INFLATION PRESSURE INDICATOR FOR VEHICLE TYRES

Abstract: An inflation pressure indicator (10) for pneumatic tyres for vehicles has a body (11, 12) mountable on the wheel to which a tyre is fitted. A piston (25) is slidably mounted in a bore (17) in the body (11, 12) and, at a preselected pressure, moves in the bore (17) against the compression spring (44) to a position adjacent a scribed mark (67) on the body (11, 12). A rotatable plug (37) is screw-threadably mounted in the bore (17) to adjust the preselected pressure. A tyre valve (29) is fitted to the piston (25) to enable the tyre to be inflated or deflated. A dust cap (13) has a secondary valve (53) which is normally closed to prevent air escaping from the indicator or the ingress of dirt into the bore (17), the secondary valve (53) being operable to open the tyre valve (29). An air hose fitting is connectable to the tyre to be inflated.

Description: TITLE : " INFLATION PRESSURE INDICATOR FOR VEHICLE TYRES " BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an inflation pressure indicator for vehicle tyres. The term vehicles includes, inter alia, passenger vehicles, trucks, tractors, motor cycles, aircraft and other vehicles fitted with pneumatic type tyres. 2. Description of the Prior Art For maximum safety, the tyres of automobiles and other vehicles must be maintained within defined inflation pressure limits set down by the tyre manufact¬ urers. If the tyres are operated when underinflated, the excess heat generated in the tyre casing as it flexes may cause the casing to fail, while overinflation of the tyre reduces the effective contact area between the tyre tread and the pavement and the risk of blow-outs is also markedly increased. Conventionally, it has been necessary to use a separate tyre pressure gauge to check the inflation pressure in the vehicle tyres. However, tests by motor¬ ing organizations have shown that the pressure gauges provided on the forecourts of garages and service stations are often inaccurate and errors of 14-28 KPa (2-4 p.s.i) have been recorded. One proposal to overcome this problem was to provide each vehicle tyre with a cap which screwed onto the tyre stem. The cap opened the tyre valve and the pressure in the tyre operated a piston which had a piston rod graduated in KPa (psi) to indicate the inflation pressure. This type of cap had a number of disadvantages. Firstly, the readings given were often inaccurate and the piston rod often became stuck due to the ingress of dust into the cap. Air leaks developed in the cap and the tyres became deflated. The caps had to be removed from the valve to enable the tyres to be inflated. Because of these and other problems, these caps were found to be not acceptable. BRIEF SUMMARY OF THE PRESENT INVENTION 5 It is an object of the present invention to provide an inflation pressure indicator for vehicle tyres which may be connected to the tyre stem or be provided with an integral spud or means to enable it to be filled to a wheel on which a tyre is mounted. 10 It is a preferred object to provide an indicator which is simple to use and which can be preset to indicate a particular (cold) inflation pressure in the tyre within e.g. a 28KPa (4 p.s.i.) range. It is a further preferred object to provide an 15 indicator which incorporates the tyre valve and enables the tyre to be inflated without the necessity to remove any portion of the indicator during such inflation. It is a still further preferred object to provide an indicator which can be operated, with a 20 suitable fitting, to enable rapid inflation of the tyre. Other preferred objects of the present invention will become apparent from the following description. In one aspect the- present invention resides in an inflation pressure indicator for pneumatic-tyres for 25. vehicles, said indicator including: a body mountable on a wheel fitted with a tyre; an axial bore in the body adapted to communicate with the interior of the tyre; a piston means slidably mounted in the axial 30 bore; sealing means between the piston means and the axial bore; compression means in the tubular body acting on the piston means in opposition to the inflation 35 pressure in the tyre; and OMPI visual indicator means in or on a substant¬ ially transparent portion of the body; so arranged that at a preselected inflation pressure in the tyre, the piston means will be moved against the compression means to a position substantially adjacent the visual indicator means. Preferably a central bore is provided in the piston means and a tyre valve, normally closing the central bore, is operable to enable the tyre to be inflated. Preferably a plug is mounted in the axial bore and the compression means include a compression spring interposed between the plug and the piston means, the plug being movable to enable adjustment of preselected inflation pressure. A bore is provided through a plug to enable the tyre to be inflated when an air hose is connected to the tubular body. Preferably a dust cap, having a fitting to receive an air hose, is removably fitted to the tubular body and is provided with a plunger operable to open the tyre valve to enable the tyre to be inflated. Preferably a second valve is mounted in the cap. The second valve normally closes a bore through the cap and is operable to enable the tyre to be inflated or to enable any air in the axial bore between the piston and plug to be vented to the atmosphere. Preferably the visual indicator means is a line scribed or marked on a substantially transparent portion of the tubular body and the piston may be coloured or marked to provide a contrast between the piston and the line. The tubular body may be screwed or vulcanized onto an existing tyre stem, may be provided with an integral spud which is engageable in a hole in the wheel rim, or may be provided with a screw-threaded portion OMPI having an abutment shoulder, the screw threaded portion extending through a hole in the wheel rim and the body being secured to the wheel rim by a suitable screw- threaded fastener. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS To enable the invention to be fully understood, a preferred embodiment will now be described with reference to the accompanying drawings, in which: . FIG. 1 is a sectional side view of the indicator; and FIG. 2 is a sectional side view of a rapid- inflation fitting. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION The indicator, generally indicated at 10, is provided in three sections - a bottom section 11, a top section 12 and a dust cap 13. The bottom section 11 has a. tubular body 14 moulded of suitable metal or plastics material. The body 14 has an axial bore 15 which is screw-threaded along its lower portion. The screw-thread 15 enables the bottom section to be fitted onto an existing tyre stem (not shown) . The top section 12, has- a tubular body 16 moulded of transparent plastics material. An axial bore 17 extends through the body and has a reduced diameter 18 at its lower end. A circumferential abutment face interconnects the two portions of the axial bore. The lower portion 20 of the body 16 has a reduced external diameter and an external circumferential abut¬ ment face 21 interconnects the lower portion 20 to the upper portion 22. A screw-thread 23 around the base of the lower portion 20 engages the screw thread 15 in the bottom section 11 to secure the two sections together, while the engagement of the abutment face 21 with the upper end wall 24 of the bottom section provides an airtight seal between the two sections. An annular piston 25, having a central bore 26 is slidably movable in the axial bore 17 and is fitted with a sealing ring 27 seated in a circumferential groove 28. A tyre valve 29 has its valve stem 30 passing through the central bore 26 in the piston. An annular sealing ring 31 is fixed to the lower end of the valve stem 30 by a screw-threaded nut 32 and engages an annular valve seat 33 around the lower end of the central bore 26 to normally close the bore. A valve head 34 is secured to the upper end of the stem 30 and a compression spring 35 fitted around the stem between the valve head 30 and an inner annular seat 36 on the piston urges the sealing ring 31 into sealing engagement with the annular .valve seat 33. An annular plug 37, with a large axial bore 38, (which receives the valve head 34) has a screw-thread 39 along its length and the lower portion of the plug is engaged in a corresponding screw thread 40 provided in the upper portion 22 of the top section 12. A transverse slot 41 across the top of the plug may be engaged by a screw-driver (not shown) to enable the plug to be screwed in or out of the top section 12. An annular rim 42 is formed around the lower end of the bore 38 and it defines an annular spring seat 43 on the bottom of the plug. A compression spring 44 is sealed and located on the plug by the spring seat 43 and annular rim 42 respect¬ ively and the lower end of the spring 44 engages an outer annular seat 45 on the piston 25. The compression spring 44 acts in opposition to the movement of the piston 25 up the axial bore 17 as the inflation pressure in the tyre is increased. The dust cap 13, moulded from a suitable plastics material, has a screw-threaded lower bore 46 which is screwed, in sealing engagement, on the upper portion of the screw-thread 39 on the plug 37, the lower end wall 47 of the dust cap and the upper end wall 48 of the top section being in sealing abutment. An annular abutment face 49 is provided at the upper end of the bore 46 to sealably support a secondary valve plate 50 which is secured in position by a circlip 51 engaged in a circumferential groove 52. The secondary valve 53 has a valve stem 54 which passes through an axial bore 55 in the valve plate and at its lower end, is provided with a foot plate 56 in the bore 38 of the plug 37 and spaced from the valve head 34. A valve seal 57 is provided intermediate the valve stem 54 to normally engage an annular valve seat 58 on the underside of the valve plate 50. An operating knob 59, having an annular rim 60, is fitted to ' the upper end of the valve stem 54 and the rim 60 is slidably movable in a coaxial bore 61 in the central portion of the dust cap. A compression spring 62, interposed between the bearing plate 50 and the annular rim 60, urges the valve seal 57 into sealing engagement with the valve seat 58 to close the bore 55, while the rim 60 engages the underside of an annular flange 63 at the upper end of bore 61. The upper portion of the dust cap is of reduced external diameter and comprises an annular ring 64 around an inlet bore 65. The knob 59 extends into the inlet bore through a bore 66 in the flange 63. A circumferential line 67 is scribed around the body 16 of the top portion 12 and may be fitted with a . paint or dye (not shown) . The indicator 10 is used as follows:- The tyre valve is removed from the valve OMPI ste and the bottom section 11 is screwed onto the valve stem using the screw thread 15. The piston 25 is urged into engagement with the abutment face 19 t by the compression spring 44. To inflate the tyre, an air hose (not shown) has its nozzle connected to the ring 64 of the dust cap. The nozzle depresses the knob 59 to open the secondary valve 53 against the compression spring 62. The valve seal 57 and the rim 60 are moved out of engagement with the seal plate 50 and annular flange 63 respectively. Air under pressure from the nozzle passes through the dust cap and plug and enters the bore 17. The air pressure overcomes the seating pressure applied by the compression spring 35 to move the seal ring 31 away from the annular seat 33 on the piston, and the air flows through the bore 18 into the tyre. Periodically, the operator checks the approx¬ imate pressure in the tyre using the gauge provided on the air hose. When a desired pressure is reached e.g. 210 KPa (30 p.s.i), the air hose is disconnected and the knob 59 returns to its original position, closing the secondary valve 53. As the air pressure on both sides of the piston 25 is substantially equal, the compression spring 35 closes the tyre valve 29, while the compression spring 44 holds the piston against the abutment face 19. The operator depresses the knob 59 to open the secondary valve 53 to bleed any air out of the bore 17 above the piston 25 in the plug 37 and dust cap 13. The inflation pressure e.g. of 210 KPa (30 p.s.i) in the tyre acting against the underside of the piston 25 will move the piston upwardly in the bore 17 against the compression spring. If the actual inflation pressure in the tyre equals the required inflation pressure, the upper face of the piston 25 willbe aligned with the scribed line 67 on the top section. If the inflation pressure is below the selected pressure, the piston will be below the line 67 and vice versa. In use, air may leak past the seal 27 into the portion of the bore 17 above the piston 25. This air will not escape to the atmosphere due to the presence of the secondary valve 53. However, as this air will apply a partial balancing force on the piston against the inflation pressure in the tyre, the piston will be moved below the scribed mark 67. Before the inflation pressure is checked (while the tyre is cold) , the knob 59 is depressed to open the secondary valve 53 to bleed the air out of the bore 17. The piston 25 will move up the bore 17 to indicate if the inflation pressure is correct. -When air is to be added to the tyre to bring the inflation pressure upto the required pressure, the air hose fitting is connected to the dust cap 13 as discussed above. When the knob 59 is depressed by the fitting, it will open the secondary valve 53, and simultaneously, open the tyre valve 29 as the foot plate 56 will move downwardly to engage the valve head 34, moving the latter to- unseat the sealing ring 31. When the fitting is removed the tyre and secondary valves 29, 53 will be closed. The operator depresses the knob 59 to bleed the air out of the bore 17 above the piston 25 and the latter moves upwardly against the compression spring 44 to indicate the inflation pressur i the tyre. To enable the indicator 10 to be used for a range of inflation pressures e.g. 196 - 224 KPa (28-32 p.s.i), the plug 37 may be screwed up or down in the top section 12. The dust cap 13 (and the second ary valve 53) are unscrewed and a screw driver fitted OMP to the transverse slot 41 in the plug. By rotating the plug e.g. one (1) turn, the preselected inflation pressure may be varied by 7 KPa (1 p.s.i). For example, if the compression spring 44 * is tensioned so that the piston 25 will be adjacent the scribed line 67 when the inflation pressure is 210 KPa (30 p.s.i), rotating the plug 37 to screw it two turns into the top section 12 will adjust the preselected inflation pressure to 224 KPa (32 p.s.i). In this manner, three different models of the indicators can be manufactured and sold to cover the most common range of inflation pressures for passenger vehicles i.e. 168 - 252 KPa (24-36 p.s.i). Alternatively, the indicators may be fixedly set at a particular inflation pressure, no means for adjusting this pressure being provided. While the bottom section 11 has been described as being screw-threaded ontoa conventional valve stem, in an alternative embodiment, it may be supplied with a plain section to be vulcanized to a tyre stem. Alternatively, the bottom section may be provided with an integral spud for direct connection to the wheel rim, or with an externally threaded portion terminated by an abutment face to be mounted on and secured to the wheel rim. The bottom section may be sold direct to tyre manufacturers, while the top section and dust cap is sold through garage and accessory shops in e.g. packs of four so that the user selects a set to suit the intended inflation pressure of his vehicles tyres and he sets the indicators to the required inflation pressures before fitting them to his vehicle. A conventional dust cap is not required with the indications as the engagement between the annular rim 60 (on the knob 59) and the annular flange 63 prevents the ingress of dirt or other material into the indicator. While it is preferred that the body 16 of the top section 12 be formed of substantially transparent material, a transparent window having a scribed or painted mark would be sufficient to enable the piston 25 to be viewed. In certain applications, e.g. truck and tractor tyres, the presence of the indicator may make inflation of the tyre very slow. To overcome this problem, the top section- 12 is unscrewed from the bottom section and the rapid inflation fitting 68 of FIG. 2 is used. The fitting 68 has an annular body 69 with a stepped axial bore 70 of increased diameter in its lower portion 71. The upper portion 72 of the body has an annular ring similar to the annular ring 64 on the dust cap. The top section 12 and dust cap 13 are removed and the fitting 68 is pushed onto the bottom section 11, the upper end wall 24 of the latter engaging an annular abutment face 73 in the fitting. An air hose is connected to the fitting and air is pumped into the tyre to a pressur above the preselected inflation pressure. The fitting is quickly removed and the top section 12 screwed into the bottom section 11. The inflati pressure of the tyre is checked as described above and additional air pumped into the tyre, or bled therefrom, until the required inflation pressure is obtained. It will be readily apparent to the skilled addressee that various changes and modifications may be mad to the embodiment described without departing from the present invention. OMP

Claims: CLAIMS: 1. An inflation pressure indicator (10) for pneumatic tyres for vehicles, said indicator (10) including: a body (11,12) mountable on a wheel fitted with a tyre; an axial bore (17) iri the body (12) adapted to communicate with the interior of the tyre; a piston means (25) slidably mounted in the axial bore (17) ; sealing means (27) between the piston means (25) and the axial bore (17) ; compression means (44) in the body (12) acting on the piston means (25) in opposition to the inflation pressure in the tyre; and visual indicator means (67) in or on a substant¬ ially transparent portion (16) of the body (12) ; so arranged that at a preselected inflation pressure in the tyre, the piston means (25) will be moved against the compression means (44) to a position substant¬ ially adjacent the visual indicator means (67) . 2. An indicator (10) as claimed in Claim 1 wherein: a central bore (26) is provided in the piston means (25) ; and a tyre valve (29) , normally closing the central bore (26) , is operable to enable the tyre to be inflated. 3. An indicator (10) as claimed in Claim 1 or Claim 2 wherein: a plug (37) is mounted in the axial bore (17); and the compression means (44) includes a compression spring (44) interposed between the plug (37) and the piston means (25) ; said plug (37) being selectively movable in the axial bore (17) to enable adjustment of the preselected inflation pressure. OMPI Yλ 4. An indicator (10) as claimed in Claim 1 wherein the body (11,12) includes: a bottom section (11) connectable to a wheel or a tyre stem; and a substantially transparent top section (12) seatably connectable to the bottom section (11) , said piston means (25) being provided in the top section (12) , the visual indicator means (67) comprising a line (67) scribed on the top section (12) . 5. An indicator (10) as claimed in Claim 4 wherein: the bottom section (11) is screw-threadably engaged with, or vulcanized onto, a tyre stem. 6. An indicator (10) as claimed in Claim 4 wherein: the bottom section includes an integral spud or fastening means for connection to the wheel. 7. An indicator (10) as claimed in Claim 2 further including: a dust cap (13) connectable to the body (12) ; a secondary valve (53) in the dust cap (13) , said secondary valve (53) normally closing the axial bore (17) and operable to bleed air from the axial bore (17) or to open the tyre valve (29) to enable the tyre to be inflated. 8. An indicator (10) as claimed in Claim 5 wherein the dust cap (13) further includes: means (64) to enable connection of the indicator (10) to an air hose fitting; and means (60,63) to prevent the ingress of dirt int the body (12) . 9. An indicator (10) as claimed in Claim 4 wherein: for rapid inflation of the vehicle tyre, the top section (12) is disconnected from the bottom section (11) ; an inflation fitting (68) is connected to the bottom section; an airhose fitting is connected to the inflation fitting (68) and the tyre is inflated; the inflation fitting (68) is removed; and the top section (12) is re-connected to the bottom section (11) to enable the inflation pressure to be indicated. OMPI

Inventors: SMITH N
Applicants: SMITH N
Application year: 1981
Main classification: B60C23
IPC codes: B60C23, G01L17