Transcript
Have you got
the drive? ACTIVITY PACK 2 TO SUPPORT ACHIEVING ALTERNATIVE B, ACTIVITY 2
OPTION 2: MECHANIC This resource developed by Volvo Trucks and their apprentice technicians will support you in achieving the Explorer Science & Technology activity badge, option 2. You’ll be able to demonstrate mechanical knowledge and explain the principles of operating an engine, gearbox and differential axle.
“At Volvo Trucks we think it is brilliant that you’ve chosen to work towards the Explorer Science & Technology badge. This resource pack is the first step in developing your mechanical knowledge, and hopefully driving your interest in technology. When working through these activities remember to work safely and check the health & safety warning boxes along the way.”
WHAT IS A DIFFERENTIAL? Explained simply, the differential is the part of a car, truck and other vehicles with wheels, that allow the driving wheels to make a turn. Only the driving wheels of a vehicle have a differential, the non- driving wheels are allowed to independently spin.
When a vehicle turns, the wheels on the outside have to rotate faster than the ones on the inside because they have to travel a longer distance. The increase in the speed of the outer wheel is balanced by a decrease in the speed of the inner wheel, allowing the vehicle to turn the corner more smoothly. Without a differential the wheels on a vehicle with a fixed axle would skid when going round a corner, causing damage to the tyre and potentially the vehicle. The differential transfers drive to 90 degrees using a sun crown wheel and pinion gear.
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Diagram 1: A truck driving in a circle
Diagram 2: A basic differential positioned between two driven wheel
The detail The drive from the engine via the propeller shaft rotates the crown wheel (yellow), which is attached to the small gear cogs (green). These are planetary gears that can rotate freely, but work together to turn large side gears (blue), which are connected to the outer and inner half shafts. If one wheel needs to rotate faster than the other, it’s these gear cogs that allow it to happen.
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How to make a simple cam You will need ACTIVITY: MAKE A SIMPLE CAM A piece of card pva glue How to make a simple cam MECHANISM mechanism
scissors
2
Have a go at making your own cam mechanism. Investigate how different shapes affect movement and discuss or will need recordYou your results.
A piece of card
pva glue
scissors
2 pieces of dowel
CAMS
wheel
20cm
A cam is a shaped piece of metal or plastic fixed to a rotating Instructions shaft – much like the propeller shaft in in the 10cm differential diagram.
How How toHow to make How make to How to a make simple a make tosimple make a simple acam simple cam a simple mechanism cam mechanism cam mechanism cam mechanism mechanism Draw out a net for an open cube on the piece How to make a simple cam mechanism
Instructions YOU WILL NEED: will u You will You need will need You will need will need need
10cm
will need piece ceAof piece AYou of card piece Acard of of card card of pva card pva pva glue pva glue pva scissors glue scissors glue scissors scissors 2 scissors pieces 2 the pieces pieces 2ofpieces of dowel 2of dowel pieces of of dowel dowel of wheel dowel wheel wheel wheel wheel wheel Apiece piece of card PVA glue scissors 22pieces of dowel blu-tak Draw out aglue net for an open cube on piece card. A piece of card
pva glue
scissors
2 pieces of dowel 20cm20cm
10cm
wheel
20cm20cm 20cm 20cm
10cm10cm
10cm10cm 10cm 10cm
INSTRUCTIONS: structions uctions Instructions Instructions Instructions Instructions 1
Draw out a net for an open cube on the piece of card.
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Carefully cut it out and score the folds.
aw out Draw out Draw aDraw net aDraw out net out for a for out net aan an open a fornet open for anan an cube for open cube open anon open cube on the cube the on cube piece on piece the the on of piece of the card. piece card. piece of card. card. of card. out a net net for open cube on the piece of of card. Carefully cut it out and score the folds. 10cm10cm
10cm10cm 10cm 10cm
Carefully cut it out and score the folds.
Carefully cut it out and score the folds.
fully refully Carefully Carefully cutcut Carefully it out itcut out cut and it and out cut itand score out and itscore out and the score and the score folds. folds. the the folds. Measure mark 5cm along 3score sides as the infolds. the folds.
3
Measure and mark 5cm along 3 sides as in the the card at th
Make up the cube, sticking the tabs with PVA glue and holding them in place with Measure and mark 5cm along 3 sides as in paperclips the diagram below. Hole punch is necessary. diagram below. Hole punch the card at these points.
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theMake card up at these points the cube, sticking the tabs with pva glue a with paperclips if necessary. This This is is thethe frameframe
Measure and mark 5cm along 3 sides as in the diagram below. Hole punch the card at these points Stick the wheel onto the bottom of the thin piece o easure sure Measure Measure and and Measure mark and mark and 5cm mark and 5cm mark along mark 5cm along 5cm 3along 5cm sides 3along sides along 3as sides 3as sides in3in the sides as the as diagram in diagram in the asthe in diagram the diagram below. below. diagram below. Hole below. Hole below. punch Hole punch Hole punch Hole punch punch
thethecard the card the atcard at these the card these at card points at these points these at these points points points
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This is the follower
Thread a cam onto the thicker dowel and thread this through the holes in the wheel onto the place bottom of the thin piece Thread a cam onto the thicker dowel and thread frame, securing it in with blu-tak the cam with the axle Thread athat cam onto theturns thicker dowel an 5 Stick 6 so of dowel. this through the holes in the frame, securing it in Stick wheel onto the bottom of the frame, thin piece of dowel.it in place with blu-tak s not bythe itself. securing place with blu-tak so that the cam turns with the not by itself. not by axle, itself. This isThis the follower is the
follower
Thread a cam onto the thicker dowel and thread this through the holes in the frame, securing it in place with blu-tak so that the cam turns with the axle, Finally, thread the follower through the hole in the top of the frame so tha not by Finally, itself. thread the follower through the hole in Your mechanism is now ready to test.
7 8 the topis of resting the frame so that wheelcam. is resting Finally, thread the follower through the h the wheel onthethe on the cam. The blu-tak will enable you changecam. the cam the wheel is resting onto the and investigate how different shapes affect the movement. Turn the a crank handle and watch the flag. How does it move? Don’t forget to record your results.
Finally, thread the follower through the hole in the top of the frame so that the wheel is resting on the cam.
Your mechanism is now ready to test. Your the mechanism isinvestigate now readyhow to test. The blu-tak will enable you to change cam and differ Overview of a Volvo Engine The blu-tak will enable you to change th A caraffect or truck the enginemovement. converts fuel into motion, so that the vehicle can move. In most vehicles, shapes movement is created by burning fuel, typically petrol or diesel, inside an movement. engine. This is known shapes affect the Turn as the a crank handle andaswatch the flag. an internal combustion engine, combustion takes place internally. Turn the a crank handle and watch the f How does it move? Don’t forget to record your results. How does it move? Don’t forget to reco Your mechanism is now ready to test. The blu-tak will enable you to change the cam and investigate how different shapes affect the movement. Turn the a crank handle and watch the flag. How does it move? Don’t forget to record your results.
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ACTIVITY: LOCATE ENGINE COMPONENTS Look through the list of basic engine components. Using the clues, see if you can locate and identify them in the picture. What do you think they might do? Piston: Located inside engine block Crankshaft: Located inside engine block Camshaft: Rotates in a circular motion Fuel filter: screens out dirt and rust particles from the fuel Conrod: Connecting rods between the piston and the crankshaft Valve: Allows passing of gasses or air into the engine Injector: Injects fuel into the cylinder (engine) Water pump: pumps water and coolant to the vehicle's engine
PETROL VS DIESEL ENGINES An engine can run on either petrol or diesel fuels.
Petrol Engine
A petrol engine is a spark ignition engine which means it uses a spark plug to ignite the fuel in the cylinder.
Diesel engine
A diesel engine is a compression ignition engine. There is no spark plug and the diesel is ignited through the immense pressure created in the cylinder. Diesel engines are most common on trucks and are the only type of engine Volvo Trucks use today. There are many differences between petrol and diesel engines. For example, diesel engines: • rev a lot lower (which means less rotations of the engine per minute) • do not have a spark plug. They work on CI (Compression Ignition). Compressed Ignition Four stroke CI Ignition
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Useful information • When a gas, liquid or solid is compressed it generates heat. This is the principle on which combustion ignition is based. • The compression stroke generates enough heat in the engine to ignite the air and fuel mixture. Therefore there is no need for a spark plug. • Petrol engines generally do not create enough compression for this type of ignition, therefore requiring a spark plug to ignite. Intake Stroke
Compression Stroke
Power Stroke
Exhaust Stroke
ELECTRIC POWERED VEHICLES Electric vehicles are known as ultra low emission vehicles, or ULEV for short. They are called ULEVs because these vehicles produce 75g or less of carbon dioxide per kilometre. At the moment, vehicles that can achieve this use electric power to directly power the wheels, from a 100% electric car to a plug-in hybrid and an extended-range electric vehicle.
What’s the difference?
• No exhaust pipe • A charging socket rather than a fuel cap • A battery instead of a fuel tank • An electric motor instead of a combustion engine
Electric motor
Power cord
Rechargeable batteries
Power outlet
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The Volvo 7900 Electric Hybrid Bus By extending our standard bus hybrid with a larger battery, we can get up to 7 km in electriconly operation and still have the versatility of the diesel vehicle. Can you spot the power outlet charging the bus?
OPTIONAL ACTIVITY: BUILD AN ELECTRIC CAR Materials Kits are available from speciality retailers, for example Maplin: MFA Geared Motor Kit.
What to do:
• Build your own electric vehicle and then race them. • You could also start adding weights on top of the cars to see how that affects the speed and battery life. • Racing will be finished when the battery runs out. • Record how long it takes for the battery to be depleted.
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ACTIVITY: TEST YOUR KNOWLEDGE Think you’ve got it? Test your knowledge 1. What is the difference between petrol and diesel engines?
2. What causes ignition in a diesel engine?
3. What is the function of the injector in a Volvo engine?
4. What component connects the piston and the crankshaft?
5. What is an ULEV? What are the benefits to using an ULEV over a petrol or diesel vehicle?
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OPTIONAL ACTIVITY: WORDSEARCH Search the grid for the main components found in an engine. CAMSHAFT CRANKSHAFT CONROD
ENGINE INJECTOR PISTON
VALVE COMBUSTION TURBO
INTAKE EXHAUST
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WHAT IS A CLUTCH? A clutch is a mechanical device that engages and disengages the power transmission. Clutches are used where the transmission of power or motion needs to be controlled, in either the amount or power or over a period of time. In a car or truck, the clutch controls the conduction of engine power to the driving wheels, allowing the vehicle to move or stop. There are occasions when the engine must be able to run without the driving wheels being affected, for example; at traffic lights or when the driver has to change gear. Here, the power transmission has to be disengaged from the engine. This is done using the clutch (1), and is called declutching. When the vehicle is running the discs (2) are pressed tightly against the flywheel (3) by the pressure plate (1). The pressure plate, a powerful steel ring, gets its pressure against the discs either from coil springs or from diaphragm springs. When the clutch pedal is depressed the pressure plate is released. The disc is then disengaged and stops rotating. The gearbox is no longer receiving power from the engine and the vehicle stops.
Useful information The disc (1) consists of a resilient steel plate with riveted fibre facings on both sides. Its purpose is to transmit the driving power of the engine to the gearbox with the aid of friction. The riveted fibre facings are made of heat-resistant material to ensure that they can stand up to the high temperatures generated when the disc is in use. The disc is designed to slip slightly when engaging to provide a smooth start. In the centre of the disc there is a hole with splines (2) in which the gearbox input shaft is attached. There a number of springs (3) around the centre of the disc which dampen vibrations. When the disc rotates it turns the gearbox input shaft, transmitting power to the gearbox.
ACTIVITY: TEST YOUR KNOWLEDGE 1. Describe the purpose of a clutch.
2. What two main parts are a clutch made up of?
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