Definitions

power-assisted steering

Torque steering

Torque steering is the influence of the engine torque on the steering for some front-wheel drive vehicles. For example, during full acceleration the steering may pull to one side, which may be disturbing to the driver. This either causes a tugging sensation in the steering wheel, or else the car veers from the intended path. As the torque steer effect is directly related to the engine torque capabilities, this problem becomes more and more evident with high output engines with strong torque in the low RPM range.

Torque steering may be confused with steering kickback.

Causes

Root causes for torque steer are:

  • Incorrect sidewall ply design allowing deformation of the tire sidewall.
  • Nonsymmetric driveshaft angles, e.g. due to
    • Nonsymmetric design of the vehicle, e.g. different driveshaft length
    • Transient movement of the engine
    • Tolerances in engine mounts
  • Different driveshaft torques left to right
  • Suspension geometry tolerances
  • Unequal traction forces due to road surface (µ-Split) in combination with kingpin offset
  • Open differentials may not equally distribute the torque between the two driveshafts, due to friction in the side gears etc. The same will be seen if a limited slip differential is used. Either way there is a tendency for the slower wheel to receive more torque.

Ways to reduce the effect of torque steer

  • Employ the use of a tire with proper sidewall ply design, mitigating the sidewall deformation.
  • Have both driveshafts of the equal length by using an intermediate shaft (or "lay shaft") on one side of the transmission. This is already implemented on most modern cars. When the driveshafts have different length and excessive torque is applied, the longer half shaft flexes more than the shorter one, thus causing one wheel to momentarily spin more slowly than the other, resulting in a steering effect. So the equal lengths of the driveshafts reduce the torque steer effect.
  • Implement double wishbone suspension or multi-link suspension.
  • Distribute the torque better between the driveshafts. Automobile transmission manufacturers like Quaife, Torsen, TrueTrac, Gold Trac offer worm-gear-based torque-biasing limited slip differentials for front-wheel drive vehicles, which help to reduce the amount of torque steer and improve cornering.
  • Reduce the amount torque from the front axle by passing part of torque to the rear axle. This is achieved on all-wheel-drive (AWD) vehicles with full-time AWD, e.g. with mechanical gear-based transaxle differential.
  • Power assisted steering (set on most modern cars) make the torque steer effect less noticeable to the driver. Steer-by-wire also hides the effect of torque steer from the driver.

Note that rear-wheel-drive vehicles do not usually suffer from the torque steer effects on the rear wheels , since the engine is not connected to the steering gear unless it has all wheel steering.

References

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