Parallel (Mechanically Coupled) Hybrid Electric Drive Train Design

Unlike the series hybrid drive train, the parallel or mechanically coupled hybrid drive train has features that allow both the engine and the traction motor to apply their mechanical power in parallel directly to the driven wheels. As mentioned in Chapter 5, the mechanical coupling has two forms: torque and speed couplings. When using conventional IC engines as the primary power source, torque coupling is more appropriate since the IC engine is essentially a torque source.