GB2171548A

GB2171548A - Tyre inflation alarms

Info

Publication number: GB2171548A
Application number: GB08604542A
Authority: GB
Inventors: Leonard Fredrick Burge; Elaine Ruth Burge
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-02-22
Filing date: 1986-02-24
Publication date: 1986-08-28
Also published as: DE3605661A1; GB2171548B; JPS61241206A; GB8604542D0

Abstract

An alarm comprises a pressure sensing means, (30) a transmitter of radiant energy, (40) and a power source (31). The device is preferably attached to the valve stem (2) of a pneumatic tyre such that the pressure sensing means (30) can sense the internal pressure of the tyre. On sensing an abnormal tyre pressure the switch activates the transmitter, (40) which transmits a signal to a receiver (13) located in the vehicle so warning the driver of the adverse pressure conditions within the tyre. A manner of coding the transmission so as to identify which tyre is defective is disclosed. <IMAGE>

Description

SPECIFICATION Tyre alarm This invention relates to an alarm device and in particular an alarm device to be used in association with a pneumatictyre.

BACKGROUND OF THE INVENTION Pneumatictyres are used on a wide variety of transport vehicles for example passenger cars, caravans, trailers, trucks, aeroplanes etc. Pneumatic tyres are costly items, particularly in the case of those for largervehicles, and any means by which replacement on a vehicle can be avoided is of significant economic advantage.

Forthe efficient and safe running of a vehicle the pressure ofthetyres has be kept within certain limits.

Iffor instance the tyre is running at below the prescribed pressure, abnormal tyre wear and low fuel economy can result. Furthermore safety can be adversely affected because accuracy of steering can be diminshed. In the extreme case total deflation can occur resulting in loss of control of the vehicle and/or irreparable damage to the tyre. Similar problems can occur if the tyre is run at pressures above the prescribed level.

A particular problem exists with largervehicles such as road transports where, because the rear vehicles are remote from the cabin, the driver is not able to detect the deflation ofthe tyre whilst travelling, with the resuitthatthe drivercontinues drivingeven though the tyre is completely deflated. Driving a vehiclewiththetyre in such a condition can and usually does result in damage or destruction of the tyre and evidence of such a situation can be readily seen on our highways where pieces oftyre are strewn on the side of the road. The vehicle owner is not only faced with the high cost ofthe tyre but also with the cost of time lost en route for wheel changes. Similar problemsoccurwithvehiclestowing caravans, trailers etc.

The development of the device which could signal the onset of abnormal tyre pressures to the occupants ofthe vehicle would be a significant contribution to lower running costs, safety and efficient use of pneumatic tyre vehicles.

SUMMARYOFTHE INVENTION The invention in its broadest sense comprises an alarm device adapted to be connected to a pneumatic tyre comprising a transmitter, a power source for the transmitter, and a pressure sensing means, the pressure sensing mans being so adapted that, when it is in contact with the interior ofthe tyre, it activates the transmitterwhen the sensed pressure in thetyre is at an abnormal level.

The alarm device of the invention may be a separate unitadaptedto be attachedtothe conventional valve stem of a tyreor alternatively, may be builtin to the valve stem.' ofth.etyre The latter form may be implemented by replacing the standard valve stem by a shortvalve stem and connecting the alarm device so that the total length of the valve stem and the attached alarm device is about the same as that of a standard valve stem. This would be particularly useful where the device is being fitted as part of the original equipment.

The power source may be any form of power supply, both forthe device itself and for the receiver, and is therefore not necessarily restricted to the use of a battery such as a nickel-cadmium battery. The power source could also be provided by magnetic induction or by use of solar cells.

Preferably the transmitter is frequency modulated.

BRIEF DESCRIPTION OF DRAWINGS Fig. lisa schematic view of a passenger vehicle showing the pressure sensing device of the present invention applied to the vehicle; Fig .2 is an exploded view of one form of alarm device ofthe invention; Fig. 3 is an exploded view of anotherform of the alarm device of the invention; Fig. 4 is an exploded view of another form of alarm device according to the invention; Fig. 5 is an exploded view ofanotherform of alarm device according to the invention which can be screwed to the normal cap thread of the tyre; Fig. 5a is a view of a connection which can be used to connectthe alarm device to a tubeless tyre.

Fig. 6 illustrates a circuit diagram of one form of transmitter useable in the alarm device ofthe invention; Fig.7 isa schematic diagram of the receiverwhich may be used in association with the alarm device of the present invention.

Fig.8 is a block diagram ofthe system; In orderthatthe invention be more readily understood we shall describe one particularform of the alarm device in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Fig. 1 ,the passengervehicle, 11 having one or more alarm devices of the present invention, includes a tyre pressure sensing andtransmitting assembly, 12 according to the invention on one or more of the vehicle wheels. A receiving device, 13 is located inthecabin ofthevehicle.

One form ofthe alarm device ofthe invention is bettershown in Fig. 2.

The components of the alarm device comprise a housing, 20 having an internallythreaded part, 21 for receiving an externally threaded valve stem, 2.

The opposed end ofthe housing includes a threaded aperture, 23 into which is threadably engaged a valve, 24.

A bore, 22 informed in the housing, 20 between the part, 21 and the part, 22 so as to provide an air passage between the valve, 24 and the internal environment of the tyre. The passage, 22 also communicates with an internally threaded part, 26 into which the switch, 30 is housed. A resilient diaphragm, 27 and an insulator, 28 The drawings) originally filed (were) informa! and the print here reproduced is taken from a later filed formal copy.

This print takes account of replacement documents submitted after the date of filing to enable the application to comply with the formal requirements of the Patents Rules 1982 is located between the body of switch 30 and the body ofthe housing, 20.

The switch, 30 is held within part 26 by externally threaded part, 36.

The switch, 30 is adapted to close the circuit between the battery, 31 and the transmitter, 40 by means of an electrical contact, 35.

In use, the housing ofthe alarm device ofthe invention is threadably engaged to the valve stem, 2.

In this form ofthe invention, the valve is removed from the valve stem before connecting the alarm device.

The device is such that air can be introduced into the tyrethrough the valve, 24 which also acts to prevent the escape ofairfrom thetyre.

The switch, 30 is conventional and has a plunger our piston, 37 having a conductive head, 39 which is adapted to close the electrical circuittothetransmit- ter, 40 when it abuts the electrical contacts, 39 of the body of the switch, 30.

The plunger, 37 is forced into contact with the diaphragm, 27 by compression spring, 38. The tension ofthe spring, 38 is selected so that the head of the plunqer, 37 closes the electrical circuit when the internal pressure ofthe tyre falls below a preset level.

The tension ofthespring may also be adjusted by means of screws.

The switch, may also be adapted so thatthe same electrical circuit or as an alternative, another electrical circuit is closed when pressure within the tyre is above a preset value.

Afurtherform of the alarm device ofthe invention is shown in Fig. 3.

Here the body, 20 ofthevalve includes an aperture, 31 a into which the battery is inserted. The switch, 30 is located in a threaded opening adjacent the battery enclosure. Electrical contact between the battery and the switch is made through the material, preferably plastic, ofthe body ofthe device.

The transmitter, 40 is located around the external peripheryofthebodyand electrical contactis madeto the transmitter by a conductor passing through the body, 20 ofthe device. A coil, 50 is mounted in the plastic body and acts as an antenna forthetransmitter, 40. Alternatively the coil may be mounted around the body.

Fig. 4shows an alarm device which can be connected to the conventional valve stem of a pneumatictyre without removal ofthe normal valve located in the valve stem. The valve body, 20 includes a pin, 19 which releases the pressure in the normal valve stem by depressing the valve, 18. A microchip transmitter is located at aperture 20a.

Fig. 5 illustrates an exploded view of one form of switch which may be used in the alarm device ofthe invention. This switch incorporates a testing means wherebythe operation of the unit can be tested.

The switch is connected to the switch receiving aperture in the body, 20 of the alarm device. The switch comprises a diaphragm, 73thatflexes under air pressure and operates the switch by moving plunger, 75. A spaced washer, 74 creates a cavityfor movement ofthe diaphragm, 73 and holds itsecure and air4ight.

The plunger, 75 displaces the conductive disk, 78 from the electrical contact, 76. Atension spring, 79 is selected such thatthe disk, 78is biased againstthe electrical contact, 76 when the pressure of the tyre falls below a preset level.

Atesting button, 80 is also pros - ued, which allows the testing of the transmitter. The switch is provided with a threaded cap, 82 which allows access to the tension spring, 79 for replacement and the whole switch construction is protected buy a soft plastic or rubber boot, 83.

It will be noted that in Fig. 5 the valve stem is made shorterthan usual so thatthe overall length ofthe stem and the attached alarm device is approximately equal to the normal length of the valve stem of a conventional pneumatictyre.

Fig. 5a shows a construction which is suitable for use with tubelesstyres, whereby the valve stem is replaced by a connection unit, 90 having a lower flangeportion,91 whichfitsinsidetherim,100ofa wheel.

Oneformoftransmittersuitableforuseinthealarm device of the invention is shown in Fig. 6. It has a single integrated circuit which is a special purpose inte- grated circuit which hasfourfunctions.

Thefirstfunction has frequency modulation generator, atoneencoderwhich is binary and which is controlled by the encoding switches shown in the schematic diagram, and a poweramplifierwhich is preferably 50 milliwatts.

The circuit also has a tone generator code call which provides an original 100 micro-second signal, which sets a receiver to receive a code and fourtone pulses each of which are fifty micro-seconds long which providethetyre codes.

The provision of a four bittyre code enables 16 tyres to be monitored, however, itwill be appreciated that if a larger number oftyres have to be monitored, then an extra signal bit can readily be incorporated.

Anothercharacteristicof thetransmittercircuitis that the tone itself can be varied. Furthermore, the frequency can be varied and normallythefrequency is controlled bythe crystal resonator, 111.

It will be seen thatthere are two parameters which can be varied in any unit, the frequency and the tone, thus it is most likely that should a vehicle having the device be passing anothervehiclewith the same device, they will have the same two parameters and as such the likelihood of incorrect calls is remote.

The output side ofthe transmitter is simply a capacitor, which prevents direct current passing to the antenna and a tuned circuit which is designed to remove any harmonics from the output, these simply being shunted to ground.

A schematic diagram of the receiver is shown in Fig.

7. It will be seen that the receiver is of standard design.

It is designed to have its operation initiated when the initial tone signal of 100 milli-seconds is transmitted, and it checks to ascertain whetherthe tone is correct.

The tone decoderthen checks the four pulses, partially to see whetherthey relate to a wheel on the particular vehicle, and secondly to indicate which wheel is concerned. The output then effects the operation of the display which may be a numberof light emitting diodes, one for each wheel, or a visual display giving an indication ofa particularwheel.

The system block diagram is shown in Fig. 8. The transmitter actuated by the pressure switch repre sented by 112 in Fig. 6.

The receiver block diagram is also shown in Fig. 8.

As indicated earlier in this description, the pressures which may be a differential pressure device which can be used to give a warning signal not only of low pressure but also of excess pressure.

Ifthis is implemented, it will be possible to provide a differentoutputforeach ofthetwo, so that the driver ofthe vehicle would be aware of the current situation.

The circuit of the transmitter chip may, for example, be fabricated on a curved or circular cross-sectioned substrate so that it may be placed round the valve and thus assist in minimising the size ofthe alarm device.

The actual shape ofthetransmitter mayvarywithin wide limits, for example it may be tablet shaped so as to fit neatly into the device. The device is adapted to screw on to the valve of the tyre and includes an air inlet adapted such that the tyre pressure may be adjusted without removal of the alarm device from the stem of the tyre and without loss of pressure.

In usethedevicewilltransmitasignal in an abnormal tyre situation to a receiver preferably situated in the cabin of the vehicle. This receiver, in reference to the one possible form of the device describedabove,could bean FM receiverwhich produces some audible orvisual warning signal to the occupants ofthe cabin. For example the receiver could emit different sounding signals in response to varying types of tyre pressure conditions. To assist the receiver in its reception ofthe signal transmitted by the device, particularly in the case of long vehicles, an aerial could be run down the spine or along the side(s) of the vehicle.

In use, using a road transport as an example,the alarm device of the invention could be attached to all tyres on the vehicle. When all tyre pressures are within the prescribed rangethe pressure sensing means holdsthetransmitter in the OFF position. However when there is a loss of pressure in one or more ofthe tyres and the pressure of the tyre(s) falls below the prescribed level, the pressure sensing means acti vates the transmitter ofthe device in question which then transmits a signal notifying a receiver, say in the cabin of the vehicle, which then issues an audible or visual alarm to the occupant. This enables the driverto stop the vehicle and inspect the tyre in question.The receiver in the cabin could be in the form of a combined visual/audio display which illustrates the tyre with abnormal tyre pressure or alternatively, an identification ofthe device emitting the signal, for example, a device number.

The device of the invention may also include a means for producing an audible signal in response to adversetyre pressures enabling a person to walk around the vehicle and identify the device and thus the tyre in question, by listening to each device in turn.

The transmitter may consist of any type of microchip in any shape, size and circuitry designed to transmit anywhere inthe radio frequency of AM or FM to produce atransmifled signal of a power needed to perform the desired result. Government regulations and specifications may determine the strength and frequency of the transmitted signal. The transmitter may produce a signal in one or more frequencies thus indicating a particular group of wheels.

The transmitter used in the alarm device of the invention may emit different signals depending on the pressure conditions of the tyre at the time. Also a number of devices could be supplied each having a transmitter transmitting at a different frequency to the others so that individual identification ofthe device can be ascertained when in use.

Many other and various forms ofthe device can also be made which will be completely satisfactory in practice and which do not depart from the invention described. For example, reference has been made to the use of a pressure valve as the pressure sensing means, whereas otherforms of means may be used, e.g. pressuretransducermeans.

It is therefore to be understood many modifications can be made in the invention without departing from the spirit and scope thereof.

Claims

1. An alarm device for connection to a pneumatic tyre comprising a transmitter, a power source for the transmitter, a pressure sensing means, the pressure sensing means being in contact with the internal atmosphere of the tyre and being adapted to activate the transmitter when the pressure of the tyre isat an abnormal level.

2. An alarm device having a body and including a transmitter, a power source for the transmitter and pressure sensing means, the pressure sensing means being so positioned in the device to be able to sense the internal pressure ofthetyre and being adapted to activate the transmitterwhen abnormal pressure is sensed, the device also having an inletforallowing air to be introduced into orexhaustedfromthetyre, without removal of the device from the tyre.

3. The device according to claim 1 wherein the transmitter is located around the body of the alarm device.

4. The device according to claim 1 in which the device is threada bly connected to the valve stem of the tyre.

5. A device according to claim 3 in which the length ofthevalvestem is reduced such thatthe overall length of the stem and the attached device is approximately the length of a normal valve stem.

6. A device according to claim 1 in which the device is connected to means for attachmentto a tubeless tyre.

7. A device according to claim 1 including a test switch for testing the operation of the transmitter.

8. A device according to claim 1 in which the transmitter is a single integrated ci rcuit which has a plurality offunctions.

9. The device of claim 7 in which the integrated circuit has a frequency modulation generator, a tone encoder which is binary and which is controlled by encoding switches and a power amplifier.

10. The device of claim 8 which has a tone generated code call which providesan original signal which sets a receiverto receive a code and a plurality oftone pulses which provide the tyre codes.

11. The device of claim 9wherein there are four bit tyre codes enabling 16 tyres to be monitored.

12. A device as claimed in claim 1 in which the pressure sensing means is a differential pressure device which detects a tyre pressure both above and below a predetermined range of pressures and activatesthetransmitter at the advent of either of these pressures.

13. A device as claimed in Claim 11 where the transmitter provides two different outputs, one for output relating to a pressure belowthe predetermined range and one for a pressure above this range.