Vehicle oxidation catalyst efficiency model for adaptive control and diagnostics

A vehicle includes a fuel tank, an internal combustion engine, an oxidation catalyst, a regenerable particulate filter in fluid communication with an outlet side of the oxidation catalyst, and a host machine. The host machine calculates an actual hydrocarbon level in the exhaust stream downstream of the particulate filter as a function of an actual energy input value and an actual output value of the oxidation catalyst, and subsequently executes a control action using the actual hydrocarbon level. A method for use aboard the vehicle includes using the host machine to calculate an actual hydrocarbon level in the exhaust stream downstream of the particulate filter, including solving a function of an actual energy input value and an actual energy output value of the oxidation catalyst, and executing a control action aboard the vehicle via the host machine using the actual hydrocarbon level.

TECHNICAL FIELD

The present invention relates to oxidation catalyst systems of the type used aboard a vehicle.

BACKGROUND

Particulate filters capture and retain microscopic particles of soot, ash, metal, and other suspended matter generated during a fuel combustion process in a vehicle. However, over time the particulate matter accumulates within the filter media, which gradually increases the differential pressure across the filter. In order to extend the life of the filter and optimize engine functionality, some particulate filters can be regenerated using heat, which may be temporarily elevated to 450 degrees Celsius or higher via an injection of fuel into the exhaust stream upstream of the filter. The spike in heat is used in conjunction with a suitable catalyst, e.g., palladium or platinum, wherein the catalyst breaks down accumulated and suspended matter into relatively inert byproducts via a simple exothermic oxidation process.

SUMMARY

A vehicle as disclosed herein includes an internal combustion engine having an exhaust port, an oxidation catalyst in fluid communication with the engine via the exhaust port, a particulate filter, and a host machine. The oxidation catalyst receives an exhaust stream from the exhaust port. The particulate filter is in fluid communication with an outlet side of the oxidation catalyst, and is selectively regenerable using heat from the oxidation catalyst. The host machine calculates an actual hydrocarbon level in the exhaust stream downstream of the particulate filter as a function of an actual energy input and output value of the oxidation catalyst, and then executes a control action determined using the actual hydrocarbon level.

A fuel injection device may be used to selectively inject fuel into the oxidation catalyst, wherein the control action includes initiating feedback control over an operation of the fuel injection device. The host machine may use a temperature model to determine the specific heat value, and temperature signals from various temperature sensors to determine the temperature of the exhaust gas at various locations within the vehicle. The host machine compares the actual energy conversion efficiency to a calibrated threshold, and may generate a diagnostic code as at least part of the control action, with the diagnostic code indicating whether the actual energy conversion efficiency exceeds or does not exceed the threshold.

A system is also provided for use aboard the vehicle noted above. The system includes an oxidation catalyst and a particulate filter. The oxidation catalyst is in fluid communication with an exhaust port of the engine, and is adapted for receiving an exhaust stream from the engine via the exhaust port. The particulate filter is in fluid communication with an outlet side of the oxidation catalyst, and is regenerable using heat from the oxidation catalyst. A host machine calculates an actual hydrocarbon level in the exhaust stream downstream of the particulate filter as a function of actual energy input and output values of the oxidation catalyst, and for subsequently executing a control action using the actual hydrocarbon level, e.g., comparing the actual hydrocarbon level to a threshold, and generating a diagnostic code and/or executing closed or open loop control over the oxidation process.

A method is also provided for use aboard the vehicle noted above. The method includes using the host machine to calculate an actual hydrocarbon level in the exhaust stream downstream of the particulate filter, in part by solving a function of an actual energy input and output value of the oxidation catalyst. Additionally, the method includes executing a control action aboard the vehicle via the host machine using the actual hydrocarbon level.

DESCRIPTION

Referring to the drawings, wherein like reference numbers correspond to like or similar components throughout the several figures, a vehicle10is shown schematically inFIG. 1. Vehicle10includes a host machine40and a diagnostic algorithm100. Algorithm100may be selectively executed by host machine40in order to calculate the actual conversion efficiency of an oxidation catalyst (OC) system13aboard the vehicle10. Host machine40is thus operable for calculating, evaluating, and controlling actual hydrocarbon levels ultimately discharged from the vehicle10into the surrounding atmosphere, doing so in part using a temperature model50as described in further detail below with reference toFIG. 2.

Vehicle10includes an internal combustion engine12, such as a diesel engine or a direct injection gasoline engine, the OC system13, and a transmission14. Engine12combusts fuel16drawn from a fuel tank18. In one possible embodiment, the fuel16is diesel fuel, and the oxidation catalyst system13is a diesel oxidation catalyst (DOC) system, although other fuel types may be used depending on the design of the engine12.

A throttle20selectively admits a predetermined amount of the fuel16and air into the engine12as needed. Combustion of fuel16generates an exhaust stream22, which is ultimately discharged from vehicle10into the surrounding atmosphere. Energy released by the combustion of fuel16produces torque on an input member24of the transmission14. The transmission14in turn transfers the torque from engine12to an output member26in order to propel the vehicle10via a set of wheels28, only one of which is shown inFIG. 1for simplicity.

OC system13is in fluid communication with the exhaust port17of engine12, such that the OC system receives and conditions a fluid in the form of a gaseous exhaust stream22as it passes in a gaseous or vapor fluidic state from the exhaust ports17of engine12through the vehicle's exhaust system. OC system13includes an oxidation catalyst30, an optional selective catalytic reduction (SCR) device32, and a particulate filter34. Particulate filter34may be configured as ceramic foam, metal mesh, pelletized alumina, or any other temperature and application-suitable material(s).

The term “condition” as employed above refers to temperature control and/or regulation of the exhaust stream22at various positions within the OC system13. To that end, the particulate filter34is connected to or formed integrally with the oxidation catalyst30. A fuel injection device36is in electronic communication with host machine40via control signals15, and is in fluid communication with the fuel tank18. Fuel injection device36selectively injects fuel16into the oxidation catalyst30as determined by the host machine40. Fuel16injected into the oxidation catalyst30is burned therein in a controlled manner to generate heat sufficient for regenerating the particulate filter34.

That is, oxidation catalyst30acts in the presence of a controlled temperature of exhaust stream22to oxidize or burn any hydrocarbons that are introduced into the exhaust stream. This provides a sufficient temperature level in the particulate filter34for oxidizing particulate matter which has been trapped by the filter downstream of the oxidation catalyst30. The particulate filter34is thus kept relatively free of potentially-clogging particulate matter.

Still referring toFIG. 1, in some embodiments an optional selective catalytic reduction (SCR) device32may be positioned between the oxidation catalyst30and the particulate filter34. SCR device32is a selective catalytic reduction device or unit operable for converting nitrogen oxides (NOx) gasses into water and nitrogen as byproducts using an active catalyst. SCR device32may be configured as a ceramic brick or a ceramic honeycomb structure, a plate structure, or any other suitable design.

Vehicle10includes the host machine40, which monitors the ongoing operation of OC system13to ensure highly efficient hydrocarbon conversion. Host machine40calculates an actual conversion efficiency of the OC system13, and uses this result to calculate actual hydrocarbon emissions from the OC system. Host machine40can then compare the results to a calibrated regulatory or other threshold and execute a control action to reflect the result.

Host machine40may be configured as a digital computer acting as a vehicle controller, and/or as a proportional-integral-derivative (PID) controller device having a microprocessor or central processing unit (CPU), read-only memory (ROM), random access memory (RAM), electrically erasable programmable read only memory (EEPROM), a high-speed clock, analog-to-digital (A/D) and/or digital-to-analog (D/A) circuitry, and any required input/output circuitry and associated devices, as well as any required signal conditioning and/or signal buffering circuitry. Algorithm100and any required reference calibrations are stored within or readily accessed by host machine40to provide the functions described below with reference toFIG. 2.

Host machine40receives temperature signals11from various temperature sensors42positioned to measure exhaust temperatures at different locations within the OC system13, including directly downstream of the oxidation catalyst30and directly upstream of the particulate filter34. In one embodiment, a temperature sensor42is positioned in proximity to the engine12or the inlet side of the oxidation catalyst30, and adapted to measure or detect an inlet temperature into the oxidation catalyst30. Additional temperature sensors42detect a corresponding outlet temperature from the oxidation catalyst30, an inlet temperature to the particulate filter34, and an outlet temperature from the particulate filter34. These temperature signals11are each transmitted by or relayed from the temperature sensors42to the host machine40. Host machine40is also in communication with the engine12to receive feedback signals44that identify the operating point of engine12, such as the throttle position, engine speed, accelerator pedal position, fueling quantity, requested engine torque, etc.

As will be described immediately below with reference toFIG. 2, the algorithm100may be executed by host machine40in order to calculate the conversion efficiency of the OC system13described above. Host machine40uses a temperature model50stored in or accessible by host machine40, and a hydrocarbon injection rate at fuel injector device36provides a total energy input, i.e., heat and chemical energy input. By measuring the actual energy output, such as by measuring the heat exiting the DOC combined with information from the temperature model50, host machine40calculates the converted fuel energy, and from this result calculates the amount of unconverted fuel exiting vehicle10in the exhaust stream22. Host machine40can then compare the actual hydrocarbon values to a calibrated threshold, e.g., a regulatory standard limit, and can execute a control action suitable to the result.

Referring toFIG. 2, algorithm100begins with steps102and104simultaneously, wherein at step102the host machine40calculates a mass flow rate, which may be calculated by multiplying the known density (ρ) of the vapor comprising the exhaust stream22, its velocity (V), and the cross-sectional area (A) of flow, or by multiplying the density (ρ) by the volume flow rate (Q). At step104a temperature sensor42measures the outlet temperature of the oxidation catalyst30and communicates this value to the host machine40as one of the temperature signals11.

Host machine40may retrieve an exhaust specific heat value from the temperature model50, and may temporarily record this value in memory. At step104, the flow rate of the fuel16is communicated to the host machine40, e.g., as part of feedback signals44. The known energy content of this fuel16is determined, such as by accessing temperature model50or a lookup table. Once all of the required values are determined in steps102and104, the algorithm100proceeds to steps106and108.

At step106, the values determined at step102are used by the host machine40to calculate the energy rate output from the oxidation catalyst30. This value is integrated with respect to time, and the value stored in memory. The algorithm100then proceeds to step110.

At step108, the values determined at step104are used by the host machine40to calculate the energy rate input into the oxidation catalyst30. This value is integrated with respect to time, as with step106above, and the value stored in memory. The algorithm100then proceeds to step110.

At step110, the values from steps106and108are used by host machine40to calculate the overall conversion efficiency of the oxidation catalyst30. The calculated efficiency is then stored in memory for use at step112. Algorithm100then proceeds to step112.

At step112, the host machine40uses the actual efficiency determined at step110to calculate the actual levels of hydrocarbons in the exhaust stream22. That is, the host machine40executes steps102-110to determine the actual efficiency value, which can be used to calculate the unconverted energy. Knowing the energy content on the input side to the oxidation catalyst30, the mass outlet of hydrocarbons contained in the exhaust stream22is readily calculated. The algorithm100then proceeds to step114.

At step114, an appropriate control action is taken by the host machine in response to any of the values calculated in steps102-112. For example, the actual levels of hydrocarbons calculated at step112may be compared to a calibrated design threshold. When hydrocarbon levels are relatively high with respect to the threshold, a corrective action may be taken.

In one embodiment, the control action may be initiation of feedback control over the rate of hydrocarbon injection into the oxidation catalyst30, and thus of the temperature generated in the subsequent burn of the fuel therein, via control signals15communicated by the host machine40to the fuel injection device36shown inFIG. 1. Other control actions may include recording of a pass/fail diagnostic code, activation of an indicator lamp (not shown), or generation of a message, or any other action conveying the need for replacement or repair of the oxidation catalyst30and/or maintenance of and/or control modification to the OC system13.

Accordingly, the host machine40calculates the actual conversion efficiency of the OC system13using the heat and chemical energy rates being input into the oxidation catalyst30, and by comparing the expected exhaust heat energy increase, e.g., as calculated using temperature model50, to the exiting heat energy content. The ratio of actual energy input to actual energy output determines the efficiency, and this value can be used to trigger one or more control actions as set forth above.