An EPS Control Strategy to Improve Steering Maneuverability on Slippery Roads

This paper proposes a new Electric Power Steering (EPS) control strategy that improves steering maneuverability especially on slippery roads. In a conventional steering system (including mechanical and hydraulic ones), poor steering wheel returnability associated with reduced alignment torque from the road may lead to awkward handling on slippery roads. In experiments with a test driver, we found that this phenomenon occurs because of the delay in the driver turning the steering wheel to avoid spinning the vehicle. This delay comes from a lower steering wheel returnability than driver expected. Increasing the steering wheel returnability will be effective in avoiding this problem. This can be realized by using the steering angle feedback or the estimated alignment torque feedback. However, the simple feedback of such values will provide drivers with poor road information when the road is slippery. We have developed a new EPS control strategy which certainly provides improved steering wheel returnability and road information on slippery roads. We have tested this control strategy using a test vehicle and confirmed that it provides improved steering maneuverability on slippery roads.