1. Field of the Invention
This invention relates to an apparatus and method for treating blow-by gas of an internal combustion engine.
2. Description of the Related Art
In an internal combustion engine built into a vehicle such as an automobile, gas containing fuel components and exhaust components (blow-by gas) leaks out of the combustion chamber into the crankcase through a space between the cylinder inner wall and the piston ring during the drive of the vehicle. Therefore, as Japanese Patent Application Publication No. 2006-299929 (JP-A-2006-299929) discloses, the internal combustion engine is provided with a blow-by gas treatment apparatus which returns the blow-by gas leaking out of the combustion chamber into the crankcase to an intake passage to treat the blow-by gas, and controls the gas flow rate of the blow-by gas based on the engine operation state.
Here, it is preferred to increase the gas flow rate as much as possible in order to let the blow-by gas within the crankcase flow promptly into the intake passage, for the purpose of preventing the oil accumulated in the crankcase from being deteriorated when the exhaust components and unburned fuel components of the blow-by gas leaking out of the combustion chamber are mixed into the oil. However, excessive increase of the gas flow rate results in increase of the amount of oil carried from the crankcase to the intake passage by the blow-by gas, which consequently increases the amount of deposit adhered to the intake passage due to this oil.
Therefore, the gas flow rate of the blow-by gas that is returned to the intake passage by the blow-by gas treatment apparatus is controlled on the basis of the engine operation state and set at an optimum value based on, for example, the two points described above. Specifically, the idea considered is to control the gas flow rate on the basis of the engine operation state to a value at which the progression degree of oil deterioration within the crankcase is kept at a standard level and at which the amount of deposit adhered to the intake passage by the blow-by gas carrying the oil to the intake passage is kept at an acceptable level.
Incidentally, even when the gas flow rate of the blow-by gas returned to the intake passage is controlled based on the engine operation state as described above, it is difficult to achieve, at high levels, suppression of the adhesion of the deposit to the intake passage caused by the blow-by gas carrying the oil to the intake passage, and suppression of the oil deterioration by treating the blow-by gas within the crankcase early. This is associated with the fact that the amount of oil carried into the intake passage by the blow-by gas is changed by how the driver of the vehicle operates the internal combustion engine and the individual difference of the internal combustion engine.
Specifically, in a case in which the amount of oil carried into the intake passage by the blow-by gas is greater than average, when the gas flow rate is controlled based on the engine operation state, although the progression degree of oil deterioration within the crankcase is kept at the standard level, the amount of deposit adhered to the intake passage by the blow-by gas carrying the oil to the intake passage exceeds the acceptable level.
On the other hand, in a case in which the amount of oil carried into the intake passage by the blow-by gas is lower than average, when the gas flow rate is controlled based on the engine operation state, the amount of deposit adhered to the intake passage by the blow-by gas carrying the oil to the intake passage considerably exceeds the acceptable level. In other words, the amount of deposit adhered to the intake passage can be kept at the acceptable level even when increasing the gas flow rate of the blow-by gas returned to the intake passage. Consequently, the progression degree of oil deterioration within the crankcase can be further kept lower than the standard level by increasing the gas flow rate. However, controlling the gas flow rate based on the engine operation state is not enough to realize the abovementioned increase of the gas flow rate, and thus the progression degree of oil deterioration within the crankcase cannot be further kept lower than the standard level.
As described above, controlling the gas flow rate based on the engine operation state does not take into consideration the fact that the amount of oil carried into the intake passage by the blow-by gas is changed by how the driver of the vehicle operates the internal combustion engine. For this reason, it is difficult to suppress the adhesion of the deposit to the intake passage and the oil deterioration within the crankcase at high levels.