Vehicle Seat Having Resilient Suspension And Constant Acting Damping Means

Abstract

A vehicle seat of the resiliently suspended type for use with earth working or agricultural implements or the like and wherein the seat itself is mounted on a parallel arm linkage arrangement and can be vertically adjusted to different heights. The seat furthermore has an air spring or the like for resiliently suspended the seat for a cushioning effect, which cushioning means can be locked out to provide a solid ride. In addition the seat has a damping means for providing a selectable stiffness or softness of the ride. This damping means is so constructed and arranged that it acts with essentially constant force on the seat regardless of the type of ride selected so that a constant force is applied by the damping means regardless of the vertical position to which the seat bounces or swings. Means are also provided for easily adjusting the vertical position of the seat so as to accommodate operators of different size.

Description

BACKGROUND OF THE INVENTION

The invention pertains to vehicle seat assemblies having a cushioned seat which is resiliently suspended for providing a comfortable ride for the operator. An air spring or the like provides the resilient suspension for the seat, and an example of this general type of parallel arm seat suspension is shown in U.S. Pat. No. 3,215,386 which issued on Nov. 2, 1965 and is entitled "Pneumatic Seat Support". The U.S. Pat. No. 3,150,855 to Carter et al which issued Sept. 29, 1964, entitled "Resilient Suspension for Vehicle Seat", also discloses a parallel arm linkage arrangement for insuring that the seat maintains a constant attitude to the vehicle regardless of its vertical position, and in addition, a shock absorber or damper is provided to damp the spring action of the air cylinder and thus retard excessive bouncing of the seat when operating in rough terrain.

Another example of a prior art device of this general type is shown in the U.S. Pat. No. 3,558,094 which issued on Jan. 26, 1971 to Radke and entitled "Vehicle Seat having Optimum Angular Motion Characteristics".

SUMMARY OF THE INVENTION

The present invention provides a resiliently suspended vehicle seat for earth working or agricultural vehicles or the like and which seat has cushioning means, for example such as an air spring. In addition the seat assembly provided by the present invention includes damping means which are so constructed and arranged so that it can be easily adjusted to provide different degrees of hardness or softness to the operator's ride, and which damping means also acts with essentially constant force on the seat regardless of the selected vertical position to which it has been moved and regardless of the vertical position of the seat when swinging or bouncing as in use in rough terrain. The constantly acting damping means provides a particularly comfortable ride and one which will not have hard bottoming or hard topping or a reduction in damping at the top.

The invention also provides the seat assembly of the above type having means for easily locking out the resilient means whereby the seat is locked in a "solid" ride position and essentially at the midpoint of its otherwise vertically swinging movement.

Another aspect of the invention provides a seat assembly of the above type having means for readily adjusting the vertical position of the seat initially so as to accommodate operators of different sizes.

Furthermore the present invention provides a seat of the above type having a cushioned seat that is pivoted at its front edge to thereby maintain the front edge of the seat at a constant point and thereby maintains the operator's feet a constant distance relative to the ground. Furthermore, the seat assembly provided by the present invention has optimum seat back rotation about the "H" point of the human body to thereby minimize vertical back scrubbing and undesirable fore and aft movement.

These and other objects and advantages will appear hereinafter as this disclosure progresses, reference being had to the accompany drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a left side elevational view showing a vehicle seat made in accordance with the present invention and showing certain hidden parts in dotted lines, the seat being in the vertically lower position;

FIG. 2 is a side elevational view of certain parts shown in FIG. 1, namely the seat support and the limit stop rod associated with the seat support, and also showing the tie rod lock-out means;

FIG. 3 is a side elevational view of other parts shown in FIG. 1, namely the damper and its connecting link to the seat, which will allow adjusting the softness of the ride;

FIG. 4 is a transverse, sectional view taken along line 4--4 in FIG. 1, certain parts being shown as broken away or removed for the sake of clarity;

FIG. 5 is a transverse, sectional view taken along line 5--5 in FIG. 4, certain sections being shown as broken away or removed for the sake of clarity;

FIG. 6 is a partial, front elevational view of the seat shown in FIG. 1 and showing certain hidden parts in dotted lines;

FIG. 7 is a side elevational view taken generally along the line 7--7 in FIG. 6, certain parts being shown as broken away or removed for the sake of clarity;

FIG. 8 is a transverse sectional view taken generally along the line 8--8 in FIG. 7 and showing the damper adjustment means and also the seat lock-out means;

FIG. 9 is a left side elevational view of a portion of FIG. 6 and is similar to the showing of FIG. 7, except that certain parts have been broken away or removed to show more clearly the damper adjusting means by means of which the softness of the seat ride can be varied;

FIG. 9a is a view somewhat similar to FIG. 9, but showing the damper adjustment means when shifted to a position in which the softest ride is obtained;

FIG. 10 is a perspective view of the cam shown in FIG. 9;

FIG. 11 is a perspective view of the seat and taken generally from the right rear upper side of the seat, certain parts being shown as broken away or removed for the sake of clarity, and other parts shown as removed from its associated part;

FIG. 12 is a fragmentary, perspective view of the seat, the view being taken from the left rear upper portion of the seat, certain parts being shown as broken away or removed for the sake of clarity;

FIG. 13 is a perspective view of the seat, the view being taken generally from the lower front left side of the seat and showing the seat when shifted to the upper position;

FIG. 14 is a left elevational view of a portion of the seat and showing the air cylinder for cushioning the seat;

FIG. 15 is a rear view and taken generally along the line 15--15 in FIG. 14 .

DESCRIPTION OF A PREFERRED EMBODIMENT

Carriage and Parallel Arm Linkage Adjustment

A vertically shiftable seat carriage is swingably mounted by parallel arm linkage so that it can rise and fall at a constant attitude. Adjustment means are also provided for fixedly adjusting the carriage in any one of a selected number of vertical positions. The adjustment can be readily made by a handle located at the forward portion of the carriage and within easy reach of the operator.

The seat assembly includes a base in the form of two cast base sections 1 and 2 which are spaced apart from one another and extend generally upwardly. These base sections have apertures 3 in their flange foot portion by means of which they can be bolted or otherwise secured to the vehicle body (not shown). A seat carriage 5 is fabricated from heavy sheet steel and is of generally U-shaped configuration having a front wall 6, a right side wall 7 and a left side wall 8. Side walls 7 and 8 extend rearwardly of the front wall and are in general parallelism with one another. The carriage is vertically and adjustably mounted on the base for vertically positioning the seat S connected thereto, and this mounting is by means of two pairs of parallel arms, one pair located on each side. One pair of arms 10 and 11 on the left side are connected to the base by shafts 12 and 13, respectively, and are then pivotally connected at their upper ends of the side wall 8 of the carriage by means of the bolt means 14 and 15, respectively, which extend through holes 14a and 15a in the side wall 8 of the carriage. The other pair of arms 20 and 21 on the right hand side of the seat are connected to the base by shaft 22 and 23, respectively and are then pivotally connected at their upper ends to the right side 7 of the carriage by the bolt means 24 and 25 which extend through holes 24a and 25a in the carriage wall 7.

The arms 10, 11 and 20, 21 form a parallel linkage connection between the base and the carriage so that the seat is maintained at a constant attitude relative to the vehicle, regardless of the vertical position thereof.

Means are provided for manually adjusting the vertical position of the carriage 5 relative to the base and this includes a pair of adjustment plates 26 and 27, one pivotally mounted on each side of the carriage 5 on their respective bolt means 14 and 24. The front end of the adjustment plates 26 and 27 are rigidly connected together by means of the handle 30 which is welded to the front ends of the adjustment plates and extends thereacross. The adjustment plates have a series of notches 31, 32, 33 and 34 along their rearward sides and these notches are adapted to receive fixed means in the form of the extending portions of shafts 13 and 23 which, as previously mentioned, also form the pivot connection between some of the parallel arms and the bases. In this manner, the operator, by swinging the forwardly extending portion 30a of the handle 30, can cause the adjustment plates to pivot about their bolt means 14 and 24, and thereby change the particular notch in which the shafts 13 and 23 are located. For example, as shown in FIG. 1, the shafts 13 and 23 are located in the rearmost notch 31, placing the seat in the lowermost position. The other extreme seat position is shown in FIGS. 11 and 12 wherein the shafts 13 and 23 are located in the forwardmost notches 34 of the adjustment plates, and this places the carriage and seat in the uppermost position.

The carriage 5 also has a centrally located, channel shaped bracket 35 (FIG. 15) welded to the inside of its front wall 6, and a pair of upwardly extending lugs 36 are in turn welded to and extend upwardly from the bracket 35, a tube 37 is welded to and between lugs 36 and forms a mounting for a pivot bolt 39 on which a sheet steel fabricated seat pivot plate 40 is pivoted. The seat S is thus pivoted on the pivot bolt 39 to the upwardly extending lugs 36 of the upper carriage 5.

The carriage also has a mounting base 41 welded or otherwise fixed thereto, as between the channel brackets 35. This base 41 forms a mounting for the lower end of an air cylinder unit AC (FIG. 1, 14 and 15) to be described.

The seat assembly SA is constructed and mounted on the upper carriage 5 as follows. A metal sheet base 50, for supporting the seat cushion 50a, has a pair of seat supports 51 and 52 which are located on opposite sides and complement one another. These supports each have a lower portion 51a and 52a between which is secured a retainer 53 for the upper end of the previously mentioned air cylinder unit AC. The supports 51 and 52 also each have an upwardly extending portion 51b and 52b, respectively, to which the seat back 57 is pivoted, as at 55. The lower end of the seat back 57 is also pivotally connected at each side to the rear ends of a pair of seat links 58 and 59. (FIGS. 1, 6, 11, 12 and 13) which in turn are pivotally mounted, adjacent their front ends to the carriage by bolt means 15 and 25, respectively. The large seat links 58 and 59 are rigidly secured together adjacent their rear ends by the cross brace 60 welded therebetween. The rear ends of seat links 58 and 59 are pivotally connected by short links 61 and 62 to a tubular member 63 extending between and connected to the lower ends 57a of the seat back 57.

Thus the seat supports 51 and 52 freely support the seat S on their horizontal surfaces 51c and the seat back 57 is pivoted to the upper ends of the seat supports at the "H" point of the operator. The seat links 58, 59 are pivotally connected at their front ends to the carriage and at their other ends to the seat back by means of the linkage connection 61, thereby causing the seat back to oscillate about the point of pivotal connection between the seat supports 51, 52 and the seat back 57.

In this manner, as the seat rises and falls, the back 57 is maintained at a constant attitude and at the proper position for comfort of the operator, more specifically, the seat back 57 pivots about its "H" point 55. This provides optimum back rotation of the back seat portion about the "H" point of the human body to thereby minimize excess back scrub and unwanted fore and aft movement.

The air cylinder unit AC is of itself conventional in character and may be of the type manufactured by Goodyear Rubber Co. and commonly referred to as an "air spring", and having a tubular rubber sleeve 65 (FIGS. 14 and 15) which rolls over a piston 66. This "air spring" acts between the seat S and the carriage 5 to form a resilient cushion for the seat.

Adjustable Damper Means

Means will now be described for adjusting the effectiveness of a seat damper D so that the character of the ride may be varied, that is to say, the degree of softness or hardness of the ride may be selected.

In any of the selected positions, the damper acts with constant force, in resisting downward and upward seat movement, regardless of the vertical position to which the seat swings. That is to say, the damping effect of the damper is substantially constant regardless of whether the seat is at the top or bottom of its bouncing or swinging movement.

The damper means includes a damper D which is of conventional character and may be of the fluid type shock absorber having a valve which meters the flow of fluid from one of its ends to the other.

The action of the damper may be selectively adjusted to provide the desired degree of softness of the ride, as follows.

The damper D is pivotally mounted at its lower end to the lower end of carriage 5 by bracket 42, and has a pivotal connection at its upper end, by a pin 69, with an intervening, channel shaped link 70 (FIG. 9), which in turn is pivoted at its other end to the seat plate 40. Thus the damper is pivotally connected to the seat through the link 70.

Means are provided for shifting the pivotal connection 69 as follows. A sliding link 72 is also pivotally connected at one end to the pin 69 and the other end of link 72 is pivotally connected on a stub shaft 73 which extends through a slot 49 in carriage wall 7. A nut 74 is threaded on the outer end of the shaft 73 and holds the shaft captive in the slot 49.

The shaft can be locked in any one of a number of positions along the slot 49, thereby changing the link of force through which the damper D acts on against movement of the seat. This locking is accomplished by an arm 75 fixed on and connecting the shaft 73 to the damper adjusting handle 48 which in turn is held captive in any one of a number of the notches 43, 44, 45, 46, or 47 in the carriage wall 7.

When the handle 48 is in the notch 46 (FIGS. 9 and 11) the line of force of the damper D is indicated by line F, which acts through the moment arm MA in respect to the point of seat pivot 39. This is the "hardest" seat adjustment position, in other words, where the firmest ride is provided by the damper D.

When the handle 48 is shifted to the foremost notch 43, the line of force through which the damper acts is indicated by F1 in FIG. 9a, acting through moment arm MA1. In this position, a softest ride is obtained because the vector product of F1 and MA1 is less than the vector product of F and MA. In other words, the line of action of the damper in the FIG. 9 position is a greater perpendicular distance from point 39 than when the damper is in the FIG. 9a, position.

However, regardless of the position to which the damper has been adjusted for any one adjustment, the damper acts with constant effectiveness against seat movement because the slide link 72 swings about an arc described by the dotted line A' in FIG. 9, and more particularly, the point of pivotal connection of the damper D to the arm 72 moves in this arc A' which practically maintains the line of force of the damper a constant distance from 39 throughout the vertical swinging movement of the tractor seat S.

In regard to the maximum amount of swinging or vertical movement of the tractor seat, this is determined by the lower stop LS (FIG. 2) and the upper stop US which are formed on the seat support members 51 and 52, and which stops abut against the limit stop rod 76 secured rigidly to and between the walls 7 and 8 of the carriage.

Seat Lock-Out Means

Lock-out means are provided for locking the seat in a "solid" or non-cushion position during operation in particularly rough conditions. This means acts to lock the seat in its approximate midpoint of travel in a vertical direction. The lock-out position is engaged with the same handle 48 which is used to adjust the effectiveness of the damper D. When the handle 48 is located in the deepest and most rearward notch 47 (FIGS. 7 and 11), the seat is in the locked position.

More specifically, a cam 77 (FIGS. 9, 10 and 12) is secured, as by welding, to the inner end of shaft 73 and is engagable with a pin 78 (FIGS. 8, 9 and 11) fixed intermediate the length of a lock-out link 79. The link 79 is journalled at its lower end on the bolt means 25; a similar link 79a (FIG. 11) is journalled on the other side on shaft 15. The links 79 and 79a are connected together by a U-shaped tie rod 80, whereby they swing in unison. When the operator shifts handle 48 into the rear notch 47, this movement causes similar rearward shifting of the associated sliding link 72, which carries with it the shaft 73 and its cam 77. As a result, the cam 77 abuts against pin 78 on link 79, swinging link 79 rearwardly, shifting the tie rod portions 80a and 80b into lock-out recesses 82 (FIGS. 1 and 2) in the rigid seat supports 51 and 52. In this position the seat is locked against movement.

RESUME

By means of the present invention, a seat assembly has been provided wherein the action of the damping means can be readily varied to provide different degrees of hardness or softness to the ride regardless of the type of ride selected. This damping means acts with essentially constant force in its damping action on the seat and regardless of the vertical position to which the seat bounces or swings during operation. Furthermore, the resilient means can be readily locked out of operation with some handle used to adjust the softness or hardness of the ride, and this locked out position occurs generally at the vertical midpoint through which the seat would otherwise swing.

In addition, the seat assembly of the present invention provides a readily adjustable means to adjust the vertical height of the seat for operators of different size, and this adjustment is effected by a simple swinging action of the conveniently located lever.

The seat assembly provided by the present invention also provides a non-linear suspension type seat wherein the operator's knees are maintained at a constant position regardless of the seat adjustment selected. Furthermore, the seat back rotates about the "H" point of the human body to thereby eliminate undesirable fore and aft movement of the back or undesirable back scrubbing on the operator in a vertical direction.

Claims

We claim:

1. A resiliently suspended vehicle seat for vehicles and comprising; a vertically shiftable carriage, means for swingably mounting said carriage in a vertical direction, a seat having a pivotal mounting adjacent its forward end to said carriage, damper means pivotally connected between said carriage and said seat and including a damper and a link having a pivotal connection with said damper, means for adjustably shifting said pivotal connection whereby the effective moment arm of said damper in respect to said seat pivotal mounting can be varied, said means for shifting said pivotal connection also being shiftably and swingably mounted on said carriage whereby said pivotal connection swings in a generally flat arc which is generally coincident with the line of force of said damper as said tractor seat rises and falls, whereby the damper has a substantially constant damping effect on said seat regardless of the vertical swinging movement of said seat.

2. The seat set forth in claim 1 wherein said means for shifting said pivotal connection includes a shiftable link having a handle attached thereto, and a series of recesses in said carriage into which said handle can be selectively positioned.

3. The seat set forth in claim 1 further characterized in that said means for shifting said pivotal connection has a cam connected therewith and a lock-out means shiftably mounted on said carriage for shifting to a position locking said seat in a fixed position, said cam being engagable with said lock out means so as to cause shifting thereof to said position when said handle is moved to a predetermined position.

4. The seat set forth in claim 2 further characterized in that said means for shifting said pivotal connection has a cam connected therewith and a lock-out means shiftably mounted on said carriage for shifting to a position locking said seat in a fixed position, said cam being engagable with said lock out means so as to cause shifting thereof to said position when said means for shifting said pivotal connection is moved to a predetermined position.

5. A vertically adjustable vehicle seat assembly comprising a mounting base member, a vertically shiftable carriage, parallel arm linkage between said base member and said carriage for vertically positioning said carriage in any one of a number of selected vertical positions; a pair of adjustment plates pivotally mounted to said carriage, one on each side of said carriage; a series of recesses in said adjustment plates, fixed means on said base member and engagable in any of said recesses when said carriage is shifted to different vertical positions, and handle means connected with said adjustment plates for swinging the latter whereby any one of said recesses in said adjustment plates may be engaged by said fixed means carried on said base member, whereby said carriage may be selectively held in any one of a number of positions to which it is vertically shifted by said parallel arm linkage.

6. The seat assembly set forth in claim 5 further characterized in that said carriage comprises a generally U-shaped member having two side portions and a bight portion connected therebetween, said handle means located across the bight portion, and said pair of adjustment plates are pivotally mounted to said carriage adjacent the bight portion, said adjustment plates extending rearwardly alongside said side portions and having said recesses adjacent the rear ends of said adjustment plates.

7. The seat assembly set forth in claim 5 including a seat pivotally connected adjacent its forward end to a forward portion of said carriage.

8. The seat assembly set forth in claim 6 including a seat pivotally connected adjacent its forward end to a forward portion of said carriage.

9. A vertically adjustable vehicle seat assembly comprising a mounting base member, a vertically shiftable carriage, parallel arm linkage between said base member and said carriage for vertically positioning said carriage in any one of a number of selected vertical positions; a seat having a pivotal mounting adjacent its forward end to said carriage, damper means pivotally connected between said carriage and said seat and including a damper and a link having a pivotal connection with said damper, means for adjustably shifting said pivotal connection whereby the effective moment arm of said damper in respect to said seat pivotal mounting can be varied, said means for shifting said pivotal connection also being shiftably and swingably mounted on said carriage so that said pivotal connection swings in a generally flat arc which is generally coincident with the line of force of said damper as said tractor seat rises and falls, whereby the damper has a substantially constant damping effect on downward movement of said seat; a pair of adjustment plates pivotally mounted to said carriage, one on each side of said carriage; a series of recesses in said adjustment plates, fixed means on said base member and engagable in any one of said recesses when said carriage is shifted to different vertical positions, and handle means connected with said adjustment plates for swinging the latter whereby any one of said recesses in said adjustment plates may be engaged by said fixed means carried on said base member, whereby said carriage may be selectively held in any one of a number of positions to which it is vertically shifted by said parallel arm linkage.

10. The seat assembly set forth in claim 9 further characterized in that said carriage comprises a generally U-shaped member having two side portions and a bight portion connection therebetween, said handle means located across the bight portion, and said pair of adjustment plates are pivotally mounted to said carriage adjacent the bight portion, said adjustment plates extending rearwardly alongside said side portions and having said recesses adjacent the rear ends of said adjustment plates.

11. A resiliently suspended vehicle seat assembly comprising; a support base, a vertically shiftable carriage, parallel arm linkage means pivotally connected between said base and said carriage for swingably moving said carriage at a constant attitude in a vertical direction, a seat having a pivotal mounting adjacent its forward end to said carriage for vertical swinging relative thereto, a pair of seat supports on which said seat freely rests, resilient cushioning means between said carriage and said seat supports for cushioning the downward vertical swinging of said seat and supports, a seat back pivotally mounted to said seat supports, a pair of seat links pivotally connected at one end to said carriage and at their other end having a link connection with said seat back whereby said seat back rotates about the point of its said pivotal mounting to said seat supports during vertical swinging of said seat.

12. The seat assembly set forth in claim 11 further characterized in that said seat supports have upper and lower stop limits, and stop means mounted on said carriage and engagable by said stop limits to define the upper and lower limits to which said seat supports can move.

13. A vertically adjustable vehicle seat assembly comprising a mounting base member, a vertically shiftable carriage, parallel arm linkage between said base member and said carriage for vertically positioning said carriage at a constant attitude and in any one of a number of selected vertical positions; a seat having a pivotal mounting adjacent its forward end to said carriage for vertical swinging relative thereto, a pair of seat supports on which said seat freely rests, resilient cushioning means between said carriage and said seat supports for cushioning the downward vertical swinging of said seat and supports, a seat back pivotally mounted to said seat supports, a pair of seat links pivotally connected at one end to said carriage and at their other end having a link connection with said seat back whereby said seat back rotates about the point of its said pivotal mounting to said seat supports during vertical swinging of said seat; a pair of adjustment plates pivotally mounted to said carriage, one on each side of said carriage; a series of recesses in said adjustment plates, fixed means on said base member and engagable in any one of said recesses when said carriage is shifted to different vertical positions, and handle means connected with said adjustment plates for swinging the latter whereby any one of said recess in said adjustment plates may be engaged by said fixed means carried on said base member, whereby said carriage may be selectively held in any one of a number of positions to which it is vertically shifted by said parallel arm linkage.

14. The seat assembly set forth in claim 13 further characterized in that said carriage comprises a generally U-shaped member having two side portions and a bight portion connected therebetween, said handle means located across the bight portion, and said pair of adjustment plates are pivotally mounted to said carriage adjacent the bight portion, said adjustment plates extending rearwardly alongside said side portions and having recesses adjacent the rear ends of said adjustment plates.

15. The seat assembly set forth in claim 13 further characterized in that said seat supports have upper and lower stop limits, and stop means mounted on said carriage and engagable by said stop limits to define the upper and lower limits to which said seat supports can move.

16. A vertically adjustable vehicle seat assembly comprising a mounting base member, a vertically shiftable carriage, parallel arm linkage between said base member and said carriage for vertically positioning said carriage at a constant attitude and in any one of a number of selected vertical positions; a seat having a pivotal mounting adjacent its forward end to said carriage, damper means pivotally connected between said carriage and said seat and including a damper and a link having a pivotal connection with said damper, means for adjustably shifting said pivotal connection whereby the effective moment arm of said damper in respect to said seat pivotal mounting can be varied, said means for shifting said pivotal connection also being shiftably and swingably mounted on said carriage to swing said pivotal connection in a generally flat arc which is generally coincident with the line of force of said damper as said tractor seat rises and falls, whereby the damper has a substantially constant damping effect on said seat regardless of the vertical swinging movement of said seat; a seat having a pivotal mounting adjacent its forward end to said carriage for vertical swinging relative thereto, a pair of seat supports on which said seat freely rests, resilient cushioning means between said carriage and said seat supports for cushioning the downward vertical swinging of said seat and supports, a seat back pivotally mounted to said seat supports, a pair of seat links pivotally connected at one end to said carriage and at their other end having a link connection with said seat back whereby said seat back rotates about the point of its said pivotal mounting to said seat supports during vertical swinging of said seat; a pair of adjustment plates pivotally mounted to said carriage, one on each side of said carriage; a series of recesses in said adjustment plates, fixed means on said base member and engagable in any one of said recesses when said carriage is shifted to different vertical positions, and handle means connected with said adjustment plates for swinging the latter whereby any one of said recesses in said adjustment plates may be engaged by said fixed means carried on said base member, whereby said carriage may be selectively held in any one of a number of positions to which it is vertically shifted by said parallel arm linkage.

17. The seat assembly set forth in claim 16 further characterized in that said carriage comprises a generally U-shaped member having two side portions and a bight portion connected therebetween, said handle means located across the bight portion, and said pair of adjustment plates are pivotally mounted to said carriage adjacent the bight portion, said adjustment plates extending rearwardly alongside said side portions and having said recesses adjacent the rear ends of said adjustment plates.

18. The seat assembly set forth in claim 16 further characterized in that said seat supports have upper and lower stop limits, and stop means mounted on said carriage and engagable by said stop limits to define the upper and lower limits to which said seat supports can move.

19. The seat assembly set forth in claim 17 further characterized in that said seat supports have upper and lower stop limits, and stop means mounted on said carriage and engagable by said stop limits to define the upper and lower limits to which said seat supports can move.