Engine equipment

Abstract

To achieve both early activation of the oxygen sensor element in the event of a thermostat water leak and optimal control of the heater's power supply prohibition. [Solution] The engine device 10 includes an engine coolant passage 27, a radiator circulation passage 32 that goes through the radiator 31, a bypass passage 33 that does not go through the radiator 31, a thermostat 36 that selectively switches the flow of coolant to the radiator circulation passage 32 or the bypass passage 33, a temperature sensor 26 that detects the temperature of the coolant, and a sub-oxygen sensor 24 having a heater 24b. The ECU 22 determines that there is a water leak in the thermostat 36 when the temperature difference between the actual coolant temperature and the simulated coolant temperature detected by the temperature sensor 26 is greater than or equal to a predetermined value, and energizes the heater 24b.

Description

Technical Field

[0001] The technology disclosed in this specification relates to an engine device.

Background Art

[0002] Conventionally, there is a heater control device including a temperature detection unit that detects the temperature of cooling water in an engine cooling water passage formed inside an engine (internal combustion engine), an oxygen sensor disposed downstream of a catalytic converter in an exhaust passage of the engine and having a sensor element that detects the oxygen concentration in exhaust gas and a heater that heats the sensor element, and a control unit that controls the heater based on the temperature of the cooling water (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the heater control device described in Patent Document 1, when the sensor element heated by the heater of the oxygen sensor is wetted by condensed water in the exhaust gas from the start of engine startup, a rapid temperature change occurs in the sensor element, and there is a possibility of element cracking. As a measure to prevent this element cracking, energization prohibition control is conceivable in which a period during which energization to the heater is prohibited is set according to the temperature of the cooling water, and energization to the heater is started after the elapse of the energization prohibition period.

[0005] On the other hand, the engine cooling system includes an engine cooling water passage formed inside the engine, a radiator circulation passage that returns the cooling water discharged from the engine cooling water passage back to the engine cooling water passage via the radiator, a bypass passage that returns the cooling water discharged from the engine cooling water passage back to the engine cooling water passage without passing through the radiator, and a thermostat that operates according to the temperature of the cooling water and selectively switches the flow of the cooling water to either the radiator circulation passage or the bypass passage. When the temperature of the cooling water is lower than a predetermined value (usually 80°C), the thermostat closes, promoting the temperature rise of the cooling water. On the other hand, when the temperature of the cooling water rises above the predetermined value, the thermostat opens, allowing the cooling water to be cooled by the radiator.

[0006] Incidentally, if a thermostat in its closed state leaks due to a hole or foreign object getting stuck, the cold coolant in the radiator will circulate into the engine coolant passages even during a cold engine start, preventing the coolant temperature from rising. As a result, the heater's power-off period, which is set according to the coolant temperature, will not end, and the oxygen sensor heater will not be powered, thus preventing the sensor element from being activated. Therefore, there is a problem in that it is difficult to achieve both the early activation of the oxygen sensor element in the event of a thermostat leak and the proper control of the heater's power-off function. Furthermore, if the sensor element is not activated, its detection accuracy will be poor, and air-fuel ratio feedback control cannot be performed, leading to a deterioration of exhaust emissions.

[0007] The problem that the technology disclosed herein aims to solve is to achieve both early activation of the sensor element of the oxygen sensor in the event of a thermostat water leak and optimization of the heater power supply prohibition control. [Means for solving the problem]

[0008] To solve the above problems, the technology disclosed herein employs the following means.

[0009] The first means is an engine device comprising: an engine coolant passage formed inside the engine; a radiator circulation passage that returns the coolant discharged from the engine coolant passage to the engine coolant passage via a radiator; a bypass passage that returns the coolant discharged from the engine coolant passage to the engine coolant passage without passing through the radiator; a thermostat that operates according to the temperature of the coolant and selectively switches the flow of the coolant to the radiator circulation passage or the bypass passage; a temperature detection unit that detects the temperature of the coolant in the engine coolant passage; and an oxygen sensor located downstream of the catalytic converter in the exhaust passage of the engine, having a sensor element for detecting the oxygen concentration in the exhaust gas and a heater for heating the sensor element, wherein the engine device is provided with a control unit that determines water leakage from the thermostat and energizes the heater when the temperature difference between the actual water temperature, which is the temperature of the coolant detected by the temperature detection unit, and the simulated water temperature, which is the temperature of the coolant mapped based on the operating state of the engine, is greater than or equal to a predetermined value.

[0010] According to the first method, when the thermostat leaks, the actual water temperature of the cooling water detected by the temperature detection unit does not rise, resulting in a discrepancy between the actual water temperature and the simulated water temperature. The control unit determines that the thermostat is leaking when the temperature difference between the actual water temperature and the simulated water temperature exceeds a predetermined value, and energizes the heater of the oxygen sensor. This makes it possible to achieve both early activation of the sensor element of the oxygen sensor when the thermostat leaks and optimal control of the heater's energization prohibition. This is effective in suppressing the deterioration of exhaust emissions caused by air-fuel ratio feedback control.

[0011] The second means is an engine device of the first means, wherein the control unit has a storage unit that stores the temperature difference between the actual water temperature and the simulated water temperature when a water leak in the thermostat is detected, and when the engine is started for the next time, the water leak in the thermostat is detected based on the temperature difference stored in the storage unit.

[0012] According to the second method, the control unit can easily determine if there is a water leak in the thermostat when the engine is started for the next time. [Effects of the Invention]

[0013] The technology disclosed herein makes it possible to achieve both early activation of the sensor element of the oxygen sensor in the event of a thermostat water leak and optimization of the heater power supply prohibition control. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram showing an engine device according to one embodiment. [Figure 2] This is a schematic diagram showing the engine cooling system with the thermostat in the closed position. [Figure 3] This is a schematic diagram showing the engine cooling system with the thermostat in the open position. [Figure 4] This figure shows the relationship between the actual water temperature, simulated water temperature, and exhaust gas volume related to a thermostat water leak. [Modes for carrying out the invention]

[0015] Hereinafter, an embodiment for carrying out the technology disclosed herein will be described with reference to the drawings.

[0016] (Overview of the engine system) Figure 1 is a schematic diagram showing an engine unit. The engine unit 10 is mounted in a vehicle such as an automobile. In the engine unit 10, an intake passage 13 and an exhaust passage 14 are connected to the combustion chamber 12 of the engine (internal combustion engine) 11.

[0017] An intake valve 15 for controlling the communication state is provided at the connection part between the combustion chamber 12 and the intake passage 13. An air cleaner 16 is arranged in the intake passage 13. Downstream of the air cleaner 16 in the intake passage 13, an electronically controlled throttle valve 17 for adjusting the amount of fresh air flowing into the combustion chamber 12 is arranged. Near the intake valve 15 in the intake passage 13, an injector 18 for supplying fuel to the combustion chamber 12 is attached.

[0018] An exhaust valve 20 for controlling the communication state is provided at the connection part between the combustion chamber 12 and the exhaust passage 14. In the exhaust passage 14, a catalytic converter 21 for purifying harmful substances (HC, CO, NOx) in the exhaust gas is arranged.

[0019] The engine 11 includes an ECU (Electronic Control Unit) 22. The ECU 22 comprehensively controls various devices related to the operation of the engine 11 based on the operation data of the engine 11 detected by a plurality of sensors. An oxygen sensor (O2 sensor) 23, 24, an air flow sensor 25, and a temperature sensor 26 are connected to the input side of the ECU 22.

[0020] Of the oxygen sensors 23, 24, the oxygen sensor 23 arranged upstream of the catalytic converter 21 in the exhaust passage 14 is referred to as the "main oxygen sensor 23", and the oxygen sensor 24 arranged downstream of the catalytic converter 21 in the exhaust passage 14 is referred to as the "sub oxygen sensor 24". The main oxygen sensor 23 has linear output characteristics with respect to the air-fuel ratio.

[0021] The sub oxygen sensor 24 has output characteristics in which the output changes abruptly on the rich side and the lean side based on the stoichiometric air-fuel ratio with respect to the air-fuel ratio. Since the detection accuracy of the sub oxygen sensor 24 is poor unless the temperature of the sensor element 24a for detecting the oxygen concentration in the exhaust gas rises to the activation temperature (for example, 750°C), it has a heater 24b for heating the sensor element 24a to promote activation. The sub oxygen sensor 24 corresponds to the "oxygen sensor arranged downstream of the catalytic converter" referred to in this specification.

[0022] The airflow sensor 25 is located immediately downstream of the air cleaner 16 and outputs a signal corresponding to the intake air flow rate. The temperature sensor 26 outputs a signal corresponding to the temperature of the coolant flowing through the engine coolant passage 27 formed inside the engine 11. The temperature sensor 26 corresponds to the "temperature detection unit" as referred to in this specification.

[0023] An injector 18 is connected to the output side of the ECU 22. The ECU 22 calculates the fuel injection amount and timing based on signals from sensors 23, 24, 25, and 26, and supplies a drive signal to the injector 18. In addition to sensors 23, 24, 25, and 26 and the injector 18, several other sensors and devices are connected to the ECU 22, but their explanation is omitted here.

[0024] As part of the control of the engine 11, the ECU 22 performs air-fuel ratio feedback control, which controls the amount of fuel injected from the injector 18 so that the air-fuel ratio of the exhaust gas becomes the target air-fuel ratio during engine 11 operation. The air-fuel ratio feedback control consists of main feedback control, which controls the amount of fuel based on the output signal of the main oxygen sensor 23, and sub-feedback control, which controls the amount of fuel based on the output signal of the sub-oxygen sensor 24. By performing air-fuel ratio feedback control, the exhaust gas purification efficiency of the catalytic converter 21 is improved. Note that the explanation of air-fuel ratio feedback control is omitted here.

[0025] Before starting air-fuel ratio feedback control after engine startup, the ECU22 energizes the heater 24b of the sub-oxygen sensor 24 to heat and activate the sensor element 24a. However, the exhaust gas from the engine 11 contains water vapor produced by the combustion reaction of fuel and air. When the temperature of the exhaust passage 14 is low immediately after engine startup, the exhaust gas containing water vapor is cooled within the exhaust passage 14, which can cause condensation of water vapor in the exhaust gas. Because this condensation could damage the sensor element 24a of the sub-oxygen sensor 24, the heater 24b is not energized until the coolant temperature reaches a certain level.

[0026] (Overview of the cooling system 30 for engine 11) Figure 2 is a schematic diagram showing the cooling system 30 of the engine 11 with the thermostat in the closed position, and Figure 3 is a schematic diagram showing the same system with the thermostat in the open position. As shown in Figure 2, the engine 11 is connected to a radiator circulation passage 32 that returns the coolant discharged from the engine cooling water passage 27 back to the engine cooling water passage 27 via the radiator 31.

[0027] The radiator circulation passage 32 consists of an upstream passage section 32a that connects the outlet of the engine coolant passage 27 to the coolant inlet of the radiator 31, a downstream passage section 32b that connects the cooling outlet of the radiator 31 to the inlet of the engine coolant passage 27, and a cooling passage within the radiator 31.

[0028] A bypass passage section 33a is installed between the middle of the upstream passage section 32a and the middle of the downstream passage section 32b. The passage that returns from the outlet of the engine cooling water passage 27 to the inlet of the engine cooling water passage 27 via the bypass passage section 33a is collectively called the bypass passage 33. The bypass passage 33 is a passage that returns the cooling water discharged from the engine cooling water passage 27 to the engine cooling water passage 27 without passing through the radiator 31.

[0029] An electrically operated water pump 34 is provided downstream of the connection point between the downstream passage section 32b and the bypass passage section 33a. The water pump 34 pressurizes the cooling water from the downstream passage section 32b and sends it to the engine cooling water passage 27. The water pump 34 is connected to the ECU 22 and is controlled based on control signals from the ECU 22.

[0030] A thermostat 36 is provided at the intersection of the downstream passage 32b and the bypass passage 33a. The thermostat 36 comprises a temperature-sensing element 36a, a thermovalve 36b, and a bypass valve 36c. The temperature-sensing element 36a is filled with wax that melts or solidifies depending on the temperature of the cooling water in contact with the temperature-sensing element 36a. The thermovalve 36b opens and closes the downstream passage 32b. The thermovalve 36b is always biased in the closing direction by a spring 36d. The bypass valve 36c opens and closes the bypass passage 33.

[0031] The thermostat 36 operates when the temperature-sensing element 36a responds to the coolant temperature, causing the thermovalve 36b and bypass valve 36c to move together, selectively switching the coolant flow to either the radiator circulation passage 32 or the bypass passage 33. Specifically, when the coolant temperature is low, the thermovalve 36b is kept closed by the biasing force of the spring 36d, while the bypass valve 36c is opened. As a result, the coolant flows through the bypass passage 33 (see arrow in Figure 2).

[0032] Furthermore, as the coolant temperature rises, the temperature-sensing element 36a displaces against the biasing force of the spring 36d, causing the opening amount of the thermo-valve 36b to gradually increase while the opening amount of the bypass valve 36c gradually decreases. Moreover, as the coolant temperature rises further, the bypass valve 36c remains closed while the thermo-valve 36b opens (see Figure 3). As a result, the coolant flows through the radiator circulation passage 32 (see arrow in Figure 3).

[0033] The thermovalve 36b maintains the coolant temperature within a predetermined range, but this range (temperature difference) is large. For this reason, the opening temperature of the thermovalve 36b is set to 75°C, for example, from the median value of the predetermined range (approximately 85°C), taking into account tolerances of the temperature sensor 26, etc. Therefore, the thermovalve 36b opens when the coolant temperature (actual water temperature detected by the temperature sensor 26) reaches 75°C or higher.

[0034] When the actual coolant temperature detected by the temperature sensor 26 reaches or exceeds the opening temperature at which the thermostat 36 opens, the ECU 22 energizes the heater 24b of the sub-oxygen sensor 24. This activates the sensor element 24a, improving the detection accuracy of the sub-oxygen sensor 24. Consequently, exhaust emissions can be improved through the implementation of air-fuel ratio feedback control.

[0035] (Characteristic configuration of this embodiment) In the engine unit 10, if water leaks from the thermostat 36 while it is in the closed state (see Figure 2), the cooled coolant in the radiator 31 flows into the engine coolant passage 27. As a result, the coolant temperature does not rise, and the heater 24b of the sub-oxygen sensor 24 is not energized. Therefore, a characteristic configuration for energizing the heater 24b of the sub-oxygen sensor 24 even when the thermostat 36 is leaking will be described.

[0036] The ECU 22 determines that there is a water leak in the thermostat 36 and energizes the heater 24b if the temperature difference between the actual water temperature, which is the temperature of the coolant detected by the temperature sensor 26, and the simulated water temperature, which is the temperature of the coolant mapped based on the operating state of the engine 11, is greater than a predetermined value. The simulated water temperature is calculated using a map that maps the amount of water temperature change every second, according to the operating state of the engine 11 (actual intake air temperature and actual intake air volume).

[0037] In other words, when the thermostat 36 leaks, the actual water temperature of the cooling water detected by the temperature sensor 26 does not rise, resulting in a discrepancy between the actual water temperature and the simulated water temperature. Actual water temperature < Simulated water temperature However, the simulated water temperature is, Simulated water temperature ≈ Actual water temperature when thermostat 36 is leak-free This is the result. The ECU 22 detects water leakage from the thermostat 36 when the temperature difference between the actual water temperature and the simulated water temperature exceeds a predetermined value, and energizes the heater 24b of the sub-oxygen sensor 24. This reduces the risk of damage to the sensor element 24a of the sub-oxygen sensor 24 due to water exposure. The ECU 22 corresponds to the "control unit" as defined herein.

[0038] As shown in Figure 2, the ECU 22 has a memory unit 22a that stores the temperature difference between the actual water temperature and the simulated water temperature when a water leak in the thermostat 36 is detected. When the engine 11 is started for the next time, the ECU 22 will determine if there is a water leak in the thermostat 36 based on the temperature difference (learned value) stored in the memory unit 22a. The ECU 22 performs the learning process at or below the opening temperature of the thermovalve 36b (for example, 75°C).

[0039] Figure 4 shows the relationship between the actual water temperature, simulated water temperature, and exhaust gas volume related to the water leakage of the thermostat 36. In Figure 4, the horizontal axis represents the hole diameter of the thermostat 36 (water leakage amount), and the vertical axis represents the coolant temperature and exhaust gas (exhaust emission). Water temperature T1 is the water temperature at which the heater 24b of the sub-oxygen sensor 24 can be energized. Lowering this water temperature T1 improves exhaust emissions, but makes the sensor element 24a more susceptible to damage. Water temperature T2 is the simulated water temperature. Exhaust gas volume R1 is the OBD (On-Board Diagnostics) regulatory value for exhaust gas. Characteristic line L1 shows the actual water temperature corresponding to the water leakage amount of the thermostat 36. Characteristic line L2 shows the exhaust gas volume corresponding to the water leakage amount of the thermostat 36.

[0040] In a normal state (where the amount of water leaking from the thermostat 36 is less than or equal to A), the heater 24b of the sub-oxygen sensor 24 is energized at the actual water temperature, activating the sensor element 24a, and thus reducing the amount of exhaust gas. However, in an abnormal state (where the amount of water leaking from the thermostat 36 exceeds A), the actual water temperature is below the temperature at which the heater 24b of the sub-oxygen sensor 24 can be energized, so the sensor element 24a is not activated, and the amount of exhaust gas increases.

[0041] In an abnormal state (where the amount of water leaking from the thermostat 36 exceeds A), if the temperature difference between the actual water temperature and the simulated water temperature exceeds a predetermined value (T2-T1), water leakage from the thermostat 36 is detected, and the heater 24b of the sub-oxygen sensor 24 is energized based on the simulated water temperature T2 (see characteristic line L1a), so the sensor element 24a is activated and exhaust emissions improve (see characteristic line L3).

[0042] (Advantages due to distinctive configuration) When the thermostat 36 leaks, if the temperature difference between the actual water temperature and the simulated water temperature exceeds a predetermined value, the leak in the thermostat 36 is detected, and the heater 24b of the sub-oxygen sensor 24 is energized. This allows for both early activation of the sensor element 24a of the sub-oxygen sensor 24 when the thermostat 36 leaks, and optimal control of the power supply prohibition of the heater 24b. This is effective in suppressing the deterioration of exhaust emissions due to air-fuel ratio feedback control. Furthermore, with the tightening of exhaust gas regulations, OBD (On-Board Diagram) detection of the thermostat 36, or water leak detection, is required, which is effective for engine systems 10 intended for the North American market, for example.

[0043] Furthermore, the ECU 22 has a memory unit 22a that stores the temperature difference between the actual water temperature and the simulated water temperature when a water leak in the thermostat 36 is detected. When the engine 11 is started for the next time, the heater 24b of the sub-oxygen sensor 24 is energized based on the temperature difference stored in the memory unit 22a. Therefore, when the engine 11 is started for the next time, the ECU 22 can easily determine if a water leak in the thermostat 36 is detected.

[0044] [Other embodiments] The technologies disclosed herein are not limited to the embodiments described above and can be implemented in various other forms. For example, the technologies disclosed herein may also be applied to control based on the temperature of the coolant in the engine coolant passage 27, such as warm-up control of the catalytic converter 21, or increasing the fuel injection amount of the injector 18. [Explanation of Symbols]

[0045] 10 Engine System 11 Engine 14 Exhaust passage 21 Catalytic Converter 22 ECU (control unit) 22a Storage section 24. Sub-oxygen sensor (oxygen sensor located downstream of the catalytic converter) 24a Sensor element 24b Heater 26. Temperature sensor (temperature detection unit) 27 Engine Coolant Passage 31 Radiator 32 Radiator circulation passage 33 Bypass passage 36 Thermostat

Claims

1. Engine cooling water passages formed inside the engine, A radiator circulation passage returns the coolant discharged from the engine coolant passage back to the engine coolant passage via the radiator, A bypass passage that returns the coolant discharged from the engine coolant passage to the engine coolant passage without passing through the radiator, A thermostat that operates according to the temperature of the coolant and selectively switches the flow of the coolant to the radiator circulation passage or the bypass passage, A temperature detection unit for detecting the temperature of the cooling water in the engine cooling water passage, An oxygen sensor is provided, which is located downstream of the catalytic converter in the exhaust passage of the engine and has a sensor element for detecting the oxygen concentration in the exhaust gas and a heater for heating the sensor element. An engine system equipped with, An engine device comprising a control unit that determines whether the thermostat is leaking and energizes the heater when the temperature difference between the actual water temperature, which is the temperature of the coolant detected by the temperature detection unit, and the simulated water temperature, which is the temperature of the coolant mapped based on the operating state of the engine, exceeds a predetermined value.

2. The engine device according to claim 1, The control unit has a storage unit that stores the temperature difference between the actual water temperature and the simulated water temperature when a water leak in the thermostat is detected, and the engine device determines the water leak in the thermostat based on the temperature difference stored in the storage unit when the engine is started for the next time.

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