GB1592518A

GB1592518A - Hydropneumatic spring

Info

Publication number: GB1592518A
Application number: GB5236677A
Authority: GB
Original assignee: Tokico Ltd
Current assignee: Tokico Ltd
Priority date: 1976-12-20
Filing date: 1977-12-16
Publication date: 1981-07-08
Also published as: FR2374563A1; DE2755816A1; JPS5376271A; BR7708440A; FR2374563B1

Description

(54) HYDROPNEUMATIC SPRING (71) We TOKICO LTD., a Japanese body corporate of 6-3, Fujimi 1-chome, Kawasaki-ku, Kawasaki-shi ,Kanagawa-ken, 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 hydropneumatic springs and, particularly, to hydropneumatic springs adapted for use with door closers, ventilating windows or the like.

Recently, hydropneumatic springs have been used frequently in controlling the opening or closing speed of members such as windows, ventilating windows or shutters. In one installation wherein a window is pivotally mounted on a frame and a hydropneumatic spring is pivotally mounted on the window and on the frame, it is usual to arrange for the spring to adopt its most extended condition when the window is in its fully open position and to adopt its most contracted condition in the door closing position. However, gas enclosed in the known hydropneumatic springs acts to extend the spring such that the window tends to open at a very high speed according to the force of the compressed gas, thereby generating a large impact force in the spring at the end of the opening movement of the window. Such impact force will sometimes damage the spring, fittings between the gas spring and the window or the frame, or the fitting between the window and the frame.

Thus, it has been required to apply some external force to the window to slow down the opening speed of the window. In preventing the aforementioned shortcomings it has been possible previously to reduce the pressure of gas enclosed in the spring which enables the force applied to the spring to be reduced when closing the window, but it has not then been possible to obtain the desired initial speed of the window during opening.

In accordance with the present invention, there is provided a hydropneumatic spring comprising a cylinder, a piston slidable in the cylinder and carried at the inner end of a piston rod whose other end projects outwardly from the cylinder, a pair of serially contiguous gas chambers defined in part by said cylinder and in part by a movable wall acting to isolate said chambers from one another, said gas chambers containing a gas under pressure and being both arranged functionally on the same side of said piston such that the gas pressure in one of them is at all times a function of the position of said piston in said cylinder, and a stop for restricting movement of the movable wall towards said one gas chamber at an intermediate point in the extension stroke of said piston.

The present invention will now be described in more detail with reference to the accompanying drawings, which are given by way of example and in which: Figure I is a schematic view of a hydropneumatic spring mounted between a frame and a window; Figure 2 is a longitudinal cross-sectional view of a prior art hydropneumatic spring; Figure 3 is a longitudinal cross-sectional view of a hydropneumatic spring according to the present invention in its most contracted condition; Figure 4 is a view similar to Figure 3 but showing the most extended condition; Figure 5 is a diagram showing the force on the piston and the stroke or the position of the piston in the cylinder; Figure 6 is a cross-sectional view of a modified hydropneumatic spring according to the present invention, and, Figure 7 is a partial cross-sectional view of a further embodiment of the present invention.

In Figure 1, a window 2 is mounted pivotally on a frame 1 around a pivot pin 3 attached to the lower end of the window. A latch 4 of a suitable construction is mounted on the upper end portion of the window for engaging the frame to hold the window in its closed position. A hydropneumatic spring having a cylinder 5 and a piston rod 6 is pivotally mounted on the window and the frame and adopts its most contracted condition as shown in full lines when the window is closed. When the window is fully open, the spring adopts its fully extended position shown in chain lines. A typical hydropneumatic spring of the prior art used in the installation of Figure 1 has a construction as shown in Figure 2. In the hydropneumatic spring of Figure 2, a free piston 7 is disposed in the cylinder 5 to define a gas chamber 8 and an oil chamber 9 in the cylinder 5. A piston 6' having a piston rod 6 secured thereto is fitted slidably in the oil chamber 9 of the cylinder 5. The gas enclosed in the gas chamber 8 at a pressure P (most extended condition acts to apply a force corresponding to P x a (wherein a is the cross-sectional area of the piston rod) on the piston in the extending direction.

When the window 2 is in its closed position the piston rod 6 receives a force a x (P + AP), wherein AP is pressure increase caused from the ingress of the piston rod.

Thus, in opening the window, a large opening force caused by the spring force a x (P + AP) plus a force due to the weight of the window will act on the window thereby moving the window at a very high speed such that the piston engages the lower end portion of the cylinder at speed at the end of the stroke, thus giving rise to a potential damage to the fittings between the hydropneumatic spring and the window or the frame or the pivot pin 3. Further, in closing the window a large force has had to be applied to overcome the projecting force a x (P + AP).

A hydropneumatic spring of the present invention shown in Figures 3 and 4 comprises a cylinder 10 and a piston rod 19 secured to a piston 14 and projecting from the lower end of the cylinder 10. A free piston 13 is slidably fitted in the cylinder 10 to define a first gas chamber 11 in the upper end portion of the cylinder 10. The free piston 13 further defines a second gas chamber 23 on the lowerside thereof, and an oil chamber 12 contiguous with the gas chamber 23 is formed in the cylinder 10 as shown. The piston 14 fitted slidably in the cylinder 1 divides the oil chamber 12 into two chambers 15 and 16. Shown at 24 is a stop formed by local deformation of the inner wall of the cylinder 10 so as to project radially inwardly for restricting the movement of the free piston 13 in the downward direction in the drawings. The pressures of the gas enclosed in the gas chambers 11 and 23 are determined such that the pressure in the chamber 11 is higher than the pressure in the chamber 23 in the most extended condition of the spring shown in Figure 4.

A passage 17 of a large effective crosssectional area and a leakage passage 18 of a small effective cross-sectional area are formed in the piston 14 to connect the oil chambers 15 and 16 with each other, and a yieldable valve member 20 is supported on the lower end surface of the piston 14 by a supporting member 21 having a stepped portion thereon. The valve member 20 acts to close the passage 17 when the piston 14 moves in the extending direction (downward in the drawings). A groove or passage 22 is formed in the supporting member 21 for enabling permanent communication of the chambers 15 and 16 through the passage 18.

When the spring of Figures 3 and 4 is mounted on the window 2 of Figure 1, it acts as follows.

When the window 2 is closed as shown in full lines in Figure 1, the spring adopts its most contracted condition as shown generally in Figure 3. The free piston 13 is moved upward from the stop 24 by a distance e. By assuming the pressure of gas in the first and the second gas chambers in this condition as P2 and P2 respectively and the crosssectional area ot the piston rod as a, since the pressures acting on the opposite sides of the free piston 13 are balanced the relation P2 = P2 is obtained. The force F2 acting on the piston rod to extend the spring is F2 = aP2 = ap2 in the closed condition of the window 2.

When the latch 4 of the window 2 is released, the spring extending force F2 becomes effective to extend the spring and the window 2 is moved in the clockwise direction in Figure 1 around the pivot pin 3; thus, the window is opened very quickly. In the spring, the volume in the gas chambers 11 and 23 will increase according to the outward movement of the piston rod 19 thus decreasing the pressure. When the piston rod 19 moves outward of the cylinder by a predetermined distance Si, the free piston 13 abuts the stop 24 with the pressure in the gas chambers 11 and 23 being p1 and P1 (P1 = Pl) respectively, which is shown in line I II in Figure 5.

Thereafter, the piston rod 19 continues to move downward in Figure 3 with the pressure and volume of the first gas chamber 11 being maintained at constant. Thus, change in volume of the cylinder due to the outward or extending movement of the piston rod is compensated solely by the second gas chamber 23, i.e. the spring extending force acting on the piston rod 19 is determined by the gas pressure in the chamber 23. The pressure in the gas chamber 23 changes at a rate higher than the aforesaid condition where the gas chambers 11 and 23 expand due to the egress of the piston rod 19. The line II - IV in Figure 5 depicts the characteristics at this stage, namely, the pressure in the gas chamber 23 at the most extended or the maximum length condition of the spring is PO, and the spring extending force acting on the piston rod in this condition if Fo = aPO.

One example of the characteristics of prior art hydropneumatic springs is shown in line I - II - III in Figure 5 wherein the movement of the free piston 5 is not restricted by a stop. In comparing the conditions III and IV, it will be clear that the projecting force acting on the piston rod at the maximum length condition can be reduced substantially according to the present invention. Therefore, it is possible to reduce the impact force acting on the spring at the end of extending stroke thus avoiding damage to fittings or to the spring itself, while attaining a high door opening speed at the initial stage. Further, the door can be closed by a relatively small force.

When the piston rod 19 moves in the spring extending direction, the passage 17 in the piston 14 is closed by the valve member 20 so as to decrease the piston speed, and when the piston rod moves in the opposite direction the valve member 20 is moved away from the passage 17 by the pressure in the chamber 15 so as to allow the upward movement of the piston without causing a large resisting force.

Figure 6 shows another embodiment of the present invention, in which an inner cylinder 25 and an outer cylinder 26 constitute the cylinder 10 of the first embodiment.

A piston 14 having a piston rod 19 is slidably fitted in the inner cylinder 25, and has a passage 17 of a large effective crosssectional area and a passage 18 of a small effective cross-sectional area for enabling communication between oil chambers 27 and 28 which are defined in the cylinder 25 and partitioned by the piston 14. A valve member 20 of a resilient material is disposed on the upper or rear face of the piston 14 where it is maintained by a support member 21 normally holding the passage 17 closed.

A passage or a groove 22 is formed in the member 21 to permit permanent communication of the chambers 27 and 28 through the passage 18. The passage 17 opens when the piston rod 19 moves inwards of the cylinder 25.

A free piston 13 is fitted slidably in an annular space defined between the cylinders 25 and 26, and a first gas chamber 29 and a second gas chamber 23 are defined on the opposite sides of the free piston 13. An oil chamber 30 contiguous with the second gas chamber 23 is also defined in the annular space. A stop 24 is secured on the inner surface of the outer cylinder 26 to restrict the movement of the free piston 13 thereby defining the maximum volume of the first gas chamber 29. A passage 31 communicates the oil chambers 28 and 30 permanently.

The hydropneumatic spring of Figure 6 acts similarly to that of the first embodiment although the piston rod 19 projects upwards of the cylinder.

Figure 7 shows a further embodiment of the present invention. In this embodiment, a first gas chamber 11 corresponding to the first gas chamber 11 in the first embodiment is defined by a deformable member 32 such as a bellows or a flexible diaphragm, and the stop 24 in the first embodiment is replaced by a plate member 33. The plate member 33 is preferably made of a porous material so as to permit free passage of the gas in the second gas chamber 23. Alternatively, a plurality of small holes may be formed through a plate member 33 made of a solid material. The plate member 33 is secured to the inner wall of the cylinder 10. Since the free piston is replaced in this embodiment by the deformable member 32, the expense of providing that piston and its seal rings is avoided and a number of machining operations necessary on the free piston sliding portion of the cylinder can be omitted.

Further, the volume of the gas chamber 11 will follow smoothly after the movement of the piston rod.

As heretofore described in detail, a hydropneumatic spring according to the present invention can, when used with a pivotable window, alleviate impact forces in the fully open condition of the window thereby reducing the risk of damage to of the gas spring, the window or the fittings therebetween. Further, the gas pressure in the extend condition of the spring can be reduced as compared with the prior art spring, and the force required in closng the window can be reduced substantially. When a free piston is incorporated to define the gas chambers, it is possible to determine clearly the point at which the effect of high pressure gas in the first gas chamber is interrupted, and to change the speed of extension of the piston rod at a desired position. When the first gas chamber is defined by a deformable member, it is possible to reduce manufacturing costs.

WHAT WE CLAIM IS: 1. A hydropneumatic spring comprising a cylinder, a piston slidable in the cylinder and carried at the inner end of a piston rod whose other end projects outwardly from the cylinder, a pair of serially contiguous gas chambers defined in part by said cylinder and in part by a movable wall acting to isolate said chambers from one another, said gas chambers containing a gas under

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. than the aforesaid condition where the gas chambers 11 and 23 expand due to the egress of the piston rod 19. The line II - IV in Figure 5 depicts the characteristics at this stage, namely, the pressure in the gas chamber 23 at the most extended or the maximum length condition of the spring is PO, and the spring extending force acting on the piston rod in this condition if Fo = aPO. One example of the characteristics of prior art hydropneumatic springs is shown in line I - II - III in Figure 5 wherein the movement of the free piston 5 is not restricted by a stop. In comparing the conditions III and IV, it will be clear that the projecting force acting on the piston rod at the maximum length condition can be reduced substantially according to the present invention. Therefore, it is possible to reduce the impact force acting on the spring at the end of extending stroke thus avoiding damage to fittings or to the spring itself, while attaining a high door opening speed at the initial stage. Further, the door can be closed by a relatively small force. When the piston rod 19 moves in the spring extending direction, the passage 17 in the piston 14 is closed by the valve member 20 so as to decrease the piston speed, and when the piston rod moves in the opposite direction the valve member 20 is moved away from the passage 17 by the pressure in the chamber 15 so as to allow the upward movement of the piston without causing a large resisting force. Figure 6 shows another embodiment of the present invention, in which an inner cylinder 25 and an outer cylinder 26 constitute the cylinder 10 of the first embodiment. A piston 14 having a piston rod 19 is slidably fitted in the inner cylinder 25, and has a passage 17 of a large effective crosssectional area and a passage 18 of a small effective cross-sectional area for enabling communication between oil chambers 27 and 28 which are defined in the cylinder 25 and partitioned by the piston 14. A valve member 20 of a resilient material is disposed on the upper or rear face of the piston 14 where it is maintained by a support member 21 normally holding the passage 17 closed. A passage or a groove 22 is formed in the member 21 to permit permanent communication of the chambers 27 and 28 through the passage 18. The passage 17 opens when the piston rod 19 moves inwards of the cylinder 25. A free piston 13 is fitted slidably in an annular space defined between the cylinders 25 and 26, and a first gas chamber 29 and a second gas chamber 23 are defined on the opposite sides of the free piston 13. An oil chamber 30 contiguous with the second gas chamber 23 is also defined in the annular space. A stop 24 is secured on the inner surface of the outer cylinder 26 to restrict the movement of the free piston 13 thereby defining the maximum volume of the first gas chamber 29. A passage 31 communicates the oil chambers 28 and 30 permanently. The hydropneumatic spring of Figure 6 acts similarly to that of the first embodiment although the piston rod 19 projects upwards of the cylinder. Figure 7 shows a further embodiment of the present invention. In this embodiment, a first gas chamber 11 corresponding to the first gas chamber 11 in the first embodiment is defined by a deformable member 32 such as a bellows or a flexible diaphragm, and the stop 24 in the first embodiment is replaced by a plate member 33. The plate member 33 is preferably made of a porous material so as to permit free passage of the gas in the second gas chamber 23. Alternatively, a plurality of small holes may be formed through a plate member 33 made of a solid material. The plate member 33 is secured to the inner wall of the cylinder 10. Since the free piston is replaced in this embodiment by the deformable member 32, the expense of providing that piston and its seal rings is avoided and a number of machining operations necessary on the free piston sliding portion of the cylinder can be omitted. Further, the volume of the gas chamber 11 will follow smoothly after the movement of the piston rod. As heretofore described in detail, a hydropneumatic spring according to the present invention can, when used with a pivotable window, alleviate impact forces in the fully open condition of the window thereby reducing the risk of damage to of the gas spring, the window or the fittings therebetween. Further, the gas pressure in the extend condition of the spring can be reduced as compared with the prior art spring, and the force required in closng the window can be reduced substantially. When a free piston is incorporated to define the gas chambers, it is possible to determine clearly the point at which the effect of high pressure gas in the first gas chamber is interrupted, and to change the speed of extension of the piston rod at a desired position. When the first gas chamber is defined by a deformable member, it is possible to reduce manufacturing costs. WHAT WE CLAIM IS:

1. A hydropneumatic spring comprising a cylinder, a piston slidable in the cylinder and carried at the inner end of a piston rod whose other end projects outwardly from the cylinder, a pair of serially contiguous gas chambers defined in part by said cylinder and in part by a movable wall acting to isolate said chambers from one another, said gas chambers containing a gas under

pressure and being both arranged functionally on the same side of said piston such that the gas pressure in one of them is at all times a function of the position of said piston in said cylinder, and a stop for restricting movement of the movable wall towards said one gas chamber at an intermediate point in the extension stroke of said piston.

2. A spring as claimed in claim 1, wherein the movable wall is a free piston.

3. A spring as claimed in claim 2 which is of a single tube type and wherein the free piston is slidably disposed in an upper portion of the cylinder, and the stop is provided by a local deformation formed on the peripheral wall of the cylinder.

4. A spring as claimed in claim 2 in which the cylinder is of a dual tube type comprising coaxial inner and outer tubes, the piston being slid ably disposed in the inner tube, and the free piston being slidably disposed in the upper portion of the annular space between the inner and the outer tubes.

5. A spring as claimed in claim 1, wherein said one gas chamber is contiguous with an oil chamber in which the piston is slidable.

6. A spring as claimed in claim 1, wherein the movable wall comprises a deformable wall, and said stop is a partition wall of a porous material secured to the cylinder.

7. A spring as claimed in claim 3 and claim 5, in which said piston carried by the piston rod is formed with a leakage passage permitting permanent oil flow between its front and rear faces and with a further passage of larger cross-section controlled by a valve closure member mounted on said piston carried by the piston rod and arranged to close said further passage during extension strokes of said piston carried by the piston rod.

8. A hydropneumatic spring constructed substantially as hereinbefore particularly described with reference to and as illustrated in Figures 3 and 4 of the accompanying drawings.

9. A hydropneumatic spring constructed substantially as hereinbefore particularly described with reference to and as illustrated in Figure 6 of the accompanying drawings.

10. A hydropneumatic spring constructed substantially as hereinbefore particularly described with reference to and as illustrated in Figure 7 of the accompanying drawings.