GB2213370A - Seat position adjustment mechanism - Google Patents

Description

1 -1 1 1 1C70 0 -MA SEAT POSITION ADJUSTMENT MECHANISM

Background of the Invention

Field of the Invention

The present invention pertains generally to the field of position adjustable vehicular seats and more particularly is directed to a mechanical seat support and position adjustment unit particularly for use with automotive adjustable seats.

State of the Prior Art

A great deal of effort has been expended in the development of mechanisms and devices which permit the adjustment of automotive seats, particularly the driver's seat, for optimum convenience, comfort and safety. Existing adjustment mechanisms include purely mechanical systems where the adjustment is achieved by means of spring loaded levers and locks, electrically powered mechanisms where threaded elements are displaced along motor driven screws, or a combination of these two. The purely mechanical systems are favored particularly at the lower end of economic scale because of their lower cost, ease of installation, and greater inherent reliability.

2 Consequently, many mechanical seat adjustment units have been developed and are in use.

Purely mechanical seat adjustment units rely on the body weight of the seat occupant to overcome an upward spring bias and thus obtain a desired shift in seat position. Upon release of a lock an adjustment in seat position occurs under spring urging to the extent allowed by the occupant, who is able to control the degree and direction of adjustment by shifting his or her body weight in relation to the adjustment mechanism.

Existing mechanical seat adjustment units suffer from certain shortcomings. One source of difficulty in spring biased mechanisms resides in the variable loading force offered by the helical springs typically employed for this purpose. A constant rate spring as is well known requires increasingly greater compressive force as the spring is compressed. Thus, as the seat is depressed from a fully raised position, the occupant encounters increasing resistance and near the fully depressed position corresponding to near full spring compression, the body weight of.a lightweight individual may be insufficient to further depress the seat because of the considerable spring force encountered. This difficulty is commonly overcome in many existing designs by providing an assist handle, i.e. a mechanical lever normally mounted on one side of the seat and operative for lowering the seat by adding leveraged 1 c 3 manual force to the occupant's weight thereby to achieve full spring compression. However, as automobiles tend to become ever more compact, it becomes increasingly difficult and impractical to provide the space required for the assist lever. On the inboard side of the forward seats a center console is frequently provided, while on the outer side of the seats there is little room between the seat and the door panel as the automobiles shrink in size. The assist lever also adds visual clutter to the vehicle interior design and 10 is undesirable for esthetic reasons as well.

For the foregoing reasons it has become desirable to provide a spring assisted seat position adjustment mechanism suitable for automotive use which is more responsive to adjustment by body weight and body movement alone without manual assist levers.

SUMMARY OF THE INVENTION

The present invention addresses the aforementioned needs by providing a seat adjustment mechanism having a base comprised of two parallel mounting rails for fastening to a seat mounting surface such as the floor board of an automotive passenger compartment, a pair of lower support beams longitudinally slidable along the mounting rails, and a pair of upper beams for supporting a seat fastened on the same. Two transverse, mutually parallel shafts are 4 journaled to and interconnect the lower beams in fixed spaced parallel relationship. Each shaft carries a rocker arm and a pair of axially spaced'apart lifter arms, which arms are fixed to and extend generally radially from the shafts. The upper beams have front ends pivotably connected on and supported between the radial outer ends of the two front shaft lifter arms, while the rear ends of the upper beams are similarly supported on the rear shaft lifter arms. Rotation of one shaft raises or lowers the corresponding end of both upper beams thereby tilting a seat supported thereon. A telescoping lock assembly is connected between the outer radial end of the rocker arm on each shaft and one of the lower beams. Each of the two lock elements is spring loaded by a constant rate spring towards a linearly extended condition so that expansion of the spring tends to rotate the shaft to which the particular rocker arm is connected, also rotating the lifter arms on the same shaft in a direction so as to elevate the ends of the upper beams supported on these lifter arms. The body weight of a seat occupant acts through the lifter arms and rocker arms to oppose thq spring loading and telescopically compress the locks. Either the front or the rear ends of the seat supporting beams may be selectively raised by releasing the appropriate lock and shifting the occupant's weight away from that end to allow the spring to extend the lock thereby lifting the corresponding end of the upper beams and tilting 1 1 the seat in the desired manner. Each lock is normally locked holding the two shafts against rotation to fix the seat in a particular position. Each lock is individually releasable through a cable release or the like and allows continuous independent adjustment of front and rear seat height within the design limits of the mechanism.

The mechanism of this invention improves over previous designs in that the geometry of the bell crank comprised of the lifter and rocker arms on each shaft is optimized in such a way that the mechanical advantage of the bell crank diminishes as the loading spring is compressed, i.e. as the loading spring force therefore increases. The net result is that the spring force actually transmitted through the rocker and lifter arms to the upper beams and ultimately upwardly to the seat remains approximately constant throughout the compression range of the spring.

In prior art designs it has been necessary to compromise in the choice of spring in order to allow relatively lightweight occupant to fully depress the and overcome the force of the spring even near full compression. This solution has required the use of a relatively weak spring such that a person weighing e.g. one hundred pounds could fully depress the seat. This, on the other hand, creates a problem for heavier weight occupants; e.g. an individual weighing a hundred and eighty pounds would find inadequate spring resistance upon release of the a seat 6 lock from an elevated seat position and would find the seat quickly dropping towards maximum depression.

This problem is overcome in the present invention which maintains an approximately even spring force throughout the . -.e adjustment range of the seat and thus allows a better compromise to be made in terms of increased spring loading force to provide more adequate seat support for heavier individuals while remaining manageable by lighter weight persons.

Still further improvement in responsiveness is achieved by arranging the rear bell cranks such that backward force applied against the seat back rest produces a force component which is added to the downward body weight force vector and thus assists in depressing the rear end of the seat adjustment mechanism. Specifically, the rear lifter arms extend from the rear transverse shaft in a generally rearward and upward direction when in maximally elevated position. Backward force against the seat back rest operates to pivot downwardly the rear lifting arms, turning the rear shaft which turns the rocker arm in the direction necessary to compress the rear loading spring and depress the rear end. A lightweight spat occupant may assist in lowering the rear of the seat by pushing back against the seat back rest. The trend towards more compact and low slung automobiles forces the driver and front passenger into an increasingly reclining position on the seats, with legs extended forward C si 7 E 1 so that it becomes easier to push back against the seat back rest than to shift one's body weight in order to apply a vertically downward force to depress the mechanism.

These and other features and advantages of this invention will be better understood from the detailed description of the preferred embodiment below considered with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a side elevational view of the seat adjustment mechanism according to this invention; Figure 2 is a top plan view of the mechanism of Figure 1 with middle portions of the transverse shafts broken away and omitted; Figure 3 is a front end view of one side of the mechanism taken along line 3-3 in Figure 2, Figure 4 is a rear end view of one side of the mechanism taken along line 4-4 in Figure 2; Figure 5 is a side view as in Figure 1 with the rear end of the mechanism in an elevated condition; Figure 6 is a side view as in Figure 1 with the front end of the mechanism in an elevated condition; Figure 7a is a vector diagram illustrating the forces acting on the rear end of the seat adjustment mechanism; 8 Figure 7b is a vector diagram illustrating the effect of force applied against the seat back rest to assist in overcoming the rear spring loading; and Figure 8 shows loading spring curves for a practical example of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the drawings, Figures 1 and 2 show the seat position adjustment mechanism 10 as having a pair of lower beams 12 slideable along mounting rails 14, and a pair of parallel upper seat supporting beams 16. The lowt--r beams 12 are interconnected in fixed spaced mutually parallel relationship by two transverse connecting shafts including rear shaft 42 and front shaft 52. The rear shaft 42 is rotatably supported by the upright legs of two rear Ubrackets 54, the bases of which are bolted to lower rails 12 by fasteners 56, or may in the alternative be welded or riveted to the same. The front transverse shaft 52 is pivoted to the upright legs 58a of front U-brackets 58, the bottoms of which are fastened to the corresponding lower beams 12. A pair of lifter arms is radially fixed to and rotatable with each of the shafts 52, 42.

A front bracket 26 and a rear bracket 28 are fixed to each upper beam 16. Each bracket is an inverted L with a horizontal leg fastened to the top surface of the upper beam 9 16 and a dependent vertical leg pivotably connected at pivot points 30 to the radial outer end of a corresponding lifter arm 22, 24. The front brackets 26 are supported on front lifter arms 22 while the rear brackets 28 are supported on rear lifter arms 24. The rear pivot points 30 are fixed on the bracket 28 while the forward pivot points 30 are linearly displaceable within a slot 32 in each bracket 26 in order to accommodate a linear displacement component of the upper beams upon rotation of the lifter arms.

Alternatively, the slot may provided at the rear pivot points for the same effect. Each shaft 42, 52 also carries a fixed radial rocker arm 40. A linear rear lock 34 is anchored at its housing end to the lower beam 12 at pivot 36 and is pivotably connected at at its opposite rod end 38 to the radially outer end of a rear rocker lever 40, the inner end of which is fixed to the rear transverse shaft 42. In the drawing, the rocker lever 40 and lifter lever 24 are shown as a unitary bell crank element but may instead be separate lever elements axially spaced along shaft 42. T linear lock element 34 includes a rod 44 axially slidable through a tubular lock housing 46, and a rear loading coil spring 48 is axially compressed between the lock housing 46 and retainer disk 50 fixed near the end of the rod 43, normally loading the lock 34 towards a telescopically extended position wherein the rod 43 is axially withdrawn from the housing 46. The lock 34 includes a mechanism he 1 internal to the lock housing 46 by which the rod 43 is normally locked to the housing 46 against axial translation relative thereto. The lock mechanism is remotely releasable through a flexible release cable (not shown) connected at its distal end to a remote release button or other actuator mounted to one side of the seat for convenient access by the seat occupant. A complete description of the construction and operation of the preferred linear lock mechanism 34 is found in commonly owned U.S. Patent 4,577,730 issued March 10 25, 1986, and the lock is available from the common assignee as product number MM65 LOXX. Figure 1 shows the rear end 20 of the mechanism 10 in fully depressed condition, the rear lock 34 in a telescopically contracted state, and rear loading spring 48 15 at maximum compression. When the rear lock 34 is remotely released from its normal locked condition, the rod 43 is urged towards a telescopically extended condition by helical coil spring 48, turning the rocker arm 40 and rotating rear shaft 42, thereby also turning the rear lifter arms 24 in a 20 counter-clockwise direction to lift the rear ends 28 of the upper beams 16 to the elevated position shown in Figure 5. The rear of the seat adjustment mechanism 10 may be returned to the depressed condition of Figure 1 by again releasing the rear lock 34, applying sufficient downward force to the 25 rear end 20 to compress and overcome the loading of rear spring 48 and thus linearly shorten the lock 34, and then

U 11 1 1 locking the device 34 in the contracted state to hold the mechanism 10 in the depressed state.

The front end of the seat adjustment device operates in a similar manner and includes a front lock 35 similar to the rear lock 34 with a lock housing 46 pivotably anchored to the same lower beam 12 at pivot point 60, as best understood by reference to Figures 2 and 3, and a lock rod 43 pivotably connected at 62 to the radially outer end of front rocker arm 40 which is radially affixed to the front transverse shaft 52. Telescopic extension of the front lock 35 under the urging of front loading spring 44 causes counterclockwise rotation of the transverse shaft 52 in Figure 1, turning the front lifter arms 22. Counter-clockwise rotation of the lifter arms 22 raises the front ends 18 of the upper beams 16 towards an elevated position shown in Figure 6. The front ends 18 can be returned to the depressed position of Figure 1 by releasing the front lock 35, applying sufficient downward force to overcome and compress front loading spring 44 and turn front shaft 43 and front lifter arms 22 clockwise, thereby telescopically shortening the front lock 35, and finally reengaging the front lock 35 to secure the mechanism in the new position.

It will be appreciated that the height adjustment of the front ends 18 and rear ends 20 of the upper beams 16 is independent of each other and is achieved by selectively releasing the corresponding locks 34, 35 by individually 12 actuatable remote releases. As a result of these independent height adjustments, a seat bolted to the upper beams 16 can be tilted up and down in the front and rear, and by combining the front and rear adjustments in a rocking motion the seat can also be raised or lowered without significantly affecting its tilt.

The loading springs 44, 48 are helical coil springs having a constant spring rate, and therefore offer linearly increasing resistance as each is compressed during depression of the corresponding end of the seat support mechanism 10. The front and rear lifter arms in the fully elevated position extend upwardly and rearwardly of the corresponding transverse shaft 52, 42. The body weight of the seat occupant applies a downward force to the ends of the lifter arms at pivot points 30 tending to rotate the shafts clockwise together with the corresponding rocker arms 40. This tendency is normally resisted by the locked condition of the front and rear locks 35, 34 which hold the mechanism 10 and the seat supported thereon in a selected position.

The downward body weight force vector F1 acts through first arm M1 presented by the lifter arms 22, 24, and is transmitted to the linear lock/spring assembly through a second arm M2 presented by the rocker arm 40 as indicated in Figures 5 and 6. Figure 7a graphically shows the force vector diagram, from which it can be seen that the net force 13 1 P3 transmitted by the ratio of arms Ml/M2 to the lock rods against spring loading force F3 is a function of the instantaneous angles a between arm M1 and vertical vector F1, and b between arm M2 and the lock rod (which is also substantially the axis of the loading spring).

The net axially compressive force F2 applied to the loading spring and opposing the spring loading force F3 is F2 = F1 M1 cos a M2 cos b The spring loading force F3 is is F3 = dL R where dL is the stroke length of the loading spring being compressed and R the spring rate characteristic of the loading spring.

The minimum force F1 required to compress the loading spring and thus depress the rear end of the seat adjustment mechanism 10 is given by F1(min) dL R M2 cos b M1 cos a The quotient in the above expression increases in nearly li-near fashion within certain ranges of angles a and h, for example, where a is between 45 and 0 degrees and b +/- 45 degrees.

The front and rear loading coils 44, 48 are wound to have a constant spring rate which approximates the negative of the "average" slope of the F2 function within the given 14 range, and a spring force in the extended state equal to the downward force which it is to oppose. The increasing spring force F3 as the loading spring is compressed during depression of the mechanism 10 is thus approximately offset by the increasing mechanical advantage of the Ml/M2 bell crank arrangement,-such that an approximately constant downward force of magnitude greater than W (min) will fully depress the mechanism. Viewed from the spring end, the bell crank net leverage diminishes as the shaft rotates towards the depressed condition, reducing the spring loading force transmitted to the seat by the lifter arms as the actual force exerted by the spring on the rocker arm increases, the two trends approximately offsetting each other to maintain a roughly constant upward force on the seat ends at all positions of the mechanism 10. Typically, the the seat requires greater spring loading as it greater portion of the occupant's body weight.

rear end of supports the Figure 8 illustrates theoretical spring curves calculated for the seat adjustment mechanism 10 for both the front and rear ends of the seat adjustment mechanism, and where the rear loading spring 48 is selected to oppose a weight of 100 pounds and the front loading spring 44 a downward weight of 30 pounds. To these theoretical curves are fitted possible i.e. practically realizable spring curves, and the loading springs 48, 44 are wound to match these possible spring curves.

R 4.

In previously known mechanisms the increase in spring force during compression resulted in a compromise in the selection of the loading spring: if a lighter weight individual was to overcome the maximum spring force necessary to fully depress the seat, the spring force at maximum seat elevation had to be reduced resulting in inadequate support for heavier individuals who tended-to drop with the seat upon release of the rear lock 34. By optimizing the geometry of the rocker angles C & D and lifter arms as here described it therefore becomes possible to use a heavier loading spring 48 than was previously practical, and thus provide better support for heavier individuals when the rear lock 34 is released, without thereby making it impossible for lighter weight persons to depress the seat adjustment mechanism 10. The same optimized geometry can be implemented with similarly improved results at the front end of the mechanism 10 to obtain substantially even spring force opposing the occupant's weight throughout the front adjustment range of the mechanism.

An additional novel feature of the improved seat adjustment mechanism 10 lies in the arrangement of the rear lifter arms such that the seat occupant can assist in depressing the rear end 20 by pushing backwards against the seat back rest which is easily achieved in a vehicle by leaning back in the seat and pushing with the feet against the floorboard or firewall of the passenger compartment.

16 1 Considerable backward force can be be applied in this manner by even a lightweight person, the effect of which is a tendency to pivot the seat about.the front pivot points 30 and to depress the rear end 20 of the mechanism 10. Figure 7b shows a force vector diagram illustrating a vector F4 applied to the seat back rest which in automobiles is typically at a 25 degree angle _q (gamma) to the vertical resulting in a downward force component F5 acting on the end of the rear lifter arms 24 represented as arm M1 in Figure 7b. Vector F5 is added to force vector F1 in figure 7a, i.e., the weight of the seat occupant to thus increase the force F2 opposing the spring loading F3 and facilitate compression of the rear spring 48. The possibility of providing such an assist is made possible by orienting the rear lifter arms upwardly and rearwardly from the rear shaft 42 so that the assist force is added to the weight vector and both vectors cooperate in turning the rear rocker arm 40 against the spring loading. Such additive effect is not possible if, for example, the rear bell crank is reversed so that the lifter arms extend upwardly and forwardly from the rear shafts 42 and the bell crank turns counter-clockwise from elevated to depressed position in the views of Figures 5 and 6. It must be appreciated that this latter arrangement would be fully operative for depressing the rear end 20 in response to occupant weight, but would not respond to the aforedescribed assist force applied against the back rest.

1k 4 17 1 Nevertheless, such a reversed rear bell crank arrangement will benefit from the optimized geometry described in connection with Figure 7a so as to obtain a nearly constant effective spring force transmitted to the rear end 20, and this optimization of the arm geometry is an improvement independent of the rearward orientation of the rear lifter arm and clockwise rotation of the rear rocker 40 during seat depression so as to add an active boost or assist force provided by the seat occupant to the occupant's weight. The useful application of the occupant provided assist further enhances the ability of a lightweight individual to overcome the loading of the rear spring 48 and therefore permits the use of still heavier loading springs which better compensate the weight of heavier persons without significant inconvenience to the lighter individuals.

The mechanism 10 will normally be provided with a suitable detent or lock for adjustably locking the lower beams 12 to the mounting rails 14, so as to permit adjustment of the seat position forward or backward along the mounting rails, for adjusting for example the spacing between a vehicle seat and the steering wheel. A variety of detent mechanisms suitable for this purpose are known and need not be described here.

The preferred embodiment is described by way of example only for purposes of clarity, and many changes, substitutions and modifications to the described embodiment 18 1 will occur to those possessed of ordinary skill in the art without thereby departing from the spirit and scope of the invention, which is limited only by the following claims.

z 4 119 v 1

Claims (1)

1 1. A six-way seat adjustment mechanism comprising:

a base; lower support means linearly slidable on said base; upper support means having a front end and a rear end; first axially telescopable lock means operatively connected between said front end and said lower support, said first lock means remotely releasable for adjusting the elevation of said front end relative to said base; second axially telescopable lock means operatively connected between said rear end and said lower support, said second lock means remotely releasable for adjusting the elevation of said rear end relative to said base; and third lock means operatively connected between said first means and said base, said third lock means releasable for slidingly repositioning said lower and upper support means relative to said base; whereby a seat on said upper support means may be adjusted in elevation, tilt and horizontal front-to-rear position relative to said base.

1 2. The device of claim 1 wherein each of said lock means is spring loaded by constant rate spring means towards an extended position, and further comprising lever means between said lock means and at least said rear end, said lever means being configured to transmit an approximately constant spring force to said upper support means throughout the compression range of said spring means.

1 3. The device of claim 2 wherein said lever means are pivoted to said lower support at a pivot point, said lever means including first and second arms extending at an angle to each other radially from said pivot point, said first arm being operatively connected to said second lock means, said second arm being connected to said rear end and arranged such that the combined net mechanical advantage of said first and second arms through their range of movement offsets the linearly increasing spring force as said spring is compressed such that said second arm transmits an approximately constant spring force to said rear end.

1 4. The device of claim 3 wherein said second arm extends rearwardly and upwardly from said pivot point in an elevated position of said rear end and pivots downwardly in response to rearward force applied to the back rest of a seat supported on said upper support means, whereby said rearward.force is at least partially added to the weight of a seat occupant to facilitate depressing the rear end of said upper support means while said second lock means is in a released condition.

z 1 1 21 5. The mechanism of claim 2 wherein each said lock means includes a rod fixed at one end to one of said base or lower support means, the other end of said rod being axially displaceable through a lock housing, said spring means being compressed between said rod and said housing, said lock housing being attached to the other of said base or lower support means, and remotely releasable means normally locking said rod against said axial displacement thereby to fix the position of said base relative to both said lower and upper support means.

6. The mechanism of claim 1 further comprising lever means connected between each of said first and second lock means for translating independent telescoping movement of said first and second lock means into changes in elevation between each of said front and rear ends respectively and said base.

7. The mechanism of claim 1 wherein said lower support means comprises two parallel rails connected by two parallel transverse shafts journaled to said rails; rocker arm means and lifter arm means affixed to each of said shafts; each of said first and second locks being connected between said rocker arm means on a corresponding one of said shafts and said lower support means; 22 said upper support means being supported between said shafts on said lifter arm means; whereby telescopic extension or contraction of said first or second lock means is translated rotation of a corresponding shaft into elevation or depression of a corresponding end of said upper support means.

8. A six-way seat adjustment mechanism comprising: a pair of parallel rails for fastening to a seat mounting surface; a pair of lower beams longitudinally slidable along said rails; a pair of parallel shafts perpendicular to and interconnecting said lower beams, said shafts being journaled for rotation to said lower beams; a rocker arm and a pair of axially spaced apart lifter arms extending radially from each said shaft; a telescopable element connected between an outer end of each said rocker arm and one of said lower beams; and seat bearing means supported between outer ends of said lifter arms; whereby telescopic extension or retraction of each of said telescopable elements raises or lowers respectively one end of said bearing means to tilt a seat supported thereon.

1 23 1 1 1 9. The mechanism of claim 8 further comprising releaseable lock means connected between at least one of said lower beams and one of said rails for selectively longitudinally positioning said lower beams and said seat bearing means along said mounting rails.

10. The mechanism of claim 8 wherein said telescopable elements are loaded towards an extended position by constant rate spring means, said rocker arm and said lifter arms on each said shafts being dimensioned and arranged for transmitting an approximately constant spring force to the corresponding ends of said seat bearing means throughout the compression range of said spring means.

11. The mechanism of claim 10 wherein said rocker arm on said rear shaft is oriented such that rearward force applied against the back rest of a seat supported on said seat bearing means cooperates with the weight of a seat occupant in overcoming said spring loading for depressing said rear end.

12. The mechanism of claim 11 wherein said rear rocker arm is oriented rearwardly and upwardly from rear shaft in a raised condition of said rear end.

24 13. The mechanism of claim 12 wherein said lifter arms on said rear shaft are oriented in a rearward and downward direction in said raised condition of the rear end.

11 1 14. A seat adjustment mechanism comprising: lower support means adapted to be secured to a mounting surface; upper support means adapted to carry a seat and having a front end and a rear end; axially telescopable lock means operatively connected between said rear end and said lower support means, said lock means remotely releasable for adjusting the elevation of said rear end relative to said lower support means; and constant rate spring means spring loading said lock means towards an extended position, and further comprising lever means between said lock means and said rear end, said lever means being configured to transmit an approximately constant spring force to said rear end throughout the 15 compression range of said spring means.

1 15. The mechanism of claim 14 wherein said lever means are further arranged and configured such that rearward force applied against the back rest of a seat supported on said upper support means cooperates with the weight of a seat occupant in overcoming said spring loading for depressing said rear end.

R -25 1 1 16. The device of claim 14 wherein said lever means are pivoted to said lower support means at a pivot point, said lever means including first and second arms extending at an angle to each other radially from said pivot point, said first arm being operatively connected to said lock means, said second arm being connected to said rear end and arranged such that the combined net mechanical advantage of said first and second arms changes between elevated and depressed positions of said rear end to offset the linearly increasing spring force as said spring is compressed such that said second arm transmits an approximately constant spring force to said rear end.

17. The mechanism of claim 14 wherein said second arm extends rearwardly and upwardly from said pivot point in an elevated position of said rear end and pivots downwardly in response to rearward force applied to the back rest of a seat supported on said upper support means, whereby said rearward force is at least partially added to the weight of a seat occupant to facilitate depressing the rear end of said upper support means while said lock means is in a released condition.

26 1 18. A seat adjustment mechanism comprising: lower support means adapted to be secured to a mounting surface; upper support means having a front end and a rear end and adapted to carry a seat secured thereon; lock means operatively connected between said rear end and said lower support means, said lock means remotely releasable for adjusting said rear end between an elevated and a depressed position relative to said lower support means; and constant rate spring means spring loading said lock means towards said elevated position, and further comprising lever means between said lock means and said rear end, said lever means being configured and arranged such that the combined net mechanical advantage of said lever means changes continuously between said elevated and depressed positions to compensate for the linearly increasing spring force as said spring is compressed and thereby transmit an approximately constant spring force to said rear end.

1 19. The mechanism of claim 17 wherein said lever means are further arranged and configured such that rearward force applied against the back rest of a seat supported on said upper support means cooperates with the weight of a seat occupant in overcoming said approximately constant spring force for depressing said rear end.

I.

20. A seat adjustment mechanism substantially as hereinbefore described with reference to the accompanying drawings.

Published 1959 at The Patent Office, Swee House. 66 71 High Holborn, London WC IR 4TP F'urther copies mkv be obtaiLned from The patent O:Mce Sales Branch, St Mary Cray, Orpington. Kent BRS 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con- 1187