Note: Descriptions are shown in the official language in which they were submitted.
~3~35
Description
Tapered Roller Dynamometer
Technical Field
This invention relates to dynamometers for testing
of vehicles, and more particularly to such dynamometers
having tapered rollers.
Background Art
Dynamometers are used in the testing of vehicles
to simulate a vehicle in motion by allowing the driving
wheels of the vehicle to rotate on two or more rollers.
The rollers absorb power from the wheels through some
mechanical (water brake) or electromechanical (eddy
current) means. This simulation of motion allows the
vehicle to be tested in place under realistic road
conditions for convenient measuring of, e.g., emissions
or other parameters. A dynamometer-like device is used
for testing vehicle brakes by supplying force (torque)
to the wheels to test the force available through the
braking system.
Dynamometer rollers manufactured to date have been
cylindrical in shape. However, front-wheel drive
vehicles have a strong tendency to move the drive
wheels off to the side of the dynamometer rollers,
creating a possible hazard. As a result, the operator
of a vehicle inspection program is often compelled to
use an experienced inspector trained in operation of a
front-wheel drive vehicle on a dynamometer. Thus, the
cost of testing a front-wheel drive vehicle on a
dynamometer is increased as compared to the cost of
CI-421-TS
- :, ...................... .: ,. . . ..
: :
2~310~
testing a rear wheel drive vehicle on the same
dynamometer.
Disclosure of Invention
Objects of the present invention include the
provision of apparatus having tapered rollers which
prevent the drive wheels of a vehicle riding thereon
from moving off of the rollers.
According to a first aspect of the present
invention, apparatus for retaining contact of a wheel
having a first and second sidewall includes a first
roller having a tapered body, the tapered body of the
first roller having a larger diameter at the first
sidewall of the wheel and having a constant or curved
taper to a smaller diameter towards the second sidewall
of the wheel.
In further accord with this aspect of the present
invention, the apparatus includes a second roller
having a tapered body, the tapered body of the second
roller having a larger diameter at the first sidewall
of the wheel and having a constant or curved taper to a
smaller diameter towards the second sidewall of the
wheel, the first roller and the second roller being
disposed adjacent to each other.
According to a second aspect of the present
invention, apparatus for retaining contact of a pair of
wheels disposed coaxially and having first and second
sidewalls includes first and second rollers disposed
coaxially, each roller having a tapered body, the
tapered body of the first roller having a larger
diameter at the first sidewall of a first wheel and
having a constant or curved taper to a smaller diameter
towards the second sidewall of the first wheel, the
- ; ~ '' ' -
,
203~035
tapered body of the second roller having a larger
diameter at a second sidewall of a second wheel and
having a constant or curved taper to a smaller diameter
towards the first sidewall of the second wheel.
In further accord with this aspect of the present
invention, the apparatus includes third and fourth
rollers disposed coaxially, each roller having a
tapered body, the tapered body of the third roller
having a larger diameter at the first sidewall of the
first wheel and having a constant or curved taper to a
smaller diameter towards the second sidewall of the
first wheel, the tapered body of the fourth roller
having a larger diameter at the second sidewall of the
second wheel and having a constant or curved taper to a
smaller diameter towards the first sidewall of the
second wheel, the first roller being disposed adjacent
to the third roller and the second roller being
disposed adjacent to the fourth roller.
According to a third aspect of the present
invention, apparatus for retaining contact of a wheel
having a first and second sidewall includes first and
second rollers, each roller having a tapered body, the
tapered body of the first roller having a larger
diameter at the first sidewall of the wheel and having
a constant or curved taper to a smaller diameter
towards the second sidewall of the wheel, the tapered
body of the second roller having a larger diameter at
the first sidewall of the wheel and having a constant
or curved taper to a smaller diameter towards the
second sidewall of the wheel, the first roller and the
second roller being disposed adjacent to each other.
According to a fourth aspect of the present
invention, apparatus for retaining contact of a pair of
,.. .
. .
.; ., , ~ .
2~13~035
wheels disposed coaxially, each wheel haviny a first
and second sidewall, includes first and second rollers,
each roller having a tapered body, the tapered body of
the first roller having a larger diameter at the first
sidewall of a first wheel and having a constant or
curved taper to a smaller diameter towards the second
sidewall of the first wheel, the tapered body of the
second roller having a larger diameter at the first
sidewall of the first wheel and having a constant or
curved taper to a smaller diameter towards the second
sidewall of the first wheel, the first and second
rollers being disposed adjacent to each other.
In further accord with this aspect of the present
invention, the apparatus includes third and fourth
rollers, each roller having a tapered body, the tapered
body of the third roller having a larger diameter at a
second sidewall of a second wheel and having a constant
or curved taper to a smaller diameter towards the first
sidewall of the second wheel, the tapered body of the ;
îourth roller having a larger diameter at the second
sidewall of the second wheel and having a constant or
curved taper to a smaller diameter towards the first
sidewall of the second wheel, the third and fourth
rollers being disposed adjacent to each other.
By creating rollers having an inward taper (e.g.,
shaped as a frustum of a cone), the tendency of the
vehicle wheels to move to one side of the rollers can
be overcome. Thus a less experienced or inexperienced
driver can perform a vehicle test on the dynamometer,
resulting in a significant cost savings to the
inspection program operator.
These and other objects, features and advantages
of the present invention will become more apparent in
' ~' '
, . :
. . .
~31~35
light of the detailed description of a best mode
embodiment thereof, as illustrated in the accompanying
drawing.
Brief Description of Drawing
Fig. 1 is a perspective illustration of a vehicle
dynamometer test station in which the tapered rollers
of the present invention may be utilized;
Fig. 2 is a schematic block diagram of the vehicle
dynamometer test station of Fig. 1;
Fig. 3 is an illustration of a prior art vehicle
dynamometer with cylindrical rollers;
Fig. 4A is an illustration of a vehicle
dynamometer having rollers with a constant taper in
accordance with the present invention;
Fig. 4B is an illustration of a vehicle
dynamometer having rollers with a curved taper in
accordance with the present invention;
Fig. 5 is an illustration of the tapered rollers
of the present invention having a set of vehicle
driving wheels thereon along with a related side force
analysis;
Fig. 6 is a cross sectional illustration of the
tapered roller of Figs. 4A and 4B; and
Fig. 7 is an illustration of the tapered rollers
of the present invention having a set of vehicle
driving wheels thereon along a related differential
speed analysis.
Best Mode For Carrying Out The Invention
In Fig. 1 is illustrated a typical vehicle test
station in which the dynamometer tapered rollers of the
present invention may be used. A tractor type truck 10
. :
:. :. ... -. ,, . ~
- ' : : :, . , : '
203~03~
is illustrated as an exemplary test vehicle. However,
it is to be understood that the present invention may
be used with any class of vehicles, including
automobiles, trucks or motorcycles. The test station
apparatus includes left and right (as viewed from the
driver's seat) test equipment assemblies 12,14, a test
console 16, and an annunciator panel 18 which is used
to display messages to the operator and/or driver
during vehicle testing (e.g., brake testing). An
exemplary brake test method is illustrated in U.S.
Patent No. 4,893,242 to Rogers et al., assigned to the
assignee of the present invention, and hereby
incorporated by reference.
Fig. 2 is a schematic block diagram of the test
station equipment illustrated in Fig. 1. Each assembly
12,14 includes a pair of rollers 20,21 and 22,23
respectively, which are tapered in accordance with the
present invention. Each roller may be independently,
rotatably mounted in the corresponding assembly 12,14.
Alternatively, each pair of opposing rollers 20,22 and
21,23 may be disposed coaxially and connected together
by corresponding axles (Figs. 3-6).
Depending upon the ultimate vehicle testing
application, one or both of the opposing pairs of
rollers 20,22 and 21,23 may be driven through gear
drive trains 24,26 by torque motors 28,30. For a brake
force test in accordance with the aforementioned U.S.
Patent to Rogers et al., the torque motors drive the
rollers at a nominally constant test speed. The signal
magnitude of the motor output torque is provided from
each tester on lines 32,34 to the console 16.
Each assembly 12,14 includes one ox more weight
scales 36,3~ placed beneath the roller assembly such
2~3~03~
that the scales may respond to, and measure the applied
axle weight. The scales are typically strain gauge
type. With the vehicle's front wheels placed on the
rollers, the scales provide the weight measurement in
the form of left and right axle weights on lines 40,42
to the console 16. The weights may then be processed
in accordance with the aforementioned U.S. Patent to
Rogers et al.
The console receives the torque and weight analog
signals from the assemblies 12,14 in a multi~channel
analog-to-digital (A/D) converter 44. The converter
provides the digital signal equivalent of each analog
signal magnitude to a console main bus 46 where it is
accessed by a signal processor 48. The processor 48
may be any of a known type personal computers (PCs),
with a keyboard 50, a video monitor 51, at least one
disk drive 52, with suitable kilobyte (kb) of RAM and
ROM storage. Also included within the console and
connected to the bus 46 is a known type printer 54,
along with an input/output (I/O) interface 58
connecting the console bus 16 to the annunciator 18.
In Fig. 3 is illustrated a prior art dynamometer
in which the rollers 20,21 and 22,23 of Fig. 1 are
cylindrical in nature with a rectangular cross section.
25 Each pair of opposing rollers 20,22 and 21,23 is
connected together by a corresponding axle 60,61. As
described hereinbefore, it is well known that
front-wheel drive vehicles have a tendency to move the
drive wheels to the side of this cylindrical type of
roller, creating a potential hazard.
In Fig. 4A is illustrated a dynamometer in which
the rollers 20,21 and 22, 23 of Fig. 1 have a constant
taper in accordance with the present invention. The
.
~' .~, : ,
..
' ' ,., ~
2~3~03~
rollers are tapered at an angle inward towards one
another so as to be shaped as a frustum of a cone.
Each roller has an outer cross sectional diameter 64
which is greater in magnitude that an inner cross
sectional diameter 66. As described hereinafter, the
tapered rollers have the ability to overcome the
tendency of the vehicle wheels to move to one side of
the dynamometer.
In Fig. 4B is illustrated a dynamometer in which
the rollers 20,21 and 22, 23 of Fig. 1 have a curved
taper in accordance with the present invention. The
curved taper affords the same advantages as the
constant taper described hereinbefore.
In Fig. 5 is illustrated a vehicle axle 70
connecting corresponding left and right (as viewed from
the driver's seat) vehicle wheels and associated tires
72,73, each with corresponding sidewalls. The
axle/tire configuration is illustrated in both a
neutral position 76 relative to each roller (i.e., with
no wheel rotation) and in a non-neutral position 78
relative to each roller (i.e., with wheel rotation
during vehicle test). For small angles or curvatures
of taper, the side force available in the non-neutral
position is a very small fraction of the vehicle axle
weight. It is to be noted that all numbers in Fig. 5
are exemplary and taken to be representative of a
vehicle/dynamometer configuration, e.g., that of Fig.
1.
The fractional side force available is negligible
as compared to the force due to friction between the
vehicle tire and dynamometer surface, which may
approach a value equal to the vehicle axle weight
(coefficient of friction of 1.0). Thus, contrary to
2~31~
intuition, the effect of tapering the dynamometer
rollers inward does not in a practical way create a
significant side force in achieving the desired
stability of vehicle position on the dynamometer.
For practical reasons (e.g., to minimize total
weight, inertia and cost), dynamometers are not
normally manufactured with solid rollers but rather
with hollow core rollers with finite wall thickness 80
(Fig. 6). Therefore the degree of taper achieved with
a metal cutting or machining process is limited, as
contrasted to the taper achievable with a more
expensive casting or molding process.
In Fig. 7 is illustrated the principle which
renders the dynamometer with tapered rollers in
accordance with the present invention an effective
means of pre~enting vehicle sideslip. Upon wheel
rotation during vehicle test, the vehicle tires will
reach the non-neutral position 78 on the tapered
rollers. In the example of Fig. 5, the horizontal
displacement (R3 - R2) of the tires 72,73 from the
neutral position is 6.25 inches. It follows that the
radius R2 of the roller at the left tire 72 position
becomes significantly larger than the radius R2, of the
roller at the right tire 73 position (approximately 10%
larger)~
Because the axle for both rollers is fixed, the
angular velocity (C~) is fixed and the wheel speed is
proportional to the radius of the roller. Therefore
the wheel on the larger roller radius R2 will operate
at a speed which is 10% faster than the wheel on the
smaller roller radius R2 " creating a "turn" inward to
a neutral, more stable position on the dynamometer. It
is this phenomenon, coupled with the angle of the tires
:. ~ . :: . .: ,:
.
: ' ' , ' ` :
. . .
~3103~
on the slope of the dynamometer, which creates the
restorative force to prevent the vehicle from being
driven off the dynamometer.
The following analysis calculates an amount of
5 linear taper for the constant tapered roller of Fig. 4A
to achieve a 5% differential speed at a 6.25 inch
displacement.
Rl = ROLLER DIAMETER / 2 (Equ. 1)
= 7.944"/2
= 3.972"
R = R - 0.33" ~Equ. 2)
= 3.972" - 0.33"
= 3.642"
3 1 (Equ. 3)
= 3.972" - 0.50"
= 3.472"
R = R - 0.67" (Equ. 4)
= 3.972" - 0.67"
= 3.302"
SPEED = (R2 ~ R2,)/ R3 (Equ. 5)
0.05 = (3.642" - R2,) / 3.472"
Rearranging Equation 5:
R2, = 3.642" - 0.05(3.472")
= 3.468"
-- 10 --
. . ~
' . , ' , ,
:, ,' :; , . ,.`, .,, ' : ~ ' :
:: . ... .. .
2~3~035
TAPER = (Rl - R2,) * (35.00" / 26.25") (Equ. 6)
= (3.972" - 3.468") * 1.33
= 0.504"
The calculation indicates that for as small a
taper as approximately 0.5 inches in 35 inches (a taper
angle of 0.82 degrees), the difference in wheel
velocities will be approximately 5%. This level o-f
taper is easily achievable by cutting (machining) the
outer wall of a hollow cylinder used in most
dynamometers as manufactured. It is to be understood
that the aforementioned analysis is equally applicable
to the roller having a curved taper in accordance with
Fig. 4B. The taper produces a significant stabilizing
effect on the location of the driven wheels of the
vehicle on the dynamometer.
The dynamometer with tapered rollers permits
front-wheel drive vehicles (in the case of emissions
tests) and all vehicles (in the case of higher speed
brake tests) to be tested on rollers in a safer and
more efficient manner than can be achieved with current
dynamometers with cylindrical rollers. This feature in
turn saves the cost and time of a specially trained
driver, permitting the general public to operate their
own vehicles on dynamometers, thereby reducing the
overall costs of performing vehicle tests on
dynamometers.
: : :, : :: , , :,;
. : . . .,~ . .: ;: .
2 ~ 3 ~
Although the invention has been illustrated and
described with resp~ct to a best mode embodiment
thereof, it should be understood by those skilled in
the art that the foregoing and various other changes,
omissions, and additions in the form and detail thereof
may be made without departing from the spirit and scope
of the invention.
We claim:
: . : .- :
:
