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Technical Paper

Transfer Function Analysis of Rear Multi-Link Suspension to Improve Ride Vibration and Road Noise

2011-05-17
2011-01-1571
The expectation of customers on ride comfort is very high and vehicle engineers also have keen interesting to improve ride vibration and road noise. As the conventional tuning parameters for the ride vibration and road noise, vibration characteristics of tire, body structure, bushing, suspension members etc. are mainly considered. But these conventional tuning parameters are sometimes not enough due to the side effects such like handling performances and durability. Therefore, instead of these conventional design and tuning parameters, suspension geometry and alignment characteristics of suspension system are selected as the alternative parameters to compromise ride vibration, road noise and vehicle dynamic performance. In this research, multi-link type rear suspension is selected for the integrated analysis of ride vibration, road impact noise and handling performance.
Journal Article

Pulley Optimization for Improved Steering Pump Airborne Noise Performance

2011-05-17
2011-01-1568
This paper discusses the optimization of an automotive hydraulic steering pump pulley design for improved in-vehicle pump NVH performance. Levels of steering pump whine noise heard inside a vehicle were deemed objectionable. Vehicle and component transfer path analyses indicated that the dominant noise path for the whine noise was airborne in nature. Subsequent experimental modal analysis indicated that the steering pump pulley was a major contributor to the amount of radiated noise produced by the pump/pulley system. CAE analysis was used to further analyze the dynamic behavior of the pulley and develop an optimized design with decreased noise radiation efficiency. The results predicted with the CAE analysis were verified in-vehicle, resulting in a vehicle with acceptable steering pump whine noise performance.
Technical Paper

Friction Force Measurement at Brake Discs

2011-05-17
2011-01-1576
Experimental researches on brake squeal have been performed since many years in order to get an insight into friction-excited vibrations and squeal triggering mechanisms. There are many different possibilities to analyse brake squeal. The different operating deflection shapes can be detected using e.g. laser vibrometer systems or acceleration sensors. Piezoelectric load cells can be used for the measurement of the normal contact force of the brake pad. The presented test setup measures not only the mean value of the friction force between brake pad and disc at a certain brake pressure, but also the superposed vibration of this force, which only occurs during a squeal event. Therefore the guide pins of the brake caliper are replaced by modified ones. The brake pads are held in position by these pins and the resulting force of the brake torque, hence the friction force, acts on these pins. The shape of the pins is optimized for measuring these forces.
Journal Article

Hot Judder - An Investigation of the Thermo-Elastic and Thermo-Plastic Effects during Braking

2011-05-17
2011-01-1575
Thermo-elastic and thermo-plastic behaviour takes place with a disc brake during heavy braking and it is this aspect of braking that this paper considers. The work is concerned with working towards developing design advice that provides uniform heating of the disc, and equally important, even dissipation of heat from the disc blade. The material presented emanates from a combination of modeling, on-vehicle testing but mainly laboratory observations and subsequent investigations. The experimental work makes use of a purpose built high speed brake dynamometer which incorporates the full vehicle suspension for controlled simulation of the brake and vehicle operating conditions. Advanced instrumentation allows dynamic measurement of brake pressure fluctuations, disc surface temperature and discrete vibration measurements.
Technical Paper

The Development of a Global Brake Insulator Damping Measurement Procedure

2011-05-17
2011-01-1574
The development and validation of a brake pad insulator damping measurement procedure by the SAE Brake NVH Standards Committee was presented at the 2010 SAE Brake Colloquium (Paper 2010-01-1685). In Europe, in 2010, the EKB Working Group identified the need to develop a similar procedure, and started some activities which lead to the release of a standard similar but different than the SAE J3001. The SAE and EKB working groups agreed that having a global standard was of paramount importance, so the 2 groups decided to meet in November of 2010 to flush out the details of the J3001 global procedure. The details of the new test procedure, test setup and recommendation for proper test practices are described in this paper. This description provides an excellent foundation for evaluating the insulator damping properties over a range of temperatures and frequencies.
Technical Paper

Modeling and Experimental Verification of Vibration and Noise Caused by the Cavity Modes of a Rolling Tire under Static Loading

2011-05-17
2011-01-1581
Tire cavity noise refers to the vehicle noise due to the excitation of the acoustic modes of a tire air cavity. Although two lowest acoustic modes are found to be sufficient to characterize the cavity dynamics, the dynamical response of these two modes is complicated by two major factors. First, the tire cavity geometry is affected by the static load applied to the tire due to vehicle weight. Second, the excitation force from the tire-road contact changes position as the tire rotates. In this paper, we first develop dynamic equations for the lowest cavity modes of a rotating tire under the static load. Based on the model, we obtain the forces transmitted to the wheel from the tire resulting from the random contact force between the tire and the road surface. The transmitted forces along the fore/aft direction and the vertical direction show two peaks at frequencies that are dependent both on the tire static load and on the vehicle speed.
Technical Paper

Experimental and Analytical Investigation of Countermeasure against Squeal in Floating Type of Car Disc Brake

2011-05-17
2011-01-1579
This paper deals with low-frequency squeal phenomena generated in floating type of car disc brake units. First, the vibration characteristics of low-frequency squeal (about 2 kHz) were investigated. Here, in order to reproduce the squeal, a bench-test apparatus consisting of an actual automotive disc brake unit was utilized, itself comprising a disc, pad, and caliper. With this, the associated frequency characteristics were experimentally determined. It was found that the squeal is caused by coupled out-of-plane vibration modes among the disc and caliper due to Coulomb friction. As an experimental countermeasure, a dynamic absorber was applied to the leading side or the trailing side of the inner caliper. It was found that squeal can be suppressed when the natural frequency of the dynamic absorber is tuned so as to be near the frequency of the squeal, and that squeal can be suppressed even without viscous damping of the dynamic absorber.
Technical Paper

Determination of Interior NVH Levels from Tire/Wheel Variations using a Monte Carlo Process

2011-05-17
2011-01-1580
Variability in design (e.g. tolerance), material, manufacturing, or other sources of variation causes significant variation in vehicle noise, vibration and harshness (NVH) response. This leads to a higher percentage of produced vehicles with higher levels of NVH leading to higher number of warranty claims and loss of customer satisfaction, which are proven costly to the original equipment manufacturers (OEM). Measures must be taken to insure less warranty claims and higher levels of customer satisfaction. As a result, original equipment manufacturers have implemented design for variation in the design process to secure an acceptable (or within specification) response. We will focus on some aspects of design variations in a tire/wheel assembly that should be considered in the design process. In particular, certain materials (e.g. rubber) are known to have variation in stiffness that is either unavoidable or proven costly if tighter control is desired.
Technical Paper

A Simplified Approach to Quantifying Gear Rattle Noise Using Envelope Analysis

2011-05-17
2011-01-1584
The present work discusses an objective test and analysis method developed to quickly quantify steering gear rattle noise heard in a vehicle. Utilizing envelope analysis on the time history data of the rattle signal, the resulting method is simple, fast, practical and yields a single-valued metric which correlates well to subjective measures of rattle noise. In contrast to many other rattle analysis methods, the approach discussed here is completed in the time domain. As applied to rattle noise produced by automotive electric steering systems, the metric produced with this analysis method correlates well with subjective appraisals of vehicle-level rattle noise performance. Lastly, this method can also be extended to rattle measurements at the component and subcomponent level.
Technical Paper

The Influence of Pad Abutment on Brake Noise Generation

2011-05-17
2011-01-1577
The paper overviews the modes of vibration of the principal component parts of a brake and their contribution to system instability during noise generation. It is shown that both in-plane and out-of-plane vibration are present and that both can be related to the vibration of the pad. It is further shown that the pad and its region often provide a solution or “fix” towards noise prevention and it is this area that forms the focus of this investigation. The collective evidence, proposals and associated theory are applied to real brake case studies when it is demonstrated that disc/pad interface “spragging” may be the source of brake noise. Measurements of the position of the dynamic centre of pressure (CoP) support the theoretical predictions that a leading CoP induces brake noise. Design proposals are suggested that may be applied early in the design phase as a means to reduce the propensity of a brake to generate noise.
Journal Article

Challenges for Tire Noise Evaluation on Common Pavements

2011-05-17
2011-01-1582
Developing common methods of noise evaluation and facilities can present a number of challenges in the area of tire/pavement noise. Some of the issues involved include the design and construction of pavements globally, the change in pavement over time, and variation in the noise produced with standard test tires used as references. To help understand and address these issues for airborne tire/pavement noise, acoustic intensity measurement methods based on the On-board Sound Intensity (OBSI) technique have been used. Initial evaluations have included measurements conducted at several different proving grounds. Also included were measurements taken on a 3m diameter tire noise dynamometer with surfaces replicating test track pavements. Variation between facilities appears to be a function of both design/construction and pavement age. Consistent with trends in the literature, for smooth asphalt surfaces, the newest surface produced levels lower than older surfaces.
Technical Paper

Noise Contribution Analysis at Suspension Interfaces Using Different Force Identification Techniques

2011-05-17
2011-01-1600
Road-tire induced vibrations are in many vehicles determining the interior noise levels in (semi-) constant speed driving. The understanding of the noise contributions of different connections of the suspension systems to the vehicle is essential in improvement of the isolation capabilities of the suspension- and body-structure. To identify these noise contributions, both the forces acting at the suspension-to-body connections points and the vibro-acoustic transfers from the connection points to the interior microphones are required. In this paper different approaches to identify the forces are compared for their applicability to road noise analysis. First step for the force identification is the full vehicle operational measurement in which target responses (interior noise) and indicator responses (accelerations or other) are measured.
Journal Article

Aerodynamic Investigation on the Effect of Varying Through-Hub Flow on a Formula One Front Wheel Assembly

2011-04-12
2011-01-1431
For open wheel race cars the front wheel flow and the interaction of its wake with downstream components is of significant importance. Considerable effort goes into the design of front wing end plates, barge boards and underfloor components in order to manage the front wheel flow. In this study a 50% scale Formula One front wheel assembly has been tested in the Durham University 2m₂ open jet wind tunnel to evaluate the effect of through-hub flow on its cooling drag and flow structures. Varying the amount of through-hub flow gave rise to a negative cooling drag trend whereby increasing the flow through the hub resulted in a decrease in drag. This observation has been explained both qualitatively and quantitatively by inlet spillage drag. Lower than optimum airflows through the brake scoop result in undesirable separation at the inside edge and hence, an increase in drag (reversing the cooling drag trend).
Journal Article

Tire and Road Input Modeling for Low-Frequency Road Noise Prediction

2011-05-17
2011-01-1690
This paper presents a modeling method for prediction of low-frequency road noise in a steady-state condition where rotating tires are excited by actual road profile undulation input. The proposed finite element (FE) tire model contains not only additional geometric stiffness related to inflation pressure and axle load but also Coriolis force and centrifugal force effects caused by tire rotation for precise road noise simulation. Road inputs act on the nodes of each rib in the contact patch of the stationary tire model and move along them at the driving velocity. The nodes are enforced to displace in frequency domain based on the measured road profile. Tire model accuracy was confirmed by the spindle forces on the rotating chassis drum up to 100Hz where Coriolis force effect should be considered. Full vehicle simulation results showed good agreement with the vibration measurement of front/rear suspension at two driving velocities.
Journal Article

Determining Isolator Damping for Minimized Response from Impulse: A Theoretical Approach

2011-09-13
2011-01-2239
Several recent product developments for vibration and motion control have needed passive viscous damping, in addition to traditional elastomer-based hysteretic damping, to be successful in their respective applications. In addition to attenuating steady-state vibration, an important function of these recent product developments is to control motion from impulsive or mechanical shock input. Examples are the cab mounts of off-highway vehicles that need damping in the vertical direction to control cab motion from ground input through the vehicle and some torsionally flexible couplings that need damping to control torque spikes from shift shocks or other transient events. In this work, the theoretical damped impulse response quantities of displacement, velocity, acceleration, force, jerk, yank, and jounce are investigated. This work shows that, for certain response quantities, there is a specific magnitude of damping that minimizes response from impulsive or mechanical shock input.
Technical Paper

Influence of Surface Modifications on Vehicle Disc Brake Squeal

2009-06-15
2009-01-1977
Squeal from brakes is a problem in the automotive industry and large efforts are made to understand the squeal tendencies. The approach taken is mainly to change the design of the caliper, fine-tune the brake pad material and finally to trim the introducing shims on the backside of the pads. Despite these efforts still no general solutions exist. To advance the situation, a deeper understanding of the actual source of excitation of the sound in the friction interface is needed. However, in the present investigation the surfaces modifications of brake disc and pad have been tested with respect to the understanding properties. The surfaces modifications are slotted pad material and coated disc. All tests have been made in a brake test stand consisting of a complete front wheel corner of a vehicle. The changes have resulted in a significant understand of the generated noise.
Technical Paper

Study on Natural Torsional Vibration Characteristics of Dual Mass - Flywheel Radial Spring Type Torsional Vibration Damper

2009-05-19
2009-01-2062
The working principle of dual mass flywheel - radial spring (DMF-RS) type torsional vibration damper was analyzed, and the design method of natural torsional vibration characteristics control of DMF-RS type torsional damper for automotive powertrains was studied herein. Based on the multi-freedom lumped mass - torsional vibration spring analysis model of powertrain, the natural torsional vibration characteristics of the system with DMF-RS type torsional damper were analyzed, and compared with the clutch type torsional vibration damper, the effectiveness of DMF-RS type torsional damper on the torsional vibration control was verified.
Technical Paper

A Test-Based Procedure for the Identification of Rack and Pinion Steering System Parameters for Use In CAE Ride-Comfort Simulations

2009-05-19
2009-01-2090
Current CAE modeling and simulation techniques in the time domain allow, by now, very accurate prediction of many ride-comfort performances of the cars. Nevertheless, the prediction of the steering wheel rotation vibration excited by, for instance, wheel unbalance or asymmetric obstacle impact, often runs into the difficulty of modeling the steering line with sufficient accuracy. For a classic rack and pinion, hydraulic assisted steering line, one of the challenges is to model the complex and non linear properties - stiffness, friction and damping - of the rack-rack case system. This paper proposes a rack model, thought for easy implementation in complex multi-body models, and an identification procedure of its parameters, based on measurements, in the operational range of the wheel unbalance excitation. The measurements have been gathered by specific tests on the components and the test set-up is also shown here.
Technical Paper

Noise Path Analysis Process Evaluation of Automotive Shock Absorber Transient Noise

2009-05-19
2009-01-2091
Shock absorber transient noise, often referred to as “chuckle” or “loose lumber”, has been a vehicle level noise and vibration concern for many years. The noise often occurs with lightly damped shock tuning under small road inputs at low speed. This transient type noise is of particular concern to the operator because it can sound like mechanical looseness in the chassis. This noise concern is generally addressed late in the design cycle and the options of a fix are limited to a change in damper tuning or added mass. A need for a wider design envelope exists to address this concern which must include noise paths into the structure and body sensitivity. The study documented in this paper walks through the process of acquiring this noise on the road and reproducing it in the lab on a 4-post hydraulic test rig.
Technical Paper

Steering Grunt Noise Robustness Improvement

2009-05-19
2009-01-2095
Grunt is a structure-born noise caused by resonance of the steering gear torsion bar (T-bar) in an HPAS (Hydraulic Power Assist Steering) system. The goal of this work was to develop techniques to quantify and predict grunt in a RV (rotary valve) steering gear system. First, vehicle testing was used to identify an objective metric for grunt: y = dynamic pressure in the return line. Then, a computer simulation was developed to predict y as a function of two known control factors. The simulation results were correlated to measurements on a test vehicle. Finally, the simulation was expanded to include two additional control factors, and grunt predictions were demonstrated on a different test vehicle.
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