FR3031154A1 - DIFFERENTIALLY REDUCING BRAKE ACTUATOR, BRAKE OR BRAKE CALIPER INCLUDING SUCH ACTUATOR, AND METHOD FOR LOOSENING SUCH BRAKE - Google Patents

Abstract

The invention proposes a linear actuator for activating a vehicle brake, in particular for a disc brake caliper. This actuator comprises a brake piston is moved in translation by a screw-nut mechanism driven by a gearbox from an electric motor. This actuator comprises an upstream reduction stage formed by an upstream epicyclic gear train (PR1) fixed ring (R1, 121), driven at its input by its sun gear (S1). The upstream planet carrier (PC1) carries the input sun gear (S2) of a double-ring differential epicyclic reduction gear (DPR). This comprises an epicyclic gear train (PR2) driven in input by its sun gear (S2), and whose satellites (P2, 141) meshing with the fixed ring (R2, 121). From this fixed ring gear, by a common PC2 planet carrier, the satellites (P3, 141) of the differential gearbox (DPR) drive a mobile ring gear (R3, 151). Its teeth are surrounded by a thread (152) cooperating with an internal thread (161) of the piston (16) to drive it in translation. Preferably, the fixed ring gear (121) is common to the two epicyclic gear trains (PR1, PR2) and the differential satellites (141) are common to the two rings (121, 151).

Description

- 1 - "Differential reduction brake actuator, brake or brake caliper including such an actuator, and method of loosening such a brake" The invention relates to a linear actuator for activating a vehicle brake, in particular for a brake caliper disc. This actuator comprises a brake piston is moved in translation by a screw-nut mechanism driven by a gearbox from an electric motor. This actuator comprises an upstream reduction stage formed by an upstream planetary gear train fixed ring gear driven at its input by its sun gear. The upstream planet carrier carries the input sun gear of a double ring differential epicyclic reduction gear. This comprises an epicyclic train driven in input by its sun gear, and whose satellites meshing with the fixed crown. From this fixed ring gear, by a common PC2 planet carrier, the satellites of the differential gearbox drive a mobile ring gear. Its teeth are surrounded by a thread cooperating with an internal thread of the piston to drive it in translation. Preferably, the fixed ring gear is common to both epicyclic gear trains and the differential satellites are common to both rings. The invention also relates to a brake including such an actuator, in particular a disk brake caliper, as well as a control method and a vehicle using such a brake or actuator.

BACKGROUND OF THE INVENTION The field of the invention is that of road vehicle brakes, in particular light and utility motor vehicles, and in particular four-wheel vehicles.

In such a vehicle, the service brake function consists mainly in slowing down the vehicle and stopping it. In most modern automobiles, the service brake is provided by drum brakes or disc brakes, or disc brakes at the front of the vehicle and rear drum vehicles. 3031154 - 2 - The parking brake function is to keep a vehicle immobilized continuously for long periods of time. The emergency brake function consists in slowing down a moving vehicle in an exceptional manner, for example in the event of failure of the service brake control circuit. Very often, this operation is performed by the same mechanism as the parking brake, and usually only on the rear brakes. For a long time, the brakes have generally been operated by hydraulic pressure for the service brakes, and for parking brakes by pulling a cable in general using a ratchet lever. Over the past ten years, it has become commonplace to provide an automated parking brake management system by a computer that controls an electric actuator. The electric actuator 15 is often located outside the brake itself, and operates for example by exerting traction on a cable instead of the manual control. Such external management has various disadvantages, for example complexity and cost of manufacture and maintenance. At the same time, it is also sought to achieve purely electric brakes, that is to say including the service brake function. Thus, it is interesting to realize a brake whose electric actuator or actuators are fully included in the basic mechanism of the brake or "brake base", "foundation brake" in English, ie the part that is directly located on or around the wheel. Whether it is disc brakes or drum brakes, kinematics of these mechanisms uses a rather small displacement but requires a rather large tightening force. For this reason, the electric motors are often chosen at high speed, which allows to limit their size and weight for a given power, but requires to provide a very large gear. For drum brakes, for example, document FR 13 63706 (not yet published) thus proposes an electric actuator separate from the hydraulic cylinder. This electric actuator applies a linear force 3031154 - 3 - by a screw-nut mechanism driven by a transmission of three outer gears, itself driven by a geared motor with two planetary gear trains in series. For disc brakes, for example, the document US Pat. No. 4,804,073 proposes a brake caliper whose housing 90 receives an electric actuator comprising a screw-nut mechanism located inside the hydraulic piston, driven coaxially by an epicyclic reduction gear. differential double crown, itself driven by a motor. As illustrated herein in FIGURE 1, with reference to FIG. 1 of this document, the 9M motor drives a 9S planetary gear which meshes with the 9P satellites of a 9PC planet carrier disposed within a fixed ring gear. 9R1, thus causing a rotation of this planet carrier 9PC according to a first reduction. The 9P satellites also mesh with a movable ring 9R2, which is thus driven in a second reduction. This movable ring is coupled in rotation with the head of a screw 9SC which penetrates inside the hydraulic chamber, and cooperates with a nut 9NU held fixed in rotation. When it is displaced in translation by the rotation of the screw, this nut 9NU presses on the piston 9PL, which thus exerts its clamping force on the rear plate 17 of a friction lining. In Fig.1, this document proposes to drive the gearbox directly by a 9M electric motor. However, the reduction of the order of 1/115 provided by such a gearbox may be insufficient, in particular to provide large forces, and / or imposes a motor size which becomes troublesome in terms of size. For this purpose, for example in FIG. 9 of the same document, it has been proposed to make a geared motor assembly comprising an additional stage of external gears, the motor of which is mounted on the piston side with a shaft coming out from the side opposite to that of the piston.

Independently of this document, as illustrated herein in FIGURE 2 with a 9AMU 9AM motor shaft assembly, such a configuration still has space constraints, and potentially a higher weight. An object of the invention is to overcome the disadvantages of the state of the art, and in particular to provide an electric actuator producing a better compromise between a large reduction and a low weight and bulk, for all types of brake and in particular for disc brakes, only electric or mixed hydraulic. This goal is sought in conjunction with advantages in terms of simplicity, cost and reliability, manufacturing and maintenance. DESCRIPTION OF THE INVENTION The invention proposes a linear actuator for activating a vehicle brake, in particular a road and / or automobile brake, in particular for a disc brake caliper. This actuator is of the type comprising a brake piston which is displaced in translation by a mechanism comprising a screw-nut mechanism transforming a rotary drive in linear displacement, which is driven by a reduction mechanism (also called a reduction mechanism) from an electric motor. According to the invention, this actuator comprises an upstream reduction stage formed by an upstream epicyclic train driven by the electric motor. This upstream reduction stage drives a double ring differential epicyclic gear 20. The movable ring of this differential epicyclic reduction gear is surrounded by a thread which it rotates. This thread surrounds the toothing of the movable ring, and cooperates with an internal thread of the piston to drive it in translation. A more precise description is the following. The upstream reduction stage, which drives the differential gearbox, is formed by an upstream epicyclic gear train comprising at its output an upstream planet carrier integral in rotation with the planetary input gear of said differential gear unit, one-piece with it or preferably fitted. in on the inside. This upstream planet carrier carries a group of upstream satellites 30 which: meshes with a so-called upstream fixed ring, integral with the actuator or stirrup housing, possibly fixed to or one-piece with it, and 3031154 -5 -0 are driven at the input by meshing with an upstream planetary gear, thus producing a so-called upstream reduction. The differential epicyclic reduction gear comprises a differential carrier carrying: a group of so-called input satellites, which are input-engaged by meshing with the input differential planetary gear, and which meshing with a differential fixed ring, thus driving said differential carrier with a first reduction operating on the same principle as the upstream reduction, and 10 o a group of output satellites, integral in rotation with the input satellites, and which meshing with a differential mobile ring, which is thus rotated to provide a second reduction which may be called "harmonic". This second reduction is determined in particular by the ratio between the radius times the number of teeth of the moving ring and the radius times the number of teeth of the fixed ring. - The screw-nut mechanism is rotated by the ring gear of said differential gear, so as to move the piston in translation along the axis of said differential epicyclic gear train, in the clamping direction, and optionally in both directions. - The screw of the screw-nut mechanism is formed in a part surrounding the toothing of said movable ring and secured to said movable ring. This screw cooperates with a fixed rotating nut which is formed inside a piece integral in translation of the piston.

As is understood, the invention combines a choice of reduction stages providing a substantial overall reduction, with a radially and axially imbricated geometrical arrangement which allows for high compactness. In particular, even if the overall reduction rate could be obtained by a simple basic accumulation of known reduction stages, the combination according to the invention has a particular nesting of the different stages between them, which makes it possible to obtain a better compromise. between compactness, weight, reduction rate and transmitted load capacity. This performance gain is all the more useful because the elements of the braking base are part of a non-suspended subassembly and whose displacement vis-à-vis the vehicle chassis increases. impact in space. These performances are obtained for many types of brakes, including types or even already marketed brake models, in particular hydraulic or mixed hydraulic / electric. They are therefore easier to obtain with good reliability and at the cost of less effort and adaptation costs, design or even assembly or even aftermarket. Although presented here in the context of a disk brake, the invention also applies to other types of brake using a linear actuator, for example a drum brake to press one or more ends of segments, in service brake and / or parking brake. The invention preferably has the following features, which may or may not be combined with one another according to the needs and constraints which govern the sizing of the actuator and / or the brake. Preferably, the fixed ring gear of the upstream epicyclic gear is one-piece with the fixed ring gear of the differential gearbox, or even with common teeth and continuous and constant diameter. For example, a greater compactness and simplicity of implementation is obtained.

According to other variants, the fixed ring gear of the upstream planetary gear train and the fixed ring gear of the differential gearbox have different diameters and / or different numbers of teeth, while possibly being formed by the same piece. This gives more flexibility and freedom in determining the reduction and load parameters of the actuator. In a preferred embodiment, the differential carrier carries a single group of so-called differential, preferably one-piece, satellites. each have a uniform and continuous toothing and constant diameter on two successive longitudinal portions so as to form both an input satellite and an output satellite. This preferred embodiment allows for example a greater compactness and simplicity of implementation. In other embodiments, the differential satellites have two different diameters on their two parts meshing with the two rings, or different numbers of teeth, or both at the same time. This gives more flexibility and freedom in determining the reduction and load parameters of the actuator. In this same preferred embodiment, the thread of the screw and the toothing of the movable ring are formed in the same piece. Preferably, the thread of the nut is formed in a bore formed inside the piston. Thus, in the preferred embodiment, it is the movable ring itself that forms the screw, which is surrounded by the piston itself forming a nut. Preferably, the actuator has dimensions determined so that the useful thread of the screw surrounds all or part of the toothing of the fixed ring, which allows for example simplicity of manufacture and compactness. Other variants are however provided, which allow more freedom in the dimensioning of the actuator, and for example a flexibility of integration into the stirrup by the choice of its external dimensions such as its elongation or its diameter or the relationship between them.

In another aspect, the invention provides a brake including or incorporating an actuator as set forth herein. In particular, the invention provides a disc brake caliper comprising a housing having at least one housing receiving such an actuator, which is arranged and arranged so that the movement of its piston 25 comes to press at least one friction lining within a support chain comprising a brake disc sandwiched between at least two friction linings in said stirrup. According to one feature, the housing of this stirrup forms a hydraulic chamber receiving the piston in a sealed manner and which is arranged to allow to apply a hydraulic pressure displacing the piston in the direction of tightening. Optionally, the teeth of the actuator are arranged to allow displacement in translation, along the axis of the gear, between the screw and the fixed ring. This clearance is obtained for example by a set of teeth 3031154 - 8 - straight or low angle, conjugated with a sufficient length of the teeth and a play in translation formed in the axial stop of the upstream input shaft. This configuration thus makes it possible: on the one hand to allow the piston to move in the direction of clamping by hydraulic actuation without electrical actuation (or a less extensive and / or time-shifted actuation), and on the other hand to produce a movement of said piston in the direction of loosening by electrical actuation (or "declamping"). It thus becomes possible to reduce the risk of residual clamping outside the braking periods, which for example reduces the consumption of the vehicle as well as the parasitic noise and the wear of the friction elements. Alternatively, the stirrup is also provided with an electric actuation only, performed by one or more actuators as discussed herein. According to another feature of the stirrup according to the invention, the upstream input shaft of the actuator is driven by an electric motor or geared motor fixed on the stirrup housing coaxially with said upstream input shaft.

Such an arrangement makes it possible to limit the lateral space requirement, for example compared to the configurations of the prior art with side motor. According to another feature, the upstream input shaft of the actuator is driven by an electric motor without intermediate reduction, for example by a DC motor or a brushless motor or a variable reluctance motor or a motor with AC controlled. The characteristics of high compactness and high reduction rates are advantageously combined with the direct mounting of a single motor to thus allow a small overall size and weight including for significant needs in terms of clamping force. According to yet another aspect, the invention proposes a method of actuating a parking brake of a brake as described herein, or a brake comprising an actuator as described herein, and which comprises a 3031154 - 9 - Drive control of the actuator by an electric motor in one direction for tightening and in the other direction for the release of said parking brake. According to a feature, such a method comprises a control 5 for driving the actuator by an electric motor in the loosening direction over a sufficient stroke to reduce by a predetermined value a clamping force applied by hydraulic actuation, o when detecting an interruption of hydraulic actuation of the service brake (for example at the end of a braking period 10 controlled by the driver), thus allowing a limitation of the residual braking, or o during a selection of a release control of the service brake by an automatic control system of the brake system, for example in the context of an anti-lock brake function ("ABS") or assisted or automated trajectory control (for example Such a control is applicable in particular for an embodiment of the brake in which the actuator has at the beginning of the stroke a clearance in translation sufficient to allow hydraulic clamping. without requiring electrical actuation. When tightened by the electric actuator, the actuation then begins, for example, by making up for this clearance. When the parking lot is loosened electrically, the loosening operation is then continued long enough to recreate this clearance.

According to another aspect of the invention, there is provided a vehicle or subassembly of a vehicle comprising an actuator or brake or brake caliper as disclosed herein, or implementing a control method such as exposed here.

Various embodiments of the invention are provided, incorporating, according to all of their possible combinations, the various optional features set forth herein. Other features and advantages of the invention will become apparent from the detailed description of an embodiment which is in no way limitative, and the attached drawings in which FIG. 1 is a longitudinal sectional view. an electric actuator on a floating mounting brake caliper according to the prior art; FIGURE 2 is a perspective view illustrating another example of an "on-side" geared motor electric actuator on a floating mount brake caliper 10 according to the prior art; FIGURE 3 and FIGURE 4 are kinematic diagrams that generically illustrate the operation of an exemplary embodiment of the actuator according to the invention; FIGURE 5 is a kinematic diagram which more accurately illustrates an example of the preferred embodiment of the invention; FIGURE 6 is an exploded perspective view illustrating an exemplary actuator according to the preferred embodiment of the invention; FIGURE 7, FIGURE 8, FIGURE 9 and FIGURE 10 are scale perspective views showing certain elements of the actuator of FIGURE 6; FIGURE 11 is a longitudinal sectional view of the actuator of FIGURE 6 in a floating mounting bracket, here with an end motor 130A mounted directly at the end; FIGURE 12 is a more detailed view of the mechanism of the actuator of FIGURE 11; FIGURE 13 is a perspective view at the scale of a longitudinal section of the mechanism of the actuator of FIGURE 11; FIG. 14 is a simplified half-view in longitudinal section of the mechanism of an actuator according to the invention in a variant with a mobile ring of a diameter different from that of the fixed ring; FIGURE 15 is a simplified half-view in longitudinal section of the mechanism of an actuator according to the invention in a variant with the thread of the screw not covering the fixed ring; FIGURE 16 and FIGURE 17 are scale perspective views illustrating a floating mounting bracket with an actuator according to the invention, with a brushless motor and respectively with a DC motor.

Description of an Exemplary Embodiment FIGURE 3 and FIGURE 4 illustrate in strictly kinematic fashion the operation of an exemplary embodiment of the actuator according to the invention, without showing the relative positions of the different parts. In these figures is illustrated a wide version of the arrangement according to the invention. For example, the input P2 and output P3 differential satellites are shown therein as integral pinions in rotation with each other but with possibly different teeth and / or diameters, as is explicitly provided for certain embodiments which will not be detailed further. In FIGURE 4, the curved arrows symbolize by way of illustration a form of representation of the "path" of the mechanical drive action throughout its "passage" through the kinematic stages.

For each stage, the two beginnings of the arrow each represent one of the inputs or kinematic references of the drive, while its end expresses the member through which this drive is transmitted to the next stage. PREFERRED EMBODIMENT FIGURE 5 schematically illustrates an example of the preferred embodiment of the invention, and includes certain room position characteristics. In particular, it is shown that the screw SC is formed by an external thread 152 which surrounds the toothing 151 of the movable ring R3. In this example, this thread 152 also surrounds the toothing 121 of the part 12 forming the two fixed rings R2 and R3. FIGURE 6 and FIGURES 7 to FIGURE 10 show the main parts of a real example of implementation of the preferred embodiment. FIGURE 11 to FIGURE 13 represent this same real example once assembled. This example of an actuator is here represented in FIG. 11 in the context of a floating mounting bracket, but could quite well be used in other types of caliper with little or no configuration modifications, even of dimensions.

In this example, the linear actuator is configured for a disc brake caliper 1. It comprises, comprising coaxially between them: an upstream epicyclic gear train PR1, comprising an upstream planet carrier PC1, 130 carrying upstream satellites P1, 131 which are driven by an upstream input planetary pinion 51, 111 and meshing with the toothing 10 121 of a fixed ring 12, thereby driving said upstream planet carrier with an upstream reduction; a differential double-ring DPR gear reducer, coaxial with the upstream planetary gear train PR1, comprising a so-called differential carrier 140, PC2 carrying a group of so-called differential satellites, each carrying a single toothing, which differential satellites: On the one hand, they are input-driven by an input sun gear 139, S2 integral in rotation with the upstream satellite carrier 30, PC1 and cooperate by meshing with the same continuous and unchanged gearing 121 of the fixed ring 12 as said epicyclic gear. DPR1 upstream to drive the differential carrier 140, PC2 according to a first reduction PR2 in a first direction of rotation, compactness gain and o other meshes with a mobile ring 152, R3 preferably of the same diameter and a number of teeth different from the fixed ring 121 that they thus rotate in a second reduction DR called "harmonic" in a sen s rotation opposite that of the differential carrier 140, PC2; and an external thread 152 carried by the outside of the movable ring 30 and cooperating with an internal thread 161 carried by the inside of the piston 16 or a cylinder integral with said piston, to form a screw-nut mechanism which moves said piston in translation in a direction depending on the direction of rotation of the upstream input planetary pinion 51, 111. In this example, the upstream planet carrier PC1, 130 is mounted on and guided in rotation by a drive shaft. guide 110 forming an axial extension of an input shaft 11, carrying the input sun gear 51, 111 of the upstream stage PR1. This input shaft 11 is here one-piece with the input pinion 111, which is for example a simplification factor. Alternatively, however, it is expected that it forms a different part. Preferably, but not obligatory, the differential satellites 141 of the differential gearbox DPR are here rotatably mounted in longitudinal windows 149 formed in an annular cage 140 surrounding the input pinion 139 of the differential gearbox DPR. In the same way, these differential satellites 141 are in a number determined to ensure a rotation guidance of the differential carrier PC2 without cooperation of said cage 140 with other parts than said differential satellites 141.

These characteristics contribute in particular to the compactness and the lightness of the whole. In the present example, the common fixed ring R1-R2 is formed by a cylinder forming a skirt 120 bearing the toothing 121 on its inner face, and having at its upstream end a flange extending radially outwards. This fixed ring 12 is fixed inside the cylindrical housing 100 of the caliper housing 10, on its end wall, which is traversed by the end 119 of the input shaft 11. The motor 19 is fixed on the other side of this same wall, and its drive shaft (not shown) is coupled coaxially in rotation with the inlet end 119 of the input shaft 11, here by complementary fitting in a form of maneuver . The upstream planet carrier 130 is traversed and guided in rotation by an internal bore mounted on a bearing surface of the guide shaft 110. The differential input planetary pinion 139 is formed by a cylinder whose inner bore is mounted integrally. in rotation on an outer surface of the upstream planet carrier 130, for example mounted tightly or on keys or splines. The movable ring is formed by an internal toothing carried by the interior of a movable cylinder 15, whose outer surface carries the thread 152 of the screw SC. The latter, on the side of the upstream planetary gear train PR1, has a smooth bore which is guided in rotation on a guide ring 191, for example made of PTFE, which is itself mounted free to rotate on a cylindrical outer bearing surface of the crown. 12. At this same end, the movable cylinder 15 is stopped in translation by a washer 192, for example made of PTFE, on which it bears to resist the support force transmitted to the internal thread 161 carried by the The piston 16, at its end opposite the engine, has a bearing face 164 which transmits its thrust 10 to the friction lining 17. In the stirrup 1, the latter is free in translation along the axis A16 of the piston and maintained in rotation about this same axis. It presents form accidents such as pins (not shown) which fit into the notches 163 carried by the bearing face of the piston, which it thus immobilizes in rotation during the rotation of the screw 152. In the example presented here, the piston carries a peripheral groove 163 hosting a circular seal protecting the intrusion mechanism. In other variants not shown here, the piston further carries a hydraulic pressure seal which cooperates with the walls 20 of the housing 100, which forms a sealed hydraulic chamber communicating with a hydraulic pressure control circuit by means of a hydraulic pressure seal. fluid inlet, in known manner. As shown in FIGURE 12, the actuator includes translational stop means which moves the piston in the loosening direction (here to the left) when the applied direction of rotation drives the screw in the opposite direction of the clamping. This characteristic makes it possible to control an active brake release movement, or "declamping". In the half-view located above the axis, these means are located so as to prevent any significant play in translation, between the screw-crown 15 and the parts 12 fixed to the stirrup housing 10, for example by a circlips 195 bearing a thrust flange 194. This configuration limits games and optimize the useful length of the toothing 151 of the ring gear. It is for example well suited to the case of a stirrup only electrically operated, or a mixed stirrup in which the electric actuator is used only for the parking brake where it ensures loosening correct even after a long immobilization. According to a variant illustrated by the other half-view of FIGURE 12 located below the axis, the teeth of the actuator are arranged to allow displacement in translation (along the axis of the gear) between the screw 15 , SC and the fixed ring 12, NU, for example with straight or low angle toothings, a sufficient length of the teeth and a play in translation between the movable crown screw 15 and the fixed parts 12. This configuration thus allows on the one hand, to allow the piston 16 to move in the direction of clamping by hydraulic actuation without electrical actuation (or a less extensive and / or time-shifted actuation), and on the other hand to produce a displacement of said piston in the direction of loosening by electric actuation 19, or "declamping". The positive loosening displacement obtained by the electric actuator requires only a small stroke, and will be, for example, caught immediately afterwards by an identical displacement in the opposite direction, making it possible to restore the clearance required for the hydraulic actuation while remaining limited for do not trigger a new tightening by itself. In the other half-view of FIGURE 12 located below the axis, this configuration is carried out as an example by a configuration of the guide shaft 110 bearing an axial stop 195 'located further to the right. to leave an axial clearance allowing a stroke D15, which is reflected in the displacement of the toothing 151 relative to the differential satellites 141. Sizing example It will now be presented a numerical example of overall reduction ratio provided by the actuator according to the invention.

This numerical example is valid for most embodiments of the invention, with the advantages of compactness (among others) that it provides. It is here developed more particularly in the case of the preferred embodiment, as illustrated with reference to FIG. 3 to FIG. 13. 3031154 - 16 - Kinematics of the upstream epicyclic gear train - PR1 The upstream epicyclic stage PR1 provides a determined upstream reduction by the following elements: - input by the upstream planetary gear S1 (111); 5 - reference by the upstream fixed crown R1 (121); - output by the upstream satellite carrier PC1 (130). In this conventional epicyclic gear train, with the symbol Z for the numbers of teeth and the symbol S2 for the rotation speeds, we obtain: 10 n if X if for the speed of rotation of the carrier PC1 Z 7 S1 Z P1 differential PC1 (130), which carries the upstream satellites P1 (131). Differential gearbox kinetics - DPR: epicyclic stage PR2 The epicyclic stage PR2 of the differential gearing DPR provides a first reduction determined by the following elements: - input by the sun gear S2 (139) integral in rotation with the upstream satellite carrier PC1 ( 130); reference by the second fixed ring R2 (121), merged in this example with the upstream fixed ring R1; - output by the differential carrier PC2 (140).

In this conventional epicyclic gear train, with the symbol Z for the numbers of teeth and the symbol S2 for the speeds of rotation, we obtain: Zs2 X for the speed of rotation of the planet carrier pc S2 ç) S2 2 Zs2 Zp2 differential PC2 ZRX S2 25 f - 42 _ 2 PC2 for the speed of rotation of the input satellites P2, Z p2 here confused with the differential satellites 141. Differential gearbox kinetics - DPR: differential stage DR The differential stage DR of the differential gearbox DPR provides a second reduction determined by the following elements: first input (in one direction of rotation) by the differential carrier PC2 (140); - second input (in the opposite direction of rotation) by P2 differential satellites (141); - Output by the mobile ring R3 (151) (in the direction of rotation of the planet carrier PC2).

In this differential stage DR: the output rotation S2R3 is derived from the rotation S2pc2 of the satellite carrier PC2 (140) and the rotation S2p3 of the output satellites P3, here merged with the differential satellites 141. - No part is fixed in this differential stage DR. The rotations ç2pc2 and S2p3 are imposed by the epicyclic stage PR2. - The rotations ç2pc2 and S2p3 are related by the Willis formula, which gives the differential velocity equation for a classical epicyclic train: S2planetary2 = Osatcarrier -S2sat * Zsat Zplanetary2 where Zplanetary2 is the ratio of numbers of leading / conducting teeth.

For such an epicyclic train, one obtains: S2planetary2 = O (1 * 1, ie Zplanetary2) S2planetary2 = S2entrance * Zentreate * (1 Zplanetaryl Zentrée + Zplanetaryl v Zplanetary2) - Considering this differential stage DR according to the principle of such an epicyclic gear train with: the movable ring R3 (151) considered to be the planetary element 2, and the fixed ring gear R2 (121) as the p / anetary element; we obtain: 1-) R3 1 .-. 2 PC2 (1-2S2 * Z S2 * (ZR2 ZR2 that is S2R3 \ 1- ZR3) = ZR3) Z82 ZR2 (ZR2 ZR3) to respond to In this relation the ratio of the stresses in the configuration of the mechanism used here is chosen in terms of the difference between the numbers of teeth between the fixed ring R2 and the ring gear R3 (151), in particular to obtain an integer number of teeth for each crown. In the particular case of the example illustrated here, these two rings E2 and E3 mesh with the same group of satellites which has the same 5 teeth for each of the two rings. These two crowns therefore have the same diameter here. To obtain a reduction, it is therefore necessary that the fixed ring R2 (121) has a number of teeth ZR2 less than the number of teeth ZR3 of the mobile ring R3 (151). This difference is realized by using two different toothing modules between these two rings, and for the satellites 141 a module that is compatible with these two different modules. Compared to a reduction gear with two conventional planetary gear trains connected in series, this differential gearbox DPR has various advantages, and for example: 15 - fewer parts (a single carrier and a single set of satellites) - less inertia for the same transmission ratio (ie reduction rate); a smaller footprint for the same transmission ratio and the same transmitted torque; Compared to a gear unit with a single epicyclic gear as used in the geared motor illustrated in FIG. 2, this differential gear unit DPR can be produced with the same dimensions but with two reduction stages instead of just one; - the same material can be used for both stages of reduction.

Sizing In the example presented here, the satellites have the following constraints: - a total of three parts, one of which is a two-stage DPR PR2 and DR - preferably different numbers of teeth for the two groups of satellites 131 and 141 - same diameter outside the satellites - different module between the two stages PR2 and DR, and therefore for the two crowns 121 and 151 - the satellites must be able to mesh with the two rings 3031154 - 19 - For the compatibility of toothing between the satellites Differences 414 and the two rings 121, 151 of different numbers of teeth: the spacing parameter ("spacing") is chosen as low as possible, and the offset parameter ("offset") is then chosen to allow 5 meshing between different modules. An example of a dimension for the configuration presented here provides the following values: For the upstream planetary gear train PR1, we use a hypothesis with input speed input input parameters Qsimax = 10000 rpm and torque Csimax = 1, 2Nm, a dimensioning proposal gives the following 10 parameters: modulus for the different elements: mpR1 = 0.7 number of teeth of the input gear 111: Zsi = 10 number of teeth of the satellites 131: Zp1 = 18 number of teeth of the fixed ring gear 121 (R1): ZRi = ZR2 = 50 For the differential epicyclic reduction gearbox DPR: Input parameters of Qs2max = 1600 rpm and torque Cs2max = 27 Nm are obtained. A dimensioning proposal gives the parameters following: - Differential input pinion 139 (S2): number of teeth ZSZ = 33 20 ms2 module = 0.6 - differential carrier 130 (PC2) and differential satellites 141: number of teeth Zp2 = 11, module mp2 = 0.6 and PC2 = 13.6 mm - fixed ring 121 (R2 and R1): number of teeth ZR2 = 50 modulus mR2 = from 0.684 to 0.7 - moving ring 151 (R3): number of teeth ZR3 = 57 modulus mR3 = 0.6 For the differential epicyclic reduction gear DPR in this dimensioning, we thus obtain a reduction ratio, ie the ratio of output rotation speed to input rotational speed of 22.2. To obtain this ratio with two conventional planetary gear trains mounted in series, it would take a much larger footprint. For all reduction stages PR1, PR2 and DR, in this dimensioning, a reduction ratio is obtained, ie the output rotational speed to engine rotation speed ratio is 135.6. The reduction rate thus obtained is thus slightly higher than that of a lateral geared motor like that of FIG. 2, of approximately 1/125. As can be seen in FIGURE 16 and FIGURE 17 respectively with a brushless motor and with a DC motor, this better rate is obtained for a space requirement and an even lower weight.

For the SC-NU screw-nut mechanism (152-161): the pitch of the threads 152 and 161 of the screw 15 (SC) and the nut 16 (NU) can be selected independently of the stresses and interdependencies of the teeth and the dimensions of the elements of the epicyclic mechanism, which makes it possible to obtain different actuator characteristics for the same global epicyclic reduction gear PR1, PR2, DR. Preferably, as illustrated in FIGURE 11 and FIGURE 16 and FIGURE 17, the actuator is driven directly by a motor 19 mounted at the end of the input shaft 11 and fixed on the caliper housing 10, without additional reducer .

The motor 19 drives the input shaft 11 by a coupling 119 at a rotation speed Qmot. The assembly of the gearbox formed by the three stages PR1, PR2 and DR provides a reduced rotational speed. This rotation speed is converted into translation by the thread 152, 161 of the screw-nut mechanism 15-16. For example, it is proposed a screw thread nut chosen at P = 2mm / turn. For such a step, in the sizing example above, such an actuator can thus provide a clamping force F16 applied by the piston 16 to the friction lining of up to 40 kN. EXEMPLARY EXAMPLES OF THE PREFERRED EMBODIMENT FIG. 14 illustrates the mechanism of an actuator according to the invention in a variant in which the movable ring 15 'bears an internal toothing 151' of a diameter different from that of the fixed ring gear. By acting on this difference in diameters, additional parameters are thus obtained which make it possible to adapt the kinematic dimensioning and / or the transmissible load. Differential satellites 141 'thus each have a first longitudinal portion 141a of a first diameter meshing with the toothing 121 of the fixed ring 12, and a second longitudinal portion 141b meshing with the toothing 151' of the ring gear 15 '. In FIGURE 15 is illustrated the mechanism of an actuator according to the invention in another variant, which can be combined with the previous one. In this variant, the thread 152 "of the screw 15" does not cover the toothing 121 of the fixed ring gear 12. As can be seen in the figure, this thread 152 "can thus be produced with a radius R152" smaller than in the embodiment of FIGURE 6 to FIGURE 13, for example substantially the same or even less than the outer radius R12 of the piece 12 forming the fixed ring 12. The radius of the internal thread 161 "of the piston 16" can be reduced accordingly . For example, greater freedom of design is obtained for the external dimensions of the actuator, which can facilitate its integration or its positioning in the brake that it activates. Of course, the invention is not limited to the examples that have just been described and many adjustments can be made to these examples without departing from the scope of the invention.

25 Nomenclature State of the art (FIGURE 1, FIGURE 2) 90 caliper housing 91 input shaft 9AM motor shaft 30 9M electric motor 9MGU geared motor assembly 9NU nut mechanism screw-nut 9P planetary gear reducer 9PL brake piston 3031154 - 22 - 9R1 first ring 9R2 second ring 9SC screw mechanism screw-nut Invention 5 PR1 upstream planetary gear train DPR epicyclic gear reducer PR2 epicyclic differential gear train DR differential stage F1 support force 10 P1 planetary gear trains upstream P2 satellites input differential planetary gear P3 output satellites of differential planetary gear PC1 planetary gear carrier of upstream planetary gear PC2 planet carrier of differential epicyclic gear train 15 R1 fixed upstream ring R2 fixed differential ring gear R3 movable ring gear S1 planetary gear of upstream planetary gear train S2 planetary gear Differential epicyclic reduction gear 20 SC v is of mechanism screw-nut NU nut of mechanism screw-nut 1 caliper 10 caliper housing 100 piston housing 25 101 caliper finger (s) 11 input shaft 110 guide shaft 111 upstream sun gear 119 end of input shaft drive 30 12 common fixed ring gear 120 fixed ring skirt 121 fixed ring gear teeth 130 upstream satellite carriers 131 upstream satellites 3031154 -23- 139 differential sun gear 140 differential gear carriers 141, 141 ' differential satellites 141a part of the differential satellite gates meshing with the fixed ring 141b part of the differential satellite gates meshing with the movable ring 149 longitudinal windows of the differential planet carrier 15, 15 ', 15 "piece forming the movable ring and the screw 151 , 151 'toothing of the ring gear 152, 152' screw thread 16, 16 'nut piece and brake piston 161 piston-nut internal thread 162 anti-rotation notches u piston 15 163 piston seal groove 164 bearing surface of the piston 17 friction lining 19 electric motor 191 guide bearing of the ring gear 20 192 axial thrust flange of the ring gear 193, 194 axial thrust washers the moving ring gear 195, 195 'axial locking circlips of the ring gear A16 brake piston pin D15 axial hydraulic actuating play 25 R12 outer radius of the fixed ring skirt R152' outer radius of the crown screw thread mobile

Claims (17)

REVENDICATIONS1. Linear actuator, in particular for disc brake calliper, by piston with a reduction gear of the type comprising: - a differential epicyclic reduction gear (DPR) comprising a differential gear carrier (PC2, 140) carrying: o a group of input satellites (P2 , 141), meshingly engaged with an input sun gear (S2, 139) and meshing with a fixed ring (R2, 121), thereby driving said planet carrier (PC2, 140) with a first reduction ( PR2), and o a group of output satellites (P3, 141), integral in rotation with the input satellites (P2, 141), and which meshes with a movable ring (R3, 151), which is thus driven by rotation to provide a second reduction (DR), which is determined by the ratio between the radius times the number of teeth of the moving ring and the radius times the number of teeth of the fixed ring; and a screw-nut mechanism (SC-NU, 152-161) driven by the mobile ring gear (R3, 151) of said differential gearbox to move a piston (16) movable in translation along the axis of said differential epicyclic gear train, in the direction of clamping, said actuator being characterized a) in that it further comprises an upstream reduction stage (PR1) driving the differential gear (DPR) by an upstream epicyclic gear train comprising an upstream carrier planet (PC1, 130) solidaire in rotation of the sun gear (S2, 139) of said differential gear, said upstream planet carrier (PC1, 130) carrying a group of upstream satellites (P1, 131) which: o meshes with a fixed gear (R1, 121 ), and o are input meshing with an upstream sun gear (S1, 111); and b) in that the movable ring gear (R3, 151) of the differential gear (DPR) drives in rotation a screw (SC, 152) formed in a part surrounding the toothing of said movable ring (R3, 151) and integral with said Mobile crown; which screw (SC, 152) cooperates with a nut (NU, 161) fixed in rotation which is formed inside a part integral with the piston or the piston (16) itself. 5 2. Actuator according to the preceding claim, characterized in that the differential carrier (PC2, 140) carries a single group of so-called differential satellites (141) which each have a uniform and continuous toothing on two successive longitudinal portions so as to form each at the same time an input satellite (P2) and an output satellite (P3). 10 3. Actuator according to any one of the preceding claims, characterized in that the thread (152) of the screw (SC) and the toothing (151) of the movable ring (R3) are formed in the same piece (15). 15 4. An actuator according to any one of the preceding claims, characterized in that the thread (161) of the nut (NU) is formed in a bore formed inside the piston (16). 5. Actuator according to any one of the preceding claims, characterized in that it has dimensions determined so that the useful thread (152) of the screw (SC) surrounds all or part of the toothing (121) of the crown fixed (12, R1, R2). 6. Actuator according to any one of the preceding claims, characterized in that the fixed ring (R1) of the upstream stage (PR1) and the fixed ring (R2) of the differential gear (DPR) are produced in the same room. (12) by a toothing (121) common and continuous. 7. Linear piston actuator (16) with reduction gear, in particular for disc brake caliper (1), comprising in a coaxial manner: an upstream planetary gear train (PR1) comprising an upstream planet carrier (PC1, 130) carrying upstream satellites (P1, 131) which are driven by an upstream input sun gear (Si, 111) and meshing with the toothing (121) of a fixed ring gear (12), thereby driving said carrier upstream satellites with upstream reduction; a double-ring differential epicyclic reduction gear (DPR), coaxial with the upstream epicyclic gear train (PR1), comprising a so-called differential carrier (140, PC2) bearing a group of so-called differential satellites, each carrying a single toothing, which differential satellites: o on the one hand are driven into input by an input sun gear (139, S2) integral in rotation with the upstream satellite carrier 10 (13, 130, PC1) and co-operate by meshing with the same toothing (121) of the fixed ring gear (12) that said upstream epicyclic gear train (DPR1) for driving the differential carrier (140, PC2) in a first reduction (PR2) in a first direction of rotation, and 15 o of on the other hand meshes with a movable ring (152, R3) that they thus drive in rotation according to a second reduction (DR) called "harmonic" in a direction of rotation opposite to that of the differential carrier (140, PC2); - An external thread (152) carried by the outside of the movable ring (15) and cooperating with an internal thread (161) carried by the inside of the piston (16) or a cylinder integral with said piston, to form a screw-nut mechanism which moves said piston in translation in a direction depending on the direction of rotation of the upstream input planetary gear (S1, 111). 25 8. Actuator according to any one of the preceding claims, characterized in that the upstream planet carrier (PC1, 130) is mounted on and guided in rotation by a guide shaft (110) forming an axial extension of a shaft d input 11 carrying the input sun gear (S1, 111) 30 of the upstream stage (PR1). Actuator according to one of the preceding claims, characterized in that the differential gearboxes (141) of the differential gearbox (DPR) are rotatably mounted in longitudinal windows (149) in an annular cage ( 140) surrounding the input gear (139) of the differential gear (DPR), and in that said differential satellites (141) are in a predetermined number to provide rotation guidance of the differential carrier (PC2) without cooperation 5 said cage (140) with other parts than said differential satellites (141). 10. Disc brake caliper (1) comprising a housing (10) having at least one housing (100) receiving an actuator according to any one of the preceding claims arranged so that the movement of its piston (16) comes to press at least one friction lining (17) within a support chain comprising a brake disk (19) sandwiched between at least two friction linings (17, 17 ') within said caliper. 15 11. A stirrup according to the preceding claim, characterized in that the housing forms a hydraulic chamber receiving the piston sealingly and which is arranged to allow to apply a hydraulic pressure moving the piston in the direction of tightening. 20 12. A stirrup according to the preceding claim, characterized in that the teeth of the actuator are arranged (eg straight or low angle toothing, sufficient length of the teeth and play in the axial stop of the upstream input shaft. ) to allow translational displacement between the screw (15, SC) and the fixed ring (12, NU) and thus: - on the one hand to allow a displacement of the piston (16) in the direction of the clamping by hydraulic actuation without electrical actuation, and - secondly produce a displacement of said piston in the direction of loosening by electric actuation (19). 30 13. A stirrup according to any one of claims 10 to 12, characterized in that the upstream input shaft (11) of the actuator is driven by a motor (19) or electric gear motor attached to the caliper housing (10) coaxially with said upstream input shaft. 3031154 - 28 - 14. A stirrup according to any one of claims 10 to 13, characterized in that the upstream input shaft (11) of the actuator is driven by an electric motor (19) without intermediate reduction, for example by a motor DC or a brushless motor or a variable reluctance motor or a controlled AC motor. Vehicle or vehicle subassembly comprising an actuator according to any one of claims 1 to 9 or a stirrup according to any one of claims 10 to 14. 16. A method of actuating a parking brake of a brake according to any one of claims 10 to 14, or a brake comprising an actuator according to any one of claims 1 to 9, characterized in that comprises driving control of the actuator by an electric motor (19) in one direction for clamping and in the other direction for loosening of said parking brake. 17. Method according to the preceding claim, characterized in that it is applied to a brake according to claim 12 and comprises a control 20 for driving the actuator by an electric motor (19) in the direction of loosening over a sufficient stroke to reduce by a predetermined value a clamping force applied by hydraulic actuation, o when detecting an interruption of hydraulic actuation of the service brake, thus allowing a limitation of the residual braking 25, or o at a selecting a service brake release command by an automatic control system of the brake system.