2007 Fiscal Year Final Research Report Summary
Complementary Behaviors of Active Steering and Traction/breaking Force Distribution and Online Optimizations
| Project/Area Number |
18560230
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Dynamics/Control
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| Research Institution | Kyoto University |
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Principal Investigator |
NISHIHARA Osamu Kyoto University, Graduate school of Informatics, Associate Professor (00218182)
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| Co-Investigator(Kenkyū-buntansha) |
HIRAOKA Toshihiro Kyoto University, Graduate School of Informatics, Research Associate (30311749)
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| Project Period (FY) |
2006 – 2007
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| Keywords | Active Steering / Four-wheel Independent Steering / Traction / Breaking Force / Real-time Optimization / Tire Workload / Friction Coefficient / Brush Model / μ-split Road |
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| Research Abstract |
This research project deals with the active control of four-wheel independent steering vehicle with respect to the tire force distribution. From the viewpoint of active safety, there is a strong need for further progress in vehicle dynamics control. In order to maintain direct yaw-moment control, traction/braking forces must be effectively distributed over the four wheels. Increasingly precise online optimization algorithms are being studied to replace the former empirical methods. According to the tire friction circle model, the tire force will not exceed the product of the vertical load on the tire with the road friction coefficient If the tire workload is optimized in minimax criterion, the optimal distribution of traction/braking force can be determined for all tires, under the natural condition that the tires have identical friction coefficients; the actual friction coefficient is not required. First of all, a simple algebraic approach is derived to isoangle steering systems appli
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cable to the front wheel active steering and the four-wheel active steering vehicles. Four-wheel independent steering means vehicles whose wheels' steering actions are totally independently controllable. In optimization of the tire workload, the distribution of tire forces is optimized between the left and right front wheels using control conditions of lateral forces at the front and the rear axles. In addition to the basic problem formulation, the complementarities between the steering and traction/breaking force distribution can be exploited to further reduce the maximum tire workload. To realize the reduction effecte, the tire force distributor must be reconstructed to take accounts of the complementarity relations between two terms, but basically the physical configuration is unchanged. The algorithm is updated and the cooperation of the steering and the traction/braking force distribution effectively reduces the maximum tire workload. Since the workload based optimization is based on the assumption that the road friction coefficient is uniform over four wheels, the μrate based optimization needs the estimated value of road friction coefficients. So we studied the friction coefficient estimation method based on the brush model. The relation between tire forces and the aligning torque is translated into the estimation formula for the road friction coefficient at the contact area. The workload minimization algorithms are translated into the μrate based approach by the replacement of the estimated vertical loads of tires by the equivalent values. These algorithms are verified by the numerical simulations using popular simulation software CarSim with the vehicle controller together with the tire force distributor implemented using the Matlab/Simulink environment. Less
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