Title: Combined tire pressure monitoring and keyless entry receiver
Abstract: A system for monitoring conditions within a tire (
Patent Number: 6,885,282 Issued on 04/26/2005 to Desai, et al.
| Inventors:
|
Desai; Tejas B. (Sterling Heights, MI);
Deniau; Jean-Christophe (Fenton, MI);
Leblanc; Melvin (Taylor, MI);
O'Connor; Steve (West Bloomfield, MI);
Van Drus; Kurt (Macomb, MI);
Abi-Nader; Patricia (Southfield, MI)
|
| Assignee:
|
Siemens VDO Automotive Corporation (Auburn Hills, MI)
|
| Appl. No.:
|
079665 |
| Filed:
|
February 20, 2002 |
| Current U.S. Class: |
340/5.61; 340/5.6; 340/5.64; 340/10.1; 340/10.2; 340/10.5; 340/5.62 |
| Intern'l Class: |
G05B 019//00; G06F 007//00 |
| Field of Search: |
340/56,561,564,101,105,562,825.72,825.69,34,102
|
References Cited [Referenced By]
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| 4734674 | Mar., 1988 | Thomas et al.
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| 5192929 | Mar., 1993 | Walker et al.
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| 5357798 | Oct., 1994 | Weinzerl et al.
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| 5463374 | Oct., 1995 | Mendez et al.
| |
| 5473938 | Dec., 1995 | Handfield et al.
| |
| 5602868 | Feb., 1997 | Wilson.
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| 5661651 | Aug., 1997 | Geschke et al.
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| 5963128 | Oct., 1999 | McClelland.
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| 6043738 | Mar., 2000 | Stewart et al.
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| 6218936 | Apr., 2001 | Imao.
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| 6232875 | May., 2001 | DeZorzi.
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| 6252498 | Jun., 2001 | Pashayan, Jr.
| |
| 6259361 | Jul., 2001 | Robillard et al.
| |
| 6271748 | Aug., 2001 | Derbyshire et al.
| |
| 6292096 | Sep., 2001 | Munch et al.
| |
| 6463798 | Oct., 2002 | Niekerk et al.
| |
| 6650236 | Nov., 2003 | Ghabra et al.
| |
| Foreign Patent Documents |
| 0671289 | Dec., 1995 | EP.
| |
| 0735219 | Mar., 1996 | EP.
| |
Primary Examiner: Edwards; Timothy
Assistant Examiner: Brown; Vernal
Parent Case Text
The present invention claims priority to U.S. Provisional Patent Application
Ser. Nos. 60/276,210 filed Mar. 15, 2001; 60/269,959 filed Feb. 20, 2001; 60/276,325
filed Mar. 16, 2001; 60/298,258 Jun. 14, 2001; 60/290,923 filed May 15, 2001 and
60/352,489, filed on Jan. 23, 2002.
Claims
1. A system for monitoring conditions within a tire comprising:
a sensor assembly disposed within each tire of a motor vehicle,
a transmitter in communication with said sensor assembly to transmit a frequency
shift keyed transmission indicative of current tire conditions;
a remote transmitter for actuating a remote keyless entry system, said remote
transmitter emitting a amplitude shift keyed transmission to actuate a function
of said keyless entry system;
a receiver assembly for receiving said frequency shift keyed transmission signal
indicative of said current tire conditions and said amplitude shift keyed transmission
signal to actuate a function from said remote transmitter, said receiver assembly
including an amplitude shift keyed receiver, and a frequency shift keyed receiver,
said amplitude shift keyed receiver and said frequency shift keyed receiver are
selectively engaged in receive incoming signals in response to a predetermined
triggering event wherein said transmission indicative of current tire conditions
includes an amplitude shift keyed wake-up signal for alerting said receiver assembly
of an incoming frequency shift keyed transmission signal such that said amplitude
shift keyed wake-up signal initiates a switch from said amplitude shift keyed receiver
to said frequency shift keyed receiver.
2. The system of claim 1, wherein said predetermined triggering event is the
current speed of the motor vehicle.
3. The system of claim 2, wherein said amplitude shift keyed receiver is engaged
to receive incoming signals for speeds below a predetermined speed threshold of
the said motor vehicle and said frequency shift keyed receiver is engaged to receive
incoming signals for speeds above said predetermined speed threshold.
4. The system of claim 1, wherein said transmitter sends said signal at predetermined
intervals, said predetermined intervals varied in response to motor vehicle speed.
5. The system of claim 1, wherein said predetermined interval is greater at speeds
above said predetermined speed threshold than below said predetermined speed threshold.
6. The system of claim 5, wherein said predetermined interval increases in response
to variation of pressure within one of said tires.
7. The system of claim 1, wherein said transmission indicative of said tire conditions
includes a plurality of data frames sent at random time intervals to prevent repeated
overlap of transmissions from two or more of said sensor assemblies.
8. The system of claim 7, wherein said random time interval is transmitted to
said receiver assembly such that said receiver assembly anticipates subsequent
data frames of said transmission indicative of said tire condition.
9. The system of claim 8, wherein said amplitude shift keyed receiver is engaged
during said random time interval.
10. A method of preventing data transmission overlap between signals emitted
from a tire pressure monitoring system and a remote keyless entry system, said
method comprising the steps of:
a. setting a receiver assembly including an amplitude shift keyed receiver and
a frequency shift keyed receiver such that incoming transmissions are received
by said amplitude shift keyed receiver; and
b. switching from said amplitude shift keyed receiver to said frequency shift
receiver in response to a triggering event, wherein said triggering event includes
receiving an amplitude shift keyed wake-up signal from said tire pressure monitoring
system.
11. The method of claim 10, further including the steps of emitting a frequency
shift keyed transmission from said tire pressure monitoring system, and emitting
an amplitude shift keyed transmission from said remote keyless entry system.
12. The method of claim 10, wherein said triggering event is further defined
as obtaining a vehicle speed above a predetermined threshold value.
13. The method of claim 10, wherein said amplitude shift keyed wake up signal
from the tire pressure monitoring system alerts the receiver assembly of a subsequent
frequency shift keyed transmission.
Description
BACKGROUND OF THE INVENTION
This invention relates to a system for monitoring conditions within a tire,
and specifically to a receiver assembly for receiving transmissions of varying
modulations from sensor assemblies within each of the tires and from a remote keyless
entry system. It is becoming increasingly desirable to continually monitor tire
pressures in a motor vehicle during operation. Such constant monitoring of tire
pressures allows an operator to maintain vehicle tire pressures within an optimal
range to optimize fuel economy and handling performance.
Conventional methods of monitoring tire pressure include positioning
a sensor within each wheel to monitor pressure. The sensor assembly typically emits
a radio frequency (RF) transmission indicative of tire conditions. A receiver disposed
within the vehicle receives the RF signal and actuates a messages or warning light
to signal the operator of tire conditions.
Many motor vehicles include a remote keyless entry system including a key fob
carried by an operator to actuate door locks or other features. The remote keyless
entry system includes a receiver disposed within the motor vehicle to receive transmissions
from the key fob and actuate vehicle systems in response to transmissions received
from the key fob. It is known in some system to utilize the same type of transmission
for the tire monitoring system as is used in remote keyless entry system.
Typically, a transmission is modulated either as an amplitude shift keyed
ASK, or a frequency shift keyed FSK radio frequency. The ASK transmission modulation
is best suited for applications in which the receiver and transmitter are relative
stationary to each other. In addition ASK transmissions are favorable when there
exists a relatively long distance between the transmitter and the receiver. However,
an ASK transmission becomes disrupted when the receiver or transmitter is moving
relative to one another. The FSK signal is suited for transmitters that are moving
relative to the receiver because the amplitude remains essentially constant for
the duration of any transmission. However, the FSK transmission has lower peak
field strength than a comparable ASK transmission. The FSK transmission is specifically
suited for use with the sensor assembly disposed within the tire and the ASK is
suited for use with the remote keyless entry system.
Accordingly, it is desirable to develop a receiver capable of receiving
both ASK and FSK transmissions to optimize the capabilities of both the tire monitoring
system and the remote keyless entry system.
SUMMARY OF THE INVENTION
An embodiment of this invention is a receiver assembly comprised of an amplitude
key shifted (ASK) receiver and a frequency shift keyed (FSK) receiver for receiving
transmissions from sensor assemblies mounted within each of the tires, and from
a remote keyless entry system.
A system for monitoring conditions within tires mounted to a motor vehicle includes
five tires, each with a sensor assembly. Each of the sensor assemblies gathers
data indicative of conditions within the tire and transmits that data to a receiver
assembly. The receiver assembly in turn forwards that data to a vehicle controller.
The vehicle controller will then process the data for display to the operator of
the motor vehicle.
Each tire mounts to a rim and each sensor assembly is mounted within the rim
and includes a valve stem and a circuit housing. The sensor assembly includes a
sensor circuit disposed within the circuit housing. The sensor circuit includes
a temperature sensor, a motion sensor and a pressure sensor. An RF transmitter
receives data gathered by the sensors, and relays that data to the receiver.
Each transmission from the various sensor assemblies includes a unique identity
code relating to a specific sensor assembly. An initialization or learning mode
defines specific sensor assemblies disposed on a specific motor vehicle. Learning
the specific identity codes of the sensor assemblies eliminates errant reception
of other transmissions from other sensor assemblies installed on other motor vehicles
within close proximity.
The data transmitted from each of the sensor assemblies to the receiver is transmitted
at predetermined intervals. There is a probability that the receiver will receive
two or more data transmissions from different sensor assemblies at the same time.
The receipt of two or more data transmission simultaneously or overlapped is known
as a data collision. The receiver will not recognize collided data or overlapping
data transmission, therefore the current invention prevents overlapping data transmissions
by varying the interval between data transmission in a random manner. Another factor
considered in preventing signal collision is the transmission rate that affects
the length of time required to transmit data indicative of tire conditions. The
faster data is transmitted and received the lower the probability of data collision.
The shorter the total transmission time, the lower the probability of signal collision.
The receiver assembly comprises an amplitude shift key (ASK) receiver and a frequency
shift keyed (FSK) receiver. The FSK receiver receives signals from the sensor assemblies.
The ASK receiver receives signals from a key fob for a remote keyless entry system
to initiate the locking or unlocking of doors.
The ASK transmissions are favorable for situations where the transmitter and
receiver are substantially stationary. The ASK radio frequency transmission is
easily disrupted by abrupt changes in received field strength and therefore are
not favorable for sending transmissions from a moving object such as the tires
of a motor vehicle. However, the ASK provides for greater signal power which is
desirable for the remote keyless entry system. The FSK transmissions are favorable
for conditions were the transmitter or receiver are moving during data transmission.
However, an FSK transmission is amplified upon receipt, effectively removing any
amplitude disturbances.
The receiver assembly switches between the ASK receiver and the FSK receiver
in response to a triggering event. The triggering event is the vehicle speed. At
speeds indicative of traveling along a roadway, the FSK receiver is engaged. As
appreciated, a motor vehicle traveling at speed along the roadway does not require
reception of ASK transmissions from a remote keyless entry transmitter to unlock
the doors of the motor vehicle. Conversely, a vehicle at rest or parked is unlikely
to spontaneously encounter a tire puncture, and therefore at lower speeds the ASK
receiver is engaged.
An intermediate condition is encountered when the motor vehicle is idling. In
this condition, the receiver assembly engages the ASK receiver due to the low speed
of the vehicle, however, the tire may become punctured or encounter a condition
that changes conditions within the tire. The signal from the sensor assemblies
includes an ASK wake up signal that proceeds the FSK signal transmitting data indicative
of current conditions within the tire. The ASK wake up signal triggers the change
over from the ASK receiver to the FSK receiver. The FSK receiver remains engaged
until the FSK transmission is completed and the ASK receiver is reengaged.
The system of this invention includes a receiver capable of receiving both ASK
and FSK transmissions to optimize the capabilities of both the tire monitoring
system and the remote keyless entry system.
BRIEF DESCRIPTION OF THE DRAWINGS
The various features and advantages of this invention will become apparent to
those skilled in the art from the following detailed description of the currently
preferred embodiment. The drawings that accompany the detailed description can
be briefly described as follows:
FIG. 1 is a schematic view of a motor vehicle including a tire monitoring and
remote keyless entry system;
FIG. 2 is a cross-sectional view of a tire including a sensor assembly;
FIG. 3 is a cross-sectional view of the sensor assembly mounted within the tire;
FIG. 4 is a side view of a sensor assembly;
FIG. 5 is a top view of the sensor assembly;
FIG. 6 is an exploded view of the sensor assembly;
FIG. 7 is a schematic view of the circuit assembly within the sensor assembly;
FIG. 8 is a schematic view of the components of a transmission from the sensor assembly;
FIG. 9 is a graphical representation of the format of data packets comprising
the transmission from the sensor assembly;
FIG. 10 is a graph illustrating the effect of transmission rate on signal overlap
in prior art systems;
FIG. 11 is a graph illustrating how increased transmission rate prevents data overlap;
FIG. 12 is a schematic view of the receiver assembly;
FIG. 13 is a schematic view of a motor vehicle and an external triggering device
to initialize the sensor assemblies;
FIG. 14 is a schematic view of a method of determining sensor assembly position; and
FIG. 15 is a schematic view of another embodiment of determining sensor assembly position.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of this invention is a system for monitoring conditions within
tires
mounted to a motor vehicle
10 shown schematically in FIG.
1. The
motor vehicle
10 includes four tires
12 along with an additional
tire
12 carried as a spare. Each of the tires
12 includes a sensor
assembly
14. Each of the sensor assemblies
14 gathers data indicative
of conditions within the tire
12 and transmits that data to a receiver assembly
16.
The receiver assembly
16 in turn forwards that data to a vehicle controller
18. The vehicle controller
18 will then process the data for display
to the operator of the motor vehicle
10 or to the remote keyless entry system
19 to actuate unlocking of doors
20 or other such functions as are
known to a worker skilled in the art. Preferably the remote keyless entry system
19 is an active system requiring actuation, such as by depressing buttons
on the key fob
22, however, it is within the contemplation of this invention
for passive remote keyless entry system that do not require a positive action by
the operator.
Referring to FIGS. 2 and 3, each tire
12 mounts to a rim
24.
Each sensor assembly
14 is mounted within the rim
24 and includes
a valve stem
26 and a circuit housing
28. The circuit housing
28
is preferably mounted within the tire
12 and the valve stem
26 extends
from the circuit housing
28 outward to provide a means of filling the tire
12 with air. A sensor circuit
46 disposed within the circuit housing
28 preferably includes a pressure sensor
36, a temperature sensor
32 and an accelerometer
34.
Referring to FIGS. 4-6, the valve stem
26 is pivotally mounted to
the circuit housing
28 to provide for use in rims
24 of various configurations.
The valve stem
26 is pivotally mounted to the circuit housing
28
and locked in a desired pivotal location by a lock nut
30. Pivotal adjustment
of the valve stem
26 relative to the circuit housing
28 allows for
use of the sensor assembly
14 with various configurations of wheel rims
24 (FIGS.
3 and
4).
FIG. 7, is a schematic view of the sensor circuit
46 disposed within
the circuit housing
28. The sensor circuit
46 includes the temperature
sensor
32, the accelerometer
34 and the pressure sensor
36.
Each of the sensors
32,
34 and
36 are of any configuration
known to a worker skilled in the art. An RF transmitter
40 receives data
gathered by the sensors
32,
34, and
36 and transmits that
data to the receiver
16.
A battery
38 powers the sensor circuit
46. A battery monitor measure
battery power and provides a warning indicator that is sent to the receiver assembly
16 when remaining battery power attains a desired level. The receiver assembly
16 forwards the low battery signal to the vehicle controller
18 and
in turn to the operator. Preferably the life of the battery
38 is of an
extended length such that any necessary battery change is infrequent throughout
the life span of the motor vehicle
10. A controller
44 controls how
the RF transmitter
40 emits data indicative of tire conditions.
The sensor circuit
46 also includes a low frequency receiver
42.
The low frequency receiver
42 receives signals generated to initiate the
transmission of an identity code
68 (FIG. 8) from the sensor assembly
14
in order to initialize and localize the sensor assembly
14. Initialization
of the sensor assembly
14 teaches the receiver assembly
16 the identity
codes of each sensor assembly
14 installed on the motor vehicle
10
so that the receiver assembly
16 can ignore transmission received from sensor
assemblies
14 of other motor vehicles. Localization teaches the receiver
16 and controller
18 the specific tire position of the sensor assembly
14 on the particular vehicle. The tire position includes left front tire,
right front tire, left rear tire, and right rear tire.
Referring to FIG. 8, a transmission
64 emitted by the sensor assembly
14 includes an ASK wakeup signal
66, an identity code
68 and
a data signal
70. The transmission
64 is a FSK transmission, except
for the ASK wake up signal
66.
Referring to FIG. 9, each data transmission
64 includes a number
of data frames
72. Preferably, three (3) data frames
72 are sent
for each transmission
64. The data transmitted from the sensor assemblies
14 to the receiver assembly
16 are transmitted at predetermined intervals
80. There is a probability that transmissions from the various sensor assemblies
14 to the receiver assembly
16 will arrive at the same time (schematically
indicated at
78). The receipt of two or more data frames
72 simultaneously
or overlapped, as shown at
78, is known as a data collision. The receiver
assembly
16 will not recognize collided or overlapping data transmission
because the overlapped data frames
78 are of a greater duration than the
receiver assembly
16 is programmed to receive. Overlapping data frames
72
cause the receiver assembly
16 to ignore the data frames
78. Repeated
data collisions would eliminate data transmitted from at least two of the sensor
assemblies
14.
The system of this invention includes a method of preventing repeated data collisions.
The sensor assemblies
14 of this invention prevent overlapping data frames
72 by varying the predetermined interval
80 between data frames
72
in a random manner. The length of the data frame
72 is preferably 50 milli-seconds
(ms) with the interval
80 varying according to the below listed equation.
Where: interval length is the length of time in ms between data frames;
- Standard length is a predetermined duration of time in ms; and
- Beta is a random variable with a value between 0 and 1.
Preferably the standard length of time is 100 ms; therefore the interval
length will vary between 100 ms and 200 ms depending on the value of beta. Each
transmission from the sensor assemblies
14 are sent with differing variable
intervals
80, such that even if one or more data packets
72 overlap
for any one transmission, subsequent data packets
72 will not overlap, thereby
preventing cyclical, or repeated overlap. As appreciated, differing intervals and
lengths of data frames are within the contemplation of this invention, and a worker
skilled in the art would recognize the application of this method to other lengths
of data transmission.
In another embodiment of this invention, the length of the variable interval
80
is transmitted to the receiver assembly
16. The receiver assembly
16
will then expect the next data packet
72 at the communicated interval. This
allows the receiver assembly
16 to switch back to the ASK receiver between
data frames
72.
Another factor considered in preventing signal collision is the transmission
rate. The faster data is transmitted and received the lower the probability of
data collision. Prior art FIG. 10 illustrates the likelihood of signal collisions
at a transmission rate of 4 kbaud. Each line represents the length of time required
to transmit each data frame
72 from each of the sensor assemblies
14.
FIG. 11 illustrates how the increase in baud rate decreases the probability of
overlapping data frames
72. Each line represents a length of time to transmit
one data frame
72 to the receiver assembly
16. The shorter the total
transmission time, the lower the probability of signal collision. Preferably, the
system of this invention includes a baud rate of 10 kbaud as shown in FIG. 11,
however, a worker skilled in the art would understand that different data transmission
rates are within the contemplation of this invention.
Referring to FIGS. 1 and 12 the receiver assembly
16 comprises an
ASK receiver
52 and a FSK receiver
58. The FSK receiver
58
receives signals from the sensor assemblies
14. The ASK receiver receives
signals from a key fob
22 for the remote keyless entry system
19
to initiate the unlocking of doors
20. The receiver assembly
16 also
includes an antenna
48 to receive transmissions from the key fob
22
and the sensor assemblies
14. The receiver assembly
16 includes a
low frequency driver
50 to emit a signal to the sensor assemblies
14
to initiate transmission by the sensor assemblies
14.
The antenna
48 is preferably of a length one quarter that of the wavelength
of the transmission received. Transmissions received by the antenna
48 proceed
through a resistor
54 to the RF receiver
16. A controller
60
controls which of the receivers
58 and
52 are engaged to receive
incoming transmissions.
Transmission from the various sensor assemblies
14 include the
unique identity code
68 (FIG. 8) relating to a specific sensor assembly
14. The initialization or learning mode defines the specific sensor assemblies
14 disposed on a specific motor vehicle. Learning the specific identity
codes
68 of each of the sensor assemblies
14 eliminates errant reception
of other transmissions from other sensor assemblies
14 installed on other
motor vehicles. Initialization occurs by matching the sensor assemblies
14
of a specific motor vehicle with the receiver assembly
16 of that motor
vehicle. The receiver assembly
16 disposed within the motor vehicle
10
will receive numerous signals from surrounding RF transmitting sources such as
radios, electrical appliances and other vehicle systems equipped with similar tire
sensing systems.
Referring to FIG. 13, an embodiment of initialization includes placing
the receiver assembly
16 (FIG. 1) in a learn mode and actuating each sensor
assembly
14 through the use of a triggering device, schematically shown
at
84. The triggering device can be a magnet, a transponder located at a
programming station or a low frequency emitter positioned on the motor vehicle.
The triggering device
84 initiates each sensor assembly
14 in sequence
to transmit the identity code
68. The sequence of initiating transmission
of the identity code
68 indicates the location of the sensor assembly
14
on the motor vehicle
10. The first sensor assembly
14 triggered is
the front left tire, the second is the front right and so on until all the tires
on the motor vehicle have been triggered to transmit the identity code
68
to the receiver assembly
16. The identity code
68 is stored sequentially
to indicate the position of the specific sensor assembly
14. The receiver
assembly
16 learns which sensor assembly
14 belongs to the specific
motor vehicle. In addition to the specific location on the sensor assembly on the
motor vehicle such as the front right or front left tire is also recorded in the
receiver assembly
16. This operation is repeated any time the tires
12
of the motor vehicle are changed or rotated.
Another embodiment of initialization requires no external trigger. Instead
an acceleration value from the motor vehicle
10 is communicated to the vehicle
controller
18 and compared to accelerometer data transmitted from each of
the sensor assemblies
14. The accelerometer
34 of each sensor assembly
14 transmits acceleration information of the tire
12. The acceleration
value of each tire
12 is compared to the acceleration value provided by
another vehicle system, such as the anti-lock braking system or transmission system
(indicated schematically in FIG. 1 at
86). If the acceleration signals are
equal within a predetermined tolerance value, the identity code
68 sent
within the transmission from the sensor assembly
14 will be recorded as
belonging to the specific motor vehicle.
The initialization or learning process using the compared values of acceleration
may be repeated whenever the motor vehicle
10 is in a non-moving position
for a predetermined length of time. The purpose of the relearning of the sensor
assembly identification codes is to allow for changing or rotating of the tires
12 and thereby the sensor assembly
14. The predetermined amount of
time allows for the possibility that one of the sensor assemblies
14 may
have been changed, for instance when a spare tire is installed.
In the instance, where a new tire, and thereby a new sensor assembly
14
is installed, the receiver assembly
16 receives the new identity code of
the new sensor assembly
14 during initial movement of the motor vehicle
10. The receiver assembly
16 compares the acceleration signal belonging
to the new identity code of the new sensor
14 and compares it to the acceleration
of the vehicle
10. If the vehicle acceleration is comparable, the receiver
assembly
16 will recognize the new sensor assembly
14 after a predetermined
amount of time or number of data frames. This is transparent to the operator of
the motor vehicle.
Referring to FIG. 14, in another embodiment of this invention, localization
of each of the sensor assemblies
14 is established by comparing data obtained
from another vehicle system
86 indicative of a turn of the motor vehicle
10. The tires
12 of a motor vehicle travel different distances when
turning. The inner tires
88 travel along a first radius indicated at r
1
and the outer tires
90 move along a second radius r
2. Acceleration
and turning data is compared to the acceleration at each wheel. Data transmitted
from a sensor assembly
14 mounted to one of the inner tires
88 of
the motor vehicle will indicate a lower acceleration than that of a sensor assembly
14 mounted to on of the outside wheels
90. Therefore, the side that
the sensor assembly
14 is positioned is indicated by the magnitude of acceleration
of that tire relative to the acceleration and direction of the motor vehicle
10.
Accelerometer correlation determines whether the sensor assembly is on the left
or right side of the motor vehicle
10, however, this does not indicate whether
the sensor assembly
14 is a front or rear tire.
In one embodiment of localization the front to rear location of the tire
12
is accomplished by detecting signal strength of the transmission sent from each
of the sensor assemblies
14. In this embodiment, the receiver assembly
16
includes front and rear antennas
92,
94. Transmissions received at
each antenna
92,
94 are measured for field strength. The rear antenna
94 will receive transmissions having higher field strength from the sensor
assemblies
14 disposed on the rear tires of the motor vehicle
10.
The front antenna
92 will receive a stronger transmission from sensor assemblies
14 disposed on the front tires of the motor vehicle
10. The field
strength data provides the data indicating the front or rear position of each sensor
assembly
14 and the acceleration data correlated to the turning radius of
the motor vehicle
10 provides the left or right position of each of the
sensor assemblies
14.
Referring to FIG. 15, another embodiment of localization combines low frequency
transmissions with correlation of acceleration to determine the position of the
sensor assemblies
14. Low frequency emitters
96 are positioned to
initiate transmission from the rear sensor assemblies
14. A transmission
from the low frequency emitter triggers the transmission of the rear sensor assemblies
14 that is then received by the receiver assembly
16 to indicate
a rear location of the tires
12. This provides the data required to determine
the front and rear position of any particular sensor assembly
14. The left
and right position is determined by correlating accelerometer data obtained from
each of the sensor assemblies
14. Further, a worker knowledgeable in the
art will recognize that other combination of low frequency initiating transmissions
and correlation of accelerometer data can be used to determine the specific location
of any of the sensor assemblies
14 disposed on the motor vehicle
10.
The receiver assembly
16 of this system is also used with the remote keyless
entry system
19. The receiver assembly
16 is configured to receive
transmission from both the sensor assemblies
14 and the key fob
22
(FIG.
1). Although a key fob
22 is specifically described it is within
the contemplation of this invention that the remote entry system
19 include
other active or passive transmitting means to initiate entry or operation of the
motor vehicle
10.
The receiver assembly
16 includes the ASK receiver
52 and the FSK
receiver
58. This configuration allows the receiver assembly
16 to
be used for both the remote keyless entry system
19 and the tire monitoring system.
ASK transmissions are favorable for situations where the transmitter and receiver
are substantially stationary. The ASK radio frequency transmission is easily disrupted
by abrupt changes in received field strength and therefore are not favorable sending
transmission from a moving object such as the tires
12 of a motor vehicle
10. The changes from received field strength can change for any number or
reasons within a motor vehicle including interference created by other onboard
systems, to the specific environment present at the time of the signal. However,
the ASK provides for greater signal power which is desirable for the remote keyless
entry system of this invention. The ASK transmission allows for higher peak output
field strength, relative to a comparable FSK transmission. However, the ASK transmission
decreases typical battery life and is therefore not desirable for applications
such as tire condition sensing that require longer battery life due to the difficulty
of changing batteries of the sensor assemblies disposed within the tire of the
motor vehicle.
FSK transmissions are favorable for conditions were the transmitter or receiver
are moving during data transmission. As appreciated, rotation of a tire will introduce
amplitude variations in the transmission caused by the changes in interference
patterns. If sensor assembly
14 data was transmitted by way of an ASK transmission,
the noise caused by rotation of the tire would cause data in the transmission to
become corrupted. However, an FSK transmission is amplified upon receipt to effectively
remove any amplitude disturbances. Further, the FSK transmission is less power
intensive and therefore more adaptable to the sensor assembly application that
requires longer battery life.
Referring to FIG. 12, the receiver assembly
16 defaults to sending
any transmission to the ASK receiver
52. The ASK receiver
52 operates
at a lower power and is therefore the default receiver that is on when the receiver
assembly
16 is activated. The ASK receiver
52 is engaged while the
motor vehicle
10 is stopped or parked. Preferably, the ASK receiver
52
is engaged in response to the speed of the motor vehicle being below a predetermined
speed. Preferably, the predetermined speed is 10 mph. Above 10 mph, the receiver
assembly
16 will change over to the FSK receiver
58. The switch is
initiated because it is unlikely that the remote keyless entry system
19
will be activated while the vehicle
10 is traveling at speed. The FSK receiver
58 will then receive transmissions from the sensor assemblies
14.
The conditions of the motor vehicle
10 traveling above the desired speed
or in a parked position provide definite indicators for the switch between FSK
and ASK receivers
58,
52. However, when the vehicle
10 is
idling, for instance in a traffic jam, but not moving at the desired speed to switch
from the ASK receiver
52 and the FSK receiver
58 the system will
not switch over to the FSK receiver
58 unless another conditions is satisfied.
Each transmission
64 (FIG. 8) includes the ASK wake up signal
66
that is sent prior to the FSK transmission. The ASK wake up signal
66 alerts
the receiver assembly
16 to incoming FSK transmission, which causes the
receiver assembly
16 to switch over to the FSK receiver
58. The switch
over allows the receiver assembly
16 to accept data indicative of tire conditions
from the sensor assemblies
14 while the automobile is parked or idling in traffic.
Preferably, each of the sensor assemblies
14 will transmit a signal
indicative of tire conditions at differing rates depending on the speed of the
motor vehicle. At speeds above a predetermined speed the sensor assemblies
14
will transmit tire condition data at a greater frequency. At lower speeds, indicative
of a parked vehicle, the sensor assemblies
14 transmit at a lower rate.
Preferably, the predetermined speed is 10 mph and the sensor assemblies
14
will transmit signals indicative of tire conditions once every minute. Below the
10 mph predetermined speed threshold the sensor assemblies
14 will transmit
signals only after sensing a change in tire pressure above a desired amount indicative
of a tire
12 losing air pressure. Once an initial loss of pressure is sensed,
the sensor assemblies
14 are triggered to transmit signals at one-minute
intervals. Although, specific speeds and intervals of data transmission are discussed,
a worker knowledgeable in the art will understand that it is within the contemplation
of this invention to use other speeds and data transmission intervals according
to specific application criteria. The selective actuation of the transmitter
40
for each sensor assembly and the switching between the ASK and FSK receivers
52,
58
prevent signal collisions between ASK and FSK transmission emitted by the remote
keyless entry system
19 and the tire monitoring system. Preventing signal
collisions optimizes function of the receiver assembly
16.
The foregoing description is exemplary and not just a material specification.
The invention has been described in an illustrative manner, and should be understood
that the terminology used is intended to be in the nature of words of description
rather than of limitation. Many modifications and variations of the present invention
are possible in light of the above teachings. The preferred embodiments of this
invention have been disclosed, however, one of ordinary skill in the art would
recognize that certain modifications are within the scope of this invention. It
is understood that within the scope of the appended claims, the invention may be
practiced otherwise than as specifically described. For that reason the following
claims should be studied to determine the true scope and content of this invention.
*
