JP2003018754A - Estimation-calculating device for battery state of charge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device which can suitably be used for an automobile having a function to stop idling, and estimation-calculates the state of charge of a battery without using a current sensor. SOLUTION: The battery state of charge(SOC) estimation-calculating device for the battery has an SOC estimation-calculating means, which estimation- calculates the SOC of the battery 9, based on the speed of an engine 1 and the time driving it or the like; a state of discharge estimation-calculating means, which estimation-calculates a state of discharge while the engine is stopped for such as idling stop or the like, based on consumed power and the operating time of power-consuming devices 32, 42 and 72, which are operated while the engine is stopped; an SOC estimation-calculating means, which estimation- calculates the SOC of the battery by arithmetically calculating a charge-and- discharge balance of the battery based on the state of charge and discharge of the battery. With such an arrangement, the SOC of the battery can be estimation-calculated without using a current sensor, and the capacity of the battery can be controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for estimating and calculating a stored charge amount of a battery, which is preferably used for an automobile having an idle stop function.

[0002]

2. Description of the Related Art Recently, some automobiles have a function (idle stop function) for stopping engine idling when the vehicle is stopped in order to improve fuel efficiency and reduce exhaust gas emissions. In an automobile having such an idle stop function, when the compressor of the air conditioner is driven only by the engine, the idle stop (that is,
There is a problem that the air conditioner also stops when the engine is stopped). As conventional techniques for solving this problem, there are Japanese Patent Laid-Open Nos. 2001-1753 and 2000-211.
There is a device disclosed in Japanese Unexamined Patent Publication No. 348, and the former intends to secure the air conditioning function at the time of idle stop by the cold storage method and the latter by the compressor driving method by the auxiliary machine driving means. Among these, the cold storage method has an advantage that energy is not consumed so much at the time of idle stop, but there is a problem that the cooling capacity becomes insufficient when the idle stop time becomes long, and the cold storage section becomes large when trying to improve the capacity. In this respect, it is preferable to use the compressor drive system by the auxiliary machine drive means that drives the compressor of the air conditioner by the auxiliary machine drive means (for example, an electric motor) during idle stop.

The device disclosed in Japanese Unexamined Patent Publication No. 2000-212348 detects the state of the refrigerant, and if the pressure or temperature is below a predetermined value, the compressor is driven by auxiliary device drive means, and if it is above a predetermined value. For example, switch to engine drive. Here, an electric motor can be considered as the auxiliary device driving means, but this device does not know the state of the battery that is the power supply source, and when the traffic jam continues, the amount of charge stored in the battery (storage of the battery). Amount of electrical energy)
There is a risk that the engine may not start due to lack of power.
In addition, the problem that the amount of charge held in the battery is insufficient at the time of idle stop when the battery is not charged is due to the use of the auxiliary device driving means of the air conditioner as described above, as well as the use of radio, audio, etc. It can also be caused by the use of power consuming equipment on the vehicle. In order to deal with such a problem, there is a method of detecting the current flow in and out of the battery and managing the amount of charge held in the battery, but this method requires the installation of a current sensor, which increases the device cost. I will end up.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to suitably use a vehicle having an idle stop function, which has a charge amount of a battery held without a current sensor. Is to provide a device for estimating and calculating.

[0005]

As a means for solving the above-mentioned problems, the present invention provides a battery charge estimation / calculation device described in each of the claims.

According to the first aspect of the present invention, based on the engine speed and the time during which the engine is driven, the power consumption of the power consuming device that is operating during engine operation, and the time during which the engine is operating. A battery charge amount estimating / calculating means for estimating and calculating the battery charge amount, and a battery discharge amount during engine stop during idle stop, etc. for the power consumption of the power consuming equipment operating during engine stop and its operating time. A battery discharge amount estimation calculation means for estimating and calculating based on the battery charge amount and a battery discharge amount based on the calculated battery charge amount and battery discharge amount; And a means for estimating and retaining a stored charge of a battery. According to this, the stored charge amount of the battery can be estimated and calculated without using the current sensor, and the battery capacity can be managed.

According to a second aspect of the present invention, in the apparatus according to the first aspect, the battery charge amount estimated and calculated by the battery charge amount estimation calculation means while the engine is stopped is less than a predetermined value. Then, there is provided a battery charge estimation / calculation device further having means for starting the engine. As a result, when it is determined that the remaining charge amount of the battery is insufficient based on the estimation calculation result of the remaining charge amount of the battery during the engine stop such as at idle stop, the engine is started to charge the battery. As a result, the stored charge of the battery is maintained, and it is possible to prevent inconvenience caused by the shortage of the stored charge of the battery.

Further, according to the invention described in claim 3, in the device according to claim 2, the amount of charge held in the battery estimated while the engine is stopped due to idle stop or the like becomes less than a predetermined value, and the engine When the battery is being charged and the battery is being charged, the battery-holding-charge estimation calculation further includes means for stopping the engine when the battery-holding charge estimated and calculated by the battery-holding-charge estimation calculating unit exceeds a predetermined value. A device is provided. According to this, when the engine is driven under the engine stop condition such as under the idle stop condition for the purpose of recovering the charged charge of the battery, the engine stops when the charged charge of the battery recovers, and the normal idle stop is performed. Since it returns to the state, it becomes possible to maintain the battery charge amount without impairing the action and effect of the idle stop function such as improvement of fuel consumption and reduction of exhaust gas emission more than necessary.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the embodiments described below, roughly speaking, in an engine control ECU, start / stop (driving time) and engine speed information of an engine and on-vehicle power consumption equipment during engine driving. The battery charge amount is estimated and calculated based on the start / stop (operating time) and power consumption information of the vehicle, and the start / stop (operating time) and power consumption information of the in-vehicle power consumption device during engine stop such as idle stop Estimating and calculating the battery discharge amount based on the estimated battery charge amount and the battery discharge amount based on the estimated battery charge amount and the estimated battery charge amount. Based on the calculation result, the engine is started / stopped under the engine stop condition such as the idle stop condition.

An embodiment of the present invention will be described in detail below with reference to the drawings. In the following description, an air conditioner (more specifically, a compressor driving motor 32 of the air conditioner and a blower to the refrigerant condensing means 41 of the air conditioner is used as a power consuming device that operates or continues to operate while the engine is stopped. The cooling fan driving motor 42 and the blower driving motor 72 that blows air to the refrigerant evaporating means 71 of the air conditioner are shown and mainly described. However, it goes without saying that other power consumption (not shown) is also shown. Devices (for example, headlights, brake lights, audios, etc.) also exist, and these also consume the electric power supplied from the battery similarly to the air conditioner.

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention for explaining an air conditioner as an example of a power consuming device that continues to operate even when the engine is stopped.

In the figure, 1 is an engine, 2 is a generator,
Reference numeral 31 indicates a compressor. The engine 1 is connected to the generator 2 and the compressor 31 by power transmission means such as a belt. The compressor 31 includes a refrigerant condensing means 41, a liquid tank 5, a refrigerant expanding means 6, and a refrigerant evaporating means 71.
And are connected in sequence and then returned to the compressor 31 again to form a refrigerating cycle as a whole and constitute a main part of the air conditioner. The arrow in the figure indicates the passage direction of the refrigerant. Further, a cooling fan and a motor 42 for driving the cooling fan are attached to the refrigerant condensing means 41, and a blower for feeding cold air into the vehicle compartment and a motor 72 for driving the blower are attached to the refrigerant evaporation means 71.

The compressor 31 also includes a compressor driving motor 32 that drives the compressor 31 when the engine is stopped such as during idle stop. The compressor driving motor 32 is connected to the compressor 31 by a known clutch mechanism (not shown) or the like only when the engine is stopped such as during idle stop. At this time, the power transmission means from the engine 1 is disconnected, and the compressor 31 is driven only by the compressor driving motor 32.

The generator 2 is connected to the battery 9 by a conductive means such as a conductive wire. Generator 2 and battery 9
Each of the relays 33, 43, 73 is connected to this conductive means for connecting to
The positive (+) terminal side of each motor 32, 42, 72 is connected via. Each of the relays 33, 43, 73 is controlled by a signal from the engine control ECU 8 which receives the air conditioner operation information from the air conditioner operation unit 11 and the air conditioner ECU 10 and the engine operation information from the engine 1, and the generator 2 or Each motor 32, 4 from the battery 9
The power supply to 2, 72 is controlled.

As described above, the engine 1 is connected to the compressor 31 and the generator 2 of the air conditioner by the power transmission means such as a belt. Therefore, while the engine 1 is being driven, the engine 1 is rotated to rotate the air conditioner. When the compressor 31 is driven, the battery 9 is charged by the electric power generated by the generator 2, and the switch of each on-vehicle power consuming device is turned on, etc. Electric power is supplied to each power consumption device. For example, when the engine is being driven and the air conditioner switch is ON, the engine control ECU 8 receives the air conditioner operation information from the air conditioner operation unit 11 and the air conditioner ECU 10 and the engine operation information from the engine 1. , Relay 43
And the relay 73 are connected and the relay 33 is cut off, the cooling fan driving motor 42 and the blower driving motor 72 are driven by the electric power from the generator 2, and the compressor 31 is driven by the rotation of the engine 1. The air conditioner works. Then, of the electric power generated by the generator 2, that which is not consumed is charged in the battery 9.

On the other hand, when the switch of the air conditioner is turned on when the engine is stopped at idle stop or the like, the compressor 31 is driven by the known clutch mechanism (not shown) as described above. 32 and the power transmission means from the engine 1 are disconnected. Further, the relay 33 is connected by the engine control ECU 8 which receives the engine operation information (engine stop) from the engine 1, and the compressor driving motor 32 is supplied with electric power to drive the compressor 31. At this time, the relay 43 and the relay 73 are connected by the engine control ECU 8 as in the case where the engine is being driven, and electric power is also supplied to the cooling fan driving motor 42 and the blower driving motor 72 to cool the cooling fan and the blower. Is driven to operate the air conditioner. As a matter of course, since the generator 2 is not operating when the engine is stopped, the electric power in this case is supplied from the battery 9.

As described above, the engine control ECU 8 is equipped with various vehicle-mounted devices that consume power from the battery 9 such as the start / stop (driving time) of the engine 1 and the number of revolutions, and the motors 32, 42, 72. Information such as start / stop (operation time) information of the power consuming device is transmitted at any time, and the generator 2
Output characteristics (see FIG. 3) and power consumption information of various in-vehicle power consumption devices are input in advance, and based on these information, the engine control ECU 8 causes the engine control ECU 8 to charge the battery while the engine is driving and discharge the battery when the engine is stopped. The charge and discharge balance of the battery can be calculated by estimating and calculating the amount and the amount, respectively. The engine control ECU 8 has a battery 9
A predetermined value (reference value) serving as a reference for determining that the stored charge amount of the battery is insufficient is input, and as described below, the engine control ECU 8 determines that the battery stored charge amount falls below this value. The engine 1 can be started even under the engine stop condition such as the idle stop condition, while the engine 1 can be stopped when the battery charge amount recovers the initial value under the condition.

Next, referring to FIG. 2, the control flow performed by the engine control ECU 8 in this embodiment will be described in more detail. The start of the operation in Fig. 2 (STAR
At the time point T), the engine 1 is started and the counting of the engine drive time Te is started.
The engine driving time Te is counted until the engine 1 is stopped next.

When the operation of FIG. 2 is started, first, at step 101, it is judged if the vehicle is in an idle stop condition. If it is not an idle stop condition,
Although the operation ends, the operation is actually started again and the operation is repeated from the beginning. on the other hand,
When it is determined that the idle stop condition is satisfied, in step 102, the engine 1 is cut by a method such as fuel cut.
Is stopped (OFF), counting of the engine stop time Tm is started from this point (step 103), and is counted until the engine 1 is driven next time. Next, at step 104, it is confirmed whether or not the switch of the air conditioner is ON, and if it is ON, the routine proceeds to step 105. In step 105, the compressor driving motor 32 is started (ON). In step 106, it is checked again whether the idle stop condition is satisfied, and if it is determined that the idle stop condition is satisfied, the process proceeds to step 107, and it is again checked whether the switch of the air conditioner is turned on. If the switch of the air conditioner is ON, the routine proceeds to step 108, where it is judged whether or not the stored charge amount of the battery 9 is in an insufficient state. That is, in step 108, the battery discharge amount U _Tm is estimated and calculated from the start / stop (operation time) of the on-vehicle power consuming devices such as the motors 32, 42, 72 and the like or the operation information during the engine stop time Tm until then. , The generator power generation amount estimated from the engine speed information during the engine drive time Te that has been counted until immediately before the engine stop (step 102) and the start / stop (operation time) or operation of the in-vehicle power consumption device The battery charge amount C _Te is estimated and calculated from the difference from the power consumption amount estimated and calculated from the information, and the charge and discharge balance of the battery 9 (= C _Te −
U _Tm : That is, the reduction amount of the retained charge amount of the battery 9) is calculated, and the retained charge amount of the battery 9 is 10 of the battery capacity Q (the retained charge amount of the battery in the fully charged state).
Check if it is decreasing by more than%. Here, the reduction amount of the charged amount of the battery 9 is 10 of the battery capacity Q.
If it is less than%, the process returns to step 106 to check again whether the idle stop condition is satisfied. Step 106
If it is determined that the idle stop condition is not satisfied, the compressor driving motor 32 is stopped in step 121, the engine 1 is started in step 122, and the engine driving time Te is counted in step 123. The operation is started and ended (that is, the operation returns to the start state and the operation is repeated from the beginning). As described above, the counting of the engine drive time Te is performed until the engine next stops.

On the other hand, in step 108, when the stored charge amount of the battery 9 has decreased by more than 10% of the battery capacity Q, it is determined that the stored charge amount of the battery 9 is insufficient, and compression is performed even during idle stop. The machine driving motor 32 is stopped (step 109), Te is reset to 0 (step 110), and the engine 1 is started (step 111). As a result, the generator 2 operates and the battery 9
Is charged. The counting of the engine drive time Te is started from the time when the engine 1 is started (step 11
2). The engine drive time Te can also be restated as the generator operating time. In step 113, it is checked again whether the idle stop condition is satisfied. If the condition is not satisfied, the operation ends (that is, the operation returns to the start state and the operation is repeated from the beginning). If the idle stop condition is satisfied, the routine proceeds to step 114, where the generator power generation amount estimated from the engine speed information of the engine 1 up to that time and the start / stop of the on-vehicle power consumption device (operation time) Alternatively, it is confirmed whether or not the battery charge amount C _Te obtained from the difference between the power consumption amount estimated and calculated from the driving information exceeds 10% of the battery capacity Q. If the battery charge amount C _Te is 10% or less of the battery capacity Q, it is determined that the battery charge amount has not yet recovered, and the process returns to step 113. When the battery charge amount C _Te exceeds 10% of the battery capacity Q, it is determined that the battery charge amount has recovered, and at that time T
e and Tm are reset to 0, the counting of Te is restarted (step 115), and the operation ends. That is, since the state returns to the start state and the operation is repeated from the beginning, if the idle stop condition is satisfied in step 101, the engine 1 is stopped again (step 102).

On the other hand, when it is confirmed in step 104 whether the switch of the air conditioner is ON, if the switch of the air conditioner is OFF, the process proceeds to step 140.
It is confirmed again whether or not the idle stop condition is satisfied without starting the compressor driving motor 32. When it is determined that the idle stop condition is not satisfied, the engine 1 is started in step 141, the counting of the engine drive time Te is started in step 142, and the operation ends (that is, the state returns to the start state, The operation is repeated from.). If it is determined in step 140 that the idle stop condition is satisfied, step 1
In step 43, it is determined whether or not the stored charge amount of the battery 9 is insufficient as in step 108.
That is, in step 143, the battery discharge amount U _Tm is estimated and calculated from the start / stop (operation time) of the on-vehicle power consumption device or the operation information during the engine stop time Tm until then, and the immediately preceding engine stop (step 10) is performed.
2) Estimated and calculated from the generator power generation amount estimated and calculated from the engine speed information during the engine driving time Te that has been counted up to the previous time, and the start / stop (operation time) or operation information of the on-vehicle power consumption device. was estimated calculating the battery charge C _Te from the power consumption, the charge-discharge balance of these battery 9 (= C _Te -U _Tm: that is, reducing the amount of held charge amount of the battery 9) by calculating, It is confirmed whether the stored charge amount of the battery 9 has decreased by more than 10% of the battery capacity Q. Here, if the reduction amount of the charged amount of the battery 9 is 10% or less of the battery capacity Q, the process returns to step 104 to check again whether the air conditioner is ON, and the operation from there is repeated. On the other hand, step 14
3, the charge amount of the battery 9 is 10% of the battery capacity Q
If it is decreasing beyond the limit, it is determined that the charge amount of the battery 9 is insufficient, and the routine proceeds to step 110, where Te is reset to 0 even during idle stop as described above (step 110), and the engine 1 Is started (step 111) and the process proceeds to step 112 and subsequent steps thereafter.

In step 107, the air conditioner is turned on.
If it is confirmed to be FF, step 131
Then, the compressor drive motor 32 is stopped. afterwards,
Proceed to step 140, and the air conditioner that starts there is O
Go to the step for FF.

In the above operation, the engine drive time Te
Once started, the counting of the engine stop time Tm is continued until the engine 1 is next stopped and driven. Unless the engine drive time Te and the engine stop time Tm are reset to 0, the values at the time when the engine 1 is stopped and driven before that are stored, and the values of the next engine drive time Te and the engine stop time Tm are stored. The counting is additionally performed when the engine 1 is stopped and driven before that.

The operation in steps 108 and 143 will be further described. In steps 108 and 143, as described above, the battery discharge amount U _Tm during the engine stop time Tm until then is estimated and calculated, and the immediately preceding engine is executed. Stop (Step 10
2) estimate calculated battery charge amount C _Te before the engine driving time in Te which had been counted until they after calculating the charge and discharge balance of the battery 9, held charge amount of the battery 9 battery capacity Q 10% It is confirmed whether or not the remaining charge amount of the battery 9 is in an insufficient state by determining whether or not the remaining charge amount is decreasing. Here, the battery discharge amount U _Tm is a consumption amount estimated and calculated based on start / stop (operation time) or operation information of the compressor driving motor 32 and other on-vehicle power consumption devices during the engine stop time Tm until then. The total amount of electric power is calculated by time integration for the target engine stop time Tm, and the battery charge amount C _Te is estimated and calculated from the rotation speed information of the engine 1 during the engine drive time Te until then. Generated power (as shown in FIG. 3 by way of example, the current generated by the generator 2 has a correlation with the number of revolutions,
The power generated by the generator 2 depends on the engine speed. ) And the power consumption estimated from the start / stop (operation time) of the in-vehicle power consumption device or the driving information,
It is calculated by time-integrating the target engine drive time Te. Further, determination formula of step 108 and step 143, Q + C _Te -U _Tm <As is clear from the fact that can be rewritten and 0.9Q, the operation at step 108 and step 143, the battery held charge amount estimated calculated In other words, it can be said that it is determined whether the stored charge amount of the battery 9 is in an insufficient state by comparing with the value of 90% of the battery capacity Q.
Further, in FIG. 2, regarding step 143, the air conditioner is always turned on during the target engine stop time Tm.
As is clear from the fact that it may be FF,
In the present embodiment, it is also assumed that the amount of charge held in the battery 9 becomes insufficient by using only the on-vehicle power consumption device other than the air conditioner, and the engine 1 is started under the idle stop condition.

Further, here, the battery capacity Q is 10 as a reference value for judging that the charged amount of the battery 9 is insufficient.
%, But this is just one example. If the amount of charge stored in the battery is greatly reduced and becomes insufficient, the starter cannot be started when the vehicle restarts, and the vehicle remains stopped, which is a serious problem. It is impossible to unambiguously determine how much of the stored charge amount will be consumed to cause such an insufficient state, because it varies depending on factors such as the temperature and the degree of deterioration of the battery, but in general, if the battery capacity Q drops by about 10%. It is possible to start the starter sufficiently.

Next, the operation in step 114 will be further described. In step 114, as described above, the battery charge amount C _Te during the engine drive time Te until then is compared with a value of 10% of the battery capacity Q. Then, it is determined whether or not the charged amount of the battery 9 has recovered. Here, the battery charge amount C _Te is, as described above, the generator generated power estimated and calculated from the rotation speed information of the engine 1 during the engine driving time Te until then and the start / stop (operation time) of the in-vehicle power consumption device. Alternatively, it is calculated by time-integrating a difference from the power consumption estimated and calculated from the driving information with respect to the target engine drive time Te. Further, the reason why the reference value for determining that the retained charge amount of the battery 9 has recovered is set to 10% of the battery capacity Q is that the retained charge amount of the battery 9 is determined to be insufficient in step 108 and step 143. The reference value corresponds to the case where the battery capacity Q is reduced by 10%, and if the battery charge amount C _Te here exceeds 10% of the battery capacity Q, the battery capacity Q (completely charged) is obtained. The stored charge amount of the battery 9 in the state (that is, the initial value) has been recovered. That is, step 114
It can be said that the operation in (3) compares the estimated calculated charge amount of the battery 9 with the battery capacity Q to determine whether the charge amount of the battery 9 has recovered.

As described above, with the above configuration and operation, the estimated charge of the battery 9 can be calculated without using the current sensor, and the capacity of the battery 9 can be managed. Further, when it is determined that the stored charge amount of the battery 9 is insufficient while the engine is stopped at the time of idle stop or the like based on the estimation calculation result of the stored charge amount of the battery 9, the engine 1 is started and the battery 9 is stored. Charge,
Inconvenience caused by insufficient charge of the battery 9 (for example, the starter cannot be started when the engine is restarted)
Can be prevented.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention for explaining an air conditioner as an example of a power consuming device that is operating even when an engine is stopped.

FIG. 2 is a control flowchart of the embodiment shown in FIG.

FIG. 3 is a diagram showing an output characteristic of a generator.

[Explanation of symbols]

1 ... engine 2 ... Generator 5 ... Liquid tank 6 ... Refrigerant expansion means 8 ... Engine control ECU 9 ... Battery 10 ... ECU for air conditioner 11 ... Air conditioner operation unit 31 ... Compressor 32 ... Motor for driving compressor 33 ... Relay for compressor driving motor 41 ... Refrigerant condensing means 42 ... Cooling fan drive motor for refrigerant condensing means 43 ... Cooling fan drive motor relay 71 ... Refrigerant evaporation means 72 ... Blower drive motor for refrigerant evaporation means 73 ... Blower drive motor relay

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasushi Suzuki             1-1, Showa-cho, Kariya city, Aichi stock market             Inside the company DENSO F-term (reference) 3G092 AC03 BA08 GA04 GB10 HF02Z                 3G093 AA01 BA21 BA22 CA04 DB19                       DB23 EA12                 5G003 AA07 BA01 EA05 GC05                 5G060 AA04 AA05 CA21                 5H030 AS08 BB10 FF41

Claims (3)

[Claims] 1. A battery charge amount while an engine is driven is based on an engine speed and a time during which the engine is driven, and a power consumption of a power consuming device that is operating during the engine and a time during which the engine is operating. Estimate and calculate the battery charge amount estimation calculation means and the battery discharge amount during engine stop due to idle stop etc. based on the power consumption of the power consuming equipment operating during engine stop and its operating time A battery discharge amount estimation / calculation unit, a battery charge amount estimated and calculated by the battery charge amount estimation / calculation unit, and a charge / discharge balance of a battery based on the battery discharge amount estimated and calculated by the battery discharge amount estimation / calculation unit. And a battery holding charge amount estimating and calculating means for calculating and estimating the battery holding charge amount. Charge amount estimation and calculation device. 2. The method according to claim 1, further comprising means for starting the engine when the stored charge amount of the battery estimated and calculated by the battery stored charge amount estimation / calculation unit becomes less than a predetermined value while the engine is stopped. Battery charge estimation and calculation device. 3. In the case where the battery charge amount estimated and calculated by the battery charge amount estimation calculation means becomes less than a predetermined value while the engine is stopped by idle stop or the like and the engine is started and the battery is charged. The device for estimating and calculating a stored charge amount of a battery according to claim 2, further comprising: a unit that stops the engine when the stored charge amount of the battery estimated and calculated by the battery-held charge amount estimation and calculation unit exceeds a predetermined value.