JP2006200414A - Exhaust temperature control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sufficiently increase an exhaust temperature by enhancing re-combustion effect in an exhaust passage in order to implement early activation of an exhaust emission purifying catalyst immediately after the start. <P>SOLUTION: When increasing the exhaust temperature, fuel cut or ignition cut is executed to a part of cylinders. At the same time, lift characteristic of an exhaust valve of the cylinder is changed to open the exhaust valve with in-cylinder pressure increased by the rise of a piston. High temperature/high pressure air or raw gas adiabatically compressed is exhausted to an exhaust passage from a combustion chamber of the cylinder. The opening timing of the exhaust valve can be in the latter stage of an exhaust stroke or of a compression stroke of the piston. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas temperature control device for an internal combustion engine used for early activation of an exhaust purification catalyst immediately after starting.

In Patent Document 1, when early activation of an exhaust purification catalyst is attempted, fuel is cut for some cylinders, so that exhaust (air) from the cylinders is supplied as secondary air to an exhaust passage and operated. It is disclosed that unburned components in the exhaust of the cylinder are reburned to raise the exhaust temperature.
JP-A-11-3111119

However, in the technique described in Patent Document 1, since the opening timing of the exhaust valve of the idle cylinder remains the same, the air compressed once in the compression stroke and expanded in the expansion stroke is discharged in the exhaust stroke. Therefore, the discharged air has a low temperature and is not preferable from the viewpoint of HC oxidation, and the reburning effect in the exhaust passage cannot be maximized.
In view of such a situation, the present invention makes it possible to exhaust air or raw gas (unburned gas mixture) from a deactivated cylinder at a high temperature, thereby enhancing the recombustion effect in the exhaust passage, and making the exhaust temperature more sufficient. An object of the present invention is to provide an exhaust temperature control device for an internal combustion engine that can be raised.

  For this reason, in the present invention, when the exhaust temperature is raised, fuel cut or ignition cut is performed for some cylinders, and the exhaust valves of the cylinders are opened in a state where the in-cylinder pressure is increased by raising the piston, Air or raw gas is discharged from the combustion chamber of the cylinder to the exhaust passage.

According to the present invention, since the exhaust valve of the idle cylinder is opened when the in-cylinder pressure becomes high, the adiabatic-compressed high-temperature and high-pressure air or raw gas can be supplied to the exhaust passage, The combustion effect can be improved.
Further, when the raw gas is supplied to the exhaust passage by the ignition cut, since the fuel is contained, a higher reburning effect can be obtained.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is an engine system diagram showing an embodiment of the present invention.
In the intake passage 2 of the engine 1, an electrically controlled throttle valve 4 that is positioned on the inlet side of the intake manifold 3 and controls the amount of intake air is installed. The opening degree of the electric throttle valve 4 is controlled by a step motor or the like that is operated by a signal from an engine control unit (hereinafter referred to as ECU) 20.

A fuel injection valve 6 for injecting fuel into the intake port 5 of each cylinder is attached to the branch portion on the outlet side of the intake manifold 3. The fuel injection valve 6 is opened by energizing the solenoid for a time determined by the pulse width based on the injection pulse signal output from the ECU 20 in synchronization with the engine rotation, and injects the fuel adjusted to a predetermined pressure. .
The air controlled by the electric throttle valve 4 and the fuel injected from the fuel injection valve 6 are sucked into the combustion chamber 9 above the piston 8 of the engine 1 when the intake valve 7 is opened.

The air and fuel sucked into the combustion chamber 9 form an air-fuel mixture, and are ignited and burned by the spark plug 10 at the ignition timing controlled by the ECU 20. The exhaust after combustion is discharged to the exhaust passage 12 via the exhaust valve 11. An exhaust purification catalyst 13 is provided at a collecting portion of the exhaust passage 12.
Of the intake valve 7 and the exhaust valve 11, at least the exhaust valve 11 is provided with a variable valve device 14 that can change its lift characteristics (open timing, etc.) for each cylinder.

As the variable valve operating device 14, a cam switching device (VVL) that includes two cams having different cam profiles and can selectively switch between them is used.
Alternatively, the valve operating angle and lift that can continuously change the valve operating angle (open period) and the lift amount by changing the posture of the link that mechanically links the cam shaft and the cam. A variable amount device (VEL) and a variable valve timing device (VTC) capable of continuously changing the central angle phase of the valve operating angle by changing the rotational phase of the crankshaft and the camshaft are used.

  For example, as shown in FIG. 2, when the ignition order is # 1 → # 3 → # 4 → # 2 in the four-cylinder engine, the exhaust passage 12 is paired with cylinders whose ignition order is not continuous. # 4 Cylinder exhaust passages (branch pipes) are merged upstream (at a short distance) (G1). Similarly, exhaust passages (branch pipes) of # 2 and # 3 cylinders are upstream (at a short distance). After joining (G2), the whole is joined (G3).

  The ECU 20 includes an accelerator opening APO detected by an accelerator pedal sensor 21, an engine speed Ne detected by a crank angle sensor 22, an intake air amount Qa detected by an air flow meter 23, and an engine detected by a water temperature sensor 24. The coolant temperature Tw, the exhaust air-fuel ratio detected by the air-fuel ratio sensor 25, the catalyst temperature Tc detected by the catalyst temperature sensor 26, and the like are input. In addition, although not shown, a signal is also input from an engine key switch having an ignition switch and a start switch.

The ECU 20 controls the opening degree of the electric throttle valve 4, the fuel injection timing and fuel injection amount of the fuel injection valve 6, the ignition timing of the spark plug 10, and the like based on the engine operating conditions detected from these input signals. . Further, the operation of the variable valve operating device 14 is controlled.
Next, control for early activation (warming-up) of the exhaust purification catalyst 13 immediately after startup will be described with reference to the flowchart of FIG.

In S1, it is determined whether there is a catalyst temperature increase request immediately after startup or the like. Specifically, the catalyst temperature sensor 26 detects the catalyst temperature Tc and determines whether it is lower than a predetermined activation temperature. The activity / inactivity may be determined by predicting the catalyst temperature from the operating conditions. If there is a catalyst temperature increase request immediately after startup, that is, if the catalyst 13 is inactive, the process proceeds to S2 and S3.
In S2, the engine is operated in the partial cylinder combustion mode. Specifically, for example, cylinders # 1 and # 3 are operating cylinders, cylinders # 2 and # 4 are deactivated cylinders, and fuel cut (fuel injection by fuel injection valve 6) is performed for cylinders # 2 and # 4 which are deactivated cylinders. Stop) or ignition cut (stop ignition by the spark plug 10). When performing fuel cut (when exhausting air), the ignition may be cut or performed, but when performing ignition cut (when exhausting raw gas), fuel is supplied. To do.

In S3, the lift characteristics of the exhaust valves 11 of the # 2 and # 4 cylinders, which are idle cylinders, are changed from the characteristic A (normal characteristics) in FIG. In other words, the opening timing of the exhaust valve 11 is delayed, and the exhaust valve 11 is set to open in the latter half (second half) of the exhaust stroke of the piston 8. In this example, the valve is opened for a predetermined period up to the vicinity of the exhaust TDC in the later stage of the exhaust stroke.
As a result, the exhaust valves 11 of the # 2 and # 4 cylinders, which are idle cylinders, open in a state where the in-cylinder pressure is increased due to the rise of the piston 8, and in the case of a fuel cut, adiabatically compressed from the combustion chamber 9 of the cylinder The high-temperature and high-pressure air can be discharged to the exhaust passage 12. The discharged high-temperature and high-pressure air is mixed with the exhaust (burned gas) of the # 1 and # 3 cylinders, which are the operating cylinders, and the unburned components (HC) in the exhaust are efficiently reburned, and the exhaust temperature Is sufficiently increased, contributing to the early activation of the catalyst 13.

In the case of ignition cut, high-temperature and high-pressure raw gas (unburned gas mixture) adiabatically compressed from the combustion chamber 9 of the cylinder can be discharged to the exhaust passage 12. The exhausted high-temperature and high-pressure raw gas is combusted while being mixed with the exhaust of the operating cylinders # 1 and # 3, and the amount of combustion increases, so that the exhaust temperature is raised sufficiently, and the catalyst 13 Significantly contributes to early activation.
When performing partial cylinder operation, it is necessary to increase the torque of the operating cylinder, including the amount of compression work that increases due to the change in the exhaust valve opening timing of the idle cylinder. Next, the fuel injection amount of the operating cylinder is set.

  Further, in the case of fuel cut, unburned components from the operating cylinder are burned with air from the idle cylinder in the exhaust passage, so that the fuel injection amount of the operating cylinder is set to a rich rich setting in terms of air-fuel ratio. In the case of the ignition cut, the fuel in the operating cylinder is burned with the air in the raw gas from the idle cylinder (and the unburned component from the operating cylinder) from the idle cylinder in the exhaust passage. The injection amount is set to stoichiometric or slightly rich in terms of air-fuel ratio.

If it is determined in S1 that there is no catalyst temperature increase request, that is, if the catalyst 13 has been warmed up, the process proceeds to S4 and S5.
In S4, the operation is performed in the all-cylinder combustion mode. That is, the fuel injection amounts of all the cylinders are set to the normal setting, and all the cylinders are ignited.
In S5, the variable valve device 14 returns the lift characteristics of the exhaust valves 11 of the # 2 and # 4 cylinders from the characteristic B of FIG. 4 to the characteristic A (normal characteristic). Note that the lift characteristics of the exhaust valves 11 of the # 1 and # 3 cylinders are always the characteristic A (normal characteristics).

Next, another embodiment of the present invention will be described.
In the above embodiment, according to the exhaust valve lift characteristics of FIG. 4, the opening timing of the exhaust valve of the idle cylinder is delayed and set to the latter stage of the exhaust stroke, so that high-temperature / high-pressure air or raw gas is generated from the combustion chamber of the cylinder. Although the gas is discharged to the exhaust passage, as another embodiment, the following control may be performed using the exhaust valve lift characteristic of FIG.

  When operating in the partial cylinder combustion mode, the lift characteristics of the exhaust valves 11 of the # 2 and # 4 cylinders, which are idle cylinders, are controlled by the variable valve device (especially VEL and VTC) 14 in S2 of the flow of FIG. The characteristic A (normal setting) in FIG. In other words, the opening timing of the exhaust valve 11 is set to be greatly advanced so that it opens in the later stage of the compression stroke of the piston 8. In this example, the valve is opened for a predetermined period near the compression TDC from the compression stroke to the expansion stroke. Even in this case, adiabatic-compressed high-temperature and high-pressure air or raw gas can be discharged to the exhaust passage 12, and the same effect can be obtained.

In the above embodiment, the cylinder groups are divided into # 1 and # 3 cylinder groups and # 2 and # 4 cylinder groups, one of which is an operating cylinder (combustion cylinder) and the other is an idle cylinder (exhaust of air or raw gas). Cylinder).
This is based on the exhaust system layout as shown in FIG. 2, and the operating cylinder and the non-operating cylinder are paired, and the exhaust passages of the paired cylinders are joined upstream (with a short distance) from the other exhaust passages. This is for burning at a high temperature and effectively raising the exhaust temperature.

  However, in this case, when the ignition order is # 1 → # 3 → # 4 → # 2, combustion-combustion-pause-pause is considered disadvantageous in terms of stability, so combustion-pause- The cylinder group of # 1, # 4 and the cylinder group of # 2, # 3 are divided so as to be combustion-pause, one is an operating cylinder (combustion cylinder), and the other is an idle cylinder (exhaust of air or raw gas) Cylinder). When the exhaust passages of all the cylinders merge at one point, exhaust and air or raw gas alternately flow into the junction, which is advantageous in terms of afterburning.

In the partial cylinder operation, it is not necessary to deactivate half of all cylinders, and at least one cylinder may be deactivated and air or raw gas may be discharged from the cylinder.
Further, the control may be performed under limited conditions for increasing the exhaust temperature due to the discharge of air or raw gas into the exhaust passage.
That is, when an electric air pump for supplying secondary air is provided and secondary air can be supplied to the exhaust passage (especially the exhaust port) by this pump, the air pump can be operated from the viewpoint of battery consumption during cranking. In the period when the battery voltage is stabilized after the end of cranking, the period until the battery voltage is stabilized, the period until the discharge amount is stabilized after the start of the air pump operation, the fuel cut or ignition cut of some cylinders, The exhaust valve opening timing of the cylinder may be changed to use exhaust air or raw gas from the cylinder.

Engine system diagram showing one embodiment of the present invention Exhaust system layout Flow chart for switching control between full cylinder operation and partial cylinder operation Lift characteristics of exhaust valve used during partial cylinder operation Lift characteristic chart of exhaust valve used during partial cylinder operation in another embodiment

Explanation of symbols

1 engine
2 Intake passage
3 Intake manifold
4 Electric throttle valve
5 Intake port
6 Fuel injection valve
7 Intake valve
8 Piston
9 Combustion chamber
10 Spark plug
11 Exhaust valve
12 Exhaust passage
13 Exhaust gas purification catalyst
14 Variable valve gear
20 ECU
21 Accelerator pedal sensor
22 Crank angle sensor
23 Air Flow Meter
24 Water temperature sensor
25 Air-fuel ratio sensor
26 Catalyst temperature sensor

Claims (4)

  When the exhaust temperature is raised, fuel cut or ignition cut is performed on some cylinders, and the exhaust valve of the cylinder is opened in a state where the cylinder pressure is increased by raising the piston, and air or air is discharged from the combustion chamber of the cylinder. An exhaust temperature control apparatus for an internal combustion engine, characterized in that raw gas is discharged into an exhaust passage.   2. An exhaust temperature control apparatus for an internal combustion engine according to claim 1, wherein the opening timing of the exhaust valve of the cylinder for performing fuel cut or ignition cut is set in the latter stage of the exhaust stroke of the piston.   2. An exhaust temperature control apparatus for an internal combustion engine according to claim 1, wherein the opening timing of the exhaust valve of the cylinder for performing fuel cut or ignition cut is set in the latter stage of the compression stroke of the piston.   The exhaust gas of the internal combustion engine according to any one of claims 1 to 3, wherein an exhaust gas purification catalyst is provided in the exhaust passage, and the exhaust gas temperature is raised when a temperature increase request is made for the catalyst. Temperature control device.

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