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Technical Paper

Virtual and Experimental Analysis of Brake Assist Systems

2006-04-03
2006-01-0477
The paper deals with the virtual and experimental analysis of two commercial Mechanical Brake Assist systems. They are described in detail, then modeled and experimentally evaluated through a Hardware-In-the-Loop test bench and road tests. Three different kinds of drivers are compared, from the point of view of the performance increase promised by Brake Assist during an emergency brake maneuver. The three driver types are based on the measurement of the behavior of real drivers, as it is presented in specific research activities in literature.
Journal Article

Vehicle Simulation for the Development of an Active Suspension System for an Agricultural Tractor

2009-05-13
2009-01-1608
The design of suspension systems for heavy-duty vehicles covers a specific field of automotive industry. The proposed work focuses on the design development of a front controllable suspension for an agricultural tractor capable to satisfy the system requirements under different operating conditions. The design of the control algorithms is based on the developed multibody model of the actual tractor, including the pitch motion of the sprung mass, the anti-dive effects during braking and forward-reverse maneuvers and the non-linear dynamics of the actuation system. For an advanced analysis, a novel thermo-hydraulic model of the hydraulic system has been implemented. Several semi-active damping controls are analyzed for the specific case study.
Technical Paper

Vehicle Dynamics Simulation to Develop an Active Roll Control System

2007-04-16
2007-01-0828
Active Roll Control (ARC) is one of the most promising active systems to improve vehicle comfort and handling. This paper describes the simulation based procedure adopted to conceive a double-channel Active Roll Control system, characterized by the hydraulic actuation of the stabilizer bars of a sedan. The first part of the paper presents the vehicle model adopted for this activity. It is Base Model Simulator (BMS), the 14 Degrees-of-Freedom vehicle model by Politecnico di Torino. It was validated through road tests. Then the paper describes the development of the control algorithm adopted to improve the roll dynamics of the vehicle. The implemented control algorithm is characterized by a first subsystem, capable of obtaining the desired values of body roll angle as a function of lateral acceleration during semi-stationary maneuvers.
Journal Article

Torque-Vectoring Control for an Autonomous and Driverless Electric Racing Vehicle with Multiple Motors

2017-03-28
2017-01-1597
Electric vehicles with multiple motors permit continuous direct yaw moment control, also called torque-vectoring. This allows to significantly enhance the cornering response, e.g., by extending the linear region of the vehicle understeer characteristic, and by increasing the maximum achievable lateral acceleration. These benefits are well documented for human-driven cars, yet limited information is available for autonomous/driverless vehicles. In particular, over the last few years, steering controllers for automated driving at the cornering limit have considerably advanced, but it is unclear how these controllers should be integrated alongside a torque-vectoring system. This contribution discusses the integration of torque-vectoring control and automated driving, including the design and implementation of the torque-vectoring controller of an autonomous electric vehicle for a novel racing competition. The paper presents the main vehicle characteristics and control architecture.
Journal Article

Torque Gap Filler for Automated Manual Transmissions: Principles for the Development of the Control Algorithm

2009-04-20
2009-01-0952
One of the most significant tasks in automotive design is related to the implementation of gearboxes capable of reducing the torque gap during the gearshift process and, at the same time, not decreasing vehicle performance from the point of view of driveline efficiency. Automated gearboxes based on torque converters ([1], [2]) satisfy the first requirement but not the second. On the other hand, manual automated gearboxes ([3], [4], [5], [6]) satisfy the requirements in terms of consumption, due to the absence of the dissipations caused by the torque converter. In fact, they consist of the basic layout of a manual transmission with hydraulic or electromechanical actuators which are adopted for the clutch and the synchronizers. However, automated manual transmissions cannot guarantee optimal longitudinal dynamics of the vehicle due to the discontinuity in torque transmission when the clutch is disengaged.
Technical Paper

Tire Thermal Model for Enhanced Vehicle Dynamics Simulation

2009-04-20
2009-01-0441
Brush models permit a more physical simulation of tire performance in comparison with models based on empirical formulas. The paper presents an empirical model for the estimation of tire temperature as function of the actual working conditions of the component. The estimated temperature values enter a tire brush model and provoke the variation of the performance in terms of tangential forces. The model can be empirically tuned through experimental data showing the variation of tire performance as function of temperature. The experimental validation of the model is dealt with in detail.
Journal Article

The Application of Control and Wheel Torque Allocation Techniques to Driving Modes for Fully Electric Vehicles

2014-04-01
2014-01-0085
The combination of continuously-acting high level controllers and control allocation techniques allows various driving modes to be made available to the driver. The driving modes modify the fundamental vehicle performance characteristics including the understeer characteristic and also enable varying emphasis to be placed on aspects such as tire slip and energy efficiency. In this study, control and wheel torque allocation techniques are used to produce three driving modes. Using simulation of an empirically validated model that incorporates the dynamics of the electric powertrains, the vehicle performance, longitudinal slip and power utilization during straight-ahead driving and cornering maneuvers under the different driving modes are compared.
Technical Paper

Shock Absorber Modeling and Experimental Testing

2007-04-16
2007-01-0855
Simulation is becoming the fundamental tool to design the main components of a vehicle. The paper describes the shock absorber model which was implemented by the Vehicle Dynamics Research Team of Politecnico di Torino. It is a modular model which can be adopted both for mono-tube and twin-tube shock absorbers. It can be used at different levels of approximation, as a function of the kind of user and his/her targets. The main data which have to be inserted in the model are fluid properties, the basic dimensions of the component and the characteristics of the orifices of the shock absorber. An experimental test bench was conceived to obtain the diagrams plotting flow rate through an orifice of a shock absorber versus the pressure drop between input and output ports. The test rig and the procedure to perform the experimental tests and insert the results in the shock absorber model are described in detail.
Technical Paper

Racing Simulation of a Formula 1 Vehicle with Kinetic Energy Recovery System

2008-12-02
2008-01-2964
This paper deals with the development of a Lap Time Simulator in order to carry out a first approximate evaluation of the potential benefits related to the adoption of the Kinetic Energy Recovery System (KERS). KERS will be introduced in the 2009 Formula 1 Season. This system will be able to store energy during braking and then use it in order to supply an extra acceleration during traction. Different technologies (e.g. electrical, hydraulic and mechanical) could be applied in order to achieve this target. The lap time simulator developed by the authors permits to investigate the advantages both in terms of fuel consumption reduction and the improvement of the lap time.
Journal Article

Optimal Wheel Torque Distribution for a Four-Wheel-Drive Fully Electric Vehicle

2013-04-08
2013-01-0673
Vehicle handling in steady-state and transient conditions can be significantly enhanced with the continuous modulation of the driving and braking torques of each wheel via dedicated torque-vectoring controllers. For fully electric vehicles with multiple electric motor drives, the enhancements can be achieved through a control allocation algorithm for the determination of the wheel torque distribution. This article analyzes alternative cost functions developed for the allocation of the wheel torques for a four-wheel-driven fully electric vehicle with individually controlled motors. Results in terms of wheel torque and tire slip distributions among the four wheels, and of input power to the electric drivetrains as functions of lateral acceleration are presented and discussed in detail. The cost functions based on minimizing tire slip allow better control performance than the functions based on energy efficiency for the case-study vehicle.
Technical Paper

Linear Analysis of the Effect of Tire Dynamics on the Overall Vehicle Performance

2010-04-12
2010-01-0090
The purpose of this paper is to deal with the frequency response of rigid and articulated vehicles subjected to a steering input. In particular, the effect of tire dynamics is considered in detail. Tire delays in lateral force generation can be modeled by adopting first or second order transfer functions. The paper compares the structure of the overall transfer functions simulating the entire vehicle. The results related to three alternative linear vehicle models are presented, in order to draw some objective conclusions about the real effect of relaxation length at low and average velocities.
Technical Paper

Hardware-In-the-Loop to Evaluate Active Braking Systems Performance

2005-04-11
2005-01-1580
The paper shortly describes an ABS/ESP Hardware-In-the-Loop (HIL) test bench built by the Vehicle Dynamics Team of the Department of Mechanics of Politecnico di Torino. It consists of a whole brake system, integrated through specific interface (e.g. wheel pressures signals) with a vehicle model running in real time on a dSPACE® board. Different commercial ABS strategies are compared, in a large spectrum of manoeuvres: slow brake apply manoeuvres, panic brake manoeuvres, μ-split brake manoeuvres, brake manoeuvres with a sudden variation of the friction coefficient between tyres and ground. The paper deals with the generation of all the signals required for activating a commercial ESP: steering wheel angle, body yaw rate, body lateral acceleration, engine control, etc… Some of them are transmitted by CAN. Typical handling manoeuvres are used to test the ESP: step steer, double step steer, ramp steer, etc… Several brake manoeuvres are simulated while turning.
Technical Paper

Friction inside Wheel Hub Bearings: Evaluation through Analytical Models and Experimental Methodologies

2007-09-16
2007-24-0138
This paper presents an experimental methodology which can be adopted to measure the friction torque of the bearings in the wheel hubs of passenger vehicles. The first section of the paper highlights the reasons why an experimental device is necessary to have an objective evaluation of the performance of the bearing in terms of friction. In particular, the high level of approximation of the current formulas for the estimation of the friction inside a single bearing is discussed and demonstrated. An analytical methodology for the evaluation of the distribution of the axial load between the two bearings of the wheel hub is presented. However, its practical application for the precise calculation of the distribution of the load has to be checked through experimental tests.
Technical Paper

Four-wheel-steering Control Strategy and its Integration with Vehicle Dynamics Control and Active Roll Control

2004-03-08
2004-01-1061
The paper presents a 4-wheel-steering (4WS) control strategy devoted to reduce the turn diameter for small longitudinal speed values and to obtain a yaw rate damping effect in dynamic manoeuvres. Moreover, the 4WS active system conceived produces compensation both for lateral wind and road irregularities. The main results obtained through a functional vehicle model are presented. 4WS was integrated with a Vehicle Dynamics Control (VDC), which was improved for turn while braking manoeuvres. The results due to integration were very good, with a reduction of both systems interventions. Finally, a VDC-4WS-Active Roll Control (ARC) integration was tried, based on only one reference body yaw rate for all the active systems. The main results obtained are presented and discussed.
Technical Paper

Experimental Validation of a Heavy Goods Vehicle Fuel Consumption Model

2011-04-12
2011-01-1234
Over the last decade the simulation of driving cycles through longitudinal vehicle models has become an important stage in the design, analysis and selection of vehicle powertrains. This paper presents an overview of existing software packages, along with the development of a new multipurpose driving cycle simulator implemented in the Matlab/Simulink environment. In order to evaluate the performance of the simulator, a MAN TGL 12.240 multi-usage delivery vehicle was fitted with a CAN-bus data logger and used to create a series of ‘real-life’ drive cycles. These were inputted into the vehicle model and the simulated fuel mass flow-rate and engine rotational speed were compared to those experimentally obtained.
Technical Paper

Enhanced Tire Brush Model for Vehicle Dynamics Simulation

2008-04-14
2008-01-0595
The aim of this paper is the conception of a tire model which allows a good fit with the physical experimental behavior of the component. In the meanwhile, the model should be simple enough to permit real time vehicle dynamics simulation, in the same way as the diffused Pacejka's model. The paper discusses the influence of the model for the estimation of contact patch properties on the overall tire forces and moments. It demonstrates that unrealistic models of the contact patch can lead to a good fit with the experimental data (in terms of forces and self-aligning moment), even if the real physics of the tire is not reproduced. A realistic model implies a significant reduction of the stiffness of the brushes as a function of the vertical load between the tire and the road surface.
Technical Paper

Electro-Mechanical Active Roll Control: A New Solution for Active Suspensions

2006-02-14
2006-01-1966
The paper presents the approach followed by Politecnico di Torino Vehicle Dynamics Research team to design an electro-mechanical Active Roll Control (ARC) system. The first part of the paper describes the targets of the system, which has to improve both comfort and handling. Different solutions for the implementation of the electro-mechanical actuation were evaluated. A prototype of the electro-mechanical Active Roll Control was built and experimentally tested in the Vehicle Dynamics Laboratory of the Department of Mechanics of Politecnico di Torino, by adopting a Hardware-In-the-Loop (HIL) test bench. The experimental results show the benefits of the system, both in a stand alone configuration and integrated with an Electronic Stability Control (ESC) system.
Technical Paper

Electro-Hydraulic Braking System Modelling and Simulation

2003-10-19
2003-01-3336
The first step toward a braking system ‘by wire’ is Electro-Hydraulic Braking System (EHB). The paper describes a method to evaluate through virtual experimentation the actual improvement in vehicle behaviour, from the point of view of both handling and comfort, including also pedal feeling, due to EHB. The first step consisted in modelling the hydraulic unit, comprehensive of sensors. Then it was conceived a control logic devoted to medium-low intensity braking manoeuvres, without ABS intervention, to determine an optimal braking force distribution and pedal feeling depending on the manoeuvre. A failsafe strategy, complete of on board diagnosis, to prevent dangerous system behaviour in the eventuality of a component failure was carried out and tested. Finally, EHB wheel pressure sensors were used to improve both ABS performance, increasing the adherence estimation, and Vehicle Dynamics Control (VDC) performance, through a more precise actuation.
Technical Paper

Driveline Layout Influence on Four Wheel Drive Dynamics

2004-03-08
2004-01-0860
The paper presents the research activity managed to investigate the dynamics of a 4WD vehicle equipped considering drivelines with different layout. The procedure developed required to conceive an on purpose simulator to compare performance through virtual experimentation. Drivelines mechanical main characteristics and performance increasing due to control strategy were evaluated. Preliminary road test were performed with a single driveline layout, to evaluate simulation reliability and limits. The paper presents the 4WD vehicle simulator, the main equations applied to model open, torque sensing and limited slip differentials, some preliminary road test results showing torque sensing driveline performance.
Journal Article

Drivability Analysis of Heavy Goods Vehicles

2010-10-05
2010-01-1981
The paper presents linear and non-linear driveline models for Heavy Goods Vehicles (HGVs) in order to evaluate the main parameters for optimal tuning, when considering the drivability. The implemented models consider the linear and non-linear driveline dynamics, including the effect of the engine inertia, the clutch damper, the driveshaft, the half-shafts and the tires. Sensitivity analyses are carried out for each driveline component during tip-in maneuvers. The paper also analyses the overall frequency response using Bode diagrams and natural frequencies. It is demonstrated that the most basic model capable of taking into account the first order dynamics of the driveline must consider the moments of inertia of the engine, the transmission and the wheels, the stiffness and the damping properties of the clutch damper, driveshaft and half-shafts, and the tires (which link the wheel to the equivalent inertia of the vehicle).
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