Regeneration control method and regeneration control device for hybrid vehicle

Abstract

To appropriately perform SOC reduction control when a slope-descending is predicted in a travel path, according to a battery temperature.SOLUTION: A hybrid vehicle includes a power generation motor generator that is driven by an internal combustion engine, and a travel motor generator that is driven by a battery. In slope-descending, power is recovered by regeneration. When a slope-descending is predicted in a travel path, SOC is reduced to target SOC in advance by EV travel or the like so that the maximum regenerative power in the slope-descending is secured. When a battery temperature is low, since a regenerative amount in the slope-descending is small, an SOC reduction amount in the SOC reduction control is made small and the target SOC is set relatively high.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] This invention relates to a regenerative control technology for a hybrid vehicle that efficiently regenerates power on a downhill road.

Background Art

[0002] In a hybrid vehicle in which drive wheels are driven by a motor generator, power regeneration is performed when driving on a downhill road, and the battery is charged. In order to avoid deterioration due to overcharging, a SOC (state of charge) that is the upper limit of use is defined for the battery. When the SOC reaches the upper limit of use during regeneration, no further charging is performed, and the regenerative power is consumed in some form.

[0003] Patent Document 1 discloses a technique of actively reducing the SOC by performing motor driving or the like before approaching a downhill road when there is a downhill road on a planned route in order to maximize energy recovery by driving on a downhill road. By reducing the SOC in advance, the margin up to the upper limit of use becomes large, and efficient energy recovery on a downhill road can be achieved.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the temperature of the battery is low in a cold region or the like, basically, due to the performance degradation of the battery, the recovery of the SOC by regeneration on a downhill road tends to decrease.

[0006] Also, generally, when the battery temperature is extremely low, the input / output current is limited by the battery controller for the purpose of avoiding degradation of the battery due to excessive input / output of current. In such a case, when the battery is at a low temperature, the increase in SOC due to regeneration on a downhill section becomes relatively small due to current limitation.

[0007] Therefore, if the SOC is decreased before the downhill section in the same way as when the battery temperature is high when the battery temperature is low, the SOC may not recover sufficiently at the end of the downhill section.

[0008] Patent Document 1 does not describe how to handle such a situation when the battery temperature is low.

Means for Solving the Problem

[0009] In the regenerative control of a hybrid vehicle according to the present invention, a downhill section on the vehicle's driving route is detected in advance, and SOC reduction control is performed to reduce the SOC of the battery in advance in preparation for regeneration on the downhill section before the start of the downhill section. The temperature of the battery is obtained by detection or estimation, and the lower the battery temperature, the smaller the amount of SOC reduction in the SOC reduction control.

Effect of the Invention

[0010] According to the present invention, when the battery temperature is low, the SOC is not excessively decreased by the SOC reduction control for decreasing the SOC of the battery in advance before the start of the downhill section, and the SOC at the end of the downhill section can be made appropriate.

Brief Description of the Drawings

[0011]

Figure 1

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Figure 4

Best Mode for Carrying Out the Invention

[0012] FIG. 1 schematically shows the configuration of a series hybrid vehicle as an example of a hybrid vehicle to which the present invention is applied. The series hybrid vehicle mainly includes a power generation motor generator 1 that operates as a generator, an internal combustion engine 2 used as a power generation internal combustion engine that drives the power generation motor generator 1 in response to a power demand, a traveling motor generator 4 that mainly operates as a motor and drives drive wheels 3, and a battery 5 that temporarily stores the generated electric power. In one embodiment, the power generation motor generator 1 is driven by the internal combustion engine 2 via a gear train 10. The drive wheels 3 are driven by the traveling motor generator 4 via a gear train 11. The electric power obtained by driving the power generation motor generator 1 by the internal combustion engine 2 is stored in the battery 5 via an inverter device (not shown). The traveling motor generator 4 is driven and controlled using the electric power of the battery 5. The electric power during regeneration of the traveling motor generator 4 is also stored in the battery 5 via an inverter device (not shown).

[0013] The operations 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 the controller 6. The controller 6 is composed of a plurality of controllers 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, which are connected so as to be able to communicate with each other. Information such as the opening degree (depression amount) of the accelerator pedal 13, the operation amount of the brake pedal 14, and the vehicle speed detected by the vehicle speed detection means 15 is input to the controller 6. Further, the battery controller 9 obtains the SOC of the battery 5 based on the voltage and current of the battery 5. Basically, when the SOC drops to a predetermined lower limit level, the internal combustion engine 2 is started via the engine controller 8 and power generation is performed. Then, when the SOC reaches a predetermined level, the internal combustion engine 2 stops. As operation modes of such a series hybrid vehicle, there are an EV mode in which the vehicle travels with the power of the battery 5 without the combustion operation of the internal combustion engine 2, and an HEV mode in which the vehicle travels while performing power generation by the combustion operation of the internal combustion engine 2. However, even when the SOC is above the lower limit level, when the required driving force of the vehicle is relatively large, the vehicle travels in the HEV mode.

[0014] The battery 5 is provided with a temperature sensor 16 for detecting the battery temperature. The temperature of the battery module itself included in the battery 5, the ambient temperature in the pack case that houses a plurality of battery modules, etc. can be used as the battery temperature. In addition, the battery temperature may be estimated by monitoring the charge and discharge amount or the like without relying on the detection using the temperature sensor.

[0015] The battery controller 9 limits the charging current and the discharging current according to the battery temperature in order to suppress the deterioration of the battery 5 due to excessive current being charged and discharged when the battery temperature is low. For example, when the battery temperature is lower than a certain predetermined temperature, the lower the battery temperature, the lower the allowable charging current and discharging current are set respectively.

[0016] In addition, a vehicle according to an embodiment is provided with a navigation system 17 that uses relatively high-precision map information and a GPS system. The map information of this navigation system 17 includes three-dimensional information of roads, that is, road gradient information. This map information may be stored in a storage device such as a hard disk of the navigation system 17, or may be provided to the navigation system 17 during travel from outside the vehicle via, for example, 5G communication or the like. With this navigation system 17, it is possible to detect a downhill road in advance on the travel route of the vehicle, and furthermore, it is possible to obtain information such as the gradient and length of the downhill road. Even when no destination is registered in the navigation system 17, it is possible to detect or predict a downhill road ahead on the current travel route.

[0017] Next, the regenerative control and SOC reduction control for a downhill road of the series hybrid vehicle configured as described above will be described. On a downhill road, regeneration is performed by driving the driving motor generator 4 by the drive wheels 3. Since it is not desirable for the SOC of the battery 5 to exceed the allowable upper limit during regeneration, in order to maximize the energy recovery by traveling on a downhill road, if there is a downhill road on the planned route, before approaching the downhill road, SOC reduction control is executed, such as performing EV mode driving to actively reduce the SOC. Since the amount of regeneration expected during downhill road travel is obtained from conditions such as the gradient and length of the downhill road, or the elevation difference between the start and end points of the downhill road, correspondingly, the target SOC at the start of the downhill road is determined so that the SOC becomes the upper limit SOC at the end of the downhill road.

[0018] Here, in this embodiment, basically, the lower the battery temperature, the smaller the amount of SOC decrease in the SOC decrease control. That is, when the battery temperature is low in a cold region or the like, the target SOC at the start of the downhill road is kept relatively high compared to when the battery temperature is high. This is because, as described above, when the battery temperature is low, the input current (charging current) to the battery 5 during regeneration on the downhill road is relatively limited, considering that the amount of SOC increase (recovery amount) due to regeneration on the downhill road becomes small.

[0019] FIG. 2 is a flowchart showing the flow of processing of the first embodiment of the SOC decrease control executed by the controller 6 when a downhill road is predicted. When a downhill road is predicted, the routine starts. In the first step 1, it is determined whether the battery temperature is lower than a certain threshold temperature. The threshold temperature is the temperature that becomes the boundary for performing or not performing the restriction of the input current based on the battery temperature described above. If it is above the threshold temperature, the input current is not restricted, and when it is lower than the threshold temperature, the input current is restricted according to the temperature. In other words, in step 1, it is determined whether it is a low-temperature state in which the input current is restricted. If the temperature threshold for starting the restriction of the input current changes due to some parameter, the determination threshold in step 1 also changes accordingly.

[0020] If the result in step 1 is NO, it proceeds to step 2, and the expected regeneration amount on the predicted downhill road is calculated. In other words, the increase amount of the battery SOC that will increase due to traveling on the downhill road is calculated. Here, the calculation is performed based on the normal restriction of the input current when the battery temperature is normal temperature.

[0021] Then, it proceeds to step 5, and based on the expected regeneration amount (SOC increase amount) on the downhill road, the target SOC at the position immediately before the downhill road (that is, the start point of the downhill road) is determined.

[0022] In accordance with the target SOC determined in this way, for example, by driving in the EV mode of the vehicle or driving appropriate auxiliary equipment, the SOC of the battery 5 is decreased, so that immediately before the downhill road, the SOC of the battery 5 has decreased to near the target SOC. Therefore, during the subsequent downhill road driving, maximum energy recovery can be achieved without exceeding the upper limit SOC of the battery 5.

[0023] On the other hand, when it is determined in step 1 that the battery temperature is lower than the threshold temperature, the process proceeds from step 1 to step 3, and the data of the input current limit based on the battery temperature performed by the battery controller 9 is read. This input current limit is set such that the maximum input current becomes smaller as the temperature is lower, as described above.

[0024] Next, in step 4, in the same manner as in step 2, the amount of regeneration expected on the predicted downhill road is calculated. In other words, the increase amount of the battery SOC that will increase due to downhill road driving is calculated. Here, the calculation is performed based on the input current limit corresponding to the battery temperature read in step 3. Therefore, the lower the battery temperature, the smaller the amount of regeneration expected on the downhill road.

[0025] Then, the process proceeds to step 5, and based on the amount of regeneration expected on the downhill road (SOC increase amount), the target SOC at the position immediately before the downhill road (that is, the starting point of the downhill road) is determined. When the battery temperature is low, since the amount of regeneration expected on the downhill road is small, the target SOC becomes a relatively high value. That is, the amount of SOC decrease in the SOC decrease control becomes smaller as the battery temperature is lower.

[0026] FIG. 4 is a characteristic diagram showing a comparison between (A) the case where the battery temperature is the normal temperature (that is, equal to or higher than the above-described threshold temperature) and (B) the case where the battery temperature is low (lower than the above-described threshold temperature) with respect to (a) the elevation change of the driving route, (b) the power consumption / regeneration amount of the driving motor generator 4, and (c) the change in the SOC of the battery 5.

[0027] The conditions of the downhill road, namely the gradient and length, are the same for both (A) and (B). In the case of (A), as shown in (b), the amount of regeneration on the downhill road is relatively large. Therefore, as shown in (c), the target SOC just before the downhill road is set low. By sufficiently reducing the SOC in this way, maximum energy recovery is possible on the downhill road.

[0028] On the other hand, in the case of (B) where the battery temperature is low, due to the limitation of the input current based on the battery temperature, as shown in (b), the amount of regeneration on the downhill road is relatively small. Therefore, as shown in (c), the target SOC just before the downhill road is set relatively high. By not excessively reducing the SOC before the downhill road in this way, the SOC can be maintained at an appropriate level at the end of the downhill road. In the example of (B) in FIG. 4, although the SOC reached at the end of the downhill road is set lower than the upper limit of use in relation to the low battery temperature, it may also be set to reach the upper limit of use as in the case of (A).

[0029] Next, FIG. 3 shows the flowchart of the second embodiment. The second embodiment takes into account the increase in the battery temperature during driving. That is, when it is assumed that the SOC reduction control is started by detecting a downhill road on the driving route at a certain point in time, during the driving with the SOC reduction control from this point until the start point of the downhill road, and during the downhill road driving with regeneration, mainly due to the charge and discharge of the battery 5, a change in the battery temperature may occur. Since the SOC of the battery 5 approaches the upper limit of use due to regeneration on the downhill road near the end point of the downhill road, if it is expected that the battery temperature will rise until the end point of the downhill road even if it is determined that the battery temperature is low at the above-mentioned certain point in time, the expected amount of regeneration during the downhill road driving becomes relatively large (in other words, it approaches the amount of regeneration when the battery temperature is at the normal temperature). In this case, even if it is determined that the battery temperature is low at the time of detecting the downhill road, it is preferable to suppress the reduction of the SOC reduction amount based on the battery temperature. Therefore, in the second embodiment, in consideration of such an increase in the battery temperature during driving, the SOC reduction amount is set according to the battery temperature.

[0030] When a downhill road is predicted, the routine starts. Similar to the first embodiment, in the first step 1, it is determined whether the battery temperature is lower than a certain threshold temperature. The threshold temperature is the temperature at which the input current is restricted based on the battery temperature described above.

[0031] If the result in step 1 is NO, proceed to step 2 and calculate the expected amount of regeneration on the predicted downhill road. In other words, calculate the increase in the battery SOC that will occur due to traveling on the downhill road. Here, the calculation is performed based on the normal input current restriction when the battery temperature is normal temperature.

[0032] Then, proceed to step 5 and determine the target SOC at the position immediately before the downhill road (i.e., the starting point of the downhill road) based on the expected amount of regeneration (SOC increase amount) on the downhill road.

[0033] Along with the target SOC determined in this way, the SOC of battery 5 is decreased, for example, by driving in the EV mode of the vehicle or driving appropriate auxiliary machines.

[0034] On the other hand, if it is determined in step 1 that the battery temperature is lower than the threshold temperature, proceed from step 1 to step 3A and predict the increase in the battery temperature due to the subsequent driving. Since the increase in the battery temperature is mainly caused by the charge and discharge of battery 5, the increase in the battery temperature can be predicted based on the prediction of charge and discharge. For example, predict the input / output current of battery 5 in the section from the current time to the point where it is predicted that the SOC of battery 5 will reach the upper limit SOC during the downhill road (e.g., the end point of the downhill road) based on map information, etc., and predict the increase in the battery temperature according to the integrated value of this input / output current.

[0035] Note that the driving section from the current time to the starting point of the downhill road (the driving section with SOC decrease control) and the driving section with regeneration from the starting point to the end point of the downhill road can be divided, and the increase in the battery temperature for each section can be calculated, and the increase in the battery temperature for the entire section can be obtained from both.

[0036] Regarding the increase in battery temperature during a driving section with SOC reduction control until the start of a downhill road, for example, the difference between the current SOC and the target SOC at the start of the downhill road (i.e., immediately before the downhill road) can be obtained and predicted based on this difference. That is, the greater the SOC difference, the greater the discharge amount, and the temperature of battery 5 increases. Note that since both the current SOC and the target SOC are parameters that change over time, this calculation is repeated, for example, every small time interval.

[0037] Next, proceed to step 3B to obtain the limit of the input current based on the battery temperature. Here, as the battery temperature, the battery temperature considering the increase in the battery temperature during driving in step 3A is used, and the limit of the input current corresponding to this battery temperature is calculated. This limit of the input current is set such that the lower the battery temperature, the smaller the maximum input current, similar to the first embodiment. However, by considering the increase in the battery temperature during driving, the predicted limit of the input current becomes relatively loose. That is, it approaches the limit of the input current under normal temperature.

[0038] Next, in step 4, in the same manner as in step 2, calculate the expected amount of regeneration on the predicted downhill road. In other words, calculate the increase in the battery SOC that will occur due to driving on the downhill road. Here, the calculation is performed based on the limit of the input current corresponding to the battery temperature obtained in step 3B. Therefore, the lower the predicted final battery temperature, the smaller the expected amount of regeneration on the downhill road.

[0039] Then, proceed to step 5 and determine the target SOC at the position immediately before the downhill road (i.e., the start of the downhill road) based on the expected amount of regeneration (SOC increase amount) on the downhill road. When the battery temperature is low, since the expected amount of regeneration on the downhill road is small, the target SOC becomes a relatively high value. However, by considering the increase in the battery temperature during driving, the target SOC becomes a relatively lower value than when not considering the increase in the battery temperature during driving. That is, the amount of decrease in the SOC reduction control is corrected in a direction where it becomes relatively larger when an increase in the battery temperature during driving is expected.

[0040] Therefore, in the example of FIG. 4, when the battery temperature at the time of predicting the presence of a downhill road is low but the increase in the battery temperature during driving is large, the characteristics are close to those in FIG. 4(A).

[0041] When the prediction of the increase in the battery temperature during driving described above is repeatedly executed, the operations in Steps 3B, 4, and 5 are also repeatedly executed. Therefore, the target SOC for the SOC reduction control will change sequentially.

[0042] As described above, one embodiment of the present invention has been described in detail. However, the present invention is not limited to the above embodiment, and various modifications are possible. For example, the present invention is not limited to a series hybrid vehicle, and can be widely applied to hybrid vehicles capable of regeneration on a downhill road, such as series-parallel hybrid vehicles and plug-in hybrid vehicles.

Explanation of Reference Numerals

[0043] 1... Generator motor for power generation 2... Internal combustion engine 4... Driving motor generator 5... Battery 6... Controller 16... Temperature sensor

Claims

1. A regenerative control method for a hybrid vehicle including a motor generator connected to a drive wheel of the vehicle and a battery, the method comprising: detecting a downhill road in a driving route of the vehicle in advance; and performing SOC reduction control for reducing the SOC of the battery in advance in preparation for regeneration on the downhill road before the start of the downhill road. In the regenerative control method, obtaining the temperature of the battery by detection or estimation, and reducing the amount of SOC reduction in the SOC reduction control as the battery temperature is lower. A regenerative control method for a hybrid vehicle.

2. obtaining a limit of the battery input current corresponding to the battery temperature, calculating an increase amount of the SOC of the battery due to regeneration on a predicted downhill road in consideration of the limit of the input current, and determining the amount of SOC reduction in the SOC reduction control corresponding to the increase amount of the SOC. The regenerative control method for a hybrid vehicle according to claim 1.

3. predicting an increase in the battery temperature during traveling with SOC reduction control until reaching the downhill road, and adding a correction in a direction in which the final amount of SOC reduction increases as the predicted increase in the battery temperature is larger. The regenerative control method for a hybrid vehicle according to claim 1 or 2.

4. predicting an increase in the battery temperature during traveling with regeneration on the downhill road, and adding a correction in a direction in which the final amount of SOC reduction increases as the predicted increase in the battery temperature is larger. The regenerative control method for a hybrid vehicle according to any one of claims 1 to 3.

5. predicting the input / output current of the battery in a section from the current time to a point where it is predicted that the SOC of the battery reaches a predetermined upper limit SOC on the downhill road, and adding a correction in a direction in which the final amount of SOC reduction increases as the integrated value of the input / output current is larger. The regenerative control method for a hybrid vehicle according to claim 1 or 2.

6. performing the prediction of the increase in the battery temperature based on a difference between the current SOC and a target SOC immediately before the downhill road by the SOC reduction control. The regenerative control method for a hybrid vehicle according to claim 3.

7. A regenerative control device for a hybrid vehicle including a motor generator connected to a drive wheel of the vehicle and a battery, the device comprising: a downhill road detection unit configured to detect a downhill road in a driving route of the vehicle in advance; a battery temperature detection unit configured to obtain the temperature of the battery by detection or estimation. An SOC reduction control that reduces the SOC of the battery in advance in preparation for regeneration on a downhill road before the start of the downhill road is executed by a control unit that reduces the SOC reduction amount as the battery temperature is lower. A regenerative control device for a hybrid vehicle comprising the same.

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