Differential explained - How differential works open, limited slip

Summary

This video explains how differential gear trains work in vehicles, particularly focusing on their importance in allowing rear wheels to rotate at different speeds during turns. It covers the function of open and limited-slip differentials, detailing the components like the pinion, ring gears, spider gears, and side gears. The video also introduces the concept of friction in limited-slip differentials, helping vehicles maintain traction on slippery surfaces. Viewers are encouraged to learn hands-on by building their own differential model with provided 3D-printable design files, with sponsorship from PCBWay for 3D printing services.

Takeaways

• 😀 Differential gear trains are crucial in vehicles, especially for distributing power to the wheels, allowing them to rotate at different speeds during turns.
• 😀 When a car moves straight, the differential ensures both rear wheels rotate at the same speed, but during turns, the wheels rotate at different speeds to avoid tire slip and damage.
• 😀 Without a differential, if both rear wheels rotate at the same speed while turning, the tires would slip, wear out, and the axle could break.
• 😀 An open differential allows the wheels to rotate at different speeds but can cause one wheel to lose traction on slippery surfaces, sending power to the wheel with less resistance.
• 😀 Limited slip differentials (LSD) prevent one wheel from slipping by limiting the difference in speed between the wheels, ensuring better traction on slippery surfaces.
• 😀 A differential consists of the main housing, a drive pinion gear, a ring gear, and two Spider gears that connect to side gears, which in turn connect to the wheel axles.
• 😀 In a basic open differential, when the car turns, the inner wheel rotates slower and the outer wheel rotates faster, allowing both to follow their respective paths without slipping.
• 😀 The gear ratio of the differential, defined by the pinion gear and ring gear teeth, affects fuel efficiency and acceleration in cars.
• 😀 Limited slip differentials use clutch packs and spring-loaded friction plates to prevent excessive wheel speed differences, temporarily locking the side gears to maintain traction.
• 😀 A limited slip differential provides better control and traction, especially on icy or slippery surfaces, by distributing power more evenly between the wheels compared to an open differential.
• 😀 To understand how a differential works, building a 3D model or using a printed version allows a hands-on experience of the gear interactions and movement.

Q & A

What is the purpose of a differential gear train in a car?

The differential gear train allows the rear wheels to rotate at different speeds, especially when turning. This prevents tire slippage and excessive wear by enabling the outer wheel to cover a longer distance during a turn.

Why do the rear wheels of a car need to rotate at different speeds when turning?

When a car turns, the inner wheel follows a shorter path than the outer wheel. To maintain traction and prevent slipping, the outer wheel must rotate faster to cover the longer distance in the same amount of time.

What happens if a differential is not installed in a vehicle?

Without a differential, both wheels would rotate at the same speed during turns, causing tire slippage and excessive wear. The car would become harder to handle, and the axle could potentially break due to the uneven forces.

What is the difference between an open differential and a limited slip differential?

An open differential allows the wheels to rotate at different speeds but can lead to a loss of traction if one wheel encounters less friction, such as on ice. A limited slip differential uses clutches to limit the speed difference between the wheels, providing better traction under slippery conditions.

How does a limited slip differential work?

A limited slip differential has additional clutch packs behind each side gear, which temporarily lock the side gears together. When there’s a speed difference between the wheels, the clutches allow for some slip, but they prevent excessive wheel spin, providing better traction on slippery surfaces.

Why are the gears in a differential typically spiral-cut?

Spiral-cut gears are used in differential assemblies because they increase the contact surface area between the gears, which helps improve efficiency and reduce noise compared to straight-cut gears.

What is the role of the spider gears in a differential?

The spider gears are small gears inside the differential that allow the side gears (connected to the axles) to rotate at different speeds. They distribute the torque between the wheels and enable the car to turn smoothly without causing tire slip.

How does the clutch-based limited slip differential prevent one wheel from losing traction?

In a clutch-based limited slip differential, the clutch friction plates and discs work together to lock the side gears when there is a significant torque difference between the wheels. This reduces wheel slip and allows the car to maintain better traction on slippery surfaces.

What is the effect of a low gear ratio in a differential?

A low gear ratio (e.g., 3.9:1) increases fuel efficiency but decreases acceleration, making it ideal for cars that prioritize fuel economy over speed. The lower ratio reduces the engine's load, enabling more efficient power transfer.

How can building a model differential help in understanding how it works?

Building a model differential provides a hands-on way to visualize how the gears interact, including how the spider gears allow different wheel speeds during turns. It helps in better understanding the mechanics of power distribution in a car's drivetrain.