WO1997003851A1 - Ameliorations apportees a des dispositifs de surveillance de pneumatiques ou en rapport avec ceux-ci - Google Patents

Ameliorations apportees a des dispositifs de surveillance de pneumatiques ou en rapport avec ceux-ci Download PDF

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Publication number
WO1997003851A1
WO1997003851A1 PCT/GB1996/001699 GB9601699W WO9703851A1 WO 1997003851 A1 WO1997003851 A1 WO 1997003851A1 GB 9601699 W GB9601699 W GB 9601699W WO 9703851 A1 WO9703851 A1 WO 9703851A1
Authority
WO
WIPO (PCT)
Prior art keywords
monitoring system
vehicle tyre
tyre monitoring
loop
signal
Prior art date
Application number
PCT/GB1996/001699
Other languages
English (en)
Inventor
Andrew Stuart-Taylor
Original Assignee
Tyresafe Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Tyresafe Limited filed Critical Tyresafe Limited
Priority to AU64668/96A priority Critical patent/AU6466896A/en
Publication of WO1997003851A1 publication Critical patent/WO1997003851A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C23/00—Devices for measuring, signalling, controlling, or distributing tyre pressure or temperature, specially adapted for mounting on vehicles; Arrangement of tyre inflating devices on vehicles, e.g. of pumps or of tanks; Tyre cooling arrangements
    • B60C23/02—Signalling devices actuated by tyre pressure
    • B60C23/04—Signalling devices actuated by tyre pressure mounted on the wheel or tyre
    • B60C23/0408—Signalling devices actuated by tyre pressure mounted on the wheel or tyre transmitting the signals by non-mechanical means from the wheel or tyre to a vehicle body mounted receiver
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C23/00—Devices for measuring, signalling, controlling, or distributing tyre pressure or temperature, specially adapted for mounting on vehicles; Arrangement of tyre inflating devices on vehicles, e.g. of pumps or of tanks; Tyre cooling arrangements
    • B60C23/005—Devices specially adapted for special wheel arrangements
    • B60C23/009—Devices specially adapted for special wheel arrangements having wheels on a trailer
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
    • B60C23/00—Devices for measuring, signalling, controlling, or distributing tyre pressure or temperature, specially adapted for mounting on vehicles; Arrangement of tyre inflating devices on vehicles, e.g. of pumps or of tanks; Tyre cooling arrangements
    • B60C23/02—Signalling devices actuated by tyre pressure
    • B60C23/04—Signalling devices actuated by tyre pressure mounted on the wheel or tyre
    • B60C23/0408—Signalling devices actuated by tyre pressure mounted on the wheel or tyre transmitting the signals by non-mechanical means from the wheel or tyre to a vehicle body mounted receiver
    • B60C23/0422—Signalling devices actuated by tyre pressure mounted on the wheel or tyre transmitting the signals by non-mechanical means from the wheel or tyre to a vehicle body mounted receiver characterised by the type of signal transmission means
    • B60C23/0433—Radio signals
    • B60C23/0447—Wheel or tyre mounted circuits
    • B60C23/0455—Transmission control of wireless signals
    • B60C23/0462—Structure of transmission protocol

Definitions

  • the present invention relates to tyre monitoring systems .
  • Tyres for heavy goods vehicles are expensive and their catastrophic failure (typically in a blow-out) can lead to dangerous incidents on the highways. Further, much time and considerable expense is wasted because tyres need to be replaced at the roadside rather than at depots.
  • pressure and temperature are important features in determining the condition of a tyre in relation to its likelihood to fail. If the air pressure within the tyre falls, it is indicative of a leak. If the pressure falls significantly, the tyre may suffer from a blow-out. An increase in temperature is indicative of poor tyre condition and can lead to increased pressure and a blow ⁇ out.
  • Embodiments of the present invention aim obviate or overcome disadvantages with the prior art whether referred to herein or otherwise.
  • a vehicle tyre monitoring system comprising a tyre status monitor adapted to be mounted on a wheel, which tyre status monitor comprises means to detect a variation in a tyre variable and means for transmitting a signal from the tyre status monitor to a signal receiving unit.
  • the monitor is adapted to be mounted between a vehicle tyre and its wheel rim.
  • the tyre variable is one or more of tyre pressure and/or tyre temperature.
  • the signal is an ultra high or very high frequency electromagnetic transmission.
  • the signal includes a wheel identification signal to indicate from which of a plurality of wheels on a vehicle the signal originates.
  • the signal includes an error signal, whereby a plurality of error signals are provided indicative of different variations in tyre status.
  • the system comprises memory means for storing at least part of the transmitted signal.
  • the memory means is adapted to store a wheel identifier and an associated error signal.
  • the system additionally comprises a user unit coupled to the signal receiving unit, which user unit comprises means to indicate receipt by the signal receiving unit of an error code.
  • the indication means indicates the tyre of a plurality of possible errors detected.
  • the indication means indicates from which wheel the signal originates.
  • the indication means comprises an audible alarm.
  • the user unit additionally comprises means for detecting ambient noise levels and means for adjusting the audible alarm dependent upon the ambient noise level.
  • an antenna circuit comprising an input feeder from which a feeder signal can be supplied to the circuit, a primary antenna loop and means to electrically couple the primary antenna loop to an emitter.
  • the primary antenna loop comprises a loop antenna substantially resonant at the frequency of the input signal.
  • the resonance remains independent of the emitter.
  • the primary antenna loop is a physically open loop.
  • the ends of the open loop comprise a capacitive element, which capacitive element may comprise a tuning termination whereby the loop is tuned to the wavelength of the input signal.
  • the capacitive element has a capacitance of about 3.3 picoFarads.
  • the capacitive tuning element comprises two generally opposed feet.
  • the input feeder of the primary antenna loop comprises two arms which join the loop at points along a side of the loop or at an end thereof.
  • a length of the arm of an input feeder is approximately in accordance with the equation:
  • Lf a length of the input feeder arm
  • L the length of a long side of the loop
  • the loop comprises at least one and preferably two long sides, and at least one and preferably two shorter side strips.
  • a long side of the loop has a length L.
  • a long side of the loop is connected to the coupling means.
  • a side strip has a length of approximately 0.2L.
  • the length of the feed line is approximately 0.2L.
  • the feed line joins a long side of the loop approximately 0.2L from one end of a long side of the loop.
  • a feeder input joins a long side of the loop approximately 0.2L from one end of a long side of the loop.
  • the length of a long side of the loop approximately satisfies the equation:
  • n is an integer
  • ⁇ is the wavelength of the input signal
  • the entire loop satisfies the above equation.
  • n 1.
  • the lengths and equations are substantially as set out above or substantially satisfied.
  • the two long sides are of substantially equal length.
  • the two short strips are of substantially equal lengths.
  • the outline of the loop is generally rectangular.
  • the primary antenna loop is coupled to the emitter by a capacitive coupling.
  • the emitter is connected to the primary antenna by a feed line, which feed line is preferably of a reactance substantially equal to that of the feed line.
  • the feed line has a length of substantially m( ⁇ /2) , where ⁇ is the wavelength of the input signal and m is an integer.
  • the emitter comprises a metallic body.
  • the circuit is adapted for an input signal of less than 200mW.
  • the circuit is mounted on a printed circuit board ("pcb") .
  • pcb printed circuit board
  • at least one track may be laid on the opposite side of the pcb.
  • the az least one track may comprise an antenna circuit, which may be as described herein.
  • the corners of the primary loop antenna are non-perpendicular. They may be rounded or at about 45°. Suitably, the corners have a length of about 0.04L.
  • the circuit is partly enclosed by a conductive body.
  • the circuit is substantially enclosed by a conductive body.
  • the conductive body comprises the emitter.
  • the conductive body is metallic.
  • a pressure sensing apparatus comprising a first electrode, a second electrode and a conductive, compressible material electrically between the first and second electrodes, whereby an electrical characteristic of the conductive, compressible material alters upon a change of pressure, and in which the apparatus further comprises means for detecting the change in an electrical characteristic of the conductive, compressible material.
  • the conductive, compressible material comprises a foam or rubber based material.
  • the foam or rubber is impregnated with a conductive material .
  • the conductive material is graphite.
  • the electrical characteristic is resistance.
  • the resistance can change by compression by the order of Mega-Ohms.
  • the minimum resistance is when the material is compressed.
  • the apparatus further comprises means for compressing the conductive, compressible material at over a predetermined pressure.
  • the apparatus further comprises means for biassing the compression means away from its compressing position.
  • the biassing means urges and moves the compression means away from its compression position.
  • the compression means comprises a plunger acting on the conductive, compressible material.
  • the biassing means comprises a spring.
  • the apparatus comprises means for mounting the apparatus to a tyre arrangement. More suitably, the apparatus forms part of a tyre pressure sensing apparatus.
  • the apparatus forms part of the first aspect of the present invention.
  • Figure 1 is a schematic illustration of a vehicle incorporating a system according to the present invention.
  • Figure 2 is a functional block diagram illustrating features of the present invention.
  • Figure 3 is a front view of a tyre monitoring apparatus according to the present invention.
  • Figure 4 is a plan view of the apparatus shown in Figure 3.
  • Figure 5 is a schematic cross-sectional illustration of a pressure element for use in the present invention.
  • Figure 6 is a circuit diagram for an absolute pressure change detection system incorporating the element shown in Figures 3 and 4.
  • Figure 7 is a schematic cross-sectional illustration of pressure element for relative pressure change sensing.
  • Figure 8 is a schematic cross-sectional illustration of a vibration sensing element for use in the present invention.
  • Figure 9 is a circuit diagram for a temperature change detection system.
  • Figure 10 is a functional block diagram showing elements of an apparatus incorporating a circuit of the present invention.
  • Figure 11 is a schematic line diagram of a circuit according to the present invention.
  • Figure 12 is a schematic functional block diagram of a receiving unit in accordance with the present invention.
  • Figure 13 is a flow diagram illustrating the operation of a part of the present invention.
  • Figure 14 is a flow diagram expanding upon part of the flow diagram of Figure 13.
  • FIG. 1 of the drawings that follow there is shown a heavy goods vehicle 2 on which is mounted a system according to the present invention.
  • the vehicle 2 includes twelve tyres of which four tyres are visible 4A - 4D in each of which is mounted (as described in more detail below) a tyre monitoring apparatus 6A - 6D respectively.
  • a radio signal receiver unit 8 is located in the cab 10 of the vehicle 2 which also includes a trailer 11.
  • the apparatus 6A - 6D monitor the condition of the tyre/wheel within which it is mounted. In particular it monitors temperature, pressure and vibration. If any of these variables exceeds or changes by more than their respective predetermined limits, an appropriate signal is transmitted to receiver unit 8 to warn the driver.
  • the apparatus 6 includes a battery power source 12 connected to a microprocessor control unit 14, which is connected to an antenna circuit 16.
  • the battery power source 12 and control unit 14 are connected to a pressure monitoring assembly 18, a vibration monitoring assembly 20 and a temperature monitoring assembly 22.
  • a tyre monitoring apparatus 6 comprising a hollow, generally cuboidal plastics housing 300 having a hinged lid 302 that can snap fit to the housing 300.
  • a pressure sensing element 24 comprising a generally cylindrical body that projects partly outside the housing 300 through a hole 305.
  • the pressure sensing element 24 is described in more detail below.
  • a printed circuit board (“pcb") 304 on which are mounted the electronic components for the apparatus 6.
  • the pcb 304 is electrically connected to pressure sensing element 24.
  • the lid 302 of the housing 300 When the lid 302 of the housing 300 is closed, it presents a concave, curved surface 306 which is intended to be placed against the rim of a vehicle wheel in use.
  • Pressure sensing element 24 comprises a main body 26 formed as a multiple piece plastic injection moulding.
  • the body 26 comprises a circular cylindrical hollow chamber 28 and a larger diameter cylindrical cavity 30 at one end thereof.
  • the hollow chamber 28 includes vent holes 32, 34 respectively at either end to allow gas to pass in and out of the chamber 28.
  • a central hole 36 at one end through which can project a piston rod 38.
  • Inside the chamber 28 is a piston head 40 connected to the piston rod 38.
  • the piston head 40 comprises a neoprene seal 42 sandwiched between two plastics slugs 44, 46.
  • the neoprene seal 42 is airtight against the chamber 28.
  • a helical spring 48 acts on slug 46 in the chamber 28 to bias the piston head 40 away from the cavity 30.
  • a spring retainer (not shown) is provided as part of the main body 26.
  • the piston rod 38 projects through the hole 36 into the cavity 30 and abuts against a conductive, graphite impregnated compressible resilient material 50 such as a conductive foam or rubber.
  • a conductive, graphite impregnated compressible resilient material 50 such as a conductive foam or rubber.
  • a typical material is high density conductive foam, available at least in the U.K. from Maplin (1994/5 catalogue order code FA82A) or a conductive rubber such as that available from Keymat Technology Ltd of London.
  • the conductive, compressible material 50 is provided in a disc of 8mm diameter and 4mm height. Electrodes 52, 54 are provided spaced apart in the conductive, compressible material 50.
  • the pressure element 24 is connected to a 6 volt dc power supply via the electrodes 52, 54 each connected to a respective dc input (not shown) .
  • the conductive, compressible material 50 In its uncompressed nominal condition, the conductive, compressible material 50 has a relatively high dc resistance, which can be of the order of 500k ⁇ to 1M ⁇ at 6 volt dc. In its most compressed state a typical resistance is 47 ⁇ (i.e. less than 50 ⁇ ) which relative to the resistance in the uncompressed state, can be regarded as zero Ohms.
  • the change in resistance responsive to pressure variation can be used to detect pressure changes.
  • the bias of spring 48 overcomes the force exerted on the piston head 40 by the air pressure and the piston head 40 is driven to the other end (ie distant from the cavity 30) of the chamber 28 by the spring 48.
  • the resistance between connectors 52, 54 therefore increases dramatically, of the order of 10,000 Ohms.
  • the reaction of the pressure sensing element 24 to pressure change, in effect between very high and zero resistance can be used as a switch in a switching circuit as described below.
  • the spring 48 can be treated and calibrated to give this response at any desired pressure.
  • a pressure change sensing circuit 60 incorporating the pressure element 24 which is indicated as a switch.
  • the circuit 60 comprises the pressure element 24 connected in series between ground (typically the negative pole of the battery) and a first resistor 62 which is in series with a positive battery pole 64 (typically a + 12 volts lithium cell stack) . Also connected to positive battery pole 64 is a second resistor 66 which is connected to the input of a first diode 68, the output of which is connected to a second diode 70, the output of which is connected to a third resistor 72 which is also connected to the input of first diode 68.
  • the output of first diode 68 is connected to ground via a capacitor 74.
  • An integrated circuit oscillator 76 is provided, the DC pin of which is connected to the input of first diode 68.
  • the output pin (Q) of oscillator 76 is connected to a programmable interface controller ("PIC") 78.
  • Threshold pin (TH) and pin (2) are connected to the output of first diode 68.
  • Reset pin (R) is connected between pressure element 24 and first resistor 62.
  • first resistor 62 limits the current flow to ground via pressure element 24 to less than 1 ⁇ A when it appears as virtually nil resistance (ie the tyre pressure is above 105 psi and the piston rod is depressed against the conductive, compressible material 50) to prevent an effective short.
  • the voltage at reset pin (R) is at ground and the output pin (Q) is also at zero volts.
  • the switch consisting of pressure element 24 goes to a high resistance.
  • the circuit of the pressure element 24 and first resistor 62 now looks electrically like a potential divider and the voltage at the DC pin is set to be approximately 60% of the supply voltage which is - In ⁇ sufficient to trigger the oscillator output of integrated circuit 76 with a mark:space ratio of on 0.2 second:off 5 seconds.
  • This is controlled by charging the capacitor 74 via the second resistor 66 at the rate of 0.7 x (capacitor of capacitor 74) x (resistance of second resistor 66) via first diode 68.
  • the first diode 68 only allows the capacitor 74 to be charged therethrough.
  • the off time is controlled by the capacitor 74 discharging through the second diode 70 and third resistor 72. The time constants for charging and discharging are kept the same.
  • the PIC 78 When the PIC 78 receives the output from output pin Q, it is activated to send a signal to the transmitter circuit (described below) with the code for a tyre pressure fault. In this way, the transmitter is only active for the duration of the Q output signal, thus conserving battery power.
  • circuit and system thus described is sensitive, adaptable and has low power consumption requirements. Further, especially the use of the conductive, compressible material 50 means that the system is not affected adversely by the substantial vibrations and 'centrifugal' forces to which the apparatus can be subjected in use.
  • the pressure sensing apparatus and circuit described can be adapted to provide a system for detecting a relative pressure change as opposed to that described above which senses when an absolute, predetermined threshold is crossed.
  • a system is described with reference to Figure 7 of the drawings that follow.
  • Figure 7 there is shown a pressure sensing element 80 similar to the lower half of the pressure sensing element 24 described above.
  • the pressure sensing element 80 comprises two electrodes 82, 84 between which is provided a conductive, graphite impregnated, compressible material 86 in a cavity 88 defined by a cavity housing 90 in which there is a vent hole 92.
  • the arrangement and configuration of the pressure sensing element 80 is substantially the same as that of the pressure sensing element 24 without the piston rod 38 and head 40 with their corresponding chamber 28. The significant difference is that the cavity 88 of the pressure sensing element 80 is open to atmosphere, whereas cavity 30 of pressure sensing element 24 is sealed airtight.
  • Pressure sensing element 80 is attached to circuit 60 ( Figure 6) in substantially the same way as pressure sensing element 24.
  • the circuit 60 operates in substantially the same way in each case, except for the way in which the signals are handled by the PIC 78.
  • the signal from pressure sensing element 80 to PIC 78 will vary in a corresponding fashion. This can then be analog-to-digital converted by the PIC 78 for processing. Although the response from the pressure sensing element 80 has been found to be nearly linear, some minor, but predictable, variations arise which can be dealt with by appropriate software in PIC 78.
  • the PIC 78 can be programmed to deal with slow and fast leaks by programming it to be responsive to the rate of change of the signal input thereto.
  • the PIC 78 can initiate the transmission of different alarm codes in this case.
  • the pressure sensing element 80 is, in effect self-calibrating. When the tyre is inflated it will cause an amount of compression of the conductive, compressible material 86 to produce a given output (Q) signal to PIC 78. By building in to the initialisation of the pressure sensing element 80 a delay, it will respond only to changes from the original, inflated pressure.
  • the pressure sensing element 80 can be used instead of pressure sensing element 24 if it is desired only to detect relative pressure changes, but it is preferred that it is used in tandem with pressure sensing element 24 both feeding their outputs to PIC 78.
  • the PIC 78 can be programmed to alert a user to a slow leak, a rapid leak and/or when the tyre pressure passes a threshold value, typically being that after which it is unsafe to continue.
  • the vibration sensing element 100 comprises a conductive base plate 102 on which is mounted a cap 104 the internal surface of which is conductive and electrically connected to the base plate 102.
  • a rod 106 electrically insulated from the base plate 102 and cap 104 by insulation 108.
  • spokes 110 extend from the rod 106 to the cap 104.
  • the spokes 110 are electrically insulated from the cap 104 by insulation 112.
  • a small ball of liquid mercury 114 is provided in the cap 104.
  • the base plate 102 and cap 104 form a first contact while the rod 106 and spokes 110 form a second contact for the vibration sensing circuit.
  • a voltage is applied across the first and second contacts which are only electrically connected, because of the size of the mercury ball 114, as the ball 114 passes the spokes 110.
  • the vibration sensing element 100 is mounted on a tyre 4 with the longitudinal axis of the rod 106 aligned with a radial axis of the tyre .
  • the centrifugal effect keeps the mercury 114 at one or other end of the cap 104, ie no electrical connection is made between the contacts, in normal usage. If a vertical (in use) vibration is induced in the tyre 4 because for instance it is becoming unbalanced, the element 100 will be shaken sufficiently for the mercury 114 to connect the first and second contacts generating a signal therefrom.
  • the output can be provided to PIC 78 for further processing.
  • a temperature change detection circuit 120 forming part of the temperature monitoring assembly.
  • the circuit 120 comprises a p-type field effect transistor 122 connected by its collector and drain between a relatively positive dc supply 124 and an output 126.
  • a relatively positive dc supply 124 and earth In series between a relatively positive dc supply 124 and earth is a reverse biased zener diode 128 and a high resistance resistor 130 (typically 10 - 47 ⁇ ) .
  • a relatively positive dc supply 124 and earth is a reverse biased zener diode 128 and a high resistance resistor 130 (typically 10 - 47 ⁇ ) .
  • a high resistance resistor 130 typically 10 - 47 ⁇
  • the circuit 120 is provided on pcb 304.
  • the breakdown voltage of the zener diode 128 varies with temperature. As the temperature rises, the breakdown voltage decreases.
  • the zener diode 128 can be chosen with values that allow breakdown to occur at virtually any desired temperature. For heavy goods vehicle applications this is set at about 85°C.
  • the transistor Before breakdown of the zener diode 128, the transistor is OFF, but when breakdown of the p-n junction of the zener diode 128 occurs above 85°C the voltage of the gate of the transistor 122 falls to turn it ON.
  • the pressure, vibration and temperature monitoring assemblies 18, 20 and 22 respectively are connected to, monitored and controlled by the PIC 78 in a manner set out in more detail below. Signals generated by the monitoring apparatus 6 are then transmitted by the antenna 16.
  • an antenna system comprising a signal generator 150 (in this case originating from PIC 78 via a driver unit) the output of which is connected to the input of an antenna circuit 152, the output of which is connected to the input of an emitter 154, here comprising a metal wheel rim.
  • the antenna circuit 152 is shown in more detail.
  • the antenna circuit 152 can been seen to comprise a feeder having two arms 156, 158 extending to a loop 160.
  • the loop 160 is not physically closed and terminates in a capacitive tuning element 162.
  • From the side of the loop 160 opposite the feeder arms 156, 158 extends a feed line 164 which terminates in a capacitive coupling element 166.
  • the antenna circuit 152 is mounted on a pcb shown generally by dashed lines 168.
  • the dimensions, and in particular the proportions, of the antenna circuit 152 are important to maintaining high performance of the circuit. These dimensions are shown in Figure 11, based on a basic length unit L. To maintain best performance of the system it has been found that the conditions set out below in equation (1) should be satisfied:
  • L is the length unit referred to above n is an integer less than or equal to 4 ⁇ is the wavelength of the input signal
  • the antenna circuit 152 in Figure 11 has a long side 170 of length L from which the feed line 164 extends for a length of 0.2L to the capacitive coupling element 166.
  • the feed line 164 is spaced a length 0.2L from one end of the long side 170.
  • the 0.8L length of the long side 170 from feed line 164 turns through 90°, via a 45° angled section 172, to a first side strip 174 of 0.2L length.
  • First side strip 174 turns through 90°, via a 45° section 176, to a second long side 178 of length L, interrupted 0.2L along from first side strip 174 by a first input feeder line 180, via 45° sections 182, 184.
  • the remainder of second long side 178 is 0.8L long, terminating at second side strip 186 which, is 0.2L long.
  • a distance of 0.04L from the feeder input side of second side strip 186 is a termination of the loop in two parallel feet 188 forming a 3.3pF capacitive tuning element 162.
  • the length X of the feeder line 180 substantially parallel to long side 178 is adjusted to provide a 50 Ohm impedance and is thus variable. It is dependent upon the feeder length and the overall wavelength of the antenna system.
  • a second feeder input line 190 is connected to the circuit at the junction of the second long side 178 and second side strip 186.
  • the second feeder input line 190 includes a strip 192 substantially parallel to the long side 178 which strip is 0.2L long.
  • Typical lengths for a 418MHz signal are 2.5mm for the lengths indicated by reference letter "A" .
  • the two long sides 170, 178 and side strips 174, 186 form the antenna loop.
  • the loop 170, 174, 178, 186 is generally rectangular in outline.
  • the primary antenna circuit 152 is essentially a closed loop system with a near centre feed and capacitive ground reference point at a specific node junction along its dipole conductor.
  • Each branch from the antenna loop 170, 174, 178, 186 acts as a resonator, resonant at specific frequencies or at specific decimals of the fundamental input signal frequency.
  • the antenna circuit as a whole is resonant because of its proportions relative to the input signal wavelength, and appears to remain so independent of the presence or properties of the emitter.
  • the system can be regarded as a loop system acting as a magnetic dipole for transmission purposes.
  • the system is most suitable for UHF or VHF transmissions at low power, typically less than 200mW.
  • the antenna system described above has been tested within a sealed steel box to which the capacitive coupling element 18 has been connected for capacitive coupling thereto.
  • the antenna loop has a directivity of 3/2 and a beam width of 90°.
  • the gain is substantially reduced, but effective transmission of the input signal is achieved without overloading the circuit.
  • the circuit described herein finds particular advantage. In that case it can use the body as the emitter and because of the configuration of the circuit, also not lose resonance as would normally be expected.
  • the performance of the system has been found to . be substantially independent of the size and shape of the emitter 154.
  • the length of feed line 164 has a length of m( ⁇ /2) , where ⁇ is the wavelength of the input signal and m is an integer. This ensures that at the junction of the feed line 164 and at the emitter there is a node of the signal.
  • the antenna circuit can be replicated on the other side of the pcb as a second antenna circuit (not shown) and connected to the first antenna circuit at the same points as feet 186.
  • the capacitance of element 162 is still desired to be 3.3pF, and this can be achieved by offsetting the second antenna circuit relative to the first antenna circuit to increase the pcb thickness therebetween.
  • an antenna tuning unit (not shown) can be attached to the feeder arms 156, 158 in which case the element 162 is instead wired through (short circuit) to form a closed loop.
  • the capacitive tuning element 162 described above in relation to Figure 11 is, however, preferred at this stage.
  • the receiver unit 8 comprises an antenna 200 for receiving signals transmitted from the monitoring apparatus 6.
  • the signals are interpreted and analysed by a PIC based microprocessor 202 to activate or ⁇ deactivate a plurality of warning lights 204 and/or an audible alarm 206.
  • the microprocessor 202 is connected to a memory device 208 and also to a liquid crystal display screen 210 via a display driver 212.
  • a microphone 214 is also connected to the microprocessor 202.
  • an on/off switch 216 and a reset button 218 are also connected to the microprocessor 202.
  • Each receiver unit 8 has a dedicated key fob 220 (with at least one spare) in the microprocessor control of which is embedded a system code corresponding to that of the receiver unit 8 to provide receiver unit 8/key fob 220 matching pairs.
  • a tyre monitoring apparatus 6 is installed in each tyre 4 of the trailer 11. Each tyre monitoring apparatus 6 is configured to the same system code to identify substantially uniquely the trailer 11.
  • the tyre monitoring apparatus 6 is secured to the rim of the tyre-carrying wheel by a strap extending around the circumference of the wheel rim.
  • the capacitive coupling element 166 of the antenna system described in relation to Figures 10 and 11 is secured adjacent the wheel rim thereby to capacitively couple to the metal wheel rim.
  • the tyres 4 are inflated to their operational pressures.
  • the receiver unit 8 is located in the cab in a convenient position for viewing by the driver without its operation distracting his attention from the road.
  • the system code from the key fob 220 is transmitted to the receiver unit 8 to be stored in memory device 208.
  • the key fob 170 transmits a program entry command chain comprising a four bit code which allows access to the PIC program input sector of the system code area. After this a further four bit code (presently 0000) is transmitted which allows entry of the code into the memory 158.
  • Each monitoring apparatus 6 is configured with a timer circuit to transmit data to the receiver unit 8 approximately once each second. This minimises the drain on the battery 12, typically a lithium battery.
  • Each transmission comprises the following elements:
  • Data is transmitted in a binary form and may be encrypted if desired.
  • the system code is unique for each vehicle (trailer, cab etc) .
  • the tyre code a number from 0-99, is unique for the tyre on the particular vehicle.
  • the system code can be hardwired into the receiver unit and monitoring apparatus.
  • the system code of the monitoring apparatus is entered into the receiver unit . This can be done by having a plate on the trailer giving the system code to be entered or by electronic means.
  • a frequency modulated signal can be superimposed on the vehicle electrical system by the monitoring apparatus to be received by the receiver unit soon after the system is initiated.
  • Dedicated system codes prevent errors caused by cross-talk.
  • the error code signal is a number from 0-9 unique for the status to be reported to the receiver unit.
  • the error code is encoded as follows:
  • the temperature circuit 120 will output a relatively high signal as the transistor 122 goes ON as explained above. This causes the next transmission from the relevant tyre 4 to include error code signal '3' .
  • the error codes 5-9 are provided for anticipated expansions of the system.
  • the key fob 220 includes buttons for (i) data log retrieval, (ii) system check and (iii) spare.
  • a vibration counter is set to zero at 402. If at 404 no system code has been set in the receiver 8, the LCD display 210 displays the message "WARNING - NO SYSTEM CODE" until such a code is entered via the key fob 220.
  • the receiver determines whether a signal has been received. If not, it continues to monitor receipt of a signal.
  • a signal includes the correct system code
  • the error code is filtered from the signal by known means.
  • the error code equals zero (TYRE OK) , no further action is taken and the system continues to monitor for received signals at 408. If, however, the error code does not equal zero, the NO branch from box 412 is followed forming a cascade analysis of the error signal.
  • the LCD display 210 is energised to display a battery low signal and an appropriate light 204 is lit. The system then returns to monitor incoming signals at 408. If the error code equals 2 (PRESSURE DROP) , at 420 the LCD display 220 is energised to display a pressure low warning and to light a corresponding light 204.
  • an audible alarm is sounded as well.
  • the signal from microphone 214 is measured to determine the ambient noise level.
  • the audible alarm 206 is then energised at a sound level a predetermined amount above the ambient level to ensure that it is clearly audible to the driver or other user but is not too loud, for instance if the vehicle is stationary and the engine idling the alarm will be quieter than the case in which the vehicle is travelling at a high speed on a motorway with in-cab noise coming from a sound system.
  • the error code is entered into the memory device 158 with a date and tyre number log entry to form a record which can be interrogated.
  • the system then returns to monitoring received signals at 408.
  • the error code equals 3 (HIGH TEMPERATURE)
  • a high temperature visual message is displayed on the LCD display 210 and an appropriate light 204 lit.
  • An alarm is sounded in the same way as for a pressure drop warning and the code is entered into the memory as described above.
  • the vibration counter if the vibration counter does not equal 5, no action is taken and the system returns, at 408, to monitoring for received signals. If, however, the vibration count equals 5, firstly at 436 the vibration counter is reset to zero. Then a vibration alert signal is displayed on the LCD display 210 together with the lighting of appropriate light 204. Once again, the audible alarm is sounded and the code data entered into the memory before the system returns to its monitoring status.
  • the system avoids or minimises false alarms that might be caused by, for instance, a rough road, an object in the vehicle's path or a cattle grid.
  • a vibration must continue for 5 seconds before the tyre vibration warning is given.
  • the unit 8 In its state monitoring received signals, the unit 8 enters its low power consumption stand-by mode at 252. Periodically it checks for data receipt at 254 and, if • none has been received returns to stand-by mode at 252.
  • the program next checks at 256 whether the 8 bit address system code transmitted from the antenna 152 matches that of the last four bits of system code received by and stored in receiver unit 8. If it does not, the program returns to the stand-by/data monitoring mode loop, described above. If the 8-bit address does not match at 256, the VT pin on the PIC 202 which controls the receiver unit 8 is disabled at 258 and the rest of the input word ignored.
  • the unit 8 receives and stored the 4 bit system code signal at 260 and, at 262, checks whether it matches the previous stored system data. If there is no match, the program returns to the stand-by/signal monitoring mode loop via VT pin disable step 258.
  • the program determines at 264 whether there have already been two such matches i.e. whether this is the third. If not the program loops back to the stand-by mode.
  • the 4 bit momentary data is output to the VT pin on the PIC 202 of microprocessor control 14.
  • the PIC 202 is thereby enabled for receipt of the error signal and subsequent processing thereof.
  • the software returns to its stand-by mode 252 to await further signals.
  • the VT pin on the PIC 202 is used to control the display and audible areas of the cab receiver unit 8 as described herein.
  • any system code data received by the unit 8 is checked three times to ensure data integrity before it is acted upon. That is signals from other vehicles with other system codes will be ignored because there will not be three matches.
  • the data rate has been set to about 200 kHz for the system code and error signal transmission. This is presently considered by be adequate for a typical heavy goods vehicle wheel speed at 80 mph. the Doppler effect during wheel rotation causes some variation, but it is not significant at this frequency.
  • the lights 204 are shown by way of example only. On the receiver unit 8 it is anticipated that a series of lights will correspond to each tyre of the vehicle and the light lit will determine both the location and nature of the problem.
  • a Bl-morph sensing element comprises a piezo-electric component the voltage across which varies with increased force corresponding to vibration. Such an element produces about 4 volts peak-to-peak output voltage for a small physical movement of the element. This output will increase to about 6 volts if a regular oscillation in the same place is present.
  • the Bl-morph sensing element may be the preferred option as it relies solely on the piezo- electric effect and has no moving parts.
  • the output of a Bl-morph element 310 is connected to a capacitor 312 via first resistor 314 of the order of 1000 ⁇ .
  • Second resistor 316 is connected between the first resistor 314 and capacitor 312, as well as to the output of capacitor 312.
  • a third resistor 318 is connected from the output of capacitor 312 and the inverting output of capacitor 312 and the inverting input of operational amplifier 320 (acting as a comparator) .
  • the non-inverting input of operational amplifier 320 is connected between first resistor 314 and capacitor 312. Between the non-inverting input and the output of operational amplifier 320 is connected fourth resistor 322.
  • First and second resistors 314, 316 act with third resistor 318 as a voltage divider to set the threshold voltage for operational amplifier (comparator) 320.
  • the resistances are chosen such that the threshold is about 3.8 volts.
  • the output of operational amplifier (comparator) 320 goes high to flag the PIC 78 that vibration is occurring.
  • Fourth resistor 322 provides an amount cf hysteresis to avoid the "flicker" effect at around 3.8, volts so that the output does not actually change until the input reaches 3 volts .
  • the PIC 78 In order for the PIC 78 to cause the antenna circuit 152 to transmit a vibration error signal, it is programmed such that the vibration signal must have been present for at least 5 seconds (as described above) and will not reset until it has stopped for a period of 10 seconds. The prevents spurious signals from momentary vibrations or balancing of the wheel caused by road effects.
  • the apparatus described above includes a vibration monitoring assembly, at this stage it is envisaged that this will not be included as, typically, heavy goods vehicle tyres tend to be out of balance by enough to trigger a vibration sensor.
  • the software capability can be present, however, and a retro-fit of this feature is possible if desired.

Abstract

Cette invention porte sur des dispositifs de surveillance de pneumatiques de véhicule, servant notamment à détecter des situations pouvant déboucher sur des éclatements potentiellement dangereux. Un dispositif de surveillance de pneumatique de véhicule selon cette invention comporte un organe de surveillance de l'état du pneumatique (6A-6D) conçu pour être monté sur une roue, cet organe (6A-6D) comprenant un équipement (6) de détection de variation dans une variable de pneumatique et un équipement de transmission (16) destiné à émettre un signal de l'organe de surveillance de l'état du pneumatique (6A-6D) à un récepteur de signaux (8).
PCT/GB1996/001699 1995-07-18 1996-07-16 Ameliorations apportees a des dispositifs de surveillance de pneumatiques ou en rapport avec ceux-ci WO1997003851A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU64668/96A AU6466896A (en) 1995-07-18 1996-07-16 Improvements in and relating to tyre monitoring systems

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9514673.4 1995-07-18
GBGB9514673.4A GB9514673D0 (en) 1995-07-18 1995-07-18 Improvements in and relating to tyre monitoring systems

Publications (1)

Publication Number Publication Date
WO1997003851A1 true WO1997003851A1 (fr) 1997-02-06

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Application Number Title Priority Date Filing Date
PCT/GB1996/001699 WO1997003851A1 (fr) 1995-07-18 1996-07-16 Ameliorations apportees a des dispositifs de surveillance de pneumatiques ou en rapport avec ceux-ci

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AU (1) AU6466896A (fr)
GB (1) GB9514673D0 (fr)
WO (1) WO1997003851A1 (fr)
ZA (1) ZA966056B (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1039286A1 (fr) * 1999-03-19 2000-09-27 Meritor Heavy Vehicle Systems, LLC Surveillance des vibrations d'une transmission
WO2011098533A1 (fr) 2010-02-10 2011-08-18 Land Rover Contrôle de pression des pneus ii
EP2749438A1 (fr) * 2010-02-10 2014-07-02 Jaguar Land Rover Limited Surveillance de la pression des pneus I

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2504675A1 (fr) * 1981-04-28 1982-10-29 Salou Alain Systeme permettant de visualiser, sans contact, l'evolution d'un parametre et applicable au suivi, en permanence, de la pression d'un pneumatique
WO1986000265A1 (fr) * 1984-06-21 1986-01-16 Transensory Devices, Inc. Systeme de detection a commutateur a distance
EP0239545A1 (fr) * 1986-01-28 1987-09-30 FIAT AUTO S.p.A. Système pour le contrôle et l'indication acoustique des conditions de travail d'un véhicule à moteur
WO1992014620A2 (fr) * 1991-02-21 1992-09-03 Ttc/Truck Tech Corp. Dispositif et procede de controle d'un pneu
WO1994020317A1 (fr) * 1993-03-11 1994-09-15 Schrader Automotive Inc. Systeme de surveillance a distance de pression de pneu utilisant une identification codee des pneus et une transmission par frequence radioelectrique, et permettant un reetalonnage lors de l'inversion ou du remplacement de pneus
EP0657314A1 (fr) * 1993-12-10 1995-06-14 Sumitomo Rubber Industries Limited Dispositif d'alarme en cas de dégonflage de pneumatique

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2504675A1 (fr) * 1981-04-28 1982-10-29 Salou Alain Systeme permettant de visualiser, sans contact, l'evolution d'un parametre et applicable au suivi, en permanence, de la pression d'un pneumatique
WO1986000265A1 (fr) * 1984-06-21 1986-01-16 Transensory Devices, Inc. Systeme de detection a commutateur a distance
EP0239545A1 (fr) * 1986-01-28 1987-09-30 FIAT AUTO S.p.A. Système pour le contrôle et l'indication acoustique des conditions de travail d'un véhicule à moteur
WO1992014620A2 (fr) * 1991-02-21 1992-09-03 Ttc/Truck Tech Corp. Dispositif et procede de controle d'un pneu
WO1994020317A1 (fr) * 1993-03-11 1994-09-15 Schrader Automotive Inc. Systeme de surveillance a distance de pression de pneu utilisant une identification codee des pneus et une transmission par frequence radioelectrique, et permettant un reetalonnage lors de l'inversion ou du remplacement de pneus
EP0657314A1 (fr) * 1993-12-10 1995-06-14 Sumitomo Rubber Industries Limited Dispositif d'alarme en cas de dégonflage de pneumatique

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1039286A1 (fr) * 1999-03-19 2000-09-27 Meritor Heavy Vehicle Systems, LLC Surveillance des vibrations d'une transmission
WO2011098533A1 (fr) 2010-02-10 2011-08-18 Land Rover Contrôle de pression des pneus ii
EP2749438A1 (fr) * 2010-02-10 2014-07-02 Jaguar Land Rover Limited Surveillance de la pression des pneus I
AU2011214368B2 (en) * 2010-02-10 2015-05-21 Jaguar Land Rover Limited Tyre pressure monitoring II

Also Published As

Publication number Publication date
GB9514673D0 (en) 1995-09-13
ZA966056B (en) 1997-02-18
AU6466896A (en) 1997-02-18

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