Method for heating an scr system using two resistive heating elements

Abstract

Method for heating an SCR system using at least two resistive heating elements, according to which each of these resistive elements is powered by a PWM signal, the two PWM signals being at least partly in phase opposition.

1 . A method for heating an SCR system, the method comprising:
 powering at least two resistive heating elements, wherein each of these resistive elements is powered by a PWM signal comprising power pulses and having a given duty cycle, the two PWM signals being at least partly in phase opposition.   
     
     
         2 . The method of  claim 1 , wherein the heating elements are metallic heating wires attached inside an injection molded shell, which is part of a urea tank. 
     
     
         3 . The method of  claim 2 , wherein the shell comprises a pump and wherein one of the heating wires is fixed in the neighborhood of the pump. 
     
     
         4 . The method of  claim 1 , wherein at least one temperature sensor is employed and if this sensor detects a temperature less than or equal to a threshold value, at least one of the heaters is powered and thereafter or at the same time, the second one is powered too, but with a PWM signal being at least partly in phase opposition with the PWM signal of the first heater whenever possible depending on the heating conditions. 
     
     
         5 . The method of  claim 1 , wherein an overlap between the power pulses of both PWM signals is optimized as a function of the respective duty cycles (heating conditions). 
     
     
         6 . The method of  claim 1 , wherein a time shift is introduced between the switching on and off of both heaters during each period of the PWM signal. 
     
     
         7 . The method according to any of the of  claim 1 , being applied to a urea tank of a vehicle comprising a battery, wherein the duty cycle of each heater is a function of the power supply voltage received from the battery, and is adapted for each heater according to the temperature and a urea level in the tank. 
     
     
         8 . The method of  claim 7 , wherein an electronic control unit (ECU) is employed to specifically activate/deactivate each of the heaters as a function of information received from sensor(s) and of the power (voltage) available on the battery.