JP6187330B2 - Hybrid car - Google Patents

Description

  The present invention relates to a hybrid vehicle including a traveling engine and a motor.

  Since a motor that generates a driving force for traveling requires a high output, such a motor or an inverter that supplies electric power to the motor generates a large amount of heat. Patent Documents 1 and 2 disclose examples of techniques for suppressing an excessive temperature rise of a motor or an inverter.

  In the technique of Patent Document 1, the engine is continuously operated when the motor temperature is equal to or higher than a predetermined temperature threshold. The hybrid vehicle of Patent Document 1 includes a mechanical pump that circulates refrigerant to the motor by the driving force of the engine, and ensures circulation of the refrigerant by the mechanical pump by continuously operating the engine. In Patent Literature 2, inverter protection control is executed when the motor is in a stalled state. The stall state means a state where electric power is supplied to the motor but the motor output and the force applied to the wheel from the outside are balanced and the motor does not rotate.

JP 2012-096584 A JP 2013-159327 A

  In a hybrid vehicle including an engine and a motor, when an excessive temperature increase of the motor or the inverter is predicted, it may be possible to protect the motor by reducing the frequency of use of the motor. However, if the frequency of use of the motor is excessively reduced, the frequency of use of the engine is increased in order to maintain the running performance, and as a result, the fuel consumption that is an advantage of the hybrid vehicle is deteriorated. On the other hand, some hybrid vehicles include a power converter that boosts the voltage of the battery and converts the boosted power into alternating current. The present specification makes use of the electrical structure peculiar to a hybrid vehicle including such a power conversion device, and provides a technology that suppresses an excessive temperature rise of the power conversion device and increases the frequency of use of the engine as much as possible. To do.

  The hybrid vehicle targeted by this specification includes an engine, first and second motors, and a power converter. The first motor is a starter motor that starts the engine. The second motor is a motor that generates a driving force for traveling. The first and second motors may have a function as a generator that generates electric power using the kinetic energy of the vehicle during braking. Further, the first motor does not need to be dedicated to the starter, and its power may be used for traveling. The power converter includes a voltage converter circuit that boosts the output voltage of the battery, a first inverter circuit that converts the boosted DC power into AC and supplies the first motor, and converts the boosted DC power into AC And a second inverter circuit for supplying the second motor. The hybrid vehicle also includes a controller that controls the power conversion device.

  Since an appropriate output torque is required to start the engine, when the engine is started, the amount of heat generated by the power converter that supplies power to the first motor (starter motor) increases. Since the hybrid vehicle repeatedly stops and restarts the engine during traveling, the amount of heat generated by the power converter increases each time the vehicle is restarted. While the power conversion device generates heat even while power is being supplied to the second motor, the amount of heat generated when the engine is restarted is added to the amount of heat generated when the second motor is used.

  The amount of heat generated when the engine is restarted is frequently added and the temperature of the power converter rises excessively. The total fuel efficiency is improved by avoiding the heat generated by the restart. Therefore, in the technology disclosed in this specification, when the temperature of the power conversion device is equal to or higher than a predetermined temperature threshold, the controller prohibits the engine from being stopped and continuously operates so that it is not necessary to restart the engine.

  If the temperature threshold is too high, there is a high possibility that the temperature of the power conversion device will rise excessively due to the restart of the engine, and if it is too low, the frequency of use of the engine will increase and fuel consumption will deteriorate.

  On the other hand, the output voltage of the voltage converter circuit is determined depending on the rotational speed of the motor and the output torque required for the first and second motors. In general, due to the electrical characteristics of a motor, when the number of revolutions is high, a current that achieves a desired torque cannot flow unless the supplied voltage is increased. The second motor is mainly used for traveling, and its rotational speed depends on the vehicle speed. That is, as the vehicle speed increases, a desired torque cannot be output unless the output voltage of the voltage converter circuit is increased. Therefore, the higher the vehicle speed, the higher the output upper limit voltage of the voltage converter circuit. Here, the calorific value of the power converter including the voltage converter circuit mainly depends on the load of the voltage converter circuit.

  In the technology disclosed in this specification, the temperature threshold value for prohibiting the engine stop is appropriately changed in consideration of the above situation of the hybrid vehicle. The controller of the hybrid vehicle disclosed in this specification sets the output upper limit voltage of the voltage converter circuit to the first voltage or higher when the vehicle speed is equal to or higher than a predetermined vehicle speed threshold, and the temperature of the power converter is the first. If the temperature is above the limit, prohibit the engine from stopping and run the engine continuously. On the other hand, when the vehicle speed is lower than the vehicle speed threshold, the controller sets the output upper limit voltage of the voltage converter circuit to a second voltage lower than the first voltage, and the temperature of the power converter is higher than the first temperature. The engine is continuously operated when the temperature is two or more. That is, when the vehicle speed is lower than the vehicle speed threshold, the engine is allowed to stop / restart up to a second temperature at which the temperature of the power converter is relatively high. The above-described control of the controller can suppress an increase in the use frequency of the engine while suppressing an excessive temperature rise of the power conversion device.

  According to the technology disclosed in this specification, an increase in the frequency of use of the engine can be suppressed when performing thermal protection of the power conversion device of the hybrid vehicle. Details and further improvements of the technology disclosed in this specification will be described in the following “DETAILED DESCRIPTION”.

It is a block diagram of the drive system of the hybrid vehicle of an Example. It is a skeleton figure of a power distribution mechanism. It is a graph which shows an example of the relationship between the rotation speed of a motor, and output torque. It is a flowchart figure of the heat protection process which a controller performs.

  A hybrid vehicle 2 according to an embodiment will be described with reference to the drawings. FIG. 1 shows a block diagram of a drive system of the hybrid vehicle 2. The hybrid vehicle 2 of the embodiment includes an engine 8 and two motors (a first motor 6 and a second motor 7) for traveling. The output of the engine 8 and the outputs of the two motors 6 and 7 are combined or distributed by the power distribution mechanism 40 and transmitted to the axle 9. The hybrid vehicle 2 generates electricity by rotating the first motor 6 with the output of the engine 8 according to the situation. Electric power obtained by power generation is charged in the battery 3. Moreover, the hybrid vehicle 2 may generate electric power by the motors 6 and 7 using the kinetic energy of the vehicle during braking and charge the battery 3 in some cases. The power distribution mechanism 40 that connects the engine 8 and the two motors 6 and 8 will be described next.

  The power distribution mechanism 40 is mainly composed of two planetary gear sets (a first planetary gear set 50 and a second planetary gear set 60). In FIG. 2, the skeleton figure of the gear structure of the power distribution mechanism 40 is shown. The planetary gear set 50 is a gear set in which a sun gear 51, a carrier 52, and a ring gear 53 are combined. The carrier 52 is connected to the output shaft of the engine 8. The sun gear 51 is connected to the output shaft of the first motor 6 (M1). An output gear 54 is coaxially fixed to the ring gear 53. The output gear 54 is engaged with the idle gear 55. The shaft of the idle gear 55 is connected to the axle 9. The output gear 64 of the second planetary gear set 60 is engaged with the idle gear 55, and the ring gear 63 of the second planetary gear set 60 is coaxially fixed to the output gear 64. The carrier 62 of the second planetary gear set 60 is fixed and does not rotate. The output shaft of the second motor 7 (M2) is coupled to the shaft of the sun gear 61 of the second planetary gear set 60.

  The torque output to the axle 9 is determined by the sum of the outputs of the engine 8, the first motor 6, and the second motor 7 by the power distribution mechanism 40 having the above configuration. Depending on the situation, the axle 9 is driven by the outputs of the engine 8 and the second motor 7 and the first motor 6 is rotated by a part of the driving force of the engine 8 to obtain electric power. Alternatively, the engine 8 and the first motor 6 and the second motor 7 may all output and obtain a large driving force. Further, the driving force may be output only by the engine 8. The above case is a drive mode called an HV mode using an engine and a motor (or only an engine). Further, when the engine 8 is stopped, the outputs of the first motor 6 and the second motor 7 can be transmitted to the axle 9. A state in which the engine 8 is stopped and the vehicle travels with at least one driving force of the first motor 6 and the second motor 7 is a driving mode called an EV mode. In other words, the HV mode is a traveling mode that uses the driving force of the engine, and the EV mode is a traveling mode that does not use the driving force of the engine.

  The hybrid vehicle 2 travels while switching between the EV mode and the HV mode depending on the vehicle speed, the accelerator opening, the remaining amount of the battery 3, and the inclination of the travel path. The maximum output of the second motor 7 is larger than the maximum output of the first motor 6, and the second motor 7 is mainly used for traveling. The first motor 6 is mainly used as a starter motor that starts the engine 8 when switching from the EV mode to the HV mode, and a generator. However, as described above, when a large driving force is required, the first motor 6 also outputs the driving force, and on the other hand, the second motor 7 along with the first motor 6 functions as a generator during braking. The electric power generated by the kinetic energy of the vehicle during braking is called regenerative electric power.

  Returning to FIG. 1, the electrical system of the hybrid vehicle 2 will be described. Electric power supplied to the two motors 6 and 7 is stored in the battery 3. The battery 3 is connected to the power conversion device 5 via the system main relay 4. The power conversion device 5 includes a voltage converter circuit 10, a first inverter circuit 21, a second inverter circuit 22, and a controller 23. The voltage converter circuit 10 has a boost function that boosts the voltage of the battery 3 and supplies the boosted voltage to the first and second inverter circuits 21 and 22, and a step-down function that lowers the voltage of the regenerative power to the voltage of the battery 3. . The AC regenerative power generated by the motor is converted to DC by the first or second inverter circuit 21 or 22 and sent to the voltage converter circuit.

  The voltage converter circuit 10 includes a series circuit of two switching elements S7 and S8, and a reactor 13 having one end connected to an intermediate point of the series circuit and the other end connected to a high potential terminal on the battery side. The filter capacitor 12 is connected between the high potential terminal on the battery side and the ground terminal. In addition, a diode for passing a reverse current is connected in antiparallel to each of the switching elements S7 and S8. Step-up is performed by the operation of the switching element S8, and step-down is performed by the operation of the switching element S7. The voltage converter circuit 10 shown in FIG. 1 is also referred to as a chopper type buck-boost converter, and its mechanism is well known, and thus detailed description thereof is omitted.

  A first inverter circuit 21 and a second inverter circuit 22 are connected in parallel to the high voltage output terminal of the voltage converter circuit 10. A smoothing capacitor 16 and a voltage sensor 15 that measures the output voltage of the voltage converter circuit 10 are connected between the high voltage output terminal and the ground terminal of the voltage converter circuit 10. The smoothing capacitor 16 is inserted to suppress the pulsation of the current input to the first and second inverter circuits 21 and 22.

  The first inverter circuit 21 converts the boosted DC power into AC power and supplies the AC power to the first motor 6. The first inverter circuit 21 has a configuration in which six switching elements S1 to S7 are connected as shown in FIG. A diode is connected in antiparallel to each switching element. The diode is called a freewheeling diode. As shown in FIG. 1, the first motor 6 and the second motor 7 are both three-phase AC motors, and the circuit configuration of the first inverter circuit 21 that outputs the three-phase AC is well known, so detailed description is omitted. To do.

  The second inverter circuit 22 converts the boosted DC power into AC power and supplies it to the second motor 7. The second inverter circuit 22 has the same circuit configuration as the first inverter circuit 21. In FIG. 1, the circuit configuration of the second inverter circuit 22 is not shown.

  The switching elements of the voltage converter circuit 10 and the first and second inverter circuits 21 and 22 are typically transistors. More specifically, IGBTs are often employed as these switching elements. A drive signal (PWM signal) for driving those switching elements is generated by the controller 23. The controller 23 determines the output distribution of the engine 8 and the motors 6 and 7 from information such as the vehicle speed, the accelerator opening, and the remaining battery level, and generates and supplies drive signals (PWM signals) to the respective switching elements. The vehicle speed is measured by a vehicle speed sensor 17 provided on the axle 9 (see FIG. 1). A sensor signal of the vehicle speed sensor 17 is also input to the controller 23.

  Further, the controller 23 controls the power converter 5 according to the temperature of several devices of the power converter 5 in order to prevent an excessive temperature rise of the voltage converter circuit 10 and the first and second inverter circuits 21 and 22. The output (that is, the output of the motors 6 and 7) is limited. The voltage converter circuit 10 has the highest load, and the controller 23 adjusts the output of the power converter 5 according to the temperature of the voltage converter circuit 10. Therefore, sensor data of the temperature sensor 14 that measures the temperature of the voltage converter circuit 10 is also collected in the controller 23. Sensor data of the voltage sensor 15 that monitors the output voltage of the voltage converter circuit 10 is also collected in the controller 23.

  In FIG. 1, the symbol VH represents the output voltage (output upper limit voltage) of the voltage converter circuit 10, the symbol Sp represents the vehicle speed, and the symbol Ts represents the measured temperature of the voltage converter circuit 10. In addition, although illustration is abbreviate | omitted, the power converter device 5 is accompanied by the liquid-cooled cooler, and the temperature of the voltage converter circuit 10 may be estimated from the temperature of a liquid refrigerant. In that case, the estimated temperature is treated as the temperature Ts of the voltage converter circuit 10.

  Here, the output characteristics of the motor will be described. The output torque of the three-phase AC motor is proportional to the supplied current, but the output torque is limited by the physical characteristics of the motor, the rotational speed, and the supplied voltage. FIG. 3 shows an example of the relationship between the rotational speed of the three-phase AC motor and the maximum output torque. Graphs Gm, G1, and G2 show the relationship between the rotational speed and the output torque when the voltages of the electric power supplied to the motor are Vm, V1, and V2, respectively. Here, the relationship between the voltages Vm, V1, and V2 is Vm> V1> V2. The maximum output torque Tm in the low rotation range is determined by the physical characteristics of the motor and is constant without depending on the voltage. On the other hand, the lower the supplied voltage, the smaller the maximum output torque in the high rotation range. Since a large current cannot be sent to the motor unless the supply voltage is increased, the characteristics shown in FIG. 3 are obtained.

  The tendency of the graph of FIG. 3 is also applicable to the first and second motors 6 and 7 of the hybrid vehicle 2. In the case of the hybrid vehicle 2, the voltage of power supplied to the motor corresponds to the output voltage of the voltage converter circuit 10. Further, as shown in FIG. 2, the second motor 7 is interlocked with the axle 9, and the rotation speed of the second motor 7 is proportional to the vehicle speed.

  When the rotation speed of the second motor 7 is high, that is, when the vehicle speed is high, in order to enable the second motor 7 to output a desired torque, the voltage of the electric power supplied to the second motor 7, that is, The output upper limit voltage VH of the voltage converter circuit 10 needs to be increased. For example, in order to enable the second motor 7 to output the maximum output torque Tm during traveling at a vehicle speed corresponding to the rotational speed R1 in FIG. 3, the output upper limit voltage VH of the voltage converter circuit 10 should be set to V1 or higher. There must be. When the output upper limit voltage of the voltage converter circuit 10 is increased, the load on the voltage converter circuit 10 is increased, and the amount of heat generation is easily increased. That is, the temperature of the power conversion device 5 including the voltage converter circuit 10 is likely to rise.

  The thermal protection of the power conversion device 5 will be described. The controller 23 monitors the temperature Ts of the voltage converter circuit 10, and when the temperature Ts increases, the use opportunity of the motor is reduced and the load of the voltage converter circuit 10 is reduced. Specifically, the usage frequency of the first motor 6 is reduced. As described above, the hybrid vehicle 2 normally travels while appropriately switching between the EV mode that travels only with the driving force of the motor and the HV mode when traveling with the driving force of the engine (and the motor). The engine 8 is stopped in the EV mode, and the engine 8 is restarted using the first motor 6 when switching from the EV mode to the HV mode. Every time the engine is restarted, the amount of heat generated by the power supplied to the first motor 6 increases. In order to avoid this increase in the amount of heat generation, the controller 23 prohibits the transition to the EV mode so that the restart of the engine 8 becomes unnecessary when the temperature Ts of the voltage converter circuit 10 exceeds a predetermined temperature threshold. . In other words, the controller 23 continuously operates the engine 8 when the measured temperature Ts of the voltage converter circuit 10 exceeds the temperature threshold. Since the output of the second motor 7 affects drivability, it should be avoided to limit it as much as possible. On the other hand, by continuously operating the engine 8, the first motor 6 is not driven as a starter motor, and the load on the voltage converter circuit 10 is reduced accordingly.

  The temperature threshold is determined in consideration of the load increment required for engine restart. On the other hand, the load of the voltage converter circuit 10 depends on the output voltage. Since the first and second inverter circuits 21 and 22 are connected in parallel to the voltage converter circuit 10, the output upper limit voltage of the voltage converter circuit 10 is required for the first and second motors 6 and 7. It is determined depending on the output upper limit torque. As described above, the second motor 7 rotates in conjunction with the axle, and the higher the vehicle speed, the more the desired torque cannot be output unless the supply voltage to the motor is increased. Therefore, when the vehicle speed is high, the output upper limit voltage of the voltage converter circuit 10 needs to be increased. Conversely, when the vehicle speed is low, there is no need to increase the output voltage of the voltage converter circuit 10.

  In the graph of FIG. 3, the maximum output torque Tm can be secured if the output upper limit voltage VH of the voltage converter circuit 10 is held at V2 while traveling at a vehicle speed corresponding to the rotational speed R2. On the other hand, for example, during traveling at a vehicle speed corresponding to the rotational speed R1, the second motor 7 cannot output the maximum output torque Tm unless the output upper limit voltage VH of the voltage converter circuit 10 is maintained at V1 or higher. That is, the output upper limit voltage VH of the voltage converter circuit 10 needs to be maintained at V1 or higher. If the output upper limit voltage VH of the voltage converter circuit 10 is different, the temperature margin of the power converter 5 is also different. That is, when the output upper limit voltage VH of the voltage converter circuit 10 is low, the temperature threshold value for continuously operating the engine 8 can be set high.

  Based on the above logic, the controller 23 sets the output upper limit voltage VH of the voltage converter circuit 10 to be equal to or higher than the first voltage V1 when the vehicle speed Sp is equal to or higher than a predetermined vehicle speed threshold, and the power converter 5 (voltage converter). The engine is continuously operated when the temperature of the circuit 10) is equal to or higher than the first temperature threshold T1. When the vehicle speed Sp is lower than the vehicle speed threshold, the controller 23 sets the output upper limit voltage VH of the voltage converter circuit 10 to be equal to or higher than the second voltage V2, and the temperature of the power converter 5 (voltage converter circuit 10) is the first. When the temperature is equal to or greater than 2 temperature threshold T2, the engine is continuously operated. Here, the second voltage V2 is lower than the first voltage V1, and the second temperature threshold T2 is higher than the first temperature threshold T1. That is, when the vehicle speed is low, there are fewer opportunities for the engine stop / restart to be prohibited compared to when the vehicle speed is high. In other words, when the vehicle speed is low, the chance of traveling in the EV mode increases. This contributes particularly to an improvement in fuel consumption during long-time low speed driving in traffic jams.

  A flowchart of the above processing is shown in FIG. The controller 23 periodically executes the heat protection process of FIG. The controller 23 monitors the vehicle speed Sp by the vehicle speed sensor 17. When the vehicle speed Sp is equal to or higher than a predetermined vehicle speed threshold, the output upper limit voltage VH of the voltage converter circuit 10 is set to the first voltage V1 (S2: YES, S3). The controller 23 monitors the temperature of the voltage converter circuit 10 with the temperature sensor 14, and continuously operates the engine 8 if the measured temperature Ts is equal to or higher than a predetermined first temperature threshold T1 (S4: YES, S8). On the other hand, when the measured temperature Ts is lower than the first temperature threshold value T1, the controller 23 permits the engine 8 to stop (S4: NO, S5).

  If the determination in step S2 is NO, that is, if the vehicle speed Sp is below the vehicle speed threshold, the controller 23 sets the output upper limit voltage VH of the voltage converter circuit 10 to the second voltage V2 (S6). As described above, the second voltage V2 is lower than the first voltage V1. At this time, the controller 23 continuously operates the engine 8 if the temperature Ts of the voltage converter circuit 10 is equal to or higher than the second temperature threshold T2 (S7: YES, S8). On the other hand, when the measured temperature Ts is lower than the second temperature threshold value T2, the controller 23 permits the engine 8 to stop (S7: NO, S5). Here, the second temperature threshold T2 is higher than the first temperature threshold T1.

  Thus, the hybrid vehicle 2 suppresses an increase in the usage frequency of the engine 8 while suppressing an excessive temperature rise of the power conversion device 5.

  Points to be noted regarding the technology described in the embodiments will be described. In the processing shown in FIG. 4, when the temperature Ts of the voltage converter circuit 10 is equal to or higher than a predetermined temperature threshold, traveling in the EV mode is prohibited and traveling in the HV mode is performed. On the other hand, when the temperature Ts of the voltage converter circuit 10 is below a predetermined temperature threshold, switching between the EV mode and the HV mode can be performed. However, it should be noted that traveling in the EV mode may be prohibited due to other requirements such as a requirement that the remaining amount of the battery 3 is low.

  The controller 23 sets the maximum upper limit voltage VH of the voltage converter circuit 10, but the voltage converter circuit 10 outputs a voltage corresponding to the torque required for the second motor 7. The upper limit of the voltage is limited to the maximum upper limit voltage VH.

  In the flowchart of FIG. 4, inequality signs representing “above (or less)” are used, but these inequality signs may be inequality signs representing “greater than (less than)”. It should be noted that it is important that a threshold is provided, and it is not important in which region the boundary is included.

  The function of the controller 23 of the embodiment may be realized in cooperation with a plurality of devices in hardware. Actually, a hybrid vehicle has a plurality of hardware controllers such as an engine controller and a battery controller. However, for the sake of brevity, the functions described in this embodiment are performed by the controller 23 of the power converter 5. Assumed that

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

2: Hybrid vehicle 3: Battery 4: System main relay 5: Power converter 6: First motor 7: Second motor 8: Engine 9: Axle 10: Voltage converter circuit 12: Filter capacitor 13: Reactor 14: Temperature sensor 15 : Voltage sensor 16: Smoothing capacitor 17: Vehicle speed sensor 21: First inverter circuit 22: Second inverter circuit 23: Controller 40: Power distribution mechanism 50: First planetary gear set 51, 61: Sun gear 52, 62: Carrier 53 63: Ring gear 54, 64: Output gear 55: Idle gear 60: Second planetary gear set

Claims (1)

Engine,
A first motor for starting the engine;
A second motor for generating a driving force for traveling;
A voltage converter circuit that boosts the output voltage of the battery; a first inverter circuit that converts the boosted DC power to AC and supplies the first motor; and the second DC power that has been boosted is converted to AC. A power converter including a second inverter circuit to be supplied to the motor;
A controller,
The controller comprises:
When the vehicle speed is equal to or higher than a predetermined vehicle speed threshold, the output upper limit voltage of the voltage converter circuit is set to the first voltage or higher, and the engine is continuously operated when the temperature of the power converter is equal to or higher than the first temperature,
When the vehicle speed is lower than the vehicle speed threshold, the output upper limit voltage of the voltage converter circuit is set to a second voltage lower than the first voltage, and the temperature of the power converter is a second temperature higher than the first temperature. In the above case, the engine is operated continuously.
A hybrid vehicle characterized by that.

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