GB2031123A - Valve structure - Google Patents

Abstract

A valve structure for inter-connecting the tyres of a set of dual tyres to equalize the pressures therein including a casing (10) having therein a cylinder (14) at one end of which is a valve seat. A piston (20) carrying a valve closure element (28) is spring urged towards said seat and the interiors of the tyres communicate with the chamber 14 via passages (18, 30) so that the air pressures therein may be used to hold said element away from the seat. Should either tyre deflate to below a predetermined pressure, the spring urges said element (28) against said seat to isolate the tyres one from the other. A warning device triggered by movement of the piston to close the valve warns the driver that he has an under inflated tyre. A semicylindrical groove (96) in the casing (10) and a bore (98) co-axial with the groove serve to receive a tyre inlet connection (104), there being a valve opening element (116) in the bore (98). <IMAGE>

Description

SPECIFICATION Valve structure THIS INVENTION relates to a valve structure for inter-connecting the two tyres of a set of dual tyres.

Dual tyres are widely used on heavy duty vehicles to increase the number of tyres which can be provided on a single axle. It is well known that certain problems are inherent in the use of such tyres. Perhaps the major problem is that, unless the tyres are both pumped to the same pressure, one of the tyres of the pair takes far more of the load than the other tyre of the pair. This is particularly true where the road over which the tyres are running has a substantial camber. In such circumstances one of the tyres of each pair can well be overloaded resulting in increased and uneven tyre wear, casing fatigue and overheating.

This problem of uneven pressures is aggravated by the fact that it is difficult to gain access to the air inlet connection of the inner tyre of the pair. This means that pumping of the inner tyre is not given the requisite attention and the tyre is often run in an underinflated condition. Consequently, not only is the tyre carrying the major portion of the load but can be doing so in an under-inflated condition.

A third problem of which applicant is aware is that, because the two tyres of the pair are close together, one of the tyres can quite well be under-inflated without the driver knowing this as the other tyre of the pair is taking the load. Thus should the two tyres of a pair be visually inspected while the vehicle is unladen, it is extremely difficult to see that one of the two tyres is not taking its full share of the load.

To overcome these problems, valve structures have been proposed which interconnect the tyres of a pair of dual tyres. These structures equalize the pressures in the tyres of the pair until one tyre deflates to a pressure below a predetermined level whereupon the tyres are isolated one from the other. In some forms of valve structure, both the tyres can be pumped from a single air inlet and in yet other forms means are provided for warning the driver if his tyres are under-inflated.

Applicant has no reason to doubt that these prior valve structures operate in a satisfactory manner, that is, they achieve pressure equalization during running and tyre isolation when required. However, in South Africa for example, applicant can only find one such valve that is available commercially and even this is not used as widely as might be expected bearing in mind the cost of heavy duty tyres and the damage which they can suffer due to the problems mentioned above. Applicant believes that the known valve structures have failed to achieve widespread acceptance because of difficulties in mounting them on the variety of wheel types and constructions which are in every day use. He is aware, for example, of one valve structure which is mounted on the outer end of the hub, that is, on the portion of the hub which projects through the outer wheel.However, many wheels today are hubless and thus this form of valve structure can only be used on a limited number of vehicles. Additionally, vehicle owners are reluctant to drill holes in the vehicle wheels or to use the wheel bolts to secure the valve structures in place. In certain circumstances, modification of the wheel to fit a valve structure could have an adverse effect on the manufacturer's guarantee on the vehicle.

The object, therefore, of the present invention is to provide a valve structure which equalizes the pressure in a pair of dual tyres and isolates the tyres from one another upon the pressure in either tyre falling to below a predetermined minimum, which valve structure can be fitted to a wheel without drilling holes, removing wheel bolts or otherwise altering the wheel construction.

Applicant is aware of one disclosure in which a valve structure intended to equalize tyre pressures and then isolate the tyres on deflation is shown with a threaded pipe leading directly from a bore in its casing to the interior of the tyre. However, this disclosure is purely diagrammatic and does not show the valve structure mounted on the conventional air inlet connection of a tyre. That this is so is clear from the fact that it does not disclose any means for opening the valve of the air inlet connection of the tyre.

According to the present invention there is provided a valve structure comprising a casing having a chamber therein, an air inlet communicating with said chamber, a normally closed valve for preventing flow out of said chamber through said air inlet, first and second air flow paths each for connection to one of the tyres of the set of dual tyres, said paths both communicating with said chamber, a valve closure element displaceable between a first position in which it seals-off said first flow path from said chamber and a second position in which it permits communication between said first flow path and said chamber, there being biassing means urging said valve closure element towards its first position and the arrngement being such that air pressure in said chamber urges said valve closure element towards its second position, said casing having a bore therein for receiving the free end of an air inlet connection of a tyre, and a valve actuating element in this bore for holding open the air inlet valve of a tyre air inlet connection entered in said bore, one of said flow paths communicating with said bore.

The biassing means can be a spring and there can be means for enabling the spring force to be varied.

The spring can act directly on a component which carries the valve closure element but it is preferred that the structure include a pivotally mounted lever, said spring acting on said lever and said lever transmitting the spring force to said valve closure element to urge the element towards its second position.

In the preferred form of the invention, the casing has a bore therein and said element is carried by a piston displaceable along the bore, said chamber being constituted by part of said bore. A transverse end face can be provided at one end of the bore, said flow paths communicating with said chamber through said transverse end face.

To ensure that the valve structure is a firm fit on a tyre inlet connection, the casing can include a part-cylindrical groove in the outer face of said casing for receiving an air inlet connection, said groove being co-axial with the bore provided to receive said air inlet connection. Clamping means can be provided for urging an air inlet connection into the groove, and the clamping means can be in the form of a rod which passes through said casing and includes a curved end, said groove and said curved end together forming an opening through which a tyre inlet connection can pass.

To provide a visual indication as to whether or not the tyres of the pair are correctly inflated, the valve structure can include first and second cylinders connected respectively to the first and second flow paths, a piston in each of the first and second cylinders, spring means for displacing each piston in the opposite direction to that in which it is displaced by pressure in the said flow paths, and telltale elements each of which moves with one of said pistons, air pressure in said flow paths serving to urge said tell-tale elements to positions in which they protrude from the casing and spring force tending to retract the elements into the casing.

The invention also extends to a combination of a valve structure as defined above and a pair of dual tyres, each of said flow paths communicating with the air receiving space of one of the tyres.

In the form of the invention which includes the first and second cylinders, a warning device including an operating member held in an inoperative condition by said tell-tale elements while said elements protrude from the casing can be provided. In this form the combination can include an electrical switch, said switch being actuated by said operating member when the member is released upon retraction of one of said tell-tale elements.

The invention also provides a retainer comprising a wire bent to form a loop and two limbs which are integral with the loop, the limbs diverging away from the loop and there being bearing portions at the free ends of the limbs, said portions extending one on each side of the plane containing the loop and the limbs.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be mde, by way of example, to the accompanying drawings in which: Figure 1 is an axial section with certain parts in elevation, through a pressure-balancing valve structure in accordance with the present invention, the section being on the line I-I of Fig. 2, Figure 2 is an end elevation of the valve structure, Figure 3 is a fragmentary section through the valve structure, the section being on the line Ill-Ill of Fig. 1, Figure 4 is a transverse section, the left half being on the line IV-IV of Fig. 1 and the right half on the line V-V, Figure 5 is a section through a connector, Figure 6 diagrammatically illustrates a warning device, Figure 7 is an axial section through a further valve structure, some components being shown partially in elevation, and Figures 8 and 9 are two views of a retainer.

The pressure-balancing valve structure of Figs. 1 to 4 comprises a casing 10 in which there are a number of cavities, passages and cylinders. The main cavity in the casing is designated 1 2 and a cylinder 14 forms part of this cavity. The cylinder 14 terminates in an end face 1 6 and a longitudinal passage 1 8 opens through the end face 1 6 to form a continuation of the cylinder 14.

Within the cylinder 14 there is a piston 20 having a disc-like central portion 22 and a stem 24 which is coaxial with the portion 22 and protrudes therefrom towards the face 1 6.

A sealing ring 26 of the lip-seal type encircles the stem 24 and seals between the piston 20 and the cylinder 1 4. The end of the stem 24 is in the form of a cone and a sealing ring 28 encircles this cone, the ring 28 being in a groove of the cone.

The sealing ring 28 co-operates with the flared mouth of a short longitudinal passage 30 which in turn communicates with a transverse passage 32. The passage 32 opens through one of the lateral faces of the casing 10 and there is an adaptor 34, integral with the casing 10, for permitting a flexible connector 36 (Figs. 2 and 4) to be secured to the casing 10 in communication with the passage 32. The connector 36 will be described in more detail hereinafter with reference to Fig.

5.

A normally closed air inlet valve 38 of the Schrader type is located in a subsidiary bore 40 which opens through the same end of the casing 10 as thte main cavity 1 2. A lateral passage 42 (Figs. 2 and 3) connects the bore 40 to a chamber 44 which encircles the stem 24 between the sealing ring 26 and the end face 16.

The main cavity 1 2 also includes a bore 46.

As is best seen in Fig. 3, a partition 48 forms part of the wall of the cylinder 14 and separates the cylinder 14 from the bore 46. Both the cylinder 14 and the bore 46 extend into the casing 10 from a common part of the main cavity 1 2. A screw 50 is within the bore 46 and passes through a nut 52. A spring 54 acts between the end of the bore 46 and the nut 52. The bore 46 is, over at least that portion of its length which receives the nut 52, of hexagonal cross-section. Thus the nut 52 cannot rotate and, when the screw 50 is turned, the nut moves axially thus varying the length of the spring 54 and hence its tension.

A lever in the form of a fulcrum block 56 is pivotally mounted on a fulcrum pin 58 which is itself a push fit in bores provided therefor on opposite sides of the cavity 1 2. An aperture 60 is provided in the block 56, this aperture registering with the head of the screw 50. The screw can thus be turned by means of a screwdriver pushed through the aperture 60. As will clearly be seen from Fig.

3, the screw 50 is urged against the block 56 by the spring 54 and the block 56 in turn bears on the piston 20 to hold the ring 28 against the flared mouth of the passage 30.

By turning the screw 50 so that its head and the nut 52 move apart, the spring force can be increased and this in turn increases the force with which the ring 28 bears on said flared mouth.

The cavity 12 is closed by a cover 62 (not shown in Fig. 1) secured to the casing 10 by screws. The screws are not shown but tapped bores which receive the screws are shown at 64 in Fig. 2.

The casing 10 includes an upward extension 66 to provide two cylinders 68 and 70.

These cylinders, which lie side-by-side with their axes vertical, open through the top face of the extension 66. A cover 72 held in place by screws 74 closes the upper ends of the cylinders 68 and 70.

Each cylinder contains a piston 76 and, as these pistons and the associated parts are identical in each cylinder, only the piston 76 illustrated in Fig. 4 will be described in detail.

This piston includes a disc-like portion 78 and a stem 80 which extends above and below the portion 78. A lip seal 82 extends around the part of the stem 80 which is below the portion 78 and seals between the piston and the cylinder. The part of the stem 80 above the portion 78 forms an indicating rod 84.

The cover 72 has an aperture 86 therein through which the rod 84 projects when the piston 76 is in its upper position. A spring 88 urges the piston 76 to the lower position shown in Fig. 4, the spring 88 acting between the portion 78 and the underside of the cover 72. The lifted positions of the rods 84 are shown in Figs. 1 and 2. An O-ring 90 seals between the rod 84 and the cover 72.

A passage 92 (Fig. 4) places the lower end of the cylinder 70 in communication with the passage 30 and a further passage 94 places the lower end of the cylinder 68 in communication with the passage 1 8.

A semi-circular groove 96 is provided in the underside of the casing 10, this groove being co-axial with the bore 98 of a boss 100 (Fig.

1) forming part of the casing 1 0. The right hand end of the bore 98, as viewed in Fig. 1, opens through an end face of the casing 10 and, at the left hand end of the bore 98, there is an inwardly directed flange 1 02.

An air inlet connection 104 for a tyre extends along the groove 96 and into the bore 98. A sealing ring 106 within the bore 98 encircles the connection 104 and a moulded element 108 is inserted into the bore 98 from its right hand end. A transverse pin 110 secures the element 108 in position and an O-ring 11 2 seals between the element 108 and the surface of the bore 98. The element 108 includes a sleeve 11 4 which bears on the sealing ring 106 and a central core 11 6 which enters the connection 104 to open, and hold open, the Schrader valve which is contained within the connection 1 04.

The passage 1 8 opens into the bore 98 and the sleeve 11 4 is formed with one or more ports 11 8 which place the interior of the sleeve 11 4 in communication with the passage 18.

A clamp 1 20 (Figs. 1 and 2) of J-shape passes through a vertical bore of the casing 1 0. The free end portion of the straight limb of the clamp 1 20 is threaded and a nut 1 22 is screwed onto this. The curved portion of the clamp 1 20 holds the connection 104 in the groove 96, this portion and the groove together forming an opening through which the connection 104 passes.

Turning now to Fig. 5, the connector 36 illustrated comprises a flexible hose 1 24 which is co-axial with a protective sheath 126. The sheath 126 is in the form of a coiled stainless steel wire. At one end of the hose 1 24 there is a nut 1 28 which is compatible with the adaptor 34 provided in conjunction with the transverse passage 32.

For part of its length the combined flexible hose 1 24 and sheath 1 26 are within a sleeve 1 30 of relatively stiff material. The sleeve 1 30 is non-rotatably secured to an internally threaded adaptor 1 32. At the inner end of the adaptor 1 32 there is an inwardly directed flange 1 34 which co-operates with an outwardly directed flange 1 36 forming part of a nipple 1 38 to which the flexible hose 1 24 is connected.

An element 1 40 of stainless steel wire is a push-fit in the bore of the nipple 1 38. the element 1 40 protruding from the nipple 1 38 to form a valve opening pin. A sealing washer 142 encircles the part of the element 140 which forms the valve opening pin and lies adjacent the outwardly directed flange 1 36 of the nipple 1 38.

The valve structure and connector described are used to inter-connect the two tyres of a set of dual tyres such as are extensively used on trucks, buses and other heavy vehicles. In Fig. 5 a set of dual tyres is illustrated, the inner tyre being referenced 1 44 and the outer tyre 146. The connection 104 is the inlet to the outer tyre 146 of the pair and the connector 36 leads to the connection (not shown) of the inner tyre of the pair. The valve structure is connected to the two tyres in the following manner.

As a first step, the flexible hose 1 24 is pushed over the adaptor 34 and then the nut 128 is screwed onto the adaptor 34. The nut 128 compresses the hose 1 24 to secure it in place. The flexible connector 36 is then attached to the inlet connection of the inner tyre 144 of the pair of dual tyres. This inlet connection is, of course, substantially identical to the inlet connection 104 and has a threaded end portion similar to that which lies inside the sleeve 114.Attachment of the connector 36 to the inlet connection of the inner tyre 144 is achieved by passing the connector 36 through aperture 148 in the rim 1 50 of the outer tyre and through aperture 1 52 of the rim 1 54 of the inner tyre, engaging the threading of the adaptor 1 32 with the threaded end portion of the inlet connection of the inner tyre and turning the adaptor 1 32 by means of the sleeve 1 30. The pin constituted by the end of the element 140 eventually opens the Schrader inlet valve of the inner tyre 144 of the pair. Thus, through the hose 124 and the passages 30 and 32, the pressure in the inner tyre 1 44 acts on the piston 20.At this stage, however, the spring 54 is effective to hold the sealing ring 28 against said flared mouth. This is because the area of the passage 30 is so small that the force exerted on the piston 20 by virtue of the air pressure in the inner tyre 144 cannot displace the piston 20 to the left to open the passage 30 and cause leakage from the inner tyre 144.

The valve structure is finally secured to the connection 104 by sliding the connection along the groove 96 until the free end of the connection enters the bore 98. The sealing ring 106 comes into sealing engagement with the connection 104 and the core 11 6 of the moulded element 108 opens the Schrader valve which is within the threaded portion at the free end of the connection 1 04. The pressure in the outer tyre 146, if sufficiently high, urges the piston 20 to the left to open the passage 30 and place the two tyres in communication via the chamber 44.

The nut 1 22 is then tightened so that the Jclamp 1 20 urges the connection 104 firmly into the groove 96. The casing 10 now occupies the position shown diagrammaticaly in Fig. 6.

In use of the valve structure, in the absence of sufficient pressure in the annular chamber 44, the spring 54 urges the sealing ring 28 against the flared mouth of the passage 30.

The valve structure thus adopts the condition illustrated in Figs. 1 to 3.

When the air inlet valve 38 is connected to an air hose, air feeds into the chamber 44.

From here it feeds along the passage 1 8 to the bore 98 and through the ports 11 8 to the annular chamber which encircles the core 11 6. As the valve of the connection 104 is held open by the core 116, air feeds along the connection 104 to the outer tyre 146.

When the pressure in the outer tyre 146, and hence in the chamber 44, has risen to a predetermined value (as will be described), the force exerted on the piston 20 in opposition to the force exerted by the spring 54 is sufficient to displace the piston 20 to the left (as viewed in Fig. 1). The sealing ring 28 lifts from the flared mouth of the passage 30 with the result that air now feeds along the passages 30 and 32 to the connector 36 and hence to the inner tyre of the pair of tyres.

The two tyres are now in communication with one another and air flowing through the valve 38 flows to both tyres which eventually reach the desired pressure as shown by the pressure gauge of the inlet hose.

To assist in an understanding of the following description, it is assumed that it is desired to operate the tyres at 85 psi (590 kPa). The force exerted by the spring 54 is then adjusted by turning the screw 50 so that a pressure of 80 psi (550 kPa) in the chamber 44 is necessary to overcome the spring force.

While both tyres remain at the desired pressure, the piston 20 remains in its lefthand position so that the tyres are in communication with one another through the valve structure. Should one tyre begin to leak, then the pressure in both tyres will fall until a pressure of 80 psi (550 kPa) exists in both. A similar pressure exists in the chamber 44 and at this stage the spring 54, acting via the fulcrum block 56, urges the piston 20 to the right so that the sealing ring 28 re-engages the flared mouth thereby to isolate the tyres one from the other. The leaking tyre will therefore continue to deflate but the other tyre will remain at 80 psi (550 kPa).

The sequence described above, which occurs in the event of a slow leak, also occurs should one tyre deflate suddenly.

As explained above, the passages 92 and 94 lead into the lower ends of the cylinders 68 and 70. Consequently, while the pressure in the tyres is sufficient to overcome the force exerted by the springs 88, the indicating rods 84 protrude upwardly from the cover 72.

Movement of either piston 76 downwardly under the influence of its spring 88 indicates that there is now insufficient pressure below that piston to overcome the spring force. Thus a mere visual inspection of the structure indicates whether or not the tyres are at the requisite working pressure. As soon as visual inspection reveals that one of the rods 84 has moved downwardly it is known that the related tyre is under-inflated, or possibly even completely flat.

The structure illustrated has a number of advantages. Firstly, the inner tyre 144 is pumped via the valve 38 which means that it is not necessary to gain access to the inner tyre. A single air inlet serves both tyres. This facilitates the checking and adjustment of tyre pressures.

While the tyres are at or above the pressure at which the structure is set to operate, pressure equalisation continually takes place.

Thus, if as can occur on a cambered road, the inner tyre tends to support more of the load, the resultant pressure increase in this tyre will be transmitted to the outer tyre. Furthermore, merely checking whether the rods 84 protrude above the cover 72 provides an indication as to whether both tyres are correctly inflated or are under-inflated.

Turning now to Fig. 6, the reference numeral 1 56 generally indicates the hub and drive shaft to which the rims 1 50 and 1 54 are secured by bolts 1 58 and numeral 1 60 indicates one of the leaf springs of the vehicle.

The leaf spring 1 60 has its ends connected to the vehicle body and carries the shaft 1 56 at its centre.

An electrical switch 1 62 is mounted on the spring 160, the switch 1 62 having a long operating arm 1 64. A guide 1 66 is secured to the wheel rim 1 54 and an operating rod 1 68 is carried by the guide 1 64. A flexible connection 1 70 leads from the rod 1 68 through the apertures 1 52 and 148 to an element 1 72 which is shown as being in the form of a ring.

The flexible connection 1 70 can comprise a chain, a cable, or a combination of chain and cable and incorporates a tension spring 1 74.

A compression spring 1 76 acts between the guide 1 66 and a washer 1 78 fast with the rod 1 68. The spring 1 74 is stronger than the spring 176.

Apart from the switch 1 62 and leaf spring 160, the structure illustrated in Fig. 6 rotates with the shaft and hub 1 56. The element 1 72 is held in the position illustrated by the rods 84. Immediately one of the rods 84 is retracted into the casing 10, the spring 1 74 pulls the element 1 72 to the left and the spring 1 76 urges the rod 1 68 to the left into a position in which, next rotation, it strikes and moves the operating arm 1 64. The switch 1 62 can be connected to an audible and/or visual warning device such as a buzzer or light in the vehicle cab.Consequently, the driver of the vehicle becomes aware, while on the road, the moment that one of his tyres has become under-inflated.

It is preferred that the driver can only switch off the warning device by means of the arm 1 64. Of course, if he switches off the device and then attempts to drive without dealing with whatever problem has arisen in connection with his tyres, the switch 1 62 is immediately actuated again and the warning device triggered once more.

The pressure-balancing valve structure of Fig. 7 comprises a casing 1 80 in which there is a main bore 182 and a subsidiary bore 184. The main bore 182 terminates in an end face 1 86 and a longitudinal passage 1 88 opens through the end face 1 86 to form a continuation of the main bore 1 82.

The surface of the main bore 182 is threaded over a portion thereof extending from its open end and is cylindrical over the remainder.

Within the cylindrical portion of the bore 182 there is a piston 1 90 having a cylindrical body 1 92 and a stem 1 94 which is co-axial with the body 1 92 and protrudes therefrom towards the end face 1 86. A sealing ring 1 96 of the lip-seal type encircles the stem 1 94 and seals between the piston 1 90 and the cylindrical bore portion.

The free end of the stem 1 94 is formed with a short blind bore which is flared adjacent its open end. A sealing element 1 98 in the form of a short cylinder is entered in the blind bore and protrudes slightly beyond the free end of the stem 1 94.

The sealing element 1 98 co-operates with a short longitudinal passage 200 which in turn communicates with a transverse passage 202.

The passage 202 opens through one of the lateral faces of the casing 1 80 and there is an adaptor (not shown) identical to the adaptor 34 for permitting the flexible connector 36 to be secured to the casing 1 80 in communication with the passage 202.

A combined air inlet and piston guide 204 enters the main bore 1 82 through its open end and is co-axial therewith. The guide 204 has a cylindrical outer portion 206, a central hexagonal portion 208, and a stem 210 which forms an extension of the portion 208.

The stem 210 enters a recess 21 2 provided in the piston 1 90. The outer portion 206 is itself extended (to the left as shown in Fig. 7) by a threaded section 214 which enables an air supply hose (not shown) to be screwed onto the guide 204.

An axial passage 21 6 passes through the guide 204 from one end to the other and, at its left hand end, the guide 204 includes a valve opening pin and a normally closed valve of the Schrader type.

An axial passage 21 8 opens through the face 220 of the recess 212 and leads through the stem 1 94 to a transverse passage 222.

The passage 222 opens into an annular chamber 224 which encircles the stem 1 94 between the sealing ring 1 96 and the end face 186 of the bore 182.

The stem 210 enters the recess 212, the portion of the stem 210 in the recess carrying a sealing ring 226 which seals between the stem 210 and the wall of the recess. The stem 210 is formed, in the portion thereof which lies outside the recess 212, with a peripheral groove 228. A pin 230 mounted in the casing 1 80 extends into the groove 228 for cooperation with the right hand face of the groove 228.

The piston 1 90 and guide 204 together form a valve member which carries the element 198.

An element 232 having a hexagonal central bore 234 and a threaded outer periphery is located in the threaded portion of the bore 1 82. The hexagonal portion 208 of the guide 204 is slid through the hexagonal central bore 234 of the element 232. Engagement between the threaded external periphery of the element 232 and the threaded portion of the bore 1 82 permits the element 232 to rotate but at the same time imposes axial motion thereon. A Circlip 236 encircles the portion 208 in a groove thereof and a spring 238 acts between the element 232 and the Circlip 236. This spring, in the absence of pressure in the annular chamber 224, holds the sealing element 1 98 against the end face 1 86 to close the short longitudinal passage 200.

A plug 240 having a cylindrical central aperture is screwed into the outer end of the bore 1 82. A transverse pin 242 pushed through a transverse bore in the casing 1 80 limits movement of the element 232 to the left. An O-ring 244 carried by the cylindrical outer portion 206 of the guide 204 seals between the plug 240 and the portion 206.

Two Circlips 246 and 248 are provided one on each side of the ring 244, these just being clear of the surface of the bore of the plug 240. The ring 244 is to prevent dust ingress.

The subsidiary bore 1 84 and the longitudinal passage 1 88 are both closed by a plug 250 which is secured in place by a suitable grub screw or pin (not shown). An O-ring 252 carried by the plug 250 seals between the casing 180 and the plug 250.

Before the subsidiary bore 1 84 is closed by the plug 250, an O-ring 254 and a moulded element 256 are inserted in the subsidiary bore. The element 256 includes a valve opening core 258.

The plug 250 is provided with a recess 260 into which the passage 1 88 opens. The element 256 has one or more bores 262 placing its interior in communication with the recess 260.

The casing 180 is formed with a partcylindrical groove 264 which serves to receive the air inlet connection 104 of the outer tyre.

The connector 36, as with the previous embodiment described, leads to the inlet connection of the inner tyre.

In use of the valve structure of Fig. 7, in the absence of sufficient pressure in the annular chamber 224, the spring 238 urges the sealing element 1 98 against the end face 1 86. The valve structure thus adopts the condition illustrated in Fig. 7.

When the combined air inlet and piston guide 204 is connected to an air hose, air feeds along the axial passage 21 6 of the guide 204 and through the passages 218 and 222 to the annular chamber 224. From hdre it feeds along the passage 188, recess 260 and bores 262 to the annular chamber which encircles the core 258. As the Schrader valve of the connection 104 is held open by the core 258, air feeds along the connection 104 to the outer tyre.

When the pressure in the outer tyre, and hence in the chamber 224, has risen to a predetermined value (as will be described), the force exerted on the piston 1 90 in opposition to the force exerted by the spring 238 is sufficient to displace the piston to the left (as viewed in Fig. 7). The sealing element 198 lifts from the face 1 86 with the result that air now feeds along the passages 200 and 202 to the connector 36 and hence to the inner tyre of the pair of tyres. The two tyres are now in communication with one another and air flowing through the combined air inlet and piston guide 204 flows to both tyres which eventually reach the desired pressure.

If it is again assumed that it is desired to operate the tyres at 85 psi (590 kPa), the force exerted by the spring 238 is then adjusted (as will be described) so that a pressure of 80 psi (550 kPa) in the chamber 224 is necessary to overcome the spring force.

While both tyres remain at the desired pressure, the piston 190 remains in its lefthand position so that the tyres are in communication with one another through the valve structure. Should one tyre begin to leak, then the pressure in both tyres will fall until a pressure of 80 psi (550 kPa) exists in both. A similar pressure exists in the chamber 224 and at this stage the spring 238 urges the piston 1 90 to the right so that the sealing element 1 98 re-engages the face 1 86 thereby to isolate the tyres one from the other. The leaking tyre will therefore continue to deflate but the other tyre will remain at 80 psi (550 kPa).

When the element 1 98 engages the face 186, it spreads slightly in the flared end of the bore in which it is received.

The piston 1 90 has two positions. In the first of these positions, that which is illustrated, the element 1 98 is against the face 1 86 so that the two tyres are isolated from one another. The amount by which the por tion 206 protrudes from the casing 1 80 is an indication of the position of the guide 204 and hence of the piston 1 90. The pin 230 is spaced from the hand face of the groove 228.

An increase in pressure in the chamber 224 sufficient to displace the piston 1 90 and guide 204 to the left against the action of the spring 238 brings the said right hand face against the pin 230 which limits movement of the piston 1 90. That this is the condition of the valve structure can be determined by noting the extent to which the portion 206 protrudes from the casing 1 80.

To calibrate the spring 238 so that the piston moves at the requisite pressure in the annular chamber 224, it is necessary to turn the combined air inlet and piston guide 204.

This has the effect of causing the element 232 to move along the threaded portion of the bore 1 82. It will be understood that, in the position illustrated, the spring force is at its weakest and that it is increased by displacing the element 232 to the right.

Once the spring position has been adjusted, air is supplied to the valve structure and passes through the connection 104. When the guide 204 moves outwardly of the casing 180, this is an indication that the valve has operated. The pressure gauge can then be consulted to see the pressure at which this occurred. If the valve operated at too high a pressure then the element 232 must be displaced to the left, and if it operated at too low a pressure then the element 234 must be displaced to the right.

In common with the structure of Figs. 1 to 4, the structure of Fig. 7 permits the inner tyre to be pumped via the single air inlet provided which means that it is not necessary to gain access to the inner tyre. In this form, merely checking the extent by which the portion 206 protrudes from the casing 1 80 indicates whether the sealing element 1 98 is or is not against the face 1 86. If not then this is an indication that both tyres are under-inflated and one or both may be flat.

A retainer 266 is illustrated in Figs. 8 and 9 and is, in use, located where shown in Figs.

1, 2 and 3. The retainer 266 is of steel wire which has inherent resilience and comprises a central loop 268 and two inclined limbs 270 diverging from the loop. At the free end of each limb 270 there is a bearing portion 272.

The portions 272 protrude in opposite directions from the central plane which contains the loop 268 and the limbs 270.

It is conventional to pass the connection 104 (and the corresponding connection of the inner tyre) through elongated slots in the wheel rims (150 and 1 54 in Fig. 6). These slots are necessary in view of the length of the connections such as 1 04. Should either an inner tube or a tyre casing burst, it can happen that the entire connection 104 is dragged into the tyre. The result is that the inner tube is cut up and the tyre casing can be sufficiently badly damaged as to be unusable. With the retainer in the position illustrated in Figs. 1, 2 and 3 the connector 104 passes through the loop 268 and the bearing portions 272 engage the wheel rim. Any tendency for the connector 104 to move through its slot into the tyre results in the limbs 270 being splayed apart so that the loop 268 tightens on the connector 104.

Thus, even if the inner tube or outer casing is punctured, there is no danger of it being destroyed by the connection 104 which is restrained by the retainer 266 against movement.

By locating the retainer 266 hard against the wheel rim, virtually all motion of the inlet connection 104 with respect to the tyre can be eliminated so as to prevent any motion which can puncture the inner tube.

Claims (17)

1. A valve structure comprising a casing having a chamber therein, an air inlet communicating with said chamber, a normally closed valve for preventing flow out of said chamber through said air inlet, first and second air flow paths each for connection to one of the tyres of the set of dual tyres, said paths both communicating with said chamber, a valve closure element displaceable between a first position in which it seals-off said first flow path from said chamber and a second position in which it permits communication between said first flow path and said chamber, there being biassing means urging said valve closure element towards its first position and the arrangement being such that air pressure in said chamber urges said valve closure element towards its second position, said casing having a bore therein for receiving the free end of an air inlet connection of a tyre, and a valve actuating element in this bore for holding open the air inlet valve of a tyre air inlet connection entered in said bore, one of said flow paths communicating with said bore.

2. A valve structure as claimed in claim 1, wherein said biassing means is a spring and there are means for enabling the spring force to be varied.

3. A valve structure as claimed in claim 2, and including a pivotally mounted lever, said spring acting on said lever and said lever transmitting the spring force to said valve closure element to urge the element towards its second position.

4. A valve structure as claimed in claim 1, 2 or 3, wherein said casing has a bore therein and said element is carried by a piston displaceable along the bore, said chamber being constituted by part of said bore.

5. A valve structure as claimed in claim 4, and including a transverse end face at one end of the bore, said paths communicating with said chamber through said transverse end face.

6. A valve structure as claimed in any preceding claim, and including a part-cylindrical groove in the outer face of said casing for receiving an air inlet connection, said groove being co-axial with the bore provided to receive said air inlet connection.

7. A valve structure as claimed in claim 6, and comprising clamping means for urging an air inlet connection into said groove.

8. A valve structure as claimed in claim 7, in which said clamping means is in the form of a rod which passes through said casing and includes a curved end, said groove and said curved end together forming an opening through which a tyre inlet connection can pass.

9. A valve structure as claimed in any preceding claim, and including first and second cylinders connected respectively to the first and second flow paths, a piston in each of the first and second cylinders, spring means for displacing each piston in the opposite direction to that in which it is displaced by pressure in the said flow paths, and telltale elements each of which moves with one of said pistons, air pressure in said flow paths serving to urge said tell-tale elements to positions in which they protrude from the casing and spring force tending to retract the elements into the casing.

1 0. The combination of a valve structure as claimed in any preceding claim and a pair of dual tyres, each of said slow paths communicating with the air receiving space of one of the tyres.

11. The combination of a valve structure as claimed in claim 6 and a pair of dual tyres, each of said flow paths communicating with the air receiving space of one of the tyres, and a warning device including an operating member held in an inoperative condition by said tell-tale elements whilst said elements protrude from said casing.

1 2. The combination as claimed in claim 11, and further including an electrical switch, said switch being actuated by said operating member when this member is released upon retraction of one of said tell-tale elements.

1 3. The combination of any one of claims 10 to 12, wherein the air inlet connection of the outer tyre is received in the bore having the valve actuating element therein and a connector leads from said casing to the air inlet connection of the inner tyre.

14. The combination claimed in claim 13, wherein said connector comprises an air hose within a sleeve, the sleeve carrying an internally threaded adaptor at one end thereof which adaptor is compatible with the air inlet connection of the inner tyre and which adaptor can be rotated by turning the sleeve.

1 5. A retainer comprising a wire bent to form a loop and two limbs which are integral with the loop, the limbs diverging away from the loop and there being bearing portions at the free ends of the limbs, said portions extending one on each side of the plane containing the loop and the limbs.

16. In combination, a retainer as claimed in claim 1 5 and a tyre inlet connection, said connection passing through said loop.

17. A valve structure substantially as herein before described with reference to Figs. 1 to 7 of the accompanying drawings.

1 8. A retainer substantially as hereinbefore described with reference to Figs. 8 and 9 of the accompanying drawings.