| CPC F02M 35/112 (2013.01) [F02M 35/10052 (2013.01); F02M 35/10308 (2013.01)] | 14 Claims |

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1. An intake manifold, comprising:
a surge tank, formed in an elongated tubular shape in a direction of a predetermined axis;
a plurality of branch pipes, extending from the surge tank; and
an upstream tubular part, continuous on an upstream side of the surge tank,
wherein the upstream tubular part comprises: an opening part, open at an upstream end of the upstream tubular part; and a flange part, formed around the opening part,
wherein the flange part comprises: an annular seal groove, formed at the flange part around the opening part; and a plurality of fastening parts, formed at the flange part around the annular seal groove to fasten a throttle unit, and
wherein a groove width of the annular seal groove is formed to decrease in a vicinity of the fastening part, the annular seal groove comprises a width-invariant region having a constant groove width and a width-gradually-variant region having a groove width that gradually and continuously varies so as to gradually decrease toward the fastening part and gradually increase away from the fastening part.
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