U.S. patent application number 10/743209 was filed with the patent office on 2004-12-30 for electric hand tool.
Invention is credited to Fuchs, Frank, Hoffmann, Erhard, Schulz, Martin, Voigt, Mike.
Application Number | 20040263008 10/743209 |
Document ID | / |
Family ID | 32404370 |
Filed Date | 2004-12-30 |
United States Patent
Application |
20040263008 |
Kind Code |
A1 |
Voigt, Mike ; et
al. |
December 30, 2004 |
Electric hand tool
Abstract
An electric hand tool is described that includes a machine
housing (1) with an electric motor (12) accommodated in the machine
housing (11) for driving a tool (13), and a fan wheel (21)
accommodated in the machine housing (11) for generating a cooling
air current that flows through the machine housing (11), which said
fan wheel creates a suction space (22) and a pressure space (23) on
opposite sides when it rotates. To increase the performance of the
electric hand tool with longer idle periods for the machine
components, purposeful cooling is carried out by providing means
for generating an additional air current, which said means are
configured such that the additional air current flows to machine
components that are located outside of or in a low-flow region of
the cooling air current.
Inventors: |
Voigt, Mike; (Gaildorf,
DE) ; Hoffmann, Erhard; (Leinfelden-Echterdingen,
DE) ; Fuchs, Frank; (Rutesheim, DE) ; Schulz,
Martin; (Stuttgart, DE) |
Correspondence
Address: |
STRIKER, STRIKER & STENBY
103 East Neck Road
Huntington
NY
11743
US
|
Family ID: |
32404370 |
Appl. No.: |
10/743209 |
Filed: |
December 22, 2003 |
Current U.S.
Class: |
310/58 ; 310/50;
310/62 |
Current CPC
Class: |
H02K 9/06 20130101; F04D
29/281 20130101; B25F 5/008 20130101 |
Class at
Publication: |
310/058 ;
310/050; 310/062 |
International
Class: |
H02K 007/14; H02K
009/00; H02K 009/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 2002 |
DE |
102 61 572.1 |
Claims
What is claimed is:
1. An electric hand tool comprising a machine housing (11), with an
electric motor (12) accommodated in the machine housing (11) for
driving a tool (13), and a fan wheel (21) accommodated in the
machine housing (11) for generating a cooling air current that
flows through the machine housing (11), which said fan wheel
creates a suction space (22) and a pressure space (23) on opposite
sides when it rotates, wherein means for generating an additional
air current are provided and configured such that the additional
air current flows onto at least one machine component that is
located outside of or in a low-flow region of the cooling air
current.
2. The electric hand tool as recited in claim 1, wherein the
electric motor (12) includes a motor winding (31) with winding
heads (311) that project outward on at least one end face of the
electric motor (12), the fan wheel (21) is located with axial
clearance in front of the end face of the electric motor (12) and
is configured such that the suction space (22) is located in front
of the end face of the electric motor (12) where the winding heads
(31) are located, and the means for generating the additional air
current have air inlets that lead into the suction space (22).
3. The electric hand tool as recited in claim 2, wherein the air
inlets are air inlet openings (24) that are configured in the wall
of the machine housing (11) on or near the end face of the electric
motor (12).
4. The electric hand tool as recited in claim 2, wherein the air
inlets are passages (25) located in a dividing wall (40; 26) that
separates the pressure space (23) from the suction space (22) and,
preferably, the passages (25) are separated from the axis of the
fan wheel by the greatest radial distance possible.
5. The electric hand tool as recited in claim 4, wherein the
dividing wall (40) is fixed in position, and is mounted on the
machine housing (11), or it is part of the machine housing
(11).
6. The electric hand tool as recited in claim 4, wherein the
dividing wall rotates with the fan wheel (21) and is an integral
part of the fan wheel (21).
7. The electric hand tool as recited in claim 6, wherein the fan
wheel (21) has a base plate (27) with a hub (271) for sliding onto
a driven shaft (15) of the electric motor (12), a cover plate (26)
that has axial clearance from the base plate (27) and forms the
dividing wall, and radially oriented fan vanes (28) that are
located between the base and cover plate (27, 26), and air outlet
openings (19) are located in the wall of the machine housing (11)
on the pressure side of the fan wheel (21) in the region of the
vane ends.
8. The electric hand tool as recited in claim 1, wherein the
electric motor (12) has a motor winding (31) with winding heads
(311) that project outward on at least one end face of the electric
motor (12), and the means for generating the additional air current
has openings in the wall of the machine housing (11) that are
located in the region of the end face of the electric motor (12) on
which the winding heads (311) are carried.
9. The electric hand tool as recited in claim 1, wherein the means
for generating an additional air current have air guide elements
(41) that divert a sub-current, as the additional air current, from
the cooling air current.
10. The electric hand tool as recited in claim 9, wherein the
electric motor (10) has a stator (30), a rotor (32) and an air gap
(33) located between the two, and the air guide elements (41) are
located in the suction space (22) and are configured such that a
sub-current is diverted to the winding heads (311) from the cooling
air current passing through the air gap (33) and into the suction
space (22).
11. The electric hand tool as recited in claim 1, wherein the means
for generating the additional air current have at least one air
duct (34) guided in the machine housing (11), and one end of the
duct is located in the cooling air stream, and the other end of the
duct is located at or near the machine component (17).
12. The electric hand tool as recited in claim 11, wherein the duct
inlet is located at or near the machine component (17), and the
duct outlet leads into the suction space (22) of the fan wheel
(21).
13. The electric hand tool as recited in claim 11, wherein the air
duct (34) is formed in the wall of the machine housing (11).
14. The electric hand tool as recited in claim 13, wherein the
machine housing (11) has two shells, and one part (341, 342) of the
air duct (34) is formed in each housing shell (111, 112) such that,
when the two housing shells (111, 112) are joined, the air duct
(34) is formed.
15. The electric hand tool as recited in claim 1, wherein the
electric motor (12) includes a commutator (37) with commutator
brushes (38), and the means for generating an additional air
current with the commutator (37) have air turbulence-generating
elements (42) around the periphery, which are arranged such that
the additional air current they generate flows across the
commutator surface.
16. The electric hand tool as recited in claim 15, wherein the air
turbulence-generating elements (42) are formed on the commutator
(37) itself.
17. The electric hand tool as recited in claim 15, wherein the air
turbulence-generating elements (42) are the fan vanes (43) of an
axial fan wheel (44) that is joined with the commutator (37) in
torsion-proof fashion.
18. The electric hand tool as recited in claim 15, wherein the
commutator brushes (38) are displaceably held in a brush cartridge
(39), and the brush cartridges (39) are equipped with cooling ribs
(47).
19. The electric hand tool as recited in claim 11, wherein the
machine component is an on/off switch (17) for the electric motor
(12) or a battery pack for supplying power.
Description
BACKGROUND INFORMATION
[0001] The present invention is directed to an electric hand tool
as recited in the preamble of claim 1.
[0002] With an electric hand tool of this type (DE 196 00 339 C1),
fan guide vanes are located on either side of a fan wheel that is
mounted on the motor shaft between the electric motor and gearbox,
in order to improve the cooling of the electric motor and a gearbox
that is located between the electric motor and a drive spindel for
a tool, which said fan guide vanes cool the electric motor and the
gearbox separately and independently of one another via
corresponding air ducts.
[0003] With an electric hand tool having an impact mechanism (DE
100 30 962 C2), an annular channel with an opening on the outside
is formed in the impact region of the snap die, which said opening
is connected to the suction side of a ventilation system of the
electric motor. The dust that is produced in the abrasive process
of removing material, which said material also penetrates the
working area of the snap die, is suctioned away from this area
through the annular channel by the vacuum generated by the
ventilation system.
ADVANTAGES OF THE INVENTION
[0004] The electric hand tool according to the invention having the
features of claim 1 has the advantage that greater performance and
longer idle periods for the machine components and the electric
hand tool as a whole can be obtained by purposefully cooling
machine components that are subject to warming and are not
ventilated at all or inadequately by the cooling air current that
is generated by the fan wheel, which is preferably driven by the
electric motor, by means of the additional air current that is
diverted from the cooling air current or injected additionally from
the outside. In contrast to the known electric hand tools, no dead
air space regions develop, in which components are not cooled. The
improved cooling can increase the performance of the electric hand
tool with the same housing cross-section, or the housing
cross-section can be reduced in size in the region of the electric
motor while retaining the same performance. No additional
production costs are incurred, since the means for the additional
air current can be designed such that they can be produced at the
same time as the machine housing or fan wheel.
[0005] Advantageous further developments and improvements of the
electric hand tool described in claim 1 are made possible by the
measures listed in the further claims.
[0006] According to an advantageous embodiment of the invention,
the electric motor has a motor winding with winding heads that
project outward on at least one end face of the electric motor, and
the fan wheel is located with axial clearance in front of the end
face of the drive motor and is configured such that the suction
space is located directly in front of the end face of the drive
motor on which the winding heads are carried. The means for
generating the additional air current have air inlets that lead
into the suction space. The fan wheel can be configured as an
axial, diagonal or radial fan wheel. This structural configuration
has the advantage that additional air is supplied through the air
inlets that lead into the suction space, which said air inlets
reach the "dead air space regions", inside the suction space, where
the winding heads are located. Said dead air space regions are
produced because the cooling air current that is drawn in by the
fan wheel flows substantially through the working air gap between
the rotor and stator and into the suction space and, from there, it
is blown over the fan wheel vanes into the pressure space without
reaching the winding heads of the motor winding that are located
toward the outside relative to the working air gap.
[0007] According to an advantageous embodiment of the invention,
the air inlets are openings that are configured in the wall of the
machine housing at or near the end face of the electric motor. With
this configuration of the air inlets, the amount of air in the
cooling air current that is flowing into the suction space is
increased by the amount of air drawn in from the outside through
the openings. At the same time, air is directed in purposeful and
efficient fashion past the winding heads without any noteworthy
additional costs being incurred.
[0008] According to an advantageous embodiment of the invention,
the air inlets are openings in a dividing wall that separates the
pressure space from the suction space, which said openings are
preferably located with the greatest radial clearance possible from
the axis of the fan wheel. The dividing wall can be fixed in
position, and it can be part of the machine housing or part of the
fan wheel, and it can rotate with said fan wheel. By means of this
"internal injection", a portion of the air flowing into the
pressure space is directed, as additional air, from the pressure
space back into the suction space. It is thereby directed past the
winding heads to be cooled without requiring any additional
components or production costs. By making the openings larger or
smaller, the amount of air flowing back into the suction space can
be controlled very well. Openings to the outside, as used in the
case of "external injection" described hereinabove, are eliminated,
which also rules out an additional contamination risk.
[0009] According to an alternative embodiment of the invention, the
means for generating the additional air current have air guide
elements that divert a sub-current, as the additional air current,
from the cooling air current to the machine components that are
poorly ventilated by the cooling air current. Although this does
not increase the cooling air current, the cooling air current is
divided into branches such that purposeful and efficient cooling of
individual machine components is obtained. The additional costs
required to produce and install the air guide elements is
minimal.
[0010] According to an advantageous embodiment of the invention,
the means for generating the additional air current have at least
one air duct guided in the machine housing; one end of the duct is
located in the cooling air stream, and the other end of the duct is
located at or near the machine component. This has the advantage
that machine components, such as electrical, electronic or
mechanical components that are not located directly in the vicinity
of the cooling air stream that is flowing through the machine, are
cooled well and therefore have a longer service life and can be
designed smaller in size. This reduces structural volume and lowers
the costs to fabricate the components. At the same time, greater
structural and design-oriented freedom is obtained in terms of
configuring the electric hand tool, since components that work fine
without cooling no longer need to be located in the immediate
vicinity of the cooling air current. Instead, they can be placed
anywhere, due to the air duct according to the invention.
Preferably, the air duct is positioned such that the duct inlet is
close to the machine component to be ventilated, e.g., the on/off
switch for the electric motor, and the duct outlet leads into the
suction space of the fan wheel.
[0011] According to a preferred embodiment of the invention, the at
least one air duct is integrated directly in the plastic wall of
the machine housing. As a result, no additional production costs
for the air duct would be incurred, since said air duct can be
formed when the machine housing is produced.
[0012] According to an advantageous embodiment of the invention,
the electric motor, which is designed as a commutator motor, e.g.,
a universal motor, has a commutator with commutator brushes. The
means for generating the additional air current have air
turbulence-generating elements that encircle the periphery of the
commutator and are configured such that the additional air current
they generate flows across the commutator surface. The air
turbulence-generating elements can be located on the commutator
itself, or they can be the fan wheel vanes of an axial fan wheel
that is joined with the commutator in torsion-proof fashion, e.g.,
it is mounted together with the commutator on the driven shaft of
the electric motor in torsion-proof fashion. Said structural
features increase the overall amount of cooling air that flows
through the machine housing, and permits optimum flow of cooling
air onto the commutator and commutator brushes. With commutator
motors having a short structural shape, the axial fan wheel is
designed as a plastic disk that is mounted in torsion-proof fashion
on the driven shaft of the drive motor, on the periphery of which
said plastic disk the fan wheel vanes are equidistantly located as
small, bent segments. The advantage of this is that, due to the
plastic disk, a sufficiently large creepage distance is retained
between the pivot bearing and the commutator, despite the short
structural shape.
[0013] According to an advantageous embodiment of the invention,
the brush cartridges for holding and guiding the commutator brushes
are equipped with cooling ribs, through which the air current
generated by the axial fan wheel flows. The large surface area of
the cooling ribs ensures substantially improved heat dissipation at
the brush cartridges and the commutator brushes, which permits in
longer idle periods for the commutator brushes.
BRIEF DESCRIPTION OF THE DRAWING
[0014] The invention is described in greater detail in the
description below with reference to the embodiments shown in the
drawing.
[0015] FIG. 1 is a schematic representation of a section of a
longitudinal cross-section of an electric hand tool,
[0016] FIG. 2 is the same depiction as in FIG. 1, according to a
further embodiment,
[0017] FIG. 3 is a view in the direction III in FIG. 2 of a
structural configuration of a fan wheel in the electric hand tool
according to FIG. 2, depicted with perspective,
[0018] FIGS. 4 show the same depiction as in FIG. 1, in accordance
to a third and 5 and fourth embodiment,
[0019] FIG. 6 is a schematic representation of a longitudinal
section of an electric hand tool according to a further
embodiment,
[0020] FIG. 7 shows a section of an enlarged section of a portion
of a wall of the machine housing of an electric hand tool that has
been modified relative to FIG. 6,
[0021] FIG. 8 is an enlarged, perspective view of the commutator of
the electric motor in the electric hand tool according to FIG. 6,
and
[0022] FIG. 9 is an enlarged, perspective view of a brush cartridge
of the electric motor in the electric hand tool according to FIG.
6.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0023] The electric hand tool, e.g., an electric hand-held drill,
shown in FIG. 1 in a sectional view and in FIG. 6 in a complete
view, includes, in known fashion, a machine housing 11, in which an
electric motor 12 for a tool 13, e.g., a drill bit, is
accommodated. As depicted in FIG. 6 in principle only, tool 13 is
clamped in a tool receptacle 14, e.g., a drill chuck, which is
mounted in torsion-proof fashion on a drive spindle, which is
driven by a gearbox (not shown in FIG. 4) by driven shaft 15 of
electric motor 12 depicted here as a commutator motor, as an
example.
[0024] As shown in FIGS. 1 and 6, electric motor 12 includes a
stator 30 with stator or field winding 31 (FIG. 1) and a rotor 32
that is mounted in torsion-proof fashion on driven shaft 15, which
said rotor is concentrically surrounded by stator 30, with an air
gap 33 between said rotor and said stator. Field winding 31 is
inserted in known fashion in axial grooves in stator 30 and
projects via winding heads 311 out of said stator on both end faces
of stator 30. A rotor winding that is inserted in rotor 32, but is
not shown in FIGS. 1 and 6, is connected to the commutator bars of
a commutator 37 that is mounted in torsion-proof fashion on driven
shaft 15. At least two commutator brushes 38 serve to conduct
current to the rotor winding, each of which said commutator brushes
is accommodated in axially displaceable fashion in a brush
cartridge 38, and each of which is pressed radially against the
commutator bars of commutator 37 using spring pressure. Brush
cartridges 38 are fixed in position on a brush holder located in
machine housing 11. An on/off switch 17 is located in an easily
accessible location in a handle 16 that is integrally formed on
machine housing 11, for switching electric motor 12 on and off
(FIG. 6).
[0025] The electric hand tool is air-cooled and includes a fan that
is configured as an axial or radial fan, for cooling electric motor
12 and gearbox, which said fan draws in air through air inlet slits
18 that are formed in the rear region of machine housing 11, and
blows air out through air outlet openings 19 that are formed in the
front region of machine housing 11. For this purpose, a fan wheel
21 is mounted--downstream of the air current and directly behind
electric motor 12--on driven shaft 15 in torsion-proof fashion, so
that fan wheel 21 is positioned between electric motor 12 and
gearbox on the side furthest from commutator 37. When fan wheel 21
rotates, it produces a suction space 22 on its side closest to
drive motor 12, and a pressure space 23 on its other side, which is
furthest from said drive motor, which said pressure space is
connected with air outlet openings 19. As a result, as indicated by
the flow arrows in FIGS. 1 and 6, air is drawn in from the
environment through air inlet openings 18 and through annular gap
33 in electric motor 12, whereby the air absorbs heat produced in
electric motor 12.
[0026] Finally, the warmed air is blown back out into the
environment through air outlet openings 19.
[0027] Due to the high internal air resistance of the electric hand
tool and the high flow speed of the air inside air gap 33, a
sufficient amount of cooling air does not always reach components
to be cooled, e.g., winding heads 311 of field winding 31 that are
shown on the left side of FIG. 1 and which are located downstream
from the cooling air current, so that said cooling air can carry
away enough heat from here. In order to eliminate this inadequacy,
air inlets that lead into suction space 22 are provided in
embodiments of the electric hand tool depicted in FIGS. 1 and 2 in
order to generate an additional air current. Due to the position of
the air inlets, the additional air is directed into suction space
22 such that the additional air flows past winding heads 311 in
suction space 22, where it absorbs a sufficient amount of heat from
winding heads 311. In the embodiment of the electric hand tool
according to FIG. 1, said air inlets are slit-shaped air inlet
openings 24 that are formed in the wall of machine housing 11
within the region of suction space 22. Air inlet openings 24 are
preferably distributed evenly around the periphery of machine
housing 11 and are located in the immediate vicinity of the end
face of electric motor 12 or its stator 30. As the air flow arrows
drawn in FIG. 1 show, when fan wheel 21 rotates, the cooling air
current as well as additional air from the environment flows
through air inlet openings 24, over winding heads 311, and into
suction space 22. Said additional air effectively cools winding
heads 311 and, therefore, field winding 31, and increases the
amount of cooling air in suction space 22.
[0028] In the embodiment of an electric hand tool shown in a
sectional view in FIG. 2, the air inlets are passages 25 that are
formed in a portion of fan wheel 21, which said portion divides
suction space 22 from pressure space 23. As the air flow arrows
drawn in FIG. 2 show, when fan wheel 21 rotates, a portion of the
air from pressure space 23 does not flow through air outlet
openings 19. Instead, the vacuum in suction space 22 causes said
portion of air to flow through passages 25 into suction space 22.
Since passages 25 are located close to the outer edge of fan wheel
21, the additional air drawn from pressure space 23 flows over
winding heads 311, and is then guided by fan wheel 21 back into
pressure space 23.
[0029] Fan wheel 21, which is shown in a sectional view of a
longitudinal cross-section in FIG. 2 as a schematic representation,
is shown in FIG. 3 in a top view with perspective in a real
embodiment as a radial fan wheel. When fan wheel 21 is mounted on
driven shaft 15, the top-view side in FIG. 3 faces electric motor
12. Fan wheel 21 includes an annular cover plate 26 that borders
suction area 22, a base plate 27--that has axial clearance from
said cover plate--with a central hub 271 for sliding onto driven
shaft 15, and radially oriented fan vanes 28 that are located
between cover plate 26 and base plate 27. Passages 25 are located
in cover plate 26 in the form of circular holes 251, 252. For
example, holes 251 having the larger diameter are located on an
outer perimeter, and holes 252 having the smaller diameter are
located on a concentric, inner perimeter having a smaller diameter.
The size of the holes and the distance between them are
purposefully selected in order to prevent an undesired reduction in
the efficiency of the radial fan caused by the injection of an
excessive volume of air from pressure space 23 into suction space
22. Locating holes 251 having the larger diameter on the outer
perimeter is advantageous because the greater portion of the air
injected into suction space 22 flows in the region of winding heads
311 of field winding 31. Passages 25 can have any cross-sectional
shape. For example, said passages can be configured as slits.
[0030] With the embodiment of the electric hand tool that is shown
as a sectional view in FIG. 4, fan wheel 21 is modified such that
cover plate 26 with passages 25 is eliminated, and the dividing
wall function of cover plate 26 is now performed by a dividing wall
40 that is fixed in position, which said dividing wall is part of
machine housing 11. Passages 25 are located in dividing wall 40 in
the same manner as described hereinabove in conjunction with cover
plate 26. Dividing wall 40, which is configured as a hollow
cylinder having the shape of a pagoda, can be designed integral
with machine housing 11, or it can be mounted, as a separate
structural component, on the wall of machine housing 11.
[0031] With the embodiment of the electric hand tool shown in FIG.
5, the air inlets in the suction space are eliminated in order to
increase the size of the cooling air mass in suction space 22 and,
instead, the additional current that flows onto winding heads 311
branches off from the cooling air current. For this purpose, at
least one air guide element 40 is located in suction space 22 such
that a sub-current of the cooling air current that flows in through
air gap 33 between stator 30 and rotor 32 into suction space 22
branches off such that it forms the additional air current that
flows onto winding heads 311. Radial fan wheel 21 is configured as
described in connection with FIG. 2, but cover plate 26 does not
contain passages. Of course, fan wheel 21 can also be configured as
shown in FIG. 4. Fixed dividing wall 40, which would then be
required, does not have passages in this case, either.
[0032] In order to also cool components in the electric hand tool
that cannot be positioned in the cooling air current that forms
between air inlet slits 18 and air outlet openings 19, such as
electrical on/off switch 17 installed in handle 16 as shown in FIG.
6, special air ducts are provided in machine housing 11, with which
air is drawn in over the electrical, electronic or mechanical
components to be cooled, such as on/off switch 17. An air duct 34
of this type is shown in FIG. 6. Said air duct extends along the
inner wall of machine housing 11 and has a duct inlet 35, which is
located in the region of on/off switch 17, and a duct outlet 36,
which leads into suction space 22. When fan wheel 21 rotates, the
vacuum that is generated in suction space 22 causes air to be drawn
in at duct inlet 35, which said air flows in from the outside due
to installation tolerances of on/off switch 17 in housing 11. Said
air flows over on/off switch 17 and past it. After it absorbs heat
at on/off switch 17, said air is drawn into air duct 34.
Advantageously, air duct 34 is integrated in the wall of machine
housing 11, as shown in FIG. 7. Machine housing 11, which is formed
via injection molding of plastic, is joined in a plane of symmetry
that passes through the longitudinal axis of the electric hand
tool. To integrate air duct 34 in machine housing 11, one half 341
or 342 of air duct 34 is configured in each housing shell 111 and
112. When the two housing shells 111 and 112 are joined, the two
duct halves 341, 342 combine to form air duct 34, as shown in a
sectional view in FIG. 7 for the region of handle 16.
[0033] In addition to air duct 34, which was described as an
example, for ventilating and cooling electrical on/off switch 17,
further air ducts having a similar configuration may be guided to
other electrical or electronic or mechanical components inside
machine housing 11. It is advantageous, for example, with an
electric hand tool that is designed as a battery pack-operated
machine, to guide an air duct to the battery pack and thereby
passively cool the battery pack. The cooling effect of air ducts 24
is independent of whether fan wheel 21 works using "external air
injection" (FIG. 1) or "internal air injection" (FIG. 2), or
whether injection of this type is eliminated altogether. In the
case of "external air injection" according to FIG. 1, air ducts 34
can be utilized instead of or in addition to air inlet openings 24
to draw in additional air from the outside.
[0034] Commutator 37 of electric motor 12 is a machine component of
the electric hand tool that is subjected to high levels of thermal
stress. In order to improve the cooling of commutator 37 and
commutator brushes 38 that ride on commutator 37, air
turbulence-generating elements 42 are located on commutator 37,
which rotate with commutator 37. Said air turbulence-generating
elements 42 can be mounted directly on commutator 37. In the
embodiment of commutator 37 shown in FIG. 8, fan vanes 43 of an
axial fan wheel 44 are air turbulence-generating elements 42, which
said axial fan wheel is mounted together with commutator 37 on
driven shaft 15 of electric motor 12. Axial fan wheel 44 is located
between a pivot bearing 45 of driven shaft 15--which said pivot
bearing is accommodated in machine housing 11--and commutator 37,
that is, on the end face of commutator 37 that is furthest from
rotor 32. Axial fan wheel 44 is preferably configured as a plastic
disk 46 that is mounted on driven shaft 15 in torsion-proof
fashion, with fan vanes 43 formed by bent axial segments mounted on
the periphery of said plastic disk. The advantage of this is that,
due to plastic disk 46, a sufficiently large creepage distance is
retained between pivot bearing 45 and commutator 37, despite a
short structural shape of electric motor 12. When driven shaft 15
rotates, fan vanes 43 generate an air current in addition to the
cooling air current that is generated by fan wheel 21, which said
additional air current flows across the surface of commutator 37
and commutator brushes 38 and increases the amount of air in the
cooling air current.
[0035] To enhance the cooling of commutator brushes 38, brush
cartridges 39 are equipped with cooling ribs 47, through which the
additional air current flows. Since the surface area of brush
cartridges 39 is greatly increased by cooling ribs 47, the
dissipation of heat from commutator brushes 38--which are held
axially inward in displaceable fashion--is markedly improved.
[0036] The invention is not limited to the embodiments described
hereinabove. For example, in the embodiment shown in FIG. 1, fan
wheel 21 can be configured such that its pressure space is located
in front of the end face of electric motor 12 on which winding
heads 311 are mounted. In this case as well, an additional air
current would be drawn over winding heads 311 through openings that
are equivalent to air inlet openings 24 in the wall of machine
housing 11, and would provide better cooling of winding heads 311.
Likewise, air ducts 34 in machine housing 11 can be positioned such
that their duct inlet is located in pressure space 23 formed by fan
wheel 21, and their duct outlet is located at the machine component
17 to be cooled.
* * * * *