EP1105651A1

EP1105651A1 - Working cylinder actuated by hydraulic fluid

Info

Publication number: EP1105651A1
Application number: EP99942808A
Authority: EP
Inventors: Xu Guo
Original assignee: Mannesmann Rexroth AG
Current assignee: Bosch Rexroth AG
Priority date: 1998-08-12
Filing date: 1999-08-03
Publication date: 2001-06-13
Also published as: WO2000009891A3; DE19836422C2; US6481331B1; WO2000009891A2; DE19836422A1

Abstract

The invention relates to a working cylinder actuated by hydraulic fluid, comprising a piston (20) to which a piston rod (35) is fixed and which can be axially displaced in a cylinder chamber between two end positions such that it inversely modifies the volume of two cylinder chambers (21, 22) on either side. A damping element (40) is arranged at least at one side of the piston (5) which when the piston moves into one of the terminal positions enters an opening between the one cylinder chamber and a cylinder connection, such that together with said opening it forms a circular throttling gap for the throttled outflow of hydraulic fluid from the cylinder chamber to the cylinder connection. To obtain a high damping capacity and in this way to be able to slow down large masses moved by the cylinder along a defined path, the outer surface of the damping element (40) in the axial direction is shaped such that when the damping element is fully immersed, it has a maximum diameter at the chamber-side start of the opening and, following a flat section having a small diameter (52) or small diameters, if the damping element is deeply immersed, across a short section has a medium diameter situated between the maximum and the small diameter.

Description

description

Pressure operated cylinder

The invention relates to a pressure-actuated working cylinder, which has the features from the preamble of claim 1, in which the piston is braked when it enters an end position by throttling the pressure medium outflow from the shrinking cylinder chamber. By throttling off the flowing pressure medium flow, a pressure is built up in the shrinking cylinder chamber, which generates a force on the piston which is opposite to the movement of the piston.

The so-called damping pressure building up in the cylinder chamber should not exceed a maximum value that is 1.5 to 2 times the nominal pressure of the working cylinder. On the other hand, the working cylinder has maximum damping capacity if the damping pressure has the maximum value over the entire damping distance. Even theoretically, this ideal course of the damping pressure can only be achieved by designing the throttle cross sections and the throttle lengths between the damping element and the passage opening if the same boundary conditions are always met, i.e. if the working cylinder e.g. is always driven at the same speed and moves the same mass. An attempt is then made to obtain the ideal end position damping for the case of the maximum speed and the greatest mass, so that the damping pressure no longer reaches the maximum value at lower speeds and smaller masses.

Pressure-actuated working cylinders with end position damping are known from a number of publications. For example, EP 0 837 250 A2 shows a working cylinder in which the damping element axially extends on its outer surface. fende and narrowing in their cross-section throttle grooves. The throttle cross section over the throttle grooves becomes smaller and smaller when the damping element is immersed in the passage opening. In addition to the throttle grooves, after the damping element has been immersed in the passage opening between the cylinder chamber and the cylinder connection, a pressure medium connection is connected via a throttle point, the hydraulic resistance of which is largely independent of the immersion depth of the damping element.

A pressure-operated cylinder with the features from the preamble of claim 1 is known from DE-OS 22 14 032. In such a working cylinder, the outer surface of the damping element is rotationally symmetrical. In the known working cylinder, an insertion bevel, the effect of which for the end position damping is negligible, is followed by a surface section with a smaller diameter, followed by a surface section with a larger diameter approximately from the center of the damping element, which extends to the end of the damping element on the piston side .

The invention has for its object to develop a pressure-operated cylinder with the features from the preamble of claim 1 so that a high damping capacity is obtained, so that a large mass can be braked in a short distance without expecting damage from pressure peaks are.

This goal is achieved with a pressure-actuated working cylinder which, in addition to the features from the preamble, also has the features from the characterizing part of patent claim 1. In a working cylinder according to the invention, viewed in the direction of immersion of the damping element into the passage opening, the damping element in front of the section with a smaller diameter has an average diameter that is between the maximum Diameter at the piston end of the damping element and the smaller diameter. This avoids that the damping pressure does not drop quickly after a steep increase at the beginning of the immersion of the damping element in the passage opening, but remains at a high level. The mean diameter is only present over a short distance compared to the length of the surface section with a small diameter, which prevents the damping pressure from exceeding the maximum permissible pressure, and therefore the working cylinder from being damaged by pressure peaks. It has been shown that with a configuration of the damping element according to the invention for a certain speed and mass, a course of the damping pressure can be achieved close to the ideal curve.

Advantageous embodiments of a pressure cylinder operated working cylinder according to the invention can be found in the subclaims.

Claims 2 and 3 contain information on advantageous configurations of the diameter.

According to claim 4, surface sections each have a fixed large diameter, a fixed small diameter and a fixed medium diameter. The diameter of the damping element does not change continuously as it progresses in the axial direction. According to patent claim 5, the second surface section advantageously merges into further surface sections with a diameter that changes continuously during the axial progression into the first surface section and into the third surface section.

Other preferred configurations result from the further subclaims. An exemplary embodiment of a pressure cylinder-operated working cylinder according to the invention and a diagram in which the damping pressure is plotted over the damping path for different speeds are shown in the drawings. The invention will now be explained in more detail with reference to these drawings.

Show it

1 shows a longitudinal section through a hydraulic working cylinder according to the invention, FIG. 2 shows a longitudinal section rotated through 90 ° with respect to FIG. 1 through a damping bushing used in the working cylinder according to FIG. 1, FIG. 3 shows a detail from FIG. 2 with a partially exaggerated representation of the outer surface of the damping bushing and FIG. 4 shows the diagram in which the measured damping pressure is plotted against the damping path for two piston speeds.

The hydraulically operated working cylinder shown in FIG. 1 is a cylinder of the so-called circular design. As essential components, the cylinder housing 10 has a cylinder tube 11, a cylinder head 12 which is placed on one end, and a cylinder base 13 which is placed on the other end of the cylinder tube 11. To fasten the cylinder tube, cylinder head and cylinder base to one another, a flange 14 is screwed onto each of the two ends of the cylinder tube 11 which are provided with an external thread and has axial threaded holes 15 distributed over 360 ° into which screws tightening the cylinder head or the cylinder base against the cylinder tube 16 are screwed in.

In the interior of the cylinder tube 11, a piston 20 is axially guided in a tightly sliding manner, which divides the interior of the cylinder tube into two cylinder chambers 21 and 22, the volumes of which change in opposite directions when the piston moves. By A cylinder connection 23 in the cylinder head 12 can supply hydraulic pressure medium to the cylinder chamber 21 and be discharged from this cylinder chamber. The radially arranged cylinder connection 23 initially opens into a chamber 24 in the cylinder head 12, which is fluidly connected to the cylinder chamber 21 via an axial passage opening 25 of a certain diameter. A pressure medium path runs similarly from a radial cylinder connection 26, a chamber 27 and an axial passage opening 28 of the cylinder bottom 13 to the cylinder chamber 22. The two passage openings 25 and 28 in the cylinder head and in the cylinder bottom have the same diameter.

The piston 20 is assembled with a piston rod 35 which passes through the cylinder head 12 to the outside and allows the chamber 24 and the passage opening 25 of the cylinder head 12 to become annular spaces. The piston 20 is pushed from the inner end over a reduced-diameter section of the piston rod 35 and is tensioned against a shoulder of the piston rod 35 with the interposition of a flange bushing 36 by means of a nut 37 screwed onto the threaded end of the piston rod 35.

Axially between the piston 20 and the collar 38 of the collar bushing 36, a damping bushing 40 is arranged thereon with axial and radial play, which serves as a throttle body and a check valve body. An identical damping bush 40 is arranged with axial and radial play between the piston 20 and a collar 39 of the nut 37.

The shape of the damping bushes is shown in more detail in FIGS. 2 and 3. A damping bush 40 has, apart from a recess 41 on its end 42 facing the piston 20, a constant inside diameter over its entire length, which is matched to the outside diameter of the collar bush 36 and the nut 37 in such a way that a radial play of, for example, 0.5 mm results. In The length of the damping bushing 40 is, for example, 0.3 mm shorter than the clear distance between the piston 20 and a collar 38, 39. On its end face 42 the damping bushing has two diametrically opposed circular segment-like recesses 43 which are not quite as deep as the recess 41 are. At that

5 piston 20 facing away from the end face 44, the damping bushing has a run-on slope 45, which ensures that the damping bushing, despite the radial play, threads into the passage opening 25 or 28. Even if one does not take into account the chamfer 45, the diameter of the outer surface 50 of the damping bush 40 is not constant over its length. The largest is the diameter in

IO of a first surface section 51 that begins directly on the end face 42. In the exemplary embodiment under consideration, the diameter in the surface section 51 is 30 μ smaller than the 48 mm diameter of the through bores 25 and 28. The first surface section 51 extends axially, in the present exemplary embodiment approximately 1 mm, further from the end face 42 of the damping

15 bushing 40 away as the recesses 43. In a second surface section 52, the outer surface 50 of the damping bushing 40 has a constant smallest diameter over a distance of approximately 8 mm, which is approximately 110 μm smaller than the diameter of the passage openings 25 and 28. Furthermore, a third axially extending surface section 53 with a constant diameter is provided.

20 hands. The diameter in the surface section 53 is approximately 80 μm smaller than the diameter of the passage openings 25 and 28. The surface section 53 directly adjoins the run-on slope 45 and extends over a length of approximately 1 to 2 mm. Its diameter lies between the diameters in the surface section 52 and in the surface section 51. Between the two surfaces

25 sections 52 and 53 there is a frustoconical surface section 54 in which the diameter increases from the diameter in the surface section 52 to the diameter in the surface section 53. Finally, in a frustoconical surface section 55, the diameter of the outer surface 50 of the damping bush 40 increases from the diameter in the surface section 52 to the diameter knife in surface section 51. The surface section 55 is axially longer than the surface section 54. Its length is approximately 6 to 7 mm, while the surface section 54 is only approximately 3 mm long. The total length of the damping bushing here is approximately 24.5 mm.

5

In the position of the piston 20 shown in FIG. 1, the damping bush 40 sits axially on the nut 37 on its collar 39. If pressure medium is now supplied to the cylinder connection 26, the damping bush 40 is displaced by its axial play towards the piston 20 by the force generated by the pressure present.

I O ben until it rests with its end face 42 on the piston. Pressure fluid can now flow into the cylinder chamber 22 through the axial gap between the end face 44 of the damping bush 40 and the collar 39 of the nut 37, through the radial gap between the damping bush 40 and the nut 37 due to the radial play, and through the recesses 43 of the damping bush 40.

15 The hydraulic resistance of the flow path described along the inner wall of the damping bush 40 is substantially lower than the hydraulic resistance between its outer surface and the wall of the passage opening 28. The piston 20 now moves with a speed corresponding to the quantity of pressure medium flowing in via the cylinder connection 26 to the Cylinder head

20 12 to, pressure medium being displaced from the shrinking cylinder chamber 21 via the passage opening 25 and the cylinder connection 23. At a certain distance of the piston 20 from the cylinder head 12, the other damping bush 40, which is guided on the collar bush 36, begins to dip into the passage opening 25. This will cause the pressure medium to flow away

25 of the flow cross section available to the cylinder chamber 21 is reduced through the through bore 25. The pressure in the cylinder chamber 21 is thereby higher than the pressure in the chamber 12 and in the cylinder port 23 of the cylinder head 12, so that the damping bush 40 is moved away from the piston 20 to the collar 38 of the collar bush 36 and with its end face 44 sits on the federal government. Like the movable body of a check valve, the damping bushing 40 thereby blocks the flow path along the radial gap between it and the collar bushing 36. The surface section 53 of the damping bushing 40 then passes into the passage opening 25 along the flow path

5 the outside of the damping bush 40 becomes very narrow and the pressure in the cylinder chamber 21 increases relatively quickly. However, after a short further travel of the piston 20, the surface sections 54 and 52 of the damping bush 40 get into the passage opening 25, thereby preventing the damping pressure in the cylinder chamber 21 from exceeding the intended maximum value

I O increases. The piston 20 is braked by the damping pressure present in the cylinder chamber 21. The surface sections 55 and 51 of the damping bush 40 are then immersed in the passage opening 25, as a result of which the hydraulic resistance along the flow path on the outside of the damping bush 40 is again greatly increased and despite the

15 wrestle speed of the piston 20 even a small amount of pressure medium to be displaced from the cylinder chamber 21 per unit of time in the cylinder chamber 21, a damping pressure is maintained close to the maximum pressure. Finally, the piston 20 reaches its end position on the cylinder head 12 at a very low speed. Extending from this end position into that in FIG. 1

20 shown starting position is done in the same way as moving out of the starting position.

The diagram according to FIG. 4 shows various curves which show a damping pressure in a cylinder chamber plotted against the damping path 25, the zero point of the damping path being placed in the beginning of the immersion of the damping bushing in a passage opening. The dashed curve 60 represents an ideal damping curve. The damping pressure rises quickly to the maximum value, remains at this value almost throughout the entire damping path and only drops steeply at the end. The curve 61 is below On the basis of certain boundary conditions, such as a maximum speed of the piston and on the basis of certain dimensions of a damping bushing designed according to the invention. The curve 62 has been recorded in an experiment which has the same boundary conditions as at

5 the calculation of curve 61 have been assumed, in particular based on the same speed of the piston and the same moving mass. Curve 63 has been recorded at a lower piston speed at the start of damping. The speed here was approximately 300 mm / s, while for the recording of curve 62 a speed of 500 mm / s

I have been driving. It can be seen that the damping pressure rises less quickly at a lower speed with the same damping bushing and the same passage opening. This is not surprising since, according to the lower speed, a smaller amount of pressure medium through the throttle flow path between the damping bush and the wall of the

15 passage opening is displaced.

Claims

Claim

1. Pressure-actuated working cylinder with a piston (20), to which a piston rod (35) is fastened and which is axially displaceable between two end positions in a cylinder chamber with opposite changes in the volume of two cylinder chambers (21, 22) on one side on one side of the piston (20) arranged damping element (40), which has a rotationally symmetrical outer surface (50) with surface sections (51, 52, 53, 54, 55) of different diameters and when the piston (20) enters one end position immersed in a passage opening (25, 28) between the one cylinder chamber (21, 22) and a cylinder connection (23, 26) and thereby with the passage opening (25, 28) an annular throttle gap for throttled outflow of pressure medium from the cylinder chamber (21, 22) to the cylinder connection (23, 26), characterized in that the outer surface (50) of the damping element (40) in the formation of the dro Selselspaltes serving area is shaped such that, when the damping element (40) is completely immersed, it has a maximum diameter at the chamber-side beginning of the passage opening (25, 28) and after a surface section (52) with a small diameter or small diameters in a large immersion depth Damping element (40) has an average diameter over a short distance, which is between the maximum diameter and the small diameter.

2. Pressure medium operated cylinder according to claim 1, characterized in that the difference between the diameter of the through bore (25,

28) and the average diameter of the damping element (40) 3 to 4 times and between the diameter of the through hole (25, 28) and the small diameter is 4.5 to 6 times as large as the difference between the diameter of the through hole (25, 28) and the largest diameter.

3. Pressure medium operated cylinder according to claim 2, characterized in that the diameter difference between the through bore (25, 28) and the damping element (40) in the region of the large diameter 10 to 40 microns, in the region of the average diameter 40 to 120 microns and in the area of the small diameter is 60 to 180 micrometers.

4. Pressure-actuated working cylinder according to any preceding claim, characterized in that the outer surface (50) of the damping element (40) has a first area section (51) which extends over a certain axial extent and has a fixed large diameter, and a second area over a certain area axially extending surface section (52) with a fixed small diameter and a third extending over a certain axial extent surface section (53) with a fixed average diameter.

5. Pressure medium operated cylinder according to claim 4, characterized in that the second surface section (52) in further surface sections (54, 55) with a continuously changing in the axial progress diameter in the first surface section (51) and in the third surface section (53) transforms.

6. Pressure medium operated cylinder according to claim 5, characterized in that the further surface sections (54, 55) are truncated cone surfaces.

7. Pressure medium operated cylinder according to claim 5 or 6, characterized in that the further surface section (55) between the second surface section (52) and the first surface section (51) is axially longer than the further surface section (54) between the second surface section (52 ) and the third surface section (53).

8. Pressure-actuated working cylinder according to one of claims 4 to 7, characterized in that the axial extent of or between the first surface section (51) and the third surface section (53) located surface sections (52, 54, 55) is substantially larger is the axial extent of the first surface section (51) or the third surface section (53).

9. Pressure medium operated cylinder according to one of claims 5 to 7, characterized in that the axial extent of the second surface section (52) is substantially greater than the axial extent of the first surface section (51) or the third surface section (53).

10. Pressure medium operated cylinder according to one of claims 4 to 9, characterized in that the axial extent of the first surface section (51) and the third surface section (53) is in the range between 1 and 3 mm, depending on the cylinder size.