Backrest height adjustment for office chair

In an office chair including a seat, a vertically extending support member having its lower end secured to said seat, and a backrest supported for vertical movement on the upper end portion of said support member, the combination therewith of improved means for adjusting the backrest vertically of said support member, said backrest adjusting means comprising

• a. a housing fixed on said backrest and supporting said backrest for vertical sliding movement on a medial portion of said support member,
• b. notch means extending vertically along a medial portion of said support member and including a vertical slot with spaced notches along opposite sides of said slot,
• c. a pawl pivotally supported on said housing and including a pair of ratchet fingers positioned below the pivot point and being engageable with said notches, said pawl being movable between an operative position with said ratchet fingers in engagement with said notches, and an inoperative position with said ratchet fingers out of engagement with said notches,
• d. an elongate tension spring attached at one end to said pawl and adjacent said ratchet fingers and at the other end to said housing and above the pivot point of said pawl, the longitudinal axis of said spring extending on one side of the pivot point of said pawl when said pawl is in said operative position to resiliently maintain said ratchet fingers in engagement with said notches, said spring extending on the opposite side of the pivot point of said pawl when said pawl is in said inoperative position to resiliently maintain said ratchet fingers out of engagement with said notches, and
• e. operator means at the upper and lower ends of said notches for engagement with said pawl, said operator means at said lower end of said notches being operable to move said pawl into said operative position and maintained in said operative position by said spring axis being positioned on one side of the pawl pivot point when said backrest and said pawl are moved to the lower end of said notches so that said backrest may be raised to the desired level and maintained in adjusted position by engagement of said ratchet fingers with said notches, said operator means at said upper end of said notch means being operable to move said pawl into said inoperative position and maintained in said inoperative position by said spring axis being positioned on the other side of the pawl pivot point when said backrest and said pawl have been moved to the upper end of said notches so that said backrest may be freely moved to its lowermost position in preparation for making a subsequent vertical adjustment of said backrest.

Vertical height adjustment means for adjusting the vertical position of a vertically adjustable member supported for vertical movement on the upper end portion of an upstanding support of a fixed base member, said vertical height adjustment means comprising

• a. a housing fixed on said vertically adjustable member, said housing surrounding and supported for vertical sliding movement on the upper portion of said upstanding support,
• b. notch means extending vertically along the upper portion of said upstanding support and including upper and lower ends, said notch means including a central vertical slot and vertically spaced notches along opposite sides of said vertical slot,
• c. a pawl pivotally supported on said housing and including ratchet finger means at one end thereof, said ratchet finger means including a pair of ratchet fingers, and an operating tongue positioned between and extending outwardly beyond said pair of ratchet fingers, said pawl being movable between an operative position with said pair of ratchet fingers in engagement with said vertically spaced notches, and an inoperative position with said pair of ratchet fingers out of engagement with said vertically spaced notches,
• d. over center spring means operatively associated with said pawl and being operative along a line of action to selectively maintain said ratchet finger means in said operative position with said ratchet finger means in resilient engagement with said notch means, or in said inoperative position with said ratchet finger means out of engagement with said notch means, the line of action of said over center spring means being positioned on one side of the pawl pivot point when in said operative position and being positioned on the other side of the pawl pivot point when in said inoperative position, and
• e. operator means associated with said upper and lower ends of said notch means for engagement with said pawl, said operator means at the lower end of said notch means being operable to move said pawl into said operative position when said vertically adjustable member and said pawl are moved to the lower end of said notch means so that said vertically adjustable member may be moved to the desired level and maintained in such adjusted position by engagement of said ratchet finger means with said notch means, said operator means at the upper end of said notch means being operable to move said pawl into said inoperative position when said vertically adjustable member and said pawl have been moved to the upper end of said notch means so that said vertically adjustable member may be freely moved to said upper end of said notch means in preparation for making a subsequent vertical adjustment of said vertically adjustable member.