Automobili Lamborghini s.p.a. OBDII MY 10 Section 3 Page 2 MISFIRE MONITORING
Automobili Lamborghini s.p.a. OBDII MY 10 Section 3 Page 3 This system allows us to detect misfire under all positive torque engine speed and load conditions, from the engine start. Due to the choices made for the exhaust system, the malfunction criteria - which is more severe - is linked to the increase of emission levels. Our misfire monitoring system is able to detect a 2.5% misfire condition which causes an emission increase exceeding 1.4 times the applicable FTP standard; this level is more severe than the one required by CARB (paragraph (e) (3.2.2)(A)). The system is able to detect which cylinder is affected by misfire in single misfire conditions; in the case of multiple misfires, the system can detect which is the affected cylinder bank. If more than 90 percent of the detected misfires occur in a single cylinder, the appropriate fault code indicating the specific misfiring cylinder is stored. If two or more cylinders individually have more than 10 percent of the total number of detected misfires, a multiple cylinder fault code is stored.
Automobili Lamborghini s.p.a. OBDII MY 10 Section 3 Page 4 Basic theory and algorithm
Automobili Lamborghini s.p.a. OBDII MY 10 Section 3 Page 5 The Lamborghini misfire detection system is based on the analysis of the pressure oscillations in the exhaust system. In normal conditions, the instantaneous exhaust pressure has a particular, well defined shape varying with load and rpm. In case of misfire, the lack of combustion in one or more cylinders produces a variation of the pressure wave shape of the exhaust that can be detected with the pressure sensors (one for each bank, installed just before the Catalytic Converters). The shape of the signal from the pressure sensor is analyzed using a FFT method, which allows us to define module and phase of exhaust pressure wave harmonics. In order to identify the various misfire conditions the first three harmonics have to be simultaneously analyzed; for the amplitude of each of these harmonics, specific reference ranges are defined, which identify regular or irregular combustion and give indications about single or multiple misfire: their thresholds values, function of rpm and load, have been identified thanks to the great quantity of data obtained from the field and from extensive testing. If misfire affects a single cylinder, that cylinder can be identified, using the analysis of the phase reference (obtained by the camshaft sensor). The introduction of the Exhaust Noise Control System (see section 16.15) who modifies exhaust sound and backpressure in function of rpm and load, imply to utilize two different threshold configurations in function of ENCS status (Bypass valve OPEN or Bypass valve CLOSED). In particular has been duplicated: -Misfire Index threshold -I Harmonic s recognition range -II Harmonic s recognition range -III Harmonic s recognition range -I harmonic phase recognition range
Automobili Lamborghini s.p.a. OBDII MY 10 Section 3 Page 6
Automobili Lamborghini s.p.a. OBDII MY 10 Section 3 Page 7 The most important part of the algorithm is the Fourier analysis of the exhaust pressure signal. The algorithm s logical steps are the following: 1. Check if engine is on. 2. If engine is on, verify if conditions (RPM, MAP, TH2O, TAIR) are suitable for misfire detection (positive torque conditions). 3. If engine conditions are suitable for misfire detection perform the next step. 4. Acquire the output signal of the pressure transducers (one for each bank of the exhaust system, positioned before the close coupled catalytic converter). 5. Perform the Fourier transform of the pressure signal over every sampled engine cycle. 6. Perform the analysis of the amplitudes of the first three harmonics (The first harmonic has a period that equals the engine cycle, the second a period that equals engine Rpm, the third a period that equals a third of the engine cycle). 7. Define a misfire index as a combination of the amplitudes of the three harmonics. 8. Perform the Misfire preliminary detection by comparing the misfire index to a stored threshold value, a function of engine Rpm, load and ENCS status. 9. If the threshold value is exceeded, identify whether the misfire is single or multiple. This detection is possible comparing the three harmonics amplitudes to their reference ranges. If all the three harmonic amplitudes are within the relevant ranges a SINGLE misfire occurred in the engine cycle. 10. Calculate the first harmonic phase and compare it with the values stored in the ECU (function of Rpm, load and ENCS status). This comparison defines the single cylinder that misfired. 11. Calculate the misfire percentage, by verifying the number of misfiring engine cycles over a predetermined number of engine cycles. 12. Verify whether the percentage reaches the value that would cause the catalyst damage. If this is true the MIL will blink until misfire is detected. At the same time, if misfire is single, the relevant fault code identifying the cylinder will be stored. A freeze frame of engine conditions will be stored too. If the misfire percentage reaches the value that would cause emission from a durability demonstration vehicle to exceed 1.5 times the applicable FTP standard, evaluated in 1000 revolution increments, according to subsection. (e) (3.2.2)(A and C), then a fault code identifying the cylinder which is undergoing misfire or a fault code relevant to multiple misfire will be stored. A freeze frame of engine conditions will be stored too. The Pending Fault code will be stored no later than the next driving cycle in which misfire is detected, unless driving conditions similar to those under which misfire was originally detected have been encountered without an indication of misfire, in which case the temporary fault code can be erased.