JP2004076695A - Variable compression ratio engine and its control - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the trouble involved in the change in compression ratio of an engine. <P>SOLUTION: At an increase in compression ratio (εi>ε(i-1)), an opening-increasing drive signal is outputted to a throttle valve driving actuator 63 (step S330) to forcedly increase the intake air quantity. In such a compression ratio-increasing state, the blow-by gas quantity to an intake pipe 50 is increased, and the air-fuel mixture carried into a combustion chamber is transited to fuel excessive side. However, since the intake air quantity is increased, such an excessive fuel is suppressed, and the disturbance of the fuel/air ratio carried to the combustion chamber after the increasing change of compression ratio is suppressed. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a variable compression ratio engine that changes the compression ratio of an engine and its control.
[0002]
[Prior art]
The variable compression ratio engine has various advantages by changing the compression ratio according to the operating conditions. For example, at a high load where knocking is likely to occur, by lowering the compression ratio, self-ignition of the fuel is suppressed, and thus the occurrence of knocking can also be suppressed. At a low load, increasing the compression ratio causes an increase in the temperature of the air-fuel mixture, thereby increasing the combustibility of the fuel. For this reason, during acceleration running or the like in which load fluctuation is likely to occur, the compression ratio is changed from the high compression ratio to the low compression ratio in accordance with the load fluctuation (fluctuation from low load to high load). I have. By performing the compression ratio control in accordance with such load fluctuations, fuel efficiency and drivability are improved.
[0003]
By the way, when operating the engine, air-fuel ratio control is generally performed so that the air-fuel ratio matches the target air-fuel ratio. A method of applying such air-fuel ratio control to a variable compression ratio engine is proposed in, for example, Japanese Patent Application Laid-Open No. 63-159624. This method sets the compression ratio to a high compression ratio in the low load range, sets the target air-fuel ratio at that time to the lean side, and sets the target air-fuel ratio to the rich side when changing from the high compression ratio to the low compression ratio. is there.
[0004]
[Problems to be solved by the invention]
However, even if the air-fuel ratio control and the compression ratio are changed in this way, the following problems are expected to occur. During operation of the engine, clearances exist between the piston and the cylinder, between the piston and the piston ring, between the piston ring and the like, and blow-by occurs in which gas in the combustion chamber passes through the clearance. The blow-by gas reaches the crank room and is returned to the intake pipe directly from the crank room or via the cylinder head.
[0005]
When the compression ratio is changed, the occurrence state of the blow-by changes, and the blow-by gas amount also changes. Immediately after the change in the compression ratio, the blow-by gas amount suddenly changes. Blow-by gas may include an unburned fuel mixture. For this reason, the blow-by gas returned to the intake pipe causes disturbance in the fuel / air ratio in the intake air entering the combustion chamber. Such a disturbance in the intake air ratio adversely affects the combustion state by the air-fuel ratio control that attempts to make the air-fuel ratio equal to the target air-fuel ratio. As a result, the residual oxygen in the exhaust gas is also disturbed. Therefore, the reliability of the air-fuel ratio control decreases due to the blow-by due to the change in the compression ratio.
[0006]
In a so-called direct injection engine, the following phenomena are expected to occur because fuel is directly blown into the combustion chamber. In a direct injection engine, during the compression stroke, it is possible that air is present in an unmixed state with the fuel spray, and this air leaks into the engine room as blow-by gas. If the compression ratio is high, the blow-by gas amount of air during the compression stroke increases, so that at the fuel ignition timing in the latter half of the compression stroke, there may be a shortage of air in the combustion chamber. If this occurs, the fuel / air ratio in the combustion chamber will be disturbed, thus causing the above-mentioned problem.
[0007]
In addition, since air-fuel ratio control generally employs a feedback control method based on residual oxygen, control for achieving the target air-fuel ratio is delayed due to disturbance of residual oxygen. Therefore, the driver may feel uncomfortable. For example, when the acceleration operation is stopped, the following may occur.
[0008]
When the depression of the accelerator pedal is suddenly released to stop the acceleration, the compression ratio is set to a high state as the load changes from a high load to a low load. In such a situation, the amount of blow-by gas increases and fuel becomes excessive, so that the deceleration state of the vehicle does not coincide with the pedal operation (loosening of the pedal), and the driver who looses the accelerator pedal may feel uncomfortable. In the case of a direct injection engine, an increase in the amount of blow-by gas causes a shortage of air and a decrease in combustion efficiency, leading to a shortage of torque and a sense of incongruity.
[0009]
The present invention has been made to solve the above problems, and has as its object to suppress problems caused by a change in compression ratio.
[0010]
[Means for Solving the Problems and Their Functions and Effects]
In order to solve at least a part of this problem, in the control method of the variable compression ratio engine according to the present invention, when the compression ratio of the engine is changed, it is determined according to the occurrence of blow-by from the crank room to the intake passage due to the change in the compression ratio. Then, the physical quantity related to the air-fuel ratio is corrected. Therefore, after the compression ratio is changed, the air-fuel ratio can be promptly corrected to the lean side or the rich side regardless of the deviation of the air-fuel ratio when the air-fuel ratio matches the target air-fuel ratio. In this case, if the amount of fuel changes due to the blow-by situation, the air-fuel ratio can be corrected to the lean side so as to increase the amount of air in order to suppress the excess fuel. Alternatively, if the air is insufficient, the air-fuel ratio can be corrected by adjusting the fuel in response to the air shortage.
[0011]
Therefore, such air-fuel ratio correction can reduce disturbance in the ratio of fuel / air entering the combustion chamber after changing the compression ratio, so that the sense of discomfort associated with the change in compression ratio can be reduced. In addition, deterioration of emission can be avoided.
[0012]
According to another variable compression ratio engine control method of the present invention for solving at least a part of the above-described problems, when the compression ratio of the engine is changed, the intake passage from the crank room is changed according to the change state of the compression ratio. Variable the amount of blow-by gas to That is, even if the blow-by gas amount fluctuates due to the change in the compression ratio, the blow-by gas flow rate to the intake passage can be variably controlled. For example, if the amount of fuel changes due to an increase in the amount of blow-by gas accompanying a change in compression ratio, the amount of fuel can be suppressed by limiting the amount of blow-by gas. In addition, if the amount of blow-by gas increases due to a change in the compression ratio and the air becomes insufficient, the amount of blow-by gas can be limited to suppress the air shortage. Conversely, if the amount of blow-by gas decreases due to a change in the compression ratio and the amount of fuel or air is disturbed, the amount of blow-by gas can be ventilated to the intake passage more than before, suppressing such disturbance. it can. For this reason, since the turbulence in the ratio of fuel / air entering the combustion chamber after changing the compression ratio can be reduced, it is possible to alleviate the sense of incongruity and avoid emission deterioration due to the change in the compression ratio.
[0013]
In the control method of the variable compression ratio engine of the present invention described above, the physical quantity correction according to the occurrence state of blow-by and the variable control of the blow-by gas amount according to the change state of the compression ratio are performed over the transition period of the compression ratio change. I can do it. This makes it possible to reduce the disturbance in the ratio of fuel and air entering the combustion chamber, and then to perform engine control with the changed compression ratio. Therefore, such engine control (for example, changing the air-fuel ratio to the target air-fuel ratio) Control, etc.) can be suitably performed.
[0014]
In order to solve at least a part of such a problem, in the variable compression ratio engine of the present invention, when the compression ratio is changed by the compression ratio variable unit, the physical quantity related to the air-fuel ratio when the air-fuel ratio control unit controls the The correction is made according to the occurrence of blow-by from the crank room to the intake passage due to the change in the compression ratio. Therefore, according to the engine of the present invention, even after the compression ratio is changed, the air-fuel ratio can be quickly corrected as described above regardless of the deviation of the air-fuel ratio when the air-fuel ratio matches the target air-fuel ratio. . Therefore, such air-fuel ratio correction can reduce the disturbance of the ratio of fuel / air entering the combustion chamber after the change of the compression ratio, so that it is possible to reduce the sense of incongruity and avoid the deterioration of the emission caused by the change of the compression ratio.
[0015]
If such correction is performed by open-loop control, it can be performed more quickly than suppression of the disturbance in the ratio of fuel / air entering the combustion chamber after the compression ratio is changed, which is preferable.
[0016]
When correcting the physical quantity related to the air-fuel ratio, at least one of the fuel injection quantity and the intake air quantity can be corrected according to the blow-by occurrence situation. For example, if the amount of fuel changes due to a blow-by situation, an increase in the amount of intake air and a correction to decrease the amount of fuel injection, or a combination of both, can suppress the excess fuel. In the case of an air shortage, it is possible to cope with the air shortage by correcting the increase in the intake air amount and the correction in decreasing the fuel injection amount, or a combination of both.
[0017]
Further, the above-described air-fuel ratio correction can be performed over the transition period of the change in the compression ratio, so that the engine control after the change in the compression ratio can be suitably performed as described above.
[0018]
In another variable compression ratio engine according to the present invention for solving at least a part of the above problems, if there is a change in the compression ratio by the compression ratio variable unit, the variable control unit changes the crank ratio in accordance with the change state of the compression ratio. Varies the amount of blow-by gas from the room to the intake passage. For this reason, even if the blow-by gas amount fluctuates due to the change in the compression ratio, as described above, it is possible to cope with excess fuel and insufficient air through limiting the blow-by gas amount and promoting ventilation. Therefore, even with the engine having this configuration, it is possible to reduce the disturbance of the ratio of fuel / air entering the combustion chamber after the compression ratio is changed, thereby alleviating the sense of incongruity and avoiding the deterioration of emission due to the change in the compression ratio.
[0019]
In such variable control of the blow-by gas amount, a throttle may be provided in the ventilation means, and the throttle opening degree of the throttle may be adjusted in accordance with the change of the compression ratio. In this way, with simple device control such as adjusting the throttle opening, it is possible to deal with excess fuel and air shortage by limiting the amount of blow-by gas and promoting ventilation, and thereby alleviate the sense of incongruity and avoid emission deterioration due to the change in compression ratio. Can be achieved.
[0020]
Further, the variable control of the blow-by gas amount can be performed over the transition period of the change in the compression ratio, so that the engine control with the changed compression ratio can be suitably performed as described above. it can.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described based on examples. FIG. 1 is an explanatory diagram schematically illustrating the configuration of the variable compression ratio engine 20 according to the first embodiment.
[0022]
As shown in the figure, the variable compression ratio engine 20 includes a cylinder block 22 and a cylinder head 24, and a cylinder 26 having a piston 28 incorporated therein. The piston 28 is connected to a crankshaft 29 through a connecting rod 27 that is configured to be bendable. The vertical reciprocating motion of the piston 28 in the cylinder is converted into a rotational movement of the crankshaft 29 via the connecting rod 27. The connecting rod 27 constitutes a compression ratio variable mechanism 30 described later, and changes the top dead center position and the bottom dead center position of the piston 28 at the same time by changing the bending degree. As a result, the variable compression ratio engine 20 can change the compression ratio. The details will be described later.
[0023]
The variable compression ratio engine 20 includes an intake pipe 50 connected to an intake port (not shown) of the cylinder head 24. The intake pipe 50 guides the fuel injected into the intake pipe flow path by the injector 52 to the combustion chamber via the intake port in a state of a mixture with air. In this case, the intake amount of air is adjusted by the throttle valve 54, and the fuel mixture ratio is adjusted. Further, the variable compression ratio engine 20 includes a blow-by gas flow path 53 extending from the crank room 23 formed by the cylinder block 22 to the intake pipe 50, and blow-by gas blown through the piston clearance from the combustion chamber of the cylinder 26. The air flows into the intake pipe 50 via the blow-by gas flow path 53. In this embodiment, the blow-by gas passage 53 is connected to the intake pipe 50 downstream of the throttle valve 54. Therefore, the blow-by gas is sucked by the negative pressure of the intake pipe 50 and flows into the intake pipe 50.
[0024]
The variable compression ratio engine 20 includes an ECU 60 that controls the compression ratio change, the driving of the throttle valve 54, and the like. The ECU 60 is configured as a logical operation circuit mainly composed of a microcomputer, and includes a throttle valve driving actuator 63, a throttle sensor 55, an accelerator sensor 61, and a rotation speed / crank angle sensor for detecting an engine speed and a crank angle. 56, an actuator (servo motor) 57 for changing the compression ratio, a compression ratio sensor 58 for detecting the compression ratio, an oxygen sensor 62 for detecting the oxygen concentration in the exhaust gas, an air flow meter 64 for detecting the amount of intake air, and the like. ing.
[0025]
Next, a configuration for changing the compression ratio will be described in detail. FIG. 2 is a schematic perspective view showing the variable compression ratio mechanism 30 including the connecting rod 27, and FIG. 3 is an explanatory diagram for explaining how the compression ratio is changed by the variable compression ratio mechanism 30.
[0026]
As shown in the figure, the variable compression ratio mechanism 30 is configured by connecting the connecting rod 27 to a first connecting rod 31 and a second connecting rod 32 on the side of the piston 28. The first connecting rod 31 is rotatably connected to a piston 28 and a piston pin 34 at a small end 33 at an upper portion thereof. The second connecting rod 32 is rotatably connected to a crank pin (not shown) of the crankshaft 29 at a lower end 35 of the second connecting rod 32. The first and second connecting rods are rotatably connected to each other via a connecting rod pin 36 at the lower end of the first connecting rod and the upper end of the second connecting rod.
[0027]
The first connecting rod 31 has a protruding portion 31a at the lower end side, and is rotatably connected to one end side of the control rod 37 by a pin 38 at the protruding portion 31a. The control rod 37 has a through hole 37a on the other end side, and a control shaft 39 is rotatably fitted into the through hole 37a.
[0028]
In addition, the variable compression ratio mechanism 30 has a control shaft guide 40, which is rotatably supported by the cylinder block 22 (see FIG. 1). The control shaft guide 40 is provided with a bearing portion 41 having a circular cross section at both ends and a plurality of locations on the way, and a connecting portion 42 formed by cutting out a crescent cross section between adjacent bearing portions 41. The same number of connecting portions 42 as the number of cylinders of the engine are prepared, and the control shaft 39 is fitted and fixed to the control shaft guide 40 so that the control shaft 39 is located in the cutout region 43 of each connecting portion. That is, the control shaft 39 is fitted and fixed at a position eccentric from the rotation center axis (center axis) X of the control shaft guide 40. Therefore, when the control shaft guide 40 rotates, the control shaft 39 swings with respect to the central axis X to change its position, whereby the control rod 37 moves the first connecting rod 31 via the pin 38 to the second connecting rod 31. The connecting rod 32 is bent and displaced. When the connecting rod 27 bends in this manner, the top dead center position and the bottom dead center position length of the piston 28 change simultaneously according to the degree of bending, and the variable compression ratio engine 20 changes the compression ratio. In this case, the change of the compression ratio, that is, the turning state of the control shaft guide 40 is controlled by the ECU 60 according to the operating state of the engine.
[0029]
The cross-sectional shape and dimensions of the connecting portion 42 are set so that the control rod 37 does not interfere with the connecting portion 42 when the control shaft 39 swings.
[0030]
As shown in FIG. 3, the compression ratio variable mechanism 30 has a servomotor 57 and a worm gear 47 as actuators for causing the control shaft 39 to swing. The worm gear 47 includes a worm 48 connected to a shaft of a servo motor 57 and a directly connected worm wheel 49 connected to the control shaft guide 40. Therefore, the control shaft guide 40 rotates with the rotation of the servomotor 57, and the rotation direction and the rotation angle are determined by the motor control.
[0031]
That is, when the worm 48 is rotated by the servomotor 57, the control shaft guide 40 rotates by an angle corresponding to the degree of rotation, and displaces the control shaft 39 and the control rod 37 as described above. The bending state of the connecting rod 27 is determined by the displacement of the control rod 37, and the compression ratio 蛩 of the engine changes. In the present embodiment, the control shaft 39 can be displaced around the central axis X of the control shaft guide 40 in a range of 90 degrees from the direction of about 3 o'clock to the direction of about 6 o'clock, and the compression ratio is smaller at the direction of 6 o'clock. Is set to be higher.
[0032]
The compression ratio sensor 58 detects the rotation angle (including the direction) of the control shaft guide 40 or the worm wheel 49, and outputs this to the ECU 60. The ECU 60 is configured to calculate an actual compression ratio 蛩 based on the sensor output.
[0033]
The ECU 60 receives sensor outputs from the various sensors described above and performs various engine controls. Among them, characteristic control performed by the variable compression ratio engine 20 of the present embodiment and related control will be sequentially described. FIG. 4 is a flowchart showing the compression ratio change control, and FIG. 5 is an explanatory diagram for explaining the contents of the compression ratio change control.
[0034]
The compression ratio change control routine shown in FIG. 4 is repeatedly executed at predetermined time intervals. First, an engine speed is read from a speed / crank angle sensor 56, and an accelerator sensor 61 for outputting an accelerator depression state and a throttle sensor 61 are provided. A torque corresponding to a sensor output from the sensor 55 or an intake pipe negative pressure sensor (not shown) is read (step S100). Subsequently, a target compression ratio εt is calculated based on the read rotation speed / torque and a map of the two and the compression ratio shown in FIG. 5 (step S110). In the present embodiment, as shown in FIG. 5, the target compression ratio is switched in three stages of a high compression region, a medium compression region, and a low compression region. In this case, a plurality of maps shown in FIG. 5 are prepared according to the conditions such as the temperature of the engine coolant, the temperature of the intake air, and the emission, and the map may be appropriately switched in accordance with the engine operating condition at that time.
[0035]
Next, the current compression ratio is read from the compression ratio sensor 58 (step S120), and whether or not the compression ratio needs to be changed is determined based on the coincidence state between the read compression ratio εi and the target compression ratio εt. A determination is made (step S130). Here, if the two compression ratios do not match, it is determined that the compression ratio needs to be changed, and the ECU 60 outputs a change command for setting the compression ratio to the target compression ratio εt to the servomotor 57 (step S140). ). More specifically, a drive signal required to set the current compression ratio εi to the target compression ratio εt is output to the servomotor 57, and the above-described processing is repeated. With such control, the variable compression ratio engine 20 changes the degree of bending of the connecting rod 27 by the compression ratio variable mechanism 30 driven by the servomotor 57, thereby changing the compression ratio of the engine.
[0036]
In the variable compression ratio engine 20, in parallel with such compression ratio change control, fuel injection control is performed as follows. FIG. 6 is a flowchart showing the fuel injection control performed by the variable compression ratio engine 20.
Even in the illustrated fuel injection control routine, it is repeatedly executed at a predetermined time, for example, at every predetermined crank angle (360 ° CA). First, the engine speed NE, the intake air amount Q, The target compression ratio εt is read (steps S200 to S220). The engine rotational speed NE and the intake air amount Q are read from the rotational speed / crank angle sensor 56 and the sensor output of the air flow meter 64, and the target compression ratio εt is determined by the compression ratio change control of FIG. . In this case, the actual compression ratio ε of the variable compression ratio engine 20 is made to match the target compression ratio εt by the compression ratio change control of FIG. 4, so that the actual compression ratio ε is used instead of reading the target compression ratio εt. Can also be read. Immediately after the compression ratio is changed in step S140 of FIG. 4, it is preferable to use the target compression ratio εt rather than the actual compression ratio ε.
[0037]
Subsequently, using the read intake air amount Q, the rotational speed NE, and the target compression ratio εt, the basic fuel injection amount TP is calculated according to the following equation (1) (step S230).
TP ← k · Q · f (εt) / NE (1)
[0038]
Here, k is a constant, and f (εt) is a coefficient determined according to the three-stage target compression ratio εt of the high compression area, the medium compression area, and the low compression area as shown in FIG. This f (εt) is predetermined and stored in a predetermined storage area of the ECU so that the value becomes smaller as the compression range becomes higher.
[0039]
In the present embodiment, as will be described later, in the compression ratio change correction control, the intake air amount Q is corrected according to the change state of the compression ratio, that is, the change state of the blow-by gas amount. Therefore, during the execution period of such a correction, the intake air amount Q read before the correction is used as it is in the calculation of the basic fuel injection amount TP by the above equation (1).
[0040]
Next, a target air-fuel ratio corresponding to the target compression ratio εt that has been read is set (step S240). The target air-fuel ratio is predetermined for each of the high-compression region, medium-compression region, and low-compression region shown in FIG. 4 and stored in a predetermined storage region of the ECU. Have been. Subsequently, the sensor output (oxygen concentration) from the oxygen sensor 62 is read (step S250), and the deviation ΔO between the sensor output and the target air-fuel ratio is read. ₂ The air-fuel ratio correction coefficient FAF is corrected in accordance with ₂ ) Is set as the air-fuel ratio correction coefficient FAF (step S260). That is, the air-fuel ratio correction coefficient FAF is a deviation ΔO between the sensor output and the target air-fuel ratio. ₂ And the feedback control is performed so that the air-fuel ratio matches the target air-fuel ratio.
[0041]
Subsequent to the calculation of the air-fuel ratio correction coefficient FAF, the actual fuel injection amount TAU is calculated by multiplying the basic fuel injection amount TP obtained in step S230 by various correction coefficients according to the following equation (2) (step S230). S270).
TAU ← TP · FAF · (1 + FWL) · α · β (2)
[0042]
Here, FWL is a water temperature increase correction coefficient, which is calculated according to a cooling water temperature THW detected by a water temperature sensor (not shown). In this calculation process, a coolant temperature increase correction coefficient FWL is obtained from the coolant temperature THW using a predetermined map provided in the ECU. This map shows the relationship between the cooling water temperature THW and the water temperature increase correction coefficient FWL. The lower the cooling water temperature THW, the larger the water temperature increase correction coefficient FWL.
[0043]
α and β are other correction coefficients, for example, correction coefficients related to intake air temperature correction, power supply voltage correction, and the like.
[0044]
When the actual fuel injection amount TAU is calculated in step S270, subsequently, the fuel injection time corresponding to the actual fuel injection amount TAU is set in a counter (not shown) that determines the valve opening time of the injector 52 (step S280). As a result, the injector 52 is driven to open for the valve opening time set in the counter. After that, the process returns to “return” and ends the process.
[0045]
Next, a description will be given of the compression ratio change correction control performed in accordance with the compression ratio change. FIG. 7 is a flowchart showing the compression ratio change correction control.
Even in the illustrated compression ratio change correction control, the control is repeated every predetermined time. Since this compression ratio change correction control is accompanied by a change in the compression ratio, the repetition time interval is determined in consideration of the time when the change in the compression ratio by the compression ratio variable mechanism 30 is completed in all the cylinders. . Accordingly, the compression ratio change correction control is not executed while the compression ratio is being changed by the compression ratio variable mechanism 30, specifically, while the connecting rod 27 is bending, that is, the bending of the connecting rod 27 is completed, that is, It is executed after the compression ratio change is completed.
[0046]
In the first process of the compression ratio change correction control, the ECU 60 reads the compression ratio εi at the start of the process from the compression ratio sensor 58, and updates and stores this in a predetermined storage area (step S300). In the compression ratio update storage, the compression ratio read by the compression ratio change correction control performed immediately before and after is updated and stored in time series. Subsequently, the compression ratio ε (i−1) is read as stored in the previous process (step S310), and this is compared with the current compression ratio εi to determine whether the compression ratio εi has increased or decreased (step S320).
[0047]
Here, if it is determined that there is no increase / decrease (εi = ε (i−1)), the process exits to “Return” and ends the process once. That is, since there is no change in the compression ratio, this routine ends without any correction, and the fuel injection in step S280 in FIG. 6 is performed as it is.
[0048]
On the other hand, if it is determined that the compression ratio is increased (εi> ε (i−1)), the ECU 60 outputs a drive signal for increasing the opening to the throttle valve driving actuator 63 (step S330), and then returns to “Return”. And the process is once ended. Therefore, through step S330, when the compression ratio increases, the fuel injection in step S280 in FIG. 6 is performed while increasing the intake air amount by forcibly driving the throttle valve 54 to the open side. . This increase in the amount of air is compared with the situation before the increase in the compression ratio.
[0049]
If it is determined that the compression ratio is reduced (εi <ε (i−1)), the ECU 60 outputs a drive signal for decreasing the opening to the throttle valve driving actuator 63 (step S340), and the process is temporarily terminated. I do. Therefore, after step S340, when the compression ratio is changed, the fuel injection in step S280 of FIG. 6 is performed while the intake air amount is reduced by forcibly driving the throttle valve 54 to the closing side. . This air amount reduction is compared with the situation before the compression ratio was reduced.
[0050]
According to the present embodiment for performing such correction, there are the following advantages.
In a situation where the compression ratio is increased (εi> ε (i−1)), the amount of blow-by gas increases along with such a change in the compression ratio, and the amount of blow-by gas reaching the intake pipe 50 from the crank room 23 via the blow-by gas passage 53 is also increased. Increase. In the mixed-intake type variable compression ratio engine 20 as in the present embodiment, since the blow-by gas contains the unburned fuel mixture, the mixture entering the combustion chamber is increased due to an increase in the blow-by gas amount to the intake pipe 50. The state shifts to the excess fuel side (air-fuel ratio rich side). If no countermeasure is taken in such a situation where the compression ratio is increased, combustion with excessive fuel occurs before and after the change of the compression ratio, so that the output of the oxygen sensor 62 is greatly disturbed. Therefore, in step S260 in FIG. 6, a sudden change in FAF is caused, and as a result, the driver feels uncomfortable due to a delay in feedback control.
[0051]
However, in the present embodiment, when the compression ratio increases, the intake air amount is increased in step S330 to set the air-fuel ratio to the lean side, so that such an excessive fuel can be suppressed. Therefore, the disturbance in the output of the oxygen sensor 62 can be suppressed through the suppression of the disturbance in the ratio of the fuel and air entering the combustion chamber after the change in the compression ratio is increased, so that the FAF does not suddenly change. Therefore, it is possible to alleviate the sense of incongruity and avoid the deterioration of emission due to the change in the compression ratio.
[0052]
Such an increase in the amount of intake air can be performed so that the degree of increase is adjusted to the degree of increase in the compression ratio, that is, the degree of increase in the amount of blow-by gas. For example, if the compression ratio is increased from the low compression range to the high compression range, the increase in the intake air amount is increased, and the change from the middle compression range to the high compression range or the change from the low compression range to the middle compression range is performed. In this case, an increase in the amount of intake air can be suppressed.
[0053]
The same applies to the situation of the reduction of the compression ratio. In consideration of the reduction of the blow-by gas amount due to the reduction of the compression ratio, the intake air amount can be reduced at step S340. Therefore, since the above-described disturbance in the ratio after the change in the compression ratio is changed can be suppressed to suppress the disturbance in the output of the oxygen sensor 62, as described above, it is possible to reduce the sense of incongruity and avoid the deterioration of the emission caused by the change in the compression ratio. it can. Note that the state of the blow-by gas amount reduction due to the reduction in the compression ratio is slower than the increase in the blow-by gas amount when the compression ratio is increased, and therefore, the processing in step S340 may be omitted.
[0054]
Since the correction of the intake air amount in steps S330 and S340 is based on the open-loop control, the effectiveness of such air amount correction is enhanced, which is effective in promptly suppressing the disturbance in the fuel / air ratio.
[0055]
In the compression ratio change correction control of FIG. 7 described above, while the compression ratio increases or decreases, the intake air amount is increased or decreased in steps S330 and 340, and the actual compression ratio (the read compression ratio in step S300) becomes steady. Then, the increase / decrease of the intake air amount is stopped. Generally, the change of the compression ratio is completed in about 100 to 300 msec. Therefore, it is possible to forcibly increase or decrease the intake air amount for a predetermined time exceeding the compression ratio change execution period, for example, for about several seconds. . With this configuration, the intake air amount is increased or decreased over a transitional period after the compression ratio is changed. Therefore, when the compression ratio has been changed, various engine controls such as fuel injection control are preferably performed. be able to. The execution time of the increase or decrease of the intake air amount can be arbitrarily set to be longer or shorter by various methods such as a dip switch or program change, and the time can be changed at a later date.
[0056]
Next, a second embodiment will be described. This embodiment is characterized in that the fuel injection amount is forcibly increased or decreased in accordance with a change in the compression ratio. FIG. 8 is a flowchart showing the fuel injection control performed by the variable compression ratio engine 20 in the second embodiment, and FIG. 9 is a flowchart showing the compression ratio change correction control in the second embodiment.
[0057]
As shown in the figure, even in the second embodiment, in the fuel injection control, as in the previous embodiment, the engine speed NE, the intake air amount Q, and the target compression ratio εt required for calculating the fuel injection amount are read (step S1). S200 to 220), the basic fuel injection amount TP is calculated by the equation (1) using these (step S230).
[0058]
Subsequent to step S230, it is determined whether or not the flag FΔε has a value of 1 (step S232). This flag FΔε is set by a compression ratio change control routine of FIG. 9 described later, and its value indicates whether or not the compression ratio has been changed.
[0059]
Here, if it is determined that FΔε = 0, it is not the phase of changing the compression ratio. Therefore, as described above, the target air-fuel ratio is set in accordance with the target compression ratio εt (step S240). Reading of sensor output (oxygen concentration) (step S250), deviation ΔO ₂ The correction setting of the air-fuel ratio correction coefficient FAF according to (Step S260). Even in this case, the deviation ΔO ₂ The air-fuel ratio is feedback-controlled so that the air-fuel ratio matches the target air-fuel ratio by correcting the air-fuel ratio correction coefficient FAF based on
[0060]
On the other hand, if it is determined that FΔε = 1, the process proceeds to step S265 because the compression ratio has changed. In this step S265, the air-fuel ratio correction coefficient used in the next step S270 is a correction coefficient FAF (Δε) determined according to the change state of the compression ratio, that is, the change state of the blow-by gas amount in the compression ratio change control routine of FIG. It is set to FAF (step S265).
[0061]
Subsequent to steps S260 and S265, the actual fuel injection amount TAU is calculated based on the equation (2) (step S270), and a fuel injection time counter corresponding to the actual fuel injection amount TAU is set (step S280). Through such processing, the actual fuel injection amount TAU is changed to FAF (ΔO) according to the compression ratio change condition (blow-by gas amount change condition). ₂ ) And FAF (Δε).
[0062]
As shown in FIG. 9, even in the compression ratio change correction control of this embodiment, the compression ratio εi is read / updated and stored (step S300), and the compression ratio ε (i−1) of the previous process is read (step S310). ) And a comparison thereof to determine whether the compression ratio has increased or decreased (step S320).
[0063]
If it is determined that there is no increase or decrease (εi = ε (i−1)), it is determined that the correction of the air-fuel ratio correction coefficient FAF according to the compression ratio change state (the change state of the blow-by gas amount) is unnecessary, and the flag is set. A value zero is set to FΔε (step S322), and this routine ends. Thus, as described above, the actual fuel injection amount TAU is equal to the deviation ΔO between the sensor output and the target air-fuel ratio. ₂ FAF (ΔO ₂ ).
[0064]
On the other hand, if the ECU 60 determines that the compression ratio increases (εi> ε (i−1)), the ECU 60 sets the correction coefficient FAF (Δε) to the reduced coefficient FAF (Δε ;−) (step S332). If it is determined that the compression ratio is reduced (εi <ε (i−1)), the correction coefficient FAF (Δε) is set to the increased coefficient FAF (Δε; +).
[0065]
In determining the decrease coefficient FAF (Δε; −) and the increase coefficient FAF (Δε; +), the degree of the increase or decrease can be adjusted in accordance with the change situation of the compression ratio, that is, the change situation of the blow-by gas amount. For example, if the compression ratio increases from a low compression range to a high compression range, the reduction coefficient FAF (Δε ;−) is assumed to have a large degree of the decrease, and the compression ratio is changed from the middle compression range to the high compression range, or the compression ratio is reduced. In the case of the change from the area to the medium compression area, the degree of reduction can be reduced. The same applies to the situation of the compression ratio reduction, and the degree of increase of the increase coefficient FAF (Δε; +) in step S342 can be determined in consideration of the reduction of the blow-by gas amount due to the reduction of the compression ratio.
[0066]
Then, after setting the decrease coefficient FAF (Δε; −) and the increase coefficient FAF (Δε; +) in steps S332 and 342, a value 1 is set in the flag FΔε (step S350), and this routine ends. . As a result, as described above, the actual fuel injection amount TAU is determined by the increase coefficient FAF (Δε; +) or the decrease coefficient FAF (Δε;-) according to the change state of the compression ratio (the increase / decrease state of the blow-by gas amount). In this case, the deviation ΔO between the sensor output and the target air-fuel ratio ₂ FAF (ΔO ₂ ) Is not adopted.
[0067]
As described above, in this embodiment, when the compression ratio increases (the blow-by gas amount increases), the injection amount is forcibly reduced to perform the fuel injection, and the compression ratio decreases (the blow-by gas amount increases). In the case of the decrease, the fuel injection is performed by forcibly increasing the injection amount. For this reason, even if the amount of blow-by gas increases due to the change in the compression ratio and the fuel mixture becomes excessively rich (air-fuel ratio rich), the fuel injection amount is reduced (step S332) to set the air-fuel ratio to the lean side. Thus, such an excessive amount of fuel can be suppressed. For this reason, by suppressing the disturbance of the ratio of fuel and air entering the combustion chamber after the change in the compression ratio is increased, it is possible to alleviate the discomfort caused by the change in the compression ratio and to avoid the deterioration of the emission.
[0068]
Note that the state of the blow-by gas amount reduction due to the reduction in the compression ratio is slow compared to the increase in the blow-by gas amount when the compression ratio is increased. Therefore, the processing in step S342 may be omitted.
[0069]
Since the correction of the coefficient FAF (Δε) in steps S332 and S342 is based on the open-loop control, the effectiveness of the coefficient correction is enhanced, which is effective in promptly suppressing the disturbance of the fuel / air ratio. .
[0070]
Also in the compression ratio change correction control of FIG. 9, similarly to FIG. 7, while the compression ratio increases or decreases, the correction coefficient of the fuel injection amount is increased or decreased in steps S332 and S342, and the actual compression ratio (step When the reading compression ratio in S300 becomes steady, the increase / decrease of the intake air amount is stopped. Therefore, even in this embodiment, as described above, it is possible to forcibly increase or decrease the correction coefficient over a predetermined time. With this configuration, the fuel injection amount is increased or decreased over a transitional period after the compression ratio is changed, so that various engine controls can be suitably performed when the compression ratio has been changed. Even in this case, the execution time for increasing or decreasing the correction coefficient can be arbitrarily set to be longer or shorter by various methods such as a dip switch or a program change, and the time can be changed at a later date.
[0071]
Next, a third embodiment will be described. This embodiment is characterized in that it has a bubble control device for controlling the opening / closing timing of an intake valve, and controls the valve opening / closing timing with the device to adjust the intake air amount. FIG. 10 is an explanatory diagram illustrating a state of control in the third embodiment.
[0072]
Also in this embodiment, the compression ratio change correction control is executed as described above, and the valve opening / closing timing is adjusted in the phase of changing the compression ratio. Now, as shown in FIG. 10, suppose that the compression ratio is increased and changed from point A in the low compression range to point B in the high compression range at a low engine speed. Then, the opening / closing curve Iv in the figure representing the opening / closing state of the intake valve in the steady state of the compression ratio is shifted to the left in the figure to become the opening / closing curve IvAB, and the opening / closing timing of the intake valve is advanced to match this curve. As a result, when the compression ratio increases from point A to point B and the amount of blow-by gas increases, the opening / closing timing is advanced to increase the amount of air taken into the combustion chamber, thereby setting the air-fuel ratio to the lean side.
[0073]
When the compression ratio is increased from point a in the low compression range to point b in the high compression range at a high engine speed, the opening / closing curve Iv of the intake valve is shifted rightward in the figure to open / close the curve Ivab. The opening / closing timing of the intake valve is delayed to match this curve. This is for the following reason.
As the engine speed increases, the inertial force acting on the air during intake with the opening of the valve increases. Therefore, even if the valve timing is delayed, the intake air amount increases due to the increase in the suction amount due to the inertial force. Thus, even when the compression ratio is increased from point a to point b, the amount of air taken into the combustion chamber can be increased, and the air-fuel ratio can be made leaner. Such a shift amount of the timing is predetermined according to the engine speed.
[0074]
Adjusting the valve timing in this manner also increases the intake air amount in the phase of the change in the compression ratio, so that the discomfort caused by the change in the compression ratio and the avoidance of the deterioration of the emission are avoided as in the above-described embodiment. be able to.
[0075]
Each embodiment described above can also be applied to a direct injection engine that directly injects fuel into a combustion chamber. In such a direct injection engine, part of the air entering the combustion chamber is replaced by blow-by gas, causing air shortage. Therefore, in order to cope with this air shortage, the throttle valve is changed according to the compression ratio change condition (blow-by gas amount change condition). The degree of opening of the valve 54 may be adjusted, or the fuel injection amount may be increased or decreased. For example, in step S330 in FIG. 7 and step S332 in FIG. 9, the air amount is increased and the coefficient is reduced (fuel injection amount is reduced) in accordance with the increase in the compression ratio. In this way, even in the direct injection engine, it is possible to reduce the discomfort caused by the change in the compression ratio and to avoid the deterioration of the emission.
[0076]
Next, another embodiment will be described. This embodiment is characterized in that the amount of blow-by gas sucked into the intake pipe 50 itself is adjusted. FIG. 11 is an explanatory diagram schematically illustrating the configuration of the variable compression ratio engine 20A according to the fourth embodiment.
[0077]
As shown in the figure, the variable compression ratio engine 20A has the same configuration as the variable compression ratio engine 20 described above in that the compression ratio is changed by the variable compression ratio mechanism 30, and differs in the following points. That is, the variable compression ratio engine 20 </ b> A includes the blow-by valve 70 in the blow-by gas passage 53 that guides the blow-by gas to the intake pipe 50, and adjusts the opening of the passage.
[0078]
In the fourth embodiment, the compression ratio change correction control is performed as follows. When the compression ratio is increased as in step S330 in FIG. 7 and step S332 in FIG. 9 described above, the blow-by valve 70 is driven to the closed side to limit the blow-by gas amount. By doing so, the amount of blow-by gas sucked into the intake pipe 50 is reduced, so that the situation of excessive fuel can be suppressed. Further, in the case of a direct injection engine, the amount of blow-by gas can be limited to suppress the shortage of air.
[0079]
Also, if the compression ratio is reduced, the blow-by valve 70 can be driven to the open side to increase the blow-by gas amount as compared to the situation before that (that is, the situation with a high compression ratio). Therefore, it is possible to prevent a large disturbance from occurring in the blow-by gas amount with respect to the intake air amount and the fuel injection amount, so that it is possible to reduce the disturbance in the ratio of the fuel / air entering the combustion chamber after changing the compression ratio. As a result, as in the above-described embodiments, it is possible to reduce disturbance in the ratio of fuel / air entering the combustion chamber after changing the compression ratio, thereby alleviating discomfort caused by the change in compression ratio and avoiding deterioration of emission. it can.
[0080]
In addition, in the variable compression ratio engine 20A, with a simple configuration in which the opening degree of the blow-by valve 70 is adjusted, it is possible to reduce the sense of incongruity and avoid the deterioration of emission due to the change in the compression ratio.
[0081]
Even in the case where the blow-by gas amount is adjusted in this way, as described above, the blow-by gas amount adjustment is performed over a transitional period after the compression ratio is changed. be able to. Further, since the state of the blow-by gas amount reduction due to the reduction of the compression ratio is slower than the increase of the blow-by gas amount when the compression ratio is increased, it is necessary to maintain the valve opening of the blow-by valve 70 when the compression ratio is reduced. You can also.
[0082]
Further, the degree of the blow-by gas amount adjustment may be determined according to the blow-by gas amount.
[0083]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described examples and embodiments, and it goes without saying that the present invention can be implemented in various modes without departing from the gist of the present invention. is there.
[0084]
For example, in each of the above-described embodiments, the presence or absence of a change in the compression ratio is determined based on the sensor output from the compression ratio sensor 58. In other words, the compression ratio at that time is read from a map as shown in FIG. 5 based on sensor outputs from the throttle sensor 55 and the rotation speed / crank angle sensor 56, and whether or not the compression ratio has been changed is determined from the change in the read compression ratio. Judgment can also be made. This eliminates the need for the compression ratio sensor 58, which can contribute to cost reduction.
[0085]
In addition, in the compression ratio change correction control in FIG. 7 and the like, the intake air amount Q and the fuel injection amount are corrected to increase or decrease according to the change state of the compression ratio. That is, a sensor (blow-by sensor) for detecting the amount of the blow-by gas is provided in the blow-by gas flow path 53, and the degree of correction of the increase / decrease of the intake air amount Q and the fuel injection amount due to the change of the compression ratio is adjusted by the output of the blow-by sensor. . By doing so, the degree of correction can be more accurately matched to the changing situation of the blow-by gas amount, so that the disturbance in the ratio of fuel / air entering the combustion chamber after changing the compression ratio can be more accurately suppressed, which is preferable.
[0086]
Further, in the above-described embodiment, the case where one of the fuel injection amount correction (coefficient correction) and the intake air amount correction is performed has been described. However, both may be performed in combination.
[0087]
In addition, the case where the compression ratio is changed by the variable compression ratio mechanism 30 having the bending connecting rod 27 has been described, but the present invention is not limited to such a configuration. For example, the position relationship between the piston 28 and a connecting rod connected to the piston 28 via a piston pin can be changed by a hydraulic mechanism so that the top dead center position and the bottom dead center position of the piston are simultaneously changed. You can also. Further, instead of the servomotor 57 and the worm gear 47, the control shaft guide 40 may be configured to be rotated by a hydraulic mechanism type helical spline.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram schematically illustrating a configuration of a variable compression ratio engine 20 according to a first embodiment.
FIG. 2 is a schematic perspective view showing a variable compression ratio mechanism 30 including a connecting rod 27.
FIG. 3 is an explanatory diagram for explaining a state of changing a compression ratio by the compression ratio variable mechanism 30.
FIG. 4 is a flowchart illustrating compression ratio change control.
FIG. 5 is an explanatory diagram for explaining the content of the compression ratio change control.
FIG. 6 is a flowchart illustrating fuel injection control performed by the variable compression ratio engine 20.
FIG. 7 is a flowchart illustrating compression ratio change correction control.
FIG. 8 is a flowchart illustrating fuel injection control performed by a variable compression ratio engine 20 according to a second embodiment.
FIG. 9 is a flowchart showing compression ratio change correction control in the second embodiment.
FIG. 10 is an explanatory diagram illustrating a state of control in a third embodiment.
FIG. 11 is an explanatory view schematically illustrating a configuration of a variable compression ratio engine 20A according to a fourth embodiment.
[Explanation of symbols]
20 ... Variable compression ratio engine
20A: Variable compression ratio engine
22 ... Cylinder block
23… Crank room
24 ... Cylinder head
26 ... Cylinder
27 ... Connecting rod
28 ... Piston
29 ... Crankshaft
30 ... Compression ratio variable mechanism
31 ... First connecting rod
31a ... Projection
32 ... second connecting rod
33 ... Small end
34 ... Piston pin
35 ... Large end
36 ... Connecting rod pin
37 ... Control rod
37a ... Through-hole
38 ... Pin
39 ... Control shaft
40 ... Control shaft guide
41 ... Bearing part
42 ... connecting part
43 ... Notch area
47 ... worm gear
48… Warm
49… Warm wheel
50 ... intake pipe
52 ... Injector
53 ... Blow-by gas flow path
54 ... Throttle valve
55 ... Throttle sensor
56 ... Rotation speed / Crank angle sensor
57 ... Servo motor
58: Compression ratio sensor
61 ... Accelerator sensor
62 ... Oxygen sensor
63 ... actuator
64 ... Air flow meter
70… Blow-by valve
X: Central axis

Claims (10)

An engine control method for changing an engine compression ratio,
Changing the compression ratio (1);
Correcting the physical quantity related to the air-fuel ratio of the engine according to the occurrence of blow-by from the crank room to the intake passage due to the change in the compression ratio. An engine control method for changing an engine compression ratio,
Changing the compression ratio (1);
A step (2) of variably controlling an amount of blow-by gas from a crank room to an intake passage according to a change state of a compression ratio. An engine control method according to claim 1 or 2, wherein:
The method of controlling a variable compression ratio engine, wherein the step (2) is performed over a transition period of the compression ratio change. An engine having compression ratio variable means for changing a compression ratio of the engine,
Air-fuel ratio control means for controlling the air-fuel ratio of the engine to match the target air-fuel ratio,
Correction means for correcting a physical quantity related to the air-fuel ratio when the air-fuel ratio control means controls the blow-by from the crank room to the intake passage due to a change in the compression ratio. Compression ratio engine. The variable compression ratio engine according to claim 4,
The variable compression ratio engine, wherein the correction unit executes the correction by open loop control. The variable compression ratio engine according to claim 4 or claim 5,
The variable compression ratio engine, wherein the correction means corrects at least one of a fuel injection amount and an intake air amount as the physical quantity according to the blow-by occurrence state. The variable compression ratio engine according to any one of claims 4 to 6, wherein
The variable compression ratio engine, wherein the correction unit performs the correction over a transition period of the compression ratio change. An engine having compression ratio variable means for changing a compression ratio of the engine,
Ventilation means for ventilating blow-by gas from the crank room to the intake passage;
A variable control means for variably controlling an amount of the blow-by gas to be ventilated according to a change state of the compression ratio. The variable compression ratio engine according to claim 8, wherein:
The variable control means,
A restrictor provided in the ventilation means,
Means for adjusting the throttle opening of the throttle. The variable compression ratio engine according to claim 8 or 9, wherein:
The variable compression ratio engine, wherein the variable control means performs variable control of the blow-by gas amount over a transition period of the compression ratio change.

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