Self-centering unit for tire removal machines, comprising a plate provided with a series of angularly equidistant radial slots, in each of which a clamping jaw is received and slides to grip the edge of a wheel rim, said clamping jaws being linked together in such a manner as to be always equidistant from the axis of said plate, at least one clamping jaw being associated with actuator means causing it to translate in a radial direction by means of a positioner device arranged to vary the working position of said clamping jaws relative to the actuator means, without modifying their travel stroke.

FIELD OF THE INVENTION

The present patent relates to a self-centering unit to be associated with tire removal machines, to maintain wheel rims locked in a horizontal position while demounting and/or mounting the corresponding tires.

PRIOR ART

The automobile industry currently markets vehicles provided with wheel rims of a diameter which exceeds the range within which traditional self-centering units operate.

To be able to also operate on large-dimension wheel rims, a self-centering unit is known comprising a horizontal plate mounted on an underlying vertical shaft of the tire removal machine. Said plate presents a circumferential series of angularly equidistant radial slots, with each of which there is associated a slide carrying a head or clamping jaw for gripping the edge of the wheel rim from the inside or outside.

The head is associated with the slide in such a manner as to be able to translate in the direction of the travel axis of the slide in order to occupy two different operative positions, locking means being present to lock the head in the chosen operative position.

Although the described device performs the function for which it is provided, it presents certain drawbacks. A first drawback is the need to individually move each head relative to the slide to adapt the self-centering unit to large-dimension wheel rims. This operation is lengthy and laborious, the operator often forgetting to move a head, with the result that when the wheel rim is gripped by the heads it is not in the correct working position and risks undergoing damage.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome the drawbacks of the known art within the context of a simple and rational solution.

The invention achieves said object by virtue of the characteristics defined in the claims.

Specifically, the invention provides a self-centering unit comprising a plate provided with a series of angularly equidistant radial slots, in each of which a clamping jaw is received and slides to grip the edge of a wheel rim, said clamping jaws being linked together in such a manner as to be always equidistant from the axis of said plate, at least one clamping jaw being associated with actuator means for translating it in a radial direction. According to the invention, between said at least one clamping jaw and said actuator means there is provided a positioner device arranged to vary the working position of said clamping jaws relative to the actuator means, without modifying their travel stroke.

In a preferred embodiment of the invention, said actuator means are associated with two opposing clamping jaws, a positioner device being interposed between each clamping jaw and the actuator means. According to the invention, said actuator means for translating the clamping jaws are at least one pneumatic cylinder-piston unit.

The characteristics and constructional merits of the invention will be apparent from the ensuing detailed description given with reference to the figures of the accompanying drawings, which illustrate a particular preferred embodiment thereof by way of non-limiting example.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Said figures show a self-centering unit1comprising a horizontal plate2to be associated with a vertical shaft3branching from the base of a usual tire removal machine, not shown.

The purpose of the shaft3is to rotate the self-centering unit1during the demounting or mounting of the tire from or on the wheel rim by the usual means with which the tire removal machine is provided.

The plate2presents four angularly equidistant identical radial slots4. In each slot4there is slidingly mounted a slide5(FIG. 1) provided on its upper side with a double acting clamping jaw6, i.e. able to lock a wheel rim7, shown by dashed and dotted lines inFIG. 3, from the inside or from the outside.

With reference toFIGS. 2,3and4, each slide5lowerly presents a threaded pin55(FIG. 4), the axis of which intersects the longitudinal axis of the corresponding radial slot4, and on which there is mounted a bushing8on which a pair of identical overlying connecting rods9are pivoted by way of an interposed spacer10. The opposing ends of the connecting rods9are hinged to the corners of two identical overlying square plates11(FIG. 2) mounted idly on the shaft3, so that the two connecting rods9of each pair are disposed symmetrical about the direction in which the corresponding clamping jaw6travels (FIG. 2). The function of the plates11and connecting rods9form linking means for linking together all the clamping jaws which grip the edge of the wheel rim7such that they are always equidistant from the axis of the shaft3of the tire removal machine.

Two opposing slides5are associated, via a positioner device20, with two cylinder-piston units12disposed on one and the other side of the shaft3, their function being to move the clamping jaws towards or away from the axis of the shaft3, to hence cause the clamping jaws to translate radially.

Said two opposing slides5present lowerly (FIG. 5) a descending central stem13which terminates with a bushing14provided with two opposing holes140and141perpendicular to the axis of the bushing. The bushing14is connected to the said positioner device20, which comprises a crankshaft15provided with a crank16, on the crankpin17on which the bushing14is mounted. The ends of the crankshaft15are connected respectively to said pneumatic cylinder-piston units12.

Rotating the crankshaft15causes the working position of the clamping jaws to vary, i.e. causes them to approach or withdraw from the axis of the shaft3without modifying the travel stroke of the clamping jaws. This advantageously enables the self-centering unit to operate even on large-dimension wheel rims, i.e. with diameters exceeding 20 inches.

The positioner device20also comprises means18for locking the crankshaft17in two opposing working positions, in which the clamping jaws are at their closest point to and farthest point from the shaft axis respectively.

With reference toFIG. 4, said means18are fixed between the arms of the crank16, and comprise a cup-shaped body19the end of which is provided with a hole190. Within the cup-shaped body19there slides a pin21, one end of which is intended to be received in one of the holes140of the bush14, whereas the opposite end emerges from the cup-shaped body via said hole190and is connected to an operating knob22. The pin is maintained normally urged into one of the holes140by a spring23mounted about the pin and contained within the cup-shaped body. Said spring23is compressed between the end of the cup-shaped body and an annular shoulder200on the pin21.

The operation of the invention is extremely simple. When the operator is to operate on large-dimension wheel rims, i.e. of diameter exceeding20inches, he sets the positioner device as shown inFIG. 3. To achieve this, starting from the position ofFIG. 7the operator extracts the pin21from the hole141and then rotates the crankshaft15through 180 degrees in a clockwise direction to bring the pin21in front of the hole140. At this point, by releasing the knob the pin penetrates into the hole and locks the clamping jaw in position. It should be noted that this operation can be performed on only one or on both of the positioner devices, depending on the diameter of the wheel rim on which to operate.

FIGS. from 8 to 10show a variant of the invention which differs from the aforedescribed embodiment with regard to the constructional form of the positioner device.

In the description of this variant of the invention, those components identical to and already described in the first embodiment of the invention are indicated by the same reference numerals.

The figures show two opposing slides presenting at their rear a descending central stem50which terminates with a bushing51(FIG. 9) connected to the cylinder-piston units12via a positioner device25.

The positioner device25comprises a crankshaft26provided with a crank27, on the crankpin28of which the bushing51is mounted. The ends of the crankshaft26are connected respectively to said pneumatic cylinder-piston units12.

Rotating the crankshaft26causes the working position of the clamping jaws to vary, i.e. causes them to approach or withdraw from the axis of the shaft3without modifying the travel stroke of the clamping jaws. This advantageously enables the self-centering unit to operate even on large-dimension wheel rims, i.e. with diameters exceeding 20 inches. The positioner device25also comprises means29for locking the crankshaft26in two opposing working positions, in which the clamping jaws are at their closest to and farthest from the shaft axis respectively.

Said locking means are associated with the bushing51, they comprising a U-shaped latch30, the base wall of which presents a rectangular aperture300to be received by and to translate on two flat portions510of the bushing51. A pin31and a spring32are positioned in the arms of the latch30. The pin31is normally received in a matching hole33in the crankpin28of the crank27by passing through a hole34in the bushing. The spring32, the function of which is to maintain the pin31within the hole33, is positioned between said arm of the latch30and a corresponding cavity35provided in the bushing wall.

Again in this case the operation of the invention is very simple. To position the device the operator moves the latch30against the action of the spring32so as to compress the spring32and hence cause the pin31to leave the hole33. The operator then rotates the crankshaft26through 180 degrees and then releases the latch to cause the pin31to enter the hole33by the action of the spring32.