The motion of all vehicles requires the expenditure of a certain quantity of mechanical energy, and in motor vehicles the system that supplies such energy (in most cases an internal combustion engine) is on board. The lack of an adequate prime mover is the main reason that mechanical vehicles could be built only at the end of the industrial revolution, and enter mass production only in the Twentieth Century, in spite of attempts dating back to ancient times. For a mechanical vehicle to be built, a prime mover able to move not only itself, but the vehicle structure and payload. | 22 PRIME MOVERS FOR MOTOR VEHICLES The motion of all vehicles requires the expenditure of a certain quantity of mechanical energy and in motor vehicles the system that supplies such energy in most cases an internal combustion engine is on board. The lack of an adequate prime mover is the main reason that mechanical vehicles could be built only at the end of the industrial revolution and enter mass production only in the Twentieth Century in spite of attempts dating back to ancient times. For a mechanical vehicle to be built a prime mover able to move not only itself but the vehicle structure and payload as well was needed. Remembering that the power needed to move the mass m at the speed V on a level surface with coefficient of friction sliding or rolling f is equal to P mgfV it is easy to conclude that the minimum value of the power mass ratio of a prime mover able to move itself is m . where a is the ratio between the mass of the engine and the total mass of the vehicle and n is the total efficiency of the mechanism which transfers the power and propels the vehicle. Prime movers with an adequate power mass ratio and transmission devices with a power rating and an efficiency high enough to allow the motion of the vehicle were not practical until the Nineteenth Century. The engine must obtain the energy required for motion from an energy source that is usually on board the vehicle. Rail vehicles often receive such energy from outside but the only road vehicles in which this occurs are trolleybusses. In most cases the energy is stored as the chemical energy of a fuel but it can be stored in the form of electrochemical energy electrical batteries or G. Genta L. Morello The Automotive Chassis Volume 2 System Design Mechanical Engineering Series Springer Science Business Media . 2009 165 166 22. PRIME MOVERS FOR MOTOR VEHICLES TABLE . Onboard energy storage. Energy density e m power density P m and general characteristics data for electrochemical energy .
