U.S. patent application number 13/680656 was filed with the patent office on 2013-03-28 for system and method for performing auto-location of a tire pressure monitoring sensor arranged with a vehicle wheel.
This patent application is currently assigned to Schrader Electronics Ltd.. The applicant listed for this patent is Schrader Electronics Ltd.. Invention is credited to John Greer, Samuel Strahan.
Application Number | 20130079977 13/680656 |
Document ID | / |
Family ID | 45003039 |
Filed Date | 2013-03-28 |
United States Patent
Application |
20130079977 |
Kind Code |
A1 |
Greer; John ; et
al. |
March 28, 2013 |
SYSTEM AND METHOD FOR PERFORMING AUTO-LOCATION OF A TIRE PRESSURE
MONITORING SENSOR ARRANGED WITH A VEHICLE WHEEL
Abstract
Auto-location systems and methods of tire pressure monitoring
sensor units arranged with a wheel of a vehicle detect a
predetermined time (T1) when a wheel phase angle reaches angle of
interest using a rim mounted or a tire mounted sensor. The systems
and methods transmit a radio frequency message associated with a
wheel phase angle indication. The wheel phase angle indication
triggers wheel phase and/or speed data such as ABS data at the
predetermined time (T1) to be stored. A correlation algorithm is
executed to identify the specific location of a wheel based on the
wheel phase and/or speed data at the predetermined time (T1). TPM
sensor parameters from a tire pressure monitoring sensor unit are
assigned to the specific location of the wheel.
Inventors: |
Greer; John; (Randalstown,
IE) ; Strahan; Samuel; (Broughshane, IE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Schrader Electronics Ltd.; |
Northern Ireland |
|
GB |
|
|
Assignee: |
Schrader Electronics Ltd.
Northern Ireland
GB
|
Family ID: |
45003039 |
Appl. No.: |
13/680656 |
Filed: |
November 19, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13222653 |
Aug 31, 2011 |
8332104 |
|
|
13680656 |
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12888247 |
Sep 22, 2010 |
8332103 |
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13222653 |
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61277334 |
Sep 22, 2009 |
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Current U.S.
Class: |
701/34.4 |
Current CPC
Class: |
B60C 23/0437 20130101;
B60C 23/0488 20130101; G06F 11/30 20130101; B60C 23/0489 20130101;
B60C 23/0416 20130101; B60C 23/0462 20130101 |
Class at
Publication: |
701/34.4 |
International
Class: |
G06F 11/30 20060101
G06F011/30 |
Claims
1. A wheel auto-location method, comprising: receiving a radio
frequency (RF) transmission that indicates a one-measurement point
during a rotation of a wheel and TPM sensor parameters, wherein the
RF transmission is associated with a phase correlation data storage
event trigger; storing a current content of a rolling window of an
antilock brake system ("ABS") data indicative of a wheel phase
angle in response to the phase correlation data storage event
trigger, wherein a time period covered by the rolling window is the
same or greater than a time period between the one-measurement
point and a receipt point of the RF transmission, and the current
content of the rolling window corresponds to the ABS data between
the one-measurement point and the receipt point of the RF
transmission; calculating the one-measurement point based on the
time period between the one-measurement point and the receipt point
of the RF transmission; determining relevant ABS data from the
current content of the rolling window of the ABS data based on the
one-measurement point over time; and applying an auto-location
algorithm to the relevant ABS data to identify a specific location
of the wheel where the TPM sensor parameters are associated with
the specific location of the wheel.
Description
PRIORITY
[0001] This application is a continuation of U.S. application Ser.
No. 13/222,653 filed Aug. 31, 2011, entitled "System and method for
performing auto-location of a tire pressure monitoring sensor
arranged with a vehicle wheel," which is a continuation-in-part of
U.S. application Ser. No. 12/888,247 filed Sep. 22, 2010, entitled
"System and method for performing auto-location of a wheel in a
vehicle using wheel phase angle information," which claims priority
to Provisional Application No. 61/277,334 filed on Sep. 22, 2009,
entitled "Use of wheel phase angle to perform auto-location in a
Tire Pressure Monitoring System." Disclosures of U.S. application
Ser. Nos. 13/222,653 and 12/888,247 and Provisional Application No.
61/277,334 are incorporated here in their entirety.
BACKGROUND
[0002] 1. Technical Field
[0003] This invention relates generally to a system and method for
performing auto-location of a wheel in a vehicle and more
particularly to a tire pressure monitoring system and method for
performing auto-location of a tire pressure monitoring sensor
arranged with a vehicle wheel using wheel phase and/or speed
data.
[0004] 2. Related Art
[0005] In tire pressure monitoring systems, performing
auto-location of a wheel is needed for a number of reasons. Tire
pressure monitoring systems generally include a tire pressure
monitoring (TPM) sensor in or at each wheel of a vehicle and a
central controller which receives tire pressure information from
each TPM sensor, to be reported to the driver of the vehicle.
Auto-location is the identification of each TPM sensor and
determination of its position on the vehicle, automatically and
without human intervention. Auto-location may be done initially
upon installation and subsequently in the event of tire rotation or
replacement. Performing auto-location involves determining the
identity or serial number of a TPM sensor in each of the wheels in
the car. In premium vehicles, knowing the identity of the TPM
sensor in each wheel allows a pressure by position display to be
implemented and shown to the driver. In basic vehicles with
different placard tire pressures for front and rear axles, it is
desirable to know TPM sensor identities and positions in order to
check pressure against a correct threshold for an applicable
axle.
SUMMARY
[0006] The present embodiments are directed to auto-location
systems and methods in which wheel phase and/or speed data is
correlated with a specific wheel to determine a location of a TPM
sensor and facilitate identification of the TPM sensor arranged
with the specific wheel on a vehicle. The present embodiments
determine the wheel location in order to determine the location of
a TPM sensor arranged with the wheel. In the present embodiments,
the auto-location of a wheel indicates auto-location of the TPM
sensor arranged with the wheel so that parameters from the TPM
sensor may be assigned to the wheel. The wheel phase and/or speed
data can be processed and correlated with wheel phase angle
information or a wheel phase angle indication from a wheel unit.
The present systems and methods are particularly well suited for
use with tire pressure monitoring systems that use rim mounted
sensors that can deduce the instantaneous wheel angle using shock
sensors. Alternatively, or additionally, the present systems and
methods can also be practiced in a tire pressure monitoring system
that uses a rim mounted sensor which is able to deduce the
instantaneous wheel angle using accelerometers. The present systems
and methods are also well suited for use with tire pressure
monitoring systems that use tire mounted sensors that deduce the
instantaneous wheel angle. This method of auto-location is not
limited to the use of accelerometric devices. For example, periodic
signals from which phase information can be deduced may also be
used. Devices such as Hall effect sensors or sensors which respond
to road strike may be used to deduce the phase information.
[0007] Advantageously, most vehicles employ antilock brake systems
("ABS"). The ABS allows independent wheel speeds to be monitored in
near real-time. In one embodiment, the wheel phase and/or speed
data includes or is based on the ABS data. Correlation between ABS
data and other data from TPM sensors can be used to locate wheel
positions where the TPM sensors are arranged. ABS sensors provide
the ABS data and may be associated with one or more wheels. As one
example, ABS sensors are associated with each wheel of a vehicle,
or with selected wheels of the vehicle. The wheel phase and/or
speed data is not limited to the ABS data. A sensor, a device, a
system, or a mechanism that may provide wheel phase and/or speed
data directly or in various forms may be used in addition to, or
instead of antilock brake systems.
[0008] In one embodiment, the identification of the wheel location,
thereby identifying the location of the TPM sensor, may require
snapshots of information at a one-measurement point during rotation
of a wheel, where a snapshot is a capture of information from a
short duration of a continuous stream of information. A radio
frequency (RF) transmission identifying the one-measurement point
is transmitted from a wheel unit and correlated to the ABS data at
the one-measurement point using a statistical processing method. A
historic trace of the ABS data at the one-measurement point is
correlated to a specific wheel location.
[0009] By way of one example, one embodiment of a wheel
auto-location method includes (i) arranging a wheel unit to be
associated with a wheel of the vehicle, the wheel unit comprising a
TPM sensor and a wheel phase angle sensor and the wheel unit
transmitting TPM sensor parameters; and (ii) arranging an ABS
sensor to be associated with each wheel of the vehicle, the ABS
sensor producing ABS data indicative of the wheel phase angle. The
ABS sensor provides wheel phase and/or speed data in this
embodiment; however, the wheel phase and/or speed data is not
limited to ABS data. In this embodiment, the wheel auto-location
method detects a first time (T1) reaching a particular wheel angle
of interest and transmits a radio frequency (RF) message at a
second time (T2). A wheel phase angle at the second time (T2) may
not be measured. The wheel auto-location method then triggers a
phase correlation data storage event based on wheel phase angle
indication. In response to the wheel phase angle indication, the
phase correlation data storage event is triggered and the current
contents of a rolling window of the ABS data is captured. The
rolling window of the ABS data is continuously maintained and the
captured current content of the rolling window is stored in
storage. After a substantial amount of the ABS data is captured, an
auto-location algorithm is executed and applied to the stored ABS
data in order to identify a specific location of the wheel.
[0010] The phase correlation data storage event trigger is
implemented with various embodiments of the wheel phase angle
indication. In one embodiment, the wheel phase angle indication
includes a function code, or a status code contained in the RF
message. Upon receipt of such RF message, the phase correlation
data storage event is triggered and the current content of the
rolling window of the ABS data is captured. In another embodiment,
the RF message uses at least a portion of bits of a temperature
data field of the RF message as the wheel phase angle indication.
The temperature data bits are recognized and the current content of
relevant ABS data is captured. Further in another embodiment,
interframe spacings of a series of RF messages operate as the wheel
phase angle indication. The interframe spacings are recognized and
the relevant ABS data is captured.
[0011] Another embodiment of the present invention includes a wheel
auto-location system that determines a location of a TPM sensor.
The system includes a wheel unit to be associated with a wheel of
the vehicle. The wheel unit includes the TPM sensor that measures
tire pressure of the wheel and a wheel phase angle sensor that
detects a first time (T1) when a wheel phase angle reaches a
particular angle of interest. The wheel unit transmits an RF
message at the second time (T2). The RF message includes an
identification of the TPM sensor and measured tire parameters such
as tire pressure. The RF message may not include an actual phase
angle. Alternatively, or additionally, the RF message includes
position or location information of the TPM sensor such as left
side or right side of a vehicle.
[0012] In this embodiment, the wheel auto-location system further
may include or may work in cooperation with an antilock brake
system ("ABS") sensor associated with each wheel of the vehicle and
operable to provide ABS data indicative of the wheel phase angle.
The ABS data may be used as wheel phase and/or speed data, but
other data that represents wheel phase and/or speed is available.
The wheel auto-location system further includes or operates in
conjunction with an Electronic Control Unit ("ECU") in
communication with the wheel unit and the ABS sensor. ABS data from
the ABS sensors are available to other components of the vehicle
such as the wheel auto-location system and the ECU. The ECU may be
operable to execute instructions of calculating the first time (T1)
based on a predetermined time delay, determining the ABS data at
the calculated first time (T1) and identifying a location of the
wheel whose ABS data matches with a predetermined criterion.
[0013] In one embodiment, the predetermined criterion is based on a
historic trace of the ABS data at the first time (T1). The
predetermined criterion is also based on a statistically
significant value of the ABS data. For example, the ECU correlates
the location of the wheel having the TPM sensor with the location
of the ABS sensor whose historic trace shows a lowest standard
deviation of ABS tooth count values at the first time (T1) over
time. Alternatively, or additionally, the ECU correlates the
location of the wheel having the TPM sensor with the location of
the ABS sensor whose historic trace shows the most consistent ABS
tooth count values at the first time (T1) over time. Alternatively,
or additionally, the ECU correlates the location of the wheel
having the TPM sensor with the location of the ABS sensor whose
historic trace shows a statistically significant trend in ABS tooth
count values at the first time (T1) over time.
[0014] The foregoing has outlined rather broadly the features and
technical advantages of the present invention in order that the
detailed description of the invention that follows may be better
understood. Additional features and advantages of the invention
will be described hereinafter which form the subject of the claims
of the invention. It should be appreciated by those skilled in the
art that the conception and specific embodiment disclosed may be
readily utilized as a basis for modifying or designing other
structures for carrying out the same purposes of the present
invention. It should also be realized by those skilled in the art
that such equivalent constructions do not depart from the spirit
and scope of the invention as set forth in the appended claims. The
novel features which are believed to be characteristic of the
invention, both as to its organization and method of operation,
together with further objects and advantages will be better
understood from the following description when considered in
connection with the accompanying figures. It is to be expressly
understood, however, that each of the figures is provided for the
purpose of illustration and description only and is not intended as
a definition of the limits of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The accompanying drawings, which are incorporated in and
form part of the specification and in which like numerals designate
like parts, illustrate embodiments of the present invention and
together with the description, serve to explain the principles of
the invention. In the drawings:
[0016] FIG. 1 illustrates one embodiment of a tire pressure
monitoring system;
[0017] FIG. 2 illustrates one embodiment of a wheel unit for use
with the tire pressure monitoring system.
[0018] FIG. 3A illustrate a wheel phase angle as a function of the
gravitational force, i.e., acceleration and FIG. 3B illustrates
phase varying signals from different sensors.
[0019] FIG. 4 illustrates one embodiment of correlation between
wheel phase angle information from the wheel unit and ABS data.
[0020] FIG. 5 is a flow chart illustrating one embodiment of a
method for performing auto-location of a wheel using wheel phase
angle information at the wheel unit.
[0021] FIG. 6 is a flow chart further illustrating the method for
performing auto-location of the wheel at an Electronic Control Unit
("ECU").
[0022] FIG. 7 is a flow chart illustrating another embodiment of
the method for performing auto-location of the wheel using wheel
phase angle information.
[0023] FIG. 8 is a flow chart illustrating another embodiment of
the method for performing auto-location of the wheel using wheel
phase angle information.
[0024] FIG. 9 is a flow chart illustrating another embodiment of
the method for performing auto-location of the wheel using wheel
phase angle information.
[0025] FIG. 10A illustrates correlation between ABS data and a
one-measurement point during a rotation of a wheel and FIG. 10B
illustrates storage of the ABS data at the one-measurement
point.
[0026] FIGS. 11A-11D illustrate various embodiments of a phase
correlation data storage event trigger based on various wheel phase
angle indications.
[0027] FIG. 12 is a flow chart illustrating one embodiment of an
auto-location method based on the ABS data at the one-measurement
point.
[0028] FIG. 13 illustrates one embodiment of ABS tooth count values
for four wheels with respect to RF transmissions from a left rear
wheel unit.
[0029] FIG. 14 is a graph illustrating ABS tooth count values of
FIG. 13.
[0030] FIG. 15A illustrates one embodiment of a standard deviation
of ABS sensor tooth count values with respect to RF transmissions
from a left rear wheel unit, and FIG. 15B illustrates one
embodiment of a trend of ABS sensor tooth count values with respect
to RF transmissions from a left rear wheel unit.
[0031] FIG. 16 illustrates one example of a standard deviation of
ABS tooth count values for four wheels with respect to RF
transmissions from left front, right front, left rear and right
rear wheels.
[0032] FIG. 17 is a flowchart illustrating one embodiment of an
auto-location algorithm.
[0033] FIG. 18 is a flowchart illustrating another embodiment of an
auto-location algorithm where not every wheel has an associated ABS
sensor.
DETAILED DESCRIPTION
[0034] The present invention is directed to systems and methods in
which a measurement from a wheel is combined or correlated with
wheel phase and/or speed data such as antilock brake system (ABS)
data to allow identification of the TPM sensors to a specific
location on a vehicle. In accordance with various embodiments of
the present invention, a tire pressure monitoring system comprises
wheel rim or tire mounted TPM sensors, typically four, and an
Electronic Control unit (ECU) that receives signals from the TPM
sensors. In addition, the system employs data presented to the ECU
from the Anti-lock Brake System (ABS).
[0035] In accordance with various embodiments of the present
invention, the identification of the TPM sensors may require
snapshots of information at one-measurement point during a rotation
of a wheel, where a snapshot is a capture of information from a
short duration of a continuous stream of information. The ECU holds
a rolling window of ABS data for all wheels or selected wheels
associated with ABS sensors. When a radio frequency (RF) data frame
is received, the ECU uses the RF data frame to store and determine
relevant ABS data from the rolling window of the ABS data. An
auto-location algorithm is applied to stored ABS data to identify a
specific location of a wheel where a TPM sensor is arranged. The
auto-location algorithm may analyze a historic trace of the ABS
data and determines a standard deviation of ABS tooth count values
with respect to each wheel of a vehicle. Alternatively, or
additionally, the auto-location algorithm may analyze a
statistically significant trend of the ABS data.
[0036] FIG. 1 illustrates a tire pressure monitoring system 100
according to a first embodiment of the present invention. The
system 100 is arranged in a standard vehicle 1 having four wheels.
Four wheels include a left front wheel (LF), a right front wheel
(RF), a left rear wheel (LR) and a right rear wheel (RR). In
another embodiment, the system 100 may be arranged in any other
vehicle having a different number of wheels. The system 100
includes wheel units 101, 102, 103 and 104 that are associated with
each wheel of the vehicle 1.
[0037] The system 100 further includes four antilock brake system
(ABS) sensors 201, 202, 203 and 204. In this embodiment, ABS
sensors 201, 202, 203, 204 are also associated with each wheel of
the vehicle 1. Accordingly, each wheel is assigned with one of the
wheel units 101, 102, 103 and 104 and one of ABS sensors 201, 202,
203 and 204. In another embodiment, ABS sensors 201, 202, 203, 204
may not be associated with all four wheels. Fewer numbers of ABS
sensors may be present in a structure of a vehicle such as a single
axle and associated with a few selected wheels.
[0038] The system 100 also includes an Electronic Control Unit
(ECU) 300 and a receiver 400. The ECU 300 is coupled to the ABS
sensors 201, 202, 203, 204 via a communication bus such as a
Controller Area Network (CAN) bus and receives ABS data from the
ABS sensors 201, 202, 203, 204. The ECU 300 includes a processor
302 and storage 304. The ECU 300 operates to store received ABS
data in the storage 304 to provide a historic ABS trace. The ECU
300 may be implemented by any suitable means, for example a
microprocessor, microcontroller, an Application Specific Integrated
Circuit (ASIC), or other suitable data processing device programmed
to perform the functions described herein. Further, the ECU 300 may
communicate with other vehicle components using any other suitable
device, either wire line or wireless. The CAN bus is an exemplary
implementation of data communication among components of the
vehicle. The ECU 300 stores computer program code. In one
embodiment, the ECU 300 executes the computer program including
instructions of calculating a first time (T1) based on a
predetermined time delay (T2-T1), storing ABS data indicative of a
wheel phase angle based on a phase correlation data storage event
trigger and determining the ABS data at the first time (T1), and
correlating a location of the wheel with a location of the ABS
sensor based on a historic trace of the ABS data at the first time
(T1).
[0039] The ECU 300 also receives data from the wheel units 101,102,
103 and 104 via the receiver 400. For example, the wheel units 101,
102, 103 and 104 transmit radio frequency or other wireless
communications conveying data and other information to the ECU 300.
The respective wheel units include a suitable radio transmission
circuit and the ECU 300 includes a suitable radio reception circuit
for radio communication. Further, the radio circuits may use an
agreed upon transmission and reception format and data encoding
technique. The ECU 300 operates to correlate the data received from
the wheel units 101, 102, 103 and 104 with the ABS data in order to
perform auto-location, as will be discussed in detail below.
[0040] Referring to FIG. 2, the structure of the wheel unit 101 is
illustrated in more detail. The wheel units 102-104 may incorporate
the same structure as that of the wheel unit 101. As shown in FIG.
2, the wheel unit 101 includes a microcontroller 202, a battery
204, a transponder coil 206, a sensor interface 207, a pressure
sensor 208, a wheel phase angle sensor 212, a transmitter 214 and
an antenna 216. In other embodiments, the wheel unit 101 may have a
different structure from the structure illustrated in FIG. 2. The
microcontroller 202 is coupled to the sensor interface 207. The
sensor interface 207 is coupled to the wheel phase angle sensor
212. In one embodiment, the wheel phase angle sensor 212 measures a
wheel phase angle at multiple different times. The wheel phase
angle sensor 212 provides measurements to the sensor interface 207.
Alternatively, or additionally, the wheel phase angle sensor 212
provides other value or information indicative of wheel phase angle
measurements. The sensor interface 207 receives the measurements of
the wheel phase angle sensor 212 in the form of an electrical
output signal. The sensor interface 207 receives the electrical
output signal and amplifies and filters the signal. The sensor
interface 207 sends the processed signal to an analog to digital
converter (not shown) in order to convert the signal into a digital
signal. The microcontroller 202 receives the digital form of the
output signal from the wheel phase angle sensor 212 for
processing.
[0041] In the illustrated embodiment, the pressure sensor 208
detects the pneumatic air pressure of the tire with which the wheel
unit 101 is associated. In alternative embodiments, the pressure
sensor 208 may be supplemented with or replaced by a temperature
sensor or other devices for detecting tire data. An indication of
the tire pressure data is sent to the microcontroller 202 via the
analog-to-digital converter (not shown).
[0042] The battery 204 is a power source of the wheel unit 101. The
transponder coil 206 detects external activation of the transponder
by a signal applied by a remote exciter and may modulate a signal
to communicate data to a remote detector from the wheel unit 101.
The wheel unit 101 provides data including tire pressure from the
pressure sensor 208 and the wheel phase angle information from the
wheel phase angle sensor 212 through the transmitter 214 and the
antenna 216 to the ECU 300 (see FIG. 1).
[0043] Upon rotation of a wheel, the wheel phase angle sensor 212
operates to measure a wheel phase angle. The wheel phase angle
measurements may not have to be against an absolute reference. The
reference may be arbitrarily selected based on accuracy capability
and ease of implementation. In other words, the phase measurements
do not have to be measured from a top of wheel, or road striking
point. In this embodiment, the key piece of information may be a
phase difference, or a phase delta of the wheel, and therefore, the
requirement is that two different phase angles are measured
relative to the same angle. Alternatively, or additionally, in
another embodiment, the key piece of information may include a
one-measurement point during a rotation of a wheel.
[0044] The wheel phase angle sensor 212 may be mounted on a rim of
the wheel, or a tire mounted sensor. Alternatively, or
additionally, the wheel phase angle sensor 212 may be arranged on
any suitable location associated with a wheel. In one embodiment,
the wheel phase angle 212 includes a rotation sensor. For example,
the rotation sensor may be a piezoelectric rotation sensor which
measures a wheel phase angle based on the gravitational force.
Specifically, as the wheel rotates, the gravitational force causes
a sensing element of the rotation sensor to experience different
forces which results in a different output signal representing a
wheel phase angle or wheel angular position. In that way, the
rotation sensor produces an output signal indicating a wheel phase
angle at a predetermined time. The output signal of the rotation
sensor may have different amplitude and/or different polarity
depending on the wheel phase angle. For instance, the rotation
sensor produces the output signal having amplitude M at 0 degree
and having the amplitude -M at 180 degree. Alternatively, or
additionally, any conventional rotation sensor may be used as the
wheel phase angle sensor 212.
[0045] In another embodiment, the wheel phase angle sensor 212
comprises a shock sensor of the type that produces an electrical
signal in response to acceleration. The electrical signal is
indicative of, or typically proportional to, the experienced change
in acceleration. Alternatively, the wheel phase angle sensor 212
may each comprise an accelerometer or a micro-electromechanical
systems (MEMS) sensor. The main difference between an accelerometer
and a shock sensor is that the output signal from a shock sensor is
related to a change of force applied to the shock sensor, whereas
the output signal from an accelerometer is proportional to the
absolute force applied. Shock sensors may be implemented, for
example, with shock sensors discussed in commonly owned U.S. Pat.
No. 7,362,218, issued Apr. 22, 2008 and entitled Motion Detection
Using A Shock Sensor In A Remote Tire Pressure Monitor System and
commonly owned U.S. Pat. No. 7,367,227, issued May 6, 2008 and
entitled Determination Of Wheel Sensor Position Using Shock Sensors
And A Wireless Solution, the disclosures of which are incorporated
here in its entirety. Accelerometer sensors may be implemented, for
example, with sensors discussed in commonly owned U.S. Pat. No.
7,010,968, issued Mar. 14, 2006 and entitled Determination Of Wheel
Sensor Position Using A Wireless Solution, the disclosure of which
is incorporated here in its entirety.
[0046] In the embodiment where shock sensors or accelerometers are
used as the wheel phase angle sensor 212, FIG. 3A is a graph
illustrating a wheel phase angle or a wheel angular position as a
function of the gravitational force or acceleration. In the
illustrated embodiment, the wheel rotates counter clockwise, and
acceleration along the z axis 304 leads acceleration along the x
axis by approximately 90 degrees. The output signal is a sinusoid
with a period equal to one revolution of the wheel. The magnitude
of the output signal is a voltage proportional to the change in
acceleration or acceleration experienced by the wheel phase angle
sensor 212 such as the shock sensors or accelerometers as they
rotate. The graph as shown in FIG. 3A is by way of example, and the
actual acceleration experienced in a moving wheel may be different
from the amount illustrated in FIG. 3A.
[0047] FIG. 3B(a) illustrates phase varying signals output from the
wheel phase angle sensor 212 which may be a shock sensor or an
accelerometer. FIG. 3B(b) illustrates phase varying signals output
from the wheel phase angle sensor 212 which may be a Hall effect
sensor, or a road striking sensor. The phase varying signals
illustrated in FIG. 3B (a) and (b) are input to the microcontroller
202. The microcontroller 202 recognizes a repeated pattern in the
phase varying signals and determines one rotation of the wheel.
Then, the microcontroller 202 determines how far through the one
rotation of the wheel it is at the first time (T1) and the second
time (T2) and determines a first phase angle (P1) and a second
phase angle (P2). Assuming that the phase-varying signal does not
change its characteristics between the first time (T1) and the
second time (T2), the first phase angle (P1) and the second phase
angle (P2) will be relative to each other, and can be used as
auto-location data.
[0048] Referring back to FIG. 2, the sensor interface 207 is
configured to provide the necessary control signals and detect the
electrical signals from the wheel phase angle sensor 212 such as
the shock sensor. As discussed above, the shock sensor detects
change in acceleration to produce an output in the form of an
electrical charge output signal. The output signal is typically in
the order of 1 mV/g. Preferably, if the wheel phase angle sensor
212 includes more than one shock sensor, shock sensors can share
the same interface 207 via multiplexing.
[0049] Through the sensor interface 207, the microcontroller 202
receives output signals representing wheel phase angle from the
wheel phase angle sensor 212. The microcontroller 202 may include,
for example a memory for data storage and a data processing unit.
The microcontroller 202 stores a received wheel phase angle, or
data related thereto, for a later transmission to the ECU 300. The
microcontroller 202 may not transmit every time the output signal
has been received. In one embodiment, the microcontroller 202
calculates and determines a difference in two wheel phase angles
measured by the wheel phase angle sensor 212. For instance, the
microcontroller 202 subtracts a first wheel phase angle measured at
a first time (T1) from a second wheel phase measured at a second
time (T2). In another embodiment, the microcontroller 202
determines the second time (T2) based on a predetermined known time
delay (T2-T1). For instance, the microcontroller 202 may consider
the first time (T1) as the one-measurement point of a wheel phase
angle during the rotation of a wheel and the second time (T2) as a
data transmission point of a radio frequency message as described
below. The microcontroller 202 may include a clock or time base, or
other circuit or module for measuring time increments and operating
at specified times or during specified time durations.
[0050] The microcontroller 202 encodes and transmits a radio
frequency message via the transmitter 214 and the antenna 216. The
radio frequency message includes, among other things, tire pressure
information, an identifier of the wheel unit 101, and wheel phase
angle information. The wheel phase angle information may include
actual wheel phase angles measured at different times. In another
embodiment, the wheel phase angle information may include wheel
phase angle measured at a transmission time, such as the second
time (T2), and a difference in wheel phase angle measured at two
different times. Alternatively, the wheel phase angle information
may include only the difference in wheel phase angles.
[0051] In another embodiment, the wheel phase angle information may
include no actual wheel phase angle. Instead, the wheel phase angle
information includes a wheel phase angle indication. As one
example, the wheel phase angle indication may include a predefined
function code which will trigger a phase correlation data storage
event. The wheel phase angle indication may be implemented by
establishing predetermined data values or patterns such as by
setting a bit which is normally unused in a RF message structure
(see FIG. 11A). Alternatively, or additionally, the wheel phase
angle indication may be implemented with a most significant bit,
which is normally set to zero (see FIG. 11B). Additionally, the
phase wheel angle indication may also include a predetermined time
delay, such as T2-T1, or any other information indicative of a
wheel phase angle (e.g., a pseudo-random number).
[0052] Referring again back to FIG. 1, the ECU 300 receives the
radio frequency message from the wheel unit 201. The ECU 300 stores
the radio frequency message, or data contained in the radio
frequency message. Such data may be stored in the storage 304 which
is a suitable data store such as a memory device. Also, the ECU 300
extracts the tire pressure, the identifier, and the wheel phase
angle information from the radio frequency message. The ECU 300
correlates the wheel phase angle information with the ABS data from
the ABS sensors 201, 202, 203, 204. In one embodiment, the ECU 300
analyzes the ABS data and determines a wheel phase angle or a wheel
phase angle difference which is indicated by and corresponds to the
ABS data. The ECU 300 compares the wheel phase angle information
from the wheel unit 101 with the wheel phase angle or the wheel
phase angle difference of the ABS data in order to determine the
closest match. Upon finding the closest match, the ECU 300 assigns
the identifier sent from the wheel unit 101 to a wheel whose ABS
data most closely matches with the wheel phase angle information
from the wheel units 101, 102, 103, 104.
[0053] In another embodiment, the ECU 300 analyzes the ABS data and
determines whether the ABS data maintains a consistent value or a
statistically significant trend at a predetermined time (e.g., T1).
Alternatively, or additionally, the ECU 300 analyzes the ABS data
and determines whether the ABS data shows a lowest standard
deviation for a particular wheel location. By using this
statistical correlation method, as will be described in detail
below, the ECU assigns the identifier sent from the wheel unit 101
to a wheel whose ABS data is the most consistent or shows the
lowest deviation, or shows the a statistically significant
trend.
[0054] Referring to FIG. 4, correlation of the wheel phase angle
information from the wheel unit 101, 102, 103, 104 with the ABS
data is further explained. In one embodiment, the wheel phase angle
sensor 212 measures a wheel phase angle multiple times. In another
embodiment, the wheel phase angle sensor 212 measures a wheel phase
angle at the one-measurement point (e.g., T1 in FIG. 4) and does
not measure the wheel phase angle at a different time (e.g., T2 in
FIG. 4). In this embodiment, the wheel phase angle sensor 212
measures a first wheel phase angle (P1) at a first time (T1) and
waits a predetermined time. The wheel phase angle sensor 212 then
transmits a radio frequency message at a second time (T2) where
T2=T1+Predetermined Time. The method with which the time T2-T1 is
predetermined will be discussed later. Alternatively, the wheel
phase angle sensor 212 measures the first wheel phase angle (P1)
and detects the first time (T1) when the wheel phase angle reaches
the first wheel phase angle (P1), which will be further described
later. In this embodiment, the wheel units 101, 102, 103, 104 may
be pre-programmed to recognize this Predetermined Time. For
example, in a tire mounted TPM sensor the act of "striking" the
ground provides an indication that the tire sensor has completed a
revolution, relative to a previous "strike." If the TPM sensor
reports the time since the last strike, then the phase of the wheel
can be deduced. It may also be desirable, although not essential,
that the period of the wheel revolution may also be sent.
[0055] In one embodiment, the Predetermined Time (T2-T1) may be
fixed and selected to ensure multiple wheel rotations between the
first time (T1) and the second time (T2). In case the difference in
wheel speed between vehicle wheels may be small, setting the value
of the Predetermined Time (T2-T1) to cover multiple wheel rotations
may improve accuracy of the auto-location. Accordingly, a tire
pressure monitoring system according to this embodiment may
sufficiently comply with accuracy requirements. Alternatively, in
another embodiment, a period between the first time and the second
time (T1, T2) may be variable, whereas a phase angle difference or
a phase delta may be fixed. This embodiment will be further
explained in detail below.
[0056] As discussed in connection with FIG. 2 above, the
microcontroller 202 calculates and determines a wheel phase angle
difference (PD) by subtracting the second wheel phase angle (P2)
from the first wheel phase angle (P1). The wheel phase angle
difference (PD) may range between 0 degree and 360 degree. In this
embodiment, the wheel units 101, 102, 103, 104 may transmit a radio
frequency message including the wheel phase angle difference to the
ECU 300. The wheel units 101, 102, 103, 104 may transmit the radio
frequency message at a time that the wheel phase angle difference
(PD) is obtained, i.e., the second time (T2). Because the wheel
units 101, 102, 103, 104 provide the wheel phase angle difference
(PD), the ECU 300 may reduce the burden of calculating the wheel
phase angle difference. Tire pressure monitoring systems are
time-critical applications, and additional time to process the
calculation of the wheel phase angle difference (PD) may introduce
uncertainty and increase inaccuracy.
[0057] As shown in FIG. 1, the ECU 300 periodically receives ABS
data from the ABS sensors 201, 202, 203, 204. Additionally, the
vehicle may include an Electronic Stability Control (ESC) system
which may be the source of other inputs, such as steering angle,
vehicle yaw, etc. to the ABS system information to help control
vehicle progress through curves in the road. For instance, the ECU
300 receives the ABS data every 40 ms. As shown in FIG. 4, a
rolling window of ABS data is stored, running from the present
point to a point in the past. In this embodiment, the rolling
window of the ABS data is stored for each wheel throughout the
entire drive. The rolling window of the ABS data is variable and
large enough to contain the first time (T1). The stored ABS data
provides a historic ABS trace between the first time (T1) and the
second time (T2). The ABS data includes information that is used to
measure a phase through which the wheel has rotated. In one
embodiment, the ABS data may include a number of ABS teeth that
pass through the ABS sensors 201, 202, 203, 204 during a
predetermined period of time. Only as one example, 48 teeth pass
through the ABS sensor 210, which indicates completion of a full
cycle. The ABS data for the number of counts may be divided by the
number of teeth per wheel which is constant. The remainder of the
number of counts divided by the number of teeth gives an estimate
of wheel angle change over any given period. Using the above
example of 48 teeth, 48/48=1 and the remainder is zero.
Accordingly, the ECU 300 determines that there is no wheel phase
angle change.
[0058] As shown in FIG. 4, the first time (T1) and the second time
(T2) may serve as time points at which correlation of wheel phase
angles (P1, P2) with ABS data shall occur. The time delay or the
time period between the first time (T1) and the second time (T2)
may be predetermined in order to ensure generation of effective
phase angle data and ABS data that result in accurate
auto-location. The time delay or the time period between the first
time (T1) and the second time (T2) may be known to the ECU 300 and
the wheel units 101-104 such that the first time (T1), the second
time (T2), the first phase angle (P1), etc. may be later calculated
and determined. Alternatively, in another embodiment, the time
period between the first time (T1) and the second time (T2) may be
variable.
[0059] Referring to FIGS. 5-8, a method for performing
auto-location of a wheel using wheel phase angle information is
explained in detail. FIG. 5 is a flow chart illustrating one
embodiment of a method for performing auto-location of a wheel
using wheel phase angle information. In particular, FIG. 5 shows
operations at the wheel unit 101 for convenience. The operations at
the wheel unit 101 may be equally applicable to the wheel units
102, 103, 104. In the embodiment illustrated in FIG. 5, the time
period between the first time (T1) and the second time (T2) is
pre-determined, whereas a phase angle difference between the first
phase angle (P1) and the second phase angle (P2) is variable.
[0060] As shown in FIG. 5, at the wheel unit 101, the first wheel
phase angle (P1) is measured at the first time (T1) and the second
wheel phase angle (P2) is measured at the second time (T2) after
passage of the predetermined time (Step 502). At the wheel unit
101, the wheel phase angle difference (PD) is calculated by
subtracting P1 from P2 (Step 504). The microcontroller 202
generates the radio frequency message including tire pressure, the
identifier of the TPM sensor 208, and the wheel phase angle
information. The radio frequency message is transmitted via the
transmitter 214 and the antenna 216 (Step 506). The radio frequency
message is transmitted a plurality of times (e.g., 5 times or 8
times) to ensure that the ECU 300 receives the message, considering
clashing and path loss. Thus, interframe spacing may be introduced
to avoid clashing, which occurs when two transmitters transmit at
the same time so as to be indistinguishable to the receiver. (Step
520). The same wheel phase angle information is duplicated in each
frame 1 to 8. If the first frame of data is not received, then the
ECU 300 must be able to calculate the time at which frame 1 was
transmitted in order for the wheel phase angle data to be accurate
(Step 520). Therefore, the transmitted frames which contain the
wheel phase angle information need a predetermined interframe
spacing known to the ECU 300. The frames may be numbered 1 through
8, or alternatively, the frame number information could be deduced
by the ECU from the interframe spacing.
[0061] In one embodiment, the wheel phase angle information
includes the first wheel phase angle (P1) and the second wheel
phase angle (P2). The wheel unit transmits the first and the second
wheel angles (P1 and P2) at the second time (T2) (Step 508). In
another embodiment, the wheel phase angle information includes the
second wheel phase angle (P2) and the wheel phase angle difference
(PD) which is transmitted at the second time (T2) (Step 510). In
further another embodiment, the wheel phase angle information
includes only the wheel phase angle difference (PD) (Step 512).
[0062] FIG. 6 is a flow chart illustrating one embodiment of the
method for performing auto-location of the wheel using wheel phase
angle information at the ECU 300. In the illustrated embodiment,
the wheel phase angle difference (PD) is received at the second
time (T2) (Step 602 and Step 512). Here it is assumed that the ECU
300 has received the first frame. The ECU 300 calculates the first
time (T1) based on the fixed time delay which is known to the ECU
300 (Step 604). The first time (T1) may need calculation to give a
reference point at which the ABS data will be analyzed. As noted
above, the period between the first time (T1) and the second time
(T2) is set up to ensure that a meaningful phase angle difference
between the measured phase angles can be obtained.
[0063] After determining the first time (T1), the ECU 300 is able
to calculate a phase angle difference for each ABS data per wheel
between T1 and T2 (Step 606). Using the example discussed above, 48
teeth of ABS teeth that have passed the period between T1 and T2
may indicate two full rotations of the wheel and the zero remainder
of 48 teeth/24 teeth indicates zero phase angle difference. The ECU
300 compares the wheel phase angle difference (PD) against the
phase angle difference for each ABS data (Step 608). In other
words, the ECU may estimate, by interpolation of the RF message
phase measurement, what the number of counts from each ABS sensor
would have been and search for a match from the ABS data for a
wheel unit that has a similar wheel angle. The purpose of the
correlation is to determine which set of ABS data matches with the
deduced phase rotation of the wheel phase angle sensor 212.
[0064] There are a number of ways to perform the interpolation. For
example, linear interpolation based on the assumption that the
vehicle speed is relatively constant may be used. For example,
every wheel on the vehicle will rotate at least 0.1% difference in
overall effective circumference. After 60 seconds at 40 kmh
(typically 5.5 Hz), the difference in angular rotation of each
wheel will likely be 0.001*5.5*60. This equates to 1/3 of a
revolution or 120 degrees. As a result, the ECU 300 assigns the
identifier to a location whose phase angle difference of ABS data
mostly closely matches to the wheel phase angle difference
transmitted from the wheel unit 101.
[0065] FIG. 7 is a flow chart illustrating another embodiment of
the auto-location method. In the illustrated embodiment, the wheel
phase angle (P2) and the wheel phase angle difference (PD) are
received at the second time (T2) (Step 702 and Step 510, as shown
in FIG. 7. It is assumed that the ECU 300 has received the first
frame. The ECU 300 calculates the first time (T1) based on the
fixed time delay known to the ECU 300 (Step 704). The calculated
first time (T1) is a reference point at which the ABS data will be
analyzed. The ECU 300 further calculates wheel phase angle (P1) by
subtracting the wheel phase angle difference (PD) from the second
phase angle (P2) (Step 706). The ECU 300 retrieves historic ABS
data that is stored and determines ABS trace at the first and the
second times (T1, T2) (Step 708). Subsequently, the ECU 300
compares wheel phase angles (P1, P2) which are transmitted from the
wheel unit against ABS data at the first and the second time (T1,
T2) (Step 710). As a result, the ECU 300 assigns the identifier to
a location whose phase angle difference of ABS data mostly closely
matches to the wheel phase angle difference transmitted from the
wheel unit (Step 712).
[0066] FIG. 8 is a flow chart further illustrating another
embodiment of the auto-location method. In the illustrated
embodiment, the wheel phase angles (P1, P2) are received at the
second time (T2) (Step 802), as shown in FIG. 8, unlike the
embodiments illustrated in FIGS. 6 and 7. The ECU 300 calculates
the first time (T1) based on the fixed time delay as the reference
point (Step 804). Subsequently, the ECU 300 retrieves stored ABS
data and determines ABS trace at the first and the second times
(T1, T2) (Step 806). The ECU 300 then compares wheel phase angles
(P1, P2) which are transmitted from the wheel unit 101 against ABS
data at the first and the second time (T1, T2) (Step 808). As a
result, the ECU 300 assigns the identifier to location whose phase
angle difference of ABS data most closely matches to the wheel
phase angle difference transmitted from the wheel unit (Step
810).
[0067] As discussed in connection with the above-described
embodiments, the wheel units 101, 102, 103, 104 measure the wheel
phase angle of the associated wheels LF, RF, LR and RR at two
different times and determine the relative phase angle difference.
The relative phase angle difference is transmitted to the ECU 300
at a later measurement time such that the relative phase angle
difference is compared with similar information extracted from the
ABS system. The ECU 300 will receive RF messages from the wheel
units 101, 102, 103, 104 including the phase angle difference and
compare the phase angle difference from the wheel units 101, 102,
103, 104 with the ABS data from the ABS sensors 201, 202, 203, 204.
The ECU 300 periodically receives the ABS data and stores a
variable rolling window of the ABS data which covers the first time
(T1) and the second time (T2). Thus, the ECU 300 may estimate, by
interpolation of the RF message phase measurement, what the ABS
data from each ABS sensor would have been between the first time
(T1) and the second time (T2) and searches for a match from the ABS
data for a wheel unit that has a similar wheel angle. The purpose
of the correlation is to determine which set of ABS data matches
with the deduced phase angle of the wheel phase angle sensor
212.
[0068] In the above-described embodiments, the ECU 300 determines
and uses as a reference point the first and the second times T1, T2
in order to perform the auto-location. The ECU 300 calculates the
first time based on the second time T2 and the fixed time delay
known to the ECU 300. The ECU 300 then determines ABS data that
corresponds to the first and the second time T1 and T2. In other
words, the above-described embodiments rely upon the first time
(T1) and the second time (T2) to define a relevant wheel phase
angle and relevant ABS data for correlation. By comparing two
different sets of data within the identical reference points, T1
and T2, accurate correlation may be obtained. Simple and accurate
implementation of correlation between the wheel phase angle
information from the wheel units 101, 102, 103, 104 and the ABS
data may be obtained. Furthermore, the period between the first
time (T1) and the second time (T2) may be easily variable to
accommodate changing situations and ensure the system accuracy
requirements.
[0069] Moreover, as the wheel units 101, 102, 103, 104 may
calculate and determine the phase angle difference, calculation
burdens on the ECU 300 may be reduced. Because a tire pressure
monitoring system is a time-sensitive application, reduced
calculation time by the ECU 300 may increase accuracy and
efficiency of such systems.
[0070] In the above-described embodiments, auto-location for
determining the location of TPM sensors is performed based on the
fixed time delay between the phase angle measurements and the
variable phase angle difference. In another embodiment, the
auto-location may also be realized by the wheel units 101, 102,
103, 104 and the ECU 300 knowing a fixed phase angle difference or
a fixed phase delta which will occur between variable measurements
times (TD=T2-T1). In other words, the phase delta is fixed, and the
period between the first time (T1) and the second time (T2), i.e.,
T2-T1 is variable. Referring to FIG. 9, the embodiment where the
phase delta is fixed and the time period (T2-T1) is variable is
explained in detail. When a wheel unit 102 decides to perform an
auto-location event, the wheel unit 102 waits until it reaches a
self-determined phase angle (P1). The wheel unit 102 then
determines the time that the self-determined phase angle (P1) is
reached and stores such time (T1) (Step 902). In this embodiment,
the wheel unit 102 is discussed only for convenience and other
wheel units 101, 103 and 104 may be equally available. After
rotating through the fixed phase delta known to the wheel unit 102
and the ECU 300, the wheel unit 102 reaches the second phase angle
P2 (P2=P1+fixed phase delta) (Step 904). The wheel unit 102
determines the time that the second phase angle P2 is reached and
stores the time (T2) (Step 904).
[0071] The wheel unit 102 transmits the identification, and Time
Difference (TD=T2-T1) (Step 906). As discussed above in conjunction
with FIG. 5, the wheel unit 102 transmits the same radio frequency
message a plurality of times to ensure that the ECU 300 receives
the radio frequency message (Step 908). The ECU 300 receives the
identification and the Time Difference (TD). The ECU 300 correlates
the Time Difference (TD) for a known phase angle with ABS
information (Step 910). The identification is assigned to the ABS
location which has swept through the fixed phase angle in the Time
Difference (TD) (Step 912). In this implementation, the fixed phase
angle does not have to be an integer number of revolutions. In
other words, the second phase angle (P2) does not have to equal
(P1+(N*360.degree.)), where N is an integer. The phase difference
(PD) could be encoded in the transmission at T2, or it could be a
pre-determined value which is known to both the wheel unit and the
ECU.
[0072] The foregoing embodiments describe that the wheel unit
transmits wheel phase angle information which includes actual
measurements, a value derived from the actual measurement, etc.
such as first phase angle P1, the second phase angle P2, and/or the
phase angel difference (PD). The wheel phase angle information,
however, is not limited to the actual measurement of the wheel
phase angle and/or the phase angle difference. The wheel phase
angle information may include any information indicative of, and/or
translatable to a wheel phase angle. Moreover, the wheel phase
angle information may include information that prompts or triggers
auto-location. For example, the wheel phase angle information may
include wheel phase angle indication. Receipt or detection of the
wheel phase angle indication may trigger the ECU to perform a phase
correlation data storage event. The ECU continuously maintains a
rolling window of the ABS data. In response to the phase
correlation data storage event, the ECU stores or captures relevant
ABS data. In one embodiment, the wheel phase angle indication may
include a predefined function code. In another embodiment, the
wheel phase angle indication may include setting a bit which is
normally unused in a RF message structure, or a most significant
bit of a certain data byte. Alternatively, or additionally, the
wheel phase angle indication may include temperature data or
interframe spacings of RF transmissions.
[0073] Moreover, the foregoing embodiments compare a wheel phase
angle difference with ABS data at two different times (T1, T2) to
perform auto-location of a wheel. Alternatively, or additionally,
the auto-location of the wheel where the TPM sensor is arranged may
require a snapshot of information at one measurement point of a
wheel phase angle during a rotation of the wheel, where a snapshot
is a capture of information from a short duration of a continuous
stream of information. The wheel unit transmits an RF message that
includes or is associated with the wheel phase angle indication.
The ECU holds a rolling window of wheel phase and/or speed data
such as ABS data for all wheels. Upon receipt of the RF message,
the ECU captures and stores a current content of the rolling window
of the ABS data. Then, the ECU determines relevant ABS data from
the rolling window at a predetermined time, i.e., T1. An
auto-location algorithm is applied to the stored ABS data in order
to identify the specific location of the wheel where the TPM sensor
is arranged. Referring to FIGS. 10-17, these different embodiments
of the wheel auto-location system and method are described
below.
[0074] FIG. 10A illustrates the one-measurement point during the
rotation of the wheel. The wheel unit 101 detects the first time
(T1) when the wheel phase angle reaches the first phase angle (P1).
The first phase angle (P1) is an angle of interest which may be set
depending on the hardware configurations of tire pressure
monitoring systems. As one example, the first phase angle (P1) may
be a zero-crossing point, i.e. zero, or a peak in order to
facilitate efficient implementation of system hardware
configurations. The first phase angle (P1) is not limited to the
zero-crossing point or the peak and any angle can be set as the
first phase angle (P1). The wheel unit 101 is described in this
embodiment by way of example, and other wheel units 102, 103, 104
can be used. The wheel unit 101 waits a predetermined time delay
(TD=T2-T1) and transmits a RF message. In this embodiment, the
controller 202 of the wheel unit 101 is programmed to know the
predetermined time delay (TD). The wheel unit 101 may not measure a
wheel phase angle at the second time (T2). Accordingly, the wheel
phase angle at the second time (T2) is undetermined in this
embodiment. In other embodiments, the wheel phase angle at the
second time (T2) may be measured. The ABS sensors 201, 202, 203,
204 transmit ABS data to the ECU 300 via the receiver 400, as
described in connection with FIG. 1 above. In another embodiment,
fewer than four ABS sensors may transmit ABS data to the ECU 300,
which will be further described below.
[0075] FIG. 10B illustrates the rolling window of the ABS data from
four wheels. The ECU 300 continuously maintains the rolling window
of the ABS data as shown in FIG. 10B. The sinusoidal wave of the
wheel phase angle at the first time (T1) and the second time (T2)
is also shown in FIG. 10B. The ECU 300 does not store or capture
each rolling window of the ABS data. Instead, the ECU 300 responds
to a phase correlation data storage event trigger and captures the
current content of the rolling window of the ABS data that spans
the first time (T1) and the second time (T2) as illustrated in FIG.
10B. The phase correlation data storage event trigger will be
described in detail below, referring to FIGS. 11A-11D. The ECU 300
repeats this capturing or storing process multiple times until a
significant number of the current contents of the ABS data is
captured and stored in order to ensure reliability.
[0076] FIGS. 11A-11D illustrate various embodiments of implementing
the phase correlation data storage event trigger. FIGS. 11A-11D
also illustrate various embodiments of implementing wheel phase
angle indication such that the phase correlation data storage event
is triggered. FIGS. 11A-11C illustrate contents of RF messages
transmitted by a wheel unit and received by the ECU. Referring to
FIGS. 11A and 11B, a first embodiment of the wheel phase angle
indication is explained. In the first embodiment, an RF message
1100 contains information corresponding to wheel phase angle
indication. In FIGS. 11A and 11B, an exemplary RF message 1100 sent
from the wheel unit 101 is illustrated. The RF message includes
digital data arranged in a number of data fields including, for
example, a synchronization field such as a data preamble, a
function code field, an identifier field, a pressure data field, a
temperature data field and an error detection and correction field
such as a checksum. Additional or fewer data fields maybe used and
the field locations in the RF message may be standardized to ensure
reliable reception of the RF message. The structure of the RF
message 1100 may vary depending upon vehicle hardware and/or
software where this embodiment of the wheel auto-location system
and method is used. In this embodiment, the function code field
corresponds to the wheel phase angle indication. The function code
field may be referred to as a status code field or a status byte
field.
[0077] As described above, the wheel unit 101 transmits the RF
message 1100 at the second time (T2) after the wheel phase angle
reaches the first phase angle (P1) and waits the predetermined time
delay (TD). The RF message 1100 may not include an actual wheel
phase angle, as shown in FIGS. 11A and 11B. The RF message of FIG.
11A includes a preamble, a function code 1110, an identification of
a wheel, tire pressure, temperature, and a checksum. The RF message
structure including the preamble, the tire pressure, the checksum,
etc. as shown in FIG. 11A uses a conventional RF message structure.
The function code 1110 may include a predefined function code which
prompts or instructs the ECU 300 to trigger a phase correlation
data storage event. The phase correlation data storage event
indicates to the ECU 300 that a current content of a rolling window
of the ABS data should be captured by the ECU 300. As described in
connection with FIG. 1 above, the ECU 300 receives ABS data from
the ABS sensors 201, 202, 203, 204. The ECU 300 is continuously
holding a rolling window of the ABS data which has dimensions the
same or greater than the predetermined time period (TD). As shown
in FIG. 10B, the ECU 300 captures the current content of the
rolling window of the ABS data in response to the phase correlation
data storage event and stores it in its storage.
[0078] Referring back to FIGS. 11A and 11B, the function code 1110
may include a bit that has been set or changed to set to trigger
the phase correlation data storage event. As one example, the bit
is normally unused in a RF message structure. As another example,
the bit includes two most significant bits of a certain data byte,
which is normally set to zero. As shown in FIG. 11A, the RF message
1100 sent from the wheel unit 101 includes wheel phase angle
indication by adding the function code 1110. For example, the RF
message 1100 is encoded to set a bit of the function code 1110 that
triggers the phase correlation data storage event. The RF message
1100 shown in FIG. 11A includes no actual phase angle. The RF
message 1100 may include the wheel phase angle indication
implemented by the function code bits 1110. The structure of the RF
message 1100 has benefits of including no wheel phase angle
information. This message structure having no wheel phase angle
information may provide flexibility as a standard frame protocol
may not need to change in order to include phase angle
information.
[0079] In FIG. 11B, the RF message 1100 may include data defining
the predetermined time delay (TD=T2-T1) 1120 using a dataframe
assigned to temperature data in addition to the function code bits
1110. The predetermined time delay may represent the wheel phase
angle. In another embodiment, the RF message 1100 may include a
pseudo-random number that indicates or is translatable to the wheel
phase angle. Various types of information which represents the
wheel phase angle may be included in the RF message 1100. For
example, the wheel phase information could be encoded into 8 bits
of data. This would allow a phase resolution of
360/255=1.41.degree. to be realized.
[0080] Another method to provide wheel phase information is to
assign a code to specific wheel phase angles. The transmitter 214
(FIG. 2) would then transmit the code which corresponds to the
particular phase angle of interest. In this embodiment, the ECU 300
stores a lookup table in the storage 304. The lookup table maps the
codes to actual phase angles, and the ECU 300 then deduces the
phase from the transmitted code. In a further embodiment, the time
delay (TD) may be one of several options known to both the wheel
units 101, 102, 103, 104 (FIGS. 1 and 2) and the ECU 300. More
specifically, the wheel units 101, 102, 103, 104 will transmit a
short code which corresponds to one of the several options. The ECU
decodes the short code, and determines which of the several options
for the time delay (TD) have been used by the wheel units 101, 102,
103, 104. In a further embodiment, the wheel units 101, 102, 103,
104 may encode the actual time delay (TD) value in the radio
frequency transmission. For example, with a resolution of 1
millisecond and eight bits of information, a time delay of 255
milliseconds could be communicated.
[0081] Referring to FIG. 11C, a second embodiment of the phase
correlation data storage event trigger is described. FIG. 11C
illustrates an RF message that includes temperature data 1130. In
this embodiment, the temperate data 1130 includes 8 bits. As shown
in FIG. 11C, 8 bits of temperature data indicate the normal
operating temperature range of the tire pressure sensor 208 (FIG.
2). The normal operating temperature generally ranges from
-40.degree. C. to +125.degree. C., and the temperature byte 1130
has the capability to indicate temperatures from -50.degree. C. to
+205.degree. C. The temperatures above +125.degree. C. may not have
any practical application. Accordingly, some of the temperature
bits are used to encode the wheel phase angle indication. By using
the example illustrated in FIG. 11C, the temperature of
+142.degree. C. corresponds to 11000000 and the two most
significant bits of the temperature byte are `11.` The temperature
of +142.degree. C. is well above the maximum operating temperature.
The code, 11000000 may be used to trigger a phase correlation data
storage event in this embodiment.
[0082] In FIG. 11D, a third embodiment of a phase correlation data
storage event trigger is illustrated. In the third embodiment, an
interframe spacing among a series of RF message transmissions
corresponds to the wheel phase angle indication and is used to
trigger the phase correlation data storage event. In this
embodiment, multiple RF message transmissions occur during the one
second transmission. For instance, the identical information is
transmitted eight times over a one second time period. The
structure of the RF message frame, the number of RF message frames
and the interframe spacings discussed in this embodiment are only
by way of example and not limited thereto. The structure of the RF
message frame, the number of RF message frames and/or the
interframe spacings may vary.
[0083] As shown in FIG. 11D, each interframe spacing between two
consecutive RF transmissions varies. In this embodiment, 109.86 ms,
189.94 ms and 159.67 ms are respectively set as interframe
spacings. The interframe spacings are encoded and known to the ECU
300. When the ECU 300 receives the first three RF transmissions
1140, 1145 and 1150, the ECU 300 recognizes the interframe spacings
of 109.86 ms and 189.94 ms. Then, the ECU 300 calculates when the
first RF transmission 1140 is received. The time that the first RF
transmission 1140 is received corresponds to the second time (T2).
The ECU 300 subsequently calculates the first time (T1) and
determines the ABS data at the first time (T1).
[0084] In FIGS. 11A-11D, various embodiments of the phase
correlation data storage event trigger are explained. However, the
wheel auto-location method is not limited to those embodiments and
other ways of implementing the phase correlation data storage event
are available. As described in connection with the embodiments of
FIGS. 11A-11D, the ECU 300 receives or recognizes the phase
correlation data storage event trigger based on the wheel phase
angle indication. The ECU 300 responds to the wheel phase angle
indication and performs the phase correlation data storage event.
As illustrated in FIG. 10B, the ECU 300 stores or captures the
current content of the rolling window of the ABS data in response
to the wheel phase angle indication. Then, the ECU 300 calculates
the first time (T1) based on the predetermined time delay (TD)
which has been known to the ECU 300. The ECU 300 determines
relevant ABS data from the ABS data stream, i.e., the stored
current content of the rolling window of the ABS data relevant to
the first time (T1). In this embodiment, the relevant ABS data
corresponds to an ABS tooth count number at the first time (T1).
The relevant ABS data is stored over time as the ECU 300 receives
the RF message 1100 multiple times and repeatedly determines and
stores the relevant ABS data. The ECU 300 stores the ABS data in
the storage 304 and executes an auto-location algorithm that
correlates the stored relevant ABS data with a specific wheel
location. The auto-location algorithm is executed to identify the
specific wheel location based on the trace of the relevant ABS data
using a statistical correlation method.
[0085] Referring to FIG. 12, one embodiment of an auto-location
method is further explained in detail. The wheel unit 101 detects
the first phase angle (P1) which is set as an angle of interest at
the first time (T1) when the first phase angle (P1) is reached
(Step 1210). The first phase angle (P1) is not limited to a
particular angle and is set depending on system hardware
configuration. Actual values of the first phase angle (P1) may
depend on a frequency of wheel rotation.
[0086] The wheel unit 101 waits for the predetermined time delay
(TD=T2-T1) where the time delay is known to the ECU 300 (Step
1215). The wheel unit 101 may not measure a phase angle other than
the measurement at the first time (T1). In this embodiment, timing
of one measurement, i.e., T1 and the predetermined time delay (TD)
may be indicative of the wheel phase angle. Actual phase angles of
the wheel may not be used.
[0087] After waiting the predetermined time delay (TD), the wheel
unit 101 transmits the RF message 1100 to the ECU 300 at the second
time (T2) (Step 1220). The RF message 1100 includes the wheel phase
angle indication. As described above, the RF message 1100 includes
predefined function code bits 1110 such that the phase correlation
data storage event will be triggered by the ECU 300.
[0088] The ECU 300 continuously maintains a rolling window of the
ABS data, the window having dimensions the same or greater than the
predetermined time delay (TD). The ECU 300 receives the RF message
1100 and recognizes the function code bits 1110 (Step 1225). When
the RF message 1100 includes the time delay (TD) data, the ECU 300
also recognizes such data. When the time delay (TD) data is
recognized, the ECU 300 stores the current values in the rolling
window of the ABS data. These current values of the rolling window
will be used by the ECU 300 to perform the phase correlation data
storage event upon receipt of the RF message 1100.
[0089] The ECU 300 calculates the first time (T1) based on the
predetermined time delay (TD) upon receipt of the RF message 1100
(Step 1230). The ECU 300 then determines an ABS tooth count for
each wheel at the first time (T1) (Step 1235). The ECU 300 stores
the ABS tooth count and repeats this process until a significant
number of the phase correlation data storage events have occurred
(Step 1240). The stored ABS tooth count values are provided as an
input to the auto-location algorithm. The output of the
auto-location algorithm is the association of a wheel unit ID with
a specific ABS sensor location on the vehicle.
[0090] Referring to FIGS. 13-17, the auto-location algorithm is
explained. FIGS. 13 and 14 illustrate one example of the ABS tooth
count values at the first time (T1) for all wheels which have been
stored by the ECU 300. With respect to a series of the RF
transmissions from a left rear wheel unit, the ABS tooth count
values at the first time (T1) from a left front ABS sensor are 93,
82, 18, 48, 71 for the first five transmissions. Likewise, the ABS
tooth count values at the first time (T1) from a right front ABS
sensor and a right rear ABS sensor are 40, 23, 62, 47, 55 and 15,
57, 20, 4, 12, respectively, for the first five transmission. On
the other hand, a left rear ABS sensor shows a statistically
significant and consistent tooth count values, i.e., 32, 30, 29,
30, 31 at the first time (T1) for the first five transmissions.
Even after 15 transmissions, the consistent tooth count values
remain unchanged. The auto-location algorithm uses the stored ABS
tooth count values as an input.
[0091] The stored ABS tooth count values as shown in FIGS. 13 and
14 enable the ECU 300 to perform statistical processing. The stored
ABS tooth count values show a historic trace of the ABS tooth count
values for each wheel. By statistically processing the trace of the
ABS tooth count values at a one-measurement point, identifying a
specific location of a wheel is achieved. One example of the
statistical processing uses a standard deviation of the ABS tooth
count values over time, as will be described in detail below.
Another example of the statistical processing may include variance.
The statistical calculation will also be designed with
consideration of ease of calculation and minimization of memory
resources.
[0092] Referring to FIGS. 15A and 15B, FIG. 15A illustrates one
example of the standard deviation for all four wheels, and FIG. 15B
illustrates one example of the tooth count values for all four
wheels with respect to the RF transmissions from the left rear
wheel. When the auto-location algorithm calculates the standard
deviation, the wheel location is associated with the location of
the ABS sensor whose ABS data shows the lowest standard deviation
(Step 1706). Referring to FIG. 16, the corresponding ABS sensor
indicates the lowest standard deviation of ABS tooth count
values.
[0093] In this embodiment, the auto-location algorithm determines a
standard deviation of a series of ABS sensor tooth count values. As
shown in FIG. 16, the ABS sensor assigned to a corresponding wheel
shows a lowest standard deviation. For instance, for the left front
(LF) wheel, the left front ABS sensor shows the lowest standard
deviation. In other words, the left front ABS sensor shows the most
consistent tooth count value at the first time (T1). Also, the left
front ABS sensor shows a statistically significant trend. Likewise,
for the right front (RF) wheel, the right front ABS sensor shows
the lowest standard deviation with regard to a series of ABS tooth
count values at the first time (T1). Thus, the ECU 300 executes the
auto-location algorithm and correlates the ABS tooth count values
with a specific wheel location. As a result, the ECU 300 assigns a
wheel unit ID to the specific wheel location which is associated
with the specific ABS sensor location.
[0094] FIG. 17 is a flowchart illustrating one embodiment of the
auto-location algorithm. As a drive of a vehicle begins, the ECU
300 receives a RF transmission including tire pressure and needs to
identify the location of a wheel associated with the RF
transmission (Step 1702). The ECU 300 checks whether a significant
number of phase correlation data storage events have occurred and a
reliable database is formed. When the reliable database is formed,
the ECU 300 activates the auto-location algorithm (Step 1702). By
way of example only, full auto-location times may be less than 5
minutes, with an average of less than 2 minutes. The auto-location
algorithm remains active through the remainder of that drive. In
this embodiment, the auto-location algorithm includes instructions
of retrieving stored ABS tooth count values at the first time (T1)
for each wheel during N consecutive RF transmission from each wheel
(Step 1704). Referring to FIG. 13, ABS tooth count values, 93, 82,
18, 48, 71 . . . are retrieved with respect to the left front
wheel. Likewise, different ABS tooth count values at the first time
(T1) are retrieved with respect to the right front, the right rear
and the left rear wheels.
[0095] In this embodiment, the auto-location algorithm further
includes calculating a standard deviation of a series of ABS tooth
count values for each wheel (step 1706). Alternatively, or
additionally, the auto-location algorithm further includes
instructions of determining a statistically significant trend of
ABS tooth count values for each wheel (step 1708). In another
further embodiment, the auto-location algorithm includes
instruction of determining dynamic thresholds of a wheel unit
associated with the tooth count values of minimum deviation.
Dynamic thresholds allow the wheel auto-location system to
dynamically change the decision parameters for the wheel assignment
logic, i.e., the value set for the standard deviation can be
changed. In one embodiment, dynamic thresholds indicate a multiple
of the minimum deviation. The association decision will be based on
the dynamic thresholds and thus will react to adverse operating
conditions. Adverse operating conditions may be present in
situations where a vehicle experiences driving on rough roads,
extreme braking, etc. It is also advantageous to permit the system
to have flexible, self-determined threshold criteria when operating
on a surface which is conducive for optimal accuracy of wheel phase
angle determination, but which results in the vehicle wheel speeds
having minimal difference.
[0096] When the auto-location algorithm determines a statistically
significant trend of ABS tooth count values, the wheel location is
associated with the location of the ABS sensor whose ABS data shows
the most consistent tooth count values or a statistically
significant trend. Referring to FIG. 15B, the left rear ABS sensor
shows the most consistent tooth count value and the lowest standard
deviation at the first time (T1) throughout the series of RF
transmission from the left rear wheel.
[0097] In the above-described embodiments, four ABS sensors are
associated with each of four wheels in the vehicle. In another
embodiment, the vehicle's ABS system does not provide wheel phase
and/or speed data for all wheels on the vehicle. FIG. 18 is a
flowchart illustrating an embodiment where front wheels are
associated with ABS sensors and the remaining wheels are not
associated with ABS sensors. Vehicle platforms may differ depending
on vehicle models, manufacturers, vehicle designs, etc. Some
vehicle platforms are installed with four ABS sensors at each wheel
of a vehicle, but other vehicle platforms may be equipped with
fewer numbers of ABS sensors. In this embodiment, the ABS system
provides information for the wheels on a front axle and does not
provide information for the wheels on a rear axle. In that case,
the ABS data for the wheels on the front axle are correlated with
the wheel phase angle indication from the wheel units mounted on
the wheels on the front axle, as described in detail in the
above-described embodiments. Accordingly, the ECU determines the
location of TPM sensors arranged with the wheels on a single
axle.
[0098] The remaining wheels are not associated with ABS sensors as
they are located on the other axle of the vehicle. With respect to
the remaining wheels, the wheel units arranged on the remaining
wheels can determine if the TPM sensor is arranged on the left or
right hand side of the vehicle. For example, the wheel unit may
compare phase signals from an accelerometric device, or other
mechanism in order to determine rotation direction, lead/lag
relationship, etc. as described in detail in commonly owned U.S.
Pat. No. 6,204,758 to Wacker et al. and U.S. Pat. No. 7,367,227 to
Stewart et al. of which disclosure is incorporated herein by its
entirety. These two patents explain that position on the left or
right of the vehicle can be discerned from the polarity of the
acceleration data, indicating direction of acceleration and
lead/lag relationship associated with clockwise or counterclockwise
rotation of a wheel associated with a TPM sensor. Such
determination is combined with determination of the front/rear
location of the TPM sensor based on the ABS data from the ABS
sensor arranged on the single axle.
[0099] As illustrated in FIG. 18, the wheel unit provides TPM
sensor parameters, a wheel ID and left/right side information (Step
1802). With regard to two wheels where ABS sensors provide ABS
data, the stored ABS tooth count values at the first time (T1) is
retrieved during N consecutive RF transmissions from front wheels
(Step 1804) as described above in connection with FIG. 17. The
statistical value of the standard deviation of a series of the ABS
tooth count values for the front wheels is calculated (step 1806).
Alternatively, or additionally, a statistically significant trend
of ABS tooth count values is determined (step 1808). The wheel ID
and the TPM sensor parameters are assigned to the ABS sensor that
shows the lowest standard deviation and based on the left/right
side information from the wheel unit (Step 1810). Alternatively,
the wheel ID and the TPM sensor parameters are assigned to the ABS
sensor that shows the most consistent values and based on the
left/right side information from the wheel unit (Step 1812). This
embodiment of using the left/right determination from the wheel
unit and the front/rear determination from the ABS sensors may
provide flexibility and increased adaptability in making and using
the tire pressure monitoring system and methods, because various
different vehicle frames from different vehicle manufacturers can
be accommodated.
[0100] In the above-described embodiment, auto-location of a TPM
sensor is also performed based on the snapshot of information at
one measurement point (i.e., T1) during a rotation of the wheel
when the time delay (TD=T2-T1) is fixed. The transmission time
(i.e., T2) is used to calculate and determine the first time (T1)
at the ECU 300. The ECU 300 determines the relevant ABS data at the
first time (T1) from the rolling window of the ABS data and stores
the relevant ABS data. In one embodiment, the relevant ABS data
includes ABS tooth count values at the first time (T1). The ECU 300
responds to the wheel phase angle indication included in the RF
message 1100 sent from the wheel unit 101. The wheel phase angle
indication may include function code bits set to trigger the phase
correlation data storage event. In response to the function code
bits, the ECU 300 captures the ABS data and determines the relevant
ABS data at the first time (T1). Once sufficient ABS data is
captured and stored, the relevant ABS data is provided as the input
to the auto-correlation algorithm. The auto-correlation algorithm
uses the statistical correlation process that considers the
standard deviation of or consistency in ABS data traces. Then, the
auto-correlation algorithm associates the specific wheel location
with the wheel location of the ABS sensor whose ABS data shows the
lowest standard deviation, or the most consistent ABS tooth count
values and determines the location of the TPM sensor arranged with
the specific wheel location.
[0101] In this embodiment, no actual wheel phase angle may be
provided to the ECU 300. Rather, the wheel phase angle indication,
which may be implemented with setting unused bits, using the
function code or the temperature data, setting interframe spacings,
or any other available mechanism, is provided to the ECU 300.
Moreover, based on information at the one-measurement point during
the rotation, the auto-location of the wheel is achieved.
Accordingly, the above-described the auto-location systems and
methods may be simplified and produce fast output. Moreover, power
consumption from the auto-location operation may be minimized.
Also, the standard data frame protocol may be used as no actual
wheel phase angle is included in the RF message data frame.
Additionally, the above-described auto-location systems and methods
are applicable to various different vehicle frames where four or
less ABS sensors are used. This may increase flexibility of the
above-described system and methods as specific ECU requirements may
be removed and different vehicle frames can be accommodated.
[0102] Although the present invention and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made herein without departing
from the spirit and scope of the invention as defined by the
appended claims. Moreover, the scope of the present application is
not intended to be limited to the particular embodiments of the
process, machine, manufacture, composition of matter, means,
methods and steps described in the specification. As one of
ordinary skill in the art will readily appreciate from the
disclosure of the present invention, processes, machines,
manufacture, compositions of matter, means, methods, or steps,
presently existing or later to be developed that perform
substantially the same function or achieve substantially the same
result as the corresponding embodiments described herein may be
utilized according to the present invention. Accordingly, the
appended claims are intended to include within their scope such
processes, machines, manufacture, compositions of matter, means,
methods, or steps.
* * * * *