JPH0361008B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an intake system for an engine.

(Prior art) Some engine intake devices utilize the inertia effect of intake air to improve volumetric efficiency.
Some engines are designed to increase engine torque as much as possible. In other words, the negative pressure wave that occurs with the start of intake is reflected at the upstream side of the intake passage leading to the atmosphere or the expansion chamber, resulting in a positive pressure wave. As a result, the air is returned toward the intake port, but by allowing this positive pressure wave to reach the intake port that is about to close, the volumetric efficiency, that is, the torque, is improved.

This intake inertia effect is affected by the natural frequency of the engine intake system,
To explain this point using a reciprocating 4-stroke engine as an example, let's say that the engine speed is Nrpm, the rotation angle of the engine output shaft while the intake port is open is α, and the natural frequency of the engine intake system is ν. , n=ν・α/6・N −(1) In equation (1), “n” is “1”, “2”, “3”...
When the natural frequency ν reaches an integer value such as ν, the peak of the natural frequency ν, that is, the intake pressure wave reaches a positive maximum value, and the tuning condition for obtaining an inertial effect is satisfied. Also, above (1)
When "n" in the formula is "0.5", "1.5", "2.5", etc., the valley of the natural frequency ν, that is, the intake pressure wave reaches its negative maximum value, and the volumetric efficiency decreases. Become. To provide a supplementary explanation of equation (1) above, the time required for the engine to rotate once is:
Since it is 60/N seconds, the engine output shaft is 1deg.
The time required to rotate is 1/6N second. "α/6N" in equation (1) means the intake stroke time during which the intake port is open. Of course, the natural frequency ν is ν=1/t, where t is the period of the intake pressure wave.

On the other hand, the natural frequency ν of the engine intake system itself has almost no dependence on the engine speed, and basically depends on the length and diameter of the intake pipe, as well as the stroke volume of the engine, which is unique to a certain engine. It is fixed uniformly. Therefore, based on the above equation (1), the natural frequency ν of the engine intake system can be calculated as follows: n is "1" at a certain engine speed,
If it is set to an integer value such as "2" or "3", the volumetric efficiency will be significantly improved at the engine speed (tuned speed) at this time.

However, as is clear from the above explanation, the inertial effect of intake air can only be expected around a certain engine rotational speed corresponding to the natural frequency of the engine intake system. In order to improve low-speed torque, the natural frequency ν of the engine intake system is usually set so that the engine rotational speed at which this inertial effect should be obtained is relatively low.

For this reason, recently, a system has been proposed in which the natural frequency of the engine intake system is changed according to the engine speed, so that the inertia effect of the intake air can be obtained not only in the low speed range but also in the high speed range. There is.
That is, as shown in Japanese Patent Application Laid-Open No. 56-115819, an enlarged chamber is connected to the intake passage, and an on-off valve is arranged between the intake passage and the enlarged chamber, so that the engine speed is low. When the on-off valve is closed, the equivalent pipe length of the engine intake system is lengthened (reducing the natural frequency ν) to obtain an inertia effect, while in the high engine speed range, the on-off valve is opened to increase the equivalent intake air. The pipe length is shortened (the natural frequency ν is increased) to obtain an inertial effect. In this conventional system, the on-off valve is always fully open when the engine speed is higher than the set speed, and when the engine speed is lower than the set speed. At this time, the on-off valve was always kept fully closed, that is, the on-off valve was switched at the only set rotation speed mentioned above. Note that this set rotation speed is selected as the engine rotation speed when the torque curve obtained when the on-off valve is fully opened and the torque curve obtained when the on-off valve is fully closed intersect, It is designed to prevent torque fluctuations caused by valve switching as much as possible.

(Problem to be Solved by the Invention) However, with the method described in the above publication, although the inertia effect can be used at both low and high engine speeds, the inertia effect cannot be expected in the middle engine speed range. On the contrary, a torque valley (a large drop in torque) would occur in this medium rotation range. In other words, in the engine mid-speed range where the on-off valve is conventionally fully closed, the intake pressure wave reaches its maximum negative value, such as the value of "n" in equation (1) above is "0.5" or "1.5". There is supposed to be a rotation range where a large drop in torque occurs.

Therefore, an object of the present invention is to change the equivalent intake pipe length, that is, the natural frequency of the engine intake system, between the low engine speed and high engine speed range due to the inertia effect. An object of the present invention is to provide an intake system for an engine that is capable of preventing a large drop in torque in the range of torque as much as possible, in other words, that is capable of obtaining torque characteristics that are as flat as possible.

(Means and actions for solving the problems) In order to achieve the above-mentioned object, the present invention has the following configuration. That is, an intake passage in which the equivalent intake pipe is lengthened, an expansion chamber connected to the intake passage to shorten the equivalent intake pipe length, and an expansion chamber arranged between the intake passage and the expansion chamber to shorten the equivalent intake pipe length. an on-off valve for switching, the on-off valve is fully closed when the engine is running at low speeds, and the on-off valve is fully open when the engine is at high speeds;
and an on-off valve control means that opens the on-off valve by a predetermined opening in a predetermined engine rotation range to change an equivalent intake pipe length, and the length of the intake passage is such that the torque when the on-off valve is in a fully closed state is It is set such that a state in which the torque exceeds the torque when the on-off valve is fully open exists multiple times in the normal rotation range of the engine, and in the engine rotation range around which the torque exceeds the torque when the on-off valve is fully closed. A rotation range sandwiched between a first rotation speed at which maximum torque is obtained and a second rotation speed at which maximum torque is obtained when the on-off valve is fully open is set as a predetermined rotation range in which the on-off valve is opened to a predetermined opening degree. , it has a structure like this.

(Example) Examples of the present invention will be described below with reference to the attached drawings.

In FIG. 1, reference numeral 1 denotes a four-cycle reciprocating engine (generally a gasoline engine). An intake port 4 and an exhaust port 5 are opened, and the intake port 4 is opened and closed by an intake valve 6, and the exhaust port 5 is opened and closed by an exhaust valve 7, respectively, in synchronization with the output shaft (crankshaft, not shown) of the engine 1. It is becoming more and more like this. In the embodiment, a plurality of pistons 2 are arranged in a direction perpendicular to the plane of the paper to form a multi-cylinder structure.

An intake passage 11 connected to the intake port 4 is connected to a main surge tank 1 that defines a main enlarged chamber 12a inside.
It has 2. The intake passage 11 on the upstream side of the main surge tank 12 is a common intake pipe 13 that constitutes one common intake passage A, and the common intake pipe 13 includes:
An air cleaner 14, an air flow meter 15, and a throttle valve 16 are arranged in this order from the upstream side. In addition, the main surge tank 12 and each intake port 4
and are connected by mutually independent intake pipes 17, the number of which corresponds to the number of cylinders. That is, the intake passage 11 downstream of the main surge tank 12 is configured as an independent intake passage B for each cylinder by the branch pipe portion 12b integrally formed with the main surge tank 12 and the independent intake pipe 17. The independent intake passages B have substantially the same length. A fuel injection valve 18 is disposed at the downstream end of each independent intake passage B.

Each of the independent intake passages B connects to the sub-enlargement chamber 2 via a communication passage 19 on the upstream side of the fuel injection valve 18.
It is connected to a sub-surge tank 20 defining 0a. The length of this communication passage 19 is short, and the length is short from the combustion chamber 3 to the main surge tank 12 (main expansion chamber 12).
The length from the combustion chamber 3 to the sub-surge tank 20 (the sub-expansion chamber 20a) is longer than the length from the combustion chamber 3 to the sub-surge tank 20 (sub-expansion chamber 20a). An on-off valve 21 is disposed in the communication passage 19, and this on-off valve 21 is continuously variable between a fully closed state and a fully open state (valve opening angle of 70°) by a proportional motor 22. The opening degree can be arbitrarily selected.

Reference numeral 23 in FIG. 1 denotes a control unit consisting of a microcomputer, into which the intake air amount signal from the air flow meter 15 and the engine rotational speed signal from the rotational speed sensor 24 are input. Further, the control unit 23 outputs power to the fuel injection valve 18 and the motor 22. In addition, fuel injection valve 1
The fuel injection amount from No. 8 is determined based on the intake air amount and the engine speed, but this point is well known and is not directly related to the present invention, so the details will be described below. Further explanation will be omitted.

Here, the equivalent intake pipe length determined by the independent intake passage B, that is, from the combustion chamber 3 to the main expansion chamber 12.
The length up to a is long as described above, and is set so that the natural frequency of intake air is small. As a result, when the opening/closing valve 21 is fully closed (opening/closing angle θ = 0°), as is clear from the above-mentioned equation (1), the inertia effect of the intake air is maintained at low engine speeds. The torque curve at this time becomes as shown by the Y1 line in FIG. 2, and shows the peak value of the torque peak due to the inertial effect when the engine speed N is _N1 and _N5 .
As is clear from this Y1 line, there is a large drop in torque in the medium speed range, especially when the engine speed is between _N1 and _N4 .

Furthermore, when the on-off valve 21 is fully open (opening/closing angle θ=70°), the equivalent intake pipe length is the short length from the combustion chamber 3 to the sub-expansion chamber 20a via the communication passage 19, and the intake pipe at this time is The natural frequency of will be large. As a result, the intake inertia effect is obtained in the high engine speed range, and the torque curve at this time is as shown by line Y3 in Figure 2.
When the engine speed N is _N3 and _N7 , the peak value of the torque peak is shown. Conventionally, in order to obtain an inertial effect in both the low rotation speed and high rotation speed ranges, when the engine speed is lower than _N13 shown in FIG. 2, the on-off valve 21 is always fully opened and Y1 While ensuring the torque characteristics shown by the line Y3, when the engine speed is higher than _N13 , the on-off valve 21 is always fully opened to obtain the torque characteristics shown by the Y3 line.

In the present invention, in the engine rotation range below _N13 , the on-off valve 21 is conventionally kept fully closed in order to prevent the large drop in torque that would inevitably occur if only the Y1 line was selected. By opening the on-off valve 21 by a predetermined angle according to the engine speed, the inertia effect is obtained as effectively as possible even in the middle engine speed range. That is, the on-off valve 21
The torque curve when is set to an intermediate opening degree, that is, θ=35°, is shown by the Y2 line in FIG. As is clear from this Y2 line, even in the engine medium rotation region, the peak value of the torque peak due to the inertial effect is shown when the engine rotation speed N is _N2 and _N6 . That is, by adjusting the valve opening angle θ,
The value of n in the above formula (1) is an integer value such as "1" or "2" (perfect matching for inertia effect), or a value close to this integer value, so that the engine speed is It becomes possible to set the natural frequency ν for "a certain engine rotation speed" in the region. In this embodiment, the opening angle θ of the on-off valve 21 is changed in accordance with the engine speed, as shown by the X-ray in FIG. Specifically, as shown in the flowchart of FIG. 3, the current engine speed N is read in step S1, and then the opening angle θ of the on-off valve 21 corresponding to this engine speed N is determined in step S2.
is read out from a map as shown in the X-ray in FIG. 2, and the motor 22 is controlled (driving the on-off valve 21) so that the valve opening angle θ read out from this map is achieved. The torque curve obtained at this time becomes as shown in FIG. 4, and it is possible to compensate for the large drop in torque in the engine mid-rotation region, which conventionally occurs, as shown by E1. In addition,
In the high rotation range, it is possible to compensate for the slight drop in torque that conventionally occurs, as shown by E2.

In this way, in the embodiment described above, the on-off valve 21
is always fully closed when the engine speed is low, lower than N ₁ , and always fully open when _{the engine speed is high, higher than N 7 .} In the rotation range, the opening degree of the on-off valve 21 is continuously variable in accordance with the engine rotation speed, as shown by the X-ray in Figure 4, so that the maximum torque can be obtained for a "certain engine rotation speed." It is designed to be controlled.

Here, the meaning of controlling the opening degree of the on-off valve 21 as described above (control based on the X-rays in Figure 2) is as follows.
This will be explained diagrammatically with reference to FIG.

First, since the natural frequency ν in equation (1) is a linear function of the engine speed N, for example, n
= "1", "1,5", "2", the three types of linear functions (straight lines) are W1 (n = 1), W2 (n =
1, 5), W3 (n = 2), while the natural frequency determined by the equivalent intake pipe length when the on-off valve 21 is fully closed is ν ₁ , and the equivalent intake pipe length when the on-off valve 21 is fully open is The natural frequency thus determined is ν ₂ (ν ₂ > ν ₁ ). Under such conditions, the on-off valve 21
W
1 or W3 line, the rotational speed corresponds to the natural frequency ν ₁ , and on the W2 line, the engine rotational speed corresponding to ν ₁ becomes the trough of the intake pressure wave (torque trough). . Similarly,
When the on-off valve 21 is fully open, the peak of the intake pressure wave occurs at an engine speed corresponding to ν ₂ on the line W1 or W3, and the trough of the intake pressure wave corresponds to ν ₂ on the line W2. Occurs at engine speed.

On the other hand, the natural frequency ν can be continuously and arbitrarily changed between ν ₁ and ν ₂ by continuously and variably changing the opening degree of the on-off valve 21.
Therefore, among the natural frequencies between ν ₁ and ν ₂ , if we want to obtain the intake inertia effect corresponding to a certain engine rotation speed, for example N ₀ , W1 or W
On the line No. 3, select the natural frequency ν ₀ corresponding to this N ₀ (see the arrow in Figure 9), and control the opening degree of the on-off valve 21 so that this ν ₀ is achieved. . If there is no corresponding natural frequency on the line W1 or W3 depending on the engine speed (a completely matched inertial effect cannot be obtained), then the natural frequency between ν ₁ and ν ₂ The opening degree of the on-off valve 21 is selected so that the natural frequency has the largest torque.

The X-rays in Figure 2 were created based on the reasons explained above. This means that the torque curve representing the torque of the engine is selected according to the engine speed.

In addition, in FIG. 9, n is "1" and
The cases of “1, 5” and “2” are shown as representative cases, but
For example, by further drawing a linear function when n is set to "2, 5" or "3", the engine speed, natural frequency, and intake pressure wave (torque) can be calculated over the entire engine speed range. This allows us to investigate the relationship in more detail.

5 to 8 show other embodiments of the present invention, and the same components as those in the previous embodiments are given the same reference numerals and their explanations will be omitted.

In this embodiment, the opening degree of the on-off valve 21 is changed to three different degrees in stages so that it can take exactly half the opening degree (valve opening angle θ=35°) in addition to fully closed and fully open. It is designed so that you can get it. Accordingly, as an actuator for driving the on-off valve 21, instead of the proportional motor 22 in the above embodiment,
As shown in FIGS. 5 and 6, a two-stage negative pressure actuator 31 is used.

The actuator 31 will be described with reference to FIG. 6. The actuator 31 is equipped with a casing 32, and inside the casing 32, first and second diaphragms 33 and 34 are arranged to face each other. It is defined by two second negative pressure chambers 35 and 36. This first diaphragm 33 is connected to the on-off valve 21 by opening the rod 37, and when the first diaphragm 33 is displaced upward in FIG.
1 is rotatably displaced in the opening direction.

A first return spring 38 is interposed between the first diaphragm 33 and the second diaphragm 34, and the second diaphragm 34 is urged downward in FIG. 6 by a second return spring 39. As a result, the first diaphragm 34 is normally placed at the lowermost position in FIG.
1 is biased to the fully closed position, and both negative pressure chambers 35,
When negative pressure is supplied to either one of the negative pressure chambers 36, the first diaphragm 33 is slightly displaced upward in FIG.
When negative pressure is supplied to both 5 and 36, the first diaphragm 33 is largely displaced upward in FIG. 6, and the on-off valve 21 is fully opened.

In FIG. 5, 40 is a negative pressure tank, and this negative pressure tank 40 is connected to the main surge tank 12 through a check valve 41.
The negative pressure in the main surge tank 12 (main expansion chamber 12a) generated as the engine 1 operates is supplied to the negative pressure tank 40 via the check valve 41. . This negative pressure tank 40
is connected to the first negative pressure chamber 35 of the actuator 31 via a first pipe 42, and an electromagnetic three-way switching valve 43 is connected to the first pipe 42.
This three-way switching valve 43, for example,
The negative pressure chamber 35 is communicated with the atmosphere, and the first negative pressure chamber 35 is communicated with the negative pressure tank 40 during excitation. Similarly, the negative pressure tank 40 is connected to the second pipe 44
It is connected to the second negative pressure chamber 36 of the actuator 31 via the second pipe 44, and an electromagnetic three-way switching valve 45 is connected to the second pipe 44. The three-way switching valve 45 also selectively communicates the second negative pressure chamber 36 with the atmosphere or with the negative pressure tank 40 depending on its demagnetization or excitation.

Here, in this embodiment, the control unit 23:
The two three-way switching valves 43 and 45 are controlled to select the degree of opening of the on-off valve 21, either fully open or half open, depending on the engine speed. The opening degree of the on-off valve 21 is selected in accordance with the engine speed so as to select the torque curve from which the largest torque can be obtained from the three torque curves Y1, Y2, and Y3 in FIG. 2. Of course, this switching of the opening degree is performed when the engine rotational speed is reached at which the torque curves that cause the switching to occur intersect. To explain this point in detail based on Fig. 2, when the engine speed N is smaller than _N11 , the Y1 line has the largest torque, so the on-off valve 21 is fully closed (opened) in response to this Y1 line. Valve angle θ = 0°). Also, the engine speed N is
Between N ₁₁ and N ₁₂ , the Y2 line has the largest torque, so the on-off valve 21 is
is half open (θ=35°). In this way, when the engine speed N is between _N12 and _N4 , the on-off valve 21 is fully closed, and when N is between _N4 and _N6 , the on-off valve 21 is fully closed. When N is between N ₆ and N ₇ , the on-off valve 21 is half open, and when N is between N ₇
When this happens, the on-off valve 21 is fully opened. A torque curve obtained by performing such control is shown in FIG. 7, and it is easily understood that the torque is improved in the regions shown by E3 and E4 in FIG.

A flowchart for controlling the opening degree of the on-off valve 21 according to the engine speed N as described above is shown in FIG. That is, in this Figure 8,
If in step S11 the current engine speed N is in the rotational range where the on-off valve 21 is fully closed, the route from step S12 or S13 to S14 is taken. In addition, when the on-off valve 21 is in a rotation range that is half open, step S15 or S16 is performed.
Take the route from to S17. Furthermore, on-off valve 2
1 is in the rotation range when fully opened, the route from step S18 or S19 to S20 is taken.

In the embodiment shown in FIGS. 5 to 8, the on-off valve 21 is designed so that it can take only one opening degree, which is an intermediate opening degree between fully closed and fully open, that is, fully closed and fully open. Although a case has been described in which a total of three types of opening degrees including the opening degree can be taken in stages, the intermediate opening degree may be set in two or three stages. However, increasing the number of possible opening degrees (number of stages) too much will end up being essentially the same as the continuously variable control shown in Figures 1 to 4, so if you take costs into consideration, it is best to minimize the number of opening degrees. It is better to use a small number of stages.

Although the embodiments have been described above, the present invention is not limited thereto, and includes, for example, the following cases.

The present invention can be similarly applied to an engine in which the intake passage 11 does not have a throttle valve 16, that is, a diesel engine. Further, the present invention is applicable not only to reciprocating engines but also to rotary piston engines.

The fuel supply device may use a carburetor instead of the fuel injection valve 18.

When the control unit 23 is configured by a computer, it may be of either a digital type or an analog type.

The engine type may be a single cylinder.

(Effects of the Invention) As is clear from the above, the present invention has the following advantages:
While improving torque due to the inertia effect of the intake air at low engine speeds and high engine speeds,
It is possible to prevent a large drop in torque in the medium rotation range and obtain characteristics that are as flat as possible.

In particular, in the present invention, the length of the intake passage is set so that a state occurs multiple times in which the torque when the on-off valve is fully closed exceeds the torque when the on-off valve is fully open in the normal rotation range of the engine. Therefore, the range of adjustment of the equivalent intake pipe length by opening the on-off valve to a predetermined opening degree is small, which is preferable in terms of shortening the length of the intake passage and making the engine more compact.

In particular, the present invention is extremely advantageous in terms of implementation, since it is sufficient to effectively utilize the conventional on-off valve as it is to change the equivalent intake pipe length and simply control the opening degree of this on-off valve.

[Brief explanation of drawings]

1 to 4 show an embodiment of the present invention, FIG. 1 is an overall system diagram, and FIG. 2 shows the engine torque and engine rotation speed according to the opening degree of the on-off valve.
A graph showing an example of controlling the opening degree of the on-off valve according to the engine speed, FIG. 3 is a flowchart showing an example of controlling the opening degree of the on-off valve by the control unit, and FIG. 4 is a graph showing an example of controlling the opening degree of the on-off valve according to the engine speed. It is a graph which shows an example of the obtained torque curve. 5 to 8 show other embodiments of the present invention, in which FIG. 5 is an overall system diagram, FIG. 6 is a sectional view showing an example of an actuator that drives an on-off valve in stages, and FIG. The figure is a graph showing the torque curve obtained by the control according to the present embodiment, Fig. 8 is a flowchart showing an example of control by the control unit, and Fig. 9 is a graph showing the engine speed and the engine speed to obtain the inertial effect of intake air. It is a graph schematically showing conditions for synchronizing the natural frequency of the intake system. A: Common intake passage, B: Independent intake passage, 1: Engine, 3: Combustion chamber, 4: Intake port, 6: Intake valve, 11: Intake passage, 19: Communication passage, 20: Sub-surge tank, 20a: Sub- Expansion chamber, 21: Open/close valve,
22: motor, 23: control unit, 24: rotation speed sensor, 31: actuator, 40: negative pressure tank, 43, 45: three-way switching valve.

Claims (1)

[Scope of Claims] 1. An intake passage in which an equivalent intake pipe is lengthened, an enlarged chamber connected to the intake passage and used to shorten the equivalent intake pipe length, and arranged between the intake passage and the enlarged chamber. , an on-off valve for switching the equivalent intake pipe length; the on-off valve is fully closed when the engine is running at low speeds, and the on-off valve is fully open when the engine is at high speeds;
and an on-off valve control means that opens the on-off valve by a predetermined opening in a predetermined engine rotation range to change an equivalent intake pipe length, and the length of the intake passage is such that the torque when the on-off valve is in a fully closed state is The state is set such that a state in which the torque exceeds the torque when the on-off valve is fully open exists multiple times in the normal engine speed range, and the maximum torque when the on-off valve is fully closed is set in the engine speed range in which the torque exceeds the torque. A rotation range sandwiched between a first rotation speed at which torque is obtained and a second rotation speed at which maximum torque is obtained when the on-off valve is fully open is set as a predetermined rotation range in which the on-off valve is opened to a predetermined opening degree. An engine intake device characterized by: