Dual-mode and Multi-mode Hybrid Transmissions
Dual-mode or multi-mode hybrid transmissions are a new trend in hybrid vehicles, aiming to merge the benefits of power-split, parallel and series hybrid transmissions with low technical complexity.
Even though the specific design can show a great variation in the details, the essence of the concept is the application of an internal combustion engine and two electric motors (M1 and M2). The engine and the M1 motor are connected with a simple mechanical gearbox, referenced as the ICE gearbox. The M2 motor can drive the wheels through a second simple mechanical gearbox, or the EM gearbox. Finally, the ICE gearbox is connected to the EM gearbox, so that both the engine and the M1 motor can be connected to the wheels with drive power going through both gearboxes.
The gearbox itself might be just a simple gearwheel pair, or a simple pair of shafts connected or disconnected via a shift mechanism, or even a multi-speed gearbox, depending on which particular vehicle is considered. Since inherently designed for hybrid vehicles, the two gearboxes form a Dedicated Hybrid Transmission (DHT).
Note that the system layout has no clutch, the vehicle is put into motion with the M2 motor, and the engine is started only if the vehicle speed is high enough the allow the engine operate above the low idle speed. Typically, reverse gear is also not included in the system, as reverse driving can be achieved in full electric mode only.
The name dual-mode hybrid comes from earlier times and highlights that the vehicle can operate either as a parallel or as a series hybrid. The term multi-mode hybrid is now more common, reflecting that the system can switch between ICE, full electric or combined (hybrid) modes.
This layout is particular flexible and enables a high number of different operating modes even without a power split device (PSD).
A possible extension to the system layout shown above is when the ICE gearbox can also drive the wheels directly. The benefit of this extension is – besides keeping all the power path options shown above – that the engine can drive the wheels either through the ICE gearbox or through the EM gearbox.
This means in case of a two-speed ICE gearbox and a two-speed EM gearbox, the engine can drive via 4 different ratios, without adding any new gears to the system.
↑ Back to the top.
← Back to the Basics.