Intake passage structure for turbocharger-equipped engine

An intake passage structure for a turbocharger-equipped engine, the intake passage structure comprising:

• a compressor of the turbocharger housed in a compressor case;
• an upstream intake passage supplying intake air into the compressor case;
• a downstream intake passage supplying the intake air supplied into the compressor case and supercharged by the compressor to an intake port of the engine;
• and
• a throttle valve disposed in the downstream intake passage, wherein
• a supercharging passage and an air relief passage are provided in the compressor case, the supercharging passage including the compressor and connecting the upstream intake passage and the downstream intake passage together, the air relief passage connecting an upstream portion of the supercharging passage upstream of the compressor and a downstream portion of the supercharging passage downstream of the compressor together without passing through the compressor, and returning a portion of the intake air supercharged by the compressor to the upstream portion of the supercharging passage upstream of the compressor,
• the air relief passage has a first passage and a second passage, each of which is in a non-linear shape,
• the first and second passages each have an air outflow port formed through an inner wall surface of the upstream portion of the supercharging passage upstream of the compressor, and
• the air outflow port of the first passage and the air outflow port of the second passage are formed through different portions of the inner wall surface in a circumferential direction of the inner wall surface so as to overlap with each other in a direction along a central axis of the upstream portion.