Method and system for detecting and mitigating self-ignition of an engine

Abstract

A method for detecting and mitigating self-ignition in a cylinder (114) of an internal combustion engine (102), the method comprising: Providing a first sensor (119) for sensing a crank angle of a crankshaft (118) of the engine (102); Providing a second sensor (152) for detecting (220) a knock intensity signal in the cylinder (114) of the engine (102); Determining (210) the crank angle using the first sensor (119); Calculating (230, 235) a knock intensity signal indicative of cylinder pressure when the crank angle is between a first predetermined crank angle and a second predetermined crank angle; Determining (230, 235) at least one property of the knock intensity signal; Comparing (240) the at least one characteristic of the knock intensity signal with at least one predetermined characteristic; Determining (245) whether the at least one characteristic of the knock intensity signal exceeds the at least one predetermined characteristic; and Performing (250) at least one mitigation measure for the auto-ignition if the at least one property of the knock intensity signal exceeds the at least one predetermined property, characterized in that performing (250) the at least one auto-ignition mitigation measure comprises adjusting (280) a position of a camshaft (18) when the engine speed is between two predetermined engine speed thresholds, which are defined as a fifth predetermined engine speed threshold (ES 5 ) and as a sixth predetermined engine speed threshold (ES 6 ) and the engine load is between two predetermined engine load thresholds, which are referred to as a fifth predetermined engine load threshold (EL5 ) and as a sixth predetermined engine load threshold (EL 6 ) is located.

Description

TECHNICAL FIELD

[0001] The present invention relates to systems and methods for controlling internal combustion engines, and more particularly to systems and methods for detecting and mitigating autoignition events in internal combustion engines. BACKGROUND

[0002] The background description presented herein is intended to provide a general context for the disclosure. The work of the presently identified inventors—to the extent described in this Background section—and aspects of the description not otherwise considered prior art at the time of filing are not, by express or implied, prior art to the present disclosure.

[0003] In a spark-ignition engine, a mixture of fuel and air flows into the piston combustion chamber during the intake process. The fuel-air mixture is compressed, and combustion is induced by a high-energy electrical spark during the ignition process.

[0004] Ignition timing affects an engine's performance, durability, power, and fuel consumption. Under certain conditions, uncontrolled or spontaneous ignition (AI) can occur. Uncontrolled ignition occurs in positive-ignition engines when an air-fuel mixture in a cylinder is ignited by an ignition source other than the ignition spark. Generally, uncontrolled ignition that occurs before top dead center (TDC) is referred to as spontaneous ignition (AI).

[0005] Uncontrolled ignition that occurs too early or too late in the combustion cycle is often responsible for excessive vibration and can potentially cause engine damage due to increased cylinder temperature and pressure. Engine control systems monitor the position of an engine's crankshaft as a means of determining crank angle. Crank angle is useful in determining when an AI event occurs.

[0006] To maintain engine aging resistance, it is important to determine when AI occurs and take corrective measures.

[0007] While detection and mitigation systems for uncontrolled ignitions after TDC are known and serve their purpose, for example, from publications DE 10 2008 041 840 A1, DE 102 01 073 A1, and DE 10 2015 107 412 A1, there is still a need for improved detection and mitigation systems and methods. More specifically, there is a need for a new and improved detection and mitigation system that identifies self-ignitions before TDC in spark-ignition engines.

[0008] It is therefore an object of the invention to improve the service life of internal combustion engines.

[0009] This object is achieved according to the invention by the features of claim 1. Advantageous further developments emerge from the subclaims. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present invention will become more fully understood with the aid of the detailed description and the accompanying drawings, in which: Fig. Figure 1 is a functional diagram for a vehicle AI detection and mitigation system according to the present invention; Fig. Figure 2 is a flowchart of a method for detecting and mitigating AI according to the present invention; Fig. 3 is a graph illustrating multiple mitigation strategies activated based on engine speed and engine load, according to the present invention; Fig. 4 is an example of a timeline graph of a crank angle window for detecting AI, according to the present invention; and Fig. 5 is an example of a graph illustrating an AI signal overlapping a knock signal window in accordance with the present invention. DETAILED DESCRIPTION

[0011] Under some circumstances, a self-ignition (AI) event can occur within an engine cylinder. AI can be described as an event in which the air / fuel mixture in the cylinder ignites before TDC and before the spark plug. AI can be initiated by an ignition source other than the ignition spark, such as hot spots in the combustion chamber, a spark plug that runs too hot for the application, or carbonaceous deposits in the combustion chamber that are incandescent by previous engine combustion events. AI can cause engine damage if not detected and corrected.

[0012] With reference to Fig. 1 illustrates a functional block diagram of a vehicle system 100 for detecting and mitigating AI, according to an embodiment of the present invention. An engine 102 generates torque to drive the wheels of a vehicle. Air is drawn into the engine 102 via an intake manifold 104. Airflow into the engine 102 is controlled by a throttle valve 106. A throttle actuator module 108 (e.g., an electronic throttle controller) controls the opening of the throttle valve 106. One or more fuel injectors 110 mix fuel with air to form a combustible fuel / air mixture. A fuel actuator module 112 controls the fuel injector(s). The injectors inject fuel directly into the cylinders, or, for example, into fuel injection ports of the cylinders.

[0013] A cylinder 114 includes a piston (not shown) connected to a crankshaft 118. Although the engine 102 is illustrated with only cylinder 114, the engine 102 may include more than one cylinder, e.g., 2, 4, 6, 8, or more. A combustion cycle in cylinder 114 may consist of four strokes: an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. An engine cycle includes one combustion cycle in each cylinder.

[0014] During the intake stroke, the piston approaches a bottom position, and cylinder 114 is supplied with fuel and air. This bottom position may be referred to as bottom dead center (BDC). During the compression stroke, crankshaft 118 drives the piston to a top position, compressing the air-fuel mixture within cylinder 114. This top position may also be referred to as top dead center (TDC). A spark plug 120 ignites the air / fuel mixture within engine 102. A spark plug actuator module 122 controls the spark plug(s).

[0015] Combustion of the fuel / air mixture during the expansion stroke propels the piston away from TDC and rotates crankshaft 118. Rotational force (i.e., torque) is a source of compression force for a compression stroke of a combustion cycle of one or more cylinders following the cylinder in a predetermined firing order. Exhaust gas from the combustion of the fuel / air mixture is expelled from cylinder 114 during the exhaust stroke.

[0016] One or more boosting devices, such as a turbocharger 127 or a supercharger, may be implemented. While only one boosting device is illustrated, multiple boosting devices may be implemented. Turbocharger 127 pressurizes air in intake manifold 104. Boost actuator module 128 controls the output of turbocharger 127. Boost may be described as the amount by which the pressure in intake manifold 104 is greater than an ambient pressure. Engine 102 transmits torque to transmission 140. Transmission 140 may include a manual transmission, an automatic transmission, an automatic manual transmission, or another suitable type of transmission.

[0017] A speed sensor 141 is mounted on or near a transmission output shaft 142 and is operable to determine engine speed as the transmission output shaft 142 rotates. Additionally, the crankshaft sensor 119 may be used to determine engine speed in addition to crank angle, but for the purposes of this disclosure, two separate sensors are used.

[0018] The transmission 140 transmits torque to one or more idler wheels (not shown) via the transmission output shaft 142 and a power train (not shown). A torque sensor or torque converter 143 is located on or near the transmission output shaft 142 for sensing engine torque or load.

[0019] An electronic control module (ECM) 160 is in communication with the speed sensor 141 for receiving an engine speed signal as input for determining an engine speed and is also in communication with the torque sensor 143 for receiving a torque signal as input for determining an engine load.

[0020] Torque sensor 143 is typically a non-contact sensor located on or near the transmission output shaft 142 and operable to detect an electric or magnetic field signal affected by changes in engine torque on the rotating transmission output shaft 142.

[0021] A manifold absolute pressure (MAP) sensor 146 is mounted within the intake manifold to measure pressure within the intake manifold 104 and generate a MAP based on the pressure within the intake manifold 104. A crankshaft sensor 119 measures the rotational position of the crankshaft 118 and provides a crankshaft position signal to the ECM 160, thereby determining the crank angle. Crank angle refers to the rotational position of the crankshaft 118 relative to a piston as it moves within the engine cylinder 114. Measured in degrees, the crank angle for a piston at top dead center (TDC) of its compression stroke, for example, is 0°.

[0022] A crank angle monitoring system of AI detection and mitigation system 100 includes ECM 160, crankshaft sensor 119, and a gear (not shown) that rotates with crankshaft 118. The gear may have N teeth, and crankshaft sensor 119 monitors the rotation of the teeth. Crankshaft sensor 119 generates pulses in the form of a crank angle signal as the teeth of the gear pass crankshaft sensor 119.

[0023] ECM 160 determines the crank angle based on the pulses in the crank angle signal. ECM 160 determines the crank angle at various rotational intervals of crankshaft 118 where AI, spark pre-ignition, or knock are known or suspected to be occurring. For example only, ECM 160, when used in conjunction with other sensors, may determine that AI is occurring during an interval between 30° and 0° before TDC of crankshaft 118 rotation.

[0024] An ambient pressure sensor 150 measures an ambient (barometric) air pressure and generates an ambient air pressure based on the measured pressure. Engine vibration sensor 152 continuously measures engine vibrations indicative of the pressure within an engine cylinder 114. According to the present invention, engine vibration sensor 152 is selectively read by the ECM 160. Additionally, according to one embodiment of the present invention, the ECM 160 determines the pressure within cylinder 114 between predetermined crank angles.

[0025] In one embodiment, engine vibration sensor 152 is a piezoelectric accelerometer, however, other sensors commonly referred to as "knock sensors" used to detect pressure or vibrations within an engine may be substituted. One or more other sensors 154 may also be implemented, such as a mass flow rate (MAF) sensor, an intake air temperature (IAT) sensor, an oil temperature sensor, an engine coolant temperature sensor, etc.

[0026] Engine actuator modules control engine actuators based on signals from the ECM 160. For example, the throttle actuator module 108 controls the throttle valve 106 based on signals from the ECM 160, the fuel actuator module 112 controls the fuel injector(s) based on signals from the ECM 160, the spark actuator module 122 controls the spark plug(s) 120 based on signals from the ECM 160, and the boost actuator module 128 controls the boost device(s) based on signals from the ECM 160. Other engine actuators, such as, for example, valve actuators, may be included and controlled based on signals from the ECM 160.

[0027] AI may occur when a driver requests an increase in engine output torque after a period of operation with intake manifold 104 vacuum less than a predetermined value. A driver may request an increase in engine output torque after a period of operation with intake manifold 104 vacuum less than the predetermined value, for example, when performing a passing maneuver, during hill climbing, and / or under other circumstances.

[0028] During the operating period when the vacuum in the intake manifold 104 is less than the predetermined value, combustible materials may accumulate within the cylinder 114 of the engine 102. Combustible materials may accumulate in crevices of the cylinders 114 of the engine 102, such as near piston ring lands, piston rings, spark plugs, etc. The associated increase in airflow into the engine 102 that occurs when the driver requests an increase in engine output torque may cause some or all of the accumulated combustible materials to ignite and cause AI. According to the present invention, the ECM 160 is programmed to initiate one or more remedial actions when AI is detected to mitigate AI. Remedial actions include, but are not limited to, cylinder fuel enrichment or deactivation, adjusting camshaft position, and preventing short-term spark retard.

[0029] With reference to Fig. 2, a flowchart of a method 200 for detecting and mitigating AI according to the present invention is shown and begins at block 205. At block 210, ECM 160 reads crankshaft sensor 119 to determine crank angle.

[0030] At block 215, ECM 160 compares the measured crank angle to a first predetermined crank angle threshold. If the measured crank angle and the first predetermined crank angle threshold are unequal, ECM 160 continues reading crankshaft sensor 119. In a preferred embodiment, the crankshaft sensor signal is continuously read by ECM 160 so that the current crank angle can be determined. If the measured crank angle is equal to the first predetermined crank angle threshold, the method proceeds to block 220.

[0031] At block 220, the ECM 160 reads the engine vibration sensor 152 to obtain an engine vibration signal. It should be understood that in one embodiment of the present invention, the engine vibration sensor 152 continuously samples the engine vibration signal, and the ECM 160 reads the engine vibration signal after the measured crank angle signal equals the first predetermined crank angle threshold.

[0032] At block 225, the ECM 160 compares the measured crank angle to a second predetermined crank angle threshold. If the measured crank angle is not equal to the second predetermined crank angle threshold, the ECM 160 continues reading the engine vibration sensor 152. If the ECM 160 determines that the measured crank angle is equal to the second predetermined crank angle threshold, the method proceeds to block 230.

[0033] Continuing at block 230, ECM 160 stops reading engine vibration sensor 152. As such, ECM 160 receives a reading from engine vibration sensor 152 from the first predetermined crank angle threshold to the second predetermined crank angle threshold in an engine vibration detection window.

[0034] In an alternative embodiment of the invention, the ECM 160 selectively reads the engine vibration sensor 152 during a period occurring between a third and a fourth predetermined crank angle threshold. According to this approach, multiple cylinder pressure windows may be sampled during a cylinder combustion cycle. After the ECM 160 stops reading the engine vibration sensor 152 at block 230, the method continues at block 235.

[0035] At block 235, ECM 160 analyzes and converts the engine vibration sensor signal read between the first and second predetermined crank angle thresholds. A signal read across the entire range of the engine vibration detection window may include an AI signal and a knock signal, which are parsed or separated according to the time of occurrence and signal characteristics. If the AI ​​signal ends after the knock signal begins, a portion of the AI ​​signal appears concurrently with the occurrence of the knock signal. Various signal characteristics, such as amplitude and frequency, allow the signals to be easily identified and parsed.

[0036] In one embodiment of the present invention, the ECM 160 includes an analog-to-digital (AD) converter circuit (not shown) to digitize the output signal of the engine vibration sensor 152. A digital signal processor (DSP) circuit (not shown) is also included in the ECM 160 to apply the FFT to the digitized output signal of the AD circuit to identify a frequency signal or "knock intensity" signal from the digital signal.

[0037] At 240, the ECM 160 compares at least one characteristic of the knock intensity signal to at least one predetermined characteristic threshold. At block 245, if the at least one characteristic of the knock intensity signal exceeds the at least one of the predetermined characteristic thresholds, the process proceeds to block 250. If the at least one knock intensity signal characteristic does not exceed the at least one predetermined characteristic threshold, the method returns to block 240. According to one embodiment of the present invention, the amplitude of the knock intensity signal is the at least one predetermined characteristic used to determine whether AI is occurring.Alternatively, the present invention determines that an AI event occurs when the amplitude of the knock intensity signal moves between a lower knock intensity minimum threshold and a maximum threshold for a predetermined number of cylinder events.

[0038] At block 250, the ECM 160 initiates AI mitigation to mitigate or terminate the occurrence of AI when the pressure signal parameters of the knock severity signal exceed the at least one predetermined set of parameters. With additional reference to Fig. 3, the present invention provides for the use of one or more mitigation techniques performed separately or in combination.

[0039] At block 255, the ECM 160 determines whether the engine speed is between a first predetermined engine speed ES 1 -Threshold and a second predetermined engine speed ES 2threshold and the engine load is between a first predetermined engine load EL 1 threshold and a second predetermined engine load EL 2 threshold (see Fig. 3). If the speed is between a first predetermined engine speed ES 1 -Threshold and a second predetermined engine speed ES 2 threshold and the engine load is between a first predetermined engine load EL 1 threshold and a second predetermined engine load EL 2 threshold, the ECM 160, at block 260, causes the injector 110 to inject additional fuel into the cylinder 114, thereby performing fuel enrichment mitigation.

[0040] At block 265, the ECM 160 determines whether the engine speed is between a third predetermined engine speed threshold ES 3and a fourth predetermined engine speed threshold ES 4 and whether the engine load is between a third predetermined engine load threshold EL 3 and a fourth predetermined engine load threshold EL 4 If the engine speed is between a third predetermined engine speed threshold ES 3 and a fourth predetermined engine speed threshold value ES 4 and the engine load is between a third predetermined engine load threshold EL 3 and a fourth predetermined engine load threshold EL 4 , the ECM shuts off fuel supply to the engine cylinder in block 270. Enriching and removing fuel in / from cylinder 114 reduces the cylinder temperature, thus avoiding a temperature that would cause AI.

[0041] At block 275, a remedial action to prevent or stop AI continues when ECM 160 determines whether the engine speed is between a fifth predetermined engine speed threshold ES 5 and a sixth predetermined engine speed threshold value ES 6 and whether the engine load is between a fifth predetermined engine load threshold EL 5 and a sixth predetermined engine load threshold EL 6 is located (see Fig. 3). If the engine speed is between a fifth predetermined engine speed threshold value ES 5 and a sixth predetermined engine speed threshold value ES 6 and if the engine load is between a fifth predetermined engine load threshold EL 5 and a sixth predetermined engine load threshold, ECM 160 performs the remedial action of adjusting the camshaft position at block 280.

[0042] Adjusting the position of the camshaft affects the actuation timing of an engine's intake and exhaust valves, which is important for controlling ignition in engine cylinder 114. If the ECM 160 determines that the engine speed is not between a fifth predetermined engine speed threshold ES 5 and a sixth predetermined engine speed threshold value ES 6 and that the engine load is not between a fifth predetermined engine load threshold EL 5 and a sixth predetermined engine load threshold EL 6 the camshaft position is not adjusted and the corrective action procedure continues at block 285.

[0043] At Block 285, and with reference to Fig. 3, ECM 160 determines whether the engine speed is between the first predetermined engine speed threshold ES 1 and a seventh predetermined engine speed threshold ES7 and the ECM 160 determines whether the engine load is between a seventh predetermined engine load threshold EL 7 and an eighth predetermined engine load threshold EL 8 If the engine speed is between the first predetermined engine speed threshold ES 1 and a seventh predetermined engine speed threshold ES 7 and if the engine load is between a seventh predetermined engine load threshold EL 7 and an eighth predetermined engine load threshold EL 8, the ECM prevents short-term spark retard from occurring in cylinder 114 at block 290. If the conditions are not met, short-term spark retard is allowed if necessary, and the detection and mitigation process returns to block 240. Removing short-term spark retard mitigates AI by advancing spark ignition and thus cooling the charge BTDC.

[0044] With reference to Fig. 4, a crank angle degree timeline 400 includes an AI detection window 402 and a knock detection window 404 according to the present invention. For example only, the total length of the crank angle degree timeline is 80° crank angle. The AI ​​detection window 402 begins at -30° crank angle and ends at 0° crank angle, thereby providing an AI detection window 402 length of 30° crank angle.

[0045] According to the present invention, ECM 160 can be operated to read pressure sensor 150 when crankshaft sensor 119 measures a crank angle of -30° and stop reading when the crank angle is 50°. Therefore, ECM 160 reads the entire 80° crank length. After that, the signal is buffered, and only the AI ​​window data between -30° and 0° is used to detect AI. The window length between 20° and 50° is used to detect knock / SPI signals.

[0046] In an alternative embodiment, the ECM 160 may read an entire detection window or a plurality of different detection windows to obtain the engine vibration sensor 152 signals that occur during a cylinder combustion cycle.

[0047] With reference to Fig. 5, a graph is provided that depicts an AI signal overlapping a knock signal window. Graph 500 depicts crank angle degrees along its X-axis and pressure in Pascals along its Y-axis. For example only, according to Fig. 4 above, the AI ​​detection window 402 occurs between -30° and 0° crank angle, and the knock detection window is shown as occurring between 20° and 50° crank angle. As illustrated, the AI ​​pressure signal 502 begins to increase at -20° crank angle until a maximum pressure level is reached at approximately -5° crank angle. Thereafter, the AI ​​pressure signal 502 begins to decrease in magnitude and frequency beyond the AI ​​detection window 402, overlapping and crossing the knock detection window 404. This example clearly shows that the magnitude and frequency of the knock pressure signal 504 are significantly lower than the AI ​​pressure signal 502, making it easily distinguishable.

[0048] After detecting and distinguishing the AI ​​pressure signal 502 from the knock pressure signal 504, the ECM 160 may then be operated to initiate remedial actions to terminate or mitigate occurrences of AI, wherein such uncontrolled detonations may result in reduced engine performance and durability or significant engine damage.

[0049] The foregoing description is merely illustrative and is in no way intended to limit the present disclosure and its applications or uses. The broad teachings of the disclosure may be embodied in numerous forms. Thus, while the present disclosure includes specific examples, the true scope of the disclosure is in no way limited thereby, and further modifications will become apparent from a study of the drawings, the specification, and the following claims. For clarity, the same reference numerals are used in the drawings to identify similar elements. As used herein, the phrase "at least one of A, B, and C" should be construed to mean a logical expression (A or B or C) using a non-exclusive logical OR (OR).It should be understood that one or more steps within a method may be performed in a different order (or simultaneously) without altering the principles of the present disclosure.

[0050] As used herein, the term module may refer to, be a part of, or include: an application-specific integrated circuit (ASIC); a discrete circuit; an integrated circuit; a combinational logic circuit; a field-programmable gate array (FPGA); a processor (shared, dedicated, or group) that executes code; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip. The term module may include memory (shared, dedicated, or group memory) that stores code executed by the processor.

[0051] The term code, as used above, may include software, firmware, and / or microcode, and may refer to programs, routines, functions, classes, and / or objects. The term common, when used above, means that some or all of the code from multiple modules may be executed using a single (shared) processor. In addition, some or all of the code from multiple modules may be stored by a single (shared) memory. In addition, some or all of the code from a single module may be stored using a group of memories.

[0052] The devices and methods described herein may be implemented in part or in whole by one or more computer programs executed by one or more processors. The computer programs include processor-executable instructions stored on at least one non-transitory, tangible, computer-readable medium. The computer programs may also include and / or be based on stored data. Non-limiting examples of the non-transitory, tangible, computer-readable medium include non-volatile memory, volatile memory, magnetic storage, and optical storage.

Claims

[1] A method for detecting and mitigating self-ignition in a cylinder (114) of an internal combustion engine (102), the method comprising: Providing a first sensor (119) for sensing a crank angle of a crankshaft (118) of the engine (102); Providing a second sensor (152) for detecting (220) a knock intensity signal in the cylinder (114) of the engine (102); Determining (210) the crank angle using the first sensor (119); Calculating (230, 235) a knock intensity signal indicative of cylinder pressure when the crank angle is between a first predetermined crank angle and a second predetermined crank angle; Determining (230, 235) at least one property of the knock intensity signal; Comparing (240) the at least one characteristic of the knock intensity signal with at least one predetermined characteristic; Determining (245) whether the at least one characteristic of the knock intensity signal exceeds the at least one predetermined characteristic; and Performing (250) at least one mitigation measure for the auto-ignition if the at least one property of the knock intensity signal exceeds the at least one predetermined property, characterized by , that performing (250) the at least one auto-ignition mitigation measure comprises adjusting (280) a position of a camshaft (18) when the engine speed is between two predetermined engine speed thresholds, which are defined as a fifth predetermined engine speed threshold (ES 5 ) and as a sixth predetermined engine speed threshold (ES 6 ) and the engine load is between two predetermined engine load thresholds, which are referred to as a fifth predetermined engine load threshold (EL 5) and as a sixth predetermined engine load threshold (EL 6 ) is located. [2] The method of claim 1, wherein calculating (230, 235) the knock intensity signal comprises converting (235) the engine vibration signal from an analog signal to a digital signal. [3] The method of claim 2, wherein calculating (230, 235) the knock intensity signal further comprises performing (235) a Fast Fourier Transform (FFT) on the digital signal to convert the digital signal into a frequency signal. [4] The method of at least one of the preceding claims, wherein performing (250) the at least one auto-ignition mitigation measure further comprises enriching (260) a fuel flow to the cylinder (114) when an engine speed is between a first predetermined engine speed threshold (ES 1) and a second predetermined engine speed threshold (ES 2 ) and an engine load is between a first predetermined engine load threshold (EL 1 ) and a second predetermined engine load threshold (EL 2 ) is located. [5] The method of at least one of the preceding claims, wherein performing (250) the at least one auto-ignition mitigation measure further comprises shutting off (270) a fuel flow into the cylinder (114) when an engine speed is between a third predetermined engine speed threshold (ES 3 ) and a fourth predetermined engine speed threshold (ES 4 ) and the engine load is between a third predetermined engine load threshold (EL 3 ) and a fourth predetermined engine load threshold (EL 4 ) is located. [6] The method of claim 4 or 5, wherein performing (250) the at least one auto-ignition mitigation measure further comprises preventing (290) a short-term ignition delay when the engine speed is between the first predetermined engine speed threshold (ES 1 ) and a seventh predetermined engine speed threshold (ES 7 ) and the engine load is between a seventh predetermined engine load threshold (EL 7 ) and an eighth predetermined engine load threshold (EL 8 ) is located.

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