Abstract:
An operational control is provided for setting an actuating variable, more particularly a set point for a motor vehicle air conditioner, having a rotary knob, having at least two contact tracks and one elastic wiper contact element that is in contact by means of at least one wiper contact with a contact track, wherein the contact tracks are joined to the rotary knob so as to be nonrotatable with respect thereto and in that the wiper contact elements are provided with an additional elastic wiper contact facing the printed circuit board.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an operational control for setting an actuating variable, more particularly a set point for a motor vehicle air conditioner, with a rotary knob, having at least two contact tracks and one spring wiper contact element that is in wiper contact with at least one contact track. 
   2. Description of the Background Art 
   Operational controls are often used in which wiper contacts are moved over contact tracks, for example in order to adjust a variable electrical resistance. The wiper contact element here can be fastened directly to the rotary knob of the operational control or can work together with the rotary knob. Such an operational control for actuating an air distribution flap in a motor vehicle air conditioning and/or ventilation device is known from EP 0 414 941 A1. In order to change the set point, a manually operated rotary control knob is moved through a certain angle and a wiper contact element is drawn over three concentric contact-making contact tracks. The wiper contact element is fastened to a separate disk that is mounted on the axis of the rotary knob. The disk carrying the wiper contact element is moved by a dog that is arranged on the rotary knob of the operational control. In order to compensate for the tolerances in the direction of the contact tracks, the ends of the wiper contacts are bent in a V-shape in the direction of the contact tracks. The wiper contact element is thereby rigidly attached to the rotary disk. 
   Another wiper contact element is disclosed in DE 101 11 400 A1. The wiper contact element here is also called a wiper, and is rotationally fixed to a gear that carries the wiper contact element. A printed circuit board is arranged directly beneath the wiper contact element. Contact tracks that the wiper contacts of the wiper contact elements slide over are applied to the printed circuit board. To improve the reliability of the contact, every wiper contact has two elastic wiper contacts. The wiper has two wiper arms, where wiper contacts are successively arranged in radial alignment on one wiper arm, while only one wiper contact is located on the other wiper arm. 
   From DE 43 19 543 A1 is known an automotive light switch with a rotary/push-pull switch accommodated in a housing for the parking and driving lights and interior illumination. In order to be able to perform additional light switch operations with such a switch, a regulating switch for headlight leveling and a regulating switch for the dashboard lighting are additionally installed in the housing. This automotive light switch is characterized in that each regulating switch constitutes an electrical switch with a resistance, adjustable by a spring wiper that is placed on the printed circuit board and is used to control the power consumption of electrical loads. The spring wiper here is arranged on the side of the printed circuit board opposite the adjusting wheel and is actuated by means of a rotatably mounted lever. The spring wiper here is mounted beneath the printed circuit board such that it can move. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a wiper contact element and an arrangement of a wiper contact element in an operational control that are of simple design and that minimize the tolerance problems between the receptacle for the wiper contact elements and the printed circuit board or the contact tracks, and thus facilitate reliable contact. Furthermore, the wiper contact element to be developed should be inexpensive to manufacture and require minimal effort to install in the operational control. 
   This object is attained in accordance with the invention in that the contact tracks are joined to the rotary knob so as to be nonrotatable with respect thereto and in that the wiper contact elements are provided with an additional elastic wiper contact facing the printed circuit board. The arrangement according to the invention of a wiper contact element that has elastic wiper contacts facing in both directions, which is to say facing the contact tracks located on the rotary knob and facing the printed circuit board, makes it possible to employ an operational control that minimizes the tolerances relative to both the printed circuit board and the contact tracks. The use of just one spring element—the term spring element is used here as a synonym for wiper contact element—makes it possible to implement the contact in an extremely economical manner and also with extremely simple design means. 
   Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein: 
       FIG. 1  is a side view of an example embodiment of a wiper contact element according to the invention; 
       FIG. 2  is a view along A from  FIG. 1  of a wiper contact element built into an operational control; 
       FIG. 3  is a top view of an underside of a rotary knob; and 
       FIG. 4  is a side view of a cross-section IV—IV of a wiper contact element. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a side view of a wiper contact element  1  in the relaxed state prior to installation. In a mounting plane  2 , the wiper contact element  1  has two laterally extending projections  3  with which the wiper contact element is held in the operational control. Extending out of the mounting plane  2  are two wiper contacts  4 ,  4 ′ facing a contact track  5 , and two wiper contacts  6 ,  6 ′ facing a printed circuit board  7 . The contact track  5  and the printed circuit board  7  are shown here only as dashed lines in order to clarify their positions with respect to the mounting plane  2 . By way of example, the wiper contact  4 ′ is shown in dashed lines in the operating position on the contact track  5 . 
   As can also be seen in  FIG. 1 , the legs  4 ,  4 ′ and  6 ,  6 ′ of the wiper contact element  1  have different dimensions. The lengthened or shortened design in accordance with the invention of the individual wiper contacts  4 ,  4 ′ and  6 ,  6 ′ makes it possible to apply different preloadings to the contact track  5  and the printed circuit board  7 . As a result of the different forces, different tolerances with respect to the mounting plane  2  can be compensated in relation to the contact track  5  and the printed circuit board  7 . Depending on the design requirements for the operational control, it may be necessary to design the legs of the wiper contacts  4 ,  4 ′ and  6 ,  6 ′ with different lengths, and thus to establish a corresponding nominal dimension between the contact track  5  and the printed circuit board  7 , to which contact is to be made. In this example embodiment, a relatively large tolerance is to be compensated in the direction of the contact track, in contrast to which only a small force can be accommodated or exerted by the longer wiper contacts  4 ,  4 ′. While a greater force is exerted by the shorter wiper contacts  6 ,  6 ′ in the direction of the printed circuit board  7  between the mounting plane  2  and the printed circuit board  7 , only a relatively small tolerance can be compensated. Depending on the design of the wiper contacts  4 ,  4 ′ and  6 ,  6 ′, which is to say different lengths of the spring arms  4 ,  4 ′ and  6 ,  6 ′, it is possible, for example, to establish a force ratio of 1 to 2, which is to say the force in the direction of the printed circuit board  7  is twice as great as the force in the direction of the contract track  5 . 
     FIG. 2  shows the view along A from  FIG. 1 , and an enlarged view  11 , of a wiper contact element  1  from  FIG. 3  of the wiper contact element  1  in the installed state. The wiper contact element  1  is connected nonrotatably to a base  9  in a through opening  8  of the base  9  beneath a rotary knob  10 . Contact tracks  11  and  12  on the underside of the rotary knob  10  are visible through the through opening  8 . The wiper contact element  1  is laid in recesses  13 ,  14  of the base  9  and is joined at points  15 ,  16  to the base. In this example embodiment, a connection to points  15 ,  16  is made by pressing a part of the plastic from which the base  9  is manufactured that projects from the base  9 . However, it is also possible to join the wiper contact element  1  to the base  9  in a removable manner. Known fastening options such as clips, snap-in attachments, screws, rivets, adhesives, etc. are available for this purpose. 
   The wiper contact element  1  is located immediately above the contact track  11  in such a manner that the two wiper contacts  4 ,  4 ′ are in connection with the contact track  11 . It can also be seen that only one contact track is contacted by the wiper contact element  1 . An additional wiper contact element  1  is necessary in order to make contact with a contact track  12 , which is located further inward at a diameter D. Thus it is possible in accordance with the invention to arrange any desired number of wiper contact elements in the base of the operational control. It is preferred to arrange three contact tracks  11 ,  12  and three wiper contact elements  1  in one operational control. 
   When the rotary knob  10 , of which only the underside is visible in FIG.  2  through the opening  8 , moves in the direction of the arrow P, the contact track  11  slides over the contacts of the wiper contacts  4 ,  4 ′ and an actuating variable of the operational control is changed. For example, if the operational control is designed as a potentiometer, three contact tracks  11 ,  12  are present on the rotary knob  10  as annular tracks. The first contact track  11 ,  12  would carry chassis, the second contact track  11 ,  12  would form a ground, and the third contact track  11 ,  12  would then be the resistive layer across which the voltage would be distributed. The diameter D of the contact tracks  11 ,  12  vary by 2 to 2.5 mm in this example embodiment. 
   The rotary knob  10  is rotatably mounted on the base  9  and is in electrical contact through the wiper contact element  1  with the printed circuit board  7 , not shown in FIG.  2 . In this configuration, the wiper contacts  6 ,  6 ′ are in almost static contact with the printed circuit board  7 . Since the rotary knob  10  is held in the base  9  against the spring force of the wiper contact element  1 , the rotary knob  10  can also be described as being float mounted. The wiper contact element  1  likewise acts against the printed circuit board  7  solely through the spring force of the wiper contacts  4 ,  4 ′ and  6 ,  6 ′. The projections  3  on the wiper contact elements  1  have a taper  17  so that the wiper contact element  1  is merely positioned and guided in the base  9 . The wiper contact element thus offers optimal tolerance compensation between the printed circuit board  7  and the contact track  5 . So that the forces from the wiper contacts  4 ,  4 ′ and  6 ,  6 ′ work optimally together, the wiper contacts  4 ,  4 ′ and  6 ,  6 ′ are opposing, which is to say they are curved in different directions opposite to one another. Thus, for example, the wiper contact  6 ′ is curved against the printed circuit board  7  and the opposing wiper contact  4 ′ is curved against the contact track  5 . For this reason, the spring force acts on a center  18  of the wiper contact element  1 , which is also indicated in  FIG. 1  by the dashed center line  18 . In addition, the wiper contacts  4 ,  6  are curved in the opposite direction. Thus not only is the force from the wiper contact element  1  kept in the center  18 , but tilting or rotation of the wiper contact element  1  is avoided by this means as well. 
   It should be noted that conventional materials can be used as materials for the wipers, wiper contact elements and wiper springs, which are used synonymously here. 
   A further advantage that results from the use of the wiper contact element  1  in accordance with the invention is that, as a result of this contact method, the position of the wiper contact element  1  relative to the contact track on the rotary knob  10  is no longer dependent on the position of the printed circuit board  7  to which the wiper contact element  1  was generally fastened. Thus, the tolerance problems between the printed circuit board  7  and the plastic parts from which the base  9  and the rotary knob  10  are manufactured have been eliminated. Moreover, the manufacturing step in which the wiper contact element  1  was fastened to the printed circuit board is eliminated. 
     FIG. 3  shows a top view of the base  9  on the underside of the rotary knob  10 . In this example embodiment, three wiper contact elements  1  are built into the rotary knob  10  at different diameters. As is clearly visible, the wiper contact elements  1  are arranged at different diameters with respect to the center point of the circular rotary knob  10  and are Arranged in order to attach the base  9  to the upper part of the rotary knob  10 . 
     FIG. 4  shows a cross-section through a wiper contact element  1  along the line IV—IV from FIG.  3 . The wiper contact element  1  rests on an area  20  in a recess  14  of the base  9 . In this case, the wiper contact element  1  is fastened to the base  9  in the area of the recess  14  by pressing a section of plastic  16  projecting from the base  9 . The entire contact spring  1  sits in the through opening  8 . 
   The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.