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Additional fuel consumption reduction during the NEDC test cycle and real life driving can be effectively achieved by quickly raising the temperatures of the powertrain’s parts, oils and coolant closer to the optimal operating temperatures. In particular, the engine cooling system today must play a bigger role in the overall thermal management of the powertrain’s fluids and metals during warm-up, idle and severe operating conditions. In responding to these additional requirements, the previously proposed cost effective split cooling system has been further evolved to expedite the powertrain’s warming up process without compromising the overall heat rejection performance during severe operating conditions. In achieving these warming and cooling functions, the coolant flow rate in the cylinder head is almost stagnant when the single thermostat is closed and at its maximum when the thermostat is fully opened.

An engine cylinder block is generally considered to be the heaviest part within a complete engine. In lowering the fuel consumption and CO2 discharge to the environment, efforts have been made around the world to reduce the weight of cylinder blocks. In general, the efforts are mostly focused on material upgrade from either cast iron to aluminum or from aluminum to magnesium. Although the material upgrade approach is effective in lowering the part weight, it is often accompanied by undesirable cost increase and manufacturing complexity. In moving forward, a new cylinder block concept is proposed that focuses more on material removal rather than material upgrade. The material removal approach is focused more on the high metal concentration areas like the bulkhead, skirt and housing for water pump and thermostat. To ensure that the material removal approach is effective and suitable for mass production, a uniquely designed crankcase inner sand core is applied.

The ongoing global trends in engine downsizing and continuous need for higher engine specific output require more heat to be transferred out of the engine and into the radiator. This higher heat rejection necessitates higher coolant flow rate which is often accompanied with higher water pump power consumption and increased coolant circuit's cavitations risk. An enhanced split cooling concept is proposed to overcome the stated limitations with more efficient and effective coolant distributions to the cylinder head and cylinder block. The proposed concept also enables the cylinder head to run cooler than the cylinder block without the need for additional thermostat or water pump. The temperature differences are achievable by optimizing the coolant flow rates going through the cylinder head and cylinder block using both the 1D and 3D simulation packages.

The test results published earlier have proven that the previously proposed engine cooling circuit when combined with exhaust heat recovery and reuse could expedite the warm-up process after cold start and has improved the fuel economy by up to 4%. With the evolution of the earlier concept, the study discussed in this paper explores further improvements to the cooling circuit to expedite the warm-up process. In particular, with some changes to the cooling circuit, the heat recovered from the exhaust gas is reusable right away to heat up the heat exchangers for engine oil, CVT oil and cabin heater. Next, the thermostat opening temperature and leakage rate can also be optimized to prolong the heat recirculation and preservation periods. Finally, the coolant flow rate across the heat recovery unit can also be varied as a function of time right after the cold-start. These additional measures although capable of improving the warm-up process come with limitations.

The drive to reduce CO2 and fuel consumption from passenger cars requires improvements from various subsystems. In particular, the ever growing importance of effective and efficient thermal management will no doubt benefit the quest for more efficient vehicle. While many established automakers have decided to increase the sophistications of the engine cooling circuits through electronics, the increase in complexity and costs are still not desirable especially for A and B passenger car segments. With this in mind, simple mechanical based cooling systems with enhanced functionalities are in high demand. To meet such demand, a simplified engine split cooling circuit previously proposed, simulated and reported seems to be promising. To further verify the indicated advantages, a prototype unit was built and physically tested using a dynamometer with motoring capability.