JP3536519B2 - Intake valve control device and control method for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-cycle spark ignition type internal combustion engine represented by a gasoline engine, and more particularly to an intake valve control device and control method for an internal combustion engine having a variable valve mechanism.

[0002]

2. Description of the Related Art Various types of variable valve mechanisms for variably controlling the opening and closing timings of intake valves and exhaust valves of a four-cycle internal combustion engine have been proposed in various types, some of which have already been put to practical use. . For example, a camshaft and a crankshaft that drives the camshaft are relatively shifted in phase relation to change the opening / closing timing of intake and exhaust valves in the same direction, or two cams having different cam profiles. There are practically used devices in which two rocker arms are provided, and the valve lift characteristics are switched between two types by selectively switching the rocker arms in which intake and exhaust valves are actually linked. Also, Japanese Patent Application Laid-Open No. 6-18 / 1994
No. 5321, applying the principle of a non-constant velocity shaft coupling,
There is disclosed a variable valve mechanism capable of continuously variably controlling a valve lift characteristic by rotating a cylindrical camshaft at an irregular speed.

One purpose of variably controlling the opening / closing timing of an intake valve is to reduce pump loss caused by a throttle valve and improve fuel efficiency, particularly in a gasoline engine. In other words, in a gasoline engine, the negative pressure of the intake pipe pressure downstream of the throttle valve develops when the load is low, so the pump loss becomes relatively large as compared with the high load. Attempts have been made to reduce pump loss at partial load by controlling.

In order to reduce the pump loss, the closing timing of the intake valve is greatly delayed at the time of partial load.
Many methods have been proposed to reduce the filling efficiency and reduce the suction negative pressure. Further, in this method, since the actual compression ratio is reduced, a mirror cycle combined with a supercharger is partially used in practice.

[0005]

However, if the intake valve closing timing is delayed to reduce the pump loss at the time of partial load as in the prior art, the pump loss is reduced,
Since the combustion is deteriorated due to a decrease in the actual compression ratio, it is not always an effective method as a fuel efficiency improving means.

SUMMARY OF THE INVENTION It is an object of the present invention to achieve both improvement of combustion by improving the actual compression ratio and prevention of increase in pump loss at the time of partial load.

[0007]

In order to achieve the above object, an intake valve control device and a control method according to the present invention provide a variable valve mechanism capable of continuously controlling the opening / closing timing of an intake valve by a control signal. In the equipped internal combustion engine, the opening timing of the intake valve is set to a position that is later than the intake top dead center when the engine is under a low load, and is gradually advanced according to an increase in the load.
At high load, the intake valve is set near the top dead center, and the closing timing of the intake valve is set near the compression bottom dead center at low engine load, and is gradually delayed according to the increase in load. And

FIG. 1 is a valve timing diagram of an intake valve, in which (a) shows the characteristics at high load (specifically, at high speed and high load), and (b) shows characteristics at low load (specifically, at low speed and low load). ) Is shown, but the characteristics under a high load are extremely common opening / closing timings. That is, in consideration of the inertia of the gas, it opens slightly before the intake top dead center and is considerably delayed from the compression bottom dead center.
Close at around 40-60 °. On the other hand, when the load is low, the opening timing is gradually delayed in accordance with the decrease in the load, and is at a position delayed from the intake top dead center. On the other hand, the closing timing is gradually advanced in accordance with the decrease in the load, and when the load is low, it is near the intake top dead center.

In the present invention, the pump loss is reduced by delaying the opening timing of the intake valve at a low load as described above.

FIG. 9 is a characteristic diagram showing the correlation between the valve lift and the pressure in the conventional example in which the intake valve opens just before the intake top dead center at the time of low load, but shows the intake valve 1 at the end of the exhaust stroke. The pressure P2 at the upstream intake port 2 (see FIG. 10) is a very large negative pressure due to the presence of a throttle valve (not shown). And the combustion chamber 3
The pressure P1 in (see FIG. 10) is substantially equal to the exhaust pressure level in the exhaust port 5 (see FIG. 10) downstream of the exhaust valve 4.
Here, when the intake valve 1 opens near the top dead center, the intake port 2
The residual gas in the combustion chamber 3 is sucked out to the intake port 2 as shown by an arrow in FIG.
The pressure in the combustion chamber 3 rapidly decreases as shown in FIG.
As a result, the piston 6 (see FIG. 10) descends from near the top dead center against a large negative pressure, and a large pump loss occurs.

On the other hand, in the present invention, the intake valve 1
Is opened during the suction stroke in which the piston 6 descends. In this case, as shown in FIG. 2, at the beginning of the suction stroke, the residual gas in the combustion chamber 3 expands with the lowering of the piston 6, and the pressure P1 in the combustion chamber 3 decreases. 9 is very slow compared to the characteristic of FIG. 9 in which the negative pressure P2 acts rapidly. Accordingly, when the intake valve 1 is opened during the intake stroke, the intake air flows into the combustion chamber 3 from the intake port 2 as shown by an arrow in FIG. Is also close to the pressure P2 of the intake port 2, but the pump loss is reduced by delaying the timing when the large negative pressure acts on the piston 6.

On the other hand, in the present invention, the closing timing of the intake valve 1 is advanced at a low load compared to a high load, and approaches the compression bottom dead center. Therefore, the actual compression ratio at low load is improved, and the combustion at low load is simultaneously improved. If the closing timing of the intake valve 1 is advanced to the bottom dead center side at a low load, an increase in pump loss occurs. However, the increase in pump loss here is caused by the above-described decrease in pump loss at the beginning of the intake stroke. Therefore, the combustion improvement effect due to the improvement in the actual compression ratio can be secured as it is without increasing the pump loss at low load as a whole.

The variable control of the opening timing and the variable control of the closing timing of the intake valve 1 as described above are described, for example, in Japanese Patent Laid-Open No. 6-18 / 1994.
It can be realized by a variable speed variable valve mechanism of a non-constant speed rotation type described in Japanese Patent No. 5321 or the like, but is of course limited to this as long as the opening timing and the closing timing can be simultaneously changed in opposite directions. Not something. However, in the above-described type in which the camshaft and the crankshaft are relatively rotated, the opening timing and the closing timing change in the same direction while the operating angle is constant. Moves in the middle of the compression stroke, and the actual compression ratio becomes excessively low, which makes it difficult to deteriorate the combustion.

[0014] In the present invention, the opening timing of the upper Symbol intake valves 1, further cylinder pressure P1 is that control the timing substantially equal to the intake pipe pressure (pressure in the intake port 2) P2.
In this way, the pressure P1 in the combustion chamber 3 does not drop sharply due to the negative pressure P2 in the intake port 2.

[0015] The pressure sensor opening timing of the intake valve 1 in this way, to cylinder pressure P1 is controlled to timing becomes substantially equal to the intake pipe pressure P2, the second aspect of the present invention, for detecting an intake pipe pressure P2 The opening timing of the intake valve 1 is controlled based on the detected pressure. According to this configuration, the intake pipe pressure P2 is directly detected.

Further, the invention according to claim 3 has pressure estimating means for estimating the intake pipe pressure P2 from the rotational speed of the internal combustion engine, the amount of intake air and the closing timing of the intake valve at that time, and based on the estimated pressure. Thus, the opening timing of the intake valve 1 is controlled. According to this configuration, the intake pipe pressure P2 is indirectly detected without using a pressure sensor. The intake pipe pressure P2 can be estimated mainly from the engine speed and the intake intake air amount. However, since the actual effective stroke changes depending on the closing timing of the intake valve 1, it is necessary to correct the intake valve closing timing. .

In the present invention, the opening / closing timing on the exhaust valve 4 side may be fixedly set or may be variably controlled.

[0018] In the structure of claim 4, the closing timing of the exhaust valve 4 is fixedly set to a position immediately after the exhaust top dead center, the valve overlap is produced at the time of engine high load, at the time of engine low load, The intake valve opening timing is later than the exhaust valve closing timing.

That is, when the engine is under low load, there is no valve overlap, and both the exhaust valve 4 and the intake valve 1 are closed at the beginning of the intake stroke when the piston 6 descends.

[0020]

According to the present invention, the pump loss at the beginning of the suction stroke is reduced by opening the intake valve during the suction stroke at a low load. At the same time, by increasing the closing timing of the intake valve, the actual compression ratio can be increased, and although there is an increase in pump loss in the middle of the intake stroke, it is covered by the reduction in pump loss at the beginning of the intake stroke. Fuel efficiency can be improved by the improvement.

In particular, the opening timing of the intake valve is determined by the cylinder pressure.
By performing control at a time when the pressure becomes substantially equal to the pipe pressure, it is possible to more reliably prevent the pressure in the combustion chamber from being rapidly reduced due to the negative pressure of the intake pipe when the intake valve is opened. The loss can be more reliably reduced.

[0022] Then, by using a pressure sensor for detecting an intake pipe pressure as claimed in claim 2, since the intake pipe pressure is detected directly, by eliminating the influence of various factors, the cylinder in the open intake valve The internal pressure and the intake pipe pressure can be accurately matched.

Further, if the intake pipe pressure is estimated as in claim 3 , a pressure sensor is not required. In addition, by taking into account the influence of the intake valve closing timing, highly accurate estimation can be performed.

According to the fourth aspect , variable control of the exhaust valve is not required, and the configuration can be simplified.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 4 is a valve timing diagram showing an example of the opening and closing timing of the intake and exhaust valves of the internal combustion engine according to the present invention. In this embodiment, the exhaust valve
Opening and closing operation is always performed with a fixed valve lift characteristic through a general valve operating mechanism. As an example, the exhaust valve opens 49 degrees before bottom dead center and closes 3 degrees after top dead center. The open period of the exhaust valve shown as theta _E. Although two exhaust valves are provided for each cylinder as shown in FIG. 3, for example, it is needless to say that the present invention is not limited to this.

On the other hand, the intake valve is opened and closed via a variable valve mechanism capable of continuously and continuously changing the opening timing and the closing timing in the opposite directions as described above. Then, at the time of high speed and high load, the intake valve opens, for example, at 3 ° before top dead center and closes at 49 ° after bottom dead center. The open period at this time is shown as θ _IH . At low speed and low load, the intake valve opens, for example, at 14 ° after top dead center and closes at 25 ° after bottom dead center. The open period of this time is shown as theta _IL.

The opening timing of the intake valve is BTDC3ＤＣ-
It changes continuously according to the load within the range of ATDC14 °. That is, when the load is reduced, the opening timing is gradually delayed. Similarly, the closing timing of the intake valve is determined by the above-mentioned ABDC49.
It changes continuously according to the load in the range of {} to ABDC25}, and as the load decreases, the closing timing gradually advances.

Therefore, at high speed and high load, BTD
The valve overlap period is between C3 # and ATDC3 #, but in a predetermined partial load region, the open period of the exhaust valve and the open period of the intake valve do not overlap.

Here, the intake valve opening timing at the time of low load is aimed at the timing at which the in-cylinder pressure at which the residual gas expands as the piston descends and the intake pipe pressure at the upstream side of the intake valve become equal. Is set.

FIG. 5 shows a PV diagram at a low load, in which the characteristics of the embodiment of the present invention are compared with those of the conventional example. The characteristics of the embodiment are shown by way of example when the valve overlap is −10 °, that is, when the opening timing of the intake valve is ATDC13 °. In the conventional example, the valve overlap is 6 °, That is, this is a characteristic in the case where the opening timing of the intake valve is BTDC3 °, which is the same as when the load is high. As is apparent from FIG. 4, in the present invention, the pressure drop at the beginning of the suction stroke is gradual,
Negative work or pump losses are reduced. Specifically, a reduction in pump loss corresponding to the region shown by hatching in FIG. 5 is achieved.

Next, an embodiment of control for controlling the opening timing of the intake valve at a timing when the intake pipe pressure and the in-cylinder pressure become substantially equal will be described with reference to FIGS. FIG.
Is a flowchart showing the flow of the control. In step 1, a target value αm of the intake valve opening timing is referred to based on an intake pipe pressure detected by an intake pipe pressure sensor (not shown) with reference to a predetermined map. Set. This target value is given, for example, as a crank angle after top dead center. Next, in step 2, the actual opening timing α at that time is compared with the target value αm. If α <αm, the routine proceeds to step 3, where it is determined that it is necessary to delay the opening timing of the intake valve, and in step 5, the actuator is controlled to delay the opening timing. If α ≧ αm, the routine proceeds to step 4, where it is determined that it is necessary to advance the intake valve opening timing. At step 5, the actuator is controlled in a direction to advance the opening timing. In this way, the intake valve opening timing is always optimally controlled.

In addition to the method of directly detecting the intake pipe pressure as described above, the intake pipe pressure can be estimated based on a predetermined map from the engine operating conditions, that is, the engine speed and the intake air intake amount. . FIG. 7 shows an example of the control characteristic of the intake valve opening timing using the engine speed and the torque as parameters, and the target value of the opening timing is set in accordance with such characteristics. In this example, the target value of the opening timing is shown as a valve overlap period (crank angle). In addition, since the actual effective stroke changes depending on the closing timing of the intake valve, it is necessary to correct it. Specifically, when the intake valve closing timing approaches the bottom dead center, the intake pipe pressure decreases even at the same rotation speed and the same intake air amount.

FIG. 8 shows an example of the control characteristic of the intake valve closing timing. As described above, the closing timing is earlier in the lower load range and approaches the bottom dead center.

[Brief description of the drawings]

FIG. 1 is a valve timing diagram showing the opening / closing timing of an intake valve according to the present invention and showing characteristics when the load is high (a) and when the load is low (b).

FIG. 2 is a characteristic diagram showing a valve lift characteristic and a pressure change according to an intake valve opening timing according to the present invention.

FIG. 3 is a characteristic diagram showing a gas flow when an intake valve is opened according to the present invention.

FIG. 4 is a valve timing diagram showing a specific example of an intake valve opening / closing timing.

FIG. 5 is a PV diagram at a low load according to the present invention.

FIG. 6 is a flowchart showing the flow of control according to the present invention.

FIG. 7 is a characteristic diagram showing control characteristics of intake valve opening timing.

FIG. 8 is a characteristic diagram showing control characteristics of intake valve closing timing.

FIG. 9 is a characteristic diagram showing a valve lift characteristic and a pressure change according to a conventional intake valve opening timing.

FIG. 10 is a characteristic diagram showing a conventional gas flow when an intake valve is opened.

[Explanation of symbols]

1 ... intake valve 2. Intake port 3. Combustion chamber

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-58-214610 (JP, A) JP-A-59-34434 (JP, A) JP-A-60-150407 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) F02D 13/02 F02B 29/08 F02D 41/04 F02D 45/00 F02D 23/00

Claims (5)

(57) [Claims] In an internal combustion engine having a variable valve mechanism capable of continuously controlling the opening and closing timing of an intake valve by a control signal, the opening timing of the intake valve is delayed from the intake top dead center when the engine is under a low load. And at the same time, gradually advance according to the increase of the load, and set it near the intake top dead center when the load is high, and set the close timing of the intake valve near the compression bottom dead center when the engine load is low. as well as, as delayed gradually with increase of the load, further, the opening timing of the intake valve, the cylinder pressure intake pipe pressure
An intake valve control device for an internal combustion engine , wherein the control is performed at a timing substantially equal to the following . 2. A has a pressure sensor for detecting an intake pipe pressure, intake valve control apparatus for an internal combustion engine according to claim 1, wherein the opening timing of the intake valve is controlled based on the detected pressure . 3. A pressure estimating means for estimating an intake pipe pressure from a rotational speed of the internal combustion engine, an intake air amount and a closing timing of the intake valve at that time, and based on the estimated pressure, an opening timing of the intake valve. 2. The intake valve control device for an internal combustion engine according to claim 1, wherein 4. The closing timing of the exhaust valve is fixedly set at a position immediately after the top dead center of the exhaust. When the engine is under a high load, valve overlap occurs. The intake valve control device for an internal combustion engine according to any one of claims 1 to 3 , wherein the valve opening timing is delayed. 5. An internal combustion engine provided with a variable valve mechanism capable of continuously controlling the opening / closing timing of an intake valve by a control signal, wherein the opening timing of the intake valve is delayed from the intake top dead center when the engine is under a low load. And at the same time, gradually advance according to the increase of the load, and set it near the intake top dead center when the load is high, and set the close timing of the intake valve near the compression bottom dead center when the engine load is low. At the same time as the load increases, and furthermore, the opening timing of the intake valve is adjusted so that the in-cylinder pressure becomes the intake pipe pressure.
A method for controlling an intake valve of an internal combustion engine, characterized in that the control is performed at a timing substantially equal to :