JPH0726994A - Intake device of engine provided with supercharger - Google Patents

Abstract

PURPOSE:To decrease an exhaust temperature so as to be held to the allowable a limited exhaust temperature or less by providing an EGR control means for enhancing the EGR ratio when the exhaust temperature rises to the prescribed allowable limited exhaust temperature due to an increase in the engine speed. CONSTITUTION:The fuel injection amounts of first and second fuel injection valves 5a, 5b of respective cylinders 1 to 6 are respectively controlled by a control unit 10. In an engine VE, the control unit 10 suitable controls the opening/closing timing of intake valves 1a, 1b, the EGR ratio, the pressurized air relief amount and the air-fuel ratio on the basis of the engine speed, the S/C discharge temperature and the exhaust temperature, so as to prevent knocking from being generated in all driving range. Thereby, when the exhaust temperature is raised to the fixed allowable limited exhaust temperature due to an increase in the engine speed during its operation, the EGR ratio is enhanced by enlarging the opening of the second EGR valve 42, and the exhaust temperature is lowered so as to be held to the allowable limited exhaust temperature or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intake system for an engine with a mechanical supercharger.

[0002]

2. Description of the Related Art An engine with a mechanical supercharger has been conventionally known, which is designed to pressurize (supercharge) intake air with a mechanical supercharger to improve intake charging efficiency and output. . However, when supercharging is performed by the mechanical supercharger as described above, there is a problem that knocking easily occurs at high load. For this reason, in such a conventional engine with a mechanical supercharger, there is a countermeasure such as retarding the ignition timing at the time of high load to improve knock resistance, but retarding the ignition timing causes a decrease in engine output. Therefore, there arises a problem that the output improvement effect due to supercharging is diminished and fuel efficiency is deteriorated.

Therefore, in an engine equipped with a mechanical supercharger and an intake valve opening / closing timing variable means (VVT) capable of changing the closing timing of the intake valve, the boost pressure is increased in a predetermined operating region. In addition, there is a proposal to improve the knock resistance by setting the closing timing of the intake valve by the crank angle and setting it at a relatively late time after the bottom dead center of the intake stroke to perform the intake valve delayed closing operation. (See, for example, Japanese Patent Laid-Open No. 63-239312). That is, when the intake valve retarded closing operation is performed after increasing the supercharging pressure, the effective compression ratio in the compression stroke becomes smaller than in the normal operation,
The temperature rise due to the compression of the air-fuel mixture in the combustion chamber is reduced,
Therefore, the temperature of the air-fuel mixture at the time of ignition is relatively low, and the knock resistance is enhanced.

[0004]

However, when the intake valve retarded closing operation is performed, the intake charge efficiency cannot be sufficiently increased in the medium / high rotation range, so that the engine output cannot be sufficiently increased. Therefore, in the middle / high speed region, there is a problem that the knock resistance cannot be enhanced by the late closing of the intake valve.

In the supercharging region, part of the exhaust gas is EGR.
An engine with a supercharger has also been proposed in which the gas is recirculated to the intake passage to lower the combustion temperature to improve knock resistance and reduce the amount of NOx generated (for example,
(See JP-A-60-237153). However, when the EGR gas is introduced into the intake passage, the intake charging efficiency decreases, which causes a problem that the engine output decreases.

By the way, in an engine with a mechanical supercharger, the discharge pressure of the supercharger increases as the engine speed increases.
(Supercharging pressure) rises, and therefore the temperature of the discharge air (discharge temperature) rises.However, if the discharge temperature becomes too high, there is a problem that the reliability of the supercharger is impaired due to thermal expansion. . Therefore, in the conventional engine with a mechanical supercharger, when the discharge temperature reaches a predetermined allowable limit discharge temperature, the pressurized air downstream of the supercharger is relieved to the intake passage upstream of the supercharger to discharge the discharge temperature. Is maintained below the allowable limit discharge temperature. However, when the pressurized air is relieved in this way, there is a problem that the power loss in the supercharger is increased and the engine output cannot be sufficiently increased.

Further, in an engine with a mechanical supercharger, the exhaust temperature (exhaust gas temperature) tends to increase, but if the exhaust temperature becomes too high, the reliability of the exhaust pipe or the catalytic converter is impaired. In the engine with a mechanical supercharger, when the exhaust gas temperature reaches a predetermined allowable limit exhaust gas temperature, the air-fuel ratio is changed to the rich side to lower the exhaust gas temperature. However, this causes a problem that the fuel efficiency is deteriorated.

Therefore, in the engine with a mechanical supercharger, after comprehensively considering the opening / closing timing of the intake valve, the supercharging pressure, the EGR, the air-fuel ratio, etc., the engine is improved while improving the knock resistance in the entire operating range. Output can be increased enough,
In addition, it is required to develop the most rational system that can improve the fuel efficiency and can keep the discharge temperature and the exhaust temperature of the supercharger within the allowable limits.

The present invention has been made in order to solve the above-mentioned conventional problems, and it is possible to sufficiently increase the engine output while preventing the occurrence of knocking in all operating regions, and to improve the fuel efficiency. It is an object of the present invention to provide an engine with a mechanical supercharger, which is capable of maintaining the discharge temperature and exhaust temperature of the supercharger within an allowable limit.

[0010]

In order to achieve the above object, a first aspect of the present invention is to provide a mechanical supercharger, at least an intake valve opening / closing timing varying means capable of changing a closing timing of an intake valve, and at least In the operating range where supercharging is performed by the mechanical supercharger, the intake valve opening / closing timing varying means is provided so that the intake valve is closed at a relatively late timing after the bottom dead center of the intake stroke in view of the crank angle, depending on the operating state. In an intake device for a mechanical supercharged engine, which is provided with an intake valve opening / closing timing control means for controlling the engine to perform an intake valve late closing operation, the intake valve opening / closing timing control means operates in a predetermined low speed range. While causing the engine to perform the intake valve late closing operation, the engine speed increased from the low speed region and the discharge temperature of the mechanical supercharger rose to a predetermined allowable limit discharge temperature. In addition, the intake valve opening / closing timing variable means is controlled so that the intake valve is closed at a timing earlier than that in the case of the intake valve late closing operation, and the engine is made to perform the intake valve early closing operation. The intake of the engine with a mechanical supercharger is characterized in that EGR control means for increasing the EGR rate is provided when the engine speed increases from the low speed region and the exhaust temperature rises to a predetermined allowable limit exhaust temperature. Provide a device. The intake valve early closing operation means that the closing timing of the intake valve is earlier than that in the intake valve late closing operation.
It is not meant to be earlier than the closing timing of the intake valve of a normal engine.

According to a second aspect of the present invention, in the intake system for an engine with a mechanical supercharger according to the first aspect, after the intake valve opening / closing timing control means performs the intake valve early closing operation, the engine speed is further increased. When the temperature rises and the discharge temperature of the mechanical supercharger rises to the allowable limit discharge temperature, supercharging control means for relieving the pressurized air downstream of the mechanical supercharger to the intake passage upstream of the mechanical supercharger, Air-fuel ratio control means is provided for changing the air-fuel ratio to the rich side when the engine speed further increases and the exhaust gas temperature rises to the above-mentioned allowable limit exhaust gas temperature after the EGR rate is increased by the EGR control means. An intake device for an engine with a mechanical supercharger is provided.

According to a third aspect of the present invention, in the intake system for a mechanical supercharger engine according to the first or second aspect, the mechanical supercharger engine uses regular gasoline as fuel. An intake system for an engine with a mechanical supercharger is provided.

According to a fourth aspect of the present invention, in the intake system for an engine with a mechanical supercharger according to any one of the first to third aspects, the EGR control means causes the EG to operate in the predetermined low speed range.
EGR is supplied when the engine speed increases from the low speed range and the exhaust temperature rises to the allowable limit exhaust temperature without supplying R. An intake system for an engine is provided.

According to a fifth aspect of the invention, in the intake system for an engine with a mechanical supercharger according to any one of the first to fourth aspects, the EGR control means makes the EGR rate higher as the engine speed is higher. Provided is an intake device for an engine with a mechanical supercharger, which is characterized in that the intake device is increased.

[0015]

EXAMPLES Examples of the present invention will be specifically described below.
As shown in FIGS. 1 and 2, first to sixth cylinders # 1 to # 6
In the 6-cylinder V-type engine VE having the above, the first, third, and fifth cylinders # 1, # 3, and # 5 are arranged on the first bank P side, and the second and fourth cylinders on the second bank Q side. , 6th cylinder # 2, # 4, #
6 are arranged. Here, each cylinder # 1 to # 6 is
Ignition is performed in the order of 1 → # 2 → # 3 → # 4 → # 5 → # 6. Therefore, the intake strokes of the cylinders # 1, # 3, and # 5 on the first bank P side do not overlap with each other, and
The intake strokes of the cylinders # 2, # 4, and # 6 on the bank Q side do not overlap with each other. In the following description, for the sake of convenience, in the vicinity of the engine body, the fifth cylinder # 5 side is referred to as “left” and the first cylinder # 1 side is referred to as “right” when viewed in the longitudinal direction of the engine VE (left and right direction in FIG. 1). I will decide.

In each of the cylinders # 1 to # 6, when the first and second intake valves 1a and 1b are opened, the air-fuel mixture is introduced into the combustion chamber 3 from the first and second intake ports 2a and 2b. The mixture is taken in, compressed by a piston (not shown), ignited and burned by a spark plug (not shown), and an exhaust valve (not shown).
Combustion gas (exhaust gas) is discharged to the exhaust port 4 when is opened. Here, first and second fuel injection valves 5a, 5b are provided facing the first and second intake ports 2a, 2b, respectively, to inject fuel into intake air in the ports to form a mixture. There is. In addition, the third to sixth in FIG.
The cylinders # 3 to # 6 have the same configuration as the first and second cylinders # 1 and # 2, and therefore, the numbering to the individual members is omitted for the sake of space.

Although not shown in detail, each cylinder # 1 to # 1
The fuel injection amount of the # 6 first and second fuel injection valves 5a, 5b is
Each of them is controlled by the control unit 10. That is, the control unit 10 can freely change the air-fuel ratio of the air-fuel mixture in each of the cylinders # 1 to # 6.

In each of the first and second banks P and Q, the first and second intake valves 1a, 1a of the cylinders # 1 to # 6 are also provided.
The first and second intake valve cams 6a and 6b mounted on the intake valve cam shaft 7 are opened and closed at a predetermined timing as described later. Here, camshaft pulleys 8 are attached to the left end portions of the intake valve camshafts 7 of the first and second banks P and Q, respectively. Although not shown, one timing belt is wound around both camshaft pulleys 8 and 8 and the crankshaft pulley attached to the crankshaft, so that both intake valve camshafts 7 and 7 are The crankshaft is rotationally driven in synchronization with the crankshaft.

Here, the intake valve opening / closing timing which can change the opening / closing timings of the first and second intake valves 1a, 1b by changing the rotational phases of the intake valve camshafts 7, 7 respectively. Variable means 9 (hereinafter, abbreviated as VVT 9 for convenience) is provided, and these VVTs 9 are controlled by the control unit 10, respectively. It should be noted that the VVT 9 is the first and second intake valves 1
Since the opening and closing timings of a and 1b are only shifted in the advance direction or the retard direction, the valve opening period (as viewed in crank angle) does not change even when the opening and closing timing is changed.

Although not shown, the exhaust valve is also the intake valve 1.
The mechanism is similar to a and 1b, and is opened and closed at a predetermined timing as described later. However, since VVT is not provided for the exhaust valve,
The opening / closing timing of the exhaust valve is fixed.

A common intake passage 12 is provided to supply air for fuel combustion to each of the cylinders # 1 to # 6 of the engine VE. The common intake passage 12 is arranged in this order from the upstream side in the flow direction of the intake air. , An air cleaner 13 for removing dust in intake air, an air flow sensor 14 for detecting the amount of intake air, a throttle valve 15 which is opened and closed in conjunction with an accelerator pedal (not shown), and a crankshaft (not shown) Driven by a mechanical supercharger 16 (supercharger)
And an intercooler 17 that cools the intake air that has been adiabatically compressed by the mechanical supercharger 16 and whose temperature has risen.

A bypass intake passage 18 is provided downstream of the throttle valve 15 to connect a portion of the common intake passage 12 upstream of the mechanical supercharger 16 and a portion downstream of the intercooler 17 to each other. A relief valve 20 that is opened and closed by an actuator 19 according to a signal from the control unit 10 is provided in the bypass intake passage 18. Here, when the temperature of the air discharged from the mechanical supercharger 16 (discharge temperature) approaches a predetermined allowable limit discharge temperature as the engine speed increases, as described later, the actuator 19 relieves the relief. The valve 20 is opened so that the intake air downstream of the intercooler is relieved upstream of the supercharger so that the discharge temperature is maintained below the allowable limit discharge temperature. here,
The allowable limit discharge temperature is set to a value at which the reliability of the mechanical supercharger 16 is impaired due to thermal expansion or the like when the temperature of the mechanical supercharger 16 becomes higher than this.

The common intake passage 12 has a first branch intake passage 21 and a second branch intake passage 2 downstream of the intercooler 17.
2, the downstream end of the first branch intake passage 21 is connected to the first surge tank 23 for the first bank P, and the downstream end of the second branch intake passage 22 is the second surge for the second bank Q. It is connected to the tank 24. Here, a first communication passage 25 that connects the left end portion of the first surge tank 23 and the left end portion of the second surge tank 24 is provided.
A communication passage opening / closing valve 26 that opens and closes the valve is provided in this. In addition, a second communication passage 27 that connects the right end of the first surge tank 23 and the right end of the second surge tank 24 is provided, and the second communication passage 27 has two communication passage shutter valves that open and close the second communication passage 27. 28a and 28b are interposed.

The first and second communication passages 25 and 27, the communication passage opening / closing valve 26, and the communication passage shutter valves 28a and 28b effectively utilize the resonance effect or the inertial effect in accordance with the engine speed, and thereby, the intake air It is provided to increase the filling efficiency. That is, when the engine speed is low, the communication passage opening / closing valve 26 and the communication passage shutter valves 28a and 28b are closed to close the common intake passage 12
From the first to the second branch intake passages 21 and 22 by using the resonance effect of the pressure wave reversal portion to improve the intake charging efficiency, and open only the communication passage shutter valves 28a and 28b during the middle rotation. 2 The intake filling efficiency is increased by utilizing the resonance effect in which the central portion of the communication passage 27 is used as the pressure wave reversal portion, and the communication passage opening / closing valve 26 and the communication passage shutter valves 28a, 28b are opened at the time of high rotation to utilize the inertia effect. The intake charging efficiency is improved.

The first surge tank 23 has a first,
The upstream ends of three sets of first and second independent intake passages 29a and 29b for the third and fifth cylinders # 1, # 3 and # 5 are connected to each other, and the first and second independent intake passages 29a and 29b are connected. The downstream ends of the cylinders are connected to the first and second intake ports 2a and 2b of the corresponding cylinders. On the other hand, the second surge tank 24 has three sets of first and second independent intake passages 2 for the second, fourth, and sixth cylinders # 2, # 4, and # 6.
The upstream ends of 9a and 29b are connected, and the downstream ends of these first and second independent intake passages 29a and 29b are connected to the first and second intake ports 2a and 2b of the corresponding cylinders, respectively. here,
In the second independent intake passage 29b of each cylinder # 1 to # 6,
An intake passage opening / closing valve 30 is provided which is closed when the load is low and generates swirl in the combustion chamber 3 to enhance the combustibility of the air-fuel mixture. The first intake port 2a is a tangential type or helical type swirl port.

The first and second fuel injection valves 5a and 5b of each of the cylinders # 1 to # 6 are provided with an assist air supply passage 31 for supplying assist air for promoting vaporization and atomization of fuel. The upstream end of the assist air supply passage 31 opens into the common intake passage 12 on the upstream side of the throttle valve 15. An assist air control valve 32, which is a three-way valve, is provided in the assist air supply passage 31, and the third terminal of the assist air control valve 32 has an upstream end located downstream of the mechanical supercharger 16. An assist air introduction passage 33 opening to the common intake passage 12 is connected. Here, the assist air control valve 32
When supercharging, the pressurized intake air is introduced as assist air through the assist air introduction passage 33, while when not supercharging, intake air at atmospheric pressure is introduced as assist air through the assist air supply passage 31. ing.

The assist air supply passage 31 branches into first and second branch assist air supply passages 31a and 31b on the way, and each fuel injection valve 5a on the side of the first bank P passes through the first branch assist air passage 31a. While the assist air is supplied to 5b, the assist air is supplied to each fuel injection valve 5a, 5b on the second bank Q side through the second branch assist air supply passage 31b. The first and second
Check valves 34 and 35 are provided in the branch assist air supply passages 31a and 31b, respectively.

The exhaust gas discharged from the combustion chamber 3 of each cylinder # 1 to # 6 to the exhaust port 4 is discharged to the atmosphere through the exhaust passage 36. The exhaust passage 3
A catalytic converter 37 for purifying the exhaust gas is provided at 6.

Lowering the exhaust temperature to improve knock resistance
An EGR system that recirculates a part of the exhaust gas as EGR gas to the intake system is provided in order to suppress the generation of knocking and reduce the amount of NOx generated. Specifically, a first EGR passage 38 is provided to recirculate the exhaust gas in the exhaust passage 36 upstream of the catalytic converter 37 as EGR gas to the common intake passage 12 downstream of the intercooler 17 during non-supercharging. A first EGR valve 39 for adjusting the EGR amount is provided in the first EGR passage 38.
Is installed.

Further, there is provided a second EGR passage 41 for returning the exhaust gas in the exhaust passage 36 downstream of the catalytic converter 37 as EGR gas to the common intake passage 12 upstream of the mechanical supercharger 16 during supercharging. Has been. Then, in the second EGR passage 41, a carbon trap 51 for removing carbon in the EGR gas and an E for cooling the EGR gas are sequentially provided from the upstream side in the EGR gas flow direction.
A GR cooler 52 and a second EGR valve 42 that adjusts the EGR gas amount (EGR rate) are interposed. Where the second E
As will be described later, the GR valve 42 is capable of freely changing the EGR gas addition rate with respect to the intake air amount, that is, the EGR rate, in accordance with a signal applied from the control unit 10. The second EG
Of course, the R valve 42 can stop the supply of EGR gas to the intake system.

The control unit 10 is composed of a microcomputer, and includes "intake valve opening / closing timing control means", "EGR control means", "supercharging control means" and "air-fuel ratio control means" described in the claims. Including engine VE
Of the intake air amount detected by the air flow sensor 14, the intake air temperature detected by the first intake air temperature sensor 45, and the throttle sensor 46.
Throttle opening (engine load) detected by, the intake air temperature downstream of the supercharger detected by the second intake air temperature sensor 47, that is, the temperature of the pressurized air discharged from the supercharger 16 (hereinafter, for convenience, S / C discharge temperature), intake air temperature downstream of the intercooler detected by the third and fourth intake air temperature sensors 48, 49, and a rotation speed sensor (not shown)
Engine speed, exhaust temperature sensor detected by
Various kinds of information such as the exhaust temperature detected by (not shown) are used as control information to perform various controls of the engine VE.

However, the control unit 10
The general engine control according to the present invention is performed by a well-known ordinary control method and is not the subject matter of the present invention, and therefore its explanation is omitted. Hereinafter, referring to FIGS. Only the intake valve opening / closing timing control, the EGR control, the supercharging control, and the air-fuel ratio control, which are related to the subject matter, will be described. That is, in the engine VE, the control unit 10 determines the opening / closing timing of the intake valves 1a and 1b, the EGR rate, the pressurized air relief amount, and the air-fuel ratio based on the engine speed, the S / C discharge temperature, and the exhaust temperature. The engine output and the fuel consumption performance are improved while preventing the occurrence of knocking in the entire operation region by the preferable control, and the S / C discharge temperature and the exhaust temperature are kept within the allowable limits.

Specifically, the first and second methods are as follows.
Fuel injection valves 5a, 5b, VVT 9, and relief valve 2
0 and the second EGR valve 42 are controlled. (1) At least in an operating region (supercharging region) where supercharging is performed by the supercharger 16, the VVT 9 causes the first and second intake valves 1a and 1b to move after the intake stroke bottom dead center in terms of crank angle in the low speed region. Is relatively late (for example, 60 ° CA after the intake stroke bottom dead center), and the intake valve retarded closing operation is performed. At this time, the effective compression ratio becomes smaller, but the supercharging pressure becomes higher by this amount, and the intake charge efficiency is sufficiently secured.
At this time, since the effective compression ratio of the air-fuel mixture in the combustion chamber 3 becomes small, the temperature rise due to the compression of the air-fuel mixture becomes small. Therefore, the temperature of the air-fuel mixture at the time of ignition becomes relatively low, and the knock resistance is improved. In addition, since the pumping loss is reduced by the intake valve late closing operation, fuel efficiency is also improved. In this case, either the EGR gas may be supplied to the intake system or the EGR gas may not be supplied. However, when the EGR gas is supplied, the EGR gas amount or the EGR rate is reduced in order to minimize the decrease in the fresh air intake amount. Is preferred. Although the S / C discharge temperature also rises as the supercharging pressure rises, since the supercharging pressure is originally low in this low speed region, there is no possibility that the S / C discharge temperature will reach the allowable limit discharge temperature. .

(2) When the engine speed gradually rises during operation in such a low speed region, the exhaust gas temperature rises with it, but the exhaust gas temperature rises to a predetermined allowable limit exhaust gas temperature. In this case, the EGR rate is increased stepwise by a predetermined amount by increasing the opening degree of the second EGR valve 42. If the EGR gas is not being supplied to the intake system in the above state (1), the supply of the EGR gas is started from this point. When the EGR rate is increased in this way, the combustion temperature of the air-fuel mixture in the combustion chamber 3 decreases, so the exhaust temperature also decreases, and the exhaust temperature is maintained below the allowable limit exhaust temperature. Therefore, the exhaust gas temperature can be maintained below the allowable limit exhaust gas temperature without lowering the fuel efficiency, and the reliability of the exhaust passage 36 or the catalytic converter 37 can be improved. Further, the knock resistance is enhanced by the increase of the EGR rate. In this case, after the EGR rate is increased stepwise, it is preferable to gradually increase the EGR rate as the engine speed increases. In addition,
The EGR rate may be increased from the region where the exhaust temperature approaches the allowable limit exhaust temperature. Thus, by increasing the EGR rate according to the engine speed, the rise in exhaust temperature can be suppressed more effectively.

(3) Also, when the engine speed gradually increases during operation in the low speed region, the supercharging pressure rises accordingly and the S / C discharge temperature rises. Is increased to a predetermined allowable discharge temperature, VVT
Due to 9, the first and second intake valves 1a, 1b are closed at an earlier timing (for example, 30 ° CA after the intake stroke bottom dead center) than in the case of the intake valve late closing operation, and the intake valve early closing operation is performed. At this time, since the effective compression ratio becomes large, the supercharging pressure becomes low by this amount, and the S / C discharge temperature drops. Therefore, the S / C discharge temperature is maintained below the allowable limit discharge temperature. In this case, knocking is suppressed by lowering the combustion temperature due to EGR and increasing the valve opening overlap between the intake valve and the exhaust valve. The term "intake valve early closing operation" as used herein means that the intake valves 1a and 1b are closed at an earlier timing than in the case of late intake valve closing operation, and at an earlier timing than a conventional ordinary engine. It does not mean that the intake valve is closed.

(4) When the engine speed further increases from the state of (2) above and the exhaust temperature again rises to the allowable limit exhaust temperature, the fuel injection of the first and second fuel injection valves 5a, 5b is performed. The air-fuel ratio is changed to the rich side by increasing the amount. As a result, the exhaust gas temperature is lowered and maintained below the allowable limit exhaust gas temperature. in this way,
First, the exhaust temperature is lowered by increasing the EGR rate, and the air-fuel ratio is changed to the rich side only when the exhaust temperature cannot be maintained below the allowable limit exhaust temperature by increasing the EGR rate. As a result, unnecessary enrichment of the air-fuel ratio can be avoided and fuel efficiency can be improved.

(5) When the engine speed further rises from the above state (3) and the S / C discharge temperature rises again to the allowable limit discharge temperature, the relief valve 20 is opened to open the intercooler downstream. Pressurized air is relieved to the common intake passage 12 upstream of the supercharger through the bypass intake passage 18. As a result, the supercharging pressure is lowered, and the S / C discharge temperature is maintained below the allowable limit discharge temperature. Thus, first, the intake valve premature closing operation is performed to lower the S / C discharge temperature, and the S / C discharge temperature can no longer be kept below the allowable limit discharge temperature by the intake valve early closing operation. Since the relief of the pressurized air is performed only when it becomes the maximum, the capacity of the supercharger 16 can be utilized to the maximum in a wide operating range, and the engine output can be sufficiently increased.

Hereinafter, referring to FIG. 3, in the case where the regular gasoline is used as the fuel, the above control is performed when the engine speed gradually increases from the extremely low speed region (almost idle region). , Exhaust temperature and S /
The change characteristics of the C discharge temperature will be described. In FIG. 3, T
₁ and T ₂ respectively represent the allowable limit exhaust temperature and the allowable limit discharge temperature, G ₁ (solid line) shows the change characteristic of the S / C discharge temperature with respect to the engine speed, and H ₁ (solid line) shows the exhaust temperature. The change characteristic with respect to the engine speed is shown. Also, G ₂
Indicates the change characteristic of the S / C discharge temperature with respect to the engine speed when the EGR rate is increased by retarding the intake valve, and G ₃ is the engine of the S / C discharge temperature when the EGR rate is not increased by retarding the intake valve. The characteristic with respect to the rotational speed is shown, and G ₄ shows the characteristic with respect to the engine rotational speed of the S / C discharge temperature when the EGR rate is increased by closing the intake valve early. Furthermore, H ₂ shows the change characteristic of the exhaust temperature with respect to the engine speed when the EGR rate is increased by closing the intake valve early, and H ₃ is the engine speed of the exhaust temperature when the EGR rate is increased by closing the intake valve late. And H ₄ shows the characteristic of the exhaust temperature with respect to the engine speed when the intake valve is late closed and the EGR rate is not increased.

As shown in FIG. 3, the engine speed gradually increases from the state where the intake valve retarded closing operation is performed in the extremely low speed region and the EGR rate is not increased (including the case where the EGR rate = 0). The exhaust temperature and S
Although the / C discharge temperature rises, the exhaust temperature _first reaches the allowable limit exhaust temperature T ₁ when the engine speed reaches N ₁ . In this way, the exhaust temperature first reaches the allowable limit because the regular gasoline with relatively low knock resistance is used as the fuel, so the ignition timing is set relatively to the retard side, so that the air-fuel mixture is left behind. This is because there is a strong tendency for the temperature of the exhaust gas to become high due to burning.
Since the intake valve retarded closing operation is performed in the region where the engine speed is N ₁ or less, the knock resistance is enhanced and the occurrence of knocking is effectively prevented.

When the engine speed reaches N ₁ , EG
The R rate is increased stepwise, and the exhaust temperature drops sharply.
In this case, since the fresh air intake amount is reduced by the amount by which the EGR rate is increased, the supercharging pressure is slightly increased to compensate for this, and thereby the S / C discharge temperature is slightly increased. In the region where the engine speed is N _{1 to} N ₂ , the intake valve retarded closing operation is performed and the EGR rate is increased, so
The knock resistance is further enhanced and the occurrence of knocking is more effectively prevented.

When the engine speed further rises from this state, S / is reached when the engine speed reaches N _2.
The C discharge temperature reaches the allowable limit discharge temperature T ₂ , and at this time point, the intake valve premature closing operation is switched to, whereby the supercharging pressure decreases and the S / C discharge temperature sharply decreases. At this time, the exhaust temperature rises slightly. The engine speed is N _{2 to} N ₃
In the region (2), the occurrence of knocking is prevented by the EGR gas. In this case, by closing the intake valve early, the valve opening overlap between the intake valve and the exhaust valve becomes large, so that the scavenging property in the combustion chamber 3 is improved, which also improves the knock resistance. . In this area, S / C
Since the discharge temperature has a margin, it is preferable to increase the amount of EGR to improve knock resistance.

As the engine speed further increases,
When the engine speed reaches N ₃ , the exhaust temperature again reaches the allowable limit exhaust temperature T ₁ , and at this time the air-fuel ratio is changed to the rich side. Since the air-fuel ratio is preferably adjusted so that the exhaust gas temperature does not exceed T ₁ , the exhaust gas temperature is maintained at approximately T ₁ when the engine speed is higher than N ₃ . In this way, the air-fuel ratio is made rich in the high rotation speed region, so that the fuel efficiency is improved.

As the engine speed further increases,
When the engine speed reaches N ₄ , the S / C discharge temperature reaches the allowable limit discharge temperature T ₂ again, and at this time, the compressed air downstream of the intercooler is relieved in the common intake passage 12 upstream of the supercharger. . Here, the relief amount of the pressurized air is S
Since the / C discharge temperature is preferably adjusted so as not to exceed T ₂ , when the engine speed is higher than N ₄ , S /
The C discharge temperature is maintained at T ₂ . in this way,
Since the relief of the pressurized air is performed in the high rotation range, the performance of the supercharger 16 can be maximized in a wide operating range, and the engine output can be increased.

In this way, the engine output can be increased while preventing the occurrence of knocking in the entire operating range,
In addition, fuel efficiency can be improved, and exhaust temperature and S
/ C discharge temperature can be kept within the allowable limit.

[0045]

According to the first aspect of the invention, since the intake valve retarded closing operation is performed in the low speed region, the effective compression ratio of the air-fuel mixture in the combustion chamber becomes small and the temperature rise due to the compression of the air-fuel mixture becomes small. Become. Therefore, the temperature of the air-fuel mixture at the time of ignition becomes relatively low, the knock resistance is enhanced, and knocking is prevented. Then, from this state, when the engine speed increases and the exhaust gas temperature rises to a predetermined allowable limit exhaust gas temperature, the EGR rate is increased, so the exhaust gas temperature decreases and is maintained below the allowable exhaust gas temperature limit. Therefore, the exhaust temperature can be maintained within the allowable limit without lowering the fuel efficiency, and the reliability of the exhaust system can be improved. Further, when the engine speed increases and the discharge temperature of the supercharger rises to the predetermined allowable limit discharge temperature, the intake valve premature closing operation is performed, so the effective compression ratio increases and the boost pressure decreases by this amount. , The discharge temperature is lowered and is maintained below the allowable limit discharge temperature. Therefore, the discharge temperature can be held within the allowable limit while the capacity of the supercharger is maximized, and the engine output can be increased.

According to the second invention, basically, the same operation and effect as those of the first invention can be obtained. Further, when the engine speed increases and the exhaust gas temperature again rises to the allowable exhaust gas temperature limit, the air-fuel ratio is changed to the rich side, whereby the exhaust gas temperature is lowered and kept below the allowable exhaust gas temperature limit. Therefore, the exhaust gas temperature is first lowered by increasing the EGR rate, and the air-fuel ratio is changed to the rich side only when the exhaust gas temperature cannot be maintained within the allowable limit. Unnecessary enrichment of the air-fuel ratio is avoided and fuel efficiency is improved. Further, when the engine speed increases and the discharge temperature again rises to the allowable limit discharge temperature, the pressurized air downstream of the supercharger is relieved in the intake passage upstream of the supercharger, which reduces the supercharging pressure. The discharge temperature is maintained below the allowable limit discharge temperature. Therefore, the discharge temperature is lowered by first performing the intake valve early closing operation,
As a result, the pressurized air is relieved only when the discharge temperature cannot be maintained within the allowable limit, so it is possible to maximize the performance of the supercharger in a wide operating range. The engine output can be increased.

According to the third invention, basically, the same operation and effect as those of the first or second invention can be obtained. Furthermore, since regular gasoline having relatively low knock resistance is used as the fuel, the exhaust temperature becomes relatively high. Therefore, when the engine speed increases from the low speed region, the exhaust temperature first reaches the allowable limit exhaust temperature, and then the discharge temperature reaches the allowable limit discharge temperature. Therefore, when the discharge temperature reaches the allowable limit discharge temperature and the intake valve premature closing operation is performed, the EGR rate is already increased, so that the knock resistance is sufficiently enhanced and the occurrence of knocking is prevented. It If the discharge temperature reaches the allowable limit first, for example, by using high-octane gasoline as the fuel, the EGR rate cannot be increased from this point until the exhaust temperature reaches the allowable limit. The knocking property will be slightly reduced.

According to the fourth invention, basically, the same action and effect as any one of the first to third inventions can be obtained. Further, since the supply of EGR gas to the intake system is stopped in the low speed region, the fresh air intake amount is increased and the engine output is increased.

According to the fifth invention, basically, the same operation and effect as any one of the first to fourth inventions can be obtained. Furthermore, since the EGR rate is increased as the engine speed increases, the increase in exhaust temperature is effectively suppressed.

[Brief description of drawings]

FIG. 1 is a system configuration diagram around an engine body of an engine with a mechanical supercharger including an intake device according to the present invention.

FIG. 2 is a system configuration diagram of an intake system of the engine shown in FIG.

FIG. 3 is a diagram showing characteristics of discharge temperature and exhaust temperature of a supercharger with respect to engine speed in the engine shown in FIG. 1.

[Explanation of symbols]

 VE ... Engine # 1 to # 6 ... First to sixth cylinders 1a, 1b ... First and second intake valves 5a, 5b ... First and second fuel injection valves 9 ... Intake valve opening / closing timing varying means 10 ... Control unit 16 ... Mechanical supercharger 20 ... Relief valve 42 ... Second EGR valve

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location F02D 21/08 311 B 7536-3G 23/00 K 7536-3G 41/02 330 D 8011-3GE 8011-3G 41/04 330 M 8011-3G 43/00 301 NHZ F02M 25/07 570 P (72) Inventor Tatsuya Uesugi 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Motor Corporation

Claims (5)

[Claims] 1. A mechanical supercharger, an intake valve opening / closing timing variable means capable of changing the closing timing of an intake valve, and an operating state at least in an operating region where supercharging is performed by the mechanical supercharger. Accordingly, the intake valve opening / closing timing for controlling the intake valve opening / closing timing variable unit to cause the engine to perform the intake valve delayed closing operation so that the intake valve is closed at a relatively late timing after the intake stroke bottom dead center when viewed from the crank angle. In an intake device for a mechanical supercharged engine provided with a control means, the intake valve opening / closing timing control means causes the engine to perform an intake valve late closing operation in a predetermined low speed region, while the engine is operated from the low speed region. When the rotational speed rises and the discharge temperature of the mechanical supercharger rises to the prescribed allowable limit discharge temperature, the intake valve operates faster than the intake valve delayed closing operation. The intake valve opening / closing timing varying means is controlled so as to be closed by the engine so that the engine performs the intake valve early closing operation. E when the temperature reaches the allowable limit exhaust temperature
An intake system for an engine with a mechanical supercharger, comprising EGR control means for increasing a GR rate. 2. The intake system for an engine with a mechanical supercharger according to claim 1, wherein the intake valve opening / closing timing control means performs an intake valve early closing operation, and then the engine speed further increases. Supercharging control means for relieving the pressurized air downstream of the mechanical supercharger to the intake passage upstream of the mechanical supercharger when the discharge temperature of the mechanical supercharger rises to the above-mentioned allowable limit discharge temperature, and EGR control means After the EGR rate is increased by, the engine speed further increases, and when the exhaust temperature rises to the allowable limit exhaust temperature, the air-fuel ratio control means for changing the air-fuel ratio to the rich side is provided. An intake device for an engine with a mechanical supercharger. 3. The intake system for a mechanical supercharged engine according to claim 1 or 2, wherein the engine with a mechanical supercharger uses regular gasoline as fuel. An intake device for an engine with a mechanical supercharger. 4. The intake system for an engine with a mechanical supercharger according to any one of claims 1 to 3, wherein the EGR control means does not supply EGR in the predetermined low speed range, When the engine speed increases from the low speed range and the exhaust temperature rises to the above-mentioned allowable limit exhaust temperature, EG
An intake device for an engine with a mechanical supercharger, which is adapted to supply R. 5. The intake system for an engine with a mechanical supercharger according to any one of claims 1 to 4, wherein the EGR control means increases the EG as the engine speed increases.
An intake device for an engine with a mechanical supercharger characterized by increasing the R ratio.