System for sensing particulate matter

Systems and methods are described for sensing particulate matter in an exhaust system of a vehicle. An example system comprises a particulate matter sensor and a guiding plate spaced away from each other in a tube capable of receiving a portion of exhaust gas in an exhaust passage.

FIELD

The present description relates generally to methods and systems for sensing particulate matter in an exhaust system.

Engine emission control systems may utilize various exhaust sensors. One example sensor may be a particulate matter sensor which indicates particulate matter mass and/or concentration in the exhaust gas. In one example, the particulate matter sensor may operate by accumulating particulate matter over time and providing an indication of the degree of accumulation as a measure of exhaust particulate matter levels.

Particulate matter sensors may encounter problems with non-uniform deposition of soot on the sensor due to a bias in flow distribution across the surface of the sensor. Further, particulate matter sensors may be prone to contamination from an impingement of water droplets and/or larger particulates present in the exhaust gases. This contamination may lead to errors in sensor output. Furthermore, sensor regeneration may be inadequate when a substantial volume of exhaust gases stream across the particulate matter sensor.

The inventors herein have recognized the above issues and identified an approach to at least partly address the issues. In one example approach, a system for sensing particulate matter in an exhaust passage of an engine is provided. The system comprises a tube positioned in an exhaust passage of an engine, a particulate matter sensor positioned within the tube, and a flow guiding plate positioned within the tube substantially parallel to a vertical axis of the tube. The guiding plate comprises a plurality of projections with surfaces of the projections defining an interior passage in proximity to the particulate matter sensor, the surfaces of the projections directing flow against the particulate matter sensor.

As one example, a particulate matter (PM) sensor may be disposed within a tube fixed to a wall of an exhaust passage. The tube may further comprise a flow guiding plate located downstream of the PM sensor. The PM sensor may comprise an electric circuit on an upstream surface directed away from the guiding plate. The PM sensor may further comprise two separate electrodes located on a downstream surface. An interior passage (e.g., a central chamber) may be located between the PM sensor and guiding plate. A sample of exhaust gas may enter the tube via an inlet located on a bottom portion of the tube. Larger particulates and/or water droplets may flow through a drainage hole directly downstream of the inlet on the bottom portion of the tube. The sample of exhaust gas may be conducted up along an outside of the guiding plate before flowing down into the central chamber The sample of exhaust gas flows through guides of the guiding plate and may be evenly distributed across the downstream surface of the PM sensor. Finally, the sample of exhaust gas may exit the tube and flow into the exhaust passage via outlets located at an interface between the guiding plate and the tube.

In this way, a PM sensor may be exposed to a more uniform flow distribution across its surface. By flowing the sample of exhaust gas from a lower portion of the tube to a higher portion of the tube, a flow rate and/or volume of exhaust gas entering the central chamber may be controlled. Further, distribution of particulate matter from the sample of exhaust gas onto the PM sensor may be more evenly distributed due to the guiding plate, which may mix and guide exhaust flow across a total surface area of the downstream surface of the PM sensor. By providing a more even and controlled flow of the sample exhaust gas onto the downstream surface, particulate filter regeneration and/or determination of degradation of the PF in the exhaust passage may occur more accurately. Further, the PM sensor may be protected from larger particulates and water droplets, as they may flow through the drainage hole due to their greater momentum. Overall, functioning of the PM sensor may be improved and may be more reliable.

DETAILED DESCRIPTION

The following description relates to systems and methods for sensing particulate matter (PM) in an exhaust flow on an engine system, such as the engine system, as shown inFIG. 1. A PM sensor assembly may include a tube with an inlet on an extension of the tube for receiving a sample exhaust flow and a drainage hole opposite the inlet on the extension, as shown inFIG. 2. An outer chamber may guide the sample exhaust flow up the tube toward a central chamber located between a PM sensor and a guiding plate, as shown inFIG. 3. The tube may further include a PM sensor located upstream of a guiding plate. The guiding plate may comprise a plurality of concave projections, protruding away from the PM sensor, as shown inFIG. 4. The guiding plate may control an exhaust flow similar to a quincunx (e.g., Galton box) and evenly distribute an exhaust flow across a surface of the PM sensor, as shown inFIGS. 5A and 5B. A method for determining if a particulate matter load of a particulate filter is greater than a threshold particulate load and if the particulate filter is degraded, as shown inFIG. 6.

FIGS. 1-5Bshow example configurations with relative positioning of the various components. If shown directly contacting each other, or directly coupled, then such elements may be referred to as directly contacting or directly coupled, respectively, at least in one example. Similarly, elements shown contiguous or adjacent to one another may be contiguous or adjacent to each other, respectively, at least in one example. As an example, components laying in face-sharing contact with each other may be referred to as in face-sharing contact. As another example, elements positioned apart from each other with only a space there-between and no other components may be referred to as such, in at least one example.

Referring now toFIG. 1, it shows a schematic diagram with one cylinder of multi-cylinder engine10, which may be included in a propulsion system of a vehicle. Engine10may be controlled at least partially by a control system including a controller12and by input from a vehicle operator132via an input device130. In this example, input device130includes an accelerator pedal and a pedal position sensor134for generating a proportional pedal position signal PP. A combustion chamber30(also termed, cylinder30) of the engine10may include combustion chamber walls32with a piston36positioned therein. Piston36may be coupled to a crankshaft40so that reciprocating motion of the piston is translated into rotational motion of the crankshaft40. Crankshaft40may be coupled to at least one drive wheel (not shown) of a vehicle via an intermediate transmission system (not shown). Further, a starter motor (not shown) may be coupled to the crankshaft40via a flywheel (not shown) to enable a starting operation of the engine10.

Combustion chamber30may receive intake air from an intake manifold44via an intake passage42and may exhaust combustion gases via an exhaust passage48. The intake manifold44and the exhaust passage48can selectively communicate with the combustion chamber30via intake valve52and exhaust valve54respectively. In some embodiments, the combustion chamber30may include two or more intake valves and/or two or more exhaust valves.

In the example depicted inFIG. 1, the intake valve52and exhaust valve54may be controlled by cam actuation via respective cam actuation systems51and53. The cam actuation systems51and53may each include one or more cams and may utilize one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT), and/or variable valve lift (VVL) systems that may be operated by the controller12to vary valve operation. The position of the intake valve52and the exhaust valve54may be determined by position sensors55and57, respectively. In alternative embodiments, the intake valve52and/or exhaust valve54may be controlled by electric valve actuation. For example, the cylinder30may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including CPS and/or VCT systems.

In some embodiments, each cylinder of the engine10may be configured with one or more fuel injectors for providing fuel thereto. As a non-limiting example, the cylinder30is shown including one fuel injector66. Fuel injector66is shown coupled to the cylinder30for injecting fuel directly therein in proportion to the pulse width of signal FPW received from controller12via electronic driver68. In this manner, fuel injector66provides what is known as direct injection of fuel into combustion chamber30. It will also be appreciated that the cylinder30may receive fuel from a plurality of injections during a combustion cycle. In other examples, the fuel injector may be mounted in the side of the combustion chamber or in the top of the combustion chamber, for example. Fuel may be delivered to fuel injector66by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail.

In the example shown inFIG. 1, engine10is configured as a diesel engine that combusts air and diesel fuel through compression ignition. In other embodiments, the engine10may combust a different fuel including gasoline, biodiesel, or an alcohol containing fuel blend (e.g., gasoline and ethanol, or gasoline and methanol) through compression ignition and/or spark ignition. Thus, the embodiments described herein may be used in any suitable engine, including but not limited to, diesel and gasoline compression ignition engines, spark ignition engines, direct or port injection engines, etc.

The intake passage42may include a throttle62having a throttle plate64. In this particular example, the position of the throttle plate64may be varied by controller12via a signal provided to an electric motor or actuator included with the throttle62, a configuration that is commonly referred to as electronic throttle control (ETC). In this manner, the throttle62may be operated to vary the intake air provided to the combustion chamber30among other engine cylinders. The position of the throttle plate64may be provided to the controller12by throttle position signal TP. The intake passage42may include a mass air flow sensor120and a manifold air pressure sensor122for providing respective signals MAF and MAP to the controller12.

Further, in the disclosed embodiments, an exhaust gas recirculation (EGR) system may route a desired portion of exhaust gas from the exhaust passage48to the intake manifold44via an EGR passage140. An amount of EGR provided may be varied by controller12via an EGR valve142. By introducing exhaust gas to the engine10, the amount of available oxygen for combustion is decreased, thereby reducing combustion flame temperatures and reducing the formation of NOx, for example. As depicted, the EGR system further includes an EGR sensor144which may be arranged within the EGR passage140and may provide an indication of one or more of pressure, temperature, and concentration of the exhaust gas. Under some conditions, the EGR system may be used to regulate the temperature of the air and fuel mixture within the combustion chamber30, thus providing a method of controlling the timing of ignition during some combustion modes. Further, during some conditions, a portion of combustion gases may be retained or trapped in the combustion chamber by controlling exhaust valve timing, such as by controlling a variable valve timing mechanism.

An exhaust system128includes an exhaust gas sensor126coupled to the exhaust passage48upstream of an emission control system70and the EGR passage140. Exhaust gas sensor126may be any suitable sensor for providing an indication of exhaust gas air/fuel ratio such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO, a HEGO (heated EGO), NOx, HC, or CO sensor.

Emission control system70is shown arranged along exhaust passage48downstream of exhaust gas sensor126. Emission control system70may be a selective catalytic reduction (SCR) system, three way catalyst (TWC), NOx trap, various other emission control devices, or combinations thereof. For example, emission control system70may include an SCR catalyst71and a particulate filter (PF)72. In some embodiments, PF72may be located downstream of the SCR catalyst71(as shown inFIG. 1), while in other embodiments, PF72may be positioned upstream of the SCR catalyst71(not shown inFIG. 1). Emission control system70may further include exhaust gas sensor162. Sensor162may be any suitable sensor for providing an indication of a concentration of exhaust gas constituents such as a NOx, NH3, EGO, or a particulate matter (PM) sensor, for example. In some embodiments sensor162may be located downstream of PF72(as shown inFIG. 1), while in other embodiments, sensor162may be positioned upstream of PF72(not shown inFIG. 1). Further, it will be appreciated that more than one sensor162may be provided in any suitable position.

As described in more detail with reference toFIG. 2, sensor162may be a PM sensor assembly comprising a PM sensor and may measure the mass or concentration of particulate matter downstream of PF72. For example, sensor162may be a soot sensor. Sensor162may be operatively coupled to controller12and may communicate with controller12to indicate a concentration of particulate matter within exhaust exiting PF72and flowing through exhaust passage48. In this way, sensor162may detect leakages from PF72.

Further, in some embodiments, during operation of engine10, emission control system70may be periodically reset by operating at least one cylinder of the engine within a particular air/fuel ratio.

Controller12is shown inFIG. 1as a microcomputer, including a microprocessor unit102, input/output ports104, an electronic storage medium for executable programs and calibration values shown as a read only memory chip106in this particular example, random access memory108, keep alive memory110, and a data bus. The controller12may be in communication with and, therefore, receive various signals from sensors coupled to the engine10, in addition to those signals previously discussed, including measurement of inducted mass air flow (MAF) from the mass air flow sensor120; engine coolant temperature (ECT) from a temperature sensor112coupled to a cooling sleeve114; a profile ignition pickup signal (PIP) from a Hall effect sensor118(or other type) coupled to the crankshaft40; throttle position (TP) from a throttle position sensor; absolute manifold pressure signal, MAP, from the sensor122; and exhaust constituent concentration from the exhaust gas sensor126. Engine speed signal, RPM, may be generated by controller12from signal PIP.

The controller12receives signals from the various sensors ofFIG. 1(e.g., exhaust gas sensor162) and employs the various actuators ofFIG. 1to adjust engine operation based on the received signals and instructions stored on a memory of the controller.

As described above,FIG. 1shows only one cylinder of a multi-cylinder engine, and each cylinder may similarly include its own set of intake/exhaust valves, fuel injector(s), spark plug(s), etc.

Turning now toFIG. 2, a schematic view of an example embodiment of a PM sensor assembly200is shown. PM sensor assembly200may be used as exhaust gas sensor162ofFIG. 1and therefore may share common features and/or configurations as those already described for exhaust gas sensor162. PM sensor assembly200may be configured to measure PM mass and/or concentration in the exhaust gas, and as such, may be coupled to a wall201of an exhaust passage (e.g., exhaust passage48). The wall201may be a geodetically highest wall of the exhaust passage.

PM sensor assembly200is shown from a downstream perspective inside an exhaust passage (e.g., exhaust passage48ofFIG. 1) such that exhaust gases are flowing from the right hand side ofFIG. 2to the left hand side ofFIG. 2as indicated by arrows. PM sensor assembly200may include a cylindrical tube202with an inlet204on an upstream surface of an extension208of the tube202. The tube202is fluidly coupled to the exhaust passage only via the inlet204, a drainage hole206, and outlets224of a guiding plate216. Therefore, exhaust gas may only enter or exit the PM sensor assembly200via the inlet204, the drainage hole206, and outlets224.

The inlet204is substantially normal to and faces the flow of oncoming exhaust gases in the exhaust passage. Thus, the inlet204may be in direct contact with exhaust flow, and exhaust gases exiting PF72may flow in an unobstructed manner towards the inlet204of the PM sensor assembly200. Further, no components may block or deflect the flow of exhaust gases from the PF72to the PM sensor assembly200. Thus, a portion of exhaust gases for sampling may be conducted via an inlet204into PM sensor assembly200. A remaining portion of exhaust gases in the exhaust passage may flow around an outer body of the PM sensor assembly200. In this way, the remaining portion of exhaust gases does not flow into the PM sensor assembly. The remaining portion of exhaust gases may be greater in quantity of the portion of exhaust gases flowing into the PM sensor assembly200. Thus, a quantity of exhaust entering the PM sensor assembly200is less than a quantity of exhaust gas flowing around and not entering the PM sensor assembly200.

The inlet204is rectangular and aligned with a vertical axis of the PM sensor assembly200. The inlet204may be located on an extension208of the tube202and thus is geodetically lower than a perforated plate216and a PM sensor214. In this way, exhaust gas flows up into the tube202of the PM sensor assembly200in order to be sampled.

The extension208may be located at a bottom (e.g., base) of the tube202and may resemble a half-cylinder shape. The extension208may be located on a downstream half of the tube202. It will be appreciated by someone skilled in the art that the extension208may be other suitable shapes.

A drainage hole206is located along the extension208downstream of and directly across from the inlet204. Water droplets and large particulates may form as a result of combustion, which may impinge onto the PM sensor214and result in inaccurate soot measurements. The drainage hole206is fluidly coupled to the exhaust passage and allows water droplets and large particulates to flow through its circular opening in order to mitigate a quantity of water droplets and large particulates impinging on the PM sensor214of the PM sensor assembly. The water droplets and large particulates are less likely to flow up into an outer chamber210due to their momentum being greater than a momentum of smaller particulates in the exhaust flow.

As described above, a portion of exhaust gas flowing through the exhaust passage flows into the PM sensor assembly200via the inlet204. A first portion of exhaust gas flowing into the PM sensor assembly200flows up along the vertical axis into an outer chamber210. A second portion of exhaust gas flowing into the PM sensor assembly200flows through drainage hole206. The second portion of exhaust gas may comprise a greater concentration of water droplets and large particulates than the first portion.

The first portion of exhaust gas flowing through the outer chamber210may be conducted up toward a top of the tube202and down into a central chamber212. An entrance to the central chamber212may be geodetically higher than an entrance to the outer chamber210. The central chamber212and the outer chamber210may be parallel and aligned with the vertical axis. Thus, a direction of exhaust flow is inverted from up the vertical axis toward a top of the PM sensor assembly200to down toward a bottom of the PM sensor assembly200when exhaust flows from the outer chamber210to the central chamber212, respectively. The central chamber212may be located between the PM sensor214and the guiding plate216. Exhaust gas may not flow from the outer chamber210, through the perforated plate216, and into the central chamber212. Thus, exhaust gas is conducted up the outer chamber210along an entire height of the guiding plate216before entering the central chamber212.

The PM sensor214may comprise an upstream surface (also referred to herein as a first surface) and a downstream surface (also referred to herein as a second surface). The first surface of the PM sensor214may face a direction of incoming exhaust flow, opposite the guiding plate216. The second surface of the PM sensor214faces a direction opposite of incoming exhaust flow, toward the guiding plate216. The first surface comprises an electric circuit. The electric circuit may be used to increase a temperature of the PM sensor214in response to a particulate load of the PM sensor214exceeding a threshold PM sensor load in order to regenerate (e.g., burn off) stored particulate matter.

The second surface comprises a first electrode220and a second electrode222. The first electrode220is depicted via solid lines and the second electrode222is depicted via small dash lines. As depicted, the first electrode220and the second electrode222are not electrically coupled to one another. Furthermore, the first electrode220and the second electrode222may not have equal resistances. As a first example, the first electrode220may have a greater resistance than the second electrode222. As a second example, the second electrode222may have a greater resistance than the first electrode220. Exhaust gas flowing through the central chamber212may deposit particulate matter onto the second surface comprising both the first electrode220and the second electrode222. As a quantity of particulate matter on the second surface increases, the first electrode220and the second electrode222may become bridged (e.g., electrically coupled). Bridged first and second electrodes220and222, respectively, may indicate a PM load of the PM sensor214is greater than the threshold PM sensor load and the electric circuit on the first surface may be activated in order to regenerate the PM sensor.

The guiding plate216is depicted via medium dash lines and a transparent checkered body. Medium dash lines are greater in length than small dash lines. The guiding plate216may guide exhaust gas through the PM sensor assembly200in order to evenly distribute particulate matter across the second surface of the PM sensor214via surfaces of the guiding plate216. Surfaces of the guiding plate216may also define a passage of the central chamber212(e.g., an interior passage). In this way, exhaust gas may flow freely between the central chamber212and the guiding plate216while depositing soot onto the second surface of the PM sensor214.

In one example, an exhaust gas flow rate increases as exhaust gas within the guiding plate216converges (e.g., flows inward) while the exhaust gas flow rate decreases as exhaust gas within the guiding plate216diverges (e.g., flows outward). The guiding plate216comprises outlets224aligned with the vertical axis on a radius on the tube202. Exhaust gas flowing down the central chamber212may exit the PM sensor assembly200only via the outlets224. As depicted, the outlets224are arc-shaped. It will be appreciated by someone skilled in the art that the outlets224may be other suitable shapes.

The guiding plate216comprises a plurality of concave projections vertically offset from one another. The projections project in a direction away from the PM sensor214. Surfaces of the projections communicate fluidly with each other and the exhaust passage and may alter an exhaust flow similar to a Galton box (e.g., a quincunx), as will be described below. Openings of the projections may be oblique to the vertical axis. In one example, the openings are exactly 45° to the vertical axis. The guiding plate216may alter an exhaust flow such that exhaust flow is promoted to flow toward a bottom portion of the central chamber212rather than flowing through the outlets224near an upper portion of the guiding plate216. In this way, particulate matter may be evenly deposited across the second surface of the PM sensor214such that bridging of the first and second electrodes220and222, respectively, is equally likely at any position of the second surface.

In the example ofFIG. 2, exhaust gas enters the PM sensor assembly200via the inlet204of the tube202. The exhaust gas may be conducted upward through the outer chamber210before flowing into the central chamber212. An entrance to the central chamber212is located directly above the guiding plate216. The exhaust gas is then conducted downward toward a bottom of the PM sensor assembly200once it enters the central chamber212and interacts with both the second surface of the PM sensor214and the guiding plate216. A flow direction of the exhaust gas is altered via the guiding plate216as the exhaust gas deposits particulate matter onto the second surface of the PM sensor. As particulate matter is deposited onto the second surface, the first electrode220and the second electrode222may become bridged (e.g., electrically connected) when a particulate matter load of the PM sensor214exceeds a threshold particulate matter load. Furthermore, a resistance of the first electrode220or the second electrode222is decreased in response to the bridging. As a result, the PM sensor214is fully loaded due to particulates leaking from a particulate filter (e.g., PF72ofFIG. 1) of the exhaust passage. Particulates may be leaking due to the particulate filter being fully loaded or degraded (e.g., cracked). A method for determining the particulate filter being fully loaded or degraded is described below with respect toFIG. 6.

PM sensor assembly200may be coupled to exhaust passage48(FIG. 1) in a suitable manner such that a top surface of PM sensor assembly200is sealed to a wall201of the exhaust passage. A top-down view of the PM sensor assembly200not being sealed to the wall of the exhaust passage such that components within the PM sensor assembly200are visible is shown below in reference toFIG. 3.

Turning now toFIG. 3, a top-down view of a PM sensor assembly300detached from a wall of an exhaust passage of a vehicle located on a flat surface is shown. The PM sensor assembly300may be used as PM sensor assembly200in the embodiment ofFIG. 2or it may be used as exhaust gas sensor162ofFIG. 1.

The top-down view of the PM sensor assembly300depicts a tube301, a first outer chamber302, a guiding plate304, a central chamber306, a PM sensor308, and a second outer chamber310. The first outer chamber302, the guiding plate304, the central chamber306, and the PM sensor308may be used as the outer chamber210, the guiding plate216, the central chamber212, and the PM sensor214in the embodiment ofFIG. 2, respectively. The PM sensor308comprises a downstream surface312, adjacent the central chamber306and an upstream surface314, adjacent the second outer chamber310. The downstream surface312comprises two electrodes indicated by a thick line316. The upstream surface314comprises an electric circuit indicated by a thick line318.

As described above, exhaust gas is conducted up the first outer chamber302before flowing into the central chamber306. The guiding plate304hermetically seals the first outer chamber302from the central chamber306for a first portion of the tube301. Exhaust gas may exit the first outer chamber302and flow into the central chamber306via an opening located directly above the guiding plate304. In this way, exhaust gas flows up an entire height of the guiding plate304before flowing through the opening to the central chamber306.

The central chamber306is located in a space between the guiding plate304and the PM sensor308. A width320of the space may be between 1-5 millimeters. In one example, the width320is exactly 1.5 millimeters. In other embodiments, the width320may be less than 1 millimeter or greater than 5 millimeters.

Exhaust in the central chamber306flows down toward a bottom of the tube301in a direction opposite the flow of exhaust in the first outer chamber302. Exhaust in the central chamber306flows into and between the guiding plate304and the downstream surface312of the PM sensor308. The downstream surface312may be composed of a material capable of receiving and storing particulate matter while also being able to withstand high temperatures. In one example, the PM sensor308may be ceramic. The first and second electrodes of the downstream surface312may become bridged as particulate matter (e.g., soot) is deposited onto the downstream surface312of the PM sensor308. The guiding plate304may comprise a material unable to store particulate matter while coming into contact with and guiding the exhaust flow in the central chamber306. In one example, the guiding plate304may be plastic (e.g., polyurethane).

The upstream surface314of the PM sensor308comprising the electric circuit may be activated in response to the first and second electrodes of the downstream surface312bridging. Activating the electric circuit may include flowing electricity through the electric circuit in order to heat the PM sensor308and regenerate the particulate matter stored on the downstream surface312. The downstream surface312may be regenerated (e.g., the electric circuit remains active) until the first and second electrodes are no longer bridged. In another example, additionally or alternatively, the electric circuit may remain active for a threshold duration of time (e.g., 20 seconds). Regenerated particulate matter (e.g., ash) may fall into the central chamber306and swept away by incoming exhaust gas.

As described above, the guiding plate304comprises a plurality of concave projections vertically offset and in fluid communication with each other. The guiding plate304may promote exhaust gas in the central chamber306to flow in a downward motion toward the bottom (e.g., a base) of the tube301. Furthermore, the guiding plate304may be in fluid communication with an exhaust passage at an interface between the guiding plate304and an outer radius of the tube301along a central axis322of the PM sensor assembly300. As an example, the guiding plate304comprises outlets along a body of the tube301such that exhaust near the interface may flow out of the tube301and into the exhaust passage. In this way, exhaust gas may be equally promoted to flow out of the tube301along a periphery of the guiding plate304, and therefore near a periphery of the PM sensor308, while also flowing down the central chamber306in order to reach the base of the tube301. By doing this, soot may be evenly deposited onto the downstream surface312comprising the first and second electrodes.

Exhaust gas in the central chamber306flows in a substantially downward direction. Exhaust gas in the central chamber306cannot flow into the second outer chamber310due to the physically coupling between the PM sensor308and the tube301. In this way, the second outer chamber310does not receive exhaust gas and is not fluidly coupled to the exhaust passage, the first outer chamber302, and/or the central chamber306. The tube301is sealed at the base such that exhaust gas flowing out of the tube301does not flow into a path of an inlet (e.g., inlet204) of the tube301

In the example ofFIG. 3, the PM sensor assembly300comprises the guiding plate304located along its center and spaced away from the PM sensor308. The PM sensor308is located upstream of the guiding plate304. Three chambers are located within the PM sensor assembly including the first outer chamber302, the central chamber306, and the second outer chamber310. The first outer chamber302and the second central chamber306are fluidly coupled and sandwich the guiding plate304. The second outer chamber is located upstream of the PM sensor308and does not receive exhaust gas. Exhaust gas in the central chamber306flows into the guiding plate304and the PM sensor308. The exhaust gas in the central chamber306may flow out of the PM sensor assembly300via exits located at the interface between the guiding plate304and the tube301before or after depositing particulate matter onto the PM sensor.

The guiding plate304comprises a plurality of concave projections which may guide an exhaust flow in the central chamber306in order to more evenly distribute exhaust flow across the downstream surface312of the PM sensor308. The concave projections will be elaborated below in reference toFIG. 4.

Turning now toFIG. 4, a face-on view of a guiding plate400from a downstream to upstream direction is depicted. In the present example, the guiding plate400is in front of and blocks a view of a central chamber and a PM sensor. The guiding plate400may be used as the guiding plate304in the embodiment ofFIG. 3or as the guiding plate216in the embodiment ofFIG. 2.

The guiding plate400may comprise a plurality of projections402. The projections402are physically coupled to adjacent projections402such that each side of the projections402is physically coupled to another side of a corresponding adjacent projection of the projections402. A close-up view403depicts a detailed structure of a single projection410.

As depicted, projection410comprises four legs A, B, C, and D. Legs A, B, C, and D, correspond to legs A, B, C, and D of a dash circled projection of the projections402located on the guiding plate400. Legs A, B, C, and D are physically coupled to other legs of adjacent projections of the projections402. In one example, leg A of projection410is physically coupled to legs of three adjacent projections402. Likewise, legs B, C, and D of projection410are each physically coupled to legs of three corresponding adjacent projections of the projections402. An area between the legs A, B, C, and D is open to the central chamber such that exhaust gas may flow freely between the guiding plate400and the central chamber.

As depicted, projection410, and thus projection402, are concave. A cross-section of the projection410may be “U-shaped.” It will be appreciated by someone skilled in the art that the projections402may be other suitable concave shapes (e.g., parabolic, V shaped, saddle, cup, etc.).

Projections402are hermetically sealed along the legs and opening arches412such that gas in the central chamber may not flow through the guiding plate400and into an outer chamber (e.g., the first outer chamber302) or vice-versa.

Opening arches412are located between each of the legs A, B, C, and D. The opening arches412are physically coupled to opening arches of other adjacent projections. For example, one of the opening arches412of the projection410may by physically coupled to a single opening arch of an adjacent projection of the projections402. In this way, the projection410may be coupled to a total of twelve adjacent legs and four opening arches of the adjacent projections. Furthermore, the projections402are physically coupled to one another obliquely to the vertical and/or horizontal axes. In this way, a pattern of the projections402on the guiding plate400may be a zig-zag.

Projections402located along a top side404of a tube (e.g., tube301) of the guiding plate400may be cut in half along the horizontal axis and open to incoming gas. For example, gas flowing from an outer chamber (e.g., outer chamber302) may flow into a central chamber (e.g., central chamber306) and or the guiding plate400via the projections located adjacent to the top side404of the projections402. Gas in the central chamber and the guiding plate400may flow back and forth between or remain in the central chamber and the guiding plate400, respectively. As will be described below, exhaust gas flowing through the projections402of the guiding plate400may flow in a zig-zag direction, similar to a Galton box.

Exhaust gas flowing through the projections402of the guiding plate400may flow out of the tube via projections402located adjacent side406A or side406B. Projections402located near side406A or side406B may be cut in half along the vertical axis and are in fluid communication with an exhaust passage. In this way, the guiding plate400comprises a plurality of outlets located along the sides406A and406B.

Exhaust gas may flow to a base408of the guiding plate400. The base of the guiding plate400may also be a base of the tube (e.g., the base of the tube is base408). Thus, the base408is hermetically sealed from the exhaust passage such that gas flowing through the guiding plate400may not flow through the base408. Said another way, the base408does not comprise outlets and is not fluidly coupled to the exhaust passage. In this way, gas flowing toward the base408may ricochet off the base408and flow toward outlets located at either side406A or side406B.

The example ofFIG. 4illustrates the guiding plate400with a plurality of projections402physically coupled to one another such that exhaust gas in the central chamber may not flow through the guiding plate400and into the outer chamber. The projections402are in fluid communication with each other and may alter an exhaust flow substantially similar to a Galton box in order to more evenly distribute exhaust flow across a face of a PM sensor. The flow of exhaust through the guiding plate400will be described in greater detail below with reference toFIG. 5.

Turning now toFIG. 5A, a guiding plate500comprising a plurality of projections502altering an example exhaust flow is shown. The guiding plate500and the projections502may be used as guiding plate400and projections402in the embodiment ofFIG. 4. The guiding plate500and the projections502are depicted via medium dashed lines.

A first example exhaust flow504is depicted via thick, large dashed lines. A second example exhaust flow506is depicted via thick, small dashed lines. Large dashed lines are longer than medium and small dashed lines. Medium dashed lines are longer than small dashed lines. A third example exhaust flow508is depicted via thick, dashed two dot lines. The third example flow508originates from a substantially similar location as the first example flow504in the present example. A fourth example exhaust flow510is depicted via thick, dashed single dot lines. It will be appreciated by someone skilled in the art that many different exhaust flow patterns may occur in the guiding plate500and that the guiding plate500is not limited to the examples described below.

The projections502of the guiding plate500adjacent a top-side512of the guiding plate500may serve as inlets and allow exhaust gas to enter a flow path of the guiding plate500. Therefore, the first, second, third, and fourth example flows504,506,508, and510, respectively, may enter the guiding plate500via the projections502adjacent the top-side512. Exhaust gas may enter the guiding plate500in a direction parallel with a central axis501. Exhaust gas flowing through projections502may exit the guiding plate500, and a PM sensor assembly (e.g., particulate matter sensor assembly200) via projections502located adjacent to sides514A or514B. In this way, projections504located adjacent sides514A or514B may be used as outlets.

The first example exhaust flow504enters the guiding plate500near the side514A. The first example exhaust flow504is substantially linear and parallel to the central axis501. The first example exhaust flow504flows out of the guiding plate500, and therefore out of the PM sensor assembly and into an exhaust passage before reaching a base516of the guiding plate500. As described above, the base516of the guiding plate500is sealed such that exhaust gas may not flow through the base516.

The second example exhaust flow506enters the guiding plate500near the side514B. The second example exhaust flow506flows obliquely to the central axis501such that it exits the guiding plate500along the side514A. In this way, the second sample exhaust flow506traverses an entire width of the guiding plate500before exiting the guiding plate500along the side514A and entering the exhaust passage housing the PM sensor assembly.

The third example exhaust flow508enters the guiding plate500near the side514A. The third example exhaust flow508flows to and away from the side514B before exiting the side514B near the base516. Portions of the third example exhaust flow508zig-zag such that a direction of the exhaust flow in a current projection of the projections502is perpendicular to a direction of exhaust flow in a previous projection of the projections502.

For example, an exhaust flow may flow through a plurality of projections502in a direction oblique to or parallel to the central axis501. Exhaust flow flowing from a first of the projections502to a second of the projections502may flow parallel to, oblique to, or perpendicular to an initial flow based on a location of the second of the projections502relative to the first of the projections502. The direction of exhaust flow may also be based on exhaust flows in a same projection of the projections502colliding. For example, exhaust flows in the projections502of the guiding plate500may collide and mix, thereby altering a direction of the exhaust flows.

The fourth example exhaust flow510enters the guiding plate500along the central axis501. The fourth example exhaust flow510flows parallel to the central axis501in a zig-zag motion. The fourth example exhaust flow510collides with the base516and begins to flow toward the side514A. The fourth example exhaust flow510flows out the side514A at a location substantially similar to the outflow of the first example exhaust flow504.

Turning now toFIG. 5B, a portion of the projections540with exhaust gas flowing through passages within the projections540is shown. Projections540may be used as a portion of the projections502ofFIG. 5A.

In one example, an exhaust flow rate through the projections540may be increased as exhaust flow is directed toward a central axis541of the projections540. Additionally or alternatively, the exhaust flow rate through the projections540may be decreased as exhaust flow is directed away from the central axis541.

Exhaust flows550and552enter a projection551of the projections540from different angles. Exhaust flow550enters the projection551from a pathway farther away from the central axis541than the exhaust flow552. Exhaust flows550and552converge within the projection551before flowing to an end of the projection551. In this way, exhaust flow550begins to flow toward the central axis501after it enters the projection551and exhaust flow552begins to flow away from the central axis501as it enters the projection551(e.g., the exhaust flows550and552may be oblique to or perpendicular to each other). The exhaust flows may divide and flow into two adjacent projections559and563geodetically lower than and in fluid communication with the projection551. Flow rates of the exhaust flows550and552may be increased as they converge (e.g., merge) within the projection551.

A portion of the converged exhaust (e.g., exhaust flow558) flows into the projection559while a remaining portion of the converged exhaust (e.g., exhaust flow560) flows into the projection563. In this way, exhaust in the projection551may be divided upstream of the projections559and563. In one example, the exhaust flow560may be greater in volume than the exhaust flow558.

Exhaust flows554and556enter a projection555from different angles. Exhaust flow554flows away from the central axis501as it enters the projection555while exhaust flow556flows toward the central axis501as it enters the projection555. A flow rate of the exhaust flows554and556may increase as the exhaust flows converge within the projection555.

A portion of the converged exhaust (e.g., exhaust flow562) flows into the projection563and combines (e.g., converges) with exhaust flow560. A remaining portion (e.g., exhaust flow564) of the converged exhaust flow in the projection555flows into the projection567. Exhaust flow562may have a greater volume of exhaust than exhaust flow564. In this way, the combined exhaust flow of the exhaust flows560and562may have a flow rate greater than a flow rate of either the exhaust flow558in the projection559or the exhaust flow564in the projection567.

Turning now toFIG. 6, a method600for determining a particulate load of a PM sensor assembly being greater than a threshold particulate load in order to regenerate the PM sensor is depicted. The method600may further depict degradation of a particulate filter in an exhaust passage is degraded based on a time interval between PM sensor regeneration being less than a threshold time interval. Instructions for carrying out method600may be executed by a controller (e.g., controller12shown inFIG. 1) based on instructions stored on a memory of the controller and in conjunction with signals received from sensors of the engine system, such as the sensors described above with reference toFIGS. 1 and 2. The controller may employ engine actuators of the engine system to adjust engine operation, according to the methods described below.

Method600may be described in reference to components depicted inFIGS. 1, 2, and 3. Specifically, the method600may the controller12, the PF72, the exhaust gas sensor162, the PM sensor assembly200, the PM sensor214, the first and second electrodes220and222, and the guiding plate216with reference toFIGS. 1 and 2, respectively.

Method600being at602to determine, estimate, and/or measure current engine operating parameters. Current engine operating parameters may include but are not limited to engine load, engine speed, vehicle speed, manifold vacuum, throttle position, exhaust pressure, and an air/fuel ratio.

At604, the method600includes measuring an electrical resistance of the first and second electrodes located on a downstream surface of the PM sensor within the PM sensor assembly. In the embodiment ofFIG. 6, the first electrode may have a greater resistance than the second electrode. However, it will be appreciated by someone skilled in the art that the second electrode may have a greater resistance than the first electrode.

At606, the method600includes determining if the electrodes are electrically connected (e.g., bridged). The electrodes may become bridged as soot is deposited onto the downstream surface of the PM sensor by exhaust flowing freely between a central chamber and a guiding plate. As the soot builds up between the first and second electrodes, the soot may touch both electrodes simultaneously and as a result, the electrodes are bridged. When the electrodes are bridged, the resistance of the first electrode may decrease to a resistance of the second electrode due to the conductivity of the soot. If the resistance of the first electrode is greater than the resistance of the second electrode, then the electrodes are not bridged and the method600proceeds to608to maintain current engine operating parameters and to not regenerate the PM sensor in the PM assembly. Furthermore, a particulate filter (PF) in an exhaust passage may not be leaking or fully loaded with PM (e.g., a PF PM load is less than a threshold PF PM load). Thus, the PF in the exhaust passage is not regenerated.

If the resistance of the first electrode is substantially equal to the resistance of the second electrode, then the electrodes are bridged and the method600proceeds to610to activate an electric circuit of the PM sensor in order to regenerate the PM sensor. The electric circuit may be electrically connected to one or more of the first and second electrodes. Thus, the electric circuit may be activated by one or more of the first and second electrodes in response to the first and second electrodes being bridged. Alternatively, the electric circuit may be activated (e.g., switched on) via the controller in response to determining that the first and second electrodes are bridged. The controller may further adjust actuators of the engine in response to activating the electric circuit. For example, the controller may adjust an engine operation in order to regenerate the particulate filter located in the exhaust passage. The adjustments may include retarding spark, decreasing an air/fuel ratio of one or more cylinders, increasing the air/fuel ratio of one or more cylinders, and/or increasing a post-injection volume. In this way, regeneration of the PM sensor of the PM sensor assembly may trigger a regeneration of the PF located in the exhaust passage based on the first and second electrodes being bridged.

At612, the method600includes disabling the PM sensor regeneration in response to the first and second electrodes no longer being bridged. The first and second electrodes may no longer be bridged after the electric circuit regenerates the PM sensor and thus, burns off at least a portion of accumulated soot on the PM sensor. By burning off the soot, the bridge between the first and second electrodes may also be burned and the resistance of the first electrode may become greater than the resistance of the second electrode. The controller may deactivate the electric circuit in response to determining the resistance of the first electrode is greater than the resistance of the second electrode. Alternatively, the first and second electrodes may be electrically coupled to the electric circuit and the circuit may be deactivated by the first and second electrodes in response to the electrodes no longer being bridged.

The regeneration of the PF in the exhaust passage may also be terminated in response to deactivating the electric circuit. The controller may adjust engine operation back to an optimal engine operation based on a current engine load. Thus, a duration of regeneration for the PM sensor and the PF are substantially equal. Additionally or alternatively, the regeneration of the PF in the exhaust passage may be terminated after a threshold duration has passed after termination of the electric circuit. For example, the electric circuit is deactivated and then after the threshold duration has passed, the controller signals actuators of the engine to return to a nominal operation in order to deactivate PF regeneration.

In one example, additionally or alternatively, the regeneration of the PF sensor and the regeneration of the PF may operate for lengths of a first threshold and a second threshold, respectively. In this way, lengths of regeneration of the PF sensor and the PF may be independent. In other words, the first threshold may not be equal to the second threshold. In one embodiment, the first threshold may be less than the second threshold (e.g., the PF is regenerated for a greater length of time compared to the PM sensor). In another embodiment, the first threshold may be greater than the second threshold (e.g., the PF sensor is regenerated for a greater amount of time than the PF).

At614, the method includes determining a time interval between a last regeneration and a current regeneration of the PM sensor. The last regeneration is defined as a regeneration event that occurred directly before a current regeneration event. The time interval may be calculated based on a duration of time between initiation of the last regeneration and initiation of the current regeneration (e.g., 120 minutes). A time interval may be less than a previous time interval as the PF in the exhaust passage (e.g., particulate filter72ofFIG. 1) becomes degraded and captures less soot. For example, the particulate filter develops leaks (e.g., cracks), which may allow a greater amount of soot to flow to the PF sensor, resulting in more frequent regenerations of the PF sensor.

At616, the method600determines if the measured time interval is less than a threshold time interval. The threshold time interval may be based on a set threshold (e.g., 200 minutes), a last time interval measured, or a percentage of the last time interval measured (e.g., 50% of the last time interval). Further, the threshold time interval may be based on a threshold that indicates that the time interval is decreasing and the PF sensor has to be regenerated at an increasing rate. Additionally or alternatively, the threshold time interval may be adjusted based on engine operating parameters. For example, the threshold time interval may be decreased as an engine load increases.

If the time interval is not less than the threshold time interval, then the method600proceeds to608to maintain current engine operation and continue monitoring the electrodes of the PM sensor.

If the time interval is less than the threshold time interval, then the method600proceeds to618to indicate the PF of the exhaust passage, upstream of the PM sensor assembly, is leaking. Indication of the PF leaking includes adjusting an engine operation and activating an indicator lamp620(e.g., in order to indicate to a vehicle operator that the PF is degraded and needs to be replaced).

As an example, a controller (e.g., controller12) may signal various actuators of an engine (e.g., throttle62of engine10) to limit a torque output of the engine in order to reduce exhaust produced to meet emissions standards. As another example, additionally or alternatively, the method600may advance one or more of a spark timing and fuel injection, increase air/fuel ratio, and/or increase EGR. By increasing EGR flow to one or more cylinders of the engine, a combustion mixture temperature(s) is decreased and a volume of fuel injection may be decreased. By doing this, an amount of soot being exhausted from one or more cylinders of the engine may be decreased.

Thus, the method ofFIG. 6provides a method comprising diverting exhaust gas from an exhaust pipe to a PM sensor assembly, where the PM sensor assembly includes a PM sensor with electrodes on a downstream surface and an electric circuit on an upstream surface. The method includes adjusting engine operation based on electrodes of the PM sensor being bridged (e.g., connected). The bridging is based on resistances of the electrodes becoming substantially equal.

In this way, a PM sensor assembly may receive a sample exhaust flow from an exhaust passage in order to determine a PM load of a PF in the exhaust passage. PM from the exhaust accumulates onto a surface of a PM sensor located within the PM sensor assembly in order to signal a regeneration and/or degradation of the PF. Exhaust gas in the PM sensor assembly is evenly distributed across the surface of the PM sensor via a guiding plate. The technical effect of using a guiding plate to evenly distribute a sample exhaust flow across a surface of a PM sensor is to increase a uniformity of PM being deposited onto the surface of the PM sensor. By doing this, an accuracy of a determination of a PF being fully loaded and/or degraded is increased.

In a first example, a system comprises a tube positioned in an exhaust passage of an engine where a particulate matter sensor is positioned within the tube and a flow guiding plate is also positioned within the tube and substantially parallel to a vertical axis of the tube. The guiding plate has a plurality of projections with surfaces of the projections defining an interior passage in proximity to the particulate matter sensor, the surfaces of the projections directing flow against the particulate matter sensor.

In a first embodiment of the first example, the system further comprises an inlet of the tube aligned with the vertical axis of the tube, and where the tube further comprises a drainage hole spaced away from the inlet, where both the drainage hole and the inlet fluidly connect an interior of the tube with the exhaust passage.

In a second embodiment, which may additionally include the first embodiment, the system of the first example additionally or alternatively includes the particulate matter sensor having a switchable electrical circuit on a first surface facing away from the guiding plate in the tube.

In a third embodiment, which may include one or more of the first and second embodiments, the system of the first example further includes the particulate matter sensor has two, unconnected electrodes on a second surface facing the guiding plate.

In a fourth embodiment, which may include one or more of the first through third embodiments, the system of the first example further comprising a central chamber aligned with a vertical axis of the tube and located between the guiding plate and the second surface of the particulate matter sensor.

In a fifth embodiment, which may include one or more of the first through fourth embodiments, the system of the first example further comprising where the plurality of outlets are located along an interface between the guiding plate and the tube.

In a sixth embodiment, which may include one or more of the first through fifth embodiments, the system of the first example further comprising where exhaust gas flows in the tube in a direction perpendicular or oblique to a direction of exhaust flow in the exhaust passage.

In a seventh embodiment, which may include one or more of the first through the sixth embodiments, the system of the first example further comprising where the projections of the guiding plate are concave and physically coupled to and in fluid communication with adjacent projections.

In a second example, a method comprising conducting a portion of exhaust gas from an engine through an opening in a tube into an outer chamber within the tube, guiding the portion of exhaust gas from the outer chamber into a central chamber located between a particulate matter sensor and a guiding plate both of which are positioned within the tube, and flowing part of the portion of the exhaust gas entering the central chamber through concave projections of the guiding plate and onto a surface of the particulate matter sensor.

In a first embodiment of the second example, the method further includes flowing the portion of exhaust gas onto a surface of the particulate matter sensor further comprises flowing the portion of exhaust gases onto one of a pair of separated electrodes located on the surface of the particulate matter sensor.

In a second embodiment of the first example, which may additionally or alternatively include the first embodiment, the method further includes where the separate electrodes are electrically coupled when a load of particulate matter from the portion of the exhaust flowing on to the separated electrode exceeds a threshold particulate matter load.

In a third embodiment, which may additionally or alternatively include one or more of the first and second embodiments, the method further includes where a resistance of the separate electrode decreases in response to electrically coupling the separate electrodes.

In a third example, a system comprises a tube positioned in an exhaust passage of an engine, a particulate matter sensor and a guiding plate positioned in the tube. The guiding plate comprises a plurality of concave projections extending away from the guiding plate, and where surfaces of the concave projections define a central chamber and are in fluid communication with each other and the exhaust passage. The particulate matter sensor comprises an upstream surface with an electric circuit and a downstream surface with separate first and second electrodes, the upstream surface communicating with the central chamber and receiving a portion of the exhaust flow which is directed onto the upstream surface by the concave projections. The system further comprises a controller with computer-readable instructions for determining when a load of particulate matter in the exhaust which is collected on the upstream surface of the sensor exceeds a threshold particulate matter load and initiating a regeneration of the particulate matter sensor.

A first embodiment of the third example, where regenerating a particulate matter filter positioned in the engine exhaust based on how frequently the particulate matter sensor is regenerated.

A second embodiment of the third example, which may additionally or alternatively include the first example, the system further comprising the particulate matter sensor, the guiding plate, and the central chamber located therebetween are in fluid communication.

A third embodiment of the third example, which may additionally or alternatively include one or more of the first and second embodiments, the system further includes where an exhaust gas sample flows freely between the particulate matter sensor, the guiding plate, and the central chamber.

A fourth embodiment of the third example, which may additionally or alternatively include one or more of the first through third embodiments, the system further includes where the guiding plate redirects exhaust flow similar to a quincunx.

A fifth embodiment of the third example, which may additionally or alternatively include one or more of the first through fourth embodiments, the system further includes where the tube and the guiding plate are hermetically sealed at a shared base.

A sixth embodiment of the third example, which may additionally or alternatively include one or more of the first through fifth embodiments, the system further includes where the tube comprises an inlet upstream of and larger than a drainage opening of the tube.

A seventh embodiment of the third example, which may additionally or alternatively include one or more of the first through sixth embodiments, the system further includes where the particulate matter sensing element is downstream of a particulate matter filter of the exhaust passage.