GB2171233A

GB2171233A - Monitoring tyre inflation

Info

Publication number: GB2171233A
Application number: GB08603945A
Authority: GB
Inventors: Tom Cooper
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-02-19
Filing date: 1986-02-18
Publication date: 1986-08-20
Also published as: GB8603945D0; GB8504244D0

Abstract

In a tire inflation alarm a switch is arranged so as to close below a predetermined pressure, whereby to activate a signal transmission system. As shown, the switch contacts 52,62 are separated by excess pressure acting on diaphragm 36, and are closed (in the absence of such pressure) by a spring 56. The switch arrangement is screwed onto an inflation valve, and has a projection 48 to depress the valve stem 16. The transmitted signal may be a coded radio signal. <IMAGE>

Description

SPECIFICATION Fluid pressure monitoring devices This invention relates to fluid pressure monitoring devices and is particularly concerned with monitoring devices for use with pneumatic tyres.

Pneumatic tyres on motor vehicles are normally checked with regard to correct inflation pressures while the vehicle is in a stationary condition by means of conventional checking procedures. However loss in pressure in the tyres while the vehicle is in motion remains a problem, and loss of pressure is highly probable due to the functional and fundamental demands placed on vehicle tyres.

According to the present invention there is provided apparatus for monitoring fluid pressure in a device, the apparatus comprising means for transmitting a monitoring signal from the apparatus to a remote location, and means operable in accordance with changes in fluid pressure in a device to change the condition of the transmitting means, the operable means being biassed into an operating mode but being maintained in a non-operating mode against the biassing force so long as the fluid pressure is above a pre-determined value.

Preferably the apparatus is designed for monitoring pressure in a pneumatic tyre, and the apparatus may be designed to operatively connect with a conventional tyre valve arrangement. The operable means preferably comprises a control member movably located in the apparatus, the control member providing a movable contact in an electrical circuit which includes the transmitting means.

Further, the control member may be so biassed as to move the movable contact to a closed position but, when the pressure in the device is above the predetermined value, the movable contact is maintained in an open condition whereby the transmitting means is non-operative.

The biassing means preferably comprises a compression spring, and the control member may comprise a flexible diaphragm.

The apparatus is preferably formed with an internally threaded neck part for location on an externally threaded part of the device. Further there may be provided means for engaging a valve part of the device whereby to maintain a through passage for fluid from the device to the apparatus to enable the fluid pressure to act upon the control member against the biassing force.

The transmitting means may comprise means for generating a carrier frequency signal, means for modulating the carrier frequency signal and generating a modulated signal, and inductive means for radiating an operating signal. Means for receiving a transmitted monitoring signal may be adapted to selectively detect the presence or absence of the monitoring signal and reject spurious signals originating from other than the transmitting means.

An embodiment of the present invention will now be described by way of example only with reference to the single figure of the accompanying drawing which is a sectional view in elevation through an apparatus according to the invention mounted on a pneumatic tyre valve.

Referring to the drawing, a pneumatic tyre (not shown) for a motor vehicle is provided with a conventional tyre valve having an externally threaded part 10 defining a seat 12 for a movable valve part 14. The latter conventionally has an outwardly extending valve stem 16.

A monitoring apparatus comprises a multipart casing formed of any suitable material and including a mounting section 20 and a switch casing 22, the former having an enlarged diameter section 24 at one end, the upper end in the drawing, defining an annular shoulder 26. The casing 22 has an externally threaded part 28 at its lower end, whereby the casing 22 can be clamped to the mounting section 20 by means of a locking nut 30 provided with an inturned flange 32 at a lower end to engage with the shoulder 26 and an internally threaded part 34 at tne upper end for engaging with the externally threaded part 28 of the casing 22. A diaphragm 36 formed of a flexible material is clamped between the upper end of the mounting section 20 and the lower end of the switch casing 22 for a purpose hereinafter described.

The mounting section 20 is open at the end remote from the switch casing 22, i.e. the lower end, and at that end is formed with an internally threaded neck 38 which is threadedly engageable on the threaded part 10 of the tyre valve whereby to secure the monitoring apparatus to the tyre. The mounting section 20 is further provided with an integrally formed partition 40 extending across the internal space at a location whereby to define a first cavity 42 opening onto the lower end of the mounting 20, and a second cavity 44 opening onto the upper end of the mounting 20 so that, in use, the cavity 44 is closed in a pressure-tight manner by the diaphragm 36.The partition 40 has a plurality of through holes 46 defined therein to communicate between the cavities 42 and 44, and on its lower side the partition 40 is provided with a fixed plunger 48 extending downwardly therefrom for a purpose hereinafter described.

The diaphragm 36 is formed of an electrically conductive material and, on the side thereof facing into the switch casing 22, the diaphragm 36 is formed with a projection 50 of substantially inverted L-shaped configuration, providing an electrical contact 52. A central boss 54 on the same side of the diaphragm 36 provides a location for one end of a compression spring 56, the other end of which locates around a boss 58 formed on an inner face of an upper wall of the switch casing 22.

An electrically conductive member 60 of elongate form extends through the upper wall of the switch casing 22 and is of substantially L-shaped configuration whereby to present a contact 62 within the casing 22. The location of the member 60 is such that the contacts 52, 62 can engage one another. An insulating member 64 is provided in the upper wall of the casing 22 and provides a through passage within which is located the member 60, whereby the latter is normally insulated from the casing 22, which is also formed of an electrically conductive material. The end of the contact member 60 outside the switch casing 22 provides a connection point for electrically connecting with an appropriate contact of a signal transmitting arrangement (not shown), which is mounted on the switch casing 22 to be electrically connected thereto.

In use, when the mounting section 20 is engaged on the threaded part 10 of the tyre valve, the plunger 48 engages with the valve stem 16 to move the valve part 14 off the seat 12 and thus release air from the tyre into the cavity 42. The air passes through the holes 46 in the partition 40 into the cavity 44 and, provided the tyre is at a desired pressure, the pressure of the air in the cavity 44 will deflect the partition 36 upwardly against the biassing force of the spring 56 and move the contact 52 out of engagement with the contact 62. In this normal operating condition the signal transmitting arrangement is not energised. When the air pressure in the tyre reduces below a predetermined value, the biassing force of the spring 56 overcomes the air pressure in the cavity 44 and moves the diaphragm 36 back to a condition where the contacts 52 and 62 are engaged.An electrical circuit to the transmitting arrangement is thereby completed through the diaphragm 36 and the switch casing 22, and through the contact member 60.

In a suitable transmitting arrangement a carrier frequency is generated by an oscillator circuit which is controlled by a tuned device. The generated signal is then passed to a modulator with the modulation signal generated by another oscillator.

The output from the modulator is then passed through a driver or matching circuit to a signal radiating assembly which comprises an inductor wound on a suitable core material such as ferrite or dust iron, the inductor forming part of a tuned circuit which is tuned to the carrier frequency. The transmitting arrangement is adapted to function at the chosen frequency regardless of environmental conditions such as ambient temperature.

Transmission can take place with a carrier frequency between 105 kHz and 115 kHz, or between 129 kHz and 139 kHz, or at any suitable frequency which may be officially allocated or officially be allowed to be used. The transmission arrangement may also modulate the carrier frequency such that a receiving arrangement (not shown) could be made to detect the modulation and recognise this to indicate a true warning signal rather than a spurious or unwanted interference signal. Several modulation techniques could be suitable for the pupose, for example amplitude modulation, frequency modulation, phase modulation, or pulse modulation. A vehicle with a plurality of wheels may be fitted with a separate transmitting arrangement on each wheel.If required, the design of the system could be made to allow for different transmission signals to be generated from each wheel such that the wheel having a low pressure tyre could be identified.

The transmitting arrangement can be powered by a battery consisting of one or more electrochemical cells using lithium type, mercury type, silver oxide type, alkaline manganese type, or any other type of technology which can be made to serve the purpose within the limited volume which the cells would be allowed to occupy. The small size of the battery would imply an equally small capacity. The switching arrangement is so designed that the battery is not suppiying the transmitting means unless the tyre inflation is below the predetermined value so that battery capacity is conserved until such time that a low pressure warning transmission signal is necessary.

The signal from the transmitting arrangement may be picked up by a receiving arrangement which may be mounted upon or within the chassis or body of the vehicle and used to control an audible or visual or any other type of warning device which will alert the vehicle driver that a drop in inflation pressure to a level below the predetermined value has occurred. The predetermined value may be set by suitable control of the switch assembly comprising the diaphragm 36 and the spring 56.

The receiving arrangement may comprise a reception inductor or aerial connected to an electronic receiver circuit and detector which could use tuned circuit, frequency tuned amplifier, hetrodyne, superhetrodyne, synchrodyne, or homodyne technology to selectively detect the presence or absence of the signal from the transmitting arrangement.

It will be appreciated that the invention provides for a continual monitoring of the tyre pressure while the vehicle is in motion or stationary. The ability of the invention to monitor the tyre pressure when the vehicle is in motion gives substantial benefits with regard to safety requirements and tyre cost effectiveness.

As the casing 22 is releasably secured to the mounting section 20, the former can be easily removed for ease of maintenance and replacement if necessary. Various other modifications may be made without departing from the invention. For example the biassing force may be provided by other than that described and shown and the apparatus may be of any other configuration, for example a T-configuration so as to reduce the height extending from the tyre.

Claims

1. Apparatus for monitoring fluid pressure in a device, the apparatus comprising means for transmitting a monitoring signal from the apparatus to a remote location, and means operable in accordance with changes in fluid pressure in a device to change the condition of the transmitting means, the operable means being biassed into an operating mode but being maintained in a non-operating mode against the biassing force so long as the fluid pressure is above a predetermined value.

2. Apparatus according to claim 1, wherein the operable means comprises a control member movably located in the apparatus, the control member providing a movable contact in an electrical circuit which includes the transmitting means.

3. Apparatus according to claim 2, wherein the control member is so biassed as to move the mov able contact to a closed position but, when the pressure in the device is above the predetermined value, the movable contact is maintained in an open condition whereby the transmitting means is non-operative.

4. Apparatus according to claim 3, wherein the biassing means comprises a compression spring.

5. Apparatus according to any of claims 2 to 4, wherein the control member comprises a flexible diaphragm.

6. Apparatus according to any of claims 2 to 5, wherein the casing of the apparatus is formed in a plurality of parts, including a first part for mounting on the device and a second part which houses an insulated fixed contact in the electrical circuit of the transmitting means, the first and second parts being releasably clamped together with the control member sealingly clamped therebetween.

7. Apparatus according to claim 6, wherein at least the second part and the control member are formed of electrically conductive material.

8. Apparatus according to any of the preceding claims, including an internally threaded neck part for location on an externally threaded part of the device.

9. Apparatus according to any of the preceding claims, wherein there is provided means for engaging a valve part of the device whereby to maintain a through passage for fluid from the device to the apparatus to enable the fluid pressure to act upon the control member against the biassing force.

10. Apparatus according to any of the preceding claims, wherein the transmitting means comprises means for generating a carrier frequency signal, means for modulating the carrier frequency signal and generating a modulated signal, and inductive means for radiating an operating signal.

11. Apparatus according to any of the preceding claims, including means for receiving a transmitted monitoring signal, the receiving means being adapted to selectively detect the presence or absence of the monitoring signal and reject spurious signals originating from other than the transmitting means.

12. A vehicle including tyre pressure monitoring apparatus according to any of the preceding claims.

13. Apparatus for monitoring fluid pressure in a device substantially as hereinbefore described with reference to the accompanying drawing.

14. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.