Week 5- Gearboxes and gear ratios

Question 1

What is the gear ratio equation?

Answer 1

-wa/ wb = tb/ta = -Tb/Ta, where t is teeth, w is angular velocity, T is torque

Question 2

What is the equation for determining the range of gear ratios?

Answer 2

Rgears = Rt/ Rl - Rt is top gear ratio and Rl is lowest gear ratio (gear 1)

Question 3

What is the requirement for maximum vehicle speed?

Answer 3

Maximum engine power (increased power = increased rpm = increased rpm at wheels)

Question 4

What is the requirement for maximum traction?

Answer 4

Maximum torque

Question 5

What is the requirement for maximum acceleration?

Answer 5

Maximum torque

Question 6

What is the requirement for the maximum economy?

Answer 6

Engine at mid-range speed under light
load with a small throttle opening

Question 7

How do we determine the top gear of a car?

Answer 7

It is determined by the top speed required for the vehicle, the gear ratio must be set so the peak power available from the engine is at the required top speed

Question 8

How is the lowest gear determined in a vehicle?

Answer 8

We determine the maximum tractive effort required and select the lowest gear. When tractive effort> tractive resistance then the vehicle will accelerate.

Question 9

How are the mid gears selected?

Answer 9

intermediate ratios are used

Question 10

What does a shorter distance between the lay shaft and the main shaft result in?

Answer 10

Increased contact stress and reduced gear life.

Question 11

What is the equation for lay shaft- main shaft distance?

Answer 11

Found on canvas

Question 12

What does a smaller module result in?

Answer 12

module is the distance between teeth on the pitch circle, a smaller module means more teeth which is less noise but a greater mass.

Question 13

How can we overcome the axial force produced by helical gears?

Answer 13

By having an adjacent helical gear to the current one to cancel it out

Question 14

What does increasing the face width of a gear result in?

Answer 14

Increased bending strength but reduces mass and gear size.

Question 15

What are the components of a drivetrain?

Answer 15

Engine, shaft, gearbox, prop shaft, final drive/ differential, drive shaft

Question 16

Why is a friction clutch required in a vehicle?

Answer 16

This is due to the fact the engine must be operating at a speed with sufficient power before
the drive to the wheels is engaged. So a dog clutch for example is insufficient

Question 17

Why is a clutch needed?

Answer 17

The engine must be disengaged from the gearbox in order to change gears, as the drive must be stopped.

Question 18

What does the prop shaft do?

Answer 18

It transmits drive from the engine to the final drive/ differential

Question 19

What are some of the required properties of the prop shaft?

Answer 19

Great torsional strength, must not sag under weight to prevent vibration.

Question 20

Why is a tubular prop shaft often preferred?

Answer 20

• Lightweight, good torsional strength, lower inertia, higher resistance to misalignment.

Question 21

What does the drive shaft do?

Answer 21

It transmits drive (torque) from differential to the wheels

Question 22

Why are universal/CV joints required?

Answer 22

These transmit drive without losses at varying angles, this is useful as it means joints do not need perfect angular alignment. If they weren’t used then shafts would bend and fracture.

Question 23

What requirements are there for universal/ CV joints?

Answer 23

High strength, compactness, and high driven angle due to, modern load springs. It must also be able to operate effectively at high engine speeds.

Question 24

Why are CV joints preferred?

Answer 24

They are preferred as they can transmit shaft speed without losses at high angles.

Question 25

Why are CV joints preferred?

Answer 25

They are preferred as they can transmit shaft speed without losses at high angles.

Question 26

What is the function of the final drive?

Answer 26

Transmits torque through an angle of 90 degrees. Steps speed down (reduction gear). Splits speed into two outputs. Allows wheels to turn at different speeds for cornering (with a differential).

Question 27

What is the purpose of a differential?

Answer 27

The differential allows the inside wheel to turn at a different speed to the outside wheel when cornering.

Question 28

Why is an LSD preferred to an open differential for some applications?

Answer 28

It sends torque to the wheel with more grip, this is better for performance. The open differential sends torque to the wheel with the least resistance.

Question 29

What are the three main drive arrangements that exist?

Answer 29

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