JPH0635842B2 - Compression ratio control method for internal combustion engine with variable compression ratio mechanism - Google Patents

Description

TECHNICAL FIELD The present invention relates to a compression ratio switching control method for an internal combustion engine having a compression ratio variable mechanism.

[Conventional technology]

In an Otto-cycle internal combustion engine, increasing the compression ratio improves combustion efficiency, improves fuel efficiency, and improves axial torque. Therefore, it is desirable to increase the compression ratio. However, if the compression ratio is increased, it is apt to ignite when the temperature rises due to adiabatic compression in the combustion chamber, and knocking easily occurs, thus limiting the increase of the compression ratio. Knocking is likely to occur at high load while a large amount of air is absorbed in the combustion chamber, and is unlikely to occur at light load with a small suction air amount and a small degree of substantial compression in the combustion chamber. It is desirable that the compression ratio, which is variable and set to be appropriate at medium and high loads, be increased at light loads. In this sense, various compression ratio variable mechanisms for internal combustion engines have been proposed in the past.

In an internal combustion engine with a variable compression ratio mechanism, it is desirable to control switching to a high compression ratio or low compression ratio side so as to follow the most efficient operating state without causing knocking.

Focusing on such a point, a technique is known in which a compression ratio variable mechanism is controlled in accordance with a signal from a knocking sensor that detects the occurrence of knocking (Japanese Patent Laid-Open No. Sho 5)
9-188056).

[Problems to be solved by the invention]

However, in the above proposed structure, since the compression ratio switching control is performed after the actual occurrence of knocking is detected by the knocking sensor, the operating state of the optimum compression ratio is always maintained without causing knocking at all. There is a problem that it is difficult.

In addition, apart from the above proposal, conventionally, in a multi-cylinder internal combustion engine with a variable compression ratio mechanism, the engine speed, load,
The compression ratio was controlled uniformly for all cylinders against knocking and the like.

However, in a multi-cylinder internal combustion engine, for each cylinder, variations in combustion chamber volume due to manufacturing accuracy, cylinder difference in cooling state,
There are cylinder differences due to various causes, such as cylinder differences due to intake air distribution, cylinder differences due to changes over time such as wear of various parts, and the like. Therefore, the control of the compression ratio can be performed only by the greatest common divisor, and there is a problem that it is difficult to maximize the ability of each individual cylinder.

An object of the present invention is to control the optimal compression ratio without generating knocking at all, and in a multi-cylinder internal combustion engine, to achieve an optimal operating condition for each cylinder. It is to provide a control method.

[Means for solving problems]

In order to achieve this object, a compression ratio control method for an internal combustion engine with a variable compression ratio mechanism according to the present invention is a compression ratio control method for an internal combustion engine with a variable compression ratio mechanism capable of switching a compression ratio between a high compression ratio and a low compression ratio. When the output signal of the combustion pressure sensor exceeds the first set pressure value indicating that the risk of knocking is increasing, the compression ratio is switched to the low compression ratio side, and the output of the combustion pressure sensor If the signal falls below the second set pressure value indicating that knocking does not occur even if the compression ratio is increased, the compression ratio is switched to the high compression ratio side.

[Work]

In such a compression ratio control method, the combustion pressure is adopted as a representative value that best represents the combustion state, and the combustion pressure is the first set pressure value, that is, there is a risk of knocking due to changes in the load and the rotational speed. When the pressure value representing the increase is exceeded, the compression ratio is switched to the low compression ratio side, and the knocking is efficiently and reliably prevented without actually causing the knocking. Further, when the combustion pressure falls below the second set pressure value, that is, the pressure value that represents a region in which knocking does not occur even if the compression ratio is increased, the combustion pressure is switched to the high compression ratio side and knocking occurs. It is possible to switch to an operating state in which fuel efficiency is high without generating any. Therefore, the engine is constantly controlled to be switched to the operating state with the highest combustion efficiency that does not cause knocking according to the combustion state.

Also, if this control is adopted for each cylinder of a multi-cylinder internal combustion engine, it becomes possible to control to an optimum operating state according to the cylinder state for each cylinder, and the most efficient and optimum engine as a whole can be controlled. A good driving condition can be obtained.

〔Example〕

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

FIG. 1 shows a control flow of a compression ratio control method according to an embodiment of the present invention, and FIGS. 2 to 4 show a schematic configuration of an apparatus when the method is applied to a multi-cylinder internal combustion engine.

First, the compression ratio variable mechanism shown as one embodiment in FIGS. 3 and 4 will be described.

In the figure, 1 is a cylinder block, 2 is a piston, 3
Is a connecting rod, and 4 is a piston pin. Between the piston pin insertion hole 5 at the small end of the connecting rod 3 and the outer circumference of the piston pin 4, the wall thickness changes in the circumferential direction, and the inner circumference circle and the outer circumference circle are eccentric to each other. An eccentric bearing 6 composed of a body is rotatably interposed.

A lock pin housing hole 7 extending in a radial extension line of the eccentric bearing 6 is formed at a position of the connecting rod 3 corresponding to the eccentric bearing 6, and the lock pin 8 is slidably provided in the hole 7. Is accommodated in the eccentric bearing 6 so as to be retractable. On the other hand, the eccentric bearing 6
Has a lock pin engaging hole 9 having a diameter that allows the lock pin 8 to be projected and retracted in a portion having a large radial thickness. When the lock pin 8 is engaged with the lock pin engaging hole 9, the piston 2 Is set to a high position with respect to the connecting rod 3 and has a high compression ratio, and when the engagement by the lock pin 8 is released, the eccentric bearing 6 freely rotates, and the piston 2 becomes a low position at the compression top dead center. A low compression ratio state can be revealed.

The lock pin 8 is driven by the pressure oil of the lubricating oil sent from the cylinder block via the oil passage.

A lock pin lock hydraulic passage 10 and a lock pin unlock hydraulic passage 11 are connected to the lock pin storage hole 7 with the lock pin 8 interposed therebetween, and the lock pin lock hydraulic passage 10 connects the lock pin 8 to the eccentric bearing 6 direction. It is opened at the position where it is biased. Further, as shown in FIG. 4, a lock pin guide groove 12 extending in the circumferential direction is formed on the outer periphery of the eccentric bearing 6 at a position corresponding to the lock pin 8, and the groove 12 has the lock pin engaging groove. A fitting hole 9 is provided.

The hydraulic passage 1 provided in the connecting rod 3
Nos. 0 and 11 communicate with oil grooves 13 and 14 provided independently of each other on the bearing circumference at the large end of the connecting rod. The oil grooves 13 and 14 are the crankshaft 1
5, an oil groove 17 independently provided on the circumference of the journal bearing of the crankshaft through an oil passage 16 in
The crankshaft 15 is connected to the shaft 18 so that the crankshaft 15 can communicate with the shaft 18 intermittently. The oil groove 17 can communicate with the lock pin lock hydraulic passage 10 through the oil groove 13, and the oil groove 18 can communicate with the lock pin unlock hydraulic passage 11 through the oil groove 14.

A high compression ratio main oil passage 19 and a low compression ratio main oil passage 20 are provided in the cylinder block 1. The high compression ratio main oil passage 19 is communicated with the oil groove 17 and has a low compression ratio. Main oil passage 20 for the oil groove 18
Is in communication with. The oil pumped up by the oil pump is sent to either the high compression ratio main oil passage 19 or the low compression ratio main oil passage 20 so that switching of the compression ratio can be controlled.

Next, FIG. 2 will be described.

In each cylinder of the multi-cylinder internal combustion engine (four cylinders in this embodiment),
Combustion pressure sensors 21a, 21b, 21c, 21d for detecting the combustion pressure in each combustion chamber are provided. The combustion pressure sensors 21a, 21b, 21c, 21
d is a CPU 22a, 22b having an independent arithmetic function,
22c and 22d are respectively connected, and the output signals of the combustion pressure sensors 21a, 21b, 21c and 21d are input. Each CPU 22a, 22b, 22c,
From 22d, a signal is sent to the aforementioned compression ratio variable mechanism,
The compression ratio switching control is performed for each of the cylinders # 1, # 2, # 3, and # 4.

Using the apparatus thus configured, the method of the present invention is carried out as follows.

FIG. 1 shows a control flow for carrying out the compression ratio control method of the present invention. This flow chart shows an interrupt routine executed for each cycle of each cylinder.

First, it is determined whether the current compression ratio state is the high compression ratio side or the low compression ratio side. This is determined by, for example, the signal of the compression ratio control system.

Next, when the high compression ratio state is determined, it is determined by the output signals of the combustion pressure sensors 21a, 21b, 21c, 21d whether the combustion maximum pressure is equal to or higher than the first set pressure value. Here, the first set pressure value is given as a value representing that the risk of knocking is increasing due to changes in the load and the number of revolutions. In other words, there is a risk of knocking if the pressure is further increased. Accordingly, when the determination is YES, the compression ratio is switched to the low compression ratio side and the compression ratio is lowered.

Further, when it is determined that the compression ratio is low, the combustion pressure is set to the second value.
It is determined whether the pressure is equal to or less than the set pressure value of. Here, the second set pressure value is given as a value representing a region in which knocking does not occur even if the compression ratio is increased. This makes Y
If it is determined to be ES, the high compression side is switched to, and the compression ratio is increased.

In order to explain this compression ratio switching control in more detail,
This is shown in FIGS. 5 and 6. FIG. 5 shows a general combustion pressure change state with respect to the crank angle, and the maximum combustion pressure is normally reached at a point slightly above the top dead center (TDC). This maximum combustion pressure is the combustion pressure sensors 21a, 21b, 21.
It is detected for each cylinder by c and 21d.

FIG. 6 shows the relationship between the engine load and the combustion pressure in the high compression ratio state A and the low compression ratio state B, respectively. Then, the above-mentioned first set pressure value is set as the P ₁ point, and is set as a point where knocking may occur if the load further increases in the high compression ratio state. On the other hand, the second set pressure value is set as point P ₂ , and at that time, there is no risk of knocking even if the low compression ratio state is switched to the high compression ratio side. In this embodiment, a slight hysteresis is given to the switching control characteristic of the compression ratio at the points P ₁ and P ₂ as shown in the figure.

As shown in FIG. 6, in the high compression ratio state A, the combustion pressure is P
_{When the number of} points exceeds ₁ , it can be switched to the low compression ratio B side.
Entry into the area C where knocking may occur is prevented in advance. Further, when the combustion pressure falls below the P ₂ point in the low compression ratio state B, the combustion pressure is switched to the high compression ratio A side, so that combustion efficiency is improved without causing knocking.

Then, this control is performed for each cylinder # 1, # as in the present embodiment.
If performed for each of # 2, # 3, and # 4, the compression ratio for each cylinder is controlled to an optimal operating state in which knocking does not occur and combustion efficiency is highest.

〔The invention's effect〕

According to the present invention, the switching of the compression ratio is performed according to the combustion pressure that is the value that most represents the operating state of the cylinder, and it is possible to always aim for the most efficient operating state within the knocking occurrence limit. Therefore, there is an effect that the compression ratio switching control can be performed so that the engine can exhibit the optimum combustion efficiency without causing knocking at all.

Further, if the present invention is applied to a multi-cylinder internal combustion engine, it is possible to aim for the highest combustion efficiency by controlling knocking for each cylinder, and it is possible to always control the engine as an optimum operating state.

[Brief description of drawings]

FIG. 1 is a flow chart of control for carrying out a method according to an embodiment of the present invention, FIG. 2 is a schematic configuration diagram of an engine when the present invention is applied to a multi-cylinder internal combustion engine, and FIG. 3 is a compression ratio. FIG. 4 is a partial vertical sectional view of the engine showing an example of the variable mechanism, FIG. 4 is a partial vertical sectional view of the engine as viewed from the direction perpendicular to the apparatus of FIG. 3, and FIG. 5 is a relationship diagram between combustion pressure and crank angle. The figure is a diagram showing the relationship between engine load and combustion pressure, showing compression ratio switching control. 2 …… Piston 3 …… Connecting rod 4 …… Piston pin 6 …… Eccentric bearing 8 …… Lock pin 10 …… Lock pin Lock hydraulic passage 11 …… Lock pin Unlock hydraulic passage 19 …… High compression ratio main Oil passage 20 ... Main oil passage for low compression ratio 21a, 21b, 21c, 21d ... Combustion pressure sensor 22a, 22b, 22c, 22d ... CPU A ... Characteristics at high compression ratio B ... Low compression ratio In case of C: Area where knocking may occur

Claims (2)

[Claims] 1. A method of controlling a compression ratio of an internal combustion engine with a variable compression ratio mechanism capable of switching a compression ratio between a high compression ratio and a low compression ratio, the risk of knocking the output signal of a combustion pressure sensor increases. When the pressure exceeds the first set pressure value indicating that the compression ratio is switched to the low compression ratio side, and there is no risk of knocking even if the output signal of the combustion pressure sensor increases the compression ratio. The compression ratio control method for an internal combustion engine with a variable compression ratio mechanism is characterized in that the compression ratio is switched to a higher compression ratio side when the set pressure value is decreased. 2. The internal combustion engine is a multi-cylinder internal combustion engine, the combustion pressure sensor is provided for each cylinder, and switching between the low compression ratio side and the high compression ratio side is controlled for each cylinder. A compression ratio control method for an internal combustion engine with a variable compression ratio mechanism according to claim 1.