F2010D022
Driving Torque Transfer System for FWD with Steering Wheel Torque Compensation
Driving torque transfer systems between right and left wheels enable to improve turning performance in everyday driving as well as vehicle stability in critical situations such as a severe lane change, whereas braking torque distribution systems work effectively mainly for stabilizing vehicle dynamics because of deceleration. Front-wheel drive especially gains greater benefits than rear/all-wheel drive from driving torque transfer systems for reducing understeer and improving yaw rate response. Through our research and development, however, a couple of difficulties were found to be overcome for applying it to front-wheel drive. The first is how to ensure compatibility between turning and stability performance by using a single controller. For example, when using yaw rate following control to improve turning performance of front-wheel drive with strong understeer, it tends to generate excessive turning yaw moment, resulting in large slip angle in transient states. On the other hand, slip angle feedback can augment stability while turning performance is restricted. To cope with the contrary, we design a two-degrees-of-freedom controller, consisting of yaw rate following and slip angle feedback, each of which specifies its respective performance independently in each operating region that is automatically determined based on a vehicle model. The proposed two-degrees-of-freedom controller works between the both regions without discontinuities and complicated parameter switching. The second one is how to reduce torque steer caused by driving torque transfer at front-wheels. Instead of designing front suspension geometry appropriately for reducing torque steer with extra weight and cost, we decide to compensate it by active control of electrical power steering, in which additive torque is given as a function of yaw rate with some modification to original assist and damping torque. As a consequence, torque steer decreases to almost zero in steady and transient states. The paper presents the concrete methods to design the two-degrees-of-freedom controller of vehicle dynamics and the steering wheel torque compensator, and demonstrates their effectiveness by simulation and experiment data.
This abstract is supplemented by a PDF, which can be viewed here.