Hybrid vehicles

Abstract

The goal is to achieve both the warm-up of the nitrogen oxide detection sensor and more accurate detection of nitrogen oxide (NOx) emissions. [Solution] The control device of the hybrid vehicle performs sensor warm-up control, which controls the engine and electric motor so that the engine operates at a relatively low, constant output until the nitrogen oxide detection sensor has warmed up. During the execution of sensor warm-up control, it also estimates the amount of nitrogen oxide emissions based on the values ​​detected from the air-fuel ratio sensor.

Description

Technical Field

[0001] The present disclosure relates to a hybrid vehicle, and more particularly to a hybrid vehicle including an engine having a nitrogen oxide detection sensor for detecting nitrogen oxides in an exhaust pipe.

Background Art

[0002] Conventionally, as this type of hybrid vehicle, a vehicle has been proposed in which an exhaust gas recirculation valve is closed until catalyst warm-up is completed, and nitrogen oxides (NOx) in the exhaust gas are adsorbed by a NOx adsorbent (see, for example, Patent Document 1). In this hybrid vehicle, while suppressing the emission of nitrogen oxides (NOx) into the atmosphere, it is possible to inspect a NOx adsorbent and a NOx desorption mechanism.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the above-described hybrid vehicle, it is necessary to warm up the nitrogen oxide detection sensor until the nitrogen oxide detection sensor sufficiently exhibits its function. However, since the warm-up of the nitrogen oxide detection sensor and the warm-up of the catalyst are not completely linked, the emission amount of nitrogen oxides (NOx) cannot be accurately detected. [[ID=……]]

[0005] The main object of the hybrid vehicle of the present disclosure is to achieve both warm-up of the nitrogen oxide detection sensor and more appropriate detection of the emission amount of nitrogen oxides (NOx).

Means for Solving the Problems

[0006] The hybrid vehicle of the present disclosure has taken the following means to achieve the above-described main object.

[0007] The hybrid vehicle of this disclosure comprises an electric motor capable of inputting and outputting power for driving, an engine, a purification device attached to the exhaust pipe of the engine for purifying exhaust gases, an air-fuel ratio sensor attached downstream of the purification device in the exhaust pipe, a nitrogen oxide detection sensor attached downstream of the air-fuel ratio sensor in the exhaust pipe for detecting nitrogen oxides in the exhaust gases, and a control device for controlling the engine and the electric motor. The control device is characterized by performing sensor warm-up control to control the engine and the electric motor so that the engine operates at a relatively low constant output until the nitrogen oxide detection sensor has warmed up, and while the sensor warm-up control is being performed, it estimates the amount of nitrogen oxide emissions based on the detected value from the air-fuel ratio sensor.

[0008] The hybrid vehicle of this disclosure includes an electric motor capable of inputting and outputting power for driving, an engine, a purification device attached to the engine's exhaust pipe for purifying exhaust gases, an air-fuel ratio sensor attached downstream of the purification device in the exhaust pipe, a nitrogen oxide detection sensor attached downstream of the air-fuel ratio sensor in the exhaust pipe for detecting nitrogen oxides in the exhaust gases, and a control device for controlling the engine and the electric motor. The control device performs sensor warm-up control, which controls the engine and the electric motor so that the engine is operated at a relatively low, constant output until the nitrogen oxide detection sensor has warmed up, and estimates the amount of nitrogen oxide emissions based on the detected value from the air-fuel ratio sensor while the sensor warm-up control is being performed. Because the engine is operated at a relatively low, constant output, the amount of nitrogen oxide emissions can be estimated more accurately based on the detected value from the air-fuel ratio sensor even while the nitrogen oxide detection sensor is warming up. As a result, it is possible to achieve both the warm-up of the nitrogen oxide detection sensor and more accurate detection of nitrogen oxide (NOx) emissions. During sensor warm-up control, the engine is operated to output a constant power, so the motor is controlled to provide input and output for any excess or deficiency in the torque required for driving as requested by the driver, based on the torque derived from the engine's constant power output.

[0009] In the hybrid vehicle of this disclosure, the control device may control the engine so that when it starts the engine when it is cold and performs the sensor warm-up control, the engine operates at a constant output at a higher output than when it starts the engine under normal conditions and performs the sensor warm-up control. In this way, the nitrogen oxide detection sensor can be warmed up earlier by the heat from the exhaust gas from the engine.

[0010] In the hybrid vehicle of this disclosure, a sensor heating device is provided to heat the nitrogen oxide detection sensor, and the control device may limit the duty cycle of the sensor heating device until a predetermined time has elapsed since the start of the sensor warm-up control when the engine is started in cold conditions and the sensor warm-up control is performed. Immediately after starting the engine in cold conditions, condensation may form around the nitrogen oxide detection sensor, causing freezing. In this case, if the sensor heating device is operated at a high duty cycle, the nitrogen oxide detection sensor will be covered in water due to the condensation. Therefore, the condensation around the nitrogen oxide detection sensor is evaporated by the heat of the engine's exhaust gas, and then the sensor heating device is operated at a high duty cycle to warm up the nitrogen oxide detection sensor. This makes it possible to suppress the inconveniences that may occur if the duty cycle of the sensor heating device is set to a high duty cycle while the nitrogen oxide detection sensor is covered in water, such as failure of the nitrogen oxide detection sensor. [Brief explanation of the drawing]

[0011] [Figure 1] A schematic diagram showing the configuration of a hybrid vehicle according to an embodiment of the present disclosure. [Figure 2] A schematic diagram showing the general configuration of engine 22. [Figure 3] A flowchart illustrating an example of engine control during sensor warm-up. [Modes for carrying out the invention]

[0012] Next, embodiments for implementing this disclosure will be described. Figure 1 is a schematic diagram showing the configuration of a hybrid vehicle equipped with an engine device as one embodiment of this disclosure. As shown in the figure, the hybrid vehicle of the embodiment comprises an engine 22, an engine ECU 24, a planetary gear 30, motors MG1 and MG2, inverters 41 and 42, a battery 50 as an energy storage device, and a hybrid electronic control unit (hereinafter referred to as "HVECU") 70.

[0013] The engine 22 is configured as a multi-cylinder (e.g., 4-cylinder or 6-cylinder) internal combustion engine that outputs power using gasoline or diesel as fuel, and is connected to the carrier of the planetary gear 30 via a damper 28. Figure 2 is a schematic diagram showing the configuration of the engine 22. As shown in the figure, the engine 22 draws air cleaned by the air cleaner 122 into the intake manifold 123, passes it through the throttle valve 124, and injects fuel from fuel injectors 126 provided for each cylinder to mix the air and fuel, and this mixture is drawn into the combustion chamber 129 via the intake valve 128. The intake mixture is then exploded and burned by an electric spark from a spark plug 130 installed for each cylinder, and the reciprocating motion of the piston 132 pushed down by the energy is converted into rotational motion of the crankshaft 26. Since the engine 22 has fuel injectors 126 that inject fuel into each cylinder, fuel cut-off can be performed for each cylinder. The exhaust gas discharged from the combustion chamber 129 to the exhaust pipe 133 via the exhaust valve 131 is discharged to the outside air via a catalytic converter 134 and a PM filter 136, and is also supplied to the intake side via an exhaust gas recirculation system (hereinafter referred to as the "EGR (Exhaust Gas Recirculation) system") 160 that recirculates the exhaust gas back into the intake. The catalytic converter 134 has a purification catalyst (three-way catalyst) 134a that purifies harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) in the exhaust gas. The PM filter 136 is formed as a porous filter using ceramics or stainless steel, and captures particulate matter (PM: Particulate Matter) such as soot in the exhaust gas. The EGR system 160 includes an EGR pipe 162 connected downstream of the catalytic converter 134 to supply exhaust gas to a surge tank on the intake side, and an EGR valve 164 located in the EGR pipe 162 and driven by a stepping motor 163. In the EGR system 160, the opening of the EGR valve 164 is adjusted to a target opening θ* corresponding to the required power Pe* required by the engine 22, thereby adjusting the return flow rate of exhaust gas as unburned gas and returning it to the intake side.

[0014] The engine ECU24 is configured as a microprocessor centered around the CPU24a. In addition to the CPU24a, it includes a ROM24b for storing processing programs, a RAM24c for temporarily storing data, and input / output ports and communication ports (not shown).

[0015] The engine ECU 24 receives, for example, the crank position from the crank position sensor 140 which detects the rotational position of the crankshaft 26, the engine water temperature Thw from the water temperature sensor 142 which detects the temperature of the engine coolant 22, the engine oil temperature Thoi from the oil temperature sensor 143 which detects the temperature of the engine oil, the cam position from the cam position sensor 144 which detects the rotational position of the camshaft that opens and closes the intake valve 128 and exhaust valve that perform intake and exhaust to the combustion chamber, the throttle opening TH from the throttle valve position sensor 146 which detects the position of the throttle valve 124, and the airflow meter 148 attached to the intake manifold. The inputs include intake air volume Qa, intake air temperature Ta from temperature sensor 149 attached to the intake manifold, intake pressure Pin from intake pressure sensor 158 that detects the pressure inside the intake manifold, catalyst temperature Tc from temperature sensor 134a attached to the catalytic converter 134, air-fuel ratio AF1 from front air-fuel ratio sensor 135a, air-fuel ratio AF2 from rear air-fuel ratio sensor 135b, differential pressure ΔP from differential pressure sensor 136a that detects the differential pressure before and after the PM filter 136 (the differential pressure between the upstream and downstream sides), detected value NOX from nitrogen oxide sensor (hereinafter referred to as "NOx" sensor) 137, and EGR valve opening EV from EGR valve opening sensor 165 that detects the opening degree of the EGR valve 164.

[0016] The engine ECU 24 outputs signals such as a drive signal to the fuel injector 126, a drive signal to the throttle motor 147 that adjusts the position of the throttle valve 124, a control signal to the ignition coil 138 which is integrated with the igniter, a control signal to the variable valve timing mechanism 150 which can change the opening and closing timing of the intake valve 128, a drive signal to the stepping motor 163 which adjusts the opening degree of the EGR valve 164, and an operation signal to the sensor heater 137a which heats the NOx sensor 137.

[0017] The engine ECU 24 communicates with the hybrid electronic control unit 70 and controls the operation of the engine 22 based on control signals from the hybrid electronic control unit 70, and outputs data regarding the operating status of the engine 22 as needed. The engine ECU 24 calculates the rotational speed Ne of the engine 22 based on the crank angle θcr from the crank position sensor 140, and calculates the load ratio (the ratio of the volume of air actually inhaled in one cycle to the stroke volume per cycle of the engine 22) KL based on the intake air volume Qa from the air flow meter 148 and the rotational speed Ne of the engine 22. The engine ECU 24 also calculates the amount of nitrogen oxides emitted and its cumulative value (cumulative nitrogen oxide emissions) based on the NOx detected from the NOx sensor 137.

[0018] As shown in Figure 1, the planetary gear 30 is configured as a single-pinion type planetary gear mechanism and includes a sun gear 31, a ring gear 32, a plurality of pinion gears 33 that mesh with the sun gear 31 and the ring gear 32 respectively, and a carrier 34 that supports the plurality of pinion gears 33 so that they can rotate and revolve freely. The rotor of the motor MG1 is connected to the sun gear 31 of the planetary gear 30. The drive shaft 36, which is connected to the drive wheels 39a and 39b via a differential gear 38, is connected to the ring gear 32 of the planetary gear 30. As described above, the crankshaft 26 of the engine 22 is connected to the carrier 34 of the planetary gear 30 via a damper 28.

[0019] Motor MG1 is configured, for example, as a synchronous generator-motor, and as described above, its rotor is connected to the sun gear 31 of the planetary gear 30. Motor MG2 is configured, for example, as a synchronous generator-motor, and its rotor is connected to the drive shaft 36. Inverters 41 and 42 are used to drive motors MG1 and MG2 and are connected to the battery 50 via a power line 54. A smoothing capacitor 57 is attached to the power line 54. Motors MG1 and MG2 are driven by the switching control of multiple switching elements (not shown) of inverters 41 and 42 by a motor electronic control unit (hereinafter referred to as "motor ECU") 40.

[0020] The motor ECU 40, although not shown in the diagram, is configured as a microcomputer centered around a CPU. The motor ECU 40 receives inputs such as the rotational positions θm1 and θm2 from rotational position detection sensors 43 and 44 that detect the rotational position of the rotors of motors MG1 and MG2, and the phase currents Iu1, Iv1, Iu2, and Iv2 from current sensors 45u, 45v, 46u, and 46v that detect the current flowing through each phase of motors MG1 and MG2. Switching control signals to multiple switching elements of inverters 41 and 42 are output from the motor ECU 40 via output ports. Based on the rotational positions θm1 and θm2 of the rotors of motors MG1 and MG2 detected by the rotational position detection sensors 43 and 44, the motor ECU 40 calculates the electrical angles θe1 and θe2, angular velocities ωm1 and ωm2, and rotational speeds Nm1 and Nm2 of motors MG1 and MG2.

[0021] The battery 50 is configured as, for example, a lithium-ion secondary battery or a nickel-metal hydride secondary battery, and is connected to the power line 54. This battery 50 is managed by a battery electronic control unit (hereinafter referred to as "battery ECU") 52. The battery ECU 52 is configured as a microcomputer centered around a CPU, although not shown in the figure. Voltage Vb of the battery 50 from a voltage sensor 51a attached between the terminals of the battery 50, current Ib of the battery 50 from a current sensor 51b attached to the output terminal of the battery 50, temperature Tb of the battery 50 from a temperature sensor 51c attached to the battery 50, etc. are input to the battery ECU 52. The battery ECU 52 calculates the state of charge SOC based on the integrated value of the current Ib of the battery 50 from the current sensor 51b.

[0022] The HVECU 70 is configured as a microcomputer centered around a CPU, although not shown in the figure. For example, an ignition signal from an ignition switch 80, a shift position SP from a shift position sensor 82 that detects the operation position of a shift lever 81, an accelerator opening Acc from an accelerator pedal position sensor 84 that detects the depression amount of an accelerator pedal 83, a brake pedal position BP from a brake pedal position sensor 86 that detects the depression amount of a brake pedal 85, vehicle speed V from a vehicle speed sensor 88, atmospheric pressure Pout from an atmospheric pressure sensor 89, etc. are input to the HVECU 70. As described above, the HVECU 70 is connected to the engine ECU 24, the motor ECU 40, and the battery ECU 52 via communication ports.

[0023] The hybrid vehicle configured in this way travels while switching between a hybrid driving mode (HV driving mode) that travels with the operation of the engine 22 and an electric driving mode (EV driving mode) that travels with the operation stop of the engine 22 (while intermittently operating the engine 22).

[0024] In HV driving mode, the HVECU 70 basically sets the driving torque Td* required for driving (required to the drive shaft 36) based on the accelerator opening Acc and vehicle speed V, and calculates the driving power Pd* required for driving by multiplying the set driving torque Td* by the rotational speed Nd of the drive shaft 36 (rotational speed Nm2 of the motor MG2). Next, it calculates the required power Pe* required for the engine 22 by subtracting the charge / discharge required power Pb* of the battery 50 (a positive value when the battery 50 is being discharged) from the driving power Pd*, and sets the target rotational speed Ne* and target torque Te* of the engine 22, and the torque commands Tm1* and Tm2* of the motors MG1 and MG2, so that the calculated required power Pe* is output from the engine 22 and the driving torque Td* is output to the drive shaft 36. Then, the target rotational speed Ne* and target torque Te* of the engine 22 are transmitted to the engine ECU 24, and torque commands Tm1* and Tm2* of the motors MG1 and MG2 are transmitted to the motor ECU 40. When the engine ECU 24 receives the target rotational speed Ne* and target torque Te* of the engine 22, it controls the operation of the engine 22 so that the engine 22 is operated based on the target rotational speed Ne* and target torque Te*. The operation control of the engine 22 includes intake air volume control, which controls the opening degree of the throttle valve 124; fuel injection control, which controls the amount of fuel injected from the fuel injector 126; and ignition control, which controls the ignition timing of the spark plug 130. In fuel injection control, the target injection amount Qf* is set by multiplying the basic fuel injection amount Qf, which is based on the rotational speed of the engine 22 and the intake manifold pressure, by a correction coefficient based on various sensor values ​​that detect the state of the engine 22. The fuel injectors 126, each provided for each cylinder, are controlled so that the amount of fuel injected from the fuel injectors 126 becomes the target injection amount Qf*. When the motor ECU 40 receives torque commands Tm1* and Tm2* from motors MG1 and MG2, it controls the switching of multiple switching elements of inverters 41 and 42 so that motors MG1 and MG2 are driven by the torque commands Tm1* and Tm2*.

[0025] In EV driving mode, the HVECU 70 sets the driving torque Td* based on the accelerator opening Acc and vehicle speed V, sets the torque command Tm1* of motor MG1 to a value of 0, and sets the torque command Tm2* of motor MG2 so that the driving torque Td* is output to the drive shaft 36, and transmits the torque commands Tm1* and Tm2* of motors MG1 and MG2 to the motor ECU 40. The control of inverters 41 and 42 by the motor ECU 40 is described above.

[0026] Next, we will describe the operation of the hybrid vehicle configured in this way, particularly the operation of the NOx sensor 137 during warm-up. Figure 3 is a flowchart showing an example of engine control during sensor warm-up performed by the engine ECU 24. This engine control during sensor warm-up is performed when the engine 22 is started.

[0027] When engine control is performed during sensor warm-up, the engine ECU 24 first determines whether or not to warm up the NOx sensor 137 (step S100). The determination of whether or not to warm up the NOx sensor 137 can be made based on whether or not the NOx sensor 137 is considered to have reached a temperature sufficient for it to function properly, based on the temperature of the NOx sensor 137 and the coolant temperature of the engine 22. If it is determined that the NOx sensor 137 does not need to be warmed up, this control is deemed unnecessary and terminated.

[0028] In step S100, when it is determined that the NOx sensor 137 should be warmed up, the amount of nitrogen oxide (NOx) emissions is estimated based on the air-fuel ratio AF2 from the rear air-fuel ratio sensor 135b (step S110). In this embodiment, the rear air-fuel ratio sensor 135b also functions as an oxygen concentration sensor, so the amount of nitrogen oxide (NOx) emissions is estimated based on the oxygen concentration in the exhaust. In addition, the engine ECU 24 of this embodiment also calculates the cumulative amount of nitrogen oxide (NOx) emissions based on the estimated amount of nitrogen oxide (NOx) emissions.

[0029] Next, it is determined whether the engine 22 is being started in a cold state (step S120). This determination can be made by checking whether the coolant temperature Tw of the engine 22 is less than a threshold Twref (which is less than 0) and whether the ambient temperature is less than a threshold Taref (which is less than 0). For example, the threshold Twref can be 0°C, and the threshold Taref can be 0°C, -10°C, -20°C, etc.

[0030] If it is determined in step S120 that it is not a cold start, the required power Pe* for the engine 22 is set to value Pe1 (step S130), and constant power operation of the engine 22 is started so that the engine 22 outputs the required power Pe* of value Pe1 (step S140). A relatively small value Pe1 can be used, which is slightly larger than that for self-sustaining operation. Constant power operation of the engine 22 is performed in order to stabilize the operation of the engine 22 and to perform a more accurate estimation of nitrogen oxide (NOx) emissions based on the air-fuel ratio AF2 from the rear air-fuel ratio sensor 135b. Then, after waiting for the NOx sensor 137 to have finished warming up or for a second predetermined time to have elapsed since the start of warming up the NOx sensor 137 (steps S200, S210), the constant power operation of the engine 22 is terminated (step S220), the estimation of nitrogen oxide (NOx) emissions based on the air-fuel ratio AF2 from the rear air-fuel ratio sensor 135b is terminated (step S230), and this control is terminated. The second predetermined time is, for example, 60 or 70 seconds, which is the time normally considered necessary for the NOx sensor 137 to warm up. In this way, by estimating the amount of nitrogen oxides (NOx) emitted based on the air-fuel ratio AF2 from the rear air-fuel ratio sensor 135b until the NOx sensor 137 has finished warming up or until the second predetermined time has elapsed since the start of the NOx sensor 137 warming up, the amount of nitrogen oxides (NOx) emitted and the cumulative amount emitted can be calculated even while the NOx sensor 137 is warming up. When the estimation of nitrogen oxides (NOx) emitted based on the air-fuel ratio AF2 from the rear air-fuel ratio sensor 135b is completed, the engine ECU 24 calculates the amount of nitrogen oxides (NOx) emitted and the cumulative amount emitted based on the NOx detected value of the NOx sensor 137. Furthermore, while the engine 22 is operating at a constant output, any excess or deficiency in the driving torque Td* due to the constant output operation of the engine 22 is covered by the torque from the motor MG2. Therefore, the HVECU 70 sets the torque obtained by subtracting the torque output to the drive shaft 36 by the constant output operation of the engine 22 from the driving torque Td* as the torque command Tm2* for the motor MG2, and the motor ECU 40 controls the switching elements of the inverter 42 based on this torque command Tm2*.

[0031] If it is determined in step S120 that it is not a cold start, the required power Pe* for the engine 22 is set to a value Pe2 which is greater than the value Pe1 (step S150), and the engine 22 is started to operate at a constant output so that it outputs the required power Pe* of value Pe2 (step S160), and the heating duty cycle D of the sensor heater 137a is limited to a relatively small value D1 or less (step S160). Here, the value Pe2 can be a value slightly larger than the value Pe1. The value D1 can be 0.1 or 0.2. The reason for setting the required power Pe* to a value Pe2 which is greater than the value Pe1 is to increase the exhaust gas from the engine 22 and evaporate the condensed water around the nitrogen oxide detection sensor at an earlier stage. Subsequently, after waiting for a first predetermined time to elapse since the warm-up of the NOx sensor 137 has started (step S190), the restriction on the heating duty cycle D of the sensor heater 137a is released (step S190). The first predetermined time is the time required for some degree of evaporation of condensed water around the nitrogen oxide detection sensor, and is shorter than the second predetermined time. Then, after waiting for the NOx sensor 137 to have finished warming up or for the second predetermined time to have elapsed since the start of warming up the NOx sensor 137 (steps S200, S210), the constant output operation of the engine 22 is terminated (step S220), the estimation of nitrogen oxide (NOx) emissions based on the air-fuel ratio AF2 from the rear air-fuel ratio sensor 135b is terminated (step S230), and this control is terminated. In this way, during cold starts, the heating duty cycle D of the sensor heater 137a is limited until a certain amount of time has elapsed for some degree of evaporation of condensed water around the nitrogen oxide detection sensor, thereby suppressing the inconveniences that would occur if the heating duty cycle D of the sensor heater 137a were high while the NOx sensor 137 is submerged in water, such as malfunction of the NOx sensor 137.

[0032] In the hybrid vehicle 20 of the embodiment described above, the engine 22 is operated at a constant output until the NOx sensor 137 has finished warming up or until a second predetermined time has elapsed since the start of the NOx sensor 137 warming up, and the amount of nitrogen oxide (NOx) emissions is estimated based on the air-fuel ratio AF2 from the rear air-fuel ratio sensor 135b. In this way, by operating the engine 22 at a constant output while the NOx sensor 137 is warming up and stabilizing the operation of the engine 22, the estimation of nitrogen oxide (NOx) emissions based on the air-fuel ratio AF2 from the rear air-fuel ratio sensor 135b can be performed more accurately. This makes it possible to achieve both the warming up of the NOx sensor 137 and more accurate detection of nitrogen oxide (NOx) emissions.

[0033] In the hybrid vehicle 20 of this embodiment, when the engine 22 is cold-started, the required power Pe* required for the engine 22 is set to a value Pe2 that is greater than the value Pe1 when it is not cold-started, and the engine 22 is operated at a constant output so that it outputs a required power Pe* of value Pe2, and the heating duty cycle D of the sensor heater 137a is limited until a certain amount of time has elapsed for the condensed water around the nitrogen oxide detection sensor to evaporate. This makes it possible to suppress the inconvenience caused by setting the heating duty cycle D of the sensor heater 137a to a high duty cycle while the NOx sensor 137 is submerged in water, such as the malfunction of the NOx sensor 137.

[0034] In the hybrid vehicle 20 of this embodiment, when the engine 22 is cold-started, the required power Pe* for the engine 22 is set to a value Pe2 that is greater than the value Pe1 that is not used when the engine is not cold-started, and the engine 22 is operated at a constant output so that it outputs a required power Pe* of value Pe2. However, even when the engine 22 is cold-started, the required power Pe* for the engine 22 may be set to the value Pe1 that is not used when the engine is not cold-started, and the engine 22 may be operated at a constant output.

[0035] In the hybrid vehicle 20 of this embodiment, the heating duty cycle D of the sensor heater 137a is limited during cold starts of the engine 22 until a certain amount of time has elapsed for the condensed water around the nitrogen oxide detection sensor to evaporate. However, the heating duty cycle D may not be limited even during cold starts of the engine 22.

[0036] In this embodiment, the engine system is mounted on a hybrid vehicle in which the engine 22 and motor MG1 are connected to the drive shaft 36 via a planetary gear 30, and motor MG2 is also connected to the drive shaft 36, and a battery 50 is connected to motors MG1 and MG2 via power lines. However, the engine system may also be mounted on a so-called single-motor hybrid vehicle or a so-called series hybrid vehicle.

[0037] The correspondence between the main elements of the embodiment and the main elements of the invention described in the section on means for solving the problem will be explained. In the embodiment, motor MG2 corresponds to "electric motor", engine 22 corresponds to "engine", catalytic converter 134 corresponds to "purification device", rear air-fuel ratio sensor 135b corresponds to "air-fuel ratio sensor", NOx sensor 137 corresponds to "nitrogen oxide detection sensor", and engine ECU 24, motor ECU 40, and HVECU 70 correspond to "control device".

[0038] Furthermore, the correspondence between the main elements of the embodiment and the main elements of the invention described in the section on means for solving the problem is merely an example to specifically explain the form in which the embodiment implements the invention described in the section on means for solving the problem, and does not limit the elements of the invention described in the section on means for solving the problem. In other words, the interpretation of the invention described in the section on means for solving the problem should be based on the description in that section, and the embodiment is merely one specific example of the invention described in the section on means for solving the problem.

[0039] Although the present disclosure has been described above using embodiments, the present disclosure is not limited in any way to these embodiments, and can of course be implemented in various forms without departing from the gist of the present disclosure. [Industrial applicability]

[0040] This disclosure can be used in industries such as the hybrid vehicle manufacturing industry. [Explanation of symbols]

[0041] 20 Hybrid vehicle, 22 Engine, 24 Engine ECU, 30 Planetary gear, 36 Drive shaft, 40 Motor ECU, 50 Battery, 52 Battery ECU, 70 HVECU, 133 Exhaust pipe, 134 Purification device, 135a Front air-fuel ratio sensor, 135b Rear air-fuel ratio sensor, 136 PM filter, 137 NOx sensor 150, MG1, MG2 Motor.

Claims

1. A hybrid vehicle comprising: an electric motor capable of inputting and outputting power for driving; an engine; a purification device attached to the exhaust pipe of the engine for purifying exhaust gases; an air-fuel ratio sensor attached downstream of the purification device in the exhaust pipe; a nitrogen oxide detection sensor attached downstream of the air-fuel ratio sensor in the exhaust pipe for detecting nitrogen oxides in the exhaust gases; and a control device for controlling the engine and the electric motor, The control device performs sensor warm-up control, which controls the engine and the electric motor so that the engine operates at a relatively low, constant output until the nitrogen oxide detection sensor has warmed up, and while the sensor warm-up control is being performed, it estimates the amount of nitrogen oxide emissions based on the value detected from the air-fuel ratio sensor. A hybrid vehicle characterized by the following features.

2. A hybrid vehicle according to claim 1, When the control device starts the engine in cold conditions and performs the sensor warm-up control, it controls the engine so that it operates at a constant output with a higher output than when the engine is started in normal conditions (not cold conditions) and the sensor warm-up control is performed. Hybrid vehicle.

3. A hybrid vehicle according to claim 1 or 2, The system includes a sensor heating device for heating the nitrogen oxide detection sensor, When the control device starts the engine in cold conditions and performs the sensor warm-up control, it limits the duty cycle of the sensor heating device until a predetermined time has elapsed since the start of the sensor warm-up control. Hybrid vehicle.

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