The present invention concerns a security cage for use especially in the inflation of large wheels of the type where the tyre can be introduced more-or-less freely over the wheel rim, and the mounting is finalised by the insertion of a bead wire ring at the outer side of the tyre with subsequent mounting of a locking ring for the closing of the bead wire ring. Wheels and tyres of this currently used type have the advantage that the tyre is easy to mount on the rim, and thus that the tyre does not need to be particularly supple in or- der for it to be forced over a rim for mounting in a self- retaining manner.

In connection with the inflation of tyres, and especially of tyres for large vehicles where an air pressure of up to 10 bar is used, use is made to an increasing degree of special security cages to prevent injury to persons and damage to equipment in the vicinity in the event of a tyre explosion during the inflation. There is a very great risk of this hap- pening especially in connection with tyres which have been renovated, in that in larger wheel service centres tyre ex- plosions may very well occur several times a week. These cages have perforated walls which will restrain parts which are flung out from the inside of the cage, and which will also break the pressure wave which arises with the explosion.

This pressure wave alone can be extremely dangerous in the immediate surroundings.

In their modern configurations, the relevant security or inflation cages, which are only slightly larger than the wheels and are typically designed to accommodate the wheels in their standing position, are provided with an"inflation robot", i. e. a control unit which controls the inflation with certain interruptions for control measurement of the pressure reached, in that the inflation is hereby controlled up to a pressure which e. g. lies one bar above the desired, set pressure, after which the pressure is automatically low- ered by deflation to the desired value. When the relevant

wheel is one with self-retaining tyre, the only thing which needs to be done inside the cage is the connection of the compressed-air pipe from the robot to the inflation nipple on the wheel, which can be done from the outside during tempo- rary opening of an intermediate section of the one side of the cage, e. g. a self-closing sliding wall section. When both this and the front with the opening for the rolling in and out of the tyre are closed, the automatic inflation can then be started while maintaining full security.

In practice, however, the situation is somewhat different in connection with the"locking ring wheels"mentioned in the introduction, in that most of the wheel mounting personnel consider it important that, during the actual inflation, they can work with the locking rings in order to ensure that these are mounted in a fully defensible manner. Those familiar with the technique will know that a control of this and a possible further working with the rings, mainly by using a hammer, can best be carried out after the side of the tyre has been brought to press outwards against the bead wire ring, and es- pecially in the cases where the rim and ring parts are so old that there are deposits of rust which can make the correct mounting or"setting"of the locking ring very difficult.

Even though the manufacturer of the security cages can certainly not recommend it, on this basis it has been ascer- tained that the operators use the said side opening in the cage for working on the locking ring with a hammer from the outside while the inflation is in progress. Despite the fact that in this side opening there are grating bars which permit both a view towards the side of the wheel and the insertion of the hands (with hammer), and which will prevent the fling- ing out of large articles from the cage, there still exists a great element of risk that, in the event of an explosion in- side the cage, the said pressure wave can be transmitted al- most unhindered through the relevant wall part.

The object of the invention is to provide a security cage which in a defensible manner can accommodate the desire con- cerning the working on the locking rings during the infla- tion.

With the invention, a surprisingly simple solution has been found to this problem, i. e. based on the observation that it will be of no use to work further on the security rings after a pressure in the order of 3 bar has been estab- lished in the tyre. If the ring is not properly in place when this pressure is reached, then the procedure should be re- peated completely from the start. Precisely this pressure of approx. 3 bar also happens to be a limit value between those pressure areas where a tyre explosion can manifest itself with a dangerous and non-dangerous pressure wave development respectively. Even a tyre explosion at slightly under 3 bar can be quite violent, but when it is ensured by means of the grating bars that large articles can not be flung out, the associated pressure wave is thus no more violent than it quickly abates and can hardly promote a really dangerous flinging-out of wheel parts, let alone constitute an actual element of danger in itself. However, the effect of the pres- sure wave will increase exponentially with the tyre pressure, and already at 4 bar it will be capable of knocking a person off his feet. At even higher pressure within the area under consideration, a person can be blown several metres away, so there is good reason to determine precisely 3 bar as a risk limit, naturally plus or minus some tenths of a bar.

This coincidence with the pressure limit for the working on the locking rings can thus be utilised in that the same work is"legalised"providing that the inflation robot has still not registered that a tyre pressure of 3 bar has been reached, but on the other hand it is"criminalised"when it is registered that this pressure has been reached. The robot can thus be programmed to stop further inflation, unless the conditions for said ring work have been suppressed. In prac- tice this will mean that by means of a sensor sequence the robot must register that the said side opening has been closed in order that the inflation can be continued. Con- versely, here there will be given a signal to the operator that he can just as well stop his work with the locking ring and start from the beginning if it is not sitting as it should.

The invention can thus be realised by the combination of establishing a sensor for"side door closed", and the pro- gramming of the inflation control to interrupt the inflation at a tyre pressure of approx. 3 bar if it is registered that the said sensor has not been activated. In the event of such an interruption in the inflation, the operator must then choose whether to close the side door in order to continue the inflation, or whether to give the control unit instruc- tions to initiate a deflation of the tyre with the object of starting the fastening of the ring from the beginning.

A security cage according to the invention is illustrated in the drawing. The cage 2 is built up with a box frame and with top and walls executed preferably with reference to #, i. e. with two layers of expanded metal netting for the break- ing of a possible pressure wave of air from inside the cage.

The cage has a front door 4 which can be opened, whereby it can accommodate a large wheel which can be rolled in to sta- bilised support on a pair of bottom rollers 6 and 8. In a side wall, the cage has a slide-or swing-door 10 which can be opened, and which can close over a wall opening 12, through which in a known manner a hand can be introduced for gripping an inflation hose 14 with an inflation nipple 16 for the placing of the nipple on the wheel air valve. This opera- tion is extremely simple, and it is therefore normal practice for use to be made of a self-closing door 10 which the opera- tor can easily hold open while this operation takes place, and which will thereafter close automatically.

The pump hose 14 extends from a control unit 18 which is fed with compressed air through a hose 20, and is otherwise arranged with diverse means for the determination of the de- sired inflation pressure, e. g. cf. #. The front door 4 can be locked with a latch 22, and a door switch 24 is provided which by a connection to the control unit 18 renders this in- operative while the door 4 is open.

With the invention, this known cage is provided with three important modifications, i. e. the side door is configured so that it can be opened to a self-holding open position in which there is easy access, not

only to place the pump nipple 16 on the wheel valve, but also to work on a locking ring system existing on the rolled-in wheel during an initial inflation of the tyre, preferably un- til the control unit 18 has registered an inflation pressure of a maximum of 3 bar; the side opening 12 is provided with a sensor 26 for "closed door", which sensor by a connection to the control unit 18 will render this inoperative for further inflation while the door 10 is open; the control unit 18 is correspondingly arranged to be rendered inoperative for further building-up of pressure in excess of the said approx. 3 bar until it has been registered that the side door 10 has been closed.

For a correct, safe and uninterrupted inflation sequence, the operator must thus ensure that the side door 10 is re- leased for the closing of this door when the work on the locking ring has been completed, since further inflation is otherwise stopped, possibly with a related generation of an "attention signal". As mentioned, the work on the wheel will be relatively free of risk and practically possible providing that the tyre pressure is less than the said approx. 3 bar, i. e. with open side door 10, while the same work will be both ineffective and dangerous if this door is held open during further increase in pressure in the tyre.

The shown embodiment of the pump cage contains a further advantageous modification, i. e. that the rearmost bottom sup- port roller 6 is connected to a front-operated pedal 28 which, when pressed down, can influence just the one end of this roller so that it is raised, whereby the rolled-in tyre can easily be induced to start rolling out.

It should be mentioned that the air pressure in the tyre is measured intermittently during necessary interruptions of the inflation. The control unit 18 houses a computer which, already after a couple of initial measurement below 3 bar, is rendered able to calculate the time at which the said 3 bar will be reached in the relevant tyre, and for a possible se- curity interruption of the inflation (if the side door is not closed), it will be the associated calculation signal which is the interrupting factor.