Browse Topic: Disc brakes
With the growing trend of electric vehicles (EVs) incorporating regenerative braking systems, many compact SUVs, including hybrids and EVs, still utilize drum brakes on the rear wheels to strike a balance between cost, performance, and durability. Drum brake squeal remains a complex and persistent challenge in the field of vehicle noise, vibration, and harshness (NVH). This issue stems from dynamic instability caused by time–dependent friction forces. Traditional linear modal analysis has been used to study the mechanisms behind drum brake squeal, focusing on harmonic vibrations in large–scale models. However, these methods often fail to accurately correlate with real world behavior due to the presence of extra, non-physical modes. To address this, time–domain analysis approaches have been explored, incorporating detailed friction models and contact mechanics. These methods consider different root causes for high and low–frequency squeal and have shown promising results in accurately predicting brake squeal behavior when validated against experimental data.
In an earlier publication, it was reported that the pad compressibility measured under 160 bars on NAO formulas keeps decreasing with increasing number of repeated measurements due to unrecoverable residual deformation of the friction material combined with increasing moisture adsorption, which increases the hardness of the friction material. This current investigation was undertaken to find out if this same phenomenon occurs for NAOs under a low pressure of 100 bars during compressibility measurements and under 700N during dynamic modulus measurements. In all cases, it is found that the same phenomenon occurs, meaning that friction materials become permanently compressed without full recovery, making them harder to compress and raising up the modulus. The dynamic modulus of friction material attached to a backplate is found to be lower as compared with the friction material without the backplate, which is caused by more rapid moisture adsorption of friction material pads without a backplate. As pad properties are continuously changing under pressure at temperature during usage, compressibilities and dynamic moduli measured for the initial quality must not be used for predicting brake performance/NVH – an important issue for AI databases.
The use of drum brakes in Battery Electric Vehicles (BEVs) offers numerous benefits, including energy efficiency, reduced brake dust emissions, and reliable performance under challenging weather conditions. The capability of regenerative braking reduces the friction brake application frequency in BEVs and therefore the brakes can be prone to corrosion and performance degradation especially considering conventional disc brake systems. The closed design of a drum brake prevents corrosion of the friction-components by sealing out water, dirt or snow. A common sealing concept is performed with a labyrinth between the gap of the rotating drum and the axle mounted backplate. A hermetical isolation of water and snow ingress into the drum cannot be achieved with this concept, so additional aerodynamic measures are necessary to deflect the air/water path and protect the inner brake components. Additionally, interfaces like wheel cylinders, electric park brake parts, brake shoe pins, and axle mountings can potentially lead to leaks on the backplate. This study highlights the impact of water/snow ingress on the example of a frozen parking brake during cold climate on-road testing. Through scientific investigation using the state-of-the-art fluorescence method, drum leakages were visualized, and the extent of water ingress was measured. Multiple multiphase CFD simulations supported the design phase of the aerodynamic measures. Subsequently, the vehicle was cooled down to -10 °C to simulate the cold climate test conditions. The frozen parking brake situation could be reproduced with this method, and beneficial aerodynamic and sealing measures were extrapolated to avoid the drum brake from freezing. The tests were conducted in the FKFS Thermal Wind Tunnel, a wind tunnel comprising a two-axle-dynamometer and water irrigation systems with UV illumination.
Disc brakes play a vital role in automotive braking systems, offering a dependable and effective means of decelerating or halting a vehicle. The disc brake assembly functions by converting the vehicle's kinetic energy into thermal energy through friction. The performances of the brake assembly and user experience are significantly impacted by squeal noise and wear behaviour. This paper delves into the fundamental mechanisms behind squeal noise and assesses the wear performance of the disc brake assembly. Functionally graded materials (FGMs) are an innovative type of composite material, characterized by gradual variations in composition and structure throughout their volume, leading to changes in properties such as mechanical strength, thermal conductivity, and corrosion resistance. FGMs have emerged as a groundbreaking solution in the design and manufacturing of brake rotors, addressing significant challenges related to thermal stress, wear resistance, and overall performance. These studies evaluate the noise and wear behaviour of disc brake assemblies made with FGMs. The paper also investigates the application of FGMs in brake rotors, highlighting their distinctive properties and the advantages they offer to automotive braking systems. The study underscores the importance of further research and development to fully leverage the benefits of FGMs in enhancing brake system performance.
The influence of moisture adsorption, prior braking, and deceleration rate on the low-speed braking noise has been investigated, using copper-free disc pads on a passenger car. With increasing moisture adsorption time, decreasing severity of prior braking or increasing deceleration rate, the noise sound level increases for the air-borne exterior noise as well as for the structure-borne interior noise. The near-end stop noise and the zero-speed start-to-move noise show a good correlation. Also, a good correlation is found between the noise measured on a noise dynamometer and on a vehicle for the air-borne noise. All the variables need to be precisely controlled to achieve repeatable and reliable results for dynamometer and vehicle braking groan noise tests. It appears that the zero-speed start-to-move vehicle interior noise is caused by the pre-slip vibration of the brake: further research is needed.
Despite efforts to reduce disc brake noise occurrence, it remains a significant concern in the automotive industry, particularly in the current era of electric vehicles, where it can be an intermittent issue. There is no standard solution available for every noise frequency, as it depends on various conditions and parameters that need to be experimentally identified and addressed. This paper specifically focuses on addressing low-frequency noise. During dynamic conditions, the contact pressure becomes uneven, leading to uneven pad wear and making the disc brake system susceptible to noise. In noise rigs, the paper selects the most suitable shim and pad geometry based on trials that analyze the interaction between the shim and pad. In conventional practice, shim modification was performed using computer-aided engineering, but obtaining accurate pressure patterns in dynamic conditions with CAE is challenging due to certain assumptions. Through dynamometer trials, the paper identifies that the critical frequency is caused by the coupling of the disc and pad mode shapes. Wear analysis reveals greater wear on the leading side of the piston, which can contribute to noise at critical frequencies. Pressure patterns were examined using Tekscan™ across different pressure ranges from 10 bar to 50 bar to understand the cause of uneven wear, confirming the bias in the caliper loading pattern. Consequently, the details of piston contact pressure were investigated, indicating higher pressure distribution on the leading end of the piston compared to the trialing side. Further analysis using finite element analysis (FEA) confirms a similar bias towards the caliper on the leading side. To modify the pressure pattern and reduce noise, a half-moon cut profile was introduced in the shim, resulting in the elimination of occurrences at 3.9 kHz.
As the vehicle electrification progresses and the demand for acoustic comfort increases, the NVH performance of brakes becomes more important theme. In-plane squeal of disc brake is one of phenomena that is difficult to countermeasure. In this study, we used array microphones to search for sound sources of in-plane squeal in order to elucidate the mechanism. The Microphones were set in the out-of-plane direction and the lateral direction of a disc in brake components on a full-sized dynamometer. In the vibration mode in which in-plane stretch vibration was dominant, the sparse and dense parts showed high sound pressure. 3D laser vibrometer was used to check displacements of the disc, and the result indicated a possibility that the sparse and dense parts could vibrate in the out-of-plane direction and generate the sound. Then, complex eigenvalue analysis (CEA) and acoustic simulation were conducted to validate the experimental results. Firstly, frequency of instability mode occurred in CEA was almost the same as that of the actual brake squeal and the mode was identified as in-plane squeal mode. Secondary, acoustic simulation resulted that areas near the sparse and dense parts in a disc had high sound pressure as similar to the sound source identified by array microphones. Finally, parametric studies of friction material property showed correlation between the CEA results and the sound pressure distribution obtained by acoustic simulation.
The braking system in a vehicle is one of the most crucial parts for proper and safe operation. It is required to slow down or stop the vehicle and work by converting the kinetic energy of the wheel to heat. It is essential to dissipate the generated heat for optimal working and the long life of the disc brakes. Heat generated is due to friction between the brake pad and disc. Due to overheating of brakes due to prolonged braking and heavy braking, brake fade occurs. This leads to boiling of the brake fluid, gassing, and glazing of brake pads, hence reducing braking performance. Therefore, in this study, we used computer simulations to determine the best design that allows for the most heat dissipation by analyzing four different conventional disc brake designs. It was found that the slotted disc brake design had the maximum value of heat transfer coefficient (87.2% more than that of the vented disc brake) and also correspondingly the most decrease in the maximum temperature (39.56% decrease than that of the vented disc brake). We used CFD to study the effects of airflow on convection and FEA for thermal analysis. This study aims to understand the heat transport behaviour, in general, and heat dissipation disc brakes in a comprehensive manner, in particular.
This SAE Recommended Practice is intended for measuring the static brake torque performance of a pnuematically actuated brake assembly, friction material, and drum/disc combination on an inertia brake dynamometer.
The brake of a vehicle is of particular importance for vehicle safety. Brake inspection is an essential part of the periodic technical inspection and contributes to road safety. The current vehicle brake inspection methods are mostly tied to brake tester and check the vehicle brake in a workspace that does not have much practical relevance. Therefore, an attempt is made to develop dynamic inspection methods for automotive brakes, which are based on driving tests. To develop these dynamic inspection methods, a vehicle model is used, which includes an empirical brake model that takes into account the various dependencies of the coefficient of friction of the friction pairing of automotive disc brakes. The model is later validated with full-vehicle brake maneuvers from different velocities and under different conditions and shows good results.
This document describes standard test methods, analysis methods, and reporting methods for measuring the resonant modes of automotive disc brake rotors and drums for design/development and production verification of these components.
This SAE Recommend Practice specifies a method for measuring the deflection of friction materials and disc brake pad assemblies in a manner more consistent with classical material compressive strain testing. This SAE test method differs from SAE J2468 in the preload and maximum load applied to the test sample when deflection is measured. It adopts the material applied stress levels found in ISO 6310 (0.5 to 8.0 MPa) using a 25 mm diameter flat plunger.
This paper addresses the brake pad particle emission during the braking process of a vehicle in motion. The frictional-constant contact between the disc brake and pads results in an increased temperature and wear of the pads. The emission of brake pad particles into the atmosphere leads to an increase in air pollution and hence becomes hazardous to the human body. In this paper, a wheel brake disc is installed in a ventilation system where the specific air flow is introduced in order to investigate the thermal performance and the emission of particles from the brake pads. A mathematical model using the fundamental parameters of the brake disc and ventilation system is established. The behavior of the heat transfer is studied using computational fluid dynamics (CFD). The particle emission rate from the pads is calculated under the assumption of uniform constant pressure distribution at the contact surface of the brake disc and pad. The results of the analysis show that circumferential airflow within the ventilation system is uniform with the rotation direction of the brake disc and that the particles of the pad are dispersed in the axial direction of airflow. The CFD simulation also shows that the airflow around the brake disc reduced the temperature of the disc by 20%. The validity of the ventilation model is verified with Finite Element Method (FEM).
This article presents a novel aero-thermal coupled simulation approach for estimating the cooling performance of automotive vented disc brakes under the scenario of emergency braking. This approach couples the quasi-steady computational fluid dynamics (CFD) analysis in the fluid domain and the transient thermal calculation in the solid domain, and no finite element method (FEM)-based calculation is involved in the simulation. An advanced coupling strategy is proposed and used in the approach to solve the problem of boundary mismatch when data exchanging between the solid and fluid domains, and a specific point-in-polygon (P-in-P) algorithm is incorporated into the approach for a precise calculation of the braking heat flux through the brake disc. This approach has been implemented to analyze the temperature change of the vented disc brake for a real vehicle, and the results show that it is able to replicate the real pattern of heat generation via friction on the surface of the brake disc and accurately predict the temperature peak inside the brake disc. Such an approach has a high potential of engineering application to estimate the cooling performance of different types of automotive frictional brakes under other more complicated scenarios.
The braking capacity of reducing the speed or even keeping the vehicle stoped is extremely important in the design of any brake system, as more than meeting legislation requirements; it directly affects the safe operation of the vehicle and its users. A fundamental component, which requires notable attention, is the friction material, which is designed to establish a compromise between mechanical properties, friction coefficient, noise propensity, deformation, wear, among others. However, braking capacity is a combined response for several of these friction material properties, along with the performance of other brake system components, such as the brake chamber, disc and caliper. This work aims to analyze firstly the influence of the friction material deformation and secondly the brake system deformation on the total stroke of the brake chamber. To the first one, three different formulations of friction material, applied to commercial vehicles, were selected. For these materials, compressibility measurements were performed, according to ISO 6310, and also subjected to static test for measuring the total stroke of the brake chamber, in an inertial dynamometer. The static test performed consists of a pressure ramp application on the brake pad with the measurement of the total chamber stroke for each of the pressures. To the second one, static test was performed using steel pads (copying the brake pad shape), with thickness simulating new and end-of-life pads. The friction material and the brake system showed a significant pressure sensitivity, with a small contribution at low pressures, increasing its contribution with pressure increase. More than it, this work allowed to understand that the formulation, pad compressibility, material thickness, brake system stiffness, temperature and chamfered pads show a significant influence on the performance, fuel consumption and reduction of pollutants), there are also improvements to be made on braking performance and reduction of early wear. These improvements must also be applied to commercial vehicles such as trucks and buses, where the brake system is subjected to heavy loads and long routes. For this type of vehicle is very important to obtain maximum brake pad durability, in order to reach customer satisfaction. For commercial vehicles, the use of disc brakes has been increasing gradually, once it is already widely applied in Europe and there is a gradual growth in North American and Asian markets. Brazil tends to follow the same path as Europe, only slower, due to drum brakes costs, which are much lower than disc brake costs. Disc brake system has greater advantages compared to the drum brake system, such as: higher braking efficiency, even on higher application temperatures; greater dissipative energy capacity during braking and, finally, greater comfort during brake pedal actuation [2]. Pedal force and displacement are important factors for the driver to modulate, regarding safety and braking efficiency. It shows that soft pedal feeling is not only unsafe due to lack of vehicle control and accidental brake lock, but can also generate longer stopping distances [3]. Technically, the term known as Pedal Sensitivity means the relationship between the force applied to the pedal, the pedal travel and the deceleration achieved by the vehicle. Normally, the vehicle's brake capacity is evaluated on a field test, considering different conditions of deceleration, force and chamber stroke.
Copper-free disc pads of 9 different compositions were made using a traditional hot molding process and tested to study frictional behavior. It is found that the friction coefficient consists primarily of two parts; one part controlled by the plastic deformation of the friction surface region of the disc and pad, and the second part controlled by the total wear of the disc and pads. As the plastic deformation and the wear are non-linear with respect to the load and sliding speed, the friction coefficient becomes a non-linear function of the load and speed. Under moderate braking conditions, the plastic deformation part is more significant in determining the friction coefficient while under more severe braking conditions, the wear contribution becomes more significant. The frictional behavior of a fade cycle is explained, and the correlation between brake squeal and disc wear is confirmed.
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