Method and device for controlling start of internal combustion engine

Abstract

An internal combustion engine (2) for power generation in a series hybrid vehicle has an EHC (17A) in an exhaust passage (11). When a main switch of the vehicle is turned on, preheating of the EHC (17A) is started, and when the temperature of the EHC (17A) reaches a start permission temperature (Tst), the start of the internal combustion engine (2) based on a start request is permitted. The catalytic activity capacity of the EHC (17A) is determined from the temperature of the EHC (17A) when the internal combustion engine (2) is started based on the start request. The amount of intake air at the time of starting the internal combustion engine (2) is adjusted so as to correspond to this catalytic activity capacity.

Description

Starting control method and device for internal combustion engine

[0001] This invention relates to a starting control technique for an internal combustion engine that includes an electrically heated catalyst in an exhaust passage, energizes the electrically heated catalyst before starting the internal combustion engine to perform preheating, and permits starting of the internal combustion engine when the catalyst reaches a certain level of activity.

[0002] As a catalyst used in the exhaust system of an internal combustion engine, an electrically heated catalyst (EHC) that can be heated up by energization, that is, the promotion of catalyst activation, is known. By starting energization of the electrically heated catalyst prior to starting the internal combustion engine, preheating of the catalyst can be performed, and emission reduction immediately after starting the internal combustion engine can be achieved.

[0003] Patent Document 1 discloses that in a configuration including a second catalyst downstream of a first catalyst that is an electrically heated catalyst, after preheating of the first catalyst is completed and the internal combustion engine starts, until the second catalyst reaches its activation temperature, the exhaust gas flow rate that can be purified by the first catalyst is restricted for a predetermined period.

[0004] However, Patent Document 1 does not describe the exhaust gas flow rate when starting the internal combustion engine. For example, in a configuration where the internal combustion engine is started based on a start request, the internal combustion engine does not necessarily start when the temperature of the electrically heated catalyst reaches a temperature corresponding to the partial activation state of the catalyst. That is, since the actual start is performed when a start request is made after starting is permitted, appropriate exhaust gas purification cannot be performed at the time of starting.

[0005] Japanese Unexamined Patent Application Publication No. 2018 - 105190

[0006] This invention is a starting control method for an internal combustion engine that includes an electrically heated catalyst in an exhaust passage, energizes the electrically heated catalyst before starting the internal combustion engine to perform preheating, and permits starting of the internal combustion engine based on a start request after preheating has started. The method includes determining the temperature of the electrically heated catalyst when the internal combustion engine starts based on a start request, and adjusting the intake air amount at the time of starting the internal combustion engine so as to correspond to the catalyst activation capacity at that time based on the temperature of the electrically heated catalyst.

[0007] By adjusting the intake air volume during engine startup to match the catalytic activity capacity of the electrically heated catalyst when the internal combustion engine actually starts based on the starting request, exhaust gas purification can be performed without excess or deficiency by the electrically heated catalyst.

[0008] Diagram illustrating the configuration of a series hybrid vehicle. Diagram illustrating the configuration of the intake and exhaust systems of an internal combustion engine. Flowchart showing the energization control of the EHC. Flowchart showing the starting control of the internal combustion engine. Characteristic diagram showing the relationship between the EHC preheating time and catalyst activity capacity. Characteristic diagram showing the relationship between catalyst activity capacity and the target exhaust flow rate at startup. Characteristic diagram showing the change in exhaust purification rate due to exhaust flow rate.

[0009] Hereinafter, an embodiment of this invention will be described in detail with reference to the drawings. Figure 1 schematically shows the configuration of a series hybrid vehicle as an example of a vehicle to which this invention is applied. The series hybrid vehicle is configured to include a power generation motor generator 1 that mainly operates as a generator, an internal combustion engine 2 used as a power generation internal combustion engine that drives the power generation motor generator 1 according to power demands, a drive motor generator 4 that mainly operates as a motor to drive the drive wheels 3, and a battery 5 that stores the generated electricity. The electricity obtained by the internal combustion engine 2 driving the power generation motor generator 1 is stored in the battery 5 via an inverter device (not shown). The drive motor generator 4 is driven and controlled using the power from the battery 5. The electricity generated during regeneration by the drive motor generator 4 is also stored in the battery 5 via an inverter device (not shown). In Figure 1, the internal combustion engine 2 and the power generation motor generator 1 are connected via a gear train, but a configuration in which the crankshaft of the internal combustion engine 2 and the rotating shaft of the power generation motor generator 1 are directly connected is also possible.

[0010] The operation of motor generators 1 and 4, the charging and discharging of battery 5, and the operation of internal combustion engine 2 are controlled by controller 6. Controller 6 consists of multiple controllers connected to each other so as to be able to communicate with one another, including motor controller 7 which controls motor generators 1 and 4, engine controller 8 which controls internal combustion engine 2, and battery controller 9 which manages battery 5. Information such as the opening of the accelerator pedal (not shown) and vehicle speed is input to controller 6. Battery controller 9 also determines the state of charge (SOC) of battery 5 based on the voltage and current of battery 5. When the SOC drops to a predetermined lower limit level, the internal combustion engine 2 is started via engine controller 8 and power generation is performed.

[0011] The driving modes of such a series hybrid vehicle include an EV mode in which the vehicle runs on electricity from the battery 5 without combustion operation of the internal combustion engine 2, and an HEV mode in which the vehicle runs while generating electricity through combustion operation of the internal combustion engine 2. Furthermore, even if the SOC is above the lower limit level, if the vehicle's required driving force is relatively large, the internal combustion engine 2 will be driven, and the vehicle will run in HEV mode. Therefore, the internal combustion engine 2 will repeatedly cycle between combustion operation and shutdown while the vehicle's main switch is on.

[0012] Figure 2 shows the configuration of the intake and exhaust systems of the internal combustion engine 2. The internal combustion engine 2 in one embodiment is a four-stroke cycle spark-ignition gasoline engine equipped with a turbocharger 13 as a supercharger, and is a so-called direct-injection type internal combustion engine in which fuel is injected directly into the cylinder by a fuel injector. A port injection type configuration is also possible.

[0013] The intake passage 12 of the internal combustion engine 2 extends through the compressor (not shown) of the turbocharger 13, and an electronically controlled throttle valve 21 that controls the amount of intake air is located downstream of the turbocharger 13. Between the turbocharger 13 and the throttle valve 21, there is a water-cooled intercooler 22, for example, to cool the supercharged intake air. The opening of the throttle valve 21 is controlled by the engine controller 8.

[0014] An exhaust turbine (not shown) of a turbocharger 13 is located in the exhaust passage 11 of the internal combustion engine 2, and an upstream catalytic converter 17 and a downstream catalytic converter 18 are located downstream of this exhaust turbine. The upstream catalytic converter 17 is a so-called manifold catalytic converter that is installed at the exhaust turbine outlet in the engine compartment of the vehicle, and the downstream catalytic converter 18 is a so-called underbody catalytic converter that is located under the floor of the vehicle.

[0015] The upstream catalytic converter 17 includes an electrically heated catalyst (hereinafter referred to as EHC) 17A and a three-way catalyst 17B arranged in series with each other, and both are housed in a single casing. In one embodiment, the EHC 17A is made by coating a three-way catalyst onto a porous monolithic ceramic carrier formed using a conductive ceramic material such as SiC, and the monolithic carrier itself generates heat when electricity is applied. A configuration using a metal carrier that generates heat when electricity is applied is also possible. The three-way catalyst 17B consists of a three-way catalyst using a general monolithic ceramic carrier. In the illustrated example, the three-way catalyst 17B is located upstream of the EHC 17A, but a configuration in which the three-way catalyst 17B is located downstream of the EHC 17A is also possible.

[0016] The downstream catalytic converter 18 includes a particulate filter (so-called GPF) 18A for collecting exhaust particulate matter and a three-way catalyst 18B using a general monolithic ceramic carrier. The particulate filter 18A may consist of, for example, a wall-flow type filter using a sealed monolithic ceramic body and may be coated with a catalytic metal.

[0017] An air-fuel ratio sensor 19 is positioned upstream of the catalytic converter 17 in the exhaust passage 11.

[0018] The engine controller 8 in Figure 1 receives detection signals from numerous sensors, either directly or via other controllers, including an air flow meter for detecting intake air volume, the air-fuel ratio sensor 19 for detecting exhaust air-fuel ratio, a crank angle sensor for detecting engine rotational speed, a water temperature sensor for detecting coolant temperature, a boost pressure sensor for detecting boost pressure, an accelerator pedal position sensor for detecting accelerator pedal depression, an atmospheric pressure sensor for detecting atmospheric pressure, and an ambient temperature sensor for detecting ambient temperature. Based on these detection signals and requests from other controllers, the engine controller 8 optimally controls the fuel injection amount and timing, ignition timing, throttle valve 21 opening, boost pressure, and the EGR rate in an exhaust recirculation device (not shown).

[0019] Next, the starting control of the internal combustion engine 2 after the vehicle has started to operate will be described. As described above, in one embodiment of the series hybrid vehicle, the internal combustion engine 2 is started in response to a power generation request. In order to purify exhaust gases by catalytic action from the initial stages of starting, in one preferred embodiment, preheating of the EHC 17A is started when the vehicle's main switch (so-called ignition switch) is turned on. When the temperature of the EHC 17A reaches the starting permission temperature Tst, which corresponds to the partially activated state of the catalyst, the starting of the internal combustion engine 2 is permitted.

[0020] After permission to start is granted, the internal combustion engine 2 is started in response to power generation requests, so the actual timing of when the internal combustion engine 2 starts is uncertain. Therefore, in one embodiment, the catalytic activity capacity of the EHC17A at the time of actual starting is determined, and the intake air volume (in other words, exhaust flow rate) at the time of starting the internal combustion engine 2 is adjusted to correspond to this catalytic activity capacity. By setting the exhaust flow rate per unit time to an appropriate value corresponding to the catalytic activity capacity, exhaust gas purification can be reliably achieved, and deterioration of emissions immediately after starting can be avoided.

[0021] The flowchart in Figure 3 shows the power supply control of the EHC17A. In step 1, the vehicle's main switch is turned on based on the driver's switch operation. In step 2, the power supply to the EHC17A is turned off. In step 3, it is determined whether the temperature of the EHC17A at that time (hereinafter referred to as the EHC temperature) is below the target preheating temperature Ttg. The target preheating temperature Ttg corresponds to the "second temperature" in the claim and is set to a temperature higher than the above-mentioned start permission temperature Tst, for example, around 500 to 600°C. If the EHC temperature is below the target preheating temperature Ttg, the process proceeds to step 4, and the power supply to the EHC17A is turned on. If the EHC temperature exceeds the target preheating temperature Ttg in step 3, the process proceeds to step 5 and beyond with the power supply to the EHC17A still off. The EHC temperature can be determined by methods such as directly detecting it by installing a temperature sensor on the EHC 17A, estimating it based on the amount of power supplied to the EHC 17A, or estimating it based on the resistance value of the EHC 17A. In one preferred embodiment, the EHC temperature is determined based on the amount of power supplied to the EHC 17A.

[0022] In step 5, it is determined whether the EHC temperature is equal to or greater than the above-mentioned start-up permission temperature Tst. If the answer is NO, the process returns to step 4 and the energization continues. If it is determined in step 5 that the EHC temperature is equal to or greater than the start-up permission temperature Tst, the process proceeds to step 6 to determine whether the EHC temperature has transitioned from a state below the start-up permission temperature Tst to a state above the start-up permission temperature Tst. That is, if the EHC temperature was below the start-up permission temperature Tst in the previous calculation cycle, and the EHC temperature is equal to or greater than the start-up permission temperature Tst in the current calculation cycle, the determination in step 6 is YES.

[0023] If the result of step 6 is YES, proceed to step 7 and turn on the start permission flag. Then, proceed from step 7 to step 8 and determine whether the EHC temperature exceeds the target preheating temperature Ttg. If the result of step 6 is NO, it means that the start permission temperature Tst has already been exceeded, so proceed from step 6 to step 8. If the EHC temperature in step 8 is less than or equal to the target preheating temperature Ttg, return from step 8 to step 4 and continue supplying power to EHC17A. If the EHC temperature in step 8 exceeds the target preheating temperature Ttg, return from step 8 to step 2 and turn off the power supply to EHC17A.

[0024] Once the EHC temperature reaches the target preheating temperature Ttg, the power supply to the EHC 17A is repeatedly switched on (step 4) and off (step 2) based on whether the EHC temperature is equal to or greater than the target preheating temperature Ttg. Therefore, the EHC temperature is maintained at the target preheating temperature Ttg until the internal combustion engine 2 starts. The preheating of the EHC 17A may be terminated at an appropriate timing after the start of the internal combustion engine 2, or it may be terminated simultaneously with the start of the internal combustion engine 2 (step 9).

[0025] The flowchart in Figure 4 shows the starting control of the internal combustion engine 2, which is executed in parallel with the energization control of the EHC17A. In the initial state when the vehicle's main switch is turned on, the internal combustion engine 2 is stopped (step 11). In step 12, calculations regarding the power generation request are performed based on the state of charge (SOC) of the battery 5 and the vehicle's driving status. Based on the results of these calculations, in step 13, it is determined whether or not there is a request to start the internal combustion engine 2 (in other words, a power generation request). If there is no request to start, the process in steps 12 and 13 is repeated, and the system waits until a request to start is made.

[0026] If a start request is received, proceed to step 14 to determine whether the start permission flag mentioned above is turned on. If the start permission flag is not turned on, return to step 11 and wait without starting until the start permission flag is turned on.

[0027] If a start request is made and the start permission flag is turned on, the process proceeds from step 14 to step 15, and the catalytic activity capacity of EHC17A at that point is calculated. The catalytic activity capacity is calculated based on the EHC temperature.

[0028] In one preferred embodiment, the catalytic activity capacity can be determined from the relationship shown in Figure 5. Figure 5(b) shows the relationship between preheating time and EHC temperature, and (a) shows the characteristics of the catalytic activity capacity corresponding to these. As shown in Figure 5, after the main switch is turned on and preheating begins, the EHC temperature reaches the target preheating temperature Ttg at time t1. In the interval up to time t1, the catalytic activity capacity is correlated with the EHC temperature, so the catalytic activity capacity can be determined based on the EHC temperature. After time t1, as described above, the current supplied to EHC 17A is controlled so that the EHC temperature maintains the target preheating temperature Ttg. However, at time t1, the entire EHC 17A is not in a fully activated state, so the catalytic activity capacity increases further as preheating continues. Therefore, as shown in Figure 5(a), in the interval from time t1 onward, the catalytic activity capacity can be determined from the EHC temperature and the preheating time up to that point. In other words, the EHC temperature corresponds to the temperature of a suitable representative point (for example, the center) within EHC17A, and even after the temperature of this representative point reaches the target preheating temperature Ttg, which corresponds to the completion of activation, localized temperature increases, i.e., the progression of activation, occur in other parts.

[0029] In addition, in this invention, the catalytic activity capacity may be estimated simply from the EHC temperature alone.

[0030] After calculating the catalytic activity capacity in step 15 of Figure 4, the process proceeds to step 16 to determine the target exhaust flow rate at startup corresponding to the catalytic activity capacity. Then, in step 17, the internal combustion engine 2 is started while adjusting the intake air volume to achieve this target exhaust flow rate.

[0031] Figure 6 shows the characteristics of the target exhaust flow rate at startup corresponding to the catalytic activity capacity. These characteristics are pre-programmed into the engine controller 8 in the form of a table or calculation formula, and the target exhaust flow rate at startup is determined based on the relationship shown in Figure 6. In other words, the relationship between the catalytic activity capacity and the exhaust flow rate that can be purified is determined in advance by experiment or simulation, and Figure 6 shows the exhaust flow rate that can be purified (exhaust flow rate per unit time) corresponding to the catalytic activity capacity.

[0032] When the internal combustion engine 2 is started, it is cranked at a predetermined constant rotational speed by the power of the power generation motor generator 1, and combustion operation begins when fuel injection and ignition are started during cranking. In other words, the internal combustion engine 2 is started. At this time, the opening of the throttle valve 21 is controlled based on the target exhaust flow rate. In other words, the intake air amount is controlled by the throttle valve 21 so that the target exhaust flow rate is achieved at the predetermined cranking rotational speed.

[0033] By controlling the intake air volume at startup to correspond to the catalytic activity capacity of the internal combustion engine 2 during actual startup, exhaust gas purification can be ensured from the initial stages of startup.

[0034] Figure 7 shows the relationship between the exhaust gas purification rate by EHC17A and the exhaust gas flow rate, with lines L1, L2, and L3 representing the characteristics of the exhaust gas purification rate when the exhaust gas flow rate is "high," "medium," and "low," respectively. For example, when the EHC temperature is a certain temperature T1, if the exhaust gas flow rate is "medium" (line L2), the target purification rate #1 can be met. However, if the exhaust gas flow rate is "high" (line L1), the exhaust gas purification rate decreases, and the target purification rate #1 cannot be met.

[0035] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment and various modifications are possible. For example, in the above embodiment, the initial starting of the internal combustion engine 2 after the vehicle's main switch is turned on was described, but the present invention can be similarly applied to subsequent restarts if preheating of the EHC 17A is performed. Furthermore, although a series hybrid vehicle was described as an example in the above embodiment, other types of hybrid vehicles may also be used, and it may even be applied to the starting of internal combustion engines other than those in hybrid vehicles.

Claims

1. An internal combustion engine starting control method comprising: an internal combustion engine equipped with an electrically heated catalyst in the exhaust passage; preheating the electrically heated catalyst by energizing it before starting the internal combustion engine; and allowing the starting of the internal combustion engine based on a starting request after preheating has started; wherein the temperature of the electrically heated catalyst when the internal combustion engine starts based on a starting request is determined, and the amount of intake air at the time of starting the internal combustion engine is adjusted based on the temperature of the electrically heated catalyst to correspond to the catalytic activity capacity at that time.

2. The method for controlling the starting of an internal combustion engine according to claim 1, wherein the starting of the internal combustion engine based on a starting request is permitted when the temperature of the electrically heated catalyst reaches a first temperature corresponding to the partially activated state of the catalyst.

3. The method for controlling the starting of an internal combustion engine according to claim 2, wherein when the temperature of the electric heating catalyst reaches a second temperature corresponding to an activated state that is higher than the first temperature before the start of the internal combustion engine, the energization of the electric heating catalyst is controlled to maintain the second temperature.

4. The method for controlling the starting of an internal combustion engine according to claim 3, wherein the catalytic activity capacity is determined from the temperature of the electric heated catalyst when the internal combustion engine is started until the temperature of the electric heated catalyst reaches the second temperature, and after the temperature of the electric heated catalyst reaches the second temperature and the temperature is maintained, the catalytic activity capacity is determined from the temperature of the electric heated catalyst when the internal combustion engine is started and the preheating time up to that point.

5. The starting control method for an internal combustion engine according to claim 1, wherein the relationship between the catalytic activity capacity and the exhaust gas flow rate that can be purified is determined in advance, and a target intake air amount corresponding to the catalytic activity capacity is determined based on this relationship.

6. A method for controlling the starting of an internal combustion engine according to claim 1, comprising motoring the internal combustion engine at a constant rotational speed during startup and controlling the throttle valve opening to adjust the amount of intake air.

7. The starting control method for an internal combustion engine according to claim 1, wherein the temperature of the electrically heated catalyst is the temperature of a representative point of the electrically heated catalyst obtained by detection using a temperature sensor, estimation based on the resistance value of the electrically heated catalyst, or estimation based on the amount of power input to the electrically heated catalyst.

8. The method for controlling the starting of an internal combustion engine according to claim 1, wherein the internal combustion engine is a power-generating internal combustion engine that drives a generator in a series hybrid vehicle.

9. An internal combustion engine starting control device comprising: an internal combustion engine equipped with an electrically heated catalyst in the exhaust passage; and a controller that energizes the electrically heated catalyst before starting the internal combustion engine to preheat it, and after preheating has started, permits starting the internal combustion engine based on a starting request, wherein the controller determines the temperature of the electrically heated catalyst when the internal combustion engine starts based on a starting request, and adjusts the amount of intake air at the time of starting the internal combustion engine to correspond to the catalytic activity capacity at that time based on the temperature of the electrically heated catalyst.

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