JP5737103B2 - Carbon removal method and spark ignition direct injection engine - Google Patents

Description

The present invention belongs to the technical field of mosquito Bon removal method and direct-injection spark-ignition engine.

  For example, in Patent Document 1, in order to increase the theoretical thermal efficiency of a spark-ignition gasoline engine, a cavity recessed in the lower surface of the cylinder head and a protrusion projecting from the piston crown surface form a central combustion chamber and a main combustion chamber. The combustion chamber as a whole is set to a compression ratio as high as about 16, and the air-fuel mixture is relatively rich in the central combustion chamber, and the air-fuel mixture is relatively lean in the main combustion chamber. Thus, an engine having a lean air-fuel mixture is described for the entire combustion chamber.

  Further, for example, in Patent Document 2, from the viewpoint of reducing cooling loss and improving thermal efficiency, a surface that forms a combustion chamber of an engine has a lower thermal conductivity than the base material and is lower than the base material. Alternatively, a technique is disclosed that is constituted by a heat insulating material in which a large number of bubbles are formed inside a material having a heat capacity per unit volume substantially equal to that of the base material. The compression ratio of the engine of this Patent Document 2 is 16.

Japanese Patent Laid-Open No. 9-217627 JP 2009-243355 A

  By the way, in the Otto cycle, which is the theoretical cycle of a spark ignition engine, the theoretical thermal efficiency increases as the compression ratio of the engine increases and as the specific heat ratio of the gas increases. For this reason, the combination of a high compression ratio and lean air-fuel mixture as described in Patent Document 1 is advantageous to some extent for improving thermal efficiency (illustration thermal efficiency). However, in this case, the illustrated thermal efficiency is maximized at a compression ratio of about 15, and even if the compression ratio is increased further, the illustrated thermal efficiency does not increase (inversely, the higher the compression ratio is, the lower the illustrated thermal efficiency is). . This is because, since the air-fuel mixture is lean, a relatively large amount of air is introduced into the cylinder. On the other hand, a large amount of air in the cylinder is greatly compressed as the compression ratio increases, and the combustion pressure and temperature are reduced. This is because it becomes significantly higher. That is, the amount of heat released through the cylinder wall and the like is increased by a high combustion pressure and combustion temperature, and the cooling loss is greatly increased. As a result, the illustrated thermal efficiency is lowered.

  In this regard, if the combustion chamber is insulated by providing a heat insulation layer having a low thermal conductivity and a low volume specific heat as described in Patent Document 2 on the wall surface of the combustion chamber, Loss can be reduced, and there is a high possibility that the illustrated thermal efficiency can be improved by a high compression ratio.

  Here, in the case of increasing the compression ratio, in addition to the heat insulating layer or instead of the heat insulating layer, if the intake air temperature is lowered and the gas temperature during combustion is lowered as much as possible, the gas It is preferable because the difference in temperature between the temperature and the temperature of the wall surface of the combustion chamber can be reduced to reduce the cooling loss. In order to lower the intake air temperature in this way, a heat insulating layer is also provided on the back side of the umbrella portion (including the valve stem) of the cylinder head intake port and intake valve so that the intake air does not receive heat from the cylinder head or intake valve. It is preferable to make it.

  However, since lubricating oil flows from the upper part of the valve stem to the back side portion of the umbrella portion in the intake valve, carbon accumulates on the heat insulating layer due to the lubricating oil. When carbon is deposited on the heat insulating layer in this way, the passage area of the intake air is reduced, so that the amount of intake air charged is reduced and the engine output is reduced.

  The present invention has been made in view of such a point, and an object of the present invention is to easily determine that carbon is deposited on a heat insulating layer provided at least on the back side of the umbrella portion of the intake valve. In addition, when it is determined that carbon is deposited, the carbon can be easily removed.

To achieve the above object, in this invention, it is a geometrical compression ratio is 18 or more, the rear portion of at least the valve head of the intake valve, the spark-ignition direct injection engine heat insulating layer is coated, targeting the decoking method for removing carbon deposited on the heat insulating layer, and the accumulated operation time detection step of detecting the cumulative operating time of a predetermined rotation number or more of the engine rotational speed is detected by the accumulated operation time detection step A carbon deposition determining step for determining that carbon is deposited on the heat insulating layer when the accumulated operation time exceeds a predetermined time; and carbon depositing on the heat insulating layer in the carbon deposition determining step. When the determination is made and the accelerator opening after the acceleration request is in a steady state equal to or less than the predetermined opening, the opening period of the intake valve and the exhaust valve is turned off. Burlap by, by introducing burned gas into the intake port, it is intended to include a carbon sintered removed by the step of tempering removed by the carbon deposited on the heat insulating layer.

Thus , the cumulative operation time at the engine speed equal to or higher than the predetermined rotation speed is detected, and when the detected cumulative operation time exceeds the predetermined time, it is determined that carbon is deposited on the heat insulating layer. Do. That is, at an engine speed equal to or higher than a predetermined speed, the temperature of the back side portion of the umbrella portion of the intake valve becomes a temperature at which carbon is likely to accumulate, and the cumulative operation time at such speed is a predetermined time. If it exceeds, carbon should have accumulated in the heat insulation layer, and it can be determined that carbon has accumulated. Therefore, it can be easily determined that carbon is deposited on the heat insulating layer.

Then, when it is determined that carbon has accumulated on the heat insulating layer, the temperature of the back side portion of the umbrella portion in the intake valve is set to a temperature high enough to burn the carbon deposited on the heat insulating layer (temperature exceeding 300 ° C. ). That is, the gas temperature in the combustion chamber increases with the acceleration request, and the high-temperature gas is caused to flow back to the intake port due to the overlap of the valve opening period of the intake valve and the exhaust valve after the acceleration request. As a result, the temperature of the back side portion of the umbrella portion in the intake valve becomes high, and the carbon deposited on the heat insulating layer can be easily burned off. By removing carbon from the heat insulating layer in this way, it is possible to suppress a decrease in the amount of intake air charged due to carbon deposition, and it is possible to suppress a decrease in engine output. In addition, the heat insulation layer can lower the intake air temperature to reduce the gas temperature during combustion as much as possible, and reduce the difference between the gas temperature and the temperature of the combustion chamber wall surface to reduce the cooling loss. Is possible. Thereby, the illustrated thermal efficiency can be improved by setting the compression ratio to 18 or higher.

Another aspect of the present invention is a spark-ignition direct injection engine in which the geometric compression ratio is 18 or more and at least a back portion of the umbrella portion of the intake valve is coated with a heat insulating layer. A cumulative operating time detecting means for detecting a cumulative operating time at an engine speed equal to or higher than a predetermined speed, and the heat insulation layer when the cumulative operating time detected by the cumulative operating time detecting means exceeds a predetermined time. The carbon deposition determining means for determining that carbon has been deposited on, the accelerator opening detecting means for detecting the accelerator opening, and the carbon deposition determining means determining that carbon has been deposited on the heat insulating layer. In this case, when it is detected by the accelerator opening detection means that the accelerator opening after the acceleration request is in a steady state equal to or less than a predetermined opening, the intake valve and the exhaust valve The overlap of the valve period, by introducing burned gas into the intake port, it is assumed that a carbon sintered removed by means of burn removed by the carbon deposited on the heat insulating layer.

This invention, similarly to the invention of the decoking process, it is possible to easily determine the carbon deposited on the insulation layer, it is possible to easily remove the carbon deposited on the sectional heat layer.

As described above, according to the decoking process of the present invention, the determination of carbon to the sectional heat layer is deposited can be easily performed, when performing this determination, facilitating carbon deposited on the heat insulating layer Can be removed. Furthermore, according to the spark ignition direct injection engine of the present invention, the same operational effects as those of the carbon removing method can be obtained.

1 is a schematic view showing a spark ignition direct injection engine according to an embodiment of the present invention. Investigate how the temperature of the back part of the umbrella part of the intake valve with the heat insulation layer on the combustion chamber side and back part of the umbrella part changes depending on the engine speed and air charge (engine load) (A) And (b) shows the temperature of the part which left | separated 5 mm and 10 mm in the axial direction of the valve stem from the combustion chamber side surface of the umbrella part, respectively. FIG. 3 is a view corresponding to FIG. 2 in the case of an intake valve not provided with a heat insulating layer, and (a) and (b) are portions separated by 5 mm and 10 mm in the axial direction of the valve stem from the surface of the umbrella portion on the combustion chamber side, respectively. Indicates the temperature. It is a flowchart which shows the control action regarding carbon deposition determination and carbon removal by an engine controller (CPU).

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

  FIG. 1 schematically shows a spark ignition direct injection engine 1 (hereinafter simply referred to as an engine 1) according to an embodiment of the present invention. In the present embodiment, the engine 1 includes various actuators attached to the engine body, various sensors, and an engine controller 100 that controls the actuators based on signals from the sensors.

  The engine 1 is mounted on a vehicle such as an automobile, and its output shaft is connected to drive wheels via a transmission, although not shown. The vehicle is propelled by the output of the engine 1 being transmitted to the drive wheels. The engine body of the engine 1 includes a cylinder block 12 and a cylinder head 13 mounted thereon, and a plurality of cylinders 11 (cylinders) are formed inside the cylinder block 12 (in FIG. 1). Only one is shown). Although not shown in the drawings, a water jacket through which cooling water flows is formed inside the cylinder block 12 and the cylinder head 13.

  A piston 15 is slidably inserted into each cylinder 11, and the piston 15 defines a combustion chamber 17 together with the cylinder 11 and the cylinder head 13. A concave cavity 15 a is formed at the center of the crown surface of the piston 15.

  Although only one is shown in FIG. 1, two intake ports 18 are formed in the cylinder head 13 for each cylinder 11, and each opens to the lower surface of the cylinder head 13 (the ceiling surface of the combustion chamber 17). Communicating with Similarly, two exhaust ports 19 are formed in the cylinder head 13 for each cylinder 11, and each communicates with the combustion chamber 17 by opening on the lower surface of the cylinder head 13 (the ceiling surface of the combustion chamber 17). The intake port 18 is connected to an intake passage (not shown) through which fresh air introduced into the cylinder 11 flows. A throttle valve 20 for adjusting the intake flow rate is interposed in the intake passage, and the opening degree of the throttle valve 20 is adjusted in response to a control signal from the engine controller 100. On the other hand, the exhaust port 19 is connected to an exhaust passage (not shown) through which burned gas (exhaust gas) from each cylinder 11 flows. Although not shown, an exhaust gas purification system having one or more catalytic converters is disposed in the exhaust passage.

  The cylinder head 13 is provided with an intake valve 21 and an exhaust valve 22 so that the intake port 18 and the exhaust port 19 can be shut off (closed) from the combustion chamber 17, respectively. The intake valve 21 is driven by an intake valve drive mechanism via a valve stem 21b provided on the back side of the umbrella portion 21a, and the exhaust valve 22 is provided via a valve stem 22b provided on the back side of the umbrella portion 22a. It is driven by the exhaust valve drive mechanism. The intake valve 21 and the exhaust valve 22 reciprocate at a predetermined timing to open and close the intake port 18 and the exhaust port 19, respectively, and perform gas exchange in the cylinder 11. Although not shown, the intake valve drive mechanism and the exhaust valve drive mechanism each have an intake camshaft and an exhaust camshaft that are drivingly connected to the crankshaft. These camshafts are synchronized with the rotation of the crankshaft. Rotate. Further, at least the intake valve drive mechanism includes a hydraulic or mechanical phase variable mechanism (Variable Valve Timing: VVT) 23 that can continuously change the phase of the intake camshaft within a predetermined angle range. ing. In addition, you may make it provide the lift variable mechanism (CVVL (Continuous Variable ValveLift)) which can change a valve lift amount continuously with VVT23.

  A spark plug 31 is disposed on the cylinder head 13. The ignition plug 31 is attached and fixed to the cylinder head 13 by a known structure such as a screw. In the present embodiment, the spark plug 31 is attached and fixed in a state inclined to the exhaust side with respect to the central axis of the cylinder 11, and the tip (electrode) thereof faces the ceiling of the combustion chamber 17. The arrangement of the spark plug 31 is not limited to this. The spark plug 31 generates a spark by the ignition system 32. The ignition system 32 receives a control signal from the engine controller 100 and energizes the spark plug 31 to generate a spark at a desired ignition timing. As an example, the ignition system 32 may include a plasma generation circuit, and the ignition plug may be a plasma ignition type plug. The use of a plasma ignition type plug with high ignition energy is advantageous in improving the ignition stability.

  An injector 33 that directly injects fuel into the combustion chamber 17 is disposed on the central axis of the cylinder 11 in the cylinder head 13. The injector 33 is fixedly attached to the cylinder head 13 with a known structure such as using a bracket. The tip of the injector 33 faces the center of the ceiling of the combustion chamber 17. The arrangement of the injector 33 is not limited to this. In the present embodiment, the injector 33 is an outer valve-opening type injector having an outer valve that opens and closes a nozzle port that injects fuel into the combustion chamber. In this outer valve-opening injector, as the lift amount of the outer valve from the state in which the nozzle port is closed is larger, the penetration of fuel spray injected from the nozzle port into the combustion chamber 17 becomes larger. Adjustment of fuel spray penetration is facilitated.

  The fuel supply system 34 includes a fuel supply system that supplies fuel to the injector 33 and an electric circuit that drives the injector 33. This electric circuit receives a control signal from the engine controller 100 and operates the injector 33 to inject a desired amount of fuel into the combustion chamber 17 at a predetermined timing.

  Here, the fuel of the engine 1 is gasoline in the present embodiment, but may be gasoline containing bioethanol or the like, and any fuel as long as it is a fuel (liquid fuel) containing at least gasoline. Also good.

  The engine controller 100 is a controller based on a well-known microcomputer, and includes a central processing unit (CPU) that executes a program, a memory that is configured by, for example, RAM and ROM, and stores a program and data, And an input / output (I / O) bus for inputting and outputting signals.

  The engine controller 100 includes at least a signal related to the intake air flow from the air flow sensor 71, a crank angle pulse signal from the crank angle sensor 72, an accelerator opening signal from the accelerator opening sensor 73 that detects the amount of depression of the accelerator pedal, And the vehicle speed signal from the vehicle speed sensor 74 is received, respectively. Based on these input signals, the engine controller 100 calculates control parameters of the engine 1 such as a desired throttle opening signal, a fuel injection pulse, an ignition signal, a valve phase angle signal, and the like. The engine controller 100 outputs these signals to the throttle valve 20 (throttle actuator that moves the throttle valve 20), the fuel supply system 34, the ignition system 32, the VVT 23, and the like.

  The geometric compression ratio ε of the engine 1 is 18 or more. The upper limit value of the geometric compression ratio ε is preferably 40, and the geometric compression ratio ε is particularly preferably 25 or more and 35 or less. In the present embodiment, the engine 1 is also an engine 1 having a relatively high expansion ratio as well as a high compression ratio, because the compression ratio = expansion ratio. In addition, you may employ | adopt the structure (for example, Atkinson cycle and a mirror cycle) used as compression ratio <= expansion ratio.

  As shown in FIG. 1, the combustion chamber 17 includes the wall surface of the cylinder 11, the crown surface of the piston 15, the lower surface of the cylinder head 13 (the ceiling surface of the combustion chamber 17), and the umbrellas of the intake valve 21 and the exhaust valve 22. A section is formed by the combustion chamber side surface (lower surface) of the portions 21a and 22a. And in order to reduce a cooling loss, the combustion chamber 17 is thermally insulated by providing the heat insulation layers 61, 62, 63, 64, and 65 on each of these surface portions (that is, the combustion chamber wall surface portion). In addition, below, when these heat insulation layers 61-65 are named generically, a code | symbol "6" may be attached | subjected to a heat insulation layer. The heat insulation layer 6 may be provided on all of the combustion chamber wall surface portion, or may be provided on a part of the combustion chamber wall surface portion. Further, in the illustrated example, the heat insulating layer 61 on the cylinder wall surface portion is provided at a position above the piston ring 14 in a state where the piston 15 is located at the top dead center. The ring 14 is configured not to slide. However, the heat insulating layer 61 on the cylinder wall surface is not limited to this configuration, and the heat insulating layer 61 may be provided over the entire stroke of the piston 15 or a part thereof by extending the heat insulating layer 61 downward. Further, although it is not a wall surface portion that directly partitions the combustion chamber 17, a heat insulating layer may be provided on the port wall surface portion near the opening on the ceiling surface side of the combustion chamber 17 in the intake port 18 or the exhaust port 19. In addition, the thickness of each heat insulation layer 61-65 illustrated in FIG. 1 does not show actual thickness, but is only an illustration, and does not show the magnitude relationship of the thickness of the heat insulation layer in each surface.

  The heat insulation structure of the combustion chamber 17 will be described in more detail. As described above, the heat insulating structure of the combustion chamber 17 is configured by the heat insulating layers 61 to 65 provided on the wall surface of the combustion chamber. These heat insulating layers 61 to 65 are configured so that the heat of the combustion gas in the combustion chamber 17 is In order to suppress discharge through the wall surface portion of the combustion chamber, the thermal conductivity is set lower than that of the metal base material constituting the combustion chamber 17. Here, for the heat insulating layer 61 provided on the wall surface portion of the cylinder 11, the cylinder block 12 is the base material, and for the heat insulating layer 62 provided on the crown surface portion of the piston 15, the piston 15 is the base material, and the cylinder head 13. For the heat insulating layer 63 provided on the lower surface portion of the cylinder, the cylinder head 13 is a base material, and for the heat insulating layers 64 and 65 provided on the surface of the intake valve 21 and the exhaust valve 22 on the combustion chamber side, Each of the valve 21 and the exhaust valve 22 is a base material. Accordingly, the base material is aluminum alloy or cast iron for the cylinder block 12, cylinder head 13 and piston 15, and heat-resistant steel or cast iron for the intake valve 21 and exhaust valve 22.

  Further, the heat insulating layer 6 is set to have a specific volume heat lower than that of the base material in order to reduce cooling loss. That is, the gas temperature in the combustion chamber 17 varies with the progress of the combustion cycle, but in a conventional engine that does not have the heat insulation structure of the combustion chamber 17, the cooling water flows in a water jacket formed in the cylinder head or cylinder block. Thus, the temperature of the wall surface of the combustion chamber is maintained substantially constant regardless of the progress of the combustion cycle.

  On the other hand, since the cooling loss is determined by cooling loss = heat transfer coefficient × heat transfer area × (gas temperature−temperature of the combustion chamber wall surface portion), the difference temperature between the gas temperature and the temperature of the combustion chamber wall surface portion is The larger the value, the larger the cooling loss. In order to suppress the cooling loss, it is desirable to reduce the difference between the gas temperature and the temperature of the combustion chamber wall surface. However, if the temperature of the combustion chamber wall surface is maintained approximately constant by cooling water, It is unavoidable that the temperature difference increases with fluctuation. Therefore, it is preferable to reduce the heat capacity of the heat insulating layer 6 so that the temperature of the combustion chamber wall surface portion changes following the fluctuation of the gas temperature in the combustion chamber 17.

Moreover, in this embodiment, as shown in FIG. 1, the heat insulation layer 21c is coated also on the back side part (including the valve stem 21b) of the umbrella part 21a of the intake valve 21. Like the heat insulating layer 6, the heat insulating layer 21c has a lower thermal conductivity than the base material and a lower volume specific heat than the base material. For example, a ceramic material such as ZrO _{2 is formed} on the base material. It is coated by plasma spraying. The ceramic material may contain a number of pores. If it does in this way, the heat conductivity and volume specific heat of the heat insulation layer 6 can be made low, so that the porosity is large. In addition, the heat insulation layer 21c and the heat insulation layer 6 may be comprised with the same material.

  By the heat insulating layer 21c, when fresh air is sucked into the combustion chamber 17, it is possible to suppress or avoid an increase in temperature due to heat received from the intake valve 21. As a result, the temperature of fresh air introduced into the combustion chamber 17 (initial gas temperature before compression) is lowered, so that the gas temperature at the time of combustion is lowered, and the temperature difference between the gas temperature and the temperature of the combustion chamber wall surface portion. This is advantageous in reducing the size. Lowering the gas temperature at the time of combustion can lower the heat transfer rate, which is advantageous for reducing the cooling loss.

  Further, in this embodiment, the port liner 181 made of aluminum titanate having a very low thermal conductivity, excellent heat insulation, and excellent heat resistance is integrally cast on the cylinder head 13, thereby The port 18 is provided with a heat insulating layer. As a result, when fresh air passes through the intake port 18, it can be suppressed or avoided that the temperature rises due to heat received from the cylinder head 13, and the temperature of the fresh air introduced into the combustion chamber 17 is further reduced. Can be lowered. The configuration of the heat insulating layer provided in the intake port 18 is not limited to the cast-in of the port liner 181, and it is not always necessary to provide the heat insulating layer in the intake port 18.

  In addition to the heat insulation structure as described above, it is possible to further reduce the cooling loss by forming a heat insulation layer by a gas layer in the combustion chamber 17. In this case, fuel is injected from the injector 11 into the combustion chamber 17 during the compression stroke so that a gas layer containing fresh air is formed at the outer peripheral portion of the combustion chamber 17 of the engine 1 and an air-fuel mixture layer is formed at the central portion. Try to spray. That is, fuel is injected into the combustion chamber 17 by the injector 33 during the compression stroke, and the penetration of the fuel spray is suppressed to such a size (length) that the fuel spray does not reach the outer periphery of the combustion chamber 17. Thus, stratification is realized, in which an air-fuel mixture layer is formed at the center of the combustion chamber 17 and a gas layer containing fresh air is formed around it. This gas layer may be only fresh air, and may contain burned gas (EGR gas) in addition to fresh air. It should be noted that there is no problem even if a small amount of fuel is mixed in the gas layer, and the fuel layer may be leaner than the gas mixture layer so that the gas layer can serve as a heat insulating layer.

  When ignition is performed by the spark plug 31 in a state where the gas layer and the air-fuel mixture layer are formed as described above, the gas mixture between the air-fuel mixture layer and the wall surface of the cylinder 11 causes the flame of the air-fuel mixture layer to be in the cylinder 11. The gas layer becomes a heat insulating layer without coming into contact with the wall surface of the cylinder 11, and the release of heat from the wall surface of the cylinder 11 can be suppressed.

  It should be noted that if the cooling loss is simply reduced, the reduced cooling loss is converted into exhaust loss and does not contribute much to the improvement in the illustrated thermal efficiency. The energy of the combustion gas corresponding to the reduced cooling loss is efficiently converted into mechanical work. That is, it can be said that the illustrated thermal efficiency is greatly improved in the engine 1 by adopting a configuration that reduces both the cooling loss and the exhaust loss.

  Here, in a low load region where the engine load is equal to or less than a predetermined value, the excess air ratio λ of the entire combustion chamber 17 is set to 2 or more, or the weight ratio G / F of gas to fuel in the cylinder is set to 35 or more. The Thereby, in the low load region, RawNOx can be reduced while achieving thermal insulation by the heat insulation layer and improving the illustrated thermal efficiency. From the viewpoint of reducing RawNOx, the excess air ratio λ ≧ 2.5 is more preferable. In addition, since the illustrated thermal efficiency reaches a peak when the excess air ratio λ = 8, the range of the excess air ratio λ is preferably 2 ≦ λ ≦ 8 (more preferably 2.5 ≦ λ ≦ 8). Note that the lean air-fuel mixture sets the throttle valve 20 on the open side, which can contribute to the improvement of the indicated thermal efficiency by reducing the gas exchange loss (pumping loss).

  On the other hand, in the high load region where the engine load is higher than the predetermined value, the excess air ratio λ = 1 in the entire combustion chamber 17 is set with priority on torque (in the mixed gas layer, the excess air ratio λ <1. ). The predetermined value may increase as the engine speed increases, and may be a constant value regardless of the engine speed.

  Since the lubricating oil flows from the upper part of the valve stem 21b to the back side portion of the umbrella portion 21a in the intake valve 21, carbon is deposited on the heat insulating layer 21c due to the lubricating oil. This carbon is easily deposited when the temperature of the back side portion of the umbrella portion 21a is within a certain temperature range (200 ° C. to 300 ° C.). When carbon is deposited on the heat insulating layer 21c in this way, the passage area of the intake air is reduced, so that the amount of intake air charged is reduced and the engine output is reduced.

  Therefore, in the present embodiment, when the engine controller 100 determines that carbon has accumulated on the heat insulating layer 6 as described later, and determines that carbon has accumulated, Remove (burn).

  That is, if the operation is performed such that the temperature of the back side portion of the umbrella portion 21a of the intake valve 21 is such that the carbon is easily deposited (200 ° C. to 300 ° C.), the carbon is deposited on the heat insulating layer 21c. It is conceivable that it can be determined that carbon is deposited on the heat insulating layer 21c based on the accumulated operation time.

  FIG. 2 shows the result of examining how the temperature of the back side portion of the umbrella portion 21a of the intake valve 21 changes depending on the engine speed (rpm) and the air charge amount ce (that is, engine load). (a) and (b) show the temperatures of the portions that are 5 mm and 10 mm apart from the combustion chamber side surface of the umbrella portion 21a in the axial direction of the valve stem 21b. FIG. 3 is a view corresponding to FIG. 2 in the case of an intake valve in which the heat insulating layer 64 and the heat insulating layer 21c are not provided, and (a) and (b) show the temperatures of the same parts as in FIG. .

  In the present embodiment, as shown in FIG. 2, the heat insulation layer 64 and the heat insulation layer 21 c prevent the temperature of the back side portion of the umbrella portion 21 a of the intake valve 21 from exceeding 300 ° C. even in a high load high rotation region. Yes. For this reason, when carbon is deposited on the heat insulation layer 21c, the carbon is not burned off and remains deposited. Then, at an engine speed (range indicated by hatching) equal to or higher than a predetermined speed (smaller as the engine load is larger), the temperature of the back side portion of the umbrella portion 21a is a temperature (200 ° C.) at which carbon is easily deposited. ~ 300 ° C). Therefore, when the cumulative operation time at the engine speed equal to or higher than the predetermined speed (which becomes smaller as the engine load increases) is detected and the cumulative operation time exceeds the predetermined time, carbon is deposited on the heat insulating layer 21c. And make a determination. The predetermined time may be a time during which carbon is deposited to such an extent as to cause a decrease in engine output, or may be a short time during which a small amount of carbon is deposited. However, if the time is short, the carbon burning operation described later is frequently performed. Therefore, it is preferable to make it as long as possible without causing a decrease in engine output. In the present embodiment, the predetermined rotational speed is made smaller as the engine load is larger, but may be a constant value (for example, 4000 rpm).

  Here, if the heat insulating layer 64 and the heat insulating layer 21c (particularly the heat insulating layer 64) are not provided, the heat of the high-temperature gas during combustion in the combustion chamber 17 is transmitted to the umbrella portion 21a in the high-load high-rotation region. As shown in FIG. 3, the temperature of the back side portion of the umbrella portion 21a (the portion 5 mm away from the combustion chamber side surface of the umbrella portion 21a in the axial direction of the valve stem 21b) exceeds 300 ° C. The temperature at a portion 10 mm away from the surface on the combustion chamber side of 21 a in the axial direction of the valve stem 21 b does not exceed 300 ° C. even in a high load high rotation region. The same applies when the heat insulation layer 64 is provided without the heat insulation layer 64. For this reason, even when the heat insulating layer 64 is provided without the heat insulating layer 64, it is meaningful to determine that carbon is deposited on the heat insulating layer 21c, and the determination can be performed in the same manner as described above ( The carbon deposition at the 10 mm apart portion has a lower influence on the engine output than the carbon deposition at the 5 mm apart portion. Therefore, the heat insulation layer 64 and the heat insulation layer 21 c are allowed to pass through the predetermined time. Can be longer than if provided).

  When it is determined that carbon is deposited on the heat insulating layer 21c as described above, the carbon deposited on the heat insulating layer 21c is burned out by performing a carbon burning operation. In the carbon burning operation, when it is determined that carbon is deposited on the heat insulating layer 21c, the accelerator opening after the acceleration request detected by the accelerator opening sensor 73 is in a steady state (0 Is included). Specifically, in the carbon burning operation, when the accelerator opening after the acceleration request becomes a steady state equal to or smaller than a predetermined opening, the intake valve 21 and the exhaust valve 22 are opened quickly by the VVT 23. By providing an overlap during the valve opening period, the burned gas is introduced into the intake port 18 to burn off the carbon deposited on the heat insulating layer 21c. That is, the gas temperature in the combustion chamber 17 becomes a high temperature exceeding 300 ° C. in accordance with the acceleration request, and the high-temperature gas can be caused to flow back to the intake port 18 by the overlap after the acceleration request. Thereby, the temperature of the back side part of the umbrella part 21a in the intake valve 21 becomes high, and the carbon deposited on the heat insulating layer 21c can be easily burned off. The carbon burning operation is performed, for example, by a predetermined number of cycles in the combustion cycle (the number of cycles in which most of the carbon deposited on the heat insulating layer 21c is burned out, and the longer the predetermined time is, the more the number is increased). The overlap period is preferably as long as possible.

  Control operations related to carbon deposition determination and carbon removal by the engine controller 100 (CPU) will be described with reference to the flowchart of FIG.

  In first step S1, it is determined whether the engine speed is equal to or higher than the predetermined speed. When the determination at step S1 is NO, the operation at step S1 is repeated, while when the determination at step S1 is YES, the process proceeds to step S2.

  In step S2, an accumulated operation time at an engine speed equal to or higher than the predetermined speed is calculated. In other words, the accumulated operation time up to the previous time (stored in the memory of the engine controller 100) is added to the current operation time (timed by a timer (not shown) provided in the engine controller 100) to obtain the accumulated operation time. Calculate time.

  In the next step S3, it is determined whether or not the accumulated operation time has exceeded a predetermined time. If the determination in step S3 is NO, the process returns to step S1, while if the determination in step S3 is YES, Proceed to S4.

  In step S4, it is determined that carbon is deposited on the heat insulating layer 21c, and in the next step S5, it is determined whether the accelerator opening after the acceleration request is in a steady state equal to or less than a predetermined opening. When the determination at step S5 is NO, the operation at step S5 is repeated. On the other hand, when the determination at step S5 is YES, the process proceeds to step S6 to perform the carbon burning operation. Here, the carbon burning operation is performed for a predetermined number of cycles in the combustion cycle so that most of the carbon deposited on the heat insulating layer 21c is burned off. In the next step S7, the cumulative operation time is reset to 0, stored in the memory, and then the process returns.

  When the accumulated operation time (accumulated operation time at an engine speed equal to or higher than the predetermined rotation speed) estimated to accumulate carbon by the control operation by the engine controller 100 exceeds a predetermined time, the heat insulating layer 21c It is determined that carbon has accumulated. When it is determined that carbon is deposited on the heat insulating layer 21c, when the accelerator opening after the acceleration request is in a steady state equal to or less than the predetermined opening, the carbon incineration operation causes the heat insulating layer 21c to Burn up the deposited carbon.

  In the present embodiment, the engine controller 100 (CPU) constitutes the cumulative operation time detecting means, the carbon deposition determining means, and the carbon burning means according to the present invention, and the accelerator opening sensor 73 constitutes the accelerator opening detecting means. Will do.

Therefore, in this embodiment, it can be easily determined that carbon is deposited on the heat insulating layer 21c, and when this determination is made, the carbon deposited on the heat insulating layer 21c can be easily removed. . Therefore, it is possible to suppress a decrease in the intake air filling amount due to carbon deposition, and it is possible to suppress a decrease in engine output. Further, the heat insulating layer 21c can reduce the gas temperature during combustion by reducing the intake air temperature as much as possible, and in combination with the heat insulating layer 6 on the wall surface of the combustion chamber, the gas temperature and the temperature of the wall surface of the combustion chamber It is possible to reduce the cooling loss by reducing the temperature difference between the two. Thereby, the illustrated thermal efficiency can be improved by setting the compression ratio to 18 or higher.

  The present invention is not limited to the embodiment described above, and can be substituted without departing from the spirit of the claims.

Here, in the above-described embodiment, as the carbon burning operation, when the accelerator opening after the acceleration request is in a steady state of a predetermined opening or less, the valve opening period overlaps between the intake valve 21 and the exhaust valve 22. Thus, the burned gas is introduced into the intake port 18, but the carbon deposited on the heat insulating layer 21c may be burned out by the carbon burning operation of the following reference example . That is , when it is determined that carbon has accumulated on the heat insulating layer 21c, the excess air ratio λ in the entire combustion chamber 17 is set to 1 or less, and the start of combustion of the air-fuel mixture is retarded at a predetermined timing of the expansion stroke. In the exhaust stroke immediately after the expansion stroke, the burned gas is introduced into the intake port 18 by the overlap. Also in the case of this reference example, the hot gas can be made to flow backward to the intake port 18. And in the case of this reference example, when the operation region when it is determined that carbon is deposited on the heat insulating layer 21c is the high load region, the carbon burning operation is performed immediately. When the operation region when the operation is performed is the low load region, the carbon incineration operation is not performed until the high load region is entered, and the entire excess air ratio λ in the combustion chamber 17 is set to 1 in the high load region. After shifting, it is preferable to perform a carbon burning operation. Then, the carbon burning operation is performed for a predetermined number of cycles in the combustion cycle (the number of cycles is such that most of the carbon deposited on the heat insulating layer 21c is burned out, and the longer the predetermined time is, the larger the number is).

  The above-described embodiments are merely examples, and the scope of the present invention should not be interpreted in a limited manner. The scope of the present invention is defined by the scope of the claims, and all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

The present invention, the geometric compression ratio is 18 or more, the rear portion of at least the valve head of the intake valve, which is useful in spark-ignition direct injection engine heat insulating layer is coated.

DESCRIPTION OF SYMBOLS 1 Spark ignition direct injection engine 21 Intake valve 21a Umbrella part 21c Heat insulation layer 73 Accelerator opening degree sensor (accelerator opening degree detection means)
100 Engine controller (cumulative operation time detection means) (carbon deposition determination means)
(Carbon burning means)

Claims (2)

In a spark ignition direct injection engine in which a geometric compression ratio is 18 or more and a heat insulating layer is coated on at least the back portion of the umbrella portion of the intake valve, a carbon removing method for removing carbon deposited on the heat insulating layer. There,
A cumulative operation time detecting step for detecting a cumulative operation time at an engine speed equal to or higher than a predetermined speed;
A carbon deposition determination step for determining that carbon is deposited on the heat insulation layer when the cumulative operation time detected in the cumulative operation time detection step exceeds a predetermined time;
When it is determined in the carbon deposition determination step that carbon is deposited on the heat insulation layer, when the accelerator opening after the acceleration request is in a steady state of a predetermined opening or less, the intake valve and the exhaust valve And a carbon burning step of burning the carbon deposited on the heat insulating layer by introducing burned gas into the intake port due to overlap of the valve opening period. A spark ignition type direct injection engine having a geometric compression ratio of 18 or more and having a heat insulation layer coated on at least a back portion of an umbrella portion of an intake valve,
An accumulated operation time detecting means for detecting an accumulated operation time at an engine speed equal to or higher than a predetermined speed;
Carbon deposition determination means for determining that carbon is deposited on the heat insulation layer when the cumulative operation time detected by the cumulative operation time detection means exceeds a predetermined time;
An accelerator opening detecting means for detecting the accelerator opening;
When it is determined by the carbon deposition determination means that carbon has accumulated on the heat insulating layer, the accelerator opening after the acceleration request is in a steady state equal to or less than a predetermined opening by the accelerator opening detection means. Carbon burnout that burns carbon deposited on the heat insulation layer by introducing burned gas into the intake port due to the overlap of the valve opening period between the intake valve and the exhaust valve. direct-injection spark-ignition engine, characterized in that it e Bei and means.

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