Seat reclining device

1. A seat reclining device comprising:

a reclining unit that includes a fixing member which is fixed to a seat cushion side and a rotating member which is fixed to the seat cushion side and is supported by the fixing member to rotate freely, and that switches freely between a locked state which restricts rotation of the rotating member in relation to the fixing member and an unlocked state which allows the rotation;

a transmission lever which is supported by the fixing member to rotate freely on a same center as the fixing member;

a release operation lever which is supported on the seat cushion side to rotate freely between a lock operation position and an unlocking operation position;

a link which includes a protruding portion, in which each end portion of the link is supported by one of the transmission lever and the release operation lever to rotate freely, and which switches the reclining unit from the locked state to the unlocked state via the transmission lever in accordance with rotation of the release operation lever from the lock operation position to the unlocking operation position; and

a holding plate that includes an unlock holding portion which is joined to a seat back side to rotate integrally therewith, the unlock holding portion extends in a circumferential direction centered on an axial line of the rotating member, and the unlock holding portion includes a circumferential rim that has a surface extending in a radial direction,

wherein the circumferential rim slides relative to the protruding portion when the release operation lever is in the unlocking operation position due to a rotational position of a seat back in relation to the seat cushion reaching an unlock holding region.

2. The seat reclining device according to claim 1 ,

wherein the holding plate is directly fixed to the rotating member.

3. The seat reclining device according to claim 1 ,

wherein end portions of the release operation lever and the link are supported to rotate freely by

an engaging protruding portion which is provided to protrude from the release operation lever, and

an engaging recessed portion into which the engaging protruding portion which is formed on the link is inserted, and which allows movement of the engaging protruding portion to allow rotation of the release operation lever to the lock operation position when the engaging protruding portion is pressed such that the reclining unit switches to the unlocked state via the link and the transmission lever in accordance with rotation of the release operation lever to the unlocking operation position, and the reclining unit is in the unlocked state together with the link and the transmission lever.

4. The seat reclining device according to claim 1 ,

wherein the fixing member and the rotating member are fixed to a cushion side frame which is on the seat cushion side and a back side frame which is on the seat back side, respectively, and

wherein the holding plate is fixed to the rotating member at a side which is closer to the fixing member than the back side frame in a width direction of a seat.

5. The seat reclining device according to claim 4 ,

wherein the unlock holding portion is displaced in a direction of the cushion side frame in the width direction of the seat.

6. The seat reclining device according to claim 4 ,

wherein the link includes a folded portion which displaces the protruding portion in a direction of the cushion side frame in the width direction of the seat.

7. The seat reclining device according to claim 1 ,

wherein the holding plate includes a release stroke adjustment range in which a release stroke of the reclining unit gradually increases as the protruding portion is progressively pushed onto the unlock holding portion.