Automotive and Engine Technology最新文献

Several studies about the calculation of the brake factor exist, with differences in the degree of detail. One of the best known from Kößler is enlarged in this paper to analyze beside the brake factor the force inside the drum in further detail. Based on this analysis a relation between brake torque and abutment forces is presented, which leads to the idea of an abutment force sensor, to determine the brake torque. To assess this relation a sensitivity analysis is carried out. The results show a low sensitivity against the friction coefficient of the lining. The effects from all other, mainly geometric parameters are discussed to assess the potential of this innovative sensor.

The focus on transient engine operation will increase to fulfill future emission requirements in the commercial vehicle sector. Accordingly, the transient turbocharger matching process is becoming increasingly important. The one-dimensional fluid dynamics (1D-CFD) simulation is established as an important development tool for matching the exhaust gas turbocharger to a combustion engine. The optimization of the modeling methodology of the combustion process and the turbocharger modeling are two key parameters to improve the reliability of the dynamic engine process simulation. In this paper, the advanced turbocharger (TC) methodology is described. This includes the determination of the adiabatic turbocharger performance from conventional hot gas test stand (HGS) measurement data, the derivation of an one-dimensional (1D) turbocharger heat transfer model and a method to physically extend the turbine map range. The adiabatic efficiencies of the turbocharger are determined with a model-based heat transfer correction of the conventional measured efficiencies from HGS measurement data. These adiabatic efficiency maps were used as a baseline to extend the conventional TC model with a heat transfer model taking into account of the engine boundary conditions in terms of temperature, pressure and mass flow rate. To assess the temperature distribution and the thermal inertia of the TC main components, in both stationary and transient engine operations, the variable geometry turbine (VGT) turbocharger hardware, installed on a medium-duty diesel engine, was equipped with several thermocouples on all accessible surfaces to make comprehensive surface temperature surveys. A 1D lumped capacitance heat transfer model (HTM) of the VGT TC was developed and validated against the experimental data from the engine test bench. To complete the advanced TC modeling, the turbine map is extended using experimental measurement data, based on extended HGS measurements, in combination with mathematically supported extrapolation. The results from the advanced turbocharger simulation methodology significantly improves the prediction of the temperature drop over the turbine in comparison to the conventional adiabatic TC simulation methodology. The validated heat transfer model also allows the analysis of the heat flow breakdown of the turbocharger. Based on the advanced turbocharger model, a tool for the improved transient turbocharger-engine matching process is given.

Tire development based on functional tire characteristics (FTC) makes it possible to objectify target values across all topics and thus contributes to a clear target agreement between tire and vehicle manufacturers. Developmental tires can be evaluated on the basis of test bench measurements, thereby decreasing development duration and financial costs. A major challenge is the ongoing tightening of conflicting targets as a result of legal and customer-related requirements. Depending on the rim and tire dimensions the characterization of these conflicting targets can be different. Therefore, when defining a tire portfolio in the early development phase, methods are required to allow an evaluation of the feasibility based on objective correlations. In this paper a method for determining the optimal rim and tire dimensions by considering the respective requirements is presented. First of all, the effects of the tire dimension on individual FTC concerning load capacity, driving dynamics and efficiency are quantified using regression models. Next, the FTC of different dimension configurations are estimated on the basis of a Monte Carlo sampling. Finally solution spaces of optimal dimension ranges are shown graphically.

This paper evaluates the fuel consumption of homogeneous and heterogeneous lean combustion in the WLTC test cycle. A lean combustion engine is combined with an electrified powertrain and the combustion processes are compared with each other. There is also a distinction with regard to the degree of electrification. First, investigations are carried out with an “engine in the loop” test bench. It turns out that, as expected, the best fuel consumption results can be achieved with heterogeneous lean combustion in combination with homogeneous lean combustion. In addition, it is shown that, in combination with P1 hybridization, low-load heterogeneous lean combustion becomes less important, but continues to contribute to an improvement in fuel consumption. Additionally, P1 hybridization increases the percentage of homogeneous lean combustion by 13%. Thus, the cycle fuel consumption is improved through electrification disproportionately for homogeneous lean combustion by 7.5%, for stoichiometric combustion by 6%. Furthermore, electrification contributes to reducing nitrogen oxide emissions by about 50% in the test cycle to 9 mg/km. The reduction can be achieved by shifting the load points from high loads with higher NOx raw emissions to lower loads with lower NOx raw emissions and by omitting heterogeneous lean combustion. In the second step, the combustion processes for two different engine displacements are compared in calculations. This allows further investigations. It turns out that, with increasing degree of electrification and decreasing engine displacement, heterogeneous lean combustion can no longer contribute to an improvement in fuel consumption and rather an expansion of homogeneous lean combustion at high loads becomes necessary. In general, thanks to the electrification of the powertrain in combination with lean combustion, the cycle fuel consumption can be greatly reduced by up to 33% to 3.76 l/100 km. Electrification does not compete with the advantages of lean combustion, but complements them. The presented results show the potential for improvement in fuel consumption for future developments in gasoline engines in hybridized powertrains.

The friction at the contact surfaces of a vehicle body vibration damper, which are moved relatively to each other, influences its transmission behavior at the start of movement (breakaway force) as well as with excitation signals of higher velocity and thus has an impact on the comfort properties of the damper. According to Vibracoustic (Die wichtigsten Kriterien für deutsche Autofahrer beim Autokauf, Springer Fachmedien Wiesbaden GmbH, Wiesbaden, 2019), for most German drivers (63%) comfort (in addition to brand and appearance) before driving dynamics (53%) and environmental compatibility (48%) is the most important criteria when evaluating a new car, which explains the importance of this vehicle characteristics. Furthermore, the friction is present with any relative movement of the damper and is, therefore, relevant for the design of the damper and the associated vertical dynamics. The friction is generally determined in the fully assembled state of the damper, including oil filling and gas pressure at a very low movement velocity to eliminate the influence of the damping force. This measurement method allows no or only inadequate statements about the friction behavior at, e.g. more dynamic excitation scenarios. As a result, the aim should be to characterize the friction properties without the influence of hydraulic damping at the start of movement or reversal of movement, as well as at higher movement velocities. Another goal is to evaluate the influence of the internal pressure of the damper on its friction behavior. The test damper used here is a commercially available monotube damper that has been modified in accordance with the requirements for these tests. The results shown below can be used as starting variables for further investigations for the targeted optimization of the friction properties and thus for the improvement of driving comfort. The reduction in damper friction promises an increase in comfort due to the improved decoupling of the vehicle body from the road excitation. Furthermore, the data obtained enable the level of detail of simulation models to be increased and serve as a basis for comparing different friction pairings and contact surfaces in the damper. For the substitution of coatings (chrome-free piston rods → environmental protection) or tube materials (aluminum matrix composites → lightweight construction) as well as for changes in the surface structure and roughness, the results enable an evaluation of the friction properties compared to conventional dampers and the adjustment of the friction pairings in the sense of the best possible functionality.

In this paper, a homogeneous lean combustion concept for gasoline engines with direct injection, small displacement and turbocharging is investigated under high-load conditions. A representative operating point was selected for this purpose. The tests were carried out on a single-cylinder research engine. In particular, the influence of the center of combustion, charge motion and pressure ratio is discussed. It has been discovered that the center of combustion has a large influence on the stability of homogeneous lean combustion at high load points. The present investigations provide a method of how to achieve an early center of combustion in knock-limited load points of homogeneous lean combustion. Early centers of combustion enable a high air–fuel ratio with good, smooth running and low NO_x emissions. In addition to the high charge motion, operation with a positive scavenging gradient and valve overlap can be applied to flush the hot internal residual gas out of the combustion chamber, whereby knocking can be reduced. With the high air–fuel ratio, specific fuel consumption can be reduced substantially and high combustion efficiency can be achieved. The results can be leveraged as a basis for future developments in gasoline engines.

In this work, the temporal and spatial rotational temperature, as an indicator of spark temperature in the gas, of an ignition spark at ambient pressure is determined. With optical emission spectroscopy, the rotational bands of the nitrogen C³Π_u → B³Π_g transition at a wavelength of 337 nm are for determination. In addition, the electrical values of the current and the voltage are measured with a digital storage oscilloscope. All measurements are performed with a common nickel spark plug and a commercial 90 mJ ignition coil. The dwell time of the coil is varied in four steps from 100 to 25% and the influence on the rotational temperature is measured. The results are split into the three spark phases: breakdown, arc discharge, and glow discharge. The results show a cold breakdown, which is independent from the dwell time. On average, arc discharge is the hottest discharge phase, while the glow discharge has a medium rotational temperature.

The effort and time demand for the calibration of electronic control systems for internal combustion engines on test benches is rising constantly for a number of years. This is mainly driven by new engines and powertrain technologies as well as by the rising quantity of series and vehicle variations. In the engine calibration process with the objective for optimization of fuel consumption and emission values, the number of parameters is large and the evaluation on a test bench is expensive. Since a certain target quantity is usually dependent on a range of various parameters, the sensitivity of system inputs on outputs should be identified. The goal of this approach is a reduction of the dimension in the design of experiments to the most important factors. In this study, the approaches by linear models, nonlinear models and mutual information are introduced and are compared with measurement data.

Driving cycles like WLTP and the consideration of real driving emissions increase the relevance of load-dependent process losses for the prediction of engine efficiency based on engine process simulation. The contribution of valve pumping work to the total gas exchange losses of an internal combustion engine is usually neglected during engine conception. However, its share of the total gas exchange power losses increases with engine load. Within this paper, the variation of load, engine speed and valve timings on valve pumping work is investigated on a theoretical basis using 1D-CFD-simulation for a three-cylinder turbo-charged gasoline engine. Further, the influence of the valve lift curve design on valve pumping work is evaluated. The consideration of valve pumping work can increase the accuracy of the engine efficiency prognosis based on engine process simulations. A comparison with results from the literature points out that 3D-CFD-based evaluations of the valve gas forces can provide even more accurate results than the conventional calculation approach which is presented within scope of this publication. Hence, future works on this subject might include the improvement of the standard calculation approach on an either physical or empirical basis considering valve and seat ring design details as parameters.

The main goal of this study was the experimental investigation of the fluid pressure in the boundary region between wet grip and hydroplaning. In order to gain an insight into the processes in the tire contact area, a test setup was developed to directly measure the fluid pressure in the water film between tire and road. The fluid pressure was measured on an asphalt track for different speeds, water heights and tire patterns on an inner drum test bench. The influence of the examined parameters on the fluid pressure is clearly visible and physically plausible. Braking tests were done in order to clarify how much the fluid pressure build up influences the overall braking performance in the boundary region between wet grip and hydroplaning.