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

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

One of the main features of 48 V vehicles is the ability to coast at high speeds with the Internal Combustion Engine (ICE) off. This can be realized due to the high torque and power the 48 V 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, State-of-Charge of the 48 V and 12 V batteries and the air-conditioning (A/C) system.
In summer, if the A/C runs with a mechanical belt-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 standstill is inefficient as fuel is consumed solely for operating the A/C. Therefore, it is beneficial for fuel consumption if the evaporator maintains low temperature for long time during coasting with ICE 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 48 V battery required for the additional A/C supply. A more cost-effective solution is to use Phase-Change-Materials (PCM) with high thermal capacity and specified melting temperature optimized for this purpose.
DENSO has developed an evaporator with modular concept to integrate PCM-filled tanks, referred to as cold-storage (CS-evaporator), which is specifically designed to maximize coasting duration of 48 V vehicles. Tests show that a fuel consumption reduction of around 5% is possible at 30 °C ambient temperature.

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