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Development of SH-AWD System using EPS Relative Steering Angle Signal

Article of Honda R&D Technical Review Vol.23 No.1

Summary

The Super Handling-All Wheel Drive (SH-AWD) system uses the steering angle value to determine the proper left and right rear wheel torque distribution ratio to enhance vehicle handling response. Cost reduction in the application of the SH-AWD system is realized by (1) replacing the conventional stand-alone absolute steering angle sensor with an EPS resolver sensor, which determines the position of the EPS power assist motor, (2) applying integration to the change in the EPS motor position over time to yield a steering angle value relative to the initial steering rack position, and (3) using a new midpoint learning algorithm to determine the true steering angle value by calculating the difference between the initial steering rack position and the straight-ahead driving position. Through this process, a steering angle value relative to the initial steering rack position is acquired and is equivalent to the value that would be provided by an absolute steering angle sensor. To determine the straight-ahead steering position, a learning period is required during which the vehicle needs to travel a minimum distance every time the ignition key is turned on. To meet all existing system and CBU performance requirements during this learning period, two algorithms were created. First, a steering angle estimation algorithm substitutes as the true steering angle to allow SH-AWD to perform normal torque distribution operation. This algorithm uses two independent calculations to prevent excessive steering angle estimation, which would distribute more torque than necessary. Second, a new vehicle stability enhancement algorithm reduces the SH-AWD rear torque amount when an unstable driving event occurs. Using these algorithms, the SH-AWD system can achieve comparable performance by acquiring steering angle data from an EPS resolver sensor as opposed to a more costly absolute steering angle sensor.

Author (organization or company)

Steve TURNER(HONDA R&D AMERICAS, INC.)

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