Cooling fin arrangement for an internally cooled brake disc

Abstract

Internally ventilated brake disc (21) for a disc brake, with two adjacent friction discs (20) which are connected to each other by webs (1, 2', 3', 4, 5', 6, 7', 8, 9, 10, 11', 12, 13') in such a way that the spaces between them form cooling channels through which cooling air can flow, characterized in that the geometric arrangement of the webs (1, 2', 3', 4, 5', 6, 7', 8, 9, 10, 11', 12, 13') is so irregular that during braking only a single standing wave can be formed over the entire circumference of the brake disc.

Description

[0001] The invention relates to an internally ventilated brake disc for a disc brake, according to the preamble of the first claim.

[0002] Approximately ninety percent of the energy lost during braking is initially absorbed as heat by the brake disc, from where it is transferred to the ambient air. High temperatures of up to 700°C can occur. To achieve better cooling, internally ventilated discs are increasingly being used alongside solid brake discs. These consist of two adjacent friction discs connected by webs running between the friction discs. Another measure to improve cooling and also improve responsiveness in wet conditions is the use of perforated or grooved brake discs. However, this is associated with higher costs and increased noise during braking.

[0003] The frictional heat generated by the friction elements of a wheel brake during braking must be dissipated to the outside environment to maintain braking effectiveness and prevent damage to the wheel brake. Otherwise, repeated braking with high braking force can lead to a reduction in braking effectiveness, known as brake fade. This is undesirable, particularly when driving at high speeds or on long downhill stretches. Therefore, there is great interest in preventing overheating of the brake friction elements, particularly the brake discs and brake pads. In this context, it is well known that the friction elements of a wheel brake can be additionally cooled, for example by directing airflow to the friction elements.

[0004] For improved heat dissipation, internally ventilated brake discs are equipped with radial cooling channels or ribs located between the two friction surfaces. This creates a centrifugal force as the brake disc rotates, causing a constant flow of air from the hub through the radial cooling openings to the outside. This promotes heat dissipation. Despite the greater width and weight, this brake disc design has become established for many passenger cars. In general, the longer the radially arranged ribs, the greater the airflow distance and the better the cooling.

[0005] Due to the installation conditions of the brake disc within the rim contour, the brake disc has a one-sided mounting flange, the disc hub. The friction ring therefore tends to shield when heated, meaning the friction surfaces transition from flat surfaces to conical surfaces. This can lead to uneven pad and disc wear due to the brake pad friction surface contacting the friction ring at specific points. Noise and judder can result. Judder is a combination of steering wheel vibration, pedal pulsation, and low-frequency noise. Shielding must be kept within limits through design measures to limit noise generation by effectively dampening high-frequency squealing and low-frequency judder.The squealing noise referred to above during braking is essentially caused by the oscillating movement of the brake caliper and brake pad, which generates vibrations in the braking system that radiate this audible sound. Brake squeal is caused by self-excited vibrations in the braking system. Even if noise reduction measures are implemented, noise can still occur if specific boundary conditions are met. This applies to certain values ​​of temperature, brake pressure, deceleration, and steering angle, as well as to numerous parameters of the interface between the brake pad and brake disc, such as the shape, position, and friction properties of the pads, the pressure distribution and moisture on the friction surface, and even the microstructural conditions of the brake pairing of pad and disc.

[0006] Furthermore, the frequency of the vibrations or bending can be specifically altered by appropriate arrangement and design of the webs. Consequently, if the shear stiffness of the webs is changed, the frequency of the vibrations and, accordingly, the resulting noise level also change.

[0007] To achieve a lower frequency, thus a softer bridge design, the bridges should be shorter in the radial direction. To achieve a higher frequency, the bridges are thickened, thus achieving greater stiffness.

[0008] EP 0 205 713 B1 describes a motor vehicle brake disc in which cooling channels are integrated to cool the brake disc by air flowing into them. Some of the necessary webs extend radially from the inner to the outer area of ​​the friction discs. Furthermore, shorter and longer webs are arranged in alternating sections, evenly distributed around the circumference of the brake disc. The total number of webs or the number of sections that are equal across the circumference can be a prime number.

[0009] Current internally ventilated brake discs have a rotationally symmetric design. The rotationally symmetrical arrangement of the cooling fins and webs on the brake discs creates natural frequencies and modal shapes in a specific way. With a symmetrical arrangement of these webs, an infinite number of standing waves can develop. The excitation of the road surface and other vibrating components in the vehicle, as well as the actual braking process, can cause the brake disc to vibrate. At a certain frequency, this creates a modal shape and a vibration state that leads to undesirable acoustic phenomena. The vibration of the brake disc can thus spread throughout the entire vehicle and, in the worst case, reach the natural frequency of a vehicle component, such as the parcel shelf. This component is then excited to vibrate, creating background noise.

[0010] Based on the prior art, the object of the present invention is to create an internally ventilated brake disc which, due to its construction, is less prone to vibrations and in which the probability of hitting natural frequencies of vehicle components is low,

[0011] The problem is solved by the features of the first claim. Further embodiments of the invention are described in the dependent claims.

[0012] According to the invention, an internally ventilated brake disc for a disc brake, with two friction discs arranged adjacent to one another, which are connected to one another by webs in such a way that their intermediate spaces form cooling channels through which cooling air can flow, is characterized in that the geometric arrangement of the webs is so irregular, in particular chaotic, that only a single standing wave can form over the entire circumference of the brake disc during braking.

[0013] This advantageously drastically reduces the likelihood of disruptive noise development caused by the excitation of natural frequencies in vehicle components, thus lowering the noise level and increasing passenger comfort. The irregular or chaotic arrangement of the standing wave is also weight-neutral. This vibration reduction measure results in less excitation of the brake disc and less energy being introduced into the vehicle system. If only a single standing wave of a single wavelength can develop across the entire circumference of the brake disc during braking, the probability of hitting the natural frequency of vehicle components is also reduced.

[0014] In a preferred embodiment of the invention, an internally ventilated brake disc is characterized in that the irregular, in particular chaotic, arrangement of the webs is achieved by a displacement alternating in direction over a certain circumferential angle of all webs with a prime number counting number based on their consecutive numbering along the circumference of the brake disc.

[0015] Advantageously, assuming a regular arrangement of the webs around the circumference of the brake disc, all prime-numbered webs are alternately offset by +2 and -2 degrees of circumferential angle on the friction discs of the brake disc. The circumferential angle amount of the alternating displacement of the webs with a prime number can also be one to five degrees for each web, in particular two degrees.

[0016] A preferred embodiment of the present invention for a brake disc is schematically illustrated in the single accompanying figure, limited to the essentials. This figure shows a longitudinal section between two friction discs, showing half a brake disc with a web arrangement according to the invention and its formation.

[0017] The figure shows, on the inside of a first friction disc 20 of an internally ventilated brake disc 21 for a motor vehicle, a chaotically arranged combination of webs 1, 2', 3', 4, 5', 6, 7', 8, 9, 10, 11', 12, and 13', and their origin from structurally regularly arranged webs 1 to 13, the division of which is shown schematically, not to scale, indicated by dashed lines. The webs 1, 2', 3', 4, 5', 6, 7', 8, 9, 10, 11', 12, and 13', whose length and shape are only indicated and not drawn to scale, connect the first annular friction disc 20 to a second friction disc adjacent in the axial direction, not visible in the partial cross-section. The webs 1, 2', 3', 4, 5', 6, 7', 8, 9, 10, 11', 12 and 13' delimit the cooling channels in the circumferential direction of the brake disc 21 between the friction disc 20 and its adjacent friction disc.

[0018] The chaotic arrangement of the webs 1, 2', 3', 4, 5', 6, 7', 8, 9, 10, 11', 12 and 13' arises from the fact that all webs 1 to 13, structurally regular arrangement, whose numbering results in a prime number, i.e. the webs with the numbering or reference number 2, 3, 5, 7, 11 and 13, are offset in their direction by two angular degrees in the circumferential direction of the brake disc 21. Thus, the offset of web 2 is counterclockwise to the left by minus two degrees relative to web 2', the offset of web 3 is clockwise to the right by plus two degrees relative to web 3' and the offset of web 5 is again counterclockwise to the left by minus two degrees relative to web 5' and so on for all further webs 7, 11, 13, whose number is a prime number when numbering webs 1 to 13.This results in the additional webs 7', 11' and 13' being constructed from the webs 7, 11 and 13 of the geometrically regular circular ring division, which are structurally omitted.

[0019] The webs 1, 2', 3', 4, 5', 6, 7', 8, 9, 10, 11', 12 and 13' or the cooling channels located between these webs 1, 2', 3', 4, 5', 6, 7', 8, 9, 10, 11', 12 and 13' can, for example, according to the prior art, each extend from a not-drawn inner diameter on the friction disc 20, in the vicinity of a not-drawn inner circumferential edge of the friction disc 20, to an outer diameter close to an outer circumferential edge 22 of the friction disc 20 of the brake disc 21.

[0020] According to the prior art, the brake disc 21 can be fixed via its inner peripheral edge to a brake disc hub (not shown) and via this to a wheel flange (not shown) of a wheel suspension of a motor vehicle.

Claims

[1] Internally ventilated brake disc (21) for a disc brake, with two friction discs (20) arranged adjacent to one another, which are connected to one another by webs (1, 2', 3', 4, 5', 6, 7', 8, 9, 10, 11', 12, 13') in such a way that the spaces between them form cooling channels through which cooling air can flow, characterized by that the geometric arrangement of the webs (1, 2', 3', 4, 5', 6, 7', 8, 9, 10, 11', 12, 13') is so irregular that only a single standing wave can arise over the entire circumference of the brake disc during braking. [2] Internally ventilated brake disc according to claim 1, characterized by that the irregular arrangement of the webs (1, 2', 3', 4, 5', 6, 7', 8, 9, 10, 11', 12, 13') is achieved by a displacement alternating in direction over a certain circumferential angle of all webs (2', 3', 5', 7', 11', 13') with a prime counting number based on their consecutive numbering along the circumference of the brake disc (21). [3] Internally ventilated brake disc according to claim 2, characterized by that the circumferential angle amount of the displacement of the webs (2', 3', 5', 7', 11', 13') alternating in direction with a counting number which is a prime number, for each web (2', 3', 5', 7', 11', 13') is one to five, in particular two, angular degrees.

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