GB2279169A

GB2279169A - A tyre pressure alarm device

Info

Publication number: GB2279169A
Application number: GB9312507A
Authority: GB
Inventors: Simon John Ford
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-06-17
Filing date: 1993-06-17
Publication date: 1994-12-21
Anticipated expiration: 2013-06-17
Also published as: GB9312507D0; GB2279169B

Abstract

The alarm device is for indicating loss of pressure and attaches to the valve of a pneumatic tyre. The device has pressure sensing means eg. switch contacts 11, 16, piston 8 and diaphragm 6 arranged to trigger a radio transmitter 12 when the tyre pressure falls below a certain value. The device has a spring biassed plunger 3 acting to open the tyre valve and to adjust to different valve core and stroke tolerances. Means are also provided to turn off the device for storage purposes. A light emiting diode 19 on top of the device warns the driver which tyre has suffered pressure loss. The signal transmitted by the device is received in the operator/driver compartment, where it is converted into visual and audible warnings. <IMAGE>

Description

A TYRE PRESSURE ALARM DEVICE DESCRIPTION The present invention relates to an alarm device. In particular, the invention relates to an alarm device for indicating loss of pressure in a pneumatic tyre.

Pneumatic tyres are widely used on many different vehicles, including motor cars, motor cycles, bicycles, trucks, trailers, caravans, buses and aeroplanes. For reasons of safety and economy, it is important to ensure that the air pressure within such tyres is correctly maintained during use. Where loss of pressure occurs, a tyre may suffer abnormal wear or failure, and the steering and fuel economy of the vehicle, to which it is fitted, will be adversely affected as a result. Many tyre deflations occur slowly and a tyre often shows little sign of pressure drop until it is completely deflated. If total deflation occurs, particularly whilst the vehicle is in motion, the tyre can be irreperably damaged or, worse still, suffer a "blow out" and the vehicle may become uncontrollable. If the tyre is fitted to a motor car, the driver will probably be aware of a "blow out" as soon as it occurs. If, however, the tyre is fitted to a caravan or a truck, for example, the driver may not realise what has happened and may continue in a vehicle that is no longer roadworthy.

A number of warning devices for measuring tyre pressure loss have been proposed, one such device being described in British Patent Specification No. 2171548.

This device is arranged for threaded connection to the valve stem of a pneumatic tyre and has an inlet for allowing air to be introduced into or expelled from the tyre, while the device is installed on the valve stem.

However, it is recommended that, before the device is fitted, the standard valve stem should be replaced by a short valve stem. Furthermore, it is also necessary to remove the valve core from the valve stem, before the device is attached to the latter, and then to refit the core into the device itself. Once fitted, the device is intended to remain in place, since its removal would require the reverse operation to be performed, and there is no means for switching the device off, short of disassembly, when the device is not attached to a tyre valve; the ambient pressure would be insufficient to prevent the alarm from being continuously triggered.

It is an object of the present invention to provide an alarm device that does not suffer from certain of the above disadvantages. In particular, it is an object of the present invention to provide an alarm device that may be deactivated when the device is not in use. It is a further object of the present invention to provide an alarm device that may be easily and reversibly fitted to the valve of any conventional pneumatic tyre, without the need to modify the valve in any way.

Accordingly, in a first aspect of the invention, there is provided an alarm device for indicating loss of pressure in a pneumatic tyre having an associated valve, comprising attachment means for attaching the device to the valve, valve actuating means for opening the valve to expose pressure sensitive means to the pressure within the tyre, signalling means arranged for producing a detectable signal in response to a tyre pressure change sensed by the pressure sensitive means, power source means to provide power for the device, and deactivation means for allowing the device to be deactivated.

In a second aspect of the invention, there is provided an alarm device for indicating loss of pressure in a pneumatic tyre having an associated valve, comprising attachment means for attaching the device to the valve and valve actuating means for opening the valve, wherein the valve actuating means comprises retractable plunger means biased towards an extended position.

In an embodiment of the invention in its first or second aspects, the attachment means is arranged for threaded connection to a valve stem, thus allowing the device to be screwed onto a valve stem in the manner of a valve stem cap. However, any other means of attachment that allows a pressure-tight seal to be achieved between the inventive device and the valve stem is also suitable. In a further embodiment of the first aspect of the invention and in its second aspect, the valve actuating means comprises retractable plunger means biased towards an extended position, preferably by spring means. Most preferably, the plunger means is arranged for depressing a core within a valve stem.

stem, so as to open the valve and expose the device to the internal pressure of the tyre. In these embodiments, the plunger is able to retract to compensate for different tolerances of valve core height and stroke. Thus, alarm devices provided in accordance with the present invention can enjoy the advantage of being able to be used on a wide range of pneumatic tyres fitted with different valves.

In another embodiment of the invention in its first aspect, the deactivation means and the pressure sensitive means have means in common. Thus, the means for preventing the signalling means from producing a detectable signal, when a tyre is at correct operating pressure, also can be the means by which the device may be deactivated, when it is not in use or is not fitted to a tyre. Preferably, the common means comprises electrical switching means arranged between the signalling means and the power source means.

Still more preferably, the pressure sensitive means can be arranged to cause the signalling means to produce a detectable signal when the tyre pressure falls below a predetermined value. In an especially preferred embodiment, the deactivation and valve actuating means also have common means. Thus, these common means can comprise a retractable spring-biased plunger, in which the spring is of sufficient resistance to allow the plunger to actuate a valve and adjust to differences in valve core height, and the plunger can be pushed into the device, against the resistance of the spring, to actuate means for preventing the signalling means from producing a signal, thereby deactivating the device.

In a preferred embodiment of the invention in its second aspect, the device further comprises pressure sensitive means, signalling means, power source means and deactivation means as defined in accordance with the invention in its first aspect. Preferably, the retractable plunger means can be moved from an extended position to a retracted position upon application of a predetermined force. Thus, whilst the application of a force of less than a predetermined value will still cause the plunger to retract to a less extended position, only a force equal to or greater than a predetermined value will cause the plunger to retract to a retracted position, as understood in the context of the present invention. In an embodiment, retraction of the plunger by the predetermined distance causes the device to be deactivated. Preferably, retraction of the plunger by a predetermined distance causes electrical switching means to open, so deactivating the device.

In the aforementioned embodiment, deactivation of the inventive device can be achieved by releasing the device from a valve and attaching it to a separate member adapted to move the valve actuating means to a deactivated position. In an alternative embodiment, the alarm device has two separate stages of attachment to a tyre valve stem, in the first of which the device is rendered operational and in the second stage the valve core head moves the valve actuating means to a deactivated position.

The pressure sensitive means may be any means by which the internal pressure of the tyre may be monitored, including any kind of pressure sensitive transducer. In a most preferred embodiment of the invention, the pressure sensing means comprises piston means arranged for maintaining electrical switching means open, at normal tyre pressures, and for allowing the electrical switching means to close, when the tyre pressure falls below a predetermined value. Preferably, the piston means are sealed in the device by diaphragm means, arranged to prevent loss of pressure from the tyre when the device is in position on a valve.

In a further embodiment, a protective casing surrounds the pressure sensitive means, the signalling means and the power source means, such that one face of the diaphragm means remains exposable to the tyre pressure. The protective casing serves to isolate the pressure sensitive means, the signalling means and the power source means from external conditions, whilst the diaphragm means provides a pressure and water-tight seal. Thus, advantageously, none of the electronic or electrical switching components of the inventive device are exposed to the elements. Furthermore, since the means for deactivating the device has means in common with the pressure sensitive means or the valve actuating means, the inventive device enjoys the advantage that, once fitted to a valve, the deactivation means can be isolated from external conditions. Thus, in a preferred embodiment, the deactivation means is arranged to be isolated from external conditions when the device is fitted to a valve.

In a third aspect of the invention, there is provided a system for indicating loss of pressure in a pneumatic tyre, comprising an alarm device according to the invention in its first or second aspect and further comprising remote receiving means for converting a signal from said device into an audible or visual warning.

In an especially preferred embodiment, the remote receiving means consists of a receiver connected to a visual or audible warning device located in the operator or driver compartment of the vehicle to which the tyre is fitted. Preferably, each alarm device also has a warning device, such as a light emitting diode, fitted to it, so that on receiving a signal that pressure loss has occurred, the driver is easily able to determine which tyre has failed.

The nature of the invention and the manner in which it may be performed will be better understood from the following detailed description of one specific embodiment thereof, by way of illustration only, and with reference to the accompanying drawings, wherein: Figure 1 is a sectional a side view of a tyre pressure alarm device according to the present invention; Figure 2 is a sectional side view of the disassembled component parts of the lower body of the tyre pressure alarm device of Figure 1; Figure 3 is a block diagram of a transmitter circuit suitable for use in the present invention; Figure 4 is a block diagram of a receiver circuit, suitable for use with the inventive device; Figure 5 is a schematic representation of a warning system comprising a tyre pressure alarm device according to the present invention.

With reference to Figures 1 and 2, a hollow lower body 1 comprises a frusto-conical middle portion 1J extending between smaller and larger diameter cylindrical sleeve portions 1K, 1L. The smaller sleeve portion 1K is internally threaded for screw thread engagement with a tyre valve (not shown). The larger sleeve portion 1L has a stepped bore which extends from hole 1E, formed through the frusto-conical middle portion 1J, opening out through a series of larger concentric bores (1A, 1B, 1C and 1D).

A rubber sealing washer 2 is located in an annular recess 1H formed between the hole 1E and the threaded part of the smaller sleeve portion 1K. A plunger 3 comprises a rod portion 3A, extending from a cylindrical portion 3C, and an annular flange 3B, which extends radially outwardly from the cylindrical portion 3C where it joins the rod portion 3A. The plunger 3 is slidably located in the lower body 1, with the rod portion 3A in the hole 1E and the cylindrical portion 3C in the bore 1A. The flange 3B is held in abuttment with the end face of the bore 1A by a coil spring 4. The coil spring 4 surrounds the cylindrical portion 3C of the plunger 3 and acts between the flange 3B and a retaining washer 5. The retaining washer 5 is located in the bore 1B and has an inner diameter sufficient to allow the passage of the cylindrical plunger portion 3C. A rubber diaphragm 6 is located in the third bore 1C and is retained in place by a top hat member 9 located in the fourth bore 1D. The top hat member 9 is a tight frictional fit within the fourth bore 1D and seats the rubber diaphragm 6. A piston 8 comprises a disc portion 8A centrally attached to one end of a cylindrical shaft 8B. An annular groove 8C is formed in and around the shaft 8B at the end remote from the disc 8A. The shaft 8B is slidably located within a bore 9C, defined through the crown of the top hat member 9G, and the disc 8A is slidably located within a bore 9B, defined within the rim portion of the top hat member 9. A coil spring 7 surrounds the shaft 8B, and is retained within a bore 9A, formed between the bores 9B and 9C.

The spring 7 acts between the crown of the top hat member 9G, surrounding the bore 9C, and the disc 8A.

An insulating washer 10 has two diametrically opposed holes, formed through its web, each for receiving one of two axially extending cylindrical contact members 11, and has a radially innermost surface 10A dimensioned to locate around the surface of the top hat member 9, radially outwards from bore 9D. A contact washer 16 has a central hole to receive the shaft 8B and is retained in place on the shaft 8B by a clip 20, which fits in the annular groove 8C.

A transmitter circuit board 12 is located within an upper body 18 (see Figure 1). The transmitter circuit conforms to the Department of Trade and Industry (Radio Communications Division) performance specification MPT 1340 (Transmitters and Receivers for use in telemetry, telecommand and in building security equipment operating in the frequency band 417.90 MHz to 418.10 MHz). An annular spacer 13 spaces a transmitter circuit board 12 and an encoder circuit board 14. The endcoder circuit board 14 uses a CMOS semiconductor encoder chip (Holtek Semiconductor INC, Taiwan HT-12ES), which allows for 256 different combinations of coding. An annular spacer 15 spaces the encoder circuit board 14 and a battery 17. The battery 17, which is cylindrical in shape, is a lithium manganese coin cell or a lithium thionyl chloride cell. The upper body 18 is hollow and substantially cylindrical.

It is attached to the lower body 1 and encloses the components (see Figure 1), isolating them from external conditions. A light emitting diode 19 protrudes through top of the upper body 18. Conductors (not shown) extend between the battery 17 and the encoder and transmitter boards 12 and 14, via contact members 11 and the contact washer 16; the latter components providing a switch between the battery 17 and the boards 12 and 14.

With reference to Figure 3, a conventional transmitter circuit of the type suitable for use in the present invention is depicted schematically. On closing the switch a voltage is applied to a CMOS semiconductor encoder chip which sends an encoded signal to a wide band frequency modulation modulator via a low pass filter. This signal is used to vary the output of a SAW oscillator. The resultant signal is passed through a 418 MHz bandpass filter before transmission from an antenna.

With reference to Figure 4, a conventional receiver circuit of the type suitable for use with the transmitter shown in Figure 3 is depicted schematically. The signal from the transmitter is received by an antenna and filtered through a 418 MHz bandpass filter. The signal is amplified by a pre-amplifier before being down-converted to an intermediate frequency of 15.92 MHz by heterodyning with a 433.92 MHz first local oscillator signal from a SAW oscillator. The intermediate frequency signal is itself down-converted by heterodyning with a 16 MHz second local oscillator signal to a second imtermediate frequency. The second intermediate signal is amplified and demodulated. The demodulated signal is applied to a 5KHz low pass filter and then amplified before being supplied to a data slicer and decoded. The CMOS decoder drives a light and/or buzzer to provide the observer with an appropriate warning.

With reference to Figure 5, the figure on the left shows a conventional tyre valve fitted with a tyre pressure alarm device according to the invention, whilst that on the right shows a possible location for a receiver and warning device in the operator compartment of a vehicle.

In use, when the tyre pressure alarm device is attached to a valve stem, it is held in such a way that the end of the valve stem is sealed to the lower body 1 by the rubber washer 2. This allows the bottom face of the plunger rod 3A to depress the valve core within the valve stem, so allowing pressure from within the tyre to escape. Pressurised air passes through a hole or clearance between 3A and lE, enters the bore lA, and then passes through the spring retaining washer 5 to the bottom face of the rubber diaphragm 6. The rubber diaphragm 6 is sealed in the bore 1C by the top hat member 9. The bottom face of the diaphragm 6 is now exposed to the pressure within the tyre causing it to be displaced upwards against the piston 8. The piston 8 resists upward displacement of the diaphragm by means of the spring 7. The spring 7 has a predetermined rate, so that when the tyre pressure on the diaphragm 6 increases beyond this rate, the piston 8 is itself displaced upwards. At the correct tyre pressure, the piston 8 holds the contact washer 16 away from the contacts 11. When the pressure within the tyre falls below the spring rate of the spring 7, the piston 8 and the diaphragm 6 move down, allowing the contact washer 16 to touch both contacts 11 and energise the transmitter circuit 12, encoder circuit 14 and light emitting diode 19. The signal generated by the transmitter and encoder circuit is collected by a receiver, which is mounted in the driver/operator compartment. The receiver collecting the correct signal emits a visual and audible alarm.

In order to allow for varying tolerances in valve core height or stroke, the plunger 3 is spring-loaded. The rate of the spring 4 is selected to be sufficient to fully open the valve, but to allow the plunger 3 to be displaced upwards when the valve core bottoms out in its stroke. This allows the tyre pressure alarm device to adjust to different valve core positions and strokes, and ensures good sealing. In order to turn the device off for storage, a suitably dimensioned threaded plug (not shown) is screwed into the smaller sleeve portion 1K, pushing the rod 3A of plunger 3 upwards against the spring 4. As the spring 4 is overcome, the cylindrical portion 3C passes through the hole in spring retaining washer 5 so that the top face of 3C contacts the bottom face of the rubber diaphragm 6. The plunger 3 now pushes up the diaphragm 6 and the piston 8, opening the switch contacts and terminating the power supply to the transmitter and the encoder circuits.

Claims

1. An alarm device for indicating loss of pressure in a pneumatic tyre having an associated valve, comprising attachment means for attaching the device to the valve, valve actuating means for opening the valve to expose pressure sensitive means to the pressure within the tyre, signalling means arranged for producing a detectable signal in response to a tyre pressure change sensed by the pressure sensitive means, power source means to provide power for the device, and deactivation means for allowing the device to be deactivated.

2. An alarm device for indicating loss of pressure in a pneumatic tyre having an associated valve, comprising attachment means for attaching the device to the valve and valve actuating means for opening the valve, wherein the valve actuating means comprises retractable plunger means biased towards an extended position.

3. An alarm device as claimed in claim 2, further comprising pressure sensitive means arranged to be exposed to the pressure within the tyre when the valve is open, signalling means arranged for producing a detectable signal in response to a tyre pressure change sensed by the pressure sensitive means, power source means to provide power for the device, and deactivation means for allowing the device to be deactivated when not in use.

4. An alarm device as claimed in claimSl or 3, wherein the deactivation means is arranged to be isolated from external conditions when the device is fitted to a valve.

5. An alarm device as claimed in any of claims 1, 3 and 4, wherein the pressure sensitive means are arranged to cause the the signalling means to produce a detectable signal when the tyre pressure falls below a predetermined value.

6. An alarm device as claimed in any of claims 1 and 3-5, wherein the deactivation and pressure sensitive means include common means for deactivating the device, or causing the signalling means to produce a detectable signal.

7. An alarm device as claimed in any of claims 1 and 3-6, wherein the deactivation and valve actuating means include common means for deactivating the device, or actuating the valve.

8. An alarm device as claimed in claim 7, wherein the common means comprises retractable plunger means biased towards an extended position.

9. An alarm device as claimed in claim 6, wherein the common means comprises electrical switching means arranged between the signalling means and the power source means.

10. An alarm device as claimed in any of claims 2, 3 and 8, wherein the plunger means are biased towards an extended position by spring means.

11. An alarm device as claimed in any of claims 2, 3, 8 and 10, wherein the plunger means moves from an extended position to a retracted position upon application of a predetermined force.

12. An alarm device as claimed in any of claims 2, 3, 8, 10 and 11, wherein the plunger means is arranged for depressing a core within a valve stem.

13. An alarm device as claimed in any of claims 2, 3, 8 and 10-12, wherein retraction of the plunger means by a predetermined distance deactivates the device.

14. An alarm device as claimed in claim 13, wherein retraction of the plunger means by a predetermined distance causes the electrical switching means to open.

15. An alarm device as claimed in any of the preceding claims, wherein the attachment means is adapted for threaded connection to the valve.

16. An alarm device as claimed in claim 9, wherein the pressure sensitive means comprises piston means arranged for maintaining the electrical switching means open, at normal tyre pressure, and for allowing the electrical switching means to close, when the tyre pressure falls below a predetermined value.

17. An alarm device as claimed in claim 16, wherein diaphragm means are arranged to seal the piston means in the device and to prevent loss of pressure from the tyre.

18. An alarm device as claimed in any claims 1 and 3-17, wherein the signalling means is a radio transmitter.

19. An alarm device as claimed in any of the preceding claims, further comprising warning means to provide a signal that said device has been activated when the tyre pressure falls below a predetermined value.

20. An alarm device as claimed in claim 19, wherein said warning means is a light emitting diode.

21. An alarm device substantially as hereinbefore described with reference to the accompanying drawings.

22. A system for indicating loss of pressure in a pneumatic tyre, comprising an alarm device as claimed in any of claims 1-21 and further comprising remote receiving means for converting a signal from said device into an audible or visual warning.