JP5052489B2 - Device for controlling the stop of an internal combustion engine - Google Patents

Description

  The present invention relates to a technique for stopping an internal combustion engine without increasing the vibration of the internal combustion engine.

  In an internal combustion engine such as a diesel engine or a gasoline engine, even if combustion stops in the combustion chamber, the piston reciprocates several tens of times until the inertia of the piston is consumed by friction, causing the engine to vibrate. In order to reduce this vibration, when the engine is stopped, the throttle valve on the intake passage is disposed at a completely closed position. However, if the throttle valve is completely closed and the intake passage is closed, negative pressure is generated in the intake passage due to inertial movement of the piston that continues for a while after the combustion is stopped. For this reason, the amount of air in the cylinder in the compression stroke is reduced, the force against inertia energy in inertial operation is weakened, and the piston tends to stop near the top dead center.

  Patent Document 1 describes that when the piston is stopped near the top dead center, the crank arm and the crank rod are in series, and the torque required to move the piston is large, so the engine startability is poor. Has been. For this reason, Patent Document 1 proposes that when the engine speed due to inertia falls below a preset value when the engine is stopped, the throttle valve is slightly opened to reduce the negative pressure in the intake passage.

  Patent Document 2 describes that the opening degree of the throttle valve is controlled more finely in order to reduce engine vibration when the engine is stopped.

  In normal engines, the intake valve starts to open several degrees before top dead center and closes several tens of degrees after bottom dead center, and the exhaust valve starts to open several tens of degrees before bottom dead center. It is set to close after a few degrees. For this reason, a section of about 10 and several degrees near the top dead center is a valve overlap section in which both the intake valve and the exhaust valve are open. In recent years, in order to improve the output and fuel consumption of an internal combustion engine, a variable valve timing and lift control system that changes the opening / closing timing or lift amount of an intake valve or an exhaust valve has been used. Even in an internal combustion engine using this mechanism, valve overlap occurs near the top dead center.

Patent Document 3 describes that the engine stop control is performed by opening the throttle valve after the engine speed has decreased below the resonance speed that falls within the resonance frequency range of the vehicle when the engine is stopped.
JP 2000-213375 A JP 2005-320909 A JP2003-214192A

  The resonance frequency of the vehicle changes with aging and varies from vehicle to vehicle. Therefore, if the timing for opening the throttle valve is constant to control the piston position when the engine is stopped, the resonance of the vehicle There is a risk of increasing resonance by opening the throttle in the frequency range.

  Therefore, there is a need for a technique that can stop the engine without increasing resonance with the vehicle.

  In order to solve the above problems, an apparatus of the present invention includes a throttle valve that controls an intake air amount of an internal combustion engine, an actuator that drives the throttle valve, and an electronic control device that controls the internal combustion engine. Prepare. The electronic control device includes a means for sending a signal for opening the throttle valve to the actuator when the rotation speed of the internal combustion engine becomes a predetermined value or less after a stop command for the internal combustion engine is generated and the throttle valve is closed; After the stop command, vibration determining means for determining whether or not vibration exceeding a predetermined reference has occurred in the internal combustion engine, and timing for opening the throttle valve after the next stop command when it is determined that the vibration has occurred Means for delaying.

  In one embodiment of the present invention, the vibration determining means performs frequency analysis using a time series data array of the rotational speed of the internal combustion engine detected by the rotational speed sensor, obtains a spectrum for a predetermined frequency, and When the value exceeds the threshold value, it is determined that vibration exceeding a predetermined standard has occurred in the internal combustion engine.

  Further, in this embodiment, the vibration determination unit performs the frequency analysis by discrete Fourier transform.

  In yet another embodiment, the means for delaying the timing for opening the throttle valve includes means for delaying the timing for opening the throttle valve and for changing the opening of the throttle valve according to the delayed timing.

  In one embodiment, as the predetermined frequency, a plurality of frequencies that may be the resonance frequency of the vehicle are set.

  In another embodiment of the present invention, the electronic control device includes a non-volatile memory that records the number of revolutions of the internal combustion engine from when the internal combustion engine stop command is generated until the internal combustion engine stops. The vibration determining means is executed after the internal combustion engine is stopped.

  In this embodiment, the vibration determination means is executed after the ignition is turned on next time. Further, the means for delaying the timing for opening the throttle valve stores a value obtained by subtracting the predetermined rotational speed for opening the throttle valve by a predetermined rotational speed as a new set rotational speed in the nonvolatile memory.

  The stop command for the internal combustion engine is generated by the electronic control unit when the ignition is turned off or when the engine automatically stops during idling.

  Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of an idle speed control device for an internal combustion engine. The engine 10 is, for example, a 4-cylinder automobile engine. A throttle valve 14 that is a main throttle valve is disposed in the intake pipe 12. The throttle valve 14 is driven by an actuator 18 in accordance with a control signal from an electronic control unit (ECU) 60. The ECU 60 sends a control signal for opening / closing the throttle valve 14 to the actuator 18 in accordance with a detection output from an accelerator pedal depression amount sensor (not shown). This method is called a drive-by-wire method, and other methods include a method in which the wire 16 is connected to an accelerator pedal and the throttle valve is directly controlled by the accelerator pedal. A throttle valve opening sensor 20 is provided near the throttle valve 14 and outputs a signal corresponding to the throttle opening θTH.

  In the vicinity of the intake port immediately after the intake manifold downstream of the throttle valve 14, an injector (fuel injection device) 24 is provided for each cylinder. The injector 24 is connected to the fuel tank via a fuel supply pipe and a fuel pump, receives gasoline fuel, and injects it into the intake port.

  An absolute pressure sensor 32 and an intake air temperature sensor 34 are provided downstream of the throttle valve 14 in the intake pipe 12 and output electric signals indicating the intake pipe absolute pressure PBA and the intake air temperature TA, respectively.

  A cylinder discrimination sensor (CYL) 40 is provided in the vicinity of the camshaft or crankshaft of the engine 10, and for example, outputs a cylinder discrimination signal CYL at a predetermined crank angle of the first cylinder. In addition, a TDC sensor 42 and a crank angle sensor (CRK) 44 are provided, and the former outputs a TDC signal at a predetermined crank angle position related to the piston top dead center (TDC) position of each cylinder. The CRK signal is output at a crank angle (for example, 30 degrees) whose cycle is shorter than that of the TDC signal.

  The engine 10 is connected to the exhaust pipe 46 via an exhaust manifold, and purifies exhaust gas generated by combustion with the catalyst device 50 and discharges it to the outside. A wide area air-fuel ratio (LAF) sensor 52 is provided upstream of the catalyst device 50, and outputs a signal proportional to the oxygen concentration in the exhaust gas in a wide range from lean to rich.

  A vehicle speed sensor 54 is disposed in the vicinity of the drive shaft that drives the wheels of the automobile, and outputs a signal every predetermined rotation of the drive shaft. The vehicle is provided with an atmospheric pressure sensor 56 and outputs a signal corresponding to the atmospheric pressure.

  The outputs of these sensors are sent to an electronic control unit (ECU) 60. The ECU 60 is composed of a microcomputer, and includes a processor CPU 60a that performs calculations, a list of control programs and various data, a ROM 60b that stores tables, and a RAM 60c that temporarily stores calculation results by the CPU 60a. The ECU 60 includes a nonvolatile memory, and stores data necessary for engine control in the next operation cycle in the nonvolatile memory. The nonvolatile memory can be composed of an EEPROM, which is a rewritable ROM, or a RAM with a backup function that retains memory by supplying a holding current even when the vehicle power is turned off.

  Outputs of various sensors are input to the input interface 60d of the ECU 60. The input interface 60d includes a circuit that shapes an input signal to correct a voltage level, and an A / D converter that converts an analog signal into a digital signal.

  The CPU 60a detects the NE rotating the engine by counting the CRK signal from the crank angle sensor 44 with a counter, and detects the running speed VP of the vehicle by counting the signal from the vehicle speed sensor 54. The CPU 60a performs calculations according to the program stored in the ROM 60b, and sends drive signals to the injector 24, the ignition device (not shown), the throttle valve / actuator 18 and the like via the output interface 60e.

  FIG. 2 shows the relationship between the engine speed NE and the resonance frequency 72 specific to the engine. FIG. 2A shows that the engine stop control started by the engine stop command is started at the time of the alternate long and short dash line 70. TH indicates the opening of the throttle valve. The throttle valve is closed simultaneously with the start of the stop control, and is opened from the starting point AA to weaken the negative pressure in the intake pipe. As indicated by an arrow 71 in the figure, the throttle valve is opened when the engine speed NE intersects the resonance frequency. When the throttle valve is opened, the engine is likely to rotate, and the torque increases momentarily to increase vibration. A curve G represents the vibration of the engine, and represents that the engine vibrates greatly where the engine speed NE intersects the resonance frequency.

  FIG. 2B shows a state in which the start point AA for opening the throttle valve after the engine stop control is started is set to the time when the engine speed becomes smaller than the resonance frequency of the engine. The throttle valve is opened after the engine speed indicated by circle 74 in the figure intersects the resonance frequency. By doing so, the engine torque is not increased in the vicinity of the resonance point, so the phenomenon of increasing resonance as shown in FIG. 2A does not occur.

  FIG. 3 shows a problem that occurs in engine stop control when the resonance frequency of the engine changes due to secular change. In FIG. 3A, the timing AA for opening the throttle valve once closed at the time point 70 when the ignition is turned off and the engine stop control is started is set after the resonance region 76. In this state, the engine resonance is not increased by opening the throttle valve.

  Even in a vehicle in which stop control is set so that the throttle valve opens at such timing, a problem arises when the engine resonance frequency changes due to secular change. As shown in FIG. 3B, when the initial resonance frequency 72 changes to the value indicated by the line 73 due to the aging of the vehicle, the time when the engine speed NE intersects the resonance frequency is delayed, and the initial resonance region 76 resonates. Changes to area 77. If the timing AA for opening the throttle valve is kept at the position shown in FIG. 3A in this state, the throttle valve is opened in the resonance region 77, and vibration is increased by the torque generated thereby. This is indicated by the vibration curve G.

  The apparatus according to the present invention detects a secular change in the resonance frequency of the engine and performs control to delay the timing for opening the throttle valve in accordance with the changed resonance frequency.

  Referring to the map of FIG. 4, in one embodiment, the timing for opening the throttle valve is delayed in accordance with the changed resonance frequency (specifically, the engine speed when the throttle valve is opened is changed to the low speed side). At the same time, the throttle valve opening (TH opening) is changed according to the delayed timing (that is, the engine speed changed to the low speed side). This map is set so that the opening degree of the throttle valve becomes lower as the engine speed at which the throttle valve is opened becomes lower, and is stored in the ECU memory.

  In one embodiment of the present invention, the engine rotational speed from the start of stop control that starts with an engine stop command until the engine stops is stored in a nonvolatile memory. Next, when the ignition is turned on and the vehicle enters the driving state, a calculation for detecting the resonance frequency of the engine in the background is performed.

  FIG. 5 shows a change in the rotational speed NE (rpm) stored in the nonvolatile memory in 1000 milliseconds from the start of the engine stop control to the stop of the engine. In this embodiment, in the eight sections (ANLY) indicated by circle 1 to circle 8 in FIG. 5, there is a high possibility of the resonance frequency being 10 Hz (corresponding to engine speed 600 rpm), 8.3 Hz (corresponding to 500 rpm), 6.7 Fourier analysis is performed for each of three frequencies (corresponding to 400 rpm), and resonance is detected depending on whether the spectrum exceeds a threshold value. FIG. 5 shows an example of frequency analysis for 10 Hz, and each of the eight sections is set to 100 milliseconds, which is a period corresponding to 10 Hz. These eight sections are shifted by 50 milliseconds of a half cycle as shown in the lower part of FIG. In the nonvolatile memory of the ECU, the number of revolutions for 1000 milliseconds until the engine stops is stored at an interval of 1 millisecond. Therefore, there is an array of 100 numerical values in one section (ANLY) of 100 milliseconds.

  FIG. 6 shows a flow of vibration detection, and FIG. 7 shows a threshold level for vibration determination. Discrete Fourier transform is performed at a frequency of 10 Hz for each of the eight sections on the time-series data of the engine speed shown in FIG. 5, that is, the array of numerical values (201). Next, a discrete Fourier transform is performed at a frequency of 8.3 Hz by the same method (203), and finally a discrete Fourier transform is performed at a frequency of 6.7 Hz (205). If the spectrum exceeds the threshold level 90 in FIG. 7 in any of the discrete Fourier transforms in these three subroutines, the vibration flag F_VIB is set to 1 (207), and the starting point AA for opening the throttle valve is set to 10 rpm. Delay by the corresponding time (209). Specifically, 10 rpm is subtracted from the set rotational speed of the starting point AA for opening the throttle valve. The updated start point AA (set rotation speed after subtracting 10 rpm) is stored in the nonvolatile memory and used as the start point AA in the next engine stop control. By repeating this process, the starting point AA is delayed by a time corresponding to 10 rpm, and moved to a point where resonance does not occur.

  FIG. 8 shows an overall flow of engine stop control. When an engine stop command is issued and the stop mode flag is set to 1 (211), check whether the engine speed NE has reached the starting speed at which the throttle valve opens (213). If YES, go to step 215. In step 215, the table is searched based on the starting point of the throttle valve, and the opening degree of the throttle valve is obtained. This throttle valve opening is set as a signal THCMD for driving the throttle valve (219). When the engine speed has not reached the engine speed corresponding to the starting point for opening the throttle valve in step 213, the throttle opening (for example, 0 degrees) during the closing of the valve is used as a signal THCMD for driving the throttle valve ( 217).

ここで、
ω₀＝２π/Ｔ Next, the discrete Fourier transform executed in the subroutines 201, 203, and 205 in FIG. 6 will be described with reference to FIG. Briefly describing the complex Fourier transform, a periodic wave of f (t) = f (tT) with T as the period is expressed by the following equation.

here,
ω ₀ = 2π / T

c _n is a complex Fourier coefficient and is expressed by the following equation.

The spectrum (magnitude, intensity) _Kn and the phase of the sine wave of the period T are obtained by the following equations. In this equation, RE means the real part and IM means the imaginary part.

  FIG. 9 shows a process for obtaining a spectrum by digital calculation based on discrete Fourier transform in the embodiment of the present invention. The calculation in the digital form of the above formula is performed. Here, 10 Hz, 8, 3 Hz, and 6.7 Hz, which may be the resonance frequency of the vehicle, are subjected to Fourier transform. This frequency is an example, and the present invention is not limited to this. In step 301, three frequencies (FREQ) to be subjected to Fourier transform are converted into angular frequency OMEGA (rad / sec). Now, when Fourier transform is performed for a frequency of 10 Hz, OMEGA = 2π × 10 (rad / sec).

  In step 303, the length TERM of the analysis section is set. In this embodiment, TERM is set to the period length of the frequency to be analyzed. When FREQ = 10Hz, TERM = (1/10) x 1000 (milliseconds) = 100 (milliseconds).

  From step 305, a loop for repeating Fourier transform is entered in each of the eight analysis sections (ANLY) shown in FIG. In step 307, the start point KST of the analysis section is set to a point advanced by 1/2 section from the start point of the previous analysis section. For the first analysis interval 1, KST is set to an initial value of 1. For the second analysis interval 2, the start point KST is a time point advanced by 1/2 interval from the initial value. In step 309, ST is set to the sampling interval of the rotational speed data. In this embodiment, the sampling interval is 1 millisecond. In step 311, n is set to a value from the start point KST of the analysis interval to (KST + TERM), that is, the end of the analysis interval, and the calculation loop is entered. That is, when the Fourier transform is performed for a frequency of 10 Hz, since the length of the section is 100 milliseconds, the calculation loop is set to n = KST, KST + 1, KST + 2, ..., KST + 99. enter. In step 313, the time t is set by multiplying the sampling interval ST, that is, 1 millisecond by n. Since ST is an integer value, t / 1000 is used in the operations of Steps 315 and 317 in order to make units of milliseconds.

  In step 315, an integral operation is performed on a numerical array at 1 millisecond intervals included in one analysis interval to obtain a real part RE of the Fourier series. In step 317, the integral operation is similarly performed to obtain the imaginary part IM of the Fourier series.

  Next, in step 321, the spectrum of Fourier transform is calculated. If the spectrum thus obtained is larger than the determination threshold VIBJUD (321), it is determined that vibration has occurred, and the flag F_VIB is set to 1 (325). When the calculation for all the analysis intervals is completed (327), the Fourier transform processing for the frequency of 10 Hz is ended.

  The above processing is performed for frequencies 8.3 Hz and 6.7 Hz, and the discrete Fourier transform subroutines 201, 203, and 205 shown in FIG. 6 are completed.

  Although the present invention has been described with respect to specific embodiments, the present invention is not limited to such embodiments.

  For example, the vibration determination means can be configured using a sensor that detects vibration, such as a piezoelectric element.

The figure which shows the whole structure of the engine of one Example of this invention. The figure which shows the relationship between the timing which opens a throttle valve in engine stop control, and engine resonance. The figure which shows a mode that the opening timing of a throttle valve is determined according to this invention. The map for changing the opening degree of a throttle valve in one Example is shown. The figure which shows the change of the engine speed in engine stop control. The figure which shows the flow which determines the vibration of an engine according to this invention. The figure which shows the example of the threshold level which determines a vibration from the spectrum obtained by Fourier-transform in one Example. The figure which shows the whole flow of engine stop control. The figure which shows the flow of the discrete Fourier transform used in one Example of this invention.

Explanation of symbols

10 Engine 14 Throttle valve 60 Electronic control unit (ECU)
72, 73 Resonance frequency

Claims (7)

A throttle valve for controlling the intake air amount of the internal combustion engine;
An actuator for driving the throttle valve;
An electronic control unit for controlling the internal combustion engine,
The electronic control device
The stop command of the internal combustion engine is generated, after the throttle valve is closed, when the rotational speed of the internal combustion engine is equal to or lower than a predetermined set rotational speed, and means for sending a signal for opening the throttle valve to the actuator,
Vibration determination means for determining whether or not vibration exceeding a predetermined reference has occurred in the internal combustion engine after the stop command;
Means for delaying the timing of opening the throttle valve after the next stop command when it is determined that the vibration has occurred;
Bei to give a,
The means for delaying the opening timing of the throttle valve has means for delaying the opening timing of the throttle valve and changing the opening degree of the throttle valve according to the delayed timing, and the opening degree of the throttle valve to be changed is: , Is set so that the lower the opening, the lower the rotational speed of the internal combustion engine at the timing of opening the throttle valve,
A device for controlling the stop of the internal combustion engine.   The vibration determination means performs frequency analysis using a time-series data array of the rotation speed of the internal combustion engine detected by the rotation speed sensor, obtains a spectrum for a predetermined frequency, and the spectrum exceeds a threshold value. The apparatus according to claim 1, wherein the apparatus determines that vibration exceeding a predetermined reference has occurred in the internal combustion engine.   The apparatus according to claim 2, wherein the vibration determination unit performs the frequency analysis by discrete Fourier transform.   The apparatus according to claim 2 or 3, wherein a plurality of frequencies that can be a vehicle resonance frequency are set as the predetermined frequency. The electronic control device includes a non-volatile memory that records the number of revolutions of the internal combustion engine from when the stop command for the internal combustion engine is generated until the internal combustion engine stops, and the vibration determination unit performs the vibration The apparatus according to any one of claims 2 to 4 , wherein the determination of whether or not has occurred is performed after the internal combustion engine has stopped. 6. The apparatus according to claim 5 , wherein the determination by the vibration determination means whether or not the vibration has occurred is executed after the ignition is turned on next time. Said means for delaying the timing of opening the throttle valve, the set rotational speed to a predetermined rotational speed value obtained by subtracting a new said set rotation speed, and stores the new setting rotational speed in the nonvolatile memory of claim 5 Or the apparatus of 6 .

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