Test Group TBM2.8VJGKEK
Catalyst Monitoring General Description - Catalyst monitoring is based on monitoring its oxygen storage capability. The engine closed loop feedback control generates lambda (air/fuel ratio) oscillations in the exhaust gas. These oscillations are dampened by the oxygen storage activity of the catalyst. The amplitude of the remaining lambda oscillations downstream of the catalyst indicates the storage capability.
- Monitoring Procedure - The conversion efficiency of both catalyst systems (cyls. 1-3 and cyl. 4-6) are separately monitored. In order to determine the efficiency the lean and rich time periods of the oxygen sensors up and downstream will be compared. See Fig 1. The smaller of the 2 ratios determined is used for further processing. The cycle counter is incriminated by one after each cycle. If the counter reaches a predetermined number of checks (235 lambda controller cycles) and the sum of all ratios determined is greater than a fixed value a fault will be stored in the computer memory. The monitoring procedure is then terminated until the engine is shut-off and started again.
- Monitoring Structure -
The catalyst monitoring functions are activated if the following conditions are fulfilled:
- Closed loop operation.
- Coolant temperature greater than 159°F (70.5°C).
- Vehicle speed between 3-75 mph.
- Catalyst temperature between 685-1162°F (353-628°C).
- Limited dynamics.
- Throttle angle less than 8.4 degrees.
- Engine speed less than 382 RPM.
- Mean lambda value less than 6 percent. See Fig 2.
- Temperature Model -
The statistical exhaust temperature as a function of air mass is stored in the ECM. For stationary operation there are the following values:
- Air mass: 10-250 kg/h
- Exhaust temperature: 246-1430°F (119-777°C)
- Block Diagram Of System -
See Fig 3.NOTE: The conversion efficiency of both catalyst systems (Cyl. 1-3 and Cyl. 4-6) are separately monitored.