Abstract:
A pile driver with an air pressure buffer comprises a pile following moving part, a rebound part, and an air pressure buffer. The pile following moving part comprises a pile cap ( 2 ) contacting the pile ( 1 ) and a piston lever ( 7 ), and the rebound part is the other part except the moving part. An air pressure buffer provided between the moving part and the rebound part is composed of a buffer piston ( 3 ), a buffer cylinder ( 4 ) and a vessel ( 5 ). The buffer cylinder ( 4 ) and the vessel ( 5 ) are intercommunicated with each other. Compressed gas ( 8 ) is filled in the vessel ( 5 ). The buffer piston ( 3 ) can slide in the buffer cylinder ( 4 ). The pile driver can save energy and accelerate the frequency of driving pile.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a liquid propellant pile driver&#39;s design and improves the piling principle and the structure of the pile driver buffer. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    The present invention is the improvement of the original invention “Liquid Propellant Pile Driver” (Application No.: CN87108193.8; Pub. No.: CN1033532). The original invention introduced a new kind of pile driver that uses liquid propellants as its piling energy. The liquid propellants combust in the combustion chamber and produce forces to push the pile into the ground through a piston lever and generate the first piling. A liquid buffer is used for absorbing the falling energy of the rebound part and producing piling force and forming the second piling. However, the inadequacy is that: a great quantity of heat is produced and the energy is wasted. 
       SUMMARY OF THE INVENTION 
       [0003]    The purpose of this invention is to overcome the inadequacy of the original invention “Liquid Propellant Pile Driver” and avoids producing the heat and wasting the energy when the liquid buffer absorbs the fall energy of the rebound part. 
         [0004]    The present invention uses air pressure buffer to replace the original liquid buffer. The piling principle is changed from almost fully plastic impact piling mode to more like a perfectly elastic impact piling mode. Accordingly, the liquid propellant pile drive with the air pressure buffer consumes less energy and has faster piling frequency. 
         [0005]    The structure of the air pressure buffer is that: at the lower portion of the pile driver, there is a buffer cylinder in which a buffer piston can move up and down; the buffer piston, buffer cylinder and a vessel which connected to the buffer cylinder form a sealed space; The space contains compressed gases or a gasbag that contains compressed gases; The buffer piston can be pressed down and forms a compressed gas spring. 
         [0006]    When the rebound part of the pile driver falls down, it compresses the compressed gas spring. During the compressed gas spring being compressed, the energy of motion is used up and the rigid impact is avoided. Because the force of the compressed gas spring is far greater than the weight of the rebound part of the pile driver, when the compressed gas spring rebounds, it pushes the rebound part up and transfers the compressed spring potential energy to the rebound part again in order to reserve the energy for next piling. Because the acting force equals to the reacting force but acting on opposite directions, the compressed gas spring produces the press force on the pile and pushes the pile into ground while the compressed gas spring is compressed and rebounding. Because it is more like a perfectly elastic impact during the compressed gas spring being compressed, the energy lost is less, and less heat is produced. The energy consume of piling is reduced. Another advantage is realizing multi hits by one ignition. 
         [0007]    The buffering force of the compressed gas spring can be adjusted. Method one is adjusting the pre-loaded pressure of the gases in the buffer by pumping in or out the gases. 
         [0008]    Method two is adjusting the pre-loaded pressure of the gases in the buffer by pumping in or out the liquid. The liquid in the buffer also plays the roles of sealing and lubricating. 
     
    
     
       DETAILED DESCRIPTION OF THE INVENTION 
       Brief Description of the Drawing 
         [0009]      FIG. 1  is the overall drawing of the liquid propellant pile driver and the pile, used to indicate the location of the pile driver buffer. 
           [0010]      FIG. 2  is the section view of the buffer and related parts in an embodiment. 
           [0011]    In the drawing:  1 . pile,  2 . pile cap,  3 . buffer piston,  4 . buffer cylinder,  5 . vessel,  6 . liquid,  7 . piston lever,  8 . compressed gas,  9 . anti-collision opening cylinder. 
       
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT 
       [0012]    The piston lever  7 , the pile cap  2  and the pile  1  in the low part of the liquid propellant pile driver are connected together and are supported by the soil underneath. The rest parts of the pile driver belong to the rebound part. 
         [0013]      FIG. 2  shows the various parts of the buffer at the stationary equilibrium position. The compressed gas  8  in the vessel  5  push the buffer piston  3  to the low dead end. The weight of the rebound part passes to the pile cap  2  and the pile  1  through the surface of the anti-collision opening cylinder  9  in the buffer piston  3 . 
         [0014]    The first piling is done by the same methods as original design. The liquid propellants combust in the combustion chamber and produce forces. The forces push the pile  1  into the ground through the piston lever  7  and push the rebound part moving upward. 
         [0015]    The second piling is done by this invention however: When the rebound part fall down from a height, the buffer piston  3  contacts the boss of the pile cap  2 , and its moving speed is as the same speed as the pile cap  2  quickly. Because the rebound part&#39;s speed is faster than the speed of the pile cap  2  and pile  1 , the buffer piston  3  separates oneself from the surface of the low dead end and starts sliding in the buffer cylinder  4 , that compresses the compressed gas  8  further. The forces generated by the compressed gas  8  push down the pile  1  into ground and push up the rebound part and reduce its falling speed in order to avoid the rigid collision. The falling down kinetic energy of the rebound part is transformed into potential energy of the compressed gas spring. When the speed of the rebound part is equal to the speed of the pile  1 , the compressing distance of the buffer piston  3  in the buffer cylinder  4  reaches the maximum. Then the compressed gas spring starts extending, pushes the rebound part moving upward and pushes the pile  1  into ground through the buffer piston  3 , the pile cap  2 , and the pile  1 . When the compressed gas spring extends completely, the buffer piston  3  moves to the low dead end and stops. The rebound part continues moving upward under the effect of inertia. The buffer piston  3  and the boss on the top of the pile cap  2  disengage. The piling force produced by gas pressure disappears. The second piling is finished. 
         [0016]    The advantages of using air pressure buffer are less energy consume and less heat generation in the buffer. Because the heat dissipation of the gas spring is very small in the fast compression and rebound, it is a good elastomer with high rebound ratio. It converts the falling down kinetic energy of the rebound part of the pile driver partially into useful work for sinking the pile and a part of the kinetic energy is returned to and raises the rebound part and can be used again in the next hit. The energy consumes in the heat is very small. The original hydraulic buffer converts the kinetic energy into thermal energy, and absorbs the kinetic energy of the rebound part without rebound. When the piling resistance is growing larger and larger, the energy consumes in the hydraulic buffer becomes more and more. So that liquid temperature in the liquid buffer rises too high and too fast to work properly. Because this elastic buffering method is used, the fuel consumed in the piling process reduces greatly. The maximum amount of the fuel injected is only one third of the original design. Not only the combustion chamber pressure is reduced, but also the heat generation in the combustion chamber is reduced. The piling force lasts longer. Because this elastic buffering method will produce pressure to the pile during compressing and extending, the piling time is as twice as longer than that of hydraulic buffer. The impulse has doubled so that the pile&#39;s penetration has more than doubled. The piling force on the pile is also more stable. The piling force is relatively even. The piling force only relates to the volume and pressure of the compressed gas  8  in the vessel  5  and the compressed distance of travel of the buffer piston  3 , but does not directly relate to the geological conditions, the weight, elasticity and the depth of the pile. The gas pressure can be adjusted according to piling requirements for piling in the best state, increasing piling speed and ensuring piling quality. Adversely, the hydraulic buffer&#39;s piling force is great influenced by the piling condition and geological conditions and more difficult to adjust. 
         [0017]    The piling frequency is higher because the rebound part rebounds immediately after hit the pile without dwell time, and the rebound part bounces up and down freely under the gravity. Adversely, the original design needs a dwell and stilling time after the rebound part falling down for liquid propellants being injected and ignited. It takes longer time and realizes twice pilings by one ignition only. The present design using the air pressure buffer instead of the original hydraulic buffer can achieve multi pilings by one ignition. When the piling resistance is big, the energy consumed in the pile is small. Most of the kinetic energy of the rebound part is rebounded. If the fuels are injected and ignited each time, the rebound part of the pile driver will jump higher and higher and finally exceed the permitted range. At this situation, the liquid propellant injections and ignitions will be stopped until the rebound height is reduced to the allowed range step by step. That is an example of multi pilings by one ignition. It is helpful to save fuel, to improve the cooling and lubrication of the combustion chamber, to reduce the exhaust noise and increase the life time of the components. The air pressure buffer can provides much larger piling forces than conventional spring without fatigue failure. 
         [0018]    The function of the anti-collision opening cylinder  9  in the low part of the buffer piston  3  is to avoid the rigid collision between the buffer piston  3  and the boss of the pile cap  2 . The gases in the anti-collision opening cylinder  9  act as an air cushion. The gases in the anti-collision opening cylinder  9  are compressed before the buffer piston  3  contacts the boss of the pile cap  2 , and produce a sufficient force to push the buffer piston  3  start moving in the buffer cylinder  4 . 
         [0019]    For safety, the present design, the air pressure buffer can remain keep part of functions of the hydraulic buffer. When the air pressure buffer can not absorb the full energy generated by the rebound part, the hydraulic buffer begins to function to absorb excessive amount energy of the rebound part, avoid damages and maintain normal operation. 
       THE SUITABILITY FOR INDUSTRY APPLICATION 
       [0020]    The present invention provides a air pressure buffer for replacing the liquid buffer on the liquid propellant pile driver. In the piling principle, the piling mode is more like a perfectly elastic impact rather than a fully plastic impact, in order to save energy and acquire faster piling frequency. The present invention is suitable for industry application.