JPS6125784A - Stroke variable mechanism of hydraulic type striking device - Google Patents
Stroke variable mechanism of hydraulic type striking deviceInfo
- Publication number
- JPS6125784A JPS6125784A JP14731884A JP14731884A JPS6125784A JP S6125784 A JPS6125784 A JP S6125784A JP 14731884 A JP14731884 A JP 14731884A JP 14731884 A JP14731884 A JP 14731884A JP S6125784 A JPS6125784 A JP S6125784A
- Authority
- JP
- Japan
- Prior art keywords
- piston
- liquid chamber
- valve
- valve control
- stroke
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Landscapes
- Percussive Tools And Related Accessories (AREA)
- Drilling And Exploitation, And Mining Machines And Methods (AREA)
- Earth Drilling (AREA)
Abstract
(57)【要約】本公報は電子出願前の出願データであるた
め要約のデータは記録されません。(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.
Description
【発明の詳細な説明】
〔産業上の利用分野〕
この発明は、さく岩槻やブレーカ等の液圧式打撃装置の
ストローク可変機構に関し、特に、ピストンの往復運動
を切換える切換弁の移動速度を弁制御通路に設けた可変
絞りで調整することにより、ピストンのストロークを可
変とし負荷条件に最適の打撃力が得られるようにする。[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a variable stroke mechanism for a hydraulic impact device such as a rock drill or a breaker, and particularly to a variable stroke mechanism for a hydraulic impact device such as a rock drill or a breaker, and in particular, a variable stroke mechanism for controlling the movement speed of a switching valve that switches the reciprocating motion of a piston. By adjusting the variable throttle provided in the passage, the stroke of the piston can be made variable to obtain the optimal striking force for the load conditions.
鉱山、採石、土木工事等で行なわれる掘削やさく孔作業
は、現場の状況により条件が一定せず、掘削対象の岩質
の変化や工法の選択に対応して常に最適条件で作業を行
なうためには、これに使用するさく岩槻やブレーカ等の
打撃装置が打撃エネルギーを調整できることが望ましい
。そこで、このような打撃装置のビストンストロークを
変更可能とするため、弁切換用の連絡通路に複数のポー
トを設け、各ポートの選択的開閉によりビストンストロ
ークを変更可能とした液圧式打撃装置が捉案されている
（特願昭５８−１７８９５２号、特公昭５４〜４８８２
号参照）。Conditions for excavation and hole drilling work carried out in mining, quarrying, civil engineering, etc. vary depending on the site situation, and work is always carried out under optimal conditions in response to changes in the rock quality of the excavation target and selection of construction methods. It is desirable that the striking device used for this purpose, such as a rock drill or breaker, be able to adjust the striking energy. Therefore, in order to make it possible to change the piston stroke of such a striking device, a hydraulic striking device has been developed in which multiple ports are provided in the communication passage for valve switching, and the piston stroke can be changed by selectively opening and closing each port. (Japanese Patent Application No. 58-178952, Japanese Patent Publication No. 54-4882)
(see issue).
しかしながら、複数ポートの開閉を選択するのみでは、
ストロークの変更が段階的となり、種々の異なる岩質に
対し最適なストロークをビストンに与えることが困難で
あり、作業能率の向上を阻古している。However, simply selecting the opening/closing of multiple ports is not enough.
The stroke is changed in stages, making it difficult to give the piston the optimum stroke for various types of rock, and hindering improvements in work efficiency.
この発明は、液圧式打撃装置における上記問題を解決す
るものである。This invention solves the above-mentioned problems in hydraulic striking devices.
而して、この発明の目的は、液圧式打撃装置のビストン
ストロークを連続的に変更することのできる液圧式打撃
装置のストローク可変機構を提供するにあり、また、こ
の発明の目的は、作業条件の変化に対応して最適のスト
ロークを与えることにより作業能率を向上させる液圧式
打撃装置を提供するにある。SUMMARY OF THE INVENTION An object of the present invention is to provide a variable stroke mechanism for a hydraulic impact device that can continuously change the piston stroke of the hydraulic impact device. An object of the present invention is to provide a hydraulic striking device that improves work efficiency by providing an optimal stroke in response to changes in the stroke.
この発明の液圧式打撃装置のストローク可変機構では、
ソリンダ内に、前後に小径部を有するピストンを摺嵌し
て前部液室と後部液室とを形成し、少くとも一方の液室
を切換弁で高圧と低圧とに切換えてピストンを往復動さ
せる液圧式打撃装置に、ピストンの往復動に伴って開閉
される制御ポートと弁制御液室とを設け、この制御ポー
トと弁制御液室とを弁制御通路で接続し、この弁制御通
路に可変絞りを介設している。In the variable stroke mechanism of the hydraulic impact device of this invention,
A piston having a small diameter portion at the front and rear is slid into the cylinder to form a front liquid chamber and a rear liquid chamber, and at least one liquid chamber is switched between high pressure and low pressure with a switching valve to cause the piston to reciprocate. A hydraulic impact device is provided with a control port and a valve control liquid chamber that are opened and closed as the piston reciprocates, and the control port and the valve control liquid chamber are connected by a valve control passage. A variable aperture is provided.
可変絞りを調整することにより制御ポートから弁制御通
路を通って弁制御液室へ供給される作動圧液の流量が変
化し、切換弁の移動速度は無段階に制御される。従って
、切換弁の移動速度を制御することにより、ピストンの
制動反転時期を任意に設定できビストンストロークは連
続的に変更可能となる。By adjusting the variable throttle, the flow rate of the operating pressure liquid supplied from the control port to the valve control liquid chamber through the valve control passage changes, and the moving speed of the switching valve is controlled steplessly. Therefore, by controlling the moving speed of the switching valve, the braking reversal timing of the piston can be arbitrarily set and the piston stroke can be changed continuously.
以下、図面を参照してこの発明の詳細な説明する。 Hereinafter, the present invention will be described in detail with reference to the drawings.
第１図は、この発明の−・実施例である液圧式打撃装置
のストローク可変機構の構成を示す縦断面図であり、シ
リンダ１内にはピストン２が前後方向へ往復動可能に摺
嵌され、シリンダ１の後部にバルブプラグ１２が嵌着さ
れている。FIG. 1 is a longitudinal cross-sectional view showing the configuration of a variable stroke mechanism of a hydraulic impact device according to an embodiment of the present invention. , a valve plug 12 is fitted to the rear of the cylinder 1.
ピストン２は、大径部２ａ、前方小径部２ｂ、後方小径
部２Ｃを有し、この径の相違により前部液室３と後部液
室４とを形成している。後方小径部２Ｃは、前方小径部
２ｂより更に径が小さく、従って、ピストン２は、後部
液室４側の受圧面積が前部液室３側の受圧面積より大で
ある。前部液室３は、高圧回路６によって液圧源１）と
接続されている。シリンダ１の後部に嵌着されているバ
ルブプラグ１２は、前方の外径を小さくして、その外周
とシリンダ１の内周との間に、円筒状の切換弁５をピス
トン２と同心状に摺嵌する弁室１７を形成している。第
２図は、弁室１７付近の拡大断面図である。弁室１７に
は、高圧ポート１３とその前方に位置する低圧ポート１
４とが設けられており、高圧ポート１３は高圧回路６に
よって液圧ｔＸ１）と接続され、低圧ポート１４は低圧
回路１０によってタンク１５に接続されている。２１は
アキュムレータである。弁室１７内には、後部液室４と
給排液孔１６で連通された給排液室１８が設けられてお
り、切換弁５には、前進位置で高圧ポート１３を給排液
室１８へ連通させる給液孔１９と、後退位置で低圧ポー
ト１４を給排液室１８へ連通さセる排液孔２０とが穿設
されている。切換弁５の前部は段付で小径となり、その
前後に弁後退液室２２と弁制御液室２３とが形成されて
いる。後部液室４と弁後退液室２２との間には、ピスト
ン２の前後進によってピストン２の大径部２ａで開閉さ
れる弁切換通路２４が設けられており、弁後退液室２２
と後部液室４とは、切換弁５に設けた後退孔２５を介し
て連通される。前部液室３には、ピストン２の前後進に
よってピストン２の大径部２ａで開開される制御ポート
２８が設けられており、この制御ポート２８と弁制御液
室２３とが弁制御通路２６で接続され、弁制御液室２３
と前部液室３とは、切換弁５に設けた制御孔２７を介し
て連通される。弁制御通路２６には、可変絞り３０が介
設されており、弁制御通路２６の流量を無段階に変化さ
せることができる。なお、弁制御通路２６には、可変絞
り３０の下流側と、制御ポート２８の後方に設けた規制
ポート２９とを接続する最大ストローク規制用バイパス
３１を備えている。ピストン２の大径部２ａには、ピス
トン２の前進位置で、規制ポート２９と弁室１７の前端
部からの連通路３２とを低圧回路ｌＯへ連通させ、ピス
トン２の後退位置で、弁室１７の前端部からの連通路３
２と弁切換通路２４とを低圧回路ＩＯへ連通させる溝３
３が設けられている。さらに、弁室１７の後端部からは
、低圧回路１０への連通路３４が設けられている。７は
ロッドである。The piston 2 has a large diameter portion 2a, a front small diameter portion 2b, and a rear small diameter portion 2C, and the difference in diameter forms a front liquid chamber 3 and a rear liquid chamber 4. The rear small diameter portion 2C has a smaller diameter than the front small diameter portion 2b, and therefore, in the piston 2, the pressure receiving area on the rear liquid chamber 4 side is larger than the pressure receiving area on the front liquid chamber 3 side. The front liquid chamber 3 is connected to the liquid pressure source 1) by a high-pressure circuit 6. The valve plug 12 fitted at the rear of the cylinder 1 has a smaller outer diameter at the front, and a cylindrical switching valve 5 is placed concentrically with the piston 2 between the outer circumference and the inner circumference of the cylinder 1. A valve chamber 17 into which the valve chamber 17 is slidably fitted is formed. FIG. 2 is an enlarged sectional view of the vicinity of the valve chamber 17. The valve chamber 17 includes a high pressure port 13 and a low pressure port 1 located in front of the high pressure port 13.
4, the high pressure port 13 is connected to the hydraulic pressure tX1) by the high pressure circuit 6, and the low pressure port 14 is connected to the tank 15 by the low pressure circuit 10. 21 is an accumulator. A liquid supply/drainage chamber 18 is provided in the valve chamber 17 and communicated with the rear liquid chamber 4 through a liquid supply/drainage hole 16. A liquid supply hole 19 that communicates with the liquid supply and drain chamber 18 and a liquid drain hole 20 that communicates the low pressure port 14 with the liquid supply and drain chamber 18 in the retracted position are bored. The front part of the switching valve 5 is stepped and has a small diameter, and a valve retreat liquid chamber 22 and a valve control liquid chamber 23 are formed before and after the front part. A valve switching passage 24 is provided between the rear liquid chamber 4 and the valve retreating liquid chamber 22, and the valve switching passage 24 is opened and closed by the large diameter portion 2a of the piston 2 as the piston 2 moves back and forth.
and the rear liquid chamber 4 are communicated with each other via a retreat hole 25 provided in the switching valve 5. The front liquid chamber 3 is provided with a control port 28 that is opened and opened by the large diameter portion 2a of the piston 2 as the piston 2 moves back and forth, and the control port 28 and the valve control liquid chamber 23 form a valve control passage. 26, the valve control liquid chamber 23
and the front liquid chamber 3 are communicated with each other via a control hole 27 provided in the switching valve 5. A variable throttle 30 is interposed in the valve control passage 26, and the flow rate of the valve control passage 26 can be varied steplessly. The valve control passage 26 is provided with a maximum stroke regulation bypass 31 that connects the downstream side of the variable throttle 30 and a regulation port 29 provided behind the control port 28 . The large diameter portion 2a of the piston 2 is provided with a regulation port 29 and a communication passage 32 from the front end of the valve chamber 17 communicating with the low pressure circuit 1O when the piston 2 is in the forward position, and a communication passage 32 from the front end of the valve chamber 17 is connected to the low pressure circuit lO when the piston 2 is in the backward position. Communication path 3 from the front end of 17
2 and the valve switching passage 24 to the low pressure circuit IO.
3 is provided. Furthermore, a communication path 34 is provided from the rear end of the valve chamber 17 to the low pressure circuit 10. 7 is a rod.
次に、動作を説明する。Next, the operation will be explained.
切換弁５が前方にある状態では、排液孔２０が閉じ給液
孔１９が開いているので、後部液室４と前部液室３とは
、共に高圧回路に連通ずる。このとき、ピストン２の後
部液室４側の受圧面積が、前部液室３側の受圧面積より
大であるから、ピストン２は、ロアドア方向へ前進する
。ピストン２か前進すると弁切換通路２４が開き、後部
液室４と弁後退液室２２とが連通されて高圧液が弁後退
液室２２へ流入する。弁制御液室２３は、弁制御通路２
６．規制ポート２９．ピストン大径部２ａの′ａ３３を
経て低圧回路ｌＯへ連通するので、切換弁５は後退する
。When the switching valve 5 is in the front, the liquid drain hole 20 is closed and the liquid supply hole 19 is open, so that both the rear liquid chamber 4 and the front liquid chamber 3 communicate with the high pressure circuit. At this time, since the pressure receiving area of the piston 2 on the rear liquid chamber 4 side is larger than the pressure receiving area on the front liquid chamber 3 side, the piston 2 moves forward toward the lower door. When the piston 2 moves forward, the valve switching passage 24 opens, the rear liquid chamber 4 and the valve retracting liquid chamber 22 are communicated with each other, and high pressure liquid flows into the valve retracting liquid chamber 22. The valve control liquid chamber 23 is connected to the valve control passage 2
6. Regulated port 29. Since it communicates with the low pressure circuit 1O via 'a33' of the piston large diameter portion 2a, the switching valve 5 is moved backward.
切換弁５が後退すると、給液孔１９が閉じ、排液孔２０
が開くため、後部液室４は低圧回路１０に連通ずる。ピ
ストン２はロッド７を打撃して前進を停止し、後部液室
４が低圧となっているため後退を始める。ピストン２が
後退すると、制御ボー）２８．規制ポート２９は順次前
部液室３と連通ずる。制御ポート２８をピストン２の大
径部２ａが通過すると、弁制御通路２６を経て弁制御液
室２３と前部液室３とが連通し、高圧液が弁制御液室２
３に流入する。弁後退液室２２は、弁室１７の前端部か
らの連通路３２を経て低圧回路１０へ連通されているの
で、切換弁５は前進を開始する。When the switching valve 5 retreats, the liquid supply hole 19 closes and the liquid drain hole 20 closes.
is opened, so that the rear liquid chamber 4 communicates with the low pressure circuit 10. The piston 2 hits the rod 7 and stops moving forward, and since the pressure in the rear liquid chamber 4 is low, it starts moving backward. When the piston 2 retreats, the control bow)28. The regulation port 29 sequentially communicates with the front liquid chamber 3. When the large diameter portion 2a of the piston 2 passes through the control port 28, the valve control liquid chamber 23 and the front liquid chamber 3 communicate with each other through the valve control passage 26, and the high pressure liquid flows into the valve control liquid chamber 2.
3. Since the valve retreat liquid chamber 22 is communicated with the low pressure circuit 10 via the communication path 32 from the front end of the valve chamber 17, the switching valve 5 starts moving forward.
切換弁５が前進すると排液孔２０を閉じ、給液孔１９を
開いて高圧回路６と後部液室４と連通させる。高圧回路
６と後部液室４とが再び連通されると後部液室４の圧力
が上昇し、慣性のために後退を続けようとするピストン
２は制動を受け、ピストン２の持つ運動エネルギーが高
圧液の形でアキュムレータ２１に蓄積される。ピストン
２の運動エネルギーが回収されるとピストン２は後退を
停止し、再び前進行程に入り同様のサイクルが繰返され
る。ここで、弁制御通路２６の可変絞り３０を調整する
と、制御ポート２８から弁制御通路２６を通って弁制御
液室２３へ流入する圧液の流量を無段階に変化させるこ
とができるため、切換弁５の前進移動速度は任意に制御
可能である。流量大で切換弁５の移動速度が天であれば
、ピストン２は早く制動反転してストロークが短かく、
流量を絞ればストロークが長くなるので、可変絞り３０
を調整することによりビストンストロークを連続的に変
化させることができる。最大ストローク規制用バイパス
３１は、可変絞り３０で流量を絞りすぎ、ビストンスト
ロークが適長になるとロッド７に過大なストレスを生起
させたり、ピストン２後部の衝突による事故を生したり
する虞れがあるため、規制ポート２９をピストン２の大
径部２ａが通過した後は弁制御通路２６の流量を増加さ
せ最大ストロークを規制するものである。When the switching valve 5 moves forward, the liquid drain hole 20 is closed and the liquid supply hole 19 is opened to communicate with the high pressure circuit 6 and the rear liquid chamber 4. When the high pressure circuit 6 and the rear liquid chamber 4 are communicated again, the pressure in the rear liquid chamber 4 increases, and the piston 2, which tries to continue retreating due to inertia, is braked, and the kinetic energy of the piston 2 is transferred to the high pressure It is accumulated in the accumulator 21 in liquid form. When the kinetic energy of the piston 2 is recovered, the piston 2 stops moving backward and starts moving forward again, repeating the same cycle. Here, by adjusting the variable throttle 30 of the valve control passage 26, the flow rate of the pressure liquid flowing from the control port 28 through the valve control passage 26 into the valve control liquid chamber 23 can be changed steplessly. The forward movement speed of the valve 5 can be controlled arbitrarily. If the flow rate is large and the switching valve 5 moves at a high speed, the piston 2 will reverse braking quickly and the stroke will be short.
If you reduce the flow rate, the stroke will become longer, so the variable orifice 30
By adjusting the piston stroke, the piston stroke can be changed continuously. If the maximum stroke regulating bypass 31 restricts the flow rate too much with the variable throttle 30 and the piston stroke becomes an appropriate length, there is a risk of causing excessive stress on the rod 7 or causing an accident due to a collision at the rear of the piston 2. Therefore, after the large diameter portion 2a of the piston 2 passes through the regulation port 29, the flow rate of the valve control passage 26 is increased to regulate the maximum stroke.
上述の如く、この発明の液圧式打撃装置のストローク可
変機構は、弁制御通路に可変絞りを介設して切換弁の移
動速度を無段階制御可能としたためピストンの制動反転
時期が任意に設定でき、ビストンストロークは連続的に
変更することができる。従って、岩質等の作業条件の変
化に対応して最適のストロークを与えることが可能であ
り、液圧式打撃装置の作業能率を向上することができる
。As mentioned above, the variable stroke mechanism of the hydraulic impact device of the present invention has a variable throttle in the valve control passage to enable stepless control of the moving speed of the switching valve, so that the braking reversal timing of the piston can be set arbitrarily. , the piston stroke can be changed continuously. Therefore, it is possible to provide an optimal stroke in response to changes in working conditions such as rock quality, and the working efficiency of the hydraulic striking device can be improved.
第１図は、この発明の一実施例である液圧式打撃装置の
ストローク可変機構の縦断面図、第２図は、弁室付近の
拡大断面図である。
図中、１はシリンダ、２はピストン、３は前部液室、４
は後部液室、５は切換弁、６は高圧回路、１０は低圧回
路、１２はバルブプラグ、１７は弁室、２３は弁制御液
室、２６は弁制御通路、２８は制御ポート、３０は可変
絞り、３１は最大ストローク規制用バイパスである。FIG. 1 is a longitudinal sectional view of a variable stroke mechanism of a hydraulic impact device according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of the vicinity of a valve chamber. In the figure, 1 is the cylinder, 2 is the piston, 3 is the front liquid chamber, 4
is a rear liquid chamber, 5 is a switching valve, 6 is a high pressure circuit, 10 is a low pressure circuit, 12 is a valve plug, 17 is a valve chamber, 23 is a valve control liquid chamber, 26 is a valve control passage, 28 is a control port, 30 is a The variable throttle 31 is a bypass for regulating the maximum stroke.
Claims (2)
摺嵌して前部液室と後部液室とを形成し、少くとも一方
の液室を切換弁で高圧と低圧とに切換えてピストンを往
復動させる液圧式打撃装置において、ピストンの往復動
に伴って開閉される制御ポートと弁制御液室とを連通さ
せる弁制御通路を設け、該弁制御通路に可変絞りを介設
したことを特徴とする液圧式打撃装置のストローク可変
機構。(1) A piston having a small diameter portion at the front and rear is slid into the cylinder to form a front liquid chamber and a rear liquid chamber, and at least one liquid chamber is switched between high pressure and low pressure with a switching valve, and the piston In a hydraulic impact device that reciprocates a piston, a valve control passage is provided that communicates a control port that is opened and closed with the reciprocation of a piston and a valve control liquid chamber, and a variable throttle is interposed in the valve control passage. The variable stroke mechanism of the hydraulic impact device features a variable stroke mechanism.
えてなる特許請求の範囲第１項記載の液圧式打撃装置の
ストローク可変機構。(2) The variable stroke mechanism for a hydraulic impact device according to claim 1, wherein the valve control passage is provided with a maximum stroke regulating bypass.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14731884A JPS6125784A (en) | 1984-07-16 | 1984-07-16 | Stroke variable mechanism of hydraulic type striking device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14731884A JPS6125784A (en) | 1984-07-16 | 1984-07-16 | Stroke variable mechanism of hydraulic type striking device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS6125784A true JPS6125784A (en) | 1986-02-04 |
| JPS6362355B2 JPS6362355B2 (en) | 1988-12-02 |
Family
ID=15427470
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP14731884A Granted JPS6125784A (en) | 1984-07-16 | 1984-07-16 | Stroke variable mechanism of hydraulic type striking device |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS6125784A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5415797A (en) * | 1991-11-06 | 1995-05-16 | Nippon Paint Co., Ltd. | Degreasing solution and degreasing method |
| JP2000037661A (en) * | 1998-07-23 | 2000-02-08 | Hitachi Constr Mach Co Ltd | Excitation apparatus |
| JP2009527370A (en) * | 2006-02-20 | 2009-07-30 | アトラス コプコ ロツク ドリルス アクチボラグ | Impact device and rock drill including the impact device |
| WO2018003668A1 (en) * | 2016-06-28 | 2018-01-04 | 古河ロックドリル株式会社 | Two-piston hydraulic striking device |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH04106249U (en) * | 1991-02-22 | 1992-09-14 | 株式会社吉野工業所 | liquid pouring container |
| JP2009019463A (en) * | 2007-07-13 | 2009-01-29 | Okumura Corp | Drill with guide rod |
-
1984
- 1984-07-16 JP JP14731884A patent/JPS6125784A/en active Granted
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5415797A (en) * | 1991-11-06 | 1995-05-16 | Nippon Paint Co., Ltd. | Degreasing solution and degreasing method |
| JP2000037661A (en) * | 1998-07-23 | 2000-02-08 | Hitachi Constr Mach Co Ltd | Excitation apparatus |
| JP2009527370A (en) * | 2006-02-20 | 2009-07-30 | アトラス コプコ ロツク ドリルス アクチボラグ | Impact device and rock drill including the impact device |
| WO2018003668A1 (en) * | 2016-06-28 | 2018-01-04 | 古河ロックドリル株式会社 | Two-piston hydraulic striking device |
| JPWO2018003668A1 (en) * | 2016-06-28 | 2019-04-18 | 古河ロックドリル株式会社 | 2-piston type hydraulic impact device |
| US11072977B2 (en) | 2016-06-28 | 2021-07-27 | Furukawa Rock Drill Co., Ltd. | Two-piston hydraulic striking device |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6362355B2 (en) | 1988-12-02 |
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