Cylinder head

A cylinder head comprising:

• a cylinder head body fixed to an upper surface of a cylinder block;
• and
• a camshaft housing fixed to an upper surface of the cylinder head body, wherein
• a camshaft is accommodated in the camshaft housing,
• the camshaft housing includes
• two longitudinal frame bars, which extend in an axial direction of the camshaft, and
• a plurality of lateral frame bars, which extend between the longitudinal frame bars,
• a bearing portion is arranged in an upper surface of each of the lateral frame bars to rotationally support the camshaft,
• each of the bearing portions is a portion recessed from the upper surface of one of the lateral frame bars,
• a bolt hole is provided in each lateral frame bar to receive a bolt that is inserted through the bolt hole to fix the camshaft housing to the cylinder head body,
• each of the bolt holes extends through one of the lateral frame bars and is arranged on an outer side of the corresponding bearing portion in a longitudinal direction of the lateral frame bar,
• the longitudinal frame bars each have a plurality of joint points at which the longitudinal frame bar is joined to the corresponding lateral frame bar,
• each longitudinal frame bar includes, between adjacent two of the joint points, a vibration reducing portion, wherein a cross-sectional area of a cross section of the vibration reducing portion that is perpendicular to a longitudinal direction of the longitudinal frame bar gradually changes in the longitudinal direction of the longitudinal frame bar,
• the vibration reducing portion includes
• an outer upper surface,
• an arcuate inner upper surface extending from an inner edge of the outer upper surface in the longitudinal direction of the lateral frame bar,
• an inward-facing surface extending downward from a lower edge of the arcuate inner upper surface and facing inward in the longitudinal direction of the lateral frame bar,
• a lower surface extending from a lower edge of the inward-facing surface toward an outer side in the longitudinal direction of the lateral frame bar, and
• an outward-facing surface extending from an edge of the lower surface on the outer side in the longitudinal direction of the lateral frame bar,
• the arcuate inner upper surface becomes curved more downward toward a middle between the two adjacent joint points such that the lower edge of the arcuate inner upper surface at the middle between the two adjacent joint points is lower than at either of the two adjacent joint points, and
• the arcuate inner upper surface becomes more recessed more outward in the longitudinal direction of the lateral frame bar toward the middle between the two adjacent joint points such that the lower edge of the arcuate inner upper surface is closer to the outward-facing surface at the middle between the two adjacent joint points than at either of the two adjacent joint points.