Mode hamper and method for testing a brake disc by vibration

Abstract

The invention relates to a modal hammer and to a method for testing a brake disc (1) by means of vibration technology. The method comprises the steps of: rotating the brake disc (1) during its engagement with the brake lining; exciting the brake disc (1) by means of knocking by an exciter, in particular by means of a modal hammer (2) and / or an electromagnet; and scanning the brake disc (1) at different points (P) with a laser vibrometer (6).

Description

Technical Field

[0001] The present invention relates to a modal hammer and a method for testing brake discs by vibration technology. In particular, the present invention relates to an improved possibility for testing the modalities of brake discs under real conditions. Background Art

[0002] Avoiding brake noise is a major challenge in the development of passenger car brake systems. In order to evaluate the noise development during the development of brake systems, brake noise test benches (BGPs) are used. A large number of braking events under different operating and environmental conditions are simulated on these BGPs in order to be able to evaluate the noise sensitivity of the brake system as comprehensively as possible (passive noise search).

[0003] Alternatively, an active noise search can be performed, in which the brake system is excited to vibrate in the audible frequency range by an additional device. In this regard, reference is made to DE 100 06 391 A1 and DE 10 2019 119 149 A1. Here, the vibration excitation must be as close as possible to the friction contact between the disk and the pad, since this is the cause of the brake noise.

[0004] Passive noise searches are very time consuming, as many experiments need to be performed on a test bench in order to obtain meaningful results. Furthermore, the results of passive noise searches are subject to fluctuations for reasons that are not fully understood.

[0005] For the analysis of the operating vibration pattern of a brake system, noise must be generated by a targeted approach to the operating state. As soon as the noise is detected by a microphone, a measurement is carried out with the aid of a Doppler laser scanning vibrometer to determine the operating vibration pattern. However, it is often difficult to maintain the noise for a sufficiently long time, so the measurement time is limited. However, since preferably several hundred measuring points must be scanned in order to correctly reconstruct the operating vibration pattern, it may be necessary to approach the respective operating state several times. Furthermore, the operating vibration pattern is only measured at the frequencies at which the noise occurs.

[0006] The test apparatuses known from the prior art have the disadvantage that the vibration behavior of the brake system of the vehicle is sometimes significantly changed by the measuring technique. However, since the additional application of small masses (10 g to 50 g) is a known measure for suppressing squeal, these known test apparatuses are not completely free of influence on the test results of the noise behavior of the brake system. Summary of the invention

[0007] It is an object of the present invention to eliminate the disadvantages known from the prior art.

[0008] According to the invention, the above-mentioned object is achieved by a method for testing a brake disc by vibration technology. Furthermore, a modal hammer for use in the method according to the invention is proposed.

[0009] The dependent claims reveal preferred developments of the invention.

[0010] According to a first aspect, a method for testing a brake disc by vibration technology is proposed. The brake disc can be provided for a passenger car brake system. In a first step, the brake disc is rotated during its engagement with the brake lining or during braking by means of the brake lining. The brake lining or the brake system can also be a brake system close to mass production or in accordance with mass production standards. In other words, the combination of brake disc and brake lining, brake caliper, etc., is tested for vibration technology properties on a test bench. The brake engagement can be carried out with a predefined braking force. The braked brake disc can be rotated, for example, by means of an electric motor. This can be operated in a speed-controlled manner so that the predefined speed of the brake disc is always maintained. In a further step, the brake disc is excited by means of an exciter, in particular automatically, preferably by means of a modal hammer. In the following, in order to maintain linguistic simplicity, it is always referred to as a modal hammer. In particular, the modal hammer can strike the brake disc in the radial direction or in the axial direction. That is, the brake disc is excited by means of the modal hammer during its movement under the action of the braking force. This results in a particularly close-to-real vibration mode for the brake disc, which can be used later. In a final step, the brake disc is scanned at various points with the aid of a laser vibrometer. In other words, a representative surface area of ​​the brake disc is scanned by the laser vibrometer with respect to its deflection during the excitation of the vibration (brake squeal). The points can be measured after a single blow with a modal hammer, with corresponding blows with a modal hammer, or during multiple blows with a modal hammer. The rotation under the action of the braking force results in a particularly realistic modal analysis, since the excitation and grinding effects caused by the brake are realistically included, the local effects of the brake on the different areas of the vibration form are maintained, centrifugal forces occur inside the brake as in real operation, and in addition, ambient air flows through the air chamber between the two sides of the brake disc. The results recorded with the aid of the laser vibrometer therefore correspond as best as possible to the real operating conditions under which brake squeal usually occurs.

[0011] By ensuring a predefined rotational speed before performing the scan, the temporally continuous measurement of different points on the brake disc can preferably produce representative results. For example, the speed can be kept constant during the scan and / or another predefined condition can be ensured. For example, a predefined temperature of the brake disc or the brake fluid can also be ensured. For this purpose, the system can be brought to a stable state in which the brake disc radiates just as much thermal energy as is absorbed by the braking process. The predefined temperature can be measured by means of a contactless measurement, by means of a grinding thermometer and / or by measuring the brake fluid temperature. After the brake disc temperature has stabilized, the measurement by means of a laser vibrometer can be enabled. Alternatively or additionally, a predefined brake pressure can be determined, which remains constant for the duration of the scan of the different points, so that the measurements of the different points on the brake disc can be combined essentially without error. Alternatively or additionally, it can be ensured that a predefined rotational position of the brake disc is established at the moment of the modal hammer impact. In this way, the modal hammer always impacts the same position on the brake disc, so that possible rotational asymmetries cannot have an influence on the measurement results. Only in response to determining the aforementioned start condition or any combination of the aforementioned start conditions is then the excitation and / or scanning of the brake disc started.By sequentially scanning the brake disc by means of the laser vibrometer the best possible measurement result can thus be ensured.

[0012] During scanning, the laser beam of the laser vibrometer can track a predefined point on the brake disc. For example, during the measurement of the point under consideration, the same point can always be irradiated by means of the laser beam. Alternatively, the laser beam can be fixedly aligned so that a circle is scanned on the brake disc. If the laser beam tracks the measurement point, the laser itself can be arranged on a device that rotates synchronously with the brake disc in order to keep the laser beam pointed at the point. Alternatively, the laser beam can be deflected onto a circular path by means of optical mirrors or the like, so that the same point on the brake disc is always scanned during the vibration damping of the brake disc.

[0013] The excitation or striking direction of the modal hammer can be realized in the radial direction and / or in the tangential direction. For example, the modal hammer can excite the (exposed) side surface of the brake disc surface engaged by the brake lining or the end surface of the brake disc surface with a free gap in a normal direction for this purpose. Here, the modal hammer can have a shank, which is aligned in the tangential direction relative to the rotation of the brake disc at the moment when the head of the modal hammer contacts the brake disc. In this way, by the brake disc "pulling" the modal hammer head in the lateral direction at the moment of impact, moments that could damage the modal hammer can be avoided, which could overstress the bearing part of the shank of the modal hammer.

[0014] The modal hammer can be designed with the aid of different measuring sensors in order to determine the characteristic variable of the impact by measuring technology and compare it with a predefined reference value. In other words, the impulse applied by the hammer or the velocity / acceleration of the hammer head at the moment of impact can be determined by measuring technology. The reference value can represent a target value of the characteristic variable, so that in response to reaching the predefined reference value, the measurement is declared "valid" or "normal" and saved, while in the case of deviations from the predefined reference value, the measurement is discarded, the measurement data are optionally not saved, and the measurement is automatically repeated if necessary.

[0015] The modal hammer can be arranged in particular in a fixed position on a test bench. In particular, the modal hammer can be arranged in a fixed position relative to one or more laser vibrometers. For example, the modal hammer can be fastened to a support (tripod) and / or at least fastened separately from the brake system in order not to affect the brake system by vibration technology during the test.

[0016] The vibration test can be adapted in particular to a scan of 3 to 3000, in particular 30 to 300, most preferably 50 to 200 measuring points. Alternatively or additionally, the brake disc can have a rotational speed of 0.5 to 10 rpm, preferably 1 to 5 rpm, most preferably 1.5 to 4 rpm. These rotational speeds correspond to the rotational speeds at which the brakes are most susceptible to squealing according to experience.

[0017] The method according to the invention can be designed such that for each of the above-mentioned measuring points on the brake disk, at least one, preferably exactly one, strike is performed by means of a modal hammer, after which the damping behavior of the brake disk at the considered point is recorded by means of a laser vibrometer. Thus, after essentially identical vibration states generated according to the invention have been induced by means of the modal hammer, the surface of the brake disk is measured continuously point by point by means of a laser vibrometer.

[0018] According to a second aspect of the invention, a modal hammer suitable for carrying out the above-described method is proposed. The modal hammer has a motor, by means of which the handle can be pivoted. The handle carries an elastic element between the motor and the head. Due to the elastic element, the head can move slightly together with the brake disk, independently of the kinematic mechanism activated by the motor, while it contacts the brake disk and adheres there if necessary. As a result, the elastic element relieves the load on the support of the handle in one or more motors, decouples the motor relative to the head by vibration technology, and can also provide information about the acting force through its deformation. In other words, the elastic element enables distance measurement so that the striking force can be derived.

[0019] In particular, the elastic element can be arranged between the motor and the shank and / or between the shank and the head of the modal hammer. Thus, particularly effective decoupling, easy installation and a long service life can be achieved. In particular, when the elastic element is arranged relative to the shank and the head, the shank and the head can be designed so that the elastic element forms a positive locking connection with both the shank and the head. This positive locking connection can be produced, for example, by a first thread (an internal thread in the elastic element) and an external thread on the circumference of the elastic element. The internal thread of the elastic element engages in the external thread in the shank, while the internal thread of the head engages in the external thread in the elastic element. Thus, a permanent connection with the head and the shank can be established by means of the elastic element. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Further details, features and advantages of the invention are apparent from the following description and the accompanying drawings. In the drawings:

[0021] Figure 1 a perspective view showing an experimental setup for carrying out the method according to the invention; and

[0022] Figure 2 A flow chart illustrating the steps of an exemplary embodiment of a method according to the invention for testing a brake disk by means of vibration technology is shown. DETAILED DESCRIPTION

[0023] Figure 1 An experimental device is shown, according to which an electric motor 7 can rotate a brake disk 1 of a brake system at a constant rotational speed. A brake caliper 5 with a brake lining (not shown) is provided to brake the rotation of the brake disk 1 during the rotation of the brake disk 1. For this purpose, the brake caliper 5 presses the brake lining (not shown) against the friction ring of the brake disk 1 by means of a brake piston (not shown). A modal hammer 2 is provided to be guided along arrow 9 to the end face of the brake disk 1 by means of an electric motor 24 which can pivot a handle 23. Here, a head 21 coupled to the handle 23 via a rubber sleeve as an elastic element 22 collides with the end face and excites the brake disk 1 to vibrate during the braking rotation. A point P is scanned by means of a laser vibrometer 6 via a laser beam 8. As a result, the vibration form of the brake disk 1 can be measured at least with respect to a circle located on the corresponding radius.

[0024] Figure 2The steps of an embodiment of a method according to the invention for testing a brake disc by means of vibration technology are shown. In step 100, the brake disc is rotated in the braking state. Before the measurement starts, the presence of a predefined rotational speed (rotational speed) is determined in step 200, a predefined temperature of the brake system (e.g. brake fluid) is determined in step 300, a predefined brake pressure is determined in step 400, and a predefined rotational position of the brake disc is determined in step 500. In response thereto, the brake disc is stimulated in step 600 by means of a tapping with a modal hammer. Here, the modal hammer stimulates the brake disc in a wideband while the brake disc is rotated by an electric motor in a braking manner. Finally, in step 700, the brake disc is scanned at different points by means of a laser vibrometer. At least after the tapping performed in step 600, a point or a circular path on the brake disc is scanned by means of the laser vibrometer. For the scanning in step 700 with respect to further points, a new tapping can be performed in each case with the modal hammer.

[0025] As an alternative to the modal hammer, the housing of the electromagnet is mounted without direct contact with the brake system. The electromagnet generates a highly dynamic magnetic field via the friction ring of the brake disc, which excites the brake system to vibrate over a wide frequency band.

[0026] This type of vibration analysis is usually performed on static objects or systems. In the new method, however, the vibrations of the brake are excited by a modal hammer or an electromagnet during operation of the brake system in order to determine the system characteristics during operation of the brake system. To this end, the modal hammer strikes the rotating friction ring at a constant speed of the friction ring and a constant brake pressure. If an electromagnet is installed, the highly dynamic magnetic field sets the rotating friction ring in motion through magnetic interaction.

[0027] By means of external excitation during braking, the noise sensitivity of the brake system can be detected over the entire frequency spectrum, even when no noise is noticeably present. For this purpose, a transfer function is formed between the surface velocity at a number of points on the brake disc and brake lining and the excitation force applied by a modal hammer or electromagnet. The surface velocity is detected without contact, for example using a Doppler laser scanning vibrometer. Both in-plane and out-of-plane movements of the components must be detected. The transfer function is used to assess the critical frequencies of the brake system. The more critical a particular frequency is with respect to the squeal, the greater the amplitude of the transfer function at the corresponding frequency.

[0028] With the new method, the noise sensitivity of the brake system can be quickly assessed across the entire frequency range. The method is therefore less time-consuming. In addition, the results of the active noise search are subject to fewer fluctuations, so the method is reproducible.

[0029] In addition to determining the modal parameters, external excitation during operation also enables the measurement of the operational vibration forms of the brake system. Controlled external broadband excitation with the aid of a modal hammer or electromagnetic exciter enables the continuous measurement of many operational vibration forms over the entire frequency range, without the need for practically any noise.

[0030] Using a modal hammer or an electromagnet, the noise sensitivity of the brake system can be tested without reaction, since the housing of the modal hammer or the electromagnet is mounted without direct contact with the brake system. In addition, the use of a modal hammer or an electromagnet is a particularly easy excitation to excite the rotating brake disk during braking over a wide frequency band, and modifications that change the vibration behavior of the brake system can be omitted. Overall, this saves costs and improves the quality of the measurement results.

[0031] List of reference numerals:

[0032] 1 brake disc

[0033] 2 Modal Hammer

[0034] 5. Brake caliper

[0035] 6Laser vibrometer

[0036] 7 Electric Motor

[0037] 8 Laser beams

[0038] 9 Arrows

[0039] 21Head

[0040] 22 Elastic element

[0041] 23 handle

[0042] 24 Electric Motor

[0043] 100 to 700 method steps

[0044] Point P

Claims

1. A method for testing a brake disc (1) by means of a vibration technique, comprising the following steps: ‧ causing the brake disc (1) to rotate (100) during engagement of the brake disc with the brake lining; ‧ exciting (600) the brake disc (1) by striking with an exciter, in particular a modal hammer (2) and / or an electromagnet; and ‧ Scanning (700) the brake disc (1) at different points (P) using a laser vibrometer (6).

2. The method according to claim 1, further comprising - determining (200) a predefined speed of said rotation, and / or - determining (300) a predefined temperature, and / or - determining (400) a predefined brake pressure, and / or - determining (500) a predefined rotational position of the brake disk (1), And in response to this - starting said excitation and / or said scanning.

3. The method according to claim 1 and 2, wherein: During the scanning, the laser beam (8) of the laser vibrometer (6) - Tracking a point (P) on the brake disc (1), or - Fixed alignment.

4. The method according to any one of the preceding claims, wherein: The excitation takes place in the radial direction and / or in the tangential direction.

5. The method according to any one of the preceding claims, wherein: The shank (23) of the modal hammer (2) is aligned tangentially with respect to said rotation of the brake disc (1).

6. The method according to any one of the preceding claims, wherein: The characteristic variable of the tapping is further determined by means of measurement technology and compared with a predefined reference value, wherein, in particular in response to reaching the predefined reference value, the measurement is declared normal and saved, but in the event of a deviation from the predefined reference value, the measurement is discarded, in particular automatically repeated.

7. The method according to any one of the preceding claims, wherein: The vibration technology test: - comprises 3 to 3000, in particular 30 to 300, preferably 50 to 200 points (P), and / or - carried out at a rotational speed of the brake disk (1) of 0.5 to 10 rpm, preferably 1 to 5 rpm, preferably 1.5 to 4 rpm.

8. The method according to claim 7, wherein: For each of the points (P), at least one, preferably exactly one, strike is performed with the modal hammer (2).

9. Modal hammer, including - Motor (24), - handle (23), - an elastic element (22), and - a head (21), wherein The elastic element (22) is arranged between the motor (24) and the head (21).

10. The modal hammer according to claim 9, wherein: Elastic element (22) - arranged between the motor (24) and the handle (23), and / or - arranged between the handle (23) and the head (21).

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