U.S. patent application number 14/051900 was filed with the patent office on 2014-02-06 for power tool.
This patent application is currently assigned to Johnson Electric S.A.. The applicant listed for this patent is Johnson Electric S.A.. Invention is credited to James Ching Sik LAU.
Application Number | 20140034348 14/051900 |
Document ID | / |
Family ID | 43307986 |
Filed Date | 2014-02-06 |
United States Patent
Application |
20140034348 |
Kind Code |
A1 |
LAU; James Ching Sik |
February 6, 2014 |
POWER TOOL
Abstract
A power tool includes a case and a motor installed within the
case. The motor has a motor housing and a rotor with shaft. A gear
train having a gear train housing and a speed reduction mechanism
is installed within the gear train housing and connected to the
shaft of the motor. The motor housing and the gear train housing
are integrally formed as a common housing and fixed relative to the
case.
Inventors: |
LAU; James Ching Sik; (Hong
Kong, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Johnson Electric S.A. |
Murten |
|
CH |
|
|
Assignee: |
Johnson Electric S.A.
Murten
CH
|
Family ID: |
43307986 |
Appl. No.: |
14/051900 |
Filed: |
October 11, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12828767 |
Jul 1, 2010 |
8567521 |
|
|
14051900 |
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Current U.S.
Class: |
173/216 |
Current CPC
Class: |
B25F 5/02 20130101; H02K
7/145 20130101; B23B 45/00 20130101; H02K 7/116 20130101 |
Class at
Publication: |
173/216 |
International
Class: |
B25F 5/02 20060101
B25F005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 1, 2009 |
CN |
200910108565.0 |
Claims
1. A power tool comprising: a case; a motor installed within the
case, the motor comprising a motor housing and a rotor including a
motor shaft; a gear train comprising a gear train housing and a
speed reduction mechanism installed within the gear train housing
and connected to the motor shaft; wherein the motor housing and the
gear train housing are integrally formed as a common housing having
a single piece monolithic construction and fixed relative to the
case, the common housing having a motor end remote from the gear
train and a gear train end remote from the motor; a fan is fixed to
the rotor and located within the common housing; inner and outer
bearing brackets are fixed to the common housing to support the
rotor via bearings, the fan being axially located between the inner
and outer bearing brackets, the outer bearing bracket closing the
motor end of the common housing and having vents for passage of air
drawn in by the fan to cool the motor; and the motor further
comprising one of a brush card and a circuit board fixed to the
inner bearing bracket.
2. The power tool of claim 1, wherein the common housing defines
radial openings to radially expose the fan.
3. The power tool of claim 1, wherein the motor is a brush motor
having brushes and a commutator, and the motor housing defines
radial openings to expose the brushes, commutator, and the fan.
4. The power tool of claim 1, wherein a pair of power leads
arranged to provide power to the one of a brush card and a circuit
board of the motor extends through a radial opening of the motor
housing to connect to a switch of the power tool.
5. The power tool of claim 1, wherein a ring gear closes the gear
train end of the common housing, the inner bearing bracket being
located between the outer bearing bracket and the ring gear.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional of co-pending application
Ser. No. 12/828,767, filed on Jul. 1, 2010, for which priority is
claimed under 35 U.S.C. .sctn.120; and this application claims
priority of Application No. 200910108565.0 filed in The People's
Republic of China on Jul. 1, 2009 under 35 U.S.C. .sctn.119; the
entire contents of all of which are hereby incorporated by
reference.
FIELD OF THE INVENTION
[0002] This invention relates to power tools such as portable
drills and electric screw drivers and in particular, to a
motor/gear train assembly for a power tool.
BACKGROUND OF THE INVENTION
[0003] A traditional power tool comprises a gear train driven by a
separate motor, the gear train and motor being installed in a case
of the power tool independently. Alternatively, the motor and gear
train may be connected together before being fitted to the case. In
either assembly method, eccentricity inevitably exists between the
gear train and the motor.
[0004] Eccentricity between the gear train and the motor means that
the alignment between the motor shaft and the gear train is not
correctly aligned increasing the friction of the connection
resulting in higher friction and greater heat generation. This
higher friction means that the power tool has a lower efficiency
and will use more power to do the same task. This is undesirable,
especially if the power tool is powered by batteries.
SUMMARY OF THE INVENTION
[0005] Hence there is a desire for a power tool in which
eccentricity between the gear train and the motor is minimized or
eliminated.
[0006] This is achieved in the present invention by using a common
housing to accommodate both the motor and the gear train.
[0007] Accordingly, in one aspect thereof, the present invention
provides a power tool comprising: a case; a motor installed within
the case, the motor comprising a motor housing and a rotor
including a motor shaft; a gear train comprising a gear train
housing and a speed reduction mechanism installed within the gear
train housing and connected to the motor shaft; wherein the motor
housing and the gear train housing are integrally formed as a
common housing and fixed relative to the case.
[0008] Preferably, a pair of power leads extend through an opening
in the motor housing adjacent the gear train and arranged to
provide power to the motor.
[0009] Preferably, the motor comprises a brush card supporting
brushes thereon for slidingly contacting a commutator of the motor,
each power lead comprising first and second ends, the first ends
being connected to a corresponding brush and the second ends being
connected to a switch of the power tool.
[0010] Preferably, a fan is fixed to the rotor, the brush card
being located between the gear train and the fan.
[0011] Preferably, the fan is disposed within the motor housing and
aligned with at least one opening in the motor housing to blow air
out of the motor housing.
[0012] Preferably, the motor is a brush motor, permanent magnets
being installed on an inner surface of the motor housing.
[0013] Preferably, the motor is a brushless motor, the motor
comprises a circuit board with control circuits for the motor
mounted thereon, each power lead comprises first and second ends,
the first ends being connected to the control circuit and the
second ends being connected to a switch of the power tool.
[0014] Preferably, a fan is fixed to the rotor, the circuit board
being located between the gear train and the fan.
[0015] Preferably, the fan is disposed within the motor housing and
aligned with at least one opening in the motor housing to blow air
out of the motor housing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] A preferred embodiment of the invention will now be
described, by way of example only, with reference to figures of the
accompanying drawings. In the figures, identical structures,
elements or parts that appear in more than one figure are generally
labeled with a same reference numeral in all the figures in which
they appear. Dimensions of components and features shown in the
figures are generally chosen for convenience and clarity of
presentation and are not necessarily shown to scale. The figures
are listed below.
[0017] FIG. 1 illustrates a power tool according to the preferred
embodiment of the present invention, with a part of a case and a
switch of the power tool removed;
[0018] FIG. 2 is a view similar to FIG. 1, with the switch mounted
in the case and a part of a housing of the gear train and motor
cutaway;
[0019] FIG. 3 is a view similar to FIG. 1, but with the entire case
and switch removed and the housing partially cutaway; and
[0020] FIG. 4 is a view of the housing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] FIGS. 1 to 3 show a power tool according to the preferred
embodiment of the present invention with various parts removed or
cut away to show the construction. The power tool comprises a case
10, a motor 30 and a gear train 50 installed in the case 10. A
chuck 16 and a torque reduction mechanism 18 are also shown. The
motor 30 comprises a motor housing 32 forming a part of a stator of
the motor and a rotor including a shaft. The gear train 50
comprises a gear train housing 52 accommodating gears driven by the
motor. The motor housing 32 and the gear train housing 52 are
integrally formed as a single structure, herein after referred to
as the housing or common housing 20. In this embodiment, the
housing 20 has a cylindrical or tubular shape. The gear train
housing 52 has a mounting base 54 which is attached to a frame 12
which is fixed to the case 10.
[0022] In FIG. 3 the housing 20 is partially sectioned to show the
motor and gear train assembly. In this embodiment, the motor 30 is
a brush motor and comprises a brush card 40 on which brushes 42 are
mounted. The brushes 42 slidably contact with a commutator 34 being
a part of the rotor of the motor 30. Permanent magnets 36 are
attached to the inner surface of the housing 32. A pair of power
leads 44 connected to the brushes 42 extends through a hole 45
(FIG. 4) in the motor housing 32 to connect to the switch 14 (FIG.
2) of the power tool.
[0023] A fan 60 is mounted to the rotor of the motor 30 and located
within the motor housing 32. The brush card 40 is located between
the gear train 50 and the fan 60. The motor housing 32 defines a
pair of openings 33 at opposite sides of a portion adjacent to the
gear train 50. The openings 33 expose the brushes 42, commutator 34
and the fan 60. Airflow generated by the fan 60 flows through the
opening 33 to an air passage formed within the case 10.
[0024] The gear train 50 comprises a speed reduction mechanism
installed within the gear train housing 52 and driven by the shaft
of the motor 30. The gear train is optionally of a planetary gear
type.
[0025] Alternatively, the motor 30 may be a brushless motor. The
brush card 40 may be a circuit board with control circuits mounted
thereon. The power leads 44 are connected to the circuit board 40
and switch 14 for supplying power to the circuit board 40.
[0026] In the present invention, the motor housing 32 and the gear
train housing 52 are integrally formed, which avoids concentricity
errors which exist when assembling two separate housings
independently. Furthermore, with the brush card/circuit board 40
being located between the motor 30 and gear train 50, the power
leads 44 extend from the brush card/circuit board 40 and connect to
the switch 14 after passing through the hole 45 in the case 10.
Compared to traditional power tools where the brush card/circuit
board 40 is located at the end of the motor remote from the
gearbox, the power leads 44 of the present invention are relatively
short as the switch 14 is located close to the brush card/circuit
board 40. This means that the resistance of the power leads is
reduced giving more power to the motor and reducing the heat
produced by the power leads. This is particularly desirable for
battery operated power tools.
[0027] While the common housing 20 may be of a plastics material,
it is preferred if the housing is made from one piece of sheet
steel which is rolled and joined at the lateral edges to form a
hollow tube. End plates or bearing brackets 22, 23, are fixed to
the housing 20 to support the rotor via bearings. The outer bearing
bracket 22 closes the motor end of the common housing and has vents
for the passage of air drawn in by the fan 60 to cool the motor.
The outer bearing bracket 22 is fixed to the housing 20 by crimps.
The brush card is fixed to the inner bearing bracket 23 which is
fixed to the housing 20 by crimping tabs into recesses in the edges
of the openings 33. A ring gear 56 of the gear train is pressed
into or otherwise fixed to and closes the gear train end of the
common housing 20.
[0028] Optionally, the housing 20 could be formed by two sheets of
electrical steel rolled into half tubes and joined together along
the lateral edges to form the common housing in a clam shell
arrangement. This simplifies assembly of the parts into the housing
and allows crimping to be avoided by fitting tabs of the bearing
brackets into slots in the housing. Tabs and slots could also be
used to fix the ring gear 56 to the housing 20.
[0029] An oil seal is provided between the inner bearing bracket 23
and the gears to prevent oil or grease from the gear train
contaminating the motor, especially the brush card and
commutator.
[0030] In the description and claims of the present application,
each of the verbs "comprise", "include", "contain" and "have", and
variations thereof, are used in an inclusive sense, to specify the
presence of the stated item but not to exclude the presence of
additional items.
[0031] Although the invention has been described with reference to
one or more preferred embodiments, it should be appreciated by
those skilled in the art that various modifications are possible.
Therefore, the scope of the invention is to be determined by
reference to the claims that follow.
* * * * *