WO2018137847A1 - Drive train - Google Patents

Abstract

The invention relates to a drive train (1) of a drive (2) for the motorized adjustment of a closure element (3) of a motor vehicle, wherein at least one frictionally locking mechanism (5, 5') is provided for making available a frictional force or a frictional moment, wherein the frictionally locking mechanism (5, 5') is a constituent part of a brake mechanism (6) or clutch mechanism (7) of the drive train (1), wherein the frictionally locking mechanism (5, 5') has two frictionally locking elements (8, 9; 8, 9') which are in frictional engagement or can be brought into frictional engagement with one another, and a pressing mechanism (10) for the generation of a pressing force (F) of the frictionally locking elements (8, 9; 8, 9') onto one another, and wherein the frictional force results from the pressing force (F) and the coefficient of friction between the frictionally locking elements (8, 9; 8, 9'), and the frictional moment results from the pressing force (F), the mean frictional radius (R_m, R_m') and the coefficient of friction between the frictionally locking elements (8, 9; 8, 9''). It is proposed that at least one of the frictionally locking elements (8, 9, 9') is configured in such a way that the influence of a decrease in the thickness (H_R) thereof on the resulting frictional force or the resulting frictional moment is compensated for at least partially.

Description

 powertrain

The invention relates to a drive train of a drive for the motorized adjustment of a VerscMusselements of a motor vehicle according to the preamble of claim 1, a drive for the motor Versteltang a VerscMusselements of a motor vehicle with such a drive train according to Speech 12 and a closure element assembly of a motor vehicle with such a drive according to spoke 14, The powertrain in question of a drive finds application in. Frame, the motorized adjustment of a VerscMusselements of a motor vehicle. Such closure elements may be, for example, doors, in particular sliding doors, or flaps, in particular tailgates, trunk lids, hoods, load compartment floors or the like, of a motor vehicle. In so far, the term "closure element" is to be understood broadly.

The drive train in question serves to guide the power flow of the driving force generated by a drive motor of the drive. Accordingly, the drive train drive components such as shafts, gears, clutches, brakes o. The like. Have.

The known drive sträng (DE 10 2014 1 14 617 AI), from which the invention proceeds, is part of a spindle drive for the motorized adjustment of a tailgate of a motor vehicle. The driveline is assigned a frictional engagement mechanism designed as a brake mechanism or as a clutch mechanism, which on the one hand permits secure holding of the tailgate in intermediate positions and, on the other hand, manual adjustment of the tailgate after overcoming the braking force of the brake mechanism. The structural design of the known powertrain basically ensures a relatively high level of operational safety and, with regard to the manual adjustability, a high level of user comfort. A challenge with regard to operational safety, however, is the fact that the frictional force provided by the frictional engagement mechanism degrades over time as a result of wear. Thus, in the known drive train in each case two connection elements of the drive train to each other for transmitting a rotary coupled, wherein one of the connecting elements comprises a first frictional engagement element which is in .Reibeingriff with a second frictional engagement element Here, the second ReibscMusselement Iber is biased by a pressure mechanism having at least one spring element against the first frictional engagement element. In the course of time, the thickness of at least one of the two frictional engagement elements is reduced due to wear, with the result that the length of the spring element (s) is increased. With increasing length of the respective spring element but at the same time decreases the spring force and accordingly the pressing force, also called normal force from. This, in turn, results in a decreasing frictional force over time or a decreasing frictional torque over time.

This may have the result that the friction force or the friction torque is no longer sufficient after some time to keep the tailgate o. The like. In intermediate positions. This leads to an impairment of operational safety.

The invention is based on the problem, the known drive train to design and further develop that a wear-related impairment of reliability is counteracted.

The above problem is solved in a drive train according to the preamble of claim 1 by the features of the characterizing part of claim 1. Essential is the fundamental consideration that by a particular shape, in particular a special geometric shape and / or a special material or a special material structure (claim 2), which is worn over time frictional engagement with a consequent declining spring force or pressure force in a frictional engagement mechanism can be at least partially compensated. Since the length of the clamped spring or springs, for example, wave springs or springs, of the eccentric mechanism increases with decreasing thickness of the respective frictional engagement element and the pressure force correspondingly decreases, according to the proposal, in order to keep the frictional force or the frictional moment as constant as possible, at least one other parameters influencing the friction force or the friction torque (friction coefficient and / or friction radius) are changed automatically. In principle, it is conceivable that at least one of the frictional engagement elements is rotatable about an axis of rotation extending in an axial direction and the urging force acts axially or radially relative to the axis of rotation. In the first case, by the proposed solution, the resulting friction torque and in the. the latter case, the resulting frictional force over the life of the Reibschlusselements be kept within a predetermined range of values, in which a sufficient reliability of a drive train, a corresponding drive and a corresponding closure element assembly of a motor vehicle is ensured. In particular, the influence of a decrease in the thickness of the frictional engagement element on the resulting frictional force or the resulting frictional torque can be compensated for at least 20%, preferably at least 50%, more preferably substantially completely (claim 3).

In a preferred embodiment according to claim 4, the cross-sectional shape (in an axial section) of the at least one of ReibschJusselemente configured such that the average radius of friction with the respective other frictional engagement frictionally engaged or engageable surface (friction surface) with decreasing thickness of at least one of Friction elements increases. By the "mean friction radius" is meant the mean distance of the friction surface from the axis of rotation, so that the geometric shape of the respective frictional engagement element can be designed such that the average friction radius increases when the frictional engagement element is worn as intended.

The particularly preferred embodiments according to claims 5 and 6 relate to ways in which the geometric shape of the respective frictional engagement element can be designed so that the average frictional radius automatically increases as it is worn.

In the embodiment according to claims 7 and 8, the drive train has at least three, preferably exactly three, frictional engagement elements which are arranged one above the other in the axial direction, that is to say that a middle frictional engagement element has a first outer frictional engagement element on the lower side and a second outer frictional engagement element on the upper side outer frictional engagement element is in frictional engagement or can be brought. In this case, at least two frictional Mechanisms provided, namely, a first frictional engagement mechanism, which comprises the central frictional engagement element and the first outer frictional engagement element, and a second frictional engagement mechanism comprising the central frictional engagement element and the second outer frictional engagement element. Here, in particular, the average frictional engagement element is the one whose thickness decreases particularly strong due to wear, which was compensated by the proposed solution such that the resulting frictional force or the resulting frictional torque is at least partially compensated.

As already indicated above, a special material structure of the frictional engagement element can serve to compensate at least in part for the influence of a decrease in the thickness of the frictional engagement element on the resulting frictional force or the resulting frictional torque.

The further preferred embodiments according to claims 9 and 10 relate to different application cases of the friction mechanism, so this may be part of a brake mechanism or part of a clutch mechanism.

According to a further teaching according to claim 1 1, which has independent significance, a drive for the motorized adjustment of a closure element of a motor vehicle is claimed which has a proposed drive train. Reference may be made to all statements relating to the drive train according to the present invention, insofar as these are suitable for explaining the drive.

A particularly slim design is shown in a construction of the drive according to claim 12, wherein the drive is designed as a spindle drive. Further preferably granules, the geometric spindle axis of the spindle and the drive shaft of the drive motor associated with the drive to be aligned.

According to a further teaching according to claim 13, which also has independent significance _» is a VerscMusselementanordnung a motor vehicle with an adjustably coupled to the body of the motor vehicle closure element and at least one proposed drive for the motorized adjustment of the Verschlusseleniei claimed. Again, reference may be made to the above statements on the proposed powertrain and the propriety drive. In particular, the drive is not designed to be self-locking and designed as a braking mechanism frictional engagement keeps the closure element with the drive off in intermediate positions, the closure element is preferably manually adjustable against the braking effect of the braking mechanism when the drive is off (claim 14).

In the following the invention will be explained in more detail with reference to a drawing showing only one exemplary embodiment. In the drawing shows

Fig. 1 in a very schematic representation of the rear area of a

 Motor vehicle with a proposed closure element assembly, the proposed drives each having a proposed drive train,

2 shows one of the drives according to FIG. 1 in the retracted state in one

 Longitudinal section

3 shows a brake mechanism of a first embodiment of the drive according to FIG. 2 in longitudinal section, FIG.

Fig. 4 shows a clutch mechanism of a second Ausführangsform of

 Drive according to FIG. 2 in longitudinal section,

Fig. 5 in the illustrations a) and b) is a detail view of the clutch mechanism of Fig. 4 each with different degrees of wear and in the illustrations a) and b) a Fig. 5 corresponding detail view of another embodiment of the clutch mechanism, each with different degrees of wear. The drive train 1 shown in the drawing is a drive 2 for the motorized adjustment of a closure element 3, here a tailgate of a Motor vehicle, assigned. The drive train 1 serves to guide the power flow of the drive force generated by a drive motor 15 of the drive 2.

The application of designed as a tailgate closure element 3 is here in the foreground. However, the proposed solution is applicable to all other types of closure elements. The exemplary list in the introductory part of the description may be referred to.

The tailgate 3 shown in FIG. 1 is assigned a total of two drives 2, which act on the two side wheels, a tailgate opening 4 and on the tailgate 3 itself. The here each designed as a spindle drive. Drive 2 end ball joints 2 a, 2 b associated with the corresponding. Ball heads at the respective. Side edge of the tailgate opening 4 and are engaged on the tailgate 3. In the following, only from the visible in Fig. 1 drive .2 talk. All designs are valid for the not visible in Fig. 1, behind lying drive and for an arrangement with only one, single drive 2 accordingly.

The drive train 1 of the drive 2 is equipped with a frictional engagement mechanism 5 (FIGS. 3 to 5) or a plurality of, preferably two, frictional engagement mechanisms 5 and 5 '(FIG. 6) for providing a frictional force. In the embodiment shown in Fig. 3 Ausm ^'currency form of Reibschlussmechanismus 5 part of a brake mechanism 6. In the case shown in Figs. 4 to 6 embodiments of the respective Reibschlussmechanismus is 5 or 5' part of a mechanism 7 couplings lung.

The brake mechanism 6 shown in Fig. 3 is used for preferably continuous braking of the drive train 1 to hold the tailgate 3 in intermediate positions. In order additionally to allow manual adjustment, the drive 2 here and preferably is not self-locking, ie can be driven back, designed, so that after overcoming the braking force, a corresponding adjustment of the tailgate 3 is possible.

The coupling mechanism 7 shown in FIGS. 4 to 6 is best suited for an arrangement in which the drive 2 is designed to be self-locking, ie not restorable. Nevertheless, manual adjustment of the rear To allow flap 3, the clutch mechanism 7 is designed as Rutsclikupplung so that roof overcoming the friction force a corresponding adjustment of the tailgate 3 is possible. In all the illustrated embodiments, the respective friction locking mechanism 5 or 5 'at least two, here and preferably exactly two, frictionally engaged or ^' bringable frictional engagement elements 8, 9 and 8, 9 \ and a pressure mechanism 10 for generating a pressing force F of Frictional engagement elements 8, 9 and 8, 9 'toward each other. It can be provided in principle that the pressing mechanism 10 forms a part of at least one of the frictional engagement elements 8, 9, 9 '. In the embodiments in Figs. 3 to 5, the single frictional engagement mechanism 5 is formed by the pairing of the frictional engagement elements 8, 9, whereas in the embodiment in Fig. 6, a frictional engagement mechanism 5 of the pair of frictional engagement elements 8, 9 and the other In the latter case, the pressing mechanism 10 is a component of both friction locking mechanisms 5, 5 In the embodiments described here and preferably, the respective friction locking mechanism 5 or 5 'generates a friction torque, the friction friction mechanism 5 is obtained from the pressing force F, which acts axially relative to the axis of rotation 20, from the relevant friction coefficient between the frictional engagement elements 8, 9 or 8, 9 'and from the respective friction radius R _m or R _m ^* can provide a frictional force when providing a radially acting on the rotational axis pressing force Any friction torque can be generated, which then results from the pressing force and from the relevant friction coefficient between the Reibschlusselementen. Specifically, the friction torque is proportional to the relevant friction coefficient and the amount of the respective pressing force F and the amount of the respective friction radius R _m or R _m 'according to the following equation:

M _friction = μ x F x (R _m or R _m '), where M _Re j _{b is} the Reibmomeiit and μ is the friction coefficient. Depending on the application, the coefficient of friction may be a static coefficient of friction or a coefficient of sliding friction between the frictional engagement elements 8, 9 or 8, 9 '. In the embodiments described here both coefficients of friction are relevant since in all the applications shown here both static friction and sliding friction occur.

What is essential now is the recognition, which can also be seen from the aforementioned equation, that a decreasing pressing force F over the course of time would result in a reduction of the friction torque if this effect were not compensated. The same applies, of course, also for the variant of a frictional force, not shown here, which results from a radially acting pressure force and the respective friction coefficient.

In order to keep the friction torque as constant as possible, the friction coefficient between the frictional engagement elements 8, 9 or 8, 9 'and / or the friction radius R _m or R _m ' is increased according to the proposal. If, according to the variant not shown here, a frictional force should be kept as constant as possible, the coefficient of friction alone would be increased with decreasing pressure force. An increase in the coefficient of friction can be achieved, for example, by the fact that the frictional engagement element in question has a multilayer structure. wherein the material of each layer causes a different coefficient of friction. As wear increases, the coefficient of friction increases automatically with each layer removed. The layers do not necessarily have to be clearly delineated layers, but it is also conceivable that neighboring layers merge into each other.

Specifically, it is proposed that at least one of the frictional engagement elements 8. 9. 9 'is configured in this way. that the influence of a decrease in its thickness H _R , that is a decrease in its dimension in the direction of the pressing force F, is at least partially compensated for on the resulting frictional force or the resulting frictional torque. The compensation takes place to at least 20%, preferably to at least 50%, more preferably substantially completely. In order to achieve the compensation in question, the cross-sectional shape and / or the material of at least one of the frictional engagement elements 8, 9 ₅ 9 \ in particular at least or exclusively of the frictional engagement element 8 with the. highest wear, be designed in a special way.

According to the proposal, the cross-sectional shape may be configured such that the mean friction radius R _m 'of the surface 1 1 or 1 Γ (friction surface) frictionally engaged or brought into frictional engagement with the respective other frictional engagement element 9, 9' increases with decreasing thickness H _{R of} the frictional engagement element 8 , A associated with decreasing thickness H _R of the frictional engagement element 8 increase in the average friction radius R _m is for a first alternative Ausftihrungsform in FIGS. 5a) and b shown) and for a second alternative embodiment shown in FIGS. 6a) and b) _"wherein the Fig. 5a) and 6a) each show the frictional engagement element 8 without wear or with only a relatively low degree of wear, whereas Fig. 5b) and 6b) the same frictional engagement element 8 after a over time over the Fig. 5a) and 6a) higher Show degree of wear.

In the embodiment shown in FIGS. 5 a) and b), the frictional engagement element 8 is shaped such that the cross section (cord cross section) of the frictional engagement element 8 is parallelogram-shaped, wherein the inner radius R 1 and the outer radius R _{a of} the frictional surface 11 of the frictional engagement element 8 coincide decreasing thickness H _{R of} the Reibschlusselements 8 increases. In principle, it is also possible that either only the inner radius R, or only the outer radius R _{a increases} with decreasing thickness H _R. In particular, the frictional engagement element 8 here and preferably is shaped so that the radial inner side 12 and the radial outer side 13 of the entire frictional engagement element 8 has an oblique course relative to the friction surface 1 1, wherein here and preferably the radial inner side 12 and the radial outer side 13 parallel to each other and straight.

In the embodiment in FIG. 6, the frictionally engaging element 8, which is mainly subject to wear, is in frictional engagement or can be brought into engagement both with a lower-side friction surface 11 and with an upper-side friction surface 11 'with a respectively adjacent frictional-engagement element 9 or 9'. The middle frictional engagement element 8 has here, since it wears both axially upper side and axially underside, radially outwardly a substantially convex or arrow-shaped contour and radially inside a substantially concave or negative-arrow-shaped contour. Again, the inner radius R, or R _t "and the outer radius R _a or R _a 'of the respective friction surface 1 1 or 1 1' decreases with decreasing the thickness H _{R of} the ReibscMusselements 8. The frictional engagement element 8 has for this purpose a lower axial end portion 14 and an upper axial end portion 14 ', wherein the lower axial end portion 14 as the frictional engagement element 8 in Figs. 5a) and b) is formed and the upper axial blind portion 14' is mirror-inverted is. with respect to a plane extending radially and orthogonal to the axis of rotation 20.

In particular, according to FIG. 6 a) and b), the middle frictional engagement element 8 has a lower axial end section 14 and an upper axial end section 14 ', whose radial inner side 12 or 12' and its radial outer side 13 or 13 'each have an oblique course relative to the friction surface 1 1 or 1 Γ of the respective end portion 14 or 14 'has. wherein, starting from the respective friction surface 1 1 or I V, the radial. Inner sides 12 and 12 'of both end portions 14 and 14' towards each other and the radial outer sides 13 and 13 'of the two end portions 14 and 14' extend away from each other.

The above-described geometric shape of the respective friction element 8 when worn causes the average friction radius R _{m to} increase with increasing wear over time. In this way, a decrease of the pressing force F of the pressing mechanism 10 that accompanies increasing wear can be compensated such that the resulting friction torque remains substantially constant.

To keep the Reibmoraent with decreasing pressing force F constant as possible or in order to keep as constant as possible in accordance with the non-illustrated variant, a friction force in the radial pressing force, as mentioned, be increased coefficient of friction between adjacent friction engagement members 8 _"9 and 8, 9 ' ,

In the following, the brake or clutch mechanisms 6, 7 illustrated in FIGS. 3 to 6 will be explained, each with a proposal as appropriate

Frictional engagement mechanism 5 or, 5 'are equipped.

In the embodiment shown in Fig. 3, at least one frictional engagement element 8 is fixedly arranged, while over the frictional engagement a braking force can be transmitted. In the embodiment illustrated in FIGS. On the other hand, it is like that. that the frictional engagement elements 8, 9 and 8. 9 'are each rotatable and rotational drive movements Iber are the frictional engagement.

Accordingly, in the embodiment shown in FIG. 3, the eccentricity mechanism 5 is part of a brake mechanism 6 which acts on a drive component of the drive train 1, here on a multi-part drive shaft 21, 22 of the drive train 1. In the embodiment shown in Fig. 3, the brake mechanism 6 is configured in the manner of a disc brake.

The brake mechanism 6 shown in FIG. 3 has two connection elements 23, 24 which are coupled to one another via a guide 25 which is non-rotatable but axially displaceable with respect to the rotation axis 20. The frictional engagement element 8 is here and preferably part of the connection element 23. The other frictional engagement element 9 is fixed relative to the rotational axis 20 rotatably, but axially displaceably mounted on a brake housing 26. The two connection elements 23, 24 are each fastened to a drive shaft section 21, 22, as indicated in FIG. 3.

Alternatively, the frictional engagement mechanism 5 may be a component of a clutch mechanism 7, as discussed above. This is shown in Fig. 4. The clutch mechanism 7 is connected between two drive components 21, 22, here two drive shaft sections 21, 22, of the drive train 1. Here, the clutch mechanism 7 is configured here and preferably as between the two Antriebskomporjenten 21, 22 of the drive train 1 overload clutch.

Also in the embodiments shown in Figures 4 to 6 and so far preferred embodiments are each two Anschl usselemente 23, 24 are provided which are rotatably coupled to each other with respect to the axis of rotation 20 via the frictional engagement of the friction mechanism 5. For this purpose, the frictional engagement element 9 is rotationally fixed relative to the axis of rotation 20, but mounted axially displaceably on the guide 27 on the connection element 24. According to the embodiment in FIGS. 5a) and 5b), the frictional engagement element 8 is a component of the connection element 23 and, according to the embodiment in FIGS. 6a) and 6b), a separate component which to both connection elements 23 and 24 movable, here rotatable, is mounted. The coupling housing 26 serves here only for the mounting of the connection element 24,

According to another teaching, which has independent significance, the above drive 2 is claimed as such. The proposed drive 2 is used in accordance with the motorized adjustment ein.es closure element 3 ein.es motor vehicle, wherein a drive train 1 is provided, which is designed according to the first-mentioned teaching. Reference should be made to all versions of the proposed powertrain 1.

In a particularly preferred embodiment shown in FIG. 2, the drive 2 is a spindle drive. The drive 2 has a drive motor 15 and a spindle spindle nut transmission 16 connected downstream of the drive motor 15 with a spindle 17 and an associated spindle nut 18 for generating linear drive movements. Indicated in FIG. 2 is the fact that in the illustrated preferred embodiment, the frictional engagement mechanism 5 of the drive 2 is connected between the drive motor 15 and the spindle spindle nut transmission 16.

According to another teaching, which also has independent significance, a closure element arrangement of a motor vehicle shown in FIG. 1 is claimed as such. The proposed closure element arrangement has a closure element 3 which is adjustably coupled to the body 19 of the motor vehicle and at least one proposed drive 2 for the motorized adjustment of the closure element 3. Please refer to all versions of the proposed drive 2.

In a particularly preferred embodiment, it is such that the drive 2 is not self-locking, so rücktreibbar, designed and that designed as a brake mechanism 6 Reibschlussmechanismus 5, the closure element 3 with switched-off drive 2 in intermediate positions, preferably in any intermediate position holds. In a particularly preferred embodiment, the closure element 3 is manually adjustable with the drive 2 off against the braking action of the brake mechanism 6. Of particular importance in this context is the fact that the arrangement as a whole is such that the brake Mechanism 6 the VerscMusselement 3 holds with the drive 2 off in intermediate positions, in particular with regard to the weight of the closure element 3 and any acting on the closure element 3 spring arrangements. Such spring arrangements may be, for example, gas spring arrangements or the like.

Claims

claims 1 . Drive train of a drive (2) for the motorized adjustment of a closure element (3) of a motor vehicle, wherein at least one frictional engagement mechanism (5, 5 ') is provided for providing a frictional force or an frictional torque, the frictional engagement mechanism (5, 5') being part of a braking mechanism ( 6) or clutch mechanism (7) of the drive train (1), wherein the frictional engagement mechanism (5, 5 ') comprises two frictional engagement elements (8, 9, 8, 9') which are frictionally engaged with each other and a pressure mechanism (10) for the production a pressing force (F) of the frictional engagement elements (8, 9, 8, 9 ') towards each other, and wherein the frictional force of the pressing force (F) and the friction coefficient between the frictional engagement elements (8. 9, 8, 9') and the frictional torque from the pressing force (F), the average frictional radius (R _rn , R _m ^l ) and the coefficient of friction between the frictional engagement elements (8, 9, 8, 9 '), characterized, in that at least one of the frictional engagement elements (8, 9, 9 ') is configured such that the influence of a decrease in its thickness (H _R ) on the resulting frictional force or the resulting frictional torque is at least partially compensated. 2. Drive train according to claim 1, characterized in that the cross-sectional shape and / or the material of the at least one of the frictional engagement elements (8, 9, 9 ') is configured such that the influence of a decrease in its thickness (H _R ) on the resulting friction force, or the resulting friction torque is at least partially compensated. Drive train according to claim 1 or 2, characterized in that the at least one of the frictional engagement elements (8, 9, 9 ") or its cross-sectional shape and / or material is configured such that the influence of a decrease in its thickness (H _R ) on the resulting friction force or the resulting friction torque to at least 20%, preferably at least 50%, more preferably substantially completely, is compensated. 4. Drive train according to one of the preceding claims, characterized in that the cross-sectional shape is configured such that the average friction radius (R _m , R _m ⁴ ) with the respective other frictional engagement element (8, 9, 9 ') in frictional engagement or engageable surface (1 1, 1 Γ) increases with decreasing thickness (H _R ) of the at least one of the frictional engagement elements (8. 9, 9'), 5. Drive train according to one of the preceding claims, characterized in that the inner radius (Rj, Rj ') and / or outer radius (R _a , R _a ') are in frictional engagement with the respective other frictional engagement element (8, 9, 9 ') or bringable surface (1 1, 1 Γ) with decreasing thickness (H _R ) of the at least one Reibschlusseiemente (8, 9, 9 ') increases. 6, drive train according to one of the preceding claims, characterized in that the radial inner side (12, 12 ') and / or radial outer side (13, 13') of at least one axial end portion (14. 14 ') of the at least one Reibschlusseiemente (8 , 9, 9 ') has an oblique course relative to the surface (I i, 1 P) in frictional engagement or engageable with the respective other frictional engagement element (8, 9, 9'), preferably in that the radially inner side (12 1 2 ') and radial outer side (13, 13') parallel to each other and / or straight, 7. Drive train according to one of the preceding claims, characterized in that "at least three frictional engagement elements (8, 9, 9 ') are provided, which have a middle frictional engagement element (8) on the underside with a first outer frictional engagement element (9) and on the upper side with a second outer frictional engagement element (9 ') is in frictional engagement or can be brought, 8, drive sträng according to one of the preceding claims, characterized in that the central frictional engagement element (8) has a lower axial end portion (14) and an upper axial end portion (14 '), the radial inner side (12, 12') and / or Radial outer side (13, 13 ') each have an oblique course relative to the respective other frictional engagement element (9, 9') in frictional engagement or engageable surface (1 1, 1 Γ) of the respective end portion (14, 14 '), preferably that, in each case starting from the surface (1 1, 1 1 ') which is in frictional engagement with the respective other frictional engagement element (9, 9'), the radial inner sides (12, 12 ') of the end sections (14, 1.4') ) towards each other and / or the radial outer sides (13, 13 ') of the end sections (14, 14') run away from one another. 9. Drive train according to one of the preceding claims, characterized in that the frictional engagement mechanism (5. 5 \) is part of a braking mechanism (6) which acts on a drive component of the drive train (1) _» preferably that the braking mechanism (6) according to Art a disc brake or in the manner of a drum brake is designed. 10. Antriebsstong according to any one of the preceding claims, characterized in that the frictional engagement mechanism (5, 5 ') is part of a clutch mechanism (7), which is connected between two drive components of the drive train (1), preferably that the clutch mechanism (7 ) configured as between two drive components of the drive train (1) overload clutch is configured. 1 1. Drive for the motorized adjustment of a closure element (3) of a motor vehicle, wherein a drive train (1) is provided according to one of the preceding Artsprüche 12. Drive according to claim 1 1, characterized in that the .Antrieb (2) is designed as a spindle drive and a. Drive motor (15) and one of the drive motor (15) downstream spindle-spindle nut transmission (16) having a spindle (17) and an associated spindle nut (18) for generating linear drive movements, preferably, that the frictional engagement mechanism (5, 5 ') of the drive train (1) is connected between the drive motor (15) and the spindle spindle nut transmission (16). 13. Closure element arrangement of a motor vehicle with an adjustably coupled to the body (19) of the motor vehicle closure element (3) and with at least one drive (2) for the motorized adjustment of the closure element (3) according to spoke 1 1 or 12th 14. Closure element arrangement according to spoke 13, characterized in that the drive (2) is not designed to be self-locking and designed as a braking mechanism (6) frictional engagement mechanism (5) holds the closure element (3) in switched off drive (2) in intermediate positions, preferably. that the closure element (3) is manually adjustable against the braking action of the brake mechanism (6) when the drive (2) is switched off.