Control method for vehicle and control device for vehicle

Abstract

A vehicle according to the present invention has an internal combustion engine (1), an electric heating catalyst (4) that is provided to an exhaust passage 2 of the internal combustion engine (1) and generates heat when energized, and a rear air / fuel ratio sensor (7) that is provided downstream of the electric heating catalyst (4) and comprises a heater that can raise the temperature of a sensor element to activate the sensor element when energized. When the electric heating catalyst (4) is energized to activate the electric heating catalyst, the energization start timing of the heater of the rear air / fuel ratio sensor (7) is delayed so as to be later than the energization start timing of the electric heating catalyst (4).

Description

Vehicle control method and vehicle control device

[0004]

[0001] The present invention relates to a vehicle control method and a vehicle control device.

[0002] For example, Patent Document 1 discloses an internal combustion engine having a catalytic converter including a three-way catalyst and a catalyst heater on the upstream side thereof, and an O2 sensor with a sensor heater located on the upstream side of the catalytic converter. The internal combustion engine of Patent Document 1 energizes the catalyst heater according to the temperature of the three-way catalyst, energizes the sensor heater according to the temperature of the O2 sensor, and starts the internal combustion engine when the three-way catalyst and the O2 sensor are each at or above the activation temperature.

[0003] However, in Patent Document 1, since the O2 sensor is located on the upstream side of the catalytic converter, there is a possibility that the sensor heater cannot be energized when there is an influence of condensed water.

[0004] Japanese Patent Laid-Open No. 8-74645

[0005] When activating the sensor element of the electric heating catalyst and the first air-fuel ratio sensor before starting the internal combustion engine, the vehicle of the present invention delays the timing of starting to energize the heater of the first air-fuel ratio sensor compared to the timing of starting to energize the electric heating catalyst. The first air-fuel ratio sensor is arranged on the downstream side of the electric heating catalyst, and by energizing the heater, it is possible to raise the temperature of its own sensor element and activate it.

[0006] According to the present invention, it is possible to activate the sensor element of the first air-fuel ratio sensor before starting the internal combustion engine, and it is possible to match the timing when the sensor element of the first air-fuel ratio sensor is activated with the timing when the electric heating catalyst is activated, and generally improve the fuel consumption (electricity cost) of the vehicle.

[0007] An explanatory diagram schematically showing the schematic configuration of a system of an internal combustion engine mounted on a vehicle to which the present invention is applied. A timing chart showing an example of changes in various state quantities at the start of vehicle travel.

[0008] Hereinafter, an embodiment of the present invention will be described in detail based on the drawings. FIG. 1 is an explanatory diagram schematically showing the schematic configuration of a system of an internal combustion engine 1 mounted on a vehicle to which the present invention is applied.

[0009] The internal combustion engine 1 is mounted in a so-called series hybrid vehicle (not shown) in which the drive wheels (not shown) are driven by an electric motor (not shown). In other words, the internal combustion engine 1 is mounted in the vehicle for power generation, and is operated to generate electricity using an on-board generator (not shown) when the battery charge level (battery SOC) of the on-board battery (not shown) becomes low. The internal combustion engine 1 is, for example, a spark-ignition internal combustion engine that uses gasoline as fuel and is connected to an on-board generator.

[0010] In the exhaust passage 2 of the internal combustion engine 1, a first catalyst 3, an electric heat-controlled catalyst (EHC) 4, and a second catalyst 5 are arranged from upstream in the direction of exhaust flow. The first catalyst 3 and the electric heat-controlled catalyst 4 constitute, for example, a manifold catalyst located near the outlet of the exhaust manifold in the exhaust passage 2. The second catalyst 5 is, for example, an underbody catalyst located under the floor of the vehicle.

[0011] The first catalyst 3 and the second catalyst 5 are, for example, three-way catalysts. A three-way catalyst can simultaneously purify NOx, HC, and CO in the exhaust gas with maximum conversion efficiency when the air-fuel ratio is within the so-called window centered around the stoichiometric air-fuel ratio.

[0012] The electrically heated catalyst 4 is a catalyst that generates heat when electricity is passed through it. For example, it has a structure in which a ceramic heating element that generates heat when electricity is passed through it is used as a catalyst support, and an appropriate catalytic metal that serves as a ternary catalyst or oxidation catalyst is coated onto its surface in a slurry.

[0013] Furthermore, in the exhaust passage 2, a front air-fuel ratio sensor 6 is provided upstream of the first catalyst 3 in the direction of exhaust flow, and a rear air-fuel ratio sensor 7 is provided downstream (outlet side) of the electric heated catalyst 4 in the direction of exhaust flow.

[0014] The front air-fuel ratio sensor 6 corresponds to the second air-fuel ratio sensor and is a so-called wide-range sensor that has a nearly linear output characteristic corresponding to the exhaust air-fuel ratio. The front air-fuel ratio sensor 6 is equipped with a heater that can be activated by increasing the temperature of its sensor element when energized. The front air-fuel ratio sensor 6's heater is energized after the internal combustion engine 1 has started.

[0015] The rear air-fuel ratio sensor 7 corresponds to the first air-fuel ratio sensor and is a sensor that detects only rich or lean air-fuel ratios by changing its output voltage ON / OFF (rich, lean) within a narrow range near the stoichiometric air-fuel ratio. The rear air-fuel ratio sensor 7 is equipped with a heater that can be activated by raising the temperature of its sensor element when energized. The rear air-fuel ratio sensor 7's heater is energized before the internal combustion engine 1 is started.

[0016] The rear air-fuel ratio sensor 7 is positioned upstream of the location where condensation occurs within the exhaust passage 2. Furthermore, the rear air-fuel ratio sensor 7 is positioned close to the electrically heated catalyst 4 and unaffected by condensation. In other words, the rear air-fuel ratio sensor 7 is positioned as close as possible to the electrically heated catalyst 4, where it is unaffected by condensation. Therefore, when the heater is energized to activate the sensor element, the rear air-fuel ratio sensor 7 can avoid the influence of condensation.

[0017] Here, the energization of the electrically heated catalyst 4 is controlled by the control unit 10, which acts as the control unit. In other words, the catalyst temperature of the electrically heated catalyst 4 can be controlled by the control unit 10. Furthermore, the energization of the front air-fuel ratio sensor 6 and the rear air-fuel ratio sensor 7 is also controlled by the control unit 10, which acts as the control unit. In other words, the temperature of the sensor elements of the front air-fuel ratio sensor 6 and the rear air-fuel ratio sensor 7 can be controlled by the control unit 10.

[0018] In other words, the vehicle has an internal combustion engine 1, an electrically heated catalyst 4, a front air-fuel ratio sensor 6, a rear air-fuel ratio sensor 7, and a control unit 10.

[0019] The control unit 10 can improve exhaust performance when starting the internal combustion engine 1 by activating the catalytic converter temperature of the electrically heated catalyst 4 prior to starting the internal combustion engine 1.

[0020] The control unit 10 is a well-known digital computer equipped with a CPU, ROM, RAM, and an input / output interface. Furthermore, when a predetermined power generation request is received, the control unit 10 drives the internal combustion engine 1 to start power generation by the generator.

[0021] The control unit 10 receives input from various sensors for various control and calculation purposes, including detection signals from the front air-fuel ratio sensor 6 and the rear air-fuel ratio sensor 7, as well as output signals from an airflow meter 11 that detects the amount of intake air from the internal combustion engine 1, and a crank angle sensor 12 that can detect the engine speed along with the crank angle of the crankshaft of the internal combustion engine 1.

[0022] Furthermore, when the control unit 10 energizes the electric heating catalyst 4 to warm it up (preheat) and activate it, it delays the timing of the start of energizing the heater of the rear air-fuel ratio sensor 7 compared to the timing of the start of energizing the electric heating catalyst 4.

[0023] Furthermore, the control unit 10 controls the amount of current supplied to the heater of the rear air-fuel ratio sensor 7 according to the temperature of the electric heating catalyst 4, so that the timing of activation of the electric heating catalyst 4 matches the timing of activation of the sensor element of the rear air-fuel ratio sensor 7. Normally, the time it takes for the electric heating catalyst 4 to activate from a cold state is longer than the time it takes for the sensor elements of the sensors to activate from a cold state.

[0024] Furthermore, the control unit 10 starts the internal combustion engine 1 after the catalyst temperature of the electrically heated catalyst 4 reaches its activation temperature and the sensor element of the rear air-fuel ratio sensor 7 reaches its activation temperature.

[0025] Figure 2 is a timing chart showing an example of changes in various state variables when a vehicle equipped with an internal combustion engine 1 starts driving. Time t1 in Figure 2 is the timing when the vehicle's ignition switch is turned on, and also the timing when preheating begins by energizing the electric heating catalyst 4. Time t2 in Figure 2 is the timing when the EHC heater duty cycle (EHC heater duty cycle), which is the duty cycle for energizing the electric heating catalyst 4, is reduced from the maximum duty cycle at startup. Time t3 in Figure 2 is the timing when the heater of the rear air-fuel ratio sensor 7 is energized. Time t4 in Figure 2 is the timing when the sensor elements of the electric heating catalyst 4 and the rear air-fuel ratio sensor 7 are activated. Time t5 in Figure 2 is the timing when the internal combustion engine 1 is started.

[0026] The electric heating catalyst 4 begins preheating at the maximum duty cycle at time t1, and at time t2, when the catalyst temperature has risen to a certain extent, it switches to a normal duty cycle (normal duty cycle) which is smaller than the maximum duty cycle, and continues preheating. The catalyst temperature of the electric heating catalyst 4 reaches the activation temperature at time t4.

[0027] The power supply to the heater of the rear air-fuel ratio sensor 7 begins at time t3, as shown by the solid line in Figure 2. Since the rear air-fuel ratio sensor 7 is located in a position unaffected by condensed water, power can be supplied to the heater even before the internal combustion engine 1 starts. The rear air-fuel ratio sensor heater duty cycle, which is the power supply duty cycle to the heater of the rear air-fuel ratio sensor 7, reaches its maximum duty cycle from time t3. The temperature of the sensor element of the rear air-fuel ratio sensor 7 (rear air-fuel ratio sensor temperature) reaches its activation temperature at time t4.

[0028] The power supply duty cycle for the heaters of the electrically heated catalyst 4 and the rear air-fuel ratio sensor 7 becomes a heat-maintaining duty cycle (heat-maintaining duty) from time t4 until time t5 when the internal combustion engine 1 is started for power generation, based on the battery request.

[0029] Furthermore, the catalyst temperature of the electric heating catalyst 4 and the temperature of the sensor element of the rear air-fuel ratio sensor 7 may fall below the activation temperature when the internal combustion engine 1 stops while the vehicle is running. Therefore, when energizing the electric heating catalyst 4 to warm it up after the internal combustion engine 1 stops while the vehicle is running, the timing of starting to energize the heater of the rear air-fuel ratio sensor 7 may be delayed compared to the timing of starting to energize the electric heating catalyst 4.

[0030] The battery SOC decreases from time t1 until time 5, when the internal combustion engine 1 starts, due to the start of power supply (preheating) to the electric heating catalyst 4 from time t1 and the start of power supply (preheating) to the rear air-fuel ratio sensor 7 from time t3.

[0031] Here, as shown by the dashed line in Figure 2 for the comparative example rear air-fuel ratio sensor heater Duty, if the power supply to the rear air-fuel ratio sensor 7 is started at time t1, the power supply time to the rear air-fuel ratio sensor 7 will be longer, resulting in a larger decrease in battery SOC. This is because the sensor element of the rear air-fuel ratio sensor 7 is activated earlier than the electrically heated catalyst 4, so power is supplied to maintain the sensor element of the rear air-fuel ratio sensor 7 at its activation temperature until the catalyst temperature of the electrically heated catalyst 4 is activated.

[0032] On the other hand, in the above-described embodiment, the activation of the sensor element of the rear air-fuel ratio sensor 7 does not precede the activation of the catalyst temperature of the electric heating catalyst 4, so the power required to maintain the temperature of the sensor element of the rear air-fuel ratio sensor 7 until the electric heating catalyst 4 is activated can be reduced.

[0033] In other words, in the above-described embodiment, the amount of power supplied to the heater of the rear air-fuel ratio sensor 7 before starting the internal combustion engine 1 can be minimized. To put it another way, in the above-described embodiment, the amount of power required to keep the sensor element of the rear air-fuel ratio sensor 7 at its activation temperature can be minimized. Therefore, in the above-described embodiment, battery power consumption is suppressed, the frequency of starting the internal combustion engine 1 for power generation can be reduced, and the EV driving range without power generation by the internal combustion engine 1 can be extended.

[0034] Furthermore, in the above-described embodiment, when the electric heating catalyst 4 is warmed up and activated before starting the internal combustion engine 1, the heater of the rear air-fuel ratio sensor 7 can be energized to activate the sensor element of the rear air-fuel ratio sensor 7. Moreover, in the above-described embodiment, by delaying the timing of the start of energizing the heater of the rear air-fuel ratio sensor 7 compared to the timing of the start of energizing the electric heating catalyst 4, it becomes possible to synchronize the timing of the activation of the sensor element of the rear air-fuel ratio sensor 7 with the timing of the activation of the electric heating catalyst 4, thereby improving the overall fuel efficiency (electricity consumption) of the vehicle.

[0035] In the above-described embodiment, the sensor element of the rear air-fuel ratio sensor 7 is activated simultaneously with the activation of the electric heating catalyst 4. Therefore, when the internal combustion engine 1 is started after the activation of the electric heating catalyst 4, it becomes possible to start air-fuel ratio feedback control according to the state of the electric heating catalyst 4 and the first catalyst 3 immediately after the internal combustion engine 1 is started. As a result, in the above-described embodiment, the exhaust performance during cold starting of the internal combustion engine 1 can be improved.

[0036] Although specific embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention.

[0037] For example, when the control unit 10 energizes the electric heating catalyst 4 to warm it up (preheat) and activate it, it may set the timing of starting to energize the heater of the rear air-fuel ratio sensor 7 to be simultaneous with or earlier than the timing of starting to energize the electric heating catalyst 4, thereby reducing the energizing duty cycle of the heater of the rear air-fuel ratio sensor 7 to less than the maximum. In this case as well, the control unit 10 can control the amount of current supplied to the heater of the rear air-fuel ratio sensor 7 according to the temperature of the electric heating catalyst 4 so that the timing of activation of the electric heating catalyst 4 matches the timing of activation of the sensor element of the rear air-fuel ratio sensor 7.

[0038] The above-described embodiment relates to a vehicle control method and a vehicle control device.

Claims

1. A vehicle control method comprising: an internal combustion engine; an electrically heated catalyst provided in the exhaust passage of the internal combustion engine and generating heat when energized; and a first air-fuel ratio sensor positioned downstream of the electrically heated catalyst and equipped with a heater capable of increasing the temperature of its own sensor element and activating it when energized, wherein, when activating the electrically heated catalyst and the sensor element of the first air-fuel ratio sensor before starting the internal combustion engine, the timing of starting to energize the heater of the first air-fuel ratio sensor is delayed compared to the timing of starting to energize the electrically heated catalyst.

2. The vehicle control method according to claim 1, wherein, if the timing of the start of energizing the heater of the first air-fuel ratio sensor is set to be simultaneous with or earlier than the timing of the start of energizing the electric heating catalyst, the energizing duty cycle of the heater of the first air-fuel ratio sensor is set to be less than the maximum.

3. A vehicle control method according to claim 1, wherein the amount of current supplied to the heater of the first air-fuel ratio sensor is controlled according to the temperature of the electric heating catalyst, and the timing of activation of the electric heating catalyst is synchronized with the timing of activation of the sensor element of the first air-fuel ratio sensor.

4. A vehicle control method according to claim 1, wherein the electric heating catalyst is energized so that the catalyst temperature of the electric heating catalyst reaches its activation temperature, and the internal combustion engine is started after the sensor element of the first air-fuel ratio sensor reaches its activation temperature.

5. The vehicle control method according to claim 1, wherein the first air-fuel ratio sensor is positioned upstream of the location where condensate is generated.

6. The vehicle control method according to any one of claims 1 to 5, wherein the internal combustion engine is mounted on the vehicle for power generation.

7. A vehicle control device comprising: an internal combustion engine; an electrically heated catalyst provided in the exhaust passage of the internal combustion engine and generating heat when energized; a first air-fuel ratio sensor positioned downstream of the electrically heated catalyst and equipped with a heater capable of increasing the temperature of its own sensor element and activating it when energized; and a control unit that, when activating the electrically heated catalyst and the sensor element of the first air-fuel ratio sensor before starting the internal combustion engine, delays the timing of the start of energizing the heater of the first air-fuel ratio sensor compared to the timing of the start of energizing the electrically heated catalyst.

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