Patent ID: 7462266
Filing Date: 2008-12-09
Classification: G01N

Abstract:
1. A nitrogen oxide concentration detection apparatus, comprising: a main body portion of a sensor having a first measurement chamber, a second measurement chamber, said first measurement chamber formed between a first oxygen pumping cell and an oxygen concentration measurement cell laminated with the first oxygen pumping cell, said first oxygen pumping cell being made of a first oxygen ion conducting solid electrolyte layer formed between porous electrodes, said oxygen concentration measurement cell comprising a second oxygen ion conducting solid electrolyte layer formed between porous electrodes, said first measurement chamber communicating via a first diffusion rate defining layer with a gas under measurement, said second measurement chamber formed between the oxygen concentration cell and a second oxygen pumping cell made of a third oxygen ion conducting solid electrolyte layer formed between porous electrodes, said second measurement chamber communicating with said first measurement chamber via a second diffusion rate defining layer filling a hole penetrating the second oxygen ion conducting solid electrolyte layer constituting said oxygen concentration measurement cell, said oxygen concentration measurement cell being formed as a lamination with the first and second oxygen pumping cells and disposed between said first and second measurement chambers and between said first and third oxygen ion conducting solid electrolyte layers; a pump current controller for pumping out oxygen from said first measurement chamber by said first oxygen pumping cell so that an output voltage of said oxygen concentration measurement cell will be constant, to control the oxygen concentration in said first measurement chamber to a constant value; a constant voltage applying unit for applying a constant voltage to said second oxygen pumping cell so as to decompose NOx components of an oxygen-pumped out gas flowed from the first measurement chamber and to pump out oxygen decomposed from the NOx components from the second measurement chamber through said third oxygen ion conducting solid electrolyte layer constituting said second oxygen pumping cell; a nitrogen oxide concentration detector for detecting a concentration of nitrogen oxides in the gas under measurement based on the current value flowing in said second oxygen pumping cell on application of said constant voltage; a heater for heating said main body portion of the sensor to a temperature capable of detecting the nitrogen oxide concentration, said heater being formed as a lamination and configured to heat the second oxygen pumping cell and the second measurement chamber and then to heat the first measurement chamber, wherein the first oxygen pumping cell, the oxygen concentration measurement cell and the second oxygen pumping cell are positioned transverse to the lamination and wherein the second oxygen ion conducting solid electrolyte layer constituting the oxygen concentration measurement cell is located between the first and second measurement chambers; a temperature detector for detecting a temperature of the oxygen concentration measurement cell by detecting an internal resistance of said oxygen concentration measurement cell, the temperature detector being configured to stop current supply control for the first oxygen pumping cell during temperature detecting; and a heater current controller for controlling a current supply to said heater so that the temperature of the oxygen concentration measurement cell detected by said temperature detector will be a pre-set target temperature so that the detected internal resistance of said oxygen concentration measurement cell will be of a value corresponding to said target temperature.