PATENT ABSTRACT
A front fork of a bicycle, which has damping function, has a lower fork having a closed bottom. An upper fork tube is inserted into the lower fork for reciprocation relative to the lower fork, which has a nozzle at a top thereof. Oil is received in a space between the lower fork and the upper fork tube. An air chamber is formed in a space between a surface of the oil and the nozzle, which a gas is issued therein and a pressure of the gas is greater than an atmospheric pressure, and a damping device, which is mounted at a bottom of the upper fork tube and under the surface of the oil, has multiple, variable oil flow paths through which oil passes as the upper and lower fork member reciprocate to provide various damping characteristics dependent on the relative speed or impact the fork members experience with respect to each other.

PATENT DESCRIPTION
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to a bicycle, and more particularly to a front fork of a bicycle with a suspension and damping apparatus. 
   2. Description of the Related Art 
     FIG. 1  shows a conventional front fork  1  with a hydraulic damping apparatus, which has an upper tube  2 , a bottom fork  3  and a valve  4  mounted at a bottom of the upper tube  2 . The valve  4  has an oil outlet  4   a  at a middle portion thereof, two apertures  4   b  at opposite sides of the oil outlet  4   a  and two plates  5  at a bottom of the valve  4  and below the apertures  4   b  respectively. A needle valve  6  is inserted into the tube  2  from a top thereof. A front end  6   a  of the needle valve  6  is aligned with the oil outlet  4   a  of the valve  4 , and a rear end  6   b  thereof is rotated to adjust a distance between the front end  6   a  and the oil outlet  4   a , such that a velocity of an oil  7  is changed to adjust the resistance. The needle valve  6  takes the impact of the oil  7  flowing upwards via the oil outlet  4   a  directly that would damage the needle valve  6  after a long time of use. In addition, the oil  7  usually has air bubbles therein while it flows in the valve  4 , and the oil  7  has a constant flow rate that the buffer capacity cannot absorb the impact of the front fork  1  gradually. 
   SUMMARY OF THE INVENTION 
   The primary objective of the present invention is to provide a front fork of a bicycle with a damping apparatus, which increases the efficiency of riding. 
   The secondary objective of the present invention is to provide a front fork of a bicycle with a simplified damping and suspension system to minimize the overall fork weight. 
   The third objective of the present invention is to provide a front fork of a bicycle with a multi-function damping system that will a) respond lightly to small bumps and low frequency oscillation; b) respond freely to large bumps and more severe impacts; c) minimize relative suspension motion induced by rider pedaling. 
   The fourth objective of the present invention is to provide a front fork of a bicycle with a variable damping apparatus, which will respond in proportion to the severity of the bumps or impacts. 
   The fifth objective of the present invention is to provide a front fork of a bicycle with a buffer apparatus, which works so as to decrease bubbles derived, and reduce noise caused by oil flowing through the restriction. 
   According to the objectives of the present invention, a front fork comprises a lower fork having a closed bottom. An upper fork tube is inserted into the lower fork for reciprocation relative to the lower fork, which has a nozzle at a top thereof. Oil is received in a space between the lower fork and the upper fork tube. A gas or air chamber is formed in a space between a surface of the oil and the nozzle, in which a gas is issued therein where pressure of the gas is greater than atmospheric pressure, and a damping device is mounted at a bottom of the upper fork tube and under the surface of the oil, has multiple oil flow paths for control of oil flowing therethrough. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of a prior art front fork assembly showing the hydraulic damping apparatus; 
       FIG. 2  is a sectional view of a preferred embodiment of the present invention; 
       FIG. 3  is a sectional view of the nozzle of the preferred embodiment of the present invention; 
       FIG. 4  is a sectional view of the damping device of the preferred embodiment of the present invention, showing the spool valve or piston at the lower position; 
       FIG. 5  is an exploded perspective view of the damping device of the preferred embodiment of the present invention, and 
       FIG. 6  is a sectional view similar to  FIG. 4 , showing the spool valve or piston at the upper most position. 
       FIG. 7  is a sectional view of a second preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As shown in  FIG. 2  to  FIG. 4 , a front fork  100  of the preferred embodiment of the present invention mainly comprises a lower fork  10 , an upper fork tube  20 , a seal assembly  30  and a damping device  40 . The front fork  100  is issued with oil  50  therein allowing space for pressurized gas  60 . 
   The lower fork  10  has a closed bottom end  12 . 
   The upper fork tube  20  is inserted into the lower fork  10  to be moved in a linear reciprocating motion with respect to the lower fork  10 . The upper fork tube  20  has a nozzle  22  at a top thereof and a lid  24  to cover the nozzle  22 . The upper fork tube  20  further has an inner threaded section  26  at an interior side thereof. 
   The seal assembly  30  is mounted at a top of the lower fork  10  between an interior side of the lower fork  10  and the exterior side of the upper fork tube  20 . The seal assembly  30  serves functions of preventing the oil  50  from leakage, maintaining a seal to preserve gas pressure  60  and sealing the lower fork  10 . 
   The damping device  40  has a column-like main member  41 , a bottom plate  42 , a ring  43 , a spool valve or piston  44 , an O-ring  45  and an elastic member, which is a spring  46  in the present invention. 
   As shown in  FIG. 5 , the main member  41  has a return hole  411  and a spool cylinder with oil vent  412 . The spool cylinder  412  has a section with a smaller diameter at the top, which is defined as a shoulder portion  412   a . The main member  41  further has two lateral holes  413  communicated with the spool cylinder  412 , an outer threaded section  414  at a bottom thereof to be engaged with the inner threaded section  26  of the upper fork tube  20  and two gaps  415  adjacent to the bottom thereof. 
   The bottom plate  42  has two protrusions  421  to be engaged with the gaps  415  of the main member  41 . The ring  43  is fitted to the plate  42  to secure it to the main member  41 . The plate further has a shaped orifice  422  and an oil inlet  423 , wherein the orifice  422  is communicated with the return hole  411 , and the orifice  422  has an upper section with a smaller diameter and a lower section with a greater diameter, and the oil inlet  423  is communicated with the spool cylinder  412 . 
   The spool valve or piston  44  is open at a top thereof and is closed at the bottom thereof. The O-ring  45  is fitted to the piston adjacent to the bottom thereof. The piston  44  is received in the spool cylinder  412  for movement from a lower position P 2 , as shown in  FIG. 4 , in which the piston  44  seals the lateral holes  413 , toward an upper position P 1 , as shown in  FIG. 6 , in which the piston  44  departs from the lateral holes  413  to allow oil flow from the lower fork  10  to the upper fork tube  20 . 
   The spring  46  is installed in the spool cylinder  412  with opposite ends urging the shoulder portion  412   a  and the piston  44  respectively. The spring  46  urges the piston  44  to the lower position P 2 . 
   The oil  50  has a viscosity, as shown in  FIG. 2 , for which a surface  52  thereof is higher than the damping device  40  for a predetermined distance, and an air chamber  60  is formed between the surface  52  and the nozzle  22 . A high-pressure gas is issued into the air chamber  60  via the nozzle  22  to make the front fork  100  having a pressure in the air chamber  60  greater than that of outside. The pressure in the air chamber  60  can be adjusted to meet a riders&#39; requirements. 
   As the fork compresses, oil flows through the damping devise  40  into the cavity of the upper fork tube  20  reducing the volume available for the pressurize gas  60 . As this gas further compresses, the force acting on the surface of the oil  52  increases exponentially. This rise in pressure also effects the damping characteristic of the spool valve  44  to increase the damping coefficient of the system as the pressure rises. The relative volume allowed for the pressurized gas  60  with respect to the intended fork stroke sets the progressive feel of the fork for the rider. This feel can be easily changed and tailored to a given rider by adding or removing small amounts of oil, and by increasing or decreasing the initial pressure of the gas  60 . 
   As shown in  FIG. 4 , when a smaller impact is exerted on the front fork  100 , some oil  50  will flow through the orifice  422 , which has a smaller flow area, but the spool valve or piston  44  is not moved because of the pressure in the air chamber  60  and the spring  46 . Under this condition, the spool valve or piston  44  seals the lateral holes  413  still, and the lower fork  10  can move only slowly relative to the upper fork tube  20 . As a result, the fork  100  responds with a high damping coefficient to smaller impacts making more of the rider&#39;s exertion delivered to motivating the bicycle, and less of the rider&#39;s exertion absorbed by the hydraulic damping, thus increasing the riders efficiency. 
   As shown in  FIG. 6 , when the front fork  100  of the present invention is exerted by a greater impact, sufficient to overcome the force of the spring  46  and the pressure in the upper fork tube  20 , the lower fork  10  is moved toward the upper fork tube  20 , and the oil  50  flows through the orifice  422  and moves the piston  44  from the lower position P 2  toward the upper position P 1 . In the movement of piston  44  from the lower position P 2  toward the upper position P 1 , the lateral holes  413  are exposed gradually such that the flow rate of the oil  50  flowing through the lateral holes  413  rises gradually and proportionally to the severity of the bump or impact. When the bump or impact is of lower severity but sufficient to overcome the combined effects of the gas  60  pressure and the spring  46 , the spool valve or piston  44  moves only enough to allow a small effective orifice by moving from the lower position P 2  upward toward the upper position P 1  but only enough to slightly open the oil port  413 . The shape of the lateral holes  413  are designed to allow progressively more flow as the spool valve or piston  44  is forced higher and higher due to the severity of the bump or impact encountered. Pressure in the air chamber  60  slows the flow speed of the oil  50  as the compression continues and applies an exponentially increasing force on both the surface of the oil  50  and the back of the spool valve  44  to give the front fork  100  of the present invention a smooth and progressive damping feel. More damping as the compression becomes greater. 
   For rebound, when the lower fork  10  is moved away from the upper fork tube  20 , the piston  44  is moved back to the lower position P 2 , and oil  50  is forced by gas  60  pressure to flow back to a space (not shown) under the damping device  40  in the lower fork  10  via the return hole  422 . Since the volume for gas  60  increases as the fork lower  10  moves away from the upper fork tube  20  and oil is forced out of the upper fork tube  20  through the damper assembly  40 , the pressure of gas  60  decreases. When gas  60  pressure is high, it provides a high force to push oil  50  through the shaped orifice  422  which gives a higher flow rate. As pressure decreases in the upper fork tube  20  at  60 , the flow rate of the oil decreases, thus reducing the rebound velocity of the lower fork  10  with respect to the upper fork tube  20 . This gives the rider a higher rebound rate when the fork is highly compressed, and a lower rebound rate when the fork is near full extension. 
   The front fork  100  of the present invention provides a smooth buffer capacity to absorb impact to provide the rider with a comfortable riding condition. The high-pressure gas issued in the air chamber  60  can reduce the oil  50  from generating bubbles therein. The pressure in the air chamber  60  is adjustable to change the flow speed of the oil  50  to meet all situations. 
   The shaped orifice  422  has a converging/diverging nozzle geometry that accelerates then decelerates the oil as it passes through. This reduces the noise induced by passing oil, and reduces the bubbles retained in the oil. 
   The front fork  100  of the present invention provides a smooth damping function for a variety of impact conditions to provide efficient riding in small bump conditions and a progressive absorption in larger bump or impact conditions. It also allows multiple ways of tuning the fork, increasing or decreasing gas  60  pressure, increasing or decreasing oil  50  quantity, for the individual requirements of each rider. 
     FIG. 7  shows a front fork  200  of the second preferred embodiment of the present invention, similar to the front fork  100  the first preferred embodiment, having a lower fork  201 , an upper fork tube  202 , an anti-leak assembly  203 , a damping device  204  and oil  205 . The upper fork tube  202  is provided with a lid  206  on a top thereof, and has a chamber  207  between the lid  206  and a level of the oil  205  and a biasing device  208  in the chamber  207 . The biasing device  208  has a float plate  208   a , a ring  208   b  and a pushing device  208   c , which is a spring, wherein the float plate  208   a  floats on the oil level, and the ring  208   b  is fitted to the float plate  208   a  and pressing an interior wall of the upper fork tube  202  to prevent the oil  205  from leakage to the chamber  207 , and the spring  208   c  has opposite ends resting the lid  206  and the float plate  208   a  to slow the speed of oil flow. The front fork  200  of the second preferred embodiment serves the same function. 
   The specification of the present invention only discloses one of the preferred embodiments according to the scope of the present invention. Any equivalent device should be still within the scope of the present invention.