Vehicle System and Design Flashcards
(167 cards)
1
Q
What is the purpose of Internal Combustion (IC) engines
A
- Convert chemical energy into mechanical energy
- Convert linear motion into rotational motion
- Be able to move a vehicle for long periods of time without failure
- Burn fuel efficiently
2
Q
What is a gearbox
A
A gearbox is a box of ratios which help make best use of our rev ranges
3
Q
What is a driveshaft
A
Takes drive to the wheels
4
Q
What are the issues of a front engine RWD layout
A
Drivetrain components have to sit through the vehicle creating vehicle packaging issues
5
Q
What is an inline engine
A
The pistons of the engine line up in a row
6
Q
What is a V engine
A
The pistons of the engine are configured in the shape of a V
7
Q
What happens in the induction phase of the 4 stroke cycle
A
- Piston starts at TDC and moves to BDC
- Inlet valve opens
- Depression inside combustion chamber forces air into the combustion chamber
- Fuel is injected
8
Q
What happens in the compression phase of the 4 stroke cycle
A
- Piston moves from BDC to TDC
- Air fuel mix is compressed raising pressure
- Spark plug is ignited at TDC
9
Q
What happens in the expansion phase of the 4 stroke cycle
A
- Piston moves from TDC to BDC
- Explosion happens in the combustion chamber, forcing the piston to move
10
Q
What happens in the exhaust phase of the 4 stroke cycle
A
- Piston moves from BDC to TDC
- Exhaust valve opens
- Any exhaust gases are pushed out of the combustion chamber
11
Q
Why is it important to get correct compression ratios
A
So that compression pressures are not too high that it causes self ignition
12
Q
What is stratified charge
A
Swirl is created in the air and fuel is injected at the very end of the compression stroke in a small amount. Used when coasting for efficiency
13
Q
How do you tell the difference between inlet and exhaust valve on the cylinder head
A
Inlet valve is bigger than exhaust valve
14
Q
What does a camshaft do
A
Rotates around, lifting the valves off their seat, to open and close.
15
Q
What is a over head valve engine
A
Camshaft sits at the bottom of the engine with the crankshaft. Mass is mainly distributed to the bottom of the engine. More moving parts
16
Q
What is a over head camshaft engine
A
Camshaft sits at the top of the engine. Has less moving parts meaning less parts can fail
17
Q
What is valve float
A
Camshaft spins too fast that the valve can never fully close
18
Q
What is valve bounce
A
Valve bounces out of control as the spring reaches its natural frequency
19
Q
What is seat pressure
A
Pressure to hold a valve closed
20
Q
What are dry sleeve engine blocks
A
Dry sleeves are pressed into cylinder bores in the block. They do not make contact with the coolant but are supported by the cylinder block walls
21
Q
What are wet sleeve engine blocks
A
Coolant is in direct contact with a wet sleeve. They are thicker to account for lack of structural support. A seal is fitted at the top and bottom to prevent coolant leakage
22
Q
What does a gudgeon pin do
A
Connects piston to the connecting rod
22
Q
What is the requirement of the fuel system
A
Correct amount of fuel is delivered to the engine at the correct time so it mixes with enough air so combustion can occur
23
Q
What is stochiometric
A
Chemically correct air fuel ratio for complete fuel combustion (about 14:1)
24
What is rich
Less air in air fuel mix. Can cause incomplete combustion and leave fuel in the combustion chamber
25
What is lean
More air in air fuel mix. Can raise combustion chamber temperatures
26
What is port fuel injection
Injects fuel into the inlet port before the valve
27
What is direct injection
Injects fuel straight into the combustion chamber
28
Why is fuel atomisation important
The better the atomisation the quicker the fire will spread between particles inside the combustion chamber
29
What is a homogeneous charge
Air and fuel mix is uniform as all the mixture is required
30
What is an inlet manifold
Ensure an adequate volume of air enters the combustion chamber and that fuel is mixed with air
31
What happens on the induction stroke of a diesel engine
- Piston moves from TDC to BDC
- Only induces air
32
What happens on the compression stroke of a diesel engine
- Piston moves from BDC to TDC
- Inject fuel near TDC
- Increased temperature and pressure is enough to ignite the fuel, no spark plug needed
33
What is diesel engine knock
Instantaneous combustion when fuel is directly injected into the combustion chamber. This is kept to a minimum by electrically controlled delivery
34
What happens in the first phase of combustion / delay phase in diesel engine
Fuel mixes with compressed air and begins to absorb heat. Little rise in pressure
35
What is phase 2 of combustion in diesel engine
Rapid pressure rise. Greater pressure rise means more engine knock experienced
36
What is phase 3 of combustion in diesel engine
Stage of continuous burning as a result of fuel still being injected into the cylinder
37
How do turbochargers work
Air from exhaust pipes enter and hit the turbine wheel causing it to rotate. This is connected to a shaft which spins the compressor wheel which forces air to be pressurised and pushes it into the intake manifold
38
What are issues of turbochargers
- Heating from exhaust gases spreading to components
- Increases exhaust back pressure
- Pressurised air heats up and expands
39
What happens in variable geometry turbochargers
Narrow vane opening
- High torque at low revs
Wide vane opening
- High torque at high revs
40
How do centrifugal superchargers work
Pulley is connected to crankshaft and gears are inside to allow the compressor blade to run at whatever speed we want whenever we want delivering a boost pressure we want
41
How do roots type superchargers work
As the roots type blades spin they pressurise the air induced
42
What are non harmful exhaust emissions
- N2 Nitrogen
- CO2 Carbon Dioxide
- H20 Water vapour
43
What are the harmful exhaust emissions
- CO Carbon monoxide
- HC Hydrocarbons
- NOX Nitrous oxides
- PM Particular matter
44
How do you increase engine efficiency
- Variable valve timing
- Variable intake systems
- Increased compression ratios
- Use of forced air induction systems (turbo and superchargers)
- Use of electric motors to reduce frictional losses
45
How do catalytic converters work
Exhaust gases flow from the engine, the catalytic converter is dipped into precious metals which convert the toxic exhaust gases into non toxic properties.
Platinum is the oxidizing agent (CO + O = CO2)
Rhodium is the reducing agent (NOx - O = N2)
46
How does exhaust gas recirculation work
Turbocharger pumps in atmospheric air. Some exhaust gases are also filtered in from the exhaust and mixed into the intake gases and sent back to the combustion chamber. This reduces the gases that are sent through the exhaust. This process doesn't apply to acceleration
47
How do we get rid of particulate matter in diesel engines
Put a filter which picks up all the carbon deposits. Then when enough has built up we spray in burning fuel which burns the carbon deposits and sends them down the exhaust pipe
48
What are the requirements of a cooling system
Remove heat generated by the combustion process. If heat removal did not occur the cylinder would overheat causing pre ignition
49
What is a sealed cooling system
Has an expansion tank which makes sure all the components are bled (air removed). This allows the coolant to flow without any air pockets. Expansion tank is high up in engine. Pressure cap is on expansion tank
50
What is a semi sealed cooling system
Expansion tank put lower in the engine. Pressure cap allows coolant to bleed out of the system when it reaches a certain pressure. As engine cools down, coolant is drawn back into radiator to make sure it is topped up and no air is present. Pressure cap is on radiator
51
How is temperature regulation achieved
Through use of thermostat. This device is usually controlled by the use of wax expansion or electronically controlled thermostats. Coolant is flowing through a bypass in the engine to get it up to the optimal temp. Once it reaches that the bypass shuts and coolant flows round. If overheating a fan turns on.
52
Why do you need uniform temperature in the engine
To avoid different cylinders having different outputs, such as some pre igniting and some not
53
Why is lubrication important in an engine
Important in keeping friction to a minimum. It can also aid internal cooling
54
What is dry friction
In the absence of a lubricant the friction, rate of wear and heat generated is high
55
What is boundary friction
The film of lubricant is not complete and the surfaces are only partially separated
56
What is fluid friction
Complete separation of the surfaces by a film of lubricant. It is the ideal condition and reduces friction to a minimum
57
What are the types of lubrication
- Hydrodynamic lubrication
- Electrohydrodynamic lubrication
- Boundary lubrication
- Hydrostatic lubrication
- Mixed film lubrication
58
What is electrohydrodynamic lubrication
Rotating part against a surface builds a wedge at the front of the rotating part, causing lift
59
What are additives
Additive packs contain friction modifiers which line the cylinder walls as they are attracted to the surface
60
What is rolling radius
2pi radius - compression
61
What does a clutch / torque converter do
Provides a break in the drive without having to stop the engine
62
Why do crankshafts rotate clockwise
As we want the wheels to rotate clockwise to provide drive
63
What are issues of more gears in a gearbox
- Requires more space
- More mechanical losses as more gears
- Need to extend output and input shafts
64
What is the function of the differential unit
- To provide a gear reduction
- To allow any paired driven wheels to travel at different speeds
65
How does a differential work
Ring gear (final drive) bolts to the diff case and the drive pinion is connected to the ring gear. Inside the case is gears which allows wheels to travel at different speeds
66
Why do road wheels on a shared axle travel at different speeds
Path of the inner wheel is shorter than the outer. It also can be due to one wheel traveling over rough ground and the other on smooth road
67
What is a limited slip differential
As the gears rotate they push away from each other
68
What is a direct shift gearbox
Input shaft is split into two, allowing 2 gears to be selected at the same time. Clutch pack is hydraulically controlled and ECU controls which gear is selected. Because it has two shafts and clutch packs it can pre select gears
69
What is the problem of an open differential
If one wheel is on a loose surface the other wheel is not going to get any drive
70
What is track width
Distance between centre of tyres on a shared axle
71
What are the requirements of a steering system
- Enable vehicle to change direction
- Ensure the vehicle can travel with ease in a straight ahead position
- Provide adequate resistance to tyre scrub when cornering or travelling in a straight line
72
What is wheelbase
Distance between centre of front and rear wheel
73
What is scrub
Push the tyre surface laterally across the road surface breaking mechanical grip
74
What are types of steering systems
- Rack and pinion
- Steering box
- Power assisted steering
- Electric power assisted steering
75
What is a steering box used for
Heavy vehicle industry as a result of its strength and ability to provide a significant gear reduction making the steering lighter
76
What is a rack and pinion used for
Light commercial and passenger vehicles as it has minimal moving parts and is compact allowing it to be fitted along the engine compartment bulkhead
77
How does a rack and pinion work
Driver turns the steering wheel, which then turns the steering column. This then is converted into linear motion by the steering rack and the track rod connected to the wheel moves to turn the steering wheel left or right
78
What is bump steer
Bump steer is a result of the steering track control arm radius and height and the suspension control arm radius and height.
79
What is a steering column
Connects the steering wheel to the steering rack / box. Normally fitted with universal joints to allow for rake adjustment and movement. The steering column contains a collapsible section to reduce the chance of crushing the driver
80
How does a steering rack work
Works on a rack and pinion gear system. As the pinion gear is turned by the steering column it pushes the rack either left or right. On the end is a shock damper assembly which absorbs energy if any contact is made to reduce chance of damage
81
What is a steering box
Worm gear is inside a re circulating ball box which have ball bearings between the worm gear and the gear. The worm gear spins which forces the gear to also rotate
82
What are spherical joints used for
Used as an alternative to rubber bushes and the ball joint as it requires less space and can provide increased accuracy for alignment purposes
83
What are ball joints used for
Used to get rid of feedback and vibrations as the ball absorbs some of the energy
84
What is a universal joint
Allow preferential positioning of steering rack and location of steering wheel. A single joint will travel through 35 degrees whilst a double joint is able to pass through 70 degrees
85
What are issues caused by vibrations in steering systems
All vibrations are transmitted to the steering wheel which increases driver fatigue and component wear. In order to reduce vibration the steering rack / box is mounted to the vehicle body
86
What do we want from wheel alignment
Wheel and tyre in a straight ahead direction to reduce rolling resistance
87
What is towing out
Front wheels are both pointing out in their respective directions
88
What is towing in
Front wheels are both pointing inwards in their respective directions
89
What is tow out good for
Cornering as one wheel is more rotated that the other
90
What is tow in good for
Straight line stability
91
What is Ackermann
Inclining the steering arms towards the centre of the vehicle
92
How do you achieve 100% Ackermann
When the convergence of the projected lines meets the centre of the rear axle
93
What is slip angle
As the tyre caucus rotates, the contact patch doesn't it distorts. The slip angle provides tow out
94
What is understeer
Front wheels are experiencing greater slip angle than the rear wheels
95
What is oversteer
Rear wheels are experiencing greater slip angle than the front wheels
96
How does hydraulic power assisted steering work
Pump is driven by crankshaft so always working whilst engine is on. Reaches a small valve which when enough torque is put into the steering wheel it rotates the spring ring allowing small valve to move and fluid to flow
97
How does electric power assisted steering work
Electric motor provides direct assistance to the steering column, meaning they do not consume unnecessary power from the engine
98
What is the purpose of a suspension system
Prevents damage to vehicles body whilst travelling over uneven ground and therefor allowing vehicles to travel at significant speed over rough ground
99
What is unsprung mass
Anything on the road wheel end of the suspension. Want this to be at minimum as possible
100
What is sprung mass
Anything on the body side of the suspension
101
What forces are acting on a vehicle
Roll - Torsional vibration about the longitudinal axis
Pitching - Vibration in the transverse axis
Yawing - Vibration in the vertical axis
102
What is ride height
Suspension system is at its optimal height to work.
103
What is bump
Tyres gain elevation causing the suspension to raise
104
What is droop
Tyres loose elevation causing the suspension to lower
105
What is ideal for ride height
Typically you want your bottom wishbone to be horizontal and as long as possible. For good camber gain the top wishbone should be about 80% of the length of the bottom
106
What is camber gain
Change in camber as the suspension moves up in down.
107
Where is ride height measured from
Centre of wheel / hub to the body of the car
108
What is rigid axle suspension used for
Heavy vehicles or contemporary off road vehicles as the suspension is required to carry substantial load or negotiate harsh road conditions
109
What is a live axle
An axle which has drive going down to it, connected to power train
110
What is a dead axle
An axle which is not connected to the power train at all
111
What is a semi floating axle
The load of the vehicle is transmitted to the suspension system through the driveshaft
112
What is a fully floating axle
All of the load is carried through the axle casing itself
113
What are the issues of coil springs on an axle
Lowers space available for vehicle packaging
114
What are the benefits of leaf springs
Sit below axle which means they do not effect vehicle packaging
115
What is a De Dion drive
The differential is mounted to the vehicles body making it part of the sprung mass. The De Dion tube runs across which can carry heavy loads
116
What is pros and cons of beam axle
Cheap and lightweight component.
What happens on one wheel happens to the other as only connected by a dead steel rod
117
What is a independent suspension
Isolates each individual wheel so that if something happens to one wheel the other does not have to experience it. Improves vehicle handling
118
How does an independent suspension work
Instead of a top wishbone, a macpherson strut is fitted. Sub frame is designed to fit suspension and power train parts so it can just be lifted up and bolted. The beams that connect the rear axle allow for complete adjustability
119
Benefits of a macpherson strut
Cheap to manufacture and assemble
120
What are problems of macpherson strut
Increases frontal area which increases drag
121
Benefits of double wishbone
Reduces frontal area reducing drag
122
What are the problems of double wishbone
Expensive, wishbones intrude into where engine components would be
123
What do we want from springs
We want to be able to traverse bumps without the suspension moving, the spring compression takes all the load. Want to choose softest spring possible whilst maintaining what vehicle needs to do
124
What is an anti roll bar
When wheels go into bump and droop, anti roll bar twists to reduce body roll
125
What is a rising rate spring
Move onto larger winding of springs dependent on the situation
126
What does a damper / shock absorber do
Ensure that the road spring does not bounce out of control
127
How does air suspension work
Air pressure is constantly changing to change the spring rate to maintain ride height
128
How does electrical active suspension work
Electromagnetic coil is switched on generating an electromagnetic field causing the ferrous particles to line up in the ports, creating resistance through it to change spring rate or damping
129
What is electromechanical rotary damper
Heat from dampers is then transferred to a 48 volt battery charging it to give extra power
130
What is castor angle
Key for straight line driving and stability. As you incline castor angle you induce jacking effect, requiring it to fall when the turning force is removed
131
What is swivel axis / kingpin inclination
Gives a scrub radius which is the offset between centre line of wheel and tyre to the swivel axis (swivel axis is the axis the tyre and wheel rotate around). If the line meets the road surface at the centre of the tyre contact patch then you have centre point steering
132
What does scrub radius effect
- Dynamic toe during acceleration and deacceleration
- Transmission of road surfaces
- Steering self centring
133
What is camber
Angle which allows for good tyre contact when vehicle is subjected to high cornering forces. We want to have a small bit of negative camber
134
What should a tyre do
Must be able to transmit longitudinal and lateral forces whilst optimising grip from the road whether wet or dry
135
What does tyre tread do
Tread is good for generating grip and also for expulsion of water
136
What does a tyre carcass do
Keeps a large contact patch between the tyre and the road
137
What is different about motorbike tyre carcass
As you go out from the centre of the tyre the temperature decreases as its used less. So the tyre is made of different compounds, getting softer as you go outwards to help with grip
138
What is the yellow dot on a tyre
Lightest point of a tyre carcass
139
What is the red dot on a tyre
Radial force variation / high point of a tyre. Should be aligned to low point of wheel (white dot)
140
Why are tyre pressures important
If under inflated, tyre carcass creates concave shape with surface, allowing for water to get underneath and aquaplaning to occur. If over inflated you reduce the tyres ability to deform which wont mould itself to the road surface. Both reduce contact patch of the tyre
141
What do different tread patterns do
Different tread patterns tend to be best in one condition, apart from daily road tyres. When not in their optimal condition they may struggle with overheating
142
What are the hysteresis losses of a road tyre
When the tyre moulds to the road surface for grip, we want it to return to its original shape. Greater the hysteresis loss the greater the rolling resistance
143
What does run flat tyre technology do
Keeps the tyre so that the driver is able to pull over and not cause an accident
144
What is neutral steer
When the front slip angle is the same as the rear slip angle
145
Why should you not swap wheels
It offsets the wheel as you move the centre line which changes your swivel axis inclination
146
What are wheel dimensions determined by
Required brake torque
147
What is a lug design
How many bolts are holding wheel onto the hub. More bolted means more stability of the wheel
148
What is a centre bore
Centre hole of the hub which slots in the wheel to ensure it is concentric and run out is minimal
149
What is the purpose of a braking system
- Stop
- Slow down
- Park
- Control stability
- Aid acceleration
150
What is the difference between primary brake (foot brake) and secondary brake (hand brake)
Primary brake is hydraulic or pneumatic, secondary is mechanical
151
What is the requirements of a braking system
Must apply an equal force to brake across any shared axle. For light vehicles this is normally distributed 70% front 30% rear brake bias
152
How does a hydraulic braking system work
Uses pistons and fluid in order to activate the brakes. A force is put into the brake which is connected to the master cylinder. A slave cylinder is connected to the callipers.
153
How does an air braking system work
Brake pedal controls a valve which allows air to go into a diaphragm chamber which presses against a pushrod, causing it to brake. Can achieve a lot higher forces, so useful for heavy duty vehicles
154
How does servo assistance work in IC / Hybrids
Once brake pedal pressed, a cup covers some ports which stops the chamber being in equilibrium. Seals of right hand side of chamber which causes a depression which pulls diaphragm right to left
155
How does a servo assistance work in EVs
Once brake pedal is pressed, motor and gears apply servo assistance
156
When do you need servo assistance
Whenever you have disc brakes
157
What is brake friction dependant on
- Nature and surface finish of the materials in contact
- Independent of the area of the surfaces in contact
- Independent of the relative velocity of the moving parts providing the velocity is not high
158
What is a hydraulic circuit
As the driver presses the brake, hydraulic fluid applies force to the brake components. As brake pedal is pressed, brake fluid reservoir is covered by the push rod, then once it moves back, gravity feeds more brake fluid through the port
159
What is the issue or a front and rear hydraulic system
If you loose the front braking system, it becomes very easy to lock up the rears
160
What is the benefit of diagonal hydraulic system
If you loose one front and one rear brake, the brake torque will still keep the car in a straight line
161
What are hydraulic brake pipes
Either rigid pipes secured to the vehicle body or flexible hoses used to connect moving parts
162
How does air braking system hand brake work
Once you loose air pressure in the chamber, no more pressure is on the diaphragm, so the spring becomes uncaged applying the parking brake
163
What happens in a brake disc
In the chamber, pressure is increased moving the piston. The calliper also moves an equal displacement in the opposite direction for equal braking force
164
What are brake pad friction materials
- Organic, work well in cold, wear quicker than disc
- Semi metallic, cope with high temp, not best in the cold
- Metallic, cope very well with high temp, do not work well when cold, noisy
-Ceramic, very good at dissipating heat so can cope with high braking force, quiet
- Carbon fibre, racing application
165
Which brake type is more efficient
Drum is more efficient than disc
166
How does a hydraulic secondary brake system work
Uses a mechanical linkage to apply the brakes. It does not apply automatically when hydraulic pressure reduces, the driver has to manually pull the electronic cable which applies the brake
