Metafuel 1 system description

Transcription

1 Metafuel 1 system description ECE R110 and ECE Euro IV compliant, full EOBD MASTER-MASTER twin ECU system for bi-fuel vehicles METAFUEL 1

2 Summary Summary...2 General description...4 METAFUEL 1 features...6 Preface...6 Injection Calculation...6 Air Mass Flow Calculation...6 AFR tuning and open loop areas...6 Closed loop controls...7 AFR self adaptation...7 Fuel quality self adaptation...7 Fuel Mass flow and Injector Opening Time calculation...8 Injection Advance Timing...8 CNG optimisation for performance, emission, driveability...8 Spark Advance optimisation for CNG...8 Additional air optimisation for CNG...8 Idle Engine Speed target...9 Canister purge management...9 Safety and Durability...9 Gasoline Fuel Pump Deactivation...9 SWITCHOVER strategy...9 Diagnosis OBD1 diagnosis EOBD diagnosis Metafuel 1 system description.doc Page 2 di 15

3 Diagnosis supervisor Diagnosis tools communication protocol Other strategies General electrical scheme Metafuel 1 system description.doc Page 3 di 15

4 General description A ECE R110 and ECE Euro IV + EOBD compliant MASTER-MASTER twin ECU system for bi-fuel vehicles The Metafuel 1 system is a Multipoint Sequential Electronic Injection system based on the Master Master concept designed to convert original Otto cycle (Spark Ignition) engine from only gasoline to Bifuel CNG-Gasoline. The Master-Master concept is based on a full featured CNG Engine Control Unit (ECU), that can operate as a Master control with the gasoline one when operating in CNG mode. While running in gasoline mode the proper ECU operates as a Master Stand Alone control. The Master CNG ECU is a complete engine control unit: it is provided with all the typical engine control strategies like fuel metering, Spark Advance Management, Idle Speed Control, Canister Purge, Lambda sensor Closed Loops (up and downstream catalyst), dedicated and shared sensor diagnosis, full EOBD diagnosis strategies set, etc. The CNG ECU can be defined as Master since it uses some drivers and actuators owned by the gasoline OEM system. For instance, the Metafuel 1 is not provided with ignition coil drivers, but actuates the right CNG Spark Advance simply by communicating the exact value to be actuated to the gasoline ECU (by means of a digital fast communication line) which is in charge to actuate it. Figure 1 - The MASTER - MASTER concept scheme of Metafuel 1 The most evident advantage, from the application point of view, is the saving in actuators as well as in sensors keeping at same time the availability in CNG mode Metafuel 1 system description.doc Page 4 di 15

5 (the added on system) of the same features of the gasoline base system: all this resulting in a performance, emissions, driveability and diagnoseability at the highest standard achievable with the engine/vehicle components. From the point of view of the gasoline ECU, only very low impact modifications to the software are required in order to set up the fast communication protocol. Along with the base simplified concept of the Master-Master twin ECU control, the OEM quality that cannot be renounced, is ensured by the full compliancy of the system components to ECE R110 Standard and by the long lasting application of them to hundreds of thousands of passenger cars, light duty and heavy duty vehicles. Finally, for those market where it is required, the European On Board Diagnosis (EOBD) system is fully featured and stand alone in CNG mode. The Metafuel 1 is provided with all the required strategies as Upstream Oxygen Sensor, Catalyst (by means of the downstream oxygen sensor), Misfire and a CNG dedicated Fuel System. The Malfunction Indicator (MI) manager can be easily set to manage the indicator directly or indirectly (as the one already present on the dashboard). The vehicle equipped with Metafuel 1 system can be homologated ECE Euro IV + EOBD. As to the EOBD robustness, it has been tested by means of endurance tests for thousands of kilometres. Metafuel 1 system description.doc Page 5 di 15

6 METAFUEL 1 features Preface As already depicted above, the Master-Master bifuel system needs a full featured CNG ECU that, only to avoid HW duplication on a twin ECU architecture, isn t provided with some actuators, like Ignition Coils, but manages all the engine control parameters: air mass flow measure (estimation), Air/Fuel ratio (open-closed loop), fuel mass flow calculation, Spark Advance, Canister Purge Mass flow, Additional Air (idle and dashpot), Air/Fuel self adaptation. Moreover to comply with EOBD regulation a very sophisticated and powerful diagnosis supervisor, jointly with state of the art core diagnosis allows the customer to define the level of diagnoseability best fitting with the application targets. For this reason, taking into account the scope of this document, just a very brief description of the control strategies is given. Reader should consider that the Metafuel 1 ECU really can act as a Master. Injection Calculation Air Mass Flow Calculation Since the gasoline ECUs standard strategies for this fundamental control are widely speed-density based, Metafuel 1 ECU, taking information from the already present TMAP sensor, estimates the air mass flow when engine operates in CNG mode. The estimation is of course corrected by the intake efficiency loss due to CNG injection, ensuring high accuracy to the open loop fuelling mode (some case of recovery or COLD after crank and WOT conditions). For best response an electrical sharing of the pressure sensor output is preferred while, due to the lower dynamics, the temperature one can be shared digitally on serial link (i.e. CAN link). AFR tuning and open loop areas A large lookup table allows applicators to define the best Air/Fuel Ratio (AFR) on the whole running conditions. Of course the closed loop area (that is possible to define on low and high engine speed and load indexes) superimposes the theoretical AFR for the application reference CNG fuel while the closed loop control is operating. Moreover the areas of WOT (in high load) and CUTOFF (in negative torque) triggered by the throttle position against engine speed are available to switch to open loop. Even not strictly necessary, a coolant temperature based strategy allows the AFR tuning while engine is warming up. Metafuel 1 system description.doc Page 6 di 15

7 Closed loop controls The Euro IV compliancy requires a very accurate AFR control by means of the upstream (mandatory) and downstream (optional) Oxygen sensors. Notwithstanding the normal ±25% authority, the dynamic of the closed loop is methane featured in order to allow the best tuning of the AFR bias required by the CNG dedicated catalysts. Catalyst chemistries of CNG dedicated catalysts require heavier AFR bias than gasoline ones in order to achieve the best conversion efficiencies. A WOT triggered half closed loop strategy can be enabled ensuring Not Lean conditions in order to avoid, at high engine speed and load, any overheating of the catalyst. Since the downstream sensor is required by EOBD Catalyst Diagnosis, the feedback of it can be used for a slow and extremely accurate (less than o.5 % error) AFR control operating as an upstream closed loop refinement. Due to the heavily different dynamics of the up and downstream Oxygen sensors, the first one must be electrically shared while the second can be acquired by means of the serial link. AFR self adaptation Based on the average error of the closed loop control, a self-adaptative values cartography allows the engine as well as components efficiency drifts compensation. The self-adaptative values are calculated and validated in closed loop conditions and then can operate as open loop corrections while needed. Also small fuel quality spreads are managed by this strategy. Fuel quality self adaptation Methane contents in commercial CNG can vary from filling station to filling station. The fuel self adaptation of the ECU can be saturated when engine, injection system and fuel drifts are all in the same direction (i.e. sum of lean condition while - 5% injectors, +5% engine intake efficiency, -2 % closed loop accuracy, -15% methane contents on CNG exceeds the usual ± 25 % authority). As Earlier experiences have shown that usually is not required by the CNG filling station fuel quality spread in many countries The spread of the fuel quality can be due to methane concentration and or to hydrocarbon blends Fuel quality can have impact mainly on the driveability if the vehicle is operating in a critical filling station network Metafuel 1 system description.doc Page 7 di 15

8 a tank filling recognition triggered strategy of AFR compensation is provided as optional (need only to be activated and tuned). The self-adptative value operates as reference AFR correction in open loop leaving to the closed loop and engine self-adptative strategy the whole authorities. Fuel Mass flow and Injector Opening Time calculation The Fuel Mass Flow calculation is very simple: since the AFR has been calculated and the Air Mass Flow has been estimated, at every TDC an AFR/AirMassFlow ratio is calculated giving the fuel amount as operation result. The Fuel amount per stroke is given as input to the CNG injector model that, taking into account CNG pressure and density in the rail (pressure / temperature sensor output) and battery voltage, produces as output the Opening Time of the injector able to deliver to the engine the right mass quantity. In real time this time is programmed onto the injection ASIC. Injection Advance Timing Safety reasons as well as performance optimisation require that the CNG delivered inside the intake manifold duct must be intaken entirely as soon as the first intake phase happens. For this reason a cartography of angle based injection advance timing is available in order to tune this feature on the engine layout and phasing. The advance angle is on the range of 180 to 520 degrees before the combustion TDC. CNG optimisation for performance, emission, driveability Spark Advance optimisation for CNG Best performance, driveability and emissions are mainly affected by the spark advance applied. A complete set of engine speed/load charts, coolant temperature lookup tables (even detailed for emission test driving style) and engine overspeed or idling detection is provided in order to tune the most effective spark advance in all conditions. The spark advance values, while computed at every TDC, are sent by means of the serial link to the gasoline ECU that, as a slave, actuates them. Additional air optimisation for CNG Nothing like additional air strategies can affect the driveability. This is mainly true in idle mode as well as in fuel deceleration shutoff (CUTOFF) where the most sensible driveability faults can happen. For this reason the additional air management of the gasoline ECU in Metafuel 1 systems is corrected by means of parallel idling and dashpot strategies besides CNG ECU. The summed additional air values computed by the CNG ECU (added or subtracted) are sent via serial link to, and managed by, the gasoline ECU which is in charge to actuate the corrected target. Metafuel 1 system description.doc Page 8 di 15

9 Idle Engine Speed target Gasoline engine operating in CNG can have some poor performance at idle (i.e. when air conditioner is on or power steering is full locked). A strategy to modify the engine speed target at idle is provided in order to counteract the problem. The summed engine speed values tuned in the CNG ECU (added or subtracted) are sent via serial link to, and managed by, the gasoline ECU which is in charge to actuate the corrected target. Canister purge management Since the Metafuel 1 is targeted to Bifuel Vehicles, a strategy to actuate the Canister Purge according to functional targets and regulations is provided. The canister purge valve opening values are calculated in closed loop (not in blind mode) in order to avoid any too rich condition while the canister is full. The canister purge valve opening values computed by the CNG ECU are sent via serial link to, and managed by, the gasoline ECU which is in charge to actuate them. Safety and Durability Gasoline Fuel Pump Deactivation In order to avoid any problem with overheating of gasoline fuel pump as well as an electrical consumption not useful, during CNG running mode, this component is deactivated with a relay under control of the CNG ECU. Reactivation is done inside the SWITCHOVER strategy taking into account all the preactivation time for fuel pressurisation before injectors activation. SWITCHOVER strategy The full customisable strategy can allow or disable switchover under user request basing on several condition like engine speed, load and coolant temperature in addition to a complete diagnosis check. Wall wetting formation model can be tuned to give the most comfortable and AFR safe switching differentiating GAS to Gasoline or vice versa switch. A complex protocol give to CNG and Gasoline ECU the complete control of all the parameters that must be checked before switching. Warm up of engine and CNG component model can be tuned in order to prevent any damage while running under very cold condition (i.e. -25 C overnight soak cranking). A forced very fast switching mode is available for diagnosis reason, customisable inside the diagnosis supervisor, in order to prevent any engine stall. Metafuel 1 system description.doc Page 9 di 15

10 Run out of GAS strategy is customisable in term of absolute threshold on tank pressure, hysteresis to allow on trip switchback and for refilling recognition. Diagnosis OBD1 diagnosis OBD1 is normally called the set of diagnosis strategies both electrical and functional relating with the status of operation of the electrically connected components. The Metafuel 1 set of diagnosis strategies cover both dedicated and shared sensors and, of course, only dedicated actuators. The list of the OBD1 diagnosis lines is shown below. Manifold Absolute Pressure as well as Throttle position sensors, shown in green background, failures allow running in CNG having a reconstruction signal model recovery available. Metafuel 1 system description.doc Page 10 di 15

11 Injector lines are shown in yellow fields because it is possible to set the number of CNG injectors failure before forcing the switchback to Gasoline. EOBD diagnosis Aim of EOBD strategy is to give an emission related vehicle failure signal to the driver (MI ON) who is in charge to recover as soon as possible to the service. As to emissions, the main target is to avoid emission system tampering or poor maintenance. Required by actual European Euro IV and future regulations, the EOBD strategies set on Metafuel 1 is fully compliant. This means that Metafuel 1 system can fulfil requirements for REAL BIFUEL VEHICLES with full driving range both on CNG and Gasoline fuel: other systems allow only dedicated application with a small (less than 20 liters) gasoline tank. The homologation procedure output is an individual certificate for CNG and Gasoline running modes. Engine family homologation procedure is allowed with Metafuel 1 system giving a very comfortable system porting within different application. Nevertheless some market/countries do not require EOBD, some lines, like Misfire 200 can be very useful because it is able to detect malfunctions of normally not under diagnosis components as i.e. the spark plugs. Diagnosis Line EOBD Components / Feature Checked Benefit of use out of regulation demand ***** high *** medium * low Misfire 200 Misfire 1000 Injection, Ignition, Engine Valves Efficiency Injection, Ignition, Engine Valves Efficiency ***** Catalyst Efficiency Diagnosis Catalyst * Upstream Oxygen Sensor EOBD Oxygen sensor *** Fuel System Upstream/Downstream oxygen sensors plausibility Load sensors, Pressure regulator, Piping, Injectors characteristics, Engine Intake Efficiency * ***** Oxygen sensors * EOBD core diagnosis strategy tuning emission related for homologation procedure testing and robustness is almost the most complex and expensive task in an Metafuel 1 system description.doc Page 11 di 15

12 application development. An only robustness for general diagnosis purpose calibration is much cheaper and give big benefits to the end user. Diagnosis supervisor A powerful and complex states machine strategy, functionally joining OBD1 and EOBD core diagnosis line outputs with recovery activation and MI ON strategy is available. Recovery activations and MI ON (modes ON 1 or ON 3) are fully customisable with system calibration tools. Diagnosis supervisor is in charge to manage also the record of failures in the EEPROM of ECU for future diagnosis tools reading. Each diagnosis line has its individual set of environmental parameters recorded. Diagnosis tools communication protocol The normal production standard protocol is the Keyword 2000 standard. SW changes are available for custom communication protocols implementation. As to the system, the CNG ECU acts as an additional ECU in the general vehicle diagnosis bus (like ABS or Automatic Gearbox ones) with its individual Address. Non proprietary EOBD compliant scan tools are already able, within European Market, to recognise and treat emission relevant information coming from the second ECU collecting and showing them in the same query/show frames of the gasoline OEM ECU. Other strategies An ECU has some low level strategies that are necessary to implement the high level functions (as the ones depicted above). The following table shows all the base functions included in the Metafuel 1 system Software. 1 Input signals SW, tied to the HW, dedicated to input signal conditioning and scaling 2 Output signals SW that takes care of the generation of pulse width, analog and digital signals 3 Injection Timing Low level real time firmware dedicated to the CNG injection hardware timing management 6 Power latch Post key-off strategy for EEPROM setting when engine is turned off Metafuel 1 system description.doc Page 12 di 15

13 General electrical scheme of the whole system Notwithstanding every application has its own gasoline components, more or less the most usual scheme that occurs while applying the Metafuel 1 system, is the one shown in the following picture. Take care that: A complete and detailed electrical scheme is dependent on the original wiring harness and components of the application. The following scheme indicates the macro breaks, shunts and connections present in the Metafuel 1 system All power actuations are remotely operated by relais and protected by fuses that are too complex to be depicted for the scope of the following scheme Except for the Metatron supplied components, all other gasoline ones are only examples figures Only electrical wired components are included in the electrical scheme Metafuel 1 system description.doc Page 13 di 15

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