Abstract:
The invention is directed to a brush attachment adapted to be attached to and detached from a shaft of a handle of an electric toothbrush, including a bristle area, a brush shank and a plug-on part disposed in the brush shank, wherein the plug-on part includes a first spring element and a second spring element which act on the shaft when the brush attachment is plugged onto the shaft. This establishes a connection without play between the brush attachment and the shaft, enabling relatively high vibration frequencies to be transmitted.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to German Patent Application No. DE 103 52 993 4, filed on Nov. 13, 2003, which is incorporated herein by reference in its entirety. 
   TECHNICAL FIELD 
   This disclosure relates to electric toothbrushes and attachments therefor. 
   BACKGROUND 
   A replaceable brush attachment for an electric toothbrush is known from U.S. Pat. No. 3,369,265. On the brush attachment are bristles in a fixed arrangement. The end of the brush attachment intended for connecting to the handle has a cavity in which provision is made for two opposite lying detent notches, both of which are arranged in the same axial position. A connecting pin of a handle equipped with corresponding detent elevations engages in these detent notches. The end of the brush attachment intended for connecting to the handle is divided by two slots into two legs which are spread apart when the brush attachment is plugged onto the connecting pin, thus permitting a snap-action effect. The end of the connecting pin engages in the end of the cavity, which is conformably shaped in flush fashion. 
   WO 00 76420 describes an electric toothbrush with a brush attachment. The latter has a coupling means formed by a rubbery component with a sawtooth serration, which frictionally engages over an extension of the housing. A clamping ring is used to achieve high retaining forces without making it difficult to push on the brush attachment. This ring is rotatably held on the brush attachment and equipped with a run-on ramp that grips the housing extension. In addition, provision is made for an anti-rotation device using a coupling sleeve. This solution is relatively elaborate in its construction and hence expensive. 
   A brush attachment of the prior-art type is known from WO 99 20202. The brush attachment can be plugged onto a handle of an electric toothbrush that has a receiving socket from which a shaft projects. An axial securing element arranged in a brush shank of the brush attachment has a first spring element that is configured like a detent finger and engageable in a groove of the shaft. A second spring element in the form of a bending bar acts on the receiving socket on the handle and is part of a sleeve inserted in the brush shank. This plug-on mechanism is intended for a brush attachment on which a bristle carrier mounted on the brush shank is to be set in oscillatory rotational motion by the shaft of the handle. 
   It is an object of the present invention to construct a brush attachment of the prior-art type such that it can also be used on a toothbrush with which dental cleaning is supported by a fast vibratory motion of the bristles. The transmission of these vibrations from the handle to the brush attachment should take place without clattering noises in the attachment area, and it should still be easy to plug on and remove the brush attachment. The plug-on mechanism should also display these advantageous characteristics at comparatively high vibration frequencies of preferably 100 to 300 Hz. 
   This object of the invention is accomplished in that the brush attachment has a plug-on part on which a first and a second spring element are arranged in an axially offset relation to each other and which act on the shaft when the brush attachment is plugged onto the shaft. 
   This solution enables a connection without play between the shaft and the brush attachment, whereby relatively high forces and torques can be transmitted. The brush attachment is supported on the shaft under bias by in particular elastic shaped elements. 
   In an advantageous further configuration of the brush attachment of the invention the first and the second spring element are arranged in the same radial position. As a result, the pressure forces of the spring elements act in the same plane, or to be more exact in the same radial direction. This is advantageous with regard to the behavior of the brush attachment when plugged onto the shaft. 
   According to an advantageous embodiment, provision is made for the first spring element to be constructed as a detent finger that extends axially and engages in an approximately V-shaped detent groove of the shaft. This arrangement can be implemented at very little cost and tells the user of the brush attachment by means of an audible and tangible snap action that the brush attachment is securely seated on the handle. 
   When, in accordance with an advantageous arrangement, the second spring element is arranged on an area close to the bristle carrier while the first spring element is arranged at a location more remote from the bristles, the second spring element can then act on the free end of the shaft. This means that only the first spring element acts at the beginning of the plug-on operation and very little resistance can be felt when plugging on. The second spring element, which is preferably calculated to have a higher pressure force, does not come into play until at the end. 
   A preferred arrangement of the detent finger wherein the finger points in the direction of the handle, has the advantage of allowing the detent groove to be deeper and bigger, as the shaft generally has a larger diameter in the vicinity of the handle. The bigger detent groove and the bigger detent finger enable a better snap action to be provided. 
   A preferred embodiment of the brush attachment of the invention wherein the second spring element is an axially aligned spring bar with a bend curved in the direction of the shaft, whereby the spring bar is arranged between two axial slots of the plug-on part, has the advantage of being an economical and durable solution. A necessary pressure force is assured even after very frequent changing of the brush attachment. 
   An even better hold is afforded by a third spring element in accordance with another advantageous configuration of the brush attachment of the invention. The third spring element is arranged in an axially offset position relative to the first two spring elements. Conveniently, the plug-on part has several, in particular three, radially offset resilient fingers that urge against the shaft in the mounted state. Through this supporting of the shaft at least three axially offset points the brush attachment is seated particularly quietly and securely on the shaft. The radial support of the plug-on part is also effected preferably at three points of the shaft. 
   According to another preferred embodiment of the brush attachment of the invention, provision is made for the brush attachment to be constructed for mounting on a shaft having several cross sectional areas, the shaft having an essentially D-shaped cross section at its forward end close to the bristle carrier and a circular cross section at its rear end close to the handle, the forward end of the shaft preferably having a flattening against which a spring element rests. This enables user-friendly attachment and good guidance of the brush attachment. On the one hand, the shaft tip has a small cross section that is inserted in a relatively large receiving opening of the plug-on part. On the other hand, the brush attachment with its bristles has the correct radial alignment. In the first moment of the plug-on movement it is even possible for the bristles to be in any radial alignment. Using a practically automatic rotary movement of the brush attachment in an already partly inserted position, a precise alignment of the bristles is achieved by means of insertion bevels and/or curves running preferably transverse to the shaft on the shaft and/or the plug-on part. The plugging on operation is thus greatly facilitated. Incorrect plugging on is impossible. 
   When the plug-on part is constructed for mounting on a shaft having at least two circular cross sectional areas of various diameters, with different spring elements resting against the different cross sectional areas, then it is possible for third spring elements, for example, to rest against an enlarged cross sectional area. Preferably provision is made for a first diameter for the first spring element and for a second, bigger diameter for the third spring element. When the brush attachment is pushed on, very little force is required initially because the third spring element does not take support upon the shaft until at the end of the push-on movement. This makes it easy to insert the plug-on part. 
   It is an advantage for the brush attachment to be encompassed by a soft-elastic padding that extends over at least a section of the brush attachment in order to equip the brush attachment with a shock-absorber function. This padding is preferably arranged in a region proximate the bristles, with a soft-elastic component preferably encompassing a hard part at least in a region opposite the bristles. This shock absorber function enables the forces acting on the teeth on contact with the bristle carrier at high frequencies of vibration to be dampened and reduced. As the result, the user does not experience the contact as bothersome or indeed painful. Drive frequencies can lie above 100 Hz and particularly between 200 and 500 Hz, for example 260 Hz or higher. Without a suitable shock absorbing effect the high acceleration could cause damage to the teeth in extreme cases. It suffices for the padding to extend over a partial area, preferably about half of a circumference and/or only in the vicinity of the brush attachment. In particular, a soft-elastic component additionally covers side areas of the brush attachment in full or in part. The padding can have a structured, in particular studded or ribbed, surface. It is optimal for the soft-elastic component to have a Shore hardness of 30 to 60 A Shore. 
   An embodiment of a brush attachment of the invention, the present invention itself as well as further advantages thereof will be explained in the following with reference to the description of the accompanying drawing. 

   
     DESCRIPTION OF DRAWINGS 
       FIG. 1  is a side view of a section of a handle of an electric toothbrush, showing a shaft; 
       FIG. 2  is a sectional view of the shaft taken along the section line A-A of  FIG. 1 ; 
       FIG. 3  is a view of a brush attachment of the invention; 
       FIG. 4  is a cross-sectional view taken along the section line B-B of  FIG. 3 ; 
       FIG. 5  is a cross-sectional view taken along the section line C-C of  FIG. 3 ; 
       FIG. 6  is a cross-sectional view taken along the section line D-D of  FIG. 3 ; 
       FIG. 7  is a view of a brush attachment of the invention similar to  FIG. 1 , but in attached condition; 
       FIG. 8  is a view of a first variant of the brush attachment of the invention, showing a partial soft-elastic padding; 
       FIG. 9  is a view of a second variant of the brush attachment of the invention, showing a partial soft-elastic padding; and 
       FIG. 10  is a view of another variant of the brush attachment of the invention, showing a complete soft-elastic padding. 
   

   In the Figures, like parts are assigned like reference characters. 
   DETAILED DESCRIPTION 
     FIG. 1  shows a connecting area of a handle  1  of an electric toothbrush for connecting to a brush attachment  13  of the invention shown in  FIG. 3 . 
   The handle  1  is comprised of a plastic housing and all components required for operation such as an electric motor, a gear unit, batteries or storage batteries, a controller and the like. These components are in the interior of the housing and not shown. 
   As illustrated in  FIG. 1 , a shaft  2  made in particular of metal projects directly out of the handle  1  and performs a small torsional oscillation about its longitudinal axis at a high frequency of 260 Hz, approximately. In other words, the shaft  2  executes a vibratory motion when driven by an electric drive mechanism. Other vibratory motions, such as those along the shaft axis  3  or a combination thereof for example, are also possible. This vibratory motion is directly transmitted to bristles  50  of the brush attachment  13 . The bristles  50  are fixedly secured to the brush attachment  13  either directly in a bristle area or by way of a replaceable bristle holder, not shown. However, the bristles  50  do not move relative to the brush attachment but only relative to the handle  1 . In other words, they move together with the brush attachment  13 . The vibratory motion of the bristles  50  is used for dental cleaning and dental care. 
   The brush attachment  13  has a brush shank  12 —preferably made of plastic—in which a plug-on part  11 —preferably also made of plastic—is fastened by positive and/or frictional engagement therewith, being in particular snap-locked in the brush shank  12  by detent means. Preferably, the brush shank  12  is shaped in an essentially tubular configuration and the plug-on part  11  is constructed as a sleeve. At one front face or end  21  of the brush attachment  13  or the plug-on part  11  is an approximately circular receiving opening in which the shaft  2  can be inserted. 
   The brush attachment  13  is thus constructed to be pluggable onto and detachable from the shaft  2  of the handle  1 . 
   The plug-on part  11  is equipped with a first spring element  35  acting directly on the shaft  2 , as shown in  FIG. 3 . This element is constructed as a detent element to engage with a detent notch  8  of the shaft  2  with a snap action. The first spring element has preferably a detent finger with an approximately V-shaped detent lug  36 , which engages in a V-shaped detent groove  8  of the shaft  2  such that the brush attachment  13  is also axially located relative to the shaft  2 , with the detent finger transmitting axial forces. The first spring element extends preferably axially in relation to the shaft  2 . With its free end the detent finger adjoins a cavity  37  of the plug-on part  11 , with material recesses  38  situated to the side of the detent finger. 
   The brush attachment  13  is equipped in addition with a second spring element  30  arranged in an axially offset position relative to the first spring element  35 . 
   According to the invention the second spring element  30  is arranged on the plug-on part  11  and acts likewise directly on the shaft  2 . As the result, the brush attachment  13 , or to be more precise the plug-on part  11 , takes support upon two axially spaced points of the shaft  2 , thus permitting the use of high drive frequencies. The axial distance A 5  (cf.  FIG. 7 ) between the first spring element  35  and the second spring element  30  amounts to preferably 5 to 20 mm, particularly around 8 to 14 mm, e.g., 12 mm, which is a good compromise between minimizing the sleeve dimensions and maximizing the noise damping. 
   As  FIGS. 4 and 5  show, the first spring element  35  and the second spring element  30  are arranged preferably in the same radial position, the second spring element  30  being arranged on an area close to the bristle carrier or the bristles  50  while the first spring element  35  is arranged at a location more remote from the bristle carrier, as illustrated in  FIG. 3 . The detent finger  35  points preferably in the direction of the handle  1 . 
   As  FIGS. 3 and 7  show, the second spring element  30  is comprised of an axially aligned spring bar with a bend curved toward the shaft  2 . This spring bar is constructed in particular as a bending bar. The spring bar lies between two axial slots  51 ,  52  or recesses  31  ( FIG. 4 ) of the plug-on part  11 . When the brush attachment  13  is plugged on, the spring bar  30  is bent slightly outwardly, its spring force operating to urge it directly against the shaft  2 , as shown in  FIG. 7 . The detent finger  35  presses likewise with its spring bar and/or detent lug  36  against the shaft  2 . The distance A 3  ( FIG. 4 ) is smaller than the distance A 1  ( FIG. 2 ). The difference is equal in particular to less than 1 mm. 
   The spring action of the bent spring bar  30  is obtained necessarily by demolding when, after the plug-on part  11  is injection-molded, a core provided in the manufacturing process for this bent shape is withdrawn. 
   The plug-on part  11  is equipped with a third spring element  22  in an axially offset position relative to the first two spring elements  30 ,  35 , which lies preferably in the vicinity of the receiving opening or is arranged on the end  21  close to the handle  1 . The first spring element  35  then lies between the second spring element  30  and the third spring element  22 . 
   As becomes apparent from  FIG. 6 , the third spring element  22  is comprised of several, in particular three, radially offset resilient fingers  53 - 55 , which in the mounted state also urge against the shaft  2 . The fingers  53 - 55  extend axially and point preferably toward the handle  1  and are relatively short, preferably only 1 to 3 mm long. Free spaces  23  exist between the fingers  53 - 55 . 
   In the non-inserted state the free ends of the fingers  53  to  55  adjoin an imaginary circular line  24  ( FIG. 6 ) with a diameter D 3 . The diameter D 1  of the shaft  2  in this area is bigger than the diameter D 3 , thus producing a radial bias between a rear section  4  ( FIG. 1 ) of the shaft  2  and the fingers  53 - 55  of the plug-on part  11 . 
   As is shown in  FIGS. 1 and 2 , the shaft  2  is constructed with several cross sectional areas, including one area with a circular cross section and a diameter D 1  in the vicinity of the handle  1  for the third spring element  22 , one area, which is roughly in the middle of the shaft  2 , with a likewise circular cross section and a somewhat smaller diameter D 2  for the first spring element  35 , and one forward area with a reduced cross section (cf. A 1  in  FIG. 2 ) for the second spring element  30  on the free end of the shaft  2 . On this forward end close to the bristle carrier the shaft  2  has an essentially D-shaped cross section. In this region are two parallel surface areas  6  and  7 . The surface area  7 , which makes contact with the second spring element  30 , is smaller, for example ¼ to ¾, in particular approximately half the size of the opposite surface area  6 . The surface area  6  lies in the vicinity of the axis  3 , while the flattening  7  or surface area  7  lies close to the circumference of a forward section  5 . The distance A 2  can be smaller than 1 mm, for example. The surface area  6  can also meet exactly with the axis  3  or even be arranged above it. The distance A 1  between the two surface areas equals preferably about 1.5 to 2.5 mm or approximately half the diameter D 2 . The diameter D 2  equals preferably 80% to 97% of the diameter D 1  and in particular 3 mm to 5 mm, for example 4 mm. The distance A 4  between the second and the third spring element  30 ,  22  is relatively large and equals preferably 20-40 mm, particularly 23-27 mm. This is favorable for the transmission of bending moments between the shaft  2  and the plug-on part  11 . 
   The third spring element  22  lies in the shaft area with the biggest diameter D 1 . The first spring element  35  lies in the area with the reduced diameter D 2 , and the second spring element  30  thus lies in the D-shaped forward area of the shaft. The plug-on part  11  encloses the D-shaped area such that the brush attachment  13  can be plugged onto the shaft  2  in a certain radial position only. 
   A plane area  29  ( FIG. 4 ) of the plug-on part  11  rests flush on the surface area  6  ( FIG. 2 ) such that high torques can be transmitted. The spring bar  30  can transmit lateral forces and bending moments between the shaft  2  and the plug-on part  11 . 
   A frontal insertion bevel  60  in the vicinity of the surface area  6  and a further insertion bevel  61  in the area of the diameter D 2  facilitate the plugging on such that the brush attachment  13  rotates into the correct position on its own. 
     FIG. 3  shows further that the plug-on part or the sleeve  11  is press-fitted into the brush shank or secured therein by frictional engagement, namely at points  14  and  15  at the ends respectively of the sleeve  11 . In axial direction the sleeve  11  is additionally fastened by positive engagement of an annular, outwardly extending fastening collar  16  with the brush shank  12 , for which a groove  17  is provided on the brush shank  12 . The sleeve  11  is thus held by in the brush shank  12  by both frictional and positive engagement therewith. 
     FIGS. 8 and 9  illustrate a very advantageous embodiment of the brush attachment  13  with soft-elastic areas. The soft-elastic construction is useful in combination with the spring element arrangement of the invention. This construction, which is shown in  FIG. 8  or  9 , can also be used in combination with a different plug-on solution. 
   The brush attachment  13  or the brush shank  12  has a soft-elastic padding  70 ,  71  or  76 . This padding extends at least over a section of the brush attachment and covers preferably at least a rear side of the area set with bristles. In other words, this padding  70  or  71  is arranged preferably in a region proximate the bristles. A soft-elastic component, which forms the padding  70  or  71 , encompasses a hard part  72  or  73 , which lies in an area opposite the bristles  50 . The padding  71  extends preferably over a partial area, preferably about half of a circumference, and exists only in the vicinity of the bristles  50 . 
   The soft-elastic component can cover in addition side areas of the brush attachment in full or in part, as shown in  FIG. 8 . 
   As illustrated in  FIG. 10 , a soft-elastic padding  76  can also enclose the brush attachment  13  in full. 
   The soft-elastic, in particular rubbery plastic mass is injection-molded using a two-component plastic injection-molding process. 
   This elastic padding can have a structured, in particular studded or ribbed, surface, such that the brush shank is particularly good to grip. 
   If the bristles  50  are omitted or replaced by massage elements, such a vibrating device with a soft-elastic component can also be used as a massaging device. 
   A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting of the invention described herein. The scope of the invention is thus indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced herein. 
   LIST OF REFERENCE CHARACTERS 
   
       
         1  handle 
         2  shaft 
         3  axis 
         4  section 
         5  section 
         6 ,  7  surface areas 
         8  detent groove 
         11  plug-on part 
         12  brush shank 
         13  brush attachment 
         14 ,  15  points 
         16  fastening collar 
         17  groove 
         21  end 
         22  third spring element 
         23  free spaces 
         24  circular line 
         30  second spring element 
         35  first spring element 
         36  detent lug 
         37  cavity 
         38  material recesses 
         50  bristles 
         51 ,  52  slots 
         53 - 55  fingers 
         61 ,  62  insertion bevels 
         70 , 71 , 76  padding 
         72 ,  73  hard part