Search Results

Squeak and rattle (S&R) are nonstationary annoying and unwanted noises in the car cabin that result in considerable warranty costs for car manufacturers. Introduction of cars with remarkably lower background noises and the recent emphasis on electrification and autonomous driving further stress the need for producing squeak- and rattle-free cars. Automotive manufacturers use several road disturbances for physical evaluation and verification of S&R. The excitation signals collected from these road profiles are also employed in subsystem shaker rigs and virtual simulations that are gradually replacing physical complete vehicle test and verification. Considering the need for a shorter lead time and the introduction of optimisation loops, it is necessary to have efficient and inclusive excitation load cases for robust S&R evaluation.

The aim of the presented research is to propose and benchmark two brake models, namely the novel dynamic ILVO (Ilmenau-Volvo) model and a neural-network based regression. These can estimate the evolution of the brake friction between pad and disc under different load conditions, which are typically experienced in vehicle applications. The research also aims improving the knowledge of the underlying mechanism related to the evolution of the BLFC (boundary layer friction coefficient), the reliability of virtual environment simulations to speed up the product development time and reducing the amount of vehicle test in later phases and finally improving brake control functions. With the support of extensive brake dynamometer testing, the proposed models are benchmarked against State-of-the-Art. Both approaches are parametrized to render the friction coefficient dynamics with respect to the same input parameters.

To give the customer an immediate impression of quality several of criteria must be fulfilled such as styling, paint finish and fitting of outer panels/closures. Therefore, higher demands on geometrical quality e.g. stability for both exterior and interior are needed. The structural part of the car body is the key element for success. Beside the visual impression, lack of noise and vibrations during driving can convince a potential buyer to become an actual customer. To achieve this, car manufacturers have to draw up an overall strategy in combination with proper working methods to be able to guarantee a stable geometrical output throughout the entire development process and during series production over the lifetime of the vehicle. On a simultaneous engineering basis, the OEM, the system/component- and the process suppliers (for the industrial system from press shop to final assembly) have to adopt a common measurement strategy.

The development of a new combustion system for a light-duty diesel engine is presented. The soot-NOx trade-off is significantly improved with maintained or improved efficiency. This is accomplished only by altering the combustion chamber geometry, and thereby the in-cylinder flow. The bowl geometry is developed in CFD and validated in single cylinder tests. Tests and simulations align remarkably well. Under identical conditions in the engine the new combustion chamber decreases smoke by 11-27%, NOx by 2-11%, and maintains efficiency as compared to the baseline geometry. The injector nozzle is matched to the new bowl using design of experiments (DoE). By this method transfer functions are obtained that can be used to optimize the system using analytical tools. The emissions show a complex dependence on the nozzle geometry. The emission dependence on nozzle geometry varies greatly over the engine operating range.

This paper describes the development of a robust and accurate method to model one-phase heat exchangers in complete vehicle air flow simulations along with a comprehensive comparison of EFD and CFD results. The comparison shows that the inlet radiator coolant temperatures obtained with CFD were within ±4°C of the experimental data with a trend in the differences being dependent on the car speed. The relative differences in cooling air mass flow rates increase with increasing car speed, with CFD values generally higher than EFD. From the investigation, the conclusion is that the methodology and modeling technique presented offer an accurate tool for concept and system solutions on the front end design, cooling package and fan. Care must be taken in order to provide the best possible boundary conditions paying particular attention to the heat losses in the engine, performance data for the radiator and fan characteristics.

Structural topology optimization is a truly interesting and important area, which has developed very rapidly and matured considerably in many fields. However, the use of topology optimization for global structures, using detailed design, is still tremendously time-consuming. From this perspective, the author sees the development of methods and tools to include optimization on simplified models during the design process as the most interesting and important step towards implementing structure topology optimization in the vehicle industry. In the design process, structures are broken down into beams and joints, and are described using a PBM (Property Based Model). Beams are described using a rectangular cross-section with the possibility of being changed in size, shape and orientation. Joints are described as flexible elements using a set of sub-elements called 2-joints that makes it possible for the joint model to change topology and stiffness.

In the continuous struggle to improve car body properties, and at the same time reduce the weight of the structure, new materials and body concepts are being evaluated. In competition with more self-evident lightweight materials such as aluminium and plastic composites, new and different grades of high-strength steels with various surface coatings are being introduced. From experience it is known that to be able to weld and join these steel grades under high-volume conditions, it is necessary to perform comprehensive testing to establish those assembly parameters which give a superior and reliable weld quality. To meet the demands of cost-effective low volume production, we can notice a tendency to move away from traditional uni-body concepts and into the direction of space-frame structures. These can preferably be manufactured out of high-strength steels by using production methods like roll-forming, hydro-forming and hot-forming.

Numerical and modeling errors in computational aerodynamics consist of multiple components. Previous investigations at Volvo have shown that low Reynolds k-ε models generally give better levels in pressure over the rear base area of the car than the corresponding wall function based model. However, these computations were carried out on car shapes without wheels. This paper presents numerical simulations of the flow field around three versions of the Volvo validation car series (VRAK). The geometry is a typical car with flat floor and simplified tires. The three car models differ by their rear shape. The configurations are: one with a nearly flat base, a fastback with a sloping rear window, and a car with a roof wing. The influence of the near wall formulation of the standard k-ε model on drag and lift is investigated. The performance of the low Reynolds number version of the cubic k-ε model by Suga [7] is also investigated.

A two-state forward dynamic programming algorithm is evaluated in a series hybrid drive-train application with the objective to minimize fuel consumption when look-ahead information is available. The states in the new method are battery state-of-charge and engine speed. The new method is compared to one-state dynamic programming optimization methods where the requested generator power is found such that the fuel consumption is minimized and engine speed is given by the optimum power-speed efficiency line. The other method compared is to run the engine at a given operating point where the system efficiency is highest, finding the combination of engine run requests over the drive-cycle that minimizes the fuel consumption. The work has included the engine torque and generator power as control signals and is evaluated in a full vehicle-simulation model based on the Volvo Car Corporation VSIM tool.

In modern vehicles, each system must meet tough demands to fulfill the many different attribute requirements, design constraints and manufacturing limitations. It becomes difficult and time-consuming to find an optimal and robust design using a traditional engineering process. Volvo Cars has for several years been using Multi-Disciplinary Optimization, MDO, that basically shows the customer attributes levels, such as NVH, ride comfort, and driveability as a function of different parameter configurations. This greatly facilitates project team understanding of the limitations and possibilities of the different systems, and has become a key enabler to achieving a good balance between different attributes. Traditionally, this type of comprehensive Design of Experiments (DOE) optimization demands huge time and computer resources. Frequently, experimental designs will not fulfill manufacturing limitations or attribute targets, making this decision process slow, tedious, and fruitless.

The objective of this paper is to investigate whether different appearance modes of the digital human models (DHM or manikins) affect the observers when judging a working posture. A case where the manikin is manually assembling a battery in the boot with help of a lifting device is used in the experiment. 16 different pictures were created and presented for the subjects. All pictures have the same background, but include a unique posture and manikin appearance combination. Four postures and four manikin appearances were used. The subjects were asked to rank the pictures after ergonomic assessment based on posture of the manikin. Subjects taking part in the study were either manufacturing engineering managers, simulation engineers or ergonomists. Results show that the different appearance modes affect the ergonomic judgment. A more realistic looking manikin is rated higher than the very same posture visualized with a less natural appearance.

Bushing elasticity is one of the most important compliance factors that significantly influence driving behavior. The deformations of the bushings change the wheel orientations under external forces. Another important factor of bushing compliance is to provide a comfortable driving experience by isolating the vibrations from road irregularities. However, the driving comfort and driving dynamics are often in conflict and need to be balanced in terms of bushing compliance design. Specifically, lateral force steer and brake force steer are closely related to safety and stability and comprises must be minimized. The sensitivity analysis helps engineers to understand the critical bushing for certain compliance attributes, but optimal balancing is complicated to understand. The combination of individual bushing stiffness must be carefully set to achieve an acceptable level of all the attributes.

In May 1998 Volvo launched its most exclusive car model so far, the Volvo S80, which is aimed to compete with upper luxury segment products. The car is produced in the new production facility in the Torslanda plant in Sweden. Among the more highlighted features were a transversely mounted in-line six cylinder engine with a specially designed gearbox, electronic multiplex technology with 18 computers in the network, and safety features like stability and traction control (STC), front seats with integrated antiwhiplash system (WHIPS) and inflatable curtain (IC) for improved side impact protection. To fulfill the product's high demands on safety, quality and environmental care, the design, materials selection and assembly of the car body with high precision had to be very carefully engineered. As in previous product-/process development a holistic and concurrent engineering approach was necessary.