59 Vehicle Architectures and Design (a) (a) (b) ICE ICE Clutch Clutch Trans- mission mission Trans- Starter Starter Gear Gear E M E M (c) (d) FIGURE 3.8 HEV P0 to P4 architectures: (a) P0 architecture with belt-starter generator; (b) P1 architecture ISG; (c) P2 architecture and (d) P3 or P4 architecture. P4 – The P4 architecture is also a post-transmission configuration with the electric machine connected through a gear mesh on the rear axle of the vehicle or in the wheels hub. Similar to P3 architecture, the electric machine is decoupled from the IC engine and rotates at a multiple of wheel speed.
In P2, P3 or P4 configurations, the electric machine is discon- nected from the IC engine through a clutch. Each of the four configurations has their advantages and disadvantages in terms of functionality, cost, fuel economy improvement and drivability. The fuel economy improvement comes from the brake regeneration operation where the size and capacity of the electric machine matters and the engine on/off operation particularly on stop and go traffic in urban areas. The improvement comes from electric-only modes reducing inefficient engine operation times at light load conditions.
For example, a 20% fuel economy improvement is expected using P0 architecture compared with the baseline vehicle that has a conventional alternator. A combination architecture may also be used to improve fuel economy and driver experience; for example, adopting a P0P4 architecture more than 30% fuel economy improvement is expected with increased driver experience. 3.2.2.3 48 V Hybrid Architectures An increasing number of HEV architectures are evolving around 48 V system serving as a low- cost hybrid alternative in the category of mild hybrids.
The 48 V architectures are a less disruptive approach of vehicle electrification for increasing fuel economy and reducing carbon emissions with a 48 V powertrain electrification. European Union has 95 g/km CO 2 emission requirement to be met by vehicle manufacturers by 2021, which cannot be achieved by improvements in ICEVs alone; this is driving the micro-hybrid demand and market in Europe with lower voltage electrified powertrain. Lower voltage and higher power battery-packs can be utilized for start–stop operation, electric pro- pulsion assist, regenerative energy capture, and supplying the ever-growing vehicle load demands.
With 15–25 kW electrification, 48 V hybrids can deliver fuel economy improvements, handle higher power auxiliaries and provide improved handling, drivability and comfort compared to ICEVs. The safety features are also well managed with 48 V systems compared to higher voltage systems. These mild hybrids bridge the gap to full hybrids and BEVs where consumers have historically been reluc- tant to purchase due to the high cost. E M Clutch Trans- ICE mission Belt Starter Gear Differential Differential Clutch E Trans- ICE M mission Starter Gear Differential Starter Differential E M Gear Trans- ICE mission Clutch Starter Gear Differential ICE Differential