1. Field of the Invention
Applicant's invention relates to suspension systems and, more specifically, to a novel front wheel suspension fork for motorcycles or bicycles.
2. Background Information
Presently, motorcycle suspensions are of two general types called the conventional type or the inverted type. Conventional type suspensions consist of a damping mechanism--for example, a combination spring, rod, and hydraulic assembly--encased in two hollow cylinders that telescope into each other. The two hollow cylinders are of different diameters so that one cylinder telescopes snugly into the other. The primary damping mechanism--the receiving tube and valving assembly--is placed in the cylinder with the larger diameter and is located at the bottom of the suspension so that shocks transferred from the wheel to the suspension can be immediately damped before traveling to the hands of the rider. Any remaining compression force not absorbed by the damping mechanism are transmitted through the rod to the hands of the rider. In actual practice, conventional suspensions are suited for absorbing small bumps and tend to bottom out on large bumps. Furthermore, these conventional suspensions tend to deform under large stresses, causing the entire suspension to flex, thus decreasing its efficiency to absorb shocks. Inverted suspensions also consist of a damping mechanism encased into two hollow cylinders. As with conventional suspensions, the primary damping mechanism is located in the lower cylinder. However, unlike the conventional suspension, this lower cylinder is the cylinder with the smaller diameter. In fact, an observer can easily distinguish a conventional suspension from an inverted suspension because, in a conventional suspension, the cylinder having the larger diameter is attached to the wheel axis while in an inverted suspension, the cylinder having the smaller diameter is attached to the wheel axis. This configuration-one with the cylinder having a smaller diameter at the bottom and the cylinder having a larger diameter at the top causes the suspension to be rigid and stiff due to the increased length and increased stiffness of the upper cylinder. This increased rigidity solves the deformation problem encountered in conventional forks. In practice, the inverted suspension design is not ideal because it can only damp out large bumps while allowing smaller vibrations to travel from the wheel to the rider's hands, making the ride uncomfortable.
The damping mechanism in today's shock absorbers comprises a rod and a receiving tube--i.e., one telescoping part--along with two hydraulic valving assemblies. One hydraulic valving assembly--the upper hydraulic valving assembly--is located on the portion of the rod permanently located inside the receiving tube. The other hydraulic valving assembly--the lower hydraulic valving assembly--is located near the bottom and inside of the receiving tube. Small orifices are located near the bottom of the receiving tube, just below the lower hydraulic valving assembly.
The entire damping mechanism, along with a coil spring encircled around the damping mechanism, is attached to and placed inside of the hollow cylinders and partially immersed with hydraulic fluid. The coil spring is also attached to the hollow cylinders. Through the small orifices, the hydraulic fluid seeps into the receiving tube, completely filling the inner cavity of the receiving tube.
When a compression force is applied to the damping mechanism, the receiving tube is forced into the rod; the mass of the rod displaces the hydraulic fluid from the inner cavity of the receiving tube; and the hydraulic fluid flows past both the upper and the lower hydraulic valving assemblies, with the portion flowing past the lower hydraulic valving assembly being expelled out of the receiving tube through the orifices at the bottom of the receiving tube. Both the top and the bottom hydraulic valving assemblies control the speed by which the hydraulic fluid pass through them, thereby controlling the damping rate.
As the external force pushes the receiving tube into the rod, the coil spring is also compressed. When the external force can push the receiving tube into the rod no further, the spring coil returns the rod and receiving tube back to their rest positions. As the rod exits the receiving tube, hydraulic fluid can either pass though the upper hydraulic valving assembly or can enter through the orifices and pass through the lower hydraulic valving assembly and refill the inner cavity of the receiving tube. The suspension is now ready to damp another road bump.
While the above described damping mechanism--i.e. one with a single telescoping part--works well against an individual compression force, it gradually loses its effect when damping compression forces of different magnitudes occurring in quick succession of each other. Because the spring may not have time to return the receiving tube to its rest position before another compression force pushes the receiving tube further into the rod, the above described damping mechanism tends to lose its effect and may even bottom out when damping rapidly successive compressions. This problem becomes especially pronounced when the mechanism must damp out both small and large compression forces in quick succession of each other.
Some motorcycle riders ride their motorcycles strictly on well paved roads where bumps are typically small and separated by lengthy stretches of road, and thus the suspension systems presently available readily satisfy their needs. However, other riders--especially dirt bike riders--tend to encounter both large and small bumps in rapid succession of each other. With today's shock absorbers, which are specifically designed to absorb either large bumps or small bumps but not both, dirt bike riders must choose to either endure small vibrations throughout the entire ride or risk bottoming out the motorcycle suspension when going over large bumps. Furthermore, today's shock absorbers work poorly when damping bumps that occur in quick succession of each other. Inventors have tried to solve the above problem without success.
U.S. Pat. No. 2,475,774 to Benson discloses an inverted suspension that uses both a light spring and a heavy spring to absorb shocks. The light spring is attached to the heavy spring and together they form the primary damping mechanism of this invention. The light spring is to be used to damp small shocks, while the heavy spring is to be used to damp large shocks. However, only one telescoping rod and one receiving tube--i.e. one telescoping part--is used for this invention. Thus, although this invention may be able to absorb both large and small shocks, it is not effective when such shocks come in quick succession of each other.
U.S. Pat. No. 4,511,156 to Offenstadt discloses of a motorcycle suspension system having an anti-skid breaking mechanism. Because this invention uses a shock absorbing mechanism having only one telescoping part, it cannot adequately absorb shocks that arrive in quick succession of each other or damp out both small and large shocks.
U.S. Pat. No. 4,561,669 to Simons discloses another inverted suspension. This invention provides a lightweight, highly rigid fork with low friction, high quality damping characteristics and no axle overhang. One spring is found throughout the entire inner length of the suspension. However, since damping is still achieved with one telescoping part, this invention cannot adequately absorb both large and small shocks, whether or not they appear in quick succession of each other.
U.S. Pat. No. 5,209,138 to Shu discloses a handlebar assembly for bicycles. This invention prevents the rod from rotating relative to the shank, thereby allowing only up and down motion and preventing any twisting motion. Again, this invention has only one telescoping part and therefore is not able to absorb shocks that come in quick succession of each other.
U.S. Pat. No. 5,398,954 to Chonan discloses a wheel suspension type front fork and a method of manufacturing the same. The advantage of this invention over the prior art is that this invention can be manufactured without a metal mold and cutting work. This invention does not provide a method for absorbing both large and small shocks.
U.S. Pat. No. 5,427,397 is again issued to Chonan. This patent discloses a wheel suspension type front fork that eliminates the need of a rebound absorption mechanism by securing the upper end of the spring coil to the lower end of the receiving tube and the lower end of the spring coil to the upper end of the sliding tube (the tube enclosing the spring), thereby preventing the receiving tube, the spring coil, and the sliding tube from springing apart from the rebounding force of the compressed spring coil. This invention uses conventional shock absorbers having only one telescoping part and therefore is not designed to absorb both large and small shocks.
U.S. Pat. No. 5,478,099 issued to Kawahara discloses a bicycle wheel fork assembly that telescopes from one side only. The advantage of this invention over other front fork assemblies is that the stiffness of the shocks in both the contraction and the expansion parts of the shock absorption cycle can be adjusted by placing a contraction adjuster on one fork, an expansion adjuster on the other fork, and a cross member that connecting the two forks. Although this invention allows the stiffness of the shocks to be adjusted and thus allows better shock absorption, it does not allow both large and small shocks to be absorbed at the same time. Furthermore, since this invention uses a damping mechanism that telescopes from one side only, it also cannot satisfactorily absorb shocks that come in quick succession of each other. Thus, this invention does not provide an adequate solution to the present problem.