Urea solution injection device

Abstract

The purpose of the present invention is to provide an exhaust purification device that is capable of adding an appropriate amount of urea solution without the need to directly measure the NOx emissions amount using an NOx measuring means. The exhaust purification device uses urea solution as a reducing agent for reducing nitrogen oxides within exhaust, and is provided with a temperature sensor, a humidity sensor, and a control device. A map is stored in the control device, and in said map the real NOx emissions amount for each rotation speed and each load of an engine occurring at a predetermined air temperature and a predetermined absolute humidity are converted using a correction formula into a reference NOx emissions amount for each rotation speed and each load of the engine while in a standard state. Using the map, the control device calculates a reference NOx emissions amount that corresponds to the rotation speed detected by a rotation speed sensor and to the load detected by a load sensor, uses the correction formula to convert the reference NOx emissions amount into the real NOx emissions amount occurring at an air temperature and an absolute humidity, and calculates a urea solution addition amount.

1 . An urea solution injection device of an exhaust purification device in which an urea solution is added as a reducing agent to exhaust gas of an internal combustion engine so as to reduce nitrogen oxide in the exhaust gas, comprising:
 a temperature sensor detecting a temperature of atmosphere;   a humidity sensor detecting an absolute humidity or a relative humidity of the atmosphere; and   a control device calculating an addition amount of the urea solution,   characterized in that   a map, which converts an actual NOx discharge amount of the internal combustion engine driven with each rotation speed and each load under predetermined temperature and absolute humidity of the atmosphere into the standard NOx discharge amount of the internal combustion engine with each rotation speed and each load under standard conditions with a correction formula is stored in the control device,   a rotation speed detection means detecting the rotation speed of the internal combustion engine and a load detection means detecting the load of the internal combustion engine are connected to the control device, and   the standard NOx discharge amount corresponding to the rotation speed detected by the rotation speed detection means and the load detected by the load detection means is calculated with the map, the standard NOx discharge amount is converted into the actual NOx discharge amount of the rotation speed and the load under the temperature of the atmosphere detected by the temperature sensor and the absolute humidity of the atmosphere detected by the humidity sensor with the correction formula by inverse operation, and the addition amount of the urea solution is calculated based on the actual NOx discharge amount.   
     
     
         2 . The urea solution injection device according to  claim 1 , wherein the addition amount is calculated in consideration of a target purification rate and a concentration of the urea solution.