Regenerative control method and regenerative control device for hybrid vehicle

Abstract

A hybrid vehicle has a first motor generator (1) for power generation driven by an internal combustion engine (2), and a second motor generator (4) for running driven by a battery (5). As a basic running mode, an S mode, an ECO mode, and a NORMAL mode are switched by a mode switch (16). In the S mode and the ECO mode, the deceleration of regenerative braking on a downhill is large, and the regenerative amount increases. A controller (6) executes SOC lowering control to lower the SOC in advance before the start of a downhill when the S mode and the ECO mode are selected if a downhill is predicted to exist in a running path, and does not execute the SOC lowering control if the NORMAL mode is selected.

Description

Technical Field

[0001] This invention relates to a regeneration control technology for hybrid vehicles that efficiently regenerate electricity on downhill roads. Background Technology

[0002] In hybrid vehicles that use an electric generator to drive the drive wheels, electricity is regenerated to charge the battery when driving downhill. A State of Charge (SOC) is defined as an upper limit for battery usage to prevent degradation caused by overcharging. If the SOC reaches this limit during regeneration, further charging is stopped, and the regenerated electricity is consumed in some form.

[0003] Patent Document 1 discloses a technique that, in order to maximize energy recovery during downhill driving, when a downhill section exists on a predetermined path, actively reduces the State of Charge (SOC) in advance by performing motor operation or similar actions before approaching the downhill section. By reducing the SOC in advance, the margin up to the maximum usage limit is increased, enabling effective energy recovery during downhill driving.

[0004] However, Patent Document 1 does not take into account the differences in driving modes with different amounts of regeneration on downhill roads and uniformly reduces SOC in advance. Therefore, it is possible that, for example, when the actual amount of regeneration on the downhill road is small, the SOC at the end of the downhill road may be low.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2000-333305 Summary of the Invention

[0006] The regeneration control of the hybrid vehicle of the present invention involves pre-detecting downhill sections in the vehicle's driving path and performing SOC reduction control to pre-reduce the battery's SOC in order to cope with regeneration on the downhill section before it begins. In this regeneration control method, the driver selects from a variety of driving modes that affect the amount of regeneration on the downhill section, and switches whether to perform the above-mentioned SOC reduction control.

[0007] By considering driving modes in this way, it is possible to avoid unnecessary pre-emptive reduction of SOC control in a certain driving mode. Attached Figure Description

[0008] Figure 1 This is a structural illustration of a hybrid vehicle according to one embodiment.

[0009] Figure 2 This is a flowchart illustrating the regeneration control process related to driving downhill.

[0010] Figure 3 This is a timing diagram used to illustrate the operation of one embodiment. Detailed Implementation

[0011] Figure 1 As an example of a hybrid vehicle applying the present invention, the structure of a series hybrid vehicle is schematically shown. The series hybrid vehicle is configured to have: an electric generator 1 for generating electricity, which mainly functions as a generator; an internal combustion engine 2, which functions as an internal combustion engine for generating electricity to drive the electric generator 1 according to a power demand; and an electric generator 4 for driving, which mainly functions as a motor to drive the drive wheels 3.

[0012] And battery 5, which temporarily stores the electricity generated by the generator. In one embodiment, the generator 1 is driven by the internal combustion engine 2 via gear train 10. Additionally, the drive wheels 3 are driven by the drive generator 4 via gear train 11. The electricity obtained by the internal combustion engine 2 driving the generator 1 is stored in battery 5 via an inverter device (not shown). The power from battery 5 is used to drive and control the drive generator 4. The electricity generated by the drive generator 4 during regeneration is also stored in battery 5 via an inverter device (not shown).

[0013] The operation of electric generators 1 and 4, the charging and discharging of battery 5, and the operation of internal combustion engine 2 are controlled by controller 6. Controller 6 consists of multiple controllers that are interconnected, including motor controller 7 which controls electric generators 1 and 4, engine controller 8 which controls internal combustion engine 2, and battery controller 9 which manages battery 5. Information such as the opening degree (push-off amount) of accelerator pedal 13, the operation amount of brake pedal 14, and the vehicle speed detected by vehicle speed detection unit 15 are input to controller 6. In addition, battery controller 9 calculates the state of charge (SOC) of battery 5 based on the voltage and current of battery 5. Basically, based on the decrease of this SOC, it requests engine controller 8 to start internal combustion engine 2. Furthermore, in a series hybrid vehicle, the state of driving using the electricity of battery 5 without combustion of internal combustion engine 2 is called EV mode, and the state of driving while generating electricity based on combustion of internal combustion engine 2 is called HEV mode. The above-mentioned EV mode and HEV mode are different concepts from the "driving mode" in the technical solution.

[0014] One embodiment of a series hybrid vehicle offers three basic driving modes regarding vehicle operation or maneuverability: "S mode," "ECO mode," and "NORMAL mode." These modes can be switched using a mode switch 16. S mode provides higher vehicle responsiveness to the accelerator pedal 13, delivering a higher torque increase when the accelerator pedal 13 is depressed and stronger regenerative braking when the accelerator pedal 13 is released. ECO mode prioritizes fuel economy compared to S mode, with a relatively gentler torque increase when the accelerator pedal 13 is depressed and relatively gentler regenerative braking when the accelerator pedal 13 is released. In both S and ECO modes, acceleration / deceleration can be performed using only the accelerator pedal 13. Furthermore, when the brake pedal 14 is depressed, so-called coordinated regenerative braking control is performed, applying a portion of the required braking force through regenerative braking and applying the insufficient portion using the friction braking mechanisms of each wheel.

[0015] The NORMAL mode provides a driving feel similar to a non-hybrid gasoline engine vehicle, offering moderate acceleration. However, it does not engage aggressive regenerative braking when the accelerator pedal 13 is disengaged (for example, it is set to a weaker regenerative braking equivalent to so-called engine braking). Furthermore, when the brake pedal 14 is depressed, coordinated regenerative braking control is not performed; instead, friction-based braking is applied. These three modes can be selected according to the driver's preference, typically switching before the vehicle begins to move.

[0016] Of the three modes mentioned above, S mode and ECO mode correspond to the "condition of large deceleration during regenerative braking on downhill roads" in the technical solution. Furthermore, S mode and ECO mode are equivalent to "regenerative braking mode," while NORMAL mode is equivalent to "normal braking mode."

[0017] Additionally, one embodiment of the series hybrid vehicle has a gear selector 17 for selecting one of multiple gears via lever operation, similar in form to a vehicle without a transmission mechanism but with an automatic transmission. The gears include, for example, "D" for forward, "R" for reverse, "P" for selection during parking and starting, "N" for establishing a power cut-off state, and "B" for temporarily applying stronger regenerative braking, such as on downhill slopes. Switching between D and B gears is possible while driving. If the driver selects B gear, for example, on a downhill slope, stronger regenerative braking is applied even when the basic driving mode is NORMAL mode and the accelerator pedal 13 is disengaged. When the basic driving modes are S mode and ECO mode, selecting B gear using gear selector 17 results in relatively stronger regenerative braking compared to the D gear. Therefore, B gear corresponds to the "condition of greater deceleration during regenerative braking on downhill slopes" in the technical solution.

[0018] Additionally, one embodiment of the vehicle includes a navigation system 19 that utilizes high-precision map information and a GPS system. The map information in the navigation system 19 includes three-dimensional road information, specifically road gradient information. This map information can be stored in a storage device such as a hard drive of the navigation system 19, and can be provided to the navigation system 19 from outside the vehicle while it is in motion, for example, via 5G communication. The navigation system 19 can be used to detect downhill sections in the vehicle's driving path in advance, and can obtain information such as the gradient and length of the downhill sections. Furthermore, even if no destination is registered in the navigation system 19, it can detect or predict downhill sections preceding the currently traveling path.

[0019] Next, the regeneration control of the series hybrid vehicle configured as described above for use on downhill roads will be explained. On downhill roads, regeneration is performed by driving the electric generator 4 via the drive wheels 3. Since it is not preferable for the state of charge (SOC) of the battery 5 to exceed the permissible usage limit during regeneration, in order to maximize energy recovery during downhill driving, when a downhill section exists on the predetermined path, SOC reduction control is implemented to proactively reduce the SOC before approaching the downhill section, such as by driving in EV mode.

[0020] In this embodiment, the decision to implement State of Charge (SOC) reduction control is switched based on the driving mode selected by the driver among various driving modes that affect the amount of regeneration on downhill roads. That is, if the driving mode is one where the estimated amount of regeneration on downhill roads is high, SOC reduction control is implemented in advance; if the driving mode is one where the amount of regeneration on downhill roads is low, SOC reduction control is not implemented.

[0021] Figure 2This is a flowchart illustrating the processing flow executed by controller 6 when a downhill road is predicted. The process begins upon predicting a downhill road. In the initial step 1, it is determined whether a driving mode requiring pre-execution of SOC reduction control should be applied for the predicted downhill road. In one embodiment, this is determined to be a driving mode requiring pre-execution of SOC reduction control when the basic driving mode is S mode or ECO mode, and when the basic driving mode is NORMAL mode but the gear is in B gear. In NORMAL mode and D gear, the amount of regeneration on the downhill road is relatively small, therefore, it is determined to be NO in step 1. In this case, the process proceeds from step 1 to step 2, without pre-execution of SOC reduction control. That is, driving continues according to the normal target SOC.

[0022] If the result in step 1 is YES, proceed to step 3 and set a flag indicating that SOC reduction control will be executed. Alternatively, SOC reduction control can be started after a suitable timing is reached, or it can be started immediately.

[0023] Next, we proceed to step 4, calculating the target SOC for the position just before entering the downhill section. That is, determining the target value to which the SOC should be reduced through SOC reduction control. This target value is essentially calculated based on different driving modes with varying regeneration amounts under the same downhill conditions, and the predicted conditions of the downhill section. In other words, the target SOC is calculated based on the expected regeneration amount supplied to battery 5 during downhill driving.

[0024] For example, in S mode and B gear, the regenerative braking is strongest relative to the same downhill slope to generate the maximum regenerative braking. In ECO mode and D gear, relatively weaker regenerative braking is required, resulting in a smaller regenerative braking amount relative to the same downhill slope; therefore, the target SOC differs. Furthermore, the slope and length of the downhill slope are input as conditions. Additionally, the elevation difference between the start and end points of the downhill slope can be set as a condition for the downhill slope. Moreover, the greater the vehicle weight, the greater the regenerative braking amount; therefore, the vehicle weight, including occupants, can be detected or estimated using appropriate methods, and the expected regenerative braking amount for downhill driving can be estimated considering this weight. The target SOC calculated in step 4 is a basic target SOC that does not consider the driver's driving tendencies.

[0025] Furthermore, the expected regeneration amount during downhill driving is actually the amount of power consumed during downhill driving. Therefore, the basic target SOC can also be calculated by taking into account the power consumption of the cabin air conditioning unit, vehicle lighting unit, windshield wipers, audio unit, navigation system 19, etc. at the current time.

[0026] Next, in steps 5-7, the basic target SOC is corrected to a more appropriate value based on the driver's driving tendencies. The driver's driving tendencies can be learned based on data such as the amount of regeneration on previous downhill roads, the amount of driving maneuvering on previous downhill roads, and vehicle acceleration. First, in step 5, it is determined whether the driver's driving tendencies have been identified (in other words, learned). In one embodiment, the driver's driving tendencies are broadly categorized into two types: a relatively stable driving tendency and a relatively aggressive driving tendency. Furthermore, the degree of each is learned. For example, based on data from previous driving, an aggressive driving tendency is determined, such as frequently switching between the accelerator pedal 13 and the brake pedal 14, situations involving such abrupt maneuvers, frequent acceleration and deceleration of the vehicle, or numerous instances of rapid acceleration and deceleration. Conversely, stable driving is determined when these situations are less frequent. Additionally, as a driving tendency related to the amount of regeneration on downhill roads, an additional factor can be added: the tendency to frequently switch from D to B gear midway downhill. Furthermore, based on past downhill regeneration data, it can determine whether the driving tendency is characterized by higher or lower regeneration. If such a driving tendency has been identified and stored, it is marked as YES in step 5; otherwise, it is marked as NO. If the result is NO, i.e., the driving tendency is unclear, then the process proceeds from step 5 to step 8. From multiple data points that associate different degrees of driving tendency with a target SOC appropriate to that tendency (in other words, the target SOC corrected for the driving tendency relative to the basic target SOC), the value corresponding to the median value of the driving tendency is determined as the final target SOC. Alternatively, the basic target SOC obtained in step 4 can be used directly.

[0027] If the driving tendency learning is complete, proceed to step 6, where the driving tendency is considered in relation to the basic target SOC to determine the final target SOC. Here, the higher the degree of the driving tendency towards stable driving, the lower the final target SOC will be set. When the tendency towards stable driving is present, there is generally less unnecessary braking on downhill sections and less re-acceleration based on the accelerator pedal 13, allowing for greater energy recovery corresponding to the elevation difference of the downhill section. Furthermore, if there is a tendency to switch to B gear midway downhill, it is still preferable to lower the final target SOC. On the other hand, when the tendency towards aggressive driving is present, there is a risk of friction braking due to braking midway downhill, or unnecessary re-acceleration, potentially reducing energy recovery. Therefore, if the driving tendency is towards aggressive driving, the target SOC at the point just before reaching the downhill section will be set higher. That is, the reduction amount in SOC reduction control will be smaller.

[0028] In the next step, 7, the target SOC, determined considering driving tendency, is limited to a range higher than the specified lower threshold. That is, the target SOC determined in step 6 is compared with the lower threshold; if it is lower than the lower threshold, the lower threshold is set as the target SOC. This avoids excessive reduction in SOC.

[0029] Based on the target SOC determined therefrom, the SOC of battery 5 is reduced through methods such as driving in EV mode and appropriate auxiliary drive, thereby reducing the SOC of battery 5 to near the target SOC just before reaching the downhill section. Therefore, during subsequent downhill driving, the upper limit SOC of battery 5 will not be exceeded, thus achieving maximum energy recovery.

[0030] Figure 3 The diagram compares the characteristics of (a) changes in altitude of the driving route, (b) power consumption / regeneration of the electric generator 4, and (c) changes in the SOC of the battery 5 in a driving mode with relatively high regeneration on downhill roads (e.g., D gear in S mode) and (B) driving mode with relatively low regeneration on downhill roads (e.g., D gear in ECO mode).

[0031] The conditions for the downhill path, namely the slope and length, are the same in both (A) and (B). In case (A), as shown in (b), the regeneration rate is higher on the downhill path. Therefore, as shown in (c), the target SOC is set lower before reaching the downhill path. This allows for sufficient SOC reduction beforehand, maximizing energy recovery on the downhill path. On the other hand, in case (B), as shown in (b), the regeneration rate is lower on the downhill path. Therefore, as shown in (c), the target SOC is set relatively higher before reaching the downhill path. This prevents excessive SOC reduction before descending the slope and maintains an appropriate SOC level before and after the downhill path.

[0032] Thus, in the above embodiments, depending on whether the driving mode involves a higher or lower regeneration rate on a downhill slope, a decision is made on whether to implement SOC reduction control to preemptively lower the battery's SOC in preparation for downhill regeneration. Even when SOC reduction control is implemented, the target SOC before reaching the downhill slope is appropriately set based on the driving mode and the driver's driving habits. Therefore, excessive SOC increases or decreases can be avoided, achieving efficient energy recovery.

[0033] The present invention has been described in detail above with respect to one embodiment, but the present invention is not limited to the above embodiment and can be modified in various ways. For example, the present invention is not limited to series hybrid vehicles, but can also be widely applied to series hybrid vehicles, parallel hybrid vehicles, plug-in hybrid vehicles, and other hybrid vehicles capable of regeneration on downhill roads.

[0034] Furthermore, in the above embodiments, S mode, ECO mode, and other specific examples of driving modes were described as driving modes, but the driving modes of the present invention are not limited to the specific names mentioned above, and also broadly include a variety of driving modes with different regeneration amounts on downhill roads.

[0035] In addition, in the above embodiments, regenerative braking is performed in S mode and ECO mode when the accelerator pedal 13 is disengaged, and coordinated regenerative braking control is performed when the brake pedal 14 is depressed. However, the regenerative braking when the accelerator pedal 13 is disengaged and the coordinated regenerative braking control when the brake pedal 14 is depressed can be switched on and off respectively.

[0036] Furthermore, in this invention, coordinated regenerative braking control during brake pedal operation is not essential, and it can be applied even to vehicles that do not have a coordinated regenerative braking control mechanism.

Claims

1. A regenerative control method for a hybrid vehicle, the hybrid vehicle comprising: an electric generator connected to the vehicle's drive wheels; and a battery, the regenerative control method being to pre-detect a downhill section in the vehicle's driving path and perform SOC reduction control by pre-lowering the battery's SOC before the downhill section begins to cope with regeneration on the downhill section, wherein... The system switches between different SOC reduction controls based on the driving mode selected by the driver from various driving modes that affect the amount of regeneration on downhill roads. Furthermore, the driving tendencies of the driver on a downhill road should at least be determined in advance. When implementing the above-mentioned SOC reduction control, the expected amount of regeneration during downhill driving is calculated in advance. Based on this expected amount of regeneration, a basic target SOC is set in such a way that the greater the expected amount of regeneration, the greater the SOC reduction. Furthermore, the basic target SOC is adjusted based on the driver's driving tendencies to determine the final target SOC. In the process of pre-determining the driver's driving tendency, it is determined whether the driver is in a first tendency of stable driving or a second tendency of active driving. In the process of correcting the basic target SOC, if it is determined that the driver's driving tendency is the first tendency, it is determined that a relatively large amount of regeneration can be expected, and the basic target SOC is corrected to be smaller, so that the amount of SOC reduction is further increased.

2. The regenerative control method for a hybrid vehicle according to claim 1, wherein, As driving modes that affect the amount of regeneration on downhill roads, they include a regenerative braking mode that performs regenerative braking during braking and a normal braking mode that mainly performs friction braking during braking. In the regenerative braking mode, SOC reduction control is performed, while in the normal braking mode, SOC reduction control is not performed.

3. The regenerative control method for a hybrid vehicle according to claim 1, wherein, As a driving mode that affects the amount of regenerative braking on downhill roads, it includes a normal driving D gear selected by the gear selector lever, and at least one second gear that enhances the deceleration of regenerative braking compared to driving in the D gear, and performs SOC reduction control in the second gear.

4. The regenerative control method for a hybrid vehicle according to any one of claims 1 to 3, wherein, When implementing the above-mentioned SOC reduction control, the greater the deceleration of regenerative braking on a downhill road, the larger the SOC reduction amount should be set.

5. The regenerative control method for a hybrid vehicle according to any one of claims 1 to 3, wherein, The driver's driving tendencies are learned based on past driving experience on downhill roads and vehicle acceleration.

6. The regenerative control method for a hybrid vehicle according to any one of claims 1 to 3, wherein, Based on past data on regeneration on downhill roads, drivers' driving tendencies are learned.

7. A regenerative control device for a hybrid vehicle, the hybrid vehicle comprising: an electric generator connected to the vehicle's drive wheels; and a battery, wherein, The regenerative control device of the hybrid vehicle has: The downhill road detection department pre-detects downhill sections that exist in the vehicle's travel path; The driving mode selection unit allows the driver to select from a variety of driving modes, including driving modes with different regeneration rates for downhill roads. as well as The control unit selectively executes SOC reduction control, which, based on the driving mode selected by the driver, pre-emptively lowers the battery's SOC before the start of a downhill drive to cope with regeneration on the downhill section. The aforementioned control unit, At least the driving tendencies of the driver on a downhill road should be determined in advance. When implementing the above-mentioned SOC reduction control, the expected amount of regeneration during downhill driving is calculated in advance. Based on this expected amount of regeneration, a basic target SOC is set in such a way that the greater the expected amount of regeneration, the greater the SOC reduction. Furthermore, the basic target SOC is adjusted based on the driver's driving tendencies to determine the final target SOC. In the process of pre-determining the driver's driving tendency, it is determined whether the driver is in a first tendency of stable driving or a second tendency of active driving. In the process of correcting the basic target SOC, if it is determined that the driver's driving tendency is the first tendency, it is determined that a relatively large amount of regeneration can be expected, and the basic target SOC is corrected to be smaller, so that the amount of SOC reduction is further increased.

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