JP2008302763A - Drive unit of hybrid vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably ensure power for starting an engine without increasing a capacity of a storage device. <P>SOLUTION: When an engine 50 is started by using power from a motor generator 54, if a temperature τb of a secondary battery 16 is equal to a prescribed value τ0 or lower in Step S102, a switching frequency fc of transistors T1, T2 of a step-up converter 18 is set to f1 in Step S103. If the temperature τb of the secondary battery 16 is lower than the prescribed value τ0 in Step S102, the switching frequency fc of the transistors T1, T2 of the step-up converter 18 is set to f2 lower than the f1 in Step S104. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a drive device for a hybrid vehicle, and more particularly to a drive device for a hybrid vehicle that can start an engine by driving a motor generator by supplying electric power from a power storage device to the motor generator.

  As a conventional drive device, a power storage device that outputs a DC voltage, a boost converter that boosts and outputs a DC voltage from the power storage device, an inverter that converts the DC voltage from the boost converter into an alternating current, and an inverter Have been proposed (for example, Patent Documents 1 and 2 below). In this drive device, power transmission can be performed between the engine and the motor generator, so that the motor generator can be driven by power supply from the power storage device to the motor generator to start the engine. it can.

JP 2003-116280 A International Publication No. 02/65628 Pamphlet Japanese Patent Laying-Open No. 2005-245086 JP 2002-153096 A

  In the above drive device, when the engine is started by supplying power from the power storage device to the motor generator, the boost converter, inverter, and so on until the discharge power of the power storage device is converted into the power of the motor generator and transmitted to the engine And loss in the motor generator. Therefore, the power transmitted to the engine is smaller than the discharge power of the power storage device by these losses. Furthermore, in an environment at an extremely low temperature, the output (electric power that can be discharged) of the power storage device is reduced, so that the power transmitted to the engine is also reduced. As a result, engine startability is reduced. If the capacity of the power storage device is increased in order to secure electric power that can start the engine, an increase in weight of the power storage device, deterioration in mountability, and cost increase are caused.

  An object of the present invention is to provide a drive device for a hybrid vehicle that can stably secure electric power capable of starting an engine without increasing the capacity of a power storage device.

  The drive device for a hybrid vehicle according to the present invention employs the following means in order to achieve the above-described object.

  A drive device for a hybrid vehicle according to the present invention includes an engine, a power storage device that outputs a DC voltage, a boost converter that boosts and outputs a DC voltage from the power storage device by a switching operation of the switching device, and a power supply to the switching device. Utilizes boost converter control means that controls the boost ratio of the boost converter by controlling the duty ratio of the switching control signal, an inverter that converts the DC voltage from the boost converter into an alternating current, and AC power from the inverter And a motor generator capable of starting the engine, comprising: a temperature detection means for detecting the temperature of the power storage device; and the boost converter control means when the engine is started by the motor generator. The temperature detected by the temperature detecting means is lower than the predetermined value. Time, and summarized in that the temperature is lower the switching frequency of the switching element than when it is the predetermined value or more.

  In one aspect of the present invention, the boost converter control means generates the switching control signal based on a comparison result between the duty ratio command and the reference carrier, and further, when the engine is started by the motor generator, the temperature detection means When the detected temperature is lower than the predetermined value, it is preferable to lower the frequency of the reference carrier than when the temperature is equal to or higher than the predetermined value.

  In one embodiment of the present invention, it is preferable that the temperature detection unit detects an outside air temperature or an engine coolant temperature instead of the temperature of the power storage device.

  ADVANTAGE OF THE INVENTION According to this invention, when starting an engine by the electric power supply from an electrical storage apparatus to a motor generator, the electric power which can start an engine can be ensured stably, without increasing the capacity | capacitance of an electrical storage apparatus.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of a drive device for a hybrid vehicle according to an embodiment of the present invention. An output shaft of an engine (internal combustion engine) 50 capable of generating power is connected to a power distribution mechanism 52. In addition to the output shaft of the engine 50, the power distribution mechanism 52 is also connected to the input shaft of the speed reducer 14 and the rotor of a motor generator (first motor generator) 54 that can generate power. Here, the power distribution mechanism 52 can be constituted by, for example, a planetary gear mechanism having a ring gear, a carrier, and a sun gear. The output shaft of the speed reducer 14 is connected to the drive wheels 19. The power distribution mechanism 52 distributes the power from the engine 50 to the drive wheels 19 and the motor generator 54. The power distributed from the power distribution mechanism 52 to the drive wheels 19 is used for driving the vehicle. On the other hand, the power distributed from the power distribution mechanism 52 to the motor generator 54 is converted into electric power generated by the motor generator 54. The electric power generated by the motor generator 54 can be supplied via the inverter 12 to the motor generator (second motor generator) 10 capable of generating power.

  The secondary battery 16 provided as a power storage device that stores electrical energy outputs a DC voltage. The secondary battery 16 here can be composed of, for example, a lithium ion battery or the like, and is provided with a temperature sensor 17 that detects the temperature τb of the secondary battery 16. Boost converter 18 boosts the DC voltage from secondary battery 16 and outputs the boosted voltage to inverter 12. Inverter 12 includes a switching element, and converts the DC voltage from boost converter 18 into AC by a switching operation of the switching element and outputs the alternating current to motor generators 10 and 54. The motor generator 10 converts AC power supplied to the windings from the inverter 12 into rotor power. The rotor of the motor generator 10 is connected to the input shaft of the speed reducer 14, and the power of the motor generator 10 is transmitted to the drive wheels 19 after being decelerated by the speed reducer 14 and used for driving the vehicle. Further, by the regenerative operation of the motor generator 10, the motive power of the drive wheels 19 (vehicle) can be converted into the generated power of the motor generator 10 and recovered into the secondary battery 16 via the inverter 12 and the boost converter 18.

  In addition, the motor generator 54 converts the AC power supplied from the inverter 12 to the windings to the power of the rotor, thereby starting the engine 50 using the power of the rotor (AC power from the inverter 12). Is possible. When engine 50 is started by motor generator 54, torque is also generated in motor generator 10 in order to receive torque from motor generator 54. Furthermore, the power generated by the motor generator 54 can be recovered to the secondary battery 16 via the inverter 12 and the boost converter 18 by the power generation operation of the motor generator 54.

  A configuration example of the boost converter 18 is shown in FIG. As shown in FIG. 2, the boost converter 18 includes two transistors (switching elements) T1, T2 connected in series so as to be on the source side and the sink side with respect to the positive side line and the negative side line of the inverter 12. Two diodes D1 and D2 connected in reverse parallel to the transistors T1 and T2, respectively, and a reactor having one end connected to one end of the secondary battery 16 and the other end connected to a connection point of the transistors T1 and T2. L. The transistor T1 is disposed between the other end of the reactor L and the output end, and the transistor T2 is disposed between the other end of the reactor L and the other end of the secondary battery 16. In boost converter 18, when transistor T 2 is turned on, a short circuit that connects secondary battery 16, reactor L, and transistor T 2 is formed, and energy is stored in reactor L in accordance with the direct current flowing from secondary battery 16. In this state, when the transistor T2 is turned off from on, the energy accumulated in the reactor L is accumulated in the capacitor 26 via the diode D1. At this time, the DC voltage of capacitor 26 (output voltage of boost converter 18) can be made higher than the DC voltage of secondary battery 16 (input voltage of boost converter 18). As described above, the boost converter 18 can boost the DC voltage from the secondary battery 16 and output it to the inverter 12 by the switching operation for driving the transistors T1 and T2 on and off.

  The electronic control unit 42 controls driving of the motor generators 10 and 54 by controlling the switching operation of the switching element of the inverter 12. Further, the electronic control unit 42 controls the boost ratio of the boost converter 18 by controlling the duty ratio D of the switching control signal for driving the transistors T1 and T2 of the boost converter 18 to be turned on and off. Here, for example, as shown in FIG. 3, based on the comparison result between the duty ratio command (target duty ratio) D0 and the reference carrier (triangular wave carrier) Vc, a switching control signal that satisfies the duty ratio D = target duty ratio D0 is obtained. Can be generated. In the configuration example of the boost converter 18 shown in FIG. 2, the duty ratio D, which is the ratio between the conduction period (T1on) of the upper transistor T1 and the conduction period (T2on) of the lower transistor T2, is D = T1on / (T1on + T2on). ) And the boost ratio of the boost converter 18 increases as the duty ratio D (= T1on / (T1on + T2on)) decreases.

  When the engine 50 is started by supplying power from the secondary battery 16 to the motor generator 54, the discharge power of the secondary battery 16 is converted into power (mechanical power) of the motor generator 54 as shown in FIG. Thus, a loss occurs in boost converter 18, inverter 12, and motor generator 54 before being transmitted to engine 50. Further, since the torque is also generated in the motor generator 10 in order to receive the torque from the motor generator 54, the motor generator 10 also has a loss. Therefore, the power transmitted to the engine is smaller than the discharge power of the secondary battery 16 by these losses. In an environment at a very low temperature, the output of the secondary battery 16 (dischargeable power) is reduced, so that the power transmitted to the engine is reduced and the friction of the engine 50 is also increased. 50 startability is reduced. Therefore, in this embodiment, when the engine 50 is started using the power of the motor generator 54, the switching operation of the boost converter 18 is performed by lowering the switching frequency of the transistors T1 and T2 of the boost converter 18 at an extremely low temperature. Reduce power loss at the time. As a result, the required output of the secondary battery 16 required for starting the engine 50 is reduced, and a decrease in the startability of the engine 50 is suppressed.

  FIG. 5 is a flowchart for explaining processing executed by the electronic control unit 42 when the engine 50 is started using the power of the motor generator 54. First, in step S101, the temperature τb of the secondary battery 16 detected by the temperature sensor 17 is read. Next, in step S102, it is determined whether or not the temperature τb of the secondary battery 16 is lower than a predetermined value τ0. Here, the predetermined value τ0 is set as a threshold value for determining whether or not the temperature τb of the secondary battery 16 is an extremely low temperature. When the temperature τb of the secondary battery 16 is equal to or higher than the predetermined value τ0 (when the determination result of step S102 is NO), the process proceeds to step S103. On the other hand, when the temperature τb of the secondary battery 16 is lower than the predetermined value τ0 (when the determination result of step S102 is YES), the process proceeds to step S104.

  In step S103, the frequency fc of the reference carrier Vc is set to f1, so that the switching frequency fc of the transistors T1 and T2 of the boost converter 18 is set to f1. Here, f1 is a value of about 10 kHz, for example. A switching control signal to the transistors T1 and T2 is generated based on the comparison result between the reference carrier Vc having the frequency fc = f1 and the duty ratio command D0, and the boosting ratio of the boost converter 18 is controlled by the switching control signal. .

  On the other hand, in step S104, the frequency fc of the reference carrier Vc is set to f2 lower than f1, so that the switching frequency fc of the transistors T1 and T2 of the boost converter 18 is set to f2. Here, f2 is a value of about 5 kHz, for example. A switching control signal to the transistors T1 and T2 is generated based on the comparison result between the reference carrier Vc having the frequency fc = f2 and the duty ratio command D0, and the boosting ratio of the boost converter 18 is controlled by the switching control signal. . For example, as shown in the loss characteristic of the boost converter 18 in FIG. 6, when the frequency fc of the reference carrier Vc is 10 kHz and the loss is 0.2 kW, the loss is reduced to 0. 0 by reducing the frequency fc of the reference carrier Vc to 5 kHz. It can be reduced to 12 kW.

  Thus, in this embodiment, when the engine 50 is started using the power of the motor generator 54, if the temperature τb of the secondary battery 16 is lower than the predetermined value τ0, the temperature τb of the secondary battery 16 is used. The frequency of the reference carrier Vc (switching frequency of the transistors T1 and T2) fc is made lower than when the value is equal to or greater than the predetermined value τ0. As a result, at a very low temperature, the power loss during the switching operation of the boost converter 18 can be reduced, so that a reduction in the power transmitted to the engine 50 due to a reduction in the output of the secondary battery 16 can be compensated. The required output of the secondary battery 16 required for starting 50 can be reduced. As a result, it is possible to stably secure electric power capable of starting the engine 50 without increasing the capacity of the secondary battery 16, and to improve the startability of the engine 50. On the other hand, when the temperature is not extremely low, the frequency of the reference carrier Vc (the switching frequency of the transistors T1 and T2) fc is increased to reduce the noise during the switching operation of the boost converter 18 and the ripple of the current flowing through the reactor L. And controllability can be improved.

  Furthermore, in this embodiment, when the engine 50 is started using the power of the motor generator 54, if the temperature τb of the secondary battery 16 is lower than the predetermined value τ0, the temperature τb of the secondary battery 16 is predetermined. It is also possible to lower the switching frequency (reference carrier frequency) of the switching element of the inverter 12 than when the value τ0 or more. Thereby, at a very low temperature, the required output of the secondary battery 16 required for starting the engine 50 can be further reduced by reducing the power loss during the switching operation of the inverter 12. As a result, the startability of the engine 50 can be further improved.

  In the above description of the embodiment, when the engine 50 is started using the power of the motor generator 54, the frequency of the reference carrier Vc (the switching frequency of the transistors T1 and T2) fc based on the temperature τb of the secondary battery 16. Was set. However, in the present embodiment, a temperature sensor that detects the outside air temperature τg may be provided instead of the temperature sensor 17 that detects the temperature τb of the secondary battery 16. In this example, when the engine 50 is started using the power of the motor generator 54, when the outside air temperature τg is lower than the predetermined value τ0, the reference carrier Vc is higher than when the outside air temperature τg is equal to or higher than the predetermined value τ0. Is reduced (the switching frequency of the transistors T1 and T2) fc. This also makes it possible to compensate for the reduction in the power transmitted to the engine 50 caused by the output reduction of the secondary battery 16 at an extremely low temperature, thereby reducing the required output of the secondary battery 16 necessary for starting the engine 50. can do. In this embodiment, a temperature sensor that detects the coolant temperature τe of the engine 50 may be provided instead of the temperature sensor 17 that detects the temperature τb of the secondary battery 16. In this example, when the engine 50 is started using the power of the motor generator 54 and the coolant temperature τe of the engine 50 is lower than the predetermined value τ0, the coolant temperature τe of the engine 50 is equal to or higher than the predetermined value τ0. The frequency of the reference carrier Vc (switching frequency of the transistors T1 and T2) fc is made lower than that when. This also makes it possible to compensate for a decrease in the power transmitted to the engine 50 due to a decrease in the output of the secondary battery 16 at an extremely low temperature.

  Moreover, the above embodiment demonstrated the case where this invention was applied with respect to the hybrid vehicle of the structure shown in FIG. However, the configuration of the hybrid vehicle to which the present invention can be applied is not limited to the configuration shown in FIG. 1, and the present invention can also be applied to, for example, a series hybrid vehicle and a parallel hybrid vehicle. Further, the configuration of the boost converter 18 to which the present invention can be applied is not limited to the configuration shown in FIG. 2, and the present invention can be applied to boost converters having configurations other than those in FIG.

  As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to such embodiment at all, and it can implement with a various form in the range which does not deviate from the summary of this invention. Of course.

1 is a diagram illustrating a schematic configuration of a drive device for a hybrid vehicle according to an embodiment of the present invention. It is a figure which shows the structural example of a boost converter. It is a figure explaining an example of the production | generation method of the switching control signal to a step-up converter. It is a figure explaining the loss generate | occur | produced until the discharge electric power of a secondary battery is converted into motive power of a motor generator, and is transmitted to an engine. It is a flowchart explaining the process performed by an electronic control unit. It is a figure which shows an example of the loss characteristic of a step-up converter.

Explanation of symbols

  10, 54 Motor generator, 12 inverter, 14 reducer, 16 secondary battery, 17 temperature sensor, 18 boost converter, 19 drive wheel, 42 electronic control unit, 50 engine, 52 power distribution mechanism, T1, T2 transistor.

Claims (3)

Engine,
A power storage device that outputs a DC voltage;
A boost converter that boosts and outputs a DC voltage from the power storage device by a switching operation of the switching element;
A boost converter control means for controlling a boost ratio of the boost converter by controlling a duty ratio of a switching control signal to the switching element;
An inverter that converts the DC voltage from the boost converter to AC and outputs,
A motor generator capable of starting the engine using AC power from the inverter;
A drive device for a hybrid vehicle comprising:
Temperature detecting means for detecting the temperature of the power storage device,
When the engine is started by the motor generator, the boost converter control means switches the switching element when the temperature detected by the temperature detection means is lower than a predetermined value than when the temperature is equal to or higher than the predetermined value. A drive device for a hybrid vehicle that lowers the frequency. The hybrid vehicle drive device according to claim 1,
The boost converter control means
Based on the comparison result between the duty ratio command and the reference carrier, the switching control signal is generated,
Further, when the engine is started by the motor generator, when the temperature detected by the temperature detecting means is lower than the predetermined value, the frequency of the reference carrier is made lower than when the temperature is equal to or higher than the predetermined value. Drive device for hybrid vehicle. A drive device for a hybrid vehicle according to claim 1 or 2,
The temperature detecting means is a hybrid vehicle drive device that detects an outside air temperature or an engine coolant temperature instead of the temperature of the power storage device.

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