Abstract:
A coupling for a blender comprises first and second clutches. The first clutch is connected to a blender motor and is adapted to be rotatably driven by operation of the motor. The second clutch is connected to a rotatable cutter assembly inside a blender jar. The first and second clutches each comprise a plurality of teeth, and each tooth comprises a drive face. Each drive face has a negative draft.

Description:
[0001]    This invention relates to a clutch used in a blender assembly for connecting the blender motor to the rotatable cutter assembly inside a blender jar.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is not uncommon for a user to turn on a blender and leave it unattended, even if just for a few seconds. If a blender jar is not secure or well-seated on its blender base, the blender jar can pop off and cause a mess.  
           [0003]    In some high use environments, for instance, commercial settings, if a blender falls off its base, then there could be a spill and a waste of valuable time. Also, a user can misuse a blender assembly by, for instance, putting a jar on its motor housing/base and turning on the motor prematurely, or similarly, pulling the jar off of the base before the motor stops rotating. In addition to the potential mess that this could cause, these abusive practices could be damaging to the appliance. One area that is commonly damaged is the coupling made up of the two clutches where the clutch teeth can become chipped or even shear off.  
           [0004]    Some efforts at solving the foregoing problems include clutches made of rubber and having vertical drive faces on the teeth of the clutches. A vertical drive face facilitates alignment of the clutch teeth upon mounting of a blender jar on the base. The tradeoff is that the vertical drive face does not necessarily grip a jar onto the base as securely as possible.  
         SUMMARY OF THE INVENTION  
         [0005]    Accordingly, it is an object of the present invention to solve the foregoing problems and provide a clutch having teeth wherein the drive face of those clutch teeth has a negative draft.  
           [0006]    In one embodiment, a coupling for a blender comprises first and second clutches. The first clutch is connected to a blender motor and is adapted to be rotatably driven by operation of the motor. The second clutch is connected to a rotatable cutter assembly inside a blender jar. The first and second clutches each comprise a plurality of teeth, and each tooth comprises a drive face. Each drive face has a negative draft. In a further variation, the first and second clutches may be comprised of metal, including cast aluminum. Each clutch may comprise four teeth, with each tooth oriented on the clutch about 90° from its adjacent teeth. The negative draft of each drive face may be in the range of 1° to 10°. The negative draft may be approximately 5°. Still further, the negative draft of each drive face can be substantially the same.  
           [0007]    In a further embodiment, a blender comprises a rotatable cutter assembly, a jar for receiving a material to be acted upon by said rotatable cutter assembly which is positioned within the jar, and a motor carried in a housing with a drive shaft. A coupling comprises first and second clutches. The first clutch is connected to the motor by the drive shaft and is adapted to be rotatably driven by operation of the motor. The second clutch is connected to a rotatable cutter assembly inside the jar. The first and second clutches each comprise a plurality of teeth, and each tooth comprises a drive face wherein each drive face has a negative draft. Alternatively, the first and second clutches may be comprised of metal, including cast aluminum. Each clutch may comprise four teeth, with each tooth oriented on the clutch about 90° from its adjacent teeth. The negative draft of each drive face can be in the range of 1° to 10°. Alternatively, the negative draft of each drive face can be approximately 5°. Still further, the negative draft of each drive face can be substantially the same. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a partially exploded view of a blender wherein clutches of the present invention are shown, one attached to the blender jar, and the other attached to a blender motor housing.  
         [0009]    [0009]FIG. 2 is a perspective view of a clutch in accordance with the present invention.  
         [0010]    [0010]FIG. 3 is a top elevation view of a clutch in accordance with the present invention.  
         [0011]    [0011]FIG. 4 is a cross sectional, side elevation view of a clutch in accordance with the present invention taken along the lines  4 - 4  shown in FIG. 3. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    Turning first to FIG. 1, there is shown a blender  10  that includes a blender jar  11  and blender motor housing  12  that are shown in dotted lines. Mounted within the blender jar  11  is a rotatable cutter assembly  15 . The rotatable cutter assembly  15  is connected via a shaft (not shown) to a clutch  14 . The clutch  14  is adapted to engage the clutch  13  that is mounted onto a drive shaft (not shown) that is rotated by a motor within the motor housing  12 .  
         [0013]    [0013]FIGS. 2 through 4 illustrate a clutch  20  that is the same as the clutches  13  and  14  shown in FIG. 1. The clutch  20  is made up of a circular plate  22  that has four teeth  21  protruding upwardly from the plane defined by the face of the plate. The center of the plate  22  is an internally threaded portion  23  that will attach the clutch  20  to a drive shaft attached to a blender motor or a shaft attached to a blender cutter assembly. Of course, any type of attachment design may be used to attach the clutch  20  to a shaft on a blender. The internally threaded portion  23  is preferred because it securely holds the clutch  20  in place yet still allows the clutch to be replaced by unscrewing it.  
         [0014]    Each tooth  21  has a drive face  30  and a trailing support portion  31 . The drive face  30  is adapted to engage a reciprocal drive face on a second clutch that is mounted on either the blender jar or the blender motor housing. The drive face  30  is typically flat in order to fully engage a reciprocal drive face on a reciprocal clutch. Alternatively, there may be slight serrations on a drive face to better encourage gripping when the reciprocal drive faces are engaged. The trailing support portion  31  angles downwardly from the side of the tooth opposite the drive face  30 . The trailing support portion  31  offers support and integrity to the tooth. In a preferred embodiment, the angle of taper of the trailing support portion  31  is approximately 40°. The tooth  21  is approximately 0.5 cm in height and the thickness of the plate  22  is approximately 2 mm. In this preferred embodiment, the clutch  20  is made of cast aluminum. Other metals, composites, coatings and rubber may alternatively be used. Cast aluminum is preferred, because it is durable and because it is relatively easy to machine. Also, if a user of a blender tries to place ajar upon a moving clutch and a motor housing, then a substantial noise is created by the aluminum contact, which will discourage this type of abuse. This is a useful safety warning. Also, the use of a durable metal such as cast aluminum makes the clutch  20  more resistant to wear than other common materials such as rubber.  
         [0015]    As seen most clearly in FIG. 4, the drive face  30  of the teeth  21  has a negative draft. That is, the portion of the drive face  30  furthest from the plate  22  extends out further than the base of the drive face adjacent the plate. Said another way, the drive face  30  forms an acute angle with the horizontal plane of the plate  22 . The negative draft allows the reciprocal teeth in a pair of clutch plates to effectively lock in place upon rotation. This negative draft tightly engages the two clutches so that they are not easily separated. When attached in operation to a blender motor housing and to a bottom of a blender jar, this negative draft means that the blender jar will be better held in place. The most favorable draft is within the range of 1° to 10° from perpendicular to the horizontal plane of the plate  22 . Preferably, the draft is approximately 5° as shown in FIG. 4. As shown, each tooth  21  has substantially the same negative draft, but there may be variations in the drafts depending on engineering design requirements. If there is too much negative draft, then the blender may be difficult to remove from the blender base. In addition to a greater stability, the negative draft can allow a designer to have the blender perform at a higher rpm with less fear of a blender jar becoming accidentally disengaged.  
         [0016]    In the preferred embodiment shown in the attached figures, there are only four teeth  21  on the clutch  20  that are oriented on the clutch about 90° from adjacent teeth. This relative few number of teeth allows play between the teeth and a more simple alignment upon placing the blender jar onto the blender base. Accordingly, four teeth are preferred, but are not necessary—fewer or more may be used.  
         [0017]    While the invention has been described with reference to specific embodiments thereof, it will be understood that numerous variations, modifications and additional embodiments are possible, and accordingly, all such variations, modifications, and embodiments are to be regarded as being within the spirit and scope of the invention.