Method and device for controlling internal combustion engine during acceleration

Abstract

In the present invention, a series hybrid vehicle includes: a power-generating motor generator (1) driven by an internal combustion engine (2); a drive motor generator (4); and a battery (5). The internal combustion engine (2) is provided with a turbocharger (11). When power generation by the internal combustion engine (2) is started due to a request to accelerate the vehicle, the ignition timing is retarded relatively further to the retarded side than a reference ignition timing in order to increase exhaust energy while the output of the battery (5) is used to perform accelerated driving for a length of time (t1 to t2) after the internal combustion engine (2) is started up. Boosting the rotational speed of the turbocharger (11) increases the output of the internal combustion engine (2) after the time (t2), yielding better acceleration performance.

Description

Method and device for controlling internal combustion engine during acceleration

[0001] The present invention relates to control of an electric power generating internal combustion engine in a series hybrid vehicle during acceleration.

[0002] In a series hybrid vehicle, the internal combustion engine drives a generator to generate electricity, which is temporarily stored in a battery and used to drive a traction motor. However, when a large amount of driving force is required, such as during full-throttle acceleration, the battery output alone is generally insufficient to provide the power required by the traction motor, so the vehicle is configured so that both the generator output and the battery output are supplied to the traction motor. In other words, when the vehicle accelerates, the internal combustion engine starts up due to a request to generate electricity, and the vehicle driving force required for acceleration is obtained using both the generator output and the battery output.

[0003] In such a configuration, if the output of the internal combustion engine (which essentially corresponds to the generator's power output) that starts and begins driving the generator in response to a request for vehicle acceleration does not rise quickly, the output (electric power) supplied to the traction motor during the vehicle acceleration process will be transiently insufficient, and the desired acceleration profile will not be achieved. In particular, if the internal combustion engine is equipped with a turbocharger, when the vehicle is requested to accelerate from a cold state, the rise in output will be slower than the original output characteristics after warming up, making the above-mentioned phenomenon more likely to occur.

[0004] Patent Document 1 discloses that in order to reduce the response delay of the turbocharger during acceleration, known as turbo lag, the ignition timing is set to MBT until the turbocharger begins supercharging work, and then the ignition timing is retarded once supercharging work begins.

[0005] However, if this technology were applied to an internal combustion engine for generating electricity in a series hybrid vehicle, the ignition timing would be retarded when supercharging begins, which would reduce the output of the internal combustion engine and ultimately the power output of the generator, which is undesirable.

[0006] JP 2012-163039 A

[0007] This invention relates to acceleration control of an internal combustion engine for generating electricity that is equipped with a turbocharger and drives a generator in a series hybrid vehicle. When the internal combustion engine starts generating electricity in response to a request for acceleration of the vehicle, after the internal combustion engine starts, the vehicle accelerates using battery output, and ignition timing is retarded relatively to the basic ignition timing to increase exhaust energy.

[0008] When a relatively high acceleration request is made, the internal combustion engine is started and power generation begins, but at this stage, acceleration driving using battery output is still possible. In other words, when the accelerator pedal is opened more and acceleration is requested, the internal combustion engine is started at a stage when there is still a margin of battery output compared to the motor output required for acceleration. Immediately after starting, ignition timing retardation is performed, which keeps the turbocharger rotation speed high and increases the temperature of the exhaust system, including the turbocharger. If ignition timing retardation is terminated in this state, high output is quickly obtained due to the supercharging effect, and high power generation output from the generator is achieved.

[0009] When the internal combustion engine starts, the generator begins generating electricity, but in the initial stage of acceleration, acceleration is achieved by battery output without relying on the generator's power output, so the reduction in output of the internal combustion engine due to ignition timing retardation does not pose a problem.

[0010] Therefore, even when acceleration of the vehicle is required from a state in which the internal combustion engine is cold, for example, a desired acceleration profile can be achieved.

[0011] 1 is a block diagram of a series hybrid vehicle; 2 is a block diagram of an internal combustion engine according to an embodiment; 3 is a flowchart showing a processing flow according to an embodiment; 4 is a time chart showing operation during acceleration of a vehicle; 5 is a block diagram showing (a) basic valve timing setting and (b) valve timing setting when ignition timing is retarded; 6 is a block diagram showing injection timing for homogeneous combustion and stratified combustion;

[0012] An embodiment of the present invention will now be described in detail with reference to the drawings. Fig. 1 schematically illustrates the configuration of a series hybrid vehicle to which the present invention is applied. The series hybrid vehicle includes a power-generating motor-generator 1 that primarily functions as a generator, an internal combustion engine 2 that serves as a power-generating internal combustion engine and drives the power-generating motor-generator 1 in response to a power demand, a traction motor-generator 4 that primarily functions as a motor and drives drive wheels 3, and a battery 5 that stores the generated power. While the figure illustrates the internal combustion engine 2 driving the power-generating motor-generator 1 via a gear train, the internal combustion engine 2 and the power-generating motor-generator 1 may alternatively be arranged in series (i.e., directly coupled) so as to rotate at the same speed without a gear train.

[0013] The electric power obtained by the internal combustion engine 2 driving the power generating motor generator 1 is stored in the battery 5 via an inverter device (not shown). The driving of the traveling motor generator 4 is controlled using the electric power of the battery 5. The electric power generated by the traveling motor generator 4 during regeneration is stored in the battery 5 via an inverter device (not shown).

[0014] The operation of the motor generators 1 and 4, the charging and discharging of the battery 5, and the operation of the internal combustion engine 2 are controlled by a controller 6. The controller 6 is composed of multiple controllers connected to each other so as to be able to communicate with each other, such as a motor controller 7 that controls the motor generators 1 and 4, an engine controller 8 that controls the internal combustion engine 2, and a battery controller 9 that manages the battery 5. Information such as an accelerator position signal (APO) generated by depression of an accelerator pedal (not shown) and vehicle speed (VSP) is input to the controller 6. The battery controller 9 also calculates the SOC of the battery 5 based on the voltage and current of the battery 5. When the SOC drops to a predetermined lower limit, the internal combustion engine 2 is started via the engine controller 8 to generate electricity. Such a series hybrid vehicle has two driving modes: an EV mode in which the vehicle runs on power 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. Even if the SOC is above the lower limit, the internal combustion engine 2 is driven and the vehicle runs in the HEV mode when the required driving force of the vehicle is relatively large. Therefore, the internal combustion engine 2 repeatedly performs combustion operation and stops of combustion operation while the main switch of the vehicle is on.

[0015] 2 shows the system configuration of the internal combustion engine 2. The internal combustion engine 2 is a four-stroke, spark-ignition internal combustion engine (a so-called gasoline engine) equipped with a turbocharger 11. A pair of intake valves 14 and a pair of exhaust valves 15 are arranged on the ceiling wall of each cylinder 13, and an ignition plug 16 is arranged in the center surrounded by these intake valves 14 and exhaust valves 15. A fuel injection valve 17 that supplies fuel into the cylinder 13 is provided below the intake valve 14. The ignition timing of the spark plug 16 and the injection timing and injection amount of fuel by the fuel injection valve 17 are controlled by the engine controller 8. Note that the internal combustion engine 2 may be a port injection type in which the fuel injection valve injects fuel into an intake port.

[0016] The intake valve 14 and the exhaust valve 15 are equipped with variable valve timing mechanisms 18, 19 that can change their opening timing (referred to as IVO and EVO, respectively) and closing timing (referred to as IVC and EVC, respectively). These variable valve timing mechanisms 18, 19 may be of any type, but for example, a mechanism that retards the phase of the camshaft relative to the phase of the crankshaft can be used.

[0017] The intake passage 21 has an intake collector 21a, and upstream of this intake collector 21a is provided an electronically controlled throttle valve 22 whose opening is controlled by a control signal from the engine controller 8. The compressor 11a of the turbocharger 11 is located upstream of the throttle valve 22, and upstream of this compressor 11a are provided an air flow meter 24, for example of a hot wire type, for detecting the intake air amount, and an air cleaner 25. Between the compressor 11a and the throttle valve 22 is provided an intercooler 26, for example of a water-cooled type, for cooling the high-temperature, high-pressure intake air. In addition, a recirculation valve 27 is provided to communicate the discharge side and intake side of the compressor 11a.

[0018] A turbine 11b of the turbocharger 11 is located in the exhaust passage 30, and a pre-catalyst device 31 and a main catalyst device 32, each of which is made up of a three-way catalyst, are disposed downstream of the turbine 11b. The main catalyst device 32 is disposed under the floor of the vehicle.

[0019] An air-fuel ratio sensor 33 that detects the air-fuel ratio is disposed upstream of the turbine 11b in the exhaust passage 30. The turbine 11b is provided with a wastegate valve 34 that bypasses part of the exhaust gas in accordance with the boost pressure in order to control the boost pressure. The wastegate valve 34 is an electrically operated valve whose opening is controlled by the engine controller 8.

[0020] The engine is also provided with an exhaust gas recirculation passage 35 that recirculates a portion of the exhaust gas from the exhaust passage 30 to the intake passage 21. The exhaust gas recirculation passage 35 is provided with, for example, a water-cooled EGR gas cooler 37 and an EGR valve 38. The engine controller 8 controls the opening of the EGR valve 38, thereby controlling the EGR rate.

[0021] In addition to the air flow meter 24 and air-fuel ratio sensor 33, detection signals from sensors such as a crank angle sensor 41 for detecting engine speed, a water temperature sensor 42 for detecting coolant temperature, a boost pressure sensor 43 for detecting boost pressure, and an atmospheric pressure sensor 44 for detecting atmospheric pressure are input to the engine controller 8. Based on these detection signals and various signals input via other controllers (for example, the accelerator opening APO, vehicle speed VSP, etc.), the engine controller 8 optimally controls the fuel injection amount and injection timing, ignition timing, the opening of the throttle valve 22, the phase of the variable valve timing mechanisms 18, 19, the boost pressure (i.e., the opening of the wastegate valve 34), the EGR rate, etc.

[0022] Next, acceleration control of the internal combustion engine 2 when the driver requests vehicle acceleration by relatively large depression of the accelerator pedal will be described. First, the operation of each component during vehicle acceleration will be described with reference to the time chart of FIG. 4. Column (a) of FIG. 4 shows the characteristics of the vehicle acceleration requested by the driver. The illustrated example shows so-called full-throttle acceleration, in which the requested acceleration rises sharply. In the latter half of the time chart, the requested acceleration decreases as the driver reduces the accelerator opening APO. Column (b) shows the output of the traction motor-generator 4 that drives the vehicle. For simplicity, various losses and efficiencies are ignored, and the power supplied to the traction motor-generator 4 is considered to be equivalent to the output (motor output) of the traction motor-generator 4. Characteristic line b1 in column (b) represents the requested motor output corresponding to the requested acceleration in column (a). Characteristic line b2 represents the characteristics of the motor output output from the traction motor-generator 4 in one embodiment. A characteristic line b3 indicates the motor output in a comparative example in which the acceleration control (i.e., ignition timing retard) of the present invention is not performed.

[0023] Column (c) shows the output of the battery 5. This basically shows the output supplied from the battery 5 to the traction motor-generator 4, but also includes the power supplied to the power-generator motor-generator 1 when the power-generator motor-generator 1 is powered. In the illustrated example, the start of the internal combustion engine 2 is requested in response to an acceleration request, and the internal combustion engine 2 is motored by the power-generator motor-generator 1 until time t1. The battery output from time t1 onwards is supplied from the battery 5 to the traction motor-generator 4. The maximum output of the battery 5 is managed by the battery controller 9. In the illustrated example, the output of the battery 5 increases from time t1 in response to the acceleration request, reaches the maximum output at time t3, and remains constant thereafter. The maximum output is set, for example, based on the SOC of the battery 5.

[0024] When the output of the battery 5 is limited to its maximum output in this way, the required motor output b1 in column (b) cannot be met, so the shortfall is made up by the output of the internal combustion engine 2, i.e., the output of the power generating motor generator 1.

[0025] Column (d) shows the rotation speed of the internal combustion engine 2, in other words, the rotation speed of the power generation motor generator 1. The characteristics of this rotation speed are controlled via the power generation motor generator 1. The initial rotation speed up to time t1 is the rotation speed of motoring due to power running of the power generation motor generator 1.

[0026] Column (e) shows the output (engine output) of the internal combustion engine 2 that drives the power-generating motor-generator 1. Here, various losses and efficiency are ignored, and the output of the internal combustion engine 2 is considered to be equivalent to the output (electric power) of the power-generating motor-generator 1. Characteristic line e1 in column (e) shows the output (engine required output) required of the internal combustion engine 2, which corresponds to the shortfall in the required motor output b1 after the output of the battery 5 reaches its maximum output, as described above. Characteristic line e2 shows the characteristics of the engine output (actual output) output from the internal combustion engine 2 in one embodiment. Characteristic line e3 shows the engine output in a comparative example in which the acceleration control (i.e., ignition timing retard) of the present invention is not performed. As shown by characteristic lines e2 and e3, the output of the internal combustion engine 2 rises at time t2, which is slightly delayed from the start of the internal combustion engine 2 (time t1), and power generation begins earlier than time t3, at which the required engine output (e1) begins to be generated.

[0027] Column (f) simply shows the crank angle position of the combustion center of gravity (so-called MB50) during the combustion cycle of the internal combustion engine 2. In comparative example f2, the engine is operated at the basic ignition timing without ignition timing retard, so MB50 is constant. In example f1, ignition timing retard is performed between times t2 and t4, and MB50 is relatively delayed. Here, time t4 is the time when the actual output (e2) of the internal combustion engine 2 intersects with the required engine output (e1) in column (e).

[0028] Column (g) shows the rotation speed of the turbocharger 11 of the internal combustion engine 2, with characteristic line g1 being the characteristic of the embodiment and characteristic line g2 being the characteristic of the reference example. In the characteristic line g1 of the embodiment, retarding the ignition timing between times t2 and t4 increases the exhaust energy given to the turbine 11b of the turbocharger 11, and the rotation speed of the turbocharger 11 increases.

[0029] 4, particularly when the internal combustion engine 2 is cold when acceleration of the vehicle is required, the output of the internal combustion engine 2 may become lower than the required engine output (e1), as shown by the characteristic line e3 in column (e). As a result, the motor output of the traction motor / generator 4 may not satisfy the required motor output (b1), as shown by the characteristic line b3 in column (b). As a result, the desired acceleration profile shown in column (a) may not be realized.

[0030] In contrast to this, in one embodiment, as shown in line (f), ignition timing retardation is performed by relatively retarding the ignition timing from the basic ignition timing immediately after starting the internal combustion engine 2. This increases the rotation speed of the turbocharger 11 as shown in line (g), and increases the output of the internal combustion engine 2 after the ignition timing retardation ends as shown by the characteristic line e2 in line (e). This increases the motor output of the traction motor / generator 4 as shown by the characteristic line b2 in line (b), making it possible to satisfy the required motor output (b1).

[0031] During the period from time t2 to time t4 when the ignition timing is retarded, the output of the internal combustion engine 2 is reduced by the ignition timing retard, as shown in (e). However, during this period, no output from the internal combustion engine 2 is required during the first half of the period from time t2 to time t3, and the required output is relatively low during the second half of the period from time t3 to time t4, so the reduction in output from the internal combustion engine 2 due to the ignition timing retard does not pose a problem. In other words, there is no adverse effect on the final motor output of the traction motor-generator 4.

[0032] At time t4, the actual output (e2) of the internal combustion engine 2 undergoing ignition timing retarding becomes equal to the required engine output (e1), and if the ignition timing retarding were continued, the actual output (e2) of the internal combustion engine 2 would become lower than the required engine output (e1). Therefore, in a preferred embodiment, the ignition timing retarding is continued until time t4, at which time the ignition timing retarding is terminated.

[0033] Next, Fig. 3 is a flowchart showing the flow of processing for the acceleration control described above. The routine shown in Fig. 3 is repeatedly executed by the controller 6. First, in step 1, a target motor output is calculated based on the accelerator opening APO determined by the driver's operation of the accelerator pedal, the vehicle speed VSP, etc. Next, in step 2, it is determined whether or not to start the internal combustion engine 2 depending on the degree of acceleration required. If it is determined that starting the internal combustion engine 2 is necessary, the process proceeds to step 3, where the internal combustion engine 2 is started.

[0034] Next, in step 4, the SOC of the battery 5 is read, and in step 5, the battery output that the battery 5 supplies to the traction motor / generator 4 is calculated. As described above, the vehicle accelerates and runs using the battery output until the battery output reaches its maximum output. Then, in the next step 6, the output required of the internal combustion engine 2 (required engine output) is calculated. This is calculated as the amount by which the battery output is insufficient to meet the required motor output.

[0035] In step 7, the conditions for permitting ignition timing retard are determined. Specifically, it is determined whether the temperature of the exhaust system including the turbocharger 11 is low, and ignition timing retard is permitted only when the temperature of the exhaust system is low. If the internal combustion engine 2 has been started repeatedly and is in a sufficiently warmed state, it is unlikely that the output of the internal combustion engine 2 will be insufficient when power generation is required due to acceleration.

[0036] If the determination in step 7 is YES, the process proceeds to step 8, where ignition timing retardation is initiated. Then, the process proceeds to step 9, where it is determined whether the actual output of the internal combustion engine 2, for which ignition timing retardation is being performed, is greater than the engine's required output. If the determination is YES, this means that the period is between times t2 and t4 in FIG. 4, so the process proceeds to step 10, where ignition timing retardation is continued. It is desirable to set the amount of ignition timing retardation relatively large within a range that does not impair combustion stability. If the determination in step 9 is NO, this means that the actual output of the internal combustion engine 2, for which ignition timing retardation is being performed, is equal to or less than the engine's required output, so the process proceeds to step 11, where ignition timing retardation is terminated. In other words, the basic ignition timing is set. This corresponds to time t4 in FIG. 4. In one embodiment, the actual output of the internal combustion engine 2 can be estimated from the rotation speed and torque of the electric power generating motor / generator 1. Alternatively, the torque of the internal combustion engine 2 may be detected by some kind of sensor.

[0037] In a preferred embodiment, the valve timing of the intake valve 14 can be changed using a variable valve timing mechanism 18 in addition to retarding the ignition timing. For example, in an internal combustion engine 2 equipped with a variable valve timing mechanism 18 on the intake valve 14 side, the basic valve timing setting during normal operation may be an early-closing valve timing setting in which the intake valve closing timing IVC is advanced to before bottom dead center (or a late-closing valve timing setting in which the IVC is delayed to after bottom dead center), as shown in Figure 5(a). Such early-closing / late-closing valve timing settings are known to be advantageous in terms of fuel economy and knocking suppression of the internal combustion engine 2.

[0038] In one embodiment, during the execution of the ignition timing retard between times t2 and t4, the intake valve closing timing IVC is set relatively closer to bottom dead center (BDC), as shown in Figure 5B, and after time t4, the normal early / late closing valve timing is set.

[0039] 5B, the air amount priority valve timing setting increases the charging efficiency and relatively increases the amount of exhaust energy given to the turbocharger 11. With this air amount priority valve timing setting, knocking is relatively more likely to occur, but since the ignition timing is retarded at the same time, knocking does not worsen.

[0040] In addition, the opening and closing timing of the exhaust valve 15 may also be changed via a variable valve timing mechanism 19 on the exhaust valve 15 side so as to maintain an appropriate valve overlap.

[0041] In a preferred embodiment, if the internal combustion engine 2 is capable of switching between stratified charge combustion and homogeneous charge combustion, the combustion mode may be switched to stratified charge combustion while the ignition timing is being retarded. Figure 6 is an explanatory diagram of the injection timing for homogeneous charge combustion and stratified charge combustion. In the case of homogeneous charge combustion, a homogeneous mixture is formed by injecting fuel during the intake stroke. In the case of stratified charge combustion, a portion of the fuel is injected during the intake stroke, and then a second fuel injection is performed near the top dead center of the compression stroke, thereby forming a stratified mixture. Stratified charge combustion allows for a larger ignition timing retard, and can supply more exhaust energy to the turbocharger 11.

[0042] Furthermore, in a preferred embodiment, while the ignition timing is being retarded, individual cylinder rich / lean control may also be performed, in which the air-fuel ratio of some cylinders is made rich and the air-fuel ratio of other cylinders is made lean so that the average air-fuel ratio of all cylinders is equivalent to the stoichiometric air-fuel ratio. With this individual cylinder rich / lean control, when the exhaust gas from the rich cylinder and the exhaust gas from the lean cylinder merge, an oxidation reaction of unburned components occurs, raising the exhaust gas temperature. This is therefore advantageous for increasing the rotation speed of the turbocharger 11.

[0043] While one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications are possible. For example, in the above embodiment, the end timing of the ignition timing retard is determined based on the magnitude relationship between the actual output of the internal combustion engine 2 during the ignition timing retard and the required engine output. However, the present invention is not limited to this. In this invention, what is important is to perform the ignition timing retard, which involves a reduction in output, at the beginning of acceleration when the vehicle is accelerated using battery output, and the timing of its end is not important. After the ignition timing retard is initiated upon starting the internal combustion engine, the ignition timing retard may be continued for an appropriate period of time. For example, the ignition timing retard may be ended after a predetermined time or a predetermined number of cycles have elapsed after starting the internal combustion engine. Furthermore, the end of the ignition timing retard may be determined based on an appropriate condition that is earlier than the time t4 described above.

Claims

1. A control method for an internal combustion engine during acceleration that is equipped with a turbocharger and is used to power a generator in a series hybrid vehicle, wherein when power generation by the internal combustion engine is initiated in response to a request for acceleration of the vehicle, after the internal combustion engine is started, the vehicle accelerates using battery output, and ignition timing is retarded relatively to the basic ignition timing in order to increase exhaust energy.

2. A control method for an internal combustion engine during acceleration as set forth in claim 1, wherein a required engine output required of the internal combustion engine is calculated from a required motor output required of the vehicle's traction motor and a battery output output from the battery, and the ignition timing retard is terminated when the actual output of the internal combustion engine becomes equal to or less than the required engine output.

3. The method for controlling an internal combustion engine during acceleration according to claim 1, wherein the ignition timing retard is terminated when a predetermined time has elapsed after the internal combustion engine has been started.

4. A control method for an internal combustion engine during acceleration as described in claim 1, which determines whether the temperature of the exhaust system including the turbocharger is low when acceleration of the vehicle is required, and permits the ignition timing retard only if the temperature of the exhaust system is low.

5. The control method for an internal combustion engine during acceleration as described in claim 1, wherein the internal combustion engine is equipped with a variable valve timing mechanism on the intake valve side that changes the intake valve closing timing, and during normal operation, the intake valve closing timing is set to an early closing / late closing valve timing setting that advances the intake valve closing timing before bottom dead center or late closing that delays the intake valve closing timing after bottom dead center, and while the ignition timing retard is being executed, the intake valve closing timing is set to an air volume priority valve timing setting that brings the intake valve closing timing relatively closer to bottom dead center.

6. A control method for an internal combustion engine during acceleration according to claim 1, wherein the internal combustion engine is capable of switching between stratified charge combustion and homogeneous charge combustion, and stratified charge combustion is used while the ignition timing is being retarded.

7. A control method for an internal combustion engine during acceleration as set forth in claim 1, wherein, during execution of the ignition timing retard, cylinder-specific rich / lean control is also performed to make the air-fuel ratio of some cylinders rich and the air-fuel ratio of other cylinders lean so that the average air-fuel ratio of all cylinders corresponds to the stoichiometric air-fuel ratio.

8. A control device for accelerating an internal combustion engine for generating electricity that is equipped with a turbocharger and drives a generator in a series hybrid vehicle, wherein, when the internal combustion engine starts generating electricity in response to a request for acceleration of the vehicle, after the internal combustion engine starts, the vehicle accelerates using battery output while retarding the ignition timing relative to the basic ignition timing in order to increase exhaust energy.

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