Patent Application
20120023903
The present invention relates to an apparatus and method for monitoring the regeneration frequency of a particulate filter adapted for removing soot from a vehicle exhaust stream.
Particulate filters are designed to remove microscopic particles of soot, ash, metal, and other suspended matter from an exhaust stream of a vehicle. Over time, the particulate matter accumulates on a substrate within the filter. In order to extend the life of the particulate filter and to further optimize engine functionality, some filters are designed to be selectively regenerated using heat.
Temperatures within the particulate filter can be temporarily increased to between approximately 450° C. to 600° C. by directly injecting and igniting fuel, either in the engine's cylinder chambers or in the exhaust stream upstream of the filter. The spike in exhaust gas temperature may be used in conjunction with a suitable catalyst, e.g., palladium or platinum, wherein the catalyst and heat act together to reduce the accumulated particulate matter to relatively inert carbon soot via a simple exothermic oxidation process.
A vehicle as disclosed herein includes an engine, a particulate filter that is regenerable using heat, and a host machine. The host machine accesses a first soot model to determine an actual soot mass in the particulate filter, e.g., a lookup table indexed by a calculated or measured differential pressure across the filter, and a second soot model to determine a modeled soot mass in the filter. The second soot model provides the modeled soot mass relative to a set of current vehicle operating points or conditions. The host machine then calculates a ratio of a change in the actual soot mass to a change in the modeled soot mass. The host machine compares the calculated ratio to a calibrated threshold, and automatically executes a control action when the calculated ratio exceeds the calibrated threshold.
The method may be embodied as an algorithm executable by the host machine. By executing the algorithm as disclosed herein, the host machine can account for varying filter regeneration trigger points, i.e., sets of generated or related signals initiating a heat-based regeneration of the particulate filter. The host machine can also account for the varying soot masses remaining in the particulate filter subsequent to an immediately prior filter regeneration event.
Suitable control actions may include setting a first diagnostic code when the calculated ratio exceeds the calibrated threshold, activating an indicator device, transmitting a message, etc. As the actual and modeled soot values can vary with vehicle operating conditions, conventional monitoring methods that set an arbitrary threshold to cover a worst case scenario may be less than optimal. The present method may therefore improve the robustness of any regeneration frequency monitoring algorithm.
A system is also provided for use aboard the vehicle noted above. The system includes a host machine and a particulate filter, which is regenerable using heat. The host machine accesses a first soot model which provides an actual soot mass remaining in the particulate filter, and a second soot model which provides a modeled soot mass remaining in the filter using a set of current vehicle operating conditions. The host machine also calculates a ratio of a change in the measured soot mass to a change in the modeled soot mass. The host machine then compares the calculated ratio to a calibrated threshold, and executes a suitable control action when the ratio exceeds the threshold.
A method is also provided that may be embodied as an algorithm and used aboard the vehicle noted above. The method includes using a first soot model to determine an actual soot mass remaining in the particulate filter, and using a second soot model to determine a modeled soot mass remaining in the filter, with the second soot model using a set of current vehicle operating conditions. The method also includes calculating a ratio of a change in the actual soot mass to a change in the modeled soot mass, comparing the ratio to a calibrated threshold, and executing a control action when the ratio exceeds the calibrated threshold.
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 drawings, wherein like reference numbers correspond to like or similar components throughout the several figures, a vehicle 10 is shown schematically in
Vehicle 10 includes an internal combustion engine 12, such as a diesel engine or a direct injection gasoline engine, an oxidation catalyst (OC) system 13 having the particulate filter 34, and a transmission 14. The engine 12 combusts fuel 16 drawn from a fuel tank 18. In one possible embodiment, the fuel 16 is diesel fuel, the oxidation catalyst system 13 is a diesel oxidation catalyst (DOC) system, and the particulate filter 34 is a diesel particulate filter (DPF), although gasoline or other fuel types may be used depending on the design of engine 12.
As noted above, algorithm 100 is executed by the host machine 40 in order to detect a condition in which a frequency of regeneration of the particulate filter 34 is higher than a threshold level required by design standards, doing so using first and second soot models 50 and 60, respectively, as set forth herein. In particular, host machine 40 directly monitors regeneration frequency using a calculated ratio of the difference in a measured or actual soot level to a simulated or modeled soot level from the first and second soot models 50 and 60, respectively, with the two models determining soot levels remaining in the particulate filter 34 in different ways, and by comparing the calculated ratio to a calibrated threshold as explained below with reference to
Host machine 40 may 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. Algorithm 100 and any required reference calibrations are stored within or readily accessed by host machine 40 to provide the functions described below with reference to
Vehicle 10 also includes a throttle 20 which selectively admits a predetermined amount of the fuel 16 and air into engine 12 as needed. Combustion of fuel 16 by the engine 12 generates an exhaust stream 22, which passes through the exhaust system of the vehicle before it is ultimately discharged into the surrounding atmosphere as shown. Energy released by the combustion of fuel 16 ultimately produces torque on an input member 24 of transmission 14. The transmission 14 in turn transfers torque from the engine 12 to an output member 26 in order to propel the vehicle 10 via a set of wheels 28, only one of which is shown in
The OC system 13 as shown in
Regeneration of the particulate filter 34 may be active or passive. As understood in the art, passive regeneration requires no additional control action for regeneration. Instead, the particulate filter is installed in place of the muffler, and at idle or low power operations, particulate matter is collected on the filter. As the engine exhaust temperatures increase, the collected material is then burned or oxidized by the exhaust stream 22. Active regeneration adds an external source of heat to complete the regeneration, along with additional control methodology.
However configured, the particulate filter 34 may be constructed of a suitable substrate constructed of, by way of example, ceramic, metal mesh, pelletized alumina, or any other temperature and application-suitable material(s). As the temperature of the exhaust stream 22 increases, particulate matter previously entrapped within the particulate filter 34 is burned or oxidized by the hot exhaust gas to form soot within the particulate filter.
Vehicle 10 may also include a fuel injection device 36 in electronic communication with the host machine 40 via control signals 15, and in fluid communication with fuel tank 18. Fuel injection device 36 selectively injects fuel 16 into the oxidation catalyst 30 or engine cylinders (not shown) when determined by the host machine 40. The injected fuel 16 is then ignited and burned in a controlled manner to generate the increased levels of heat necessary for regenerating the particulate filter 34.
Still referring got
The second soot model 60 provides the modeled soot mass in a different manner, i.e., doing so using a set of current vehicle operating conditions and not using the differential pressure across the particulate filter 34. Second soot model 60 uses feedback signals 44 describing the operating point of engine 12 and other suitable vehicle operating data points. Such points may include oxygen levels, throttle position, engine speed, accelerator pedal position, fueling quantity, requested engine torque, exhaust temperatures, elapsed time since the start of the last regeneration event, the particular driving mode such as highway driving, city driving, and/or other recognized modes or combinations of modes as determined by monitoring parameters such as engine speed, engine loading, braking, etc.
Host machine 40 also receives signals 11 from various sensors 42 positioned throughout the vehicle 10 describing various measured values, e.g., exhaust temperatures, pressure, oxygen levels, etc., at different locations within the OC system 13, including directly upstream and downstream of the oxidation catalyst 30 and directly upstream and downstream of the particulate filter 34. These signals 11 are each transmitted by or relayed to the host machine 40. Host machine 40 is also in communication with the engine 12 to receive the feedback signals 44 indentifying the operating point of the engine, values which are used in particular by the second soot model 60 as described below.
Referring to
In particular, beginning at step 102 the host machine 40 first determines whether a set of initialization conditions are present, i.e., whether a regeneration event is presently commanded. Step 102 may be satisfied by detecting a discrete on/off regeneration trigger signal generated internally by the host machine if the host machine is configured to control the regeneration process, or by another vehicle controller if configured otherwise. The algorithm 100 proceeds to step 104 after detection of the regeneration trigger signal or other initialization condition.
At step 104, the host machine 40 determines the actual soot mass in the particulate filter 34. In one possible embodiment, the host machine 40 directly reads or calculates the differential pressure across the particulate filter 34 using signals 11 from the sensors 42 positioned at the inlet and outlet sides of the particulate filter, in this case configured as temperature transducers or other suitable temperature sensors, and then references the first soot model 50 using the pressure drop to determine an actual soot mass value. This value is temporarily recorded in memory, and the algorithm 100 proceeds to step 106.
At step 106, the host machine 40 processes the feedback signals 44 and any other required signals 11 to calculate a change in the modeled soot mass, with the modeled soot mass determined with reference to the second soot model 60 described above. This change occurs over the time interval between the present regeneration trigger signal and the initiation of the immediately prior filter regeneration event. Host machine 40 also calculates the change in actual soot mass within the particulate filter 34 over the same time interval, this time with reference to first soot model 50, and then proceeds to step 108 after temporarily recording the two change values in memory.
At step 108, the host machine 40 calculates a ratio of the change values calculated at step 106, i.e., the change in modeled soot mass and the change in actual soot mass in the elapsed interval since the last regeneration event, and temporarily records the value of this ratio in memory before proceeding to step 110.
At step 110, the host machine 40 compares the ratio from step 108 to a calibrated threshold. If the recorded ratio exceeds the calibrated threshold, the host machine 40 proceeds to step 112, and otherwise proceeds to step 114.
At step 112, host machine 40 sets a first diagnostic code indicating that the ratio exceeds the calibrated threshold. Such a result could mean that there is more soot present within the particulate filter 34 than expected by the second soot model 60, a result which may be caused by an air leak or an engine malfunction, and which therefore warrants further investigation. Additional control actions at step 112 may include activating an indicator device 38 to alert an operator, transmitting a message within vehicle 10, transmitting a message outside of the vehicle using a vehicle telematics unit, and/or taking any other action suitable for signaling the need to inspect, maintain, or replace the particulate filter 34.
At step 114, the host machine 40 sets a second diagnostic code indicating that the calculated ratio does not exceed the calibrated threshold. Algorithm 100 may continue to execute in a suitable control loop to minimize variability, i.e., all regeneration events must maintain at least a minimum level of efficiency, thus making the algorithm robust for any given control system calibration, as well as a wider variety of control system calibrations.
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.
