A Torsen differential works by using worm gears and spur gears to distribute torque between the axles, favoring the wheel with more traction. Unlike a standard "open" differential, it limits wheel spin.
Understanding the Torsen Differential
The Torsen differential is a type of limited-slip differential (LSD) that relies on gears rather than clutches to distribute torque. This design offers several advantages over open differentials and other types of LSDs.
Basic Operation
Here's a breakdown of how it works:
- Gear Design: The core of a Torsen differential is its use of worm gears and spur gears. Worm gears can transmit torque at a high angle, and they have a unique property: they can easily turn the spur gear but resist being turned by the spur gear. This is key to the Torsen's operation.
- Torque Biasing: In normal driving conditions (straight line or gentle turns), the Torsen differential behaves much like an open differential, allowing the wheels to rotate at different speeds. However, when one wheel loses traction, the magic happens. Because of the worm gear design, torque is automatically biased towards the wheel with more traction.
- Limited Slip Action: If one wheel starts to spin freely (due to ice, mud, or being lifted off the ground), the Torsen differential resists this. The worm gears prevent the torque from solely going to the spinning wheel. Instead, a significant portion of the torque is redirected to the wheel with grip.
- No Complete Lock-Up: While the Torsen differential limits slip, it doesn't completely lock the axles together like a spool. This is important for maintaining drivability and handling, especially on pavement. The amount of torque bias is determined by the Torque Bias Ratio (TBR) of the differential. For example, a TBR of 3:1 means that the wheel with the most traction can receive up to 3 times the torque of the wheel with the least traction.
Torsens in Front and/or Rear Axles
Torsen differentials can be installed in both front and rear axles, offering improved traction and handling characteristics depending on the vehicle's drivetrain configuration.
- Rear Axle: A Torsen in the rear axle helps reduce wheel spin during acceleration, improving straight-line performance and cornering grip, especially in rear-wheel-drive vehicles.
- Front Axle: In front-wheel-drive vehicles, a Torsen in the front axle mitigates torque steer (the tendency of the steering wheel to pull to one side during acceleration) and improves traction out of corners.
- All-Wheel Drive (AWD): Some AWD vehicles use Torsen differentials in both the front and rear axles and/or the center differential to optimize torque distribution and maximize traction in various driving conditions.
Advantages of Torsen Differentials
- Smooth and Predictable: Torsen differentials offer a smooth and predictable torque transfer, making them suitable for both street and track use.
- Durable: With fewer wear items compared to clutch-type LSDs, Torsen differentials are known for their durability and long lifespan.
- Quiet Operation: They operate relatively quietly compared to some other types of LSDs, which can produce noise during engagement.
Disadvantages of Torsen Differentials
- Zero Traction Scenario: If one wheel is completely off the ground or has absolutely zero traction, a Torsen differential may not be able to transfer any torque to the other wheel. This is because it needs some resistance to bias torque effectively.
- Cost: Torsen differentials can be more expensive than open differentials or some other types of LSDs.
Example: Cornering Dynamics
Consider a vehicle cornering. According to the provided reference, friction in the differential will oppose motion, and that will work to slow the faster side and speed up the slower/inner side. In a vehicle equipped with a Torsen differential, this friction is managed to distribute torque effectively. The outer wheel needs to rotate faster than the inner wheel. The Torsen helps ensure that the outer wheel receives adequate torque, preventing excessive wheel spin on the inner wheel and improving cornering grip.
| Feature | Description |
|---|---|
| Gear Type | Worm gears and spur gears |
| Torque Biasing | Automatically biases torque to the wheel with more traction |
| Limited Slip | Prevents excessive wheel spin by resisting the flow of torque to the wheel with less traction |
| Applications | Front axles, rear axles, and center differentials in AWD vehicles |
| Advantages | Smooth operation, durability, quietness |
| Disadvantages | Can struggle with zero traction scenarios, higher cost |
