Control method for vehicle and control device for vehicle

Abstract

A vehicle comprises an internal combustion engine (1), a compressor (22) of a turbocharger (21) disposed in an intake passage (2) of the internal combustion engine (1), an intercooler (24) positioned on the downstream side of the compressor (22), an EGR passage (35) that recirculates a portion of exhaust gas to the upstream side of the compressor (22), and an EGR valve (36) that is disposed in the EGR passage (35) and controls the flow rate of recirculated EGR gas. When the temperature of the intercooler (24) is lower than a prescribed temperature set in advance, or when the humidity of intake air is higher than a prescribed value set in advance, the vehicle reduces the torque of the internal combustion engine (1) and controls the EGR valve (36) so as to achieve an EGR rate at which condensed water is not generated in a state of reduced torque.

Description

Vehicle control method and vehicle control device

[0008]

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

[0002] For example, in Patent Document 1, when recirculating exhaust through an exhaust recirculation passage during cold operation of an engine, the opening degree of a tumble control valve that generates a tumble flow in a combustion chamber is made smaller than the opening degree during warm operation of the engine, thereby increasing the flow velocity of the intake air flowing through the intake passage, blowing off the condensed water generated in the intake passage, and suppressing the freezing of the condensed water. A technique is disclosed.

[0003] However, Patent Document 1 only addresses countermeasures against condensed water when a part of the recirculated exhaust is returned to the intake manifold provided with the tumble control valve. That is, Patent Document 1 does not consider countermeasures against condensed water in a system where the recirculated exhaust is upstream of the supercharger and an intercooler is arranged downstream of the supercharger.

[0004] That is, in a system equipped with a supercharger and an intercooler in the intake system and performing exhaust gas recirculation (EGR) by returning a part of the exhaust upstream of the supercharger, there is room for further improvement in suppressing the generation of condensed water.

[0005] Japanese Unexamined Patent Application Publication No. 2010 - 163937

[0006] When the temperature of an intercooler arranged in the intake passage of an internal combustion engine is low or the humidity is high, the vehicle of the present invention reduces the torque of the internal combustion engine and controls an EGR valve arranged in an EGR passage that returns a part of the exhaust so that the EGR rate is such that condensed water does not occur in this state.

[0007] According to the present invention, when the temperature of the intercooler is low or the humidity is high, it is possible to suppress the generation of condensed water in the intercooler, and at the same time, it is possible to improve the fuel consumption by improving the thermal efficiency by introducing EGR gas into the intake passage.

[0008] Explanatory drawing schematically showing the system configuration of an internal combustion engine to which the present invention is applied. Timing chart showing changes in various parameters at the time of cold start of an internal combustion engine.

[0009] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0010] Figure 1 is a schematic diagram illustrating the system configuration of an internal combustion engine 1 to which the present invention is applied. The internal combustion engine 1 is, for example, installed in a so-called series hybrid vehicle for power generation, and has an intake passage 2 and an exhaust passage 3.

[0011] The intake passage 2 is connected to the combustion chamber 5 of the internal combustion engine 1 via the intake valve 4. The exhaust passage 3 is connected to the combustion chamber 5 of the internal combustion engine 1 via the exhaust valve 6. The internal combustion engine 1 is, for example, a direct injection type, and a fuel injector (not shown) and a spark plug 7 are provided for each cylinder to inject fuel into the cylinder.

[0012] The intake passage 2 is provided with an air cleaner 11 for collecting foreign matter in the intake air, an air flow meter 12 for detecting the amount of intake air, an electric first throttle valve 13, and an electric second throttle valve 14 located upstream of the first throttle valve 13.

[0013] The airflow meter 12 is located upstream of the second throttle valve 14. The air cleaner 11 is located upstream of the airflow meter 12. The first throttle valve 13 controls the amount of intake air to the internal combustion engine 1 according to the load. The second throttle valve 14 is equivalent to a pressure control valve and controls the intake pressure upstream of the compressor 22, which will be described later. The second throttle valve 14 is located upstream in the direction of intake air flow from the connection point between the intake passage 2 and the EGR passage 35, which will be described later.

[0014] The exhaust passage 3 is equipped with an upstream exhaust purification device 17 and a downstream exhaust purification device 18. The upstream exhaust purification device 17 consists of, for example, a three-way catalytic converter. The downstream exhaust purification device 18 also consists of, for example, a three-way catalytic converter and is located downstream of the upstream exhaust purification device 17.

[0015] Furthermore, a turbocharger 21 is provided in the intake passage 2 and the exhaust passage 3 as a supercharger. The turbocharger 21 has a compressor 22 provided in the intake passage 2 and a turbine 23 provided in the exhaust passage 3. The compressor 22 and the turbine 23 are arranged coaxially and rotate together as a single unit. The compressor 22 is positioned upstream of the first throttle valve 13 and downstream of the second throttle valve 14. The turbine 23 is positioned upstream of the upstream exhaust gas purification device 17.

[0016] Furthermore, an intercooler 24 is provided downstream of the first throttle valve 13 in the intake passage 2 to cool the intake air compressed (pressurized) by the compressor 22 and improve charging efficiency.

[0017] An exhaust bypass passage 31 is connected to the exhaust passage 3, which bypasses the turbine 23 and connects the upstream and downstream sides of the turbine 23. The downstream end of the exhaust bypass passage 31 is connected to the exhaust passage 3 at a position upstream of the upstream exhaust gas purification device 17. An electric wastegate valve 32 that controls the exhaust gas flow rate within the exhaust bypass passage 31 is located in the exhaust bypass passage 31. Reference numeral 33 in Figure 1 indicates the intake collector.

[0018] The internal combustion engine 1 is capable of exhaust gas recirculation (EGR), which involves introducing (recirculating) a portion of the exhaust gas from the exhaust passage 3 into the intake passage 2 as EGR gas. An EGR passage 35 is connected to both the intake passage 2 and the exhaust passage 3. The EGR passage 35 branches off from the exhaust passage 3 and is connected to the intake passage 2. One end of the EGR passage 35 is connected to the exhaust passage 3 at a position between the upstream exhaust gas purification device 17 and the downstream exhaust gas purification device 18, and the other end is connected to the intake passage 2 at a position downstream of the second throttle valve 14 and upstream of the compressor 22. The EGR passage 35 is equipped with an electric EGR valve 36 for adjusting (controlling) the flow rate of EGR gas within the EGR passage 35, and an EGR cooler 37 capable of cooling the EGR gas.

[0019] The internal combustion engine 1 is controlled by a control unit 41, which acts as a control unit, to prevent condensation from forming in the intercooler 24.

[0020] The control unit 41 corresponds to the control unit and is a well-known digital computer equipped with a CPU, ROM, RAM, and input / output interface. In addition to the airflow meter 12 described above, the control unit 41 receives detection signals (detected values) from various sensors, including a crank angle sensor 42 capable of detecting the engine speed along with the crank angle of the crankshaft of the internal combustion engine 1, an accelerator position sensor 43 that detects the amount the accelerator pedal is depressed (accelerator position APO) representing the required load state of the internal combustion engine 1, an atmospheric pressure sensor 44 that detects atmospheric pressure, a pressure sensor 45 that detects the intake pressure in the intercooler 24, a temperature sensor 46 that detects the temperature of the intercooler 24, a humidity sensor 47 that detects the humidity of the intake air in the intercooler 24, and a water temperature sensor 48 that detects the temperature of the coolant in the internal combustion engine 1. The control unit 41 uses the detected value of the accelerator position sensor 43 to calculate the required load (engine load) of the internal combustion engine 1.

[0021] The atmospheric pressure sensor 44 is located, for example, in the intake passage 2 upstream of the second throttle valve 14.

[0022] The pressure sensor 45, temperature sensor 46, and humidity sensor 47 are located, for example, in the intake passage 2 downstream (outlet side) of the intercooler 24. The pressure sensor 45 detects the pressure of the intake air that has passed through the intercooler 24. The temperature sensor 46 detects the temperature of the intake air that has passed through the intercooler 24. The humidity sensor 47 detects the humidity of the intake air that has passed through the intercooler 24.

[0023] The control unit 41 estimates the intake pressure inside the intercooler 24 from the intake pressure on the outlet side of the intercooler 24 detected by the pressure sensor 45.

[0024] The control unit 41 estimates the temperature of the intercooler 24 and the intake air temperature inside the intercooler 24 from the intake air temperature on the outlet side of the intercooler 24 detected by the temperature sensor 46.

[0025] The control unit 41 estimates the intake air humidity inside the intercooler 24 from the intake air humidity on the outlet side of the intercooler 24 detected by the humidity sensor 47.

[0026] The control unit 41 estimates whether the internal combustion engine 1 is warmed up or cold based on the coolant temperature of the internal combustion engine 1 detected by the water temperature sensor 48.

[0027] Based on detection signals from various sensors, the control unit 41 optimally controls the opening degree of the EGR valve 36, as well as the fuel injection amount and timing of the fuel injection valve (not shown), the ignition timing of the spark plug 7, the opening degree of the first throttle valve 13, the opening degree of the second throttle valve 14, the opening degree of the wastegate valve 32, and the opening degree of the EGR valve 36.

[0028] Then, based on detection signals from various sensors, the control unit 41 further reduces the torque of the internal combustion engine 1 to a level below the torque at which condensation is suppressed, if the temperature of the intercooler 24 is lower than a predetermined temperature, or if the humidity of the intake air is higher than a predetermined value. At the same time, it controls the EGR valve 36 so that the EGR rate is such that condensation does not occur when the torque of the internal combustion engine 1 is reduced in this way.

[0029] Furthermore, if the temperature of the intercooler 24 is lower than a predetermined temperature, or if the humidity of the intake air is higher than a predetermined value, the control unit 41 reduces the torque of the internal combustion engine 1 to below the upper limit (maximum value) of the torque at which condensation does not occur, and controls the EGR valve 36 so that the EGR rate is such that condensation does not occur when the torque of the internal combustion engine 1 is reduced in this way.

[0030] Here, the case where the temperature of the intercooler 24 is lower than a predetermined temperature means that it is lower than the temperature of the intercooler 24 when the internal combustion engine 1 is warmed up. In other words, the case where the temperature of the intercooler 24 is lower than a predetermined temperature means that the internal combustion engine 1 is in a cold state.

[0031] Furthermore, high humidity refers to situations where the amount of water vapor in the air surrounding the vehicle is high, such as during rainy or cloudy weather.

[0032] Furthermore, the EGR rate such that no condensation is generated when the torque of the internal combustion engine 1 is reduced is calculated based on atmospheric pressure, intake pressure in the intercooler 24, temperature of the intercooler 24, and intake air humidity in the intercooler 24.

[0033] Since the internal combustion engine 1 is used exclusively for power generation, it is basically operated at the operating point that provides the best fuel efficiency. The operating point is determined by the engine speed and torque. When reducing the torque of the internal combustion engine 1 to prevent condensation from forming, as described above, the torque is reduced relative to the torque at the best fuel efficiency point while maintaining the engine speed at the best fuel efficiency point.

[0034] In more detail, when the internal combustion engine 1 is cold, the torque is reduced compared to the torque under the operating conditions for the best fuel efficiency in order to prevent condensation from forming in the intercooler 24.

[0035] Furthermore, when the internal combustion engine 1 is cold, the torque is set to the level that provides the best fuel efficiency, according to the EGR rate which is set so that condensation does not occur in the intercooler 24. This torque is calculated by the control unit 41.

[0036] Figure 2 is a timing chart showing the changes in various parameters during cold-start of the internal combustion engine 1 when the temperature of the intercooler 24 is lower than a predetermined temperature. In Figure 2, the internal combustion engine 1 starts at time t0 and operates at a predetermined constant rotational speed from time t0 onward.

[0037] The CAC temperature, which is the temperature of the intercooler 24, gradually rises after the internal combustion engine 1 is started.

[0038] In the internal combustion engine 1 of the above-described embodiment, when the temperature of the intercooler 24 is low, the torque of the internal combustion engine 1 is set even lower than the torque at which condensation generation is suppressed. The characteristic curve Tp shown as a solid line in Figure 2 shows an example of the torque of the internal combustion engine 1 in the present invention, where the torque of the internal combustion engine 1 is further reduced below the torque at which condensation generation is suppressed when the temperature of the intercooler 24 is low. The characteristic curve Tc shown as a dashed line in Figure 2 shows an example of the torque of a comparative example in which the torque of the internal combustion engine 1 is set to a torque at which condensation generation is suppressed when the temperature of the intercooler 24 is low.

[0039] Furthermore, in the internal combustion engine 1 of the above embodiment, when the temperature of the intercooler 24 is low, the EGR rate is increased by the amount by which the torque of the internal combustion engine 1 is reduced. This is because reducing the torque of the internal combustion engine 1 makes it less likely for condensate to form, and as a result, more EGR gas can be introduced into the intake passage 2.

[0040] The characteristic curve Ep, shown as a solid line in Figure 2, shows an example of the EGR rate of the internal combustion engine 1 in the present invention, where the EGR rate is increased by the amount by which the torque of the internal combustion engine 1 is reduced when the temperature of the intercooler 24 is low. Here, the EGR rate shown by characteristic curve Ep is set so as not to generate condensate in the intercooler 24. The characteristic curve Ec, shown as a dashed line in Figure 2, shows an example of the EGR rate in a comparative example where the torque of the internal combustion engine 1 is set to a torque that suppresses the generation of condensate when the temperature of the intercooler 24 is low. Here, the EGR rate shown by characteristic curve Ec is set so as not to generate condensate in the intercooler 24. Note that the EGR rate shown as a dashed line in Figure 2 shows the EGR rate when there is no restriction to suppress the generation of condensate when the temperature of the intercooler 24 is low.

[0041] When the temperature of the intercooler 24 is low, the fuel consumption rate of the internal combustion engine 1 can be improved by controlling the EGR valve 36 so as to reduce the torque of the internal combustion engine 1 and to set the EGR rate such that no condensed water is generated in the state where the torque is reduced. The characteristic line Cp shown by the solid line in FIG. 2 shows an example of the fuel consumption rate in the present invention when the torque of the internal combustion engine 1 is the characteristic line Tp and the EGR rate of the internal combustion engine 1 is the characteristic line Ep. The characteristic line Cc shown by the broken line in FIG. 2 shows an example of the fuel consumption rate in a comparative example when the torque of the internal combustion engine 1 is the characteristic line Tc and the EGR rate of the internal combustion engine 1 is the characteristic line Ec. Note that the fuel consumption rate shown by the one-dot chain line in FIG. 2 shows the fuel consumption rate when no restriction is imposed to suppress the generation of condensed water when the temperature of the intercooler 24 is low.

[0042] In FIG. 2, when the temperature of the intercooler 24 rises and the EGR rate increases, the reduced torque is gradually increased to return to the original value. Times t2 and t3 are the timings when the torque is increased stepwise. The EGR rate temporarily decreases stepwise in correspondence with the increased torque at the timings of times t2 and t3.

[0043] As shown by the characteristic line Cp in FIG. 2, the internal combustion engine 1 of the above-described embodiment sets the torque of the internal combustion engine 1 lower than the torque at which the generation of condensed water is suppressed when the temperature of the intercooler 24 is low, while increasing the EGR rate of the internal combustion engine 1 by the amount by which the torque is set low, whereby the fuel consumption rate can be improved.

[0044] When the humidity of the intake air is high, the internal combustion engine 1 of the above-described embodiment sets the torque of the internal combustion engine 1 lower than the torque at which the generation of condensed water is suppressed, while increasing the EGR rate of the internal combustion engine 1 by the amount by which the torque is set low, whereby the fuel consumption rate can be improved in the same manner as when the temperature of the intercooler 24 is low.

[0045] In other words, in the hybrid vehicle of the above-described embodiment, the generation of condensed water in the intercooler 24 can be suppressed when the temperature of the intercooler 24 is low or when the humidity of the intake air is high, and fuel efficiency can be improved by improving the thermal efficiency of the internal combustion engine 1 through the introduction of EGR gas into the intake passage 2.

[0046] 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.

[0047] For example, the present invention is not limited to series hybrid vehicles, but can also be applied to hybrid vehicles that can drive the vehicle's drive wheels using an electric motor.

[0048] 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; a supercharger located in the intake passage of the internal combustion engine; an intercooler located downstream of the supercharger; an EGR passage for recirculating a portion of the exhaust gas upstream of the supercharger; and an EGR valve located in the EGR passage for controlling the flow rate of the recirculating EGR gas, wherein when the temperature of the intercooler is low or the humidity is high, the torque of the internal combustion engine is reduced, and the EGR valve is controlled so that the EGR rate does not generate condensate in this reduced torque state.

2. The vehicle control method according to claim 1, wherein the case where the temperature of the intercooler is low is a case where the temperature of the intercooler is lower than the temperature of the intercooler when the internal combustion engine is warmed up.

3. A vehicle control method according to claim 1, which calculates an EGR rate in which condensate is not generated based on atmospheric pressure, intake pressure in the intercooler, temperature of the intercooler, and intake air humidity in the intercooler.

4. The vehicle control method according to claim 1, wherein the internal combustion engine is mounted on a hybrid vehicle capable of driving the drive wheels using an electric motor, and the internal combustion engine is operated under the operating conditions that result in the best fuel efficiency.

5. The control method for the vehicle according to claim 4, wherein the hybrid vehicle is a series hybrid vehicle.

6. The vehicle control method according to claim 5, wherein the internal combustion engine is operated at the point of best fuel consumption, and when the torque of the internal combustion engine is reduced to prevent the generation of condensate, the torque of the internal combustion engine is reduced relative to the torque at the point of best fuel consumption while maintaining the engine speed at the point of best fuel consumption.

7. A vehicle control method according to claim 1, wherein, in the case of a cold engine, the torque of the internal combustion engine is reduced compared to the torque under the operating conditions for the best fuel efficiency, so as not to generate condensate.

8. A vehicle control method according to claim 1, which calculates the torque of the internal combustion engine that provides the best fuel efficiency, according to the EGR rate set so that condensate does not form when the engine is cold.

9. A vehicle control device comprising: an internal combustion engine; a supercharger located in the intake passage of the internal combustion engine; an intercooler located downstream of the supercharger; an EGR passage for recirculating a portion of the exhaust gas upstream of the supercharger; an EGR valve located in the EGR passage for controlling the flow rate of the recirculating EGR gas; and a control unit that reduces the torque of the internal combustion engine when the temperature of the intercooler is low or the humidity is high, and controls the EGR valve so that the EGR rate does not generate condensate when the torque is reduced.

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