Patent Application
20090115372
The present invention relates to a discharge control system for controlling discharge from a plurality of electric rechargeable cells included in a electric storage pack so as to make uniform residual capacities or states of charge of the respective electric rechargeable cells.
A electric storage pack for supplying electric power to a motor or the like is equipped on a vehicle such as EV (Electric Vehicle) or HEV (Hybrid Electrical Vehicle). The electric storage pack includes a plurality of electric rechargeable cells which are connected in series.
The electric storage pack 10 shown in
Each discharge switch unit has a discharge resistor R and a switch Sw which are connected in series. The voltage detection units S1 to Sm detect voltages at both ends of the cell (a cell voltage) with which it is connected in parallel. The control unit 21 on/off controls the respective switches of the discharge switch units in accordance with determination results by the voltage detection units S1 to Sm.
Further, the electric storage pack 10 has a charge control unit which is not shown. The charge control unit controls to prevent the overcharge of the respective cells (an overcharge preventive control) when the electric storage pack 10 is charged. The cell voltages of the respective cells vary depending on the state of using the electric storage pack 10 and/or qualities of the respective cells. Therefore, the charge control units implements an overcharge preventive control based on the cell having a highest cell voltage. In addition, lithium ion electric rechargeable cells or nickel-hydrogen electric rechargeable cells are used as the cells installed in the electric storage pack 10, and the overcharge preventive control is necessary particularly when the lithium ion electric rechargeable cells are used.
In this way, since the overcharge preventive control of the electric storage pack 10 is carried out based on the cell having the highest cell voltage, as shown in
Therefore, in the electric storage pack 10 shown in
For example, refer to Japanese Unexamined Patent Publications JP-A-8-19188 and JP-A-2003-164069.
In the electric storage pack 10 described above, heat is produced in association with making uniform the cell voltages of the cells. Namely, in the electric storage pack 10, electric power stored in the cells is consumed wastefully by making uniform the cell voltages of the cells. Further, as has been described above, the integrated circuit made up of the discharge switch units Cc1 to Ccm, the voltage detection units S1 to Sm and the control unit 21 is provided in an interior of the electric storage pack 10. Since some constituent elements are included in the integrated circuit whose properties change depending on ambient temperatures, the discharge resistors R1 to Rm desirably have a smaller heat value.
According to Joule's law, the heat value of a resistor is proportional to “electric current2×resistance value.” Therefore, resistors having a large resistance value are used for the discharge resistors R1 to Rm. Since the larger the resistance value of a discharge resistor, the smaller a discharge current, a quantity of heat generated in the discharge resistor is reduced. However, with a small discharge current, a longer time has to be spent in making uniform the cell voltages of the cells. Therefore, the resistance values of the discharge resistors R1 to Rm are determined based on a balance between the heat values of the discharge resistors and the time spent in making uniform the cell voltages. In any case, since heat is generated in the discharge resistors R1 to Rm in association with making uniform the cell voltages of the cells, a high-level of countermeasures against heat like heat dissipation or heat resistance need to be taken for the electric storage pack 10 so as to prevent the integrated circuit from being badly affected by the heat.
The invention provides a discharge control system which can consume energy stored in a electric storage pack with good efficiency.
According to a first aspect of the invention, a discharge control system for a electric storage pack (for example, a electric storage pack 100 in an embodiment) has a plurality of electric rechargeable cells (for example, lithium ion electric rechargeable cells C1 to Cn in the embodiment) connected in series and a feeding circuit for driving a load which the circuit is connected discharge lines from the electric rechargeable cells, including a plurality of cell voltage detection units (for example, voltage detection units S1 to Sn in the embodiment) for detecting respective cell voltages of the plurality of electric rechargeable cells, a switch group (for example, a discharge switch unit 111) including a plurality of switches (for example, switches SW1 to SW2n in the embodiment) which are respectively connected between the electric rechargeable cells, and a control unit (for example, a control unit 121 in the embodiment) which designates a electric rechargeable cell having a highest cell voltage in the electric rechargeable cells possessed by the electric storage pack as a group in accordance with detection results by the cell voltage detection units and forms a discharge line from the electric rechargeable cell of the group to the feeding circuit by controlling the switches of the switch group individually.
Furthermore, according to a second aspect of the invention, the electric rechargeable cells may comprise lithium ion electric rechargeable cells.
In addition, according to a third aspect of the invention, the switch group may have a first switch group including a plurality of first switches (for example, switches SW1 and SW2, SW4, . . . , SW2n−2 in the embodiment) which are connected to a negative side input terminal of the feeding circuit, and a second switch group including a plurality of second switches (for example, SW3, SW5, . . . , SW2n−1 and SW2n) which are connected to a positive terminal of the feeding circuit, and wherein the control unit closes any one of first switches in the first switch group and any one of second switches in the second switch group, so as to form a discharge line from the plurality of electric rechargeable cells to the feeding circuit.
Additionally, according to a fourth aspect of the invention, the control unit may select the electric rechargeable cell to be designated as forming the group so that a discharge voltage of the electric rechargeable cell designated as forming the group falls within a voltage range which can drive the load.
Furthermore, according to a fifth aspect of the invention, when a different electric rechargeable cell becomes a electric rechargeable cell having a highest cell voltage as a result of discharge from the electric rechargeable cell designated as forming the group, the control unit may designate the different electric rechargeable cell as a different group and forms a discharge line from the different electric rechargeable cell of the different group to the feeding circuit.
According to a sixth aspect of the invention, when a electric rechargeable cell having a lowest cell voltage in electric rechargeable cells designated as forming the group becomes a electric rechargeable cell having a lowest cell voltage in the plurality of electric rechargeable cells possessed by the electric storage pack as the result of discharge from the electric rechargeable cell designated as forming the group, the control unit may designate a electric rechargeable cell having a highest cell voltage in the electric rechargeable cells possessed by the electric storage pack as forming a different group and forms a discharge line from the electric rechargeable cell of the different group to the feeding circuit.
In addition, according to a seventh aspect of the invention, the control unit may exclude a group which is designated as forming a group including a electric rechargeable cell having a lowest cell voltage in the electric rechargeable cells possessed by the electric storage pack from the group to be selected.
Additionally, according to an eighth aspect of the invention, the switch group may have a first switch group including a plurality of first switches (for example, SW1 and SW2, SW4, . . . , SW2n−2 in the embodiment) which are connected to a negative side input terminal of the feeding circuit, and a second switch group including a plurality of second switches (for example, SW3, SW5, . . . , SW2n−1 and SW2n) which are connected to a positive side terminal of the feeding circuit, and wherein the control unit may close any one of first switches in the first switch group and any one of second switches in the second switch group, so as to form a discharge line from a electric rechargeable cell having a highest cell voltage in the plurality of electric rechargeable cells possessed by the electric storage pack to the feeding circuit.
Furthermore, according to a ninth aspect of the invention, when the cell voltage of the electric rechargeable cell having the highest cell voltage becomes equal to a cell voltage of a electric rechargeable cell having a lowest cell voltage in the plurality of electric rechargeable cells possessed by the electric storage pack as a result of discharge from the electric rechargeable cell having the highest voltage, the control unit may switch the discharge line.
In addition, according to a tenth aspect of the invention, when the cell voltage of the electric rechargeable cell having the highest cell voltage becomes equal to a value resulting from subtraction of a predetermined value from the cell voltage of a electric rechargeable cell having a second highest cell voltage in the plurality of electric rechargeable cells possessed by the electric storage pack as a result of discharge from the electric rechargeable cell having the highest voltage, the control unit may switch the discharge line.
Furthermore, according to an eleventh aspect of the invention, the cell voltage detection units may detect continuously or periodically cell voltages of the plurality of electric rechargeable cells, and wherein the control unit continuously controls the switches in accordance with detection results by the cell voltage detection units.
Hereinafter, embodiments of the invention will be described by reference to the drawings. A electric storage pack which will be described in the following embodiments is such as to be equipped on a vehicle such as EV (Electric Vehicle) and HEV (Hybrid Electric Vehicle) to supply electric power to a motor or the like. In addition, a plurality of electric rechargeable cells connected in series are provided in the electric storage pack. In the embodiments which will be described hereinafter, lithium ion electric rechargeable cells are used as such electric rechargeable cells. However, as other embodiments, nickel-hydrogen electric rechargeable cells, electric double-layer capacitors, capacitors and the like may be used. In addition, it should be understood that when used in this specification, “discharge” means not energy output for supplying electric power from the electric storage pack to the motor but energy output for making uniform cell voltages of the respective cells installed in the electric storage pack.
An output voltage of the electric storage pack 100 of this embodiment is a high output voltage (for example, 100 to 200V), and an output voltage of the battery 17 is an output voltage for auxiliaries (for example, a low voltage of 12V). The output voltage of the electric storage pack 100 is transformed from direct current to alternating current by the inverter 11 for supply to the motor 13. The output voltage of the electric storage pack 100 is reduced low enough to charge the battery 17 by the DC-DC converter 15. Electric power is supplied to the electric motor 109 by discharge from cells installed in the electric storage pack 100, and an airflow produced by the cooling fan driven by the electric motor cools the electric storage pack 100.
In addition, the operation of the electric motor is ensured by a drive voltage of 9 to 14V. Not only in this embodiment but also in other embodiments, the auxiliary is not limited to the cooling fan electric motor but may be an electric motor for a coolant pump or an electric motor for a blower of an air cleaner. In addition, a destination to the supply of electric power by the cell discharge is not limited to the electric motor 109 which is the rotary induction load but may be a feeding circuit for feeding a capacity variable load. The capacity variable load includes a hot wire used in a seat heater, a lamp used as a back light for an instrument cluster, a Peltier element, an air cleaner and the like. Furthermore, electric power resulting from cell discharge may be supplied not only to the electric motor 109 but also to the electric motor 109 and other auxiliaries at the same time.
The electric storage pack 100 shown in
Here, a single output voltage range of the cells C1 to Cn is in the range of 2.5 to 4.0V. Note that a relationship between SOC (State of Charge) and output voltage of a lithium ion battery is substantially linear, and in the electric storage pack equipped on the vehicle, charging and discharging are repeated within a predetermined range of residual capacity (SOC) of the cells.
The discharge switch unit 111 has switches SW1 to SW2n which are connected between the cells. In addition, the switches SW1 and SW2, SW4, . . . , SW2n−2 are connected to a negative side input terminal of the electric motor 109, while the switches SW3, SW5, . . . , SW2n−1 and SW2n are connected to a positive side input terminal of the electric motor 109.
The voltage detection units S1 to Sn detect voltages at both ends of the cells with which they are connected in parallel (cell voltages). In addition, the voltage detection units S1 to Sn detect cell voltages of the cells continuously or periodically and send detection results to the control unit 121.
The control unit 121 determines the SOC of the respective cells based on the detection results sent from the voltage detection units S1 to Sn. In addition, as has been described above, the relationship of SOC and output voltage of the lithium ion battery is substantially linear and a relationship of SOC and output voltage of each cell is also substantially linear. The control unit 121 on/off controls individually the switches SW1 to SW2n within the discharge switch unit 111 based on latest detection results in relation to SOC so that the SOC of the cells, that is, cell voltages of the cells become the same in level. By the on/off control of the switches SW1 to SW2n by the control unit 121, a continuous discharge line is established from at least one cell to the electric motor 109. Consequently, electric power is supplied to the electric motor 109 from the cell that is included in a closed circuit made by the on/off control by the control unit 121. For example, when the control unit 121 closes the switches SW1, SW3 and opens the other switches, electric power is supplied to the electric motor 109 from the cell C1. In addition, when the control unit 121 closes the switches SW4, SW2n and opens the other switches, electric power is supplied to the electric motor 109 from the cells C3 to Cn.
Hereinafter, on/off controls by the control unit 121 possessed by the electric storage pack 100 of the first embodiment will be described in detail separately with respect to “group setting,” “different group setting,” “group selection,” and “group switching.”
Firstly, a group setting by the control unit 121 according to the first embodiment will be described by reference to
As is shown in
If the result of the determination at step S102 determines that the accumulated cell voltage is equal to or smaller than 9V, the group setting operation proceeds to step S105. At step S105, the control unit 121 designates, of two cells which lie adjacent to a group of cells which is designated as the group, a cell having a higher cell voltage as forming the same group, and thereafter, the group setting operation returns to step S102. In addition, if the result of the determination at step S103 determines that the accumulated cell voltage is equal to or larger than 14V, the group setting operation proceeds to step S106. At step S106, the control unit 121 designates, of two cells which lie at both ends of the group of cells which is designated as forming the group, a cell having a lower cell voltage as a cell to be excluded from the group, and thereafter, the group setting operation returns to step S102.
Note that in the group setting described above, it is desirable to have fewer cells within one group. For example, in the case of a cell voltage being 3.0V shown in
In addition, the control unit 121 may select the number of cells that are designated as forming a group in accordance with variation in cell voltage (a difference between a maximum cell voltage and a minimum cell voltage). Namely, the control unit 121 designates a larger number of cells when the variation is small, while selecting a smaller number of cells when the variation is large. For example, in the case of the cell voltage of 3.0V shown in
Hereinafter, a case will be described in which the group setting based on the flow described by reference to
Next, the control unit 121 determines whether or not an accumulated cell voltage of the cells 5 to 7 is larger than 9V. If the accumulated cell voltage of the cells 5 to 7 is larger than 9V, the control unit 121 determines whether or not the accumulated cell voltage of the cells 5 to 7 is smaller than 14V. If the accumulated cell voltage of the cells 5 to 7 is smaller than 14V, the control unit 121 sets the cells 5 to 7 into one group and then on/off controls the switches of the discharge switch unit 111 so that a discharge line is formed from the cells 5 to 7 to the electric motor 109.
If an accumulated cell voltage of the cells 4 to 7 is equal to or larger than 14V in such a state that the cells 4 to 7 are set into one group, the control unit 121 designates, of the two cells lying at both ends of the cells 4 to 7 which are designated as forming the group, the cell 4 having a lower cell voltage as a cell to be excluded from the group.
Next, a different group setting by the control unit 121 of the first embodiment will be described by reference to
As is shown in
If the result of the determination at step S112 determines that the accumulated cell voltage of the group B is equal to or smaller than 9V, the different group setting operation proceeds to step S114. At step S114, the control unit 121 designates a cell which lies adjacent to the cell group which is designated as the group B and is not designated as forming the group A as forming the group B and thereafter the different group setting operation returns to step S112. In addition, the result of the determination at step S113 determines that the accumulated cell voltage of the group B is equal to or larger than 14V, the different group setting operation proceeds to step S115. At step S115, the control unit 121 designates the cell of the cells designated as forming the group B which was last designated as forming the group B as a cell that is to be excluded from the group B, and thereafter, the different group setting operation returns to step S112.
Hereinafter, a case will be described in which the different group setting based on the flow described by reference to
Next, the control unit 121 determines whether or not an accumulated cell voltage of the cells 5, 4, 3 is larger than 9V. If the accumulated cell voltage of the cells 5, 4, 3 is larger than 9V, the control unit 121 then determines whether or not the accumulated cell voltage of the cells 5, 4, 3 is smaller than 14V. If the accumulated cell voltage of the cells 5, 4, 3 is smaller than 14V, the control unit 121 sets the cells 5, 4, 3 into the group B which is different from the group A. If the accumulated cell voltage of the cells 5, 4, 3 is equal to or larger than 14V, the control unit 121 designates the cell 3 which was last designated as forming the group B in the cells 5, 4, 3 as a cell that is to be excluded form the group B.
Next, a group selection by the control unit 121 of the first embodiment will be described by reference to
Next, a first group switching by the control unit 121 of the first embodiment will be described by reference to
As is shown in
In addition, at step S122, while whether or not the cell voltage of the cell 5 is equal to or larger than the cell voltage of the cell 2 is determined and the groups are switched at the point in time at which the cell voltage of the cell 5 becomes lower than the cell voltage of the cell 2, a hysteresis may be provided in switching the groups. Namely, switching to the different group is not implemented at a instant point in time at which the cell voltage of the cell 5 becomes lower than the cell voltage of the cell 2, but is implemented at a point in time at which the cell voltage of the cell 5 becomes smaller than a value which results from subtracting an overshoot value from the cell voltage of the cell 2. Because of this, since in the event that the overshoot value is large, the number of times of switching the groups is reduced, a smooth control results, and in the event that the overshoot value is small, the residual capacities can be made uniform by frequent group switchings.
In the first group switching that has been described above, while the cell voltage of the cell in the cells designated as forming the group which has the highest cell voltage is compared with the cell voltage of the cell in the cells installed in the electric storage pack 100 which has the second highest cell voltage, as a second group switching, the groups may be switched in accordance with a result of a comparison between a lowest cell voltage in the cells designated as forming the group and a lowest cell voltage in the cells installed in the electric storage pack 100.
Hereinafter, the second group switching by the control unit 121 of the first embodiment will be described by reference to
As is shown in
By executing the second group switching, it becomes possible to prevent the generation of a cell having a cell voltage which is lower than the lowest cell voltage in the cells installed in the electric storage pack 100.
The on/off control by the control unit 121 that has been described heretofore may include functions which will be described later.
<Increase/Decrease in Cell Number Matching Electric Power Demand from Load>
While this embodiment has been described using the cooling fan electric motor 109 as the example of the rotary induction load which consumes electric power discharged from the electric storage pack 100, the load consuming the electric power from the electric storage pack 100 is not limited to the cooling fan electric motor 109 but may be an auxiliary such as a coolant pump electric motor and a blower electric motor of an air cleaner or a feeding circuit for feeding a capacity variable load such as a hot wire or a lamp. However, since required electric power differs depending on auxiliaries, the control unit 121 changes the threshold used at steps S102, S103 in the flowchart shown in
For example, since the electric motor 109 requires a driving voltage of 8 to 14V, the groups are set in such a manner that their accumulated voltage falls within the range of 8 to 14V. However, when driving an auxiliary which requires a driving voltage of 11 to 17V, the control unit 121 selects the cells which are to be designated as forming the groups in such a manner that their accumulated cell voltage falls within the range of 11 to 17V. In addition, the control unit 121 may change the thresholds in accordance with a quantity of air produced by the cooling fan driven by the electric motor 109.
<Addition of Cell in Association with Reduction in Cell Voltage>
The cell voltages of the cells which have carried out the discharge of required electric power drop. Since electric power to be supplied to the load is reduced when the cell voltages are reduced, there can be caused a situation in which electric power required by the load cannot be supplied. Because of this, when the cell voltages are reduced, a cell is added to the group which is discharging so that the cell also discharges so as to secure electric power to be supplied to the load. The cell to be added is a cell having a higher cell voltage of two cells which lie adjacent to the group of cells which are designated as forming the group.
As has been described heretofore, according to the electric storage pack 100 of the embodiment, electric power discharged from the cells by the on/off control of the switches of the discharge switch unit 111 by the control unit 121 is used to drive the electric motor 109. In this way, electric power that is transformed into heat at the resistors in the conventional electric storage pack is used effectively. In addition, while electric power is supplied from the battery 17 to the electric motor 109 in the conventional electric storage pack, in this embodiment, electric power discharged from the cells is supplied to the electric motor 109. Because of this, power consumption from the battery 17 can be reduced. As has been described above, the battery 17 is charged with electric power from the electric storage pack 100 which is reduced in voltage by the DC-DC converter 15, and power loss is generated at the DC-DC converter 15. Because of this, the reduction in consumption of electric power from the battery 17 can indirectly realize a reduction in consumption of electric power from the electric storage pack 100.
In addition, when comparing the speed at which electric power discharged from the cells is transformed into heat in the resistors with the speed at which the electric power is consumed in the electric motor 109, the speed at which the electric power is consumed in the electric motor 109 is faster markedly. Thus, the discharging time can be shortened compared with the conventional electric storage pack. Furthermore, when comparing the heat value resulting when electric power discharged from the cells is transformed into heat in the resistors with the heat value resulting when the electric power is consumed in the electric motor 109, the heat value resulting when the electric power is consumed in the electric motor 109 is smaller markedly. Consequently, the high level of countermeasures taken against heat in the conventional electric storage pack does not have to be taken any more, and the integrated circuit made up of the discharge switch unit 111, the voltage detection units S1 to Sn and the control unit 121 is little affected by heat.
In addition, when comparing the electric storage pack 10 shown in
While in the first embodiment, the continuous discharge line is formed from at least one cell to the cooling fan electric motor 109 which is the rotary induction load by the on/off control of the switches SW1 to SW2n by the control unit 121, in a second embodiment, a discharge line is formed from a cell of cells installed in a electric storage pack 100 which has a highest cell voltage to an electric motor 109. Although a relationship between the electric storage pack, part of an electric drive system and auxiliaries is substantially the same as that of the first embodiment shown in
Hereinafter, a discharge control by a control unit of the second embodiment will be described by reference to
As is shown in
When the discharge line is formed, since electric power is discharged from the cell specified at step S141 to the electric motor 109, the cell voltage of the cell drops. Next, at step S143, the control unit determines whether or not the cell voltage of the cell specified at step S141 is equal to a cell voltage of a cell in the cells installed in the electric storage pack 100 which has a lowest cell voltage. When the cell voltage of the cell specified at step S141 drops to be equal to the smallest cell voltage, the discharge control operation returns to step S140.
Hereinafter, a case will be described in which the discharge control based on the flow described by reference to
As shown in
In this way, the control unit of the second embodiment continues to control the switching of discharge lines from the respective cells to the electric motor 109 until the respective cell voltages of the cells installed in the electric storage pack finally drop to the cell voltage of the cell 4 to thereby eliminate variations in cell voltage by repeating the discharge control described above.
A third embodiment is identical to the second embodiment in that a discharge line is formed from a cell having a highest cell voltage in cells installed in a electric storage pack 100 to an electric motor 109 but is different therefrom in timing at which discharge lines are switched. Namely, while in the second embodiment, discharge continues until the cell voltage of the discharging cell drops to the cell voltage of the cell having the lowest cell voltage in the cells installed in the electric storage pack, in the third embodiment, discharge continues until the cell voltage of a discharging cell drops to be a voltage resulting from subtraction of a predetermined voltage from the cell voltage of a cell having a second highest cell voltage in the cells in the electric storage pack.
Although a relationship between the electric storage pack of the third embodiment, part of an electric drive system and auxiliaries is substantially the same as that of the first embodiment shown in
Hereinafter, a discharge control by the control unit of the third embodiment will be described by reference to
As is shown in
When the discharge line is formed, electric power is discharged from the cell specified at step S151 to the electric motor 109, the cell voltage of the cell drops. Following this, at step S154, the control unit determines whether or not the cell voltage of the cell specified at step S151 is equal to a voltage resulting from subtraction of a predetermined voltage from the cell voltage of the cell specified at step S152 (hereinafter, referred to as a “reference voltage”). When the cell voltage of the cell specified at step S151 drops to become equal to the reference voltage, the discharge control operation returns to step S150.
Hereinafter, a case will be described in which the discharge control based on the flow described by reference to
When the cell voltage of the cell 5 drops to the cell voltage of the cell 2 having the second highest cell voltage in the cells installed in the electric storage pack as shown in
When the discharge line is formed from the cell 2 to the electric motor 109, the cell voltage of the cell 2 drops. The control unit maintains the discharge line so formed until the cell voltage of the cell 2 drops to the cell voltages of a cell 3 and the cell 5 which are having the second highest cell voltage as shown in
In this way, the control unit of the second embodiment continues to control the switching of discharge lines from the respective cells to the electric motor 109 until the respective cell voltages of the cells installed in the electric storage pack finally drop to the cell voltage of the cell 4 to thereby eliminate variations in cell voltage by repeating the discharge control described above.
For example, since when only one cell needs to discharge, the discharge voltage of the electric storage pack 100 does not reach a voltage needed to drive the electric motor 109, the electric motor 9 is not driven. As this occurs, no cell discharge by the electric motor 19 is carried out. However, since the resistor R0 is connected to the electric motor 109 in parallel, discharge current flows to the resistor R0 when the control unit 121 closes the switch SW0. Consequently, when the discharge voltage of the electric storage pack 100 does not reach the voltage needed to drive the electric motor 109, the cell discharge by the resistor R0 can be performed.
In addition, the resistor R0 of the embodiment may be a variable resistor. In the case of a variable resistor being used as the resistor R0, the control unit 121 adjusts a resistance value of the variable resistor in accordance with a level of discharge voltage of the electric storage pack 100. In addition, the embodiment may take a form in which a plurality of sets of the resistor R0 and the switch SW0 may be provided parallel, each set having a different resistance value. In this case, the control unit closes a switch for the set selected based on the level of discharge voltage of the electric storage pack 100.
According to the first to eleventh aspects of the invention, since electric power discharged from the electric rechargeable cells for the purpose of making uniform the cell voltages thereof, energy stored in the electric storage pack can be consumed with good efficiency.
While the invention has been described in connection with the exemplary embodiments, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing form the present invention, and it is aimed, therefore, to cover in the appended claim all such changes and modifications as fall within the true spirit and scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-285422 | Nov 2007 | JP | national |
