Actuator for motor-vehicle seat adjuster

A motor-vehicle seat displaceable relative to a fixed support in a motor vehicle between a pair of end positions is powered by a motor whose output shaft may be rotatable in only a single predetermined rotational sense. Mechanism is provided having an input rotatable in one direction for displacing the seat on the support of the motor-vehicle from one end position into the other end position and rotatable in the other opposite direction for displacing the seat on the support from the other end position into the one end position. A motion-converting transmission is connected between the output shaft of the motor and the input of the displacement mechanism for automatically driving this input alternately in the one direction and in the other direction on continuous rotation of the motor output shaft in only the one sense. This motion-converting transmission may comprise a crank so that the motor-vehicle seat is automatically displaced from the one end position into the other and then back into the one position without the actuating motor having to stop.

Cross-Reference to Related Application 
This application is related to the commonly assigned and copending 
application Ser. No. 833,334 of A. Reinmoeller, whose entire disclosure is 
herewith incorporated by reference. 
BACKGROUND OF THE INVENTION 
The present invention relates to an actuator for a seat. More particularly 
this invention concerns an electrically powered adjuster for a 
motor-vehicle seat. 
At least the driver's seat of a motor vehicle is usually displaceable 
horizontally relative to a support on the vehicle between a rear end 
position and a forward end position relative to the direction of travel to 
compensate for drivers of different height and to allow each drive to 
select that seat position most comfortable for him or her. It is also 
known to provide a tilting mechanism which automatically tilts the seat 
upwardly and forwardly as it is displaced from the rear end position 
toward the front end position, as typically the driver who likes his or 
her seat close to the wheel is relatively short and also likes the seat to 
be raised somewhat. 
In the above-cited commonly owned patent application an arrangement is 
disclosed which automatically effects this horizontal displacement and 
tilting displacement synchronously. In this arrangement a reversible 
direct-current motor is operated by a reversing switch so that the user 
can merely push the switch in one direction to advance the seat in the 
corresponding direction and can push the switch in the opposite direction 
to similarly displace the seat in the opposite direction. The switch is 
normally not of the maintain type so that when released the motor is 
automatically deenergized and stops. 
Nonetheless a problem with such an arrangement is that the switch is 
normally actuated for at least a limited period of time after the seat has 
reached an end position, as the user does not immediately ascertain that 
the seat has stopped moving so continues to hold the switch over for a 
short time. In order to prevent against overloading of the motor and the 
entire structure the electric motor is therefore normally provided with a 
thermal overload switch that automatically cuts the motor out when it 
heats up as a result of straining to displace the seat which can no longer 
move against an abutment defining an end position. It is also necessary in 
such an arrangement to overdimension the mechanism that displaces the seat 
between the rear and tilted-down end position and the forward and 
tilted-up position in order to insure that prior to automatic switching 
off of the motor by the thermal overload arrangement the mechanism is not 
damaged. 
It has been suggested to overcome this problem by the provision of limit 
switches which automatically shut off or reverse the motor when it reaches 
an end position. Such an arrangement has proven itself so failure-prone in 
practice that it has never been used widely. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide an improved 
adjuster for a seat. 
Another object is to provide an improved adjuster for a motor-vehicle seat 
displaceable relative to a fixed support in the motor vehicle between a 
pair of end positions. 
A further object is the provision of such an actuator which can be produced 
at lower cost than the above-described type of actuator. 
These objects are attained according to the present invention in a 
motor-vehicle seat of the above type wherein mechanism has an input 
rotatable in one direction for displacing the seat on the support from one 
of its end positions toward the other end position and in the other 
opposite direction for displacing the seat on the support from the other 
end position toward the one end position. According to this invention 
means is provided including a motion-converting transmission which is 
connected between the output of a motor that is rotatable in a 
predetermined rotational sense and the input of the displacement mechanism 
for driving this input alternately in the one direction and then in the 
other direction on continuous rotation of the output only in its 
predetermined rotational sense. According to this invention the 
motion-converting transmission automatically switches the input of the 
displacement mechanism between directions on displacement of the seat into 
the respective end position without stopping of rotation of the output of 
the motor in its predetermined rotational sense. 
Thus in accordance with the instant invention the seat automatically moves 
into its one end position and then back toward the other end position if 
the switch for the actuating motor is held on. Thus it is possible to use 
an actuating motor which need only be unidirectional, and to provide a 
simple single-pole single-throw switch for operating such a motor. The 
mechanism that displaces the seat need not be overdimensioned, as it will 
never be forced to absorb all of the torque of the motor when the seat 
comes to its end positions. What is more it is possible to dispense with 
the thermal overload feature altogether, or to set it at a higher level so 
that it only operates when the seat becomes jammed due to external causes. 
Thus the entire arrangement according to this invention can be produced at 
much lower cost than the hitherto known actuator. 
According to a further feature of this invention the motion-converting 
transmission includes an eccentric crank which is operatively connected to 
the output of the motor and a connecting rod which is connected to this 
crank and operatively connected to the input of the mechanism that 
displaces the seat. This connecting rod may be constituted as a rack that 
is continuously maintained in mesh with a pinion carried on an output 
shaft that in turn is connected to the input of the seat-displacement 
mechanism. A guide pivotal about the output shaft carrying this output 
pinion surrounds the connecting rod and is provided with a 
friction-reducing member on which the connecting rod can slide while in 
mesh with the output pinion. 
The seat-displacement mechanism includes a support rail pivoted at its 
front end on the support of the seat and raisable at its rear end by means 
of a segment and pinion mechanism. A slide rail longitudinally slidable 
along this support rail is displaceable relative thereto by a rack and 
pinion which is operated jointly and synchronously with the segment and 
pinion. These two pinions are interconnected by a gear train contained in 
a mechanism housing bolted to the support rail. The transmission in turn 
is provided in a transmission housing that is bolted to the mechanism 
housing, and the motor itself is bolted to the transmission housing. Thus 
the entire assembly is supported on the support rail, and is pivotal 
therewith. With such an arrangement it is possible to do without a complex 
universal joint interconnecting a motor fixed to the motor-vehicle floor 
and the displacement mechanism. Of course the seat can comprise two such 
mechanisms having slide rails and the like, one for each side of the seat, 
in order to make the sliding of the seat as smooth as possible. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of a specific embodiment when read in 
connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in FIGS. 1-3 a motor vehicle normally displaceable in a horizontal 
direction D is provided with a support 10 provided relative to the 
direction D at its front end with a pivot 11 defining a horizontal axis A 
perpendicular to the direction D. At its rear end the fixed support 10 is 
provided with a rack member 12 having a throughgoing cut-out 13 and formed 
with a vertical array of teeth 14 forming a short gear segment. 
The motor-vehicle seat is supported on each of its sides on a respective 
guide-rail assembly 15 each of which comprises a respective lower support 
rail 16 extending backwardly from and pivoted at its front end at the 
pivot 11 and an upper slide rail 17 displaceable by means of rollers 
parallel to and on top of the support rail 16. The motor-vehicle seat is 
bolted to the two upper slide rails 17 which can only move parallel to the 
lower rails 16 but cannot move in any other direction relative thereto. 
Each such slide rail 17 is provided with a rack 18 having downwardly 
directed teeth and fixed to each support rail 16 is a mounting plate 19. 
A mechanism housing 20 is bolted by means of screws 21 to one of the plates 
19, here the right-hand plate 19 relative to the direction D. This housing 
20 contains displacement mechanism 22 including pinions 23 and 24 
respectively in mesh with the segment 14 and rack 18. The pinion 23 is 
carried on a shaft 25 journalled in the mounting plate 19 and also 
carrying a small-diameter gear 26 and a large-diameter gear 27, all of the 
gears 24, 26 and 27 being angularly fixed for joint rotation. Splined on 
the shaft 25 is a connecting tube 28 that extends perpendicular to the 
direction D from the right-hand side of the seat actuating mechanism to 
the left-hand side where it is fitted over a splined shaft 29 journalled 
in the other mounting plate 19 and carrying a respective gear 23 meshing 
with the other segment 14. An intermediate gear 30 carried on a shaft 31 
journalled in the housing 20 meshes with the small-diameter gear 27 and 
the large-diameter gear 26 meshes with a small-diameter gear 32 carried on 
a shaft 33 journalled in the mounting plate 19 and jointly rotatable with 
a large-diameter gear 34. An intermediate gear 35 carried on a further 
shaft 36 in the mounting plate 19 meshes on one side with the 
large-diameter gear 34 and on the other side with a gear 37 connected via 
a shaft 39 rotatable in a journal 38 in the plate 19 to the gear 24. 
Another connecting tube 40 is fitted over the shaft 39 for joint rotation 
of the gears 24 on both sides of the seat in mesh with the respective 
racks 18. 
The above-described gear trains are so constructed that as the gears 23 
rotate to raise the support rail 16 about the pivot 11 the gears 24 slide 
the rail 17 forwardly. When the rail 16 is in its uppermost position the 
rail 17 is in its frontmost position, and similarly when the rail 16 is in 
its lowermost position the rail 17 is in its rearmost position. This is 
achieved by appropriate dimensioning of the gears 23, 26, 32, 34, 35 and 
24. 
A motion-converting transmission 41 held in a housing formed by a pair of 
housing halves or plates 42 and 43 is secured by screws 64 to the housing 
20. A direct-current electric motor 44 is in turn secured by means of 
screws 65 to the outer plate 43 of the housing 42, 43. 
More particularly as shown in FIGS. 4-6 the mechanism 41 includes an input 
pinion 46 carried on the output shaft 45 of the motor 44. A large-diameter 
gear 47 carried on a shaft 49 on the plate 42 is unitary with a 
small-diameter gear 48 that in turn meshes with the teeth on the outer 
periphery of a large-diameter gear 50 carried on a shaft 51 fixed to the 
plate 42. This gear 50 carries offset from the axle 51 an eccentric crank 
52 on which is mounted a connecting rod 53 formed along its upper edge as 
a rack 54. A guide 55 holds this rack 54 in mesh with the teeth of an 
output pinion 58 carried on a shaft 57 extending through the plate 42. 
Together the structure 50-57 constitutes a crank drive or mechanism 66 
that converts continuous rotary motion of the gear 50 into oscillatory 
rotary motion of the gear 58 as will be described below. 
This gear 58 is fixed on a shaft 57 having an end 59 coupled as shown in 
FIG. 2 via a tube 60 to the shaft 31 of the gear 30 that itself meshes as 
shown in FIG. 3 with the small-diameter gear 27 fixed on the shaft 25 of 
the one pinion 23. 
Furthermore as shown in FIG. 6 the guide 55 is constituted as a split fork 
61 embracing and surrounding the connecting rod 53 and provided in its 
interior with a synthetic-resin slide body 62 of polytetrafluoroethylene 
so that the connecting rod 53 can easily slide in the guide 55. 
As mentioned above the synchronizing and actuating assembly 63 constituted 
by the mechanism 22 and transmission 41 need only be provided on one side 
of the seat, as the coupling tubes 28 and 40 insure that the pinions 23 
and 24 rotate synchronously on the other side of the seat. Thus 
synchronous operation of the mechanisms on both sides of the seat is 
insured with minimal duplication of structure. 
The transmission 41 is dimensioned according to this invention by 
appropriate dimensioning of the gears 46, 47, 48 and 50 as well as proper 
spacing of the axis of the eccentric 52 from the axis of the pin 51 so 
that for each full rotation of the large-diameter gear 50 the seat will 
move from its one end position into the other end position and then back 
into its original end position. Thus with the motor output shaft 45 
rotating continuously in a single direction the connecting rod 54 will 
rotate the gear 58 in one direction during 180.degree. of rotation of the 
gear 50, and during the next 180.degree. of rotation of the gear 50 the 
connecting rod will rotate the gear 58 in the opposite direction. What is 
more the change in speed of displacement, that is the acceleration, of the 
seat as it moves from the one end position to the other will vary 
sinusoidally with the seat slowly moving into its rest position and slowly 
moving therefrom, but moving somewhat faster intermediate this rest 
position. Thus the seat will move to its one end and come to a sudden 
stop, but instead will slow down as it approaches its end position and 
then slowly accelerate in the opposite direction away from this end 
position during continuous steady-speed rotation of the output shaft 45. 
This type of adjustment makes for extremely comfortable use of the seat 
and allows the mechanism described above to be dimensioned relatively 
lightly as it will not be subject to considerable strain. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
mechanisms differing from the types described above. 
While the invention has been illustrated and described as embodied in a 
motor-vehicle seat actuator, it is not intended to be limited to the 
details shown, since various modifications and structural changes may be 
made without departing in any way from the spirit of the present 
invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can by applying current knowledge 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.