The present disclosure herein relates to a chain tensioner, and more particularly, to a chain tensioner that adjusts tensile force of a chain by using coil springs. 
A timing drive system of a vehicle includes a belt drive system and a chain drive system.  Since the chain system has durability greater than that of the belt system, the chain drive system is mainly used for the timing drive system of the vehicle. 
The timing chain of the chain drive system may connect a crank sprocket connected to a crank shaft and cam sprockets, which are respectively connected to cam shafts, to each other.  Thus, the timing chain may transmit driving force of the crank shaft to the cam shafts.  However, a predetermined portion of the timing chain may be released when the timing chain is driven by the driving force of the crank shaft.  Thus, the chain drive system may include a chain tensioner that adjusts tensile force of the timing chain.  In general, a hydraulic tensioner that receives an oil pressure to adjust the tensile force of the timing chain by using pushing force of a piston.  However, studies on a chain tensioner that adjusts the tensile force of the timing chain by using other force, but not the oil pressure are ongoing.