JPS6060223A - Engine for automobile - Google Patents

Abstract

PURPOSE:To enhance response to accelerating an engine which is supplied with lean mixture at the time of low-speed operation and to increase the engine output, by making the volume of an intake passage from the position thereof located on the downstream side of a throttle valve to the position of an intake valve equal to or smaller than 1/3 of the total stroke volume of the engine, and delaying the valve closing time of the intake valve at the time of high-speed operation of the engine. CONSTITUTION:In an engine which is supplied with lean mixture at the time of steady, low-speed operation and supplied with rich mixutre at the tine of high-output operation, the volume of an intake passage 28 from the position thereof located on the downstream side of a throttle valve 31 to the position of an intake valve 26 is selected to be equal to or smaller than 1/3 of the total stroke volume of the engine. Further, the valve closing timing of the intake valve 26 is varied according to the engine speed. That is, the valve closing timing of the intake valve 26 at the low-speed operation of the engine is set at the position near the bottom dead point while it is delayed at the time of high-speed operation of the engine. Thus, since the volume of the intake passage on the downstream side of the intake valve is small, it is enabled to enhance response for accelerating an engine and to raise the charging efficiency by the pulsation effect of intake-air flow.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to an automobile engine, and more specifically, to improve fuel efficiency and reduce harmful emissions by burning a lean mixture during low-speed steady driving and a rich mixture when driving at high output. The present invention relates to an automobile engine that is designed to improve drivability while also achieving the following.

(Prior Art) Coupled with the recent demands for resource conservation and low fuel consumption, making exhaust gas pollution-free is one of the biggest challenges for automobile engines.

In general, the generation of HC, CO in exhaust gas is due to incomplete combustion within the engine cylinder, and their generation can be significantly reduced if sufficient air is supplied and combustion is performed efficiently at high temperatures. This also leads to improved engine combustion efficiency. On the contrary,
Reducing the generation of NOx in the exhaust gas inherently lowers the maximum temperature of the combustion cycle, which tends to be at odds with improving engine combustion efficiency.

Conventionally, one known countermeasure is to change the mixture ratio. This method burns as lean a mixture as possible and efficiently burns the mixture, thereby eliminating harmful components in the exhaust gas ( This aims to reduce IIC, Co, NOx).

Conventional automobile engines that use this method are:
For example, there is one described in Japanese Patent Publication No. 57-12011. This engine will be explained based on FIGS. 1 to 3. Reference numeral 1 indicates a cylinder head, and the cylinder head 1 is provided with an intake/exhaust valve 2.3 and three spark plugs 4.5.6. This cylinder head 1 defines a combustion chamber 9 together with a piston 8 movably housed in a cylinder 7, and an air-fuel mixture is supplied to the combustion chamber 9 from a carburetor through an intake passage (not shown). The carburetor is equipped with an atomization device or a heating vaporization device to promote combustion, and normally produces a lean mixture with a mixture ratio of about 20, with very little HC, Co, and NOx, and a rich mixture during acceleration etc. supply. Ignition signals are supplied to the spark plugs 4.5.6 from distributors 12.13.14 whose contacts rotate in synchronization with the crankshaft 11 in the crankcase 10, and these ignition signals cause the spark plugs to 4.5.6 all fire at the same time.

Such automobile engines maintain the mixture ratio at around 20, simultaneously ignite three spark plugs 4.5.6 to counter the delay in combustion speed caused by the dilution of the mixture, and maintain the flame speed itself. Although the flame propagation is slow, by propagating the flame from three directions, combustion is completed within a predetermined crank angle, eliminating the loss of output due to combustion delays and engine malfunctions due to ignition errors, thereby achieving practical output characteristics.

In addition, by efficiently burning the air-fuel mixture at a mixture ratio of around 20, where NOx generation is low, as described above, fuel efficiency is improved while reducing NOx in exhaust gas and minimizing HC and CO.

However, such conventional automobile engines operate with a lean mixture with a mixture ratio of about 20 during low-speed steady driving, and enrich the mixture only when driving at full power when the throttle valve is fully open to avoid a lack of output. Since the mixture ratio of the air-fuel mixture supplied through the intake passage in response to the operation of the throttle valve changes slowly when transitioning from low-speed steady driving to power driving, the downstream side of the throttle valve changes slowly. After intake passage (eg, intake manifold) number λ, the remaining lean mixture is supplied, the rich mixture is supplied. As a result, the start-up of the engine is delayed for a moment, resulting in what is called a pause in acceleration. As a result, there is a problem in that the vehicle cannot be smoothly accelerated against the driver's intention, resulting in poor drivability.

(Purpose of the Invention) Therefore, the present invention sets the intake passage volume from the downstream side of the throttle valve to the intake valve to 1/3 or less of the total engine displacement, and also adjusts the closing timing of the intake valve according to the engine speed. By controlling the mixture ratio of the air-fuel mixture supplied into the cylinder in response to the operation of the throttle valve, it prevents the breathing phenomenon during acceleration, and also reduces the filling efficiency of the air-fuel mixture that decreases at low speeds. The purpose is to increase the engine's drivability.

(Structure of the Invention) The automobile engine according to the present invention is supplied with a lean air-fuel mixture during low-speed steady running, and a rich air-fuel mixture during power running. The above-mentioned automobile engine has the intake passage volume from the throttle valve downstream to the intake valve set to 1/3 or less of the total engine displacement, and is provided with a valve opening/closing timing variable means for varying the closing timing of the intake valve. By closing the intake valve near bottom dead center at low speeds and later than bottom dead center at high speeds, changes in the mixture ratio of the air-fuel mixture supplied into the cylinder in response to throttle valve operation are quickly controlled. This is to improve the filling efficiency of the air-fuel mixture that flows at low speeds.

(Example) Hereinafter, the present invention will be explained based on the drawings.

4 to 6 are diagrams showing a first embodiment of the present invention, and show an example in which the present invention is applied to an in-line four-cylinder engine.

First, to explain the configuration, reference numeral 21 indicates an engine in which four cylinders 22 are arranged in series, and the cylinder head 23 of the engine 21 has an intake boat 24 and an exhaust boat 25 that communicate with the combustion chamber in each cylinder 22. is formed. These intake boats 24 and exhaust boats 25 are opened and closed by intake valves 26 and exhaust valves 27, respectively.

Further, an intake passage 28 is connected to each cylinder 22 via an intake boat 24, and an exhaust passage 29 is connected via an exhaust boat 1-25. The intake passage 28 communicates with the outside air via an air cleaner (not shown), and a carburetor 30 and a throttle valve 31 are sequentially disposed in the middle of the passage from the upstream side. Further, the intake passage 28 has a gathering portion 32 located downstream of the throttle valve 31, and four branch portions 33 that branch from the gathering portion 32 and communicate with the combustion chambers in each cylinder 22. , the length β (see FIG. 5) of the branch portion 33 is set as short as possible. The volume of the intake passage 28 from the downstream side of the throttle valve 31 to the intake valve 26 (
That is, the total volume of the collecting part 32 and the four branch parts 33) is the total exhaust gas 1 (4 (11i1 no I) of the engine 21.
It is set to 1/3 or less of the total volume of J 7 da 22 volumes. The carburetor 30 supplies the air-fuel mixture at a predetermined mixture ratio to the intake passage 28 set as described above according to the opening degree of the throttle valve 3. is O
- 3/4), use a lean mixture with a mixture ratio of about 20, and during power running (referring to the range where the throttle valve 31 opening degree exceeds 3/4 to 4/4). Mixing ratio 14.7 (
A rich mixture at or below the stoichiometric air-fuel ratio is supplied.

Further, the intake valve 26 is connected to the valve opening/closing timing variable means 3 shown in FIG.
4, the valve closing timing is made variable. The valve opening/closing timing variable means 34 includes a rocker arm 36, one end of which contacts a valve drive cam 35 that rotates in synchronization with engine rotation, and the other end of which contacts a stem engine F' 26a of the intake valve 26. The rotation shaft 37 of the rocker arm 36 is held movable in substantially the axial direction of the intake valve 26, and the spring 38
The lever 39 is urged upwardly in the direction away from the rocker arm 36, and the actuator 41, which is embedded in a bracket 40 fixed to the cylinder head 23 and is the tip thereof, comes into contact with the end of the lever 39, as shown in the figure. It has a hydraulic pivot 42 that moves in the vertical direction to change the separation distance between the rocker arm 36 and the reno 39.

This valve opening/closing timing variable means 34 changes the movement distance of the actuator 41 by changing the control oil pressure supplied from the oil gear rally 43 to the first hydraulic chamber 44 of the hydraulic pivot 42 based on the engine rotation speed. The swinging fulcrum of the rocker arm 36 is moved along the back surface of the rocker arm 36 by changing the distance between the rocker arm 36 and the lift amount and opening/closing timing of the intake valve 26. That is, engine 2
1 is in the low rotation range, the control hydraulic pressure supplied from the oil gear rally 43 is smaller than the hydraulic pressure in the second hydraulic chamber 45 and the biasing force of the coil spring 46, and the actuator 41 does not move downward, preventing the lever 39 and rocker arm 36 from moving downward. Separation distance is large. Therefore, as the valve drive cam 350 rotates, the rocker arm 36 rotates in the clockwise direction in the figure while moving its fulcrum, but in this case, the fulcrum of the rocker arm 36 does not move to the vicinity of the apex of the bent portion of the arm 36. . Therefore, the lift amount (depression amount) of the intake valve, which is urged in the valve closing direction by the valve spring 47, is small, and the valve opening timing is delayed and the valve closing timing is early. On the other hand, when the engine 21 is in a high rotation range, the control oil pressure is greater than the oil pressure in the second hydraulic chamber 45 and the biasing force of the coil spring 46, and the check valve 4B closes, causing the control oil pressure to flow into the second hydraulic chamber 45. is introduced and the actuator 41 moves downward to narrow the distance between the lever 39 and the rocker arm 36. In this case, the rocker arm 36 gradually changes its fulcrum by the rotation of the valve drive cam 35.
Rotate in the clockwise direction in the figure while moving it to the vicinity of the apex of the bending part 6.

Therefore, as the lift amount of the intake valve increases, the valve opening timing becomes earlier and the valve closing timing becomes later.

Note that a plurality of spark plugs (shown in the diagram) are attached to the cylinder head 23 at positions facing each cylinder 22 for each cylinder 22, and these spark plugs ignite for each cylinder 22 at the same time.

Next, the operation will be explained, but first, the principle of the present invention will be explained.

Figure 7 shows a typical car engine with a total displacement of 18
00cc, rotation speed 150Orpm, ) Luk 3kg・
FIG. 3 is a diagram showing the relationship between the mixture ratio and the fuel consumption rate when exhaust gas recirculation (EGR) is performed so as to obtain a NOx reduction rate of 90% when m is 1. As is clear from this figure, as the mixture ratio becomes leaner, the fuel consumption rate decreases, and the EG
The amount of R is also decreasing. In particular, when the mixture ratio is around 20, the combustion temperature decreases, the generation of NOx decreases, and the fuel consumption rate becomes extremely low. However, a practical engine that can achieve a NOx reduction rate of 90% without performing any EGR and can be operated at a mixture ratio of 20 or more has not yet been realized. There are two main reasons for this.The first reason is that when operating at a mixture ratio of 20 or more, a large breathing phenomenon occurs when the engine accelerates, resulting in poor drivability.The second reason is that In order to prevent the breathing phenomenon, for example, if the length of the intake passage is shortened, the air-fuel mixture filling efficiency decreases at low speeds, which also deteriorates drivability.

In other words, in an engine that performs such lean combustion, as shown in FIG. Mixing ratio 14-1 during low speed steady driving
If the engine is operating with an air-fuel mixture near the stoichiometric air-fuel ratio of about 5, the mixture will be enriched as shown by the broken line B in Figure 8, and the same will be shown by the broken line C1 in Figure 8C. As a result, the engine output can be increased quickly (no breathing phenomenon occurs). On the other hand, during low-speed steady driving, the mixture ratio is 20
If you are operating with a fairly lean mixture, the solid line B in Figure 8
2, the mixture can finally be enriched at timing t2, which is delayed from acceleration timing t, and as shown by solid line C2 in Figure 8C, the increase in engine output is delayed and the acceleration response is delayed ( time lag) T occurs (that is, a large breathing phenomenon occurs). The reason for this is, as explained in the section on prior art, that during acceleration, the mixture ratio must be enriched to the same level or higher than the stoichiometric air-fuel ratio in order to secure sufficient engine output for acceleration. This is because the mixture ratio changes slowly with respect to the opening degree change of the throttle valve, so a response delay inevitably occurs in the mixture ratio change.

By the way, in order to eliminate such a problem, it is clear that the rich mixture should be promptly supplied into the cylinder at the acceleration timing t1 when the throttle valve is fully opened. For example, if the volume of the intake passage from downstream of the throttle valve to the intake valve is reduced to 1/3 or less of the total engine displacement, the acceleration response delay can be reduced to a value that does not cause any practical problems. This fact has been established through experiments. Section 9.1
Figure 0 is a diagram showing the experimental results for an engine with a total displacement of 1800 cc. In FIG. 9, curve D2 shows the acceleration characteristics from a lean mixture in a conventional intake passage whose volume is 800 cc (approximately 1/2 of the total displacement), and curve D3 shows the acceleration characteristics from a lean mixture in the conventional intake passage whose volume is 600 cc (about 1/2 of the total displacement). 1/3 of the volume), the curve 1 indicates the case where the volume is 450cc (1/4 of the m displacement), and the curve 1 indicates the case where the volume is 800cc and the rich mixture near the stoichiometric air-fuel ratio. It shows the acceleration characteristics of In addition, in Figure 1θ, if the case where the acceleration response delay is a value T that does not cause any practical problem is when the volume is 800cc and acceleration is performed from a rich mixture, then the acceleration response delay from a lean mixture is 80
When changing from 0cc to 600CC'-450cc, the values change to E2, E3, and E-4 on the solid line in the figure, respectively. From the above, if the volume is set to at least ⅓ or less of the total engine displacement, the acceleration response delay can be eliminated.

However, in order to reduce the intake passage volume, it is common to shorten the length of the intake passage from the viewpoint of intake resistance.
In this case, a new problem arises: the pulsating effect of the intake air cannot be utilized in the low rotation range, and the air-fuel mixture filling efficiency decreases (resulting in a decrease in engine output, which worsens drivability, especially when driving at low speeds). Occurs. This is the second
This falls under the following reason. That is, when the length of the intake passage is changed in the range of 0 to 3 m as shown in Fig. 11, the shorter the length L, the more the filling efficiency in the high rotation range is increased due to the pulsation effect of the intake air. , it decreases in the low rotation range. Here, there is a relationship expressed by the following equation between the length of the intake passage and the tuned rotational speed NO at which the intake pulsation effect can be obtained.

However, n cylinder number a: speed of sound (m/sec'l) The above equation shows that as the length of the intake passage becomes shorter, the tuned rotation speed No. increases and the filling efficiency in the low rotation range decreases. .

On the other hand, the filling efficiency has a correlation (that is, the inertia effect of intake air) shown in FIG. 12 with respect to the closing timing of the intake valve. In this figure, the curve F1 shows the filling efficiency at the valve closing timing of energization (for example, near 52 degrees after the bottom dead center), and the curve F2 shows the filling efficiency at the early valve closing timing (near the bottom dead center). If the speed is accelerated, charging efficiency in the low rotation range will be increased. This is due to the following reasons. That is, at the bottom dead center of the intake culm, the cylinder internal pressure is lower than the intake passage pressure due to a delay in intake air inflow (intake inertia). Therefore, since the intake air is still flowing in, the filling efficiency will be higher if the closing timing of the intake valve is delayed. After passing the bottom dead center, compression by the piston begins and the pressure begins to rise,
Eventually, the cylinder internal pressure becomes equal to the stroke passage pressure. If the intake valve is still open at this point, the cylinder internal pressure will now become higher than the intake passage pressure, and what was once sucked into the cylinder will be pushed back into the intake passage. Therefore, in order to obtain maximum filling efficiency, the intake valve should be closed at the instant when the cylinder internal pressure becomes equal to the intake passage pressure. When the rotational speed is high, the delay in intake air inflow is large, so the valve closing timing for obtaining maximum charging efficiency is delayed. On the other hand, when the engine speed is low, the maximum filling efficiency can be obtained by closing the intake valve early. Such a phenomenon is generally referred to as the inertia effect of intake air.

The present invention prevents delay in acceleration response by setting the intake passage volume to 1/3 or less, while variably controlling the closing timing of the intake valve according to the rotation speed to increase filling efficiency in the low rotation range. , is based on the principle of obtaining a practical engine with a lean mixture.

Next, the operation of the engine according to this embodiment will be explained.

During low-speed, fixed-seat driving, the air-fuel mixture is diluted to a mixture ratio of about 20 and is supplied into the cylinder 22 from the air passage 28 through the intake valve 26. At this time, the closing timing of the intake valve 26 is advanced by the valve opening/closing timing variable means 34.
As shown by curve G in the figure, it is approximately in the vicinity of bottom dead center (BDC) (TDC in FIG. 13 indicates top dead center). For this reason, the lean mixture can be filled into the cylinder 2 with high filling efficiency.
Supplied within 2 days. This lean air-fuel mixture is ignited by multiple spark plugs at predetermined ignition timing, and burns in about the same combustion completion time as a general practical engine. therefore,
Sufficient engine output can be obtained, and at the same time, NOx can be reduced and fuel efficiency can be improved.

Next, when the throttle valve 31 is fully opened at a predetermined acceleration timing, the air-fuel mixture is enriched to near the stoichiometric air-fuel ratio by the carburetor 30, and is supplied into the cylinder 22 through the intake passage 4.

At this time, the volume of the intake passage 28 on the downstream side of the throttle valve 31 is reduced, that is, it is set to 1/3 or less of the total displacement of the engine 21, and the rich mixture is immediately transferred to the cylinder 22.
supplied within. Therefore, the engine output can be quickly increased without causing a delay in acceleration response to the operation of the throttle valve 31, and a smooth transition to power running can be achieved. In addition, if the engine 21 is in a high rotation range during this output running, the valve opening/closing timing variable means 34 controls the intake valve 21.
As shown by curve G2 in Fig. 13, the valve closing timing of No. 6 is delayed to near the bottom dead center 1° and 52°, and the air-fuel mixture is supplied into the cylinder 22 with high filling efficiency by fully utilizing the inertia effect of the intake air. Ru. Furthermore, at this time, since the length of the intake passage 28 is short, the intake air is also affected by the pulsation effect of the intake air.

Therefore, the engine output in the high rotation range can be further improved.

On the other hand, when the engine is in a low engine speed range, the closing timing of the intake valve 26 is advanced, and the peak of the filling efficiency shifts to the low engine speed range due to the inertia effect of the intake air. Therefore, engine output during low-speed power running can also be improved.

Next, FIGS. 14 to 16 are diagrams showing a second embodiment of the present invention, and in this embodiment, the configuration of the valve opening/closing timing variable means 51 is different from the previous embodiment. That is, one end of a rocker arm 52 is in contact with the stem end 26a of the intake valve 26, and the other end of the rocker arm 52 is in contact with a valve drive cam 53 that rotates in synchronization with engine rotation. Valve drive cam 5
3 has a high speed cam portion 53a and a low speed cam portion 53b which are sequentially arranged along the axial direction of the camshaft 54. Further, the rocker arm 52 is movable along the axial direction of the rocker shaft 55.
The movement is performed by an electromagnetic actuator 5 having a solenoid 56.
This is done by controlling the energization to 7 based on the engine speed. When the solenoid 56 of the electromagnetic actuator 57 is energized at high engine speed, it moves the rocker arm 52 upward in FIG.
The other end is brought into contact with the high-speed cam portion 53a and curve H is shown in FIG.
2, the intake valve 26 is lifted (delaying the valve closing timing). On the other hand, when the power to the solenoid 56 is cut off during low engine speed, the rocker arm 52 is moved downward and the other end is connected to the low speed cam. The intake valve 26 is brought into contact with the portion 53b to lift the intake valve 26 as shown by curve H8 in FIG. 16 (to advance the valve closing timing).

The rocker arm 52, valve drive cam 53, and electromagnetic actuator 57 collectively constitute a valve opening/closing timing variable means 51. The other parts are the same as those in the previous embodiment.

Therefore, in this embodiment, the same effects as in the previous embodiment can be obtained, but since the opening timing of the intake valve 26 is constant, the valve overlap with the exhaust valve 27 does not change. This has the advantage that the inertia of intake air when the valve is opened can be efficiently utilized.

Although the above embodiments are examples in which the present invention is applied to an engine equipped with a carburetor, the present invention is not limited to a carburetor, but can also be applied to an engine equipped with an electronically controlled fuel injection device, for example. Of course.

Furthermore, the present invention is not limited to engines that perform combustion with a lean mixture during low-speed steady running, but can also be applied to, for example, engines that perform combustion with a mixture near the stoichiometric air-fuel ratio and recirculate a large amount of exhaust gas. . In this case, it is also possible to improve acceleration response and charging efficiency during low-speed power running.

(Effects) According to the present invention, acceleration response can be improved, and the air-fuel mixture filling efficiency at low speeds can be increased, and engine drivability can be improved.

In addition, in each of the above embodiments, the closing timing of the intake valve is varied according to the engine speed, so that not only the pulsation effect of the intake air but also the inertia effect can be used during high-speed power running, and the engine output can be increased. On the other hand, when driving at low speed, the engine output can be improved due to the inertia effect of the intake air. As a result, drivability during power running can be improved.

[Brief explanation of drawings]

1 to 3 are diagrams showing conventional automobile engines,
Fig. 1 is a plan view of the cylinder head, Fig. 2 is a sectional view of the cylinder part, Fig. 3 is a sectional view of the main part of the cylinder part, and Fig. 4 to 6-1 are automatic small engine according to the present invention. FIG. 4 is a plan view thereof, FIG. 5 is a sectional view taken along the line V-V in FIG. 4, and FIG. 6 is a sectional view showing the valve opening/closing timing variable means. 7 to 13 are diagrams for explaining the operation of the same embodiment, and FIG. 7 is a diagram showing the relationship between the mixture ratio, fuel consumption rate, and exhaust gas recirculation amount, and FIG. 8 a to C
9 is a diagram showing the relationship between the opening degree of the throttle valve, the mixture ratio, and the nearsin output, FIG. 9 is a diagram showing the acceleration characteristic with respect to the intake passage volume, and FIG. 10 is a diagram showing the acceleration response delay with respect to the intake passage volume. , FIG. 11 is a diagram showing the relationship between the engine speed and charging efficiency with respect to the length of the intake passage, FIG. 12 is a diagram showing the relationship between the engine speed and charging efficiency with respect to the intake valve closing timing, and FIG. 13 is a diagram showing the relationship between the engine speed and charging efficiency with respect to the intake valve closing timing. 14 to 16 are diagrams showing the second embodiment of the automobile engine according to the present invention, and FIG. 14 is a plan view showing the valve opening/closing timing variable means. FIG. 15 is a sectional view showing the valve opening/closing timing variable means, and FIG. 16 is a diagram showing the intake valve opening/closing timing. 21---Engine, 26---Intake valve, 28---M-Intake passage, 3I-One throttle valve, 34.51---Valve opening/closing timing variable means. Figure 1 Figure 2 Figure 9 Figure 10 Figure 1

Claims (1)

[Claims] In automobile engines that are supplied with a lean mixture during low-speed steady running and a rich mixture when running at high power, the intake passage volume from downstream of the throttle valve to the intake valve is calculated as 1 of the total engine displacement.
/3 or less, and a valve opening/closing timing variable means is provided to vary the closing timing of the intake valve, so that the intake valve closes near bottom dead center at low speeds and later than bottom dead center at high speeds. An automobile engine characterized by: