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Technical Paper

Optimization of Gear Whine, Efficiency, and Durability of a Manual Transaxle

2009-05-19
2009-01-2064
Development of modern powertrains used in car and truck applications is more competitive than ever before. Powertrains and components previously considered to be advanced technology, such as hybrids and dual-clutch transmission technology, are now commonplace, being designed and manufactured in all worldwide markets. In order to stay competitive, powertrain OEMs must simultaneously optimize attributes such as performance, cost, weight, durability, fuel economy and NVH while producing new, desirable designs with reduced product development timelines. Oftentimes, the ideal solution for optimization of gear whine will result in an unexpected deterioration of durability, and vice versa. An advanced software tool was previously developed for the design of transmissions and transaxles, including analysis of the vibration, efficiency and durability performance under specified speeds and loads.
Technical Paper

A High Performance Passive Muffler Valve

2009-05-19
2009-01-2039
A new passive muffler valve has been developed that offers the advantages of both the current passive and active valves without their major drawbacks. Like current passive valves this new valve provides high restriction at low to medium engine speeds for improved noise control. But with a near over-center spring action and unique flap shape, this high performance valve has minimal pressure drop at high engine speeds, closer to the active valve pressure drop performance. The in-line design of the valve makes it ideal for low restriction OE mufflers, resonators, and aftermarket performance mufflers. The new valve design is uncomplicated, with few components and has been tested extensively for durability utilizing both bench and vehicle level testing.
Journal Article

A Simulation and Optimization Methodology for Reliability of Vehicle Fleets

2011-04-12
2011-01-0725
Understanding reliability is critical in design, maintenance and durability analysis of engineering systems. A reliability simulation methodology is presented in this paper for vehicle fleets using limited data. The method can be used to estimate the reliability of non-repairable as well as repairable systems. It can optimally allocate, based on a target system reliability, individual component reliabilities using a multi-objective optimization algorithm. The algorithm establishes a Pareto front that can be used for optimal tradeoff between reliability and the associated cost. The method uses Monte Carlo simulation to estimate the system failure rate and reliability as a function of time. The probability density functions (PDF) of the time between failures for all components of the system are estimated using either limited data or a user-supplied MTBF (mean time between failures) and its coefficient of variation.
Journal Article

Reliability Prediction for the HMMWV Suspension System

2011-04-12
2011-01-0726
This research paper addresses the ground vehicle reliability prediction process based on a new integrated reliability prediction framework. The integrated stochastic framework combines the computational physics-based predictions with experimental testing information for assessing vehicle reliability. The integrated reliability prediction approach incorporates the following computational steps: i) simulation of stochastic operational environment, ii) vehicle multi-body dynamics analysis, iii) stress prediction in subsystems and components, iv) stochastic progressive damage analysis, and v) component life prediction, including the effects of maintenance and, finally, iv) reliability prediction at component and system level. To solve efficiently and accurately the challenges coming from large-size computational mechanics models and high-dimensional stochastic spaces, a HPC simulation-based approach to the reliability problem was implemented.
Journal Article

Time-Dependent Reliability of Random Dynamic Systems Using Time-Series Modeling and Importance Sampling

2011-04-12
2011-01-0728
Reliability is an important engineering requirement for consistently delivering acceptable product performance through time. As time progresses, the product may fail due to time-dependent operating conditions and material properties, component degradation, etc. The reliability degradation with time may increase the lifecycle cost due to potential warranty costs, repairs and loss of market share. Reliability is the probability that the system will perform its intended function successfully for a specified time interval. In this work, we consider the first-passage reliability which accounts for the first time failure of non-repairable systems. Methods are available in the literature, which provide an upper bound to the true reliability which may overestimate the true value considerably. Monte-Carlo simulations are accurate but computationally expensive.
Technical Paper

Design Optimization Under Uncertainty Using Evidence Theory

2006-04-03
2006-01-0388
Early in the engineering design cycle, it is difficult to quantify product reliability due to insufficient data or information to model uncertainties. Probability theory can not be therefore, used. Design decisions are usually, based on fuzzy information which is imprecise and incomplete. Recently, evidence theory has been proposed to handle uncertainty with limited information. In this paper, a computationally efficient design optimization method is proposed based on evidence theory, which can handle a mixture of epistemic and random uncertainties. It quickly identifies the vicinity of the optimal point and the active constraints by moving a hyper-ellipse in the original design space, using a reliability-based design optimization (RBDO) algorithm. Subsequently, a derivative-free optimizer calculates the evidence-based optimum, starting from the close-by RBDO optimum, considering only the identified active constraints.
Technical Paper

Vehicle accelerator pedal development using CAE analysis

2005-11-22
2005-01-4108
In the competitive automotive market, industries are looking to reduce the product cost and its launch time. This work presents a vehicle accelerator pedal development using CAE tools to evaluate the design proposal and also a unique physical test performed in the final design. The objective of CAE analysis is to simulate the fatigue loading of the accelerator pedal bracket and dash area due to the accelerator pedal duty cycle. The simulation goal is to predict the likelihood of a fatigue failure and its severity in the accelerator dash mount with an estimative of the fatigue life. After the CAE design evaluation, it was performed a rig test and vehicle durability test, in order to approve the accelerator pedal new design. This job allowed saving engineer and physical test cost in a short development cycle.
Technical Paper

The Fault Avoidance and The Fault Tolerance Approaches for Increasing the Reliability of Aerospace and Automotive Systems

2005-11-22
2005-01-4157
In this work we discuss the fault avoidance and the fault tolerance approaches for increasing the reliability of aerospace and automotive systems. This includes: the basic definitions/concepts (reliability, maintainability, availability, redundancy, etc.), and characteristics (a priori analysis, a posteriori analysis, physical/hardware redundancy, analytical/software redundancy, etc.) of both approaches, their mathematical background and models (exponential, Weilbull, etc.), their basic theory, their methods and techniques (fault trees, dependence diagrams, Markov chains, etc.), some of their standards (SAE-ARP4761, AC 25.1309, etc.) and simulation environments (Cafta, etc.), and their applications to the reliability analysis and reliability improvement of aerospace and automotive vehicles. This is illustrated by some examples driven from the aerospace and automotive industries.
Technical Paper

Analysis of Vehicle Power Supply Systems Using System Simulation

2006-04-03
2006-01-0299
Due to the introduction of new safety and comfort systems in modern automobiles, stability of the vehicle electrical system is increasingly important. The increasing number of electrical components demands that additional electrical energy be provided from robust, reliable supply sources in vehicles. When designing such systems, simulation is the development tool that is used to quickly obtain information regarding electrical system stability, battery charge level, and the distribution of power to the consumer systems. This paper describes how the Saber simulation environment from Synopsys Corporation helps develop increasingly demanding and complex vehicle power systems. A Volkswagen vehicle power net serves as an illustration.
Technical Paper

Predictive Monitoring and Failure Prevention of Vehicle Electronic Components and Sensor Systems

2006-04-03
2006-01-0373
Vehicle electronics and sensor systems have become indispensable parts in providing safety, comfort, personal communication mobility and many other advanced functions in today's vehicles. As a result, reliability requirements for these critical parts have become extremely important. To meet these requirements, more advanced technologies and tools for degradation monitoring and failure prevention are needed. Currently, the development of diagnostics and prognostics techniques, which employ accurate degradation quantification by appropriate sensor selection, location decision, and feature selection and feature fusion, still remains a vital and unsolved issue. This paper addresses several realistic concerns of failure prevention in vehicle electronics and sensor systems. A unified monitoring and prognostics approach that prevents failures by analyzing degradation features, driven by physics-of-failure, is suggested as a general framework to overcome the unsolved challenge.
Technical Paper

The Validation Process - One Key Element of Reliability Management

2005-04-11
2005-01-1778
Due to increasing durability requirements driven by engine emission regulations such as Euro 5 and US'07, the reliability of the engine cooling equipment, especially of charge-air-to-air-cooler (CAC), has to be increased as well. Behr is using reliability management in order to meet these requirements. “Reliability” is defined as the fulfillment of quality requirements over the life cycle and under specific application conditions. At Behr, the reliability management is organized as a “House of Reliability” (HOR). The mission profile includes up-to-date customer requirements, loads and statistical experience from the field and helps to create relevant test specifications for the validation testing. Validation is one key element of the HOR. If the test specifications are not connected to the field, the testing will not lead to a reliable product and to customer satisfaction. The process of gathering load collectives for mission profiles is therefore very important.
Technical Paper

Risk Assessment

2005-04-11
2005-01-1779
Probabilistic risk assessment is an attempt to quantify design and or manufacturing risks associated with use of a specific product or technology. Risk assessment consists of three main elements: scenarios, frequencies and consequences. Scenarios entail a list of all of the possible sequences of events. Frequencies represent the relative probability the scenario will occur whereby consequences are the expected outcome given the scenario does in fact happen. This paper, taken from a design perspective, will discuss a variety of risk assessment tools including event sequence diagrams, fault trees and maximum likelihood estimates. Application techniques will be explored allowing product-engineering teams to quantify product risks, subsequently determining the likelihood of product success.
Technical Paper

Treatment of Confidence levels When Allocating System Reliability Requirements

2005-04-11
2005-01-1776
Reliability allocation of system objectives for Reliability validation purposes must account for Confidence levels. Misallocating Confidence levels can lead to unrealistic and unmanageable objectives, resulting in increased development times and associated costs. Therefore, it is necessary to correctly model both Reliability and Confidence levels. Unfortunately, modeling for anything more complex than the simplest pass/fail test criteria can become quite complex in a multi-component system. The easiest case to model is time-censored testing with no failures. But time-censored testing with no failures is just a small subset of all viable validation strategies. Given that the validation strategy for each component can be different, trying to isolate a single one-size-fits-all model is extremely difficult. For these complex scenarios, computer simulation provides the best approach to calculating true system performance.
Technical Paper

A Comparative Study of Bayesian-Based Reliability Prediction Methodologies

2005-04-11
2005-01-1777
As new technology is introduced into automotive engineering, the level of uncertainty regarding system robustness increases. With it reliability assessment tools that account for such uncertainty is expected to gain increased attention. This can naturally lead to Bayesian-based tools. This paper examines three reliability assessment methodologies that operate in the Bayesian framework. Two of them are geared towards electronic parts and assemblies, with the remaining one being geared towards systems in general. In doing so, they were critiqued in terms of four dimensions: (1) basic architecture, (2) input factors, (3) handling of qualitative data, and (4) failure rate updating mechanisms.
Technical Paper

Solution Verification Linked to Model Validation, Reliability, and Confidence

2005-04-11
2005-01-1774
The implementation of Verification and Validation (V&V) of a computational model of a physical system can be simply described as a 4-step process. One of the steps in the 4-step process is that of Solution Verification. Solution Verification is the process of assuring that a model approximating a physical reality with a discretized continuum (e.g. finite element) code converges in each discretized domain to a converged answer on the quantity of validation interest. The modeling reality is that often we are modeling a problem with a discretized code because it is neither smooth nor continuous spatially (e.g. contact and impact) or in relevant physics (e.g. shocks, melting, etc). The typical result is a non-monotonic convergence plot that can lead to spurious conclusions about the order of convergence, and a lack of means to estimate residual error or uncertainty.
Technical Paper

A Bayesian Approach for Aggregating Test Data Across Sub-Populations

2005-04-11
2005-01-1775
In the process of conducting a reliability analysis of a system, quite often the population of interest is not homogenous; consisting of sub-populations which arise as production operations are adjusted, component suppliers are changed, etc. While these sub-populations are each unique in many ways, they also have much in common. It is also common for data to be available from a variety of different test regimes, e.g. environmental testing and fleet maintenance observations. Hierarchical Bayesian methods provide an organized, objective means of estimating the reliability of the individual systems, the sub-population reliability as well as the reliability of the entire population. This paper provides an introduction to a Bayesian approach that can be extended for more complicated situations.
Technical Paper

Definition of the Relationship Between Clutch Facing on Vehicle and Bench Testing Using Reliability and DOE

2005-04-11
2005-01-1766
1. SUMMARY There is a large variation in the results of the durability of friction facings in field applications and in most cases there is very little information about the conditions in which the vehicle operated and therefore it was decided to developed a test procedure capable of containing all the different conditions of a vehicle. For this works statistical applications such as DOE (Experimental Design for Experiment) were used to help in planning and to obtain of equations of the tests results and Weibull curves for statistical analysis and comparison of failure mode. By this mean, it was possible to determine a correlation of the results on wear between the bench test and mileage covered on vehicle up to total wear. Therefore it is new possible to estimate the durability of friction facing on vehicles based on bench tests and also obtain knowledge about the behave of the material relative to energy and working temperature.
Technical Paper

Validation Test Optimization Based on a Statistical Approach for Diesel Engine Cylinder Heads Reliability

2005-04-11
2005-01-1780
This paper describes a statistical method of test sizing optimization, used by RENAULT for diesel engine cylinder heads validation. Based on mission profiles, tests results and damage computations, the paper describes an application of the “Stress Strength” method combined with a sampling plan. Associated with degradation measurements (crack length), it allows to estimate the future field reliability and to optimize the validation test sizing: number of parts to be tested, test duration, confidence level, supplier risk and test acceptance criterion. It permits to obtain less expensive validation tests while demonstrating high level of reliability.
Technical Paper

Reliable Diesel Engine Design Based on a New Numerical Method

2005-04-11
2005-01-1762
On their own market, European car manufacturers must face high constraints, especially in three domains: environmental issues, reliability and development time reduction. For environmental issues, they have to combine fuel economy and low exhaust emissions. Diesel engines are a very cost effective way to reduce fuel consumption. However, to satisfy new standards on exhaust emissions, Diesel particulate filters and NOx traps will be necessary. These devices, associated with downsizing, will severely increase thermal and mechanical loads on engine main parts. Reliability has a great impact on brand image. The competition on this point leads to longer warranty periods and mileage targets, associated with lower failure rates. Development time reduction allows accelerating models renewal, which is also an important factor of competitiveness.
Technical Paper

Impact of Optimality Criteria on Metamodeling Accuracy Under Scarce Sampling Plans

2005-04-11
2005-01-1761
Metamodeling has been widely used in place of complex numerically intensive simulations to perform design reliability assessment and optimization. Due to cost and time constraints, most complex simulations can only afford a limited number of runs with a relatively large number of factors. The accuracy of a metamodel is affected by the degree of the underlying non-linearity, the sample size, the sampling strategy, and the type of the metamodel. In this study, the effect of the DOE optimality criteria on the accuracy of the Kriging metamodel is investigated under scarce sampling plans. Uniformity optimization is performed using some of the most popular uniformity measures, such as Centered Discrepancy (CL2), Maximin, and Entropy criteria. Case studies consist of eight analytical closed-form functions drawn mostly from real engineering applications with five to seven factors each and various degrees of non-linearity.
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