JP2014105652A - Engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark ignition/in-cylinder injection type internal combustion engine that avoids knocking and operates at high thermal efficiency.SOLUTION: A spark ignition/in-cylinder injection type internal combustion engine controls a fuel injection timing θinj so as to be set to a predetermined timing in a compression stroke, and controls an ignition timing θig. More specifically, when it is determined that knocking occurs, the spark ignition/in-cylinder injection type internal combustion engine delays the fuel injection timing θinj by a first predetermined amount (α) (see a step 250), and calculates a generation heat amount Q due to combustion of fuel. In a case where the calculated generation heat amount Q is smaller than a predetermined threshold Qth, the spark ignition/in-cylinder injection type internal combustion engine advances the fuel injection timing θinj by a second predetermined amount (α, α1) (see a step 290), and delays the ignition timing θig by a third predetermined amount (β) (see a step 285).

Description

  The present invention relates to an engine control device applied to an in-cylinder fuel injection spark ignition internal combustion engine.

  2. Description of the Related Art Conventionally, an internal combustion engine in which fuel such as gasoline is directly injected into a cylinder and an air-fuel mixture formed in the cylinder is ignited by a spark from a spark plug is widely known. Such an engine is also referred to as a “cylinder fuel injection spark ignition internal combustion engine”, a “direct injection engine”, or a “cylinder injection engine”.

  Incidentally, even in a cylinder injection type engine, knocking occurs due to various factors such as a fuel octane number and a deposit amount. Knocking is generally avoided by retarding the ignition timing. However, as the ignition timing is retarded, the ignition timing is further away from MBT (Minimum Advance for Best Torque), so the engine torque decreases.

  Therefore, one of the conventional control devices (hereinafter also referred to as “conventional device”) applied to the in-cylinder injection engine is to change not only the ignition timing but also the injection timing when knocking occurs. The occurrence of knocking is avoided while reducing the amount of decrease in engine-generated torque (see, for example, Patent Document 1).

  More specifically, the conventional device injects fuel during the intake stroke for the purpose of lowering the intake air temperature by vaporizing the fuel and improving intake charging efficiency, and if knocking occurs, the ignition timing is set. Be retarded. Further, the conventional device, when knocking cannot be suppressed and the retard amount of the ignition timing becomes larger than the threshold value, the injection timing is shifted to the first half of the compression stroke and the ignition timing is advanced. While avoiding occurrence of this, it is avoided that the torque drop becomes large. According to the above publication, the ignition timing can be advanced when the injection timing is retarded so as to be in the first half of the compression stroke, so that a reduction in engine torque can be avoided in the first half of the compression stroke. It is described that because the fuel mixing state deteriorates due to injection, knocking is less likely to occur, and therefore the ignition timing can be brought close to MBT. Since MBT is also the ignition timing that maximizes the engine torque, it can also be referred to as the “maximum torque ignition timing”, and because it is also the ignition timing that maximizes the thermal efficiency of the engine, it is referred to as “maximum thermal efficiency generation ignition timing”. It can also be called.

JP 2002-339848 A (particularly paragraph 0024)

  By the way, when fuel injection is performed during an intake stroke in a direct injection type engine, the latent heat of vaporization of the fuel is used for cooling the intake air. Therefore, since the intake air amount can be increased, the engine generated torque can be improved. However, the fuel injection during the intake stroke causes a decrease in thermal efficiency compared to the fuel injection during the compression stroke.

  More specifically, if fuel injection is performed during the compression stroke, the latent heat of vaporization of the fuel can be used to avoid knocking. Therefore, since the ignition timing can be set close to MBT, high thermal efficiency can be ensured. Therefore, the inventor performs fuel injection during the compression stroke, and appropriately adjusts the fuel injection timing and ignition timing during the compression stroke, thereby operating the in-cylinder injection engine with high thermal efficiency while avoiding knocking. Invented an engine control device that can do this.

  An engine control device according to the present invention (hereinafter also referred to as “the present device”) includes a fuel injection valve that directly injects fuel into a cylinder, and an air-fuel mixture formed in the cylinder by the injected fuel. The present invention is applied to an internal combustion engine including an ignition plug that generates a spark for ignition.

Furthermore, the device of the present invention
A determination unit for determining whether knocking has occurred in the engine;
Control for setting the fuel injection timing, which is the timing for injecting the fuel from the fuel injection valve, to a predetermined timing in the compression stroke, and for controlling the ignition timing, which is the timing for generating the spark from the spark plug And
Is provided.

  In addition, when it is determined that the knocking has occurred, the control unit retards the fuel injection timing by a first predetermined amount, calculates the amount of heat generated by the combustion of the fuel, and the calculated amount of generated heat is When it becomes smaller than a predetermined threshold value, the fuel injection timing is advanced by a second predetermined amount and the ignition timing is retarded by a third predetermined amount.

  According to the device of the present invention, since fuel injection is performed during the compression stroke, the ignition timing in normal time (a state in which knocking has not occurred) can be brought close to the maximum thermal efficiency generation ignition timing (MBT). Therefore, the thermal efficiency of the engine can be kept high. Further, when knocking occurs, the fuel injection timing is retarded in preference to the ignition timing.

  Note that “the fuel injection timing is retarded in preference to the ignition timing” means “only the fuel injection timing is retarded while the ignition timing is maintained”, “the ignition timing is a minute amount. The fuel injection timing is retarded by a considerable amount for the purpose of suppressing knocking. That is, “the fuel injection timing is retarded in preference to the ignition timing” means “the fuel injection timing is retarded while the ignition timing is substantially maintained”.

  Here, the reason why the control unit of the device of the present invention retards the fuel injection timing during the compression stroke when knocking occurs as described above will be described with reference to FIG. A curve C in FIG. 3 shows “relationship between ignition timing and engine torque” when the engine is operated in an operation region in which knocking may occur (for example, a low rotation high load region). When the engine is operated in such an operation region, the ignition timing at which knocking occurs is considerably retarded from MBT. Therefore, in general, the ignition timing (basic ignition timing) set in normal operation (operation in which knocking has not occurred) is set to a value retarded by a relatively large amount from MBT. As a result, when the ignition timing is retarded by a certain amount dθ with the occurrence of knocking, the engine torque decrease amount d becomes relatively large.

  Therefore, if the ignition timing is retarded when knocking occurs, the amount of torque reduction increases and the thermal efficiency decreases. Therefore, the device of the present invention retards the fuel injection timing (prior to the ignition timing) when knocking occurs. When the injection timing during the compression stroke is changed to the retard side, the time from the injection timing to the ignition timing is shortened, so the time during which heat is transferred from the cylinder inner wall to the air-fuel mixture is shortened. As a result, the temperature of the air-fuel mixture that has decreased due to the latent heat of vaporization of the injected fuel can be maintained at a low temperature until the air-fuel mixture is ignited. Furthermore, if the fuel injection timing is changed to the retarded angle side, the time during which the fuel is exposed to a high-temperature and high-pressure environment before combustion starts is shortened, so that one of the causes of knocking (self-ignition) occurs. The decomposition of the fuel (the decomposition of the fuel into a substance having a low molecular weight) is suppressed.

  From the above, by changing the injection timing during the compression stroke to the retard side, the occurrence of knocking is suppressed without substantially retarding the ignition timing. On the other hand, the delay of the fuel injection timing does not significantly reduce the thermal efficiency compared to the delay of the ignition timing. Therefore, the device of the present invention can suppress the occurrence of knocking while avoiding a large decrease in engine torque (and hence thermal efficiency).

  However, if the amount of retardation of the fuel injection timing during the compression stroke becomes excessive as knocking continues, the time from the fuel injection timing to the ignition timing (fuel diffusion time) becomes extremely short, and the fuel in the cylinder It cannot spread sufficiently. As a result, the thermal efficiency decreases. In other words, when it is necessary to further suppress the occurrence of knocking when the retardation amount of the fuel injection timing is a certain value, the ignition timing is retarded rather than performing further retardation of the fuel injection timing. The decrease in torque (and hence thermal efficiency) is smaller.

  Therefore, when it is determined that the knocking has occurred, the control unit of the present invention retards the fuel injection timing by a first predetermined amount, calculates the amount of heat generated by the combustion of the fuel, and the calculated amount of generated heat is the predetermined amount. The fuel injection timing is advanced by a second predetermined amount and the ignition timing is retarded by a third predetermined amount when it becomes smaller than the threshold value.

  According to this, since it is possible to avoid a decrease in thermal efficiency due to an excessive delay of the fuel injection timing, it is possible to suppress the occurrence of knocking while reducing the amount of decrease in thermal efficiency as a result.

  Other objects, other features, and attendant advantages of the present invention will be readily understood from the description of each embodiment of the present invention described with reference to the following drawings.

FIG. 1 is a schematic cross-sectional view of an internal combustion engine to which an engine control device (this device) according to an embodiment of the present invention is applied. FIG. 2 is a flowchart showing a routine executed by the CPU of the present apparatus. FIG. 3 is a graph showing the relationship between the ignition timing and the torque generated by the engine. FIG. 4 is a graph showing the in-cylinder pressure with respect to the crank angle and the value P · ^Vκ with respect to the crank angle. FIG. 5 is a map showing an operation region that is referred to by the CPU of a modification of the present apparatus.

  Hereinafter, an engine control device according to an embodiment of the present invention (hereinafter also referred to as “the present device”) will be described with reference to the drawings.

(Outline configuration)
FIG. 1 is a schematic view of an internal combustion engine 10 to which the present apparatus is applied. The engine 10 is a so-called “in-cylinder injection type—spark ignition—gasoline—multi-cylinder (four-cylinder) internal combustion engine”. Although FIG. 1 shows only a cross section of a specific cylinder, other cylinders have the same configuration.

  The internal combustion engine 10 supplies air to the cylinder block portion 20 including a cylinder block, a cylinder block lower case, an oil pan and the like, a cylinder head 30 fixed on the cylinder block portion 20, and the cylinder block portion 20. The intake system 40 and the exhaust system 50 for releasing the exhaust gas from the cylinder block unit 20 to the outside are included.

  The cylinder block portion 20 includes a cylinder bore (cylinder) 21, a piston 22, a connecting rod 23, and a crankshaft 24. The piston 22 reciprocates in the cylinder, and the reciprocating motion of the piston 22 is transmitted to the crankshaft 24 via the connecting rod 23, whereby the crankshaft 24 rotates. The top surface of the piston 22, the wall surface of the cylinder bore 21, and the lower surface of the cylinder head 30 define a combustion chamber 25.

  The cylinder head 30 includes an intake port 31 that communicates with the combustion chamber 25, an intake valve 32 that opens and closes the intake port 31, an intake valve drive device 33 that includes an intake camshaft that opens and closes the intake valve 32, and an exhaust gas that communicates with the combustion chamber 25. Port 34, exhaust valve 35 for opening and closing exhaust port 34, exhaust camshaft 36 for driving exhaust valve 35, ignition plug (ignition plug) 37, igniter 38 including an ignition coil for generating a high voltage applied to ignition plug 37, and fuel A fuel injection valve (in-cylinder injection valve, fuel injector) 39 for directly injecting the fuel into the combustion chamber 25 is provided.

  The intake system 40 includes an intake manifold 41 including an intake manifold that communicates with the intake port 31 and forms an intake passage together with the intake port 31, an air filter 42 provided at an end of the intake pipe 41, and an intake pipe 41. A throttle valve 43 having a variable opening cross-sectional area of the passage and a throttle valve actuator 43a including a DC motor constituting throttle valve driving means are provided.

  The exhaust system 50 includes an exhaust manifold 51 communicating with the exhaust port 34, an exhaust pipe (exhaust pipe) 52 connected to the exhaust manifold 51, “an upstream side three-way catalyst 53 and a downstream side disposed on the exhaust pipe 52. A three-way catalyst 54 "is provided.

  On the other hand, this system includes a hot-wire air flow meter 61, a throttle position sensor 62, a cam position sensor 63, a crank position sensor 64, a coolant temperature sensor 65, a knock sensor 66, an in-cylinder pressure sensor 67, and an accelerator opening sensor 68. .

The hot-wire air flow meter 61 detects the mass flow rate per unit time of the intake air flowing through the intake pipe 41 and outputs a signal representing the mass flow rate Ga.
The throttle position sensor 62 detects the opening of the throttle valve 43 and outputs a signal representing the throttle valve opening TA.

The cam position sensor 63 outputs one pulse every time the intake camshaft rotates 90 degrees, 90 degrees, and 180 degrees from a predetermined angle.
The crank position sensor 64 outputs a pulse every time the crankshaft 24 rotates 10 degrees. A pulse output from the crank position sensor 64 is converted into a signal representing the engine rotational speed NE by an electric control device 70 described later. Further, the electric control device 70 obtains the crank angle (absolute crank angle θ) of the engine 10 based on signals from the cam position sensor 63 and the crank position sensor 64.

The coolant temperature sensor 65 detects the coolant temperature of the engine 10 and outputs a signal representing the coolant temperature THW.
The knock sensor (knocking detection unit) 66 detects vibration generated by knocking generated in the engine 10 and sends a signal representing the vibration.

  One in-cylinder pressure sensor 67 is provided for each of the plurality of cylinders. The in-cylinder pressure sensor 67 detects the gas pressure (in-cylinder pressure) in the corresponding combustion chamber 25 (that is, each of which is disposed), and sends a signal representing the in-cylinder pressure P (= Pc). ing. The in-cylinder pressure P of each cylinder is acquired by the electric control device 70 every time the crank angle changes by a minute angle Δθ. Further, the acquired in-cylinder pressure P is stored in the RAM 73 described later in the form of in-cylinder pressure P (θ) in association with the crank angle θ of the corresponding cylinder.

  The accelerator opening sensor 68 detects the operation amount of the accelerator pedal 81 operated by the driver, and outputs a signal representing the operation amount Accp of the accelerator pedal 81. The operation amount Accp of the accelerator pedal 81 is one parameter representing the magnitude of the “load” of the engine 10.

  The electric control device 70 is a known microcomputer including a CPU 71, a ROM 72, a RAM 73, a backup RAM 74, an interface 75 including an AD converter, and the like.

  The interface 75 is connected to the sensors 61 to 68, and supplies signals from these sensors to the CPU 71. Further, the interface 75 sends a drive signal to the intake valve drive device 33, the throttle valve actuator 43a, etc. in accordance with an instruction from the CPU 71, sends an injection instruction signal to the fuel injection valve 39 of each cylinder, and igniters for each cylinder. An ignition signal is sent to 38.

  The electric control device 70 controls the throttle valve actuator 43a so that the throttle valve opening TA increases as the operation amount Accp of the accelerator pedal 81 increases. Further, the electric control device 70 determines whether or not knocking has occurred in the engine 10 based on a signal from the knock sensor 66 in accordance with a known method.

(Outline of knocking suppression control)
Next, an outline of the knocking suppression control executed by the present apparatus will be described.

  This apparatus controls the ignition timing θig, which is a timing at which a spark is generated from the spark plug 37 and the air-fuel mixture in the cylinder is ignited. This device determines a fuel injection amount, which is the amount of fuel injected from the fuel injection valve 39, based on the intake air amount Ga and the engine rotational speed NE in accordance with a known method. Further, the present apparatus injects “determined fuel injection amount of fuel” from the fuel injection valve 39 and controls the fuel injection timing θinj (= start timing of fuel injection), which is the timing of injecting the fuel. However, this apparatus sets the fuel injection timing θinj during the compression stroke. That is, this apparatus injects fuel from the fuel injection valve 39 provided in the cylinder in the compression stroke. In addition, as described below, when it is determined that knocking has occurred, this apparatus controls the ignition timing θig and the fuel injection timing θinj. The control of the ignition timing θig and the fuel injection timing θinj is also referred to as “knocking suppression control”.

  More specifically, this device retards the fuel injection timing θinj by a first predetermined amount when knocking occurs. If knocking still occurs in this state, the fuel injection timing θinj is further retarded by a first predetermined amount. As described above, the present apparatus basically retards the fuel injection timing θinj by the first predetermined amount until knocking disappears.

  If the fuel injection timing θinj during the compression stroke is changed to the retard side to suppress knocking, the time from the fuel injection timing θinj to the ignition timing θig is shortened, so heat is transferred from the cylinder inner wall to the mixture. The time spent is shortened. As a result, the temperature of the air-fuel mixture decreased by the latent heat of vaporization of the injected fuel can be maintained at a “lower temperature” until the air-fuel mixture is ignited. Therefore, knocking is less likely to occur than when the fuel injection timing θinj is not retarded.

  Furthermore, if the fuel injection timing θinj is changed to the retard side, the time during which the fuel is exposed to a high-temperature and high-pressure environment before the combustion starts is shortened, which is one of the factors that cause knocking (self-ignition). Decomposition of the fuel, which is one of them (decomposition of the fuel into a substance having a low molecular weight) is suppressed. Therefore, knocking is less likely to occur.

  From the above, since the occurrence of knocking is suppressed by changing the fuel injection timing θinj during the compression stroke to the retard side, the ignition timing θig can be maintained at an ignition timing (basic ignition timing θigb) close to MBT. .

  Incidentally, as described with reference to FIG. 3, in the operation region where knocking may occur, the basic ignition timing θigb is set to a timing delayed by a considerable amount from the MBT. Therefore, the retard of the ignition timing θig for suppressing knocking greatly reduces the torque of the engine 10. On the other hand, the retardation of the fuel injection timing θinj does not greatly reduce the torque of the engine 10 while exhibiting the knocking suppression effect. Therefore, according to the present apparatus, it is possible to suppress the occurrence of knocking while avoiding a large decrease in the torque (and hence thermal efficiency) of the engine 10.

  However, if the retard amount of the fuel injection timing θinj during the compression stroke is excessive, the time from the fuel injection timing θinj to the ignition timing θig becomes extremely short, and the fuel cannot be sufficiently diffused in the cylinder. As a result, the thermal efficiency decreases. In other words, when the retard amount of the fuel injection timing θinj is a relatively large value, it is more effective to retard the ignition timing θig than to retard the fuel injection timing θinj further. Therefore, the decrease in thermal efficiency is small.

  Therefore, when it is determined that knocking has occurred, the apparatus retards the fuel injection timing θinj by a first predetermined amount, calculates the amount of heat generated by the combustion of the fuel, and the calculated amount of generated heat is greater than a predetermined threshold value. When it becomes smaller, it is determined that the thermal efficiency has decreased because the fuel injection timing θinj has been retarded too much. In such a case, the present apparatus advances the fuel injection timing θinj by a second predetermined amount (when the first predetermined amount is equal to the second predetermined amount, the fuel injection timing θinj is returned to the previous value). At the same time, the ignition timing θig is retarded by a third predetermined amount. As a result, this apparatus can avoid a decrease in thermal efficiency due to an excessive delay of the fuel injection timing θinj, and as a result, it is possible to suppress the occurrence of knocking while reducing the amount of decrease in thermal efficiency.

(Actual operation)
Next, the actual operation of this apparatus will be described. In the present system, the basic fuel injection timing θinjb and the basic ignition are set such that knocking does not occur and the thermal efficiency of the engine 10 is maximized with respect to the engine operating state determined based on the load KL of the engine 10 and the engine speed NE. The time θigb is determined in advance by experiments or the like, and the data is stored in the ROM 72 in the form of a lookup table (Mapθigb (KL, NE), Mapθinjb (KL, NE)).

The load (load factor, filling factor) KL is obtained by the following equation (1). Instead of the load KL, an accelerator pedal operation amount Accp or an air amount (in-cylinder intake air amount Mc) that one cylinder sucks in one intake stroke may be used as the load KL. In the equation (1), Mc is the in-cylinder intake air amount, ρ is the air density (unit is (g / l)), L is the exhaust amount of the engine 10 (unit is (l)), and “4” is the engine. The number of cylinders is 10.

KL = (Mc / (ρ · L / 4)) · 100% (1)

1. The fuel injection timing control CPU 71 (hereinafter simply referred to as “CPU”) applies a load KL and an engine rotational speed NE to a table Mapθinjb (KL, NE) by executing a routine not shown in the drawing. The injection timing θinjb is determined. Further, the CPU performs a fuel injection amount Finj (= Mc / theoretical air-fuel ratio) by a known method from the load KL, the engine speed NE (or the cylinder intake air amount Mc) and the target air-fuel ratio (in this example, the theoretical air-fuel ratio). ).

In addition, the CPU retards (corrects) the basic fuel injection timing θinjb by an injection timing correction amount (injection delay amount) dθinj separately calculated by a routine described later, and sets the retarded fuel injection timing θinj to the retarded fuel injection timing θinj. To inject fuel (start fuel injection). That is, the CPU determines the fuel injection timing θinj according to the following equation (2). The reference for the fuel injection timing θinj is the compression top dead center of each cylinder. The value of the fuel injection timing θinj increases as the fuel injection timing θinj is advanced from the compression top dead center.

Fuel injection timing θinj = Basic fuel injection timing θinjb−Injection delay amount dθinj (2)

2. Ignition Timing Control The CPU determines a basic ignition timing θigb by executing a routine (not shown) and applying the load KL and the engine speed NE to the table Mapθigb (KL, NE).

Further, the CPU retards (corrects) the basic ignition timing θigb by an ignition timing correction amount (ignition delay amount) dθig separately calculated by a routine described later, and performs ignition at the retarded ignition timing θig. Do. That is, the CPU determines the ignition timing θig according to the following equation (3). The reference of the ignition timing θig is the compression top dead center of each cylinder. The value of the ignition timing θig increases as the ignition timing θig is advanced from the compression top dead center.

Ignition timing θig = Basic ignition timing θigb−Ignition retardation amount dθig (3)

3. Knocking suppression control The CPU executes a “knocking suppression control routine” shown in the flowchart of FIG. 2 every time a predetermined time (predetermined crank angle) elapses. Therefore, when the predetermined timing is reached, the CPU starts the process from step 200 in FIG. 2 and proceeds to step 210, where the operation region to which the “operation state of the engine 10 determined by the load KL and the engine speed NE” belongs is determined in this routine. It is determined whether or not it has changed since the previous execution.

  At this time, if the operating region has changed, the CPU makes a “Yes” determination at step 210 to proceed to step 220 to set the injection retardation amount dθinj to “0”. Next, the CPU proceeds to step 230, sets the ignition retardation amount dθig to “0”, proceeds to step 295, and once ends this routine. As a result, the ignition timing θig is set to the basic ignition timing θigb, and the fuel injection timing θinj is set to the basic fuel injection timing θinjb.

  On the other hand, if the operating region has not changed at the time when the CPU executes the process of step 210, the CPU makes a “No” determination at step 210 and proceeds to step 240 to determine whether knocking has occurred. Determine. At this time, if knocking has not occurred, the CPU makes a “No” determination at step 240 to directly proceed to step 295 to end the present routine tentatively. Accordingly, the injection retard amount dθinj and the ignition retard amount dθig are not changed. Therefore, in this case, both the injection retard amount dθinj and the ignition retard amount dθig are maintained at “0”.

  On the other hand, if knocking has occurred at the time when the CPU executes the process of step 240, the CPU makes a “Yes” determination at step 240 and sequentially executes the processes of steps 250 to 280 described below. Do.

  Step 250: The CPU increases the injection retardation amount dθinj by a positive predetermined value α (first predetermined amount). The predetermined value α is a constant value. However, the predetermined value α may be a value that changes according to the operating state (KL, NE). For example, the predetermined value α may be a value that increases as the load KL increases and increases as the engine speed NE decreases.

  Step 260: The CPU reads the generated heat quantity Q calculated separately. The generated heat quantity Q is calculated based on the in-cylinder pressure P as described later. A method for calculating the amount of generated heat Q is well known (for example, see JP 2010-144484 A).

Step 270: The CPU calculates the threshold heat quantity Qth by applying the separately calculated fuel injection amount Finj to the function fq. This function fq is a positive coefficient smaller than 1 (for example, 0.6), which is obtained when combustion is performed at “expected thermal efficiency” when the fuel injection amount is “Finj”. A function for calculating a value obtained by multiplying by .about.0.9). The threshold heat quantity Qth may be obtained by a look-up table using the load KL and the engine speed NE as parameters. For example, the threshold heat quantity Qth can be calculated so as to increase as the load KL increases and decrease as the engine speed NE increases.
Step 280: The CPU determines whether or not the generated heat quantity Q is equal to or greater than the threshold heat quantity Qth.

  If the generated heat quantity Q is equal to or greater than the threshold heat quantity Qth, the CPU makes a “Yes” determination at step 280 to directly proceed to step 295 to end the present routine tentatively. Therefore, in order to avoid knocking, the fuel injection timing θinj is retarded from the basic fuel injection timing θinjb by the injection delay amount dθinj (in this case, the value α), and the ignition timing θig is maintained at the basic ignition timing θigb.

  If the CPU starts the process of this routine again from step 200 in a state where the operation region does not change, the CPU makes a “No” determination at step 210 to proceed to step 240. If knocking has not occurred at this stage, the CPU makes a “No” determination at step 240 to directly proceed to step 295. Therefore, if knocking does not occur, the fuel injection timing θinj is not further changed to the retard side.

  On the other hand, if knocking still occurs at the time when the CPU executes the process of step 240, the CPU proceeds to step 250 to step 280. Accordingly, the fuel injection timing θinj is further retarded by the predetermined value α.

  By the way, if the generated heat quantity Q is less than the threshold heat quantity Qth at the time when the CPU executes step 280, the fuel diffusion time becomes extremely short and the fuel cannot be sufficiently diffused in the cylinder. It can be determined that the thermal efficiency is reduced. Therefore, in this case, the CPU makes a “No” determination at step 280 to proceed to step 285 to increase the ignition retardation amount dθig by a positive predetermined value β (third predetermined amount). The predetermined value β is a constant value. However, the predetermined value β may be a value that changes according to the operating state (KL, NE). For example, the predetermined value β may be a value that increases as the load KL increases and increases as the engine speed NE decreases.

  Next, the CPU proceeds to step 290 to decrease the injection retardation amount dθinj by a positive predetermined value α (second predetermined amount = first predetermined amount). That is, the CPU advances the fuel injection timing θinj by a predetermined value α. As a result, the injection retardation amount dθinj increased by the predetermined value α in step 250 is returned to the value before the increase. Thereafter, the CPU proceeds to step 295 to end the present routine tentatively. In step 290, the CPU may decrease the injection retardation amount dθinj by a positive value α1 (second predetermined amount) different from the predetermined value α. The value α1 is preferably larger than 0 and smaller than the predetermined value α.

  As described above, the CPU retards the ignition timing θig instead of retarding the fuel injection timing θinj when the fuel injection timing θinj is greatly retarded due to the occurrence of knocking and the generated heat amount Q becomes less than the threshold heat amount Qth. Therefore, the occurrence of knocking is suppressed.

4). Outline of Calculation Method of Generated Heat Quantity Q Next, an outline of a calculation method of the generated heat quantity Q will be described.
FIG. 4A shows how the in-cylinder pressure P changes with respect to the crank angle θ. FIG. 4B shows the state of change of “P (θ) · V (θ) ^κ ” by a solid line, and the amount of heat generated (integrated amount of generated heat) Q in the combustion chamber 25 by a broken line. . In FIG. 4, the crank angle 0 indicates “compression top dead center”, the region where the crank angle θ is a negative value indicates before compression top dead center (BTDC), and the region where the crank angle θ is a positive value After compression top dead center (ATDC). P (θ) is the in-cylinder pressure P at the crank angle θ, V (θ) is the combustion chamber volume at the crank angle θ, and κ is the specific heat ratio of the gas in the combustion chamber 25.

From FIG. 4B, it is understood that the change pattern (dashed line) of the generated heat quantity Q substantially coincides with the change pattern (solid line) of P (θ) · V (θ) ^κ . That is, the heat generation amount Q can be acquired based on P (θ) · V (θ) ^κ .

Therefore, the apparatus as a heat generation amount Q, and calculates the [Delta] P · V ^kappa shown in FIG. 4 (B). More specifically, the control device obtains P (θs) · V (θs) ^κ when the crank angle θ is a θs degree crank angle before compression top dead center (for example, θs = 60 degree crank angle). To do. Furthermore, this apparatus acquires P (θe) · V (θe) ^κ when the crank angle θ is a θe degree crank angle after compression top dead center (for example, θe = 40 degree crank angle). Thereafter, the apparatus acquires the difference (that is, the value obtained by subtracting P (θs) · V (θs) ^κ from P (θe) · V (θe) ^κ ) as the amount ΔP · V ^κ , and the amount ΔP · V ^κ is adopted as the generated heat quantity Q.

  When the crank angle θ is the θs degree crank angle before the compression top dead center, both the intake valve 32 and the exhaust valve 35 are closed in the compression stroke toward the target combustion stroke (expansion stroke) and the ignition timing is reached. It is a time when it has advanced sufficiently. That is, the time when the air-fuel mixture does not generate any heat. The time point when the crank angle θ is the θe degree crank angle after compression top dead center is a predetermined time later than the latest time when the combustion of the air-fuel mixture in the target combustion stroke is substantially finished, and the exhaust valve 35 This is a time advanced from the valve opening time.

In this apparatus, the maximum of “P (θ) · V (θ) ^κ ” when the crank angle θ is between the crank angle θs degrees before compression top dead center and the crank angle θe degrees after compression top dead center. The value MAX and the minimum value MIN may be acquired, and the difference (MAX−MIN) may be acquired as the quantity ΔP · ^Vκ .

That is, the present apparatus, at least at the start combustion of the mixture (e.g., ignition timing, or, when the P · V ^kappa begins a rapid rise) at the end of combustion from (e.g., the P · V ^kappa in subsequent ignition timing A heat generation amount estimation means for estimating (acquiring) a generated heat quantity Q, which is an amount of heat generated with combustion of the air-fuel mixture, based on the value ΔP · V ^κ during a period until the start of the decrease) I can say.

As described above, this device is
A determination unit (knock sensor 66, step 240 in FIG. 2) for determining whether knocking has occurred in engine 10;
The fuel injection timing θinj, which is the timing for injecting fuel from the fuel injection valve (39), is controlled to be set to a predetermined timing in the compression stroke, and the ignition timing θig, which is the timing for generating a spark from the spark plug (37). A control unit (electric control device 70) for controlling
Is provided.
Furthermore, the control unit
When it is determined that knocking has occurred, the fuel injection timing θinj is retarded by a first predetermined amount (α) (see step 250 in FIG. 2), and the amount of generated heat Q due to fuel combustion is calculated and calculated. When the generated heat quantity Q is smaller than a predetermined threshold value Qth, the fuel injection timing θinj is advanced by a second predetermined amount (α, α1) (step 290 in FIG. 2) and the ignition timing θig is set to a third predetermined amount ( β) The angle is retarded (step 285 in FIG. 2).

  Therefore, the occurrence of knocking can be suppressed without causing a significant decrease in the thermal efficiency of the engine 10.

  The present invention is not limited to the above embodiment, and various modifications can be employed within the scope of the present invention. For example, this device executes the above-described knocking suppression control when the operating state of the engine 10 belongs to the region A (low rotation high load region) shown in FIG. 5, and the operating state of the engine 10 is shown in FIG. When knocking occurs in the indicated region B (high rotation / low load region), the ignition timing θig may be retarded without retarding the fuel injection timing θinj.

  In other words, this apparatus is used when the load KL of the engine 10 is larger than the “threshold load that decreases as the engine speed decreases (see KLth = f1 (NE) in FIG. 5)” (that is, the region A). When it is determined that knocking has occurred, the fuel injection timing θinj is retarded in preference to the ignition timing θig, and control based on the generated heat quantity Q is executed, and the engine load is smaller than the threshold load KLth. In this case (that is, in the region B), when it is determined that knocking has occurred, the ignition timing θig may be retarded in preference to the fuel injection timing θinj. In the region C shown in FIG. 5, knocking does not occur even when the ignition timing θig is set to MBT.

As described above, when the operating state of the engine 10 belongs to the high rotation low load region (region B), the knocking suppression by the ignition timing θig is executed.
(1) When the operating state of the engine 10 belongs to the high rotation / low load region, knocking is unlikely to occur in the first place, so the basic ignition timing θigb is close to MBT, and therefore the torque decreases even if the ignition timing θig is retarded. The amount is small, and
(2) When the operating state of the engine 10 belongs to the high rotation and low load region, the time from the fuel injection timing to the ignition timing (fuel diffusion time) is short. Therefore, if the fuel injection timing θinj is retarded, the fuel diffusion time The torque drop amount becomes large due to shortage,
based on.

  Further, the present apparatus determines whether or not knocking has occurred based on the signal from the knock sensor 66, but determines whether or not knocking has occurred based on the signal from the in-cylinder pressure sensor 67. May be configured. Further, the amount of generated heat may be calculated by a method different from the method described above.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 25 ... Combustion chamber, 31 ... Intake port, 32 ... Intake valve, 34 ... Exhaust port, 35 ... Exhaust valve, 37 ... Spark plug, 39 ... Fuel injection valve, 66 ... Knock sensor, 67 ... In-cylinder pressure Sensor, 70 ... electric control device, 71 ... CPU.

Claims (1)

Applied to an internal combustion engine comprising: a fuel injection valve that directly injects fuel into a cylinder; and an ignition plug that generates a spark for igniting an air-fuel mixture formed in the cylinder by the injected fuel,
A determination unit for determining whether knocking has occurred in the engine;
Control for setting the fuel injection timing, which is the timing for injecting the fuel from the fuel injection valve, to a predetermined timing in the compression stroke, and for controlling the ignition timing, which is the timing for generating the spark from the spark plug And
In an engine control device comprising:
The controller is
When it is determined that the knocking has occurred, the fuel injection timing is retarded by a first predetermined amount, the amount of heat generated by the combustion of the fuel is calculated, and the calculated amount of generated heat is smaller than a predetermined threshold value. The fuel injection timing is advanced by a second predetermined amount and the ignition timing is retarded by a third predetermined amount,
An engine control device configured as described above.

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