1. Field of the Invention
The present invention relates to an air intake apparatus of a vehicle, which guides fluid accumulated in a portion of a surge tank into a cylinder of an internal combustion engine.
2. Description of Related Art
In the following description, a top-to-bottom direction refers to a top-to-bottom direction (vertical direction) upon installation of the vehicle air intake apparatus in a vehicle placed on a horizontal plane without tilting. Also, an upper side and an lower side refers to an upper side and a lower side in the vertical direction upon the installation of the vehicle air intake apparatus in the vehicle placed on the horizontal plane without tilting.
A previously known vehicle air intake apparatus has a surge tank, which is formed by enlarging a passage cross-sectional area of an intake passage, which conducts air to cylinders of the engine.
In a case where an exhaust gas recirculation (EGR) apparatus is provided to recirculate a portion of exhaust gas, which flows in an exhaust passage, into the intake passage as EGR gas, due to presence of high content of water and/or oil in the EGR gas, the water and/or oil may condense as condensed fluid (more specifically liquid) in the surge tank of the vehicle air intake apparatus upon volume expansion of the air, which contains the EGR gas. The condensed fluid of water and/or oil may be guided to the lower portion of the surge tank by the gravitational force.
In a case where a lower edge of a connection between the surge tank and a corresponding one of intake branches (an intake passage that guides the air from the surge tank to the corresponding cylinder) is located on an upper side of a lower portion (bottom portion) of the surge tank, the condensed fluid of water and/or oil may be accumulated in the lower portion of the surge tank. Therefore, this condensed fluid, which is accumulated in the lower portion of the surge tank, cannot be guide to the cylinder of the engine.
Furthermore, there is also known another type of vehicle air intake apparatus, which has an intercooler placed in the intake passage that guides the condensed fluid, which is accumulated in the portion of the intake passage, into the cylinder of the engine.
The intercooler cools the air, which is drawn into the intake passage. When the air, which is drawn into the intake passage, is cooled, water and/or oil contained in the drawn air may condense as condensed fluid (more specifically liquid) and may be accumulated in the lower portion of the intercooler.
Japanese Unexamined Patent Publication No. 2005-226476A teaches a technique of guiding the condensed fluid of water and/or oil, which is accumulated in the lower portion of the intercooler, into the cylinder of the engine.
This technique is provided for a case where the intercooler is placed on the upstream side of a throttle valve in the flow direction of the air in the intake passage. The lower portion of the intercooler is connected to a portion of the intake passage (the portion being depressurized via the throttle valve during the time of running the engine) through a drain conduit while bypassing the throttle valve. The condensed fluid of water and/or oil is guided into the cylinder of the engine by using a pressure difference (differential pressure) between the upstream side of the throttle valve and the downstream side of the throttle valve (the pressure of the air on the upstream side of the throttle valve>the pressure of the air on the downstream side of the throttle valve).
As discussed above, the technique of Japanese Unexamined Patent Publication No. 2005-226476A uses the pressure difference (differential pressure) between the upstream side of the throttle valve and the downstream side of the throttle valve. Therefore, in the case where the surge tank is placed on the upstream side of the throttle valve, it is possible to use the pressure difference (differential pressure) between the upstream side of the throttle valve and the downstream side of the throttle valve. However, in another case where the surge tank is placed on the downstream side of the throttle valve in the intake passage, one portion of the intake passage, which is located on the downstream side of the throttle valve, is connected to another portion of the intake passage, which is located on the downstream side of the throttle valve, through the drain conduit. Therefore, in such a case, the pressure difference (differential pressure) between the upstream side of the throttle valve and the downstream side of the throttle valve cannot be used, so that the condensed fluid of water and/or oil accumulated in the lower portion of the surge tank cannot be guided into the cylinder of the engine.
Furthermore, in the technique of Japanese Unexamined Patent Publication No. 2005-226476A, the drain conduit is provided to guide the air into the cylinder of the engine while bypassing the throttle valve. Therefore, it is not possible to accurately control the quantity of the air drawn into the cylinder of the engine in the idling time of the engine, during which the throttle valve is fully closed.