Fig. 1 Composition of power steering 2.Steering wheel characteristic for vehicle speed There is a necessity that the assistance torque that assists in the steering wheel torque is adjusted according to the vehicle speed because of safety and the steer feeling improvement. The adjustment of this assistance torque is especially important for the motorcycle. A big assistance torque is necessary when vehicle speed is high, and small assistance is necessary when it is low as shown in Figure 2. Therefore, there is necessity to investigate the relation between a speed of the vehicle and a necessary assistance torque by the experiment. Fig. 2 Assistance torque and Steering wheel torque 3. Experimental equipment We experiments with the experiment machine. Figure 3 shows Kawasaki ZRX400. This experimental vehicle is the most general size in the two-wheeled motor vehicle in Japan now. Table 1 shows details of the experimental vehicle. The steering wheel torque is measured by using Kyowa Electronic Instruments KFG-3-120-D16-11L3M2S that shows in Figure 4. The measurement place of the swerve is a part in a parallel direction and the vertical direction against the steering wheel axis near the handlebar. It is shown in Figure 4. Because the gauge picks up an extra transformation when 492
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