JP4239813B2 - Compression ratio control device and compression ratio control method for internal combustion engine - Google Patents

Description

  The present invention relates to compression ratio control of an internal combustion engine provided with a variable compression ratio mechanism that makes an engine compression ratio variable with a change in piston top dead center position.

In an internal combustion engine equipped with a variable compression ratio mechanism that makes the engine compression ratio variable, a low compression ratio is set on the low load side and a low compression ratio on the high load side, thereby avoiding knocking and reducing the fuel consumption rate. Can be improved. As a variable compression ratio mechanism, for example, in Patent Document 1, a volume chamber connected to a combustion chamber is separately provided, and an effective combustion chamber remaining at the time of piston compression top dead center by intermittently connecting both connecting passage portions depending on operating conditions. A mechanism is disclosed in which the engine compression ratio can be changed without changing the operating position of the piston by making the volume variable. Patent Document 2 discloses a mechanism that makes the engine compression ratio variable by changing the top dead center position of the piston instead of changing the combustion chamber volume on the cylinder head side. In this mechanism, the top dead center position of the piston is high when the compression ratio is high, and the top dead center position of the piston is low when the compression ratio is low. In this way, the latter mechanism that makes the engine compression ratio variable with the change of the piston top dead center position is not provided with a separate volume chamber in the cylinder head, compared to the former mechanism that makes the combustion chamber volume variable. This is advantageous in that a large change range of the engine compression ratio can be secured and the piston stroke characteristic itself can be optimized.
JP 07-229431 A JP 2002-70601 A

  However, the variable compression ratio mechanism that makes the engine compression ratio variable with changes in the piston top dead center position has been uniquely found to have the following problems.

  As shown in FIG. 10, a piston 38 that moves up and down in conjunction with the crankshaft is fitted in a cylinder (liner) 51 of the cylinder block. Since the inner wall surface of the cylinder 51, i.e., the cylinder bore surface 39, is always exposed to very high-temperature combustion gases and combustion products, it is very important to ensure lubricity as compared to other lubrication parts of the engine. Therefore, the cylinder bore surface 39 is lubricated with engine oil so that the piston slides smoothly with low friction while maintaining high compression and air tightness. In addition, the cylinder bore surface 39 is generally subjected to special processing called so-called honing processing, in which a large number of minute irregularities are formed so that a good and thick oil film can be held. Confidentiality and smooth sliding of the piston 38 are ensured.

  In the variable compression ratio mechanism that makes the engine compression ratio variable with the change in the piston top dead center position described above, the piston top dead center position changes according to the set state of the engine compression ratio, specifically, high compression. The ratio is high and the low compression ratio is low. Therefore, the area where the piston 38 and the piston ring 52 are in contact with the cylinder bore surface 39 inevitably changes. When the compression ratio is low, the piston top dead center position remains at a lower position than when the compression ratio is high. Therefore, in the difference region ΔTDC between the piston top dead center position at the time of high compression ratio and low compression ratio, During the engine operation, the piston 38 and the piston ring 52 repeatedly slide, while during the engine operation at the low compression ratio, the piston 38 and the piston ring 52 are maintained in a non-contact state without reaching. Therefore, the cylinder bore surface 39 in the differential region ΔTDC is mainly subjected to removal of combustion products (sludge) 50 and lubrication by engine oil by the piston ring 52 during operation at a high compression ratio, while at a low compression ratio. During this operation, it is always exposed to high-temperature combustion gas. The amount of adhesion / deposition of the combustion product 50 basically increases in proportion to the continuous operation (integrated) time at a low compression ratio as shown in FIG. Further, it is more easily promoted under an operating condition in which the air-fuel ratio in which the combustion product itself in the combustion gas increases is high. Therefore, the combustion product 50 continues to accumulate on the bore surface 39 in the difference region ΔTDC in proportion to the continuous operation (integration) time at the low compression ratio.

  The sludge 50 adhering to and accumulating on the bore surface 39 in the differential region ΔTDC in this way is swept up at once by the top ring 52 of the piston 38 when shifting to the high compression ratio. It is easy to clog the ring groove or the oil return hole of the oil ring 53. Even if the amount of sludge accumulation is not extremely large, if it becomes a sludge piece of a certain size, there is a possibility that it will be difficult to be smoothly excreted from the narrow piston land part, and the small sludge piece is repeatedly generated, resulting in low compression While the continuous operation time of the ratio continues for a long time, it gradually accumulates around the piston ring and may act in a direction that impedes the movement of the piston ring 52. Therefore, it is necessary to remove the sludge accumulated on the bore surface 39 in the differential region ΔTDC as small and as few steps as possible.

  In particular, the honed bore surface 39 is formed with a large number of irregularities in order to increase the retention of the oil film. Therefore, it is very difficult to completely remove sludge once the oil film has been cut and clogged to the fine groove below it, even if the piston ring 52 slides on it again later. It is. Since it is more difficult to form an oil film again on the bore surface that has been flattened because the honing surface is buried, it is highly important to remove sludge accumulated in the differential region ΔTDC at an early stage.

  The present invention has been made in view of the problems uniquely found in this way, and is a problem peculiar to a variable compression ratio mechanism that makes the engine compression ratio variable with changes in the piston top dead center position. The main purpose is to easily and effectively remove sludge accumulated on the inner surface of the cylinder in the region ΔTDC.

  A piston that moves up and down in the cylinder in conjunction with the rotation of the crankshaft, a variable compression ratio mechanism that makes the engine compression ratio variable by changing the top dead center position of the piston, and an engine compression ratio according to the engine operating state Compression ratio control means for controlling When a predetermined condition is satisfied, the piston top dead center position is forcibly and temporarily increased.

  According to the present invention, when a predetermined condition is established, the piston top dead center position is forcibly and temporarily increased, so that sludge accumulated on the cylinder inner surface in the differential region of the piston top dead center position can be easily reduced. Can be removed. Therefore, it is possible to prevent the sludge from excessively accumulating in the above-described differential region, and to avoid problems such as sludge clogging and excessive wear due to this.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 schematically shows an example of a variable compression ratio mechanism 1 that makes the engine compression ratio variable with a change in the top dead center position of the piston 38. The crankshaft 31 includes a plurality of journal portions 32, a crankpin 33, and a counterweight portion 31a. The journal part 32 is rotatably supported by a main bearing of a cylinder block as an engine body. The crank pin 33 is eccentric from the journal portion 32 by a predetermined amount. The piston 38 is fitted to the cylinder 51 of the cylinder block with substantially no gap, and moves up and down in the cylinder 51 in conjunction with the rotation of the crankshaft 31. An intake valve 43 that opens and closes the intake port 44 in synchronization with the rotation of the crankshaft 31 and an exhaust valve 45 that opens and closes the exhaust port 46 in synchronization with the rotation of the crankshaft 31 are disposed above the piston. ing.

  The variable compression ratio mechanism 1, which is a multi-link type piston-crank mechanism that links the piston 38 and the crankshaft 31, includes a lower link 34 that is rotatably fitted to the crankpin 33, and the lower link 34 and the piston 38. , And a control link 40 having one end connected to the lower link 34, and the engine compression ratio can be varied by changing the motion constraint condition of the lower link 34 via the control link 40. And

  The lower link 34 has a substantially T-shape, and the crank pin 33 is fitted in a substantially central connecting hole configured to be split from a main body 34a and a cap 34b. The upper link 35 is rotatably connected to the lower link 34 by a connecting pin 36 at the lower end side, and is rotatably connected to the piston 38 by a piston pin 37 at the upper end side. The control link 40 has an upper end side rotatably connected to the lower link 34 by a connecting pin 41, and a lower end side rotatably connected to, for example, an appropriate position of a cylinder block as an engine body via a control shaft 42. Specifically, the control shaft 42 is supported by the engine body so as to rotate about the small diameter portion 42b, and the lower end portion of the control link 40 is rotatable on the large diameter portion 42a that is eccentric to the small diameter portion 42b. Is fitted.

  The rotation position of the control shaft 42 is changed and held by the compression ratio control actuator 11. When the rotational position of the control shaft 42 is changed by the compression ratio control actuator 11, the axial center position of the large diameter portion 42a that is eccentric with respect to the small diameter portion 42b, in particular, the relative position with respect to the engine body changes. As a result, the swing support position at the lower end of the control link 40 changes, the motion restraint condition of the lower link 34 changes, the stroke characteristics of the piston 38 change, and the engine compression ratio changes.

  The engine control unit 10 sets a target compression ratio as will be described later, and outputs a command signal corresponding to the target compression ratio to the variable compression ratio actuator 11 to control its operation. As a result, the variable compression ratio actuator 11 drives the variable compression ratio mechanism 1 toward the target compression ratio.

  FIG. 2 is a flowchart showing the target compression ratio setting routine, and FIG. 3 shows a flag setting routine used in the routine of FIG. These routines are repeatedly executed by the engine control unit 10 every predetermined period (for example, every 10 ms).

  Referring to FIG. 3, in step (denoted as S in the figure) 1, it is determined whether the vehicle is operating at a low compression ratio. For example, what is necessary is just to determine whether the target compression ratio is a state below a predetermined value. Alternatively, the actual compression ratio may be detected / estimated based on sensors or engine operating conditions, and it may be determined whether the actual compression ratio is equal to or less than a predetermined value. If the operation is in the low compression ratio, 1 is added to the value CONT_Lowε of the continuous operation measurement timer for measuring the continuous operation (integration) time in the low compression ratio (step 2). If not operating at a low compression ratio, the continuous operation time timer CONT_Lowε is cleared to 0 (zero) (step 7), and a continuous operation time flag FLG_LowεTime described later is cleared to 0 (step 8). In step 3, it is determined whether the continuous operation time flag FLG_LowεTime is 1. If the flag FLG_LowεTime is not 1, the process proceeds to step 4 to determine whether the continuous operation time timer CONT_Lowε exceeds a predetermined limit value (limiter) described later. If the continuous operation time CONT_Lowε at the low compression ratio exceeds the limit value, the continuous operation time flag FLG_LowεTime is set to 1 (step 5), and the continuous operation time timer CONT_Lowε is cleared to 0 (step 6).

  Referring to FIG. 2, in step 11, engine speed rNe calculated based on the detection signal of crank angle sensor 12 is read. In step 12, the accelerator opening degree rAPO detected by the accelerator opening degree sensor 13 is read. In step 13, it is determined whether the continuous operation time flag FLG_LowεTime is set to 1, that is, whether the continuous operation (integration) time at the low compression ratio is longer than the limit value.

  If the continuous operation time CONT_Lowε at the low compression ratio does not exceed the limit value, the process proceeds to step 14, and the engine operating state is obtained by referring to and searching the setting map of FIG. 4 using the engine speed rNe and the accelerator opening rAPO. An appropriate basic target compression ratio tε0 is calculated. Generally, the basic target compression ratio tε0 is lowered as the load increases. In the following step 15, the basic target compression ratio tε0 is set to the target compression ratio tε (first target compression ratio setting means).

  If the continuous operation time CONT_Lowε exceeds the limit value, the process proceeds to step 16 where a predetermined high compression ratio # tMAX_ε is calculated and set as the target value tε2 of the compression ratio. In step 7, this value tε2 is set to the target compression ratio tε. (Second target compression ratio setting means). The above # tMAX_ε is the compression ratio at which the piston top dead center position is the highest, and is typically the maximum compression ratio. Thereby, the forced high compression ratio operation in which the engine compression ratio is forcibly set to a high compression ratio is performed. In step 18, it is determined whether the above-described forced high compression ratio operation is maintained for a specified time # CONT_Max_ε using an appropriate counter or timer. When the forced high compression ratio operation is performed for the specified time # CONT_Max_ε, the process proceeds to step 9, the continuous operation time flag FLG_LowεTime is cleared to 0, and the forced high compression ratio operation is terminated.

  FIG. 5 is a time chart in the case where the limit value in step 4 is simply set to the fixed value Limit_LowεTime. As shown in the figure, when the continuous operation integration time CONT_Lowε at the low compression ratio exceeds the limit value, the target compression ratio is forcibly set to the maximum compression ratio # tMAX_ε for a predetermined period # CONT_Max_ε, and the piston top dead center position To be maximized. Thereby, the sludge 50 accumulated in the differential region ΔTDC of the piston top dead center position can be easily removed at a small number of stages.

  FIG. 6 shows a routine for changing and correcting the limit value according to the engine water temperature and the air-fuel ratio, and FIG. 9 is a time chart in that case. In step 31, the target air-fuel ratio tλ calculated and set according to the engine operating state is read. In step 32, the engine water temperature rTw detected by the water temperature sensor 14 is read.

  In step 33, as shown in FIG. 7, a water temperature correction table TBL_Tw_hos is searched based on the engine water temperature rTw, and a limit value water temperature correction factor GAIN_Tw_hos is calculated. As shown in FIG. 7, as the engine water temperature is lower, the sludge adhesion amount increases. Therefore, the water temperature correction factor GAIN_Tw_hos is decreased so as to lower the limit value.

  In step 34, as shown in FIG. 8, the air-fuel ratio correction table TBL_λ_hos is searched based on the actual air-fuel ratio rλ estimated or detected based on the target air-fuel ratio tλ, and the limit value air-fuel ratio correction rate is obtained. GAIN_λ_hos is calculated. As shown in FIG. 8, as the air-fuel ratio becomes lower (darker), the sludge adhesion amount increases. Therefore, the air-fuel ratio correction rate GAIN_λ_hos is reduced so as to lower the limit value.

  In step 35, the basic limit value # Limit_LowεTime is multiplied by the water temperature correction factor GAIN_Tw_hos and the air-fuel ratio correction factor GAIN_λ_hos to calculate the final limit value Limit_LowεTime2.

  By performing the calculation processing of FIGS. 2 and 3 using such limit value Limit_LowεTime2, as shown in FIG. 9, the low compression ratio until the shift to the forced high compression ratio operation is made according to the water temperature and the air-fuel ratio. The operation time is adjusted appropriately. For example, the limit value increases as the water temperature rises, and the low compression ratio operation time until shifting to forced high compression ratio operation becomes longer. In addition, as the actual air-fuel ratio becomes richer, the limit value decreases, and the low compression ratio operation time until the shift to forced high compression ratio operation is shortened.

  The technical ideas that can be grasped from the above embodiments are listed together with their effects.

  (1) A piston 38 that moves up and down in the cylinder 51 in conjunction with the rotation of the crankshaft 31, a variable compression ratio mechanism 1 that makes the engine compression ratio variable with a change in the top dead center position of the piston 38, and a target The target compression ratio tε is set based on the compression ratio control means (10, 11) for controlling the operation of the variable compression ratio mechanism 1 toward the compression ratio tε and the engine operating state including the engine load and the engine speed. When the first target compression ratio setting means (steps 14 and 15) and a predetermined condition are satisfied, the target compression ratio tε is forcibly and temporarily set to a predetermined high compression ratio tε2 = # tMAX_ε. Target compression ratio setting means (steps 16 to 18).

  With this configuration, the basic target compression ratio tε0 is obtained when the sludge 50 is deposited on the bore surface 39, when it is actually deposited, or when it is estimated that it has accumulated. Regardless of the value, the forced high compression ratio operation in which the target compression ratio tε is forcibly and temporarily set to a predetermined high compression ratio tε2 is performed, so that the sludge accumulation amount 50 on the bore surface 39 in the difference region ΔTDC is obtained. It can be easily removed at a few early stages. Therefore, sludge clogging, excessive wear, and the like due to sludge accumulation in the differential region ΔTDC can be prevented.

  (2) A measurement means (steps 2 and 7) for measuring the continuous operation time CONT_Lowε at the low compression ratio is provided, and the predetermined condition is that the continuous operation time CONT_Lowε at the low compression ratio exceeds a predetermined limit value. This is the case (step 4).

  Thus, by using the continuous operation time CONT_Lowε at the low compression ratio for the determination of the forced high compression ratio operation, it is possible to accurately estimate the sludge accumulation amount 50 on the bore surface 39 in the difference region ΔTDC. The limit value is preferably set based on an amount of sludge accumulated per hour under each operating condition obtained in advance through experiments. Further, by simply setting the above limit value to the fixed value Limit_LowεTime, it is possible to reduce the calculation load and the memory usage.

  (3) Water temperature detection means (water temperature sensor 14) for detecting the engine water temperature rTw, and first limit value correction means (steps 33, 35) for correcting the limit value Limit_LowεTime2 to the lower side as the engine water temperature rTw decreases. Have. As a result, when the amount of sludge accumulation is likely to increase more than in the normal post-warm state, such as at the time of low water temperature immediately after starting, the limit value Limit_LowεTime2 becomes lower, and the operation shifts to forced high compression ratio operation. The continuous operation time CONT_Lowε at a low compression ratio until becomes shorter. Thus, forced high compression ratio operation can be performed more appropriately according to the water temperature conditions.

  (4) Second limit value correcting means (steps 34 and 35) for correcting the limit value Limit_LowεTime2 to the lower side as the air-fuel ratio rλ is lowered. As a result, the lower the air-fuel ratio (the darker), that is, the easier the sludge accumulates, the lower the limit value Limit_LowεTime2, and the continuous operation time CONT_Lowε until the shift to the forced high compression ratio operation is made. It is shortened. Therefore, the forced high compression ratio operation can be appropriately performed according to the air-fuel ratio.

  (5) The variable compression ratio mechanism 1 includes a lower link 34 that is rotatably fitted to the crankpin 33 of the crankshaft 31, an upper link 35 that links the lower link 34 and the piston 38, and a lower link 34. A control link 40 having one end connected thereto, and the engine compression ratio is made variable by changing the motion restraint condition of the lower link 34 via the control link 40.

  Such a variable compression ratio mechanism 1 has the following operational effects in addition to being able to continuously change and control the engine compression ratio according to the engine operating state. Since it is a multi-link type piston-crank mechanism in which the piston 38 and the crank pin 33 are linked by a plurality of link parts (upper link and lower link), the single link type of the piston and the crank pin linked by a single connecting rod. Compared to the piston-crank mechanism, the stroke characteristic of the piston itself can be brought close to an appropriate characteristic such as a simple vibration characteristic. Since the control link 40 is disposed so as to extend substantially downward from the lower link 34, the control shaft 42 can be disposed in a crankcase obliquely below the crankshaft 31 having a relatively large space. Therefore, the control shaft 42 and its actuator and the control link 40 can be easily accommodated and arranged in the crankcase, and the engine mountability is excellent.

  As described above, the present invention has been described based on the specific embodiments. However, the present invention is not limited to the above-described embodiments, and includes various modifications and changes without departing from the spirit of the present invention. . For example, in the above embodiment, the limit value is corrected based on the water temperature and the air-fuel ratio. However, the present invention is not limited to this. Further, although the limit value is corrected based on the actual air-fuel ratio rλ, the limit value may be more simply corrected based on the target air-fuel ratio tλ. Furthermore, the engine may be shifted to the high compression ratio operation immediately after the engine is started or before the engine is stopped under other specific conditions.

The block diagram which shows the variable compression ratio mechanism which concerns on one Example of this invention. The flowchart which shows the setting routine of the target compression ratio which concerns on a present Example. A flag setting routine used in the routine of FIG. Basic target compression ratio setting map. Time chart when the limit value is fixed. A routine for correcting the limit value by the water temperature and the air-fuel ratio. Explanatory drawing of the water temperature correction factor of a limit value. Explanatory drawing of the air-fuel ratio correction factor of a limit value. A time chart when the limit value is corrected by the water temperature and the air-fuel ratio. Explanatory drawing of the subject peculiar to the mechanism which makes an engine compression ratio variable with the change of a piston top dead center position. The characteristic view which shows the relationship between the continuous operation time of a low compression ratio, and sludge accumulation amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Variable compression ratio mechanism 10 ... Engine control unit 38 ... Piston 39 ... Cylinder bore surface 51 ... Cylinder (liner)

Claims (5)

A piston that moves up and down in the cylinder in conjunction with the rotation of the crankshaft;
A variable compression ratio mechanism that makes the engine compression ratio variable with a change in the top dead center position of the piston;
Compression ratio control means for controlling the operation of the variable compression ratio mechanism toward the target compression ratio;
First target compression ratio setting means for setting the target compression ratio based on an engine operating state including an engine load and an engine speed;
A second target compression ratio setting means for forcibly and temporarily setting the target compression ratio to a predetermined high compression ratio when a continuous operation time at a low compression ratio exceeds a predetermined value ;
A compression ratio control apparatus for an internal combustion engine. Water temperature detecting means for detecting engine water temperature;
First value correction means for correcting the predetermined value to a lower side as the engine water temperature becomes lower;
The compression ratio control device for an internal combustion engine according to claim 1 , comprising: Second value correcting means for correcting the predetermined value to the lower side as the air-fuel ratio becomes lower;
Compression ratio control apparatus for an internal combustion engine according to claim 1 or 2 having a. The variable compression ratio mechanism includes a lower link that is rotatably fitted to a crank pin of the crankshaft, an upper link that links the lower link and the piston, and a control link that is connected to the lower link at one end. The compression ratio control device for an internal combustion engine according to any one of claims 1 to 3 , wherein the engine compression ratio is made variable by changing a motion constraint condition of the lower link via the control link. A piston that moves up and down in the cylinder in conjunction with the rotation of the crankshaft, a variable compression ratio mechanism that makes the engine compression ratio variable by changing the top dead center position of the piston, and an engine compression ratio according to the engine operating state In a compression ratio control method for an internal combustion engine comprising:
A compression ratio control method for an internal combustion engine, characterized by forcibly and temporarily increasing a piston top dead center position when a continuous operation time at a low compression ratio exceeds a predetermined value .

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