FR3105326A1 - ELECTROMECHANICAL DRUM BRAKE ACTUATOR - Google Patents

Abstract

Actuator for an electromechanical brake, said electromechanical brake comprising two friction members (3, 4) intended to come into contact with a drum integral in rotation with the wheel, said actuator (10) being intended to apply said friction members (3, 4). 4) against the drum, said actuator (10) comprising a first element (16) forming a screw, a second element (18) forming a nut and cooperating with the first element (16), said first (16) and second (18) element being movable relative to each other along a longitudinal direction (Y), the second element (18) being intended to be driven in rotation by an electric motor, a coil spring (26) and means of spring preload (26) mounted at least in part in the spring (26). Figure for the abstract: Figure 2.

Description

ACTUATOR FOR ELECTROMECHANICAL DRUM BRAKE

TECHNICAL FIELD AND PRIOR ART

The present invention relates to an actuator for an electromechanical drum brake.

In most current automobiles, the service brake is provided by disc brakes and/or drum brakes.

They perform the service braking function, aimed at slowing down, or even stopping, the motor vehicle. The parking brake or parking brake function aimed at immobilizing a stationary vehicle and the emergency brake function are generally obtained with the system ensuring the parking brake.

The application of the parking brake can be obtained by pulling on a lever located in the passenger compartment which is connected to a mechanism located in a drum brake or a disc brake, via a brake cable. The mechanism tends to spread the brake shoes of the drum brakes to apply them against the drums. In the case of a disc brake, the pads are clamped to the brake disc.

To improve driver comfort and parking brake application safety, the automotive industry has developed an electric parking brake.

For example, an actuator provided with an electric motor is arranged at least on each rear brake, and causes the brakes to apply.

For example, the driver presses a button on the dashboard to activate the electric parking brake.

Electric parking brake systems include direct current electric motors, the implementation of such motors being recommended for example by the German Association of the Automotive Industry in its "VDA Recommendation".

In the case of a disc brake, it is generally the piston which is moved by the actuator and which presses the brake pads against the brake disc. In the case of a drum brake, the actuator is for example arranged between the brake shoes and serves as a fixed point when applying service braking via a wheel cylinder. The actuator is for example of the screw-nut type and spreads the segments. The actuator has two pistons that press against the brake shoes. Moving the pistons away from each other causes the piston rings to press against the drum. The pistons are configured to be movable in translation and fixed in rotation.

In general, one of the pistons is formed by the screw which is locked in rotation and the other piston is carried by the nut and is free to rotate relative to it. During an activation phase of the parking brake, the nut is rotated by the electric motor, it moves in translation, causing the two pistons to move apart.

The actuator also comprises a means that is elastically deformable along the axis of the actuation movement, called an elastic element, also called a "spring pack" in English, to provide the function of stabilizing the forces in the support chain. This element is for example described in the document FR3016010.

Depending on the forces transmitted in the direction of displacement of the actuator, this elastic element has a determined stiffness to provide a stroke making it possible to maintain or restore sufficient support of the segments against the drum in different circumstances or changing situations.

In particular, this elastic element is thus capable of storing, by compression during an activation of the actuator while the device is in the first braking position, a quantity of mechanical energy sufficient to maintain or bring the device into the second braking position if the support of the brake cylinder is interrupted after activation of the actuator without requiring activation of the actuator again.

Such a situation occurs, for example, when the driver stops the vehicle and keeps it stationary using the service brake, then engages the parking brake before releasing the service brake control, for example when stopping to parking on a slope. This elastic reserve makes it possible to fill the strokes which are necessary for the transition from one braking position to another, for example from simplex mode to duo servo mode, while ensuring a sufficient load to meet the needs of immobilization of the vehicle .

It is therefore an object of the present invention to provide a new electromechanical actuator structure for a drum brake incorporating an elastic element or “spring pack”.

The object stated above is achieved by an actuator comprising two pistons intended to come and apply a spreading force on each of the brake shoes, a screw-nut assembly for separating the pistons from each other, elastic means capable of storing a certain quantity of energy during operation of the brake, means for applying a preload to the elastic means. Said preloading means are mounted at least partly inside the elastic means and ensure a preloading of said elastic means by exerting a compressive force on said elastic means.

By implementing means arranged inside the elastic means, an unoccupied space is used. Thus the size is reduced compared to means external to the elastic means.

In a very advantageous example, the preloading means comprise a first axial element comprising a part bearing on one longitudinal end of the elastic means and a second part passing through the elastic means, a second element bearing on the other longitudinal end of the elastic means and means for axially locking the first element with respect to the second element in the longitudinal direction applying the desired preload to the elastic means.

The first element and the second element are configured to allow compression of the elastic means beyond the preload.

The subject of the present invention is therefore an actuator for an electromechanical brake, said electromechanical brake comprising at least one friction member intended to come into contact with a drum integral in rotation with the wheel, said actuator being intended to apply said friction member against the drum, said actuator comprising a first element forming a screw, a second element forming a nut and cooperating with the first element, the said first and second elements being movable relative to each other along a longitudinal direction, the first element or the second element being intended to be driven in rotation by an electric motor, elastic means, means for preloading the elastic means resting on the longitudinal ends of the elastic means. The first element and the second element are arranged partly in the elastic means, and the preloading means are mounted at least partly in the elastic means.

Preferably, the preloading means comprise the first element or the second element which is intended to be driven in rotation.

The preloading means are advantageously such that they have a variable length between a maximum length and a minimum length, the maximum length fixing the preload of the elastic means.

For example, the preloading means comprise at least two parts able to slide relative to each other along the longitudinal direction. One of the parts may include a slot extending in the longitudinal direction, and the other of the parts may include a pin secured axially to the other part and intended to slide in the slot.

One of the parts can be the second element and the other part can be a connecting part between the second element and a washer resting against one of the ends of the elastic means, the actuator can also include locking means to axially lock the connecting piece and the washer.

For example, the locking means comprise two half-keys cooperating with a locking element of the connecting piece and a central passage of the washer.

The second element may comprise a flange resting on one end of the elastic means provided with a toothing intended to mesh with a toothed wheel driven by the electric motor.

The elastic means comprise for example a helical spring.

The present invention also relates to an electromechanical brake comprising at least one friction member intended to come into contact with a friction part integral in rotation with the wheel, at least one actuator according to the invention, said actuator being intended to apply said friction member against said friction piece, and a geared motor activating the actuator.

The actuator is advantageously configured to apply at least one parking brake, and the brake may include a second actuator to apply a service brake.

The brake is a drum brake comprising a drum, a plate, two segments, the actuator being fixed on the plate.

The present invention also relates to a method of manufacturing the actuator according to the invention, comprising:

- the assembly of the two parts,

- placing the two parts in the elastic means from one end of the elastic means,

- installation of the washer bearing against the other end of the elastic means,

- compression of the elastic means,

- installation of locking means,

- assembly of the first element and the second element.

The present invention will be better understood on the basis of the following description and the appended drawings in which:

is a perspective view of an example of a hydraulic drum brake with an electric parking brake to which the elastic element according to the invention applies,

is a longitudinal sectional view of an example of an actuator.

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

In FIG. 1, a "dual-mode" drum brake 1 can be seen in an exemplary embodiment of the invention.

The drum brake 1 comprises a drum (not shown) integral in movement with the wheel (not shown), a plate 2 of revolution of axis X equipped with a first and a second segment in an arc of circles 3 and 4 radially movable so as to be able to be pressed against the cylindrical internal face of a drum, not shown.

The segments 3 and 4 each comprise a core 3a, 4a of flat sheet metal in the shape of a portion of a circular crown which carries a brake lining 3b, 4b, and are mounted diametrically opposite with their ends bearing both on a wheel cylinder 6 hydraulic and on a mechanical actuator 10 carried by the plate 2. These segments 3 and 4 are also biased towards each other by two return springs 8 and 9, and pressed against the plate 2 each by a so-called reminder.

A wear take-up link 7 extends along wheel cylinder 6 with a first end resting on web 3a of first segment 3 and a second end resting on web 4a of second segment 4, when the brake is at rest.

The wheel cylinder 6 is intended to be actuated during use of the drum brake 1 according to a first so-called "simplex" mode of operation, which provides progressive braking particularly suitable for braking the vehicle in service. It comprises a hydraulic chamber closed at its ends by two pistons which move apart when the hydraulic pressure increases and pushes the associated ends of segments 3 and 4.

The mechanical actuator 10 ensures, for its part, the parking or parking and emergency braking by spreading the associated ends of the segments to ensure rapid and powerful locking of the wheels of the vehicle according to a so-called "duo-servo" mode of operation. , in particular when the wheel cylinder 6 is inactive. This actuator is driven by an electric motor 22. In the example shown, the wheel cylinder comprises two opposite pistons, which each actuate one of the segments 3, 4 by moving their two ends 3.1 apart from each other, 4.1 facing each other, that is to say those located on the same side of the axis of rotation X, here called "moving ends" and located at the top of figure 3. At its opposite end, said abutment end, each segment rests on the plate 2 by an anchoring element integral with the plate, and thus forming an abutment for this segment. The anchoring element transmits at least part of the braking torque between segments and plate. The anchoring element of the two segments is produced by the actuator 10.

The actuator 10 extends along a Y axis perpendicular to the X axis of the platter and parallel to the platter. It comprises a box 12 fixed to plate 2 on the side of the first face. The housing includes a housing extending along the Y axis and opening out at the two longitudinal ends of the housing 12. A drive assembly is housed in the housing 12.

The drum brake also comprises an actuator drive device, fixed to the face of the plate opposite to the face on the side of which the actuator 10 is mounted.

The drive device is an electric motor 22 which is advantageously associated with a reduction gear.

A passage (not visible) is made through the plate 2 to allow transmission of the drive from the drive device to the drive assembly of the actuator 10.

In Figure 2, one can see a view in longitudinal section of an embodiment of the actuator 10.

The drive assembly is of the screw-nut type. It comprises two support elements or pistons 16, 20 intended to form a fixed point for the ends 3.2, 4.2 of the brake shoes 3, 4 respectively in service braking, and to apply a force to the ends 3.2, 4.2 in braking parking by being moved out of the housing along the Y axis. The housing 12 has two openings aligned along the Y axis and in which are mounted the pistons 16 and 20 to slide.

The screw-nut system comprises a first threaded element 16, one longitudinal end of which comprises a head forming the first piston 16, and another longitudinal end carrying the thread 21.

The screw-nut system comprises a second element 18 comprising an internal thread, designated nut, receiving the first threaded element, the first and second elements interacting with each other to form the screw-nut system. This screw-nut system produces the linear movement under the effect of a rotation of the second element 18 relative to the first piston 16. It transforms the torque received by the second element 18 into two opposing axial forces on each of the elements 16, 18 respectively.

The second element 18 comprises a flange 18.1 provided with a toothing 18.2, intended to cooperate with a toothed wheel driven by the geared motor.

In addition, as can be seen in Figure 2, the actuator 10 also comprises elastically deformable means 26 along the axis of the actuation movement, also called "spring pack" in English to provide the force stabilization function in the chain of support. The diameter of the drum varies, in particular increases with temperature. The elastic means 26 ensure that if the hot parking brake is applied, it can be released after the brake has cooled, despite the constriction exerted by the drum.

The elastic means 26 comprise a spring, advantageously a helical spring 26. The elastic means will be designated “spring” in the following description for simplicity.

The spring is, in the rest state of the drum brake, preloaded. Means for preloading the spring or preloading means are provided. In the example shown, the preloading means advantageously use the second element of the screw-nut system, whose collar 18.1 bears against a longitudinal end 26.1 of the spring 26. The preloading means comprise a washer 28 bearing against the other longitudinal end 26.2 of the spring and connecting means 30 for axially connecting the second element 18 and the washer 28 so as to compress the spring 26, while allowing the spring to undergo additional compression. Advantageously the washer 28 has the shape of a cap, the edge 28.2 of which bears against the end of the spring 26 and the cap 28.3 penetrates into the spring 26. The positioning of the washer 28 against the spring 26 is then improved.

In the example shown and very advantageously, the connecting means 30 comprise a connecting piece 32 comprising a body 33 provided with a slot 34 extending longitudinally and receiving a pin 36 axially secured to the second element, the pin 36 extending perpendicular to the longitudinal axis.

The second element 18, in the example shown, comprises a threaded sleeve 18.3 housed in the spring 26 and the flange 18.1 resting on a longitudinal end of the spring 26 and forming a base for the sleeve 18.3.

Advantageously, the outer diameter of the sleeve 18.3 is close to the inner diameter of the spring 26, ensuring guidance of the spring.

The slot 34 extends longitudinally over a length greater than the diameter of the pin, for example at least twice as long .

The cooperation of the slot 34 and the pin 36 allows relative axial movement between the connecting piece 32 and the second element 18. The pin is positioned axially in the sleeve 18.3 beyond the threaded zone usable by the screw-nut system . It will be understood that the pin has a length such that it does not come into contact with the spring so as not to interfere with the operation of the brake. Indeed, the second element 18 carrying the pin rotates on itself in the spring 26.

The connecting means also comprise locking means 40 for locking the connecting piece 32 with respect to the washer 28 at least in a direction of separation of the connecting piece 32 and the second element 18 from each other. .

In the example shown, the locking means 40 comprise two tapered half-keys 41 cooperating with a locking element 42 of the connecting piece extending from the body 33 and with the central passage of the washer 28. The central passage 28.1 of the washer 28 is of flared shape to cooperate with the frustoconical shape of the two half-keys 41 and ensure axial immobilization of the two half-shells and of the connecting piece with respect to the washer 28. The locking element 42 is then enclosed in the two half-keys 41 thanks to the cooperation of the contour of the central passage 28.1 of the washer and the outer surface of the half-keys 41. Locking is advantageously confirmed by the reaction of the preloaded spring. In the example shown, the inner surface of the half-keys 41 have one or more grooves intended to cooperate with one or more annular ribs carried by the locking element. Alternatively, the grooves are carried by the locking element and the ribs are carried by the two half-keys.

The locking element passes through the washer 28 and is intended to come into contact with the second piston 20. An axial clearance is provided between the locking element 42 and the end of the second piston 20 opposite the end in contact with the segment.

The preloading means are on the one hand compact because they are arranged in the spring and partly use already existing parts. In addition, assembly is relatively easy.

As a variant, the locking means comprise a frustoconical shaped nut and the locking element comprises a thread. Preferably, the screw-nut connection is braked, for example by no thread lock, or stopped for example by a punch to eliminate any risk of unscrewing due to vibrations.

As a further variant, the locking element is immobilized axially in the washer by plastic deformation. According to another variant, an axial locking implementing a pin is possible between the locking element and the washer.

The axial dimension of the preload means defines the preload value of the spring.

For example, the spring is compressed so that its length in the preloaded state is on the order of 80% of its unloaded length.

Preferably, the spring preload is chosen equal to at least 30% of the input force of the drum brake in duo-servo mode.

As a further variant, the preloading means are separate from the screw-nut system. They are for example arranged around the screw-nut system.

Alternatively, the light and the pin are interchanged. The light is formed in the threaded sleeve and the pin is carried by the connecting piece.

According to another variant, the first and the second element are inverted, it is the screw which is driven in rotation by the electric motor and it is this which participates in the application of the prestress.

An example of a spring preload method will now be described.

The second element 18 and the connecting piece 32 are assembled. For this, the body 33 of the connecting piece 32, comprising the slot 34, is introduced into the free end of the threaded socket 18.3 and the pin 36 is inserted transversely into the socket and passes through the slot 34 of the connecting piece 32 For this, a transverse hole is made in the sleeve 18.3. The axial location of the pin in the socket defines the maximum axial dimension of the preloading means. The pin is advantageously blocked in the hole making the connecting piece captive with respect to the second element 18.

The threaded sleeve 18.3 of the second element 18 is introduced into the spring 26 until the flange 18.1 comes to bear against one end 26.1 of the spring 26.

Washer 28 is mounted bearing against the other end 26.2 of spring 26.

A compressive force is exerted between collar 18.1 and washer 28 so that locking element 42 passes through washer 28 and protrudes from the other end of spring 26. Then the two half-keys 41 are fitted around the locking element 42. The compression force is released. The relaxation of the spring 26 causes a sliding of the two half-keys 41 in the central passage 28.1 of the washer 28 and ensures their tight maintenance around the locking element 42, ensuring an axial locking of the locking element 41 in the washer 28 and maintaining the preload.

The manufacture of the actuator then continues in a known manner.

An example of the operation of the spring package will now be described.

During comfort braking, the driver presses the brake pedal, pressurized brake fluid is sent to the wheel cylinder causing the shoes to press against the drum. The driver brakes until the vehicle comes to a stop.

The driver decides to apply the parking brake. It activates the control dedicated to this function located in the passenger compartment. The electric motor is activated, the second element is rotated via the collar. The first and second element deviate from each other. First, the clearance between the locking element and the second piston is closed, and then the spring is compressed.

The driver releases his action on the brake pedal, the action of the wheel cylinder on the segments ends and the spring takes over from the wheel cylinder. It restores its load to the pistons 16 and 20, and keeps the segments under pressure on the drum.

In the example shown, the actuator comprises two pistons moving away from each other during a braking action. In another example, the actuator comprises a single movable piston, the screw for example being fixed.

In an exemplary embodiment, the actuator is implemented for application to service braking.

The invention applies to a drum brake with hydraulic service brake and electric parking brake, and also to a drum brake with electric service braking and electric parking brake.

REFERENCE LIST

1: drum brake

2: tray

3: first segment

3.1, 3.2: ends of the first segment

4: second segment

4.1, 4.2: ends of the second segment

3a, 4a: souls

3b, 4b: brake pads 3b, 4b

6: water wheel cylinder

7: wear take-up rod

8, 9: return springs

10: mechanical actuator

12: housing

16: first plunger

18: second element

18.1: collar

18.2: collar toothing

18.3: threaded sleeve

20: second plunger

21: thread

22: electric motor

26: elastically deformable element

26.1, 26.2: longitudinal end of the spring

28: washer

28.1: central passage

28.2: puck edge

28.3: cap

30: connecting means

32: connecting piece

33: body

34: light

36: pin

40: means of locking

41: half key

42: locking element

X, Y: axes

Claims (13)

Actuator for electromechanical brake, said electromechanical brake comprising at least one friction member (3, 4) intended to come into contact with a drum integral in rotation with the wheel, said actuator (10) being intended to apply said friction member (3 , 4) against the drum, said actuator (10) comprising a first element (16) forming a screw, a second element (18) forming a nut and cooperating with the first element (16), said first (16) and second (18) element being movable relative to each other along a longitudinal direction (Y), the first element (16) or the second element (18) being intended to be driven in rotation by an electric motor, means elastic means (26), means for preloading the elastic means (26) resting on the longitudinal ends of the elastic means, characterized in that the first (16) and the second (18) element are arranged partly in the elastic means ( 26), and in that said preloading means are mounted at least partly in the elastic means (26). Actuator according to Claim 1, in which the preloading means comprise the first element (16) or the second element (18) which is intended to be driven in rotation. Actuator according to Claim 2, in which the preload means are such that they have a variable length between a maximum length and a minimum length, the maximum length fixing the preload of the elastic means (26). Actuator according to Claim 3, in which the preloading means comprise at least two parts capable of sliding relative to each other along the longitudinal direction. Actuator according to Claim 4, in which one of the parts comprises a slot (34) extending in the longitudinal direction (Y) and the other of the parts comprises a pin (36) axially integral with the other part and intended to slide in the slot (34). Actuator according to Claim 5, in which one of the parts is the second element (18) and the other part is a connecting part (32) between the second element (18) and a washer (28) bearing against the one of the ends of the elastic means (26), the actuator also comprises locking means (40) for axially locking the connecting piece (32) and the washer (28). Actuator according to Claim 6, in which the locking means (40) comprise two half-keys (41) cooperating with a locking element of the connecting piece (32) and a central passage (28.1) of the washer (28) . Actuator according to one of Claims 1 to 7, in which the second element (18) comprises a flange resting on one end of the elastic means (26) provided with a toothing intended to mesh with a toothed wheel driven by the electric motor. Actuator according to one of the preceding claims, in which the elastic means (26) comprise a coil spring. Electromechanical brake comprising at least one friction member (3, 4) intended to come into contact with a friction part integral in rotation with the wheel, at least one actuator according to one of the preceding claims, the said actuator (10) being intended in applying said friction member (3, 4) against said friction piece, and a geared motor activating the actuator. Electromechanical brake according to the preceding claim, in which the actuator (10) is configured to apply at least one parking brake, and in which the brake comprises a second actuator (6) to apply a service brake. Electromechanical brake according to Claim 10 or 11, in which the brake is a drum brake comprising a drum, a plate (2), two shoes (3, 4), the actuator being fixed to the plate (2). Method of manufacturing the actuator according to one of Claims 1 to 9, comprising:
- the assembly of the two parts,
- placing the two parts in the elastic means from one end of the elastic means,
- installation of the washer resting against the other end of the elastic means,
- compression of the elastic means,
- installation of locking means,
- assembly of the first element and the second element.