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Technical Paper

Properties and Limitation of an Oxide Coated Aluminum Brake Rotor

2018-10-05
2018-01-1877
The electrification of the powertrain and the thereto related recuperation of the electric engine saves the energy in the battery and thus reduces the thermally dissipated brake energy, which leads to lower brake rotor temperatures compared to combustion engine vehicles (ICEVs). These new conditions enable to reconsider brake disc concepts. Including lightweight design in heavy battery electric vehicles (BEVs) and the increasingly reliant corrosion resistance of brake rotors, Aluminum is a promising approach for new brake disc concepts. In the past, Aluminum brake disc concepts have already been deployed. For instance Aluminum Metal-Matrix Composite (Al-MMC) concepts in the Lotus Elise S1 and on the rear axle of the Volvo V40 [1]. The presented concept is a different approach and separates the friction system from the bulk Aluminum brake disc, achieved by coating of the friction rings.
Technical Paper

Investigations of the Measurement Layout for Brake Particle Emissions

2018-10-05
2018-01-1885
Non-exhaust emissions in general and brake particle emissions in particular have become very relevant during the last years. Even if many investigations and efforts are under progress, no common test standards exist so far. Many mechanisms and possible impacts are not fully understood either. Hence, the authors continued their investigations by using an already refined and proved test setup, which is the base for further characterizations and enhancements. The presented studies include the characterization of three different friction couples (using the same brake system) for two different test cycles (namely a modified AK Master and a WLTP) in terms of particle number concentration. Additionally, the major differences of the modified AK Master and the WLTP are investigated and analyzed. Finally, results of particle mass characterizations introduced. A brief summary and some conclusions are presented in the final chapter.
Technical Paper

Estimation of Transport Efficiency for Brake Emissions Using Inertia Dynamometer Testing

2018-10-05
2018-01-1886
There is vast literature and peer-reviewed methods to estimate losses1 during aerosol sampling. However, there are no current published models for transport losses during laboratory measurement for brake emissions. This paper presents an open source (Microsoft® Excel) Macro using three different models (Particle Loss Calculator - PLC - from the Max Planck Institute [1]; AeroCalc [2] from the United States Center for Disease Control and Prevention; and SAE AIR6504™:2017-10 [3] for calculation of non-volatile particulate matter penetration). The fourth model (LINK) provides the average value from the three initial models. The LINK PALS2 Microsoft® Excel Macro (or ‘Macro’ for short version) also includes calculations for isokinetics not included on any of the three initial models.
Technical Paper

A Study on Safety Intelligent Driving System for Heavy Truck Downhill in Mountainous Area

2018-10-05
2018-01-1887
Mountainous area makes up more than half of the whole land area of China, the road of which is full of ups and downs. Heavy commercial vehicles as the main means of transport in mountainous areas, braking torque recession, even brake failure, often happens because of the overheating in long downhill journey, which seriously threatens the safety of the driving. Therefore, this paper presents an intelligent assistance system based on Geographic Information System and vehicle dynamics. The main brake duration and heat generation can be effectively reduced through adjusting the speed at the slope top, applying the engine auxiliary brake in the initial stage and choosing braking strategy appropriately, in order to prolong the downhill driving distance and improve the safety during continuous braking. This paper characterizes and analyses the road gradients and their effects on braking heat generation.
Technical Paper

Construction of a Multiple Driving Affective Scale

2018-10-05
2018-01-1888
The authors’ goal is to develop brakes that are more satisfying to users in sensory aspects by explaining the relationship between people’s state of mind and a vehicle’s physical quantities. However, there are no scales to measure such feeling. In this study, a psychological scale was constructed to measure the affective state of general automobile drivers, for the purpose of clarifying the effects of brake characteristics on the affective state. To construct the affective scale, two experiments were conducted. In the first experiment, a comparison of four types of vehicles was performed and then an interview survey was conducted to collect a broad sample of terms used to evaluate the affective state. From the results, it was hypothesized that the evaluation terms were divided into eight categories.
Technical Paper

Improvement of the Assessment Methods for the Braking Dynamics with ABS Malfunction

2018-10-05
2018-01-1881
The bulk of automobiles are equipped with ABS currently. Having of automatic devices that prevent vehicle wheels from locking and skidding does not require consideration of the normal reactions on the front and rear vehicle axles wheels’ changes dynamics. However, ABS malfunction is possible for various reasons, and in this case the braking system must provide the safety vehicle braking. To provide this, it is necessary to return to the problem of choosing the rational braking forces distribution between the wheels of the front and rear axles.
Technical Paper

A New Model Describing the Formation of Heat Cracks in Brake Discs for Commercial Vehicles

2018-10-05
2018-01-1882
During the development process of brake discs for commercial vehicles, heat cracks are a frequent problem. Since no profound model to forecast the occurrence of cracks has been presented yet, their prediction is hardly ever possible. The standardized heat crack test puts the brake disc under severe thermomechanical load and therefore forces it into cracking. In this paper, results from a series of heat crack tests on the dynamometer are presented, which provide insight into the hidden processes that accelerate or slow down the heat crack propagation in brake discs. This includes an extensive experimental setup using a thermographic camera, a set of capacitive displacement sensors, a pyrometer, and sliding thermocouples as well as a unique eddy-current heat crack detector that was developed at TU Darmstadt. Continuous monitoring of disc deformation, surface temperature, and crack propagation at high sampling rates provides the base for a new, profound causal model.
Technical Paper

System Identification Method for Brake Particle Emission Measurements of Passenger Car Disc Brakes on a Dynamometer

2018-10-05
2018-01-1884
Besides particulate emissions from engine exhausts, which are already regulated by emission standards, passenger car disc brakes are a source of particulate matter. With the current car fleet it is estimated that up to 21% of the total traffic related PM10 emissions in urban environments originate from brake wear and reduction of brake dust emissions is subject of current research. For the purpose of reducing brake dust emissions by choosing low-emission operating points of the disc brake, the knowledge of the emission behavior depending on brake pressure, wheel speed, temperature and friction history is of interest. According to the current state of research, theoretical white box modeling of the emission behavior is complicated due to the complexity of tribological contact between pad and disc. Thus experimental black box modeling is supposed to describe emission behavior.
Technical Paper

Optimization of Slot Disc Shape for Improving Brake Fade Performance

2018-10-05
2018-01-1883
Due to improvements in vehicle powertrain performance, friction material fade performance is becoming an important topic. For this reason, needs for studies to improve thermal characteristics of the brake system is increasing. Methods for improving the fade characteristics have several ways to improve the thermal characteristic of friction materials and increase disc capacity. However, increasing disc capacity(size) have some risk of weight and cost rise, and friction factor improvements in friction material tend to cause other problems, such as increasing squeal wire brush noise and increasing metal pick up on disc surface. Therefore, a slot disc study is needed to overcome the problems discussed previously. Currently, there is few research history for slot disc related to fade and metal pickup improvements.
Technical Paper

A Mathematical Model of the Braking Dynamics of a Car

2018-10-05
2018-01-1893
The braking efficiency of a vehicle is its most important operational property. However, in practice, researchers utilize simplistic physical-mathematical models for the process of vehicle braking that leads to accuracy reduction of these models predictions. The literature data show that the error in assessing braking efficiency can reach 30%. One of the main indicators of the efficiency of a braking system is deceleration. Most accurately, this value can be determined by experimental measurements. However, this is not always possible due to various technical reasons. The existing models typically ignore the impact of the car design and its speed on deceleration. They also either neglect air resistance completely or account only for its horizontal component. This paper presents an improved mathematical model written in the differential form that takes into account the impact of the lifting or downforce components of the aerodynamic forces.
Technical Paper

Instabilities Induced by Thermal-Mechanical Couplings in Clutch and Brake Discs

2018-10-05
2018-01-1894
The interaction between thermal buckling and thermoelastic instability (TEI) can play an importance role in frictionally-excited hot spot development in automotive disc brakes. In this study the distributions of temperature variations were obtained from the eigenmodes based on the classical TEI analyses. The critical buckling temperatures and the associated deformation modes were subsequently computed using the commercial software ABAQUS. The effects of sliding speed, coefficient of friction and boundary conditions have been investigated for both banding and focal modes. It is concluded that the TEI induced temperature variations can significantly alter the distribution of thermal stresses, and that there could exist a strong coupling between TEI and thermal buckling under some conditions. Although the analyses were performed in the settings of clutch applications, the conclusions are applicable to brake discs as well because of the shared similarities.
Technical Paper

Identification and Resolution of Vehicle Pull and Steering Wobble Using Virtual Simulation and Testing

2018-10-05
2018-01-1895
A vehicle drifts due to several reasons from its intended straight path even in the case of no steering input. Vehicle pull is a condition where the driver must apply a constant correction torque to the steering wheel to maintain a straight-line course of the vehicle. This paper presents an investigation study into the characteristics of a vehicle experiencing steering drift. The aim of the work is to study vehicle stability and the causes of vehicle drift/pull during straight line to minimize vehicle pull level and hence optimize safety measures. A wobble in the steering wheel feels like the steering wheel is shaking to the left and right. This may get worse, if speed increases. This paper focuses on modelling and evaluating effects of suspension parameters, differential friction, brake drag variation, Unbalanced mass in the wheel assembly and C.G. location of the vehicle under multibody dynamic simulation environment.
Technical Paper

Performance Evaluation of Two Wheeler Brake System Using Coupled Thermo-Mechanical Simulation

2018-10-05
2018-01-1896
Safety aspect has been a key requirement in designing braking system. However, non-safety aspect like NVH and thermal performance are gaining equal importance. High engine capacity (cc) motorcycles are prone to thermal and NVH issues as braking energies are more. Therefore, virtual validation of brake disc system by considering both dynamic and thermal load with predefined assumptions is a toughest challenge when confronted with reality boundary conditions. Thus, the paper comes in a unique way of coupling dynamic and thermal load executed between multi body dynamics (MBD) and heat transfer equation which will convey results closer to real time scenario. MBD solves motion and the dynamic influence on heat transfer is calculated using “sliding boundary condition”. A series of repeated braking condition are performed on front brake disc of motorcycle. The results obtained from the analysis shows critical temperature rise.
Technical Paper

Modeling Articulated Brake Component Wear to Assist with Routing Decisions

2018-10-05
2018-01-1890
Very few activities the brake engineer engages in can induce as much vexation as trying to find a satisfying routing for the flexible brake components such as hoses, wheel speed sensors, and electric parking brake cables. Ever increasing wheel end content, ever decreasing space, more complex suspensions, and bulkier (but lighter weight) suspension components provide quite the morass through which the components must be routed through. When routing is finalized - and free of any major issues - there frequently remains some combinations of articulation position and component tolerances that allow a light “friendly” touch between components (such as a sensor wire and a surface of a bracket or strut tube), or near misses where clearance exists but raises “what if” questions around what would happen if the tolerances would stack up slightly differently on another vehicle.
Technical Paper

Correlation of Objective and Subjective Evaluation in Automotive Brake Pedal Feel

2018-10-05
2018-01-1889
In order to establish the correlation between objective and subjective evaluation of brake pedal feel for passenger cars, road tests of brake pedal feel were carried out and an evaluation method was proposed. In the road tests, subjective scores and objective measurements were obtained under the conditions of uniform and emergency braking. The objective measurements include pedal preload, low deceleration pedal force and travel, moderate deceleration pedal force and travel, brake response time and brake linearity. Using the theory of analytic hierarchy process (AHP), the design process of the evaluation method was established. Key setups including the hierarchical structure model, the judgement matrix and the score calculation method of objective measurements were described in detail. Then, the correlation between subjective and objective scores was analyzed. It can be concluded that the evaluation method is effective and it can be applied to brake pedal feel assessment and adjustment.
Technical Paper

A Study of the Disc Scoring Generation Principle and Reduction (II)

2018-10-05
2018-01-1891
In the latest paper [10], we presented our work based on experiments studying MPU (Metal Pick Up) of the pad and scoring(scratching) of the disc. The main component of MPU was iron “Fe”. If the roughness of the disc was small, the content of iron “Fe” was increased and the segregation of that was decreased especially in initial condition. In this study, we extended our study based on the results by adding some additional factors such as the location of the roughness of the disc, the coefficients brake pad friction, and disc slots. We made various discs of different roughness boundaries and slots, and pads of pad friction coefficients; and conducted two types of tests for whether a slot is present or not with the other same conditions to confirm the impact of the scoring. We find and believe that our experimental data should serve a useful guideline for reducing MPU of the pad and scoring of the disc.
Technical Paper

On the Wear Dependence of Low-Frequency and High-Frequency Brake Squeal

2018-10-05
2018-01-1902
The dynamics of disc brakes, and in particular their NVH behavior, have long been the focus of research. Measurements by Rhee et al. show that brake pad wear has a significant influence on the occurrence of low and high frequency squealing [1]. It is suspected that low frequency squealing is more likely to occur when the wear difference between the inner and outer brake pads is high. If the two pads incur comparable wear, however, the prevalence of high frequency squealing increases. In order to investigate this hypothesis, this paper focuses on a simplified model of a commercial brake system. First, the friction force between the inner pad and the disc is iteratively adjusted, while the force between the outer pad and the disc is held constant. In a second step, the inner pad’s wear is iteratively increased, while the wear on the outer pad remains unaffected.
Technical Paper

Adaptronic Actuator to Minimize the Pins Misalignment on Pin-on-Disc Testers

2018-10-05
2018-01-1892
The Automated Universal Tribotester (AUT) represents a fully automated reduced scale brake dynamometer and was developed by the Institute of Dynamics and Vibrations at TU Braunschweig. The setup is based on the pin-on-disc principle. The downscaled test specimen is brought to contact to the disc, loaded and guided via the load unit, which was specifically designed for this purpose. It is laid out as a combination of parallel and serial leaf springs, facilitating a friction free and horizontal motion. The stiffness in radial and tangential directions are much higher than in normal orientation. If the test specimen has a two-dimensional, flat contact surface, the misalignment of the pin in a Pin-on-Disc setup is a phenomenon that appears even in very stiff and robust Pin-on-Disc testers. The measured friction forces are not sensitive to the tilting movement, but the wear processes that take place in the contact zone are.
Technical Paper

Effects of the Metal Surface Profile to the Sliding Properties between Rubber and Metal and Applying That to Wheel Bearing Seals

2018-10-05
2018-01-1904
Cartridge seals are frequently utilized in wheel bearings where a high level of reliability is required. The cartridge seal combines two components; a seal with flexible rubber lips and a stamped metal slinger that provides a surface for the seal lips to contact without being exposed directly to foreign substances. This paper provides a fundamental evaluation of the sliding properties of rubber seal lips relative to the slinger metal surface profile and evaluates the performance of rotating torque and muddy water endurance from a recommend metal surface profile (developed by advanced fundamental evaluation) of the slinger. Seals with the recommend metal surface profile showed approximately 30% lower torque at the rotating speed from 400 rpm to 800 rpm, which are the speeds representative of automotive city driving. At the same time, the durability performance against muddy water was almost equivalent to the seals without this metal surface.
Technical Paper

Bearing Life Evaluation for Automotive Wheel Bearings Using Design of Experiments

2018-10-05
2018-01-1903
Automotive wheel bearings have primary functions of translating the rotating motion of the wheels into linear vehicle motion while bearing the vehicle weight. Bearing life is affected by many parameters such as bearing geometry, vehicle and bearing technical specifications, driving conditions, lubrication conditions, material properties, and so on. In this paper, both the basic bearing rating life and modified bearing rating life were evaluated using design of experiments. Bearing lives were calculated by the international standard, and the factors affecting bearing life were investigated. Sequential experimental designs were applied. First, screening experiments were performed to analyze the factors affecting bearing life. Next, confirmation experiments were carried out to determine accurate effects of the selected factors from the screening experiments. As a result, contact angle and curvature of inner ring were significant at a 95% of significance level.
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