JP4208994B2 - 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 a target air-fuel ratio of an air-fuel mixture to a leaner fuel side than a 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 mixture in the combustion chamber is stratified by devising the shape of the combustion chamber and intake port and the fuel injection method, and as a result, an air-fuel mixture with a high fuel concentration is made 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. Also, the multi-cylinder in-cylinder injection engine can be operated with a lean air-fuel ratio 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 region, the throttle valve opening speed or the engine speed change speed increases as the vehicle accelerates, and when the driver is making an output request, lean combustion cannot respond to the output request. There is a need to change the stoichiometric, I had to abort the lean combustion.
[0006]
[Problems to be solved by the invention]
In the above-described multi-cylinder in-cylinder injection engine, when the vehicle travels down a gentle slope, the throttle valve is not fully closed, and the engine speed is increased, and the engine is running at a low load. However, if the amount of change in the rotational speed of the engine exceeds a predetermined amount, it is determined that the vehicle is accelerating, and lean combustion is prohibited. Therefore, even if the engine load can be operated at a lean air-fuel ratio, there is a possibility that the engine cannot actually be operated at a lean air-fuel ratio, and the fuel efficiency has not been drastically improved at present. there were.
[0007]
The present invention has been made in view of the above situation, and an object of the present invention is to provide an internal combustion engine capable of further improving fuel efficiency by increasing the frequency of operation in the lean region.
[0008]
[Means for Solving the Problems]
The configuration of the present invention for achieving the above object is the area where the lean area is prohibited by the lean area permission means when the downhill condition is determined by the downhill determination means based on the driving situation. Even during driving, the operation in the lean region is permitted, and the frequency of driving in the lean region is increased to further improve fuel efficiency.
[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 the 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 as a fuel supply means is attached to each cylinder. An injection port of the fuel injection valve 4 is opened in the combustion chamber 5, and fuel injected from the fuel injection valve 4 via the driver 20 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. An intake side camshaft 13 and an exhaust side camshaft 14 are rotatably supported on the upper part of the cylinder head 2, and the intake valve 11 is driven by the rotation of the intake side camshaft 13. The exhaust valve 12 is driven by the rotation. 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 vane type crank angle sensor 17 that outputs a crank angle signal SGT at a predetermined crank position (for example, 75 degrees BTDC and 5 degrees BTDC) of each cylinder is provided, and the crank angle sensor 17 can detect the engine rotation speed. Yes. The camshafts 13 and 14 that rotate at half the number of revolutions of the crankshaft are provided with an identification sensor 18 that outputs a cylinder identification signal SGC, and the cylinder identification signal SGC can identify which cylinder the crank angle signal SGT belongs to. It is said that. In the figure, reference numeral 19 denotes an ignition coil that applies a high voltage to the spark plug 3.
[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 includes an air cleaner 23, a throttle body 24, a stepper motor type first air bypass valve 25, and an air flow sensor 26. The air flow sensor 26 detects an intake air amount, and for example, a Karman vortex type flow sensor is used. A boost pressure sensor can be attached to the surge tank 22 and the intake air amount can be obtained from the intake pipe pressure detected by the boost pressure sensor.
[0015]
The intake pipe 40 is provided with a large-diameter air bypass pipe 27 that bypasses the throttle body 24 and intakes air to the intake manifold 21, and the air bypass pipe 27 is provided with a linear solenoid type second air bypass valve 28. Yes. The air bypass pipe 27 has a flow passage area similar to that of the intake pipe 40, and when the second air bypass valve 28 is fully opened, intake of an amount required in the low and medium speed range of the direct injection engine 1 is possible.
[0016]
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. A throttle voltage corresponding to the opening degree of the throttle valve 29 is output from the throttle position sensor 30 that detects the opening degree of the throttle valve 29, and the opening degree of the throttle valve 29 is recognized based on the throttle voltage. Yes. The throttle body 24 is provided with an idle switch 31 that detects the fully closed state of the throttle valve 29 and recognizes the idling state of the in-cylinder injection engine 1.
[0017]
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 a large-diameter EGR pipe 36, and a stepper motor type EGR valve 37 is provided in the EGR pipe 36.
[0018]
The fuel stored in the fuel tank 41 is sucked up by the electric low-pressure fuel pump 42 and fed to the in-cylinder injection engine 1 side through the low-pressure feed pipe 43. The fuel pressure in the low pressure feed pipe 43 is regulated to a relatively low pressure (low fuel pressure) by a first fuel pressure regulator 45 provided in the return pipe 44. The fuel supplied to the in-cylinder injection engine 1 side is supplied to each fuel injection valve 4 by a high-pressure fuel pump 46 via a high-pressure feed pipe 47 and a delivery pipe 48.
[0019]
The high-pressure fuel pump 46 is, for example, a swash plate axial piston type, driven by the exhaust-side camshaft 14 or the intake-side camshaft 13, and a discharge pressure that is equal to or higher than a predetermined pressure even during idling operation of the direct injection engine 1. Can be generated. The fuel pressure in the delivery pipe 48 is adjusted to a relatively high pressure (high fuel pressure) by the second fuel pressure regulator 50 provided in the return pipe 49.
[0020]
An electromagnetic fuel pressure switching valve 51 is attached to the second fuel pressure regulator 50, and the fuel pressure switching valve 51 can release the fuel in the ON state to reduce the fuel pressure in the delivery pipe 48 to a low fuel pressure. Reference numeral 52 in the drawing is a return pipe for returning a part of the fuel used for lubrication and cooling of the high-pressure fuel pump 46 to the fuel tank 41.
[0021]
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 controls the driver 20, the ignition coil 19, the EGR valve 37, and the like.
[0022]
In addition to the various sensors described above, a number of switches (not shown) and the like are connected to the input side of the ECU 61, and various warning means and devices (not shown) are also connected to the output side.
[0023]
In the above-described in-cylinder injection engine 1, when the in-cylinder injection engine 1 is in the cold state, when the driver turns on the ignition key, the low-pressure fuel pump 42 and the fuel pressure switching valve 51 are turned on and the fuel injection valve 4 is turned on. Low fuel pressure fuel is supplied. Next, when the driver performs a start operation of the ignition key, the in-cylinder injection engine 1 is cranked by a cell motor (not shown), and at the same time, fuel injection control by the ECU 61 is started.
[0024]
At this time, a mode in which fuel is injected in the intake stroke is selected under the control of the ECU 61, and the fuel is injected so as to achieve a relatively rich air-fuel ratio. At the time of such start-up, the second air bypass valve 28 is closed to substantially the fully closed vicinity. Accordingly, intake of air into the combustion chamber 5 is performed via the clearance of the throttle valve 29 and the first air bypass valve 25. The first air bypass valve 25 and the second air bypass valve 28 are centrally managed by the ECU 61, and the respective valve opening amounts are determined according to the required amount of intake air that bypasses the throttle valve 29.
[0025]
When the start of the in-cylinder injection engine 1 is completed in this way and the in-cylinder injection engine 1 starts the idle operation, the high-pressure fuel pump 46 starts the rated discharge operation, and the ECU 61 turns off the fuel pressure switching valve 51. Thus, high pressure fuel is supplied to the fuel injection valve 4. The required fuel injection amount at this time is obtained from the discharge pressure of the high-pressure fuel pump 46 and the valve opening time of the fuel injection valve 4.
[0026]
Until the cooling water temperature detected by the water temperature sensor 16 rises to a predetermined value, fuel is injected in the same manner as at the start. The first air bypass valve 25 controls the idle rotation speed according to the increase / decrease in the load of auxiliary equipment such as an air conditioner. When the O ₂ sensor 34 is activated after a predetermined cycle has elapsed, air-fuel ratio feedback control is started according to the output voltage of the O ₂ sensor 34. Thereby, harmful exhaust gas components are favorably purified by the catalyst 35.
[0027]
The ECU 61 calculates the current fuel injection region from the fuel injection map of FIG. 2 based on the target output correlation value obtained from the throttle voltage corresponding to the opening of the throttle valve 29, for example, the target average effective pressure Pet and the engine speed. Search to determine the fuel injection mode. Thereby, 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 coil 19 is driven and controlled. At the same time, opening / closing control of the first air bypass valve 25, the second air bypass valve 28, and the EGR valve 37 is also performed.
[0028]
In the low load range such as during idling or low speed running, the late injection lean mode (compressed lean mode) in FIG. 2 is selected as the lean region for the fuel injection region. In this case, the first air bypass valve 25 and the second air bypass valve 28 are controlled, and the target air-fuel ratio corresponding to the target average effective pressure Pet is set based on the throttle voltage and the engine speed so as to obtain a lean air-fuel ratio. The Then, a fuel injection amount corresponding to the target air-fuel ratio is set, and the fuel injection valve 4 is driven and controlled to perform fuel injection corresponding to the fuel injection amount.
[0029]
In a medium load region such as when driving at a constant speed, depending on the load state and engine speed, the lean region in FIG. 2 in the previous injection lean mode (intake lean mode) or a region in which the lean region is prohibited (lean prohibited region) ) To enter the stoichiometric feedback mode. In the first-stage injection lean mode, the first air bypass valve 25 is controlled in the same manner as a normal idle speed control valve, the target air-fuel ratio is calculated according to the intake air amount signal from the air flow sensor 26 and the engine speed, The fuel injection amount is controlled to achieve a lean air-fuel ratio.
[0030]
In the stoichiometric feedback mode, the first air bypass valve 25 is controlled in the same manner as a normal idle speed control valve, and the second air bypass valve 28 is fully closed to increase the output excessively in the same manner as in the previous injection lean mode. In addition, the EGR valve 37 is controlled, and the fuel injection amount is controlled by performing air-fuel ratio feedback control according to the output voltage of the O ₂ sensor 34 so that the target air-fuel ratio becomes the stoichiometric air-fuel ratio.
[0031]
Further, in a high load region such as during rapid acceleration or high speed traveling, the open loop mode in FIG. 2 is set. In this case, the second air bypass valve 28 is closed, the target air-fuel ratio is set from the map so that the air-fuel ratio becomes relatively rich, and the fuel injection amount is controlled according to the target air-fuel ratio.
[0032]
At the time of driving in which the throttle valve 29 is substantially fully closed during traveling to inertial traveling or stopping, the fuel cut mode in FIG. 2 is set. In this case, the supply of fuel into the combustion chamber 5 is stopped. In the fuel cut mode, when the engine rotation speed is lower than the return rotation speed, the fuel supply into the combustion chamber 5 is resumed (fuel return) in the late injection lean mode. Further, even when the driver depresses the accelerator pedal, the fuel cut mode is immediately stopped, and the fuel supply into the combustion chamber 5 is resumed by the predetermined mode.
[0033]
The above-described in-cylinder injection engine 1 includes a downhill determination unit that detects whether or not a downhill condition of the vehicle is satisfied based on the driving situation, that is, based on the target average effective pressure Pet and the vehicle speed, and a lean region Lean area permitting means for permitting driving in the lean area when the descending slope determining means detects that the downhill condition of the vehicle is satisfied even when the vehicle is operating in the prohibited area. That is, when the vehicle travels down a gentle slope, the amount of change in the engine speed is low, even though the throttle valve 29 is not fully closed but the engine speed is increasing. When the engine exceeds a predetermined amount, operation in the lean region is enabled regardless of the amount of change in the rotational speed of the engine.
[0034]
That is, the ECU 61 stores a downhill determination value Pe as a target average effective pressure Pet with respect to the vehicle speed as a map. That is, as shown in FIG. 3, the downhill determination value Pe is set as a target average effective pressure that is lower than the load value P when the vehicle is traveling in the normal fourth speed with respect to the same vehicle speed. And even if it is driving | operating in the area | region where the lean area | region was prohibited, ECU61 will be in the state, when the target average effective pressure with respect to a vehicle speed falls below the downhill determination value Pe (when it becomes a downhill determination area | region). Has a function of permitting the operation in the lean region when it stays for a predetermined time or more.
[0035]
The detailed state of the function that permits the operation in the lean region when it becomes the downhill determination region will be described based on FIGS. 4 to 7. 4 to 7 show flowcharts of the operation permission control.
[0036]
As shown in the figure, it is determined whether or not the lean operation is being performed in step S1, and if the lean operation is being performed, it is determined whether or not the idle switch is on in step S21. If the idle switch is on, the step is performed. In step S22, the idle switch is counted up. In step S23, it is determined whether the idle switch-on timer has exceeded a predetermined value. If it is determined in step S23 that the idle switch-on timer exceeds the predetermined value, it is determined in step S24 whether or not the engine speed exceeds a predetermined value that allows fuel cut, and exceeds the predetermined value. If it is determined, the control is ended in the fuel cut mode in step S25. If it is determined in step S21 that the idle switch is off, the idle switch on timer is cleared and the process proceeds to step S2.
[0037]
Next, in step S2, it is determined whether or not the amount of change ΔTPS of the throttle valve 29 is greater than or equal to a predetermined value. If it is determined in step S2 that the change amount ΔTPS is greater than or equal to a predetermined value, it is determined that acceleration has started, and stoichiometric operation is performed in step S3. If it is determined in step S2 that the change amount ΔTPS is less than the predetermined value, the acceleration is not started and the load is not increased, and the process returns.
[0038]
If it is determined in step S1 that the engine is not leaning, it is determined in step S31 whether or not the idle switch is on. If the idle switch is on, the idle switch is counted up in step S32, and in step S33. It is determined whether or not the idle switch-on timer exceeds a predetermined value. If it is determined in step S33 that the idle switch-on timer exceeds a predetermined value, it is determined in step S34 whether or not the engine speed exceeds a predetermined value that allows fuel cut, and exceeds the predetermined value. If it is determined, the control is terminated in step S35 as a fuel cut mode. If it is determined in step S31 that the idle switch is off, the idle switch on timer is cleared and the process proceeds to step S4.
[0039]
In step S4, it is determined whether or not the engine speed change amount ΔNe is less than a predetermined value. If it is determined that the change amount ΔNe is less than the predetermined value, the ΔNe timer is counted in step S5, and it is determined in step S6 whether the count value of the ΔNe timer is less than the predetermined value. If it is determined in step S6 that the count value of the ΔNe timer is equal to or greater than the predetermined value, the process proceeds to step S7 shown in FIG. 7 to execute the lean operation. That is, the stoichiometric operation is performed until a certain amount of time has elapsed in which the change amount ΔNe of the engine rotation speed is less than the predetermined value.
[0040]
If it is determined in step S4 that the engine speed change amount ΔNe is equal to or greater than the predetermined value, the ΔNe timer is cleared in step S8, and whether or not the target average effective pressure Pet is greater than or equal to the downhill determination value Pe in step S9. To be judged. If it is determined in step S6 that the count value of the ΔNe timer is less than the predetermined value, it is determined in step S9 whether or not the target average effective pressure Pet is equal to or greater than the downhill determination value Pe. If it is determined in step S9 that the target average effective pressure Pet is equal to or greater than the downhill determination value Pe, the downhill determination timer is cleared in step S10, and the stoichiometric operation is executed in step S3.
[0041]
That is, the change amount ΔNe of the engine rotation speed is less than a predetermined value, but the target average effective pressure Pet is equal to or higher than the downhill determination value Pe with respect to the vehicle speed (when acceleration is not started but the load is relatively high). When the change amount ΔNe of the engine speed is equal to or greater than a predetermined value and the target average effective pressure Pet is equal to or greater than the downhill determination value Pe with respect to the vehicle speed (when the load is relatively high at the start of acceleration), the stoichiometric operation is performed. .
[0042]
On the other hand, if the target average effective pressure Pet is determined to less than the downhill determination value Pe at step S9, as shown in FIG. 7, it counts the downhill determination timer in Step S11 in downhill determination timer in Step S12 It is determined whether the count value is equal to or greater than a predetermined value. If it is determined in step S12 that the count value of the downhill determination timer is less than the predetermined value, that is, the predetermined time has not elapsed since it is determined that the target average effective pressure Pet is less than the downhill determination value Pe. In this case, the routine proceeds to step S3 in FIG. 6 and the stoichiometric operation is executed. When the count value of the downhill determination timer in step S12 is determined to be equal to or greater than the predetermined value, i.e., from its target average effective pressure Pet is determined that less than the downhill determination value Pe (downhill determination area) When the state stays for a predetermined time or longer, the process proceeds to step S7 and the lean operation is executed.
[0043]
The above-described step S9 constitutes downhill judging means for judging whether or not the downhill condition of the vehicle is satisfied, and step S11 and step S12 constitute lean area permission means. That is, when it is determined that the target average effective pressure Pet with respect to the vehicle speed is less than the downhill determination value Pe and it is determined that the downhill condition of the vehicle is satisfied, it is determined in step S1 that the lean operation is not being performed. However, even when driving in the lean-prohibited area, driving in the lean area is permitted.
[0044]
As described above, in the in-cylinder injection engine 1 of the present embodiment, the target average effective pressure Pet is reduced downhill even under a situation where the change amount ΔNe of the engine speed is large and the operation is performed in the lean prohibition region. If it is less than the judgment value Pe, that is, if the load is low and the operation in the lean region is possible, the operation in the lean region is executed when the state stays for a predetermined time or more. For this reason, the frequency of the driving | running | working in a lean area | region increases, and a further fuel-consumption improvement can be aimed at.
[0045]
In the above-described embodiment, it is determined whether or not the vehicle downhill condition is satisfied by comparing the target average effective pressure Pet and the downhill determination value Pe. It is also possible to determine whether the downhill condition is satisfied by other means, such as determining whether the downhill condition of the vehicle is satisfied. 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 internal combustion engine of the present invention is operating in an area where the lean area is prohibited by the lean area permission means when the downhill determination means determines that the downhill condition of the vehicle is satisfied based on the driving situation. However, since the operation in the lean region is permitted, the frequency of the operation in the lean region can be increased. As a result, it is possible to further improve fuel efficiency.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a multi-cylinder direct injection internal combustion engine as an internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a fuel injection control map.
FIG. 3 is a downhill determination map.
FIG. 4 is a flowchart of operation permission control.
FIG. 5 is a flowchart of operation permission control.
FIG. 6 is a flowchart of operation permission control.
FIG. 7 is a flowchart of operation permission control.
[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 6 Cylinder 7 Piston 8 Cavity 9 Intake port 10 Exhaust port 11 Intake valve 12 Exhaust valve 61 ECU

Claims (2)

An internal combustion engine having a lean combustion stopping means that stops lean combustion and burns at a stoichiometric air-fuel ratio when the throttle valve opening speed or the engine speed change speed exceeds a predetermined speed in a lean region where lean combustion is performed. ,
Internal combustion engine, characterized in that descent of the vehicle is provided with a stop means for Ru to perform the lean combustion is stopped the lean combustion stop means when it is detected. The internal combustion engine according to claim 1,
When the target average effective pressure Pet obtained from the throttle voltage corresponding to the throttle valve opening falls below a predetermined downhill determination value Pe when the stop means stays for a predetermined time or longer, the stop means An internal combustion engine that detects that the engine is running.

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