JP2566232B2 - Valve timing controller for engine with supercharger - Google Patents

Description

The present invention relates to a valve timing control device for a supercharged engine.

(Prior Art) A system in which a supercharger is provided in an intake system of an engine is generally known (see, for example, JP-A-59-39927). Generally, in an engine with a supercharger, the exhaust gas temperature is high, so by making the air-fuel ratio rich (increasing the air-fuel mixture concentration) in the high-speed operating range, the exhaust gas temperature can be kept high. Controls are made to keep it below the limit.

In the case of an engine with a supercharger, keep the geometric compression ratio (cylinder volume at piston bottom dead center / clearance volume at piston top dead center) lower than that of an engine without a supercharger. Abnormal combustion (knocking) in high-load operating range
Trying to avoid. That is, the geometric compression ratio
It is normal to set the closing timing of the intake port to 7.0 to less than 8.5 at the time when 20 to 40 degrees in crank angle has passed from the bottom dead center and set the effective compression ratio to about 6.5 to 8.25.

(Problems to be Solved by the Invention) As described above, in a supercharged engine, there is a problem that fuel efficiency deteriorates because the air-fuel ratio is made rich in a high-speed operation region, and a low compression ratio is used. Is also not preferable in terms of fuel efficiency because the thermal efficiency will be deteriorated.

Therefore, in the present invention, in a turbocharged engine, use adiabatic expansion instead of enriching the air-fuel ratio as a cooling means for preventing an excessive rise in exhaust gas temperature in a high-speed operation region. It is what However, in that case, the following problems newly arise.

That is, in order to cool the combustion gas by adiabatic expansion, the intake port may be closed late to shorten the substantial stroke of the piston in the compression stroke, and thus the stroke of the expansion stroke may be relatively long. Since the compression period is shortened, conversely, the temperature rise due to compression cannot be obtained, and the combustibility deteriorates.

Further, after the expansion stroke, the combustion gas is not completely discharged and a part of the combustion gas remains in the combustion chamber. However, since this residual gas is high in temperature, the temperature of the air-fuel mixture to be burned next rises, and abnormal combustion occurs. In addition, there is a problem in that the charging efficiency of intake air is reduced by the amount of residual gas.

(Means for Solving the Problem) In order to solve the above problems, in the present invention, the combustion gas is cooled by adiabatic expansion by the late closing of the intake port, and the intake charge amount in the case of the late closing of the intake port. Is sufficiently covered by supercharging with a supercharger and cooling of the supercharged air with an intercooler.However, if residual gas remains in the combustion chamber at that time, the intake charge amount will decrease accordingly. In the engine equipped engine, the phenomenon that the supercharging pressure becomes higher than the exhaust pressure in the low rotation and high load operating region is utilized to eliminate the residual combustion gas by scavenging.

Specifically, the solution means of the present invention is a supercharged engine equipped with a turbocharger for supercharging intake air to the engine and an intercooler for cooling supercharged air from the turbocharger. At, the geometric compression ratio of the engine is
In addition to being set to 8.5 or more, the closing timing of the intake port specified when the valve lift amount of the intake valve becomes 1 mm is set to the time when 50 degrees or more in crank angle has elapsed from the bottom dead center of the piston. I shall. Further, in an operating region in which the supercharging pressure on the low rotation and high load side exceeds the exhaust pressure, a means for advancing the opening timing of the intake port compared to other operating regions to increase the overlap between the valve opening periods of the intake side and the exhaust side. Shall be provided.

(Operation) That is, in the present invention, since the closing timing of the intake port is late, the piston stroke in the compression stroke is shortened and the piston stroke in the expansion stroke is relatively long, and cooling by adiabatic expansion of the combustion gas can be achieved. . And
Even if the closing timing of the intake port is delayed, the geometric compression ratio is high, so the effective compression ratio necessary for ensuring combustion stability is obtained, and the clearance volume of the cylinder at the piston top dead center is The reduction in the amount of residual gas in the combustion chamber also contributes to ensuring the combustion stability.
Also, due to the late closing of the intake port, pumping loss in the light load operation region (negative work in the intake stroke)
Can be reduced.

In this case, regarding the setting of the closing timing of the intake port, the specification that the crank angle is 50 degrees or more after the piston bottom dead center is given because the piston displacement (the piston moving speed is This is to keep the intake port open up to a relatively high crank angle). Further, the geometrical compression ratio is specified to be 8.5 or more in order to sufficiently compensate for the decrease in the effective compression ratio due to the delay in the closing timing of the intake port.

On the other hand, in the present invention, in the operating region in which the boost pressure on the low rotation and high load side exceeds the exhaust pressure, the overlap of the valve opening period between the intake side and the exhaust side becomes large, so that it remains at the end of the exhaust stroke. The combustion gas being discharged is scavenged by supercharging, the charging efficiency of intake air is increased, and it is possible to compensate for a decrease in the effective compression ratio and a decrease in the intake charge amount, which results in a late closing of the intake port.

In the present invention, the opening / closing timing of the intake / exhaust port is defined as a valve closed state with no substantial intake / exhaust when the valve lift amount is 1 mm. For example, when the intake port closing time is 50 degrees in crank angle from the bottom dead center, it means that the valve lift amount becomes 1 mm at the time of 50 degrees.

(Effect of the Invention) Therefore, according to the present invention, in the turbocharged engine, the intake port closing timing is delayed while the combustion stability is ensured by controlling the high geometric compression ratio and the intake port opening timing. Since the combustion gas can be cooled by effectively utilizing the adiabatic expansion, it is possible to prevent an excessive rise in the exhaust gas temperature without using the enrichment of the air-fuel ratio, and it is possible to improve the fuel efficiency in the high speed operation region.

Further, in an operating region where the supercharging pressure on the low rotation speed and high load side exceeds the exhaust pressure, the scavenging of the combustion gas due to the supercharging is promoted, so a sufficient intake charge amount can be obtained at the time of acceleration even at a low supercharging pressure. The output is improved, the fuel efficiency is improved, and the residual gas is reduced in combination with the above-mentioned high geometric compression ratio. Knocking performance will also be improved.

(Example) Hereinafter, the Example of this invention is described based on drawing.

In the supercharged engine shown in FIG. 1, 1 is a 4-cycle engine body, and 2 is a turbocharger. From the upstream side of the intake passage 3, a compressor 2a of the supercharger 2, an intercooler 5, and a throttle valve 6 are sequentially installed to follow the surge tank 7, and from the surge tank 7, the first and second intake air of each cylinder are provided. First and second opening and closing with valves 8 and 9
The first and second passages 12 and 13 are connected to the intake ports 10 and 11, respectively. A shutter valve 14 for opening and closing the passage is provided in each second passage 13, and a fuel injection valve 15 directed to the first and second intake ports 10 and 11 is provided on the downstream side of the shutter valve 14. ing.

Further, each cylinder has a first exhaust valve 16 and a second exhaust valve 1,1 respectively.
It is provided with first and second exhaust ports 18 and 19 that are opened and closed at 7.
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 above engine is set to 8.5 or more. Regarding the opening / closing timing of the intake ports 10 and 11 which is specified when the valve lift amount becomes 1 mm,
As shown in the figure, the first intake valve 8 opens the first intake port 10 immediately before the piston top dead center (TDC), and closes when the crank angle exceeds 50 degrees from the piston bottom dead center (BDC). The timing of the second intake valve 9 is set by the camshaft so that the second intake port 11 opens earlier than the case of the first intake valve 8 and the second intake port 11 closes at the same time as the first intake valve 8. . And the second intake port 11
With regard to the above, the shutter valve 14 is controlled to be opened / closed by the control means 23, and the shutter valve is provided only in the operating region on the low rotation / high load side where the supercharging efficiency is high and the supercharging pressure exceeds the exhaust pressure as shown by the hatched lines in FIG. The opening operation of 14 introduces intake air into the combustion chamber. That is, the control means 23, based on the signal of the intake pipe pressure detected by the pressure sensor 24 provided in the surge tank 7 and the engine speed signal detected by the rotation sensor 25, operates the shutter valve 14 in the low rotation and high load operation region.
The actuator 26 is designed to output an open signal.

Then, based on the settings of the geometrical compression ratio and the intake port closing timing, the effective compression ratio of the engine (the cylinder internal volume at the start of compression / the clearance volume at the piston top dead center) is
As shown in Fig. 4, a solid line is drawn with a diagonal line to the right to indicate the setting area.
It is about 6.5 to 8.25. The area shown by the slanted lines in the figure is the setting range of the conventional engine with a supercharger. 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 of 6.5 to 8.25 can be obtained. Regarding the intake port closing timing, when the crank angle is 50 degrees after the piston bottom dead center, as shown in FIG. 6, the piston displacement ratio (piston displacement x / total piston stroke) with respect to the crank angle change. (x st) is the point when it rapidly increases.

Therefore, in the case of the above embodiment, the piston stroke in the expansion stroke becomes relatively longer than the same stroke in the compression stroke due to the delay of the intake port closing timing, the combustion gas is effectively cooled by the adiabatic expansion, and the exhaust gas temperature is It will be kept below the heat-resistant limit temperature of the exhaust system parts. That is,
It is not necessary to enrich the air-fuel ratio in the high-speed operation range, and fuel efficiency can be improved. Further, since the intake ports 10 and 11 are closed after the displacement rate of the piston suddenly becomes large, the pumping loss at a light load can be effectively reduced.
Moreover, regardless of the delay in the intake port closing timing, the geometric compression ratio is increased to secure the effective compression ratio and the residual gas in the combustion chamber in the exhaust stroke is reduced, so that the combustion stability is secured. Or, improvement can be achieved, and it becomes possible to suppress the effective compression ratio to a low value or to further delay the intake port closing timing.

On the other hand, in the operating region where the supercharging pressure on the low rotation and high load side is higher than the exhaust pressure, the opening operation of the shutter valve 14 causes the second intake port 11 to perform the intake action, and the opening period of the intake side and the exhaust side is exceeded. Since the wrap becomes large, combustion gas is scavenged by supercharging, and the geometric compression ratio is high,
The residual gas in the combustion chamber is further reduced. And
Due to this reduction of residual gas, the intake chamber is filled with a large amount of intake air even at a low supercharging pressure, which improves output and fuel efficiency, while suppressing an increase in the temperature of the air-fuel mixture due to residual gas, as well as knocking resistance. Be improved. The effective compression ratio can be prevented from becoming excessively high by adjusting the relationship between the intake port closing timing and the geometric compression ratio. Further, the discharge of the unburned gas when the overlap is increased and the scavenging is performed can be prevented by performing the fuel injection after the exhaust ports 18 and 19 are 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 may do it. As a result, the cooling efficiency due to the adiabatic expansion of the combustion gas in the low rotation and high load operation region can be further enhanced, the effective compression ratio can be reduced, and the occurrence of knocking can be prevented more reliably.

Further, 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 the effective compression is achieved on the light load side. The ratio is increased to make the air-fuel ratio leaner or the combustion stability is improved. Only on the high load side, the closing timing of the intake port is delayed to reduce the effective compression ratio while effectively cooling the combustion gas. You may be able to do it.

Further, in the above embodiment, the opening / closing timing of the intake port is controlled by the second intake valve 9 using the shutter valve 14, but a valve stop mechanism is provided in the second intake valve to control this in the same manner as the shutter valve. Alternatively, the phase of the second intake valve can be arbitrarily changed by a motor on the intake cam side, and the intake side and the exhaust side can be changed as the load increases as shown by the equiphase lines in FIG. Control may be performed such that the overlap of the valve opening periods with and gradually increases.

When a method of changing the valve phase by a motor is adopted, not only the second intake valve but also the first intake valve may be controlled at the same time. Of course, the present invention can be implemented not only in the two-valve system, but also in an engine having one intake valve.

Further, the control of the above-mentioned overlap may be performed by directly detecting the supercharging pressure and the exhaust pressure by the sensors and comparing them, and when changing the overlap amount, the closing timing of the exhaust port should be changed. Good.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings show an embodiment of the present invention, FIG. 1 is an overall configuration diagram of an engine with a supercharger, FIG. 2 is a diagram showing timing characteristics of intake valves, and FIG. 3 is a turbo type. FIG. 4 is a characteristic diagram showing an overlap expansion region in the case of a supercharger, and FIG. 4 is a characteristic diagram showing a setting region of the present invention and a conventional example with respect to the relationship between the geometric compression ratio, the intake port closing timing, and the effective compression ratio, FIG. 5 is a characteristic diagram showing a set region relating to the geometric compression ratio and the intake port closing timing, FIG. 6 is a diagram showing a relationship between a crank angle and a piston displacement ratio, and FIGS. 7 and 8 are intake valves. It is a figure which shows the other example of the timing characteristic of. 1 ... Engine body, 2 ... Supercharger, 3 ... Intake passage,
8 ... 1st intake valve, 9 ... 2nd intake valve, 10 ...
1st intake port, 11 …… Second intake port, 14 …… Shutter valve, 18,19 …… Exhaust port.

Claims (1)

(57) [Claims] 1. A supercharged engine comprising a turbocharger for supercharging intake air to the engine and an intercooler for cooling supercharged air from the turbocharger, the engine geometry being The dynamic compression ratio is set to 8.5 or more, and the closing timing of the intake port specified when the valve lift of the intake valve becomes 1 mm is when the crank angle exceeds 50 degrees from the bottom dead center of the piston. It is set, and in the operating region where the supercharging pressure on the low rotation and high load side exceeds the exhaust pressure, the intake port opening timing is set earlier than in other operating regions so that the intake side and exhaust side open period overlaps. A valve timing control device for an engine with a supercharger, characterized in that a means for enlarging is provided.