Note: Descriptions are shown in the official language in which they were submitted.
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Electric Toothbrush with Rotary B~istle Supporting
Structure
i''
Tllis illv~lLiorl reiates to an electric toothbrush
with a handle section comprising an electric motor drive.
A brush section is adapted to be connected to the handle
section, with the brush section including a shaft having
means for delivering a torque to a bristle supporting
structure, with a bristle supporting structure b~ing ro-
tatably carried at an end of the brush section remote
from the handle section. The bristle supporting struc-
ture comprises means for receiving a torque and means for
mounting bristles, with an axis of rotation of the
bristle supporting structure being disposed at an angle,
particularly at approximately right angles, to a longitu-
dinal center line of the brush section.
A toothbrush incorporating the features identified
is already known from international patent application
publication number WO 84/02453 or from U.S. Pat. No.
4,619,009 having issued from this application. The
bristle carrier of this toothbrush has a bearing section
carried in a bearing bore at the head end of the brush
section. The brlstle carrier is located by means of a
slide lock engaging in an annular groove of the bearing
section. The bristle carrier is driven by means of a
drive shaft extending through a mounting tube and having
bevel gear teeth at its head end. These bevel gear teeth
mesh with gear teeth on the bristle carrier, with these
gear teeth being arranged on the bristle carrier directly
underneath a mounting plate of the bristle carrier. The
axis of rotation of the bristle carrier beir.g disposed at
right angles to the longitudinal axis of the mounting
tube, the mounting plate and the means for receiving the
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torque of the bristle carrier are both arranged on one
side of the longitudinal center line of the mounting tube
or brush section.
,,,~
This known arrangement has the following disadvan-
tages: Not only the rotary parts which include the drive
shaft and the bristle carrier, but also the locking de-
vice and the bearing mount of the bristle carrier are
subject to major wear. In this connection, it is to be
considered in particular that toothbrushes are conven-
tionally used in combination with tooth cleaning agents
containing abrasives to a greater or lesser degree. For
these reasons, it is advisable to reduce the number of
friction points or the size' of the friction surfaces as
much as possible. On the other hand, such provisions may
cGntribute to a prolonged life of this known toothbrush
as are suitable to ensure a safe function of the tooth-
brush while allowing a certain amount of wear of the
movable parts. This will be explained in more detail in
the following with reference to FIG. 4 of the prior art
identified. After prolonged use, the bearing section 7
or the bearing bore 11 will experience a certain amount
of attrition so that the bristle carrier 31, as a result
of the special arrangement of the gears 10 and 20 of the
gear drive 19 and the resultant radial force components
acting on the bristle carrier 31, will be tilted out of
the ideal axis of rotation in the direction of the side
wall 6. With progressive wear of the bearing parts, the
engagement of the gears 10 and 20 wi]l become less and
less until, from a certain moment, they are completely
out of mesh. The known toothbrush is then no longer
usable and has to be replaced.
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It is an object of the present invention to avoid
the disadvantages of the prior art mentioned in the fore-
going. The object is particularly to reduce friction
while, in addition, the mea~s for torque transmissi~n ~re
to be arranged such that the operating capability of the
toothbrush is maintained even in the presence of a
certain amount of wear of the ~ovable parts.
This requirement is satisfied by an electric tooth-
brush incorporating the features initially referred to,
in which the means for receiving the torque and the means
for mounting the bristles are in relative opposite
arrangement on the bristle supporting structure below
and, respectively, above thé longitudinal center line of
the brush section, and in which the rneans for delivering
the torque of the shaft engage in overlapping fashion in
the bristle supporting structure in the area intermediate
the torque-receiving means and the means for mounting the
bristles. By these means, the shaft with the torque-
delivering means serves at the same time an interlocking
function for the bristle supporting structure, because
the shaft engages in overlapping fashion in the bristle
supporting structure between the torque-receiving means
and the means for mounting the bristles on the bristle
supporting structure. This completely eliminates the
need to provide an additional interlocking arrangement
for the bristle supporting structure with the attendant
increased wear of the bearing parts.
Because the bristle supporting structure is mounted
on a shaft of the brush section and the torque-receiving
means are arranged on the bristle supporting structure in
the area of a low end of the shaft, the radial forces
acting on the shaft of the bristle supporting structure
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as d result of the torque transmission in the gear train
are introduced in the shaft at a location where the
tilting or bending moments which they produce are mini-
mal. By these means, fric~ion of the bearinq parts as
well as wear are reduced.
A particularly advantageous configuration is ob-
tained by arranging the torque-transmitting means in such
a matlner that the transmission of torques to the bristle
supporting structure occurs above a low end of a shaft
for mounting the bristle supporting structure and below
the longitudinal center line of the brush section.
Although the radial forces occurring during torque trans-
mission act on the bristle supporting structure axially
as a tilting moment, causing actual tilting of the
bristle supporting structure after corresponding wear of
the bearing parts, this tilting movement of the rotary
shaft of the bristle supporting structure does not result
in disengagement of the torque-delivering and torque-
receiving means. On the contrary, the torque-
transmitting means have shown to mesh even closer when
ti]ting of the xotary shaft occurs. In contrast to the
embodiment OL the prior art, this special arrangement for
introducin~ the torque has the effect that attrition of
the movable parts tends to cause the torque-transmitting
means to move in the direction of a closer mesh.
Configuring the torque-transmitting means as bevel
gear teeth has the advantage of affording controllability
of manufacture and relative ease of computation of the
geometry. The arrangement of a mounting plate opposite
the bevel gear teeth of the bristle support;ng structure
for the mounting of bristles or tufts of bristles ensures
a free structure and optimization of the bristle pattern
~r~ 4j
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with respect to the cleaning effect of the toothbrush of
the invention. Configuring the bevel gear teeth of the
shaft as a bevel gear segme~t makes it possible to reduce
the overall length of the hrllsh section while maint~lning
the above-mentioned advantages. The bristle supporting
structure which is driven to rotate in an angular range
of about +/-35, reversing direction in alternating
sequence, ensures an intensive cleaning effect by the
toothbrush. The use of sintered metal for the torque-
transmitting means reduces the wear of these components
which are subjected to high loads. The splined connec-
tion of these sintered metal parts to the shaft and the
mounting plate which are both made of industrial plastics
ensures a transmission of the necessary torques by areal
impact. The provision of apertures in a mounting tube of
the brush section ensures that cleaning and drying of the
toothbrush after brushing poses no problems and that also
during brushing no or only a minor pumping action occurs
within the brush section as a result of the direction-
reversing rotary motion of the bevel gear segment of the
shaft. By this means, the entry of tooth cleaning agents
in the bearings can be largely avoided or, if tooth
cleaning agents have already entered the bearings, they
can be removed from the bearings after brushing is com-
pleted. Wedge-shaped beadings provided on the shaft in
the area of the apertures of the mounting tube of the
brush section cause water that has entered the shaft area
to be centrifuged to the outside away from the wedge-
shaped beadings. By this means, liquid which has entered
the mounting tube is largely prevented from travelling
tllrough the entire mounting tube to the handle section,
the major part thereof being previously removed from the
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mountlng tube by the centrifugal rings. This, too, con-
tributes substantially to a reduced wear of the brush
section caused the entry of tooth cleaning agents in
the body.
Further advantages of the invention will become
apparent from the subse~uent description of an embodiment
in conjunction with the drawings.
In the drawings,
FIG. 1 is a schematic view of a toothbrush of the
inverltion illustrating an embodiment thereof;
FIG. 2 is a longitudi~al sectional view of the for-
ward end of the brush section of the toothbrush of FIG.
1, with the shaft being shown not sectioned; and
FIG. 3 is a top plan view of the sleeve section,
the pin, the bevel gear teeth and the shaft, sectioned
along the line A-A of FIG. 2.
In the Figures, reference numeral 20 identifies an
electric toothbrush. The toothbrush 20 comprises a
handle section 22 and a brush section 24 which is adapted
to be coupled together with the handle section 22. The
handle section 22 houses an accumulator 26 or, alterna-
tively, a battery, an electric motor 28 and a translating
device 30 for converting the continuous rotary motion of
the electric motor 28 into a rotary motion reversing di-
rection in alternating sequence. On the outside of the
handle section is a switch 32 for activating the tooth-
brush 20. The brush section 24 comprises a hollow
mounting tube 36 receiving a shaft 34. The mounting
tube 36 and the shaft 34 are adapted to be connected to
the handle section 22 by a coupling means 40 not shown in
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greater detail. Arranged at the end of the brush section
24 remote from the handle section 22 is a bristle
supporting structure 38 witjh, a mounting plate 44 for re-
ceivinq bristles 45 or t~l~t.s of bristles~ At its ^nd
opposite the mounting plate 44, the bristle supporting
structure 38 includes bevel gear teeth 46 meshing with a
bevel gear segment 48 arranged at the head end of the
shaft 34. The axis of rotation of the bristle supporting
structure 38 defines an angle with respect to the axis of
rotation of the shaft 34 of approximatel-y 90. It will
be understood that this angle may also assume values of
between 30 and 120 without limiting ~he scope of the
invention. The bevel gear train 42 comprised of the
bevel gear teeth 46 and 4~ transmits the torque of the
direction-reversing rotary shaft 34 to the bristle
supporting structure 38 which is preferably arranged at
right angles to the shaft 34. The range of the angle of
rotation covered b~y the bristle supporting structure 38
may assume values on the order of between +/-20 and +/-
100, the preferred angle being, however, +/-35,
approximately.
As becomes more clearly apparent from the repre~en-
tation of FIG. 2, the hollow conical mounting tube 36
tapers in the di:rection towards the head end remote from
the handle section 22. The head end of the mounting tube
36 is configured as an upwardly open cup shaped socket
50. In a transition area 51, the inside diameter of the
mounting tube 36 diminishes abruptly to about three
fourths of its original diameter, This bearing surface
serves, in connection with the ring 60 and the circlip
62, for axially securing a shaft member 75 which is
arranged in the transition area 51 of the mounting tube
36. At its end close to the cup-shaped socket 50, the
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shaft memher 75 includes a bevel gear segment 48. The
bevel gear segment 48 is arranged at the end of the shaft
member 75 close to the b~ tom area of the cup-shaped
socket 50 below ~ l~ngi tU~l nal center line 5 of th~
brush section 24. The cross section of the shaft member
75 in the abruptly diminished area is identified by ref-
erence numeral 74. The diameter of the shaft member 75
increases from a small diameter in its upper area
abruptly to a larger diameter in its lower area, with the
small diameter being maintained over an angular range of
approximately 250~ and the large diameter being main-
tained over an angular range of 110. This construction
enables the shaft member tp perform rotations of about
+/-35, reversing direction in alternating sequence. At
its end remote from the bevel gear segment 48, the shaft
member 75 has cylindrical peripheral dimensions adapted
to the inside diameter of the mounting tube 36. The
shaft member terminates in a hub 49 having splines 80 on
its inner circumference. The inner circumferential line
of the splines extends in an approximately sinusoidal or
rosette patternj thereby ensurin~ an optimum areal torque
transmission from the shaft 34 whose head end has an
outer splined section adapted to fit into the inner
splined section 80 of the shaft member 75. The shaft
member 75 i9 preferably made of sintered metal, while the
shaft 34 is an injection-molded part made of industrial
plastics. Arranged in the center of the bottom of the
cup-shaped socket 50 is a frusto-conical elevation 63
having a centrally arranged blind-end bore 57 serving to
clampingly receive a shaft 56 which i5 preferably made of
a non-abrasive material as, for example, steel. The
shaft 56 defines a right angle with respect to the shaft
34 and serves to carry the rotary bristle supporting
structure 38. In the present embodiment, the bristle
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supporting structure 38 is a two-piece structure, com-
prising a pin 59 having an annular shoulder 61 integrally
formed therewith and a sleeve section 58 fitting over the
pin 59 and having a mountirlq plate 44 integrally formed
therewith which extends above the cup-shaped socket 50,
covering it. In the transition area intermediate the an-
nular shoulder 61 and the pin 59, bevel gear teeth 46
meshing with the bevel gear segment 48 are provided. The
bevel gear teeth 46 are arranged in the area of the low
end 53 of the shaft 56. Preferably, the accurate axial
positioning of the bevel gear teeth 46 is in such an area
that the transmission of torques to the bevel gear teeth
46 occurs a small distance above the low end 53. The pin
59 has its bottom end recessed in the manner of a central
frustum of a cone, enabling part of the elevation 63 to
engage in this recess, with a small gap being maintained
between the elevation 63 and the pin S9. The pin 59, the
annular shoulder 61 and the bevel gear teeth 46 are
preferably an integral sintered metal part, while the
sleeve section 58 and the mounting plate 44 are an
injection-molded part made of industrial plastics.
For the transmission of the necessary torques from
the pin 59 to the sleeve section 58, these are provided
with splines 81 as shown in FIG. 3. The bevel gear teeth
46 and the splines 81 which are arranged on the center
part of the pin 59 as a one-sided eccentric dovetail are
clearly recognizable. The sleeve 58 fitting over the pin
i1as a corresponding one-sided, eccentric dovetailed
structure, thereby providing a sufficient surface for
transmission of the torques to the mounting plate 44.
Axial securing of the mounting plate 44 or the sleeve
sec:tion 58 relative to the pin 59 is accomplished by
injection-molding around it, gluing. or ultrasonic
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welding. Extending through the center of the pin S9 is a
blind-end bore 55 serving to receive the free end of the
shaft 56. Bores for accommodating individual bristles 45
or tufts of bristles are pr~vi~e~ in the mountlng plate
44.
In the off-center bottom area of the cup-shaped
socket 50, the housing is provided with apertures 64, 65.
Like apertures are in the housing wall area of the
mounting tube 36. Apertures in the area of the shaft 34
are identiEied by reference numerals 66 and 67. The
housing of the mounting tube 36 includes further
apertures not shown in the drawings, these being disposed
i~ the upper housing section 68 in the side wall area
above the shaft member 75.
The brush section 24 is assembled as described in
the following. The bristle supporting structure 38 is
inserted into the cup-shaped socket 50 of the mounting
tube 36 from above and placed down upon the free end of
the shaft 56. The eccentrically arranged dovetailed
splined section is aligned in the direction of the front
end of the brush section 24 adjacent to the side wall 47.
Throuyh the opening of the mounting tube 36 at the han~le
end, the shaft member 75 is inserted in the mounting tube
36 by means of a tool, such that the shaft member 75
abuts the bearing surface in the transition area 51. By
virtue vf the fact that the shaft member 75 is only pro-
vided with a bevel gear segment 48, its teeth not extend-
ing over the entire circumference, the bevel gear segment
48 is to be oriented in a predetermined angular position
relatlve to the longitudinal center line 52. The shaft
member 75 is subsequently secured axially by means of the
ring 60 and the circlip 62, for example, a notched ring.
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The bevel gear segment 48 fitting over the bevel gear
teeth 4~ of the bristle supporting structure, the bristle
supporting structure 38 i~ also secured against axial
displacement relative to the shaf. ~u. Findlly~ ~ne
shaft 34 is inserted in its mount in the area of the hub
49 of the shaft member 75. The transmission of torques
from the shaft 34 to the shaft member 75 is ensured by
the splines 80 in the area of engagement of the shaft 34
in the shaft member 75. By means not shown in greater
detail in the drawings, also the shaft 34 is secured
against axial displacement relative to the longitudinal
center line 52. The shaft 3~ is adapted to be coupled
together with a drive shaft~of the handle section 22, and
the mounting tube 36 is adapted to be coupled to the
housing of the handle section.
Owing to the advantageous arrangement of the shaft
3~ or the shaft member 75 with respect to the bevel gear
teeth 46 of the bristle supporting structure 3~, the
shaft 34 or the shaft member 75 not only fulfil an axial
securing function for the bristle supporting structure,
but further advantages result as will be described in the
following. As becomes readily apparent from general ref-
erence manuals on kinematics or bevel gear designs, the
force acting on a driven gear which essentially acts nor-
mal to the tooth surfaces can be broken down into its
components circumferential force, axial force and radial
force. It is the circumferential force which is the
force component by which the torque received by the
driven gear is determined. Axial force and radial force
are lost forces which, while contributing nothing to the
amount of the torque transmitted, place a load on partic-
ularly the bearings of the driven gear. In the present
embodiment, the axial force acts along the axis of rota-
. . .
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tion 54 of the bristle supporting structure in the direc-
tion of the bottom section of the cup-shaped socket 50.
This axial force is taken iup by the abutment means be-
tween the head end of the shaft 56 and the head area ~f
the blind-end bore 55. In this area, barely visible wear
of the bearing occurs, because tooth cleaning agents can
hardly penetrate in this area because of the precise fit
between shaft 56 and blind-end bore 55. By contrast, the
radial forces exert a bending moment on the shaft 56
which naturally increases with the distance between the
point of force application to the shaft and the fastening
point of the shaft. Thus, it will be advantageous to
introduce the force or torque in the bristle supporting
structure 38 in such an axial area which is as close as
possible to the fastening point of the shaft 56. This
provision minimizes the bending moments acting on the
shaft 56 as a result of the radial force components
occurring in the transmission of torques. It is particu-
larly advantageous to introduce the force in the bevel
gear teeth 46 in an axial area of the rotary shaft 56
lying a small distance above the fastening point of the
shaft 56. The tilting moment on the shaft 56 resulting
from the radial force components causes the shaft 56 to
tilt in the direction of the side wall 47 of the cup-
shaped socket 50. In consequence, also the annular
shoulder 61 with the superposed bevel gear teeth 46 tilts
about this angle, leaving its ideal position. However,
this brings the teeth of the bevel gear segment 48 and
the bevel gear teeth 46 into even closer me~h. Assuming
that over time the teeth of the bevel gear train 42 are
abraded or worn down by the action of tooth cleaning
agents and that the clearance between the shaft 56 and
the blind-end bore 55 increases also, torque transmission
is possible over a prolonged period of time, because the
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tilting moments acting on the shaft 56 as a result of the
radial forces act in the direction of a c]oser mesh of
the teeth of the gear train 42~ With this advantageous
arrangement of the teeth of'the gear train 42 relativ~ to
each other and relative to the fastening point of the
shaft 56, it is possible to prolong the life of the brush
section 24 even in the presence of a certain degree of
wear.
The apertures 66 and 67 in the mounting tube 36 and
the apertures 64 and 65 in the bottom of the cup-shaped
socket 50 serve to facilitate cleaning of the brush sec-
tion, which involves the removal of tooth cleaning agents
and other extraneous material. The apertures at 68 above
the shaft member 75 in the upper side wall area of the
mounting tube 36 underneath the mounting plate 44 are
only secondary to the cleaning of the brush section 24.
The shaft member 75 being configured as indicated by the
cross section 74, it acts like a pump while oscillating,
forcing liquid matter contained in this area not only
into the cup-shaped socket 50 but also in the direction
of the shaft 34 through the gap maintained between the
shaft member 75 and the inner wall of the mounting tube
36. To relieve this pressure, apertures are provided in
the housing sect:Lon 68 of the mounting tube 36 above the
shaft Inember 75. Since in spite of this means the possi-
bility of liquid mixed with extraneous material entering
the interior of the mounting tube 36 past the shaft
mernber 75 and penetrating along the shaft 34 in the
coupling area 40 between the handle section 22 and the
brush section 24 cannot be eliminated entirely, wedge-
shaped beadings 70, 71, 72 are provided on the shaft 34
in the area of the apertures 66 and 67 of the mounting
tube 36. If liquid mixed with extraneous material passes
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over these beadings 70, 71, 72, the increased centrifuyal
force acting at these beadings will cause the major part
of the liquid and extraneo~s material to be centrifuged
away from the shaft 34 and'through th~ anertll~es 66, 57
out of the mounting tube 36. The beadings 70, 71, 72
thus have the effect of centrifugal rings for the removal
of foreign particles and liquid from the interior of the
mounting tube 36. This provision, too, adds to ensure an
increased functional reliability and wear resistance of
the brush section 24.
The embodiment of the invention was described with
reference to a toothbrush in which the bristle supporting
stxucture 38 rotates perpe'ndicular to the longltudinal
center line 52 of the brush section 24 at an angle of
approximately ~/-35, reversing direction in alternating
sequence. It will be appreciated, however, that the in-
vention is not limited to this particular embodiment and
that it is with equal advantage suitable for use with
continuously rotating toothbrushes arranged at angles
other than right angles with respect to the longitudinal
center line of the brush section.
