Pile driver

Abstract: This invention relates to a pile driver wherein an attachment frame 1 is fixed to a work-arm 12 of an appropriate construction equipment that serves as a base machine 11, a vibration cylinder 4 actuated and controlled by an electro-hydraulic servo-valve 5 is mounted on the attachment frame through a buffer rubber 3, and a counter weight 2 and a chucking means 6 for gripping a pile to be driven K are provided on the axial ends, that is, on the cylinder base and on the forward end of the piston 41, the pile being to be held in such a manner that the drive direction coincides with the axis of the vibration cylinder.

Description: This invention relates to pile driver comprising a pile driving device construction equipment provided at the end of a work-arm that serves as a base machine for operation against the ground. A conventional pile driver of this type is known which comprises, as a base machine, a construction equipment such as an excavator having a work-arm for drilling, crushing and other works against the ground, and a rotating eccentric weight type pile driving device attached at the end of the arm. This type of pile driver drives a pile into the ground under the force which is a superposition of the centrifugal force due to rotation of the eccentric weights, a portion of the gravity force acting on the base machine, and the hydraulic force from the hydraulic cylinder mounted on the base machine. In this type of pile driver, it is obvious that, since the driving force is generated by rotation of eccentric weights, to get a greater driving force, it is necessary to increase either the mass of the eccentric-weights or the revolution rate or the eccentric throw, which however, means necessarily greater loads on the axles supporting the eccentric weights, on the bearings supporting the axles rotatability, and on the frame holding the bearings and the power transmission mechanism. To avoid this inconvenience, a new type pile driver has been proposed by the same inventors as of the present invention, disclosed in the EP-A-0 276 845 cf. the pre-characterising portion of claim 1. The main feature of this pile driver is that the alternating force from the vibration cylinder is not attenuated when a pull-up or pull-down force is exerted by any other construction machine such as a crane truck, a leader etc. To achieve this object, the pile driver comprises a self-equilibration cylinder arranged vertically in series with the vibration cylinder. The object of the invention is to provide a high-frequency type pile driver that not only is exempt from the drawbacks of the prior art which causes vibration public hazard but also can exert effectively large driving force or pull out force when attached to a work-arm of a construction equipment. The invention solves the object by a pile driver as defined in claim 1; advantageous features are introduced in the dependent claims. It is described in the following description by way of example and with reference to the drawings, which show in Fig. 1 a side sectional view of an embodiment of the invention; Fig. 2 a side sectional view showing a servo control system that controls the vibration cylinder; Fig. 3 a side sectional view showing a typical example of an electro-hydraulic servo-valve; Fig. 4 a side elevational view of an embodiment of the invention in a pile driving operation; and Fig. 5 a side sectional view similar to Fig. 1, showing another embodiment of the invention. An embodiment of the invention will be described with reference to Fig. 1 to Fig. 4. In Fig. 1 numeral 1 designates an attachment frame of arch shape, which is fixed to the forward end of a work-arm 12 of the base machine 11 (Fig. 4) by means of a fixing axle 1A. As a base machine, a rather heavy construction equipment such as an excavator or a road ripper having a work-arm 12 to carry out drilling, pounding and other operation is suited. Inside the arch of the attachment frame 1 is fixed a frame 3A through a buffer rubber 3, and a vibration cylinder 4 is provided in the frame 3A with the piston 41 directed downward. At the lower end of said piston 41 is fixed a chucking means 6 for gripping a pile K to be driven. To the piston 41 is fixed a counter weight 2 at the end of the vibration cylinder 4 opposite with respect to the chucking means 6, that is at the base end of the cylinder, as shown in Fig. 2. The chucking means 6 is provided in such a manner that the pile K is gripped to be in alignment with the axis of the vibration cylinder 4. To the vibration cylinder 4 is attached an electro-hydraulic servo-valve 5 for actuation and control thereof; on the side surface is attached a displacement sensor 7 to detect the displacement of the piston 41. A signal generator 8 is provided to generate control signals to actuate and control said electro-hydraulic servo-valve 5. The signal generator can generate, as shown in Fig. 2, control signals of various wave forms ; rectangular, sinusoidal, and others. The signals generated by the signal generator 8 are transmitted to the electro-hydraulic servo-valve 5 via a servo-amplifier 10. Also, a feedback signal circuit 9 connecting between the piston displacement sensor 7 and the servo-amplifier 10 is provided to form a servo control system that controls the vibration cylinder 4 through the electro-hydraulic servo-valve 5. The outline of action of said servo control system is as follows; the actuation signal from the signal generator 8 moves a spool 52 in the electro-hydraulic servo-valve 5 in accordance with polarity and magnitude of electric current of the signal, which, in turn, shifts the piston 41 of the vibration cylinder 4 upward or downward(Action of the electro-hydraulic servo-balve 5 Will be described later with reference to Fig. 3). The direction and magnitude of this displacement of the piston 41 is detected by the piston displacement sensor 7 and a feedback signal (voltage) proportional to sensed quantity is transmitted to the servo-amplifier 10. In the servo-amplifier 10, the signal (voltage) from the signal generator 8 and said feedback signal are compared, and the difference is transmitted as an input electric current to the electro-hydraulic servo-valve 5, which moves the piston 41 in the direction to lessen the difference. Thus, the piston 41 of the vibration cylinder 4 is made to vibrate profiling the wave form of the signal from the signal generator 8. The signal desired to be generated from the generator 8, that is, the operation condition of the pile driver can be easily set by turning the adjusting dial (not shown) attached thereto. Since, to the vibration cylinder is fixed the counter weight 2, a reaction force that is proportional to acceleration of the cylinder 41 is generated by the vibration of said cylinder 41, which is transmitted to the pile K through the chucking means 6 fixed to the lower end of the piston 41. The force transmitted possesses the same frequency as the piston 41, is proportional to the mass of the counter weight 2, and is directed to be in alignment with the axis of the vibration cylinder that is, the axis of the pile K. With its attached servo-valve 5 and piston displacement sensor 7, the vibration cylinder 4, the counter weight 2 and the chucking means 6 is supported by a support frame 3A connected to the attachment frame 1 through a buffer rubber 3 whereby the chucking means 6 is directly connected to said support frame 3A. Fig. 5 shows another embodiment of the invention, which is different from the embodiment described hereinabove only in that the direction of the vibration cylinder 4 is reversed in so far as the counter weight 2 is fixed to the end of the piston 41 while the chucking means 6 is fixed to the base of the vibration cylinder 4. With this modified embodiment, the operation is quite the same with the above embodiment. Here, with reference to Fig. 3, the construction and action of the electro-hydraulic servo-valve 5 will be described. The electro-hydraulic servo-valve comprises, roughly speaking, a four-port spool valve part, a torque motor part, and a primary hydraulic amplifier part. The four-port spool valve part consists of a sleeve 51 and a spool 52 that engages slidably inside said sleeve 51. The spool 52 possesses land portions on the both ends and effects communication or disconnection among the four ports; the entrance port P for hydraulic oil, the return port R to a tank, and a pair of passages A and B which lead to an actuator or the vibration cylinder 4 in this case. The member that is shown as a tube below the spool 52 is a filter which has fixed orifices 60 at the both ends. The torque motor part consists of a permanent magnet 58, an electromagnetic coil 56, and an armature 57. The armature 57 is mounted to be rotatable about the central axle on which is exerted a torque due to a torsion spring 55, and a flapper 54 is fixed on the opposite side of said armature 57 with respect to said central axle. A feedback spring 59 is attached at the end of said flapper and the other end thereof is engaged with the center of the spool 52 through an appropriate ball. On both sides of the flapper are provided a pair of nozzles 53 facing each other. which are severally in communication with the end faces of the spool 52 (let the pressures on them be P₁ and P₂ ), and a flow passage for a part of oil entering from the port P is formed by way of the fixed orifices 60 on the both sides. The flapper 54, the pair of nozzles 53 and the fixed orifices described above constitue the primary hydraulic amplifier. When the input signal current to the electro-hydraulic servo-valve 5 is zero, the armature 57, hence the flapper 54, is at the central position as shown, and the back pressures P₁ and P₂ behind the nozzles 53 are equal, which keeps the spool at the central position shown in Fig. 3. Now let a small electric current (input signal) of either polarity (plus or minus) increase through the electromagnetic coil 56 to change the magnetic field of the permanent magnet 58, and let thereby the armature 57 be turned to one direction, to the left for example, then the flapper will move to the right and will cause a higher back pressure P₂ on the right nozzle than the pressure P₁ on the left nozzle (P₂ > P₁), which moves the spool 52 to the left. The displacement of the spool 52 continues until the back pressures on the nozzles again come to an equilibrium which is effected by pulling back the flapper 54 by the feedback spring 59. The commumication relationship among the four ports of the four-port spool valve part when the spool 52 stops is such that oil flows in the path: the entrance port P → A → the vibration cylinder 4 → B → the return port R. If the port A is in communication with the head side of the vibration cylinder 4, then the piston 41 extends out in responce to the above said input signal. If the polarity of the input signal is reversed, the action is similar but the spool moves to the right by a quantity. Thus, in an electro-hydraulic servo-valve, the spool moves a distance in the direction corresponding to the sign (plus or minus) and in proportion to the magnitude of the input signal, which also means the output flow to be proportional to the input electric current. In this manner, the use of the electro-hydraulic servo-valve 5 makes it possible to operate and control a large-capacity actuator by means of small electric current of the order of milliampere. Moreover, the electro-hydraulic servo-valve permits a faithful profiling of magnitude and polarity of the input electric current of the input signal, and, the machine can follow well up to several tens of herz of frequency variation, keeping the counter weight 2 at about the center of the vibration under the cooperative action of the servo control system consisting of the piston displacement sensor 7, the signal generator 8, the feedback signal circuit 9 and the servo-amplifier 10. In Fig. 3 is shown a two-stage, most typical electro-hydraulic servo-valve to facilitate comprehension of the work principle; if an actuator of greater capacity is to be controlled, a three-stage electro-hydraulic servo- valve can be adopted. Of course, with a three-stage electro-hydraulic servo-valve, the work principle that the output flow is controlled through displacement of the spool which is made to be proportional to the input electric current, is the same with the typical servo-valve described above. In actual pile driving operation, the base machine 11 is set with the front wheels raised as shown in Fig. 4 so that most of the weight therof is transferred to the pile K through the attachment frame 1. To say more accurately, it is more convenient if the distance between the vertical line of the pile and the base machine 11 is as short as possible. The force that acts on the pile K is, therefore, superposition of the reaction force from the vibration cylinder 4 described above, tile gravity force on the counter weight, and most part of the machine weight itself, On the other hand, if the base machine is sufficiently fixed, instead of making use of the machine weight as shown in Fig. 4, it is possible to complement the driving force on the pile K by forcing the end of the work-arm in the direction of the pile axis by means of a hydraulic cylinder mounted on the machine. Also, the works-arm can be readily made use of for pulling out a pile K from the ground although this depends on the kind of the base machine 11.

Claims: A pile driver comprising a pile driving device provided at the end of a work-arm (12) of an appropriate construction equipment that serves as a base machine (11), said pile driving device having a pile driving vibration cylinder (4) supported on an attachment frame (1) that is to be fixed to the end of said work-arm (12), further having a counter weight (2) provided at the axial end of said vibration cylinder (4) opposite the ground and a chucking means (6) for gripping a pile K to be driven at the other axial end of said vibration cylinder (4) facing the ground, and further a servo control system which consists of an electro-hydraulic servo-valve (5) that actuates and controls said vibration cylinder (4), a piston displacement sensor (7) that detects displacement of the piston (41) of said vibration cylinder (4), a signal generator (8) that generates input signals to said electro-hydraulic servo-valve (5), a feedback signal circuit (9) that transmits the detected signal from said piston displacement sensor to said electro-hydraulic servo-valve (5) and a servo-amplifier (10) that compares the signal from said signal generator (8) and the signal from said piston displacement sensor (7); characterized in that the assembly comprising the vibration cylinder (4), the counter weight (2), and the chucking means (6) is supported by a support frame (3A) connected to the attachment frame (1) through a buffer rubber (3), and that said chucking means (6) is directly connected to said support frame (3A). A pile driver claimed in claim 1 characterized in that said vibration cylinder (4) is fixed to said attachment frame (1) in such a manner that the extension side of the piston (41) thereof faces the ground. A pile driver claimed in claim 1 characterized in that said vibration cylinder (4) is fixed to said attachment frame (1) in such a manner that the extension side of the piston (41) thereof faces the direction opposite the ground.

Inventors: KUMAI SEIZO, SANO YUJI, SHIMADA FUBITO, TASAKI YASUO, KUMAI, SEIZO, SANO, YUJI, SHIMADA, FUBITO, TASAKI, YASUO
Applicants: KENCHO KOBE CO LTD, TAKAHASHI ENG KK, KABUSHIKI KAISHA TAKAHASHI ENGINEERING, KENCHO KOBE CO., LTD.
Application year: 1991
Main classification: E02D7
IPC codes: E02D7, B06B1