Electric parking brake having a gearing unit

Abstract

A gearing unit of a motor vehicle actuator, in particular an electric parking brake, includes a gearing housing in which a driven first shaft and a driving second shaft having fixed rotational axes are located. A first toothed wheel is mounted on the first shaft and a second toothed wheel is mounted on the second shaft. The first toothed wheel and the second toothed wheel engage with one another through a third toothed wheel. The housing for the third toothed wheel has at least two spatially offset bearing points in order to adjust a transmission ratio between the first shaft and the second shaft. An electric parking brake having a gearing unit is also provided.

Claims

1. An electric parking brake of a motor vehicle, the electric parking brake comprising: a spindle being displaceable in an axial direction of said spindle; a spindle nut rotatably mounted on said spindle; a support device supporting said spindle nut, said support device having limited resilient flexibility, said support device having at least first and second spring elements being disposed in series with one another in a force transmission chain and being configured to be placed under stress during a transmission of force, and said first spring element having a lower stiffness than said second spring element; said first spring element being configured to be placed under stress under action of a first support force over a first spring travel; a first mechanical engagement device preventing a spring travel beyond said first spring travel and an absorption of force by said first spring element over and above said first support force; said second spring element being formed by a spring module having a second spring; a second mechanical engagement device prestressing said second spring with a second support force for placing said second spring under further stress only when said second support force has been exceeded; a travel sensor indirectly or directly detecting a displacement; a gearing unit including a gearing housing, a driven first shaft and a driving second shaft disposed in said gearing housing, said shafts each having a stationary axis of rotation, a first gearwheel attached to said first shaft and a second gearwheel attached to said second shaft, a third gearwheel through which said first gearwheel and said second gearwheel engage one another, said gearing housing having a displaceable bearing point or at least two spatially offset bearing points, between said first shaft and said second shaft, for said third gearwheel; and an electric motor driving said spindle nut through said gearing unit.

2. The electric parking brake according to claim 1, wherein said bearing points are disposed along a straight adjustment line.

3. The electric parking brake according to claim 2, wherein said axes of rotation lie on said straight adjustment line.

4. The electric parking brake according to claim 2, wherein said third gearwheel has an axle journal, and said bearing point includes a movable slide with an opening into which said axle journal can be inserted.

5. The electric parking brake according to claim 1, wherein said first gearwheel is integrally formed on said first shaft.

6. The electric parking brake according to claim 1, wherein said second shaft has a journal for holding said second gearwheel.

7. The electric parking brake according to claim 1, wherein said gearwheels have at least one of mutually parallel toothings or helical toothings.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a diagrammatic, longitudinal-sectional view of an electric parking brake;

(2) FIG. 2 is a perspective view of a gearing unit with a third gearwheel removed;

(3) FIG. 3 is a plan view of the gearing unit; and

(4) FIG. 4 is a plan view of the gearing unit according to FIG. 3 with a changed transmission ratio.

DETAILED DESCRIPTION OF THE INVENTION

(5) Referring now in detail to the figures of the drawings, in which parts corresponding to one another are denoted by the same reference signs, and first, particularly, to FIG. 1 thereof, there is seen a sectional side view of an electric parking brake 2 of a motor vehicle, having a spindle nut 4 which, as a force generating element, interacts with a spindle 6. The spindle nut 4 is mounted so as to be rotatable and is supported on an axial bearing 8. The spindle nut 4 carries, on its outer side, a helically toothed second gearwheel 10 of a gearing unit 12. In other words, the spindle nut 4 forms a second shaft 14 to which the second gearwheel 10 is attached. The second gearwheel 10 has, in the center, an opening 16 which corresponds to the cross section of the spindle nut 4, within which opening the spindle nut 4 in the form of a journal is disposed in a form-locking and rotationally secure manner.

(6) The spindle nut 4 can be driven, through a third gearwheel 18, by a first shaft 20, which is the rotor shaft of an electric motor 22. In this case, the free end of the rotor shaft 20 is provided with cut-out grooves 28 running in spiral fashion along an axis of rotation 26 to form a first gearwheel 24. In other words, the first gearwheel 24 is integral with the first shaft 20, and the outer diameter of the first gearwheel 24 is equal to the diameter of the first shaft 20.

(7) The electric motor 22 is fastened at the end thereof to a gearing housing 30, within which the gearwheels 10, 18, 24 are situated and which projects into a spindle housing 32 in which the spindle nut 4, the spindle 6 and the axial bearing 8 are disposed. The axial bearing 8 is typically in the form of a rolling bearing and is supported on a second spring element 34, which in turn, in the illustrated state, is supported on a first spring element 36 in an axial direction 38. The first spring element 36 is in the form of a helical spring which coaxially surrounds the spindle 6 or its displacement travel during rotation of the spindle nut 4.

(8) Reference sign 40 denotes a sleeve which surrounds and protects the spindle 6 in the region of the spring elements. A Bowden cable receptacle 42 is attached to that end of the spindle 6 which faces toward the sleeve 40. A non-illustrated Bowden cable engages into the Bowden cable receptacle 42 for the actuation of brake pads which act on a brake disk and through the use of which a movement of the motor vehicle is prevented.

(9) If the spindle 6 moves in the direction of the arrow 38, the Bowden cable is pulled, or the tensile force is increased. In this case, a force acts on the spindle 6 and the spindle nut 4 in the direction of an arrow 44. In the event of a movement of the spindle 6 in the direction of the arrow 44, the pulling action is eliminated, and the tensile force is reduced.

(10) During the course of the force generation, the spindle nut 4 is supported on the first spring element 36 and on the second spring element 34. The first spring element 36 is in the form of a spring which is softer, with a lower spring constant, than the spring of the second spring element 34, so that the first spring 36 is compressed first, and to a greater extent than the spring of the second spring element 34. The first spring 36 is supported on a first stop 46 which is formed by using a step of the spindle housing 32.

(11) In the case of a low tensile force being generated, and a corresponding support force being applied by the first spring 36, the latter is compressed to an extent by virtue of the second spring element 34 being moved, undeformed, toward the first spring 36. When the first spring travel has been traveled through, a first end retention element 48 of the second spring element 34 abuts against a stationary second stop 50. At this point in time, a second end retention element 52 of the second spring element 34 also moves in the direction of the arrow 44, without the second spring element 34 being compressed or expanded in the axial direction of the spring.

(12) Correspondingly, the axial bearing 8 moves to an extent, typically in the region of 2 mm, in the direction of the arrow 44, in such a way that the spindle nut 4 also performs this movement. The toothing of the second and third gearwheels 10, 18 permits such a relative movement of the two gearwheels with respect to one another in the axial direction 44.

(13) If, by further rotation of the spindle nut 4, the tensile force is increased, the first spring 36 is not compressed any further because the first end retention element 48, which together with the second mechanical stop 50 forms a first mechanical engagement device, abuts against a fixed stop. The first spring 36 does not absorb any further forces beyond the corresponding partial compression.

(14) With a further increase in the tensile force or the support force, a further movement in the axial direction takes place only when the second spring element 34 is compressed in the axial direction 44 when the level of the second support force is reached.

(15) FIG. 2 shows the gearing unit 12 in a perspective view, wherein the third gearwheel 18 and a cover of the gearing housing 30 have been removed. Both the axis of rotation 26 of the first shaft 20 and an axis of rotation 54 of the second shaft 14 run in parallel through the box-shaped main body of the gearing housing 30, and are both perpendicular to the base thereof and also stationary. A movable slide 56 which is also introduced into the base has an opening 58. The plane of extent of the preferably circular opening 58 in this case is substantially parallel to the plane of extent of the second gearwheel 10 and perpendicular to the axes of rotation 26, 54. The slide 56 is displaceable along a straight adjustment line 60 between the first shaft 20 and the second shaft 14, wherein the central point of the circular opening 58 lies on the straight adjustment line 60. The straight adjustment line 60 is furthermore perpendicular to the axes of rotation 26, 54 and intersects them.

(16) The non-illustrated cover of the gearing housing 30 likewise has such a slide 56, as illustrated in FIG. 3. In this case, the gearing unit 12 is shown in a front view with the third gearwheel 18 installed. The third gearwheel is parallel to the second gearwheel 10. Only the slide 56 of the cover of the gearing housing 30 is shown. The third gearwheel 18 has two axially running axle journals 62 (see FIG. 1), each of which is inserted through the opening 58 of the respective slide 56. Consequently, the third gearwheel 18 is disposed between the two slides 56, which are substantially parallel to the third gearwheel 18. The two slides 56 and the opening 58 thereof, which has a cross section corresponding to that of the respective axle journal 62, thus form a bearing point 64 for the third gearwheel 18. Due to the mobility of the slides 56 along the respective straight adjustment line 60, it is made possible for the bearing point 64 to be moved between the two axes of rotation 26, 54.

(17) In this case, the position of the bearing point 64 and the radius of the gearwheels 10, 24 determine a transmission ratio 66 between the first shaft 20 and the second shaft 14. FIG. 3 shows a first transmission ratio 66 and FIG. 4 shows a further transmission ratio 66. In order to vary the transmission ratio 66, in a first step, the cover of the gearing unit 12 is removed and the third gearwheel 18 is removed. In a further working step, a winged nut 68 fastened to the free end of the spindle 6 is removed. The winged nut 68 prevents the spindle nut 4 from being unscrewed from the spindle 6 during normal operation, as is seen in FIG. 1. In a further working step, the second gearwheel 10 is removed from the gearing unit 12 and is replaced with a new second gearwheel 10. For adjustment purposes, the bearing point 64 is displaced in such a way that the axis of rotation of the third gearwheel 18 is situated centrally between the first gearwheel 24 and the now new second gearwheel 10. This is realized by positioning the two slides 56. In a further step, a new third gearwheel 18 is inserted, and the gearing housing 30 is closed.

(18) The transmission ratio 66 shown in FIG. 3 is such that a rotational movement of the first shaft 24 leads to a relatively slow rotational movement of the second shaft 14. By contrast, in the case of the transmission ratio 66 illustrated in FIG. 4, an identical rotational movement of the first shaft 24 causes an increased rotational speed of the second shaft 14. This is achieved due to the reduced radius of the second gearwheel 10 and the increased radius of the third gearwheel 18. This has the effect that, in the case of the gearing unit 12 shown in FIG. 4, the bearing point 64 has been shifted in the direction of the second shaft 14.

(19) Rather than the transmission ratio 66 being varied after assembly has already taken place this is, for example, already taken into consideration at the initial assembly stage, and a suitable second and third gearwheel 10, 18 are selected. Due to the different transmission ratio 66, the gearing unit 12 shown in FIG. 3 transmits a relatively high force, so that even a vehicle of relatively high weight can be secured by using the electric parking brake 2. In a motor vehicle with a relatively low weight, a gearing unit 12 shown in FIG. 4 is adequate. If use is made of the same electric motor 22 with the same actuation device, the exertion of force by the gearing unit on the Bowden cable is faster, so that the motor vehicle is already secured by using the parking brake 2 at an early point in time.

(20) The invention is not restricted to the exemplary embodiments described above. Rather, a person skilled in the art may also derive other variants of the invention therefrom without departing from the subject matter of the invention. In particular, it is also the case that all individual features described in conjunction with the exemplary embodiments may also be combined with one another in a different way without departing from the subject matter of the invention.