GB2413777A

GB2413777A - Impact mechanism for power tool

Info

Publication number: GB2413777A
Application number: GB0509188A
Authority: GB
Inventors: Gerhard Meixner; Thilo Henke; Juergen Lennartz
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2004-05-07
Filing date: 2005-05-05
Publication date: 2005-11-09
Also published as: GB0509188D0; CN1693034A; FR2869825A1; DE102004022623A1; US20050247462A1

Abstract

A hand-held power tool is equipped with an impact mechanism which comprises a striker 1 which can be axially reciprocated in a guide tube 2, a spring mechanism 4 exerting a force on the striker 1 being present, with which the striker 1 can be displaced in a movement in the direction of a tool 3. The impact mechanism produces a very high single impact energy with a relatively low impact frequency, as after each impact the striker 1 is displaced in a movement against the force of the spring mechanism 4, in order to load said spring mechanism, and as the striker 1 is abruptly released again after the loading of the spring mechanism 4, so that it flies in the direction of the tool 3. The spring mechanism may be a chamber 4 filled with a compressible medium or one or more compression and/or tension springs (15,16,fig.2). The mechanism for moving the striker 1 against the force of the spring mechanism 4 may include a rod 8 connected to the striker 1, with a hook 14 which may be driven and released by a drive wheel 10.

Description

24 1 3777 Hand-held power tool with an impact mechanism

Prior Art

The present invention relates to a hand-held power tool - preferably a rotary and/or impact hammer - with an impact mechanism which comprises a striker which can be axially reciprocated in a guide tube, a spring mechanism exerting a force on the striker being present, with which the striker can be displaced in a movement in the direction of a tool which can be inserted in the hand-held power tool.

Such a pneumatic impact mechanism carrying out repetitive impact movements for an electro-pneumatic rotary and/or impact hammer, as appears in DE 198 10 088 C1, consists of an eccentric drive, a piston and a striker. A rotary movement is converted by these three elements into an impact movement. The striker moves axially back and forth in a guide tube in the following manner: the piston moved forwards by the eccentric drive compresses the air cushion between the piston and the striker, whereby said striker flies freely onto the tool inserted in the machine. The striker transfers its impact energy to the tool and receives an impulse there in the backwards direction. At the same time, the piston is also moved back by the eccentric drive, whereby a certain vacuum is generated in the air cushion between the piston and the striker. As soon as the piston has reached its dead centre position and the striker flies again onto the piston, the air cushion between the two is compressed, leading to a compression, with the result that subsequently, when the piston again moves forward, the striker now flies forward with an even greater speed onto the tool. With such a pneumatic impact mechanism, the piston and the striker move with the same frequency. A high single impact energy with a low impact frequency is not possible with such an impact mechanism.

The same applies to a so-called spring driven impact mechanism, as is known from EP 544 865 B1. In this connection, a spring steel angle is displaced into oscillating motion by an eccentric drive and this spring steel drives the striker forwards in the direction of the tool or a ram present between the tool and the striker. The rebound energy of the striker is stored in the stirrup spring and, as with a pneumatic impact mechanism, is released again during the forward movement.

The object of the invention is thus to provide an impact mechanism of the type specified above which can be made with the simplest technical means possible and with which a high single impact energy can be produced with a low impact frequency.

Advantages of the Invention The aforementioned object is achieved by the features of claim 1, in that means are present which displace the striker after each impact in a movement against the force of a spring mechanism in order to load said spring mechanism, and in that the means abruptly release the striker again after the loading of the spring mechanism, so that, driven by the spring mechanism, it flies in the direction of the tool. As the striker is actively moved after each impact against the force of the spring mechanism, after its subsequent release the striker obtains very high energy for a new impact.

Advantageous embodiments of the invention appear in the sub-claims.

An appropriate drive for the striker creates a frictional connection with the striker after an impact has been carried out and moves it against the force of the spring mechanism and again releases the frictional connection as soon as the striker has reached a defined position in its movement against the force of the spring mechanism.

A more advantageous spring mechanism consists of a compression chamber filled with a compressible medium and which is located in the guide tube on the side of the striker facing away from the tool. The compression chamber can be filled with a gas, preferably air or even a fluid.

The compressible medium - gas or fluid - constantly remains in the compression chamber and only certain leakages from the compression chamber have to be compensated. A pump can additionally be provided which supplies a compressible medium to the compression chamber to compensate for leakages. The pumping capacity of this pump can be very low as it only has to compensate for leakages in the compression chamber. Such a small pump requiring low volume and weight can be integrated in the hand- held power tool.

A further advantageous spring mechanism can consist of one or more compression springs and/or tension springs which are supported, on the one hand, on the striker and, on the other hand, on a rigid shoulder in the direction of movement of the striker.

Drawings The invention will hereinafter be described in more detail with reference to two embodiments shown in the drawings, in which: Fig. 1 is a longitudinal section through a rotary or impact hammer with an impact mechanism and a spring mechanism configured as a compression chamber and Fig. 2 is a longitudinal section through a rotary or impact hammer with an impact mechanism and a spring mechanism consisting of compression/ tension springs.

Description of the Embodiments

Fig. 1 shows a longitudinal section through a hand-held power tool with an impact mechanism. This hand-held power tool is, for example, a rotary and/or an impact hammer. In the diagrammatic view of the hand-held power tool only the impact mechanism, the subject of the invention, is shown.

Any other functional assemblies which are normally present in a hand-held power tool, are not shown.

The impact mechanism consists in the known manner of a striker 1 which is mounted in a guide tube 2 in a reciprocating manner. A tool 3, for example, a drill bit or chisel, is inserted in a tool holder of the handheld power tool. When the striker 1 flies forwards onto the tool 3, the striker 1 transfers its impact impulse to the tool 3.

Between the tool 3 and the striker 1 in the guide tube 2 a ram (not shown here) can also be arranged which transmits the impact impulse received by the striker 1 onto the tool 3.

The forward movement of the striker 1 in the direction of the tool 3 inserted in the hand-held power tool is produced by a spring mechanism of which the force is directed onto the striker 1 in the direction of forward movement. In the embodiment shown in Fig. 1, this spring mechanism is a compression chamber 4 filled with a compressible medium and which is located in the guide tube 2 on the side of the striker 1 facing away from the tool. The compression chamber 4 is defined by the side wall of the guide tube 2, the striker 1 sliding in the guide tube and a rear wall 5 present on the guide tube 2 on its end facing away from the tool 3. Between the striker 1 and the side wall of the guide tube 2 a seal 6 is incorporated which prevents the compressible medium from being able to escape from the compression chamber 4.

The compressible medium can be a fluid or a gas. Preferably the compression chamber 4 is filled with air. In order to compensate for leakages in the compression chamber 4, a pump 7 is attached to the compression chamber 4 via which the compressible medium can be supplied to the compression chamber 4 to compensate for leakages. As it only has to compensate for leakages of the compressible medium, a small pump 7 with low pumping capacity is sufficient which, due its low weight and volume, can be easily housed in the hand-held power tool.

The impact mechanism comprises a drive which, after each impact on the tool 3, displaces the striker 1 in a movement against the force of the spring mechanism and, as a result, loads the spring mechanism. Said drive is designed such that it abruptly releases the striker 1 again after the loading of the spring mechanism, so that the striker 1, driven by the spring mechanism, flies in the direction of the tool. As the spring mechanism is not only loaded by the rebound force of the striker 1 but actively highly loaded by the separate drive, on the release of the spring mechanism the striker 1 obtains a very high impact force.

Thus a very high single impact energy can be generated, even with a relatively low impact frequency.

The aforementioned drive in the embodiment shown in Fig. 1 is explained as follows: A rod 8 extending in the direction of the longitudinal axis of the guide tube 2 is connected to the striker 1 on its side facing away from the tool 3, which rod is guided through the rear wall 5 of the guide tube 2. A seal 9 between the rod 8 and the through passage in the rear wall 5 of the guide tube 2 prevents the leakage of compressible medium from the compression chamber 4. The rod 8 terminates outside the compression chamber 4 in the vicinity of a drive wheel 10 which can be rotated about an axis which is perpendicular to the longitudinal axis of the guide tube 2. The drive wheel is displaced in rotation by the shaft 11 of a motor not shown, for example via a spur gear (not shown in the drawings). On the drive wheel 10, displaced relative to the rotational axis 12 of the drive wheel, a journal 13 is located which protrudes perpendicular to the plane of projection of the drive wheel 10. The end of the rod 8 facing the drive wheel 10 is configured as a hook 14, such that the journal 13 can move into the hook 14 when the drive wheel 10 rotates. When the striker 1 moves backwards after the impact on the tool, the rod is pushed with the hook 14 in the direction of the drive wheel 10. The journal 13 of the rotating drive wheel 10 thus slides into the hook 14 and drives the rod 8 with the striker 1 in the rotational direction of the drive wheel 10 - clockwise in the embodiment -, so that the striker 1 is moved toward the rear wall 5 of the guide tube 2 and thus the medium in the compression chamber 4 is compressed. The result thereof is that the pressure greatly increases on the striker 1 in the direction toward the tool 3. As soon as the drive wheel 10 has carried out a half rotation and, as a result, the journal 13 has reached a position 13' which is furthest away from the guide tube 2, the journal 13 again slides out of the hook 14. At this moment, the striker 1 is released and can move toward the tool 3 for a further impact, driven by the pressure of the compression chamber 4. The speed of the drive wheel 10 can be set, such that when the striker 1 moves backwards again after an impact, the hook 14 is always positioned at the end of the rod 8 just above the journal 13 of the drive wheel 10.

Instead of the previously operated drive which pulls the striker 1 via the rod 8 against the force of the spring mechanism, a drive can also be provided which pushes the striker 1 against the force of the spring mechanism. The drive could then be arranged on the side of the striker 1 facing the tool. Apart from the drive for the striker 1, disclosed by way of example, any other mechanism can be used which moves the striker 1 against the force of the spring mechanism after each individual impact in order to load the spring mechanism.

A cross-section of a hand-held power tool is shown diagrammatically in Fig. 2, in which the spring mechanism does not, as in the embodiment of Fig. 1, consist of a compression chamber but in which one or more tension and/or compression springs are used. Apart from the spring mechanism, all other function elements are the same as in the embodiment of Fig. 1 previously disclosed and in Fig. 2 are also provided with the same reference numerals as in Fig. 1.

As Fig. 2 shows, a compression spring 15 is used in the space of the guide tube 2 between the striker 1 and the rear wall 5 of the guide tube and which is supported on the one hand on the rear wall 5 of the guide tube 2 and on the other hand on the striker 1. Alternatively to this compression spring 15, or additionally thereto, a tension spring 16 can also be provided on the side of the striker 1 facing the tool 3. This tension spring is, on the one hand, connected to the striker 1 and, on the other hand, to a shoulder of the guide tube 2. Instead of only one compression spring 15 and/or tension spring 16, a plurality of compression and/or tension springs can also be used which give the striker 1 the required impact force.

Claims

Claims 1. Hand-held power tool - preferably a rotary and/or impact hammer

- with an impact mechanism which comprises a striker (1) which can be axially reciprocated in a guide tube (2), a spring mechanism (4, 15, 16) exerting a force on the striker (1) being present, with which the striker (1) can be displaced in a movement in the direction of a tool (3) which can be inserted in the hand-held power tool, characterized in that means (8, 10, 13, 14) are present which displace the striker (1) after each impact in a movement against the force of the spring mechanism (4, 15, 16), in order to load said spring mechanism, and in that the means (8, 10, 13, 14) abruptly release the striker (1) again after the loading of the spring mechanism (4, 15, 16), so that, driven by the spring mechanism (4, 15, 16), it flies in the direction of the tool (3).
2. Hand-held power tool according to claim 1, characterized in that the means (8, 10, 13, 14) consist of a drive which creates a frictional connection with the striker (1) after an impact is carried out and moves it against the force of the spring mechanism (4, 15, 16) and which again releases the frictional connection as soon as the striker (1) has reached a defined position in its movement against the force of the spring mechanism (4, 15, 16).
3. Hand-held power tool according to claim 1 or 2, characterized in that the spring mechanism (4, 15, 16) consists of a compression chamber (4) filled with a compressible medium and which is located in the guide tube (2) on the side of the striker (1) facing away from the tool (3).
4. Hand-held power tool according to claim 3, characterized in that a compressible medium can be supplied to the compression chamber (4) via a pump (7).
5. Hand-held power tool according to claim 1 or 2, characterized in that the spring mechanism (14, 15) consists of one or more compression springs (15) and/or tension springs (16), which are supported on the one hand on the striker (1) and on the other hand on a rigid shoulder (5, 17) in the direction of movement of the striker.
6. A hand-held power tool substantially as herein described with reference to the accompanying drawings.