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FIELD OF THE INVENTION 
     The present invention relates to window opening control devices, often referred to as vent stops, which can be actuated to limit the extent to which a window sash may be opened. This enables the sash to be opened enough for ventilation while limiting the opening to a desired maximum size. More particularly, the invention relates to vent stops incorporating a pivoting stop element. 
     BACKGROUND OF THE INVENTION 
     Pivoting vent stops are in general well known devices that are designed to be mounted on sash rails of double hung windows or other slidable window arrangements in a position to allow a window sash to be opened to, but not beyond, a predetermined position. A typical pivoting vent stop includes a housing arranged to be mounted in a sash frame, a tumbler pivotally mounted in the housing and movable between retracted and extended positions, a spring for biasing the tumbler toward its extended position, and some form of retention means for retaining the tumbler in a retracted position. When the tumbler is retracted, a window sash may slide over the housing and thus be moved to fully open position. When the tumbler is in an extended position, however, it engages the sash after partial opening thereof and blocks further opening movement. When it is necessary or desirable to fully open the sash, the tumbler is pushed back into its housing and held in a retracted position until needed. 
     An early form of pivoting vent stop is reflected in the Szapucki et al U.S. Pat. No. 6,572,158, which incorporates a pivoted tumbler biased toward an extended position by a spring. In order to retain the tumbler in a retracted position, when desired, the tumbler can be pressed inward and then slid on a loose pivot connection until an end portion of the tumbler lies underneath a lip on the housing. The tumbler is released, when desired, by sliding the tumbler in an opposite direction to free the end portion and allow the tumbler to be pivoted outward by the biasing spring. A shortcoming of this type of device is the inconvenience of manipulating the tumbler for locking and unlocking it in or releasing it from a retracted position. 
     A different form of pivoting vent stop is represented by the Liang et al U.S. Pat. Nos. 7,600,796 and 7,637,544. In each of these devices, a tumbler is pivotally mounted in a housing and biased to a projected position by a spring. A separate, spring-biased latch mechanism is contained within the housing to engage the tumbler, when retracted, and retain it in a retracted position until the user desires to release it into an extended or locking position. A push-button type of release is provided for the latch mechanisms, such that the tumbler can be retracted by pressing on the projected end of the tumbler, and released by pressing on the push button release for the latching mechanism. A shortcoming of these designs is their relative complexity and corresponding higher cost, as well as a somewhat larger physical size to accommodate the presence of the release mechanism. 
     Yet another form of pivoting vent stop is represented by the Liang et al U.S. Pat. Nos. 7,530,611 and 8,235,430. Each of these devices utilizes a special spring element which is attached to a pivoted tumbler and has a horizontally extending portion that slides over a contoured bottom of the housing in which the tumbler is mounted. The combination of the sliding spring and the contoured housing bottom is intended to cause the tumbler to be self-retaining in retracted or extended positions without the need for special locking and/or releasing mechanisms. This arrangement, while having certain desirable functional features has the shortcoming of requiring extra parts and the assembly operations associated therewith, which adds extra cost to a highly cost-sensitive product. 
     There remains a need for a pivoted vent stop that is fully functional but which nevertheless requires an absolute minimum of parts, resulting in lower manufacturing and assembly costs. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an advantageous form of pivoting vent stop which is comprised of only two parts: a housing, and a tumbler pivotally mounted within the housing. The two parts are formed of injection molded plastic material and thus suitable for production on an economical basis. The vent stop of the invention incorporates a novel construction by which the two parts thereof cooperate to provide an integrally formed resilient detent arrangement whereby the tumbler is self-retaining in either of its retracted or extended positions. The design and structure of the new device is such that the two parts thereof, after molding, may be assembled by simply pressing the tumbler part into the housing part, whereupon the tumbler is pivotally mounted within the housing and the detent features are automatically functional. 
     As a feature of the invention, portions of the housing and portions of the tumbler cooperate resiliently to form a two-position detent, allowing the tumbler to be manually pivoted between its retracted and extended positions and automatically retained in either of those positions. This desirable function is achieved in the device of the invention without the use of added spring elements that are found in prior art devices and which add significantly to the cost of production. 
     In a particularly preferred form of the invention, the desired resilient detent action is derived from the side walls of the housing, which are formed of a plastic material having suitable strength and resilience. The housing side walls are formed with detent recesses therein which receive detent projections extending laterally from the tumbler and spaced radially from the pivot axis of the tumbler. The detent recesses are disposed along an arcuate path followed by the detent projections during pivoting movements of the tumbler. The recesses are formed with end portions, corresponding to recessed and extended limit positions of the tumbler, and with a restricted intermediate portion. When the tumbler is pivoted from one limit position to the other, the detent projections pass through the restricted intermediate portion of the detent recess and resiliently displace such restricted portions in order to pass through. A modest degree of force is required to cause the detent projections to pass through the restricted portion, and the tumbler is thus automatically retained in either of its limit positions until intentionally moved by pressing on one end or the other of the tumbler. 
     To particular advantage, the detent recesses comprise primary openings through the opposed side walls of housing, and secondary openings on at least one side, and preferably both sides of the primary openings. The secondary openings, together with the primary openings, define resiliently displaceable side wall portions that are deflected within the planes of the respective side walls, to allow passage of the detent projections through the restricted portions of the detent openings. 
     For a more complete understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment of the invention, and also to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is orthographic view of a vent stop mechanism according to the invention, shown with the tumbler in a retracted position. 
         FIG. 2  is an orthographic view, similar to  FIG. 1 , showing the tumbler in a projected or extended position. 
         FIG. 3  is a side elevational view of the mechanism of  FIG. 1 , with the tumbler in a retracted position. 
         FIG. 4  is a side elevational view similar to  FIG. 3 , showing the tumbler in an extended position. 
         FIGS. 5 and 6  are longitudinal cross-sectional views, corresponding to  FIGS. 3 and 4 , showing the tumbler in retracted and extended positions, respectively. 
         FIG. 7  is a side elevational view of the housing without a tumbler installed therein. 
         FIGS. 8 and 9  are cross-sectional views as taken generally along lines  8 - 8  and  9 - 9 , respectively, of  FIG. 7 . 
         FIG. 10  is in orthographic view of the housing part without a tumbler installed therein. 
         FIG. 11  is a top plan view of the housing part. 
         FIGS. 12 and 13  are side elevational and bottom plan views, respectively, of the tumbler part by itself. 
         FIG. 14  is an orthographic view of the tumbler part of  FIGS. 12 and 13 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings, the numeral  20  designates generally a housing part of the two-part vent stop device of the invention. The housing forms an upwardly opening cavity  21  which receives a tumbler  22 . It will be understood that, throughout this specification, directional terms such as “upward”, “downward”, “laterally” and the like are referenced to the representational orientation of the device as shown in the drawings, and are used for convenience only and not in a limiting manner. In actual practice, the vent stop may be used in any orientation called for by its mounting in a window sash. 
     In the illustrated and preferred form of the device, the housing  20  is formed with a top plate or flange  23 , which surrounds and extends outward from upper edges of the sidewalls  24 ,  25  and end walls  26 ,  27  of the housing. The housing also includes a bottom wall  28 . Integral mounting clips  29 ,  30  are provided at each end of the housing  20 , extending outward and upward from bottom portions of the respective end walls  26 ,  27 . Upper portions of the mounting clips  29 ,  30  underlie opposite end extremities of the flange  23 , as shown in, for example,  FIG. 7 . The lower portions of the mounting clips extend integrally from lower portions of the housing end walls and are designed to flex inwardly toward the end walls. The housing  20  is intended to be mounted in a hollow sash frame or stile (not shown), which is provided with an opening (not shown) closely fitting the side walls  24 ,  25  of the housing  20  and extending somewhat beyond the end walls  26 ,  27 , although not as far as the end extremities of the flange  23 . When the housing is pressed into the sash opening, upper portions of the mounting clips  29 ,  30  initially flex inwardly, toward the housing end walls, allowing the tops of the clips to pass through the opening. Once through the opening, the clips flex outwardly to underlie or partly underlie the outer wall of the sash, depending upon the thickness of the outer wall. The housing is thus locked in place, with the flange  23  snuggly seated on the outer surface of the sash wall. The described manner of mounting the housing is well known and well understood by those skilled in the art. 
     In accordance with aspects of the invention, the housing side walls  24 ,  25  are provided with axially, aligned circular through openings  31 ,  32  for the pivotal mounting of the tumbler  22 . The tumbler, which is injection molded of plastic material, is formed with integrally molded cylindrical pivot pins  33 ,  34 , which are received in the respective pivot openings  31 ,  32  and provide for pivotal mounting of the tumbler in the housing about a predetermined pivot axis. 
     As shown particularly in  FIGS. 1-6 , the tumbler  22  has two limit positions in the housing  20 , a fully retracted position, shown in  FIGS. 1, 3 and 5 , and an extended position, shown in  FIGS. 2, 4 and 6 . As indicated in the drawings, the pivot axis of the tumbler is asymmetrically positioned, such that one end  35  of the tumbler (the left end as viewed in  FIGS. 1-6 ) is of considerably greater length than the other end  36 . When the tumbler is pivoted to its retracted limit position, the upper surfaces of both end portions  35  and  36  of the tumbler are substantially flush with the upper surfaces of the flange  23 , allowing a window sash to slide freely over the top of the flange and the retracted tumbler. In the extended limit position of the tumbler, the end portion  35  thereof is projected outward from the flange  23  and presents an abutment surface  37  thereof generally at right angles to the sash frame in which the device is mounted. The abutment surface is positioned to engage the upper or lower sash frame member (in a typical, vertically sliding window) to limit the extent to which the sash may be opened. The vent stop device typically is positioned in such manner as to limit opening movement of a window sash to a desired maximum, typically about 4 inches 
     In the illustrated form of the invention, the retracted limit position of the tumbler  22  is determined in part by means of an extension  38  of the bottom  39  of the tumbler. As shown in  FIG. 5 , the extension  38  has a bottom surface  40  that engages the bottom wall  28  to limit pivotal retracting movement of the tumbler. Once in the retracted position, the tumbler is held in that position by a unique detent means to be described. The extension  38  extends a short distance beyond the abutment surface  37  and provides an outer surface  41  that can function as a secondary stop feature. If forces greater than normal were to be applied to a sash in an opening direction, the extension surface  41  will engage the face of the sash and assist in maintaining its position. 
     As shown particularly in  FIG. 6 , the short end  36  of the tumbler, which is recessed when the tumbler is in its extended limit position, has downwardly facing surfaces  42 ,  43 , which engage with upwardly facing surfaces  44 ,  45  of the housing bottom wall to form a strong positive limit stop to pivoting movement of the tumbler in the extending direction. This is arranged to strongly resist pivoting movement of the tumbler in response to sash pressure on the abutment surface  37 . Additionally, the recessed end  36  of the tumbler, when the tumbler is in its extended position, has a surface portion  46  which bears against the inner surface of the end wall  26 . This serves to transmit longitudinally directed forces, applied against the tumbler via the abutment surface  37 , into the housing end wall, partially isolating such forces from the pivot pins  33 ,  34  and the respective pivot openings  31 ,  32  in the housing side walls. The housing  20 , being supported by the wall of sash frame, can readily withstand the forces transmitted thereto by the surface portion  46  of the tumbler. 
     In accordance with an important aspect of the invention, the tumbler  22  and housing  20  are provided with novel, self-contained detent features providing a desired over-centering spring action and serving to retain the tumbler  22  is its respective retracted or extended positions without requiring additional springs or other parts that would add cost and complexity of the device. To this end, the tumbler  22  is provided on opposite sides with detent projections  47 ,  48  which are spaced a short distance from the pivot axis formed by the pivot pins  33 ,  34 . In a representative but non-limiting example, in which a tumbler of approximately 1.4 inches in length is configured to pivot through an angle of about 22.5°, the detent projections may be spaced from the pivot axis a distance of approximately 0.250 inch. The detent projections, which conveniently but not necessarily are of cylindrical form, have a diameter of about 0.125 inch, extend a short distance (e.g., 0.057 inch) outward from the side walls  49  of the tumbler and project through detent openings  50  in the opposite side walls  24 ,  25  of the housing. In the described but non-limiting example, the side walls of the housing may have a typical thickness of about 0.059 inch, it being understood that such side walls will have a small taper (e.g., 1°) to accommodate the molding processes. 
     As illustrated particularly in  FIG. 7 , the detent opening is formed with upper and lower end portions  51 ,  52  of a size and shape to receive the detent projections  47 ,  48  in the respective limit positions of the tumbler. To advantage, the end portions are of circular form, of just slightly larger diameter than the diameter of the detent projections. The positioning of the detent recesses is such, in relation to the diameter of the detent projections, that the circular end portions  51 ,  52  slightly overlap to form partially restricted intermediate portion  53   s . For example, circular end portions  51 ,  52  of 0.127 inch in diameter may be spaced apart a distance of 0.097 inch, such that the end portions overlap about 0.030 forming openings  50  having somewhat of a figure eight configuration. In the illustrated embodiment, the central side edge portions  54  of the opening closest to the pivot axis are rounded slightly, and the opposite central side edge portions  55  are rounded to a somewhat greater degree, such that the figure eight configuration is slightly asymmetrical, as illustrated in the drawings, but with a width dimension in the restricted intermediate portions  53  of slightly less than the diameter of the detent projections  47 ,  48 . As a non-limiting example, the width dimension of the restricted portions  53  may be about 0.110 inch in conjunction with detent projections of 0.150 inch diameter. The arrangement is such that, when the tumbler  22  is pivoted between its limit positions, the projections must be forced through the restricted portions  53 . In addition, once passed through the restricted portions, the detent projections are resiliently urged into their new limit positions with somewhat of a snap action and retained in their new positions, such that the tumbler  22  is always snuggly retained on one or the other of its two limit positions. 
     In accordance with a feature of the invention, secondary openings  56 ,  57  are formed in one or both of the housing side walls  24 ,  25 , spaced closely adjacent to the opposite sides of the detent openings  50  therein. The respective secondary openings  56 ,  57  preferably are contoured to follow the side edge contours of the detent openings  50  and extend substantially from the top to the bottom of the detent openings. In the illustrated embodiment, the secondary openings extend to points slightly above and slightly below the top and bottom extremities of the detent openings  50 . The detent openings  50  and their respective secondary openings  56 ,  57  define between them resiliently displaceable side wall portions  58 ,  59  which, at their upper and lower ends, are integral with the housing side walls  24 ,  25  while being resiliently displaceable in their mid portions to accommodate passage of the detent projections  47 ,  48  through the restricted mid portions  53  of the detent openings. In an exemplary but non-limiting example, the displaceable side wall portions may have a width of about 0.030 inch from top to bottom. Persons skilled in the art will, however, be aware that the width dimension of the detent openings  50  in their restricted portions  53  and the width dimensions of the displaceable side wall portions  58 ,  59  may be somewhat variable depending on the desired level of force required to pivot the tumbler from one limit position to the other. The functional principles of operation will remain the same, regardless of such dimensional variations. 
     To facilitate and expedite assembly of the two-part vent stop of the invention, the respective housing side walls  24 ,  25  are provided on inner surfaces thereof with two sets of opposed vertically disposed slots  60 ,  61  which are aligned vertically with the pivot openings  31 ,  32  and the detent openings  50  respectively. The width of the first pair of slots  60  is such as receive the pivot pins  33 ,  34  of the tumbler, while the width of the second pair of slots  61  is such as to receive the detent projections  47 ,  48 . As shown in  FIGS. 8 and 9 , the vertical slots are inclined downward and inward and merge at their lower ends with the inner surfaces of the housing side walls. At their upper extremities the inclined slots  60 ,  61  extend into the flange  23  and have a maximum width, at the top, approximately equal to the end-to-end dimension of the pivot pins  33 ,  34  and the detent projections  47 ,  48 . In the illustrated example, the slots  60 ,  61  are inclined at an angle of about 8° and merge with the inside side wall surfaces at a level slightly below the upper extremities of the respective pivot openings  31 ,  32  and detent openings  50 , as can be seen in  FIGS. 8 and 9 . 
     In accordance with an aspect of the invention, a tumbler  22  and housing  20  are assembled by inserting a tumbler part way into the housing cavity  21 , with the pivot pins  33 ,  34  and the detent projections  47 ,  48  aligned with the slots  60 ,  61 . The tumbler is then pressed into to cavity, causing the pivot pins and detent projections to slide downward within the inclined slots. This causes the housing side walls to be progressively and resiliently displaced outwardly, until the pivot pins and detent projections are aligned with their respective openings  31 ,  32  and  50 , at which time the housing side walls return to their normal configuration, engaging and permanently retaining the tumbler in operative relation within the housing. 
     In order to actuate the tumbler  22  from a recessed position ( FIG. 1 ) to an extended position ( FIG. 2 ) the exposed upper surface  62 , at the short end of the tumbler is depressed with a finger or thumb a sufficient distance to cause the detent projections  47 ,  48  to pass through the restricted portions  53  of the detent openings  50 . Once the detent projections pass through the restricted portions, the resilient action of the displaceable side wall portions  58 ,  59  will cause the tumbler to continue pivoting into its extended limit position. Preferably, the housing flange  23  is provided, at the end of the housing in which the short end  36  of the tumbler is positioned, with a U-shaped recess  63 , which allows the tumbler surface  62  to be easily depressed sufficiently by the user&#39;s finger assure the full pivotal motion of the tumbler. Typically, a small recess  64  is provided in the upper edge of the tumbler in order to separate the pressing surface  62  from the exposed upper surface  65  of the long end  35  of the tumbler. This facilitates visually identifying the surface  62  to be pressed when actuating the tumbler. 
     Because of the multiple requirements of, and functions performed by the housing  20 , it is preferably formed of an engineering plastic material having substantial strength and resiliency. A preferred material for this purpose is CELCON® acetal copolymer, available from Ticona, of Summit, N.J. A preferred material for the tumbler is nylon. 
     The invention represents a significant improvement in vent stop devices because it provides all of the necessary functions of such a device without compromise—indeed with certain improvements—yet is formed of only two parts. Prior art devices performing similar functions typically have required the provision and assembly of at least three individual parts. Because of the nature and utilization of vent stop devices, purchasers thereof (typically window manufacturers) are very price conscious. The device of the present invention, requiring only two parts and a minimal, easily automated assembly step, enables a significant reduction in the manufacturing cost of the device with no sacrifice of performance. Whereas heretofore, a separate spring element has been required to achieve the desired action of the tumbler, the device of the present invention derives the necessary spring action from the interaction of the housing and tumbler, and preferably by forming resiliently displaceable portions of the housing side walls, which control movements of the tumbler between its retracted and extended limit positions. 
     The vent stop device of the invention not only derives all the necessary functionality with a mechanism of only two parts, but additionally enables a fully functional device to be assembled by simply pressing one part together with the other. 
     It should be understood, of course, that the preferred embodiment of the invention herein illustrated and described is intended to be representative of the invention and it will be recognized by those skilled in the art that certain variations may be made therein without departing from the teachings of the disclosure. In this respect, although the described embodiment of the invention is indicated to have detent features in both side walls of the housing, it is acceptable in many cases if at least one side has a detent recess. Accordingly, reference should be made to the following appended claims in determining the full scope of the invention.

Summary:
A fully functioning, pivoting vent stop for sliding windows has only two parts, a housing and a pivoting tumbler, both formed of injection molded plastic material. The tumbler is pivotally mounted in the housing and has integral detent elements cooperating with detent elements on the housing walls to position the tumbler in recessed or extended limit positions. The cooperating detent elements also provide an over-centering spring action as the tumbler is actuated between its limit positions. Assembly of the two-part device is achieved in a highly simplified and economical manner by configuring an internal cavity in the housing with inclined slots in the internal side walls of the housing. This enables the tumbler to be resiliently pressed into the cavity, temporarily displacing the housing side walls outwardly, until the cooperating pivot and detent elements are fully engaged.