Hybrid electric vehicle and control method thereof

Abstract

To suppress stability of a vehicle from deteriorating and effectively suppress vibration noise of the vehicle due to an internal combustion engine.SOLUTION: A hybrid electric vehicle comprises an internal combustion engine, a main driving shaft that is driven by a first electric motor, a sub driving shaft that is driven by a second electric motor, and an electronic control unit. The electronic control unit executes driving torque distribution control by which requested vehicle torque based on accelerator aperture is distributed into main shaft torque and sub shaft torque. In the driving torque distribution control, the electronic control unit, when the requested vehicle torque is less than a first threshold, restricts torque of the internal combustion engine from increasing, in accordance with the requested vehicle torque, and increases a sub-shaft distribution ratio from the requested vehicle torque to the sub shaft torque as the requested vehicle torque increases, while limiting the main shaft torque to be less than an upper-limit value of the main shaft torque; and when the requested vehicle torque is above the first threshold and is less than a second threshold, increases the main shaft torque and the sub shaft torque as the requested vehicle torque increases, while limiting the sub shaft distribution ratio to be less than the upper-limit value of the distribution ratio.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a hybrid electric vehicle (HEV) and a control method thereof. [Background technology]

[0002] Patent Document 1 discloses a hybrid electric vehicle equipped with an internal combustion engine and first and second electric motors as a power source. In this vehicle, in order to suppress vehicle vibration noise, when one of the absolute values ​​of the rotation speeds of the first and second electric motors is within a resonant rotation speed range including the vehicle's resonant frequency and the other is outside the resonant rotation speed range, the two electric motors are controlled to reduce the torque output from one electric motor and satisfy the required torque.

[0003] Patent Document 2 discloses a hybrid electric vehicle equipped with an internal combustion engine and two electric motors as power sources. In this vehicle, in order to suppress vehicle vibration noise, when the target rotation speed and target torque of the internal combustion engine are in a booming noise region, torque commands for the two electric motors are set so that a required torque is output to the drive shaft outside a predetermined region in the booming noise region. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2008-265599 A [Patent Document 2] JP 2008-230510 A Summary of the Invention [Problem to be solved by the invention]

[0005] According to the techniques described in the above-mentioned Patent Documents 1 and 2, the operating point of the electric motor is changed to suppress vehicle vibration noise, but the operating point of the internal combustion engine is not changed. Therefore, it is not possible to effectively suppress vibration and noise caused by explosions in the internal combustion engine and transmitted to the vehicle body via the engine mount. In addition, it is required that the control of the drive torque for suppressing vehicle vibration noise is performed in a manner that does not reduce vehicle stability.

[0006] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a hybrid electric vehicle and a control method thereof that can effectively suppress vehicle vibration noise caused by an internal combustion engine while suppressing a decrease in vehicle stability. [Means for solving the problem]

[0007] A hybrid electric vehicle according to the present disclosure includes a main drive shaft, an auxiliary drive shaft, and an electronic control unit. The main drive shaft is connected to the main drive wheels and is driven by an internal combustion engine and a first electric motor. The auxiliary drive shaft is connected to the auxiliary drive wheels and is driven by a second electric motor. The electronic control unit controls a main shaft torque, which is the torque of the main drive shaft, and a countershaft torque, which is the torque of the countershaft. The electronic control unit executes a drive torque distribution control for distributing a vehicle required torque based on an accelerator opening to the main shaft torque and the countershaft torque. In the drive torque distribution control, when the vehicle required torque is less than a first threshold value, the electronic control unit increases a countershaft distribution ratio from the vehicle required torque to the countershaft torque in response to an increase in the vehicle required torque while limiting an increase in the torque of the internal combustion engine in response to the vehicle required torque and limiting the main shaft torque to less than a main shaft torque upper limit value, and when the vehicle required torque is equal to or greater than the first threshold value and less than a second threshold value, increases the main shaft torque and the countershaft torque in response to an increase in the vehicle required torque while limiting the countershaft distribution ratio to less than a distribution ratio upper limit value.

[0008] The hybrid electric vehicle may include a battery that supplies power to the first and second electric motors, and the electronic control unit may limit the vehicle required torque used in the drive torque distribution control so that the lower the output of the battery is, the lower the vehicle required torque is.

[0009] In the drive torque distribution control, when the vehicle required torque is equal to or greater than a second threshold value, the electronic control unit may increase the main shaft torque in response to an increase in the vehicle required torque while limiting the counter shaft torque to less than the counter shaft torque upper limit value.

[0010] A control method for a hybrid electric vehicle according to the present disclosure controls a hybrid electric vehicle including a main drive shaft connected to main drive wheels and driven by an internal combustion engine and a first electric motor, and a secondary drive shaft connected to secondary drive wheels and driven by a second electric motor. The control method executes a drive torque distribution control for distributing a vehicle required torque based on an accelerator opening to a main shaft torque which is the torque of the main drive shaft and a secondary drive shaft torque which is the torque of the secondary drive shaft. In the drive torque distribution control, when the vehicle required torque is less than a first threshold value, the control method increases a secondary shaft distribution ratio from the vehicle required torque to the secondary shaft torque in response to an increase in the vehicle required torque while limiting an increase in the torque of the internal combustion engine and limiting the main shaft torque to less than a main shaft torque upper limit value. In the drive torque distribution control, when the vehicle required torque is equal to or greater than the first threshold value and less than a second threshold value, the control method increases the main shaft torque and the secondary shaft torque in response to an increase in the vehicle required torque while limiting the secondary shaft distribution ratio to less than a distribution ratio upper limit value. Effect of the Invention

[0011] According to the hybrid electric vehicle and the control method thereof disclosed herein, when the vehicle required torque is less than a first threshold value, the countershaft distribution ratio is increased in response to the increase in the vehicle required torque while limiting the increase in the torque of the internal combustion engine and limiting the main shaft torque to less than the main shaft torque upper limit value. This limits the increase in the load on the engine mount, thereby suppressing the deterioration of the vehicle vibration noise caused by the internal combustion engine. Furthermore, when the vehicle required torque is equal to or greater than the first threshold value and less than a second threshold value, the main shaft torque and the countershaft torque are increased in response to the increase in the vehicle required torque while limiting the countershaft distribution ratio to less than the distribution ratio upper limit value. By limiting the increase in the countershaft distribution ratio in this manner, it is possible to suppress a decrease in vehicle stability caused by excessive distribution of the vehicle required torque to the auxiliary drive shaft. [Brief description of the drawings]

[0012] [Figure 1] 1 is a diagram illustrating an example of a configuration of a hybrid electric vehicle according to an embodiment; [Diagram 2] 4 is a flowchart showing a process flow relating to drive torque distribution control according to the embodiment. [Diagram 3] 1 is a diagram showing a basic relationship between a main shaft torque Tms and an engine torque limit value Tel. FIG. [Figure 4] FIG. 10 is a diagram for explaining a problem caused by a battery output and a measure to limit a vehicle required torque Tvr. [Diagram 5] 13 is a flowchart showing a procedure for calculating a minor shaft distribution ratio Ktr. [Figure 6] 6 is a diagram for explaining details of the minor shaft distribution ratio Ktr determined by the process of the flowchart shown in FIG. 5. FIG. [Figure 7] 11 is a diagram showing an example of the relationship between the main shaft torque Tms and the engine torque limit value Tel when the vibration noise suppression standard is relaxed. FIG. [Figure 8] FIG. 4 is a diagram showing the relationship between main shaft torque Tms and vehicle acceleration. [Figure 9] FIG. 4 is a diagram showing the relationship between the total drive torque Tv and the engine torque limit value Tel. [Figure 10] 7A to 7C are diagrams illustrating the operation of the drive torque distribution control according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In the following embodiments, when the number, quantity, amount, range, etc. of each element is mentioned, the technical idea of ​​the present disclosure is not limited to the mentioned number unless otherwise specified or clearly specified in principle. Furthermore, the structures, steps, etc. described in the following embodiments are not necessarily essential to the technical idea of ​​the present disclosure unless otherwise specified or clearly specified in principle.

[0014] 1. Example of hybrid electric vehicle configuration 1 is a diagram illustrating an example of a configuration of a hybrid electric vehicle 10 according to an embodiment. The hybrid electric vehicle (hereinafter also referred to as "HEV") 10 includes an internal combustion engine 12, an electric motor 14 (first electric motor), and an electric motor 16 (second electric motor) as power sources. The internal combustion engine 12 is, for example, a spark ignition engine. More specifically, as an example, the electric motors 14 and 16 are configured as three-phase AC motor generators capable of generating electricity.

[0015] The HEV 10 also includes a main drive shaft 18, main drive wheels 20, a secondary drive shaft 22, and secondary drive wheels 24. As an example, the main drive wheels 20 are the two front wheels of the HEV 10, and the secondary drive wheels 24 are the two rear wheels. Conversely to this example, the main drive wheels may be the two rear wheels of the EV, and the secondary drive wheels may be the two front wheels.

[0016] The main drive shaft 18 is driven by the output torques of the internal combustion engine 12 and the electric motor 14. More specifically, as an example, the internal combustion engine 12 and the electric motor 14 are arranged coaxially. The output torques of the internal combustion engine 12 and the electric motor 14 are transmitted to the main drive shaft 18 via a differential gear 26. The main drive shaft 18 is a rotation shaft of the main drive wheels 20.

[0017] The auxiliary drive shaft 22 is independent of the main drive shaft 18 and is driven by the output torque of the electric motor 16. More specifically, the output torque of the electric motor 16 is transmitted to the auxiliary drive shaft 22 via a differential gear 28. The auxiliary drive shaft 22 is a rotation shaft of the auxiliary drive wheels 24.

[0018] In the example shown in Fig. 1, one electric motor is used to drive the main drive shaft 18. However, the number of electric motors provided together with the internal combustion engine to drive the main drive shaft may be multiple. Specifically, for example, a planetary gear type power split mechanism may be used together with the internal combustion engine and two electric motors to drive the main drive shaft.

[0019] The HEV 10 further includes a battery 30, an electronic control unit (ECU) 32, and power control units (PCUs) 34 and 36. The battery 30 stores power to be supplied to the electric motors 14 and 16. The ECU 32 is configured to control the internal combustion engine 12 and the electric motors 14 and 16. The PCUs 34 and 36 are power conversion devices including inverters for driving the electric motors 14 and 16, respectively, and control the electric motors 14 and 16 based on commands from the ECU 32.

[0020] The battery 30 is charged, for example, using electric power generated by the electric motor 14 that is rotationally driven using the power of the internal combustion engine 12. The battery 30 is also charged using electric power generated by regenerative braking using at least one of the electric motors 14 and 16. Furthermore, the HEV 10 may be configured to be able to charge the battery 30 using external electric power. In other words, the HEV 10 may be a plug-in hybrid electric vehicle.

[0021] The ECU 32 has a processor and a storage device. The storage device stores various data including maps used for various controls of the internal combustion engine 12 and the electric motors 14 and 16, and various control programs. The processor reads out and executes the control programs from the storage device, thereby realizing various processes by the ECU 32 for the above-mentioned various controls. Note that there may be multiple ECUs 32.

[0022] The ECU 32 also receives sensor signals from sensors 38 mounted on the HEV 10. The sensors 38 include, for example, a vehicle speed sensor, an accelerator position sensor, a crank angle sensor, a battery temperature sensor, and a battery current sensor. The ECU 32 can calculate the engine speed based on the signal from the crank angle sensor. The ECU 32 can also calculate a State Of Charge (SOC) indicating the charging rate of the battery 30 based on an integrated value of the charging and discharging current of the battery 30 detected by a battery current sensor.

[0023] 2. Drive torque distribution control The HEV 10 configured as described above is an electric 4WD vehicle in which the main drive wheels 20 are driven by the internal combustion engine 12 and the electric motor 14, and the auxiliary drive wheels 24 are driven by the electric motor 16. With this type of electric 4WD HEV 10, the generation of "vehicle required torque Tvr," which is the drive torque required of the HEV 10, can be shared between the main drive shaft 18 and the auxiliary drive shaft 22 by controlling the output torque of the internal combustion engine 12 and the electric motors 14 and 16.

[0024] More specifically, in the drive torque distribution control, the drive torque shared by the main drive shaft 18 and the auxiliary drive shaft 22 can be determined by distributing the vehicle required torque Tvr to each shaft according to a predetermined distribution ratio. In this embodiment, a "auxiliary shaft distribution ratio Ktr" is used as an example of such a distribution ratio, as described later.

[0025] In the HEV 10, the internal combustion engine 12 and the electric motor 14 are assembled into a unit and mounted on the vehicle body via an engine mount (powertrain mount). The vibration characteristics of the internal combustion engine 12 are determined by the magnitude of the explosion and the interval between explosions. The magnitude of the explosion is proportional to the engine torque Te, and the interval between explosions is proportional to the engine speed. The engine vibrations thus generated are attenuated when passing through the engine mount before being transmitted to the vehicle body. If this attenuation is insufficient, passengers are more likely to feel the vibrations and noises caused by the engine vibrations (hereinafter referred to as "vibration and noise of the HEV 10").

[0026] It is also known that an excessive load on the engine mount reduces the vibration damping rate in the engine mount, which increases vibration and noise in the HEV 10. In addition, a load corresponding to the sum of the engine torque Te and the torque Tm1 of the electric motor 14 acts on the engine mount.

[0027] In order to effectively suppress vibration noise of the HEV 10, in this embodiment, the driving torque distribution control described below is executed.

[0028] 2 is a flowchart showing a process flow relating to the drive torque distribution control according to the embodiment. The process of this flowchart is repeatedly executed by the ECU 32 while the HEV 10 is traveling.

[0029] <Calculation of vehicle required torque Tvr> 2, first, in step S100, the ECU 32 calculates the vehicle required torque Tvr. The vehicle required torque Tvr is a vehicle driving torque required for driving the HEV 10 (in other words, a total required torque), and is calculated based on the accelerator opening. More specifically, as an example, the ECU 32 calculates the vehicle required torque Tvr based on the accelerator opening and the vehicle speed detected by the accelerator position sensor and the vehicle speed sensor, respectively. Thereafter, the process proceeds to step S102.

[0030] <Calculation of required torque after limit Tvrl> In step S102, the ECU 32 calculates a limited required torque Tvrl, which is a limit value of the vehicle required torque Tvr.

[0031] Fig. 3 is a diagram showing the basic relationship between the main shaft torque Tms and the engine torque limit value Tel. The main shaft torque Tms is the output torque of the main drive shaft 18, and has a value corresponding to the sum of the engine torque Te and the motor torque Tm1 (torque of the electric motor 14). The engine torque limit value Tel corresponds to the upper limit of the engine torque Te that is tolerable for vibration noise (NV) of the HEV 10. The dashed line in Fig. 3 corresponds to a straight line obtained when the main shaft torque Tms and the engine torque limit value Tel have a one-to-one relationship.

[0032] The vibration generated by the internal combustion engine 12 when generating a certain torque is larger than the vibration generated by the electric motor 14 when generating the same torque. Therefore, when the required main shaft torque Tms increases with an increase in the vehicle required torque Tvr (in other words, when the damping rate of the engine mount decreases), if the ratio of the engine torque Te to the main shaft torque Tms is high, the vibration transmitted to the vehicle body via the engine mount increases compared to when the ratio is low. Therefore, in order to suppress the vibration noise of the HEV 10, it is necessary to limit the engine torque Te so that the ratio of the engine torque Te to the main shaft torque Tms decreases with an increase in the required main shaft torque Tms. Therefore, in the characteristics shown in FIG. 3, the engine torque limit value Tel decreases with an increase in the main shaft torque Tms in a high torque region where the main shaft torque Tms is higher than a certain value.

[0033] As described with reference to Fig. 3, when the main shaft torque Tms is increased, the engine torque Te is reduced (limited). Therefore, in this embodiment, in order to suppress a reduction in the total driving torque Tv of the front and rear wheels (main driving wheels 20 and auxiliary driving wheels 24), a part of the vehicle required torque Tvr is distributed to the electric motor 16 connected to the auxiliary driving shaft 22, which is a shaft separate from the main driving shaft 18, by using "driving torque distribution control". More specifically, by using the driving torque distribution control, the distribution ratio of the driving torque to the auxiliary driving shaft 22 is increased according to the magnitude of the vehicle required torque Tvr (for details, see step S104 described later). This limits the increase in the load on the engine mount, and suppresses an increase in vibration noise of the HEV 10.

[0034] However, the torque (motor torques Tm1 and Tm2) that can be output by the electric motors 14 and 16 is limited by the output of the battery 30. This gives rise to the following problem. Fig. 4 is a diagram for explaining the problem caused by the battery output (Fig. 4(A)) and the countermeasure therefor, that is, the limitation of the vehicle required torque Tvr (Fig. 4(B)).

[0035] The vehicle required torque Tvr is proportional to the accelerator opening. As shown in FIG. 4A, the vehicle drive torque Tv (output torque) increases as the vehicle required torque Tvr increases according to the accelerator opening. Whether the vehicle drive torque Tv according to the vehicle required torque Tvr can be generated even after the vehicle required torque Tvr reaches a value Tvr1 that is affected by the engine torque limit depends on the battery output. Specifically, in the example of the battery output "small" shown in FIG. 4A, the decrease (limitation) of the engine torque Te cannot be compensated for by the increase of the motor torques Tm1 and Tm2 immediately after the value Tvr1 is reached. In addition, in the examples of the battery output "medium" and "large", there is a torque region in which the generation of the vehicle drive torque Tv according to the vehicle required torque Tvr can be continued even after the value Tvr1 is reached. However, in both examples, although there is a difference according to the battery output, the vehicle drive torque Tv according to the vehicle required torque Tvr cannot be generated soon. In this way, when the accelerator pedal is depressed, the reduction (limitation) of engine torque Te for vibration suppression cannot be compensated for by an increase in motor torques Tm1 and Tm2 due to insufficient battery output, and the total drive torque Tv of HEV 10 may decrease.

[0036] In response to such a problem, in this embodiment, the vehicle required torque Tvr is limited according to the battery output. Specifically, as shown in FIG. 4B, in an example where the battery output is "small", the vehicle required torque Tvr is limited by a value Tvr1 at which the engine torque Te is not expected to increase due to the influence of the engine torque limit. In this example, the value Tvr1 corresponds to the limited required torque Tvrl. In addition, in an example where the battery output is "medium", the vehicle required torque Tvr is limited by a maximum value Tvr2 at which the generation of the vehicle drive torque Tv according to the vehicle required torque Tvr can be continued due to the increase in the motor torques Tm1 and Tm2. In this example, the value Tvr2 corresponds to the limited required torque Tvrl. Similarly, in an example where the battery output is "large", the vehicle required torque Tvr is limited by a maximum value Tvr3. As can be seen from these examples, the vehicle required torque Tvr is limited more greatly as the battery output is lower. By limiting the vehicle required torque Tvr in this manner in accordance with the battery output, it is possible to suppress the decrease (limitation) of the engine torque Te caused by the increase in the main shaft torque Tms accompanying the increase in the vehicle required torque Tvr, and the decrease in the total drive torque (vehicle drive torque) Tv caused by insufficient battery output.

[0037] Based on the above knowledge, in step S102, the ECU 32 calculates the post-limitation required torque Tvrl based on the battery output and the engine speed.

[0038] Here, the limit value of the vehicle required torque Tvr (post-limitation required torque Tvrl) and the engine torque limit value Tel are mutually dependent. For this reason, it is difficult for the ECU 32 to constantly calculate the post-limitation required torque Tvrl based on the engine torque limit value Tel. Therefore, a "post-limitation required torque map" that determines the post-limitation required torque Tvrl (i.e., the maximum value of the total drive torque Tv that can be output) from the battery output and engine speed is calculated and stored in advance in the storage device of the ECU 32.

[0039] More specifically, the post-restriction required torque map is set based on an engine torque limit map (a map that defines the relationship as shown in FIG. 3), the relationship between the total drive torque Tv and the front / rear distribution ratio, and the efficiency of the electric motor 16. Note that the battery output (i.e., the maximum allowable power that may be discharged from the battery 30) used in calculating the post-restriction required torque Tvrl in step 102 is calculated as a value according to the state of the battery 30 (e.g., SOC and temperature).

[0040] By using the above-mentioned post-limitation required torque map, the ECU 32 can calculate the post-limitation required torque Tvrl by a simple calculation from the battery output and the engine speed.

[0041] <Calculation of distribution ratio> In step S104 following step S102, the ECU 32 executes the process of the flowchart shown in the following Fig. 5 to calculate (determine) the countershaft distribution ratio Ktr. The countershaft distribution ratio Ktr is a specific example of a distribution ratio for distributing the vehicle required torque Tvr to the main drive wheels 20 and the countershaft 22. Fig. 5 is a flowchart showing a calculation procedure of the countershaft distribution ratio Ktr. Fig. 6 is a diagram for explaining the details of the countershaft distribution ratio Ktr determined by the process of the flowchart shown in Fig. 5.

[0042] 5, first, in step S200, the ECU 32 sets a basic distribution ratio Ktrbs as a provisional distribution ratio Ktrrq, which is a provisional value of the countershaft distribution ratio Ktr used in the calculation process of the countershaft distribution ratio Ktr. The basic distribution ratio Ktrbs is determined in advance as a basic value of the countershaft distribution ratio Ktr. As shown in FIG. 6, the basic distribution ratio Ktrbs is determined so as to be constant against changes in the post-limitation required torque Tvrl, for example.

[0043] Next, in step S202, the ECU 32 calculates the NV distribution ratio Ktrnv for suppressing noise and vibration (NV) of the HEV 10. The NV distribution ratio Ktrnv is calculated according to the following formula (1). Ktrnv=1-Tpfnvgd / Tvrl (1)

[0044] The torque value Tpfnvgd in formula (1) corresponds to the lower limit of the region of the vehicle required torque Tvr where it is desired to suppress an increase in the main shaft torque Tms in order to suppress vibration and noise of the HEV 10. According to formula (1) and FIG. 6, the NV distribution ratio Ktrnv becomes zero when the post-restriction required torque Tvrl is equal to the torque value Tpfnvgd. As the post-restriction required torque Tvrl becomes larger with respect to the torque value Tpfnvgd, the NV distribution ratio Ktrnv becomes higher (i.e., the vehicle required torque Tvr distributed to the auxiliary drive shaft 22 becomes larger). The lower limit of the NV distribution ratio Ktrnv is zero, and is restricted from becoming less than zero.

[0045] Next, in step S204, the ECU 32 determines whether the provisional distribution ratio Ktrrq (here, the basic distribution ratio Ktrbs) is lower than the NV distribution ratio Ktrnv. As a result, if the provisional distribution ratio Ktrrq is lower than the NV distribution ratio Ktrnv, the process proceeds to step S2006 and step S208 in that order. In step S206, the ECU 32 updates the provisional distribution ratio Ktrrq by the NV distribution ratio Ktrnv. That is, the lower limit of the countershaft distribution ratio Ktr is guarded by the NV distribution ratio Ktrnv so as to suppress deterioration of vibration and noise of the HEV 10.

[0046] On the other hand, if the provisional distribution ratio Ktrrq is equal to or greater than the NV distribution ratio Ktrnv in step S204, the process proceeds to step S208 without updating the provisional distribution ratio Ktrrq.

[0047] In step S208, the ECU 32 determines whether the provisional distribution ratio Ktrrq (here, the basic distribution ratio Ktrbs or the NV distribution ratio Ktrnv) is higher than the first upper limit distribution ratio Ktrgd. If the countershaft distribution ratio Ktr becomes too high, there is a risk that vehicle stability may deteriorate. The first upper limit distribution ratio Ktrgd is determined in advance as an upper limit value of the countershaft distribution ratio Ktr that can satisfactorily ensure vehicle stability. More specifically, the first upper limit distribution ratio Ktrgd is determined to be constant, for example, regardless of the vehicle required torque Tvr, as shown in FIG. 6.

[0048] If the provisional distribution ratio Ktrrq is higher than the first upper limit distribution ratio Ktrgd in step S208, the process proceeds to steps S210 and S212. In step S210, the ECU 32 updates the provisional distribution ratio Ktrrq by the first upper limit distribution ratio Ktrgd. That is, the upper limit of the countershaft distribution ratio Ktr is guarded by the first upper limit distribution ratio Ktrgd so as to suppress deterioration of vehicle stability caused by the countershaft distribution ratio Ktr becoming too high.

[0049] On the other hand, if the provisional distribution ratio Ktrrq is equal to or less than the first upper limit distribution ratio Ktrgd in step S208, the process proceeds to step S212 without updating the provisional distribution ratio Ktrrq.

[0050] In step S212, the ECU 32 determines whether the provisional distribution ratio Ktrrq (here, the basic distribution ratio Ktrbs, the NV distribution ratio Ktrnv, or the first upper limit distribution ratio Ktrgd) is higher than the second upper limit distribution ratio Ktrmg. The second upper limit distribution ratio Ktrmg is another upper limit value of the countershaft distribution ratio Ktr that is determined in advance in consideration of the torque that can be output by the electric motor 16 on the auxiliary drive shaft 22 side. More specifically, as shown in FIG. 6, the second upper limit distribution ratio Ktrmg is determined so as to decrease as the vehicle required torque Tvr increases. In addition, the torque region in which the second upper limit distribution ratio Ktrmg is set is located on the high torque side compared to the torque region in which the NV distribution ratio Ktrnv is set.

[0051] If the provisional distribution ratio Ktrrq is higher than the second upper limit distribution ratio Ktrmg in step S212, the process proceeds to step S214 and then step S216. In step S214, the ECU 32 updates the provisional distribution ratio Ktrrq by the second upper limit distribution ratio Ktrmg. That is, the upper limit of the countershaft distribution ratio Ktr is protected by the second upper limit distribution ratio Ktrmg so that the countershaft distribution ratio Ktr is not determined to exceed the torque that the electric motor 16 can output.

[0052] On the other hand, if the provisional distribution ratio Ktrrq is equal to or less than the second upper limit distribution ratio Ktrmg in step S212, the process proceeds to step S216 without updating the provisional distribution ratio Ktrrq.

[0053] In step S216, the ECU 32 determines the provisional distribution ratio Ktrrq as the final countershaft distribution ratio Ktr.

[0054] <Front and rear distribution> 2, in step S106 following step S104, the ECU 32 calculates a required main shaft torque Tmsr, which is a required value of the main shaft torque Tms, and a required countershaft torque Tssr, which is a required value of the countershaft torque Tss, in order to distribute the vehicle drive torque Tv between the front and rear. The countershaft torque Tss is the output torque of the counter drive shaft 22, and has a value corresponding to the torque of the electric motor 16 (motor torque Tm2).

[0055] Specifically, as shown in the following formula (2), the required main shaft torque Tmsr is the product of the limited required torque Tvrl and a value (1-Ktr) obtained by subtracting the countershaft distribution ratio Ktr from 1. The required countershaft torque Tssr is the product of the limited required torque Tvrl and the countershaft distribution ratio Ktr. Tmsr = Tvrl × (1 - Ktr) (2) Tssr = Tvrl × Ktr (3)

[0056] <Calculation of engine torque limit value Tel> Next, in step S108, the ECU 32 calculates the engine torque limit value Tel based on the post-limitation required torque Tvrl and the engine speed.

[0057] As already explained, the basic relationship between the main shaft torque Tms and the engine torque limit value Tel is expressed as shown in Fig. 3. Here, when the degree of acceleration request from the driver is high, it is considered that acceleration performance takes precedence over suppression of vibration noise of the HEV 10, and as a result, the standards for suppression of vibration noise can be relaxed.

[0058] FIG. 7 is a diagram showing an example of the relationship between the main shaft torque Tms and the engine torque limit value Tel when the vibration noise suppression standard is relaxed. The dashed line in FIG. 7 shows the basic characteristic shown in FIG. 3 (without relaxation taking into account vehicle acceleration). In the example shown in FIG. 7, the engine torque limit value Tel is increased compared to the basic characteristic (dashed line) in a torque region where the main shaft torque Tms is high. In other words, the restriction on the engine torque Te taking into account vehicle acceleration is relaxed. By using the characteristic shown in FIG. 7 instead of the basic characteristic when the degree of acceleration request is high, it is possible to suppress a decrease in the vehicle drive torque Tv and an increase in discharge from the battery 30 caused by the restriction on the engine torque Te.

[0059] However, the acceleration of the HEV 10 (vehicle acceleration (total vehicle acceleration)) is obtained by the main shaft torque Tms and the counter shaft torque Tss. FIG. 8 is a diagram showing the relationship between the main shaft torque Tms and the vehicle acceleration. As shown in FIG. 8, the vehicle acceleration obtained during acceleration basically increases as the main shaft torque Tms increases. In addition, the torque region in which the increase in the main shaft torque Tms is limited by the NV distribution ratio Ktrnv includes torque values ​​where the vehicle acceleration has a range with respect to the main shaft torque Tms, as shown by the symbol A in FIG. 8. For this reason, the map of the engine torque limit value Tel using the main shaft torque Tms as an argument cannot appropriately manage the relationship between the vehicle acceleration and the vibration noise.

[0060] 9 is a diagram showing the relationship between the total drive torque Tv and the engine torque limit value Tel. The total drive torque (vehicle drive torque) Tv is a value according to the sum of the engine torque Te, the main shaft motor torque Tm1, and the counter shaft motor torque Tm2. Therefore, by using the total drive torque Tv, the relationship between the vehicle acceleration (total vehicle acceleration) and the drive torque can be appropriately managed to address the above-mentioned issue.

[0061] Therefore, in step S108, an "engine torque limit map" based on the post-limitation required torque Tvrl, which is the required value after limiting the total drive torque Tv, is used to calculate the engine torque limit value Tel. When using this map, the magnitude of the main shaft torque Tms that contributes to the vibration and noise of the HEV 10 is calculated in advance from the total drive torque and the assumed countershaft distribution ratio Ktr, and is reflected in the map. More specifically, this engine torque limit map is constructed in advance by adding the engine speed as an argument to the relationship between the post-limitation required torque Tvrl and the engine torque limit value Tel as shown in Figure 9, and is stored in the storage device of the ECU 32. Therefore, in step S108, the ECU 32 calculates the post-limitation required torque Tvrl. l By a simple calculation based on the engine speed and the vehicle acceleration, the engine torque limit value Tel can be calculated while reflecting the relaxation of the limit on the engine torque Te taking into account the vehicle acceleration.

[0062] <Engine torque limit> Next, in step S110, the ECU 32 calculates the required engine torque Ter, and then executes a process of protecting the upper limit of the calculated required engine torque Ter with the engine torque limit value Tel. More specifically, the ECU 32 calculates the required engine torque Ter as a value according to the required main shaft torque Tmsr and the required countershaft torque Tssr in accordance with a predetermined rule. Then, when the calculated required engine torque Ter is less than the engine torque limit value Tel, the ECU 32 limits the required engine torque Ter to be equal to the engine torque limit value Tel.

[0063] Fig. 10 is a diagram showing the operation of the driving torque distribution control according to the embodiment. According to the driving torque distribution control using the countershaft distribution ratio Ktr set as shown in Fig. 6 and the engine torque limit map (step S108), the main shaft torque Tms and the countershaft torque Tss change as shown in Fig. 10 in response to the change in the vehicle required torque (total required torque) Tvr.

[0064] Specifically, the region (horizontal axis) of vehicle required torque Tvr less than threshold value TH1 (corresponding to an example of the "first threshold value" according to the present disclosure) in Fig. 10 includes a first torque region and a second torque region. Also, Fig. 10 shows, as the region (vertical axis) of main shaft torque Tms, an NV suppression region in which main shaft torque Tms needs to be limited to suppress vibration noise of the HEV 10.

[0065] The first torque region corresponds to a torque region corresponding to a main shaft torque Tms lower than the NV suppression region. In this first torque region, the main shaft torque Tms and the counter shaft torque Tss are distributed from the vehicle required torque Tvr in accordance with the basic distribution ratio Ktrbs, and increase as the vehicle required torque Tvr increases.

[0066] The second torque region is located on the high torque side with respect to the first torque region, and corresponds to a torque region corresponding to the main shaft torque Tms included in the NV suppression region. In the second torque region (the same applies to the third and fourth torque regions described below) corresponding to the NV suppression region, an increase in the requested engine torque Ter is limited by the engine torque limit value Tel calculated according to the above-mentioned engine torque limit map in order to suppress vibration noise. According to this engine torque limit value Tel, an increase in the requested engine torque Ter is limited according to the vehicle requested torque Tvr (more specifically, the limited requested torque Tvrl).

[0067] In the second torque region, the main shaft torque Tms is limited to be less than the main shaft torque upper limit value in accordance with the NV distribution ratio Ktrnv. The NV distribution ratio Ktrnv is set to increase as the vehicle required torque Tvr increases, as shown in Fig. 6. Therefore, in the second torque region, the main shaft torque Tms is limited to be less than the main shaft torque upper limit value, while the counter shaft torque Tss increases as the vehicle required torque Tvr increases.

[0068] Further, the region of the vehicle required torque Tvr equal to or greater than the threshold value TH1 in Fig. 10 includes a third torque region and a fourth torque region. Like the second torque region, the third and fourth torque regions also correspond to torque regions corresponding to the main shaft torque Tms included in the NV suppression region.

[0069] In the third torque region, the countershaft distribution ratio Ktr is limited so as not to exceed a first upper limit distribution ratio Ktrgd (corresponding to an example of the “distribution ratio upper limit value” according to the present disclosure), while the main shaft torque Tms and the countershaft torque Tss increase in response to an increase in the vehicle required torque Tvr.

[0070] The fourth torque region is located on the high torque side of the third torque region. In addition, the third torque region corresponds to a torque region where the vehicle required torque Tvr is equal to or greater than a threshold value TH1 and less than a threshold value TH2 (corresponding to an example of the "second threshold value" according to the present disclosure), and the fourth torque region corresponds to a torque region where the vehicle required torque Tvr is equal to or greater than the threshold value TH2. In the fourth torque region, the countershaft torque Tss is limited to be less than the countershaft torque upper limit in accordance with the second upper limit distribution ratio Ktrmg, while the main shaft torque Tms increases in accordance with an increase in the vehicle required torque Tvr.

[0071] 3.Effects As described above, according to the drive torque distribution control of this embodiment, in the second torque region (see FIG. 10), the increase in the required engine torque Ter is limited according to the vehicle required torque Tvr, and the main shaft torque Tms is limited to less than the main shaft torque upper limit value. The countershaft distribution ratio Ktr is increased according to the increase in the vehicle required torque Tvr. This limits the increase in the load on the engine mount, thereby suppressing the deterioration of the vibration and noise of the HEV 10 caused by the internal combustion engine 12.

[0072] In the third torque region, the main shaft torque Tms and the counter shaft torque Tss increase in response to an increase in the vehicle required torque Tvr while the counter shaft distribution ratio Ktr is limited so as not to exceed the first upper limit distribution ratio Ktrgd. By limiting the increase in the counter shaft distribution ratio Ktr in this manner, it is possible to suppress deterioration of the vehicle posture caused by an excessive distribution of the vehicle required torque Tvr to the auxiliary drive shaft 22.

[0073] As described above, the driving torque distribution control of this embodiment makes it possible to provide the HEV 10 that can effectively suppress vibration noise caused by the internal combustion engine 12 while suppressing a decrease in vehicle stability.

[0074] In addition, the vehicle required torque Tvr used to calculate the engine torque limit value Tel in the drive torque distribution control is limited as the above-mentioned limited required torque Tvrl so that it becomes lower as the battery output becomes lower. This makes it possible to suppress a decrease in engine torque Te (in other words, excessive engine torque limitation) caused by an increase in main shaft torque Tms accompanying an increase in vehicle required torque Tvr, and to suppress a decrease in total drive torque (vehicle drive torque) Tv caused by insufficient battery output.

[0075] According to the drive torque distribution control, in the fourth torque range, the countershaft torque Tss is limited to be less than the countershaft torque upper limit, while the main shaft torque Tms is increased in accordance with an increase in the vehicle required torque Tvr. This allows the drive force to be appropriately distributed in the high torque range in consideration of the torque that can be output by the electric motor 16 on the auxiliary drive shaft 22 side.

[0076] 4. Other embodiments 4-1. Application to HEVs equipped with a gearbox The "drive torque distribution control" according to the present disclosure may be applied to a hybrid electric vehicle in which an internal combustion engine is combined with a transmission mechanism. In such an HEV, the transmission characteristics and resonance band of the drive system change depending on the gear stage of the transmission mechanism. In consideration of such changes, at least one of the engine torque limit map and the post-restriction required torque map may be set for each gear stage in consideration of the transmission characteristics and resonance band of the drive system at each gear stage. With this configuration, it is possible to perform optimal torque restriction at each gear stage by switching at least one of the engine torque limit map and the post-restriction required torque map according to the selected gear stage.

[0077] 4-2. Optimization of vibration and noise performance and dynamic performance The memory device of the HEV's ECU may store, in addition to the normal engine torque limit map having the above-mentioned settings, a second engine torque limit map in which the limits are relaxed so as to prioritize power over vibration and noise.

[0078] According to this configuration, by switching from the normal map to the second map under specific conditions, it becomes possible to selectively realize the vibration noise performance and power performance that meet the driver's expectations. The specific condition here is met, for example, when the driver selects the sports mode (power mode), the circuit mode, or the manual mode (manual shift mode). The specific condition may also be met when the HEV is towing or traveling on a steep hill.

[0079] 4-3. Suppression of vibration and noise deterioration by considering the output limit of the electric motor on the countershaft The countershaft distribution ratio Ktr (front / rear distribution ratio) is used to design the engine torque limit map as described above (see step S108). Here, the electric motor 16 on the countershaft side may require output limitation due to factors such as overheating. In such a case, the front / rear distribution ratio may differ from the assumed value, and as a result, the relationship between vehicle acceleration and vibration noise may be lost. Therefore, the storage device of the ECU may store a third engine torque limit map that assumes that all of the vehicle required torque Tvr is distributed to the main drive shaft 18, in addition to the normal engine torque limit map.

[0080] According to this configuration, when the electric motor 16 is subjected to output restriction due to a factor such as overheating, the map is switched to the third engine torque limit map, thereby suppressing the deterioration of vibration noise caused by an unintended front / rear distribution ratio. In addition, the switching between the normal map and the third map may be performed gradually by, for example, linear interpolation according to the degree of overheating of the electric motor 16. This makes it possible to avoid a sudden change in the front / rear distribution ratio caused by a sudden switching of the map. [Explanation of symbols]

[0081] 10 Hybrid Electric Vehicle (HEV) 12 Internal combustion engine 14 Spindle side electric motor 16 Electric motor on the countershaft side 18 Main drive shaft 20 Main drive wheel 22 Sub-drive shaft 24 Secondary drive wheel 26, 28 Differential gear 30 Battery 32 Electronic Control Unit (ECU) 34, 36 Power control unit (PCU) 38 Sensors

Claims

1. a main drive shaft coupled to the main drive wheels and driven by the internal combustion engine and the first electric motor; an auxiliary drive shaft connected to the auxiliary drive wheels and driven by a second electric motor; an electronic control unit for controlling a main shaft torque, which is a torque of the main drive shaft, and a counter shaft torque, which is a torque of the counter drive shaft; A hybrid electric vehicle comprising: the electronic control unit executes a drive torque distribution control for distributing a vehicle required torque based on an accelerator opening degree to the main shaft torque and the counter shaft torque, In the drive torque distribution control, the electronic control unit When the vehicle required torque is less than a first threshold value, an increase in the torque of the internal combustion engine is limited in accordance with the vehicle required torque, and the main shaft torque is limited to less than a main shaft torque upper limit value, while a countershaft distribution ratio from the vehicle required torque to the countershaft torque is increased in accordance with an increase in the vehicle required torque, When the vehicle required torque is equal to or greater than the first threshold value and less than a second threshold value, the main shaft torque and the countershaft torque are increased in accordance with an increase in the vehicle required torque while limiting the countershaft distribution ratio to less than a distribution ratio upper limit value; an upper limit value of the torque of the internal combustion engine at which vibration and noise of the hybrid electric vehicle can be tolerated in the driving torque distribution control is referred to as an engine torque limit value; In the drive torque distribution control, the electronic control unit calculates the engine torque limit value that is relaxed when the degree of the driver's acceleration request is high compared to when the degree of the driver's acceleration request is low, based on a post-limitation required torque that is a limit value of the vehicle required torque and a relationship established in advance between the engine rotation speed and the engine torque limit value. A hybrid electric vehicle characterized by:

2. the hybrid electric vehicle includes a battery that supplies power to the first and second electric motors; The electronic control unit limits the vehicle required torque used in the drive torque distribution control so as to be lower as the output of the battery becomes lower.

2. The hybrid electric vehicle of claim 1.

3. In the drive torque distribution control, when the vehicle required torque is equal to or greater than the second threshold value, the electronic control unit increases the main shaft torque in response to an increase in the vehicle required torque while limiting the counter shaft torque to less than a counter shaft torque upper limit value.

3. A hybrid electric vehicle as claimed in claim 1 or 2.

4. A method for controlling a hybrid electric vehicle including a main drive shaft connected to main drive wheels and driven by an internal combustion engine and a first electric motor, and an auxiliary drive shaft connected to auxiliary drive wheels and driven by a second electric motor, comprising the steps of: executing a drive torque distribution control for distributing a vehicle required torque based on an accelerator opening degree to a main shaft torque which is a torque of the main drive shaft and a sub-shaft torque which is a torque of the sub-drive shaft; in the drive torque distribution control, when the vehicle required torque is less than a first threshold value, an increase in torque of the internal combustion engine is limited in accordance with the vehicle required torque, and the main shaft torque is limited to less than a main shaft torque upper limit value, while a countershaft distribution ratio from the vehicle required torque to the countershaft torque is increased in accordance with an increase in the vehicle required torque; In the drive torque distribution control, when the vehicle required torque is equal to or greater than the first threshold value and less than a second threshold value, the main shaft torque and the countershaft torque are increased in response to an increase in the vehicle required torque while limiting the countershaft distribution ratio to less than a distribution ratio upper limit value. Including, an upper limit value of the torque of the internal combustion engine at which vibration and noise of the hybrid electric vehicle can be tolerated in the driving torque distribution control is referred to as an engine torque limit value; The control method further includes, in the drive torque distribution control, calculating the engine torque limit value that is relaxed when a degree of acceleration request by a driver is high compared to when the degree of the acceleration request is low, based on a post-limitation required torque that is a limit value of the vehicle required torque and a relationship established in advance between the engine rotation speed and the engine torque limit value.

23. A method for controlling a hybrid electric vehicle comprising:

Images