Planetary reducer with at least one axial force transmission component forming a radially eccentric force path

Abstract

The present invention relates to a reducer (1) for an electric parking brake, the reducer (1) comprising a drive shaft (3), at least one reduction stage, and a cylindrical body (14), which, together with an outer planetary gear (2) of the reducer, forms a screw-nut mechanism. The reducer (1) also comprises at least one axial force transmission part (16, 11) located between the bearing ring (20) of the drive shaft (3) and the cylindrical body (14) to transmit an axial force applied via either the bearing ring (20) or the cylindrical body (14) to either the bearing ring (20) or the cylindrical body (14). The axial force transmission part (16, 11) prevents buckling of the drive shaft (3) by defining a radially eccentric axial force transmission path.

Description

[Technical field]

[0001] The present invention relates to a planetary speed reducer, for example for an electric parking brake actuator in an automotive vehicle. [Background technology]

[0002] A conventional floating caliper electric parking brake is disclosed in Patent Document 1 and in FIG. 1 of this specification.

[0003] In a manner known per se, the brake of Fig. 1 comprises a planetary reducer, the external sun gear of which forms a piston 100 translatable along a longitudinal axis A100. An input torque generated by an electric motor is transmitted to said piston 100 via a drive shaft 200, shown separately in Fig. 2, and a planetary gear train connected in series. An output planet carrier 300 of said reducer comprises an external thread, which, in cooperation with an internal thread formed by an internal thread 400 of the piston 100, converts the rotation of the planet carrier 300 into a translation of the piston 100 along the longitudinal axis A100. Such translation allows, by cooperating with a finger 500 of a caliper arranged facing the piston 100, to press the brake pads against the brake disc.

[0004] In this conventional speed reducer, a drive shaft 200 carries a sun gear 600 which meshes with a planet gear 700 of a first gear train. A planet carrier 900 of the first gear train carries a sun gear 950 which meshes with a planet gear 970 of a second gear train. The drive shaft 200 has a downstream portion 800 which passes through openings in the planet carrier 900 and the sun gear 950 and is thus received at one end within a cavity in the output planet carrier 300. This allows the shaft 200 to rotate relative to the planet carriers 300 and 900 and relative to the sun gear 950.

[0005] In this configuration, when mechanical forces are applied to the piston 100 during braking, the forces are picked up by the drive shaft 200. These forces can lead to the shaft 200 buckling. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] French Patent Application Publication No. 3031058 Summary of the Invention [Problem to be solved by the invention]

[0007] One object of the invention is to limit the risk of buckling of the drive shaft of such planetary reducers, in particular to allow a reduction in the diameter of said drive shaft.

[0008] More generally, the invention aims at reducing the mass and cost of such planetary reducers. [Means for solving the problem]

[0009] To this end, one object of the present invention is to a drive shaft rotatably driven about a longitudinal axis by a motor, the drive shaft comprising an internal sun gear having the longitudinal axis as an axis of rotation; With internal teeth that form a female thread Inner teeth A gear is fixed so as to be rotatable about the longitudinal axis. Inner teeth Gears and a gear wheel comprising one or more planet carriers and one or more planet gears carried by said one or more planet carriers; A cylindrical body configured to be rotated around the longitudinal axis by the gear when the drive shaft is rotated around the longitudinal axis, and when the cylindrical body rotates around the longitudinal axis, Inner teeth The gear is driven in translation along the longitudinal axis. Inner teeth a cylindrical body having an external thread cooperating with the internal thread of the gear; It is a planetary reducer equipped with

[0010] According to the present invention, the drive shaft has a shoulder forming a bearing ring radially outside the internal sun gear, and the reducer has at least one axial force transmission part interposed between the bearing ring and the cylindrical body to transmit an axial force acting on one of the support ring and the cylindrical body to the other of the bearing ring and the cylindrical body.

[0011] The at least one transmission part allows recovery of a portion of the axial forces experienced by the reducer in order to relieve the load on the drive shaft, for example during braking if the reducer belongs to a brake actuator.

[0012] The invention thus makes it possible to reduce the diameter of the drive shaft, particularly in the portion adjacent the bearing ring, thereby reducing the mass and cost of said reducer compared to conventional reducers.

[0013] In one embodiment, said at least one axial force transmission part may bear on the one hand against said bearing ring, preferably via a friction washer, and on the other hand against one of the planet carriers of said gear wheels.

[0014] In one embodiment, said at least one axial force transmitting part may include one or more radial openings, each forming a housing for each planet gear of said gear wheels.

[0015] In one embodiment, the at least one axial force transmitting component comprises arms, said arms defining said radial opening therebetween.

[0016] In one embodiment, the gear comprises a first planet carrier and a second planet carrier, the reducer comprises a first axial force transmission part interposed between the bearing ring and the first planet carrier to transmit an axial force applied to one of the bearing ring and the first planet carrier to the other of the bearing ring and the first planet carrier, and the second planet carrier forms a second axial force transmission part interposed between the first planet carrier and the cylindrical body to transmit an axial force applied to one of the first planet carrier and the cylindrical body to the other of the first planet carrier and the cylindrical body.

[0017] In one embodiment, the reducer is configured to rotate about the longitudinal axis. Inner teeth a ring gear integral with the gears, the second planet carrier forming a free cage carrying planet gears that mesh with both the internal teeth of the ring gear and the internal teeth of the cylindrical body, the internal teeth of the ring gear having a number of teeth different from the number of teeth of the internal teeth of the cylindrical body.

[0018] In one embodiment, the second axial force transmission part may bear against the first planet carrier on the one hand, preferably via a friction washer, and against a bearing surface of the cylindrical body on the other hand, preferably via a friction washer.

[0019] Another subject of the invention is an electric brake actuator, comprising a reducer as defined above and an electric motor arranged to drive said drive shaft in rotation about said longitudinal axis.

[0020] Another subject of the invention is a disc brake, preferably a floating caliper brake, such as a parking brake or a service brake, comprising an electric brake actuator as described above.

[0021] Another subject of the invention is a motor vehicle equipped with a disc brake as described above.

[0022] Other advantages and features of the present invention will become apparent from the following detailed non-limiting description.

[0023] The following detailed description refers to the accompanying drawings. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic partial longitudinal sectional view of an electric parking brake equipped with a planetary reduction gear of a known type. [Diagram 2] FIG. 2 is a schematic perspective view of a drive shaft of the brake reducer of FIG. [Diagram 3] FIG. 3 is a schematic partial vertical sectional view of a planetary reducer according to the present invention. [Figure 4] 4 is a schematic perspective view of an axial force transmission portion of the reducer shown in FIG. [Diagram 5] FIG. 5 is a schematic, partially exploded perspective view of the reducer of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Figures 3 and 5 show a planetary reducer 1 according to the invention, which can be used in the automotive sector, for example in electromechanical brakes fitted with disc brakes, in particular disc brakes of the floating caliper type, or more generally in electromechanical actuators for converting rotary motion into translational motion.

[0026] With reference to FIG. 3, the reducer 1 forms a piston that is translationally movable along a longitudinal axis A1. Inner teeth Gear 2 (Hereinafter referred to as "External sun gear 2") The piston 2 is fixed in rotation about said longitudinal axis A1 by any conventional means, for example by inserting a pin belonging to a brake caliper into a corresponding notch made in the piston 2.

[0027] The translational movement of the piston 2 along the longitudinal axis A1 is caused by an electric motor (not shown) which transmits an input torque to the drive shaft 3 of the reducer 1. The rotational motion of this shaft 3 about axis A1 is converted into a translational motion of the piston 2 via gears and motion converters which will be described below.

[0028] More specifically, in this embodiment, the drive shaft 3 is adapted to be connected to an electric motor such that when the shaft of the motor rotates about axis A1, the drive shaft 3 is driven to rotate about axis A1.

[0029] The drive shaft 3 comprises a first internal sun gear 4 which is integral with said shaft 3 for rotation about an axis A1. In this embodiment, the sun gear 4 and the shaft 3 are formed as a single piece.

[0030] The external sun gear 2 is provided with internal teeth 5 which form circumferentially spaced longitudinal grooves for meshing with the planetary gears whilst forming an internal thread adapted to cooperate with the external thread of the motion conversion member (see below).

[0031] The reducer 1 comprises a first planet carrier 6 which includes three openings 7 eccentric to the axis A1 and at 120° to each other. Each of these openings 7 receives a journal 8 carrying a respective planet gear 9 in order to ensure guiding of the rotation of said planet gear 9 (see FIG. 5).

[0032] The planetary gears 9 mesh with both the first internal sun gear 4 and with the longitudinal groove formed by the internal teeth 5 of the external sun gear 2. As a result, therefore, that the rotation of the sun gear 4 of the shaft 3 about its axis A1 drives each planetary gear 9 in rotation about its journal 8, while each post gear 9 drives in rotation along a circumferential path about axis A1 and thus drives the first planet carrier 6 in rotation about axis A1.

[0033] The reducer 1 thus makes it possible to drive the first planetary carrier 6 in rotation about its longitudinal axis A1 at a rotational speed lower than the rotational speed of the drive shaft 3.

[0034] In the embodiment of figures 3 and 5, the reducer 1 comprises a second reduction stage, the input of which consists of a second internal sun gear 10 carried by the first planet carrier 6. This sun gear 10 is integral with the planet carrier 6 so as to be rotatable about axis A1. In this embodiment, the sun gear 10 and the planet carrier 6 are formed as a single part.

[0035] The gearbox 1 of figures 3 and 5 comprises a second planet carrier 11, which forms a free cage carrying the planet gears 12, in this example three. In a known manner, the cage 11 has a substantially tubular shape and includes radial openings which extend in an axially central part, each radial opening being thus axially defined by a respective axial end part of the two lateral sides of the cage. Each of these radial openings forms a housing for one of the planet gears 12. To carry each planet gear 12 and to reliably guide their rotation, a respective shaft is passed axially through each opening. These shafts are received in corresponding holes in the two axial end parts of the cage and are thereby connected to the cage.

[0036] 3, the reducer 1 comprises a ring gear 13 with external and internal teeth. The external teeth engage with the longitudinal groove formed by the internal teeth 5 of the external sun gear 2. The ring gear 13 and the external sun gear 2 are therefore integral with each other so as to be rotatable about the axis A1. The internal teeth of the ring gear 13 are configured to mesh with the planetary gears 12, defining a contact point located radially inward with respect to the internal teeth 5 of the external sun gear 2. That is, the internal teeth of the ring gear 13 are configured to offset the longitudinal groove formed by the internal teeth 5 of the external sun gear 2 radially inward of the reducer 1.

[0037] Said radial offset is necessary in this embodiment because the planetary gears 12 also mesh with teeth formed in a cavity in the motion converter member 14. This cavity has a radial dimension that is smaller than the inner radial dimension of the external sun gear 2 (see FIG. 3 and below).

[0038] In this embodiment, the motion converter 14 is in the form of a cylinder with an external thread 15 which cooperates with an internal thread formed by the internal teeth 5 of the external sun gear 2. As a result of this cooperation, a rotational movement of the cylinder 14 about the axis A1 causes a translational movement of the external sun gear 2 along the axis A1. The cylinder 14 and the piston 2 thus form a reversible screw-nut mechanism.

[0039] The cavity of the cylinder 14 is configured to accommodate a portion of the cage 11 such that the planetary gear 12, via its first axial portion, meshes with teeth formed in this cavity.

[0040] The ring gear 13 is axially adjacent to the cylindrical body 14 so that the planetary gears 12 mesh with the internal teeth of the ring gear 13 via their second axial portions.

[0041] Thanks to this configuration, when the sun gear 10 rotates about the axis A1, each planetary gear 12 is driven in rotation about its own rotation axis while being driven along a circumferential orbit about the axis A1, so that the free cage 11 is driven in rotation about the axis A1.

[0042] If the number of internal teeth of the ring gear 13 were the same as the number of teeth formed in the cavity of the cylinder 14, the rotation of the sun gear 10 about its axis A1 would not drive the cylinder 14 in rotation about its axis A1. In fact, in that case the teeth of the cylinder 14 would be axially aligned with the internal teeth of the ring gear 13, so that the planetary gears 12 would simply roll within the teeth of the cylinder 14 when rotating.

[0043] Thus, in this embodiment, the ring gear 13 has a smaller number of internal teeth than the number of teeth formed in the cavity of the cylindrical body 14, thereby achieving a relatively large reduction ratio.

[0044] The reducer 1 thus makes it possible to drive the cylinder 14 in rotation about its longitudinal axis A1 at a rotational speed lower than the rotational speed of the sun gear 10 and even lower compared to the drive shaft 3.

[0045] Therefore, the reducer 1 reduces the rotational speed by increasing the torque.

[0046] The present invention makes it possible to recover axial forces acting on the reducer 1, for example when the piston 2 exerts a braking force.

[0047] For this purpose, the reducer 1 includes a force transmission part 16 as shown in FIG.

[0048] In this embodiment, the part 16 has a generally tubular shape defining a central opening 19 dimensioned to allow the drive shaft 3 to pass therethrough and to allow relative rotation of the shaft 3 with respect to the part 16.

[0049] In this embodiment, the force transmitting part 16 comprises an annular circumferentially solid first part 17 and a second part comprising three axially extending arms 18. The arms 18 define radial openings between them, each opening forming a housing for a respective planetary gear 9.

[0050] To achieve force recovery, the drive shaft 3 is provided with a shoulder 20 forming a bearing ring radially outside the internal sun gear 4 .

[0051] The part 16 is interposed between said bearing ring formed by a shoulder 20 of the shaft 3 and the planet carrier 6 in order to transmit the axial forces acting on the planet carrier 6 to and from the bearing ring 20 to the planet carrier 6, while at the same time preventing said axial forces from passing through the radially central part of the shaft 3, in particular those parts located on either axial side of the shoulder 20. As a result, the risk of buckling of the drive shaft 3 when using the gear reducer 1 is significantly reduced or eliminated.

[0052] More precisely, said first part 17 of the force transmission part 16 forms a bearing surface 21 which bears against a bearing surface 22 formed by the bearing ring 20 via a friction washer 23. The axial arm 18 of the force transmission part 16 defines a bearing surface 24 which bears against a bearing surface 25 of the planet carrier 6.

[0053] The friction washer 23 makes it possible to limit the wear of the bearing ring 20 and the force transmitting part 16 when they rotate relative to one another.

[0054] Furthermore, the two axial end portions of the free cage 11 each form a bearing surface 26, one of which bears, via a friction washer 28, against a bearing surface 27 of the planet carrier 6 and the other of which bears, via a friction washer 29, against a bearing surface formed by the bottom of the cavity in the cylinder 14.

[0055] The free cage 11 thus interposed between the planet carrier 6 and the cylindrical body 14 forms a second axial force transmission part, by means of which the axial forces acting on the cylindrical body 14 can be transmitted to the planet carrier 6 or, conversely, the axial forces acting on the planet carrier 6 can be transmitted to the cylindrical body 14.

[0056] The friction washers 28 and 29 make it possible to limit wear of the planet carrier 6, the free cage 11 and the member 14 as they rotate relative to one another.

[0057] 3 thus makes it possible to transmit an axial force acting on the cylinder 14, for example when the piston 2 is subjected to a braking force, to the bearing ring 20 via the two axial force transmission parts 11 and 16 interposed between the bearing ring 20 and the cylinder 14, while at the same time preventing the path of this axial force from passing through a portion of the longitudinal axis A1 and thus of the drive shaft 3, which has a relatively small diameter compared to the diameter of its shoulder 20. The function of transmitting forces via this eccentric path is also ensured in the other direction, i.e. when an axial force acts on the bearing ring 20. The two axial force transmission parts 11 and 16 then enable the axial force acting on the bearing ring 20 to be transmitted to the cylinder 14.

[0058] The above description is given by way of example and is in no way limiting. For example, in an embodiment not shown here, the reducer 1 may comprise a single reduction stage. In this case, the planetary carrier 6 does not comprise the second internal sun gear 10 but is directly connected to the cylinder 14, so that the cylinder 14 and the planetary carrier 6 are integral with each other so as to be rotatable about the axis A1. Of course, in such a single-stage reduction embodiment, the reducer 1 does not comprise the free cage 11, the planetary gear 12 and the friction washers 28 and 29.

[0059] In other embodiments not shown here, the reducer 1 comprises a second reduction stage different from the one presented by way of example in Fig. 3. For example, the planetary gear 12 is not carried by the free cage 11 but directly by the member 14. In order to ensure recovery of the axial forces between the planet carrier 6 and this member 14, in this case the reducer 1 may comprise an additional axial force transmission part similar to part 16, which is interposed between the planet carrier 6 and the member 14. [Explanation of symbols]

[0060] A100 Longitudinal axis 100 External sun gear / piston 200 Drive shaft 300 Output Planet Carrier 400 Internal teeth of external sun gear 500 Caliper Finger 600 Sun Gear 700 Planetary Gear 800 Downstream part of drive shaft 900 Planet carrier of the first gear train A1 Longitudinal axis 1 Planetary reducer 2 External sun gear / piston 3 Drive shaft 4 First internal sun gear 5 Internal teeth of external sun gear 6 First Planet Carrier 7 Opening for the journal of the first planet carrier 8 Journal of the first planet carrier 9 Planet gear of first planet carrier 10 Second internal sun gear 11 Second planet carrier / free cage / second axial force transmission part 12 Planet gear of second planet carrier 13 Ring Gear 14 Cylinder / Motion conversion member / Screw 15 Cylindrical external thread 16 (First) Axial Force Transmission Part 17 First part of axial force transmission component / solid part 18 Second part / arm of axial force transmission part 19 Central opening of axial force transmission part 20 Drive shaft shoulder / bearing ring 21 Bearing surface of axial force transmission component 22 Bearing surface of bearing ring 23 Friction washer 24 Bearing surface of axial force transmission parts 25 First planet carrier bearing surface 26 Bearing surface of second planet carrier 27 First planet carrier bearing surface 28 Friction washer 29 Friction washer

Claims

1. a drive shaft (3) configured to be driven in rotation about a longitudinal axis (A1) by a motor, the drive shaft (3) comprising an internal sun gear (4) configured to rotate about said longitudinal axis (A1); An internal gear (2) having internal teeth (5) forming a female thread, the internal gear (2) being unable to rotate about the longitudinal axis (A1); a gearbox comprising one or more planet carriers (6, 11) and one or more planet gears (9, 12) carried by said one or more planet carriers (6, 11); a cylindrical body (14) configured such that when the drive shaft (3) is rotated about the longitudinal axis (A1), the gear rotates the cylindrical body (14) about the longitudinal axis (A1), the cylindrical body (14) having a male thread (15) cooperating with the female thread of the internal gear (2) such that when the cylindrical body (14) rotates about the longitudinal axis (A1), the internal gear (2) is driven in translation along the longitudinal axis (A1); A reducer (1) comprising: The drive shaft (3) has a shoulder (20) forming a bearing ring radially outside the internal sun gear (4), and the reducer (1) has at least one axial force transmission part (16) interposed between the bearing ring (20) and the cylindrical body (14) to transmit an axial force acting on one of the bearing ring (20) and the cylindrical body (14) to the other of the bearing ring (20) and the cylindrical body (14).

2. 2. The reducer (1) according to claim 1, wherein the at least one axial force transmission part (16) on the one hand bears against the bearing ring (20).

3. 3. The reducer (1) according to claim 2, wherein the at least one axial force transmission part (16) bears on the one hand against the bearing ring (20) via a friction washer (23) and on the other hand against one of the planet carriers (6) of the gear wheels.

4. The reducer (1) according to any one of claims 1 to 3, wherein the at least one axial force transmission part (16) comprises one or more radial openings, each of said radial openings forming a housing for each planetary gear (9) of said gear wheels.

5. 5. The reducer (1) according to claim 4, wherein the at least one axial force transmitting part (16) comprises arms (18), said arms (18) defining said radial opening therebetween.

6. 6. The speed reducer (1) according to any one of claims 1 to 5, wherein the gears comprise a first planetary carrier (6) and a second planetary carrier (11), the speed reducer (1) comprises a first axial force transmission part (16) interposed between the bearing ring (20) and the first planetary carrier (6) in order to transmit axial forces acting on one of the bearing ring (20) and the first planetary carrier (6) to the other of the bearing ring (20) and the first planetary carrier (6), and the second planetary carrier (11) forms a second axial force transmission part interposed between the first planetary carrier (6) and the cylindrical body (14) in order to transmit axial forces acting on one of the first planetary carrier (6) and the cylindrical body (14) to the other of the first planetary carrier (6) and the cylindrical body (14).

7. 7. The speed reducer (1) according to claim 6, further comprising a ring gear (13) integral with the internal gear (2) so as to be rotatable about the longitudinal axis (A1), the second planet carrier (11) forming a free cage carrying planet gears (12) meshing with both the internal teeth of the ring gear (13) and with the internal teeth of the cylindrical body (14), the internal teeth of the ring gear (13) having a number of teeth different from the number of teeth of the internal teeth of the cylindrical body (14).

8. 8. The reducer (1) according to claim 6 or 7, wherein the second axial force transmission part (11) bears on the one hand against the first planet carrier (6) and on the other hand against a bearing surface of the cylindrical body (14).

9. 9. The reducer (1) according to claim 8, wherein the second axial force transmission part (11) bears against the first planet carrier (6) via a friction washer (28).

10. 10. The reducer (1) according to claim 8 or 9, wherein the second axial force transmission part (11) bears against a bearing surface of the cylindrical body (14) via a friction washer (29).

11. An electric brake actuator comprising: a reducer (1) according to any one of claims 1 to 10; and an electric motor configured to rotate the drive shaft (3) about the longitudinal axis (A1).

12. A disc brake comprising the electric brake actuator according to claim 11.

13. The disc brake of claim 12, wherein the disc brake is a floating caliper brake.

14. A motor vehicle comprising a disc brake according to claim 12.

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