JPH0586913A - Intake system of engine - Google Patents

Abstract

PURPOSE:To provide an intake system for an engine with a supercharger provided with a variable valve timing mechanism and a variable intake mechanism, for effectively preventing knocking at the time of quick acceleration from a low rotational and low load region, and for improving acceleration responsiveness. CONSTITUTION:An opening valve overlap of an intake device A of an engine E with a supercharger, provided with a hydraulic variable valve timing mechanism 21, a P port 4 for constantly feeding air to a combustion chamber, and with an S port 5 provided with an opening and closing valve 39, is made small in a low load and low rotation region, and is made large in the other regions, while the opening and closing valve 39 is closed in a low rotation region, and is opened in the other regions. A control means (control unit 23) is also provided, by which the opening and closing valve 39 is forcibly opened for a fixed period at the time of quick acceleration from a condition where the opening valve overlap is small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine intake device.

[0002]

2. Description of the Related Art Generally, in an engine, combustion stability deteriorates in a low speed region. Therefore, in order to improve this, a first intake port (hereinafter, referred to as P port) that constantly supplies air to each combustion chamber and a second intake port (hereinafter, (This is called S port)
And a so-called variable intake mechanism in which the on-off valve is closed and air is supplied to the combustion chamber only from the P port in a predetermined low rotation region (for example, JP-A-64-104920). (See Japanese Patent Publication). In an engine provided with such a variable intake mechanism, normally, the P port and the S port are eccentric to the center of the cylinder in opposite directions and open to the combustion chamber. Therefore, in a predetermined low rotation region where air is supplied to the combustion chamber only from the P port, a swirl (swirl flow) is generated in the combustion chamber, and the swirl enhances the combustibility of the air-fuel mixture, thereby improving the combustion stability. The height is increased and knocking is prevented. It should be noted that the on-off valve is opened in an operating region other than the predetermined low rotation region, air is sufficiently supplied to the combustion chamber from both P and S ports, and the engine output is increased.

On the other hand, in an engine equipped with a mechanical supercharger, knocking is likely to occur at high loads. Therefore, in an engine equipped with a mechanical supercharger, usually, the overlap of the valve opening period between the exhaust valve and the intake valve (hereinafter referred to as the valve opening overlap) is set to be relatively large, and The residual gas is scavenged by the air flowing into the combustion chamber from the port to prevent knocking. However, when the valve opening overlap is increased in this way, there is a problem that combustion stability deteriorates due to internal EGR in a low rotation / low load region, for example, an idle region. In addition, even under a high load, the air-fuel mixture is blown through from the intake port to the exhaust port during the valve opening overlap period, the HC concentration (hydrocarbon concentration) in the exhaust gas becomes high, and the fuel efficiency decreases. There is such a problem. In addition, the above-mentioned blow-through becomes remarkable especially in a pent roof type four-valve engine.

On the other hand, for example, in a four-valve engine provided with two intake valves and two exhaust valves, a pair of intake / exhaust valves arranged substantially symmetrically with respect to the center of the cylinder bore. An engine has been proposed in which the opening overlap of the exhaust valve is set large and the opening overlap of the other set of intake and exhaust valves is set small (see, for example, JP-A-61-58920). In this engine, since the valve-to-valve distance of the intake / exhaust valves with a large valve opening overlap becomes relatively long, it is possible to reduce the blow through of the air-fuel mixture. In the four-valve engine provided with the variable intake mechanism having the P and S ports as described above, the valve opening overlap between the intake valve of the P port and the exhaust valve at the point-symmetrical position. Has been proposed, in which the intake valve of the S port and the exhaust valve at the position symmetrical with the intake valve of the S port are set to a small opening overlap.
(See, for example, JP-A-61-218726). However, in the above-mentioned conventional engine disclosed in Japanese Patent Laid-Open No. 61-58920 or Japanese Patent Laid-Open No. 61-218726, basically, intake / exhaust valves having a large valve opening overlap exist. Therefore, there is a problem that deterioration of combustion stability in the low rotation speed / low load region cannot be completely prevented.

Therefore, a variable valve timing mechanism for changing the opening / closing timing of the intake valve or the exhaust valve is provided.
In the low speed / low load range, the valve opening overlap between the intake valve and the exhaust valve is set small, and in the other areas, the valve open overlap is set large to ensure combustion stability in the low speed / low load range. Has been proposed and an intake system for an engine has been proposed in which both of the above are ensured and the scavenging performance in a high load region is improved. Then, if a variable intake mechanism is further provided in the intake device equipped with such a variable valve timing mechanism and air is supplied to the combustion chamber only from the P port in the low rotation region to generate swirl, the low rotation region The flammability can be greatly improved.

[0006]

By the way, a variable valve timing mechanism is usually accompanied by a relatively large response delay, and such a response delay is particularly remarkable in a hydraulic variable valve timing mechanism (for example, 1 to 2). Seconds). And
In an engine intake device including the variable valve timing mechanism and the variable intake mechanism as described above, for example, during rapid acceleration from a low rotation / low load region where the valve opening overlap is small, the operating state of the engine opens immediately. It enters the operating range (high load range) where the overlap should be large. However, since the variable valve timing mechanism is accompanied by a delay in response, the valve opening overlap does not immediately increase, and sufficient scavenging is not performed during this period. On the other hand,
In such a low speed region, intake air is supplied only from the P port and swirls are generated, but at such low speeds and high loads, if swirls are generated without sufficient scavenging, the spark plug surroundings However, there is a problem in that the air-fuel mixture becomes ignited and the ignition performance deteriorates, while the residual gas ignites the air-fuel mixture, which causes knocking and deteriorates the acceleration performance or the acceleration response. The present invention has been made to solve the above-mentioned conventional problems, and in an intake system for a supercharged engine provided with a variable valve timing mechanism and a variable intake mechanism, a low rotation speed
An object of the present invention is to provide an intake system for an engine, which can effectively prevent the occurrence of knocking at the time of rapid acceleration from a low load region and can improve acceleration performance or acceleration response.

[0007]

In order to achieve the above object, the first aspect of the present invention is capable of changing the overlap of the valve opening period between the intake valve and the exhaust valve (valve opening overlap). In an engine provided with a valve timing means, a first intake port that constantly supplies air to the combustion chamber, and a second intake port that has an on-off valve, the valve opening overlap is set to a predetermined low rotation and low load. The valve opening overlap control means for controlling the variable valve timing means so as to be small in the area and large in the other area, and the opening / closing valve are controlled to be closed in a predetermined low rotation area and opened in the other areas. An opening / closing valve control means and an opening / closing valve opening means for forcibly opening the opening / closing valve for a predetermined period at the time of sudden acceleration from an operating region where the valve opening overlap is set small are provided. Providing an intake system for an engine characterized by and.

A second aspect of the present invention is the engine intake system according to the first aspect, wherein the variable valve timing means is
Provided is an intake device for an engine, which is hydraulic variable valve timing means.

A third aspect of the present invention provides an engine intake system according to the first or second aspect of the invention, characterized in that a mechanical supercharger driven by the engine is provided. To do.

According to a fourth aspect of the invention, in the intake system for an engine according to the second or third aspect of the invention, the opening / closing valve is opened by the opening / closing valve opening means at the time of sudden acceleration from an operating region where the valve opening overlap is set small. An intake system for an engine, wherein the period is a period until the operation of the variable valve timing means is completed.

[0011]

EXAMPLES Examples of the present invention will be specifically described below.
As shown in FIGS. 1 to 3, an intake device A for supplying air is provided to an intake two-valve / exhaust two-valve engine E. In each cylinder 1 of the engine E, basically, when the first and second intake valves 2 and 3 are opened, the air-fuel mixture is introduced into the combustion chamber 6 from the first and second intake ports 4 and 5. The mixture is taken in, compressed by the piston 7, and then ignited and burned by the ignition plug 8, and the first and second exhaust valves 9,
Combustion gas is discharged from the first and second exhaust ports 11 and 12 when the valve 10 is opened.

On the upper surface (cylinder head portion) of the cylinder 1, a first intake port 4 (hereinafter referred to as P port 4) opened and closed by a first intake valve 2 and an opening and closing by a second intake valve 3 are provided. A second intake port 5 (hereinafter referred to as S port 5), a first exhaust port 11 opened and closed by a first exhaust valve 9, and a second exhaust port 12 opened and closed by a second exhaust valve 10. Is provided. Here, both the P and S ports 4,5 are the intake side half of the cylinder 1.
The first and second exhaust ports 1 are located in the right half of FIG.
1 and 12 are the exhaust side half of the cylinder 1 (the left half in FIG. 2)
It is located in. An ignition plug 8 is arranged at the center of the cylinder 1. The P port 4 opens to the cylinder 1 in a substantially circumferential direction of the cylinder,
In a predetermined low rotation region (region 2 in FIG. 8), the air flowing into the combustion chamber 6 from the P port 4 swirls along the inner peripheral surface of the cylinder to generate swirl. here,
The P port 4 may be formed in a helical shape to generate swirl.

The first and second intake valves 2 and 3 are opened and closed at a predetermined timing in synchronization with a crankshaft (not shown) by a plurality of intake valve cams 16 attached to an intake side camshaft 15. It has become so. Similarly, the first and second
The exhaust valves 9 and 10 are also opened and closed by a plurality of exhaust valve cams 18 attached to the exhaust side cam shaft 17. A hydraulic variable valve timing mechanism 21 is provided on the exhaust side camshaft 17, and the variable valve timing mechanism 21 operates according to a signal applied from the control unit 23 to the hydraulic mechanism 22.
The rotation phase of the exhaust side camshaft 17 can be changed. That is, the first and second exhaust valves 9, 10
Opening and closing timing of the intake valve 2, 3 and exhaust valve 9,
The valve opening overlap between 10 and 10 can be changed.

Here, each intake valve 2, 3 and each exhaust valve 9, 10
The opening / closing timing of the variable valve timing mechanism 21 has the characteristic shown in FIG. 7 when the phase of the exhaust valve side camshaft 17 is retarded, that is, when the valve opening overlap is large. Is set to. That is, the valve-opening overlap between the first intake valve 2 and the first exhaust valve 9 which are in point-symmetrical positions with respect to the center of the cylinder bore is relatively large (a ₂ ), and the first valve in the point-symmetrical position is located. 2 The valve opening overlap between the intake valve 3 and the second exhaust valve 10 is almost zero. Further, the valve opening overlap between the first intake valve 2 and the second exhaust valve 10 which face each other is medium (a ₁ ). The valve opening overlap between the second intake valve 3 and the first exhaust valve 9 that face each other is also medium. In such a configuration, the valve-to-valve distance between the first intake valve 2 and the first exhaust valve 9 having the largest valve opening overlap becomes long, so blow-through of the air-fuel mixture is reduced. On the other hand, when the phase of the exhaust side camshaft 17 is advanced by the variable valve timing mechanism 21, the valve opening overlaps between the intake valves 2 and 3 and the exhaust valves 9 and 10 become smaller.

The intake device A is provided with a common intake passage 24. In the common intake passage 24, an air cleaner 25 for removing suspended dust in intake air and an intake air amount in order from the upstream side in the intake flow direction. Air flow meter 26 for detecting
A throttle valve 27 that is opened and closed in conjunction with an accelerator pedal (not shown), and a Rishorum type mechanical supercharger 28 that is driven by the engine E are provided. In order to adjust the supercharging pressure, a bypass intake passage 29 that bypasses the supercharger 28 is provided, and a bypass opening / closing valve 30 that is opened / closed by a diaphragm type actuator 31 is provided in the bypass intake passage 29. There is.
Further, an intercooler 32 for cooling air is provided in the common intake passage 24 downstream of the supercharger 28, and the common intake passage 24 downstream of the intercooler 32 is not shown in detail but is independent for each cylinder. It is connected to the intake passage. The independent intake passage is branched into a first independent intake passage 35 having a downstream end communicating with the P port 4 and a second independent intake passage 36 having a downstream end communicating with the S port 5.

A fuel injection valve 37 is arranged in a partition wall that separates the first independent intake passage 35 and the second independent intake passage 36, and the fuel injected from the fuel injection valve 37 is formed in the partition wall. The fuel is supplied to the first and second independent intake passages 35 and 36 through a bifurcated fuel injection passage 38 that opens to both the first and second independent intake passages 35 and 36. Further, an opening / closing valve 39 for opening / closing the second independent intake passage 36 (S port 5) is provided, and the opening / closing valve 39 is an electromagnetic actuator 41 according to a signal from the control unit 23 via a link mechanism 40. It is designed to be opened and closed by. As will be described later, the control unit 23 closes the open / close valve when the operating state of the engine E is in the region 2 in FIG. 8 and opens it when it is in the region 3. Here, when the on-off valve 39 is closed, air (mixture) is supplied to the combustion chamber 6 only from the P port 4, swirl is generated in the combustion chamber 6, and basically the combustibility of the mixture is generated. Is increased. On the other hand, when the on-off valve 39 is open, P, S
Sufficient air is supplied to the combustion chamber 6 from both ports 4 and 5,
The engine output is sufficiently increased.

A control unit 23 including a microcomputer is provided for performing predetermined control of the engine E and the intake system A. The control unit 23 includes an intake air intake amount Q detected by an air flow meter 26, The throttle opening TVO detected by the throttle sensor 45, the cam phase of the exhaust side camshaft 17 detected by the phase sensor 46, the engine speed N detected by a speed sensor (not shown), etc. are input as control information. It is supposed to be done.
Here, the control unit 23 is a comprehensive control means for the engine E and the intake system A, and is configured to perform various predetermined controls. The variable valve timing mechanism, which is related to the gist of the present application, will be described below. Only the switching control of 21 (that is, the valve opening overlap control) and the opening / closing control of the opening / closing valve 39 (that is, the swirl control) will be described.

(1) Valve Opening Overlap Control The control method of valve opening overlap control will be described below with reference to the flow chart shown in FIG. At step # 1, the engine speed N and the intake air amount Q are read as control information. Next, in step # 2, it is determined whether or not the operating state of the engine E is within the region where the valve opening overlap should be increased. In this embodiment, the valve opening overlap is set to be small in the low rotation / low load region as shown by the region 1 in FIG. This is because if the valve opening overlap is increased in the low rotation speed / low load region, combustion stability deteriorates due to blowback or internal EGR.
In areas other than this, the valve opening overlap is set large to perform sufficient scavenging to prevent knocking. In this case, as described above, the first intake valve 2 and the first exhaust valve 9, which have the largest valve opening overlap, are located in a point-symmetrical position with respect to the center of the cylinder bore. It is possible to prevent the blow-through of the vehicle and improve the emission performance and fuel efficiency performance.

If it is determined in step # 2 that the operating state of the engine E is in the region where the valve opening overlap should be increased, that is, the region other than the region 1 (YES), the overlap flag F is determined in step # 3. ₁ is added to 1 The overlap flag F ₁ is a flag indicating whether or not the valve opening overlap is large, and is set to 1 when the valve opening overlap is large, and is set to 0 when the valve opening overlap is small. Be done. Then, in step # 4, the hydraulic mechanism 22 (variable valve timing mechanism 2
1) Valve timing control signal (VTC signal)
Is turned on, the phase of the exhaust side camshaft 17 is retarded, and the valve opening overlap becomes large. This effectively scavenges air and prevents knocking.
Then, the process returns to step # 1.

On the other hand, if it is determined in step # 2 that the operating condition of the engine E is in the region 1 (NO), the valve timing flag F _{1 is set} to 0 in step # 5, and then the step is continued. At # 6, the VTC signal to the hydraulic mechanism 22 is turned off, and the valve opening overlap is reduced. This improves combustion stability. After this, step # 1
Return to.

(2) Open / close valve control (swirl control) The open / close valve control will be described below according to the flowchart shown in FIG.
A control method of (swirl control) will be described. Step # 11
Then, the engine speed N, the intake air amount Q, and the timer count value T are read as control information. Next, at step # 12, it is determined whether or not the operating state of the engine E is within the region where the on-off valve 39 should be opened. In the present embodiment, basically, the opening / closing valve 39 is closed in the region 2 (including the region 1) in FIG. 8, that is, in the operating region in which the rotational speed shifts to the high rotational speed side when the load is low although the rotational speed is low. The open / close valve 39 is opened in the other region, that is, the region 3. That is, in the low rotation / medium / high load range or the light load range, the combustibility deteriorates, so the on-off valve 3
9 is closed and air is supplied to the combustion chamber 6 only from the P port 4 to generate swirl and enhance combustibility. Further, in the other region, that is, the region 3, the on-off valve 3
9 is opened, and sufficient air is supplied to the combustion chamber 6 from both the P and S ports 4 and 5 to increase the engine output.

If it is determined in step # 12 that the operating state of the engine E is in the region where the on-off valve 39 should be opened, that is, region 3 (YES), the on-off valve flag F ₂ is incremented by 1 in step # 13. Be taken. The on-off valve flag F ₂ is a flag indicating whether or not the on-off valve 39 is open. When the on-off valve 39 is open, 1 is set,
When closed, 0 is set. Subsequently, the opening / closing valve 39 is opened in step # 14. As a result, sufficient air is supplied to the combustion chamber 6 and the engine output is increased. Then, the process returns to step # 1.

On the other hand, in step # 12, the operating state of the engine E is the region where the on-off valve 39 should be closed, that is, the region 2
If it is determined that the valve is on (NO), the on-off valve flag F _{2 is set} to 0 in step # 15, and then step # 1.
At 6, it is compared / determined whether the timer count value T is 0 or not. As described above, in the region 2, the on-off valve 39 is closed to generate the swirl to enhance the combustibility.
The region 2 includes a region with a small valve opening overlap (region 1) and a region with a large valve opening overlap. In this case, in the low load region where the valve opening overlap is small in the region 2, the internal EGR is reduced and the combustion stability is enhanced due to the small valve opening overlap, and the combustion stability is further enhanced by the swirl. On the other hand, in the high load region where the valve opening overlap is large, the scavenging is promoted due to the large valve opening overlap to prevent knocking from occurring, and the swirl enhances the combustibility and the engine output.

However, when the operating state of the engine E is within the region 1 and therefore the valve opening overlap is small and the accelerator pedal is suddenly depressed to start the rapid acceleration, the operating state of the engine is as shown in FIG. As indicated by the arrow A ₁ in the middle, the valve opening overlap changes almost instantly. However, the hydraulic variable valve timing mechanism 21 is usually accompanied by a response delay of about 1 to 2 seconds. Note that the electromagnetic variable valve timing mechanism is shorter than the hydraulic type,
After all, there is a delay in response. Therefore, high load operation is performed in a state where the valve opening overlap is small for some period after the start of rapid acceleration. In this case, knocking is likely to occur because the scavenging property is poor, but in addition to this, when swirl is generated, the air-fuel mixture around the spark plug becomes lean and the ignitability deteriorates, causing knocking. Therefore, at the time of rapid acceleration from the state where the valve opening overlap is small (region 1), the on-off valve 39 is opened to stop the swirl generation for a period corresponding to the response delay of the variable valve timing mechanism 21, and knocking occurs. I try to prevent it. In this embodiment, in this case, the on-off valve 39 is forcibly opened for the predetermined time T ₀ . The T ₀ is set according to the engine speed N, as will be described later. Then, the elapsed time after the start of the rapid acceleration is counted by the timer, and when the count is up, the on-off valve 39
The forced opening of the valve is stopped. The setting of the set value T ₀ and the counting of the timer are performed by the timer count routine shown in FIG. 6, as will be described later.

If it is determined in step # 16 that T = 0 (YES), it means that it is not during rapid acceleration, so step # 1
At 7, the on-off valve 39 is closed. After this, step # 11
Return to. On the other hand, if it is determined that T ≠ 0 (N
O), the opening / closing valve 39 is opened in step # 14. FIG. 9 shows the characteristics of the valve opening overlap (J ₁ ) and the opening / closing valve opening / closing state (J ₂ ) with respect to time during such rapid acceleration. In the example shown in FIG. 9, the variable valve timing mechanism 21 starts operating at t ₁ after the start of acceleration, and the switching is completed at t ₂ . For reference, FIG. 9 also shows the characteristics of the valve opening overlap (J ₃ ) and the opening / closing valve opening / closing state (J ₄ ) with respect to time as shown by arrow A ₂ in FIG. There is. In this way, knocking due to the response delay of the variable valve timing mechanism 21 is prevented. Then, the process returns to step # 11.

In the above embodiment, the opening / closing valve 39 is forcibly opened for the predetermined time T ₀ at the time of sudden acceleration, but the variable valve timing mechanism 21 is determined from the cam phase detected by the cam phase sensor 46. It is also possible to detect the operating state of and open the on-off valve 39 compulsorily until the switching operation of the variable valve timing mechanism 21 is completed. With this configuration, even if the engine temperature (oil temperature) or the characteristic of the variable valve timing mechanism 21 varies, the on-off valve control can be accurately performed.

(3) Timer Count Routine The timer count routine will be described below with reference to the flowchart shown in FIG. In this timer count routine, when rapid acceleration is started while the valve opening overlap is small and the opening / closing valve 39 is closed, the timer count value is set to a predetermined value T ₀ and thereafter the count value T is decremented. However, the count is stopped when it reaches 0. .. At step # 21, the throttle opening TVO and the current timer count value T are read.

Next, at step # 22, it is compared and judged whether or not T = 0. If T ≠ 0 (NO), the timer is already counting, so at step # 27, T is a predetermined value. Decrement by ΔT and continue counting.
If it is determined in step # 22 that T = 0 (YE
S), whether or not the overlap flag F ₁ has changed from 0 to 1 in step # 23, that is, the operating state of the engine E changes from the region where the valve opening overlap should be reduced (region 1) to the valve opening overlap. It is compared and judged whether or not it has changed to a region where the throttle opening should be increased, and in step # 24, the throttle opening T
Based on the angular acceleration of VO, it is compared and judged whether or not the rapid acceleration is started, and in step # 25 it is compared whether or not the on-off valve flag F ₂ is 0, that is, whether or not the on-off valve 39 is closed.・ Judged. Then, when F ₁ changes from 0 to 1, rapid acceleration is started, and the opening / closing valve 39 is closed (YES in all steps # 23 to # 25), the timer is set in step # 26. The value T ₀ is set. This T ₀ is a function of the engine speed N, as shown by the curve K ₁ in FIG. That is, the hydraulic pressure of the hydraulic mechanism 22 (variable valve timing mechanism 21) is
As shown by the curve K ₂ , the value rises as the engine speed increases, and the response delay of the variable valve timing mechanism 21 becomes shorter as the hydraulic pressure increases, so T ₀ is made smaller as the engine speed increases. I am trying. After this,
Return to step # 21.

As described above, according to the present invention, knocking due to a response delay of the variable valve timing mechanism 21 can be effectively prevented at the time of rapid acceleration from a state where the valve opening overlap is small, and acceleration response is enhanced. ..

[0030]

According to the first aspect of the present invention, when the opening / closing valve is closed, the opening / closing valve is forcibly opened at the time of rapid acceleration from a state where the valve opening overlap is small, and the swirl generation is stopped. Therefore, even if the scavenging property is deteriorated due to the response delay of the variable valve timing means, knocking does not occur, the engine output is increased, and the acceleration responsiveness is improved.

According to the second invention, basically, the same operation and effect as those of the first invention can be obtained. Furthermore, since the variable valve timing means is a hydraulic type with a large response delay, the above effect is particularly effective.

According to the third invention, basically, the same effect as that of the first or second invention can be obtained. Further, since the mechanical supercharger is provided and knocking easily occurs at the time of high load, the above effect is particularly effective.

According to the fourth invention, basically, the same operation and effect as those of the second or third invention can be obtained. Further, the open / close valve is forcibly opened according to the response delay of the variable valve timing means, and the generation of swirl is not stopped more than necessary, so the combustibility is enhanced.

[Brief description of drawings]

FIG. 1 is a system configuration diagram of an engine and an intake device showing an embodiment of the present invention.

FIG. 2 is a partial cross-sectional plan view around the intake / exhaust ports of the engine and the intake system shown in FIG.

3 is an elevational cross-sectional explanatory view around intake / exhaust ports of the engine shown in FIG. 1. FIG.

FIG. 4 is a flowchart showing a control method of valve opening overlap control.

FIG. 5 is a flowchart showing a control method of on-off valve control.

FIG. 6 is a flowchart showing a timer count routine.

FIG. 7 is a diagram showing opening / closing timings of an intake valve and an exhaust valve.

FIG. 8 is a diagram showing a valve opening overlap characteristic and an opening / closing valve opening / closing characteristic.

FIG. 9 is a diagram showing a valve opening overlap state and an opening / closing valve opening / closing state during acceleration.

FIG. 10 is a diagram showing characteristics of a set value of a timer and hydraulic pressure with respect to an engine speed.

[Explanation of symbols]

 A ... Intake device E ... Engine 2, 3 ... 1st, 2nd intake valve 4 ... P port 5 ... S port 6 ... Combustion chamber 9, 10 ... 1st, 2nd exhaust valve 21 ... Variable valve timing mechanism 22 ... Hydraulic pressure Mechanism 23 ... Control unit 28 ... Mechanical supercharger 39 ... Open / close valve

Claims (4)

[Claims] Claim: What is claimed is: 1. Variable valve timing means capable of changing the overlap of the valve opening period between the intake valve and the exhaust valve (valve opening overlap), and first intake air for constantly supplying air to the combustion chamber. In the engine provided with the port and the second intake port provided with the opening / closing valve, the variable valve timing means for decreasing the valve opening overlap in a predetermined low rotation / low load region and increasing it in other regions. And an opening / closing valve control means for controlling the opening / closing valve to be closed in a predetermined low rotation region and opened in other regions, and an operating region in which the valve opening overlap is set small. An intake device for an engine, which is provided with an opening / closing valve opening means for forcibly opening the opening / closing valve for a predetermined period at the time of sudden acceleration. 2. The intake system for an engine according to claim 1, wherein the variable valve timing means is a hydraulic variable valve timing means. 3. The intake system for an engine according to claim 1 or 2, further comprising a mechanical supercharger driven by the engine. 4. The intake system for an engine according to claim 2 or 3, wherein a period during which the on-off valve is opened by the on-off valve opening means at the time of sudden acceleration from an operating region where the valve opening overlap is set small. An intake device for an engine, which is a period until completion of operation of the variable valve timing means.