Hybrid vehicle

Abstract

To provide a hybrid vehicle that ensures the transition to motor-driven travel while suppressing hesitation.SOLUTION: A control device which switches between engine-driven hybrid travel with a clutch engaged and motor-driven travel with the clutch released: calculates a predicted upper limit which is an output upper limit of a battery when an engine is started by a motor during the hybrid travel; sets a determination value on the basis of the predicted upper limit; determines that transition to motor-driven travel is prohibited when a vehicle speed during the hybrid travel exceeds a determination value; and permits transition to the motor-driven travel when the vehicle speed is equal to or less than the determination value. A setting section sets the vehicle speed which results in a sufficient output value to reach the predicted upper limit as the determination value. The determination value is obtained by adding a predetermined margin value which decreases as the vehicle speed decreases to a required output value. The required output value is a battery's output value per unit time at each vehicle speed capable of maintaining the motor-driven travel when the engine start-up is completed and decreases as the vehicle speed decreases.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a hybrid vehicle.

Background Art

[0002] There is a hybrid vehicle that switches between hybrid driving powered by an engine and motor driving powered by a motor (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When shifting from motor driving to hybrid driving, the engine is cranked by the motor, which is the driving power source, to start the engine. Here, depending on the output upper limit value of the battery, there may be a hesitation in which the power of the motor is insufficient when starting the engine, resulting in a decrease in the acceleration of the hybrid vehicle. Therefore, when the output upper limit value of the battery during hybrid driving is low, it is conceivable to not permit the shift from hybrid driving to motor driving and continue hybrid driving. However, if the frequency of not permitting the shift to motor driving increases, the driving time of the engine becomes long, which may deteriorate fuel consumption and exhaust emissions.

[0005] Therefore, an object of the present invention is to provide a hybrid vehicle that suppresses hesitation and ensures a shift to motor driving.

Means for Solving the Problems

[0006] The above object is achieved by a hybrid vehicle including: an engine; a clutch disposed on a power transmission path from the engine to wheels; a motor disposed on the power transmission path from the clutch to the wheels and capable of starting the engine by cranking the engine with the clutch engaged; a battery that outputs electric power to the motor; a control device that switches between a hybrid running mode in which the vehicle runs by the power of the engine with the clutch engaged and a motor running mode in which the vehicle runs by the power of the motor with the clutch disengaged. The control device includes: a calculation unit that calculates a predicted upper limit value which is a predicted value of an output upper limit value of the battery when starting of the engine by the motor during motor running is completed during hybrid running; a setting unit that sets a determination value based on the predicted upper limit value; and a determination unit that determines non-permission of a shift to the motor running mode when a vehicle speed during hybrid running is higher than the determination value, and determines permission of a shift to the motor running mode when the vehicle speed during hybrid running is equal to or lower than the determination value. The setting unit sets, as the determination value, a vehicle speed at which a full output value becomes the predicted upper limit value, the full output value is a value obtained by adding a predetermined margin value to a required output value, the required output value is an output value per unit time of the battery for each vehicle speed at which running can be maintained by the motor when starting of the engine is completed, the required output value decreases as the vehicle speed decreases, and the margin value decreases as the vehicle speed decreases.

[0007] The hybrid vehicle may further include a transmission disposed on the power transmission path from the motor to the wheels, and the margin value may decrease as a gear ratio in the transmission increases.

[0008] The calculation unit may calculate the predicted upper limit value based on a state of charge (SOC) of the battery and an amount of power consumption of the battery from start to completion of starting of the engine by the motor.

[0009] Based on the rotational speed of the motor during the hybrid drive, the torque of the motor required for the motor drive at the rotational speed of the motor, the cranking torque required for cranking the engine by the motor, and the cranking period which is the period from when the cranking of the engine by the motor is started until combustion is started in the engine by the motor, the calculation unit may calculate the power consumption.

Advantages of the Invention

[0010] It is possible to provide a hybrid vehicle that suppresses hesitation and ensures a shift to motor drive.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0012] [Schematic Configuration of Hybrid Vehicle] FIG. 1 is a schematic configuration diagram of a hybrid vehicle 1. In the hybrid vehicle 1, a clutch 30, a motor 40, and a transmission 50 are sequentially provided in the power transmission path from the engine 10 to the drive wheels 70. The engine 10 and the motor 40 are mounted as driving sources for the hybrid vehicle 1 to travel. The engine 10 may be, for example, a gasoline engine or a diesel engine. The transmission 50 and the left and right drive wheels 70 are connected via a differential gear 60. The transmission 50 includes a torque converter 51 and an automatic transmission 52. The automatic transmission 52 may be a stepped transmission or a continuously variable transmission.

[0013] The clutch 30 is provided between the engine 10 and the motor 40 on the same power transmission path. The clutch 30 receives hydraulic pressure supply from the released state and engages to connect the power transmission between the engine 10 and the motor 40. The clutch 30 is released in response to the stop of hydraulic pressure supply to cut off the power transmission between the engine 10 and the motor 40.

[0014] The motor 40 is connected to the battery 90 via the PCU 80. The motor 40 functions as a driving power source for the hybrid vehicle 1 in response to power supply from the battery 90. Further, the motor 40 also functions as a generator that charges the battery 90 in response to power transmission from the engine 10 or the drive wheels 70. The motor 40 can start the engine 10 by cranking the engine 10 when the clutch 30 is engaged.

[0015] The PCU 80 is controlled by the ECU 100 described later. In the case of a power running operation in which the motor 40 outputs torque, the PCU 80 converts the DC voltage of the battery 90 into an AC voltage and adjusts the power supplied to the motor 40. In the case of a regenerative operation in which the motor 40 generates power, the PCU 80 converts the AC voltage from the motor 40 into a DC voltage and adjusts the regenerative power supplied to the battery 90.

[0016] The hybrid vehicle 1 is provided with an ECU (Electronic Control Unit) 100 as a control device for the vehicle. The ECU 100 is an electronic control unit including an arithmetic processing circuit that performs various arithmetic processes related to the running control of the vehicle, and a memory in which control programs and data are stored. The ECU 100 is an example of a control device for the hybrid vehicle 1. The ECU 100 functionally realizes a calculation unit, a setting unit, and a determination unit, which will be described in detail later.

[0017] An oil temperature sensor 11, a rotation speed sensor 41, an SOC sensor 91, and a temperature sensor 92 are electrically connected to the ECU 100. The oil temperature sensor 11 detects the temperature of the lubricating oil of the engine 10. The rotation speed sensor 41 detects the rotation speed of the motor 40. The SOC sensor 91 detects the SOC (State of Charge) of the battery 90. The temperature sensor 92 detects the temperature of the battery 90. Incidentally, when the SOC sensor 91 is not provided, the ECU 100 may calculate the SOC based on the current value and voltage value of the battery 90.

[0018] The ECU 100 runs the hybrid vehicle 1 either in motor drive or hybrid drive. In motor drive, the ECU 100 stops the engine 10, disengages the clutch 30, and runs by the power of the motor 40. In hybrid drive, the clutch 30 is engaged and the vehicle runs at least by the power of the engine 10. Also, in hybrid drive, the output of the motor 40 can assist the driving of the engine 10.

[0019] The switching between motor drive and hybrid drive is performed based on the required torque for the hybrid vehicle 1 obtained from the vehicle speed and the accelerator opening. For example, when the required torque is less than the starting threshold for starting the engine 10, motor drive with the engine 10 stopped is selected to improve fuel efficiency. When the required torque is equal to or greater than the starting threshold for starting the engine 10, hybrid drive with the engine 10 started is selected.

[0020] [Motor Drive Transition Control] Figure 2 is a flowchart illustrating motor driving transition control. The ECU 100 determines whether the hybrid vehicle 1 is in hybrid driving (step S1). If the answer in step S1 is No, this control ends.

[0021] If the answer in step S1 is Yes, the ECU 100 executes a calculation process for calculating the predicted upper limit value of the battery 90 (step S2). The predicted upper limit value is a predicted value of the output upper limit value of the battery 90 when the start of the engine 10 by the motor 40 is completed during motor driving. The output upper limit value is the upper limit value that the battery 90 can output per unit time. The specific content of the calculation process will be described later. Step S2 is a process executed by the calculation unit.

[0022] Next, the ECU 100 determines whether the predicted upper limit value has been calculated (step S3). If the answer in step S3 is Yes, the ECU 100 determines whether the predicted upper limit value is equal to or greater than the lower limit value (step S4). The lower limit value will be described later. If the answer in step S3 or S4 is No, the ECU 100 does not permit the transition to motor driving (step S7).

[0023] If the answer in step S4 is Yes, the ECU 100 sets a determination value (step S5). The determination value is set as follows. FIG. 3A is an exemplary diagram of a map defining the relationship between the vehicle speed and the battery output value in this embodiment. This map is pre-stored in the ROM of the ECU 100. FIG. 3A shows the required output value and the sufficient output value. The required output value is the output value per unit time of the battery 90 for each vehicle speed at which running can be maintained by the motor 40 when the start of the engine 10 is completed. The sufficient output value is a value obtained by adding a predetermined margin value to the required output value. The margin value is a value appropriately determined in consideration of fluctuations in the output of the battery 90 and the like. The required output value decreases as the vehicle speed decreases. For this reason, the sufficient output value also decreases as the vehicle speed decreases. The vehicle speed when the sufficient output value becomes the predicted upper limit value is set as the determination value. As described above, the sufficient output value decreases as the vehicle speed decreases. Therefore, the lower the predicted upper limit value of the battery 90, the lower the set determination value. Incidentally, although it will be described in detail later, the margin value also decreases as the vehicle speed decreases, and decreases as the gear ratio of the automatic transmission 52 increases. Step S5 is an example of the process executed by the setting unit.

[0024] Incidentally, FIG. 3A shows the above-described lower limit value. The lower limit value is the minimum value of the sufficient output value at which the shift to motor running is permitted. Therefore, as described above, if the answer in step S4 is No, the shift to motor running is not permitted (step S7).

[0025] After the execution of step S5, the ECU 100 determines whether or not the vehicle speed of the hybrid vehicle 1 is equal to or lower than the determination value (step S6). If the answer in step S6 is No, the ECU 100 determines not to permit the shift to motor running (step S7). If the answer in step S6 is Yes, the ECU 100 determines to permit the shift to motor running (step S8). Steps S7 and S8 are examples of the processes executed by the determination unit.

[0026] As shown in FIG. 3A, the determination value decreases as the predicted upper limit value decreases. In other words, the lower the predicted upper limit value, the wider the non-permissible range in which the shift to motor driving is not permitted. As a result, hybrid driving is continued, and hesitation during the shift from motor driving to hybrid driving can be suppressed.

[0027] Here, a comparative example in which the margin value is constant will be described. FIG. 3B is an exemplary diagram of a map defining the relationship between the vehicle speed and the battery output value in the comparative example. As shown in FIG. 3B, when the margin value is constant, the determination value is set to a lower value than in the case of the present embodiment shown in FIG. 3A. Therefore, the permissible range in which the shift to motor driving is permitted in the comparative example is narrower than in the present embodiment. Here, when the vehicle speed of the hybrid vehicle 1 is low, the acceleration with respect to the accelerator operation amount is large. That is, even if hesitation occurs at a low vehicle speed, acceleration can be immediately ensured by the accelerator operation. Therefore, the driver hardly feels the occurrence of hesitation. Therefore, in the present embodiment as shown in FIG. 3A, the margin value decreases as the vehicle speed decreases. As a result, the shift to motor driving is permitted within a range of vehicle speeds in which the driver hardly feels the occurrence of hesitation.

[0028] Also, as shown in FIG. 3A, the larger the gear ratio of the automatic transmission 52, in other words, the lower the gear position of the automatic transmission 52, the margin value decreases stepwise. This is because the lower the gear position, the larger the acceleration with respect to the accelerator operation amount, and the driver hardly feels the occurrence of hesitation. The shift to motor driving is permitted within a range of gear positions in which the driver hardly feels the occurrence of hesitation.

[0029] FIG. 4 is an exemplary diagram of a map defining the relationship between the vehicle speed and the battery output value in the modified example. In the modified example, the automatic transmission 52 is a continuously variable transmission. In this case, the larger the gear ratio of the automatic transmission 52, the continuously the margin value decreases. Also in this case, the larger the gear ratio, the larger the acceleration with respect to the accelerator operation amount, and the driver hardly feels hesitation.

[0030] [Calculation Control of Prediction Upper Limit Value] Next, the calculation control of the prediction upper limit value described above will be explained. FIG. 5 is a flowchart illustrating the calculation control of the prediction upper limit value. First, the ECU 100 calculates the current output upper limit value of the battery 90 based on the SOC and temperature of the battery 90 (step S21). FIG. 6 is an exemplary diagram of a map defining the output upper limit value according to the SOC and temperature of the battery 90. FIG. 6 shows the cases where the SOC is high and where the SOC is low. As shown in FIG. 6, the higher the temperature of the battery 90, the more the output upper limit value of the battery 90 increases up to a predetermined value. When the temperature of the battery 90 is equal to or higher than the predetermined value, the output upper limit value of the battery 90 becomes constant. Also, the higher the SOC, the more the output upper limit value increases.

[0031] Next, the ECU 100 acquires the motor rotation speed, which is the current rotation speed of the motor 40, and estimates the motor torque, which is the torque required for the motor 40 to run at the acquired motor rotation speed (step S22). The estimation of the motor torque is performed, for example, based on a map according to the motor rotation speed.

[0032] Next, the ECU 100 calculates the upper limit torque that the motor 40 can output based on the output upper limit value calculated in step S21 and the motor rotation speed acquired in step S22 (step S23).

[0033] Next, the ECU 100 calculates the cranking torque and the cranking period required for cranking the engine 10 by the motor 40 (step S24). The cranking torque is calculated based on the temperature of the lubricating oil of the engine 10. The lower the temperature of the lubricating oil of the engine 10, the more the cranking torque increases. The cranking period is the period from when the cranking of the engine 10 by the motor 40 starts until combustion starts in the engine 10. The cranking period is calculated based on the cranking torque and the motor rotation speed.

[0034] Next, it is determined whether the upper limit torque calculated in step S23 is greater than the sum of the cranking torque calculated in step S24 and the motor torque estimated in step S22 (step S25). If the result in step S25 is No, this control ends. In this case, the predicted upper limit value is not calculated, and it is determined that the transition to motor driving is not permitted.

[0035] If the result in step S25 is Yes, the ECU 100 calculates the power consumption of the battery 90 from the start to the completion of the start of the engine 10 by the motor 40 (step S26). This power consumption is the total power consumption by the motor 40, accessories, air conditioner, etc. during the cranking period. The output value of the battery 90 per unit time is calculated based on the sum of the cranking torque and the motor torque. Next, the output value of the battery 90 per unit time by the accessories and the air conditioner is calculated. The power consumption is calculated based on the value obtained by multiplying the sum of these output values by the cranking period.

[0036] Next, a predicted upper limit value is calculated based on the power consumption calculated in step S26 (step S27). Specifically, the power consumption is converted into SOC. Next, the converted SOC is subtracted from the current SOC of the battery 90. The output upper limit value calculated by referring to the map in FIG. 6 based on the subtracted SOC and the temperature of the battery 90 is calculated as the predicted upper limit value.

[0037] As described above in detail with respect to the embodiments of the present invention, the present invention is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Explanation of Signs

[0038] 1 Hybrid vehicle 10 Engine 30 Clutch 40 Motor 90 Battery 100 ECU (Control device, calculation unit, setting unit, determination unit)

Claims

1. An engine, a clutch disposed on a power transmission path from the engine to the wheels, a motor disposed on the power transmission path from the clutch to the wheels and capable of starting the engine by cranking the engine with the clutch engaged, a battery that outputs power to the motor, a control device that switches between hybrid driving in which the vehicle travels by the power of the engine with the clutch engaged and motor driving in which the vehicle travels by the power of the motor with the clutch disengaged, and the control device includes a calculation unit that calculates a predicted upper limit value, which is a predicted value of an output upper limit value of the battery when starting of the engine by the motor is completed during motor driving while in hybrid driving; a setting unit that sets a determination value based on the predicted upper limit value; a determination unit that determines non-permission of a shift to motor driving when a vehicle speed during hybrid driving is higher than the determination value and determines permission of a shift to motor driving when the vehicle speed during hybrid driving is equal to or lower than the determination value, wherein the setting unit sets, as the determination value, a vehicle speed when a full output value becomes the predicted upper limit value, the full output value is a value obtained by adding a predetermined margin value to a required output value, the required output value is an output value per unit time of the battery for each vehicle speed at which driving can be maintained by the motor when starting of the engine is completed, the required output value decreases as the vehicle speed decreases, and the margin value decreases as the vehicle speed decreases. A hybrid vehicle.

2. The hybrid vehicle according to claim 1, further comprising a transmission disposed on the power transmission path from the motor to the wheels, wherein the margin value decreases as a gear ratio in the transmission increases.

3. The hybrid vehicle according to claim 1 or 2, wherein the calculation unit calculates the predicted upper limit value based on a state of charge (SOC) of the battery and a power consumption amount of the battery from start to completion of starting of the engine by the motor.

4. The calculating unit calculates the power consumption based on the rotational speed of the motor during the hybrid running, the torque of the motor required for the motor running at the rotational speed of the motor, the cranking torque required for cranking the engine by the motor, and the cranking period which is the period from when the cranking of the engine by the motor is started until combustion is started by the engine. The hybrid vehicle according to claim 3.

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