Vehicle Durability Test Research Articles

Optimized determination of vehicle durability test specification correlated with user-targeted fatigue life using the multi-index decision-making approach

Optimized determination of vehicle durability test specification correlated with user-targeted fatigue life using the multi-index decision-making approach

Kinematic analysis and bearing capacity optimization of fully decoupled two-rotation mechanisms

Abstract. The existing vehicle durability test platform has low accuracy in reproducing the road spectrum and cannot meet the demand for high-accuracy road spectrum reproduction. In order to meet the need for high accuracy in road spectrum reproduction of vehicle durability tests, this paper is based on an analysis of the factors affecting the accuracy of the test platform. From the perspective of mechanism innovation, a fully decoupled two-rotation parallel mechanism with large load-bearing capacity for vehicle durability testing is proposed in this paper. A new solution is provided to improve the road spectrum reproduction accuracy of the test platform. Based on the requirement of reproduction accuracy of a real road spectrum, inverse kinematics, velocity Jacobians, and workspaces of mechanisms are analyzed. The inverse kinematics and velocity Jacobian analysis of parallel mechanisms can lay a research foundation for the subsequent calculation of load-bearing capacity indexes. The design of the parallel mechanism is based on the performance requirements of large load capacity and complete decoupling. A new index for evaluating the global average carrying capacity of a mechanism is proposed. Based on this index and the atlas method, the dimensional parameters of the mechanism have been optimized. A finite-element simulation study is carried out, and it is proved that the optimized fully decoupled two-rotation parallel mechanism can satisfy the bearing capacity requirements of the platform test. The large load capacity and fully decoupled mechanism proposed in the research work of this paper can improve the road spectrum reproduction accuracy of the vehicle durability test platform and has good application prospects in the field of vehicle durability tests.

Assessment of the Possibility of Validating the Durability Testing Method for Large-Sized Vehicles Based on Changes in Shock Absorber Characteristics—Preliminary Tests

The use of road simulators in vehicle durability tests enables a significant reduction in time related to the implementation of a new product. However, there is still a need to improve the methods of these tests in order to obtain a full correlation between the time of the tests on the simulator with respect to the mileage of the vehicle in real road conditions. The aim of this work is a validation and improvement of the durability testing method for large-sized vehicles. Comparative tests of shock absorbers dismantled from semi-trailers with different mileage and shock absorbers dismantled from semi-trailers after durability tests conducted at the MTS test bench are presented. The relationship between the maximum damping force and the displacement speed of the shock absorber piston was examined. Additionally, the influence of the shock absorber temperature on the damping force was analyzed. As a result of the tests, the dynamic characteristics of the shock absorbers were determined and the relationship between the maximum damping force and the mileage of the trailers was determined. It was found that the load on the trailers during their operation has a significant impact on the change in the characteristics of the shock absorbers. What is new in this publication is the validation of the methodology for conducting durability tests previously proposed by the authors based on the selected component, which is the shock absorber. The authors have not yet encountered in the literature any attempt to validate the methodology for conducting durability tests for large-sized vehicles.

Type Synthesis of Fully Decoupled Three Translational Parallel Mechanism with Closed-Loop Units and High Stiffness

In order to solve the problem of weak stiffness of the existing fully decoupled parallel mechanism, a new synthesis method of fully decoupled three translational (3T) parallel mechanisms (PMs) with closed-loop units and high stiffness is proposed based on screw theory. Firstly, a new criterion for the full decoupled of PMs is presented that the reciprocal product of the transmission wrench screw matrix and the output twist screw matrix of PMs is a diagonal matrix, and all elements on the main diagonal are nonzero constants. The forms of the transmission wrench screws are determined by the criterion. Secondly, the forms of the actuated and unactuated screws can be obtained according to their relationships with the transmission wrench screws. The basic decoupled limbs are generated by combination of the above actuated and unactuated screws. Finally, a closed-loop units construction method is investigated to apply the decoupled mechanisms in a better way on the high stiffness occasion. The closed-loop units are constructed in the basic decoupled limbs to generate a high-stiffness fully decoupled 3T PM. Kinematic and stiffness analyses show that the Jacobian matrix is a diagonal matrix, and the stiffness is obviously higher than that of the coupling mechanisms, which verifies the correctness of the proposed synthesis method. The mechanism synthesized by this method has a good application prospect in vehicle durability test platform.

Fatigue Durability Development for Cab of Light Truck Based on Virtual Proving Ground Technology

<div class="section abstract"><div class="htmlview paragraph">The boundary load of the light truck cab fatigue analysis is the force of the cab mounting system, which cannot be directly measured. In the absence of a physical prototype, the fatigue load of the cab cannot be extracted through virtual iteration. Aiming at the problem of fatigue analysis in the early stage of the car-free cab, the virtual proving ground technology is used to extract fatigue load and do fatigue analysis in this paper. Using the virtual road as the excitation, the simulation analysis of the whole vehicle virtual proving ground is carried out, and the wheel center load and the cab mounting force are obtained. Comparing the simulation load with the signal required on the proving ground, it is found that the extracted virtual load is consistent with the actual vehicle load in the time domain and frequency domain. The retention of pseudo-damage of the six-component load of the wheel center can meet the precision control requirements of the vehicle load decomposition. The fatigue life prediction of the cab based on the simulation results of the virtual proving ground, and the comparison with the durability test results of the whole vehicle in the proving ground show that the high-risk area predicted by the fatigue simulation is consistent with the cracking position in the actual vehicle durability test, which can guide the fatigue performance design of the cab. Compared with the traditional technology, the virtual proving ground technology uses a fully digital model to extract a higher-precision fatigue load spectrum at an early stage, which can be used for life prediction and structural design optimization.</div></div>

Optimized Vehicle Durability Testing by Means of an Intelligent Test Driver Guidance System

Vehicle manufacturers use special test courses which must be endured damage-free by the vehicle prototype until a compulsory mileage is reached. The driving instructions of this durability road test cannot always be implemented in a reproducible manner, for example due to the influence of driver, weather conditions or route closures. Furthermore, a test course based on many years of experience can only be slowly adapted to new trends in customer usage behavior.This article presents a new type of driver guidance system which, depending on the loads already endured, indicates the test driver the optimal driving instructions to reach a customer-oriented load target. The route calculation is dynamically adapted according to the actually generated and measured loads. For this purpose, the system accesses the relevant in-vehicle sensor data and combines it with road segments of a digital map. In this way, a database of the loads which were achieved on each road segment, is filled. This information is used as input of a heuristic algorithm which determines the best combination of road segments ahead for reaching the load target. As the load database is updated with every road segment driven on during the test, a learning process takes place that continuously adapts the route determination to driving style and changed road conditions. Thus, by monitoring the measured loads and by using the artificial intelligence of the driver guidance system, the customer-oriented load target of the durability road test is optimally achieved resulting in a high testing quality.

A study on the high-efficiency mixer of the SCR system

A new mixer for a diesel engine after-treatment system is developed to meet the requirements of China VI emission regulation. As for the structure of the mixer, it is surrounded by spiral blades, and the center is staggered with small blades, which is conducive to the crushing of urea droplets and can make the droplets fully mixed with air, improve the conversion efficiency of nitrogen oxides (NOx) and reduce ammonia leakage. The numerical analysis, engine bench test, and vehicle road test were carried out on the after-treatment system equipped with the new mixer. The numerical calculation results show that the velocity uniformity index of the selective catalytic reduction (SCR) carrier can reach 0.98, as well as the ammonia uniformity can reach 0.95, meanwhile, the low wall film height shows excellent anti-crystallization properties. engine bench test results are consistent with numerical results. The crystallization status of the mixer after the vehicle durability test is acceptable and well performed.

Modified Quasi-Newton Optimization Algorithm-Based Iterative Learning Control for Multi-Axial Road Durability Test Rig

The iterative learning control (ILC) based on the linear frequency-domain model has been employed to replicate the road conditions for the vehicle durability testing in the laboratory. Generally, the vehicle and the multi-axial hydraulic test rig behave strong nonlinearities, which requires a large number of iterations to correct the tracking error. Hence, the process of drive file (i.e., the input signals which drive the actuators of the test rig) generation is time-lengthy and tedious. A method that combines the ILC with the Quasi-Newton algorithm over the complex space (QNILC) is developed to speed up the drive file construction for the multi-axial vibration test rig. The impedance matrix can be updated with Broyden’s method to reduce the modeling errors and make the iteration more robust. An auxiliary estimating loop is inserted into the iteration process to attain an optimal learning gain. The convergence of the proposed method has been proven to be monotonic. This approach is validated through simulation, where the target signals are the real-life spindle forces gathered from the wheel force transducer. The simulation results demonstrate that the QNILC can improve the convergence rate and increase the tracking accuracy than the current offline ILC. The QNILC reduces the iteration number from nine down to five to converge to the desirable index compared with the offline ILC using gain 0.5. The new method based on the optimization algorithm can extend to other repetitive tracking processes.

Road Load Identification and Accelerated Life Testing of Engine Mounts

Internal combustion engine mounts in a ground vehicle experience a very complicated loading situation. The loads mainly depend on the combination of engine vibration, engine torque, and vehicle motion especially in irregular road and maneuver conditions. Fatigue life estimation of rubber components is more complicated than metal components because of nonlinear viscoelastic behavior of rubber. Hence, analytical and numerical methods to estimate the loading and fatigue life of engine mount rubber components are not employed as often as in metal components. A new approach has been proposed to validate engine mount rubber components using accelerated fatigue life testing. Accurate identification of service loads is the key factor for a successful engine mount development and validation process. A multi-axial load sensor was developed to measure the engine mount loading in six degrees of freedom for a rear wheel drive heavy duty truck. Developed load sensors were installed onto a heavy duty truck and engine mount loading was measured during vehicle durability test. Measured loading data were processed using rainflow cycle counting technique to generate the accelerated fatigue life test profile. Failure of the engine mount rubber observed in vehicle durability test was successfully replicated in accelerated life test. This approach can also be employed for validation of different rubber components available in suspension and driveline sub-systems.

A Novel Approach for Accelerated Life Testing of Ground Vehicle Components

Accelerated life testing has major impact on the success of a ground vehicle development program. Accelerated life testing profile should represent the customer usage so that optimum design can be achieved. A novel approach incorporating finite element analysis and vehicle durability test data into single axis accelerated life test profile generation was developed in this study. The proposed approach was successfully applied to the engine mount bracket of a heavy duty truck engine and it is validated by vehicle and rig tests. The accelerated life testing procedure developed in this study is applicable to many components of ground vehicles. It is possible to test components at high confidence level and low cost with this approach.

Custom Design Multi-Axial Engine Mount Load-Cell Development for Road Load Identification and Fatigue Life Estimation

Copyright © 2016 SAE International. Internal combustion engines are attached on the vehicle body using engine mounts composed of two cast iron brackets and a rubber isolator connecting them. Engine mount road load identification during vehicle durability tests on proving ground is a critical task for engine mount development. Using standard multi-axial load-cell is not possible unless major design revisions on the vehicle body or engine block are done. Using wheel force transducers and vehicle dynamic simulation tools need extensive model tuning work to get accurate load information. Hence, a custom multi-axial load-cell design is preferred for the engine mount load identification of a BCar I4 engine. The developed load-cell engine mount bracket can be installed without doing any design changes on the vehicle. Design, durability analysis, instrumentation, calibration and vehicle installation of custom designed six degree of freedom multi-axial load cell have been performed. Strain and acceleration measurements have been conducted on vehicle durability test track. Data have been processed to obtain forces and moments in six degree of freedom on the engine mounts. The loading information was used for fatigue life estimation.

Fatigue Life Prediction of Z Type Leaf Spring and New Approach to Verification Method

In this study, fatigue life prediction and the correlation of Z Type leaf springs were investigated. Leaf springs are tested with different loads until failure and component S-N curve is constructed to take account of process effects. Rate measurement on test rig is completed for first FE correlation. Collected time based strain data is used for the second FE correlation. WFT loads are applied to the FE model hardpoint and compared damage effects so expected test rig specification is determined. After completion of the vehicle durability test, the remaining life of the part is determined via component test rig for third correlation.

Measurement and Simulation of Random Vibro-Impact Responses at Brake Guide Pins

This study firstly conducted measurement of load history profiles at brake guide pins using strain gages subject to random road load history obtained from vehicle durability tests. Then, this study developed a simple mathematical model capable of estimating guide pin load history using the principle of energy conservation for a given road load profile. The model took into account the effect of impact that occurs from a range of acceleration levels and frequency content of the road input. The mathematical model also utilized the measured stiffness of the guide pin specimens and strain versus load relationship to increase the accuracy of the predictions. The estimated loads at a brake guide pin subject to a given random road load history were then computed using the mathematical model and compared to the load history obtained from the measurement. This study also compared cumulative fatigue damages calculated using Smith-Watson-Topper equation with the measured and predicted load profiles at the guide pin. The comparison study showed that the developed simple model is applicable to predict load profiles for fatigue life calculation at brake guide pins.

Design of Multifunctional Electric Wheel Test-Bed

This paper introduces a multifunctional electric wheel test-bed which focuses on vehicle dynamics (especially for testing the relation between tire force and slip ratio with large cornering force) and durability test of the electric wheel. On the basis of the functional requirements we propose some design specifications, with which mechanical structure and control system design as well as finite element analysis of the test-bed are conducted. The finite element analysis results show that the stress of the whole mechanism especially the critical parts is less than the yield stress limit with enough tolerance, suggesting that the test-bed meets the design specifications.

Equivalence Study for Special Purpose Vehicle Durability Test on Different Program Ground

The number of special purpose vehicle increase quickly recent year, so more Program Grounds were needed to performed the durability test. Now more than one Program Ground owned the qualification to perform the test. To secure the test results were uniform in different Program Grounds, a equivalence analysis method based on fatigue theory was given in the paper. The acceleration signals on vehicle were taken as the basic parameters in the method. At last, a high mobility vehicle was used to collecting the vibration signals on two different Program Grounds.The equivalence relationship was analyzed.

Failure analysis and design of a front bumper using finite element method along with durability and rig tests

This work presents a case study that comprises the application of the Finite Element Method (FEM) to the design of a front bumper to predict possible failures caused by fatigue. Stress distribution and damage estimates were obtained by using FEM together with rig tests results. Vehicle durability tests were also performed, and geometric changes were proposed in the design of the component analysed based on the simulation results obtained from FEM. A good agreement between experimental data and FEM predictions was found. The case study and results demonstrate that time and cost can be reduced in the course of the product development phase in the automotive industry. FEM also can be used to support decision-making during the design phase of the product.

Development of an air spring engine mount system for a medium duty truck

A collaborative research project between universities, a public laboratory, vehicle engineering and testing companies was formed and a prototype vehicle with a diesel engine mounted on four air springs was designed. Concurrently, Genetic Algorithm (hereafter GA) was also implemented to optimize the parameters related to the engine mounting layout, the calculations of the stiffness matrix and the inverse stiffness matrix to prevent the coupled of lateral and rolling vibrational modes, and to obtain the displacement of each mounting point. Finally, the best engine mounting layout was selected for the installation of four air springs to minimize torque roll. Also, the original engine mount layout with cushion rubbers was completely changed to enable installation of four air springs, two lateral and tension rods, and four shock absorbers for the reduction of large engine movements against transient engine torque at engine start and stop, and gear changes. Two leveling valves were also attached to the frame to maintain engine height against large engine torque. As a result, the engine vertical vibration level at 19.1 Hz dropped below 20% of the level designed with the cushion rubber installed on the current vehicle and the engine displacement with the largest torque was within the limit. Further study such as vehicle durability testing is necessary, but the air spring is very useful as a vibration isolation tool for diesel engine mounting layouts.

A technique for developing a high accuracy durability test for a Light Truck on a Six Degree-of-Freedom Road Test Simulator

A technique for developing a high accuracy laboratory durability test for a light-duty pickup truck on an MTS Six Degree-of-Freedom Light Truck (LT) Road Test Simulator (RTS) is presented. On the vehicle being studied, various transducers were instrumented. On-road data was acquired for drive file development on a RTS. Vehicle transducer responses from the road were used as targets to be achieved on the simulator. Several simulation schemes using different vehicle transducer configurations as control channels were attempted and the correlation of transducer responses between those achieved on the simulator and the on-road data was analysed. The configuration that produced the best correlation with on-road responses was adopted to develop the drive files used for subsequent vehicle durability testing.

Extended PEMFC Durability From MEAs Based On A New Reinforced Membrane

A key requirement for the adoption of PEMFCs is demonstration of improved durability from the MEA. Most MEA failures have been ascribed to rupture of the membrane as a result of mechanical stress and chemical attack. Johnson Matthey Fuel Cells has developed a reinforced membrane impregnated with PFSA ionomer solution. In 30-cell stack tests the membrane has a high performance and shows a 6-fold improvement in durability compared to commercially available unreinforced membranes, under demanding automotive operating conditions. The improved durability is ascribed to an increased tear resistance and to an improved response to the change in dimensions during the hydration/dehydration cycles present during vehicle durability testing. Initial testing in large-scale single cells highlighted that MEA durability can be compromised by poor gasket design. Edge protection films were designed to overcome the impact of the gasket on durability with thinner films providing prolonged durability.