JPS6133677B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a portable power tool, ie, a power hand tool hammer, which is driven by an internal combustion engine having a crankshaft and a flywheel connected to the crankshaft.

Hand tools of this type are used, for example, at fairly large scale demolition sites and at remote construction sites where there is no power supply. They have the advantage of being more maneuverable than electric tools. However, known internal combustion engine operated tools are considerably heavier than conventional power tools. Furthermore, they are much more noisy and vibrate than power tools.

It is therefore extremely difficult to work with such known tools for long periods of time. This is on the one hand to compensate for imbalances in the drive motor, and on the other hand to compensate for delays in the power transmission of the internal combustion engine without a significant reduction in speed. Therefore, in order to prevent an increase in engine speed and a consequent increase in unpleasant noise when the tool is lifted from the working surface, the known tool is equipped with a throttling mechanism, which reduces the engine speed to idling speed. Common. The operation of this throttle mechanism can be manual or automatic. The flywheel must have an extra rotational moment or inertia to prevent the engine from stalling from low idle speeds during such idle periods or when reapplying the tool to the work surface. For this purpose, for example, the flywheel can be made larger. However, in the power hand tool according to the present invention, the size of the flywheel must be limited in terms of weight and space.

Most of the internal combustion engine-driven hand tools currently in use are so-called high-speed engines, which provide the necessary power only at relatively high operating speeds.
However, this results in extremely loud noises and violent vibrations, which can eventually become a health hazard and render the tool useless. Furthermore, so-called low-speed engines require large and heavy flywheels, making them unsuitable as portable tools.

The object of the invention is to provide a power hand tool which can be operated at low engine speeds and which is light in weight.

In order to achieve this object, the present invention is characterized in that a speed change gear is provided between the crankshaft and the flywheel, and the speed of the flywheel is made higher than the speed of the crankshaft by this speed change gear.
Since the energy capacity of the flywheel is proportional to the square of the rotational speed, the addition of a variable speed gearing can save the overall weight of the tool and also reduce the engine speed.

If the tool is small, the flywheel also performs other functions. Therefore, it is common to design the flywheel to also act as a fan, generating airflow to cool the engine. This arrangement allows for a considerable air flow generated by the increased speed of the flywheel resulting from the use of the variable speed gearing, and even when the tool is used for a considerable period of time, the engine will not run despite the small diameter flywheel. It can be cooled sufficiently. Additionally, the flywheel may also act as a generator to generate the ignition spark, thereby maintaining the ignition voltage somewhat constant at low engine speeds. The variable speed gearing, which increases the speed of the flywheel relative to the speed of the crankshaft, also has the advantage of stabilizing the entire tool as a result of the gyroscope effect of the flywheel. Therefore, unintentional tilting of the entire tool caused by eccentric forces during use can be significantly reduced. Furthermore, the vibration of the tool during operation is also reduced.

For reasons of size and weight, the transmission gearing should be constructed as compact as possible. It is therefore advantageous to design this transmission gear as a planetary gear. Furthermore, the planetary gear can be configured to be coaxial with the crankshaft, so that the appearance of the hand tool is not impaired.

For better power transmission and for dimensional reasons, the web or support of the planetary gear set is driven by the crankshaft, the annular member of the planetary gear set is fixed to the housing of the tool, and the sun gear of the planetary gear set is fixed to the housing of the tool. It is best to connect it to the flywheel. A preferred design of the planetary gear system allows for two or more planetary gears to be mounted on a web or support in order to obtain an even force distribution.

For practical reasons, there is a limit to the transmission ratio between the crankshaft and the flywheel. The addition of the variable speed gearing offsets the savings in flywheel weight itself. The speed of the flywheel is therefore considerably higher than the speed of the crankshaft. On the other hand, the rotational speed of the flywheel should not be too high at the rated speed of the engine, that is, the normal speed. This is because if the gyroscope effect of the flywheel is too large, proper handling of the tool becomes extremely difficult. In order to obtain a suitable intermediate value, it is preferable to set the speed change ratio of the speed change gear device to about 1:3. Of course, when the flywheel supports a magnet that induces a current in the ignition coil, the gear ratio should be selected so that the output rotation speed is an integral multiple of the input rotation speed. For example, when the gear ratio is 1:3, the flywheel rotates three times for one revolution of the crankshaft, producing three ignition voltage pulses. At this time, an interrupter (not shown) placed on the crankshaft closes a contact point every revolution of the crankshaft to introduce ignition voltage, so that one ignition occurs during one stroke of the internal combustion engine. do. Thus, a pulse of ignition voltage must be present whenever the interrupter causes a contact to close and ignite. Therefore, it is necessary that the output rotation speed be an integral multiple of the input rotation speed.

The invention will be explained with reference to the drawings.

Housing 1 for a drill hammer or chisel hammer as an example of an internal combustion engine driven power tool as shown.
will be established. A handle 2 is attached to the rear end of this housing 1.
Place. A tool holder 3 is provided at the end of the housing 1 on the side away from the handle 2. A crankshaft 4 of a drive engine is rotatably mounted in a housing 1. The connecting rod 5 is tightened to the crank pin 4a of the crankshaft 4. This connecting rod 5 is connected to a piston 6 of a drive engine. At the upper end of the crankshaft 4, the crank 7 is connected to the crankshaft 4 through a threaded portion 4b. This crank 7 is provided with a crank pin 7a, and a connecting rod 8 of a striking mechanism of the tool is rotatably tightened to this crank pin 7a. This connecting rod 8 is connected to a drive piston 9 of the striking mechanism. This drive piston is guided into the sleeve 10.

The end of the crankshaft 4 on the side away from the threaded portion 4b is surrounded by a planetary gear device. The web or support 11 of the planetary gear set is fixed to the crankshaft 4 without twisting. A planetary gear 13 is supported on this web 11, and each planetary gear has a corresponding shaft 1.
Place it in 2. Each planetary gear meshes with a fixed toothed annular member 14 connected to the housing 1 on the one hand;
On the other hand, the sun gear 1 mounted on the flywheel 15
5a. A flywheel and a sun gear 15a connected thereto are rotatably attached to the crankshaft 4 by a bearing bush 16. The speed of the flywheel is increased compared to the speed of the crankshaft by means of a planetary gear system consisting of the web or support 11, the planetary gear 13, the toothed ring 14 and the sun gear 15a.

As is clear from the sectional view of FIG. 2, the web or support 11 has three shafts 12 and three
A number of planetary gears are provided. Furthermore, as is clear from this drawing, the planetary gear 13 is connected to the toothed annular member 1 on the one hand.
4, and on the other hand meshes with the centrally located sun gear 15a. This configuration with three planetary gears is just one example. Instead of three planetary gears, one, two or more than three planetary gears can be provided. Furthermore, although a hammer drill is shown in the drawings, the invention can also be applied to other configurations of hand tools driven by internal combustion engines, such as power drills or power saws.

[Brief explanation of the drawing]

FIG. 1 is a partially sectional side view showing an embodiment of the internal combustion engine-driven power tool of the present invention as a drill hammer or chisel hammer, and FIG.
It is an enlarged sectional view on a line. DESCRIPTION OF SYMBOLS 1...Housing, 2...Handle, 3...Tool holder, 4...Crankshaft, 4a, 7a...Crank pin, 4b...Threaded portion, 5, 8...Connecting rod, 6...Piston, 7 ... Crank, 9 ... Drive piston, 10 ... Sleeve, 11 ... Support body, 12 ... Shaft, 13 ... Planetary gear, 14 ... Fixed toothed annular member, 15 ... Flywheel, 15
a...Sun gear, 16...Bearing bush.

Claims (1)

[Scope of Claims] 1. In a portable power tool driven by an internal combustion engine provided with a crankshaft and a flywheel connected to the crankshaft, a speed change that increases the speed of the flywheel compared to the speed of the crankshaft. An internal combustion engine-driven power tool, characterized in that a gear device is disposed between the crankshaft and the flywheel. 2. The internal combustion engine-driven power tool according to claim 1, wherein the speed change gear device is a planetary gear device. 3. A web or support of the planetary gear set is driven by the crankshaft, a toothed annular member of the planetary gear set is secured to the housing of the power tool, and a sun gear of the planetary gear set is coupled to the flywheel. An internal combustion engine-driven power tool according to claim 2, characterized in that: 4. The internal combustion engine-driven power tool according to any one of claims 1 to 3, characterized in that the speed change gear device has a speed change ratio of 1:3. 5. The internal combustion engine-driven power tool according to any one of claims 1 to 4 above, characterized in that the power tool is a drill hammer or a chisel hammer.