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The real cycle simulation is an important tool to predict the engine efficiency. To evaluate Extended Expansion SI-engines with a multi-link cranktrain, the challenge is to consider all concept specific effects as best as possible by using appropriate submodels. Due to the multi-link cranktrain, the choice of a suitable heat transfer model is of great importance since the cranktrain kinematics is changed. Therefore, the usage of the mean piston speed to calculate a heat-transfer-related velocity for heat transfer equations is not sufficient. The heat transfer equation according to Bargende combines for its calculation the actual piston speed with a simplified k-ε model. In this paper it is assessed, whether the Bargende model is valid for Extended Expansion engines. Therefore a single-cylinder engine is equipped with fast-response surface-thermocouples in the cylinder head. The surface heat flux is calculated by solving the unsteady heat conduction equation.

As for passenger cars, the overall noise and vibration comfort in commercial trucks and busses becomes an increasingly important sales argument. In order to effectively reduce the noise and vibration levels it is required to identify possible NVH issues at an early stage in the vehicle development process. For this reason a so-called “Virtual Transfer Path Analysis” (VTPA) method has been implemented which combines the results obtained from the conventional multi-body simulation and finite element method approaches. The resulting VTPA tool enables Daimler Trucks to systematically investigate and predict the complex interaction between powertrain excitation and the resulting vehicle response well before hardware prototypes become available. An overview of the theory is presented as well as the practical application and outcome of the technique applied in a past product development.

The increasing functionality and complexity of future electric/electronic architectures requires efficient methods and tools to support design decisions, which are taken in early development phases 6. For the past four years, a holistic approach for architecture development has been established at Mercedes-Benz Cars R&D department. At its core is a seamless design flow, including the conception, the analysis and the documentation for electric/electronic architectures. One of the actual challenges in the design of electric/electronic architectures concerns communication behavior and network topologies. The increasing data exchange between the ECUs creates high requirements for the networks. With the introduction of FlexRay 21 and Ethernet the automotive network architecture become a lot more heterogeneous. Especially gateways must fulfill many new requirements to handle the strict periodic schedule of FlexRay and the partly event-triggered communication on CAN-busses 23.

The reliability of electronic components is of increasing importance for further progress towards automated driving. Thermal aging processes such as electromigration is one factor that can negatively affect the reliability of electronics. The resulting failures depend on the thermal load of the components within the vehicle lifetime - called temperature collective - which is described by the temperature frequency distribution of the components. At present, endurance testing data are used to examine the temperature collective for electronic components in the late development stage. The use of numerical simulation tools within Vehicle Thermal Management (VTM) enables lifetime thermal prediction in the early development stage, but also represents challenges for the current VTM processes [1, 2]. Due to the changing focus from the underhood to numerous electronic compartments in vehicles, the number of simulation models has steadily increased.

In this paper the latest status of the Vehicle Thermal Management (VTM) simulation at the Mercedes-Benz Car Group is shown. First of all VTM is nowadays a routine simulation application and secondly it is embedded in a standard process which starts with the CAD data collection and ends with standard reporting of the simulation results and thirdly VTM is now an integrated simulation application in terms of VTM includes the classical underhood-underbody analysis, the analysis of electric/electronic components, the brake temperature analysis and last not least the thermal comfort of passengers. There is also a close link to the tests of vehicle hardware. Beside the operational simulation process there is a process installed which guarantees good quality of the results.

The need for a consistent and reliable calculation of thermodynamic property of refrigerants has been a topic of research since the past decade. This paper reports a study of various cubic equations of state for a refrigerant being used in automotive air-conditioning applications. The thermodynamic property of refrigerant 1,1,1,2 tetrafluoroethane (commercially known as R134a) is estimated for this purpose. A comparative analysis is made on three sets of equations of state. They are Redlich Kwong equation (RK), Peng Robinson equation (PR) and Patel Teja equation. It is found that the Patel-Teja and Peng-Robinson equations are accurate in the operating region of automotive air-conditioning system. Using these literature based equations and Maxwell correlations, thermodynamic models are developed. They estimate thermodynamic properties of saturated liquid/vapor, sub-cooled liquid and superheated vapor phases.

In the proposed work the transient thermal modeling of a vehicle cabin has been performed. Therefore, a reduced model has been developed based on a one-node discretization of the cabin air. The conduction in the solid parts is accounted for by a one-dimensional heat transfer approach, the radiation exchange between the surfaces is based on view factors adopted from a 3D reference and the convective heat transfer from the cabin surfaces to the cabin air is conducted with the help of heat transfer coefficients calculated in a 3D reference simulation. The cabin surface is discretized by planar wall elements, including the outer shell of the cabin and inner elements such as seats. Each wall element is composed of several homogeneous material layers with individual thicknesses. Investigations have been conducted on the temporal and spatial resolution of the layer structure of these wall elements, for the 3D model as well as for the reduced one.

A raise of efficiency is the strongest selling point concerning the total cost of ownership (TCO), especially for commercial vehicles (CV). Accompanied by legislations, with contradictive development demands, satisfying solutions have to be found. The analysis of energy losses in modern engines shows three influencing parameters. Wall heat transfer (WHT) losses are awarded with the highest optimization potential. Critical for the occurrence of these losses is the WHT, which can be described by representing coefficients. To reduce WHT accompanying losses a decrease of energy transfer between combustion gas and combustion chamber wall is necessary. A measurement of heat fluxes is necessary to determine the WHT relations of the combustion chamber in an engine. As this has not been done for a Heavy-Duty (HD) engine, with peak pressures up to 250 bar, an increased in-cylinder turbulence and high exhaust gas recirculation (EGR)-rates before, it is presented in the following.

Air-cooled fin and tube heat exchangers are used as a condenser in the conventional automotive Heating Ventilation & Air-Conditioning (HVAC) systems. In this study, the use of liquid cooled plate heat exchanger as a condenser in the automotive HVAC systems has been investigated. In the proposed configuration, the cabin heat absorbed by the refrigerant in HVAC system is rejected to the coolant through a liquid cooled condenser and then to the ambient air through a low temperature radiator. Hence, the proposed configuration combines heat rejection from HVAC system with a low temperature radiator circuit of power train cooling. Mixture of Ethylene glycol & Water (coolant), which is used in power train cooling system, is used as secondary fluid in the condenser.

In the digital prototype development process of a new Mercedes-Benz, thermal protection is an important task that has to be fulfilled. In the early stages of development, numerical methods are used to detect thermal hotspots in order to protect temperature sensitive parts. These methods involve transient full Vehicle Thermal Management (VTM) simulations to predict dynamic vehicle heat-up during critical load cases. In order to simulate thermal control mechanisms, a coupled 1D to 3D thermal vehicle model is built in which the coolant and oil circuit of the engine, as well as the exhaust flow are captured in detail. When performing a transient 3D VTM analysis, the conduction and radiation phenomena are simulated using a transient structure model while the convective phenomena are co-simulated in a steady state fluid model. Both models are brought to interaction at predetermined points by an automatized coupling method.

An accurate model to predict the formation of fogging and defogging which occurs for low windshield temperatures is helpful for designing the air-conditioning system in a car. Using a multiphase flow approach and additional user-defined functions within the commercial CFD-software STAR-CCM+, a model which is able to calculate the amount of water droplets on the windshield from condensation and which causes the fogging is set up. Different parameters like relative humidity, air temperature, mass flow rate and droplet distributions are considered. Because of the condition of the windshield's surface, the condensation occurs as tiny droplets with different sizes. The distribution of these very small droplets must be obtained to estimate numerically the heat transfer coefficient during the condensation process to predict the defogging time.

Fuel cells convert a fuel together with oxygen in a highly efficient electrochemical reaction to electricity and water. Automotive fuel cell systems mainly use compressed onboard stored hydrogen as fuel. Oxygen from ambient air is fed to the cathode of the fuel cell stack by an air supply subsystem. For its current and next generation air supply subsystem NuCellSys has employed screw type compressor technology, which in the automotive area initially was developed for supercharged internal combustion (IC) engines. As NVH expectations to fuel cell vehicles differ very much from IC-engine driven vehicles, specific efforts have to be taken to address the intense noise and vibration profile of the screw compressor. This paper describes different counter measures which have been implemented into the NuCellSys next generation air supply subsystem.

A system for controlled heat generation in exhaust pipeline is studied, consisting of fuel injector and oxidation catalyst (plus connecting pipes). A 3D-CFD software (StarCD) coupled with a tailored 1D model of catalytic monolith channel (XMR) are employed for simulations of realistic, fully 3D system geometry. Exhaust gas flow, fuel injection, and distribution at the catalyst inlet is solved by 3D-CFD, while the processes inside individual representative channels are simulated by the effective 1D model. The 3D-CFD software calls iteratively the 1D channel model with proper boundary conditions and solves 3D temperature profile over the monolith, utilizing local enthalpy fluxes (including gas-solid heat transfer and reaction enthalpy) calculated by the 1D channel model. Seven representative hydrocarbons are used for characterisation of Diesel fuel composition with respect to catalytic oxidation kinetics.

The electric turbocharger is a promising type of air supply unit for future automotive fuel cell drive systems. It comprises of a centrifugal compressor, a variable geometry turbine and a permanent magnet synchronous motor assembled on a single shaft. Compared to other types of vehicular fuel cell air supplies, like for example a screw or roots compressor, it needs less installation space and has lower weight while also causing less noise and vibration. This paper presents a validated mechanistic model of the electric turbocharger. The stationary compressor model is based on a set of aerodynamic loss models with surge and stone wall line prediction capability. Similarly, the stationary variable axial turbine is a detailed station based model derived from aerodynamic losses at the turbine wheel and the stator blades. The aerodynamic losses incorporated in the compressor and the turbine models are implemented under MATLAB/Simulink and show a good correlation with the experimental data.

Safety-critical embedded software has to satisfy stringent quality requirements. All contemporary safety standards require evidence that no data races and no critical run-time errors occur, such as invalid pointer accesses, buffer overflows, or arithmetic overflows. Such errors can cause software crashes, invalidate separation mechanisms in mixed-criticality software, and are a frequent cause of errors in concurrent and multi-core applications. The static analyzer Astrée has been extended to soundly and automatically analyze concurrent software. This novel extension employs a scalable abstraction which covers all possible thread interleavings, and reports all potential run-time errors, data races, deadlocks, and lock/unlock problems. When the analyzer does not report any alarm, the program is proven free from those classes of errors. Dedicated support for ARINC 653 and OSEK/AUTOSAR enables a fully automatic OS-aware analysis.

This paper summarizes a common project of Mercedes-Benz and FKFS (Research Institute of Automotive Engineering) to apply numerical methods to thermal soak issues in a very early stage of the development phase of a new car. “Thermal soak” results from driving the vehicle at high load followed by shutting off the engine and a cool down phase. After stopping, the underhood flow is only driven by natural convection. The thermal soak behaviour is discussed in principal and the numerical challenges are summarized. Four different issues are identified: the need for a transient computation including transient thermal load pattern, a method to compute natural convection in the underhood after the shutdown of the engine, the complex geometry and the lack of a single computational program to consider all three modes of heat transfer, which results in a coupled numerical approach.

Aerodynamic design and thermal management are some of the most important tasks when developing new concepts for the flow around tractor-trailers. Today, both experimental and numerical studies are an integral part of the aerodynamic and thermal design processes. A variety of studies have been conducted how the aerodynamic design reduces the drag coefficient for fuel efficiency as well as for the construction of radiators to provide cooling on tractor-trailers. However, only a few studies cover the combined effect of the aerodynamic and thermal design on the air temperature of the under hood flow [8, 13, 16, 17, 20]. The objective of this study is to analyze the heat transfer through forced convection for a scaled Cab-over-Engine (CoE) tractor-trailer model with under hood flow. Different design concepts are compared to provide low under hood air temperature and efficient cooling of the sub components.

This paper investigates the pressure drop with and without condensation inside a charge air cooler. The background to this investigation is the fact that the stored condensate in charge air coolers can be torn into the combustion chamber during different driving states. This may result in misfiring or in the worst-case lead to an engine failure. In order to prevent or reduce the accumulated condensate inside charge air coolers, a better understanding of the detailed physics of this process is required. To this end, one single channel of the charge air side is investigated in detail by using an experimental setup that was built to reproduce the operating conditions leading to condensation. First, measurements of the pressure drop without condensation are conducted and a good agreement with experimental data of a comparable heat exchanger reported in Kays and London [1] is shown.

Since 2013 the new Daimler Aeroacoustic Wind Tunnel (AAWT) is in operation at the Mercedes-Benz Technology Center in Sindelfingen, Germany. This construction was the second stage of a wind tunnel center project, which was launched in 2007 and started with the climatic wind tunnels including workshop and office areas. The AAWT features a test facility for full-scale cars and vans with a nozzle exit area of 28 m2, a five-belt system, and underfloor balance to measure forces with best possible road simulation. With a remarkable low background noise level of the wind tunnel, vehicle acoustics can be investigated under excellent conditions using high-performance measurement systems. An overview is given about the building and the design features of the wind tunnel layout. The aerodynamic and aeroacoustic properties are summarized. During the first years of operation, further improvements regarding the wind tunnel background noise and vehicle handling were made.

An overview of Daimler?s progression to advance powertrain technology in a growth industry shows many different solutions to improvement in transportation. Daimler continues to make breakthroughs in technology development and application building on 125 years of automotive development. Optimization of current powertrains will enable a significant gain in CO2/mi reductions, that dependent on product mix can be augmented with additional technologies. There is however no bypass to some form of electrification, enabling efficiency gains and alternative forms of power supply. Development of hybrid powertrains continues in an established manner and enhanced development of further electrified powertrains are in development. Organizationally and technically, significant skills and adjustments need to continue to be undertaken enabling OEMs and in particular the supply base to develop optimized solutions efficiently. The outlook is bright for novel component development and innovation.