Patent ID: 8047175

Claim:
An in-line four-cylinder engine for a vehicle including a crankshaft having first crank pins of two cylinders, wherein the first crank pins are provided on a common first virtual plane and are arranged with a 180° phase difference, and having second crank pins of another two cylinders, wherein the second crank pins are provided on a second virtual plane different by a 90° phase from the first virtual plane and are arranged with a 180° phase difference, the in-line four-cylinder engine comprising: a crankshaft satisfying a formula of (k L −0.25)(0.25−k R )≅D R /D L , wherein, when a crank web for each of at least two cylinders is divided between a pair of half crank webs facing a crank pin, wherein k L , k R denote balance ratios of the both half crank webs (wherein k L ≠0.25, k R ≠0.25) and D L , D R denote distances from the center in a longitudinal direction of the crankshaft to the respective half crank webs, the crank webs for the four cylinders of the engine are set so that a track of a vector of a primary inertial couple is formed into a substantially circular shape; and a primary balancer for generating a couple vector offsetting a vector of the first inertia couple.