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POLITECNICO DI TORINO Analysis of the Effect of Tire Inflation Pressure on Vehicle Dynamics and Control Strategies

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POLITECNICO DI TORINO Analysis of the Effect of Tire Inflation Pressure on Vehicle Dynamics and Control Strategies POLITECNICO DI TORINO Collegio di Ingegneria Meccanica, Aerospaziale, dell'Autoveicolo e della Produzione Corso di Laurea Magistrale in Automotive Engineering (Ingegneria dell’Autoveicolo) Tesi di Laurea Magistrale Analysis of the effect of tire inflation pressure on vehicle dynamics and control strategies Relatori Candidato Prof. Stefano d’Ambrosio Carlo Di Pasquale Prof. Nicola Amati Novembre/Dicembre 2018 II Introduction Tires, being the interface between the vehicle on the road have a huge influence on vehicle performance: through the tires the vehicle is able to exert traction, braking and cornering forces. A key parameter in particular that affects tire capabilities is inflation pressure. According to the National Highway Traffic Safety Administration (NHTSA) more than a quarter of automobiles travel with underinflated tires in the U.S. [1], while a study by Michelin and Kwik Fit evidenced a percentage of the 40% in the U.K. [2]. An under-inflation creates not only safety issues, affecting the handling of the vehicle, but results also in an increased tire wear and fuel consumption (due to a bigger rolling resistance): a reduction of 0,5 bar from the recommended inflation pressure brings to a growth of rolling resistance of about the 10% bringing to an increase of consumptions of the 1-2% [3]. The ATCP (Active Tire Pressure Control) team has the goal to develop a system capable to monitor and maintain a desired pressure, that can be regulated according to the working conditions of the vehicle. The opportunities of a pressure control are several: from on optimization of consumptions (and consequently CO2 emissions) to a control of the cornering and braking behaviour of the vehicle. In this thesis, the effect of pressure on the main tire parameters is analysed using Pacejka’s MF 5.2 model. Then the analysis focus on the vehicle dynamics, ensuring a safe operation of the vehicle throughout the range of pressure considered and checking configurations that optimize the braking and cornering performance of the vehicle. Different manoeuvre simulations were performed on the software Adams Car for a passenger car (Fiat Grande Punto) and a light duty vehicle (Iveco Daily). Experimental tests performed on track permitted to tune and validate the Grande Punto model. Finally, an overview of the interaction between different strategies of pressure control was made. III Index 1 An active tire pressure control…………………………………………….1 1.1 The ATPC team………………………………………………….………………………………………….…...1 1.2 Rolling Resistance……………………………………………………………………………………………….2 1.3 Contact Patch……………………………………………………………………………………………………..4 1.4 Tire wear…………………………………………………………………………………………………………….5 2 Preliminary theory concepts……………………………………………….8 2.1 Tires……………………………………………………………………………………………………………………8 2.1.1 Structure and characteristics…………………………………………………………………………………………………8 2.1.2 Wheel’s reference system and forces acting on the tire………………………………………………………11 2.1.3 Pacejka’s Magic Formula MF 5.2……………………………………………………………………………………...….15 2.1.4 Improved Magic Formula to take in account inflation pressure changes MF 6.2………………….17 2.2 Longitudinal dynamics………………………………………………………………………………………18 2.2.1 Load distribution………………………………………………………………………………………………………………….18 2.2.2 Braking in ideal conditions…………………………………………………………………………………………………..20 2.3 Lateral dynamics………………………………………………………………………………………………20 2.3.1 Low speed or kinematic steering………………………………………………………………………………………….21 2.3.2 Ideal steering ………………………………………………………………………………………………………………………22 2.3.3 Simplified approach for high speed cornering …………………………………………………………………….25 2.3.4 High speed cornering 282.3.5 Definition of understeer and oversteer………………………………..32 3 The effect of inflation pressure on tire performance……………35 3.1 Tire 185/65 R 15 ………………………………………………………………………………………………35 3.1.1 Longitudinal analysis……………………………………………………………………………………………………………35 3.1.2 Lateral analysis…………………………………………………………………………………………………………………….37 3.1.3 Self aligning moment…………………………………………………………………………………………………………..38 IV 3.1.4 Summary table of the results……………………………………………………………………………………………….39 3.2 Tire 225/65 R 16 ………………………………………………………………………………………….…..40 3.2.1 Longitudinal analysis……………………………………………………………………………………..…………….………40 3.2.2 Lateral analysis……………………………………………………………………………………………..……………….…….41 3.2.3 Self aligning moment ..………………………………………………………………………………………….…………….43 3.2.4 Summary table of the results……….………………………………………………………..……………………………44 3.3 Tire 195/75 R 16……………………………………………………………………………………………….44 3.3.1 Longitudinal analysis …………………………………………………………………………………………………………..44 3.3.2 Lateral analysis…………………………………………………………………………………………………………………….46 3.3.3 Self aligning moment…………………………………………………………………………………………………………..48 3.3.4 Summary table of the results……………………………………………………………………………………………….49 4 Effect of inflation pressure on vehicle dynamics……..…………..50 4.1 Fiat Grande Punto…………………………………………………………………………………………….50 4.1.1 Braking………………………………………………………………………………………………………………………………..50 4.1.2 Analysis of braking results and literature overview………………………………………………………………53 4.1.3 Lateral Dynamics………………………………………………………………………………………………………………….54 4.1.3.1 Step Steer……………………………………………………………………………………………………………………………………….55 4.1.3.2 Steering Pad……………………………………………………………………………………………………………………………………58 4.1.4 Analysis of lateral dynamics results……………………………………………………………………………………..60 4.2 Iveco Daily………………………………………………………………………………………………………..60 4.2.1 Braking (225/65 R16)…………………………………………………………………………………………………………..60 4.2.2 Braking (195/75 R16)…………………………………………………………………………………………………………..63 4.2.3 Analysis of braking results and literature overview………………………………………………………………65 4.2.4 Lateral dynamics (225/65 R16)…………………………………………………………………………………………….66 4.2.4.1 Step Steer……………………………………………………………………………………………………………………………………….66 4.2.4.2 Steering Pad……………………………………………………………………………………………………………………………………69 4.2.5 Lateral dynamics (195/75 R16)…………………………………………………………………………………………….70 4.2.5.1 Step Steer……………………………………………………………………………………………………………………………………….70 4.2.5.2 Steering Pad……………………………………………………………………………………………………………………………………73 V 4.2.6 Analysis of lateral dynamics results and literature overview………………………………………………..73 5 Vehicle Dynamics Strategies……………………………………………….75 5.1 Passenger Car (Grande Punto)………………………………………………………………………….75 5.1.1 Longitudinal dynamics…………………………………………………………………………………………………………75 5.1.2 Lateral dynamics………………………………………………………………………………………………………………….77 5.1.3 Interaction between strategies……………………………………………………………………………………………79 5.2 Light duty vehicle with 225/65 R16 tires (Daily)………………………………………………..81 5.2.1 Longitudinal dynamics…………………………………………………………………………………………………………81 5.2.2 Lateral dynamics………………………………………………………………………………………………………………….82 5.2.3 Interaction between strategies……………………………………………………………………………………………83 5.3 Light duty vehicle with 195/75 R16 tires (Daily)………………………………………………..85 5.3.1 Longitudinal dynamics…………………………………………………………………………………………………………85 5.3.2 Lateral dynamics………………………………………………………………………………………………………………….86 5.3.3 Interaction between strategies……………………………………………………………………………………………87 6 Conclusions………………………………………………………………………..90 7 Bibliography……………………………………………………………………….91 8 List of figures………………………………………………………………………92 9 List of tables……………….………………………………………………………99 VI 1 An active tire pressure control In this chapter is made an overview of the ATPC team targets and field of operation. 1.1 The ATPC team The ATPC (Active Tire Pressure Control) team, born in 2013 has the aim to develop an active system to manage the tire inflation pressure under specific vehicle working conditions. The use of a pressure control system allows better performances in the warm up of the tires, fuel consumption, safety and driveability [3]. The management is performed through an automatic, electro-pneumatic central tire inflation system: a schematic layout is presented in Figure 1.1 [3]. FIGURE 1.1. Electro-pneumatic layout of the ATPC system with air compressor (1); ejector (9); central electro-valves: one on the compressor line (7) and one on the vacuum line (8); vent valve (2); four pipelines for the connection of the tires to the central part (10), including a solenoid valve (3), pressure transducer (11), rotating pneumatic joint (6), and an on-wheel valve or valve unit (4). The inflation pressure has in fact influence on the adherence and on the wear of the tire (changing size and shape of the contact patch) but also on rolling resistance (that has a great contribution to the resistance to motion). Several strategies can be implemented to improve performance and consumptions. 1 In the following chapters the effect of inflation pressure on the main tire parameters affecting vehicle dynamics will be investigated with the aim of: • Ensuring that fuel economy strategies don’t affect in a dangerous way the dynamic of the vehicle • Developing strategies to improve the performance of the vehicle or to maintain constant the vehicle dynamic with the change of its load condition • Check a possible compatibility between the different strategies 1.2 Rolling Resistance The tire and the ground are not rigid, so deformations occur in the contact zone. During tire motion new material is continuously entering in this zone, deforming and springing back. The energy expended for this process is not completely recovered because of the internal damping of the material [4]. These dissipations are the main causes for rolling resistance and in the case of a pneumatic tire rolling on tarmac or concrete are localized mainly in the tire itself [4]. The distribution of the
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