U.S. patent application number 13/609695 was filed with the patent office on 2014-03-13 for tire sidewall load estimation system and method.
The applicant listed for this patent is John Michael Fenkanyn, Amrita Patel, Kanwar Bharat Singh, Peter Jung-min Suh. Invention is credited to John Michael Fenkanyn, Amrita Patel, Kanwar Bharat Singh, Peter Jung-min Suh.
Application Number | 20140069181 13/609695 |
Document ID | / |
Family ID | 49118424 |
Filed Date | 2014-03-13 |
United States Patent
Application |
20140069181 |
Kind Code |
A1 |
Singh; Kanwar Bharat ; et
al. |
March 13, 2014 |
TIRE SIDEWALL LOAD ESTIMATION SYSTEM AND METHOD
Abstract
A system and method of estimating a load bearing on a vehicle
tire includes an inflation pressure measuring sensor attached to
the tire for measuring a tire cavity inflation pressure level; and
one or more piezofilm deformation measuring sensors mounted to one
or both of the tire sidewalls. The deformation measuring sensor
generates within the tire footprint a deformation signal having
signal power level indicative of a level of sidewall deformation
within the footprint contact patch. Power-to-load maps adjusted for
tire inflation pressure are generated and stored for the tire, the
maps correlating a range of load levels to a range of signal power
levels whereby operatively enabling a load level to be identified
for each signal power level on an inflation pressure adjusted
basis.
Inventors: |
Singh; Kanwar Bharat; (Stow,
OH) ; Fenkanyn; John Michael; (Akron, OH) ;
Patel; Amrita; (Copley, OH) ; Suh; Peter
Jung-min; (Copley, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Singh; Kanwar Bharat
Fenkanyn; John Michael
Patel; Amrita
Suh; Peter Jung-min |
Stow
Akron
Copley
Copley |
OH
OH
OH
OH |
US
US
US
US |
|
|
Family ID: |
49118424 |
Appl. No.: |
13/609695 |
Filed: |
September 11, 2012 |
Current U.S.
Class: |
73/146.3 |
Current CPC
Class: |
B60C 2019/004 20130101;
B60C 23/064 20130101; B60C 23/0408 20130101 |
Class at
Publication: |
73/146.3 |
International
Class: |
B60C 23/04 20060101
B60C023/04 |
Claims
1. A method of estimating a load on a vehicle tire, comprising: (A)
attaching at least one deformation measuring sensor to at least one
sidewall of the vehicle tire, the deformation measuring sensor
generating a cyclical deformation signal having a signal power
level indicative of a deformation of the one sidewall in the tire
under a rolling condition; (B) attaching a tire inflation pressure
measuring sensor to the vehicle tire, the inflation pressure
measuring sensor measuring tire inflation pressure within a tire
cavity and generating detected inflation level data; (C)
electronically storing power-to-load maps adjusted for tire
inflation pressure for the tire, the maps correlating a range of
load levels to a range of signal power levels whereby operatively
enabling a load level to be identified for each signal power level
adjusted for tire inflation pressure; (D) measuring a detected
signal power level of a deformation signal from the deformation
measuring sensor; (E) measuring a detected inflation level from the
tire cavity by means of the tire inflation pressure measuring
sensor; (F) extracting from the signal power-to-load maps a tire
pressure level-adjusted estimated load level corresponding to a
detected signal power level.
2. The method of claim 1, wherein further comprising attaching at
least one inner deformation measuring sensor in an axially inwardly
located tire sidewall and attaching at least one outer deformation
measuring sensor in an axially outwardly located tire sidewall; and
measuring a detected inner signal power level from the inner
deformation measuring sensor; and measuring a detected outer signal
power level from the outer deformation measuring sensor; and
averaging the detected inner signal power level with the outer
signal power level to create an averaged detected signal power
level.
3. The method of claim 2, wherein further comprising using the
averaged detected signal power level to extract from the signal
power-to-load maps an estimated load level corresponding to the
averaged detected signal power level at the detected inflation
level.
4. The method of claim 1, wherein further comprising comparing the
estimated load level from the signal power-to-load maps to an
overload threshold load level; and generating a warning signal in
the event that the estimated load level exceeds the overload
threshold load level.
5. The method of claim 1, wherein attaching at least one
deformation measuring sensor in at least one sidewall of the
vehicle tire comprises attaching a cantilever piezofilm strain
sensor to the tire one sidewall.
6. A system of estimating a load bearing on a vehicle tire,
comprising: (A) a vehicle tire having a tire cavity and supporting
a load; (B) an inflation pressure measuring sensor attached to the
tire for measuring a tire cavity inflation pressure level; (C) at
least one deformation measuring sensor mounted to at least one of
the tire sidewalls, the deformation measuring sensor comprising a
piezoelectric sensor rotating with the tire sidewall through a tire
footprint, the deformation measuring sensor generating within the
tire footprint a deformation signal having signal power level
indicative of a level of sidewall deformation within the footprint
contact patch; (D) electronically stored power-to-load maps
adjusted for tire inflation pressure for the tire, the maps
correlating a range of load levels to a range of signal power
levels whereby operatively enabling a load level to be identified
for each signal power level adjusted for tire inflation pressure;
and (E) electronic means for extracting from the signal
power-to-load maps a tire pressure level-adjusted estimated load
level corresponding to a detected signal power level.
7. The system of claim 6, wherein the deformation measuring sensor
comprises a piezoelectric strain sensor.
8. The system of claim 7, wherein the piezoelectric strain sensor
comprises a piezofilm strain sensor.
9. The system of claim 6, wherein further comprising at least one
deformation measuring sensor mounted to a first sidewall and at
least a second deformation measuring sensor mounted to an opposite
second sidewall, the first and the second sidewall deformation
measuring sensors each measuring a bending of the respective first
and second opposite sidewalls within a rolling tire footprint and
generating respectively a first signal having a first detected
signal power level and a second signal having a second detected
signal power level.
10. The system of claim 9, wherein the means for extracting from
the signal power-to-load maps an estimated load level operatively
applying an average of the first and the second detected signal
power levels to extract the estimated load from the signal
power-to-load maps.
11. The system of claim 10, wherein further comprising comparator
means operatively comparing the estimated load to an overload
threshold load level and generating a warning signal in the event
that the estimated load level exceeds the overload threshold load
level.
12. A system of estimating a load bearing on a vehicle tire,
comprising: (A) a vehicle tire having a tire cavity and supporting
a load; (B) an inflation pressure measuring sensor attached to the
tire for measuring a tire cavity inflation pressure level; (C) at
least a first deformation measuring sensor mounted to a first tire
sidewall and at least a second deformation measuring sensor mounted
to an opposite second tire sidewall, the first and second
deformation measuring sensors comprising a piezoelectric sensor
rotating with the tire sidewall through a tire footprint, the first
and the second deformation measuring sensors generating within the
tire footprint respectively a first deformation signal having first
signal power level and a second deformation signal having a second
signal power level, the first the second signal power levels each
indicative of a level of respective sidewall deformation within the
footprint contact patch. (D) electronically stored tire inflation
pressure-adjusted power-to-load maps for the tire, the maps
correlating a range of load levels to a range of signal power
levels whereby operatively enabling a load level to be identified
for each signal power level; and (E) electronic means for
extracting from the signal power-to-load maps an estimated load
level corresponding to a detected signal power level based upon a
combined average of the first and the second signal power
levels.
13. The system of claim 12, wherein the system comprising a
plurality of spaced apart first deformation measuring sensors
mounted to the first sidewall and a plurality of spaced apart
second deformation measuring sensors mounted to the second
sidewall.
14. The system of claim 13, wherein the electronic means for
extracting from the signal power-to-load maps operatively averages
a combination of signal power levels from the first and the second
plurality of deformation measuring sensors.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to tire monitoring systems
for collecting measured tire parameter data during vehicle
operation and, more particularly, to systems for estimating vehicle
tire loading through a tire sidewall based upon such
measurements.
BACKGROUND OF THE INVENTION
[0002] Vehicle-mounted tires may be monitored by tire pressure
monitoring systems (TPMS) which measure tire parameters such as
pressure and temperature during vehicle operation. Data from TPMS
tire-equipped systems is used to ascertain the status of a tire
based on measured tire parameters and alert the driver of
conditions, such as low tire pressure or leakage, which may require
remedial maintenance. Sensors within each tire are either installed
at a pre-cure stage of tire manufacture or in a post-cure assembly
to the tire.
[0003] Other factors such as tire loading are important
considerations for vehicle operation and safety. It is accordingly
further desirable to measure tire loading and communicate load
information to a vehicle operator in conjunction with the measured
tire parameters of pressure and temperature.
SUMMARY OF THE INVENTION
[0004] In one aspect of the invention, a system and method of
estimating a load bearing on a vehicle tire is provided. The system
includes an inflation pressure measuring sensor attached to the
tire for measuring a tire cavity inflation pressure level; and one
or more piezofilm deformation measuring sensors mounted to a tire
sidewall. The deformation measuring sensor generates within the
tire footprint a deformation signal having signal power level
indicative of a level of sidewall deformation within the footprint
contact patch. Power-to-load maps adjusted for tire inflation
pressure are generated and stored for the tire, the maps
correlating a range of load levels to a range of signal power
levels whereby operatively enabling a load level to be identified
for each signal power level on an inflation pressure adjusted
basis.
[0005] In another aspect of the invention, a deformation measuring
sensor is mounted to each of the sidewalls and an average of the
signal power level from each sensor is used in referencing the
power-to-load maps in order to identify a corresponding load level
on a tire inflation pressure adjusted basis.
DEFINITIONS
[0006] "ANN" or "Artificial Neural Network" is an adaptive tool for
non-linear statistical data modeling that changes its structure
based on external or internal information that flows through a
network during a learning phase. ANN neural networks are non-linear
statistical data modeling tools used to model complex relationships
between inputs and outputs or to find patterns in data.
[0007] "Aspect ratio" of the tire means the ratio of its section
height (SH) to its section width (SW) multiplied by 100 percent for
expression as a percentage.
[0008] "Asymmetric tread" means a tread that has a tread pattern
not symmetrical about the center plane or equatorial plane EP of
the tire.
[0009] "Axial" and "axially" means lines or directions that are
parallel to the axis of rotation of the tire.
[0010] "Chafer" is a narrow strip of material placed around the
outside of a tire bead to protect the cord plies from wearing and
cutting against the rim and distribute the flexing above the
rim.
[0011] "Circumferential" means lines or directions extending along
the perimeter of the surface of the annular tread perpendicular to
the axial direction.
[0012] "Equatorial Centerplane (CP)" means the plane perpendicular
to the tire's axis of rotation and passing through the center of
the tread.
[0013] "Footprint" means the contact patch or area of contact
created by the tire tread with a flat surface as the tire rotates
or rolls.
[0014] "Groove" means an elongated void area in a tire wall that
may extend circumferentially or laterally about the tire wall. The
"groove width" is equal to its average width over its length. A
grooves is sized to accommodate an air tube as described.
[0015] "Inboard side" means the side of the tire nearest the
vehicle when the tire is mounted on a wheel and the wheel is
mounted on the vehicle.
[0016] "Lateral" means an axial direction.
[0017] "Lateral edges" means a line tangent to the axially
outermost tread contact patch or footprint as measured under normal
load and tire inflation, the lines being parallel to the equatorial
centerplane.
[0018] "Net contact area" means the total area of ground contacting
tread elements between the lateral edges around the entire
circumference of the tread divided by the gross area of the entire
tread between the lateral edges.
[0019] "Non-directional tread" means a tread that has no preferred
direction of forward travel and is not required to be positioned on
a vehicle in a specific wheel position or positions to ensure that
the tread pattern is aligned with the preferred direction of
travel. Conversely, a directional tread pattern has a preferred
direction of travel requiring specific wheel positioning.
[0020] "Outboard side" means the side of the tire farthest away
from the vehicle when the tire is mounted on a wheel and the wheel
is mounted on the vehicle.
[0021] "Peristaltic" means operating by means of wave-like
contractions that propel contained matter, such as air, along
tubular pathways.
[0022] "Piezoelectric Film Sensor" a device in the form of a film
body that uses the piezoelectric effect actuated by a bending of
the film body to measure pressure, acceleration, strain or force by
converting them to an electrical charge.
[0023] "Radial" and "radially" means directions radially toward or
away from the axis of rotation of the tire.
[0024] "Rib" means a circumferentially extending strip of rubber on
the tread which is defined by at least one circumferential groove
and either a second such groove or a lateral edge, the strip being
laterally undivided by full-depth grooves.
[0025] "Sipe" means small slots molded into the tread elements of
the tire that subdivide the tread surface and improve traction,
sipes are generally narrow in width and close in the tires
footprint as opposed to grooves that remain open in the tire's
footprint.
[0026] "Tread element" or "traction element" means a rib or a block
element defined by having a shape adjacent grooves.
[0027] "Tread Arc Width" means the arc length of the tread as
measured between the lateral edges of the tread.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The invention will be described by way of example and with
reference to the accompanying drawings in which:
[0029] FIG. 1 is a diagrammatic view of a tire in cross-section, a
rolling tire showing azimuth degree designations; and a graph of
load dependence in which shear strain in the tire is graphed
against azimuth for three different tire loads.
[0030] FIG. 2 is a total signal power per revolution graph from the
piezoelectric sensor bending with the tire sidewall, showing
normalized power (db) against Revolution Number (N) for the three
representative load level cases selected for illustration.
[0031] FIG. 3 is a diagrammatic representation of a tire in
cross-section, a rolling tire showing azimuth degree designations;
and a slip angle dependence study graph of shear strain vs. azimuth
(Deg) for three slip angle data lines at a tire load of 1000
pounds.
[0032] FIG. 4 is a total signal power per revolution graph from the
piezoelectric sensor bending with the tire sidewall, showing
Normalized Power (db) graphed against Revolution Number (N) for the
three representative slip angles selected for illustration at 1000
pounds of load.
[0033] FIG. 5 is a diagrammatic representation of a tire in
cross-section during cornering, a rolling tire showing azimuth
degree designations; and a slip angle dependence study graph of
shear strain vs. azimuth (Deg) for three slip angle data lines at a
tire load of 1000 pounds.
[0034] FIG. 6A is a graph of Normalized Power vs. Revolution Number
[N] for an inner sidewall sensor-3 for the three slip angles at a
tire load of 1000 pounds.
[0035] FIG. 6B is a graph of Normalized Power vs. Revolution Number
[N] for an outer sidewall sensor-5 for the three slip angles at a
tire load of 1000 pounds.
[0036] FIG. 6C is a graph of Average Power showing Normalized Power
[dB] vs. Revolution Number [N].
[0037] FIG. 7 is a diagrammatic representation of a cornering tire
with inner sidewall sensor-3 and outer sidewall sensor-5 in
position and a chart of Average Power showing Normalized Power [dB]
vs. Revolution Number [N] for three different load levels.
[0038] FIG. 8A is a graph showing shear strain vs. Azimuth [Deg] in
a tire sidewall developed using a FEA Virtual Sensor Signal.
[0039] FIG. 8B is a Sensor Data Set graph showing Acceleration {V}
vs. Azimuth [Deg] from a Piezosensor Signal.
[0040] FIG. 9A is a diagrammatic representation of Sensor Location
along a tire inner surface and the mounting locations of the
enumerated sensors.
[0041] FIG. 9B is a schematic representation view of a
Piezosensor.
[0042] FIG. 10A is graphs of experimental data of applied load,
tire pressure, and signal amplitude for tire speed of 10 mph, at
110 psi.
[0043] FIG. 10B is graphs of experimental data for tire speed of 20
mph at 110 psi.
[0044] FIG. 10C is graphs of experimental data for tire speed of 30
mph at 110 psi.
[0045] FIG. 10D is graphs of experimental data for tire speed of 40
mph at 110 psi.
[0046] FIG. 11A is graphs of experimental data of applied load,
tire pressure, and signal amplitude for tire speed of 10 mph, at
100 psi.
[0047] FIG. 11B is graphs of experimental data for tire speed of 20
mph at 100 psi.
[0048] FIG. 11C is graphs of experimental data for tire speed of 30
mph at 100 psi.
[0049] FIG. 11D is graphs of experimental data for tire speed of 40
mph at 100 psi.
[0050] FIG. 12A is graphs of experimental data of applied load,
tire pressure, and signal amplitude for tire speed of 10 mph, at 90
psi.
[0051] FIG. 12B is graphs of experimental data for tire speed of 20
mph at 90 psi.
[0052] FIG. 12C is graphs of experimental data for tire speed of 30
mph at 90 psi.
[0053] FIG. 12D is graphs of experimental data for tire speed of 40
mph at 90 psi.
[0054] FIG. 13 is a Results Summary graph showing signal amplitude
vs. speed for three different loading levels and three different
inflation levels.
[0055] FIG. 14 is a flow diagram of the system operation for
determining an overload condition in a vehicle.
[0056] FIG. 15 is a functional block diagram of the Algorithm
employed by the system.
[0057] FIG. 16 is a graph demonstrating the process of contact
patch length estimation using a derivative waveform.
DETAILED DESCRIPTION OF THE INVENTION
[0058] Referring to FIGS. 1, 5, 15, a system 10 for estimating tire
load from tire deflection measurement and tire pressure is shown in
diagrammatic form. The system 10 is incorporated into a tire 12 of
conventional construction, having a tread component 14 at a tire
crown region which contacts a ground surface 18 during rolling
operation. The tire 12 mounts to a rim 16 in conventional manner.
At least one tire deformation measuring sensor 20 mounts to an
inner sidewall 26. Other sensors, including a like-configured tire
deformation measuring sensor 22 may be mount to an outward sidewall
28. The sensors 20, 22 may be affixed by adhesive to an innerliner
30 defining a tire cavity 24. The sensors 20, 22 are preferably
piezoelectric bending sensors, or other suitable strain sensors
commercially available, of a type operational to bend and
reconfigure when subjected to a bending force and each generate an
electrical signal 32, 33 respectively, indicative of the magnitude
of bending reconfiguration in the sensor body. The bending signals
32, 33 are thus indicative of the magnitude of the bending strain
within the sidewall to which the sensor is attached. When the
bending force is removed, the sensor resumes its original
configuration. For the tire application shown, a piezoelectric
bending sensor such as bending film sensor commercially offered by
Measurement Specialties, Inc. located at 1000 Lucas Way, Hampton,
Va. 23666 may be employed. The piezoelectric sensor functionally
mounts flush to a surface and a piezoresistive film sensor body,
when subjected to a bending force, bends and generates a signal
proportional to the magnitude of bending force on the body.
[0059] With the sensor signal(s) 32, 33 is a measurement of tire
inflation pressure by a tire pressure monitoring system (TPMS)
mounted to the tire, of a type commercially available. The TPMS
system includes a pressure sensor that mounts to a tire in
communication with an internal tire air cavity and functions to
measure the air pressure within the tire cavity and transmit the
measured pressure data to a receiver. The measurement of the TPMS
may further include a temperature sensor that measures tire
temperature. Measured pressure value 36 of the tire cavity 24 is
transmitted by the TPMS system to a data processor for recordation
and analysis. Should the pressure falls below a minimum threshold,
a warning will be generated to the vehicle operator.
[0060] The system and apparatus 10 feeds the tire deformation
sensor signal(s) 32, 33 to a signal processing unit 38 for
processing in order to ascertain from the signal an average signal
power estimation 40. The sensors 20, 22, respectively mounted to
the inner and outer sidewalls, 26, 28, provide an inner sidewall
signal 32 and an outer sidewall signal 33 which is used in the
estimation of average signal power 40. From stored memory files,
and signal power load maps stored in such memory 42, an estimated
tire loading is derived using a tire load estimation algorithm 44.
Should the estimated loading exceed a recommended level, a warning
signal may be generated and communicated back to the operator of
the vehicle.
[0061] FIG. 14 represents in block diagram form the sequence of
system operation. At the start 46, the vehicle is checked 48, and
motion detected 50. The tire pressure is read 52, and the average
sensor signal power is calculated 54. If the value of the estimated
load based upon the average sensor signal power exceeds a threshold
56, a warning 58 is sent and the system recycles 60 and concludes
62 when the estimated load is below the threshold value.
[0062] With reference to FIGS. 1 and 2, the tire 12 is adapted to
include the inner sensor 20 mounted to an inward sidewall 28. The
tire belt(s) 64, located beneath the tread 14, is connected to the
beads 66 of the tire through the sidewalls 26, 28. An increase in
the applied vertical load on the tire leads to vertical
displacement of the wheel with respect to the tire belt. The
sidewalls then shear the beads in the opposite direction at the
entry and exit of the contact area. FIG. 1 shows a graph
illustrating the effect of the vertical component on the strain on
the sidewall in straight line driving for three load levels: 1000,
1300, and 1600 pounds. The signal 32 generated by the sensor 20
demonstrates the magnitude of shear strain which the sidewall
experiences for the three load levels.
[0063] As seen in FIG. 2, the total signal power per revolution is
shown by the data points for the three load levels examined. A
strong correlation between the shear strain amplitude on the tire
sidewall and the load on the tire is demonstrated. The straight
line driving condition reflected in the data and graphs of FIGS. 1
and 2 is modified in FIGS. 3 and 4 to examine the effects due to
lateral sidewall deflection during cornering of the vehicle. As
seen in FIG. 3, during cornering, a substantial difference in the
sidewall strain levels under constant loading conditions is
present. Comparison of the graphs of FIGS. 1 and 3 reveal the
strain level differential detected between straight and cornering
driving conditions. In FIG. 3, results of a slip angle dependence
study are shown in graphical form for three slip angle conditions,
+/-3 degrees and zero at a constant tire load of 1000 pounds. The
graph of shear strain vs. azimuth (deg.) shows the effect of a
change in slip angle on the measured strain. This variation must be
accounted for in utilizing signal power during a cornering maneuver
as will be appreciated from the data point presentation of FIG. 4
for the exemplary three slip angle settings utilized. FIG. 4 shows
normalized power [dB] vs. revolution number [N] at constant loading
of 1000 pounds.
[0064] In FIG. 5, the graph and diagram is shown for a sensor 22
mounted to the outside tire sidewall 28 during cornering. The
inside and the outside sidewalls may thus be monitored for strain
simultaneously. The slip angle dependence study graph 32 of FIG. 5
shows shear strain vs. azimuth [Deg.] at constant load (1000
pounds) for the three slip angles used. The inner sidewall graph of
FIG. 3 may be compared with the outer sidewall graph of FIG. 5 to
understand the effect of slip angle on the shear strain signal on
both sides of the tire during cornering. For comparison purposes,
the data points for normalized power vs. revolution number [N] for
the inner sidewall sensor and the outer sidewall sensor are shown
side by side in FIGS. 6A and 6B, respectively. The average power is
further shown in FIG. 6C as normalized power [dB] vs. Revolution
Number [N]. It will be appreciated that, for the three slip angle
conditions, the normalized power is approximately constant and
equal.
[0065] FIG. 7 shows the data points for average power for the three
slip angle conditions resulting from averaging the power from the
inner sidewall sensor 20 and the outer sidewall sensor 22 during
cornering. In the data point comparison graph of FIG. 7, three load
levels are shown and the normalized power [dB] for each level at
the three slip angle settings are shown. The normalized power for
each load is a constant for each slip angle but the constant varies
depending on tire loading. The normalized power constant thus may
be used as indicative of the loading level on the tire pursuant to
the subject invention.
[0066] A finite element analysis (FEA) virtual sensor signal 68
shows the shear strain within the tire sidewall in FIG. 8A and the
Piezosensor Signal 32 data set is shown in FIG. 8B as validation of
the concept. It will appreciated by the graphs of FIGS. 8A and 8B
that the strain data from the tire mounted piezoelectric sensors is
indicative of the shear strain within the tire sidewall region.
[0067] FIG. 9A shows the test location of multiple sensors (12
sensors shown for illustration) along a tire sidewall and the
enumerated mounting location of each. Sensor 10 results will be
analyzed. FIG. 9B shows a representative sensor of a type
commercially available, known within the industry as a cantilever
piezofilm (Water) sensor. The results of the experimental data at
110 psi and 10 mph are shown in FIG. 10A. For the applied loads,
the signal amplitude vs. rotation number may be averaged to derive
the constant amplitude under each load condition. In FIG. 10B, the
data for 110 psi and 20 mph are given; in FIG. 10C, data for 110
psi and 30 mph; and in FIG. 10D, data for 110 psi and 40 mph. The
experimental results indicate that the level of sensor strain
amplitude is a constant for each applied load level. Accordingly,
the correlation between measured sensor strain amplitude and load
level may be stored in a database and, once the measured sensor
strain amplitude within a sidewall is known, the load level may be
determined therefrom.
[0068] FIGS. 11A through D show the experimental test data for tire
speeds between 10 and 40 mph at 10 mph gradients, respectively,
under tire inflation of 100 psi. It will be noted by comparing the
110 psi against the 100 psi data, that changes in tire inflation
pressure will alter the measured sensor signal amplitudes for the
applied loads. Consequently, tire pressure must be know in order to
interpret the strain sensor amplitude and deduce the applied load
on the tire therefrom. The Monitoring System mounted to each tire
thus provides the tire pressure measurement necessary to identify
the appropriate sensor strain to applied load table stored in the
database. FIGS. 12A through D show the experimental test data for
tire speeds between 10 and 40 mph at 10 mph gradients,
respectively, with a tire inflation of 90 psi. Again, the data
verifies that changes in tire inflation pressure in a tire will
alter the measured sensor signal amplitudes from that tire for the
different applied loads.
[0069] FIG. 13 sets forth the Results Summary for the different psi
settings examined at the three applied load levels. The threshold
signal amplitude is identified in broken line 72. The system, as
will be understood, can successfully detect an overload condition
when the applied load exceeds the preset threshold limit. The
overload condition can then prompt a warning to the driver in
addition in addition to precisely estimating the dynamic tire
load.
[0070] As explained previously, FIG. 14 shows the overload warning
system in a block level diagram. The threshold data is stored in
memory. The tire pressure 52 and the average sensor signal power 54
are continuously monitored and measured in a tire in order to
provide data necessary to identify the applicable threshold look-up
table in memory to use. The loading on the tire is determined from
appropriate memory tables. The tire may further be identified by
type and size through a tire RFID identification device attached to
the tire. A table is then consulted in memory and used to establish
the applicable threshold value for the tire type and size of
interest and its inflation level. The actual applied load value is
then compared against the threshold load value (step 56) to
determine whether an overload condition exists.
[0071] FIG. 15 shows the algorithm proposed in a functional block
diagram form. A singular strain gauge 20 may be mounted to a tire
sidewall, or a pair of sensors 20, 22 mounted to inward and
opposite sidewalls of each tire. Alternatively, multiple pairs of
sensors may be mounted to each tire in order to analyze the loading
on the tire from various tire locations. The sensor signal(s) 32,
33 are averaged to derive an average signal power estimation 40.
Average signal power is estimated to account for the variations in
the signal during a cornering maneuver. As shown in the test data,
the average signal power is a constant even during a cornering
maneuver. Signal-Power-Load Maps are stored in memory from
empirical studies of the type discussed previously herein. The tire
load estimation algorithm takes from Signal Power-Load Maps 42
stored in memory the loading level appropriate for the Signal Power
and measured tire pressure detected. The loading level so obtained
may then be used to analyze the overload condition. Tire loading
data may further be used to analyze load distribution of the
vehicle from tire to tire.
[0072] It will be appreciated that the subject proposed algorithm
which relies on sidewall deformation measurement has decided
advantages over systems which use a tire crown based approach In a
crown based approach, the load is characterized using patch length
information. FIG. 16 shows patch length estimation using a
derivative waveform for three sets of loading levels. The top graph
shows the longitudinal strain wave form and its differential
waveform. The contact patch length varies as will be noted for each
load level so, theoretically, measuring patch length will yield
loading information on the tire. In FIG. 16, the patch length or
contact patch is indicated at numeral 74, with the leading edge of
the patch at 76. Precise patch length estimation, however, can be
challenging since sophisticated signal processing techniques are
required to precisely find the leading and trailing edge of the
signal to estimate the patch length accurately. Moreover, under
certain conditions (e.g. during aquaplaning), the tire crown
deformation is drastically different from deformation under normal
conditions, for the same tire load.
[0073] From the foregoing, it will be understood that a system and
method of estimating a load bearing on a vehicle tire is provided.
The system includes an inflation pressure measuring sensor attached
to one or both of the tire for measuring a tire cavity inflation
pressure level; and one or more piezofilm deformation measuring
sensors mounted to one or both of the tire sidewalls. The
deformation measuring sensor(s) generate within the tire footprint
a deformation signal having signal power level indicative of a
level of sidewall deformation within the footprint contact patch.
Power-to-load maps adjusted for tire inflation pressure are
generated and stored for the tire, the maps correlating a range of
load levels to a range of signal power levels whereby operatively
enabling a load level to be identified for each signal power level
on an inflation pressure adjusted basis. In the system embodying a
plurality of deformation measuring sensors, mounted to both
sidewalls, an average of the signal power level from each sensor is
used in referencing the power-to-load maps in order to identify a
corresponding load level on the tire on an inflation pressure
adjusted basis.
[0074] Variations in the present invention are possible in light of
the description of it provided herein. While certain representative
embodiments and details have been shown for the purpose of
illustrating the subject invention, it will be apparent to those
skilled in this art that various changes and modifications can be
made therein without departing from the scope of the subject
invention. It is, therefore, to be understood that changes can be
made in the particular embodiments described which will be within
the full intended scope of the invention as defined by the
following appended claims.
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