Bicycle with rhomboidal gear

Abstract: A bicycle is disclosed with a rhomboidal (preferably 60 o - 120 o ) drive sprocket gear (10) and a circular driven sprocket on the rear driven wheel (26). This gear arrangement varies the overall power input from the drive sprocket (10) to the driven gear (32). The shape of the drive sprocket (10) and the location of the drive pedal (27) changes the gear ratio so that a low gear ratio is utilized during the horizontal portion of movement of the cyclist's legs and a high gear ratio is utilized during the vertical movement of the legs. The gear ratio with the rhomboidal gear (10) is relatively constant during horizontal movement and abruptly changes at the approach to and during vertical movement of the cyclist's legs. While the rhomboidal gear is shown primarily for bicycles it may be used in other systems for converting reciprocal to rotary movement with a change in gear ratio.

Description: FIELD OF THE INVENTION This invention relates generally to bicycles and drive sprocket gears and more particularly to a bicycle having a drive sprocket gear of a shape providing an abrupt change in gear ratio on change in pedal movement from a horizontal direction to a vertical direction. BRIEF DESCRIPTION OF THE PRIOR ART Bicycles with a pedal driven sprocket gear driving a gear on the rear wheel were developed in the third quarter of the 19th century. In riding a bicycle, as the rider moves the pedals through a complete rotation, there are portions of the cycle of power application which are more effective than others. In particular, when either of the pedals is at the top of its rotation and slightly forward of center, the cyclist can easily apply a strong downward force with considerable effect in the application of torque to the drive sprocket. On the other hand, when the pedal is pointed straight down, there is little or no torque being applied to the sprocket Thus, during vertical movement, force is applied effectively, and during horizontal movement, there is little or no force applied. During the last century, attempts were made to improve the gear relationships by making the drive sprocket gear elliptical in shape. This allegedly gave improved performance during certain portions of the operation of the drive sprocket. The use of elliptical drive procket gears has been suggested from time to time up to the present date. There are several patents which disclose various types of bicycles with elliptical or oblong gears. Metz U.S. Patent 513,589 discloses a bicycle with an elliptical drive sprocket gear. Scovell U.S. Patent 515,449 discloses a bicycle with an oblong drive sprocket gear. Schaum et al U.S. Patent 530,058 discloses a bicycle with an elliptical drive sprocket gear having means to compensate for variations in tension of the drive chain. Delacroix U.S. Patent 885,082 discloses another bicycle with an elliptical drive sprocket gear and means for compensating for slack in the drive chain during operation. Hattan U.S. Patent 3,259,398 discloses another bicycle with elliptical drive sprocket and having a system of idler gears for compensating for slack in the drive chain at different positions of operation. Durham U.S. Patent 3,899,932 discloses another elliptical drive gear with a special gear tooth design for preventing derailing of the drive chain. Neumann DE 3 709 482 discloses a bicycle with a quasi-elliptical sprocket gear and Rocca GB Patent 18,888 discloses a bicycle with a quadrilateral chain wheel. The present invention is distinguished over the prior art in that there is no previous disclose of the use of drive sprocket gears having distinct rectilinear sections connected by circular sections which provide for an abrupt change in gear ratio at desired points in the movement of the sprocket gear. This invention is distinguished from the prior art in providing a bicycle having a rhomboidal drive sprocket gear and a circular driven sprocket on the rear driven wheel. This gear arrangement varies the overall power input from the drive sprocket to the driven gear. The shape of the drive sprocket and the location of the drive pedal changes the gear ratio so that a low gear ratio is utilized during the horizontal portion of movement of the cyclist's legs and a high gear ratio is utilized during the vertical movement of the legs. The gear ratio with the rhomboidal gear is constant during horizontal movement and abruptly changes at the approach to and during vertical movement of the cyclist's legs. While the rhomboidal gear is shown primarily for bicycles it may be used in other systems for converting reciprocal to rotary movement with a change in gear ratio. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a new and improved bicycle with a drive sprocket gear of improved design and construction. It is another object of this invention is to provide a new and improved bicycle with a drive sprocket gear of improved design and construction wherein the gear ratio is changed during rotation of the sprocket. Another object of this invention is to provide a new and improved bicycle with a drive sprocket gear of improved design and construction driving a conventional circular gear on the rear driven wheel. Another object of this invention is to provide a new and improved bicycle with a drive sprocket gear having rectilinear sections connected by circular sections whereby the gear ratio is relatively constant during horizontal movement and abruptly changes at the approach to and during vertical movement of the cyclist's legs. Still another object of this invention is to provide a new and improved bicycle with a drive sprocket gear having rectilinear sections connected by circular sections whereby the gear ratio abruptly changes at the approach to and during vertical movement of the cyclist's legs. Still another object of this invention is to provide a new and improved bicycle with a drive sprocket gear of rhomboidal design and construction. A further object of this invention is to provide a new and improved bicycle with a drive sprocket gear of rhomboidal design and construction driving a conventional circular gear on the rear driven wheel. A further object of this invention is to provide a new and improved bicycle with a rhomboidal drive sprocket gear having rectilinear sections connected by circular sections whereby the gear ratio is relatively constant during horizontal movement and abruptly changes at the approach to and during vertical movement of the cyclist's legs. Other objects of the invention will become apparent from time to time throughout the specification and claims as hereinafter related. The above noted objects and other objects of the invention are accomplished by a novel bicycle having a rhomboidal drive sprocket gear as claimed in Claim 1. This gear arrangement varies the overall power input from the drive sprocket to the driven gear. The shape of the drive sprocket and the location of the drive pedal changes the gear ratio so that a low gear ratio is utilized during the horizontal portion of movement of the cyclist's legs and a high gear ratio is utilized during the vertical movement of the legs. The gear ratio with the rhomboidal gear is relatively constant during horizontal movement and abruptly changes at the approach to and during vertical movement of the cyclist's legs. While the rhomboidal gear is shown primarily for bicycles it may be used in other systems for converting reciprocal to rotary movement with a change in gear ratio. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view of a rhomboidal drive sprocket gear having rectilinear sections connected by curved sections. Fig. 2 is a side elevation of a bicycle having the rhomboidal gear of Fig. 1 driving a circular rear sprocket gear, with the gear and pedals shown at the point of maximum gear ratio as the pedals are moved downward. Fig. 3 in a side elevation of a bicycle having the rhomboidal gear of Fig. 1 driving a circular rear sprocket gear, with the gear and pedals shown at the point of minimum gear ratio as the pedals are moved horizontally. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings by numerals of reference, and more particularly to Fig. 1, there is shown a sprocket gear 10 for a bicycle which has a central opening 11 and a radial slotted opening 12 for connection to an axle, crank arm and pedal. Sprocket gear 10 is rhomboidal in shape, preferably having 60° angles at the acute angled ends and 120° angles at the obtuse angled sides, also called a 60° - 120° rhomboid, of rigid sheet metal or equivalent, e.g., sheet plastic, etc., having flat side portions 13, 14, 15 and 16. Curved portion 17 connects side portions 13 and 14. Curved portion 18 connects side portions 15 and 16. Curved portion 19 connects side portions 13 and 16. Curved portion 20 connects side portions 14 and 15. A plurality of equally spaced teeth 21 extend around the entire periphery of the gear 10. The gear 10 has a major axis extending from the center of the curved portion 17 to the center of the curved portion 18. The gear 10 has a minor axis extending from the center of the curved portion 19 to the center of the curved portion 20. In Figs. 2 and 3, the rhomboidal sprocket gear 10 is shown in use on a bicycle 21 in different stages of operation. The bicycle 21 has the usual frame 22, seat 23 and handle bars 24. Frame 22 is supported on a front wheel 25 and rear wheel 26 for movement along the ground. A pair of pedals 27 and 28 are supported on crank arms 29 and 30 journaled at 31 on frame 22. Rhomboidal sprocket gear 10 is secured to and operated by crank arms 29 and 30 and journaled at 31 for rotation on frame 22. Crank arms 29 and 30 are secured to rhomboidal sprocket gear 10 in slotted opening 12 about 45° ahead of the major axis of the sprocket. The rhomboidal construction of sprocket gear 10 and the location of pedals 27 and 28 and crank arms 29 and 30 relative to the sprocket gear result in the application of force by the cyclist being greatest when the major axis of the sprocket is at the top of its stroke and least when the minor axis is at the top. This has the effect of allowing the cyclist to apply the greatest amount of force at the highest gear ration and the least amount of force at the lowest gear ratio. There are two distinctly different gear ratios, a high gear ratio between the sprocket teeth at the major axis and the rear driven gear, and a low gear ratio between the sprocket teeth at the minor axis and the rear driven gear. The change in gear ratios is abrupt and not a continuous change as in the case on an oblong or elliptical sprocket gear. OPERATION While the operation of this invention should be obvious from the foregoing description, it will be restated for clarity and for a better understanding of the advantages of the rhomboidal sprocket gear. In order to understand the advantages of sprocket gear 10 better, one should consider the way in which an ordinary circular sprocket gear works on a bicycle. The power requirement from a circular sprocket gear remains the same for all quadrants of the circular motion of the driving pedals when maintaining a constant speed on the bicycle. The best source of power comes in the up and down strokes of the cyclist's legs in the same manner as the reciprocal movement of the piston on a motor or engine. The forward and backward movement of the legs is not very productive of power. In the rhomboidal sprocket gear 10 of this invention, there is a marked decrease in the power requirements in the forward and rearward movement of the legs because the diameter of the sprocket becomes smaller as the pedals come circular from the downward movement to horizontal movement. Conversely, there is a marked increase in requirements at the top of the stroke as the pedals come circular from application of horizontal force to application of vertical force, which is at that time in the cycle where the maximum force is available. By placing the pedals 27 and 28 and crank arms 29 and 30 ahead of the major axis (preferably 45° ahead) it becomes possible to shift application of downward force to the point where the maximum moment arm exerts the most circular force, i.e. torque. The location of the pedals 45° ahead of the major axis of the sprocket gear 10 produces a great improvement of power produced by the cyclist, although it is not yet known where the optimum location of the pedals should be. It should also be noted that the velocity of the drive chain varies considerably as it passes over the teeth of the rhomboidal sprocket gear 10. This results in a desired repetitive loading and unloading of the driving force. With this sprocket gear, there is no change in gear ratio when the flat sides of the sprocket are moving the drive chain, while the gear ratio increases abruptly when force is being transmitted from the major axis of the sprocket gear and decreases abruptly when the force is being transmitted from the minor axis of the sprocket gear. For the same number of teeth as a circular sprocket, there is a net result of lower overall power input requirements for the same speed and distance travelled. The rhomboidal sprocket gear 10 operates with the low gear ratio (ratio of minor axis of sprocket gear to rear driven gear) when the legs are moving backward and forward and with the high gear ratio (ratio of major axis or sprocket gear to rear driven gear) when the legs ar moving up and down. The change between the low gear ratio and the high gear ratio is abrupt as distinguished from oblong or elliptical gears where the gear ratios are constantly changing. The teeth on the flat sides of the rhomboidal sprocket gear are not load transmitting teeth and could be eliminated if desired. While this invention has been shown fully and completely with special emphasis on certain preferred embodiments, it should be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein. While the rhomboidal gear is shown primarily for bicycles it may be used in other systems for converting reciprocal to rotary movements with a change in gear ratio and the invention extends thereto.

Claims: A cycle (21) comprising a frame (22), a seat (23) and handlebars (24), a rear wheel (26) supported on said frame (22), a front wheel (25) supported on said frame (22) and controlled by said handlebars (24), a driven gear (32) supported on said frame (22) for rotation with and driving said rear wheel (26), a sprocket gear (10) supported for rotation on said frame (22), crank arms (29, 30) and pedals (27, 28) supported thereby, supported on said frame (22) for rotary motion and secured to said sprocket gear (10) for rotating it by pedal operated motion, a drive chain (33) surrounding and inter-connecting said sprocket gear (10) and said drive gear (32) for transferring motion and force therebetween characterised in that said drive sprocket gear (10) is constructed as a rhomboid gear having four distinct rectilinear sides connected by substantially curved sections, the rhomboidal construction sprocket gear (10) and the location of pedals (27, 28) and crank arms (29, 30) relative to the sprocket gear result in the application of force by the cyclist being greatest when the major axis of the sprocket is substantially vertical. A cycle (21) according to Claim 1 characterized in that said sprocket gear (10) is a 60°-120° rhomboid. A cycle (21) according to Claim 1 or Claim 2 characterized in that said sprocket gear (10) is constructed of rigid sheet material. A cycle (21) according to any of Claims 1-3 characterized in that the sprocket gear (10) is an elongated rhomboidal shape having major and minor axes, and four regions of circular curvature located at the respective ends of each axis, and further comprising anchoring holes (12) for securing pedals (27, 28) thereon said pedals being positioned at an acute angle to and forward of the said major axis. A cycle (21) as claimed in Claim 4 characterized in that the pedals (27, 28) are positioned substantially at 45° ahead of the major axis of the rhomboid. A cycle (21) as claimed in any preceding claim characterized in that the major and minor axes of the rhomboidal sprocket gear (10) intersect at an angle of substantially 90°. A cycle as claimed in any preceding claim characterized in that the rectilinear portions of the sprocket gear (10) are devoid of teeth, the load being transmitted entirely through the teeth on the substantially circular sections of the rhombus. A cycle as claimed in any preceding claim characterized in that the proportions of the rhomboidal sprocket gear (10) are such that there is substantially no slack in said drive chain (33) during rotation of the pedals (27, 28).

Inventors: RUNNELS DAVID J, RUNNELS, DAVID J.
Applicants: RUNNELS DAVID J, RUNNELS, DAVID J.
Application year: 1992
Main classification: B62M9
IPC codes: B62M9, B62M3