72 Electric and Hybrid Vehicles Velocity (m/s), Force (N/100), Power (kW) FIGURE 3.17 Tractive power and force requirements with a combination of constant force and constant power modes of acceleration. With this approach, the IC engine size should be determined first for the Akron hybrid vehicle, and then the remainder of the 130 kW power required can be met by an electric motor. The IC engine power can be calculated from ρ P t 2 TR ( ) = + V m g m sin β gC 1 + A C F D V m + gC 0 (3.7) 2 where V is the rated velocity or cruising speed.
The HEV IC engine can be sized for the engine power required to maintain a steady expressway velocity of x mi/h (say 75 mi/h), up an y % grade (say 3%), and against an z mi/h (say 20) headwind at high-engine fuel efficiency. The engine power at highway speeds should also have good fuel effi- ciency; an IC engine’s best fuel efficiency operating point is not necessarily at its maximum power capability point. Therefore, the IC engine can be selected with highway power capability less than the engine’s maximum power rating for acceptable fuel efficiency.
3.5.3.3 Maximum Velocity The power requirement from the propulsion system at maximum velocity is F v TR ⋅ max , which is sup- plied by a combination of the IC engine and the electric motor. The power requirement for maxi- mum velocity is ρ P F TR ,max = ⋅ TR v m max m = + gv ax sin β + 3 + mgC A 1 F D C v max m mgv C ax 0 (3.8) 2 With the IC engine and electric motor sized to meet the acceleration and cruising speed require- ments, it has to be verified that the combination of the two can meet the vehicle maximum velocity requirements. If the combined power is less than the power required for maximum velocity, then one of the power plants size should be increased.