Vehicle drum brake and manufacturing process
By adding visco-elastic shear or additional masses to the segments of drum brakes, the issue of vibrations and noise is addressed, achieving reduced noise and consistent brake performance without extensive part modifications.
Patent Information
- Application Number
- FR2022013282
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2022-12-13
- Publication Date
- 2025-02-07
- Estimated Expiration
- 2042-12-13
AI Technical Summary
Existing drum brakes generate undesirable vibrations and noise during braking due to resonance frequencies caused by friction forces, leading to screeching noises, and previous methods to mitigate this issue are incomplete and require extensive part resizing.
Incorporating visco-elastic shear or additional masses on the segments of the drum brake to increase the segment mass and shift resonance frequencies, thereby reducing vibrations and noise.
The solution effectively reduces vibrations and noise by adjusting resonance frequencies, ensuring consistent brake performance without requiring extensive part resizing.
Smart Images
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Abstract
Description
Title of the invention: “Vehicle drum brake and manufacturing method”
[0001] The invention relates to a vehicle drum brake comprising a disc-shaped plate having an internal face to which are fixed a wheel cylinder and a support member called a fixed point, at diametrically opposite positions, a first and a second segment respectively comprising a core to the external edge of which is fixed a sole usually called a sheet metal rim, curved cylindrically and provided with a braking lining, each core having a first end bearing on a piston of the wheel cylinder and a second end bearing on the fixed point. A drum is rotatably mounted relative to the plate and provided with a peripheral friction skirt.The drum brake comprises an actuator provided with a parking brake lever which allows the vehicle to be immobilized, this lever being carried by the core of one of the segments, said lever being provided with a first end mounted free to rotate at a bore, with the first end of said core, and a second end to which is fixed one end of a brake cable, which, when tensioned, pulls the second end of the lever, causing rotation of the lever in order to separate the segments.
[0002] Each of the first ends of the cores comprises a bore provided to receive a part of the free rotational assembly of the first end of the lever with the first end of the corresponding core.
[0003] The invention also relates to a method of manufacturing such a drum brake. State of the art
[0004] A drum brake is a braking device that is arranged in a vehicle to slow down or even block the rotation of the wheel by friction. Thus, a drum brake of this type can be used as a service brake to slow down or stop the vehicle, and also as a parking brake to ensure the immobilization of the vehicle when parked.
[0005] Such a drum brake comprises a fixed plate having an internal face to which are fixed a wheel cylinder and a support member called a fixed point, at diametrically opposite positions. This plate carries a first and a second segment having ends brought into support on the wheel cylinder and on the fixed point by two springs to grip them together. The first segment comprises a sheet metal core having the shape of a crown portion, to the external edge of which is welded or crimped a sole usually called a rim made of cylindrically curved sheet metal, and intended to carry a brake lining. This core has one end resting on a piston of the wheel cylinder, and another end resting on the fixed point. The second segment has the same general structure.
[0006] These segments are radially movable to be pressed against an internal face of a rotating wheel drum so as to generate a braking torque. The wheel cylinder comprises a chamber closed by two pistons which move apart upon an increase in hydraulic pressure, to move the ends of the segments apart. In addition, a wear adjustment rod runs along the wheel cylinder, having one end resting on a lever carried by the first segment and another end resting on the core of the second segment when the brake is at rest. This rod incorporates a mechanism which increases its length as the linings wear, so that the brake control stroke remains unchanged during the life of the brake.
[0007] A lever carried by the core of the segment is actuated by an actuator which controls the parking brake. This lever has one end connected in rotation by a connection to a first end of the core, and another free end to which a brake cable head is secured. This lever bears in the vicinity of the connection on the end of the connecting rod. When the cable is tensioned, it pulls the free end of the lever which then moves away from the rim, to press on the connecting rod in order to move the segments apart so as to press them against the peripheral friction skirt of the drum.
[0008] During a braking action, the drum brake and in particular its plate undergo several forces.
[0009] First, an input force is observed at the contact between the wheel cylinder piston and the first end of the core.
[0010] Secondly, an application force is present at the contact of the brake linings with the peripheral friction skirt of the drum.
[0011] Thirdly, a braking force is exerted, in thrust, at the point of contact of the braking lining with a stop of the plate corresponding to the guide wall.
[0012] Fourth, a reaction force is exerted at the point of contact of the second end of the core with the fixed point.
[0013] The forces undergone by the platform during braking involve vibrations which generate more or less significant noises disturbing the acoustic environment of the driver.
[0014] Controlling and predicting vibrations and noise levels of braking systems have therefore become important criteria.
[0015] In the case of a braking system, the main source of excitation is the friction of the brake linings which is the origin of the squealing noise.
[0016] During a braking action, the brake linings come into contact with the peripheral friction skirt of the drum. The entire drum brake is then put vibrating and is likely to generate a squealing noise between 1 kHz and 15 kHz.
[0017] Each element constituting the drum brake has several natural modes to which a resonance frequency corresponds. The appearance of the squeal comes from the fact that a resonance frequency of a natural mode is close to the frequency of the squeal noise.
[0018] In order to reduce or even eliminate this noise, a first response consisted of isolating each of the elements of the system, then determining the natural frequency of each of the natural modes of these elements, then determining which elements have frequencies close to that of the squealing noise and finally structurally modifying each of the elements so that the resonance frequencies are far from the frequency of the squealing noise.
[0019] However, it appears that this design method does not provide complete satisfaction in all cases, since some brakes designed in this way still generate a squealing noise. In addition, this method has a huge impact on manufacturing processes since it requires resizing the parts for each brake model.
[0020] The inventors have also established that the cause of the squealing noise lies in the coupling of the natural modes due to friction forces.
[0021] This is why the inventors worked on predicting the vibration behavior of drum brakes using complex modal analysis methods using discretized finite element models. Presentation of the invention
[0022] The invention provides a drum brake in which at least one of the cores of the segments comprises means for damping by friction, viscoelastic shear or other means and / or one or more additional masses fixed to said core so as to increase the mass of said segment with the aim of thus shifting the natural frequencies of the segment, and / or so as to dampen the vibrations of the segment when the drum brake is in service.
[0023] More particularly, the invention relates to a drum brake comprising a disc-shaped plate having an internal face to which are fixed a wheel cylinder and a support member called a fixed point, at diametrically opposite positions, a first and a second segment respectively comprising a core to the external edge of which is fixed a sole usually called a sheet metal rim, curved cylindrically and provided with a braking lining, each core comprising a first end bearing on a piston of the wheel cylinder and a second end bearing on the fixed point, the drum brake comprising an actuator provided with a parking brake lever which allows the vehicle to be immobilized, this lever being carried by the core of one of the segments, said lever being provided with a first end mounted free to rotate at a bore, with the first end of said core, and a second end to which is fixed one end of a brake cable, which when tensioned, pulls the second end of the lever, causing rotation of the lever in order to separate the segments, each of the first ends of the cores comprising a bore provided to receive a part of the free-rotating mounting of the first end of the lever with the first end of the corresponding core, the drum brake comprising means for reducing vibrations, which are fixed on at least one of the cores of the segments.
[0024] Various embodiments of the invention are provided, integrating according to all of their possible combinations the different optional characteristics set out here.
[0025] According to a first aspect of the invention, the means for reducing vibrations comprise one or more additional masses fixed to at least one of the cores of the segments so as to increase the mass of said segment, thus shifting the natural frequencies of the segment, and / or so as to dampen vibrations when the drum brake is in service.
[0026] According to a second aspect of the invention, the means for reducing vibrations comprise vibration damping means such as friction or viscoelastic shear dampers, fixed to at least one of the cores of the segments.
[0027] According to a first embodiment, the means for reducing vibrations are fixed to at least one of the cores of the segments by gluing, welding, screwing, riveting, or crimping.
[0028] According to a second preferred embodiment, the drum brake comprises a first washer forming an additional mass, and fixed on one of the bores of the first ends of the cores.
[0029] According to this preferred embodiment, the first washer forming an additional mass is advantageously fixed to the bore of the first end of the core carrying the lever, by means of the part of the free rotational mounting of the first end of the lever with the first end of the corresponding core.
[0030] According to a variant of this preferred embodiment, the drum brake comprises a first and a second washer each forming an additional mass, and each fixed respectively on the bore of the first ends of the cores.
[0031] Preferably, the means for reducing vibrations comprise one or more additional masses representing a total mass of between 15 and 40% of the mass of the segment.
[0032] Advantageously, the means for reducing vibrations comprise one or several additional steel masses so as to significantly increase the mass of the core and thus ensure a sufficient shift in the natural frequencies of the segment.
[0033] According to an improvement, the means for reducing vibrations comprise one or more additional masses made of a damping material for attenuating vibrations, such as an elastomer.
[0034] The invention also relates to a method for manufacturing a drum brake in accordance with an embodiment of the invention, the means for reducing vibrations comprising one or more additional masses, in which at least:
[0035] - at a stage of determining the resonance frequencies of the natural modes of the segments and all other parts making up the drum brake,
[0036] - at a step of determining the value of the at least one additional mass as well as its positioning on the cores of the segments, so as to distance the resonance frequencies of the segments from the resonance frequencies of all the other parts constituting the drum brake,
[0037] - at a step in which the at least one additional mass is fixed on the core cor respondent.
[0038] Preferably, the ratio (R) between the highest resonant frequency and the lowest resonant frequency is at least equal to 1.12 and preferably greater than 1.15. Brief description of the drawings
[0039] 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:
[0040] [Fig-1]: [Fig.l] represents a plan view of a drum brake according to the state of the technique, intended to be mounted on a motor vehicle wheel;
[0041] [Fig.2]: [Fig.2] represents a perspective view of a parking brake lever of the drum brake according to the state of the art;
[0042] [Fig.3]: [Fig.3] represents a plan view of the segments of a drum brake according to the state of the art, the right segment carrying a parking brake lever;
[0043] [Fig.4]: [Fig.4] represents a sectional view of the first end of the segments of a drum brake according to the state of the art, the right segment carrying a parking brake lever;
[0044] [Fig.5]: [Fig.5] represents a plan view of a drum brake according to the invention, intended to be mounted on a motor vehicle wheel;
[0045] [Fig.6]: [Fig.6] represents a plan view of the segments of a drum brake according to the invention, the straight segment carrying a parking brake lever;
[0046] [Fig.7]: [Fig.7] represents a sectional view of the first end of the segments of a drum brake according to the invention, the right segment carrying a parking brake lever. Description of the embodiments
[0047] A drum brake 1 according to the state of the art is shown in [Fig. 1]. Such a drum brake 1 comprises a fixed plate 2 having an internal face to which are fixed a wheel cylinder 6 and a support member called fixed point 7, at diametrically opposite positions. This plate 2 carries a first and a second segment 3 and 4 having ends brought into support on the wheel cylinder 6 and on the fixed point 7 by two springs 8 and 9 to clamp them together. The first segment 3 comprises a core 12A made of sheet metal having the shape of a crown portion, to the outer edge of which is welded or crimped a sole usually called a rim 13 made of cylindrically curved sheet metal, and which carries a brake lining 14. This core 12A comprises a first end 15A bearing on a piston of the wheel cylinder 6, and a second end 16A bearing on the fixed point 7.
[0048] Similarly, the second segment 4 comprises a core 12B made of sheet metal having the shape of a crown portion, to the outer edge of which is welded or crimped a sole usually called a rim 13 made of cylindrically curved sheet metal which carries a brake lining 14. This core 12B comprises a first end 15B bearing on a piston of the wheel cylinder 6, and a second end 16B bearing on the fixed point 7.
[0049] The drum brake also comprises a drum (not shown in the figures) mounted to rotate relative to the plate 2 and provided with a peripheral friction skirt.
[0050] The segments 3 and 4 are radially movable to be pressed against an internal face of the rotating drum so as to generate a braking torque.
[0051] The wheel cylinder 6 comprises a chamber closed by two pistons which move apart upon an increase in the hydraulic pressure, to move the ends of the segments 3, 4 apart. In addition, a wear compensation rod 17 runs along the wheel cylinder 6 and has a first end 18 bearing on a lever 21 carried by the first segment 3 and a second end 19 bearing on the core of the second segment when the brake is at rest. This rod 17 incorporates a mechanism which increases its length as the linings wear, so that the brake control stroke remains unchanged during the life of the brake.
[0052] As shown in Figures 2, 3 and 4, the lever 21 carried by the core 12 of the segment 3 is actuated by an actuator which controls the parking brake. This lever 21 comprises a first end 24 linked in rotation by a connection 22 to a first end 15A of the core 12A, and a second free end 23 to which a brake cable head 5 is secured. The cable 5 is housed partly in guide means such as a helical spring 26 carried by the plate 2 on its internal face.
[0053] This lever 21 is supported in the vicinity of the connection 22 on the end 18 of the connecting rod 17. When the cable is put under tension, it pulls the free end 23 of the lever 21 which then moves away from the rim 13, to press on the connecting rod 17 in order to move the segments 3 and 4 apart so as to press them against the drum.
[0054] The actuating lever 21 is formed by a plate extending longitudinally, and more particularly intended to extend, once mounted in the drum brake, in a plane parallel to the plate 2.
[0055] As shown in Figures 5 and 6 and in accordance with the invention, the drum brake comprises means for reducing or canceling unwanted vibrations and noise, typically damping means by friction, shear of elastomeric materials, viscoelasticity or the like and / or one or more additional masses 29, 29A, 29B fixed to at least one of the cores of the segments 3, 4.
[0056] The presence of these additional masses induces an increase in the mass of the segment(s) 3, 4, which has the consequence of shifting the natural frequencies of the segment(s) provided with the additional masses.
[0057] Thus, it is possible to adjust the value of the additional mass so as to shift the natural frequencies of the segment more or less.
[0058] Advantageously, the additional mass(es) 29, 29A, 29B are made of steel so as to significantly increase the mass of the segment and thus ensure a sufficient shift in the natural frequencies of the segment.
[0059] Advantageously, these additional masses may have properties making it possible to dampen vibrations when the drum brake is in service.
[0060] Thus, it is possible to adjust the composition of the additional mass so as to adjust its damping properties.
[0061] Advantageously, the additional mass(es) 29, 29A, 29B are made of a damping material to attenuate vibrations, such as an elastomer.
[0062] According to a first embodiment, the additional mass(es) 29 are fixed by gluing, welding, screwing, riveting, crimping on at least one core 12A, 12B.
[0063] Preferably, the additional mass(es) are fixed to the core of the segment carrying the lever 21 insofar as the connection between this segment and the lever constitutes a source of vibrations.
[0064] According to a second embodiment, a first washer 29A, 29B forming an additional mass is fixed on one of the bores 22A, 22B of the first ends 15A, 15B of the cores 12A, 12B, for example by means of a screw.
[0065] In the case where it is the first end 15A of the core 12A carrying the lever 21, it is advantageous to use, as shown in [Fig.7], the part 30 of the free rotational mounting of the first end 24 of the lever 21 with the first end of the core 12A.
[0066] According to a variant of the second embodiment shown in Figures 6 and 7, the drum brake comprises a first and a second washer 29A, 29B each forming an additional mass, and each fixed respectively on the bore 22A, 22B of the first ends 15A, 15B of the cores 12A, 12B.
[0067] It is understood that the use of the bores 22A, 22B makes it possible to simplify the fixing of the additional masses on the cores of the segments and to attenuate the vibrations at the level of the connection between the segment 3 and the lever 21.
[0068] In order to ensure a sufficient shift in the natural frequencies of the segment, all of the additional masses represent a mass of between 15 and 40% of the mass of the segment.
[0069] The invention also proposes steps which are incremented following the conventional steps of manufacturing a drum brake.
[0070] Thus, it is planned to proceed according to the invention to at least one step of determining the resonance frequencies of the natural modes of the segments 3, 4, and of all the other parts constituting the drum brake.
[0071] Then, the value of the additional masses 29, 29A, 29B and / or the vibration dampers is determined as well as their positioning on the cores of the segments 3, 4, so as to distance the resonance frequencies of the segments from the resonance frequencies of all the other parts constituting the drum brake.
[0072] Then, the location where the additional mass(es) 29, 29A, 29B must be fixed is defined.
[0073] Finally, the additional masses 29, 29A, 29B are fixed at the determined location on the cores 12A, 12B.
[0074] Preferably, the ratio (R) between the highest resonant frequency and the lowest resonant frequency is at least equal to 1.12 and preferably greater than 1.15.
[0075] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention.
[0076] Nomenclature
[0077] 1 - drum brake
[0078] 2 - fixed tray
[0079] 3 - first segment
[0080] 4 - second segment
[0081]
[0082]
[0083]
[0084]
[0085]
[0086]
[0087]
[0088]
[0089]
[0090]
[0091]
[0092]
[0093]
[0094]
[0095]
[0096]
[0097]
[0098] 5 - brake cable 6 - wheel cylinder 7 - support member called fixed point 8, 9 - springs 12A, 12B - webs 13 - base / rim 14 - brake lining 15A, 15B - first ends of the webs resting on the wheel cylinder 16A, 16B - second ends of the webs resting on the fixed point 17 - wear adjustment rod 18, 19 - ends of the rod 21 - parking brake operating lever 23 - free end of the lever 24 - rotationally linked end of the lever 26 - helical spring 27A, 27B - support element 29A, 29B, 29 - additional vibration damping masses 30 - part of the free rotational mounting of the first end of the lever with the first end of the core.
Claims
Claims
1. Drum brake (1) comprising: - a disc-shaped plate (2) having an internal face to which are fixed a wheel cylinder (6) and a support member (7) called a fixed point, at diametrically opposite positions, - a first and a second segment (3, 4) respectively comprising a core (12A, 12B) to the external edge of which is fixed a sole (13) usually called a sheet metal rim, curved cylindrically and provided with a brake lining (14), each core (12A, 12B) having a first end (15A, 15B) bearing on a piston of the wheel cylinder (6) and a second end (16A, 16B) bearing on the fixed point (7), - the drum brake comprising an actuator provided with a parking brake lever (21) which allows the vehicle to be immobilized, this lever (21) being carried by the core (12A) of one of the segments (3, 4), said lever being provided with a first end (24) mounted free to rotate at a bore (22A), with the first end (15A) of said core (12A), and a second end (23) to which one end of a brake cable (5) is fixed, which, when tensioned, pulls the second end (23) of the lever (21), causing a rotation of the lever (21) in order to separate the segments (3, 4), - each of the first ends (15A, 15B) of the cores (12A, 12B) comprising a bore (22A, 22B) provided to accommodate a part (30) of the free rotational assembly of the first end (24) of the lever with the first end of the corresponding core, characterized in that the drum brake comprises means for reducing vibrations, fixed on at least one of the cores of the segments (3, 4), the brake comprising a first washer (29A, 29B) forming an additional mass, and fixed on at least one of the bores (22A, 22B) of the first ends (15A, 15B) of the cores (12A, 12B).
2. Drum brake (1) according to claim 1, characterized in that the means for reducing vibrations comprise one or more additional masses (29, 29A, 29B) fixed on at least one of the cores of the segments (3, 4) so as to increase the mass of said segment and thus shift the natural frequencies of the segment, and / or so as to dampen vibrations when the drum brake is in service.
3. Drum brake (1) according to claim 1 or 2, characterized in that the means for reducing vibrations comprise vibration damping means such as friction or viscoelastic shear dampers, fixed on at least one of the cores of the segments (3, 4).
4. Drum brake according to any one of the preceding claims, characterized in that the means for reducing vibrations are fixed to at least one of the cores of the segments (3, 4) by gluing, welding, screwing, riveting, or crimping.
5. Drum brake according to any one of the preceding claims, characterized in that it comprises a first washer (29A, 29B) forming an additional mass, and fixed on the bore (22A) of the first end (15A) of the core (12A) carrying the lever (21), by means of the part of the free rotational mounting of the first end (24) of the lever with the first end of the corresponding core.
6. Drum brake according to any one of the preceding claims, characterized in that it comprises a first and a second washer (29A, 29B) each forming an additional mass, and each fixed respectively on the bore (22A, 22B) of the first ends (15A, 15B) of the cores (12A, 12B).
7. Drum brake according to any one of the preceding claims, characterized in that the means for reducing vibrations comprise one or more additional masses representing a total mass of between 15 and 40% of the mass of the segment.
8. Drum brake according to any one of the preceding claims, characterized in that the means for reducing vibrations comprise one or more additional steel masses so as to significantly increase the mass of the core and thus ensure a sufficient shift in the natural frequencies of the segment.
9. Drum brake according to any one of the preceding claims, characterized in that the means for reducing vibrations comprise one or more additional masses made of a damping material for attenuating vibrations, such as an elastomer.
10. A method of manufacturing a drum brake according to one of any of the preceding claims, the means for reducing vibrations comprising one or more additional masses, characterized in that at least: - at a stage of determining the resonance frequencies of the natural modes of the segments (3, 4), and of all the other parts constituting the drum brake, - at a step of determining the value of the at least one additional mass (29, 29A, 29B) as well as its positioning on the cores (12A, 12B) of the segments, so as to distance the resonance frequencies of the segments (3, 4) from the resonance frequencies of all the other parts constituting the drum brake, - at a step in which the at least one additional mass (29, 29A, 29B) is fixed on the corresponding core.
11. Method of manufacturing a drum brake according to the preceding claim, characterized in that the ratio (R) between the highest resonant frequency and the lowest resonant frequency is at least equal to 1.12 and preferably greater than 1.15.