A variety of emissions, such as nitrogen oxides (e.g., NO and NO2), are emitted in exhaust gases of internal combustion engines. In order to decrease emissions from motor vehicles, emissions are regulated via use of exhaust system components, such as catalytic converters. Additionally, various gas sensors, including NOx sensors, are employed to detect the emissions in exhaust gases.
During operation, accurate measurement of NOx in the exhaust gases may depend on temperature control of a NOx sensor. U.S. Pat. No. 6,228,252 describes a method to correct NOx concentration measurement of a NOx sensor via temperature detection of the sensor. In the cited reference, temperature detection of the NOx sensor is implemented by measuring internal resistance of a gas concentration measurement cell, as internal resistance is temperature dependent. Depending on a measured offset of the NOx sensor temperature from a target temperature, the NOx concentration measurement may be adjusted. An offset from the target temperature of the sensor may occur, for example, due to a sudden change in the temperature of the exhaust gases. Thus, temperature of a NOx sensor may be detected and, in the event of an offset, the NOx measurement may be corrected without additional temperature sensing components.
In the event of cold start of a motor vehicle, a NOx sensor operates accurately after it warms-up and reaches an activation temperature, sometimes referred to as a light-off temperature, before it can accurately measure the amount of NOx contained in the emissions. During the warm-up period, which can have a duration of up to several hundred seconds, the NOx concentration measurements may be affected by an initial (e.g., ambient) temperature of the sensor causing an erroneous NOx reading. As such, the NOx sensor reading is generally ignored during this time. The above reference, while addressing temperature variation of the sensor during operation, fails to address the ambient temperature detection affect on the sensor during warm-up.
The inventor herein has recognized the above problems and has devised an approach to address them. Thus, a method for adjusting the NOx measurement of a NOx sensor in response to the ambient temperature is disclosed. The method comprises adjusting an engine operating condition in response to a NOx indicative reading of the NOx sensor, the NOx indicative reading being compensated for ambient temperature effects on the NOx sensor. In this manner, the effect of ambient temperature on the NOx readings of a NOx sensor may be reduced during warm-up of the sensor and it may be possible to obtain accurate NOx readings during the sensor warm-up.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.