Abstract:
A plastic jaw or striker with downwardly facing teeth is pivotally mounted to a plastic base with mating upwardly facing teeth. A plastic trigger hangs from the base, and a coil spring extends between the jaw and the base rearward of the trigger. The spring holds the jaw in the set position, by engaging the rear of the jaw against the rear of the base. The trap is tuned to be not overly sensitive, avoiding springing of the trap by vibrations or insubstantial rodent entry. The spring or tension axis does not go through the trigger, simplifying construction and arrangement of parts. The open position is limited by the jaw engaging the base. The jaw is just over-center when set, such that a small movement towards closure does not trigger it. The trigger requires fairly large movement, facilitated by the raised pivot axis, to trigger the trap. When closed the teeth interdigitate, closing against each other without any shear, thus striking and crushing rodents caught between the teeth, but minimizing damage to children or pets inadvertently actuating the trap.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     BACKGROUND OF THE INVENTION 
     The present invention relates to rodent traps in general, and more particularly to traps employing a base, a jaw, a trigger, and a spring between the base and the jaw. 
     Bait containing rodenticide is widely used to control or eliminate rodent populations, however, there are circumstances where mechanical traps are desirable. Traps are useful within large structures or where water is available within a structure such that rodents which consume rodenticide are likely to die within the confines of a structure. Typically, rodenticide causes rodents to become thirsty before death, causing them to leave the typical home or building in search of water. If the rodents do not leave the structure before dying they often die in inaccessible locations. The decay of dead rodents will produce an undesirable stench within a building. 
     Mechanical traps also allow visual assessment of rodent population. Even where bait containing rodenticide is used, traps may be employed to monitor rodent population. Mechanical traps are also used where foodstuffs could be contaminated by rodenticide. 
     In homes where small children or pets are present, mechanical traps do not expose non-targeted animals and children to poison. 
     Mechanical traps, however, have liabilities. They may be constructed of sheet metal which tends to corrode. Corrosion may affect the reliable operation of a trap and will certainly limit its operating life, particularly in damp environments. Mechanical traps also can cut a rodent caught within the trap, causing bleeding which soils the trap and the structure surrounding the trap. Mechanical traps can also be difficult to set. A rodent trap requires a sensitive trigger which often means they are very sensitive to slight movements when being set, and sometimes will be accidently triggered when being positioned. Many mechanical traps also can become enmeshed with the trapped rodent, making discharge of the dead rodent from the trap difficult, thus complicating trap reuse. Where children or pets are present, any trap which will produce an open wound which may become infected is undesirable. 
     One class of traps typically made of sheet metal, but in some cases constructed of plastic, has four pieces: a base, a jaw pivotally mounted on the base, a trigger mounted on the base, and a coil spring extending between the base and the jaw. This type of trap may be arranged so that the trigger which moves the jaw a small amount and which brings the line of effort produced by the spring through the pivot center, causing the trap to close. Traps based on this basic form have been known since at least the patent to Evans, U.S. Pat. No. 2,138,092, issued in 1938. Traps of the Evans type combined simplicity with the absence of a trigger catchment or sere. This type of trap can often be manipulated externally by pivoting the jaw with respect to the base to release a dead rodent or to set the trap. 
     Although such traps are known, improvements in manufacturing simplicity, use of plastic materials, ease of operation, and reduction in too sharp edges remain desirable goals. 
     SUMMARY OF THE INVENTION 
     The rodent trap of this invention has three molded plastic parts: a base, a jaw pivotally mounted on the base, and a trigger mounted on the base. A coil spring extends between the base and the jaw. The base is substantially rectangular; however, the front portion has somewhat greater width than rear portion, and has rounded teeth which extend around three sides. Rearward of the teeth, the sides extend upwardly forming flanges which support small stub shafts which define a pivot axis. The upper jaw mounts to the stub shafts for pivotal movement about the pivot axis. The upper jaw has a forward portion having teeth that are opposed to and which interdigitate with the lower teeth. The jaw rocks on the pivot axis from a position where the jaw teeth engage the base teeth, to a position where a rearmost portion of the jaw engages a rearward portion of the base. A coil spring is connected between the forward portion of the jaw and a rearward portion of the base. The coil spring defines a tension axis which moves through the pivot axis as the upper jaw is pivoted on the base. The tension axis passes through the pivot axis shortly before the rearmost portion of the upper jaw comes to rest against the rearmost portion of the base. 
     A trigger is pivotally mounted to the side flanges of the base, forming a second pivot axis below and rearward of the first pivot axis. The trigger has a frontwardly extending tongue and a rearwardmost portion which engages against depending flanges which are integral with the upperjaw. When the trap is opened with a rearwardmost portion of the jaw engaging the rearwardmost portion of the base, the jaw flanges push against the rearwardmost portion of the trigger pivoting the tongue to a raised position. When a rodent pushes the tongue downward, the rearwardmost portion of the trigger rotates about the second axis, pushing against the flanges and causing the upper jaw to rotate about the first pivot axis, bringing the axis of tension below the first pivot axis and causing the teeth of the upper jaw to forcefully close against the teeth of the base. 
     It is an object of the present invention to provide a rodent trap that is easily set and easily opened to remove dead rodents. 
     It is another object of the present invention to provide a rodent trap which can be used many times. 
     It is a further object of the present invention to provide a rodent trap which can be set with one hand. 
     It is a still further object of the present invention to provide a mouse trap strong enough to kill a mouse yet not harm pets or children. 
     It is a yet further object of the present invention to provide a rodent trap which is not easily triggered accidentally by vibration. 
     Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded isometric view of the rodent trap of this invention. 
     FIG. 2 is a cross-sectional view of the rodent trap of FIG. 1 shown in a set position. 
     FIG. 3 is a cross-sectional view of the rodent trap of FIG. 2 closed upon the limb of a rodent. 
     FIG. 4 is an exploded isometric view of the rodent trap of this invention with respect to a specially configured rodent bait station. 
     FIG. 5 is a front elevational view of the trap of FIG.  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring more particularly to FIGS. 1-5, wherein like numbers refer to similar parts, a rodent trap  20  is shown in FIGS. 2 and 3. The trap  20  has a plastic base  22  to which a plastic upper jaw or striker  24  is pivotally mounted. A plastic trigger  26  is also pivotally mounted to the base, and a coil spring  28  extends between the striker and the base. As shown in FIG. 1, the upper jaw  24  has spaced side walls  30  which define shaft engagement holes  32 . The shaft engagement holes  32  ride on stub shafts  34  which project outwardly of flanges  36  which extend upwardly from the sides  38  of the base  22 . The stub shafts  34  pivotally mount the upper jaw  24  about a horizontal first pivot axis  40 . 
     A coil spring  28  has a first hook  42  which attaches the spring  28  to the upper jaw  24  by extending around a short shaft  44  mounted below a slot  46  in the forward portion  48  of the upper jaw  24 . The coil spring  28  has a second hook  50  which attaches to the base  22  by engaging a short shaft  52  supported between two upstanding ears  54 . The shaft  52  and the ears  54  are integrally formed with the bottom wall  56  of the base  22 . The spring  28  defines an axis  58  through which the tension produced by the spring  28  acts. As the upper jaw  24  of the trap  20  moves from the open, set position shown in FIG. 2, to the closed position shown in FIG. 3, the axis of tension  58  moves through the first pivot axis  40 . When the tension axis  58  is below the first pivot axis  40 , energy stored in the spring  28  is transformed into kinetic energy of the rotating upper jaw  24  by the work the spring does as the trap  20  closes. 
     The trap is set, or a dead mouse is released from the trap, by simply pinching the rear portion  60  of the jaw  24  toward the rear portion  62  of the base  22  in a way analogous to opening a clothespin, until a rearwardmost downwardly facing surface  64  on the jaw  24  abuts an upwardly facing rearwardmost surface  66  on the base, as shown in FIG.  2 . The rear portion  60  of the jaw  24  has an upwardly protruding horizontal ridge  61  which facilitates gripping the upper jaw. The axis of tension  58  is above the first axis of rotation  40  when the trap  20  is set. The jaw  24  is actually held open by the spring  28  and substantial rotation of the jaw  24  is required before the axis of tension is sufficiently past the axis of rotation to cause the trap  20  to begin closing. The surfaces  64 ,  66  may be moved apart about {fraction (1/16)}th of an inch before the spring  28  will pull the trap shut. This positioning of the tension axis above the axis of rotation and friction created by the stub shafts  34  rotating in the holes  32 , prevents the trap from closing due to vibration or other small shocks. Resistance to premature closing due to shock or vibration allows the trap  20  to be set and then placed. This feature is particularly important when the trap is placed within a bait station  68 , as shown in FIG. 4, where the bait station  68  is closed and then set in a position of use. Premature actuation of the trap  20  then requires unlocking the lid  114  from the base  112  of the bait station and resetting the trap. The bait station  68  is disclosed in the application entitled Bait Station With Interior Mechanical Rodent Trap, by applicants Rick Leyerle et al., filed on the same date as this application, and the disclosure of which is incorporation by reference herein. To facilitate positive positioning of the trap  20  within the bait station  68 , the base of the trap may be provided with downwardly opening holes  106  which engage over protrusions  110  which extend upwardly from the bottom of the bait station. The bait station  68  may be of the type which alternatively holds rodent bait units  116 . 
     In conventional mouse traps which employ two jaws connected by a coil spring, in which the spring moves over center of a pivot axis to close the trap, it is common for the trigger to extend between where the upper jaw comes together with the base, or to have a catchment which holds the upper jaw in place. This results in the trigger passing around or under the spring or spring mount and typically results in sensitivity to shock or vibration. 
     As shown in FIG. 1, the trigger  26  has a rectangular tongue  70  which extends forward within the forward portion  72  of the base  22 . The tongue  70  is joined to a rear trigger plate  74  at an angle of about one-hundred and sixty degrees. Side flanges  76  extend upwardly from the rear trigger plate  74  and the tongue  70 . An array of pins  118  may be molded on the tongue to aid in retaining bait on the tongue. Short stub shafts  78  extend sidewardly from the side flanges  76  and fit within holes  80  formed in the side walls  30  of the base  22 . The stub shafts  78  define a trigger pivot axis  81 . The rearmost edge  82  of the rear trigger plate  74  engages two interior jaw flanges  84  which extend downwardly from the rear portion  60  of the jaw  24 . A small rearwardly opening recess  86  in the trigger plate  74  prevents the trigger  26  from engaging the ears  54  which support the spring engaging shaft  52 . 
     In the set position, as shown in FIG. 2, the depending flanges  84  have nearly vertical edges  88  which engage with the rear edge  82  of the trigger plate  74  forcing it forward and thus causing the trigger  26  to pivot about an axis defined by the stub shafts  78 , and raising the tongue  70  to the set position. The motion of the trigger plate rear edge  82  about the trigger pivot axis  81  is relatively large because the rear edge  82  is spaced a substantial distance below the pivot axis  81  and the motion against the flanges  84  is substantially tangent to the trigger plate&#39;s  74  rotation about the pivot axis  81 . The motion of the trigger plate  74  is forcefully amplified because the lever arm, that is the distance from the trigger axis  81  to the tip  90  of the trigger tongue  70 , is relatively large. The result of this trigger arrangement is that relatively light pressure by a rodent is required to depress the tongue  70  of the trigger plate  74  yet the rearmost edge  82  of the trigger plate moves strongly and a substantial distance against the flanges  84  mounted to the upper jaw  24 . This means a rodent trap  20  can be at the same time easily triggered by a rodent and resistant to triggering by vibration and mild shock. 
     The design of the trigger  26  is such that no part of the trigger spring  28  is surrounded by the trigger. This simplifies assembling and reduces possibility of interference between the trigger  26  and the spring  28 . 
     The base  22  has an overall rectangular shape which is made up of a rear rectangle  92  which includes the flanges  36  and the rear portion  62  of the base, and a forward rectangle  94  which is wider than the rear rectangle so that the front edge  96  and the two side edges  98  of the base are matched in width to the front edge  100  and side edges  102  of the upper jaw  24 , so that the upper and lower edges meet when the trap is closed. Typically, in prior art traps, the jaws telescope one within the other, creating a cutting action between jaws, which although effective at killing mice, increases the inherent hazard to adults, children, and pets who may be cut by accidental engagement with such traps. 
     The trap  20  edges  96 ,  98 ,  100 ,  102  forming the teeth are relatively thick having wall thicknesses, where the teeth are formed, of approximately {fraction (1/10)}th of an inch. The teeth  104  are rounded, sinusoidal, interdigitate and are opposed. The spaces between teeth are formed by lower margins which are part of the rounded teeth. Opposed means that the teeth rest upon each other, while interdigitate means that the upper teeth fit between the lower teeth. The base  22  upper jaw  24  and the trigger  26  may be constructed of injection molded ABS plastic, which, together with the arrangement and shape of the teeth, results in a trap  20  that avoids shearing action which could cut or injure a pet or child. As shown in FIG. 3, a portion of a rodent such as a mouse  108  is crushed between the upper jaw and the base, without shearing. Shearing is prevented by the teeth  104  being opposed, i.e. upper and lower teeth not sliding past each other but biting down, the upper upon the lower. Moreover, the thickness of the teeth, approximately {fraction (1/10)}th of an inch, and teeth being constructed of plastic, results in crushing rather than shearing action. 
     It should be understood that for catching mice, an appropriate size for the trap  20  is about three inches along the length of the base. The spring should have an extension of 0.182 inches and a spring constant of about twenty-nine pounds per inch. For a mouse trap the teeth  104  should have valley to valley spacing of about 0.209 inches and a height of about 0.062 inches. The valleys between teeth being somewhat more rounded at a radius of 0.069 verses a radius of 0.049 for the peaks. Furthermore, as best shown in FIG. 1, base  22  front portion is three-sided, providing a front entry for rodents, and two rearwardly extending side entries for rodents, each of the front and side entries having upwardly protruding teeth. The upper jaw  24  forward portion has a front top array of teeth, and two rearwardly extending arrays of teeth. In the closed position, the upper jaw teeth are closed upon and interdigitated with the base teeth, with the upper jaw front array of teeth overlying the base front entry, and the upperjaw side arrays of teeth overlying the base side entries. 
     It should be understood that the sensitivity of the trap may be adjusted by slight changes in the position of the edges  88  of the flanges  84 . This facilitates adjusting the injection mold used to manufacture the trap jaw to achieve desired sensitivity. Furthermore, the molds may be adjusted to elevate or decrease the upwardly facing rearwardmost surface  66  of the base, to adjust the preferred set position of the trap. In some circumstances, then, the upwardly facing rearwardmost surface  66  may be found on an upwardly protruding tab. 
     In a preferred embodiment, the trap  20  is tuned to have a range of sensitivity most adapted to entrap the targeted rodent. A trap  20  which is overly sensitive may be actuated before the rodent has fully entered the trap, while a trap which is not sensitive enough may never close on the rodent. Due to friction and other factors, the spring  28  may not extend in a completely straight line from the first hook  42  to the second hook  50 . If the spring  28  bows upwardly towardly the striker  24 , the sensitivity is reduced, if it bows downwardly toward the base  22 , sensitivity is increased. To prevent the loss of sensitivity from upward bowing, a bridge or tab  120  is formed in the underside of the striker, immediately rearward of the slot  46 . As shown in FIGS. 2,  3  and  5 , the tab  120  protrudes downwardly sufficiently to engage the spring  28  or the first hook of the spring, or to be closely spaced above the spring when the trap is in the set position. The tab  120  prevents undesired upward bowing of the spring. 
     It is understood that the invention is not limited to the particular construction and arrangement of parts herein illustrated and described, but embraces such modified forms thereof as come within the scope of the following claims.