Bowstring cam arrangement for compound long bow or crossbow
A compound bow or crossbow employs bowstring cams with bowstring cam grooves and power cord cam grooves. Preferably a pair of generally identical power cord cam grooves are positioned axially above and below the bowstring cam groove. The power cords are anchored to a fixed anchor point, e.g., a pylon, on the near end of the riser or on the near side of the crossbow bar or stock. The power cords do not cross over to the other limb. The reduction in the number of cam wheels and pulleys and in the number of strings or cords results in greater efficiency and higher transfer of energy from the bow to the arrow or bolt. There is no drop-off in pull weight at full draw. The bolt or arrow accelerates throughout the travel of the bowstring, resulting in significantly higher velocity.
1. A pulley system for a bow having a riser with at least one limb attached at one end on each side of a medial plane of the riser, the pulley system comprising:
at least one cam pivotally mounted to a free end of each of the limbs on each side of the medial plane of the riser, each of the cams comprising a bowstring cam groove and upper and lower power cord cams located above and below the bowstring cam groove;
a bow string wound on the bowstring cam grooves and travels in the respective bowstring cam grooves to be wound and unwound therefrom; and
upper and lower power cords having distal ends attached to fixed anchor points on the bow on opposite sides of the medial plane and wound on upper and lower power cord cam grooves of the upper and lower power cord cams, respectively, such that the upper and lower power cords do not extend across the medial plane to the riser,
wherein the power cord cam grooves and the bowstring cam grooves are programmed such that the draw weight on the bow string increases from full brace position to full draw position without weight drop-off.
2. The pulley system of claim 1 wherein the upper and lower power cord cam grooves are configured to retain the upper and lower power cords out of a bowstring plane extending through the bowstring cam groove.
3. The pulley system of claim 1 wherein the upper and lower power cord cam grooves are configured to direct the upper and lower power cords away from a bowstring plane extending through the bowstring cam groove.
4. The pulley system of claim 1 wherein proximal ends of the upper and lower cords are attached to the upper and lower power cord cams, respectively.
5. The energy storage system of claim 1 wherein each of the limbs comprise first and second limbs arranged in a spaced apart configuration with the cams located between the pair of limbs, respectively.
6. The pulley system of claim 1 wherein the cams are not coupled by synchronizing cords or strings.
7. An energy storage system for a bow comprising:
a riser having a medial plane;
at least one limb attached to the riser on each side of the medial plane;
a cam pivotally mounted to a free end of each of the limbs on each side of a medial plane of the riser, each of the cams comprising a bowstring cam groove and upper and lower power cord cams located above and below the bowstring cam groove of the cam;
a bow string wound on the bowstring cam grooves and travels in the respective bowstring cam grooves to be wound and unwound therefrom; and
upper and lower power cords having distal ends attached to fixed anchor points on the bow on opposite sides of the medial plane and wound on upper and lower power cord cam grooves of the upper and lower power cord cams, respectively, such that the power cords do not extend across the medial plane of the riser, wherein the power cord cam grooves and the bowstring cam grooves are programmed such that the draw weight on the bow string increases from full brace position to full draw position without weight drop-off.
8. The energy storage system of claim 7 wherein the upper and lower power cord cam grooves are configured to direct the upper and lower power cords away from a bowstring plane extending through the bowstring cam grooves.
9. The energy storage system of claim 7 wherein the upper and lower power cords minimize torsional deformation of the pairs of bow limbs as the bow string moves from a full brace position to a full draw position.
10. The energy storage system of claim 7 wherein each of the limbs comprise first and second limbs arranged in a spaced apart configuration with the cams located between the pair of limbs, respectively.
11. The energy storage system of claim 7 wherein the cams are not coupled by synchronizing cords or strings.
12. A method of configuring an energy storage portion for a bow comprising the steps of:
coupling at least one limb on each side of a medial plane of a riser;
attaching at least one cam to each of the limbs, each of the cams comprising a bowstring cam groove and upper and lower power cord cams located above and below the bowstring cam groove of the cam;
attaching distal ends of upper and lower power cords to fixed anchor points on the bow on opposite sides of the medial plane, so the upper and lower power cords are wound on upper and lower power cord cam grooves of the upper and lower power cord cams, respectively, such that the power cords do not extend across the medial plane of the riser; and
attaching a bowstring to the bowstring cam grooves in the cams to be wound and unwound in the respective bowstring cam grooves, wherein the power cord cam grooves and the bowstring cam grooves are programmed such that the draw weight on the bow string increases from full brace position to full draw position without weight drop-off.
13. The method of claim 12 comprising the upper and lower power cord cam grooves directing the upper and lower power cords away from a bowstring plane extending through the bowstring cam groove.
14. The method of claim 12 comprising the upper and lower power cords minimizing torsional deformation of the pairs of bow limbs as the bow string moves from a full brace position to a full draw position.
15. The method of claim 12 comprising configuring each of the limbs as first and second limbs arranged in a spaced apart configuration with the cams located between the pair of limbs, respectively.
16. The method of claim 12 wherein the cams are not coupled by synchronizing cords or strings.
17. A bow comprising:
a riser with at least one limb attached at one end on each side of a medial plane of the rise;
at least one cam pivotally mounted to a free end of each of the limbs on each side of the medial plane of the riser, each of the cams comprising a bowstring cam groove and upper and lower power cord cams located above and below the bowstring cam groove;
a bow string wound on the bowstring cam grooves and travels in the respective bowstring cam grooves to be wound and unwound therefrom; and
upper and lower power cords having distal ends attached to fixed anchor points on the bow on opposite sides of the medial plane and wound on upper and lower power cord cam grooves of the upper and lower power cord cams, respectively, such that the upper and lower power cords do not extend across the medial plane to the riser,
wherein the power cord cam grooves and the bowstring cam grooves are programmed such that the draw weight on the bow string increases continuously to full draw.
18. The bow of claim 17 wherein the upper and lower power cord cam grooves are configured to retain the upper and lower power cords out of a bowstring plane extending through the bowstring cam groove.
19. The bow of claim 17 wherein the upper and lower power cord cam grooves are configured to direct the upper and lower power cords away from a bowstring plane extending through the bowstring cam groove.
20. The bow of claim 17 wherein proximal ends of the upper and lower cords are attached to the upper and lower power cord cams, respectively.
21. The bow of claim 17 wherein the cams are not coupled by synchronizing cords or strings.
22. The bow of claim 17 wherein the bow is one of a bow or a crossbow.