Seat lifter device

1. A seat lifter device comprising:

a seat support member;

a front link including first and second ends, the first end being rotationally coupled to a front section of the seat support member;

a rear link including first and second ends, the first end being rotationally coupled to a rear section of the seat support member;

a frame member including a front section rotationally coupled to the second end of the front link and a rear section rotationally coupled to the second end of the rear link at a position rearward of the coupling portion between the seat support member and the rear link, wherein a seat back is supported at a rear end portion of the frame member;

a cushion member including part of a seat cushion, the cushion member including a front section rotationally coupled to the frame member and a rear section rotationally coupled to the rear link at a position further separated from the coupling portion between the seat support member and the rear link than the coupling portion between the rear link and the frame member; and

a rotation transmitting member for rotating one of the front link and the rear link.

2. The seat lifter device according to claim 1 , wherein

the rear link is one of a pair of rear links facing each other in a seat widthwise direction,

the seat lifter device further comprises a beam member, the beam member including a pair of shaft portions, which are secured to the rear links and provide the coupling portions between the rear links and the frame member, and an eccentric portion, which has an axis displaced from the axis of the shaft portions and extends between the shaft portions, and

the rear section of the cushion member is rotationally coupled to the rear links via the eccentric portion.

3. The seat lifter device according to claim 1 , wherein

the rear link is one of a pair of rear links facing each other in a seat widthwise direction,

the seat lifter device further comprises a beam member, which extends in the seat widthwise direction and is secured to the rear links, the beam member having an axis that extends through a pair of coupling portions between the rear section of the cushion member and the rear links, and

the rear section of the cushion member is rotationally coupled to the rear links via the beam member.

4. The seat lifter device according to claim 2 , wherein the cushion member includes:

a cushion pan rotationally coupled to the frame member, the cushion pan forming the front section of the cushion member; and

a spring member forming the rear section of the cushion member, the spring member including a front end portion engaged with the cushion pan and a rear end portion rotationally engaged with the beam member.

5. The seat lifter device according to claim 3 , wherein the cushion member is a cushion pan, and the rear section of the cushion pan is rotationally coupled to the beam member.

6. The seat lifter device according to claim 1 , further comprising a tilt mechanism that vertically moves the front section of the cushion member with respect to the rear section of the cushion member, wherein the front section of the cushion member is coupled to the frame member via the tilt mechanism.