WO1997004971A1

WO1997004971A1 - Vehicle tyre deflation detector

Info

Publication number: WO1997004971A1
Application number: PCT/EP1996/003328
Authority: WO
Inventors: Garry David Leslie Starck
Original assignee: Alternatives Engineering Cc
Priority date: 1995-07-31
Filing date: 1996-07-29
Publication date: 1997-02-13
Also published as: AU6738596A

Abstract

A deflation detector for detecting when the tyre (10) becomes deflated and for indicating to the driver of the vehicle that the tyre is deflated comprises a plunger member (48) subject to the pressure in the tyre and a transmitter (72) controlled by said member to emit a signal when the pressure in the tyre falls below a predetermined amount. The transmitter is carried by the wheel rim (14) and includes an electric circuit incorporating a pair of contact terminals (66) one of which is connected to a source of power (74) for the transmitter. The plunger member is movable by the pressure in the tyre against a spring (58) bias to a first position in which it holds the contact terminals apart and a second position in which it permits the contact terminals to move into electrical contact thereby to permit power to be supplied to the transmitter. In a modification the plunger is connected to operate a rheostat that gives a signal which is dependent upon the pressure in the tyre.

Description

Vehicle Tyre Deflation Detector

This invention relates to tyres for motor vehicles and the like. The invention is concerned with a deflation detector for detecting when the tyre becomes deflated and for indicating to the driver of the vehicle that the tyre is deflated.

Many devices have been suggested for detecting when a tyre on a vehicle has become deflated. These include, among many others, devices which permit air to pass through the tyre valve where its pressure is detected, devices which measure the relative rotational speed of wheels on a vehicle and optoelectronic devices to testing the tyres. Most, if not all, of such devices incorporate a transmitter for sending a signal receivable in the cabin of the vehicle when the pressure in the tyre drops. So far however, as far as the applicant has been able to ascertain, no such device has been sufficiently successful for it to be adopted generally by the motor industry.

According to one aspect of the invention there is provided apparatus for detecting whether the pressure in a tyre on a wheel rim has fallen below a predeter¬ mined amount including a member subject to the pressure in the tyre and a transmitter controlled by said member to emit a signal when the pressure in the tyre falls below a predetermined amount characterised in that the transmitter is carried by the wheel rim and includes an electric circuit incorporating resistance variation means which affects the signal, and in that the said member is movable relative to the resistance variation means by the pressure in the tyre against a bias, the said member being operatively connected to the resis¬ tance variation means so that when the pressure in the tyre is at a pre-set level then the resistance vari¬ ation means will provide a first resistance and when the pressure in the tyre has fallen a prescribed amount the resistance variation means will provide a second resistance.

The resistance variation means may comprise a rheostat or the like. Preferably however the resis¬ tance variation means may comprise a switch where one of the aforesaid resistances is zero i.e. when the switch is closed and the other of the aforesaid resistances is infinite i.e. when the switch is open. The said first resistance is preferably infinite so that the transmitter will be disconnected from the power supply when the tyre pressure is at the pre-set level and the second resistance is zero when the pressure in the tyre has fallen the prescribed amount so that power will be supplied to the transmitter causing it to emit a signal.

The said member is preferably in the form of a plunger having one end subject to the pressure in the tyre and being biassed by a spring to move against said pressure. The resistance variation means preferably comprises a pair of terminals biassed into contact with each other and the other end of the plunger being movable to engage at least one, and preferably both, of the terminals to move them apart.

According to another aspect of the invention there is provided apparatus for detecting whether the pressure in a tyre on a wheel rim has fallen below a predetermined amount including a member subject to the pressure in the tyre and a transmitter controlled by said member to emit a signal when the pressure in the tyre falls below a predetermined amount characterised in that the transmitter is carried by the wheel rim and includes an electric circuit incorporating a pair of contact terminals one of which is connected to a source of power for the transmitter, and in that the said member is movable by the pressure in the tyre against a bias to first position in which it holds the contact terminals apart and a second position in which it permits the contact terminals to move into electrical contact thereby to permit power to be supplied to the transmitter.

Two embodiments of the invention will now be described by way example and with reference to the accompanying drawings. In the drawings:-

Figure 1 is a partial section through a motor vehicle tyre embodying a detector of the invention,

Figure 2 is a longitudinal section through the detector of Figure 1,

Figure 3 is a diagrammatic side view of a truck incor¬ porating a plurality of tyres as illustrated in Figures 1 and 2,

Figure 4 is a diagrammatic view showing a receiver and display device, detectors

Figure 3 is a modified detector of the invention and,

Figure 4 is diagrammatic electronic circuit.

Referring now to Figure 1 there is shown a motor vehicle wheel 10 carrying a tyre 12. The wheel rim 14 carries a sensor and transmitting device 16 of the invention (hereinafter referred to as the "sensor") so that it protrudes into the space defined by the tyre 12.

The sensor 16 comprises a rubber casing 18 (see

Figure 2) which passes through an opening 20 in the rim 14. The casing 18 has an upper frusto conical part 22 protruding outside the tyre and terminating in a cylindrical end part 24. Below the frusto conical part 22 is a slot 26 into which the edge of the rim 14 about an opening 20 enters. Below the slot 26 there is a low, enlarged diameter frusto conical inner por- tion 28 of a larger cone angle than the part 22. At the end of the frusto conical portion 28 is a flat surface 30 surrounded by a low circular rim 32. A thin veneer 34 (shown enlarged for clarity) covers the frusto conical portion 28 and extends over the flat surface 30 and serves to prevent air escaping through the sensor 16. This veneer 34 engages against the inside of a the tube 36 within the tyre.

There is a cylindrical inner chamber 38 extending along the length of the casing 18. An internally stepped bush 40 is provided within the chamber 38, having its free end 42 flush with the end 30 of the member. The bush 40 has a cylindrical internal passage 44 that extends to a throat 46 about midway along the length of the chamber 38.

A plunger 48 is co-axially located within the passage 44. The plunger 48 comprises a plastics, electrically non-conductive material, preferably "Tufnol". It has a conical end 50 remote from the tyre 12 and its other, inner, end 52 is threaded into a hard plastic head 54. Midway along its length, and within the chamber 38, the plunger 48 has an integral flange 56 which serves as an abutment for a compression spring 58. The other end of the spring 58 butts against a washer 60 which in turn butts against the surface of the throat 46.

A locking seal 62 fits into the open end of the chamber 44 so that its end face is co-planer with the face 42. The seal 62 has a frusto conical end 63 which fits into a corresponding groove in the material 40 which in effect locks it in position. The locking seal 62 has a through bore in which the plunger 48 is a sliding fit.

Within the end part 24 of the casing 18 is a printed circuit board 64. A pair of electrical contact terminals 66 are mounted on the PCB 64 by a pair of springs 68 respectively. The springs 68 bias the terminals 66 into engagement. Thus the terminals 66 form in effect an on/off switch, there being a zero resistance between them when they are in contact and an infinite resistance when they are moved apart from one another. The corners of the contact terminals 66 closer to the end face 30 of the sensor have a taper 70. The conical end 50 of the plunger 48 is located between these surfaces 70 and holds the ter¬ minals 66 apart. These terminals 66 are connected via the springs 68 to the electrical connections of a transmitter (indicated generally at 72) mounted on the PCB 64. One of the terminal contacts 66 connects directly with a button battery 74 which provides power for the transmitter.

The button battery 74 is mounted in the casing 18 near its inner end. The battery 74 is held in place by a circular plug 76 which has downward flanges 78 and which is a snap fit in the free end of the end part 24. The transmitter can be of any conventional design as will be appreciated by those skilled in the art which is small enought to fit into the casing 18 anmd will not be described further.

The sensor operates as follows. The plastic head 54 acts through the flexible veneer cover 34 against the tube 36 and is urged by the spring 58 outwardly of the casing 18. As the plunger 48 is moved outwardly, the conical end 50 moves backwardly from the two terminals 66 which are urged by the springs 68 into engagement thereby connecting the battery 74 to the electrical circuit of the trans- mitter 72 which now emits a signal. Once the tube 36 is inflated, it engages the head 54 of the plunger 48.

When it, the tube 36, is properly inflated to the pre-set pressure it will move the plunger 48 inwardly against the bias of the spring 58 to move the con- tacts 66 apart, thereby disconnecting the electrical circuit of the transmitter 72 from its source of power 74. This is the condition which the sensor 16 takes while the tube 12 is properly inflated.

Should the tube become deflated a below the pre¬ set level (which is the appropriate pressure for the tyre) by a prescribed amount (say five tenths of a bar below the pre-set level), the force of the spring 58 overcomes the effect of the tube 36 to move the plunger 48 outwardly and allows the contacts 66 to move into engagement, i.e. the closed switch position. This provides electric power to the circuit of the transmit¬ ter 72 which now emits a signal as described above.

It is self-evident that the strength of the spring 58 is chosen so that it will move the plunger 48 as described above at the appropriate pressures.

Reference is now made to Figures 3 and 5. In these Figures there is a shown a truck 74 comprising a "horse" 76 and trailer 78. Each tyre 80 of the truck is the same as the tyre 10. Within the cabin 82 of the "horse" 76 is a radio receiver 84 (see Figure 4) which is powered by the vehicle battery 85 and is connected to a display board 86 conveniently mounted on the dashboard (not shown). The display board 86 comprises one or more light emitting diodes L.E.D.s that can display the number of any tyre which has become deflated. Thus when the pressure in a tyre 12 falls a prescribed amount below the pre-set desired level by the aforesaid prescribed amount, a radio signal will be sent to receiver 84 as described above. The receiver 84 will then give a signal to the display board so that the number of the tyre 80 which is deflated will appear on the display board 86. If more than one tyre 80 has become deflated then the numbers will alternately be displayed on the display board 86. If desired, the display board may also flash, or may have a separate flashing light, to alert the driver that a tyre has become deflated so that he will check the display board to ascertain which tyre has become deflated.

A modified display board 88 is shown in Figure 6. This display board comprises a number of lights 90 that are capable of being illuminated. Each light 90 corresponds to a tyre of the truck and will be illu¬ minated should the tyre deflate and the appropriate signal sent as described above.

In a further modification of the display board, this may comprise a single light which will inflate should any one of the tyres deflate warning the driver to take remedial action including finding out which tyre has deflated by inspection. A modified sensor and transmitter 92 is illus¬ trated in Figure 7. The sensor 92 comprises a multi¬ part casing 94. The casing 94 comprises a lower part 96 terminating at a low frusto-conical inner portion 97. The part 96 has a cylindrical bore 98 that terminates at an end face 100 having a narrow aper¬ ture 102 therethrough to form a throat. This throat 102 comprises a first cylindrical portion 104 and then a frusto-conical continuation 106. The open end of the bore 98 contains a sealing bush 108 which has a larger frusto-conical head 110 that fits into a complementary groove in the wall of the bore 98.

A plunger 114 sealingly passes through the bush 108. It has a double frusto-conical head 116 at the inner portion 96. Along its length it carries a washer 118 held in place by a cross-pin 120. A compression spring 122 acts between the washer 118 and the end face 100, conveniently through a washer (not shown), thereby biassing the plunger 114 outwardly.

The double head 116 of the plunger 114 has an upper head part 128 sealing against a concave frusto¬ conical end face of the bush 108 and the lower head part 130 sealing against the inside portion of a concave frusto-conical face 132 of the inner por- tion 96. An air tight flexible seal 134 covers the face 132 to prevent air pressure escaping through the sensor 92.

The outer end 136 of the plunger 114 is of conical shape with an acute cone angle which is the same as that of the frusto-conical bore continuation 104. It engages the movable member of a rheostat shown diagram¬ matically at 138 forming part of a transmit¬ ter indicated generally at 140. When the plunger 114 is moved fully outwardly by the tyre pressure, the end 136 engages the bore continuation 106 to limit further movement of the plunger.

The transmitter 140 is mounted on a PCB 142 which is housed in a cylindrical transmitter housing 144. A battery 146 is carried in the housing 144 near its inner end and is held in place by a screw-in cap 148.

A frusto-conical housing clamp 150 fits tightly over the casing 94. It has a triangular section internal ridge 152 that fits into a correspondingly shaped groove in the outside surface of the casing 94. The clamp 150 has a slightly larger upper cylindrical bore 154 that firmly holds the transmitter housing 144 in position abutting the casing 94.

The rheostat 138 forms part of the circuitry of the radio transmitter 140 the construction of which will be appreicated by those skilled in the art. It is arranged so that it sends a signal when depends upon the position of the conical end 136 of the plunger 114. When the plunger is in the position most remote from the tyre, the signal sent will indicate that the tyre is fully inflated. When the plunger 114 is in the furthest position moved by the spring 122, the signal emitted indicates that the tyre is significantly deflated. The intermediate positions of the plunger will cause the rheostat 138 to affect the transmitter so that signals of different strengths are emitted so that the driver will see from the display board that the tyre is deflated to a lesser degree. Remedial action can thus be taken at an early stage.

It will be seen that when fitting the sensor 92 to the wheel rim 14, the casing 94 is passed through the opening in the rim 14with the inner portion 96 pressed firmly against the rim to seal therewith. The housing clamp 150 is then fitted to the casing 94 to secure it in position. The transmitter housing 144 is now fitted into the bore 154 where it is firmly held in position.

The invention is not limited to the precise constructional details hereinbefore described and illustrated in the drawings. For example, the housing arrangement of the Figure 7 embodiment may be used with the first described embodiment and vice versa. The materials from which the parts are made may vary.

Claims

1. Apparatus for detecting whether the pressure in a tyre (10, 80) on a wheel rim (14) has fallen below a predetermined amount including a member (48, 114) subject to the pressure in the tyre and a transmitter (72, 140) controlled by said member to emit a signal when the pressure in the tyre falls below a predeter¬ mined amount characterised in that the transmitter (72, 140) is carried by the wheel rim (14) and includes an electric circuit incorporating resistance variation means (66, 138) which affects the signal, and in that the said member (48, 114) is movable relative to the resistance variation means (66, 138) by the pressure in the tyre against a bias, the said member being operatively connected to the resistance variation means so that when the pressure in the tyre is at a pre-set level then the resistance variation means will provide a first resistance and when the pressure in the tyre has fallen a prescribed amount the resistance variation means will provide a second resistance.

2. Apparatus as claimed in any one of the preceding claims characterised in that the member (48, 114) is in the form of a plunger having one end (54, 130) subject to the pressure in the tyre and being biassed by a spring (58,122) to move against said pressure.

3. Apparatus as claimed in claim 1 or 2 characterised in that the resistance variation means comprises a rheostat (138) or the like.

4. Apparatus as claimed in claim 1 or 2 characterised in that the resistance variation means comprises a switch where one of the aforesaid resis¬ tances is zero and the other of the aforesaid resis¬ tances is infinite (see Fig 2) .

5. Apparatus as claimed in claim 4 characterised in that the first resistance is the infinite resis¬ tance.

6. Apparatus as claimed in claim 4 or 5 characterised in that the switch preferably comprises a pair of terminals ( 66) biassed into contact with each other and said other end (136) of the plunger (114) is movable to engage at least one of the terminals to move the terminals apart.

7. Apparatus for detecting whether the pressure in a tyre (10) on a wheel rim (14) has fallen below a predetermined amount including a member (48) subject to the pressure in the tyre and a transmitter (72) controlled by said member to emit a signal when the pressure in the tyre falls below a predetermined amount characterised in that the transmitter (72) is carried by the wheel rim and includes an electric circuit incorporating a pair of contact terminals (66) one of which is connected to a source of power for the transmitter, and in that the said member (48) is movable by the pressure in the tyre against a bias to first position in which it holds the contact terminals apart and by the said bias to a second position in which it permits the contact terminals to move into electrical contact thereby to permit power to be supplied to the transmitter.

8. Apparatus as claimed in claim 6 characterised in that the said member (48) engages both of the terminals (66) to move them apart.

9. Apparatus as claimed in any one of the preceding claims characterised in that the siad membner

(48) is adapted to engage an inflatable tube within the tyre.

10. Apparatus as claimed in any one of claims 1 to 9 characterised in that the said member is adapted to be subject to pressure in a tubeless tyre.

11. Apparatus as claimed in any one of the preceding claims characterised by a spring acting on the said member to provide the said bias.

12. Apparatus as claimed in any one of the preceding claims in which the plunger is mounted in a housing characterised in that the end of the housing subject to pressure in the tyre is covered by a flexible sealing member.