Impostazione progettuale dell'autoveicolo
Forze e momenti agenti su un veicolo, forze di contatto pneumatico-strada, forze e momenti aerodinamici.
Prestazioni longitudinali del veicolo, distribuzione dei carichi al suolo e trasferimento del carico, potenza richiesta per il movimento, potenza disponibile, scelta di i rapporti di trasmissione, le prestazioni massime (velocità, accelerazione, pendenza superabile); consumo di carburante, frenata e distribuzione della potenza frenante sulle ruote.
Dinamica laterale del veicolo. Sterzo cinematico e modelli di base. Comportamento di sotto e sovrasterzo, influenza del vento trasversale.
Sottosistemi del veicolo. Analisi funzionale e dettagli costruttivi dei più comuni sottosistemi veicolari (sospensioni, ammortizzatori, sistema di sterzo, sistema frenante,..) e loro comportamenti cinematici.
Architetture e componenti per trazione anteriore, posteriore, integrale.
Architetture e componenti per un veicolo elettrico, ibrido e a fuel cell.
Architetture telaio, metodologie di progettazione e nuovi materiali.
Cenni sui sistemi attivi, loro componenti e logiche di controllo: ABS, TCS, ESP, Frenata rigenerativa.
Impostazione progettuale dell'autoveicolo
- The vehicle: definition, reference systems, degrees of freedom, characteristic quantities.
- Tire mechanics
Limits of the Coulomb friction model in tire-road contact, hypothesis of flexible wheel on rigid ground. Effect of tire stiffness, inflation pressure and vertical load on contact patch dimension and average pressure. Structure of a tire and manufacturing process.
Brush model in conditions of simple longitudinal and lateral slip: stress distribution in the contact footprint, trends of the ground forces and of the self-aligning moment and sensitivity to the vertical load and the wheel-road friction coefficient. Steering axis position and its effects on straight driving stability and on sensitivity to the limit adhesion condition. Linearized behavior: dependence of cornering stiffness and longitudinal slip stiffness on vertical load. Cornering stiffness of an axle. Combined slip and interaction between longitudinal and lateral force. Empirical models, ply steer and conicity. Losses in a pneumatic tire: drift losses, slip losses and hysteresis.
- Longitudinal dynamics of the vehicle
Estimation of the center of gravity position (longitudinal and vertical) with dedicated experimental tests.
Traction: motion equations, vertical loads and load transfers, resistances to the motion of a vehicle at constant speed. Estimation of the loss coefficients by coast-down test. Power available from the powertrain and inertial power. Kinetic energy and translating apparent mass of a vehicle.
Electric motors (operating quadrants, efficiency) and thermal engines for motor vehicles (specific consumption maps, efficiency, E-line, fuel consumption calculation).
Transmission: components for a 2WD vehicle. Why a gearbox? Ideal traction hyperbola and characteristic traction force on the wheels for stepped and stepless transmission. Range of transmission ratios typical for automotive gearbox: example of a 6-speed DCT and 8-speed AT. Classification of transmissions, schemes and constructional drawing (MT, DCT, AT, CVT).
Maximum slope that can be overcome by a vehicle equipped with different drivetrain layouts: FWD,
RWD, ideal AWD, fixed torque distribution AWD. Optimized torque distribution ratio for a given grip condition. Effect of adherence conditions and torque distribution factor on performance.
Epicyclic gears and their use as differentials between wheels and axles.
Performance: acceleration, elasticity, gear ratio to maximize acceleration.
Criteria for the selection of the minimum and maximum transmission ratios and of the intermediate ratios of a gearbox: geometric and progressive ratio selection (theory and numerical exercise).
- Braking mechanics
Dynamic loads under braking. Ideal braking and braking with wheels locking on a single axle. Constant deceleration curves. Real braking with fixed brake force distribution. Braking efficiency. Graphic check of axle locking when the vehicle loading and grip change. Fixed distribution between the braking forces of the two axles: friction utilization and braking efficiency. Brake system design specifications. Braking correctors (pressure reducing valve, with fixed and variable calibration), EBD. Verifications required by ECE 13 regulations. Stopping time and distance of a vehicle. Approval limits for service and emergency braking. Components of a passive hydraulic braking system: brake booster and tandem master cylinder. Characteristic curve pressure-Force. Brake boost gain. Effect of the degree of vacuum on p-F, F-stroke characteristics. Response delay and speed of manoeuvre execution: Emergency Valve Assist, Hydraulic Brake Assist. Active systems that act on the brakes: ABS (layout, low and high level control logic).
- Lateral dynamics of a vehicle
Kinematic and dynamic steering. Bicycle model: kinematic and dynamic analysis of steady-state motion during cornering. Understeer and sideslip angle equation and related gradients.
Linear lateral dynamics: steady-state cornering response for understeering, neutral and oversteering vehicles; gains of curvature, yaw rate, lateral acceleration and sideslip angle; critical speed, instability and balance in counter-steering.
Nonlinear lateral dynamics: axle nonlinearity effect; understeer characteristic and real vehicle attitude; sensitivity to the driving torque, load transfers and setting of the anti-roll bars.