ELECTROMAGNETIC BRAKE WITH IMPROVED OPERATING SAFETY

Abstract

Electromechanical brake for a motor vehicle comprising a body, an electromechanical actuator moving at least one brake pad, said actuator comprising an electric motor (8), a reducer, a screw-nut system (12) and a piston (4), the screw-nut system transforming the rotational movement of the motor into a translational movement of the piston (4), the brake also comprising energy storage means (S) ensuring the release of the brake at least in a malfunction phase, the storage means (S) comprising a spring system mounted on a pinion (24) of the reducer and a crown provided with notches, the pinion (24) being rotatable relative to said crown, the spring system comprising a spiral spring (26), one end of which is fixed to the pinion (24) and the spring system comprising a tab extending radially outwards and cooperating with a notch of said crown. [Fig.1]

Description

Title of the invention: ELECTROMAGNETIC BRAKE WITH IMPROVED OPERATING SAFETY TECHNICAL FIELD AND PRIOR ART

[0001] The present invention relates to an electromechanical brake for a motor vehicle.

[0002] An electromechanical brake comprises an electric actuator and at least one pad intended to come into contact with an element integral in rotation with the wheel to brake it. The electric actuator comprises an electric motor and a piston which is moved for example by means of a screw-nut system when the motor is actuated.

[0003] The electromechanical brake can be fully electrically actuated both for service braking and for parking and emergency braking, this brake is designated in English terminology "electro mechanical brake" or "EMB"; or be electrically actuated for parking and emergency braking and be hydraulically actuated for service braking.

[0004] An important safety criterion for braking systems is the ability to release each brake in the event of a malfunction, for example of the electric motor. In fact, the brakes are used to provide anti-lock braking and / or electronic trajectory control functions. However, if one of the brakes is defective and remains in the applied position, the stability of the vehicle may be compromised.

[0005] Document US 9,677,632 describes an electromechanical brake comprising a device ensuring the release of the brake in the event of a brake malfunction. The release device comprises a spiral spring which is, on the one hand, connected to a shaft moved in rotation by the motor and on the other hand connected to an anchoring element which is fixed relative to the brake. Thus, when the brake is activated for application, the spiral spring stores energy which will be released if the electric motor does not ensure the release of the brake, the spring causing the shaft to rotate in the opposite direction and a retraction of the piston.

[0006] Furthermore, in order to take into account the wear of the pad and avoid overstorage of energy, a mechanism is provided to ensure that substantially the same amount of energy is stored in the spring regardless of the state of wear of the pad. This mechanism is relatively complex. Statement of the invention

[0007] It is therefore an aim of the present application to provide an electro-brake mechanics for a motor vehicle comprising means ensuring its release in the event of a malfunction, having a simplified structure compared to the brakes of the state of the art and having a simplified assembly.

[0008] The object of the present invention is achieved by an electromechanical brake comprising a body, an electrically actuable actuator, a piston movable by the actuator and at least one friction element movable by the piston. The actuator comprises an electric motor, a reducer and a shaft movable in rotation by the electric motor via the reducer. The actuator also comprises means for converting the rotational movement of the shaft into a translational movement of the piston. The brake also comprises means for storing energy when the brake is actuated in the braking phase, this energy being released when the brake is released or releasable to move the shaft in rotation in the release direction in the event of a malfunction of the actuator.The storage means comprise a spiral spring, one end of which is rotationally fixed to the shaft, the storage means also comprising a tab fixed to the spring which cooperates with a toothed crown fixed relative to the brake body.

[0009] The tab is either formed directly by one end of the spiral spring, or by an element of a housing in which the spring is mounted.

[0010] The brake has the advantage of simplified assembly. In fact, the storage means can be pre-assembled, for example on a pinion of the reducer.

[0011] The storage means allow the brake to be released in the event of a malfunction, in particular of the actuator, by releasing the energy stored in the storage means. This energy, which is also released during normal release of the brake under the effect of the actuator, also helps to relieve the electric motor, which is assisted by the released energy. Since the actuator is less stressed, it presents less risk of failure and is safer. The safety of the vehicle equipped with this brake is therefore improved.

[0012] Furthermore, since the storage means are relatively simple to produce, they are more robust, which helps to make the brake even safer.

[0013] Very advantageously, the storage means comprise two mobile parts rotating with the shaft by which one end of the spring is made integral in rotation with the shaft, the parts being rotated successively by the shaft so that the shaft can rotate by at least 600° without creating interference between the spring and an element ensuring the preloading of the spring.

[0014] Very advantageously, the brake comprises a capsule integrating the spiral spring and comprising a tab cooperating with the ratchet system. The implementation of such a capsule makes it possible to simplify the assembly of the spring in the brake, the spring being pre-assembled in the capsule, and also makes it possible to retain the ratchet function while using a thin spring to limit the torque applied to the motor.

[0015] The present invention then relates to an electromechanical brake for a motor vehicle comprising a body, an electromechanical actuator intended to move at least one brake pad, said actuator comprising an electric motor, a reducer, a screw-nut system and a piston, the screw-nut system being configured to transform the rotational movement of the motor into a translational movement of the piston, the brake also comprising energy storage means intended to ensure the release of the brake at least in a malfunction phase, the storage means comprising a spring system mounted on a pinion of the reducer and a crown provided with notches on its inner periphery, the pinion being movable in rotation relative to said crown, the spring system comprising a spiral spring, one end of which is fixed to the pinion,the spring system comprising a tab extending radially outwards and cooperating with a notch of said crown.

[0016] In an exemplary embodiment, the tongue is formed by the outer end of the spiral spring.

[0017] In another exemplary embodiment, the spring system comprises a housing housing the spiral spring, the outer end of the spiral spring being fixed to the housing, and the housing comprises a tab cooperating with a notch of said crown.

[0018] The tab is advantageously integral with a side wall of the housing.

[0019] Preferably, the storage means comprise a preloading element cooperating with the outer end of the spiral spring, so that when the brake is assembled the spring is in a given preloaded state.

[0020] The storage means advantageously comprise a first part permanently fixed in rotation to the pinion and a second part carrying the preloading element and free to rotate relative to the first part over a certain angular travel, such that in a first braking phase only the first part is driven in rotation and in a second braking phase the second part is driven in rotation by the first part.

[0021] For example, the second portion is received within the first portion and is rotationally guided thereby, and the first portion includes a radial projection configured to contact a radial projection of the second portion.

[0022] Preferably, the rotational displacement during the first phase is at least 300° and the rotational displacement during the second phase is of the order of 300°.

[0023] Another object of the present invention is a method of assembling an electromechanical brake according to the invention, comprising:

[0024] - assembly of the piston and the screw-nut system in the brake body and putting into place of the electric motor and at least part of the reducer,

[0025] - mounting the spring system on a pinion,

[0026] - installation of the pinion between the reducer and the screw-nut system so that the nut is integral in rotation with the screw,

[0027] - positioning the crown so that the tab of the spring system cooperates with a crown notch.

[0028] In an exemplary embodiment, the spiral spring is mounted directly on the pinion.

[0029] In another exemplary embodiment, the assembly method comprises pre-assembling the spring system including mounting the spiral spring in the housing and fixing one end of the spiral spring to the housing, and when the crown is put in place the tab of the housing cooperates with a notch of the crown. BRIEF DESCRIPTION OF THE FIGURES

[0030] The following description will be better understood with the aid of the attached drawings in which: - [Fig.l] is a sectional view of an example of an electromechanical brake incorporating energy storage means, - [Fig.2] is a perspective view of energy storage means according to an example of the present invention shown in isolation, - [Fig.3] is a front view of a portion of the energy storage means in a pre-charged state, - [Fig.4] is a perspective view of the pinion implemented in the means of figures 2 and 3, - [Fig.5] is a view of the toothed crown implemented in the means of figures 2 and 3 shown alone, - [Fig.6] is a perspective view of part of the storage means according to another exemplary embodiment, - [Fig.7] is an exploded view of the storage means of [Fig.6], - [Fig.8A], - [Fig.8B], and - [Fig.8C] are front views of different operating states of the storage means of [Fig.6], - [Fig.9] is a perspective view of another example of storage means according to the invention, - [Fig. 10] is a perspective view of a capsule implemented in the means of [Fig.9], - [Fig. 11] is a detailed view of the cooperation of the capsule with the notched crown. DETAILED DESCRIPTION OF EMBODIMENTS

[0031] In [Fig.l], we can see an example of an electromechanical disc brake integrating energy storage means.

[0032] The disc brake comprises a body formed by a caliper 2, in which a piston 4 is mounted in translation along an axis X, an electromechanical actuator 6 comprising an electric motor 8, a shaft 10 driven in rotation by the electric motor, a screw-nut system 12 transforming the rotational movement of the shaft into a translational movement which is applied to a piston 4. The elements of the actuator are housed partly in a casing C.

[0033] In the example shown, the screw-nut system is a ball screw-nut system. The screw-nut system comprises the shaft 10 forming the screw and a nut 16 locked in rotation intended to push the piston along the longitudinal axis X. A screw-nut system without balls does not depart from the scope of the present application.

[0034] The brake also comprises two brake pads 18 intended to come into contact with the opposite faces of a brake disc (not shown) under the action of the piston 4.

[0035] The electric motor 8 transmits the rotational movement to the shaft via a reducer 20. In the example shown, the reducer comprises at least one pinion 22 in direct engagement with the output shaft of the motor, one pinion 24 in direct engagement with the shaft 10, an intermediate pinion meshing with the pinion 22 and the pinion 24. In the example shown, the pinion 24 comprises on one face a projecting element penetrating into a longitudinal end of the shaft, for example of polygonal shape, for example square, ensuring rotational attachment of the pinion 24 and the shaft 10. As a variant, it is the shaft which penetrates into the pinion 24.

[0036] The reducer is preferably irreversible, but a reversible reducer does not depart from the scope of the present invention.

[0037] The brake also comprises energy storage means S intended to store energy during a tightening phase and to release this energy during a loosening phase, or when the actuator is unable to move the shaft to ensure loosening, for example in the event of a breakdown of the electric motor or a fault in the control of the actuator.

[0038] In Figures 2 to 4, a first example of the means S can be seen comprising a spiral spring 26, a first end 26.1 of which is connected to the shaft 10 and a second end 26.2 of which is connected to the body of the brake.

[0039] In the example shown, the first end 26.1 is the inner end of the spiral spring 26 which is fixed on a face of the pinion 24, and the second end 26.2 is the outer end which is connected to the body of the brake.

[0040] Furthermore, the spiral spring 26 is oriented so that in the braking phase the spiral spring is compressed and in the releasing phase the spring discharges. The energy elastic stored in the spring is sufficient to, in the event of a failure, move the piston 4 back.

[0041] In the example shown in Figures 2 to 4, one of the faces of the pinion 24 comprises two projecting pins 25 extending parallel to the longitudinal axis X and the first end 26.1 of the spring comprises a beak received between the two pins 25 and at least partially surrounding one of the pins 25. Any other connecting means falls within the scope of the present application.

[0042] In a particularly advantageous manner, the storage means S are configured to ensure the storage of the same quantity of energy regardless of the state of wear of the brake pads and the disc. Indeed, without any particular means, the quantity of energy stored in the spring would be increasingly greater as the brake pads became worn.

[0043] To avoid this and to maintain substantially the storage of the same quantity of elastic energy, the second end 26.2 of the spring 26 which is connected to the body of the brake so as to allow its compression when the pinion 24 rotates in the application phase, sees its angular position changed as the pads wear.

[0044] For this purpose, the storage means comprise a crown 9 provided on its inner face with notches 30 and the second end 26.2 of the spring 26 is curved outwards forming a tongue 27 extending substantially radially towards the outside of the spring and cooperating with notches 30. The notches 30 are structured so as to form with the tongue 27 a ratchet system. The crown 9 is immobilized in rotation relative to the casing and is mounted on the side of the face of the pinion 24 receiving the spiral spring 26 so as to surround the spiral spring.

[0045] Each notch 30 has a gently sloping face 30.1 allowing the tab to cross the notch in one direction and a steeper sloping face 30.2 preventing the tab from moving in the opposite direction.

[0046] The angular distribution of the notches is such that beyond a certain quantity of excess energy stored from a given value which corresponds to a certain increase in the wear of the pads and / or the disc, the tab 27 jumps a notch 30 and releases this excess elastic energy.

[0047] The crown 9 and in particular the notches are made of a material that is sufficiently hard to limit wear by friction. The crown is advantageously made of steel covered with a hard treatment, for example comprising a nickel alloy, a nitride or the like.

[0048] Very advantageously, the pinion 24 has on its face carrying the spiral spring 26 a projecting element 32 parallel to the axis X and arranged so as to cooperate with the tongue 27. The element 32 is positioned so as to ensure a certain preload of the spring. Indeed, a preload of the spring is provided so as not to apply a force which would be applied to the motor in addition to the friction forces of transmission and the resistive torque. The element 32 will be referred to as the "preloading element". The arrangement of the preloading element with respect to the pins 25 is such that the mounting of a given spiral spring ensures automatic preloading to the desired value without requiring additional adjustment. In [Fig. 3], the spring can be seen mounted preloaded on the pinion 24. In this example, the preloading element has a lateral face 32.1 perpendicular to the face of the pinion forming a stop for the tab 27. The angle between the lateral face 32.1 and the face of the pinion is preferably equal to 90°, -0° and +2°, and the lateral face 32.1 is inclined at most 45° with respect to the face of the pinion, and preferably from 30° to + / - 5°.

[0049] Also advantageously shown in Figures 2 to 4, the preloading element performs a function when replacing the brake pads. During the replacement operation, the screw-nut system is fully screwed back in; in fact, during operation and to take wear into account, the piston takes an increasingly forward position. When the screw-nut system is screwed back in, the preloading element, by its lateral face 32.1, comes to bear against the tab to allow it to jump the notches 30.

[0050] In a particularly advantageous embodiment shown in FIGS. 6 to 8C, in which the storage means comprise a preloading element, the storage means are configured to allow sufficient rotation of the shaft and a stroke of the piston ensuring maximum braking, in particular when the pads are at the limit of wear, without there being any harmful interference between the tab of the spring and the preloading element.

[0051] A pinion 24' of axis XI is composite so that the pinion 24' can rotate sufficiently before contact between the preloading element and the spring tab takes place. The pinion 24' comprises a first part 24.1' provided with the teeth and the pins 25 and a second part 24.2' provided with the preloading element 32'.

[0052] The first part 24.1' comprises on its outer periphery the teeth of the pinion 24', and on one face 34, the pins 25 and an annular recess 36 of longitudinal axis XL

[0053] The annular recess 36 delimits in the center of the part a shaft 38 around which the second part 24.2' is able to rotate. The shaft 38 in the example shown is stepped and has a shoulder 40.

[0054] The second part 24.2' has a ring shape comprising a first face 42 provided on its outer periphery with the preloading element 32' extending parallel to the axis XL. The second part 24.2' comprises a second stepped face 43 comprising a central part 45 of smaller diameter intended to be housed in the annular recess 36 and an outer part 44 intended to rest on the contour of the first part 24.1'.

[0055] The radially inner periphery of the second part 24.2' and the stepped shaft 38 of the first part 24.1' are configured to ensure, over a first angular stroke, free rotation of the first part 24.1' relative to the second part 24.2', and over a second angular stroke, integral rotational movement of the first 24.1' and the second part 24.2'.

[0056] In the example shown, the radially inner periphery of the second part 24.2' comprises a projection 46 extending radially inwards and the stepped shaft of the first part (24.1') comprises on its shoulder a projection 48 extending radially outwards.

[0057] The relative displacement of the first and second parts is as follows:

[0058] The second part is arranged on the first part 24.1' so that the part central part 45 is housed in the annular recess 36 of the first part 24.1', the cooperation of the central part and the portion of larger diameter of the stepped shaft 38 ensures rotational guidance of the second part 24.2' relative to the first part 24.1'.

[0059] In [Fig.8A], one can see the relative angular arrangement of the first 24.1' and the second 24.2' part in an initial state, the brake is not applied. The radial projection 48 bears against a lateral face of the radial projection 46 so that the first part 24.1' can, in a first phase, move freely in rotation in the counterclockwise direction. The first part 24.1' moves freely without driving the second part 24.2' until its other lateral face comes to bear against the other lateral face of the projection 48. The preloading element 32 remains stationary since it is integral with the second part. The first part 24.1' has made almost a complete turn, i.e. 360° minus the angular extent of the projection 48 ([Fig.8B]).

[0060] In a second phase, during which the first part 24.1' continues its movement in the counterclockwise direction, it drives the second part 24.2' in rotation due to the two projections 46, 48 pressing against each other. The preloading element 32 is then moved. The two parts 24.1', 24.2' can perform a rotation of a significant angle, for example up to 300°, without risking contact between the preloading element 32 and the tongue of the spring ([Fig.8C]).

[0061] The spiral spring 26 being fixed by its outer end 26.1 to the first part 24.1' and to the crown which is fixed to the case, it is loaded during the first phase and the second phase.

[0062] Thus the shaft can rotate at least 600° and provide the piston with a maximum stroke allowing maximum braking to be achieved even when the pad is at the wear limit.

[0063] In Figures 9 to 11, an advantageous embodiment can be seen in which the storage means comprise a storage capsule facilitating both the brake assembly and further improving the operation of the storage means.

[0064] The storage capsule comprises a housing 50 and the spiral spring 26 housed in the housing 50.

[0065] The housing 50 has a relatively thin shape intended to be housed on the pinion 24 and inside the ratchet crown.

[0066] The housing 50 is largely inscribed in a circle and comprises a bottom 52 and a side wall 54. The bottom 52 has a central opening 56 for the passage of the pins 25. The side wall 54 is not continuous, it comprises at least a first discontinuity 57, one 58 of the ends of the side wall 54 projecting from the circle and forming a tongue intended to cooperate with the ratchet crown in place of the tongue of the spring.

[0067] In the example shown, the side wall 54 comprises a second discontinuity 60 allowing the outer end of the spring to be fixed to the housing, for example by pinching, the outer end of the spring being folded. The inner end is, for its part, fixed to the pins of the pinion.

[0068] Any other attachment of the outer end of the spring to the housing is possible, for example by means of a pin, in a similar manner to the attachment to the pinion.

[0069] Alternatively, the inner end is attached to the housing and the outer end is attached to the pinion.

[0070] The housing 50 is held on the nut via the attachment of the spring to the nut.

[0071] The capsule operates in a similar manner to the balance spring alone. Energy is stored in the balance spring and the ratchet function is provided by the cooperation of the case tongue with the ratchet crown.

[0072] The case 50 is made of a material offering both a certain rigidity and a certain elasticity similar to those of the tongue of the spiral spring.

[0073] Alternatively, the housing 50 is made of standard plastic material and a spring-loaded metal tab is attached to the side wall of the housing.

[0074] The implementation of such a capsule has the advantage of facilitating the assembly of the brake. Indeed, the spiral spring 26 is mounted in the housing. Then the housing is arranged on the pinion 24 or the pinion 24' and the inner end of the spring 26 is fixed on the pins 25 of the nut. The implementation of such a capsule avoids having to handle the spiral spring in the free state in which it has a large diameter.

[0075] Furthermore, it may be desirable to reduce the dimensions of the spring, in particular the thickness of the spirally wound strip to reduce the torque exerted by the spring. However, by reducing the thickness of the strip, the tab which performs the ratchet function may no longer be sufficiently rigid. By providing the ratchet function through the housing, this rigidity problem is resolved.

[0076] The method of assembling a brake according to the invention comprising storage means of [Fig.2] is as follows:

[0077] The spring is fixed by its inner end to the nut forming a sub-assembly. The piston and the screw-nut system are mounted in the caliper. The nut is then mounted in the brake body, coaxially with the threaded shaft of the screw-nut system and so that they are integral in rotation, the toothed crown is mounted on and around the spring, the tab penetrating into a notch.

[0078] The electric motor and other elements of the reducer are mounted in the housing.

[0079] The housing cover is put in place, thus closing the housing.

[0080] In the brake comprising storage means according to [Fig.6], the capsule is pre assembled by mounting the spring in the housing and securing its outer end to the side wall of the housing 50.

[0081] The capsule is then positioned on the nut, the inner end of the spring being secured to the nut. The other steps are similar to the steps described in relation to the brake comprising the storage means of [Fig.2].

[0082] In the examples shown, the pins 25 and the element 32 are made in a single piece with the pinion 24. As a variant, the spring 26 is mounted on a plate comprising the pins and the preloading element and the plate is immobilized in rotation on the pinion 24.

[0083] The present invention applies to electromechanical brakes for which service braking and advantageously parking braking are obtained by controlling the electric motor. REFERENCES

[0084] 2: stirrup 4: piston 6: electromechanical actuator 8: electric motor 9: crown 10: tree 12: screw-nut system 16: nut 18: brake pads 20: reducer 22, 24, 24': gable 24.1 ': first part 24.2': second part 25: pawns 26: spiral spring 26.1: outer end 26.2: second end 27: tab 30: notch 30.1, 30.2: face 32, 32': preload element 32.1: lateral face 32.2: slope 34: face 36: annular recess 38: stepped tree 40: shoulder 42: first side 43: second side 44: outer part 45: central part 46, 48: radial projection 50: case 52: background 54: side wall 56: central opening 57: first discontinuity 60: second discontinuity C: crankcase S: energy storage means X, XI: axis

Claims

Claims

1. Electromechanical brake for a motor vehicle comprising a body, an electromechanical actuator intended to move at least one brake pad, said actuator comprising an electric motor (8), a reduction gear, a screw-nut system (12) and a piston (4), the screw-nut system being configured to transform the rotational movement of the motor into a translational movement of the piston (4), the brake also comprising energy storage means (S) intended to ensure the release of the brake at least in a malfunction phase, the storage means (S) comprising a spring system mounted on a pinion (24, 24') of the reduction gear and a crown (9) provided with notches (30) on its inner periphery, the pinion (24, 24') being rotatable relative to said crown (9), the spring system comprising a spiral spring (26) one end (26.1) is fixed on the pinion (24, 24'), in which the spring system comprises a tab (27) extending radially outwards and cooperating with a notch (30) of said crown (9).

2. Electromechanical brake according to claim 1, wherein the tab (9) is formed by the outer end of the spiral spring (26).

3. Electromechanical brake according to claim 1, in which the spring system comprises a housing (50) housing the spiral spring (26), the outer end of the spiral spring being fixed to the housing (50), and in which the housing (50) comprises a tab cooperating with a notch (30) of said crown (9).

4. An electromechanical brake according to claim 3, wherein at least the tab is integral with a side wall of the housing (50).

5. Electromechanical brake according to one of claims 1 to 4, in which the storage means comprise a preloading element (32, 32') cooperating with the outer end of the spiral spring (26), so that when the brake is assembled the spring is in a given preloaded state.

6. Electromechanical brake according to claim 5, in which the storage means comprise a first part (24.1') permanently secured in rotation to the pinion (24') and a second part (24.2') carrying the preloading element (32') and free to rotate relative to the first part (24.1') over a certain angular travel, such that in a first braking phase only the first part (24.1') is driven in rotation and in a second braking phase the second part (24.2') is rotated by the first part (24.1').

7. An electromechanical brake according to claim 6, wherein the second part (24.2') is received in the first part (24.1') and is rotationally guided thereby, and wherein the first part (24.1') comprises a radial projection (48) configured to come into contact with a radial projection (46) of the second part (24.2').

8. An electromechanical brake according to claim 6 or 7, wherein the rotational displacement during the first phase is at least 300° and the rotational displacement during the second phase is of the order of 300°.

9. Method of assembling an electromechanical brake according to one of the preceding claims, comprising: - assembling the piston and the screw-nut system in the body of the brake and installing the electric motor and at least part of the reducer, - mounting the spring system on a pinion, - installing the pinion between the reducer and the screw-nut system so that the nut is rotationally integral with the screw, - installing the crown so that the tab of the spring system cooperates with a notch of the crown.

10. A method of assembling according to claim 9 an electromechanical brake according to claim 2, in which the spiral spring is mounted directly on the pinion.

11. A method of assembling according to claim 9 an electromechanical brake according to claim 3 or 4, comprising pre-assembling the spring system comprising mounting the spiral spring in the housing and fixing one end of the spiral spring to the housing, and in which when the crown is put in place the tab of the housing cooperates with a notch of the crown.

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