Drum brake actuating device incorporating a ball screw mechanism

Abstract

Device for actuating a drum brake incorporating a ball screw mechanism 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, characterized in that said actuating means (6) comprise a worm screw (60) mechanically driven by the rotary motor, as well as a ball screw nut mechanism (62, 63A, 63B) in connection (64A, 64B) with the end of the at least one segment, said ball screw nut mechanism being multi-threaded.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 abstract: Fig. 1.

Description

Title of the invention: Device for actuating a drum brake incorporating a ball screw mechanism

[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. 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 in abutment against the friction track. As is known, these actuation 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 support 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, said actuating means comprising a worm screw mechanically driven by the rotary motor, as well as a ball screw nut mechanism connected to the end of the at least one segment, said mechanism of ball screw nut 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 ball screw nut mechanism so as to exert or release support on the end of the at least one segment, the at least one screw cooperating in screwing with said nut along multiple threads.

[0018] Various embodiments of the invention are provided, integrating according to all of their possible combinations the different optional characteristics set out here.

[0019] According to a first preferred aspect of the invention, the at least one screw cooperates in screwing with said nut along two threads.

[0020] Advantageously, the two threads are out of phase by 180 degrees.

[0021] The two ball recirculation circuits are arranged in the body of the nut of the ball screw nut mechanism preferably in a diametrically opposed manner.

[0022] This configuration makes it easier to install the ball recirculation circuits in the nut.

[0023] According to a second preferred aspect of the invention, the ball screw nut mechanism comprises two reverse pitch screws, each connected respectively to the end of a first and a second braking segment.

[0024] The use of a double-threaded ball screw nut mechanism makes it possible to obtain a translation of the ball screw twice as long for one revolution, which implies that the speed of the rotary motor can be divided by two.

[0025] This also implies that by maintaining the original speed of the rotary motor, a response time divided by two is obtained.

[0026] In other words, for the same amount of energy, we obtain a segment spacing twice as large for a reaction time half as long.

[0027] According to a second preferred aspect of the invention, the worm screw is a globular screw.

[0028] Preferably, the globular screw is configured to engage at least 20% of the circumference of the worm screw.

[0029] 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.

[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 segment spacing.

[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. List of figures

[0033] 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:

[0034] [Fig-1] is a schematic view of a drum brake, in the axis of rotation of the drum.

[0035] [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.

[0036] [Fig.3] is a schematic perspective view of [Fig.2].

[0037] [Fig.4] is a partial schematic perspective view of a gear mechanism of a actuating device according to one embodiment of the invention.

[0038] [Fig.5] is a partial schematic perspective view of a ball mechanism of an actuating device according to an embodiment of the invention.

[0039] [Fig.6] is another partial schematic perspective view of a ball mechanism of an actuating device according to an embodiment of the invention.

[0040] [Fig.7] is another schematic view of a meshing of an actuating device according to an embodiment of the invention. Description of an exemplary embodiment

[0041] 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.

[0042] 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.

[0043] 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 about 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.

[0044] 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.

[0045] 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.

[0046] In this example, the drum brake is arranged to operate in simplex mode when actuated as a service brake.

[0047] 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).

[0048] 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 an inner surface of the drum.

[0049] 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.

[0050] The actuating means 6 comprise a mechanically driven endless screw 60 only by the rotary motorization around the axis (z), as well as a ball screw nut mechanism in connection with the respective ends 15A, 15B of the segments 3A, 3B.

[0051] The ball screw nut 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 nut mechanism so as to exert or release support on the ends 15A, 15B of the segments.

[0052] Ball screw mechanisms allow a rotational movement to be transformed into a translational movement.

[0053] The use of ball screw mechanisms makes it possible to significantly reduce friction compared to a simple screw-nut mechanism. These ball screw mechanisms are particularly relevant for power transmissions and precision movements.

[0054] 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.

[0055] Ball screw mechanisms are also preferred when reversibility of the rotation / translation conversion is desired.

[0056] 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).

[0057] According to the invention, said ball screw nut mechanism has multiple threads. In other words, the nut 62 cooperates in screwing with the at least one screw 63A, 63B according to a thread with several threads, in the sense that in the distance of a helical pitch, comprises this plurality of threads. The nut also comprises several ball recirculation circuits 630 arranged inside the nut and each dedicated to one of the threads.

[0058] The helical pitch, or axial feed per revolution, expresses the distance over which the screw is extracted from the nut (or driven in) when the nut is rotated 360°. Therefore, in the case of a single-thread thread, the feed is identical to the pitch of the profile while for a multi-thread thread, the feed is equal to the product of the pitch of the profile by the number of threads.

[0059] Preferably, and in relation to figures 2, 3, 5 and 6, the ball screw nut mechanism comprises two threads.

[0060] The two threads are preferably 180 degrees out of phase, in the sense that they "start" and "end" with a 180 degree offset.

[0061] Thus, the ball screw nut mechanism comprises two recirculation circuits 620 of the balls 630, arranged in the body of the nut 62 of the ball screw nut mechanism. in a diametrically opposed way.

[0062] This configuration makes it easier to install the ball recirculation circuits in the nut.

[0063] Preferably, and in relation to figures 2, 3, 5 and 6, the ball screw nut 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.

[0064] 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 in the figures which is fixed relative to a support plate.

[0065] The connection 64A between the end 15A of the first segment 3A and the connection 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).

[0066] According to another embodiment not shown in the figures, the ball screw nut 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.

[0067] The use of a double-threaded ball screw nut mechanism makes it possible to obtain a translation of the ball screw twice as long for one revolution, which implies that the speed of the rotary motor can be divided by two.

[0068] This also implies that by maintaining the original speed of the rotary motor, a response time divided by two is obtained.

[0069] In other words, for the same amount of energy, we obtain a segment spacing twice as large for a reaction time half as long.

[0070] The meshing of the toothed wheel 61 can be achieved by a cylindrical worm screw as shown in [Fig.5], this worm screw being driven directly by the rotary motor.

[0071] However, according to a preferred embodiment and shown in [Fig.4], the worm screw 60, meshing with the toothed wheel 61, is a globoid screw, the axis of rotation of which is the (z) axis.

[0072] 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.

[0073] In other words, globular screws are screws whose diameter is larger at the ends than in the center. They allow torque to be transmitted with less play and resistance.

[0074] As shown in Figures 4 and 7, the globular screw 60 is configured to mesh with at least 20% of the circumference of the worm screw 61.

[0075] 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.

[0076] The meshing of the toothed wheel 61 with the worm screw 60 forms a wheel and worm screw mechanism, which 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. Thus, the brake remains in particular in an applied position which ensures the parking brake function (simplex in this embodiment).

[0077] The worm wheel mechanism allows for particularly quiet and shock-free engagement.

[0078] However, it will be necessary to adjust the low-friction material pairs (example: steel screw with bronze wheel) and the lubrication to minimize friction.

[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 abutment ends of the segments from each other, while their movable ends would remain in contact with each other by means of an intermediate element movable relative to the plate, and said abutment ends would come to bear only one at a time against an anchoring element fixed relative to the plate. Nomenclature

[0083] 1 drum brake

[0084] 12A, 12B segment souls

[0085]

[0086]

[0087]

[0088]

[0089]

[0090]

[0091]

[0092]

[0093]

[0094]

[0095]

[0096]

[0097]

[0098]

[0099] 13A, 13B soles / rims 14A, 14B friction linings 15A, 15B upper ends of segments 16A, 16B lower ends of segments 2 support plate 3A, 3B segments 4 fixed point 6 actuating means 60 worm screw 61 toothed wheel 62 nut of the ball screw mechanism 620 recirculation circuits of the ball screw mechanism 63A, 63B ball screws of the ball screw mechanism 630 balls of the ball screw mechanism 64A, 64B connection between the upper ends of the segment and the associated ball screw

Claims

Claims

1. 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 (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 ball screw nut mechanism (62, 63A, 63B) in connection (64A, 64B) with the end (15A, 15B) of the at least one segment, said ball screw nut mechanism being provided with at least a screw (63A,63B) cooperating in screwing with a nut (62) on which is mounted a toothed wheel (61) meshed with 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 ball screw nut mechanism so as to exert or release support on the end (15A, 15B) of the at least one segment, the at least one screw cooperating in screwing with said nut along multiple threads.,

2. Device for actuating a drum brake according to claim 1, characterized in that the at least one screw cooperates in screwing with said nut along two threads.

3. Device for actuating a drum brake according to claim 2, characterized in that the two threads are out of phase by 180 degrees.

4. Device for actuating a drum brake according to claim 2 or 3, characterized in that the ball screw nut mechanism comprises two recirculation circuits (620) of the balls, arranged in the body of the nut (62) of the ball screw nut mechanism in a diametrically opposite manner.

5. Device for actuating a drum brake according to any one of the preceding claims, characterized in that the ball screw nut 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 segment.

6. Device for actuating a drum brake according to any one of the preceding claims, characterized in that the worm screw (60) is a globular screw.

7. Device for actuating a drum brake according to the preceding claim, characterized in that the globular screw is configured to engage at least 20% of the circumference of the worm screw (61).

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 of a brake according to claim 8, for performing a service brake braking function.

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