A chair back assembly includes a back shell member including laterally extending top, bottom and side portions cooperating to define an open space therebetween, where a portion of the back shell member is located in a lumbar region, a cover having a first surface and a second surface opposite the first surface, wherein the cover covers at least a portion of the open space, and a back frame assembly operably supporting the back shell member and movable between upright and reclined positions, wherein the back frame assembly causes the back shell to flex in a fore-to-aft direction as the back frame assembly is moved between the upright and reclined positions independent of an external force being exerted on the back shell member, and where the lumbar portion of the back shell member remains spaced from the back frame as the back frame is moved between the upright and reclined positions.

Disclosed is an underframe with an improved structure. The underframe includes an underframe body, an operating handle, a reclining pull rope and a gas spring pull rope, a cushion back-and-forth moving mechanism being installed on the outer side of the underframe body, the operating handle being installed through a left outer wall of the underframe body at a lower end of the cushion back-and-forth moving mechanism, a backrest installed on a rear end of the underframe body through a backrest connecting rod; and a reclining elastic adjusting mechanism is arranged at a front end of an inner wall of the underframe body, a backrest angle adjusting mechanism is arranged at the inner wall of the underframe body on a right side of the reclining elastic adjusting mechanism, a cushion height adjusting mechanism is fixedly connected in the underframe body.

A chair according to the present invention has a reference position P located midway in a front-back direction in a movable range of a seat 2. The chair includes a return force generation mechanism 4 configured to generate a return force in a direction to return the seat 2 moved from the reference position P at least in the front-back direction to the reference position P. The return force generation mechanism 4 includes an elastic member 40 configured to increase the return force in the direction to return the seat to the reference position P as the amount of movement of the seat from the reference position P increases.

The invention relates to a chair which functions by means of a deflection that is mutually synchronous between a backrest (9) and a seat (25) over a range between a respective zero position of back inclination (R.sub.0) and of seat inclination (S.sub.0) and a respective maximum back inclination (R.sub.max) and maximum seat inclination (S.sub.max). The mechanism (2) that causes synchronous deflection has a spring unit (6) arranged therein. The base support (50) of a carrier unit (5) is rigidly fastened to the underframe (1), which is intended to be set on the floor. A stationary first axis of rotation (D1) and a stationary second axis of rotation (D2) extend through the base support (50). A back carrier (91) is articulated on the first axis of rotation (D1). A third axis of rotation (D3), which moves around the first axis of rotation (D1) when the mechanism (2) is adjusted, extends through the back carrier (91). A base plate (3) lies movably on the base support (50) at the front of the base plate and is articulated on the third axis of rotation (D3) at the rear of the base plate. The base support (50) is designed in the shape of a U, having a center part (54) and two arms (53) extending upward from the center part, which arms each have a shaped piece (55) protruding upward, which shaped pieces each engage in an associated opening (34) in the base plate (3). When the mechanism (2) is deflected, a relative displacement between the stationary shaped pieces (55) and the openings (34) arises. The two openings (34) are oriented in the direction of the seat depth (T) and thus at right angles to the transversely extending axes of rotation (D1, D2, D3).

Some embodiments relate to a chair including a base, a hub, and a seat frame. The hub is supported by the base and includes first and second side mounts and first and second covers. The first side mount is positioned on a first side of the chair and includes a back portion and a bottom portion. The first cover is coupled to the first side mount to define a first channel with the first side mount. The seat frame includes a first lateral member having a lower portion and an upper portion that is pivotally coupled to the back portion of the first side mount and is configured to angulate relative to the lower portion. The lower portion of the first lateral member is slidably received in the first channel such that two sides and a bottom of the lower portion received within the first channel are substantially hidden.

A chair includes a leg 1, a seat 5 including a pressure receiving surface PS, a backrest 6, and a support mechanism SM. The seat 5 can move in the front-rear or left-right direction along a predetermined trajectory and to downwardly incline a tip side of the seat 5 in a movement direction in accordance with a movement of the seat 5 from a predetermined reference position (S). The support mechanism SM includes a return-force generation unit configured to generate, in accordance with an amount of movement, a return force in a direction in which the seat 5 moved from the reference position (S) in the front-rear or left-right direction is returned to the reference position (S), and movably supports the backrest 6 in the left-right direction together with a movement of the seat 5 in the left-right direction.

A tilt mechanism for a chair comprises a base, a first support configured to support a chair seat and mounted to the base, a second support configured to support a chair back and pivotably coupled to the base about the first pivot axis, a link element pivotably coupled to the second support about a second pivot axis, and a shaft attached to the first support. A first guide slot is provided at the base and a second guide slot is provided at the link element. The shaft is supported in the first guide slot and the second guide slot.

A tilt mechanism for a chair comprises a base, a first support configured to support a chair seat and mounted to the base, a second support configured to support a chair back and pivotably coupled to the base about the first pivot axis, a link element pivotably coupled to the second support about a second pivot axis, and a shaft attached to the first support. A first guide slot is provided at the base and a second guide slot is provided at the link element. The shaft is supported in the first guide slot and the second guide slot.

A body support assembly includes a seat assembly and backrest assembly supported by a tilt control assembly. Methods of using and assembling the body support assembly are provided.

A tilt locking device for a chair, comprising a housing configured for connection to one of a seat and a frame; a first rotatable locking member, rotatable about a first axis and biased in a first direction about the first axis, the first rotatable locking member is configured for interlocking with a notch member; a rotatable activation member, rotatable about a second axis, the rotatable activation member is configured to abut and rotate the first rotatable locking member in a second direction opposite the first direction into interlocking with the notch member.