JPH0338411B2 - - 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 with a turbocharger equipped with 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 3.
(See Publication No. 119325).

That is, each cylinder has an intake valve 1A whose closing timing is relatively early and an intake valve 1B whose closing timing is relatively late, and two intake ports 2A and 2B that lead to these intake valves 1A and 1B.
A fuel injector 3 for supplying fuel to the intake port 2A is provided, and a butterfly-type on-off valve 4 is provided to the other intake port 2B. Further, a turbocharger (not shown) is provided in a single intake passage upstream from the branch point of the intake ports 2A, 2B of each cylinder.

By closing the on-off valve 4 when the engine is running at low speed, a large swirl is generated in the combustion chamber 5 by utilizing the intake air flowing only from the intake port 2A along the circumferential wall of the combustion chamber 5, resulting in combustion at low speeds. In addition, by setting the closing timing of the intake valve 1A earlier, the actual compression ratio is increased to improve fuel efficiency and output.

On the other hand, when the engine is at high speed, by opening the on-off valve 4 and opening the two intake ports 2A and 2B,
In addition to reducing the intake resistance, the actual compression ratio is lowered by the intake valve 1B with a late closing timing to suppress knocking, and the intake air filling efficiency is increased using turbocharger supercharging and inertia supercharging to improve the output.

In addition, exhaust valves 6A, 6B and exhaust ports 7A, 7B
Two spark plugs 8 are provided near the center of the combustion chamber 5.

<Problems to be Solved by the Invention> By the way, the intake system for such a turbocharged internal combustion engine has the following problems.

First, the behavior of the compression stroke at low speed and high speed of the engine will be explained with reference to FIG.

In the figure, in the low speed range when the on-off valve 4 is closed, even if the piston 9 rises as shown in A until the intake valve 1A closes, the intake air flows backward from the intake port 2A (especially when the intake inertia is small). (at low speeds), compression actually starts when the intake valve 1A closes as shown in B. At this time, while the intake valve 1B is still open, a small amount of air-fuel mixture moves to the intake port 2B as the pressure in the combustion chamber 5 increases (the volume of the intake port 2B downstream of the on-off valve 4 is
Although it is small compared to the volume, the amount of air-fuel mixture movement is proportional to this volume). After this, the intake valve 1B closes as shown in C, but there is no major change and compression continues.

On the other hand, in the high-speed range where the on-off valve 4 is open, the intake air in the combustion chamber 5 at stage B is
As the pressure rises, the air flows backward from the intake port 2B through the on-off valve 4, so there is no pressure rise in the combustion chamber 5, and compression actually starts after the intake valve 1B is closed.

In this way, the actual compression ratio of the engine changes by opening and closing the on-off valve 4. Here, the on-off valve 4 is closed at low speeds mainly to improve practicality (fuel efficiency, stability, etc.) in the low speed range, and at high speeds, the intake air filling efficiency may decrease if only the intake port 2A is used. It opens to ensure output, but at low speeds, even when the throttle valve is fully open, the turbocharger does not increase rotation because the exhaust flow rate is small, and below 1500 rpm, the boost pressure is almost equal to atmospheric pressure (that is, there is no supercharging). On the other hand, at medium speeds and above, the rotation of the turbocharger increases, so a sufficiently stable boost pressure can be obtained.
On the contrary, the current situation is to maintain the boost pressure at a constant value by relieving exhaust gas in order to suppress an excessive rise in the boost pressure.

In this way, in addition to the actual compression ratio change due to the opening and closing of the on-off valve 4, there is a difference in compression conditions due to the difference in boost pressure at low speed and high speed, and as a result, the compression pressure at the top dead center of the combustion chamber 5 changes. They are different.

It is well known that the higher the compression pressure, the more likely knocking will occur.

Furthermore, when the compression pressure is the same, engine characteristics tend to cause knocking to occur more easily at low speeds than at high speeds. In other words, knotting is a phenomenon in which heated unburnt air-fuel mixture spontaneously ignites during the process of combustion of the air-fuel mixture. The smaller the combustion speed is, the more likely it is to occur, and the higher the speed, the less it occurs.

From the above points, in order to obtain good drivability while suppressing knocking over the entire engine operating range from low speed to high speed, it is necessary to appropriately set each engine specification. Appropriate settings have not necessarily been made in conventional institutions of this type, including prior-application cases.

The present invention was made with attention to the above-mentioned actual situation, and by appropriately setting each engine specification based on performance analysis, it is possible to suppress knocking over the entire operating range while achieving good output and fuel efficiency. It is an object of the present invention to provide an intake system for an internal combustion engine that achieves high performance.

<Means for solving the problem> For this reason, the present invention provides a combustion chamber volume V 1 when the intake valve on the side with a relatively early closing timing closes, and a combustion chamber volume V ₁ when the intake valve on the side with a relatively early closing timing closes, and the intake valve on the side with a relatively late closing timing. The combustion chamber volume V ₂ when closed, and the intake port volume V _P on the downstream side of the on-off valve,
The set value P _T of the supercharging pressure of the turbocharger in the engine high speed range where the on-off valve is opened is (V ₂ +V _P /V ₁ +V _P ) ^k・P _T /P ₀ > 1 where, k: specific heat ratio of air , P ₀ : The configuration is set to satisfy the relationship of atmospheric pressure.

<Function> With such a configuration, the compression pressure P ₁ at the top dead center when the engine is running at high speed will be larger than the compression pressure P ₂ at low speed (the reason will be explained in the examples). It is possible to balance the occurrence rate of knotting in the engine, thereby increasing the engine's base compression ratio (piston bottom dead center volume/piston top dead center volume), thereby suppressing knocking over the entire operating range. It is possible to improve fuel efficiency and output performance at the same time.

<Example> Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 1 shows the configuration of an embodiment, and shows an internal combustion engine 1.
For each cylinder of 1, a low-speed intake valve (hereinafter referred to as the first intake valve) 12A has a relatively early closing timing, and a high-speed intake valve (hereinafter referred to as the first intake valve) that has a relatively late closing timing and is set in the middle of the compression stroke. (hereinafter referred to as the second intake valve) 12B,
First and second intake ports 13A and 13B independently lead to these first and second intake valves 12A and 12B, respectively.
will be provided.

Further, the first intake port 13A is provided with a fuel injector 14 as a fuel supply means, and the second intake port 13B is provided with an on-off valve 15 that closes in a low speed range of the engine 11 and opens in a high speed range, as will be described later. A turbocharger 17 driven by an exhaust turbine is mounted upstream of the throttle valve 16 of the intake passage 13, which is unified upstream of the branching point of the first and second intake ports 13A, 13B.

The on-off valve 15 has a support shaft 15a connected to an output rod 18a of a diaphragm actuator 18 via a link mechanism, and the actuator 1
When the supercharging pressure from the turbocharger 17 led to the pressure operating chamber 18b of No. 8 exceeds the pressure near the intercept point where the engine rotational speed rapidly increases, the output rod 18a extends against the biasing force of the return spring 18c and opens and closes. The valve 15 is switched from closed to open.

In addition, two exhaust valves 19A and 19B are provided for each cylinder.
and exhaust ports 20A, 20B, the combustion chamber 21
A spark plug 22 is provided at the center of the ignition plug 22.

Here, various specifications of the engine as a configuration according to the present invention are set as follows. That is, the first intake valve 12
The volume of the combustion chamber 21 when A is closed is V ₁ , the volume of the combustion chamber 21 when the second intake valve 12B is closed is V ₂ ,
The volume of the downstream portion of the on-off valve 16 of the second intake port 13B is V _P , and the combustion chamber 2 at the top dead center position of the piston 23
When the volume of 1 is V ₀ , the boost pressure of turbocharger 17 at low speed is P ₀ (atmospheric pressure), the boost pressure of turbocharger 17 at high speed is P _T (set value), and the specific heat ratio of air is k, the following formula is obtained. Set so that it holds true.

(V ₂ +V _P /V ₁ +V _P ) ^k ·P _T /P ₀ >1 (1) Next, the operation of this embodiment having such a configuration will be explained.

When the on-off valve 15 is open, compression of the air-fuel mixture taken into the combustion chamber 21 starts from the time when the second intake valve 12B is closed, so the compression ratio ε ₁ is as follows: ε ₁ =V ₂ / V ₀ ...(2) becomes.

On the other hand, when the on-off valve 15 is closed, the compression takes place in two stages () The compression ratio ε ₂₁ from when the first intake valve 12A closes to when the second intake valve 12B closes is: ε ₂₁ =V ₁ +V _P /V ₂ +V _P ...(3) () The compression ratio after the second intake valve 12B closes is ε ₁ , so the compression ratio ε ₂ of these two stages as a whole is ε ₂ = ε ₂₁ × ε ₁ =V ₂ /V ₀ ×(V ₁ +V _P /V ₂ +V _P )……(4
) By the way, the on-off valve 15 is switched on and off in the medium speed range, and as shown in FIG. 2, in the low speed range where the on-off valve 15 is closed, the boost pressure is close to atmospheric pressure _P0 , In the high speed range where the valve opens, the boost pressure is stabilized and maintained at the set value P _T.

For this reason, the throttle valve 16, where the knotting is the most severe,
The compression pressure at the top dead center of the piston 23 when fully open is: At high speed, P ₁ = P _T (V ₂ /V ₀ ) ^k ...(5) At low speed, P ₂ = P ₀ [(V ₂ /V ₀ ) × (V ₁ +V _P /V ₂ +V _P )] ^k ...(6).

At the same compression pressure, as mentioned above,
Since there is a greater tendency for knocking to occur at low speeds than at high speeds, by setting P ₂ <P ₁ (7), it is possible to balance the knocking occurrence rates at low speeds and at high speeds.

Here, by substituting equations (5) and (6) into equation (7) and transforming it, equation (1) is obtained.

In other words, formula (7) is satisfied by setting each specification so as to satisfy formula (1). and,
In this way, by balancing the knocking occurrence rate at low speeds and high speeds, the base compression ratio of the engine 11 can be increased, thereby suppressing knocking over the entire operating range and improving fuel efficiency.
This allows the output to be maintained well.

Incidentally, contrary to equation (7), if P ₂ > P ₁ is set, the knocking resistance at low speeds will be extremely deteriorated, and the base compression ratio will have to be lowered, resulting in lower fuel efficiency and The output also deteriorates.

Next, an example of calculation when the present invention is applied to a specific engine will be shown.

(Base) Compression ratio ε = 9.0, total displacement 1800c.c. 4-cylinder 4-stroke engine, V _P = 70c.c., first intake valve closing timing 30° after bottom dead center, second intake valve Assuming that the valve close timing is 70° after bottom dead center, V ₀ = 1800/(9-1) = 56.25 [cc] V ₁ ≒ (450 + 56.25)・(1 + cos30°)/2 = 472.34 [cc] V ₂ ≒ (450+56.25)・(1+cos70°)/2 =339.70 [cc] ∴(V ₂ +V _P /V ₁ +V _P ) ^k = (409.7/542.34) ^1.4 = 0.67
5 In this case, in order to satisfy equation (1), P _T /P ₀ > 1/0.675≒1.481 In other words, the set value of boost pressure at high speed should be 365.5
Although it needs to be greater than mmHg, since the set value of the supercharging pressure is generally about 375 mmHg or more, there is no problem in applying the present invention.

<Effects of the Invention> As explained above, according to the present invention, the specifications of the engine and turbocharger are set so that the compression pressure at top dead center is smaller at low speed than at high speed. By balancing the occurrence rate of knocking at high speeds and high speeds, it is possible to increase the base compression ratio of the engine, which has the effect of suppressing knocking over the entire operating range and increasing fuel efficiency and output. can get.

[Brief explanation of drawings]

FIG. 1A is a longitudinal cross-sectional view showing the structure of an embodiment of the present invention, FIG. 1B is a cross-sectional view showing the structure around the combustion chamber of the above embodiment, and FIG. FIG. 3 is a cross-sectional view showing the main part configuration of an example of the prior art, and FIG. 4 is a diagram showing the state of the compression stroke of the prior art. 11... Internal combustion engine, 12A... First intake valve, 1
2B...Second intake valve, 13...Intake passage, 13A
...first intake port, 13B...second intake port, 15...opening/closing valve, 17...turbocharger, 18...actuator, 21...combustion chamber.

Claims (1)

[Scope of Claims] 1 Each cylinder includes two intake valves with different closing timings and two intake ports leading to these two intake valves, and an intake port leading to the intake valve with a relatively later closing timing. In an intake system for an internal combustion engine, the intake system includes an on-off valve that is controlled to open and close so as to close in a low engine speed range and open in a high engine speed range, and a turbocharger in an intake passage upstream from a branch point of each intake port, The combustion chamber volume V ₁ when the intake valve on the side with a relatively early closing timing closes, the combustion chamber volume V ₂ when the intake valve on the side with a relatively late closing timing closes, and the intake air on the downstream side of the opening/closing valve. The port volume V _P and the set value P _T of the turbocharger supercharging pressure in the engine high speed range where the on-off valve is opened are: (V ₂ +V _P /V ₁ +V _P ) ^k・P _T /P ₀ > 1 However, An intake system for an internal combustion engine, characterized in that it is set to satisfy the following relationship: k: specific heat ratio of air, P ₀ : atmospheric pressure.