Abstract:
A shock absorbing tire and wheel assembly, particularly suitable for civil engineering plant comprises interconnected outer ( 15 ) and inner ( 14 ) chambers. The chambers are interconnected by passages which preferentially allow flow from the outer chamber ( 15 ) to the inner chamber ( 14 ). The passages preferably include at least one passage ( 21 ) which permits flow in either direction between the chambers and at least one passage ( 22 ) which permits flow from the outer chamber to the inner chamber, but prevents or restricts reverse flow. The passages ( 22 ) may be fitted with flap valves ( 23 ).

Description:
BACKGROUND AND BRIEF SUMMARY OF THE INVENTION 
     The present invention relates generally to tire and wheel assemblies suitable for vehicles and other items fitted with wheels. The preferred embodiments of the invention are particularly useful for earth moving and excavating vehicles with low pressure tires, but the invention is not limited to this application and will have numerous other applications. 
     According to one aspect of the present invention a tire and wheel assembly comprises a plurality of chambers for containing pressurised fluid, at least two of the chambers being interconnected by means enabling flow of fluid between one chamber and the other, the connecting means allowing fluid to pass preferentially from the one chamber to the other so providing a shock absorbing effect when the tire passes over an obstruction. 
     The pressurised fluid will, in general, be air or other gas or vapour or a mixture of air or gas or vapour or a combination of any of the foregoing with a liquid. 
     A non-mechanical shock absorber within the tire enables earth moving and excavating vehicles to retain structural strength for excavating with the facility to travel faster on site roads or public roads. This reduces cycle times on site and transport times between sites leading to increased productivity. 
     By virtue of the fact that fluid passes preferentially from one chamber to the other the tire and wheel assembly of the present invention has a shock absorption facility which is particularly suitable for use on earth moving and excavating vehicles. 
     Multi-chamber tires have been proposed hitherto. Most of them have been devised with safety in mind and as a result the individual chambers are interconnected such that air passes freely from the inner chamber to the outer chamber during inflation and use until a puncture or blow-out when gas or air loss is restricted from the inner chamber. 
     The tire and wheel assembly of the preferred embodiment of the present invention has at least one first passage interconnecting outer and inner chambers enabling substantial free flow of air or other gases between the chambers. In order to ensure that air or other gases flow preferentially from outer to inner chambers at least one second passage may be provided which allows air or other gases to pass from the outer to the inner chambers only. This may be achieved by using a one-way valve in at least some of the second passages. 
     The ratio between the free flow path and the one way flow path and the relative sizes of outer and inner chambers will be determined by experiment and possibly varied according to the particular application for which the tire is designed. It is presently envisaged that the total one way flow path will have greater cross-sectional area than the two way flow path. 
     In one preferred embodiment of the invention a plurality of passages interconnect the outer and inner chambers some of which allow one-way air or gas flow only. The passages may be identical with the exception that some of them are provided with one way valves. As noted above in the case of several identical passages it is presently envisaged that there will be more “one-way” passages than “two-way” passages. 
     The use of one-way valves is a simple way of ensuring preferential flow of gas from one chamber to another. Alternatively valve or restrictor designs may be available which themselves define a two-way flow path with preferential flow in one direction. For example, a plurality of flap valves may be provided, the flap of each valve being formed with a through passage. With such an arrangement the flap valves will open to allow relatively free flow of fluid in one direction, and the through passages will permit restricted flow in the opposite direction. 
     The tire and wheel assembly itself may define a single chamber divided into outer and inner chambers by a dividing wall or walls extending across the single chamber. The dividing wall may be a sheet secured to or integral with the tire. Alternatively the inner chambers may be partially or completely surrounded by the outer chamber. Either way the tire may be designed to sit on a wheel rim with the wheel rim defining one wall of one or more of the chambers. For example a single inner chamber may be designed as a complete inner tube which is partially or completely enclosed by a tire and wheel assembly defining the outer chamber or the means defining both outer and inner chambers may be the wheel rim with the outer chamber partially surrounding the inner chamber. 
     In all the foregoing examples of the invention it may be necessary for inner chambers to be reinforced to prevent collapse under excess pressure in the outer chamber and to encourage air or other gases to flow from the outer chamber to the inner chambers. 
     Alternatively the inner chamber may be fabricated to form a single or a series of rigid chambers each assembled and connected radially to form a single rigid construction attached to the wheel rim. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Several embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings which for clarity feature only one inner chamber. In the drawings: 
     FIG. 1 is a cross-sectional view of a first tire and wheel assembly according to the invention comprising a single chamber divided by a transverse wall. 
     FIG. 2 is a cross-sectional view of a second tire and wheel assembly according to the invention in which both the outer and inner chambers are defined by the tire and wheel assembly. 
     FIG. 3 is a cross-sectional view of a third tire and wheel assembly according to the invention in which the inner chamber is a rigid chamber enclosed by the outer tire and wheel assembly. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a so called “tubeless” tire having a tire body  10  which defines an open chamber which is closed by the wheel rim  11 . Reference numeral  12  indicates the tread portion. The chamber is divided by means of a cylindrical dividing wall  13  into an outer chamber  15  and an inner chamber  14 . The tire is inflated via valve  16  with compressed air or other gases and may, optionally, be partially filled with a liquid. 
     The tire body  10  is made from reinforced rubber and rubber additives and the dividing wall  13  may also be made similarly. FIG. 1 shows one example of how the dividing wall  13  may be attached to the tire body  10 . The tire body  10  has opposing inwardly facing flanges  17 ,  18  to which the wall  13  is attached. Suitable reinforcing means generally indicated by reference numerals  19  and  20  possibly in the form of annular plates serve to retain the dividing wall with respect to the tire body  10 . 
     The dividing wall  13  is provided with several through passages at locations spaced around the circumference. These include a number of free flow passages  21  one of which is illustrated in FIG. 1 and a number of one-way passages  22 . The passages  22  are closed by one-way valves one of which is indicated by reference numeral  23  which enable air of other gases to pass from the outer chamber  15  to the inner chamber  14  only. Thus air or other gases may pass freely from one chamber to the other via the through passages  21  but by virtue of the additional passages  22  air or other gases pass more readily from the outer chamber to the inner chamber. Thus the air or other gases are redistributed under pressure on the tread  12  in response to bumps in the road or other running surface. 
     In contrast to some known multi-chamber tires, the tire of the present invention has the advantage that by virtue of the passage  21  a single filler valve can be used to fill both chambers  14  and  15 . 
     The valves  23  are illustrated as simple flap valves which may be made from rubber and vulcanised to the dividing wall  13 . Any type of one-way valve may be used however. 
     In the embodiments of the invention shown in FIGS. 2 and 3 like parts have been indicated with like reference numerals. In FIG. 2 a tire body  10  for a tubeless tire is provided with a smaller tire body  30  which is housed inside the tire body  10 . The tire body  30  defines an open chamber which is closed by the wheel rim  11 . The holes  21  and  22  which interconnect the inner and outer chambers  14  and  15  are provided in the inner tire body  30 . The inner tire body  30  may be made from a material which is more flexible than the material of the tire body  1 O. For example the inner tire body  30  may be made from the same material as a traditional inner tube. The inner tire body  30  is preferably vulcanised to the outer tire body  10  to prevent it from, moving with respect to the tire body  10  though this may not be necessary. 
     If the tire body  30  is made from a material which is more flexible than the main tire body  10  some additional strengthening may be necessary in the region which divides the inner and outer chambers. This is illustrated as an annular reinforcing plate  31 . The plate  31  is provided with holes which are aligned with the holes  21  and  22  in the inner tire body  30 . It should be noted that there is a gap between the edge of the plate  31  and the tire body  10  to allow for some flexing of the tire body  10 . The edges of the plate  31  are rounded to minimise any wear which may occur if the plate  31  touches the tire body  10 . It will be appreciated that the inner tire body  30  may be replaced by a complete inner tube which does not completely fill the tire body  10 . In other words the inner tire body may completely define the inner chamber  14  rather than the chamber  14  being closed by the wheel rim  11 . 
     FIG. 3 illustrates a further embodiment of the invention designed for use with two-part wheel rims in which the inner chamber  14  is defined by a rigid housing enclosed within the tire and wheel assembly. The wheel rim is in two parts  11   a  and  11   b  secured together by means of countersunk screws one of which is indicated at reference numeral  35 . The inner chamber  14  is defined by a rigid annular chamber which is in this example rectangular in cross-section. The annular chamber  14  is formed by a first wall portion  36  which is generally C shaped in cross-section and defines three walls of the chamber  14  and a second circular lid portion  37 . The first wall portion  36  is provided with the holes  21  and  22 . The lid portion  37  is attached to the wall portion  36  by several shouldered screws  38  secured by locking nuts  39 . The walls of the chamber  14  are formed in two parts for practical purposes but the provision of the cover  37  has the advantage that it enables access to the one-way valves  23  for example for maintenance. 
     It will be noted that the wheel portion  11   a  is provided with an annular shoulder  40  against which the wall portion  36  is located. An opposing shoulder  41  for retaining the wall portion  36  in place is provided on wheel rim portion  11   b . Any gaps between the wall portion  36  and the wheel rim  11   a  may be sealed by suitable sealant e.g. mastic sealant. 
     It is likely that the tire  10  will not flex enough to enable it to be positioned around the rigid inner chamber  14  and therefore it is envisaged that the wall potion  36  and the lid portion  37  will each be formed in at least two part-circular portions which are bolted and flanged together. Thus in order to assemble the wheel and tire assembly of FIG. 3 the tire body  10  would be positioned with respect to the wheel rim portion  11   a . The chamber  14  comprising portions  36  and  37  would then be assembled inside the tire body  10  and the second wheel rim portion  11   b  would then be screwed to the first wheel rim portion  11   a.    
     It will be noted that in all the foregoing embodiments of the invention the holes  21  and  22  interconnecting the inner and outer chambers  14  and  15  extend radially. It will be appreciated that the holes could extend in other directions particularly in the embodiment of FIG. 3 in which the holes could extend in the same direction as the screws  38  i.e. parallel to the wheel axle. 
     In all embodiments the holes  21  and  22  will be positioned so as to maintain the dynamic balance of the wheel.