Patent ID: 12214774

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, in the drawings, the dimensions, ratios, and the like of the respective parts may not be shown so as to completely coincide with the actual ones. Further, in some drawings, details are omitted. Further, the scale of each element depicted between the figures may be different.

Outline of the Hybrid Electric Vehicle

FIG.1is a schematic configuration diagram of a hybrid electric vehicle1. In the hybrid electric vehicle1, a K0 clutch14, a motor generator15, a torque converter18, and a transmission19are provided in this order in a power transmission path from an engine10corresponding to an internal combustion engine to the drive wheels13. The engine10and the motor generator15are mounted on the hybrid electric vehicle1as driving sources for traveling. The engine10is an example of an internal combustion engine, for example, a series three-cylinder gasoline engine, but the number of cylinders and the arrangement method of cylinders are not limited thereto. In addition, the internal combustion engine may be a diesel engine using light oil as a fuel. K0 clutch14, the motor generator15, the torque converter18, and the transmission19are provided in the transmission unit11. The transmission unit11and the left and right drive wheels13are drivingly connected to each other via a differential12.

K0 clutch14is provided between the motor generator15and the engine10on the power transmission path. K0 clutch14is supplied with hydraulic pressure, and is brought into an engaged state from a released state. K0 clutch14is engaged to connect the power transmission between the engine10and the motor generator15. When the hydraulic pressure is stopped, K0 clutch14is released to shut off power transmission between the engine10and the motor generator15. The engagement state is a state in which both engagement elements of K0 clutch14are coupled to each other and the engine10and the motor generator15have the same speed. The disengaged state is a state in which both engagement elements of K0 clutches14are separated from each other. Depending on the state in which the engagement hydraulic pressure is supplied, K0 clutch14may be in a slip state in which the speed of the engine10side does not coincide with the speed of the motor generator15side. K0 clutch14corresponds to a disconnection clutch.

The motor generator15is connected to the battery16via an inverter17. The motor generator15functions as a motor that generates a driving force of the vehicle in response to power supply from the battery16. The motor generator15also functions as a generator that generates electric power to charge the battery16in response to power transmission from the engine10and the drive wheels13. The electric power exchanged between the motor generator15and the battery16is adjusted by the inverter17. The use of the battery16may be limited depending on the temperature, such as at a cryogenic temperature. The temperature at which the use is restricted is set for each specification of the actual machine. The motor generator15corresponds to an electric motor.

The inverter17is controlled by an ECU100to be described later, and converts a DC voltage from the battery16into an AC voltage. The inverter17converts the AC voltage from the motor generator15into a DC voltage. In the case of the power running operation in which the motor generator15outputs torque, the inverter17converts the DC voltage of the battery16into an AC voltage and adjusts the power supplied to the motor generator15. In the case of the regenerative operation generated by the motor generator15, the inverter17converts the AC voltage from the motor generator15into a DC voltage and adjusts the electric power supplied to the battery16. The battery16is mainly used as a power source for traveling of the hybrid electric vehicle1.

The torque converter18is a fluid coupling having a torque amplification function. The transmission19is a stepped automatic transmission in which the gear ratio is switched in multiple stages by switching the gear stages, but the present disclosure is not limited thereto, and may be a continuously-type automatic transmission. The transmission19is provided between the motor generator15and the drive wheels13on the power transmission path. The motor generator15and the transmission19are coupled to each other via the torque converter18. The torque converter18is provided with a lock-up clutch20that receives a supply of hydraulic pressure and is in an engaged state to directly couple the motor generator15and the transmission19.

The transmission unit11is further provided with an electric oil pump21and a hydraulic control mechanism22. Hydraulic pressure generated by the electric oil pump21is supplied to K0 clutch14, the torque converter18, the transmission19, and the lockup clutch20via the hydraulic control mechanism22. The hydraulic control mechanism22is provided with hydraulic circuits of K0 clutch14, the torque converter18, the transmission19, and the lockup clutch20, and various hydraulic control valves for controlling the hydraulic pressures. A wet clutch may be provided instead of the torque converter18.

The hybrid electric vehicle1includes an auxiliary battery23separately from the battery16. The hybrid electric vehicle1includes a starter24for starting the engine10. The starter24is driven by an auxiliary battery23. The battery16may be limited in use, for example, when the temperature of the environment in which the vehicle is placed is very low, but the auxiliary battery23can be used even in such a case. The engine10can be started by a starter24driven by an auxiliary battery23. The auxiliary battery23can also be used for driving the electric oil pump21.

The hybrid electric vehicle1includes a mechanical oil pump25. The mechanical oil pump25operates when the output shaft of the motor generator15rotates. Therefore, the mechanical oil pump25is not driven when the engine10or the motor generator15is stopped. The mechanical oil pump25is not driven when the motor generator15is stopped and K0 clutch14is released even when the engine10is in operation. Like the electric oil pump21, the mechanical oil pump25can supply the hydraulic pressure to K0 clutch14, the torque converter18, the transmission19, and the lock-up clutch20via the hydraulic control mechanism22.

The hybrid electric vehicle1is provided with an Electronic Control Unit (ECU)100as a control device of the vehicle. ECU100is an electronic control unit including an arithmetic processing unit that performs various arithmetic processing related to travel control of vehicles, and a memory that stores control programs and data.

ECU100controls driving of the engine10and the motor generator15. Specifically, ECU100controls the torque and the speed of the engine10by controlling the throttle opening degree, the ignition timing, and the fuel injection quantity of the engine10. ECU100controls the torque and the speed of the motor generator15by controlling the inverters17to adjust the amount of transfer of electric power between the motor generator15and the battery16. ECU100controls driving of K0 clutch14, the lock-up clutch20, and the transmission19through control of the hydraulic control mechanism22.

Signals from the ignition switch71, the crank angle sensor72, and the motor sensor73are inputted to ECU100. The crank angle sensor72detects the speed of the crankshaft of the engine10. The motor rotation speed sensor73detects the rotation speed of the output shaft of the motor generator15. ECU100issues a drive command to the starter24when the ignition switch71is turned on.

ECU100causes the hybrid electric vehicles to travel in either the motor mode or the hybrid mode. In the motor mode, ECU100releases K0 clutch14and travels by the power of the motor generator15. At this time, the engine10may be in a stopped state. In the hybrid mode, ECU100switches K0 clutch14into engagement and runs at least with the power of the engine10. For example, when the hybrid electric vehicle1is placed in a cryogenic environment and the use of the battery16is restricted, K0 clutch14is also brought into an engaged state when the hybrid electric vehicle1is allowed to travel only by the driving force of the engine10.

K0 Clutch Engagement Control

Next, with reference toFIGS.2and3, the control will be described in the case where both the engine10and the motor generator15are stopped, the hybrid electric vehicle1is shifted to the travelable state. Here, it is assumed that a predetermined time has elapsed after the hybrid electric vehicle1stops in a state where both the engine10and the motor generator15are stopped. It is assumed that the hybrid electric vehicle1is in a state in which the hydraulic pressure is removed at a position where the supply of the hydraulic pressure is required after a predetermined time has elapsed after the stop. The environment in which the hybrid electric vehicle1is placed is a cryogenic environment in which the use of the battery16is restricted. In this case, since the hybrid electric vehicle1cannot operate the motor generator15, the engine10is started in order to set the hybrid electric vehicle1in a travelable state. Since the motor generator15cannot be used to start the engine10, the engine10is started using the starter24driven by the auxiliary battery23. When the hybrid electric vehicle1is in the stopped state, since K0 clutch14is in the released state, K0 clutch engagement control is performed in order to make the hybrid electric vehicle1in the travelable state. Hereinafter, K0 clutch-engagement control will be described in detail. Referring toFIG.3, K0 clutch-engagement control includes a preparation control performed in a period T1and a slip control performed in a period T2. Further, K0 clutch engagement control includes engagement completion control (see the step S6inFIG.2) performed at the time t6which is the end of the period T2.

ECU100determines whether or not there is a startup request for the engine10in the step S1. Specifically, ECU100determines whether or not the ignition switch71is turned on. ECU100repeats the process of step S1when a negative determination (No) is made in step S1until an affirmative determination (Yes determination) is made in step S1. When an affirmative determination is made in step S1, ECU100proceeds to step S2.

ECU100issues a drive command to the starter24in step S2. Thus, the starter24is driven from the time t1to the time t2, the speed of the engine10is increased, and the start of the engine10is completed. The number of revolutions of the engine10after starting is maintained at a preset idle number of revolutions.

ECU100drives the starter24in the step S2to start the engine10, and then performs the preparation control to engage K0 clutch14in the step S3. This preparation control is a control for raising the hydraulic pressure in the hydraulic control mechanism22that engages K0 clutch14prior to the slip control described in detail later, and is sometimes referred to as packing. By performing the preparation control, the hydraulic pressure in the oil passage for supplying the hydraulic pressure to K0 clutch14is increased, and K0 clutch14can immediately shift to the engaged condition. In the present embodiment, the preparation control is performed in the period T1from the time t3to the time t5. The end of the period T1, that is, the time t5, may be a time when at least one of a decrease in the speed of the engine10or an increase in the speed of the motor generator15is detected. The reason why the speed of the engine10decreases or the speed of the motor generator15increases is that it can be determined that K0 clutch14can be engaged. In the present embodiment, the time point at which the decrease in the speed of the engine10is detected is set as the time t5.

In the present embodiment, the length of the period T1and the instruction hydraulic pressure are set in advance according to the hardware configuration of the hybrid electric vehicle1, such as the engine10, K0 clutch14, and the hydraulic control mechanism22, and the starting target period. This makes it possible to appropriately raise the state of the hydraulic pressure in accordance with the configuration of the hybrid electric vehicle1. When ECU100starts the preparation control from the time t3, the actual pressure of the hydraulic pressure for engaging K0 clutch starts to gradually increase from the time t4after a delay from the time t3.

ECU100proceeds to the step S4when the preparation control performed in the step S3is completed. ECU100initiates slip control in step S4. The slip control is performed in the period T2from the time t5to the time t6. During the time t5, the speed of the engine10is maintained at the idle speed. On the other hand, the motor generator15is not in operation, and its speed is 0 (zero). In the slip control, K0 clutches14are gradually engaged so that the speeds of the motor generator15and the engine10in which the differential rotation is occurring coincide with each other. During this time, the rotational element of K0 clutch14on the engine-10side and the rotational element of the motor-generator15side are slipped. As a result, the speed of the motor generator15gradually increases, while the speed of the engine10decreases as the speed of the motor generator15increases. At this time, the number of revolutions of the engine10is controlled so as to maintain a higher number of revolutions than the lower limit speed for avoiding the stop of the engine10. Specifically, the instruction hydraulic pressure for engaging K0 clutch14is controlled so as to maintain the speed of the engine10at a higher speed than the lower limit speed. The higher the engagement hydraulic pressure of K0 clutch14, the faster the speed of the motor generator15can be increased. However, on the other hand, a drop in the speed of the engine10tends to be rapid. When the speed of the engine10drops sharply and falls below the lower limit speed, there is a possibility that the engine10is stopped in a so-called engine stall state. Therefore, in the present embodiment, the instruction hydraulic pressure is set so that the speed of the engine10does not fall below the lower limit speed during the slip control. As a result, the engine10is prevented from being stopped. The lower limit speed is set in accordance with the specifications of the engine10, such as the idle speed.

In the period T2, the instruction hydraulic pressure is gradually increasing. The ascending speed is set so that the speed of the engine10does not reach the lower limit speed under the influence of the drag torque and the rotational inertia of the rotating elements after the motor generator15.

Here, the instruction hydraulic pressure during the slip control will be described in more detail. Referring toFIG.3, during the time t5from which the slip control is performed to the time t6(period T2), the instruction hydraulic pressure gradually increases. The time t5is a starting point of the slip control. That is, the time t5is a timing at which the control is switched from the preparation control to the slip control. The instruction hydraulic pressure is temporarily lowered from the instruction hydraulic pressure during the preparation control so far in the time t5. In other words, the instruction hydraulic pressure in the preparation control is an instruction hydraulic pressure equal to or higher than the instruction hydraulic pressure at the start point of the slip control. That is, the instruction hydraulic pressure in the preparation control is the same as or higher than the instruction hydraulic pressure at the start of the slip control. With such an instruction hydraulic pressure, it is possible to shorten the period T1required for the preparation control, and as a whole, it is possible to shorten the period for enabling the hybrid electric vehicle1to travel.

Here, with reference toFIG.4, the instruction hydraulic pressure during the slip control will be described. The instruction hydraulic pressure during the slip control may be a pulse wave as shown inFIG.4. In this way, the engine10can be easily prevented from being stopped by using a pulse wave in which the increase and the decrease of the instruction hydraulic pressure are repeated. The speed of the engine10is likely to decrease when the hydraulic pressure for engaging K0 clutch14is suddenly increased. Therefore, the change in the number of revolutions can be made gentle by setting the instruction hydraulic pressure as a pulse wave and providing a timing for lowering the instruction hydraulic pressure. Although the pulse wave shown inFIG.4is rectangular, the waveform of the pulse wave is not limited to this, and may be other waveforms such as a square wave or a sine wave. Further, a continuous waveform other than the pulse wave or a fine stepped waveform may be used, and the waveform of the instruction hydraulic pressure during the slip control may be appropriately selected without being limited to a specific waveform.

ECU100proceeds to step S5after starting the slip control in step S4. In the step S5, ECU100determines whether the difference rotation is smaller than a preset difference rotation threshold Δ1. The differential rotation is a difference between the speed of the engine10and the speed of the motor generator15. The speed of the engine10is acquired by the crank angle sensor72. The speed of the motor generator15is acquired by the motor speed sensor73. The differential rotational thresholds Δ1 are set in advance in view of the magnitude of shocks generated when K0 clutch14is engaged so that the speed of the engine10and the speed of the motor generator15coincide with each other, and the performance and properties of the engine10.

When a negative determination is made in step S5, ECU100repeats the process of step S5until an affirmative determination is made in step S5. When an affirmative determination is made in step S5, ECU100proceeds to step S6.

ECU100performs engagement completion control in S6of steps. The engagement completion control is a control for raising the instruction hydraulic pressure for engaging K0 clutch14by the hydraulic control mechanism22to the instruction hydraulic pressure at which the engagement of K0 clutch14is completed. The engagement completion means that the speeds of the engine10and the motor generator15coincide with each other, and the rotational element of K0 clutch14on the engine10side and the rotational element of the motor generator15side do not slip and are synchronized with each other. In the present embodiment, the slipping control is ended at the time t6, and the engagement completion control is performed. In the engagement completion control, the instruction hydraulic pressure rises to the fully engaged hydraulic pressure. Accordingly, the speed of the engine10and the speed of the motor generator15coincide with each other in the time t7. As described above, K0 clutch-engagement control is completed, and the hybrid electric vehicle1is ready to travel.

Here, the instruction hydraulic pressure in the engagement completion control is set in accordance with the rotational torque of the engine10. This suppresses slipping in K0 clutch14and allows the engine10and the motor generator15to be connected to each other.

In the present embodiment, the engagement completion control is performed at the time t6when the difference rotation is smaller than the difference rotation threshold Δ1. Therefore, in the present embodiment, the period T3from the time t5to the time t7is a rotation synchronization period in which the rotation speed of the engine10and the rotation speed of the motor generator15are synchronized. On the other hand, the period during which the slip control is performed may be managed in time. That is, the engagement completion control may be performed when a predetermined time set in advance has elapsed from the time t5at which the slip control is started. In this case, it is also assumed that the speed of the engine10and the speed of the motor generator15coincide with each other before the engagement completion control is performed. However, by performing the engagement completion control thereafter, the hybrid electric vehicle1can be brought into a travelable state.

Effects

According to the present embodiment, since the instruction hydraulic pressure for engaging K0 clutch14is set as the instruction hydraulic pressure to be maintained at a speed higher than the lower limit speed of the engine10, it is possible to avoid stopping the engine10.

Further, according to the present embodiment, by performing the preparation control prior to the slip control, it is possible to shorten the time required for bringing the hybrid electric vehicle1into a travelable state. Further, the period of the preparation control can be shortened by setting the instruction hydraulic pressure in the preparation control to an instruction hydraulic pressure higher than the instruction hydraulic pressure at the start point of the slip control.

Further, since the instruction hydraulic pressure is given by the pulse wave, the internal combustion engine is effectively prevented from being stopped.

Modification

Next, referring toFIG.5, a modification of a control device (ECU)100for vehicles will be described. The flowchart illustrated inFIG.5is a flowchart in which the details of the slip control (step S4) in the flowchart illustrated inFIG.2are changed. In this variant, feedback control is implemented in the slip control. In the flow chart shown inFIG.5, the process from step S1to step S3in the flow chart shown inFIG.2is omitted, but in this modification, the process from step S1to step S3is performed in the same manner. Note that, since the time chart itself for the modification is common to the time chart shown inFIG.3, the time chart shown inFIG.3is also referred to as appropriate in the following description.

ECU100increases the instruction hydraulic pressure for engaging K0 clutch14in step S41(time t5inFIG.3). ECU100determines whether or not the speed of the engine10is equal to or lower than the lower limit avoidance speed in the step S42performed following the step S41. Here, the lower limit avoidance speed is a speed higher than the lower limit speed. When the speed of the engine10reaches the lower limit speed, the engine10is more likely to stop, but by setting the lower limit avoidance speed, it is possible to detect a state before such a state is reached.

When an affirmative determination is made in step S42, ECU100proceeds to step S43. ECU100, in a stepped S43, lowers the instruction hydraulic pressure for engaging K0 clutch14. As a result, it is possible to prevent the speed of the engine10from falling to the lower limit speed, and as a result, it is possible to prevent the engine10from stopping. The amount of decrease in the instruction hydraulic pressure can be appropriately set by adaptation or simulation by an actual machine. ECU100performs the process of step S43and then performs the process of step S42again.

When a negative determination is made in step S42, ECU100proceeds to step S44. ECU100continues to increase the instruction hydraulic pressure in step S44. ECU100proceeds to step S5after performing the process of step S44. The steps S5and S6are similar to the flow chart shown inFIG.2, and ECU100performs engagement completion control at time t6in the time chart shown inFIG.3, and ends the series of control.

According to this modification, since the instruction hydraulic pressure for engaging K0 clutch14is controlled while comparing the engine speed with the lower limit avoidance speed, it is possible to avoid the engine speed from reaching the lower limit speed. As a result, the engine10can be prevented from being stopped.

Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present disclosure described in the claims.