Control device for internal combustion engine

Abstract

To provide a controller of an internal combustion engine capable of reducing a PN emission amount at low temperature.SOLUTION: A controller of an internal combustion engine of the present invention performs control to: more reduce a load on the internal combustion engine when a temperature of cooling water that cools the internal combustion engine is low than when the water temperature is high; and increase a rotational speed of the internal combustion engine.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a control device for an internal combustion engine.

Background Art

[0002] Patent Document 1 discloses a technique for suppressing the load of an engine in order to reduce emissions when the cooling water for cooling the engine has a low water temperature and the catalyst warm-up retard angle is present.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Under the operating conditions of the engine, when the temperature is low and the volatility of the fuel deteriorates (conditions where each part such as the engine body, lubricating oil, and cooling water is cold), and when the load of the engine is high, there is a problem that the number of particulate matter (PN: Particulate Number) contained in the exhaust gas increases.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a control device for an internal combustion engine capable of reducing the PN emission amount at low temperatures.

Means for Solving the Problems

[0006] In order to solve the above-described problems and achieve the object, the control device for an internal combustion engine according to the present invention performs control to lower the load of the internal combustion engine and increase the rotational speed of the internal combustion engine when the water temperature of the cooling water for cooling the internal combustion engine is low, as compared with when the water temperature is high.

[0007] This allows the engine load to be reduced at low temperatures when fuel volatility is reduced, thereby avoiding operation in the high load range where PN emissions are high, and reducing PN emissions at said low temperatures.

[0008] In the above, the control may be such that the internal combustion engine is operated while avoiding a predetermined low rotation speed and high load region in which the amount of PN discharged from the internal combustion engine becomes equal to or greater than a predetermined amount.

[0009] This makes it possible to minimize the increase in the rotation speed of the internal combustion engine while avoiding a predetermined low rotation speed and high load region, thereby suppressing noise that accompanies an increase in the rotation speed of the internal combustion engine.

[0010] In addition, in the above, the control may be performed by determining the load on the internal combustion engine and the rotation speed of the internal combustion engine using an operating point map of the internal combustion engine that shows the relationship between the water temperature, the load on the internal combustion engine, and the rotation speed of the internal combustion engine.

[0011] This makes it possible to determine the load and rotation speed of the internal combustion engine according to the temperature of the cooling water that cools the internal combustion engine. [Effects of the Invention]

[0012] The control device for an internal combustion engine according to the present invention has the effect of avoiding operation in a high load range where PN emissions are high by reducing the load at low temperatures when fuel volatility deteriorates, thereby reducing PN emissions at low temperatures. [Brief explanation of the drawings]

[0013]

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DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of a control device for an internal combustion engine according to the present invention will be described. Note that the present invention is not limited to the present embodiment.

[0015] FIG. 1 is a control system diagram of an engine 1 according to an embodiment. As shown in FIG. 1, an intake passage 21 and an exhaust passage 22 are respectively provided in communication with an engine 1 which is an internal combustion engine mounted on a vehicle. In the intake passage 21, an air cleaner 6 for filtering intake air, an air flow sensor 5 which is an air amount detecting means for detecting the intake air amount, and a throttle valve (not shown) for adjusting the intake air amount (engine load) are arranged. In the exhaust passage 22, a catalyst device 7 and a muffler 8 for purifying the exhaust gas discharged from the engine 1 are arranged.

[0016] The engine 1 is also provided with a rotation sensor 4 that detects the rotation speed of the engine 1, and a water temperature sensor 3 that detects the temperature of the engine coolant that cools the engine 1. The rotation sensor 4 detects the rotation speed of the engine 1, for example, from the rotation angle or rotation speed of a flywheel 12 provided at the end of a crankshaft 11 of the engine 1. The water temperature sensor 3 detects the temperature of the engine coolant flowing through a cooling device (not shown) provided in the engine 1, for example.

[0017] An engine speed signal from the speed sensor 4 and a water temperature signal from the water temperature sensor 3 are input to an electronic control unit 2 that controls the engine 1. The electronic control unit 2 also receives an intake air volume signal from an air flow sensor 5 and a throttle opening signal from a throttle sensor (not shown) that detects the opening of a throttle valve. The electronic control unit 2 is then able to control the operating state (speed and load) of the engine 1 based on these various signals.

[0018] Next, an overview of the amount of PN discharged when the engine 1 is operating will be described with reference to Figures 2, 3, and 4. Figure 2 is a diagram showing the range of PN discharged when the engine coolant is at a low water temperature. Figure 3 is a diagram showing the range of PN discharged when the engine coolant is at a medium water temperature. Figure 4 is a diagram showing the range of PN discharged when the engine 1 is fully warmed up. Note that symbol L1 in Figures 2 and 3 is a boundary line that indicates the boundary between the range where PN discharged is particularly high and the range where PN discharged is low at low water temperatures. Furthermore, symbol L2 in Figures 2 and 3 is a boundary line that indicates the boundary between the range where PN discharged is particularly high and the range where PN discharged is low at medium water temperatures.

[0019] As shown in FIGS. 2 and 3, the PN emission amount tends to be larger as the operating state of the engine 1 is on the low rotational speed side and the high load side. Conventionally, it is known that the PN emission amount increases by increasing the load of the engine 1. On the other hand, it is possible to reduce the PN emission amount by increasing the rotational speed of the engine 1. Further, as shown in FIGS. 2, 3, and 4, the lower the temperature of the engine cooling water, the larger the region where the PN emission amount is particularly large on the low rotational speed side and the high load side of the operating state of the engine 1, and as the engine 1 warms up and the temperature of the engine cooling water rises, the region with a large PN emission amount shrinks.

[0020] Therefore, in order to reduce the PN emission amount discharged during engine operation, the electronic control unit 2 restricts the load of the engine 1 according to the temperature of the engine cooling water, and controls the engine 1 so as to avoid the region where the PN emission amount is particularly large when the temperature of the engine cooling water is low. That is, as PN suppression control, when the temperature of the engine cooling water is low, the electronic control unit 2 reduces the load of the engine 1 and increases the rotational speed of the engine 1 as compared with when the temperature of the engine cooling water is high, and avoids a predetermined low rotational speed and high load region where the PN emission amount from the engine 1 becomes equal to or more than a predetermined amount, and can execute control for operating the engine 1.

[0021] FIG. 5 is a diagram showing an operating point map of the engine 1 in a first control example of PN suppression control. For example, as a first control example of PN suppression control, the electronic control unit 2 uniformly reduces the load of the engine 1 regardless of the rotational speed of the engine 1 according to the temperature of the engine cooling water so as to avoid the region where the PN emission amount is particularly large, as shown in FIG. 5. At the same time, in order to ensure the required output of the engine 1, the rotational speed of the engine 1 is controlled so that the operating point is P1 at low water temperature, the operating point is P2 at medium water temperature, and the operating point is P3 at full warm-up. In the first control example of PN suppression control, the lower the temperature of the engine cooling water, the smaller the load of the engine 1, and the higher the rotational speed of the engine 1 to obtain the same required output.

[0022] FIG. 6 is a diagram showing an engine operation line in a second control example of PN suppression control. Note that the required output shown in FIG. 6 is the same as the required output shown in FIG. 5. As a characteristic of the PN emission amount, when the rotational speed of engine 1 is increased, the PN emission amount of engine 1 can be reduced even under high load conditions. Therefore, the electronic control unit 2 may control the operating state of engine 1 as follows. That is, as a second control example of PN suppression control, for example, as shown in FIG. 6, the electronic control unit 2 avoids low rotational speed and high load so that the increase in the rotational speed of engine 1 is minimized and the PN emission amount can be reduced, and performs control to limit the rotational speed and load of engine 1 according to the water temperature of the engine coolant. In FIG. 6, the electronic control unit 2 controls the load and rotational speed of engine 1 so that the operating point is P11 at a low water temperature, P12 at a medium water temperature, and P13 at full warm-up. Note that the operating point P11 is an operating point with a higher load and a lower rotational speed than the operating point P1 shown in FIG. 5, the operating point P12 is an operating point with a higher load and a lower rotational speed than the operating point P2 shown in FIG. 5, and the operating point P13 is an operating point with the same load and rotational speed as the operating point P3 shown in FIG. 5.

[0023] Thus, in the second control example of PN suppression control, compared with the first control example, the load of engine 1 can be increased in a region with a small PN emission amount for the same required output of engine 1. Therefore, in the second control example of PN suppression control, by suppressing the increase in the rotational speed of engine 1 to the minimum, it is possible to suppress the deterioration of noise due to the increase in the rotational speed of engine 1.

[0024] FIG. 7 is a diagram showing an outline of the control flow of PN suppression control. As shown in FIG. 7, the electronic control unit 2 determines the load and the rotational speed of engine 1 by using an operating point map of engine 1 that shows the relationship between the water temperature of the engine coolant, the load of engine 1, and the rotational speed of engine 1, which enables reduction of the PN emission amount, based on the output request from the user such as the depression amount of the accelerator pedal and the water temperature of the engine coolant (engine water temperature). Note that this operating point map of engine 1 is stored, for example, in a storage device provided in the electronic control unit 2, which is obtained in advance for each water temperature or temperature range of the engine coolant through experiments or the like. In addition, in a hybrid vehicle equipped with a motor that generates a driving force for vehicle driving in addition to engine 1, the required output to engine 1 itself may be reduced by motor assist.

[0025] FIG. 8 is a diagram showing a first control example and a second control example of PN suppression control, and a time chart without PN suppression control. In FIG. 8, the required output of engine 1 is the same for the first control example and the second control example of PN suppression control, and for the case without PN suppression control.

[0026] As shown in FIG. 8, without PN suppression, the rotational speed of engine 1 can be set to the lowest rotational speed and the noise is most suppressed, but engine 1 is operated at an engine operating point where the PN emission amount is particularly large in the regions on the low rotational speed side and the high rotational speed side, resulting in the largest PN emission amount. On the other hand, in the first control example and the second control example of PN suppression control, since engine  1 is operated at an engine operating point that avoids the regions where the PN emission amount is particularly large, it can be seen that both can reduce the PN emission amount compared to the case without PN suppression control, as shown in FIG. 8 . Also, in the first control example and the second control example of PN suppression control, the PN emission amounts are almost the same, but it can be seen that the second control example, which can increase the load of engine 1 and lower the rotational speed of engine 1, can suppress the noise more than the first control example.

[0027] Next, the differences from the emission reduction control will be described. There is catalyst warm-up as a control for restricting the engine speed and load during cold operation. The differences and division of labor between the control according to this embodiment and the catalyst warm-up control are defined.

[0028] FIG. 9 is a diagram showing a time chart of control with only catalyst warm-up control and with PN suppression control.

[0029] The electronic control unit 2 can execute catalyst warm-up control, which is control for effectively warming up the catalyst provided in the catalyst device 7 by the exhaust gas in order to effectively purify HC, CO, and NOx (hereinafter referred to as the three components) contained in the exhaust gas and enhance its activity. In the catalyst warm-up control, the temperature of the catalyst is actually measured or estimated, and the engine 1 is operated while continuing controls such as "load suppression" and "ignition timing retard" until the temperature of the catalyst reaches the activation temperature Tc. Then, after the temperature of the catalyst reaches the activation temperature Tc and the catalyst becomes active, the engine 1 is operated at a load corresponding to the output request without suppressing the load of the engine 1. On the other hand, since the catalyst cannot purify PN, the PN emission amount cannot be reduced by the catalyst warm-up control. Therefore, as shown in FIG. 9, in the case of only catalyst warm-up suppression, if the required load at the end of catalyst warm-up is high, the engine 1 is operated at a high load, and the PN emission amount increases.

[0030] The PN emission amount decreases as the temperature of the engine 1 rises, in other words, as the temperature of the engine coolant water rises. Therefore, in the PN suppression control, the temperature of the engine coolant water is monitored, and the control is continued until the temperature of the coolant water reaches a temperature Tp or higher at which the PN emission amount decreases and the output suppression of the engine 1 becomes unnecessary.

[0031] In general, the temperature of the catalyst reaches the activation temperature Tc earlier than the engine coolant temperature rises to the temperature at which the PN emission amount decreases. Also, since the catalyst warm-up control significantly deteriorates fuel consumption, it is not preferable to continue it for a long time. Therefore, as in the PN suppression control shown in FIG. 9, when the catalyst warm-up control and the PN suppression control are required simultaneously, it is preferable to prioritize the catalyst warm-up control and execute the PN suppression control after the catalyst warm-up control is completed. Note that in the catalyst warm-up control, generally the load of engine 1 is low and does not reach the load of engine 1 at which the PN emission amount basically increases. Therefore, even if the catalyst warm-up control is performed prior to the PN suppression control, it is possible to reduce the PN emission amount.

[0032] FIG. 10 is a flowchart showing an example of the PN suppression control executed by the electronic control unit 2. First, the electronic control unit 2 determines whether the engine is ON (step S1). When the electronic control unit 2 determines that the engine is not ON (No in step S1), it ends a series of controls. On the other hand, when the electronic control unit 2 determines that the engine is ON (Yes in step S1), it determines whether the catalyst warm-up control is OFF (step S2). When the electronic control unit 2 determines that the catalyst warm-up control is not OFF (No in step S2), it ends a series of controls. On the other hand, when the electronic control unit 2 determines that the catalyst warm-up control is OFF (Yes in step S2), it acquires the water temperature of the engine coolant (step S3). Next, the electronic control unit 2 acquires the output request of engine 1 (step S4). Next, the electronic control unit 2 determines the load and the rotational speed of engine 1 from the operating point map of engine 1 showing the relationship between the water temperature of the engine coolant at which the PN emission amount can be reduced, the load of engine 1, and the rotational speed of engine 1 (step S5). Next, the electronic control unit 2 controls the operation of engine 1 at the determined load and rotational speed (step S6). Thereafter, the electronic control unit 2 ends a series of controls.

[0033] By implementing PN suppression control, the electronic control unit 2 can avoid operating the engine 1 in a high load region where the PN emission is high by reducing the load of the engine 1 at low temperatures when the volatility of the fuel deteriorates, and can reduce the PN emission at the low temperatures.

Description of Signs

[0034] 1 Engine 2 Electronic control unit 3 Water temperature sensor 4 Rotation sensor 5 Airflow sensor 6 Air cleaner 7 Catalytic converter 8 Muffler 11 Crankshaft 12 Flywheel 21 Intake passage 22 Exhaust passage

Claims

A control device for an internal combustion engine, which is provided with a catalyst in a catalyst device for purifying exhaust gas discharged from the internal combustion engine, and performs catalyst warm-up control for warming up the catalyst by the exhaust gas to enhance its activity, and PN suppression control for reducing the load of the internal combustion engine and increasing the rotational speed of the internal combustion engine when the water temperature of the cooling water for cooling the internal combustion engine is low, as compared with when the water temperature is high, wherein the control device is capable of executing the above. When the catalyst warm-up control and the PN suppression control are simultaneously required, the catalyst warm-up control is prioritized, and the PN suppression control is executed after the catalyst warm-up control is completed. A control device for an internal combustion engine, characterized by the above.

2. The PN suppression control is characterized in that the internal combustion engine is operated while avoiding a predetermined low rotational speed and high load region where the PN emission amount from the internal combustion engine becomes equal to or more than a predetermined amount. The control device for an internal combustion engine according to claim 1.

3. The PN suppression control is characterized in that the load and the rotational speed of the internal combustion engine are determined and performed using an operating point map of the internal combustion engine showing the relationship between the water temperature, the load of the internal combustion engine, and the rotational speed of the internal combustion engine. The control device for an internal combustion engine according to claim 1 or 2.

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