DESCRIPTION

The present invention relates to a hand tool for breaking the bead of tyres of the kind described in the introductory part of claim 1.

Tools of the said kind are known to be operated by pneumatic or hy- draulic means-

Tools of the described kind can be used for breaking the tyres from their rim without removing the wheel from the vehicle, e.g. a trac¬ tor.

In known tools the movable pressure plate is mounted on the piston rod of a pneumatic or hydraulic cylinder.

This gives the tool a large width and hence it often needs much space for the breaking of tyres on the internal side facing the body of the vehicle, where space is often restricted.

From the description of U.S.A. patent No. 4.850.413 a hand tool is known for the breaking of a tyre from its rim. The tool comprises two plate-shaped arms which are wedge-shaped at the front end, and which in their initial position rest against each other. By means of a clamping mount and a tightening screw oriented in the direction of the arms, the arms can be forced down between the rim and the side of the tyre to a position in which the pointed front end of the arms is in contact with the internal, plane side of the rim. By means of another tightening screw oriented at right angles to the arms\' longitudinal direction the movable arm can be turned in rela¬ tion to the stationary arm, thus releasing the tyre from its rim. This known tool is difficult to operate, especially in releasing the tyre on the internal side facing the vehicle. The former tightening screw is placed under the rim and is accessible only -yith difficulty. The latter tightening screw is oriented at right angles to the arms and takes up much space. Furthermore, it is subjected to pressure and must therefore be of sturdy dimensions. Finally, fine-adjustment of the tool for different rim sizes

is difficult to make.

It is one purpose of the invention to describe a hand tool which takes up essentially less space in the width than known tools. This is achieved by embodying the tool as described in the characterizing part of claim 1.

Claim 2 describes an example of a push/pull mechanism.

By what is described in claim 3 it is achieved that the tool can be used without extra equipment in the shape of hydraulic pumps or com¬ pressors. Such equipment is often not at hand for repair work in the field, thus making it necessary to dismount the wheel from the vehicle, transport it to the workshop, repair it, transport it back and re-attach it to the vehicle, which is a time-consuming exercise.

By the procedure described in claim 4 it is achieved that the tool also can be used in breaking a tyre mounted on twin wheels.

Claim 5 describes a preferred embodiment of a retaining fixture for a hand tool according to the invention.

The invention is explained in detail in the following with reference to the drawing in which

fig. 1 shows an embodiment of a hand tool according to the invention for breaking a tyre from its rim, seen from above,

fig. 2 shows the hand tool, seen from below,

fig. 3 is a sectional view after the line I-I in fig. 1 with certain parts not shown and in the initial position in which the movable part of the pressure plate is flush with the sta- tionary part, and

fig. 4 is similar to fig. 3 with the exception that the movable part of the pressure plate is staggered in relation to the stationary part.

fig. 5 shows a section after line II-II in fig. 3.

As shown in the drawing the hand tool is embodied with a pressure plate consisting of a stationary part 1 and a movable part 2. The movable part 2 has an indentation 3 which can take up the stationary part 1 so that the movable part 2 can be aligned flush with the stationary part 1 in the starting or initial position in which the pressure plate is inserted between a tyre and its rim.

Furthermore, the tool is embodied with a retaining fixture 4 which has a set screw 5 with a circular part 6 which during the breaking operation of a tyre from a rim rests against the rim flange.

According to the invention the tool is embodied as a pair of scissors with two arms 7, 8, of which the arm 7 is stationary during the breaking operation, and the other arm 8 is movable. The arms 7, 8 can turn in relation to each other on a common pivot 9, at the rear end, positioned low on the movable arm 8.

The stationary arm 7 is at its rear end mounted on a plate 10 which is pivoting on the pivot 9.

As shown in the drawing the movable arm 8 has a U-shaped cross- section whereby it can accommodate the stationary part 7 in the zero position of the tool.

Outside the stationary arm 7 is mounted a push/pull mechanism 11 in such a way in the plate 10 that it can turn in relation to it.

At the front end the push/pull mechanism 11 is swingably hinged on each side to an internal, hinged toggle lever 12 and to an external, hinged toggle lever 13 on a through-going pivot 14.

The hinged lever 12 is swingably hinged on a pivot 15 to the lower part of the stationary arm 7 close to the stationary part 1 of the pressure plate.

The hinged lever 13 is swingably hinged on a pivot 16 to the lower part of the movable arm 8.

The pivot 15 is situated in front of the pivot 16. In the initial po¬ sition in which the movable part 1 of the pressure plate is flush with the stationary part 2, the _. pivot 15 is situated a little lower than or level with the pivot 16.

The push/pull mechanism 11 can be embodied as a pneumatic or a hy¬ draulic cylinder. As shown in the drawing it can also be embodied as a screw spindle, which can be extended by turning the screw head 17 counter-clockwise, and shortened by turning the screw head in the opposite direction.

As shown, the screw spindle 11 is pull activated during the breaking operation. The screw spindle can therefore be of small dimensions.

The stationary arm 7 can be embodied as a tube in which an arm 18 on the retaining fixture 4 can be slidably mounted. The arm 18 is slid- able by means of a screw spindle with a screw head 19. The arm 18 can be detachably mounted so that the tool can be used also for breaking tyres mounted on twin wheels.

It goes without saying that the tool can be activated by an electric hand drill engaging the screw heads 17 or 19 with socket spanner.