Adjustable seat

An adjustable seat having a seat cushion and a backrest which are both secured to an underframe. The seat further includes a hydrostatic system of incompressible fluid contained within a closed circuit. The hydrostatic system includes individual actuators which bear against the seat cushion or both the seat cushion and backrest to adjust the inclination thereof. A shutoff member is provided to alternately allow and prevent movement of fluid within the closed circuit to change and then maintain a desired inclination.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a novel type of adjustable seat. 
2. Discussion of the Background Art 
As is known, a seat is essentially formed of a seat cushion and of a 
backrest, both secured to an underframe. A suitable mechanism makes it 
possible to adjust the inclination of the seat cushion and/or of the 
backrest. Adjustable seats have many applications, particularly as seats 
for offices, workshops, laboratories, for the disabled, for the sick, as 
well as in vehicles or aircraft. 
These seats equipped with backrests generally call upon mechanisms formed 
of articulations, of springs, and of systems for locking by clamping. 
Although widely used, this solution has the drawback of requiring numerous 
components, which leads to a high cost, particularly a high assembly cost, 
and to a relatively large size. Moreover, it is difficult to build into 
these seats complementary functions such as adjustment of the damping. 
Finally, on an ergonomic level, the control of the locking members is 
generally deemed to be unsatisfactory. 
Seats have also been proposed in which the inclination mechanism is 
controlled by electric motors. This solution, although satisfactory, is 
very expensive and requires the presence of a source of energy. 
Document U.S. Pat. No. 2,615,499 described a chair in which each leg 
includes a hydrostatic system, which can slide vertically, these various 
hydrostatic systems being connected up in a closed circuit in pairs, 
respectively on the right-hand side and on the left-hand side, so as to 
incline the chair, respectively the seat-cushion and backrest assembly, 
either forward or backward. Here, the hydrostatic system which forms the 
actual leg, and replaces the castors or the runners, rests directly on the 
ground, which allows the whole seat assembly only forward or backward 
inclination movements, in the manner of a rocking chair. 
The invention overcomes these drawbacks. It envisages a novel type of 
inclinable seat, which is reliable and comfortable in all positions, in 
which the mechanism is simple, effective, small, easy to actuate by the 
user and which remains of attractive cost. 
This adjustable seat, formed of a seat cushion and of a backrest which are 
secured to an underframe and which comprises a hydrostatic mechanism for 
adjusting the inclination of the seat cushion and/or of the backrest, is 
one wherein the hydrostatic inclination mechanism bears respectively on a 
base arranged on the top of the underframe and on the underside of the 
seat cushion (or of the backrest). 
In other words, the invention consists in using the hydrostatic 
transmission, which is moreover well known, and has been for a long time, 
to incline the seat cushion or the backrest, and no longer the legs 
themselves as is described in document U.S. Pat. No. 2,615,499 mentioned 
in the preamble. 
As is known, a hydrostatic system is a system formed by a plurality of 
actuating devices connected together by pipelines filled with a fluid in 
equilibrium, in the manner of communicating vessels. In that way, if one 
of the actuating devices is lowered, the others rise in proportion through 
the transfer of fluid contained in the circuit. Preferably, moreover, this 
fluid is an incompressible fluid, such as oil or water. 
In general, the actuating device is of the single-acting hydraulic actuator 
or flexible actuator type, in which the chamber containing the hydraulic 
fluid is connected to a base which is fixed onto the underframe. A 
hydraulic circuit of incompressible fluid connects the various chambers 
together. In that way, when one of the chambers lowers on one side, the 
chambers of the associated actuators automatically rise correspondingly, 
through the transfer of liquid in this circuit. 
In a first advantageous embodiment, the hydrostatic system is formed of 
three single-acting actuators forming a triangle the base of which is 
arranged on the side of the rear of the seat cushion (or of the backrest), 
the vertical axis passing through the center of the gravity of the seat 
and of its load being arranged inside this triangle to ensure good 
equilibrium of the seat. 
In another embodiment, the hydrostatic system includes six single-acting 
flexible actuators, arranged on either side of a bearing plate forming a 
base secured to the top of the underframe, namely respectively: 
four actuators arranged in a square, resting under the seat cushion and on 
the base for the inclination of this seat cushion; 
two actuators arranged under the bearing plate forming a base and on the 
support plate of the backrest for the inclination of this backrest. 
These six actuators are connected one by one and in closed circuit to a 
distribution chamber. 
In a preferred embodiment, the chambers of the actuators are connected 
together by a circuit including a shutoff member actuatable by the user, 
such as, for example, a tap, a locking screw or a valve, controlled by a 
lever, or even by any other means to control the, transfer of the liquid 
from one chamber to another. In an advantageous variant, the circuit may 
also be equipped with distributors, flow limiters, pressure accumulators 
or motorized pumps, depending on the additional functions which it is 
desired to obtain. Generally, all the known functions of hydraulic 
circuits may be used successfully. 
In another embodiment, the seat cushion and the backrest are articulated 
about a horizontal spindle secured to the underframe, and the hydrostatic 
system, also secured to the underframe, is formed of a plurality of 
actuators acting respectively on the underside of the seat cushion and on 
the backside of the backrest, these various actuators being connected 
together by a common circuit in which the shutoff member is arranged so 
that the inclination of the seat cushion and of the backrest are 
synchronized when the shutoff member is open, and locked when it is closed 
.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1 to 3, the seat comprises, in a symbolized manner, 
respectively a seat cushion (1) having a rear face (2) and a front face 
(3), and an underframe (4) to which it is secured by any suitable known 
means which are not represented. The underside face (5) of the seat 
cushion (see FIG. 3) comprises three hydrostatic actuators, referenced 
respectively (10, 11, 12) and arranged in a triangle. Two (10, 11) of 
these actuators forming the base of the triangle are arranged on the side 
of the rear face (2), whereas the apex (12) is arranged towards the front 
(3), so that (see FIG. 2) the vertical axis passing through the center of 
gravity (G) of the seat and of its load is arranged inside this triangle 
(10, 11, 12). The seat cushion (1) is secured to the underframe by a 
suitable mechanism comprising a base symbolized by the reference (15) 
(FIG. 3). 
Each single-acting hydrostatic actuator comprises, in a known manner, a rod 
(16, 16', 16") secured to the underside (5) of the seat cushion (1), a 
chamber (17, 17', 17") and a piston (18, 18', 18"). The incompressible 
hydrostatic liquid, such as water or oil, fills each chamber and these 
chambers are connected together by pipelines (20, 21, 22) respectively 
ending in a shutoff member (23) which can be actuated by a suitable member 
(24). The shutoff member (23) may consist of a tap, a distributor or a 
valve, actuated by the user by means of the member (24) arranged at the 
most suitable ergonomic location, such as, for example, the armrest of the 
seat or one of the lower lateral edges of the seat cushion. 
In the equilibrium position (see FIG. 4), all the rods (16, 16', 16") have 
substantially the same length. When the user wishes to modify his 
inclination position, he opens the shutoff member (23) by actuating the 
lever (24), and by leaning his body more on one actuator than on another. 
In that way, he inclines the seat cushion (1) (see FIG. 5). At this 
moment, an actuator, for example the actuator (16), is pushed in; but the 
opposite actuators (16', 16") rise in proportion, so that by the transfer 
of the fluid in the circuits (20, 21, 22) there is always equilibrium in 
the circuit. When the user reckons that the seat cushion is in an ideal 
position, all he has to do is release the shutoff member (23). Thus, the 
circuit remains in equilibrium and the seat cushion (1) (see FIG. 5) 
remains immobilized in a position which is inclined in a way which is best 
adapted to the position sought at a given time. 
When the user wishes, for some reason, to modify the inclination of the 
seat cushion (1) again, all he has to do is to open the shutoff member 
(23) and, when the new position is reached, to lock it again as before. 
Thus, the seat according to the invention is perfectly adapted to the 
inclination modifications, and this being as a function either of the 
user's desire, or of his disabilities, or of his need to change position 
to make a task easier. 
In an embodiment shown in FIG. 6, the seat, denoted by the general 
reference (30), comprises a seat cushion (31) similar to (1) and a 
backrest (32), both secured by a chassis (33) to the underframe (34). By 
virtue of a clevis (35, 36), the seat cushion (31) and the backrest (32) 
are articulated about two horizontal spindles, respectively (37, 38), 
secured to the underframe (34). The seat cushion (31) has, on its 
underside, a first single-acting actuator (40) connected to a similar 
actuator (41) acting on the back face of the backrest (32). These two 
actuators (40, 41) are connected together by a circuit (43, 44) in which a 
shutoff valve (45) actuatable by the user is arranged. Thus, by acting on 
the valve (45), the fluid is transferred from one branch of the circuit 
(43) to the other (44). It follows that the inclination of the seat 
cushion (31) gives rise to a coordinated inclination of the backrest (32). 
Thus, these two inclinations are synchronized. 
FIG. 7 illustrates another embodiment of the invention, in which, as in 
FIGS. 1 to 5, the pistons still act on the underside (5) of the seat 
cushion (1) no longer on a horizontal portion, but perpendicularly on 
inclined lateral portions (50, 51). The inclination of these lateral 
portions (50, 51) is such that the meeting point (P) of their extension 
substantially coincides with the virtual axis of rotation (P) of the seat 
cushion (1) arranged above this seat cushion, therefore close to the 
user's center of gravity (G). This arrangement ensures good stability and 
an increased feeling of comfort for the user. 
FIGS. 8 to 13 illustrate, as already stated, a practical embodiment of the 
invention. This seat, denoted by the general reference (100), is shown 
with the backrest in a vertical position in FIG. 8 and with the backrest 
in a backward-inclined position in FIG. 9. This seat (100) comprises an 
underframe (101), a plate (102) for supporting the backrest (103), which 
plate is articulated in a clevis (104) about a horizontal spindle (105) 
secured to the underframe and a seat cushion (106) which rests on a rigid 
plate (107). 
According to one characteristic of the invention, the seat (100) also 
includes a rigid bearing plate (110) fixed securely to the underframe 
(101) by means of a suitable framework. This fixed bearing plate (110), 
which forms the base, is arranged under the seat-cushion plate (107) and 
above the backrest-support plate (102). On either side of this fixed 
bearing plate (110) is arranged the characteristic hydrostatic system 
shown in detail in FIGS. 10 to 12, namely four seat-cushion actuators 
(115, 116, 117, 118) arranged in a square between the seat-cushion plate 
(107) and the bearing plate (110), and two backrest actuators (120, 121) 
arranged at the front and at the rear between the bearing plate (110) and 
the backrest-support plate (102). 
The hydrostatic system (130) detailed in FIG. 10 is formed of a plurality 
of individual pockets made from a sheet of polyvinyl chloride (PVC), 
welded on-all four sides, trapping the end of a PVC tube (131 to 136) 
respectively, which is also welded into the pocket. The other ends of 
these tubes are connected to a distribution chamber (140), itself coupled 
to a tube (141) for filling with fluid (water, oil). 
The references (111, 112, 122) denote orifices for fixing the 
actuation-forming chambers onto the compatible plates (102, 107, 110). In 
a variant, these pockets may be fixed onto these plates by some other 
system, such as a tape-and-hook assembly (113) known under the registered 
Trademark "VELCRO". 
References (150) and (151) denote a shutoff member respectively for 
shutting-off the seat-cushion circuit (150) and the backrest circuit 
(151). In one embodiment, this shutoff member may consist of a pair of 
parallel tubes (155, 156) forming a clamp which are brought together (or 
moved apart) by a closure (or opening) screw (157), depending on the 
desired inclination movement. 
The various actuator-forming pockets (115-118, 120, 121), with their 
coupling tube (131-136) distribute in (140), are filled with fluid by 
means of a pipe (141) which is then closed. These various pockets are then 
positioned on the bearing plate (110) as is shown in FIGS. 12 and 13, 
namely the seat cushion one (115-118) on the top and the backrest one 
(120-121) underneath. 
When the user wishes to incline the backrest backward, as is shown in FIG. 
9, he opens the corresponding shutoff member (151), for example by 
unscrewing the screw (157), thereby moving the two parallel rods (155, 
156) apart. By pressing, by means of his back, on the backrest (103) the 
user automatically transfers the fluid (oil or water) from the front 
pocket (121) to the rear pocket (120). 
Once he has found the correct inclination for the backrest (103) he closes 
the corresponding clamp (151) again. To tilt the backrest forward, for 
example to return it to the normal position as shown in FIG. 8, the 
process is reversed. The forward return of the backrest is facilitated in 
a conventional manner by a return spring, as in existing mechanisms. 
Modifying the seat cushion is obtained in the same way, but by actuating 
the corresponding shutoff member (150). 
In another practical embodiment, the two shutoff members (150, 151) can be 
synchronized, for example by means of a suitable hydraulic circuit. 
Thus, depending on the various configurations of the shutoff system, very 
varied behaviour can be obtained. 
When it is desired to move the seat cushion sideways without intervention, 
that is to say without closing the circuit, which cannot be achieved with 
current devices, part of the body weight is transferred to the side toward 
which it is desired to lean. By virtue of the equal pressure, distribution 
takes place automatically, which considerably improves comfort. 
Since the fluid is incompressible, the movements are controlled adjustably 
and are damped out, which attenuates the consequences of abrupt movements. 
Likewise, when the height of the seat cushion (106) is varied with respect 
to the underframe (101), the front-rear inclination of this seat cushion 
(106) is automatically compensated for. 
Since a better distribution of the loads over the seat cushion is thus 
obtained, the weight of the occupant's legs is taken up better, which 
correspondingly relieves the spinal column and eases the blood 
circulation. 
The device according to the invention makes it possible to change position 
naturally and easily, and to automatically regain optimum adjustment, 
which could not be achieved until now. 
The device according to the invention has numerous advantages compared with 
those known to date with an inclination mechanism. There may be mentioned: 
reduced size of the components of the mechanism, 
reliable and accurate mechanism, 
easy and ergonomic location of the unlocking control, that is to say the 
shutoff control, lower cost, 
great flexibility of use as regards the adjustments and damping, which 
ensures better comfort, 
an absence of noise during the adjustment movements, 
the fact that the seat adapts itself, which makes it possible to optimize 
the adjustments, by virtue of the equal pressure. 
In that way, these seats can be used successfully in all the applications 
of inclinable seats, for professional comfort needs, for the sick, the 
handicapped, and even in the automobile industry. 
While this invention has been described in detail with reference to certain 
preferred embodiments, it should be appreciated that the present invention 
is not limited to those precise embodiments. Rather, in view of the 
present disclosure which describes the best mode for practicing the 
invention, many modifications and variations would present themselves to 
those of skill in the art without departing from the scope and spirit of 
this invention, as defined in the following claims.