The basic architecture of a parallel hybrid transmission. Electrical power is applied in parallel with the combustion engine power. The electrical torque is applied at the wheel axle, but it could also be applied to the engine flywheel. In this test, the vehicle accelerates, maintains the faster speed, and then decelerates back to the original speed. The power management strategy uses just electrical power to effect the maneuver, the combustion engine only delivering the power required to maintain the original speed.

The basic architecture of a power-split hybrid transmission. The planetary gear, along with the motor and generator, acts like a variable ratio gear. In this test, the vehicle accelerates, maintains the faster speed, and then decelerates back to the original speed. The power management strategy uses just stored electrical power to effect the maneuver, the combustion engine only delivering the power required to maintain the original speed.

The basic architecture of a series hybrid transmission. All mechanical power from the engine is converted to electrical power via the generator. In this test, the vehicle accelerates, maintains the faster speed, and then decelerates back to the original speed. The power management strategy uses just stored electrical power to effect the maneuver, the combustion engine only delivering the power required to maintain the original speed.

The basic architecture of a two mode hybrid transmission. It consists of three planetary gear sets and four clutches. This combination permits four fixed gear ratios plus two power-split modes. The power split modes are used to transition between fixed gear ratios and for heavy acceleration/deceleration. The fixed ratios help with efficiency when cruising. For the first power split (input-split regime), only Clutch 1 is engaged. For the second power split (compound-split regime), only Clutch 2 is engaged. Engaging two clutches simultaneously removes one degree of freedom and hence results in a fixed ratio.