This example shows 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 enagaged. Engaging two clutches simultaneously removes one degree of freedom and hence results in a fixed ratio.
In this example, the Strategy subsystem defines a set of rules that determine when to change between transmission modes during a steady acceleration profile. A full vehicle control strategy would also need to include control of electrical power as a function of speed, driver demand and battery state.
The plot below shows the speeds of the engine, motor-generator shafts, and vehicle speed as it progresses through each of the modes of a two mode hybrid powertrain. The modes include fixed gears and split modes where the flow of power is split at the input to the powertrain or both at the input and output (compound split).
The plot below shows the gear ratio of the two mode hybrid powertrain transmission. The two electric motors enable the set of planetary gears to act as a continuously variable transmission.