JPH11117779A - Variable compression ratio mechanism for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable compression ratio mechanism for an internal combustion engine capable of accurately variably controlling a compression ratio in a combustion chamber in a simpler structure. SOLUTION: A piston 12 provided in an engine 11 is formed with a piston mainbody 22 and a head 23. The head 23 is rotatably connected to the piston mainbody 22 with its female screw portion 23a threaded to the male screw portion 22a of the piston mainbody 22. A magnet 24 is arranged on the upper face of the head 23. The head 23 is rotationally moved by electrifying magnets 25a-25d, 26a-26d, 27a-27d and 28a-28d in a gasket 15 provided in the engine 11 at preset timings by a controller 31. The head 23 is moved up and down by the screw operation of the head 23 to vary a compression ratio in the combustion chamber 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable compression ratio mechanism for an internal combustion engine that varies a compression ratio in a combustion chamber of the internal combustion engine in accordance with an operation state of the internal combustion engine.

[0002]

2. Description of the Related Art Generally, in an internal combustion engine, when the compression ratio in a combustion chamber is increased, the combustion pressure is increased, the thermal efficiency is increased, and the output is improved. However, on the other hand, if the compression ratio is excessively increased, the combustion pressure becomes too high, which causes knocking. On the other hand, the combustion pressure generated in the combustion chamber is different between the low load and medium load operation states and the high load operation state, and the combustion pressure in the high load operation state is higher than the combustion pressure in the low load and medium load operation states. Become. Therefore, usually, the occurrence of knocking in a high-load operation state is prevented by setting a lower compression ratio in the combustion chamber.

[0003] However, setting the compression ratio in the combustion chamber in accordance with the high load operation state inevitably lowers the output performance at low load and medium load. Generally, the improvement of the knocking resistance and the improvement of the output performance are incompatible with each other.

Therefore, conventionally, for example, JP-A-63-186
As in the variable compression ratio mechanism described in Japanese Patent Application Laid-Open No. 926, the compression ratio is made variable to achieve both anti-knock performance and output performance. Incidentally, in this variable compression ratio mechanism, a hydraulic mechanism is provided on the piston, and the compression ratio is changed by changing the height of the piston by the hydraulic mechanism. Therefore, according to the variable compression ratio mechanism,
When the engine load is low or the engine speed is low, the compression ratio can be increased to increase the output, and when the engine load is high or the engine speed is high, the compression ratio can be reduced to prevent knocking. Become like

[0005]

As described above, it is possible to achieve both the antiknock performance and the output performance by making the compression ratio variable. However, in the above-mentioned conventional variable compression ratio mechanism, a hydraulic mechanism is used. Since the height of the piston is made variable by using the structure, the structure is complicated and the cost is increased. Further, since the characteristics of the hydraulic pressure change depending on the temperature, the hydraulic characteristics are likely to vary, and it is difficult to finely adjust the compression ratio. In addition, a high-performance pump and hydraulic circuit capable of supplying and maintaining a hydraulic pressure against the combustion pressure are required.

The present invention has been made in view of such circumstances, and has as its object to provide a variable compression ratio of an internal combustion engine capable of more accurately adjusting the compression ratio in a combustion chamber with a simpler configuration. It is to provide a mechanism.

[0007]

To achieve the above object, according to the first aspect of the present invention, the compression ratio in the combustion chamber is increased by moving the piston head relative to the piston body in the direction of movement. In the variable compression ratio mechanism of the internal combustion engine, the head portion of the piston has a plurality of magnets on a peripheral edge thereof and is screwed to the piston body, and generates a magnetic field in the combustion chamber by energization. The gist of the invention is that the head unit moves relative to the piston body in the direction of movement of the head unit by the rotation of the head unit based on the guidance of the magnetic field generated by the magnetic field generation unit.

According to such a configuration, the head can be relatively moved with a relatively small force, and fine adjustment of the compression ratio is also facilitated. In addition, the configuration is simplified as compared with a variable compression ratio mechanism using hydraulic pressure.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a sectional view showing a variable compression ratio mechanism of the present embodiment, and FIG. 2 is a schematic plan view for explaining the operation of the variable compression ratio mechanism. As shown in FIG. 1, a piston 12 is provided on a cylinder block 11a of the engine 11 so as to be reciprocally movable.
Through a crankshaft 14 which is an output shaft of the engine 11. The reciprocating movement of the piston 12 is converted into rotation of the crankshaft 14 by the connecting rod 13.

A cylinder head 16 is provided at an upper end of the cylinder block 11a via a gasket 15, and a combustion chamber 17 is formed between the cylinder head 16 and the piston 12. The cylinder head 16 is provided with an intake port 18 and an exhaust port 19 communicating with the combustion chamber 17, and the intake port 18 and the exhaust port 19 are provided with an intake valve 20 and an exhaust valve 21, respectively. These intake valves 20
The exhaust valve 21 is opened and closed by a cam (not shown) to communicate and shut off the intake port 18 and the combustion chamber 17 and the exhaust port 19 and the combustion chamber 17 respectively. Also,
An ignition plug 29 is disposed on the cylinder head 16 so as to be exposed to the combustion chamber 17.

In the engine 11 having such a structure, four strokes of intake, compression, combustion / expansion, and exhaust are performed in the combustion chamber 17 in order to obtain the power. First, in the intake stroke, the mixed gas is sucked into the combustion chamber 17 through the intake port 18 by opening the intake valve 20 and moving down the piston 12.
Next, in the compression stroke, the piston 12 that has reached the bottom dead center moves upward together with the closing of the intake valve 20, whereby the volume of the combustion chamber 17 is reduced, and the mixed gas filled in the combustion chamber 17 is compressed. Is done. In the subsequent combustion / expansion process, a spark is ignited from the ignition plug 29, and the compressed mixed gas is ignited. Thereby, the mixed gas in the combustion chamber 17 explodes, and the piston 12 is pushed down in the direction of the bottom dead center by the combustion expansion of the mixed gas, so that power is applied to the engine 11. Then, in the exhaust stroke, the mixed gas after combustion is sent out from the exhaust port 19 as exhaust gas with the opening of the exhaust valve 21 and the upward movement of the piston 12.

On the other hand, the piston 12 comprises a piston body 22 and a head 23. A male screw part 22a is formed at the upper end of the piston body 22, and a female screw part 2 corresponding to the male screw part 22a is formed at the lower end of the head part 23.
3a are formed. And the above-mentioned head part 23
The female screw portion 23a is engaged with the piston main body 22 so as to rotate and move up and down by being screwed to the male screw portion 22a. Further, a magnet (permanent magnet) 24 is provided on the upper surface of the head portion 23. As shown in detail in FIG. 2, four magnets 24 are arranged on the outer edge of the upper surface of the head portion 23 at 90 ° intervals. At this time, the magnets adjacent to each other are arranged so as to have different polarities toward the outer edge of the head portion. That is, the magnets 24a and 24c
The poles and the magnets 24b and 24d are arranged to be S poles.

As shown in FIG. 2, the gasket 15 has electromagnets 25a to 25g as a magnetic field generating mechanism.
25d, 26a-26d, 27a-27d, 28a-2
8d are arranged at equal intervals. Electromagnet 25
The coils wound around a to 25d are respectively connected in series and connected to the control device 31. Similarly, the other electromagnets 26a to 26d, 27a to 27d, 28
The coils wound around a to 28d are also connected in series and connected to the control device 31 (not shown). In addition, each said electromagnet 25a-25d, 26a-26d, 2
Each of the coils 7a to 27d and 28a to 28d has an S pole on the head portion 23 side of the electromagnets 25a to 28a and 25c to 28c when a current I is applied to the respective coils in the arrow direction shown in FIG. , Electromagnets 25b to 28b, 25d to 2
8d is wound on the side of the head section 23 so that the N pole is excited (electromagnets 26a to 26d, 27a to 27).
d, 28a to 28d are not shown).

Next, the operation and action of the variable compression ratio mechanism of the present embodiment having the above-described configuration will be described with reference to FIGS. 3 (a) and 3 (b)
FIG. 4 is a schematic diagram schematically showing an operation state of the variable compression ratio mechanism of the present embodiment, FIG. 4 is a time chart showing energization timing for each electromagnet, and FIG. 5 schematically shows a movement amount of the head unit. It is a schematic diagram.

First, as shown in FIG. 2, the control device 31 controls the electromagnets 25a to 25d by the control device.
A current I is applied to each coil in the direction of the arrow shown in FIG.
Thereby, the head 23 of the electromagnets 25a and 25c is
The S pole is excited on the side, and the N pole is excited on the head 23 side of the electromagnets 25b and 25d. Therefore, at a predetermined crank angle near the top dead center of the piston 12, the magnets 24a, 24c are attracted to the electromagnets 25a, 25c, and the magnets 24b, 24d are attracted to the electromagnets 25b, 25d.
24d is drawn.

Next, the control device 31 causes the coils of the electromagnets 25a to 25d to be energized from
It switches to energization to each coil of 6a-26d. Thereby, as shown in FIG. 3A, the electromagnets 26a, 26c
The S pole is excited on the head 23 side of the electromagnet 26.
The N pole is excited on the head 23 side of b and 26d.
For this reason, the magnets 24a, 24a,
24c is drawn, and the magnets 24b, 24d are about to be drawn to the electromagnets 26b, 26d. As a result, the head section 23 rotates (rotates clockwise in the figure) in the direction of the arrow shown in FIG. 3A, and as shown in FIG. 26a-26d
Move to the position corresponding to.

Subsequently, as shown in FIG. 4, when the energization is sequentially switched to the electromagnets 27a to 27d and 28a to 28d, the magnets 24a to 24d are attracted to the electromagnets excited by the energization. As a result, the head 23 rotates. That is, as shown in FIG. 4, each coil of the electromagnets 25a to 25d is
By sequentially energizing the coils of 28d, the head unit 23 rotates (rotates clockwise in the figure) in the directions of the arrows shown in FIGS. 3 (a) and 3 (b).

Then, by energizing the coils of the electromagnets 28a to 28d, the magnet 24a
a, 28c, the magnet 24b is the same as the electromagnet 28b,
After moving to the position 28d, as shown at point P in FIG. 4, the direction of the current I is reversed, and the current is switched again to the coils of the electromagnets 25a to 25d. Thereby, the magnets 24b and 24d are attracted to the electromagnets 25c and 25a, and the magnets 24a and 24d are drawn.
24c is attracted to the electromagnets 25b and 25d, and the head section 23 continues to rotate rightward. In addition, the respective electromagnets 25a to 25d, 26a to 26d, 27a to 27
If the order of energizing the coils d, 28a to 28d is reversed, the head 23 rotates left in FIG. That is, the operating principle for rotating the head section 23 is the same as the operating principle of the stepping motor.

As described above, the head section 23 is provided with the electromagnets 25a to 25d, 26a to 26d, 27a to 27
d, 28a to 28d, and is rotated by energization of each coil, and as shown in FIG.
The height of the head portion 23 is changed by the screw action between the a and the male screw portion 22a of the piston body 22. That is, the head portion 23 becomes lower when the head portion 23 rotates clockwise, and becomes higher when the head portion 23 rotates counterclockwise. for that reason,
The compression ratio in the combustion chamber 17 is changed by moving the head portion 23 in the height direction. For example, when the head portion 23 moves downward by a height h from the position indicated by the two-dot chain line in FIG. 5, the volume in the combustion chamber 17 at the top dead center increases by the height h. The compression ratio inside becomes lower.

The compression ratio in the combustion chamber 17 which can be varied in this way is, as shown in the map of FIG.
The optimum compression ratio ε is obtained from E and the intake pressure PM. Accordingly, the head unit 23 is moved by the control device 31 to a position where the optimum compression ratio ε based on the engine speed NE and the intake pressure PM at that time is obtained.

As described in detail above, according to the present embodiment, the following effects can be obtained. The compression ratio in the combustion chamber 17 can be variably set to the optimum compression ratio ε according to the engine speed NE and the intake pressure PM of the engine 11, that is, the operating state of the engine 11. Moreover, the movement of the piston 12 in the height direction of the head portion 23 is performed by a screw action between the head portion 23 and the piston body 22. Therefore, the head portion 23 can be reliably moved relative to the piston main body 22 even with a relatively weak force. Further, since the amount of movement of the head portion 23 in the height direction is smaller than the amount of rotation of the head portion 23, fine adjustment of the compression ratio in the combustion chamber 17 can be easily performed.

Since the structure for varying the compression ratio in the combustion chamber 17 is based on the same principle as the operation principle of the stepping motor, the structure is different from that of a conventional variable compression ratio mechanism using hydraulic pressure. It can be simplified and the manufacturing cost can be reduced. In addition, since the response is better than the conventional variable compression ratio mechanism, it is possible to accurately change the compression ratio to a desired one.

The structure for making the compression ratio in the combustion chamber 17 variable is based on the same principle as the operation principle of the stepping motor, so that there is no problem of deterioration and maintenance-free.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. In the present embodiment, members having the same configuration as that of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

As shown in FIG. 7, this embodiment differs from the first embodiment in that the electromagnets 25a to 25a
5d, 26a to 26d, 27a to 27d, 28a to 28
d is the gasket 15 and the cylinder block 1
1a.

According to such a configuration, in addition to the same operations and effects as those of the first embodiment, the head portion 23 can be rotated even if it is not near the top dead center of the piston 12. Therefore, the compression ratio in the combustion chamber 17 can be made variable over a wide range of crank angles. Therefore, it is possible to immediately change the compression ratio to a desired one even when the operating state changes suddenly.

The above embodiments may be modified as described below, and the same operation and effect can be obtained in such a case. In the above embodiments, the gasket 15
Alternatively, between the gasket 15 and the cylinder block 11a, a total of 16 electromagnets 25a to 25d, 26a to
26d, 27a to 27d and 28a to 28d are provided,
The number of these electromagnets is increased or decreased. When the number of the electromagnets is increased in this manner, the amount of rotation of the head 23 can be more finely controlled, and the compression ratio in the combustion chamber 17 can be more finely controlled. When the number of the electromagnets is reduced, the manufacturing of the magnetic field generating mechanism is facilitated and the amount of rotation of the head unit 23 in one step is increased, so that the compression ratio in the combustion chamber 17 is reduced. Responsiveness can be improved when abruptly changing.

The male screw portion 22a of the piston body 22
And, the pitch of the female screw portion 23a of the head portion 23 is changed. If the pitch is reduced, the compression ratio in the combustion chamber 17 can be delicately controlled. If the pitch is increased, the male screw portion 22a and the female screw portion 23 can be controlled.
a becomes easy, and the response when the compression ratio in the combustion chamber 17 is rapidly changed can be improved.

In the first and second embodiments,
The control of the compression ratio in the combustion chamber 17 is controlled based on the engine speed NE and the intake pressure PM shown in FIG. In other words, the combustion chambers 17 in the first and second embodiments described above.
Is controlled based only on the engine speed NE and the intake pressure PM, and is not controlled based on other knocking occurrence factors. That is, the set value of the compression ratio set in each of the above embodiments is set to a value including a margin for preventing knocking from occurring even under the condition where other knocking occurrence factors are most likely to cause knocking. ing. Such other knocking occurrence factors include the water temperature THW of the engine 11, and usually, when the engine temperature is low such as immediately after the start of the engine 11, that is, when the water temperature THW is low, knocking hardly occurs. Therefore, as shown in FIG.
The compression ratio Δε1 based on the water temperature THW of the engine 11 detected by a water temperature sensor (not shown) mounted on the
Is added as a correction value to the compression ratio ε obtained based on the engine speed NE and the intake pressure PM in each of the above embodiments, and the compression ratio is controlled to ε + Δε1. That is, control is performed such that the set value of the compression ratio in the combustion chamber 17 is set to a value at which a knock limit that changes with the water temperature THW of the engine 11 is learned. Thus, the engine 11
If the compression ratio is set in accordance with the temperature condition, the output performance of the engine 11 can be further improved without knocking, particularly when the engine 11 is at a low temperature. Moreover, when the compression ratio is set to be high when the engine 11 is at a low temperature, the thermal efficiency increases, so that the warm-up operation time can be shortened.

As described above, the compression ratio in the combustion chamber 17 in the first and second embodiments is controlled based only on the engine speed NE and the intake pressure PM, and is controlled based on other knocking factors. Has not been. Such other knocking factors include the octane number of the fuel used for the engine 11. Therefore, a knock sensor is provided in the engine 11, and after the engine 11 is warmed up, the throttle valve is fully opened (WOT; Wide).
Open Throttle) The octane number of the fuel is estimated from the occurrence of knocking in the operating state, and as shown in FIG. 9, the compression ratio Δε2 corresponding to the estimated octane number is used to determine the engine speed NE and the intake pressure in each of the above embodiments. The compression ratio ε obtained based on the PM is given as a correction value to control the compression ratio to be ε + Δε2. That is, control is performed such that the set value of the compression ratio in the combustion chamber 17 is set to a value at which a knock limit that changes with the octane number of the fuel used for the engine 11 is learned. With this configuration, when “high-octane gasoline” generally used as fuel for the engine 11 is used, the output performance can be further improved. Also, when changing from "high-octane gasoline" to "regular gasoline" with a low octane number, knocking is reliably generated by changing the compression ratio when using "high-octane gasoline" to the compression ratio when using "regular gasoline" Can be prevented.

As described above, the compression ratio in the combustion chamber 17 in the first and second embodiments is controlled based only on the engine speed NE and the intake pressure PM, and is controlled based on other knocking factors. Has not been. Such other knocking factors include the ignition timing in the combustion chamber 17. Usually, the ignition timing is the ignition timing (MBT; Minimum) for extracting the maximum torque from the engine.
There is a Spark Advance for Best Torque, and it is ideal to set the ignition timing to this MBT. Therefore, in each of the above embodiments, the engine speed NE and the intake pressure PM
At the compression ratio ε obtained based on
In the case where knocking does not occur even after setting to BT, the compression ratio ε is further increased, and control is performed so that the compression ratio is increased to just before the knock limit. That is,
Control is performed such that the set value of the compression ratio in the combustion chamber 17 is set to a value at which a knock limit that changes with the ignition timing of the engine 11 is learned. By doing so, the output performance of the engine 11 can be further improved.

If the control of the compression ratio based on the water temperature THW, the control of the compression ratio based on the octane number, and the control of the compression ratio based on the ignition timing are simultaneously performed, the output performance of the engine 11 can be improved. Can be improved. In addition, since the mechanism for changing the compression ratio is based on the same principle as the operation principle of the stepping motor, the responsiveness is good when controlling such a compression ratio, and the compression ratio in the combustion chamber 17 is accurately determined. Can be varied.

In each of the above embodiments, each of the electromagnets 25a to 25d, 26a to 26d, 27a as a magnetic field generating mechanism is used.
As shown in FIG. 2, each coil is wound around one electromagnet in one direction in each of the coils 27a and 28a to 28d. And wind the coil in both directions.
Then, the energizing direction is fixed, and the current I is applied only to one side of the coil wound in each direction, and the current is applied to the other side at point P shown in FIG. Switch. That is, the operating principle of the magnetic field generating mechanism is made equal to that of the hybrid type stepping motor.

While the embodiments have been described above, technical ideas other than the claims that can be grasped from the embodiments will be described below together with their effects. (A) In the variable compression ratio mechanism for an internal combustion engine according to claim 1, the relative movement of the head portion with respect to the piston body is controlled in accordance with a compression ratio in which a knock limit of the internal combustion engine is learned. Variable compression ratio mechanism of an internal combustion engine.

In this way, it is possible to more accurately control the water temperature, the octane number of the fuel used, and the ignition timing in the internal combustion engine to an optimum compression ratio that does not exceed the knock limit.

[0037]

According to the first aspect of the present invention, the head can be relatively moved with a relatively small force and the fine adjustment of the compression ratio can be easily performed. In addition, the configuration can be simplified as compared with a variable compression ratio mechanism using hydraulic pressure.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a variable compression ratio mechanism according to a first embodiment.

FIG. 2 is a plan view schematically showing an electrical configuration of the variable compression ratio mechanism of the first embodiment.

FIG. 3 is a schematic diagram schematically showing an operation mode of the variable compression ratio mechanism of the first embodiment.

FIG. 4 is a time chart showing a state of energizing each electromagnet of the variable compression ratio mechanism of the first embodiment.

FIG. 5 is a schematic diagram schematically showing a moving amount of a head unit of the variable compression ratio mechanism of the first embodiment.

FIG. 6 is a two-dimensional map showing a setting mode of a compression ratio variably set by the first embodiment.

FIG. 7 is a sectional view showing a variable compression ratio mechanism according to a second embodiment.

FIG. 8 is a graph showing a relationship between a water temperature and a compression ratio corrected by another embodiment.

FIG. 9 is a graph showing a relationship between a fuel octane number and a compression ratio corrected according to another embodiment.

[Explanation of symbols]

11 ... engine, 12 ... piston, 15 ... gasket,
17: combustion chamber, 22: piston body, 22a: male screw part, 23: head part, 23a: female screw part, 24: magnet,
25a to 25d, 26a to 26d, 27a to 27d, 2
8a to 28d: electromagnet (magnetic field generating mechanism); 31: control device.

Claims (1)

[Claims] 1. A variable compression ratio mechanism for an internal combustion engine that varies a compression ratio in a combustion chamber by moving a head portion of a piston relative to a piston body in a movement direction of the piston body. A plurality of magnets, which are screw-engaged with the piston main body, and a magnetic field generating mechanism that generates a magnetic field in the combustion chamber when energized, wherein the head is based on induction of a magnetic field generated by the magnetic field generating mechanism. A variable compression ratio mechanism for an internal combustion engine, wherein the head portion moves relative to the piston body in the direction of movement by rotation of the portion.