Ball screw drive and associated electromechanical actuator

Abstract

A ball screw of an electromechanical brake comprising a ball screw nut disposed on a spindle, wherein the spindle includes complementary tracks formed on the spindle and the ball screw nut. The ball screw further includes a race that includes a plurality of ball pockets spaced apart from one another and a protruding section that includes a concave bearing surface, a ball housed between the concave bearing surface and an end section of a first spring element for a main load direction, and a second spring element for a return stroke direction, wherein the second spring element includes a second spring end section in contact with an opposite side of the bearing surface.

Claims

1. A ball screw comprising: a ball screw nut disposed on a spindle, wherein the ball screw includes a first and second spring element disposed axially offset to one another and disposed such that the first and second spring element generate reset forces acting in the same direction; and complementary tracks formed on the spindle and the ball screw nut, in which a ball is accommodated in a race and the first spring element for generating a reset force are disposed, wherein the ball is disposed between the race and the first spring element.

2. The ball screw of claim 1, wherein a diameter of the ball disposed between the race is large enough that the ball is a supporting ball.

3. The ball screw of claim 1, wherein a diameter of the ball disposed between the race and the first spring element is small enough that the ball is not a supporting ball.

4. The ball screw of claim 1, wherein the race includes at least one concave bearing surface adapted to an outer contour of the ball.

5. The ball screw of claim 1, wherein the ball screw includes the first and second spring elements disposed such that the first and second spring elements generate opposing reset forces.

6. The ball screw of claim 1, wherein a length of the first spring element is between one half of a circumference and approximates three quarters of the circumference of the track.

7. The ball screw of claim 1, wherein the complimentary tracks on the spindle and the ball screw nut are configured to accommodate balls in the race to be retained therein.

8. The ball screw of claim 1, wherein the race includes ball pockets that are radially offset.

9. A ball screw of an electromechanical brake, comprising: a ball screw nut disposed on a spindle, wherein the spindle includes complementary tracks formed on the spindle and the ball screw nut; a race that includes a plurality of ball pockets spaced apart from one another and a protruding section that includes a concave bearing surface; a ball housed between the concave bearing surface and an end section of a first spring element for a main load direction; and a second spring element for a return stroke direction, wherein the second spring element includes a second spring end section in contact with an opposite side of the bearing surface.

10. The ball screw of the electromechanical brake of claim 9, wherein a diameter of the ball includes an outer diameter configured to roll on the tracks when the ball screw is moved.

11. The ball screw of the electromechanical brake of claim 9, wherein the first or second spring element retains a raceway configured to allow the ball to roll when the spindle moves in relation to the ball screw nut.

12. The ball screw of the electromechanical brake of claim claim 9, wherein the ball pockets are radially offset toward the outside of a circumferential surface of the race.

13. The ball screw of the electromechanical brake of claim claim 9, wherein the ball pockets are configured to retain the ball on the spindle such that the ball screw nut can be removed without the ball falling.

14. The ball screw of the electromechanical brake of claim claim 9, wherein the plurality of ball pockets are radially offset toward an inside with respect to the race.

15. The ball screw of the electromechanical brake of claim claim 9, wherein the race includes a bearing surface of a section extending in an axial direction of the race, wherein a second spring element is disposed on an opposite side of the bearing surface and the second spring element exerts a force directed opposite the force generated by a first spring element.

16. The ball screw of the electromechanical brake of claim claim 9, wherein the spring element is a helical compression spring.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a first exemplary embodiment of a ball screw in a perspective, partially cutaway view;

(2) FIG. 2 shows a perspective view of the race of the ball screw shown in FIG. 1;

(3) FIG. 3 shows a side view of the race shown in FIG. 2;

(4) FIG. 4 shows another exemplary embodiment of a ball screw in a perspective, partially cutaway view;

(5) FIG. 5 shows the race of the ball screw shown in FIG. 4, in a side view;

(6) FIG. 6 shows a race of a ball screw;

(7) FIG. 7 shows another perspective view of the race shown in FIG. 6; and

(8) FIG. 8 shows a modified embodiment of a race of a ball screw.

DETAILED DESCRIPTION

(9) The ball screw 1 shown in FIG. 1 comprises a spindle 2, a portion of which is shown in FIG. 1. The spindle 2 has tracks 3. In addition, the ball screw 1 comprises a ball screw nut 4, also referred to as a linear actuator nut. The cylindrical ball screw nut 4 has internal tracks 5, which are adapted to the tracks 3 of the spindle 2, such that balls can be accommodated in the interior of the ball screw nut 4. The ball screw 1 comprises a race 6, through which the rollers formed as balls are guided. It can be seen in FIG. 1 that the race 6 comprises numerous axially adjacent rows of ball pockets 7, spaced apart from one another, and in which a ball can be received in each case.

(10) In this case, the race 6 may be produced from steel sheet metal, and designed as a stamped bending part. In the view in FIG. 1, a joint 8 running in the axial direction can be seen, wherein the free ends of the race 6 adjoining one another are welded together. In order to avoid plastic deformation, the race 6 can optionally be subjected to a heat treatment, depending on the forces acting on the ball screw 1.

(11) The ball screw 1 has a first spring element 9, which may be designed as a helical compression spring, and may be received between the complementary tracks 3, 5 of the spindle 2 and the ball screw nut 4. In the depicted exemplary embodiment, the first spring element 9 extends over approximately one half of the circumference of the tracks, i.e. over ca. 180. It can be seen in FIG. 1 that an end section 10 of the first spring element 9 does not bear directly on the race 6, but rather on a ball 11. On its opposite side, the ball 11 bears on a concave bearing surface 12 of the race 6. The race 6 has a section 13 there, extending in the axial direction, on which the bearing surface 12 for the ball 11 is formed. In this exemplary embodiment, the ball 11 may be a supporting ball such that its outer diameter may roll on the tracks 3, 5 when the ball screw 1 is moved.

(12) The first spring element 9 shown in FIG. 1 is dedicated to the main load direction. The spring element 9 retains a raceway for the balls, such that they may roll instead of slide when the spindle 2 moves in relation to the ball screw nut 4.

(13) Because the end section 10 of the first spring element 9 bears on the ball 11, the end section 11 is centered, by means of which it is prevented from ending up in an intermediate space between the race 6 and one of the two tracks 3, 5. This may be possible with conventional ball screws, in which the end section of the spring element bears directly on the race.

(14) FIGS. 2 and 3 show the race 6, wherein FIG. 2 is a perspective view and FIG. 3 is a side view. The race 6 is shown without balls therein, which are placed in the ball pockets 7 in the assembled state.

(15) A second spring element 14 is shown in FIG. 1, which likewise bears on the protruding section 13 of the race 6. However, the second spring element 14 bears on the opposite side of the bearing surface 12 on the section 13, such that the second spring element 14 exerts a force directed opposite the force generated by the first spring element 9. The second spring element 14 is dedicated to the return stroke direction, whereas the first element 9 is dedicated to the main load direction. The second spring element 14, dedicated to the return stroke direction, is subjected to substantially lower loads than the first spring element, such that a ball between the end section 15 of the second spring element 14 and the bearing surface can be eliminated. Likewise, a specially shaped bearing surface like that provided on the opposite side for the ball 11 is not needed for the end section 15 of the second spring element 14. In certain applications, even the second spring element 14 can be eliminated.

(16) FIG. 4 shows another exemplary embodiment of a ball screw 16, which is substantially identical to the ball screw 1 shown in FIG. 1. For this reason, identical components shall not be explained in detail again at this point. The ball screw 16, in conforming to the first exemplary embodiment, comprises a spindle 2 with tracks 3, and a ball screw nut 4 with tracks 5. Balls (not shown) are received in the complementary tracks 3, 5, guided by a race 17. The first spring element 9, the ball 11 and the second spring element 14 are accommodated between the tracks. There is an end section of the spring element 14 below the first spring element 9, which bears on the ball screw nut 4.

(17) In differing from the ball screw 1 shown in FIG. 1, the ball screw 16 shown in FIG. 4 has a third spring element 18, disposed on the axial side of the ball screw nut 4 opposite the first spring element 9. A ball 21 is disposed between an end section 19 of the third spring element 18 and a bearing surface 20 of the race 17, which is identical to the ball 11. The opposite end of the third spring element 18, which is hidden in FIG. 4, bears on the ball screw nut 4. In modified embodiments, this end can also bear on another (not shown) element, e.g. a pin or a disk press-fitted therein.

(18) It can be seen in FIG. 4 that the two spring elements 9, 18 are disposed parallel to one another, and generate parallel forces. As a result of the bearing surface 20, formed like the bearing surface 12, the end section 19 of the third spring element 18 is prevented from being displaced into a free space between the race 17 and one of the tracks 3, 5. As a result of the parallel spring elements 9, 18, the overall force generated by the spring elements 9, 18 is increased and set to a specific value. In other exemplary embodiments, a third parallel spring may also be provided.

(19) FIGS. 5, 6, and 7 show a side view and parallel views of the race 17. The concave bearing surfaces 12, 20 for the balls 11, 21 can be seen in FIG. 5. It can be seen in FIG. 5 that a bearing surface 22 for the second spring element 14 is designed as a straight, axial edge, such that a concave bearing surface is not provided for the second spring element 14. A few supporting balls 23 are shown in FIGS. 5, 6, and 7 in each case, which are guided by the race 17. The race 17 has ball pockets 7, which are radially offset toward the inside with respect to the race 17. In this manner, balls 23 are retained in the ball screw nut 4 by the race 17, such that the spindle 2 can be screwed out, without the supporting balls 23 falling out.

(20) Differing therefrom, FIG. 8 shows a race 24 of another design, which, in conforming to the race 17, comprises circle segment-shaped bearing surfaces 12, 20 for balls 11, 21, which each center a spring element. Furthermore, the race 24 includes the axial bearing surface 22.

(21) In differing from the race 17, the race 24 has ball pockets 25, which are radially offset toward the outside with respect to the circumferential surface of the race 24. As a result of this special design of the ball pockets 25, the supporting balls 23 are retained on the spindle 2 by the race 24, such that the ball screw nut 4 can be removed without the balls 23 falling off. The balls 23 are retained, offset toward the inside with respect to their equator, by the ball pockets 25 that are offset toward the outside.

(22) The ball screws 1, 16 are components of an electromechanical brake, wherein the spindle 2 is coupled to an electric drive motor. The rotation of the drive motor is converted to a displacement of the ball screw nut 4, by means of which a piston pushes against a brake pad, resulting in the brake pad being pressed against a brake disk.

LIST OF REFERENCE SYMBOLS

(23) 1 ball screw

(24) 2 spindle

(25) 3 track

(26) 4 ball screw nut

(27) 5 track

(28) 6 race

(29) 7 ball pocket

(30) 8 joint

(31) 9 spring element

(32) 10 end section

(33) 11 ball

(34) 12 bearing surface

(35) 13 section

(36) 14 spring element

(37) 15 end section

(38) 16 ball screw

(39) 17 race

(40) 18 spring element

(41) 19 end section

(42) 20 bearing surface

(43) 21 ball

(44) 22 bearing surface

(45) 23 ball

(46) 24 race

(47) 25 ball pocket