Patent Description:
Internal combustion engines combust an air/fuel mixture within cylinders to drive pistons that rotatably turn a crankshaft to generate drive torque. Abnormal combustion of the air/fuel mixture can cause vibration of the engine (e.g., seismic waves through the engine structure), which is known as "knock. " There are two primary types of engine knock: (<NUM>) end-gas auto ignition (also known as "spark knock") and (<NUM>) low speed pre-ignition (LSPI) knock (also known as "mega knock"). LSPI knock refers to a stochastic, abnormal start of combustion prior to spark discharge. Specifically, oil ingestion or chemical pre-reactions due to time, pressure, and temperature may cause auto-ignition, which creates pressure waves that collide causing knock.

LSPI knock is often orders of magnitude higher than spark knock. A typical knock control strategy is spark retardation. This control strategy, however, is not effective against LSPI knock and is actually detrimental in mitigating LSPI knock. This is because during LSPI knock, combustion has already been initiated prior to the spark discharge, and thus retardation of the spark timing provides the cylinder charge even more time for auto-ignition to occur. Accordingly, while such knock detection and control systems work for their intended purpose, there remains a need for improvement in the relevant art. Document <CIT> generally describes two or more sensors for monitoring LSPI and end-ignition knock. In this known solution one of the sensors may be used to detect both LSPI and spark knock, but only in some specific operating conditions of the engine. Other solutions are known from <CIT>, <CIT> and <CIT>.

According to a first aspect of the invention, a knock detection and control system is presented as set forth in claim <NUM>.

According to a second aspect of the invention, a knock detection and control method is presented, as set forth in claim <NUM>.

In some implementations, the LSPI knock monitoring window is positioned before the appropriate MFB location and the spark knock monitoring window is positioned after the appropriate MFB location. In some implementations, the LSPI and spark knock monitoring windows are separated by a controller reset window. In some implementations, the controller is configured to reset its signal amplifications and detection thresholds during the controller reset window. In some implementations, each distinct monitoring window has distinct signal amplifications and detection thresholds associated therewith.

In some implementations, the controller is configured to further mitigate the detected LSPI knock by controlling airflow into the engine. In some implementations, the controller is configured to further mitigate the detected LSPI knock by limiting or decreasing a torque output of the engine. In some implementations, the controller is configured to mitigate the detected spark knock by performing spark retardation.

Further areas of applicability of the teachings of the present disclosure will become apparent from the detailed description, claims and the drawings provided hereinafter, wherein like reference numerals refer to like features throughout the several views of the drawings. It should be understood that the detailed description, including disclosed embodiments and drawings referenced therein, are merely exemplary in nature intended for purposes of illustration only and are not intended to limit the scope of the present disclosure, its application or uses.

As previously mentioned, conventional spark retardation is detrimental in mitigating low speed pre-ignition (LSPI) knock. One LSPI knock detection technique involves utilizing an ionization current sensor on an ignition coil (also known as "ion sensing"). This technique, however, is both costly (due to the additional sensor) and unreliable. Accordingly, systems and methods for improved knock detection and control are presented. The techniques implemented by these systems and methods are capable of distinguishing between conventional spark knock and LSPI knock using an engine's knock sensor. More particularly, a knock signal generated by the knock sensor is monitored using two distinct monitored windows for LSPI knock and spark knock, respectively. In some implementations, each monitoring window has its own associated signal amplifications and detection thresholds. LSPI mitigation can also involve controlling different actuators (DI fuel injectors, throttle, etc.) to mitigate detected LSPI knock.

Referring now to <FIG>, a diagram of an example engine system <NUM> is illustrated. The engine system <NUM> includes an engine <NUM> configured to combust an air/fuel mixture to generate drive torque. Non-limiting examples of the engine <NUM> include a spark ignition direct injection (SIDI) engine, but it will be appreciated that the techniques of the present disclosure could be applicable to any suitable engine comprising a knock sensor, such as a port fuel injection (PFI) engine. In some implementations, the engine <NUM> could be a gasoline compression ignition engine (homogeneous charge compression ignition (HCCI), partially pre-mixed charge compression ignition (PPCI), pre-mixed charge compression ignition, etc.). The engine <NUM> draws air into an intake manifold <NUM> through an induction system <NUM> that is selectively regulated by a throttle valve <NUM>. The air in the intake manifold <NUM> is distributed to a plurality of cylinders <NUM> and therein combined with fuel injected by respective DI fuel injectors <NUM>. While four cylinders are shown, it will be appreciated that the engine <NUM> could have any suitable number of cylinders. In some implementations, the engine <NUM> includes a boost system <NUM> (a turbocharger, a supercharger, etc.).

The air/fuel mixture in the cylinders <NUM> is compressed by pistons (not shown) and combusted by spark generated by respective spark plugs <NUM>. For a smaller (e.g., <NUM> cylinder) configuration of the engine <NUM> with the boost system <NUM>, a compression ratio of the cylinders <NUM> may be relatively high. The combustion of the air/fuel mixture within the cylinders <NUM> drives the pistons (not shown), which rotatably turn a crankshaft <NUM> to generate drive torque. The drive torque is then transferred, e.g., via a transmission (not shown), to a drivetrain <NUM>. A knock sensor <NUM> is configured to generate a knock signal indicative of vibration of the engine <NUM> caused by abnormal combustion. In one exemplary implementation, the knock sensor <NUM> is an accelerometer-based sensor that is mounted to a block of the engine <NUM>. The abnormal combustion, if unaccounted for, causes noticeable vibrations (noise, vibration, and/or harshness, or NVH) and/or could damage the engine <NUM>.

Exhaust gas resulting from combustion is expelled from the cylinders <NUM> into an exhaust system <NUM> configured to treat the exhaust gas before releasing it into the atmosphere. For example, unburnt fuel from the abnormal combustion could cause increase emissions that must then be handled by the exhaust system <NUM>. A controller <NUM> (an application-specific integrated circuit (ASIC), one or more processors and a non-transitory memory storing executable instructions, etc.) controls operation of the engine system <NUM>, such as controlling the throttle valve <NUM> (airflow), the DI fuel injectors <NUM> (fuel), and the spark plugs <NUM> (spark). The controller <NUM> also receives the knock signal from the knock sensor <NUM>. The controller <NUM> is configured to detect knock of the engine <NUM> using the knock signal. According to the techniques of the present disclosure, the controller <NUM> is configured to detect both (i) LSPI knock and (ii) spark knock using the knock signal, which will be described in greater detail below. While not shown, it will be appreciated that the controller <NUM> is configured to receive other inputs, such as a crank angle measurement (e.g., in crank angle degrees, or CAD) from a crankshaft position sensor (not shown).

Causes of LSPI events are numerous. Extended and reoccurring LSPI can lead to thermal runways and surface (cylinder wall) ignition. Possible causes of LSPI events include: (<NUM>) hot combustion chamber deposits that flake off and ignite the cylinder charge because the flaking deposit is exposed to long resonance times and elevated pressure, which causes it to ignite, (<NUM>) oil droplets from the piston crevice enter into the combustion chamber of the cylinder <NUM> and act as a localized octane reducer causing auto-ignition prior to the spark discharge, and (<NUM>) auto-ignition prior to the spark discharge due to the boundary conditions, such as in gasoline compression ignition engines. Some engines overcome these surface ignition problems with improved hardware, engine design, and calibration. LSPI events, however, are still problematic in boosted engines with very retarded combustion phasing and high combustion ratios (long resonance times at elevated pressure) operating at low speed and high load.

For a particular monitoring window, the knock signal is processed according to associated parameters (signal amplifications, detection thresholds, etc.). In one exemplary implementation, the knock signal is filtered, rectified, and its energy is integrated across the monitoring window to obtain a single value. The window could be calibrated throughout the engine speed range. Based on a fast Fourier transform (FFT), the "knocking frequency" is isolated, which allows monitoring of first and second order pressure oscillations occurring in a particular frequency range (e.g., <NUM>-<NUM> kilohertz (kHz)). As previously discussed herein, only one monitoring window is typically active at a time. Before a new window is active, there may be a reset period for the controller <NUM>. Thus, by implementing two distinct monitoring windows separated by a controller reset window, a single controller <NUM> is capable of detecting both LSPI knock and spark knock using a single knock sensor <NUM>.

Referring now to <FIG>, a timing diagram <NUM> of example monitoring windows <NUM>, <NUM> for a knock signal received from the knock sensor <NUM> is illustrated. The timing diagram <NUM> corresponds to a combustion event (i.e., a combustion stroke) of a particular cylinder <NUM>, but it will be appreciated that spark knock monitoring could extend into an expansion stroke of the cylinder <NUM> as described in greater detail below. As shown, the monitoring windows <NUM>, <NUM> are determined with respect to actual spark angle <NUM> and an appropriate mass fraction burn (MFB) location <NUM>. This appropriate MFB location could be a <NUM>% MFB location (also known as "CA50"), as opposed to with respect to engine top dead center (TDC). It will be appreciated however, that the appropriate MFB location may not be the <NUM>% location (i.e., it could be before or after the <NUM>% MFB location). The term "actual spark angle" refers to a crankshaft angle/position at which the spark occurs. This is a known/scheduled value for the controller <NUM>. Conventional knock detection, in comparison, utilizes a single monitoring window, which is fixed for every particular engine speed. As shown, the LSPI knock window <NUM> is positioned before the appropriate MFB location <NUM> and the spark knock window <NUM> is positioned after the appropriate MFB location <NUM>. This is because LSPI heat release and resultant cylinder pressure oscillations happen earlier in the engine cycle compared to spark knock.

In one exemplary implementation, the following durations/offsets/delays for determining/positioning the monitoring windows <NUM>, <NUM> are obtained using predetermined lookup tables stored at the controller <NUM>. From the actual spark angle <NUM>, the LSPI knock window <NUM> is determined to be from (i) an offset value <NUM> before the actual spark angle <NUM> until (ii) a delay <NUM> from the actual spark angle until the appropriate MFB location, plus or minus a tolerance. A controller reset window ("CRW") <NUM> is positioned between the LSPI knock window <NUM> and the spark knock window <NUM>. The length of the controller reset window <NUM> is calibrated such that it is long enough for a worst-case reset of the controller <NUM> to load parameters (signal amplifications, detection thresholds, etc.) for the spark knock window <NUM>. The spark knock window <NUM> then extends from an end of the controller reset window <NUM> into an expansion stroke of the cylinder <NUM> (i.e., after an end of a combustion stroke of the cylinder <NUM>). The spark knock window <NUM> could also be described as extending until the end of combustion, plus a safety margin. By extending the spark knock window <NUM> into the expansion stroke of the cylinder <NUM>, late/extended spark knock ringing is able to be monitored. Subsequent control to mitigate/suppress the detected LSPI knock and/or the detected spark knock is described in greater below.

Referring now to <FIG>, a flow diagram of an example knock detection and control method <NUM> is illustrated. At <NUM>, the controller <NUM> receives, from the knock sensor <NUM> of the engine <NUM>, a knock signal indicative of a vibration of the engine <NUM> caused by abnormal combustion. At <NUM>, the controller <NUM> determines distinct monitoring windows for LSPI knock and spark knock, respectively. At <NUM>, the controller <NUM> monitors the knock signal using the distinct monitoring windows. As previously discussed herein, this involves utilizing distinct signal amplifications and detection thresholds for LSPI knock and spark knock, respectively. At <NUM>, the controller <NUM> determines whether knock exceeding a threshold is detected in the LSPI knock window <NUM>. If true, the method <NUM> proceeds to <NUM> where LSPI knock is detected. If false, the method <NUM> proceeds to <NUM>. At <NUM>, the controller <NUM> implements LSPI counteracting measures, such as those discussed previously herein and in further detail below. The method <NUM> then ends or returns to <NUM>. At <NUM>, the controller <NUM> determines whether knock exceeding a threshold is detected within the spark knock window <NUM>. If true, the controller <NUM> detects spark knock at <NUM>. At <NUM>, the controller <NUM> mitigates the spark knock by delaying or retarding spark timing. The method <NUM> then ends or returns to <NUM>.

For detected spark knock, for example, the controller <NUM> could perform spark retardation. For detected LSPI knock, on the other hand, the controller <NUM> could utilize other torque control actuators (e.g., airflow and/or fuel control actuators). In one exemplary implementation, one or more of the following torque control techniques could be utilized to mitigate the detected LSPI knock. A first attempt could be made by the controller <NUM> to mitigate the detected LSPI knock by controlling the DI fuel injectors <NUM>, which represent a fast path for torque control. A subsequent (second) or alternative attempt could be made by the controller <NUM> to mitigate the detected LSPI knock by controlling the throttle <NUM>, which represents a short-term slow path for torque control. A subsequent (third) or alternative attempt could be made by the controller <NUM> to mitigate the detected LSPI knock by limiting or decreasing engine torque output (e.g., an incoming torque request), which represents a long-term slow path for torque control.

Claim 1:
A knock detection and control system for a direct injection (DI) engine (<NUM>) provided with DI fuel injectors, the system comprising:
a single knock sensor (<NUM>) configured to generate a knock signal indicative of a vibration of the engine (<NUM>), which may be caused by abnormal combustion; and
a controller (<NUM>) configured to:
receive the knock signal,
determine, with respect to a crank angle of the engine, two distinct monitoring windows (<NUM>,<NUM>) for low speed pre-ignition (LSPI) knock and spark knock, respectively, based on (i) the actual spark timing (<NUM>) and (ii) an appropriate mass fraction burn (MFB) location (<NUM>), wherein the two distinct monitoring windows (<NUM>, <NUM>) are separated by a controller reset window (<NUM>);
monitor the knock signal using the two distinct monitoring windows (<NUM>,<NUM>),
detect (<NUM>,<NUM>) one of LSPI knock and spark knock based on the monitoring, and
control the engine (<NUM>) to mitigate the detected LSPI knock or spark knock, wherein the controller (<NUM>) is configured to mitigate the detected LSPI knock by controlling the DI fuel injectors of the engine,
characterised in that said controller reset window (<NUM>) is calibrated such that it is long enough for a worst-case reset of the controller (<NUM>) to load parameters for the spark knock window (<NUM>),
and that the controller (<NUM>) is configured to reset signal amplifications and detection thresholds during the controller reset window (<NUM>), each distinct monitoring window (<NUM>, <NUM>) having distinct signal amplifications and detection thresholds associated therewith.