type of vehicle you drive and consult the vehicle manufacturer’s manual
- Some employers specify that manufacturers ‘pre-programme’ gearboxes with drive modes such as: