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Technical Paper

A Study on Rear Disc Brake Groan Noise Immediately After Stopping

1 In this study, we investigated a new type of groan noise that is different from other conventional types of groan noises during braking. This groan noise occurs immediately after stopping the vehicle. We investigated the behaviors of the pads and caliper on the vehicle with two types of pads. By comparing the data, we assumed that μ characteristics of those pads during the stopping event are different. Then we examined the friction surface of the pads in order to study the root cause. In conclusion, we determined that the shape of the contact plateaus of the brake pad surface contributed to this groan noise.
Technical Paper

Analysis of Friction Coefficient Variation with Moisture between Friction Surfaces

If a vehicle is left in a humid environment, the coefficient of friction between the brake pads and discs increases, generating a discomforting noise during braking called brake squeal. It is assumed that this increase in the coefficient of friction in a humid environment is the effect of moisture penetrating between the brake friction surfaces. Therefore, this paper analyzes the factors causing coefficient of friction variation with moisture between the friction surfaces by dynamic observation of these surfaces. The observation was achieved by changing the disc materials from cast iron to borosilicate glass. One side of the glass brake disc was pushed onto the brake pad and the sliding surface was observed from the opposite side by a charge coupled device (CCD) camera. First, a preliminary test was carried out in a dry state using two pad materials with different wear properties to select the appropriate pad for observing the friction surfaces.
Technical Paper

Brake Master Cylinder for Secure Brake Feel and Improved System Failure Performance

The brake master cylinder for a heavy weight vehicle which can offer the optimal braking effect and brake feel has been developed. This brake master cylinder has mechanical type work-bore switching mechanism without electric control system between the conventional master cylinder and the conventional vacuum type booster, it combines enough braking effect during a vacuum failure condition with the secure brake feel during the normal condition. This master cylinder operates in large bore during the normal operation and enables secure brake feel. It operates in smaller bore during a vacuum failure condition and enhances braking effect. The work-bore switching unit has a sealing pressure chamber of a large diameter, the work-bore switching action is carried out by open/close operation of the bore switching valve which has built-in this unit.
Technical Paper

Comparison of Pad Stiffness under Static Pressure and Vibration with Small Amplitude

It is necessary to consider both pad stiffness in static and dynamic situations to develop brake pads that create effective braking and squeal less. Brake pads that have a high degree of static stiffness generally respond well when braking. A past study clarified that stiffness when vibration is added to a pad differs from static stiffness. This pad stiffness in dynamic situations depends on braking pressure and it is one of the causes of squeal generation. This research clarified that pad stiffness depends on the amplitude of excitation and its frequency, which was measured by using an experimental apparatus. This apparatus gave sufficient displacement to a pad for measuring static stiffness and gave vibration with sufficient frequency and amplitude to assess the stiffness of the pad when squeal was generated. First, the static stiffness of the pad was measured by adding static pressure.
Technical Paper

Considering the Dynamic Pad Stiffness in FEM Analysis of Disk Brake Squeal

This study aims to incorporate the dynamic stiffness of pads into the finite element method (FEM) used for brake design in order to improve the accuracy of FEM analyses. In the first step, the vibration caused by a disk brake squeal is simulated in order to measure the dynamic stiffness of the brake pads. We then compare this result with the static stiffness result obtained from a past static compressive strain and show that these different modes of stiffness have different characteristics. The dynamic stiffness of the pad is higher than the static stiffness and is greatly dependent on pressure load. The next step is to show, from the squeal experiments using a simple squeal tester and FEM analysis, that it is dynamic stiffness and not static stiffness of the pads that correlates to squeal.
Technical Paper

Development of New Brake Control System With Gear Pump Modulator

In recent years, there has been a growing need for excellent automobile safety. The number of vehicle with active safety systems such as ABS, Brake Assist and VSC (Vehicle Stability Control) is dramatically increasing. A current brake control systems tend to generate activating noise and uncomfortable brake pedal feeling, which they have to restrain its positive use during ordinary braking. To improve this point, a new brake control system has been developed. This paper introduces the configuration, functions and effects of the system. The new hydraulic modulator adopts a gear pump (trochoid pump) and linear solenoid valves. This allows the modulator to be controlled silently and smoothly. As a result, it becomes possible to apply hydraulic pressure in the normal operating range at any time and a high level of performance is realized. Several new benefits were added to the current control system.
Journal Article

Development of New Electronically Controlled Hydraulic Unit for Various Applications

The use of hybrid, fuel cell electric, and pure electric vehicles is on the increase as part of measures to help reduce exhaust gas emissions and to help resolve energy issues. These vehicles use regenerative-friction brake coordination technology, which requires a braking system that can accurately control the hydraulic brakes in response to small changes in regenerative braking. At the same time, the spread of collision avoidance support technology is progressing at a rapid pace along with a growing awareness of vehicle safety. This technology requires braking systems that can apply a large braking force in a short time. Although brake systems that have both accurate hydraulic control and large braking force have been developed in the past, simplification is required to promote further adoption.
Technical Paper

Development of Regenerative Cooperative Braking System with Conventional ESC

HEV and EV markets are in a rapid expansion tendency. Development of low-cost regenerative cooperation brake system is needed in order to respond to the consumers needs for HEV and EV. Regenerative cooperation brake system which HEV and EV are generally equipped with has stroke simulator. We developed simple composition brake system based on the conventional ESC unit without the stroke simulator, and our system realized a low-cost regenerative cooperation brake. The key technologies are the quiet pressurization control which can be used in the service application, which is to make brake force depending on brake travel, by gear pump and the master cylinder with idle stroke to realize regenerative cooperation brake. Thanks to the key technologies, both the high regenerative efficiency and the good service brake feeling were achieved.
Technical Paper

Development of an Electronically Controlled Brake System for Fuel-efficient Vehicles

To solve various environmental problems, fuel-efficient vehicles that reduce CO2 emissions as well as exhaust gas emissions have been developed. In such vehicles, a regenerative brake is used to further reduce fuel consumption. Because the market size for such vehicles is expanding, a brake system is required that can be used in a wide range of vehicles extending from internal combustion engine vehicles (ICEVs) to electric vehicles (EVs). In addition, issues such as deceleration fluctuation and brake pedal fluctuation arise because the regenerative brake force is dependent on the vehicle speed. This paper presents a brake system configuration and its element technologies that can replace existing brake systems in different vehicles ranging from ICEVs to EVs. The proposed system can realize a regenerative cooperative brake not only by replacing the brake booster unit but also without replacing the modulator.
Journal Article

Evaluation of Friction Phenomena of Brake Pads by Acoustic Emission Method

Brake pads are composite materials made from dozens of ingredients intended to simultaneously satisfy various performances such as brake effectiveness, wear, noise and vibrations. For this reason, the friction phenomena that occur during braking are complicated. It is important to clarify the friction phenomena, but that is not easy because the associated complexities as mentioned above. We looked to acoustic emission (AE) as an online evaluation method of friction phenomena. AE is a non-destructive testing method that measures elastic stress waves caused by the deformation and fracturing of materials. In fact, it has been reported that the difference between abrasive wear and adhesive wear of a metal can be identified from the change in the frequency spectrum of AE signals. In this study, we verify whether differences in the friction phenomena of brake pads are detectable by the AE method. Three kinds of brake pads were used in the experiments.
Technical Paper

Evaluation of an Energy Dissipation Mechanism by Friction for Brake Shims

Brake squeal is uncomfortable noise that occurs while braking. It is an important issue for automobile quality to prevent brake products from squealing. Brake shims are widely used to reduce squeal occurrence rate. In particular, laminated shims can effectively suppress squeal via the viscoelastic damping of an adhesive layer. However, there are cases where the damping performance at low temperature and the durability performance at high temperature deteriorate. In that regard, we thought of applying frictional damping to shims instead of relying on a temperature-sensitive adhesive layer. To study the application of frictional damping for shims, it is necessary to clarify the characteristics thereof. In order to quantify the damping performance of shims, loss factor has been generally measured with a bending mode tester. However, the influence of friction cannot be evaluated because it is measured under pressure-free condition.
Technical Paper

Influence of Pad Surface Texture on Disc Brake Squeal

The prevention of brake squeal is a significant task in brake development, because brake squeal is bothersome to users and consequently reduces a vehicle's commercial value. Due to the progress made by researchers in their efforts to gain insight into the mechanisms and causes of brake squeal, the number of brake squeal complaints has declined. However, brake squeal can appear long after the vehicle is produced, without any early sign. In order to maintain long-term high satisfaction among the vehicle owners, it is important to find the factors that create a gradual increase in the occurrence of brake squeal. In this study, we focus on the stiffness factor of brake pads. Also, brake-pad wear due to braking is virtually impossible to completely eliminate. Here, we examine the correlation between pad stiffness and squeal occurrence. This study presents experimental and analytical results of the influence of pad surface texture on disc brake squeal.
Technical Paper

Online Estimation of Vehicle Stability Factor for Electronic Stability Control

Electronic stability control (ESC) is becoming a standard technology in passenger cars, and because of its effectiveness in reducing serious traffic accidents, its use is spreading to commercial vehicles. ESC is activated by comparing the target vehicle behavior, which is analyzed based on driver operation, with the actual vehicle behavior, which is detected by onboard sensors. The target vehicle behavior is analyzed with an initial steer characteristic (such as a vehicle stability factor Ks) representing a vehicle turning characteristic (understeer, neutral steer, or oversteer). Because Ks changes depending on the payload loading states (such as vehicle mass and location of center of gravity), it varies considerably for commercial vehicles. We analyzed the influence of error in Ks on ESC performance and established a method for the online estimation of Ks. ESC includes the restriction functions of oversteer and understeer.
Technical Paper

Squeal Noise Improvement by High Damping & High Stiffness under Layer Material

The purpose of this research is to clarify how damping characteristics of Under Layer (hereafter “UL”) material in the brake pads (hereafter “PAD”) influences brake squeal noise performance. In this study, UL material structure and dynamic viscoelasticity, for two different types of UL formulations are investigated. In addition, PAD damping ratio and squeal noise performance for multiple UL formulations are verified. As a result, the raw material orientation is determined based on manufacturing method, and it causes the UL material’s anisotropic properties. Dynamic viscoelasticity are dependent on the direction in which they are measured. In particular, the loss modulus, which is the damping element of dynamic viscoelasticity, is higher in the direction of the raw material orientation for the high damping and high stiffness UL formulation. In addition, it was confirmed that this loss modulus in the direction of the raw material orientation is effective for bending vibration.
Technical Paper

Study of Brake Squeal - Classification for Vibration Modes of Mounting Bracket

In the studies of disc brake squeal, the vibration modes on squealing were measured, and calculated [1, 2 and 3]. By those results to the disk rotor, it is clear that the specific type of the modes affect the squeal generation. It is not clear whether mounting bracket mode shapes contribute to squeal, because the mounting bracket mode shapes cannot be classified in the same way as the rotor mode shapes. In this paper, by using FEM modal analysis the vibration modes of the mounting bracket are classified systematically. And by adopting this classification to the vibration mode of mounting on squealing, it is confirmed that the specific type of modes of mounting affect the squeal generation.