Control method for hybrid vehicle and control device for hybrid vehicle

Abstract

In this control method for a hybrid vehicle that comprises an engine and a battery, when it is necessary to drive the engine as a heat source for space heating of the hybrid vehicle, the output of the engine is reduced when the SOC of the battery is equal to or greater than a first threshold compared to when the SOC of the battery is lower than the first threshold, and the first threshold is changed in accordance with the cooling water temperature of the engine.

Description

Control Method for Hybrid Vehicle and Control Device for Hybrid Vehicle

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

[0002] A control method for a hybrid vehicle is known in which the output of an engine is reduced when the state of charge (SOC) of a battery becomes less than or equal to a threshold value during in-vehicle heating (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2022-75286

[0004] In the control method for a hybrid vehicle described in Patent Document 1, since the threshold value of the battery charge amount for reducing the output of the engine is a fixed value, even if the fuel consumption increases continuously due to the combustion requirement of the engine for heating when the battery charge amount is less than or equal to the fixed value, the output of the engine is not reduced and the engine continues to burn, which may reduce the fuel efficiency of the engine.

[0005] An object of the present invention is to provide a control method for a hybrid vehicle and a control device for a hybrid vehicle that can suppress a decrease in the fuel efficiency of an engine due to heating.

[0006] In one aspect of the present invention, when it is necessary to drive an engine as a heat source for heating a hybrid vehicle, when the SOC of the battery is greater than or equal to a first threshold value, the output of the engine is reduced more than when the SOC of the battery is less than the first threshold value, and the first threshold value is changed according to the coolant temperature of the engine.

[0007] It is a schematic configuration diagram of a vehicle. It is a block diagram of a control device for a vehicle. It is a flowchart of a control method for a vehicle. It is a diagram showing an operating point of an engine. It is a diagram showing the relationship between the outside air temperature and the air conditioning set temperature and the priorities of heating and fuel efficiency.

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a vehicle 10. The vehicle 10 is a so-called series-type hybrid vehicle that supplies power generated by a generator 33 using the power of an engine 31 to a battery 21 and drives wheels 25 to travel by rotating an electric motor 23 with the power of the battery 21.

[0009] The vehicle 10 is equipped with a drive unit 20, a power generator 30, an air conditioning unit 40, and a control device 50.

[0010] The drive unit 20 comprises a battery 21, an inverter 22, an electric motor 23, a reduction gear 24, and wheels 25. The inverter 22 converts the direct current input from the battery 21 into alternating current and outputs it to the electric motor 23. The inverter 22 also converts the alternating current input from the electric motor 23 into direct current and inputs it to the battery 21. The electric motor 23 is driven according to the input from the inverter 22 and generates the driving force and regenerative braking force of the vehicle 10. The reduction gear 24 comprises a transmission 24A and a differential gear 24B, and reduces the output of the electric motor 23 and transmits it to the wheels 25.

[0011] The power generation device 30 includes an engine 31, a speed increaser 32, a generator 33, and an inverter 34.

[0012] The engine 31 is mechanically connected to the generator 33 via a speed increaser 32. The engine 31 is used not as a power source to drive the vehicle 10, but as a power source to drive the generator 33 and generate electricity.

[0013] The generator 33 is configured to generate electricity by rotating using power from the engine 31, and to charge the battery 21. The generator 33 can use the power from the battery 21 to rotate the output shaft of the engine 31 to crank it when starting the engine 31, to perform motoring by rotating the engine 31 as a load to consume power when the State of Charge (SOC) of the battery 21 is high, and to close the throttle valve of the engine 31 to generate negative pressure in the intake passage when negative pressure is needed for brake pedal assist.

[0014] The air conditioning system 40 is a device that provides air conditioning for the interior of the vehicle 10, including heating, cooling, and ventilation. The air conditioning system 40 supplies warm air to the interior by blowing air into a circulation path of cooling water, which is heated by the engine 31. The air conditioning system 40 includes an air conditioning control unit 41, an HVAC (Heating-Ventilation-Air Conditioning) unit 42, and a cooling circuit 43.

[0015] The air conditioning control unit 41 is equipped with, for example, operating devices such as a touch panel, various buttons, and various switches, and is configured to allow operations such as switching between heating, cooling, and ventilation in the vehicle 10's interior, and changing the set temperature of the air conditioning.

[0016] The HVAC 42 supplies warm or cool air to the room in response to operations performed on the air conditioning control unit 41. Information about operations performed on the air conditioning control unit 41 (hereinafter referred to as air conditioning operation information) is output from the HVAC 42 to the control device 50. Air conditioning operation information includes, for example, the set temperature of the air conditioning and whether or not the defroster is operating. If the set temperature for heating is higher than the room temperature, or if the set temperature for heating is increased, and it is necessary to raise the coolant temperature, the HVAC 42 outputs a signal requesting a rise in coolant temperature due to heating to the HVAC 42 and the control device 50. The HVAC 42 and the engine 31 are connected by a cooling circuit 43 that circulates between them.

[0017] The cooling circuit 43 circulates the coolant for the engine 31 to cool the engine 31 and other equipment.

[0018] The control device 50 includes an ambient temperature sensor 60A, a cooling water temperature sensor 60B, and a controller 70.

[0019] The outside temperature sensor 60A detects the outside temperature of the vehicle 10.

[0020] The coolant temperature sensor 60B detects the temperature of the coolant in the engine 31.

[0021] Figure 2 is a control block diagram of the controller 70. The controller 70 controls the engine 31 and the generator 33, as well as the electric motor 23. The controller 70 is implemented by a computer equipped with, for example, a storage device 71 such as ROM (Read Only Memory) and RAM (Random Access Memory), an arithmetic unit 72 composed of a processor such as a CPU (Central Processing Unit) and a GPU (Central Graphics Processing Unit), and an input / output unit such as an input / output interface. The inverters 22 and 34, the engine 31, the air conditioning unit 40, the outside temperature sensor 60A, and the coolant temperature sensor 60B are electrically or communicatively connected to the controller 70.

[0022] The storage device 71 stores computer programs for operating the controller 70, various maps used for control, and various parameter values. Examples of maps stored in the storage device 71 include maps defining the relationship between the air conditioning set temperature, the outside temperature, and the target coolant temperature. Parameter values ​​stored in the storage device 71 include characteristic values ​​of the engine 31, the electric motor 23, and the generator 33, as well as various threshold values ​​used in control.

[0023] The calculation unit 72 includes a heating water temperature rise request determination unit 73, an operating point change threshold setting unit 74, an engine control unit 75, a target coolant temperature setting unit 76, a target coolant temperature arrival determination unit 77, and a power generation control unit 78.

[0024] The heating water temperature rise request determination unit 73 determines, based on air conditioning operation information and cooling water temperature rise request signals from the air conditioning unit 40, whether or not there is a request for a rise in the cooling water temperature due to heating, that is, whether or not it is necessary to drive the engine 31 as a heat source for heating.

[0025] The operating point change threshold setting unit 74 sets an operating point change threshold as a first threshold for determining whether or not to change the operating point of the engine 31, based on the coolant temperature of the engine 31. The operating point change threshold setting unit 74 decreases the operating point change threshold when the coolant temperature is low and increases the operating point change threshold when the coolant temperature is high. The operating point of the engine 31 is defined by the torque and rotational speed of the engine 31.

[0026] The engine control unit 75 controls the engine 31 based on the state of charge (SOC) of the battery 21 and the operating point change threshold. When the engine 31 needs to be driven as a heat source for heating, if the SOC of the battery 21 is below the operating point change threshold, the engine control unit 75 sets the operating point of the engine 31 to the normal operating point with the highest power generation efficiency, and allows the engine 31 to generate power at a fixed point using the generator 33 at the normal operating point. On the other hand, when the engine 31 needs to be driven as a heat source for heating, if the SOC of the battery 21 is above the operating point change threshold, the engine control unit 75 sets the operating point of the engine 31 to the low-output operating point, lowering the output of the engine 31 to a level lower than when the SOC of the battery 21 is below the operating point change threshold. The SOC of the battery 21 is obtained by the controller 70 either by acquiring it from the battery 21 or by calculating it from the temperature, voltage, and current of the battery 21.

[0027] The target coolant temperature setting unit 76 sets the target coolant temperature based on whether the defroster is operating, the air conditioning set temperature, and the outside temperature. The target coolant temperature is also a second threshold for stopping the engine 31 when the coolant temperature of the engine 31 reaches a temperature suitable for heating. In this embodiment, the target coolant temperature setting unit 76 sets a first target coolant temperature used when the defroster is operating, a second target coolant temperature used when the defroster is not operating but heating is prioritized, and a third target coolant temperature used when the fuel efficiency of the engine 31 is prioritized over heating. Fuel efficiency is the fuel consumption rate of the engine 31 per unit amount of fuel or per unit distance traveled by the vehicle 10. Each target coolant temperature is set according to the outside temperature, with higher temperatures when the outside temperature is low and lower temperatures when the outside temperature is high.

[0028] The first target coolant temperature is set based on the ambient temperature. If the defroster is operating, heating must be prioritized, so it is set higher than the third target coolant temperature, which is used when fuel efficiency is prioritized. The second and third target coolant temperatures are set based on the air conditioning set temperature and the ambient temperature. If the air conditioning set temperature is equal to or greater than the priority threshold, which is set as the third threshold for each ambient temperature, it is determined that heating should be prioritized over fuel efficiency, and the second target coolant temperature is set. If the air conditioning set temperature is less than the priority threshold, it is determined that fuel efficiency should be prioritized over heating, and the third target coolant temperature is set. The second target coolant temperature is set lower than the first target coolant temperature and higher than the third target coolant temperature.

[0029] The target coolant temperature determination unit 77 determines whether the engine 31's coolant temperature has reached the target coolant temperature based on the target coolant temperature and the engine 31's coolant temperature.

[0030] The power generation control unit 78 controls the generator 33 according to the operating point set by the engine control unit 75.

[0031] Figure 3 is a flowchart of the control performed by the controller 70. The control routines shown in the flowchart are pre-programmed and installed in the controller 70. The controller 70 repeatedly executes the following control routines according to the program, for example, in calculation cycles of about 10 to 100 milliseconds.

[0032] In step S1 of Figure 3, the controller 70 acquires the outputs of the air conditioning unit 40 and sensors 60A and 60B, namely air conditioning operation information, a coolant temperature rise request signal, the outside temperature, and the coolant temperature.

[0033] In step S2, the heating water temperature rise request determination unit 73 determines whether or not there is a request for a rise in the cooling water temperature due to heating, based on the air conditioning operation information and cooling water temperature rise request signal from the air conditioning unit 40. If it is determined in step S2 that there is no request for a rise in the cooling water temperature due to heating, the engine control unit 75 stops the engine 31 in step S13 and then terminates control. If it is determined that there is a request for a rise in the cooling water temperature due to heating, the process proceeds to step S3.

[0034] In step S3, the operating point change threshold setting unit 74 sets the operating point change threshold based on the coolant temperature of the engine 31. When the coolant temperature of the engine 31 is low, it is expected that the air conditioning system 40 will continue to request an increase in the coolant temperature due to heating, i.e., that the engine 31 will continue to burn due to heating. Therefore, by making the operating point change threshold smaller, the output of the engine 31 is reduced at an early stage at a low SOC, thereby suppressing the fuel consumption of the engine 31. On the other hand, when the coolant temperature of the engine 31 is high, it is expected that the engine 31 will soon stop burning due to heating. Therefore, by making the operating point change threshold larger, the engine 31 is operated at the normal operating point up to a high SOC, thereby suppressing the fuel consumption of the engine 31.

[0035] In step S4, the engine control unit 75 determines whether the State of Control (SOC) of the battery 21 is equal to or greater than the operating point change threshold. If, in step S4, it is determined that the SOC is not equal to or greater than the operating point change threshold, in step S5, the engine control unit 75 sets the operating point of the engine 31 to the normal operating point, and the power generation control unit 78 causes the generator 33 to generate power at the normal operating point.

[0036] On the other hand, if in step S4 it is determined that the SOC is above the operating point change threshold, in step S6 the engine control unit 75 sets the operating point of the engine 31 to a low-power operating point, and the power generation control unit 78 causes the generator 33 to generate low power at the low-power operating point. In this embodiment, when the SOC of the battery 21 is above the operating point change threshold, the engine control unit 75 reduces the output of the engine 31 along a line (hereinafter referred to as the α line) that connects the most efficient operating points for each output of the engine 31, as shown in Figure 4. The α line is also called the fuel efficiency optimal line because it connects the most efficient operating points for each output of the engine 31, i.e., the points with the best fuel efficiency on the isopower lines of the engine 31 for each output of the engine 31.

[0037] In step S7 of Figure 3, the target coolant temperature setting unit 76 determines whether or not the defroster is operating. If it is determined in step S7 that the defroster is operating, the target coolant temperature setting unit 76 sets a first target coolant temperature in step S8 based on the ambient temperature. The first target coolant temperature is set according to the ambient temperature, being higher when the ambient temperature is low and lower when the ambient temperature is high.

[0038] On the other hand, if it is determined in step S7 that the defroster is not operating, the target coolant temperature setting unit 76 determines in step S9 whether to prioritize heating over fuel consumption based on the air conditioning set temperature and the outside temperature. In this embodiment, the target coolant temperature setting unit 76 determines whether to prioritize heating over fuel consumption using the priority determination threshold shown in Figure 5. In Figure 5, a priority determination threshold for determining the priority between heating and fuel consumption is set for each outside temperature. If the air conditioning set temperature is equal to or greater than the priority determination threshold, heating is prioritized over fuel consumption. If the air conditioning set temperature is less than the priority determination threshold, fuel consumption is prioritized. If it is determined in step S9 that heating should be prioritized over fuel consumption, the target coolant temperature setting unit 76 sets a second target coolant temperature based on the outside temperature in step S10. Otherwise, in step S11, it sets a third target coolant temperature based on the outside temperature. The second target coolant temperature is set lower than the first target coolant temperature and higher than the third target coolant temperature.

[0039] In step S12, following steps S8, S10, and S11, the target coolant temperature determination unit 77 determines whether the engine coolant temperature is equal to or greater than the target coolant temperature. If it is determined in step S12 that the engine coolant temperature is not equal to or greater than the target coolant temperature, the process returns to step S3. If it is determined that the engine coolant temperature is equal to or greater than the target coolant temperature, in step S13 the engine control unit 75 stops the engine 31 and then terminates the control.

[0040] According to the embodiment as described above, the operation point change threshold of the SOC of the battery 21 for reducing the output of the engine 31 is changed according to the coolant temperature of the engine 31. Therefore, when the coolant temperature is low and the combustion requirement of the engine 31 due to heating continues, by reducing the operation point change threshold, the output of the engine 31 can be reduced at an early stage with a low SOC, and the decrease in the fuel consumption of the engine 31 due to heating can be suppressed.

[0041] According to the embodiment, when the SOC of the battery 21 is greater than or equal to the operation point change threshold, in order to reduce the output of the engine 31 along the α line connecting the most efficient operation points for each output of the engine 31, the fuel consumption suppression effect of the engine 31 can be enhanced.

[0042] According to the embodiment, when heating is prioritized, the target coolant temperature is increased compared to when heating is not prioritized. Therefore, the engine 31 is not stopped until a higher coolant temperature is reached, and the room temperature can be quickly increased by heating.

[0043] As described above, the best configuration, method, etc. for implementing the present invention are disclosed in the above description, but the present invention is not limited thereto. That is, the present invention is mainly illustrated and described with respect to specific embodiments, but without departing from the scope of the technical idea and purpose of the present invention, those skilled in the art can make various modifications to the above-described embodiments in terms of shape, material, quantity, and other detailed configurations. In addition, the descriptions limiting the shape, material, etc. disclosed above are exemplified for ease of understanding of the present invention and do not limit the present invention. Therefore, the description using the names of members with some or all of the limitations on those shapes, materials, etc. removed is included in the present invention.

[0044] The vehicle 10 may be a parallel hybrid vehicle, and the wheels 25 may be driven by the electric motor 23 and the engine 31. The vehicle 10 may be an all-wheel drive vehicle, a front-wheel drive vehicle, or a rear-wheel drive vehicle.

[0045] The transmission 24A may have a fixed gear ratio, or may be configured to be stepwise switchable to a plurality of gear ratios, or may be configured to be continuously switchable in gear ratio like a CVT (Continuously Variable Transmission).

[0046] The engine control unit 75 may reduce the output of the engine 31 not along the α line, or may partially reduce the output of the engine 31 along the α line.

[0047] The target coolant temperature setting unit 76 may set the first target coolant temperature and the second target coolant temperature to the same value, or may set the first target coolant temperature and the second target coolant temperature to different values at some outside air temperatures and to the same value at other outside air temperatures.

[0048] The coolant may be water, may be oil, or may be something else.

[0049] 10... vehicle (hybrid vehicle), 21... battery, 31... engine, 50... control device, 70... controller

Claims

1. A control method for a hybrid vehicle equipped with an engine and a battery, wherein, when it is necessary to drive the engine as a heat source for heating the hybrid vehicle, the output of the engine is reduced when the SOC of the battery is above a first threshold, compared to when the SOC of the battery is below the first threshold, and the first threshold is changed according to the coolant temperature of the engine.

2. A control method for a hybrid vehicle according to claim 1, wherein when the State of Control (SOC) of the battery is equal to or greater than the first threshold, the output of the engine is reduced along a line connecting the most efficient operating points for each engine output.

3. A control method for a hybrid vehicle according to claim 1 or claim 2, wherein when the coolant temperature of the engine is equal to or greater than a second threshold, the engine is stopped, and when heating is prioritized, the second threshold is raised higher than when heating is not prioritized.

4. A control method for a hybrid vehicle according to claim 3, wherein the case in which heating is prioritized is when the defroster is operating or when the air conditioning set temperature is above a third threshold set for each outside temperature.

5. A control device for a hybrid vehicle equipped with an engine and a battery, comprising a controller for controlling the engine, wherein, when it is necessary to drive the engine as a heat source for heating the hybrid vehicle, the controller reduces the output of the engine when the SOC of the battery is above a first threshold, compared to when the SOC of the battery is below a first threshold, and changes the first threshold according to the coolant temperature of the engine.

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