JPS63195325A - Valve timing control device for engine with supercharger - Google Patents

Abstract

PURPOSE:To achieve the enhancement in charging efficiency, by advancing the opening timing of an intake port in such an operating region as the supercharged pressure is greater than the exhaust pressure. CONSTITUTION:The first and the second intake ports 10, 11 which are opened or closed by the first and the second intake valves 8, 9 are connected to each cylinder respectively, and a shutter valve 14 is provided in the second intake passage 13 which is communicated with the second intake port 11. In the operating region in which the supercharged pressure is greater than the exhaust pressure, the shutter valve 14 is opened to increase the overlap in the valve opening timing on both the intake side and the exhaust side. Thus, the charging efficiency of intake air can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a valve timing control device for a supercharged engine.

(Prior art) It is generally known that a supercharger is provided in the intake system of an engine (for example, see Japanese Patent Laid-Open No. 59-39927).
. By the way, in a supercharged engine, the exhaust gas temperature is generally high, so the air-fuel ratio is enriched (increasing the mixture concentration) in the high-speed operation range, and the exhaust gas temperature is lowered to the heat resistance limit of the exhaust system parts. Control is in place to keep it below.

In addition, in the case of a supercharged engine, its geometric compression ratio (
Abnormal combustion (knocking) in high-load operating ranges is avoided by keeping the cylinder internal volume at the bottom dead center of the piston / clearance volume at the top dead center of the piston) lower than that of an engine without a supercharger. That is, by setting the geometric compression ratio to less than 7.0 to 8.5 and setting the opening timing of the intake port to a point in time when the crank angle has passed from bottom dead center to 20 to 40 degrees, the effective compression ratio is set to 6.5 to 8.5. It is normal to set it to about 8.25.

(Problems to be Solved by the Invention) As mentioned above, supercharged engines have the problem of poor fuel efficiency due to the enrichment of the air-fuel ratio in high-speed operating ranges, and the problem of poor fuel efficiency when using a low compression ratio. This is also unfavorable from the point of view of fuel efficiency, as thermal efficiency deteriorates.

Since the purpose of enriching the air-fuel ratio is to prevent an excessive rise in exhaust gas temperature, the present invention attempts to utilize adiabatic expansion as an alternative cooling means, but even in that case, the following problems still occur. .

In other words, in order to cool the combustion gas through adiabatic expansion, the intake port can be closed late to shorten the actual stroke of the piston in the compression stroke, and therefore, the stroke in the expansion stroke can be made relatively long. Since the compression period is shortened, the temperature increase due to compression cannot be achieved and combustibility deteriorates.

In addition, after the expansion stroke, the combustion gas is not completely exhausted and some remains in the combustion chamber, but since this residual gas is high temperature, it tends to increase the temperature of the next combusted air-fuel mixture, which can lead to abnormal combustion. At the same time, there is a problem in that the filling efficiency of intake air is also lowered by the amount of residual gas.

(Means for Solving the Problems) The present invention provides, as means for solving the above problems, a supercharged engine whose geometric compression ratio is 8.5 or more.
The closing timing of the intake port is set when 50 degrees or more of the crank angle has passed from the bottom dead center of the piston.
A supercharged engine equipped with a means for opening the intake port earlier than in other operating regions in an operating region where the boost pressure exceeds the exhaust pressure to increase the overlap between the valve opening periods on the intake side and the exhaust side. The present invention provides a valve timing control device.

(Function) That is, in the present invention, due to the late intake port closing timing, the piston stroke in the compression stroke becomes short and the piston stroke in the expansion stroke becomes relatively long.
Cooling can be achieved by adiabatic expansion of combustion gas. Even if the above-mentioned closing timing is late, the geometric compression ratio is high, so the effective compression ratio necessary to ensure combustion stability is obtained, and the cylinder clearance volume at the piston top dead center is reduced, so that the combustion chamber The reduction in residual gas also contributes to securing the above-mentioned combustion stability. In addition, since the closing timing is late, it is possible to reduce the pumping loss (negative work in the intake stroke) in the light load operation region.

In this case, regarding the above closing timing setting, the crank angle is 50°.
The reason for specifying 1° or more is to keep the intake port open until the piston displacement (crank angle at which the piston movement speed becomes relatively high) provides a relatively large pumping loss reduction effect. Also, the geometric compression ratio is 8.
The reason for specifying 5 or more is to make it possible to sufficiently compensate for the decrease in the effective compression ratio due to the delay in the closing timing.

On the other hand, in the present invention, in the operating region where the boost pressure exceeds the exhaust pressure, the overlap between the valve opening periods on the intake side and the exhaust side becomes large, so that the combustion gas remaining near the end of the exhaust stroke is Air is scavenged with air, increasing the filling efficiency of intake air,
It is possible to compensate for a decrease in the effective compression ratio and a decrease in the intake air filling amount due to the late opening timing of the intake port.

Note that, in this specification, the opening/closing timing of the intake/exhaust ports is explained by regarding the time of the valve lift m1 tma as a closed state where there is no substantial intake/exhaust. for example,
When the intake port close timing is 50 degrees in crank angle from bottom dead center, it means that the valve lift amount becomes 1 city at this 50 degrees.

(Effects of the Invention) Therefore, according to the present invention, combustion stability is ensured by a high geometric compression ratio and control of the intake port opening timing, while adiabatic expansion is effectively utilized by delaying the intake port closing timing. Since the combustion gas can be cooled and the exhaust gas temperature can be prevented from rising excessively, it is possible to prevent the air-fuel ratio from becoming richer and improve fuel efficiency in high-speed driving ranges.

In addition, scavenging of combustion gas by supercharging air is promoted,
Even with low boost pressure, a sufficient charging amount and therefore power can be obtained during acceleration, improving fuel efficiency, and combined with the above-mentioned high geometric compression ratio, reducing residual gas,
An increase in the temperature of the mixture due to this residual gas is suppressed, and the knocking resistance is also improved.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

In the supercharged engine shown in FIG. 1, 1 is a 4-stroke engine main body, and 2 is a turbo supercharger. The intake passage 3 has a compressor 2a of the supercharger 2, an intercooler 5, and a throttle valve 6 interposed in this order from the upstream side, and continues to a surge tank 7. From this surge tank 7, the first and second The first and second passages 1 are connected to the first and second intake ports lo and 11 which are opened and closed by the intake valves 8 and 9.
2°13 are in a row. Each second passage 13 has a shutter valve 14 for opening and closing the passage. A fuel injection valve 15 is provided downstream of the shutter valve 14 and directed toward the first and second intake ports 10.11.

Each cylinder also has a first and a second exhaust valve 16.
It has first and second exhaust ports 18, 19 which are opened and closed at 17. A turbine 2b of the supercharger 2 is installed in an exhaust passage 20 connected to each cylinder, and a wastegate valve 22 is installed in a passage 21 that bypasses the turbine 2b.

Therefore, the geometric compression ratio of the engine is set to 8.5 or higher. Regarding the opening/closing timing of the intake ports 10 and 11, as shown in Fig. 2, the first intake valve 8 cranks the first intake port 10 from just before the piston top dead center (T, DC) to the piston bottom dead center (BDC). The second intake valve 9 opens the second intake port 11 earlier than the first intake valve 8, and closes the second intake bow hll at the same time as the first intake valve 8. The timing is set by the camshaft. The second intake port 11 is controlled by the control means 23 using the shutter valve 14 on the low-speed, high-load side where the supercharging efficiency is high and the supercharging pressure exceeds the exhaust pressure, as shown by diagonal lines in FIG. Intake air is introduced into the combustion chamber only in the operating range. That is, the control means 23 controls the shutter valve 14 in the low rotation and high load operating region based on the intake pipe pressure detected by the pressure sensor 24 provided in the surge tank 7 and the engine rotation speed detected by the one revolution sensor 25.
An open signal is output to the actuator 26 of the actuator 26.

Then, based on the above geometric compression ratio and intake port closing timing settings, the effective compression ratio of the above engine (internal cylinder volume at the beginning of compression/clearance volume at piston top dead center) is as shown in Figure 4. Draw a solid line diagonally downward to the right to indicate the setting area6.
．． It is set at about 5 to 8.25. Note that the area indicated by broken diagonal lines in the figure is the setting range of a conventional supercharged engine.

From FIG. 4, it can be seen that if the relationship between the geometric compression ratio and the intake port closing timing is set in the region shown in FIG. 5, the effective compression ratio 6.5 to 8.25 can be obtained. Regarding the above-mentioned intake port closing timing, when the crank angle is 50 degrees after the bottom dead center of the piston, the piston displacement ratio (piston displacement amount This is the point in time when X5C) suddenly increases.

Therefore, in the above embodiment, due to the delay in the intake port closing timing, the piston stroke in the expansion stroke becomes relatively longer than the same stroke in the compression stroke, the combustion gas is effectively cooled by adiabatic expansion, and the exhaust gas temperature is reduced. This means that the temperature can be kept below the heat-resistant limit temperature of exhaust system parts. That is, it is not necessary to enrich the air-fuel ratio in the high-speed driving range, and fuel efficiency can be improved. Also 1. Intake port 10. '11 is closed after the piston displacement rate increases rapidly, so it is possible to effectively reduce the pumping loss under light loads. Furthermore, despite the delay in the intake port closing timing, the geometric compression ratio is increased to ensure an effective compression ratio, and residual gas in the combustion chamber during the exhaust stroke is reduced, ensuring combustion stability. Or improvements can be made, and it becomes possible to keep the effective compression ratio low or further delay the intake port closing timing.

On the other hand, in the operating range where the boost pressure is higher than the exhaust pressure, the second intake port 11 exhibits an intake action due to the opening movement of the shutter 014, and the overlap between the valve opening periods on the intake side and the exhaust side increases, so the supercharging The combustion gas is scavenged by air, and the geometric compression ratio is high, so that the residual gas in the combustion chamber can be further reduced. And by reducing this residual gas.

The combustion chamber is filled with a high amount of intake air even at low boost pressure, which improves output and fuel efficiency, suppresses the rise in air-fuel mixture temperature due to residual gas, and improves knocking resistance. Note that by adjusting the relationship between the intake port closing timing and the geometric compression ratio, it is possible to prevent the effective compression ratio from becoming excessively high. In addition, when the overlap is increased and scavenging is performed, unburned gas is discharged from the exhaust port 18.
．． This can be prevented by injecting fuel after the valve 19 is closed.

In the above embodiment, both the first and second intake ports 10 and 11 are closed at the same time, but as shown in FIG. 7, the second intake valve closes the second intake port later than the first intake valve. You can do it like this.

This further increases the engine cooling efficiency through adiabatic expansion of the combustion gas in the low-speed, high-load operating range, and also lowers the effective compression ratio, thereby making it possible to more reliably prevent knocking.

In addition, as shown in Fig. 8, the first intake valve closes the intake port earlier than the second intake valve (between the piston bottom dead center and the crank angle of 50 degrees), so that effective compression is achieved on the light load side. Lean air-fuel ratio by increasing the ratio
It is also possible to improve the combustion stability and to delay the closing timing of the intake port only on the high load side to effectively cool the combustion gas while lowering the effective compression ratio. In the embodiment, a shutter valve 14) is used to control the opening/closing timing of the intake port to the second intake valve 9, but a valve stop mechanism is provided to the second intake valve to control it in the same way as the shutter valve. It is also possible to change the (fi phase) of this second intake knob/rube arbitrarily by a motor on the intake cam side, as shown in Fig. 3.
As the load increases, as the load increases, as shown by the equal phase line at m (the wrap may be controlled so that it gradually increases), the mechanical overload is driven by the engine crankshaft. Even when a charger is used, the present invention can be carried out in substantially the same manner as in the case of the turbocharger described above. In the case of the second mechanical supercharger, unlike a turbo supercharger, a high X supercharging pressure can be obtained over a wide rotation speed range, so
As shown in FIG. 9, the above-mentioned overlap II control knob automatically becomes larger at higher engine speeds. Additionally, due to the delay in the intake port closing timing, the amount of intake air filling tends to be low in general, but with a 1 mechanical supercharger, a sufficient amount of filling can be obtained through supercharging at the same time as 11 acceleration, so there is no particular problem with acceleration. Moreover, due to the enlargement of the oaturu wrap mentioned above, the amount of charge is increased by scavenging air at low rotation speeds and high loads, and the force of reducing supercharging pressure1 and the driving resistance of the supercharger are also reduced, which increases engine torque and reduces fuel consumption. Improvements can be made.

In addition, when adopting a method of changing the valve phase using a motor, it is possible to control not only the second intake valve but also the first intake valve at the same time. The present invention can also be carried out in other industries.

In addition, the above-mentioned overlap control may be performed by detecting the boost pressure and exhaust pressure with sensors and directly comparing the two.Furthermore, when changing the amount of overlap, the timing of closing the exhaust port may be changed. You can also strain it.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and Fig. 1 is an overall configuration diagram of a supercharged engine, Fig. 2 is a diagram showing the timing characteristics of the intake nozzle, and Fig. 3 is a diagram showing the case of a turbo supercharger. Fig. 4 is a characteristic diagram showing the setting range of the present invention and the conventional example regarding the relationship between the geometric compression ratio, intake port closing timing, and effective compression ratio, and Fig. 5 is the geometric Characteristic diagram showing the setting range regarding the theoretical compression ratio and intake port closing timing,
Figure 6 is a diagram showing the relationship between the crank angle and the displacement rate of the piston, Figures 7 and 8 are diagrams showing other examples of intake valve timing characteristics, and Figure 9 is a diagram showing the relationship between the crank angle and the displacement rate of the piston. FIG. 3 is a diagram similar to FIG. 3 in the case of a machine. ■・・・Engine body, 2・・・Supercharger,
3... Intake passage, 8... First intake valve, 9... Second intake valve, 10...
...First intake port, 11...Second intake port, 14...Shutter valve, 18.19...
...Exhaust port. Figure 2 Figure 3 Figure 4 Figure 5 Figure 7 Figure 8

Claims (1)

[Claims] (1) In an engine equipped with a supercharger, the geometric compression ratio of the engine is set to 8.5 or higher, and the intake port closes at the point when 50 degrees or more of the crank angle has passed from the bottom dead center of the piston. The engine is equipped with a means to increase the overlap between the valve opening periods on the intake side and the exhaust side by opening the intake port earlier than in other operating areas in the operating range where the boost pressure exceeds the exhaust pressure. A valve timing control device for a supercharged engine, characterized by: