JP2004156542A - Internal combustion engine having variable compression ratio mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To mitigate degradation of the fuel economy by using an electric motor in changing the compression ratio, and to prevent generation of knocking associated with the change of the compression ratio. <P>SOLUTION: A control shaft control circuit 31 rapidly completes the change of the compression ratio by applying the maximum voltage to an electric motor 32 when decreasing the compression ratio, while the compression ratio is changed in a highly efficient manner by applying the voltage of the maximum efficiency when increasing the compression ratio. When decreasing the compression ratio, generation of knocking may be prevented by adjusting the ignition timing in advance. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an internal combustion engine having a variable compression ratio mechanism.
[0002]
[Prior art]
DESCRIPTION OF RELATED ART Conventionally, the internal combustion engine which has the variable compression ratio mechanism which can change a compression ratio is known (for example, patent documents 1-5).
[0003]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-54873 [Patent Document 2]
JP 2002-115571 A [Patent Document 3]
JP 2001-289079 A [Patent Document 4]
JP 2001-214770 A [Patent Document 5]
JP-A-7-26981
[Problems to be solved by the invention]
Many variable compression ratio mechanisms use an electric motor as a drive unit when changing the compression ratio. In a variable compression ratio mechanism using an electric motor, the inertia of the electric motor is often large, and to change the compression ratio at high speed requires a considerably large amount of electric power. For this reason, if the compression ratio is frequently changed, there is a problem that fuel efficiency is reduced.
[0005]
In addition, in an internal combustion engine using a variable compression ratio mechanism, there is a problem that knocking is likely to occur unless the compression ratio is changed at high speed.
[0006]
The present invention has been made to solve the above-described conventional problems, and has as its first object to provide a technique for mitigating a decrease in fuel consumption caused by using an electric motor for changing a compression ratio. . It is a second object of the present invention to provide a technique for preventing occurrence of knocking due to a change in compression ratio.
[0007]
[Means for Solving the Problems and Their Functions and Effects]
To achieve at least a part of the above object, a first internal combustion engine of the present invention includes:
A cylinder and a piston constituting a combustion chamber;
A variable compression ratio mechanism capable of changing the compression ratio of the combustion chamber,
With
The variable compression ratio mechanism has an electric motor used when changing a compression ratio, and a control circuit that controls the electric motor,
The control circuit changes drive power supplied to the electric motor according to a direction in which a compression ratio changes.
[0008]
In this internal combustion engine, the drive power supplied to the electric motor is changed in accordance with the direction in which the compression ratio is changed, so that drive power suitable for the direction in which the compression ratio is changed (increase or decrease) can be supplied to the electric motor. As a result, it is possible to alleviate a decrease in fuel efficiency due to the use of the electric motor.
[0009]
When the compression ratio is reduced, the control circuit completes the change of the compression ratio faster than when increasing the compression ratio over the entire compression ratio change or at least during a part of the change. The electric motor may be controlled so as to perform the control.
[0010]
If the reduction of the compression ratio is delayed, a high compression ratio is maintained in a state where a low compression ratio is desired, so that the possibility of occurrence of knocking increases. Therefore, if the change of the compression ratio is completed at a higher speed when lowering the compression ratio, it is possible to prevent the occurrence of knocking.
[0011]
The control circuit may apply a higher voltage to the electric motor when decreasing the compression ratio than when increasing the compression ratio.
[0012]
When a high voltage is applied to the electric motor, the number of revolutions of the electric motor increases, so that the compression ratio can be changed at a higher speed.
[0013]
Further, the control circuit may apply the highest voltage to the electric motor when decreasing the compression ratio, and apply the highest efficiency voltage to the electric motor when increasing the compression ratio.
[0014]
In this way, the reduction of the compression ratio can be completed at a high speed, and the increase of the compression ratio can be performed with high efficiency.
[0015]
The present invention can be realized in various aspects. For example, an internal combustion engine, a control method and a control device for an internal combustion engine, a computer program for realizing the control method and the control device, and a computer program , A data signal including the computer program and embodied in a carrier wave, and the like.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
A. First embodiment:
Next, embodiments of the present invention will be described based on examples. FIG. 1 is a conceptual diagram showing a configuration of an internal combustion engine 10 as one embodiment of the present invention. The internal combustion engine 10 has a combustion chamber including a cylinder 20 and a piston 21. The cylinder head 22 is provided with an intake valve 41, an exhaust valve 42, and a spark plug 51.
[0017]
The piston 21 is connected to the connecting rod 23. The connecting rod 23 has a configuration in which first and second connecting rod members 231 and 233 are connected by a connection pin 232, and can be bent at the connection portion. The upper end of the first connecting rod member 231 is connected to the piston 21 by the piston pin 24, and the lower end of the second connecting rod member 233 is connected to the crank 11. The lower end of the first connecting rod member 231 is further connected to a control rod 26 by a connecting pin 25. The other end of the control rod 26 is connected to a control shaft 27 provided on the periphery of a rotatable worm wheel 28. The control shaft 27 is installed parallel to the central axis 29 at a position eccentric from the central axis 29 of the worm wheel 28. The worm wheel 28 meshes with the worm 33, and when the worm 33 is rotated by the electric motor 32, the worm wheel 28 is also rotated around the central axis 29. When the worm wheel 28 is rotated, the control shaft 27 revolves around the central axis 29. The worm wheel 28 is provided with a rotation position sensor 34 for detecting the rotation position of the worm wheel 28.
[0018]
A control shaft control circuit 31 (also referred to as a "variable compression ratio control circuit 31") provided in an ECU (Electronic Control Unit) 30 controls the electric motor 32 to move the position of the control shaft 27 to approximately the 3 o'clock position. The position of the connecting rod 23 can be adjusted by positioning in a section at a position of about 6 o'clock. When the degree of bending of the connecting rod 23 changes, the positions of the top dead center and the bottom dead center of the piston 21 in the cylinder 20 also change. Therefore, the compression ratio of the combustion chamber can be changed by adjusting the degree of bending of the connecting rod 23. As can be understood from this description, the connecting rod 23, the control rod 26, the worm wheel 28, the control shaft control circuit 31, the electric motor 32, and the worm 33 constitute a variable compression ratio mechanism as a whole.
[0019]
This variable compression ratio mechanism is substantially the same as that disclosed in Japanese Patent Application Laid-Open No. 2000-54873 disclosed by the present applicant. However, any other mechanism can be adopted as the variable compression ratio mechanism.
[0020]
The ECU 30 further includes an ignition control circuit 35 for controlling the ignition state of the ignition plug 51. The ECU 30 is supplied with signals indicating various parameters such as an engine speed, a throttle opening (accelerator pedal depression amount), an intake air amount, a cylinder cooling water temperature, and the like from various sensors. The ECU 30 controls the compression ratio and the ignition state according to these various parameters.
[0021]
FIG. 2 is a graph showing the relationship between the applied voltage of the electric motor 32, the rotation speed, and the efficiency. In this graph, it is assumed that the applied current and the load are constant. In a normal electric motor, the applied voltage and the rotation speed are in a proportional relationship, so that when the load on the motor is constant, the maximum rotation speed Nf is obtained when the maximum voltage Vmax that can be applied is applied. However, the maximum efficiency ηmax of the electric motor is achieved when a maximum efficiency voltage Vef smaller than the maximum voltage Vmax is applied. Therefore, the rotation speed Ns at the maximum efficiency voltage Vef is smaller than the maximum rotation speed Nf.
[0022]
By the way, in general, the higher the compression ratio, the better the thermal efficiency and the better the fuel efficiency, but the higher the compression ratio, the more the knocking tends to occur. Therefore, when the load on the internal combustion engine is small, the possibility of knocking is low. Therefore, by setting a high compression ratio, fuel efficiency can be improved. On the other hand, when the load is large, it is preferable to prevent knocking by setting the compression ratio low. As can be understood from this, the change from the high compression ratio to the low compression ratio is performed when the internal combustion engine changes from a low load to a high load. Therefore, if the change of the compression ratio is delayed, the load becomes high and the compression ratio becomes high, and knocking easily occurs. For this reason, when changing from a high compression ratio to a low compression ratio, it is preferable to complete the change of the compression ratio in as short a time as possible. On the other hand, when changing the compression ratio from the low compression ratio to the high compression ratio, even if it takes some time to change the compression ratio, there is no problem since knocking does not occur. Therefore, in this case, it is preferable to operate the electric motor as efficiently as possible to improve fuel efficiency.
[0023]
FIG. 3 is a flowchart showing a control procedure of the engine according to the first embodiment of the present invention. In step S1, the ECU 30 reads the previously set compression ratio εp (that is, the current compression ratio) from a memory (not shown), and in step S2, the engine speed, throttle opening, intake air amount, cylinder coolant temperature. Detects the operating state of the engine. In step S3, the ECU 30 calculates an appropriate compression ratio target value εt for the operating state of the engine detected in step S2. This calculation can be realized using, for example, a map or a lookup table that receives a combination of values of a plurality of parameters that define the operating state and outputs a target value of the compression ratio.
[0024]
In step S4, the target value εt of the compression ratio is compared with the current value εp. When the target value εt is smaller than the current value εp (ie, when decreasing the compression ratio), the control shaft control circuit 31 applies the maximum voltage Vmax to the electric motor 32 and changes the compression ratio in a short time as possible. Is completed (step S6). As a result, a state of a high load and a high compression ratio can be prevented, so that knocking can also be prevented. When the target value εt of the compression ratio is equal to the current value εp, a holding current / voltage is supplied to the electric motor 32 so as to keep the compression ratio as it is (steps S5 and S7). When the target value εt of the compression ratio is larger than the current value εp (ie, when increasing the compression ratio), the high efficiency voltage Vef is applied to the electric motor 32 to change the compression ratio as efficiently as possible. (Step S8). As a result, it is possible to prevent a reduction in fuel efficiency due to supplying unnecessary voltage and current to the electric motor 32.
[0025]
As described above, in the first embodiment, when the compression ratio is reduced, the change of the compression ratio is completed at a higher speed than when the compression ratio is increased, so that the occurrence of knocking is prevented and the fuel consumption is reduced. The drop can be prevented.
[0026]
B. Second embodiment:
FIG. 4 is a flowchart showing a control procedure of the engine according to the second embodiment of the present invention. The only difference from the first embodiment is that step S10 is added after steps S7 and S8 and step S11 is added before step S6. Other procedures and the configuration of the engine are the same as those of the first embodiment. Is the same as
[0027]
In the second embodiment, when the target value εt of the compression ratio is smaller than the current value εp (that is, when decreasing the compression ratio), the ignition control circuit 35 first sets the optimum ignition timing for the target value εt of the compression ratio. Is determined, and the ignition timing is retarded by a predetermined angle α with respect to the optimum ignition timing (step S11). The reason for retarding the ignition timing is to prevent knocking from occurring. The retardation amount α can be set to any positive value other than 0. Then, the maximum voltage Vmax is applied to the electric motor 32, and the change of the compression ratio is completed in as short a time as possible (step S6). As described above, when the compression ratio is reduced, the electric motor 32 is driven at the maximum speed, and the ignition timing is adjusted so that knocking does not easily occur. Therefore, occurrence of knocking can be more reliably prevented. The reason why the correction of the ignition timing is performed before the driving of the electric motor 32 is that the correction of the ignition timing has a quicker response, and is therefore preferable from the viewpoint of preventing occurrence of knocking. However, both may be performed simultaneously. Note that, depending on the characteristics of the internal combustion engine, the occurrence of knocking may be prevented by advancing the ignition timing in some cases.
[0028]
When the target value εt of the compression ratio is equal to the current value εp, or when the target value εt is larger than the current value εp, after steps S7 and S8, the ignition control circuit 35 corresponds to the target value εt of the compression ratio. The optimal ignition timing is set (step S10).
[0029]
As described above, in the second embodiment, while the target value εt of the compression ratio is smaller than the current value εp (that is, knocking is likely to occur), the ignition timing is retarded (step S11). If the target value εt is equal to or greater than the current value εp, the optimal ignition timing is set. As a result, knocking can be prevented when the compression ratio is reduced, and the internal combustion engine can be operated with high efficiency when the compression ratio is maintained or increased.
[0030]
C. Modification:
The present invention is not limited to the above-described examples and embodiments, but can be implemented in various modes without departing from the gist of the invention, and for example, the following modifications are possible.
[0031]
C1. Modification 1
In the above embodiment, the electric motor 32 is always driven at the maximum speed when the compression ratio is reduced. However, the electric motor 32 may be driven at the maximum speed only when knocking is likely to occur. good. For example, when the current value εp of the compression ratio is larger than a predetermined determination value, the electric motor 32 may be driven at the maximum speed. Alternatively, the current value εp of the compression ratio is larger than the first determination value, and the difference (εp−εt) or ratio (εp / εt) between the current value εp and the target value εt is larger than the second determination value. If larger, the electric motor 32 may be driven at the maximum speed. With this configuration, the compression ratio is changed at a high speed only when necessary to prevent knocking, so that a reduction in fuel efficiency can be prevented.
[0032]
C2. Modified example 2:
In the above embodiment, the voltage value supplied to the electric motor 32 is changed according to the compression ratio. However, depending on the type of the electric motor 32, the current value or the frequency of the driving power may be changed instead of the voltage value. Thus, the operating speed of the electric motor 32 may be changed. That is, it is preferable that the internal combustion engine of the present invention includes a control circuit that changes drive power supplied to the electric motor in accordance with a change state of the compression ratio. Further, it is preferable that the control circuit controls the electric motor such that the change of the compression ratio is completed at a higher speed when the compression ratio is decreased than when the compression ratio is increased. Note that the operation of applying a relatively high voltage to the electric motor to rapidly reduce the compression ratio may be performed throughout the entire compression ratio change, or may be performed during a partial period during the change of the compression ratio. Is also good. In the latter case, the compression ratio may be changed at a speed almost the same as or slightly slower than when the compression ratio is increased during other periods during the change of the compression ratio.
[0033]
C3. Modification 3:
In the present invention, a mechanism having a drive unit other than the electric motor may be adopted as the variable compression ratio mechanism. Also in this case, it is preferable that the variable compression ratio mechanism completes the change of the compression ratio faster when decreasing the compression ratio than when increasing the compression ratio. In this manner, occurrence of knocking due to delay in lowering the compression ratio can be prevented.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing a configuration of an internal combustion engine 10 as one embodiment of the present invention.
FIG. 2 is a graph showing a relationship between an applied voltage of an electric motor 32, a rotation speed, and efficiency.
FIG. 3 is a flowchart illustrating an engine control procedure according to the first embodiment of the present invention.
FIG. 4 is a flowchart showing an engine control procedure according to a second embodiment of the present invention.
[Explanation of symbols]
Reference Signs List 10 internal combustion engine 11 crank 20 cylinder 21 piston 22 cylinder head 23 connecting rod 24 piston pin 25 connection pin 26 control rod 27 control shaft 28 worm wheel 29 central shaft 30 ECU
31 ... Control shaft control circuit (variable compression ratio control circuit)
32 electric motor 33 worm 34 rotational position sensor 35 ignition control circuit 41 intake valve 42 exhaust valve 51 ignition plugs 231 and 233 connecting rod member 232 connection pin

Claims (4)

An internal combustion engine,
A cylinder and a piston constituting a combustion chamber;
A variable compression ratio mechanism capable of changing the compression ratio of the combustion chamber,
With
The variable compression ratio mechanism has an electric motor used when changing a compression ratio, and a control circuit that controls the electric motor,
The internal combustion engine, wherein the control circuit changes drive power supplied to the electric motor according to a direction in which a compression ratio changes. The internal combustion engine according to claim 1,
The internal combustion engine, wherein the control circuit controls the electric motor to complete the change of the compression ratio faster when decreasing the compression ratio than when increasing the compression ratio. The internal combustion engine according to claim 2,
When decreasing the compression ratio, the control circuit applies a higher voltage to the electric motor than when increasing the compression ratio, throughout the compression ratio change, or at least during a part of the change, Internal combustion engine. The internal combustion engine according to any one of claims 1 to 3, wherein
The internal combustion engine, wherein the control circuit applies a maximum voltage to the electric motor when decreasing a compression ratio, and applies a maximum efficiency voltage to the electric motor when increasing a compression ratio.

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