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This article describes both a computer-aided engineering tool - a computer model - utilized in accelerating design tasks and also the process of building a powertrain design knowledge. The computer model, which integrates engineering and analysis phases into the design process, has been developed to enable rapid evaluation of new powertrain concepts. The model determines the basic geometry of engine and transmission subsystems and components, and allows automation of the engineering and analysis processes. Examples of application of the tool in evaluation of powertrain concepts and the design of components and subsystems are also given.

Powertrain Engineering Tool (PET) [1, 2, 3], developed at Ford Powertrain and Vehicle Research Laboratory, is a powertrain computer model that allows rapid development of preliminary powertrain component geometry, and evaluation of engine performance and friction. Based on specified design objectives such as engine torque, power and geometric constraints, PET calculates the powertrain component geometry by employing its integrated design rules and a non-linear SQP-based (Sequential Quadratic Programming) geometry optimizer. PET also generates parametric solid models of powertrain systems based on its integrated dynamic component assembly schemes and solid modeling database. The cranktrain system consists of high-speed moving and rotating components. Complex dynamic analysis is typically required to achieve optimum cranktrain component design. This paper discusses development of a systematic approach in the calculation of optimal cranktrain component geometry.

This paper presents some of the design rules used to calculate critical geometry of engine components, and the object-oriented component hierarchy system in PET. This paper also presents parametric solid model assembling schemes used to dynamically construct an assembly of whole powertrain systems. Some examples of powertrain concept design, such as the estimation of friction, packaging, and moving component clearances, will be presented. The computational efficiency of this concept design method will be compared to traditional methods also.

A computer model for the design of automobile engines is being developed to enable an evaluation of engine concepts for new vehicles. The model automates the design process and helps in the reduction of the product development cycle. The model determines the basic geometry of engine sub-systems (crank-train, valve-train, etc.) and allows simultaneous evaluation of different engine configurations and different arrangements of engine components. The engine design model consists of two modules. The first module is a computer program that contains design rules and is used to determine the critical geometry of engine components. The second module is CAD (Computer Aided Design) software that uses geometry data from the first module for generation of parametric 3-d solid models of engine components. By simple changes in geometry of components a new 3-d engine configuration is generated and available for evaluation and analysis of component dimensions, masses and other desired properties.

Intake-generated flow fields and subsequent combustion characteristics were studied respectively in a reciprocating piston water analog flow apparatus and in firing engines. Three 1.6L, I4, 4-valve engine cylinder heads were tested with and without one intake port blocked to generate six distinctly different inducted flow fields. Fluid velocity distributions and flow field structure (“zero mean motion”, “swirl”, and “tumble”) were determined at BDC of the induction stroke using 2-D or 3-D particle tracking velocimetry. Swirl ratios based on steady-flow data were also obtained. The burn duration for each case was determined from cylinder pressure data. The results show that burn duration decreased with increases in tumble or swirl strength. Previously observed correlations between burn duration and swirl hold if swirl is the major component of the large-scale motion.

This experimental investigation is an initial step in separating the influences of swirl and inducted kinetic energy on combustion in a homo - geneous charge engine. By rotation of the intake port about the axis of the intake valve, the swirl ratio was varied from zero to 2,8 while maintaining constant intake port flow, and hence constant inducted kinetic energy. Combustion data were obtained at a low speed, light load operating point (1500 RPM/60 psi IMEP) with MBT spark timing. The effects of the increase in swirl were a 25% decrease in ignition delay, a 10% decrease in combustion duration, and a significant improvement in combustion stability. Estimates were made on the effect of swirl on turbulence intensity (10% increase) and integral length scale (10% decrease). Both the increase in swirl and the use of a near-central spark plug location improved the lean operability.

LDA measurements of the flow in a motored engine near TDC of compression have been obtained, along with burnrate data in a firing engine having a near-central spark plug location. Results are reported for two different intake ports and four intake valve lifts varying from 25% to 100% of full lift. Opposite trends of swirl vs valve lift were found for the two ports, and the rms velocity fluctuation was found to be relatively insensitive to changes in valve lift. Regression analysis of the burn duration data was conducted, with swirl ratio and rms as independent variables. The analysis indicated that burn duration decreases with an increase in swirl ratio and/or rms velocity fluctuation. In light of the experimental findings, a new conceptual model is proposed regarding the effect of valve lift on the dissipation of turbulent velocity via changes in the length scale.

An Engine Simulation Model was used to study the effect of in-cylinder swirl level on turbulence intensity and burn rate while holding the inducted kinetic energy constant. Experimental measurements of burn rate for three different swirl levels were obtained and compared with model predictions. The turbulence model used previously did not include wall shear effects and showed little enhancement of turbulence due to swirl, causing small changes in predicted burn rate when the swirl level was changed. An improved turbulence model is proposed which includes production of turbulence due to wall shear effects. Turbulence intensity predictions from the improved model resulted in excellent agreement between the measured and predicted burn rates as swirl level was changed. In addition, the model was used to predict the effect of swirl levels on ISFC. Results showed that ISFC changes were overall small for the range of swirl levels considered.