This epicyclic drive is pretty innovative. The prius drive train never locks any of the elements meaning that there is a ratio of at all times between the 3 elements sun planets and ring, at some point the ice engine must start spinning its part or the smaller motor gen overspeeds. The volt drives its epicyclic differently and has 3 clutches to stop and start different elements at different speeds. at all times the primary electric drive motor must supply torque, however above 70 mph the primary motor starts to over speed so the second motor is clutched in and together with the sun and ring gears they lower the speed of the primary motor to an acceptable level. when the battery is depleted a second clutch closes and the engine is coupled to the smaller motor/generator providing torque to it as well as the ring gear which previously was driven solely by the smaller motor/gen now the smaller motor consumes torque to generate electricity for sustaining the battery pack level and simultaneously to power the primary electric motor. The deficit of previously supplied torque from the smaller motor/gen is now mechanical supplied via the clutch and ring gear this is genius. The third clutch is to disconnect the smaller motor/gen from the ring gear at low speeds and allow the ice to turn it as a true generator in pure series hybrid mode again genius. This is a series electric + mechanical parallel+ electric cvt system the best of all the current hybrid modes. Should be a winner technically.
It should be noted that they purposely left out clutch 4 which would have allowed the ICE to turn the wheels directly as this would void the EV tax credit. A clutch on the sun gear to disconnect the primary electric drive motor and a band clutch or one way gear to hold the planet carrier would allow the ICE a direct mechanical connection to the epicyclic output geared for hyway speed at the final ratio would have allowed even greater hwy mileage since sending torque via the motor/gen to the inverter to the primary drive motor in electric cvt mode at hwy speed is inherently less efficient than a direct drive but alas they need the tax credit so this clutch was left out.