Particulate sensor system

#The present disclosure relates to a self-regenerating particulate sensor, and more particularly, to a self-regenerating sensor capable of detecting particulates emitted from an exhaust gas. Incomplete combustion of heavy hydrocarbon compounds, such as heavy oils, diesel oil, and the like leads to particulate formation. In the operation of internal combustion engines, “smoking” of the engine leads to ambient air pollution although the carbon monoxide and hydrocarbon emission of the exhaust gases from the internal combustion engine itself are very low. It is, therefore, desirable to detect the formation of particulates in the exhaust of the engine and to provide an output signal that can then be used to indicate the presence of particulates and further to be used as a sensing or control signal, for example in a control loop, to automatically adjust air, or the supply of fuel for complete combustion and to prevent excess particulate formation.

#Currently exhaust gases can be sensed by optical sensors; however, such sensors are more suited to fixed locations, for example smokestacks, and are not readily adaptable to automotive use, particularly in view of the rugged and highly variable ambient operating conditions associated with automotive use, including wide swings in temperature, temperature gradients, shock, vibration, and the like. It would, therefore, be desirable to provide a more robust sensor capable of directly sensing exhaust particulates.

#In the past, a sensing plate has been used for detecting exhaust particulates, wherein the sensing plate changes the electrical conductivity of a sensor by the formation of a carbon bridge between electrodes. To refresh the sensor, the deposited particulates are burned off by means of a catalyst with extra oxygen in the engine exhaust. Such sensors, however, are not completely practical because the strong reduction effect of the particulates can damage the electrode and detach the electrode from the sensing plane. Current sensors are furthermore unable to control both the temperature surrounding the sensor and the rate of the exhaust flow. This inability is disadvantageous as it allows for the condensation of humidity or moisture on the sensor, which leads to the gradual deterioration of the sensor; thus preventing the sensor from controlling the particulate deposition process, which in turn prevents the sensor from being a direct mechanism by which particulates may be removed from the exhaust. A further problem with current sensors is that they are primarily limited to use with direct current methods of sensing conductivity. Such methods are problematic in that the electrical properties are highly non-liner, thereby making it difficult to control the rate of exhaust flow.

#Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike:

#FIG. 1 is a schematic showing an exemplary embodiment of the sensor;

#FIG. 2 is a flow diagram showing the circuitry of the particulate sensor system;

#The present disclosure relates to a particulate sensor system capable of self-regeneration and for use as a sensing or control signal to automatically remove particulate matter from exhaust emission devices. The particulate sensor system comprises a sensor in electrical communication with a sensor circuit, which operates to detect the level of particulate matter in the environment surrounding the sensor. The particulate sensor system may be calibrated to detect a specific amount of particulate accumulation on the sensor, at which point the particulate sensor system removes the particulates (self-regeneration) by signaling a heater disposed in the sensor. Additionally, the particulate sensor system may be designed such that after a predetermined number of self-regeneration cycles, particles condensed on an exhaust system can also be removed. It is noted that each self-regeneration cycle can be determined based on the size dimensions of the sensor; in general, the smaller the sensing area (e.g., the substrate surface upon which the sensing electrodes are positioned) and the smaller the volume at the tip of the sensor (e.g., that portion of the sensor where the sensing electrodes are positioned), the less time is needed for each self-regeneration cycle. Additionally, a temperature sensor may be advantageously used to maintain the external temperature surrounding the sensor at a point higher than the condensation point of water but lower than the condensation point of the particulates such that the particulates can condense on the sensor without an accompanying condensation of water. Preferably the external temperature maintained by the heater is above the temperature of water condensation, and below the burn-off temperature of the deposited particulates.

#The particulate sensor system can self-regenerate by a signal comprising an electrical communication between at least two sensing electrodes and a heater. A signal is transmitted from the sensing electrodes to the heater when the electrical resistance between the sensing electrodes drops to a predetermined threshold amount. Such a drop in resistance is caused by particulate condensation on the sensor. The signal activates the heater to increase its thermal energy output, thereby causing the removal of the particulates from the sensor. As the particulates are removed from the sensor, the resistance gradually increases. The increasing resistance can be employed to signal the heater to decrease its thermal energy output, or the thermal energy output can be maintained until the resistance reaches a selected level, or thermal energy output may be controlled at timed intervals.

#In general, the sensor comprises a sensing element and a heating element, wherein the sensing element may comprise, but is not limited to, at least two sensing electrodes, and optionally a guard electrode; and, wherein the heating element may comprise, but is not limited to, a temperature sensor, and a heater. The sensor may include a multi-layered structure comprising the sensing element, the temperature sensor, the heater, and a combination comprising at least one of the foregoing, contained in a single structure formed, e.g., by multi-layer technology.