JP7775845B2 - Hybrid vehicle engine start control device - Google Patents

Description

The present invention relates to an engine start control device for a hybrid vehicle.

Hybrid vehicles are known that have a clutch, motor, and automatic transmission arranged in this order from the engine side to the drive wheels on the power transmission path between the engine and the drive wheels (see, for example, Patent Document 1).

JP 2008-179283 A

Such hybrid vehicles run on the motor with the engine stopped and the clutch disengaged. If the torque required for the hybrid vehicle during such motor running exceeds the start threshold for starting the engine, the motor torque is used to start the engine via the clutch. For this reason, when running on the motor, the starting torque required to start the engine must be secured as surplus motor torque. As a result, the motor running range in which the vehicle can run on the motor is the range obtained by dividing the maximum motor torque by the above-mentioned surplus torque, which narrows the motor running range and may result in poor fuel economy.

The present invention therefore aims to provide an engine start control device for a hybrid vehicle that ensures a motor-driven driving range.

The above objective can be achieved by an engine start control device for a hybrid vehicle in which a clutch, motor, and automatic transmission are provided in that order from the engine side to the drive wheels side on a power transmission path between the engine and the drive wheels, the engine start control device including: a start request determination unit that determines whether the torque required for the hybrid vehicle is equal to or greater than a start threshold for starting the engine while the hybrid vehicle is running on the motor with the engine stopped and the clutch disengaged; and a start control unit that, when a positive determination is made by the start request determination unit, executes upshift start processing to start the engine via the clutch using the inertia torque increased by upshifting the automatic transmission.

The system may include a motor torque determination unit that determines whether the surplus torque obtained by subtracting the motor torque from the motor's maximum torque is less than the starting torque required to start the engine, and a start threshold change unit that, if a positive determination is made by the motor torque determination unit, changes the start threshold to a value greater than when a negative determination is made by the motor torque determination unit. The start control unit may execute the upshift start process when a positive determination is made by the motor torque determination unit and the start request determination unit, and execute a motoring start process that uses the motor torque to start the engine via the clutch without upshifting the automatic transmission when a negative determination is made by the motor torque determination unit and a positive determination is made by the start request determination unit.

The system may include an inertia torque determination unit that determines whether the predicted inertia torque predicted before the upshift start process is executed is equal to or greater than the start torque required to start the engine, and a start threshold change unit that, if a positive determination is made by the inertia torque determination unit, changes the start threshold to a value greater than when a negative determination is made by the inertia torque determination unit. The start control unit may execute the upshift start process when a positive determination is made by the inertia torque determination unit and the start request determination unit, and may execute a motoring start process that uses the torque of the motor to start the engine via the clutch without executing an upshift of the automatic transmission when a negative determination is made by the inertia torque determination unit and the start request determination unit.

The start control unit may downshift the automatic transmission when the engine start is completed during the upshift start process.

The start control unit may adjust the torque of the motor according to the magnitude of the inertia torque during the upshift start process.

This invention provides an engine start control device for a hybrid vehicle that ensures a motor-driven driving range.

FIG. 1 is a schematic diagram of a hybrid vehicle. FIG. 2 is a flowchart showing an example of engine start control. FIG. 3 is a flowchart showing an example of an upshift start process. FIG. 4 is a timing chart showing an example of the upshift start process. FIG. 5 is a flowchart showing a modified example of engine start control. FIG. 6 is a flowchart showing a modified example of the upshift start process. FIG. 7 is a timing chart showing a modified example of the upshift start process.

[General configuration of hybrid vehicle]
FIG. 1 is a schematic diagram of a hybrid vehicle 1. In the hybrid vehicle 1, a K0 clutch 14, a motor 15, and a transmission 18 are provided in this order in a power transmission path from an engine 10 to drive wheels 13. The engine 10 and the motor 15 are mounted as a driving source for running the hybrid vehicle 1. The engine 10 is, for example, a V6 gasoline engine, but the number of cylinders is not limited thereto, and it may be an in-line gasoline engine or a diesel engine. The K0 clutch 14, the motor 15, and the transmission 18 are provided in a transmission unit 11. The transmission unit 11 and the left and right drive wheels 13 are drivingly connected via a differential 12. The transmission 18 includes a torque converter 19 and an automatic transmission 20.

The K0 clutch 14 is provided between the engine 10 and the motor 15 on the power transmission path. When the K0 clutch 14 receives a supply of hydraulic pressure from a disengaged state, it switches to an engaged state, connecting the power transmission between the engine 10 and the motor 15. When the hydraulic pressure supply is stopped, the K0 clutch 14 switches to a disengaged state, cutting off the power transmission between the engine 10 and the motor 15. The engaged state is a state in which both engagement elements of the K0 clutch 14 are connected and the engine 10 and the motor 15 are rotating at the same speed. The disengaged state is a state in which both engagement elements of the K0 clutch 14 are disengaged.

The motor 15 is connected to the battery 16 via the inverter 17. The motor 15 functions as a motor that generates driving force for the vehicle in response to power supplied from the battery 16, and also functions as a generator that generates regenerative power to charge the battery 16 in response to power transmitted from the engine 10 and drive wheels 13. The power exchanged between the motor 15 and the battery 16 is regulated by the inverter 17.

The inverter 17 is controlled by the ECU 100, which will be described later, and converts the DC voltage from the battery 16 into AC voltage, or converts the AC voltage from the motor 15 into DC voltage. During power running, in which the motor 15 outputs torque, the inverter 17 converts the DC voltage from the battery 16 into AC voltage and adjusts the power supplied to the motor 15. During regenerative running, in which the motor 15 generates power, the inverter 17 converts the AC voltage from the motor 15 into DC voltage and adjusts the regenerative power supplied to the battery 16.

The torque converter 19 is a fluid coupling with a torque amplification function. The automatic transmission 20 is a stepped automatic transmission that changes the gear ratio in multiple stages by changing gear positions, but is not limited to this and may also be a continuously variable automatic transmission. The automatic transmission 20 is located on the power transmission path between the motor 15 and the drive wheels 13. The motor 15 and automatic transmission 20 are connected via the torque converter 19. The torque converter 19 is provided with a lock-up clutch 19a that receives a supply of hydraulic pressure and enters an engaged state, directly connecting the motor 15 and automatic transmission 20. Note that a wet clutch may be provided instead of the torque converter 19 or lock-up clutch 19a.

The transmission unit 11 is further provided with an oil pump 21 and a hydraulic control mechanism 22. The hydraulic pressure generated by the oil pump 21 is supplied to the K0 clutch 14, torque converter 19, automatic transmission 20, and lock-up clutch 19a via the hydraulic control mechanism 22. The hydraulic control mechanism 22 is provided with hydraulic circuits for each of the K0 clutch 14, torque converter 19, automatic transmission 20, and lock-up clutch 19a, as well as various hydraulic control valves for controlling their operating hydraulic pressures.

Hybrid vehicle 1 is equipped with an ECU (Electronic Control Unit) 100, which serves as the vehicle's control device. ECU 100 is an electronic control unit that includes a processing circuit that performs various calculations related to vehicle driving control, and memory that stores control programs and data. ECU 100 is an example of an engine start control device, and functionally implements a start request determination unit, start control unit, motor torque determination unit, and start threshold change unit, which will be described in detail below.

The ECU 100 controls the operation of the engine 10 and the motor 15. Specifically, the ECU 100 controls the torque and rotation speed of the engine 10 by controlling the throttle opening, ignition timing, and fuel injection amount of the engine 10. The ECU 100 controls the power torque, regenerative torque, and rotation speed of the motor 15 by controlling the inverter 17 to adjust the amount of power exchanged between the motor 15 and the battery 16. The ECU 100 also controls the operation of the K0 clutch 14, lock-up clutch 19a, and automatic transmission 20 through control of the hydraulic control mechanism 22. The lock-up clutch 19a engages when the vehicle speed is above a predetermined value and disengages when the vehicle speed is below that value.

Signals are input to the ECU 100 from an ignition switch 71, crank angle sensor 72, motor rotation speed sensor 73, accelerator position sensor 74, vehicle speed sensor 75, SOC sensor 76, and gear position sensor 77. The ignition switch 71 detects the on/off state of the ignition. The crank angle sensor 72 detects the rotation speed of the crankshaft of the engine 10, i.e., engine rotation speed. The motor rotation speed sensor 73 detects the rotation speed of the output shaft of the motor 15, i.e., motor rotation speed. The accelerator position sensor 74 detects the accelerator pedal position, which is the amount of depression of the accelerator pedal by the driver. The vehicle speed sensor 75 detects the traveling speed of the hybrid vehicle 1. The SOC sensor 76 detects the SOC (State of Charge), which indicates the charge level of the battery 16. The gear position sensor 77 detects the gear position established in the automatic transmission 20.

The ECU 100 drives the hybrid vehicle in either the motor driving mode or the hybrid driving mode. In the motor driving mode, the ECU 100 stops the engine 10, disengages the K0 clutch 14, and drives the vehicle using power from the motor 15. In the hybrid driving mode, the K0 clutch 14 is engaged and the vehicle drives using at least the power from the engine 10.

The driving mode is switched based on the torque required for the hybrid vehicle 1, which is calculated from the vehicle speed and accelerator pedal position. For example, if the required torque is less than the start threshold for starting the engine 10, a motor driving mode is selected in which the engine 10 is stopped to improve fuel efficiency. If the required torque is equal to or greater than the start threshold, a hybrid driving mode in which the engine 10 is driven is selected. Therefore, if the required torque exceeds the start threshold while driving in the motor driving mode, the engine 10 must be started as follows:

[Engine start control]
2 is a flowchart showing an example of engine start control. This control is repeatedly executed at predetermined intervals while the ignition is on. The ECU 100 determines whether the driving mode is the motor driving mode (step S1). If the answer is No in step S1, this control is terminated. Step S1 is an example of processing executed by the start request determination unit.

If the answer is Yes in step S1, the ECU 100 determines whether the surplus torque of the motor 15 is less than the starting torque required to start the engine 10 (step S2). The surplus torque can be calculated by subtracting the current motor torque from the maximum torque that the motor 15 can output. The motor torque may be calculated based on the power supplied to the motor 15, or may be detected by a sensor. The maximum torque of the motor 15 is predetermined based on the motor rotation speed. Step S2 is an example of processing executed by the motor torque determination unit.

Therefore, if the answer to step S2 is No, the surplus torque of the motor 15 is deemed to be equal to or greater than the starting torque of the engine 10, and the ECU 100 sets the threshold for starting the engine 10 to a predetermined starting threshold α (step S3). Next, the ECU 100 determines whether the torque required for the hybrid vehicle 1 is equal to or greater than α (step S4). Step S4 is an example of processing executed by the start request determination unit. If the answer to step S4 is No, this control is terminated.

If step S4 is Yes, the ECU 100 executes motoring start processing (step S5). The motoring start processing is processing that starts the engine 10 via the K0 clutch 14 using motor torque without performing an upshift of the automatic transmission 20. In the motoring start processing, the K0 clutch 14 is engaged and the motor torque is increased by the amount required to crank the engine 10, thereby starting the engine 10. Step S5 is an example of processing executed by the start control unit.

If the answer is Yes in step S2, the surplus torque of the motor 15 is deemed to be insufficient relative to the starting torque of the engine 10, and the ECU 100 sets the threshold for starting the engine 10 to a predetermined starting threshold β (step S6). Here, the starting threshold β is set to a value greater than the starting threshold α. Step S6 is an example of processing executed by the starting threshold change unit.

Next, the ECU 100 determines whether the torque required for the hybrid vehicle 1 is equal to or greater than the start threshold value β (step S7). Step S7 is an example of processing executed by the start request determination unit. If the result in step S7 is No, this control is terminated.

If step S7 returns Yes, the ECU 100 executes an upshift start process (step S8). The upshift start process is a process that starts the engine 10 via the K0 clutch 14 using the inertia torque that increases when the automatic transmission 20 performs an upshift. The inertia torque is the torque that acts in the rotational direction of the input shaft of the automatic transmission 20 when the rotation speed of the input shaft of the automatic transmission 20 decreases due to the automatic transmission 20 performing an upshift. In the upshift start process, the inertia torque is used to start the engine 10, so there is no need to increase the motor torque compared to the motoring start process. Step S8 is an example of a process executed by the start control unit.

In this way, even if the excess torque of the motor 15 is less than the starting torque of the engine 10, the engine 10 can be started by raising the starting threshold value from α to β and utilizing the inertia torque. As a result, the motor running range can be secured, improving fuel efficiency.

Upshift start processing is executed only if the answer is Yes in step S2. This prevents the driver from feeling uncomfortable due to unnecessary repetition of the upshift start processing.

Engine start control is not limited to the above example, and may be performed, for example, as follows: When the required torque is equal to or greater than the start threshold value α in motor driving mode, motoring start processing may be performed if the surplus torque is greater than the start torque, and when the surplus torque is less than the start torque, upshift start processing may be performed if the required torque is equal to or greater than the start threshold value β.

In step S2, it may be determined whether the excess torque is lower than the value obtained by adding a predetermined margin to the starting torque, taking into account calculation errors in the excess torque and starting torque.

[Upshift start processing]
Figure 3 is a flowchart showing an example of the upshift start process. Figure 4 is a timing chart showing an example of the upshift start process. Figure 4 shows changes in the rotation speeds of the motor 15 and transmission 18, the rotation speed of the engine 10, the torque of the output shaft of the automatic transmission 20, the inertia torque, the torque of the motor 15, and the hydraulic pressure command value for the K0 clutch 14. Note that since the lock-up clutch 19a is engaged during driving in the motor driving mode, the motor rotation speed and the transmission rotation speed match.

The ECU 100 starts hydraulic control of the K0 clutch 14 (step S11, time t1). This hydraulic control of the K0 clutch 14 is different from the hydraulic control of the K0 clutch 14 during normal starting, and is hydraulic control for upshift starting processing. Details will be described later.

Next, the ECU 100 initiates an upshift of the automatic transmission 20 (step S12). When the upshift is initiated, the torque phase begins in the automatic transmission 20, and the output shaft torque of the automatic transmission 20 begins to decrease (time t2). When the inertia phase begins in the automatic transmission 20, the output shaft torque of the automatic transmission 20 becomes substantially constant, the motor/transmission rotation speed begins to decrease, and the inertia torque begins to increase (time t3). The ECU 100 determines whether the increase in inertia torque due to this upshift has started (step S13). Specifically, it is determined that the increase in inertia torque has started when the rate of decrease in the rotation speed of the motor 15 is equal to or greater than a predetermined value. If the answer to step S13 is No, the processing of step S13 is executed again.

If step S13 returns Yes, the ECU 100 controls the hydraulic pressure command value for the K0 clutch 14 to a command value that engages the K0 clutch 14 (step S14, time t3). This transitions the K0 clutch 14 from a disengaged state to a slipped state. In other words, hydraulic control of the K0 clutch 14 during the upshift start process involves waiting for the inertia torque to increase due to the upshift, and then controlling the hydraulic pressure command value for the K0 clutch 14 to a command value that engages the K0 clutch 14. The ECU 100 also adjusts the motor torque (step S15, time t3). When the inertia torque is greater than the starting torque required to start the engine 10 by a predetermined value or more, the motor torque is reduced by that amount. This allows the engine 10 to start with appropriate torque. Step S15 is an example of processing executed by the start control unit. As a result, the engine speed begins to increase via the slipped K0 clutch 14 due to the inertia torque and motor torque (time t4).

Next, the ECU 100 determines whether starting of the engine 10 is complete (step S16). For example, when the engine speed reaches or exceeds a speed at which autonomous operation is possible, it is determined that starting of the engine 10 is complete. If the answer is No in step S16, step S16 is executed again. If the answer is Yes in step S16, the ECU 100 adjusts the motor torque (step S17, time t5). The motor torque adjustment here is performed by reducing the motor torque by the amount of increase from the inertia torque before the upshift. This makes it possible to suppress the occurrence of shock to the hybrid vehicle 1 due to starting of the engine 10. Step S17 is an example of processing executed by the start control unit.

When the motor/transmission rotation speed decreases and matches the engine rotation speed, and the K0 clutch 14 engages, the inertia torque begins to decrease (time t6). Due to the adjustment of the motor torque in step S17 described above, the motor torque increases in response to the decrease in inertia torque (time t6) and returns to its original value (time t7). In this way, the upshift start process ends.

Upshifting may involve changing to a gear ratio one step lower, such as from third to fourth, or may involve changing to a gear ratio several steps lower, such as from third to fifth. For example, if there is a risk that the increased inertia torque that occurs when upshifting from third to fourth will be insufficient for the starting torque of the engine 10, then upshifting from third to fifth may be performed.

[Modification of engine start control]
FIG. 5 is a flowchart showing a modified example of engine start control. FIG. 5 corresponds to FIG. 2. If step S1 is Yes, it is determined whether the predicted inertia torque, which is predicted to increase due to the execution of the upshift start process, is equal to or greater than the starting torque of the engine 10 (step S2a). The predicted inertia torque can be predicted, for example, from the current gear position and the rotation speed of the output shaft of the automatic transmission 20, and the gear position and the target rotation speed of the output shaft of the automatic transmission 20 after the upshift is completed. It is also preferable to calculate the predicted inertia torque taking into account torque loss due to the execution of the upshift. Such predicted inertia torque is determined based on experimental results. If step S2a is Yes, the processes from step S6 onward are executed as in the above-described embodiment.

If step S2a is No, steps S3 and S4 are executed, and if step S4 is Yes, the ECU 100 executes motoring start processing (step S5a). Unlike the above-described embodiment, the motoring start processing in this modified example ensures motor torque by performing a downshift. This allows the engine 10 to start. Step S2a is an example of processing executed by the inertia torque determination unit.

Engine start control is not limited to the above example, and may be performed, for example, as follows: When the required torque exceeds the start threshold value α in motor driving mode, motoring start processing may be performed if the predicted inertia torque is lower than the start torque; and when the predicted inertia torque is equal to or greater than the start torque, upshift start processing may be performed if the required torque exceeds the start threshold value β.

In step S2a, it may be possible to determine whether the predicted inertia torque is equal to or greater than the starting torque plus a predetermined margin, taking into account calculation errors in the predicted inertia torque and starting torque.

[Modification of upshift start processing]
Fig. 6 is a flowchart showing a modified example of the upshift start process. Fig. 7 is a timing chart showing a modified example of the upshift start process. Figs. 6 and 7 correspond to Figs. 3 and 4, respectively. Furthermore, steps S11 to S14 and times t1 to t4 described above are the same as those in Figs. 3 and 4 except for the motor torque, and therefore their explanation will be omitted.

After executing step S14, the ECU 100 determines whether starting of the engine 10 is complete (step S16). If the answer is No in step S16, step S16 is executed again. If the answer is Yes in step S16, the ECU 100 determines whether the degree of progress of the upshift is equal to or less than a threshold value (step S18). For example, the degree of progress of the upshift is determined to be greater the smaller the difference between the current rotation speed of the output shaft of the automatic transmission 20 and the target rotation speed of the output shaft of the automatic transmission 20 at the completion of the upshift. Here, the threshold value is set to the upper limit of the degree of progress at which a downshift is possible, as described below. If the answer is No in step S18, this process ends.

If step S18 returns to Yes, the ECU 100 initiates a downshift (step S19). That is, the automatic transmission 20 is returned to the gear position before the upshift. This causes the rate of increase in the engine 10 speed to decrease, the output shaft torque of the automatic transmission 20 to begin to increase, and the inertia torque to begin to decrease (time t5a). By performing a downshift in this way, the output shaft torque of the automatic transmission 20 can be increased, ensuring the driving force of the hybrid vehicle 1 when the engine is started. The ECU 100 also adjusts the motor torque (step S20). The motor torque adjustment here is performed by increasing the motor torque by the amount of the decrease in inertia torque from before the upshift. This also ensures the driving force of the hybrid vehicle 1 when the engine is started. Steps S19 and S20 are an example of processing performed by the start control unit.

Once the downshift is complete, the motor/transmission rotation speed remains approximately constant, and the inertia torque begins to rise toward the value before the upshift (time t6a). Due to the adjustment of the motor torque in step S20 described above, the motor torque decreases in accordance with the decrease in inertia torque (time t6a), and then returns to its original value (time t7a). Note that while the example shown in Figure 7 shows the case where the K0 clutch 14 is engaged at time 7a, this is not limited to this, as long as it occurs after the engine 10 has been started.

In the above embodiment, either the upshift start process or the motoring start process is executed depending on the determination results of step S2 and step S2a, but this is not limited to this. In other words, the upshift start process may be executed at all times when a request to start the engine 10 is made, without executing the determinations of steps S2 and S2a.

In the above embodiment, a hybrid vehicle is controlled by a single ECU 100, but this is not limited to this. The above-described control may also be performed by multiple ECUs, such as an engine ECU that controls the engine 10, a motor ECU that controls the motor 15, a clutch ECU that controls the K0 clutch 14, and a T/MECU that controls the transmission 18.

Although the present invention has been described in detail above with reference to specific embodiments, the present invention is not limited to these specific embodiments, and various modifications and variations are possible within the scope of the invention as set forth in the claims.

REFERENCE SIGNS LIST 1 Hybrid vehicle 10 Engine 14 K0 clutch 15 Motor 18 Transmission 20 Automatic transmission 100 ECU (engine start control device, start request determination unit, start control unit, motor torque determination unit, start threshold change unit, inertia torque determination unit)

Claims (3)

1. An engine start control device for a hybrid vehicle in which a clutch, a motor, and an automatic transmission are provided in this order from an engine side to a drive wheel side on a power transmission path between the engine and the drive wheel,
a start request determination unit that determines whether a torque required for the hybrid vehicle is equal to or greater than a start threshold for starting the engine while the hybrid vehicle is running using the motor with the engine stopped and the clutch released;
a start control unit that, when a positive determination is made by the start request determination unit, executes an upshift start process to start the engine via the clutch by utilizing an inertia torque that increases due to an upshift of the automatic transmission;
an inertia torque determination unit that determines whether or not a predicted inertia torque predicted before execution of the upshift start process is equal to or greater than a start torque required to start the engine;
a start-up threshold value changing unit that changes the start-up threshold value to a value greater than that when a negative determination is made by the inertia torque determining unit when a positive determination is made by the inertia torque determining unit,
The start control unit executes the upshift start processing when a positive determination is made by the inertia torque determination unit and the start request determination unit, and executes a motoring start processing that starts the engine via the clutch using the torque of the motor without executing an upshift of the automatic transmission when a negative determination is made by the inertia torque determination unit and a positive determination is made by the start request determination unit . 2. The engine start control device for a hybrid vehicle according to claim 1 , wherein the start control unit executes a downshift of the automatic transmission when starting of the engine is completed in the upshift start process. 2. The engine start control device for a hybrid vehicle according to claim 1 , wherein the start control unit adjusts the torque of the motor in accordance with the magnitude of the inertia torque in the upshift start process.