SHOCK ABSORBING DEVICE FOR HYDRAULIC CYLINDER

Abstract: A shock absorbing device for a hydraulic cylinder including a shock absorbing hole (4) formed in an end wall (2) of cylinder, a passageway (6) having a port (5) opening in the shock absorbing hole at its inner peri­ pheral surface (5A) and a shock absorbing member (13) attached to the piston (11) and aligned with the shock absorbing hole so that it enters the hole during shock absorbing stroke. The shock absorbing member (13) throttles the flow of fluid in the hole (4) to perform a first stage shock absorption and then throttle the flow of fluid through the port (5) to perform a second stage shock absorption.

Description: SHOCK ABSORBING DEVICE FOR HYDRAULIC CYLINDER BACKGROUND OF THE INVENTION This invention relates to a shock absorbing device for a hydraulic cylinder capable of imparting to a piston the function of absorbing the force of shocks in a plurality of stages at the terminating portion of a stroke of the piston of the hydraulic cylinder. In the majority of hydraulic cylinders operated hydraulically, it is usual practice to move the piston rod assembly at high speed to increase operation efficiency. The piston rod assembly moving at high speed has high kinetic energy, so that it is necessary to provide means for absorbing high energy of inertia to bring same to a halt at the end of its stroke. If the piston rod assembly were allowed to impinge on the end wall of the' cylinder when it is brought to a halt, a high force of impact would be exerted on the end wall to thereby cause considerable damage thereto. Thus a shock absorbing device for absorbing the energy of inertia possessed by the piston rod assembly has been provided to absorb the force of shocks at the end of the stroke of the piston. One type of shock absorbing device known in the art is disclosed in Japanese Patent Application Laid-Open No. 35478/72 (corresponding to US Application serial No. 128,822). This shock absorbing device comprises a cylindrical shock absorbing port formed in the end wall of the cylinder housing in a manner to extend axially and communicating at one end with the cylinder chamber and at the other end with a suction and exhaust passageway, and a cylindrical shock absorbing member mounted on the piston and adapted to be inserted in the shock absorbing port at the end of the stroke of the piston to reduce the area of the channel in the shock absorbing port. The device functions such that high resistance is offered to a stream of working fluid discharged, in the terminating stages of the stroke of the piston, from the cylinder chamber through the shock absorbing port by the piston as the shock absorbing member enters the shock absorbing port, to thereby restrict the flow rate of the discharged fluid to impart a shock absorbing function to the piston. Some disadvantages are associated with this device of the prior art. First, the effectiveness of the shock absorbing function may vary depending on the relation between the length of the cylindrical portion of the cylindrical shock absorbing member and the length of the shock absorbing port. To increase the shock absorbing function would require an increase in the lengths. This however, would increase the overall length of the cylinder. Conversely, in the case of a cylinder of restricted cylinder length, it would be necessary to forgo the benefit of shock absorbing function. Secondly, the shock absorbing device of the prior art has a shock absorbing characteristic such that the instant the shock absorbing member enters the shock absorbing port, deceleration of very high order would take place in the piston and no great deceleration would occur thereafter. Stated differently, the device would only perform a shock absorbing function or energy absorbing function in a single stage. Thus a very high force of impact would be exerted on the hydraulic cylinder the instant the shock absorbing member enters the shock absorbing port, and a high force of impact would be applied to the end wall of the cylinder housing when the piston impinges thereon when it is brought to a' halt. Thirdly, the provision of the axially extending shock absorbing port and the suction and discharge passageway communicating with the end portion of the shock absorbing member in the end wall of the cylinder housing would increase the axial length of the end wall of the cylinder housing. Fourthly, it is only in the annular throttling passageway defined between the inner peripheral surface of the shock absorbing port and the outer peripheral surface of the shock absorbing member that the shock absorbing function is performed, so that the clearance between the inner and outer peripheral surfaces constituting the throttling passageway would exert great influences on the shock absorbing performance. Thus it would become necessary to increase the precision with which working and assembling are performed, which would be troublesome. SUMMARY OF THE INVENTION This invention has been developed for the purpose of obviating the aforesaid disadvantages of the prior art. Accordingly, one of the objects of the invention is to provide a shock absorbing device for a hydraulic cylinder which is free from the defects of the shock absorbing device for a hydraulic cylinder of the prior art described in the background of the invention. Another object of the invention is to provide a shock absorbing device for a hydraulic cylinder operative to absorb the energy of inertia of the piston assembly at least in two stages. According to the invention, there is provided, in a hydraulic cylinder comprising a housing including a cylindrical side wall and at least one end wall, and a piston assembly including a piston slidably arranged in the housing for axial sliding movement for cooperating with the housing to define therein a working space, a shock absorbing device comprising means for defining a shock absorbing hole formed in the end wall and extending axially of the housing, passageway means communicating with the shock absorbing hole, and a shock absorbing member mounted on the piston assembly in a manner to align with the shock absorbing hole and adapted to enter the shock absorbing hole in terminating stages of a stroke of the piston to throttle the flow of fluid in the shock absorbing hole, characterized in that said passageway means comprises a port opening in the shock absorbing hole at its inner peripheral surface defining the hole, said port being located in a position in which the area of its opening is reduced by the shock absorbing member. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view of a hydraulic cylinder incorporating therein the shock absorbing device comprising one embodiment of the invention; Figs. 2 and 3 are sectional views showing, on an enlarged scale, the shock absorbing device of Fig. 1 mounted on the head cover side with the piston located in different operation positions; Fig. 4 is a sectional view showing, on an enlarged scale, the shock absorbing device of Fig. 1 mounted on the head cover side; Fig. 5 is a diagrammatic representation of the shock absorbing characteristic of the embodiment shown in Figs. 2 and 3; Figs. 6 and 7 are sectional views of the shock absorbing device comprising another embodiment, shown as mounted on the head cover side with the piston located in different operation positions; ; Fig. 8 is a graph showing the piston speed and the head cover acceleration in the shock absorbing stroke of the embodiment shown in Figs. 6 and 7; Fig. 9 is a diagrammatic representation of the pressure characteristic of the embodiment shown in Figs. 6 and 7 exhibited in the shock absorbing stroke; Fig. 10 is a graph showing the piston speed and the head cover acceleration of a shock absorbing device of the prior art in the shock absorbing stroke; Fig. 11 is a sectional view of the shock absorbing device comprising still another embodiment mounted on the rod cover side similar to the embodiment shown in Figs. 6 and 7; Figs. 12 and 13 are sectional views of modifications of the embodiment shown in Fig. 6; ; Figs. 14 and 15 are sectional views of the shock absorbing device comprising still another embodiment mounted on the head cover side with the piston located in different operation positions; Fig. 16 is a sectional view of the shock absorbing device comprising still another embodiment mounted on the rod cover side similar to the embodiment shown in Figs. 14-15; Figs. 17-19 are sectional views of the shock absorbing device comprising still another embodiment mounted on the head cover side with the piston located in different operation positions; Fig. 20 is a graph showing the piston speed and the head cover acceleration of the embodiment shown in Figs. 17-19 in the shock absorbing stroke; Fig. 21 is a sectional view of the shock absorbing device comprising a further embodiment mounted on the rod cover side similar to the embodiment shown in Figs. 17-19; and Figs. 22 and 23 are sectional views of modifications of the embodiments shown in Figs. 17-19. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 1, the hydraulic cylinder comprises a cylinder housing including a cylinder 1 and a head cover 2 and rod cover 3 secured to opposite ends of the cylinder 1. The head cover 2 is formed therein with a shock absorbing hole 4 adapted to receive therein a shock absorbing member subsequently to be described, a port 5 opening in the shock absorbing hole 4 at its side, and a supply and discharge passageway 6 communicating with the port 5. Likewise, the rod cover 3 is formed therein with a shock absorbing hole 7, a port 8 and a supply and discharge passageway 9. The rod cover 3 guides a rod 10 for sliding movement, and the rod 10 has a piston 11 defining hydraulic chambers A and B in the cylinder 1 in which it is slidably fitted. A nut 12 for securing the piston 11 to the rod 10 and the shock absorbing member 13 are located at an end surface of the piston 11 on the head cover 2 side, and another shock absorbing member 14 is located at an end surface of the piston 11 in contact therewith. V j The shock absorbing members 13 and 14 may be in the form of shock absorbing plungers formed integrally with the rod 10 or piston 11. Alternatively, shock absorbing rings held by the rod 10 through rubber rings may be used. As shown on an enlarged scale in Figs. 2 and 3, the shock absorbing hole 4 includes a cylindrical inner peripheral surface 4A at which the port 5 opens in the shock absorbing hole 4. Meanwhile, the shock absorbing member 13 is aligned with the shock absorbing hole 4 and has a cylindrical outer peripheral surface 13A of an outer diameter slightly smaller than the diameter of the inner peripheral surface 4A. Thus, as the shock absorbing member 13 is received in the shock absorbing hole 4, a minuscule annular gap or throttle passageway C is defined between the inner peripheral surface 4A of the shock absorbing hole 4 and the outer peripheral surface 13A of the shock absorbing member 13. The port 5 is positioned such that, as shown in Fig. 3, it is closed by the outer peripheral surface 13A of the shock absorbing member 13 at the end of a stroke of the piston 11. Likewise, as shown in Fig. 4, the shock absorbing hole 7 formed in the rod cover 3 includes a cylindrical inner surface 7A, and the shock absorbing member 14 includes a cylindrical outer peripheral surface 14A. The outer peripheral surface 14A of the shock absorbing member 14 cooperates with the inner peripheral surface 7A of the shock absorbing hole 7 to define therebetween an annular gap D and closes the port 8. Operation of the shock absorbing device shown and described hereinabove will be described. Upon a pressure fluid being fed into the chamber B from the supply and discharge passageway 9 via the port 8, the piston 11 moves rightwardly in the figure at high speed in a compression stroke and enters a shock absorbing stroke, in which the forward end of the shock absorbing member 13 enters the shock absorbing hole 4 to define the annular throttle passageway C between the inner peripheral surface 4A of the shock absorbing hole 4 and the outer peripheral surface 13A of the shock absorbing member 13. This throttles the flow of the pressure fluid from the chamber A to the supply and discharge passageway 6 via the shock absorbing hole 4, so that a high pressure prevails in the chamber A to offer high resistance to the movement of the piston 11. At the same time, the resistance offered by the flow of the pressure fluid through the throttle passageway C is conducive to rapid deceleration of the piston 11. This condition is represented in Fig. 5 by a curve PP'. Then a shock absorbing function mainly attributed to resistance to the flow offered by the throttle passageway C is performed, and the piston 11 shows slow deceleration as indicated by a curve P'Q. During this shock absorbing operation, the shock absorbing member 13 continues its movement into the shock absorbing hole 4 and the length of the annular throttle passageway C increases with an attendant increase in the resistance offered thereby to the flow of the pres sure fluid. However, the deceleration of the piston 11 is not so high. A position represented by Q in Fig. 5 is a position (shown in Fig. 2) in which the forward end of the shock absorbing member 13 is positioned against the port 5. Further movement of the shock absorbing member 13 into the shock absorbing hole gradually reduces the area of the opening of the port 5 as it is closed by the outer peripheral surface 13A of the shock absorbing member 13. This creates a high resistance offered to the pressure fluid as it flows through the port 5 into the supply and discharge passageway 6 from a space 4B in the hole 4 after it has flown through the annular throttle passageway C into the space 4B, to thereby decelerate the piston 11. The flow resistance offered by the port 5 grows by leaps and bounds as the area of the opening of the port 5 is reduced, so that the piston 11 shows a rapid deceleration as indicated by a curve QR in Fig. 5. A point R shown in Fig. 5 is a point at which the outer peripheral surface 13A of the shock absorbing member 13 fully closes the port 5 (as shown in Fig. 3) immediately before the piston 11 reaches the end of the stroke. Thereafter the piston assembly reaches the end of the stroke and abuts against the end wall of the cylinder 1, thereby being brought to a halt (as represented by a point T in Fig. 5). As described hereinabove, in this embodiment, it is possible to decelerate the piston 11 until its speed is reduced to a very low level by a shock absorbing operation performed in two stages, shock absorption in the first stage being performed by the action of the throttle passageway C (represneted by a curve PQ) and shock absorption in the second stage being performed by the throttling action of the passageway C and the port 5 (represented by the curve QR). Meanwhile, in the shock absorbing device of the prior art described hereinabove, shock absorption is performed only by the throttling action of the throttle passageway C. Thus the piston speed is reduced as indicated by a curve PQS. As a result, the piston still has high speed when it reaches the end of its stroke and a high force of impact is produced at the end of its stroke. To reduce the speed of the piston satisfactorily at the end of its stroke, one has only to reduce the gap between the shock absorbing member and the shock absorbing hole or the width of the throttle passageway C and increase its length. This would entail an increase in the overall length of the cylinder and make it necessary to increase the precision with which machining and assembly of the parts are performed. The shock absorbing device of the prior art incorporating therein the aforesaid improvements has a shock absorbing characteristic such that the speed is reduced abruptly as indicated by a dash-and-dot line PR in Fig. 5. Thus, it will be appreciated that the embodiment of the present invention is superior to the device of the prior art in that a better shock absorbing characteristic is obtained without requiring to increase the precision of machining and assembling of the parts and to increase the length of the cylinder. The aforesaid description refers to the shock absorbing device mounted on the head cover 2 side. The shock absorbing device mounted on the rod cover 3 side operates in like manner, so that the description thereof shall be omitted. In the embodiment shown and described hereinabove, the inner peripheral surface of the shock absorbing hole and the outer peripheral surface of the shock absorbing member are both cylindrical in shape. However, the invention is not limited to this specific shape and one or both of them may be tapering. The use of a tapering inner peripheral surface and/or an outer peripheral surface causes a reduction in the cross-sectional area of the annular gap C or D defined therebetween as the shock absorbing member progressively enters the shock absorbing hole, thereby increasing the shock absorbing effect. Figs. 6 and 7 show an embodiment distinct from the embodiment shown in Figs. 2 and 3. In Figs. 6 and 7, parts similar to those shown in Figs. 2 and 3 are designated by like reference characters and their description is omitted. In this embodiment also, a shock absorbing hole 21 having a cylindrical inner peripheral surface 21A is formed in the head cover 2, and a port 23 of a suction and discharge passageway 22 opens in the shock absorbing hole 21 at the inner peripheral surface 21A. Meanwhile the shock absorbing member 13 has a cylindrical outer peripheral surface 13A cooperating with the inner peripheral surface 21A of the shock absorbing hole 21 to define therebetween an annular throttle passageway C and operating to close the port 23. In this embodiment, -the shock absorbing hole 21 extends farther than the port 23 to form a back pressure chamber 24, and the shock absorbing member 13 is constructed such that, as shown in Fig. 7, the forward end of the cylindrical outer peripheral surface 13A moves past the port 23 to enter the back pressure chamber 24 at the end of a stroke of the piston and cooperates with the inner peripheral surface 21A of the shock absorbing hole 21 to define adjacent and posterior to the port 23 a minuscule annular gap or annular throttle passageway E. The annular throttle passageway E functions such that when the shock absorbing member 13 enters the back pressure chamber 24, the pressure fluid in the latter is restricted in its flow to the port 23 to thereby generate a pressure in the back pressure chamber 24. In operation, as the piston 11 progressively moves rightwardly in Fig. 6, the shock absorbing member 13 enters the shock absorbing hole 21. Flow of the pressure fluid from the chamber A to the port 23 is suddenly restricted by the throttle passageway C, to perform shock absorption of the first stage. Further movement of the shock absorbing member 13 into the shock absorbing hole 21 results in gradual reduction in the opening of the port 23 as it is closed by the outer peripheral surface 13A of the shock absorbing member 13, thereby perform shock absorption of the second stage. The shock absorbing member 13 continues its movement into the shock absorbing hole 21 even after the former has fully closed the port 23, to generate a high pressure in the back pressure chamber 24, which offers resistance to the movement of the shock absorbing member 13 into the shock absorbing hole 21. Combined with the resistance offered by the high pressure in the back pressure chamber 24, the resistance offered by the throttle passageway E to the flow of the pressure fluid from the back pressure chamber 24 through the throttle passageway E to the port 23 performs shock absorption of the third stage. Thus the shock absorbing device of the embodiment in conformity with the invention performs shock absorption in three stages. Figs. 8 and 9 are graphs showing shock absorbing characteristics of the embodiment shown in Figs. 6 and 7 as actually measured. In Fig. 8, a curve (a) represents a change in piston speed, and points i, ii, iii and iv indicate positions in which shock absorption is initiated immediately before the shock absorbing member 13 enters the shock absorbing hole 21, the shock absorbing member 31 begins to close the port 23 of the suction and discharge passageway 22, the shock absorbing member 13 has completely closed the port 23 and the piston 11 has reached the end of its stroke, respectively. Meanwhile, a curve (2) represents a change in the acceleration of the head cover 2. In Fig. 9, P1, P2, P3 and P4 represent the internal pressure of the hydraulic chamber B (see Fig. 1), the internal pressure of the hydraulic chamber A, the internal pressure of the back pressure chamber 24 and the internal pressure of the supply and discharge passageway 22 (see Fig. 7) respectively. In the graphs shown in Figs. 8 and 9, a section i - ii represents a first stage shock absorption in which the internal pressure P2 of the chamber A gradually rises and offers resistance to the piston 11 while the latter is decelerated by the throttling action of the throttle passageway C. A section ii - iii represents a second stage shock absorption in which in addition to the aforesaid shock absorption, the port 23 of the suction and discharge passageway 22 is gradually throttled and the piston is decelerated. A section iii - iv represents a third stage shock absorption in which, following full closure of the port 23, the back pressure P3 is produced in the back pressure chamber 24 to decelerate the piston 11. Fig. 10 is a graph showing the data obtained with the shock absorbing device of the prior art relying on the throttle passageway alone for effecting-shock absorption. As shown, a curve (a) represents a change in the speed of the piston, and a curve (b) indicates a change in the acceleration of the head cover 2. In Fig. 10, it will be seen that in the shock absorbing device of the prior art, shock absorption is performed only in one stage and that even at the end of a shock absorbing operation, the piston 11 still has a substantial speed as indicated at a point X The piston 11 is brought to a halt at the end of its stroke by impinging on the head cover 2, so that a high force of impact is exerted on the head-cover 2 and high acceleration is generated in the head cover 2 as indicated at a point Y. On the other hand, in the embodiment shown in Figs. 6 and 7, smooth deceleration of the piston 11 can be obtained as shown in Fig. 8 and a good shock absorbing characteristic is exhibited. The change in the acceleration of the head cover 2 is almost nil as indicated by the curve (b), indicating that no high force of impact is exerted thereon. Fig. 11 shows a modification of the shock absorbing device mounted on the rod cover 3 side. In the figure, the cylindrical outer peripheral surface 14A of a shock absorbing member 14 extends beyond V V - a port 32 opening in a shock absorbing hole 31 at its inner peripheral surface 31A into a back pressure chamber 33, to define annular throttle passageways D and F on opposite sides of the port 32. Like the embodiment shown in Figs. 6 and 7, the embodiment shown in Fig. 11 performs shock absorption in three stages. In the embodiments shown in Figs. 6, 7 and 11, the shock absorbing hole and the shock absorbing member have cylindrical inner and outer peripheral surfaces respectively. However, the invention is not limited to this form of the shock absorbing hole and member, one or both of the shock absorbing hole and member may be tapering in form. Fig. 12 shows a modification of the embodiment shown in Figs. 6 and 7. This modification has a tapering groove 41 formed in a portion of the cylindrical outer peripheral surface 13A of the shock absorbing member 13 facing the port 23. The tapering groove 41 has a progressively increasing depth in going toward the forward end of the shock absorbing member 13. Thus as the shock absorbing member 13 enters the shock absorbing hole 21 and closes the port 23, the tapering groove 41 provides a channel for the pressure fluid to flow to the port 23, thereby avoiding sudden deceleration of the piston. The depth of the tapering groove 41 is reduced as the shock absorbing member 13 enters the shock absorbing hole 21, so that the throttling effect increases and a good deceleration characteristic a can be exhibited. Moreover, when the piston moves from its position shown in Fig. 12 leftwardly as pressure fluid is supplied through the supply and discharge passageway, pressure fluid is immediately supplied from the port 23 through the tapering groove 41 to the back pressure chamber 24. As compared with the embodiment shown in Figs. 6 and 7 in which pressure fluid is supplied to the back pressure chamber 24 through the throttle passageway E alone, the embodiment shown in Fig. 12 is capable of quickly and smoothly effecting movement of the shock absorbing member 13, out of the shock absorbing hole 21. Fig. 13 shows an embodiment which comprises, in addition to the parts of the embodiment shown in Figs. 6 and 7, a first ancillary passageway mounting a check valve 42 allowing pressure fluid to flow from the supply and discharge passageway 22 to the chamber A, and a second ancillary passageway mounting a check valve 43 allowing pressure fluid to flow from the supply and discharge passageway 22 to the back pressure chamber 24. In this embodiment also, the pressure fluid from the suction and discharge passageway 22 is fed into the chamber A and the back pressure chamber 24 through the check valves 42 and 43 respectively when the pressure fluid is supplied from the supply and discharge passageway 22 and the piston 11 has moved into an expansion stroke, to thereby enable movement of the shock absorbing member 12 out of the hole 21 to be smoothly effected. Figs. 14 and 15 show a still another embodiment in which a shock absorbing hole 50 is defined by a cylindrical inner peripheral surface 50A and a tapering inner peripheral surface 50B extending beyond the port 23 and a back pressure chamber 51 is defined by a tapering inner peripheral surface 50B. Meanwhile the shock absorbing member 13 has a cylindrical outer peripheral surface 13A of a length Lc substantially equal to the length Lt of a cylindrical inner peripheral surface 50A and a tapering outer peripheral surface 13B at the forward end of the former. The tapering outer peripheral surface 13B operates in such a manner that it enters the back pressure chamber 51 and cooperates with the tapering inner peripheral surface 50B to define between the surfaces 13B and 50B an inclined annular gap or throttle passageway G. In operation, the rightward movement of the piston 11 causes the shock absorbing member 13 to enter the shock absorbing hole 50, to allow the throttle passageway G to perform a first stage shock absorption. The first stage shock absorption. lasts while the cylindrical outer peripheral surface 13A of the shock absorbing member 13 moves in a stroke covering the distance corresponding to the length Ls of the throttle passageway. Then as the shock absorbing member 13 further moves, the area of the opening of the port 23 is gradually reduced by the cylindrical outer peripheral surface 13A of the shock w v U v wr J J absorbing member 13, to thereby perform a second stage shock absorption. At the end of the second stage shock absorption, the tapering outer peripheral portion 13B of the shock absorbing member 13 enters the back pressure chamber 51 as shown in Fig. 15, to cause a back pressure to be generated therein. At the same time, the pressure fluid in the back pressure chamber 51 flows through the throttle passageway G into the port 23, so that resistance is offered by the passageway G to the flow of the pressure fluid. Thus, the shock absorbing action performed by the throttling of the port 23 gradually by the cylindrical outer peripheral portion 13A of the shock absorbing member 13 and the shock absorbing action performed by the back pressure in the back pressure chamber 51 and the throttle passageway G are set in motion simultaneously, to thereby bring about rapid deceleration of the piston 11. At this time, as the tapering outer periperal surface 13B,of the shock absorbing member 13 nears the tapering inner peripheral surface 50B of the shock absorbing hole 50, the cross-sectional area of the throttle passageway G shows a sudden reduction and the resistance offered to the flow of the pressure fluid therethrough rapidly increases. Thus a positive shock absorbing action can be performed to bring the piston 11 to a halt. The tapering surfaces 13B and SOB defining the throttle passageway G may be parallel to each other or angles of inclination a and may be equal to each other as shown in Fig. 14. However, the angle of inclination ss of the shock absorbing hole 50 is preferably greater than the angle of inclination a of the shock absorbing member 13. When a < ss, a thin blade orifice can be formed between the forward end of the tapering outer peripheral surface 13B of the shock absorbing member 13 and the tapering inner peripheral surface 50B of the shock absorbing hole 50, so that it is possible to offer resistance to the pressure fluid flowing through the orifice without the fluid being influenced much by the temperature and viscosity of the fluid. Fig. 16 shows an embodiment in which the same concept as incorporated in the embodiment shown in Figs. 14 and 15 is incorporated in a shock absorbing device mounted on the rod cover side. In this embodiment, a tapering inner peripheral surface 60B is formed in a portion of a shock absorbing port 60 extending beyond a port 32. The operation of this embodiment is similar to that of the embodiment shown in Fig. 14, so that detailed description shall be omitted. Figs. 17, 18 and 19 show still another embodiment in which, as in the embodiment shown in Fig. 6, the shock absorbing member 13 has a cylindrical outer peripheral surface 13A and a tapering outer peripheral surface 13B, while a shock absorbing hole 70 has a cylindrical inner peripheral surface 70A and 'J'J'J'J'tj V V \ t 2 o} a port 23 opening in the hole 70 at the cylindrical inner peripheral surface 70A. The shock absorbing hole 70 is additionally formed with an annular stepped portion 70C disposed beyond the inner peripheral surface 70A between it and an inner peripheral surface 70B of smaller diameter than the inner peripheral surface 70A, as distinct from the shock absorbing hole 21 shown in Fig. 6. The stepped portion 70C is located in a position spaced apart from the entrance of the shock absorbing hole' 70 a distance corresponding to the length Lc of the cylindrical portion of the shock absorbing member 13. In operation, as the cylindrical outer peripheral surface 13A of the shock absorbing member 13 enter., the shock absorbing hole 70, a throttle passageway C is defined between the cylindrical outer peripheral surface 13A and the inner peripheral surface 70A of the shock absorbing hole 70, so that the throttle passageway C performs a first stage shock absorption. This shock absorbing action lasts while the cylindrical outer peripheral surface 13A moves a distance corresponding to the length Ls of the throttle passageway C-. Further movement of the shock absorbing member 13 causes the cylindrical outer peripheral portion 13A to gradually close the opening of the port 23, to additionally perform a shock absorbing action by the throttling of the flow of the pressure fluid through the port 23, -to thereby perform a second stage shock absorption. Furthermore, as the cylindrical outer peripheral surface 13A of the shock absorbing member 13 moves past the opening of the port 23 as shown in Fig. 18, the forward end of the shock absorbing member 13 enters a back pressure chamber 71, to cause a back pressure to be generated therein. Thus the resistance offered to the flow of the pressure fluid by the back pressure in the back pressure chamber 71 and by the throttle passageway E perform a shock absorbing action, thereby setting in motion a third stage shock absorption. When further movement of the shock absorbing member 13 brings same to a position shown in Fig. 19, an annular orifice H is defined between the tapering outer peripheral surface 13B of the shock absorbing member 14 and the stepped portion 70C of the shock absorbing hole 70. Thus as the area of the orifice H is reduced, the back pressure in the back pressure chamber 71 rises because the latter is brought to a closed condition, to thereby offer increased resistance to the shock absorbing member 13. At the same time, the resistance offered to the flow of the pressure fluid from the back pressure chamber 71 to the throttle passageway E through the orifice H performs a shock absorbing action, thereby enabling a fourth stage or last stage shock absorption to be performed. As described hereinabove, in the embodiment shown in Figs. 17-19, shock absorption is carried out in four stages, to enable smooth deceleration of the piston 11 to be obtained. Fig. 20 shows the results of actual measurements of a change in the speed of the piston and a change in the acceleration of the head cover done in the embodiment shown in Figs. 17-19. In the figure, a curve (a) represents the speed of the piston, and a curve (b) indicates the acceleration of the head cover. As can be clearly seen in the figure, this embodiment enables smoother deceleration of the piston 11 to be obtained than the embodiment shown in Fig. 8. The concept of the embodiment shown in Figs. 17-19 can, of course, be incorporated in a shock absorbing device mounted on the rod cover 3 side. Fig. 21 shows an embodiment of this concept in the shock absorbing device mounted on the rod cover 3 side, in which a shock absorbing hole 80 has a cylindrical inner peripheral surface 80A of a major diameter, a cylindrical inner peripheral surface 80B of a minor diameter and a stepped portion 80C interposed therebetween. The stepped portion 80C operates in such a manner that a minuscule annular orifice is defined between the tapering outer peripheral surface 14B of the shock absorbing member 14 and the stepped portion 80C. In this embodiment also, shock absorption is performed in four stages, like the embodiment shown in Figs. 17-19. Figs. 22 and 23 show modifications of the embodiment shown in Fig. 17. Like the embodiment shown in Fig. 12, the modification shown in Fig. 22 is formed with a tapering groove 41 in the shock absorbing member 13. In the modification shown in Fig. 23, check valves 42 and 43 are mounted in first and second ancillary passageways, as in the embodiment shown in Fig. 13. In these modifications of the embodiment shown in Fig. 17, the advantage of being able to readily move the shock absorbing member 13 out of the hold is offered as described by referring to the embodiment shown in Figs. 12 and 13. While preferred embodiments of the invention have been shown and described hereinabove, it is to be understood that they are merely for purposes of illus tration and not limiting the scope of the invention. It will be apparent that various changes and modifi cations may be made therein without departing from the spirit and scope of the invention which is defined in the appended claims.

Claims: 'J'J'JLtj u u u u t v J WHAT IS CLAIMED IS: 1. In a hydraulic cylinder comprising a housing including a cylindrical side wall and at least one end wall, and a piston assembly including a piston slidably arranged in said housing for sliding axial movement for cooperating with the housing to define therein a working space, a shock absorbing device comprising: means for defining a shock absorbing hole formed in the end wall and extending axially of the housing; passageway means communicatinc with the shock absorbing hole; and a-shock absorbing member mounted on the piston assembly in a manner to be aligned with the shock absorbing hole and adapted to enter the shock absorbing hole in terminating stages of stroke of the piston to throttle the flow of fluid in the shock absorbing hole; characterized in that said passageway means comprises: a port (5, 8, 23, 32) opening in the shock absorbing hole (4, 7, 21, 31, 50, 60, 70, 80) at its inner peripheral surface defining the hole, said port being located in a position in which the area of its opening is reduced by the shock absorbing member (13, 14). 2. A shock absorbing device as claimed in claim 1, wherein the inner peripheral surface of said shock absorbing hole is cylindrical in form, and said shock absorbing member has a cylindrical outer peripheral surface of a diameter slightly smaller than the diameter of said inner peripheral surface of said shock absorbing hole. 3. A shock absorbing device as claimed in claim 1 or 2, wherein said shock absorbing hole includes a back pressure chamber (24, 33, 51, 71) extending beyond said port (23, 32), said port and said back pressure chamber being positioned such that said shock absorbing member enters said back pressure chamber to thereby create a shock absorbing pressure in said back pressure chamber. 4. A shock absorbing device as claimed in claim 3, wherein an inner peripheral surface defining said back pressure chamber includes a cylindrical portion adjacent said port, and said shock absorbing member includes a cylindrical outer peripheral surface portion cooperating with said cylindrical portion of said back pressure chamber when entering the cylindrical portion, to define therebetween a minuscule annular gap (E, F). 5. A shock absorbing device as claimed in claim 3, wherein an inner peripheral surface defining said back pressure chamber includes a tapering surface portion (50B, 60B) adjacent the port (23, 32) and said shock absorbing member includes a tapering outer peripheral surface portion (13B) entering said tapering surface portion to define a minuscule annular gap (G) therebetween. 6. A shock absorbing device as claimed in claim 5, wherein said tapering outer peripheral surface portion (13B) of said shock absorbing member has an angle of inclination a smaller than the angle of inclination ss of the tapering inner peripheral surface portion (50B) of said back pressure chamber. 7. A shock absorbing device as claimed in claim 3, wherein an inner peripheral surface defining said back pressure chamber (71) includes a cylindrical surface portion (70A) adjacent said port (23), and a stepped surface portion (70C) contiguous therewith, and said shock absorbing member includes a cylindrical outer peripheral surface portion (13A) entering said cylindrical surface portion (70A) to define a minuscule annular gap (E) therebetween, and a tapering surface portion (13B) contiguous with said cylindrical outer peripheral surface portion, said tapering surface portion (13B) being adapted to cooperate with said stepped surface portion to define therebetween a minuscule gap (H) at the end of a stroke of movement of said shock absorbing member. 8. A shock absorbing device as claimed in any one of claims 3 to 7, wherein said shock absorbing member is formed at a portion of the outer peripheral surface thereof facing said port with a tapering groove (41) extending axially of the shock absorbing member, said tapering groove having a cross-sectional area progressively increasing in going toward end of said shock absorbing member adjacent said back pressure chamber. 9. A shock absorbing device as claimed in any one of claims 3 to 8, further comprising a first ancillary passageway communicating said passageway means with said working space and mounting a one-way valve (42) allowing the fluid to flow from said passageway means to said working space, and a second ancillary passageway communicating said passageway means with said back pressure chamber and mounting a one-way valve (43) allowing the fluid to flow from said passageway means to said back pressure chamber.

Inventors: HASHIMOTO, HISAYOSHI, OCHIAI, MASAMI, TAMURA, MORIO
Applicants: HITACHI CONSTRUCTION MACHINERY CO., LTD.
Application year: 1982
Main classification: F15B15
IPC codes: F15B15