Engine control device

Abstract

The present invention provides an engine control device that can suppress the occurrence of thermal shock to the high-temperature catalytic converter when the fuel supply is cut off after high-load operation. [Solution] The vehicle has an engine 3 provided in the vehicle and connected to an intake system 1 and an exhaust system 2, a catalytic converter 4 provided in the exhaust system 2, and a heating means 5 that heats the air flowing into the catalytic converter 4 by heating the air passing through at least one of the intake system 1 and the exhaust system 2, and the heating means 5 controls the heating of the air when the fuel supply to the engine 3 is cut off while the vehicle is running.

Description

Technical Field

[0001] This invention relates to an engine control device.

Background Art

[0002] A vehicle engine is provided with a catalytic device for purifying its exhaust gas. In recent years, various requirements for the catalytic device have been increasing, such as improving the exhaust gas purification ability, miniaturizing to reduce the amount of precious metals, and enhancing durability.

[0003] For example, in the configuration described in Patent Document 1 below, when fuel cut control of the engine is performed after high-load running, relatively low-temperature air that has passed through the combustion chamber along with the fuel cut is blown onto the catalyst that has become high-temperature due to high-load running to cool this catalyst, thereby preventing the catalyst from becoming high-temperature and the catalyst performance from deteriorating. Further, the transmission is shifted to the low-speed side to increase the engine rotation speed, and more air is blown to enhance the cooling efficiency (see paragraphs 0011 to 0014 of Patent Document 1, etc.).

[0004] Also, in the configuration described in Patent Document 2 below, when the temperature of the catalyst becomes a predetermined value or higher, the fuel injection amount is increased to lower the temperature of the exhaust gas exhausted from the combustion chamber, thereby suppressing the high-temperature rise of the catalyst (see paragraphs 0041 to 0042 of Patent Document 2, etc.).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the configuration shown in Patent Document 1, when relatively cold air is blown onto the surface of a hot catalyst, shock-induced thermal stress (cold and thermal shock) due to thermal distortion is likely to occur in the catalyst, potentially leading to problems such as cracking of the catalyst layer. This risk is particularly increased when a large amount of cold air is blown onto it. In addition, in the configuration shown in Patent Document 2, since the engine is running, cold and thermal shock like that in Patent Document 1 is less likely to occur, but the fuel injection amount is increased, which may worsen fuel efficiency.

[0007] Therefore, the object of this invention is to provide an engine control device that can suppress the occurrence of thermal shock in a high-temperature catalytic converter when the fuel supply is cut off after high-load operation. [Means for solving the problem]

[0008] In order to solve the above problems, this invention provides: An engine installed in the vehicle and connected to the intake and exhaust systems, A catalytic converter is provided in the exhaust system, A heating means for heating the air flowing into the catalytic converter by heating the air passing through at least one of the intake system and the exhaust system, An engine control device (first configuration) is configured that has such a heating means and controls the heating of air when the fuel supply to the engine is cut off while the vehicle is running.

[0009] In the first configuration, The heating means can be configured (second configuration) in which an exhaust gas recirculation passage for recirculating exhaust gas from the exhaust system to the intake system and an exhaust gas recirculation cooler provided in the exhaust gas recirculation passage are opened to mix the air that has passed through the exhaust gas recirculation cooler with the air flowing through the intake system, thereby heating the air flowing through the intake system.

[0010] In the first or second configuration, The heating means may be an intercooler provided in the intake system, and a cooling water circulation pump is driven to circulate the intercooler cooling water flowing through the intercooler, thereby circulating the intercooler cooling water at a temperature higher than the temperature of the air flowing through the intake system, and a heating control is performed to heat the air passing through the intercooler (third configuration).

[0011] In the first configuration, The heating means can be configured as follows (fourth configuration): an exhaust gas recirculation passage for recirculating exhaust gas from the exhaust system to the intake system, an exhaust gas recirculation cooler provided in the exhaust gas recirculation passage, and an intercooler provided in the intake system, wherein heating control is performed by opening an exhaust gas recirculation valve provided in the exhaust gas recirculation passage to mix the air that has passed through the exhaust gas recirculation cooler with the air flowing through the intake system, and when the exhaust pressure of the air passing through the exhaust system falls below a predetermined pressure, the exhaust gas recirculation valve is closed and a cooling water circulation pump is driven to circulate the intercooler cooling water flowing to the intercooler, thereby circulating the intercooler cooling water at a temperature higher than the temperature of the air flowing through the intake system and heating the air that has passed through the intercooler.

[0012] In the fourth configuration, The heating means may be the engine, and the heating control may be configured such that when the temperature of the intercooler coolant falls below a predetermined temperature, the coolant circulation pump is stopped, and the fuel supply to the engine is temporarily interrupted to restart combustion (fifth configuration).

[0013] In any of the configurations from the first to the fifth configuration, When the fuel supply to the engine is cut off while the vehicle is in motion, in addition to the heating control, an intake volume reduction control is performed to reduce the amount of air flowing through the intake system (sixth configuration).

[0014] In the sixth configuration, The intake air amount reduction control can be configured (seventh configuration) to be performed by upshifting the transmission to reduce the engine speed.

Advantages of the Invention

[0015] In this invention, there is heating means for heating the air flowing into the catalyst device through the intake system and the exhaust system. When the fuel supply to the engine is cut during driving, the heating control of the air by the heating means is performed. Therefore, relatively low-temperature air is blown onto the high-temperature catalyst device, and the generation of a thermal shock in this catalyst device can be suppressed.

Brief Description of the Drawings

[0016] [Figure 1] It is a block diagram showing an embodiment of an engine control device according to this invention. [Figure 2] It is a flowchart showing an example of the flow of heating control applied to the engine control device shown in FIG. 1. [Figure 3] It is a flowchart showing an example of the flow of intake air amount reduction control applied to the engine control device shown in FIG. 1.

Embodiments for Carrying Out the Invention

[0017] An embodiment of an engine control device A according to this invention will be described based on the drawings. As shown in FIG. 1, this engine control device A is provided in a vehicle and includes an engine 3 connected to an intake system 1 and an exhaust system 2, a catalyst device 4 provided in the exhaust system 2, and heating means 5 for heating the air flowing into the catalyst device 4 by heating the air passing through at least one of the intake system 1 and the exhaust system 2 as main components. The engine control device A is provided with a supercharger 6 and an exhaust gas recirculation passage 7 for recirculating exhaust gas from the exhaust system 2 to the intake system 1.

[0018] The intake system 1 is provided with a fresh air intake port 8, an air cleaner 9, a compressor 10 of a supercharger 6, an intercooler 11, and a throttle valve 12. An outside air temperature sensor 13 for measuring the outside air temperature is provided at the fresh air intake port 8, a flow rate sensor 14 for measuring the flow rate of the air passing through the air cleaner 9 is provided on the downstream side of the air cleaner 9, a compressor temperature sensor 15 for measuring the temperature of the air introduced into the compressor 10 is provided on the upstream side of the compressor 10, an intercooler pressure and temperature sensor 16 for measuring the pressure and temperature of the air passing through the intercooler 11 is provided on the downstream side of the intercooler 11, and an intake pressure and temperature sensor 18 for measuring the pressure and temperature of the air introduced into the intake manifold 17 is provided on the downstream side of the throttle valve 12, respectively.

[0019] A cooling water passage 19 through which intercooler cooling water for cooling the intercooler 11 flows is connected to the intercooler 11. A cooling water circulation pump 20 for circulating the intercooler cooling water is provided in the cooling water passage 19. Further, a cooling water temperature sensor 21 for measuring the water temperature of the intercooler cooling water before being introduced into the intercooler 11 is provided in the cooling water passage 19.

[0020] The exhaust system 2 is provided with a turbine 22 of a supercharger 6, a wastegate valve 23 for adjusting the flow rate of the air (exhaust gas during combustion of the engine 3) introduced into the turbine 22, a catalyst device 4, a filter device 24 for removing fine particles in the exhaust gas, and a muffler 25. An oxygen concentration sensor 26 for measuring the oxygen concentration in the exhaust gas is provided on the downstream side of the turbine 22, a filter upstream temperature sensor 27 for measuring the temperature of the air introduced into the filter device 24 is provided on the upstream side of the filter device 24, and a differential pressure sensor 28 for measuring the differential pressure between the upstream side and the downstream side of the filter device 24 is provided in the filter device 24, respectively.

[0021] The exhaust gas recirculation passage 7, which connects the exhaust system 2 and the intake system 1, includes an exhaust gas recirculation cooler 29 for cooling the recirculated gas, a filter device 30, and an exhaust gas recirculation valve 31 for adjusting the flow rate of the recirculated gas. The exhaust gas recirculation passage 7 is connected to the downstream side of the catalytic converter 4 and the upstream side of the compressor 10. Upstream of the exhaust gas recirculation valve 31 in the exhaust gas recirculation passage 7, a recirculated gas temperature sensor 32 is provided to measure the temperature of the recirculated gas passing through the exhaust gas recirculation valve 31. The exhaust gas recirculation passage 7 is also provided with a differential pressure sensor 33 to measure the differential pressure between the upstream and downstream sides of the exhaust gas recirculation valve 31. The exhaust gas recirculation cooler 29 is connected to a cooling water passage 34 through which exhaust gas recirculation cooler cooling water flows to cool the exhaust gas recirculation cooler 29.

[0022] When the vehicle is running with engine 3 in operation, the intercooler coolant reaches a steady state of approximately 30-40°C, while the exhaust gas recirculation cooler coolant reaches a steady state of approximately 80°C, which is roughly the same as the engine coolant temperature.

[0023] During high-load operation of engine 3, the temperature of the catalytic converter 4, along with the temperature of the coolant, is often high. When the accelerator is released during this high-load operation, fuel supply cut control may be performed to improve fuel efficiency while driving. At the time of this fuel supply cut, the throttle valve 12 is closed, but since engine 3 continues to rotate, a small amount of air inevitably flows into the intake system 1 and exhaust system 2. Moreover, since no combustion occurs in engine 3, the air that passes through engine 3 and is sent to catalytic converter 4 is at a lower temperature than during combustion in engine 3. As a result, when this low-temperature air passes through the high-temperature catalytic converter 4, shock thermal stress (cold and thermal shock) based on thermal distortion occurs, which may cause malfunctions such as cracking of the catalytic converter layer.

[0024] To avoid this problem, in this configuration, heating control is performed to heat the air passing through the catalyst device 4 before it passes through, for example, as shown in the flowchart in Figure 2.

[0025] In this heating control, first, it is determined whether fuel supply cut-off control was performed during driving (step S1), whether the temperature of the catalytic converter 4 is higher than a predetermined temperature (step S2), and whether the ambient temperature is lower than a predetermined temperature (step S3). The predetermined temperature of the catalytic converter 4 and the predetermined ambient temperature can be appropriately determined based on experiments and experience, taking into account the temperature difference between the two predetermined temperatures that may cause thermal shock. The temperature of the catalytic converter 4 can be estimated from the value of the filter upstream temperature sensor 27 or from the value of a separate temperature sensor installed upstream of the catalytic converter 4.

[0026] If any one of the following conditions is met: fuel supply cut-off control is not performed (NO side in step S1), the temperature of the catalytic converter 4 is lower than a predetermined temperature (NO side in step S2), or the ambient temperature is higher than a predetermined temperature (NO side in step S3), the risk of thermal shock occurring in the catalytic converter 4 is relatively low, and therefore the series of flows is terminated without performing heating control.

[0027] On the other hand, if fuel supply cut-off control is performed (YES side of step S1), the temperature of the catalytic converter 4 is higher than a predetermined temperature (YES side of step S2), and the outside air temperature is lower than a predetermined temperature (YES side of step S3), the exhaust gas recirculation valve 31 is opened (step S4). As a result, the high-temperature air that has passed through the exhaust gas recirculation cooler 29 (heating means 5) (which also includes exhaust gas immediately after fuel supply cut-off) is mixed with the low-temperature air taken in from the fresh air intake 8, and this low-temperature air is heated.

[0028] After a short period of time has elapsed since the fuel supply cut-off control was performed, the amount of exhaust gas sent from the engine 3 to the exhaust system 2 decreases, and consequently, the exhaust pressure in the exhaust system 2 decreases. If this exhaust pressure falls below the internal pressure of the intake system 1, a problem occurs in which air from the intake system 1 flows back into the exhaust gas return passage 7. Therefore, a determination is made as to whether this exhaust pressure has fallen below a predetermined pressure (step S5). This predetermined pressure can be appropriately determined within a pressure range slightly higher than the internal pressure of the intake system 1 (a pressure range in which backflow does not occur).

[0029] If the exhaust pressure in exhaust system 2 has not fallen below a predetermined pressure (NO side of step S5), the exhaust gas recirculation valve 31 is kept open. On the other hand, if this exhaust pressure has fallen below a predetermined pressure (YES side of step S5), the exhaust gas recirculation valve 31 is closed (step S6).

[0030] Furthermore, a determination is made as to whether the temperature of the intercooler coolant is above a predetermined temperature (step S7). If this temperature is above the predetermined temperature (YES in step S7), the coolant circulation pump 20 provided in the coolant passage 19 of the intercooler 11 is activated (step S8). As a result, the air taken in from the fresh air intake 8 is heated as it passes through the intercooler 11 (heating means 5). If the coolant circulation pump 20 is already operating, control is performed to increase its operating speed.

[0031] On the other hand, if the temperature of the intercooler coolant is lower than a predetermined temperature (including when it has decreased due to heat transfer to the air) (NO side of step S7), the coolant circulation pump 20 is stopped (or kept stopped). This predetermined temperature can be appropriately determined within a temperature range higher than the temperature of the air before it passes through the intercooler 11 (a temperature range in which heat transfer from the intercooler 11 to the air is possible). In addition, it is possible to control the coolant circulation pump 20 to maintain rotation at a predetermined low rotational speed without completely stopping it.

[0032] As described above, if heating is still required even after heating by the exhaust gas recirculation cooler 29 and the intercooler 11, the fuel supply cut control to the engine 3 is temporarily suspended and combustion of the engine 3 is resumed (step S10). The suspension of fuel supply cut control continues until the engine 3 has warmed up to a certain extent, and the fuel supply cut can be resumed, for example, after a predetermined number of combustion cycles or after a predetermined time has elapsed. This allows the low-temperature air sent to the engine 3 (heating means 5) through the intake system 1 to be heated by the engine 3.

[0033] If further heating is required, the wastegate valve 23 is closed, allowing the air that has passed through the engine 3 to be sent to the turbine 22 (step S11). As a result, the residual heat from the turbine blades, which are hot after high-load operation, heats the air sent to the turbine 22 (heating means 5). However, since the flow of cold air into the hot turbine 22 may cause thermal shock to the turbine 22, it is preferable that the heating of the air by the turbine 22 occurs after heating by the exhaust gas recirculation cooler 29 and the intercooler 11, and after the temperature of the turbine 22 has decreased slightly.

[0034] In the flowchart above, considering that the duration of exhaust pressure in the air (exhaust gas) passing through the exhaust gas recirculation passage 7 is usually shorter than the duration of the intercooler coolant temperature, heating by the exhaust gas recirculation cooler 29 is performed first, followed by heating by the intercooler 11. However, it may also be possible to reverse the order of the two heating processes or to perform both heating processes simultaneously. Note that interrupting the fuel supply cut-off control, which consumes a certain amount of additional fuel, and heating by residual heat from the turbine blades, which generates a certain thermal load, may be omitted.

[0035] In addition to the heating means 5 described above (exhaust gas recirculation cooler 29, intercooler 11, engine 3, turbine 22), other heating means 5 may also include, for example, a heating coating provided on the inner surface of the intake manifold 17 (port) that generates heat when an electric current is applied, an electrically heated catalytic converter equipped with a heater for heating the catalyst, and glow plugs used in diesel engines.

[0036] Furthermore, in order to avoid malfunctions caused by thermal shock, in this configuration, intake volume reduction control is performed in conjunction with the heating control described above. For example, intake volume reduction control is performed to reduce the amount of air flowing through the intake system 1 shown in the flowchart of Figure 3.

[0037] In this intake volume reduction control, similar to the heating control flow described above, it is first determined whether fuel supply cut-off control was performed during driving (step S21), whether the temperature of the catalytic converter 4 is higher than a predetermined temperature (step S22), and whether the ambient temperature is lower than a predetermined temperature (step S23). The predetermined temperature of the catalytic converter 4 and the predetermined ambient temperature can be appropriately determined based on experiments and experience, taking into account the temperature difference that may cause thermal shock.

[0038] If any one of the following conditions is met: fuel supply cut-off control is not performed (NO side in step S21), the temperature of the catalytic converter 4 is lower than a predetermined temperature (NO side in step S22), or the ambient temperature is higher than a predetermined temperature (NO side in step S23), the risk of thermal shock occurring in the catalytic converter 4 is relatively low, and therefore the series of flows is terminated without intake volume reduction control.

[0039] On the other hand, if fuel supply cut-off control is performed (YES side of step S21), the temperature of the catalytic converter 4 is higher than a predetermined temperature (YES side of step S22), and the ambient temperature is lower than a predetermined temperature (YES side of step S23), the transmission shifts up (step S24). When the transmission shifts up, the rotational speed of the engine 3 decreases in conjunction with this, and the amount of intake air from the intake system 1 decreases. As a result, the amount of air passing through the high-temperature catalytic converter 4 decreases.

[0040] As the transmission shifts up and fuel supply cut-off control continues, the engine speed of engine 3 gradually decreases along with the vehicle speed. Therefore, a determination is made as to whether the engine speed of engine 3 has fallen below a predetermined speed (step S25). If the engine speed of engine 3 is higher than the predetermined speed (NO side of step S25), the transmission shift position is maintained. On the other hand, if the engine speed of engine 3 is lower than the predetermined speed (YES side of step S25), the transmission is shifted down (step S26) to increase the engine speed of engine 3. This predetermined speed can be appropriately determined on the premise that engine 3 can be driven stably.

[0041] Furthermore, the above intake volume reduction control can also be performed independently at a different timing from the heating control (for example, before or after the heating control).

[0042] The engine control device A described above has a heating means 5 that heats the air flowing into the catalytic converter 4 by heating the air passing through at least one of the intake system 1 and the exhaust system 2. The device is configured to control the heating of the air by the heating means 5 when the fuel supply to the engine 3 is cut off while the vehicle is running. This prevents the catalytic converter 4 from being exposed to relatively cold air, thus suppressing the occurrence of thermal shock in the catalytic converter 4.

[0043] Furthermore, the engine control device A described above has a heating means 5 which consists of an exhaust gas recirculation passage 7 that recirculates exhaust gas from the exhaust system 2 to the intake system 1, an exhaust gas recirculation cooler 29 provided in the exhaust gas recirculation passage 7, and an intercooler 11 provided in the intake system 1. Heating control is performed by opening the exhaust gas recirculation valve 31 provided in the exhaust gas recirculation passage 7 to mix the air that has passed through the exhaust gas recirculation cooler 29 with the air flowing through the intake system 1. When the exhaust pressure of the air passing through the exhaust system 2 drops below a predetermined pressure, the exhaust gas recirculation valve 31 is closed and a cooling water circulation pump 20 that circulates the intercooler cooling water flowing to the intercooler 11 is driven to circulate the intercooler cooling water at a temperature higher than the temperature of the air flowing through the intake system 1 to heat the air passing through the intercooler 11. Thus, the air can be efficiently heated by the exhaust gas recirculation cooler 29, which has a short duration as a heating means 5, and the intercooler 11, which has a relatively long duration as a heating means 5. Furthermore, by applying the different heating methods 5 sequentially with a time difference rather than simultaneously, the air can be heated for a relatively long period of time.

[0044] Furthermore, the engine control device A temporarily interrupts the fuel supply cut to the engine 3 and restarts combustion, employing the engine 3, which has been heated by the combustion, and the turbine 22 (turbine blades), which have become hot after high-load operation, as heating means 5. Therefore, even if the heating of the air by the exhaust gas recirculation cooler 29 and the intercooler 11 is insufficient, the air can be additionally heated.

[0045] Furthermore, since the above-mentioned heating means 5 (exhaust gas recirculation cooler 29, intercooler 11, engine 3, and turbine 22) all utilize the existing configuration of the vehicle, the occurrence of additional costs can be suppressed.

[0046] Furthermore, the engine control device A described above is configured to reduce the amount of air intake flowing through the intake system 1 in addition to the heating control when the fuel supply to the engine 3 is cut off while the vehicle is running. This reduces the amount of low-temperature air blown onto the high-temperature catalytic converter 4, thereby suppressing the occurrence of thermal shock to the catalytic converter 4. In particular, the configuration reduces the amount of air intake by shifting up the transmission to lower the rotational speed of the engine 3, making the control easy to implement.

[0047] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. Accordingly, the scope of the invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0048] 1. Intake System 2. Exhaust System 3 Engines 4. Catalytic converter 5 Heating means 6. Supercharger 7. Exhaust gas recirculation passage 8. New air intake 9. Air cleaner 10 Compressors 11 Intercooler 12 Throttle valve 13. Outdoor temperature sensor 14 Flow Sensor 15. Compressor temperature sensor 16 Intercooler pressure and temperature sensor 17 Intake Manifold 18. Intake pressure and temperature sensor 19 Cooling Channel 20 Cooling water circulation pump 21 Cooling water temperature sensor 22 Turbines 23 Wastegate Valve 24 Filter device 25 Muffler 26. Oxygen concentration sensor 27 Filter upstream temperature sensor 28 Differential pressure sensor 29 Exhaust gas recirculation cooler 30 Filter device 31 Exhaust gas return valve 32 Reflux Gas Temperature Sensor 33 Differential pressure sensor 34 Cooling Channel A Engine control unit

Claims

1. An engine installed in the vehicle and connected to the intake and exhaust systems, A catalytic converter is provided in the exhaust system, A heating means for heating the air flowing into the catalytic converter by heating the air passing through at least one of the intake system and the exhaust system, An engine control device having a heating means that controls the heating of air when the fuel supply to the engine is cut off while the vehicle is running.

2. The control device for an engine according to claim 1, wherein the heating means is an exhaust gas recirculation passage for recirculating exhaust gas from the exhaust system to the intake system and an exhaust gas recirculation cooler provided in the exhaust gas recirculation passage, and heating control is performed by opening an exhaust gas recirculation valve provided in the exhaust gas recirculation passage and mixing the air that has passed through the exhaust gas recirculation cooler with the air flowing through the intake system to heat the air flowing through the intake system.

3. The control device for an engine according to claim 1, wherein the heating means is an intercooler provided in the intake system, and heating control is performed to circulate the intercooler cooling water at a temperature higher than the temperature of the air flowing through the intake system by driving a cooling water circulation pump to circulate the intercooler cooling water flowing through the intercooler, thereby heating the air passing through the intercooler.

4. The control device for an engine according to claim 1, wherein the heating means comprises an exhaust gas recirculation passage for recirculating exhaust gas from the exhaust system to the intake system, an exhaust gas recirculation cooler provided in the exhaust gas recirculation passage, and an intercooler provided in the intake system, wherein heating control is performed by opening an exhaust gas recirculation valve provided in the exhaust gas recirculation passage to mix the air that has passed through the exhaust gas recirculation cooler with the air flowing through the intake system, and when the exhaust pressure of the air passing through the exhaust system falls below a predetermined pressure, the exhaust gas recirculation valve is closed and a coolant circulation pump is driven to circulate the intercooler coolant flowing to the intercooler to heat the air passing through the intercooler by circulating the intercooler coolant at a temperature higher than the temperature of the air flowing through the intake system.

5. The control device for an engine according to claim 4, wherein the heating means is the engine, and when the temperature of the intercooler coolant falls below a predetermined temperature, the coolant circulation pump is stopped, and the fuel supply to the engine is temporarily interrupted and combustion is restarted, thereby performing heating control.

6. The engine control device according to any one of claims 1 to 5, wherein, in addition to the heating control, when the fuel supply to the engine is cut off while the vehicle is in motion, intake volume reduction control is performed to reduce the amount of air intake flowing through the intake system.

7. The engine control device according to claim 6, wherein the intake volume reduction control is performed by shifting the transmission up to reduce the engine speed.

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