Patent Application
20120222399
The invention generally relates to a method of operating a vehicle, and more specifically to a method of controlling an exhaust gas treatment system for an engine of the vehicle.
Exhaust gas treatment systems for internal combustion engines may include an oxidation catalyst for treating a flow of exhaust gas from the engine. If the internal combustion engine is a diesel engine, then the oxidation catalyst may be referred to as a Diesel Oxidation Catalyst (DOC). The oxidation catalyst is a flow through device that consists of a canister containing a substrate or honeycomb-like structure. The substrate has a large surface area that is coated with an active catalyst layer. As the exhaust gases traverse the active catalyst layer, carbon monoxide, gaseous hydrocarbons and liquid hydrocarbon particles, i.e., unburned fuel and/or oil, are oxidized, thereby reducing harmful emissions.
However, in order for the active catalyst layer to oxidize the carbon monoxide, gaseous hydrocarbons and liquid hydrocarbon particles, the active catalyst layer must be at or above a light-off temperature. Often, once the active catalyst layer reaches the light-off temperature, additional hydrocarbons are injected into the flow of exhaust gas through either late post fuel injection or a hydrocarbon injector. The additional hydrocarbons injected into the flow of exhaust gas may be ignited to further heat the flow of exhaust gas.
The performance of the oxidation catalyst degrades over time with usage of the vehicle due to the loss of the active catalyst material and/or sintering caused by high exhaust gas temperatures. This degradation may cause an increase in the light-off temperature, which may lead to quenching of the oxidation catalyst. Quenching of the oxidation catalyst is defined as the cessation of hydrocarbon oxidation that occurs when the temperature of the active catalyst layer decreases below the light-off temperature. Quenching of the oxidation catalyst may cause excessive hydrocarbons to slip past the oxidation catalyst, thereby reducing the performance of the exhaust gas treatment system, or may result in collection of hydrocarbons on the substrate of the oxidation catalyst, which may lead to excessive temperatures once the light-off temperature is reached and the collected hydrocarbons begin to oxidize.
A method of operating a vehicle is provided. The method includes tracking a usage of an oxidation catalyst, and relating the tracked usage of the oxidation catalyst to a temperature offset value. A current burn threshold temperature is adjusted by the temperature offset value to define an adjusted burn threshold temperature. Hydrocarbons are injected into a flow of exhaust gas when a temperature of the oxidation catalyst is equal to or greater than the adjusted burn threshold temperature to regenerate the oxidation catalyst.
A method of controlling an exhaust gas treatment system of a vehicle having an engine is also provided. The method includes tracking a usage of an oxidation catalyst, and relating the tracked usage of the oxidation catalyst to a temperature offset value. A current burn threshold temperature is adjusted by the temperature offset value to define an adjusted burn threshold temperature. The method further includes detecting a request to regenerate the oxidation catalyst. A temperature of the flow of exhaust gas is sensed to determine if the temperature of the flow of exhaust gas is equal to or greater than the adjusted burn threshold temperature. Hydrocarbons are injected into a flow of exhaust gas when a temperature of the oxidation catalyst is equal to or greater than the adjusted burn threshold temperature to regenerate the oxidation catalyst. The method further includes identifying when the temperature of the oxidation catalyst drops below the adjusted burn threshold temperature to detect when the oxidation catalyst is quenched, and stopping the injection of hydrocarbons into the flow of the exhaust gas when the oxidation catalyst is quenched. The adjusted burn threshold temperature is compared to a maximum burn threshold temperature to determine if the adjusted burn threshold temperature is less than or equal to the maximum burn threshold temperature. A number of occurrences the oxidation catalyst is determined to be quenched at the adjusted burn threshold temperature is tracked. The adjusted burn threshold temperature is permanently increased when the number of occurrences is greater than a pre-defined limit and the adjusted burn threshold temperature is less than the maximum burn threshold temperature.
Accordingly, by gradually increasing the temperature at which the hydrocarbons are injected into the flow of exhaust gas in relation to the degradation of the oxidation catalyst, i.e., the adjusted burn threshold temperature, the oxidation catalyst may not become quenched. Preventing the oxidation catalyst from becoming quenched helps avoid extreme temperatures and/or temperature gradients across the oxidation catalyst and/or other components of the exhaust gas treatment system downstream of the oxidation catalyst. This extends the useful life of the oxidation catalyst and/or the other components of the exhaust gas treatment system as the performance of the oxidation catalyst degrades.
The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.
Referring to
The exhaust gas treatment system includes an oxidation catalyst. If the engine is a diesel engine, then the oxidation catalyst may be referred to as a Diesel Oxidation Catalyst (DOC). The oxidation catalyst is a flow through device that consists of a canister containing a substrate or honeycomb-like structure. The substrate has a large surface area that is coated with an active catalyst layer. The oxidation catalyst treats the flow of exhaust gas from the engine to reduce the toxicity of the exhaust gas, i.e., to reduce toxic emissions of the exhaust gas, including but not limited to, nitrogen oxides (NO), carbon monoxide (CO) and/or hydrocarbons (HC). As the exhaust gases traverse the active catalyst layer, carbon monoxide, gaseous hydrocarbons and liquid hydrocarbon particles, i.e., unburned fuel and/or oil, are oxidized, thereby reducing harmful emissions. The active catalyst material may include Platinum Group Metals (PGM), and convert a percentage of the nitrogen oxides in the exhaust gas into nitrogen and carbon dioxide or water, as well as oxidizes a percentage of the carbon monoxide to carbon dioxide and oxidizes a percentage of the unburnt hydrocarbons to carbon dioxide and water.
The active catalyst layer must be heated to a light-off temperature of the catalyst before the active catalyst layer becomes operational and oxidizes the nitrogen oxides, the carbon monoxide and the unburnt hydrocarbons. Accordingly, the exhaust gas must heat the active catalyst layer to the light-off temperature before the reaction between the active catalyst layer and the exhaust gas begins. In order to rapidly heat the oxidation catalyst and/or other components of the exhaust gas treatment system, including but not limited to a particulate filter and/or a selective catalytic reduction unit, hydrocarbons may be injected into the flow of exhaust gas. The hydrocarbons are ignited to generate heat within the exhaust gas, which is transferred to the oxidation catalyst and/or the other components of the exhaust gas treatment system. The hydrocarbons may be injected through a late post injection process or through a hydrocarbon injector. The hydrocarbons are injected after the oxidation catalyst has reached a burn threshold temperature, which is greater than the light-off temperature, to ensure that the injected hydrocarbons are oxidized across the active catalyst layer.
The performance of the oxidation catalyst degrades or lessens with usage due to loss of catalyst material from the active catalyst layer, and also due to sintering of the substrate. As the oxidation catalyst degrades with usage, the light-off temperature of the oxidation catalyst increases. If the light-off temperature of the oxidation catalyst increases to a temperature above the burn threshold temperature, the hydrocarbons would slip through the oxidation catalyst and/or become trapped on the substrate of the oxidation catalyst without oxidizing. To avoid this situation, the method 20 described herein increases the burn threshold temperature in accordance with the usage of the oxidation catalyst to accommodate the decreased performance and the increased light-off temperature of the oxidation catalyst, thereby ensuring that the hydrocarbons are not injected into the exhaust gas when the oxidation catalyst is not at the light-off temperature.
The method 20 includes tracking a usage of the oxidation catalyst, generally indicated by box 22, over the lifetime of the exhaust gas treatment system. Tracking the usage of the oxidation catalyst may include but is not limited to tracking a total mileage of the vehicle, tracking an operating temperature history of the oxidation catalyst during the usage of the vehicle, or tracking a period of time the oxidation catalyst is operating within each of a plurality of pre-defined temperature ranges. Accordingly, the amount of time the oxidation catalyst is operating within each specific temperature range may be tracked. The oxidation catalyst may degrade faster when operated at higher temperatures for longer periods of time. As such, tracking the different operating conditions in which the oxidation catalyst operates provides a more accurate estimation of the degradation of the oxidation catalyst, thereby providing a more accurate estimate to correct therefore.
The tracked usage of the oxidation catalyst is related to a temperature offset value, generally indicated by box 24. The temperature offset value is a temperature value that is related to, i.e., associated with, the degree or level of degradation predicted to have occurred in the oxidation catalyst for any given amount of usage. The temperature offset value may be determined and/or associated with degrees of degradation found in the oxidation catalyst through testing or modeling of the exhaust gas treatment system. Relating the tracked usage of the oxidation catalyst to the temperature offset value may include but is not limited to referencing a relationship relating the temperature offset value to at least one of the total mileage of the vehicle, the operating temperature history of the oxidation catalyst or the time the oxidation catalyst is operated within the pre-defined temperature ranges. The relationship may be referenced, for example, through a look-up table or by solving an equation relating the temperature offset value to at least one of the total mileage of the vehicle, the operating temperature history of the oxidation catalyst or the time the oxidation catalyst is operated within the pre-defined temperature ranges.
The method 20 further includes adjusting a current burn threshold temperature, generally indicated by box 26, by the temperature offset value to define an adjusted burn threshold temperature. The current burn threshold temperature is adjusted by adding the temperature offset value to the current burn threshold temperature. Accordingly, because the temperature offset value accounts for the decrease in performance of the oxidation catalyst, adding the temperature offset value to the current burn threshold temperature increases the temperature at which the hydrocarbons are injected into the exhaust gas, thereby decreasing the possibility that the increased light-off temperature of the oxidation catalyst associated with the degradation of the oxidation catalyst does not rise above the burn threshold temperature.
This process is continuously followed throughout the lifetime of the vehicle until a maximum burn threshold temperature is reached. Accordingly, the adjusted burn threshold temperature may be defined as a revised current burn threshold temperature, and then re-adjusting by the temperature offset value to define a re-adjusted burn threshold temperature. It should be appreciated that the temperature offset value continuously changes in accordance with the usage of the vehicle. As such, as the oxidation catalyst continues to degrade, the temperature offset value continues to increase in value until the adjusted burn threshold temperature equals the maximum burn threshold temperature.
The method 20 further includes detecting a request to regenerate the oxidation catalyst, generally indicated by box 28. The request to regenerate the oxidation catalyst may come from a vehicle controller or the like. The request to regenerate the oxidation catalyst triggers the exhaust gas treatment system to inject the hydrocarbons into the exhaust gas to heat the oxidation catalyst to burn off particles trapped thereon.
The method 20 further includes sensing a temperature of the flow of exhaust gas, generally indicated by box 30, to determine if the temperature of the flow of exhaust gas is equal to or greater than the adjusted burn threshold temperature. The temperature of the exhaust gas may be sensed upstream and downstream of the oxidation catalyst, and the difference therebetween used to determine the temperature of the oxidation catalyst.
Once the vehicle has determined that the oxidation catalyst is at a temperature equal to or greater than the adjusted burn threshold limit, the method 20 further includes injecting the hydrocarbons, generally indicated by box 32, into the flow of exhaust gas. As described above, the hydrocarbons may be injected through a post late injection process, which injects the hydrocarbons into the exhaust gas within a cylinder bore of the engine, or through a hydrocarbon injector which injects the hydrocarbons into the exhaust gas downstream of the engine and upstream of the oxidation catalyst.
The method 20 further includes detecting when the oxidation catalyst is quenched, generally indicated by box 34. The oxidation catalyst is quenched when the temperature of the active catalyst layer decreases below the light-off temperature causing the cessation of hydrocarbon. Detecting when the oxidation catalyst is quenched includes identifying when the temperature of the oxidation catalyst drops below the adjusted burn threshold temperature. The sensed temperature of the exhaust gas upstream and downstream of the oxidation catalyst may be used to identify or determine when the temperature of the oxidation catalyst drops below the adjusted burn threshold temperature.
If it is determined that the temperature of the oxidation catalyst has dropped below the adjusted burn threshold temperature and the oxidation catalyst is now quenched, then the method 20 further includes stopping the injection of hydrocarbons, generally indicated by box 36, into the flow of the exhaust gas. The injection of hydrocarbons into the flow of exhaust gas prevents the hydrocarbons from slipping past the oxidation catalyst and/or accumulating on the substrate of the oxidation catalyst.
If the injection of the hydrocarbons into the flow of exhaust gas is stopped, then the method 20 may further include comparing the adjusted burn threshold temperature to the maximum burn threshold temperature, generally indicated by box 38, to determine if the adjusted burn threshold temperature is less than or equal to the maximum burn threshold temperature. If the adjusted burn threshold temperature is less than the maximum burn threshold temperature, generally indicated at 40, then the method 20 may include temporarily increasing the adjusted burn threshold temperature, generally indicated by box 42, to complete regeneration cycle of the oxidation catalyst. If the adjusted burn threshold temperature is equal to or greater than the maximum burn threshold temperature, generally indicated at 44, then no action is taken, generally indicated by box 46.
When the adjusted burn threshold temperature is less than the maximum burn threshold temperature, generally indicated at 48, the vehicle may track a number of occurrences, generally indicated by box 50, in which the oxidation catalyst is determined to be quenched at the adjusted burn threshold temperature. The tracked number of occurrences in which the oxidation catalyst is determined to be quenched is compared to a pre-defined limit, generally indicated by box 52, to determine if the number of occurrences is greater than the pre-defined limit, indicating that the light-off temperature of the oxidation catalyst has increased above the current burn threshold. If the number of occurrences is greater than the pre-defined limit, generally indicated at 54, then the method 20 may further include permanently increasing the adjusted burn threshold temperature, generally indicated by box 56, even though the usage of the vehicle does not dictate the increase in the burn threshold temperature. If the number of occurrences is less than the pre-defined limit, generally indicated at 58, then once the vehicle determines that the oxidation catalyst is at a temperature equal to or greater than the adjusted burn threshold limit, generally indicated by box 30, the vehicle restarts the injection of the hydrocarbons, generally indicated by box 32, into the flow of exhaust gas, and the process is repeated.
While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.
