EP0068495B1

EP0068495B1 - Shock absorbing device for hydraulic cylinder

Info

Publication number: EP0068495B1
Application number: EP82105779A
Authority: EP
Inventors: Hisayoshi Hashimoto; Masami Ochiai; Morio Tamura
Original assignee: Hitachi Construction Machinery Co Ltd
Current assignee: Hitachi Construction Machinery Co Ltd
Priority date: 1981-06-30
Filing date: 1982-06-29
Publication date: 1986-03-12
Also published as: DE3269801D1; EP0068495A1

Description

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 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 US-A-3 704 650. 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 thottling 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 consitituting 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.
In DE-A-2 603 041 a cushioning means for cushioning the end portion of the stroke of a piston in a hydraulic cylinder is shown, comprising a cushioning member, such as a spear projecting axially from the head end of a piston or a sleeve projecting axially from the rod end of the piston and disposed around the piston rod, which, during the cushioned portion of the piston stroke, enters a cylinder head bore to define therewith a restricted passage through which fluid is displaced from the cylinder. When entering the cylinder head bore the cushioning member gradually covers the lateral fluid port opening into the cylinder head bore. An additional damping chamber is provided at the end of the cylinder head bore, which chamber becomes operative when the lateral fluid port is closed by the cushioning member.
US-A-4064788 describes a cushioning means comprising a cushioning spear with successively tapered steps having crests made smaller in diameter from one step to the next, the most forward end step being the smallest in diameter.
Both cushiohing means discussed above fail to throttle the fluid flow discharged from cushioning chamber just before the stroke end is reached. Therefore it remains a remarkable force of impact of the piston against the end wall of a hydraulic cylinder.
It is an object of the invention to provide a shock absorbing device for hydraulic cylinders with an improved cushioning effect during the period just before the stroke end is reached conducting to a remarkable reduced force of impact of the piston against the end wall of the hydraulic cylinder.
According to the invention this object is solved in a shock absorbing means of the kind referred to in the precharacterizing part of patent claim 1 and 2 the features disclosed in the characterizing parts of patent claims 1 or 2, respectively.
The subclaims 3 to 5 describe preferred embodiments of the shock absorbing means according to the invention.

Brief Description of the Drawings

Figs. 1 and 2 are sectional views of the shock absorbing device comprising one embodiment of the invention mounted on the head cover side with the piston located in different operation positions;
Fig. 3 is a sectional view of the shock absorbing device comprising another embodiment mounted on the rod cover side similar to the embodiment shown in Figs. 1 and 2;
Figs. 4―6 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. 7 is a graph showing the piston speed and the head cover acceleration of the embodiment shown in Figs. 4―6 in the shock absorbing stroke;
Fig. 8 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. 4―6; and
Figs. 9 and 10 ares sectional views of modifications of the embodiments shown in Figs. 4―6.

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 (Fig. 3) secured to opposite ends of the cylinder 1. The head cover 2 is formed therein with a shock absorbing hole 50 adapted to receive therein a shock absorbing member subsequently to be described, a port 23 opening in the shock absorbing hole 50 at its side, and a supply and discharge passageway 22 communicating with the port 23. Likewise, the rod cover 3 (Fig. 3) is formed therein with a shock absorbing hole 60, a port 32 and a supply and discharge passageway. 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. 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.
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 generally 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 defined therebetween as the shock absorbing member progressively enters the shock absorbing hole, thereby increasing the shock absorbing effect.
In the embodiment shown in Figs. 1 and 2 the 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 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. 2, 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 peripheral 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 50B defining the throttle passageway G may be parallel to each other or angles of inclination a and β may be equal to each other as shown in Fig. 1. However, the angle of inclination β of the shock absorbing hole 50 is preferably greater than the angle of inclination a of the shock absorbing member 13. When a < 13, 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. 3 shows an embodiment in which the same concept as incorporated in the embodiment shown in Figs. 1 and 2 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. 1, so that detailed description shall be omitted.
Figs. 4, 5 and 6 show still another embodiment in which, 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 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. 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 cylin- dricai portion of the shock absorbing member 13.
In operation, as the cylindrical outer peripheral surface 13A of the shock absorbing member 13 enters 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. 5, 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. 6, 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. 4―6, shock absorption is carried out in four stages, to enable smooth deceleration of the piston 11 to be obtained. Fig. 7 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. 4―6. 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 a very. smooth deceleration of the piston 11 to be obtained.
The concept of the embodiment shown in Figs. 4―6 can, of course, be incorporated in a shock absorbing device mounted on the rod cover 3 side. Fig. 8 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. 4―6.

Figs. 9 and 10 show modifications of the embodiment shown in Fig. 4.

The modification shown in Fig. 9 is formed with a tapering groove 41 in the shock absorbing member 13. In the modification shown in Fig. 10, check valves 42 and 43 are mounted in first and second ancillary passageways. 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 71 as shown in Fig. 10. 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 71 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 70 to be smoothly effected.
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 70 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 70, so that the throttling effect increases and a good deceleration characteristic can be exhibited. Moreover, when the piston moves from its position shown in Fig. 9 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 71. The embodiment shown in Fig. 9 is capable of quickly and smoothly effecting movement of the shock absorbing member 13, out of the shock absorbing hole 70.
In these modifications of the embodiment shown in Fig. 4, the advantage of being able to readily move the shock absorbing member 13 out of the hold is offered.

Claims

1. A hydraulic cylinder comprising a housing including a cylindrical side wall (1) and at least one end wall (2; 3), a piston assembly including a piston (11) slidably arranged in said housing for sliding axial movement for cooperating with the housing to define therein a working space (A, B), and a shock absorbing device comprising:

a shock absorbing hole (50; 60) formed in the end wall (2; 3) and extending axially of the housing,

a shock absorbing member (13; 14) mounted on the piston assembly in a manner to be aligned with the shock absorbing hole (50; 60) and adapted to enter the shock absorbing hole (50; 60) in terminating stages of stroke of the piston (11) to throttle the flow of fluid from the working space (A, B) into the shock absorbing hole (50; 60), and supply and discharge passageway means (22) communicating with the shock absorbing hole (50; 60) and having a port (23, 32) opening in the shock absorbing hole (50; 60) at its inner peripheral surface, said port being located in a position in which the area of its opening can be reduced by the shock absorbing member (13; 14), said shock absorbing hole including a back pressure chamber (51) 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; characterized in that the inner peripheral surface defining said back pressure chamber (51) includes a tapering surface portion (50B, 60B) adjacent the ports (23, 32) and said shock absorbing member (13, 14) includes a tapering outer peripheral surface portion (13B) entering said tapering surface portion to define a minuscule annular gap (G) therebetween.

2. A hydraulic cylinder comprising a housing including a cylindrical side wall (1) and at least one end wall (2; 3), a piston assembly including a piston (11) slidably arranged in said housing for sliding axial movement for cooperating with the housing to define therein a working space (A, B), and a shock absorbing' device comprising:

a shock absorbing hole (70; 80) formed in the end wall (2; 3) and extending axially of the housing,

a shock absorbing member (13; 14) mounted on the piston assembly in a manner to be aligned with the shock absorbing hole (70; 80) and adapted to enter the shock absorbing hole (70; 80) in terminating stages of stroke of the piston (11) to throttle the flow of fluid from the working space (A, B) into the shock absorbing hole (70; 80), and supply and discharge passageway means (22) communicating with the shock absorbing hole (70; 80) comprising a port (23; 32) opening in the shock absorbing hole (70; 80) at its inner peripheral surface, said port being located in a position in which the area of its opening can be reduced by the shock absorbing member (13; 14), said shock absorbing hole indluding a back pressure chamber (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; characterized in that the inner peripheral surface defining said back pressure chamber (71) includes a cylindrical surface portion (70A, 80A) adjacent said port (23, 32), and a stepped surface portion (70C, 80C) contiguous therewith, and said shock absorbing member (13, 14) includes a cylindrical outer peripheral surface portion (13A, 14A) entering said cylindrical surface portion (70A, 80A) to define'a minuscule annular gap (E) therebetween, and a tapering surface portion (13B) contiguous with said cylindrical outer peripheral surface portion (13A, 14A), 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.

3. A shock absorbing device as claimed in claim 1, characterized in that said tapering outer peripheral surface portion (13B) of said shock absorbing member (13) has an angle of inclination (a) smaller than the angle of inclination (β) of the tapering inner peripheral surface portion (50B) of said back pressure chamber (51).

4. A shock absorbing device as claimed in claim 1 or 2, characterized in that said shock absorbing member (13) is formed at a portion of the outer peripheral surface thereof facing said port (23) with a tapering groove (41) extending axially of the shock absorbing member, said tapering groove having a cross-sectional area progressively increasing towards the end of said shock absorbing member (13) adjacent said back pressure chamber (51, 71).

5. A shock absorbing device as claimed in claim 1 or 2, further comprising a first ancillary passageway communicating said passageway means (22) with said working space (A) 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 (71) and mounting a one-way valve (43) allowing the fluid to flow from said passageway means to said back pressure chamber.