Patent ID: 12240425

DETAILED DISCLOSURE OF PARTICULAR EMBODIMENTS

InFIG.3, a “dual mode” drum brake2in an exemplary embodiment of the invention can be seen.

The drum brake1includes a drum (not represented) movably integral with the wheel (not represented), an X-axis revolving backing plate2fitted with a first and a second arc-of-circle shoes3and4, the shoes being radially movable so that they can be pressed against the cylindrical inner face of a drum not represented.

The shoes3and4each include a web3a,4amade of flat sheet in the form of a portion of a circular crown which carries a brake lining3b,4b, and are mounted diametrically opposite each other with their ends bearing on both a hydraulic wheel cylinder6and a mechanical actuator10carried by the backing plate2. These shoes3and4are further biased towards each other by two return springs8and9, and each pressed against the backing plate2by a so-called side spring.

A wear adjustment connecting rod7extends along the wheel cylinder6, having a first end bearing on the web3aof the first shoe3and a second end bearing on the web4aof the second shoe4when the brake is at rest.

The wheel cylinder6is for being actuated when the drum brake1is used according to a first so-called “simplex” operating mode, which ensures progressive braking particularly adapted to brake the vehicle in service. It comprises a hydraulic chamber closed at its ends by two pistons which move away from each other when the hydraulic pressure increases and pushes the associated ends of the shoes3and4.

The mechanical actuator10, in turn, ensures parking and emergency braking by moving the associated ends of the shoes apart to ensure rapid and powerful locking of the vehicle wheels according to a so-called “duo-servo” operating mode, especially when the wheel cylinder6is inactive. This actuator is driven by an electric motor22. In the example represented, the wheel cylinder includes two opposite pistons, each of which actuates one of the shoes3,4by spacing apart their two ends3.1,4.1facing from each other, that is those located on the same side of the axis of rotation X, here referred to as the “movable ends” and located at the top ofFIG.3. At its opposite end32,4.2, called the stop end, each shoe bears on the backing plate2by an anchoring element integral with the backing plate, thus forming a stop for this shoe. The anchoring element transmits at least part of the braking torque between the shoes and backing plate. The anchoring element of both shoes is formed by the actuator10.

The actuator10extends along an axis Y perpendicular to the axis X of the backing plate and parallel to the backing plate. It includes a casing12which is attached to the backing plate2on the side of the first face. The casing includes a housing formed by a through bore13extending along the axis Y and opening at both longitudinal ends of the casing12. A drive assembly is housed in the bore13.

The drive assembly is, for example, of the screw-nut type, such as that described in application WO2015/101486. It includes two bearing elements16,20for forming a fixed point for the ends3.2,4.2of the brake shoes3,4respectively in service braking, and applying a force on the ends3.2,4.2in parking braking by being moved towards outwardly of the casing along the axis Y.

The drum brake also includes a drive device22for the actuator, attached to the other face side of the backing plate opposite the face to the side of which the actuator10is mounted.

The drive device is an electric motor which may or may not be associated with a motor reducer.

A passageway (not illustrated) is provided through the backing plate2to allow drive transmission from the drive device to the drive assembly of the actuator10.

InFIG.4, an example drum brake actuator10according to the invention can be seen. It includes a first threaded element16and a second element18having an internal thread receiving the first threaded element16, the first and second elements interacting with each other to form a screw-nut system. This screw-nut system produces the linear movement under the effect of a rotation of the second element18relative to the first element16. It transforms torque received by the second element18into two opposite axial forces on each of the elements16,18respectively.

The first element16forms a piston bearing against the brake shoe3and a second piston20is interposed between the brake shoe4and the second element18. The second element18is to be rotatably driven by a toothed wheel24rotated by the drive device. In the example represented, the first element18is mounted in the toothed wheel24and is rotatably secured relative thereto by means of splines.

In this embodiment, the thread angle of this screw-nut system is chosen so that the force transmission obtained is irreversible, by choosing a thread angle which is less than the friction angle of the pair of materials used to make these two elements.

This choice of a screw-nut system, combined with the choice of such a thread angle, produces an irreversibility that provides the locking function in the parking braking position. That is, a force received by the pistons16,20from the shoes3,4is blocked by the non-slip between the threads of both elements of the screw-nut system. It is thus not transmitted to the motor system, making it unnecessary to block the motor or to keep it under load.

Further, as is visible inFIG.4, the actuator10also includes an elastically deformable element along the axis of the actuation motion, so-called elastic element or also spring pack, to provide the function of force stabilisation in the bearing chain. In this exemplary embodiment, this elastic element is made by one of both pistons, in this case the second piston20. Depending on the forces transmitted in the direction of movement of the spreader, this elastic element has a determined spring constant to provide a stroke allowing to maintain or restore sufficient bearing of the shoes against the drum under different circumstances or changes of situation.

Alternatively, the spring pack is arranged between the second piston20and the second element18.

In particular, this elastic element is thus likely to store, by compression in the actuation assembly upon activating the actuator while the device is in the first braking position, a sufficient quantity of mechanical energy to maintain or bring the device into the second braking position if bearing of the wheel cylinder6is interrupted after activation of the actuator10without the need to activate the actuator again.

Such a situation occurs, for example, when the driver stops the vehicle and holds it stationary using the service brake, and then engages the parking brake before releasing the service brake control, for example when stopping to park on a slope. This elastic reserve compensates for the strokes required to move from one braking position to another, for example from simplex to duo-servo mode, while providing sufficient load to meet the needs for bringing the vehicle to a standstill.

The stroke of this elastic element also makes it possible, during a variation in the dimensions of elements3,4of the drum brake, and without activation of the actuator10:to maintain the bearing force of the shoes3,4against the friction track in the case of dimensional variations in one direction, for example in the case of thermal shrinkage of the shoes or of the elements of the mechanical chain creating this bearing, such as the pistons or the mechanism which moves them apart, or for example in the case of thermal expansion of the drum; andto limit the increase in forces in the mechanism in the case of dimensional variations in the other direction, which may be caused, for example, by thermal shrinkage of the drum when it cools down when stationary after having been heated as a service brake during a journey.

This elastic element thus makes it possible to limit and most often avoid any need for automatic reactivation of the system during parking, also called “re-clamping”, which can be energy consuming and subject to malfunctions that may have serious consequences.

In embodiments where motion of the actuator is achieved by an irreversible type mechanism, the elastic element is located downstream of the irreversible mechanism.

In the example inFIG.4, the elastic element is here provided by the second piston20which comprises a piston head202having rearwardly a skirt within which a piston bottom203can slide. The piston head202and the piston bottom203bear against each other by means of a compressible elastic structure201, in this case an advantageously pre-stressed stack of conical steel washers, known as “Belleville” washers. The assembly is held together by crimping the end of the skirt around the rear of the piston bottom203.

According to the invention, the drum brake includes means26forming a stop for at least one of the movable elements of the actuator10, during the parking brake release phase.

The movable element has a release position Pr from which, in the brake release phase, it is certain that the parking brake has been released. The means26are arranged in the actuator in a position Pb beyond the release position Pr in the release phase.

The term “movable elements of the actuator” refers to the elements of the actuator that are moved upon applying the parking brake and releasing the same.

According to a first example, the stop means are arranged between the spring pack and the body of the actuator10.

When the actuator is activated to release the parking brake, the second element18slides along the axis Y of the actuator towards the first piston16, the second piston20moves in the direction S2 under the action of the shoe4which is brought back inwardly by the return spring8. Further, the spring pack relaxes, causing the piston bottom203of the piston20to move in direction S2. The actuator is in a state where the brake is released, the bottom203of the second piston20is in the position Pr. The bottom203continues to move to bear against an axial stop and reach the rest position Pb. The position Pb of the stop26is such that the bottom203bears against it, when the spring pack is completely released. In the example represented, the stop26is a shoulder formed in the bore13of the actuator casing12. The end of the second element18for contacting the second piston20slides in a reduced diameter portion of the bore13.

The position Pb of the bottom203is then still the same at each release of the parking brake. This position is known to within the manufacturing clearance.

Consequently, at the beginning of each activation of the parking brake, the position of the second piston20is known to within the manufacturing clearance. Its position, upon activating the actuator10, can then be estimated relatively accurately by counting the number of revolutions of the second element18which is known from the number of revolutions of the motor and the reduction ratio between the motor and the second element18. The estimation uncertainty due to the uncertainty of the position of one of the actuator elements in the rest state is eliminated. The position Pb is downstream of the position Pr in the direction of movement of the movable element in the brake release phase.

In another exemplary embodiment represented inFIG.5, the actuator110includes stop means formed by a tooth126on the thread of the first piston16against which the longitudinal end18.1of the second element18, oriented on the side of the first piston16, bears when the actuator is in the released position. The tooth126is schematically represented inFIG.5.

The operation of the brake according to the invention will now be described from the example ofFIG.5and with the schematic representation of the movement D of the second element18inFIG.2.

The positions inFIG.2are the positions of the longitudinal end18.1of the second element18for contacting the tooth126.

It is considered that the parking brake is applied (FIG.5). The first element is in the position Ps. The pistons16and20are moved away from each other and apply the brake shoes against the drum. The longitudinal end18.1of the second element18is in the position Pf, when the parking brake is applied.

If the driver decides to deactivate the parking brake, he or she controls the activation of the actuator10, for example by pressing a button, the second element18is rotated via the electric motor and the toothed wheel, so that the pistons16and20slide towards each other. The second piston16, in particular its threaded rod, slides in the second element18, the piston head16.1moving closer to the longitudinal end18.1of the second element. The second element18turns until the pistons16,20have travelled a stroke towards each other which is considered sufficient to ensure the parking brake release, the longitudinal end18.1of the second element18then has the position Pr. The second element18is then turned until the tooth126bears against the longitudinal end18.1of the second element, the longitudinal end18.1of the second element18is in the position Pb. A control unit UC then measures an increase in the current across the motor, and controls the power supply to the motor to be stopped. The actuator is stopped.

The position of the tooth126is advantageously chosen so that the contact between the tooth and the second element18takes place just after the release stroke has been travelled in order to obtain a very compact brake.

Thus, when designing the brake, in particular the actuator, the axial dimension of the actuator is chosen so that the second element18can travel the distance between Pr and Pb. As the position Pb is known to within the manufacturing clearance, the length of the actuator can be optimised and there is no need to provide an additional margin to take account of the uncertainty of the position of the second element in the released position. The distance between Pb and Pr is at least equal to the manufacturing clearance. InFIG.2, this distance is slightly greater than the clearance j.

InFIG.1, the movement of the second element18in an actuator of the state of the art can be seen. A rest position assumed by the second element is an estimated position Pe, which is estimated with an error margin e. Dimensioning of the actuator takes account of the error margin e and the manufacturing clearance j for the position Pb′ of the stop. Considering an actuator of the type shown inFIG.5, the length of the actuator of the state of the art is at least 2e greater than that of the actuator according to the invention inFIG.5.

By virtue of the invention, a reduction of 2 mm in the length of the actuator can be achieved.

Further, by optimising the stroke of the first element, i.e. by reducing it, the application of the parking brake during the next activation of the parking brake will be faster, as the first element has a shorter distance to travel.

According to another exemplary embodiment, a stop is provided on the body of the actuator against which the first element18bears in the stop position.

The present invention is also applicable to an electromechanical disc brake.

The present invention applies to floating caliper disc brakes and fixed caliper disc brakes.

In the examples described, the movable element(s) of the actuator move along an axis and possibly rotate about that axis. In another example, the actuator has at least one part that is only rotatably movable, for example of the cam type, the stop forming an angular stop. The stop means interrupt a rotational motion only.

In the example ofFIG.4, the stop means form an axial stop for the spring pack. In the example shown inFIG.5, the stop means form a rotational stop and interrupt a translational movement. Further alternatively, the stop means form an axial stop for an element that is both rotatably and translationally movable.

An exemplary method for making the brake shown inFIG.5will now be described.

Firstly, the minimum movement of the movable element(s) of the actuator is determined to make sure that the brakes are released. From this minimum movement, the position that the movable element(s) have to reach in the release phase, for the brake to be released, is determined. This position is the position Pr inFIG.2.

The position of the stop Pb is then determined relative to the position Pr, taking account of the manufacturing clearance j. The minimum distance between Pr and Pb is at least equal to j.

The stop means are made on the body of the actuator or another part of the actuator, so that the movable part contacts the stop in the position Pb, i.e. Pr+j. The various parts of the actuator are adapted to this movement, especially the casing which has a greater compactness.

In the case of a movable element having a rotational movement only, the movement is an angular movement.

The present invention applies to all electromechanical brakes that are partly or entirely electrically actuated. It applies to brakes in which parking and/or service braking is achieved by electrical actuation. In the case of an electromechanical brake, in which service braking is provided by an electrical actuator, contact between at least one movable element of the actuator and the stop means takes place at each complete release of the service braking.

REFERENCES

1drum brake2backing plate3first shoe4second shoe3a,4awebs3b,4bbrake linings6hydraulic wheel cylinder7wear adjustment connecting rod8,9return springs10mechanical actuator12actuator casing13actuator bore16first element/first piston16.1head of the second piston18second element18.1longitudinal end of second element20second piston22electric motor24toothed wheel26/126stop means201spring pack202head of the second piston203top of the second pistonX, Y axese error marginj manufacturing clearancePb, Pb′ stop positionPf braking positionPr release positionUC Control unit