Browse Topic: Brake linings
This paper’s aim is to explain alternative friction lining formulations based on inorganic polymer binders for the production of new, future-proof brake friction materials. The aspects of high-temperature stability in the fading tests of the AKM- and AMS tests, as well as the reduction in PM10 emissions compared to classic organic friction materials, make these materials particularly fascinating for future use. Additionally, the energy savings potential of this type of friction lining could be of particular importance when sustainability considerations further influence our development activities in friction brake related applications.
During validation of a new brake lining on a light duty truck application, the brake rotor exhibited high lateral runout on the friction surfaces. As the engineering team investigated the issue more carefully, they noticed the rotor lateral runout was also changing from revolution to revolution. The team ran testing on multiple light pickup vehicles and found differences in the amount of rotor runout variation. The rotor lateral runout and runout variation can cause vibration and pulsation of the passenger seat and the steering wheel. To identify the root cause of the high level of rotor lateral runout and runout variation, measurement data was collected and analyzed from the vehicle level test. During further analysis, some of the runout variation corresponded to a wheel bearing internal frequency. The bearing internal geometry was studied to confirm what factors affected the runout variation. The team also conducted testing to see how the mating components may have affected the wheel bearing. In addition to the vehicle testing, fixtures were built to perform brake corner bench testing. This testing showed that both the total runout and runout variation increased as more mating components were added. Brake corners from two different vehicles were bench tested. The major difference between the vehicles was the mounting location of the splash shield. On one vehicle the splash shield is mounted (sandwiched) between the knuckle and the bearing’s outer ring flange and on the other vehicle, the splash shield is directly mounted with screws to the knuckle (not sandwiched). Splash shield distortion due to compression near the knuckle bolts and the bearing outer ring contact surface, caused the larger total runout value and the higher variation. The study also proved that continuous assembly/disassembly will increase the distortion on the mating parts, which leads to the greater total runout and variation values.
This SAE Recommended Practice is intended for qualification testing for brake drums used on highway commercial vehicles with air brakes using an inertia-dynamometer procedure. This document consists of two distinct tests: Part A, durability and speed maintenance test, and Part B, heat check drag sequence test. Each test can be considered to be an independent evaluation of the brake drum which tests different properties.
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.
With the spread of new trends such as autonomous driving and vehicle subscription service, drivers may pay less attention to the maintenance of the vehicle. Brake pads being safety critical components, the wear condition of all service brakes is required by regulation to be indicated by either acoustic of optical devices or a means of visually checking the degree of brake lining wear [1]. Current application of the wear indicator in the market uses either sound generating metal strip or wire harness based pad wear sensor. The former is not effective in generating clear alarm to the driver, and the latter is not cost effective, and there is a need for more effective and low cost solution. In this paper, a pad wear monitoring system using MOC(Motor On Caliper) EPB(Electric Parking Brake) ECU is proposed. An MOC EPB is equipped with a motor, geartrain and an ECU. The motor current when applying the parking brake is influenced by the mechanical load at the brake pad side of the system. So, by analyzing the time history of the current it is possible to measure the clearance between brake pad and disc induced by the pad wear. From the measurement of the low load interval along with the mechanical specifications of the geartrain (e.g. lead of the screw), pad wear can be calculated. A sequential procedure for pad wear measurement mode is also proposed. A HILS test bench using production MOC actuator was setup and the measurement accuracy was evaluated across various conditions such as amount of wear, supply voltage, and temperature. The result is shown and a further discussion about practical aspects of the technology is added.
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.
The aim of this paper was the proposal of a numerical procedure for the structural evaluation and durability validation of brake shoes, employing fatigue and finite element softwares that are able to predict the failure locations (and number of cycles to failure) with acceptable accuracy. The software Abaqus was used in the calculation of the stress and strain fields whereas the software fe-safe was employed in the evaluation of fatigue life. Accelerated tests were performed on a bench test that has been designed to match the operating conditions of the vehicles were the brake shoes are assembled. In those cases where only local plasticity is expected (rather than generalized plasticity) the procedure can somewhat be simplified by running linear elastic finite element analysis (instead of full non-linear), which is often called pseudo-elastic analysis [1]. Then the pseudo stresses and strains are corrected at post-processing time by means of the Neuber’s rule and Ramberg-Osgood equation [2]. The fractographies of the tested components suggest brittle failure mode, which requires a method like SWT (Smith-Watson-Topper) for the mean stress correction [10]. The full brake assembly was considered in the simulations. All the contacts are non-linear and the material of the brake lining is orthotropic. In the present context experimental life to failure is defined as the arithmetic mean of the failed samples (there were three of them). The numerical and experimental results (in terms of life) differ by no more than 52%, and the failure locations correlate really well. The developed numerical procedure has shown to be sufficiently accurate to replace the experimental tests. Therefore it can be used in a more comprehensive study where the sensitivity to geometry, material and loads can be investigated.
The static coefficient of friction between lining and shoe plays a fundamental role in the lining fixing project, which is the most important parameter for the riveted joint calculation. For the lining riveting, the rivet needs to ensure that friction material and shoe remain in contact through the normal force applied on the surfaces, but the rivet should not be exposed to shear forces. Thus, the brake torque transmission must occur through the static coefficient of friction between lining and shoe, not allowing relative slips or movements between the pair in contact. Therefore, the present study aims to understand the influence of the static friction coefficient between lining and shoe as a function of the lining internal superficial roughness, from the evaluation of different roughness conditions - contact area with shoe -. The static coefficient of friction between lining and shoe is a complex measurement to be performed, due to the cylindrical geometry of the drum brake system, so for the present study, a measuring device based on plane geometry will be proposed. Thus, three different friction materials were evaluated, and each one of them had a different formulation and mechanical properties, such as hardness, shear strength, impact resistance, dynamic coefficient of friction, and stiffness. Plane samples were made for each of these friction materials, with three different surface finishing obtained by changing the machining parameters - speed and feed -, generating different surface roughness profiles. For each friction material sample, three sequential tests were performed in order to measure the static coefficient of friction, using a universal testing machine and a flat counter piece with the same material and painting of the shoe. For the test, a specific device was developed, allowing the application of tangential force only on the friction material, keeping the counter piece fixed. From this study, it was possible to conclude that each friction material tested has its level of static coefficient of friction, nevertheless, the superficial roughness did not show influence over static CoF. The static coefficient of friction shows a variation up to 14% for the same friction material and surface condition, being higher than the variation of the same material under different surface conditions.
In order to have a detailed insight of a vehicle dynamics and performance of a car and its influencing parameters, it is common to use simulation programs to get this job done. The purpose of this work is to model the longitudinal dynamics of a Formula SAE prototype in Matlab/Simulink® environment, focusing on the braking dynamics and on the incorporation of collected data from the brake lining materials. The model was designed to receive data from a Formula SAE prototype, which are used in the interaction of subsystems, such as, brakes, sprung mass, aerodynamics and tires. The implementation of the three degrees of freedom for the sprung mass and the non-linear model used for the tires assure a better precision in the model. The brake bench tests were made in a machine that simulates the braking process and was defined as a Krauss testing procedure, which could be used to evaluate the coefficient of friction variation versus temperature. This data was implemented in the model, and through it the reliability and the precision could be improved. Besides the implementation of the real data from the parts and the interaction between the systems, it is crucial the validation of such tool compared to the real behavior of the car. The validation of the model results was made comparing the real test data of the ES09 prototype from the Formula Cefast Team in a straight-line braking carried out in the competition of this category. The data compared between the model and the test validation were the rear wheel speed, the longitudinal acceleration, the prototype speed, the braking distance and the the braking time. The results could represent the car braking behavior precisely, with low values of errors and little discrepancies, such as the percentage error of longitudinal acceleration as 4,8%, the braking distance percentage error as 2,5% and the braking time percentage error as 8%.
In Brazil, 20% of the accidents involve commercial vehicles, the high load capacity and the big dimension of commercial vehicles, such bus and trucks, become this situation even more dangerous. To prevent crashes, robust parts and product validation methodologies are essential for a safer and cheaper transport. The drum brake is widely used in commercial transport, due to the cheaper cost of production. The disadvantage of the drum brake system it’s his low thermal dissipation, to decrease the vehicle velocity, the brake converts kinetic energy in thermal energy, causing loss of efficiency, degradation of material mechanical properties and life reduction, these thermal effects can be even more dangerous under extreme conditions, as overload, speeding, over adjustment (dragging), and bad system maintenance. Due the fact that the temperature affects significantly the vehicle performance, especially in drum brakes system, the friction pair is tested under the worst road scenarios, manufacturers often use dynamometers to safely reproduce severe load conditions applied in brake systems. The challenge is to comprehend and reproduce the thermal and mechanical effects on brake drums using Computer Aided Engineering (CAE) to develop safer and cheaper solutions for the commercial vehicles industry. This paper aims to show a case study for a drum brake system, studying the most common failures in dynamometers and their representation in finite element models, allowing an effective prototype project design before the component production. The main target of this study is to search solution ideas for the most common brake drum failures and a better knowledge of combined thermal and mechanical loads acting in the brake structure.
Accurate measurements of brake friction materials are critical to understanding brake behaviors during testing. Current methods typically utilize a hand gauge (or a machine, in some cases) to sample various discrete points on the brake lining. This approach limits measurements to planar wear characteristics, taper and thickness, and excludes more complex measurements such as cupping. The limited number of points means that a single errant point measurement or the choice of point locations can have a large impact on the reported wear measurement. This paper will describe a method for utilizing a Coordinate Measurement Machine (CMM) fitted with a laser line scanning tool to generate a point cloud of data that can then be compared to an earlier measurement of the same piece or to a math model. This method produces thousands of data points which allows for more accurate volumetric wear calculations and color maps of the entire friction face. A gage R&R for this method is presented along with some of the challenges involved in fixturing and aligning brakes pads for analysis.
This study evaluated the performance of a new approach for detecting problems with commercial vehicle brakes based on the analysis of sounds emitted during braking. Commercial vehicle brakes emit ultrasonic energy inaudible to humans as part of the friction process, and the spectral distribution of these sounds is highly dependent on the mechanical condition of the brakes. Data collected from a commercial vehicle fleet found that the acoustic signature changes as friction linings wear. This conforms with the acoustic theory that the resonant frequency of an object increases with its decrease in mass. The use of this information to inform maintenance operations is promising in that the scheduling of visual brake inspections could be based on acoustic wear patterns rather than arbitrary time intervals and the observation of anomalous signals that might indicate more immediate concerns. This could reduce maintenance labor and address issues more quickly as compared to visual inspections based on time intervals.
The mechanism of automobile brake hot spots is unclear, which is a problem in the brake industry. Complex coupling between friction, heat, contact, and structure is the main difficulty in revealing the mechanism of brake hot spots. This paper proposes a new way to study the mechanism of hot spots by analyzing the deformation behavior of brake discs under asymmetric mechanical loading. The actual brake is simplified into a brake disc and friction lining system, and a transient dynamic finite element model under asymmetric mechanical loads is established to analyze the deformation characteristics of the brake disc. The normal deformation of the brake disc under asymmetric mechanical loads consists of two parts: low-frequency bending deformation and high-frequency waviness deformation, which are caused by the squeezing effect of the asymmetric brake pressure on the brake disc and the constraint modal vibration of the brake disc. The influence of the rotation speed, magnitude and asymmetric distribution of mechanical loads on the normal deformation of the brake disc is analyzed. It is observed that the deformation has both a critical speed and critical mechanical load. When the rotation speed or mechanical load exceeds critical values, the disc exhibits stable high-frequency waviness deformation, which propagates in the circumferential direction with high speed. However, the propagation speed is not affected by the rotation speed or the magnitude and asymmetric distribution of mechanical loads, and it is very sensitive to the Young's modulus of the brake disc. The research in this paper provides a reference for the analysis of the coupling behavior of brake friction, heat, contact, and structure, and it is helpful to explore the mechanism of brake hot spots.
It is important for assessing the service life of the braking mechanisms of passenger cars that are in operation is the establishment of the speed and the value of the permissible wear of the friction surfaces, which ensures the durability of the brake. The purpose of the study is to assess effect of area friction surfaces on resource of vehicle braking mechanisms. This will extend the service life of the disc brakes on cars. In the work, the regularities of wear of mating parts of disc brakes were established depending on the change in the geometric parameters of the friction surfaces and operating modes during their operation. It was found that the service life of disc brakes can be increased by 1.16 times with an increase in the area of frictional contact by 15 %, for passenger cars DAEWOO LANOS and LADA PRIORA. A comparative assessment of the wear of the new DAEWOO LANOS and LADA PRIORA brake pads, which perform cyclic emergency braking, is provided. Recommendations have been formulated that will increase the resource of disc brakes. It is recommended to increase the disc-pad friction contact area by using curved surfaces. This will increase the width of the friction surface, which is limited by the inner and outer radii of the disc, without increasing the thickness of the friction bodies.
One of the top problems that every Indian automobile manufacturer struggles to manage is the clutch early failure less than 30000 Km. This is mainly due to the extreme heating of the friction lining due to the real-world user profile in the Indian market and users inappropriate driving behaviors like Overloading the goods more than the manufacturer’s recommendation, non-recommended attachments and increased wheel size, Thick traffic leading to high level of clutch modulation and Clutch riding while running and launching the vehicle at higher gears. Although many simulation and testing are done during the development phase, above listed real world user profile and customer driving habits are inevitable by any automobile manufacturer. Hence the prime goal of this experimental research is to indicate or alert the user on the clutch thermal condition due to the driving habit and to encourage the user on right driving habits. This objective is met through a standalone electronic system that consists of a set of thermocouples, a micro controller unit (ECU) and a digital LCD display. Analog output of the thermocouple is fed into the ECU which contains the wear calculation logic to convert the temperature input to the heat energy dissipated through flywheel surface during every clutch engagement. ECU then estimates the friction lining temperature caused due to the heat energy and calculates the wear of the friction lining. Finally, the percentage of facing lining worn due to the launch events along with the clutch housing temperature will be displayed through the LCD display which is fixed in the instrument panel. Hence, by using this system, it is expected that the user awareness with respect to the right driving behavior can be improved and thereby the clutch facing life, hence the reduced cost of warranty incurred by the manufacturer.
Agricultural Tractors consisting of a conventional manual transmission and dry friction clutch are mostly assembled with a mechanical type of clutch release mechanism where a defined amount of free play needs to be maintained between the clutch and Release Mechanism. A defined free play is required for efficient operation of clutch, Release Bearing as well as to ensure the durability of the system. As the clutch disc wears the free play between diaphragm spring or levers (as the case may be) and the release bearing is reduced. The rate at which the clutch disc wears is dependent on many factors like working condition of the tractor, grade of the friction lining material, experience of the driver, etc. This makes it very difficult to predict the exact timeline when the free play needs to be adjusted even though an approximate indication is given in instruction manuals. In today’s situation the adjustment of the free play is carried out manually and approximately. Many times, the adjustment activity is neglected, and this leads to early failures of the clutch release bearings and / or clutch. The purpose of this solution is to ensure that the free play adjustment is automatically carried out ensuring longer life of components. The system used for automation consists of a sensorized bearing, smart logic controller, and an actuator motor. As the adjustment would be carried out digitally, it would check and ensure the required free play is always available in the system, as well as eliminate manual intervention. The same can be extended to other areas of applications like commercial vehicles etc. where a mechanical release system is used. This paper describes the innovative ways to automatically maintain a fixed value of free play between the Diaphragm Spring fingers and the clutch release bearing at any point of time as well as to automate this process without manual intervention.
A new approach for detecting problems with vehicle brakes by analyzing sounds emitted during braking events is proposed. Vehicle brakes emit acoustic energy as part of the braking process; the spectra of these sounds are highly dependent on the mechanical condition of the brake and can be used to detect problems. Acoustic theory indicates that as brake linings wear thinner the resonant frequency of the shoe or pad increases, potentially enabling the monitoring of lining wear through passive acoustic sensors. To test this approach, passive acoustic sensors were placed roadside at the exit of a transit bus facility for 9 months. The sensors collected almost 10,000 recordings of a fleet of 160 vehicles braking over a variety of conditions. Spectra of vehicles that had brake work performed during this period were analyzed to compare differences between new and worn friction linings. It was found that the spectra changes as friction linings wear, in concurrence with acoustic theory, where resonant frequencies increased as the brake linings wore thinner. The use of this information in predictive maintenance could significantly reduce the maximum time a problem could go undetected between periodic inspections.
This SAE Recommended Practice (RP) applies to the validation process for test systems used to measure deflection (compressibility, creep, or swell and growth) of friction materials and friction material assemblies. The materials or assemblies can fit passenger cars, light trucks, and commercial vehicles equipped with hydraulic or air brake systems, using disc or drum brakes.
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