Method and system for plausibility testing of a knock sensor

Abstract

Method for an engine, comprising: Generating a vibration via an actuator in the absence of engine combustion, the actuator comprising part of an acoustic vehicle notification system and generating acoustic vehicle notifications in response to a vehicle speed being below a threshold and the engine being off; and Indicating knock sensor degradation of a knock sensor based on an amplitude of a knock sensor output in response to the generated vibration.

Description

REGIONThe present description relates generally to methods and systems for determining knock sensor degradation and adjusting operation in response thereto.GENERAL STATE OF THE ART / SUMMARYEngine knock is caused by spontaneous combustion of the air-fuel mixture in compressed tail gases caused by the original combustion ignition event in a combustion chamber. Knock sensors may be used to detect knock conditions, such as due to carbon accumulation within the combustion chamber. The knock sensor may be a passive piezoelectric device that outputs a voltage in response to the received acoustic vibration. A high amplitude knock sensor output may indicate a knock event. To ensure engine performance, a plausibility check for the knock sensor may be used.Attempts to address knock sensor plausibility checks include determining knock sensor degradation based on sensor output during engine operation. An exemplary approach is shown by Hernandez et al. in U.S. Pat. No. 7,222,607 B2. Therein, the knock energy of each knock sensor is calculated and a knock sensor fault is determined if the knock energy is below an experimentally determined threshold. Further prior art is known from publications DE 10 2008 019 674 A1 and DE 100 33 586 A1.However, the inventors herein have recognized potential issues with such systems. As one example, the knock sensor output energy may be below a threshold under certain conditions, although the knock sensor is functioning properly. For example, knock sensor output may be low and near zero during a vehicle idle-off or hybrid electric vehicle (EV) mode. Under these conditions, previous approaches may result in false positive diagnostics. Further, plausibility checks based on knock energy may be time consuming, as a reliable knock energy calculation may require large sampling points of the knock sensor output.It is therefore an object of the present invention to provide an improved method for determining knock sensor degradation and adjusting operation in response thereto.This object is achieved by the features of the independent claims. Advantageous refinements of the invention are described in the dependent claims.In one example, the issues described above may be overcome by a method for an engine, comprising: generating vibration via an actuator in the absence of engine combustion; and indicating knock sensor degradation based on knock sensor output in response to the generated vibration. In this way, knock sensor degradation in an engine may be reliably determined.As an example, a method may include recording an engine vibration during engine combustion and generating an excitation signal by adding a pulse signal to the recorded engine vibration. When the vehicle is still operating and combustion events are stopped in all engine cylinders, an actuator may be actuated with the excitation signal to generate a structural and / or sound vibration. The oscillation may simulate the noise or oscillations of engine knock during engine combustion and trigger a knock sensor (e.g., if the processed output of the knock signal were detected by the electronic control system as engine knock). The vibration, which may include sound vibration, may also notify pedestrians and / or vehicle drivers that the vehicle is running when there is no noise from engine combustion. Based on the response of the knock sensor, sensor degradation may be indicated. For example, knock sensor degradation may be indicated if the amplitude of the knock sensor output corresponding to the excitation pulse signal is below a threshold. In this way, a plausibility check for a knock sensor may be reliably performed when there is no combustion event in the engine cylinder (e.g., when the engine is at rest and no combustion cycles are being performed). Since knock sensor degradation is determined by a check whether the sensor responds to a pulse signal generated by a controller in this example, the plausibility check may be completed in a short time. In one example, knock sensor degradation may be reliably determined by adjusting the amplitude of the acoustic vibration to be within a threshold range of the same level as noise generated from engine knock. Further, by comparing the amplitude of the excitation signal to the amplitude of the knock sensor output, degradation in sensitivity of the knock sensor may be compensated. In one example, the actuator for generating the sound vibration may be incorporated into an acoustic vehicle alerting system (AVAS) already present in the HEV. Therefore, the method can be implemented with low adjustment of the vehicle system.It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely in the claims following the detailed description. Further, the claimed subject matter is not limited to implementations that eliminate disadvantages noted above or in any part of the present disclosure.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 shows an example engine system. FIG. 2 shows an example method for carrying out a plausibility check for a knocking sensor of an engine. FIG. 3 illustrates timelines of various engine operating parameters during implementation of the example method.DETAILED DESCRIPTIONThe following description relates to systems and methods for performing a plausibility check of an engine knock sensor in an engine system, such as the engine system shown in FIG. 1. FIG. 2 shows an example method for detecting knock sensor degradation. During engine operation, an actuator is excited to produce vibration in the absence of engine combustion. If the knock sensor is not sensitive to vibration, sensor degradation may be determined. Variation of engine operating parameters during implementation of the example method is illustrated in FIG. 3.FIG. 1 illustrates an example embodiment of a combustion chamber or cylinder of the internal combustion engine 10. The engine 10 may receive control parameters from a control system including the controller 12 and input from a vehicle operator 130 via an input device 132. In this example, the input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. Cylinder 14 (also referred to herein as a combustion chamber) of engine 10 may include combustion chamber walls 136 in which piston 138 is positioned. The piston 138 may be coupled to the crankshaft 140 such that reciprocating motion of the piston is translated into rotational motion of the crankshaft. The crankshaft 140 may be coupled to at least one drive wheel of the passenger vehicle via a transmission system (not shown). Further, a starter motor may be coupled to crankshaft 140 via a flywheel (not shown) to enable a cranking operation of engine 10.The cylinder 14 may receive intake air via a series of intake air passages 142, 144, and 146. The intake air passage 146 may communicate with other cylinders of the engine 10 in addition to the cylinder 14. In some embodiments, one or more of the intake passages may include a boosting device, such as a turbocharger or a compressor. For example, FIG. 1 shows engine 10 configured with a turbocharger including a compressor 174 disposed between intake air passages 142 and 144, and an exhaust turbine 176 disposed along an exhaust passage 148. Compressor 174 may be at least partially powered by exhaust turbine 176 via a shaft 180, where the boosting device is configured as a turbocharger. A wastegate (not shown) may be coupled in the turbocharger via exhaust turbine 176. Specifically, the wastegate may be included in a bypass passage coupled between an inlet and an outlet of the exhaust turbine 176. By adjusting a position of the wastegate, an amount of boost provided by the turbine may be controlled. The wastegate may be coupled to an electromechanical actuator, which may receive commands from a controller 12. However, in other examples, such as where engine 10 is equipped with a compressor, exhaust turbine 176 may be omitted where appropriate, and compressor 174 may be powered by mechanical inputs from an electric motor or the internal combustion engine.A throttle 20 (also referred to as intake throttle 20) including a throttle 164 may be provided along an intake passage of the engine to vary the flow rate and / or pressure of intake air provided to cylinders of the engine. For example, throttle 20 may be disposed downstream of compressor 174, as shown in FIG. 1, or alternatively may be provided upstream of compressor 174.Exhaust passage 148 may receive exhaust gases from other cylinders of engine 10, in addition to cylinder 14. Exhaust gas sensor 128 is shown coupled to exhaust passage 148 upstream of emission control device 178. The sensor 128 may be selected from various suitable sensors for providing an indication of exhaust gas air-fuel ratio, such as a linear oxygen sensor or UEGO (universal exhaust gas oxygen) sensor, a two-state oxygen sensor or EGO (as shown), a HEGO (heated EGO) sensor, a NOx, HC, or CO sensor. Emission control device 178 may be a three way catalyst (TWC), NOx trap, various other emission control devices, or combinations thereof.The exhaust temperature may be estimated by one or more temperature sensors (not shown) disposed in the exhaust passage 148. Alternatively, exhaust temperature may be inferred based on engine operating conditions such as speed, load, air-fuel ratio (AFR), spark retard, etc. Further, exhaust temperature may be calculated by one or more exhaust gas sensors 128. It may be noted that the exhaust temperature may alternatively be estimated by any combination of methods for temperature estimation.An exhaust gas recirculation (EGR) system (not shown) may be used to direct a desired portion of the exhaust gas from the exhaust passage 148 to the intake air passage 142 upstream of the compressor 174. An amount of EGR flow may be controlled by an EGR valve. Alternatively, as internal EGR, a portion of the combustion gases may be retained in the combustion chambers by controlling the timing of the exhaust and intake valves. In yet another alternative, exhaust gases may be directed from a location upstream of the exhaust turbine to a location downstream of the compressor.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, which are disposed in an upper portion of cylinder 14. 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 an upper portion of the cylinder.Intake valve 150 may be controlled by controller 12 by cam actuation via cam actuation system 151. Similarly, exhaust valve 156 may be controlled by controller 12 via cam actuation system 153. Cam actuation systems 151 and 153 may each include one or more cams and 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 controller 12 to vary valve operation. The position of intake valve 150 and 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 electric 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, including CPS and / or VCT systems. In still other embodiments, the intake and exhaust valves may be controlled by a common valve actuator or system or variable valve actuation actuator or system.Cylinder 14 may have a compression ratio that is the volume ratio between piston 138 at bottom dead center and top dead center. Conventionally, the compression ratio is in the range of 9:1 to 10:1. however, in some examples where other fuels are used, the compression ratio may be increased. This can occur, for example, when fuels with a higher octane number or fuels with a higher latent enthalpy of vaporization are used. The compression ratio may also be increased using direct injection due to its effect on engine knock.In some embodiments, each cylinder of engine 10 may include a spark plug 192 to initiate combustion. Ignition system 190 may provide spark to combustion chamber 14 via spark plug 192 in response to a pre-ignition signal SA from controller 12 under selected operating modes. However, in some embodiments, spark plug 192 may be omitted, such as when engine 10 may initiate combustion by auto-ignition or by injecting fuel, which may be the case with some diesel engines.In some embodiments, each cylinder of engine 10 may be configured with one or more fuel injectors to supply fuel thereto. As a non-limiting example, cylinder 14 is shown including a fuel injector 166. Fuel injector 166 is shown coupled directly to cylinder 14 to directly inject fuel therein in proportion to the pulse width of signal FPW received from controller 12 via electronic driver 168. In this manner, fuel injector 166 provides so-called direct injection (hereinafter also referred to as "DI" (direct injection)) of fuel into combustion cylinder 14. Although FIG. 1 shows fuel injector 166 as a side injector, it may also be disposed over the piston, such as near the position of spark plug 192. Such a position may improve mixing and combustion when the engine is operated with an alcohol-based fuel, as some alcohol-based fuels have lower volatility. Alternatively, the injector may be positioned above and near the intake valve to improve mixing. Fuel may be supplied to fuel injector 166 from a high pressure fuel system 8 including fuel tanks, fuel pumps, and a fuel rail. Alternatively, fuel may be provided at a lower pressure by a single stage fuel pump, in which case the timing of direct fuel injection during the compression stroke may be more limited than when using a high pressure fuel system. Further, although not shown, the fuel tanks may include a pressure transducer that provides a signal to the controller 12. It should be appreciated that fuel injector 166 may be a port injector that provides fuel into the port upstream of cylinder 14 in an alternative embodiment.It will also be appreciated that while the depicted embodiment illustrates the engine being operated by injecting fuel via a single direct injector, in alternative embodiments the engine may be operated by using two injectors (e.g., a direct injector and a port injector) and varying a relative injection amount from each injector.Fuel tanks in the fuel system 8 may contain fuel with different properties, such as with different fuel compositions. These differences may include different alcohol contents, different octane numbers, different heat of vaporization, different fuel mixtures and / or combinations thereof, etc.Fuel may be supplied to the cylinder by the injector during a single cycle of the cylinder. Further, the distribution and / or relative fuel amount supplied by the injector may vary depending on operating conditions. Moreover, for a single combustion event, multiple injections of the delivered fuel may be performed per cycle. The plurality of injections may be performed during the compression stroke, intake stroke, or any suitable combination thereof. Additionally, fuel may be injected during the cycle to adjust the ratio of air to injected fuel (AFR) of combustion. For example, fuel may be injected to provide a stoichiometric AFR. An AFR sensor may be included to provide an estimate of the AFR within the cylinder. In one example, the AFR sensor may be an exhaust gas sensor, such as an EGO sensor 128. By measuring an amount of residual oxygen (for lean mixtures) or unburned hydrocarbons (for rich mixtures) in the exhaust gas, the sensor may determine the AFR. Thus, the AFR may be provided as a lambda (λ) value, i.e., as a ratio of the actual AFR to stoichiometry for a respective mixture. Thus, a lambda value of 1.0 indicates a stoichiometric mixture, mixtures richer than stoichiometric mixtures have a lambda value below 1.0, and mixtures leaner than stoichiometric mixtures have a lambda value above 1.Engine 10 may include a knock sensor coupled to each cylinder 14 for detecting abnormal cylinder combustion events, such as knock, low speed pre-ignition (LSPI), and high speed pre-ignition (HSPI). In one embodiment, one or more knock sensors 90 may be coupled to selected locations of the cylinder block 15. For example, the knock sensor may be directly coupled to the outer wall of the cylinder block 15. In yet another embodiment, one or more knock sensors 90' may be coupled to the intake manifold 144. For example, the knock sensor may be directly coupled to the wall of the intake manifold and protrude into an interior of the intake manifold.The engine 10 may further include an audible vehicle notification system (AVAS) 9. As hybrid electric vehicles are very quiet, the AVAS system 9 may actuate an actuator to generate vibration to provide messages to pedestrians and / or the vehicle operator during vehicle operation. As an example, the AVAS system may be activated and generate audible vehicle messages when the vehicle speed is below a threshold and the engine of the vehicle is deactivated. As another example, the AVAS system may be activated when the vehicle is moving in reverse in electric mode. In one example, the actuator for generating the vibration may be a loudspeaker. In one embodiment, the actuator 123 may be coupled to the cylinder block 15. The actuator may be directly coupled to the outer wall of the cylinder block 15. In another embodiment, actuator 123' may be coupled to intake manifold 144. The actuator may be directly coupled to the wall of the intake manifold and protrude into an interior of the intake manifold. In this way, vibration generated by the actuator may resonate within the cylinder block. In yet another embodiment, the actuator may be positioned outside of all combustion chambers of the engine. In one embodiment, both knock sensor 90 and actuator 123 are coupled to the cylinder block. The actuator may generate acoustic vibration simulating knocking sound of the cylinder to which it is coupled, and the knocking sensor may detect engine knocking of the cylinder to which it is coupled. In another embodiment, both knock sensor 90' and actuator 123' are coupled to the intake manifold. The knock sensor may detect engine knock in any cylinder of a multi-cylinder engine. Positioning the knock sensor and the actuator close to each other (both coupled to the cylinder block or both coupled to the intake manifold) may ensure that acoustic vibration generated by the actuator may reach the knock sensor. In another embodiment, the knock sensor may be coupled to each cylinder block and the actuator may be coupled to the intake manifold. By coupling the actuator to the intake manifold, only one actuator is required for a multi-cylinder engine system to generate the acoustic vibration to determine knock sensor degradation. The acoustic vibration generated by the actuator may simulate engine knock in any cylinder of the multi-cylinder engine. In another embodiment, the knock sensor may be coupled to the intake manifold and the actuator may be coupled to each of the cylinder blocks. The AVAS system may further include a recording device for recording engine vibration. In one embodiment, the recording device can be integrated into the actuator. By coupling the actuator to the cylinder block or intake manifold, engine knock noise may be generated and resonated in the cylinder block or intake manifold.As described above, FIG. 1 shows only one cylinder of a multi-cylinder engine. Thus, each cylinder may similarly include its own set of intake / exhaust valves, fuel injector(s), spark plug, etc.Controller 12 is shown as a microcomputer, including microprocessor unit 106, input / output ports 108, an electronic storage medium for executable programs and calibration values shown as read only memory chip 110 in this particular example, random access memory 112, keep alive memory 114, and a data bus. Controller 12 may receive various control signals from sensors coupled to engine 10, in addition to those signals previously discussed, including measurement of inducted mass air flow (MAF) from mass air flow sensor 122; engine coolant temperature (ECT) from temperature sensor 116 coupled to cooling sleeve 118; a profile ignition pickup signal (PIP) from Hall effect sensor 120 (or other type) coupled to crankshaft 140; a throttle position (TP) from a throttle position sensor; an absolute manifold pressure (MAP) signal from sensor 124, a cylinder AFR from EGO sensor 128, and abnormal combustion from knock sensor 90. Manifold pressure signal MAP from a manifold pressure sensor may be used to provide an indication of vacuum or pressure in the intake manifold.The read-only memory 110 of a storage medium may be programmed with computer readable data representing instructions executable by the processor 106 for performing the methods described below as well as other variants that are anticipated but not expressly listed. The controller 12 thus receives signals from the various sensors of FIG. 1 and employs the various actuators of FIG. 1 to adjust engine operation based on the received signals and instructions stored on a memory of the controller. For example, adjusting the amplitude of the generated sound vibration may include adjusting the actuator 123.FIG. 2 shows an example method 200 for carrying out a plausibility check for a knocking sensor. The method generates vibration to simulate engine knock noise. If the knock sensor is functioning properly, a high amplitude knock sensor output may be detected in response to the vibration. In one embodiment, the actuator may be part of an AVAS of an HEV.Instructions for carrying out method 200 and the remaining methods included herein may be executed by a controller (such as controller 12 of FIG. 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 to FIG. 1. The controller may employ engine actuators of the engine system to adjust engine operation according to methods described below.At step 201, engine operating conditions may be determined by the controller when the vehicle is operating. The controller detects measurements from various sensors in the engine system and estimates operating conditions including engine load, engine torque demand, engine speed, engine crank angle, and engine spark timing.At step 202, method 200 determines whether an engine combustion event is halted. For example, method 200 may determine that engine combustion is stopped if combustion does not occur in any of the engine cylinders within their respective engine cycle. As another example, method 200 may determine that engine combustion is stopped if the spark plugs in all cylinders have been deactivated. As another example, method 200 may determine that engine combustion is stopped if the engine is in electric vehicle mode, where the vehicle is propelled only by torque produced by an electric motor. As another example, method 200 may determine that engine combustion is stopped if the engine is stopped (i.e., engine speed is zero). As yet another example, method 200 may determine that engine combustion is stopped if the vehicle is in idle-disconnect. In the absence of a combustion event, the method 200 proceeds to step 204 where the recorded engine vibration is charged. For example, the engine vibration may be loaded from a non-volatile memory. Engine vibration may include engine noise due to engine combustion. The engine vibration may also include noise generated by the traveling vehicle. If engine combustion has not been stopped, method 200 proceeds to step 203.At step 203, the method 200 determines whether to record engine vibration. As an example, engine vibration may be recorded if no recorded engine vibration is stored on the non-volatile memory. As another example, the recorded engine vibration may be recorded if the recorded engine vibration has not been updated for a period of time.The controller may also determine whether the current engine condition is suitable for recording the engine vibration. In one embodiment, the controller may record engine operation when engine knock is not present. As an example, the controller may record engine vibration when spark retard is low and engine knock is unlikely to occur. As another example, the controller may record engine vibration when the engine load is below a threshold. In another embodiment, the controller may record engine vibration during stable engine operation. For example, stable engine operation may be determined if the variation in torque demand is within a threshold range. In another embodiment, the controller may record engine vibration during low ambient noise. The ambient noise may include, for example, noise generated without reference to the operation of the vehicle. In another embodiment, the controller may record engine vibration based on the road condition. For example, the controller may record engine vibration when the vehicle is traveling on a fixed road when the noise generated by friction between the vehicle wheels and the road is low.If method 200 determines not to capture engine vibration, method 200 proceeds to step 205 where engine operating conditions are continuously monitored. Otherwise, if the method 200 determines to record the engine vibration, the method 200 proceeds to step 206.At step 206, engine vibration may be recorded via a recording device. The engine vibration may include the sound vibration generated from engine combustion. Engine vibration may also include noise generated due to engine operation, such as friction between engine components. As an example, the recording device may be a microphone for converting sound vibration into a voltage signal. As another example, the recording device may be a piezoelectric device. In one embodiment, the recording device may be positioned in the engine intake manifold. In another embodiment, the recording device may be coupled to the engine block.At step 207, method 200 determines whether a plausibility check for the knock sensor needs to be performed. As an example, the plausibility check for the knock sensor may be performed after a predetermined period of time. As another example, the plausibility check for the knock sensor may be performed if the duration since the most recent plausibility check is above a threshold. If it is determined that the plausibility check is not being performed, the method 200 proceeds to step 209. Otherwise, the method 200 proceeds to step 208.At step 208, an actuator (such as actuator 123 or 123' in FIG. 1 ) is actuated with an excitation signal to generate a structural and / or acoustic vibration. In one example, the excitation signal may be a pulse signal or a ping signal. In another example, the excitation signal may include the recorded motor vibration from step 206. In one embodiment, the controller 12 may generate the excitation signal by adding a pulse signal to the recorded motor vibration signal and send the excitation signal to the actuator. The actuator can then convert the excitation signal into the oscillation. The vibration generated from the pulse signal may simulate engine knock during engine combustion, while the vibration generated from the recorded engine vibration may reflect vibration during engine operation. In one example, the vibration may be structural vibration. In another example, the actuator may be a speaker and the vibration is sound vibration. In another example, the actuator may alternatively be a piezoelectric device. In one embodiment, the actuator is part of the AVAS system. In another embodiment, the actuator may be positioned in the intake manifold. In another embodiment, the actuator may be coupled to the engine block. In yet another embodiment, the actuator may be integrated into the recording device.The amplitude of the generated vibration may be adjusted by the controller. In one embodiment, the amplitude of the generated vibration may be tuned to be within a threshold range of the same level as noise generated from engine knock. In one embodiment, the amplitude of the generated vibration may be adjusted based on the position of the recording device and the position of the actuator. For example, the amplitude of the generated vibration may be increased with an increasing distance between the recording device and the actuator. In another embodiment, the amplitude of the generated vibration may be based on the sensitivity of the knock sensor. For example, the amplitude may be decreased with decreased sensitivity of the knock sensor, such that the generated vibration may trigger a response if the knock sensor is healthy.If method 200 determines not to perform a plausibility check for the knock sensor, method 200 proceeds to step 209, where the actuator is only excited with the recorded engine vibration.At step 210, method 200 monitors knock sensor output and determines knock sensor degradation based on the knock sensor output. In one embodiment, knock sensor degradation may be determined if the magnitude of the knock sensor output is below a threshold. The threshold value may decrease, for example, with reduced amplitude of the generated sound vibration. In another embodiment, the reproduced engine vibration may be first removed from the knock sensor output before being compared to the threshold. As an example, the reproduced engine vibration may be removed by filtering the knock sensor output with a high pass filter. As another example, the reproduced engine vibration may be removed from the knock sensor output by subtracting the recorded engine vibration from the knock sensor output. By removing the reproduced engine vibration from the knock sensor output, the signal-to-noise ratio of the knock output due to the impulse excitation can be increased. If knock sensor degradation is not detected, method 200 proceeds to step 211 to clear diagnostic code related to knock sensor degradation. Otherwise, if knock sensor degradation is determined, method 200 proceeds to step 212.At step 212, the diagnostic code relating to knock sensor degradation may be determined and stored in the controller. Further, a knock sensor compensation factor may be calculated based on the knock sensor output and used to compensate for the knock sensor output. For example, the knock sensor compensation factor may be proportional to the amplitude of the excitation pulse and proportional to the inverse of the amplitude of the knock sensor output in response to the pulse excitation. The knock sensor compensation factor may reflect the degree of knock sensor degradation. For example, an increased knock sensor compensation factor indicates a decreased sensitivity of the knock sensor. The knock sensor output may be compensated by multiplying the knock sensor output by the knock sensor compensation factor. The compensated knock sensor output may then be analyzed to detect engine knock. Further, method 200 may inhibit spark retard in response to knock sensor degradation to prevent engine knock. For example, method 200 may determine the cylinder to which the degraded knock sensor corresponds and inhibit spark retard of the determined cylinder.FIG. 3 shows timelines of engine operating parameters during implementation of the method shown in FIG. 2. The x-axes are time and increase from left to right. The first plot from the top shows torque demand 310. The torque demand increases as indicated by the y-axis. The second plot from the top shows an engine combustion event in a representative engine cylinder. The vertical columns (such as 321 and 322) indicate individual combustion events. The third plot from above shows engine vibration 330. The direction of the y-axis indicates increasing engine vibration. The fourth plot from the top shows a signal recorded by a recording device. The recorded signal 340 may be a voltage signal. The fifth plot from above shows the excitation signal 350. The excitation signal may be sent to actuate an actuator to generate a sound vibration. The excitation signal may be a voltage signal. The sixth plot from the top shows knock sensor output 360. The knock sensor output may be a voltage signal.From T 0 to T 1 the engine has periodic burns. The variation in torque demand 310 is high. Consequently, the fluctuation of the engine vibration is large. During this period, no signal is recorded and the actuator is not actuated. The magnitude of the knock sensor output is low, indicating the absence of engine knock.From T 1 to T 2 the engine combustion is continued. The torque demand decreases and is within a range determined by thresholds 311 and 312. Since the variation in torque demand 313 is within a threshold range, the controller determines that the engine is in steady state operation. During stable engine operation, the fluctuation of the engine vibration 330 decreases as compared with T 0- T 2. From T 1 on, engine vibration has been recorded and stored on the controller's nonvolatile memory.At time T 2 the torque demand falls to zero. For example, the torque demand may drop to zero during an idle shutdown of the vehicle. As another example, the torque demand may drop to zero when an HEV is in EV mode. The engine combustion is stopped from time T 2 on. Note that, although the second plot from the top shows a representative engine cylinder, combustion has been halted from T 2 to T 3 in each individual engine cylinder. The duration from T 2 to T 3 is not shorter than one engine cycle. The excitation signal is a mathematical function of the recorded signal 340, and a pulse signal (or "ping" signal) 351 is sent to the actuator. For example, the excitation signal may be an addition of a scaled recorded motor vibration and a pulse signal. An exemplary excitation signal with high amplitude periodic pulses is depicted in FIG. 3. Alternatively, the excitation signal may include a single pulse. In response to each pulse of the excitation signal, the knock sensor outputs a high amplitude oscillation. If the amplitude of the oscillation is above a threshold 361, the controller determines that the knock sensor passes the plausibility check. Otherwise, knock sensor degradation is indicated.A compensation factor may be determined based on the amplitude of the excitation signal (A ein) and the amplitude of the knock sensor output (A aus). For example, the compensation factor may be proportional to A ein / A aus. The compensation factor may be multiplied by the knock sensor output to compensate for the sensitivity loss of the knock sensor over time.In this way, knock sensor degradation may be determined robust and reliable by exciting it with a sound pulse. The technical effect of performing a plausibility check for a knock sensor in the absence of engine combustion is that knock sensor degradation may be determined directly and quickly. The technical effect of using an actuator coupled to the intake manifold to excite the knock sensor is that the acoustic vibration generated may simulate knocking sound from any cylinders of the engine system. The technical effect of using an actuator coupled to the cylinder block to excite the knock sensor is that the acoustic vibration generated may simulate the knocking sound from the cylinder to which the actuator is coupled. The technical effect of the actuator playing recorded engine vibration is that pedestrians and the vehicle operator may be notified when noise due to vehicle operation is low. Furthermore, the plausibility check for a knocking sensor with little system modification can be carried out economically via an AVAS system.As one embodiment, a method for an engine, comprising: generating vibration via an actuator in the absence of engine combustion; and indicating knock sensor degradation based on knock sensor output in response to the generated vibration. In a first example of the method, knock sensor degradation is indicated if the magnitude of the knock sensor output is below a threshold and the actuator is positioned outside of all combustion chambers of the engine. A second example of the method optionally includes the first example, and further includes wherein the generated vibration is a sonic vibration. A third example of the method optionally includes one or more of the first and second examples, and further includes wherein the actuator is part of an audible vehicle notification system and generates audible vehicle messages in response to a vehicle speed being below a threshold and the engine being off. A fourth example of the method optionally includes one or more of the first through third examples, and further includes wherein the knock sensor is coupled to an intake manifold. A fifth example of the method optionally includes one or more of the first through fourth examples, and further includes wherein the knock sensor is coupled to an engine block. A sixth example of the method optionally includes one or more of the first through fifth examples, and further includes prohibiting spark retard in response to an indication of knock sensor degradation. A seventh example of the method optionally includes one or more of the first through sixth examples, and further includes wherein the actuator is coupled to an engine intake manifold. An eighth example of the method optionally includes one or more of the first through seventh examples, and further includes wherein the actuator is coupled to an engine block. A ninth example of the method optionally includes one or more of the first through eighth examples, and further includes recording an engine vibration during engine combustion and generating a vibration including the recorded engine vibration. A tenth example of the method optionally includes one or more of the first through ninth examples, and further includes wherein engine vibration is recorded during stable engine operation.As another embodiment, a method for an engine, comprising during engine combustion, recording an engine vibration; in the absence of engine combustion, electrically exciting an actuator with an excitation signal, the excitation signal including the recorded engine vibration and a pulse signal; and indicating knock sensor degradation based on a knock sensor output. In a first example of the method, further comprising recording engine vibration while the variation of a torque demand is within a threshold range. A second example of the method optionally includes the first example, and further includes indicating knock sensor degradation by comparing the knock sensor output to the excitation signal. A third example of the method optionally includes one or more of the first and second examples, and further includes indicating knock sensor degradation by filtering the knock sensor output to remove a signal in response to the recorded engine vibration. A fourth example of the method optionally includes one or more of the first through third examples, and further includes wherein the acoustic pulse signal is a periodic signal.As yet another embodiment, a vehicle system comprising: an engine; an actuator coupled to the engine; a knock sensor coupled to the engine; a controller configured with computer readable instructions stored on non-transitory memory to: generate, in the absence of engine combustion, a sound vibration via the actuator; and indicate degradation of the knock sensor based on the output of the knock sensor. In a first example of the system, the acoustic vibration is generated during an engine off condition. A second example of the system optionally includes the first example and further includes wherein the vehicle system is a hybrid electric vehicle and the sound vibration is generated during an electric vehicle mode. A third example of the system optionally includes one or more of the first and second examples, and further includes wherein the generated acoustic vibration includes a pulse and the amplitude of the pulse is tuned based on the sensitivity of the knock sensor.It should be appreciated that the example control and estimation routines included herein may be used with various engine and / or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and executed by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various illustrated acts, acts, and / or functions may be performed in the order illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but rather is provided for ease of illustration and description. One or more of the illustrated acts, operations, and / or functions may be repeatedly performed depending on the particular strategy being employed. Further, the described acts, operations, and / or functions may graphically represent code programmed to non-transitory memory of the computer readable storage medium in the engine control system, wherein the described acts are performed by executing the instructions in a system including the various engine hardware components in combination with the electronic controller.It should be understood that the configurations and routines disclosed herein are exemplary in nature and these specific embodiments are not to be interpreted in a limiting sense as numerous variations are possible. For example, the above technology may be applied to V6, I4, I6, V12, 4-cylinder horizontally opposed, 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.The following claims particularly set forth certain combinations and sub-combinations which are considered novel and non-obvious. These claims may refer to "a" element or "a first" element or the equivalent thereof. Such claims should be understood to include inclusion of one or more such elements and neither require nor exclude two or more such elements. Further combinations and sub-combinations of the disclosed features, functions, elements and / or characteristics may be claimed by altering the present claims or by filing novel claims in this or a related application. Such claims, whether broader, narrower, equal or different in scope from the original claims, are further considered to be within the scope of the present disclosure.

Claims

A method for an engine, comprising: generating vibration via an actuator in the absence of engine combustion, the actuator comprising a portion of an acoustic vehicle communication system and generating acoustic vehicle messages in response to a vehicle speed being below a threshold and the engine being off; and indicating knock sensor degradation of a knock sensor based on an amplitude of a knock sensor output in response to the generated vibration.The method of claim 1, wherein knock sensor degradation is indicated if the magnitude of the knock sensor output is below a threshold, and wherein the actuator is positioned outside of all combustion chambers of the engine.The method of claim 1, wherein the generated vibration is a sonic vibration.The method of claim 1, wherein the knock sensor is coupled to an intake manifold.The method of claim 1, wherein the knock sensor is coupled to a cylinder block.The method of claim 1, further comprising prohibiting spark retard in response to an indication of knock sensor degradation.The method of claim 1, wherein the actuator is coupled to the interior of an engine intake manifold.The method of claim 1, wherein the actuator is coupled to an engine block.The method of claim 1, further comprising recording an engine vibration during engine combustion and generating the vibration including the recorded engine vibration.The method of claim 9, wherein the engine vibration is recorded during stable engine operation.A hybrid vehicle system, comprising: an engine; an actuator coupled to the engine; a knock sensor coupled to the engine; a controller configured with computer readable instructions stored on non-transitory memory to: in the absence of engine combustion, during an electric vehicle mode in which the hybrid vehicle is driven only by torque generated by an electric motor, generate a sound vibration via the actuator, and indicate degradation of the knock sensor based on the amplitude of an output of the knock sensor.The system of claim 11, wherein the acoustic vibration is generated during an engine off condition.The system of claim 11, wherein the generated acoustic vibration includes a pulse and an amplitude of the pulse is tuned based on sensitivity of the knock sensor.

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