Brake disc for a motor vehicle

Abstract

A brake disc for a motor vehicle is described, wherein the brake disc is internally ventilated, wherein the brake disc has an inner brake plate and an outer brake plate which are connected to each other by a plurality of connecting webs, wherein at least one of the brake plates has a plurality of hollow chambers, wherein the hollow chambers are filled with a coolant, wherein the volume of coolant under normal ambient conditions is less than the volume of the respective hollow chamber.

Description

[0001] A brake disc for a motor vehicle is described.

[0002] Brake discs for motor vehicles of the type mentioned above are known in the prior art.

[0003] Braking systems in motor vehicles are one of the fundamental components of a motor vehicle’s safety concept.

[0004] Braking systems must be capable of safely slowing the vehicle down to a standstill with high deceleration values, even at high speeds. The vehicle's kinetic energy is converted into thermal energy by generating friction within the braking system. Basically, two different systems have prevailed: drum brakes and disc brakes. Almost all modern vehicles are equipped with disc brakes on at least the front axle.

[0005] A limiting factor in the performance of braking systems is their operating temperature range. Above a certain temperature limit, the braking systems can be damaged or deceleration can decrease (so-called fading). Very high temperatures can cause glazing of the brake pads and warping of brake discs and drums. For this reason, it is important that the resulting heat can be dissipated from the braking systems as quickly as possible.

[0006] The kinetic energy to be dissipated increases linearly with the weight of the vehicle and with the square of the speed. Due to their heavy batteries, electric vehicles are often considerably heavier than conventional vehicles in the same vehicle category and are generally aerodynamically optimized to minimize airflow around the braking systems. Therefore, the braking systems of electric vehicles are often subject to particularly high loads, as they have to dissipate more energy and are less well cooled.

[0007] Various approaches are known for optimizing the performance of braking systems. One approach is to equip disc brakes with internally ventilated discs, which can dissipate significantly more energy in the same amount of time than solid discs. The size of the brake discs is also a crucial factor. The larger the brake disc, the more friction surface it can provide and the more energy it can absorb and dissipate. However, very large braking systems lead to an increase in the unsprung mass of the vehicle, which impairs suspension comfort and dynamics and increases energy consumption during acceleration.

[0008] In addition, various high-temperature-resistant materials are known for disc brakes, such as ceramic brake discs with corresponding brake pads. Ceramic brake discs can operate at significantly higher temperatures than conventional steel brake discs, which is why they have become established in racing and are sometimes used in sports cars on public roads. However, compared to conventional brakes, ceramic brake systems are very expensive to manufacture and maintain, and are also much more susceptible to damage.

[0009] In addition, various approaches are known to dissipate energy in braking systems using other physical principles.

[0010] From DE 29 50 057 A1 a vehicle wheel with a disc brake is known, comprising a brake disc fastened to a hub, which can be cooled according to the principle of heat pipes which are integrated in the interior of the brake disc and which have their heat-absorbing part in the radial region of the braking surface and their heat-emitting part which can be exposed to ambient air in a part of the brake disc lying radially inside thereof, wherein only a single heat pipe system is provided within the brake disc, which heat pipe system communicates freely with one another with regard to all of its hollow space parts, and a connection is provided between them which reduces the heat transfer between the brake disc and the hub.

[0011] DE 34 39 119 A1 discloses a rotor for a rotating electrical machine having a field winding arranged around a shaft and a pair of claw-shaped poles arranged to axially enclose the field coil from opposite sides, wherein a plurality of cylindrical portions are formed projecting on the outer side surfaces thereof, that the cylindrical portions are formed concentrically with respect to the shaft, and that cooling fins are arranged on the corresponding cylindrical portions and are fastened by means of mortising through openings formed in the fins concentrically with the cylindrical portions, wherein the fins are further fastened to corresponding ones of the respective claw-shaped poles by means of welding.

[0012] However, existing braking systems still reach their physical limits.

[0013] The task therefore arises of further developing brake discs for motor vehicles in such a way that brake discs are specified that allow higher braking performance with lower weight than conventional brake discs.

[0014] The object is achieved by a brake disc according to claim 1. Further embodiments and developments are the subject of the dependent claims.

[0015] A brake disc for a motor vehicle is described, wherein the brake disc is internally ventilated, wherein the brake disc has an inner brake plate and an outer brake plate which are connected to one another by a plurality of connecting webs, wherein at least one of the brake plates has a plurality of hollow chambers, wherein the hollow chambers are filled with a cooling liquid, wherein the volume of cooling liquid under normal ambient conditions is less than the volume of the respective hollow chamber.

[0016] By using brake discs with a number of hollow chambers filled with a certain volume of coolant, the thermal conductivity of the brake disc can be significantly increased compared to a conventional brake disc without a hollow chamber and without coolant. The coolant causes the coolant to evaporate when heat energy is introduced into the hollow chamber when temperatures above the boiling point of the coolant are reached. This evaporation absorbs far more heat energy than would be possible through normal heat conduction within the brake disc material alone, allowing considerably more heat to be dissipated in a shorter time than with conventional brake discs. The coolant can temporarily store this heat and efficiently release it to other surfaces that are not subject to any heat input.This is the case with internally ventilated brake discs on the respective side of the internal ventilation, so that the use of brake discs with a plurality of hollow chambers is surprisingly particularly suitable for internally ventilated brake discs.

[0017] The brake disc can be made of various materials, particularly gray cast iron. Gray cast iron is an iron material with a high graphite carbon content. This material exhibits very good thermal conductivity, good damping properties, and very good compressive strength. Gray cast iron is hard and brittle. The most common type of gray cast iron is lamellar graphite cast iron, in which the graphite carbons are present in the form of thin, irregular lamellae. These lamellae act like notches in the material structure and give the material its characteristic properties: comparatively low tensile strength but very high compressive strength.

[0018] Brake discs are typically cast. The material, particularly gray cast iron, is melted and then poured into molds that determine the basic shape of the brake disc. After casting, the resulting blanks undergo a controlled cooling process to minimize stresses in the material. The blanks are then machined to achieve their final shape and precise dimensions. This includes turning, milling, and drilling to smooth the surface and create the necessary mounting holes.

[0019] After machining, heat treatment is performed to achieve the required material properties. This treatment increases the hardness and strength of the brake disc, which increases its service life and performance. Finally, the brake disc undergoes a quality control inspection, where it is tested for dimensional accuracy, surface quality, and structural integrity.

[0020] To produce the hollow chambers, the brake disc can be cast in several parts, which are then joined together, for example by friction welding.

[0021] In particular, the hollow chambers can be hermetically sealed so that the coolant cannot escape.

[0022] Typically, a very small amount of coolant is sufficient, in particular less than 5% of the volume of the hollow chamber (under normal ambient conditions and 20°C), and especially less than 2% of the volume. This allows for very good thermal conductivity and minimizes the rotating mass.

[0023] Particularly suitable are coolants that are liquid at normal temperatures and do not react with the brake disc material. One possible coolant is water. Water is liquid at 20°C and evaporates at 100°C, which is within the normal operating temperature range of brake discs. Additives can be added to the water to prevent it from reacting with the brake disc material.

[0024] Depending on the type of sealing of the hollow chambers, the coolant can be introduced before or during the sealing process. For this purpose, filling openings can be provided during production, which are then sealed with a material bond, for example, with a plug or a weld point.

[0025] On the one hand, such a brake disc has a considerably higher thermal conductivity than conventional internally ventilated brake discs and, on the other hand, the hollow chambers make it lighter than internally ventilated brake discs with solid brake plates, even if these are perforated or slotted, since the wall thicknesses of the brake plates in question are smaller than those of solid discs.

[0026] In a first further embodiment, it is provided that both the inner brake plate and the outer brake plate have a plurality of closed hollow chambers.

[0027] This makes the brake disc even lighter than one in which only one of the brake calipers is equipped with hollow chambers. Furthermore, more even heat dissipation can be achieved, preventing temperature differences on the inside and outside of the brake disc and thus preventing potential damage.

[0028] In a further further embodiment, it is provided that a majority or all connecting webs are hollow, wherein these connecting webs connect a hollow chamber of the inner brake plate with a hollow chamber of the outer brake plate.

[0029] This makes it possible to combine two hollow chambers—one hollow chamber of an inner brake disc and one hollow chamber of an outer brake disc—into a single volume. This provides the coolant with more surface area to condense and dissipate heat. Heat dissipation via surfaces where no heat is introduced can thus be optimized. In particular, the connecting bridges bridge the internally ventilated area, where they are exposed to a comparatively cool airflow, allowing for particularly efficient heat dissipation at these surfaces.

[0030] In a further further embodiment, it is provided that the connecting webs are designed as connecting cylinders.

[0031] Cylinders are easy to manufacture using the casting process, cause less imbalance than other geometries, have a large outer surface and also avoid stress peaks in the material when the brake disc is subjected to physical loads.

[0032] In a further refinement, it is provided that the coolant has a boiling point that is lower than a permissible maximum operating temperature of the brake disc.

[0033] In this way, additional heat dissipation via the coolant can begin before the materials of the brake system, especially the brake disc, reach their permissible operating temperature limits.

[0034] In a further further embodiment, it is provided that at least one of the hollow chambers and / or at least one of the hollow connecting webs has at least one porous inner wall.

[0035] This significantly increases the internal surface area of ​​the hollow chambers compared to smooth surfaces, thus increasing the available area through which heat can be transferred from the brake disc material to the coolant. This allows more coolant to evaporate per unit of time than on smooth surfaces. Furthermore, the internal surfaces of the hollow chambers are better wetted with coolant than on smooth surfaces.

[0036] In a further further embodiment, it is provided that at least one of the hollow chambers and / or at least one of the hollow connecting webs has at least one inner wall with a capillary structure.

[0037] This allows for a better distribution of the coolant over the inner surfaces of hollow chambers and / or connecting webs.

[0038] In particular, it has been shown that the use of porous capillary structures is suitable for very good distribution of the coolant and good heat transfer.

[0039] In a further further embodiment, it is provided that a radially inner contact surface to a rim is provided on the outer brake plate, wherein at least one hollow chamber is provided axially within the contact surface.

[0040] In such an arrangement, the rim can be used as a heat dissipating element by transferring heat from the brake disc to the rim via the contact surface, whereby the rim is usually exposed to an air flow through which heat dissipation is possible efficiently.

[0041] In a further further embodiment, it is provided that the connecting webs are each supported by means of at least one separating web on the inner brake plate and / or the outer brake plate.

[0042] In this way, the mechanical stability of the brake disc can be increased.

[0043] In a further further embodiment, it is provided that the hollow chambers are designed to be radially circumferential.

[0044] Radially encircling hollow chambers allow the construction of a brake disc without imbalance.

[0045] Further advantages, features, and details will become apparent from the following description, which – where appropriate with reference to the drawings – describes at least one embodiment in detail. Identical, similar, and / or functionally equivalent parts are provided with the same reference numerals.

[0046] They show schematically: Fig. 1 a side view of a brake disc; Fig. 2 an enlargement from Fig. 1; Fig. 3 the heat dissipation concept of the brake disc Fig. 1; Fig. 4 a partially transparent perspective sectional view of the brake disc from Fig. 1, and Fig. 5 a perspective view of the brake disc from Fig. 1.

[0047] Fig. 1 shows a side view of a brake disc 2.

[0048] The brake disc 2 is internally ventilated and has an inner brake plate 4 on an inner side 1 and an outer brake plate 6 on an outer side A.

[0049] A hub 8 is provided radially inward, to which the brake disc 2 is mounted on a motor vehicle wheel suspension.

[0050] Fig. 2 shows an enlargement of the brake disc 2 in section D from Fig. 1.

[0051] In the inner brake plate 4 and in the outer brake plate 6, a series of concentric hollow chambers 12 are arranged, each filled with a small amount of cooling liquid 14, e.g. water.

[0052] The hollow chambers 12 on the side of the inner brake disc 4 and on the side of the outer brake disc 6 are each arranged at the same height and connected to one another via a hollow connecting web 10, so that the respective hollow chambers 12 each form a common closed volume. The hollow chambers 12 together with the hollow connecting webs 10 each form different large hollow chamber volumes VH, which are considerably larger than the volumes VK of coolant 14 with which the hollow chambers 12 are filled.

[0053] The cooling liquid 14 can be transported back and forth between the hollow chambers 12 on the inner brake plate 4 and the outer brake plate 6.

[0054] Fig. 3 shows the heat dissipation concept of the brake disc 2.

[0055] During braking, brake pads of a brake system rest on the outer sides of the inner brake disc 4 and outer brake disc 6, thereby generating friction with the brake disc 2. This friction leads to heating of the gray cast iron material of the brake disc 2. The heat reaches the hollow chambers 12 via the outer sides of the inner brake disc 4 and outer brake disc 6. The coolant 14 then evaporates on a part of the inner surfaces 18 of the hollow chambers 12 opposite the heat input surfaces and is distributed in vapor form within the corresponding internal volume of the hollow chambers 12.

[0056] The respective internal volumes of the hollow chambers 12 and the connecting webs 10 also have surfaces through which no heat is transferred during braking. The coolant 14 can condense on these surfaces, thereby transferring energy to the metal of the brake disc 2. This energy can be dissipated at the non-braked surfaces, particularly in the area of ​​the internal ventilation, including the connecting webs 10.

[0057] The inner surfaces 18, 20 of hollow chambers 12 and connecting webs 10 are each equipped with a porous capillary structure, which can be introduced during the casting of the brake disc 2. The porous capillary structures on the inner surfaces 18, 20 increase the available contact area between the material of the brake discs 2 and the coolant 14, thereby achieving better evaporation of the coolant 14 and thus higher heat transfer. Furthermore, the coolant 14 can be better distributed in the hollow chamber and connecting webs, as it is distributed by capillarity.

[0058] To support the connecting webs 10 and to stabilize the brake disc 2, separating webs 16 are provided, which allow axial force transmission from the respective outer surfaces of the brake disc 2 to the connecting webs 10.

[0059] Fig. 4 shows a section of the brake disc 2 in a sectional perspective view.

[0060] It can be seen that the hollow chambers 12 are designed to be radially circumferential and that the connecting webs 10 as well as the separating webs 16 are each designed to be cylindrical.

[0061] Fig. 5 shows a perspective view of the brake disc 2 viewed from the outside A.

[0062] The brake disc 2 has a large contact surface 22 against which a rim can rest, so that the contact surface 22 can serve to dissipate heat.

[0063] For this purpose, in certain embodiments, hollow chambers 12 may also be provided inside the contact surface 22, which increase the heat transfer to the contact surface 22.

[0064] Although the invention has been illustrated and explained in detail by means of preferred embodiments, the invention is not limited by the disclosed examples, and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention. It is therefore clear that a multitude of possible variations exist. It is also clear that the embodiments mentioned by way of example are truly only examples and should not be construed as limiting the scope, possible applications, or configuration of the invention in any way.Rather, the preceding description and the description of the figures enable the person skilled in the art to implement the exemplary embodiments in concrete terms, whereby the person skilled in the art, with knowledge of the disclosed inventive concept, can make various changes, for example with regard to the function or the arrangement of individual elements mentioned in an exemplary embodiment, without departing from the scope of protection defined by the claims and their legal equivalents, such as a further explanation in the description. List of reference symbols 2 brake discs 4 inner brake disc 6 outer brake plate 8 Hub 10 connecting bridge 12 hollow chambers 14 Coolant 16 Divider 18 Inner surface of hollow chamber 20 Inner surface connecting bridge 22 contact surface A outside D Detail I Inside VH volume hollow chamber VK volume of coolant QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 29 50 057 A1

[0010] DE 34 39 119 A1

[0011]

Claims

[1] Brake disc (2) for a motor vehicle, wherein the brake disc (2) is internally ventilated, wherein the brake disc (2) has an inner brake plate (4) and an outer brake plate (6) which are connected to one another by a plurality of connecting webs (10), characterized by that at least one of the brake plates (4, 6) has a plurality of hollow chambers (12), wherein the hollow chambers (12) are filled with a cooling liquid (14), wherein the volume (VK) of cooling liquid (14) under normal ambient conditions is less than the volume (VH) of the respective hollow chamber (12). [2] Brake disc (2) according to claim 1, characterized by that both the inner brake plate (4) and the outer brake plate (6) have a plurality of closed hollow chambers (12). [3] Brake disc (2) according to 2, characterized bythat a majority or all of the connecting webs (10) are hollow, said connecting webs (10) connecting a hollow chamber (12) of the inner brake plate (4) to a hollow chamber (12) of the outer brake plate (6). [4] Brake disc (2) according to one of the preceding claims, characterized by that the connecting webs are designed as connecting cylinders (10). [5] Brake disc (2) according to one of the preceding claims, characterized by that the cooling liquid (14) has a boiling point which is lower than a permissible maximum operating temperature of the brake disc (2). [6] Brake disc (2) according to one of the preceding claims, characterized by that at least one of the hollow chambers (12) and / or at least one of the hollow connecting webs (10) has at least one porous inner wall (18, 20). [7] Brake disc (2) according to one of the preceding claims, characterized bythat at least one of the hollow chambers (12) and / or at least one of the hollow connecting webs (10) has at least one inner wall with a capillary structure. [8] Brake disc (2) according to one of the preceding claims, characterized by that a radially inner contact surface (22) to a rim is provided on the outer brake plate (6), wherein at least one hollow chamber (12) is provided axially within the contact surface (22). [9] Brake disc (2) according to one of the preceding claims, characterized by that the connecting webs (10) are each supported by means of at least one separating web (16) on the inner brake plate (4) and / or the outer brake plate (6). [10] Brake disc (2) according to one of the preceding claims, characterized by that the hollow chambers (12) are designed to be radially circumferential.

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