The invention relates to a runflat device for a motor vehicle, enabling a considerable distance to be traveled at relatively high speed with a tuneless tire that is partially or totally deflated.
In general, for fitting to civilian vehicles, runflat devices need to be suitable for being mounted on standard wheel rims, which means one-piece rims of the drop-center type.
Presently-known runflat devices are generally constituted by a rolling ring which is clamped around the rim of the wheel inside the tire. The ring is constituted either by a single, relatively flexible piece from which a splice has been removed, or else by at least two rigid pieces in the form of circular arcs or sectors. To mount the ring in a clamped configuration around the rim, it is necessary to provide assembly and clamping fastener means between the two free ends of the split ring or between the facing ends of the ring sectors. Assembly and clamping fastener means are rigid and they are constituted by mechanical elements such as nuts-and-bolts, for example.
Unfortunately, experience shows that it is such rigid fastener means that constitute the weak links in runflat devices (e.g. Due to fatigue phenomena). Furthermore, mounting a runflat device is an operation that requires the operator to be trained, in particular because of the small amount of space available for the tool that is required for clamping the ring onto the rim.
According to document FR-97/13618 in the name of the Applicant, the runflat device is made up in such a manner as to eliminate assembly and clamping fastener means. It comprises at least one open inner ring of relatively rigid material for mounting on the rim, and a continuous outer ring that is substantially in extensible and that is engaged on the inner ring so as to clamp it and fix it to the rim.
In an improvement disclosed in document FR-98/04225, likewise in the name of the Applicant, the ring is made up of three pieces, namely: two first annular pieces that are open at respective slices and that are designed to be mounted one on the other around the rim, and a third annular piece that is continuous and coaxial about the two preceding pieces, said third piece serving to clamp the system built up in this way onto the rim.
An object of the invention is specifically to avoid problems associated with assembly and clamping fastener means between the two free ends of a ring or between sectors of a ring.
To this end, the invention provides a runflat device for a motor vehicle, the device comprising a ring for mounting inside a tire on a one-piece non-standard wheel rim that presents a drop center, an inner flange and an outer flange, said ring being made as at least two sectors each having a radially inner zone and a radially outer zone, wherein the sectors of the ring are independent of one another, and wherein each sector is fixed to the rim via its radially inner zone.
In general, the radially inner zone of each sector of the ring is terminated by a circularly actuate footing designed to bear against the bottom of the drop center, and said footing presents an inner lateral flange and an outer lateral flange, the inner flange being received in a lateral groove in the drop center while the outer flange matches the profile of the drop center and cooperates with the means for fixing the sector of the ring on the rim.
In the invention, each sector of the ring is secured to the wheel rim by means of screws or by means of a clamping belt.
In a first embodiment of the invention, fixing screws are used which pass through the outer flange of the footing of each sector of the ring and penetrate into tapped blind holes formed in the thickness of the wheel rim from the bottom of the drop center.
Advantageously, the tapped blind holes are machined obliquely in the thickness of the rim to facilitate screw-fitting operations.
In a second embodiment of the invention, fixing screws are used which pass through tapped holes machined laterally through the rim and opening out into the drop center so as to bear in clamped manner against the outside faces of the sectors of the ring.
In addition, the inner flanges of the footings of the sectors of the ring bear against an O-ring placed in the lateral groove of the drop center and designed to accommodate the lateral tolerances of the various parts of the assembly, while each fixing screw has an enlarged head which bears against the rim via a sealing ring.
In a third embodiment of the invention, the means for fixing the sectors of the ring on the rim are constituted by a clamping belt which surrounds the outer flanges of the sectors of the ring.