Battery control method for hybrid vehicle and hybrid vehicle

Abstract

To surely guarantee a guaranteed output as a battery output in the time of the battery low temperature, and reduce a frequency of start and stop of an internal combustion engine in the time of the normal temperature in a hybrid vehicle.SOLUTION: There is provided a hybrid vehicle in which EV travel, power generation by an internal combustion engine and the like are controlled such that the SOC of a battery is kept between the SOC upper limit target value SOCH and the SOC lower limit target value SOCL. The SOC upper limit target value SOCH is a constant value with respect to the battery temperature but the SOC lower limit target value SOCL becomes a higher value as the temperature becomes lower. Therefore, a corresponding battery output PL is equal to or greater than a guaranteed output Plim in the time of the battery low temperature. The SOC control range ΔSOC between the SOC upper limit target value SOCH and the SOC lower limit target value SOCL becomes wider as the battery temperature becomes higher. Therefore, the frequency of start and stop of the internal combustion engine is reduced.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a battery control technique for a hybrid vehicle. [Background technology]

[0002] There are several types of hybrid vehicles known, including series hybrids and parallel hybrids. Regardless of the type, in most cases, the vehicle's driving, which consumes battery power, and the power generation via the internal combustion engine are controlled so that the battery's SOC is maintained within a certain range. In other words, when the vehicle is driven by the traction motor (so-called EV driving), the battery's SOC decreases. When regeneration occurs due to deceleration of the vehicle, the battery's SOC increases. When the internal combustion engine is driven to generate power, the battery's SOC also increases. By repeating these operations, the battery's SOC is maintained within a certain range while the vehicle is driving.

[0003] Patent Document 1 discloses a battery control method that changes the target value of the SOC control center according to the battery temperature so that the battery output remains constant regardless of the battery temperature. Specifically, the target value of the control center is set so that the SOC control center is about 50% at room temperature and decreases as the battery temperature increases. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-345165 Summary of the Invention [Problem to be solved by the invention]

[0005] While Patent Document 1 describes the SOC control center as a characteristic that corresponds to battery temperature, it does not disclose that the SOC control range, i.e., the range between the upper and lower SOC target values, is changed according to battery temperature. It is therefore assumed that the SOC control range remains constant while the control center changes according to battery temperature. Therefore, for example, the maximum EV driving distance when the SOC is at the upper SOC target value is essentially constant, regardless of battery temperature. In other words, the frequency with which the internal combustion engine operates for power generation or charging is essentially the same whether the SOC control center is high when the battery is cold or low when the SOC control center is low.

[0006] The object of this invention is to provide battery control for a hybrid vehicle that can reliably ensure the minimum required battery output when the battery is low, while reducing the operating frequency of the internal combustion engine at normal or high temperatures. [Means for solving the problem]

[0007] The present invention provides a battery control method for a hybrid vehicle including an internal combustion engine, a generator that can be driven by the output of the internal combustion engine, a traction motor, and a battery that supplies power to the traction motor, in which vehicle travel by the traction motor and drive of the internal combustion engine are controlled so that the SOC of the battery is maintained between a predetermined SOC upper limit target value and a predetermined SOC lower limit target value, the method comprising: The SOC upper limit target value and the SOC lower limit target value are set in accordance with the battery temperature so that the SOC control range between the SOC upper limit target value and the SOC lower limit target value is relatively wide on the high temperature side, and the SOC lower limit target value is relatively high on the low temperature side. death, Furthermore, the SOC upper limit target value is set to a value according to the battery temperature so that it is relatively low on the high temperature side. do. [Effects of the Invention]

[0008] According to this invention, the SOC lower limit target value is set to a high value when the battery temperature is low, thereby ensuring the minimum required battery output. On the other hand, when the battery temperature is relatively high, the SOC lower limit target value is lowered and the SOC control range between the SOC lower limit target value and the SOC upper limit target value is expanded, thereby reducing the frequency of operation of the internal combustion engine for power generation or charging. Furthermore, by setting the SOC upper limit target value to a value corresponding to the battery temperature so that it is a relatively low value on the high temperature side, the progression of battery degradation can be suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating a system configuration of a hybrid vehicle according to an embodiment of the present invention; [Figure 2] This is a characteristic diagram showing the upper and lower limit SOC target values ​​and the corresponding battery output characteristics relative to the battery temperature. [Figure 3] This is a characteristic diagram showing the upper and lower limit SOC target values ​​and the corresponding battery output characteristics relative to the battery temperature when it is determined that the battery has deteriorated. [Figure 4] FIG. 4 is a diagram illustrating data showing a correlation between battery temperature and outside air temperature. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described in detail with reference to the accompanying drawings. Figure 1 shows a schematic configuration of a series hybrid vehicle as an example of a hybrid vehicle to which the present invention is applied.

[0011] A series hybrid vehicle is configured to include a power-generating motor-generator 1 that operates primarily as a generator, an internal combustion engine 2 used as a power-generating internal combustion engine that drives the power-generating motor-generator 1 in response to a power generation demand, a traction motor-generator 4 that operates primarily as a motor to drive drive wheels 3, and a battery 5 consisting of a secondary battery such as a lithium-ion battery that temporarily stores the generated power. In one embodiment, the power-generating motor-generator 1 is driven by the internal combustion engine 2 via a gear train 10. 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 traction motor-generator 4 is driven and controlled using the power from the battery 5. Electric power generated by the traction motor-generator 4 during regeneration is stored in the battery 5 via an inverter device (not shown).

[0012] 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 that they can 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 the accelerator pedal position and vehicle speed (not shown) 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. The battery 5 is also equipped with a battery temperature sensor 12 that detects the battery temperature. The vehicle is equipped with an outside air temperature sensor 13 that detects the outside air temperature. The controller 6 obtains information about the battery temperature and the outside air temperature from these sensors 12 and 13.

[0013] Furthermore, the hybrid vehicle of the embodiment is equipped with a communication device 11 as a so-called connected system that communicates with a cloud server (not shown) and other vehicles traveling in the vicinity. As will be described later, data relating to the correlation between the outside air temperature and the battery temperature can be exchanged via this communication device 11.

[0014] Such a series hybrid vehicle has two driving modes: an EV driving mode in which the vehicle runs on power from the battery 5 without combustion operation (i.e., power generation or charging) of the internal combustion engine 2, and an HEV driving mode in which the vehicle runs while generating power through combustion operation of the internal combustion engine 2. The battery controller 9 manages the charging and discharging of the battery 5 so that the SOC of the battery 5 is maintained between a predetermined SOC upper limit target value and a predetermined SOC lower limit target value. For example, if the SOC decreases due to EV driving and falls below the SOC lower limit target value, the internal combustion engine 2 is started via the engine controller 8 and power is generated. This power generation by the internal combustion engine 2 is terminated, for example, when the SOC approaches the SOC upper limit target value. Regenerative power is also controlled by an appropriate method so that the SOC of the battery 5 does not exceed the SOC upper limit target value.

[0015] Here, in one embodiment of the hybrid vehicle, the SOC lower limit target value and the SOC control range (the width between the SOC upper limit target value and the SOC lower limit target value) are variably set according to the battery temperature, and the SOC control range is relatively wider on the high temperature side, and the SOC lower limit target value is relatively higher on the low temperature side.

[0016] FIG. 2 shows the relationship between the SOC upper limit target value SOCH and the SOC lower limit target value SOCL and the battery temperature in one embodiment (left axis). As shown in the figure, the SOC upper limit target value SOCH is a constant value regardless of the battery temperature and is set to a value slightly lower than 100%, for example, between 90% and 80%. In contrast, the SOC lower limit target value SOCL is set to a lower value as the battery temperature increases. For example, at extremely low temperatures of approximately -30°C, the value is higher than 50%, and at extremely high temperatures of approximately 60°C, the value is lower than 50%. Note that in the illustrated example, the SOC lower limit target value SOCL is depicted as decreasing linearly with increasing temperature, but this does not necessarily have to be a linear characteristic in the present invention. Furthermore, the characteristic may be substantially constant at temperatures higher or lower than the illustrated temperature range.

[0017] As a result of the characteristic that the SOC upper limit target value SOCH remains constant and the SOC lower limit target value SOCL tends to decrease with respect to the battery temperature, the SOC control range ΔSOC between the SOC upper limit target value SOCH and the SOC lower limit target value SOCL becomes wider as the battery temperature increases, as shown by ΔSOC1, ΔSOC2, and ΔSOC3 in FIG. 2.

[0018] Figure 2 also shows the battery output [kW] versus battery temperature. For secondary batteries such as lithium-ion batteries, battery output generally decreases as the SOC decreases, and even for the same SOC, the battery output decreases as the battery temperature decreases. Line PH shows the battery output characteristic corresponding to the SOC upper target value SOCH, and line PL shows the battery output characteristic corresponding to the SOC lower target value SOCL (right axis). These battery outputs, particularly the battery output PL corresponding to the SOC lower target value SOCL, are equal to or greater than the guaranteed output Plim, the minimum required for a hybrid vehicle, even at extremely low temperatures, such as -30°C. In other words, the battery temperature characteristic of the SOC lower target value SOCL is determined so that the battery output PL does not fall below the guaranteed output Plim even at the lowest conceivable battery temperature. At the guaranteed output Plim, there is essentially no degradation in driving performance, and normal acceleration performance, for example, can be achieved.

[0019] In this way, in the above embodiment, the SOC lower limit target value SOCL is set relatively high when the battery temperature is low, so that a battery output equal to or greater than the minimum required guaranteed output Plim is guaranteed even when the battery temperature is below freezing. On the other hand, when the battery temperature is relatively high, the SOC control range ΔSOC is widened, so that, for example, long-distance driving in EV driving becomes possible, and the internal combustion engine 2 is started less frequently for charging. In other words, the internal combustion engine 2 does not start and stop frequently, which improves emissions from the internal combustion engine 2 and improves vehicle quality related to noise and vibration caused by starting and stopping the internal combustion engine 2.

[0020] Here, when the SOC of the battery 5 falls below the SOC lower limit target value SOCL and the internal combustion engine 2 is generating electricity, it is desirable to set the target rotation speed and target torque of the internal combustion engine 2 so that the noise caused by power generation does not exceed the background noise level generated by the vehicle. It is desirable to set the target rotation speed and target torque of the internal combustion engine 2 to an operating point as close as possible to the optimal fuel efficiency point of the internal combustion engine 2. During HEV driving, which involves the operation of the internal combustion engine 2, louder noise is generated than during EV driving due to vibrations and noise caused by combustion in the internal combustion engine 2, operating noise from the valve mechanism, etc., and operating noise from the gear train 10 and the power generation motor / generator 1. The noise caused by the operation of the internal combustion engine 2 generally becomes louder the higher the rotation speed of the internal combustion engine 2. Background noise generated by the vehicle mainly consists of airflow noise, tire noise, etc. generated while the vehicle is running, and the level of noise generated even during EV driving with the internal combustion engine 2 stopped essentially corresponds to the background noise level. By keeping the noise generated by the internal combustion engine 2 and the like due to power generation below the background noise level, the driver or passengers will feel less uncomfortable, and the quality of the vehicle will improve.

[0021] Since the background noise level generated by the vehicle correlates with vehicle operating conditions such as vehicle speed, it is possible to set the target rotation speed and target torque of the internal combustion engine 2 according to these vehicle operating conditions such as vehicle speed. Alternatively, for example, the background noise level may be measured using a microphone inside the vehicle cabin during the last EV run, and the operating point of the internal combustion engine 2 may be set accordingly.

[0022] Note that if the target rotation speed and target torque of the internal combustion engine 2 are set so that the noise caused by power generation does not exceed the background noise level generated by the vehicle, the power generation output may end up being insufficient. For this reason, it may be possible to control the noise caused by power generation so that it does not exceed the background noise level only when the battery temperature is relatively high (for example, 0°C or higher) and there is a margin for battery output, and to allow power generation that exceeds the background noise level when the battery temperature is low (for example, below freezing point).

[0023] As described above, power generation by the internal combustion engine 2 is basically initiated when the SOC of the battery 5 falls below the SOC lower limit target value SOCL, and the vehicle transitions from EV driving to HEV driving. However, in one embodiment, when the driver selects the EV fixed mode as the driving mode, or when the vehicle is traveling at a high speed under a high load (for example, while traveling on an expressway with an uphill slope), the transition to HEV driving may not be made, and EV driving may be permitted until the SOC of the battery 5 drops to a predetermined SOC allowable limit. The SOC allowable limit is set to a value lower than the SOC lower limit target value SOCL and corresponds to the limit SOC at which the internal combustion engine 2 can be started. Note that this SOC allowable limit may be a constant value that does not change with battery temperature, or may be set to a higher value as the battery temperature decreases, taking into account the fact that battery output decreases at low temperatures.

[0024] Furthermore, when EV driving is permitted with an SOC below the SOC lower limit target value SOCL, it is preferable to provide the driver with information about the possible EV driving distance from now when the SOC of the battery 5 approaches the above-mentioned SOC allowable limit, for example, by displaying on a screen or by voice, etc. The above-mentioned possible EV driving distance is calculated according to the battery temperature as the EV driving distance until the SOC limit is reached.

[0025] In this way, by allowing EV driving under conditions where the SOC temperature is below the target SOC lower limit SOCL in accordance with the driver's intention, it is possible to set the basic target SOC lower limit SOCL relatively high when the battery is cold, as shown in Figure 2.

[0026] Next, Figure 3 shows the relationship between the SOC upper limit target value SOCH and the SOC lower limit target value SOCL and the battery temperature when the battery 5 is determined to be degraded. When the battery 5 is degraded, as shown in the figure, the SOC upper limit target value SOCH is corrected so that the higher the battery temperature, the lower the value becomes. When the battery temperature is low, the SOC upper limit target value SOCH is approximately the same as when the battery is new (Figure 2), and gradually decreases as the battery temperature rises. This takes into account the fact that when the battery 5 is degraded, a high SOC when the battery is hot will likely further accelerate the degradation. The characteristics of the SOC lower limit target value SOCL are the same as when the battery is new.

[0027] Furthermore, the SOC control range ΔSOC becomes wider as the battery temperature increases, as shown by ΔSOC11, ΔSOC12, and ΔSOC13 in Figure 3. In other words, the change in the SOC upper limit target value SOCH with respect to battery temperature is more gradual than the change in the SOC lower limit target value SOCL. However, the SOC control range ΔSOC when the battery is high temperature (e.g., ΔSOC13) is relatively smaller than when the battery is new (e.g., ΔSOC3).

[0028] In this way, by changing the SOC upper limit target value SOCH in accordance with the battery temperature when the battery 5 is degraded, the progress of degradation of the battery 5 can be suppressed while maintaining the same effects as when the battery is new.

[0029] The degree of deterioration of the battery 5 can be measured by various known methods. For example, when the degree of deterioration exceeds a certain threshold, the settings of the SOC upper limit target value SOCH, etc. shown in Fig. 2 are switched to the settings of the SOC upper limit target value SOCH, etc. shown in Fig. 3.

[0030] Alternatively, the value of the SOC upper limit target value SOCH corresponding to each temperature may be changed continuously according to the measured degree of deterioration of the battery 5.

[0031] Although FIG. 3 shows the SOC upper limit target value SOCH as having a linear characteristic with respect to the battery temperature, the present invention is not limited to this, and the SOC upper limit target value SOCH may have a non-linear characteristic.

[0032] Next, FIG. 4 is an explanatory diagram showing the correlation between the battery temperature detected by the battery temperature sensor 12 and the outside air temperature sensor 13, respectively, and the outside air temperature. In one embodiment of a hybrid vehicle, the battery temperature and the outside air temperature are detected and data showing the correlation between the two is stored in a storage device inside or outside the vehicle. This data is used to estimate the battery temperature based on the outside air temperature. In FIG. 4, the horizontal axis represents the battery temperature and the vertical axis represents the outside air temperature, and a large number of measurement data points are shown. By storing a large number of data points, lines L1 and L2 that encompass the data points can be obtained, and for example, a line L0 can be obtained in the middle of the two points. Simply put, the battery temperature T2 relative to the outside air temperature T1 can be estimated using the correlation of this line L0.

[0033] The battery temperature estimated from the outside air temperature in this manner can be used, for example, to determine whether the battery temperature sensor 12 is abnormal, to provide a fail-safe in the event of a malfunction of the battery temperature sensor 12, or to correct or modify control based on the temperature detected by the battery temperature sensor 12.

[0034] In one embodiment, for example, while the vehicle is being driven, the sensors 12 and 13 repeatedly measure the battery temperature and the outside air temperature and generate data indicating the correlation between the two, and a large amount of data is stored in the storage device within the controller 6. Then, using the correlation between the two based on this data, estimation of the battery temperature based on the outside air temperature is performed in parallel.

[0035] Furthermore, in the above embodiment, data indicating the correlation between the measured battery temperature and the outside air temperature is transmitted to, for example, an external cloud server via the communication device 11. The cloud server side constructs the relationship between the battery temperature and the outside air temperature based on a large amount of data, and provides, for example, information on the battery temperature corresponding to the outside air temperature while driving to each vehicle, including the vehicle itself. By collecting a large amount of data in this way using an external cloud server or the like, it is possible to obtain a highly accurate estimation of the battery temperature. Data may also be collected for each vehicle model, and the correlation between the battery temperature and the outside air temperature may be determined for each vehicle model.

[0036] In this embodiment, even if the battery temperature sensor 12 fails, the above-described control of the SOC control range according to the battery temperature can be continued.

[0037] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment and various modifications are possible. For example, although the above embodiment has been described using a series hybrid vehicle as an example of a hybrid vehicle, the present invention can be widely applied to any type of hybrid vehicle as long as the battery is charged by power generated by an internal combustion engine. [Explanation of symbols]

[0038] 1...Power generating motor generator 2...Internal combustion engine 3...Drive wheels 4...Traction motor generator 5. Battery 6...Controller 7...Motor controller 8...Engine controller 9...Battery controller 11...Communication equipment 12...Battery temperature sensor 13...Outside air temperature sensor

Claims

1. A battery control method for a hybrid vehicle including an internal combustion engine, a generator that can be driven by output of the internal combustion engine, a traction motor, and a battery that supplies power to the traction motor, wherein driving of the vehicle by the traction motor and driving of the internal combustion engine are controlled so that the SOC of the battery is maintained between a predetermined SOC upper limit target value and a predetermined SOC lower limit target value, setting the SOC upper limit target value and the SOC lower limit target value according to the battery temperature so that an SOC control range between the SOC upper limit target value and the SOC lower limit target value is relatively wide on the high temperature side and the SOC lower limit target value is relatively high on the low temperature side; Furthermore, the SOC upper limit target value is set to a value according to the battery temperature so that it is a relatively low value on the high temperature side. A method for controlling a battery in a hybrid vehicle.

2. 2. The battery control method for a hybrid vehicle according to claim 1, wherein when the SOC of the battery falls below the target SOC lower limit value while the vehicle is running and power is generated by the internal combustion engine, a target rotation speed and a target torque of the internal combustion engine are set so that noise caused by power generation does not exceed a background noise level generated by the vehicle.

3. 3. A battery control method for a hybrid vehicle as described in claim 1 or 2, wherein the battery temperature and the outside air temperature are detected, data showing the correlation between the two is stored in a storage device inside or outside the vehicle, and this data is used to estimate the battery temperature based on the outside air temperature.

4. 4. The battery control method for a hybrid vehicle according to claim 1, wherein when a driver selects an EV fixed mode as the driving mode or during high-load high-speed driving, EV driving is permitted with the internal combustion engine stopped until the SOC of the battery falls to a predetermined SOC allowable limit that is lower than the SOC lower limit target value.

5. 5. The battery control method for a hybrid vehicle according to claim 4, further comprising providing a driver with information regarding a possible EV driving distance depending on the battery temperature when the SOC of the battery approaches the allowable SOC limit.

6. A battery control method for a hybrid vehicle comprising an internal combustion engine, a generator that can be driven by the output of the internal combustion engine, a traction motor, and a battery that supplies power to the traction motor, in which the vehicle's running by the traction motor and the driving of the internal combustion engine are controlled so that the SOC of the battery is maintained between a predetermined SOC upper limit target value and an SOC lower limit target value, setting the SOC upper limit target value and the SOC lower limit target value according to the battery temperature so that an SOC control range between the SOC upper limit target value and the SOC lower limit target value is relatively wide on the high temperature side and the SOC lower limit target value is relatively high on the low temperature side; When the driver selects an EV fixed mode as the driving mode, or during high-load high-speed driving, EV driving is permitted with the internal combustion engine stopped until the SOC of the battery decreases to a predetermined SOC allowable limit that is lower than the SOC lower limit target value, When the SOC of the battery approaches the SOC allowable limit, information regarding the possible EV driving distance depending on the battery temperature is provided to the driver. A method for controlling a battery in a hybrid vehicle.

7. an internal combustion engine; a generator that can be driven by the output of the internal combustion engine; A traction motor; a battery that supplies power to the drive motor; a controller that controls the vehicle's running by the driving motor and the drive of the internal combustion engine so that the SOC of the battery is maintained between a predetermined SOC upper limit target value and a predetermined SOC lower limit target value; A hybrid vehicle comprising: the controller sets the SOC upper limit target value and the SOC lower limit target value in accordance with the battery temperature so that an SOC control range between the SOC upper limit target value and the SOC lower limit target value is relatively wide on the high temperature side and the SOC lower limit target value is a relatively high value on the low temperature side, and further the SOC upper limit target value is set to a value in accordance with the battery temperature so that it is a relatively low value on the high temperature side.

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