Unexamined Published Japanese Utility Model Application (Kokai) No. Hei 4-116233 and Unexamined Published Japanese Utility Model Application (Kokai) No. Hei 4-37025 disclose seat lifter mechanisms that include a pair of links that connect vehicle floor side members with seat lower arm members, an operating member provided with a spring coupler and held on the seat lower arm members, and torsion bars (or a coil spring) that urge the seat upwardly. The spring coupler controls the urging force of the torsion bars so that the seat is not lifted up by the links. When the control of the spring coupler is released, the urging force of the torsion bars is transmitted to the links and the seat is lifted up by the links against the weight of the seat and weight of the passenger.
However, in these known type of seat lifter devices, because the urging force of torsion bar (or coil spring) is directly applied to the links, the torsion bar (or coil spring) must possess a large capacity to compensate for the weight of the seat and the passenger. The torsion bar (or coil spring) is thus rather large in size and quite relatively heavy. The links are also rather large and heavy.
To improve and achieve better passenger safety and comfort, there is a tendency nowadays to increase the vehicle seat weight through the attachment of seatbelts and other parts. Therefore, the large capacity torsion bar (or coil spring) must be applied and so the size and weight of the parts increases.
In light of the foregoing, a need exists for a seat lifter device that is not susceptible to the same disadvantages and drawbacks as other known seat lifter devices.