Patent Publication Number: US-6220114-B1

Title: Control knob positioning device having tactile feedback

Description:
TECHNICAL FIELD 
     The present invention relates to control device subassemblies and, in particular, to an automotive HVAC control device having tactile feedback. 
     BACKGROUND OF THE INVENTION 
     Operation controls for heating ventilation and air conditioning (HVAC) systems in automobiles often provide tactile feedback to the operator. The feedback represents finite incremental changes or gradients as, for example, the temperature control knob is rotated clockwise from “cold” to “hot.” In some applications, instead of a knob, a sliding scale is used which, for example, when moved from left to right provides tactile feedback of finite incremental changes from “cold” to “hot.” One common method of providing this tactile, mechanical, feedback is to move a spring steel or plastic ball across a series of detents. 
     Referring to FIG. 1, there is shown one embodiment of providing tactile feedback in an HVAC detent application. The assembly includes a ball  10  positioned atop a coil spring  14 . The ball  10  is held into place by grease  12  or a similar tacky substance such that the stainless steel ball adheres to the spring during handling. The other end of the coil spring is attached, directly or indirectly, to a control knob or sliding indicator. In operation, the ball  10 , which can be steel or plastic, will tend to engage a detent  15  due to the biasing force of the spring  14 . As the knob is rotated, or slider moved laterally, the ball  10  will engage in each detent  15  with which it axially aligns, thereby providing tactile feedback as each detent  15  contacts the ball  10 . The ball, spring, and detent also act to maintain the position of the control indicator. 
     The prior art ball and spring assembly of FIG. 1 has several drawbacks when used for HVAC system detent applications, however. In particular, the ball and spring can become easily separated when handled or in operation. In addition, the grease required to hold the ball to the spring collects dirt which can reduce the wear characteristics of the ball, particularly in the case of a plastic ball. The grease also has a tendency to contaminate other components of the system and the assembly environment in general. The difficulty in handling the separate ball, spring, and grease assembly also increases the overall assembly costs. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a solution to the above mentioned problems. 
     According to the present invention, the foregoing and other objects and advantages are attained by a control device having tactile feedback which includes an elongated tubular bullet housing and a coil spring slidably engaged in said housing. The housing includes a semi-spherical cap enclosing one end. The cap is biased by the coil spring against a scale having a plurality of detents which represents gradients along the scale. The coil spring provides a biasing force such that, during relative movement between the housing and the scale, the end cap disengages each detent as it moves away and engages each detent as it becomes axially aligned with said housing. 
     In another embodiment, the housing includes an interior notch such that upon insertion of the coil spring into the housing, the coil spring and housing engage so as to prevent the separation of the coil spring and housing during handling of the assembly. 
     One advantage of the present invention is the reduced likelihood that the housing and spring separate during handling or operation as compared to the prior art spring and ball assembly. 
     Another advantage is reduced costs and easier assembly handling because the lack of grease as compared to the prior art spring and ball assembly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of this invention, reference should now be had to the embodiments illustrated in greater detail in the accompanying drawings and described below by way of examples of the invention. In the drawings: 
     FIG. 1 is a perspective view of a prior art ball and spring assembly; 
     FIG. 2 is a perspective view of one embodiment of the bullet housing and spring assembly of the present invention; and 
     FIG. 3 is a front elevation view of one embodiment of the bullet housing and spring assembly of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning to FIG. 2, there is shown one embodiment of the bullet-shaped housing and spring assembly of the present invention. The assembly includes a bullet-shaped housing  20  and an elongated coil spring  22 . The housing  20  has an elongated tubular body  24  which is open at one end  26  and enclosed at the other end by a semi-spherical cap  28 . Preferably, the outside diameter of the compression spring  22  has a close tolerance with the inside diameter of the hollow housing  20  such that once the spring  22  is inserted into the housing  20 , the housing  20  and spring  22  become an integral part. This reduces the likelihood that the spring  22  and housing  20  will become separated during handling or operation. 
     The semi-spherical cap  28  and elongated tubular body  24  of the housing  20  are preferably formed as a single part. In addition, the semi-spherical cap  28  is preferably polished stainless steel. It has been found that polished stainless steel provides adequate wear properties in low-wear applications such as HVAC detent applications. Thus, in detent applications for HVAC systems, the wear rate of the polished stainless steel cap  28  is nominal and no grease is required for lubrication. Because no grease is required to either improve the wear rate of the outer surface of the cap  28  or to keep the coil spring  22  and housing  20  together. The assembly cost of the housing and spring subassembly is less than that of the spring, ball, and grease assembly of the prior art. 
     As an alternative embodiment, the housing  20  can include a notch  30  along the elongated tubular body  24  to engage the coil spring  22  upon insertion into the housing  20 . Once engaged, the notch  30  prevents the coil spring  22  from separating from the housing  20 . The notch  30  could take several forms such as a flange about the circumference of the opening  26  of housing  20  or a detent in the side wall of the tubular body  24  of housing  20 . 
     As shown in FIG. 3, in operation, the housing  20  and spring  22  assembly is operatively connected to a control knob or sliding indicator represented as control device  32 . Control device  32  is typically a circular knob or an upstruck member slildably engaged in a groove on the instrument panel housing  34 . Relative movement of the control device  32  causes the end cap  28  of housing  20  to move relative to the plurality of detents  30  formed in the scale member  33 . The scale member  33  represents, for example, the temperature scale for an automotive HVAC system. Thus, rotation of the control device  32  in the case of a knob, or sliding of the control device  32  in the case of an upstruck member indicates the operator&#39;s desire to change the temperature. At all times, the spring  22  biases the end cap  28  against the detent  30  which is axially aligned with the subassembly. As the end cap  28  and detents  30  move relative to one another, the end cap  28  engages and disengages respectively, with each axially aligned detent  30 . Of course, depending upon the application, either the scale member  32  is fixed, and the bullet and spring assembly move relative to the scale member  32 , or vice versa. 
     From the foregoing, it will be seen that there has been brought to the art a new and improved bullet and spring assembly which overcomes the drawbacks of the prior art ball, spring, and grease assembly. 
     While the invention has been described in connection with one or more embodiments, it will be understood that the invention is not limited to those embodiments. On the contrary, the invention covers all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the appended claims.