ECU Software and System Design for NOx

ABSTRACTWith evolution of emission norms in diesel engines, NOx emission limits became more stringent and can be met only with specific NOx emission control systems. The NOx control systems in heavy duty diesel engines are monitored for OBD regulations in on-highway applications.Additionally driver warning and inducement requirements for NOx emission control systems are to be complied in both on-highway and off-highway applications. The driver inducement requirements are defined with intent to enforce and ensure correct operation of NOx control system. The NOx control systems and inducement measures are implemented in engine Electronic Control Unit (ECU)software to be compliant to legislation.The paper focuses on driver inducement requirements for NOx emission control systems. The paper summarizes the inducement requirements with a system overview and software design to meet driver inducement requirements for EUVI legislation and CARB/EPA compliance. Besides, the impact of the EPA legislation “Heavy-Duty Highway Program: Revisions for Emergency Vehicles and SCR Maintenance” on the software and system design is explained. The impact of this legislation on software design and possible approaches for short term relief measures using diagnostic tester, smart card and/or information from GPS systems are presented.INTRODUCTIONThe commercial vehiclesare powered by large diesel engines, which normally run leaner resulting in higher NOx emissions. The NOx limits of current emission legislations are quite stringent and there are solutions available to meetthis requirement. The trend to address this requirement seems to be the combination of Exhaust Gas Recirculation (EGR)and Selective Catalytic Reduction (SCR) systems as depicted in Fig 1. [1]The SCR system uses aqueous ammonia (Adblue) as a reduction agent and sprays the same into exhaust to reduce NOx with a SCR catalyst (after treatment). The EGR recirculates the exhaust gas into the cylinder to reduce NOx during the combustion process. The EGR and SCR control and monitoring algorithms are defined in engine Electronic Control Unit (ECU) software.According to OBD (On Board Diagnostics) legislations, the emission control systems are to be monitored for OBD compliance. The OBD system monitors virtually every component that can affect the emission performance of the vehicle. The OBD monitoring is done to ensure that the vehicle remains as clean as possible over its entire life, and assists repair technicians in diagnosing and fixing problems with the computerized engine controls. If a problem is detected, the OBD system illuminates a Malfunction Indicator lamp (MIL) on the vehicle instrument panel to alert the driver. [2]The SCR functionality is defined in ECU software,effectiveness of SCR systems depends on reduction agent availability and quality of reduction agent. If reduction agent not available and is of inferior quality, then the SCR systems are not effective although there are no defective components.Apart from that the consumption and regular refill incurs additional cost on driver, so there is a possibility to tamper the system to reduce this additional cost. The factors such as no reduction agent, poor quality and system tampering reduce the effectiveness of NOx control system. In view of this, theECU Software and System Design for NOx Control Driver Inducements2013-01-2385Published 09/24/2013N. Santosh DattaRobert Bosch Engineering and Business Solutions Ltd.Copyright © 2013 SAE Internationaldoi:10.4271/2013-01-2385legislations in US and EU have introduced the specific driver inducement approach to ensure correct operation of NOx control measures along with OBD (which monitors for defective components). In case of errors such as no reagent quantity, inferior quality and system tampering, the legislations propose specific driver warning system design to forewarn the driver. After the warning system is active, a time to correct the malfunction or refill the urea is specified. If the error is not rectified or reduction agent is not replenished even after warning, driver inducements to limit the vehicle/engine performance are initiated. As per the legislations, the performance limitations are to be induced in increasing order of engine de-rating and in specific time intervals. [2][3] The EPA guidance also specifies the monitoring of repeat offense to discourage the repeat use of poor quality reagent and tampering. [4]Besides, EPA is proposing short-term relief from emission control system performance inducements for any non-road vehicles operating in temporary emergency service and also proposing amendments to its heavy-duty diesel engine programs that would specifically allow engine manufacturers to request to deploy specific emission controls or settings for emergency vehicles (such as Ambulance and Fire trucks).[6] The NOx emission control systems are typically embedded into electronics i.e. engine ECU software. The ECU software has to be enhanced to meet NOx monitoring requirements for driver inducements and also to allow short term relief from inducements in case of emergency. The subsequent chapters describe the System requirements for inducements and an approach for software design to meet these requirements. NOXCONTROL MONITORING -WARNING/INDUCEMENTSystem OverviewAccording to EU legislation [2], the NOx emission control systems are to be maintained under all environment conditions which occur in EU. The NOx emission control monitoring is to be operational, when engine coolant temperature is greater than 70degC, altitudes less than 1600m and at environment temperatures between −7 to 35degC. The legislation also specifies that the SCR system with frozen tank reduction agent shall be operational after 70mins (under test conditions).The system overview for inducement and warning system is as depicted in figure 2. The ECU software monitors for the incorrect operation and tampering. If any error is found and confirmed, the software will trigger warning by turning on warning lamp. The warning is to be indicated using a separate lamp (other than MIL/service lamp) or through Text display/ Audible alarms. It shall act as a preludebefore escalating driver inducements. The warning inducement system for US is similar to EU requirements.Figure 2. System OverviewAfter the warning system activation, if the error is not addressed or healed for defined time, the inducements for engine/vehicle de-rate are triggered. The inducement logic escalates the driver inducements with respect to time. Though the purpose of inducement escalations is same in both US and EU legislations, the activation scheme is different in certain aspects. As per EU activation scheme, the inducement logic activates the driver inducements in two steps Level 1 (e.g. 25% torque limitation) and Level 2 (e.g. creep mode). In case of EPA guidance, thedriver inducements are increased Figure 1. NOx Control Systems EGR and SCR [1]incrementally and usually can go up to three stages, Level1 (e.g. 25% torque reduction at 1%/min), Level 2 (e.g. 40% torque reduction at 1%/min) and Final inducement (creep mode).The CARB/EPA also enforces repeat offense monitoring. The goal of repeat offense is to discourage repeated tampering or repeated attempts at filling poor quality reagent. The inducement logic functionality is to be customized to support repeat offense counter function.Software DesignThe NOx control system is monitored for low reagent level, incorrect reagent quality, interruption of dosing, too low reagent consumption, SCR tampering (removal of any necessary sensors required for correct operation) and impeded EGR valve (mainly referred in EU legislation). The faults belonging to any of the error classes mentioned above activate driver warning and inducement systems.The software is designed to meet the driver inducement requirements mentioned in system overview. The modular overview for software design is as shown in Figure 3. The ‘monitoring’ module probes for the malfunction and tampering. The defect status from monitoring is transmitted to module ‘Diagnostic System Management’ (DSM). The DSM debounces the inputs from monitoring module and the pending/active error status is transmitted to ‘inducement counters’ module. The “inducement counters” block includes inducement logic, increments the counter with respect to time, evaluates the status of level1/2/3 and transmits the status back to DSM. Based on these inputs, DSM coordinates the driver warning inducement and torque limitations. The diagnostic data and inducement counter data is stored in EEPROM and can be retrieved using a diagnostic tester. The software design includes set of calibratable parameters for different thresholds, timers etc., to provide flexibility to adapt changing/different legislations.MonitoringThe first module in the signal flow monitors the errors for reagent tank level, reagent quality, reagent consumption and dosing interruption, tampering and impeded EGR valve.The filtered tank level is required from tank level sensor and this information is displayed on the dashboard. The filtered tank level is monitored for warning, level1, level2 thresholds and empty tank. If the tank level falls below these thresholds, the status is transmitted to DSM. The thresholds are designed as calibratable parameters and are to be defined to allow sufficient time for refilling the reduction agent before initiating creep mode.The reagent quality is monitored either through quality information from urea quality sensor or based on information from NOx sensor.The deviations in average reagent consumption to the commanded consumption are monitored either over defined engine operation time (e.g. 48 hrs) or over demanded consumption volume (e.g. 15ltrs). The defined engine operation time or demanded consumption volume is configured as calibratable parameters in software. The deviation is monitored and if the deviation exceeds the thresholds, the status is sent to DSM.The errors for dosing interruption and tampering are monitored based on the SCR system status and any signal faults. The EGR signal status is monitored for any errors related to impeded EGR valve.Diagnostic System Management (DSM)DSM includes functions to debounce the error, inhibition of functions based on the error, communication with diagnostic tester, activation of warning lamps, fault storage. The module DSM receives the errors from monitoring, after debouncing the errors, error status (potential, active/confirmed) is sent to the module inducement counters. The inducement counter module after incrementing the defect counters, gives the feedback on the status of counters to DSM. The DSM module based on defects and status of inducement counters activates the warning lamp. Further based on status of inducement levels and trigger conditions, the DSM inhibits the functions to enforce inducement measures.Figure 3. Software DesignInducement countersThe ‘inducement counters’ module forms the core of inducement logic. The inducement logic is realized using an incrementing counter with respect to time. A separate counter is defined for individual errors like reagent quality monitoring, low reagent consumption, interruption of dosing,blocked EGR valve and tampering. In case of errors reported from DSM, the counters keep incrementing. The counters store the cumulative operation hours of NOx control faults,based on the fault status received from DSM. If the counter exceeds defined level, it activates defect paths of inducement system stages 1/2/Final. The module includes the logic to set/reset the inducement levels. The defect paths are then transmitted to DSM. The flow chart for inducement counter logic (specific for EU legislation) is as depicted below.The inducement counter stores the value of counters and ‘NoFaultTimer’ (Time to indicate that the error is healed),values in EEPROM at the end of driving cycle. In the next driving cycle, the values from EEPROM are used to initialize the counter and ‘NoFaultTimer’ values.In principle, the implementation of inducement counter will remain same for US legislation, with adaptations for final inducement and repeat offense.Upon detecting subsequent repeated offenses which occurs within a defined period of time (e.g. 40 engine hours) of the previous offense, the engine derating occurs immediately and will reach the final inducement within shorter time interval(e.g. 30mins for EPA and 60 min for CARB).Figure 4. Flow chart for inducement counterInducement measureThe inducement measures are activated based on fault status from DSM and counter information. The warning system will be turned ON, when the fault is present and counter is greater than zero. If the level1/2 status is set, then the inducement measures such torque limitations will be set. As per EU legislation, torque limitations for Level 1/2 will not be active until the trigger conditions are met. The trigger conditions are engine restart, Ignition OFF & ON, vehicle parking for 1hr and stationary vehicle. In case of EPA legislations, the inducement measures are set immediately and torque reduction is induced using a ramp. But the final inducement (creep mode) is activated after the trigger conditions are met.When final inducement is set, normal engine operation inhibited. The reset to normal mode is allowed by factory ordealership tools or through self healing.Figure 5. Pseudo code for inducement activation.Inducement Activation SchemeThe complete inducement system response in case of errors for EU and CARB are described with the examples in this section. The examples describe the state requests, transitions and the inducement activations.Note: The examples contain the values for torque limitation and time intervals. These values of torque limitation, counter times are only indicative, the actual relevant values for given legislation are to be referred from latest and corresponding legislation.Inducement activation - EUThe inducement activation scheme as per EU legislation [2]is depicted in Figure 6. The inducement counter starts once the fault is confirmed. The counter keeps incrementing to denote the activation time, when the activation crosses a certain time (e.g. 10hrs), the engine de-rating (e.g. - 25%torque limitation) will be activated after stationary vehicle.The status “waiting” depicted in Fig 6 indicates waiting for trigger condition before inducement. If the error is healed, the inducement counter will be frozen and shall be reset only if the error does not reoccur until stipulated time (e.g. 36hrs). If the error is still not healed or if it reoccurs before counter is set to zero, the inducement counter keeps incrementing and will result in severe driver inducement after crossing the level 2 threshold. The torque limitations for level 1 and creed mode are active only after trigger conditions such as ‘engine re-startor parking or re-fuelling’ are met. During the creep modevehicle speed is limited (e.g. 20 kmph).Figure 6. Inducement activation example (EU)Inducement activation - USThe inducement activation scheme (if no repeat offense) for US legislation is in similar lines to EU activation scheme, but usually with additional inducement level. The inducement counter starts incrementing once the fault status is present. If the error persists, inducement counter increments and torque inducements for level 2 and final inducement will come into force. If the error is healed in between the inducement counter will be reset to zero. However if the error re-occurs (same error for EPA and any error for CARB) with in 40hrs (as an example), the de-rating level is directly increased to level 2 and the final inducement will occur within smaller window of time (e.g. one hour). The example for activation scheme in case of repeat offense counter is as shown inFigure 7.Figure 7. Inducement activation - Repeat Offense (US)SHORT TERM RELIEF FOR EMERGENCY VEHICLESThe legislation for driver inducements is to ensure and enforce correct functioning of NOx control system. However there are concerns about unusual circumstances where performance inducements could hinder equipment andvehicle performance in emergency conditions [7]. In order to overcome this aspect, EPA is proposing revisions to its heavy-duty diesel regulations that would enable emergency vehicles, such as dedicated ambulances and fire trucks, to perform their mission-critical life-saving work without risking that abnormal conditions of the emission control system could lead to decreased engine power, speed or torque. Besides, EPA is proposing short-term relief from emission control system performance inducements for any non-road compression ignition engine powered vehicles operating in temporary emergency service. The proposal has provisions for a short-term emergency bypass of the normal emission controls, including inducement strategies, which could result in a loss of power of an engine; thus, allowing the equipment to temporarily perform emergency-related work. [6]The new rules do allow for engine manufacturers to apply for the use of auxiliary emissions control devices (AECDs) that could be applied to an engine in emergency vehicles. The auxiliary emission control devices to be used only during emergency and in other times emission control systems shall function as desired. [7]In case of non-road machinery, the “○Notice of Proposed Rulemaking (published June 8, 2012)” cites as below, [6]• AECD must be designed so that it cannot be activated without the specific permission of the certificate holder.AECD must require the input of a temporary code or equivalent security feature.• The AECD must become inactive within 24 engine hours of becoming active (or other period approved in unusual circumstances).• The manufacturer must show that the AECD deactivate emission controls (such as inducement strategies) only to the extent necessary to address the expected emergency situation.AECD InterfacesThe AECDs are interfaced in vehicle to activate emergency status and in turn to avail short term relief from driver inducements. The various sources are considered to ensure flexibility in emergency activation status. The summary of possible or proposed interfaces is as shown in figure 8.In case, of emergency vehicles such as Ambulance, Fire-engines, Police vehicles etc., the AECD is proposed to be interfaced using a switch connected to either ECU or instrument cluster. The intention to use a direct switch without security is to provide easy access to bypass the inducements.In non-road machinery, various other options are explored.These options provide the flexibility to activate short term relief measures during emergencies. During the large scale emergencies (such as earth quakes or floods), the emergency status switch can be transmitted for required duration through GPS or by sending the emergency release code through SMS.In case of local emergency (like clearing a rubble), the emergency status can be sent either using a smart card (through smart card reader in instrument cluster) or diagnostic tester.It is assumed that the instrument cluster in non-road machinery is equipped with smart card reader, a keypad or touch screen to enter the emergency activation code and the possibility to read the emergency information from GPS system. Although it is possible to receive the emergency status through multiple sources in instrument cluster, the interface for engine ECU is same and status is transmittedover CAN.Figure 8. AECD Interface possibilitiesSoftware AdaptationsThe software of driver inducement is adapted to bypass the driver inducements for short time during emergency. The information to activate emergency status is available either through CAN and/or as switch input connected to ECU. The software design for emergency activation is as indicated inFigure 9.Figure 9. Software Adaptations for inducement bypass The emergency activation module evaluates the status of emergency. The inducement counter block is customized to include the features such as emergency reset to support the bypass of driver inducements.Emergency status evaluationThe emergency status is available either over CAN or through the switch. The module evaluates all possibilities and includes a configurable switch to prioritize the activation request (in case of multiple requests).The emergency switch is hardwired either to ECU or to instrument cluster. If the switch is interfaced with instrument cluster, then switch status is transmitted to ECU over CAN.The switch shall be designed as mono stable/pulsed switch to ensure no permanent activation and to perform diagnostics.The switch evaluation consists of verifying the input pulse within the given pulse times (Calibratable parameters).The emergency status is received through multiple sources in instrumentation cluster. The instrumentation cluster will process the requests and sends the emergency activation status over CAN to engine ECU. The typical CAN frame contains the information as shown in table 1. The data byte 8shall have checksum based on common security algorithm implemented in engine ECU and emergency cluster. The default duration of emergency duration will be considered as 24hrs, unless explicitly specified.Table 1. CAN Frame structureThe emergency status can also be activated by Diagnostic tester. The emergency status is triggered using the service “Routine control” and the routine will be triggered after clearing the specific security access. The routine control service will include “time and date” and “Duration emergency activation” as data bytes. The information such as time and date of emergency activation and duration are stored in EEPROM.Inducement counter adaptationThe inducement logic functionality is adapted based on emergency status. If the emergency status is active, then the inducement level is bypassed for a stipulated amount of time.A timer runs to check the emergency activation duration and compare it with the requested duration. The timer value shall be stored in non-volatile memory and compared with requested emergency duration. The emergency activation remaining time is computed and the same is transmitted to instrument cluster. Once the timer is elapsed or emergency status is released, inducement logic is activated.The emergency activation status when active, stores the activation duration, date and time of activation in EEPROM.The EEPROM stores the information for configurable number of emergency activations. The stored information is configured, so as to retrieve using diagnostic tester. When the emergency status is active, the data is sent to instrument cluster to turn on the lamp to indicate the emergency activation status to the operator.SUMMARY/CONCLUSIONSThe NOx driver inducement legislation is defined to ensure the correct operation of NOx control systems and to help the driver to comply with the emission norms. The functionality to support NOx driver inducement systems is implemented in ECU software. The software design is derived based on system overview and legislation requirements. The implementation of “inducement counter, Monitoring and DSM” form the core of software to meet these requirements. The software is modular, with a flexibility to adapt for short term bypass of inducement in case of emergency. The possible interfaces to convey the emergency activation and inducement short term bypass are proposed.In summary, the approach to meet the legislation requirements for driver inducements in ECU software is presented in this paper.REFERENCES1. /article/10657806/egr-meets-scr2. /obd/basic.htm3. Commission Regulation (EU) No 582/2011 of 25 May 2011 implementing and amending Regulation (EC) No595/2009 of the European Parliament and of the Council with respect to emissions from heavy duty vehicles (Euro VI) and amending Annexes I and III to Directive 2007/46/EC of the European Parliament and of the Council - Annexure XIII. 4. /fdsys/pkg/FR-2011-06-07/pdf/2011-13851.pdf5. /msprog/onroadhd/documents/epa-arb_scr_workshop_7-20-10.pdf6. /fdsys/pkg/FR-2012-06-08/pdf/2012-13087.pdf7. /articles/print/ volume-18/issue-1/departments/fama-forum/emergency-vehicles-and-the-epa.html CONTACT INFORMATIONN. Santosh DattaSoftware and System EngineerECU Powertrain projectsRobert Bosch Engineering and Business Solutions Ltd India #123, Industrial Layout, Hosur Road, Koramangala Bangalore-560095, Indiasantosh.datta@ ACKNOWLEDGMENTS• Dr.Hauke Wendt - ‘Senior OBD analyst Commercial Vehicles’ from Robert Bosch GmbH, for providing valuable inputs on driver inducements.• Mr. Michael Kolitsch - ‘Exhaust System engineer’ from Robert Bosch GmbH, for supporting with relevant information on SCR and EGR systems.• Mr. Vadiraj Krishnamurthy - Principle Consultant, Robert Bosch Engineering and Business Solution Ltd India, for reviewing the document.DEFINITIONS/ABBREVIATIONS AdBlue- Aqueous Ammonia Solution, also referred as Diesel Exhaust Fluid (DEF)AECD - Auxiliary Emission Control DeviceCAN - Controller Area NetworkCARB - California Air Resources BoardDSM - Diagnostic System Managemente.g. - ‘exempli gratia’ (for example)ECU - Electronic Control UnitEEPROM- Electrically Erasable & Programmable Read Only MemoryEGR - Exhaust Gas Re-circulationEPA - Environment Protection AgencyEU - European UnionOBD - On Board DiagnosticsSCR - Selective Catalytic ReductionThe Engineering Meetings Board has approved this paper for publication. 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