Patent Description:
<CIT> describes a method for indicating the remaining capacity of a rechargeable battery. The method includes a process for correcting an estimation error of the remaining capacity of the rechargeable battery when using a large current. To perform the correction, the remaining capacity is calculated from an accumulated value of the discharge current and the battery voltage. When the battery voltage decreases to a set voltage, a correction is made to the remaining capacity that is calculated with the battery voltage.

<CIT> describes a method for measuring the remaining capacity of a rechargeable battery. The method includes a remaining capacity computation process performed in correspondence with different situations, namely, before an electrical load is supplied with power (i.e., when power is not supplied), when the electrical load is supplied with power, and after the electrical load is supplied with power.

In the remaining capacity measurement for the rechargeable battery of the above embodiments, the inventors of the present invention have noticed that during usage of the rechargeable battery, the computation result of the remaining capacity deviates greatly from the actual remaining capacity. Thus, for example, when the rechargeable battery is supplying a large current to the electrical load, it would be difficult to accurately estimate the remaining capacity of the rechargeable battery.

In the techniques of the above publications, an electric instrument may indicate that the remaining capacity of the rechargeable battery is low even though the actual remaining capacity is high enough to permit discharging of the rechargeable battery. Such an incorrect indication would prompt the user of the electric instrument to replace the rechargeable battery. On the other hand, an electric instrument may indicate that the remaining capacity of the rechargeable battery is sufficient even though the actual remaining capacity is low such that discharging of the rechargeable battery should be prohibited. Such an incorrect indication would result in the user continuing the use of the electric instrument. This would lead to over-discharging of the rechargeable battery.

<CIT> describes a treatment cylinder is attached to a fixing member, and a hook <NUM> is attached to a cover edge. The fixing member is connected to a lifting-up member which lifts up the hook <NUM> to upright posture. A piston rod of the treatment cylinder is connected to a pusher which pushes and tilts the lifting-up member toward a seat frame, and then pushes the hook toward the seat frame to hook the hook on a retaining rim of the seat frame.

<CIT> describes a battery-operated power tool that has a state of charge indicator (or "fuel gauge") to show the 'at rest' state of charge of the battery. The power tool may have a switch assembly to electrically connect the motor to the battery. When the switch assembly is activated the state of charge of the battery may be measured and displayed on the fuel gauge before electrically connecting the motor and the battery, with the display being stopped before the switch is deactivated. The power tool may comprise a movable spindle for supporting a tool element, a housing supporting the motor and a drive mechanism connected to the spindle, a battery connected to the rear of the housing and a fuel gauge for displaying the 'at rest' state of charge of the battery.

<CIT> describes after stopping feeding a main load with power and a further short time lapse, a remaining capacity is indicated for a specified time. The detecting operation of the remaining capacity is conducted in a period from the power feed stop to the remaining capacity indication with an indication showing in operation for detecting the remaining capacity.

<CIT> describes a device for determining a charge condition of an electric storage battery connected to a consumer has a unit for detecting an operational value of the battery from which a charge condition can be derived, the unit being operative for detecting a terminal voltage of the battery and deriving the charge condition exclusively from such voltage values which are applied on output terminals of the battery when a level of current taken from the consumer reaches a predetermined value.

<CIT> describes a method for determining a recovery voltage in a battery includes detecting a transient increased current draw event drawing current from the battery, the transient increased current draw event starting at a start time and ending at an end time; and in response to detecting the transient increased current draw event, waiting until time and/or voltage criteria are met to determine recovered battery voltage. An implantable pulse generator (PG) device for stimulating a human organ includes a battery, a power sink drawing current from the battery, wherein drawing increased current from the battery for transient periods causes battery voltage to decrease; and a status indicator detecting a transient increased current draw event and waiting a minimum time duration after the transient increased current draw event to measure battery voltage in order to determine a recovery voltage.

<CIT> describes when a remaining capacity of a battery is displayed by remaining capacity display control means, operation state discrimination function discriminates an operation state of an apparatus and also discriminates whether battery output voltage is greater than discrimination value when the apparatus is in reception indication operation. If the battery output voltage is greater than the discrimination value, remaining capacity of the battery corresponding to the battery output voltage in a standby state immediately before the start of the reception indication operation is displayed on LCD. If the battery output voltage is equal to or smaller than the discrimination value, the remaining capacity of the battery corresponding to the battery output voltage of this time is displayed as it is on the LCD. It is an object of the present invention to provide a battery meter that obviates or limits the announcement of incorrect remaining capacity information of a rechargeable battery and a power tool including a battery meter.

Preferred embodiments are described in the dependent claims. One aspect of the present invention is a tool main body that comprises a battery meter for use with a rechargeable battery that supplies power to an electrical load. The battery meter includes a voltage measurement unit for measuring an inter-terminal voltage of the rechargeable battery, an announcement unit for announcing rechargeable battery remaining capacity information based on the measurement of the inter-terminal voltage, and an announcement request switch for outputting an announcement request for requesting announcement of the remaining capacity information. The announcement unit is configured to announce the remaining capacity information when the announcement request is received during a period in which the electrical load is not supplied with power, and not announce the remaining capacity information regardless of whether or not the announcement request is received during a period in which the electrical load is supplied with power.

Preferably, the announcement unit is configured to generate the remaining capacity information when the announcement request is received during a period in which the electrical load is not supplied with power, and announce the remaining capacity information, which is generated when the announcement request is received, throughout a set announcement period even when the inter-terminal voltage changes after the announcement request is received.

Preferably, the announcement unit includes a recovery prediction function or a recovery prediction map for predicting recovery of the inter-terminal voltage when the supply of power to the electrical load is stopped. Further, the announcement unit is configured to predict a recovered inter-terminal voltage with the recovery prediction function or the recovery prediction map when the supply of power to the electrical load is stopped, and generate the rechargeable battery remaining capacity information based on the prediction of the recovered inter-terminal voltage.

Preferably, when the supply of power to the electrical load is started during an announcement of the rechargeable battery remaining capacity information, the announcement unit interrupts the announcement of the rechargeable battery remaining capacity information.

Preferably, the announcement unit includes an indicator that visually indicates the rechargeable battery remaining capacity information.

Preferably, the announcement unit includes a voice generator that generates a voice to announce the rechargeable battery remaining capacity information.

Preferably, the electrical load is the motor.

A further aspect of the present invention is a power tool including an electrical load and the aforementioned battery meter.

As will be appreciated, other aspects, embodiments, and/or configurations of the disclosure are possible utilizing, alone or in combination, one or more of the features set forth above or described in detail below.

The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:.

One embodiment of a power tool <NUM> will now be described.

<FIG> shows a chargeable drill driver, which is one example of the power tool <NUM>. The power tool <NUM> includes a tool main body <NUM> and a battery pack <NUM>, which is attached to the tool main body <NUM> in a removable manner. The tool main body <NUM> includes a housing <NUM> and an electric circuit <NUM>, which is accommodated in the housing <NUM> (refer to <FIG>).

The housing <NUM> includes a barrel <NUM>, a chuck <NUM>, and a grip <NUM>. The electric circuit <NUM> is accommodated in, for example, the barrel <NUM>. The chuck <NUM> holds a removable tool bit (e.g., drill).

A trigger lever <NUM> is coupled to, for example, an upper portion 13a of the grip <NUM> near the barrel <NUM>.

The trigger lever <NUM> is used to set the torque applied to the tool bit (e.g., drill). The torque is increased in accordance with the pulled amount of the trigger lever <NUM>. A spring may be used to outwardly urge the trigger lever <NUM> from the grip <NUM>. The trigger lever <NUM> is pulled into the grip <NUM> when operated. The trigger lever <NUM> outputs a trigger signal Str having a level that is in accordance with the pulled amount. The pulled amount is, for example, the movement distance of the trigger lever <NUM> when the trigger lever <NUM> is pulled.

The grip <NUM> includes a lower portion 13b (side farther from the barrel <NUM>) and a middle portion 13c. The lower portion 13b is wider than the middle portion 13c. The lower portion 13b of the grip <NUM> includes a lower surface, to which a battery pack <NUM> is attached in a removable manner, and an upper surface, on which an indicator 27b and an announcement request switch <NUM> are arranged.

The indicator 27b includes, for example, three light emitting diodes (LEDs), namely, first to third LEDs <NUM> to <NUM>. In the illustrated example, the first to third LEDs <NUM> to <NUM> are arranged in a single line.

The announcement request switch <NUM> is operated by the user of the power tool <NUM>. The announcement request switch <NUM> may be, for example, a push button that is moved in a pushing direction to a pushed position when pushed and returned to an original normal position when released.

The battery pack <NUM> and the electric circuit <NUM> of the power tool <NUM> will now be described with reference to <FIG>.

The battery pack <NUM> incorporates a rechargeable battery <NUM>. The rechargeable battery <NUM> may be any rechargeable battery cell, such as a lithium-ion rechargeable battery, a lithium rechargeable battery, or a nickel-metal hydride battery. The battery pack <NUM>, or the rechargeable battery <NUM>, includes a positive electrode <NUM> and a negative electrode <NUM> that are configured to be connectable to the electric circuit <NUM> of the power tool <NUM>. The rechargeable battery <NUM> includes one or more battery cells <NUM>. In the illustrated example, the battery cells <NUM> are connected in series.

The electric circuit <NUM> of the power tool includes a circuit main body <NUM> and a battery meter <NUM>. The circuit main body <NUM> includes a motor <NUM> (electric motor), a drive circuit <NUM>, and a main body control unit <NUM>.

The motor <NUM> is a driving device that rotates the tool bit (e.g., drill). In comparison with the drive circuit <NUM> and the main body control unit <NUM>, the motor <NUM> consumes a large amount of power. The power supplied from the rechargeable battery <NUM> is mainly consumed by the motor <NUM>. Thus, the motor <NUM> substantially acts as the main electrical load of the rechargeable battery <NUM> and is referred to as the electrical load that most dominantly affects the estimation of the remaining capacity C.

The main body control unit <NUM> receives the trigger signal Str, generates a control signal for controlling the motor <NUM> in accordance with the level of the trigger signal Str, and provides the control signal to the drive circuit <NUM>. The main body control unit <NUM>, for example, increases the power supplied to the motor <NUM> as the level of the trigger signal Str increases. When the trigger signal Str is null, the main body control unit <NUM> supplies the motor <NUM> with substantially no power. In a non-restrictive example, the control signal may be a pulse width modulation (PWM) signal.

The drive circuit <NUM> supplies the motor <NUM> with power that is in accordance with the control signal received from the main body control unit <NUM>.

The main body control unit <NUM> determines whether or not power is supplied to the motor <NUM> based on, for example, the level of the trigger signal Str from the trigger lever <NUM>, the amount of current supplied to the motor <NUM>, or the rotation speed of the motor <NUM>. When power is supplied to the motor <NUM>, the main body control unit <NUM> provides an announcement unit <NUM> with a power supply determination signal SX indicating that the motor <NUM> is being supplied with power.

The main body control unit <NUM> receives an announcement request signal SC from the announcement request switch <NUM> and transmits the announcement request SC to the announcement unit <NUM>. In a different example, the announcement request switch <NUM> directly provides the announcement request SC to the announcement unit <NUM> and does not transmit the announcement request SC via the main body control unit <NUM>.

The battery meter <NUM> will now be described. The battery meter <NUM> includes a voltage measurement unit <NUM>, the announcement unit <NUM>, and the announcement request switch <NUM>.

The voltage measurement unit <NUM> measures the potential difference between a positive terminal 29a and a negative terminal 29b of the electric circuit <NUM> and provides the main body control unit <NUM> with a measurement signal indicating the potential difference. The potential difference between the positive terminal 29a and the negative terminal 29b corresponds to the inter-terminal voltage Vt of the rechargeable battery <NUM>. The positive terminal 29a is connected to the positive electrode <NUM> of the battery pack <NUM>, or the rechargeable battery <NUM>. The negative terminal 29b is connected to the negative electrode <NUM> of the battery pack <NUM>, or the rechargeable battery <NUM>.

Referring to <FIG>, the announcement request switch <NUM> is operated by the user of the power tool <NUM>. When operated, the announcement request switch <NUM> sends an announcement request SC to the announcement unit <NUM> to request the announcement unit <NUM> to announce information related to the rechargeable battery remaining capacity C (hereinafter, referred to as the remaining capacity information). For example, the announcement request switch <NUM> provides the main body control unit <NUM> with the announcement request SC when pushed and does not output the announcement request SC when not pushed (normal condition).

The announcement unit <NUM> includes an announcement controller 27a and the indicator 27b. Based on the announcement request SC and the power supply determination signal SX, the announcement controller 27a determines whether or not to indicate the remaining capacity information of the rechargeable battery <NUM> with the indicator 27b. When determining to announce the remaining capacity information of the rechargeable battery <NUM>, the announcement controller 27a indicates the remaining capacity information on the indicator 27b.

In accordance with the determination result of the announcement controller 27a, the indicator 27b indicates the remaining capacity information. The announcement controller 27a controls the lighting of the first to third LEDs <NUM> to <NUM>. For example, the announcement controller 27a activates or deactivates each of the first to third LEDs <NUM> to <NUM> in accordance with the rechargeable battery remaining capacity C.

The indication of the rechargeable battery remaining capacity C will now be described with reference to <FIG> shows the relationship of the inter-terminal voltage V of the rechargeable battery <NUM> and the rechargeable battery remaining capacity C when the discharge current of the rechargeable battery <NUM> is substantially zero. The rechargeable battery remaining capacity C decrease as the inter-terminal voltage Vt of the rechargeable battery <NUM> decreases. This allows the main body control unit <NUM> to estimate the rechargeable battery remaining capacity C based on the inter-terminal voltage Vt of the rechargeable battery <NUM>.

<FIG> is a table showing an indication example of the rechargeable battery remaining capacity C.

When the inter-terminal voltage Vt of the rechargeable battery <NUM> is lower than voltage V1, the rechargeable battery remaining capacity C is less than capacity C1 (level <NUM>). In this case, the first LED <NUM> is intermittently illuminated.

When the inter-terminal voltage Vt of the rechargeable battery <NUM> is higher than or equal to voltage V1 and less than voltage V2, the rechargeable battery remaining capacity C is greater than or equal to capacity C1 and less than capacity C2 (level <NUM>). In this case, the first LED <NUM> is continuously illuminated.

When the inter-terminal voltage Vt of the rechargeable battery <NUM> is higher than or equal to voltage V2 and less than voltage V3, the rechargeable battery remaining capacity C is greater than or equal to capacity C2 and less than capacity C3 (level <NUM>). In this case, the first and second LEDs <NUM> and <NUM> are continuously illuminated.

When the inter-terminal voltage Vt of the rechargeable battery <NUM> is higher than or equal to voltage V3, the rechargeable battery remaining capacity C is greater than or equal to capacity C3 (level <NUM>). In this case, the first to third LEDs <NUM> to <NUM> are continuously illuminated.

Changes in the inter-terminal voltage Vt of the rechargeable battery <NUM> will now be described.

<FIG> shows changes in the inter-terminal voltage Vt of the rechargeable battery <NUM> when the supply of power to the motor <NUM> is started. At time t1, the user operates the trigger lever <NUM> to start the supply of power to the motor <NUM>. Due to relatively large inrush current, the inter-terminal voltage Vt of the rechargeable battery <NUM> decreases temporarily and rapidly increases to show an extreme drop. Thereafter, the inter-terminal voltage Vt of the rechargeable battery <NUM> gradually and slightly increases as power is continuously consumed by the motor <NUM>.

<FIG> shows changes in the inter-terminal voltage Vt of the rechargeable battery <NUM> when the supply of power to the motor <NUM> is stopped. At time t2, the user releases the trigger lever <NUM> and stops the supply of power to the motor <NUM>. This gradually and slightly increases the inter-terminal voltage Vt of the rechargeable battery <NUM>. The slight voltage increase occurs because the discharge current is large when the motor <NUM> operates, the voltage drop caused by the internal resistance of the rechargeable battery <NUM> is large, and the estimated or measured inter-terminal voltage Vt (measured value) is lower than the inter-terminal voltage (true value) corresponding to the actuator remaining capacity Cr.

A problem that arises when indicating the rechargeable battery remaining capacity C based on the inter-terminal voltage Vt of the rechargeable battery <NUM> will now be described.

When the motor <NUM> consumes a large amount of motor <NUM>, that is, when the discharge current of the rechargeable battery <NUM> is large, the inter-terminal voltage (measured value) of the rechargeable battery <NUM> during operation of the motor <NUM> is lower than the inter-terminal voltage (true value) corresponding to the actual rechargeable battery remaining capacity Cr. Further, the voltage difference between the inter-terminal voltage Vt (measured value) of the rechargeable battery <NUM> during operation of the motor <NUM> and the inter-terminal voltage (true value) corresponding to the actual rechargeable battery remaining capacity Cr is large such that it cannot be ignored when estimating the rechargeable battery remaining capacity C. Thus, when estimating the rechargeable battery remaining capacity C based on the inter-terminal voltage Vt of the rechargeable battery <NUM> measured during operation of the motor <NUM>, the estimated value would be lower than the actual rechargeable battery remaining capacity Cr. The low estimated value would lead to the following problem during usage of the power tool <NUM>.

For example, if the user checks the rechargeable battery remaining capacity C when operating the power tool <NUM> and the rechargeable battery remaining capacity C is low, the user would replace the battery pack <NUM> with another battery pack. However, the rechargeable battery remaining capacity C when the power tool <NUM> is operating is indicated as being lower than the actual rechargeable battery remaining capacity Cr. Thus, the user would be replacing the battery pack <NUM> based on an incorrect estimation result of the rechargeable battery remaining capacity. When the rechargeable battery remaining capacity C is indicated during operation of the power tool <NUM>, the battery pack <NUM> may be replaced even though the battery pack <NUM> can still be used. In this manner, even though the battery pack <NUM> is still usable, the user would replace the battery pack <NUM>. This increases the number of times the battery pack <NUM> is replaced. Further, the user would erroneously believe that the power loss is large in the power tool <NUM>, and the frequent battery pack replacement would be inconvenient for the user.

In this regard, the power tool <NUM> of the present embodiment performs a process that stops the indication of the rechargeable battery remaining capacity C when the motor <NUM> is operating. One example of the process will now be described.

A process for starting a remaining capacity announcement will now be described with reference to <FIG>. The announcement unit <NUM> performs the remaining capacity announcement starting process in predetermined cycles.

In step S110, the announcement controller 27a determines whether or not the motor <NUM> is being supplied with power. The determination is based on the power supply determination signal SX from the main body control unit <NUM>. For example, when receiving the power supply determination signal SX, the announcement controller 27a determines that the motor <NUM> is being supplied with power. When the power supply determination signal SX is not received, the announcement controller 27a determines that the motor <NUM> is not being supplied with power.

When the motor <NUM> is being supplied with power (YES in step S110), the announcement controller 27a ends the remaining capacity announcement starting process.

When the motor <NUM> is not being supplied with power (NO in step S <NUM>), in step S120, the announcement controller 27a determines whether or not the announcement request SC has been received.

When the announcement request SC has not been received (NO in step S120), the announcement controller 27a ends the remaining capacity announcement starting process.

When the announcement request SC has been received (YES in step S120), in step S130, the announcement controller 27a measures the inter-terminal voltage Vt of the rechargeable battery <NUM>.

In step S140, the announcement controller 27a generates the remaining capacity information based on the measured inter-terminal voltage Vt and announces the remaining capacity information. The remaining capacity information indicates the level of the rechargeable battery remaining capacity C. The remaining capacity information is indicated based on the level of the rechargeable battery remaining capacity C shown in the row at the left end of <FIG>.

A process for stopping the remaining capacity announcement will now be described with reference to <FIG>. The announcement unit <NUM> performs the remaining capacity announcement stopping process while announcing the rechargeable battery remaining capacity C.

In step S210, the announcement unit <NUM> determines whether or not the remaining capacity information is being announced. When the remaining capacity information is not being announced (NO in step S210), the announcement unit <NUM> ends the remaining capacity announcement stopping process. The announcement unit <NUM> may be configured not to perform the remaining capacity announcement stopping process when the remaining capacity information is not being announced.

When the remaining capacity information is being announced (YES in step S210), in step S220, the announcement unit <NUM> determines whether or not the announcement time of the remaining capacity information is longer than a predetermined set announcement period Tx. The set announcement period Tx is set to be long enough to allow the user to acknowledge the remaining capacity information.

When the announcement time of the remaining capacity information is longer than the set announcement period Tx (YES in step S220), the remaining capacity information should have been acknowledged by the user. Thus, the announcement unit <NUM> stops the announcement of the remaining capacity information. Under normal situations, the remaining capacity information is announced throughout the set announcement period Tx.

Even if the inter-terminal voltage Vt of the rechargeable battery <NUM> changes during the announcement of the remaining capacity information, the remaining capacity information, which is set during step S <NUM> during the remaining capacity announcement starting process, is continuously announced without being changed until the set announcement period Tx ends or an announcement stopping command is received.

When the announcement time of the remaining capacity information is shorter than or equal to the set announcement period Tx (NO in step S220), in step S230, the announcement unit <NUM> determines whether or not power is being supplied to the motor <NUM>. For example, when the power supply determination signal SX is received from the main body control unit <NUM>, the announcement controller 27a determines that the motor <NUM> is being supplied with power.

When the motor <NUM> is being supplied with power (YES in step S230), in step S250, the announcement unit <NUM> stops the announcement of the remaining capacity information. As described above, the announcement is stopped because the estimation accuracy of the rechargeable battery remaining capacity C, which is based on the inter-terminal voltage Vt, is low when power is being supplied to the motor <NUM>.

When the motor <NUM> is not being supplied with power (NO in step S230), in step S240, the announcement unit <NUM> determines whether or not an announcement request SC has been received.

When an announcement request SC has not been received (NO in step S240), the announcement unit <NUM> returns to step S220.

When an announcement request SC has been received (YES in step S240), in step S260, the announcement unit <NUM> performs the remaining capacity announcement starting process. When he remaining capacity announcement starting process is started, the previous announcement time and the previous remaining capacity information are reset or initialized, and the announcement time and the inter-terminal voltage Vt are measured from the beginning. When the remaining capacity announcement starting process is performed, the remaining capacity announcement stopping process is terminated.

For example, the announcement of the remaining capacity information is continued throughout the set announcement period Tx. However, when the motor <NUM> is supplied with power during the announcement of the remaining capacity information, the announcement is interrupted. When a new announcement request SC is received during the announcement of the remaining capacity information, the remaining capacity announcement starting process is performed as long as the motor <NUM> is not supplied with power.

The operation of the battery meter <NUM> will now be described with reference to <FIG>.

Time t11 in <FIG> indicates the timing in which the announcement unit <NUM> receives the announcement request SC when the motor <NUM> is not being supplied with power. At time t11, the remaining capacity announcement starting process indicates the remaining capacity information of the rechargeable battery <NUM> with the indicator 27b. For example, when the inter-terminal voltage Vt of the rechargeable battery <NUM> is higher than or equal to voltage V3, the first to third LEDs <NUM> to <NUM> are continuously illuminated. The remaining capacity information is indicated during the period from time t11 to time t12, which is when the set announcement period Tx ends.

At time <NUM>, the supply of power to the motor <NUM> starts. At time t14, the announcement unit <NUM> receives an announcement request SC when the motor <NUM> is being supplied with power. In this case, since the motor <NUM> is being supplied with power, due to the remaining capacity announcement starting process, the indicator 27b does not indicate the remaining capacity information of the rechargeable battery <NUM> even though the announcement request SC has been received. Accordingly, the first to third LEDs <NUM> to <NUM> remain deactivated.

The processing performed when the remaining capacity information of the rechargeable battery <NUM> is being indicated as the supply of power to the motor <NUM> starts will now be described with reference to <FIG>.

At time t21, which is before power is supplied to the motor <NUM>, the announcement unit <NUM> receives an announcement request SC. Thus, at time t21, the remaining capacity announcement starting process indicates the remaining capacity information of the rechargeable battery <NUM> with the indicator 27b.

At time t22, the supply of power to the motor <NUM> is started. Time t22 is before the set announcement period Tx ends, or before t23. However, the determination of step S230 in the remaining capacity announcement stopping process interrupts the indication of the remaining capacity information. In this manner, when the motor <NUM> is supplied with power, the remaining capacity information of the rechargeable battery <NUM> is not indicated.

The processing performed when the announcement request switch <NUM> is successively pushed immediately after the supply of power to the motor <NUM> stops will now be described. The double-dashed line in <FIG> show changes in the inter-terminal voltage Vt of the rechargeable battery <NUM>.

At time t31, the supply of power to the motor <NUM> is stopped. At each of times t32, t33, and t34, the announcement request switch <NUM> is pushed, and the announcement request SC is provided to the announcement unit <NUM>. In <FIG>, the period between time t32 and time t33 and the period between time t33 and time t34 are shorter than the set announcement period Tx. Thus, while the remaining capacity information generated at time t31 is being announced, the announcement unit <NUM> starts announcing the remaining capacity information that is newly generated at time t32. Then, while the remaining capacity information generated at time t32 is being announced, the announcement unit <NUM> starts announcing the remaining capacity information that is newly generated at time t33.

When the supply of power to the motor <NUM> is stopped, the inter-terminal voltage Vt of the rechargeable battery <NUM> may gradually increase. Thus, the remaining capacity information indicated by the indicator 27b is updated at time t32, time t33, and time t34.

For example, as shown in <FIG>, the inter-terminal voltage Vt measured at time t32, time t33, and time t34 may be voltage V11, voltage V12, and voltage V13, respectively. Further, voltage V11 and voltage V12 may be between voltage V2 and voltage V3 in the table of <FIG>, and voltage V13 may be higher than or equal to voltage V3 in the table of <FIG>. In this case, the indicator 27b continuously illuminates two LEDs, namely, the first LED <NUM> and the second LED <NUM>. Then, the indicator 27b continuously illuminates three LEDs, namely, the first LED <NUM>, the second LED <NUM>, and the third LED <NUM>.

The advantages of the present embodiment will now be described.

The inter-voltage Vt of the rechargeable battery <NUM> when power is being supplied to the motor <NUM> is lower than the actual inter-terminal voltage of the rechargeable battery <NUM>, that is, the inter-terminal voltage Vt when discharging is not performed. Thus, when power is being supplied to the motor <NUM>, the remaining capacity information is not announced regardless of whether or not the announcement request SC is received. This obviates or limits the announcement of incorrect remaining capacity information of the rechargeable battery <NUM> to the user.

(<NUM>) In the present embodiment, as shown in <FIG>, when the announcement unit <NUM> announces the remaining capacity information, the announcement unit <NUM> announces the remaining capacity information generated when the announcement request SC is received without changing the remaining capacity information throughout the set announcement period Tx.

This allows for stable announcement of the remaining capacity information.

If the remaining capacity information were to be changed in accordance with changes in the inter-terminal voltage of the rechargeable battery <NUM>, the information indicated by the indicator 27b would be frequently changed. For example, when the inter-terminal voltage Vt increases and decreases around voltage V2, which is shown in <FIG>, the indication of the indicator 27b would be frequently changed. This would result in the user erroneously determining that the rechargeable battery <NUM> is unstable. Thus, by stabilizing the indication of the remaining capacity information, the user would not erroneously determine that the rechargeable battery <NUM> is unstable.

(<NUM>) In the present embodiment, as shown in <FIG>, if the announcement unit <NUM> receives a signal indicating that power is being supplied to the motor <NUM> when announcing the remaining capacity information of the rechargeable battery <NUM>, the announcement unit <NUM> stops announcing the remaining capacity information of the rechargeable battery <NUM>.

For example, when the supply of power to the motor <NUM> is started, the rechargeable battery remaining capacity C starts to decrease. Thus, if the remaining capacity information of the rechargeable battery <NUM> were to be continuously announced when the supply of power to the motor <NUM> starts, incorrect remaining capacity information of the rechargeable battery <NUM> would be announced to the user. In the above embodiment, if the supply of power to the motor <NUM> starts when the remaining capacity information of the rechargeable battery <NUM> is being announced, the announcement is stopped. This obviates or limits the announcement of such incorrect remaining capacity information.

(<NUM>) In the present embodiment, the announcement unit <NUM> includes the indicator 27b, which indicates the remaining capacity information of the rechargeable battery <NUM>. This allows for the user to view the remaining capacity information of the rechargeable battery <NUM>.

(<NUM>) In the present embodiment, the main electrical load of the rechargeable battery <NUM> is the motor <NUM>. The motor <NUM> consumes a large amount of power, and changes are large in the amount of the consumed current. Due to the voltage drops in the internal resistance of the rechargeable battery <NUM> that cannot be ignored, the rechargeable battery remaining capacity C estimated when the motor <NUM> is being driven easily becomes incorrect. Thus, by applying the battery meter <NUM> of the present embodiment to the electric circuit <NUM> including the motor <NUM>, the announcement of incorrect remaining capacity information of the rechargeable battery <NUM> may be obviated or limited.

(<NUM>) The power tool <NUM> of the present embodiment includes the battery meter <NUM>. This allows for the announcement of incorrect remaining capacity information of the rechargeable battery <NUM> to be obviated or limited.

In the above embodiment, whenever the remaining capacity announcement starting process is executed, the inter-terminal voltage Vt of the rechargeable battery <NUM> is measured, and the remaining capacity information based on the inter-terminal voltage Vt is indicated by the indicator 27b. Thus, as shown in <FIG>, during the period the inter-terminal Vt recovers immediately after the supply of power to the motor <NUM> is stopped, the indication of the indicator 27b would change if the announcement request switch <NUM> were to be pushed a number of times. Although the announcement request switch <NUM> would be seldom pushed a number of times during the period the inter-terminal voltage Vt recovers, such changes in the indication of the indicator 27b may result in the user determining that the rechargeable battery remaining capacity C is increasing. Thus, it is preferable that changes be decreased in the indication of the indicator 27b when the rechargeable battery remaining capacity C increases. Accordingly, during the recovery of the inter-terminal voltage Vt immediately after the supply of power to the motor <NUM> stops, the recovered inter-terminal voltage Vt may be predicted, and the remaining capacity information may be announced based on the prediction.

For example, the announcement unit <NUM> may be configured to include a recovery prediction function (double-dashed line in <FIG>) for predicting the recovered inter-terminal voltage Vt. The recovery prediction function is set through discharge tests or the like conducted on the rechargeable battery <NUM>. Further, the recovery prediction function is configured to calculate the inter-terminal voltage Vt after a predetermined period by inputting an initial inter-terminal voltage Vt.

The operation of the announcement unit <NUM> will now be described with reference to <FIG>.

<FIG> is a chart for predicting the recovered inter-terminal voltage Vt immediately after the supply of power to the motor <NUM> is stopped.

When predicting the recovered inter-terminal voltage Vt, the inter-terminal voltage Vt is measured immediately after the supply of power to the motor <NUM> is stopped, and the voltage V22 obtained through the measurement is input as an initial value to the recovery prediction function. Further, the terminal voltage Vt after a predetermined time (i.e., time t43), which is voltage V23, is predicted. In the prediction, the predicted inter-terminal voltage Vt may be corrected based on the inter-terminal voltage Vt immediately before the supply of power to the motor <NUM> is started (voltage V21 at time t41). Further, the amount of current supplied to the motor <NUM> may be accumulated during the period from when the supply of power to the motor <NUM> starts (time t41) to when the supply of power stops (time t42), and the predicted inter-terminal voltage Vt may be corrected based on the accumulated value.

In this example, when the supply of power to the motor <NUM> is stopped, the recovered inter-terminal voltage Vt after the supply of power to the motor <NUM> is stopped is predicted using the recovery prediction function. Then, the remaining capacity information of the rechargeable battery <NUM> is generated based on the predicted inter-terminal voltage Vt.

More specifically, when the announcement request switch <NUM> is pushed immediately after the supply of power to the motor <NUM> is stopped, the remaining capacity information that is announced is estimated from the predicted inter-terminal voltage Vt. Thus, the remaining capacity information is stably indicated by the indicator 27b. This obviates or limits the user erroneously determining that the rechargeable battery remaining capacity C is increasing.

In the above example, a recovery prediction function is used to predict the recovered inter-terminal voltage Vt when the inter-terminal voltage recovers immediately after the supply of power to the motor <NUM> stops. However, a recovery prediction may be used in lieu of the recovery prediction function. The recovery prediction map, for example, associates the inter-terminal voltage Vt immediately after the supply of power to the motor <NUM> stops with the recovered inter-terminal voltage Vt after a predetermined period.

In the above embodiment, the determination of whether or not the motor <NUM> is supplied with power is performed based on the power supply determination signal SX output from the main body control unit <NUM>. In other words, the main body control unit <NUM> substantially determines whether or not power is being supplied to the motor <NUM>. However, the announcement unit <NUM> may determine whether or not power is being supplied to the motor <NUM>.

In the above embodiment, the indicator 27b visually indicates and announces the remaining capacity information of the rechargeable battery <NUM> so that the user may check the remaining capacity information of the rechargeable battery <NUM>. However, the means for announcing the remaining capacity information of the rechargeable battery <NUM> is not limited in such a manner. For example, a voice may be generated to announce the remaining capacity information of the rechargeable battery <NUM>. In this case, the power tool <NUM> is provided with a voice generator formed by a speaker or the like instead of the indicator 27b. Alternatively, the indicator 27b and the voice generator may both be provided in the power tool. In such cases, a voice is generated to announce the remaining capacity information of the rechargeable battery <NUM> to the user.

In the above embodiment, the announcement unit <NUM> is located outside the main body control unit <NUM> but may be located inside the main body control unit <NUM>.

In the above embodiment, the voltage measurement unit <NUM> is located outside the announcement unit <NUM> but may be located inside the voltage measurement unit <NUM>.

The power tool <NUM> is not limited to a chargeable drill driver and may be, for example, a chargeable saw, a chargeable air pump, a chargeable cutter, a chargeable blower, and a chargeable chain saw.

In the above embodiment, the battery meter <NUM> is applied to the electric circuit <NUM> including the motor <NUM> but may be applied to an electric circuit <NUM> including an electrical load other than the motor <NUM>. For example, the electrical load may be an electric heating device (nichrome wire, heating coil, or the like).

Claim 1:
A tool main body (<NUM>) comprising an electrical load (<NUM>), the tool main body (<NUM>) comprising a battery meter (<NUM>) for use with a rechargeable battery (<NUM>) configured to supply power to the electrical load (<NUM>), the battery meter (<NUM>) comprising:
a voltage measurement unit (<NUM>) for measuring an inter-terminal voltage (Vt) of the rechargeable battery (<NUM>);
an announcement unit (<NUM>) for announcing rechargeable battery remaining capacity information based on the measurement of the inter-terminal voltage (Vt); and
an announcement request switch (<NUM>) for outputting an announcement request (SC) for requesting announcement of the remaining capacity information, wherein:
the announcement unit (<NUM>) is configured to
announce the remaining capacity information when the announcement request (SC) is received during a period in which the electrical load (<NUM>) is not supplied with power, and
wherein the tool main body (<NUM>) is characterized in that
the announcement unit (<NUM>) is configured to
not announce the remaining capacity information regardless of whether or not the announcement request (SC) is received during a period in which the electrical load (<NUM>) is supplied with power,
wherein the tool main body (<NUM>) is further configured such that,
during a period in which the electrical load (<NUM>) is not supplied with power, at each of times (t32, t33) when the announcement request switch (<NUM>) is pushed, the announcement request (SC) is provided to the announcement unit (<NUM>) and the remaining capacity information is updated at each of the times even if a period between two times when the announcement request switch (<NUM>) is pushed is shorter than a set announcement period (Tx).