Diesel oxidation catalyst (DOC) temperature sensor rationality diagnostic

This application claims the benefit of U.S. Provisional Application No. 60/670,526, filed on Apr. 12, 2005. The disclosure of the above application is incorporated herein by reference.

The present invention relates to engine exhaust treatment systems, and more particularly to a temperature sensor rationality diagnostic for an exhaust treatment system including a diesel oxidation catalyst (DOC).

Diesel engines are internal combustion engines that combust an air and fuel mixture reciprocally drive pistons slidably disposed within cylinders producing drive torque. Diesel engines typically have a higher efficiency than gasoline engines due to the increased compression ratio of the diesel combustion process and the higher energy density of diesel fuel. Consequently, diesel engines commonly achieve better gas mileage than equivalently sized gasoline engines. Vehicle manufacturers incorporate emission control devices into the exhaust treatment systems of diesel engines to reduce emissions.

An exemplary exhaust treatment device includes a diesel oxidation catalyst (DOC). A DOC is an exhaust flow through device that includes a honey-comb formed substrate having a large surface area coated with a catalyst layer. The catalyst layer includes precious metals including, but not limited to, platinum and palladium. As the exhaust flows over the catalyst layer, carbon monoxide, gaseous hydrocarbons and liquid hydrocarbon particles are oxidized to reduce emissions.

The DOC may be adversely affected when the temperature of the exhaust exceeds a threshold. Inlet and outlet temperature sensors are typically associated with the DOC to monitor exhaust temperatures. Proper functioning of the temperature sensors is required to enable the vehicle control system to monitor exhaust temperature. Because the temperature sensors work over a large operating range (e.g., −40° C. to 800° C.) it has traditionally been difficult to ensure accuracy over the entire range.

Accordingly, the present invention provides a temperature sensor rationality control system for an exhaust treatment system having an oxidation catalyst. The temperature sensor rationality control system includes an oxidation catalyst inlet temperature sensor that generates an inlet temperature signal and an oxidation catalyst outlet temperature sensor that generates an outlet temperature signal. A control module determines whether a difference based on the inlet temperature signal and the outlet temperature signal is below a difference threshold when an exhaust temperature is within a threshold range.

In other features, the exhaust temperature is greater than the first threshold temperature and is less than the second threshold temperature when a plurality of vehicle operating parameters are within respective threshold ranges. The vehicle operating parameters include engine running time, current fuel rate, exhaust mass flow, engine RPM, coolant temperature and no DPF regeneration occurring. The exhaust temperature is greater than the first threshold temperature and is less than the second threshold temperature when a plurality of vehicle operating parameters are within the respective threshold ranges for a threshold period of time.

In another feature, the exhaust temperature is calculated based on at least one of an engine RPM, a primary fuel rate, an injection timing, a turbo boost level, a post fuel rate and an exhaust gas recirculation (EGR) value.

In still other features, the difference is determined based on a delayed inlet temperature value. The delayed inlet temperature value is determined based on at least one of a calibration factor, a previous delayed inlet temperature value and the inlet temperature signal. The calibration factor is determined from a look-up table based on an exhaust flow rate and a fueling rate.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of an engine system including an exhaust treatment system having a diesel oxidation catalyst (DOC) according to the present invention; and

FIG. 2 is a flowchart illustrating exemplary steps executed by the temperature sensor rationality control of the present invention.

The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.

Referring now to FIG. 1 , an exemplary vehicle 10 is illustrated including an engine 12 that drives a transmission 14 through a coupling device 16 (e.g., clutch, torque converter) and an exhaust treatment system 18 . More specifically, air is drawn into an intake manifold 20 through a throttle 22 . The intake manifold 20 distributes air into cylinders (not shown). The air is mixed with fuel and the air/fuel mixture is combusted within the cylinders to drive pistons (not shown), producing drive torque. Exhaust generated by the combustion process is exhausted from the engine 12 and into the exhaust treatment system 18 through an exhaust manifold 24 .

The exhaust treatment system 18 includes a diesel oxidation catalyst (DOC) 26 and a diesel particulate filter (DPF) 28 that reduce emissions. More specifically, a catalyst layer of the DOC 26 induces reaction of the exhaust once the DOC 26 has achieved a threshold or light-off temperature (T LO ). Carbon monoxide, gaseous hydrocarbons and liquid hydrocarbon particles are oxidized over the catalyst layer to reduce emissions. The DPF 28 traps soot particles therein preventing the soot from escaping to atmosphere. The DPF 28 periodically undergoes a regeneration process, whereby the soot trapped therein is burned off.

A control module 30 regulates operation of the engine and executes the temperature sensor rationality control of the present invention. More specifically, the control module 30 regulates engine fueling and the throttle 22 to achieve a desired engine torque output based on signals generated by various sensors, as described herein.

A manifold absolute pressure (MAP) sensor 32 disposed within the intake manifold is responsive to MAP and generates a MAP signal based therein. An engine speed sensor 34 generates an engine speed (RPM) signal and a coolant temperature 36 sensor generates a coolant temperature (T COOL ) signal. The exhaust treatment system 18 includes a DOC inlet temperature sensor 38 and a DOC outlet temperature sensor 40 . The inlet temperature sensor 38 generates an inlet temperature (T IN ) signal and the outlet temperature sensor 40 generates an outlet temperature (T OUT ) signal.

The temperature sensor rationality control of the present invention determines temperature accuracy after the exhaust temperature (T EXH ) has achieved a threshold temperature (T THR ) and is still below T LO . T EXH is determined based on engine operating conditions and/or a thermal model, as discussed in detail below. The thermal model compensates for the temperature difference (T DIFF ) between T IN and T OUT caused by the thermal capacity of the DOC 26 . More specifically, in order to compensate for the thermal capacity of the DOC 26 , T OUT is compared to a delayed T IN (T INDEL ). T INDEL is determined from the following relationship:

T INDEL ( k )= T INDEL ( k −1)×α+(1−α)× T IN

where k is the current time step, k−1 is the previous time step and α is a calibration factor determined from a look-up table based on an exhaust flow rate and a fueling rate.

The value of T EXH , relative to T THR and T LO , can be determined using various methods. In one method, engine operating parameters are compared to respective thresholds. If the engine operating parameters are each within their respective thresholds, T EXH is considered to be greater than T THR and less than T LO . If any of the engine operating parameters outside of their respective thresholds, T EXH is considered to be either less than T THR or greater than T LO . Exemplary engine operating conditions include, but are not limited to, engine running time, current fuel rate, exhaust mass flow, engine RPM, T COOL , no sensor faults indicated, no DPF regeneration occurring and whether each of these conditions are met for a threshold period of time. For example, if the engine running time (t RUN ) exceeds a threshold running time (t RUNTHR ), the current fueling rate (FR CURR ) is within a threshold fueling rate range defined by lower and upper fueling rate thresholds (FR LOTHR ,FR UPTHR ), an exhaust mass flow (m EXH ) is within a threshold mass flow range defined by lower and upper thresholds (m EXHLO ,m EXHUP ), the engine RPM is within a threshold range defined by lower and upper thresholds (RPM LOTHR ,RPM UPTHR ), T COOL is within a threshold range defined by lower and upper thresholds (T COOLLOTHR ,T COOLUPTHR ), there are no sensor faults, there is no DPF regeneration occurring and the operating conditions are within their respective threshold for a threshold time, T EXH is considered to be within the range defined between T THR and T LO .

It is alternatively anticipated that T EXH can be calculated as a function of engine operating conditions. Exemplary engine operating conditions include, but are not limited to, engine RPM, primary fuel rate, injection timing, turbo boost, post fuel rate, exhaust gas recirculation (EGR). An exemplary relationship is defined as:

T EXH =[f (RPM, FR PRIM , t INJ , boost, FR POST , EGR)+Offset]× k AMB ×k VEH

where Offset is a temperature offset based on a learned function of the outlet temperature sensor, k AMB is an ambient condition factor based on an ambient temperature and k VEH is a vehicle condition factor based on vehicle speed and exhaust architecture. It is anticipated that the relationship can be modified to provide a maximum T EXH (T EXHMAX ) and/or a minimum T EXH (T EXHMIN ).

The temperature rationality diagnostic control determines the accuracy of the temperature sensors 38 , 40 and can detect a failed sensor or unintended DOC reaction based on T DIFF . T IN and T OUT are compared to T EXH . If either T IN or T OUT are within a threshold range of T EXH , the sensors are operating normally. If either T IN or T OUT are outside of the threshold range of T EXH , the sensors are faulty. Alternatively, if T DIFF is below a threshold difference (T DIFFTHR ), the sensors are operating correctly. If T DIFF is below T DIFFTHR , the sensors are faulty.

Referring now to FIG. 2 , exemplary steps executed by the temperature sensor rationality control will be described in detail. In step 200 , control sets a fault count (FC) equal to zero. In step 202 , control determines whether test conditions are met. As described in detail above, the test conditions include T EXH being within a threshold range defined by T THR and T LO and/or engine operating conditions being met that would indicate T EXH is within the threshold range. If the test conditions are met, control continues in step 204 . If test conditions are not met, control loops back.

In step 204 , control determines T IN based on the inlet temperature sensor signal. In step 206 , control determines α based on exhaust flow rate and fueling rate. Control determines T INDEL based on T IN , a previous T INDEL and α in step 208 . In step 210 , control determines T DIFF as the absolute value of the difference of T INDEL and T OUT .

In step 212 , control determines whether T DIFF exceeds T DIFFTHR . If T DIFF exceeds T DIFFTHR , control continues in step 214 . If T DIFF does not exceed T DIFFTHR , control continues in step 216 . In step 214 , control increases FC. In step 218 , control determines whether FC exceeds a threshold FC (FC THR ). If FC exceeds FC THR , control sets a FAULT status in step 220 and control ends. If FC does not exceed FC THR , control continues in step 222 . Control determines whether a test time (t TEST ) exceeds a test time threshold (t THR ) in step 222 . If t TEST exceeds t THR , control sets a PASS status in step 224 and control ends. If t TEST does not exceed t THR , control loops back to step 202 .

Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.