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VARIABLE RATIO (VR)

Variable Ratio (VR) steering racks from Bishop provide remarkable improvements in:

Primary Safety

  • more relaxing to drive at high speeds ensuring less fatigue and greater safety;
  • improved control during radical avoidance maneuvers and skid recover;
  • increased driver confidence in lateral placement of vehicle.

Driver Comfort

  • reduced need to change position of hands on steering wheel;
  • reduced turns lock-to-lock ensures easier parking.

Bishop’s VR steering racks, which are manufactured on its specifically developed Warm Forging process, have the largest ratio curve flexibility, which can achieve fast ratio changes and multiple ratio changes.


STEERING RACK PRODUCT

Y-Shape Steering Racks

Bishop’s Y-Shape Rack design reduces rack roll, thus improving steering stiffness (precision). The inherently wider teeth of a Y-Rack can be up to 110% of the shaft diameter, providing maximum ratio flexibility, even tooth load distribution and superior rack tooth strength. The stronger cross section in the teeth area often enables reduction in shaft size diameter with associated cost and weight reductions.


D-Shape Steering Racks

The Bishop’s D-Shape Rack design makes Bishop’s VR available to all applications and offers a higher level of tooth accuracy, thereby maximizing the VR potential for a given size and configuration. This rack type is ideal for existing applications where VR is required, as the features of the existing rack design can be easily reproduced or improved. Due to the use of the warm forging process, there is still freedom in shape and cross section design. 


ActivRakTM

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An ActivRakTM VR rack has a unique form of Bishop’s VR, where the rack gain characteristic is tuned to achieve a particular vehicle yaw gain target. This yaw gain target is consistent with what might be achieved using an angle overlay active steering system but at negligible cost and without any additional components or systems. An ActivRakTM VR rack has typically gain increase greater than 25% in less than 170° pinion rotation from the on-centre position, in main case in 90° or less.


M-Curve VR

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BishopVR offers the possibility for multiple ratio changes - an application with 2 or more ratio changes is referred to as an 'M-Curve' VR. Some existing power assistance systems cannot support the fast ratios required for improved vehicle dynamics at full lock. The use of a second (slower) ratio at lock directly reduces the assistance torque required at lock in column driven assisted steering systems (CEPAS). This same approach reduces the rack speed at lock in rack driven assisted steering systems (REPAS or HPAS), indirectly achieving a similar benefit. The result is increased steering performance without increasing the power assistance requirement.