Squeal Vibration Research Articles

Prediction of wheel squeal noise under mode coupling

Wheel squeal vibration and noise amplitude under the effects of mode coupling and rising and falling creep behavior is investigated and predicted using an efficient analytical model. Based on previous research, a simplified modal dynamics model for wheel squeal noise amplitude is enhanced to include two coupled modes. Closed form analytical solutions for the vibration and squeal noise amplitude are determined under combined squeal mechanisms of full sliding falling friction and mode coupling. The analytical predictions are then compared with numerical time domain simulations of squeal vibrations with nonlinear creep and sound pressure level amplitude over a range of angle of attacks and contact angles for the inner and outer wheels in a curve. As an example, the effect of rail dynamics on squeal amplitude is quantified by comparing results with and without the mode coupling and the conditions and occurrences of stiffness and viscous mode coupling (where the stability is determined by the coupled structural complex stiffness, due to the closeness of the uncoupled modes, and damping, respectively) are clearly identified and quantified. The viscous mode coupling from the rail is shown to significantly reduce and/or eliminate conventional wheel squeal, for the inner and outer wheels, at higher contact angles defined by the friction coefficient. It can otherwise amplify (up to approximately 5 dB) or cause squeal, under high rail damping for the leading outer wheel. Conversely, it is shown that under only a small range of contact angles and closely matched uncoupled modes, stiffness mode coupling causes very high amplitude squeal beyond the scope of the simplified creep model. Rail mass and damping only models are shown to represent the occurrences of stiffness and viscous mode coupling, respectively, where the optimum amplitudes are dependent upon the complex stiffness and rail damping, respectively. The scope of the efficient analytical model is quantified and shown to be limited by excessive non-proportional damping and very high squeal amplitudes associated with reverse full sliding. The analytical model is shown to provide insight into the effects of mode coupling dynamics on wheel squeal noise amplitude and possibly help explain the enigma that squeal occurs seemingly unreliably in the field.

Squeal propensity characterization of brake lining materials through friction noise measurements

Disc brake systems are a technology widely adopted within the automotive and rail industry, especially when high performance is needed. The interaction between the disc and the pads is responsible for friction-induced vibrations, leading often to squeal noise emission. Squeal vibrations are generated by the onset of an unstable mode, which is triggered by an external excitation. Local phenomena occurring at the contact interface, and resulting in friction noise, can be responsible of the dynamic excitation triggering the squeal instability. This work proposes a new approach for characterizing friction lining materials, by measuring the friction noise coming from the contact between different pad materials and a disc rotor, in order to quantify and compare the attitude of materials to trigger squeal. Then, a parametrical analysis has been carried out with the aim of highlighting the influence of the main parameters on the friction noise. When testing the same set of materials on a full brake disc system, the measured friction noise indexes resulted to be strongly correlated with the squeal occurrence, validating the proposed characterization method for the squeal propensity of lining materials.

Modelling and mitigation of wheel squeal noise under friction modifiers

The prediction of wheel squeal vibration and noise under the presence of friction modifiers is investigated using an efficient analytical model. The enhanced modelling is used to determine instantaneous rolling contact traction-creep curves from quasistatically measured ones using a two disk testrig under dry and friction modified conditions. The analytical solution is then compared with both numerical and experimental measurements of squeal vibrations and sound pressure level amplitude over a range of angle of attacks. Squeal is shown to occur in both the dry and friction modified conditions at about the same steady state amplitude. The robustness of the model is further verified under a much lower speed and the amplitudes, occurrence and non-occurrence of squeal is well predicted within measurement error. The model is shown to provide efficient quantified insight into why squeal noise may and may not occur under oil-based friction modification. Subsequently the model is used to determine an optimised region of the measured quasistatic traction-creep curve within which friction modification can eliminate wheel squeal.

Automotive brake squeal analysis with rotating finite elements of asymmetric disc in time

The new finite element brake squeal model is proposed where the finite elements of a real brake disc rotate in time. Contact nodal forces between the rotating disc and stationary pads are allocated to the moving contact area at every time step. When the proposed model is applied to an asymmetric automotive brake disc, it becomes the periodic time-varying brake system. The stability boundary of the discrete time-varying system is numerically calculated by the Floquet theory. Also, the quasi-static linearized eigenvalue analysis is conducted to show that the unstable modes repeatedly appear at the short interval of the disc rotation angle. The results are consistent with the angle-dependent local phenomenon of squeal termed squeal periodicity in the squeal experiment. In the nonlinear time-domain analysis, the squeal vibration increases and then decays in time for the rotating mode shape functions. It demonstrates that the rotation of an asymmetric disc can change the nonlinear squeal behavior as well as the linear stability character drastically.

A new instability index for unstable mode selection in squeal prediction by complex eigenvalue analysis

During these last decades the modal instability of systems, generated by frictional contact forces, has been the subject of a huge amount of works in friction induced vibration literature. Linear and nonlinear numerical analyses have been largely investigated to predict and reproduce squeal vibrations. While nonlinear transient analysis needs large computational efforts, results of Complex Eigenvalue Analysis (CEA) suffer from an over-prediction issue and it is not able to predict correctly the mode that will become effectively unstable in case of several unstable eigenvalues. Because the CEA has been adopted as an efficient tool for brake design, a more reliable index is here proposed, from the CEA outputs and energetic considerations, to identify the mode that will become effectively unstable. A modular lumped model is developed to reproduce friction induced vibrations. The use of the eigenvalue real part, as discriminant of the system instability, is here combined with information coming from the eigenvectors, projected on the equilibrium position, to account for the energy flows involved in the squeal phenomena. This approach allows to define a Modal Absorption Index (MAI). The MAI allows for comparing unstable modes of the same system and is applied in this paper to predict, by CEA outputs, the unstable mode that will effectively result in squeal vibrations.

Finite element modeling for stick-slip pattern of squeal modes in disc brake

This paper provides the finite element modeling for describing the nonlinear stick-slip response of squealing modes in a disc brake system. The analytical nonlinear contact kinematics is applied to each contact node of the finite element disc and pads. Numerical results show that a portion of the contact area can undergo the stick-slip oscillation. Depending on the size of the stick-slip zone, the corresponding squeal vibration can be either the pure harmonic or periodic oscillation. Particularly, the squeal mode arising from the pad rigid mode generates the periodic stick-slip limit cycle in its steady-squealing response, as opposed that the disc squeal modes become the pure harmonic response.

VEHICLE BRAKING ASSEMBLY WITH REDUCED SQUEAL

The present disclosure relates to a vehicle braking assembly with reduced squeal, having: a brake pad operative to apply a braking force to a brake rotor or drum, the brake pad being subject to vibration during braking; and a damper attached to the pad, configured to force a squeal reducing vibration in the brake pad, the damper including: (i) a first mass; (ii) a second mass connected to the first mass by a first shaft; and (iii) a third mass connected to the first mass by a second shaft.

Finite element modelling for the investigation of in-plane modes and damping shims in disc brake squeal

Squeal propensity of the in-plane modes and the constrained-layer type damping shims for disc brake system is investigated by using the finite element method. Theoretical formulation is derived for a rotating disc in contact with two stationary vibrating pads attached to the damping shim components. By the conversion from the theoretical to FE brake model, the full equations of motion for the actual disc brake system describes the disc rotation, the in-plane friction characteristics and damping shims in association with squeal vibration. It is concluded from the results that the in-plane torsion modes can be generated by the negative friction slope, but they cannot be controlled by the damping shims. The in-plane radial mode is also investigated and found to be very insensitive in squeal generation.

Dynamic surface characteristics during disc brake squeal: non-linear modelling and simulation

This article studies the non-linear dynamic behaviour of a disc brake system during squealing induced by a disc doublet mode. The disc brake system is modelled as a rotating annular plate in contact with annular sector-friction material. In order to investigate the possibility of detachment over the contact area between the disc surface and friction material during squealing, the lift-off condition is applied to this model. Also, the non-linearity arising from the contact stiffness is considered on the basis of the load–deflection test for the friction material. Numerical results show that the vibration after the onset of squeal reaches the limit cycle. In the steady-squealing response, several interesting phenomena are observed: the stick-slip and lift-off over the specific regime of the contact area. It is shown that the dynamic surface pattern rotates due to the forward travelling wave of the squealing surface. However, the mark of the surface pattern does not seem to move because the speed of the travelling wave fluctuates at a double frequency of squeal vibration.

Squeal vibrations, glass sounds, and the stick-slip effect

The origin of the squeal acoustic emissions when a chalk is rubbed on a blackboard or better on a ceramic plate, and those when a wet finger is rubbed on a smooth surface, such as a glass surface, is sought in the stick-slip effect between the rubbing surfaces. In the case of the squealing chalk, the stick-slip effect is anchored by shear modes of vibration in about a 0.3 mm thick chalk powder band at the rubbing interface, while in the case of the wet finger on glass, by such modes in a band comprising the finger skin. Furthermore, there are the interfacial bands at the contact areas that result in the decrease of the friction coefficient with relative velocity of slide, i.e., the condition for the stick-slip effect to occur. Such bands are basically composed of the asperities on the surface of the chalk band and of the epidermis ridges and the water layer, respectively.

ディスク・パッド間圧力の均一化によるディスクブレーキ鳴きの低減(機械力学,計測,自動制御)

The pressure between a disk and a pad become un-uniform when the pad inclines due to the moment of frictional force applied when braking. The pad stiffness also becomes un-uniform because the stiffness depends on the pressure. The influence of the un-uniformity of the stiffness between the disk and the pad on squeal generation is examined by using a surface-contact-analysis model. To facilitate the stability analysis, the model consisted of a minimum element that can reproduce the squeal vibration. Specifically, the model was composed of a disk with one degree of freedom (out-of-plane direction) and a pad-caliper with two degrees of freedom (rotational and translational). The disk and the pad-caliper are connected by a distributed spring. The analytical result clarified that the coupled vibration of the disk and the pad-caliper became unstable when the pad stiffness was un-uniform, and the self-excited vibration (squeal) was then generated. Additionally, the influence of the un-uniformity of the pressure between the disk and the pad on squeal generation was examined by executing squeal tests. The moment of the frictional force could be counterbalanced by enlarging the load added to the trailing side edge of the pad, which resulted in uniform pressure between the disk and the pad. The results of the squeal test clarified that squeal was not generated when the pressure between the disk and the pad was adjusted to become uniform.

Contact surface topography and system dynamics of brake squeal

Brake noise is an example of noise caused by vibrations induced by friction forces. During brake operation, the friction between the pad and the disc can induce a dynamic instability in the system. Brake squeal can occur in the frequency range between 1 and 20 kHz, and more. Approaches to this problem are usually confined to the analysis of the system dynamics or to the tribological studies (analysis of the contact surfaces). In a previous dynamic analysis, the squeal events treated in this paper were identified to be dynamic instabilities of the brake system. This paper presents an experimental tribological analysis performed in parallel to the dynamic one and aimed to highlight the role of the contact problems in the squeal phenomena. The topography of the contact surface after braking phase with and without squeal is presented. The features of the third body and the surface topography were found to be completely different in the two cases. After squeal events the topography of the surface and the internal structure of the pad material close to the contact show several cracks and material exfoliations; on the contrary, after braking without squeal the contact surfaces were found to be smooth and compact. The analysis of the system vibrations during squeal and the numerical analysis of the contact stresses allow to relate these features to the fatigue excitation due to the local oscillation of the contact stresses at the contact surface at the squeal frequencies. The surface topography after squeal, by revealing several fatigue evidences, points out a further problem, i.e., the possible increasing of wear rates that are consequent to the squeal vibrations.

Influence of Pad Chamfering on Disk Brake Squeal

This study presents experimental and analytical results about the influence of pad chamfering on squeal vibration in the disk-pad-caliper system, which is modeled after an actual disk brake. In the leading side of contact area, the disk and the pad-caliper vibrate with the same amplitude and the same phase at a point. We call this point “contact point”. Chamfering of the pad on the leading edge decreases the sound pressure level of squeal and moves the contact point from the leading side to the center of the pad. On the other hand, chamfering of the pad on the trailing edge has no relation to the squeal vibration. To clarify the influence of chamfering on squeal, we analyzed the disk-pad-caliper system as a surface contact analysis model, which combined the disk with pad-caliper by distributed springs.

Surface Contact Analysis Model for Squeal on Disk Brake

This study presents the stability analysis of squeal vibration on disk brakes by a surface contact analysis model. In experimental results, the sound pressure level and the frequency of squeal depend on thrust pressure. We think the cause of this phenomenon is that the stiffness of the pad depends on thrust pressure in contact region. Therefore, we propose to use the surface contact analysis model which combines a disk with a pad-caliper by distributed springs. Based on the actual squeal vibration, the disk has translational motion while the pad-caliper has both translational and rotational motions. The analytical results by this model are in good agreement with the experimental results.

709 ディスクブレーキの鳴きに及ぼす摩擦接触部の動剛性の影響

This study presents experimental and analytical results of squeal vibration in the disk-pad-caliper system which is modeled based on an actual brake. The frequency of squeal becomes higher as the thrust pressure grows large. To clarify this phenomenon, we examine the dynamic stiffiness between disk and pad. As a result of the experiment, dynamic stiffness grows large when the thrust pressure grows large. Then we analyzed the disk-pad-caliper system as a distributed dynamic stiffness model. This model considers the distribution of the thrust pressure and the dynamic stiffness in the contact region.

Squeal Vibration in Disk Brake

This study presents experimental and analytical results of squeal vibration in the disk-pad-caliper system, which is modeled after an actual disk brake. The system consists of a disk clamped along an inner edge and a pad supported by a plate spring (caliper). The frequency of squeal becomes higher as the thickness of the plate spring becomes large, and as the thrust load grows large. The squeal vibration of the disk near the contact area between the disk and the pad has translational motion, and the squeal vibration of this pad-caliper has translational and rotational motion. The disk and the pad-caliper vibrate with the same amplitude and the same phase at a point in the contact area. Therefore we analyzed the disk-pad-caliper system as a pin-disk model, which combined the disk with the pad-caliper by the point.

614 ディスクブレーキの鳴きに及ぼす摩擦接触部の動剛性の影響(モデル化・摩擦機構,振動基礎(1))

This study presents experimental and analytical results of squeal vibration in the disk-pad-caliper system, which is modeled after an actual disk brake. The frequency of squeal becomes higher as the thrust load grows large. We think this phenomenon originates in that the stiffness of a contact region becomes hard according to load. Therefore we measured stiffness of a contact region in the experiment conditions imitating the situation which squeal vibration generated. And we analyzed the disk-pad-caliper system as a distributed spring model based on experiment result This model expresses that the mode of vibration and a sound pressure level is dependent on load.

1122 ディスクブレーキの鳴き発生のモデリング

This study presents experimental and analytical results of squeal in the disk-pad-caliper system, which is modeled after an actual disk brake. The system consists of a disk clamped along an inner edge and a pad supported by a plate spring (caliper). It is shown that the squeal vibration of the disk near a contact area has translational motion, and the squeal vibration of pad-caliper has translational motion and rotational motion. Squeal vibration of the disk-pad-caliper system near a contact area has same amplitude and phase at a point. Therefore we analyzed the disk-pad-caliper system as a pin-disk model, which combined the disk with the pad-caliper by a point.

A predictive tool to evaluate disc brake squeal propensity. Part 2: System linearisation and modal analysis

This paper is the second in a series of three that together describe an integrated theoretical approach to the analysis of disc brake squeal. Within this paper, the specific problems of system linearisation and complex modal analysis are addressed. The likelihood of squeal noise occurrence is quantified by the definition of a single indicator derived from the system eigenvalues. Mode shape analysis permits study of the motion linked to each mode and a technique is presented that reconstructs a true picture of the complex mode through the combination of its real and imaginary components. Typical results are presented for stable and unstable modes of vibration which lead to the proposal of a mechanism that gives rise to the unstable squeal vibration.

BRAKE VIBRATION ANALYSIS WITH THREE-DIMENSIONAL PULSED ESPI

The measurement of brake squeal vibrations is a serious problem, because the rotating disc does not allow any physical contact with the sample during measurement. When using non contact scanning techniques (e.g. vibrometers) still problems occur if non steady vibrations are present. Furthermore, the recent interest of researchers has focused not only on the onedimensional out-of plane deformation, but on the determination of the three-dimensional vibration behavior, especially the analysis of the in-plane component of the vibration. PulsESPI has already been presented as non contact and full tield measuring technique, which provides complete maps of the vibration of any component of the brake during test. Brake discs, drums, calipers, pads have been measured with this technique. The component under investigation -e.g. a rotating brake disc with engaged caliper is illuminated by two very short laser pulses with a predetermined time separation. The images at these two laser illuminations are recorded with a special high speed camera (PulsESPI camera) and analyzed in a computer. The calculated result is a deformation map of each point of the brake disc and caliper which describes the movement of the individual points of the brake between these two laser pulses. Therefore, this technique literally freezes two moments of the movement of the brake and gives an instantaneous view of the overall deformation. Recent developments have produced 3D-PulsESPI systems, which provide the complete three-dimensional vibration map of the brake. Special algorithms are used in order to separate the rotation component of the brake disc from the in-plane vibrations. Using this 3D-PulsESPI technique completely automatic brake squeal inspection systems have been designed, which capture the squealing signal, automatically fire the laser and provide the complete deformation map of the component under test. In this paper, we describe this promising new PulsESPI technique and give examples of recent applications in the field of brake squeal analysis.