JP5316102B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine provided with a variable valve gear that makes a valve overlap variable, and more particularly, to an improvement in control at a cold start.

  In an intake port injection type fuel injection device that injects fuel toward the intake port, the temperature of the inner wall of the intake port is low when the engine is cold, so that the atomization of fuel deteriorates and the fuel wall flow increases. In order to cope with this, it is known that the residual gas in the combustion chamber is positively returned to the intake port and the atomization of the fuel is promoted using the heat. For example, Patent Document 1 discloses a special configuration in which a part of the intake air flowing into the cylinder is returned to the intake port via the second intake valve, but the intake valve opening timing is delayed. Even in a general internal combustion engine equipped with an intake valve with a variable valve system that can move forward, a part of the heat of the combustion chamber is utilized by advancing the intake valve opening timing to expand the valve overlap. Atomization can be promoted.

  In addition, a so-called intake stroke injection technique is also known in which fuel is injected during a period overlapping with an intake valve opening period in which the flow velocity of intake air passing through the intake valve is high in order to suppress a cold fuel wall flow.

JP 63-18149 A

  When a variable valve system is used, the variable valve system cannot be driven and the valve overlap cannot be sufficiently expanded due to various limitations for a very short time immediately after the cold start of the engine. . For example, if the variable valve mechanism is of a hydraulic drive type, the variable valve mechanism cannot be moved until the engine is started and the lubricating oil pressure of the engine sufficiently rises. Even if not a hydraulic drive type, there is a case where the drive of the variable valve apparatus is not permitted until the normal operation of the mechanically driven variable valve apparatus is ensured.

  In such a case, the valve overlap cannot be secured sufficiently during that time, and the fuel wall flow due to the deterioration of atomization of the fuel injected into the intake port as described above temporarily increases. There is a problem that HC deteriorates.

  Further, in general intake stroke injection technology, when combined with a variable valve operating device, there is a problem that HC increases or operability deteriorates depending on the state of valve overlap.

  In the control apparatus for an internal combustion engine according to the present invention, the valve overlap between the fuel injection valve that injects fuel toward the intake port of the internal combustion engine and the exhaust valve closing timing depends on the engine operating conditions. Therefore, a variable valve operating device that changes the intake valve opening timing, an injection timing control means that changes the fuel injection end time according to the engine operating conditions, and a means that detects the engine temperature condition are provided.

  When the engine is cold-started, immediately after starting with a minimum overlap, a first stage of controlling to a predetermined injection end timing at which HC is minimum with respect to the intake valve opening timing at that time, and the variable motion A second stage for controlling to a predetermined injection end timing at which HC is minimized under each intake valve opening timing in response to the intake valve opening timing that sequentially changes when driving of the valve device is started; And a third stage for controlling the injection end timing to a timing before the normal intake valve opening timing when the temperature reaches a predetermined temperature.

In one preferred form, Oite the first stage floor above, the injection end timing becomes the intake stroke injection which is delayed from the intake valve opening timing.

  When the engine is started, the engine is started with a minimum overlap. After the complete explosion, as a first stage, the injection end timing is controlled to be a predetermined injection end timing. Since the change of the injection timing is not accompanied by the operation of a mechanical mechanism unlike the variable valve operating device, the execution can be started immediately. At this time, the injection end timing is before or in the vicinity of the intake valve opening timing, and the atomization of the fuel is promoted using the high-speed intake flow passing through the intake valve. When the driving of the variable valve apparatus starts, as the second stage, the injection end timing is controlled to the optimum point at which HC is minimum with respect to the actually changing intake valve opening timing. Thereby, the transient deterioration of HC is avoided. When the engine temperature reaches a predetermined temperature, the process proceeds to the third stage, and the injection end timing is returned to the normal timing before the intake valve opening timing.

  According to the present invention, transient deterioration of HC due to the wall flow on the wall surface of the intake port from the cold start of the engine to the completion of warm-up can be suppressed to a minimum.

The system block diagram of the control apparatus of the internal combustion engine which concerns on this invention. The characteristic view which shows the characteristic of HC and combustion stability with respect to valve overlap and injection end timing. Explanatory drawing which showed the transfer of the 1st, 2nd, 3rd step in FIG. 2 with the arrow. The valve timing chart which showed the opening / closing timing of the intake / exhaust valve. The flowchart which shows the flow of control of one Example. The time chart which shows changes, such as the injection end time after a start.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration explanatory view showing a system configuration of an internal combustion engine according to the present invention. The internal combustion engine 1 has an intake valve 3 and an exhaust valve 4, and as a variable valve operating apparatus for the intake valve 3, A first variable valve mechanism (VEL) 5 capable of continuously expanding / reducing the lift / operation angle of the intake valve 3 and a phase variable capable of continuously delaying the central angle of the operation angle. A mechanism, that is, a second variable valve mechanism (VTC) 6. The intake passage 7 is provided with an electronically controlled throttle valve 2 whose opening degree is controlled by an actuator such as a motor. The first and second variable valve mechanisms 5 and 6 and the electronic control throttle valve 2 are controlled by the control unit 10.

  A fuel injection valve 8 for injecting fuel into the intake port is disposed in the intake passage 7, and an amount of fuel corresponding to the intake air amount is injected from the fuel injection valve 8.

  The control unit 10 includes an accelerator opening signal APO from an accelerator opening sensor 11 provided on an accelerator pedal operated by a driver, an engine rotation speed signal Ne from an engine rotation speed sensor 12, and an intake air amount sensor. An intake air amount signal from 13, a coolant temperature signal Tw from the water temperature sensor 14, and the like are input. Based on these signals, the control unit 10 performs fuel injection amount, fuel injection timing, ignition timing, throttle valve opening. The fuel injection valve 8, the spark plug 9, the throttle valve 2, the first and second variable valve mechanisms 5, 6 and the like are controlled by calculating the degree, the operating angle target value, the center angle target value, and the like.

  The mechanical configuration of the first variable valve mechanism 5 and the second variable valve mechanism 6 is well known (for example, JP 2007-285308 A, JP 2002-256905 A, etc.). Here, both the first and second variable compression ratio mechanisms 5 and 6 are hydraulically driven, and the lubricating oil pressure of the engine is used as a hydraulic pressure source. In the present invention, it is sufficient that the variable valve operating device delays at least the opening timing of the intake valve 3, and for example, only one of the first and second variable compression ratio mechanisms 5 and 6 is used. Alternatively, other types of variable valve gears may be used.

  Next, the control at the time of cold start which is the main part of the present invention will be described.

  FIG. 4 shows an example of the valve timing of the intake valve 3 realized by the variable valve gears 5 and 6, and FIG. 4 (a) shows the atomization of the fuel spray by blowing back the residual gas when cold. In order to promote, the characteristic example when the valve overlap of the intake-exhaust valves 3 and 4 is ensured comparatively large is shown. Specifically, the valve overlap is 14 ° CA.

  On the other hand, FIG. (B) is an example of characteristics when the load is high. The opening timing of the intake valve 3 is on the most retarded side, and therefore the valve overlap is minimum, for example, −6 ° CA. . The variable valve gears 5 and 6 are configured to return to this characteristic (b) when the engine is not supplied with hydraulic pressure. Therefore, when the engine is started, the start is basically performed with this characteristic (b). Done. Then, after the engine is started, until the hydraulic pressure becomes sufficiently high, the variable control of the valve lift characteristic is not started, and during that time, the operation with the characteristic (b) is continued. When the variable control is started, the intake valve opening timing is gradually advanced, the valve overlap is expanded, and the characteristic (a) is changed.

  FIG. 2 shows the relationship between (i) HC emissions and (ii) combustion stability and the magnitude of the valve overlap as described above when the engine is cold. Here, the valve overlap is 14 °. Only the characteristic (a) of CA and the characteristic (b) of −6 ° CA are shown as representatives. The horizontal axis indicates the injection timing, particularly the injection end timing, as a variable. The left side of the drawing is the advance side, the right side is the retard side, and one scale is 20 ° CA. Also, in the figure, for reference, a fixed exhaust valve closing timing (EVC), an intake valve opening timing (shown as IVO (a)) at the characteristic (a), and an intake valve opening at the characteristic (b) The timing (shown as IVO (b)) is illustrated.

  As shown in the figure, when the engine is cold, if the valve overlap is small (−6 ° CA), the atomization of the fuel is bad, so there is a tendency that the HC emission amount is large, and the valve overlap is large as a whole (for example, 14 In the case of ° CA), HC is reduced due to the improvement of atomization due to the heat of the residual gas. However, when the valve overlap is small as in the characteristic (b), if the injection end timing is delayed to approach the intake valve opening timing, the HC emission amount decreases rapidly, and the injection end timing becomes the intake valve opening timing. The minimum point (P1) is reached when it is slightly delayed. However, as is apparent from the figure, if the injection end timing is excessively late, HC deteriorates conversely and combustion stability also deteriorates.

  As the valve overlap increases, the minimum point of the HC emission amount when the injection end timing is changed moves to the advance side. Although it is not necessarily clear in the figure, in the characteristic (a) where the valve overlap is 14 ° CA, the point P2 is a minimum point.

  Therefore, in the present invention, as shown by arrows Y1, Y2, and Y3 in FIG. 3, the injection end timing is variably controlled in accordance with the change in the valve overlap so that the HC discharge amount is minimized. IT0 in FIG. 3 indicates the normal injection end timing after warm-up, and as shown in the figure, fuel injection starts and ends within a period in which the intake valve 3 is closed. Further, at the start (cranking), fuel injection is performed at this injection end timing IT0. Therefore, although the operation at the time of cold start is started at the point P3 in FIG. 3, since the HC discharge amount is large at this point P3, the injection end timing is immediately retarded so as to go to the minimum point P1. That is, as the first stage, the transition as indicated by the arrow Y1 is performed. This change in the injection timing can be executed immediately because it does not require mechanical operation like the variable valve gears 5 and 6. Eventually, when the lubricating oil pressure of the engine rises and driving of the variable valve gears 5 and 6 starts, the HC under each valve overlap corresponds to the valve overlap (intake valve opening timing IVO) that changes sequentially. The injection end timing is gradually advanced in a form in which the predetermined injection end times at which the minimum is reached, that is, the respective minimum points are connected. This is the second stage, and a transition as indicated by an arrow Y2 is made. Thereafter, when the engine temperature condition reaches a predetermined condition, the injection end timing is returned to the normal injection end timing IT0 as indicated by an arrow Y3 as a third stage. Thereby, as is apparent from FIG. 3, the amount of HC emission is minimized, and the transient deterioration of combustion stability can be reliably avoided.

  FIG. 5 is a flowchart showing a flow of control performed at the time of cold start. First, as in step 1, the engine is started with the characteristic (b) of FIG. The injection end time is the normal injection end time IT0. When the explosion is completed and the operation shifts to the self-sustained operation, the process proceeds to Step 2 where the injection end timing IT is retarded to be a predetermined injection end timing at which the HC emission amount is minimized under the characteristic (b) (first stage) . In step 3, the drive of the variable valve gears 5 and 6 is permitted based on the passage of a predetermined time or the detection of the hydraulic pressure. Thereby, the variable valve gears 5 and 6 actually operate toward the characteristic (a) in FIG. In step 4, the intake valve opening timing that changes with the operation of the variable valve gears 5 and 6 is sequentially read, and HC is minimized under each intake valve opening timing corresponding to the intake valve opening timing. Control is performed at a predetermined injection end timing (second stage). When the engine temperature condition reaches a predetermined condition, in step 5, the injection end timing is returned to the normal injection end timing IT0 (third stage). Further, when the warm-up is completed, in step 6, the variable valve gears 5 and 6 are shifted to normal control, and, for example, the valve overlap is reduced depending on the operating conditions.

  FIG. 6 is a time chart showing an example of the intake valve opening timing IVO and the injection end timing IT that are changed by the control as described above after the cold start, and shows the engine rotational speed REV, the vehicle speed V, and the cooling water temperature Tw. The changes are also shown. The engine starts at the time T0 in the figure, and immediately shifts to the first stage, and the intake stroke injection is performed until the time T1. At the time of T1, the driving of the variable valve gears 5 and 6 is permitted, and at the same time, the process proceeds to the second stage, and the intake valve opening timing IVO is advanced while minimizing the HC discharge amount, for example, 14 ° CA. Overlap. Thereafter, based on the cooling water temperature Tw, at the time point T2, as a third stage, the delay of the injection end timing ends and returns to the reference injection end timing IT0. Similarly, based on the cooling water temperature Tw, at time T3, the variable valve gears 5 and 6 shift to normal control, and the valve overlap is reduced.

DESCRIPTION OF SYMBOLS 3 ... Intake valve 5, 6 ... Variable valve operating apparatus 8 ... Fuel injection valve 10 ... Control unit 14 ... Water temperature sensor

Claims (4)

A fuel injection valve that injects fuel toward the intake port of the internal combustion engine;
A variable valve gear that changes the intake valve opening timing in order to make the valve overlap between the exhaust valve closing timing and the engine operating conditions,
An injection timing control means for changing the fuel injection end timing according to the engine operating conditions;
Means for detecting engine temperature conditions;
In a control device for an internal combustion engine comprising:
A first stage of controlling to a predetermined injection end timing at which HC is minimum with respect to the intake valve opening timing immediately after starting with a minimum overlap at the time of cold start of the engine;
A second stage of controlling to a predetermined injection end time at which HC is minimized under each intake valve opening timing in response to the intake valve opening timing that sequentially changes when driving of the variable valve device starts. When,
And a third step of controlling the injection end timing to a timing before the normal intake valve opening timing when the engine temperature reaches a predetermined temperature.   2. The control apparatus for an internal combustion engine according to claim 1, wherein in the first stage, the injection end timing is intake stroke injection delayed from the intake valve opening timing. 3. The control apparatus for an internal combustion engine according to claim 2, wherein at the end of the second stage, the injection end timing is more advanced than the intake valve opening timing.   4. The control apparatus for an internal combustion engine according to claim 1, wherein the actuator of the variable valve operating apparatus is a hydraulic drive mechanism.

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