Week 5 definitions

Question 1

What does an idler gear do?

Answer 1

It allows for reversing by reversing the gear direction in the gearbox

Question 2

What happens if a gearbox needs more than 6 gears? In what type of vehicles is this usually found?

Answer 2

An additional gearbox is needed, this is usually found in commercial vehicles.

Question 3

What is usually the lowest gear ratio range for both commercial vehicles and passenger vehicles?

Answer 3

3-4.5 for passenger cars and 5-8 for commercial vehicles

Question 4

What do more gears result in?

Answer 4

Improved fuel economy, performance,increased complexity and greater mass.

Question 5

What does increasing lay shaft distance lead to? What is Ka, Temax , G1st and nt in the equation for layshaft distance?

Answer 5

It leads to a reduction in gear stress, which increases gear life. Ka is the application factor, Te max is the maximum engine torque, G1st is the first gear ratio, and nt is the application efficiency.

Question 6

Gears definition: What is pitch point?

Answer 6

The point where pitch circle diameters interact

Question 7

Gears definition: What is circular pitch (PC)?

Answer 7

Distance along the pitch circle diameter between teeth.

Question 8

What is the diametral pitch (PD)?

Answer 8

The number of teeth per mm of diameter of pitch circle

Question 9

What is the module? What is this equal to?

Answer 9

It is the pitch circle diameter per tooth. Equal to 1/ PD or Pc/pi

Question 10

What is the pressure angle?

Answer 10

The angle between the tooth face and gear wheel tangent.

Question 11

Why would you replace spur gears with helical gears?

Answer 11

Due to the high amounts of noise generated with spur gears, helical gears are much quieter.

Question 12

What is helix angle?

Answer 12

It is the angle between the helix gear and the axis line of the gear.

Question 13

What is face width?

Answer 13

It is the axial length along gear teeth

Question 14

What does a higher helix angle lead to?

Answer 14

A reduction in bending strength

Question 15

What does increasing face width lead to?

Answer 15

Increased strength, but also an increase in gear mass and size.

Question 16

Name all the parts of the drivetrain.

Answer 16

Engine goes to clutch, goes to gearbox, goes to prop shaft, goes to final drive/ differential goes to drive shaft to wheels.

Question 17

Why is a clutch needed and what does it do?

Answer 17

When changing gears the engine needs to be disconnected. The clutch disconnects the engine to allow for this.

Question 18

Why isn’t a dog clutch used?

Answer 18

The engine doesn’t produce high power at low speeds. Therefore the engine needs to be moving, this means that a dog clutch is not viable as it would cause a sudden jolt, as it cannot transmit torque smoothly, hence a friction clutch is used so smooth torque transmission using two plates.

Question 19

What type of clutch is used in cars?

Answer 19

Friction clutch for smooth torque transmission

Question 20

What does the prop shaft stand for? What are some important prop shaft properties

Answer 20

Propellor shaft. It needs to have strong resistance to the twisting action of the driving torque. It must not sag under its own weight- if the center of mass is not aligned with the center of rotation, vibrations will occur.

Question 21

Why is a tubular prop shaft often preferred?

Answer 21

Due to the lower weight, Higher resistance to misalignment, Good torsional strength, and lower inertia.

Question 22

What are composite prop shafts used for?

Answer 22

Often reserved for motorsport due to their high costs.

Question 23

What does the drive shaft do?

Answer 23

It transmits torque from the final drive/ differential to the wheels.

Question 24

What is the significance of universal/ CV joints?

Answer 24

They allow torque to be transmitted through varying angles, so shafts and joints do not have to be in perfect alignment.

Question 25

What would happen if universal joints aren’t used?

Answer 25

Then prop shaft and drive shafts would bend and fracture.

Question 26

What are some requirements of a universal/ CV joint?

Answer 26

Strength as high torque must be transmitted with minimal friction energy losses, Compactness due to limited space, large drive angle due to great suspension in the current vehicle, shaft balance- joint must maintain good alignment. Operation speed- joint must operate at sufficient speeds.

Question 27

What is a commonly used CV joint?

Answer 27

Birfield CV joint

Question 28

What are the final drive’s main functions?

Answer 28

Transmits torque through 90 degrees. Step down speed as a reduction gear. Split single input into two outputs. Allow for inside and outside wheels to turn at different speeds (with differential)

Question 29

What type of gear are used for the final drive?

Answer 29

Conventional gears not useful, bevel and worm gears are needed.

Question 30

What does the differential do?

Answer 30

It allows wheels to turn at different speeds when cornering, due to differing distances covered by each wheel.

Question 31

Why is it not desirable to have an open differential in some circumstances?

Answer 31

As an open differential will always send the torque to the wheel with the least resistance. For example in a puddle, the open differential will send lots of torque to the wheel in the puddle and barely any to the other wheel. The other wheel needs more power as it can more easily propel the vehicle forwards but the open differential does not account for this.

Question 32

What type of differential is more effective than open differential? How does it work?

Answer 32

LSD (Lower slip differential). It works by limiting the speed difference between the wheels.

Question 33

What are the three types of gearboxes?

Answer 33

Automatic ,manual and continuously variable transmission.

Question 34

What type of gear system is used in an automatic gearbox

Answer 34

An epicyclic gear system.

Question 35

What does a continuously variable transmission gearbox mean?

Answer 35

Uses a belt and two cone-shaped pulleys, this means that there are an infinite number of gears.

Question 36

What are the three main drive arrangements?

Answer 36

Rear wheel drive, front drive and four-wheel drive.

Question 37

What are the advantages/ disadvantages of rear-wheel drive?

Answer 37

-Easy access for maintenance and servicing.
-Reduced passenger space
-Good traction in dry conditions, poor traction under acceleration and wet surfaces

Question 38

What are the advantages/ disadvantages of front-wheel drive?

Answer 38

-More compact arrangements make front wheels popular for manufacturers
-Increased passenger space
-Reduced traction under acceleration or hill starts
-Increased traction on wet surfaces
-Difficult to access for maintenance and servicing

Question 39

What are the advantages/disadvantages of four-wheel drive?

Answer 39

Improved traction but extra weight, cost and complexity.