Hybrid vehicle control method and hybrid vehicle control device

Abstract

A method for controlling a hybrid vehicle comprising: a running electric motor; a battery for supplying electric power to the running electric motor; and a power generation engine capable of supplying electric power to the battery and the running electric motor, wherein, in an operating state in which a fuel consuming device that helps improve fuel consumption performance is not operating, the engine is operated at an engine speed higher than in an operating state in which the fuel consuming device is operating.

Description

Technical Field

[0001] The present invention relates to a control method and a control device for a hybrid vehicle. Background Art

[0002] JP2010-100103A discloses a method for operating an engine at an inefficient operating point (e.g., an operating point off the optimal fuel consumption line) to accelerate engine warm-up. This control method utilizes heat loss due to reduced engine efficiency to accelerate engine warm-up.

[0003] However, in the control disclosed in the above document, the engine is operated at an inefficient operating point until warm-up is completed, which degrades fuel consumption performance. Summary of the Invention

[0004] Therefore, an object of the present invention is to provide a control method and a control device capable of improving fuel consumption performance during engine warm-up.

[0005] According to one aspect of the present invention, a control method for a hybrid vehicle is provided. The hybrid vehicle includes: a propulsion motor; a battery that supplies power to the propulsion motor; and a generator engine capable of supplying power to the battery and the propulsion motor. In this control method, in an operating state in which fuel-consuming devices that contribute to improved fuel efficiency are not operating, the engine is operated at a higher engine speed than in an operating state in which the fuel-consuming devices are operating. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 This is a schematic diagram of the control system of a series hybrid vehicle.

[0007] Figure 2 It is a graph showing the optimal fuel consumption line.

[0008] Figure 3 This is a control block diagram for engine speed control.

[0009] Figure 4 Yes Figure 3 A control block diagram showing the processing contents of the α-line operation unit.

[0010] Figure 5 Yes Figure 3 A block diagram showing the processing contents of the engine speed coordination unit.

[0011] Figure 6 This is a timing chart when the control of this embodiment is executed.

[0012] Figure 7 This is a timing chart when warm-up is completed after the minimum hold time has elapsed.

[0013] Figure 8 This is a timing diagram when warm-up is completed before the minimum hold time elapses. DETAILED DESCRIPTION

[0014] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0015] (System Structure)

[0016] Figure 1 This is a schematic configuration diagram of a control system for a series hybrid vehicle, which is a premise of the present embodiment.

[0017] The series hybrid vehicle includes a driving motor 8, a battery 11 that supplies power to the driving motor 8, and a generator engine 13 that can supply power to the battery 11 and the driving motor 8. The power supplied to the battery 11 and the driving motor 8 is mainly generated by the generator motor 10 driven by the engine 13.

[0018] The control system of this series hybrid vehicle mainly includes a vehicle control module (VCM) 1, an engine control module (ECM) 12, a vehicle dynamics controller (VDC) 5, and a battery controller (LBC) 4. These are connected for information communication via a so-called controller area network (CAN).

[0019] The VCM 1 includes a required power generation calculation unit 2, which includes an α-line calculation unit 2A that calculates the optimal fuel consumption line (hereinafter also referred to as the α-line); a target power generation engine operation calculation unit 3, which includes an engine speed coordination unit 3A; and an engine mode determination unit 6 that determines the operating mode of the engine 13. The configuration within the VCM 1 is functionally represented as a block diagram and does not represent the physical structure. The α-line will be described later.

[0020] The motor drive target calculation unit 4 receives inputs of the wheel speed from the VDC 5, the accelerator position from an accelerator position sensor (not shown), the actual rotational speed of the traction motor (also referred to as the actual motor speed) from the motor inverter 7, and the upper limit motor torque from the required power generation calculation unit 2. Based on the input values, the required power generation calculation unit 2 calculates the target torque (also referred to as the target motor torque) and the required drive power generation for the traction motor 8 using a known method. The target motor torque is then input to the motor inverter 7, which then controls the traction motor 8 based on the target motor torque.

[0021] The power generation request calculation unit 2 receives inputs such as the engine coolant temperature and actual engine speed from the ECM 12, the battery 11's SOC, the upper limit for discharge power, and the upper limit for charge power from the LBC 4, and a quiet mode signal or a charging mode signal from a mode selector (not shown). Based on these inputs, the power generation request calculation unit 2 calculates the upper limit motor torque, target generated power, and other parameters. Details of the alpha-ray calculation unit 2A will be described later.

[0022] The target generator engine operation calculation unit 3 calculates the target engine speed and target engine torque based on the target generated power and the engine mode flag determined by the engine mode determination unit 6. The target engine speed is input to the generator inverter 9, which controls the generator motor 10 based on the target engine speed. The target engine torque is input to the ECM 12, which controls the engine 13 based on the target engine torque and the fuel cutoff flag determined by the engine mode determination unit 6.

[0023] (Overview of Engine Control)

[0024] As part of engine control for a series hybrid vehicle, the ECM 12 basically operates the engine 13 for charging based on the state of charge (SOC) of the battery 11. In this case, the ECM 12 prioritizes fuel efficiency and operates the engine 13 at the operating point on the optimal fuel efficiency line (also called the α line) where the fuel efficiency is lowest. The optimal fuel efficiency line is an operating line connecting the operating points with the highest fuel efficiency for each output.

[0025] Furthermore, for example, when the engine 13 is started from a cold state, control is known to operate the engine 13 at an operating point deviating from the α line to promote warm-up. This control reduces fuel efficiency, or in other words, increases heat loss, by operating the engine 13 at an operating point deviating from the α line. Consequently, the amount of heat received by the engine 13 is increased, promoting warm-up.

[0026] However, according to the above control, the operating point deviates from the α line, so that the fuel consumption performance is degraded.

[0027] Therefore, in the present embodiment, in order to suppress a decrease in fuel consumption performance, the engine 13 is operated at an operating point on the α line even in the operating state before warming up.

[0028] However, the engine 13 is equipped with a variable valve train (VTC), an exhaust gas recirculation system (EGR), and a knock control system as devices that contribute to improving fuel consumption performance (fuel consumption devices). The α line differs when these devices are in operation and when they are not in operation. For example, after a cold start of the engine 13, the α line differs between the operating state in which the fuel consumption devices such as VTC and EGR are not in operation and the operating state in which the fuel consumption devices are in operation after warm-up is completed. If the engine coolant temperature is compared between the state at medium water temperature after a cold start and before warm-up is completed and the state after warm-up, the following is shown: Figure 2 As shown, the operating point with the lowest fuel consumption rate at medium water temperature (point A in the figure) has a higher engine output than the operating point after warming up (point B in the figure). Here, the engine output is proportional to the engine speed.

[0029] Taking this into consideration, in this embodiment, the α line used is switched depending on whether fuel consuming devices are activated or deactivated to suppress degradation of fuel consumption during warm-up of the engine 13. The following describes in detail the engine control at medium water temperature in this embodiment.

[0030] (Engine control at medium water temperature)

[0031] Figure 3 This is a control block diagram of the α line calculation unit 2A and the engine speed coordination unit 3A for performing engine control at medium water temperature in this embodiment. Figure 3 A power generation coordination unit and an engine torque coordination unit are also shown, but these are not structures unique to the present invention.

[0032] The α-line calculation unit 2A outputs a fixed-point output to the power generation coordination unit, outputs the α-line rotational speed and the lower limit rotational speed to the engine rotational speed coordination unit 3A, and outputs the α-line torque to the engine torque coordination unit.

[0033] The fixed-point output is the engine output at the operating point of the engine 13 .

[0034] The α-line speed is the engine speed at the operating point when the engine 13 is operated at the operating point on the α-line. Figure 2 The α line speed is calculated based on the engine output at the operating point A. If it is after warming up, the α line speed is calculated based on Figure 2 The α-line speed is calculated using the engine output at the operating point B.

[0035] The lower limit speed is a lower limit value of the engine speed calculated by calculation described later.

[0036] The α-line torque is the engine torque at the operating point when the engine 13 is operated at the operating point on the α-line. The α-line torque is calculated based on the engine output at the operating point A or the operating point B on the α-line, for example, similar to the α-line speed.

[0037] The characteristic feature of this embodiment is that the α line calculation unit 2A calculates the lower limit rotation speed and outputs it to the engine rotation speed coordination unit 3A. The processing in the engine rotation speed coordination unit 3A will be described later.

[0038] Figure 4 2A is a control block diagram showing a function for calculating the lower limit rotation speed in the α-line calculation unit 2A.

[0039] Based on the engine coolant temperature, the α-line calculation unit 2A determines whether to use the α-line at an intermediate coolant temperature (i.e., an operating state in which fuel-consuming devices are not operating) or the α-line after warm-up (i.e., an operating state in which fuel-consuming devices are operating). The α-line flag is set to zero for the intermediate coolant temperature, and to one for the warm-up state. The engine state determination unit 40 reads the α-line flag and determines whether the engine 13 is in a combustion state or a non-combustion state. The non-combustion state includes idling. The engine state determination unit 40 sets the state flag to 1 if the engine is in a non-combustion state and to 0 if the engine is in a combustion state.

[0040] The initial warm-up determination unit 41 determines whether the initial warm-up in the current trip is complete. A single trip is defined as the period from ignition-on (i.e., hybrid system power is on) to ignition-off (i.e., hybrid system power is off). The initial warm-up determination unit 41 sets a warm-up completion flag to 1 if the initial warm-up in the current trip is complete, and sets the warm-up completion flag to 0 if the initial warm-up is not yet complete.

[0041] The flag determination unit 42 determines whether the following conditions hold: the status flag is zero and the warm-up completion flag is zero. If this condition holds, the lower limit setting unit 43 determines (sets) the lower speed limit. Furthermore, if the start-up reset flag, indicating the start of a trip, is input, the lower limit setting unit 43 clears the aforementioned flags.

[0042] When the lower speed limit is set, the rate processing unit 44 sets the engine speed change rate when the engine speed limit based on the lower speed limit is released after warm-up is completed, and outputs the setting information and the change rate to the switch 45.

[0043] Switch 45 selects the medium water temperature lower speed limit if a lower speed limit is set, and otherwise selects -9999 as the speed, outputting the selected value to engine speed coordination unit 3A. A speed of -9999 means there is no lower speed limit. The medium water temperature lower speed limit is, for example, approximately 2000 rpm.

[0044] Figure 5 3A is a control block diagram showing a function for setting the engine speed in the engine speed coordination unit 3A.

[0045] The engine speed coordination unit 3A determines the engine speed in three stages.

[0046] In the first stage, the engine speed based on the α line is compared with the engine speed limited by a limit value determined by the driving force and vehicle speed, and the lower one is selected. This limit value is the upper limit of the engine speed to make the engine operating sound less noticeable when the driving force is low or the vehicle speed is low. In this embodiment, the limit value that changes according to the driving force and vehicle speed is pre-mapped, and the limit value is determined based on this map.

[0047] In the second stage, the selected engine speed, the fuel consumption requirement lower speed limit, the charging mode lower speed limit, and the sound and vibration requirement lower speed limit are compared, and the highest engine speed is selected. The fuel consumption requirement lower speed limit is the lower limit engine speed determined based on the α line at the medium water temperature.

[0048] The charge mode lower speed limit is the lower limit of the engine speed when the charge mode (described later) is in operation. The charge mode is an operating mode, activated by the driver's switch operation, to increase the SOC of the battery 11. Even when the charge mode is not in operation, if the battery 11's SOC drops to the lower discharge limit, the engine 13 is controlled to increase power generation. However, in the charge mode, if the battery 11's SOC is below the upper charge limit, the engine speed is increased to increase power generation, regardless of the SOC.

[0049] The sound and vibration required lower limit speed is an engine speed at the lower limit that satisfies a requirement for suppressing noise and vibration (so-called sound and vibration requirement).

[0050] In the third stage, the heating request upper limit speed, the charging mode upper limit speed, the SOC management upper limit speed, and the engine speed selected in the second stage are compared, and the lowest engine speed is selected.

[0051] The heating request upper limit speed is the upper limit engine speed when performing heating control, which is used to raise the engine coolant temperature to meet the heating requirement. When operating at an operating point on the α line during heating control, the engine 13 generates less heat, making it difficult for the engine coolant temperature to rise. In other words, the engine 13 must operate for a longer time to raise the engine coolant temperature. Furthermore, this increased engine 13 operation time could lead to an excessive increase in the battery 11's SOC. Therefore, when performing heating control, to prevent an excessive increase in the battery 11's SOC, the heating request upper limit speed is set lower than the operating point on the α line. However, simply reducing the engine speed could degrade fuel efficiency. Therefore, the heating request upper limit speed is set at an engine speed that can suppress an excessive increase in the battery 11's SOC and a decrease in fuel efficiency. Specifically, the setting is based on the specifications of the engine 13, the capacity of the battery 11, and other factors.

[0052] The SOC management upper limit speed is the upper limit of the engine speed when performing SOC management control, which is control for converging the SOC of the battery 11 within the range of the dischargeable lower limit value to the chargeable upper limit value. SOC management control is commonly performed in hybrid vehicles, so its description is omitted.

[0053] The aforementioned heating-required upper speed limit, charging-mode upper speed limit, and SOC management upper speed limit are all engine speeds designed to prevent an excessive increase in the SOC of the battery 11. Specifically, in this embodiment, even if the fuel consumption-required lower speed limit is selected in the second phase, if the engine speed required to prevent an excessive increase in the SOC of the battery 11 is lower in the third phase, the engine speed ultimately selected will be the engine speed required to prevent an excessive increase in the SOC of the battery 11. Furthermore, the heating-required upper speed limit changes as the warm-up of the engine 13 is completed.

[0054] Figure 6 This is a timing chart when the control of the present embodiment is executed. In the engine output graph and the engine work graph in the figure, the solid line represents the case where the control of the present embodiment is executed, while the dashed-dotted line represents a comparative example, specifically, the case of warming up at the aforementioned operating point with poor fuel efficiency. As mentioned above, since engine output and engine speed are proportional, the engine output graph can be replaced with engine speed.

[0055] At time T1, a warm-up request is generated for the engine 13, and accordingly, the engine output increases. At this time, in the present embodiment, since the engine 13 is operating at an engine speed based on the α line for the intermediate water temperature or at a higher engine speed, the engine output (engine speed) is higher than that of the comparative example. The warm-up request continues until time T2 when the engine coolant temperature becomes slightly lower than the warm-up threshold. Furthermore, the termination of the warm-up request at time T2, even though the warm-up threshold has not been reached, is based on other controls performed in parallel with the control of the present embodiment. Therefore, if there is no such request, the warm-up request continues until the engine coolant temperature reaches the warm-up threshold. Furthermore, if the engine starts operating before time T1, this is an operation corresponding to a catalyst warm-up request flag set by a program different from the control of the present embodiment.

[0056] After stopping at time T2, the engine 13 is restarted at time T3. This is based on a request for SOC control of the battery 11, such as the selection of the charging mode. Since warm-up is not yet complete, the engine 13 is running at the same engine speed as at time T1-T2.

[0057] Then, at time T4, the engine coolant temperature reaches the warm-up threshold. However, the engine output does not immediately decrease. This is because a minimum hold time for the lower speed limit is established in this embodiment. This minimum hold time is required because, for example, when the engine is immediately started and warmed up, if the engine speed fluctuates rapidly, it can be inconvenient for the driver. The specific minimum hold time is set based on availability, for example, approximately 3-5 seconds.

[0058] After the minimum holding time has elapsed, the engine speed is reduced at the change rate set by the aforementioned rate processing unit 44 .

[0059] When warming up the engine 13 is complete at time T4, the initial warming-up completion flag becomes 1. Therefore, even if the engine coolant temperature again falls below the warming-up threshold during this trip, the control of this embodiment is not executed. This is because, once warming up is complete, if the engine speed varies each time the engine is started, it could cause discomfort to the driver.

[0060] Here, refer to Figure 7 、 Figure 8 A method of reducing the engine speed after the engine is warmed up will be described.

[0061] Figure 7 Indicates that warm-up is complete after the minimum hold time has elapsed. Figure 8 Indicates a situation where preheating is completed before the minimum hold time has elapsed.

[0062] When preheating is completed after the minimum hold time, if Figure 7 As shown in FIG, when the preheating is completed, the restriction of the lower speed limit based on the engine speed is released, and the engine speed is reduced. On the other hand, if the preheating is completed before the minimum holding time has passed, as shown in FIG. Figure 8 As shown in FIG, when the minimum holding time has passed, the limit of the lower speed limit based on the engine speed is released, and the engine speed is reduced. In addition, the timing of the minimum holding time starts each time the warm-up operation is started. For example, Figure 8 The timing starts when the engine 13 is started at time T3.

[0063] The speed of change when reducing the engine speed can be set arbitrarily. For example, the speed of change can be set to a level that does not cause discomfort to the driver or the like due to a sudden reduction in the engine speed.

[0064] (Effect)

[0065] As described above, according to this embodiment, a control method for a hybrid vehicle is provided. The hybrid vehicle includes: a propulsion motor 8; a battery 11 that supplies power to the propulsion motor 8; and a generator engine 13 that can supply power to both the battery 11 and the propulsion motor 8. In this control method, in an operating state where fuel consuming devices are not operating, which contributes to improved fuel efficiency, the engine is operated at a higher engine speed than in an operating state where the fuel consuming devices are operating. In other words, the lower limit speed of the engine 13 is increased in the operating state where the fuel consuming devices are not operating compared to the operating state where the fuel consuming devices are operating. This is because, in the operating state where the fuel consuming devices are not operating, for example, to avoid knocking, the ignition timing of the engine 13 is retarded compared to the operating state where the fuel consuming devices are operating. Raising the engine speed reduces the likelihood of knocking, thereby reducing the amount of retardation. According to this embodiment, fuel efficiency can be improved in the operating state where the fuel consuming devices are not operating, in other words, in an operating state where the engine coolant temperature is below a warm-up threshold.

[0066] In this embodiment, whether the fuel consuming device is in an operating state is determined based on the engine coolant temperature. This allows the use of a water temperature sensor included in a general engine 13 to determine whether the fuel consuming device is in an operating state.

[0067] In this embodiment, once the initial warm-up is complete after a trip begins, the engine speed is maintained in the operating state with fuel-consuming devices operating, even if the engine coolant temperature decreases during the trip. This prevents the driver from feeling uncomfortable due to the engine speed changing each time the engine 13 is started.

[0068] In this embodiment, if the engine speed is set in the operating state with fuel consuming devices not in operation, the engine speed is maintained for a predetermined minimum holding time. This can prevent the driver from feeling annoyed by the upper limit of the engine speed in a short period of time.

[0069] In this embodiment, the upper limit engine speed for suppressing an excessive increase in the state of charge (SOC) of the battery 11 is compared with the lower limit speed in an operating state with fuel-consuming devices not in operation, and the engine is operated at the lower engine speed. This can suppress an excessive increase in the SOC of the battery 11.

[0070] In this embodiment, the upper limit engine speed is an engine speed for suppressing an excessive increase in the SOC of the battery 11 when the engine 13 is operated to raise the engine coolant temperature in response to a heating request. Thus, even during operation with a low engine coolant temperature, an excessive increase in the SOC of the battery 11 can be suppressed while still satisfying the heating request.

[0071] While the embodiments of the present invention have been described above, the above embodiments merely illustrate a part of application examples of the present invention and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments.

Claims

1. A method for controlling a hybrid vehicle comprising: a running electric motor; a battery for supplying electric power to the running electric motor; a power generation engine capable of supplying electric power to the battery and the running electric motor; and a fuel consumption device provided by the engine and contributing to improved fuel consumption performance, wherein: The operating state of the engine includes an operating state in which the fuel consuming device is operating and an operating state in which the fuel consuming device is not operating. Based on the engine coolant temperature, determining whether the fuel consuming device is in an operating state; In the operating state in which the fuel consuming device is not working, the engine is operated at an operating point on the fuel consumption optimal line in the operating state in which the fuel consuming device is not working; in the operating state in which the fuel consuming device is working, the engine is operated at an operating point on the fuel efficiency optimal line in the operating state in which the fuel consuming device is working, and in the operating state in which the fuel consuming device is not working, the engine is operated at an engine speed higher than that in the operating state in which the fuel consuming device is working.

2. The control method for a hybrid vehicle according to claim 1, wherein: If the initial warm-up is completed after the start of a trip, the engine speed is maintained in the operating state in which the fuel consuming devices are operating even if the engine coolant temperature decreases during the trip.

3. The control method of a hybrid vehicle according to claim 1, wherein: If the engine speed in the operating state in which the fuel consuming device is not in operation is set, the engine speed is maintained for a predetermined minimum holding time.

4. The method for controlling a hybrid vehicle according to any one of claims 1 to 3, wherein: An upper limit engine speed for suppressing an excessive increase in the battery charge rate is compared with the engine speed in an operating state in which the fuel consuming device is not in operation, and the engine is operated at the lower engine speed.

5. The control method of a hybrid vehicle according to claim 4, wherein: The upper limit engine speed is an engine speed for suppressing an excessive increase in the charge rate of the battery when the engine is operated to increase the engine coolant temperature in response to a heating request.

6. The control method of a hybrid vehicle according to claim 1, wherein: The hybrid vehicle is configured as a series hybrid vehicle.

7. A control device for a hybrid vehicle comprising: a running electric motor; a battery for supplying electric power to the running electric motor; a power generation engine capable of supplying electric power to the battery and the running electric motor; and a fuel consumption device provided by the engine and contributing to improved fuel consumption performance, wherein: The operating state of the engine includes an operating state in which the fuel consuming device is operating and an operating state in which the fuel consuming device is not operating. The hybrid vehicle control device includes a control unit that controls the travel motor, the charge rate of the battery, and the engine. The control unit determines whether the fuel consuming device is in an operating state based on the engine coolant temperature, and in an operating state where the fuel consuming device is not operating, causes the engine to operate at an operating point on a fuel consumption optimal line in the operating state where the fuel consuming device is not operating; and in an operating state where the fuel consuming device is operating, causes the engine to operate at an operating point on a fuel efficiency optimal line in the operating state where the fuel consuming device is operating, and in an operating state where the fuel consuming device is not operating, causes the engine to operate at an engine speed higher than that in the operating state where the fuel consuming device is operating.

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