7 3/8 x 9 1/4 T echnical / Build Your Own Electric Vehicle / Leitman / 373-2 / Chapter 5
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Build Your Own Elec tric Vehicle
Figure 5-6 Simplified EV drivetrain layout.
Difference in Motor vs. Engine Specifications Comparing electric motors and internal combustion engines is not an “apples to apples” comparison. If someone offers you either an electric motor or an internal combustion engine with the same rated horsepower, take the electric motor—it’s far more powerful. Also, a series wound electric motor delivers peak torque upon startup (zero RPM), whereas an internal combustion engine delivers nothing until you wind up its RPMs. An electric motor is so different from an internal combustion engine that a brief discussion of terms is necessary before going further. There is a substantial difference in the way an electric motor and an internal combustion engine are rated in horsepower. Figure 5-7’s purpose is to show at a glance that an electric motor is more powerful than an internal combustion engine of the same rated horsepower. All internal combustion engines are rated at specific RPM levels for maximum torque and maximum horsepower. Internal combustion engine maximum horsepower ratings are typically derived under idealized laboratory conditions (for the bare engine without accessories attached), which is why the rated HP point appears above the maximum peak of the internal combustion engine horsepower curve in Figure 5-7. Electric motors, on the other hand, are typically rated at the continuous
Drivetrain type Front wheel drive Rear wheel drive
Manual Differential transmission Driveshaft drive Drive axle 0.96 not required .097 .098 0.96 0.99 .097 .098
Table 5-8 Comparison of F ront and Rear Wheel Drivetrain Efficiences
Overall efficiency 0.91 0.90
