U.S. patent application number 09/352406 was filed with the patent office on 2002-04-25 for engine starter with a thermostat for thermal protection.
Invention is credited to IWAMOTO, ATSUYA, SHIROYAMA, SHIGERU, YAGI, KATSUNORI.
Application Number | 20020047354 09/352406 |
Document ID | / |
Family ID | 11945399 |
Filed Date | 2002-04-25 |
United States Patent
Application |
20020047354 |
Kind Code |
A1 |
IWAMOTO, ATSUYA ; et
al. |
April 25, 2002 |
ENGINE STARTER WITH A THERMOSTAT FOR THERMAL PROTECTION
Abstract
A starter comprises a thermostat for detecting increases in the
temperature of brushes and interrupting the energizing of the
starter, and a heat conducting member secured to the thermostat for
conducting the heat of one of the brushes, the heat conducting
member being attached to the brush. The heat conducting member may
also be formed integrally with a brush holder. The heat conducting
member may additionally be secured to a bracket so as to hold a
base therebetween. The heat conducting member may also be composed
of a metallic material having superior thermal conductivity, and
may be copper or brass. An electrically insulating sheet may be
held between the brush holders and the base as heat insulating
material for preventing the transfer of heat from the brushes to
the base. An electrically insulating tube may also be interposed
between the thermostat and a first leg of the heat conducting
member.
Inventors: |
IWAMOTO, ATSUYA; (TOKYO,
JP) ; SHIROYAMA, SHIGERU; (TOKYO, JP) ; YAGI,
KATSUNORI; (TOKYO, JP) |
Correspondence
Address: |
SUGHRUE MION ZINN MACPEAK & SEAS
2100 PENNSYLVANIA AVENUE N W
WASHINGTON
DC
20037
|
Family ID: |
11945399 |
Appl. No.: |
09/352406 |
Filed: |
July 14, 1999 |
Current U.S.
Class: |
310/68C |
Current CPC
Class: |
H02K 11/25 20160101;
F02N 11/10 20130101 |
Class at
Publication: |
310/68.00C |
International
Class: |
H02P 009/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 26, 1999 |
JP |
11-17488 |
Claims
What is claimed is:
1. An engine starter comprising: a starter motor for starting an
engine, said starter motor including a brush and a brush holder;
and a control circuit for controlling said starter motor, said
control circuit including a thermostat for deenergizing said
starter motor when the temperature of said starter motor exceeds a
predetermined temperature; said engine starter further comprising:
a heat conducting member, having a first end thermally coupled to
said brush and a second end thermally coupled to said thermostat,
for conducting heat from said brush to said thermostat.
2. The engine starter as claimed in claim 1, wherein said
thermostat is secured to said heat conducting member and wherein
said heat conducting member is a substantially only means for
mechanically supporting said thermostat.
3. The engine starter as claimed in claim 2, wherein said heat
conducting member supports said thermostat within said starter
motor with a thermally insulating air gap defined therearound.
4. The engine starter as claimed in claim 1, wherein said heat
conducting member is a substantially "L"-shaped metal member having
first and second legs of "L", said first leg being thermally
coupled to and extending from said brush in a substantially radial
direction of the starter motor, and said second leg extending in a
substantially axial direction of the starter motor and
substantially along said thermostat.
5. The engine starter as claimed in claim 4, wherein said second
leg has a bend portion for positioning said thermostat on said
second leg.
6. The engine starter as claimed in claim 4, wherein said
thermostat and said second leg of said heat conducting member are
wrapped together by an adhesive tape.
7. The engine starter as claimed in claim 4, wherein an
electrically insulating material is interposed between said
thermostat and said second leg of said heat conducting member.
8. The engine starter as claimed in claim 1, wherein said first end
of said heat conducting member is embedded within said brush.
9. The engine starter as claimed in claim 1, wherein said first end
of said heat conducting member is an integral, continuous extension
of said brush holder.
10. The engine starter as claimed in claim 9, wherein said first
end of said heat conducting member extends from a mounting flange
of said brush holder.
11. The engine starter as claimed in claim 9, wherein a thermally
insulating material is interposed between said rear bracket and
said first end of said heat conducting member.
12. The engine starter as claimed in claim 1, wherein said first
end of said heat conducting member is mechanically fastened to said
brush holder.
13. The engine starter as claimed in claim 12, wherein said first
end of said heat conducting member is held between a rear bracket
of the starter motor and said brush holder secured to each
other.
14. The engine starter as claimed in claim 13, wherein a thermally
insulating material is interposed between said rear bracket and
said first end of said heat conducting member.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a starter provided with a
thermostat.
[0003] 2. Description of the Related Art
[0004] A starter is activated by the action of switching on a start
switch of a key switch, whereby an engine is ignited and started.
Once the engine is ignited and started, the starter is deactivated
by the action of switching off the start switch of the key switch.
At that time, for reasons such as incomplete return of the key
switch, etc., the start switch may not be switched off and the
starter may continue to be energized even after the engine has been
started, whereby the starter generates heat and is damaged by that
heat.
[0005] For that reason, in conventional techniques a thermostat is
built into the starter to detect the ambient temperature within the
starter and terminate operation of the starter if the ambient
temperature within the starter exceeds a predetermined temperature
in order to prevent excessive continuous energizing of the
starter.
[0006] Actual examples of such starters include starters with a
thermostat built directly into one of the brushes and starters with
a thermostat disposed beside one of the brushes.
[0007] FIG. 7 is a cross-section showing an example of a starter
with a thermostat disposed beside one of the brushes.
[0008] In the figure, the shaft 103 of an armature 101 comprising
commutator segments 102 disposed plurally around the circumference
thereof and constituting a motor portion is supported by a bearing
104 so as to be able to rotate freely. The bearing 104 is inserted
into and supported by a recess portion 105a disposed in a
thin-walled rear bracket 105 which houses the armature 101.
[0009] Brushes 106 which contact the commutator segments 102 and,
together with the commutator segments 102, constitute contacts for
supplying electric current to the armature 101 are disposed in
positions facing the commutator segments 102. Lead wires 110 are
connected to the brushes 106. The brushes 106 are pressed against
the commutator segments 102 with a predetermined pressure by
springs 107 and are supported by brush holders 108. The brush
holders 108 are disposed at four positions equidistantly spaced
around the circumference of the armature 101 and are secured to a
base 109 by rivets (not shown). A female thread is disposed in the
base 109, and the base 109 and the rear bracket 105 are secured to
each other by inserting a bolt from the outer end surface of the
rear bracket 105 into a bore (not shown) disposed in the end of the
rear bracket 105 so that the bolt engages the female thread
disposed in the base 109. In this way, the brush holders 108 are
supported by the rear bracket 105.
[0010] The brushes 106 are heated by heat generated by friction
between the brushes 106 and the commutator segments 102 and by heat
generated by the motor portion of the starter which is conducted to
the brushes 106. A long, slender, rod-shaped thermostat 160 for
detecting increases in the temperature of the brushes due to brush
heat being the heat contained in the brushes 106 and interrupting
the energizing of the starter is disposed in the vicinity of the
brushes 106 radially outside the brushes 106 relative to the
armature 101 such that the longitudinal direction of the thermostat
160 is parallel to the axial direction of the armature 101.
[0011] Within the thermostat 160 which comprises a hollow
pipe-shaped steel terminal 165 having a closed end, one tip of a
lead wire 161 which is one of two lead wires indicated by broken
lines in the figure is connected to one end of a bimetallic element
162, and a contact 163 is disposed on the other end of the
bimetallic element 162. Another contact 166 is disposed on one tip
of the other lead wire 164. The bimetallic element 162 deforms such
that above a predetermined temperature the contacts 163, 166 are
open and on or below the predetermined temperature the contacts
163, 166 are closed.
[0012] The two lead wires 161, 164 lead from the steel terminal 165
to the outside, extending so as to be insulated from each other,
and a male terminal 167 is connected to the tip of each of the lead
wires 161, 164. A connector 168 is integrally formed by molding
resin such that the two lead wires 161, 164 are covered.
[0013] An O-ring 169 is disposed on the cylindrical outer
circumferential portion 168a of the connector 168. A flat
plate-shaped flange 168b extends from the vicinity of the center of
the connector 168. The connector 168 which is integrated with the
thermostat 160 is secured to the rear bracket 105 by inserting a
bolt 115 into a bore 168c disposed in the flange 168b and engaging
a female thread 105a disposed in the rear bracket 105.
[0014] A hollow cylindrical resin holder 116 having a closed end
fits over the steel terminal 165 of the thermostat 160 and is
disposed on an outer circumferential portion of the steel terminal
165.
[0015] However, in many starters with a thermostat disposed in the
vicinity of the brushes, the brush heat is transferred to the
thermostat by radiation through air and it takes time for the brush
heat to be transferred as far as the thermostat, making the
temperature increases in the thermostat slower than the temperature
increases in the brushes. For that reason, in some cases the
starter may possibly be damaged by heat before the operation of the
starter is terminated by the action of the thermostat.
[0016] Furthermore, in starters with a thermostat built into one of
the brushes, installation of the thermostat is difficult because
the thermostat is embedded in the brush, and even if installation
is possible the brush has to be enlarged, making the starter
larger.
SUMMARY OF THE INVENTION
[0017] The present invention aims to solve the above problems and
an object of the present invention is to provide a compact starter
with superior heat transfer efficiency wherein the brush heat is
conducted directly to the thermostat by means of a heat conducting
member interposed between one of the brushes and the
thermostat.
[0018] In order to achieve the above object, according to one
aspect of the present invention, there is provided an engine
starter comprising:
[0019] a starter motor for starting an engine, the starter motor
including a brush and a brush holder; and
[0020] a control circuit for controlling the starter motor, the
control circuit including a thermostat for deenergizing the starter
motor when the temperature of the starter motor exceeds a
predetermined temperature;
[0021] the engine starter further comprising:
[0022] a heat conducting member, having a first end thermally
coupled to the brush and a second end thermally coupled to the
thermostat, for conducting heat from the brush to the
thermostat.
[0023] According to another aspect of the present invention, the
thermostat is secured to the heat conducting member and the heat
conducting member is a substantially only means for mechanically
supporting the thermostat.
[0024] According to another aspect of the present invention, the
heat conducting member supports the thermostat within the starter
motor with a thermally insulating air gap defined therearound.
[0025] According to another aspect of the present invention, the
heat conducting member is a substantially "L"-shaped metal member
having first and second legs of "L", the first leg being thermally
coupled to and extending from the brush in a substantially radial
direction of the starter motor, and the second leg extending in a
substantially axial direction of the starter motor and
substantially along the thermostat.
[0026] According to another aspect of the present invention, the
second leg has a bend portion for positioning the thermostat on the
second leg.
[0027] According to another aspect of the present invention, the
thermostat and the second leg of the heat conducting member are
wrapped together by an adhesive tape.
[0028] According to another aspect of the present invention, an
electrically insulating material is interposed between the
thermostat and the second leg of the heat conducting member.
[0029] According to another aspect of the present invention, the
first end of the heat conducting member is embedded within the
brush.
[0030] According to another aspect of the present invention, the
first end of the heat conducting member is an integral, continuous
extension of the brush holder.
[0031] According to another aspect of the present invention, the
first end of the heat conducting member extends from a mounting
flange of the brush holder.
[0032] According to another aspect of the present invention, the
first end of the heat conducting member is mechanically fastened to
the brush holder.
[0033] According to another aspect of the present invention, the
first end of the heat conducting member is held between a rear
bracket of the starter motor and the brush holder secured to each
other.
[0034] According to another aspect of the present invention, a
thermally insulating material is interposed between the rear
bracket and the first end of the heat conducting member.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a cross-section of a mounting structure of a
thermostat for a starter according to Embodiment 1 of the present
invention;
[0036] FIG. 2 is a cross-section of a mounting structure of a
thermostat for a starter according to Embodiment 2 of the present
invention;
[0037] FIG. 3 is a perspective view of a brush holder for a starter
according to Embodiment 2 of the present invention;
[0038] FIG. 4 is a cross-section of a mounting structure of a
thermostat for a starter according to Embodiment 3 of the present
invention;
[0039] FIG. 5 is a perspective view of a heat conducting member for
a starter according to Embodiment 3 of the present invention;
[0040] FIG. 6 is a connection diagram for a starter circuit using a
starter according to Embodiment 1 of the present invention; and
[0041] FIG. 7 is a cross-section of a mounting structure of a
conventional thermostat for a starter.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0042] Embodiment 1
[0043] FIG. 1 is a cross-section of a mounting structure of a
thermostat for a starter according to an embodiment of the present
invention. In FIGS. 1 to 5, parts or portions the same as or
similar to those in FIGS. 6 and 7 will be given the same
numbering.
[0044] In FIG. 1, the shaft 103 of an armature 101 comprising
commutator segments 102 disposed plurally around the circumference
thereof and constituting a motor portion is supported by a bearing
104 so as to be able to rotate freely. The bearing 104 is inserted
into and supported by a recess portion 105a disposed in a
thin-walled rear bracket 105 which houses the commutator segments
102.
[0045] Four generally parallelopiped brushes 106, 206 which contact
the commutator segments 102 and, together with the commutator
segments 102, constitute contacts for supplying electric current to
the armature 101 are disposed evenly around the circumference of
the armature 101 in positions facing the commutator segments
102.
[0046] A heat conducting member 218 which is an "L"-shaped brass
flat plate is embedded into one of these brushes and secured by
adhesive to form a heat conducting brush 206. One leg of the
"L"-shaped heat conducting member 218 extends in the radial
direction and has an inner end embedded into the brush 206. The
other leg of the "L" of the heat conducting member 218 extends into
the axial direction along a thermostat 260 which will be described
later.
[0047] The brushes 106, 206 are provided with lead wires 110 (FIG.
7) and are pressed against the commutator segments 102 with a
predetermined pressure by springs 107 (FIG. 7) and are each
slidably supported by brush holders 108. The brush holders 108 are
disposed at four positions equidistantly spaced from each other
around the circumference of the armature 101 and are secured to a
base 109 by rivets (not shown).
[0048] Here, an electrically insulating sheet 220 being an
electrically insulating member is disposed as heat insulation
between the brush holder 108 into which the heat conducting brush
206 is inserted and the base 109. Use is made of the fact that this
electrically insulating sheet 220 has poor thermal conductivity, so
that heat from the heat conducting brush 206 is less likely to be
conducted to the rear bracket 105 through the base 109 and thus
more likely to be transferred to the heat conducting member
218.
[0049] A thread hole is disposed in the base 109, and the base 109
and the rear bracket 105 are secured to each other by inserting a
bolt from the outer end surface of the rear bracket 105 into a bore
(not shown) disposed in the end of the rear bracket 105 so that the
bolt engages the thread hole disposed in the base 109. In this way,
the brush holders 108 are supported by the rear bracket 105. The
rear bracket 105 is connected to a yoke 215 by means of
unillustrated bolts with packing 214 and a plate 213 interposed
therebetween.
[0050] A long, slender, rod-shaped thermostat 260 is disposed
alongside the axial leg of the heat conducting member 218. The
thermostat 260 is covered by an electrically insulating tube 222 so
as not to be in direct contact with the heat conducting member 218,
and is secured to the heat conducting member 218 by adhesive tape
223.
[0051] The heat conducting member 218 is a substantially only means
for mechanically supporting the thermostat 260.
[0052] Consequently, the thermostat 260 is electrically insulated
from the brush 206 and the rear bracket 105.
[0053] Moreover, the heat conducting member 218 supports the
thermostat 260 within the starter motor 150 (FIG. 6) with a
thermally insulating air gap defined around the thermostat 260.
[0054] Consequently, the thermally insulating air gap makes the
transfered heat to the thermostat 260 less likely to escape.
[0055] Since the construction of the contacts within the thermostat
260 is the same as for those in the thermostat 160 in FIG. 7, the
following explanation will be based on FIG. 7. One tip of a lead
wire 161 which is one of two lead wires is connected to one end of
a bimetallic element 162, and a contact 163 is disposed on the
other end of the bimetallic element 162. Another contact 166 is
disposed on one tip of the other lead wire 164. The bimetallic
element 162 deforms such that above a predetermined temperature the
contacts 163, 166 are open and on or below the predetermined
temperature the contacts 163, 166 are closed.
[0056] The two lead wires 161, 164 lead from the steel terminal 165
to the outside, extending so as to be insulated from each other,
and are connected to a connector 168 molded from resin so as to
cover the two lead wires 161, 164.
[0057] An O-ring 169 is disposed on a cylindrical outer
circumferential portion of the connector 168. A retaining ring 266
composed of a center-bored disk-shaped flat plate is secured in the
vicinity of the center of the connector 168.
[0058] FIG. 6 shows an example of a connection diagram for a
starter circuit using a starter with a thermostat built
therein.
[0059] In the figure, 151 is a battery power source, 157 is a start
switch disposed in a key switch, 152 is an auxiliary switch
provided with a contact 153 and an electromagnetic coil 154, 155 is
a magnet switch, 156 is a main contact for switching on and off a
main current to a starter motor 150 being a direct-current motor
for starting an engine (not shown), and 158 is an attracting coil
functioning dually to generate a resistance allowing a minute
current to flow to the motor during engagement of a pinion gear
(not shown) of the starter and to generate an attracting force to
cause the pinion gear to engage with the ring gear (not shown) of
the engine. The thermostat 260 secured to the heat conducting
member 218 is connected in series to the electromagnetic coil
154.
[0060] Because the contacts of the thermostat 260 are closed when
the starter is not generating excessive heat, the electromagnetic
coil 154 is energized when the start switch 157 is switched on,
closing the contacts 153 and switching on the auxiliary switch 152.
At the same time, electric current flows through the attracting
coil 158 of the magnet switch 155, and as the current passes to the
starter motor 150, the pinion gear is shifted and brought into
engagement with the ring gear. If the pinion gear properly engages
the ring gear, the main contact 156 closes and the main current
flows to the starter motor 150, starting the engine.
[0061] However, for reasons such as incompleteness of the return of
the key switch, etc., there are cases where the start switch 157
may not be switched off and the starter motor 150 may continue to
rotate even after the engine has been started. In such cases, brush
heat is conducted immediately to the thermostat 260 through the
heat conducting member 218 and the temperature around the
thermostat 260 rises rapidly. When the thermostat 260 rises above
the predetermined temperature, the contacts of the thermostat 260
open, terminating the flow of current through the electromagnetic
coil 154, whereby the auxiliary switch 152 is switched off,
terminating the supply of current to the attracting coil 158 and
the starter motor 150, so that the starter does not generate
excessive heat. Because the electrically insulating sheet 220 is
disposed between the brush holder 108 into which the brush 206
mounted with the thermostat 260 is inserted and the base 109, heat
is less likely to escape to the base 109 and thus brush heat is
more likely to be conducted to the thermostat 260. Consequently,
the thermostat 260 is more likely to detect increases in the
temperature of the brush 206 without loss of time.
[0062] Moreover, the electrically insulating tube 222 is not
required if the two lead wires 161, 164 of the thermostat 260 are
electrically insulated from the steel terminal 165 of the
thermostat 260, or even if one of the lead wires is electrically
connected to the steel terminal 165 provided that the polarity
thereof matches that of the brush 206.
[0063] Furthermore, the material of the heat conducting member 218
is not limited to brass provided that the material has a good
thermal conductivity, and copper may also be used because it is
similar to brass in its workability. Carbon steel, stainless steel,
spring steel, etc., may also be used.
[0064] In addition, the brush holders 108 may be secured directly
to the rear bracket 105 without the intermediation of the base
109.
[0065] Embodiment 2
[0066] FIG. 2 is a cross-section of a mounting structure of a
thermostat for a starter according to another embodiment of the
present invention. The portion of FIG. 2 where the thermostat is
mounted is different from that of FIG. 1. That is to say, in FIG.
1, the heat conducting member 218 on which the thermostat is
mounted is secured to the brush 206, but in FIG. 2, a brush holder
308 has a portion corresponding to the heat conducting member is
formed integrally with the holder portion.
[0067] FIG. 3 is a perspective view showing the shape of the brush
holder 308 in detail.
[0068] The brush holder 308 is composed of brass and comprises:
flange portions 308a for securing the brush holder 308 to the base
109 by riveting; a brush receiving portion 308b covering the brush
106 on three sides; and a heat conducting portion 308c to which the
thermostat 260 is secured for conducting heat from the brush 106 to
the thermostat 260. In other words, the brush holder 308 has a heat
conducting portion 308c added to the brush holder 108 in FIG. 1.
The heat receiving portion 308c is formed by extending one of the
flange portions 308a in the same plane and in the radial direction
then bending it in the axial direction to form a thermostat
mounting portion 308d, and in addition the end thereof is bent in
the radial direction to form a bending portion 308e so as to
position the thermostat 260 on the thermostat mounting portion
308d. The heat receiving portion 308c may be a separate member from
the brush holder 308 and may be fastened to the flange portion 308a
by welding or using bolts.
[0069] Returning to FIG. 2, the thermostat 260 covered by an
electrically insulating tube 222 is secured to the thermostat
mounting portion 308d of the brush holder 308, so as not to be in
direct contact with the thermostat mounting portion 308d and
consequently is electrically insulated from the brush 206 and the
rear bracket 105.
[0070] Embodiment 3
[0071] FIG. 4 is a cross-section of a mounting structure of a
thermostat for a starter according to yet another embodiment of the
present invention. Comparing the structure of a heat conducting
member 418 of this embodiment with that shown in FIGS. 2 and 3, it
is understood that the heat conducting member 418 shown in FIG. 4
is separete from brush holder 108 and the heat conducting member
418 is held between the brush holder 108 and the base 109 which are
secured together by rivets.
[0072] FIG. 5 is a perspective view showing the shape of the heat
conducting member 418 in detail. The heat conducting member 418 is
made of a brass flat plate, is provided with a radially extending
flat surface portion 418a having bores 418c for securing by rivets
designed to be held between one of the brush holders 108 and the
base 109, part of which extends and then bends perpendicularly to
axially extend to form a thermostat mounting portion 418b, and the
end thereof bends perpendicularly to extend in the radial
direction. The thermostat mounting portion 418b may be a separate
member from the heat conducting member 418 and may be fastened to
the flat surface portion 418a by welding or bolts.
[0073] Returning to FIG. 4, the heat conducting member 418 is held
between one of the brush holders 108 and the base 109, and is
firmly secured by rivets. An electrically insulating sheet 220 is
held between the heat conducting member 418 and the base 109.
[0074] According to one aspect of the present invention, there is
provided an engine starter comprising:
[0075] a starter motor for starting an engine, the starter motor
including a brush and a brush holder; and
[0076] a control circuit for controlling the starter motor, the
control circuit including a thermostat for deenergizing the starter
motor when the temperature of the starter motor exceeds a
predetermined temperature;
[0077] the engine starter further comprising:
[0078] a heat conducting member, having a first end thermally
coupled to the brush and a second end thermally coupled to the
thermostat, for conducting heat from the brush to the
thermostat.
[0079] According to another aspect of the present invention, the
thermostat is secured to the heat conducting member and the heat
conducting member is a substantially only means for mechanically
supporting the thermostat.
[0080] Consequently, those can enable the brush heat to be
immediately conducted to the thermostat, making the thermal
conductivity to the thermostat superior. Because temperature of the
thermostat is not raised by the atmosphere around the brush, it is
less likely to be affected by external air temperature, providing a
stable thermostat action.
[0081] According to another aspect of the present invention, the
heat conducting member supports the thermostat within the starter
motor with a thermally insulating air gap defined therearound,
enabling to making the transfered heat to the thermostat less
likely to escape.
[0082] According to another aspect of the present invention, the
second leg has a bend portion for positioning the thermostat on the
second leg, enabling the thermostat to be positioned on the heat
conducting member facilely.
[0083] According to another aspect of the present invention, an
electrically insulating material is interposed between the
thermostat and the second leg of the heat conducting member,
ensuring electrical insulation from the thermostat, regardless of
the type of thermostat.
[0084] According to another aspect of the present invention, the
first end of the heat conducting member is embedded within the
brush and because the thermostat is therefore not embedded directly
in the brush, the size of the brush is not increased, enabling the
provision of a compact a engine starter.
[0085] According to another aspect of the present invention, the
first end of the heat conducting member is an integral, continuous
extension of the brush holder, enabling the heat conducting member
for securing the thermostat to be provided without increasing the
number of parts.
[0086] According to another aspect of the present invention, the
first end of the heat conducting member extends from a mounting
flange of the brush holder, enabling existing brush holders and
brushes to be used without modification.
[0087] According to another aspect of the present invention, a
thermally insulating material is interposed between the rear
bracket and the first end of the heat conducting member, making
brush heat less likely to escape to the base, further improving
thermal conductivity to the thermostat.
* * * * *