Optimized discrete level sensing system for vehicle reductant reservoir

Abstract

An example emissions-control system of a vehicle includes a reservoir configured to contain a reductant solution, and an SCR device disposed in the exhaust system and configured to consume the reductant solution. The example emissions-control system further includes a base sensor responsive to whether a volume of the reductant solution exceeds a base volume, wherein the base volume is a sum of a dead volume of the reservoir plus a standard volume, and one or more elevated sensors corresponding to one or more elevated volumes. The example emissions-control system further includes an emissions sensor responsive to a NOX level in the exhaust system, and a misformulation indicator operatively coupled to the emissions sensor and to at least one of the base sensor and an elevated sensor, and configured to indicate when an excess NOX emission follows, within an interval, an increase in the volume of the reductant solution above the base volume or an elevated volume. The example emissions-control system may further include an insufficiency indicator operatively coupled to the base volume sensor and configured to indicate when the volume of the reductant solution becomes less than the base volume.

1 . A method of evaluating a reductant solution stored on-board a vehicle in a reservoir, the vehicle having a reductant-delivery system for delivering the reductant solution to an SCR device in an exhaust system of the vehicle, the method comprising:
 varying a reductant-solution delivery rate in response to a reductant-solution concentration to maintain emissions-control performance;   distinguishing misformulation of the reductant solution from other emissions-control system errors based on a volume change in the reservoir in combination with an emissions-control performance assay.   
   
   
       2 . The method of  claim 1 , wherein the reductant-solution delivery rate is varied among a plurality of rates, which include a nominal rate and a maximum rate greater than the nominal rate. 
   
   
       3 . The method of  claim 2 , wherein misformulation of the reductant solution is indicated when an excess NOX emission occurs within an interval following the volume change, the interval including a time to deplete and refill a nominal operating amount of ammonia in the SCR device. 
   
   
       4 . The method of  claim 2 , wherein the volume change comprises an increase in the volume of liquid in the reservoir above at least one of a base volume and an elevated volume, where the base volume is greater than a dead volume of the reservoir, and the elevated volume is a product of the base volume times a positive-integer exponentiated ratio of the maximum rate to the nominal rate. 
   
   
       5 . The method of  claim 2 , wherein the base volume is a sum of the dead volume of the reservoir plus a standard volume, and the standard volume is a volume of reductant solution in a purchasable container of reductant solution appropriately matched to the SCR device. 
   
   
       6 . The method of  claim 2 , wherein maximum rate is substantially twice the nominal rate. 
   
   
       7 . An emissions-control system operatively coupled to an exhaust system of a vehicle, the emissions-control system comprising:
 a reservoir configured to contain a liquid;   an SCR device disposed in the exhaust system;   a reductant-delivery system configured to draw the liquid from the reservoir at a nominal rate and at a maximum rate, greater than the nominal rate, and further configured to pump the liquid to the SCR device;   a base sensor responsive to whether a volume of liquid in the reservoir exceeds a base volume greater than a dead volume of the reservoir;   an elevated sensor responsive to whether the volume of liquid in the reservoir exceeds an elevated volume, where the elevated volume is a product of the base volume times a ratio of the maximum rate to the nominal rate;   an emissions sensor responsive to a NOX level in the exhaust-system; and   a misformulation indicator operatively coupled to the emissions sensor and to at least one of the base sensor and the elevated sensor, and configured to indicate when an excess NOX emission follows, within an interval, an increase in the volume of liquid in the reservoir above at least one of the base volume and the elevated volume.   
   
   
       8 . The emissions-control system of  claim 7 , wherein the liquid comprises a reductant solution appropriately matched to the SCR device. 
   
   
       9 . The emissions-control system of  claim 7 , further comprising an insufficiency indicator operatively coupled to the base sensor and configured to indicate when the volume of liquid in the reservoir falls below the base volume. 
   
   
       10 . The emissions-control system of  claim 7 , where the elevated sensor is one in a series of elevated sensors corresponding to a series of elevated volumes, wherein each elevated volume E i  is given by E i =B×R i , where B is the base volume, R is a ratio of the maximum rate to the nominal rate, i is an integer greater than zero, where each elevated sensor is responsive to whether the volume of liquid in the reservoir exceeds a corresponding elevated volume; and
 where the misformulation indicator is further configured to indicate when an excess NOX emission follows, within the interval, an increase in the volume of liquid in the reservoir above any elevated volume in the series of elevated volumes.   
   
   
       11 . The emissions-control system of  claim 7 , wherein the base sensor is responsive to whether a level of liquid in the reservoir approaches a threshold level to within a tolerance interval, where the base volume B is related to the threshold level Lo according to 
     
       
         
           
             
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     where S(h) is a surface area of the liquid in the reservoir when a surface of the liquid is a height h above a lowest point inside the reservoir. 
   
   
       12 . The emissions-control system of  claim 11 , wherein the tolerance interval is not symmetric about the threshold level. 
   
   
       13 . The emissions-control system of  claim 11 , wherein the tolerance interval is chosen such that a response of the base sensor to an addition of the standard volume of liquid to the reservoir, when the volume of liquid in the reservoir is initially below the base volume, occurs statistically at a 3σ level, based on expected operating conditions of the vehicle. 
   
   
       14 . The emissions-control system of  claim 7 , wherein the elevated sensor is responsive to whether a level of liquid in the reservoir approaches a threshold level to within a tolerance interval, where the elevated volume E i  is related to the threshold level L i  according to 
     
       
         
           
             
               
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     where S(h) is a surface area of the liquid in the reservoir when a surface of the liquid is a height h above a lowest point inside the reservoir. 
   
   
       15 . A method to detect at least one of an insufficient reductant solution and a misformulated reductant solution in vehicle, the method comprising:
 containing the reductant solution in a reservoir equipped with a level-sensing system, comprising:
 a base sensor responsive to whether a volume of liquid in the reservoir exceeds a base volume, where the base volume is a sum of a dead volume of the reservoir plus a standard volume, and 
 a series of elevated sensors corresponding to a series of elevated volumes, wherein each elevated volume is a product of the base volume times a positive integer power of two, and wherein each elevated sensor is responsive to whether the volume of liquid in the reservoir exceeds a corresponding elevated volume; 
   indicating that the reductant solution is insufficient when the volume of liquid in the reservoir becomes less than the base volume; and   indicating that the reductant solution is misformulated when an excess NOX emission follows, within an interval, an increase in the volume of liquid in the reservoir above any elevated volume in the series of elevated volumes.   
   
   
       16 . The method of  claim 15 , wherein the excess NOX emission includes a NOX level failing to respond expectedly to an increasing rate of withdrawal of reductant solution from the reservoir. 
   
   
       17 . The method of  claim 15 , further comprising initiating a warning chain when the volume of liquid in the reservoir becomes less than the base volume. 
   
   
       18 . The method of  claim 15 , further comprising applying other diagnostics when the excess NOX emission is detected, but does not follow, within the interval, an increase in the volume of liquid in the reservoir above any elevated volume in the series of elevated volumes. 
   
   
       19 . The method of  claim 15 , further indicating that reductant solution has been added to the reservoir when the volume of liquid in the reservoir exceeds the base volume. 
   
   
       20 . The method of  claim 19 , further comprising suspending the warning chain when the volume of liquid in the reservoir exceeds the base volume.