Hybrid vehicle

Abstract

The present invention addresses the problem of achieving both warm-up of a nitrogen oxide detection sensor and more appropriate detection of the amount of nitrogen oxide (NOx) discharged. [Solution] A control device for a hybrid vehicle executes sensor warm-up control in which warm-up of a nitrogen oxide detection sensor is completed, and estimates an emission amount of nitrogen oxide on the basis of a detection value from an air-fuel ratio sensor during execution of the sensor warm-up control until the warm-up of the nitrogen oxide detection sensor is completed, and estimates the emission amount of nitrogen oxide on the basis of the detection value from the air-fuel ratio sensor during execution of the sensor warm-up control. The engine and the electric motor are controlled such that the engine operates and travels at a relatively low constant power.

Description

Technical Field

[0001] The present invention relates to a hybrid electric vehicle, and more specifically, to a hybrid electric vehicle having an engine equipped with a nitrogen oxide detection sensor on the exhaust pipe for detecting nitrogen oxides in the exhaust. Background Technology

[0002] Conventional hybrid vehicles have included the following configuration: until the catalytic converter has warmed up, the exhaust return valve is closed, and nitrogen oxides (NOx) in the exhaust gas are adsorbed using a NOx adsorbent (see, for example, Patent Document 1). In this hybrid vehicle, atmospheric emissions of nitrogen oxides (NOx) can be suppressed, and the NOx adsorption material and NOx desorption mechanism can be inspected.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2010-168994 Summary of the Invention

[0004] However, in the aforementioned hybrid vehicles, although the nitrogen oxide detection sensor needs to be warmed up until it is fully functional, the warm-up of the nitrogen oxide detection sensor and the warm-up of the catalyst are not completely synchronized, so the amount of nitrogen oxides (NOx) emitted cannot be accurately detected.

[0005] The main objective of the hybrid electric vehicle of the present invention is to achieve both warm-up of the nitrogen oxide detection sensor and more accurate detection of nitrogen oxide (NOx) emissions.

[0006] The hybrid electric vehicle of the present invention employs the following scheme to achieve the aforementioned main objectives.

[0007] The hybrid electric vehicle of the present invention comprises: an electric motor capable of inputting and outputting power for driving; an engine; a purification device installed on the exhaust pipe of the engine and purifying the exhaust; an air-fuel ratio sensor installed downstream of the purification device on the exhaust pipe; a nitrogen oxide detection sensor installed further downstream than the air-fuel ratio sensor on the exhaust pipe and detecting nitrogen oxides in the exhaust; and a control device for controlling the engine and the electric motor. The hybrid electric vehicle is characterized in that…

[0008] The control device performs sensor warm-up control, and during the execution of the sensor warm-up control, it estimates the amount of nitrogen oxide emissions based on the detection value from the air-fuel ratio sensor. During the sensor warm-up control, the engine and the electric motor are controlled to operate at a relatively low power constant power and drive until the nitrogen oxide detection sensor has completed warm-up.

[0009] The hybrid electric vehicle of the present invention includes: an electric motor capable of inputting and outputting power for driving; an engine; a purification device installed on the exhaust pipe of the engine to purify the exhaust; an air-fuel ratio sensor installed downstream of the purification device on the exhaust pipe; a nitrogen oxide (NOx) detection sensor installed further downstream than the air-fuel ratio sensor on the exhaust pipe to detect NOx in the exhaust; and a control device that controls the engine and the electric motor. The control device performs sensor warm-up control, and during the execution of sensor warm-up control, estimates the amount of NOx emitted based on the detection value from the air-fuel ratio sensor. In the sensor warm-up control, the engine and the electric motor are controlled to operate at a relatively low, constant power until the NOx detection sensor has completed warm-up. Because the engine operates at a relatively low, constant power, the amount of NOx emitted can be more accurately estimated based on the detection value from the air-fuel ratio sensor, even during the warm-up period of the NOx detection sensor. As a result, it is possible to achieve both warm-up of the NOx detection sensor and more accurate detection of NOx emissions. In addition, during the sensor warm-up control period, since the engine operates in a constant power output mode, the insufficient or excessive torque required by the driver during driving and the torque based on the constant power of the engine are input and output by the electric motor through the control of the electric motor.

[0010] In the hybrid electric vehicle of the present invention, when the control device starts the engine and performs the sensor warm-up control in a cold state, it can control the engine to operate at a constant power with a higher power output compared to when the engine is started and the sensor warm-up control is performed in a non-cold state (i.e., normal state). This allows the nitrogen oxide detection sensor to be warmed up earlier using heat from the engine exhaust.

[0011] In the hybrid electric vehicle of the present invention, a sensor heating device may be included to heat the nitrogen oxide detection sensor. When the control device starts the engine in a cold state and performs sensor warm-up control, the duty cycle of the sensor heating device is limited until a predetermined time has elapsed since the start of the sensor warm-up control. When the engine is started in a cold state, condensation may sometimes form around the nitrogen oxide detection sensor. In this case, if the sensor heating device operates at a high duty cycle, the nitrogen oxide detection sensor will become wet due to condensation. Therefore, the heat from the engine exhaust evaporates the condensation around the nitrogen oxide detection sensor, and then the sensor heating device operates at a high duty cycle to warm up the nitrogen oxide detection sensor. This suppresses adverse conditions, such as nitrogen oxide detection sensor malfunction, caused by setting the duty cycle of the sensor heating device to a high duty cycle during the period when the nitrogen oxide detection sensor is wet. Attached Figure Description

[0012] Figure 1 This is a schematic structural diagram illustrating the structure of a hybrid electric vehicle according to an embodiment of the present invention.

[0013] Figure 2 This is a schematic structural diagram showing the structure of engine 22.

[0014] Figure 3 This is a flowchart illustrating an example of engine control during sensor warm-up. Detailed Implementation

[0015] Next, the methods (implementation methods) for carrying out the present invention will be described. Figure 1 This is a schematic structural diagram showing the structure of a hybrid electric vehicle equipped with an engine device as an embodiment of the present invention. As shown, the hybrid electric vehicle of this embodiment includes: an engine 22; an engine ECU 24; a planetary gear 30; electric 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.

[0016] The engine 22 is configured as a multi-cylinder (e.g., 4-cylinder or 6-cylinder, etc.) internal combustion engine that uses gasoline, light oil, etc. as fuel to output power, and is connected to the planet carrier of the planetary gear 30 via the damper 28. Figure 2This is a schematic structural diagram showing the structure of engine 22. As shown, engine 22 draws in air purified by air filter 122 into intake manifold 123 and forces it through throttle valve 124. Fuel is injected from fuel injection valves 126 provided for each cylinder, mixing the air and fuel. This mixture is then drawn into combustion chamber 129 via intake valve 128. The intake mixture is then ignited by an electric spark from spark plugs 130 installed in each cylinder, converting the reciprocating motion of piston 132, driven by its energy, into rotational motion of crankshaft 26. Because engine 22 has fuel injection valves 126 that inject fuel for each cylinder, fuel cut-off can be achieved for each cylinder. Exhaust gas from combustion chamber 129, discharged through exhaust valve 131 to exhaust pipe 133, is discharged to the outside air via catalyst device 134 and PM filter 136, and is supplied to the intake side via exhaust gas recirculation device (hereinafter referred to as "EGR (Exhaust Gas Recirculation) system") 160, which recirculates exhaust gas back to the intake air. Catalyst device 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. PM filter 136 is formed into a porous filter made of ceramic or stainless steel to capture particulate matter (PM) in the exhaust gas. EGR system 160 includes: EGR pipe 162, which is connected downstream of catalyst device 134 for supplying exhaust gas to pressure regulating chamber on the intake side; and EGR valve 164, which is disposed on EGR pipe 162 and driven by stepper motor 163. In the EGR system 160, the return flow of exhaust gas, which is a non-combustible gas, is regulated and returned to the intake side by adjusting the opening of the EGR valve 164 to a target opening θ* corresponding to the required power Pe* required by the engine 22.

[0017] The engine ECU24 is configured as a microprocessor centered on CPU24a. In addition to CPU24a, it also has ROM24b for storing processing programs, RAM24c for temporary data storage, input / output ports (not shown), and communication ports.

[0018] In the engine ECU 24, inputs include, for example, crankshaft position from crankshaft position sensor 140 (detecting the rotational position of crankshaft 26), engine coolant temperature Thw from coolant temperature sensor 142 (detecting the temperature of coolant in engine 22), engine oil temperature Thoi from oil temperature sensor 143 (detecting the temperature of engine oil), cam position from cam position sensor 144 (detecting the rotational position of the camshaft that opens and closes the intake valve 128 or exhaust valve for intake and exhaust in the combustion chamber), throttle opening TH from throttle position sensor 146 (detecting the position of throttle valve 124), intake air volume Qa from air flow meter 148 installed in the intake manifold, and temperature sensor 146 from the intake manifold. The sensors include: intake air temperature Ta from sensor 149; intake air pressure Pin from intake pressure sensor 158 which detects the pressure inside the intake manifold; catalyst temperature Tc from temperature sensor 134a installed in catalyst unit 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 which detects the pressure difference across PM filter 136 (pressure difference between upstream and downstream sides); NOX from nitrogen oxide sensor (hereinafter referred to as "NOx" sensor) 137; and EGR valve opening EV from EGR valve opening sensor 165 which detects the opening of EGR valve 164.

[0019] The engine ECU 24 outputs, for example, drive signals to the fuel injection valve 126, drive signals to the throttle motor 147 that adjusts the position of the throttle valve 124, control signals to the ignition coil 138 integrated with the igniter, control signals to the variable valve timing mechanism 150 that can change the opening and closing timing of the intake valve 128, drive signals to the stepper motor 163 that adjusts the opening of the EGR valve 164, and operating signals to the sensor heater 137a that heats the NOx sensor 137.

[0020] The engine ECU 24 communicates with the hybrid electronic control unit 70, controlling the operation of the engine 22 via control signals from the hybrid electronic control unit 70, and outputting data related to the operating status of the engine 22 as needed. The engine ECU 24 calculates the engine speed Ne of the engine 22 based on the crankshaft angle θcr from the crankshaft position sensor 140, or calculates the load rate (the ratio of the volume of air actually drawn in during one cycle to the stroke volume of the engine 22 in each cycle) KL based on the intake air volume Qa from the air flow meter 148 and the engine speed Ne. Furthermore, the engine ECU 24 also calculates the amount of nitrogen oxides emitted and its cumulative value (cumulative nitrogen oxide emissions) based on the NOx detection value from the NOx sensor 137.

[0021] like Figure 1 As shown, the planetary gear 30 is configured as a single-pinion planetary gear mechanism, comprising: a sun gear 31; an internal ring gear 32; multiple pinions 33 meshing with the sun gear 31 and the internal ring gear 32 respectively; and a planet carrier 34 supporting the multiple pinions 33 for rotation and revolution. The rotor of the motor MG1 is connected to the sun gear 31 of the planetary gear 30. A drive shaft 36, connected to the internal ring gear 32 of the planetary gear 30 via a differential gear 38 and drive wheels 39a and 39b, is connected to the internal ring gear 32 of the planetary gear 30. As described above, the crankshaft 26 of the engine 22 is connected to the planet carrier 34 of the planetary gear 30 via a damper 28.

[0022] Motor MG1 is configured, for example, as a synchronous generator motor, with its rotor connected to the sun gear 31 of the planetary gear 30, as described above. Motor MG2 is configured, for example, as a synchronous generator motor, with its rotor 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 power line 54. A smoothing capacitor 57 is mounted on the power line 54. Motors MG1 and MG2 are driven to rotate by a motor electronic control unit (hereinafter referred to as "motor ECU") 40 through switching control of multiple switching elements (not shown) in inverters 41 and 42.

[0023] Although not shown, the motor ECU 40 is configured as a CPU-centric microcomputer. The motor ECU 40 receives inputs such as rotational position detection sensors 43 and 44 (θm1, θm2) that detect the rotational positions of the rotors of motors MG1 and MG2, and phase current sensors 45u, 45v, 46u, and 46v (Iu1, Iv1, Iu2, Iv2) that detect the current flowing through each phase of motors MG1 and MG2. The motor ECU 40 outputs switching control signals to multiple switching elements of inverters 41 and 42 via output ports. Based on the rotational positions θm1 and θm2 of the rotors of motors MG1 and MG2 from 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.

[0024] 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. The battery 50 is managed by a battery electronic control unit (hereinafter referred to as the "battery ECU") 52. Although not shown, the battery ECU 52 is configured as a CPU-centric microcomputer. The battery ECU 52 receives inputs such as the voltage Vb of the battery 50 from a voltage sensor 51a mounted between the terminals of the battery 50, the current Ib of the battery 50 from a current sensor 51b mounted at the output terminal of the battery 50, and the temperature Tb of the battery 50 from a temperature sensor 51c mounted on the battery 50. The battery ECU 52 calculates the state of charge (SOC) based on the accumulated value of the current Ib from the current sensor 51b.

[0025] Although not shown, the HVECU70 is configured as a CPU-centric microcomputer. For example, the HVECU70 receives inputs such as an ignition signal from the ignition switch 80, a shift position SP from the shift position sensor 82 (detecting the operating position of the shift lever 81), a throttle opening Acc from the throttle pedal position sensor 84 (detecting the amount of pressure applied to the accelerator pedal 83), a brake pedal position BP from the brake pedal position sensor 86 (detecting the amount of pressure applied to the brake pedal 85), a vehicle speed V from the vehicle speed sensor 88, and an atmospheric pressure Pout from the atmospheric pressure sensor 89. As described above, the HVECU70 is connected to the engine ECU 24, the electric motor ECU 40, and the battery ECU 52 via a communication port.

[0026] The hybrid vehicle configured in this way drives while switching between a hybrid driving mode (HV driving mode) that runs with the engine 22 running and an electric driving mode (EV driving mode) that runs with the engine 22 stopped.

[0027] In HV driving mode, the HVECU70 basically sets the required driving torque Td* (required for drive shaft 36) based on the throttle opening Acc and vehicle speed V. It then multiplies the set driving torque Td* by the rotational speed Nd of drive shaft 36 (the rotational speed Nm2 of motor MG2) to calculate the required driving power Pd*. Next, it subtracts the required charging / discharging power Pb* of battery 50 (positive when discharging from battery 50) from the driving power Pd* to calculate the required power Pe* for engine 22. To ensure that the calculated required power Pe* is output from engine 22 and the driving torque Td* is output to drive shaft 36, it sets the target rotational speed Ne* and target torque Te* of engine 22, and the torque commands Tm1* and Tm2* of motors MG1 and MG2. Then, it sends the target rotational speed Ne* and target torque Te* of engine 22 to engine ECU24, and the torque commands Tm1* and Tm2* of motors MG1 and MG2 to motor ECU40. If the engine ECU 24 receives the target speed Ne* and target torque Te* of the engine 22, it performs operation control of the engine 22 to make the engine 22 operate according to the target speed Ne* and target torque Te*. As part of the engine 22 operation control, it performs intake air volume control by controlling the opening of the throttle valve 124, fuel injection control by controlling the fuel injection quantity from the fuel injection valve 126, and ignition control by controlling the ignition timing of the spark plug 130. In fuel injection control, the target injection quantity Qf* is set by multiplying the basic fuel injection quantity Qf based on the engine speed and intake manifold pressure by a correction factor based on various sensor values ​​detecting the state of the engine 22, and the fuel injection valve 126, which is provided for each cylinder, is controlled so that the fuel injection quantity from the fuel injection valve 126 becomes the target injection quantity Qf*. If the motor ECU40 receives torque commands Tm1* and Tm2* from motors MG1 and MG2, it will control the switching of multiple switching elements of inverters 41 and 42 to drive motors MG1 and MG2 according to the torque commands Tm1* and Tm2*.

[0028] In EV driving mode, HVECU70 sets the driving torque Td* based on the throttle opening Acc and vehicle speed V, sets the torque command Tm1* of motor MG1 to 0, and sets the torque command Tm2* of motor MG2 to output the driving torque Td* to drive shaft 36. The torque commands Tm1* and Tm2* of motors MG1 and MG2 are then sent to motor ECU40. The control of inverters 41 and 42 by motor ECU40 is as described above.

[0029] Next, the operation of the hybrid vehicle thus configured will be explained, especially the operation of the NOx sensor 137 during warm-up. Figure 3This is a flowchart illustrating an example of engine control during sensor warm-up, executed by engine ECU 24. This engine control during sensor warm-up is executed when engine 22 is started.

[0030] If engine control is performed during sensor warm-up, the engine ECU 24 first determines whether to warm up the NOx sensor 137 (step S100). The determination of whether to warm up the NOx sensor 137 can be based on factors such as the temperature of the NOx sensor 137 and the coolant temperature of the engine 22, by considering whether the temperature level is sufficient for the NOx sensor 137 to function effectively. If it is determined that warming up the NOx sensor 137 is not necessary, this control is deemed unnecessary and terminated.

[0031] In step S100, when it is determined that the NOx sensor 137 is being warmed up, the amount of nitrogen oxides (NOx) emitted 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, thus estimating the amount of nitrogen oxides (NOx) emitted based on the oxygen concentration in the exhaust. Furthermore, the engine ECU 24 in this embodiment also calculates the cumulative amount of nitrogen oxides (NOx) emitted based on the estimated amount of nitrogen oxides (NOx) emitted.

[0032] Next, it is determined whether the engine 22 is started from a cold state (step S120). The determination of whether it is a cold start can be made by determining whether the engine 22's coolant temperature Tw is a value less than 0 and below a threshold value Twref, and whether the outside air temperature is a value less than 0 and below a threshold value Taref. For example, the threshold value Twref can be 0°C, and the threshold value Taref can be 0°C, -10°C, -20°C, etc.

[0033] When a non-cold start is determined in step S120, the required power Pe* for engine 22 is set to a value Pe1 (step S130), and constant power operation of engine 22 begins by outputting the required power Pe* of value Pe1 from engine 22 (step S140). The value Pe1 can be a relatively small value that is slightly larger than that used for independent operation. Constant power operation of engine 22 is used to more accurately estimate the amount of nitrogen oxides (NOx) emissions based on the air-fuel ratio AF2 from the rear air-fuel ratio sensor 135b by stabilizing the operation of engine 22. Then, after waiting for the NOx sensor 137 to complete warm-up or for a second predetermined time to elapse since the start of NOx sensor 137 warm-up (steps S200, S210), constant power operation of engine 22 ends (step S220), and the estimation of nitrogen oxides (NOx) emissions based on the air-fuel ratio AF2 from the rear air-fuel ratio sensor 135b ends (step S230), thus ending this control. The second specified time refers to the time generally considered required for the NOx sensor 137 to warm up, such as 60 seconds or 70 seconds. Thus, by elapsed for the second specified time after the NOx sensor 137 has finished warming up or since the start of its warm-up, the amount of nitrogen oxides (NOx) emitted is estimated based on the air-fuel ratio AF2 from the rear air-fuel ratio sensor 135b. Even during the warm-up period of the NOx sensor 137, the amount and cumulative amount of nitrogen oxides (NOx) emitted can be calculated. Furthermore, if the estimation of nitrogen oxide (NOx) emissions based on the air-fuel ratio AF2 from the rear air-fuel ratio sensor 135b ends, the engine ECU 24 calculates the amount and cumulative amount of nitrogen oxides (NOx) emitted based on the NOx detection value of the NOx sensor 137. Moreover, during the constant power operation of the engine 22, the torque from the electric motor MG2 compensates for any deficiency or excess in the driving torque Td* caused by the constant power operation of the engine 22. Therefore, the HVECU70 sets the torque obtained by subtracting the torque output to the drive shaft 36 from the driving torque Td* through the constant power operation of the engine 22 as the torque command Tm2* for the motor MG2, and the motor ECU40 controls the switching elements of the inverter 42 according to the torque command Tm2*.

[0034] When a cold start is determined in step S120, the required power Pe* for engine 22 is set to a value Pe2, which is larger than Pe1 (step S150), and engine 22 begins constant power operation by outputting the required power Pe* of value Pe2 from engine 22 (step S160), and the heating duty cycle D of sensor heater 137a is limited to a relatively small value D1 or less (step S170). Here, value Pe2 can be a value slightly larger than Pe1. Value D1 can be 0.1 or 0.2. Thus, setting the required power Pe* to a value Pe2, which is larger than Pe1, is to increase the exhaust gas from engine 22 so that the condensate around the NOx detection sensor evaporates as soon as possible. Next, after waiting for a first predetermined time to elapse since the start of warm-up of NOx sensor 137 (step S180), the limitation on the heating duty cycle D of sensor heater 137a is released (step S190). The first predetermined time is a certain time required for the condensate around the NOx detection sensor to evaporate, and is a shorter time than the second predetermined time. Then, after waiting for the NOx sensor 137 to finish warming up or for a second predetermined time to elapse since the start of the NOx sensor 137 warm-up (steps S200, S210), the constant power operation of the engine 22 ends (step S220), and the estimation of the amount of nitrogen oxides (NOx) emitted based on the air-fuel ratio AF2 from the rear air-fuel ratio sensor 135b ends (step S230), thus ending this control. In this way, during cold starts, by limiting the heating duty cycle D of the sensor heater 137a until a certain time is required for the condensate around the NOx sensor to evaporate, adverse conditions such as NOx sensor 137 malfunctions caused by setting the heating duty cycle D of the sensor heater 137a to a high duty cycle during the period when the NOx sensor 137 is wet can be suppressed.

[0035] In the hybrid vehicle 20 described above, after the NOx sensor 137 has completed warm-up or after a second predetermined time has elapsed since the start of warm-up, the engine 22 is operated at a constant power, and the amount of nitrogen oxides (NOx) emitted is estimated based on the air-fuel ratio AF2 from the rear air-fuel ratio sensor 135b. Thus, by operating the engine 22 at a constant power during the NOx sensor 137 warm-up period, the operation of the engine 22 is stabilized, and the amount of nitrogen oxides (NOx) emitted based on the air-fuel ratio AF2 from the rear air-fuel ratio sensor 135b can be estimated more accurately. Therefore, it is possible to balance the warm-up of the NOx sensor 137 with more accurate detection of nitrogen oxide (NOx) emissions.

[0036] In the hybrid vehicle 20 of the embodiment, during a cold start of the engine 22, the required power Pe* for the engine 22 is set to a value Pe2 that is larger than the value Pe1 during a non-cold start. This allows the engine 22 to operate at a constant power output, with the required power Pe* being Pe2. The heating duty cycle D of the sensor heater 137a is limited until a certain amount of time is required for the condensate around the NOx detection sensor to evaporate. This suppresses adverse conditions such as NOx sensor 137 malfunction caused by setting the heating duty cycle D of the sensor heater 137a to a high duty cycle while the NOx sensor 137 is wetted.

[0037] In the hybrid vehicle 20 of the embodiment, it is configured such that when the engine 22 is cold-started, the required power Pe* of the engine 22 is set to a value Pe2 that is larger than the value Pe1 when it is not cold-started, so that the engine 22 operates at a constant power output by outputting the required power Pe* of value Pe2. However, it is also possible to configure it such that even when the engine 22 is cold-started, the required power Pe* of the engine 22 is set to the value Pe1 when it is not cold-started, so that the engine 22 operates at a constant power output.

[0038] In the hybrid vehicle 20 of the embodiment, it is configured such that when the engine 22 is cold-started, the heating duty cycle D of the sensor heater 137a is limited until a certain amount of time is required for the condensate around the nitrogen oxide detection sensor to evaporate. However, it is also possible to configure it so that the heating duty cycle D is not limited when the engine 22 is cold-started.

[0039] In one embodiment, the engine unit is designed to be mounted in a hybrid vehicle in which an engine 22 and a motor MG1 are connected to a drive shaft 36 via a planetary gear 30, and a motor MG2 is connected to the drive shaft 36. A battery 50 is connected to the motors MG1 and MG2 via power lines. However, the engine unit may also be mounted in a so-called single-motor hybrid vehicle or a so-called series hybrid vehicle.

[0040] The correspondence between the main elements of the implementation method and the main elements of the invention described in the means for solving the problem section will be explained. In the implementation method, the motor MG2 corresponds to "electric motor", the engine 22 corresponds to "engine", the catalyst device 134 corresponds to "purification device", the rear air-fuel ratio sensor 135b corresponds to "air-fuel ratio sensor", the NOx sensor 137 corresponds to "nitrogen oxide detection sensor", and the engine ECU 24, motor ECU 40 and HVECU 70 correspond to "control device".

[0041] Furthermore, the correspondence between the main elements of the implementation method and the main elements of the invention described in the "Means for Solving the Problem" column is merely an example of how the implementation method is used to carry out the invention described in the "Means for Solving the Problem" column, and therefore does not limit the elements of the invention described in the "Means for Solving the Problem" column. That is, the interpretation of the invention described in the "Means for Solving the Problem" column should be based on the description in that column; the implementation method is simply a specific example of the invention described in the "Means for Solving the Problem" column.

[0042] The present invention has been described above using embodiments, but the present invention is not limited to such embodiments, and can of course be implemented in various ways without departing from the spirit of the present invention.

[0043] Industrial availability

[0044] This invention can be used in industries such as the manufacturing of hybrid vehicles.

[0045] Symbol Explanation

[0046] 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, MG1, MG2-Motor.

Claims

1. A hybrid electric vehicle comprising: an electric motor capable of inputting and outputting power for driving; an engine; a purification device mounted on the exhaust pipe of the engine and purifying the exhaust; an air-fuel ratio sensor mounted downstream of the purification device on the exhaust pipe; a nitrogen oxide detection sensor mounted further downstream than the air-fuel ratio sensor on the exhaust pipe and detecting nitrogen oxides in the exhaust; and a control device for controlling the engine and the electric motor, characterized in that... The control device performs sensor warm-up control, and during the execution of the sensor warm-up control, it estimates the amount of nitrogen oxide emissions based on the detection value from the air-fuel ratio sensor. During the sensor warm-up control, the engine and the electric motor are controlled to operate at a relatively low power constant power and drive until the nitrogen oxide detection sensor has completed warm-up.

2. The hybrid electric vehicle according to claim 1, characterized in that, When the control device starts the engine and executes the sensor warm-up control in a cold state, compared to when it starts the engine and executes the sensor warm-up control in a non-cold state (i.e., normal state), it controls the engine to operate at a constant power with a higher power.

3. The hybrid electric vehicle according to claim 1 or 2, characterized in that, have: A sensor heating device is used to heat the nitrogen oxide detection sensor. When the control device starts the engine and performs the sensor warm-up control in a cold state, 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.

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