Method and device for controlling acceleration of internal combustion engine

Abstract

In the present invention, a series hybrid vehicle includes: a motor generator (1) for power generation driven by an internal combustion engine (2); a motor generator (4) for traveling; and a battery (5). When power generation by the internal combustion engine (2) is started in response to a request for acceleration, acceleration traveling is performed using the output of the battery (5) after the internal combustion engine (2) has been started, while the rotational speed of the internal combustion engine (2) is increased through the traction operation of the motor generator (1) for power generation. At a time (t3) when the output of the battery (5) reaches the maximum output, the motor generator (1) for power generation is controlled from the traction operation to a regeneration side. By increasing the rotational speed in advance, the output of the internal combustion engine (2) promptly ramps up.

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, when a request for vehicle acceleration is made from a cold internal combustion engine, 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 describes a parallel hybrid vehicle in which the driving force is generated by combining the output of an internal combustion engine and the output of a motor, in which the motor is operated to compensate for the response delay of the turbocharger of the internal combustion engine, known as turbo lag.

[0005] However, even if such technology is applied to a series hybrid vehicle, which has limited battery output to begin with, the vehicle's acceleration performance cannot be improved unless the output of the internal combustion engine and, ultimately, the output of the generator can be increased.

[0006] Japanese Patent Application Publication No. 11-148388

[0007] This invention is a control method during acceleration of an internal combustion engine for generating electricity that drives a generator in a series hybrid vehicle, in which, when the vehicle is required to accelerate and the internal combustion engine begins to generate electricity, after the internal combustion engine is started, the vehicle is accelerated using battery output, and the rotation speed of the internal combustion engine is increased by powering the generator in conjunction with the combustion operation of the internal combustion engine.

[0008] When a relatively high acceleration request is made, the internal combustion engine is started to generate electricity, but in the early stages, 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, the internal combustion engine speed is increased by the generator powering. If the generator is controlled from powering to regenerative, i.e., generating, state when the internal combustion engine speed is high in this way, high output from the internal combustion engine can be obtained immediately, and high power output from the generator can be obtained.

[0009] When the internal combustion engine starts, the generator enters a power running state, but in the initial stage of acceleration, acceleration is achieved by battery output without relying on the generator's power output, so the lack of power output 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] The present invention relates to a series hybrid vehicle, an internal combustion engine, and a method for accelerating a vehicle.

[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 internal combustion engine 2 in the illustrated example is also equipped with variable valve timing mechanisms 18, 19 that can change the opening and closing timings of the intake valve 14 and the exhaust valve 15. The internal combustion engine 2 may be configured without the variable valve timing mechanisms 18, 19.

[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 depressing the accelerator pedal relatively deeply 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. Characteristic line b3 represents the motor output in a comparative example in which the acceleration control (i.e., the initial rotation speed increase) of the present invention is not performed.

[0023] Column (c) shows the rotational speed of the internal combustion engine 2, in other words, the rotational speed of the power-generator motor-generator 1. The rotational speed characteristics are controlled via the power-generator motor-generator 1. Characteristic line c1 shows the rotational speed characteristics in one embodiment. Characteristic line c2 shows the rotational speed characteristics in a comparative example in which the acceleration control of the present invention (i.e., the initial rotational speed increase) is not performed. In the characteristic line c1 of the embodiment and the characteristic line c2 of the reference example, the initial rotational speed increase until time t1 represents motoring by powering the power-generator motor-generator 1 to start the internal combustion engine 2. At time t1, the predetermined starting rotational speed is reached, and combustion operation of the internal combustion engine 2 begins with the start of fuel injection and ignition. In the comparative example c2, the rotational speed then increases as the internal combustion engine 2 continues combustion operation. In contrast, in the characteristic line c1 of the embodiment, the rotational speed increases by powering the power-generator motor-generator 1 while the internal combustion engine 2 continues combustion operation until time t3. More specifically, the rotation speed is gradually increased until time t2 after time t1, and is maintained constant from time t2 to time t3. The increase in rotation speed due to power running of the power generating motor generator 1 ends at time t3.

[0024] Column (d) shows the output of the battery 5. This basically represents 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 motor-generator 1 is powered. Characteristic line d1 represents the characteristics of one embodiment, and characteristic line d2 represents the characteristics of a comparative example in which the acceleration control (i.e., initial rotation speed increase) of the present invention is not performed. In the illustrated example, start of the internal combustion engine 2 is requested in response to an acceleration request, and the internal combustion engine 2 is motored for start-up by the power-generator motor-generator 1 until time t1. Furthermore, in the characteristic line d1 of the embodiment, the power-generator motor-generator 1 is powered to increase the rotation speed until time t3, resulting in a higher battery output than in the comparative example d2. Time t3 is the timing at which the output of the battery 5 reaches its maximum output in the characteristic line d1 of the embodiment. In the comparative example d2, the maximum output is reached slightly later than time t3. After reaching the maximum output, the output of the battery 5 is maintained at this maximum output until the end of acceleration. The maximum output is set, for example, based on the SOC of the battery 5.

[0025] 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.

[0026] Column (e) shows the output (engine output) of the internal combustion engine 2 that drives the generator 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 generator 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., initial speed increase) of the present invention is not performed. As shown by characteristic lines e2 and e3, in the comparative example in which the speed increase due to powering of the generator motor-generator 1 is not performed, the output of the internal combustion engine 2 rises slightly after the start of the internal combustion engine 2 (time t1), and power generation begins earlier than time t4, at which the engine required output (e1) begins to be generated.

[0027] Column (f) shows the rotation speed of the turbocharger 11 of the internal combustion engine 2, with characteristic line f1 being the characteristic of the embodiment and characteristic line f2 being the characteristic of the reference example. In the characteristic f1 of the embodiment, as shown in column (c), the rotation speed of the internal combustion engine 2 is higher than that of the comparative example, and therefore the rotation speed of the turbocharger 11 is higher.

[0028] 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.

[0029] In contrast to this, in one embodiment, as shown in section (c), the rotation speed of the internal combustion engine 2 is increased by powering the power-generating motor-generator 1 as soon as the internal combustion engine 2 starts combustion operation. As a result, the rotation speed of the internal combustion engine 2 is increased at the time when power generation starts (time t3), and the rotation speed of the turbocharger 11 also increases as shown in section (g), and the output of the internal combustion engine 2 after power generation starts increases as shown by the characteristic line e2 in section (e). As a result, the motor output of the traction motor-generator 4 increases as shown by the characteristic line b2 in section (b), and the required motor output (b1) can be satisfied.

[0030] Naturally, no power output is obtained while the rotation speed is increased by powering the power-generating motor-generator 1. However, during this period (times t1 to t3), as shown by the characteristic line e1 in column (e), no power output is required, and the vehicle can accelerate according to the acceleration request in column (a) using only the output of the battery 5. Therefore, there is no adverse effect on the final motor output of the traction motor-generator 4.

[0031] At time t3, when the output of the battery 5 including the power running of the power generating motor generator 1 reaches the maximum output, the increase in the rotation speed due to the power running of the power generating motor generator 1 is terminated.

[0032] 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.

[0033] Next, in step 4, the SOC of battery 5 is read, and in step 5, the battery output that battery 5 supplies to traction motor / generator 4 and power generation motor / generator 1 (in the case of power running) is calculated. As described above, the vehicle is accelerated and driven using the battery output until the battery output reaches its maximum output. Then, in the next step 6, the output required of internal combustion engine 2 (required engine output) is calculated. This is calculated to correspond to the shortfall in battery output compared to the required motor output.

[0034] In step 7, the conditions for permitting an increase in rotation speed due to powering of the power-generating motor-generator 1 are determined. Specifically, it is determined whether or not the temperature of the exhaust system including the turbocharger 11 is low, and an increase in rotation speed is permitted only if 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.

[0035] In another embodiment, a prediction is made to determine whether the output of the internal combustion engine 2 (characteristic line e3 in FIG. 4) when the rotation speed is not increased by powering the power-generating motor-generator 1 satisfies the required engine output (characteristic line e1 in FIG. 4) in response to the requested acceleration, and if the required engine output is not satisfied, an increase in the rotation speed of the internal combustion engine 2 by powering the power-generating motor-generator 1 is permitted.

[0036] If the determination in step 7 is YES, the process proceeds to step 8, where it is determined whether the battery output is less than the maximum output. If this determination is YES, the process proceeds to step 9, where the rotation speed of the internal combustion engine 2 is increased by powering the electric power generation motor generator 1. As a result, as shown in FIG. 4, at the beginning of acceleration, the rotation speed of the internal combustion engine 2 is increased while the vehicle is accelerated using battery output. If the determination in step 8 is NO, the process proceeds to step 10, where the powering of the electric power generation motor generator 1 is terminated and the vehicle is controlled to the regeneration side. As a result, electric power generation by the electric power generation motor generator 1 is started.

[0037] Although 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 internal combustion engine 2 is equipped with a turbocharger 11, but the present invention is equally applicable and useful to an internal combustion engine that does not have a supercharger. However, an internal combustion engine equipped with a turbocharger is more likely to suffer from transient power shortages when the engine is cold, etc.

[0038] Furthermore, in the above embodiment, the increase in rotation speed due to powering of the generator motor-generator 1 is terminated when the battery output reaches its maximum output, but the present invention is not limited to this. In this invention, what is important is to use the generator motor-generator 1 to increase the rotation speed of the internal combustion engine 2 in advance at the beginning of acceleration when the vehicle is accelerated using battery output, and the timing of the end of this process is not important. After the rotation speed increase begins upon start of the internal combustion engine, the rotation speed increase may be continued for an appropriate period of time. For example, the rotation speed increase may be terminated when a predetermined time or a predetermined number of cycles has elapsed after start of the internal combustion engine. Furthermore, the end of the rotation speed increase may be specified under an appropriate condition that is earlier than the time t3 described above.

Claims

1. A control method for an internal combustion engine for generating electricity that drives a generator in a series hybrid vehicle during acceleration, wherein when the vehicle is requested to accelerate and the internal combustion engine starts generating electricity, after the internal combustion engine is started, the vehicle accelerates using battery output, while increasing the rotation speed of the internal combustion engine by powering the generator in conjunction with the combustion operation of the internal combustion engine.

2. A method for controlling an internal combustion engine during acceleration as set forth in claim 1, wherein the rotation speed of the internal combustion engine is increased using surplus electric power remaining after subtracting the electric power required for acceleration from the electric power that can be output from the battery.

3. The method for controlling an internal combustion engine during acceleration according to claim 1, wherein the increase in the rotational speed of the internal combustion engine is terminated when the battery output reaches a maximum output.

4. The method for controlling an internal combustion engine during acceleration according to claim 1, wherein the increase in the rotational speed of the internal combustion engine is terminated when a predetermined time has elapsed since the increase in the rotational speed of the internal combustion engine began.

5. A control method for an internal combustion engine during acceleration as set forth in claim 1, comprising: determining an engine output required of the internal combustion engine from a motor output required of the vehicle's traction motor and a battery output required of the battery; determining whether the output of the internal combustion engine when the rotation speed is not increased by powering the generator for the requested acceleration satisfies the engine output requirement; and increasing the rotation speed of the internal combustion engine if the engine output requirement is not satisfied.

6. The method for controlling an internal combustion engine during acceleration according to claim 1, wherein the internal combustion engine is equipped with a turbocharger.

7. A method for controlling an internal combustion engine during acceleration in a hybrid vehicle as described in claim 6, which determines whether the temperature of the exhaust system including the turbocharger is low when acceleration of the vehicle is required, and allows an increase in the rotation speed of the internal combustion engine only if the temperature of the exhaust system is low.

8. A method for controlling an internal combustion engine during acceleration as set forth in claim 1, wherein, when a start of the internal combustion engine is requested, combustion operation is initiated while motoring the generator to a predetermined starting rotation speed, and after the start of combustion operation, the rotation speed is increased to a rotation speed relatively higher than the starting rotation speed.

9. A control device for accelerating an internal combustion engine for generating electricity that drives a generator in a series hybrid vehicle, which, when the vehicle is required to accelerate and the internal combustion engine begins to generate electricity, after the internal combustion engine starts, accelerates using battery output while increasing the rotation speed of the internal combustion engine by powering the generator in conjunction with the combustion operation of the internal combustion engine.

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