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Abstract Reliability analysis of a large-scale system under random dynamic loads can be a very time-consuming task since it requires repeated studies of the system. In many engineering problems, for example, wave loads on an offshore platform, the excitation loads are defined using a power spectral density (PSD) function. For a given PSD function, one needs to generate many time histories to make sure the excitation load is modeled accurately. Global and local approximation methods are available to predict the system response efficiently. Each way has their advantages and shortcomings. The combined approximations (CA) method is an efficient method, which combines the advantages of local and global approximations. This work demonstrates two methodologies that utilize CA to reduce the cost of crude or separable Monte Carlo simulation (MCS) of linear dynamic systems when the excitation loads are defined using PSD functions.

Abstract To gain a better understanding of the characteristics of corrugation, including the development and propagation of corrugation, and impact of vehicle and track dynamics, a computational model was established, taking into account the nonlinearity of vehicle-track coupling. The model assumes a fixed train speed of 300 km/h and accounts for vertical interaction force components and rail wear effect. Site measurements were used to validate the numerical model. Computational results show that (1) Wheel polygonalisation corresponding to excitation frequency of 545-572 Hz was mainly attributed to track irregularity and uneven stiffness of under-rail supports, which in turn leads to vibration modes of the bogie and axle system in the frequency range of 500-600 Hz, aggregating wheel wear. (2) The peak response frequency of rail of the non-ballasted track coincides with the excitation frequency of wheel-rail coupling; the resonance results in larger wear amplitude of the rail.

Road vibrations cause fatigue failures in vehicle components and systems. Therefore, reliable and accurate damage and life assessment is crucial to the durability and reliability performances of vehicles, especially at early design stages. However, durability and reliability assessment is difficult not only because of the unknown underlying damage mechanisms, such as crack initiation and crack growth, but also due to the large uncertainties introduced by many factors during operation. How to effectively and accurately assess the damage status and quantitatively measure the uncertainties in a damage evolution process is an important but still unsolved task in engineering probabilistic analysis. In this paper, a new procedure is developed to assess the durability and reliability performance, and characterize the uncertainties of damage evolution of components under constant amplitude loadings.

The objective of this project was to compare the fuel consumption and traction performances of 6 × 2 and 6 × 4 Class 8 tractors. Two approaches have been considered: evaluation of 6 × 2 tractors, modified from 6 × 4 tractors, and evaluation of OEM 6 × 2 tractors. Compared to the 6 × 4 tractors, which are equipped with a rear tandem with both drive axles, the 6 × 2 tractors have a rear tandem axle with one drive axle, and one non-drive axle, also called dead axle. The 6 × 2 tractor configurations are available from the majority of Class 8 tractor manufacturers. The SAE Fuel Consumption Test Procedures Type II (J1321) and Type III (J1526) were used for fuel consumption track test evaluations. Traction performances were assessed using pull sled tests to compare pulling distance, maximum speed, and acceleration when pulling the same set sled on similar surface.

This paper focuses on the manufacturer's conflict in the conceptual design of commercial vehicles between highly customized special vehicles and the greatest possible degree of standardization. Modularity and standardization are crucial success factors for realizing high variance at the best cost efficiency in development and production as well for achieving the highest quality standards at reduced efforts for technical validation. The presented virtual design approach for commercial vehicle concepts allows for purposeful design and integration of new concepts and technologies on the component level in an existing product portfolio - not neglecting manufacture's portfolio requirements concerning standardization and modularity. The integrated tool chain helps to bring trade-offs to a head that exist in balancing between dedicated vehicles with best customer-relevant characteristics and standardized vehicles with the highest degree of commonality.

Self-steered or caster steered axles are commonly used to support load on multi-axle commercial vehicles. Such axles can allow more payload to be hauled in some vehicle configurations under the existing bridge formulas. These self-steered axles cannot generate a side load, and serve to unload surrounding fixed axles that do generate lateral forces to turn the vehicle with payload. Since the tire's ability to generate a side load is dependent upon its load, the use of caster-steered auxiliary axles can upset the balance (or the understeering) properties of the vehicle. This work will define the effect of adding a caster steered auxiliary axle and compare it with a steerable axle that positively controls the steer angle and thereby generates a lateral force. This work assumes the reader has a basic knowledge of the well publicized “bicycle” model, and particularly its extension to multi-axle vehicles.

Due to recent infrastructural development and emerging competitive automotive markets, there is seen a huge shift in customer’s demand and vehicle drivability pattern in commercial vehicle industry. Now apart from ensuring better vehicle durability and best in class tyre life and fuel mileage, a vehicle manufacturer also has to focus on other key attributes like driver’s safety and ride comfort. Thus, for ensuring enhanced drivability, key parameters for ensuring better vehicle handling includes optimization of bump steer and brake steer. Both bump steer and brake steer are vehicle’s undesirable phenomenon where a driver is forced to constantly make steering wheel correction in order to safely maneuver the vehicle in the desired path.

This paper discusses the test setup and methodology required to validate complete lift axle assembly for simulating the real time test track data. The correlation of rig vs track is discussed. The approach for reduction of validation time by eliminating few of the non-damaging tracks/events, its correlation with real life condition is discussed, and details are presented. With increased competition, vehicle development time has reduced drastically in recent past. Bench test procedure using accelerated test cycle discussed in this paper will help to reduce development time and cost. Process briefed in this paper can also be used for similar test specification for other structural parts or complete suspension system of heavy commercial vehicles.

With the continuous development of various technologies in the field of electric vehicles, more and more mature products are put into the market. Among them, electric commercial vehicle has been supported by many preferential policies because of its wide use and high energy utilization and has developed rapidly in recent years. At present, the electric drive-train systems of commercial vehicles can be divided into motor direct drive, integrated el-axle and distributed e-wheel drive. The first type only uses motor to replace the engine, and the other parts have little change. This method has low transmission efficiency and loose structure, which is a temporary transition scheme. The drive types of integrated E-axle and distributed E-wheel have their own advantages and disadvantages, which way to become the mainstream of the future have not yet been decided.

This paper describes the work performed in predicting and measuring the contribution of oil churning to the no-load losses of a commercial truck axle at typical running speeds. A computational fluid dynamics (CFD) analysis of the churning losses was conducted. The CFD model accounts for design geometry, operating speed, temperature, and lubricant properties. The model calculates the oil volume fraction and the torque loss caused by oil churning due to the viscous and inertia effects of the fluid. CFD predictions of power losses were then compared with no-load measurements made on a specially developed, dynamometer-driven test stand. The same axle used in the CFD model was tested in three different configurations: with axle shafts, with axle shafts removed, and with ring gear and carrier removed. This approach to testing was followed to determine the contribution of each source of loss (bearings, seals, and churning) to the total loss.

Highway transportation using truck is an important transport mode of goods and product to their destination. Commercial vehicle is expensive mode of transportation so it will be protected from failure. For Heavy duty truck they are fully loaded at one side of transportation and other side empty transportation. In such case lift axle grounded when truck is loaded and when truck is empty it is in lift condition. Lift axle is play important role while loading so it is important that it should not fail. Many times lift axle fails at weld location due several load come on the axle. In this paper study of weld failure to vertical, braking and lateral load come on lift axle when truck is in loading condition. Weld failure check in CAE analysis with various load cases and compare with actual physical vehicle failure. Weld failure correlation well correlate when actual loading are consider in analysis. For analysis loading data is measure from RLDA data that will be used for analysis.

Adjuster rings are used in commercial vehicle axle assembly to preload differential bearings and provide support in the axial direction. Adjuster along with the carrier and bearing cap combined to form a threaded joint. Adjuster with external threads engages with internal threads formed in carrier and bearing cap. Preload in differential assembly maintains the system rigidity and helps to maintain an optimized hypoid gear engagement. An adequate preload is important to achieve a desirable bearing life. Reduction in thread engagement at adjuster joint fully or partially will cause a reduction in preload and can lead to gear misalignment. This can cause severe durability concerns. In some cases, it is observed that under vehicle operating loads adjuster ring is backed off from its assembled condition by bending the split pin (split pin is, positive lock, used to maintain adjuster position) and adjuster threads were stripped off.

Heavy commercial vehicle axle shafts are designed for torsion load. Typically, axle shaft fracture mode during the test is torsional in nature through either shaft body diameter or spline end. However, some of the field return axles shows fracture mode on axle shaft flange. This fracture mode does not resemble with a typical lab test torsional fracture. Metallurgical investigation report indicated that the fracture mode is bending in nature. This paper thus focuses on detail study of change in boundary condition and load transfer path under abusive vertical bending load on axle. A detail finite element analysis is performed to understand stress state change in axle shaft under this condition. A fracture hypothesis is proposed based on observations of finite element analysis results. A detail case study is presented depicting correlation of proposed hypothesis with physical fracture mode.

Lift axle is essentially provided in commercial vehicles to increase the vehicle’s load-carrying capacity. The axle is lowered in the case of a high payload and the load is evenly distributed among the wheels both on fixed axles and the lift axle. This ability to lift the axle implies better maneuverability in turns, better fuel consumption, and less wear and tear on the tires and brake shoes. Also, it will reduce the damage to the road surfaces. This lowering and lifting of the lift axle are controlled by a series of valves together called the Lift Axle Control System (LACS). This LACS must consider the vehicle load condition, the ignition state, and gear state to decide if the axle must be lifted or lowered. This paper deals with the modeling and simulation of the LACS system at the vehicle level and optimize the design for the respective desired design solution.

Bogie-type suspensions for trucks are comprised of two axles and a central spring pack on each side of the truck chassis. Bogie suspensions have a good load distribution between the axles and are used for severe applications in trucks, in off-road conditions thereby subjecting them to extreme stain and load. In today’s competitive market scenario, it of utmost importance to minimize down time in commercial vehicles as it directly corresponds to loss in business which leads to customer dissatisfaction. It is therefore essential to optimize and select the right material for each component in the bogie suspension system. This paper deals with the material selection and testing of one such component - Bogie Wear Pad. The bogie wear pad undergoes sliding friction throughout its lifetime during loading and unloading of bogie suspension. Three different materials are selected and their wear is measured under the same conditions of loading.

Despite numerous research efforts, there is no reliable and widely accepted tool for the prediction of erosion prone material surfaces due to collapse of cavitation bubbles. In the present paper an Erosion Aggressiveness Index (EAI) is proposed, based on the pressure loads which develop on the material surface and the material yield stress. EAI depends on parameters of the liquid quality and includes the fourth power of the maximum bubble radius and the bubble size number density distribution. Both the newly proposed EAI and the Cavitation Aggressiveness Index (CAI), which has been previously proposed by the authors based on the total derivative of pressure at locations of bubble collapse (DP/Dt>0, Dα/Dt<0), are computed for a cavitating flow orifice, for which experimental and numerical results on material erosion have been published. The predicted surface area prone to cavitation damage, as shown by the CAI and EAI indexes, is correlated with the experiments.

Using lift axles enables fleet to increase the load capacity of a vehicle, eliminating the need for multiple trips, thus reducing operational costs. In a project to assess the potential of reducing fuel consumption and greenhouse gas (GHG) emissions by lifting axles on unloaded semi-trailers, lift axle regulations in various jurisdictions and the studies that led to these regulations were analyzed. The SAE Fuel Consumption Test Procedures Type II (J1321) was used for fuel consumption track test evaluations. The tests were conducted on unloaded two-axle van semi-trailers, four-axle van semitrailers, and B-trains, and resulted in fuel savings of 1.3% to 4.8%, depending on vehicle configuration and the number of axles lifted during the test.

This paper presents an analysis of coupled longitudinal and lateral dynamics of a 4×4 hybrid-electric off-road vehicle (HEV) with two passive driveline systems, including drivelines with (i) an interaxle open symmetrical differential in the transfer case and (ii) a locked transfer case, i.e., positive engagement of two axles. The axle differentials are open. As the study proved, lateral dynamics of the 4×4 HEV, characterized by the tire side forces, vehicle lateral acceleration, yaw rate and tire gripping factors can be impacted by the tire longitudinal forces, whose magnitudes and directions (positive-negative) strongly depend on the driveline characteristics. At the same time, the tire side forces impact the relation between the longitudinal forces and tire slippages.

The most recent 2010 emissions standards for heavy-duty engines have established a tailpipe limit of oxides of nitrogen (NOX) emissions of 0.20 g/bhp-hr. However, it is projected that even when the entire on-road fleet of heavy-duty vehicles operating in California is compliant with 2010 emission standards, the National Ambient Air Quality Standards (NAAQS) requirement for ambient particulate matter and Ozone will not be achieved without further reduction in NOX emissions. The California Air Resources Board (CARB) funded a research program to explore the feasibility of achieving 0.02 g/bhp-hr NOX emissions.

The research on the characteristics of vehicle movement is the premise to guarantee the smooth operation of electric vehicles, and it’s also the basis for developing the vehicle ability in depth. Therefore, it’s essential to study on the vehicle movement characteristics. And steering on ramp is a typical working condition for tracked vehicle. Firstly, the kinematics and dynamics of tracked vehicle during the steering process on ramp are analyzed in detail aiming at the problem that it’s complex and difficult to describe the process of steering, and the dynamics model of tracked vehicle is established in the condition of the offset of instantaneous steering center and the sliding of the track and other factors. Second, the relationships between driving force, steering radius and slop are obtained by simulation, and the variation rules of these parameters are analyzed. Finally, the model of steering on ramp is verified using electric tracked vehicle.