Note: Descriptions are shown in the official language in which they were submitted.
CA 02208121 1997-06-18
TEMPERATURE SENSORS FOR P~RTNGS
FIELD OF THE INVENTION
This invention relates to the field of temperature
sensors and specifically for temperature sensors for bearings.
The invention has particular application to wheel bearings for
vehicles.
BACKGROUND OF THE INVENTION
The wheels of transport trucks are designed to carry many
heavy loads over long distances safely. However, it is not
uncommon for a wheel of a tractor trailer to break off of the
trailer during use and cause damage to other vehicles on the
road. One cause for a wheel to snap off of the truck is the
seizure of the wheel bearings in the wheel.
When a wheel bearing malfunctions, the temperature of the
bearing increases dramatically. Temperatures within the wheel
hubs can reach extreme levels as a result of bearing failures.
Causes for bearing failures include loose mounting bolts, lack
of lubricant, contamination, or other causes of high friction.
Excessive temperatures can also be generated by the braking
systems for example during constant application of braking
pressure on long downgrades or heavy use of the truck brakes
in panic braking situations. Often, drivers are not aware of
excessively high temperatures in the wheel bearings or that
wheel failure is imminent.
Although temperature monitoring systems for wheel
bearings are known for use with railroad car wheel journals,
these systems are not easily adaptable for use with trucks or
other roadway vehicles and can not be retrofit onto trucks in
a simple and economical manner.
There, therefore, remains a need for a wheel bearing
temperature monitoring system for use with tractor trailer
trucks and other vehicles. There also remains a need for such
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a system which can be easily and economically retrofit into
existing vehicles.
SUMMARY OF THE INVENTION
The present invention overcomes the disadvantages of
known systems and provides a system for monitoring the
temperature change of wheel bearings in each wheel of tractor
trailer trucks or other vehicles. The system can easily and
economically be retrofit into existing vehicles.
According to the present invention then, there is
provided a system for monitoring temperature changes in wheel
bearings comprising a plurality of sensors for monitoring the
change in temperature of wheel bearings, positioned in close
proximity to the wheel bearings to be monitored, each of said
sensors adapted to alter the flow of voltage therethrough in
relation to the temperature change; display means for
indicating whether the temperature of the wheel bearings is
above or below pre-determined temperatures; and electronic
means operatively coupled to each of said sensors and to said
display means for receiving the change in voltage in each of
said sensors, comparing said voltage to a pre-determined
value, and signalling said display means to display an
appropriate signal.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the present invention will now
be further described in greater detail and will be better
understood when read in conjunction with the accompanying
drawings, in which:
Figure 1 shows the electronic box and display box of one
embodiment of the present invention.
Figure 2 shows the attachment of a sensor in one
embodiment of the present invention to the axle of a truck.
Figure 3 is a block diagram of circuits representing the
systems installed onto a trailer and truck.
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Figure 4 are diagrams of the circuit board remote sensors
and radio frequency link and parts list for the radio
frequency sensor system used in one embodiment of the present
invention.
DETAILED DESCRIPTION
Referring to the drawings, the present invention is a
system 1 for monitoring the temperature in wheel bearings on
the wheels of a tractor trailer truck. The system 1 comprises
an electronic control box 3, a display box 5 electronically
connected to the control box 3, and temperature sensors
operably connected to the electronic control box 3.
The system 1 monitors the temperature in the bearings of
each wheel of the trailer and signals the driver when the
temperature in the wheeI bearings rises. The display box 5
is contained in the cab of the tractor trailer truck and has
a variety of display options indicating different temperature
ranges of the bearings in the wheels. The display box 5 also
includes an alarm having a buzzer and flashing red light for
signalling the driver when dangerous temperatures are reached.
In a preferred embodiment, the display options include
indicator lights 7, 9 ranging from solid green indicating the
bearings temperature is within a normal, safe range to
flashing red indicating that the temperature of the bearings
have reached dangerous levels. When dangerous temperatures
are reached, the alarm activates the buzzer and flashing red
light in the display box 5 to indicate that the driver should
cease use of the wheels until the bearings cool down to a safe
temperature and maintenance is performed.
Optionally a LCD display may be utilized to display the
status of input from the sensors.
The system 1 monitors the temperature of the bearings in
each wheel of the trailer and truck through temperature
sensors mounted to the back side (downwind side) of the axle
of each wheel. The sensor is preferably positioned
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approximately 1 to l 1/2 inches from the inside edge of the
bearing closest to the centre of the vehicle. To mount the
sensor as shown in Figure 2, the wheel is removed and the
sensor lead is thread through the brake drum area and the dust
cover. The sensor is surrounded with thermally conductive
material which adheres to the axle area. A stainless steel
band may be placed around the thermally conductive material
and sensor holding it in position until the material cures
thereby ensuring that the sensor r~; ns in the proper
position while the wheel is replaced. The sensor's lead is
tied off to the terminal strip in the control box 3 and the
wheel may be replaced as per regulatory standards.
Depending upon the system and sensors used in the present
invention, the temperature sensors have an electrical current
travelling through them which changes according to the change
in temperature of the wheel bearings. As the temperature of
the bearings rises, the electrical current in the sensors
varies approximately 2.2 millivolts per degree of temperature
change of the bearings. Sensors and control boxes suitable
for use in the present invention are commercially available
at a number of retail outlets and will be described in greater
detail below.
The electronic control box 3 is an enclosure mounted on
the truck. The box 3 receives a 12 volt DC power supply from
the truck engine or ancillary power supply. The sensors are
wired to the control box by two-wire low voltage wiring. The
control box 3 contains a number of circuits including an
electronic circuit, comparison circuit, coincidence circuit,
detection circuits, and display drivers. The comparison
circuit and coincidence circuits are set at pre-determined
values. The circuits used in the present invention are common
circuits well known in the art and widely available at many
commercial outlets. Alternatively, the system may be
computerized and the control box may include computer chips
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containing appropriate circuitry, as will be described in
greater detail below.
The electronic circuit receives signals from the sensors
relating to their voltage level and compares the level to the
pre-set values in the comparison circuit. Changes in the
voltage level from the comparison circuit values signal the
display drivers to activate the appropriate display in the
display box 5. At the same time, the coincidence circuit, set
at a pre-determined value, monitors the voltage level of the
electronic circuit to determine when to initiate and
deactivate the alarm in the display box 5 in the truck cab.
The display box 5 is mounted in the truck cab in view of
the driver. It is connected by cable 11 to the electronic
control box 3. The display box 3 contains several indicator
lights 7, 9 as well as the alarm buzzer. The lights include
a single multicolour light emitting diode display 9 as well
as single indicator lights 7 for each sensor on the trailer
and truck wheels. The single multicolour light emitting diode
display 9 is connected to the display drivers in the
electronic control box 3 and activated by the electronic
circuit. As the voltage in the sensors change due to the
change in temperature of the wheel bearings, the electronic
circuit signals the display drivers to illuminate the light
of the appropriate colour in the diode display. As the
temperature in the bearings reaches the pre-set value of the
comparison circuit, for example 70~C, the green indicator
light 9 will start to flash and turn amber. This warning
allows a driver to take precautions to avoid further
temperature rise and investigate the cause of the problem.
Continued heating of the bearing will turn the same light red.
When the pre-set value of the coincidence circuit, for example
100~C, is exceeded signalling that dangerous temperatures have
been reached in the wheel bearings, the alarm is activated
setting off the flashing red light and buzzer. The red light
and buzzer alarms can only be turned off by shutting down the
- - -
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power supply or allowing the wheel bearings to cool off. Each
wheel sensor is monitored individually to allow the problem
area to be immediately identified.
The system 1 includes a number of testing procedures to
signal a malfunction in the system. When the system 1 is
powered on through the ignition switch or other power supply,
the system 1 checks all of the sensor inputs using a series
of detection circuits to identify any problems. The detection
circuits activate the appropriate light displays in the
display box 5 to inform the driver of the nature of the
malfunction in the system. A steady green light indicates
that the system 1 is functioning properly. No lights
indicates a problem in the control 3 or display box 5 or the
connection to the power supply. A flashing green light
indicates that a sensor has an open circuit, for example
caused by a loose wire. A flashing red light indicates that
a sensor has a short circuit for example caused by pinched or
crossed wires. Obviously, other colour displays and
arrangements may be used. The display box 5 includes a manual
push button. When this button is manually depressed, all
lights will be tested and indicate if the system 1 is
functioning properly. The lights will return to their regular
colour when the push button is released.
The present invention may incorporate radio frequency
(RF) transmitters and microchip processors allowing for easier
retrofit of existing vehicles and easier exchange between
trailers and trucks. Figure 3 shows one arrangement
incorporating radio frequency transmitters and microchip
processors. Two systems are set up, one mounted on the
trailer and one on the truck. The trailer system comprises
a number of temperature sensors mounted on the wheel axles.
These sensors send information to a microprocessor which
relays the information to a radio frequency transmitter and
LED display. The system on the truck also includes sensors
on each wheel axle and a microprocessor to receive information
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from these sensors. This system further includes a radio
frequency link receiver to receive coded signals from the
radio frequency transmitter with the information gathered from
the trailer sensors. The truck system further includes a LED
display in the truck cab which informs the driver whether the
wheel bearings are within a safe operating temperature.
The microprocessor used in Figure 3 is an 8-bit CMOS
microcontroller with A/D converter. A diagram of the circuit
board remote sensors and RF link is shown in Figure 4 along
with the associated parts list for the systems shown. The
microprocessor model, PIC 16C74, is manufactured by Microchip
Technology Inc. TN and is commercially available. The
temperature sensors used on Figure 3 and shown in Figure 4B
is the LM35 model manufactured by National Semiconductor
CorporationTN. This sensor is a precision integrated-circuit
temperature sensor whose output is linearly proportional to
Celsius temperature.
A remote control system designed by MING Engineering &
Products Inc. TN may also be incorporated into the present
invention. This system comprises an encoder and transmitter
mounted on the trailer unit and a receiver and decoder
circuitry or modules mounted on the truck unit. The encoder
contains circuitry to transmit a coded signal. The signal can
contain anywhere from 8 to 18 bits giving up to 380 million
possible codes. The transmitter sends a coded signal from the
encoder circuit by means of a selected transmitting media such
as radio frequency. The receiver's input is connected to an
antenna which receives serial data information sent by the
radio frequency transmitter. The receiver's output is
connected to the decoder's serial data input for analyzation
of the coded signal received. The decoder will analyze the
coded signal input from the receiver to confirm a match of the
coded signal sent by the transmitter/encoder system. Upon
accepting a match of the coded signal, a valid transmission
can then occur.
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The present invention has a wide range of applications
beyond trucks. For instance industrial/commercial motor
bearings (electric) may be monitored. Refrigeration and
heating systems may also be monitored.
With additional sensors the present invention can track
liquid level, vibration, line (motion) speed, light, sound
levels, distance anywhere a plurality of sensors are required
for monitoring.
Sensor points can be daisy chained through RF coded
signals for additional monitoring sources.
The above-described embodiments of the present invention
are meant to be illustrative of preferred embodiments of the
present invention and are not intended to limit the scope of
the present invention. Various modifications, which would be
readily apparent to one skilled in the art, are intended to
be within the scope of the present invention. The only
limitations to the scope of the present invention are set out
in the following appended claims.
