JPH0574690B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a technique for improving the intake system of an internal combustion engine having two intake valves for each cylinder.

<Prior art> As an intake system of this type of internal combustion engine, for example,
There is something like the one shown in Figure 4 (Patent Application 1983-
No. 60918).

To explain this, the opening timing of the low-speed intake valve 1 and high-speed intake valve 2 provided for each cylinder is changed, and the low-speed intake port 3 and high-speed intake port 4 that communicate with these intake valves 1 and 2 are changed. A high-speed intake port 4 is provided independently and is equipped with a high-speed intake valve 2 that has a large overlap with the exhaust valve 5.
An on-off valve 6 is provided at the intake port 3, and one intake throttle valve 8 is interposed in the intake passage 7 upstream of both the low-speed and high-speed intake ports 3 and 4.

In an operating range where the intake air flow rate is less than a predetermined value, the on-off valve 6 is fully closed to create a strong swirl inside the combustion chamber by utilizing the airflow flowing only from the low-speed intake port 3 along the combustion chamber peripheral wall. The aim is to improve combustibility by generating flow.

On the other hand, when the intake air flow rate exceeds a predetermined value, as the flow rate increases, that is, the rotational speed
As the load increases, the opening degree of the on-off valve 6 is gradually increased to gradually increase the opening area of the high-speed intake port 4, and the on-off valve 6 is almost fully opened in the maximum output range of the engine, so that the opening/closing can be performed. Unburnt HC immediately after opening valve 6
The aim is to improve intake air filling efficiency while suppressing increases in emissions.

By the way, in the above-mentioned device, when the on-off valve 6 is closed, the air pressure close to the atmospheric pressure on the upstream side of the intake throttle valve 8 is passed through the fresh air introduction passage 9 in which an orifice is inserted in the high-speed intake port 4 portion on the downstream side. Fresh air is inhaled between the time when the high-speed intake valve 2 closes and the time when it opens again,
The differential pressure with the exhaust pressure is reduced to prevent the exhaust from flowing into the high-speed intake port 4 during the overlap period with the exhaust valve 5, thereby significantly reducing the amount of burnt gas mixed in the air-fuel mixture. Efforts are being made to improve combustion performance.

<Problems to be Solved by the Invention> However, as described above, even in the case of preventing backflow of exhaust gas by introducing fresh air, there is still room for improvement as described below.

That is, in the configuration described above, since both the low-speed and high-speed intake ports 3 and 4 are provided downstream of the intake throttle valve 8, the on-off valve 6 is closed during idling.
The upstream pressure of is equal to the intake negative pressure.

For this reason, when fresh air is introduced into the high-speed intake port 4 and the pressure inside the intake port 4 is increased to near atmospheric pressure, the differential pressure across the on-off valve 6 increases, causing problems with the sealing performance of the on-off valve 6. It's coming.

By the way, when the opening/closing properties of the on-off valves 6 of a plurality of cylinders are controlled by the same rotary shaft 10, the following problem occurs when the sealing performance of the on-off valves 6 is improved.

Generally, the cylinder head is made of aluminum, and the housing of the on-off valve 6 is also preferably made of aluminum in order to reduce its weight.

However, it is difficult to make the rotating shaft 10 sufficiently large in diameter (which creates resistance to air intake), and the rotating shaft 10 is made of aluminum because it has to be ground down to a flat surface in order to install the on-off valve 6 and holes for the mounting screws are formed. It is difficult to use steel in terms of strength, so it is necessary to use iron-based materials.

In this case, depending on the operating condition of the engine, the temperature of each component including the cylinder head may vary from -20°C at the start in winter to ++20°C at high speed.
It varies in the range of around 150° up to around 130°C, therefore,
Each of the components will be affected by heat.

The coefficient of thermal expansion is about twice as different between iron and aluminum, and if the on-off valve 6 is attached to the rotating shaft 10 with almost no gap between it and the high-speed intake port 4 at room temperature, in the operating region where the temperature rises. At a certain high speed,
The difference between the amount of expansion in the axial direction of the rotating shaft 10 due to thermal expansion and the amount of expansion in the same direction of the housing of the on-off valve 6 increases, and accordingly, the on-off valve 6 bites into the wall surface of the high-speed intake port 4, causing the valve to open. A problem arises in that the engine becomes disabled and the output of the engine decreases.

For this reason, it is necessary to provide a certain amount of clearance in advance between the on-off valve 6 and the wall of the high-speed intake port 4, which inevitably deteriorates the sealing performance.

If sufficient sealing performance is not achieved, the introduced fresh air will leak from the on-off valve 6 into the intake passage 7 on the upstream side, causing variations in the pressure in the high-speed intake port 4 of each cylinder. .

In this case, the proportion of residual gas differs for each cylinder, which may cause variations in combustion and unstable rotation.

The present invention was developed in view of these conventional problems, and by reducing the pressure difference between the upper and downstream sides of the on-off valve, the leakage of fresh air introduced downstream of the on-off valve is suppressed. An object of the present invention is to provide an intake device for an internal combustion engine that improves combustion performance during idling as much as possible by increasing the effect of preventing blowback of exhaust gas.

<Means for Solving the Problems> For this reason, the present invention provides a low-speed intake passage having a low-speed throttle valve and communicating with the low-speed intake valve, and a high-speed intake passage having a high-speed throttle valve and connecting the downstream portion of the intake passage to the low-speed intake valve. The high-speed intake passage leads to the high-speed intake valve for each cylinder, and the high-speed intake passage is connected to the high-speed intake passage for each cylinder. The minimum opening degree of the high-speed throttle valve is set to be larger than the minimum opening degree of the on-off valve, and the opening area of the on-off valve is adjusted to the increase or decrease in the engine intake air flow rate. The present invention has a configuration in which a control means is provided to increase or decrease the opening degree of the high-speed throttle valve.

<Effect> Next, the effect of this configuration will be explained.

When driving at low speeds, including idling,
The on-off valve and high-speed throttle valve have a minimum opening degree,
Only the low speed throttle valve is open. The minimum opening degree of the high-speed throttle valve is set larger than the minimum opening degree of the on-off valve.

When the high-speed intake valve closes near the middle of the compression stroke in this state, the high-speed intake port on the downstream side of the on-off valve is in a negative pressure state, while the upstream side of the on-off valve is closed via the high-speed throttle valve. It communicates with the atmosphere.

For this reason, fresh air close to atmospheric pressure flows into the high-speed intake port through the gap between the on-off valve and the high-speed intake port, and as a result, the pressure inside the high-speed intake port gradually increases until the next high-speed By the time the air intake valve opens, the pressure rises to near atmospheric pressure.

On the other hand, when the high-speed intake valve is opened, the combustion chamber is filled with residual exhaust gas at approximately atmospheric pressure.

Therefore, until the top dead center of the exhaust stroke is reached, the residual exhaust gas in the combustion chamber is prevented from blowing back into the high-speed intake port sealed by the on-off valve, and most of it is discharged to the exhaust port.

In addition, during high-speed operation, the on-off valve is switched from closed to open, and after that, the high-speed throttle valve is controlled by the control means and gradually begins to open according to the increase in the intake air flow rate, and the intake air is also drawn from the high-speed intake port. will be held.

<Example> The example shown in FIGS. 1 to 3 will be described below. The same elements as those in the conventional example will be described with the same reference numerals as in FIG. 4.

In the combustion chamber of each cylinder of the engine, there are a pair of high-speed intake valves 2 that open earlier than the closing timing of a pair of exhaust valves 5 with equal opening and closing timings, and a low-speed intake valve 1 that opens later than the opening timing of the exhaust valves 5. , is provided.

The intake passages leading to the low-speed and high-speed intake valves 1 and 2 are configured as follows.

That is, the downstream end of the intake pipe 11 whose upstream end is connected to an air cleaner (not shown) branches into two, and a low-speed manifold 12 and a high-speed manifold 13 are connected to the two downstream ends, respectively.

A low-speed throttle valve 14 is installed at the downstream end of the intake pipe 11 to which the low-speed manifold 12 is connected, and a high-speed throttle valve 15 is installed to the downstream end of the intake pipe 11 to which the high-speed manifold 13 is connected. be done.

In addition, each branch part that branches from the low-speed manifold 12 and the high-speed manifold 13 by the number of cylinders has a low-speed intake port 16 leading to the low-speed intake valve 1 of each cylinder, and a high-speed intake port leading to the high-speed intake valve 2 of each cylinder. It is connected to the air intake port 17.

As a result, a low-speed intake passage from a branch part of the intake pipe 11 to a low-speed intake valve 1 via a low-speed manifold 12 and a low-speed intake port 16, and a high-speed intake passage from a branch part of the intake pipe 11 to a high-speed manifold 13.
and the high-speed intake valve 2 via the high-speed intake port 17.
A high-speed intake passage leading to the high-speed intake passage is provided independently.

Further, the high-speed intake port 17 is provided with an on-off valve 6 that closes in a low-speed range including at least idling and is controlled to open and close in a high-speed range according to changes in operating conditions.

This on-off valve 6 is connected to the high-speed intake port 17 with a predetermined leakage amount (40 to 60/min at a differential pressure of 500 mmHg).
It is installed with a gap formed so as to provide a leakage amount of about min.

Here, the opening degree of the support shaft 21 of the low-speed throttle valve 14 is adjusted in conjunction with the accelerator pedal according to the driver's intention. In addition, the support shaft 2 of the high-speed throttle valve 15
2 is connected to a stepping motor 23, and the stepping motor 23 is driven and controlled, for example, as shown in FIG. 3, by an output signal from a control circuit 24 inputting the engine operating state.

In this case, in the low speed range when the on-off valve 6 is closed, the high-speed throttle valve 15 is at the minimum opening (however, the opening is sufficiently larger than the minimum opening when the on-off valve 6 is closed); The opening degree is gradually increased from the point where the valve 6 opens halfway on and off, giving the characteristic that it becomes fully open in the high speed region as the intake air flow rate increases.

In addition, the stepping motor 23 and the control circuit 24
The control means is constituted by:

Next, the effect of this configuration will be explained.

During low-speed operation, including idling, which is detected by the intake negative pressure detected by the pressure sensor and the engine rotational speed detected by the speed sensor, the on-off valve 6 and the high-speed throttle valve 15 are The opening degree is the minimum, and only the low speed throttle valve 14 is open. The minimum opening degree of the high-speed throttle valve 15 is
The opening degree is set larger than the minimum opening degree of the on-off valve 6.

In this state, near the middle of the compression stroke, the high-speed intake valve 2
When closed, the high-speed intake port 17 on the downstream side of the on-off valve 6 is in a negative pressure state, while the upstream side of the on-off valve 6 communicates with an air cleaner (not shown) via the high-speed throttle valve 15. .

Therefore, fresh air close to atmospheric pressure flows into the high-speed intake port 17 through the gap between the on-off valve 6 and the high-speed intake port 17, and as a result, the pressure inside the high-speed intake port 17 gradually increases. The pressure then rises to near atmospheric pressure by the time the high-speed intake valve 2 opens.

On the other hand, when the high-speed intake valve 2 is opened, the combustion chamber is filled with residual exhaust gas at approximately atmospheric pressure.

Therefore, until reaching the top dead center of the exhaust stroke, the residual exhaust gas in the combustion chamber is prevented from blowing into the high-speed intake port 17 sealed by the on-off valve 6.
Most of it is discharged to the exhaust port.

As a result, the proportion of residual exhaust gas that enters the combustion chamber in the subsequent intake stroke can be reduced as much as possible, and the combustion improvement effect can be sufficiently enhanced.

The downstream end of the intake pipe 11 is branched into two, and a low speed throttle valve 14 is linked to the accelerator pedal.
By providing this in the low-speed intake passage, the on-off valve 6
The upstream side is kept close to atmospheric pressure even at low speeds, and therefore fresh air can be prevented from leaking from the downstream side of the on-off valve 6 to the upstream side.

In this way, by preventing the leakage of fresh air to the upstream side of the on-off valve 6, it is possible to suppress variations in the pressure inside the high-speed intake port 17 on the downstream side, which equalizes the proportion of residual exhaust gas in each cylinder and improves combustion. Variations can be eliminated,
Rotational stability such as idling is maintained.

In detail, the high speed manifold 13
When the upstream side of the on-off valve 6 is communicated with the atmosphere via the high-speed throttle valve 15, the high-speed intake valve 2 opens during the intake stroke, so the downstream side of the on-off valve 6 becomes negative intake pressure, and the difference with the upstream side increases. Although the pressure increases, the intake stroke is only 1/4 of the total stroke, and the differential pressure can be resolved in the remaining 3/4 stroke. In addition, from when the intake valve of a certain cylinder closes until the next one opens, other cylinders sequentially undergo their intake strokes, and are affected by negative intake pressure through the opening/closing valve 6 of the cylinder in the intake stroke. However, by setting the minimum opening degree of the high-speed throttle valve 15 to be larger than the minimum opening degree of the on-off valve 6, it is possible to increase the influence of atmospheric pressure and ensure a rise to near atmospheric pressure. Furthermore, since a high-speed throttle valve is provided upstream of the on-off valve, even if deposits adhere to the on-off valve due to blowback and the minimum opening becomes large, the high-speed throttle valve upstream will prevent swirl in the combustion chamber. generation is not disturbed.

In addition, since the low-speed intake valve 1 is also open during the intake stroke, the high-speed intake port 17 downstream of the on-off valve 6 is in communication with the low-speed manifold 12, and gas enters and exits, so the pressure for each cylinder is This will eliminate the variation in .

Furthermore, it has the advantage that fresh air can be introduced downstream by simply forming a gap between the on-off valve 6 and the high-speed intake port 17, and there is no need to provide a communication pipe like in the past, reducing costs and layout. It is also advantageous in terms of

In addition, by lengthening the low-speed manifold 12 and low-speed intake port 16 and shortening the high-speed manifold 13 and high-speed intake port 17,
It is also possible to improve the filling rate by matching the intake pulsation characteristics at low speeds and high speeds to the respective operating ranges, and this can also be delicately controlled by adjusting the opening of the high speed throttle valve 15. .

On the other hand, during high-speed operation exceeding a predetermined value detected by intake negative pressure and engine rotational speed, the on-off valve 6 is switched from closed to open by an actuator (not shown), and from then on, the control circuit 2 A signal is sent to the stepping motor 23, and the high-speed throttle valve 15 begins to gradually open.

In this way, when the high-speed intake port 17 opens, the opening timing is earlier than that of the low-speed intake valve 1.
Since intake is performed in conjunction with the high-speed intake valve 2 whose closing timing is significantly delayed, the reduction in the effective compression ratio suppresses the rise in the compression top dead center temperature and pressure of the intake air, thereby suppressing the occurrence of knocking. Further, due to the effect of reducing the intake air flow resistance due to the opening of the high-speed intake port 17, it is possible to improve the filling efficiency and improve the output.

Here, in this embodiment, the high speed throttle valve 1
5, the opening degree is gradually changed in response to changes in engine operating conditions, so that the intake air flow rate from the high-speed intake port 17 is suppressed from increasing all at once. It is possible to prevent the air-fuel ratio from becoming excessively enriched and increase the generation of unburned HC, prevent engine torque fluctuations, and obtain stable characteristics.

It is also possible to omit the high-speed throttle valve 15 and gradually open the on-off valves 6, but in this case, the openings of the plurality of on-off valves 6 may vary at the beginning when the openings are small, and This causes variations in the intake air flow rate.

In this regard, in this embodiment, one high-speed throttle valve 1
5, the opening degree is controlled, so variations between cylinders are eliminated.

<Effects of the Invention> As explained above, according to the present invention, the on-off valve is closed in a low speed region such as during idling, and the high speed intake passage is provided independently from the low speed intake passage. The fresh air upstream of the high-speed throttle valve, which is maintained at near atmospheric pressure without being affected by the negative pressure of In this way, the pressure was raised to near atmospheric pressure by introducing it downstream through the
It prevents exhaust gas from blowing back and improves fuel efficiency and output characteristics. Also, from when the intake valve of a certain cylinder closes until the next one opens, other cylinders undergo their intake strokes one after another, and are affected by negative intake pressure through the gap between the opening and closing valves of the cylinders in the intake stroke. However,
By setting the minimum opening degree of the high-speed throttle valve to be larger than the minimum opening degree of the on-off valve, it is possible to increase the influence of atmospheric pressure and ensure a rise to near atmospheric pressure. Furthermore, since a high-speed throttle valve is provided upstream of the on-off valve, even if deposits adhere to the on-off valve due to blowback and the minimum opening becomes large, the high-speed throttle valve upstream will prevent swirl in the combustion chamber. generation is not disturbed. In addition, by controlling the opening of the high-speed throttle valve, variations in the pressure on the downstream side of the opening/closing valve for each cylinder, and therefore variations in combustibility, are eliminated, and stable rotational performance can be obtained.

[Brief explanation of drawings]

Figures 1A and 1B each show an embodiment of the present invention, where A is a plan sectional view showing the state at low engine speed, and B
2 is a cross-sectional plan view showing the state of the engine at high speed, FIG. 2 is a diagram showing the structure of the high-speed and low-speed throttle valve parts used in the above embodiment, and FIG. 3 is the opening characteristics of the high-speed throttle valve. FIG. 4 is a plan sectional view showing a conventional intake system for an internal combustion engine. 1...Intake valve for low speed, 2...Intake valve for high speed, 5
...Exhaust valve, 6...Opening/closing valve, 11...Intake pipe, 1
2...Low speed manifold, 13...High speed manifold, 14...Low speed throttle valve, 15...High speed throttle valve, 16...Low speed intake port, 17...
High-speed intake port, 23...stepping motor, 24...control circuit.

Claims (1)

[Scope of Claims] 1. An intake system for an internal combustion engine including a high-speed intake valve and a low-speed intake valve for each cylinder, wherein a downstream portion of the intake passage is provided with a low-speed throttle valve and a low-speed intake valve. A low-speed intake passage leading to the high-speed intake valve and a high-speed intake passage having a high-speed throttle valve and leading to the high-speed intake valve are branched and are closed in a low-speed range including at least idling, and are closed in a high-speed range under operating conditions. An on-off valve that is controlled to open and close according to the change in speed is provided at a port near the high-speed intake valve of each cylinder of the high-speed intake passage, and the minimum opening of the high-speed throttle valve is set larger than the minimum opening of the on-off valve. An intake system for an internal combustion engine, further comprising a control means for controlling the opening degree of the high-speed throttle valve to increase or decrease in accordance with an increase or decrease in the engine intake air flow rate in the opening region of the on-off valve.