Scholarly article on topic 'Simulation and Experimental Study of Selected Parameters of the Multifunction Steering Wheel in the View of Users’ Abilities and Accuracy of Vehicle Maneuvers'

Simulation and Experimental Study of Selected Parameters of the Multifunction Steering Wheel in the View of Users’ Abilities and Accuracy of Vehicle Maneuvers Academic research paper on "Mechanical engineering"

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Abstract of research paper on Mechanical engineering, author of scientific article — Włodzimierz Choromański, Iwona Grabarek, Maciej Kozłowski

Abstract Individual adjustment of the controls, that are part of the driver interface, for people with different levels of disability requires a specific design approach. Individualization in this respect may result in a larger group of people being able to control the car. The subject of the analysis is a multifunction steering wheel designed for people with paresis of the lower motor system. It is designed to let the driver steer the car and perform the key control functions with the use of the upper limbs only. The designers did their best to make sure that driving the car is as intuitive as possible. The design of the steering wheel is heavily parameterized, i.e. a number of its parameters can be adjusted. Among them is the ratio between the turning angle of the steering wheel and the angle of the front wheels. This feature has been subject to examination in dynamic simulators and simulation studies during special tests.

Academic research paper on topic "Simulation and Experimental Study of Selected Parameters of the Multifunction Steering Wheel in the View of Users’ Abilities and Accuracy of Vehicle Maneuvers"

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Procedía Manufacturing 3 (2015) 3085 - 3091

6th International Conference on Applied Human Factors and Ergonomics (AHFE 2015) and the

Affiliated Conferences, AHFE 2015

Simulation and experimental study of selected parameters of the multifunction steering wheel in the view of users' abilities and accuracy of vehicle maneuvers

Wlodzimierz Choromanski, Iwona Grabarek*, Maciej Kozlowski

Warsaw University of Technology, Koszykowa st. 75,Warsaw, 00-662, Poland

Abstract

Individual adjustment of the controls, that are part of the driver interface, for people with different levels of disability requires a specific design approach. Individualization in this respect may result in a larger group of people being able to control the car. The subject of the analysis is a multifunction steering wheel designed for people with paresis of the lower motor system. It is designed to let the driver steer the car and perform the key control functions with the use of the upper limbs only. The designers did their best to make sure that driving the car is as intuitive as possible. The design of the steering wheel is heavily parameterized, i.e. a number of its parameters can be adjusted. Among them is the ratio between the turning angle of the steering wheel and the angle of the front wheels. This feature has been subject to examination in dynamic simulators and simulation studies during special tests.

© 2015 PublishedbyElsevierB.V.Thisisan openaccess article under the CC BY-NC-ND license

(http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of AHFE Conference

Keywords: Multifunction steering wheel; Vehicle's maneuvers; Experimental study

1. Introduction

The progressive aging process of the population, resulting in the increase of the number of people with reduced mobility as well as the increase in the number of people with various disabilities resulting from the modern civilization diseases - this is a problem whose solution must be reflected in the currently designed modern systems

* Corresponding author. Tel.:+48-601228458. E-mail address: igr@wt.pw.edu.pl

2351-9789 © 2015 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of AHFE Conference

doi:10.1016/j.promfg.2015.07.855

and means of transport. It is also an important social problem because ensuring mobility is synonymous with the possibility of participating in social life with all its consequences. Within the framework of "Eco-Mobility" project (implemented under the Innovative Economy Operational Programme, co-financed by the European Regional Development Fund) we have focused on vehicles whose essential element is the individual fitting to the needs of potential users, both drivers and passengers. This paper concentrates on "drivers of different efficiency" and the possibility of fitting the steering devices to their needs in order to provide them with independent use and steering of a car. An "eco-car" vehicle was designed and its preprototype was created in 2013.

The eco-car is an electric car designed for rent and moving around the city center with maximum speed of 50 km/h and range approx. 100 km [1,2]. Apart from the driver there an be three other passengers in the car, including one in a wheelchair - electric or active one. A person with limited efficiency of lower limbs may serve as the driver from the position of the wheelchair. The entry of a person with manually driven wheelchair to the cabin may be performed through a floorpan previously lowered to street level, from behind on a special ram or on both sides. The car is equipped with special fastening systems in order to immobilize people in wheelchairs. An intelligent driver interface allows for an easy configuration of the car depending on the driver's level of physical ability. The basic assumption behind the designed car was equipping it with a "steer by wire" system with a set standard input signal. This means no mechanical connection between the steering wheel (or other operational steering system) and the wheel steering system of the car. This solution allows driving the car with upper limbs (driver-by-wire, break-by-wire), which significantly increases the number of users. Adjusting the control panel with steering devices provides fitting its position in accordance with the range of driver's limbs. The steering wheel designed analyzed in this paper is heavily parameterized, that is, it is possible to modify a number of its parameters. One of them is the relationship between the angle of steering wheel and turning wheels. This characteristic was the subject of research on dynamic simulators and in simulation studies.

2. Designing and functions of eco-car's steering wheel

The analysis on how to drive an eco-car assumed using different input steering devices. Results of a survey conducted along both able-bodied and disabled users strongly suggested the attachment of respondents to the traditional solution - the steering wheel. The main factor in favour of this traditional form, in the opinion of users, is the 'stabilizing' of wheel while driving - significant both for able-bodied and disabled, which provides better control of the vehicle. The users' expectations were reflected in the design of multifunctional steering wheel, adapted to steering the vehicle only using arms. This is the basic assumption adopted in designing a "universal" vehicle equally serving both able-bodied people and persons who cannot use classic brake and acceleration pedals. Further development of this idea was moving the steering devices of all basic functions of the vehicle to the steering wheel. This was somewhat forced due to design reasons and ergonomic limitations, because the proposed system of signalling acceleration significantly limited the usability of the so-called composite switch placed by the steering wheel column. The design of new steering wheel included mostly a design of new ergonomic panel with buttons and a mechanism steering the acceleration and braking of the vehicle. It was assumed that accelerating and braking would happen through pressure in the direction of the steering wheel of the rings placed within the range of the

Fig. 1. Eco-car preprototype.

Fig. 2. Multifunctional steering wheel: a) model of the steering wheel in Catia program; b) steering panel with a steering wheel in the preprototype of eco-car.

driver' fingers, called "o-rings". Giving other steering signals placed in the steering wheels was implemented in the form of buttons, coupled with an electric output system of the base kit. The buttons were incorporated into the prepared design of the steering wheel panel so that launching appropriate functions was performed using both thumbs. Gripping surfaces are placed on a circular rim, concentric with the middle of the steering wheel and the rings, placed above the brake ring (closer to the driver). The design includes seven buttons for steering such functions as: turn signals, turning the lights on and off, turning wipers on and off, emergency lights and centrally located horn.

Figure 2a shows a model of multifunctional steering wheel and 2b a steering wheel along with a steering panel, both of which are included in the eco-car prototype. Studies on the relationship between angle of steering wheel and tires were carried out in dynamic simulators. Model and simulation studies were also performed.

3. Dynamics mode: human-car-environment

Simulation studies using a dynamics model focused on the analysis of of the dynamics of a double lane change manoeuvre which was used in building tests for the dynamic car simulator. The car's driving properties are determined mostly by contact properties of the tires, as well as the dynamic properties of the suspension. in electric cars, the driving properties may additionally depend on the quality of software of SBW (Steer by wire), BBW (Break by wire) and DE (electronic differential for motors placed in tires). The model takes into account all of these requirements. It is of electro-mechanical nature. Fig.3. shows the model's basic systems: a) a block system of the the car's mechanical model, b) speed control system. The mechanical model, whose structure is shown in fig. 3a has the following basic elements isolated: WFL, WFR - front tires left and right, WRL, WRR - rear tires left and right with electric motors placed in wheels, SFL, SFR - suspension systems with Mcpherson's column front left and right, SFL, SFR - trailing rear suspension systems left and right, B - body with centerpoint in point B, A - front point of the body block, D - rear point of the body block. Simulation studies used MBS-type software. To describe the contact properties of rubber tires we used a library package TNO Delft TYRE. Issues related to the design of suspension system models for Eco-Car and parameterization of the mechanical models was presented in papers h [6], [7] [1 ], [2]. Fig. 3b shows the topology of speed control system (providing speed difference in motor control system), called "electronic differential". The presented topology corresponds to the regulation system with speed difference adjustment. The method of selection of controller settings was presented in [8].

" [n] y [m]

Fig. 3. Dynamic model systems: a) MBS Model, b) regulation system DE with speed difference adjustment. (a) markings: WFL, WFR - front tires left and right, WRL, WRR - rear tires left and right with electric motors placed in wheels, SFL, SFR - suspension systems with McPherson column front left and right, SRR, SRL - trailing rear suspension systems left and right, B - body with ceterpoint in point B, A - front point of the body block, D - rear point of the body block. Additional markings: L - wheelbase, d -wheel setting; (b) markings: RW - speed regulator, RD -speed difference regulator, S1, S2 - electric traction motors, r1, r2 - traction motors regulators, ArnzC - average speed set, rnzl, rnz2 - angular motor speeds set, Arnl2 - speed difference set, ml,m2 - angular motors speeds.

t [s] x [m]

Fig. 4. Double lane change manoeuvre: a) Steering waveforms, b) Paths of movement. (a) markings ^ref - steering angle of dynamics model, ^Ref

- angle of the direction of movement of the dynamics model. (b) markings: Tref- path of the dynamics model moment, L - manoeuvre length, H

- lane width.

In case of experimental studies of the steering system, the studies of dynamics model are applicable in setting the so-called reference trajectory. Reference trajectory is understood as the trajectory of a model doing the manoeuvre in a perfect manner. Fig. 4. shows how to obtain the reference trajectory of model movement for double lane change manoeuvre: a) steering wheel waveform (steering angle), b) path of the movement.

4. Research on dynamic car simulator

Studying the dependence between steering wheel angle and wheels turning was carried out in dynamic simulators. As it was mentioned before, the eco-car design and is physical prototype use a specific steering wheel -multifunctional (hereinafter referred to as eco-steering wheel) - adapted to driving the car by people with locomotor disabilities as well as able-bodied persons, or having universal characteristics. The problem of driving a car by disabled people is complex. Literature reports the attempts to use a joystick [10] or special steering wheel [9]. Universality is particularly hard to achieve. The main problem is lack of usefulness of this type of steering systems. For this reason, it was necessary to do experimental research. The main aim of this experiment was assessing the

correctness of maneuvers performed driving a car using a standard steering wheel (wheel and pedals) and eco-steering wheel. Another important issue was defining the torsion ratios in steering wheel/tire system for eco-steering wheel allowing a correct maneuver.

4.1. Research methodology

The research group in the experiment are men aged 20-23 years, holding a driver's license. Its size is 16 people. It was assumed that the experiment will include comparative study of simulator drives with two types of steering wheel. The main difference between the eco-steering wheel system and classic steering wheel system with pedals is that the functions of braking and acceleration are carried out "manually". When using eco-steering wheel in driving conditions requiring a simultaneous change of speed and direction of movement, the driver must perform actions requiring a different motor coordination than the one used in classic system with pedals. This issue has also been included in the study. The design and software of the eco-steering wheel allows for a programmed change of angle degree: steering wheel angle - steering angle of the tires (but not while driving). The studies included two degrees of steering system angles: 180/35 and 120/35. Selection of the test nature and parameters was made using the experience from stochastic-technic stability of the ar (performed on simulation models). As a results, two types of tests were proposed:

• test 1 - a "route" type drive including studies of steering stability in driving conditions with constant speed,

including such "constant fragments" as: straight section (1), curve (2), double lane change maneuver (3),

second straight section (4) and avoiding a collision with a pedestrian (5),

• test 2 - a "slalom" or "serpentine" type drive, requiring a simultaneous change of speed and direction of

movement on repeating, "deepening" curves of the road.

The task of a driver involved in the experiment is following the reference line of movement with the vehicle. The line is marked in a lane by additional markers placed along the track and it is visible to the driver performing the experiment. The course of the reference trajectory, and the orientation of reference line along the lane should be a result of calculations using the car's dynamics model. Since the drive experiment in the simulator is performed on a model different than eco-car, a slightly different way of determining this line was adopted. The reference trajectory is the "trace" of simulator drive of an experienced driver-instructor. The basic values to be evaluated are: distribution of experimental trajectory deviation (from reference line), the course of the speed and the course of the steering wheel angle. Based on the measured parameters the following measures will be analyzed: m1 - applies to the trajectory deviations of the driven car from reference line, meaning it includes the rms deviations from reference line in a specific section, m2 - applies to deviations from imposed speed of movement in individual sections, m3 -total measure, taking into account the specified weight displacement h and speed v expressed as dimensionless variables. The other measures such as using the brake and acceleration pedal (shifter) will be assessed in the second order. After finishing the tests, the subjects filled a survey with questions of the functionality of eco-steering wheel and ease of driving the car with it. Obtained opinions will be used in the process of the eco-steering wheel design modification. Figure 5 shows a research station in dynamic simulator and an image of reference line visible to the subject.

Fig. 5. Dynamic car simulator: a) research station; b) reference line.

4.2. Studies of steering wheel torsion functionality - pilot research

Fig. 6 shows the distributions of deviations from reference line in three experimental drives: a) normal steering wheel with pedals, b) Eco-steering wheel with steering ratio 180/35, c) Eco-steering wheel with steering ratio 120/35. In all drives a large deviation from the reference line of the track is visible in the moment of human intrusion on the road (section 5). In fig. 6 along the path marked 4, that is in a straight section, significant differences are visible in the course of the deviation of the car's geometric center point from the reference line. These differences are mainly different character of the variation of "signal" describing distance.

Fig. 6. Charts of deviations from reference line from three experimental drives: a) normal steering wheel with pedals, b) eco-steering wheel with steering ratio 120/35, c) eco-steering wheel with steering ratio 180/35. Fragments of path marked: 1 - straight section, 2, curve, 3 - passing, 4 -straight section, 5 - human intrusion.

Fig. 7. Results of fit analysis performed for signals shown in fig. 6 for the period of drive along a straight section (4): a) normal steering wheel, b) eco-steering wheel with steering ratio 120/35, c) eco-steering wheel with steering ratio 180/35.

Fig. 7 shows the results of fft analysis made for deviation waveforms in these periods of drive: a) normal steering wheel, b) eco 120/35, c) eco 180/35. The deviation signal of a car driven with eco-steering wheel contains a larger number of harmonic alternating components than the signal using normal steering wheel. This signifies the "rummaging" of the car. The phenomenon increases with the decreasing ratio of the angular SBW system. It may mean that the driving conditions for a car with eco-steering wheel in a straight section are worse than for a normal steering wheel.

Acknowledgements

This article was financed from ECO-Mobility project WND-POIG.01.03.01-14-154/09. Project co-financed from European Regional Development Fund within the framework of Operational Programme Innovative Economy.

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