Method for producing a composite brake drum

Abstract

The invention relates to a method for producing a composite brake drum (1), wherein - a friction ring (2) is produced as a metal cast part, - a brake pot (3) made of a lightweight metal alloy is cast around the friction ring (2) at least with oversized dimensions, as a result of which a composite brake drum blank with an axis of rotation (8) is produced, - the composite brake drum blank is pre-processed at least on its outer circumference (7) with oversized dimensions, - an imbalance of the pre-processed composite brake drum (1), comprising the brake pot (3) and the friction ring (2) of the pre-processed composite brake drum (1), is determined, - the outer circumference (7) of the brake pot (3) is post-processed and the rotational axis (8) of the composite brake drum (1) is displaced by a radial offset (a) towards the axis of gravity (10) such that the determined imbalance is at least partially compensated for, - the brake pot (3) is then fully circumferentially finished, and - screw openings (9) for wheel screws are introduced. As a result, the composite brake drum (1) can be balanced and produced simply, cost-effectively and in a manner which is suitable for a series production.

Description

[0001] Method for producing a composite brake drum

[0002] The present invention relates to a method for producing a composite brake drum. The invention also relates to a composite brake drum produced by such a method, as well as to a drum brake comprising such a composite brake drum and a motor vehicle, in particular an electric vehicle, comprising such a drum brake.

[0003] When a motor vehicle brakes, the braking effect is primarily provided by the brakes on the front wheels. According to the state of the art, disc brakes are usually provided on all four wheels, although in electric vehicles in particular the brakes on the rear wheels are used even less than in vehicles powered by conventional combustion engines, as the braking effect is largely achieved through recuperation in order to increase the range of the electric vehicle. This means that in electric vehicles the disc brakes on the rear wheels are used less and show greater wear due to corrosion, e.g. in the form of scoring, which requires replacement more sooner than in vehicles powered by conventional combustion engines.

[0004] One approach to preventing or reducing premature failures due to wear and tear caused by corrosion is to equip disc brakes with corrosion-inhibiting coatings; another is to use drum brakes on the rear axle instead of disc brakes.

[0005] For this reason, drum brakes are increasingly being used on the rear wheels of motor vehicles, especially electric vehicles. These easily deliver the required braking performance while being significantly less susceptible to corrosion. Another major advantage of such drum brakes is that the brake dust generated during braking remains within the drum brake, resulting in lower particulate matter emissions into the environment compared to disc brakes.

[0006] Common drum brakes typically have a brake drum made of a steel / cast iron material, which results in a considerable weight. To reduce the weight of such brake drums, one possible solution is the use of so-called composite brake drums. These consist of a friction ring made of a relatively wear-resistant steel / cast iron material, which is encased in a brake chamber made of a light metal alloy. Since a friction ring has rough sections on its outer circumference, a positive interlocking with the molten metal of the brake chamber can be achieved, thus firmly bonding the friction ring and the brake chamber.

[0007] From EP 1 292 781 A1 a method for producing a brake drum by attaching a friction element to an inner circumferential surface of a support element made of an Al alloy is known, wherein the method is divided into the following steps: producing an Al-based composite material, forming the Al-based composite material by extrusion into a cylindrical element, cutting the cylindrical element to a width of the brake drum and inserting the friction element into a casting mold and encapsulating the friction element with the Al alloy.

[0008] WO 2020 / 144250 A1 discloses an assembled composite brake drum for motor vehicles comprising a base component with a flange plane as the hub interface and a wall component. The joined components are coaxially torque-locked together via a joining interface with a centering collar, with one joint of the joining interface aligned radially with the flange plane. This allows for an assembled composite brake drum with precise concentricity.

[0009] A disadvantage of the composite brake drums known from the prior art, however, is that an imbalance in the high-density, cast-in friction ring made of a cast iron material cannot be compensated for with balance compensation cuts or holes in the light metal brake pot, which has a significantly lower density. The option of creating additional holes / balancing cuts and / or subsequently introducing corresponding weights into the brake pot also has a negative effect on the strength and heat distribution in the brake pot or friction ring, leading to corresponding hot spots, which in turn cause vibrations and increased wear. Likewise, the creation of balance compensation cuts directly on the friction element before encapsulating it with the brake pot material has a negative effect on heat distribution and also leads to hot spots, which in turn cause vibrations and increased wear.

[0010] The present invention therefore addresses the problem of providing a method for producing a composite brake drum, by means of which, in particular, the disadvantages known from the prior art can be at least reduced or completely eliminated.

[0011] This problem is solved according to the invention by the subject matter of independent claim 1. Advantageous embodiments are the subject matter of the dependent claims.

[0012] The present invention is based on the general idea of ​​compensating for an existing imbalance during the manufacture of a composite brake drum, preferably exclusively by shifting a rotational axis relative to a center of gravity axis through mass displacement, thereby at least reducing the number of weight compensation cuts or bores, and preferably even eliminating them. In the method according to the invention, a rotational axis corresponding to an original hub axis of a composite brake drum that has not been machined or has only been machined, is shifted radially toward the center of gravity axis and thus to a definitively new rotational axis after determining the imbalance of the machined composite brake drum. The imbalance can preferably be compensated for exclusively by shifting the rotational axis relative to the center of gravity axis (mass displacement).In the method according to the invention for producing a composite brake drum, a friction ring, in particular made of cast iron, is first produced as a metal casting, preferably using a centrifugal casting process. Such a friction ring can, for example, be made of gray cast iron in order to minimize wear occurring during frictional contact with a brake pad. The friction ring can also be produced using a steel casting process. In order to reduce the overall weight of the composite brake drum, the friction ring is encased in a brake pot made of a light metal alloy, at least with an oversize on a hub and on an outer circumference, preferably with an oversize at all points, thus producing a composite brake drum blank with a rotational axis. The oversize can, of course, also be provided at other points.This composite brake drum blank is then pre-machined at least on its outer circumference, where the excess dimension, in particular of 1.0 mm to 1.5 mm, is present. The pre-machining is also carried out by clamping it on the cast rotation axis. The composite brake drum blank is preferably pre-machined axially and radially on all surfaces and diameters with the aforementioned excess dimension. This means that the pre-machined composite brake drum has the described excess dimension at least for the further implementation of the method according to the invention. The composite brake drum pre-machined in this way is then clamped onto a balancing machine via the rotation axis on the hub and an imbalance of the pre-machined composite brake drum with the brake pot and the friction ring is determined.

[0013] The pre-machined composite brake drum blank is therefore clamped in the balancing machine via the rotational axis. The position of the rotational axis corresponds to the center of gravity of the composite brake drum before or after pre-machining. The position of the rotational axis can also be defined by the oversized hub of the composite brake drum blank. The composite brake drum blank can be machined in such a way that the rotational axis is not shifted before or after pre-machining. The brake pot is then remachined on the outer circumference, i.e. on an outer diameter, and the rotational axis of the composite brake drum is shifted by a radial offset a towards the center of gravity axis in such a way that the determined imbalance is at least partially compensated. The brake pot is then finish-machined, preferably over its entire circumference, with the finish-machining taking place while clamped over the remachined outer diameter.The position of the final rotation axis thus corresponds to the center of gravity, at least partially compensating for any remaining imbalances. This is easily achieved thanks to the oversize light metal alloy provided on the pre-machined composite brake drum. Screw holes for wheel bolts and, in particular, a countersunk fixing hole are then created.

[0014] With the method according to the invention, it is thus possible for the first time to easily and reliably balance a composite brake drum consisting of a friction ring with a high density and a brake pot with a significantly lower density, in particular even preferably without the need for weight compensation cuts or bores previously known from the prior art.Due to the fact that the friction ring has a significantly higher density than the brake pot, providing counterweight cuts or holes exclusively in the brake pot would be of limited or even non-existent effectiveness. For example, the aluminum used for the light metal alloy of the brake pot has only a fraction of the density of the cast iron material used for the brake ring. Therefore, a counterweight cut or hole in the light metal material intended to compensate for an imbalance in the friction ring would have to be comparatively large. Such large counterweight cuts or holes, i.e., material removal, are not even possible with conventional composite brake drums because the required material is not available on the brake pot.The method according to the invention therefore makes it possible for the first time to compensate for the imbalance of the composite brake drum by simply radially offsetting the rotational axis of the oversized and pre-machined composite brake drum toward the center of gravity axis. By shifting the rotational axis toward the center of gravity axis, the friction ring, with its heavier material than the brake pot, can also be used to compensate for the imbalance, since shifting the axis of the composite brake drum also shifts the axis of the friction ring and thus the friction ring as well. This makes it possible to preferably avoid, or at least reduce, large weight compensation cuts or bores, which have a negative impact on heat distribution in the brake drum and lead to corresponding hot spots.Likewise, weight compensation cuts or holes that have to be arranged directly on the friction ring before it is cast around the brake pot, which have a negative effect on heat distribution and also lead to hot spots, can be reduced, or preferably avoided altogether.

[0015] In an advantageous development of the method according to the invention, the rotation axis of the hub of the (pre-machined) composite brake drum is radially shifted by a radial offset a of 0.05 mm < a < 0.6 mm. Tests have shown that even such a small radial displacement of the rotation axis is sufficient to compensate for the imbalance of the composite brake drum, and in particular the imbalance of the friction ring, preferably completely.

[0016] In a particularly preferred embodiment of the method according to the invention, an aluminum alloy is used as the light metal alloy. Aluminum alloys are corrosion-resistant and significantly lighter than gray cast iron or cast iron in general, so that the components of the composite brake drum, in particular, which require little or no force to transmit, can be manufactured with such an aluminum alloy. Alternatively, a magnesium alloy can also be used as the light metal alloy. Magnesium is resilient, strong, and fully recyclable, making it ideal for weight reduction.

[0017] The advantages of aluminum and magnesium include high rigidity with a good strength-to-mass ratio, high thermal conductivity, temperature resistance, and high corrosion resistance. The high thermal conductivity of aluminum and magnesium alloys, in particular, helps prevent hot spots. The good recyclability of aluminum and magnesium also increases sustainability.

[0018] The brake chamber is preferably ground and / or turned during remachining. Additionally or alternatively, the friction ring can be remachined, particularly ground and / or turned, before being encapsulated with the light metal alloy. This is usually done on the inside of the brake ring, which will later interact with a brake pad. Grinding and / or turning can achieve a perfectly round shape for both the brake chamber and the friction ring, thus reducing wear.

[0019] In a further advantageous embodiment of the method according to the invention, material is removed from the brake pot in order to at least partially compensate for any remaining imbalance that could not be compensated for by the radial displacement of the rotation axis; this is referred to as "fine balancing" depending on the application. Such material removal can be achieved, for example, by the previously described turning or grinding process. Additionally or alternatively, at least one counterweight cut or a bore can be made, by means of which, for example, material is removed at a precisely predefined location in order to reliably compensate for any remaining small imbalance.

[0020] In a particularly preferred embodiment of the method according to the invention, the friction ring is balanced before being encapsulated with the light metal alloy to produce the brake drum. During the centrifugal casting process, the friction ring is given a comparatively rough outer surface, which allows for optimal meshing with the material, i.e., the light metal alloy, of the brake drum. However, the disadvantage of such a rough outer surface is that it can create an imbalance that must be compensated for accordingly.In the method according to the invention, such an imbalance can preferably be compensated exclusively by the radial offset a of the rotational axis. Additionally or alternatively, after the friction ring has been manufactured, counterweight cuts or holes can also be provided on it, particularly on its end face, so that it is outside the thermal load of a friction surface toward the screw-on flange. This allows, for example, pre-balancing of the friction ring, which reduces the radial offset a of the rotational axis that must be subsequently applied in the method according to the invention.

[0021] In another particularly preferred embodiment of the method according to the invention, a cast iron material, in particular gray cast iron, is used for the metal casting, in particular for centrifugal casting, of the friction ring. Gray cast iron has the great advantage of high corrosion resistance, economical production, and high compressive strength. Furthermore, its very good flow properties and extremely high wear resistance make it particularly suitable for such a friction ring. Alternatively, it is of course also conceivable for the friction ring to be manufactured from cast steel using the centrifugal casting process. In general, in centrifugal casting, material is poured into a rotating mold by a centrifugal axis and solidifies at up to 120 times the acceleration due to gravity.The comparatively high rotational forces and the solidification from the outside to the inside result in a particularly dense and pure structure, which makes components produced by centrifugal casting extremely robust and wear-resistant.

[0022] The present invention is further based on the general idea of ​​providing a composite brake drum manufactured according to the method described in the previous paragraphs. This allows the advantages described with regard to the method according to the invention to be transferred to the composite brake drum according to the invention. Specifically, these advantages lie in a comparatively simple way of producing composite brake drums of high quality and at the same time cost-effectively, which compensates for even larger imbalances.Particularly in the case of composite brake drums, in which two components with different densities are combined, namely usually a friction ring with a comparatively high density and a brake pot with a comparatively low density, compensation for an imbalance in the friction ring could only be achieved by a comparatively large removal of material from the brake pot, which is not available at all in conventional composite brake drums.

[0023] The present invention is further based on the general idea of ​​using the composite brake drum according to the invention described in the previous paragraph in a drum brake according to the invention, which makes it not only high-quality but also cost-effective to manufacture. Such a drum brake can in turn be used in a motor vehicle, in particular in an electric vehicle, which offers the great advantage that, particularly in electric vehicles, the rear wheel brakes, which are subject to little load due to the recuperation primarily used for braking, can be designed significantly more cost-effectively and also significantly more wear-resistant than would be possible with disc brakes. Disc brakes, in particular, exhibit unfavorable corrosion behavior with infrequent use, as is typically the case with the rear wheels of an electric vehicle.The use of drum brakes can also reduce the amount of particulate matter emitted into the environment, as this remains in the brake chamber and does not escape into the environment.

[0024] Further important features and advantages of the invention emerge from the subclaims, from the drawings and from the associated description of the figures based on the drawings.

[0025] It is understood that the features mentioned above and those to be explained below can be used not only in the respective combination specified, but also in other combinations or on their own, without departing from the scope of the present invention. Components mentioned above and those to be mentioned below of a higher-level unit, such as a device, a device, or an arrangement, which are designated separately, may form separate parts or components of this unit or be integral areas or sections of this unit, even if this is shown differently in the drawings.

[0026] Preferred embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description, wherein the same reference numerals refer to the same or similar or functionally identical components.

[0027] They show, schematically

[0028] Figure 1 shows a method according to the invention for producing a composite brake drum with individual process steps,

[0029] Figure 2 shows a composite brake drum produced according to the method according to the invention for a drum brake according to the invention of a motor vehicle according to the invention.

[0030] According to Figure 1, a method according to the invention for producing a composite brake drum 1 (see Figure 2) comprises a total of seven method steps A to G.

[0031] In a first process step A, a friction ring 2 is produced as a metal casting, in particular using a centrifugal casting process or a steel casting process. By producing the friction ring 2 using a centrifugal casting process, the friction ring 2 can be achieved with extremely high wear resistance and an extremely high density. During centrifugal casting, an acceleration of up to 120 times gravity is used for this purpose through a corresponding rotation of a mold forming the shape for the friction ring 2. The comparatively high centrifugal forces and the solidification directed from the outside inwards create the particularly dense and pure structure.As a material for the friction ring 2, for example, gray cast iron or cast steel can be used, wherein gray cast iron in particular has a high corrosion resistance, which is of great advantage in particular in the area of ​​drum brakes 4 in a motor vehicle 5 according to the invention, in particular in an electric vehicle, since such drum brakes 4 are often exposed to high de-icing salt loads in winter.

[0032] In the subsequent process step B, the friction ring 2 is encapsulated with a brake pot 3 made of a light metal alloy, at least with an oversize on a hub 6 and an outer circumference 7, thereby producing a composite brake drum blank with a rotational axis 8. The friction ring 2 is encapsulated with the light metal alloy with an oversize on at least a hub 6 and an outer circumference 7, so that the hub 6 has a smaller inner diameter after the light metal alloy has been cast than is later required. This oversize also enables a later shift of the rotational axis 8 to a center of gravity axis 10 to compensate for an imbalance.Due to the comparatively rough outer surface of the friction ring 2 created during the centrifugal casting process of the friction ring 2, a particularly effective toothing and thus an extremely strong connection with the material of the brake pot 3 can be achieved, since the liquid metal of the brake pot 3 flows into undercuts in the rough outer surface of the friction ring 2 during its manufacture and also otherwise forms an extremely positive connection with the outer surface of the friction ring 2.

[0033] Subsequently, in method step C, the composite brake drum blank is pre-machined at least on its outer circumference 7, where it has an excess of in particular 1.0 mm to 1.5 mm. An excess of between 1.0 mm and 1.5 mm is sufficient to later compensate for the imbalance of the friction ring 2 or the brake pot 3, preferably completely, without the need for further so-called weight compensation cuts or bores. In a first clamping operation, the composite brake drum 1 is machined with an excess on all surfaces on the axis of rotation 8 and then, in method step D, is clamped on a balancing machine, in particular a balancing dome, again via its axis of rotation 8, and an imbalance of the composite brake drum 1, which consists of the brake pot 3 and the friction ring 2, is determined. The balancing process of the composite brake drum 1 is repeated twice on a reversal or180°, whereby at the end of this balancing process a result for the existing imbalance is determined.

[0034] In the subsequent method step E, the outer circumference 7, i.e. an outer diameter, is now reworked and the axis of rotation 8 of the composite brake drum 1 is shifted by a radial offset a towards its center of gravity axis 10 so that the previously determined imbalance is at least partially compensated. The imbalance determined in method step D was previously compensated with weight compensation cuts or bores and / or weights. In the method according to the invention, the unbalance is now compensated at least predominantly, preferably entirely, by shifting the axis of rotation 8 of the composite brake drum 1. To compensate for the unbalance, the axis of rotation 8 can be shifted in the direction of the center of gravity axis 10 (unbalance) so that the axis of rotation 8 is closer to the center of gravity axis 10 (unbalance).A displacement of the rotation axis 8 in one direction can be achieved by removing material in this direction from an outer circumference of the brake pot 3. The material removal that compensates for the imbalance causes a displacement of the rotation axis 8. When balancing vehicle wheels, however, weights are attached opposite the determined imbalance. A radial displacement of the rotation axis 8 means a perpendicular displacement of the rotation axis 8 to its axial direction. In concrete terms, in the method according to the invention, the displacement of the rotation axis 8 relative to the center of gravity axis 10 also causes a displacement of the original hub of the composite brake drum blank to the final hub of the composite brake drum 1.

[0035] The “rotation axis 8” corresponds to the hub axis of the composite brake drum 1 after pre-machining, while the hub axis corresponds to the final center of gravity axis 10 of the composite brake drum 1 after finish machining.

[0036] Subsequently, in process step F, the brake pot 3 is machined to its final dimensions on all surfaces and diameters. This can be done, for example, by turning and / or grinding, with the shifted rotation axis 8, i.e., the center of gravity axis 10, being used as the axis of rotation.

[0037] In process step G, screw openings 9 are now drilled for wheel bolts to be inserted later and, for example, a hole 11 for a fixing screw of the brake drum on the vehicle hub.

[0038] With the method according to the invention, the previously mandatory "weight compensation cuts or bores" can thus at least be reduced, since balancing via such weight compensation cuts or bores in such a composite brake drum 1 would under certain circumstances not even be possible due to the material that would have to be removed from the brake pot 3. This is due in particular to the fact that the density of the material of the brake pot 3 is only a fraction of the density of the material of the friction ring 2, so that a multiple of the material would always have to be removed from the brake pot 3 in order to compensate for an imbalance in the friction ring 2.

[0039] A radial displacement of the rotational axis 8 of the composite brake drum 1 can be between 0.05 mm and up to 0.6 mm, which, according to tests, is sufficient to compensate for the imbalance of the friction ring 2 or the brake pot 3, preferably completely, without the need for further so-called weight compensation cuts or bores.

[0040] The alloy used for the brake chamber 3 can be, for example, an aluminum alloy or a magnesium alloy, with an aluminum alloy in particular having the great advantage of both high strength and low weight. Aluminum alloys also have high corrosion resistance, which is particularly advantageous when used on drum brakes 4 exposed to de-icing salts on a motor vehicle 5 according to the invention.

[0041] In a further advantageous embodiment of the method according to the invention, material can additionally be removed from the brake pot 3, in particular in the form of a weight compensation cut or a bore, in order to be able to compensate for a slight imbalance that cannot be compensated for by the radial displacement of the rotation axis 8. Such material removal can, for example, be carried out as a weight compensation cut or bore, which, however, would be significantly greater without the radial offset a of the rotation axis 8 according to the invention. By means of the radial displacement of the rotation axis 8 according to the invention, an existing imbalance can be compensated for much more easily than by corresponding weight compensation cuts or bores, for which the material present on the brake pot 3 would possibly not be sufficient.

[0042] In a further advantageous embodiment of the manufacturing method according to the invention, the friction ring 2 is balanced before being encapsulated with the light metal alloy of the brake pot 3. This allows for a pre-balancing of the friction ring 2, whereby the radial offset a produced by the method according to the invention, i.e., the radial displacement of the rotation axis 8, can be smaller. For this purpose, a corresponding material removal can be provided on the front side of the friction ring 2, in particular as a weight compensation cut or bore.

[0043] Balancing of the friction ring 2 can also be achieved by offsetting its friction ring axis (not shown). For this purpose, the friction ring 2 can be mounted on a mandrel of a balancing machine, and any existing imbalance can be determined there. The determined imbalance is then at least partially compensated for by radially offsetting the friction ring axis, analogous to the method according to the invention.

[0044] Using the method according to the invention, a composite brake drum 1 according to the invention and a drum brake 4 equipped therewith can be manufactured cost-effectively and suitable for series production. In particular, the radial offset a of the rotational axis 8 used in the method according to the invention also allows for comparatively easy compensation of imbalances in the comparatively dense and thus heavy friction ring 2.

Claims

Claims 1. A method for producing a composite brake drum (1 ), in which - a friction ring (2) is manufactured as a metal casting, - the friction ring (2) is cast around with a brake pot (3) made of a light metal alloy at least with an oversize on a hub (6) and on an outer circumference (7), thereby producing a composite brake drum blank with a rotation axis (8), - the composite brake drum blank is pre-machined with an oversize at least on its outer circumference (7), - the pre-machined composite brake drum (1) is clamped on a balancing machine and an imbalance of the pre-machined composite brake drum (1) with the brake pot (3) and the friction ring (2) is determined, - the brake pot (3) is reworked on the outer circumference (7) and the rotation axis (8) of the composite brake drum (1) is shifted by a radial offset (a) towards a center of gravity axis (10) in such a way that the determined imbalance is at least partially compensated, - the brake pot (3) is then finished, - Screw holes (9) for wheel bolts are provided.

2. Method according to claim 1, characterized in that the axis of rotation (8) of the composite brake drum (1) is radially displaced by a radial offset a of 0.05 mm < a < 0.6 mm.

3. Method according to claim 1 or 2, characterized in that that an aluminum alloy or a magnesium alloy is used as the light metal alloy for the brake pot (3).

4. Method according to one of the preceding claims, characterized in that - that the brake pot (3) is ground and / or turned during reworking, - that the friction ring (2) is reworked, in particular ground and / or turned.

5. Method according to one of the preceding claims, characterized in that material is removed from the brake pot (3) in order to be able to at least partially compensate for any remaining imbalance.

6. Method according to claim 5, characterized in that the material removal is carried out as at least one weight compensation cut or as at least one bore.

7. Method according to one of claims 1 to 6, characterized in that the friction ring (2) is balanced before being encased in the light metal alloy to produce the composite brake drum blank.

8. Method according to claim 7, characterized in that balancing of the friction ring (2) is carried out by offsetting its friction ring axis.

9. Method according to claim 7 or 8, characterized in that a material removal is carried out on the front side of the friction ring (2), in particular as a weight compensation cut or bore.

10. Method according to one of the preceding claims, characterized in that a cast iron material, in particular grey cast iron, is used for metal casting of the friction ring (2).

11. Composite brake drum (1) manufactured according to the method according to one of the preceding claims.

12. Drum brake (4) with a composite brake drum (1) according to claim 11.

13. Motor vehicle (5), in particular an electric vehicle, with a drum brake (4) according to claim 12. *****

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