Crossbow

Abstract

A crossbow including first and second flexible limbs attached to a center rail. A first cam is mounted to the first bow limb and rotatable around a first axis. A draw string is received in string guide journals and is secured to first and second cams. The draw string unwinds from the string guide journals as it translates from a released configuration to a drawn configuration. Power cables are received in first and second power cable take-up journals on each of the first and second cams. As the crossbow is drawn from the released configuration to the drawn configuration the first and second power cables wrap onto the respective first and second power cable take-up journals and are displaced along the first and second axes away from the first and second planes of rotation of the first and second draw string journals.

What is claimed is: 
     
         1 . A crossbow comprising:
 first and second flexible limbs attached to a center rail;   a first string guide mounted to the first flexible limb by a first axle mount and rotatable around a first axis located a fixed distance from the first flexible limb by the first axle mount, the first string guide comprising a first draw string journal having a first plane of rotation perpendicular to the first axis, and first upper and lower helical power cable journals on opposite sides of the first draw string journal;   a second string guide mounted to the second flexible limb by a second axle mount and rotatable around a second axis located a fixed distance from the second flexible limb by the second axle mount, the second string guide comprising a second draw string journal having a second plane of rotation perpendicular to the second axis, and second upper and lower helical power cable journals on opposite sides of the second draw string journal;   a draw string received in the first and second string guide journals, wherein the draw string unwinds from the first and second string guide journals as it translates from the released configuration to a drawn configuration;   a pair of first power cables having first ends received in the first upper and lower helical power cable journals and second ends attached to attachment points on the crossbow; and   a pair of second power cables having first ends received in the second upper and lower helical power cable journals and second ends attached to attachment points on the crossbow,   wherein the first and second upper and lower helical power cable journals displace the pairs of power cables along the first and second axes relative to the first and second planes of rotation, respectively, the first and second pairs of power cables wrap around the respective first and second upper and lower helical power cable journals, and the first and second axes move continuously toward the center rail as the drawstring is moved from the released configuration to the drawn configuration, and the first and second pairs of power cables unwrap from the respective first and second upper and lower helical power cable journals as the drawstring is moved between the drawn configuration to the released configuration.   
     
     
         2 . The crossbow of  claim 1  wherein the pair of first power cables are attached to attachment points on a first side of the center rail and the pair of second power cables are attached to attachment points on a second side of the center rail. 
     
     
         3 . The crossbow of  claim 1  wherein the first and second pairs of power cables are attached to power cable attachments that extend above surfaces of the first and second string guides and the power cable attachments pass under the respective first and second pairs of power cables as the draw string is moved between the released configuration and the drawn configuration. 
     
     
         4 . The crossbow of  claim 1  wherein the first and second string guides rotate at least 270 degrees when the draw string is moved from the released configuration to the drawn configuration. 
     
     
         5 . The crossbow of  claim 1  wherein an arrow engaged with the draw string in the drawn configuration is suspended above the center rail. 
     
     
         6 . The crossbow of  claim 1  wherein a separation between the first axis and the second axis in the drawn configuration is about 6 inches to about 8 inches. 
     
     
         7 . The crossbow of  claim 1  comprising:
 a cocking mechanism captured to slide on the center rail, wherein the cocking mechanism slides into engagement with the draw string in the released configuration; 
 a rotating member coupled to a flexible tension member attached to the cocking mechanism; and 
 a cocking handle configured to rotate the rotating member to retract the flexible member, whereby the cocking mechanism slides to a retracted position and moves the draw string to the drawn configuration in response to rotation of the cocking handle. 
 
     
     
         8 . The crossbow of  claim 7  comprising a torque control mechanism with an integral clutch that limits output torque applied to the rotating member by the cocking handle such that rotating the cocking handle after the cocking mechanism is in the retracted position causes the cocking handle to slip to limit torque applied to the cocking mechanism. 
     
     
         9 . A crossbow comprising:
 first and second flexible limbs attached to a center rail;   a first string guide mounted to the first flexible limb by a first axle mount and rotatable around a first axis located a fixed distance from the first flexible limb by the first axle mount, the first string guide comprising a first draw string journal having a first plane of rotation perpendicular to the first axis, and first upper and lower power cable journals on opposite sides of the first draw string journal each comprising a path that is not co-planar with the first plane of rotation;   a second string guide mounted to the second flexible limb by a second axle mount and rotatable around a second axis located a fixed distance from the second flexible limb by the second axle mount, the second string guide comprising a second draw string journal having a second plane of rotation perpendicular to the second axis, and second upper and lower power cable journals on opposite sides of the second draw string journal each comprising a path that is not co-planar with the second plane of rotation;   a draw string received in the first and second string guide journals, wherein the draw string unwinds from the first and second string guide journals as it translates from the released configuration to a drawn configuration;   a pair of first power cables having first ends received in the first upper and lower power cable journals and second ends attached to attachment points on the crossbow, and   a pair of second power cables having first ends received in the second upper and lower power cable journals and second ends attached to attachment points on the crossbow,   wherein the first and second upper and lower power cable journals displace the pairs of power cables along the first and second axes relative to the first and second planes of rotation, respectively, the first and second pairs of power cables wrap onto the respective first and second upper and lower power cable journals, and the first and second axes move continuously toward the center rail as the draw string is moved from the released configuration to the drawn configuration, and the first and second pairs of power cables unwrap from the respective first and second upper and lower power cable journals as the drawstring is moved between the drawn configuration to the released configuration.   
     
     
         10 . The crossbow of  claim 9  wherein the first and second pairs of power cables are attached to power cable attachments that extend above surfaces of the first and second string guides and the power cable attachments pass under the respective first and second pairs of power cables as the draw string is moved between the released configuration and the drawn configuration. 
     
     
         11 . The crossbow of  claim 9  wherein a separation between the first axis and the second axis in the drawn configuration is about 6 inches to about 8 inches. 
     
     
         12 . The crossbow of  claim 9  comprising:
 a cocking mechanism captured to slide on the center rail, wherein the cocking mechanism slides into engagement with the draw string in the released configuration; 
 a rotating member coupled to a flexible tension member attached to the cocking mechanism; and 
 a cocking handle configured to rotate the rotating member to retract the flexible member, whereby the cocking mechanism slides to a retracted position and moves the draw string to the drawn configuration in response to rotation of the cocking handle. 
 
     
     
         13 . The crossbow of  claim 12  comprising a torque control mechanism with an integral clutch that limits output torque applied to the rotating member by the cocking handle such that rotating the cocking handle after the cocking mechanism is in the retracted position causes the cocking handle to slip to limit torque applied to the cocking mechanism. 
     
     
         14 . A method of operating a crossbow comprising the steps of:
 locating a draw string in first and second draw string journals on first and second cams mounted to first and second flexible limbs by first and second axle mounts, the first and second flexible limbs are attached to a center rail, the first and second draw string journals having first and second planes of rotation that are perpendicular to first and second axes of rotation located fixed distances from the first and second flexible limbs by the first and second axle mounts, respectively, and first and second upper and lower helical power cable take-up journal on opposite sides of the first and second draw string journals comprising paths that are not co-planar with the first and second planes of rotation;   translating the draw string from the released configuration to a drawn configuration so the draw string unwinds from the draw string journals as the first and second cams rotate around the first and second axes;   wrapping first and second pairs of power cables onto the first and second upper and lower helical power cable take-up journals and moving the first and second axes continuously toward the center rail as the draw string translates from the released configuration to the drawn configuration, the first and second pairs of power cables having first ends attached to the first and second cams and second ends attached to static attachment points on the crossbow;   displacing the first and second pairs of power cables along the first and second axes relative the first and second planes of rotation as the bow string is translated from the released configuration to the drawn configuration; and   unwrapping the first and second pairs of power cables from first and second upper and lower helical power cable take-up journals as the draw string translates from the drawn configuration to the released configuration.   
     
     
         15 . The method of  claim 14  comprising rotating a cocking handle operatively coupled to a cocking mechanism to retract the draw string to the drawn configuration. 
     
     
         16 . The method of  claim 15  comprising activating a torque control mechanism in the cocking handle to limit torque applied to the cocking mechanism.