Browse Publications Technical Papers 2018-37-0023
2018-05-30

Maximizing Coasting of 48V Vehicles with Cold-Storage Evaporator 2018-37-0023

One of the main features in 48V vehicles is the ability to coast at high vehicle speeds with the Internal Combustion Engine (ICE) off due to the high torque and power the 48V motor-generator provides which allows a quick and smooth re-cranking of the ICE. The coasting feature reduces the fuel consumption depending on frequency and duration of the coasting events. This depends in turn on driving pattern, driving style and the State-of-Charge (SoC) of the 48V and 12V batteries as well as the air-conditioning system. In summer, if the air-conditioning runs with a mechanically driven compressor, the cabin inlet air temperature from the evaporator inevitably increases during each coasting event as the ICE turns off and cannot operate the compressor. If the evaporator temperature reaches a certain threshold at which the cabin comfort is noticeably affected, the ICE is re-cranked for resuming air-conditioning. This operation during vehicle deceleration and vehicle stop is inefficient as fuel is consumed solely for maintaining the air-conditioning and auxiliaries. Therefore, it is beneficial for fuel consumption if the evaporator maintains the set temperature for long time during coasting and the ICE is off. One way to overcome this is to use an electrical compressor independently operated from the powertrain. However, this is a cost intensive solution, due to higher cost of electrical compressors and increased capacity of the 48V battery for maintaining the additional supply for the air-conditioning. A more cost effective solution is to use Phase-Change-Materials (PCM) with high thermal capacity and a specified melting temperature optimized for this purpose. DENSO has developed an evaporator with modular concept to integrate PCM-filled slots with thermal storage (cold-storage), specifically designed to maximize coasting of 48V vehicles. Results show that a fuel consumption benefit of 5% is possible on modified NEDC at 35°C ambient temperature.

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