The electronic control system of the engine is very complicated. Any component in the system is faulty, or the wire is broken, the pins are loose or the contact is poor, which will cause the whole system to malfunction, resulting in a sharp increase in pollutant emissions. It is difficult to achieve this by relying solely on traditional testing tools. Therefore, modern engine electronic control systems are equipped with a self-diagnostic system called the On-Board Diagnostic System (OBD), the On-Board Diagnosis system. This article refers to the address: http:// Ignition engine OBD meaning The main point of the on-board diagnostic system (OBD) is to constantly monitor the abnormality of various data of the system, find out the fault information, take temporary remedial measures on the one hand, and send the fault information to the RAM in the ECU on the other hand, record it, wait The maintenance personnel will review and ascertain the cause of the failure, and if necessary, notify the driver via the Malfunction Indicator MI. There is also a fault indicator called a MIL (Malfunction Indicator Lamp). The most important difference between OBD and traditional car engine fault diagnosis is that the latter is only to find faults, restore their function, and intentionally or unconsciously ignore the problem of emissions; OBD guarantees that there is no engine failure. And the emissions are worsened. OBD should be understood in several ways: on the one hand, it is a technology of emission control; on the other hand, it is a function of emission control; the central task of OBD is emission control. OBD is not only important for new vehicle type certification, but also for emission control of in-use vehicles. However, OBD is not a panacea. In fact, many aspects of OBD technology have yet to be refined and developed. This is because the emission of a certain pollutant can be caused by many reasons: first, the control reasons, such as excessive HC and CO emissions may be due to poor start control, or lack of fire, or variable valve system control failure. , or evaporative emission control failure, or secondary air system control failure. Second, these problems may be caused by failure of electronic components, or poor contact of wires or connectors, or short circuits and open circuits. Third, it may also be due to mechanical failures, such as mechanical failure of the variable valve system, excessive wear of the piston, piston ring and cylinder wall, mechanical failure of the crankcase forced ventilation system or failure of the separator of the lubrication system, even May be caused by the failure of the three-way catalytic converter. Therefore, the situation on the site will be very complicated. At least the current OBD system has no way to directly link the excess of a certain pollutant discharge to a certain fault one-to-one correspondence. At best, it can only guess which areas of the engine may be problematic based on the monitored fault information when certain conditions are met, and then rely on knowledge and experience to find and solve problems through step-by-step manual inspection. It can be seen that the use of OBD to find out the cause of excessive engine emissions is a complicated process, which has both strict logic and considerable uncertainty; both inevitability and contingency. However, as long as the entire system of the entire engine is restored to normal operation, the problem of excessive emissions will naturally be solved. OBD development history The concept of OBD was first introduced by General Motors (GM) in 1982. The California Air Resources Board (CARB) adopted the standards set by the Society of Automotive Engineers (SAE) in 1985, requiring all vehicles sold in California to have basic on-board diagnostics from the 1988 model year. Later, the US Environmental Protection Agency (EPA) required that all new cars sold in the United States must meet the relevant on-board diagnostic technical requirements since 1991. This is what was later called OBDI, which is the initial stage of OBD development. OBDI can only monitor the operation of some components and some circuit faults related to emissions, and its diagnostic function is limited. In addition, the data communication protocol for obtaining on-board diagnostic information and the diagnostic interface for connecting external devices and ECUs are not standardized. Later, on the basis of OBDI, the Society of Automotive Engineers (SAE) standardized the technical details of communication protocols and diagnostic interfaces, and developed into the second generation of on-board diagnostic system, namely OBDII. In order to meet the stricter emission regulations that began in 1992, the California Air Resources Board (CARB) requires that some cars sold in California from the 1994 model year, all cars sold in California from the 1996 model year, must OBDII is also used, also known as CARB-OBDII. CARB's jurisdiction is limited to California, so CARB-OBDII is only implemented in California. The US Environmental Protection Agency (EPA) has jurisdiction throughout the United States, and it has been implementing EPA-OBDII throughout the United States since the 1996 model year. Currently implemented in the United States is an improved version of OBDII. Compared to OBDI, OBDII is integrated as part of the engine's electronic control system to continuously monitor various data on emissions-related systems and components. OBDII stipulates that major faults or abnormal emission values ​​must be displayed to the driver through the fault indicator; the fault information is stored in the fault information memory in the RAM and, if necessary, automatically corrected; before the exhaust gas enters the three-way catalytic converter The concentration of harmful toxic substances must not exceed 1.5 times the FTP limit. Compared with OBDI, OBDII has made great progress in diagnostic function and standardization. The communication protocol between the fault indicator, the diagnostic interface, the external device and the ECU, and the fault code are normalized by the corresponding standards. In addition, OBDII can provide more data for external devices to read, including fault codes, real-time data of some important signals or indicators, and freeze frame information, as shown in Table 1. Since January 1, 2000, all new gasoline vehicles that are listed for sale in EU member states must meet the requirements of the European Onboard Diagnostic System (EOBD), the European On Board Diagnosis. The requirements for EOBD are relatively loose, such as not diagnosing fuel tank evaporative emissions. It is worth mentioning that CARB-OBDII-certified cars can be accepted by countries and regions that implement EOBD; however, cars that have passed EOBD certification cannot be accepted by CARB-OBDII countries and regions. The EOBD system only requires the first four items of the nine fault monitoring functions of CARB-OBDII (engine misfire, oxygen sensor, catalytic converter and evaporative emission control system monitoring) to be monitored, and the powertrain is connected to the computer. It is possible to cause all components and systems that exceed the following EOBD limits in the Type I emission test for the entire vehicle type certification test: CO: 3.2g/km HC: 0.4g/km NOX: 0.6g/km In addition, monitor all components and systems connected to the computer and involve emissions, and at least monitor the connection status of the circuit. The specific monitoring objects vary depending on the configuration of each system. The OBDIII system, a new generation of OBD system under development, can automatically notify the management department of information such as the fault and location of the vehicle through wireless cellular communication, satellite communication, and global positioning system GPS using the in-vehicle small wireless transceiver system. According to this information, the management department can issue instructions to it for maintenance. If it is overdue, it can be punished. On-board diagnosis started late in China. China's emission regulations are generally referred to as OBD and do not distinguish between OBDI and OBDII. However, China's emission regulations basically borrow EU emission regulations, so China's OBD system is almost equivalent to the EOBD system. On April 5, 2005, the State Environmental Protection Administration promulgated the GB 18352.3-2005 standard "Light Vehicle Pollutant Emission Limits and Measurement Methods (China Stage III and IV)", and the new listing and sales since July 1, 2007 This standard is implemented for stereotyped vehicles, and OBD is the content that must be implemented in the national III and national IV emission regulations, thus clarifying the relevant requirements for OBD functions in China. The OBD part of this standard basically copied the EU standards, which is no different from EOBD. At this point, OBD has appeared in China's regulatory standards for the first time as a mandatory requirement. At present, the newly produced cars in China are equipped with OBD systems. It should be noted that the OBD systems on these domestic cars do not necessarily have all the possible OBD functions on the car. OBD related regulations China's legal basis for light vehicle engine OBD is GB 18352.3-2005 standard "Light vehicle pollutant emission limits and measurement methods (China III, IV stage)." The GB 18352.3-2005 standard stipulates that the OBD system refers to the on-board diagnostic system for emission control. It must be able to identify areas where faults may exist, and store the information in the memory of the electronic control unit in the form of fault codes. All emissions-related fault diagnostic data is obtained from the OBD system via a serial interface for standard diagnostic connections, including all fault codes for component inspection, diagnostics, maintenance or repair related to vehicle emissions. The standard also specifies a range of ISO and/or SAE standards that emission control diagnostic systems must comply with. These standards relate to digital information exchange, data communication network interfaces, emissions related systems, diagnostic connection connectors and associated circuits, and definitions of diagnostic fault codes. OBD fault monitoring and judgment criteria 1. Tasks for fault monitoring The work of OBD is based on fault monitoring. The task of fault monitoring has four aspects: (1) Monitor the hardware of the electronic control system itself, such as various sensors and actuators, including faults or short circuits of the circuit. (2) Whether the monitoring is not an electronic control system, but it is the service object of the electronic control system, and the hardware closely related to the discharge, such as the three-way catalytic converter, is faulty. (3) Monitor whether the engine working process is normal, such as whether there is a misfire or not. (4) Monitor whether the mechanical condition of the engine is normal, such as whether the oil level is too low, and whether the coolant is too small. 2. Fault monitoring range The range of ignition engine fault monitoring specified by CARB-OBDII is as follows: (1) Engine misfire monitoring (2) Oxygen sensor monitoring (3) Three-way catalytic converter monitoring (4) Evaporative emission control system monitoring (5) Fuel injection system monitoring (6) Monitoring of engine components such as sensors and actuators (some of which are also monitored in OBDI) (7) Exhaust gas recirculation system monitoring (8) Secondary air system monitoring (9) Monitoring of air conditioning systems (chlorofluorocarbon refrigerants). It can be seen that the objects monitored by CARB-OBDII are directly related to the engine except for the air conditioning system (refrigerant). The EOBD system only requires the key monitoring of the first four items of the above CARB-OBDII nine fault monitoring functions (engine misfire, oxygen sensor, three-way catalytic converter and evaporative emission control system monitoring), and the computer in the powertrain. All parts and systems that are connected and may cause emissions exceeding the EOBD limit in the Type I emission test for the entire vehicle type certification test are monitored. 3. OBD system for fault determination criteria In the OBD system, if the ECU infers from various sensor signals that the failure of the component or system associated with the emissions at the time has resulted in emissions exceeding the limits listed in Table 2, or the OBD system does not meet the basic diagnostic requirements, Then it is considered that a malfunction has occurred. For vehicles burning LPG or natural gas NG, the same emission contaminant limits as for gasoline vehicles are used. OBD system function The function of the OBD system is to implement monitoring and diagnosis of the engine electronic control system. The scope of monitoring and diagnostics depends on regulatory requirements, the function of the engine's electronic control system, and the requirements of the automotive manufacturer and engine electronic control system supplier. 1. The main monitoring and diagnostic functions of the OBD system Even with the same regulatory requirements, the monitoring and diagnostic functions and strategies of OBD systems manufactured by different manufacturers are not the same. Here are some typical monitoring and diagnostic features: (1) Integrated monitoring of electronic devices Monitor all emissions-related sensors, actuators, and power output stages within the OBD system framework. The OBD system monitors electronic devices from the following aspects: ◠Trustworthiness of input and output signals ◠Is it shorted to ground? ◠Is the power supply positive short circuit ◠Whether it is open circuit. (2) Oxygen sensor monitoring ◠Front oxygen sensor voltage characteristic offset and adaptive value monitoring ◠Oxygen sensor heating monitoring ◠Front oxygen sensor response time monitoring ◠Post-oxygen sensor control limit monitoring ◠Post-oxygen sensor dynamic characteristics monitoring (3) Three-way catalytic converter monitoring Today's monitoring of all catalytic converters is based on the monitoring of oxygen storage capacity. To this end, an oxygen sensor must be placed in front of and behind the catalytic converter. (4) Evaporative emission control system monitoring Including monitoring of the evaporative emission control system canister purge valve failure and system leakage failure, at least the connected state of the circuit must be monitored. (5) lack of fire monitoring A lack of fire refers to a ignited engine that fails to burn due to a spark plug not being ignited, fuel metering is not accurate, compression pressure is too low, or any other reason. The lack of fire can be caused by a variety of reasons, including fuel, air and ignition, such as excessive or excessive mixture, spark plug burnout or electrical contact failure. A lack of fire causes a large amount of HC to enter the three-way catalytic converter through the exhaust manifold and burn there, generating a large amount of heat sufficient to physically (melt) or chemically damage the catalytic converter. In addition, this unburned mixture, once discharged from the machine, is an additional pollution to the environment. Even a few isolated fires can cause high HC emissions. Experience has shown that when the fire rate is 2%, HC emissions will increase from the original regulatory limit to 50% above the regulatory limit, as shown in Figure 1. If the engine is out of flame for more than 17%, the catalytic converter will be damaged. Therefore, the electronic control unit must be able to perform misfire monitoring. The lack of fire monitoring is an important indicator that OBDII is different from OBDI. (6) Exhaust gas recirculation (EGR) system monitoring This includes monitoring of EGR valve underflow faults and EGR valve pin position sensor circuit faults. (7) Electronic throttle monitoring (8) CAN data bus monitoring (9) Secondary air flow monitoring (10) Absolute pressure limit monitoring of intake manifold 2. Extension of OBD system monitoring function The monitoring range of the OBD system must meet at least the minimum requirements of the regulations. GB 18352.3-2005 requirements in this regard are all around the emission control. However, in order to facilitate the maintenance, repair and safety of the vehicle, the actual function of the OBD system often exceeds the requirements of the regulations. This is mainly manifested in two aspects: First, the monitoring targets are more than required by regulations. Engine parts can be divided into two categories: the first type is that parts that are damaged or fail to cause emissions to exceed the OBD limit or cause other monitoring functions to fail; the second type is that damage or failure does not cause emissions to exceed OBD limits or parts that cause other monitoring functions to fail. The regulations only stipulate that the OBD system must be able to monitor the first type of components, but it does not require monitoring of the second type of components. However, the actual monitoring range of the OBD system often covers a part of the second type of components. Second, the conditions for implementing monitoring are more lenient than the requirements of the regulations. The regulations only require that the monitoring function of the OBD system be activated under certain conditions. In fact, even if the scope of the conditions is exceeded, as long as the OBD system can perform reliable monitoring, it will often start its monitoring function. For example, the regulation GB 18352.3-2005 clearly stipulates that the maximum speed of the misfire monitoring is 4500 r/min or the smaller than the highest speed occurring during the type I emission test in the new model certification, 1000 r/min. . However, as long as the OBD system can reliably perform misfire monitoring, the monitoring function will not be turned off even when the speed exceeds the specified range. 3. Temporary shutdown of OBD system functions The OBD system can temporarily and partially disable the OBD function in the following cases: (1) When the fuel tank liquid level does not reach 20% of the nominal capacity of the fuel tank, the manufacturer can turn off the OBD function. (2) When the monitoring performed when starting the engine at an ambient temperature below -7 ° C or above 2500 m is unreliable, the manufacturer can turn off the OBD function under these conditions. (3) When the engine is started at an ambient temperature exceeding a certain value, it may cause a misdiagnosis. The manufacturer may also require the OBD function to be turned off under these conditions. (4) When the unevenness of the road surface reaches a certain level and the transmission shifts, the misfire monitoring is turned off. (5) A vehicle equipped with a power take-off device that allows the affected monitoring system to be shut down when the power take-off is working and affecting the monitoring system.
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