Air driven reductant dosing system

Abstract

A dosing system for delivering reductant into an exhaust gas treatment system of an internal combustion engine using an air driven hydraulic pump, which includes a pressure pump tank and a liquid supply tank, for closed-loop controlling reductant pressure, and a three-stage PWM control method for dosing rate control. Reductant residue in the dosing system is purged by using compressed air, and when the air driven hydraulic pumps is positioned inside a reductant tank, heating means in the reductant tank can also be used for heating the air driven hydraulic pump. The closed-loop pressure control together with the three-stage PWM control allow dosing accuracy insensitive to pressure variations in compressed air, thereby a variety of compressed air sources can be used.

What is claimed is: 
     
         1 . An apparatus for delivering reductants into an exhaust gas system of an internal combustion engine comprising:
 a reductant tank;   a compressed air source;   a liquid supply tank having a first inlet port fluidly coupled to said reductant tank through a check valve, a second inlet port fluidly coupled to said compressed air source, a first outlet port for releasing compressed air from said liquid supply tank, and a second outlet port for reductant inside said liquid supply tank to flow out;   a pressure pump tank comprising a liquid inlet port fluidly coupled to said second outlet port of said liquid supply tank through a check valve, and a liquid outlet port;   an injector with a reductant inlet fluidly coupled to said liquid outlet port of said pressure pump tank for controlling reductant flow rate to said exhaust gas system;   a pressure control means controlling air flow to said liquid supply tank configured to control reductant pressure in said liquid supply tank by refilling air to said liquid supply tank through said second inlet port, and releasing air through said first outlet port,   and a dosing rate control means configured to energize open said injector for a period of time in a periodically repeating cycle in releasing reductant to said exhaust gas system.   
     
     
         2 . The apparatus of  claim 1 , wherein said pressure control is further configured to control reductant pressure in said liquid supply tank higher than that in said pressure pump tank in refilling said pressure pump tank, and configured to release air in said liquid supply tank in refilling said liquid supply tank. 
     
     
         3 . The apparatus of  claim 1 , further comprising:
 a pressure sensor for providing sensing values indicative to a reductant pressure in said pressure pump tank.   
     
     
         4 . The apparatus of  claim 3 , wherein said pressure control is further configured to control reductant pressure in said liquid supply tank according to at least said sensing values obtained from said pressure sensor. 
     
     
         5 . The apparatus of  claim 3 , wherein said pressure pump tank further comprises a gas inlet port fluidly coupled to said compressed air source and said pressure control is further configured to control reductant pressure in said pressure pump tank according to at least said sensing values obtained from said pressure sensor. 
     
     
         6 . The apparatus of  claim 5 , wherein said pressure pump tank further comprises a gas outlet for releasing air from said pressure pump tank. 
     
     
         7 . The apparatus of  claim 3 , wherein said dosing rate control means is further configured to energize said injector open for a period of time in a periodically repeating cycle according to at least said sensing values obtained from said pressure sensor. 
     
     
         8 . The apparatus of  claim 1 , further comprising:
 a fluid bypass path including a reductant passage and a control valve, wherein said fluid bypass path fluidly couples said reductant inlet of said injector to said reductant tank.   
     
     
         9 . The apparatus of  claim 8 , wherein said pressure control means is further configured to control reductant pressure in said pressure pump tank by opening said control valve in said fluid bypass path to release reductant from said pressure pump. 
     
     
         10 . A method for controlling reductant delivery rate of a reductant dosing system including a pressure pump tank with a liquid outlet port, an injector with a reductant inlet fluidly coupled to said liquid outlet port of said pressure pump tank, a pressure sensor for providing sensing values indicative to reductant pressure in said pressure pump tank, a first signal generator generating a first PWM signal, in a repeating cycle of which, a dosing target value is generated, a second signal generator generating a second PWM pulse signal, the duty cycle of which is determined by a second duty cycle value, and a third signal generator generating a third PWM signal for energizing and de-energizing said injector, comprising:
 calculating a dosing amount value indicative to an amount of reductant released in said repeating cycle of said first PWM signal after said injector is energized open, according to at least said sensing value obtained from said pressure sensor;   generating said second duty cycle value according to at least said dosing amount value and said dosing target value,   and setting duty cycle for said third PWM signal generator according to as least said second duty cycle value.   
     
     
         11 . The method of  claim 10 , further comprising:
 setting said second duty cycle value to a first value if a sum of said dosing amount value and a threshold, which is indicative to an amount of reductant released when said second duty cycle value is 100%, is lower than said dosing target value;   setting said second duty cycle value to a second value if the sum of said dosing amount value and said threshold is higher than said dosing target value, and said dosing amount value is lower than said dosing target value, and   setting said second duty cycle value to a third value if said dosing amount value is higher than said dosing target value.   
     
     
         12 . The method of  claim 10 , further comprising:
 at a moment in a repeating cycle of said first PWM signal, setting said third duty cycle value to a first value if a time period starting from a starting moment of said repeating cycle to said moment in said repeating cycle is shorter than a pre-determined threshold, and said second PWM signal is in its high state, otherwise, setting said third duty cycle value to a second value if said time period is longer than said pre-determined threshold, and said second PWM signal is in its high state, and setting said third duty cycle value to a third value if said second PWM signal is in its low state.   
     
     
         13 . A method for controlling a reductant dosing system including a reductant tank, a compressed air source, a liquid supply tank having a first inlet port fluidly coupled said reductant tank through a check valve, a second inlet port fluidly coupled to said compressed air source, a first outlet port for releasing compressed air from said liquid supply tank, and a second outlet port for reductant inside said liquid supply tank to flow out, a pressure pump tank comprising a liquid inlet port fluidly coupled to said second outlet port of said liquid supply tank through a check valve, and a liquid outlet port, a pressure sensor for providing sensing values indicative to reductant pressure in said pressure pump tank, and an injector with a reductant inlet fluidly coupled to said liquid outlet port of said pressure pump tank for controlling reductant flow rate to said exhaust gas system, comprising:
 releasing air in said liquid supply tank through said first outlet port to refill said liquid supply tank;   feeding compressed air into said liquid supply tank through said second inlet port to press reductant in said liquid supply tank into said pressure pump tank, and   energizing said injector open for a period of time in a periodically repeating cycle when said sensing values obtained from said pressure sensor are higher than a pre-determined threshold.   
     
     
         14 . The method of  claim 13 , wherein said pressure pump tank in said reductant dosing system further includes a gas inlet port fluidly coupled to said compressed air source. 
     
     
         15 . The method of  claim 14 , further comprising:
 feeding compressed air into said pressure pump tank through said gas inlet port to compensate air loss.   
     
     
         16 . The method of  claim 14 , wherein said pressure pump tank in said reductant dosing system further includes a gas outlet port for releasing air. 
     
     
         17 . The method of  claim 16 , further comprising:
 maintaining reductant pressure in said pressure pump tank within a pre-determined range by releasing air from said pressure pump tank through said gas outlet port and feeding compressed air into said pressure pump tank through said gas inlet port according to said sensing values obtained from said pressure sensor.   
     
     
         18 . The method of  claim 17 , wherein an upper limit of said pre-determined range is set lower than a pressure of said compressed air. 
     
     
         19 . The method of  claim 13 , wherein said reductant dosing system further comprises a fluid bypass path including a reductant passage and a control valve, wherein said fluid bypass path fluidly couples said reductant inlet of said injector to said reductant tank. 
     
     
         20 . The method of  claim 19 , further comprising:
 releasing reductant back to said reductant tank through said fluid bypass path by opening said control valve.