GB2458523A

GB2458523A - Portable machine tool with device for holding striker in idling position

Info

Publication number: GB2458523A
Application number: GB0900936A
Authority: GB
Inventors: Harald Schindler; Andreas Riedel
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2008-03-18
Filing date: 2009-01-20
Publication date: 2009-09-23
Anticipated expiration: 2029-01-20
Also published as: CN101537511A; DE102008000727A1; GB2458523B; GB0900936D0

Abstract

A portable machine tool, such as a rotary and/or percussion hammer, comprises a percussion mechanism that has an axially movable striker 4 driven via an air spring, and an axially movable percussion pin 8. The percussion pin is arranged between the striker and a tool 12 to transmit percussive impulses of the striker to the tool when the tool is pressed against an abutment, and has a device 70 for positioning and holding the striker in a defined idling position when the machine tool is idling. The device for positioning and holding the striker comprises means for frictionally and/or positively fixing the striker in the idling position; and/or for braking the movement of the striker-before the idling position is reached. Preferably, the device for positioning and holding the striker comprises at least an arresting and/or damping element (74, fig 3), which comes into engagement with the striker in the idling position. The arresting and/or damping element may project through a wall opening in a striker guide 6, in order to come into frictional engagement with the striker.

Description

Description Title

Portable machine tool, in particular rotary or percussion hammer, having a striker-catching device and/or striker-damping device The invention relates to a portable machine tool according to the precharacterising clause of Claims 1 and 2, in particular a rotary or percussion hammer.

Prior art

Conventional rotary or percussion hammers have a percussion mechanism with a striker which is driven via an air spring and moves to and fro in a striker guide in percussive operation, and as it does so impacts with great energy on a striking pin or plunger arranged between the striker and the tool, in order to transmit via the striking pin or plunger a percussive impulse to a drilling or chiselling tool inserted in a tool holder of the rotary or percussion hammer and from this tool on to a workpiece to be worked on, such as for example masonry. In percussive operation, the tool is held in a working position by a pressing force applied to the rotary or percussion hammer by the operator, and in this position is pressed against the workpiece by its front end, while its rear end projects into the movement path of the striking pin. When the rotary or percussion hammer is withdrawn or when the tool encounters no more resistance, for example after breaking through the workpiece, the tool moves out of contact with the striking pin. This state is referred to as idling to distinguish it -2 from the percussive operation, since no further percussive impulses are transmitted to the tool by the striking pin.

On idling, the striker is to be brought quickly and reliably into a defined idling position, in order to avoid a further to-and-fro movement of the striker, since, owing to so-called idle strokes, this may on the one hand lead to damage to the rotary or percussion hammer due to overloading and on the other hand is felt to be of poor quality by many operators. In order to avoid idle strokes, conventional rotary or percussion hammers have a device usually referred to as an idling control, with the aid of which the striker can be positioned and held in the idling position on idling. The basic principle of such an idling control consists in moving the striker forwards in the striker guide beyond its striking position in percussive operation, i.e. in the direction of the tool, until it frees idling bores in the striker guide, through which bores air can enter the interior of the striker guide behind the striker from the environment. As a result, the air spring situated there loses the ability to suck in the striker. Variants of idling controls are known as striker, tube or sleeve controls.

Experience has shown, however, that merely introducing idling bores into the striker guide is not always sufficient to position and hold the striker in the idling position so that it can no longer be sucked in by the air spring. The reason for this is that the striker may be accelerated rearwards by the impact on the striking pin or a damping device serving for damping the movement of the striker and provided in the striker guide, so that it moves back beyond the idling bores again. As a result, the striker is once again sucked in, leading to the idle strokes which are damaging to the rotary or percussion hammer and regarded as being of poor quality, as described above.

With this as the starting point, the object on which the invention is based is to improve a machine tool of the type mentioned at the outset such that it reliably prevents sucking-in of the striker on idling of the machine tool and/or reduces the kinetic energy of the striker before the impact on the striking pin or the damping device, in order thereby to avoid a rebound of the striker beyond the idling position.

Disclosure of the invention

This object is achieved according to a first variant of the invention in that the device for positioning and holding the striker comprises means for frictionally and/or positively fixing the striker in the idling position.

This variant of the invention is based on the idea of mechanically arresting the striker in the idling position on idling by the frictional and/or positive fixing, so that it is firmly held in the idling position in the event of a rearward acceleration and cannot move beyond this position rearwards in the sucking-in direction. The solution according to the inventièn can be implemented in both rotary and percussion hammers. In addition, the mounting or the demounting of the means for frictionally and/or positively fixing the striker in the idling position is relatively simple to accomplish. Last but not least, these means can also be adapted without difficulty such that on a renewed transition from idling to percussive operation a desired start-up behaviour of the striker can be ensured.

A second variant of the invention provides that a device for positioning and holding the striker comprises means for braking the movement of the striker before the idling position is reached. This variant of the invention is based on the idea of braking the forward movement of the striker before the idling position is reached, in order thereby to damp the impact of the striker on the striking pin and thereby to reduce the impact energy and thus also the rebound energy of the striker. The means for braking the movement of the striker before the idling position is reached are preferably formed by the same means which are also used for frictionally and/or positively fixing the striker in the idling position.

Other refinements of a hand tool according to the invention comprise an axially movable striking pin arranged between the striker and a tool. As a result, a greater flexibility in the design of a powerful percussion mechanism is achieved.

According to a preferred refinement of the invention, the means for frictionally and/or positively fixing the striker in the idling position and/or for braking the movement of the striker before the idling position is reached are arranged in the longitudinal direction of a striker guide guiding the striker in such a manner that they do not come into contact or engagement with the striker in percussive operation.

A further preferred refinement of the invention provides that the means for frictionally and/or positively fixing the striker and/or for braking the movement of the striker comprise at least one arresting and/or damping element which preferably projects into the interior of the striker guide and comes into engagement frictionally and/or positively with the striker. While it is, in principle, sufficient to provide a single arresting and/or damping element, preferably a plurality of arresting and/or damping elements are used, which come into engagement, at equal angular spacings from one another, with a circumferential surface of the striker in order to centre the striker in the striker guide.

Preferably, the means for frictionally and/or positively fixing the striker and/or for braking the movement of the striker further comprise an elastically deformable spring element which is expediently unloaded in percussive operation, while it is elastically deformed on idling by the frictional and/or positive engagement of the striker with the arresting and/or damping element(s), ensuring through its elastic restoring force that the arresting and/or damping element(s) is or are pressed against the striker.

Advantageously, the at least one arresting and/or damping element extends through a wall opening of the striker guide into the interior of the striker guide, where it expediently comes into engagement by a preferably rounded inner end with the striker in order to firmly hold or brake the latter, while the spring element is advantageously -6 arranged on the outside of the striker guide and acts on the at least one arresting and/or damping element in order to press the inner end of said element against the striker within the striker guide.

The arresting and/or damping element(s) and the spring element, expediently designed as an open or closed spring ring, may be provided in the form of separate components or as an integrated component.

Where a positive engagement is provided between the at least one arresting and/or damping element and the striker, this is expediently achieved in that the or each arresting and/or damping element engages, in the idling position, in an opposite catching indentation of the striker, which is preferably designed as a groove running all the way round on the striker.

Since sucking-in of the striker by the air spring can be prevented by the mechanical fixing of the striker in the idling position, it would be possible, in principle, to dispense with an additional idling control. However, a preferred refinement of the invention provides that besides the mechanical fixing there is also an idling control present as well, which comprises an idling opening communicating with the air spring in the idling position of the striker.

Brief description of the drawings

The invention is explained in more detail below with the aid of some exemplary embodiments illustrated in the drawing, in which: Fig. 1 shows a longitudinal sectional view of parts of a rotary or percussion hammer in percussive operation; Fig. 2 shows a longitudinal sectional view corresponding to Fig. 1, but on idling of the rotary or percussion hammer; Fig. 3 shows an enlarged view of the detail III from Fig. 2, showing a striker-catching device for the mechanical fixing of the striker in an idling position; Fig. 4 shows a cross-sectional view along the line 1V-IV of Fig. 3; Fig. 5 shows a view similar to Fig. 3, but with a different striker-catching device; Fig. 6 shows a cross-sectional view along the line VI-VI of Fig. 5; Fig. 7 shows a view similar to Figs. 3 and 5, but with yet another striker-catching device; Fig. 8 shows a cross-sectional view along the line VIII-VIII of Fig. 7.

Embodiments of the invention The rotary or percussion hammer, only partially illustrated in the drawing, comprises an elongated hammer tube 2, which has a rear section 6 with a large inside diameter serving as a guide for a striker 4 of a percussion mechanism (not illustrated) of the rotary or percussion hammer, a middle section 10 with a somewhat smaller inside diameter serving as a guide for a striking pin 8 or plunger of the percussion mechanism, and a front section 14 with an inside diameter somewhat smaller still serving as a tool holder for a drilling or chiselling tool 12. The striker 4, the striking pin 8 and the drilling or chiselling tool 12 are each dimensioned such that they are guided axially movably within the associated section 6, 10 and 14, respectively, of the hammer tube 2.

As is best illustrated in Figures 3 to 8, the striker 4 has an outer cylindrical circumferential surface 16, the outside diameter of which is matched to the inside diameter of the rear section 6 of the hammer tube 2. In the circumferential surface 16, a plurality of circumferential grooves 18, 20, 22 arranged axially spaced apart from one another can be made, one 22 of which serves for receiving an 0-ring seal 24 which bears sealingly against an adjacent cylindrical inner surface 26 of the section 6. The front end 28 of the striker 4 adjacent to the striking pin B is tapered.

When the drilling or chiselling tool 12 is pressed by the operator against an abutment, such as for example masonry or a workpiece, in percussive operation of the rotary or -9 percussion hammer, i.e. with the percussion mechanism switched on, the striker 4 is moved forwards and backwards within the section 6 of the hammer tube 2. The movement of the striker 4 is produced by means of an excitation piston (not illustrated) of the percussion mechanism, which piston is moved axially in a reciprocating manner by an electric drive motor (not illustrated) of the rotary or percussion hammer. The axial reciprocating movement of the excitation piston is transmitted to the striker 4 via an air spring (not illustrated) *arranged between the excitation piston and the striker 4 in the hammer tube 2. In other words, pressure fluctuations are produced in the air spring by the axial reciprocating movement of the excitation piston and lead to a corresponding axial forward and backward movement of the striker 4.

The striking pin 8 has a widened middle part 30 which is guided in the middle section 10 of the hammer tube 2 and from which there protrudes forwards and rearwards in each case a cylindrical end part 32, 34 with a smaller outside diameter. The middle part 30 has in its cylindrical circumferential surface 36 two grooves 38, 40 running all the way round, in each of which an 0-ring seal 42, 44 is inserted. Situated between the middle part 30 and the end part 32 adjacent to the drilling or chiselling tool 12 is a conically tapered idling shoulder 46, which bears against a complementary annular shoulder 48 between the middle section 10 and the front section 14 of the hanner tube 2 on idling of the rotary and percussion hammer. The cylindrical rear end part 34 of the striking pin 8 projects into the rear section 6 of the hammer tube 2, where its free end lies opposite the tapered front end 28 of the striker 4.

For the damping of the axial movement of the striking pin 8, a damping device 50 is inserted fixedly in the front end of the rear section 6 of the hammer tube 2. The damping device 50 is composed of a plurality of damping rings 52, 54, 56, 58 made of an elastomeric material which are arranged one behind the other in the axial direction in the hammer tube 2 and which are firmly held by a retaining ring 60. The damping device 50 has the task of damping the rebound of the striking pin 8 when the latter reaches its rear end position, in which a rearwardly facing rebound shoulder 62 on the middle part 30 of the striking pin 8 strikes the frontmost damping ring 52. The cylindrical rear end part 34 of the striking pin 8 extends through an opening 64 surrounded by the damping rings 52, 54, 56, 58.

The drilling or chiselling tool 12 has a rear shank part 66, which is guided axially movably in the front section 14 of the hammer tube 2. When the tool 12 is pressed by the operator against the abutment in percussive operation, it is displaced by the pressing force into a rear end position, in which it projects by its rear end a little way into the middle section 10 of the hammer tube 4 and bears by its rear end against the adjacent front end of the striking pin 8, as illustrated in Fig. 1. When the striker 4 then impacts on the striking pin 8, the percussive impulse is transmitted by the striking pin 8 into the drilling or chiselling tool 12.

On idling of the rotary or percussion hammer, i.e. when the rotary or percussion hammer is withdrawn by the operator or when the drilling or percussion tool 12 encounters no more resistance, the striker 4, the striking pin 8 and the tool 12 are each moved into a front end position by the pressure of the air spring. As illustrated in Fig. 2, the rear end of the drilling or chiselling tool 12 is, in this position, no longer in contact with the striking pin 8, which bears by its front idling shoulder 46 against the complementary annular shoulder 48 between the front section 14 and the middle section 10 of the hammer tube 2. The striker 4 is idling in its defined idling position, in which it bears by a forwardly facing shoulder 49 against the rearmost damping ring 58 of the damping device 50.

In this position, no further percussive impulse is to be exerted on the striking pin 8 by the striker 4, since this may cause damage to the rotary or percussion hammer on the one hand and may be felt by the operator to be of poor quality on the other hand.

For this purpose, as is known, the rotary or percussion hammer has a so-called idling control which, in the embodiment illustrated in the drawing, comprises a plurality of idling bores 68 in the hammer tube 2, by which the interior of the hammer tube 2 communicates with the environment. The axial position of these idling bores 68 in the hammer tube 2 is chosen such that in the idling position of the striker 4 they are always situated behind the 0-ring seal 24, as illustrated in Fig. 2, while in percussive operation they are always arranged in front of the 0-ring seal 24, as illustrated in Fig. 1. Unlike in percussive operation, the air spring thus communicates in the idling position of the striker 4 with the idling bores 68, whereby the pressure fluctuations in the air spring are reduced. This in turn has the result that the air spring loses its ability to suck in the striker 4, whereby the latter no longer moves to and fro even with the percussion mechanism switched on.

However, experience has shown that the striker 4 when moving into the idling position may, owing to an impact on the striking pin 8 or the damping device 50, undergo a rearwardly directed acceleration which is sufficiently large to move the 0-ring seal 24 rearwards beyond the idling bores 68 again. Since this results in renewed sucking-in of the striker 4 and thus undesired idle strokes, the rotary or percussion hammer illustrated has, besides the idling control, a striker-catching device and/or striker-damping device 70. The striker-catching device and/or striker-damping device 70 serves, on the one hand, to catch and firmly hold the striker 4 in the idling position illustrated in Fig. 2 by mechanical action, so that it can no longer move rearwards out of the idling position despite the rebound forces exerted on it by the striking pin 8, but, on the other hand, also has the effect that the forward movement of the striker is braked before the idling position is reached, in order thereby to damp its impact on the striking pin and thus also reduce the rebound forces exerted on it by the striking pin.

In the embodiment illustrated in Figures 1 to 4, the striker-catching device and/or striker-damping device 70 comprises a spring ring 72 surrounding the hammer tube 2 on the outside thereof in the circumferential direction, on the inner circumference of which spring ring there are formed four cylindrical projections 74 which protrude radially inwards at preferably equal angular spacings and each project through a complementary bore 76 in the section 6 of the hammer tube 2 into the interior of the same. The axial position of the spring ring 72 along the hammer tube 2 is chosen such that the projections 74 protrude inwards into the interior of the hammer tube 2 without contact with the striker 4 in percussive operation of the rotary and percussion hammer, as illustrated in Fig. 1, but move during the forward movement of the striker 4 into its idling position by way of a cylindrical circumferential surface 78 of the striker 4. As is best illustrated in Fig. 4, the outside diameter of the circumferential surface 78 is greater than the distance between the rounded ends 80 of the projections 74 lying diametrically opposite each other in pairs, whereby the projections 74 are, on the one hand, pushed radially outwards by the striker 4 with elastic widening of the previously unloaded spring ring 72, while, on the other hand, they are pressed by their rounded inner ends 75 against the circumferential surface 78 of the striker 4 owing to the elastic restoring forces of the widened spring ring 72. This has the effect that the striker 4 is firstly braked by the frictional engagement with the projections 74 of the striker-catching device and/or striker-damping device 70 and then arrested or firmly held in the idling position.

In the case of the striker-catching device and/or striker-damping device 70 in Figures 5 and 6, the hammer tube 2 has two diametrically opposite conical openings 82 instead of four cylindrical bores 76, in each of which openings a steel ball 84 is inserted such that it projects a little way inwards into the interior of the hammer tube 2. The two -14 steel balls 84 are pushed inwards by a ring spring 86 which is under spring pretension, is placed around the outside of the hammer tube 2 and is of C-shaped cross-section (Fig. 6). In order to fix the ring spring 86 in the circumferential direction, it has two protrusions 88 for receiving the steel balls 84, which, just like the steel balls 84, are arranged at an angular spacing of preferably degrees. In this embodiment, the striker 4 is provided in the cylindrical circumferential surface 78 with a shallow recessed catching or circumferential groove 90 which lies preferably exactly opposite the steel balls 84 in the idling position, so that the steel balls 84 come into engagement not only frictionally but also positively with the striker 4.

In the case of the striker-catching device and/or striker-damping device 70 in Figures 7 and 8, there is provided only a single cylindrical pin 92 which projects through an associated bore 94 in the section 6 of the hammer tube 2 into the interior of the same, where its rounded inner end 96 is pushed by a spiral-shaped spring ring 98 surrounding the hammer tube 2 into frictional and positive engagement with a catching or circumferential groove 100 of the striker 4, which groove lies opposite the pin 92 in the idling position of the striker 4. The pin 92 has a widened outer end 102 which is provided with an opening 104 for receiving the spring ring 98 of circular cross-section.

Like the spring rings 72 and 86 of the striker-catching devices and/or striker-damping devices 70 from Figures 1 to 6, the spring ring 98 of the striker-catching device and/or striker-damping device 70 in Figures 7 and 8 is also elastically widened when the striker 4 moves forwards into -15 the idling position and the pin 92 comes into engagement frictionally and positively with the catching or circumferential groove 100.

When the drilling or chiselling tool 12 is once again pressed by the operator against an abutment in the idling position illustrated in Fig. 2, it is displaced rearwards within the tool holder 14, whereby the striking pin 8 is also displaced rearwards in the middle section 10 of the hammer tube 2. The displacement of the striking pin 8 in turn leads to the frictional and/or positive engagement between the striker 4 and the striker-catching device and/or striker-damping device 70 being released and the striker 4 itself being displaced so far rearwards until the 0-ring seal 24 is again situated behind the idling bores 68. With the percussion mechanism switched on, this results in the rotary and percussion hammer resuming the percussive operation.

Claims

Claims 1. Portable machine tool, in particular rotary and/or percussion hammer, having a percussion mechanism comprising an axially movable striker driven via an air spring, whereby percussive impulses of the striker are transmitted to the tool when the tool is pressed against an abutment in a percussive operation of the machine tool, and having a device for positioning and holding the striker in a defined idling position when the machine tool is idling, wherein the device for positioning and holding the striker (4) comprises means (70) for frictionally and/or positively fixing the striker (4) in the idling position.
2. Portable machine tool, in particular rotary and/or percussion hammer, having a percussion mechanism comprising an axially movable striker driven via an air spring, whereby percussive impulses of the striker are transmitted to the tool when the tool is pressed against an abutment in a percussive operation of the machine tool, and having a device for positioning and holding the striker in a defined idling position when the machine tool is idling, in particular according to Claim 1, wherein the device for positioning and holding the striker (4) comprises means (70) for braking the movement of the striker (4) before the idling position is reached.
3. Machine tool according to Claim 1 or 2, wherein the percussion mechanism further comprises an axially movable striking pin arranged between the striker and a tool.
4. Machine tool according to one of Claims 1 to 3, wherein the means (70) comprise at least one arresting and/or damping element (74, 84, 92) which comes into engagement with the striker (4) in the idling position or before the idling position is reached.
5. Machine tool according to Claim 4, wherein the arresting and/or damping element (74, 84, 92) projects into the interior of a striker guide (2, 6) and comes into engagement frictionally and/or positively with the striker (4).
6. Machine tool according to Claim 5, wherein the arresting and/or damping element (74, 84, 92) projects from outside through a wall opening (76, 82, 94) of the striker guide (2, 6) into the interior of the same.
7. Machine tool according to Claim 5 or 6, wherein the arresting and/or damping element (74, 84, 92) is radially movable in relation to the striker guide (2, 6).
8. Machine tool according to one of Claims 2 to 7, wherein the arresting and/or damping element (84, 92) engages, in the idling position, in an opposite catching indentation (90, 100) of the striker (4).
9. Machine tool according to Claim 8, wherein the catching indentation is a groove (90, 100) running all the way round on the striker (4).
10. Machine tool according to one of the preceding claims, wherein the means (70) comprise at least one elastically deformable spring element (72, 86, 98).
11. Machine tool according to Claim 10, wherein the spring element (72, 86, 98) is arranged outside the striker guide (2, 6).
12. Machine tool according to Claim 10 or 11, wherein the spring element (72, 86, 98) at least partly surrounds the striker guide (2, 6) on the outside thereof.
13. Machine tool according to one of the preceding claims, wherein the means (70) for frictionally and/or positively fixing the striker (4) and/or for braking the movement of the striker (4) before the idling position is reached do not come into contact with the striker (4) in percussive operation.
14. Machine tool according to one of the preceding claims, wherein the device (68, 70) for positioning and holding the striker (4) further comprises at least one idling opening (68) communicating with the air spring in the idling position of the striker (4).
15. A portable machine tool substantially as herein described with reference to the accompanying drawings.