Method and systems for optically sensing particulate matter
AssigneeFord Global Technologies, LLC
InventorsNathan Kempema, David Bilby
Life of this patent
Estimating the term…
Abstract
Methods and systems are provided for a particulate matter sensor. In one example, the particulate matter sensor may include a light source, a waveguide aligned with the light source to receive incident light from the light source, and a photodetector positioned to receive light the incident light from the waveguide. The incident light may be reflected off a reflective surface of the waveguide more than one time to generate a plurality of evanescent waves. The plurality of evanescent waves may interact with particulate matter in exhaust gas, causing the incident light to be attenuated.
Claims11
A method for operating an optical particulate matter sensor to diagnose a status of a diesel particulate filter, comprising:
- directing a beam of light from a light source to a waveguide of the optical particulate matter sensor, and reflecting the beam of light at a first face of a first reflecting surface, the first reflecting surface included in the waveguide and having a second face for receiving particulate matter in exhaust gas, the second face opposite of the first face;
- energizing an electric device to increase deposition of the particulate matter at the second face of the first reflecting surface;
- and
- receiving the beam of light at a photodetector, after reflection of the beam of light at a second reflecting surface, to determine a concentration of the particulate matter in the exhaust gas based on attenuation of the beam of light;
- wherein the beam of light is attenuated by generation of an evanescent wave when the beam of light is reflected at the first reflecting surface, wherein directing the beam of light from the light source to the waveguide includes emitting the beam of light continuously from the light source to a first refracting surface of the waveguide, the first refracting surface adjacent to the first reflecting surface, wherein receiving the beam of light at the photodetector, after reflection of the beam of light at the second reflecting surface, includes receiving the beam of light after the beam of light is reflected at a side of the waveguide configured with a reflective coating, the side of the waveguide opposite of the first refracting surface and adjacent to the first reflecting surface, and wherein determining the concentration of the particulate matter in the exhaust gas based on attenuation of the beam of light includes determining a change in voltage at the photodetector with time to estimate a slope of the change and comparing the slope to a calibration curve to infer the concentration of the particulate matter.
A method for operating an optical particulate matter sensor to diagnose a status of a diesel particulate filter, comprising:
- directing a beam of light from a light source to a waveguide of the optical particulate matter sensor, and reflecting the beam of light at a first face of a first reflecting surface, the first reflecting surface included in the waveguide and having a second face for receiving particulate matter in exhaust gas, the second face opposite of the first face;
- energizing an electric device to increase deposition of the particulate matter at the second face of the first reflecting surface;
- and
- receiving the beam of light at a photodetector, after reflection of the beam of light at a second reflecting surface, to determine a concentration of the particulate matter in the exhaust gas based on attenuation of the beam of light;
- wherein the beam of light is attenuated by generation of an evanescent wave when the beam of light is reflected at the first reflecting surface, wherein directing the beam of light from the light source to the waveguide includes emitting the beam of light in pulses from the light source, through a first mirror, to a first refracting surface of the waveguide, the first refracting surface adjacent to the first reflecting surface, wherein receiving the beam of light at the photodetector, after reflection of the beam of light at the second reflecting surface, includes receiving the beam of light after the beam of light is reflected at a second mirror positioned at an opposite side of the waveguide from the first mirror, transmitted through the first mirror, and refracted from a beam splitter, and wherein determining the concentration of the particulate matter in the exhaust gas based on attenuation of the beam of light includes monitoring exponential decay of the beam of light at the photodetector until an intensity of the beam of light decays to 1/e2 of an initial intensity of the beam of light.
Dependencies are inferred from the claim text.