GB2087804A - Apparatus for equalizing the pressures of pneumatic tyres - Google Patents

Abstract

Apparatus for equalising the pressures of the pneumatic tyres on a multiple-tyred wheel comprises an inflation valve 1 in fluid connection with a plurality of equalising valves 9 9' connected one to each tyre inflation nipple, the equalising valve on each tyre permitting air pressure to equalise between the tyres but being adapted to close in the event of a sudden loss of pressure from another tyre. In the illustrated arrangement for a dual-tyre wheel each valve 9, 9' is connected at 11 via a hose 4, 4' to the inflation valve 1 and is connected at 14 to the respective tyre, a piston 16 in the valve body having a bleed passage 19 allowing air to pass for pressure equalization. If one tyre is punctured the pressure of air in the undamaged tyre forces the piston 16 associated therewith against a seat 16 so sealing the undamaged tyre. The valves 9, 9' will also close if the hoses 4,4' are damaged. Pressure switch 3 activates a radio transmitter 6 if a fault develops. <IMAGE>

Description

SPECIFICATION Apparatus for connection to pneumatic tyres This invention relates to an apparatus for connection to pneumatictyres, and more particularly to apparatus for equalising the pneumatic tyre pressures on a multiple wheel.

Vehicles designed to carry heavy loads, such as lorries, trailers, low loaders and the like, commonly have multiple wheels which each comprise two pneumatic tyres. In order for such multiple wheels to work efficiently, it is essential that the tyre pressures are closely similar. Unfortunately this is by no means easy to achieve in practice. The inner tyre tends to run hotter than the outer tyre, both by reason of its proximity to the brake drum and because it is less efficiently cooled by the slip-stream. In consequence the inner tyre pressure rises faster than the pressure in the outer tyre, and the inner tyre takes an undue proportion of the load, thus accentuating the temperature and pressure difference between the two tyres. Eventually the inner tyre may fail.

From British Patent Specification No. 1,511,294 it is known to connect the two tyres of a twin wheel by pressure lines to a single central valve, thus equalising the pressure in the two tyres. The central valve may be designed to permit one tyre to remain inflated if the other is punctured. The drawback of this device is the vulnerability of the pressure lines, which may suffer e.g. from perishing, fatigue failure, or from accidental or malicious damage. In the event of any damage to these pressure lines or their connections, either tyre may become deflated without being punctured.

The present invention provides apparatus for equalising the pneumatictyre pressures on a multiple wheel, comprising an inflation valve in fluid connection with a plurality of equalising valves for mounting in sealing connection one on each pneumatic tyre inflation nipple, the equalising valve on each tyre permitting air pressure to equalise between the tyres but being adapted to close in the event of a sudden loss of pressure from another tyre.

The equalising valves are mounted directly onto the tyre inflation nipples. Thus damage to or leakage from a pressure line between the two tyres will not result in either tyre deflating; the only effect will be a loss of equalisation. In view of the paramount importance of properly inflated tyres to the safety of heavy vehicles, the present invention give a significant safety advantage compared to the known construction described above.

Each equalisation valve may comprise a sliding member, e.g. a piston or the like, adapted to seal onto a seating in the event of a large pressure differential, there being an air bleed, e.g. a groove or channel in the sliding member or its housing, for permitting equalisation of a small pressure differential. The sliding member may be free-floating or may be urged by light spring pressure away from said seating. The seating may, for exampl, comprise a resilient 0-ring. The sliding member is preferably a piston having a conical orfrusto-conical head.

To provide more positive equalisation of small pressure differentials under static conditions, i.e.

when the wheel is stationary, there may be an auxiliary sliding member arranged to urge said sliding member away from said seating. The cross sectional areas of the sliding member and auxiliary sliding member exposed respectively to the pressures to be equalised should preferably be approximately the same. This construction obviates any tendency for the sliding member to seal onto its seating and be unresponsive to a small excess pressure in the pressure line. There may be a groove or channel in the auxiliary sliding member or its housing, to serve as an air bleed.

The equalisation valves are mounted directly on the inflation nipples of the tyres, or may even be integral therewith. In a preferred embodiment, the equalisation valves are adapted to be screwed onto a standard inflation nipple. The Schrader insert in the inflation nipple is either removed, or is maintained opened by an internal projection on the equalisation valve.

The equalisation valves may be connected to the inflation valve via pressure lines, or the inflation valve may be directly attached to one equalisation valve, there being a pressure line for connection to the inflation nipple of the other tyre. Although the invention is described herein in relation to its use on twin wheels, it is of course equally applicable to multiple wheels having any number of tyres.

In a preferred embodiment of the invention, means are provided to warn the driver of an abnormal pressure condition. At its simplest, this may comprise means for giving a visual indication of the pressure existing at the inflation valve, e.g. a miniature pressure gauge or a device exhibiting a coloured or other warning signal in the event of an abnormal pressure condition, e.g. when the pressure falls below a determined value.

However the preferred warning device is a pressure switch connected to a radio transmitter. The pressure switch is arranged to activate the transmitter in the event of an abnormal pressure condition, and the warning signal is received by the driver or other person in charge of the multiple wheel. In the case of a vehicle, the receiver will be placed in the drivers cab and will warn the driver immediately there is a loss of pressure in any tyre to which the device is connected. Moreover this system is operative immediately on coupling of a tractor to a trailer fitted with the appropriate transmitters. The use of a radio link to monitor pneumatic tyre pressures on a moving vehicle is of course well-known perse and it is not necessary to describe this aspect of the invention in detail.

Two embodiments of the invention will now be described by way of illustration only with reference to the accompanying drawings wherein: Figure 1 is a plan view, partially schematic, of an apparatus according to the invention; Figure2 is an enlarged cross-section through one of the equalising valves; and Figures 3 and 4 are a plan and cross-sectional view respectively of another equalising valve, the crosssection being taken along the line A-a.

Referring now to Figure 1, the apparatus compris es an inflation valve 1, having a conventional Schrader insert mounted on a plenum chamber 2.

Conneccted to the plenum chamber are a pressure switch 3, having a spring-loaded diaphragm and being designed to close below a predetermined (and preferably adjustable) pressure; and two pressure lines 4, 4' connected to the plenum chamber by screwed nipples 5, 5'. Closure of the pressure switch activates the radio transmitter 6 which is a miniature self-contained device having an output in the milliwatt range and being powered by mercury cells, or the like, having a lifetime of several years.

The pressure lines 4, 4', which may be of conventional steel braided hose, are connected by elbow pieces 7, 7' and threaded collars 8, 8' to the equalising valves 9, 9'. The equalising valves are themselves screwed onto the inflation nipples 20, 20' of the two tyres of a twin wheel (not shown). The plenum chamber 2, pressure switch 3 and radio transmitter 6 may be attached to any convenient point on the wheel, preferably close to the hub to minimise out-of-balance forces, the inflation valve 1 being conveniently positioned for connection to an air line when required.

Referring now to Figure 2, each equalising valve comprises a housing 10 having a threaded portion 11 of reduced diameter designed to receive the collar 8 or 8'. Into the other end of the housing is screwed a plug 12 having a central bore 13 and an internally threaded portion 14 designed to screw onto a standard inflation nipple. A resilient washer 15 is seated in an undercut recess at the internal end of the threaded portion 14. An 0-ring or other resilient seal may be provided between the housing 10 and the plug 12 to ensure an airtight seal.

Freely floating within the housing 10 is piston 16 having a conical head 17 for cooperation with an 0-ring seating 18 of neoprene rubber. Piston 16 has a groove 19 extending longitudinally along the length of the piston and diametrically across the flat end face thereof. A groove may instead be provided in the inner circumferential wall of housing 10.

When the apparatus is connected to the tyres of a twin wheel, the tyres may be simultaneously inflated via inflation valve 1 and during use, pressures in the tyres will be equalised via the bleed grooves 19. In the event of a sudden loss of pressure due to a puncture or damage to the integrity of the pressure lines 4, 4', the piston 16 will be urged bythe pressure in the undamaged tyre into sealing engagement with seating 18, thus prevent loss of pressure from this tyre. Simultaneously the pressure switch 3 will activate the transmitter 6 and warn the driver that a fault condition has developed.

Referring now to Figures 3 and 4, the connection between the housing 10 and the plug 12 is sealed by an 0-ring 20. The bleed groove 19 is in this embodi ment provided in the inner walk of housing 10. An auxiliary piston having a head 21 and rod 22 is housed in an extension 23 of housing 10. The head 21 has a longitudinal groove (not shown) to serve as an air bleed. The pistons 16 and 21 have the same cross-sectional area. The rod 22 of the auxiliary piston transmits any pressure differential acting on the piston head 21 to lift piston 16 from its seating 18, thus facilitating pressure equalisation.

Claims (14)

1. Apparatus for equalising the pneumatic tyre pressures on a multiple wheel, comprising an inflation valve in fluid connection with a plurality of equalising valves for mounting in sealing connection one on each pneumatic tyre inflation nipple, the equalising valve on each tyre permitting air pressure to equalise between the tyres but being adapted to close in the event of a sudden loss of pressure from another tyre.

2. Apparatus according to claim 1 wherein each equalising valve comprises a sliding member adapted to seal onto a seating in the event of a large pressure differential, and an air bleed for permitting equalisation of a small pressure differential.

3. Apparatus according to claim 2 wherein said air bleed comprises a groove or channel in the sliding member of its housing.

4. Apparatus according to claim 2 or 3 wherein said sliding member comprises a piston having a conical orfrusto-conical head for sealing onto said seating.

5. Apparatus according to any of claims 2 to 4 comprising an auxiliary sliding member arranged to urge said sliding member away from said seating, the cross-sectional areas of said sliding member and said auxiliary sliding member exposed respectively to the pressures to be equalised being approximately the same.

6. Apparatus according to claim 5 wherein a groove or channel in said auxiliary sliding member or its housing serves as an air bleed.

7. Apparatus according to any of the preceding claims wherein said equalisation valves are adapted to be screwed onto a standard inflation nipple.

8. Apparatus according to any of claims 1 to 6 wherein said equalisation values are integral with said inflation nipples.

9. Apparatus according to any of the preceding claims wherein said inflation valve is directly attached to one equalisation valve.

10. Apparatus according to any of the preceding claims including means to provide a warning of an abnormal pressure condition.

11. Apparatus according to claim 10 wherein said means to provide warning comprises means giving a visual indication of an abnormal condition of pressure at said inflation valve.

12. Apparatus according to claim 10 wherein said means to provide warning comprises a pressure switch arranged to activate a radio transmitter in the event of an abnormal pressure condition.

13. Apparatus according to claim 1, substantially as described herein.

14. Apparatus according to claim 1, substantially as illustrated in Figures 1,2 or 3 of the accompanying drawings.