FIELD OF INVENTION
This invention relates to a test jig and a method for determining center of
gravity of vehicle seat. -
BACKGROUND OF THE INVENTION
In certain automotive testes, CG of the seat is required to be determined for
application of load therethrough. The center of gravity (CG) of an object is the
point from which if suspended, the object always remains stable by getting
balanced. This is also called center of mass of the object, or the theoretical
point at which the entire weight of the object is assumed to be concentrated.
A general shaped object requires a simple mechanical way to determine its
center of gravity.
When the object is balanced using a string on an edge, the point at which the
object is balanced is the center of gravity. Another more complicated way is a
two-step method, which is as follows:
Hanging the object from any point followed by dropping a weighed string from
the same point. Thereafter, a line is drawn on the object along the string.
The procedure is repeated from another point on the object followed by drawing
of two lines on the object. The center of gravity is the point where the lines
intersect. This procedure works well for irregularly shaped objects that are
hard to balance.
Thus, in case of two dimensional objects, an experimental method for locating
the center of mass in a particular plane is to suspend the object from two
locations and drop plumb lines from the suspension points. The intersection of
the two lines is the center of mass located in the plane formed by the two
points and the plumb lines.
The shape of an object might already be mathematically determined, but it may
be too complex to use a known formula. In this case, the complex shape can be
sub divided into simpler, more elementary shapes, whose centers of mass are
easy to find. In case, the total mass and center of mass can be determined for
each area, the center of mass of the whole object is the average of the CGs.
'f'his method can even work for objects with holes, which can be accounted for
as negative masses.
Further, a direct development of the planimeter known as an integraph, or
integeometer, can be used to establish the position of the centroid or center of
mass of an irregular two-dimensional object. This method can be applied to a
shape with an irregular, smooth or complex boundary where other methods are
too difficult to use. It was usually used by ship builders to compare with the
required displacement and centre of buoyancy of a ship and ensure whether it
would not capsize.
For three dimensional object:
In case, the mass of the object is not uniformly distributed, calculus should be
used to determine center of gravity. The symbol S dw is used to denote the
integration of a continuous function with respect to weight. Then the center of
gravity can be determined from cg * W = a * S dw.. . eq. 1
Where, a is the distance from a reference line, dw is an increment of weight,
and W is the total weight of the object. To evaluate the best seat design, it is
required to determine how the weight varies geometrically.
However, this theory is very tedious to apply for determining the C.G of
irregular three dimensional objects.
Further, drawbacks are as follows:-
1. Limitation of accuracy and requirement of more iteration for applying the
concept.
2. In some cases, the properties of materials like seat cushions, recliner
mechanism, are not available since these are propriety parts.
Necessity of the Center of gravity of vehicle seat:-
As per IS 15 139 standard:
a) 3 point belt should sustain a load of 13500N for 0.2s.
b) 2 point belt should sustain a load of 22500N for 0.2s.
c) 20 times weight of seat to be applied on the center of gravity of seat, if an
anchorage point is on the seat.
Therefore, precise location of C.G is required to be determined. Hence, the
present invention proposes a test jig and method for determining center of
gravity of vehicle seat precisely.
OBJECTS OF THE INVENTION
Primary object of the present invention is to provide a test jig and a method for
determining center of gravity of vehicle seat, which overcomes disadvantages
associated with the prior art.
Another object of the present invention is to provide a test jig and a method for
determining center of gravity of vehicle seat which is simple.
Further object of the present invention is to provide a test jig and a method for
determining center of gravity of vehicle seat which is reliable.
SUMMARY OF THE INVENTION
According to this invention, there is provided a test jig for determining center of
gravity of vehicle seat comprising of a pivot mounted with a frame having
provision for mounting of vehicle seat on one side, on the other side of which a
dead weight is provided for balancing weight of the seat.
Further, according to this invention there is also provided a method for
determining center of gravity of vehicle seat comprising steps of:- balancing a
test jig, mounting the seat on the jig, balancing weight of the seat with a
counter weight to determine centre of gravity of the seat.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Further objects and advantages of this invention will be more apparent from
the ensuing description when read in conjunction with the accompanying
drawings and wherein:
Fig. 1 shows: use of load balancing equation for determining C.G of vehicle
seat.
Fig. 2 shows: set up of the present invention to determine C.G of seat.
Fig. 3 shows: seat mounting points for mounting of vehicle seat.
Fig. 4 shows: test jig mounted with vehicle seat according to the present
invention.
Fig. 5 shows: various components of the test jig.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING DRAWINGS
Conventional methods of determining C.G are difficult to apply for threedimensional
big objects like automobile seats. However, C.G can also be
determined using computer modeling but constraint is unavailability of
rnaterial properties of all components used in automobile seats. Hence, the
present invention discloses a test jig and method for determining center of
gravity of vehicle seat to obviate the above discussed problems.
The method allows easy and accurate measurement of C.G for test purposes.
The method uses basic principles of physics to avoid cumbersome
calculations/ processes.
The invention comprising of a test jig for mounting the vehicle seat to
determine its center of gravity. Now, reference may be made to fig. 1 in, which
load balancing equation of L, w, = L, w, is used to obtain C.G of the seat.
Where W1 = weight of the seat
W2 = counter balance weight for balancing weight of the seat.
L2 - Distance of counter balance weight from the pivot point on the jig.
L1 - Distance of CG of the seat from the pivot point.
Now, reference may be made to fig. 2 wherein the set up comprising of a
mounting (M) for mounting the seat thereon to obtain its C.G. During the
tcsting, the seat (S) is mounted facing downward and outwardly from the set
The seat mounting points (M) are indicated in fig. 3 for mounting seat thereon
by means of seat mounting fasteners (F) wherein weight of said seat is W1 as
shown in fig. 2.
Said jig is balanced under maximum weight of the seat relying on the balancing
theory of L2>L1 as already discussed to fix the pivot point (P) of jig.
Balancing of the seat of weight W1 is carried out with the help of dead weight of
particular weight W2 by sliding it from pivot point (P) towards the end. The
weight of dead weight is such that, it is comfortable for user to balance the
scat.
The seat is balanced with the dead weight at a particular distance (h)fro m the
pivot point as shown in figure 2 by sliding the dead weight from the pivot point.
The point of balancing is indicated by the sprit leveler (L).
The distance L:! is noted from the measuring tape of the jig.
After knowing three factors i.e. W1, W2 and L2, Li is determined by using the
equation
Thus, L1, indicates the point, at which entire weight of the seat is concentrated
i.e. centre of gravity of seat.
However, following required to be considered before determination of C.G:-
1. Test jig should be balanced before mounting the seat.
2. Seat is required to be mounted as ideal case as in the vehicle. It's four
mounting locations are maintained accordingly (X, Y, Z plane coordinates).
3. Condition of seat for which C.G is found:
a) Recliner in the design position.
b) Seat slider in the test position.
The test jig of the invention is as shown in fig. 4 and 5, in which a stand (1) is
provided to support a pivot point (2) provided at the end of a longitudinal
member (3) as shown in the fig. 5. The longitudinal member constituting a rod
is mounted below a frame (4). The frame is provided with a measuring tape (5)
starting from the pivot point upto the distal end of the frame. Further, a sprit
level (6) is provided on the frame to confirm balancing of the seat.
Again, at one end of the frame, there is provision for seat mounting (7) with a
plurality of seat mounting points (M) for mounting of vehicle seat, in which seat
mounting position can be adjusted.
To balance the seat, a dead weight (W2) is supported on a roller arm (A) across
the frame, wherein the arm is connected with a roller (R) at both ends. So that,
said arm is slidable from the pivot point upto the end of said frame. So that,
required distance (L2) can be obtained to determine C.G of the seat (W1)
provided at a distance (Ll) from the pivot point.
. I I " ,
-.
The dead weight is preferably made of rubber. Further, a ball bearing (B) is
provided in the test jig.
The test jig can be made of any material such as Iron. It can be manufactured
by the method of forging, casting without restricting scope of the invention to
the same. Thus, other materials and methods readily apparent to person
skilled in the art are understood to be within scope of the invention.
Test Results
I SPECIFICATION 1 SAMPLE I SAMPLE 2
I I
/ C.G from recliner spring 1 65 mm
I center I I I
I CAD calculation
I 1 62 mm
I
171 mm - - - - - - - . - ****** I Percentage Correlation 1 95.16 1 94.36
Thus, the jig is provided to evaluate the C.G. of the seat. This jig's calculated
value is more reliable than the theoretically estimated value, since there are
variations between actual properties of materials and those provided in the
CAD.
" , / < " &: ,-"J'Fdg\L
1 3 NOV 2013
The jig and above mentioned process can also be used to calculate C.G of
objects/ test parts other than automotive seats.
It is to be noted that the present invention is susceptible to modifications,
adaptations and changes by those skilled in the art. Such variant embodiments
employing the concepts and features of this invention are intended to be within
the scope of the present invention, which is further set forth under the
following claims:

WE CLAIM:

1. Test jig for determining center of gravity of vehicle seat comprising of a
pivot mounted with a frame having provision for mounting of vehicle seat
on one side, on the other side of which a dead weight is provided for
balancing weight of the seat.
2. Test jig as claimed in claim 1, wherein the pivot with the frame is
mounted on a stand.
3. Test jig as claimed in claim 1 or 2, wherein a measuring tape is provided
on the frame starting from the pivot point upto end of the frame.
4. Test jig as claimed in any of the preceding claims, wherein a sprit level is
provided on the frame for confirming balancing of the vehicle seat.
5. Test jig as claimed in any of the preceding claims, wherein the dead
weight is supported on a roller arm across the frame, in which a roller is
provided at each end of said arm to slide the dead weight from the pivot
for balancing the seat.
6. A method for determining center of gravity of vehicle seat comprising
steps of:-
- balancing a test jig
- mounting the seat on the jig
- balancing weight of the seat with a counter weight to determine
centre of gravity of the seat.
7. A method for determining center of gravity as claimed in claim 6, wherein
the seat is mounted on the jig according to the design co-ordinates of the
seat mount.
8. A method for determining center of gravity as claimed in claim 6 or 7,
wherein the seat is mounted on datum point and its all supporting
fasterners are counter weighed while mounting the seat on the test jig.
9. A test jig and a method for determining center of gravity of vehicle seat
substantially as herein described with reference to the accompanying
drawings.