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VARIABLE RATIO FOR EPAS (EPAS VR)

All of the vehicle dynamics benefits of VR in manual and power steering apply equally to electric steering applications. However, VR also offers additional design benefits for Column or Pinion and Rack driven electric steering applications.

Two main obstacles with electric steering are electric current requirements and motor size (torque rating). Steering geometries usually result in higher forces to turn the wheels during parking maneuvers (at lock) compared to straight ahead (on center) driving. VR allows designers to optimize the steering ratio of the rack and pinion for on center driving and parking.

In Column or Pinion assisted systems, this means increasing the mechanical advantage off center (parking). In Rack assisted systems this means slowing the rack speed down off center (parking). Both approaches reduce the electric current and motor torque requirements of the system. Such ratio curves are known as EPAS VR.

As multiple ratio changes are possible with VR, combination of a ‘Vehicle Dynamics’ VR (i.e. ActivRakTM) with an EPAS VR can be achieved using an M-Curve VR.

VR has the largest ratio curve flexibility, which can achieve fast ratio changes and multiple ratio changes.