U.S. patent application number 11/741285 was filed with the patent office on 2008-03-27 for mechanical percussion mechanism.
Invention is credited to Siew Yuen Lee, Manfred Lutz, Chin Aun Ng, Sim Teik Yeoh.
Application Number | 20080073092 11/741285 |
Document ID | / |
Family ID | 37514130 |
Filed Date | 2008-03-27 |
United States Patent
Application |
20080073092 |
Kind Code |
A1 |
Yeoh; Sim Teik ; et
al. |
March 27, 2008 |
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.
Inventors: |
Yeoh; Sim Teik;
(Butterworth, MY) ; Lee; Siew Yuen; (Penang,
MY) ; Lutz; Manfred; (Filderstadt, DE) ; Ng;
Chin Aun; (Penang, MY) |
Correspondence
Address: |
Striker, Striker & Stenby
103 East Neck Road
Huntington
NY
11743
US
|
Family ID: |
37514130 |
Appl. No.: |
11/741285 |
Filed: |
April 27, 2007 |
Current U.S.
Class: |
173/48 |
Current CPC
Class: |
B25B 21/02 20130101;
B25D 11/08 20130101 |
Class at
Publication: |
173/48 |
International
Class: |
E02D 7/02 20060101
E02D007/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 27, 2006 |
DE |
202006014850.7 |
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.
Description
CROSS-REFERENCE TO A RELATED APPLICATION
[0001] 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
[0002] The invention relates to a mechanical percussion mechanism
for a handheld power tool, in particular a rotary percussion
screwdriver.
[0003] 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.
[0004] 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
[0005] It is therefore an object of the present invention to
provide a mechanical percussion mechanism which avoids the
disadvantages of the prior art.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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
[0018] 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
[0019] 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
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
* * * * *