JP2007077840A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress generation of an unburnt HC quantity by early activation of an exhaust emission purification catalyst. <P>SOLUTION: This internal combustion engine 1 is provided with: a variable valve train 16 for variably controlling a lift characteristic and an opening/closing timing characteristic of an inlet valve and an outlet valve in response to an engine operation condition; and a turbocharger 2 for executing supercharging by driving a turbine by an exhaust gas; and is so controlled that, in a cooling idle time, a lift amount and an opening period of an exhaust vale are reduced, an inlet valve opening period is increased and charging pressure is increased, relative to those in a warming idle time. Thereby, push-out loss in an exhaust process is relatively drastically increased and the internal combustion engine 1 is inevitably operated in a high-load state, whereby a further large quantity of a hot exhaust gas can be provided and the exhaust emission purification catalyst 17 can be activated in a further early stage. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an internal combustion engine having an exhaust purification catalyst in an exhaust system, and in particular, a variable valve mechanism capable of variably controlling the valve lift characteristics of an intake valve and an exhaust valve, and supercharging by driving a turbine with exhaust gas. The present invention relates to an internal combustion engine equipped with a turbocharger that performs the above.

In Patent Document 1, in an internal combustion engine equipped with an exhaust gas turbine, at least one of the phases of an intake valve or an exhaust valve is changed to increase the amount of exhaust gas in response to an acceleration request, and the turbine rotation of the exhaust gas turbine A variable valve timing device is disclosed in which the rise of the number is made faster.
JP-A-9-125994

  However, in the technique of Patent Document 1, the exhaust valve is controlled so that the lift amount and the valve opening period of the exhaust valve are reduced at the time of cold idling and the opening time of the exhaust valve is retarded compared to the warm idling. In addition, the exhaust valve lift amount, the opening degree, and the central angle are not properly controlled so as to maximize the exhaust heat energy amount in the process of increasing the supercharging pressure that is delayed by the turbocharger rotational speed increase delay. Therefore, the exhaust flow rate at the beginning of cold idle operation is limited by the exhaust valve opening, so the exhaust flow rate cannot be increased, and the exhaust heat energy amount used for catalyst temperature rise can be increased. Therefore, there is a possibility that the unburned HC amount discharged before the catalyst is activated is increased because the rate of increase in the catalyst temperature is slow. Further, when the catalyst temperature and the water temperature are rising in the transition period from the cold idling operation to the warm idling operation, the exhaust heat energy discharged becomes excessive, and the fuel consumption may be deteriorated.

  Therefore, the internal combustion engine of the present invention is controlled to reduce the lift amount and the valve opening period of the exhaust valve at the time of cold idling, increase the intake valve opening period, and increase the supercharging pressure at the time of cold idling. It is characterized by being.

  By making the exhaust valve lift amount at the time of cold idling smaller than the exhaust valve lift amount after warm-up, high temperature and high pressure exhaust gas is forcibly exhausted by the lift of the piston through the slightly open exhaust valve gap. Therefore, the extrusion loss of the exhaust gas in the exhaust stroke is greatly increased. Therefore, in order to maintain the same shaft torque and engine rotation speed as after warm-up, it is necessary to increase the amount of fuel and perform a higher load operation. As a result, a larger amount of high-temperature exhaust gas is discharged, and the exhaust purification catalyst can be activated early.

  Also, if not only reducing the lift amount of the exhaust valve but also delaying the opening timing of the exhaust valve until after the bottom dead center, the burnt gas burned in the expansion stroke is compressed again after the bottom dead center, resulting in high temperature and high pressure. Thus, the exhaust extrusion work is further increased as compared with the case where only the lift amount is reduced. As a result, higher-temperature exhaust gas is discharged, and the temperature of the exhaust purification catalyst rises rapidly.

  When the supercharging pressure is further increased, a larger amount of exhaust gas is discharged.

  According to the present invention, the exhaust valve lift amount and the valve opening period are reduced during cold idling, the exhaust valve opening timing is retarded, the intake valve opening period is increased, and the supercharging pressure is increased. Extrusion loss in the process is greatly increased, and the internal combustion engine is inevitably operated at a higher load, so that a larger amount of high-temperature exhaust gas can be obtained, and the exhaust purification catalyst can be used earlier. Can be activated.

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

  FIG. 1 shows the configuration of an intake / exhaust system of an internal combustion engine 1 according to the present invention. As shown in the figure, the internal combustion engine 1 includes a turbocharger 2 as a supercharger. The turbocharger 2 has a configuration in which an exhaust turbine 4 located in the exhaust passage 3 of the internal combustion engine 1 and a compressor 6 located in the intake passage 5 are coaxially arranged, and the supercharging pressure is set according to operating conditions. In order to control, an exhaust bypass valve 7 for bypassing a part of the exhaust from the upstream side to the downstream side of the exhaust turbine 4 is provided. An intercooler 8 is interposed on the downstream side of the compressor 6 in the intake passage 5 as intake air cooling means for cooling intake air whose temperature has increased by the compressor 6. This intercooler 8 is configured, for example, as a water-cooled type, and the amount of cooling can be adjusted by controlling the circulation of the cooling water.

  An exhaust purification catalyst 17 for exhaust purification is interposed in the exhaust passage 3 downstream of the exhaust turbine 4. The exhaust purification catalyst 17 is provided with a catalyst temperature sensor 18 as temperature detection means for detecting the catalyst temperature. The internal combustion engine 1 further includes a water temperature sensor 19 for detecting the coolant temperature, an accelerator opening sensor 20 for detecting the opening of the accelerator pedal, and a vehicle speed sensor 21 for detecting the vehicle speed. These detection signals are respectively input to an engine control unit (hereinafter referred to as ECU) 22.

  The internal combustion engine 1 is a four-cycle gasoline engine, and includes a variable valve mechanism 16 that variably controls the opening and closing timings of the intake valve and the exhaust valve by a control signal from the ECU 22.

  The variable valve mechanism 16 includes, for example, a lift / operation angle variable mechanism 12 that changes the lift / operation angle of the intake valve, and a phase that advances or retards the phase of the center angle of the lift (phase with respect to the crankshaft). Although it is configured as a combination of the variable mechanism 13, various known types can be applied. An example of the lift / operating angle variable mechanism is described in, for example, Japanese Patent Application Laid-Open No. 11-107725. In this variable valve mechanism 16, the opening / closing timing of the intake valve can be controlled independently by changing the lift / operating angle at the same time and simultaneously delaying the entire lift. It is possible to obtain the opening / closing timing of the corresponding intake valve. In particular, by changing the opening timing of the intake valve, the valve overlap can be changed in magnitude, and the recirculation amount of the internal exhaust gas recirculation can be variably controlled.

  FIG. 2 shows a comparison between the valve lift characteristics of the intake / exhaust valves when the internal combustion engine 1 is cold idling and the valve lift characteristics of the intake / exhaust valves when the engine is warm idle.

  As shown in FIG. 2, the variable valve mechanism 16 of the internal combustion engine 1 according to the present embodiment is more exhausted at the time of cold idling (thick solid line in the figure) than at the time of warm idling (thin solid line in the figure). Control is performed to reduce the lift amount and valve opening period of the valve, retard the exhaust valve opening timing, and increase the lift amount and intake valve opening period of the intake valve. Further, as shown in the timing chart of FIG. 3, the turbocharger 2 causes the supercharging pressure at the time of cold idling (cold idling supercharging pressure) to become the supercharging pressure at the warm idling idling (idle superheat at warm up). It is controlled to be larger than (supply pressure). In other words, the internal combustion engine 1 is controlled so that the supercharging pressure increases at the time of cold idling than at the time of warm idling.

  A specific control example of the variable valve mechanism 16 at the time of cold start will be described in detail using the timing chart of FIG.

  The internal combustion engine 1 is controlled so as to have a cold idle speed when the engine is cold, and is controlled so as to have a warm idle speed smaller than the cold idle speed when the engine is warm. In the present embodiment, after the start of combustion, the time until the engine rotational speed reaches the idle rotational speed during warm-up is referred to as cold idling.

  The supercharging pressure by the turbocharger 2 increases in the first control section after the start of combustion until the engine speed reaches the cold idle speed.

  In the first control section, the exhaust valve lift amount and the valve opening period are controlled to substantially increase. In other words, the lift amount and the valve opening period of the exhaust valve are controlled to increase as the catalyst temperature rises.

  Here, there is a correlation between the catalyst temperature and the cooling water temperature, and the cooling water temperature does not have the same value as the catalyst temperature, but the temperature change tendency after the engine start is substantially similar. That is, the catalyst temperature can be estimated from the cooling water temperature, and the cooling water temperature can be estimated from the catalyst temperature. Therefore, the temperature of at least one of the cooling water temperature and the catalyst temperature is detected, and control is performed so that the lift amount and the valve opening period of the exhaust valve increase according to the temperature rise of at least one of the cooling water temperature and the catalyst temperature. You may make it do.

  Further, the phase of the lift center angle of the exhaust valve and the phase of the lift center angle of the intake valve are controlled so as to be retarded in the first control period described above. In the first control section, the intake air amount is controlled to increase relatively as the catalyst temperature increases. Note that the intake air amount in the first control section may be controlled to relatively increase in accordance with the temperature rise of at least one of the cooling water temperature and the catalyst temperature.

  In the process of increasing the engine rotational speed from the cold start to the cold idle idle speed after starting, the exhaust temperature is raised immediately after starting the cold start as the exhaust valve small lift amount / small valve opening period setting. After that, when the supercharging pressure is still low, the exhaust heat energy is maximized by setting the exhaust valve to a small lift amount and a small valve opening period so that the exhaust outflow speed from the exhaust valve is almost sonic. Rapid increase in temperature.

When the lift characteristics of the exhaust valve are reduced and the exhaust valve closing timing is retarded, the ignition timing is retarded to increase the exhaust temperature. In view of this, it is desirable to start retarding the ignition timing after the exhaust valve has been made smaller and the exhaust valve closing timing retarded. By detecting the cooling water temperature rise or catalyst temperature rise that occurs and increasing the exhaust valve lift amount and valve opening period according to the cooling water temperature rise or catalyst temperature rise, the exhaust flow rate from the exhaust valve is regulated by the exhaust valve opening area. By avoiding this, and increasing the exhaust heat energy amount applied to the exhaust gas flow rate increase / exhaust purification catalyst 17, the catalyst temperature rise can be further accelerated.

Then, the engine torque is increased by increasing the exhaust valve lift amount and the valve opening period in accordance with the boost pressure increase at the start of the boost pressure increase after the start of idling at the time of cooling. Further, after the catalyst temperature rises and reaches the catalyst activation temperature (second control section), the amount of exhaust heat energy necessary for the temperature rise of the exhaust purification catalyst 17 can be reduced. Increase the lift amount and valve opening period to reduce exhaust extrusion loss. Along with this, by reducing the intake valve lift amount in order to keep the engine speed constant, the exhaust heat energy amount is reduced, the exhaust purification catalyst 17 is activated, and at the same time, deterioration of fuel consumption can be avoided.

  Furthermore, after the catalyst temperature reaches the catalyst activation temperature, the phase of the lift valve center angle of the intake valve is advanced so that the intake valve closing timing is moved away from the bottom dead center as the catalyst temperature rises. The phase of the lift center angle is controlled to advance in accordance with the increase in the catalyst temperature. Therefore, it is possible to suppress an increase in the intake air amount in accordance with the increase in the supercharging pressure during cold idling.

  The technical idea of the present invention that can be grasped from the above embodiment will be listed together with the effects thereof.

  (1) A variable valve mechanism that variably controls the lift characteristics and opening / closing timing characteristics of the intake and exhaust valves according to the engine operating state, and a turbocharger that performs supercharging by driving the turbine with exhaust gas, At the time of cold idling, control is performed such that the lift amount and valve opening period of the exhaust valve are reduced, the intake valve opening period is increased, and the supercharging pressure is increased as compared with warm idling. As a result, the internal combustion engine is operated under a high load condition, so that a larger amount of high-temperature exhaust gas can be obtained and the exhaust purification catalyst can be activated earlier.

  In addition, it is desirable to set an appropriate ignition timing and an appropriate in-cylinder gas flow so as to improve fuel efficiency during engine operation after warm-up, and excessively increase the in-cylinder gas flow to improve combustion stability. This is undesirable because it increases cooling and pumping losses. On the other hand, during the temperature control of the exhaust when cold, priority is given to promoting early activation of the catalyst by raising the exhaust temperature rather than fuel consumption, so it is desirable to allow a significant retard of the ignition timing. . Therefore, during the temperature rise control of the exhaust when cold, the intake valve lift amount is larger than after warm-up, the intake air amount is increased, and the engine load is increased to improve the combustion stability and the ignition timing retarded greatly. It is effective to enable the exhaust temperature by.

  (2) The internal combustion engine according to (1), further comprising temperature detection means for detecting at least one of a cooling water temperature of the internal combustion engine or a catalyst temperature of an exhaust purification catalyst that performs exhaust purification, and when cooling, Control is performed so as to increase the lift amount / valve opening period of the exhaust valve in accordance with the temperature rise of at least one of the water temperature and the catalyst temperature. This makes it possible to relatively reduce exhaust extrusion loss in response to an increase in cooling water temperature or catalyst temperature, thereby increasing the exhaust gas flow rate, resulting in further increase in supercharging pressure and combustion gas amount. Therefore, the exhaust purification catalyst can be activated early, and at the same time, deterioration of fuel consumption can be avoided.

  (3) The internal combustion engine according to (1), further including temperature detection means for detecting at least one of a cooling water temperature of the internal combustion engine or a catalyst temperature of an exhaust purification catalyst that performs exhaust purification, Control is performed so as to increase the lift amount / valve opening period of the exhaust valve and retard the phase of the lift central angle of the exhaust valve in accordance with the temperature rise of at least one of the water temperature and the catalyst temperature.

  (4) The internal combustion engine according to the above (1) is controlled so that the exhaust valve opening timing is retarded at the time of cold idling than at the time of warm idling.

  (5) The internal combustion engine according to any one of the above (1) to (4) includes temperature detection means for detecting a catalyst temperature of an exhaust purification catalyst that performs exhaust purification, and the catalyst temperature is activated when it is cold. After reaching the temperature, the intake air amount is controlled to be relatively decreased as the catalyst temperature increases.

  (6) The internal combustion engine according to any one of the above (1) to (5) includes a temperature detection unit that detects a catalyst temperature of an exhaust purification catalyst that performs exhaust purification, and the exhaust catalyst is activated when cold. After reaching the temperature, the lift central angle of the intake valve is controlled to advance in accordance with the increase in the catalyst temperature. As a result, an increase in the intake air amount can be suppressed.

  (7) The internal combustion engine according to any one of (1) to (6) includes temperature detection means for detecting a catalyst temperature of an exhaust purification catalyst that performs exhaust purification, and the exhaust catalyst is activated in cold air. After reaching the temperature, control is performed to advance the lift center angle of the exhaust valve.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 5 is an explanatory view showing a comparison between the valve lift characteristics of the intake / exhaust valve during cold idling of the internal combustion engine according to the present invention and the valve lift characteristics of the intake / exhaust valve during warm-up idle. 4 is a timing chart of various parameters from when the internal combustion engine according to the present invention is started up to when it is warmed up.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Turbocharger 16 ... Variable valve mechanism

Claims (7)

  A variable valve mechanism that variably controls the lift characteristics and opening / closing timing characteristics of the intake and exhaust valves according to the engine operating state, and a turbocharger that performs supercharging by driving the turbine with exhaust gas. An internal combustion engine that is controlled to reduce the lift amount and valve opening period of the exhaust valve, to increase the intake valve opening period, and to increase the supercharging pressure as compared with the warm-up idle time.   A temperature detecting means for detecting at least one of a cooling water temperature of an internal combustion engine or a catalyst temperature of an exhaust purification catalyst that performs exhaust purification is provided, and responds to an increase in temperature of at least one of the cooling water temperature or the catalyst temperature during cooling. The internal combustion engine according to claim 1, wherein the internal combustion engine is controlled to increase a lift amount and a valve opening period of the exhaust valve.   A temperature detecting means for detecting at least one of a cooling water temperature of an internal combustion engine or a catalyst temperature of an exhaust purification catalyst that performs exhaust purification is provided, and responds to an increase in temperature of at least one of the cooling water temperature or the catalyst temperature during cooling. The internal combustion engine according to claim 1, wherein the internal combustion engine is controlled to increase the lift amount / valve opening period of the exhaust valve and retard the phase of the lift center angle of the exhaust valve.   2. The internal combustion engine according to claim 1, wherein the exhaust valve opening timing is controlled to be retarded at a cold idling time than at a warm idling time.   Equipped with a temperature detection means that detects the catalyst temperature of the exhaust purification catalyst that performs exhaust purification. After the catalyst temperature reaches the catalyst activation temperature in the cold state, the intake air amount is relatively decreased as the catalyst temperature increases. The internal combustion engine according to any one of claims 1 to 4, wherein the internal combustion engine is controlled to operate.   A temperature detection means for detecting the catalyst temperature of the exhaust purification catalyst that performs exhaust purification is provided.After the exhaust catalyst reaches the catalyst activation temperature in cold air, the lift central angle of the intake valve is adjusted according to the increase in the catalyst temperature. The internal combustion engine according to claim 1, wherein the internal combustion engine is controlled to advance.   A temperature detection means for detecting the catalyst temperature of the exhaust purification catalyst that performs exhaust purification is provided, and is controlled to advance the lift central angle of the exhaust valve after the exhaust catalyst reaches the catalyst activation temperature in cold air. The internal combustion engine according to any one of claims 1 to 6, wherein

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