HYBRID VEHICLE EXHAUST DIAGNOSTICS

Abstract

A method for a hybrid vehicle having an engine (10), comprising: inhibiting engine shutdown and enabling deceleration fuel cut-off (312, 326) to perform a monitoring test while the vehicle speed is above a speed threshold; in response to an engine down-regulation request when a vehicle speed is above a first speed threshold: inhibiting engine shutdown; enabling deceleration fuel cut-off (312); monitoring a rich-to-lean transition in an air / fuel sensor in an exhaust of the vehicle; and indicating sensor degradation based on the rich-to-lean transition in the air / fuel sensor; and in response to an engine down-regulation request when a vehicle speed is above a second speed threshold that is less than the first: inhibiting engine shutdown; enabling deceleration fuel cut-off (326);Monitoring a rich-to-lean transition upstream and downstream of a catalyst (178) in an exhaust of the vehicle; and indicating catalyst degradation based on the rich-to-lean transition upstream and downstream of the catalyst (178).

Description

[0001] Reduced engine operating times in hybrid vehicles allow for fuel savings and the benefits of lower fuel emissions. However, shorter engine operating times may result in insufficient time to complete various on-board diagnostic procedures. These include, for example, diagnostic procedures for various engine exhaust sensors, exhaust catalyst monitoring, and so on.

[0002] An exemplary approach for enabling completion of on-board diagnostic routines includes maintaining or resuming engine operation for a duration to complete the routines. Another exemplary approach is shown by Matsuoka et al. in US Pat. No. 6,446,614 B1, wherein an engine is maintained in a steady state during engine operation so that a diagnostic routine can run. KRKR 10 2011 0 062 135 A discloses an apparatus and method for monitoring an oxygen sensor of a hybrid vehicle. DE 10 2012 222 408 A1 discloses a diagnostic system and method for oxygen sensors in hybrid vehicles. DE 10 2010 050 060 A1 discloses systems and methods for diagnosing oxygen sensors and catalytic converters of exhaust systems. US 2011 / 0 120 095 A1 discloses a system and method for monitoring catalyst efficiency and downstream oxygen sensor performance.

[0003] The inventors recognized that these approaches are associated with problems. For example, starting an engine or maintaining an engine in a steady state to perform diagnostic routines can impair vehicle operation and negatively impact consumer perceptions of engine runtimes in hybrid vehicles. Furthermore, fuel efficiency may be lower with approaches that indiscriminately start or extend engine runtime to perform diagnostic tests while the hybrid vehicle is operating.

[0004] It may also be desirable to perform deceleration fuel shutoff (DFSO), which interrupts the engine's fuel supply to expose a sensor or catalyst to greater extremes of air / fuel mixtures, to ensure highly reliable fault code settings when diagnosing faults in exhaust system components, such as air / fuel sensors and catalysts. For example, due to the minimal engine runtime in hybrid vehicles, such vehicles may be configured to shut down the engine in response to driver throttle release, and exhaust system sensors may not be exposed to the rich and lean air / fuel mixtures required for monitoring.

[0005] In one example, some of the noted problems may be addressed by a method of operating a hybrid vehicle comprising inhibiting engine shutdown and enabling deceleration fuel cut-off to perform a monitoring test while vehicle speed is above a speed threshold, wherein, in response to an engine down-regulation request when vehicle speed is above a first speed threshold, the following are performed: inhibiting engine shutdown; enabling deceleration fuel cut-off; monitoring a rich-to-lean transition in an air / fuel sensor in an exhaust of the vehicle; and indicating sensor degradation based on the rich-to-lean transition in the air / fuel sensor;and in response to an engine downshift request, when a vehicle speed is above a second speed threshold that is less than the first, performing the following: inhibiting engine shutdown; enabling deceleration fuel cutoff; monitoring a rich-to-lean transition upstream and downstream of a catalyst in an exhaust of the vehicle; and indicating catalyst degradation based on the rich-to-lean transition upstream and downstream of the catalyst.;

[0006] In this way, diagnostic routines can be performed using a DFSO to sufficiently expose exhaust gas sensors to rich and lean air / fuel mixtures to provide more accurate diagnostics for exhaust system components while reducing the impact of the monitoring routines on vehicle operation. Furthermore, such an approach can increase fuel savings by inhibiting engine downshifts until the diagnostic monitor is operational. Because the engine is not forced to maintain sub-threshold speeds, consumer satisfaction with hybrid vehicle operation can increase.

[0007] It should be noted that the above summary is intended to present, in a simplified manner, a selection of concepts that are further described in the detailed description. It is not intended to identify important or essential features of the claimed subject matter, the scope of which is determined solely by the claims following the detailed description. Furthermore, the claimed subject matter is not limited to embodiments that overcome any disadvantages noted above or elsewhere in this disclosure. Fig. 1 shows an example vehicle system. Fig. 2 shows an example engine. Fig. 3 shows an exemplary method for operating a hybrid vehicle according to the disclosure. Fig. 4 shows an exemplary method of operating a hybrid vehicle according to the disclosure.

[0008] The following description relates to systems and methods for operating an electric hybrid vehicle, such as the electric plug-in hybrid vehicle according to Fig. 1. Such hybrid vehicles may include an engine such as the one described in Fig. 2, which can be selectively operated during certain conditions. For example, the engine can be operated or "ramped up" to meet torque requests, or shut down or "ramped down" during other conditions. For example, the engine can ramp down in response to a driver release of the throttle, where the driver interrupts or reduces a torque request, e.g., by adjusting an accelerator pedal. Engine ramp up occurs when the engine is spun by a generator to a target speed, e.g., ~1000 RPM, and is fueled and ignited until the engine starts. However, in hybrid vehicles, engine ramp up occurs independent of vehicle start, which may be accomplished from an alternative voltage source. Engine ramp down occurs when the engine is stopped but the vehicle continues to run.

[0009] Because hybrid vehicles may have shorter engine runtimes, as previously mentioned, sensor and catalyst diagnostic tests may not have enough time to be fully completed and may not be subjected to the air / fuel transitions required to accurately diagnose exhaust system components while reducing the impact of monitoring routines on vehicle operation. As discussed in Fig. 3 and Fig. Therefore, as shown in Figure 4, during certain non-intrusive conditions, engine down-speed may be inhibited and deceleration fuel shutoff (DFSO) may be enabled while the vehicle is running to perform diagnostic tests of exhaust system components such as exhaust gas sensors and catalysts. For example, engine down-speed may be inhibited and deceleration fuel shutoff (DFSO) may be enabled only when the diagnostic monitor is operational and the vehicle speed is above a speed threshold.

[0010] Fig. 1 shows an example vehicle operating system 100. A vehicle operating system 100 includes a fuel combustion engine 10 and a motor 20. As a non-limiting example, the engine 10 includes an internal combustion engine and the motor 20 includes an electric motor. The motor 20 may be configured to use or consume a different energy source than the engine 10. For example, the engine 10 may consume a liquid fuel (e.g., gasoline) to produce engine power, while the motor 20 may consume electrical energy to produce engine power. A vehicle including propulsion system 100 may thus be referred to as a hybrid electric vehicle (HEV). In particular, the propulsion system 100 is illustrated herein as a plug-in hybrid electric vehicle (PHEV).

[0011] A vehicle operating system 100 may be driven in a variety of ways depending on the vehicle's operating conditions. Some of these models may allow the engine 10 to be maintained in an off (or deactivated) state when fuel combustion in the engine is interrupted.

[0012] For example, in selected operating conditions, the motor 20 may drive the vehicle via the drive wheel 30 while the motor 10 is deactivated.

[0013] During other operating conditions, the engine 10 may be deactivated while the motor 20 is driven to charge the energy storage device 50 through regenerative braking. In this case, the motor 20 may receive torque from the drive wheel 30 and convert the vehicle's kinetic energy into electrical energy for storage in the energy storage device 50. The motor 20 may thereby provide a generator function in some embodiments. However, in other embodiments, a dedicated energy conversion device, herein a generator 60, may instead receive torque from the drive wheel 30 and convert the vehicle's kinetic energy into electrical energy for storage in an energy storage device 50.

[0014] During other operating conditions, the engine 10 may be powered by combusting fuel received from the fuel system 40. For example, the engine 10 may be powered to propel the vehicle via the drive wheel 30 while the engine 20 is deactivated. During other operating conditions, both the engine 10 and the engine 20 may each be powered to propel the vehicle via the drive wheel 30. A configuration in which both the engine and the electric motor can selectively propel the vehicle is referred to as a parallel-type vehicle operating system. It should be noted that in some embodiments, the engine 20 may propel the vehicle via a first set of drive wheels and the engine 10 may propel the vehicle via a second set of drive wheels.

[0015] In further embodiments, the vehicle operating system 100 may be configured as a series-type vehicle operating system, where the engine does not directly drive the drive wheels. Rather, the engine 10 may be operated to drive the motor 20, which in turn drives the vehicle via the drive wheel 30. For example, during selected operating conditions, the engine 10 may drive the generator 60, which in turn provides electrical energy to the one or more motors 20 or the energy storage device 50. As another example, the engine 10 may be operated to drive the motor 20, which in turn provides a generator function to convert the output energy into electrical energy, with the electrical energy being stored in the energy storage device 50 for later use by the engine.The vehicle operating system may be configured to switch between two or more of the described drive modes depending on the operating condition.

[0016] A fuel system 40 may include one or more fuel storage tanks 44 for storing fuel onboard the vehicle and for providing fuel to the engine 10. For example, the tank 44 may store one or more liquid fuels, including, but not limited to: gasoline, diesel, and alcohol fuels. In some examples, the fuel may be stored as a mixture of two or more different fuels onboard the vehicle. For example, the fuel tank 44 may be configured to store a mixture of gasoline and ethanol (e.g., E10, E85, etc.) or a mixture of gasoline and methanol (e.g., M10, M85, etc.), with these fuels or fuel mixtures being supplied to the engine 10. Still other suitable fuels or fuel mixtures may be supplied to the engine 10 where they are burned to produce output power.The engine output may be used to propel the vehicle and / or recharge the energy storage device 50 via the motor 20 or the generator 60.

[0017] The fuel tank 44 may include a fuel level sensor 46 for sending a signal related to a fuel level in the tank to the control unit (or controller) 12. The fuel level sensor 46 may include a float connected to a variable resistor, as shown. Alternatively, other types of fuel level sensors may be used. The level of fuel stored in the fuel tank 44 (e.g., as determined by the fuel level sensor) may be communicated to the vehicle operator, for example, via a fuel gauge or indicator light, indicated as 52. The fuel system 40 may periodically receive fuel from an external fuel source. For example, if the fuel level in the fuel tank drops below a threshold, a fuel tank refill request may be made in response, and the vehicle operator may stop the vehicle to refill.Fuel may be pumped into the fuel tank from a fuel dispenser 70 via a fill line 48 that forms a passage from a fill door 62 located on an exterior body of the vehicle.

[0018] The vehicle system may include various sensors and monitoring units that require regular evaluation. These include, for example, a VCI monitoring unit, an EGR monitoring unit, an EGO sensor, a fuel monitoring unit, an air-fuel ratio imbalance monitoring unit, an FAOS sensor, and other routines such as leak detection routines. Regular on-board diagnostic routines may be performed to confirm the sensor / monitoring unit's functionality. Furthermore, to meet federal emissions requirements, on-board diagnostic (OBD) routines may need to be performed within a vehicle's operating cycle. For this reason, some diagnostic routines require the engine to be running to be fully performed.Others do not require engine operation and can be performed in one drive cycle while a vehicle is in electric mode. At least some of the diagnostic routines are conveniently performed in full when engine operation varies between engine-on and engine-off modes. As shown in . Fig. 3 and Fig. Therefore, as shown in Figure 4, during certain non-intrusive conditions, engine down-regulation may be inhibited and deceleration fuel shutoff may be enabled while the vehicle is running to perform diagnostic tests of exhaust system components such as exhaust gas sensors and catalysts. For example, engine down-regulation may be inhibited and deceleration fuel shutoff (DFSO) may be enabled only when the diagnostic monitor is operational and the vehicle speed is above a speed threshold.

[0019] A control unit 12 may communicate with one or more engines 10, an engine 20, a fuel system 40, an energy storage device 50, and a generator 60. In particular, the control unit 12 may receive feedback from one or more of the engines 10, the engine 20, the fuel system 40, the energy storage device 50, and the generator 60 and send control signals to one or more of them in response. The control unit 12 may further receive an indication of an operator-requested vehicle operating system output from a vehicle operator 130. For example, the control unit 12 may receive feedback from a pedal position sensor 134 that communicates with pedal 132. Pedal 132 schematically refers to an accelerator pedal (as shown) or a brake pedal.

[0020] An energy storage device 50 may include one or more batteries and / or capacitors. The energy storage device 50 may be configured to store electrical energy to be supplied to other electrical loads (other than the engine) located onboard the vehicle, including a passenger compartment heating and air conditioning system (e.g., HVAC system), an engine starting system (e.g., starter motor), headlights, passenger compartment audio and video systems, etc.

[0021] The energy storage device 50 may periodically receive electrical energy from an external voltage source 80 that is not located within the vehicle. As a non-limiting example, the vehicle operating system 100 may be configured as a plug-in hybrid electric vehicle (HEV), wherein electrical energy is supplied to the energy storage device 50 from the voltage source 80 via an electrical energy transfer cable 82. During a charging operation of the energy storage device 50 from the voltage source 80, the electrical energy transfer cable 82 may electrically connect the energy storage device 50 and the voltage source 80. While the vehicle operating system is operating to propel the vehicle, the electrical energy transfer cable 82 between the voltage source 80 and the energy storage device 50 may be disconnected.The control unit 12 may estimate and / or control the amount of electrical energy stored in the energy storage device, referred to herein as the state of charge (SOC).

[0022] In further embodiments, the electrical power transmission cable 82 may be omitted, with the electrical energy being received wirelessly in the energy storage device 50 from the voltage source 80. For example, the energy storage device 50 may receive electrical energy from the voltage source 80 via one or more of electromagnetic induction, radio waves, and electromagnetic resonance. Therefore, it should be appreciated that any suitable approach may be used to charge the energy storage device 50 from the external voltage source 80. In this way, the motor 20 may propel the vehicle using a different energy source than the fuel used by the engine 10.

[0023] As in Fig. 2, the control unit 12 may receive data inputs from various sensors, process the data inputs, and trigger various actuators in response to the processed data inputs based on instructions or code programmed therein that correspond to one or more routines. An exemplary control routine is described herein with reference to Fig. 3 described.

[0024] Fig. 2 shows an exemplary embodiment of a combustion chamber or cylinder of the internal combustion engine 10. The engine 10 may receive control parameters from a control unit, including the control unit 12, and inputs from a vehicle operator 130 via an input device 132. In this example, an input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. The cylinder (also referred to herein as the "combustion chamber") 14 of the engine 10 may include combustion chamber walls 136 with a piston 138 disposed therein. The piston 138 may be connected to a crankshaft 140 to translate the reciprocating motion of the piston into rotational motion of the crankshaft. The crankshaft 140 may be connected to at least one drive wheel of the passenger vehicle via a gear system.In addition, a starter motor may be connected to the crankshaft 140 via a flywheel to enable starting of the engine 10.

[0025] Cylinder 14 may receive air supply via a series of air intake passages 142, 144, and 146. Air intake passage 146 may communicate with other cylinders of engine 10 in addition to cylinder 14. In some embodiments, one or more of the air intake passages may include a thrust device such as a turbocharger or supercharger. Fig. For example, Figure 2 shows an engine 10 configured with a turbocharger including a compressor 174 disposed between intake passages 142 and 144 and an exhaust turbine 176 disposed along exhaust passage 148. Compressor 174 may be powered at least partially by an exhaust turbine 176 via a shaft 180, with the thrust device configured as a turbocharger. In further examples, such as where engine 10 is provided with a supercharger, exhaust turbine 176 may optionally be omitted, with compressor 174 powered by mechanically supplied power from an electric motor or the engine. A throttle 162, including a throttle plate 164, may be provided along an intake passage of the engine to vary the flow rate and / or pressure of air supplied to the cylinder of the engine.For example, the throttle 162 may be downstream of the compressor 174, as shown in . Fig. 2, or alternatively provided upstream of the compressor 174.

[0026] The exhaust passage 148 may receive exhaust gases from additional cylinders of the engine 10 in addition to cylinder 14. An exhaust gas sensor 128 is shown connected to the exhaust passage 148 upstream of the emissions control device 178. The sensor 128 may be selected from various suitable sensors to provide indications of an exhaust air / fuel ratio, such as a linear oxygen sensor or UEGO (universal or wideband exhaust oxygen), a two-phase oxygen sensor or EGO (as shown), a HEGO (heat EGO), a NOx, HC, or CO sensor, for example. The emissions control device 178 may be a three-way catalyst (TWC), a NOx trap, various other emissions control devices, or combinations thereof. In addition, a downstream catalyst monitor (CMS) sensor 179 may be connected in the exhaust at a position downstream of the catalyst 178.The sensor 179 may be selected from various suitable sensors to provide information about an exhaust air / fuel ratio, such as a linear oxygen sensor or UEGO (universal or wideband exhaust oxygen), a two-phase oxygen sensor or EGO (as shown), a HEGO (heat EGO), a NOx, HC or CO sensor, for example.

[0027] The exhaust temperature may be estimated by one or more temperature sensors (not shown) disposed in the exhaust passage 148. Alternatively, the exhaust temperature may be determined based on engine operating conditions such as speed, air / fuel ratio (AFR), and spark retard.

[0028] Each cylinder of engine 10 may include one or more intake valves and one or more exhaust valves. For example, cylinder 14 is shown including at least one intake poppet valve 150 and at least one exhaust poppet valve 156. In some embodiments, each cylinder of engine 10, including cylinder 14, may include at least two intake poppet valves and at least two exhaust poppet valves disposed in a top portion of cylinder 14.

[0029] The intake valve 150 may be controlled by cam actuation via a cam actuation system 151 by the control unit 12. Similarly, the exhaust valve 156 may be controlled by a cam actuation system 153 by the control unit 12. Cam actuation systems 151 and 153 may each include one or more cams and may include one or more cam profile circuits (CPS), variable cam timing (VCT), variable valve timing (VVT), and / or variable valve lift (WL) systems driven by the control unit 12 to vary valve operation. The position of the intake valve 150 and the exhaust valve 156 may be determined by valve position sensors 155 and 157, respectively. In alternative embodiments, the intake and / or exhaust valves may be controlled by electrical valve actuation.For example, cylinder 14 may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation with CPS and / or VCT systems. In further embodiments, the intake and exhaust valves may be controlled by a common valve actuator or actuation system or a variable valve timing actuator or actuation system.

[0030] Cylinder 14 may have a compression ratio that is the ratio of volume when piston 138 is at the bottom center or top center. Conveniently, the compression ratio is in the range of 9:1 to 10:1. In some examples where different fuels are used, the compression ratio may be higher. This is the case, for example, when using higher octane fuels or fuels with higher latent heat of vaporization. The compression ratio may also be higher when using direct injection due to its effect on engine knock.

[0031] In some embodiments, a cylinder of engine 10 may include a spark plug 192 for initiating the combustion process. An ignition system 190 may provide an ignition spark to combustion chamber 14 via spark plug 192 during select engine operating modes in response to an advance ignition signal SA from control unit 12. However, in some embodiments, spark plug 192 may be omitted, such as when engine 10 initiates the combustion process through auto-ignition or fuel injection, as is the case with some diesel engines.

[0032] In some embodiments, each cylinder of engine 10 may be configured with one or more fuel injectors to provide fuel thereto. As a non-limiting example, cylinder 14 is shown with an injector 166. The illustrated injector 166 is directly connected to cylinder 14 to inject fuel directly therein in proportion to the pulse width of the FPW signal received from controller 12 via electrical driver 168. In this manner, injector 166 provides what is known as direct injection (hereinafter also referred to as "DI") of fuel into combustion cylinder 14. Fig. 2 shows the injector 166 as a side-mounted injector, but it may also be located above the piston, such as near the position of the spark plug 192. Such a position may improve mixing and combustion when driving the engine with an alcohol-based fuel due to the lower volatility of some alcohol-based fuels. Alternatively, the injector may be located above and near the intake valve to improve mixing. The fuel may be supplied to the injector assembly 166 from a high-pressure fuel system 8, which includes fuel tanks, fuel pumps, and a fuel delivery element. Alternatively, the fuel may be supplied by a single-stage fuel pump at a lower pressure, in which case the timing of the direct fuel injection may be more limited during the compression stroke than in cases where a high-pressure fuel system is used.Further, although not shown, the fuel tanks may include a pressure transducer that provides a signal to the control unit 12. As can be seen, in an alternative embodiment, the injector 166 may be a port injector that provides fuel to the intake port upstream of the cylinder 14.

[0033] As described above, Fig. 2 represents only one cylinder of a multi-cylinder engine. Therefore, the cylinder can include its own set of intake / exhaust valves, fuel injector(s), spark plug, etc.

[0034] Fuel tanks in fuel system 8 may contain fuel with different fuel properties, such as different fuel compositions. These differences may include different alcohol content, different octane rating, different latent heat of vaporization, different fuel blends, different fuel volatility, and / or combinations thereof, etc.

[0035] The control unit 12 is in Fig. 2 as a microcomputer comprising a microprocessor unit 106, input / output ports 108, an electronic storage medium for executable programs and calibration values, illustrated in this particular example as read-only memory 110, a random access memory 112, an auxiliary memory 114, and a data bus. The read-only memory 110 of the storage medium may be programmed with computer-readable data representing instructions to be executed by the processor 106 to perform the methods and routines described below, as well as other previously mentioned variations not specifically listed.The control unit 12 may receive various signals from sensors connected to the engine 10, in addition to the signals already discussed, including measuring the inducted mass air flow (MAF) by the mass air flow sensor 122; the engine cooling temperature (ECT) by the temperature sensor connected to a cooling sleeve 118; a profile ignition pickup signal (PIP) by a Hall effect sensor 120 (or other type) connected to the crankshaft 140; throttle position (TP) by a throttle position sensor; a boost pressure (MAP) signal by a sensor 124; cylinder AFR by an EGO sensor 128; exhaust AFR by a CMS 179; and abnormal combustion by a knock sensor and crankshaft acceleration sensor. An engine speed signal, RPM, may be generated by the control unit 12 from a PIP signal.Boost pressure signal MAP from a boost pressure sensor can be used to provide an indication of vacuum or pressure in the intake manifold.

[0036] Based on inputs from one or more of the aforementioned sensors, the control unit 12 may adjust one or more actuators such as the injector 166, the throttle 162, the spark plug 192, intake / exhaust valves and cams, etc. The control unit may receive input data from the various sensors, process the input data, and activate the actuators in response to the processed input data based on the instructions or codes programmed therein corresponding to one or more routines. An exemplary control routine is described herein with respect to Fig. 3 shown.

[0037] Fig. 3 shows an exemplary method 300 for inhibiting engine derating and enabling DFSO during selected vehicle operating conditions so that monitoring routines can be performed to analyze exhaust system components. As described above, during selected vehicle operating conditions, e.g., when the vehicle speed is above a speed threshold and when entry conditions for performing a monitoring routine are met, engine shutdown can be postponed for a duration, the provision of fuel to the engine can be interrupted, and rich-to-lean transition ratios through the exhaust system can be tracked to determine if there is deterioration in one or more exhaust system components, e.g., one or more sensors or catalysts. This fuel interruption occurs at a time when, in a hybrid vehicle, the engine would normally be shut down, e.g.,in response to an engine downshift request, such as the driver's throttle release. The engine must continue to rotate to move the lean transition through the exhaust and allow for observation by the monitoring element.

[0038] The sensor and catalyst monitoring routines described herein depend on transitions between air / fuel ratios by exhaust system components and, thus, on changes in engine operation while the engine is running. The engine is not started or ramped up solely to perform a diagnostic test. Therefore, at 302, method 300 includes determining whether the engine is running. If the engine is running at 302, method 300 proceeds to 304.

[0039] At 304, method 300 determines whether an engine down request occurs. An engine down request may occur in a hybrid vehicle in response to a variety of operating conditions. In one example, an engine down request may include a driver throttle release, where a torque request is interrupted or reduced by a driver input, such as via an accelerator pedal. As another example, an engine down request may be dependent on vehicle load and / or vehicle speed. For example, an engine down request may occur in response to a vehicle load and / or vehicle speed that is below a threshold. An engine down request may also be generated based on operating conditions of the engine 20, operating conditions of the generator 50, and / or a state of charge of the energy storage device 50.In some examples, an engine down-regulation request may be generated each time the driver releases the throttle.

[0040] If an engine downtime request occurs at 304, method 300 proceeds to 306. At 306, method 300 includes determining whether sensor test entry conditions are met. For example, an exhaust sensor test may be scheduled to be performed on one or more exhaust gas sensors in the vehicle's exhaust. For example, exhaust sensor 128 may be periodically tested to determine whether its response to changes in air / fuel ratio is substantially accurate.

[0041] Sensor test entry conditions can be based on a variety of engine and vehicle operating conditions, as well as a sensor monitoring schedule. For example, if no sensor test has been performed for a certain period of time, a sensor test can be scheduled to be performed at the next best opportunity when a derate request is triggered and other entry conditions are met. Furthermore, the sensor test entry conditions can be met based on how long the engine has been running. Thus, the sensor test entry conditions can include engine runtime greater than a threshold duration.

[0042] Sensor test entry conditions may also be based on vehicle speed, e.g., the vehicle's propulsion speed in a forward or reverse direction. For example, sensor test entry conditions may include a vehicle speed above a first speed threshold, e.g., above 47 mph. In this way, as described below, engine downregulation may be inhibited only when the vehicle speed is above this first threshold vehicle speed, thus increasing consumer satisfaction with the hybrid vehicle.

[0043] The entry conditions can also be based on whether engine downregulation is currently inhibited or how long the engine downregulation has been inhibited. For example, if the engine has been inhibited for less than a threshold duration, e.g., less than five minutes, the engine can continue to be inhibited to perform the sensor test as described below. However, if the engine has been inhibited for longer than the threshold duration, e.g., more than five seconds, the engine should be turned off and the monitoring routine should not occur. These entry conditions can be used to ensure that the engine is only inhibited during conditions where the sensor monitor is operational and the vehicle condition allows for non-intrusive inhibition of engine downregulation, so that the engine is not left on when not desired.

[0044] If sensor test entry conditions are met at 306, method 300 proceeds to 308. In some examples, method 300 may include determining whether the engine temperature is above a threshold temperature at 308. For example, the engine coolant temperature, as determined by temperature sensor 116, may be used to determine whether the engine temperature is above a threshold temperature. In this way, method 300 ensures that the engine is sufficiently warmed up to perform the monitoring routine.

[0045] If the engine temperature is not above the threshold temperature at 308, method 300 proceeds to 318 to not inhibit engine derating. For example, engine operation may be interrupted in response to the engine derating request while the vehicle remains operating. If the engine temperature is above the threshold temperature at 308, method 300 proceeds to 310.

[0046] At 310, method 300 includes downregulating the engine. For example, in response to the downregulation request, engine shutdown may be postponed for a duration so that the sensor test can be performed to diagnose faults in the sensor. To provide larger air / fuel swings to the sensor monitor while inhibiting engine downregulation, method 300 includes, at 312, enabling DFSO. Activating DFSO may include cutting off fuel to the engine while the engine is running and while inhibiting engine downregulation. By initiating DFSO and inhibiting engine downregulation, a rich-to-lean air / fuel ratio transition may be monitored by the exhaust gas sensor during the sensor test to test the sensor, as described below.

[0047] At 314, method 300 includes performing sensor monitoring. For example, the monitoring test may include monitoring a rich-to-lean transition in the air / fuel sensor in an exhaust of the vehicle. For example, while engine down-regulation is inhibited and DFSO is enabled, air / fuel sensor readings from exhaust sensor 128 may be monitored and sensor degradation in response to the rich-to-lean transition at an air / fuel sensor may be indicated. For example, the rich-to-lean transition on the sensor may be compared to an expected transition to determine if the sensor has degraded. Furthermore, in some examples, the rich-to-lean transition measured by the sensor may be compared to one or more predetermined transition patterns to diagnose a type of failure that may be present in the sensor.

[0048] At 316, method 300 includes determining whether the sensor test exit conditions are met. The sensor test exit conditions may be based on a period of time that the sensor test has been in progress while inhibiting engine downtime and enabling DFSO. In some examples, engine downtime may be inhibited for a duration less than a threshold duration such that vehicle operation is not significantly impacted by keeping the engine on for a duration after the downtime request. Further, in some examples, the sensor test exit conditions may be based on whether the sensor test is complete or has collected sufficient data to effectively diagnose the sensor. If the sensor test exit conditions are not met at 316, method 300 continues to perform the sensor monitoring of 314.

[0049] If the sensor test exit conditions are met at 316, method 300 proceeds to 318 to discontinue the inhibition of engine derating. For example, after the monitoring test is completed, the engine may be shut down while the vehicle is still operating. For example, after the sensor monitoring is completed, vehicle operation for propelling the vehicle may be discontinued, and an additional voltage source in the hybrid vehicle may instead be used to propel the vehicle at non-zero speed or to continue operating the vehicle.

[0050] If an indication of a sensor failure is found during the sensor test, in some examples, a message may be sent to an onboard diagnostic device or a fault code may be set to alert the vehicle driver to initiate maintenance procedures. In some examples, if sensor degradation is detected, mitigation measures may be implemented. For example, sensor readings from the degraded sensor may be adjusted based on a difference between a measured and expected transient, so that a corrected sensor reading can be used to diagnose additional exhaust system components, such as catalytic converters.

[0051] Returning to 306, if the sensor test entry conditions are not met at 306, method 300 proceeds to 320. At 320, method 300 includes determining whether the catalyst monitoring unit entry conditions are met. A catalyst monitor may be performed to determine whether a catalyst in the exhaust, e.g., catalyst 178, has degraded. For example, the catalyst monitor may be performed to determine the storage capacity or age of the catalyst.

[0052] As with the sensor test entry conditions, the catalyst monitoring unit entry conditions may be based on a variety of engine and vehicle operating conditions, as well as a catalyst monitoring schedule. For example, if a catalyst test has not been performed for a certain period of time, a catalyst test may be scheduled to be performed at the next best opportunity when a derate request is triggered and other catalyst monitoring unit entry conditions are met. Furthermore, the catalyst monitoring unit entry conditions may be based on how long the engine has been running. Thus, the sensor test entry conditions may include engine run time greater than a threshold duration.

[0053] Catalyst monitoring unit entry conditions may also be based on vehicle speed. For example, catalyst monitoring entry conditions may include a vehicle speed that is above a second speed threshold, e.g., above 27 m / h. In some examples, this second threshold speed may be lower than the first threshold speed for a sensor test described above. In this way, as described below, engine downregulation may only be inhibited when the vehicle speed is above this first threshold vehicle speed, so that consumer satisfaction with the hybrid vehicle may be increased. The entry conditions may also be based on whether engine downregulation is currently inhibited or how long the engine downregulation has been inhibited. For example, if the engine has been inhibited for less than a threshold duration, e.g.,less than five seconds, to perform the catalyst test as described below. These entry conditions can be used to ensure that the engine is only inhibited during conditions where the catalyst monitor is operational and the vehicle condition allows for non-intrusive inhibition of engine downshift, so that the engine does not remain on when not desired.

[0054] Catalyst monitor entry conditions may be further based on air / fuel sensor readings from sensors upstream and / or downstream of the catalyst. For example, the catalyst monitor entry conditions may include exhaust gas sensors upstream and downstream of the catalyst indicating "rich." For example, entry conditions for monitoring catalyst 178 may include an upstream sensor 128 and a downstream sensor 179 both indicating substantially "rich" or both indicating a threshold amount of richness in the exhaust gas.

[0055] For example, the timing of the fuel shutoff can affect the magnitude of the air-fuel ratio fluctuations observed by the catalyst monitor sensors. Starting the fuel supply when the upstream and downstream exhaust sensors are essentially rich will measure a large difference. Conversely, cutting off the fuel supply when both the upstream and downstream exhaust sensors are already lean will result. Starting when both the CMS 179 and the EGO sensor 128 are rich or richer than a threshold will cause the CMS reading to first show rich and then, after the fuel supply is shutoff, transition to lean. This transition can be used to diagnose the catalyst. The engine must continue to run to move the lean transition through the exhaust and allow the monitor to observe.The catalyst monitor is based on CMS voltage readings from the CMS 179. Thus, entry conditions for catalyst monitoring may include the CMS voltage being above a rich voltage threshold.

[0056] If catalyst monitor entry conditions are not met at 320, method 300 proceeds to 318 to not inhibit engine downregulation. For example, in response to the engine downregulation request, the engine is shut down and catalyst monitoring is not performed. For example, engine shutdown may not be inhibited if exhaust gas sensors upstream and downstream of the catalyst indicate lean. If catalyst monitor entry conditions are not met at 320, method 300 proceeds to 322.

[0057] At 322, method 300 may include determining whether the engine temperature is above a threshold temperature. For example, the engine coolant temperature, as determined by temperature sensor 116, may be used to determine whether the engine temperature is above a temperature threshold. Thus, method 300 may ensure that the engine is sufficiently warmed up to perform the monitoring routine. If the engine temperature is not above the temperature threshold at 322, method 300 proceeds to 318 to not inhibit engine derating and to shut down the engine. However, if the engine temperature is above the threshold temperature at 322, method 300 proceeds to 324.

[0058] At 324, method 300 includes inhibiting engine downshift. For example, engine shutdown may be inhibited in response to exhaust gas sensors upstream and downstream of the catalyst indicating rich. At 326, method 300 includes enabling DFSO. Enabling DFSO may include shutting off fuel to the engine while the engine is running and inhibiting engine downshift. Upon initiating DFSO and inhibiting engine downshift, a rich-to-lean air-fuel ratio transition may be monitored by the catalyst monitoring unit sensors to perform catalyst diagnostics, as described below.

[0059] At 328, method 300 includes performing catalyst monitoring. For example, a rich-to-lean transition upstream and downstream of a catalyst in an exhaust of the vehicle may be monitored, and catalyst degradation may be indicated based on the rich-to-lean transition downstream of a catalyst. For example, the rich-to-lean transition downstream of the catalyst may be compared to an expected transition to determine whether the catalyst has degraded, e.g., to determine catalyst storage capacity or age.

[0060] At 330, method 300 includes determining whether the catalyst test exit conditions are met. The catalyst test exit conditions may be based on a period of time that the catalyst test has been running while inhibiting engine downshifting and enabling DFSO. In some examples, engine downshifting may be inhibited for a duration less than a threshold duration such that vehicle operation is not significantly impacted by keeping the engine on for a duration after the downshift request. Further, in some examples, the sensor test exit conditions may be based on whether the sensor test is complete or has collected sufficient data to effectively diagnose the sensor. If the sensor test exit conditions are not met at 330, method 300 continues to perform the sensor monitoring of 328.

[0061] If the catalyst test exit conditions are met at 330, method 300 proceeds to 318 to discontinue the inhibition of engine derating. For example, after the monitoring test is completed, the engine may be turned on while the vehicle is still operating. For example, after catalyst monitoring is completed, vehicle operation for propelling the vehicle may be discontinued, and an additional voltage source in the hybrid vehicle may instead be used to propel the vehicle at non-zero speed or to continue operating the vehicle.

[0062] If an indication of catalyst deterioration is found during the catalyst test, e.g. if the age of the catalyst is above a threshold or if the storage capacity is below a storage threshold, in some examples a message may be sent to an on-board diagnostic device or a fault code may be set to alert the driver of the vehicle that maintenance procedures need to be initiated.

[0063] Fig. 4 shows an exemplary method, such as method 300 described above, for operating a hybrid vehicle to inhibit engine downregulation during selected vehicle operating conditions to perform exhaust sensor and catalyst monitoring tests. At 402, Fig. 4 shows an example diagram of a vehicle speed as a function of time. At 404, Fig. 4 shows an example diagram of engine operation, e.g. whether the engine is switched on or off, as a function of time. At 406, Fig. 4 a controlled DFSO, e.g., whether the DFSO is activated (on) or deactivated (off) as a function of time. At 408, Fig. 4 shows exemplary air / fuel readings of an exhaust sensor positioned downstream of a catalyst in the exhaust, e.g., a CMS 179 positioned downstream of the catalyst 178. At 410, Fig. 4 example air / fuel readings from an exhaust sensor located upstream of the catalyst in the exhaust, e.g., an air / fuel sensor 128.

[0064] Before time t0 in Fig.4, the vehicle is driven in an engine-on mode, with the engine being used to at least partially propel the vehicle. During this time, as shown in the diagram at 402, the vehicle speed is below the second speed threshold v2. For example, engine down-regulation may not be inhibited below this second speed threshold.

[0065] At time t0, the engine downshift request occurs. For example, the vehicle driver may apply an accelerator pedal to initiate an engine shutdown event at t0. As shown in diagram 404, the engine is shut down at t0, and the vehicle is operated between times t0 and t1 using an auxiliary voltage source while the engine is deactivated. However, because the vehicle speed is below the speed threshold v1 between times t0 and t1, the engine downshift is not postponed during this period, and no diagnostic tests are performed on exhaust components.

[0066] At time t1, an engine up-regulation request occurs. For example, at time t1, a driver may apply throttle to request higher engine speed. Thus, at t1, the engine is activated to meet the torque request. Between times t1 and t2, the vehicle speed increases above the speed threshold v2, and at t2, an engine down-regulation request occurs, e.g., when the vehicle driver again applies throttle. In this case, because the vehicle speed is above the speed threshold v2 and both the CMS and the A / F sensor indicate "rich," as shown in plots 408 and 410, respectively, catalyst monitoring may be initiated, inhibiting engine down-regulation and enabling DFSO. Catalyst monitoring is then performed between times t2 and t3, while engine down-regulation is postponed and DFSO is enabled.At t3, the exit conditions for catalyst monitoring are met, e.g., catalyst monitoring is complete or a time threshold has expired. Thus, at t3, engine downregulation is no longer postponed, and the engine is shut down.

[0067] At t4, another engine ramp-up occurs, e.g., in response to a driver acceleration, so the engine is activated to meet the torque request. Between times t4 and t5, the vehicle speed increases above the first speed threshold v1, which is above the second speed threshold v2. At t5, another ramp-down request is executed, e.g., when the driver eases off the throttle, and the sensor monitor can be initiated, since the vehicle speed is above v2, to postpone the engine ramp-down and activate DFSO. The readings from the A / F sensor between times t5 and t6, shown at 410, can then be used to diagnose the sensor. At time t6, the exit conditions for the sensor test are met, and the engine ramp-down is no longer postponed, so the engine is shut down again at t6.

[0068] By operating a hybrid vehicle to inhibit engine downshifting during selected vehicle operating conditions to perform exhaust sensor and catalyst monitoring tests while simultaneously activating the DFSO, as described above, diagnostic routines can be performed using the DFSO to sufficiently expose exhaust gas sensors to rich and lean air / fuel mixtures to perform more accurate diagnostics for exhaust system components while reducing the impact of the monitoring routines on vehicle operation. Furthermore, with such an approach, fuel savings can be increased by inhibiting engine downshifting only when the diagnostic monitoring units are operational. Furthermore, because the engine is not forced to maintain sub-threshold speeds, consumer satisfaction with hybrid vehicle operation can increase.

[0069] It should be noted that the example control and estimation routines included herein may be used with various transmission and / or vehicle system configurations. The specific routines described herein may represent one or more of a number of processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, and the like. Various disclosed acts, operations, or functions may therefore be performed in the order presented, in parallel, or in some cases omitted. Likewise, the processing order is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the described operations or functions may be performed repeatedly depending on the type of strategy employed.Furthermore, the described processes may graphically represent a code that is programmed on the computer-readable storage medium in the engine control unit.

[0070] It should be understood that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered limiting, as numerous modifications are possible. For example, the technology outlined above may be technically applicable to V-6, I-4, I-6, V-12, 4-cylinder, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations and other features, functions, and / or characteristics disclosed herein.

[0071] The following claims particularly point out certain combinations and sub-combinations that are considered novel and non-obvious. These claims may refer to "a" or "a first" element, or an equivalent thereof. Such claims are to be construed as encompassing one or more such elements, without requiring or excluding two or more such elements. Further combinations and sub-combinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or submitting new claims in this or a related application. Such claims, whether broader or narrower, or either the same or different in scope with respect to the original claims, are also considered to be within the scope of the present disclosure.

Claims

[1] Method for a hybrid vehicle with an engine (10), comprising: Inhibiting engine shutdown and enabling deceleration fuel shutoff (312, 326) to perform a monitoring test while the vehicle speed is above a speed threshold; in response to an engine down-regulation request when a vehicle speed is above a first speed threshold: Inhibiting engine shutdown; activating a deceleration fuel cut-off (312); Monitoring a rich-to-lean transition in an air / fuel sensor in an exhaust of the vehicle; and Indicating sensor degradation based on the rich-to-lean transition in the air / fuel sensor; and in response to an engine down-regulation request when a vehicle speed is above a second speed threshold which is lower than the first: Inhibiting engine shutdown; activating a deceleration fuel cut-off (326); monitoring a rich-to-lean transition upstream and downstream of a catalyst (178) in an exhaust of the vehicle; and Indication of catalyst deterioration based on the rich-to-lean transition upstream and downstream of the catalyst (178). [2] The method of claim 1, wherein inhibiting engine shutdown to perform a monitoring test in response to an engine derate request is performed while the engine (10) is running and an engine temperature is greater than a temperature threshold. [3] A method according to claim 2, wherein the engine down-regulation request is generated in response to a driver throttle release. [4] The method of claim 1, further comprising shutting down the engine (10) once the monitoring test is completed. [5] The method of claim 1, wherein inhibiting engine shutdown is performed in response to exhaust gas sensors upstream and downstream of the catalyst (178) indicating "rich", and wherein the method further comprises not inhibiting engine shutdown when the exhaust gas sensors upstream and downstream of the catalyst (178) indicate "lean".

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