Device for actuating a drum brake incorporating a wheel and worm mechanism, associated method and vehicle.

Abstract

Device for actuating a drum brake incorporating a wheel and worm mechanism, associated method and vehicle. The invention relates to a device for actuating a drum brake for a vehicle, in particular a road vehicle, comprising actuating means (6) fixed to a plate (2) and mechanically driven by a rotary motor around a drive axis, so as to separate one end (15A, 15B) of at least one braking segment (3A, 3B) mounted on the plate (2), itself movable in rotation relative to the drum, and to place said segment against a friction track carried by an inner surface of the drum, said worm (60) comprising a multi-start type thread. The invention also relates to a drum brake and to a vehicle comprising such an actuating device, as well as to a use of such an actuating device. Figure for the abstract: Fig. 1

Description

Title of the invention: Device for actuating a drum brake incorporating a wheel and worm screw mechanism, associated method and vehicle.

[0001] The invention relates to a device for actuating a drum brake for a vehicle, in particular a road vehicle, comprising actuating means fixed to a plate and mechanically driven by a rotary motor around a drive axis, so as to separate one end of at least one braking segment mounted on the plate, itself movable in rotation relative to the drum, and to place said segment against a friction track carried by an inner surface of the drum.

[0002] The invention also relates to a drum brake comprising such an actuating device as well as to its use for a service braking function in simplex mode, and to its manufacturing method. State of the art

[0003] In most current automobiles, braking is provided by drum brakes or disc brakes, and often both with disc brakes at the front and drum brakes at the rear.

[0004] Drum brakes are typically used in motor vehicles to provide three types of braking:

[0005] - service braking, which consists of slowing down and / or immobilizing the vehicle, ty stinging via a brake pedal;

[0006] - parking braking, which allows the vehicle to be immobilized when stationary and to to keep immobilized continuously for long periods of time, typically by operating a hand lever or control button;

[0007] - emergency braking, which consists of slowing down and / or immobilizing the vehicle in the event of failure of the service brake, and which is typically provided by the same device as the parking brake.

[0008] A typical drum brake comprises a drum coaxial with the wheel, mounted integrally on the wheel, and having a skirt carrying an internal friction track. This skirt covers a mechanism mounted on a support plate, which is coaxial with the axis of the wheel hub and is integral with the half-train carrying the hub. This mechanism comprises two segments in arcs of a circle mounted face to face around the axis of rotation of the drum. On their external surface, friction linings press on the drum track when they are moved outwards.

[0009] To obtain braking, these segments are separated by actuating means. which press on one of their ends to place the linings against the friction track. As is known, these actuating means are most often achieved by a "wheel cylinder" fixed to the plate and formed by a hydraulic jack, often with two opposing pistons.

[0010] It is also known to electrically activate the braking segments of a drum brake.

[0011] However, the actuators still have drawbacks or needs for improvement, for example concerning the size and weight of the motors and actuators, which are part of the unsprung elements and must be arranged close to the wheel hub.

[0012] In particular, electric motors often have a significant mass, which increases with the required power. Their high rotational speed, at least for the most economical motors and in the context of very low voltage of a vehicle, also requires a significant speed reduction to obtain the necessary actuating force.

[0013] Thus, it is necessary to produce actuation means having improved characteristics, particularly in terms of efficiency.

[0014] An aim of the present invention is to propose a drum brake actuating device which is motorized, which has good performance in terms of size and / or unsprung mass, but also in terms of braking load performance and / or speed of application, while showing sufficient reliability and economy characteristics.

[0015] Another object of the present invention is to propose an economical device, offering a reduced number of parts, ease and economy of manufacture and / or assembly and / or maintenance, while retaining the advantages of the simplex mode.

[0016] The invention also seeks to allow a variety and ease of adaptation of this device in a vehicle and flexibility of integration in a process of assembly of such a vehicle. Statement of the invention

[0017] The invention relates in particular to a device for actuating a drum brake for a vehicle, in particular a road vehicle, comprising actuating means fixed to a plate and mechanically driven by a rotary motor around a drive axis, so as to separate an upper end of at least one braking segment mounted on the plate, itself movable in rotation relative to the drum, and to place said segment against a friction track carried by an inner surface of the drum, characterized in that said actuating means comprise a worm screw mechanically driven by the rotary motor, as well as that a screw nut mechanism in connection with the end of the at least one segment, said screw nut mechanism being provided with at least one screw cooperating in screwing with a nut on which is mounted a toothed wheel meshed by said worm screw, so that the rotation of said worm screw causes, depending on its direction of rotation, the unscrewing or screwing of the screw nut mechanism so as to exert or release support on the end of the at least one segment, said worm screw comprising a multi-start type thread.

[0018] The transmission ratio r being usually defined as the ratio between the number of teeth Zv of the worm screw and the number of teeth Zr of the wheel, i.e. r = Zr / Zv, it follows that the use of a thread with n starts, i.e. with n threads, makes it possible to divide the transmission ratio by n.

[0019] It is also possible to reduce the number of teeth on the wheel, which makes it possible to obtain a wheel with a smaller footprint for an unchanged transmission ratio.

[0020] The use of a multi-start type thread makes it possible to improve resistance to stresses with a gain in terms of wear, to transmit a constant torque which also presents a gain in terms of shocks and consequently noise. This configuration also allows great flexibility of installation without increasing the number of parts.

[0021] Various embodiments of the invention are provided, integrating according to all of their possible combinations the different optional characteristics set out here.

[0022] According to a first preferred aspect of the invention, the thread of the worm screw comprises two thread starts offset by 180 degrees.

[0023] According to a first embodiment, the worm screw is a cylindrical screw.

[0024] According to a second embodiment, the worm screw is a globular screw.

[0025] Preferably, the globular screw is configured to engage at least 20% of the circumference of the worm screw.

[0026] The use of a globular spur gear instead of a simple spur gear allows more than one tooth to be used to transmit torque, thereby reducing mechanical stress and wear over the service life.

[0027] According to another preferred aspect of the invention, the helix angle [3r] of the toothed wheel is less than 6 degrees, so that the wheel and worm mechanism is irreversible, i.e. self-locking.

[0028] According to yet another preferred aspect of the invention, the helix angle [3r of the toothed wheel is greater than 10 degrees, so that the wheel and worm mechanism is reversible.

[0029] Thus, it is possible to adapt the actuating device with either a function of reversibility is an irreversibility function, simply by changing the nut carrying the toothed wheel and the worm screw.

[0030] The invention also relates to a drum brake for a vehicle or vehicle subassembly, in particular a road vehicle, comprising segments provided with friction linings capable of being separated from one another to interact by friction with a drum to perform a braking function, characterized in that it comprises an actuating device in accordance with one of the embodiments of the invention, which is arranged to produce said separation of the segments.

[0031] The invention also relates to a vehicle or vehicle subassembly comprising an actuating device in accordance with one of the embodiments of the invention or a brake equipped with such a device.

[0032] The invention also relates to a use of such an actuating device or such a brake, to perform a first service brake braking function.

[0033] The invention also relates to a method for manufacturing an actuating device or a brake according to an embodiment of the invention, for performing a service brake braking function, the method comprising at least one step in which a helix angle [3r] of the toothed wheel is chosen to be less than 6 degrees, so that the worm wheel mechanism is irreversible, or greater than 10 degrees, so that the worm wheel mechanism is reversible. List of figures

[0034] Other features and advantages of the invention will emerge from the detailed description of a non-limiting embodiment, and from the appended drawings in which:

[0035] [Fig-1] is a schematic view of a drum brake, in the axis of rotation of the drum.

[0036] [Fig.2] is a partial schematic view of a drum brake, in the axis of rotation of the drum, illustrating an actuating device according to an embodiment of the invention.

[0037] [Fig.3] is a schematic perspective view of [Fig.2].

[0038] [Fig.4] is a schematic view of a meshing of an actuating device in accordance with an embodiment of the invention. Description of an exemplary embodiment

[0039] The embodiment described here corresponds to an actuating device according to the invention, which is implemented as a service brake actuator, within a drum brake operating in simplex mode.

[0040] It should be noted that all the characteristics of the actuating device, presented here as the first actuator within a drum brake can also be implemented in a similar or even identical actuator to produce other types of drum brake.

[0041] With reference to [Fig.l], the drum brake 1 causes a braking torque between the drum (not shown here) and a plate 2 extending in a plane defined by the axes (x) and (y) in rotational movement relative to each other around an axis of rotation (z). In a conventional road vehicle, the plate 2 is fixed in rotation on the chassis of the vehicle, generally by means of a suspended train or half-train. The drum is integral with the wheel, and is fixed in translation and guided in rotation around the axis (z) by the hub and its bearings, not shown here.

[0042] In service brake mode, the braking torque is created by absorption of energy under the effect of friction between: - on the one hand, the friction track carried by an inner surface of said drum, - and on the other hand friction linings 14A, 14B carried respectively by a first and a second segment 3A, 3B.

[0043] This friction is likely to be obtained by spreading the segments outwards under the effect of actuating means 6 fixed to the plate 2. From the rest position, the actuating means 6 thus bring the mechanism into the service braking position, and the return to the rest position can also be achieved under the effect of said actuating means 6, or by means of return springs which return the ends 15A, 15B of the segments 3A, 3B to their initial position when the actuating means are deactivated. Each of the segments 3A, 3B comprises a sheet metal core 12A, 12B having the shape of a crown portion, to the outer edge of which is welded or crimped a sole usually called a rim 13A, 13B made of cylindrically curved sheet metal, and intended to carry a friction lining 14A, 14B.

[0044] In this example, the drum brake is arranged to operate in simplex mode when actuated as a service brake.

[0045] According to the simplex mode, during a braking operation, the actuating means 6 simultaneously separate the upper ends 15A and 15B of the segments 3A and 3B from each other. Such a separation of the ends 15A and 15B simultaneously causes a pivoting of the segments 3A and 3B in the plane (x, y).

[0046] The actuating means 6 are therefore fixed to the support plate 2 and mechanically driven by a rotary motor around a drive axis, so as to separate the ends 15A, 15B of the braking segments 3A, 3B, themselves mounted on the plate 2, itself movable in rotation relative to the drum, and to place said ends of the segments against a friction track carried by a inner surface of the drum.

[0047] At the opposite end 16A, 16B, called the lower end or stop end, each segment transmits the braking torque to the plate 2 by an anchoring element 4 secured to the plate, and thus forming a stop for this segment. In this example, the anchoring element of the two segments can be produced by a housing provided with an actuator provided to actuate a parking brake function or an emergency brake function.

[0048] The actuating means 6 comprise a worm screw 60 mechanically driven by the rotary motor around the axis (z), as well as a ball screw mechanism connected to the respective ends 15A, 15B of the segments 3A, 3B.

[0049] The ball screw mechanism is provided with a toothed wheel 61 meshed in rotation around the axis (x), by said worm screw 60, so that the rotation of the worm screw 60 causes, depending on its direction of rotation, the unscrewing or screwing of the ball screw mechanism so as to exert or release support on the ends 15A, 15B of the segments.

[0050] Ball screw mechanisms allow a rotational movement to be transformed into a translational movement.

[0051] According to an alternative embodiment, the ball screw mechanism could be replaced by a screw-nut mechanism.

[0052] However, the use of ball screw mechanisms allows friction to be significantly reduced compared to a simple screw-nut mechanism. These ball screw mechanisms are particularly relevant for power transmissions and precision movements.

[0053] Replacing the friction present in a conventional screw / nut mechanism with a bearing makes it possible to reduce wear on the surfaces, and therefore mechanical play.

[0054] Ball screw mechanisms are also preferred when reversibility of the rotation / translation conversion is desired.

[0055] The ball screw mechanism used for the actuating means 6 comprises a nut 62 and at least one screw 63A, 63B, cooperating in screwing with said nut. The nut 62 and the at least one screw 63A, 63B extend along the axis (x).

[0056] Preferably, and in relation to figures 2, 3, 5 and 6, the ball screw mechanism comprises two screws 63A, 63B with reverse pitch, each connected respectively 64A, 64B with the end 15A, 15B of a first 3A and a second 3B braking segments.

[0057] The rotation of the nut 62 in one direction then causes the translation of the two screws 63A, 63B, along the axis (x) in opposite directions. The nut 62 is in sliding pivot connection with a housing not shown here which is fixed relative to a support plate.

[0058] The link 64A between the end 15A of the first segment 3A and the link 64B between the end 15B of the second segment 3B are plane support connections, so that they allow the pivoting of the segments during the translation of the ball screws 63A, 63B along the axis (z).

[0059] According to another embodiment not shown in the figures, the ball screw mechanism may comprise only one screw and one nut. In this case, the screw is in pivot connection with the end of one of the segments while the nut is also in pivot connection with the end of the other segment. The nut is not fixed relative to the support plate, since the ball screw and the nut are in translation along the axis (x) and in opposite directions.

[0060] The meshing of the toothed wheel 61 with the worm screw 60 makes it possible to obtain high reduction ratios (up to 1 / 200) and offers possibilities of irreversibility. In other words, the meshing can be self-locking in the sense that the toothed wheel 61 cannot drive the worm screw 60.

[0061] The worm wheel mechanism allows for particularly quiet and shock-free engagement.

[0062] However, it will be necessary to adjust the pairs of low-friction materials (example: steel screw with bronze wheel) and the lubrication to minimize friction.

[0063] The table below summarizes, in connection with [Fig.4], the characteristics of the wheel and worm mechanism used: angular velocity CO in rad.s 1 ; co = irN / 30 number of revolutions nn in revolutions per minute or rpm 1 number of teeth on the screw Zv Zv = 1,2,3 ... number of teeth on the wheel ZR Zv + ZR > 40 helix angle of the wheel Pr [3R + [3V = 90° helix angle of the screw Pv irreversibility if [3V < 6° direction of the helices the same for the screw and the wheel real module wheel mn normalized (see table): mn screw = mn wheel axial module screw mx mx = px / ir = mn / cos [3R =mn / sin [3V real wheel pitch Pn pn = Jtmn wheel apparent pitch Pt pt = pn / cos [3r = irmt axial pitch of the screw Px px = pt (axial pitch screw = apparent wheel pitch) helix pitch Pz pz = Zv.px pitch diameter screw dv dv = Pz / ^-tan [3r ​​and a°'875 / 3 < dv < a°'875 / l,7 wheel pitch diameter Or dR= mtZR center distance aa = ! / 2(dv + dR) actual pressure angle Qn usual value: an = 14°30', 20°, 25° and 30°; common to the screw and the wheel screw axial pressure angle Qx ax = at (wheel) screw head diameter daV daV = dv + 2mn screw foot diameter dfv dfv = dv - 2.5mn projection ha ha = mn hollow hf hf = 1.25 mn tooth height hh = 2.25 mn = ha + hf Screw length LL ± 5px to 6px

[0064] The meshing of the toothed wheel 61 can be achieved by a cylindrical worm screw, this worm screw being driven directly by the rotary motor.

[0065] However, according to a preferred embodiment and shown in [Fig.3], the worm screw 60, meshing with the toothed wheel 61, is a globoid screw, the axis of rotation of which is the (z) axis.

[0066] A globular screw is understood to mean a screw whose thread tops (and bottoms) define a toric surface. This configuration makes it possible to increase the contact surface with the toothed wheel 61.

[0067] In other words, globular screws are screws whose diameter is larger at the ends than at the center. They allow torque to be transmitted with less play and resistance.

[0068] The globular screw 60 is preferably configured to mesh with at least 20% of the circumference of the worm screw 61.

[0069] The use of a globular gear instead of a simple gear allows more than one tooth to be used to transmit torque, thereby reducing mechanical stress and wear over the service life.

[0070] According to one aspect of the invention, the worm screw 60, whether cylindrical or globular, comprises a multi-start type thread.

[0071] Preferably, the worm screw 60 has a thread with two starts, offset by 180 degrees. In other words, two threads of identical pitch and angle are produced, starting in a diametrically opposite manner.

[0072] The transmission ratio r being usually defined as the ratio between the number of teeth Zv of the worm screw and the number of teeth Zr of the wheel, i.e. r = Zr / Zv, it follows that the use of a two-start thread, i.e. with two nets allow the transmission ratio to be divided by two.

[0073] It is also possible to reduce the number of teeth on the wheel, which makes it possible to obtain a wheel of less bulk for an unchanged transmission ratio.

[0074] The use of a multi-start type thread allows in summary to improve the resistance to constraints with a gain in terms of wear, to transmit a constant torque which also presents a gain in terms of shocks and consequently noise. This configuration also allows great flexibility of implantation without increasing the number of parts.

[0075] According to another aspect of the invention, the helix angle [3r of the toothed wheel 61 is less than 6 degrees, so that the wheel and worm mechanism is irreversible. Irreversible means that the toothed wheel cannot drive the worm. This results in a self-locking mesh.

[0076] In the case where it is intended that the wheel and worm mechanism is reversible, the helix angle [3r of the toothed wheel 61 is chosen to be greater than 10 degrees. The toothed wheel 61 is a straight wheel with helical teeth. The transmission of movement is carried out between two non-current orthogonal axes.

[0077] Thus, it is possible to adapt the actuating device with either a reversibility function or an irreversibility function, simply by changing the nut carrying the toothed wheel and the worm screw.

[0078] This translates, in the case of a manufacturing method of a brake actuation device, into a step of choosing the helix angle [3r of the toothed wheel.

[0079] The actuating device according to the invention is preferably arranged in a drum brake for a vehicle or vehicle subassembly, in particular a road vehicle, to perform a service brake braking function in simplex mode, i.e. by separating the segments 3A, 3B provided with the friction linings 14A, 14B to interact by friction with the drum.

[0080] The actuating device according to the invention could however be arranged to provide another braking function, in particular a parking or emergency brake, according to a duo servo type mode, within a drum brake providing the braking function, in particular a service brake, according to a "simplex" type operation.

[0081] According to this arrangement, the actuating device would be integrated into the actuator intended to actuate a parking brake or emergency brake function.

[0082] The actuating device would then be arranged to separate the stop ends 16A, 16B of the segments from each other, while their movable ends would remain in contact with each other by means of a movable intermediate element. opposite the plate, and that said abutment ends would come to bear only one at a time against the anchoring element 4 fixed relative to the plate.

[0083] The choice of an irreversible wheel and worm mechanism is interesting for a locking function in the parking braking position. That is to say that a force received by the segments 3A, 3B is blocked since the worm cannot be driven by the toothed wheel 61. It is thus useless to keep the motorization in operation to prevent the segments 3A, 3B from returning to the rest position. Nomenclature

[0084] 1 drum brake

[0085] 12A, 12B segment souls

[0086] 13A, 13B soles / rims

[0087] 14A, 14B friction linings

[0088] 15A, 15B upper ends of the segments

[0089] 16A, 16B lower ends of the segments

[0090] 2 support trays

[0091] 3A, 3B segments

[0092] 4 fixed point

[0093] 6 actuation means

[0094] 60 worm screws

[0095] 61 gear wheel

[0096] 62 ball screw mechanism nut

[0097] 63A, 63B ball screw of the ball screw mechanism

[0098] 64A, 64B connection between the upper ends of the segment and the associated ball screw

Claims

1.

2.

3.

4.

5.

6.

7. Claims Device for actuating a drum brake (1) for a vehicle, in particular a road vehicle, comprising actuating means (6) fixed to a plate (2) and mechanically driven by a rotary motor about a drive axis (z), so as to separate an upper end (15A, 15B) of at least one braking segment (3A, 3B) mounted on the plate (2), itself movable in rotation relative to the drum, and to place said segment against a friction track carried by an inner surface of the drum, characterized in that said actuating means (6) comprise a worm screw (60) mechanically driven by the rotary motor, as well as a screw-nut mechanism (62, 63A, 63B) in connection (64A, 64B) with the end (15A, 15B) of the at least one segment, said screw-nut mechanism being provided with at least one screw (63A, 63B) cooperating in screwing with a nut (62) on which is mounted a toothed wheel (61) meshed by said worm screw (60),so that the rotation of said worm screw (60) causes, depending on its direction of rotation, the unscrewing or screwing of the screw nut mechanism so as to exert or release pressure on the end (15A, 15B) of the at least one segment, said worm screw (60) comprising a multi-start type thread., Device for actuating a drum brake according to claim 1, characterized in that the thread of the worm screw (60) has two thread starts offset by 180 degrees. Device for actuating a drum brake according to claim 1 or 2, characterized in that the worm screw (60) is a cylindrical screw. Device for actuating a drum brake according to claim 1 or 2, characterized in that the worm screw (60) is a globular screw. Device for actuating a drum brake according to the preceding claim, characterized in that the globular screw is configured to mesh at least 20% of the circumference of the worm screw (61). Device for actuating a drum brake according to any one of claims 1 to 5, characterized in that the helix angle [3r of the toothed wheel (61) is less than 6 degrees, so that the wheel and worm mechanism is irreversible. A drum brake actuating device according to any one of claims 1 to 5, characterized in that the helix angle [3r of the toothed wheel (61) is greater than 10 degrees, so that the mechanism of wheel and worm screw is reversible.

8. Drum brake for a vehicle or vehicle subassembly, in particular a road vehicle, comprising segments (3A, 3B) provided with friction linings (14A, 14B) capable of being separated from one another to interact by friction with a drum to perform a braking function, characterized in that it comprises an actuating device according to any one of the preceding claims, which is arranged to produce said separation of the segments.

9. A vehicle or vehicle subassembly comprising an actuating device according to any one of claims 1 to 7 or a brake according to claim 8.

10. Use of an actuating device according to any one of claims 1 to 7 or a brake according to claim 8, for performing a service brake braking function.

11. A method of manufacturing an actuating device according to any one of claims 1 to 7 or a brake according to claim 8, for performing a service brake braking function, characterized in that it comprises at least one step in which a helix angle [3r of the toothed wheel (61) is chosen to be less than 6 degrees, so that the wheel (61) and worm (60) mechanism is irreversible, or greater than 10 degrees, so that the wheel (61) and worm (60) mechanism is reversible.

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