Parameters and Conditions For Closed Loop Operation

.20.00.00 Parameters And Conditions For Closed Loop Operation

General
The highest conversion efficiency of the catalyst is given in a small window of air-fuel mixture close to the ratio of Lambda = 1. Therefore a combination of two (three for SULEV) control loops is used to achieve the conditions for highest conversion capability of the catalyst. The first control loop uses the signal of the first Oxygen sensor (pre catalyst) to correct the air fuel ratio by adjusting the injection time. The second and third control loop uses the signals of the middle (SULEV) and post catalyst Oxygen sensors. These control loops perform a fine-tuning of the air / fuel ratio to optimise the catalytic conversion.
The first control loop has a quicker response time than the post control loops, which are depending on the death time of the exhaust systems. Therefore the adjustment ranges for the post control loops are restricted and the response time is larger than the one of the first control loop.

Conditions for closed loop operation of the first control loop
The main condition for closed loop is a proper heated up Oxygen sensor and the dew point must be exceeded. To guaranty the Oxygen sensor readiness the heat-up strategy starts depending on engine temperature first on a low level of heater power. Upon the exhaust temperature reaches a level where no liquid water is expected to be in the exhaust system the heater power is controlled to achieve normal ceramic temperature of the Oxygen sensor. The ceramic temperature has to be >350 degrees C for binary and >685 degrees C linear sensors. Specific temperatures are mentioned in the individual summary tables of the concepts.
Additional heat-up of the Oxygen sensor is caused by the thermal energy of the exhaust gas. The engine management system evaluates permanently engine temperature and thermal energy introduced to calculate the exhaust temperature based on a model. The main value therefore is the integrated air mass after engine start. Upon the integrated air mass exceeds an applicable threshold, depending on engine start temperature, the due point is exceeded. In that case, the heater power will be increased until the sensor readiness is achieved and sensor is considered to be ready for closed loop control.

The criteria for sensor readiness of a binary sensor are:
- No fault from heater final stage check
- Sensor signal is out of a range 0,4V
- Heater power > 50% within a certain time (typically 8-10 s)

The criteria for sensor readiness of the linear are:
- No fault from LSU-Heater, LSU-Signals and LSU-IC
- LSU is heated up to a ceramic-temperature of > 685 Degrees C or the internal sensor resistor Ri < 130 Ohms.

Parameters evaluated to begin closed loop (first control loop)
The target is to begin closed loop operation in a very early state after engine start. However closed loop is delayed if engine is operated according the catalyst heat-up strategy. In the table below the importance parameters are listed.

Continuity of closed loop operation (first control loop)
The closed loop operation is the most dominant operation mode for the fuel system. Despite that fact, there are operating conditions of the engine where closed loop control must be temporary disabled.

Typical Values
Given a normal cold started FTP (around 20 degrees C) most of the concepts reaches the closed loop condition for the first control loop within 20s to 60s. Additionally closed loop is forced depending on engine start temperature after a maximum time.

Vehicles produced in MY 2004 and MY 2005

Engine Start Temperature Time, when closed loop is forced
Temperature> 10 Degrees C 120 s
Temperature >-6.7 Degrees C 300 s
and < 10 Degrees C