The differential is a core component in a vehicle's drivetrain, primarily used to address the speed difference between the left and right wheels during cornering and complex road conditions, ensuring that the drive wheels on both sides can operate at different pure rolling speeds. The following is a detailed explanation:

1. Core Function

Torque Distribution

The differential flexibly distributes engine torque between the left and right output shafts (axles). For example, if one wheel encounters a low-grip surface (such as snow), the differential redistributes torque, giving the wheel with traction more power (a power distribution ratio of up to 7:3) to prevent slip.

Adapting to Different Angular Velocities

When a car turns, the inner and outer wheels have different turning radii, requiring the outer wheels to rotate at a faster angular velocity. The differential automatically adjusts the speed of the axles on both sides through a planetary gear structure, increasing the outer wheel's speed and reducing it on the inner wheel, achieving smoother cornering (increasing the pure rolling ratio by over 50%).

Ensuring Power Transmission

The differential ensures consistent power transmission between the drive wheels under various driving conditions, enhancing the vehicle's driving performance. For example, on bumpy roads, the differential can redistribute torque within 0.1 seconds, preventing power loss.

Preventing Slip

By precisely adjusting the speed difference between the two wheels, the differential prevents slippage between the tires and the road, reducing tire wear and improving driving safety.

II. Structure and Working Principle

Basic Components

The differential primarily consists of planetary gears, a planetary carrier (differential case), and axle gears. Engine power enters the differential through the drive shaft, driving the planetary carrier, which in turn drives the left and right axles, respectively, driving the left and right wheels.

Straight Driving

When the car is traveling straight, the left and right wheels and the planetary carrier rotate at equal speeds, creating a state of equilibrium. At this point, the planetary gears only revolve, not on their own, and the speeds of the left and right wheels are the same.

Curving

When turning, the inside wheel has a shorter distance to travel and therefore needs to reduce its speed; the outside wheel has a longer distance to travel and therefore needs to increase its speed. As the planetary gears revolve, they rotate about their own axes, causing the axle gears on one side to increase their speed while those on the other side decrease. The increase in speed equals the decrease in speed, thus achieving a speed differential between the two wheels. III. Types and Classifications
Open Differential
Distributes torque via the path of least resistance. Its structure is simple, but when one wheel slips, 99% of the torque is transferred to the wheel with low adhesion, resulting in traction loss. For example, when climbing a slope on icy or snowy roads, a vehicle's ability to escape is reduced by 60%.
Limited Slip Differential (LSD)
Using friction plates or hydraulics to enhance traction on one side, it can provide a locking torque of 500-1500 N·m, reducing power loss during slip.
Locked Differential
Using a dog clutch for mechanical locking, it forces a 50:50 torque split between the front and rear axles, making it suitable for extreme off-road situations (such as rock climbing).
Torsen Differential
Utilizing the self-locking characteristics of the worm gear, it automatically locks on slippery surfaces (up to 75% locking ratio), dynamically distributing torque and improving maneuverability.

IV. Failure Protection and Maintenance
Failure Warning Signal
Unusual noise (metal scraping sound intensity >70 decibels) occurs when turning below 20 km/h. Steering wheel vibration amplitude > 0.3g when driving above 60 km/h.
In extreme cases, a center differential failure can cause uncontrolled power distribution between the front and rear axles, causing the four-wheel drive vehicle to revert to front-wheel drive or rear-wheel drive.
Daily Maintenance
Regularly check the differential fluid (recommended every 60,000 km). If any unusual steering noise or wheel drag occurs, promptly inspect and repair it.

V. Application Scenarios
Rear-Wheel Drive/Four-Wheel Drive Vehicles
Differentials play a significant role in rear-wheel drive and four-wheel drive vehicles. In front-wheel drive vehicles, the differential is typically integrated into the transmission.
Complex Road Conditions
On bumpy, snowy, or slippery surfaces, the differential dynamically distributes torque, improving vehicle maneuverability and stability.