In English

Tyre Library for Vehicle Energy Model

Pooja Ramachandra Hegde ; Vamshi Krishna Gunda
Göteborg : Chalmers tekniska högskola, 2017. Diploma work - Department of Applied Mechanics, Chalmers University of Technology, Göteborg, Sweden, ISSN 1652-8557; 2017:64, 2017.
[Examensarbete på avancerad nivå]

A growing need to minimize fuel consumption motivates research towards energy loss due to tyre components. Performing tyre tests to determine the nature of these losses for every scenario may turn out to be expensive. Magic tyre formula is widely accepted to give comparable results to real world but the model is not motivated with physical principles. An effective tyre model motivated through physical principles that can predict the tyre output characteristics is needed. The key contributors to torque loss in tyres which are rolling resistance and tyre slip losses are studied in this thesis work. The aim of the project was to study the effect of tyre slip and rolling resistance on longitudinal force generation for hard and soft surfaces. The work presented here on is an attempt at arriving at a physical model by improving the basic brush tyre model for hard ground and extending the Bekker-Reece terramechanics theories for deformable ground. The models are built with Matlab scripts and Simulink which gives the user complete flexibility to tune parameters with more test data and customize the models with new additions. The brush tyre model was improved from the basic model by incorporating different values of friction coefficients for stick region and slip region in the contact patch. Further add-ons for the model with semi-empirical equations are developed by varying friction coefficient with inflation pressure and varying friction coefficient with longitudinal slip to provide the user flexibility to tune parameters in cases where test data is available. The rolling resistance is modelled with an impact loss model that captures variation of rolling resistance force with speed and accounts for a non-zero value of rolling resistance at zero speed. The model used for soft ground is an extension to Bekker’s sinkage theory for deformable surfaces and Reece’s model that relates sinkage rate of wheel with contact patch pressure. There is also an attempt to introduce an empirical relationship for a special case of tyre and road deforming simultaneously. The obtained simulation results were compared with available test data for validation. The results show that the extended brush model without the add on is reliable and produces comparable results with test data up to a slip range of 30% where passenger cars operate in normal driving conditions. The model with add-on activated and tuned with test data gives closely matching results for full range of slip. Results for rolling resistance shows that the model captures the nonlinearities for rolling resistance with speed effectively while also having an offset from the origin as desired. Different tyre types are studied here and typical values for the model parameters are tabulated. Simulation results for deformable ground show comparable results with results from research papers conducted for dry sand and soft loam. The model replicates the desirable trends and motivates the obtained results through physical concepts.

Nyckelord: tyre models, Brush model, Soft ground modelling, Bekker-reece model, rolling resistance, terramechanics, traction, tyres

Publikationen registrerades 2017-08-31. Den ändrades senast 2017-08-31

CPL ID: 251559

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