Lars Drugge

A method to find correlations between steering feel and vehicle handling properties using a moving base driving simulator

There have been several investigations to find out how drivers experience a change in vehicle-handling behaviour. However, the hypothesis that there is a correlation between what the driver perceives and vehicle- handling properties remains to be verified. To define what people feel, the human feeling of steering systems was divided into dimensions of perception. Then 28 test drivers rated different steering system characteristics of a semi-trailer tractor combination in a moving base-driving simulator. Characteristics of the steering system differed in friction, damping, inertia and stiffness. The same steering system characteristics were also tested in accordance with international standards of vehicle-handling tests resulting in characteristic quantities. The instrumental measurements and the non-instrumental ratings were analysed with respect to correlation between each other with the help of regression analysis and neural networks. Results show that there are correlations between measurements and ratings. Moreover, it is shown that which one of the handling variables influence the different dimensions of the steering feel.

Adoption of different pantographs’ preloads to improve multiple collection and speed up existing lines

The current collection using more than one pantograph is needed in railway operation to provide power to non-electrically connected traction units and, in some cases, to reduce current density on the collector strips that heavily influences the wear on the contacting bodies. The multiple current collection may become a critical condition due to the mechanical disturbances produced on the trailing pantographs by the interaction between the first pantograph and the catenary. The present-day evolution of pantograph preload regulating systems, exploiting pressure-controlled servo-valves driven by electronic units, allows a diversification of the preloads of front and rear pantographs. In this work, a suitable solution to improve multiple pantograph collection quality is analysed by the use of a lower mean force on the leading pantograph aimed at reducing the oscillations of contact wire the trailing pantograph is subjected to. This would improve the current collection quality of the trailing pantograph, and could be pursued even admitting a slight worsening of front pantographs performances.

Study of Critical Sections in Catenary Systems During Multiple Pantograph Operation

Abstract To improve the dynamic behaviour of a catenary system, the sections that limit the speed have to be found. A survey was made to gather information about critical sections of the catenary-pantograph system. Interviews with personnel at the Swedish National Rail Administration were performed and problem areas that need consideration were found and are presented. The purpose of this study was to find out how much of these critical sections affect the system and to suggest improvements to the design. Section overlaps and section insulators, both in combination with the usage of multiple pantographs, were modelled, and simulations have been performed at different speeds and for different catenary systems. As a result of this research, a better base could be built on how to ease the operation with multiple pantographs.

An interactive model of a pantograph-catenary system

SUMMARY The overhead electrification system for high speed trains is modeled by a three degree of freedom pantograph and an infinite homogeneous and elastically supported beam. Travelling wave solutions for the beam with a moving load are used to derive an equivalent stiffness for the pantograph model. The model is new in that it takes account of transverse motion due to catenary zig-zag effects. Finite element solutions are also obtained for the moving load problem. The results show that transverse zig-zag effects are the primary expected motion in this system. The calculations also show the expected importance of critical wave speeds in these systems.

Ride comfort simulation of a wheel loader with suspended axles

Wheel loaders are used in a variety of tasks. The traditional design of the vehicle is unfavourable from a ride comfort standpoint, as the unsuspended axles lead to high vibration levels. This study investigates the possibility to reduce driver vibrations by introducing suspended wheel axles. A multibody simulation model is used to study vibration levels with and without suspension. Results show that vertical and longitudinal vibrations are reduced significantly when comparing with the unsuspended vehicle. Less reduction is attained in the lateral direction, mainly because of high roll stiffness and the high placement of the driver seat.

Snaking stability of articulated frame steer vehicles with axle suspension

A known problem of articulated vehicles is that snaking oscillations may occur at high speed. For ride comfort reasons, it is desirable to introduce suspended axles on articulated vehicles such as wheel loaders which are traditionally built without wheel suspension. This paper investigates how this may affect the snaking stability, by studying the vehicle dynamic behaviour of a multibody simulation model with and without suspension. Results show that an axle suspension may have a slightly destabilising effect, although the difference is small and can be offset by a stiffer or more damped steering system.

Links between subjective assessments and objective metrics for steering, and evaluation of driver ratings

During the development of new vehicles, finding correlation links between subjective assessments (SA) and objective metrics (OM) is an important part of the vehicle evaluation process. Studying different correlation links is important in that the knowledge gained can be used at the front end of development, during testing and when creating new systems. Both SA from expert drivers using a rating scale of 1–10 and OM from different tests measured by a steering robot were collected using standard testing protocols at an automotive manufacturer. The driver ratings were evaluated and the correlations were analysed using regression analysis and neural networks through a case study approach. Links were identified and were compared with related research.

Findings from subjective evaluations and driver ratings of vehicle dynamics: steering and handling

This paper investigates subjective assessments (SA) of vehicle handling and steering feel tests, both numerical and verbal, to understand drivers’ use of judgement scales, rating tendencies and spread. Two different test methods are compared: a short multi-vehicle first-impression test with predefined-driving vs the standard extensive single-vehicle free-driving tests, both offering very similar results but with the former saving substantial testing time. Rating repeatability is evaluated by means of a blind test. Key SA questions are identified by numerical subjective assessment autocorrelations and by generating word clouds from the most used terms in verbal assessments, with both methods leading to similar key parameters. The results exposed in this paper enable better understanding of SA, allowing improving the overall subjective testing and evaluation process, and improving the data collection and analysis process needed before identifying correlations between SA and objective metrics.

Utilisation of optimisation solutions to control active suspension for decreased braking distance

This work deals with how to utilise active suspension on individual vehicle wheels in order to improve the vehicle performance during straight-line braking. Through numerical optimisation, solutions have been found as regards how active suspension should be controlled and coordinated with friction brakes to shorten the braking distance. The results show that, for the studied vehicle, the braking distance can be shortened by more than 1 m when braking from 100 km/h. The applicability of these results is studied by investigating the approach for different vehicle speeds and actuator stroke limitations. It is shown that substantial improvements in the braking distance can also be found for lower velocities, and that the actuator strokes are an important parameter. To investigate the potential of implementing these findings in a real vehicle, a validated detailed vehicle model equipped with active struts is analysed. Simplified control laws, appropriate for on-board implementation and based on knowledge of the optimised solution, are proposed and evaluated. The results show that substantial improvements of the braking ability, and thus safety, can be made using this simplified approach. Particle model simulations have been made to explain the underlying physical mechanisms and limitations of the approach. These results provide valuable guidance on how active suspension can be used to achieve significant improvements in vehicle performance with reasonable complexity and energy consumption.

A path tracking driver model with representation of driving skill

A flexible and intuitive non-linear driver model is proposed, which allows setting of physically relevant parameters for representation of both typical high and typical low skill drivers in a path ...