EP0250781B1 - Hydraulic force-transmitting element - Google Patents

Description

The invention relates to a hydraulic power transmission element with a cylinder which is open in an axial direction, a piston arranged therein, which projects beyond the cylinder opening and which, together with the cylinder, delimits a cylinder space, and with a single cylinder cylinder piston which extends essentially in the axial direction. Unit concentrically surrounding annular corrugated bellows, which has several bellows waves with troughs and wave peaks and the two bellows ends are each tightly connected to one of the parts forming the cylinder-piston unit, a variable pressure medium volume being formed between the cylinder-piston unit and the bellows is connected to the cylinder chamber via at least one opening or recess in the cylinder and / or piston with the interposition of a check valve closing under excess pressure in the cylinder chamber.

Such power transmission elements with bellows made of metal known from DE-OS 35 06 730 are used, for example, to which the invention is not limited, in internal combustion engines in the valve drive as an intermediate element between the cams of the camshaft and the valves, in order to automatically occur wear and temperature-related changes in length to ensure a play-free power transmission. As a closed system, they are independent of a pressurized oil supply and consequently also of the running and maintenance of the machine. In addition, there are no pressure oil losses to the outside. The effect of wear on the valve seat is that the total length of the cylinder-piston unit must be axially shortened, that is, the displacement of pressure oil from the cylinder chamber is required, which essentially takes place via the sliding seat between the cylinder and the piston. A corresponding pressure oil displacement results when the engine is stopped and the cam is positioned under the action of the force of the valve spring. The amount of pressurized oil displaced in the course of time and while the engine is at a standstill must be absorbed by the bellows space formed by the bellows element without the internal pressure increasing above a limit value there. On the other hand, a loss of pressure oil in the cylinder chamber, which results when the machine is at a standstill due to the reduction of the excess pressure in the cylinder chamber, can be sucked in or compensated for immediately from the reservoir in the bellows chamber via the check valve while the machine is running, without the internal pressure in the bellows chamber below to lower a certain limit. Likewise, the bellows space compensates for temperature-related changes in volume of the pressure medium, so that the transmission element as a whole always ensures a play and maintenance-free connection between the cam and the valve stem.

In the known case, two bellows arranged concentrically to one another are provided to form the bellows space, which are located in an annular space surrounding the cylinder piston unit, the outer wall of which is concentric with the cylinder piston unit and is formed by a jacket connected, for example, to the cylinder base. Here, the ends of the bellows, which are located at substantially the same height, are connected to the piston on the one hand and to the casing on the other hand, while their opposite ends are fastened to a common ring plate which is arranged axially displaceably in the said annular space and is also below corresponding change in length of the bellows axially adjusted according to the pressure medium volume to be absorbed by the bellows chamber. Due to this indirect, tight connection between the piston and cylinder via the two bellows and the ring plate connected between them, the wall that closes off the bellows chamber from the surroundings can also carry out or participate in the oscillatory movements that occur with each valve-moving power transmission due to the mutual axial adjustment Cylinder and piston result.

The function of this force transmission element would result in a correspondingly reverse manner if the distance between two components involved in the force transmission would increase in the course of operation. Then, if the bellows were shortened, a volume of pressure medium would not have to be taken in gradually from the bellows, but a volume of pressure medium would have to be gradually released with a corresponding increase in the length of the bellows.

The disadvantages of this known design are the requirement for two bellows and the ring plate connecting them to one another, and also the need for the jacket which closes the entire structural unit to the outside and is connected to the cylinder in accordance with the example described above. This results in a considerable amount of space in the radial direction, the need for a significant number of components only to represent the bellows space for accommodating the pressure medium volume, and in view of the inevitability of two bellows, the need to seal them with the adjacent components using a total of four weld seams connect to. Overall, this leads to a construction which is expensive in terms of both material and manufacturing costs.

The object of the invention is to modify and simplify a power transmission element of the type mentioned above and described in more detail above in such a way that to form the bellows space while reducing the total pressure medium volume and reducing the vibrating masses, only the use of a bellows with at least one specially designed Bellows shaft is required and there is a reduction in the cost of material and manufacturing, and in terms of space, a reduction in the size of the force transmission element and thus a corresponding saving in space at the installation site.

This task is based on a power transmission element of the type mentioned solved in that at least one of the troughs of the bellows adjacent to two flanks has an inner diameter smaller than that of the other troughs and / or that at least one of the wave peaks of the bellows adjacent to two flanks has a larger outer diameter than the other wave peaks.

From EP-A 0 169 437 it is known to design a hydraulic power transmission element of the generic type with only one bellows. In this known bellows, however, only the end runs out via a snap ring on the end of the piston and is fixed there accordingly, so that it cannot perform any functions in the sense of the object on which the invention is based.

By means of the measures according to the invention, only one bellows is initially used, the ends of which are attached directly to the cylinder and to the piston on the one hand, and thus directly and alone surrounds the cylinder-piston unit without additional components having to be used. However, this measure alone would not yet be a problem solution, since a bellows serving to compensate for axial movement between the cylinder and piston cannot be shortened in length at the same time and can be filled with an additional pressure medium volume without a significant increase in internal pressure, as is the case when cylinders and Pistons are pushed into each other while reducing the cylinder space. Rather, the problem is solved only by the fact that at least one, preferably of course several, of the troughs or wave peaks of the bellows have an inner diameter or larger outer diameter that is significantly smaller than that of the other wave troughs or wave peaks. This leads to the fact that with an axial shortening of the bellows with a simultaneous increase in the volume to be accommodated as a result of the associated pressure increase, the flanks of the bellows shafts, which are larger in the outer diameter or smaller in the inner diameter, exert a correspondingly greater axial compressive force than the flanks of the others because of their larger area Bellows waves, so that as a result not only do all the flanks inflate due to the increase in the volume of pressure medium to be absorbed, but also the base points or vertices of the flanks which are larger in the radial direction move away from one another or move towards one another at the expense of the other bellows waves. However, the volume released within or in addition to the larger bellows waves in the radial direction is also greater than the volume that may be displaced by the axial compression of the other bellows waves and then to be absorbed by the larger bellows waves, so that overall in or next to the larger ones in the radial direction Bellows waves an additional volume is available. This is done, which is to be emphasized in particular, without a significant pressure increase within the bellows compared to a bellows of the same size waves, which would have to absorb an additional pressure medium volume only by inflating the wave flanks.

In other words, it is according to the invention that the bellows shafts, which are larger or smaller in inner diameter, in addition to the flaring of their flanks which occurs equally for all bellows shafts due to the pressure medium increase caused by the additional volume, also with their base points or vertices at the expense of the other bellows shafts move axially in such a way that an additional volume is released in or next to the bellows waves larger in the radial direction, which is also larger than the volume possibly displaced in the other bellows waves, which essentially allows the bellows waves larger in the radial direction to accommodate an additional one Deliver volume, while the other bellows waves serve to absorb the movement resulting from the simultaneous shortening of the total length of the bellows.

The other bellows shafts must also be dimensioned accordingly in their radial extension, i.e. they must be designed so that their sum in terms of flexibility and service life alone is sufficient to accommodate the axial change in length of the cylinder-piston unit during operation, while the bellows shafts, which are larger in the radial direction, are sufficient their number and radial extension are essentially to be interpreted to the size of the additional volume to be accommodated, which results from the shortening of the total length of the bellows, the volume displaced from the cylinder space and the increase in the pressure medium volume with increasing temperature. Compared to the known design, however, the total volume of pressure medium required between two spaces formed by two bellows is also avoided by the invention.

It is expedient to design the inner diameter of all the troughs of the bellows in the same way, as will generally also result from the cylindrical outer contour of the cylinder-piston unit. This also keeps the pressure medium volume as small as possible compared to bellows shafts of different inner diameters. Depending on the circumstances of the individual case, however, it may also be appropriate for the outer diameter of all the shaft peaks of the bellows to be the same.

In the case of several bellows shafts with peaks of larger outside diameter or troughs of smaller inside diameter, these can be arranged next to one another. However, it is advantageous that in the case of a plurality of bellows shafts with peaks having a larger outer diameter or troughs of smaller inner diameter, one of the other bellows shafts is arranged between them, i.e. not all bellows shafts which are larger in the radial direction are grouped on the one hand and all other bellows shafts on the other hand are grouped side by side.

In the sense of this idea, it can be particularly expedient that in the case of several bellows shafts with peaks having a larger outside diameter or troughs having a smaller inside diameter, a bellows shaft with a reduced outside diameter of their shaft peak or enlarged inside diameter compared to the other bellows waves knife of their trough is arranged. Thus the ratio of the axial adjustment of the base points or the apexes of the shaft flanks caused by the pressure medium pressure is shifted even more in favor of the bellows shafts with the larger outside diameter or smaller inside diameter.

In a further development of the invention, the bellows length can be divided into a first section with shafts of the other diameter of its shaft summit and a second section with shafts of the larger and the reduced outer diameter of its summit or the smaller and the enlarged inner diameter of its wave trough, so that the said one the first section essentially serves to compensate or accommodate the change in length of the bellows, while the said second section essentially serves to simultaneously accommodate an enlarged volume. In order to intensify this effect, it can be advantageous that said second section is blocked against length changes, so that it remains unaffected by the change in the overall length of the bellows. Such blocking can take place, for example, in that between the two bellows sections mentioned, a rigid support part engages in the trough there, which is fastened together with the free end of the second bellows section to the cylinder or to the piston.

Another constructive realization of the principle on which the invention is based and which has been described above in detail, depending on the circumstances of the individual case, can also consist in the fact that the outside diameter of the shaft peaks and / or the inside diameter of the troughs of the bellows shafts continuously from the smallest value to one over the bellows length greatest value is formed gradually, if necessary. Here, there are progressively continuous or gradual transitions in the longitudinal direction of the bellows between the inclusion of the change in length of the bellows and the inclusion of an additional volume.

In practice, for example, in the case of a bellows with five bellows shafts of larger outer diameter and six other bellows shafts, based on a bellows inner diameter of 1.0, a bellows length of 2.2, an outer diameter of the tips of the other bellows shafts of 1.4 and an outer diameter of the peaks of the larger bellows waves of 1.8. In another case with a bellows section blocked with respect to a change in length with three bellows shafts with a larger outside diameter of their summit and four bellows shafts with a reduced outside diameter with their summit as well as a bellows section with four other bellows shafts not blocked with regard to length change, this resulted in a bellows length of 1.0 with a bellows length of 2 , 2 an outer diameter of the reduced bellows waves of 1.4, the other bellows waves of 1.6 and the bellows waves with a larger outer diameter of their peak of 1.8. It goes without saying that there will be significant changes with respect to the orders of magnitude mentioned only by way of example, depending on the changed ratio, for example, the additional volume to be accommodated to the total length of the bellows or the ratio of the total length of the bellows to the size of the axial length change to be accommodated .

• Fig. 1 eine erste Ausführungsform eines Kraftübertragungselementes im axialen Halbschnitt;
• Fig. 2 eine gegenüber dem Beispiel gemäß Fig. 1 geänderte Balgausführung;
• Fig. 3 ein Kraftübertragungselement mit einer Balgausführung der anhand der Fig. 2 dargestellten Art im axialen Halbschnitt und
• Fig. 4 bis 7 weitere Balgausführungen im axialen Halbschnitt.

Further details of the invention result from the following description of embodiments, which are shown in the drawing. The drawing shows:

• Figure 1 shows a first embodiment of a power transmission element in axial half section.
• FIG. 2 shows a bellows design modified compared to the example according to FIG. 1;
• Fig. 3 shows a power transmission element with a bellows design of the type shown in FIG. 2 in axial half-section and
• Fig. 4 to 7 further bellows designs in axial half section.

Fig. 1 shows in axial half section the cylinder 1 and the axially displaceable in its bore and thus guided relative to the cylinder 1 piston 2 of a power transmission element, for example between the cam of a camshaft and the valve stem of the valve of an internal combustion engine, for example the cam in contact the end face 3 of the cylinder and the valve stem may be in contact with the end face 4 of the piston 2. Cylinder 1 and piston 2 form a cylinder space 5, which is connected to the outside thereof by an axial bore 6 and a radial bore 7 of the cylinder-piston unit thus formed. The bore 6 is closed by the ball 8 of a check valve that closes under excess pressure in the cylinder chamber 5 and is pressed against the valve seat 10 by a spring 9, which is supported against the bottom of a cage 11. The cage 11 sits in a recess 12 of the piston 2 and is held against the bottom 13 of this recess by a spring 14, which in turn is supported against the cylinder 1. The cage 11 has openings 15, via which the cylinder space 5 is connected to the valve.

As can also be seen from the drawing, cylinder 1 and piston 2 form a respective collar 16 and 17 with the same outside diameter, with which the ends of a bellows, designated as a whole with 18, are welded, which concentrically surrounds the unit formed by cylinder 1 and piston 2. The bellows 18 consists of bellows shafts 19 arranged alternately next to one another and bellows shafts 20 provided with a noticeably larger outer diameter of their shaft peaks, all bellows waves starting from a uniform inner diameter of their shaft peaks which essentially corresponds to the outer contour of the cylinder-piston unit. The system closed by the bellows 18 is filled with a hydraulic pressure fluid.

If one thinks of the machine parts engaging on the end faces 3 and 4, between which a reciprocating power transmission takes place, this power transmission takes place by means of the cylinder-piston unit shown without play, since the cylinder-piston unit under the action of the spring 14 when pressure medium is drawn in from the space formed by the bellows 18 into the cylinder space 5, its length is increased until any play is compensated for in relation to the machine parts. This state generally corresponds to the installed state, where there may be too much pressure medium in the cylinder space 5, which can crawl outwards and into the space formed by the bellows 18 via the sliding seat between the cylinder 1 and the piston 2. This means that the element, which is hydraulically hard during operation, relieves the excess pressure in the cylinder chamber 5 when the external static load is on, so that the element no longer builds up any counterforce when the machine parts are stationary.

In the same way, further pressure fluid reaches the bellows 18 from the cylinder space 5 when the distance between the machine parts mentioned decreases due to wear, that is, the length of the cylinder-piston unit shown must be shorter.

However, this results in the need for a reduction in the length of the bellows 18, which in itself means a reduction in the volume contained in the bellows, and on the other hand the need not only to compensate for this volume resulting from the reduction in length, but also to compensate for or absorb the volume the cylinder space 5 additionally displaced volume.

So that this requirement can be met by the one bellows tightly connected to cylinder 1 and piston 2, this bellows has some bellows shafts 20 which are enlarged in the outer diameter of their summit compared to the other bellows shafts 19 and which, in the manner described in detail above, have an additional volume absorption by the bellows 18 allow without significant internal pressure increase, while the other bellows shafts 19 essentially or at least largely predominantly perform the task of accommodating the length reduction of the bellows and the axial displacement of the base points of the bellows shafts 20.

Fig. 2 shows a radial half section and in isolation, a bellows 21 with the same inner diameter of the troughs for all bellows and the outer diameter of their wave peaks compared to the other bellows waves 22 larger bellows 23 and adjacent bellows 24 with last compared to the other bellows 22 reduced outer diameter of their wave peak . As can be seen from FIG. 2, the larger bellows shafts 23 are always spaced apart from one another by a smaller bellows shaft 24, as is also the case in the example according to FIG. 1.

In the example according to FIG. 2, the bellows shafts 24 with a reduced outer diameter of their shaft summit serve, even more than was the case with FIG. 1, to enable the flanks of the bellows shafts 23 with an enlarged outer diameter of their shaft summit to move axially away from one another, since at one determined pressure prevailing in the bellows 21, the axial force components exerted by the flanks of the small bellows shafts 24 are substantially lower than those exerted by the flanks of the large bellows shafts 23. The volume displaced by compressing the bellows shafts 24 is considerably smaller than the volume which arises in the bellows shafts 23 as their flanks diverge, so that the bellows shafts 23 can correspondingly take up an additional volume.

FIG. 3 shows the installation of a bellows of the type described with reference to FIG. 2 in a cylinder-piston unit according to FIG. 1. The latter is provided with the designations used in FIG. 1, so that in this respect also the description of the function refer to Fig. 1.

In Fig. 3, the bellows, designated as a whole by 25, is tightly connected to the cylinder 1 with the free end of its section with bellows shafts 26 having a larger outer diameter of its shaft top and bellows shafts 27 with a reduced diameter of its shaft top, while the free end of its section is connected to the other bellows shafts 28 the piston 2 is tightly connected. In addition, the bellows section connected to the cylinder 1 is bridged by a support body 29 which is fastened on the one hand to the cylinder 1 with the bellows end and on the other hand engages with its free end 30 in the trough 31 separating the two bellows sections from one another and thus prevents that in relation to FIG Fig. 3 right bellows section can perform a change in length. This bellows section in the manner already explained with reference to FIG. 2 with respect to the shafts 23 and 24 serves exclusively to accommodate an additional pressure medium volume, while the bellows section having the other bellows shafts 28 serves practically exclusively to accommodate the change in length which occurs when the cylinders move axially 1 and piston 2 in the sense of shortening the total length of the cylinder-piston unit.

4 and 5 show a simplified representation of bellows 32 and 33 in axial section, in which, in reverse of the relationships described with reference to FIGS. 1 to 3, the bellows shafts 34 and 35 have an inner diameter which is smaller than that of the other bellows shafts 36 and 37 . The statements made above apply mutatis mutandis to the function of these bellows.

In the case of the bellows 38 shown in FIG. 6, on the other hand, the arrangement is such that, with the inner diameter of the troughs remaining the same, the outer diameter of the wave peaks of the bellows shafts 39 increases continuously over the bellows length, so that the bellows waves are seen to an increasing extent from left to right an additional volume can serve.

Finally, the latter applies mutatis mutandis to the bellows 40 shown in FIG. 7, in which both the outer diameter of the wave crests and the inner diameter of the wave troughs of the bellows waves 41 increase over the bellows length, which also increases the ring area formed by the wave flanks accordingly.

Claims (9)

1. Hydraulic force-transmission element having a cylinder (1) open in one axial direction, a piston (2) arranged therein and protruding beyond the cylinder opening, which piston together with the cylinder (1) defines a cylinder chamber (5), and having a single bellows (18, 21, 25, 32, 33, 38, 40) corrugated in annular form, concentrically surrounding the cylinder-piston unit and extending substantially in the axial direction, which bellows comprises a plurality of bellows corrugations (19, 20, 22, 23, 24, 26, 27, 28, 34, 35, 36, 37, 39, 41) with corrugation troughs and corrugation peaks, and the two bellows ends of which are each tightly connected with one of the parts (1, 2) forming the cylinder-piston unit, while between the cylinder-piston unit and the bellows (18, 21, 25, 32, 33, 38, 40) a variable pressure medium volume is formed which is connected with the cylinder chamber (5) through at least one opening or aperture (6, 7) in the cylinder (1) and/or piston (2), with interposition of a non-return valve (8) which closes under excess pressure in the cylinder chamber (5), characterised in that at least one of the corrugation troughs, each adjoining two flanks, of the bellows (18, 21, 25, 32, 33, 38, 40) comprises an internal diameter smaller than that of the other corrugation troughs and/or in that at least one of the corrugation peaks, each adjoining two flanks, of the bellows (18, 21, 25, 32, 33, 38, 40) has a larger external diameter than the other corrugation peaks.

2. Hydraulic force-transmission element according to claim 1, characterised in that the internal diameters of all corrugation troughs of the bellows (18, 21, 25, 38) are equal.

3. Hydraulic force-transmission element according to claim 1, characterised in that the external diameters of all corrugation peaks of the bellows (32, 33) are equal.

4. Hydraulic force-transmission element according to claim 1, characterised in that in the case of several bellows corrugations with peaks of larger external diameter and/or corrugation troughs of smaller internal diameter (34) these are arranged side by side.

5. Hydraulic force-transmission element according to claim 1, characterised in that in the case of several bellows corrugations with peaks of larger external diameter (20) and/or corrugation troughs of smaller internal diameter (35), at least one of the other bellows corrugations (19, 37) is arranged between these.

6. Hydraulic force-transmission element according to claim 1, characterised in that in the case of several bellows corrugations (23, 26) with peaks of larger external diameter and/or corrugation troughs of smaller internal diameter, between these there is arranged in each case a bellows corrugation (24, 27) with reduced external diameter of its corrugation peak and/or enlarged internal diameter of its corrugation trough, in comparison with the other bellows corrugations (22, 28).

7. Hydraulic force-transmission element according to claim 6, characterised in that the bellows length is divided up into a first section with corrugations (22, 28) of the other diameter of their corrugation peak and a second section with corrugations of the enlarged (23, 26) and of the reduced (24, 27) external diameter of its peak and of the smaller and of the enlarged internal diameter of its corrugation trough.

8. Hydraulic force-transmission element according to claim 7, characterised in that the second section is blocked against variation of length.

9. Hydraulic force-transmission element according to claim 1, characterised in that the external diameter of the corrugation peaks and/or the internal diameter of the corrugation troughs of the bellows corrugations (39, 41) are made graduating over the bellows length continuously from a minimum value to a maximum value, optionally steplessly.

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