JP2012030685A - Driving system of hybrid vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving system of a hybrid vehicle having a compact motor miniaturized without a boosting system.SOLUTION: The driving system of the hybrid vehicle includes a switch 7 for connecting and disconnecting a power line 9 between a battery 3 and a motor 1; a switching unit 28 for switching the switch 7 when a speed of a vehicle 10 reaches a predetermined vehicle-speed threshold; a vehicle-speed threshold changing unit 29 for changing the vehicle-speed threshold on the basis of the temperature of a battery 3 when the temperature of the battery 3 is higher than a predetermined value; and an electronic control device 13 that actuates the switch 7 for disconnection when the temperature of the battery 3 is higher than the predetermined value and the speed of the vehicle 10 is higher than the vehicle-speed threshold, and supplies power generated by a generator 2 to the motor 1, to drive the motor 1.

Description

  The present invention relates to a drive system for a hybrid vehicle.

  In recent years, a motor mounted on a hybrid vehicle tends to be downsized for the purpose of reducing the weight of the vehicle and reducing the cost. As a method for downsizing the motor, a method of downsizing a motor to be mounted by increasing the reduction gear ratio, increasing the rotation speed of the motor, and reducing the torque of the motor is employed. In the case of this method, a high voltage is required to increase the rotation speed of the motor, so a boosting system that boosts the battery voltage is required (for example, see Patent Document 1 below).

  Conventionally, a hybrid vehicle mode switching control device that performs switching control of a vehicle traveling mode in accordance with the state of charge of a battery or the like is known (see, for example, Patent Document 2 below).

JP 2007-330022 A JP 2008-1114835 A

  However, the boosting system described above is composed of a large reactor, a semiconductor element, and the like, and if the boosting system is used to reduce the size of the motor, the vehicle will increase in weight and cost. There's a problem.

  In addition, even when the vehicle is in a steady driving state, especially in a driving state that does not require boosting, energy loss always occurs in the semiconductor elements in the boosting system, and this energy loss reduces energy efficiency. There is a problem that the cruising distance decreases.

  Further, the above-described conventional vehicle mode switching control includes a hybrid vehicle in which a motor is driven with a low voltage and a vehicle is driven with a high voltage. It wasn't.

  In view of the above, an object of the present invention is to provide a hybrid vehicle drive system capable of reducing the size of a motor without using a booster system.

A hybrid vehicle drive system according to a first aspect of the present invention for solving the above problems
A motor for driving the vehicle;
A battery for supplying power to the motor;
A generator driven by a combustion engine to generate electricity;
Battery temperature detecting means for detecting the temperature of the battery;
Vehicle speed detection means for detecting the speed of the vehicle;
A power line for transmitting moving power between the battery, the motor and the generator;
A switch for switching connection / disconnection of the power line between the battery and the motor;
Switch switching means for switching the switch when the speed of the vehicle reaches a predetermined vehicle speed threshold;
Vehicle speed threshold changing means for changing the vehicle speed threshold based on the temperature of the battery when the temperature of the battery is higher than a predetermined value;
When the temperature of the battery is greater than the predetermined value and the vehicle speed is greater than the vehicle speed threshold, the switch is turned off to supply the power generated by the generator to the motor to drive the motor. And a control means for controlling.

A hybrid vehicle drive system according to a second aspect of the invention for solving the above-described problems is the hybrid vehicle drive system according to the first aspect of the invention,
The vehicle speed threshold value changing means changes the vehicle speed threshold value so as to decrease as the temperature of the battery increases.

A hybrid vehicle drive system according to a third aspect of the present invention for solving the above problems is the hybrid vehicle drive system according to the first or second aspect of the invention,
Further comprising generator temperature detection means for detecting the temperature of the generator;
When the battery temperature is equal to or lower than the predetermined value, the vehicle speed threshold value changing means changes the vehicle speed threshold value based on a rate of increase in temperature per minute time of the generator temperature calculated from the generator temperature,
The control means performs the control when the temperature of the battery is equal to or lower than the predetermined value and the speed of the vehicle is greater than the vehicle speed threshold value.

  The present invention can provide a drive system for a hybrid vehicle that can reduce the size of a motor without using a booster system.

1 is a schematic diagram illustrating a configuration of a main part of a drive system for a hybrid vehicle according to the present invention. 1 is a schematic diagram illustrating a configuration of a drive system for a hybrid vehicle according to the present invention. It is a control block diagram of the drive system of the hybrid vehicle which concerns on this invention. It is the figure which showed the driving mode switching map in the drive system of the hybrid vehicle which concerns on this invention. It is the flowchart which showed the procedure of the process of switching control of driving modes in the drive system of the hybrid vehicle which concerns on 1st Example of this invention. It is the flowchart which showed the procedure of the process of switching control of driving modes in the drive system of the hybrid vehicle which concerns on 2nd Example of this invention. It is the figure which showed the change of the temperature with respect to the time of a generator and a battery.

  Hereinafter, a drive system for a hybrid vehicle according to the present invention will be described with reference to the drawings.

A hybrid vehicle drive system according to a first embodiment of the present invention will be described below.
First, an apparatus configuration of a hybrid vehicle drive system according to the present invention will be described.
FIG. 2 is a schematic diagram illustrating a configuration of a hybrid vehicle drive system according to the present embodiment.
As shown in FIG. 2, the hybrid vehicle drive system according to the present embodiment includes a motor 1 that drives wheels 11 to drive the vehicle 10, a generator 2 that generates electric power consumed by the motor 1, and a motor 1. A battery 3 for storing electric power for driving, a motor / generator control unit 4 for controlling the motor 1 and the generator 2, an internal combustion engine 12 for driving the generator 2, and an electronic control for controlling various devices mounted on the vehicle 10. It is comprised by the apparatus (control means) 13 grade | etc.,.

FIG. 1 is a schematic diagram illustrating a configuration of a main part of a drive system for a hybrid vehicle according to the present embodiment.
As shown in FIG. 1, the motor / generator control unit 4 includes a generator-side inverter 5 that converts a three-phase AC current generated by the generator 2 into a DC current, and three DC currents from the battery 3 and the generator-side inverter 5. A motor-side inverter 6 that converts the current into a phase alternating current to drive the motor 1, a switch 7 such as a relay that switches ON / OFF of the electrical connection between the battery 3, the generator-side inverter 5, and the motor-side inverter 6, and a battery 3 and a smoothing capacitor 8 for stably supplying power from the generator-side inverter 5 to the motor-side inverter 6. In addition, the battery 3, the motor 1, and the generator 2 are electrically connected to each other through a power line 9.

FIG. 3 is a control block diagram of the drive system for the hybrid vehicle according to the present embodiment.
As shown in FIG. 3, in the hybrid vehicle drive system according to the present embodiment, a vehicle speed detector (vehicle speed detection means) 20 such as a sensor that detects the rotational speed of the wheel 11 that detects the traveling speed of the vehicle 10, and A motor temperature detector 21 that detects the temperature of the motor 1, a generator temperature detector (generator temperature detection means) 22 that detects the temperature of the generator 2, a battery voltage detector 23 that detects the voltage of the battery 3, and the battery 3 A battery current detector 24 for detecting the current of the battery 3, a battery temperature detector (battery temperature detecting means) 25 for detecting the temperature of the battery 3, and a battery control means 26 for controlling the battery 3.

  The battery control unit 26 includes an SOC calculation unit 27 that calculates a state of charge (SOC) of the battery 3. The battery control means 26 is connected to the battery voltage detector 23, the battery current detector 24, and the battery temperature detector 25. Then, the battery control means 26 is based on the battery voltage detected by the battery voltage detector 23, the battery current detected by the battery current detector 24, and the battery temperature detected by the battery temperature detector 25. To calculate the SOC. In the present embodiment, the SOC is indicated as a percentage with the full charge of the battery 3 being 100 [%].

  The electronic control unit 13 includes switch switching means 28 for switching the switch 7 installed in the motor / generator control unit 4. The electronic control device 13 is connected to the vehicle speed detector 20, the motor temperature detector 21, the generator temperature detector 22, the battery control means 26, and the motor / generator control unit 4.

The electronic control unit 13 then detects the vehicle speed detected by the vehicle speed detector 20, the motor temperature detected by the motor temperature detector 21, the generator temperature detected by the generator temperature detector 22, and the SOC calculated by the battery control means 26. Based on the above, the switch switching means 28 switches the switch 7 of the motor / generator control unit 4 between ON and OFF.
The above is the apparatus configuration of the hybrid vehicle drive system according to the present embodiment.

Next, traveling mode switching control in the hybrid vehicle drive system according to the present embodiment will be described.
FIG. 4 is a diagram illustrating a travel mode switching map in the hybrid vehicle drive system according to the present embodiment.
As shown in FIG. 4, in the hybrid vehicle drive system according to the present embodiment, when the vehicle speed is less than a predetermined value α and the SOC is equal to or higher than the predetermined value β (region indicated by A in FIG. 4), The EV traveling mode is set in which the vehicle 10 travels only with electric power.

As shown in FIG. 1A, in the EV travel mode, the electronic control unit 13 turns on the switch 7 by the switch switching means 28 and turns off the generator-side inverter 5, that is, does not operate the generator-side inverter 5. ON the motor side inverter 6, i.e. by actuating the motor side inverter 6, it travels by driving the motor 1 only by the current I _b from the battery 3.

  In the present embodiment, for example, when the normal speed range of the vehicle 10 is less than 100 [km / h], “α = 100 [km / h]” and the battery 3 needs to be charged. When the SOC to be determined is 30 [%], if “β = 30 [%]”, EV driving is performed when the vehicle speed is less than 100 [km / h] and the SOC is 30 [%] or more. At this time, for example, if the voltage of the battery 3 is 200V, the motor 1 is driven with a voltage of 200V.

  Thereby, when the SOC is sufficient, the EV travel mode can be set. Therefore, the exhaust gas is not discharged and the vehicle can travel with a low load on the environment.

  Further, when the vehicle speed is less than the predetermined value α and the SOC is less than the predetermined value β (region indicated by B in FIG. 4), the vehicle 10 is caused to travel with the same voltage as the battery voltage generated by the generator 2, and at the same time A low-voltage series travel mode in which the battery 3 is charged with the same voltage as the battery voltage generated by the generator 2 is set.

As shown in FIG. 1B, in the low voltage series travel mode, the electronic control unit 13 turns on the switch 7 by the switch switching means 28 and turns on the generator side inverter 5, that is, operates the generator side inverter 5. , ON the motor side inverter 6, i.e. by actuating the motor side inverter 6, it runs by driving the motor 1 by the current I _g of the battery voltage and the same voltage generated by the generator 2 and the power generation by simultaneously generator 2 battery charging the battery 3 by the current I _g of voltage and the same voltage.

  In the present embodiment, for example, when the normal speed range of the vehicle 10 is less than 100 [km / h], “α = 100 [km / h]” and the battery 3 needs to be charged. When the SOC to be determined is 30 [%], if “β = 30 [%]”, and the vehicle speed is less than 100 [km / h] and the SOC is less than 30 [%], the low voltage series running is Become. At this time, for example, assuming that the voltage is 200 V, the motor 1 is driven by the power generated by the generator 2 and travels, and the battery 3 is charged at the same time. The motor 200 is driven with the same voltage of 200 V as that of the battery 3.

  Thus, when the SOC decreases, the EV traveling mode can be shifted to the low voltage series traveling mode, and the decreased SOC can be recovered by the generated power of the generator 2. Therefore, it is possible to avoid an extreme decrease in SOC.

  Further, when the vehicle speed is equal to or higher than the predetermined value α (region indicated by C in FIG. 4), the high voltage series travel mode is set in which the vehicle 10 is traveled only by the high voltage power generated by the generator 2.

As shown in FIG. 1C, in the high voltage series travel mode, the electronic control unit 13 turns off the switch 7 by the switch switching means 28 and turns on the generator side inverter 5, that is, operates the generator side inverter 5. , ON the motor side inverter 6, i.e. by actuating the motor side inverter 6, only by the current I _g of the high voltage from the generator 2 to travel by driving the motor 1.

  In this embodiment, for example, when the normal speed range of the vehicle 10 is less than 100 [km / h], when “α = 100 [km / h]”, the vehicle speed is 100 [km. / H] and higher voltage series travel. At this time, for example, if the voltage generated by the generator 2 is 600V, the motor 1 is driven with a high voltage of 600V.

  Here, in the high voltage series travel mode, the electronic control unit 13 turns off the switch 7, but by turning off the switch 7, the electrical connection between the battery 3 and the motor 1 or the battery 3 and the generator 2 Will be cut off. As a result, the motor 1 and the generator 2 are disconnected from the battery 3 and are not affected by the voltage of the battery 3. Therefore, the generator 2 can generate power higher than the voltage of the battery 3 without being affected by the battery 3, and this generated power can be supplied to the motor 1. Therefore, the motor 1 can be driven with a high voltage without using a boosting system.

  In the present embodiment, as an example, the predetermined value α and the predetermined value β have been described as being set to constant values, but the predetermined value α is changed according to the SOC, or the predetermined value according to the vehicle speed. It is also possible to set as a function for changing β. That is, it is possible to give an inclination to the boundary line of each region shown in FIG.

Next, the procedure of the travel mode switching control in the hybrid vehicle drive system according to the present embodiment will be described.
FIG. 5 is a flowchart showing the procedure of the travel mode switching control in the hybrid vehicle drive system according to the present embodiment.
As shown in FIG. 5, in step P10, the electronic control unit 13 detects the vehicle speed and the SOC. After executing step P10, the electronic control device 13 executes step P11.

  In step P11, the electronic control unit 13 determines whether the detected speed is less than a predetermined value α. When the detected speed is less than the predetermined value α, the electronic control device 13 executes Step P12. Further, when the detected speed is not less than the predetermined value α, the electronic control unit 13 executes Step P15 described later.

  In step P12, the electronic control unit 13 determines whether the detected SOC is equal to or greater than a predetermined value β. When the detected SOC is equal to or greater than the predetermined value β, the electronic control device 13 executes Step P13. Further, when the detected SOC is not equal to or greater than the predetermined value β, the electronic control device 13 executes Step P14.

  In step P13, as shown in FIG. 1A, the electronic control unit 13 turns on the switch 7 by the switch switching means 28, turns off the generator-side inverter 5, that is, does not operate the generator-side inverter 5, The inverter 6 is turned on, that is, the motor-side inverter 6 is operated to set the traveling mode of the vehicle 10 to EV traveling.

  In step P14, as shown in FIG. 1 (b), the electronic control unit 13 turns on the switch 7 by the switch switching means 28, turns on the generator-side inverter 5, that is, operates the generator-side inverter 5, and the motor-side inverter. 6 is turned on, that is, the motor-side inverter 6 is operated, and the running mode of the vehicle 10 is set to the low voltage series running.

In step P15, as shown in FIG. 1 (c), the electronic control unit 13 turns off the switch 7 by the switch switching means 28, turns on the generator-side inverter 5, that is, operates the generator-side inverter 5, and the motor-side inverter. 6 is turned on, that is, the motor-side inverter 6 is operated to set the travel mode of the vehicle 10 to the high-voltage series travel.
The above is the procedure of the travel mode switching control in the hybrid vehicle drive system according to the present embodiment.

  As described above, according to the hybrid vehicle drive system of the present embodiment, in the high-voltage series travel mode, the electronic control unit 13 turns off the switch 7, but turns off the switch 7. The electrical connection between the battery 3 and the motor 1 or the electrical connection between the battery 3 and the generator 2 is disconnected. As a result, the motor 1 and the generator 2 are disconnected from the battery 3 and are not affected by the voltage of the battery 3.

  Therefore, the generator 2 can generate power that is equal to or higher than the voltage of the battery 3 without being affected by the voltage of the battery 3, and this generated power can be supplied to the motor 1. Therefore, a hybrid vehicle drive system capable of supplying a high voltage current to the motor 1 without using a booster system can be realized.

  Therefore, by using the hybrid vehicle drive system according to the present embodiment, a relay or the like is newly required as the switch 7, but compared with the case where a booster system composed of a large reactor or a semiconductor element is used. It is possible to reduce the weight and cost of the vehicle body.

  Further, by using the hybrid vehicle drive system according to the present embodiment, energy loss due to the semiconductor elements can be eliminated and energy efficiency can be improved, so that the cruising distance can be improved.

A second embodiment of the hybrid vehicle drive system according to the present invention will be described below.
The hybrid vehicle drive system according to this embodiment has substantially the same configuration as that of the hybrid vehicle drive system according to the first embodiment. However, as shown in FIG. The vehicle speed threshold value changing means 29 for correcting the predetermined value α based on the difference between the temperature and the temperature of the battery 3 and the charging threshold value changing means 30 for correcting the predetermined value β are provided. The vehicle speed and the SOC, the temperature of the generator 2 and the battery 3 The difference is that the vehicle speed threshold changing unit 29 corrects the predetermined value α based on the difference from the temperature, and the charging threshold changing unit 30 corrects the predetermined value β. That is, the areas A, B, and C shown in FIG. 4 are changed based on the temperature of the battery 3 and the rate of increase of the temperature per minute time of the generator 2. By changing the areas of the regions A, B, and C, it is possible to mitigate an increase in the temperature of the generator 2 and the temperature of the battery 3 more than necessary.

FIG. 7 is a diagram showing a change in temperature with respect to time of the generator 2 and the battery 3. In FIG. 7, the temperature of the generator 2 is indicated by a solid line, and the temperature of the battery 3 is indicated by a broken line.
In the present embodiment, for example, when the temperature of the battery 3 is low, the area of the region A shown in FIG. 4 is increased, and when the temperature of the battery 3 is high, the temperature per minute time of the generator 2 increases. Depending on the rate, the area of the region A shown in FIG. 4 is reduced.

  Thus, it is possible to switch the running mode so as to moderate the temperature rise accurately in consideration of both the temperature rise of the generator 2 and the temperature rise of the battery 3. Therefore, an excessive temperature rise of generator 2 and battery 3 can be mitigated, and deterioration of generator 2 and battery 3 can be mitigated.

The procedure of the driving mode switching control in the hybrid vehicle drive system according to the present embodiment will be described.
FIG. 6 is a flowchart showing the procedure of the travel mode switching control in the hybrid vehicle drive system according to the present embodiment.

As shown in FIG. 6, in step P20, the electronic control unit 13 detects the vehicle speed and the SOC. The electronic control device 13 executes Step P21 after executing Step P20.
In step P21, the electronic control unit 13 detects the battery temperature and the generator temperature. After executing step P21, the electronic control device 13 executes step P22.

In Step P22, the electronic control unit 13 determines whether or not the detected battery temperature is less than a predetermined value _Tr . When the detected battery temperature is less than the predetermined value _Tr , the electronic control device 13 executes Step P23. In addition, when the detected battery temperature is not less than the predetermined value _Tr , the electronic control device 13 executes Step P25 described later.

In Step P23, the electronic control unit 13 calculates an increase rate T _g ′ of the generator temperature per minute time δt by the following equation (1). The electronic control device 13 executes Step P24 after executing Step P23.

式（２），（３）において、Ｆ₁₁，Ｆ₁₂は所定の関数を意味する。 In step P24, the vehicle speed threshold value changing means 29 calculates a correction value α ′ (vehicle speed threshold value) of the predetermined value α by the following formula (2) based on the calculated increase rate T _g ′ per minute time δt. The charging threshold value changing means 30 calculates a correction value β ′ (charging threshold value) of the predetermined value β by the following equation (3). The electronic control unit 13 executes Step P26 after executing Step P24.

In the expressions (2) and (3), F ₁₁ and F ₁₂ mean predetermined functions.

式（４），（５）において、Ｆ₂₁，Ｆ₂₂は所定の関数を意味する。 In step P25, the electronic control unit 13 calculates the correction value α ′ (vehicle speed threshold) of the predetermined value α based on the detected battery temperature Tb by the following equation (4), and changes the charging threshold. The means 30 calculates a correction value β ′ (charge threshold) of the predetermined value β by the following equation (5). The electronic control unit 13 executes Step P26 after executing Step P25.

In formulas (4) and (5), F ₂₁ and F ₂₂ represent predetermined functions.

  In Step P26, the electronic control unit 13 determines whether or not the detected speed is less than the correction value α ′ (vehicle speed threshold). When the detected speed is less than the correction value α ′ (vehicle speed threshold value), the electronic control unit 13 executes Step P27. Further, when the detected speed is not less than the correction value α ′ (vehicle speed threshold), the electronic control unit 13 executes Step P30 described later.

  In Step P27, the electronic control unit 13 determines whether or not the detected SOC is equal to or greater than the correction value β ′ (charge threshold). If the detected SOC is equal to or greater than the correction value β ′ (charge threshold), the electronic control unit 13 executes Step P28. On the other hand, when the detected SOC is not equal to or greater than the correction value β ′ (charge threshold), the electronic control unit 13 executes Step P29.

  In step P28, as shown in FIG. 1A, the electronic control unit 13 turns on the switch 7 by the switch switching means 28, turns off the generator-side inverter 5, that is, does not operate the generator-side inverter 5, and The inverter 6 is turned on, that is, the motor-side inverter 6 is operated to set the traveling mode of the vehicle 10 to the EV traveling mode.

  In step P29, as shown in FIG. 1 (b), the electronic control unit 13 turns on the switch 7 by the switch switching means 28, turns on the generator-side inverter 5, that is, operates the generator-side inverter 5, and the motor-side inverter. 6 is turned on, that is, the motor-side inverter 6 is operated to set the travel mode of the vehicle 10 to the low voltage series travel mode.

In step P30, as shown in FIG. 1 (c), the electronic control unit 13 turns off the switch 7 by the switch switching means 28, turns on the generator-side inverter 5, that is, operates the generator-side inverter 5, and the motor-side inverter. 6 is turned on, that is, the motor-side inverter 6 is operated to set the travel mode of the vehicle 10 to the high voltage series travel mode.
The above is the procedure of the travel mode switching control in the hybrid vehicle drive system according to the present embodiment.

  As described above, according to the hybrid vehicle drive system of the present embodiment, in addition to the effects exhibited by the hybrid vehicle drive system of the first invention, the temperature of the battery 3 and the temperature of the generator 2 per minute time Since the travel mode of the vehicle 10 can be appropriately switched based on the increase rate of the battery, it is important to protect the more expensive battery 3 while protecting both the battery 3 and the generator 2 from performance degradation and damage due to temperature rise. can do.

  The hybrid vehicle drive system according to each of the above-described embodiments will be described as an example applied to a series hybrid vehicle, but can also be applied to a parallel hybrid vehicle.

  The present invention can be used, for example, for a hybrid vehicle drive system, in particular, a series hybrid vehicle drive system.

DESCRIPTION OF SYMBOLS 1 Motor 2 Generator 3 Battery 4 Motor / generator control unit 5 Generator side inverter 6 Motor side inverter 7 Switch 8 Smoothing capacitor 9 Power line 10 Vehicle 11 Wheel 12 Internal combustion engine 13 Electronic control unit (control means)
20 Vehicle speed detector (vehicle speed detection means)
21 Motor temperature detector 22 Generator temperature detector (generator temperature detection means)
23 battery voltage detector 24 battery current detector 25 battery temperature detector (battery temperature detection means)
26 Battery control means 27 SOC calculation means 28 Switch switching means 29 Vehicle speed threshold value changing means 30 Charging threshold value changing means

Claims (3)

A motor for driving the vehicle;
A battery for supplying power to the motor;
A generator driven by an internal combustion engine to generate electricity;
Battery temperature detecting means for detecting the temperature of the battery;
Vehicle speed detection means for detecting the speed of the vehicle;
A power line for transmitting moving power between the battery, the motor and the generator;
A switch for switching connection / disconnection of the power line between the battery and the motor;
Switch switching means for switching the switch when the speed of the vehicle reaches a predetermined vehicle speed threshold;
Vehicle speed threshold changing means for changing the vehicle speed threshold based on the temperature of the battery when the temperature of the battery is higher than a predetermined value;
When the temperature of the battery is greater than the predetermined value and the vehicle speed is greater than the vehicle speed threshold, the switch is turned off to supply the power generated by the generator to the motor to drive the motor. And a control means for controlling the hybrid vehicle drive system. 2. The drive system for a hybrid vehicle according to claim 1, wherein the vehicle speed threshold value changing means changes the vehicle speed threshold value so as to decrease as the temperature of the battery increases. Further comprising generator temperature detection means for detecting the temperature of the generator;
When the battery temperature is equal to or lower than the predetermined value, the vehicle speed threshold value changing means changes the vehicle speed threshold value based on a rate of increase in temperature per minute time of the generator temperature calculated from the generator temperature,
3. The control unit according to claim 1, wherein the control unit performs the control when the temperature of the battery is equal to or lower than the predetermined value and the speed of the vehicle is greater than the vehicle speed threshold. The hybrid vehicle drive system described.

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