JP2022063697A - Internal combustion engine - Google Patents

Abstract

To improve knocking resistance while curbing a reduction in filling efficiency.SOLUTION: In an internal combustion engine comprising an intake valve (1) and a valve activation device (5) which activates the intake valve (1), the valve activation device (5) causes the intake valve (1) to have lift characteristics where an upward crank angle period from a start crank angle (IVO) which is a commencement of a valve opening action to a central angle which maximizes a lift amount is identical with a downward crank angle period from the central angle to an end crank angle (IVC) which is a termination of the valve opening action and a time area obtained by integrating the lift amount of the intake valve (1) with respect to the crank angle period is smaller in the downward crank angle period than in the upward crank angle period.SELECTED DRAWING: Figure 2

Description

The present invention relates to an internal combustion engine.

It is known to improve the filling efficiency as a measure for improving the output of the internal combustion engine. In order to improve the filling efficiency, it is effective to increase the size of the intake valve or increase the lift amount. However, since the combustion chamber has dimensional restrictions, if the intake valve is made larger, the exhaust valve must be made smaller. That is, increasing the size of the intake valve may lead to a decrease in exhaust efficiency. If the lift amount is increased, the intake valve and the exhaust valve may interfere with each other during the valve overlap period. Further, if the lift amount is increased, a large valve recess is required to avoid interference between the intake valve and the piston, which may lead to a decrease in the compression ratio.

Patent Document 1 discloses a lift amount and lift characteristics for solving these problems and improving the filling efficiency. Specifically, it is disclosed that the lift amount is set to the maximum lift amount that can avoid the interference between the intake valve and the exhaust valve and the increase in the size of the valve recess. Regarding the lift characteristics, the lift curve for the exhaust valve should be asymmetrical with the maximum lift position biased toward the advance angle side, and the lift curve for the intake valve should be asymmetrical with the maximum lift position biased toward the retard angle side. Is disclosed.

Patent No. 6398548

However, if the lift curve of the intake valve is set as described in the above document, the filling efficiency is improved, but the in-cylinder temperature at the compression top dead center becomes high, so that knocking is likely to occur. In order to avoid knocking, it is necessary to take measures that lead to a decrease in output, such as a retardation angle of the ignition timing. That is, according to the above document, although the filling efficiency is improved, the knocking resistance is lowered, and as a result, the output may not be improved.

Therefore, an object of the present invention is to improve knocking resistance while suppressing a decrease in filling efficiency.

According to an aspect of the present invention, there is provided an internal combustion engine including an intake valve and a valve operating device for driving the intake valve. In this internal combustion engine, the lift characteristics of the intake valve by the valve operating device are the ascending period, which is the crank angle period from the starting crank angle, which is the start of the valve opening operation, to the central angle, which is the maximum lift amount, and the valve opening from the central angle. The time obtained by integrating the lift amount of the intake valve with the crank angle period, which is equal to the descent period, which is the crank angle period to the end crank angle, which is the end of the operation, and the descent period is larger than the ascending period. It is characterized by having a small area and a first lift characteristic.

According to the above aspect, the knocking resistance can be improved while suppressing the decrease in the filling efficiency.

FIG. 1 is a schematic configuration diagram of an intake valve and a valve operating device. FIG. 2 is a lift curve diagram showing the lift characteristics of the intake valve according to the first embodiment. FIG. 3 is a diagram showing the relationship between the crank angle and the in-cylinder temperature. FIG. 4 is a lift curve diagram showing the lift characteristics of the intake valve according to the second embodiment. FIG. 5 is an operating area map for explaining the switching of the lift characteristics in the third embodiment.

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

[First Embodiment]
The first embodiment will be described with reference to FIGS. 1 to 3. The internal combustion engine according to the present embodiment is a spark-ignition 4-cycle engine having one or more cylinders. An intake port and an exhaust port are open in the combustion chamber of the internal combustion engine. An intake valve 1 and an exhaust valve (not shown) are arranged at the openings of the intake port and the exhaust port, respectively.

FIG. 1 is a schematic configuration diagram of an intake valve 1 and a valve operating device 5 for driving the intake valve 1.

The intake valve 1 includes a valve head 1A that opens and closes an opening of an intake port, and a rod-shaped valve stem 1B in which a valve head 1A is arranged at one end.

The valve operating device 5 has a camshaft 2 that is rotationally driven by the power of an internal combustion engine, a valve lifter 3 that is in contact with the camlob 2A and converts the rotational motion of the camshaft 2 into reciprocating motion, and an intake valve 1 in the valve closing direction. It is configured to include a valve spring 4 for urging a force. A cam lob 2A is integrally formed on the cam shaft 2. The shape of the cam lob 2A in FIG. 1 shows that of a general internal combustion engine for the sake of simplicity.

FIG. 1 shows a state in which the intake valve 1 is closed. When the camshaft 2 rotates in the direction of the arrow in the drawing from this state, the intake valve 1 remains closed while the base circle portion of the camlob 2A and the valve lifter 3 are in contact with each other. Then, when the contact portion with the valve lifter 3 becomes a portion protruding from the base circle of the cam lob 2A, the pressing force by the cam lob 2A overcomes the elastic force of the valve spring 4, the valve lifter 3 is pressed, and the intake valve 1 is opened. As the camshaft 2 continues to rotate, the lift amount of the intake valve 1 continues to increase until the amount of protrusion of the camlob 2A from the base circle becomes maximum, and then decreases. The lift amount is reduced because the valve lifter 3 is pressed against the cam lob 2A by the elastic force of the valve spring 4. After that, when the contact portion with the valve lifter 3 becomes the base circle again, the intake valve 1 is closed.

In the present embodiment, the rotary motion of the cam lob 2A is converted into a reciprocating motion by the valve lifter 3 to press the valve stem 1B, but the so-called direct-acting valve valve device 5 is used, but the present invention is not limited to this. .. For example, it may be an internal combustion engine of a type in which the rotary motion of the cam lob 2A is converted into a swing motion by using a so-called rocker arm to press the valve stem 1B.

The change in the lift amount of the intake valve 1 according to the rotation of the camshaft 2 described above, that is, the lift characteristic depends on the shape of the cam lob 2A (hereinafter, also referred to as a cam profile).

FIG. 2 is a lift curve diagram showing the lift characteristics of the intake valve 1. The horizontal axis of FIG. 2 is the crank angle, and the vertical axis is the lift amount. The solid line in FIG. 2 shows the lift curve according to the lift characteristic (first lift characteristic) of the present embodiment, the broken line shows the lift curve according to the lift characteristic of the modified example of the present embodiment, and the alternate long and short dash line shows the comparative example. The lift curve is shown according to the lift characteristics. The modified examples are included in the scope of the present invention as in the present embodiment, whereas the comparative examples are not included in the same scope.

The general lift characteristics are intermediate (central angle in the figure) from the beginning of the valve opening operation (IVO in the figure) to the end of the valve opening operation (IVC in the figure) of the intake valve 1 as in the comparative example. The maximum lift amount is obtained, and the lift curve from the IVO to the central angle and the lift curve from the central angle to the IVC are symmetric with respect to the central angle. That is, the length of the ascending period from the IVO to the central angle is equal to the length of the descending period from the central angle to the IVC, and the lift amount of the intake valve 1 is integrated with the crank angle period between the ascending period and the descending period. The time areas obtained by this are equal.

On the other hand, in the lift characteristics of the present embodiment, the ascending period and the descending period have the same length, but the time area is smaller in the descending period than in the ascending period. In other words, the lift curve during the down period has a thinner shape than the lift curve during the up period.

The effect of having the lift characteristics as described above will be described with reference to FIG.

FIG. 3 is a diagram showing the relationship between the in-cylinder temperature and the crank angle for each lift characteristic of the intake valve 1 obtained by simulation. Similar to FIG. 2, the solid line shows the lift characteristic of the present embodiment, the broken line shows the lift characteristic of the modified example, and the alternate long and short dash line shows the lift characteristic of the comparative example. The crank angle C1 in the figure is the ignition timing.

This simulation was performed at the same engine speed and filling efficiency for all lift characteristics. The filling efficiency was adjusted to be the same by changing the supercharging efficiency of the turbocharger.

As shown in FIG. 3, in the entire crank angle region including the crank angle C1, the in-cylinder temperature has a relationship of the present embodiment <modification example <comparative example. That is, by setting the lift characteristics of the present embodiment and the modified example, the in-cylinder temperature is lower than the lift characteristics of the comparative example at the ignition timing and its vicinity.

This is because the situation is similar to the case of early closing of the intake valve that advances the IVC in order to reduce the effective compression ratio during the descent period, and the amount of intake air during the descent period decreases compared to the comparative example. Considered. However, in the lift characteristic of the present embodiment, the length from the central angle to the IVC is the same as the length from the IVO to the central angle as in the lift characteristic of the comparative example. This is because changing the IVC has a large effect on the intake air amount, and when the IVC is advanced as in the case of premature closing of the intake valve, the intake air amount is significantly reduced. That is, in the lift characteristic of the present embodiment, it is possible to suppress a decrease in filling efficiency as compared with the case where the intake valve is closed prematurely. The length from the central angle to the IVC and the length from the IVO to the central angle do not have to be exactly the same, but may be substantially the same.

As described above, according to the lift characteristics of the present embodiment, the ignition timing and the in-cylinder temperature in the vicinity thereof can be lowered as compared with the lift characteristics of the comparative example. The fact that the temperature inside the cylinder decreases means that knocking is less likely to occur. Further, the fact that knocking is unlikely to occur means that there is a margin for advancing the ignition timing. That is, by adopting the lift characteristics of the present embodiment, it is possible to suppress the occurrence of knocking while ensuring the filling efficiency, and further, by the amount that the occurrence of knocking is suppressed, the ignition timing is advanced to the internal combustion engine. It is also possible to improve the output.

The degree to which the lift curve is thinned is determined in consideration of the susceptibility to knocking and the amount of decrease in filling efficiency. The susceptibility to knocking depends on the bore diameter of the cylinder and the size of the geometric compression ratio. Therefore, for example, depending on the size of the geometric compression ratio, even with the lift characteristics of the modified example in which the lift curve in the descent period is not as thin as in the present embodiment, the effects of suppressing the occurrence of knocking and improving the output can be sufficiently obtained. There is also.

As described above, according to the present embodiment, the intake valve 1 and the valve operating device 5 for driving the intake valve 1 are provided, and the lift characteristic of the intake valve 1 by the valve operating device 5 is the start of the valve opening operation. The ascending period, which is the crank angle period from the start crank angle (IVO) to the central angle, which is the maximum lift amount, and the descending period, which is the crank angle period from the central angle to the end crank angle (IVC), which is the end of the valve opening operation. The internal combustion characteristic is that the time area obtained by integrating the lift amount of the intake valve 1 with the crank angle period is smaller in the descending period than in the ascending period. The institution is provided. By setting the first lift characteristic, the in-cylinder temperature at the ignition timing and its vicinity can be lowered as compared with the conventional lift characteristic in which the time areas of the ascending period and the descending period are equal, so that the knocking resistance can be improved. Further, during the descent period, although the time area is small, the IVC is not advanced. That is, the crank angle period from the central angle to the IVC remains equal to the crank angle period from the IVO to the central angle in the ascending period. As a result, although the filling efficiency is reduced by reducing the time area, the amount of reduction can be suppressed.

[Second Embodiment]
The second embodiment will be described with reference to FIG.

In this embodiment, the basic configuration of the internal combustion engine is the same as that in the first embodiment, but the lift characteristic (first lift characteristic) of the intake valve 1 is different from that in the first embodiment. More specifically, the lift characteristics in the down period are the same as those in the first embodiment, but the lift characteristics in the up period are different. Hereinafter, this difference will be mainly described.

FIG. 4 is a lift curve diagram showing the lift characteristics of the intake valve 1. The horizontal axis of FIG. 4 is the crank angle, and the vertical axis is the lift amount. The solid line in FIG. 4 shows the lift characteristics of the first embodiment, the one-dot chain line shows the lift characteristics of the comparative example, and the two-dot chain line shows the lift characteristics of the present embodiment. The lift curve during the ascending period of the comparative example is as shown by the solid line. The lift curve of the descent period of the present embodiment is the same as that of the first embodiment, that is, as shown by the solid line.

As shown in FIG. 4, the lift curve of the ascending period of the present embodiment is thicker than the lift curve of the ascending period of the first embodiment. That is, the time area of the ascending period according to the lift characteristics of the present embodiment is larger than the time area of the ascending period due to the lift characteristics of the first embodiment and the comparative example.

Reducing the time area during the descent period is a factor that reduces the filling efficiency and the gas flow strength in the cylinder. However, according to the present embodiment, since the time area during the ascending period is increased, it is possible to compensate for the decrease in the filling efficiency and the gas flow strength in the cylinder.

Here, the shape of the lift curve based on the lift characteristics of the comparative example will be described.

The lift curve of the comparative example has an upper limit shape that can ensure functional reliability on the premise that the lift curve in the ascending period and the lift curve in the descending period are symmetrical with respect to the central angle. The term "ensuring functional reliability" as used herein means that the intake valve 1 does not jump or bounce. Further, the "upper limit shape" refers to a shape in which the maximum intake air amount can be obtained while ensuring the functional reliability, in other words, the functional reliability is ensured and the time area is maximized.

That is, the lift curve immediately after the IVO in the ascending period in the comparative example is symmetrical with the lift curve immediately before the IVC for preventing bounce. Therefore, the rate of increase in the lift amount immediately after the IVO is limited to prevent bounce during the descent period, although there is room for increasing it because it is not necessary to consider bounce in the valve opening operation.

On the other hand, when the lift curve is asymmetrical between the ascending period and the descending period as in the present embodiment, the rate of increase in the lift amount immediately after the IVO is set as shown by the two-dot chain line in FIG. There is no problem even if it is larger than the increase rate determined from the viewpoint of ensuring functional reliability. In the lift characteristic of the present embodiment, the period near the maximum lift amount during the ascending period is longer than that of the comparative example, so that the jump is less likely to occur.

As described above, according to the present embodiment, the time area of the ascending period of the first lift characteristic is the same as the start crank angle (IVO), the end crank angle (IVC) and the maximum lift amount, and the maximum lift amount is the same as that of the first lift characteristic. Assuming that the lift characteristics of the ascending period and the lift characteristics of the descending period are symmetrical with respect to the central angle, the time area of the ascending period of the upper limit lift characteristics (comparative example above) that can ensure functional reliability. A larger internal combustion engine is provided. As a result, the knocking resistance can be improved as in the first embodiment, and further, by increasing the intake air amount in the ascending period, the filling efficiency is lowered due to the decrease in the intake air amount in the descending period, and the in-cylinder gas flow strength is reduced. Can be compensated for.

[Third Embodiment]
The third embodiment will be described with reference to FIG.

The internal combustion engine of the present embodiment is different from the first embodiment in the configuration and function of the valve operating device 5. Hereinafter, this difference will be mainly described.

The valve timing device 5 of the present embodiment has a so-called variable valve timing mechanism that switches between two lift characteristics. Then, the controller (not shown) switches between the two lift characteristics according to the operating state. The operating state referred to here is the engine speed and the engine load.

A known variable valve mechanism is used to switch between the two lift characteristics. For example, a mechanism for driving an intake valve 1 via a rocker arm, wherein the camshaft 2 has a plurality of camlobs 2A having different profiles, and the rocker arm is similar to that disclosed in Japanese Patent Application Laid-Open No. 10-121916. Uses a mechanism in which the camlob 2A that follows is hydraulically switched.

In the present embodiment, the first lift characteristic of the first embodiment or the second embodiment and the second lift characteristic described as a comparative example in the first embodiment and the like are switched according to the operating state.

FIG. 5 is an operating area map of an internal combustion engine. The vertical axis is the net mean effective pressure (BMEP) as the engine load, and the horizontal axis is the engine speed. The parameter corresponding to the engine load is not limited to the net average effective pressure, and may be, for example, the accelerator pedal opening degree.

In the low load region, knocking is unlikely to occur, and the output of the internal combustion engine is mainly limited by the amount of gas that can be inhaled. That is, the higher the filling efficiency, the higher the output of the internal combustion engine.

On the other hand, knocking is likely to occur in a high load region, so that the output of the internal combustion engine is limited to avoid knocking. That is, even if the filling efficiency is increased, the output is limited by performing the ignition timing retard angle or the like in order to avoid knocking.

Therefore, in the present embodiment, the second lift characteristic which is advantageous from the viewpoint of filling efficiency is used in the low load region, and the first lift characteristic which is advantageous from the viewpoint of avoiding knocking is used in the high load region. That is, the controller identifies the current operating point from the engine load and engine rotation speed detected using various sensors, etc., selects the first lift characteristic if the operating point is in the high load region, and is in the low load region. If so, select the second lift characteristic.

Here, the separation between the high load region and the low load region will be described.

The high load region, the low load region, and the boundary are set in advance based on the results of experiments and the like. Specifically, it is set by the following method.

As described above, the low load region is a region where the second lift characteristic which is advantageous from the viewpoint of filling efficiency is used, and the high load region is a region where the first lift characteristic which is advantageous from the viewpoint of avoiding knocking is used. Therefore, the internal combustion engine is operated while changing the operating state with the second lift characteristic selected, and vibration is detected by a knock sensor (not shown) in each operating state. The region where the detected vibration level does not exceed the preset knock limit is defined as the low load region, and the region where the detected vibration level exceeds the preset knock limit is defined as the high load region.

As described above, in the present embodiment, the valve operating device 5 has the first lift characteristic and the second lift characteristic in which the lift characteristic in the ascending period and the lift characteristic in the descending period are symmetrical with respect to the central angle. An internal combustion engine that switches according to the conditions is provided. As a result, in addition to the same effects as in the first embodiment, the intake valve 1 can be further driven with lift characteristics more suitable for the operating state of the internal combustion engine. That is, in the operating region where the knocking resistance becomes the bottleneck of the performance of the internal combustion engine, the occurrence of knocking is suppressed by setting the first lift characteristic, and in the operating region where the intake air amount becomes the bottleneck of the performance of the internal combustion engine. The intake air amount can be secured by making the two-lift characteristic.

In the present embodiment, the ascending period of the first lift characteristic and the ascending period of the second lift characteristic may have the same lift curve, and the ascending period of the first lift characteristic is the ascending period of the second lift characteristic. The time area may be larger than that. Which of the above is selected as the first lift characteristic is arbitrary, and is selected according to, for example, the maximum torque in the design of the internal combustion engine.

It is needless to say that the present invention is not limited to the above-described embodiment, and various changes can be made within the scope of the technical idea described in the claims.

1 Intake valve 2 Camshaft 3 Valve lifter 4 Valve spring 5 Valve system

Claims (5)

Intake valve and
The valve operating device that drives the intake valve and
In an internal combustion engine equipped with
The lift characteristics of the intake valve by the valve operating device
The ascending period, which is the crank angle period from the start crank angle, which is the start of the valve opening operation, to the central angle, which is the maximum lift amount, and the crank angle period, which is the end crank angle from the central angle to the end of the valve opening operation. The first lift characteristic is equal to a certain descent period, and the descent period has a smaller time area obtained by integrating the lift amount of the intake valve with the crank angle period than the ascending period. An internal combustion engine characterized by. In the internal combustion engine according to claim 1,
The time area of the ascending period of the first lift characteristic is
The start crank angle, the end crank angle, and the maximum lift amount are the same as the first lift characteristic, and the lift characteristic in the ascending period and the lift characteristic in the descending period are symmetrical with respect to the central angle. An internal combustion engine that is larger than the time area of the ascending period of the upper limit lift characteristic that can ensure functional reliability, if assumed. In the internal combustion engine according to claim 1 or 2.
The valve operating device switches between the first lift characteristic, the lift characteristic in the ascending period, and the second lift characteristic in which the lift characteristic in the descending period is symmetrical with respect to the central angle, depending on the operating state. institution. In the internal combustion engine according to claim 3,
An internal combustion engine in which the ascending period of the first lift characteristic and the ascending period of the second lift characteristic have the same lift curve. In the internal combustion engine according to claim 3,
An internal combustion engine having a larger time area in the ascending period of the first lift characteristic than in the ascending period of the second lift characteristic.

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