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Vehicle Dynamics.pptx
- 1.
- 2. Dynamics: The study ofthings in motion the branch of mechanics concerned with the motion of bodies under the action of forces.
- 3. Vehicle dynamics •The studyof vehicles in motion and forces associated with the motion • Vehicle dynamics is a part of engineering based on classical mechanics, • but it may also involve • physics, electrical engineering, chemistry, communications, psychology etc.
- 4. History of VehicleDynamics • 1769 - French military engineer, Nicholas Joseph Cugnot (1725-1804), built a three-wheeled, steam-driven vehicle for pulling artillery pieces. • 1784- a steam-powered vehicle by the Scottish engineer, James Watt (1736-1819), • 1802 - Richard Trevithick (1771-1833), an Englishman, developed a steam coach that traveled from Cornwall to London. • 1886 - The first practical automobiles powered by gasoline engines by Karl Benz (1844-1929) and Gottlieb Daimler ( 1834-1900) • Rene Panhard, Emile Levassor, Armand Peugeot, Frank and Charles Duryea, Henry Ford, and Ransom Olds • 1908 the automotive industry established in the United States with Henry Ford manufacturing the Model T and the General Motors Corporation being founded. • European companies like Daimler, Opel, Renault, Benz, and Peugeot
- 5. Why vehicle Dynamicsstudy is required • Safety- high speed manoeuvring, braking and cornering • Comfort- occupant feels • Vehicle designed considering the dynamics are safer, more comfortable and fun to drive. • Long life of vehicle system
- 6. Systems critical tovehicle dynamics • Tires: A considerable portion of the vehicle dynamics is focused • Steering system Control wheel geometry and movement • Suspension system isolate the occupant compartment from the disturbance from the road. • Braking system • Frame / body
- 7. Dynamics are consideredaccording to the use of the vehicle • Ride : vehicle response to vibration and disturbances caused by the road and other sources • Handling : vehicle response to the driver’s input of steering and manoeuvring maintaining the stability. • For a Vehicle designer, Ride and Handing are generally conflicting
- 8. Degrees of Freedom Thenumber of independent parameters that define its configuration in terms of location or motion. Movement along X direction Movement along Y direction Movement along Z direction Rotation about X axis Rotation about Y axis Rotation about Z axis
- 9. Centre of gravity •Point where the mass of body is concentrated • Location of centre of gravity is the single most important parameter which governs the overall dynamics • Fore and alt location of centre of gravity determines the weight distribution • Height of CG determines how the vehicle behaves in turns and lateral bumps
- 10. Vehicle Axis System •right-hand orthogonal coordinate system • Required to form the frame of reference for the analysis of motion • x – Forward of the vehicle • y - Lateral out the right side of the vehicle • z - Downward with respect to the vehice • p - Roll velocity about the x axis • q - Pitch velocity about the y axis • r - Yaw velocity about the z axis
- 11. Earth Fixed co-ordinatesystem and Euler angles • Vehicle attitude and path the vehicles takes during a maneuver are defined with respect to a fixed coordinate system outside the vehicle.
- 12. Concept of sprungand un-sprung mass • The portion of the vehicle supported by the spring is called sprung mass - body • The portion of the vehicle including tyres and suspension not supported by the spring is called un-sprung mass • Spring determines how the vibration are transferred and damped from road to the body • Un-sprung mass is desired to be low as possible
- 13. Newtons first lawof motion • An object will stay in rest or uniform motion unless acted upon by an unbalanced force. • Object at rest or uniform motion = Balanced force The resistance of object to change the state of rest or motion is called intertia.
- 14. Second law ofmotion • Object at equilibrium will not accelerate. • Acceleration = unbalanced forces • F = mass x acceleration • Net force = vector sum of all the forces acting • For rotational Torque = I x α • I- moment of inertia • α- Angular acceleration
- 15. Newton’s third lawof motion • Every action has equal and opposite reaction • A body at equilibrium is possible due to the reaction force.
- 16. Forces on wheels •Longitudinal Force (Fx)/ Tractive Force • Lateral Force (Fy)- • Normal Force (Fz) • Overturning Moment (Mx) • Rolling Resistance Moment (My) • Aligning Moment (Mz) Slip Angle (a) • Camber Angle (g)-
- 17. External Forces actingon a vehicle • Aerodynamic Drag : Body force impinged by the air • Road Disturbances : irregulates of road and tyre contact • Cornering forces : reaction forces while taking turn • Major sources of the resistance • Aerodynamic = • Rolling • Gradient
- 18. Equation of motionof a vehicle • Traction forces - driving resistance • the rolling resistance of the front and rear tires Fr), • the aerodynamic drag (Fw) • grade climbing resistance (Fg) • acceleration resistance (Fa)
- 19. Internal loads Static : Weightof the vehicle acts in the downwards direction at CG Wheel reactions Accelerating: Force at the tire pact moves vehicle with D’Alembert’s force Deaccelerating : brakes pads contact the disc Cruising: Aerodynamics and rolling resistance Cornering : Centrifugal force and reaction at wheels
- 20. Transmission Efficiency • Transmission:reduce the speed and increase the torque • new fuel-efficient, turbocharged, downsized engines with fewer cylinders and to diesel engines with higher torque fluctuation
- 21. Tractive Forces onDriving Wheel • Surface adhesion and the hysteresis mechanism. • Sliding frictional force: tyre and road surface rub each other • Adhesive force : Intermolecular bonds between tyre and road surface
- 22. Traction Characteristics • Underacceleration and braking, additional slip is observed • acceleration and braking forces are generated by producing a differential between the tire rolling speed and its speed of travel. • r = Tire effective rolling radius • w = Wheel angular velocity • V = Forward velocity
- 23. Braking vs LongitudinalSlip • Longitudinal stiffness tends to be low when the tire is new and has full tread depth, increasing as the tire wears.
- 24. Peak coefficient andslide coefficient versus load • On a dry road, when the slip approaches approximately 15-20 percent, the friction force will reach a maximum (typically in the range of 70 to 90 percent of the load) as most tread elements are worked most effectively without significant slip. • On wet roads the peak friction force will typically be in the range of 25 to 50 percent of the vertical load. • On ice-covered roads the peak friction will be only 10 to 15 percent of the vertical load and will be reached at only a few percent slip.
- 25. Tractive forces accordingto the tire road grip • Longitudinal traction required for braking and stopping distance • Peak coefficient - limit for braking when the wheels do not lock up. • Sliding coefficient – braking contribution from locked wheels
- 26. Response under differentroad condition • The performance of tires on wet surfaces depends on the surface texture, water depth, tread pattern, tread depth, tread material, and operating mode of the tire. Tyre Tread is given to facilitate the flow of water preventing the hydroplaning Tread types- ribbed, siped and smooth
- 27. Tread Design onpeak and sliding coefficient friction
- 28. Hydroplaning • The liftcomponent of the hydrodynamic force is equal to the vertical load acting on the tire. • Fh = ρf ×A×V2
- 29. Normal reaction ofthe road • Vertical dynamics- ride and road holding • The axles and associated wheel move as rigid bodies and impose excitation forces on the sprung mass. • input -excitations and output- vibrations • Transmissibility – gain – ratio of output to input- ratio of response amplitude to excitation amplitude • ratio may be one of forces, displacements, velocities or accelerations
- 30. Quarter car model •An Isolated Quarter Car Model • Ks = Suspension stiffness • Kt = Tire stiffness • Ride Rate • In the absence of damping, the bounce natural frequency • M = Sprung mass • W = M g = Weight of the sprung mass • g = Acceleration of gravity
- 31. Quarter car model •When damping is present, the resonance occurs • good ride the suspension damping ratio on modem passenger cars usually falls between 0.2 and 0.4 • With a damping ratio of 0.2, the damped natural frequency is 98% of the undamped natural frequency, and = at 0.4 damping, the ratio is about 92%. • The ratio of W/K represents the static deflection of the suspension due to the weight of the vehicle.