CH634899A5 - Hydraulic telescopic actuators. - Google Patents

Description

634 899

PATENT CLAIMS

1. Hydraulic telescopic lifting cylinder with a full piston and at least one hollow piston, in the bottom of which a check valve is provided, which closes an overflow channel leading from the pressure chamber of the lifting cylinder to the interior of the hollow piston, characterized in that in the bottom

(14) of the hollow piston (2) a mushroom-shaped differential piston (18) with a throttle channel (26) is provided, which slides in a mushroom-shaped cylinder chamber (15), the pressure chamber end (16) of which opens into the overflow channel (17), wherein the piston foot (19) as the valve body of the check valve closes the overflow channel (17) at a dead center of the differential piston (18).

2. Hydraulic telescopic lifting cylinder according to claim 1, characterized in that in the pressure chamber end (16) of the cylinder chamber (15) sits as a valve body of the check valve, a valve ball (28) and that the mouths of the overflow channel (17) and the throttle channel (26) are designed as valve seats (29).

3. Hydraulic telescopic lifting cylinder according to claim 1 or 2, characterized in that in the region of the bottom (14) of the hollow piston (2) a securing element (25) limiting the stroke of the differential piston (18) is arranged.

4. Hydraulic telescopic lifting cylinder according to one of claims 1 to 3, characterized in that in the differential piston (18) a the throttle channel (26) with the cylinder chamber

(15) connecting shunt channel (27) is provided.

5. Hydraulic telescopic lifting cylinder according to one of claims 1 to 4, characterized in that the differential piston (18) under the action of a spring element acting between the piston foot (19) and the bottom (14) of the hollow piston (2) in the cylinder chamber (15) is pressed.

6. Hydraulic telescopic lifting cylinder according to one of claims 1 to 5, characterized in that the differential piston (18) on both its piston foot (19) and on its piston head (20) carries ring seals (23).

7. Hydraulic telescopic lifting cylinder according to claim 6, characterized in that the cylinder chamber (15) is provided with a vent hole (24) which is hermetically sealed after the differential piston (18) has been inserted.

8. Hydraulic telescopic lifting cylinder according to one of claims 1 to 7, characterized in that the cross-sectional area of the piston head (20) exceeds that of the piston foot (19) by at least one order of magnitude.

9. Hydraulic telescopic lifting cylinder according to one of claims 1 to 8, characterized in that in the differential piston (18) an automatic one-way valve is provided which the throttle channel (26) to the interior (9) of the hollow piston (2)

opens.

10. Hydraulic telescopic lifting cylinder according to claim 9, characterized in that the one-way valve has a ball (31) loaded by a compression spring (30) as the valve body.

The innovation relates to a hydraulic telescopic lifting cylinder with a full piston and at least one hollow piston, in the bottom of which a check valve is provided, which closes an overflow channel leading from the pressure chamber of the lifting cylinder to the interior of the hollow piston.

The innovation is used for telescopic lifting cylinders with any number of telescopic stages and it is particularly suitable for telescopic synchronous lifting cylinders for the actuation of hydraulic lifts.

With telescopic lifting cylinders, pressure oil losses are unavoidable. Such losses occur on the seals between the lifting cylinder and the pistons of the units; pressure oil either escapes into the open or it flows from an annular space between two pistons into the pressure space in the lifting cylinder. A loss of pressure oil manifests itself in the fact that the telescope stage in question is no longer fully extended and is used, for. B. the telescopic lifting cylinder to drive an elevator, then the car no longer reaches the top stop, the passengers can no longer get out and the elevator system is faulty.

To compensate for the pressure losses in the individual telescopic stages in the region of the lowest positions of the pistons in the cylinder walls, it is known to provide annular grooves, with the aid of which the pressure spaces can be connected to one another when the pistons are moved even further downward from their retracted position will. In this position, pressure oil can then pass through the ring grooves e.g. overflow from the pressure chamber of the lifting cylinder into the annular space between the pistons, which compensates for the pressure oil losses. However, in order to move the pistons into this special position, special measures are necessary, for example hydraulic lifts must be brought regularly by hand at short intervals into a pressure oil compensation position that is below the lowest retracted position. This means that the elevator has to be put out of operation for a certain period of time.

Furthermore, it is known to arrange check valves in the bottom of the hollow cylinder or cylinders of telescopic lifting cylinders, the activity of which is released by a tappet. The release takes place when the pistons are again moved into a lower, special position, in which the plunger stands on the bottom of the lifting cylinder or the next larger hollow cylinder. Here, too, the inevitable compensation of pressure oil losses does not take place on its own, but the devices equipped with check valves also require regular, time-consuming maintenance.

It is the task of the present innovation to propose measures so that the compensation of pressure oil losses during the operation of a telescopic lifting cylinder takes place continuously automatically.

To solve the problem, a hydraulic telescopic lifting cylinder of the type mentioned at the outset is used and the problem is solved in that a mushroom-shaped differential piston with a throttle channel is provided in the bottom of the hollow piston, which slides in a mushroom-shaped cylinder chamber, the pressure chamber side of which End opens into the overflow channel, the piston foot as the valve body of the check valve closes the overflow channel in a dead center of the differential piston. This differential piston, which acts as a check valve, is automatically controlled by the pressure of the pressure oil in the annular space between the lifting cylinder and the hollow piston, so that pressure oil from the pressure chamber of the lifting cylinder by means of the overflow channel always replaces the pressure oil losses when the full piston is retracted due to pressure oil Lack has already taken its lowest position before the running-in process of the entire unit has ended. The full piston then sits on the hollow piston, which means that the pressure in the annulus is almost zero. Since there is still pressure in the pressure chamber of the lifting cylinder, the differential piston can now open so that pressure oil overflows. Hydraulic telescopic lifting cylinders, which are equipped with the innovation, require no maintenance with regard to their pressure oil losses.

In a preferred embodiment of the invention, a valve ball is seated above the differential piston in the end of the cylinder chamber on the pressure chamber side, and the orifices of the overflow duct and throttle duct are designed as valve seats. This makes it easy to solve the sealing problems of the check valve

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master and dimension the differential piston optimally regardless.

A securing element which limits the stroke of the differential piston can be arranged in the region of the bottom of the hollow piston, thereby reliably preventing malfunctions.

A shunt channel connecting the throttle channel to the cylinder head space is advantageously provided in the differential piston. This measure ensures that the valve ball forming a body of the check valve is lifted off its valve seat, the mouth of the throttle channel.

In order to avoid undesired opening of the overflow channel under the action of dynamic loads on the telescopic lifting cylinder, the differential piston is pressed into the cylinder space with the aid of a spring element. An air-free space beneath the piston head of the differential piston advantageously serves as the spring element, for which purpose the differential piston expediently carries ring seals both on its piston foot and on its piston head.

In order to enable the differential piston to be inserted into the cylinder chamber, it is expedient to provide it with a vent hole which is sealed tightly after it has been inserted.

It has been shown that - if an undesired opening or closing of the check valve is to be avoided with certainty - the cross-sectional area of the piston head must expediently exceed that of the piston foot by at least an order of magnitude.

In a further embodiment of the innovation, an automatic one-way valve is provided in the differential piston, which opens the throttle channel to the interior of the hollow piston. With this one-way valve, the closing process of the check valve can be advantageously influenced.

It is structurally very simple if a ball loaded by a compression spring is preferably used as the valve body of the one-way valve, but a commercially available, suitable check valve can also be used as well.

A preferred embodiment of the innovation is shown in the accompanying drawing, which is explained in more detail below. The drawing shows a hydraulic telescopic synchronous lifting cylinder in a longitudinal section.

In a lifting cylinder 1, a hollow piston 2 and in turn a full piston 3 are arranged displaceably. The lifting cylinder 1 has a pressure chamber 4, in which a pressure line 5 leads. If the pressure chamber 4 is pressurized with pressure oil by a pump (not shown) via the pressure line 5, then the hollow piston 2 moves in the axial direction. In the annular space 6 between the lifting cylinder 1 and the hollow piston 2 there is also pressure oil, which is separated by the seal 7 from the pressure oil in the pressure chamber 4. Now moves the hollow piston 2 axially, then the pressure oil of the annular space 6 is pressed through the openings 8 into the interior 9 of the hollow piston 2, where it also shifts the full piston 3 in the axial direction. The telescopic lifting cylinder is dimensioned in such a way that with a constant flow and constant pressure of the pump, the extension and retraction speed of the solid piston 3 is uniform, the hollow piston 2 and the solid piston 3 extending and retracting simultaneously; the same applies if the unit has several hollow pistons.

A seal 10 between the lifting cylinder 1 and the hollow piston 2 and a further seal 11 between the hollow piston 2 and the solid piston 3 are intended to prevent the pressure oil from escaping. The full piston 3 has at its upper end a stop plate 12 which limits the retraction and stop lugs 13 which limit the extension.

The hollow piston 2 has a high base 14 which contains a mushroom-shaped cylinder space 15 which is arranged centrally

is arranged and the end 16 opens into an overflow channel 17 which leads to the pressure chamber 4. A mushroom-shaped differential piston 18 slides in the cylinder space 15.

The differential piston 18 has a cylindrical piston foot 5 19 and a likewise cylindrical piston head 20, the diameter of the piston head 20 being slightly more than three times larger than that of the piston foot 19, so that the cross-sectional area of the piston head 20 or its surface 21 is the cross-sectional area or the surface 22 of the piston foot 19 exceeds by a whole 10 orders of magnitude. The piston foot 19, like the piston head 20, carries seals 23 which, in the form of sealing rings, are inserted in grooves provided for this purpose in the jacket of the piston foot 19 and piston head 20.

So that the air displaced by the differential piston 18 can escape from the cylinder space 15 during insertion, a vent hole 24 is provided which, after insertion and at the dead center of the differential piston 18 on the pressure chamber side (ie when the differential piston 18 has assumed its lowest position in the drawing), is airtight is closed 20. This has the effect that - as soon as forces act on the differential piston 18 that lift it from this extreme position - there is an increasingly air-diluted space under the piston head 20, with the result that a growing counterforce 25 occurs, which affects the differential piston 18 in the cylinder space 15 holds in the dead center. The effect is the same as with a spring element, for example a compression spring, through which the differential piston 18 is pressed into the cylinder space 15. The stroke of the differential piston 18 is limited by a securing element 30 in the form of a spring ring inserted into an inner groove.

The differential piston 18 is penetrated by a throttle channel 26. A shunt duct 27 branches off from the throttle duct 26 and connects the throttle duct 26 to the cylinder space 15, namely 35 to the end 16 thereof.

A valve ball 28 sits above the differential piston 18, namely between the surface 22 of the piston foot 19 and the ceiling of the cylinder chamber 15. The orifices of the overflow channel 26 are designed as conical valve seats 29. 40 An independent one-way valve in the form of a ball 31 loaded by a compression spring 30 opens the throttle channel 26 of the differential piston 18 to the interior 9 of the hollow piston 2.

The function of the telescopic lifting cylinder described above is as follows:

45 As a result of unavoidable leaks, the amount of pressure oil enclosed in the annular space 6 and in the interior 9 of the hollow piston 2 becomes smaller during operation, and the full piston 3 can therefore no longer extend fully. As a result, the stop plate 12 of the full piston 3 strikes the head 50 of the hollow piston 2 (in the area of the seal 11) when the hollow piston 2 is fully retracted. In this position, the pressure of the enclosed quantity of pressure oil drops to almost zero and the differential piston 18 is raised against the action of the counterforce resulting from the air-diluted space under the piston head 20 because the check valve (with the valve ball 28) is under the pressure of the pressure oil in the pressure chamber 4 has opened. The automatic one-way valve (the ball 31 loaded by the compression spring 30) in the differential piston 18 also opens under this pressure. Now 60 pressure oil flows from the pressure chamber 4 into the pressure oil quantity (reduced by the leaks) in the annular space 6 and in the interior 9 and it is as long refilled until their pressure has increased to such an extent that the differential piston 18 closes the check valve (27) again and the two pressure chambers 65 are thus separated from one another again.

The check valve (19, 28, 29) is opened by the pressure oil of the pressure chamber 4 being applied to the spherical cap of the valve block which closes the overflow channel 17

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io gel 28 presses and the valve ball 28 and the differential piston 18 loaded on it lifts as soon as the counterforce and the pressure of the amount of pressure oil in the annular space 6 and in the interior 9 allow this. The pressure oil now flows from the pressure chamber 4 through the overflow channel 17 and past the valve ball 28 into the end 16 of the cylinder chamber 15. There, the pressure oil that has flowed in has a considerably larger area than the spherical cap, namely the surface 22 of the piston foot 19 of the differential piston 18 , before, and it is able to further raise the differential piston 18 against the increasing counterforce,

because (at the same pressure of the pressure oil) the surface area has increased. As long as the valve ball 28 keeps the mouth of the throttle duct 26 closed, the pressure oil which has penetrated into the end 16 of the cylinder space 15 flows through the bypass duct 27 into the throttle duct 26; thereby 15 the pressure on both sides of the valve ball 28 becomes equal and it lifts off the valve seat 29 on the piston foot 19 and releases the mouth. The pressure oil flowing through the throttle channel 26 - the cross-section of which is selected in accordance with the dimensions of the differential piston 18 such that the flowing pressure oil finds sufficient resistance 20 so that the pressure can build up over the surface 22 - by opening the ball 31 lifts against the compression spring 30, and it thus enters the interior 9 of the hollow piston 2.

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If, at the end of the refilling process, the pressure at the top of the differential piston 18 is almost as great as that at the bottom, then the automatic one-way valve closes by pressing the ball 31 onto its seat by the compression spring 30, so that the throttle channel 26 is closed. Now the force that presses on the surface 21 of the differential piston 18 becomes greater because, after the one-way valve has closed, the pressure at the top of the differential piston 18 has an enlarged area available. This force now moves the differential piston 18 - additionally supported by the counterforce of the air-diluted space under the piston head 20 - into the cylinder space 15, so that the piston foot 19 presses the valve ball 28 onto its seat 29 and the check valve is closed. If hollow pistons 2 and full pistons 3 are now extended again, the pressure of the pressure oil standing in the annular space 9 and in the interior 9 rises sharply, which causes the differential piston 18 to be pressed more strongly onto the valve ball 28.

In special cases, e.g. B. in telescopic lifting cylinders with low pressure in the pressure chamber 4 or very fast moving pistons, it may be appropriate that the direction of force of the spring element acting on the differential piston 18 is directed so that it has a tendency to get out of the cylinder chamber 15 move.

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