Turbocharger with variable nozzle mechanism

The present invention relates to a turbocharger having a turbine housing accommodating a turbine wheel rotated by receiving exhaust gas blown onto the turbine wheel from an internal combustion engine and a variable nozzle mechanism.

Japanese Laid-Open Patent Publication No. 2006-125588 discloses a turbocharger having a variable nozzle mechanism. The variable nozzle mechanism regulates the flow rate of the exhaust gas blown onto a turbine wheel accommodated in a turbine housing through selective opening and closing of a plurality of nozzle vanes arranged in a gas passage. The variable nozzle mechanism includes a nozzle ring and a nozzle vane drive mechanism. The nozzle vane drive mechanism includes a rotatable unison ring and a plurality of arms, which pivot when the unison ring rotates. Specifically, when the arms pivot as the unison ring rotates, the nozzle vanes, which are connected to the arms, pivot. A support ring is provided between the nozzle ring and the unison ring. The support ring is secured to the nozzle ring, and the unison ring is pressed against the support ring by an annular stopper member secured to the support ring.

If the variable nozzle mechanism thermally expands and interferes with the turbine housing after the engine has been started, the variable nozzle mechanism may deform and hamper proper operation of the nozzle vanes. However, the variable nozzle mechanism is supported by the turbine housing through the support ring. This structure prevents the variable nozzle mechanism from interfering with the turbine housing despite thermal expansion of the variable nozzle mechanism, which occurs after starting of the engine.

In the turbocharger of the above publication, exhaust gas enters an accommodating chamber that accommodates the nozzle vane drive mechanism. Thus, immediately after the engine is started, moisture contained in the exhaust gas may condense and the water may be retained on the bottom of the accommodating chamber. Unless the engine is stopped immediately after starting of the engine, the water on the bottom evaporates through heating of the exhaust gas. However, if the engine is stopped under a low temperature immediately after the engine has been started, the water may be frozen. This hinders the nozzle vane drive mechanism from operating. Thus, if the engine is re-started in this state, the nozzle vane drive mechanism may be damaged.

Accordingly, it is an objective of the present invention to provide a turbocharger having a variable nozzle mechanism that prevents a nozzle vane drive mechanism from being damaged by frozen water.

To achieve the foregoing objective and in accordance with one aspect of the present invention, a turbocharger including a variable nozzle mechanism accommodated in an accommodating chamber is provided. The turbocharger has a turbine wheel rotated by receiving an exhaust gas blown from an internal combustion engine against the turbine wheel and a turbine housing accommodating the turbine wheel. The variable nozzle mechanism includes a nozzle ring defining a gas passage through which the exhaust gas is guided to the turbine wheel, a nozzle vane supported by the nozzle ring to vary a flow area of the gas passage, a nozzle vane drive mechanism that drives the nozzle vane, and a support ring connected to the nozzle ring. The nozzle vane drive mechanism is accommodated in the accommodating chamber while being spaced from the nozzle ring by the support ring. The turbocharger includes a drain passage extending through a lower portion of the support ring and reaching the gas passage. The drain passage is located downward from the nozzle vane drive mechanism.

Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.