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Description  |
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BACKGROUND OF THE INVENTION
The invention relates to vehicle seats and particularly to the field of
vibration isolation. In road vehicles, such as trucks, as well as
off-the-road vehicles, such as tractors and scrapers, it is quite
conventional to isolate vertical vibrations by mounting the seat on a
resilient suspension. It is also common to provide fore and aft isolation
by mounting the seat bottom on tracks which can slide fore and aft with
the occupant against springs. Such fore and aft isolation systems can
usually be locked out when desired since under severe vibration conditions
they can hit their end stops and cause the operator's feet to move rapidly
relative to the pedals in the vehicle and thus reduce, rather than
increase, his ability to control the vehicle. Shock absorbers or other
damping devices can reduce the aforementioned problem but they also reduce
the ability to isolate vibrations. Also, when the vehicle is on either an
up or down slope, the weight of the operator and seat can cause the seat
to slide to one end of its isolation travel path.
The above-noted deficiencies of commercially available fore and aft
isolator mechanisms would seem to suggest that a system which would permit
good pedal contact at all times while minimizing violent back and forth
movement of the operator's torso and heart would be highly desirable.
SUMMARY
It is among the objects of the present invention to provide a vibration
isolation mechanism for a vehicle seat which will provide a substantial
portion of the operator comfort advantages of available fore and aft
isolation mechanisms as well as additional operator vibration isolation,
at least in the critical heart region, during the periods of excess
vibration when conventional mechanisms are ordinarily locked out of
operation. Another object is to provide a considerable amount of fore and
aft isolation in situations where there is insufficient space in the
vehicle to mount a seat with a conventional fore and aft isolation unit.
It is a further object to provide a back cushion angular vibration
isolator which is of simple construction and easy to install. A still
further object is to provide a back cushion angular vibration isolator
which forms a portion of a back angle adjustment mechanism so that
isolation is provided at any angle of back adjustment.
These and other objects and advantages are attained by the seat back angle
adjustment and isolation mechanism of the present invention. The seat back
angle is adjusted by eccentric cams which are mounted in pairs of channels
carried by the seat back frame in a fashion quite similar to that
disclosed in U.S. Pat. No. 4,008,920 to O. H. Arndt, assigned to a common
assignee, the disclosure of which is incorporated by reference herein. In
the aforementioned patent, the seat back angle is adjusted by angularly
rotating a circular cam plate which is eccentrically mounted for rotation
about an axis which is spaced from and fixed relative to a pivot axis for
the seat back. The cam plate is captured between a pair of guide rails in
the form of a channel formed as part of the seat back frame. Since opposed
peripheral edges of the circular cams engage, or at least substantially
engage, both guide rails at once, rotation of the cams about their
eccentric axes will cause the seat back to tilt about its pivot axis
through a predetermined range of adjustment. In the present invention, an
axially elongated, cylindrically surfaced cam is mounted at each side of
the seat back frame for rotation about a support rod having an
eccentrically positioned axis which is mounted for rotation in the seat
frame. The cylindrical cams are positioned between the parallel, opposed
flanges or side rails of a pair of generally vertical channel portions
formed on or attached to the seat back frame. However, the diameter of the
cams is substantially smaller than the distance between the flanges so as
to form a space between the cam and one flange when the cam is contacting
the other flange. The space is filled with a resilient means such as an
elastomer pad or metal spring which is affixed to the one flange. The
elastomer pads preferably are made of a durable material such as Buna N
rubber having a durometer of about 35 or 70 Shore A that can withstand the
environment to which the seat is subjected. They also preferably have a
spring rate which is sufficient to provide substantial seat back
deflection when subjected to loading by seat occupants of varying weights.
The loading situation can be typically described as one wherein vehicle
fore and aft or rotational pitching vibrations force the seat back
forwardly against the occupant's back or rearwardly away from it. The
major force of the forward impact of the seat back against the occupant is
absorbed by the elastomer pads so as to cause the seat back to tilt
rearwardly from its normal position, thus leaving the occupant at a
relatively fixed position in space. As the vibration force switches
direction to tend to drive the seat back rearwardly, the energy absorbed
in the deflected elastomeric pads will cause the seat back to be driven
forwardly while remaining in contact with the occupant's back. The net
result is that the occupant will experience very little fore and aft
pitching movement, thus greatly increasing his comfort since it is known
that the comfort of the seat occupant is related to the magnitude of
acceleration. The greater the acceleration, the less time one can endure
it and perform effectively.
A conventional fore and aft isolator provides for about 2" of total travel
or about 1" forward or backward movement from its centered position.
Typically, such an isolator includes springs which are displaced 1" by a
30 pound load. Since the isolator is usually under the seat, it sees not
only the entire weight of the occupant but also the entire weight of the
seat. Accordingly, it is quite sensitive to variations in operator weight
and to changes in the angle of the road surface relative to horizontal. In
the seat back isolator of the present invention, the vast bulk of the seat
weight and most of the weight of the operator do not exert a horizontal
force component on the seat back. Thus, better control can be provided for
occupants of differing weights.
It is preferable for operator comfort that the angle of the seat back be
maintained at about the same angle during use regardless of the weight of
the particular occupant. If the resilient members associated with the back
angle isolator have a constant spring rate, it is obvious that the back
angle, if not separately adjusted, would probably be too close to the
vertical for a light weight occupant and too tilted to the rear for a
heavier occupant. The present invention discloses a back angle adjuster
which permits the back angle to be adjusted by the occupant while the
occupant is comfortably seated. If a seat manufacturer did not wish to
provide for back angle adjustment, the resilient members could be
adjustably preloaded to assume a desired angle when occupied by occupants
of differing weights or they could be especially shaped to provide a
non-linear spring rate which would cause them to become stiffer and
stiffer as they were deflected. In the latter case, the light occupant
could enjoy the comforts of a much larger range of deflection than would
be the case if a spring having a constant rate spring were used which
would only fully deflect from the loading exerted by a heavy occupant.
Even when a back angle adjustment feature is provided, as disclosed
herein, it is usually desirable to provide a certain amount of preload or
compression of the resilient members when the seat is unoccupied. This
preloading has several advantages, including a reduction in the overall
amount of travel which must be provided for the top of the seat back.
Space is usually at a premium in a truck cab. To conserve it, rather than
have the top of the seat back move 4.5", for example, I prefer to preload
the resilient means so that a 3" movement of the top of the seat back will
absorb the same energy as a 4.5" movement of an unpreloaded back. Another
advantage of preloading is that some occupants will not cause the seat
back to resiliently deflect by the normal horizontal force component
exerted by their back on the seat when they are seated comfortably. Thus,
the seat back angle will not always need to be adjusted after an occupant
sits down. Still another advantage of preloading is that the seat back
will have no tendency to rattle when unoccupied.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a bottom sectional view of the tilting, locking and vibration
isolation mechanism taken on line 1--1 of FIG. 3;
FIG. 2 is a fragmentary side view of a seat incorporating the invention;
and
FIG. 3 is a fragmentary rear perspective view showing a seat back
incorporating the invention.
DETAILED DESCRIPTION
FIG. 1 shows a detailed cross-section of my improved seat adjusting and
vibration isolating mechanism 10 while FIG. 2 shows the relationship of
the seat adjuster and isolator 10 to a seat consisting of a seat back 12,
a seat cushion 14 and a seat frame 16. The seat frame 16 includes a pair
of upwardly extending seat back mounting portions 18 which include a first
aperture 20 in which a pivot rod 22 is mounted and retained by means such
as E-rings (not shown). The pivot rod 22 also passes through a first
aperture 26 (FIG. 3) in each of a pair of angle members 28, 28' which are
rigidly attached to the seat back 12. Referring to FIG. 2, one can
appreciate that the seat back member 12 can be moved back to various
angles of tilt relative to the seat cushion 14 by pivoting it about the
pivot rod 22. The amount of fixed pivotal movement which can take place,
as distinguished from resilient isolation movement, is controlled by
adjuster and isolator mechanism 10 which, as seen in FIG. 1, includes a
hexagonal rod member 32 mounted in bearings 34 in second apertures 36
formed in the seat back mounting portions 18 of the frame 16. A pair of
cylindrical cam members 38 are welded eccentrically of their axes to a
spacer tube 39 which is fastened to the hexagonal rod 32 by a pin 40 so
that two diametrically opposed portions of the members will be spaced from
the rod 32 by different amounts to provide eccentric peripheral cam
surfaces 38'. First portions of the outer peripheral cam surfaces 38' of
the cam members 38 engage elastomeric pads 41 which are supported by the
rear wall portions 42 while second diametrically opposed portions
simultaneously engage the front wall portions 43. The parallel, opposed
wall portions 42, 43 form a channel or guide track in the angle members
28, 28' which are rigidly attached to the seat back 12. An elongated slot
44 (FIG. 2) formed in the pivotable angle member 28 permits the seat back
12 to tilt forwardly and backwardly about the pivot rod 22 without
interferring with the hexagonal rod 32. A rotation of the cam member 38
over an approximately 180.degree. range from the FIG. 2 position will
cause the seat back 12 to progressively pivot about pivot rod 22 from its
forwardmost to its rearwardmost fixed position of adjustment. The seat
back is positively retained in any one of about 10 positions of adjustment
throughout this range by means of a pair of locking pins 54 which are
carried by knob 56 and are adapted to engage in any pair of diametrically
opposed apertures 58 in a circle of such apertures formed in the rear
upwardly extending portion 18 of the frame 16.
In operation, the knob 56 is pulled axially outwardly by the seat occupant
against the force of spring 60 as shown in dotted lines in FIG. 1. Once
the locking pins 54 are clear of the frame portion 18 the knob 56 can be
very easily rotated over a 180.degree. range to cause a simultaneous
rotation of the cam members 38 and a consequent pivoting of the angles 28,
28' and tilting of the seat back 12. When a desired adjustment position
has been reached, the operator merely releases the knob 56 and the spring
60 will cause the pins 54 to engage in one of the opposed pairs of holes
58. The spring 60 is retained between the interior portion of the knob 56
and a cover plate 62 while the cover plate 62 is retained on the hexagonal
rod 32 by means of an E-ring 64.
The elastomeric pads 41 are shown as being slightly compressed and are thus
preloaded so that a predetermined amount of force must be applied by a
seat occupant in the direction of the arrow in FIG. 2 before the seat back
12 will start to move rearwardly. Thus, all occupants of less than a
certain weight would normally not deflect the seat. As previously
discussed, this situation reduces the amount of seat back movement that
must be accommodated, reduces the need to vary the fixed seat back angle
for different occupants, and prevents rattling when the seat is not
occupied. The thickness of the pad 41 and the distance it can be depressed
are selected in accordance with the distance which the seat back can be
permitted to move and the respective distances between the top of the seat
back and the pivot shaft 22 and between the pivot shaft 22 and the portion
of the cam periphery 38' which engages the pad 41. For example, if the top
of the seat back 12 can move 3" and it is located 18" from the pivot shaft
22, the pad 41 would be compressed 0.5" if its contact point with the cam
surface 38' were 3" from the pivot shaft 22. Preferably, a stop member
(not shown) is provided to limit the compression of the pad 41. The
durometer of the pad 41, its size, the area of contact of the contact
surface 38' of the cam 38 with the pad 41, the degree of peloading, and
the distances of the pad from the pivot shaft 22 are all selected so that
a predetermined amount of seat loading in the direction of the arrow can
be accommodated in the deflection range which is available. Obviously,
when there is a large distance over which loading can be absorbed, the pad
41 can be selected to have a lower spring rate than when space is more
restricted. The lower spring rate would be more comfortable to the lighter
occupant since he could deflect such a spring over a greater distance than
he could deflect a stiffer spring.
An example of one satisfactory construction which provides good isolation
utilized pads 41 of Buna N rubber having a durometer of 40 Shore A which
are 1.2" thick, 1.2" wide and 1.9" high. The cams 38 have a 1.5" outer
diameter and a width of 0.75" in contact with the pads 41. The pads are
compressed or preloaded by 34 pounds each, causing a 0.22" deflection. The
maximum compression of the pads before a limit stop (not shown) is
contacted is 134 pounds each, providing a total deflection of 0.5", or 100
pounds and 0.28" beyond the preload compression. If one considers the
loading of the seat back 12 by the occupant to be at a distance of 12"
from the pivot axis 22 and if the pads 41 are compressed at a point 3"
from the pivot axis, the lengths of the upper and lower lever arms
relative to the axis 22 bear a relationship of 4:1. Thus, if each pad 41
is fully compressed by a load of 134 pounds, the pair of pads will absorb
268 pounds which can be applied by applying a load of 67 pounds at a point
12" above the axis 22. The pads can thus absorb 1.86 g of acceleration for
a large or 95th percentile man weighing 221 pounds who would normally
exert a 36 pound static force on the seat back. An average or 50th
percentile man weighing 166 pounds and exerting a 27 pound static force
could have 2.5 g of acceleration absorbed and a light or 5th percentile
man weighing 105 pounds could have 3.9 g of acceleration absorbed. The
preceding figures are based on the assumption that about 76% of a person's
weight is carried by the seat and 24% by the floor and that about 22% of a
person's weight which is applied to the seat is applied to the seat back
when he is seated comfortably. In the present example, the light, or 5th
percentile man, who weighs 105 pounds will not cause the seat back to
deflect when he sits down since the 17 pounds he applies to the seat back
at a point 12" above rod 22 will exactly equal the 34 pound preload
applied to each of the pads 41 at a point 3" below the rod 22. Thus,
lighter occupants will not have to adjust the seat back angle from its
normal position.
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