In Hybrid vehicles, employing the start-stop functionality, the IC Engine automatically shuts down at zero speeds and restarts instantaneously in order to reduce the engine idling time; thereby reducing fuel consumption and emissions. The range of fuel economy gains from the start-stop system are about 5 to 10 percent as compared to non-start-stop systems. When the engine automatically stops as a result of the start stop system; the compressor which is a part of the automobile refrigeration system also stops running since the engine crankshaft pulley and the compressor are coupled by means of a serpentine belt which forms a part of the FEAD (Front End Accessory Drive) system. Thus, the air-conditioner stops working and the cabin temperature rises. The engine needs to restart to run the compressor if the cabin temperature exceeds a certain threshold value of discomfort. However, the engine restart is almost redundant rather paradoxical to the functionality of start-stop. In cold countries, the problem is not so severe. However, the issue arises in hot and tropical countries where the average temperatures during summer are above 30C. Since, restarting the engine is not a viable solution; alternative means were explored in order to solve the cabin cooling issue.

An inherent advantage of mild hybrid vehicles was exploited to combat the issue. Since, we do have a motor in the HEVs, the idea was to decouple the engine completely from the FEAD system and use this motor to drive the accessories including the compressor. The mechanism to facilitate the decoupling was the Electromagnetic Clutch. An EMC was developed and tested to solve the issue. When the engine is running i.e. at non-idling conditions; the clutch is engaged while during stops it is disengaged, thus declutching the engine from the FEAD system.

Abstract:

The worldwide scenario of road transport is moving towards a new generation of vehicles with enhanced power train able to guarantee a further increase in the automobile fuel economy. One of the technical solutions guaranteeing a significant fuel economy improvement is represented by the so-called mild-hybrid power train able to operate the Stop & Start function and, in the most sophisticated version, to recuperate the braking energy. The Stop & Start function allows stopping the engine automatically at car idle condition viz. traffic signals. This feature presents a problem because current AC-compressors would also stop working as the engine stops; thus increasing the temperature inside the car cabin. As hybrid vehicles also have mostly sufficient electrical energy available there is a possibility to run the compressor by an electric motor. Anyway, the hybrid and pure electric traction will probably be the new generation of power train in order to warrant the lower environmental impact however; their costs will be demanding as well. Hence, all the vehicle auxiliary systems have to be reviewed in order to assure and

ensure the same performance as the actual production vehicle in terms of comfort and usability; but with a lower power consumption to minimize the impact on vehicle autonomy.

In this report, we will focus on the AC system and we will provide an overview on the solutions realized by some car makers to solve the cooling issue during ‘Stops’ and summarize their limitations as to why they cannot be used in tropical countries like India. Finally, we would suggest some innovative solutions or proposals which would overcome the stated limitations and effectively solve the cooling problem.

Refer the attached document for more details