Week 2 Session 7

1) Compare the different architectures of HEV.

• Series hybrid
• Parallel hybrid
• Split-power hybrid
• Compound hybrid

Series hybrid

• ICE and EM are connected in series
• Basic components: ICE, electric generator (EM1),
electric motor (EM2), and ESS (battery)
• Only EM provides torque to the final drive

Discuss the Series hybrid layout Pro's:

• ICE always operates at peak efficiency range
• Efficiency loss can be further reduced due to fewer gear pairs and absence of transmission
• Outstanding towing capacity at low speed
• Big EM2 motor is able to capture more regen braking
• Control system is relatively simple

Discuss the Series hybrid layout Con's:

• Overall efficiency suffers especially at high speed
• EM can only output a portion of its maximum power at low speed, reversely increases EM size and costs.
• EM2 needs to meet all driving needs, increasing cost, weight, and installation space
• ICE is not engaged in final driving

Suitable applications

mining vehicle, city bus (with frequent start-stop applications).

Parallel hybrid

• Engine and electric motor are connected with fixed speed ratio.
• Both ICE and EM can provide torque to final driving, separately or together.
• Usually includes a transmission.

Discuss the Parallel hybrid layout Pro's:

• Total efficiency is higher doing cruising and highway driving
• Required relatively small EM
• Large design flexibility

Discuss the Parallel hybrid layout Con's:

• Complicated system with many variables
• ICE does not always operate at peak efficiency
• Battery cannot be charged at standstill

Example vehicles: Honda insight Hybrid, VW Jetta Hybrid, Acura RLX Hybrid, Nissan Pathfinder Hybrid

Split-power hybrid

• Double connection between the engine and the final drive: mechanical and electrical.
• Consist of one or more power split device (PSD).

Discuss Split-power hybrid layout Pro's:

• Maximum flexibility to switch between electric and ICE power
• Allows for a smaller, and more efficient ICE design

Discuss Split-power hybrid layout Con's:

• Highly complex system, more expensive than parallel hybrid
• Efficiency transmitted over the electrical path is lower

Example vehicles: Toyota Prius, Lexus CT200h, Lexus RX400h.

Compound hybrid

• Able to operate in more than one basic hybrid mode in a single architecture.
• May include Series/parallel, series/power split, parallel-parallel, and many other configurations.
• Increased cost and complexity.