The present disclosure relates to a cooling apparatus for an internal combustion engine that includes an oil warmer, which performs heat exchange between engine coolant and transmission lubricant.
Japanese Laid-Open Patent Publication No. 2003-286846 discloses a cooling apparatus that includes an oil cooler (oil warmer), which performs heat exchange between coolant of an internal combustion engine and lubricant of a transmission. The apparatus includes a warmer passage, which extends from the outlet of an engine internal passage, through which coolant flows, to the inlet of the internal passage. The oil warmer is located in the middle of the warmer passage. The warmer passage includes an induction pipe for drawing coolant into the oil warmer and a discharge pipe for discharging coolant from the oil warmer. The warmer passage is also connected to a bypass pipe, which extends from the induction pipe to the discharge pipe while bypassing the oil warmer. A thermostat is provided in the discharge pipe at a part to which the bypass pipe is connected. The thermostat is closed to cut off the flow of coolant from the oil warmer to the downstream side of the thermostat in the discharge pipe.
The thermostat includes a shape-memory plastic and is mechanically opened at about 80° C. Thus, when the temperature of coolant that flows from the outlet of the internal coolant passage of the engine into the induction pipe is lower than 80° C., the coolant bypasses the oil warmer and flows into the inlet of the internal coolant passage via the bypass passage. In contrast, when the temperature of coolant flowing into the induction pipe is higher than or equal to 80° C., the thermostat is opened to allow the coolant to flow into the oil warmer.
This apparatus allows the heat of coolant to be transferred to lubricant on condition that the warm-up of the internal combustion engine has progressed.
When the temperature of coolant has reached about 80° C. due to starting of the engine, the temperature inside the oil warmer may still be significantly lower than 80° C. If the coolant temperature reaches 80° C. in this state so that the thermostat is opened, a great amount of coolant, the temperature of which is significantly higher than that of the oil warmer, flows into the oil warmer. This may cause a thermal shock in the oil warmer.