Hand power tool

A hand power tool has a machine housing, a drive motor accommodated in the machine housing, a drive train connected with the drive motor and provided with a tool receptacle for rotation of a tool insertable in the tool receptacle, a detecting device for detecting an uncontrolled operation of the hand power tool by detecting a blocking of the tool in a workpiece with a resulting impact-like turning of the machine housing, a blocking device provided for the drive train and releasable by the detecting device, the locking device having a locking toothing arranged in the drive train and a blocking member movably supported in the machine housing and form-lockingly engagable in the locking toothing so as to non-rotatably fix the drive train relative to the machine housing, the detecting device being formed so that it produces an electrical release signal in an uncontrolled operation, the blocking device being releasable by the electrical release signal, and further has electromagnet device actuatable by the release signal so that the locking member is engagable by the electromagnet device into the locking toothing.

BACKGROUND OF THE INVENTION 
The present invention relates generally to hand power tools. 
More particularly, it relates to a hand power tool which has a machine 
housing, a drive motor arranged in the housing, a drive strand connecting 
the drive motor with a tool receptacle for rotation of a tool inserted in 
the tool receptacle, and a detection device for detecting an uncontrolled 
operation of the hand power tool. 
Hand power tools of the above mentioned general type are known in the art. 
One of such hand power tools is disclosed in the German patent document DE 
43 00 021 A1. The drive spindle in this hand power tool is blocked in an 
impact-like manner when the machine housing unintentionally starts to 
rotate. For releasing the blocking process, a mass member guided 
displaceably in the machine housing is provided. In the case of blocking, 
it releases a locking member for engagement in a toothing of the drive 
spindle. This solution has the disadvantage that the mass member always 
causes vibrations as a result of the operation, and moreover gravitation 
action is caused by the operation, so that in an unfavorable operational 
positions, only a relatively inaccurate and late release of the blocking 
device is possible. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a hand 
power tool, 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 hand machine tool in which the detection device for detecting an 
electrical release signal in uncontrolled blocking case is formed so that 
the blocking device is releasable by an electrical release signal and the 
locking member is engageable directly or indirectly into the locking 
toothing by an electromagnet actuated by the release signal. 
When the hand power tool is designed in accordance with the present 
invention, it has the advantage that an almost delay-free blocking release 
which is free from undesirable influences is guaranteed. 
The novel features which are considered as characteristic for the present 
invention are set forth in particular in the appended claims. The 
invention itself, however, both as to its construction and its method of 
operation, together with additional objects and advantages thereof, will 
be best understood from the following description of specific embodiments 
when read in connection with the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 is a view showing a hand power tool which in this embodiment is a 
drilling implement 10. The drilling implement 10 has an electric drive 
motor 11 arranged in a machine housing 12. The drive motor 11 has a motor 
shaft 16 rotatable about a motor axis 21. A handle 13 and an auxiliary 
handle 14 are provided on the machine housing 2. 
A drive moment taken from the drive motor 11 is transmitted by a pinion 17 
seating on the motor shaft 16 to a toothed gear, and then transmitted from 
it through an overloading coupling 19 to an intermediate shaft 20. The 
intermediate shaft 20 located substantially parallel to the motor axis 21 
is in a transmission connection with a drilling spindle 23 through a bevel 
gear transmission 22. The drilling spindle 23 is provided at a side with a 
tool receptacle 26 for a drilling tool 27 which operates for machining of 
a work piece 28. The motor shaft 16, pinion 17, toothed gear 18, 
overloading coupling 19, intermediate shaft 20 and drilling spindle 23 
together form a drive train for rotatably driving the tool receptacle 26 
or the tool 27 received in it. The machine housing 12 and the drilling 
spindle 23 can additionally receive a not shown impact mechanism, so that 
the drilling implement 10 can be also used as an impact drilling machine 
or a drill hammer. 
A blocking device 30 for the drive train of the drilling tool 10 is 
arranged in the machine housing 12. The blocking device 30 has a locking 
member 31 which is axially guided relative to the machine housing 12. The 
locking member 31 is provided at one side with a locking tooth 33 which 
can engage in a corresponding locking toothing 32 in the intermediate 
shaft 20. The locking member 31 is displaced by a spring 34 in direction 
to the locking toothing 32. 
A locking pin 38 which is displaceable substantially perpendicularly to the 
displacement direction of the locking member 31 engages behind a shoulder 
projection 39 on the locking member 31 and serves as an abutment for the 
locking member 31. Therefore, the locking tooth 33 remains out of the 
engagement of the locking toothing 32. The locking pin 38 is provided with 
a cylindrical expansion 37 which forms an armature 40 of an electromagnet 
41. 
In operation of the drilling implement 10, the operator holds it by the 
handle 13 or in some cases also additionally by the auxiliary handle 14. 
The operator must therefore counteract a torque which engages the tool 27 
and acts around the drilling spindle axis 44. When during the operation 
the tool 27 is fixed in the workpiece 28, the drilling implement 10 
obtains an impact-like acceleration around the drilling spindle axis 44. 
Thereby the drilling implement 10 can jump from the hand of the operator 
and cause injuries to people or damages to the drilling implement 10. 
Such an uncontrolled blocking case is detected by a sensor 46. The sensor 
46 is formed for example as an acceleration pick-up. The signal produced 
by the sensor 46 is monitored in an evaluating device 47. When a 
predetermined threshold value is exceeded, the evaluating device 47 
activates the electromagnet 41, and its armature 40 is pulled against the 
spring force 42. The locking pin 38 is pressed out of the shoulder 
projection 39 and releases the locking member 31 for engagement into the 
locking toothing 32. 
With the form-locking engagement of the locking tooth 33 in the locking 
toothing 32, the drive train is blocked in an impact-like way relative to 
the machine housing 12. Simultaneously, the drive motor 11 can be turned 
off via a motor control 48. In this case an excessive drive moment can be 
reduced by the overloading coupling 19 which can be formed as a separating 
coupling. 
The blocking device 30 is shown in FIG. 2. It can be seen that the 
intermediate shaft 20 is rotatably received in the machine housing 12 
through a bearing 21. The locking toothing 33 is provided at the end side 
in the intermediate shaft 20, and the locking member 31 can engage with 
its locking tooth 31 into the locking toothing 33. The spring 34 brings 
the locking member 31 with its shoulder projection 39 in abutment against 
the locking pin 38. The locking pin 38 is displaced by a pressure spring 
42 in direction toward its locking position. The armature 40 is surrounded 
partially by a winding 43. After applying an electrical action to the 
winding 43 through terminals 50, 51 the armature 40 is pulled axially 
against the force of the spring 42. 
The locking toothing 32 of the intermediate shaft 20 is shown in FIG. 3. 
The locking toothing 33 is composed of six teeth 53 which extend radially 
outwardly and are inclined in a rotary direction 52. The teeth 53 have a 
substantially radially oriented locking surface 54 and a free surface 55. 
The corresponding locking tooth 33 of the locking member 31 is provided 
with a corresponding locking surface 54a and a corresponding free surface 
55b. The locking surface 54a of the locking tooth 33 is oriented 
substantially parallel to a displacement axis 56 of the locking member 31, 
which is located substantially at a right angle to a rotary axis 57 of the 
intermediate shaft 20. Because of the right-angled arrangement of the 
displacement direction 56 and the rotary axis 57, a fast working 
engagement without undesired overarresting of the locking tooth 33 in the 
locking toothing 32 is possible. 
FIG. 4 shows a restoring device 65 the locking member 31. The restoring 
device 60 has a longitudinally displaceably restoring slider 61 which is 
fixedly connected at one side with an actuation button 62. The actuation 
button 62 extends outwardly from the machine housing 12 and therefore can 
be actuable by the operator of the drilling implement 10 from outside. The 
restoring slider 61 is provided with a restoring cam 63 which extends 
substantially perpendicular to the actuation direction of the restoring 
slider 61 and substantially in the restoring direction of the locking 
member 31. When the locking tooth 33 of the locking member 31 is in 
engagement with the locking toothing 32, the locking member 31 is 
returnable by pressing of the actuating button 62 and thereby by the 
longitudinal displacement of the restoring slider 61. The restoring cam 63 
during actuation of the restoring slider 61 in the actuation direction 64 
comes to abutment against a corresponding cam 66 which is formed on the 
locking member 31 as shown in FIG. 5. During further actuation of the 
restoring slider 61, the cams 63, 66 slide on one another, and the locking 
member 31 is displaced in the restoring direction 65 against the force of 
the spring 34 so that the locking tooth 33 runs completely from the 
locking toothing 32. The height of the cams 63, 66 is selected so that the 
shoulder projection 39 can again engage behind the locking pin 38 and the 
locking member 31 can again come to abutment against the locking pin 38. 
The restoring slider 61 is simultaneously withdrawn by restoring spring 67 
to the initial position shown in FIG. 4. The blocking device 40 of the 
drilling device 20 is thereby made ready for a further release. 
The second embodiment shown in FIG. 6 is different from the first 
embodiment by the restoring device 60. The same and identically operated 
parts which also are provided in the third embodiment are identified with 
the same reference numerals. 
The drilling implement 10 shown in FIG. 6 is provided with an automatic 
restoring device 60'. The restoring device 60' has a restoring slider 61' 
which is located axis-parallel to the displacement axis 56 of the locking 
member 31. The restoring slider 61 is connected with an armature 70 of an 
electromagnet 71. The electromagnet 71 is formed as a ring magnet which 
concentrically surrounds the armature 70. The armature 70 is prestressed 
by a spring 72 in the displacement direction of the locking member 31 and 
forced in an axial position with a small magnetic overlap. When the 
electromagnet 71 is electrically activated, the armature 70 is pulled 
opposite to the spring 72. The restoring slider 61' moves opposite to the 
engaging direction of the locking member 31 from it and displaces its 
locking tooth 33 from the locking toothing 32. The locking member 31 is 
displaced so far until the locking pin 38, under the action of the spring 
42, can engage behind the shoulder projection 39 on the locking member 31. 
The blocking device 30 is again brought to the initial position. For the 
purpose of illustration, in FIG. 6 the restoring slider 61' and the 
blocking pin 38 are shown in one plane. However, actually they are located 
in different planes so as not to interfere during operation. 
A pin 58 engages in a longitudinal groove 59 in the locking member 31 and 
prevents turning of the locking tooth 33 relative to the locking toothing 
32, so that a blocking engagement is always possible. The securing against 
co-rotation is performed in a different manner, for example by a 
four-cornered shape of the locking member 31. A position sensor 74 
monitors the adjusting position of the locking member 31. When the locking 
member 31 is located in its initial position, this is recognized by the 
position sensor 74, and the electromagnet 71 is turned off by the 
evaluating device 47 so that the spring pulls back the restoring slider 61 
to its initial position. The position sensor 74 can be also used for 
monitoring the blocking position of the locking member 31 so that after 
reaching the blocking position a turning-off signal produced by it turns 
off the drive motor 11. 
In the third embodiment shown in FIG. 7, the both electromagnets 41, 71 of 
FIGS. 6 are replaced by a signal magnet plate 80. A separate restoring 
device 65, 65' is therefore not necessary. The magnet plate 80 has two 
permanent magnets 83, 84 located at an end side and opposite to one 
another. They are provided with overlapping projections 83a, 84b between 
which an armature 82 is displaceably supported. The overlapping 
projections 83a, 83b form an opposite end position for the armature 82. 
Moreover, the armature 82 is surrounded by two ring-shaped coils 85, 86. 
When the armature 82 is supplied with current they are set in one or 
another end position. When the coils 85, 86 are not supplied with current, 
one of the oppositely directed pulling forces of the permanent magnet 83, 
84 prevails, so that two stable end positions are produced for the 
armature 82. 
The locking member 31 is provided at the rear side with a receiving opening 
87 which receives an armature rod 81 connected with the armature 82. The 
armature rod 81 engages with axial play in the receiving opening 87. A 
pressure spring 88 is arranged between the armature rod 81 and the locking 
member 31 and forces the locking member 31 away from the armature rod 81 
in direction to the locking toothing 32. The locking member 31 is axially 
secured by an inner ring 89 which cooperates with a ring collar 20 of the 
armature rod 81. 
In FIG. 7 the armature rod 81 with the locking member 31 is located in its 
disengaged position. By actuation of the electromagnets 85, 86, the 
armature 82 can be brought by blocking the intermediate shaft 20 into its 
opposite end position located near the intermediate shaft 20. The pressure 
spring 88 guarantees that the armature 83, independently from the 
penetration depth of the locking tooth 33 into the locking toothing 32, 
always reaches its end position in which it develops a high holding force. 
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 types described above. 
While the invention has been illustrated and described as embodied in hand 
power tool, 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.