Torsen differential
Torsen are differential gear with self-locking effect that the group of locking differentials belong. Today they are mainly as a center differential in four-wheel vehicles used, especially in the Audi quattro -models.
The name "Torsen" is derived from the English words for " torque " ( Tor que) and "sensitive" ( sen sitive). This made-up word describes the torque-sensing properties of these limited slip differentials.
The principle invention dates back to 1918. The developer of type A was Vern Gleasman, who applied for a patent for the differential in 1958. In Germany, Torsen has been a registered trademark of JTEKT Corporation based in Osaka ( Japan ) since 1983 . The Torsen system was first launched in 1983 in the HMMWV . From 1986 it was used by Audi and in the Lancia Delta HF 4WD .
technology
Like all limited slip differentials , the Torsen differential is in principle an open differential whose ability to balance torque between the output shafts is impaired by its low efficiency.
The first two types of Torsen are mainly represented on the market today:
- In type A , the differential gears (planetary gears) and the side gears (output) are designed as helical gears, i.e. the teeth are at an angle of 45 ° to the axis and the axes are perpendicular to each other. The sliding movement in the toothing and the simple storage cause high friction losses, which generate the desired locking effect if a speed difference occurs on the output side.
- With type B , the axles of all wheels are parallel, which is why it is sometimes called a “parallel axle differential”. The toothing is designed as a helical toothing (helical toothing) with extremely large helix angles. Here, too, forces arise in the toothing, which press the face of the gears against the housing. A large part of the friction occurs there.
- The type C is constructed as a planetary gear. Due to the large helix angles of the gears and oblique splines, large axial forces arise in the differential, which generate the desired locking torque via friction disks. The type C can be combined with an open differential to a compact unit. With type C the torque distribution is not 50:50, as is usual with other axle differentials; therefore the type C is used exclusively as a central differential between the axles (especially at Audi).
Type A achieves much higher locking values than type B. As with all torque-sensing differentials, if there is no ESP , hardly any propulsion is generated when the wheel is raised. In vehicles without ESP, this can have effects when starting off. In such situations, you can remedy this by applying the brakes slightly, which distributes the power to all wheels. The ESP compatibility and the influence on the driving dynamics in the sporting area are advantageous.
Construction type A
Instead of the four bevel gears in an ordinary differential gear, the Torsen uses several helical gears with a pitch of about 45 degrees , which, coupled to one another via pairs of spur gears at the two ends of the helical gears, engage in the two helical drive shafts. This allows speed differences to be compensated; The locking effect is created by the high power dissipation inherent in the helical gears and by additional friction disks.
Influence on the driving dynamics
Torsen differentials lock depending on the transmitted torque. With Torsen differentials (as with all torque-sensing limited slip differentials ) one can differentiate between several operating modes:
- In train operation, the vehicle is driven by the engine. If an axle transmits less drive force, i.e. if there is a loss of traction , the Torsen differential automatically transfers more drive force to the more slowly rotating axle (i.e. usually those with more traction). If an axle or a wheel is raised (or is standing on ice as smooth as a mirror), the locking effect of the Torsen differential remains ineffective - the wheel or axle with the least traction will spin. A differential lock or traction control can help here.
- In overrun mode, the engine is towed, i.e. driven by the vehicle. If you take your foot off the gas, the flow of forces in the Torsen differential is reversed. If the driver has disengaged it, it acts like an open (unlocked) differential and the axles are largely decoupled. This enables the ABS and ESP to intervene undisturbed.
- When cornering, the Torsen differential distributes more and more drive forces to the slower rotating axle, which is mostly the rear axle. If the rear axle loses traction, Torsen automatically provides more power on the front axle.
application
The first Audi Quattro all-wheel drive vehicles from 1980 onwards were initially fitted with manually lockable differentials of the conventional type, which were then replaced by type A Torsen differentials in the course of the model upgrade in 1986. In Audi - and VW -Allrad vehicles that were based on transverse-mounted to the driving direction front engines were Visco and Haldex couplings installed.
From 1990 a Torsen transmission was installed in the Rover 220 Coupé 2.0 Turbo .
The third RX-7 generation (FD) from Mazda (1992-2002) has a Torsen rear axle differential installed, as is the 1.9-liter Mazda MX-5 (NB) and the Honda S2000 . The Toyota GT86 and Subaru BRZ , developed in cooperation with Subaru and Toyota and presented in 2012, also have a Torsen rear axle differential.
Among the front-wheel drive vehicles in the series a Torsen differential was installed, including the Ford Focus RS and the special series "Championship White Edition" of the Honda Civic Type R .
Peugeot installed a limited-slip Torsen differential in its RCZ R released in 2014. The Peugeot 308 GTi also has a Torsen differential.
Torsen differentials are still used as center differentials, especially in Audi vehicles with longitudinally installed engines, as an important feature and image carrier.