JP2004293411A - Variable compression ratio internal-combustion engine and control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve startability in a variable compression ratio internal-combustion engine. <P>SOLUTION: Under circumstances of the variable compression ratio engine 10 where the engine is to be stopped not for the sake of the eco-running control, the compression ratio is raised (step S110) or lowered (step S130) depending on the temperature of engine-cooling water, and then the engine is stopped (step S140). Under circumstances where the engine is to be stopped not for the sake of the eco-running, but just out of driver's intention of turning-off the key, etc., the compression ratio is raised (step S110), and the engine is stopped (step S140). Thus, at the time of starting the engine, there is no need to change the compression ratio, because the compression ratio has been changed in advance of the engine-starting. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an internal combustion engine capable of changing a compression ratio and a control device therefor.
[0002]
[Prior art]
In recent years, various internal combustion engines having a function of changing a compression ratio have been proposed. When the compression ratio is set high, power can be efficiently obtained, but knocking is likely to occur. Therefore, the compression ratio is changed according to the operating conditions. Specifically, when the load on the internal combustion engine is low, knocking is unlikely to occur, so the compression ratio is set high. On the other hand, when the load of the internal combustion engine is high, knocking is likely to occur, so the compression ratio is set low.
[0003]
In such a conventional internal combustion engine (variable compression ratio engine), it has been proposed to change the compression ratio based on the temperature of the engine cooling water at the time of engine start to enhance the startability (for example, see Patent Document 1).
[0004]
[Patent Document 1]
JP-A-3-164538
[0005]
[Problems to be solved by the invention]
However, in the above-described conventional variable compression ratio engine, when starting the engine, it is necessary to wait for the engine to start until the change to the target compression ratio at the time of starting is completed. Therefore, an extra time is required for starting the engine only for the standby time, and there is room for further improvement in the startability.
[0006]
SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to improve the startability when starting a variable compression ratio engine.
[0007]
[Means for Solving the Problems and Their Functions and Effects]
In order to solve at least a part of this problem, the first internal combustion engine capable of changing the compression ratio and the control method thereof according to the present invention control the compression ratio changing mechanism when a stop request of the internal combustion engine is detected. Thus, the compression ratio is changed to the target compression ratio at the time of starting the internal combustion engine, and the operation of the internal combustion engine is stopped.
[0008]
Therefore, when the operation of the internal combustion engine is stopped based on the request for stopping the internal combustion engine, the compression ratio can be changed in advance before the next start of the internal combustion engine, and the changed compression ratio can be changed in the next start of the internal combustion engine. It is possible to set the target compression ratio at the start in preparation for the above. Therefore, at the next start, time for changing the compression ratio is not required, and startability is improved. The following example can be shown as an example of such an improvement in startability.
[0009]
In the prior art disclosed in the related art, the compression ratio remains as it was when the internal combustion engine was stopped, and the compression ratio was changed at the next start according to the temperature of the cooling water. Now, suppose that the compression ratio was low when the internal combustion engine was stopped. Since the cooling water temperature decreases as the internal combustion engine cools down after the stoppage, in the above-described conventional technology, it is necessary to change the compression ratio from a low compression ratio when the internal combustion engine is stopped to a high compression ratio at the next start-up. Since the degree of change is large, the time is long. However, according to the present invention, it is possible to previously change the compression ratio (high compression ratio = target compression ratio at startup) according to the next startup when the operation of the internal combustion engine is stopped. Startability is improved.
[0010]
In the first internal combustion engine of the present invention described above, the following aspects can be adopted. That is, the target compression ratio when the engine is restarted after the engine is stopped is determined according to the situation in which the engine is stopped, and the compression ratio is changed in advance under the stopped state of the engine so as to reach the target compression ratio thus determined. I do. With this configuration, the compression ratio is changed prior to the start of the engine in preparation for the next engine start (restart) determined by the state of the engine stop, so that the startability at the next engine start can also be improved.
[0011]
Further, as another aspect, an automatic stop means for automatically stopping the operation of the internal combustion engine when a predetermined automatic stop condition is satisfied based on the state of the vehicle or the operation history of the internal combustion engine during the operation of the internal combustion engine, Manual stop means for stopping the operation of the internal combustion engine based on the intention of stopping the internal combustion engine, the stop request detection by the stop request detection means, the stop request based on the automatic stop means, the manual stop means The stop-time change control by the stop-time control means is different from the stop request based on the automatic-stop means when the stop-change request is detected based on the manual-stop means. It can be implemented differently.
[0012]
In order to achieve such a different compression ratio (target compression ratio at the time of starting), the target compression ratio at the start is set to a lower compression ratio at the time of the stop request by the automatic stop means than at the time of the stop request by the manual stop means. That is, a low compression ratio can be set when a stop request is made by the automatic stop unit, and a high compression ratio can be set when a stop request is made by the manual stop unit.
[0013]
Even if the target compression ratio is changed in response to the stop request by the automatic / manual stop means, the compression ratio is changed prior to the start of the internal combustion engine in preparation for the next start of the internal combustion engine. In addition, the startability at the next start of the internal combustion engine can be improved.
[0014]
Further, by changing the target compression ratio in response to a stop request from the automatic / manual stop means, there are the following advantages.
For example, when the vehicle is temporarily stopped at a signal, a railroad crossing, or the like, an automatic stop condition is satisfied, a stop request is issued by the automatic stop unit, and the stop of the internal combustion engine is controlled. When the driver performs a shift operation or an accelerator operation in response to a signal change or a train passage, the automatic stop condition is canceled, and thus the internal combustion engine is controlled to start. Therefore, the stop period during which the stop request is issued by the automatic stop means and the internal combustion engine is stopped by this is expected to be relatively short, so that the cooling water temperature significantly decreases during the internal combustion engine stop period. Is hard to get up.
[0015]
For this reason, when a stop request is issued by the automatic stop means, since the cooling water temperature of the internal combustion engine hardly decreases, the compression ratio at the time of stopping the internal combustion engine is set to the next start of the internal combustion engine. Previously, it can be changed to the low compression ratio side (starting target compression ratio). Therefore, at the next start of the internal combustion engine, the operation of the internal combustion engine can be restarted (started) at the compression ratio on the low compression ratio side, and the vibration at the start due to the internal pressure (compression ratio) in the cylinder becoming too high. Increase can be suppressed. As a result, at the time of starting the internal combustion engine after the stop request is issued by the automatic stop means, the start-up vibration of the internal combustion engine can be reduced, so that it is possible to prevent the driver from feeling uncomfortable, which is preferable.
[0016]
On the other hand, a situation in which a stop request is issued not by the automatic stop means but by the manual stop means is considered to be, for example, a situation in which the driver stops the internal combustion engine and gets off the vehicle. The stop period of the internal combustion engine due to the driver's intention is expected to be relatively long, unlike the case of the automatic stop means, and the cooling water temperature of the internal combustion engine is expected to decrease relatively significantly.
[0017]
For this reason, when a stop request is issued by the manual stop means, the compression ratio at the time of stopping the internal combustion engine is increased before the next start of the internal combustion engine because the cooling water temperature of the internal combustion engine is greatly reduced. It can be changed to the compression ratio side (starting target compression ratio). Therefore, at the next start of the internal combustion engine, in the internal combustion engine with insufficient warming-up, the in-cylinder temperature can be increased because the compression ratio is on the high compression ratio side, and the startability can be improved. As a result, even when the internal combustion engine is started after the stop request is issued by the manual stop means, the startability can be further improved, which is preferable.
[0018]
Further, when the internal combustion engine is stopped by the automatic stop means in the above-mentioned automatic / manual stop means, a different target compression ratio at start-up based on an output of a warm-up sensor for detecting a warm-up state of the internal combustion engine. It can be made to be.
[0019]
With this configuration, even if the internal combustion engine is stopped based on the automatic stop means, if a change occurs in the internal combustion engine warm-up state, for example, since the internal combustion engine is stopped for a long time, the internal combustion engine is warmed up. Is insufficient, the starting target compression ratio at that time can be set to a starting target compression ratio different from that when the internal combustion engine is sufficiently warmed up. For this reason, if the internal combustion engine is not sufficiently warmed up while the internal combustion engine is stopped based on the automatic stop means, the compression ratio at the time of stopping the internal combustion engine is changed to the high compression ratio side (before starting the next internal combustion engine). (Start-time target compression ratio). Therefore, when starting the internal combustion engine after the internal combustion engine is stopped based on the automatic stopping means for a long time, the internal combustion engine can be started by raising the fuel temperature by the compression ratio on the high compression ratio side and burning the fuel. In this case, the startability can be further improved, which is preferable.
[0020]
The order of execution of the stop-time change control and the engine stop control by the stop-time control means is arbitrary, but both controls can be executed in this order.
With this configuration, the compression ratio change for the next start can be performed under the operating condition of the internal combustion engine before the stop, and thus the compression ratio change is performed in a state where the internal pressure in the cylinder is high due to fuel combustion. Therefore, when the compression ratio changing mechanism is driven in the same direction as the direction in which the internal pressure acts, a high internal pressure in the cylinder can be used to assist the driving force of the compression ratio changing mechanism, and the driving force can be reduced. Can be.
[0021]
Further, a piston position detecting means for detecting a piston position in a cylinder provided in the internal combustion engine, a cylinder that is in an expansion stroke at the time of starting the internal combustion engine is determined from the detected piston position, and fuel is supplied to the determined cylinder. Start-up ignition means for injecting and igniting and burning is provided, and then the stop-time change control is executed so that the start-time target compression ratio becomes a compression ratio on the high compression ratio side. It is also possible to control the execution of the starting ignition means to start the internal combustion engine.
[0022]
This has the following advantages.
When the internal combustion engine is stopped, the piston and the crankshaft are driven by inertia because the piston receives the internal pressure in the cylinder generated by fuel combustion immediately before the stop. Thus, the piston and the crankshaft driven by inertia stop at a balance between a force based on the internal pressure in the cylinder and a force opposing the force (for example, frictional force between the piston and the crankshaft). In this case, the force based on the internal pressure in the cylinder decreases as the coasting rotation advances, and eventually disappears, whereas the above-mentioned frictional force is almost constant. It is known that it is easy to take the crank angle at the position where the crank angle exceeds the lower dead center.
[0023]
In the above aspect, when the compression ratio is changed upon detection of the stop request, the target compression ratio at the start is set to a high compression ratio, so the internal pressure increases, so that when the engine is stopped, the piston exceeds the top dead center. The probability of falling to the bottom dead center is higher than when the compression ratio is low. Therefore, the piston tends to stop at a process position of the expansion stroke, for example, at a position near a crank angle of 90 °.
[0024]
Therefore, when the internal combustion engine is restarted, the starting ignition means injects fuel into the cylinder that is in the expansion stroke and ignites and burns, so that in the fuel injection cylinder, fuel injection and combustion occur in the expansion stroke. Will be. Therefore, the internal combustion engine cranks through the expansion stroke. When cranking occurs, the internal combustion engine starts. As a result, according to this aspect, it is possible to start the engine (starter motorless start) without causing cranking by the starter motor.
[0025]
At the time of cranking at the time of such starter motorless start, the compression ratio acts to prevent cranking. Therefore, if the compression ratio is changed to a low compression ratio after the internal combustion engine is stopped and before the next internal combustion engine is started, cranking during starter motorless start can be easily caused, so that startability is further improved, and The reliability of starterless motor start is also improved.
[0026]
When the piston is located at the bottom dead center side from the middle position between the top dead center and the bottom dead center in the cylinder which is in the expansion stroke at the start, the starter motor is changed to the execution control of the starting ignition means. Alternatively, the internal combustion engine can be started using the above.
[0027]
In this case, even if the piston position is on the bottom dead center side, the internal combustion engine can be started by the starter motor without any trouble.
[0028]
Further, as another aspect, when there is a start request of the internal combustion engine, the compression ratio changing mechanism is controlled to change the compression ratio to the actual compression ratio at start according to the output of the warm-up sensor. When stopping the operation of the internal combustion engine based on the request to stop the internal combustion engine, the compression ratio can be set to an intermediate compression ratio in advance before the next start of the internal combustion engine.
In this case, at the time of a start request of the internal combustion engine, it is sufficient to change the compression ratio from the intermediate compression ratio that has been changed in advance to the actual compression ratio at the time of starting, so that the degree of change in the compression ratio can be reduced. Therefore, the time required for changing the compression ratio at the time of starting the internal combustion engine is reduced, and the startability is improved accordingly.
[0029]
Further, in order to solve at least a part of the above problem, in the internal combustion engine having the second compression ratio according to the present invention, the starting of the internal combustion engine at the time of starting according to the warm-up state of the internal combustion engine detected by the warm-up sensor. Before the internal combustion engine is started, a compression ratio changing mechanism is controlled to change the compression ratio to the target compression ratio at start.
[0030]
Also according to the second internal combustion engine of the present invention, the compression ratio is previously changed to the target compression ratio at the start according to the state of warming up of the internal combustion engine. It becomes unnecessary. Therefore, startability is improved. In addition, since the compression ratio that is changed in advance reflects the state of warming up the internal combustion engine at the next start, the startability is further improved.
[0031]
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 showing a configuration of an engine system including a variable compression ratio engine 10 according to the first embodiment.
[0032]
As shown in the figure, the engine system according to the present embodiment is connected to an in-cylinder injection type variable compression ratio engine 10, a control unit 40 for controlling an operation state thereof, and a crankshaft (not shown) of the variable compression ratio engine 10. And various sensors for detecting the operating state of the transmission 60 and the engine. The variable compression ratio engine 10 includes a cylinder block 12 having a plurality of cylinders 11 therein, a piston 13 reciprocating in the cylinder 11, a crankcase 14 arranged at the bottom of the cylinder block 12, and a cylinder block 12 (cylinder block 12). 11) is provided with a cylinder head 15 arranged above.
[0033]
The variable compression ratio engine 10 is provided with a variable compression ratio mechanism 20 that can arbitrarily set a compression ratio within a predetermined range. The variable compression ratio mechanism 20 changes the compression ratio by moving the cylinder block 12 relative to the crankcase 14 in the movement direction of the piston 13 (the axial direction of the cylinder 11). Specifically, eccentric cams (not shown) arranged on both longitudinal sides of the cylinder block 12 are driven by an actuator 21 (for example, a motor) provided on the cylinder block 12 side, and the cylinder block 12 is moved to the crankcase 14. Away from or close to. By moving the cylinder block 12 away from the crankcase 14, the compression ratio is reduced.
[0034]
The cylinder head 15 has an intake port 16 and an exhaust port 17 for each cylinder 11. Each intake port 16 is provided with an intake valve 161 driven by an intake cam IC to open and close the intake port 16, and each exhaust port 17 is driven by an exhaust cam EC to open and close the exhaust port 17. An exhaust valve 171 is provided.
[0035]
A branch end of an intake pipe 18 is connected to each intake port 16, and a branch end of an exhaust pipe (exhaust manifold) 19 is connected to each exhaust port 17. An intake control valve 30 that controls the amount of intake air flowing into the combustion chamber is arranged in the intake pipe 18.
[0036]
The variable compression ratio engine 10 in this embodiment is an in-cylinder injection type internal combustion engine, and a fuel injection valve IJ is disposed at a position corresponding to each cylinder 11 of the cylinder head 15. Each fuel injection valve IJ is supplied with high-pressure fuel pressurized by the pressurization pump 31 via a fuel delivery pipe FD. The pressure increasing pump 31 is, for example, a mechanically driven pump or a pump driven by a motor, and can increase the fuel pressure to an arbitrary pressure within a predetermined fuel pressure range.
[0037]
In addition, a spark plug 32 for spark ignition is arranged on the cylinder head 15 at a position corresponding to each cylinder 11.
[0038]
The control unit 40 has an arithmetic processing function, a map, a storage function for storing programs, and the like. The control unit 40 includes an accelerator position sensor 50 for detecting an amount of depression of an accelerator pedal, a vehicle speed sensor 51 for detecting a vehicle speed, a crank position sensor 52 for detecting an engine speed, and a fuel pressure (fuel injection) in a fuel delivery pipe FD. Pressure), a brake position sensor 54 for detecting an amount of depression of a brake pedal, a shift position sensor 55 for detecting a shift position of a transmission, and a coolant for detecting an engine warm-up state by a coolant temperature. Various sensors such as a temperature sensor 56 are connected, and signals from the various sensors that detect the operating state of the variable compression ratio engine 10 are input. The control unit 40 is connected to the fuel injection valve IJ, the actuator 21 of the variable compression ratio mechanism 20, the intake control valve 30, the boost pump 31, and the ignition plug 32. The control unit 40 controls the driving of each device such as the fuel injection valve IJ based on the input from each sensor described above, and controls the operation of the engine.
[0039]
For example, the control unit 40 calculates the engine load from a map or the like based on the sensor outputs from the accelerator position sensor 50 and the vehicle speed sensor 51, and controls the compression ratio to change according to the load. When the compression ratio is changed, the drive of the actuator 21 of the variable compression ratio mechanism 20 is controlled so as to achieve the target compression ratio. Further, the control unit 40 determines the suspension state of the vehicle (for example, waiting for a signal or stopping at a railroad crossing) based on sensor outputs from the accelerator position sensor 50, the brake position sensor 54, the vehicle speed sensor 51, and the shift position sensor 55, At the time of such a temporary stop, engine control (so-called eco-run control) for automatically stopping the engine is performed. In this eco-run control, when the control unit 40 receives a shift operation or an accelerator operation after the automatic stop of the engine by a sensor signal from the shift position sensor 55 or the accelerator position sensor 50, the control unit 40 restarts the engine. The control unit 40 controls the fuel injection timing, the fuel injection pressure, the ignition timing, and the like based on the output from each of the sensors, not only in the case of the eco-run control, but also in the case of the engine control while the vehicle is running. The amount of intake air is appropriately controlled.
[0040]
Next, the compression ratio control of the variable compression ratio engine 10 performed by the engine system of the first embodiment will be described. FIG. 2 is a flowchart showing the state of the control at the time of stopping the compression ratio performed by the engine system of the first embodiment.
The control at the time of stopping the compression ratio is repeatedly performed at predetermined time intervals. First, it is determined whether an engine stop request has been issued prior to the engine stop (step S100). This routine ends without performing any processing. In other words, the processing described below that involves changing the compression ratio when the engine is stopped is executed in a situation where the engine is stopped based on the request to stop the engine. The engine stop request is output, for example, when a predetermined condition for executing the automatic stop of the engine by the eco-run control (not shown) is satisfied, or an operation based on the driver's intention, for example, an ignition switch OFF operation (engine stop signal) and the like. , The presence or absence of an engine stop request can be determined from the state.
[0041]
If it is determined in step S100 that there is an engine stop request (that is, if it is determined that the engine is stopped), the current engine stop is performed under the condition that the vehicle is temporarily stopped due to waiting for a traffic light or the like. It is determined whether or not the control is based on the above-described eco-run control (step S105). This determination can be made based on the output from the various sensors described above, or based on the state of the flag set in the above-described eco-run control. Since the engine stop request based on the driver's intention to stop can be directly determined by the OFF signal of the ignition switch, the stop request based on the eco-run control and the stop request based on the driver's intention to stop can be easily distinguished.
[0042]
If a negative determination is made here that the engine is not stopped by the eco-run control, the control unit 40 controls the drive of the actuator 21 of the variable compression ratio mechanism 20 so that the compression ratio becomes a high compression ratio ε (target compression ratio at start-up). The compression ratio of the variable compression ratio engine 10 is increased (step S110). In setting the compression ratio to the high compression ratio ε, it is possible to change the compression ratio to a predetermined high compression ratio εH, or to change the compression ratio to a compression ratio higher than the current compression ratio by a predetermined difference. You can also.
[0043]
On the other hand, if an affirmative determination is made in step S105, it is determined whether or not the engine coolant temperature input from the coolant temperature sensor 56 is equal to or higher than a predetermined value (step S120). The process proceeds to S110 to increase the compression ratio. However, when it is determined that the cooling water temperature is equal to or higher than the predetermined temperature, the drive of the actuator 21 of the variable compression ratio mechanism 20 is controlled so that the compression ratio becomes a low compression ratio ε, and the compression ratio of the variable compression ratio engine 10 is reduced. Is set to a low value (step S130). As described above, when the compression ratio is set to the low compression ratio ε, the compression ratio can be changed to a predetermined low compression ratio εL, and the compression ratio is changed to a compression ratio lower by a predetermined difference than the current compression ratio. You can also.
[0044]
In changing the compression ratio in the compression ratio changing process (steps S110 and S120) subsequent to step S120, a target compression ratio (starting target compression ratio) may be set according to the engine water temperature. it can.
[0045]
After the compression ratio is changed in steps S110 and S130, an engine stop process including stop of fuel injection and plug ignition is performed (step S140), and the above process is repeated.
[0046]
As described above, in the present embodiment, when a situation occurs in which the variable compression ratio engine 10 is stopped, the compression ratio is changed in height (steps S110 and S130), and the operation of the variable compression ratio engine 10 is stopped (steps S110 and S130). Step S140). For this reason, when the variable compression ratio engine 10 thus stopped is started next, since the compression ratio has already been changed, the time for driving and controlling the variable compression ratio mechanism 20 for changing the compression ratio at the time of starting is reduced. It becomes unnecessary. Therefore, according to the variable compression ratio engine 10 (engine system) of the present embodiment, the startability at the time of restart after stopping the engine can be improved.
[0047]
Further, the manner of changing the compression ratio when the engine is stopped is different depending on whether the stop state of the engine is based on the eco-run control or not based on the eco-run control. Therefore, there are the following advantages.
[0048]
First, a case where the engine is stopped based on the eco-run control will be described. Such a situation in which the engine is stopped is considered to be a situation in which the driver, for example, getting off the vehicle, intends to stop the engine. Usually, the engine stop period due to the driver's intention is expected to be relatively long, and the engine cooling water temperature is expected to decrease significantly during this engine stop period.
[0049]
In this embodiment, in such a situation where the engine is stopped based on the driver's intention (No in step S105), the compression ratio at the time of stopping the engine is changed to the high compression ratio side before the next engine start. (Step S110). Therefore, when the engine is started next time after stopping the engine based on the driver's intention, although the warm-up of the variable compression ratio engine 10 is insufficient, the temperature of the fuel is increased due to the high compression ratio. The engine can be started by burning the fuel in a state where the pressure is increased. As a result, when starting the engine after stopping the engine based on the driver's intention instead of based on the eco-run control, the startability can be further improved, which is preferable.
[0050]
On the other hand, in a situation in which the engine is automatically stopped by the eco-run control based on the temporary stop of the vehicle such as when waiting for a traffic light (Yes in step S105), the compression ratio is increased to a high compression ratio in accordance with the cooling water temperature reflecting the engine stop period. (Step S110) or the low compression ratio (step S130), and then the engine is stopped. For this reason, when the operation stop (vehicle stop) of the variable compression ratio engine 10 by the eco-run control is completed in a short time and restarted, the variable compression ratio engine 10 is sufficiently warmed up, and the compression ratio is set to the next time. Before the engine restart, the compression ratio is changed to the low compression ratio side (step S130). Therefore, at the time of the next engine restart, the variable compression ratio engine 10, which is already at the low compression ratio side, can be started, so that the startability is improved and the following advantages are provided.
[0051]
If the compression ratio is increased while the engine is sufficiently warmed up, the fuel will burn in a high temperature state due to an increase in the internal pressure (compression ratio) in the engine cylinder, causing knocking and inadvertent vibration of the engine. However, in the present embodiment, if the engine has been warmed up due to the short engine stop time due to the eco-run control, the compression ratio is set to a low compression ratio (step S130). At the time of starting, the vibration at the start of the variable compression ratio engine 10 can be reduced, so that it is possible to prevent the driver from feeling uncomfortable, which is preferable.
[0052]
Further, if the engine stoppage based on the eco-run control is not sufficient to warm up the engine for a long time (No in step S120), the compression ratio at the time of engine stop is shifted to the high compression ratio side before starting the next engine. It is changed in advance (step S110). Therefore, if the engine is stopped based on the eco-run control and the warm-up is insufficient, the in-cylinder temperature can be increased by setting a high compression ratio when the engine is subsequently restarted. It can be enhanced and is preferred.
[0053]
In the present embodiment, the engine stop process (step S140) is performed following the compression ratio change (steps S110 and S130) in preparation for the next start. I did it. Therefore, the compression ratio is changed when the internal pressure in the engine cylinder is higher due to fuel combustion. The variable compression ratio mechanism 20 having the configuration shown in FIG. 1 drives the cylinder block 12 to be separated from the crankcase 14 when the compression ratio is changed to a lower compression ratio side, and the direction of this drive is determined by the internal pressure in the engine cylinder. There is the same as the direction to do. Therefore, when the compression ratio is changed to the low compression ratio side (step S130), the high internal pressure in the cylinder can be assisted by the compression ratio changing mechanism 20 (actuator 21), and the driving force of the actuator 21 can be reduced.
[0054]
Next, another embodiment will be described. The engine system of the second embodiment is not different from the first embodiment in the device configuration including the variable compression ratio engine 10, and the content of the control of stopping the compression ratio is different. FIG. 3 is a flow chart showing a state of control at the time of stopping the compression ratio performed by the engine system of the second embodiment. FIG. 4 is a diagram showing a change in the compression ratio at the time of restarting the engine after the engine is stopped by the control at the time of stopping the compression ratio. It is a flowchart which shows the mode of control.
[0055]
The control at the time of stopping the compression ratio shown in FIG. 3 is repeatedly performed at predetermined time intervals. First, as in the first embodiment, the current situation is to stop the engine based on the engine stop request. It is determined whether or not the engine is in a situation (step S200). If the engine is not in a stopped state, the routine ends without performing any processing.
[0056]
On the other hand, if it is determined that the engine is stopped, the actuator 21 of the variable compression ratio mechanism 20 is drive-controlled so that the compression ratio becomes the intermediate range compression ratio ε, and the compression ratio of the variable compression ratio engine 10 is changed. (Step S210). After the change of the compression ratio, engine stop processing including stop of fuel injection and plug ignition is performed (step S220), and the above processing is repeated. As described above, when setting the compression ratio to the intermediate compression ratio ε, it is convenient to change the compression ratio to a predetermined intermediate region compression ratio εM (for example, an intermediate value) included in a possible compression ratio range.
[0057]
After the engine is stopped in this way, the variable compression ratio engine 10 is restarted by some start signal, for example, a signal or a flag issued in a start process in the eco-run control, for example, by a driver turning on an ignition switch. In the compression ratio change control at the time of restarting the engine in FIG. 4, first, it is determined whether or not the current situation is a situation in which the engine is to be started (restarted) based on the above-described start signal (step S230). Here, this routine is terminated without performing any processing unless it is in the restarting state.
[0058]
On the other hand, if it is determined that the engine is being started (restarted), it is determined whether or not the engine coolant temperature input from the coolant temperature sensor 56 is equal to or higher than a predetermined value (step S240). If a negative determination is made here, the actuator 21 of the variable compression ratio mechanism 20 is drive-controlled so that the compression ratio becomes the high compression ratio ε, and the compression ratio of the variable compression ratio engine 10 is increased (step S250). Thereafter, the cell motor (not shown) is driven to crank the piston to start the variable compression ratio engine 10 (step S260), and the routine is once ended.
[0059]
On the other hand, if it is determined in step S240 that the coolant temperature is equal to or higher than the predetermined temperature, it is determined whether the engine is warmed up or not at the coolant temperature (step S270). Here, if the warm-up is sufficient, the compression ratio of the variable compression ratio engine 10 is changed to a low compression ratio in the following step S280, and then the engine is started in step S260. However, if the warm-up is insufficient, the engine is started in step S260, so the compression ratio at the time of starting the engine remains the compression ratio in the intermediate range changed in step S210 in FIG.
[0060]
The second embodiment described above has the following advantages.
In the situation where the engine is stopped, the compression ratio is changed to the compression ratio in the intermediate range before the next restart of the engine (step S210). Therefore, the compression ratio is changed to the high compression ratio or the low compression ratio at the next start of the engine. Even if it is necessary to do so (steps S250 and S280), only the difference from the compression ratio in the middle range needs to be changed at the time of the start. Therefore, in steps S250 and S280, the time required for changing the compression ratio (the driving time of the variable compression ratio mechanism 20) can be reduced, and the startability can be improved accordingly.
[0061]
In the present embodiment, when a negative determination is made in step S270, the engine is started (restarted) in step S260 without changing the compression ratio. For this reason, as described in the first embodiment, the startability is further improved by the fact that the compression ratio does not need to be changed when starting the engine. Further, if the cooling water temperature is equal to or higher than the predetermined temperature at the start of the engine (Yes at step S240), the compression ratio is not changed to the low compression ratio, but only when the engine warm-up is sufficient. The ratio is changed (step S280). For this reason, the variable compression ratio engine 10 starts starting (operating) at a low compression ratio in a state where the warm-up is sufficient, and in this case, an increase in the vibration at the start due to an excessive increase in the internal pressure in the cylinder. Can be suppressed. Therefore, as described in the first embodiment, the start-up vibration of the variable compression ratio engine 10 can be reduced so that the driver does not feel uncomfortable.
[0062]
Next, a third embodiment will be described. Even in the engine system of the third embodiment, the device configuration including the variable compression ratio engine 10 is not different from that of the first embodiment, and the content of the control of the compression ratio when the engine is stopped is different. FIG. 5 is a flowchart showing the state of the stop control of the compression ratio performed by the engine system of the third embodiment.
[0063]
Although the control at the time of stopping the compression ratio shown in FIG. 5 is repeatedly performed at predetermined time intervals, the control is executed during the period when the operation of the variable compression ratio engine 10 is already stopped. There are two features. In the illustrated control at the time of stopping the compression ratio, first, it is determined whether or not the current situation is that the engine has already been stopped (step S300). If the engine is running, this routine is executed without performing any processing. To end. That is, the processing described below involving the change of the compression ratio is executed in a state where the engine is stopped. Whether the engine is stopped or not is determined, for example, based on a set value of a flag indicating that the engine is automatically stopped by eco-run in eco-run control (not shown), or by turning off the ignition switch by the driver. It can be determined by the presence or absence of an operation (engine stop signal) or the like. Alternatively, it is also possible to determine that the engine has been stopped by detecting the vibration of the engine in combination with these signals and considering the detected output.
[0064]
On the other hand, if it is determined that the engine is already stopped, it is determined whether the engine coolant temperature input from the coolant temperature sensor 56 is equal to or higher than a predetermined value (step S310). If the determination is affirmative, the routine ends once without performing any processing. If the determination is negative, the drive control of the actuator 21 of the variable compression ratio mechanism 20 is performed so that the compression ratio becomes a high compression ratio ε. Then, the compression ratio of the variable compression ratio engine 10 is increased (step S320), and the above processing is repeated. In this case, when changing the compression ratio, a value of a target compression ratio (start-time target compression ratio) may be set according to the engine coolant temperature.
[0065]
According to the third embodiment as well, the compression ratio is changed prior to the next restart of the engine in a situation where the engine has been stopped, so that the startability is improved. In addition, the compression ratio should be changed according to the cooling water temperature that reflects the engine warm-up situation. If the cooling water temperature is low and warm-up is insufficient, restart the engine at a high compression ratio. ing. That is, even in a situation where the engine has been stopped, for a short time after the engine is stopped, the cooling water temperature is kept high and the warm-up is sufficient, and the compression ratio is not changed to the high compression ratio side. Therefore, when the engine is restarted, the operation of the engine can be prevented from being performed at the high compression ratio, so that the fuel whose temperature is relatively high due to the warm-up is further compressed (high compression ratio) to further increase the temperature. Can be suppressed. As a result, when the engine is restarted, as described above, the start-up vibration of the variable compression ratio engine 10 can be reduced, so that it is possible to prevent the driver from feeling uncomfortable, which is preferable.
[0066]
On the other hand, when the engine stop period is long, the cooling water temperature decreases and warm-up becomes sufficient. In such a case, the compression ratio is changed to a higher compression ratio in step S320. As described above, if the stop period is prolonged, the internal pressure in the engine cylinder also decreases until the pressure approximates the atmospheric pressure. Does not work (see FIG. 1). By the way, in order to set the compression ratio to a high compression ratio, the variable compression ratio mechanism 20 drives the cylinder block 12 and the cylinder head 15 closer to the crankcase 14. This change in the compression ratio drives the actuator 21 with the electric power of the battery, but a load is applied to the battery due to the engine stop period. However, the self-weight of the cylinder block 12 and the cylinder head 15 acts in a direction corresponding to the driving direction of the above-described members, so that the driving force (battery power) of the actuator 21 can be assisted by the self-weight of the members, and the load on the battery is reduced. can do.
[0067]
Next, a fourth embodiment will be described. Even in the engine system of the fourth embodiment, the device configuration including the variable compression ratio engine 10 is not different from that of the first embodiment. Start control is different. FIG. 6 is a flowchart showing the state of control when the compression ratio is stopped performed by the engine system of the fourth embodiment, and FIG. 7 is a flowchart showing the state of start control performed by the engine system of the fourth embodiment.
[0068]
Even in the stop-time control of the compression ratio shown in FIG. 6, the process is repeated at predetermined time intervals. First, as in the first embodiment, whether the current situation is a situation in which the engine is to be stopped. It is determined whether or not it is not (step S400). If the engine is not stopped, the routine ends without performing any processing.
[0069]
On the other hand, if it is determined that the engine is stopped, the actuator 21 of the variable compression ratio mechanism 20 is drive-controlled so that the compression ratio becomes the high compression ratio ε, and the compression ratio of the variable compression ratio engine 10 is increased (step S410). After the compression ratio is changed, engine stop processing including stop of fuel injection and plug ignition is performed (step S420). After the engine is stopped by this processing, variable compression is performed so that the compression ratio becomes the low compression ratio ε. The compression ratio of the ratio engine 10 is changed (step 420), and the above processing is repeated.
[0070]
After the engine is stopped in this way, the variable compression ratio engine 10 is restarted by the above-described start signal. The start control at the time of restarting the engine shown in FIG. 7 is started in response to the start signal. First, based on the output from the crank position sensor 52, the crank angle becomes close to 90 ° (for example, 90 ° ± 5 °). It is determined whether or not there is (step S460). Here, if an affirmative determination is made, the process shifts to an ignition start process not using a starter motor (not shown) (step S460), and this routine ends. The ignition start processing in step S460 includes a step of injecting fuel from the fuel injection valve IJ into the cylinder when the engine is restarted, and a step of igniting the fuel with the ignition spark of the ignition plug 32. The starter motor is not driven. Even in such a starter motorless start, since the crank angle at that time is around 90 °, the fuel injection, spark ignition and fuel combustion are performed during the expansion stroke of the piston 13, so that the fuel combustion pressure This causes the piston to transition to a stroke following the expansion stroke, causing cranking of the engine. The engine is started by the cranking thus caused.
[0071]
On the other hand, if a negative determination is made in step S450, the piston is also expected to be located at the bottom dead center side even during the expansion stroke, so that the starter motor starting with cranking by the starter motor and fuel injection / spark ignition is performed. The process is performed (step S470), the engine is started, and this routine ends.
[0072]
According to the fourth embodiment described above, the engine is stopped after the compression ratio is changed to a high compression ratio, so that the piston can be stopped at a position where the crank angle is close to 90 ° with high probability as described above. . Therefore, even if the start is performed by the starter motorless start process, the reliability of the start can be improved, and the startability can be improved as described above because the compression ratio does not need to be changed at the time of the start. Moreover, since the frequency of the affirmative determination in step S450 can be increased, the execution frequency of the above-described starter motorless start processing can be increased. Therefore, even when the battery capacity is reduced, the engine can be started by the starter motorless start processing. Further, since the use frequency of the starter motor associated with the starter motor start processing can be reduced, the capacity and size of the battery can be reduced.
[0073]
Further, in this embodiment, although the compression ratio is set to a high compression ratio, the compression ratio is set to low before starting the engine, and then the engine is started. At the time of cranking at the time of starting the engine, the compression ratio acts to hinder the cranking, but the low compression ratio does not significantly impair cracking. For this reason, cranking at the time of starting the engine can be performed smoothly, which is advantageous in improving the startability. In particular, in the case of a starter without a starter motor, the cranking is performed by the fuel combustion pressure, and therefore, the reliability of the start is enhanced, which is preferable.
[0074]
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.
[0075]
For example, the variable compression ratio engine includes a variable compression ratio mechanism 20 that changes the compression ratio by moving the cylinder block 12 with respect to the crankcase 14 in the movement direction of the piston 13 (the axial direction of the cylinder 11). However, it is not limited to this. In other words, the variable compression ratio mechanism employs various configurations, such as a configuration in which the connecting rod is bendable between the piston and the crankshaft, and a compression ratio is changed by changing the degree of the bending to change the vertical dead center position of the piston. Can be taken.
[0076]
Further, in the above-described embodiment, when the compression ratio is stopped, the engine is stopped after the compression ratio is changed.However, the engine is stopped first, and then the compression ratio is changed. It can also be done.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram schematically showing a configuration of an engine system including a variable compression ratio engine 10 according to a first embodiment.
FIG. 2 is a flowchart illustrating a state of control at a stop of a compression ratio performed by the engine system of the first embodiment.
FIG. 3 is a flowchart illustrating a state of control at a stop of a compression ratio performed by an engine system according to a second embodiment.
FIG. 4 is a flowchart showing a state of a compression ratio change control at the time of restarting the engine after the engine is stopped by the control at the time of stopping the compression ratio.
FIG. 5 is a flowchart illustrating a state of control at the time of stopping a compression ratio performed by an engine system according to a third embodiment.
FIG. 6 is a flowchart illustrating a state of control at the time of stopping a compression ratio performed by an engine system according to a fourth embodiment.
FIG. 7 is a flowchart showing a state of start control performed by the engine system of the fourth embodiment.
[Explanation of symbols]
10. Variable compression ratio engine
11 ... Cylinder
12 ... Cylinder block
13 ... Piston
14 ... Crankcase
15 ... Cylinder head
16 ... intake port
17… Exhaust port
18 ... intake pipe
20: Variable compression ratio mechanism
21 ... Actuator
30 ... intake control valve
31 ... Pressure pump
32 ... Spark plug
40 ... Control unit
50 ... Accelerator position sensor
51… Vehicle speed sensor
52 ... Crank position sensor
53 ... Fuel pressure sensor
54 ... Brake position sensor
55 ... Shift position sensor
56… Cooling water temperature sensor
60 ... Transmission
161: Intake valve
171: Exhaust valve
EC: Exhaust side cam
FD: Fuel delivery pipe
IC: intake side cam
IJ: Fuel injection valve

Claims (9)

A method for changing and controlling a compression ratio of an internal combustion engine having a compression ratio changing mechanism for changing a compression ratio,
A stop-time changing step of controlling the compression ratio changing mechanism to change the compression ratio to a target compression ratio at the time of starting the internal combustion engine when the stop request of the internal combustion engine is detected; and stopping the operation of the internal combustion engine. And a control method for an internal combustion engine capable of changing a compression ratio. An internal combustion engine capable of changing a compression ratio,
A compression ratio changing mechanism for changing the compression ratio;
Stop request detecting means for detecting a request to stop the internal combustion engine,
When the stop request is detected, a stop-time change control for controlling the compression ratio change mechanism to change the compression ratio to a target compression ratio at the time of starting the internal combustion engine, and an engine for stopping the operation of the internal combustion engine An internal combustion engine comprising: stop control means for performing stop control. The internal combustion engine according to claim 2,
Automatic stop means for automatically stopping the operation of the internal combustion engine when a predetermined automatic stop condition is satisfied based on the situation of the vehicle or the operation history of the internal combustion engine during operation of the internal combustion engine;
A manual stop means for stopping the operation of the internal combustion engine based on the driver's intention to stop the internal combustion engine,
The stop request detection means,
Detecting a stop request based on the automatic stop means and detecting a stop request based on the manual stop means in a distinguished manner,
The stop time control means,
An internal combustion engine that executes the stop-time change control such that the start-time target compression ratio is different between when a stop request is detected based on the automatic stop means and when a stop request is detected based on the manual stop means. The internal combustion engine according to claim 3,
The stop time control means,
An internal combustion engine in which the target compression ratio at the time of starting is set lower when a stop request is detected based on the automatic stop means than when a stop request is detected based on the manual stop means. The internal combustion engine according to claim 3,
A warm-up sensor that detects a warm-up state of the internal combustion engine,
The stop time control means,
An internal combustion engine that executes the stop time change control when detecting a stop request based on the automatic stop means so that the target compression ratio at start is different based on an output of the warm-up sensor. The internal combustion engine according to claim 2,
Piston position detection means for detecting a piston position in a cylinder of the internal combustion engine,
Starting ignition means for judging a cylinder to be in an expansion stroke at the time of starting the internal combustion engine from the detected piston position and injecting fuel into the judged cylinder to ignite and burn;
Ignition control means for controlling the start-time ignition means,
The stop time control means,
The stop change control is performed by setting the start target compression ratio to a compression ratio on the high compression ratio side,
The ignition control means,
An internal combustion engine that executes and controls the starting ignition means when the internal combustion engine is started. The internal combustion engine according to claim 6,
The ignition control means,
When the piston is located at the lower dead center side from the intermediate position between the top dead center and the bottom dead center in the cylinder which is in the expansion stroke at the time of starting, the starter motor is used instead of the execution control of the starting ignition means. The internal combustion engine that attempts to start the internal combustion engine. The internal combustion engine according to claim 2,
A warm-up sensor for detecting a warm-up state of the internal combustion engine,
When there is a start request of the internal combustion engine, a start-time control unit that controls the compression ratio changing mechanism to change the compression ratio to a start actual compression ratio according to the output of the warm-up sensor,
The stop time control means,
An internal combustion engine that executes the stop-time change control by setting the start-time target compression ratio to an intermediate compression ratio. An internal combustion engine capable of changing a compression ratio,
A compression ratio changing mechanism for changing the compression ratio;
A warm-up sensor for detecting a warm-up state of the internal combustion engine,
Start-time target compression ratio at the start of the internal combustion engine, a start-time compression ratio setting means for setting according to the output of the warm-up sensor,
An internal combustion engine comprising compression ratio control means for controlling the compression ratio changing mechanism to change the compression ratio to the target compression ratio at the start before the internal combustion engine starts.

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