GB1584792A

GB1584792A - Oscillator actuated hydraulic percussion device

Info

Publication number: GB1584792A
Application number: GB2397577A
Authority: GB
Original assignee: Mitsui Engineering and Shipbuilding Co Ltd
Current assignee: Mitsui Engineering and Shipbuilding Co Ltd
Priority date: 1976-06-09
Filing date: 1977-06-08
Publication date: 1981-02-18
Also published as: DE2726118A1; DE2726118C3; FR2354460B1; DE2726118B2; FR2354460A1

Description

(54) AN OSCILLATOR ACTUATED "HYDRAULIC PERCUSSION DEVICE (71) We, MITSUI ENGINEERING AND SHIPBUILDING COMPANY LIMITED, a Japanese Company of 6-4 Tsukiji 5-chome, Chuo Ku, Tokyo, Japan, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - This invention relates to oscillator actuated hydraulic percussion devices and in particular oscillator actuated hydraulic percussion devices which are provided with means for controlling the stroke of the piston which strikes a boring tool.

Conventional hydraulic percussion devices in practical use have been self-actuating type in which reciprocating motion of the piston which strikes the boring tool is caused by the switching of hydraulic pressure in a double acting cylinder by means of a spool valve actuated by changes in the position of the piston. Such devices have suffered from several drawbacks. First, since the period of the spool is determined by the period of the reciprocating motion of the piston, the striking frequency and the striking energy cannot be varied independently of each other. In other words, if the hydraulic pressure supplied to the piston is reduced in order to decrease the striking energy, the striking frequency is also reduced due to a reduction in the velocity of the piston. Accordingly, it is difficult to obtain efficient boring which can be adapted to geological variation.

Particularly, in the case of rotary percussion drills, it is necessary to maintain an optimum combination of drill RPM, striking frequency, striking energy, feed, etc., and to change the RPM of the drill in accordance wtih variations in the striking frequency in order to achieve efficient boring. Complicated and expensive control devices are required in order to accomplish this end.

Furthermore, some reports state that when the piston strikes the boring tool, the efficiency of the energy transmission to the rod is improved if the period of time (hereinafter referred to as the push time)during which the piston pushes against the boring tool after initial contact is made is increased to some extent. In conventional devices, however, this push time is almost non-existant.

Furthermore, since conventional devices are of the self-actuating type, a dead point exists. Therefore, the device may fail to start, depending upon the relative positions of the piston and the spool when the device is stopped. Accordingly, it is frequently necessary to attach a separate starter device in order to insure starting.

Furthermore, in such devices which are equipped with bladder type of diaphram type accumulators for the purpose of recovering energy from the return stroke of the piston and using it in the impulse stroke in order to increase efficiency, the striking frequency cannot be increased to any great extent due to problems in the accumulator response and durability.

In addition, conventional oscillator actuated hydraulic impulse devices use oscillation exciters which suffer from certain drawbacks when used in industrial equipment.

Specifically, mechanical oscillation exciters which utilize an eccentric mass are excessively large in terms of structural size.

Electrical oscillation exciters are easier to control and can achieve high oscillation frequency, but make it difficult to obtain a large power output. Devices which utilize a motor and air pressure generate excessive noise. Devices utilizing electrohydraulic servo valves can achieve a large power output but are expensive and unsuitable for use in construction and mining machinery which is operated under harsh environmental conditions.

On the other hand, devices for generating oscillating pressure which utilize the self-excited oscillation of a hydraulic valve have been proposed. Oscillation exciters which utilize such devices as sources of pilot pressure have been able to compensate for previously mentioned drawbacks, but such devices are still unsatisfactory in some respects for use in percussion machinery such as hydraulic rock drills, hydraulic breakers, etc. Specifically, since the pressure variation of the oscillating pressure is small, this type of device cannot be used as a source of pilot pressure in machinery which is required to develop a large power output.Furthermore, if the device is designed such that the boring tool is struck at the point of maximum piston velocity in order to obtain a high striking energy, a considerable amount of time is required for the piston switching valve switch so that the piston begins its return stroke after striking the boring tool. This leads to an excessive increase in the amount of idle time during which the piston is in contact with the boring tool which in turn results in a decrease in efficiency rather than an increase.

Patricularly, in cases where this type of device is used in a rotary percussion drill in which the bit is caused to revolve by means of a motor, etc., bit abrasion becomes excessive. Furthermore, in order to achieve satisfactory efficiency, it is necessary to gradually store up energy during the return stroke of the piston by means of a spring (coil spring or accumulator, etc.) to release this energy in a rapid surge during the impulse stroke so that the piston is accelerated to a high velocity before it strikes the boring tool. For the above reasons, it is desirable that the time required for the impulse stroke of the piston be shorter than the time required for the return stroke.In conventional devices for generating oscillating pressure, however, the period of time during which a high pressure is maintained and the period of time during which a low pressure is maintained are approximately equal. Accordingly, the duration of impulse stroke and the duration of the return stroke are approximately equal.

Accordingly, it is a general object of the present invention to provide an oscillator actuated hydraulic percussion device which efficiently transmits energy from the piston to the boring tool for various geological conditions.

It is another object of the present invention to provide a hydraulic percussion device for use in mountainous areas.

It is another object of the present invention to provide a hydraulic percussion device which utilizes the self-exciter oscillation of the hydraulic valve as a source of pilot pressure.

The present invention provides a hydraulic percussion boring device comprising: a differential cylinder; a piston provided in said cylinder and together with said cylinder forming a forward and a rear chamber, said piston further being configured such that the working area of said piston in said forward chambers is larger than the working area of said piston in said rear chamber; a means for supplying a constant high hydraulic pressure to said rear chamber; an oscilator; a first means for generating a signal indicative of the changed position of said piston; and a spool valve for switching hydraulic pressure into said forward chamber whereby reciprocating motion of said piston for striking a boring tool is created, said spool valve being activated in response to said oscillator and said first means.

The above mentioned and other features and objects of the present invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings and in which: - FIGURE 1 is a cross section of a rotary percussion drill which utilizes embodiment of a hydraulic percussion device in accordance with the teachings of the present invention; FIGURE 2 is a magnified cross section of the embodiment of FIGURE 1 during the return stroke of the piston; FIGURE 3 is a magnified cross section similar to that of FIGURE 2 illustrating the operation of the embodiment of FIG URE 1 during the impulse stroke of the piston; FIGURE 4 is a magnified cross section of an impulse mechanism of a further embodiment of a hydraulic impulse device in accordance with the teachings of the present invention; ; Referring to FIGURES 1 through 4, shown therein is a rotary percussion drill utilizing a hydraulic impulse device in accordance with the teachings of the present invention. The rotary percussion drill consists of a drill rotating mechanism 201, a drill impulse mechanism 202 and a drill 203. The drill rotating mechanism 201 includes a hydraulic motor 204, gears 205 through 207, revolving sleeve 208 with an attached gear, a hydraulic pressure source 209 and a tank 210. The drill 203 is provided in the revolving sleeve 208 such that it can simultaneously revolve and reciproW cate. FIGURE 2 is a magnified portion of FIGURE 1 illustrating the drill impulse mechanism 202.The drill impulse mechanism 202 includes a differential cylinder 211, a piston 212 which strikes the drill 203, a spool valve 213, an oscillator 214, and an accumulator 215, a check valve 216, a hydraulic pressure source 217, a tank 218 and lines which interconnect these components.

Piston 212 is provided within cylinder 211 such that it slides back and forth. The piston 212 has two step parts 219 and 220 which together with the cylinder walls form respectively the forward cylinder chamber 221 and the rear cylinder chamber 222. The diameter of the shaft of the piston 212 is smaller on the side of the forward cylinder chamber 221 than on the side with the rear cylinder chamber 222 such that the piston area is greater on the side of the forward cylinder chamber 221. Furthermore, the air tight integrity of cylinder 211 is maintained by means of an air tight piston bearing 223.

The spool valve 213 is of the two piston three port type. A spool 224 is provided within spool valve 213 such that it can slide back and forth. The spool 224 is maintained in a neutral position by springs 227 and 228 which are respectively installed in pilot pressure chambers 225 and 228 provided at both ends of the spool 213.

Oscillator 214 receives appropriate fluid via line 229 and delivers an alternating hydraulic pressure to pilot pressure chambers 225 and 226 of spool valve 213 via lines 230 and 231. Furthermore, oscillator 214 is designed such that the fluid expelled by the reciprocating motion of the spool 224 is returned to the oscillator 214 via lines 231 and 230 and unloaded via line 232 along with the fluid expended by the oscillation of the oscillator 214.

Furthermore, the oscillator 214 may be of any type, e.g. electrical or mechanical, hydraulic, etc., so long as it is able to cause reciprocating motion of the spool 224.

Rear cylinder chamber 222 is coupled to hydraulic pressure source 217 via line 233, check valve 216 and line 234. Furthermore, accumulator 215 is coupled to line 233 at a point between check valve 216 and rear cylinder chamber 222 via line 235. Furthermore, ports 236, 237 and 238, which are for the purpose of obtaining a pilot pressure used to detect the change in position of the piston 212, are provided in the rear cylinder chamber 222 at points towards the midpoint of the cylinder 211. These ports are coupled to pilot pressure chamber 225 of spool valve 213 via line 239.

In addition, forward cylinder chamber 221 is coupled to spool valve 213 via line 240 and to hydraulic pressure source 217 via the spool valve 213 and line 241 and is unloaded via spool valve 213 and line 242.

For the purposes of the following descrip; tion, it is assumed that the piston 212 in FIGURE 2 has contacted drill 203 and is about to begin its return stroke. At this time, since high pressure is present in rear chamber 222, a pilot pressure reaches the pilot pressure chamber 225 of the spool valve 213 via port 236 and line 239 and the spool valve 213 is switched without any signal from the oscillator 214. Accordingly, a pressure is applied to both the forward cylinder chamber 221 and the rear cylinder chamber 222 and the piston 212 begins its return stroke as a result of the difference in the piston areas of the two chambers.

At this time, the fluid expelled from the rear cylinder chamber 222 by the piston 212 is stopped by the check valve 216 and is caused to accumulate in accumulator 215.

When the signal from the oscillator 214 is received at the end of return stroke of the piston 212, the spool valve 213 assumes the attitude shown in FIGURE 3, thereby causing the forward cylinder chamber 221 to be unloaded such that a force of Pb x At acts on piston surface on the side of the forward cylinder chamber 221 (where Pb is the back pressure in the forward cylinder chamber 221). At this time, a force P x Ar is applied to the piston surface on the side of the rear cylinder chamber 222. Since Pb iS much less than P, it follows that Pb times Af is less than P times Ar.

Accordingly, the piston 212 begins its impulse stroke. The potential energy which was stored in the accumulator 215 during the return stroke is converted into kinetic energy of the piston 212 during the impulse strke.

By repeating the above described strokes, the piston 212 delivers successive blows to the drill 203. Meanwhile, revolution of the drill 203 is caused by the hydraulic motor independently of the reciprocating motion of the piston 212.

In this embodiment, since the striking frequency is determined by the oscillation frequency of the oscilator 214, it can be varied by varying the pressure delivered to the oscillator 214. On the other hand, the striking energy can be varied by varying the pressure delivered to the piston 212 by the hydraulic pressure source or the pressure of the gas enclosed in the accumulator 215.

Furthermore, the drill RPM can be varied by adjusting the amount of supply flow to the hydraulic motor. In addition, push time can be varied by adjusting the actuation timing of the signal from port 236.

Accordingly, the striking frequency, strik- ing energy, drill RPM and push time can be varied independent of each other and it is therefore possible to achieve boring which can be adapted to the hardness of the rock without using any of the complicated devices such as variable pumps, etc., required by conventional models.

Furthermore, in this embodiment the ratio of the piston area Af on the side of the forward cylinder chamber 221 to the piston area Ar on the side of the rear chamber 222 is established such that Ar divided by Ar is greater than 1 but less than 2.

This is done in order to insure that successive delivery of satisfactory blows to the drill and for the following reasons. In the hydraulic impulse device provided -'by this invention, the spool valve 213 receives an alternating signal from the oscillator 214 which is completely unaffected by the position of the piston 212 and also receives a signal from the rear cylinder chamber 222 when the piston 212 has completed its impulse stroke. The return stroke is actuated by the signal from the rear cylinder chamber 222 while the change over to the impulse stroke is accomplished by means of a signal from the oscillator 214. However, there is a phase difference between the signal from the oscillator 214 and the signal created by the change in the position 212 and the magnitude of the difference is uncertain.

Accordingly, if the piston 212 return signal from the oscillator 214 (for example) lags far behind the signal created by the change in the position piston 212, the signal which switches the piston 212 over to the impulse stroke also lags far behind, thereby causing the piston to be pushed back too far.

As a result, the return piston signal from the oscilator 214 wil be received in the middle of the impulse stroke before the piston 212 reaches the drill 203 and the piston 212 will be caused to return. The result is an undesirable state which the piston 212 reciprocates but does not strike the drill 203.

In order to overcome this problem, it is advisable to decrease the velocity of the piston 212 during the return stroke such that the signal created by the change in position of the piston 212 will be received before the piston return signal from the oscillator 214 is received. In order to accomplish this, it is necessary that the amount of time required for the return stroke of the piston 212 be greater than the amount of time required for the impulse stroke of the piston 212. In order to satisfy this condition, it is only necessary to insure that the force which acts on piston 212 during impulse stroke is greater than the force in operation during the return stroke.

The following relationship satisfies this condition: PAr minus Pb A, is greater than PA, minus PAr. Where P" is the back pressure present in forward cylinder chamber 221. Assuming for the sake of simplicity that Pb equals zero, it follows that Af divided by Ar is less than 2. However, since Af is greater than A" the following condition is obtained: Af divided by Ar is greater than 1 but less than 2.

Furthermore, in this embodiment a multiple number of ports are installed along the line of piston 212 advance in order to obtain the pilot pressure which actuates the spool valve 213 from the rear cylinder cham ber222. Since these ports can be selectively opened or closed by means of plug 243, the timing of the actuation of the spool valve 213 by the pilot pressure and therefore the push time can easily be varied. - Furthermore, it would also be possible to vary the actuation timing of the pilot pressure and thereby the push time by installing a var- iable throttle valve 245 at an intermediate point along the line and varying the amount of restriction (as shown in FIGURE 4) instead of installing a multiple number of ports.

By use of the invention the time required for reciprocating motion of a piston can be adjusted to an optimum value for use in percussion machinery such as hydraulic rock drills, hydraulic breakers, etc. As a result, the energy of the piston can be transmitted to the rock with a high degree of efficiency and the idle time (the time during which the piston is in contact with the boring tool but is not performing any work) can be reduced. Furthermore, this invention can be used in rotary percussion drills in which the bit is caused to revolve by means of a motor. In addition, this invention is able to generate a pilot pressure on which the pressure variation is quite large.

The invention is not limited to the details of the foregoing examples.

WHAT WE CLAIM IS: - 1. A hydraulic percussion boring device comprising: a differential cylinder; a piston provided in said cylinder and together with said cylinder forming a forward and a rear chamber said piston further being configured such that the working area of said piston in said forward chambers is larger than the working area of said piston in said rear chamber; a means for supplying a constant high hydraulic pressure to said rear chamber; an oscillator; a first means for generating a signal indicative of the changed position of said piston; and a spool valve for switching hydraulic pressure into said forward chamber whereby reciprocating motion of said piston for striking a boring tool is created, said spool valve being activated in response to said oscillator and said first means.

2. A hydraulic percussion boring device according to claim 1 wherein the ratio of the piston working area in said forward chamber to the piston working area in said rear chamber is greater than one but less than two.

3. A hydraulic percussion boring device according to claim 1 wherein said first means comprises: a port provided in said cylinder, said port being provided in said

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. piston area Ar on the side of the rear chamber 222 is established such that Ar divided by Ar is greater than 1 but less than 2. This is done in order to insure that successive delivery of satisfactory blows to the drill and for the following reasons. In the hydraulic impulse device provided -'by this invention, the spool valve 213 receives an alternating signal from the oscillator 214 which is completely unaffected by the position of the piston 212 and also receives a signal from the rear cylinder chamber 222 when the piston 212 has completed its impulse stroke. The return stroke is actuated by the signal from the rear cylinder chamber 222 while the change over to the impulse stroke is accomplished by means of a signal from the oscillator 214. However, there is a phase difference between the signal from the oscillator 214 and the signal created by the change in the position 212 and the magnitude of the difference is uncertain. Accordingly, if the piston 212 return signal from the oscillator 214 (for example) lags far behind the signal created by the change in the position piston 212, the signal which switches the piston 212 over to the impulse stroke also lags far behind, thereby causing the piston to be pushed back too far. As a result, the return piston signal from the oscilator 214 wil be received in the middle of the impulse stroke before the piston 212 reaches the drill 203 and the piston 212 will be caused to return. The result is an undesirable state which the piston 212 reciprocates but does not strike the drill 203. In order to overcome this problem, it is advisable to decrease the velocity of the piston 212 during the return stroke such that the signal created by the change in position of the piston 212 will be received before the piston return signal from the oscillator 214 is received. In order to accomplish this, it is necessary that the amount of time required for the return stroke of the piston 212 be greater than the amount of time required for the impulse stroke of the piston 212. In order to satisfy this condition, it is only necessary to insure that the force which acts on piston 212 during impulse stroke is greater than the force in operation during the return stroke. The following relationship satisfies this condition: PAr minus Pb A, is greater than PA, minus PAr. Where P" is the back pressure present in forward cylinder chamber 221. Assuming for the sake of simplicity that Pb equals zero, it follows that Af divided by Ar is less than 2. However, since Af is greater than A" the following condition is obtained: Af divided by Ar is greater than 1 but less than 2. Furthermore, in this embodiment a multiple number of ports are installed along the line of piston 212 advance in order to obtain the pilot pressure which actuates the spool valve 213 from the rear cylinder cham ber222. Since these ports can be selectively opened or closed by means of plug 243, the timing of the actuation of the spool valve 213 by the pilot pressure and therefore the push time can easily be varied. - Furthermore, it would also be possible to vary the actuation timing of the pilot pressure and thereby the push time by installing a var- iable throttle valve 245 at an intermediate point along the line and varying the amount of restriction (as shown in FIGURE 4) instead of installing a multiple number of ports. By use of the invention the time required for reciprocating motion of a piston can be adjusted to an optimum value for use in percussion machinery such as hydraulic rock drills, hydraulic breakers, etc. As a result, the energy of the piston can be transmitted to the rock with a high degree of efficiency and the idle time (the time during which the piston is in contact with the boring tool but is not performing any work) can be reduced. Furthermore, this invention can be used in rotary percussion drills in which the bit is caused to revolve by means of a motor. In addition, this invention is able to generate a pilot pressure on which the pressure variation is quite large. The invention is not limited to the details of the foregoing examples. WHAT WE CLAIM IS: -

1. A hydraulic percussion boring device comprising: a differential cylinder; a piston provided in said cylinder and together with said cylinder forming a forward and a rear chamber said piston further being configured such that the working area of said piston in said forward chambers is larger than the working area of said piston in said rear chamber; a means for supplying a constant high hydraulic pressure to said rear chamber; an oscillator; a first means for generating a signal indicative of the changed position of said piston; and a spool valve for switching hydraulic pressure into said forward chamber whereby reciprocating motion of said piston for striking a boring tool is created, said spool valve being activated in response to said oscillator and said first means.

cylinder such that said port opens at the end of an impulse stroke of said piston; a flow line coupling said port to said spool valve ; and a variable throttle valve provided in said flow line whereby the actuation time of said spool valve may be varied by varying said variable throttle.

4. A hydraulic percussion boring device according to claim 1 wherein said first means comprises: a plurality of ports prou vided in said rear chamber of said cylinder along the line of movement of said piston, each of said ports being coupled to said spool valve; and means for selectively open ing and closing each of said plurality of ports whereby the actuation timing of said spool valve can be varied by selectively opening and closing said plurality of ports.

5. A hydraulic percussion boring device substantially as hereinbefore described with reference to any of the accompanying drawings.