Patent Publication Number: US-9427878-B2

Title: Spring assisted knife

Description:
The present application relates to folding knives. Specifically, the application relates to providing a spring to assist the blade of a folding knife to open and close. 
     Spring assisted folding knives are known in the art. Typically, a folding knife comprises a handle with a hollow section between two side walls of a handle. An pin, or axle, is provided at the distal end of the handle, about which a blade is configured to pivotingly rotate. The blade has a closed condition in which the blade is rotated about the pin to reside between the two side walls of the handle. In this condition the knife is safe to handle and to store. The blade has an open condition, in which the blade is rotated about the pin to extend distally away from the handle. In this condition, the knife is ready for use, which may include cutting, piercing, slicing etc. In some knives, a spring is included to provide a biasing force for urging the blade open when the blade is in a closed condition, and for urging the blade closed when the blade is not in a closed condition. In some knives, a spring may take the form of a leaf spring, in which a cantilevered tip of the leaf spring biases a cam shaped surface on the blade, thereby providing a bias to prevent the blade from opening when it is closed, and to prevent the blade from closing when it is open. In other knives, a spring may take the form of a helical spring, and may be positioned to the side of the blade within the handle of the knife. However, these knives known in the art are beset by problems. Leaf springs are limited in that they cannot be configured to bias a closed blade into an open condition. Helical springs positioned to the side of the blade within the handle are prone to collect dirt that is inaccessible to the user, and which is therefore difficult to clean out. As such, the dirt may eventually prevent the spring from operating correctly. 
     Thus, there is a need in the art for a folding knife with a spring that assists opening and closing of the blade, while addressing the described problems in the art. The present invention addresses these and other needs. 
     SUMMARY OF THE INVENTION 
     In a preferred embodiment, the invention is a folding knife comprising a handle which includes a left cover and a right cover that are separated from each other by a space and that are connected to each other by at least one pin. A blade is provided, configured to rotate around an axle extending between the left cover and the right cover, the blade defining a means for attachment spaced apart from the axle by an offset distance. A helical torsion spring having an elongate axis is provided. The spring surrounds the pin, the spring having a first end that is fixed to the handle and a second end that is free to move in relation to the handle. A connecting element is provided that connects the free end of the spring to the means for attachment on the blade. In some embodiments, the means for attachment is a protrusion. In some embodiments, the connecting element defines a distal slot sized to receive the protrusion, and a proximal slot sized to receive the second end of the spring. Preferably, the helical torsion spring&#39;s elongate axis and the pin are aligned parallel with the axle. 
     In other embodiments, the invention is a folding knife comprising a handle which includes a left cover and a right cover which are separated from each other by a space. A blade is provided, configured to rotate in a plane about an axle, the blade defining a means for attachment spaced apart from the axle by an offset distance. A helical torsion spring is provided, with an elongate axis located in the space between the left cover and the right cover, the spring being positioned with the elongate axis perpendicular to the plane, the spring having a first end that is fixed in relation to the handle and a second end that is free to move in relation to the handle. An elongate connecting element is provided that connects the free end of the spring to the means for attachment on the blade. In some embodiments, the means for attachment is a protrusion. In some embodiments, the connecting element defines a distal slot sized to receive the protrusion, and a proximal slot sized to receive the second end of the spring. 
     In yet other embodiments, the invention is a folding knife comprising a handle which includes a left cover and a right cover that are separated from each other by a space and that are connected to each other by at least one pin. A blade is provided, configured to rotate around an axle extending between the left cover and the right cover, the blade defining a means for attachment spaced apart from the axle by an offset distance. A spring is provided, having a first end fixed to the handle and a second end that is free to move in relation to the handle. An elongate connecting element is provided having an elongate axis, the connecting element connecting the free end of the spring to the means for attachment on the blade, wherein the elongate axis extends above a central axis of the axle when the blade is in an open condition, and wherein the elongate axis extends below the central axis of the axle when the blade is in a closed condition. In some embodiments, the spring is a torsion spring positioned with an axis that is parallel with the central axis of the axle. In some embodiments, the spring is positioned to surround one of the at least one pin. In some embodiments, the means for attachment is a protrusion from the blade. Preferably, the connecting element defines a distal slot sized to receive the protrusion, and a proximal slot sized to receive the second end of the spring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevational view of a folding knife having features of the invention, shown in an open condition. 
         FIG. 2  is a side elevational view of the folding knife shown in  FIG. 1 , with a front side cover removed to show features of the invention, and shown in an open condition. 
         FIG. 3  is a top view of the folding knife seen in  FIG. 2 , with a front side cover removed to show features of the invention. 
         FIG. 4  is a side elevational view showing a detail of  FIG. 2 . 
         FIG. 5  is a side elevational view showing a detail of  FIG. 2 . 
         FIG. 6  is a view of the folding knife seen in  FIG. 2 , in partially exploded configuration to show features of the invention. 
         FIG. 7  is a side elevational view of the folding knife of  FIG. 2 , shown in a closed condition. 
         FIG. 8  is a sectional view of the folding knife in the condition shown in  FIG. 7 , taken substantially along the line A-A in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF SOME OF THE EMBODIMENTS 
     With reference to the figures, a spring assisted knife is described having features of the invention. An embodiment of the invention is shown in  FIG. 1 , which discloses a folding knife  10  having a handle  12  and a blade  14 . In some embodiments, the handle  12  may include a right cover  16  and a left cover  18 , which are removably attached by screws  26  to the handle. In some embodiments, a right liner  20  and a left liner  22  are included in the handle, and may be made of metal or other hard compound. Between the liners is situated an elongate space  28  ( FIG. 3 ) which is sized to receive the blade  14  when the blade is in a closed condition. 
     The blade  14  is configured to pivot about an axle  24  that is captured by opposing liners  20 ,  22  in the handle. The blade may rotate between an open condition (shown in  FIGS. 1-2 ) in which the blade extends distally for use, and a closed condition (shown in  FIG. 7 ), in which the blade  14  resides in the space  28  for storage and safety. The end of the blade that surrounds the axle  24  includes a tang  38 , which is effectively a continuation of the blade around the perimeter of a hole cut in the blade to receive the axle  24 . Onto the tang  38 , a protrusion  40  is attached. In some embodiments, the protrusion is attached in the form of a squeeze rivet. It will be appreciated that the protrusion  40  is offset from the center of the axle  24  by an offset distance “L” as identified in  FIG. 4 . 
     The two liners  20 ,  22  may be held in alignment with each other by a first pin  30  and a second pin  32  ( FIG. 6 ), and additional pins if needed. The liner may be made of metal or other suitable hard material. The pins may be tightened in position by the screws  26 . 
     A helical torsion spring  34  is positioned to enclose the first pin  30 , as may best be seen in  FIG. 3 . The helical spring has an elongate free end  42  which extends downwardly. The spring also has a fixed end  44  which is held stationary by being inserted into a small hole in the right liner  20 . In this position, the spring is easily accessible to the user, who may consequently ensure that no dirt or grit is entering the spring and interfering with its operation. 
     The left liner  22  may be configured to define an elongate opening  36 . A small channel  50  (seen in  FIG. 8 ) may be cut or otherwise formed in the left cover  18  that follows the same perimeter as the opening  36 . 
     Turning to  FIG. 2 , an elongate connector element  46  is provided. The connector element defines an elongate distal slot  48 , and an elongate proximal slot  49 . The distal slot  48  is configured to receive the protrusion  40  on the tang  38  (detail view in  FIG. 4 ) and the proximal slot  49  is configured to receive the free end  42  of the spring  34  (detail view in  FIG. 5 ). Thus, the connector element connects the blade  14  with the spring  34 . In the open condition, as seen in  FIGS. 2, 4, and 5 , the free end  42  of the spring urges the connector element  46  proximally, and hence urges the protrusion  40  proximally. This bias tends to urge the blade to the open condition. (However, the blade may be held in a locked open condition by a liner lock  52  of a kind that is known in the art.) 
     It will be appreciated by those of ordinary skill in the art that, as the blade  14  rotates about the axle  24 , the protrusion  40  rotates about the axle  24  with enhanced offset “L” as identified in  FIG. 4 . Thus, if the blade is moved from the open condition towards a closed condition ( FIG. 7 ), the protrusion  40  will initially move in a substantially distal direction, away from the spring  34 . It will be appreciated that, consequently, the spring will tend to resist the rotation of the blade from an open towards a closed condition during the initial closing movement of the blade. However, once the blade has rotated beyond a critical point (shown as point “P” in  FIG. 4 ), it will not be necessary to apply a manual force to rotate the blade towards the closed condition by hand, and the spring will take over and will on its own cause the protrusion to move proximally by a small amount, and hence will cause the blade to move towards the final closed position ( FIG. 7 ) without manual assistance. Conversely, once the blade is closed ( FIG. 7 ), a user may apply a manual force to rotate the blade towards the open position. It will be appreciated with reference to  FIG. 7  that the user need only rotate the blade by a few degrees against the bias applied by the torsion spring towards the open position ( FIG. 2 ), before the protrusion reaches the critical point “P”, whereupon the force applied by the spring will tend to snap the blade to the open condition without any further force applied by hand. The critical point, as indicated as point “P” on  FIG. 4 , is in effect a point which lies on an intersection between the circumference of the axle  24  and a line extending from the second end  42  of the spring through the centerline B-B (see  FIG. 8 ) of the axle. 
     In order for the blade  14 , in combination with the protrusion  40  and the connector element  46 , to move beyond the critical point described above, the connector element  46  must be able to slide alongside and past the axle  24 , as shown by comparing  FIG. 2  with  FIG. 7 —and as also shown in  FIG. 8 , which is a sectional view taken through  FIG. 7 . Specifically, with reference to  FIG. 2  showing the blade in an open condition, it may be seen that the elongate axis C-C of the connector element  46  is positioned so that when extended, it lies above the central axis of the axle  24  of the knife; whereas, with reference to  FIG. 7  showing the blade in a closed condition, it may be seen that the elongate axis C-C of the connector element  46  is positioned so that it lies below the central axis of the axle  24  of the knife. 
     Stated another way, the connector element  46  must be configured in relation to the other elements of the knife so that the connector element  46  is movable to cross over the center line B-B of the axle  24  when it moves from an open condition to a closed condition. This feature provides the knife with the advantage of a system in which the connector element  46  urges the blade towards a closed condition when the blade is closed, and towards an open condition when the blade is open. 
     Thus, the present invention discloses new and useful features of a spring assisted knife that overcome problems in the prior art. 
     Although preferred illustrative variations of the present invention are described above, it will be apparent to those skilled in the art that various changes and modifications may be made thereto without departing from the invention. It is intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the invention.