EP2366908B1 - Actuator - Google Patents

Description

The invention relates to an actuator according to the preamble of patent claim 1.

Preferred but not limiting application of such actuators are e.g. Butterfly valves or ball valves in the beverage bottling industry. In such disc valves or ball valves is often in at least one end position or movements of the closure element in or out of the end position to produce a very large or the maximum switching torque from the actuator, the one-sided against spring force or double-sided with pressure medium, e.g. Compressed air, can be acted upon.

At the EP 1 222 403 A known generic actuator both guide rods are simultaneously and similarly loaded by the piston to transmit the reaction torque from the switching torque in the housing, regardless of the respective, depending on the stroke direction of the piston direction of the reaction torque. Both equally long guide rods are anchored in the same cover, eg welded. During the stroke movement of the piston, the free bending spiral lengths of the guide rods change inversely as the guide lengths. The free bending spiral length is the decisive parameter for the bending loads or bending stresses to which the guide rod is subjected mainly in the area of anchoring in the cover but also in the penetration area into the guide. Regardless of the magnitude of the reaction torque, the bending loads on each guide bar are greatest when the free bend sweep length is greatest. Since it can not be ruled out, depending on the design and function of the valve switched by the actuator, that the reaction torque at the piston is highest when the free bending gyration at both guide rods is greatest, there is a risk of wear in the area of the anchorages and also in the mouth areas of the guides and there up the guide rods. To take this circumstance into account, the guide rods are made of extremely heavy-duty and expensive material in the known actuator further. In addition, the piston skirt is reinforced by a metallic outer support tube, whereby the number of parts of the actuator is increased inappropriately. Further, because of cost reasons, the lid in which the two guide rods are anchored, is not made of the same expensive material as the guide rods themselves, the welding of two different materials is problematic, possibly such that an automated welding process can not be performed. Nevertheless, the risk of breakage in the respective weld remains acute, and at the same time in both guide rods, since both guide rods are anchored in the same lid and at the same time in the operation of the actuator subject to maximum bending forces when their free Biegewirklängen grow together. Often, the guide rods must be time-consuming rectified after welding, so they run properly in the guides.

At the EP 1 613 848 B1 ( DE 60 2004 001 988 T2 ) known actuator four guide rods are anchored in the housing. A pair of guide rods is anchored in one end in one cover, the other pair single end in the other lid, wherein the free ends of the guide rods in the stroke direction of the piston do not overlap each other. In the mouths of the guides plastic sliding bushes are arranged. Depending on the direction of the reaction torque, which depends on the stroke direction of the piston, only one pair transfers the reaction torque during the forward stroke, while the other pair transmits the opposite reaction torque to the housing during the return stroke of the piston. While the two guide rods of the one pair collect the reaction torque together, their free bending sweeps change over the stroke and vice versa the guide lengths are similar, ie, the sum of the free bending sweeps and the sum of the two guide lengths of these reaction torque transmitting guide rods vary depending on the stroke of the piston , Thus, the bending loads of the guide rods are greatest when their free Biegewirklängen are also the largest. This requires a very stable design of the anchorages of the guide rods. The four guide rods, which are radially equidistant from the piston axis, are diametrically opposed to each other in pairs, with one pair of guide rods circumferentially placed relatively close to a guide rod of the other pair, further limiting the amount of radians usable for the linkages in the piston skirt inexpedient. The actuator is, mainly because of the four guide rods multipart and requires a time and cost intensive production.

Further prior art is contained in US 6,793,194 B1 . EP 1 222 403 A2 ,

The invention has for its object to provide an actuator of the type mentioned, which is very reliable, structurally simple and yet inexpensive.

The stated object is achieved with the features of claim 1.

Since the end of a guide rod in a lid and the end of the other guide rod are anchored in the other cover of the housing, in each end position of the piston, the free bending spiral length of a guide rod is a minimum, so that the bending loads and bending stresses of this guide rod are also minimal while at the same time its guide length is a maximum, so the specific surface pressure between the guide and the guide rod remains small, even if then the reaction torque to be transmitted is a maximum. The guide rod, whose free Biegewirklänge is a minimum, thus relieves the other guide rod, the free Biegewirklänge is then a maximum. This reduces overall the bending loads and bending stresses for the two guide rods, both in the anchoring areas and in the mouths of the guides. This is accompanied by a reduction in the wear of the guide rods in the guides. In the stroke movement of the piston from the respective end position, although the free Biegewirklänge the guide rod increases whose free Biegewirklänge initially amounted to a minimum, but at the same time decreases the free Biegewirklänge the other guide rod, so that over the stroke of the piston, the reaction torque while reducing the bending forces is easily transmitted for both guide rods. The anchoring areas, such as welding areas, are less heavily loaded, which reduces the risk of damage and at the same time noticeably increases operational safety and process reliability. Due to the lower bending loads of the guide rods they can be made of a cost-effective material, possibly of the same material as the lid. This simplifies the anchoring, for example by welding. The actuator consists of only a small number of parts and can be produced inexpensively, since, for example, the production of the anchoring area can be automated, and the guide rods may not need any messages. Since the respective reaction torque is introduced into the housing in a particularly stable manner in both stroke end positions of the piston, the torques to be transmitted by the actuator to the functional element, for example the closure member of a disk valve, can be very precisely predicted in terms of their values and characteristics and on the switching behavior of the disk valve vote, for example so that these torques have their, preferably plateau-like, maxima at the stroke end positions of the piston.

In an expedient embodiment, the free ends of the two guide rods overlap in the stroke direction. The overlap may, preferably, correspond to about one third of the outside diameter of the piston, or a multiple of the strength of the guide rods. As a result, the guide length and the guide rod is relatively large and thus sustainable, the free Biegewirklänge is a maximum.

It is advantageous if the given in a respective Kolbenendstellung in the housing free maximum bending sweep length of a guide rod between about half to two-thirds of the Kolbenaußendurchmessers and / or about twice the overlap of the free ends of the two guide rods. This relatively short free bending spiral length reduces the bending loads of this guide bar to a moderate degree, anyway supported through the then with minimal free Biegewirklänge very stable load-absorbing other guide rod.

Particularly important is the sum of the guide lengths and the sum of the free Biegewirklängen of both guide rods in and out of the guides regardless of the direction of the reaction torque on the piston or the stroke direction of the piston over the entire piston stroke constant. This is particularly important in terms of a uniform and not locally concentrated wear in the guides or on the guide rods.

In an expedient embodiment, the guide rods are placed axially symmetrically and diametrically opposite with respect to the piston axis. In this way, the reaction torque is received symmetrically and transmitted into the housing.

Further, it is advantageous if the piston has a piston plate and a piston skirt containing the scenes and the guides, one guide their open mouth in the piston plate and its blind end in the piston skirt, whereas the other guide their open mouth in the piston skirt and her having blind end in the piston plate. Although the two guide rods are immersed in the pistons from different sides, the formation of the guides ensures that pressure can not pass from one side of the piston to the other via the guides or linkages. In addition, this results in a largely symmetrical piston formation with sufficient meat around those areas in which forces are transmitted.

In an expedient embodiment, the piston can be acted upon by pressure medium via a pressure medium connection and against a return spring and / or on both sides via opposite pressure medium connections. In one variant, the piston movement takes place in a stroke direction by the pressure pulse from the pressure medium connection, and in the opposite direction by the return spring, optionally depending on either complete pressure relief in the pressure medium connection or a controlled pressure relief. In this case, the actuator can be used so that, e.g. an actuated disc valve is opened by pressurizing the piston and closed by the return spring (normally closed = NC) or vice versa (normally open = NO). In the other case, the piston in each stroke direction by a pressure pulse of a pressure medium, e.g. Compressed air, operated.

Depending on the degree of opening, for example a disk valve, the torque to be transmitted depends on the angular position relative to a zero position. The torque is usually the lowest within, for example, a 90 ° rotational adjustment between about 22 ° and 68 °. For this purpose, the slope of each backdrop is usually steeper in both initial ranges but the same chosen as in an intermediate region of the backdrop. However, practice shows that, for example, when the compressed air is applied to the piston against a return spring, and provision of the piston with the return spring, the torque from the displacement of the transverse axis in both initial areas of the scenes are different. To avoid this, the slopes of the scenery in the initial areas are expedient steeper than in the intermediate area and chosen differently, so that the torque generated at the spring return and the torque generated upon application of compressed air at least largely the same size. Thus, it is advantageous to avoid overloading in the scenes, the bearing of the functional element and the actuator shaft and the connections of the functional element in the valve. In addition, each set the same switching values or switching behavior in different ways, for example, operated by the actuator switching valve, for example, when the disc valve is designed by the actuator air-opening but spring-closing or air-closing but spring opening.

In an expedient embodiment, the pitch angles in the initial regions differ by about 2% to 10%, preferably about 5%, and the pitch angle in the intermediate section is about 60% of the pitch angles in the initial regions. Preferably, the steepest pitch angle is about 66 °, the pitch angle in the intermediate area about 38.9 ° and the less steep pitch angle about 63 °. With this difference, the pitch angle in the two initial areas can be at least largely produce the same torques when compressed air and spring return.

In this case, the largest pitch angle can be provided in an initial region where, in the stroke end position of the piston and at the slightest force of the return spring, the transverse axis engages the link.

Since the forces arising in the power transmission in the piston are distributed over a large area and only moderate, in an expedient embodiment of the piston can be made of cost-effective and easy to process high-density polyamide. The polyamide does not require fiber reinforcement, which, however, should not be excluded, e.g. to provide a glass fiber reinforcement in the piston.

Suitably, each cover has a single receptacle for a guide rod end. The guide rod is anchored with its end in the receptacle by welding, screwing, shrinking, gluing or caulking. Anchoring can be done in an automated workflow be prepared and thereby with high precision, so that a message of the anchored guide rods is unnecessary.

Particularly expedient, cost-effective and optimal in terms of the quality of anchoring the guide rod is anchored with its end in the receptacle of the lid by friction welding, preferably automated friction welding. The friction welding process leads to a nearly monolithic anchoring and makes it possible to perform an exact positioning and alignment of the guide rod in the lid during friction welding, so that a message of the guide rod can be omitted.

Thanks to the bending loads or bending stresses of the guide rods, which are reduced as a result of the design, they can be made of a cost-effective material, e.g. from a steel of specification 1.4301 or an at least substantially similar material.

In view of ease of manufacture, it may be appropriate to use as a guide rods circular cylindrical solid rods, and form the guides as blind holes in the piston. However, this should not exclude to use as guide rods and hollow sections or tubes and the latter aufzustecken on provided on the lids pin and e.g. anchored by friction welding.

Fig. 1

einen Achsschnitt eines Aktors in einer Endstellung,

Fig. 2

eine Abwicklung des Außendurchmessers eines Kolbens des Aktors mit einem charakteristischen Verlauf einer Kulisse, und

Fig. 3

ein Diagramm zum vom Aktor erzeugten Drehmomentverlauf über einen nur beispielhaft mit 90° gewählten Schaltwinkel.

An embodiment of the subject invention will be explained with reference to the drawings. Show it:

Fig. 1

an axial section of an actuator in an end position,

Fig. 2

a development of the outer diameter of a piston of the actuator with a characteristic course of a backdrop, and

Fig. 3

a diagram of the torque curve generated by the actuator over a selected example only with 90 ° switching angle.

The actuator A is used for Drehverstellen a rotatable functional element G, for example, a closure element of a disc valve V or ball valve, for example in the beverage industry, where the functional element G for rotational adjustment over a certain angle of rotation (eg 90 °) requires a certain torque and torque curve, the or The actuator A generates and applies. The required switching torque can be a maximum for example in the movement of the functional element G in or out of an end position. The actuator is in the embodiment in Fig. 1 fluid-actuated For example, by means of compressed air, in a stroke direction against a return spring, but could also be druckmittelbeaufschlagbar double-sided, or driven by another, a linear motion generating drive element, and generates from the linear drive movement, the rotational movement of the functional element G. When the Actuator A in a stroke direction by compressed air against the return spring and in the other direction by the return spring, the switched valve, eg a disc valve, either compressed air closing and spring opening or spring closing and compressed air opening be designed (NC = normally closed, or NO = normally open).

The actuator A has in the embodiment shown, for example, a circular cylindrical housing 1, which consists of a cylindrical sleeve 5, e.g. metal, and upper and lower covers 5, 3 closing the sleeve 5, e.g. made of a metal such as steel, is closed. The two covers 3, 4 are inserted into the sleeve 5 and fixed for example by laser welding.

In the housing 1, a piston 2 is linearly reciprocable, in the embodiment shown, for example by compressed air via a pressure medium connection 11 in the lid 3 in a stroke direction against the force of a return spring 17 created between the piston 2 and the other cover 4 is, in the opposite stroke direction by the return spring 17 zurückstellbar as soon as the pressurization is canceled or reduced.

The piston 2 may be made of metal or metal and plastic or only of plastic, and is suitably made of a polyamide in a high-density setting and without fiber reinforcement. The piston 2 has a piston plate 10 and a piston skirt 9 integral therewith, which surrounds an inner cavity 12 in which the upper end of an actuator shaft 25 is immersed, which is rotatably mounted in the cover 4, for example by means of a bearing 22, and optionally seals. In the skirt 9 there are two diametrically opposite, opposite directions, e.g. helical splines 13 molded, in which engage the ends of a fixed in the actuator shaft 25 transverse axis 8. The sliders 13 may be circumferentially angular over a radian, e.g. of 90 ° or more or less. Their slope can be uniform or variable. Its axial length is for example greater than the total stroke of the piston 2 in the housing. 1

About the engagement of the transverse axis 8 in the scenes 13, the piston 2 converts its linear lifting movement into a rotational movement of the actuator shaft 25, wherein the actuator shaft 25 generates a constant or varying torque over the rotation angle, provided that the piston 2 is prevented during its strokes at a relative rotation about the piston axis.

For the latter purpose, two guide rods 6a, 6b are installed in the actuator A, which engage displaceably in guides 18a, 18b of the piston 2. The guide rods 6a, 6b, e.g. Solid rods with circular cylindrical cross section, e.g. made of a steel of specification 1.4301, or an equivalent material, are parallel to each other and as well as the guides 18a, 18b parallel to the axis of the piston 2 and to its stroke direction. The guide rods 6a, 6b are e.g. placed symmetrically and diametrically opposite with respect to the piston axis and each anchored at one end.

The one guide rod 6a is anchored with its upper end, for example in a recessed receptacle 14 in the upper lid 3 and cantilevered with its other end free. The other guide rod 6b, however, is anchored at one end in, for example, a receptacle 15 of the lower lid 4 and projects with its free end opposite to a guide rod 6a. The free ends of both guide rods 6a, 6b overlap in a central region of the actuator A, for example with an overlap, which may be slightly shorter than a guide length xb, with the shown in the upper end position of the piston 2, the free end of the guide rod 6b in the Guide 18b is guided. In the same operating position, however, the guide length xa of the one guide rod 6a in the guide 18a is substantially equal to the projection length of the guide rod 6a.

The two guides 18a, 18b are, for example, identical blind holes, wherein the guide 18a has its mouth 20 in the top of the piston plate 10 and a blind end 19 at the lower end of the piston skirt 9. On the other hand, the guide 18b has its open mouth 20 on the lower side of the piston skirt 9 and its blind end 19 adjacent to the top of the piston plate 10, such that no pressure-transmitting communication between the underside of the piston plate 10 and the top thereof takes place through the guides 18a, 18b can. In addition, the piston plate 10 is sealed by a circumferential ring seal 21 on the inner wall of the sleeve 5. In the embodiment shown, the space below the piston plate 10, in which the return spring 17 is arranged, having a vent opening.

When the piston 2 from the in Fig. 1 shown end position toward the other end position generates the conversion of the linear movement in the rotational movement of the functional element G, which is transmitted with a torque via a coupling end 7 of the actuator shaft 25, via the scenes 13 and the transverse axis 8, a reaction torque on Piston 2, whose direction depends on the stroke direction. This reaction torque is removed from the two guide rods 6a, 6b in the housing 1, more precisely the cover 3, 4. The guide rods 6a, 6b subjected to bending stresses, which are mainly transmitted from the anchors 16 in the receptacles 14, 15, and partly arise where the guide rods 6a, 6b enter the guides 18a, 18b.

A variable which determines the height of the bending loads of the guide rods 6a, 6b is the so-called free bending spiral length of each guide rod, ie the length which exists during the transmission of the reaction torque between the mouth of the respective guide 18a, 18b and the respective anchoring 16. In the shown one end position in Fig. 1 the free bending warp length ya of the guide rod 6a is minimum or even zero, whereas the free bending warp length yb of the other guide rod 6b has an extent corresponding, for example, to half to two thirds of the outer diameter of the piston 2 or approximately twice the guide length xb. The guide length xb may correspond, for example, to about one third of the outside diameter of the piston, or a multiple of the strength of the guide rods 6a, 6b, eg about three times the thickness.

Since in the end position shown the free bending yaw length ya is a minimum or zero, arises when generating the torque for the functional element G from the reaction torque on the piston 2 only a minimal bending load for the guide rod 6a, actually only a shear stress transverse to the longitudinal direction of the guide rod 6a The guide rod 6a consequently transmits a major part of the reaction torque into the cover 3. However, the other guide rod 6b, in which it is subjected to bending loads due to the free bending-wave length yb, also assists, because of the guide length xb but also introduces a portion of the reaction torque in the other cover 4.

The sum of the guide lengths xa + xb of the two guide rods 6a, 6b in the guides 18a, 18b has a certain value, but remains constant over the stroke of the piston 2, since the guide length xb increases to the same extent as the guide length xa of the guide rod 6a decreases, and vice versa. The situation is similar with the free bending-wave lengths ya, yb, whose sum ya + yb also remains constant over the stroke of the piston 2.

Overall, this means that by opposing the anchoring of the ends of the two guide rods 6a, 6b in the covers 3, 4, the bending loads or bending forces for the guide rods 6a, 6b resulting from the reaction torque of the piston are reduced, in particular for each of the shorter or no free bending wave length having guide rod 6a or 6b, which then transmits a major part of the reaction torque when their guide length xa and xb is optimally large, which is a low specific surface pressure in the transmission of the main part of the reaction torque brings, and thus a reduced wear between the guide rods 6a, 6b and the guides 18a, 18b. Since over the stroke of the piston 2, the sum of the guide lengths and the sum of the free Biegewirklängen remains constant, the bending loads of the guide rods do not or hardly, and wear between the guide rods and the guides is even or distributed over a large area. This allows the use of a cost-effective material, such as a steel of specification 1.4301 for the guide rods 6a, 6b, which may optionally be the material of the cover 3, 4. Furthermore, since the sum of the guide lengths xa, xb of the two guide rods always remains constant, the piston 2 also requires no reinforcements in order to better absorb local load peaks.

The guide rods 6a, 6b can be welded, screwed, glued, shrunk or caulked in the receptacles 14, 15. A preferred method of anchoring is friction welding. For this purpose (formation of the welding areas 16 in the receptacles 14, 15), each guide rod is rotated in a tool under axial pressure in the receptacle 15 of the lid 3, 4, until under heat generated by friction, a welding process takes place, resulting in a nearly integral and monolithic welding region 16 leads, in which at least a significant part of the front end face and also a part of the peripheral surface of the end of the respective guide rod 6a, 6b with the material of the lid 3, 4 is welded. This friction welding process can be automated and offers the additional advantage of already performing a precise alignment of the guide rod 6a, 6b with respect to the axis of the lid 3, 4 and thus of the housing 1 during friction welding, whereby a message after welding can be dispensed with. This offers manufacturing advantages and on the one hand leads due to the high quality of the welding area 16, e.g. between very similar or the same materials, and the reduced bending loads for the guide rod 6a, 6b to increase the operational or process reliability of the actuator A. In addition, an automated welding process, it could alternatively be laser welded, perform inexpensively.

The diameter of the piston 2 or its stroke length and the length of the housing 1 depend on the applications and the required torques for the functional element G. Different torques for the functional element G may require actuators of different diameter (piston diameter), provided that a pressure medium actuation (With compressed air) is made, either a one-sided pressure medium applied against the return spring 17 or alternatively a double-sided alternating pressure medium.

In an alternative embodiment, the two guide rods 6a, 6b could be arranged not diametrically opposite each other but at arbitrary mutual angular displacements, e.g. with regard to a larger angle of rotation. The transverse axis 8 can engage in the scenes 13 via sliding shoes or plain bearings or bearings to improve the friction conditions here. Furthermore, the guide rods 6a, 6b could have any external cross-sections which fit into the guides and / or be formed as hollow profiles or tubes. Actuator A may contain a continuous lubricant supply for lubricating the areas in which relative movements take place with simultaneous transmission of power. A tube as a guide rod 6a, 6b could be plugged in an alternative, not shown, on a pin provided on the cover 3, 4 and e.g. be anchored by friction welding. The pin thus forms a local integrated reinforcement in and adjacent to the anchoring area, or could even extend over a substantial portion of or the entire length of the pipe. This could also be a measure to make the messages of the guide rods 6a, 6b dispensable.

Fig. 2 shows a development of the outer periphery of the piston 2 with the example, only indicated by its center line 21 backdrop 13. The gate 13 has initial areas 21a, 21c and an intermediate region 21b. The slope of the slide 13 (the included with a radial axis perpendicular to the piston axis angle) is in the initial region 21 a largest (slope angle W1), in the intermediate region 21 b smallest (slope angle W2), and is in the other initial region 21 c greater than in Intermediate area 21 b, but smaller than in the initial area 21 a (pitch angle W3). In a specific embodiment, the pitch angle W1 may be about 66 °, the pitch angle W2 about 39 ° or 38.9 °, and the pitch angle W3 about 63 °. That is, the pitch angles W1 and W3 differ by about 5%, while the pitch angle W2 is only about 60% of the pitch angles W1, W2. Between the areas 21 a, 21 b and 21 c clean rounded transitions are provided.

In the embodiment in FIG Fig. 1 is therefore the largest pitch angle W1, for example, in the initial region 21 a, in which engages the end of the transverse axis 8 of the actuator shaft 25 in the upper Hubendstellung shown piston 2, as soon as the piston is acted upon by the pressure medium connection 11 with pressure medium. On the other hand, the transverse axis 8 enters the other initial area 21c with the slightly smaller pitch angle W3 when the Return spring 17, the piston 2 straight back into the in Fig. 1 shown upper Hubendstellung brings.

By the in Fig. 2 indicated course of the backdrop 13 (expediently two diametrically opposed scenes 13 are provided in the skirt 9) is achieved in the operation of the actuator A, a torque curve, as in Fig. 3 is indicated schematically. On the vertical axis in Fig. 3 the torque (Nm) is indicated, while the horizontal axis represents the angular range in degrees. There is a largely symmetrical torque curve (curve 22) given, in which the torque reaches its maximum value M _max respectively at the two end positions of the piston, these maxima are almost plateau-like and at the same height, ie, the torque maxima are at least in about the same size. The torque M _max is for example about 40 Nm, while the minimum of the torque M _{min is} about only 10 Nm. The reaction torque transmitted by the piston 2 to the guide rods 6a, 6b extends correspondingly, ie, the strongest reaction torque then makes the most particularly stable support on the guide rods 6a, 6b used profitably. This in Fig. 3 schematically indicated M _min could be flatter than shown and eg plateau-like.

Claims (15)

1. Actuator (A) for a rotating function element (G), in particular a closing element of a disk valve or a ball valve (V), having a housing (1) comprising at least one pressure means supply (11) and being closed at both ends by covers (3, 4), a piston (2) being guided to reciprocate in the housing (1) in a sealing manner, the piston (2) containing diametrically opposed, convolution-like guiding grooves (13) for a transverse axis (8) of an actuator shaft (25) rotatably mounted in a cover (4), submerging into the piston (2) and rotatably driven by the piston (2) with torques in opposite directions, and having two parallel guide rods (6a, 6b) firmly anchored in the housing each only at one end, the guide rods (69, 66) engaging in guides (18a, 18b) extending in the direction of the piston stroke and ending blind within the piston stroke, characterized in that the one guide rod (6a) is anchored in the one cover (3), and the other guide rod (6b) is anchored in the other cover (4), and that the two guides (18a, 18b) end blind in opposite directions in the piston (2).
2. Actuator according to claim 1, characterized in that the free ends of the two guide rods (6a, 6b) overlap in the direction of the piston stroke, preferably with an overlap approximately corresponding to one third of the piston's outer diameter.
3. Actuator according to claim 1 or 2, characterized in that in a respective piston stroke end position the free effective bending length (ya, yb) of only one guide rod (6a, 6b) amounts to between approximately half to nearly two thirds of the piston's outer diameter, and/or approximately to twice the overlap of the free ends of the two guide rods (6a, 6b).
4. Actuator according to at least one of the preceding claims, characterized in that the sum of the guide lengths (xa, xb) of both guide rods (6a, 6b) in the guides (18a, 18b), preferably also the sum of the free effective bending lengths (ya, yb), is constant over the piston stroke independent of the direction of the reaction torque at the piston (2) or the stroke direction of the piston (2).
5. Actuator according to at least one of the preceding claims, characterized in that the guide rods (6a, 6b) are placed in the covers (3, 4) with respect to the piston axis axially symmetrically and diametrically opposed.
6. Actuator according to at least one of the preceding claims, characterized in that the piston (2) comprises a piston plate (10) and a piston skirt (9) containing the guiding grooves (13) and the guides (18a, 18b), one guide (18a) having an open mouth (20) in the piston plate (10) and its blind end (19) in the piston skirt (9), and the other guide (18b) having an open mouth (20) in the piston skirt (9) and its blind end (19) in the piston plate.
7. Actuator according to claim 1, characterized in that the piston (2) is to be actuated in one stroke direction from a pressure means supply (11) against a readjusting spring (17), and in the other stroke direction by the readjusting spring (17), and/or that it is to be actuated at both sides by pressure means supplies disposed at opposed sides in the housing (1).
8. Actuator according to at least one of the preceding claims, characterized in that each guiding groove (13) comprises in starting regions (21 a, 21 c) different but greater pitch angles (W 1, W3) - with respect to a radial plane perpendicularly through the piston axis - than the pitch angle (W2) in an intermediate region (21 b) between the starting regions (21 a, 21 c), preferably such that the torques transmitted from the actuator shaft (25) to the function element (G) by engagement of the transverse axis (8) in the starting regions (21 a, 21 c) at least approximately have the same maxima (M_max), independent of the action of the pressure means or the readjusting spring (17) on the piston (2).
9. Actuator according to claim 8, characterized in that the pitch angles (W1, W3) in the starting regions (21a, 21 c) differ by about 2% to 10%, preferably by about 5%, and that the pitch angle of slope (W2) in the intermediate region (21 b) amounts to about 60% of the pitch angles (W1, W3), where preferably the pitch angle (W1) amounts to about 66°, the pitch angle (W2) amounts to approximately 40° or 38.9°, and the pitch angle (W3) amounts to about 63°.
10. Actuator according to claim 9, characterized in that the greatest pitch angle (W1) is provided in the starting region (21 a) in which in the stroke end position of the piston (2), the transverse axis (8) engages with the lowest acting force of the readjusting spring (17).
11. Actuator according to claim 1, characterized in that the piston (2) is made of high-density polyamide, preferably without fiber reinforcement.
12. actuator according to at least one of the preceding claims, characterized in that each cover (3, 4) comprises either a depressed or a pin-shaped mounting (14, 15) for a guide rod end, and that the guide rods (6a, 6b) are inserted into the mountings (14) or placed over the mountings (14) and are welded, screwed, shrunk, glued or calked there.
13. Actuator according to claim 12, characterized in that the respective guide rod (6a, 6b) is anchored in a welding region (16) in or on the mounting (14) of the cover (3 or 4) by friction welding, preferably automated friction welding, preferably at the front side and at the outer or inner periphery.
14. Actuator according to claim 1, characterized in that at least the guide rods (6a, 6b) preferably consist of a steel of specification 1.4301 or a metal alloy comparable to this specification.
15. Actuator according to at least one of the preceding claims, characterized in that the guide rods (6a, 6b) are equally dimensioned, circular cylindrical solid material rods or tubes and that the guides (18a, 18b) are blind holes.

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