Timing chain drive system

A timing chain drive system comprising a driving sprocket, a driven sprocket, and a timing chain in mesh with both sprockets and having a span traveling from the driven sprocket to the driving sprocket, said span being in tension and transmitting rotation from the driving sprocket to the driven sprocket at a predetermined speed ratio so that the rotations of the driving and driven sprockets are synchronized in a predetermined relationship;

• wherein the speed of said driving sprocket fluctuates cyclically;
• wherein at least one of said sprockets has sprocket teeth the pitch of which cyclically increases and decreases over the circumference thereof;
• wherein the timing chain disengages from the driven sprocket at a disengagement point, and engages with the driving sprocket at an engagement point;
• wherein, if the pitch of the teeth of the driven sprocket increases and decreases cyclically, the pitch at the disengagement point is smallest when the rotational speed of the driving sprocket is maximum;
• and
• wherein, if the pitch of the teeth of the driving sprocket increases and decreases cyclically, the pitch at the engagement point is greatest when the rotational speed of the driving sprocket is maximum;
• whereby the influence of the cyclic fluctuations in the speed of the driving sprocket on tension in said span of the timing chain is reduced.