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1.6 Subsystem interaction and analytical engine system design process
1.6.3 Advanced analytical engine system design process
Simultaneous engineering process
The advanced analytical engine system design process is characterized by systems engineering, simultaneous (or concurrent) engineering and advanced product quality planning (APQP). Simultaneous engineering is a design and/
or manufacturing process where cross-functional teams strive for a common goal. It reduces development cycle time by replacing the sequential series of phases by a simultaneous engineering process. In the sequential process, the results are relayed from one area to the next area for execution. In the simultaneous process, all the subsystem/component areas carry out their design work concurrently with a unified system design specification.
Conflicting or slow sequential
design assumptions
used by different subsystems
without system analysis
Reconcile assumptions
and revise design
specs
Many engine problems discovered Conflicting
designs
Integration, testing, and calibration – Combustion – Performance – Emissions – Aftertreatment – Vehicle integration – Mechanical
durability – NVH Mechanical design (hardware)
– Cylinder head (valves, ports) – Power cylinder and piston assembly – Connecting rod
– Crankshaft
– Valvetrain and camshaft – Intake manifold – Exhaust manifold – Turbocharger
– EGR system (cooler, valve) – Intake throttle valve – Cooling system – Water pump – Charge air cooler – Oil cooler and oil pump – Aftertreatment
– Fuel system
– Engine brake and exhaust brake – Starter and alternator
Engine electronic control design (software)
– Air-path control strategy – Fuel-path control strategy – Controller design – Sensors
– Actuators – ECU
1.26 Empirical engine design process.
APQP is a structured process of defining and establishing the steps necessary to assure a product satisfies customer expectations (APQP reference manual, 1995). In the initial phase of the program great effort is spent in engine system design by using advanced simulation tools to analyze the functional requirements. Then, the system design specifications are issued to the subsystem design teams. Because the primary risk factors have been analyzed and resolved, and the critical interface and functional analysis have been completed by the system design team, the subsystem engineers can start their designs with a much lower risk of failure. APQP uses process planning to ensure the design changes or the corresponding development efforts continuously decrease from the beginning of the engine program to the end for a smooth transition to the start of production.
The engineering product development process has evolved from the traditional slow process to today’s accelerated process where the research and advanced engineering functions are combined. Organizational processes and project management for production engineering were introduced by Menne and Rechs (2002) in detail, including a summary of key checkpoints for a program. A simultaneous engineering process of detailed subsystem packaging and structural designs was provided by Dubensky (1993). Design and process tools were elaborated by Carey (1992) and Gale et al. (1995).
Diesel engine design details were introduced by Merrion (1994).
Engineering functions in engine development
For each engine component, the engineering job functions can be classified into three types, namely analysis, design, and testing. The analysis function can be further divided into two main subareas: thermal/fluid performance and mechanical structure. It is usually impossible for one person or one department to carry out all the three job functions for all the components.
In large engineering organizations usually the work functions of analysis, design, and testing are carried out in different departments. Cross-functional cooperation is the key to success.
The job function of analysis can be defined as an activity to generate design specifications and analyze problems for the four engine design attributes (performance, packaging, durability, and cost) with advanced calculation tools. The traditional job function of design can be defined as an activity to realize the design specifications with computer aided design (CAD) tools, drawings, and prototypes. The job function of testing can be defined as an activity to validate the design specifications with experimental means.
In a product development process, design stays as a central role receiving support from analysis and testing. Simulation is a part of analysis. It supplies detailed information about many parameters which are difficult or impossible to measure, for example, heat transfer in all components, composition of gas
flows, and instantaneous pressure or flow through valves or in manifolds. When setting up an engine test, it is often beneficial to conduct simulation before testing to verify whether the test objectives can be met. Testing can confirm engine system design specifications or identify deficiencies. Many factors can render inaccurate system modeling results: model quality, assumptions, incorrect input data of the component or subsystem, etc. Simulation model tuning and comparison with experimental data are always necessary. Only after a successful model validation can the model be used with confidence to produce system design results. The analysis and testing functions should be partners reinforcing each other. The system design engineer needs to actively participate in the planning of testing to help define the objectives and procedures of the testing in order to discover any problems as early as possible. Test planning and analysis is a primary responsibility for system engineers.
Diesel engine system design is a new integrated function. The systems engineering theory (Armstrong, 2002) believes that the system engineers must release the system from the design departments. Because the majority efforts of diesel engine ‘system design’ are placed on producing system performance (or functional) design specifications, it is natural to consider the simulation analysis work conducted by a ‘system analysis’ engineer as the diesel engine ‘system design’ work instead of ‘system analysis’ work.
In other words, most system engineers are design engineers, and they are granted design authority for the entire system. They use advanced simulation software as their design tools. They are not just the simulation or analysis engineers in a supporting role. As the importance of diesel engine system design emerges in product development, the job function of engine performance analysis assumes a dominant role in the engine design process. The system testing engineers run test cells to validate the whole engine system. Their work complements the work of system design engineers.
Advanced analytical engine system design process
A work flow process of advanced analytical engine design and development from concept to production is illustrated in Fig. 1.27. The input and output of the functional areas are interactive and affect each other, as shown by the double-headed arrows in the figure. The program management located in the middle controls the specified program schedule and budget. The efficiency of the engine development process depends on how clearly technical specifications or design/development changes are organized and cascaded by the system team to the component teams within a given organization.
Although the technical communication channels between different functional areas are complex, overall there is an optimum ‘top–down’ process as shown by the thicker block arrows. In the old era when technical specifications were generated with crude hand calculations, precise design and optimization were
Customer needs, vehicle design requirements, engine functional objectives, design constraints Technology evaluation and development: combustion, aftertreatment, EPSI
Engine system concept analysis (EPSI, structural, design layout, cost)
DrivabilityCost Noise Program lead NVH testing Production design releaseManufacturing tooling development Preproduction builds and production release
Mechanical durability testing Vehicle integration testing
NOx Packaging
Fuel economy
Design criteria DurabilityPM Mechanical design Design analysis (EPSI, CFD, structural, NVH) Engine control design
Combustion, performance, aftertreatment, emissions dyno testing and calibration 1.27 Simultaneo engineering processes.
impossible. Today, with the effective use of computer simulations of engine thermodynamic cycle performance, it is feasible to accurately predict air system performance and subsystem interactions. Such a function of analytical system integration needs to be placed at the very top of the development chain. A common objective in engine development is to continue improving the upstream analysis capability and minimizing the costs in the prototype testing stages, as pointed out by Hoag (2006) in his detailed description of the engine development path. Figure 1.28 shows a more detailed process of analytical engine system design. Figure 1.29 illustrates the technical scope and examples of diesel engine system design.
Figure 1.30 illustrates the process of automotive powertrain definition, which links the engine system design to its upper level, the powertrain system design. Planning is the first step in a typical engine program. The vehicle- level requirements are cascaded down to generate the design targets at the engine level. After the engine system design specifications are determined, the design targets are then broken down further to the individual component level. A wide range of criteria must be considered, including performance (acceleration, fuel economy), emissions, cost, weight, packaging, and reliability. Often there are trade-offs between different criteria, for example, between 0–60 mph acceleration and fuel economy at different engine displacement. A larger swept volume (displacement) usually gives better naturally aspirated breathing capability so that the vehicle acceleration is faster. But during the driving cycle the larger engine runs more frequently at a lower BMEP level, hence the fuel consumption becomes worse. In this
‘top-down’ process, changing program targets or system design specifications will disrupt the development process and require extra modifications outside the agreed scope of modification freedom. Therefore, it is essential to define the program targets carefully by foreseeing future requirements and produce engine system design specifications accurately so that the extra modifications can be avoided as much as possible. Figure 1.31 shows an example of a powertrain design decision tree.