Screw pinion and screw gear transmission

Abstract

A threaded pinion (1) for a screw gear transmission, comprising at least one tooth (7), characterized in that the tooth (7) has an hourglass-shaped configuration and has a continuously varying tooth profile over its course.

Description

[Technical Field]

[0001] The present invention relates to a screw pinion for a screw gear transmission and to a screw gear transmission comprising such a screw pinion, which may in particular be provided as a steering transmission for a steering system of a motor vehicle.

[0002] Many automobiles are equipped with power assist steering systems that generate an assist torque when steering, thereby reducing the steering moment applied to the steering column by the driver.

[0003] Known power-assisted steering systems are based on a steering transmission that converts the drive power of a hydraulic or electric steering motor and transmits it, for example, to a steering column. Such a steering transmission may be configured in the form of a screw gear transmission or a worm transmission. In this case, the steering transmission comprises a gear that may be directly or indirectly connected to the steering column and a pinion in the form of a screw pinion or worm that meshes with the gear and is driven by the steering motor via a shaft.

[0004] Worm transmissions and screw gear transmissions are gear transmissions in which the rotation axes of the gears and the pinions are offset from each other and therefore do not extend parallel to each other (as in spur gear transmissions) or intersect each other (as in bevel gear transmissions). According to the present invention, the difference between one worm transmission and the other screw gear transmission is that the worm transmission has an axis-crossing angle of 90°, while the screw gear transmission has an axis-crossing angle that is not equal to 90°. In this case, the "axis-crossing angle" refers to the angle between 0° and 90° formed between the two shaft axes when projected onto a plane extending parallel to both shaft axes.

[0005] Due to the permanently smooth relative movement between the tooth flanks of their transmission elements, worm and screw gear transmissions are distinguished by a relatively quiet operating behavior compared to gear transmissions that are essentially characterized by rolling bearing contact. Furthermore, worm or screw gear transmissions may have a relatively high load-bearing capacity compared to gear transmissions, which is supported by the relatively large overlap of the engaging teeth of the transmission components. This relatively large overlap of the teeth usually results from the fact that in screw gear or worm transmissions, more teeth are simultaneously engaged than in gear transmissions of comparable size.

[0006] The relatively large overlap of the gear teeth results in relatively small contact stresses in the contact areas, which in turn essentially results in relatively little wear and plastic deformation. This significantly reduces the negative impact of wear and deformation on the service life of the gear. The same applies to the configuration of gear backlash. In automotive steering systems, it is desirable to avoid gear backlash because it would otherwise result in noticeable acoustic effects. If such gear backlash cannot be avoided, it may be considered to compensate for it by incorporating a backlash compensation element. However, this is associated with significant constructional effort and functional disadvantages.

[0007] Therefore, the goal may be to maximize the overlap of the gear tooth rows in order to avoid incorporating backlash compensation elements or to at least make it structurally simple to construct the backlash compensation elements.

[0008] Worm gears are typically configured with a cylindrical worm and an hourglass-shaped worm wheel, or with an hourglass-shaped worm and a cylindrical worm wheel. In the hourglass-shaped worm wheel, the teeth of the worm wheel are configured with a concave progression in the longitudinal direction that is adapted to the diameter of the corresponding cylindrical worm. In contrast, in the hourglass-shaped worm, the tooth tip circle and base circle each describe a single circular segment when viewed in an axial cross section (along the rotation axis of the worm). Worm gears with hourglass-shaped worms can be superior to worm gears with cylindrical worms in that they have a larger overlap of the tooth rows and therefore a larger load-bearing capacity.

[0009] A 90° cross-axis angle in worm transmissions is often a disadvantage when used in steering systems for motor vehicles, since it provides insufficient flexibility in utilizing the available construction space. This limitation does not exist in screw gear transmissions with cross-axis angles not equal to 90°. Furthermore, a 90° cross-axis angle in worm transmissions leads to the construction of worm wheels with helical teeth, which requires more manufacturing effort than gears with straight teeth that may be used as screw gears in screw gear transmissions. However, known screw gear transmissions have the disadvantage that, for geometric reasons, only cylindrical threaded pinions can be used, which have only a relatively small overlap of the teeth with the corresponding screw gears.

[0010] The problem underlying the present invention is to provide a screw gear transmission with as large an overlap of the tooth rows as possible.

[0011] This problem is solved by a screw gear transmission according to claim 10, which comprises a screw pinion according to claim 1. A steering system for a motor vehicle, which comprises a steering transmission in the form of a screw gear transmission according to the invention, is the subject of claim 14. Advantageous configurations of the screw pinion according to the invention, the screw gear transmission according to the invention and the steering system according to the invention are the subject of further claims and / or will become apparent from the following description of the invention.

[0012] The threaded pinions according to the invention for screw gear transmissions have at least one tooth crest, possibly several, in this case preferably two, characterized by an hourglass-shaped configuration, whereby, when viewed in an axial section (cutting plane along the longitudinal axis or rotation axis) of each of the threaded pinions, at least the tooth tips and preferably also the tooth roots of the tooth profile describe an arc directed toward the rotation axis of the threaded pinion (i.e., concave), which may in particular be (each) part of an ellipse. This is also referred to according to the invention as an (elliptical) tooth tip curve or (elliptical) tooth root curve. In this case, on the (elliptical) tooth tip curve, there is located a point, with respect to each tooth profile, of at least the tooth tips, which is at the greatest distance from the rotation axis of the threaded pinion. On the other hand, at least the point of each contour of the bottom of the toothing interspace (formed between two adjacent sections of at least one tooth crest) that is visible in each axial section is located on the (elliptical) root curve. Preferably, the entire bottom of the contour of each toothing interspace that is visible in each axial section is located on the (elliptical) root curve.

[0013] The screw gear transmission according to the present invention comprises, in addition to the screw pinion according to the present invention, a screw gear, which may preferably be cylindrical, in tooth engagement with the screw pinion, with the rotation axis of the screw pinion and the rotation axis of the screw gear having an intersecting axis angle unequal to 90°.

[0014] The invention therefore specifies an hourglass-shaped configuration of the threaded pinion in a screw gear transmission, which is made possible by at least one tooth crest of the threaded pinion, and in the case of several tooth crests, all of these tooth crests, over their (respective) entire extent, having a continuously varying tooth profile, so that when viewed in each axial section (i.e. in each cutting plane along the rotation axis of the threaded pinion), there is only one different tooth profile (i.e. the outer profile of the cutting surface of at least one tooth crest in each axial section).

[0015] The screw gear transmission according to the invention combines the flexibility in terms of the use of construction space that can be provided by an axis intersection angle not equal to 90° with the advantage of a relatively large overlap of the tooth rows, which up to now could only be achieved with worm transmissions equipped with hourglass-shaped worms, but in this case with an axis intersection angle of 90°.

[0016] A preferred embodiment of the screw gear transmission according to the invention can specify that the screw gear is configured with straight teeth, so that all teeth of the screw gear run parallel to the axis of rotation of the screw gear, which can be advantageous with regard to the manufacturability of the screw gear and thus the manufacturing costs of the screw gear and thus the entire screw gear transmission.

[0017] The crossing axis angle in the screw gear transmission according to the present invention may be preferably between 60° and less than 90°, for example 75°, which can have an advantageous effect on the power characteristics of the screw gear transmission and / or on the most compact possible construction of the screw gear transmission. Furthermore, particularly with such a crossing axis angle, it is advantageous to realize a combination with a screw gear having straight teeth.

[0018] The advantageous tooth engagement in the screw gear transmission according to the invention can be achieved by having all tooth profiles of the threaded pinion, and possibly all but one, asymmetric and therefore each having two unequal tooth flank geometries. One symmetrical tooth profile, which may be configured as an involute, may be located in particular in the middle of the (nominal) tooth crest extension (i.e., in the middle of the total extension of at least one tooth crest) and / or may form a transition between different, in particular contrasting, asymmetries that the tooth profiles may have in both extension directions starting from the middle of the tooth crest extension. The symmetrical tooth profile may advantageously serve as the starting point for producing the threaded pinion, in particular at least one tooth crest, for example by milling.

[0019] The advantageous tooth engagement in the screw gear transmission according to the invention can further be achieved in that, starting from the middle of the tooth crest extension range in the threaded pinion, the tooth flanks located on the outside (or further from the middle of the tooth crest extension range) in each case (i.e. in both directions of extension) have an increasing concavity over the respective partial extension range of the tooth crest, and / or the tooth flanks located on the inside (or closer to the middle of the tooth crest extension range) of the individual tooth profiles have an increasing convexity over the respective partial extension range of the tooth crest. In this case, it can be specified that the rate of increase of the concavity of the tooth flanks located on the outside in each case is greater than the rate of increase of the convexity of the tooth flanks located on the inside.

[0020] The corresponding asymmetry of the tooth profile can be advantageously made visible and / or detectable by setting measuring balls of different diameters in the tooth crests, with the centers of the measuring balls joined together to form a straight line. In this case, the diameter of the measuring balls can be selected arbitrarily, preferably such that contact with the root of the tooth crest is avoided. In this case, due to the asymmetry of the tooth profile, the straight line has an increasing slope relative to the perpendicular of each root curve over the extent of each tooth crest.

[0021] The intermediate extent of at least one tooth crest can preferably be located, with respect to the extension of the rotation axis of the threaded pinion, at an axis intersection of the threaded pinion, where the axis intersection is a point on the rotation axis of the threaded pinion and the rotation axis of the crosshair gear, respectively, defined by the shortest distance between the two axes.

[0022] Preferably, it may be specified that at least one tooth crest of the threaded pinion has a continuously varying distance of the measuring ball center point from the corresponding tooth root curve over its entire extension, where "measuring ball center point" means the center of the (measuring) ball, which is dimensioned so that when rolling in the intermediate tooth chamber formed between adjacent sections of at least one tooth crest, it only comes into contact with the tooth flank (and not with the bottom of the intermediate tooth chamber).

[0023] The advantageous tooth engagement in the screw gear transmission according to the invention can furthermore be achieved in that at least one tooth crest of the threaded pinion has, over its entire extent, a continuously varying tooth height, which is manifested by a shortest distance between the tip and root contours within each individual tooth profile.

[0024] Furthermore, in the screw gear transmission according to the invention, advantageous tooth engagement can be achieved by the tooth crest having a continuously varying tooth tip shape over its entire extension. In this case, this variability in the tooth tip shape can be caused in particular by changes in the tooth tip thickness and / or the tooth tip radius. The tooth tip is the part of the tooth profile that is located in the region of the tooth tip curve. Symbols for representing the dimensions of the tooth tip thickness, tooth tip radius and tooth curve radius (the distance between the rotation axis and the tooth tip curve) are shown in Figure 16.

[0025] The present invention also relates to a steering system including a steering transmission that is the screw transmission according to the present invention or that includes the screw transmission according to the present invention. The steering system may further include a steering motor, which may be configured, in particular hydraulically or electrically, rotationally coupled to the screw pinion. The screw gear of the screw transmission may further be non-rotatably coupled to a steering shaft of the steering system, in particular a steering column, or rotationally coupled to the steering shaft. The steering system according to the present invention may be configured, in particular, as a power-assisted steering system, in which the steering motor can generate an assist torque, thereby reducing (possibly temporarily to zero) the steering moment applied to the steering column by the driver of a vehicle equipped with the power-assisted steering system to steer the vehicle. Alternatively, the steering system may be configured such that the steering motor always generates all the steering moment required for steering, in particular to realize a so-called steer-by-wire function, in which there is no mechanical connection between the steering wheel (if present) and the steerable wheels of the steering system or vehicle.

[0026] The invention also relates to a motor vehicle equipped with a steering system according to the invention.

[0027] The invention will be explained in detail below based on the configuration examples shown in the drawings. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a side view of a screw gear transmission according to the present invention. [Figure 2] FIG. 2 is a cross-sectional view of the cross-sectional view of the screw gear transmission taken along the cutting plane II-II in FIG. 1. [Figure 3]1A and 1B are axial cross-sectional views of a superimposed threaded pinion of a screw gear transmission and a comparably dimensioned cylindrical worm (with a thinner wire arrangement), each with a rotation angle defined as 0°. [Figure 4] FIG. 4 is an enlarged view of the section designated by reference numeral IV in FIG. 3 relative to the reference coordinate system, where the axial zero value (on the x-axis) corresponds to the mid-range of the tooth crest in this axial cross-section. [Figure 5] 5 is an axial cross-sectional view of the threaded pinion and cylindrical worm shown in FIG. 4 at a rotation angle of 90°. [Figure 6] 4 and 5, all tooth profiles of the threaded pinion according to the invention which are located to the left of the axial zero value and which are fully visible are translated to the middle of the tooth crest extension range (in this case, the tooth profile located in the middle of the tooth crest extension range in FIG. 4 has been omitted). [Figure 7] 4 and 5, all tooth profiles of a fully visible threaded pinion according to the invention, which are located to the right of the axial zero value, are translated to the middle of the tooth crest extension range (in this case, the tooth profile located in the middle of the tooth crest extension range in FIG. 4 is taken into account). [Figure 8] 6 shows the progression of the radius of curvature of the tooth flanks over the corresponding tooth height for all tooth profiles of the threaded pinion according to the invention which are located to the left of the axial zero value in FIGS. 4 and 5 and which are fully visible. [Figure 9] 6 shows the variation of the radius of curvature of the tooth flanks over the corresponding tooth heights of all tooth profiles of the threaded pinion according to the invention which are located to the right of the axial zero value in FIGS. 4 and 5 and which are fully visible. [Figure 10] 1 shows an axial section of a threaded pinion combined with a measuring ball, in which two positions of the measuring ball are shown. [Figure 11] 5 shows a corresponding part of an hourglass-shaped worm (with a thinner line arrangement) instead of a cylindrical worm, for comparison with the threaded pinion according to the invention, in correspondence with FIG. 4. [Figure 12] FIG. 1 is a radial cross-sectional view of a threaded pinion and a cylindrical worm (dashed line arrangement) at the middle of the tooth crest extension range. [Figure 13] 13 is a radial cross-sectional view of a threaded pinion and a cylindrical worm (dashed line arrangement) at a position displaced by two tooth pitches compared to the radial cross-sectional view shown in FIG. 12. FIG. [Figure 14] 13 is a radial cross-sectional view of a threaded pinion and a cylindrical worm (dashed line arrangement) at a position shifted by three tooth pitches compared to the radial cross-sectional view shown in FIG. 12. FIG. [Figure 15] 14 is a radial cross-section of the threaded pinion and hourglass-shaped worm (dashed line arrangement) shown in FIG. 13. [Figure 16] FIG. 1 shows a section with a tooth tip of one tooth profile including symbols to indicate dimensions. [Figure 17] 2 is an axial cross-section of a threaded pinion combined with measuring balls each having a different ball diameter, the measuring balls being shown at three different x-positions within the range of the tooth ridges.

[0029] 1 and 2 show a screw gear transmission according to the present invention, which comprises an hourglass-shaped screw pinion 1 and a screw gear 2 which is cylindrical and has a straight tooth arrangement. Due to its configuration as a screw gear transmission, the rotation axis 3 of the screw pinion 1 and the rotation axis 4 of the screw gear 2 form an axis intersection angle δ which is not equal to 90°, specifically an axis intersection angle δ of 75°. The screw gear transmission is used as a steering transmission for a steering system 21 of a motor vehicle.

[0030] In Figure 3, the threaded pinion 1 is shown in an axial section, similar to Figure 2, in an orientation with respect to rotation (about the axis of rotation 3 of the threaded pinion 1) defined as 0°. Figure 3 additionally shows a conventional cylindrical worm 5 of comparable dimensions, also in axial section, superimposed in a thinner line arrangement.

[0031] 4 shows the section designated by the reference number IV in FIG. 3 in an enlarged view relative to a reference coordinate system whose horizontal axis (x-axis) runs parallel to the (collinear) rotation axes 3, 6 of the threaded pinion 1 and the cylindrical worm 5 and whose vertical axis (y-axis) runs radially to said rotation axes 3, 6. The zero value of the horizontal axis (x=0) is assigned to the middle extension 9 of the tooth threads 7, 8 of the threaded pinion 1 and the cylindrical worm 5, respectively, which middle extension 9 is exactly in the middle of the total helical or helical extension of the individual tooth threads 7, 8 of the threaded pinion 1 and the cylindrical worm 5, respectively, and which, in the screw gear transmission according to the invention, is located at the axis intersection 10 of the threaded pinion 1 (see FIG. 1). In the illustrated configuration, the threaded pinion 1 and cylindrical worm 5 are arranged offset by 180° relative to their respective rotation axes 3, 6, but otherwise have identical two teeth 7, 8 each.

[0032] FIG. 5 shows an axial cross section of the threaded pinion 1 and the cylindrical worm 5, each with a rotation angle of 90°, so that the zero value of the horizontal axis of the reference coordinate system is located in the middle of the tooth row intermediate space 11 of each tooth ridge 7, 8, respectively.

[0033] As is already clear from FIGS. 3 to 5, the threaded pinion 1 according to the present invention is excellent in the following features.

[0034] Each tooth crest 7 of the threaded pinion 1 has a continuously varying tooth profile over its entire extension range, whereby in the (nominal) middle of the tooth crest extension range 9 of the tooth crest 7 an involute tooth profile may arise that is substantially identical to the (constant over the entire extension range) tooth profile of the tooth crest 8 of the cylindrical worm 5. This is evident from the substantially exact overlap of the tooth profile profiles located at the zero value of the horizontal axis in Figure 4.

[0035] Starting from the midpoint of the tooth crest extension 9, the tooth flanks 12 located on the outside in both directions of extension have a concave surface that increases over the partial extension of each individual tooth crest 7. In contrast, the tooth flanks 13 located on the inside each have a convex surface that increases over the partial extension of each individual tooth crest 7, with the rate of increase of the concavity of the tooth flanks 12 located on the outside being greater than the rate of increase of the convexity of the tooth flanks 13 located on the inside.

[0036] Due to the continuously different variations in the shape of the different tooth flanks 12, 13, it becomes clear that all tooth profiles of the individual tooth crests 7 are configured asymmetrically, with the exception of the tooth profile profile located in the respective intermediate crest range 9. This asymmetry can be seen even more clearly in FIGS. 6 to 9 and 17. In FIG. 6, all tooth profiles shown (completely) to the left of zero on the horizontal axis in FIGS. 4 and 5, respectively, and therefore in the negative range, are superimposed by translation to the intermediate crest range 9. In this case, the tooth profile profile located in the intermediate crest range 9 in FIG. 4 is not taken into account. Correspondingly, in FIG. 7, all tooth profiles shown (completely) to the right of zero on the horizontal axis in FIGS. 4 and 5, respectively, and therefore in the positive range, are superimposed by translation to the intermediate crest range, in this case, the tooth profile profile located in the intermediate crest range 9 in FIG. 4 is taken into account.

[0037] FIG. 17 shows that the symmetrical asymmetry of the tooth profile (left flank vs. right flank) in both directions of extension (1. x = 0 → x > 0 or 2. x = 0 → x < 0) results in a straight line 22 defined by the ball centers of several measuring balls 14 with different ball diameters. Starting from the midpoint of the tooth crest extension 9 (x = 0), this straight line 22 is gradually inclined relative to the perpendicular (or perpendicular) 23 of the root curve 16 over the individual partial extensions of the tooth crest 7. In this case, the change in inclination in both directions of extension is opposite to each other. FIG. 17 only shows the change in inclination in one direction of extension (1. x = 0 → x > 0). In the other direction of extension, a mirror-symmetric change in the inclination of this straight line occurs. Such an inclination angle θ between the straight lines 22 and 23 occurs only in the lead pinion according to the invention. In the case of an hourglass-shaped worm with an axis crossing angle Σ=90° and a cylindrical worm with an axis crossing angle <=90°, the straight lines 22 and 23 always coincide.

[0038] 6 and 7, it can also be seen that the tooth crests 7 of the threaded pinion 1 according to the invention each have a continuously varying tooth height h over their entire extension. In particular, the thickness s a1 and tooth tip roundness ρ a1 A continuously varying tooth tip profile can also be observed (see also Figure 16).

[0039] 8 and 9 show the respective progressions, and thus the change, of the radius of curvature t (on the horizontal axis) of the tooth flanks 12, 13 over the tooth height h (vertical axis). In this case, the progression of the left tooth flanks, which are grouped on the right side of each diagram, is shown with a thicker line thickness, while the progression of the right tooth flanks, which are grouped on the left side of each diagram, is shown with a thinner line thickness. Also, in FIG. 8, the tooth profile profile to the left of zero (x=0) in FIGS. 4 and 5 is considered, while in FIG. 9, the tooth profile profile to the right of and at zero is considered. The increase in the concavity of the tooth flank 12, which is located on the outer side in each direction of extension, is clearly noticeable. The increase in the convexity of the tooth flank 13, which is located on the inner side in each direction of extension, is, although certainly present, relatively small. For comparison, in FIGS. 8 and 9, the progression of the radius of curvature of a cylindrical worm is additionally shown by dashed line sequences.

[0040] The tooth ridges 7 of the threaded pinion according to the invention are such that, over their entire extension, the distance P of the measuring ball centre 15 to the corresponding root curve 16 varies continuously, each in relation to the coordinate x. f This means that in FIG. f,x=0 ) and x=15mm(P f,x=15 ) are shown in two exemplary positions of the corresponding measuring ball 14.

[0041] The threaded pinion 1 according to the invention is further characterized in that the tooth profile describes an elliptical tooth tip curve 17 and a tooth root curve 16. This is particularly evident from Figure 11, which shows one tooth tip curve 17 and one tooth root curve 16. In addition to this, or instead of the cylindrical worm 5, a comparably dimensioned hourglass-shaped worm 18 is shown in thinner lines, whose tooth profile, which, like the cylindrical worm 5, is constant or invariant over its entire extension, describes a circular tooth root curve 19 and a tooth tip curve 20.

[0042] The continuously varying tooth profile of the tooth crest 7 of the threaded pinion 1 according to the invention can also be seen clearly in Figures 12 to 15, which show the threaded pinion 1 in radial cross-section (i.e., a cut section perpendicular to the rotation axis 3). In this case, Figure 12 shows a radial cross-section of the (identical) intermediate crest extension 9 of the tooth crest 7 (the axial zero point shown in Figures 4 and 5), Figure 13 shows a radial cross-section of the intermediate crest extension 9 at a position shifted in the positive direction of the horizontal axis by two pitches T of the tooth crest 7, and Figure 14 shows a radial cross-section of the intermediate crest extension 9 at a position shifted in the positive direction of the horizontal axis by three pitches T of the tooth crest 7. In this case, Figures 12 to 14 also show corresponding radial cross-sections of the cylindrical worm 5, which is also shown in Figures 3 to 5, for comparison.

[0043] 12 to 14 show the continuously varying tooth profile of the tooth crest (at three exemplary positions), in this case with particular clarity its asymmetry, except for the tooth profile in the intermediate tooth crest extension range 9 (see FIG. 12), and the continuously varying tooth height h of the tooth crest 7.

[0044] FIG. 15 shows a radial section of the threaded pinion 1 according to the invention shown in FIG. 13 in comparison with the corresponding radial section of the hourglass-shaped worm 18 already shown relatively in FIG. 11.

Claims

1. A threaded pinion (1) for a screw gear transmission, comprising at least one tooth (7), Threaded pinion (1) having an hourglass-shaped configuration, characterized in that the tooth ridges (7) have a continuously varying tooth profile over their entire extension.

2. 2. The threaded pinion (1) according to claim 1, characterized in that all or all but one of the tooth profiles are asymmetric.

3. 3. The threaded pinion (1) according to claim 1 or 2, characterized in that, starting from the middle of the tooth crest extension (9), the tooth flanks (12) located on the outside respectively have an increasing concavity over the partial extension of each of the tooth crests (7).

4. 4. The threaded pinion (1) according to claim 1, wherein, starting from one / certain tooth crest intermediate extension range (9) in the longitudinal axis direction, the tooth flanks (13) located inwardly respectively have an increasing convexity over the partial extension range of each of the tooth crests (7).

5. 5. The threaded pinion (1) according to claims 3 and 4, characterized in that the rate of increase of the concavity of each of the outer tooth flanks (12) is greater than the rate of increase of the convexity of each of the inner tooth flanks (13).

6. 6. The threaded pinion (1) according to claim 1, wherein the tooth tips and / or the tooth roots of the tooth profile describe portions of an ellipse when viewed in the respective axial cross section.

7. 7. The threaded pinion (1) according to claim 1, wherein the at least one tooth crest (7) has a continuously varying distance (m) of the measuring ball center point relative to the root curve over its entire extension.

8. 8. The threaded pinion (1) according to claim 1, wherein the at least one tooth (7) has a continuously varying tooth height (h) over its entire extent.

9. 9. The threaded pinion (1) according to claim 1, wherein the tooth crests have a continuously varying tooth tip shape over their entire extent.

10. A screw gear transmission comprising a screw pinion (1) according to any one of claims 1 to 9 and a screw gear (2).

11. 11. The screw gear transmission according to claim 10, wherein the screw gear (2) is configured with straight teeth.

12. 12. The screw gear transmission according to claim 10, wherein one / a particular intermediate tooth crest extension region (9) of the threaded pinion (1) is located overlapping the axis intersection point (10) of the threaded pinion (1).

13. 13. A screw gear transmission according to claim 10, wherein the screw gear (2) is cylindrical.

14. A steering system for a motor vehicle, comprising a steering transmission which is or includes a screw gear transmission according to any one of claims 10 to 13.

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