Energy absorbing device, seat belt retractor and seat belt apparatus

1. An energy absorbing device disposed between two relatively rotating objects, the rotating objects being referred to as one object and the other object, comprising:

a casing connected to one object;

a first clutch disc of an annular shape disposed to be reciprocatable in a rotation axis direction in the casing;

a second clutch disc of an annular shape disposed inside the first clutch disc to be reciprocatable in the rotation axis direction in the casing; and

a clutch plate of an annular shape connected to the other object and having an engaging surface that faces both the first clutch disc and the second clutch disc, wherein

the clutch plate has engaging teeth with ridges and grooves arranged in a circumferential direction of the engaging surface,

the first clutch disc has engaging outer teeth on a surface which faces the engaging surface so as to be engageable with the engaging teeth,

the second clutch disc has engaging inner teeth on a surface which faces the engaging surface so as to be engageable with the engaging teeth, and

the engaging outer teeth and the engaging inner teeth alternately engage with the engaging teeth so as to absorb an energy generated by relative rotation between one object and the other object.

2. The energy absorbing device according to claim 1 , further comprising a plurality of oscillation members arranged in a circumferential direction to be able to oscillate inwardly and outwardly in a radial direction between the first clutch disc, the second clutch disc, and the casing so that the oscillation members swing to alternately reciprocate the first clutch disc and the second clutch disc in the rotation axis direction.

3. The energy absorbing device according to claim 2 , wherein the casing includes a plurality of partition members that partition disposed positions of the oscillation members.

4. The energy absorbing device according to claim 3 , wherein each of the plurality of partition members includes a projection that partitions a disposed position of the first clutch disc and a disposed position of the second clutch disc.

5. The energy absorbing device according to claim 4 , wherein the first clutch disc includes a locking section that protrudes inward in a radial direction and is disposed between the partition members, and the second clutch disc includes a locking sections that protrudes outward in a radial direction and is disposed between the partition members.

6. The energy absorbing device according to claim 1 , wherein the clutch plate is disposed in the casing to be rotatable relatively to the casing, and the casing includes a cover plate that regulates movement of the clutch plate in the rotation axis direction.

7. A seat belt retractor comprising:

a spool that retracts a webbing that restrains an occupant; and

a base frame that rotatably holds the spool, wherein

an energy absorbing device is disposed between the base frame or a component fixed to the base frame and the spool, and the energy absorbing device is the energy absorbing device according to claim 1 .

8. A seat belt apparatus comprising:

a webbing that restrains an occupant to a seat;

a seat belt retractor that retracts the webbing;

a belt anchor that fixes the webbing to a vehicle body;

a buckle provided on a side face of the seat; and

a tongue disposed on the webbing, wherein

the seat belt retractor is the seat belt retractor according to claim 7 .