SPINDLE DRIVE AND AN ACTUATOR COMPRISING A SPINDLE DRIVE

Abstract

A spindle drive (1) having a spindle (2) with a spindle thread (2a), and spindle nut (3) with a nut thread (3a). The spindle thread (2a) and the nut thread (3a) form a movement thread (4) having a crown clearance (5), a root clearance (6) and a flank clearance. The spindle (2) and the spindle nut (3) can be centered by virtue of a reduced crown clearance (5) and/or a reduced root clearance (6).

Claims

1-14. (canceled)

15. A spindle drive comprising: a spindle (2, 22) with a spindle thread (2a, 22a); a spindle nut (3, 23) with a nut thread (3a, 23a); the spindle thread (2a, 22a) and the nut thread (3a, 23a) forming a movement thread (4, 24) having a crown clearance (5, 25), a root clearance (6, 26) and a flank clearance (9); and the spindle (2, 22) and the spindle nut (3, 23) being centered by at least one of a reduced crown clearance (5, 25) and a reduced root clearance (6, 26).

16. The spindle drive according to claim 15, wherein the movement thread is a trapezoidal thread (4, 24).

17. The spindle drive according to claim 15, wherein at least one of the crown clearance (5, 25) and the root clearance (6, 26) is designed as either a sliding fit or a displacement fit (2b, 3b).

18. The spindle drive according to claim 15, wherein the nut thread (3a) has a reduced root circle diameter (D.sub.F1).

19. The spindle drive according to claim 15, wherein the spindle thread (2a) has an enlarged crown circle diameter (d.sub.K1).

20. The spindle drive according to claim 15, wherein the nut thread (3a) has a reduced crown circle diameter (D.sub.K1).

21. The spindle drive according to claim 15, wherein the spindle thread (2a) has an enlarged root circle diameter (d.sub.F1).

22. The spindle drive according to claim 15, wherein at least one of the crown clearance (5, 25) and the root clearance (6, 26) is smaller than a radial portion of the flank clearance (9).

23. The spindle drive according to claim 15, wherein the spindle thread (2a) has a crown circle surface (2b) and flanks (2c, 2d), and a first transition contour (7, 11) is arranged between the crown circle surface and the flanks of the spindle thread, the nut thread (3a) has a root circle surface (3b) and flanks (3c, 3d), and a second transition contour (8, 12) is arranged between the root circle surface and the flanks of the nut thread, and a circumferential gap (10, 13) is located between the first and the second transition contours (7, 8; 11, 12).

24. The spindle drive according to claim 23, wherein the first and the second transition contours have different radii (R, r).

25. The spindle drive according to claim 23, wherein the first and the second transition contours are chamfers (11, 12).

26. The spindle drive according to claim 15, wherein the spindle thread (2a, 22a) has cylindrical crown circle surfaces (2b) and the nut thread (3a, 23a) has cylindrical root circle surfaces (3b), and the crown circle surfaces (2b) and the root circle surfaces (3b) form corresponding sliding surfaces.

27. An actuator for a rear axle steering system, with a spindle drive (1, 21) comprising: a spindle (2, 22) with a spindle thread (2a, 22a); a spindle nut (3, 23) with a nut thread (3a, 23a); the spindle thread (2a, 22a) and the nut thread (3a, 23a) forming a movement thread (4, 24) having a crown clearance (5, 25), a root clearance (6, 26) and a flank clearance (9), and the spindle (2, 22) and the spindle nut (3, 23) being centered by at least one of a reduced crown clearance (5, 25) and a reduced root clearance (6, 26).

28. A rear axle steering system with an actuator with a spindle drive (1, 21) comprising: a spindle (2, 22) with a spindle thread (2a, 22a), a spindle nut (3, 23) with a nut thread (3a, 23a), the spindle thread (2a, 22a) and the nut thread (3a, 23a) forming a movement thread (4, 24) having a crown clearance (5, 25), a root clearance (6, 26) and a flank clearance (9), and the spindle (2, 22) and the spindle nut (3, 23) being centered by at least one of a reduced crown clearance (5, 25) and a reduced root clearance (6, 26).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Example embodiments of the invention are illustrated in the drawing and are described in more detail below, so that further features and/or advantages can emerge from the description and/or the drawing, which show:

[0020] FIG. 1: A view of a spindle drive with a reduced crown clearance of the movement thread,

[0021] FIG. 2: An enlarged illustration of the reduced crown clearance,

[0022] FIG. 2a: A detail X from FIG. 2, with enlarged transition contours (radii),

[0023] FIG. 3: A further embodiment for transition contours (chamfers), and

[0024] FIG. 4: A further embodiment of the invention for a spindle drive with a reduced root clearance.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] FIG. 1 shows, as a first embodiment of the invention, a section of a spindle drive 1 with a spindle 2 having a spindle thread 2a and a spindle nut 3 having a nut thread 3a and a rotational axis a. The spindle or bolt thread 2a, together with the nut thread 3a, form a movement thread 4 preferably in the form of a trapezoidal thread and which in its geometry derives from a known trapezoidal thread according to DIN 103. Concentricity exists when the axes of the spindle thread 2a and the nut thread 3a coincide with the rotational axis a. The standardized trapezoidal thread has a crown clearance 5 and a root clearance 6, which are also called radial clearances. In addition, the standardized trapezoidal thread has a flank clearance also known as the axial clearance. The standardized trapezoidal thread is flank-centered, i.e. displacement of the thread axes of the spindle and nut threads is absorbed by the flanks so that there is no radial contact between the crown circle of the spindle thread and the root circle of the nut thread. The spindle thread 2a according to the invention has a crown circle diameter d.sub.K0 that corresponds to the crown circle diameter of the standardized trapezoidal thread. The nut thread 3a has a root circle diameter D.sub.F1 which is smaller compared with the root circle diameter D.sub.F0 of the standardized nut thread, i.e. D.sub.F1<D.sub.F0. Due to the reduction of the root circle diameter of the nut thread 3a, the crown clearance 5 is reduced to a sliding contact, so that the spindle thread 2a by virtue of its crown circle d.sub.K0 is centered relative to the root circle D.sub.F1 of the nut thread 3a. If the concentricity between the spindle 2 and the nut 3 is impaired, a radial sliding contact takes place, i.e. the radial clearance becomes practically zero; at the same time, howeveras explained below in reference to FIG. 2a flank clearance also known as axial clearance is still present. The root clearance 6 between the spindle thread 2a and the nut thread 3a corresponds to the root clearance 6 of a standardized trapezoidal thread and is therefore unchanged.

[0026] FIG. 2 shows an enlarged view of the reduced crown clearance between the spindle thread 2a and the nut thread 3a. The trapezoidal profile of the spindle thread 2a has a cylindrical crown circle surface 2b and two flanks 2c, 2d, which merge into one another via a first transition contour 7. The trapezoidal profile of the nut thread 3a has a cylindrical root circle surface 3b and two flanks 3c, 3d, which merge into one another via second transition contours 8. As can be seen from the drawing, the crown circle surface 2b is in contact with the root circle surface 3b with no clearance, i.e. there is a sliding contact between the cylindrical surfaces 2b, 3b which form a slide bearing. The known crown clearance of the standard thread is here reduced practically to zero. Preferably, between the cylindrical outer or crown circle surface 2b and the cylindrical inner or root circle surface 3b there is a sliding or displacement fit, by which the minimum and maximum crown clearance are defined.

[0027] FIG. 2 further shows an axial clearance 9, also called flank clearance 9, i.e. a distance in the axial direction between the flank 2d of the spindle thread 2a and the flank 3d of the nut thread 3a. From this representation it can be seen that with the reduced crown clearance according to the invention there can be no jamming of the flanks 2d, 3d or 2c, 3c since the radial fraction of the axial clearance 9 is always larger than the radial fraction of the flank clearance. The root clearance 6 already mentioned above can also be seen clearly here.

[0028] FIG. 2a shows a detail X from FIG. 2, i.e. the transition contours 7, 8 in an enlarged representation. The two transition contours 7, 8 are formed as radii r, R, wherein the radius r on the nut thread 3a is smaller than the radius R on the spindle thread 2a, so that between the two transition contours 7, 8 there is a circumferential gap 10. This avoids sticking or wear in the corner area.

[0029] FIG. 3 shows a further embodiment for the transition contours, in this case in the form of a first chamfer 12 on the nut thread 3a and a second chamfer 11 on the spindle thread 2a. Between the two chamfers 11, 12 there is a gap 13.

[0030] FIG. 4 shows another embodiment of the invention for a spindle drive 21 having a spindle 22 with a spindle thread 22a, a spindle nut 23 with a nut thread 23a and a rotational axis a. The spindle thread 22a and the nut thread 23a form a movement thread 24 in the form of a trapezoidal thread, which is derived from a standardized trapezoidal thread. The standard thread would have a crown clearance 25 and a root clearance 26, also called radial clearance. In this variant according to the invention the root clearance 26 is reduced, and this indeed preferably to a sliding or displacement fit. The crown clearance 25 is kept the same. Thus, the centering of the spindle 22 relative to the nut 23 takes place by virtue of the reduced root clearance 26, which is preferably produced by the following alternative change to the standard thread. A change is made in the spindle thread, and concerns an enlargement of the root circle diameter d.sub.F0 of the standard thread to the root circle diameter d.sub.F1 according to the invention. The crown circle diameter D.sub.K0 of the nut thread 23a remains unchanged, as also does the crown clearance 25. A further change is made in the nut thread and consists in making the crown circle diameter D.sub.K0 of the standard thread smaller, reducing it to the crown circle diameter D.sub.K1, so that the relationship D.sub.K1<D.sub.K0 applies. Correspondingly, for the first variant d.sub.F1>d.sub.F0 also applies.

[0031] A further, more theoretical variant not illustrated in the drawing would be that both the crown clearance and the root clearance are reduced.

INDEXES

[0032] 1 Spindle drive [0033] 2 Spindle [0034] 2a Spindle thread [0035] 2b Crown circle surface [0036] 2c Flank [0037] 2d Flank [0038] 3 Spindle nut [0039] 3a Nut thread [0040] 3b Root circle surface [0041] 3c Flank [0042] 3d Flank [0043] 4 Movement thread [0044] 5 Crown clearance [0045] 6 Root clearance [0046] 7 First transition contour [0047] 8 Second transition contour [0048] 9 Flank clearance [0049] 10 Gap [0050] 11 Chamfer [0051] 12 Chamfer [0052] 13 Gap [0053] 21 Spindle drive [0054] 22 Spindle [0055] 22a Spindle thread [0056] 23 Spindle nut [0057] 23a Nut thread [0058] 24 Movement thread [0059] 25 Crown clearance [0060] 26 Root clearance [0061] a Rotational axis [0062] d.sub.K0 Crown circle diameter, spindle (standard) [0063] d.sub.K1 Crown circle diameter, spindle, enlarged [0064] d.sub.F0 Root circle diameter, spindle (standard) [0065] d.sub.F1 Root circle diameter, spindle, enlarged [0066] D.sub.K0 Crown circle diameter, nut (standard) [0067] D.sub.K1 Crown circle diameter, nut, reduced [0068] D.sub.F0 Root circle diameter, nut (standard) [0069] D.sub.F1 Root circle diameter, nut, reduced [0070] r Radius of transition contour [0071] R Radius of transition contour