JP7707790B2 - Regenerative control method and regenerative control device for hybrid vehicle - Google Patents

Description

This invention relates to a regenerative control technology for hybrid vehicles that efficiently regenerates power on downhill roads.

In hybrid vehicles, where the drive wheels are driven by a motor generator, power is regenerated when traveling downhill and charged into the battery. To prevent deterioration due to overcharging, the battery has a set SOC (state of charge) that sets an upper limit for usage. If the SOC reaches the upper limit during regeneration, no further charging will occur and the regenerated power will be consumed in some way.

Patent Document 1 discloses a technique for actively lowering the SOC by running the vehicle on the motor before approaching a downhill road when there is a downhill road on the planned route, in order to maximize the amount of energy recovered when traveling downhill. By lowering the SOC in advance, the margin up to the upper limit of use is increased, allowing for efficient energy recovery on downhill roads.

JP 2000-333305 A

When the battery temperature is low in cold regions, the battery's performance generally declines, which tends to reduce the recovery of SOC through regeneration on downhill roads.

In addition, when the battery temperature is extremely low, the battery controller generally limits the input and output current to avoid battery degradation due to excessive current input and output. In such cases, when the battery temperature is low, the increase in SOC due to regeneration on downhill roads becomes relatively small due to the current limit.

Therefore, if the SOC is lowered before going downhill when the battery temperature is low, just as it is when the battery temperature is high, the SOC may not recover sufficiently by the time the downhill section ends.

Patent document 1 does not mention how to respond when the battery temperature is low.

The present invention relates to a regeneration control for a hybrid vehicle, which detects a downhill road in a travel route of the vehicle in advance, and performs SOC reduction control to reduce the SOC of a battery in advance in preparation for regeneration on the downhill road before the vehicle starts traveling downhill,
The temperature of the battery is detected or estimated, and the lower the battery temperature is, the smaller the amount of SOC reduction in the SOC reduction control is made.

According to this invention, when the battery temperature is low, the SOC is not excessively reduced by the SOC reduction control that reduces the battery SOC in advance before the start of the downhill road, and the SOC at the end of the downhill road can be made appropriate.

1 is a diagram illustrating the configuration of a hybrid vehicle according to an embodiment; 5 is a flowchart showing a process flow of a first embodiment of SOC reduction control before a downhill road. 10 is a flowchart showing a process flow according to a second embodiment. 4 is a time chart for explaining the operation of one embodiment.

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. The series hybrid vehicle is configured to include a power generating motor generator 1 that mainly operates 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 demand, a running motor generator 4 that mainly operates as a motor to drive the drive wheels 3, and a battery 5 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. The drive wheels 3 are driven by the running motor generator 4 via a gear train 11. The 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 running motor generator 4 is driven and controlled using the power of the battery 5. The power generated by the running motor generator 4 during regeneration is stored in the battery 5 via an inverter device (not shown).

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 the controller 6. The controller 6 is composed of multiple controllers connected to each other so that they can communicate with each other, such as the motor controller 7 that controls the motor generators 1 and 4, the engine controller 8 that controls the internal combustion engine 2, and the battery controller 9 that manages the battery 5. The controller 6 receives information such as the opening (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. The battery controller 9 also calculates the SOC of the battery 5 based on the voltage and current of the battery 5. Basically, when the SOC falls to a predetermined lower limit level, the internal combustion engine 2 is started via the engine controller 8 to generate electricity. Then, when the SOC reaches a predetermined level, the internal combustion engine 2 is stopped. The driving modes of such a series hybrid vehicle include an EV mode in which the vehicle runs on the power of the battery 5 without the combustion operation of the internal combustion engine 2, and an HEV mode in which the vehicle runs while generating electricity through the combustion operation of the internal combustion engine 2. However, even if the SOC is above the lower limit level, the vehicle will run in the HEV mode when the required driving force of the vehicle is relatively large.

The battery 5 is equipped 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 inside a pack case that houses multiple battery modules, etc., can be used as the battery temperature. In addition, the battery temperature may be estimated by monitoring the charge/discharge amount, without relying on detection using a temperature sensor.

The battery controller 9 limits the charging current and discharging current according to the battery temperature in order to suppress deterioration of the battery 5 caused by excessive charging and discharging current when the battery temperature is low. For example, when the battery temperature is lower than a certain predetermined temperature, the allowable charging current and discharging current are set to lower values as the battery temperature decreases.

The vehicle of the embodiment is also equipped with a navigation system 17 that uses relatively high-precision map information and a GPS system. The map information of the navigation system 17 includes three-dimensional information of roads, i.e., road gradient information. The 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 from outside the vehicle while the vehicle is traveling, for example, via 5G communication. The navigation system 17 can detect in advance any downhill roads on the vehicle's travel route, and can also obtain information such as the gradient and length of the downhill road. Note that even if a destination is not registered in the navigation system 17, it is possible to detect or predict downhill roads ahead on the currently traveled travel route.

Next, the regeneration 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, the driving motor generator 4 is driven by the drive wheels 3 to perform regeneration. Since it is undesirable for the SOC of the battery 5 to exceed the allowable upper limit during regeneration, in order to maximize the energy recovery by driving on a downhill road, if there is a downhill road on the planned route, SOC reduction control is executed to actively reduce the SOC by driving in EV mode before approaching the downhill road. The expected regeneration amount when driving on a downhill road is calculated 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, and accordingly, a target SOC at the start point of the downhill road is determined so that the SOC at the end point of the downhill road is the upper limit SOC.

Here, in this embodiment, the lower the battery temperature, the smaller the SOC reduction amount in the SOC reduction control is. In other words, when the battery temperature is low, such as in cold regions, the target SOC at the start of a 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 a downhill road is limited to a relatively small value, so that the SOC increase (recovery amount) due to regeneration on a downhill road is small.

Figure 2 is a flowchart showing the flow of processing of a first embodiment of the SOC reduction control executed by the controller 6 when a downhill road is predicted. When a downhill road is predicted, the routine starts, and 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 is the boundary between whether or not to limit the input current based on the battery temperature described above. If the temperature is equal to or higher than the threshold temperature, the input current is not limited, and if the temperature is lower than the threshold temperature, the input current is limited according to the temperature. In other words, in step 1, it is determined whether the temperature is low enough to limit the input current. If the temperature threshold at which the input current limit is started changes due to some parameter, the judgment threshold in step 1 also changes accordingly.

If the answer is NO in step 1, proceed to step 2 and calculate the amount of regeneration expected on the predicted downhill road. In other words, calculate the increase in battery SOC that will increase when driving on a downhill road. Here, the calculation is performed based on the normal input current limit when the battery temperature is at a normal temperature.

Then, proceed to step 5 and determine the target SOC at the position just before the downhill road (i.e., the start point of the downhill road) based on the amount of regeneration (increase in SOC) expected on the downhill road.

By lowering the SOC of the battery 5 according to the target SOC determined in this way, for example by driving the vehicle in EV mode or by driving appropriate accessories, the SOC of the battery 5 will have dropped to close to the target SOC just before the downhill road. Therefore, when driving downhill thereafter, maximum energy recovery can be achieved without exceeding the upper usage SOC of the battery 5.

On the other hand, if 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, where data on the input current limit based on the battery temperature performed by the battery controller 9 is read. As described above, this input current limit is set so that the maximum input current is smaller as the temperature is lower.

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

Then, proceed to step 5, and determine the target SOC at the position just before the downhill road (i.e., the start point of the downhill road) based on the amount of regeneration (increase in SOC) expected on the downhill road. When the battery temperature is low, the amount of regeneration expected on the downhill road is small, so the target SOC is a relatively high value. In other words, the amount of SOC reduction in the SOC reduction control is smaller the lower the battery temperature.

Figure 4 is a characteristic diagram showing (a) the change in altitude of the driving route, (b) the amount of power consumed/regenerated by the driving motor generator 4, and (c) the change in the SOC of the battery 5, comparing (A) the case where the battery temperature is normal (i.e., equal to or higher than the threshold temperature described above) with (B) the case where the battery temperature is low (lower than the threshold temperature described above).

The conditions of the downhill road, i.e. the gradient and length, are the same for both (A) and (B). In the case of (A), the amount of regeneration on the downhill road is relatively large, as shown in (b). Therefore, the target SOC just before the downhill road is set low, as shown in (c). By lowering the SOC sufficiently in this way, it is possible to recover the maximum amount of energy on the downhill road.

On the other hand, when the battery temperature is low (B), the amount of regeneration on the downhill road is relatively small as shown in (b) due to the input current limit based on the battery temperature. Therefore, the target SOC immediately before the downhill road is set relatively high as shown in (c). By not lowering the SOC excessively before the downhill road in this way, the SOC can be maintained at an appropriate level at the end of the downhill road. Note that in the example of (B) in Figure 4, the SOC reached at the end of the downhill road is set lower than the upper limit SOC due to the low battery temperature, but it may be set to reach the upper limit SOC as in the case of (A).

Next, FIG. 3 shows a flowchart of the second embodiment. The second embodiment also takes into consideration the rise in battery temperature during driving. That is, if a downhill road is detected on the driving route at a certain point in time and SOC reduction control is started, during driving with SOC reduction control from this point to the start point of the downhill road, and during driving on the downhill road with regeneration, the battery temperature may change mainly due to charging and discharging of the battery 5. 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, even if the battery temperature is determined to be low at the above-mentioned certain point in time, if the battery temperature is expected to rise by the end point of the downhill road, the regeneration amount expected during driving on the downhill road will be relatively large (in other words, it will approach the regeneration amount when the battery temperature is at a normal temperature). In this case, even if the battery temperature is determined to be low at the time of detecting the downhill road, it is preferable to suppress the reduction in the SOC reduction amount based on the battery temperature. Therefore, in the second embodiment, the SOC reduction amount according to the battery temperature is set taking into consideration such a rise in battery temperature during driving.

The routine starts when a downhill road is predicted, and in the same way as in the first embodiment, the first step 1 is to determine whether the battery temperature is lower than a certain threshold temperature. The threshold temperature is the temperature that is the boundary between whether or not to limit the input current based on the battery temperature as described above.

If the answer is NO in step 1, proceed to step 2 and calculate the amount of regeneration expected on the predicted downhill road. In other words, calculate the increase in battery SOC that will increase when driving on a downhill road. Here, the calculation is performed based on the normal input current limit when the battery temperature is at a normal temperature.

Then, proceed to step 5 and determine the target SOC at the position just before the downhill road (i.e., the start point of the downhill road) based on the amount of regeneration (increase in SOC) expected on the downhill road.

The SOC of the battery 5 is reduced in accordance with the target SOC determined in this manner, for example, by driving the vehicle in EV mode or by operating appropriate accessories.

On the other hand, if it is determined in step 1 that the battery temperature is lower than the threshold temperature, the process proceeds from step 1 to step 3A, where a rise in battery temperature due to future driving is predicted. Since a rise in battery temperature is mainly caused by charging and discharging the battery 5, the rise in battery temperature can be predicted based on the prediction of charging and discharging. For example, the input/output current of the battery 5 in the section from the current time to a point on a downhill road where the SOC of the battery 5 is predicted to reach the upper usage SOC (e.g. the end of the downhill road) can be predicted based on map information, etc., and the rise in battery temperature can be predicted according to the integrated value of this input/output current.

In addition, the battery temperature rise for each section may be calculated by dividing the driving section into a section from the current time to the start of the downhill road (a driving section involving SOC reduction control) and a section involving regeneration from the start of the downhill road to the end of the downhill road, and the battery temperature rise for the entire section may be calculated from the two.

Regarding the rise in battery temperature in a driving section involving SOC reduction control up to the start of a downhill road, for example, a 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 calculated and a prediction can be made based on this difference. In other words, the larger the SOC difference, the greater the discharge amount and the higher the temperature of the battery 5. Note that since both the current SOC and the target SOC are parameters that change over time, this calculation is repeatedly performed, for example, every small period of time.

Next, proceed to step 3B to determine the input current limit based on the battery temperature. Here, the battery temperature that takes into account the battery temperature rise during driving in step 3A is used as the battery temperature, and the input current limit corresponding to this battery temperature is calculated. As in the first embodiment, this input current limit is set so that the maximum input current is smaller the lower the battery temperature, but by taking into account the battery temperature rise during driving, the predicted input current limit is relatively relaxed. In other words, it approaches the input current limit under normal temperatures.

Next, in step 4, as in step 2, the predicted amount of regeneration expected on a downhill road is calculated. In other words, the increase in battery SOC that will increase as a result of driving on a downhill road is calculated. Here, the calculation is performed based on the input current limit according to the battery temperature determined in step 3B. Therefore, the lower the predicted final battery temperature, the smaller the amount of regeneration expected on a downhill road.

Then, proceed to step 5, and determine the target SOC at the position just before the downhill road (i.e., the start of the downhill road) based on the amount of regeneration (increase in SOC) expected on the downhill road. When the battery temperature is low, the amount of regeneration expected on the downhill road is small, so the target SOC is a relatively high value. However, by taking into account the increase in battery temperature while driving, the target SOC is a relatively lower value than when the increase in battery temperature while driving is not taken into account. In other words, the amount of reduction in the SOC reduction control is revised to be relatively larger when an increase in battery temperature while driving is expected.

Therefore, in the example of Figure 4, even if the battery temperature is low when a downhill road is predicted, if the battery temperature rises significantly while driving, the characteristics will be closer to those of Figure 4 (A).

When the above-mentioned prediction of the battery temperature rise during driving is repeatedly performed, the calculations of steps 3B, 4, and 5 are also repeatedly performed. Therefore, the target SOC for the SOC reduction control changes successively.

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, the present invention is not limited to series hybrid vehicles, but can be widely applied to hybrid vehicles capable of regenerating on downhill roads, such as series-parallel hybrid vehicles and plug-in hybrid vehicles.

REFERENCE SIGNS LIST 1...power generating motor generator 2...internal combustion engine 4...traveling motor generator 5...battery 6...controller 16...temperature sensor

Claims (7)

A regeneration control method for a hybrid vehicle including a motor generator connected to drive wheels of the vehicle and a battery, the regeneration control method detecting a downhill road in a travel route of the vehicle in advance and performing SOC reduction control to reduce the SOC of the battery in advance in preparation for regeneration on the downhill road before the vehicle starts traveling downhill,
The temperature of the battery is detected or estimated, and the lower the battery temperature is, the smaller the SOC reduction amount in the SOC reduction control is.
A method for controlling regeneration in a hybrid vehicle. Calculate the limit of the battery input current corresponding to the above battery temperature,
A predicted increase in the battery's SOC due to regeneration on a downhill road is calculated taking into account the input current limit.
A SOC reduction amount in the SOC reduction control is determined in response to the SOC increase amount.
The regenerative control method for a hybrid vehicle according to claim 1 . A rise in battery temperature during driving accompanied by SOC reduction control until a downhill road is reached is predicted;
The greater the predicted increase in battery temperature, the greater the final SOC decrease amount is corrected.
3. A regenerative control method for a hybrid vehicle according to claim 1. Predicts the rise in battery temperature while driving downhill with regeneration,
The greater the predicted increase in battery temperature, the greater the final SOC decrease amount is corrected.
The regenerative control method for a hybrid vehicle according to any one of claims 1 to 3. Predicting input/output currents of the battery in a section from the current time to a point on a downhill road where the SOC of the battery is predicted to reach a predetermined upper limit SOC;
The larger the integrated value of the input/output current is, the larger the final SOC decrease amount is corrected.
3. A regenerative control method for a hybrid vehicle according to claim 1. The prediction of the increase in the battery temperature is performed based on the difference between the current SOC and a target SOC immediately before the downhill section based on the SOC reduction control.
The regenerative control method for a hybrid vehicle according to claim 3. A regenerative control device for a hybrid vehicle including a motor generator connected to a drive wheel of the vehicle and a battery,
a downhill road detection unit that detects in advance a downhill road on a travel route of the vehicle;
a battery temperature detection unit for detecting or estimating the temperature of the battery;
a control unit that executes an SOC reduction control for reducing the SOC of the battery in advance in preparation for regeneration on a downhill road before the start of a downhill road, the SOC reduction amount being reduced as the battery temperature is lower;
A regenerative control device for a hybrid vehicle comprising: