Instantaneous Power Requirements of A Vehicle P M V Subbarao Professor Mechanical Engineering Department Match the Horse to the Car….

Comprehensive Test Driving Cycle for Design of Horse for A Vehicles

Driving on Busy Roads : Braking & Safety In general, if we're talking normal driving situations the rule of thumb you should follow is to keep the car in gear for the most amount of time. Downshifting is good, but most people do not downshift when stopping. This can either just be laziness!!! It is also driven by the fact that when you need to slow down reasonably fast you might just not have enough time to row through the gears.  Best way to do is, brake in gear until the car about the slowest speed for whatever gear it is in, then clutch in, go into neutral and keep braking further.

Forces To be Overcome by an Automobile

Resistance Forces on A Vehicle The major components of the resisting forces to motion are comprised of : Acceleration forces (Faccel = ma & I forces) Aerodynamic loads (Faero) Gradeability requirements (Fgrade) Chassis losses (Froll resist ).

Aerodynamic Force : Flow Past A Bluff Body Composed of: Turbulent air flow around vehicle body (85%) Friction of air over vehicle body (12%) Vehicle component resistance, from radiators and air vents (3%) http://www.buildyourownracecar.com/race-car-aerodynamics-basics-and-design/

Aerodynamics Lift, Drag and Down Force

Aerodynamic Drag on Vehicle Dynamic Pressure: Drag Force: Aero Power

Instantaneous Power Requirement to Overcome Drag Cd = coefficient of drag  = air density  1.2 kg/m3 A = projected frontal area (m2) V = vehicle velocity (m/sec) Vw = head wind velocity

Purpose  Shape  Design Drag

Shape & Components of Drag

Some examples of Cd: The typical modern automobile achieves a drag coefficient of between 0.30 and 0.35. SUVs, with their flatter shapes, typically achieve a Cd of 0.35–0.45. Notably, certain cars can achieve figures of 0.25-0.30, although sometimes designers deliberately increase drag in order to reduce lift. at least 0.6 - a typical truck 0.57 - Hummer H2, 2003 0.51 - Citroën 2CV over 0.5 - Dodge Viper 0.44 - Toyota Truck, 1990-1995

Drag Coefficient for Sports Cars 0.195 - General Motors EV1, 1996 0.19 - Alfa Romeo BAT Concept, 1953 0.19 - Dodge Intrepid ESX Concept , 1995 0.19 - Mercedes-Benz "Bionic Car" Concept, 2005 ([2] mercedes_bionic.htm) (based on the boxfish) 0.16 - Daihatsu UFEIII Concept, 2005 0.16 - General Motors Precept Concept, 2000 0.14 - Fiat Turbina Concept, 1954 0.137 - Ford Probe V prototype, 1985

Transient Nature of Aerodynamic Drag

Effect of Overtaking on Aerodynamic forces : Overtaking Vehicle is behind the main Vehicle

Effect of Overtaking on Aerodynamic forces : Overtaking & Main Vehicles at same Position

Effect of Overtaking on Aerodynamic forces : Overtaking Vehicle is ahead of the Main Vehicle

Effect of relative velocity on the variation in the aerodynamic Drag coefficient

Force System on A Rolling Wheel

Road Conditions & Rolling Resistance

Rolling Resistance Composed primarily of Resistance from tire deformation (90%) Tire penetration and surface compression ( 4%) Tire slippage and air circulation around wheel ( 6%) Wide range of factors affect total rolling resistance The magnitude of this force is Approximated as: Rolling resistance of a vehicle is proportional to the component of weight normal to the surface of travel

Typical Values of Coefficient of Rolling Resistance Contact Type Crr Steel wheel on rail 0.0002...0.0010 Car tire on road 0.010...0.035 Car tire energy safe 0.006...0.009 Tube 22mm, 8 bar 0.002 Race tyre 23 mm, 7 bar 0.003 Touring 32 mm, 5 bar 0.005 Tyre with leak protection 37 mm, 5 bar / 3 bar 0.007 / 0.01

Effect of Road Condition on Crr

Grade Resistance Composed of Gravitational force acting on the vehicle For small angles, θg Fg θg mg

Total Vehicular Resistance at Constant Velocity   AR = air resistance [N] RR = rolling resistance [N]             GR = gradient resistance [N] TR = total resistance [N]