MECHANICAL PERCUSSION MECHANISM

Abstract

A mechanical percussion mechanism for a percussion drive of a tool insert in a handheld power tool has a rotatably supported drive shaft, a percussion body connected to the drive shaft in a manner fixed against relative rotation and supported axially movable relative to the drive shaft, a rotatably supported driven shaft connected to the drive shaft in a manner fixed against relative rotation, the percussion body having drive cams and the driven shaft having drive cams, which drive cams of the percussion body and the driven shaft are bringable into operative connection for a percussion drive of the tool insert, and an axial stop provided for the percussion body.

Description

CROSS-REFERENCE TO A RELATED APPLICATION

The invention described and claimed hereinbelow is also described in German Patent Application DE 202006014850.7 filed on Sep. 27, 2006. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119(a)-(d).

BACKGROUND OF THE INVENTION

The invention relates to a mechanical percussion mechanism for a handheld power tool, in particular a rotary percussion screwdriver.

From the prior art, such as German Patent Disclosure DE 10 2004 032 789 A1, rotary percussion screwdrivers with a V-groove rotary percussion mechanism are known. In general, rotary percussion mechanisms convert the continuous power output of the drive motor into a percussionlike rotary pulse, and the energy output of the motor is temporarily stored in a mass and abruptly delivered to the tool insert, such as a drill bit, by means of a pulse of high power intensity. In V-groove rotary percussion mechanisms in particular, the rotary motion is transmitted to a weight mass (rotary percussion weight), and the rotary percussion weight is supported in such a way that an axial motion is possible. The control of the axial motion is done by V-grooves and slaving balls. A spring assures the restoration of the rotary percussion weight.

In practice, it is found that an impact, for instance if the rotary percussion screwdriver is unintentionally dropped, can impart such a strong impetus to the rotary percussion weight that it is displaced axially, counter to the restoring force of the spring, so far on the drive shaft that the slaving balls are set free and fall out of the grooves. After that the percussion mechanism can no longer be actuated, and hence the power tool has to be replaced or repaired.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a mechanical percussion mechanism which avoids the disadvantages of the prior art.

In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a mechanical percussion mechanism for a percussion drive of a tool insert in a handheld power tool, the mechanical percussion mechanism comprising a rotatably supported drive shaft; a percussion body connected to said drive shaft in a manner fixed against relative rotation and supported axially movable relative to said drive shaft; a rotatably supported driven shaft connected to said drive shaft in a manner fixed against relative rotation, said percussion body having drive cams and said driven shaft having drive cams which drive cams or said percussion body and said driven shaft are bringable into operative connection for a percussion drive of the tool insert; and an axial stop provided for said percussion body.

The mechanical percussion mechanism according to the invention has the advantage that even in the event of a strong impact, for instance from unintentional or improper handling, the percussion body will not be excessively deflected axially along the drive shaft. This is particularly advantageous whenever the percussion mechanism, for rotary slaving of rotationally supported components, has freely movable or in other words loose slaving elements, such as slaving balls, which could be set free by a strong axial displacement. The capability of axial motion on the part of the percussion body is limited according to the invention by the provision that the percussion mechanism is provided with an axial stop.

The mechanical percussion mechanism of the invention serves the purpose of percussively driving a tool insert of a handheld power tool, such as a rotary percussion screwdriver. The percussion mechanism includes a rotatably supported drive shaft. It further includes a percussion body, which is connected to the drive shaft in a manner fixed against relative rotation and is supported axially movably relative to the drive shaft. The percussion mechanism furthermore includes a rotatably supported driven shaft, which is connected to the drive shaft in a manner fixed against relative rotation. The percussion body has drive cams, which for the percussive driving of the tool insert can be brought into operative connection with driven cams of the driven shaft. The tool insert, such as a screwdriver bit, is located in a tool receptacle that can be driven by the driven shaft.

The mechanical percussion mechanism is in particular a rotary percussion mechanism, and very particularly a V-groove rotary percussion mechanism. However, the invention, may also be suitable for other mechanical percussion mechanisms, especially other rotary percussion mechanisms.

The percussion body is connected to the drive shaft in a manner fixed against relative rotation, in particular via at least one slaving element. The at least one slaving element is in particular a roller body, preferably a ball. The rotary slaving may be done such that either the percussion body is driven by an electric motor and the rotary motion of the percussion body is transmitted to the drive shaft via slaving elements, or the drive shaft is driven by an electric motor and the rotary motion of the drive shaft is transmitted to the percussion body by means of slaving elements. For instance, in a V-groove rotary percussion mechanism known per se, an electric motor drives a drive shaft, which is connected to the percussion mechanism in a manner fixed against relative rotation via slaving balls. The slaving balls are located in V-grooves in the drive shaft.

The driven shaft of the percussion mechanism of the invention is also supported rotatably, and the driven shaft is connected to the drive shaft in a manner fixed against relative rotation. This can be done for instance directly, by providing that the drive shaft is connected to the driven shaft in a manner fixed against relative rotation, for instance via a form lock. However, the rotary slaving can also be done indirectly, by providing that as in the V-groove rotary percussion mechanism, the percussion body driven by the drive shaft transmits the rotary motion to the driven shaft. This is done via the drive cam of the percussion body and the driven cams of the driven shaft. To that end, the restoring force of a compression spring presses the percussion body in the direction of the driven shaft, so that the driven cams act as slaving elements.

For the percussive drive of the tool insert, the percussion body is additionally supported axially movably on the drive shaft. A restoring element, preferably a compression spring, for instance in the form of a helical spring, is also provided, which keeps the percussion body prestressed. Depending on the construction of the mechanical percussion mechanism, the percussion body may be prestressed either in the direction of the driven shaft or in the direction of the drive motor. For instance, in a V-groove rotary percussion mechanism known per se, the percussion body is prestressed in the direction of the driven shaft by a helical spring, as a restoring element.

The drive end of the helical spring is located for instance on the housing of the drive motor or the end plate of a bearing for the drive shaft. The mode of operation of a mechanical percussion mechanism, and in particular how the drive cams can be operatively connected to the driven cams of the drive shaft for the percussive drive of a tool insert by means of a longitudinal motion of the percussion body so that energy can be transmitted via the drive cams to the driven cams, is familiar to one skilled in the art and will therefore not be described in detail here.

In a preferred embodiment, the stop is embodied as a spring element. The spring element is preferably formed from an elastic material, in particular an elastomer, such as rubber or soft foam. However, the spring element may also be a spring, such as a helical spring or cup spring, of metal or plastic. A spring element as a stop has the advantage that the axial motion of the percussion body is not merely limited by the stop but also damped.

The stop is also preferably embodied annularly or in disklike form. In particular, the stop is displaced annularly or in disklike form around the drive shaft. The annular or disklike stop is then preferably supported on the drive shaft. For instance, it may be slipped onto the drive shaft and optionally glued there.

Because of the annular or disklike embodiment of the stop, particularly as an annular or disklike spring element, the largest possible area of the percussion body comes into contact with the stop when the percussion body meets the stop, and thus the stop can damp the axial motion especially well.

In an embodiment of the mechanical percussion mechanism of the invention in which the percussion body is prestressed in the direction of the driven shaft via a restoring element, the axial stop prevents excessive axial deflection of the percussion body in the direction of the drive motor. Accordingly, in this embodiment, the stop is located in the region of the drive end of the drive shaft. In the alternative embodiment in which the percussion body is prestressed in the direction of the drive motor, the axial stop prevents an excessive deflection of the percussion body in the direction of the driven shaft. For that purpose, the stop is located in the region of the driven end of the drive shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the drive train of a handheld power tool in accordance with the present invention, with a mechanical rotary percussion mechanism, in an exploded view; and

FIG. 2 is a cross section through the mechanical rotary percussion mechanism of FIG. 1 in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the exploded view of FIG. 1, the drive train of a rotary percussion screwdriver is shown, with a mechanical percussion mechanism 50. Hereinafter, only the essential components will be discussed.

An electric motor 10 (shown schematically) includes an armature shaft 12, on which a gear wheel, serving as a drive pinion 31, is located, in a manner fixed against relative rotation. The drive pinion 31 forms one part of a two-stage planetary gear 30 and drives planet wheels 32 with the first gear stage. The planet wheels 32 roll inside a ring gear 36. As a result, a first sun wheel 33 is rotated, which in turn, via a set of teeth 34, drives further planet wheels 35 of the second gear stage. The planet wheels 35 roll inside the ring gear 36 and drive a second sun wheel 37. The second sun wheel 37 is connected to the drive shaft 51 of the mechanical percussion mechanism 50 in a manner fixed against relative rotation.

To that end, in FIG. 1, the sun wheel 37 is embodied in the form of pins in one piece with the drive shaft 51. The drive shaft 51 is supported, on its end toward the gear, in a bearing 52, preferably a roller bearing, in particular a deep-groove ball bearing. The two-stage planetary gear 30, the bearing 52, and part of the drive shaft 51 are received in a separate housing 20 of plastic. On the gear end, the housing 20 is provided with a cap, also of plastic, as a cover element 22. The cover element 22 has a central opening 23 for receiving the armature shaft 12. On the diametrically opposed end, the bearing end, of the housing 20, the drive shaft 51 protrudes out of the housing 20.

The mechanical percussion mechanism 50 of FIG. 1 is a V-groove rotary percussion mechanism. It includes a rotatably supported drive shaft 51 with slaving elements 57 in the form of slaving balls in a V-groove 58. Via the slaving elements 57, a percussion body 56 is connected to the drive shaft 51 in a manner fixed against relative rotation, so that the drive shaft 51, driven by the electric motor 10 via the planetary gear 30, sets the percussion body into rotary motion. Simultaneously, the percussion body 56 is axially movably supported on the drive shaft 51. The percussion body 56 has drive cams 53. Via the percussion body 56 with the drive cams 53, a rotatably supported driven shaft 59 is connected to the drive shaft 51 in a manner fixed against relative rotation via driven cams 54.

In nonpercussive driving, the percussion body 56 is prestressed in the direction of the driven shaft 59 via a compression spring 55. Then the drive cams 53 engage the driven cams 54 in such a way that the rotary motion of the percussion body 56 is transmitted to the driven shaft 59. The driven shaft 59 is likewise supported in a bearing 61. A shim 24 serves to receive and fix the compression spring 55 and also to protect the housing 20 against heating and wear from the friction of the compression spring 55. For receiving a tool insert (not shown), the driven shaft 59 is connected to a tool receptacle 62. The percussion mechanism 50 is received in a housing part 63, preferably of metal. A housing screen 64 of an elastic plastic covers at least some of the housing part 63.

The mode of operation of a V-groove rotary percussion mechanism will not be discussed in detail here, since it is familiar enough to one skilled in the art. As to the mode of operation, it will merely be indicated that by means of a screw (not shown) contacting a workpiece, the torque demand increases abruptly, and the rotary motion of the driven shaft 59 is blocked. The percussion body 56 driven by the drive shaft 51 continues to rotate and is pressed by the slaving elements 57 in the V-shaped grooves 58 in the direction of the drive end of the drive shaft 51, counter to the restoring force of the compression spring 55. In the process, the drive cams 53 of the percussion body 56 meet the driven cams 54 of the driven shaft 59, and the energy of the percussion body 56, stored as a result of the rotation, is therefore transmitted to the driven shaft 59. As a result of this longitudinal motion, the drive cams 53 slip farther on the driven cams 54 and slide past them.

For the sake of greater simplicity, the mechanical percussion mechanism 50 is shown in FIG. 1 without a stop. However, in the cross section of FIG. 2 an axial stop 70 can be seen clearly. In the embodiment of FIG. 2, the axial stop 70 is formed by an annular or disklike spring element made from an elastomer. The diameter of the disklike elastomer spring element is less than the diameter of the compression spring 55, and thus the stop 70 can be located inside the compression spring 55. The stop 70 is supported on the drive shaft 51 in a manner fixed against relative rotation and rests on the shim 24. As a result, the maximum axial deflection of the percussion body 56 on the drive shaft 51 counter to the compression force of the compression spring 55 is limited in the direction of the drive end of the drive shaft 51.

Without an axial stop 70, the percussion body 56 could be moved still farther axially in the direction of the drive end of the drive shaft 51, so that the slaving elements 57 could be set free and fall out of the V-grooves 58.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the type described above.

While the invention has been illustrated and described as embodied in a mechanical percussion mechanism, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.

Claims

1. A mechanical percussion mechanism for a percussion drive of a tool insert in a handheld power tool, the mechanical percussion mechanism comprising a rotatably supported drive shaft; a percussion body connected to said drive shaft in a manner fixed against relative rotation and supported axially movable relative to said drive shaft; a rotatably supported driven shaft connected to said drive shaft in a manner fixed against relative rotation, said percussion body having drive cams and said driven shaft having drive cams, which drive cams on said percussion body and said driven shaft are bringable into operative connection for a percussion drive of the tool insert; and an axial stop provided for said percussion body.

2. A mechanical percussion mechanism as defined in claim 1, wherein said stop for said percussion body is configured as a spring element.

3. A mechanical percussion mechanism as defined in claim 1, wherein said stop for said percussion body is composed of an elastic material.

4. A mechanical percussion mechanism as defined in claim 3, wherein said stop for said percussion body is composed of an elastomer.

5. A mechanical percussion mechanism as defined in claim 1, wherein said stop for said percussion body is configured as an annular stop.

6. A mechanical percussion mechanism as defined in claim 5, wherein said annular stop is supported on said drive shaft.

7. A mechanical percussion mechanism as defined in claim 1, wherein said percussion body is connected to said drive shaft in a manner fixed against relative rotation via at least one slaving element.

8. A mechanical percussion mechanism as defined in claim 7, wherein said at least slaving element is configured as a roller body.

9. A mechanical percussion mechanism as defined in claim 8, wherein said at least one slaving element is configured as a ball.

10. A handheld power tool, comprising a tool insert which is percussively driven; and a mechanical percussion mechanism for a percussive drive of said tool insert, said mechanical percussion mechanism including a rotatably supported drive shaft, a percussion body connected to said drive shaft in a manner fixed against relative rotation and supported axially movable relative to said drive shaft, a rotatably supported driven shaft connected to said drive shaft in a manner fixed against relative rotation, said percussion body having drive cams and said driven shaft having drive cams, which drive cams of said percussion body and said driven shaft are bringable into operative connection for the percussion drive of said tool insert, and an axial stop provided for said percussion body.