U.S. patent number RE37,832 [Application Number 09/636,652] was granted by the patent office on 2002-09-10 for electromotive chain saw.
This patent grant is currently assigned to Makita Corporation. Invention is credited to Masaki Kondo, Makoto Mizutani, Kazuya Nakamura.
United States Patent |
RE37,832 |
Nakamura , et al. |
September 10, 2002 |
Electromotive chain saw
Abstract
The chain of an electromotive chain saw is quickly stopped by
the combined use of an electric brake and a mechanical brake when a
trigger member is turned off. The rear end of a brake band disposed
to tighten a brake drum by operating a hand guard is secured to a
bent rod. When the trigger member is released, the brake band is
normally tightened around the outer periphery of a brake drum by
the urging force of a coil spring. When the trigger member is
released, a circuit provided with a brake winding is closed,
thereby applying a dynamic braking force. When the dynamic brake
force is applied, a centrifugal clutch is released quickly and the
speed of stopping the brake drum is accelerated.
Inventors: |
Nakamura; Kazuya (Anjo,
JP), Mizutani; Makoto (Anjo, JP), Kondo;
Masaki (Anjo, JP) |
Assignee: |
Makita Corporation (Anjo,
JP)
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Family
ID: |
16845830 |
Appl.
No.: |
09/636,652 |
Filed: |
August 9, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
704492 |
Aug 20, 1996 |
05791057 |
Aug 11, 1998 |
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Foreign Application Priority Data
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Sep 4, 1995 [JP] |
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7-226484 |
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Current U.S.
Class: |
30/381; 30/382;
83/DIG.1 |
Current CPC
Class: |
B27B
17/083 (20130101); H02P 3/04 (20130101); Y10S
83/01 (20130101) |
Current International
Class: |
B27B
17/00 (20060101); B27B 17/08 (20060101); H02P
3/00 (20060101); H02P 3/04 (20060101); B27B
017/00 () |
Field of
Search: |
;30/381,382
;83/DIG.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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31 50 769 |
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30 35 185 |
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3510471 |
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34 19 152 |
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3639650 |
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DE |
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9212059.8 |
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4330850 |
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DE |
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195-42-603 |
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196-14-212 |
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DE |
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35 30 685 |
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0 236 749 |
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EP |
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0743 147 |
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EP |
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1 351 546 |
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1 536 595 |
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GB |
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55-18031 |
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57-154299 |
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JP |
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59-28297 |
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JP |
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59-134504 |
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Sep 1984 |
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JP |
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60-127103 |
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Jul 1985 |
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JP |
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62-25484 |
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Jun 1987 |
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JP |
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1-43207 |
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JP |
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657401 |
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JP |
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Jul 1995 |
|
JP |
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Other References
Response to the Communication of a Notice of Opposition, dated Oct.
5, 2000 for European Patent No. 0 761 398 filed Apr. 19, 2001.
.
National Swedish Board of Occupational Safety and Health. "Petrol
Driven Power Chain Saws", published Jun. 1977: 1-18. .
Herausgegeben vom Bendesinstitut fur Berufsbildung. "Arbeiten mit
Maschinen I" 1984: 14 pp. (Concise explanation provided in English
translation of Makita's Opposition). .
International Standard ISO 6535. "Forestry machinery--Portable
chain saws--Chain brake--Performance" First Edition; Jun. 15, 1983:
6 pp. .
Comite Europeen de Normalisation Electrotechnique (CENELEC).
"Hand-held Motor Operated Tools" Part II Particular Specifications;
Section L: Chain Saws; dated Mar. 1, 1988: 12 pp. .
Comite Europeen de Normalisation Electrotechnique (CENELEC). "1995
Catalogue of European Standards": 9 pp. .
Opposition Statement and Translation of Makita against German
Patent No. P35 30 685 to Andreas STIHL. Nov. 26, 1999: 14 pp. .
Opposition Statement and Translation of Dolmar GmbH against German
Patent No. P 35 30 685 to Andreas STIHL. Nov. 30, 1999: 15 pp.
.
Opposition Statement and Translation of Andreas STIHL AB & Co.
against EPO 0 761 398, Sep. 14, 2000; 23 pp. (Corresponds to US
4,791,057). .
Opposition Statement against EP 0 743 147 B1, May 4, 2000 by Black
and Decker; (Corresponds to US 5,709,032 to Mizutani, 7 pp., cited
in previous information Disclosure Statement..
|
Primary Examiner: Rachuba; M.
Attorney, Agent or Firm: David & Bujold, P.L.L.C.
Claims
What is claimed is:
1. An electromotive chain saw comprising; a guide bar having a
track extending around a periphery thereof; a cutting chain being
supported by said track of said guide bar and being rotatable
therearound; an electric motor, having an armature, being
drivingly-connected to said cutting chain, via a drive mechanism,
to rotate said cutting chain about the periphery of said bar along
said track, and said drive mechanism including a brake drum
drivingly connected to said cutting chain for rotation with said
cutting chain; a mechanical brake being arranged to engage with
said brake drum, said mechanical brake having a disengaged position
in which said mechanical brake is disengaged from said brake drum
and permits rotation thereof, and said mechanical brake having an
engaged position in which said mechanical brake engages with said
brake drum and exerts a braking force on a surface of said brake
drum to stop the rotation of thereof and, in turn, stop rotation of
said cutting chain rotated thereby; a dynamic brake circuit being
electrically coupled to said armature of said electric motor to
supply power thereto and rotate said cutting chain, in an operation
position of said dynamic brake circuit, and said dynamic brake
circuit having a braking position in which said dynamic brake
circuit applies a braking force to said armature of said electric
motor to stop rotation thereof; and a common trigger member being
directly linked to both said dynamic brake circuit and said
mechanical brake such that actuation of said common trigger member
to an ON position concurrently actuates both said mechanical brake
to said disengaged position and said dynamic brake circuit to said
operation position while actuation of said common trigger member to
an OFF position concurrently actuates both said mechanical brake to
said engaged position and said dynamic brake circuit to said
braking position whereby both said dynamic brake force on said
armature of said electric motor and said braking force on said
brake drum are concurrently applied.
2. The electromotive chain saw according to claim 1, further
including a hand brake device comprising a hand guard, a linkage
and a steel brake band, said linkage connects a forward end of said
brake band to said hand guard, said brake band is wound around a
circumference of said brake drum, and said hand brake device is
operated by pushing said hand guard away from an operator such that
a spring is extended thereby pulling an end of said brake band to
tighten said brake band and exert a braking force opposite in
direction to the braking force exerted by said mechanical brake
resulting in extended life for said brake band.
3. The electromotive chain saw according to claim 1, wherein said a
bent rod couples said common trigger member to said mechanical
brake.
4. The electromotive chain saw according to claim 3, wherein said
mechanical brake is located in a clearance of a chain saw case
using said bent rod without increasing the size of said chain
saw.
5. The electromotive chain saw according to claim 1, wherein a
rotary drive force is supplied to a drive sprocket from said
electric motor via a centrifugal clutch mechanism when a rotational
speed of said electric motor exceeds a predetermined number of
rotations, and said rotary drive force disconnects said drive
sprocket from said electric motor via said centrifugal clutch
mechanism when the rotational speed of said electric motor is lower
than said predetermined number of rotations.
6. The electromotive chain saw according to claim 1, wherein rotary
drive force is transmitted from said electric motor to a drive
sprocket via a clutch mechanism; said clutch mechanism comprises an
engagement member formed on said brake drum, an engaging member
rotated by said electric motor rotating with a rotation shaft, said
engaging member is slidable in an axial direction on said rotation
shaft and engages with said engagement member on said brake drum;
an urging member for pushing and urging said engaging member
against said brake drum; and a clutch release member which releases
the engagement of said engaging member on said brake drum by
sliding said engaging member back against said urging member when
said trigger member is moved from said ON position to said OFF
position.
7. The electromotive chain saw according to claim 1, wherein said
mechanical brake comprises a movable member operatively connected
to said common trigger member and secured to a second end of a
brake band, which extends around a circumference of said brake
drum, such that said brake band is pulled and tightened around said
brake drum when said trigger member is in said OFF position, and
said brake band is released and loosened from said brake drum when
said trigger member is in said ON position.
8. The electromotive chain saw according to claim 1, wherein said
mechanical brake is provided with a brake shoe for engaging with an
outer periphery of said brake drum.
9. The electromotive chain saw according to claim 2, in which said
mechanical brake is provided with a brake shoe for engaging with an
inner periphery of said brake drum.
10. The electromotive chain saw according to claim 9, wherein when
said common trigger member is in said OFF position, said brake shoe
contacts said brake drum to apply said braking force to said brake
drum and when said common trigger member is in said ON position,
said brake shoe is removed from contact with said brake drum
thereby removing said braking force from said brake drum.
11. The electromotive chain saw according to claim 1, further
comprising a trigger link brake circuit having: a main winding and
a brake winding provided in a field slot; a single-pole
double-throw switch for driving and braking said electric motor,
used to change between supplying a drive current to said armature
and said main winding and supplying a counter electromotive force
arising on said brake winding; and a single pole switch for
disconnecting said brake winding from said main winding when said
single-pole double-throw switch is changed over to supplying the
drive current to said armature and said main winding.
12. The electromotive chain saw according to claim 11, wherein said
electric motor, provided with said trigger link brake circuit,
comprises a single-phase series commutator motor, when driving said
electromotive chain saw, said single pole switch is changed over to
open the connection of said brake winding with said armature and
said main winding, a clutch mechanism is engaged, and said
single-pole double-throw switch is changed over to connect a power
source with said armature and said main winding, and when braking
said electromotive chain saw, said single-pole double-throw switch
is changed over to open the connection of the power source with
said armature and said main winding and to connect said brake
winding with said armature, said clutch mechanism is disengaged,
and said single pole switch is changed over to connect said brake
winding with said armature.
13. The electromotive chain saw according to claim 12, wherein when
driving said electromotive chain saw, after said single pole switch
is changed over to open the connection of said brake winding with
said armature and said main winding, said clutch mechanism is
engaged and subsequently said single-pole double-throw switch is
changed over to connect a power source with said armature and said
main winding, and when braking said electromotive chain saw, after
said single-pole double-throw switch is changed over to open the
connection of the power source with said armature and said main
winding and concurrently to connect said brake winding with said
armature, said clutch mechanism is disengaged, and subsequently
said single pole switch is changed over to connect said brake
winding with said armature.
14. The electromotive chain saw according to claim 1, wherein said
brake mechanism is a steel brake band wound around a circumference
of said brake drum, when said trigger member is in said OFF
position said steel brake band is tightened resulting in
application of said braking force to said brake drum, and when said
trigger member is in said ON position said steel brake band is
loosened from said brake drum thereby removing said braking force
from said brake drum..Iadd.
15. A chain saw comprising: an electric motor having an armature, a
cutting chain driven by the electric motor, a brake drum coupled to
the cutting chain, a mechanical brake adapted to engage the brake
drum, the mechanical brake having a first position, in which the
mechanical brake is disengaged from the brake drum to permit the
brake drum to freely rotate, and a second position, in which the
mechanical brake engages the brake drum to exert a mechanical
braking force on the brake drum, an electric brake circuit
electrically coupled to the electric motor, the electric brake
circuit having a first mode, in which the electrical braking force
is not applied to the electric motor, and a second mode, in which
the electric brake circuit applies an electrical braking force to
the electric motor, and a common trigger coupled to both the
electric brake circuit and the mechanical brake, the common trigger
having a first trigger position and a second trigger position, the
first trigger position causing the mechanical brake to disengage
from the brake drum and the electric brake circuit to operate in
the first mode, and the second trigger position causing the
mechanical brake to engage the brake drum and the electric brake
circuit to operate in the second mode, wherein the electric brake
force is applied the electric motor concurrently with the
mechanical braking force applied to the brake drum when the common
trigger is in the second trigger position. .Iaddend..Iadd.
16. A chain saw according to claim 15, wherein the common trigger
is directly coupled to both the electric brake circuit and the
mechanical brake, the first trigger position corresponds to an ON
position and the second trigger position corresponds to an OFF
position. .Iaddend..Iadd.
17. A chain saw according to claim 15, further comprising a clutch
coupled to the cutting chain, the electric motor and the common
trigger, wherein the clutch disengages the electric motor from the
cutting chain when the common trigger is in the second trigger
position. .Iaddend..Iadd.
18. A chain saw comprising: an electric motor, a cutting chain
driven by the electric motor, a brake drum coupled to the cutting
chain, a mechanical brake adapted to apply a mechanical braking
force to the brake drum, an electric brake adapted to apply an
electrical braking force to the electric motor, and a common
trigger coupled to both the electric brake and the mechanical brake
and adapted to simultaneously actuate both the electric brake and
the mechanical brake, the common trigger having an ON position and
an OFF position, wherein the mechanical braking force and the
electrical braking force act concurrently with one another to stop
the cutting chain and the electric motor, respectively, from
rotating when the common trigger is in the OFF position.
.Iaddend..Iadd.
19. A chain saw according to claim 18, wherein in the ON position
the common trigger concurrently causes the mechanical brake to move
to a disengaged position and the electric brake to not apply the
electrical braking force to the electric motor, and in the OFF
position the common trigger concurrently causes the mechanical
brake to apply the mechanical braking force to the brake drum and
the electric brake to apply the electrical braking force to the
electric motor. .Iaddend..Iadd.
20. A chain saw according to claim 19, further comprising a clutch
coupled to the cutting chain, the electric motor and the common
trigger, wherein the clutch disengages the electric motor from the
cutting chain when the common trigger is in the OFF position.
.Iaddend..Iadd.
21. A chain saw according to claim 18, further comprising a clutch
coupled to the cutting chain, the electric motor and the common
trigger, wherein the clutch disengages the electric motor from the
cutting chain when the common trigger is in the OFF position.
.Iaddend..Iadd.
22. A chain saw comprising: an electric motor, a cutting chain
driven by the electric motor, first means for applying a mechanical
braking force to stop the cutting chain, second means for applying
an electrical braking force to stop the electric motor, and third
means for simultaneously actuating both the first means and the
second means in order to concurrently apply the electrical braking
force to stop the electric motor and the mechanical braking force
to stop the cutting chain. .Iaddend..Iadd.
23. A chain saw according to claim 22, wherein the means for
simultaneously actuating both the first means and the second means
is a trigger switch. .Iaddend..Iadd.
24. A chain saw according to claim 23, wherein the trigger switch
has an ON position and an OFF position, in the ON position the
first means does not apply the mechanical braking force to stop the
cutting chain and the second means does not apply the electrical
braking force to the electric motor, and in the OFF position the
first means applies the mechanical braking force to stop the
cutting chain and the second means applies the electric braking
force to the electric motor. .Iaddend..Iadd.
25. A chain saw according to claim 24, further comprising a clutch
coupling the cutting chain to the electric motor, wherein the
clutch disengages the electric motor from the cutting chain when
the trigger switch is in the OFF position. .Iaddend..Iadd.
26. A chain saw according to claim 22, further comprising a clutch
coupling the cutting chain to the electric motor, wherein the
clutch disengages the electric motor from the cutting chain when
the first means and the second brake means have been simultaneously
actuated. .Iaddend..Iadd.
27. An apparatus as in claim 22, further comprising a power switch
coupled to the third means, wherein movement of the power switch to
an OFF position simultaneously and concurrently operates both the
first means and the second means via the third means to quickly
stop the rotation of the cutting chain. .Iaddend..Iadd.
28. The apparatus as in claim 27, further comprising a handguard
coupled to the third means, wherein movement of the handguard to an
OFF position simultaneously and concurrently operates both the
first means and the second means via the third means to quickly
stop the rotation of the cutting chain. .Iaddend..Iadd.
29. The apparatus as in claim 28, further comprising a clutch
coupled to the cutting chain, the electric motor and the third
means, wherein the clutch disengages the electric motor from the
cutting chain when the third means is activating the first and
second means. .Iaddend..Iadd.
30. The apparatus as in claim 22, further comprising a handguard
coupled to the third means, wherein movement of the handguard to an
OFF position simultaneously and concurrently operates both the
first means and the second means via the third means to quickly
stop the rotation of the cutting chain. .Iaddend..Iadd.
31. The apparatus as in claim 30, further comprising a clutch
coupled to the cutting chain, the electric motor and the third
means, wherein the clutch disengages the electric motor from the
cutting chain when the third means is activating the first and
second means. .Iaddend..Iadd.
32. An apparatus comprising: a cutting chain; an electric motor
coupled to the cutting chain; a brake drum; a mechanical brake
coupled to the brake drum, wherein activation of the mechanical
brake results in a braking force on the brake drum that stops
rotation of the cutting chain; an electrical brake circuit coupled
to the electric motor, wherein activation of the electronic brake
results in a dynamic braking force on the electric motor; and a
trigger member coupled to the mechanical brake and the electronic
brake circuit, wherein movement of the trigger member to an OFF
position simultaneously and concurrently operates both the
mechanical brake and the electronic brake circuit to quickly stop
the rotation of the cutting chain. .Iaddend..Iadd.
33. The apparatus as in claim 32, further comprising a power switch
coupled to the trigger member, wherein movement of the power switch
to an OFF position simultaneously and concurrently operates both
the mechanical brake and the electrical brake via the trigger
member to quickly stop the rotation of the cutting chain.
.Iaddend..Iadd.
34. The apparatus as in claim 33, further comprising a handguard
coupled to the trigger member, wherein movement of the handguard to
an OFF position simultaneously and concurrently operates both the
mechanical brake and the electrical brake via the trigger member to
quickly stop the rotation of the cutting chain. .Iaddend..Iadd.
35. The apparatus as in claim 34, further comprising a clutch
coupled to the cutting chain, the electric motor and the trigger
member, wherein the clutch disengages the electric motor from the
cutting chain when the trigger member is in the OFF position.
.Iaddend..Iadd.
36. The apparatus as in claim 32, further comprising a handguard
coupled to the trigger member, wherein movement of the handguard to
an OFF position simultaneously and concurrently operates both the
mechanical brake and the electrical brake via the trigger member to
quickly stop the rotation of the cutting chain. .Iaddend..Iadd.
37. The apparatus as in claim 36, further comprising a clutch
coupled to the cutting chain, the electric motor and the trigger
member, wherein the clutch disengages the electric motor from the
cutting chain when the trigger member is in the OFF position.
.Iaddend.
Description
FIELD OF THE INVENTION
This invention relates to an electromotive chain saw.
BACKGROUND OF THE INVENTION
In a conventional electromotive chain saw, a hand guard for
protecting an operator's hands is provided in front of a handle.
Additionally, a brake band is wound around a brake drum for
stopping the operation of a cutting chain. By operating the hand
guard and pulling one end of the brake band, the brake drum is
tightened with the brake band, thereby stopping the cutting
chain.
However, in such electromotive chain saws, even after a trigger
member is released and a motor drive switch is turned off, the
inertial rotation of the motor often results in the rotation of the
cutting chain for several seconds. If the rotating chain contacts
or hits the ground, it is often damaged, thereby requiring the
replacement of the chain itself. The material in process is also
inadvertently damaged. Furthermore, the operator cannot go to the
subsequent steps of work until the chain is completely stopped.
Thus, the work efficiency is deteriorated.
To solve the aforementioned problem, it is proposed in Japanese
examined and published patent application No. 657401 that a circuit
having a brake winding is provided in an electromotive motor and
the circuit is closed when a trigger member is released, for the
purpose of dynamic braking without any impact.
Such gradual stopping of the chain achieved in the proposal fails
to satisfy a recent demand for stopping the chain quickly, for
example, within one second after the trigger member is
released.
SUMMARY OF THE INVENTION
Wherefore, an object of the present invention is to provide a brake
device for a chain saw that can quickly stop the rotation of a
cutting chain when a trigger member is released.
To achieve this or other object, the present invention provides an
electromotive chain saw, having an electric motor for providing a
rotary drive force to a drive sprocket on which a cutting chain is
wound, a trigger member for energizing the electric motor when
turned on and for stopping the electric motor when turned off, a
trigger link mechanical brake for being engaged with a brake drum
secured to the drive sprocket when the trigger member is turned off
and for being disengaged from the brake drum when the trigger
member is turned on, and a trigger link brake circuit for
cooperating with the trigger member and applying a dynamic braking
force to the electric motor when the trigger member is turned
off.
In operation of the electromotive chain saw, when the trigger
member is turned off, both the trigger link mechanical brake and
the trigger link brake circuit are operated. The mechanical braking
of the brake drum and the electric braking of the electric motor
are concurrently carried out. As a result, the cutting chain is
stopped directly stopped by the trigger link mechanical brake and
indirectly by the trigger link brake circuit, more quickly as
compared with the provision of only the trigger link brake circuit
or only the trigger link mechanical brake.
The number of rotations of the electric motor can be quickly
decreased, in the electromotive chain saw in which the rotary drive
force is transmitted from the electric motor via a centrifugal
clutch mechanism to the drive sprocket. This occurs, when a
predetermined number of rotations of the electric motor is reached
or exceeded and no rotary drive force is transmitted to the drive
sprocket when the number of rotations is lower than the
predetermined number of rotations. Since the centrifugal clutch is
quickly released, the load on the trigger link mechanical brake can
be reduced. Therefore, the cutting chain can be instantly stopped
and the trigger link mechanical brake results in increased
durability.
Instead of the centrifugal clutch mechanism, the clutch mechanism
can be composed of a plurality of engagement teeth formed on the
brake drum, an engagement member rotated together with a rotation
shaft rotated by the electric motor and slidable in an axial
direction relative to the rotation shaft for engaging with the
engagement teeth on the brake drum, and an urging member for
pushing and urging the engagement member toward the brake drum. The
electromotive chain saw is further provided with a clutch release
member for releasing the engagement of the clutch mechanism by
pushing back the engagement member against the urging member when
the trigger member is moved from its ON position to its OFF
position.
In the conventional electromotive chain saw having the clutch
release member, the cutting chain can be instantly stopped with a
mechanical brake force when the trigger member is turned off. This
occurs while gradually stopping the inertial rotation of the
electric motor. In the present invention, the cutting chain and the
electric motor are concurrently stopped, thereby eliminating
discomfort given to an operator when the electric motor is
inertially rotated even after the cutting chain is stopped.
In addition, a further advantage of the present invention is
provided by the provision of the aforementioned dynamic braking. In
actual operation of the conventional electromotive chain saw, when
the released trigger member is turned on immediately after turning
off, if the motor is still inertial rotated, the rotating clutch
components are going to be engaged with one another and the rotary
drive force of the electric motor is applied to an engagement
detent and other components, thereby impairing the durability of
the clutch mechanism. However, in the present invention, the
electric motor is also stopped by the dynamic braking. Therefore,
the durability of the engagement detent and other clutch components
is enhanced.
In the electromotive chain saw, a conventional brake band can be
wound around the brake drum, and a trigger link mechanical brake
can be provided. By operating a hand guard and pulling the
connected end of the brake band, the brake drum is tightened with
the brake band, thereby stopping the cutting chain against the
rotary drive force of the electric motor. Also, by releasing the
trigger member, the cutting chain is stopped directly by the
trigger link mechanical brake and indirectly by the trigger link
brake circuit.
The trigger link mechanical brake of the electromotive chain saw is
provided with an operable member secured to an end of the brake
band, for cooperating with the trigger member, such that the brake
band is pulled and tightened when the trigger member is released
and the brake band is released or loosened when the trigger member
is turned on.
An operable member is provided which is secured to one end of the
brake band having the other end operatively connected to the hand
guard, for cooperating with the trigger member. This adds only a
slight structural change to the conventional structure and requires
no complicated mechanical arrangement. When the trigger member is
released, the end of the brake band, opposite the end operatively
connected with the hand guard, is pulled, thereby tightening the
brake band for stopping the cutting chain. Therefore, when braking
by the trigger link mechanical brake is employed a frictional force
is applied to the opposed part of the brake band resulting in a
frictional force at the time of braking by the operation of the
hand guard.
The trigger link mechanical brake can be provided with a brake shoe
for engaging with the outer periphery of the brake drum, an urging
member for normally urging or pressing the brake shoe to the brake
drum, and a pulling member for disconnecting the brake shoe from
the brake drum against the urging member when the trigger member is
depressed or turned on.
The brake shoe is provided separately from the brake band and is
operatively connected to the hand guard. When the trigger member is
released, the brake shoe applies a braking force without giving any
frictional force to the brake band.
Alternatively, the trigger link mechanical brake can be provided
with a brake shoe operatively connected to the trigger member for
engaging with the inner periphery of the brake drum. When the
trigger member is released, the brake shoe is pushed onto the brake
drum, and when the trigger member is turned on, the brake shoe is
disconnected from the brake drum.
The trigger link brake circuit of the electromotive chain saw is
provided with a main winding and a brake winding both in a field
slot. The supply of a drive current to an armature and the main
winding and the supply of a counter electromotive force arising
with the brake winding to the armature are changed over with a
single-pole double-throw switch, thereby driving and braking the
electric motor. When the single-pole double-throw switch is changed
over such that the drive current is supplied to the armature and
the main winding, one end of the brake winding is disconnected from
the armature via the single-pole double-throw switch, and the other
end of the brake winding is disconnected from the main winding via
a single pole switch.
During the operation of the electromotive chain saw, in the trigger
link brake circuit, the brake winding is disconnected from the main
winding by the single pole switch, and the brake winding is
disconnected from the armature by the single-pole double-throw
switch. Therefore, even when the main winding and the brake winding
are wound in the same field slot, the brake winding and the main
winding are completely insulated via the single pole switch and
thus will not deteriorate and no field layer shortage thus occurs.
Therefore, to provide the sufficient capabilities of the brake
winding, the number of windings can be increased. The trigger link
brake circuit is highly durable while it also fulfills its braking
performance. For this purpose, the inexpensive single pole switch
is provided, eliminating the need for a two-pole double-throw
switch, which is cost effective.
To operate the electromotive chain saw, in the trigger link brake
circuit, the single pole switch is switched over such that the
brake winding is disconnected from the armature and the main
winding. The clutch mechanism is engaged. Subsequently, the
single-pole double-throw switch is changed over such that the power
source is connected with the armature and the main winding.
To apply a braking force to the electromotive chain saw, the
single-pole double-throw switch is changed over such that the power
source is disconnected from the armature an the main winding and
the brake winding is connected with the armature. The clutch
mechanism is disconnected. Subsequently, the single pole switch is
changed over such that the brake winding is connected with the
armature.
When the electric motor is in operation and the single-pole
double-throw switch is turned on, in the switching approach, no
connection is made between the brake winding and the main winding,
therefore, no field layer shortage arises.
Furthermore, when the chain saw is in operation, after the clutch
mechanism is engaged, the single-pole double-throw switch is
changed over to connect the power source with the main winding and
the armature, and the electric motor is driven. When the chain saw
is braked, after the single-pole double-throw switch is changed
over to disconnect the power source from the main winding and the
armature, the clutch mechanism is disengaged. The engagement and
disengagement of the clutch mechanism can thus be easily carried
out and the durability of the engagement detent can be
enhanced.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described, by way of example, with
reference to the drawings, in which:
FIG. 1 is a partly broken front view of an electromotive chain saw
according to a first embodiment of the invention;
FIG. 2 is a plan view of the chain saw of the first embodiment;
FIG. 3 is an enlarged view of a mechanical brake device
interconnected with a hand guard of the chain saw of the first
embodiment;
FIG. 4 is a circuit diagram of an electric brake device of the
chain saw;
FIG. 5 is a partly broken front view of a chain saw according to a
second embodiment of the invention;
FIG. 6 is an enlarged view of a brake shoe in the chain saw of the
second embodiment;
FIG. 7A is a plan view, FIG. 7B is a partly broken rear view, FIG.
7C is a cross-sectional view showing the securing of a wire, and
FIG. 7D is a perspective view showing a block member for securing
the wire, of the chain saw of the second embodiment;
FIG. 8 is a partly broken front view of a chain saw according to a
third embodiment of the invention;
FIG. 9 is a partly broken plan view of the chain saw according to
the third embodiment of the invention;
FIG. 10A is a cross-sectional view showing the clutch engagement,
FIG. 10B is a cross-sectional view showing the clutch disengagement
and FIG. 10C is an explanatory view showing the movement of a
swingable detent when the clutch is engaged or disengaged, of the
chain saw according to the third embodiment;
FIG. 11A is an explanatory view of the interconnection of the
clutch and the brake device in the chain saw of the third
embodiment; and FIG. 11B is a perspective view of a single pole
switch;
FIG. 12 is a circuit diagram of an electric brake device in the
chain saw of the third embodiment; and
FIG. 13 is a circuit diagram of an electric brake device in a chain
saw according to a modification.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in FIG. 1, in an electromotive chain saw 10 of the first
embodiment, a chain CH is wound around a guide bar GB extending
from a housing and is driven with an electric motor M (as shown in
FIG. 8) and a not-shown centrifugal clutch built into the housing.
The electromotive chain saw 10 is manually held with a forward
handle 11 and a rearward handle 13. The grip of the rearward handle
13 is provided with a movable trigger lever 15. A hand guard 17 is
disposed in front of the forward handle 11, with a hand guard brake
device 20 built therein, which is operated by turning the hand
guard 17 in the direction shown by arrow 16 in FIG. 3. The trigger
lever 15 is normally urged, by a spring having a switch built
therein, in the direction shown by an arrow 14 in FIG. 1, and is
brought in contact with a push button 19a of a power switch 19 of
the electric motor when depressed.
As shown in FIG. 3, the hand guard the brake device 20 applied in
cooperation with the hand guard 17 is formed with a steel brake
band 23 wound around a brake drum 21, also serving as a centrifugal
clutch drum, securely attached onto a sprocket SP. The hand guard
brake device 20 is also provided with a linkage 25 for connecting a
forward end 23a of brake band 23 to the hand guard 17. The linkage
25 is formed with a forward end link plate 31 interposed between
engagement projections 17a, 17b of hand guard 17. The forward end
link plate 31 is interconnected with a middle link plate 33 by a
rearward jaw 32. The middle link plate 33 is further interconnected
with a rear end link plate 35 which is urged forwards by a coil
spring 34.
When the hand guard 17 is in an initial position as shown by a
solid line in FIG. 3, the link plates 31, 33, 35 are aligned,
thereby pushing against the coil spring 34, loosening the brake
band 23 and permitting the brake drum 21 to rotate. When the hand
guard 17 is rotated in the direction shown by the arrow 16 in FIG.
3, the projection 17a of hand guard 17 lowers downward the forward
end link plate 31, as shown by a two-dotted line. As a result, the
middle link plate 33 is disengaged from the rearward jaw 32 and is
rotated, thereby pulling the rear end link plate 35 forwards. The
coil spring 34 is thus immediately extended, thereby quickly
tightening the brake band 23. The brake drum 21 is forced to stop
and the chain CH is also stopped.
As shown in FIGS. 1, 2 and 3, a rear end 23b of brake band 23 is
fixedly hooked on a bent rod 41, such that a mechanical brake
device 40 is formed for being operated with the power switch 19
when the trigger lever 15 is released. The bent rod 41 is
reciprocatably supported in a body case 10a. The rear end of bent
rod 41 is secured to the rear end of coil spring 43 via a washer 45
and a double nut 46. The forward end of coil spring 43 is secured
to part of the body case 10a. The bent rod 41 is thus urged
rearwardly by the coil spring 43.
The rear end of the bent rod 41 is engaged with an upwardly
extending lever 51a of a movable member 51 rotatable about a
rotational center 52. The movable member 51 is engaged with the
forward end of the trigger lever 15 by its rearward lever 51b
extending perpendicularly from the upwardly extending lever 51a.
The trigger lever 15 is rotatably supported on a support 15a, and a
forward end 15b, remote from the support 15a and is largely moved
by turning on or off the power switch 19.
In operation, when the power switch 19 is turned off, as shown by
the solid line in FIG. 3, the movable member 51 of the brake device
40 is moved in a counterclockwise direction as seen in the figure
by means of the force of the coil spring 43, thereby pulling the
bent rod 41 rearwardly. Therefore, the brake band 23 is pulled or
tightened, thereby applying a braking force onto the brake drum
21.
When the trigger lever 15 is depressed and the power switch 19 is
turned on, as shown by a two-dotted line in FIG. 3, the movable
member 51 is pushed in a clockwise direction as seen in the figure.
The rear end of the bent rod 41 is thus pushed forwards. The
compression of coil spring 43 permits the bent rod 41 to slide
forwards. Accordingly, the brake band 23 is loosened, aided by the
restoring force of its steel construction.
The chain saw 10 is provided with an electric drive and brake
device 60 as shown in FIG. 4. The electric drive and brake device
60 is composed of a drive circuit 61 for supplying a drive current
to a main winding MW and an armature by a single-pole double-throw
switch SW when the trigger lever 15 is turned on and of a brake
circuit 62 for supplying a counter electromotive force arising on a
brake winding BW to the armature by the single-pole double-throw
switch SW when the trigger lever 15 is released.
In the first embodiment, when the trigger lever 15 is released, the
aforementioned mechanical brake device 40 and the electric drive
and brake device 60 for dynamic braking shown in FIG. 4 are
operated concurrently. While a braking force is mechanically
applied to the brake drum 21, the inertial rotary force of the
electric motor is diminished by the dynamic braking, quickly
decreasing the number of rotations of the electric motor and
releasing the centrifugal clutch. Since the centrifugal clutch is
disconnected, no inertial force of the electric motor is
transmitted, thereby contributing to the mechanical stop of brake
drum 21. Therefore, when the trigger lever 15 is released, no
rotary drive force is transmitted to the brake drum 21. When the
brake band 23 is tightened around the stopped brake drum 21, only
the inertial rotary force of the chain CH is loaded on the brake
band 23. The chain CH can be quickly stopped and the durability of
brake drum 21, brake band 23 and chain CH can be enhanced.
The hand guard brake device 20 cooperates with the hand guard 17
and the rear end 23b of the brake band 23 is operatively connected
via the bent rod 41 with the mechanical brake device 40. Such brake
mechanism is achieved with a minimum number of components and such
a simple mechanical structure.
The mechanical brake device 40 cooperates with the power switch 19
and exerts a braking or tightening force to the brake band 23 in
the direction opposite to the force exerted to the brake band 23 by
the operation of hand guard 17. When the hand guard brake device 20
is operated, the frictional faces of brake band 23 and brake drum
21 are deviated from those when the mechanical brake device 40 is
operated. The frictional face of brake band 23 is prevented from
being worn quickly by the operation of the hand guard 17 for
braking.
Furthermore, as shown in FIGS. 1 and 2, the mechanical brake device
40 is formed in a clearance in the vicinity of side walls of the
body case 10a using the bent rod 41, without increasing the size of
the chain saw 10.
A second embodiment is now explained. The second embodiment is the
same as the first embodiment in that the brake circuit 62 for
dynamic braking as shown in FIG. 4, the hand guard brake device 20
operatively connected to the hand guard 17, and the centrifugal
clutch are provided. The components having the same reference
numerals as those of the components of the first embodiment are not
explained hereinafter. only the aspect of the second embodiment
different from the first embodiment, the structure of the
mechanical brake device operated when the trigger lever is let off,
is explained.
In a chain saw 110 according to the second embodiment, as shown in
FIGS. 5 and 6, a mechanical brake device 140 is composed of a brake
shoe 141 which can be swung on a support 142a and can be engaged
with the periphery of brake drum 21. The mechanical brake device
140 is also composed of a coil spring 143 for urging the brake shoe
141 to engage with the brake drum 21, and a wire 145 connected at
one end to a free end 142b of brake shoe 141 and connected at the
other end to a forward end 115c of trigger lever 115.
The wire 145 is inserted through a protective tube 147 having both
ends securely positioned in a body case 110a. The trigger lever 115
is swingable on a support 115d between a connected end of wire 145
and a trigger contact 115a.
The trigger lever 115 is connected with the wire 145 by engaging a
cylindrical block 145a at the end of wire 145 into a hole 115b
shown in FIG. 7B in the trigger lever 115, in the same manner as in
securing a bicycle brake wire. A forward end 145b of wire 145 is
connected with the brake shoe 141, as shown in FIG. 7C, by
inserting the forward end 145b in a tapered square hole 141b in a
brake shoe body 141a, attaching a block 151 from underneath, and
fastening the block 151 with a screw 153 such that the forward end
145b of wire 145 is fastened between the block 151 and the tapered
face defining the square hole 141b. An upper part of square hole
141b communicates with an oval groove 141c having a sufficiently
small width for preventing the screw 153 from falling off. As shown
in FIG. 7D, the block 151 is a specially configured square nut
having a slit 151a for receiving the wire 145 in a tapered face
151b.
In operation of mechanical brake device 140, as shown by a solid
line in FIG. 6, when the power switch 19 is turned off and the
trigger lever 115 is in its OFF position, the wire 145 is loosened,
and the brake shoe 141 is pushed by an urging force of coil spring
143 onto the periphery of brake drum 21, thereby applying a braking
force such that the chain CH is prevented from rotating.
When the power switch 19 is turned on, as shown by a two-dotted
line in FIG. 6, the wire 145 is pulled or tightened while the
trigger lever 115 is moved to its ON position, thereby pulling the
brake shoe 141 against the urging force of coil spring 143 and
permitting the brake drum 21 to rotate. The drive force can be
transmitted from the electric motor to the chain CH.
In the chain saw 110 of the second embodiment, by depressing the
trigger lever 115 and turning on the power switch 19, the brake
drum 21 is permitted to rotate, thereby rotating the chain CH. By
letting off the trigger lever 115 and turning off the power switch
19, the brake shoe 141 applies a braking force to the brake drum
21, thereby instantly halting the inertial rotation of chain
CH.
As aforementioned, in the second embodiment, by turning off the
power switch 19, the brake drum 21 is stopped by a frictional force
applied by the brake shoe 141, thereby quickly stopping the chain
CH.
The brake shoe 141, operatively connected to the hand guard 17, is
provided separately from the brake band 23 of hand guard brake
device 20. Therefore, the mechanical brake device 140 operatively
connected with the power switch 19 can be added without affecting
the conventional structure. The conventional structure can be
easily modified in design to incorporate the mechanical brake
device 140.
The mechanical brake device 140 operatively connected with the
power switch 19 is provided with the components different from
those of the mechanical brake device 20 operatively connected with
the hand guard 17. The face of the brake band 23 for receiving the
frictional force applied when the hand guard 17 is operated is
prevented from being worn too quickly.
Furthermore, as shown in FIGS. 5 and 7, the mechanical brake device
140 is formed in a clearance in the vicinity of side walls of the
body case 110a using the wire 145, without increasing the size of
the chain saw 110.
The brake shoe 141 requires no restoring properties different from
the brake band 23. The material of the mechanical brake device 140
is selected just by selecting a friction coefficient and
consideration of durability. When the brake shoe 141 is pushed
against the periphery of brake drum 21 for braking, the power
switch 19 is turned off and no strong drive force is applied to the
brake drum 21. Accordingly, the material of the brake shoe 141 is
chosen to have a sufficiently large friction coefficient. The
braking capabilities of mechanical brake device 140 can be
optionally designed.
In the same manner as in the first embodiment, when the trigger
lever 115 is released, the mechanical brake device 140 and the
brake circuit 62 are operated concurrently. While a braking force
is mechanically applied to the brake drum 21, the inertial rotary
force of the electric motor is diminished by dynamic braking,
quickly decreasing the number of rotations of the electric motor
and releasing the centrifugal clutch. When the trigger lever 15 is
released, no rotary drive force is transmitted to the brake drum
21. Therefore, without exerting excessive force to the brake shoe
141, the chain CH can be quickly stopped. The durability of brake
drum 21, brake shoe 141 and chain CH can be enhanced.
A third embodiment is now explained referring to FIGS. 8-12. The
third embodiment is the same as the first embodiment in that the
electric drive and brake device 60 for dynamic braking as shown in
FIG. 4, and the hand guard brake device 20 operatively connected to
the hand guard 17 are provided. The components having the same
reference numerals as those of the components of the first
embodiment are not explained hereinafter. The aspects of the third
embodiment different from the first embodiment, the clutch
mechanism, the mechanical brake device operated when the trigger
lever is released and the circuit structure of the electric drive
and brake device, are explained.
In an electromotive chain saw 560 according to the third embodiment
shown in FIG. 8, a trigger-linked mechanical brake 570 is driven
with a linkage when a trigger member 585 is released, thereby
disconnecting a clutch 590 and stopping the brake drum 521. The
hand gaurd brake device, operated by turning the hand guard 17 in
the direction shown by the arrow 16, is identical to the
corresponding device of the first embodiment.
As shown in FIGS. 10A-C and 11A-B, the trigger-linked mechanical
brake 570 is composed of a brake shoe 571, a metal support fitting
573 having a shape similar to that of a tennis racket for
supporting the brake shoe 571, a swingable lever 575 connected with
a pin 578b to an arm 573a of metal support fitting 573, and a
clutch 590 turned on or off with a frame 573b of metal support
fitting 573.
As shown in FIG. 10C, the frame 573b of metal support fitting 573
is partly bent into an M-shaped part 573c. The formed M-shaped part
573c is in contact with the top of a swingable detent 577 secured,
as seen in FIG. 11A, with a rivet 576b to a block 576a in a
housing. The swingable detent 577 is normally urged by a spring
577a clockwise as seen in the figure. As shown in FIG. 11A, the
frame 573b is restricted in its movement, or guided, by a screw
578a securely inserted in a long hole 573d formed in the frame
573b.
As shown in FIG. 11A, the metal support fitting 573 and the
swingable lever 575 are interconnected with a pin 578b engaged in a
longitudinal hole 575a. When the swingable lever 575 is moved, the
metal support fitting 573 can be slid smoothly.
A brake shoe 571 is fixedly supported on an arm 573e raised on the
root surface of arm 573a of metal support fitting 573, and urged or
pushed against an inner periphery of brake drum 521 by a coil
spring 579 housed in a case 576c formed adjacent the raised arm
573e.
A free end 575b of swingable lever 575 is connected with a pin 578c
to one end 580a of a link rod 580. The other end 580b of link rod
580 is connected with a pin 578d to the tip of an arm 585a of
trigger member 585.
As shown in FIGS. 8 and 11A, the trigger member 585 is rotated
about a support 585c at the forward end of a tab 585b which can be
manually depressed. The support 585c is interposed between the tab
585b and the arm 585a, as shown in FIG. 11A. When the trigger
member 585 is depressed, the arm 585a is rotated clockwise about
the support 585c, thereby pushing the link rod 580 forward as shown
by a two-dotted line in FIG. 11A. When the trigger member 585 is
released, the trigger member 585 is rotated counterclockwise by the
urging force of pushing button 613 of power switch SW1 and the
urging force of the coil spring 579 behind the brake shoe 571,
thereby returning the link rod 580 to the initial position, as
shown by a solid line in FIG. 11A.
When the trigger member 585 is depressed, a compression load is
applied to the link rod 580. Therefore, the link rod 580, formed by
pressing a metal plate, is bulged in its middle so as to have an
improved buckling strength.
As shown in FIGS. 10A and 10B, the clutch 590 is composed of a male
clutch member 593 formed integral with and rotatable about a
rotation shaft 591 and slidable in an axial direction, a female
clutch member 595 provided on the brake drum 521, and a coil spring
597 for urging the male clutch member 593 toward the female clutch
member 595. One pair of axial grooves 591a are spaced apart at an
angle of 90 degrees from the other pair of grooves 591a, about the
rotation shaft 591. Grooves 593a are formed in the male clutch
member 593, corresponding to the grooves 591a. The male clutch
member 593 is fixedly attached to the rotation shaft 591 via steel
balls 592 received between the grooves 591a and 593a, such that the
male clutch member 593 is integral with the rotation shaft 591
about the rotation axis and is also slidable in the axial
direction. The male clutch member 593 is provided with a jaw 593b
having an outer diameter of sufficient size to contact the
swingable detent 577. When the swingable detent 577 is depressed by
the M-shaped part 573c, the jaw 593b is also depressed, thereby
releasing the clutch 590.
The operation of trigger-linked mechanical brake 570 is now
explained referring to FIGS. 10 and 11.
When the trigger member 585 is released, the link rod 580 and the
swingable lever 575 are in the position shown by a solid line in
FIG. 11A. The M-shaped part 573c is lowered to depress the
swingable detent 577 as shown in the upper figure of FIG. 10C. In
the clutch 590, as shown in FIG. 10B, the male and female clutch
members 593 and 595 are disconnected from each other, and no rotary
force is transmitted from the rotation shaft 591 to the brake drum
521 and the sprocket SP. In addition, the brake shoe 571 is moved
to the position shown by a solid line in FIG. 11A such that the
brake shoe 571 is urged by the coil spring 579, thereby stopping
the brake drum 521 and the sprocket SP. Therefore, when the trigger
member 585 is released, the clutch 590 is immediately released, and
the brake force is applied by the brake shoe 571, thereby instantly
stopping the chain CH.
When the trigger member 585 is depressed, the link rod 580 and the
swingable lever 575 are moved to the position shown by a two-dotted
line in FIG. 11A. The M-shaped part 573c applies no depressing
force to the swingable detent 577 as shown in the lower figure of
FIG. 10C. The swingable detent 577 is rotated clockwise as seen in
FIG. 10C by the urging force of the coil spring 597 via the jaw
593b of male clutch member 593 and by the urging force of spring
577a. In the clutch 590, as shown in FIG. 10A, the male and female
clutch members 593 and 595 are engaged with each other. The brake
shoe 571 is returned to the position shown by the two-dotted line
in FIG. 11A, in which the coil spring 579 is compressed. No brake
force is applied to the brake drum 521 and the sprocket SP any
longer. Therefore, when the trigger member 585 is depressed, the
clutch 590 is immediately engaged and no brake force is applied by
the brake shoe 571. Drive force is instantly transmitted from the
motor M to the sprocket SP, thereby rotating the chain CH.
An electric drive and brake device 600 according to the third
embodiment includes, as shown in FIG. 12, a brake circuit of a
single-phase series commutator motor. In the electric drive and
brake device, a main winding MW for driving an armature M and a
brake winding BW for braking the armature M are provided in the
same field slot. The armature M is driven or braked by changing
over the connection of the armature M with the main winding MW and
the brake winding BW via a single-pole double-throw switch SW1. In
the electric drive and brake device 600 a single pole switch SW2 is
provided between a common contact X of main winding MW relative to
armature M and the brake winding BW. When the armature M is driven,
the single pole switch SW2 and the single-pole double-throw switch
SWl are switched over as shown by a solid line in FIG. 12. When the
armature M is braked, the single pole switch SW2 and the
single-pole double-throw switch SWl are switched over as shown by a
dotted line in FIG. 12.
As shown in FIGS. 8 and 11A, the single-pole double-throw switch
SW1 and the single pole switch SW2 are housed in the rearward
handle 13 of the chain saw.
As shown in FIG. 11A, the single-pole double-throw switch SW1 is a
switch block provided with three contacts A, B and C in a housing
611. When a push button 613 is projected from the housing 611, the
contact A is connected to the contact C, and when the push button
613 is depressed into the housing 611, the contact B is connected
to the contact C. Also as shown in FIGS. 11A and 11B, the single
pole switch SW2 is a switch block provided with two contacts P and
Q in a housing 621. When a push button 623 is projected from the
housing 621, the contact P is connected to the contact Q, and when
the push button 623 is depressed into the housing 621, the contact
P is disconnected from the contact Q. The push buttons 613 and 623
are normally urged by a not-shown spring in the housings 611 and
621 to project from the housings 611 and 621, respectively.
The trigger member 585 is provided in the rearward handle 13 such
that the trigger member 585 can contact the push buttons 613, 623,
respectively. When the trigger member 585 is depressed in the
rearward handle 13, both the push buttons 613, 623 are depressed in
the housings 611, 621, respectively. When the trigger member 585 is
released, the push buttons 613 and 623 are projected from the
housing 511 and 521, respectively.
In the third embodiment, when the trigger member 585 is depressed,
the contact P is first disconnected from the contact Q in the
single pole switch SW2. Subsequently, in the single-pole
double-throw switch SW1, the contact A is disconnected from the
contact C and the contact B is connected to the contact C. When the
trigger member 585 is released, first in the single-pole
double-throw switch SW1, the contact B is disconnected from the
contact C, and the contact A is connected to the contact C.
Subsequently, in the single pole switch SW2, the contact P is
connected to the contact Q.
In the third embodiment, when the trigger member 585 is depressed,
after the male and female clutch members 593 and 595 are engaged
with each other, the single-pole double-throw switch SW1 is changed
over to the closed circuit connecting the electric power and the
electric motor, thereby driving the electric motor. When the
depressed trigger member 585 is released, the single-pole
double-throw switch SW1 is changed over to the open circuit for
disconnecting the electric power from the electric motor, thereby
placing the electric motor in the inoperative condition.
Subsequently, the male and female clutch members 593 and 595 are
disengaged from each other. Therefore, while the electric motor is
driven, no engagement or disengagement of the clutch members are
performed, thereby enhancing the durability of the clutch detent
members.
In the third embodiment, when the trigger member 585 is released,
the clutch 590 is disconnected, and a mechanical braking force is
applied by the brake shoe to the brake drum. Therefore, without
loading much frictional force on the brake shoe, the chain can be
stopped quickly. Also, the electric drive and brake device for
dynamic braking is operated, thereby instantly stopping the
inertial rotation of the electric motor. In the third embodiment,
since the clutch 590 is forceably disconnected, the brake drum is
not braked by the electric brake circuit and the electric motor
itself is dynamically braked. However, the operator can recognize
the chain as well as the motor instantly stopping, and can operate
the chain saw comfortably. The clutch is mechanically disconnected
before the electric motor is stopped. Therefore, only the inertial
rotation of the electric motor is stopped through dynamic braking,
and the period of time required for stopping the electric motor can
be advantageously reduced. It can be appreciated that the third
embodiment provides a function of stopping the electric motor
quickly.
If, after disconnecting the clutch, no electric drive and brake
device is operated, the electric motor will be inertially rotated
for several seconds, without any load of the chain put thereon. If
the trigger member is again depressed during such inertial
rotation, the inertially rotating male clutch member 593 will be
engaged with the mechanically stopped female clutch member 595. The
drive force of the electric motor acting on the engagement of the
clutch members will deteriorate the durability of the clutch
members 593, 595.
In the third embodiment, however, the chain is instantly stopped by
the trigger-linked mechanical brake and concurrently the electric
motor is instantly stopped by the electric brake circuit 600. If
the chain saw is again driven immediately after stopped, the male
and female clutch members 593 and 595 are engaged with each other
while the electric motor is stopped. No drive force of the electric
motor acts on the clutch engagement and the durability of the
clutch members 593, 595 is prevented from impairment. Since, in the
actual operation of the chain saw, the trigger member 585 may be
repeatedly turned on and off, the aforementioned advantage of the
enhanced durability is remarkably effective in the electromotive
chain saw provided with the trigger-linked mechanical brake having
the aforementioned clutch disconnecting mechanism.
In the third embodiment the inner and outer peripheries of the
brake drum are in contact with the brake device 570 operable when
the trigger member is released and the hand guard brake device 20
operatively connected with the hand guard 17, respectively. These
brake devices can be provided without increasing the size of the
brake drum 521 or the entire size of the chain saw. These brake
mechanisms can coexist in a compact structure.
In the third embodiment, by providing the M-shaped part 573c, as
the clutch first begins to be released, and after the clutch is
released, the braking force is applied. The time the clutch is
released deviates from the time the braking force is applied.
Therefore, a braking force can be easily applied. In the
embodiment, the clutch is released and the brake device 570 is
operated, using the action of a lever. The trigger member 585 can
be depressed without requiring a strong depression force, thereby
giving an operator comfort.
In a modified electric drive and brake device or circuit 600,
during the operation of the chain saw, the brake winding BW can be
disconnected from the main winding MW and the armature M via the
single pole switch SW2. In this case, since the main winding MW and
the brake winding BW, provided in the same field slot, are
disconnected from each other via the single pole switch SW2, the
windings fail to be deteriorated and no field layer shortage
occurs. Therefore, to provide sufficient braking capabilities of
brake winding BW, the number of windings of brake winding BW can be
increased. The modified brake circuit can form a highly durable,
highly capable brake device. Furthermore, the modified brake
circuit can be inexpensively formed by adding an inexpensive
single-pole switch to the brake circuit of the first embodiment,
obviating the necessity of a two-pole double-throw switch.
A further modified brake circuit, as shown in FIG. 13, can be
formed from the circuit shown in FIG. 4. A single-pole double-throw
switch HSW, closed when the hand guard 17 is operated, is provided
between the single-pole double-throw switch SW1 and the armature M.
In the circuit, when the hand guard brake device 20 is operatively
connected with the hand guard 17, the switch HSW is turned as shown
by a dotted line in FIG. 13, for dynamic braking. When either
switch SW1 or HSW is activated, the brake winding BW is changed
over for dynamic braking.
The electric drive and brake device 600 of the third embodiment can
be used in the first and second embodiments.
In the third embodiment, the single pole switch SW2 is turned on or
off by the arm 585a of trigger member 585. The single pole switch
SW2 can be positioned such that the switch SW2 can be turned on or
off by moving the link rod 580 provided with a projection.
This invention has been described above with reference to the
preferred embodiments as shown in the figures. Modifications and
alterations may become apparent to one skilled in the art upon
reading and understanding the specification. Despite the use of the
embodiment for illustration purposes, the invention is intended to
include all such modifications and alterations within the spirit
and scope of the appended claims.
* * * * *