Telescopic screw jack for the adjustment of an element such as a vehicle seat

The jack comprises a tubular primary screw (10) provided with an outer screw thread and an inner screw thread having opposite thread hands, a secondary screw (11) cooperative with the inner screw thread and having an end (11a) articulated to a fixed point, a nut (9) fixed in rotation and connected to move in translation with the element to be adjusted and cooperative with the outer screw thread, a speed reducer associated with a motor (M) for driving the primary screw (10) in rotation, and means for preventing a rotation of the speed reducer (13) relative to the nut (9). These means comprise an articulated compass structure (18) having two branches (18a, 18b) articulated together. One of the branches is also articulated to the speed reducer (13) while the other branch is articulated to a part (9) of the jack which is fixed in rotation. The compass structure (18) considerably reduces the friction and improves the efficiency of the jack.

The present invention relates to a telescopic screw jack for the adjustment 
of an element such as a motor vehicle seat. 
A jack of this type is known in particular from the French patent No. 79 01 
741 (publication No. 2 447 494) which comprises a primary tubular screw 
provided with an outer screw thread, an inner screw thread having opposite 
thread hands, a secondary screw cooperative with the inner screw thread 
and having an end which is articulated to a fixed point, a nut fixed 
against rotation, connected to move in translation with the element to be 
adjusted and cooperative with the outer screw thread, a speed reducer 
associated with driving means for driving the primary screw in rotation, 
and means for preventing a rotation of the motor-speed reducer device 
relative to the general axis of the jack, i.e. the common axis of the two 
screws and the nut. 
The telescopic jack of the present invention may also be of the type 
disclosed in the French patent application No. 87 13 917 of Oct. 8, 1987 
in the name of the Applicant. 
The anti-twist means with which the jack of the aforementioned French 
patent is provided may be replaced by a rod fixed to the housing of the 
speed reducer and engaged moreover in the nut fixed against rotation. 
However, these known solutions have the common drawback of creating 
considerable friction which has an adverse effect on the efficiency of the 
telescopic jack since the work they perform is appreciable. 
The invention has for object to provide a jack of the aforementioned type 
in which the anti-twist means are so arranged as to create a minimum 
amount of friction and thereby ensure that the jack has an efficiency 
which is markedly higher than that of the known prior jacks. 
According to the invention, the means for preventing the rotation of the 
speed reducer relative to the nut comprise an articulated compass 
structure having two branches articulated together, one of said branches 
being also articulated to the speed reducer while the other branch is 
articulated to a part of the jack which is fixed in rotation. 
The torque tending to rotate the speed reducer about the axis of the 
primary screw is therefore transmitted to said part fixed in rotation, 
which is preferably the nut, by the pins articulating the branches of the 
compass structure to the speed reducer and to the part fixed in rotation 
and the pin articulating the branches together, which considerably reduces 
friction. 
According to an embodiment of the invention, the two branches of the 
compass structure are articulated together by a pin orthogonal to the 
general axis of the primary screw, the nut and the secondary screw and 
transversely offset relative to this general axis.

The jack shown in the drawings is a telescopic screw jack adapted to adjust 
the position of an element such as for example a vehicle seat whose 
longitudinal position or height above the floor is desired to be adjusted. 
This jack (FIGS. 1 to 3) comprises a primary tubular screw 10 provided with 
an outer screw thread and an inner screw thread of opposite thread hands, 
a secondary screw 11 cooperative with the inner screw thread of the 
primary screw 10 and having an end 11a articulated to a fixed point such 
as a bracket 11b rigid with the floor of a vehicle (not shown), a nut 9 
fixed in rotation, connected to move in translation with the element (not 
shown) to be adjusted and cooperative with the outer screw thread of the 
primary screw 10, a speed reducer 13 associated with an electric motor M 
for driving the primary screw 10 in rotation and in translation along the 
axis X--X of the latter, and anti-twist means for preventing a rotation of 
the speed reducer 13 relative to the nut 9. 
The speed reducer 13 comprises a worm wheel 14 through which a smooth end 
portion of the screw 10 extends, this end portion being rigid with the 
worm wheel, and a worm 15 tangent to the wheel 14, these two component 
parts being mounted in the housing 16. The worm 15 is driven by the motor 
M in the known manner, for example by a flexible rotary coupling F. 
The nut 9 is disposed in a housing B fixed to a slide G which is connected 
to move in translation with the element to be adjusted. The slide G may, 
for example, slide on a slideway fixed to the floor of a vehicle and carry 
a seat (not shown) whose position is to be adjusted. 
This jack may advantageously be similar to that disclosed in the 
aforementioned French patent application and therefore will not be 
described in more detail. 
The means for preventing a rotation of the speed reducer 13 relative to the 
nut 9, i.e. a twisting of the speed reducer about the axis X--X of the 
screws 10 and 11 and the nut 9 under the effect of the torque applied when 
the speed reducer 13 operates, comprise an articulated compass structure 
18a consisting of two branches or yokes 18a, 18b which are articulated 
together by a pin 19. 
The branch 18a is also articulated to the speed reducer 13, and the second 
branch 18b is articulated to a part of the jack which is fixed in 
rotation, namely the nut 9 in the presently-described embodiment. Each 
branch 18a, 18b has a generally Y (see FIG. 2a) or U shape whose base is 
extended by a projecting central end portion 30, 31 provided with a 
respective opening 32, the articulation pin 19 extending through these 
openings. The pin 19 is orthogonal to the general axis X--X and is 
transversely offset relative to this axis. Each branch 18a, 18b is 
constituted by two arms 18a1, 18a2, 18b1, 18b2 constituting a yoke, the 
ends of these arms being provided with openings and being articulated to 
distinct pins placed on each side of the primary screw 10 to allow the 
passage of the latter. 
Thus, the arms 18a1, 18a2 are each articulated to pins 20a, 20b fixed to 
the housing 16, and the arms 18b1, 18b2, are articulated to respective 
pins 21a, 21b fixed to the nut 9. Geometric axes 20, 21 respectively 
correspond to the pins 20a, 20b and 21a, 21b. 
The telescopic jack just described operates in the following manner: 
The fixed motor M drives through the flexible shaft F, the worm 15 and the 
worm wheel 14 the primary screw 10 in rotation about the axis X--X of the 
latter. As the screw 11 is fixed and the hands of the inner and outer 
screw threads of the screw 10 are opposite, the nut 9, its housing B, the 
slide G and the element to be adjusted move in translation along the axis 
X--X to the extent of the sum of the two thread pitches of the screw 
threads of the screw 10 upon each rotation of the latter. At the same 
time, the speed reducer 13 moves with the screw 10 to the extent of a 
single thread pitch of the latter relative to the fixed screw 11. There is 
consequently a relative displacement of the speed reducer 13 relative to 
the nut 9 and consequently a pivoting of the arms of the compass structure 
18 on one hand about the pins 20a, 20b, and 21a, 21b, and on the other 
hand about the pin 19. 
The fact that the pin 19 is orthogonal but not concurrent with the axis 
X--X of the screw 10 permits this relative axial displacement of the speed 
reducer 13. The reaction torque is transmitted to the part 9 which is 
fixed in rotation through the geometric axis 20, the branch 18a, the pin 
19, the branch 18b and the geometric axis 21. 
This transmission of the reaction torque through the two branches of an 
articulated compass structure considerably reduces friction as compared 
with known prior arrangements. Indeed, the sliding friction of the known 
arrangements is here replaced by pivoting friction which involves a much 
smaller amount of work. 
In the second embodiment (FIG. 4) of the jack, the yokes 18a, 18b forming 
the compass structure of FIGS. 1 to 3 are replaced by two branches 
constituted by links 22 and 23 articulated together by the common pin 19 
and having ends which are respectively articulated to pins 24 and 25 
carried by the speed reducer 13 and the nut 9a. 
The two links 22, 23 are contained in a general plane parallel to the axis 
X--X and their ends remote from the pin 19 are guided by flat surfaces 16a 
and 9b respectively provided on the housing 16 and the nut 9a which 
constitute support surfaces for the compass structure thus formed. 
The links 22, 23 have sufficient sectional size and the pins 24, 25 have a 
sufficient length to resist the developed forces. 
In the third embodiment of the invention (FIG. 5), the means for preventing 
the speed reducer 13 from turning relative to the nut 9 comprise a spring 
strip 26 bent into a V shape and consequently having two arms whose ends 
26a, 26b are respectively fixed to the speed reducer 13 and to a part of 
the jack which is fixed in rotation, namely the nut 9. The width 1 of this 
strip 26 is much larger than its thickness so that its bending inertia 
about an axis Y--Y parallel to the strip 26, i.e. in the direction of its 
bend, is very low. 
On the other hand, its bending inertia about an axis Z--Z perpendicular to 
the axis Y--Y is very high, i.e. in the direction which opposes the 
rotation of the speed reducer 13 relative to the nut 9. 
In the embodiment shown in FIG. 6, the spring strip 27 has a plurality of 
arms bent in the form of an accordion, namely four arms 27a, 27b, 27c, 
27d, the ends 27a1 and 27d1 of the strip 27 being respectively fixed to 
the speed reducer 13 and to the nut 9. It will be understood that the 
number of bends in the strip 27 may vary, the latter having moreover 
bending characteristics similar to those of the strip of FIG. 5.