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Steering redundancy for self-driving vehicles using differential braking
Published in Johannes Edelmann, Manfred Plöchl, Peter E. Pfeffer, Advanced Vehicle Control AVEC’16, 2017
The scrub radius is a lateral displacement between the tyre’s center of rotation, caused by the kingpin axis intersection with with the road plane, and the centerline of the tyre. When the center of rotation is outside of the centerline of the tyre, the scrub radius is defined as negative, otherwise it is positive. See Figure 5 for clarification. The differential brake test described in Section 3.2 was conducted with hands-on the steering-wheel, where the driver fixed the steering-wheel angle to zero. The test is here repeated but now with hands-off the steering-wheel i.e. no steering-wheel torque is applied during the test event. As shown in Figure 6, the steering-wheel angle is no longer zero caused by the (positive) scrub radius. At the end of the manoeuvre, when vehicle speed is lower, the steering angle is significantly increased up to 65°. This will in turn, contribute to even higher cornering curvature. The large steering-wheel angle corresponds to approximately 0.07 rad (= 4°) wheel angle, which confirms that the small angle approximation made in Equations 1 and 2 is relevant. The experiment clearly demonstrate that the scrub radius effect substantially influences the physical limit of maximum cornering curvature. It should be mentioned that the scrub radius effect can be modeled and included in the vehicle model. This would be beneficial since such a model would predict the curvature better, but at the expense of a more complex model. The scrub radius is however uncertain since it for example varies for different wheel hubs, and consequently, the model becomes sensitive for the scrub radius parameter.
Chassis systems
Published in Tom Denton, Advanced Automotive Fault Diagnosis, 2020
The scrub radius is the distance between the contact point of the steering axis with the road and the wheel centre contact point. The purpose of designing in a scrub radius is to reduce the steering force and to prevent steering shimmy. It also helps to stabilise the straight-ahead position. It is possible to design the steering with a negative, positive or zero scrub radius as described in Table 7.3.
Chassis systems
Published in Tom Denton, Automobile Mechanical and Electrical Systems, 2018
The scrub radius is the distance between the contact point of the steering axis with the road surface plane and the wheel centre contact point. The functions of the scrub radius are to reduce the steering force, prevent shimmy and stabilize the straight-ahead position.
Steering redundancy for self-driving vehicles using differential braking
Published in Vehicle System Dynamics, 2018
The scrub radius is a lateral displacement between the tyre's centre of rotation, caused by the kingpin axis intersection with with the road plane, and the centreline of the tyre. When the centre of rotation is outside of the centreline of the tyre, the scrub radius is defined as negative, otherwise it is positive. See Figure 6 for clarification. The differential brake test described in Section 3.2 was conducted with hands-on the steering-wheel, where the driver fixed the SWA to zero. The test is here repeated but now with hands-off the steering-wheel, that is, no steering-wheel torque is applied during the test event. As shown in Figure 7, the SWA is no longer zero caused by the (positive) scrub radius. At the end of the manoeuvre, when vehicle speed is lower, the steering angle is significantly increased up to 65 degrees. This will in turn, contribute to even higher cornering curvature. The large SWA corresponds to approximately 4 degrees wheel angle, which confirms that the small angle approximation made in Equations (1) and (2) is relevant. The experiment clearly demonstrate that the scrub radius effect substantially influences the physical limit of maximum cornering curvature. It should be mentioned that the scrub radius effect can be modelled and included in the vehicle model. This would be beneficial since such model predicts the curvature better. The scrub radius is however uncertain since it for example varies for different wheel hubs, and consequently, the model becomes sensitive for the scrub radius parameter.