| 1. |
- Juhlin, Magnus, 1975-, et al.
(author)
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A Vehicle Parameter Study on Crosswind Sensitivity of Buses
- 2004
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In: SAE technical paper series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191. ; :2004-01-2612
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Journal article (peer-reviewed)abstract
- Incidents with heavy vehicles have brought the issue of directional stability of buses under the influence of crosswind gusts into focus. In this work the directional stability of buses when exposed to crosswind gusts has been investigated by performing a parameter study on a MBS vehicle-model combined with a generalised crosswind gust model. The study shows that the most important parameters are the magnitude of the yaw moment overshoot at gust entry and the weight distribution in combination with the location of the aerodynamic pressure centre.
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| 2. |
- Juhlin, Magnus, 1975-, et al.
(author)
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Aerodynamic loads on buses due to crosswind gusts – On-road measurements
- 2008
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In: Vehicle System Dynamics. - : Taylor & Francis. - 0042-3114 .- 1744-5159. ; 46, s. 827-835
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Journal article (peer-reviewed)abstract
- Bus and coach traffic is considered to be one of the safest means of travelling. Still, there is a problem with accidents due to crosswind gusts. Therefore it is a need of improving the crosswind performance of buses. As a part of the work with improving the crosswind performance a method for estimating the aerodynamic loads on a bus when exposed to natural crosswind is proposed. The method is based on measurements of the vehicle response and the tire forces from which the aerodynamic loads are estimated using inverse simulations. The results are also shown to agree well with the results of other studies based on wind tunnel measurements. The estimated aerodynamic loads are intended to be used in a future study on crosswind sensitivity using a moving base simulator.
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| 3. |
- Juhlin, Magnus, 1975-
(author)
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Assessment of crosswind performance of buses
- 2009
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Doctoral thesis (other academic/artistic)abstract
- When driving a vehicle on the road, the driver has to compensate continuously for small directional deviations from the desired course due to disturbances such as crosswinds, road irregularities and unintended driver inputs. These types of deviations have a tiring effect on the driver and should therefore be minimised. When the magnitude of these disturbances increases, especially with crosswind, the directional deviation might become so large that the driver will have difficulties in compensating for it, and will thereby affect the traffic safety. The objective of this research work is to increase the understanding of the crosswind sensitivity of buses and to find solutions to the problem of improving the safety of buses with respect to crosswind performance. The work presented in this thesis contributes to increased knowledge about the directional stability of buses under the influence of crosswind gusts through parameter studies using detailed vehicle simulation models, through full-scale experiments and through studies of the effect of steering feel on the subjective and objective evaluation of crosswind performance. A natural crosswind gust model has been derived from wind tunnel measurements and implemented in a multi-body dynamics simulation tool. The aerodynamic loads of the crosswind gust model have been applied on a detailed vehicle model and the behaviour of the vehicle model has been studied for various vehicle configurations in both open- and closed-loop manoeuvres. The vehicle model, with parameters corresponding to real vehicle data, has been validated and the agreement with measurements is good. A method for estimating the aerodynamic loads on a bus due to crosswind on a road section is also presented. Aerodynamic loads under real conditions were estimated using this method and these data were thereafter used in a study where the effect of steering feel on the subjective and objective evaluation of crosswind performance was investigated using a moving-base driving simulator, with the aim of finding a relationship between steering feel and crosswind sensitivity. The thesis covers the influence of changing chassis-related parameters and aerodynamics-related parameters on the crosswind sensitivity, as well as the influence of the setting of the steering system on the crosswind performance of the driver-vehicle system. The results identify areas of high potential for improving the crosswind sensitivity of buses, such as the centre of gravity location and the yaw moment overshoot at gust entry. Furthermore, the study shows the importance of having a vehicle that facilitates prompt driver corrections for reducing the lateral deviation under crosswind excitation; i.e. it is shown that a steering system with the possibility of changing the yaw rate gradient referencing the steering-wheel input when the vehicle is subjected to a sudden crosswind has a good potential for improving the crosswind performance of the driver-vehicle system.
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| 4. |
- Juhlin, Magnus, 1975-
(author)
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Directional stability of buses under influence of crosswind gusts
- 2004
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In: Vehicle System Dynamics. - London : Taylor & Francis. - 0042-3114 .- 1744-5159. ; 41, s. 93-102
-
Journal article (peer-reviewed)abstract
- Incidents with heavy vehicles have put the issue of directional stability of buses under influence of crosswind gusts into focus. In this work the directional stability of buses when exposed to crosswind gusts has been investigated by using a MBS vehicle model combined with a generalised crosswind gust model and results from static wind tunnel measurements. The simulations carried out show the importance of the aerodynamic properties of buses as well as the importance of a proper weight distribution. It is also shown how important the driver model is in order to get realistic directional deviation in simulations and thereby also how important the driver is in order to keep the directional deviation to a minimum in real life situations.
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| 5. |
- Juhlin, Magnus, 1975-, et al.
(author)
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The effect of steering feel on the crosswind performance of buses - Part I : Subjective assessment
-
Journal article (other academic/artistic)abstract
- The steering feel is considered to be an important part of the on-centre handling characteristics of vehicles. Therefore, the steering feel is of interest when improving the crosswind performance of buses. In the present paper a methodology is proposed that utilizes a moving-base driving simulator to study the influence of steering feel on the subjective judgement of bus drivers regarding crosswind performance. Results achieved when using this method show that there exists a correlation between the steering feel and the subjective evaluation of crosswind performance. When the drivers are driving a bus with low crosswind sensitivity, it is shown that low yaw rate gradients are preferred for both the steering wheel torque and the steering wheel angle. For more crosswind-sensitive vehicles, the demand for higher yaw rate gradients increases. That is probably due to the increased need for corrections and the fact that more prompt driver corrections are facilitated by higher yaw rate gradients. It can therefore be concluded that, in order to help the driver in a crosswind situation, it would be valuable to be able to change the steering feel characteristics of the vehicle.
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| 6. |
- Juhlin, Magnus, 1975-, et al.
(author)
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The effect of steering feel on the crosswind performance of buses - Part II : Objective assessment and correlation with subjective judgements
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Journal article (other academic/artistic)abstract
- The steering feel is considered to be an important part of the on-centre handling characteristics of vehicles and therefore of interest when improving the crosswind performance of buses. In this paper a methodology is proposed which uses a moving-base driving simulator for studying the influence of steering feel on the objective judgement of crosswind performance. The results obtained with this method show that there exists a correlation between the steering feel and the objective evaluation of crosswind performance. The objective results show that the lateral deviation due to a crosswind gust is reduced for all levels of crosswind sensitivity when the yaw rate gradients referencing both the steering-wheel angle and the steering-wheel torque are increased, thereby minimising the maximum required steering power. This is in contrast to the subjective results, which showed that low yaw rate gradients were preferred when the centre of gravity was in the most forward position. The results presented in this study imply a great potential in using an adaptive steering system, since the steering feel that objectively is most suitable under crosswind excitation is not subjectively preferred for all the centre of gravity positions.
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