U.S. patent application number 09/739908 was filed with the patent office on 2001-07-05 for road surface friction measuring method and device therefor.
This patent application is currently assigned to National Aerospace Laboratory of Science & Technology Agency. Invention is credited to Kai, Takashi, Sotozaki, Tokuo, Ueda, Tetsuhiko.
Application Number | 20010006002 09/739908 |
Document ID | / |
Family ID | 18487966 |
Filed Date | 2001-07-05 |
United States Patent
Application |
20010006002 |
Kind Code |
A1 |
Ueda, Tetsuhiko ; et
al. |
July 5, 2001 |
Road surface friction measuring method and device therefor
Abstract
Provided is a road surface friction coefficient measuring method
and device for measuring the friction coefficient of road surfaces
such as roads and runways, and which can be used by being mounted
on a general car. This device has a spindle 5 detachably connected
to the wheel of a travelling wheel 3 of a car, a support arm 6
oscillatably connected to the spindle, and a measuring wheel
supported rotatably by the support arm. Provided to the support arm
6 are a vertical load generating mechanism for applying a vertical
load to be added to the self weight of the measuring wheel 8, a
first detection unit for detecting the vertical load that is
applied to the measuring wheel from the road surface, a rotation
transmission mechanism for transmitting to the measuring wheel the
rotation of the spindle so as to provide a circumferential velocity
difference between the travelling wheel and the measuring wheel,
and a second detection unit for detecting the rotational resistance
incurred by the measuring wheel from the road surface. The road
surface friction coefficient is calculated with a computing unit
based on the self weight of the measuring vehicle including the
detected values of these detection units and the arm.
Inventors: |
Ueda, Tetsuhiko; (Tokyo,
JP) ; Sotozaki, Tokuo; (Tokyo, JP) ; Kai,
Takashi; (Tokyo, JP) |
Correspondence
Address: |
ARMSTRONG,WESTERMAN, HATTORI,
MCLELAND & NAUGHTON, LLP
1725 K STREET, NW, SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
National Aerospace Laboratory of
Science & Technology Agency
Tokyo
JP
|
Family ID: |
18487966 |
Appl. No.: |
09/739908 |
Filed: |
December 20, 2000 |
Current U.S.
Class: |
73/9 |
Current CPC
Class: |
B60T 8/172 20130101;
G01N 19/02 20130101 |
Class at
Publication: |
73/9 |
International
Class: |
G01N 019/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 1999 |
JP |
11-366897 |
Claims
What is claimed is:
1. A road surface friction coefficient measuring method, comprising
the steps of: providing a measuring wheel on the outside of the
travelling wheel of a car via a support arm provided oscillatably
about the axis line of said travelling wheel; generating frictional
force of said measuring wheel to the ground surface by rotatably
driving said measuring wheel so as to have a prescribed difference
in circumferential velocity with said travelling wheel; generating
a vertical load to be added to the self weight of said measuring
wheel by applying a prescribed vertical load to said measuring
wheel; and measuring said frictional force and said vertical load
and calculating the road surface friction coefficient based on said
measured values.
2. A road surface friction measuring device, comprising: a spindle
connected and secured to the outside of a travelling wheel of a car
on the axis line to the axle; a support arm one end of which is
rotatably connected about the axis line of said spindle and the
other end of which is provided to be vertically ocsillatable; a
measuring wheel rotatably supported about the axis line parallel to
the spindle at a position apart from the spindle at said other end
of said support arm; a rotation transmission mechanism for
transmitting to the measuring wheel the rotation of the spindle so
as to provide a prescribed difference in circumferential velocity
between said travelling wheel and measuring wheel; a vertical load
generating mechanism for applying a vertical load to be applied to
the self weight of said measuring wheel; first detection means for
detecting said vertical load; second detection means for detecting
the frictional force upon said measuring wheel slipping and
rotating on the road surface; and computing means for calculating
the slip friction coefficient to the road surface and measuring
wheel based on the detected values respectively obtained from the
first detection means and second detection means and the self
weight of the measuring wheel including the arm.
3. A road surface friction measuring device according to claim 2,
wherein said spindle is detachably mounted on the wheel of the
travelling wheel.
4. A road surface friction measuring device according to claim 2 or
claim 3, wherein said rotation transmission mechanism comprises one
among a gear train transmission mechanism, chain transmission
mechanism, bevel gear transmission mechanism, or belt transmission
mechanism.
5. A road surface friction measuring device according to claim 2 or
claim 3, wherein said vertical load generating mechanism comprises
a disk brake mechanism in which a brake disk is secured to said
spindle side and a caliper is provided on the support arm side, so
that braking force is applied to said travelling wheel from said
support arm, a vertical load to be added to the self weight of the
measuring wheel is generated as a reactive force.
6. A road surface friction measuring device according to claim 2 or
claim 3, wherein said vertical load generating mechanism is of a
structure in which a power generator is provided to said support
arm side and braking force is obtained from power generated by
rotating said power generator with said spindle.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is directed to a road surface friction
coefficient measuring method and device therefor to be utilized in
managing the surface of roads on which vehicles such as a car
travel or of airport runways.
[0003] 2. Description of the Related Art
[0004] Conventionally, the measurement of the road surface friction
coefficient for managing roads and airport runways was ordinarily
conducted by running a measuring vehicle comprising a measuring
device. For example, with the measuring vehicle 31 shown in FIG. 4
and FIG. 5, a front-wheel-drive vehicle is remodeled and a
measuring wheel 33 for measuring the friction coefficient of the
road surface G is provided inside the rear trunk room 32. This
measuring wheel 33 comprises at the periphery thereof a tire having
proximate characteristics of a tire of cars or aircraft that travel
on the road surface G, and is mounted on the axle 35 of the
travelling wheel 34 via a support arm 36.
[0005] The front end of the support arm 36 is rotatably connected
to the axle 35 and the rear end thereof supporting the measuring
wheel 33 is vertically oscillatable. The measuring wheel 33
contacts the road surface G pursuant to its own weight and the
weight of the support arm 36 at the time of measurement. Moreover,
rotation of the rear travelling wheel 34 is transmitted to the
measuring wheel 33 via a rotation transmission mechanism not shown
provided within the support arm 36. Here, when the travelling wheel
34 rotates on the road surface G without slipping due to the
difference in the circumferential velocity of the measuring wheel
and the circumferential velocity of the travelling wheel, the
measuring wheel 33 is structured so as to rotate while slipping on
the road surface G at a prescribed slip ratio.
[0006] When the measuring wheel 33 travels on the road surface G
while slipping, the rotational resistance incurred by the measuring
wheel 33 due to the friction with the road surface G is detected by
a torque detection means provided within the aforementioned
rotation transmission mechanism. A computing device 37 successively
calculates the sliding friction of the road surface G to the
measuring wheel 33 pursuant to the value detected by the torque
detection means described above and the value of the vertical load
of the measuring wheel 33 on the road surface incurred by the
support arm 36 and its own weight. This calculation result is
indicated on the display installed in the measuring vehicle or
printed with a printer. Further, a measurement method wherewith a
tractional car is equipped with the above-mentioned measurement
device has also been conducted heretofore.
[0007] Moreover, as another conventional method of measuring the
friction coefficient of the road surface, a method is known wherein
a tractional measuring vehicle with a pair of wheels mutually
facing opposite directions obliquely to the travelling direction is
connected to the rear portion of a vehicle to be tracted along the
road surface. In this tractional measuring car, the mutually
inclined wheels are rotatably mounted respectively to a pair of
frames connected in an approachable/separable manner. A load cell
is disposed between these frames and this load cell detects the
frictional force acting upon the horizontal direction of the
respective wheels inclined from the road surface when the
tractional measuring car travels on the road surface. The friction
coefficient is thereby calculated based on this detected value and
the value of the vertical load acting upon the respective wheels
from the road surface due to the self weight of the tractional
measuring car.
[0008] In addition, as another method for measuring the road
surface friction coefficient, known is a method of running a
vehicle equipped with an accelerometer on the road surface to be
measured and measuring the friction coefficient from the
deceleration (negative acceleration) upon applying brakes.
[0009] With the aforementioned method of measuring the friction
coefficient of a road surface utilizing the measuring car shown in
FIG. 4 and FIG. 5, the measuring car has a special structure in
which a measuring wheel is provided inside the trunk room, and
there is a problem in that the costs for remodeling the vehicle
body becomes high. Further, upon measuring the friction coefficient
of a road surface by tracting a tractional measuring vehicle with a
car, it is necessary to make the measuring vehicle heavy to a
certain degree such that the wheel can obtain the vertical load
from the road surface. As a result, there is a problem in that the
size of the measuring vehicle becomes large and the influence of
the tractional car becomes great. Moreover, with the tractional car
having a pair of wheels arranged obliquely to the travelling
direction, there is a problem in that such type of tractional car
is inappropriate for measuring snow/ice road surfaces because, in
addition to the frictional force acting from the resisting force
upon the wheels oblique to the travelling direction of the
measuring vehicle, the resisting force arising from proceeding
while scraping the snow and ice is also applied.
[0010] Further, with the method of measuring the friction
coefficient of a road surface with a car equipped with an
accelerometer, there is a problem in that differences arise in the
measured values due to the manner of applying the brakes. In
addition, it is not possible to use this method for continuous
measuring the friction coefficient of airport runways, and there is
a problem in that this method can only be used in a limited
context.
SUMMARY OF THE INVENTION
[0011] An object of the present invention is to resolve the
problems of the conventional technology described above, and to
provide a road surface friction coefficient measuring method and
device therefor which can be used by being easily installed in a
general car and is capable of measuring the friction coefficient of
various road surfaces, such as roads and runways, at a high degree
of accuracy.
[0012] A road surface friction coefficient measuring method
according to the present invention for achieving the aforementioned
object comprises the steps of: providing a measuring wheel on the
outside of the travelling wheel of a car via a support arm provided
oscillatably about the axis line of the travelling wheel;
generating frictional force of the ground surface to the measuring
wheel by rotatably driving the measuring wheel so as to have a
prescribed difference in circumferential velocity from the
travelling wheel; applyingg a vertical load to be added to the self
weight of the measuring wheel by applying a prescribed vertical
load to the measuring wheel; and measuring the frictional force and
the vertical load and calculating the road surface friction
coefficient based on the measured values.
[0013] And a road surface friction measuring device according to
the present invention for achieving the aforementioned road surface
friction coefficient measuring method comprises: a spindle
connected and secured to the outside of a travelling wheel of a car
on the axis line to the axle; a support arm in which one end
thereof is rotatably connected about the axis line of the spindle
and the other end thereof is supporting the axle of measuring
wheel; a measuring wheel rotatably supported about the axis line
parallel to the spindle at a position apart from the spindle at the
other end of the support arm; a rotation transmission mechanism for
transmitting to the measuring wheel the rotation of the spindle so
as to provide a prescribed circumferential velocity difference
between the travelling wheel and measuring wheel; a vertical load
generating mechanism for applying a vertical load to be added to
the self weight of the measuring wheel; first detection means for
detecting the vertical load; second detection means for detecting
the frictional force upon the measuring wheel slipping and rotating
on the road surface; and computing means for calculating the slip
friction coefficient to the road surface and measuring wheel based
on the detected values respectively obtained from the first
detection means and second detection means and the self weight of
the measuring wheel including the arm.
[0014] By mounting the spindle detachably on the wheel of the
travelling wheel, the device can be easily installed in a general
car. Employed as the rotation transmission mechanism may be one
among a gear train transmission mechanism, chain transmission
mechanism, bevel gear transmission mechanism, or belt transmission
mechanism. The vertical load generating mechanism may, for example,
comprise a disk brake mechanism in which a brake disk is secured to
the spindle side and a caliper is provided on the support arm side,
apply braking force to the travelling wheel from the support arm,
and generate a vertical load to be added to the self weight of the
measuring wheel as a reactive force. In addition, adequately
employed as a vertical load generating mechanism may be a structure
in which a power generator is provided to the support arm side and
which obtains braking force by power generation upon rotating the
power generator with the spindle, or a structure having a counter
wheel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a side view showing the schematic structure of a
car equipped with a road surface friction measuring device of the
present invention;
[0016] FIG. 2 is a front view showing the schematic structure of a
car equipped with a road surface friction measuring device of the
present invention;
[0017] FIG. 3 is a plan schematic of the substantial parts
thereof;
[0018] FIG. 4 is a side view showing the schematic structure of a
car equipped with a conventional road surface friction measuring
device; and
[0019] FIG. 5 is a plan view showing the schematic structure of a
car equipped with a conventional road surface friction measuring
device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] The embodiments of the present invention are now described
in detail with reference to the relevant drawings. FIG. 1 is a side
view of a car equipped with the road surface friction measuring
device of the present invention, and FIG. 2 is the front view
thereof and FIG. 3 is a typical plan view of the substantial parts
thereof. The road surface friction measuring device 1 is used by
being detachably secured and connected to the wheel of a travelling
wheel 3 on one side of the measuring vehicle 2. As the measuring
vehicle 2 used for measuring the road surface friction coefficient,
general vehicles such as passenger cars may be used.
[0021] The road surface friction measuring device 1 of this
embodiment has a spindle 5 on the outside of the rear travelling
wheel 3, which is the drive wheel, mounted on the axle 4 (FIG. 3)
thereof. The spindle 5 is detachably secured to the travelling
wheel 3 so as to protrude toward the outside of such travelling
wheel 3 in a cantilever manner. In this embodiment, a mounting
flange 5' is formed on one end of this spindle 5 and detachably
secured to the wheel 13 of the travelling wheel with a plurality of
bolts 14, and the spindle 5 rotates integrally with the axle 4.
Nevertheless, the means for connecting the axle 4 and spindle 5 is
not limited thereto. Moreover, one end of a support arm 6 is
rotatably connected about the axis line of the spindle 5 via a ball
bearing 7, and the other end of the support arm 6 is directed
toward the front of the measuring vehicle so as to be capable of
oscillating within the vertical plane about the spindle 5.
[0022] A measuring wheel axis 9, to which the measuring wheel 8 is
secured in parallel to the axis line of the spindle 5, is rotatably
supported by the other end of the support arm 6. Mounted on the
periphery of the measuring wheel 8 is a tire with characteristics
similar to the tire of the car traveling on the road surface G.
Moreover, when the road surface G to be measured is a runway,
mounted on the measuring wheel 8 may be a tire with characteristics
of the tire of aircraft landing on and taking off from this road
surface G.
[0023] The measuring wheel axis 9 to which the measuring wheel 8 is
secured is structured to receive the transmission of the rotation
of the spindle 5 via a rotation transmission mechanism built in the
support arm 6.
[0024] In this embodiment, the rotation transmission mechanism is
structured of an inboard bevel gear 10 secured to the spindle 5, an
outboard bevel gear 11 secured to the measuring axis 9, and bevel
gears 19 and 20 secured to the drive shaft 12 connected between the
inboard and outboard bevel gears. With the rotation transmission
mechanism, the measuring wheel 8 is made to rotate at a smaller
circumferential velocity than that of the travelling wheel 3 when
the travelling wheel 3 rotates in connection with the running of
the measuring vehicle 2.
[0025] Moreover, provided between the support arm 6 and the spindle
5 is a disk brake as the vertical load generating mechanism for
applying a prescribed vertical load by the support arm 6 to the
spindle 5. This disk brake has a brake disk 15 secured to the
spindle 5 and a caliper 16 supported on the support arm side.
Between the caliper 16 and the support arm 6, a load cell 21 as the
first detection means of the present invention is provided for
detecting the reactive force incurred upon the caliper 16
sandwiching the brake disk 15 from both sides and braking.
[0026] When the measuring vehicle 2 is running on the road surface
G, the brake disk applies rotational resistance by braking the
spindle and makes the momentum that presses the measuring wheel 8
against the road surface G to the support arm 6 as a counteraction.
Therefore, the measuring wheel 8 is pressed against the road
surface G by the momentum and the self weight of the support arm 6
and measuring wheel 8, and the counteraction thereof acts as the
vertical load of the measuring wheel 8.
[0027] Meanwhile, the measuring wheel 8 slips on the road surface G
at a prescribed slip ratio due to the difference in the
circumferential velocity of the travelling wheel 3 and the
measuring wheel 8. Thereupon, rotational resistance is added to the
measuring wheel 8 due to the frictional force incurred by the
measuring wheel 8 from the road surface G in accordance with the
vertical load. In this embodiment, the rotational resistance is
detected as the torque imparted to the drive shaft. Specifically,
the rotational resistance is detected with a load cell or strain
gauge 22 as the second detection means of this invention mounted on
the shaft.
[0028] The detection outputs of the first detection means and the
second detection means are sent to the microprocessor inside the
measuring vehicle 2 via a signal cable not shown. Thereafter,
calculation processing is conducted to such detection outputs in
order to obtain the slip friction coefficient of the road surface G
to the measuring wheel 8. The calculation results may be indicated
on a display installed in the measuring vehicle 2 or printed by
connecting the microprocessor to a printer.
[0029] Furthermore, although the microprocessor constitutes the
computing means in this embodiment, the microprocessor may be
installed in a car or built in the support arm. Moreover, a
personal computer such as a laptop computer may be connected to the
computing means in order to input the signals output from the first
detection means and the second detection means via an interface
compatible therewith. In the event of installing the computing
means in the vehicle, the transmission of signals between the first
detection means/second detection means and the computing means can
be conducted via wire or wireless by utilizing a signal cable,
telemeter, and so on.
[0030] The road surface friction measuring device of this
embodiment is structured as described above and can measure the
friction coefficient of a road surface by being connected to a
vehicle body and running on a road or runway without having to
specially remodel a general vehicle such as a passenger car. The
measurement of the road surface friction coefficient is conducted
by mounting the road surface friction measuring device on the
outside of the travelling wheel of a car and running such car.
[0031] By the travelling wheel 3 of the car rotating without
slipping on the road surface, the spindle 5 integrally rotates
therewith and such rotation is transmitted to the measuring wheel 8
via the rotation transmission mechanism. The measuring wheel 8
rotates at a rotational speed so as to generate a predetermined
difference in the circumferential velocity from the travelling
wheel 3 of the car. Therefore, a prescribed slip ratio is applied
pursuant to the difference in the circumferential velocity of the
travelling wheel of the car and the measuring wheel, frictional
force acts upon the moving measuring wheel 8 from the road surface,
and this becomes the rotational resistance of the measuring wheel
8. The force which applies the slip ratio is equivalent to the
ground surface frictional force.
[0032] The force which applies the slip ratio is detected by the
second detection means. A strain gauge 22 attached to the drive
shaft is used as the second detection means in this embodiment and,
by detecting the rotational torque acting upon the transmission rod
pursuant to the strain gauge, the rotational resistance of the
measuring wheel is measured and the ground surface frictional force
acting upon the measuring wheel from the road surface is indirectly
measured.
[0033] Further, while measuring the road surface friction
coefficient, brake is applied to the spindle 5 by the vertical load
generation mechanism (disk brake in this embodiment) for applying a
vertical load from the support arm 6 side to the spindle. Pursuant
to this counteraction, momentum that presses the measuring wheel 8
to the road surface G acts upon the support arm 6 provided facing
the forward traveling direction. Nevertheless, the braking force of
the spindle resulting from the vertical load generating mechanism
for applying a vertical load must be within a range which will not
cause a large slip to the travelling wheel 3. In addition to the
load from the momentum, load from the self weight of the support
arm 6 and measuring wheel 8 also acts upon the road surface, and
the counteraction of these loads is applied as the vertical load
necessary in measuring the road surface friction coefficient. By
detecting the reactive force incurred by the caliper 16 provided to
the support arm 6 with the first detection means, the vertical load
added to the measuring wheel 8 is indirectly measured.
[0034] The detected value of the aforementioned first detection
means relates to the size of the vertical load incurred by the
measuring wheel from the road surface, and the detected value of
the second detection means relates to the frictional force acting
upon the measuring wheel from the road surface. Thus, by inputting
to the computing means these detected values as well as the self
weight of the measuring wheel, the computing means calculates the
added vertical load incurred by the measuring wheel from the road
surface upon correcting the weight of the support arm and measuring
wheel in view of the detected value of the first detection means,
calculates the frictional force acting upon the measuring wheel
from the road surface corresponding to the detected value of the
second detection means, and calculates the slip friction
coefficient of the road surface to the measuring wheel.
[0035] Although a preferred embodiment of the present invention was
described above, this invention is not limited to the
aforementioned embodiment and may be changed within the range of
the technical idea thereof.
[0036] For instance, without restriction to the bevel gear rod
mechanism of the aforementioned embodiment as the rotation
transmission mechanism, employed may be a chain transmission
mechanism, gear train transmission mechanism, or belt transmission
mechanism such as a timing belt. Moreover, as the vertical load
generating mechanism, without restriction to the mechanism which
generates a vertical load by applying braking force to the
travelling wheel side from the support arm side and using the
counteraction thereof, employed may be a suitable mechanism for
generating to the support arm the rotational momentum in the
direction of pressing the measuring wheel to the road surface, or a
mechanism which adds a direct vertical load with a plumb bob.
Further, in addition to the brake disk mechanism for generating a
vertical load by applying braking force to the travelling wheel
side from the support arm side and using the counteraction thereof,
employed may be, for example, an electronic brake having a
structure in which a power generator is provided to the support arm
side, and which obtains braking power by power generation by
rotating the spindle thereby, and so forth.
[0037] As described above, according to the road surface friction
coefficient measuring method and device therefor of the present
invention, there is no need to use a costly special vehicle that is
remodeled for measuring the road surface friction coefficient. As
the present invention may be used by connecting it to a travelling
wheel of ordinary vehicles such as passenger cars, it is possible
to measure the road surface friction coefficient easily, and with
low cost.
[0038] As it is possible to add a prescribed vertical load to be
added to the self weight of the measuring wheel, the bouncing of
the measuring wheel can be reduced and changes in the vertical load
of the measuring wheel can be detected thereby. As a result, the
road surface friction measuring device can be downsized as the
weight thereof can be reduced, and the precision is improved.
[0039] Moreover, as the road surface friction is calculated based
on the vertical load and rotational resistance acting from the road
surface on the measuring wheel that is constantly facing the
travelling direction, the measurement is not influenced by the
characteristics of the travelling wheel or the braking operation of
the vehicle itself conducting the measurement as when measuring the
road surface friction coefficient from the deceleration of a car
utilizing an accelerometer. Further, it is possible to obtain
highly accurate measurement results even on snow/ice roads.
* * * * *