Chain transmission device for driving camshaft

A chain transmission device for driving a camshaft, comprising:

• a driving sprocket mounted to a crankshaft;
• a driven sprocket mounted to a camshaft;
• a timing chain looped over the driving sprocket and the driven sprocket;
• a pivotable chain guide provided on one side of a slack side of the timing chain, and retaining a plurality of rotatable rollers for guiding movements of the timing chains so as to be spaced from each other in a direction in which the timing chain is moved;
• and
• a chain tensioner for applying an adjustment force to a remote end of the chain guide remote from a center of pivoting movement of the chain guide, thereby pressing the rollers against the timing chain,
• wherein the driving sprocket and the rollers are designed such that
• a ratio (D1/D2) between a pitch circle diameter D1 of the driving sprocket and an outer diameter D2 of the rollers is within a range of 5/3 to 5/1.