PILE DRIVER

Abstract: The present invention provides a pile driver com­ prising a vibration cylinder (3) and a self-equilibration cylinder (7) so provided vertically in series with each other that the axes of their respective rods lie on the center line passing through the center of gravity of an inertial weight (1), the rods of the vibration and self-equilibration cylinders being coupled to each other, the vibration cylinder having provided therein a changeover valve (10) to supply and discharge a pressurized fluid to and from the vibration cylinder, the self-equilibration cylinder having provided therein a control valve (11) responsive to the rod of either the self-equilibration cylinder or vibration cylin­ der to supply and discharge the pressurized fluid to and from a control chamber in the self-equilibration cylinder. The piston of the self-equilibration cylinder is supported with a low rigidity to the inertial weight by means of accumulators (14) provided as communicating with the control chambers in the self-equilibration cylinder, and also the self-equilibration cylinder or vibration cylinder has pro­ vided at the lower end of the rod thereof a chuck (17) which grasps the pile.

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to a pile driver utilizing a vibration cylinder receiving a fluid pressure as energy source to generate a mechanical vibration under which a pile is driven into the ground. Description of the Prior Art: A pile driver according to the preamble of claim 1 using a vibration cylinder has been proposed in the West Germany Patent No. 28 21 339 , in which, as shown in Figure 1, the vibration cylinder itself has a function of self-equilibration and a pile P is coupled with a piston 101 of a vibration cylinder 100 by means of a chuck 102, an inertial weight 103 being coupled with the other end of the vibration cylinder 100 in line with the pile P, whereby a vibratory force of a periodic function is generated between the inertial weight 103 and the pile P which in turn will be driven into a ground E. In the conventional pile driver, however, the vibratory force is damped when the inertial weight is applied with a pull-down force by any other construction machine such as crane truck, leader, etc. SUMMARY OF THE INVENTION The present invention has an object to overcome the above-mentioned drawbacks of the prior-art pile drivers by providing a pile driver of which the inertial weight can be pulled up and down by any other construction machine without damping the alternate vibratory force of the vibration cylinder. The above object can be attained by providing a pile driver utilizing a fluid pressure as energy source to generate a mechanical vibration under which a pile is driven into the ground in which the pile driver comprises an intertial weight, a vibration generating mechanism including a vibration cylinder and a change over valve to supply and discharge a pressurized fluid to and from the vibration cylinder, and a chuck which is provided at the lower end of a rod of the vibration cylinder to grasp the pile, characterized in that said vibration cylinder and a self-equilibration cylinder are so provided vertically in series with each other that the axes of their respective rods lie on the center line passing through the center of gravity of said inertial weight, the rods of the vibration and self-equilibration cylinders are coupled to each other, the self-equilibration mechanism has provided therein a control valve responsive to the rods of the self-equilibration cylinder to supply and discharge the pressurized fluid to and from a control chamber in the self-equilibration cylinder and the piston of the self-equilibration cylinder is supported with a low rigidity to the inertial weight by means of accumulators provided as communicating with the control chambers in the self-equilibration cylinder or a spring provided in the self-equilibration cylinder. According to the present invention, the vibration cylinder and self-equilibration cylinder are so provided in series with each other that the axes of the rods thereof lie on the center line passing through the center of gravity of the inertial weight, a control valve is provided which operates in response to the rod of the vibration cylinder to supply and discharge the pressurized fluid to and from the control chamber in the self-equilibration cylinder, and the piston of the self-equilibration cylinder is supported with a low rigidity to the inertial weight by means of the accumulators provided as communicating with the control chamber or the spring provided inside the self-equilibration, whereby the piston of the self-equilibration cylinder is held in position within the inertial weight and also has a damping effect. As a result, it can be avoided that the vibration cylinder has its alternate vibratory force reduced due to the displacement of the piston of the self-equilibration cylinder. Also, owing to the damping effect of the self-equilibration cylinder, the weight of the inertial weight is conveyed to the pile without being damped so that the pile is effectively driven into the ground. Especially, when the inertial weight is applied with a pull-down or pull-up force by any other construction machine, no vibration is conveyed to the pull-down or pull-up equipment and the vibratory force is conveyed to the pile as a driving force or extraction force resulted from the superposition on the pull-up or pull-down force without being cancelled by the pull-up or pull-down force. These and other objects and advantages of the present invention will be better understood from the ensuing description made by way of example of the embodiment of the present invention with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows an example of conventional pile driver; Figure 2 shows the basic construction of the pile driver according to the present invention; Figure 3 shows the self-equilibration cylinder in which a spring is provided; Figure 4 is a partially sectional view showing a preferred embodiment of the present invention; Figure 5 is a sectional view showing by way of example a changeover valve and responsive control valve; Figure 6 is a sectional view showing the details of the changeover valve; Figure 7 is a sectional view showing the details of the responsive control valve; Figure 8 is a circuit diagram of the hydraulic circuit; and Figure 9 is a simplified explanatory diagram showing the pull-up and pull-down of the inertial weight. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in Figure 2, the pile driver according to the present invention comprises an intertial weight 1, a vibration generating mechanism 2 composed of a vibration cylinder 3 having rods 4 and 5, and a self-equalibration mechanism 6 composed of a self-equalibration cylinder 7 having rods 8 and 9, these cylinders 3 and 7 being so disposed vertically in series with each other that the axes of the rods 4 and 5 and those of the rods 8 and 9 lie on the center line passing through the center of gravity of the inertial weight 1. The rods 5 and 8 are integrally formed into a one-piece structure. The vibration cylinder 3 is provided with a changeover valve 10 to produce an alternate vibratory force. The vibration cylinder 3 and the changeover valve 10 form together the vibration generating mechanism 2. The self-equilibration cylinder 7 is provided with a control valve 11 responsive to the rods 8 and 9 of the self-equilibration cylinder 7 to supply and discharge a pressurized fluid to and from the self-equilibration cylinder. As shown in Figure 2, there are provided accumulators 14 communicating with oil chambers 12 and 13 in the self-equilibration cylinder 7. Owing to the spring effect due to the volume change of these accumulators 14, the vertical vibration of the piston 15 of the self-equilibration cylinder 7 is prevented from being conveyed to the inertial weight 1, or to prevent the alternate vibratory force from being reduced by the inertial weight 1, the piston 15 of the self equilibration cylinder 7 is flexibly (with a low rigidity) coupled to the inertial weight 1. This is intended to avoid that the vibration of the piston 15 due to the vibration cylinder 3 would be restricted (pile driving force would be reduced) if the inertial weight 1 is coupled to the piston 15 with a high rigidity by means of a pressurized fluid of a relatively small compressibility. If it is assumed that the amplitude of the vibration due to the vibration cylinder 3 is less than ± 2 mm, the rigidity of the spring effect due to the accumulators 14 should desirably be more than 20 mm when the vibratory force of the vibration cylinder 3 is maximum. Such spring effect of the self-equilibration cylinder 7 can be attained by providing floating pistons 21 as fitted on the rods 8 and 9, respectively, on the opposite sides of the piston 15 and also providing springs 22 between the floating pistons 21 and the piston 15, respectively as shown in Figure 3. The rod 4 of the vibration cylinder 3 has provided at the lower end thereof a chuck 17 which grasps a pile 16. Also, the vibration cylinder 3 has oil chambers 19 and 20 on the opposite sides, respectively, of the piston 18. A preferred embodiment of pile driver according to the present invention will be described with reference to Figure 4. This embodiment is provided with a suspender 23 consisting of a hook 24 to be supported by a crane or the like, and a suspender body 25 having a C-shaped section and which is supported by the hook 24. The inertial weight 1 is to be attached to the suspender body 25 with such a rubber cushion 26 placed betwen them that the vibration of the inertial weight 1 will not be conveyed directly to the suspender body 25. The entire cylinders are made by relatively thick materials, and a sound-proof cover (skirt) 27 which also works as inertial weight is provided outside the cylinders. These are intended to reduce the manufacturing costs of the cylinders as a whole while isolating the sound and protecting the valves. As the above-mentioned changeover valve 10, a servo-controlled valve which operates with an electric signal is used as shown in Figures 5 and 6. This changeover valve 10 is provided inside the valve body 28 therof with a four-way valve 30 accomodating a spool 29 of which the shaft 29A is connected to a spool displacement detector 31 and which is driven by a electro-hydraulic servo valve 32. The position of the spool 29 is converted into an electric signal which is fed back to a differential amplifier 33, and the spool 29 is moved following up with an instruction signal applied to the differential amplifier 33. Therefore, by applying the instruction signal as an electric waveform to the differential amplifier 33, the frequency and amplitude of vibration waveform to the displacement of the spool 29 can be simply controlled. In Figure 6, the reference numeral 34 indicates an oil port and 35 indicates a return port. Ports 36 and 37 communicate with the vibration cylinder 3. The flow direction and flow rate of the oil under pressure to the vibration cylinder 3 can be controlled by the four ports 34 thru 37 bades on the position of th spool 29. The self-equilibration mechanism 6 is constructed as shown in Figures 5 and 7. The self-equilibration cylinder 7 has control oil chambers 12 and 13 on either side, respectively, of the piston 15 and accumulators 14 communicating with the control oil chambers 12 and 13, respectively. There is also provided a responsive control valve 11 to supply and discharge a pressurized oil to and from the oil chambers 12 and 13 through oil paths 40 and 39 communicating with the oil chambers 12 and 13, respectively. The responsive control valve 11 is a four-way valve using a spool 42 and works to connect any of pressurized oil supply port P and discharge port T to the oil path 43 or 44 provided within the responsive control valve and which communicate with the oil paths 39 and 40, respectively, according to the position of the spool 42. The spool 42 of the responsive control valve 11 is forced upward by a spring 46 and the upper end of the shaft 42A of the spool 42 is projected outside of the valve body 45. There is retained by the spring as in contact with the upper end of the spool shaft 42A one end of a member 48 pivotably installed to a fulcrum bracket 47 provided on the top of the self-equilibration cylinder body 38. The other end of the member 48 is in contact with the rod 9 of the self-equilibration cylinder 7 (which serves in the same manner as the rods 4 and 5 of the vibration cylinder). The fulcrum bracket 47 and member 48 form together a coupling means 41. The spool 42 moves in response to the rods of the self-equilibration cylinder 7 and vibration cylinder 3. The self-equilibration cylinder 7 has various functions; however, one of them will be described below: Namely, the oil pressure in the oil chambers 12 and 13 of the self-equilibration cylinder 7 is controlled as in the following. Assume that the pistons 15 and 18 vibrate at a high frequency of more than 20 Hz and with an amplitude of less than ± 2 to 3 mm. The spool 42 of the responsive control valve 11 coupled to the pistons 15 and 18 by means of the coupling means 41 vibrate vertically. The self-equilibration mechanism 6 is so arranged as not to respond to the vibration. For no response with any small amplitude, the four-way valve is designed to have an overlap structure, or such an arrangement is made that even when the oil in the control oil chambers 12 and 13 is supplied and discharged at a high frequency owing to the compression of the accumulators 14, the pressure in the chambers will change little. However, if the rod 4 is applied with an external force, not the above-mentioned vibration of high frequency, or a pull-down force acts on the inertial weight, so that the pistons 15 and 18 vibrate at positions displaced upward, the spool 42 of the responsive control valve 11 is pressed down by the coupling means 41. Thus, the oil chamber 13 in the self-equilibration cylinder is supplied with the oil from the oil supply port P through the oil paths 43 and 39, with the result that the oil pressure is raised, while the oil in the oil chamber 12 at the opposite side is discharged to the oil discharge port T through the oil paths 44 and 40 so that the oil pressure is lowered. Therefore, the piston 15 is pushed down and returned from the position upwardly displaced to the center. As described in the foregoing, the pistons always vibrate nearly at the center as shown. Another function of the self-equilibration cylinder 7 is to provide a damping effect, namely, to prevent, owing to the compression of the accumulators 14 communicating with the oil chambers 12 and 13 of the self-equilibration cylinder 7, the vibration of the pistons 15 and 18 caused by the vibration cylinder 3 from being conveyed to the inertial weight 1 so that the vibration of the piston 18 is not restricted by the inertial weight 1. In the embodiment shown in Figure 5, the changeover valve 10 is not provided in the vibration cylinder 2 as in the West Germany Patent No. 28 21 339.0-09 but outside the vibration cylinder 3, which leads to a simplified construction of the piston 18 of the vibration cylinder 3. Thus, the manufacturing costs of, especially, a large cylinder can be considerably reduced. By assembling both the vibration cylinder 3 and self-equilibration cylinder 7 in the inertial weight, it is possible to prevent the vibration and noise of both these cylinders from being propagated to the surrounding. In a pile driver in which, in addition to the frequency control element, an amplitude control element, namely, a servo-controlled valve is used as the changeover valve 10 according to the present invention, it is possible to control the amplitude of the pile 16 from zero to the maximum independently of the frequency. Thereby, it is possible to eliminate the shock to the crane, etc. by reducing to zero the amplitude at start and stop of the pile driver. Also, by changing the amplitude of the pile vibration, the vibration of the ground can be minimized when piles are driven into a complicate ground. For example, when the pile cannot be easily driven into the ground, the amplitude of pile vibration is increased. In case the pile can be easily driven into the ground, the amplitude is limited to a minimum necessary one. Furthermore, since the changeover valve 10 can be closed and opened following up with the waveform of electric signal, a changeover like a simple sinusoidal waveform can be done, and a changeover like a rectangular waveform can be done as well. The pile driving ability can be improved owing to the hammer effect by changing the pressure in the vibration cylinder abrubtly at time of driving a pile into the ground. Further, by controlling the opening and closing of the changeover valve so that the opening area follows up with a sinusoidal waveform, it is possible to reduce the high frequency component in the vibration waveform, whereby it is possible to reduce the noise generated by the chuck 17 and pile 16 as well. The experiments proved that the noise could be reduced a maximum of 10 dB. The cylinders 3 and 7 are disposed vertically in series with each other so that the axes of their respective rods 4 and 5, and 8 and 9 (the rods 5 and 8 are integrally formed into a one-piece structure) lie on the center line passing through the center of gravity of the inertial weight 1. The responsive control valve 11 is provided which responds to the rods 4 and 5 of the vibration cylinder 3 to supply and discharge the pressurized fluid to and from the oil chambers 12 and 13 of the self-equilibration cylinder 7. The piston 15 of the self-equilibration cylinder 7 is supported to with a low rigidity by means of the accumulators 14 communicating with the oil chambers 12 and 13 or by means of the spring 22 provided in the self-equilibration cylinder 7. Thus the piston 15 of the self-equilibration cylinder 7 is held in position and has a damping effect. As a result, the alternate vibratory force of the vibration cylinder 3 is prevented from being reduced due to the displacement of the piston 15 of the self-equilibration cylinder 7. Owing to the damping effect of the self-equilibration cylinder 7, the weight of the inertial weight 1 is conveyed to the pile without being damped, whereby the pile can be effectively driven into the ground. Especially, even when a pull-down or pull-up force is applied to the inertial weight 1 by a construction machine, the vibration is not conveyed to the pull-down or pull-up equipment, and the vibratory force can be conveyed to the pile 16 as a driving force or extraction force resulted from superposition on the pull-down or pull-up force without being cancelled by the pull-down or pull-up force. Generally, the pile driver according to the present invention is advantageous in that it is of a sound-proof structure, the alternate vibratory force of the vibration cylinder 3 can be conveyed to the pile 16 without being reduced and that the inertial weight 1 can be pulled down or up so that the pile driver itself may not be heavy. Figure 8 shows a hydraulic circuit which supplies and discharges the pressurized fluid to and from the oil chambers 19 and 20, and 12 and 13 of the vibration cylinder 3 and self-equilibration cylinder 7, respectively. In Figure, the reference numeral 49 indicates a filter, and 50 indicates a reducing valve. When a pile 16 is driven by the pile driver having been described in the foregoing, the pile 16 is grasped at the head thereof by the chuck 17, the vibration cylinder 3 is put into operation to convey to the pile 17 an alternate vibratory force as a reaction force due to the inertial effect of the inertial weight 1. And the pile 16 is applied with the total weight of the inertial weight 1 as a static weight and also with a pull-down force F1 when the inertial weight 1 is pulled down by a pull-down equipment 51 such as a winch, etc. as shown in Figure 9. Since the vibratory force of the vibration cylinder 3 is conveyed to the pile without being reduced (owing to damping effect and self-equilibration function to the self-equilibration cylinder), the weight W of the inertial weight 1, pull-down force F1 and the alternate vibratory force of the vibration cylinder 3 are superposed on each other and applied to the pile 16. Especially, in case a concrete pile 16 is driven into the ground by a conventional pile driver, the pile head is applied with a compressive force and tractive force alternately and the pile is likely to be broken when the tensile force is applied since the concrete is weak against a tensile force while being strong against a compressive force. However, when a concrete pile is driven into the ground by the pile driver according to the present invention, the tensile force of the vibration cylinder 3 to the concrete pile is reduced by pulling down the inertial weight by means of the pull-down equipment 51, so that the concrete pile can be driven into the ground without being broken. When the pile 16 is to be extracted, the pull-up force indicated with F2 in Figure 9 is applied to the inertial weight 1 by a pull-up equipment 52. The pile can be easily extracted with a static component (F2-W) of the extraction force and the alternate vibratory force applied as superposed on each other to the pile.

Claims: A pile driver utilizing a fluid pressure as energy source to generate a mechanical vibration under which a pile (16) is driven into the ground in which the pile driver comprises an intertial weight (1), a vibration generating mechanism (2) including a vibration cylinder (3) and a change over valve (10) to supply and discharge a pressurized fluid to and from the vibration cylinder (3), and a chuck (17) which is provided at the lower end of a rod (4) of the vibration cylinder to grasp the pile (16), characterized in that said vibration cylinder (3) and a self-equilibration cylinder (7) are so provided vertically in series with each other that the axes of their respective rods (4, 5, 8, 9) lie on the center line passing through the center of gravity of said inertial weight (1), the rods (4, 5, 8, 9) of the vibration and self-equilibration cylinders (3, 7) are coupled to each other, the self-equilibration mechanism (6) has provided therein a control valve (11) responsive to the rods (8, 9) of the self-equilibration cylinder (7) to supply and discharge the pressurized fluid to and from a control chamber (12, 13) in the self-equilibration cylinder (7) and the piston (15) of the self-equilibration cylinder (7) is supported with a low rigidity to the inertial weight (1) by means of accumulators (14) provided as communicating with the control chambers (12, 13) in the self-equilibration cylinder (7) or a spring (22) provided in the self-equilibration cylinder (7). A pile driver according to claim 1, in which as said changeover valve (10), a servo-controlled valve is used which acts with an electric signal.

Inventors: KUMAI, SEIZO, TASAKI, YASUO
Applicants: KABUSHIKI KAISHA TAKAHASHI ENGINEERING
Application year: 1988
Main classification: E02D7
IPC codes: E02D7, E02D13