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Vehicles and Infrastructures for a Safe Drive

ABSTRACT: Safe drive is based on the relationships existing among driver, road and vehicle. Virtual instruments and experimental facilities are available to design and carry out road infrastructures and vehicles. Those instruments and facilities are not employed to prepare a driver to use a vehicle according to its physical limits due to vehicle dynamics in dependence on the operating conditions, first of all the infrastructure status. Fundamentally, the ensemble vehicle-infrastructure is a sophisticate instrument for the mobility used by a driver generally scarcely conscious about the relationships existing among driver inputs, vehicle dynamics and operating conditions. The critical element in the safe drive is the driver yet. Significant improvements can be determined conceiving research laboratories also from the point of view of possibilities to use innovative methodologies and facilities, conceived and applied to new vehicles and to technologically up-to-date infrastructure, to train drivers for a safe drive.

Keywords: Vehicle, Pavement, Safety, Hardware-in-the-loop (HIL)

Prof. Mauro Velardocchia, Dipartimento di Meccanica Politecnico di Torino

INTRODUCTION

The vehicle-road infrastructure is a sophisticate system conceived for the mobility, used by a driver generally scarcely conscious about the relationships existing among driver inputs, vehicle dynamics and operating conditions. On the other hand, the vehicles are designed to be as much as possible safe, minimally dependently on the driver, hoping for he using the vehicle with at least a minimum competence and rationality level. From the point of view of drive safety, the critical point of the vehicle-infrastructure-driver continues to be the driver.

How the research on the vehicles has improved the safe drive? Fundamentally, chronologically, from the point of view of passive and on active safety.

Passive safety can be considered as those actions exerted for example on drive belts or on structural vehicle characteristics to optimize the accident energy dissipation. The actions carried on by a passive safety system are generally related with an accident. The effects provoked by a passive safety system are in the perspective of damage reduction.

In terms of prevention, the vehicles more recently benefits of active chassis control systems possibilities introduced as capacity to adapt the vehicle dynamics to the drive operating conditions, to carry out as best as possible the driver commands. That systems act on brakes, steering, suspensions, transmissions to help the driver to actually realize his commands. A number of international organizations documents the vehicle safety abrupt increasing due to the presence of chassis control systems as, for example, the Anti-lock Braking Systems (ABS) and the Electronic Stability Control (ESC). The evaluation of the efficacy following to the adoption of such systems is so evident and positive to strongly suggest to become them obligatory for homologation.

The research in the field is not limited to the so-called stand alone chassis control systems. Many research centers investigate on the possible safety increasing obtainable through an integration among various chassis control systems. Similarly, a lot of researches are managed as far as the potentiality that safety can benefits integrating through the communication network the informations exchangeable from many vehicles. New products are continuously presented in the field of sensors, actuators and systems to increase the driver safety. In the future is reasonable to foresee not a revolution in the field of safety but a progressive improvement due to a continuous introduction of new provisions and equipment economically sustainable by car manufacturers and their customers. Similar improvement, as the paper exemplifies, can be joined sharing and integrating the competences coming from the vehicle and the infrastructure research activities.

That promising situation unfortunately regards not directly the problem constituted by a driver not prepared to drive in a safety way, also in presence of excellent vehicles and infrastructures. How the research can help to overcome the problem related with driver education? Vehicle research centers use excellent technologies to design and validate experimentally new vehicles but nothing of that technological availability is used to prepare a new driver for a safe drive. It could be possible to apply the virtual and experimental methodologies used to design a vehicle also to teach to drive safely depending on the operating conditions, generally related with vehicle dynamics and road characteristics and traffic. The experiences carried out in the Vehicle Dynamics Laboratory and during specific courses conceived for safety drive, documents the possibility to increase the level of confidence of a young driver with vehicle dynamics and operating conditions, especially related with the road status. This learning, operated through experimental equipment and road tests, shows significant improvement of consciousness as far as the potentialities related with the vehicle dynamics. In the future a research Laboratory, available also to support a learning process for a safe drive especially conceived for young drivers, could contribute significantly to cope with the problem related with the scarce ability that drivers frequently demonstrate as capacity to correctly use the vehicle and the road infrastructure.

VEHICLE DYNAMICS AND CHASSIS CONTROL SYSTEMS LABORATORY

Politecnico di Torino’s Vehicle Dynamics and Chassis Design group researches focus on vehicle dynamics, chassis design and chassis control systems. The main aims concern vehicle performance, active safety, systems and components for fuel saving, diagnosis and reliability. The research group was constituted (1997) by Mauro Velardocchia and currently includes two professors, one researcher and seven assistant researchers. The research activity is mainly funded by industrial contracts. In 2004 the group founded the Vehicle Dynamics and Chassis Control Systems Laboratory (VDL) which grants support to around twenty mechanical engineers per year to carry out their Laurea Thesis. The generality of researches are managed both through virtual tests and experimental validation, generally carried out in the VDL. Virtual tests are based on mathematical simulators developed by the research group. The experimental tests benefits of ten Hardware-in-the-loop (HIL) test benches designed and carried out inside the VDL. Every HIL test bench of the VDL is equipped with a vehicle dynamics model developed by the research group and can integrate the physical hardware constituted both by the electro-mechanical system (braking, steering, suspension, transmission) and by the Electronic Control Unit (ECU) either commercially available and integrated in the test bench or specifically designed. Used by all the test benches are the results of research activities concerning the tyre. The researches in the field of tyre-pavement are supported and validated thanks the co-operation of VDL with tyre and car manufacturers. Among a number of relationships with Universities, the research group mainly co-operates with the Center for Automotive Research (Ohio State University) for the themes of energy saving and the University of Surrey at Guildford for studies on the dynamics of race cars. In the Politecnico di Torino, strong relationships exist with research groups active on Pavements and Road infrastructure, ICT and Energetic.

Vehicle Dynamics Laboratory (VDL)

The VDL especially supports the research group investigations concerning passive and active chassis systems devoted to braking (ABS, ESC, EHB, EMB), suspensions (ARC, CDC), transmissions (AMT, AWD, EVT), steering (4WS, AFS). The test benches are generally conceived and carried out according to a Hardware-in-the-loop (HIL) layout. Moreover, specific test benches are devoted to shock absorbers, hub bearings, differentials and transmissions and driveline components characterization. Some HIL test bench is remotely manageable via web and works are in progress to integrate the various test benches to investigate about the chassis control systems real-time co-operation, so validating the very promising results obtained by virtual analysis.

Figure 1 shows, as first example, an HIL test bench devoted to Electronic Stability Control (ESC) studies. The test bench allows to measure objectively the performance obtainable by a commercial ESC and to investigate how original control strategies can involve even better performance, especially when conceived integrated with the control actions due to other chassis control systems acting at the same time on the vehicle dynamics. Moreover, this kind of test bench results especially useful to validate the fail-safe, diagnosis and recovery procedures, so significantly reducing the necessity to manage a large number of road tests, frequently in operating conditions difficult or dangerous to be reproduced in a proving ground. Figure 1a shows the HIL ESC test bench and Figure 1b presents, as example, an experimental result concerning the positive effect determined by the ESC in terms of yaw rate dynamics consequent to an abrupt manoeuvre of step steer.

Figure 2 shows an example of HIL Active Roll Control (ARC) test bench devoted to study the vehicle dynamics dependence on the availability of anti-roll bar variable as preload and torsional stiffness. This kind of chassis control system, studied in the VDL considering different layout, has the characteristic to act not in an emergency maneuver as, vice-versa, usually happens to an ESC. An ARC chassis control system permits to modify the vehicle dynamics in the sense of determine a better handling and, consequently, a dynamic behaviour which results safer than without ARC. Figure 2a shows a photo of an ARC carried out applying active anti-roll bar both on the front and on the rear of the vehicle. The control strategy coordinates the two active systems. Figure 2b presents how relevant can be the vehicle dynamics obtainable, exemplified by the yaw rate better behaviour.

Figure 3 shows an example of HIL test bench carried out to investigate the effect of a steering system characteristics on the feeling perceived by a driver depending on the road characteristics and the vehicle overall design. Figure 3a shows the system carried out and Figure 3b presents an example concerning the steering torque dependence on the lateral acceleration. The behaviour of this characteristic is important to evaluate how a driver will feel the vehicle dynamics through the torque applied by his hands on the steering wheel. The Figure shows the dependence of the former characteristic on different tyres. Similarly, a different operating condition due to, e.g., pavement irregularities, can modifies the tyre capability to apply its forces, so determining a change in the same characteristic.

Figure 1a. Electronic Stability Control (ESC) Hardware-in-the-loop (HIL) test bench

Figure 1b. Experimental result with HIL ESC test bench

VEHICLE AND INFRASTRUCTURE

The activities, shortly described in the following, are examples of the co-operation existing between the Vehicle Dynamics Laboratory and the Road and Pavement (Prof. E. Santagata) research groups of Politecnico di Torino. The contributions coming from the vehicle and from the infrastructure fields are shared to determine more precise virtual analysis and experimental methodologies than usually otherwise obtainable by the research groups operating alone.

Figure 2a. Active Roll Control (ARC) Hardware-in-the-loop (HIL) test bench

Figure 2b. Experimental result with HIL ARC test bench

Figure 3a. Hardware-in-the-loop (HIL) test bench for steering systems

Figure 3b. Experimental result with HIL test bench for steering system

Experimental comparison in pavement-vehicle interactions

Pavement-vehicle interaction is a dynamic topic both in mechanical design and road maintenance. It is of increasing interest to design operative experimental instrumentations able to measure road irregularities, in order to schedule and repair road worsening. Two different mechanical devices were designed, carried out and compared, in order to measure road surface macroscopic irregularities and artificial bumps. Such systems are relatively light and compact to be installed on board of a vehicle. A first mechanical device is called ROMEO: its design is defined to measure suspension vertical travel by means of six degrees of freedom. A vertical transducer is used to evaluate the relative displacement between wheel spin axis and chassis, while a triaxial and a monoaxial accelerometers are implemented to measure road bumps on wheel hub and on differential. The wheel angular velocity is acquired too.

The second mechanical device, called VET6 (Vehicle Elasto-kinematic Transducer 6 degrees of freedom), allows to experimentally estimate kinematic parameters of vehicle suspension (translations and angular rotations) and in particular suspension vertical travel, by means of five potentiometers and an encoder mounted on a five arm frame. In a first stage, some experimental testes are used to identify elastic and dissipative properties of the vehicle suspension in time domain with artificial bumps of known profile. Therefore, the two mechanical devices are tested to measure irregularities of unknown profile and to reproduce road surface.

Figure 4a. ROMEO system used to measure road irregularities

Figure 4b. VET6 system used to measure suspension elasto-kinematic and road profile

Road and pavement design depending on vehicle dynamics

Road and pavement design traditionally considers the forces due to a vehicle concentrated uniformly on the road. At the same time, usually the vehicle design considers the road flat or, eventually, with a longitudinal slope. The synthesis parameter usually employed by vehicle engineers regards the adherence supposed between pavement and tires. This general way of resuming the main characteristics of a vehicle from the road designers and vice-versa, prevent the possibility of a more accurate design, capable to consider more detailed characteristics of the vehicle and of the road.

The research activity managed at Politecnico di Torino between the formerly indicated groups enriched the virtual analysis considering some more detailed data both coming from the road and from the vehicle. The methodology adopted was based on a vehicle dynamics virtual simulator which included a very detailed model of a road. Some corrective actions devoted to, e.g., the driver model, were required to permit the virtual simulator works given reliable results. The main interesting results regarded the possibility to investigate about the relationships existing between the vehicle dynamics and road design characteristics like, for example, the transition curves. It was demonstrated how a different mathematical formulation of such curves can modifies from the vehicle dynamics side the lateral acceleration behaviour and, reasonably, its stability and safety and, from the point of view of road design, the load distribution due to the vehicle.

Figure 5a presents an example of mathematical description adopted to consider the effect of different transition curves on the vehicle dynamics. Figure 5b shows the counterstroke due to different transition curve formulas, in the example clotoid and sinusoid. The same Figure 5b presents a comparison among the counterstroke computed according to a model not considering the vehicle dynamics, indicated as kinematic model, and two models that use the vehicle dynamics and different driver models. In particular, it is presented the counterstroke due to a driver (instantaneous) which react instantaneously to maintain the desired trajectory and the result obtained by a driver (predictive) which observe the road seeing ahead twenty-five meters, so anticipating the dynamic effect due to the road. It is evident how to share competencies from road and vehicle can allow to be more precise than preventing to act in that direction.

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Figure 5a. Road mathematical model to study the transition curve

Figure 5b. Example of counterstroke due to different transition curve models

Laboratory for safe drive

The former chapters of the paper exemplified how the virtual analysis and test facilities strongly support the vehicle and the infrastructure design from the point of view of establish operating conditions favourable to a safer mobility. The critical element in the safe drive is yet the driver. Significant improvements can be determined conceiving research laboratories also from the point of view of possibilities to use innovative methodologies and facilities to train drivers for a safe drive. How to carry out this idea? Probably conceiving laboratories to be attended and used by young drivers to learn through virtual computing and test facilities the main relationships existing among driver-road-vehicle. This could be one of the possible future for an infrastructure and vehicle laboratory, to be conceived also for new drivers training. A laboratory conceived in University with this main aim could benefit of the research activities for vehicle and infrastructure, proposing their result for training.

CONCLUSIONS

The theme of a safe drive was presented exemplifying how a research laboratory can support through virtual computing and test facilities the development of new systems conceived to equip a vehicle. The equipment can regard hardware components like sensors and actuators or electro-hydraulic control unit of chassis control systems and software devoted to integrate stand-alone chassis control systems or the information exchangeable among many vehicle. The role of integration of competencies between vehicle and infrastructure for a safer mobility was exemplified considering some studies in progress at Politecnico di Torino. The paper proposes to use the laboratories developed to experimentally support the research in the fields of vehicle and infrastructure also to train especially young new drivers to be more conscious as far as the potentiality of vehicle and infrastructure, so contributing to maintain the feeling of a pleasant drive, reducing significantly the possibility to provoke an accident.

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