GB2052162A

GB2052162A - Electrical contact devices for monitoring the pressure in tyres of motor vehicle wheel

Info

Publication number: GB2052162A
Application number: GB8017702A
Authority: GB
Original assignee: Moto Meter AG
Current assignee: Moto Meter AG
Priority date: 1979-06-08
Filing date: 1980-05-30
Publication date: 1981-01-21
Also published as: DE2923258A1; FR2458408A1; IT1131292B; GB2052162B; FR2458408B1; IT8022621A0

Abstract

An electrical contact device provided for monitoring the tyre pressure of a motor vehicle wheel comprises a hollow shaft 1 fixed to the wheel rim 4 in a pressure-tight manner with an end projecting into the tyre interior and carrying a metal diaphragm 12 to be acted upon by the tyre pressure and engageable by a contact pin 27 arranged in the shaft, electrically insulated therefrom and extending through a pressure chamber 9. A duct 18 formed in the shaft is closable by a closure member 21 and, when open, connects the interior of the tyre with the pressure chamber to balance the pressure on opposite sides of the diaphragm before it is sealed. <IMAGE>

Description

SPECIFICATION Improvements in or relating to electrical contact devices for monitoring the pressure in tyres of motor vehicle wheels The invention relates to an electrical contact device for monitoring the pressure in a tyre of a motor vehicle wheel, of the type comprising a shaft arranged to be fixed in a pressure-tight manner to a rim of the wheel with an end extending into the interior of the tyre and being fixed to a metal diaphragm to be loaded by the pressure prevailing in the tyre, and a metal contact pin which is arranged in the shaft in an electrically insulated manner and which extends through a pressure chamber provided in the shaft behind the diaphragm to the back face of the diaphragm facing away from the interior of the tyre so as to abut against the diaphragm in an electrically conducting manner when the tyre is inflated to normal pressure.

In devices of this type previously proposed (German patent applications P 28 18 027.0 and P 28 34 808.5) the pressure chamber located behind the metal diaphragm is either connected to the atmosphere, so that atmospheric pressure prevails in the chamber, or a conduit is provided which is closable by a valve and through which pressure can be produced in the pressure chamber which lies above atmospheric pressure. The production in the pressure chamber disposed behind the diaphragm of a pressure lying above the atmospheric pressure is desirable for the reason that thereby the reverse resilience of the diaphragm can be stabilised and the influence of the temperature on the functioning of the contact device can be reduced.However, in such a contact device, the production of an increased pressure in the pressure chamber necessitates the connection of a pump and a pressure-tight valve. In this case it is not always possible to detect with desirable accuracy what pressure is prevailing in the pressure chamber at any given moment and whether, in particular, the same is exactly equal to the pressure prevailing in the interior of the type.

According to the invention, there is provided an electrical contact device for monitoring the pressure in a tyre of a wheel of a motor vehicle, comprising a shaft arranged to be fixed to a rim of the wheel in a pressure-tight manner with an end projecting into the interior of the tyre and being fixed to a metal diaphragm to be loaded by the pressure prevailing in the tyre, and a metal contact pin which is arranged in the shaft in an electrically insulated manner and which extends through a pressure chamber provided in the shaft behind the diaphragm to the back face of the diaphragm facing away from the interior of the tyre so as to abut against the diaphragm in an electrically conducting manner when the tyre is inflated to normal pressure, the shaft having formed therein a duct which is closable by a closure member and which, when the closure member is open, provides a pressure conducting connection between the interior of the tyre and pressure chamber behind the diaphragm.

It is thus possible to provide an electrical contact device of the type referred to above which ensures by means oa simple measure that in the pressure chamber located behind the diaphragm the same pressure prevails as in the interior of the tyre, without the need for providing a special valve in the device or for employing an air pump for this purpose.

By briefly opening the closure member, the same pressure prevails in front of and behind the diaphragm, whereby the reliability of functioning of the device, in particular the accurate response thereof upon a drop pressure in the interior of the tyre, is considerably improved.

The invention will be further described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a sectional view of an electrical contact device for monitoring the pressure in the tyre of a motor vehicle; Figure 2 is a sectional view of the device of Figure 1, with a cap removed and a closure member open; Figure 3 shows another constructional form in sectional view: Figure 4 shows the constructional form of Figure 3 in the open state; Figuie 5 is a sectional view on the line 5 to 5 in Figure 1; and Figure 6 is a partial sectional view of the wheel of a motor vehicle with the contact device inserted.

As shown in Figure 1, an electrical contact device for monitoring the pressure in a tyre of a motor vehicle wheel comprises a circularcylindrical hollow shaft 1 of metal with an external screwthread 2. At its end which is located at the top in Figure 1, the shaft is enlarged in a plateshaped manner and is inserted in a bore 3 of a rim 4 of the motor vehicle wheel in such a manner that the back face of the plate-shaped enlargement lies against the inside of the rim. At this location, an O-ring 5 is inserted in an annular recess on the back face of the plate for the purpose of pressure-tight closure (see also Figure 6). The shaft 1 is retained on the rim 4 in a secure and pressure-tight manner by means of two nuts 6, 7 which are screwed upon the external screwthread 2 of the shaft 1. A metal connection contact 8 is inserted between the nuts 6, 7.On the inside of the rim, that is to say in the interior space of the tyre, the plate-shaped enlargement of the shaft 1 comprises a recess 9 with a conically extending bottom. For the purpose of enlarging the volume of the recess 9, the bottom is provided with circular ring-shaped grooves or channels ii.

A circular disc-shaped metal diaphragm 12 is supported on the rim of the recess 9. A ring 13, preferably of metal, lies upon the side of the rim of the diaphragm 1 2 which side is located at the top in Figure 1. By flanging-over the upper rim 14 of the shaft 1, the ring 1 3 presses the rim of the diaphragm 12 firmly onto its seat. The ring 13 comprises an inner bore 1 5 of relatively small diameter and is of a configuration on its inner side facing the diaphragm 12 such that a generally conical gap 1 6 remains free between this inner side and the diaphragm. When the tyre pressure drops, the elastic metal diaphragm 12 can bend resiliently into this gap. The oppositely disposed recess 9 in the shaft 1 is alternatively referred to as pressure chamber.It is connected to the inner bore of the hollow shaft 1 by means of a bore 17.

A duct 1 8 is provided in the plate-shaped enlargement of the shaft 1 leading from the outer wall of the plate-shaped enlargement as far as the inner bore of the shaft 1.

A closure member in the form of a bush 21 of metal is screwed into the bore 20 of the shaft 1 provided with an internal screwthread 19. The bush 21 contains in a pressure-tight manner a further bush 10 of electrically insulating material, such as synthetic resin material. In the position shown in Figure 1 the bush 21 closes the duct 18 relatively to the pressure chamber 9 and its front side lies against a seal 22 in a pressure-tight manner, the seal 22 projecting also into the bore 17.

O-rings 23 which are arranged in annular grooves of the bush 21 serve for further sealing.

The underside of a head 24 of the bush 21 is constructed for example as a hexagonal head and lies against the end face of the shaft 1 facing away from the diaphragm 12. As shown in Figure 1, additionally an O-ring 26 may be disposed between the ring 13 and the rim of the diaphragm for additional pressure-tight mounting of the diaphragm 12.

An axially extending metal contact pin 27 in the bush 10 is effected by a fitting slide seat in the upper region of the bush 10 produced from a synthetic resin, and by an accurately fitting fine screwthread 28 in the lower region of the bush 10. At its end face remote from the diaphragm 12, the contact pin 27 comprises a slot 29 for receiving therein a screwdriver.

A cap 31 of a synthetic resin or other electrically insuiating material is screwed on the external screwthread 2 of the shaft 1, and a split sleeve 32 of metal is inserted therein. An electrically conducting connection contact 34 of metal is connected to the sleeve 32 by means of a rivet or a screw 33. On its inside, the sleeve 32 comprises a projecting ledge 35 of acutely tapering cross-section which, when the cap 31 is placed upon the shaft 1, comes to lie against the outside of the head of the contact pin 27 and produces an electrically conductive connection between the connection contact 34 and the contact pin 27. The position of the contact pin 27 relative to the diaphragm 12 may be adjusted precisely, and under certain circumstances readjusted, by means of the fine screwthread 28.

The connection contacts 8 and 34 are constructed for example in the form of freely projecting lugs or soldering lugs for connection to connecting wires.

The device described functions in the following manner. As shown in Figure 6, the device is fixed obliquely to the wheel rim 4 in such a manner that it projects into the interior space 30 subjected to pressure of the tyre 36 fixed to the rim 4. Thereby the side of the diaphragm 1 2 which faces the ring 13 is loaded by the pressure prevailing in the tyre 36. After removal of the cap 31, the bush 21 is then unscrewed from the shaft 1 , for example by means of a spanner applied to the head 24 thereof, to such an extent that a direct connection is established with the pressure chamber 9 located on the back face of the diaphragm 12 by way of the duct 1 8, the internal bore of the shaft 1 and the bore 17, (see Figure 2). Thereby the same pressure prevails on both sides of the diaphragm 12.Thereafter the bush 21 is returned again to its normal position illustrated in Figure 1 and thereby the pressure chamber 9 is closed in a pressuretight manner. Finally the cap 31 (Figure 1) is screwed back again onto the shaft 1 of the device.

In operation, an electrical connection is produced between the connection contacts 8 and 34 by means of at least one wire loop or coil attached to the rim 4 and revolving therewith, and forms a closed current circuit with the contact pin 27 abutting the metal diaphragm 12. If the pressure prevailing in the interior space 30 of the tyre 36 then drops below a certain value, the pressure difference occurring between the pressure chamber 9 and the interior space 30 of the tyre causes the diaphragm 12 assisted by its elastic properties to be lifted off the contact pin 27 and the electrically conductive connection is interrupted at this location thereby. This interruption can be detected and brought to attention in a manner known per se, so that it is rendered possible to detect lowering of the pressure in the tyre 36 in good time and thereby to counteract a possible danger.

The detection of the interruption of the contact between the metal diaphragm 1 2 and the contact pin 27 may be effected for example by inductive means, in that the wire winding connected to the connection contacts 8 and 34 is made to travel past a sensor attached to the chassis of the respective motor vehicle, in particular a heavy goods vehicle, the sensor responding to the interruption of the electric current circuit between the contact pin 27 and the metal diaphragm 12.

Such sensors with associated indicator devices are described for example in the DEMOS 25 23 488.

In this case it is essential for the accurate operation of the described device that, after the tyre 36 has been pumped up to the prescribed pressure, exactly the same pressure is produced also in the pressure chamber 9 by temporarily screwing out the bush 21. In this way a defined starting position is obtained in the measuring system of the device and the device is relatively insensitive to temperature changes because of the equal pressure prevailing on both sides of the diaphragm. However it responds immediately to drop of the air pressure in the tyre 36 in a reliable manner.

The ring 13 serve not only for securely clamping the diaphragm 12 on the end of the shaft 1 which is enlarged in a plate-shaped manner, but also for protecting the sensitive diaphragm 1 2 against unintentional mechanical influences, for example during insertion of the device into the wheel rim 4.

The constructional form shown in Figures 3 and 4 differs from that shown in Figures 1 and 2 substantially by the fact that the duct 1 8 is angled downwards and consists of a radially extending portion and an axially extending portion which is directed downwards in Figure 3. The seal 22 lies at its front end against the outlet opening of the duct 1 8 and seals the same directly. Therefore the O-ring seals 23 provided in Figures 1 and 2 may be omitted in this constructional form. Upon turning the bush 21 out of the shaft 1 (Figure 4) the seal 22 is released under the effect of the pressure prevailing in the duct 18, so that a pressure compensation can take place between the interior space of the tyre and the pressure chamber-9 through the bore 17. In the constructional form shown in Figures 3 and 4, the seal 22 is constructed in the form of a ring seal and does not possess a limb protruding into the bore 17, as in the seal 22 in Figures 1 and 2.

Claims

1. An electrical contact device for monitoring the pressure in a tyre of a wheel of a motor vehicle, comprising a shaft arranged to be fixed to a rim of the wheel in a pressure-tight manner and an end projecting into the interior of the tyre and being fixed to a metal diaphragm to be loaded by the pressure prevailing in the tyre, and a metal contact pin which is arranged in the shaft in an electrically insulated manner and which extends through a pressure chamber provided in the shaft behind the diaphragm to the back face of the diaphragm facing away from the interior of the tyre so as to abut against the diaphragm in an electrically conducting manner when the tyre is inflated to normal pressure, the shaft having formed therein a duct which is closable by a closure member and which, when the closure member is open, provides a pressure conducting connection between the interior of the tyre and the pressure chamber behind the diaphragm.

2. A device as claimed in claim 1. in which the closure member for the duct comprises a metal bush arranged to be screwed into the shaft, the bush serving for the electrically isolated mounting of the contact pin.

3. A device according to claim 1 or 2, in which the contact pin is adjustable in the bush.

4. A device as claimed in claims 1, 2 or 3 in which the diaphragm is retained on the shaft by a ring which is pressed firmly into the shaft by a flanged-over rim of the shaft.

5. A device as claimed in claim 4, in which a seal is inserted between the ring and the diaphragm.

6. A device as claimed in any one of claims 1 to 5, in which a hexagon head is provided on the closure member for the purpose of adjustment thereof.

7. A device as claimed in any one of the preceding claims, in which a cap of electrically insulating material and having a connection contact is placed upon the end of the shaft distant from the duct and the diaphragm, the connection contact being in electrically conductive connection with the contact pin.

8. A device as claimed in claim 7, in which the connection contact is in the form of. a lug attached to a sleeve inserted in the cap, the sleeve lying in an electrically conducting manner against the end of the contact pin remote from the diaphragm.

9. A device as claimed in any one of the preceding claims, in which the shaft is connectable to the rim of the wheel by means of at least one screw nut and with the intervention of a seal.

10. A device as claimed in claim 9, in which the screw nut or nuts which serve for fixing the shaft to the rim retain a further connection contact.

11. A device as claimed in any one of the preceding claims, in which the duct comprises a portion which extends substantially radially and a portion which extends substantially axially in the shaft, the axially extending portion being sealable by a seal.

12. An electrical contact device for monitoring the pressure in a tyre of a wheel of a motor vehicle, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.