JP2022175175A - In-vehicle power supply device - Google Patents

Abstract

To provide an in-vehicle power supply device in which rotational speed of a cooling fan capable of efficiently cooling the inside of the device can be controlled.SOLUTION: An in-vehicle power supply device comprises: a first Duty determination unit 41 obtaining first Duty as a controlled variable of a rotational speed of a cooling fan 5 appropriate for inside temperature of the in-vehicle power supply device; a second Duty determination unit 42 obtaining second Duty as a controlled variable of the rotational speed of the cooling fan 5 appropriate for output electric power of the in-vehicle power supply device; and a fan Duty determination unit 43 comparing the first Duty and the second Duty thereby determining Duty on the side for heightening the rotational speed of the cooling fan 5 as indication Duty. The cooling fan 5 is controlled by the indication Duty determined by the fan Duty determination unit 43. Thus, the device inside can be efficiently cooled.SELECTED DRAWING: Figure 1

Description

The present invention relates to an in-vehicle power supply device. In particular, the present invention relates to improvements in controlling the rotational speed of a cooling fan for cooling (dissipating heat) the inside of an apparatus.

Conventionally, a power supply device such as an inverter as disclosed in Patent Document 1 includes a cooling fan to prevent the internal temperature of the device from excessively rising due to heat generated by various electronic devices associated with power supply. It is Further, as a cooling fan provided in this type of power supply device, there is also known one whose rotational speed is controllable. Patent Document 1 discloses operating a cooling fan according to the output of an inverter and adjusting the rotational speed of the cooling fan according to the temperature near the inverter (the rotational speed of the cooling fan is adjusted according to the temperature near the inverter). changing in multiple stages) is disclosed.

Japanese Patent Application Laid-Open No. 2004-111090

However, in Patent Document 1, control of the cooling fan according to the output of the inverter and control of the cooling fan according to the temperature in the vicinity of the inverter (corresponding to the internal temperature of the power supply device) are independent of each other. It's becoming

The inventor of the present invention makes it possible to efficiently cool the inside of the device by linking the output of the inverter and the internal temperature of the power supply device with the control of the cooling fan (without operating the cooling fan more than necessary). The present invention has been achieved by paying attention to the problem of suppressing an excessive rise in the internal temperature of the device.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and its object is to provide an in-vehicle power supply device capable of controlling the rotational speed of a cooling fan capable of efficiently cooling the inside of the device. be.

The solution of the present invention for achieving the above object is based on an in-vehicle power supply device having a cooling fan and a cooling system for cooling the inside of the device by the operation of the cooling fan. This vehicle-mounted power supply device includes temperature detection means, output power detection means, a first control amount candidate determination section, a second control amount candidate determination section, an instruction control amount determination section, and a cooling fan control section. The temperature detection means detects the temperature inside the device. The output power detection means detects the output power of the vehicle-mounted power supply device. The control amount first candidate determination unit determines, as a control amount first candidate, a control amount for the rotation speed of the cooling fan according to the temperature inside the device detected by the temperature detection means. The control amount second candidate determination unit determines, as a control amount second candidate, a control amount for the rotational speed of the cooling fan according to the output power detected by the output power detection means. The instruction control amount determination unit determines, as an instruction control amount, one of the first control amount candidate and the second control amount candidate that increases the rotational speed of the cooling fan. The cooling fan control section controls the cooling fan with the command control amount determined by the command control amount determining section.

With this specific item, the first control amount candidate (control amount of the cooling fan rotation speed according to the temperature inside the device) and the second control amount candidate (control amount of the cooling fan rotation speed according to the output power of the on-vehicle power supply device) , and the candidate with the higher rotation speed of the cooling fan is selected as the indicated control amount to control the cooling fan. This not only controls the rotation speed of the cooling fan according to the temperature rise inside the device, but also allows the large output power of the on-board power supply device to reduce It predicts (predicts) that the temperature inside the device will rise (rapid rise), and realizes the rotation speed control of the cooling fan accordingly. It is possible to realize rotation speed control of the cooling fan that suppresses an increase in the temperature.

Further, as another means for achieving the above object, the vehicle-mounted power supply device includes temperature detection means, output current detection means, a first control amount candidate determination section, a second control amount candidate determination section, and an indicated control amount. A configuration including a determination unit and a cooling fan control unit is also possible. The temperature detection means detects the temperature inside the device. The output current detection means detects the output current of the vehicle-mounted power supply device. The control amount first candidate determination unit determines, as a control amount first candidate, a control amount for the rotation speed of the cooling fan according to the temperature inside the device detected by the temperature detection means. The control amount second candidate determination unit determines, as a control amount second candidate, a control amount for the rotational speed of the cooling fan according to the output current detected by the output current detection means. The instruction control amount determination unit determines, as an instruction control amount, one of the first control amount candidate and the second control amount candidate that increases the rotational speed of the cooling fan. The cooling fan control section controls the cooling fan with the command control amount determined by the command control amount determining section.

This particular matter not only controls the rotation speed of the cooling fan in response to the temperature rise inside the device, but also allows the output current of the on-vehicle power supply device to be large even if the temperature inside the device has not yet risen. Therefore, it is possible to foresee that the temperature inside the apparatus will rise in the future, and to realize the rotational speed control of the cooling fan accordingly.

Further, when the second control amount candidate is determined according to the output power of the on-vehicle power supply device, the first control amount candidate is determined when the temperature inside the device detected by the temperature detection means is equal to or higher than a predetermined value. is determined so that the rotation speed of the cooling fan gradually increases as the temperature increases, and the second control amount candidate It is determined to start the operation of the cooling fan when the output power becomes equal to or higher than the value and to keep the rotation speed of the cooling fan constant until the output power becomes equal to or lower than the second predetermined value.

This is because the first control amount candidate is a control amount of passive control for coping with the fact that the temperature inside the apparatus actually rises, while the second control amount candidate This is because the control amount is an active control for coping with the fact that the internal temperature is expected to rise. In other words, the first candidate for the control amount is set so that the rotation speed of the cooling fan gradually increases as the temperature inside the device rises so that the temperature inside the device does not rise excessively when the temperature inside the device actually rises. is determined by On the other hand, the second control amount candidate is such that the output power of the on-vehicle power supply device is set to the first value so as to suppress the rise (rapid rise) of the temperature inside the device before the temperature inside the device rises. The cooling fan is started to operate when the output power exceeds a predetermined value, and the rotation speed of the cooling fan is kept constant until the output power becomes equal to or less than the second predetermined value. By selecting an appropriate control method according to the situation from among these two types of control methods and controlling the rotation speed of the cooling fan, the inside of the apparatus can be efficiently cooled.

Further, when the second control amount candidate is determined according to the output current of the on-vehicle power supply device, the first control amount candidate is selected when the temperature inside the device detected by the temperature detection means is equal to or higher than a predetermined value. is determined so that the rotation speed of the cooling fan gradually increases as the temperature increases, the second control amount candidate It is determined to start the operation of the cooling fan when the output current is equal to or higher than the value and to keep the rotation speed of the cooling fan constant until the output current becomes equal to or lower than the second predetermined value.

In this case as well, the inside of the device can be efficiently cooled by selecting an appropriate control method according to the situation from among the two types of control methods and executing the rotation speed control of the cooling fan.

In the present invention, the first control amount candidate (the control amount of the rotation speed of the cooling fan according to the internal temperature of the device) and the second control amount candidate (the control amount of the cooling fan rotation speed according to the output power of the on-vehicle power supply device) Alternatively, the control amount of the rotation speed of the cooling fan according to the output current of the on-vehicle power supply device) is compared, and the candidate with the higher rotation speed of the cooling fan is used as the indicated control amount to control the cooling fan. This makes it possible to efficiently cool the inside of the device.

2 is a block diagram showing a schematic configuration of a cooling system in the vehicle-mounted power supply device according to the embodiment; FIG. It is a figure which shows an example of a 1st Duty map. It is a figure which shows an example of a 2nd Duty map. FIG. 4 is a flow chart diagram showing a procedure of cooling fan control; It is a figure which shows the experimental result which compared the transition of the apparatus internal temperature in embodiment with the transition of the apparatus internal temperature in a comparative example. FIG. 11 is a block diagram showing a schematic configuration of a cooling system in a vehicle-mounted power supply device according to a modification;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, the present invention is applied to an inverter, which is an in-vehicle power supply device that supplies power to various devices of a vehicle (not limited to various in-vehicle auxiliary equipment, but also including a driving motor in an electric vehicle or a hybrid vehicle). A case will be described. Since the structures and functions of various electronic devices that make up the inverter are well known, descriptions thereof will be omitted here. Further, in the present embodiment, an example will be described in which the rotational speed of a cooling fan for cooling an on-vehicle power supply device is subjected to duty control.

- Schematic configuration of cooling system in on-vehicle power supply equipment -
FIG. 1 is a block diagram showing a schematic configuration of a cooling system 1 in a vehicle-mounted power supply device according to this embodiment. As shown in FIG. 1, the cooling system 1 in the vehicle-mounted power supply device includes an internal temperature sensor (temperature detection means) 2, an output power detection device (output power detection means) 3, and a cooling fan control unit 4.

In addition, the cooling fan control unit 4 includes a first duty determination unit (control amount first candidate determination unit) 41, a second duty determination unit (control amount second candidate determination unit) 42, a fan duty determination unit (instruction control amount determination unit ) 43 and a cooling fan control unit 44 .

The internal temperature sensor 2 is a sensor that detects the temperature inside the vehicle-mounted power supply device (for example, inside the casing of the vehicle-mounted power supply device), and a thermistor, a thermocouple, or the like is applied. The internal temperature sensor 2 is connected to the first duty determination section 41 by a signal line, and information on the internal temperature of the vehicle-mounted power supply device detected by the internal temperature sensor 2 is transmitted to the first duty determination section 41 .

The output power detection device 3 detects the output power of the vehicle-mounted power supply device. The method of detecting the output power by the output power detection device 3 is not particularly limited. Estimating the output power from the operating states of various devices connected to the vehicle-mounted power supply device can be mentioned. The output power detection device 3 is connected to the second duty determination unit 42 by a signal line, and information on the output power of the vehicle-mounted power supply device detected by the output power detection device 3 is transmitted to the second duty determination unit 42 .

The first duty determination unit 41 receives information on the internal temperature of the vehicle-mounted power supply device detected by the internal temperature sensor 2, and performs a first duty (rotation of the cooling fan 5 according to the temperature inside the device) according to the information on the internal temperature. A duty that determines the speed, which is referred to as the first control amount candidate in the present invention, is obtained.

Specifically, the first Duty map shown in FIG. 2 is stored in the first Duty determination unit 41, and the internal temperature, which is the information received from the internal temperature sensor 2, is applied to the first Duty map. 1Duty is required. This first duty map obtains the duty as 0% until the internal temperature, which is the information received from the internal temperature sensor 2, reaches a predetermined criterion t1 (for example, 90 ° C.), and this internal temperature becomes a predetermined criterion t1 or more. In this case, as the internal temperature increases, the duty is obtained as a gradually larger value. Also, the maximum value of the first duty is set to a predetermined value D1 (for example, 90%). These values are not limited to this.

The first duty determination unit 41 is connected to the fan duty determination unit 43 by a signal line, and the first duty information obtained by the first duty determination unit 41 is transmitted to the fan duty determination unit 43 .

The second duty determining unit 42 receives information on the output power of the vehicle-mounted power supply device detected by the output power detection device 3, and sets a second duty (a cooling fan according to the output power of the vehicle-mounted power supply device) according to the information on the output power. 5, which is the duty that determines the rotation speed of the control unit 5, and the control amount second candidate in the present invention) is obtained.

Specifically, the second Duty determination unit 42 stores the second Duty map shown in FIG. The second duty is obtained by fitting. This second duty map sets the duty to 0 until the output power of the in-vehicle power supply device, which is information received from the output power detection device 3, reaches a predetermined criterion (first predetermined value in the present invention) W1 (for example, 500 W). %, and when the output power of this vehicle-mounted power supply device reaches or exceeds a predetermined criterion W1, a predetermined Duty (D2 in FIG. 3; for example, 90%) is obtained. These values are not limited to this. Further, a hysteresis is provided in the second duty map, and when the output power of the in-vehicle power supply device is equal to or higher than the predetermined criterion W1 and the predetermined duty is required, the output power of the in-vehicle power supply device is determined according to the criterion W1 Lower predetermined value (second predetermined value in the present invention) W2 (for example, 300 W) until the predetermined Duty is maintained, when the output power of the vehicle-mounted power supply device is reduced to the predetermined value W2 Duty is set to 0%. This value is not limited to this.

The second duty determination unit 42 is connected to the fan duty determination unit 43 by a signal line, and the second duty information obtained by the second duty determination unit 42 is transmitted to the fan duty determination unit 43 .

The fan duty determination unit 43 receives the information (first duty) from the first duty determination unit 41 and the information (second duty) from the second duty determination unit 42, and determines the higher one of the first duty and the second duty, which are these information. (Duty for which the rotation speed of the cooling fan 5 is higher) is selected as the instruction duty (instruction control amount referred to in the present invention) used for controlling the cooling fan 5 . This selection operation corresponds to the operation of "determining, as the indicated control amount, the candidate with the higher rotational speed of the cooling fan out of the first control amount candidate and the second control amount candidate".

The fan duty determination unit 43 is connected to the cooling fan control unit 44 by a signal line, and the duty selected by the fan duty determination unit 43 (the higher one of the first duty and the second duty) is applied to the cooling fan control unit 44. sent to.

For example, when the internal temperature of the onboard power supply device is ta in FIG. 2 and the output power of the onboard power supply device is Wa in FIG. 3, both the first duty and the second duty are 0%, and the fan duty determination unit The information transmitted from 43 to the cooling fan control unit 44 is Duty=0%.

Further, when the internal temperature of the onboard power supply device is tb in FIG. 2 and the output power of the onboard power supply device is Wa in FIG. 3, the first duty is 50%, and the second duty is 0%. Therefore, the information transmitted from the fan duty determination unit 43 to the cooling fan control unit 44 has a duty of 50%.

Further, when the internal temperature of the onboard power supply device is ta in FIG. 2 and the output power of the onboard power supply device is Wb in FIG. 3, the first duty is 0% and the second duty is 90%, for example. Therefore, the information transmitted from the fan duty determination unit 43 to the cooling fan control unit 44 has a duty of 90%.

Further, when the internal temperature of the vehicle-mounted power supply device is tb in FIG. 2 and the output power of the vehicle-mounted power supply device is Wb in FIG. Therefore, the information transmitted from the fan duty determination unit 43 to the cooling fan control unit 44 has a duty of 90%. In this situation, when the output power of the vehicle-mounted power supply device is reduced to Wc in FIG. 3, the first duty is 50%, and the second duty is 0%. The information transmitted from to the cooling fan control unit 44 has a duty of 50%.

The cooling fan control unit 44 receives the information (Duty) from the fan duty determination unit 43, and controls the cooling fan 5 to rotate according to this information duty (the higher one of the first duty and the second duty). Controls the cooling fan 5.

- Cooling fan control -
Next, a procedure for controlling the cooling fan by the cooling system 1 in the vehicle-mounted power supply device configured as described above will be described.

FIG. 4 is a flow chart showing the procedure of cooling fan control. As shown in FIG. 4, in the cooling fan control, first, in step ST1, the internal temperature of the vehicle-mounted power supply device and the output power of the vehicle-mounted power supply device are detected. The internal temperature of the vehicle-mounted power supply device is detected by the internal temperature sensor 2 , and the information on the internal temperature of the vehicle-mounted power supply device is transmitted to the first duty determination unit 41 . Further, the output power of the vehicle-mounted power supply device is detected by the output power detection device 3 , and the information of the output power of the vehicle-mounted power supply device is transmitted to the second duty determination unit 42 .

In step ST2, the first duty determining section 41 determines the first duty using the first duty map, and the second duty determining section 42 determines the second duty using the second duty map. Information on each duty determined by these duty determination units 41 and 42 is transmitted to the fan duty determination unit 43 .

In step ST3, the fan duty determination unit 43 determines whether or not the first duty is higher than the second duty. For example, when the internal temperature of the vehicle-mounted power supply device is tb in FIG. 2 and the output power of the vehicle-mounted power supply device is Wa in FIG. 3, the first duty is higher than the second duty. will be judged. On the other hand, for example, when the internal temperature of the vehicle-mounted power supply device is ta in FIG. 2 and the output power of the vehicle-mounted power supply device is Wb in FIG. 3, the first duty is lower than the second duty. Then, a NO determination is made.

If a YES determination is made in step ST3, the process moves to step ST4, the information of the first duty is transmitted to the cooling fan control unit 44, and the cooling fan control unit 44 controls the rotational speed of the cooling fan 5 by this first duty. do. On the other hand, if the determination in step ST3 is NO, the process moves to step ST5, the information on the second duty is transmitted to the cooling fan control unit 44, and the cooling fan control unit 44 controls the rotational speed of the cooling fan 5 according to the second duty. will be controlled.

In this way, the control of the rotational speed of the cooling fan 5 by the first duty (control when the first duty is higher than the second duty) and the control of the rotational speed of the cooling fan 5 by the second duty (the first duty is lower than the second duty The cooling fan 5 is operated while the control in the case is selected to dissipate heat from the vehicle-mounted power supply device, thereby avoiding an excessive rise in the internal temperature of the vehicle-mounted power supply device.

- Effects of Embodiment -
As described above, in the present embodiment, the first duty (the control amount of the rotation speed of the cooling fan 5 according to the temperature inside the device) and the second duty (the rotation speed of the cooling fan 5 according to the output power of the vehicle-mounted power supply device) control amount), and the cooling fan 5 is controlled using the duty that increases the rotation speed of the cooling fan 5 as the instruction duty. This makes it possible to efficiently cool the inside of the device.

FIG. 5 is a diagram showing experimental results comparing changes in temperature inside the device according to the present embodiment and changes in temperature inside the device in a comparative example (for example, one in which the rotation speed of the cooling fan is controlled only by the first duty). be. As is clear from FIG. 5, it was confirmed from this experiment that the inside of the device was cooled more efficiently in this embodiment than in the comparative example.

Further, in the present embodiment, the first duty is when the temperature inside the device detected by the internal temperature sensor 2 is equal to or higher than a predetermined criterion t1, and as the temperature increases, the rotation speed of the cooling fan 5 gradually increases. On the other hand, the second duty starts the operation of the cooling fan 5 when the output power of the in-vehicle power supply device detected by the output power detection device 3 is equal to or greater than a predetermined criterion W1, and the in-vehicle power supply device It is assumed that the rotation speed of the cooling fan 5 is determined so as to be kept constant until the output power becomes equal to or less than the predetermined value W2. This is because the first duty is a control amount of passive control for responding to the fact that the temperature inside the device actually rises, while the second duty is the amount of control of passive control for responding to the fact that the temperature inside the device rises in the future. This is because it is an active control amount for coping with what has been foreseen. That is, the first duty is determined so that the rotation speed of the cooling fan 5 gradually increases as the temperature increases so that the temperature inside the device does not rise excessively in a situation where the temperature inside the device is actually high. be done. On the other hand, in the second duty, before the temperature inside the device rises, the output power of the in-vehicle power supply device is a predetermined criterion W1 or more so as to suppress the temperature rise (rapid rise) inside the device. When this occurs, the operation of the cooling fan 5 is started, and the rotation speed of the cooling fan 5 is determined to be kept constant until the output power becomes equal to or less than the predetermined value W2. By selecting an appropriate control method according to the situation from the two types of control methods described above and controlling the rotation speed of the cooling fan 5, the inside of the apparatus can be efficiently cooled.

-Modification-
Next, a modified example will be described. Here, only differences from the above-described embodiment will be described.

FIG. 6 is a block diagram showing a schematic configuration of the cooling system 1 in the vehicle-mounted power supply device according to this modification. As shown in FIG. 6, in the cooling system 1 of the vehicle-mounted power supply device according to this modification, an output current detection device 6 is provided in place of the output power detection device 3 in the above-described embodiment. This output current detection device 6 detects the output current of the vehicle-mounted power supply device. For example, there is a configuration in which an in-vehicle power supply device is equipped with a current sensor. The output current detection device 6 is connected to the second duty determination unit 42 by a signal line, and information on the output current of the vehicle-mounted power supply device detected by the output current detection device 6 is transmitted to the second duty determination unit 42 .

In this modification, the second duty determining unit 42 receives information on the output current of the vehicle-mounted power supply device detected by the output current detection device 6, and determines the second duty (vehicle-mounted power supply device) according to the information on the output current. The duty for determining the rotational speed of the cooling fan 5 according to the output current of , which is the second candidate for the controlled variable in the present invention, is obtained. For example, a map similar to the second duty map shown in FIG. 3 in the embodiment is stored, and the output current of the vehicle-mounted power supply device, which is the information received from the output current detection device 6, is applied to the map. 2Duty is required. The second duty determined by this map is also determined in the same manner as the second duty map in the above embodiment.

Other configurations and controls are the same as in the above-described embodiment.

Also in this modified example, the same effects as in the case of the above-described embodiment can be obtained.

-Other embodiments-
It should be noted that the present invention is not limited to the above-described embodiments and modifications, and all modifications and applications within the scope of the claims and their equivalents are possible.

For example, in the embodiment and the modified example, the case where the rotational speed of the cooling fan is duty-controlled has been described as an example. Control of the rotation speed of the cooling fan in the present invention is not limited to duty control, and the rotation speed may be controlled by changing the drive voltage.

INDUSTRIAL APPLICABILITY The present invention is applicable to rotation speed control of a cooling fan in an in-vehicle power supply device.

1 Cooling system in vehicle-mounted power supply device 2 Internal temperature sensor (temperature detection means)
3 Output power detection device (output power detection means)
41 First Duty Determination Unit (First Control Amount Candidate Determination Unit)
42 second duty determination unit (control amount second candidate determination unit)
43 fan duty determination unit (instruction control amount determination unit)
44 cooling fan control unit 5 cooling fan 6 output current detection device (output current detection means)
W1 first predetermined value of output power W2 second predetermined value of output power

Claims (4)

An in-vehicle power supply device comprising a cooling fan and a cooling system that cools the inside of the device by the operation of the cooling fan,
temperature detection means for detecting the temperature inside the device;
output power detection means for detecting output power of the vehicle-mounted power supply device;
a control amount first candidate determination unit that determines, as a control amount first candidate, a control amount for the rotation speed of the cooling fan according to the temperature inside the device detected by the temperature detection means;
a control amount second candidate determination unit that determines, as a control amount second candidate, a control amount of the rotational speed of the cooling fan according to the output power detected by the output power detection means;
an instruction control amount determination unit that determines, as an instruction control amount, one of the first control amount candidate and the second control amount candidate that increases the rotational speed of the cooling fan;
a cooling fan control unit that controls the cooling fan with the command control amount determined by the command control amount determination unit;
An in-vehicle power supply device comprising: An in-vehicle power supply device comprising a cooling fan and a cooling system that cools the inside of the device by the operation of the cooling fan,
temperature detection means for detecting the temperature inside the device;
output current detection means for detecting an output current of the vehicle-mounted power supply device;
a control amount first candidate determination unit that determines, as a control amount first candidate, a control amount for the rotation speed of the cooling fan according to the temperature inside the device detected by the temperature detection means;
a control amount second candidate determination unit that determines, as a control amount second candidate, a control amount of the rotation speed of the cooling fan according to the output current detected by the output current detection means;
an instruction control amount determination unit that determines, as an instruction control amount, one of the first control amount candidate and the second control amount candidate that increases the rotational speed of the cooling fan;
a cooling fan control unit that controls the cooling fan with the command control amount determined by the command control amount determination unit;
An in-vehicle power supply device comprising: In the vehicle-mounted power supply device according to claim 1,
The first control amount candidate is determined such that when the temperature inside the apparatus detected by the temperature detecting means exceeds a predetermined value, the rotation speed of the cooling fan gradually increases as the temperature increases. while
The second control amount candidate causes the cooling fan to start operating when the output power detected by the output power detection means is equal to or greater than a first predetermined value, and the output power is equal to or less than a second predetermined value. An in-vehicle power supply device, wherein the rotation speed of the cooling fan is determined to be maintained constant until In the vehicle-mounted power supply device according to claim 2,
The first control amount candidate is determined such that when the temperature inside the apparatus detected by the temperature detecting means exceeds a predetermined value, the rotation speed of the cooling fan gradually increases as the temperature increases. while
The second control amount candidate causes the cooling fan to start operating when the output current detected by the output current detecting means is equal to or greater than a first predetermined value, and the output current is equal to or less than a second predetermined value. An in-vehicle power supply device, wherein the rotation speed of the cooling fan is determined to be maintained constant until

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