Patent Abstract:
The invention relates to a lifting mechanism for spring-assisted actuation of a covering means of a dishwasher such as a door or shutter, having at least one lever which is mounted on a shaft and is connected to a tension spring. Arranged, in this case, between the lever and the spring is a mechanical control means which brings about a more or less constant lever arm between an articulation point of the spring and the shaft over an angle of rotation of the shaft of up to approximately 100°.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a spring-assisted lifting mechanism, such as a door or shutter, for a dishwasher. 
     2. Discussion of the Related Art 
     The spring-assisted lifting mechanism is used, in dishwashers for the catering trade, to facilitate the operation of raising a covering means covering the dishwashing chamber. The spring-assisted lifting mechanism is intended to bring about a smooth-running movement of the covering means between a bottom position and a top position, the covering means being retained in the bottom position by its own weight and the [sic] retained in the top position by a spring force. 
     A known spring-assisted lifting mechanism for a covering means of a catering-trade dishwasher comprises two levers mounted on a shaft, the covering means being mounted in a rotatable and displaceable manner on the first lever, and a tension spring acting at the end of the second lever. The shaft, on which the levers are mounted, is fixed on the frame of the dishwasher via the second lever, with the aid of the spring, a moment is applied to the shaft. This moment brings about or assists a rotation of the shaft and/or of the first lever, with the result that an opening movement of the covering means is facilitated. In order to ensure vertical movement of the covering means, the covering means is guided, on the rear side, in a guide fitted on the frame of the dishwasher. 
     However, this lifting mechanism has considerable disadvantages. For example, a high force is necessary for the purpose of opening the covering means since, in this position of the lifting mechanism, the spring only acts on the shaft with a small effective lever length. As the covering means is opened to an increasing extent, the effective lever length increases, with the result that the lifting force acting on the covering means becomes greater and greater. During this opening operation, the operator initially senses a high resistance because the opening movement is only assisted to a minimal extent. Since the operator applies the force in accordance with the necessary opening force, the covering means is often displaced upward against a stop at high speed. This takes place because, on account of the improving lever arm between the spring and the shaft, the force which is to be applied by the operator decreases as the degree of opening increases. It is also the case that during closure of the covering means the properties of the mechanism result in an undesired, disadvantageous force profile. This is manifested in that first of all a large force and then an increasingly smaller force has to be applied in order to move the covering means from the top position into the bottom position. This characteristic of the lifting mechanism results in the operator first of all having to apply a large force in order to set the covering means in motion and then, on account of the resistance becoming lower, has difficulties in slowing down the covering means before the bottom position has been reached. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to develop a spring-assisted lifting mechanism which, in all positions of the covering means, provides a load-relieving moment, which is adapted to the requirements of the operator, and thus allows exact, high-precision operation of the covering means with a small manual force. 
     The spring-assisted lifting mechanism for the covering means according to the invention comprises a control means which is arranged between the second lever and the tension spring a which brings about a more or less constant effective lever between an articulation point of the spring and the shaft over an angle of rotation of the shaft of up to approximately 100 degrees. This achieves the situation where the opening movement of the covering means is assisted by a virtually constant force, with the result that a force profile which is not, expected by the operator is not produced either during raising or during lowering of the covering means. 
     According to a preferred embodiment of the invention the control means is configured as an intermediate lever which is connected to the second lever and the tension springs In this case said intermediate lever at times is retained freely between the articulation points and at other times butts rotatably and displaceably against a support. This design allows a cost-effective, straightforward and space-saving embodiment of the lifting mechanism with more or less constant spring assistance. 
     An advantageous embodiment of the subject matter of the invention makes provision for the control means to be configured as a triangular compensating lever or toggle lever. Such a configuration of the control means allows the shaft to be used as a support and thus the design to be particularly straightforward. 
     According to a variant of the subject matter of the invention, it is provided that [sic] to design control means as a bolt which is mounted in two guide means and on which the spring is fastened. The guide means are formed by a slot in the second lever and by a fixed guide. This likewise makes it possible to provide a constant torque on the shaft since the effective lever remains constant. 
     A further variant of the subject matter of the invention provides that the second lever has a cam-like head, over the end side of which there runs a cable or band, the spring being fastened at the free end of said cable or band. If the end side of the cam is designed such that it is located on a circle around the shaft, then it is also possible in this case, with the aid of the spring, to apply a constant moment to the shaft. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further details of the invention are described, with reference to schematically illustrated exemplary embodiments, in the drawing, in which: 
     FIG. 1 shows a schematic side view of a dishwasher with the door closed, 
     FIG. 2 shows a detailed illustration of the lifting mechanism marked by “X” in FIG. 1, 
     FIG. 3 shows a schematic illustration of the dishwasher with the door half open, 
     FIG. 4 shows a detailed illustration of the lifting mechanism of the dishwasher when the door is half open, 
     FIG. 5 shows a schematic illustration of the dishwasher with the door open, 
     FIG. 6 shows a detailed illustration of the lifting mechanism when the door is open, 
     FIG. 7 shows a schematic illustration of a variant of the lifting mechanism, and 
     FIG. 8 shows a schematic illustration of a further variant of the lifting mechanism. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a schematic side view of a dishwasher  1 . The dishwasher  1  comprises a substructure  2  with feet  3  and a side part  4  which is fastened on the substructure  2 . The dishwasher  1  also has a covering means  4   a , which is configured as a door  5  which has a handle  6 . Seated in the side part  4  is a bearing  7  which is configured as a shaft  8 . Two levers  9 ,  10  are fastened on the bearing  7  or on the shaft  8 . The lever  9  connects the shaft  8  to a rotatable bearing bolt  11  which is fitted on the door  5 . The lever  9  is mounted displaceably in a guide  13  of the shaft  12 . During opening of the door  5 , the lever  9  slides back and forth in the guide  13  of the bearing bolt  11  by way a region  14  (cf. FIG.  3  and FIG.  5 ). The vertical movement of the door  5  is ensured by a vertical guide (not illustrated) which is arranged between the door and the side part. 
     It can be seen from FIG. 2 that the lever  10  is connected rotatably to a control means  16  at an articulation point  15 . The control means  16  is configured as a compensating lever  16 a or triangular lever  17  which has a base  18 , a side  19  and a side  20 . Suspended at a further articulation point  21  of the triangular lever  17  is a spring  22  which has a longitudinal axis  22   a . The spring  22  is designed as a tension spring  23  and is supported in the side part  4  of the dishwasher  1  (see FIG.  1 ). The shift  8  has a surface  24  against which the triangular lever  17  butts by way of the side  19 . The spring  22 , the triangular lever  17 , the lever  10 , the bearing  7  and the lever  9  form a lifting mechanism  25 . The lifting mechanism  25  assists an operator during opening and closing of the door  5  and also helps retain the door  5  in the open position. For opening purposes, the operator has to overcome the weight  26  (cf. FIG. 1) of the door  5  by the manual force  27  applied by him/her (cf. FIG.  1 ), the operator being assisted here by the spring force  28  (cf. FIG. 1) of the spring  22 . 
     The functioning of the lifting mechanism  25  is described hereinbelow with reference to FIGS. 1 to  6 . FIGS. 1,  3 ,  5  and  2 ,  4 ,  6  respectively show the door  5  of the dishwasher  1  and the lifting mechanism  1  [sic] in a closed position  29 , in a half-open position  30  and in an open position  31 . 
     As can be seen from FIG. 5, the weight  26  of the door  5  acts on the bearing  7  with a lever H 1 . The force opposing the weight  26  is applied by the manual force  27  and the spring force  28 . 
     It can be seen in FIG. 2 that the spring  22  acts on the bearing  7  via the triangular lever  17  and the lever  10 . The spring  22  thus acts on the bearing  7  with an effective lever E 1  since the triangular lever is supported at a point P on the surface  24  of the shaft  8  by way of its side  19 . By virtue of the lever  10 , the triangular lever  17  is blocked such that only joint rotation of the triangular lever  17  with the shaft  8  can take place. 
     Until approximately the half-open position  30  of the door  5  has been reached, the triangular lever  17  butts against the surface  24  of the shaft  8  by way of the point P, said surface forming a support  24   a  for the triangular lever  17 . On the way into the half-open position  30 , the triangular lever  17  rotates jointly with the shaft  8 . This means that the moment by which the spring  22  acts on the bearing  7  remains approximately equal between the closed position  29  and the half-open position  30  since the articulation point  21  of the spring  22  only moves through a small angle on a circular path around the bearing  7 . This means that the effective lever E 2  illustrated in FIG. 4 is only slightly smaller than the effective lever E 1  illustrated in FIG.  2 . By virtue of the rotation of the triangular lever  17  about the bearing  7 , the articulation point  15  of the lever  10  has also been displaced, with the result that the lever A 2  corresponds approximately to the lever E 2 . In the closed position  29  of the door  5 , the lever A 1  was still considerably smaller than the lever E 1  of the triangular lever  17  (cf. FIG.  2 ). 
     During further displacement of the door  5  into the open position  31 , the lever  10  with its effective lever A 2  then becomes determinative since the point P moves away from the surface  24  of the shaft  8 . This is because the spring  22  then no longer subjects the triangular lever  17  to any moment about the articulation point  15  and it is thus also the case that there is no longer any force which presses the triangular lever  17  onto the shaft  8  at point P. 
     A variant which is not illustrated provides that the triangular lever  17  butts against the surface  24  of the shaft  8  by way of an articulation indent configured as a recess on the triangular lever  17 . This means that the triangular lever  17  has surface contact with the shaft  8 . 
     FIG. 6 illustrates the position of the lever mechanism  25  which the latter assumes in the open position  31  of the door  5 . It can be seen that the effective lever A 3  is determined by the lever  10 . This means that the effective lever A 3  has become slightly greater than the effective lever A 2  (cf. FIG. 4) since the lever  10  has moved on a circular path around the bearing  7  between the half-open position  30  and the open position  31  of the door  5 . Comparing FIGS. 2 and 6, it can be seen that, in the closed position  29  of the door  5 , the spring  22  is stressed to a more pronounced extent by a distance LZ 1 +LZ 3  in relation to the open position  31 , this resulting in the door  5  being subjected to a somewhat more pronounced moment in the closed position  29 . 
     Overall, between the closed position  29  and the half-open position  30 , the lever mechanism  25  brings about a sinusoidal decrease in the effective lever-arm length by means of which the spring  22  acts on the shaft  8 . Between the half-open position  30  and the open position  31  of the door  5 , the lifting mechanism  25  brings about a sinusoidal increase in the effective lever-arm length by means of which the spring  22  acts on the shaft  8 . By virtue of the spring stressing decreasing during the opening operation, the spring  22  acts on the lever mechanism  25  with a decreasable force. Thus, during opening of the door  5 , the shaft  8  is subjected to a moment which, as the door  5  is opened to an increasing extent, decreases slightly to approximately the central position of said door. Between the central position and the open position of the door  5 , the moment acting on the shaft  8  increases again slightly. 
     FIG. 7 shows a schematic illustration of a variant of the lifting mechanism  25 . Analogously to the lifting mechanism  25  illustrated in FIGS. 1 to  6 , the lifting mechanism  40  illustrated in FIG. 7 likewise has a first lever  9 , a second lever  10 , a bearing  7  and a shaft  8 . The dishwasher  1  has not been illustrated here since the lifting mechanism  40  illustrated in FIG. 7 is likewise provided for the dishwasher  1  illustrated in FIGS. 1,  3  and  6 . 
     The second lever  10  has a slot  42  which is configured as a guide  41  and in which a bolt  43  is mounted in a displaceable manner. Fastened on the bolt  43 , at an articulation point  43 a, is a tension spring  44  which draws the bolt  43  in the direction of the arrow  45  and is supported in the side part  4  (not illustrated here). Furthermore, the bolt  43  is mounted in a guide  46 , formed in the side part  4 , such that it can be displaced in the vertical direction. Mounting the bolt  43  in the guides  41  and  46  ensures that an effective lever A 10 , by means of which the bolt  43  and the spring  44  act on the shaft  8  via the second lever  10 , remains more or less constant in an angle range  47 . The bolt  43  and the guides  41 ,  46  here form a control means  16 . 
     An exemplary embodiment of the subject matter of the invention which is not illustrated provides for the guide  46  to be of curved design. This makes it possible for the profile of the moment acting on the shaft  8  to be freely determined and adapted to the force profile favorable for an operator. 
     FIG. 8 shows, by way of the lifting mechanism  60 , a further variant of the lifting mechanism  25 . This lifting mechanism, in turn, has a first lever  9 , a second lever  10 , a bearing  7  and a shaft  8 . The second lever  10  has a cam-like head  61  which exhibits an end side  62  with a rounded surface  63 . On the end side  62  it is possible to see a connecting means  64  which is configured as a band  65  with an end  66  and an end  67 . The band  65  is fastened at an articulation point  68   a  with the aid of a fastening means  68 . A spring  69  is articulated at the end  67  of the band  65 . The spring  69  forces the band  65  in the arrow direction  70  and is itself supported in the side part  4  (not illustrated here). 
     In the case of the lifting mechanism  60 , a force  71 , which the spring  69  exerts on the band  65  in the direction of the arrow  70 , is deflected on the rounded surface  63  of the cam-like head  61 . By virtue of the deflection, the force  71  acts on the fastening means  68  in the arrow direction  72  and thus acts on the shaft  8  with an effective lever All. The effective lever  11  [sic], by means of which the force  71  acts on the shaft  8 , remains constant during rotation of the second lever  10  over an angle range  73  since the force  71  always acts on the fastening means  68  tangentially to the rounded surface  63 . The cam-like head  61 , the connecting means  64  and the band  65  here form a control means  16 . 
     A further exemplary embodiment which is not illustrated provides for the end side  62  of the cam-like head  61  to be provided with elevations and depressions, with the result that the configuration thereof can influence the lever arm by means of which the spring  69  acts on the shaft  8 . According to the invention, the connecting means is pressed into the depressions of the end side  62  by a mating means. 
     The invention is not restricted to exemplary embodiments which have been illustrated or described. They also cover the developments of the invention within the context of the claims.

Technology Classification (CPC): 0