This invention relates to a headrest of the kind which is movable relative to the backrest of a seat on which it is mounted.
With headrests of the above kind, movement usually varies the elevation of the headrest relative to the backrest, but it is also known to have a facility for fore and aft adjustment of the headrest position. It will be convenient to hereinafter describe the invention by reference to an adjustable headrest mounted on a vehicle seat, but it is to be understood that the invention has wider application and can by applied to seats of all kinds.
It is known to provide vehicle seats with headrests which are capable of adjustment so that the elevation of the headrest is varied. It is also known to provide headrests with a fore and aft adjustment facility. In some cases headrests are arranged to be adjustable both in relation to elevation and fore and aft disposition. Furthermore, it is known to provide such headrests with drive systems through which adjustment of the headrest position is effected.
In U.S. Pat. No. 4,830,434, a drive system is used for adjusting the headrest elevation, but not the fore the aft position. In the arrangements disclosed by U.S. Pat. Nos. 5,052,754 and 5,222,784, a drive system is provided for both types of adjustment. The drive system disclosed by each of the three U.S. patents is relatively complicated.
Vehicle manufacturers typically offer customers a choice of options concerning seating arrangements, including headrest adjustment. Options relating to the headrest may include manual adjustment, power adjustment, two-way adjustment (fore and aft, or up and down), four-way adjustment (both fore and aft, and up and down) and position memory. Given the varying requirements of those options it is generally not possible to offer all options without substantial variation in cost. By way of example, different options may require different seat backrest constructions or different headrest mounting systems.
The present invention seeks to provide a headrest which is capable of four-way adjustment and which is amendable to relatively simple construction. At least in preferred forms, the invention seeks to utilise a modular system such that principal components of the headrest can be utilised in a headrest capable of two-way (height only) adjustment.
An adjustable headrest according to one aspect of the invention includes a frame structure which can be secured on a mounting system for up and down movement relative to an associated seat backrest, and which includes a height adjuster section and a fore/aft adjuster section. The height adjuster section is secured on the mounting system for relative up and down movement of the frame structure. The fore/aft adjuster section is engaged with the height adjuster section for relative movement providing fore/aft adjustment. The headrest has drive means which includes two drive systems which control height adjustment and fore/aft adjustment respectively. The fore/aft drive system includes an adjustment member which is constrained substantially to up and down movement and which is engaged with the fore/aft adjuster section so as to permit fore/aft movement of the fore/aft adjuster section relative to the height adjuster section and the adjustment nut.
Thus, according to the invention, there is provided an adjustable headrest, for a seat backrest having an associated mounting system, wherein the headrest includes a frame structure adapted to be secured on the mounting system for up and down movement relative to the seat backrest, the frame structure including a height adjuster section and a fore/aft adjuster section; the fore/aft adjuster section is engaged with the height adjuster section for relative movement providing fore/aft adjustment; wherein the headrest further includes drive means which has a height adjustment drive system for controlling height adjustment of the headrest by moving the height adjuster section and fore/aft adjustment drive system for controlling fore/aft adjustment of the headrest by moving the fore/aft adjuster section; and wherein the fore/aft drive system has an adjustment member or nut which is constrained substantially to up and down movement and which is engaged with the fore/aft adjuster section so as to permit fore/aft movement of the fore/aft adjuster section relative to the height adjuster section and the adjustment nut.
The fore/aft adjuster section may be engaged with the height adjuster section by first engagement means which precludes relative movement therebetween in a direction for height adjustment, but which enables relative movement therebetween in a direction for fore/aft adjustment. The first engagement means may comprise at least one projection, rib or fin on one of the sections which is located in a slot which is defined by the other section and which extends in the fore/aft direction. The adjustment member or nut may be engaged with the fore/aft adjuster section by engagement means which constrains relative movement therebetween to movement along a direction which is inclined with respect to directions for both height and fore/aft adjustment to provide thereby fore/aft adjustment due to relative movement between the height and fore/aft adjuster sections being precluded in a direction for height adjustment. The second engagement means may be similar to the first engagement, but with the or each slot extending in the inclined direction. In each of the engagement means, the or each slot may be a groove, channel or the like, or a spacing between projections, ribs or fins defined by the component having the or each slot.
In one arrangement, the height adjuster of the frame structure is engaged with the fore/aft adjuster by having at least one projecting portion, such as a tab or the like, which engages in or with an elongate slot or track which is defined by the fore/aft adjuster and which extends in the fore/aft direction, i.e. in the direction required for the fore/aft adjustment. Similarly the adjustment nut is engaged with the fore/aft adjuster by having at least one projecting portion, such as a tab or the like, which engages in or with an elongate slot or track defined by the fore/aft adjuster and which extends in the fore/aft direction but is inclined at an angle to the slot or track engaged by the height adjuster. For engagement of one or each of the height adjuster and the adjustment nut with the fore/aft adjuster, a complementary method of this engagement can be used, but this can tend to limit the extent of fore/aft movement or provide a less compact arrangement. Thus, the height adjuster may define at least one track or slot in or with which a projecting portion of the fore/aft adjuster engages, while the adjustment nut may define at least one track or slot in or with which a projecting portion of the fore/aft adjuster engages.
In one embodiment, the drive system for fore/aft adjustment is an electrically powered drive means operable to raise and lower the adjustment nut, that is, to move it in the direction for height adjustment, relative to the height adjuster of the frame structure. Preferably the drive means includes an electric motor and a rotatable screw-threaded spindle drivingly connected to the motor, such as through a worm drive. The motor and spindle may be secured on the height adjuster, with the spindle co-operatively engaging a screw-threaded bore defined by or secured to the adjustment nut. The spindle is disposed in the direction of height adjustment such that, with rotation of the spindle by the drive motor, the adjustment nut is caused to travel along the spindle. Because of the respective engagement between the fore/aft adjuster of the frame structure and each of the height adjuster and the adjustment nut, the travel of the adjustment nut causes the fore/aft adjuster to move in the fore/aft direction, relative to the height adjuster, to provide fore/aft adjustment of the headrest.
The drive system for height adjustment may be as disclosed in PCT/AU97/00325. Thus, the drive system may include an electrically powered drive means operable to raise and lower the height adjuster of the frame structure, and hence the headrest, relative to the mounting system. Preferably the drive means includes an electric motor and a rotatable screw-threaded spindle drivingly connected to the motor, such as through a worm drive. The motor and spindle may be secured on or in relation to one of the height adjuster and the mounting system, while the spindle may co-operatively engage a screw-threaded nut defined by or secured on or in relation to the other one of the height adjuster and the mounting system.
The arrangement for fore/aft adjustment for the headrest of the invention differs from known arrangements, in particular those known arrangements using a tilting or nodding action. The arrangement of the invention enables fore/aft adjustment which is more effective for a greater height range for users. Moreover, throughout that range, the headrest can be maintained in a constant orientation, as the fore/aft adjustment can be and most preferably is substantially linear. For this, the or each groove or track by which the height adjuster of the core structure engages the fore/aft adjuster most preferably is substantially linear, with the groove or track most preferably substantially perpendicular to the direction of height adjustment.
As indicated, the or each groove or track by which the adjustment member engages the fore/aft adjuster of the frame structure is inclined with respect to the or each groove or track by which the height adjuster engages the fore/aft adjuster. The inclination may be such that the grooves or tracks converge in the forward direction, such that as the adjustment nut is raised or lowered, the headrest is adjusted respectively in the forward or rearward direction. The angle at which the grooves or tracks converge may, for example, be from about 20xc2x0 to 40xc2x0, and determines the magnitude of fore/aft adjustment per unit length variation in the height of the adjustment nut.
In one embodiment the headrest is adapted for use with a mounting system including a post, or each of two laterally spaced posts, secured to the seat backrest and projecting beyond the upper edge of the backrest. For ease of description, the more usual arrangement of two laterally spaced posts is assumed in the following. The headrest frame structure may be mounted on both of the posts for relative sliding movement thereon in the axial direction of the posts. A cross member may extend between and be secured to the upper end portion of each of the posts, in which case the drive system for controlling height adjustment of the headrest may extend between that cross member and the height adjuster of the frame structure.
A power headrest according to the invention can be provided with a memorised position facility, and/or with a rapid-drop facility. Also, at least one support post of a powered headrest can form or include part of the electrical circuit through which the or each drive system is controlled. Still further, the or each post can form part of two or more individual circuits including (for example), the elevation circuit control, an upper memorised position circuit, and a lower memorised position circuit and/or corresponding fore/aft position circuits.