WO2010083848A1

WO2010083848A1 - Gear shift assembly with a detent mechanism

Info

Publication number: WO2010083848A1
Application number: PCT/EP2009/000382
Authority: WO
Inventors: Kenneth Skogward
Original assignee: Kongsberg Automotive AB
Current assignee: Kongsberg Automotive AB
Priority date: 2009-01-22
Filing date: 2009-01-22
Publication date: 2010-07-29
Anticipated expiration: 2011-07-22

Abstract

The present invention refers to a gear shift assembly comprising a gear shift lever (1) and a detent mechanism, wherein the gear shift lever (1) is manually movable between predetermined positions, wherein the detent mechanism comprises a detent surface (17) and a detent element (15) biased towards the detent surface (17), wherein the detent surface (17) defines a path (19) along which a contact surface (21) of the detent element (15) is able to slide in contact with the detent surface (17) when the gear shift lever (1) is moved between the predetermined positions, and wherein the detent surface (17) comprises concave-shaped recesses (25a, 25b, 25c, 25d, 25e) each defining a stable position of the detent element (15) along the path (19) when the gear shift lever (1) is in a corresponding predetermined position, wherein the contact surface (21) of the detent element (15) is convex-shaped having a maximal radius of curvature (R₂) in the sliding direction which is substantially smaller than the minimal radius of curvature (R₁) of the path (19) within the recesses (25a, 25b, 25c, 25d, 25e) of the detent surface (17).

Description

Gear shift assembly with a detent mechanism

The present invention refers to a gear shift assembly comprising a gear shift lever and a detent mechanism, wherein the gear shift lever is manually movable between predetermined positions, wherein the detent mechanism comprises a detent surface and a detent element biased towards the detent surface, wherein the detent surface defines a path along which a contact surface of the detent element is able to slide in contact with the detent surface when the gear shift lever is moved between the predetermined positions, and wherein the detent surface comprises concave-shaped recesses each defining a stable position of the detent element along the path when the gear shift lever is in a corresponding predetermined position.

Such a gear shift assembly is typically used in vehicles with automatic or manual gear shift systems, where a shift lever is pivotable or shiftable over a series of predetermined positions which correspond to transmission gears or programs, re- spectively, such as park (P) , reverse (R) , neutral (N) , drive (D) or low gears (1, 2) . A detent mechanism is typically used to stabilise the shift lever in the predetermined positions.

A gear shift assembly comprising a gear shift lever and a de- tent mechanism is known from WO 2008/086162. The detent mechanism described therein comprises a detent plunger which is resiliently biased towards a detent profile. The detent plunger is mechanically connected to the gear shift lever such that it moves along the detent profile when the gear shift lever is moved between predetermined positions. At its tip the detent plunger comprises a roller ball which is in contact with a zigzag-shaped detent profile defining V-shaped recesses such that the roller ball is able to slide or roll along the detent profile. The roller ball snaps into a V-shaped recess to stabilise the detent plunger and the gear shift lever con- nected thereto in a predetermined position which corresponds to a transmission gear or program, respectively, such as park (P), reverse (R), neutral (N), drive (D) or low gears (1, 2) .

A similar example of a gear shift assembly comprising a gear shift lever and a detent mechanism is known from US 5,904,121. The detent profile described therein defines recesses in the form of circular segments such that a detent element in form of a roller ball is able to slide or roll along the detent profile and to snap into a U-shaped recess in the detent profile to stabilise the gear shift lever in a predetermined position which corresponds to a transmission gear or program, respectively.

A disadvantage of the known gear shift assemblies is that the snapping of a detent element into a recess makes an undesired noise and a haptic feedback to the driver which is experienced to be harsh. Moreover, the snapping causes wear and abrasion to the detent surface and/or the contact surface of the detent element which snaps into the recesses.

This problem has previously been solved by adding damping elements to the detent mechanism or acoustic insulation to the assembly. An example a dampening device for the detent surface is disclosed in US 2008/0083294. However, such a dampening device requires a large amount of additional parts, a complicated setup with several materials and higher production costs.

It is therefore the object of the present invention to provide an improved and simple gear shift assembly which allows moving of the shift lever between predetermined positions such that the driver receives an acoustically and hapticly smooth transition between gears. This object is solved by the inventive gear shift system according to the features of claim 1. Preferred embodiments of the invention are subject of the dependent claims.

According to a first aspect of the present invention a gear shift assembly comprising a gear shift lever and a detent mechanism is provided. The gear shift lever is manually movable between predetermined positions and the detent mechanism comprises a detent surface and a detent element biased towards the detent surface. The detent surface defines a path along which a contact surface of the detent element is able to slide in contact with the detent surface when the gear shift lever is moved between the predetermined positions. The detent surface comprises concave-shaped recesses each defining a stable position of the detent element along the path when the gear shift lever is in a corresponding predetermined position. The invention is characterised in that the contact surface of the detent element is convex-curved having a maximal radius of curvature in the sliding direction which is^' substantially smaller than the minimal radius of curvature of the path within the recesses of the detent surface.

The inventive detent surface has the shape of a two- dimensional curved hyper-surface which includes local minima defining the recesses. The hyper-surface may be defined as a two-dimensional function of distance to a suspension point of the detent element. The inventive contact surface of the detent element is defined by all those points of the surface of the detent element which have at least at one position of the gear shift lever contact with the detent surface. Surface points of the detent element which are not in contact with the surface at any position of the gear shift lever are therefore not part of the contact surface. The path on the detent surface is a continuous line or band defined by all those points of the detent surface which have at least at one position of the gear shift lever contact with the contact surface of the detent element. Points of the detent surface which are not in contact with the contact surface of the detent element at any position of the gear shift lever are therefore not part of the path. As the path extends through all recesses of the detent surface the path also includes local maxima with regard to the distance to a suspension point of the detent element. These local maxima of the path may coincide with the local maxima of the recess, but may also be located at another detent surface point within a recess.

The maximal radius of curvature of the contact surface and the minimal radius of curvature of the path within the recesses of the detent surface are to be determined in the sliding direc- tion, i.e. the direction of relative movement between the contact surface of the detent element and the detent surface. The shape of the contact surface and/or the detent surface in any other direction may be chosen arbitrarily. It turned out that a maximal radius of curvature of the contact surface which is about 5%, preferably 10%, smaller than the minimal radius of curvature of the path within the recess is sufficient. Therefore, "substantially smaller" in this respect means more than 5%, preferably about 10% smaller.

Mathematically speaking, the curvature of a path travelled along as a function of time corresponds to the change of the rotation angle with respect to the change of arc length. Defining d(y) as the distance of a contact point to a suspension point S of the detent element as a function of the space coor- dinate y, the value of curvature κ(y) may be defined as

4l+(d\y)γ wherein d^r (y) and d" (y) are the first and second derivatives of the function d(y) .

A first function may be defined as the distance of a point of the path to the suspension point. A second function may be defined as the distance of a point of the contact surface to the suspension point. The first function has a local maximum within a recess. The second function also has a maximum. Assuming that the contact surface slides along the path in a forward direction, the contact surface may follow, within a recess, a right hand bend which corresponds to a negative curvature. Conversely, in the backward direction it may follow, within a recess, a left hand bend which corresponds to a positive curvature. Either way, the maximal absolute value of the curvature of the first function is, within a recess, substantially smaller than any absolute value of the curvature of the second function.

Although the term "radius" is used to quantify the curvature, the curvature does not need to be circular. The curvature may, however, at any infinitesimal section be approximated by a circular curvature having a certain radius . The radius of the curvature at a certain point may then be defined as the radius of that circle which tangentially touches the function at that point and having the same curvature as the function at that point. The curvature of a circle is the reciprocal of its radius R, i.e. κ(y)=l/R. Therefore, the absolute value of the curvature in terms of radius is larger for smaller values of κ(y) and smaller for larger values of κ(y) . At those points where the surface is even the absolute value of curvature in terms of radius is infinite, where the value of κ(y) is zero. At those points where the surface has a sharp bend the absolute value of curvature in terms of radius is zero, where the value of κ(y) is infinite. As the minimal radius of curvature of the path within the recesses of the detent surface must be larger than the minimal radius of curvature of the contact surface, the path does not include any sharp bend within a recess. However, a sharp bend may be located at those points of the path which are not located within a recess, e.g. between the recesses.

The used inventive detent mechanism has the advantageous effect that the contact surface of the detent element slides smoothly into each recess without abruptly hitting a wall of a recess. Thereby, an unintentional noise is prevented and the haptic feeling of the gear shift transition is smooth. The contact surface of the detent element smoothly swings into a stable position in which the contact surface has reached a local extremum of the path. Although this position is less sta- ble than in a V-shaped recess or a recess essentially matching in shape with the contact surface, this position is stable enough to stabilise the gear shift lever in the predetermined position.

It is preferred that each predetermined position of the gear shift lever, including the end positions, corresponds to such a smooth and stable position of the contact surface of the detent element in a corresponding recess of the detent surface. Preferably, also the path between the recesses follows a smooth and differentiable curve to provide a smooth acoustic and haptic feeling at any point of movement of the gear shift lever .

In a preferred embodiment of the invention either the detent surface or the detent element is mechanically connected to the gear shift lever such that the detent surface or the detent element, respectively, moves relative to the detent element or the detent surface, respectively, when the gear shift lever is manually moved between the predetermined positions. The path preferably comprises at least a first and a second section, wherein the first section is fully comprised within a first even hyperplane and the second section is fully comprised within a second even hyperplane, wherein the first even hyperplane and the second even hyperplane cross at a common straight line which crosses the path between the first section and the second section. Preferably, the common straight line is the vertical and/or the first even hyperplane and the second even hyperplane cross at a right angle. Therefore, the path is not restricted to an even hyperplane but may change the direction between a first section and a second section. The path may also branch out to provide more than two sections of the path.

In a preferred embodiment of the invention the path within the recesses is curved in form of a segment of a circle, an ellipse, a parabola or another differentiable concave-shaped one-dimensional function. Accordingly, the contact surface of the detent element may be curved in form of a spherical shell, a shell of a spherical segment, a shell of a cylinder, a shell of a cylinder segment, a shell of an ellipsoid, a shell of an ellisoid segment or another convex-shaped differentiable two- dimensional function.

It is appreciated that the inventive detent mechanism is not only restricted to be used in a gear shift assembly, but may also be used to stabilise any pivotable and/or movable elongate member in predetermined positions, e.g. a hand brake lever, a mirror or seat adjustment lever or a headrest bracket.

According to a second aspect of the present invention a detent mechanism for stabilising a pivotable and/or movable elongate member in predetermined positions is provided, wherein the detent mechanism comprises a detent surface and a detent element biased towards the detent surface, wherein the detent surface defines a path along which a contact surface of the detent element is able to slide in con- tact with the detent surface when the elongate member is moved between the predetermined positions, and wherein the detent surface comprises concave-shaped recesses each defining a stable position of the detent element along the path when the gear shift lever is in a corresponding predetermined position, characterised in that the contact surface of the detent element is convex-shaped having a maximal radius of curvature in the sliding direction which is substantially smaller than the minimal radius of cur- vature of the path within the recesses of the detent surface.

It is appreciated that all previously described advantageous variations of the inventive detent mechanism used in the gear shift system also apply for a detent mechanism used to stabi- use any pivotable and/or movable elongate member in predetermined positions.

In the following a preferred embodiment of the invention is discussed in further detail with reference to the accompanying figures.

Figs. Ia and Ib show a perspective view and side view, respectively, of a preferred embodiment of the inventive gear shift assembly.

Figs. 2 and 3 show a cross-sectional side view of the preferred embodiment of the inventive detent mechanism at two different stable positions of the detent element.

Fig. 4 shows a detail of Fig. 3. Fig. 5 shows a function of the distance to a suspension point and the absolute value of the curvature thereof, i.e. \κ(y) \ .

Figs. 6 and 7 show for comparison the same as is shown in Fig. 4 and 5, respectively, for a mechanism known from the prior art.

Figs. Ia and Ib show a gear shift lever 1 in form of a longi- tudinal member which is pivotally suspended to a bracket (not shown) which is fixed to the chassis of a vehicle (not shown) . A Cartesian coordinate system is shown to illustrate the forward direction as the positive y-axis, the right-hand sideways direction as the positive x-axis and the upper vertical direc- tion as the positive z-axis. The gear shift lever 1 extends essentially vertically within a certain range of pivot angles. The gear shift lever 1 comprises a spherical surface defining a ball 3 to be received in a ball joint socket (not shown) to which the gear shift lever 1 is pivotally suspended. The cen- tre of the ball 3 may be defined as the suspension point S of the gear shift lever 1. A first section 5 of the gear shift lever 1 extends from the ball 3 upwards to a handle 7 which is to be grasped by a driver in order to shift gears or transmission programs. A second section 9 of the gear shift lever 1 extends downwards from the ball 3 towards a profile 11 which is fixed to the chassis of the vehicle (not shown) . The second section 9 of the gear shift lever 1 comprises a hollow tubular end portion 13 which contains inside a detent element 15 in form of a plunger protruding out of the end portion 13 of the second section 9 of the gear shift lever 1.

The profile 11 extends essentially in the horizontal xy-plane and defines on its top a detent surface 17 which has the form of a two-dimensional hyper-surface that may be parameterised as z(x,y). The detent surface 17 defines a path 19 which acts as a guide for a contact surface 21 of that portion of the detent element 15 which protrudes out of the end portion 13 of the second section 9 of the gear shift lever 1. The degree of freedom for pivotal movements of the gear shift lever 1 is therefore restrained by the path 19.

The path 19 has a first section 23 which extends essentially along the y-axis through four successive recesses 25a, 25b, 25c, 25d defined by the detent surface 17. The first section 23 of the linear path 19 is therefore comprised within a first even hyper-plane, i.e. the yz-plane. The contact surface 21 of the detent element 15 is shown in contact with the path 19 in the most backward recess 25a. This corresponds to a most forward position of the handle 7 of the gear shift lever 1. The contact surface 21 may slide forward along the first section 23 of the path 19 through the four successive recesses 25a, 25b, 25c, 25d upon a movement of the gear shift lever 1 induced by manually pulling the handle 7 of the gear shift lever 1 backwards. When the contact surface 21 is located in any of the recesses 25a, 25b, 25c, 25d the gear shift lever 1 is stabilised in a predetermined position that corresponds to a certain transmission gear or program.

The path 19 further comprises a second section 27 which ex- tends essentially along the x-axis between two recesses 25d, 25e defined by the detent surface 17. The second section 27 of the linear path 19 is therefore comprised within a second even hyper-plane, i.e. the xz-plane. When the handle 7 of the gear shift lever 1 is in a most backward position and the contact surface 21 resides within the most forward recess 26d, the driver may pull the handle 7 of the gear shift lever 1 sideways to the left such that the contact surface 21 follows the second section 27 of the path 19 sideways to the right towards the recess 25e. There may be an arbitrary pattern of path sec- tions connected to each other in a similar way. The path 19 could also branch out.

In Figs. 2 and 3 a cross-sectional side view of the detent mechanism is shown at two different stable positions of the detent element 15, i.e. when the contact surface 21 resides in the most backward recess 25a and when the contact surface 21 resides in the second-most forward recess 25c, respectively. The detent element 15 in form of a plunger is longitudinally movable inside the hollow tubular end portion 13 of the second section 9 of the gear shift lever 1. A spiral spring 29 surrounding the plunger is used to urge the detent element 15 outwards against the detent surface 17. The detent element 15 comprises a protruding head with a semi-spherical surface of which those points which have contact with the detent surface at any position of gear shift lever 1 define the contact surface 21. The contact surface 21 is at any position of the gear shift lever 1 in a sliding contact with the detent surface 17. The contact surface 21 may slide between the most backward re- cess 25a to the most forward recess 25d upon manual pulling of the handle 7 of the shift lever 1. The manual force must overcome the spring force needed to compress the spiral spring 29 when the contact surface 21 is moved between the recesses 25a, 25b, 25c, 25d. The detent element 15 then moves in a longitu- dinal direction relative to the hollow tubular end portion 13 of the second section 9 of the gear shift lever 1 when the gear shift lever 1 is shifted between its predetermined positions. Where the path 19 allows the detent element 15 to move outwards the spring force of the spiral spring 29 may be strong enough to move the gear shift lever 1 automatically into its adjacent predetermined position.

Within each recess the path 19 follows a circular path segment having a radius of curvature that is substantially larger than the radius of curvature of the contact surface 21. Between the recesses 25a, 25b, 25c, 25d the path follows six straight path segments 31a, 31b, 31c, 31d, 31e, 31f, which are located in pairs between the recesses 25a, 25b, 25c, 25d. The two straight path segments of each pair 31a/31b, 31c/31d, 31e/31f are connected to each other by a sharp bend, whereas the other ends of each pair are tangentially connected with adjacent circular segments of the recesses 25a, 25b, 25c, 25d. Thereby, a smooth transition between the straight path segments 31a, 31b, 31c, 31d, 31e, 31f and the circular path segments is guaranteed. The transition between the recesses via the sharp bends between the two straight path segments of each pair 31a/31b, 31c/31d, 31e/31f is also smooth, because the contact surface 21 is convex-shaped. When the contact surface 21 slides along the path 19 no abrupt collision of surfaces oc- curs. Therefore, an unintentional noise is prevented and the haptic feeling of the gear shift transition is smooth. Due to the sharp bends between the two straight path segments of each pair 31a/31b, 31c/31d, 31e/31f stable or metastable positions between the recesses 25a, 25b, 25c, 25d are minimised such that the gear shift lever 1 is stabilised in the predetermined positions only and not in-between.

The detailed view of Fig. 4 illustrates the difference in curvatures between the contact surface 21 and the circular path segment of the path 19 in the recess 25c. The contact surface 21 is located in a stable position within the recess 25c. A movement of the contact surface 21 in either direction along the path 1? requires the detent element 15 to be pushed inwards against the spring force of the spiral spring 29. The circular path segment of the path 19 within the recess 25c has a radius of curvature of Ri . The spherical surface of the contact surface 21 has a radius of curvature of R₂, wherein R₂ is substantially smaller than R₁. The other recesses 25a, 25b, 25d, 25e may comprise a circular path segment with the same radius of curvature of R₁. Therefore, the contact surface 21 is able to smoothly slide along the complete path 19.

Fig. 5 illustrates the difference in curvatures between the contact surface 21 and the path 19 within the recesses 25a, 25b, 25c, 25d in terms of a first function F₁ and a second function F₂. The first function F₁ is defined as the distance d between a suspension point S of the detent element 15 and a point of the path 19 along the y-direction. The second func- tion F₂ is defined as the distance d between a suspension point S of the detent element 15 and a point of the contact surface 21 along the y-direction. The second function F₂ is repeatedly shown comparison with the first function F₁ at the recesses recesses 25a, 25b, 25c, 25d. Above the functions F₁, F₂ the ac- cording absolute value of curvature κ(y) is shown for each function within the recesses 25a, 25b, 25c, 25d. The absolute value of curvature fc(y) of the second function corresponds to the reciprocal of the radius of curvature R₂ of the spherical surface of the contact surface 21, i.e. 1/R₂. The absolute value of curvature κ(y) of the first function corresponds to the reciprocal of the radius of curvature R₁ of the circular path segment of the path 19, i.e. 1/R₁, which is substantially smaller than 1/R₂. Between the recesses 25a, 25b, 25c, 25d the curvature of the path 19 is irrelevant and may take extreme values of zero or infinity.

For comparison the Figs. 6 and 7 show the same as is shown in Figs. 4 and 5, respectively, for a mechanism known from the prior art. The V-shaped recesses 25a, 25b, 25c, 25d have a sharper bend. This implies that the spherical surface of the contact surface 21 has a radius of curvature of R₂, wherein R₂ is substantially larger than radius of curvature of R₁ of the circular path segment of the path 19 within the recess 25c. Accordingly, the absolute value of curvature κ(y) of the first function corresponding to the reciprocal of the radius of cur- vature R₁ of the circular path segment of the path 19, i.e. 1/Ri, is larger than the absolute value of curvature κ(y) of the second function corresponding to the reciprocal of the radius of curvature l/R_∑- The mechanism known from the prior art would induce a noisy collision of the contact surface 21 with the detent surface 17 when the detent surface slides into a stable position. A driver holding the handle 7 of the gear shift lever 1 experiences a harsh and abrupt haptic feeling of the transition between the predetermined positions of the gear shift lever 1. These disadvantages are overcome by the inventive gear shift assembly.

Claims

1. A gear shift assembly comprising a gear shift lever (1) and a detent mechanism, wherein the gear shift lever (1) is manually movable between predetermined positions, wherein the detent mechanism comprises a detent surface (17) and a detent element (15) biased towards the detent surface (17), wherein the detent surface (17) defines a path (19) along which a contact surface (21) of the detent element

(15) is able to slide in contact with the detent surface

(17) when the gear shift lever (1) is moved between the predetermined positions, and • wherein the detent surface (17) comprises concave- shaped recesses (25a, 25b, 25c, 25d, 25e) each defining a stable position of the detent element (15) along the path (19) when the gear shift lever (1) is in a corresponding predetermined position, characterised in that the contact surface (21) of the detent element (15) is convex-shaped having a maximal radius of curvature (R₂) in the sliding direction which is substantially smaller than the minimal radius of curvature (Ri) of the path (19) within the recesses (25a, 25b, 25c, 25d, 25e) of the detent surface (17) .

2. A gear shift assembly according to claim 1, wherein either the detent surface (17) or the detent element (15) is mechanically connected to the gear shift lever (1) such that the detent surface (17) or the detent element (15), respectively, moves relative to the detent element (15) or the detent surface (21) , respectively, when the gear shift lever (1) is manually moved between the predetermined positions .

3. A gear shift assembly according to claim 1 or 2, wherein the path (19) comprises at least a first and a second section, wherein the first section is fully comprised within a first even hyperplane {yz) and the second section is fully comprised within a second even hyperplane (xz) , wherein the first even hyperplane (yz) and the second even hyperplane (xz) cross at a common straight line (z) which crosses the path (19) between the first section and the second section.

4. A gear shift assembly according to claim 3, wherein the common straight line (z) is the vertical and/or the first even hyperplane {yz) and the second even hyperplane (xz) cross at a right angle.

5. A gear shift assembly according to any preceding claim, wherein the path (19) branches out.

6. A gear shift assembly according to any preceding claim, wherein the path (19) within the recesses (25a, 25b, 25c, 25d, 25e) is curved in form of a circular segment, an ellipse, a parabola or another differentiable concave-shaped one-dimensional function.

7. A gear shift assembly according to any preceding claim, wherein the contact surface (21) of the detent element (15) is curved in form of a spherical shell, a shell of a spherical segment, a shell of a cylinder, a shell of a cylinder segment, a shell of an ellipsoid, a shell of an ellisoid segment or another convex-shaped differentiable two-dimensional function.

8. A detent mechanism for stabilising a pivotable and/or movable elongate member (1) in predetermined positions, wherein the detent mechanism comprises a detent surface (17) and a detent element (15) biased towards the detent surface (17), wherein the detent surface (17) defines a path (19) along which a contact surface (21) of the detent element

(15) is able to slide in contact with the detent surface

(17) when the elongate member (1) is moved between the predetermined positions, and wherein the detent surface (17) comprises concave- shaped recesses (25a, 25b, 25c, 25d, 25e) each defining a stable position of the detent element (15) along the path (19) when the elongate member (1) is in a corresponding predetermined position, characterised in that the contact surface (21) of the detent element (15) is curved having a maximal radius of curvature (R₂) in the sliding direction which is substantially smaller than the minmal radius of curvature (Ri) of the path (19) within the recesses (25a, 25b, 25c, 25d, 25e) of the detent surface (17) .

9. A detent mechanism according to claim 8, wherein either the detent surface (17) or the detent element (15) are mechanically connected to the elongate member (1) such that the detent surface (17) or the detent element (15), respectively, moves relative to the detent element (15) or the detent surface (17), respectively, when the elongate member (1) is manually moved between the predetermined positions .

10. A detent mechanism according to claim 8 or 9, wherein the path (19) comprises at least a first and a second section, wherein the first section is fully comprised within a first even hyperplane {yz) and the second section is fully comprised within a second even hyperplane (xz) , wherein the first even hyperplane (yz) and the second even hyper- plane (xz) cross at a common straight line (z) which crosses the path (19) between the first section and the second section.

11. A detent mechanism according to claim 10, wherein the common straight line (z) is the vertical and/or the first even hyperplane (yz) and the second even hyperplane (xz) cross at a right angle.

12. A detent mechanism according to any of the claims 8 to 11, wherein the path (19) branches out.

13. A detent mechanism according to any of the claims 8 to 12, wherein the path (19) within the recesses (25a, 25b, 25c, 25d, 25e) is curved in form of a circular segment, an ellipse, a parabola or another differentiable concave-shaped one-dimensional function.

14. A detent mechanism according to any of the claims 8 to 13, wherein the contact surface (21) of the detent element

(15) is curved in form of a spherical shell, a shell of a spherical segment, a shell of a cylinder, a shell of a cylinder segment, a shell of an ellipsoid, a shell of an ellisoid segment or another convex-shaped differentiable two-dimensional function.