Rear Oxygen Sensor Monitoring

Transcription

1 Automobili Lamborghini s.p.a. OBDII MY 08 Section 7 Page 44 Rear Oxygen Sensor Monitoring

2 Automobili Lamborghini s.p.a. OBDII MY 08 Section 7 Page 45 Oxygen Sensor Heater Monitoring

3 Automobili Lamborghini s.p.a. OBDII MY 08 Section 7 Page 46 Basic theory and algorithm

4 Automobili Lamborghini s.p.a. OBDII MY 08 Section 7 Page 47 The Lamborghini Engine management system has in its OBD II system two heated oxygen sensors, one for each bank, after the catalyst (see figure in CATALYST MONITORING section Basic theory). The lambda sensor s behavior is like that one of a voltage generator with its equivalent circuit. The impedance of this circuit is a function of temperature and is extremely high when the sensor is cold. We adopted a pull-up circuit enclosed in the Lamborghini LIE 2003 ECU in parallel to the sensor circuit, in order to monitor the heater circuit. When the pull-up circuit is switched on, the output of the sensor is a function of O 2 content, temperature and aging. Eliminating the effect of O 2 content and being aged constantly over the test, the output voltage gives an indication of temperature only. When the sensor is cold, the impedance of the pull-up circuit is lower than the impedance of the sensor; in this case the output voltage is that of the pull-up circuit (almost 0.5 V). On the other hand, when the sensor is warm, the impedance of the sensor becomes lower than the pull-up circuit impedance; in this case the level of the output voltage generated by the sensor is in proportion to the O2 content of the exhaust. During engine warm-up, the heater warms the sensor quickly. If the heater does not work, the warming of the sensor is achieved only by the heat from the exhaust gases, and it is slower. The Lamborghini Heater diagnostic looks for the time needed to heat up the sensor from engine on (that is the time to get the output voltage different from pull-up). The heater is judged operative when the time is lower than a threshold obtained from our experimental data. If greater than the threshold, it is considered to be inoperative. Please notice that there is no difference among the two test groups under this point of view. The behavior in the warm up phase depends only from the sensor which is the same in the two applications.

5 Automobili Lamborghini s.p.a. OBDII MY 08 Section 7 Page 48 Mode/Service 6 communication In the following chart there are the data related to Lambda on/off (rear) Heater monitoring strategy in accordance whit specification SAEJ1979 allowing access to the results for on-board diagnostic monitoring tests of specific components/systems that are not continuously monitored. J1979 LAMBDA HEATER MONITOR SERVICE $06 DATA INIT Value Treshold Error Conversion Test ID Comp ID Bit TTL Description Timer for inactive zone sensor 2 bank left 2 0,1 0.1sec/lsb Timer for inactive zone sensor 2 bank right 2 0,1 0.1sec/lsb

6 Automobili Lamborghini s.p.a. OBDII MY 08 Section 7 Page Rear oxygen sensor monitoring Functional aspects

7 Automobili Lamborghini s.p.a. OBDII MY 08 Section 7 Page Basic theory

8 Automobili Lamborghini s.p.a. OBDII MY 08 Section 7 Page 51 The Lamborghini engine management system is equipped with a secondary oxygen sensor for each bank for use as an OBD-II system-monitoring device to achieve compliance with the catalyst monitoring requirements. In addition to the heater monitoring (see the chapter Oxygen sensor Heater monitoring ); the sensor is checked when inactive, locked lean, locked rich and with a Transient Test. The Transient test, based on the activity of the sensor, is performed as part of the diagnostic. Purpose of the transient test is to check if the rear O2 sensor s signal is deep enough (its amplitude is able to cover the full range of the nominal sensor characteristic which is used for catalyst monitoring) and fast enough to guarantee a correct catalyst efficiency monitoring.

9 Automobili Lamborghini s.p.a. OBDII MY 08 Section 7 Page Transient Test : Algorithm for diagnosis

10 Automobili Lamborghini s.p.a. OBDII MY 08 Section 7 Page 53 Rear O2 sensor s transient test combines two aspects: - Coherence in timing and amplitude among the shape of front UEGO sensor and rear oxygen sensors (please remember that Lamborghini uses the rear oxygen sensor for catalyst diagnosis only and that monitor is run comparing the signal of front and rear sensors). - Switching behavior: During the rich to lean transition, the switching time of a healthy sensor is very short. The transition time from 0.55 to 0.25V must be shorter than 150msec. The monitor runs during every fuel cut. In case of error detected, a fault accumulator is incremented according with which failure has been detected (Coherence or switching behavior) At the end of every trip, if no error has been validated, the fault accumulators are reset to zero. More in detail: IF Fuel cut on AND Lambda value of the front UEGO sensor above 1 (fuelling lean) THEN General TT countdown on (the general countdown is set to 2 sec) IF Rear O2 sensor signal < 0.55 THEN Switching TT countdown on (the switching countdown is set to 150ms) IF Switching TT countdown = 0 AND rear O2sensor signal > 0.25V THEN Switching TT Fault Accum = Switching TT Fault Accum + 1 ELSE IF General TT countdown = 0 AND rear O2sensor signal > 0.15V THEN General TT Fault accum = General TT Fault Accum + 1 IF General TT Fault Accum > 30 5 OR Switching TT Fault Accum > 20 5 THEN P0140 (P0160) fault code is stored. ELSE Transient test monitor enabling conditions not met. Please notice that the coherence check is run using the comparison among front and rear sensors because those two sensor are used to run the Catalyst efficiency monitor and because this system allows Lamborghini to reduce the effect of transport time through exhaust pipes. In fact, triggering the main countdown with the front UEGO sensor signal allow to consider, in the calibration of the timer, only the transport time due to catalyst volume plus the oxygen storage effect of the catalyst itself.

11 Automobili Lamborghini s.p.a. OBDII MY 08 Section 7 Page 54 In the image below you can find a sample of how the strategy works. Table describes the meaning of the flag values which appear in the graph. Pict Parameter Description Meaning CO Status Value of the state machine which manage Cut Off procedure OBD2_TTPostState Value of the state machine which manage Switching TT check 4 = Waiting time (condition met but injection still on) 1 = Ramp in (fuel injection is progressively switched off to get a smooth behaviour from the engine) 2 = Complete fuel cut (injection off) 3 = Ramp out (fuel injection is progressively switched on to get a smooth behaviour from the engine) 1 = Cut off procedure has started 2 = Complete fuel Cut 3 = Switching TT Countdown on, first (Upper) Voltage threshold of 0.55 has been crossed 4 = Voltage below lower threshold of 0.25V (no error possible) Table

12 Automobili Lamborghini s.p.a. OBDII MY 08 Section 7 Page Test procedures and results

13 Automobili Lamborghini s.p.a. OBDII MY 08 Section 7 Page 56 Pict As shown in picture above, tests have been performed with aged sensors and catalyst converters at limit efficiency, aged on the field ( 1.73 * Nmog limit and 1.44 * Nox limit for V10 engine, 1.71 * Nmog limit and 1.56 * Nox limit for V12). Due to the fact that both rear O2 sensors and catalyst efficiency monitoring strategy is the same among the two Lamborghini Test Groups, also the calibrations for the transient test strategy are the same. Using aged sensors, we noticed: - among 14 rear O2 sensors with more than miles, 5 are considered out of efficiency with the strategy described above. - None of the 5 sensors out of efficiency exceed a switching time of 130 msec. - Every aged sensor has a switching time among 80 and 130 msec (40 msec is the mean switching time of a brand new sensor), and we found out aged sensors still efficient that have a switching time of msec and non efficient aged sensors with a switching time of 100 msec. - The lower limit for general Transient test check (0.15V) is a limit, with 0.17V it is impossible to detect a non efficient catalyst with Lamborghini catalyst efficiency monitoring strategy. Lamborghini understands that 14 aged sensors is a small number for statistics, but for our small production number it is impossible to have more parts to check. For those reasons the experience we made on those parts does not allow us to define a correct calibration for the switching time strategy. In fact, we have both efficient and non efficient rear O2 sensor with the same switching time. So the switching time strategy, which has been introduced in Lamborghini Engine management software, has been calibrated at 150 msec to avoid misdetection.