Mechanical Engineering: Gearing and Torque

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Questions and Answers

What is the relationship between the torque of gear B and gear A?

TB = TA

TB = 2 TA (correct)

TB = 0.5 TA

TB = 3 TA

What is a key characteristic of a sliding mesh type gear box?

It provides the highest transmission efficiency. (correct)

It can engage multiple pairs of gears simultaneously.

It requires expensive materials for construction.

All gears are permanently fixed.

What must be done before shifting gears in a sliding mesh type gearbox?

Change the gear oil.

Increase engine speed.

Stop the tractor. (correct)

Engage the parking brake.

In a system of gear rotation, how does the additional gear affect the rotation direction?

It keeps the same rotation direction as the driving gear. Signup and view all the answers

What is NOT a limitation of sliding mesh type gearboxes?

It allows for multiple gear shifts simultaneously. Signup and view all the answers

Which of the following gear types is commonly used in indigenous tractors?

Sliding mesh gear Signup and view all the answers

Which shafts in a sliding mesh gearbox are usually parallel to each other?

Main and counter shafts. Signup and view all the answers

What mechanism is used to ensure only one pair of gears engages at a time?

Spring-loaded detent balls. Signup and view all the answers

What is the primary function of the gearbox in a tractor?

To reduce wheel speed and allow for variable tractive effort Signup and view all the answers

The horsepower delivered to the rear wheels is directly affected by which of the following?

Torque and speed of rotation Signup and view all the answers

If gear A has 10 teeth and is rotating at 100 rpm, what will be the speed of gear B with 20 teeth?

50 rpm Signup and view all the answers

How does increasing the torque at the wheels affect the speed required?

It requires lower speed for increased torque Signup and view all the answers

What will happen if a tractor's engine power is delivered directly to the rear wheels?

The tractor will run at constant high speed with fixed tractive effort Signup and view all the answers

What principle does gearing utilize to transmit motion between shafts?

The principle of gear trains Signup and view all the answers

What is the mathematical representation of horsepower delivered to the rear wheels?

$\frac{2 \pi \times Torque \times rpm}{4500}$ Signup and view all the answers

What is the result of doubling the number of teeth on the driven gear?

The speed of the driven gear becomes half of the driving gear Signup and view all the answers

What is a primary feature of the constant mesh transmission?

The gears remain in constant mesh regardless of the vehicle speed. Signup and view all the answers

What is necessary for shifting gears in a constant mesh transmission to prevent damage?

The tractor needs to be stopped. Signup and view all the answers

Which component in a synchromesh transmission helps to equalize gear speeds before engagement?

A cone-type friction clutch. Signup and view all the answers

What is a disadvantage of the synchromesh gear box compared to sliding mesh gear boxes?

It has lower power transmission efficiency. Signup and view all the answers

What advantage does the constant mesh transmission have over sliding mesh type gear box regarding gear engagement?

No wear and tear during gear engagement. Signup and view all the answers

Why is the synchromesh transmission rarely used in tractors?

Because it is less efficient than constant mesh gear boxes. Signup and view all the answers

How do helical gears benefit the operation of constant mesh transmissions?

They improve gear shifting noise and effort. Signup and view all the answers

Which statement correctly describes an operational characteristic of synchromesh transmissions?

They enable gear shifting without stopping the tractor. Signup and view all the answers

Study Notes

Horsepower & Torque

Horsepower delivered to rear wheels is dependent on torque and engine speed.
Higher torque requires lower engine speeds, and vice versa, for constant engine horsepower.

Necessity of Gearbox

Tractive effort needed for rear wheels varies depending on load and ground conditions.
Direct engine power delivery results in constant, high speeds and fixed tractive effort—not ideal for tractors.
Tractors require high torque at low engine speed, while engines operate at high speed and low torque.
Gearboxes are used to reduce engine speed, leading to torque multiplication for desired tractive effort.

Principle of gearing

A gear train transmits motion between shafts via gear wheels.
If a driving gear (A) has 10 teeth and a driven gear (B) has 20 teeth, and gear A rotates at 100 RPM, gear B's speed is calculated as:
- Speed of driven gear = (Speed of driving gear * Number of teeth on driven gear) / Number of teeth on driving gear
- Speed of driven gear = (100 RPM * 10 teeth) / 20 teeth = 50 RPM
This shows that doubling the teeth on the driven gear halves the speed, but doubles the torque.
The direction of rotation of the driven gear is opposite to the driving gear.
In a compound gear train, the final gear rotates in the same direction as the driving gear.
The final driven gear's speed depends on the product of gear ratios of each pair.

Types of Gearboxes:

Sliding Mesh Gearbox: Most common in indigenous tractors.
- Main and counter shafts are parallel to the clutch shaft, with a third shaft for reverse gear.
- Gears on the counter shaft are fixed, while those on the main shaft slide to engage with appropriate counter shaft gears.
- Gearshift rails and forks are used for gear changes.
- Detent balls or other devices ensure only one gear pair engages at a time.
- Provides 3-4 forward speeds and 1 reverse speed.
Advantages:
- High transmission efficiency
- Simple design
- Cost-effective
Limitations:
- Suitable for small tractors only
- Hard to move large gears
- Large teeth can interfere and cause damage while shifting
- Tractor must be stopped before shifting to avoid damage.
Constant Mesh Gearbox: Similar to sliding mesh, but the gears on the main and counter shaft are always in mesh.
- Gears on the main shaft are mounted on bushings, allowing them to rotate freely with the counter shaft gear in neutral.
- Spline sleeve couplings, controlled by the gear lever, engage or disengage gears.
- Coupling device movement locks a free gear onto the main shaft, getting drive through the driven gear.
- Slightly less efficient than the sliding mesh due to friction between rotating parts.
- The tractor needs to be stopped before shifting to avoid damage.
Advantages:
- Constant gear mesh reduces wear and tear and damage during gear changes
- Helical gears minimize shifting noise and effort.
Limitations:
- Tractor must be stopped before shifting to avoid damage.
Synchromesh Gearbox: Basically a constant mesh with an added synchronizer device to equalize speeds before engagement.
- Common in automobiles, rare in tractors.
- Allows for shifting while the tractor is moving.
- Synchronizer regulates speed of gears and shafts before changing gears.
- Small cone-type clutches are used for synchronization.
Advantages:
- Shifting without damage, even while the tractor is moving
- Popular for tractors used for highway transport
Disadvantages:
- Lower power transmission efficiency compared to sliding mesh
- Higher cost

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Description

This quiz explores the fundamentals of horsepower, torque, and the necessity of gearboxes in mechanical systems. Understand how gear ratios affect speed and the importance of balancing engine characteristics for optimal performance, especially in agricultural machinery. Test your knowledge on the principles of gearing and tractive effort.