US3861743A

US3861743A - Adjustable seat for railway carriages and the like

Info

Publication number: US3861743A
Application number: US347448A
Authority: US
Inventors: Jean Louis Danton
Original assignee: Compin SA
Current assignee: Compin SA
Priority date: 1970-04-27
Filing date: 1973-03-30
Publication date: 1975-01-21
Anticipated expiration: 1992-01-21
Also published as: GB1285019A; FR2088851A5; DE2109001B2; NL7105583A; DE2109001C3; DE2109001A1; CH524983A

Abstract

An adjustable seat adapted particularly for railway carriages and the like, comprising seat and seat-back combination having a dual connection to a fixed base structure, including, on one hand, towards the front and under the seat a sliding and swivelling connection of slideblock and slideguide and, on the other hand, towards the bottom and at the back of the seat-back a connection with tie-rods pivoting between a transverse spindle of the base structure and a transverse spindle of the seat and seatback structure, further including an elastic member such as an extensible rubber cord, exerting a tractive force between the front of the seat-back structure and the back of the fixed base structure, the dimensions and proportions of the seat and of the elastic member providing for an equilibrium balance of the seat in all of its adjusted positions.

Description

United States Patent 1 Danton 1 Jan. 21, 1975 1 ADJUSTABLE sEAT FOR RAILWAY cARRlAoEs AND THE LIKE [75] inventor: Jean Louis Danton, Boulogne,

France [73] Assignee: Etablissements Compin, Paris,

France 221 Filed: Mar. 30, 1973 211 Appl. No.: 347,448

Related US. Application Data [30] Foreign Application Priority Data Apr. 27, 1970 France 70.15357 [52] US. Cl. 297/329, 297/344 [51] Int. Cl. A471: 1/02 [58] Field of Search 297/300, 302, 310, 317,

3,170,728 2/1965 Barenyi 248/395 X 3,305,264 2/1967 Gunn t t A 297/346 3,572,818 3/1971 Lohr u 297/317 X 3,603,638 9/1971 McGregor et a1. 248/429 X FOREIGN PATENTS OR APPLlCATlONS 1,270,662 0/1961 France H 297/346 Primary ExaminerRoy D. Frazier Assistant Examiner-William E. Lyddane Attorney, Agent, or FirmWaters, Roditi, Schwartz & Nissen [57] ABSTRACT An adjustable seat adapted particularly for railway carriages and the like, comprising seat and seat-back combination having a dual connection to a fixed base structure, including, on one hand, towards the front and under the seat a sliding and swivelling connection of slideblock and slideguide and, on the other hand, towards the bottom and at the back of the seat-back a connection with tie-rods pivoting between a transverse spindle of the base structure and a transverse spindle of the seat and seat-back structure, further including an elastic member such as an extensible rubber cord, exerting a tractive force between the front of the seatback structure and the back of the fixed base structure, the dimensions and proportions of the seat and of the elastic member providing for an equilibrium balance of the seat in all of its adjusted positions 7 Claims, 11 Drawing Figures PATENIEU JANZ I IQYS SHEET 1 OF B PATENTEDJANZI I975 SHEET t [If 8 FATENTEB MHZ] i975 SHEET 70F 8 PATENTED JANE] I975 SHEET 8 0F 8 ADJUSTABLE SEAT FOR RAILWAY CARRIAGES AND THE LIKE FIELD OF THE INVENTION The present application is a continuation-in-part Application of Ser. No. 113,907; filed Feb. 9, 1971, now abandoned.

The present invention relates to an adjustable seat, particularly adapted for use in railroad cars. More particularly, the invention relates to a seat which may readily be adjusted by tipping a seat-and-back assembly of the seat in conformance with the dual movement of a slot which is formed beneath the front of the seat and of a tie-rod fastened at the rear of the seat back.

DISCUSSION OF THE PRIOR ART Tippable seats of generally this type have been described, in particular in French Pat. No. 823,912 with the purpose of reducing the frontage occupied by the seat, in effect, during adjustment, the top of the seat back moved almost vertically without disturbing any passenger who was seated behind that particular seat. However, such prior art seats were of comparatively heavy construction, considering the state of the art at that time, and during adjustment, with the seat being unlocked, the frictional forces were sufficient to prevent any involuntary tipping over. However, pursuant to present-day technological developments, seats are now made of considerably lighter construction and, upon the seat being unlocked, there is evolved the risk of its rapidly and inadvertently tipping in one or another direction depending upon the position and weight of its occupant, such as a child, or possibly a heavy adult.

SUMMARY OF THE INVENTION It is, accordingly, an object of the present invention to eliminate the drawbacks encountered in prior art adjustable seats, and to thereby eliminate any risks to any occupant during the adjustment of the seat.

A more particular object of the present invention lies in the provision of a seat which may be adjusted by tipping the entire seat-and-back assembly, thereby permitting a neutral or quasi-neutral balance equilibrium to be obtained for the whole seat-and-back-assemblyandoccupant combination irrespective of the weight of the occupant and of the adjusted position of the seat.

The invention is essentially predicated on the applicants determination that, by appropriately designing the dual front-slot and rear tie-rod connecting structure, a curve is obtained for the path of the center of gravity of the adjustable seat-and-occupant combination which at first is almost horizontal and then extends slightly downwardly, but at a slower rate of traverse. Furthermore, this path of the center of gravity may be effectively compensated for by the extension curve of an elastic means, such as a rubber cord, which is under initial tension acting as a tractive force between the seat front and the rear of its base structure.

Consequently the present invention eliminates the need for complex and expensive seat locking devices which are frequently required in order to maintain the adjustable seat in a particular adjusted position.

Accordingly, the adjustable seat, which is particularly applicable for use in railroad cars, comprises a one-piece seat-and-back construction which incorporates a dual connection to a fixed base structure of the seat. The connection includes, first, a forwardly and beneath the seat located swivable slideway connection formed by a slideblock and slider guide and, secondly a downwardly and behind the seat-back connection provided through tie-rods swivably supported between a transverse spindle of the base structure and a transverse spindle of the seat-and-back structure, with the connections according to the invention comprising firstly an elastic member, such as a rubber cord, exerting a tractive pull between the front of the said seatand-back structure and the rear of the fixed base structure and, secondly, predetermining the size and proportions of the seat and of the elastic means so as to assure the neutral equilibrium of the seat irrespective of its adjusted position or occupancy.

According to another embodiment of the invention, the elastic means operates by exerting a tractive force between, firstly, the front of the seat-and-back structure and, secondly, downwardly and behind the seat back, and with at least one lengthwise extension of the tie rods of the swivable tie-rod connection extending toward the transverse spindle of the base structure opposite the seat-and-back structure.

However, this arrangement when utilized in cars in which dining svice is provided, is generally subject to the problem when the passenger sits upright, he is of necessity in the far back position of the seat whereby, when the seat is adjusted into a forward position, the passenger is reclining too far back for comfortable dining.

Accordingly, a further object of the invention is to provide a seat structure which permits the passenger to assume a position simultaneously upright and forwardly, suitable for dining requirements.

Consequently, according to a further feature of the invention, the adjustable seat is provided with, in addition to the slideblock and slider guide connection, at least one tie-rod connection which is pivotally mounted first at one end on a spindle integrally fastened to the seat back, and secondly at the other end on a movable slide located adjacent a ramp integrally fastened to the fixed seat base structure, including an elastic means, such as a spring, exerting a tractive force between the front of the seat-andback structure and an extension of the tie rod located toward the slide opposite the tie rod, and with the slide being able to assume, alongside the ramp, at least two regulated stationary positions, in effect, a far-back position and a forward position, pertaining which the predetermined size and proportions of the seat and of the elastic means assure their neutral equilibrium with respect to any seat-and-back-assembly-and-occupant combination irrespective of the adjusted positions of the combination.

It is important to note that an object of the invention lies in providig maximum comfort for the passenger, while allowing him to adjust the position of his seat as desired without each time having to operate a locking device. Further, there are no longer problems as to any arrangements providing for a straight forward and simple translatory movement, such as those facilitating adjustment of a driver's with respect to a steering column of an automobile responsive to the driver's size.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention will now be described in greater detail, in conjunction with the accompanying drawings, in which:

FIGS. 1 and 2 illustrate diagrammatically in side elevation an adjustable seat according to the invention, with the seat being shown in an upright position in FIG. I and in a rearwardly inclined position in FIG. 2;

FIG. 3 is a partly schematic detail drawing, on an enlarged scale, of the central portion of FIGS. 1 and 2, showing through five equidistant representative positions, the positions of the various members and of the center of gravity during the adjustment cycle of the seat;

FIG. 4 is a curve showing the tractive force developed by the rubber cord for the five positions of FIG.

FIG. 5 illustrates diagrammatically in side elevation, a seat with attachment of the elastic means onto an extension of one of the tie rods of the pivotable tie-rod connection;

FIG. 6 is a diagrammatic side elevation of a seat permitting an occupant to assume a position both upright and at full length;

FIG. 7 is a diagrammatic cross-sectional view of the ramp housing the slide associated with a guide which is adapted to lock the slide; and

FIGS. 8, 9, l and 11 are diagrammatic elevational side views of the seat of FIG. 6, illustrating different relative positions of the seat-and-back unit for each of two adjusted positions of the seat.

DETAILED DESCRIPTION Referring now to FIG. 1, which shows the seat in its upright position pursuant to the invention, the seat includes a base structure 1 supporting on its front portion a fixed pin 2 around which a movable slideblock 3 is adapted to rotate. On its rear portion, there is supported a pin 4 on which there is adapted to turn a tierod linkage which is connected to the seat-back by a pin 6. The fixed cushion-and-back unit comprises a double eushion-and-back framework 7 supporting an elastic sheet on its forward end. This sheet acts as a support for the resilient portion of the upholstery 8, there imparting to the seat a suitable configuration for satisfactory passenger comfort. The cushion-and-back framework 7 supports toward its front a guide 9 wherein the shoe 3 of the base structure 1 may slide between a rear stop 11 and a front stop 12 for effective travel within guide 9. An elastic means, formed of a rubber cord I4, is attached, on the one hand, to the front of the frame 7 by a hook l5 hooked into a suitable housing 16 and, on the other hand, to the rear of the base structure I by means of a hook 17.

In FIG. 1 the guide 9 is pushed back until the front stop 12 butts against the slideblock 3 of the base structure l and the tie-rod linkage 5 projects straight up, thereby positioning the pin 6 in its topmost position, in effect, the seat pad is thus pushed back and the seatback straightened up to its maximum extent.

When the occupant desires to adjust the seat from the upright to the extended or rearward position, he moves the cushion forward, causing slideblock 3 to slide in guide 9, with the tie-rod linkage 5 then retaining the seat-back so that the top thereof moves appreciably in the vertical plane and increasing the inclination of the back relative to the vertical axis. This extended position, illustrated in FIG. 2, in which the seat components are designated with the same reference numerals, affords the occupant better support in the lumbar region and therefore imparts him a feeling of ease and comfort.

In adjusting from an upright (as in FIG. I) to an extended position (as in FIG. 2}, the center of gravity of the seat and its occupant is slightly lowered, imparting a somewhat greater ease of seat manipulation in one direction than in the other, however, as previously stated, the invention provides neutral equilibrium in each of these positions and in the intermediate positions through an elastic means which is described in further detail hereinbelow,

Referring now to FIG. 3, which is an enlarged scale detail drawing; five equidistant representative adjusted positions of the seat are illustrated, and identified by the designations 0 (extended), b, c. d. r (upright) for each member; pin 2 in guide 9, hook I5 of the rubber cord 14, and pin 6 of the tie-rod linkage 5. FIG. 3 also illustrates the five corresponding positions of the center of gravity G of the seat-and-occupant combination. It is noted that in FIG. 3, as a nonlimitative example, the size and positions of the slide slot 9 and tie-rod linkage 5, restrict the extend of swivel of the latter between approximately l0 in front of the vertical (upright position r) and approximately 30 in front of the vertical (extended position a); whereby the path of the center of gravity G is, as previously stated, at first almost horizontal (starting fron Gr) then curved slightly downwardly (on arriving at Ga), while the intervals between successive adjusted seat positions successively decrease (interval GrGd is larger than those following, and par ticularly larger than the final interval GhGa). During this movement the rubber cord 14 is extended or stretched (from lSr to having reference to the curve of FIG. 4 showing the lengths L of the rubber cord 14 plotted along the x-axis and its tractive effort F along the y-axis. It becomes apparent that this effort F which, of course, acts in an opposite direction with respect to the lowering of G, increases progressively (due to an initial tension being imparted to the rubber cord 14) and uniformly from position r towards position a, so as to exactly correspond to the compensation required by the plotted path of the center of gravity G (FIG. 3).

It is noted that the arrangements, proportions and contours necessary for obtaining such a result are based on an extensive study of the dynamics of the adjustable seat and clearly varies from the known art, the latter of which is directed chiefly into research pertaining to translatory motion of the seat-and-back for which a locking means is indispensable.

Referring now to FIG. 5; the seat is constructed of a permanent base 31 supporting toward its front a fixed pin 32 having pivotably supported thereon a movable slideblock 33, and supporting at its rear a pin 34 on which is pivotably supported a tie-rod linkage 35 which is connected to the seat-back by a pin 36. This tie-rod linkage is extended beyond the pin 34 by a lever arm 37, the fixed seat-and-back unit being composed of a double seat-and-back framework 38 supporting an elastic sheet on its front portion. The seat-and-back framework 38 supports on its front portion a guide 39 within which the slideblock 33 of the base 3| may slide between a rear stop 41 and a front stop 42 limiting the travel within guide 39. An elastic means formed of a rubber cord 44 is attached at one end thereof to the front of the moving frame 38 by a hook 45 hooking into a suitable recess 46 and at its other end to a lever arm 37 by means ofa hook 47. In the case where the adjustable seat includes several tie-rod connections, the cord 44 may also be attached to a stay or cross-bar uniting all of the lever arms which are similar to lever arm 37. The tractive action of the elastic means 44 on the lever arm 37 impart to the seat-and-back-and-occupant combination an improved neutral equilibrium, and concurrently facilitates the ready return of the seat to its rear position.

Referring now to FIG. 6, the seat is constructed of a unitary seat-and-back structure provided with a dual connection to a fixed seat base, such as, toward the front and beneath the seat, a movable slideblock and guide connection including a mobile slideblock 51 pivotably supported on a fixed pin 53 mounted on the base 54, and of a guide 55 wherein the slideblock 51 is adapted to slide in a travel path limited by a front stop 56 and a rear stop 57.

A second connection includes a tie rod 58 which is 'pivotably mounted, on the one hand, about a pin 59 integrally formed with the seat-back 60 and, on the other hand, on a pin 6! located on a slide 62 which is movable along a ramp 63 integrally formed with the base 54. Extending parallel with the ramp 63 and along a side face of the slide 62, a guide 64 is attached thereto, and on which a skid 65 is supported while fitted on the top end of an arm 66 of a first-class lever 67. The lever 67 is bent into a slight V-shape, and pivotally supported at its fulcrum on a pin 68 integrally fastened with the base 54. The guide 64 has two grooves or recesses 69 and 70 in which the skid 65 of the lever arm 66 may engage, so as to provide for suitable positioning of the slide 62 on the ramp 63, and thereby locking the slide 62 into a position corresponding to one or the other of grooves 69 and 70. The retention of the skid 65 against the guide 64, and its engagement in either of the grooves 69 or 70 is established by the resultant couple (torsional force) generated by a spring pulling between the lever arm 71, homologous to the lever arm 66 and the base 54. it becomes apparent that such a result may be obtained by a torsion spring fitted onto pin 68, or by a compression spring extending between lever arm 66 and the base 54. The disengagement of the skid 65 externally of either one or other of the grooves 69 or 70, in which it was previously engaged, may be effected by simply exerting an upward vertical force, on lever arm 71 in opposition to the previously mentioned resultant couple. In order to prevent the angle of tie rod 58 and seat-back 60 not being able to recover beyond a predetermined limit, an adjustable stop 72 is brought to bear on a plate 73 attached to tie rod 58.

The elastic means is composed of a spring which exerts a pull between the seafront 74 and an extension 75 of the tie rod 58 located toward the slide 62 opposite the tie rod 58.

The operation of the seat unit is such that for stan dard use thereof, the slide 62 is locked in the rear position, with the skid 65 of lever arm 66 being positioned in groove 69. In this position, partly illustrated in broken lines in FIG. 6, with the pin for swiveling tie rod 58 on slide 63 being in a position illustrated by reference numeral 78, the seat acts in the identical manner described in connection with the seat illustrated in FIG. 5.

In order to reach the dining position. slide 62 is unlatched by action on the lever arm 71, and is advanced along ramp 63 until the skid 65 engages in the groove 70, in consequence of which, the pin rotating the tie rod 58 on slide 62 moves into the fixed position designated by reference numeral 79.

During the course of this movement, since the angle between the seat-back 60 and the tie rod 58 is being decreased, the stop 72 comes into contact with the plate 73 of tie rod 58 and the seat-and-back assembly is projected forwardly, the guide 55 being moved into a for ward position as it slides relative to the slide-block 5|.

A new usable range of adjustment is obtained, whereby the seat may be imparted a more forwardly and horizontal position, and with the back being also more forwardly and at the same time vertically straightened.

The inclination of ramp 63 as well as the position of the various sliding elements of the seat are, of course, so calculated as to attain as comfortable a position for dining as is possible.

Furthermore, the slide 62 may be supplied, in lieu of a guide 64, with a rack having teeth which are adapted to mesh with teeth arranged on the lever arm 66 instead of the skid 65. In that instance, the slide 62 may enter a plurality of fixed positions along ramp 63.

Referring now to FIG. 7, a slide 62 which is of parallelpipedal shape is guided, by its members, along two

channel sections

80 and 81 of the sloping ramp 63, by means of associated bearing balls 82 on the two longitudinal side faces of the slide 62, and on the internal face of the core of the two

channel sections

80 and 8|. The upper surface of this slide 62 is rigidly connected to the web of a U-section bearing 83 to which is attached, on the one hand, extending transversely to the two legs 84 and 85, the pin 86 for swiveling the tie rod 58 and, on the other hand, to the outer surface of the leg 85, a metal angle iron 87. This metal angle iron carries the channel guide 64. The web of this guide, as well as the corresponding portion of angle iron 87, comprises the two grooves 69 and utilized for locking the slide 62.

In order to avoid any error in interpreting the description, normal servive positions of the seat refers to all positions of the seat obtained for the far-back position of the slide 62 along the ramp 63, and dining (or meal) positions" all positions of the seat obtained for the forward position of the slide 62 along ramp 63.

FIG. 8 is a diagrammatic section of a seat similar to that of FIG. 6, illustrating two relative positions of the seat, namely, in solid line designated by reference numeral 88, a normal service position in which the seat is pushed back and the back is straight up, and in broken line designated by reference numeral 89, another normal position in which the seat is moved forward and the back is inclined.

Similarly, FIG. 9 illustrates in solid line, through reference numeral 90, a seat in normal service position according to which the seat is pushed back and the back straight up, and in broken line through reference numeral 91, a dining position according to which the seat is moved forward and the back slightly inclined.

The two positions shown in solid lines in FlGS. l0 and 11 through reference numeral 92, correspond to a dining position in which the seat is pushed back and the back is straight up.

The position shown in broken line in FIG. 10 through reference numeral 93, is a normal service position similar to that shown in full line in FIG. 2 by reference numeral 88.

Finally, the position shown in broken line in FIG. 11 through reference numeral 94, is a dining position similar to that shown in broken line in FIG. 9 by reference numeral 91.

While there has been shown what is considered to be the preferred embodiment of the invention, it will be obvious that modifications may be made which come within the scope of the disclosure of the specification.

What I claim is:

1. An adjustable seat, particularly for railroad cars and the like, comprising an adjustable unitary seat-andback structure; a fixed base; a dual connection between said fixed base and said seat-and-back, a first of said connections including, toward the front and beneath the seat, a slideway fastened to said seat-and-back structure so as to be movable therewith, said slideway having a slideblock and a slider guide slidably mounting said slideblock, a fixed pin fastened to said base, said slideblock being rotatably connected to said pin; the other of said connections including, downwardly and behind the seat-back, a transversely extending pin on said base and a transversely extending pin on said seatand-back structure, a tie rod linkage swivably sup ported between said pin on said base and said pin on said seat-and-baek structure facilitating tilting of said seat-and-back structure relative to said base; an elastic member connected between the front of said seat-andback structure and the rear ofsaid fixed base and exerting a tractive force therebetween, said seat and said elastic member being sized and proportioned so as to ensure a neutral equilibrium to a seat-and-back-and' occupant combination in any adjusted position of said seat; and means limiting travel of said tie-rod linkage between said fixed base and said seat to between two positions of said tie-rod linkage forwardly of a vertical axis.

2. A seat as claimed in claim I, said elastic member comprising a rubber cord.

3. A seat as claimed in claim 1, said means limiting travel of said tie-rod linkage to between said two positions of said tie-rod linkage in the range of about l0 to forwardly of said vertical axis, said elastic member exerting said force with an initial tension between a point of the seat proximate to and above said slider guide and a point on said fixed base structure proximate to and below said transverse pin on said fixed base, the tractive force of the elastic member acting in a direction opposed to a lowering of the center of gravity of the seat-and-back-and-occupant combination, and said force increasing progressively and uniformly in response to an initial tension imparted to said elastic member at a progressively lower increase from a straight-up seat position toward an extended seat position so as to provide corresponding compensation for the path of movement of said center of gravity. thereby imparting neutral equilibrium to the seat-and-backand-occupant combination.

4. A seat as claimed in claim I, said elastic member exerting a force between the front of said seat-andback structure and the back of the seat; and at least one longitudinal extension of the tie rod linkage being located so as to extend toward said transverse pin on said seat-and-back structure.

5. A seat as claimed in claim 1, comprising at least one further tie-rod linkage connection pivotably mounted at a first end thereof on one end ofa pin integrally fastened to the seat back, and at its other end, to a slide movable along a ramp integrally fastened to said fixed base, said elastic member exerting a pull between the front of said seat-and-back structure and an extension on said further tie rod linkage, and being located toward said slide opposite said tie rod linkage, said slide adapted to be moved along said ramp into at least two regulatable fixed positions defining, respectively, a farback seat position and a forward seat position, the size and proportions of the seat and of said elastic member ensuring neutral equilibrium of the seat-and-back-andoccupant combination, irrespective of the postions of said combination.

6. A seat as claimed in claim 5, comprising locking means for said slide including a guide attached to a side face of said slide and extending parallel to said ramp, at skid supporting said guide, said skid being mounted on the top end of an arm of a V-shaped lever; a spindle integrally fastened to said fixed base, said lever being fulcrumed on said spindle, said guide having two stepped grooves adapted to have said skid engaged therein so as to lock said slide into a position corresponding to one or the other of said grooves; and spring means retaining the skid against the guide and in engagement in one of said grooves in response to a resultant torque force generated by the action of said spring means.

7. A seat as claimed in claim 6, said guide comprising a toothed rack; said lever having teeth on at least one arm thereof adapted to interdigitate with said toothed rack.

Claims

1. An adjustable seat, particularly for railroad cars and the like, comprising an adjustable unitary seat-and-back structure; a fixed base; a dual connection between said fixed base and said seat-and-back, a first of said connections including, toward the front and beneath the seat, a slideway fastened to said seat-andback structure so as to be movable therewith, said slideway having a slideblock and a slider guide slidably mounting said slideblock, a fixed pin fastened to said base, said slideblock being rotatably connected to said pin; the other of said connections including, downwardly and behind the seat-back, a transversely extending pin on said base and a transversely extending pin on said seat-and-back structure, a tie rod linkage swivably supported between said pin on said base and said pin on said seat-and-back structure facilitating tilting of said seatand-back structure relative to said base; an elastic member connected between the front of said seat-and-back structure and the rear of said fixed base and exerting a tractive force therebetween, said seat and said elastic member being sized and proportioned so as to ensure a neutral equilibrium to a seat-andback-and-occupant combination in any adjusted position of said seat; and means limiting travel of said tie-rod linkage between said fixed base aNd said seat to between two positions of said tie-rod linkage forwardly of a vertical axis.

2. A seat as claimed in claim 1, said elastic member comprising a rubber cord.

3. A seat as claimed in claim 1, said means limiting travel of said tie-rod linkage to between said two positions of said tie-rod linkage in the range of about 10* to 30* forwardly of said vertical axis, said elastic member exerting said force with an initial tension between a point of the seat proximate to and above said slider guide and a point on said fixed base structure proximate to and below said transverse pin on said fixed base, the tractive force of the elastic member acting in a direction opposed to a lowering of the center of gravity of the seat-and-back-and-occupant combination, and said force increasing progressively and uniformly in response to an initial tension imparted to said elastic member at a progressively lower increase from a straight-up seat position toward an extended seat position so as to provide corresponding compensation for the path of movement of said center of gravity, thereby imparting neutral equilibrium to the seat-and-back-and-occupant combination.

4. A seat as claimed in claim 1, said elastic member exerting a force between the front of said seat-and-back structure and the back of the seat; and at least one longitudinal extension of the tie rod linkage being located so as to extend toward said transverse pin on said seat-and-back structure.

5. A seat as claimed in claim 1, comprising at least one further tie-rod linkage connection pivotably mounted at a first end thereof on one end of a pin integrally fastened to the seat back, and at its other end, to a slide movable along a ramp integrally fastened to said fixed base, said elastic member exerting a pull between the front of said seat-and-back structure and an extension on said further tie rod linkage, and being located toward said slide opposite said tie rod linkage, said slide adapted to be moved along said ramp into at least two regulatable fixed positions defining, respectively, a far-back seat position and a forward seat position, the size and proportions of the seat and of said elastic member ensuring neutral equilibrium of the seat-and-back-and-occupant combination, irrespective of the postions of said combination.

6. A seat as claimed in claim 5, comprising locking means for said slide including a guide attached to a side face of said slide and extending parallel to said ramp, a skid supporting said guide, said skid being mounted on the top end of an arm of a V-shaped lever; a spindle integrally fastened to said fixed base, said lever being fulcrumed on said spindle, said guide having two stepped grooves adapted to have said skid engaged therein so as to lock said slide into a position corresponding to one or the other of said grooves; and spring means retaining the skid against the guide and in engagement in one of said grooves in response to a resultant torque force generated by the action of said spring means.