Patent Publication Number: US-8966802-B1

Title: Trigger return and drop pendulum

Description:
FIELD OF THE INVENTION 
     This invention relates to an improved trigger mechanism for firearm fire control. 
     BACKGROUND 
     Trigger sensation (i.e., trigger pull weight, creep and feel) and safety are important issues in the operation of a firearm&#39;s fire control. Too often in the design of firearm fire control mechanisms, these two factors are seen as being in opposition to one another in that an increase in safety of operation comes at the expense of a decrease in trigger sensation and vice versa. However, it is both desirable and possible to improve both the safety and trigger sensation of firearms, using an improved trigger mechanism according to the invention disclosed in this specification that does not require a two-stage trigger feel found objectionable by many shooters. 
     SUMMARY 
     One aspect of the invention relates to a trigger assembly for a firearm. The firearm has a reciprocating component. In one example embodiment, the trigger assembly comprises a sear movably mounted within the assembly. The sear has a stop surface engageable with the reciprocating component for holding the reciprocating component in a cocked configuration. The sear further comprises a sear cam. A lever is movably mounted within the assembly. The lever has a contact surface. The sear cam engages the lever. A trigger is movably mounted within the assembly. The trigger has an action surface movable into and out of engagement with the contact surface upon motion of the trigger. A lever return spring acts on the lever and biases the contact surface out of engagement with the action surface. A trigger return pendulum is movably mounted within the assembly. The trigger return pendulum has a trigger cam engageable with the trigger. A lever cam is engageable with the lever. A head cam follower is engageable with the reciprocating component. In this example embodiment, motion of the reciprocating component acts through the head cam follower of the trigger return pendulum and forces the lever cam into engagement with the lever, and the trigger cam into engagement with the trigger, to return the lever and the trigger to a configuration of engagement between the action surface and the contact surface. 
     In a particular example embodiment, the sear is pivotably mounted on a sear fulcrum. By way of example, the stop surface is angularly oriented relatively to a line of motion of the reciprocating component to permit the reciprocating component to pivot the sear about the sear fulcrum upon motion of the reciprocating component along the line of motion against the stop surface. 
     In another example embodiment, the lever is pivotably mounted on a lever fulcrum. In a further example embodiment, the sear cam engages the lever on one side of the lever fulcrum and the contact surface is positioned on the one side of the lever fulcrum. 
     In a specific example embodiment, the trigger is pivotably mounted on a trigger fulcrum. By way of example, the trigger comprises an actuation arm and a projection extending transversely thereto. The projection is engageable with the trigger cam. By way of example, the trigger may be balanced about the trigger fulcrum. 
     In another example embodiment, the trigger return pendulum is pivotably mounted on a trigger return pendulum fulcrum. By way of a further example, the lever cam engages the lever on an opposite side of the lever fulcrum from the contact surface. In another example, the trigger return pendulum fulcrum is positioned at one end of the trigger return pendulum, and the lever cam is positioned at an opposite end of the trigger return pendulum. In this example the trigger cam is positioned between the ends of the trigger return pendulum. 
     A particular example embodiment further comprises first and second plates attached to one another in spaced apart relation. In this example, the sear, the lever, the trigger and the trigger return pendulum are mounted between the sideplates. By way of further example, the sear fulcrum, the lever fulcrum, the trigger fulcrum and the trigger return pendulum fulcrum each comprises a respective pin extending between the sideplates. 
     The invention further encompasses a trigger assembly for a firearm having a reciprocating component wherein the trigger assembly comprises first and second sideplates arranged in parallel, spaced apart relation. In this example, a sear pin extends between the first and second sideplates. A sear is pivotally mounted on the sear pin. The sear has a stop surface engageable with the reciprocating component for holding the reciprocating component in a cocked configuration. The sear further comprises a sear cam. A lever pivot pin extends between the first and second sideplates. A lever is pivotally mounted on the lever pivot pin. The lever has a contact surface. The sear cam engages the lever. A trigger pivot pin extends between the first and second sideplates. A trigger is pivotally mounted on the trigger pivot pin. The trigger has an action surface movable into and out of engagement with the contact surface upon motion of the trigger. A lever return spring acts on the lever and biases the contact surface out of engagement with the action surface. A trigger return pendulum pin extends between the first and second sideplates. A trigger return pendulum is pivotally mounted on the trigger return pendulum pin. The trigger return pendulum has a trigger cam engageable with the trigger. A lever cam is engageable with the lever. A head cam follower is engageable with the reciprocating component. In this example embodiment, motion of the reciprocating component acting through the head cam follower of the trigger return pendulum forces the lever cam into engagement with the lever and the trigger cam into engagement with the trigger to return the lever and the trigger to a configuration of engagement between the action surface and the contact surface. 
     In a particular example embodiment, the stop surface is angularly oriented relatively to a line of motion of the reciprocating component to permit the reciprocating component to pivot the sear about the sear pin upon motion of the reciprocating component along the line of motion against the stop surface. By way of example, the sear cam engages the lever on one side of the lever pivot pin and the contact surface is positioned on the one side of the lever pivot pin. In a particular example embodiment, the trigger comprises an actuation arm and a projection extending transversely thereto. In this example embodiment, the projection is engageable with the trigger cam. Further by way of example, the trigger may be balanced about the trigger pivot pin. In an example embodiment, the lever cam engages the lever on an opposite side of the lever pivot pin from the contact surface. Further by way of example, the trigger return pendulum pin may be positioned at one end of the trigger return pendulum, the lever cam may be positioned at an opposite end of the trigger return pendulum, and the trigger cam may be positioned between the ends of the trigger return pendulum. 
     The invention further encompasses a firearm. In a particular example embodiment, the firearm comprises a reciprocating component and a trigger assembly comprising a sear movably mounted within the assembly. The sear has a stop surface engageable with the reciprocating component for holding the reciprocating component in a cocked configuration. The sear further comprises a sear cam in this example embodiment. A lever is movably mounted within the assembly. The lever has a contact surface. The sear cam engages the lever. A trigger is movably mounted within the assembly. The trigger has an action surface movable into and out of engagement with the contact surface upon motion of the trigger. A lever return spring acts on the lever and biases the contact surface out of engagement with the action surface. A trigger return pendulum is movably mounted within the assembly. The trigger return pendulum has a trigger cam engageable with the trigger. A lever cam is engageable with the lever, and a head cam follower is engageable with the reciprocating component. In this example embodiment, motion of the reciprocating component acting through the head cam follower of the trigger return pendulum forces the lever cam into engagement with the lever, and the trigger cam into engagement with the trigger to return the lever and the trigger to a configuration of engagement between the action surface and the contact surface. 
     By way of example, the sear is pivotably mounted on a sear fulcrum. In an example embodiment, the stop surface is angularly oriented relatively to a line of motion of the reciprocating component to permit the reciprocating component to pivot the sear about the sear fulcrum upon motion of the reciprocating component along the line of motion against the stop surface. By way of example, the lever may be pivotably mounted on a lever fulcrum. 
     In an example embodiment, the sear cam engages the lever on one side of the lever fulcrum and the contact surface is positioned on the one side of the lever fulcrum. By way of further example, the trigger may be pivotably mounted on a trigger fulcrum. In a particular example embodiment the trigger comprises an actuation arm and a projection extending transversely thereto, the projection being engageable with the trigger cam. In this example embodiment, the trigger may be balanced about the trigger fulcrum and the lever may be balanced about the lever fulcrum. By way of example, the trigger return pendulum may be pivotably mounted on a trigger return pendulum fulcrum. In an example embodiment, the lever cam engages the lever on an opposite side of the lever fulcrum from the contact surface. 
     In a particular example embodiment, the trigger return pendulum fulcrum is positioned at one end of the trigger return pendulum, the lever cam is positioned at an opposite end of the trigger return pendulum, and the trigger cam is positioned between the ends of the trigger return pendulum. 
     By way of further example, the firearm may comprise first and second sideplates attached to one another in spaced apart relation. The sear, the lever, the trigger and the trigger return pendulum are mounted between the sideplates in this example. By way of example, the sear fulcrum, the lever fulcrum, the trigger fulcrum and the trigger return pendulum fulcrum each may comprise a respective pin extending between the sideplates. In a particular example embodiment, the firearm comprises a bolt action rifle and the reciprocating component comprises a firing pin head. In another example embodiment, the firearm comprises a semi-automatic rifle and the reciprocating member comprises a bolt carrier. By way of further example, the firearm may comprise an automatic rifle and the reciprocating member may comprise a bolt carrier. In another example embodiment, the firearm comprises a pistol and the reciprocating member comprises a slide. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded isometric view of an example embodiment of a trigger mechanism according to the invention; 
         FIG. 2  is a right side assembled view of the trigger mechanism shown in  FIG. 1 ; 
         FIGS. 3-5  are side views of example firearms with which the trigger mechanism according to the invention may be used; and 
         FIGS. 6-8  are right side views illustrating operation of the trigger mechanism of  FIG. 1  in a bolt action rifle. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an exploded view of an example trigger assembly  10  for a firearm according to the invention. Trigger assembly  10  comprises first and second sideplates  12  and  14  arranged in a parallel, spaced apart relation. A sear  16  is movably mounted within the assembly  10  between sideplates  12  and  14 . In this example embodiment, sear  16  is pivotably mounted on a sear fulcrum comprising a sear pin  18  extending between sideplates  12  and  14 . Sear  16  comprises a stop surface  20  that is engageable with a surface  22  of a reciprocating component  24 , shown in  FIG. 2 . In this example, the reciprocating component is a firing pin head  26  of a bolt action rifle  28  (see  FIG. 3 ), but in other example embodiments the reciprocating component may comprise a bolt carrier  30  of an automatic or semi-automatic rifle  32  (see  FIG. 4 ) or the slide  34  of a semi-automatic pistol  36  (see  FIG. 5 ). As shown in  FIG. 2 , stop surface  20  holds the reciprocating component  24  in a cocked position when engaged with surface  22 , the reciprocating component being reciprocally movable relatively to sear  16  along a line of motion show by arrow  38  parallel to a firing axis  39  of the firearm. It is advantageous to orient the stop surface angularly with respect to the line of motion  38  as the angular geometry facilitates release of the reciprocating component  24  and pivoting of the sear  16  when the sear pivots on its fulcrum/pin  18  as described below. 
     As shown in  FIGS. 1 and 2 , a sear cam  40  is mounted on sear  16 . In this example embodiment, the sear cam  40  comprises a lobe projecting away from the stop surface  20  and engaging a lever  42 . Lever  42  is movably mounted within the assembly  10  between sideplates  12  and  14 . Mounting is via a lever pivot pin  44  extending between the sideplates to provide a lever fulcrum permitting pivoting motion. A contact surface  46  is positioned on lever  42  on the same side of the lever pivot pin  44  that the sear cam  40  engages the lever. A trigger  48  is movably mounted within the assembly  10  between sideplates  12  and  14 . Trigger  48  is mounted on a trigger pivot pin  50  that extends between the sideplates and provides a trigger fulcrum permitting pivoting motion of trigger  48 . An action surface  52  is positioned on the trigger  48 . Upon pivoting of trigger  48  about its pin  50 , the action surface  52  is movable into and out of engagement with the contact surface  46  of the lever  42  (compare  FIGS. 6 and 7 ). With reference again to  FIGS. 1 and 2 , a lever return spring  54  biases the lever  42  in a counterclockwise sense (when viewed from the right side of the firearm) to force the lever&#39;s contact surface  46  away from the action surface  52  of the trigger  48 . A trigger pull spring  47  biases the trigger in a counterclockwise sense about its pin  50  and a trigger overtravel screw  49  limits the clockwise rotation of the trigger about pin  50 . When trigger  48  pivots to move the action surface  52  out of engagement with the contact surface  46 , lever  42  pivots clockwise under the action of sear  16 . Sear  16  rotates counterclockwise from the force of firing pin head  26  acting along line of motion  38  through engagement between surface  22  of the firing pin head  26  and angled stop surface  20  of the sear  16 . Counterclockwise rotation of sear  16  forces clockwise rotation of lever  42  (overcoming its biasing spring  54 ) through engagement between the sear cam  40  and the lever  42 . 
     Trigger  48  comprises an actuation arm  56  (the curved portion that receives a finger of a shooter) and a projection  58  that extends transversely to the actuation arm  56 . It is advantageous to balance the trigger  48  about the trigger pivot pin  50  so that there is no net torque from the part&#39;s mass about the trigger fulcrum; i.e., the trigger will not tend to rotate under the influence of gravity or inertial forces. Balancing the trigger helps prevent unintended discharge of the firearm when dropped. It is also advantageous to balance lever  42  about its fulcrum pin  44  so that there is no net torque from the part&#39;s mass about the lever fulcrum. Balancing the lever also helps prevent unintended discharge of the firearm when dropped. A safety  51  having a safety/trigger detent screw  53  is mounted on sideplate  12 . 
     A trigger return pendulum  60  is movably mounted within the assembly  10  between sideplates  12  and  14 . Trigger return pendulum  60  is mounted on a trigger return pendulum pin  18  that extends between the sideplates and provides a fulcrum permitting pivoting motion of the trigger return pendulum  60 . (In this example embodiment the trigger return pendulum  60  shares the same pin as the sear  16 .) Trigger return pendulum  60  comprises a trigger cam  62 , a lever cam  64 , and a head cam follower  66 . In the example embodiment disclosed herein, the trigger return pendulum fulcrum (pin  18 ) is positioned at one end  68  of the trigger return pendulum  60 . Lever cam  64  and the head cam follower  66  are positioned at an opposite end  70  of the trigger return pendulum from the fulcrum, and the trigger cam  62  is positioned between ends  68  and  70  of the trigger return pendulum  60 . With this configuration of trigger return pendulum  60  the lever cam  64  can engage the lever  42  on an opposite side of the lever pivot pin  44  from the lever&#39;s contact surface  46 , and the trigger cam  62  can engage the trigger projection  58  upon pivoting motion of the trigger return pendulum about pin  18 . As shown in FIGS.  2  and  6 - 8 , the head cam follower  66  is engageable with a cam  72  on the reciprocating component  24  when the action of the firearm is worked as described below. 
     Operation of the trigger assembly  10  is described with reference to  FIGS. 6-8 . As shown in  FIG. 6 , the firearm is ready to fire. The firing pin head  26  (i.e., reciprocating component  24 ) is held in the cocked position (i.e., firing pin spring  74  compressed between the firing pin  76  and the rifle&#39;s tail piece  78 ) by the stop surface  20  of sear  16  engaging the surface  22  of the firing pin head  26 . In this state, the firing pin  76  is prevented from moving toward the chamber  80  by the sear  16 . Sear  16  is prevented from rotating counterclockwise about its fulcrum pin  18  because the action surface  52  of trigger  48  engages the contact surface  46  of the lever  42  and holds the sear cam  40  against the lever  42 . Trigger cam  62  of trigger return pendulum  60  rests on the projection  58  of the trigger  48 , and the lever cam  64  of the trigger return pendulum is positioned adjacent to a portion of lever  42  on the opposite side of the lever pivot pin  44  from the lever contact surface  46 . 
     As shown in  FIG. 7 , a pull of trigger  48  rotates the trigger about trigger pivot pin  50  and disengages action surface  52  from the contact surface  46  of the lever  42 . Lever  42  is forced to rotate clockwise under the action of the force of the firing pin spring  74  acting through the angled stop surface  20  of sear  16 , which communicates this force to the lever  42  through contact between the sear cam  40  and the lever. Clockwise rotation of the lever  42  permits counterclockwise rotation of the sear  16 , causing the stop surface  20  to fall off of the surface  22  of the firing pin head  26 . This permits the firing pin head  26  to move along its line of motion  38  parallel to the firing axis  39  under the force of its spring  74 . Firing pin  76  is thus driven toward chamber  80  to discharge a chambered round. 
     As shown in  FIG. 8 , the firing pin head  26  is drawn along its line of motion  38  away from chamber  80 . For the bolt action rife ( FIG. 3 ) this is accomplished by rotating the bolt to unlock it from the barrel and manually pulling the bolt away from the chamber. Motion of the bolt away from chamber  80  extracts the spent cartridge from the chamber and opens the action of the rifle, allowing another round to be chambered. As the firing pin head moves along its line of motion  38  away from the chamber  80  the cam  72  engages the head cam follower  66  on the trigger return pendulum  60 . Engagement between the cam  72  and the head cam follower  66  causes the trigger return pendulum  60  to rotate counterclockwise about the pin  18 . During rotation of the trigger return pendulum  60 , the lever cam  64  first engages the lever  42 , causing it to rotate counterclockwise about lever pivot pin  44 . Rotation of the lever  42  causes it to engage the sear cam  40  and rotate the sear  16  about pin  18 , moving the stop surface  20  of the sear into a position where it will again engage surface  22  of the firing pin head  26  to hold it in the cocked position. Rotation of the lever  42  also moves the contact surface  46  of the lever  42  into a position where it can again engage the action surface  52  of trigger  48 . Further during counterclockwise rotation of the trigger return pendulum  60 , the trigger cam  62  engages the projection  58  of the trigger  48 , causing the trigger to rotate counterclockwise to bring its action surface  52  into engagement with the contact surface  46  of the lever  42 . The geometry of the trigger return pendulum  60 , the lever  42  and the trigger  48  are such that the lever and trigger move smoothly into position without binding to ensure engagement between the action surface  52  and the contact surface  46  once the bolt is closed and the rifle is brought once again into the fire configuration ( FIG. 6 ) wherein surface  22  of bolt head  26  is engaged with stop surface  20  of sear  16 . Once these surfaces are engaged, the sear  16  is stable, supported by contact between the sear cam  40  and the lever  42 , and, until the trigger is again pulled, able to reliably hold the firing pin head  26  in the cocked position of  FIG. 6 . Motion of firing pin head  26  along its line of action  38  causes trigger  48  and lever  42  to be influenced into engagement through each motion of opening and closing the bolt. 
     Trigger return pendulum  60  also acts as a “drop pendulum” to prevent inadvertent discharge of the firearm if dropped. As shown in  FIG. 6 , the trigger cam  62  is engaged with the projection  58  of trigger  48  when the firearm is cocked. Inertial forces acting on the mechanism as a result of the firearm being dropped will tend to keep the trigger cam  62  engaged with the projection  58 , thereby preventing rotation of the trigger (which is also balanced, further inhibiting any tendency to rotate). Inertial forces which might tend to rotate the trigger return pendulum  60  clockwise so that trigger cam  62  lifts off the projection  58  will be countered by the head cam follower  66  contacting and bouncing off of the firing pin head  26 .