Control system for internal combustion engines

Abstract

This invention provides an internal combustion engine control system that can protect the air-fuel ratio sensor from excessive temperature rise. [Solution] The control system for an internal combustion engine is a control system for an internal combustion engine mounted on a vehicle, and comprises a fuel injection device, an air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust of the internal combustion engine, a heater for warming up the air-fuel ratio sensor, and a control device for controlling the internal combustion engine, wherein the control device performs fuel cut control to stop fuel injection from the fuel injection device, and when performing the fuel cut control, performs heater control to turn on the heater and raise the voltage of the heater from zero to a predetermined value at a predetermined slope.

Description

Technical Field

[0001] The present disclosure relates to a control system for an internal combustion engine.

Background Art

[0002] Conventionally, there has been known a control system for an internal combustion engine that controls a heater to suppress a temperature drop of an air-fuel ratio sensor caused by low-temperature exhaust gas. In the control system for an internal combustion engine disclosed in Patent Document 1, duty control is performed on a heater to raise the voltage thereof to a predetermined voltage.

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] In the control system for an internal combustion engine of Patent Document 1, when performing duty control on the heater, the voltage applied to the air-fuel ratio sensor is immediately raised to a predetermined voltage. When the heater is controlled in this manner, the temperature of the air-fuel ratio sensor may rise excessively.

[0005] An object of the present disclosure is to provide a control system for an internal combustion engine that can protect an air-fuel ratio sensor from excessive temperature rise.

Means for Solving the Problem

[0006] The control system for an internal combustion engine according to this disclosure is a control system for an internal combustion engine mounted on a vehicle, comprising: a fuel injector; an air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust gas of the internal combustion engine; a heater for warming up the air-fuel ratio sensor; and a control device for controlling the internal combustion engine, wherein the control device performs fuel cut control to stop fuel injection from the fuel injector, and when performing the fuel cut control, performs heater control to turn on the heater and raise the voltage of the heater from zero to a predetermined value at a predetermined slope. [Effects of the Invention]

[0007] This internal combustion engine control system prevents the heater temperature from overshooting and, consequently, the air-fuel ratio sensor from overheating, by increasing the heater voltage at a predetermined rate. As a result, it is possible to provide an internal combustion engine control system that can protect the air-fuel ratio sensor from excessive temperature rise. [Brief explanation of the drawing]

[0008] [Figure 1] A system diagram of a hybrid vehicle according to one embodiment of the present disclosure. [Figure 2] A system diagram of an engine according to one embodiment of the present disclosure. [Figure 3] A graph showing the duty cycle control in heater control according to one embodiment of the present disclosure. [Figure 4] A flowchart illustrating a control procedure performed by a control device according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0009] Hereinafter, one embodiment of this disclosure will be described with reference to the drawings.

[0010] As shown in Figures 1 and 2, the control system 1 of vehicle (an example of a hybrid vehicle) C comprises an engine (an example of an internal combustion engine) 2, a motor (FrM) 3, a generator (GEN) 4, a drive battery (BT) 6, a transaxle 8, an inverter 12 that controls the motor 3 and generator 4, an accelerator pedal 14 operated by the user of vehicle C, a charger 16 that can be connected to an external power source, an external power supply device 18 that can supply power to external devices such as home appliances, a control device 20, and a fuel tank 22. Vehicle C in this embodiment is a plug-in hybrid electric vehicle (PHEV) equipped with external charging, which allows power from an external power source to be stored in the drive battery 6 by the charger 16, and external power supply, which allows power from the drive battery 6 to be supplied to external devices by the external power supply device 18.

[0011] As shown in Figure 1, the engine 2 is connected to the generator 4 and drives the generator 4. Furthermore, in this embodiment, the engine 2 can drive the wheels (an example of drive wheels) C1 via the transaxle 8. The engine 2 in this embodiment is an inline four-cylinder gasoline engine. The engine 2 receives fuel from the fuel tank 22 and consumes it by burning it.

[0012] As shown in Figure 2, the engine 2 includes a fuel injector 40, an exhaust gas purification device 42, an oxygen sensor 44 (an example of an air-fuel ratio sensor), and an air flow sensor 46. The fuel injector 40 in this embodiment includes an intake port injection valve 40a that injects fuel into the intake port 41 and an in-cylinder injection valve 40b that injects fuel into the cylinder N. The exhaust gas purification device 42 purifies the exhaust gas of the engine 2. The oxygen sensor 44 detects the air-fuel ratio in the exhaust gas by detecting the oxygen concentration in the exhaust gas. The air flow sensor 46 measures the amount of air Q supplied to the engine 2.

[0013] The oxygen sensor 44 experiences a decrease in sensitivity as the temperature drops. Therefore, the oxygen sensor 44 has a heater 44a to warm up the sensor element. The heater 44a is duty-cycle controlled by the control device 20.

[0014] Returning to Figure 1, the motor 3 is connected to the wheel C1 via the transaxle 8 and axle 10, and drives the wheel C1. The motor 3 in this embodiment is a three-phase AC motor having multiple coils and multiple permanent magnets. The motor 3 is also driven by the rotation of the wheel C1 to generate electricity (regenerative power). Therefore, the motor 3 is a motor-generator capable of both powering and generating electricity. The generator 4 is connected to the engine 2 and can drive the engine 2. The generator 4 motorizes the engine 2 while powering with electricity from the drive battery 6. On the other hand, the generator 4 is driven by the engine 2 to generate electricity while the engine 2 is running. Therefore, the generator 4 is a motor-generator capable of both powering and generating electricity.

[0015] The drive battery 6 outputs power to the motor 3 and the generator 4. Power generated by the motor 3 and the generator 4 is also input to the drive battery 6. Furthermore, external power is input to the drive battery 6 via the charger 16. In this embodiment, the drive battery 6 is composed of multiple lithium-ion batteries.

[0016] The transaxle 8 has a plurality of gears (not shown) and a clutch 8a. The engine 2 is connected to the generator 4 and the axle 10 via the transaxle 8. When the clutch 8a is open, the transaxle 8 disconnects power transmission between the engine 2 and the axle 10, and when the clutch 8a is engaged, it transmits power from the engine 2 to the axle 10.

[0017] The inverter 12 controls the motor torque of the motor 3 by converting the DC power supplied from the drive battery 6 into AC power and adjusting the power supplied to the motor 3. Furthermore, when the motor 3 is regenerating, the inverter 12 controls the regenerative torque of the motor 3 by converting the AC power supplied from the motor 3 into DC power and adjusting the power supplied to the drive battery 6.

[0018] The control device 20 is a device electrically connected to the motor 3 via the engine 2 and the inverter 12, and controls the engine 2 and the motor 3. The control device 20 is actually an ECU (Electronic Control Unit) configured by a microcomputer including an arithmetic unit, a memory, an input / output buffer, and the like. The control device 20 controls the vehicle C based on maps and programs stored in the memory.

[0019] The vehicle C of the present embodiment has traveling modes such as an EV mode, a series mode, and a parallel mode. When the vehicle C is in the EV mode, the vehicle C drives the wheels C1 by driving the motor 3 with electric power from the drive battery 6 while the engine 2 is stopped. When the vehicle C is in the series mode, the clutch 8a is disconnected, the generator 4 is driven by the engine 2, and the motor 3 is driven using the electric power generated by the generator 4 to drive the wheels C1. When the vehicle C is in the parallel mode, the clutch 8a is engaged, and the wheels C1 are driven via the axle 10 using the power of the engine 2. The control device 20 of the vehicle C switches between the respective traveling modes according to the depression state of the accelerator pedal 14, controls the motor 3 and the generator 4 via the inverter 12, and also controls the engine 2.

[0020] Furthermore, the vehicle C of the present embodiment has an external power supply mode. In the external power supply mode, when the connector 18a is connected to an external device, the control device 20 uses the external power supply device 18 to supply electric power from the drive battery 6 to the external device. If the state of charge SOC (State Of Charge, an example of the charged amount) of the drive battery 6 becomes equal to or less than the minimum charge rate SOCmin during the external power supply mode, the control device 20 disconnects the clutch 8a, starts the engine 2 to drive the generator 4, stores the electric power generated by the generator 4 in the drive battery 6, and executes an engine power generation external power supply mode in which the electric power is also supplied to the external device.

[0021] The control device 20 further executes regenerative motoring. Regenerative motoring is control that, when the driving battery 6 cannot accept electric power generated by the regeneration of the motor 3, consumes electric power by driving the engine 2 with the generator 4, thereby enabling acceptance of the electric power generated by the regeneration of the motor 3. The control device 20 executes regenerative motoring when the state of charge SOC of the driving battery 6 is equal to a predetermined state of charge SOCt (an example of a predetermined charge amount). The predetermined state of charge SOCt is, for example, approximately 90 percent.

[0022] During regenerative motoring, air sucked by the engine 2 flows through an exhaust pipe including the exhaust purification device 42. As a result, the oxygen sensor 44 is cooled (see FIG. 2 for all of the above).

[0023] The control device 20 executes fuel cut control that stops fuel injection from the fuel injection device 40. Fuel cut control is control that does not perform fuel injection even when the engine 2 is rotating. The control device 20 executes fuel cut control when executing regenerative motoring. In addition, the control device 20 may also execute fuel cut control when the vehicle C decelerates in the parallel mode.

[0024] The following describes the heater control performed by the control device 20. Figure 3 is a graph showing the duty cycle control in this embodiment. Figures 3(a) to (c) all show the passage of time on the horizontal axis, Figure 3(a) shows the engine speed Re on the vertical axis, Figure 3(b) shows the temperature OT of the oxygen sensor 44 (see Figure 2) on the vertical axis, and Figure 3(c) shows the output of the heater 44a (see Figure 2) (in this embodiment, the voltage applied to the heater 44a) on the vertical axis. As shown in Figure 3(a), for example, when regenerative motoring occurs or when the vehicle C decelerates in parallel mode, the engine speed Re decreases over time. At this time, as shown by the solid line in Figure 3(b), the oxygen sensor 44 is cooled as the exhaust temperature decreases, and the temperature OT decreases over time. When the temperature OT decreases, the control device 20 turns on the heater 44a and starts heater control. If heater control is not performed during regenerative motoring, as described later, the temperature OT of the oxygen sensor 44 will fall below the temperature OTa at which the oxygen sensor 44 becomes inactive, as shown by the dashed line in Figure 3(b), and it will no longer be possible to detect the air-fuel ratio.

[0025] Furthermore, as shown by the dashed line in Figure 3(c), if the control device 20 immediately raises the voltage to a predetermined value (1.0V in this embodiment), the temperature OT of the oxygen sensor 44 will overshoot on the temperature rise side, as shown by the dashed line in Figure 3(b), which may cause the oxygen sensor 44 to overheat.

[0026] Therefore, as shown by the solid line in Figure 3(c), in heater control, the control device 20 of this embodiment, when turning on the heater, gradually increases the heater voltage from zero to a predetermined value by a predetermined slope α, that is, by a predetermined increase in the output per unit time. As a result, as shown by the solid line in Figure 3(b), the overshoot of the temperature OT of the oxygen sensor 44 can be suppressed. Furthermore, the control device 20 sets the heater voltage to zero from time t1, when the temperature OT begins to decrease, until time t2, after a predetermined period has elapsed, and then increases the voltage of the heater 44a from zero to a predetermined value after time t2. As a result, the overshoot of the temperature OT can be further suppressed.

[0027] When the control device 20 performs heater control after operating the engine 2 at high power, it extends a predetermined period (from time t1 to time t2 in Figure 3). After the engine 2 has been operating at high power, the temperature of the engine 2 (e.g., water temperature) is high. Therefore, the air passing through the oxygen sensor 44 is also relatively high in temperature. Accordingly, the control device 20 suppresses the overshoot of the temperature OT of the oxygen sensor 44 by extending the predetermined period. The predetermined period should be the period until the temperature OT of the oxygen sensor 44 decreases and reaches the inert temperature. High-power operation should be, for example, 50 percent or more of the maximum output of the engine 2.

[0028] In heater control, the control device 20 changes a predetermined slope α (see Figure 3(c)) according to the amount of air supplied to the engine 2. More specifically, the control device 20 increases the predetermined slope α as the amount of air Q measured by the air flow sensor 46 increases. The energy required to raise the temperature OT of the oxygen sensor 44 (the output of the heater 44a in this embodiment) increases as the exhaust flow rate and, consequently, the amount of air Q measured by the air flow sensor 46 increases. Therefore, the control device 20 increases the slope α of the voltage applied to the heater 44a as the amount of air Q measured by the air flow sensor 46 increases. As a result, the oxygen sensor 44 is quickly warmed up by the heater control.

[0029] Next, the control procedure executed by the control device 20 will be explained using the flowchart in Figure 4. In this embodiment, the control device 20 starts the control procedure when an ignition switch (not shown) is turned on.

[0030] In step S1, the control device 20 determines whether or not vehicle C will decelerate. If the control device 20 determines that vehicle C will decelerate (step S1 YES), it proceeds to step S2.

[0031] In step S2, the control device 20 determines whether the charge level SOC is equal to or greater than a predetermined charge level SOCt. If the control device 20 determines that the charge level SOC is equal to or greater than a predetermined charge level SOCt (step S2 YES), it proceeds to step S3.

[0032] In step S3, the control device 20 performs regenerative motoring. During regenerative motoring, the control device 20 performs fuel cut control. In this embodiment, in step S3, the control device 20 performs regenerative motoring and fuel cut control, and then proceeds to step S4.

[0033] In step S4, the control device 20 performs the heater control described above. After performing the heater control, the control device 20 returns. That is, in this embodiment, the control device 20 continues the heater control while regenerative motoring is being performed.

[0034] On the other hand, if the control device 20 determines in step S1 that vehicle C does not decelerate (step S1 NO), the process proceeds to step S5.

[0035] In step S5, the control device 20 performs normal control. Here, normal control means that when the exhaust temperature is below a predetermined exhaust temperature and a temperature rise of the oxygen sensor 44 by the heater is required, the heater is turned on by a control that sets a predetermined slope α (see Figure 3(c)) to 90 degrees, and the heater is not turned on when a temperature rise of the oxygen sensor 44 by the heater is not required. Such normal control is performed when the temperature OT of the oxygen sensor 44 may fall below the inert temperature during control different from regenerative motoring. A case in which the oxygen sensor 44 may fall below the inert temperature is, for example, when the outside air temperature of the vehicle C is low and the engine 2 is in a cold state.

[0036] If the control device 20 determines in step S2 that the charge level SOC is less than a predetermined charge level SOCt (step S2 NO), the control device 20 proceeds to step S5 and performs normal control. When the charge level SOC is less than a predetermined charge level SOCt, the power generated by the regeneration of the motor 3 is charged into the drive battery 6, and therefore regenerative motoring is not performed. For this reason, the control device 20 controls the temperature of the oxygen sensor 44 by normal control. The control device 20 returns after performing normal control.

[0037] As described above, the control system 1 of this disclosure can protect the air-fuel ratio sensor from excessive temperature rise.

[0038] <Other Embodiments> Although embodiments of the present disclosure have been described above, the present disclosure is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. In particular, the various modifications described herein can be combined as needed.

[0039] The above embodiment describes an example of performing heater control during regenerative motoring, but the disclosure is not limited thereto. For example, if vehicle C is in an environment such as a long deceleration or a long downhill slope, and fuel cut control is performed for a relatively long time, the control device 20 may perform heater control.

[0040] In the above embodiment, an example in which an oxygen sensor 44 is used as an example of an air-fuel ratio sensor was described, but this disclosure is not limited thereto. The air-fuel ratio sensor can be any type that can detect the air-fuel ratio and is warmed up by a heater.

[0041] In the above embodiment, the output of the heater 44a was controlled by the magnitude of the voltage, but it may also be controlled by the duty cycle, which is the period during which the voltage is supplied. In this case, the control device 20 should increase the duty cycle from zero at a predetermined rate. [Explanation of symbols]

[0042] 1: Control system, 2: Internal combustion engine, 3: Motor, 4: Generator 6: Drive battery, 20: Control device, 40: Fuel injection device, 44: Air-fuel ratio sensor (oxygen sensor), 44a: Heater C: Vehicle, Duty: Voltage, Q: Air volume, α: Inclination

Claims

1. A control system for an internal combustion engine mounted on a vehicle, Fuel injection system and An air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust gas of the internal combustion engine, A heater for warming up the air-fuel ratio sensor, A control device for controlling the internal combustion engine, Equipped with, The control device performs fuel cut control to stop fuel injection from the fuel injector, and when performing the fuel cut control, it performs heater control to increase the output of the heater to a predetermined value at a predetermined slope when turning on the heater. Control system for internal combustion engines.

2. The control device increases the predetermined inclination as the amount of air supplied to the internal combustion engine increases in the heater control. The control system for an internal combustion engine according to claim 1.

3. When the control device performs heater control after the internal combustion engine has been operating at high output, it reduces the predetermined incline. The control system for an internal combustion engine according to claim 1.

4. The control device raises the output of the heater to a predetermined value after a predetermined period of time has elapsed. The control system for an internal combustion engine according to claim 1.

5. The control device extends the predetermined period when it performs heater control after the internal combustion engine has been operating at high output. The control system for an internal combustion engine according to claim 4.

6. A generator that is driven by the aforementioned internal combustion engine and generates electricity, A drive battery for storing the electricity generated by the aforementioned generator, A motor that rotates using electricity generated by the aforementioned generator and drives the drive wheels of the vehicle, Furthermore, The control device executes the heater control when the drive battery has a predetermined charge level or higher. A control system for an internal combustion engine according to any one of claims 1 to 5.

7. The control device performs the heater control during motoring, in which the internal combustion engine is driven by the generator. The control system for an internal combustion engine according to claim 6.

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