JP3690139B2 - Lean combustion internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an internal combustion engine in which fuel efficiency characteristics are improved by controlling the air-fuel ratio to a leaner combustion side than the stoichiometric air-fuel ratio.
[0002]
[Prior art]
In recent years, in order to improve fuel consumption by improving the fuel consumption rate, an internal combustion engine (engine) that can be operated with an air-fuel ratio leaner than a stoichiometric air-fuel ratio, that is, a lean air-fuel ratio has been developed and put into practical use. Yes.
[0003]
Normally, in an engine that can be operated as a lean air-fuel ratio, the shape of the combustion chamber and intake port and the combustion injection method are devised to stratify the mixture in the combustion chamber, thereby allowing the mixture with high fuel concentration to be as close to the ignition plug as possible To improve ignitability. As described above, when the air-fuel mixture can be suitably stratified, it becomes possible to increase only the fuel concentration of the air-fuel mixture in the vicinity of the spark plug and to reduce the air-fuel ratio as a whole, that is, to make it lean. In addition, the air-fuel ratio can be freely controlled over a wide range.
[0004]
Recently, various multi-cylinder in-cylinder injection engines that inject fuel directly into the combustion chamber have been proposed in place of the intake pipe injection engine that injects fuel into the intake pipe in order to reduce harmful exhaust gas components and improve fuel efficiency. Has been. In the multi-cylinder in-cylinder injection engine, an intake stroke injection mode in which fuel injection is mainly performed in an intake stroke and a compression stroke injection mode in which fuel injection is mainly performed in a compression stroke are switched according to an operation state. Yes. Even in a multi-cylinder in-cylinder injection engine, a lean combustion operation (lean operation) is possible according to the operating state.
[0005]
Also in the intake stroke injection mode and the compression stroke injection mode, an intake stroke lean air-fuel ratio mode (intake lean mode) and a compression stroke lean air-fuel ratio mode (compressed lean mode) controlled as a lean air-fuel ratio are set. In the lean mode that is executed in the relatively low load operating region, the lean valve combustion speed or the engine rotational speed change speed becomes large as when the vehicle is accelerating. However, since the output request cannot be met, it is necessary to change the air-fuel ratio to non-lean operation such as stoichio, and the lean mode is stopped.
[0006]
[Problems to be solved by the invention]
In the above-described multi-cylinder in-cylinder injection engine, acceleration determination and steady state determination are performed based on a change rate of the throttle valve opening, an accelerator pedal opening speed, or an engine rotation speed based on a predetermined value based on a preset operation mode. It is carried out. For this reason, for example, when the accelerator is frequently stepped on frequently due to variations in the driving operation due to the driver's heel or the like, a driving situation in which acceleration is frequently determined and the frequency of lean driving decreases is generated. When an operating situation occurs in which the frequency of lean operation is reduced, there is a risk that even in a cylinder injection engine made to improve fuel efficiency, the frequency of lean operation decreases and fuel efficiency cannot be improved.
[0007]
The present invention has been made in view of the above situation, and an object of the present invention is to provide a lean combustion internal combustion engine capable of performing a lean operation at a predetermined frequency regardless of variations in a driver's driving operation.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the configuration of the present invention calculates the frequency of the lean combustion operation by the lean combustion operation frequency calculation means, and compares the calculated lean combustion operation frequency with a preset lean combustion operation frequency. In the case where it is determined that the lean combustion operation frequency calculated is lower than the set lean combustion operation frequency, the acceleration determination value is increased by the acceleration determination value changing means to make it difficult to change to the non-lean combustion operation. Increase the frequency of lean burn operation. As a result, the frequency of lean burn operation is increased without being affected by the driver's habit and driving conditions, and fuel efficiency is further improved.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. In the illustrated embodiment, a multi-cylinder in-cylinder injection internal combustion engine in which fuel is directly injected into a combustion chamber is described as an example of a lean combustion internal combustion engine. FIG. 1 shows a schematic configuration of a multi-cylinder direct injection internal combustion engine according to an embodiment of the present invention, and FIG. 2 shows a fuel injection control map.
[0010]
The configuration of a multi-cylinder in-cylinder injection internal combustion engine will be described with reference to FIG. As the multi-cylinder in-cylinder internal combustion engine, for example, an in-cylinder in-line four-cylinder gasoline engine (in-cylinder injection engine) 1 that directly injects fuel into a combustion chamber is applied. The in-cylinder injection engine 1 has a combustion chamber, an intake device, an exhaust gas recirculation device (EGR device) and the like designed exclusively for in-cylinder injection.
[0011]
A spark plug 3 is attached to each cylinder of the cylinder head 2 of the in-cylinder injection engine 1 and an electromagnetic fuel injection valve 4 is attached to each cylinder. An injection port of the fuel injection valve 4 is opened in the combustion chamber 5 so that the fuel injected from the fuel injection valve 4 is directly injected into the combustion chamber 5. A piston 7 is supported on the cylinder 6 of the direct injection engine 1 so as to be slidable in the vertical direction, and a hemispherical cavity 8 is formed on the top surface of the piston 7. The cavity 8 generates a reverse tumble flow opposite to the normal tumble flow in the intake air flow.
[0012]
An intake port 9 and an exhaust port 10 facing the combustion chamber 5 are formed in the cylinder head 2. The intake port 9 is opened and closed by driving the intake valve 11, and the exhaust port 10 is opened and closed by driving the exhaust valve 12. A large-diameter exhaust gas recirculation port (EGR port) 15 branches obliquely downward from the exhaust port 10.
[0013]
A water temperature sensor 16 for detecting the cooling water temperature is provided in the vicinity of the cylinder 6 of the direct injection engine 1. Further, a crank angle sensor 17 that outputs a crank angle signal at a predetermined crank position of each cylinder is provided, and the crank angle sensor 17 can detect the engine rotation speed. That is, the change rate of the engine speed can be detected.
[0014]
An intake pipe 40 is connected to the intake port 9 via an intake manifold 21, and the intake manifold 21 is provided with a surge tank 22. The intake pipe 40 is provided with an air cleaner 23, an air flow sensor 26 for detecting the intake air amount, and a throttle body 24. The intake pipe 40 is provided with an air bypass pipe (not shown) that bypasses the throttle body 24 and intakes the intake manifold 21.
[0015]
The throttle body 24 is provided with a butterfly throttle valve 29 that opens and closes the flow path, and a throttle position sensor 30 that detects the opening of the throttle valve 29. The throttle position sensor 30 outputs a throttle voltage corresponding to the opening degree of the throttle valve 29, and the opening degree of the throttle valve 29 is recognized based on the throttle voltage. That is, the rate of change of the throttle valve 29 is recognized.
[0016]
On the other hand, an exhaust pipe 33 is connected to the exhaust port 10 via an exhaust manifold 32, and an O ₂ sensor 34 is attached to the exhaust manifold 32. Further, the exhaust pipe 33 is provided with a catalyst 35 and a muffler (not shown). The EGR port 15 is connected to the upstream side of the intake manifold 21 via the EGR pipe 36, and an EGR valve 37 is provided in the EGR pipe 36.
[0017]
The vehicle is provided with an electronic control unit (ECU) 61. The ECU 61 includes an input / output device, a storage device for storing a control program, a control map, and the like, a central processing unit, a timer, and counters. The ECU 61 performs comprehensive control of the cylinder injection engine 1. Detection information of various sensors is input to the ECU 61. The ECU 61 determines the fuel injection mode, the fuel injection amount, the ignition timing, the EGR gas introduction amount, and the like based on the detection information of the various sensors. 4, the spark plug 3, the EGR valve 37 and the like are driven and controlled.
[0018]
In the in-cylinder injection engine 1 described above, the intake flow that flows into the combustion chamber 5 from the intake port 9 forms a reverse tumble flow, and fuel is injected from the fuel injection valve 4 after the middle of the compression stroke to use the reverse tumble flow. On the other hand, a small amount of fuel is collected only in the vicinity of the spark plug 3 disposed at the center of the top of the combustion chamber 5, and an extremely lean air-fuel ratio is obtained at a portion separated from the spark plug 3. By setting only the vicinity of the spark plug 3 to the stoichiometric air-fuel ratio or a rich air-fuel ratio, fuel consumption is suppressed while realizing stable stratified combustion (stratified super lean combustion).
[0019]
When high output is obtained from the in-cylinder injection engine 1, the fuel from the fuel injection valve 4 is injected into the intake stroke so as to be uniform throughout the combustion chamber 5 and premixed combustion is performed. Of course, since the theoretical air-fuel ratio or the rich air-fuel ratio can provide a higher output than the lean air-fuel ratio, fuel injection is performed at a timing at which fuel atomization and vaporization are sufficiently performed, High output is obtained efficiently.
[0020]
The ECU 61 determines the fuel injection mode by searching the current fuel injection region from the fuel injection map of FIG. 2 based on the operating load Pe and the engine speed Ne according to the opening of the throttle valve 29, and The fuel injection amount corresponding to the target air-fuel ratio in each fuel injection mode is determined, and the fuel injection valve 4 is driven and controlled according to the fuel injection amount, and the ignition control of the spark plug 3 and the opening / closing control of the EGR valve 37 are performed. Is also implemented.
[0021]
In the low load region such as during idling or low speed running, the late injection lean mode (compression lean mode) in FIG. 2 is selected as the fuel injection region. In the compression lean mode, fuel injection is performed during the compression stroke (particularly in the latter half of the compression stroke) in order to achieve lean operation by stratified super-lean combustion and improve fuel efficiency.
[0022]
In a medium load region such as during high-speed traveling, the fuel injection region is selected from the first-term injection lean mode (intake lean mode) or stoichiometric feedback mode in FIG. In the intake lean mode, fuel injection is performed during the intake stroke in order to achieve lean operation by premixed combustion. In the stoichiometric feedback mode, fuel injection is performed during the intake stroke in order to achieve stoichiometric operation (theoretical air-fuel ratio operation) by premixed combustion and to improve the output from the intake lean mode.
[0023]
In a high load region such as during rapid acceleration or high speed traveling, the fuel injection region is selected from the open loop mode in FIG. In the open loop mode, rich operation by premixed combustion is realized and the output is improved compared to the stoichiometric feedback mode. Further, in the region where the throttle valve is substantially fully closed due to inertial traveling or traveling to stop, the fuel injection region becomes the fuel cut mode in FIG. 2, and the supply of fuel into the combustion chamber 5 is stopped. .
[0024]
As shown in FIG. 3, in the in-cylinder injection engine 1 described above, when the change rate of the opening degree of the throttle valve 29 serving as the acceleration operation unit exceeds a predetermined value (acceleration determination value), the acceleration determination unit 71 accelerates the acceleration state. And when the operation is determined to be in the acceleration state during the operation in the intake lean mode or the compression lean mode (lean mode) as the lean combustion operation, the operation mode is changed to the stoichiometric operation as the non-lean combustion operation. Changed to feedback mode or open loop mode (non-lean mode). Then, when the rate of change of the engine rotation speed detected by the crank angle sensor 17 falls below a predetermined value (steady state determination value), the acceleration determination unit 71 determines that it is in a steady state, and the operation mode is changed to the lean mode.
[0025]
In addition, as shown in FIG. 3, when the water temperature sensor 16 detects that the water temperature has become operable in the lean mode and the operation in the lean mode is executed, the lean region timer 73 operates and the lean mode The lean operation timer 74 is activated while the operation at is being executed. Based on the count values of the lean region timer 73 and the lean operation timer 74, the lean mode frequency is calculated by the calculating means 75 as the lean combustion frequency calculating means. That is, the frequency (lean operation frequency: lean frequency) at which the lean operation is actually performed in the region where the operation in the lean mode (lean operation) is possible is calculated.
[0026]
The lean frequency calculated by the calculating means 75 is compared with a preset lean combustion operation frequency (set lean frequency) preset by the comparing means 76. When there is a difference between the set lean frequency and the lean frequency, the changing unit 77 as the acceleration determination value changing unit changes the predetermined value of the rate of change of the opening degree of the throttle valve 29 for determining the acceleration state. . Further, the predetermined value of the rate of change of the engine speed for determining the steady state is changed.
[0027]
That is, when it is determined that the lean frequency is low, the predetermined value of the rate of change of the opening degree of the throttle valve 29 is greatly changed to delay the change of the operation mode to the non-lean mode during acceleration. In addition, the predetermined value of the rate of change of the engine rotation speed is greatly changed so as to accelerate the change to the lean mode when the steady state is reached. This makes it difficult to change to the non-lean mode when accelerating, even when the driver performs an operation that is easily determined to be in an accelerated state due to driving habits, etc., and shortens the non-lean mode when shifting to the steady state. Therefore, lean operation can be ensured at a certain frequency.
[0028]
Further, when it is determined that the lean frequency is high, the predetermined value of the rate of change of the opening degree of the throttle valve 29 is changed to be small so that the operation mode is changed to the non-lean mode at the time of acceleration. Further, the predetermined value of the change rate of the engine rotation speed is changed to a small value to delay the change to the lean mode when the steady state is reached. As a result, even in the case of a driver who performs an operation that is difficult to be determined as an acceleration state due to a driving habit or the like, the mode is changed to the non-lean mode at the time of acceleration and the non-lean mode at the time of shifting to the steady state. Is lengthened. While the lean operation tends No _x in comparison with non-lean operation is often discharged, reduced lean frequency by reducing the acceleration determination value if it is determined that lean frequency is large (increase the non-lean operation) By doing so, the emission amount of No _x is suppressed and the exhaust gas performance is improved.
[0029]
A detailed state of the function of calculating the lean frequency and changing the acceleration determination value will be described with reference to FIGS. FIGS. 4 to 6 are flowcharts of the lean mode determination control, and FIG. 7 is a time chart showing the operation state of the lean region timer and the lean timer.
[0030]
A determination situation by the acceleration determination means 71 will be described with reference to FIG.
[0031]
As shown in the figure, it is determined whether or not the water temperature WT detected by the water temperature sensor 16 in step S1 exceeds the lean operation permission water temperature WTL. If the water temperature WT exceeds the lean operation permission water temperature WTL, step S2 is performed. It is then determined whether or not the current operation mode is lean operation. If it is determined in step S2 that the engine is in a lean operation, it is determined in step S3 whether or not the rate of change ΔTPS of the opening of the throttle valve 29 detected by the throttle position sensor 30 exceeds the acceleration determination value. If the value is exceeded, the acceleration state is set and the operation mode is set to the non-lean mode in step S4.
[0032]
If it is determined in step S2 that the current operation mode is not lean operation, it is determined in step S5 whether or not the engine rotation speed change rate ΔNe detected by the crank angle sensor 17 is less than a steady determination value. If the engine speed change rate ΔNe is less than the steady state determination value, the steady state is set and the operation mode is set to the lean mode in step S6.
[0033]
Based on the above steps, acceleration determination and steady determination during lean operation are performed.
[0034]
Based on FIGS. 5 to 7, the calculation of the lean frequency and the situation in which the acceleration determination values ΔTPS α, ΔTPS β, TPS γ and the steady determination values ΔNeα, ΔNeβ, ΔNeγ are set based on the lean frequency will be described. Note that the magnitude of the acceleration judgment value is ΔTPS α <ΔTPS β <TPS γ, and the magnitude of the steady judgment value is ΔNeα <ΔNeβ <ΔNeγ.
[0035]
As shown in FIG. 5, it is determined in step S11 whether or not the water temperature WT exceeds the lean operation permission water temperature WTL. If the water temperature WT exceeds the lean operation permission water temperature WTL (after point A in FIG. 7), In step S12, it is determined according to the map of FIG. 2 whether or not the current operation region is a lean region. When the water temperature WT is equal to or lower than the lean operation permission water temperature WTL, and when the current operation region is not the lean region, if the lean region timer 73 described later is counting, the count is stopped and the process returns.
[0036]
If it is determined in step S12 that the current operation region is a lean region, the lean region timer 73 is turned on in step S13 to start counting (after point B in FIG. 7), and whether or not the lean operation is performed in step S14. Is judged. If it is determined in step S14 that the operation is lean, the lean operation timer 74 is turned on in step S15 to start counting (points B, D, and F in FIG. 7), and the process proceeds to step S16. If it is determined in step S14 that the lean operation is not being performed, if the lean operation timer 74 is counting, the count is stopped and the process proceeds to step S16 as it is (lean operation timer 74OFF: between points C and D in FIG. 7). , Between point E and point F).
[0037]
In step S <b> 16, the lean frequency is calculated based on the count value T of the lean region timer 73 and the count value t of the lean operation timer 74. That is, the frequency of lean operation in the lean region is calculated by the following equation.
Lean frequency = (t / T) × 100
In the example of FIG.
Lean frequency = {(t ₁ + t ₂ + t ₃ ) / T} × 100
It becomes.
[0038]
After the lean frequency is calculated in step S16, as shown in FIG. 6, whether or not a predetermined time set as a time for the calculated lean frequency to stabilize has elapsed since the lean region timer 73 started counting. Is determined in step S17. If a predetermined time has elapsed since the start of the count of the lean region timer 73, it is determined in step S18 whether or not the calculated lean frequency is greater than the target lean frequency in the operation mode at that time.
[0039]
If it is determined in step S18 that the lean frequency is greater than the target lean frequency, an acceleration determination value ΔTPS α and a steady determination value ΔNeα are selected in step S19. Since the acceleration judgment value ΔTPS α and the steady judgment value ΔNeα are set to small values, if it is judged that the lean frequency is large, the operation mode is changed to the non-lean mode at the time of acceleration and the steady state It becomes slow to change to lean mode when it becomes.
[0040]
If it is determined in step S18 that the lean frequency is not greater than the target lean frequency, it is determined in step S20 whether the lean frequency is less than the target lean frequency. If it is determined in step S20 that the lean frequency is smaller than the target lean frequency, an acceleration determination value ΔTPS γ and a steady determination value ΔNeγ are selected in step S21. Since the acceleration judgment value ΔTPS γ and the steady judgment value ΔNeγ are set to large values, the operation mode is changed to the non-lean mode at the time of acceleration, and the lean mode is changed to the steady state. Can be expedited.
[0041]
When it is determined in step S17 that the predetermined time has not elapsed since the lean area timer 73 started counting, and in step S20, the lean frequency is not smaller than the target lean frequency, that is, the lean frequency becomes the target lean frequency. If it is determined that they are equal, the acceleration determination value ΔTPS β and the steady determination value ΔNeβ are selected in step S22. Since the acceleration judgment value ΔTPS β and steady judgment value ΔNeβ are set to normal values, the operation mode is changed to the non-lean mode in the normal state during acceleration, and the lean mode is set to the normal state when the steady state is reached. Changed to
[0042]
As described above, in the in-cylinder injection engine 1 of the present embodiment, when it is determined that the lean frequency is greater than the target lean frequency, the acceleration determination value ΔTPS α and the steady determination value ΔNeα set to small values are selected. When the vehicle is accelerated, the change of the operation mode to the non-lean mode is accelerated, and the change to the lean mode is delayed when the steady state is reached. As a result, even in the case of a driver who performs an operation that is difficult to be determined as an acceleration state due to a driving habit or the like, the mode is changed to the non-lean mode at the time of acceleration and the non-lean mode at the time of shifting to the steady state. Becomes longer.
[0043]
Further, in the in-cylinder injection engine 1 of the present embodiment example, when it is determined that the lean frequency is smaller than the target lean frequency, the acceleration determination value ΔTPS γ and the steady determination value ΔNeγ set to large values are selected, and at the time of acceleration The change of the operation mode to the non-lean mode is delayed, and the change to the lean mode is accelerated when the steady state is reached. This makes it difficult to change to the non-lean mode when accelerating, even if the driver is performing an operation that is easily determined to be in an accelerated state due to driving habits, etc., and shortens the non-lean mode when shifting to the steady state. Thus, lean operation is ensured at a certain frequency, and fuel consumption can be further improved.
[0044]
In the above-described embodiment, when the lean frequency is calculated, when the water temperature WT exceeds the lean operation permission water temperature WTL and the current operation region is the lean region, the lean region timer 73 is turned on and the count is performed. However, when the water temperature WT exceeds the lean operation permission water temperature WTL (point A in FIG. 7), the lean region timer 73 may be turned on to start counting. Further, as a condition for turning on the lean region timer 73, output information of the O ₂ sensor 34 attached to the exhaust manifold 32 can be used.
[0045]
Further, in the above embodiment, the rate of change of the throttle valve opening is used as the acceleration determination value, but the opening speed of the accelerator pedal may be used, and is not limited to this, and is a parameter that correlates with the driver's acceleration request. Other parameters may be used if any. Further, although the present invention has been described as being applied to the direct injection engine 1 that directly injects fuel into the combustion chamber 5 as an internal combustion engine, the present invention can also be applied to an internal combustion engine that injects fuel into an intake pipe. In addition, the present invention can be applied not only to the four-cylinder in-cylinder injection engine 1 but also to a single-cylinder engine or a V-type six-cylinder engine.
[0046]
【The invention's effect】
The lean combustion internal combustion engine of the present invention calculates the frequency of the lean combustion operation by the lean combustion operation frequency calculation means, compares the calculated lean combustion operation frequency with the preset lean combustion operation frequency by the comparison means, When it is judged that the lean combustion operation frequency calculated is lower than the set lean combustion operation frequency, the acceleration judgment value is increased by the acceleration judgment value changing means, so it is difficult to change to the non-lean combustion operation. The frequency of lean burn operation can be increased. As a result, the frequency of lean burn operation can be increased without being affected by the driver's habit and driving conditions, and fuel efficiency can be further improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a multi-cylinder in-cylinder injection internal combustion engine as a lean combustion internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a fuel injection control map.
FIG. 3 is a configuration diagram of a control block.
FIG. 4 is a flowchart of a lean mode determination situation.
FIG. 5 is a flowchart of lean frequency calculation and acceleration determination value setting control.
FIG. 6 is a flowchart of lean frequency calculation and acceleration determination value setting control.
FIG. 7 is a time chart showing an operation state of a lean area timer and a lean timer.
[Explanation of symbols]
1 Multi-cylinder in-cylinder injection internal combustion engine (in-cylinder injection engine)
2 Cylinder head 4 Fuel injection valve 5 Combustion chamber 61 ECU
71 Acceleration determining means 72 Operation mode changing means 73 Lean region timer 74 Lean operation timer 75 Calculation means 76 Comparison means 77 Changing means

Claims (1)

Acceleration determination means for determining acceleration when the operation amount of the acceleration operation means exceeds an acceleration determination value;
In a lean combustion internal combustion engine comprising: an operation mode changing means for changing from a lean combustion operation that operates at an air-fuel ratio leaner than a stoichiometric air-fuel ratio to an unlean combustion operation when acceleration is determined by the acceleration determining means;
Lean combustion operation frequency calculation means for calculating the frequency of lean combustion operation;
A comparison means for comparing the calculated lean combustion operation frequency with a preset lean combustion operation frequency,
A lean combustion internal combustion engine comprising: an acceleration determination value changing means for increasing the acceleration determination value when it is determined by the comparison means that the lean combustion operation frequency calculated is lower than the set lean combustion operation frequency organ.

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