JP4960656B2 - Battery control device and program - Google Patents

Description

  The present invention relates to a technique for controlling discharge of a secondary battery such as a nickel hydride battery or a lithium ion battery mounted in an electric vehicle, a hybrid electric vehicle, or the like as a power source of a motor or a drive source of various loads.

  When using a secondary battery such as a nickel metal hydride secondary battery or a lithium secondary battery, overdischarge must be avoided. If the secondary battery is significantly overdischarged, gas is generated by electrolysis of the electrolyte inside the battery, which affects the life of the secondary battery.

  In Patent Document 1, the number of times when the battery voltage of the secondary battery measured at a predetermined time interval becomes equal to or lower than a preset threshold voltage is measured, and when the measured number of times reaches a predetermined threshold, the secondary battery is measured. A technique for preventing overdischarge of the secondary battery by stopping the discharge from the battery is disclosed.

JP 2001-95158 A

  By the way, the secondary battery is often composed of a plurality of battery blocks. The battery block includes, for example, a plurality of unit cells or a plurality of battery modules in which a plurality of unit cells are connected in series. In the secondary battery configured as described above, the battery capacity and the battery voltage may vary between the battery blocks depending on the use environment and the like. In this case, if the threshold voltage is set low, a battery block that falls into an overdischarge state appears in the battery block, which may affect the battery performance and battery life of the secondary battery.

  On the other hand, in order to maximize the battery performance of the secondary battery, it is desirable to set the threshold voltage as low as possible.

  In the present invention, the battery block that falls into an overdischarge state is prevented from appearing in the battery block group constituting the secondary battery while exhibiting the battery performance of the secondary battery as much as possible.

  A battery control device according to the present invention is a battery control device that controls the discharge of a secondary battery configured by combining a plurality of battery blocks, and a charge state estimation unit that estimates a charge state of the battery block, A reference voltage setting unit that sets, for each battery block, a reference voltage that is a criterion for determining whether or not to perform overdischarge prevention processing on the secondary battery based on a charge state of the battery block; and at least one battery block A counter unit that counts the number of times that the terminal voltage has fallen below the reference voltage, a timer unit that counts the time counted by the counter unit, and a predetermined number of times the counter unit is counted within the time counted by the timer unit And an overdischarge prevention processing unit that performs an overdischarge prevention process when the above is counted.

  In one aspect of the battery control device according to the present invention, the charging state estimation unit estimates a charging state of the secondary battery, and the over-discharge prevention processing unit includes the secondary state estimated by the charging state estimation unit. When the charge state of the battery falls below a predetermined lower limit charge state, the coefficient is the number of times that the terminal voltage of at least one battery block falls below the reference voltage of the corresponding battery block within the time counted by the timer unit The overdischarge prevention process is performed in response to the counter unit counting a predetermined number of times or more.

  In one aspect of the battery control device according to the present invention, the charge state estimation unit estimates a charge state of the secondary battery, the reference voltage setting unit sets a reference voltage of the secondary battery, and When the charge state of the secondary battery estimated by the charge state estimation unit exceeds a predetermined upper limit charge state, the discharge prevention processing unit is connected to the terminal of the secondary battery within the time counted by the timer unit. The overdischarge prevention process is performed in response to the counter unit counting the number of times that the voltage has fallen below the reference voltage of the secondary battery counting more than a predetermined number.

  In one aspect of the battery control apparatus according to the present invention, the battery control device includes a variation measuring unit that measures variations in the terminal voltage between the battery blocks, and the overdischarge prevention processing unit is configured to measure the terminal voltage measured by the variation measuring unit. If the variation of the battery block does not fall within a predetermined allowable range, the counter that counts the number of times that the terminal voltage of at least one battery block falls below the reference voltage of the corresponding battery block within the time counted by the timer unit The overdischarge prevention process is performed in response to the section counting a predetermined number of times or more.

  In one aspect of the battery control device according to the present invention, the reference voltage setting unit includes a variation measuring unit that sets a reference voltage of the secondary battery and measures a variation in terminal voltage between the battery blocks, and the variation When the variation of the terminal voltage measured by the measuring unit is within a predetermined allowable range, the counter unit is configured such that the terminal voltage of the secondary battery is the reference voltage of the secondary battery instead of the terminal voltage of the battery block. The overdischarge prevention processing unit performs overdischarge prevention processing in response to the counter unit counting a predetermined number of times or more within the time counted by the timer unit. It is characterized by.

  In one aspect of the battery control device according to the present invention, the reference voltage setting means sets a higher reference voltage as the state of charge indicates a lower rate.

  ADVANTAGE OF THE INVENTION According to this invention, it can prevent that the battery block which falls into an overdischarge state appears from the battery block group which comprises a secondary battery, exhibiting the battery performance of a secondary battery as much as possible.

  A best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described with reference to the drawings, taking a hybrid electric vehicle as an example. In addition, although this embodiment demonstrates the hybrid electric vehicle which is one of the electric vehicles to an example, this embodiment is applicable also to the other electric vehicle provided with a motor (electric motor) as a drive source.

  FIG. 1 is a diagram illustrating a schematic configuration of a hybrid electric vehicle according to the present embodiment. In FIG. 1, a vehicle ECU 10 controls an inverter 50 and an engine electronic control unit (hereinafter referred to as engine ECU) 40. The engine ECU 40 controls the engine 60. The battery electronic control unit (hereinafter referred to as battery ECU) 20 receives information such as the battery voltage V, the charge / discharge current I, and the battery temperature T from the secondary battery 30 and estimates the SOC of the secondary battery 30. Further, the battery ECU 20 transmits battery information such as the SOC and battery temperature of the secondary battery 30 to the vehicle ECU 10. Further, the battery ECU 20 controls opening and closing of the switch element of the cutoff switch circuit 38 based on the battery voltage V. The vehicle ECU 10 controls charging / discharging of the secondary battery 30 by controlling the engine ECU 40, the inverter 50, and the like based on various battery information.

  The secondary battery 30 supplies power to the motor 52 via the cutoff switch circuit 38. The inverter 50 converts the DC power supplied from the secondary battery 30 into AC power and supplies the AC power to the motor 52 when the secondary battery 30 is discharged.

  The engine 60 transmits power to the wheels via the power split mechanism 42, the speed reducer 44, and the drive shaft 46. The motor 52 transmits power to the wheels via the speed reducer 44 and the drive shaft 46. When the secondary battery 30 needs to be charged, a part of the power of the engine 60 is supplied to the generator 54 via the power split mechanism 42 and used for charging.

  The cutoff switch circuit 38 is provided between the secondary battery 30 and the inverter 50, and based on an opening / closing instruction transmitted from the battery ECU 20, the switch element for electrically connecting the secondary battery 30 and the inverter 50 is opened / closed. I do. By opening this switch element, power transmission between the secondary battery 30 and the inverter 50 is interrupted. That is, the discharge of the secondary battery 30 is stopped by opening the switch element. In this embodiment, the battery ECU 20 transmits an opening / closing instruction to the cutoff switch circuit 38. However, in response to a switch opening / closing request from the battery ECU 20, other ECUs such as the vehicle ECU 10 send to the cutoff switch circuit 38. Alternatively, an opening / closing instruction may be transmitted.

  The vehicle ECU 10 includes information on the operating state of the engine 60 from the engine ECU 40, operating information such as an accelerator pedal operation amount, a brake pedal operation amount, a shift range set by a shift lever, SOC from the battery ECU 20, and the like. Based on various battery information, a control command is output to engine ECU40 or inverter 50, and engine 60 and motor 52 are driven. On the other hand, when the battery ECU 20 determines that a situation such as overcharge or overdischarge of the secondary battery 30 causes a significant deterioration in battery life occurs based on the battery voltage V of the secondary battery 30, the battery ECU 20 Send a release instruction. Thereby, power transmission between the secondary battery 30 and the inverter 50 is interrupted, and deterioration of the battery life can be minimized.

  As shown in FIG. 2, the secondary battery 30 is configured by connecting battery blocks B1 to B20 in series. Battery blocks B <b> 1 to B <b> 20 are accommodated in a battery case 32. Each of the battery blocks B1 to B20 is configured by electrically connecting two battery modules in series. Further, each battery module is configured by electrically connecting six unit cells in series. Has been. As each single battery, a nickel metal hydride battery, a lithium ion battery, or the like can be used. In addition, the number of battery blocks, battery modules, and single cells is not particularly limited. The configuration of the secondary battery 30 is not limited to the above example.

  Further, a plurality of temperature sensors 34 are arranged in the battery case 32. The plurality of temperature sensors 34 are arranged so that a plurality of battery blocks having relatively close temperatures are grouped as one group, or one battery block having a relatively different temperature from any of the battery blocks is grouped as one group. This is done by arranging two temperature sensors 34. The grouping is performed by measuring the temperature of each battery block by a prior experiment or the like. In the present embodiment, M (M is an integer) number of temperature sensors 34 are provided, and the temperatures measured by the temperature sensors 34 are expressed as temperatures T (1) to T (M), respectively.

  In FIG. 2, the voltage measurement unit 22 measures the terminal voltage of the secondary battery 30. In the present embodiment, the voltage measurement unit 22 measures the terminal voltages Vb (1) to Vb (20) of the battery blocks B1 to B20. The voltage measuring unit 22 generates voltage data specifying the terminal voltages Vb (1) to Vb (20) and outputs them to the control unit 26. The output of the voltage data to the control unit 26 is performed at a preset period (for example, 100 ms), and the control unit 26 stores the voltage data in the storage unit 28. The control unit 26 calculates the battery voltage V by totaling the terminal voltages Vb (1) to Vb (20) indicated in the voltage data stored in the storage unit 28.

  The current measuring unit 23 measures the charging / discharging current I during charging / discharging of the secondary battery 30. In the present embodiment, the current measuring unit 23 converts the analog signal output from the current sensor 35 into a digital signal, and based on this, the current input to the secondary battery 30 during charging, and the secondary battery 30 during discharging. Current data for specifying the output current is generated and output to the control unit 26. In addition, the current measurement unit 23 generates current data, for example, when charging is negative and when discharging is positive. Current data from the current measurement unit 23 to the control unit 26 is also performed at a preset period (for example, 100 ms), and the control unit 26 also stores the current data in the storage unit 28.

  The temperature measurement unit 24 measures the battery temperature of the secondary battery 30. In the present embodiment, the analog signal output from each temperature sensor 34 set for each group is converted into a digital signal, and based on this, temperature data for specifying the battery temperature for each group is generated, and this is used as the control unit 26. Output to. The output of the temperature data to the control unit 26 by the temperature measurement unit 24 is also performed at a preset period (for example, 100 ms), and the control unit 26 also stores the temperature data in the storage unit 28. For example, the control unit 26 obtains the battery temperature T by obtaining an average value of the temperatures T (1) to T (M) indicated in the temperature data stored in the storage unit 28.

  The charge state estimation unit 261 in the control unit 26 estimates the charge state of the secondary battery 30 (hereinafter referred to as SOC (State Of Charge)) based on the battery voltage V, the charge / discharge current I, the battery temperature T, and the like. A known technique may be used for the SOC estimation method, for example, the SOC is estimated by the following method, that is, a pair of the battery voltage V and the charge / discharge current I in a predetermined period (for example, 60 sec). A plurality of data is acquired and stored, and a first-order approximation line (voltage V-current I approximation line) is obtained from the paired data by regression analysis, and the V-intercept of the V-I approximation line is set to the battery voltage V0 (no load). In addition, the integrated value 電流 I of the current I is calculated, and the polarization voltage Vp of the battery is obtained from the function of the battery temperature T, the battery voltage V0, and the current integrated value ∫I, and the polarization voltage Vp is calculated from the battery voltage V0. Subtract the electromotive force E of the battery Mel. Next, with reference to the electromotive force -SOC characteristics prepared in advance, and estimates the SOC from the determined electromotive force E.

  In the hybrid electric vehicle configured as described above, in the present embodiment, the secondary battery 30 exhibits a sufficient discharge capability, and prevents a battery block that enters an overdischarge state from appearing in the battery blocks B1 to B20. To do. The conventional battery ECU 20 prevents overdischarge by stopping the discharge of the secondary battery 30 when, for example, the battery voltage V falls below the reference voltage Vt a predetermined number of times in a predetermined period. However, as shown in FIG. 3, the terminal voltage Vb of each battery block constituting the secondary battery 30 varies more widely between the battery blocks as the SOC value decreases. Therefore, if the reference voltage Vt is set to a relatively low value in order to maximize the performance of the secondary battery 30, even if the battery voltage V is larger than the reference voltage Vt, there is an overdischarge state in the battery block. There is a risk that a battery block will fall into the box.

  Therefore, in the present embodiment, the charging state estimation unit 261 estimates the SOC for each battery block, and the reference voltage setting unit 262 uses the reference voltages Vtb (1) to Vtb (20) (hereinafter, for each battery block based on each SOC). If it is not necessary to distinguish between them, it is referred to as Vtb). Further, the counter unit 263 counts the number of times that the terminal voltage Vb of at least one battery block has fallen below the reference voltage Vtb, and the number of times counted by the counter unit 263 in a predetermined period (for example, 1 sec) counted by the timer unit 264 Is over a predetermined number (for example, 10 times), the overdischarge prevention processing unit 265 executes an overdischarge prevention process. Here, the overdischarge prevention process is a process for suppressing the secondary battery 30 from falling into an overdischarge. For example, the battery ECU 20 transmits an opening instruction to the cutoff switch circuit 38. Thereby, the power transmission between the secondary battery 30 and the inverter 50 is interrupted, and the discharge of the secondary battery 30 is stopped. Therefore, the overdischarge of the secondary battery 30 can be prevented.

  For example, the battery ECU 20 estimates the SOC for each battery block, and sets the reference voltage Vtb for each battery block with reference to a reference map as shown in FIG.

  Also, as shown in FIG. 3, when the state of charge indicated by the SOC of the secondary battery 30 is relatively high, the variation in the terminal voltage Vb between the battery blocks is relatively small. Therefore, if the battery voltage V is higher than the reference voltage Vt, the possibility that a battery block that falls into an overdischarge state appears is low. Accordingly, when the SOC of the secondary battery 30 is larger than a predetermined reference value, the battery ECU 20 causes the battery voltage V to fall below the reference voltage Vt for a predetermined number of times (for example, 10 times) in a predetermined period (for example, 1 sec). When the SOC of the secondary battery 30 is less than or equal to a predetermined reference value, the terminal voltage Vb of at least one battery block is set to the reference voltage Vtb a predetermined number of times in a predetermined period (for example, 1 sec). For example, the overdischarge prevention treatment may be performed when the number is less than 10).

  Further, the battery ECU 20 may change the determination method as to whether or not to perform the overdischarge prevention process depending on whether or not the variation in the terminal voltage Vb between the battery blocks is within a predetermined allowable range.

  FIG. 5 is a flowchart showing a procedure for setting the reference voltage Vtb or the battery voltage reference voltage Vt for each battery block.

  In FIG. 5, the battery ECU 20 detects the terminal voltage Vb for each battery block by referring to the voltage data stored in the storage unit 28 (S100). Next, the battery ECU 20 determines whether or not the variation in the terminal voltage Vb is within an allowable range (S102). For example, a variation measuring unit (not shown) that measures the variation of the terminal voltage Vb between the battery blocks is provided in the control unit 26, and the variation measuring unit indicates the maximum voltage value from the detected terminal voltage Vb group. The terminal voltage Vbmax and the terminal voltage Vbmin indicating the minimum voltage value are specified, and the difference between the specified terminal voltage Vbmax and the terminal voltage Vbmin is obtained. The battery ECU 20 determines that the variation in the terminal voltage Vb is within an allowable range when the difference obtained by the variation measuring unit is within a predetermined difference.

  When the variation of the terminal voltage Vb is within the allowable range (the determination result in step S102 is affirmative “Y”), the battery ECU 20 determines whether or not the reference voltage setting unit 262 performs overdischarge prevention processing. A predetermined reference voltage Vt is set for the secondary battery 30 as a reference (S104). On the other hand, when the variation in the terminal voltage Vb exceeds the allowable range (the determination result in step S102 is negative “N”), the battery ECU 20 estimates the SOC in units of battery blocks in the charge state estimation unit 261 ( S106) Referring to the reference map as shown in FIG. 4, the reference voltage setting unit 262 sets each reference voltage Vtb corresponding to each battery block based on each SOC (S108).

  Whether or not the battery ECU 20 performs the overdischarge prevention process according to the charge state of the secondary battery 30 and the magnitude of the variation between the terminal voltages of the battery block by periodically executing the above process. The judgment criteria can be changed.

  FIG. 6 is a flowchart showing a procedure for determining whether or not the battery ECU 20 performs the overdischarge prevention process based on the determination criteria set according to the procedure shown in FIG.

  In FIG. 6, first, the battery ECU 20 determines whether or not a reference voltage is set for each battery block (S200). As a result of the determination, when the reference voltage is set for each battery block (the determination result of step S200 is affirmative “Y”), the battery ECU 20 performs overdischarge prevention processing based on the terminal voltage for each battery block. It is determined whether or not to execute (S202). More specifically, the battery ECU 20 detects the terminal voltage Vb for each battery block by referring to the voltage data stored in the storage unit 28, and compares the terminal voltage Vb and the reference voltage Vtb for each battery block. Thus, the counter unit 263 counts the number of times that the terminal voltage Vb is lower than the reference voltage Vtb. The counter unit 263 counts the number of times that the terminal voltage Vb has fallen below the reference voltage Vtb in a predetermined period (for example, 1 sec) counted by the timer unit 264, and the counted number is a predetermined reference number (for example, 10 times). When the battery block exceeding () appears, the battery ECU 20 determines to execute the overdischarge prevention process.

  On the other hand, when the reference voltage Vt for the secondary battery 30 is set (the determination result of step S200 is negative “N”), the overdischarge prevention process is executed based on the battery voltage V of the secondary battery 30. It is determined whether or not (S204). More specifically, the battery ECU 20 calculates the battery voltage V by referring to the voltage data stored in the storage unit 28 and summing up the terminal voltages Vb of the battery blocks indicated in the voltage data. Next, the battery ECU 20 compares the battery voltage V with the reference voltage Vt by the counter unit 263, and counts the number of times that the battery voltage V is lower than the reference voltage Vt. The battery ECU 20 determines to perform the overdischarge prevention process when the number of times counted by the counter unit 263 exceeds a predetermined reference number (for example, 10 times) in a predetermined period (1 sec) counted by the timer unit 264.

  As a result of the determination in step S202 or step S204, when it is determined that the overdischarge prevention process is to be executed (the determination result in step S206 is affirmative “Y”), the battery ECU 20 uses the overdischarge prevention processing unit 265 to prevent overdischarge. The process is executed (S208). The overdischarge prevention processing unit 265 transmits an opening instruction to the cutoff switch circuit 38, for example, cuts off the power transmission between the secondary battery 30 and the inverter 50, and stops the discharge of the secondary battery 30.

  As described above, in the present embodiment, the battery ECU 20 estimates the SOC for each battery block as necessary, sets the reference voltage Vtb for each battery block based on each SOC, and determines the terminal voltage Vb of at least one battery block. When the reference voltage Vtb falls below a predetermined number of times (for example, 10 times) in a predetermined period (for example, 1 sec), overdischarge prevention processing is executed. Thereby, according to this embodiment, when the SOC of the secondary battery 30 shows a high ratio and the variation in the terminal voltage Vb for each battery block is small, the reference voltage Vt is set to a lower value and the secondary battery 30 is set. The performance of can be exhibited as much as possible. On the other hand, when the SOC of the secondary battery 30 is low and the terminal voltage Vb varies widely for each battery block, the reference voltage Vtb is set for each battery block, and the overdischarge prevention process is performed for each battery block. Since the presence / absence is determined, it is possible to prevent some battery blocks from falling into an overdischarged state.

  In the above, the battery ECU 20 can be realized by installing a program for implementing various processes shown in FIGS. 5 and 6 in the microcomputer and executing the program.

  That is, the microcomputer has various memories such as a CPU, ROM, RAM, and EEPROM, a communication bus, and an interface. The processing program stored in the ROM as firmware in advance is read out and sequentially executed by the CPU. The reference voltage Vtb for each battery block is stored in advance in the memory, and the CPU compares the terminal voltage Vb for each block input from the sensor via the interface and stored in the memory with the reference voltage Vtb stored in advance in the memory. To do. The CPU stops discharging the secondary battery 30 when the terminal voltage Vb of at least one battery block falls below the reference voltage Vtb by a predetermined number (for example, 10 times) or more in a predetermined period (for example, 1 sec). That is, the CPU transmits an opening instruction to the cutoff switch circuit 38 via the interface.

It is a figure which shows schematic structure of the hybrid electric vehicle which concerns on this embodiment. It is a figure which shows the functional block for demonstrating a secondary battery and battery ECU. It is a figure which shows the relationship between the terminal voltage of a battery block, and SOC. It is a figure which shows the relationship between the terminal voltage of a battery block, and a reference voltage. It is a flowchart which shows the process sequence performed when battery ECU sets a reference voltage. It is a flowchart which shows the process sequence performed when battery ECU performs an overdischarge prevention process.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Vehicle ECU, 20 Battery ECU, 30 Secondary battery, 36 Heating device, 40 Engine ECU, 42 Power split mechanism, 44 Reduction gear, 46 Drive shaft, 50 Inverter, 52 Motor, 54 Generator, 60 Engine

Claims (7)

A battery control device for controlling discharge of a secondary battery configured by combining a plurality of battery blocks,
A charge state estimation unit for estimating a charge state of the battery block;
A reference voltage setting unit that sets, for each battery block, a reference voltage that is a criterion for determining whether or not to perform an overdischarge prevention process on the secondary battery based on a charge state of each battery block;
A counter unit that counts the number of times that the terminal voltage of at least one battery block falls below the reference voltage;
A timer unit that counts the time counted by the counter unit;
An overdischarge prevention processing unit that performs an overdischarge prevention process when the counter unit counts a predetermined number of times or more within the time counted by the timer unit;
A battery control device comprising: The battery control device according to claim 1,
The charging state estimation unit estimates a charging state of the secondary battery,
The overdischarge prevention processing unit
When the charge state of the secondary battery estimated by the charge state estimation unit falls below a predetermined lower limit charge state, the terminal voltage of at least one battery block corresponds within the time counted by the timer unit. The counter unit that counts the number of times that the battery block has fallen below the reference voltage performs overdischarge prevention processing in response to counting a predetermined number of times or more.
A battery control device. The battery control device according to claim 1,
The charging state estimation unit estimates a charging state of the secondary battery,
The reference voltage setting unit sets a reference voltage of the secondary battery,
The overdischarge prevention processing unit
When the charge state of the secondary battery estimated by the charge state estimation unit exceeds a predetermined upper limit charge state, the terminal voltage of the secondary battery is reduced within the time counted by the timer unit. The counter unit that counts the number of times that the voltage falls below the reference voltage of the battery performs overdischarge prevention processing in response to counting a predetermined number of times or more.
A battery control device. The battery control device according to claim 1,
A variation measuring unit that measures variations in terminal voltage between the battery blocks,
The overdischarge prevention processing unit
When the variation of the terminal voltage measured by the variation measuring unit does not fall within a predetermined allowable range, the terminal voltage of at least one battery block falls within the time counted by the timer unit and the corresponding battery block An overdischarge prevention process is performed in response to the counter unit counting the number of times the reference voltage has been dropped below a predetermined number of times.
A battery control device. The battery control device according to claim 1,
The reference voltage setting unit sets a reference voltage of the secondary battery,
A variation measuring unit that measures variations in terminal voltage between the battery blocks,
When the variation of the terminal voltage measured by the variation measuring unit is within a predetermined allowable range, the counter unit determines that the terminal voltage of the secondary battery is the voltage of the secondary battery instead of the terminal voltage of the battery block. The overdischarge prevention processing unit counts the number of times that the reference voltage has fallen below, and the overdischarge prevention processing unit performs overdischarge prevention processing in response to the counter unit counting a predetermined number of times or more within the time counted by the timer unit. Do,
A battery control device. The battery control device according to any one of claims 1 to 5,
The reference voltage setting unit includes:
A battery control device that sets a higher reference voltage as a state of charge indicates a lower rate. A program for causing a computer to execute a battery control method for controlling discharge of a secondary battery configured by combining a plurality of battery blocks,
A charging state estimation step for estimating a charging state of the battery block;
A reference voltage setting step for setting, for each battery block, a reference voltage that is a criterion for determining whether or not to perform an overdischarge prevention process on the secondary battery based on a charge state of each battery block;
An overdischarge prevention processing step of performing the overdischarge prevention processing in response to the number of times that the terminal voltage of at least one battery block has fallen below a reference voltage corresponding to the battery block reaching a predetermined number of times in a predetermined period;
For causing the computer to execute.

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