Migration of Powertrain Electronics to On-Engine and On-Transmission

Transcription

1 SAE TECHNICAL PAPER SERIES Migration of Powertrain Electronics to On-Engine and On-Transmission Glen W. De Vos and David E. Helton Delphi Delco Electronics Systems International Congress and Exposition Detroit, Michigan March 1-4, Commonwealth Drive, Warrendale, PA U.S.A. Tel: (724) Fax: (724)

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3 Migration of Powertrain Electronics to On-Engine and On-Transmission Copyright 1999 Society of Automotive Engineers, Inc. Glen W. De Vos and David E. Helton Delphi Delco Electronics Systems ABSTRACT The general trend for the mounting location of powertrain electronics reflects a migration from the traditional passenger and engine compartments to on the engine and transmission. This paper will explore the underlying reasons for this trend, the potential system level benefits of on-engine and on-transmission mounting, and the resulting challenges for the electronic hardware design and development. Additionally, three strategies for managing this transition will be presented and compared. Figure 1). The primary factors contributing to this increase in ECU content are related to both emissions legislation and market drivers. Examples of emissions legislated functional growth are enhanced evaporative recovery systems, heater control on catalysts, air injection, and enhanced diagnostics. Several market drivers for functional growth are direct injection, electronic throttle control, and up integration of ignition control as well as other functions which previously operated as stand alone ECUs. INTRODUCTION For the first generation of automotive Engine Control Modules (ECM) in the late 1970s, the passenger compartment was the logical mounting location. Containing relatively limited functionality and input/output (I/O), these electronic control units (ECU) were typically located either in or below the dashboard. As powertrain control system complexity and control module functional content grew, it became more difficult to find acceptable locations within the passenger compartment. Additionally, the routing of the ECU wire harness from the passenger compartment through the bulkhead to the engine compartment became increasingly problematic. With its bulky connector(s), large number of wires, higher current levels, and overall length, the ECU wire harness created vehicle level assembly issues and increased the potential for electromagnetic and radio frequency interference (EMI/RFI) related problems. Consequently, by the late 1980 s, the mounting location for engine and powertrain ECUs began to move from the relatively benign and protected passenger compartment to the much harsher underhood environment of the engine compartment. As of model year 1999, a substantial percentage of production Engine (ECM), Transmission (TCM), and Powertrain Control Modules (PCM) are located in the engine compartment. However, growth in ECU functional content and I/O has continued at a significant rate (refer to Figure 1. Functional Growth: ECU I/O vs. Calendar Year Throughout this period, the engine compartment also experienced an increase in complexity and content. Once again, finding a suitable location for the ECU and its wire harness(s) presented significant challenges for the numerous engineering organizations involved with the vehicle underhood packaging of the engine and its surrounding components. With model year 1998 s introduction of multiple vehicles utilizing engine mounted ECMs, we see a significant expansion of the migration of powertrain control modules from their remote locations within the engine compartment to the severe environment of on-engine. 1

4 THE MIGRATION OF THE CONTROL MODULE TO ON-ENGINE AND ON-TRANSMISSION LOCATIONS SUPPORTING FACTORS Mounting any product on the engine or transmission potentially exposes that product to the most severe environmental conditions found on the vehicle. The matter is further complicated when the product contains sophisticated and sensitive electronic components. Consequently, there must be compelling reasons for pursuing an on-engine or on-transmission ECU mounting strategy. While each vehicle and its associated powertrain must be evaluated on a case-by-case basis, in general, the factors supporting on-engine and on-transmission ECU mounting are described as follows. Powertrain Sub-system Modular Assembly and Test Strategies With a remotely mounted ECU, Engine Management System (EMS) integration and test occurs at the vehicle assembly level. Consequently, any EMS related integration issues (test failures, programming, etc.) are identified at the end of the line in the vehicle assembly plant. EMS assembly and test prior to installation in the vehicle or on the engine significantly reduces the number of potential failure modes encountered during the downstream processes. Additionally, significant improvements in vehicle and powertrain assembly processes are possible with these pre-tested modules. Optimization of Wire Harness Routing, Wire Count, Harness Length, and Mass Wire harness length and partitioning for ECUs mounted remotely from the powertrain can lead to assembly difficulties, added mass, and increased likelihood of EMI/RFI problems. Additionally, higher current applications such as Electronic Throttle Control (ETC) and Direct Injection (DI) increase the need to reduce harness length due to higher current and voltage requirements. Proper EMS inter-connect partitioning and on-engine ECU mounting directly facilitate minimizing harness length, mass, and EMI/RFI. Powertrain and Engine Management System Architecture Trends Throughout the 1980 s and 1990 s the general trend has been toward upward-integration of functional content into the ECM or PCM. Initially, the introduction of electronic controls into the powertrain control system represented the first significant placement of microprocessor based electronics in the vehicle architecture. Naturally, as vehicle subsystems migrated from mechanical to electronic control, the powertrain controller became the target platform of choice for integration. This integration trend further strengthened over the last decade due to the ever-increasing demand for more functionality due to higher complexity engine management systems. Today, many powertrain control systems have been forced to re-distribute the control electronics into several ECUs due to the unmanageable complexity of a single ECU solution. Advancements in controller miniaturization, enhanced automotive serial data communications, and environmental capability have enabled the vehicle architecture to range from highly integrated to fully distributed systems. Emergence of Electronics Packaging Technologies Required for Higher Temperature Operation and ECU Miniaturization Regardless of the intended mounting location, there has been significant pressure to reduce the ECU form factor. As shown in Figure 2 and 3, the use of wire bonded and flip chip integrated circuits on high density ceramic and laminate substrates achieves significant increases in packaging density. Additionally, highly efficient IC thermal management systems have been developed to minimize the ECU s internal temperature rise to allow for operation at elevated ambient temperatures. In general, products utilizing conventional packaging technologies (FR-4 circuit boards, packaged devices, etc.) are potentially too large to be mounted directly onengine or on-transmission. Figure 2. IC Packaging Comparison Figure 3. On-Engine ECM While not stated explicitly, all of the above factors support the overall goal of reducing total vehicle costs while improving quality, performance, and reliability. 2

5 POWERTRAIN CONTROL SYSTEM DEVELOPMENT REQUIREMENTS In order to realize the benefits outlined in the previous section, there are significant technical requirements and product development issues that must be addressed. Simply relocating an ECU from its remote location to the powertrain without accounting for the environmental requirements, sensitivity to form factor and system functional partitioning will more than likely be unsuccessful. Additionally, relocation of the ECU may change the working relationships of those involved in the powertrain system engineering and development. to the component). At temperatures above 125 C, many of these components (electrolytic capacitors, ceramic resistors, inductors, etc.) must either be significantly derated or replaced with higher temperature capable functional equivalents (at additional cost). In some cases, such as non-volatile memory, suitable higher temperature capable equivalents may not be commercially available. Additionally, at ambient temperatures above 105 C, the connector pin-terminal de-rating requirements may significantly reduce current carrying limits and require either the use of multiple wires or larger pin-terminals. Table 1. Typical Environmental Requirements ENVIRONMENTAL REQUIREMENTS The most significant areas of concern for any product mounted in the engine compartment are the temperature, vibration, and fluid exposure requirements. As shown in Figure 4 and Table 1, both the temperature and vibration requirements for on-engine and on-transmission mounting increase substantially compared to remote locations in either the passenger or the engine compartment. Figure 4. Examples of potential in-vehicle temperatures Operating Temperature Requirements For most remote engine compartment locations, the maximum ambient air temperature will be 105 C (including transient events). On the engine and transmission, however, mounting surface and ambient air temperatures of 140 C may be encountered with transients that reach 150 C. While these temperatures may not be an issue for electrical components which historically have been located on the engine (various sensors, ignition modules, etc.), they exceed the current operating temperature limits for many of the electronic components utilized by ECMs, TCMs, and PCMs. In general, most ECU components are capable of operating in a local ambient of either 125 C or 135 C (the temperature internal to the controller in immediate proximity Fortunately, the powertrain is not a thermally isotropic body and there are locations that offer acceptable temperature conditions. For example, the intake manifold (depending on specific design and beauty cover features) normally contains suitable ECU mounting locations with peak temperatures limited to 125 C. As a rule, the maximum allowable ambient temperature for a specific control module can be determined by subtracting the total temperature rise (the sum of device level, internal, and external temperature rise) from the limiting component s maximum operating temperature. In some cases, it may be constrained by a 150 C junction temperature limit for an IC. In other cases, it may be a 115 C maximum operating temperature for an electrolytic capacitor. Regardless of mounting location, ECU steady state and transient temperature behavior should be fully characterized at the vehicle level to insure that the maximum operating temperatures do not exceed the individual component ratings. 3

6 In addition to the ECU and its mounting structure, the connection system and wire harness must be properly supported to avoid wire chaffing, breakage, or other failure modes induced by excessive relative motion between the control module and the harness. Figure 5. Simplified thermal model of ECU Vibration Requirements While the transition from the passenger to the engine compartment did not significantly change the level of ECU vibration exposure, the move to on-engine substantially increases this requirement. For on-engine and on-transmission locations, the lower frequency energy level (less than 500 Hz) is dominated by the periodic motion of the engine and powertrain components. Consequently, the input energy follows engine RPM and its harmonics, generally exhibiting sinusoidal behavior. Additionally, during periods of extended driving at constant RPM (e.g. highway travel), the input energy will effectively dwell at a fixed frequency. Higher frequency energy vibration (up to 2 khz) is dominated by the response behavior of the powertrain and its structural elements (transmission housings, valve covers, etc.) and generally exhibits random behavior. Typical vibration test requirements for on-engine and ontransmission ECU mounting locations have a lower frequency sinusoidal sweep component with acceleration levels of 30 Gs and a higher frequency random component with acceleration levels of 10 Grms. Specific test level and duration should be evaluated and verified on a case by case basis with actual on-engine measurements. Given the severity of these requirements, the mechanical design of the ECU and its mounting hardware or features (brackets, bosses, etc.) must provide sufficient integrity to avoid vibration failures. As a general rule, the vibration resonant response frequencies of the various mechanical systems should be above the low frequency component (above 500 Hz) and not coincident with one another. For example, Figure 6 shows an ECU and its mounting bracket with the desired separation of the resonant frequencies for the mounting bracket, ECU enclosure, and internal structure. Ideally, these resonant frequencies should be well above 500 Hz and separated by one octave. 1 Figure 6. Mechanical System Example Fluid Exposure Requirements Mounting locations on the external surface of the powertrain require similar fluid compatibility and exposure levels in comparison to remote engine compartment locations. Internally mounted ECUs, however, may be exposed to fluids, residue, and other materials not typically encountered in remote locations. For example, an ECU mounted internal to the transmission may see prolonged exposure to high temperature transmission fluid (potentially containing electrically conductive particulate). ECU FORM FACTOR As functional content and complexity of the powertrain has increased (both on and off the engine), physical space suitable for ECU mounting and wire harness routing has become very limited. Consequently, minimizing the physical size of the ECU and harnesses simplifies the task of finding a suitable location. The physical size of the ECU is determined primarily by its functional content, connection system configuration (wire count, connector type and number) and packaging 4

7 technology. As previously described, advances in packaging technology such as flip chips, high density substrates, and their supporting thermal management systems have enabled significant progress in increasing product packaging density. On-engine capable connection systems have also experienced density improvements with 0.64 mm square and round pins on mm centerlines representing the current state of the art. Finally, effective system functional partitioning facilitates optimization of individual ECU size and I/O with respect to their intended locations. CENTRALIZED ECU STRATEGY The centralized ECU strategy involves moving the existing ECM or PCM from its remote location to one on the powertrain with no functional re-partitioning. With this approach, the primary issue is to ensure that the mechanical design of the control module is capable of meeting the environmental and form factor requirements. POWERTRAIN CONTROL SYSTEM DEVELOPMENT The move to on-engine and on-transmission ECUs may constrain or influence the feature/functional partitioning within the control system as well as the development relationships between customers and suppliers. ECU Feature/Function Partitioning As previously stated, in order to maintain an optimal ECU physical size, the feature/function content of an on-engine ECU is limited to the control required by the target sub-system. In the case of a powertrain control system, this typically dictates an ECM for base engine controls, a TCM for base transmission controls, as well as other dedicated subsystem ECUs (e.g. an ETC module (ETM) for electronic throttle control). Powertrain Control System Development Partnerships Separation of the ECU from its related sub-system allows for independent specification, sourcing, development, and validation of the powertrain control system components. Conversely, integrating the ECUs with their respective sub-systems tightly couples these activities. Consequently, the relationships between the various powertrain development partners must be closely coordinated. Additionally, there exists the potential need for change with respect to the roles and responsibilities of the various engineering and commercial organizations. STRATEGIES FOR ON-ENGINE AND ON- TRANSMISSION MOUNTING OF POWERTRAIN CONTROL MODULES As outlined in the previous sections, managing the migration of the powertrain control electronics to on-engine and on-transmission is not a simple task. Outlined below are three approaches representing increasing levels of functional, physical, and developmental integration. Figure 7. Centralized ECU Strategy Advantages of the centralized ECU strategy are: Relatively simple ECU mechanical specifications and interface requirements. Facilitates pre-test and pre-assembly strategy at the powertrain assembly level. Disadvantages of this strategy are: Achieving required form factor and acceptable harness routing for PCMs and ECMs with high levels of functional content and I/O. Limited material/component cost-savings resulting from minimal physical integration. Limited pre-test capability at the subsystem level due to centralized control (e.g. PCMs). In summary, the centralized ECU strategy facilitates engine assembly and test, but does not exploit the potential advantages offered through control system functional partitioning or ECU physical integration. DISTRIBUTED ECU STRATEGY This strategy involves redefining the system partitioning for the various powertrain control modules to facilitate increased levels of functional and physical integration. The mounting locations of the individual ECUs would be determined by their functional relationships. As the example in Figure 8 indicates, a PCM with its associated functions could be repartitioned into an ECM, TCM and ETC control module. Each ECU would be externally mounted to its associated subsystem. 5

8 Improved EMI/RFI performance through reduced interconnect lengths and improved routing. Disadvantages of this strategy are: Complex ECU physical interface requirements. Complex product development process. Limited application of ECUs to other powertrain systems due to highly specific designs. Potential for severe environmental requirements. Figure 8. Example of Distributed ECU Strategy Advantages of the distributed ECU strategy are: Relatively simple ECU mechanical specification and interface requirements. Fully facilitates pre-assembly and pre-test strategy for the engine and sub-system modules. Improved harness routing and assembly as a result of optimized system partitioning. Reduced ECU form factor as a result of optimized system partitioning. Disadvantages of this strategy are: Limited material/component cost-savings resulting from minimal physical integration. In summary, the distributed ECU strategy facilitates powertrain subsystem assembly and test prior to engine or vehicle assembly as well as optimization of the control system wire harness. Additionally, the functional partitioning strategy directly supports the implementation of distributed control architectures. INTEGRATED - DISTRIBUTED ECU STRATEGY The integrated - distributed ECU strategy extends functional distribution to include physical integration of the ECU with its associated subsystem. As an example, the ETC module would be integrated into the throttle body (directly connected to the throttle position sensor and motor). Additionally, the ECM could be integrated with the intake manifold (potentially using the intake airflow for cooling and the manifold features to provide part of the ECU enclosure). Finally, the TCM would be integrated internal to the transmission (eliminating internal interconnect levels and providing a direct connection to the transmission solenoids). Advantages of the integrated-distributed ECU strategy are: Optimal implementation of powertrain subsystem assembly and test. Potential material cost-savings through physical integration and elimination of interconnect levels, physical enclosures, etc. Figure 9. Integrated Distributed ECU Strategy In summary, the integrated - distributed ECU strategy maximizes performance and potential system cost savings (both material and process related). However, the powertrain development process becomes increasingly complex and ECU operational environments are potentially very severe (refer to Figure 10). Figure 10. Strategy Comparison SUMMARY AND CONCLUSIONS Powertrain assembly and test strategies, wire harness optimization, and engine management architecture trends increase the need for flexibility with respect to control system ECU mounting. While there will continue to be applications with ECUs located remotely in either the passenger or engine compartment, there is a clear demand for ECUs with on-engine and on-transmission capability. 6

9 The technical and commercial challenges for on-engine and on-transmission mounting are significant. When implemented properly, substantial system cost savings and performance improvements will be realized. Successful implementation, however, requires utilizing the appropriate strategy to address all issues with respect to environmental requirements, functional partitioning, and control system development relationships. No one strategy will universally apply and each situation must be evaluated carefully to understand which approach is most appropriate given the vehicle application, control system requirements, and the development partner capabilities. ACKNOWLEDGMENTS The author wishes to thank the following individuals for their assistance and contributions: John Hearn, Scott Baxter, Darrel Peugh, and Sarah Bristol. CONTACT Glen W. De Vos Delphi Delco Electronics Systems One Corporate Center Kokomo, IN DEFINITIONS, ACRONYMS, ABBREVIATIONS ECU: Electronic Control Unit ECM: Engine Control Unit ETC: Electronic Throttle Control ETM: Electronic Throttle Module I/O: Input / Output PCM: Powertrain Control Module TCM: Transmission Control Module REFERENCES AND ADDITIONAL SOURCES 1. Steinberg, D., Vibration Analysis for Electronic Equipment, John Wiley & Sons, New York,