Chain tensioner

1. A chain tensioner comprising:

a lever including a sliding contact surface, which is configured to come into sliding contact with a chain, and a boss portion; and

a torsion coil spring including a coil portion fitting into the boss portion, a fixed-side support arm extending from one end of the coil portion, and a lever-side support arm extending from the other end of the coil portion, wherein

the fixed-side support arm is configured to abut against a contact portion which is a fixed member and the lever-side support arm is configured to abut against a contact surface provided on the lever to apply a biasing force of the torsion coil spring to the lever for applying tension to the chain via the sliding contact surface,

the fixed-side support arm includes

a locking portion, and

a pressing portion,

the lever includes a spring housing portion configured to house the locking portion, and an engaging portion integrally formed with the level and configured to lock the locking portion housed in the spring housing portion in a state in which a biasing force is applied,

the fixed-side support arm is configured to move from a first position to a second position, the first position being a position where the locking portion is housed in the spring housing portion and is locked by the engaging portion, the second position being a position where the locking of the locking portion by the engaging portion is released and the locking portion is removed from the spring housing portion, and

the torsion coil spring is configured such that the fixed-side support arm moves in an unwinding direction of the torsion coil spring in response to a release of the locking of the locking portion by the engaging portion.

2. The chain tensioner according to claim 1 , wherein

the chain and the chain tensioner are housed in a chain case, and a releasing protrusion is provided on a case cover that covers an open portion of the chain case, and

when the chain case is covered with the case cover, the releasing protrusion presses the pressing portion to release the locking of the locking portion with the engaging portion.

3. The chain tensioner according to claim 1 , wherein the contact portion has a tapered surface, which has a downward gradient toward a side opposite to a pressing direction to the pressing portion, and a flat spring contact surface continuous with a lower end of the tapered surface.

4. The chain tensioner according to claim 1 , wherein

the locking portion is formed of a linear portion extending from the coil portion in a tangential manner,

the spring housing portion is formed of a recess portion that houses the linear portion, and

the pressing portion is bent from the locking portion and extends beyond the engaging portion to a side opposite to the spring housing portion.

5. The chain tensioner according to claim 1 , wherein

the locking portion is formed of a portion that is obtained by bending a tip end of an extension portion extending from the coil portion in a tangential manner and extends in an axial direction of the coil portion,

the spring housing portion is formed on a rising surface of a coupling portion that couples an arched portion having the sliding contact surface to the boss portion, and

the pressing portion is formed of a portion that is obtained by bending a tip end of the locking portion beyond the engaging portion and extends in a direction away from the coil portion.

6. The chain tensioner according to claim 4 , wherein the engaging portion is formed of a protruding portion that protrudes to cover a spring biasing side of the spring housing portion, and

the engaging portion is inclined such that a protruding amount of a side surface of the locking portion in a removal direction decreases in a direction from a tip end toward the coil portion.