Brake disc for a motor vehicle

Abstract

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 each other by a plurality of connecting webs (10), wherein 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 coolant (14), wherein the volume (VK) of coolant (14) under normal ambient conditions is less than the volume (VH) of the respective hollow chamber (12), wherein both the inner brake plate (4) and the outer brake plate (6) have a plurality of closed hollow chambers (12), characterized in that a plurality or all of the connecting webs (10) are hollow, wherein these connecting webs (10) connect a hollow chamber (12) of the inner brake plate (4) with a hollow chamber (12) of the outer brake plate (6).

Description

[0001] This describes a brake disc for a motor vehicle.

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

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

[0004] Braking systems must be capable of safely slowing down a vehicle with high deceleration values, even at high speeds, or bringing it to a complete stop. This is achieved by converting the vehicle's kinetic energy into heat energy through friction within the braking system. Two main systems have become established: drum brakes and disc brakes. Almost all modern vehicles are equipped with disc brakes, at least on the front axle.

[0005] A limiting factor in the performance of braking systems is their operating temperature range. Above a certain temperature threshold, the braking system can be damaged, or braking performance can decrease (known as brake fade). At very high temperatures, brake linings can glaze over, and brake discs and drums can warp. Therefore, it is crucial that the heat generated by the braking system is dissipated 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 categories and are generally aerodynamically optimized to minimize airflow around the brakes. Therefore, the brakes of electric vehicles are often subjected to particularly high stress, as they have to dissipate more energy and are also less effectively cooled.

[0007] Several approaches exist to optimize the performance of braking systems. One is to equip disc brakes with internally ventilated discs, which can dissipate significantly more energy in the same amount of time than solid discs. Another crucial factor is the size of the brake discs. The larger the brake disc, the greater the frictional surface area, and therefore the more energy can be absorbed and dissipated. However, very large brake systems increase the unsprung mass of the vehicle, which impairs ride comfort and vehicle dynamics, and increases energy consumption during acceleration.

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

[0009] Furthermore, various approaches are known to reduce 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 attached to a hub, which can be cooled according to the principle of heat pipes integrated inside the brake disc and which have their heat-absorbing part in the radial area of ​​the braking surface and their heat-emitting part, which is exposed to ambient air, in a radially located part of the brake disc, wherein only a single heat pipe system, freely communicating with each other with respect to all its cavity parts, is provided within the brake disc and a connection between these is provided to reduce the heat transfer between the brake disc and the hub.

[0011] DE 34 39 119 A1 discloses a rotor for a rotating electric machine with a field winding arranged around a shaft and a pair of claw-shaped poles arranged such that they axially enclose the field coil from opposite sides, wherein several cylindrical sections are formed on the outer side surfaces of the same, that the cylindrical sections are concentric with respect to the shaft, and that cooling fins are arranged on the corresponding cylindrical sections and are attached by mortising through openings formed in the fins concentric to the cylindrical sections, wherein the fins are further attached to the respective claw-shaped poles by welding.

[0012] DE 10 2016 207 876 A1 discloses a brake disc, in particular for a motor vehicle, with a base disc made of a first material and with a wear-reducing coating (made of a second material). It is provided that the first material is a light metal and the second material is an oxide layer.

[0013] US 2005 / 0279595A1 describes a refrigerant-cooled rotor and an associated method and system for cooling a rotor. The rotor in question is an at least partially hollow, ring-shaped enclosure containing the refrigerant. The rotor is typically used to provide a surface against which another device comes into frictional contact. The refrigerant absorbs and releases frictional heat at the rotor surface in a continuous heat transfer cycle to limit the maximum rotor temperature. By evaporating and condensing within the rotor, the refrigerant provides a regenerative heat sink for cooling.

[0014] However, existing braking systems still reach their physical limits.

[0015] The task therefore is to further develop brake discs for motor vehicles in such a way that brake discs are specified which allow higher braking performance at a lower weight than conventional brake discs.

[0016] The problem is solved by a brake disc according to claim 1. Further embodiments and developments are the subject of the dependent claims.

[0017] 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.

[0018] By using brake discs with multiple 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 hollow chambers and without coolant. The coolant causes it to evaporate within the hollow chambers when heat energy is introduced and temperatures exceed the coolant's boiling point are reached. This evaporation absorbs far more heat energy than would be possible through normal heat conduction within the brake disc material alone, allowing significantly 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 areas that are not experiencing heat input.This is the case with internally ventilated brake discs on the respective side of the internal ventilation, so the use of brake discs with a plurality of hollow chambers is surprisingly particularly suitable for internally ventilated brake discs.

[0019] Brake discs can be made from various materials, most notably gray cast iron. Gray cast iron is an iron alloy 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-carbon is 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.

[0020] Brake discs are generally cast. The material, usually 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 internal stresses. 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.

[0021] After machining, the brake disc undergoes heat treatment to achieve the required material properties. This treatment increases the hardness and strength of the brake disc, thus extending its lifespan and improving its performance. Finally, the brake disc is subjected to quality control, where it is checked for dimensional accuracy, surface quality, and structural integrity.

[0022] To produce the hollow chambers, the brake disc can be cast in several parts, which are then joined together by material bonding, for example by friction welding.

[0023] The hollow chambers can be hermetically sealed, so that the coolant cannot escape.

[0024] Generally, a very small amount of coolant is sufficient, in particular less than 5% of the volume of the cavity (under normal ambient conditions and 20°C), and especially less than 2% of the volume. This allows for very good thermal conductivity and keeps the rotating mass low.

[0025] Coolants that are liquid at normal temperatures and do not react with the brake disc material are particularly suitable. Water is one possible coolant. Water is liquid at 20°C and evaporates at 100°C, which is within the typical operating temperature range of brake discs. Additives can be added to the water to prevent it from reacting with the brake disc material.

[0026] Depending on the method of sealing the hollow chambers, the coolant can be introduced before or during the sealing process. For this purpose, filling openings can be provided during manufacturing, which are subsequently sealed using a material-bonded method, such as a plug or a weld.

[0027] On the one hand, such a brake disc has a significantly higher thermal conductivity than conventional internally ventilated brake discs, and on the other hand, due to the hollow chambers, it is lighter than internally ventilated brake discs with solid brake plates, even if these are drilled or slotted, since the wall thicknesses of the brake plate in question are less than those of solid discs.

[0028] Furthermore, it is provided that both the inner brake plate and the outer brake plate have a plurality of closed hollow chambers.

[0029] This allows the brake disc in question to be even lighter than a brake disc where only one of the brake plates is equipped with hollow chambers. Furthermore, more even heat dissipation can be achieved, which prevents temperature differences on the inner and outer surfaces of the brake disc and thus potentially prevents damage.

[0030] Furthermore, it is provided that a majority or all of the connecting webs are hollow, with these connecting webs connecting a hollow chamber of the inner brake plate to a hollow chamber of the outer brake plate.

[0031] In this way, it is possible to connect two hollow chambers—one from an inner brake disc and one from an outer brake disc—into a single volume. This provides the coolant with a larger surface area for condensation and heat dissipation. Heat transfer via the surfaces where no heat input occurs can thus be optimized. In particular, the connecting webs bridge the internally ventilated area and are exposed to a comparatively cool airflow there, resulting in particularly efficient heat dissipation at these surfaces.

[0032] In a further, more advanced embodiment, it is provided that the connecting webs are designed as connecting cylinders.

[0033] Cylinders are easy to manufacture using the casting process, cause less imbalance than other geometries, have a large outer surface area and also avoid stress peaks in the material under physical loads on the brake disc.

[0034] In a further refinement, it is provided that the coolant has a boiling point that is lower than the maximum permissible operating temperature of the brake disc.

[0035] 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.

[0036] In a 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.

[0037] In this way, the inner surface area of ​​the hollow chambers is significantly increased compared to smooth surfaces, thus increasing the available area for heat transfer from the brake disc material to the coolant. This allows more coolant to evaporate per unit of time than on smooth surfaces. Furthermore, the inner surfaces of the hollow chambers are better wetted with coolant than smooth surfaces.

[0038] In a 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.

[0039] This allows for better distribution of the coolant across the inner surfaces of hollow chambers and / or connecting webs.

[0040] 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.

[0041] In a further embodiment, it is provided that a radially inner contact surface for a rim is provided on the outer brake plate, wherein at least one hollow chamber is provided axially within the contact surface.

[0042] 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, with the rim typically being exposed to an airflow through which efficient heat dissipation is possible.

[0043] In a 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.

[0044] This increases the mechanical stability of the brake disc.

[0045] In a further, more advanced embodiment, it is provided that the hollow chambers are designed to be radially circumferential.

[0046] Radially circumferential hollow chambers allow for the construction of a brake disc without imbalances.

[0047] Further advantages, features, and details will become apparent from the following description, in which – possibly with reference to the drawing – at least one embodiment is described in detail. Identical, similar, and / or functionally equivalent parts are marked with the same reference numerals.

[0048] 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 Fig. 1, as well as Fig. 5 a perspective view of the brake disc from Fig. 1.

[0049] Fig. Figure 1 shows a side view of a brake disc.

[0050] The brake disc 2 is internally ventilated and has an inner brake plate 4 on an inner side I and an outer brake plate 6 on an outer side A.

[0051] A hub 8 is provided radially inside, on which the brake disc 2 is mounted on a motor vehicle wheel suspension.

[0052] Fig. Figure 2 shows a magnification of the brake disc 2 in section D. Fig. 1.

[0053] 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 coolant 14, e.g. water.

[0054] The hollow chambers 12 on the side of the inner brake plate 4 and on the side of the outer brake plate 6 are each arranged at the same height and connected to each other 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.

[0055] The coolant 14 can be transported back and forth between the hollow chambers 12 on the inner brake plate 4 and on the outer brake plate 6.

[0056] Fig. Figure 3 shows the heat dissipation concept of the brake disc 2.

[0057] During braking, brake pads of a brake system contact the outer sides of the inner brake plate 4 and outer brake plate 6, generating friction with the brake disc 2. This friction heats the gray cast iron material of the brake disc 2. The heat is transferred via the outer sides of the inner brake plate 4 and outer brake plate 6 into the hollow chambers 12. The coolant 14 then evaporates on a portion of the inner surfaces 18 of the hollow chambers 12 opposite the heat input surfaces and spreads as vapor within the corresponding internal volume of the hollow chambers 12.

[0058] Furthermore, the relevant internal volumes of the hollow chambers 12 and the connecting webs 10 have surfaces through which no heat input occurs during braking. The coolant 14 can condense on these surfaces and thereby transfer energy to the metal of the brake disc 2. This energy can be dissipated at the non-braked surfaces, in particular in the area of ​​the internal ventilation including the connecting webs 10.

[0059] The inner surfaces 18, 20 of the hollow chambers 12 and connecting webs 10 are each equipped with a porous capillary structure that can be incorporated 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 brake disc material 2 and the coolant 14, thereby achieving better evaporation of the coolant 14 and thus higher heat transfer. Furthermore, the coolant 14 can distribute itself more effectively within the hollow chambers and connecting webs due to capillary action.

[0060] To support the connecting webs 10 and to stabilize the brake disc 2, separating webs 16 are provided, which allow an axial force transmission from the respective outer surfaces of the brake disc 2 to the connecting webs 10.

[0061] Fig. Figure 4 shows a section of the brake disc 2 in a cutaway perspective view.

[0062] It can be seen that the hollow chambers 12 are formed radially around the perimeter and that the connecting webs 10 as well as the separating webs 16 are each cylindrical in design.

[0063] Fig. Figure 5 shows a perspective view of the brake disc 2 as seen from the outside A.

[0064] 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.

[0065] In certain configurations, it may be provided that hollow chambers 12 are also provided inside the system surface 22, which increase the heat transfer to the system surface 22.

[0066] Although the invention has been further illustrated and explained in detail by means of preferred embodiments, the invention is not limited by the disclosed examples, and other variations can be derived from them by a person skilled in the art without departing from the scope of protection of the invention. It is therefore clear that a multitude of possible variations exist. It is also clear that the embodiments mentioned as examples are truly only examples and are not to be understood in any way as limiting, for example, the scope of protection, the possible applications, or the configuration of the invention.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 leaving the scope of protection defined by the claims and their legal equivalents, such as a further explanation in the description. Reference symbol list 2 brake discs 4 inner brake plate 6 outer brake plate 8 hub 10 Connecting bridge 12 Hollow chamber 14 Coolant 16 dividing bridge 18 Inner surface of hollow chamber 20 Inner surface connecting web 22 Plant area A Outside D Detail Inside VH Volume Hollow Chamber VK volume coolant

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 each other by a plurality of connecting webs (10), wherein 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 coolant (14), wherein the volume (VK) of coolant (14) under normal ambient conditions is less than the volume (VH) of the respective hollow chamber (12), wherein both the inner brake plate (4) and the outer brake plate (6) have a plurality of closed hollow chambers (12), characterized by , that a plurality or all of the connecting webs (10) are hollow, wherein these connecting webs (10) connect a hollow chamber (12) of the inner brake plate (4) with a hollow chamber (12) of the outer brake plate (6). [2] Brake disc (2) according to the preceding claim, characterized by , that the connecting webs are designed as connecting cylinders (10). [3] Brake disc (2) according to any of the preceding claims, characterized by , that the coolant (14) has a boiling point that is lower than a permissible maximum operating temperature of the brake disc (2). [4] Brake disc (2) according to any 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). [5] Brake disc (2) according to any 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 inner wall with a capillary structure. [6] Brake disc (2) according to any 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). [7] Brake disc (2) according to any 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). [8] Brake disc (2) according to any of the preceding claims, characterized by , that the hollow chambers (12) are designed radially circumferentially.

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