DE2508267A1 - Hydraulic pressure medium control system - has control piston operated via fingers connected with power input - Google Patents

Abstract

The hydraulic pressure medium control system for a double acting servomotor, especially steering of motor vehicles, has two control pistons acting as valve components to control the hydraulic feed or outlet to or from the working chambers. The control pistons are operated via fingers which are connected with a power input component and which engage in recesses in the pistons. In the neutral position of the control piston, a device generates a given pre-pressure in the working chambers of the servo-motor. The recesses (51, 52) in the pistons are so measured with respect to the finger (50, 49) that from a neutral position, there is a dead passage (x, x1, y, y1) between control piston and finger in both operating directions. A spring (76) is arranged between each control piston (37, 38) and a trhust bearing (77) fixed to the housing and is so tensioned that it balances the force exerted by the pre-pressure on the reaction face.

Description

Subject: Hydraulic pressure medium control system The invention relates to on a hydraulic pressure medium control system for route control of a double acting servomotor, in particular for power steering of motor vehicles a control valve device, the two control pistons as valve members for controlling the inflow of pressure medium from a pressure source to the working spaces or the Outflow of pressure medium from the working spaces of the servomotor into a drain includes, each of which has a control piston assigned to a working chamber of the servomotor is and also with means for manually actuating the control piston in Dependent of a relative movement between a force input member and a thus over elastically resilient connecting means connected force output member, which with the active part of the servo motor, e.g. B. connected to its working piston is, the displacement of the active work part on the control valve device is traceable and the control piston with the pressure in the working spaces of the servo motor acted upon reaction surfaces are provided, such that each work space one such reaction surface is assigned, the actuation of the control piston via with the force input member connected fingers or the like takes place in recesses the control piston intervene and take it along in both adjustment directions in are capable and with a device that is already in the neutral position the control piston has a certain pre-pressure in the working spaces of the servo motor generated.

In a similar pressure fluid control system of the "closed-center design" (DOS 2 262 575) the form was generated by the control piston at the front Operated by a two-sided lever with the interposition of helical springs were so that the coil springs were biased in the neutral position and the pressure on the reaction surface of the spring acted against it.

To achieve a non-reinforced, purely mechanically transmitted Part of the force from the force input element to the force output element were between the control piston and lever plunger provided, which only after a certain relative movement between The lever and control piston came into firm mechanical contact with them. An application these principles on control pistons, which are not frontal, but through in recesses engaging fingers are actuated and with regard to this actuation z. B.

in German Patent 1,133,642 would be described lead to a construction in which the springs are supported on the fingers and on the side facing the reaction surface of a control piston in the latter Work against a stop inside. The interior would have to face the reaction space be sealed and between finger and control piston would have to be in both directions of actuation to pass a certain game. Such a construction is in itself fully functional and also fulfills the requirements regarding pre-pressure in the neutral position, mechanical power transmission share without amplification below a response threshold and automatic return of the steered wheels to the straight ahead position. Yet there are cases in which the described arrangement of the spring is disadvantageous proves. One of these cases occurs when the control piston is used as one or multi-part stepped piston is formed and the reaction surface is the end face with the smaller diameter is. Since it is often not, especially with large forms is possible to accommodate the spring within such a small diameter would have to the larger diameter part of the piston made unnecessarily long which would increase the size of the entire control valve device. The second disadvantageous case occurs when there is a reaction force limitation with the help of a pressure relief valve arranged inside the control piston should be provided. Since such a pressure relief valve is certain axial Has dimensions, additional installation space would have to be provided for the spring. The same disadvantages arise when applying the principles described on a control valve device of the "open-center design". The pen is here though not necessary to generate a pre-pressure per se, as this is already due to the throttling effect of the circulating pressure medium arises.

However, the spring can be independent of fluctuations in the flow rate and the viscosity bring about a constancy of the admission pressure and thus the steering behavior improve in different environmental conditions.

It is therefore the object of the invention to provide hydraulic pressure medium control systems of the type mentioned to be designed so that with n "closed-center designs" a certain pre-pressure in the working areas of the servomotor already in the neutral position the control piston is achieved, a mechanical power transmission portion without hydraulic Gain below a response threshold is possible or in parallel next to one increased hydraulic component is possible and finally the automatic reset the steered wheels can be achieved in the straight ahead position. With n "open center designs" a flow and viscosity-independent constancy of the admission pressure is to be achieved. The design should be possible in a simple, cheaper and space-saving manner, especially when a pressure limiting device arranged inside the control piston to limit the reaction pressures or if there is "tolerance", the Reaction surface on the step with the smaller diameter of a stepped control piston is attached in one or more parts.

This object is achieved according to the invention in that the Dimensioned recess in a control piston opposite the finger or the like is that, starting from a neutral position, there is a dead gear between control pistons and fingers present in both directions of actuation is at least of the order of magnitude the relative travel of the control piston in relation to the finger when it is automatically reset of the steered wheels with a predetermined return speed or in the Order of magnitude of the relative distance to reach mechanical contact between finger and control piston and a spring between control piston and one housing fixed abutment and so biased at least in the neutral position is that it is the equilibrium of the force exerted by the pre-pressure on the reaction surface holds.

As long as there is no contact between fingers and in the dead corridor Control piston arises, this acts like the piston of a pressure control valve, which keeps the pressure in the associated working space at a constant value. This pressure from 2 to 5 bar, for example, is the admission pressure. However, if the finger comes into contact with the control piston, this is in the sense of a manually operated three-position, three-way valve ls positively actuated. The influence is with the comparatively small control paths the spring is negligible if one uses a spring with a low spring constant chooses. Although the support of the spring on a housing fixed abutment is a principle results in a different construction than with a support on the finger, one obtains in practice the same mode of action. Due to the support on the housing man the advantageous possibility of placing the spring on the end face facing away from the reaction surface act to sen caer but they are in a countersink starting from this end face to guide in the interior of the control piston with part of its length.

Further advantages and features can be found in the description and the subclaims evident.

The invention is based on the exemplary embodiments shown in the figures explained in more detail.

Figure 1 shows a pressure medium control system in partly symbolic form Shape with a cut along its axis and perpendicular to the control piston Control valve device.

FIG. 2 shows a section along the section line C-D from FIG.

FIG. 3 shows a similar section for a control valve device the open-center design.

A pump 1 sucks pressure medium from a reservoir 2 and promotes it in a pressure line 3, which is connected to a pressure line via a check valve 4 5 is connected. The pressure in the pressure line 3 is controlled by a pressure relief valve 6 limited. Furthermore, there is between the pressure line 3 and the storage container 2 a shut-off valve 7 attached, which depending on the pressure in the pressure line 5 is switched via a control line 8. The pressure line 5 to which a pressure accumulator 9 is connected, opens within a connection body 10 in a connection not shown, which with an annular groove P inside the Connection body is connected.

The annular groove P is adjacent to two further annular grooves A and B, which are connected to connections also not shown in detail, of which lines 11 and 12 lead to connections A1 and B1 of a servo motor 13. For the sake of simplicity, the pressure line 5 and the lines 11 and 12 are up to the annular grooves P, A and B drawn. The servo motor 13 has inside a piston 14 which is firmly connected to piston rods 15 and 16 on both sides and so divides working spaces 17 and 18 inside the servomotor 13. In the work room Connection A1 opens out in 17, while connection B1 opens out in working space 18. The piston rod 16 is in operative connection with the steered wheels, of which a wheel 19 is shown. The operative connection is indicated by the dash-dotted line 20 shown symbolically. The annular grooves A, B and P have transverse bores 21, 22 and 23 opposite, which are located in a sleeve 24 with a certain radial Game is arranged in the interior of the connection body 10, the resulting The gap is sealed by means of seals 25. The sleeve 24 has an internal bore 26 on. The transverse bores 21, 22 and 23 open into concentric to the bore 26 Annular grooves 27, 28 and 29. The sleeve 24 has a very small radial play penetrated by a force output member 30, which the connecting body 10 after protrudes outside and is designed as a pinion 31 there. As if through a dash-dotted line Line 32 indicated, the pinion 31 acts on a connected to the piston rod 15 Toothed segment 33 a. The pinion 31 is propagated in a journal 34, the is stored in a warehouse not shown. The force output member 30 is also mounted in the connecting body 10 by means of a bearing 35. In one of the Connection body 10 to the other side protruding part 36 is the force output member 30 provided for receiving two control pistons 37 and 38. The force output link 30 is with a inner bore 39 is provided, in which a torsion bar 40 protrudes, which with the aid of a transverse pin 41 is connected to the force output member 30 connected is. The torsion bar 40 is at its other end by means of a cross pin 42 firmly connected to a force input member 43, which by means of bearings 44 and 45 is mounted within a sleeve 46 that is fixedly connected to the part 36. In a cavity 47 forming between the bushing 46 and part 36 is the force input member 43 formed into a two-sided lever 48, which at its ends with axially parallel directed fingers 49 and 50 is provided, which will be described in more detail Way engage in recesses 51 and 52 within the control piston 37 and 38 with play.

The part 36 and the sleeve 46 are covered by a pot-shaped cover 53 enclosed at a distance, which is attached in a sealed manner to the connection body 10 and at its bottom 54 a penetration 56 sealed by means of a seal 55 for the force input member 43. The force input member 43 is with a Steering wheel 57 connected, as indicated by an action line 58.

The free space within the cover 53 is denoted by 59 and via a line T emanating from a connection not shown in detail connected to the reservoir 2. The control pistons 37 and 38 are made up of several individual parts composed. The control piston 37 has a tight fit in a bore 60 of the Part 36 slidably arranged control part 61, which two by an annular groove 62 has separate shoulders 63 and 64. Inside it has the control part 61 a through hole 65, which is partially threaded, into which a pin-like extension 66 of a piston part 67 is screwed. To avoid the piston part 67 has double centerings opposite the bore surrounding it 60 has a certain radial play and is perpendicular to its axis with the recess 51 provided, in which the finger 50 engages with all-round play. On his the peg-like extension 66 facing away from the end face comes the piston part 67 in contact with an individual part of the control piston designated as the reaction piston 68 37.

The reaction piston 68 is on its free end face of a Reaction space 69 is limited, which is opposite to space 59 by a sealing plug 70 which is held in position by a screwed cover plate 71 will. Inside the reaction flask 68, a piston 72 is slidably disposed, the is loaded by a spring 73, the other end of which is supported on the piston part 67. In the interior of the piston 72, a relief channel 74 is arranged, which leads from the reaction chamber 69 goes out and, after a certain stroke of the piston 72, moves into a spring 73 receiving bore 75 opens, which in turn with the space 47 and the space 49 and so that the line T is in communication. A spring 76 is arranged in the bore 65, which is supported on an abutment 77 fixed to the housing. In the area of the annular groove 62 A pressure channel 78 opens, the channels 79 lying outside the plane of the drawing in force from output member 30 with the annular groove 29 and thus with the annular groove P in connection stands. For a better understanding, the pressure channel 78 is also designated by P. In the neutral position of the control piston 37, the shoulder 64 closes a channel 80, via channels 81, also not shown in detail, in the force output element 30 is connected to the annular groove 27 and thus also to the annular groove A. Of the Channel 80 is therefore additionally designated with A. A channel 82 connects the channel 80 with the reaction space 69. That between the finger 50 and that of the reaction flask 68 facing side of the recess 51 existing game is denoted by x, while the play between fingers 50 and the side of the recess facing the control part 61 51 is denoted by y. The edges of shoulder 64 are called control edges 83 and 84, the control edge 83 of the annular groove 62 being adjacent. In the approach 66 a transverse bore 85 is attached, which for receiving a plastic stopper 86 or the like ient. The plastic plug 86 extends up to on both sides into the thread and therefore serves as an anti-twist device.

The control piston 38 is complete with the control piston 37 identical, so that corresponding parts have the same reference numbers but with a prime obtain. The channel 78 resp.

P accordingly opens into an annular groove 62 ', while the shoulder 64' one Channel 80 'closes in a neutral position, which via a channel 81' with the Annular groove 28 or the annular groove B is connected. For the sake of simplicity, the Channel 80 'is labeled B.

To explain the function, it is initially assumed that the pressure accumulator 9 was emptied, the pump 1 does not feed and no external forces on the steered Wheels 19 act. Since the working spaces 17 and 18 as well as the reaction spaces 69 and 69 'would then be depressurized, the springs 76 and 76' would the control piston 37 and 38 until they hit fingers 50 and 49. In such a In position, the control edges 83 and 83 'would make the connections P-A and P-B to have.

If now the pump 1 began to promote, these connections would Pressure medium flow into the working spaces 17 and 18 and cause a pressure increase there, which among other things also in the communicating with the work rooms 17 and 18 Reaction spaces 69 and 69 'propagates. There the pressure increases after overcoming the biases of the springs 76 and 76 'a displacement of the control piston 37 and 38 against the force of the springs. The power is transmitted from the reaction piston 68 or

681 via the piston part 67 or 67 'with the peg-like extension 66 or 66 'on the spring 76 or 76' and at the same time on the control part 63 or 63 '. The displacement of the control piston 37 and 38 takes place with increasing throttling of connections P-A and P-B take place until the control edges 83 and 83 'break these connections. The expression "interrupt" is like that here to understand that although there is no great flow, it is downstream of the Control edges 83 and 83 'leaks occurring are replaced, so that the pressure in the reaction rooms 69 and 69 'remains constant. This switch position is shown in FIG. The print is the "form". If now the steering wheel 57 is moved clockwise, the force input member 43 and move the lever 48 with the fingers 49 and 50 in a clockwise direction. The torsion bar 40 is somewhat tensioned, so that a relative movement between the force input member 43 and force output member 30 takes place. Move according to this relative movement the fingers 49 and 50 are also relative to the piston parts 67 'and 67. The games x 'and y become smaller. A distinction must now be made between two cases. The first Assume that the vehicle is moving on black ice, for example that the force required to steer is very low and the existing bias of the torsion bar is sufficient to move the wheels 19 and the servo piston 14, who should perform a movement to the left. This increases the work space 18, so that the pressure prevailing there is reduced at least for a short time. the The force in the reaction space 70 'is therefore also somewhat less and the spring 76' pushes the control piston into a position in which the control edge 83 'makes the connection P-B opens a little more.

It should be noted that this does not result in any amplification but only the drop in the form is compensated. In the opposite way the working space 17 is reduced in size, as a result of which there and in the reaction space 70 an increase in pressure arises.

This increase in pressure causes the control piston 37 to be displaced against the force of the spring 76 until the control edge 84 opens and the connection A-Thersteller so that pressure medium flows back from the working space 17 to the reservoir 2 can. The control piston 37 therefore also acts as a piston of a pressure regulating valve. Around Now to come to the explanation of the second case, it is assumed that the tension of the torsion bar 40 is not sufficient to cause the steered wheels 19 to move achieve. The fingers 49 and 50 will then move relative to the piston parts 67 ' and move 67 until the games x 'and y have disappeared and mechanical contact has taken place. With a further movement of the fingers 49 and 50, the control pistons 37 and 38 are then forcibly dragged along. Included Finally, the control edge 83 'opens the connection P-B. Pressure medium can be used for Flow to work space 18, build up pressure there and make the intended shift of the servo piston or the movement of the wheels 19. Since in the system 18, B1, 12, B, 22, 28, 81 ', 80' (-B) if there is a positive admission pressure, the overflow occurs of pressure medium without hissing or other noise generation. Likewise be Prevents air excretion and the servo piston 14 is hydraulically clamped. The amount of pressure increase depends on the force applied to the steering wheel 57, which from the reaction force applied in the reaction space 70 'above the pre-pressure depends on the reaction flask 68 '.

The mechanical contact between the finger 50 and the piston part 67 causes the control piston 37 to be displaced in such a way that the control edge 84 establishes the connection from the channel 80 to the bore 60, which in this area with the room 59 is connected (see Figure 1). In other words, it is the work space 17 connected to the line T, which corresponds to the connection A-T.

The pressure increase in the working space 18 can be reached at most the opening pressure of the pressure relief valve 6 increase. The increase in pressure in the Reaction space 69 'and thus the reaction force is, however, at a lower value limited'da at this value the piston 72 'relative to the reaction piston 68' so far is shifted against the force of the spring 73 'that the relief channel 74' opens into the bore 75 '. Since the influx of pressure medium from the channel 82 'in the Reaction chamber 70 'takes place in a throttled manner, there is an undesirably strong outflow prevented by pressure medium.

Finally, it should be noted that the automatic reset of the steered wheels in the straight ahead position causes similar processes to that Steering described above without hydraulic reinforcement. The only difference is that once the servo piston 14 through the force output member 30 is moved and on the other hand by external forces acting on the wheels. The possibility the automatic reset is particularly important if instead of the Torsion bar 40 'prestressed connecting means are used. To a certain To enable resetting speed, the games x and x 'must be a predetermined Have height, because of the size of this game, the flow cross-section from A to T resp.

depends from B to T. The size of the games y and y 'depends on which purely mechanical power transmission component until the onset of the hydraulic one Servo assistance is desired.

The games should not be made unnecessarily large, as they are then Failure of the hydraulic system can lead to unsafe steering behavior. It should be clear be that a rotation of the steering wheel 57 counterclockwise or in another External forces acting in the direction on the steered wheels 19 have the same effects in each case for the other control piston.

There is therefore no need for a detailed description. Since it is in the production of the fingers 49 and 50 and the recesses 51 and 52 around the Production of cylindrical profiles is a relatively simple matter keep tight tolerances. This means that the overall game x and y is also very precise can be tolerated. However, it is practically impossible without adjustment the correct games x and y and at the same time the correct position of the control edges 83 and 84 to achieve. With the help of the thread in the through hole 65 this can Difficulty to be resolved. The torsion bar 40 is expediently after Drawing dimensions drilled and pinned, while piston part 67 and control part 61 are also initially screwed as shown in the drawing, which, for example, by Insertion of a gauge between the piston part 67 and Shoulder 64 can be punished. The plastic stopper 86 prevents an automatic Loosen after de assembly or

during operation. After installing the control piston 61 and 61 ' (what was said above naturally also applies to the control piston 61 ') is the entire Control valve device mounted on a test stand with the cover 53 loosened, the allows the simulation of certain driving conditions. The games x and y are not straight forward measured and adjusted, but result from the measured pressures and torques. If predetermined setpoints are not reached, the control part 61 can help of a tool. The finger 50 serves as an anti-twist device for the piston part 67. With such an adjustment process, the Change the preload of the spring 76. In general, this can be accepted. Should However, if the change in preload is unavoidable, it is advisable to use the spring 76 to act directly on the control parts 61, since this opposite the abutment 77 assumes a fixed zero position.

In Figure 3, the same section as shown in Figure 2 is shown with the only difference that now control pistons 37 'and 38' of the open-center design are shown. The control parts 61 "and 61 '"' have control edges 83 "and 83 "'resp.

84 "and 84" 'shoulders 64 "and 64"'. The shoulders 64 " and 64 "'are dimensioned in their axial extension so that they are in the neutral position the control piston 37 'and 38' do not completely close the channels 80 and 80 '. That Pressure medium flowing into the annular grooves 62 "and 62" 'via the channel 78 therefore has the possibility of forming a certain back pressure in the channel 80 or in to flow into the channel 80 ', there also build up a certain dynamic pressure and otherwise past the control edges 84 ″ and 84 ″ ″ over the space 47, the space 59 and the line T to flow back to the reservoir 2. The back pressure in the Channels 80 and 80 'also propagate into reaction spaces 69 and 69' and act there against the force of the springs 76 and 76 'such that regardless of the respective Viscosity of the pressure medium, the pressure in channel 78 and any manufacturing tolerances that may occur the gaps at the control edges 83 '' and 83 '' 'resp.

84 '' and 84 '' 'adjust themselves in such a way that the pressure in channels 80 and 80 'or, in other words, the form is kept constant. This pressure control is maintained until fingers 50 and 49 touch piston parts 67 and 67 '.

If the movement of fingers 49 and 50 is clockwise, the piston part 67 is moved downwards so that the gap at the control edge 83 '' ' enlarges and grows in the channel 81 '(B), since at the same time the gap at the Control edge 84 '' 'is reduced in size and thus complicates the outflow of pressure medium. At the same time, the piston part 67 is moved upwards, so that the gap at the control edge 83 "is reduced and the flow of pressure medium is throttled more.

This reduction corresponds to an enlargement of the gap at the Control edge 84 ″, so that pressure medium can increasingly flow out of the channel 80 and causes a slight pressure drop there. The result is that in the working space 18 a Pressure increase takes place, but in the working chamber 17 the pressure drops. The servo piston 14 therefore moves to the left and assists the movement initiated by the steering wheel 57. Again, turning it counterclockwise has the same functions for the other control piston or the other work space.

In this case, too, all parts are first assembled the 'drawing dimensions. The setting of the control part 61 'relative to the piston part 67 is never again carried out on a test bench.

The invention is not limited to the exemplary embodiments shown restricted. So it is quite possible to have the control pistons in one piece or from two Manufacture consisting of parts.

It is also possible to control the control sections with the help of 3/3-way valves to design common piston shapes differently. It is still not necessarily necessary to use fingers that engage in bores in the control piston.

It is just as well conceivable to make grooves starting from the outer jacket, in which double-sided levers or the like engage. After all, they can The helical springs used are of course replaced by differently shaped springs will. Finally it should be noted that it does not matter for the idea of the invention whether a single steering valve or a so-called block steering with integrated Gearboxes are used or whether the torsion bar shown is prestressed by Lanyard is replaced.

Claims (7)

Patent claims: 1. - Hydraulic pressure medium control system for route control of a double-acting servomotor, especially for power steering of motor vehicles, the two control pistons as valve members for controlling the flow of pressure medium from a pressure source to the working spaces or the drainage of pressure medium includes the working spaces of the servomotor in a sequence, one of which in each case Control piston is assigned to a working space of the servomotor and furthermore with means for manual actuation of the control piston depending on a relative movement between a force input member and a connecting means which is thus elastically flexible connected force output element, which is connected to the active part of the servomotor, z. B. is connected to its working piston, the displacement of the active Is partially traceable to the control valve device and the control piston with from Pressure in the working spaces of the servomotor provided reaction surfaces acted upon are in such a way that such a reaction area is assigned to each working space, wherein the actuation of the control piston is connected to the force input member Finger or the like takes place, which engage in recesses of the control piston and these are able to take along in both adjustment directions and one Device is present that is already in the neutral position of the control piston a certain pre-pressure generated in the working spaces of the servomotor, thereby characterized in that the recess (51, 52) in a control piston (37, 38, 37 ', 38 ') relative to the finger (50, 49) or the like is dimensioned so that starting from a neutral position to a dead gear (games x, x ', y and y') between control pistons (Piston part 67 and 67 ') and fingers (50, 49) in both directions of actuation is at least present in the order of magnitude of the relative travel of the control piston (37, 38, 37 ', 38') opposite the finger (50, 49) with automatic return of the steered wheels (19) a predetermined return speed or in the order of magnitude of the relative distance to reach a mechanical contact between finger (50, 49) and control piston (piston part 67, 67 ') and a spring (76, 76') between the control piston (37, 38, 37 ', 38') and a housing-fixed abutment (77) arranged and at least in the neutral position so is pretensioned so that the pressure applied to the reaction surface (cross-section of the Reaction chamber 69 and 69 ') exerted force keeps the equilibrium. 2. - Hydraulic pressure medium control system according to claim 1, characterized characterized in that the spring (76, 76 ') in an end face opposite the reaction space (69, 69') outgoing bore (65, 65 ') within the control piston (37, 38, 37', 38 ') with part of its length is guided and against a fixed to the housing (part 36) connected against 7), which supports the control piston (37, 38, 37 ', 38') receiving bore (60, 60 ') at least partially covers. 3. - Hydraulic pressure medium control system according to claim 1 or 2, characterized in that all control edges necessary for controlling the pressure medium (83, 83 ', 83' ', 83' '', 84, 84 ', 84' ', 84' '') on that of the reaction space (69, 69 '), related to the finger (50, 49), facing away from the control piston (37, 38, 37 ', 38 '). 4. - Hydraulic pressure medium control system after one or more of the preceding claims, characterized in that the fingers (50, 49) in one with the storage container (2) communicating space are arranged. 5. - Hydraulic pressure medium control system according to claim 3, dadurcn characterized in that the control piston (37, 38, 37 ', 38') consists of at least two together There is screwable parts, one of which is the Ausnehmt gene (51, 52) having Piston part (67, 67 ') and the other one is the control edges (83, 84; 83', 84 '; 83' ', 84 "t 83 '"', 84 "') having control part (61, 61' 61", 61 "'). 6. - dydraulic pressure medium control system according to claims 5, thereby characterized in that the piston part (67, 67 ') opposite the inn surrounding bore (65, 65 ') has radial play that avoids double centering. 7. - Hydraulic pressure medium control system according to claim 5 or 6, characterized in that between the piston part (67, 67 ') and the control part (61, 61', 61 ", 61" §) an anti-rotation device (plastic stopper 86, 86 ') is arranged.