The mechanical output of the electric motor is connected to the driveline such that it can be used in conjunction with the engine or just as a pure EV. This means that the electric motor can be used to assist the engine and hence the engine can be optimised for fuel efficiency. It also means that the vehicle has a larger battery pack so that it can be used as a pure EV.
Needs review: this page currently repeats the plug-in hybrid description already covered in more depth under Hybrid System Type. It would benefit from real-world PHEV examples (specific vehicle battery/engine configurations) and supporting citations, matching the depth of the Hybrid System Type and Hybrid Battery Pack pages.
Hybrid System Block Diagrams
A high level definition of the hybrid system type. The pros and cons and a look at the battery.
The mechanical output could be to the wheels of a vehicle, the propeller of a boat or aircraft. The requirements for each system will influence the sizing of the system and the balance between battery storage capacity and onboard fuel storage. Thus changing the pros and cons of each system to some extent.
See also: Hybrid Battery Pack for an example of a mixed-chemistry pack designed specifically for PHEV and EREV use.
See also: Extended Range Electric Vehicle, SAE J1772, BYD Shark PHEV