SE517634C2 - Device for handheld machines - Google Patents

Abstract

The device is equipped with at least one flyweight (30) which is fastened to the crankshaft of the internal combustion engine or on elements rotatable on the crankshaft. This ensures that a torque is created by the developing unbalance which is as large as the torque forces acting upon the machine, but in the opposite direction. The development of the torque forces is fed back to the reaction forces. Centrifugal forces emanating from the balance weight (20), and the torque forces developing on the flyweight are oppositely directed to the torque forces developing by reason of the reaction forces.

Description

The Pizos device comprises at least one device so rotatably mounted on the engine crankshaft or devices that it is capable of giving rise to a torque which is substantially equal to, but opposite to, the torques acting on the engine body. which arise as a result of the reaction forces arising in the tool assembly due to centrifugal forces from the balancing weight or balancing weights (20), whereby the moments arising from the imbalance counteract the torques arising from the reaction forces.

According to one aspect of the invention, this is achieved by the mass of the weight or weights, its / their distance to the center line of the crankshaft, its / their position along the crankshaft and its / their orientation relative to the balance weight or weights being so selected that they give rise to a rotating moment. is essentially as large as the moment generated by the reaction forces but opposite to this.

Further aspects and advantages of the invention will become apparent from the detailed description of a possible embodiment as well as from the subsequent 'patent laws.

BRIEF DESCRIPTION OF THE DRAWINGS In the following description of a preferred embodiment, reference will be made to the accompanying drawings, of which Fig. 1 shows a schematic view above a hand-held combustion engine-driven work tool, Fig. 2 shows a detail view from the side of a piston / crankshaft arrangement. internal combustion engine.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the ur gures, there is schematically shown a working tool with an engine body 10 comprising an un cylindrical internal combustion engine 12. The internal combustion engine 12 comprises in a conventional manner a piston 14 in a cylinder 15 connected to a crank rod 16 which is rotatable. on a crankshaft 18. The crankshaft 18 is provided with balance weights 20 which are located on the opposite side of the crankshaft relative to the crankshaft mounting. These balance weights 20 are arranged to compensate for the forces which arise in the vertical direction when the piston 14 moves up and down in the cylinder 15, which forces would otherwise propagate in the engine body as vibrations. To one end of the crankshaft 18 and thus at a distance a from the center line y of the piston and from the plane of movement d of the connecting rod, which coincides with the center line y of the piston, is a tool (not shown), such as a saw chain or cutting disc, drivably mounted on a tool carrier 22, such as a saw bar or cutting arm, via, for example, gears, centrifugal couplings, V-belts and the like. The work tool is also arranged with suitable handles 24 for the user, preferably placed above and behind the motor body 10 seen in relation to the tool.

When the engine is in operation, the balance weights 20 compensate for the forces from the piston which are directed in the direction of movement of the piston. During the rotation of the crankshaft 18, however, the balance weights 20 will give rise to central gallbladders F ,, F, directed horizontally from the rearward and rearward, i.e. to the left and right in the eye. 1. These forces are absorbed in part by the inertia forces in the engine body and in part by the inertia forces in the tool assembly (tools, tool carriers, protective caps, etc.) and transmit a forward and backward movement on the machine depending on the position of the balance weights during rotation. The forces from the balance weights lead to a counter-reaction of the tool unit and a counter-reaction force R and R, respectively, of this. Since the tool carrier is arranged at a distance a from the plane of movement d of the connecting rod, which plane the forces of the balance weights 20 act in, the reaction forces will give rise to a rotating moment MR, = R, x a and MR, = R, x a on the engine body and thus the machine.

The center of gravity tp of the machine is approximately in the cylinder and the center of rotation vc of the machine coincides approximately with the center of gravity. Since the forces change direction during the rotation, the rotating moment will also change direction and thus form vibrations in the machine whose furnace amplitude increases the further from the center of rotation you get. You thus get relatively large vibrations in the rear handle and in the tool.

By providing means which compensate for the reaction forces, the vibrations generated are significantly reduced. This is done by applying a deviation moment M ,,,, MD, to the crankshaft with respect to the turning body of the machine body.

This can be done with one or more counterweights 30 arranged on the crankshaft at a certain distance r from the center line c of the crankshaft and at a certain distance b from the plane of movement d of the connecting rod and oriented in a certain relation to the balance weights 20. The position or weights 30 are adjusted so the resulting torque, ie the center of gravity D ,, D, fi of the weights times the distance r to the center of rotation, 10 15 20 25 517 634 4 Pizos corresponds to the torque torque of the reaction crane but with opposite torque direction. The counterweight / counterweights can be placed in any position on the crankshaft or devices rotatably mounted on the crankshaft. If the counterweight / counterweights are placed on the opposite side of the center of rotation as the line of attack of the reaction forces lies, the counterweight / counterweights 180 ° are arranged in opposite phase to the balance weights. If, on the other hand, the counterweight (s) are placed on the same side as that of the reaction line's line of attack, the counterweight (s) are arranged in phase with the balance weights. An apprenticeship for practical reasons is on a flywheel on the crankshaft. Based on empirical experiments, it has been established that the counterweight / counterweights do not need to be placed exactly in phase and opposite phase, but can be within a range of 80 °.

In experiments with a machine comprising an internal combustion engine in the size class 90 cm3, it has been found that a balancing weight of at least 100 gmr, preferably SOOgmmn, and a deviation torque of at least SOOOgmmz, preferably 20.0O0gmn12, give clear improvements on the machine.

With the help of appropriately selected weights and placement, a significant reduction in the impact of the reaction cranes on the machine is obtained. This results in less vibration which provides a better working environment and less risk of night damage to the machine. Other advantages are that the basic construction of the machine does not need to be changed, which is an advantage for older constructions where the design can be implemented directly. In new construction, no great consideration needs to be given to where the crankshaft's normal balance weights are placed in relation to the engine body's center of gravity. In addition, the tool unit and other machine parts can be made lighter.

It is to be understood that the invention is not limited to the embodiment described above and shown in the drawings, but may be modified within the scope of the appended claims.

Claims (4)

10 15 20 25 517 634 5 'PATENT REQUIREMENTS Device in hand-held machines comprising an internal combustion engine (10) with a piston (14), connecting rod (16) and crankshaft (18) with at least some balancing weight (20) for the piston, and a tool assembly (22) connected to the motor, characterized by that the device comprises at least one imbalance (30) arranged so on the crankshaft of the engine or devices rotatably mounted to the crankshaft that it is capable of giving rise to a torque which is substantially equal to, but opposite to, the torques acting on the engine body arising from as a result of the reaction forces arising from the tool assembly due to the centering forces from the balancing weight or balancing weights (20), the moments arising from the imbalance counteracting the torques arising from the reaction cranes. Device according to claim 1, characterized in that said imbalance (30) is arranged substantially in phase or substantially 180 ° in opposite phase with the balancing weight or balancing weights (20). Device according to claim 1, characterized in that said imbalance (30) comprises at least one weight (30) arranged at a distance (r) fi from the center line (c) of the crankshaft and at a distance (b) fi from the plane of movement (d) of the connecting rod . Device according to claim 3, characterized in that the mass of the weight or weights (30), its / their distance (s) to the center line (c) of the crankshaft, its position (b) along the crankshaft (18) and its / their orientation relative to the balance weight or balance weights (20) are so selected that they give rise to a rotating moment which is substantially as large as the moment generated by the reaction forces but opposite to it.