Auxiliary battery charging apparatus

CROSS REFERENCE TO RELATED APPLICATION

0001This application claims priority to Japanese Application No. 2011-077935 filed Mar. 31, 2011.

TECHNICAL FIELD

0002The present invention relates to an auxiliary battery charging apparatus for charging an auxiliary battery that is installed in a vehicle in addition to a main battery.

BACKGROUND

0003<figref idref="DRAWINGS">FIG. 1</figref> illustrates an existing auxiliary battery charging apparatus.

0004An auxiliary battery charging apparatus <b>40</b> in <figref idref="DRAWINGS">FIG. 1</figref> is installed in a vehicle such as a hybrid vehicle, an electric vehicle, etc., and includes a main battery <b>41</b> and a DC/DC converter <b>42</b> for dropping an output voltage of the main battery <b>41</b> and charging an auxiliary battery <b>43</b>.

0005It is necessary for the main battery <b>41</b> to output a relatively high voltage to provide electric power to a motor/generator <b>44</b>. Therefore, with a higher voltage of the main battery <b>41</b>, the parts such as an inductor, a capacitor, etc. configuring the DC/DC converter <b>42</b> become larger. Therefore, concerns are rising that the auxiliary battery charging apparatus <b>40</b> becomes larger.

0006The main battery <b>41</b> is configured to connect a plurality of rechargeable battery cells in series so that the output voltage can be increased; however, as much as possible, it is necessary to eliminate variations between the output voltages of the rechargeable battery cells in order to reduce the overall degradation.

0007Accordingly, to eliminate as much as possible the variation between the output voltages of the rechargeable battery cells, the existing auxiliary battery charging apparatus <b>40</b> in <figref idref="DRAWINGS">FIG. 1</figref> comprises: a cell-monitoring cell balance circuit <b>45</b> which equalizes the output voltages of the rechargeable battery cells; and an ECU <b>46</b> which controls the operation of the cell-monitoring cell balance circuit <b>45</b>.

0008As an example, as a technique to equalize the output voltages of rechargeable battery cells (hereinafter referred to as “cell balancing”), there is a so-called active-system cell balancing wherein the output voltages of the rechargeable battery cells are equalized by discharging or charging the rechargeable battery cells via a transformer (see, for example, Japanese Laid-open Patent Publication No. 2001-339865).

SUMMARY

0009The present invention aims at providing an auxiliary battery charging apparatus capable of suppressing the increase in size of the apparatus while reducing the variations between the output voltages of each of a plurality of rechargeable battery cells configuring a main battery.

0010The auxiliary battery charging apparatus according to the present invention includes: a main battery provided with first and second rechargeable battery cells connected to each other in series; a first transformer provided with a first coil and a second coil connected to the first rechargeable battery cell; a second transformer provided a third coil connected to an auxiliary battery and a fourth coil connected to the second rechargeable battery cell; a first switch provided between the first rechargeable battery cell and the second coil; a second switch provided between the second rechargeable battery cell and the fourth coil; a third switch provided between the first coil and the third coil; a fourth switch provided between a connection point of the third switch and the third coil and the auxiliary battery; a voltage source for applying a voltage to the first coil; and a control circuit for, when the auxiliary battery is charged, turning off the third switch, turning on the fourth switch, and turning on and off the second switch, thereby electrically connecting the third coil to the auxiliary battery, placing the first coil in an open state, and electromagnetically coupling the third and fourth coils, and when each output voltage of the first and second rechargeable battery cells is equalized, turning on the third switch, turning off the fourth switch, and turning on and off the first and second switches respectively, thereby electrically connecting the first and third coils, placing the auxiliary battery in the open state, and electromagnetically coupling the first through fourth coils.

0011Thus, the variations between the output voltages of each rechargeable battery cell of the main battery can be suppressed. Furthermore, since the auxiliary battery can be charged using the rechargeable battery cell of a part of each rechargeable battery cell of the main battery, it is not necessary to provide a DC/DC converter for charging the auxiliary battery by dropping the output voltage of the main battery, thereby suppressing the increase in size of the apparatus.

0012In addition, when the main battery is not used, the control circuit can turn on and off the second switch, turn off the third switch, turn on the fourth switch, and charge the auxiliary battery, and then turn on and off the first and second switch respectively, turn on the third switch, and turn off the fourth switch, thereby equalizing the output voltages of the first and second rechargeable battery cells.

0013Furthermore, when the second rechargeable battery cell is charged, the control circuit can turn on and off the fourth switch, turn on the second switch, turn off the third switch, and electromagnetically couple the third and fourth coils, thereby electrically connecting the third coil to the auxiliary battery.

BRIEF DESCRIPTION OF THE DRAWINGS

0014<figref idref="DRAWINGS">FIG. 1</figref> illustrates an existing auxiliary battery charging apparatus;

0015<figref idref="DRAWINGS">FIG. 2</figref> illustrates the auxiliary battery charging apparatus according to an embodiment of the present invention;

0016<figref idref="DRAWINGS">FIG. 3</figref> is an example of the cell monitoring cell-balance/charge circuit according to an embodiment of the present invention; and

0017<figref idref="DRAWINGS">FIG. 4</figref> is a schematic diagram of an example of a timing chart of turning on and off each switch.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

0018<figref idref="DRAWINGS">FIG. 2</figref> illustrates the auxiliary battery charging apparatus according to an embodiment of the present invention. The same configuration as the configuration of the existing auxiliary battery charging apparatus <b>40</b> illustrated in <figref idref="DRAWINGS">FIG. 1</figref> is assigned the same reference numerals.

0019An auxiliary battery charging apparatus <b>1</b> illustrated in <figref idref="DRAWINGS">FIG. 2</figref> includes the main battery <b>41</b>, a cell monitoring cell-balance/charge circuit <b>2</b> for equalizing the output voltage of each of a plurality of serially connected rechargeable battery cells configuring the main battery <b>41</b>, and charging the auxiliary battery <b>43</b> (for example, a lead storage battery etc.) using a part of the rechargeable battery cells of the main battery <b>41</b>, and an ECU (electronic control unit) <b>3</b> (control unit) for controlling the operation of the cell monitoring cell-balance/charge circuit <b>2</b>. It is assumed that the auxiliary battery charging apparatus <b>1</b> according to the present embodiment is installed in the vehicle such as a hybrid vehicle, an electric vehicle, a fork lift tracks, etc. It is also assumed that the entire output voltage of a part of the rechargeable battery cells used in charging the auxiliary battery <b>43</b> is set as the voltage (for example, 12V) as high as the voltage of the fully charged auxiliary battery <b>43</b>. Furthermore, it is assumed that the auxiliary battery <b>43</b> provides power to electrical equipment such as a control circuit for controlling the drive of the motor/generator <b>44</b>, a car navigation, etc.

0020Thus, since the auxiliary battery charging apparatus <b>1</b> according to the present embodiment includes the cell monitoring cell-balance/charge circuit <b>2</b>, the variations between the output voltages of the rechargeable battery cells the main battery <b>41</b> can be suppressed.

0021In addition, since the auxiliary battery charging apparatus <b>1</b> according to the present embodiment is configured to charge the auxiliary battery <b>43</b> using a part of rechargeable battery cells of the main battery <b>41</b>, it is not necessary to include the DC/DC converter <b>42</b> as with the existing auxiliary battery charging apparatus <b>40</b> illustrated in <figref idref="DRAWINGS">FIG. 1</figref>, thereby suppressing the increase of the size of the apparatus.

0022<figref idref="DRAWINGS">FIG. 3</figref> is an example of the cell monitoring cell-balance/charge circuit <b>2</b>. It is assumed that the main battery <b>41</b> is configured by serially connecting n modules <b>5</b> (a module <b>5</b>-<b>1</b> (first rechargeable battery cell), a module <b>5</b>-<b>2</b> (first rechargeable battery cell), . . . , a module <b>5</b>-<i>n</i>-<b>1</b> (first rechargeable battery cell), and a module <b>5</b>-<i>n </i>(second rechargeable battery cell)) each configured by three serially connected battery cells <b>4</b> (for example, a rechargeable battery cell such as a lithium ion rechargeable battery cell, a nickel-metal hybrid rechargeable battery cell, etc.). The number of battery cells <b>4</b> configuring one module <b>5</b> is not limited to three.

0023The cell monitoring cell-balance/charge circuit <b>2</b> illustrated in <figref idref="DRAWINGS">FIG. 3</figref> includes a transformer <b>6</b> (first transformer), a transformer <b>7</b> (second transformer), n switches <b>8</b> (a switch <b>8</b>-<b>1</b> (first switch), a switch <b>8</b>-<b>2</b> (first switch), . . . , a switch <b>8</b>-<i>n</i>-<b>1</b> (first switch), and a switch <b>8</b>-<i>n </i>(second switch)), a switch <b>9</b> (third switch), a switch <b>10</b>, a switch <b>11</b> (fourth switch), and a voltage source <b>12</b>.

0024The transformer <b>6</b> includes a first coil <b>13</b> (first coil), and a plurality of second coils <b>14</b> (a second coil <b>14</b>-<b>1</b>, a second coil <b>14</b>-<b>2</b>, . . . , and second coil <b>14</b>-<i>n</i>-<b>1</b>) (second coil) connected in parallel to the modules <b>5</b>-<b>1</b> through <b>5</b>-<i>n</i>-<b>1</b> other than the module <b>5</b>-<i>n </i>in the modules <b>5</b>-<b>1</b> through <b>5</b>-<i>n. </i>

0025The transformer <b>7</b> includes a first coil <b>15</b> (third coil) connected to the auxiliary battery <b>43</b>, and a second coil <b>16</b> (fourth coil) connected to the module <b>5</b>-<i>n. </i>

0026The switch <b>8</b>-<b>1</b> is provided between the module <b>5</b>-<b>1</b> and the second coil <b>14</b>-<b>1</b>, the switch <b>8</b>-<b>2</b> is provided between the module <b>5</b>-<b>2</b> and the second coil <b>14</b>-<b>2</b>, . . . , the switch <b>8</b>-<i>n</i>-<b>1</b> is provided between the module <b>5</b>-<i>n</i>-<b>1</b> and the second coil <b>14</b>-<i>n</i>-<b>1</b>, and the switch <b>8</b>-<i>n </i>is provided between the module <b>5</b>-<i>n </i>and the second coil second coil <b>16</b>.

0027The switch <b>9</b> is provided between the first coil <b>13</b> of the transformer <b>6</b> and the first coil <b>15</b> of the transformer <b>7</b>.

0028The switch <b>10</b> is provided between the first coil <b>15</b> and the ground (for example, a virtual ground connected to the body of a vehicle).

0029The switch <b>11</b> is provided between the connection point of the switch <b>9</b> and the first coil <b>15</b> and the auxiliary battery <b>43</b>.

0030Assume that the ratio of the number of turns of the first coil <b>13</b> to the total number of turns of the second coils <b>14</b>-<b>1</b> through <b>14</b>-<i>n</i>-<b>1</b> is 1:1, the ratio of the number of turns of the second coils <b>14</b>-<b>1</b> through <b>14</b>-<i>n</i>-<b>1</b> to the number of turns of the second coil <b>16</b> is 1:1, and the ratio of the number of turns of the first coil <b>15</b> and the number of turns of the second coil <b>16</b> is 1:1.

0031The voltage source <b>12</b> can be configured as, for example, illustrated in <figref idref="DRAWINGS">FIG. 3</figref>, by a voltage follower circuit connected to the first coil <b>13</b> with the output of the main battery <b>41</b> input to the positive input terminal of an operational amplifier <b>17</b>, and the output of the operational amplifier <b>17</b> input to the negative input terminal of the operational amplifier <b>17</b> through a resistor <b>18</b>. Thus, by configuring the voltage source <b>12</b>, a voltage substantially equal to the output voltage (for example, 200V) of the main battery <b>41</b> can be applied to the first coil <b>13</b>.

0032The switches <b>9</b> through <b>11</b> are configured by, for example, switching elements such as relays, MOSFETs (metal oxide semiconductor field effect transistor) etc. The switch <b>9</b> is turned on and off according to a control signal SS<b>1</b> output from the ECU <b>3</b>, the switch <b>10</b> is turned on and off according to a control signal SS<b>2</b> output from the ECU <b>3</b>, and the switch <b>11</b> is turned on and off according to a control signal SS<b>3</b> output from the ECU <b>3</b>. When the switch <b>9</b> is turned on from the off state, the first coil <b>13</b> is electrically connected to the first coil <b>15</b>. When the switch <b>10</b> is turned on from the off state, the first coil <b>15</b> is electrically connected to the ground. When the switch <b>11</b> is turned on from the off state, the connection point of the switch <b>9</b> and the first coil <b>15</b> is electrically connected to the auxiliary battery <b>43</b>. Therefore, when each of the switches <b>9</b> through <b>11</b> is turned off, each of the first coils <b>13</b> and <b>15</b> and the auxiliary battery <b>43</b> is placed in the open state. When the switch <b>9</b> is turned off, and each of the switches <b>10</b> and <b>11</b> is turned on, the first coil <b>13</b> is placed in the open state, and the first coil <b>15</b> and the auxiliary battery <b>43</b> are electrically connected. Furthermore, when each of the switches <b>9</b> and <b>10</b> is turned on, and the switch <b>11</b> is turned off, the first coils <b>13</b> and <b>15</b> are electrically connected, the first coil <b>15</b> and the ground are electrically connected, and the auxiliary battery <b>43</b> is placed in the open state.

0033Each of the switches <b>8</b>-<b>1</b> through <b>8</b>-<i>n </i>is configured by, for example, a switching element such as a MOSFET etc., and is turned on and off according to the control signals S<b>1</b> through Sn output from the ECU <b>3</b>. It is assumed that the duty of each of the control signals S<b>1</b> through Sn is, for example, 50%.

0034When the output voltage of each of the modules <b>5</b>-<b>1</b> through <b>5</b>-<i>n </i>is equalized (cell balance is attained), each of the switches <b>9</b> and <b>10</b> is turned on, the switch <b>11</b> is turned off, and each of the switches <b>8</b>-<b>1</b> through <b>8</b>-<i>n </i>is turned on and off Then, the first coils <b>13</b> and <b>15</b> are electrically connected, the auxiliary battery <b>43</b> is placed in the open state, an alternating current passes through the second coils <b>14</b>-<b>1</b> through <b>14</b>-<i>n</i>-<b>1</b> and the second coil <b>16</b>, and the first coil <b>13</b>, the second coils <b>14</b>-<b>1</b> through <b>14</b>-<i>n</i>-<b>1</b>, the first coil <b>15</b>, and the second coil <b>16</b> are electrically connected. In this case, for example, when the voltage of the second coil <b>16</b> is higher than the output voltage of the module <b>5</b>-<i>n</i>, a current passes from the second coil <b>16</b> to the module <b>5</b>-<i>n</i>, and the module <b>5</b>-<i>n </i>is charged. In addition, for example, when the voltage of the second coil <b>14</b>-<b>1</b> is lower than the output voltage of the module <b>5</b>-<b>1</b>, a current passes from the module <b>5</b>-<b>1</b> to the second coil <b>14</b>-<b>1</b>, and the module <b>5</b>-<b>1</b> is discharged. Then, if the output voltages of the modules <b>5</b>-<b>1</b> through <b>5</b>-<i>n </i>are settled as an average voltage of the output voltages of the modules <b>5</b>-<b>1</b> through <b>5</b>-<i>n </i>respectively by charging and discharging each of the modules <b>5</b>-<b>1</b> through <b>5</b>-<i>n </i>respectively, that is, if the output voltage of each of the modules <b>5</b>-<b>1</b> through <b>5</b>-<i>n </i>is substantially the same voltage, each of the switches <b>8</b>-<b>1</b> through <b>8</b>-<i>n </i>is turned off, thereby terminating the cell balance. Thus, the output voltage of each of the modules <b>5</b>-<b>1</b> through <b>5</b>-<i>n </i>can be equalized.

0035During the cell balance, in the ECU <b>3</b>, the output voltage of each of the modules <b>5</b>-<b>1</b> through <b>5</b>-<i>n </i>can be monitored, and each of the switches <b>8</b>-<b>1</b> through <b>8</b>-<i>n </i>can be turned on and off until the output voltages of the modules <b>5</b>-<b>1</b> through <b>5</b>-<i>n </i>can be lower than the upper limit threshold Vthl (a value higher by a specified value than the average value of output voltages of the modules <b>5</b>-<b>1</b> through <b>5</b>-<i>n</i>), and higher than the lower limit threshold Vth<b>2</b> (a value lower by a specified value than the average value of the output voltages the modules <b>5</b>-<b>1</b> through <b>5</b>-<i>n</i>).

0036<figref idref="DRAWINGS">FIG. 4</figref> is a schematic diagram of an example of a timing chart of turning on and off each of the switches <b>8</b>-<b>1</b> through <b>8</b>-<i>n </i>and the switches <b>9</b> through <b>11</b>. When an ignition signal IG output from the upper ECU etc. for controlling the entire vehicle indicates a high level, that is, in the state in which the main battery <b>41</b> is used by the motor/generator <b>44</b> when the vehicle is driven etc., it is assumed that the control signals SS<b>1</b> through SS<b>3</b> indicate a low level, and the switches <b>9</b> through <b>11</b> are turned off.

0037First, if the ignition signal IG changes from the high level to the low level, that is, the main battery <b>41</b> changes into the state in which it is not used, for example, in the parking state of a vehicle, etc., the ECU <b>3</b> sets the control signal SS<b>1</b> as the low level, and the control signals SS<b>2</b> and SS<b>3</b> as the high level. Then, the switch <b>9</b> is turned off, the switches <b>10</b> and <b>11</b> are turned on, the first coil <b>15</b> and the auxiliary battery <b>43</b> are electrically connected, and the first coil <b>13</b> enters the open state. Furthermore, the ECU <b>3</b> turns off the switches <b>8</b>-<b>1</b> through <b>8</b>-<i>n</i>-<b>1</b> according to the control signals S<b>1</b> through S<i>n</i>−1, and turns on and off the switch <b>8</b>-<i>n </i>according to the control signal Sn. Then, an alternating current passes through the second coil <b>16</b>, and the first coil <b>15</b> and the second coil <b>16</b> of the transformer <b>7</b> are electromagnetically coupled to each other. In this case, if the voltage of the first coil <b>15</b> is higher than the voltage of the auxiliary battery <b>43</b>, a current passes from the first coil <b>15</b> to the auxiliary battery <b>43</b>, thereby charging the auxiliary battery <b>43</b>. The frequency of the control signal Sn in this case can be set based on the inductance of each of the first coil <b>15</b> and the second coil <b>16</b> and the amount of charge per unit time of the auxiliary battery <b>43</b>.

0038Then, when the monitored voltage of the auxiliary battery <b>43</b> reaches the voltage indicating the full charge, the ECU <b>3</b> sets the control signals SS<b>1</b> and SS<b>2</b> at a high level, and sets the control signal SS<b>3</b> at a low level. Then, the switches <b>9</b> and <b>10</b> are turned on, the switch <b>11</b> is turned off, the first coil <b>13</b> and the first coil <b>15</b> are connected, and the auxiliary battery <b>43</b> is placed in the open state. The ECU <b>3</b> turns on and off the switches <b>8</b>-<b>1</b> through <b>8</b>-<i>n </i>according to the control signals S<b>1</b> through Sn, and equalizes the output voltages of the modules <b>5</b>-<b>1</b> through <b>5</b>-<i>n</i>. Thus, after charging the auxiliary battery <b>43</b>, the variations between the output voltages of the modules <b>5</b>-<b>1</b> through <b>5</b>-<i>n </i>can be suppressed.

0039Thus, in the auxiliary battery charging apparatus <b>1</b> according to the present embodiment, the on and off state of the switch <b>8</b>-<i>n </i>and the switches <b>9</b> through <b>11</b> provided for the cell monitor cell-balance/charge circuit <b>2</b> can be controlled, thereby charging the auxiliary battery <b>43</b> using the module <b>5</b>-<i>n </i>which is a part of the modules <b>5</b>-<b>1</b> through <b>5</b>-<i>n </i>in the main battery <b>41</b>.

0040According to the embodiment above, after charging the auxiliary battery <b>43</b>, the output voltages of the modules <b>5</b>-<b>1</b> through <b>5</b>-<i>n </i>are equalized. However, after equalizing the output voltages of the modules <b>5</b>-<b>1</b> through <b>5</b>-<i>n</i>, the auxiliary battery <b>43</b> can be charged. With the configuration, the auxiliary battery <b>43</b> can be charged by the stable output voltage of the module <b>5</b>-<i>n. </i>

0041In addition, according to the present embodiment, the switch <b>9</b> is turned off, the switches <b>10</b> and <b>11</b> are turned on, and the switch <b>8</b>-<i>n </i>is turned on and off, thereby charging the auxiliary battery <b>43</b>. However, the switch <b>9</b> can be turned off, the switch <b>8</b>-<i>n </i>and the switch <b>11</b> can be turned on, and the switch <b>10</b> is turned on and off, thereby charging the module <b>5</b>-<i>n </i>by supplying power to the module <b>5</b>-<i>n </i>from the auxiliary battery <b>43</b> through the transformer <b>7</b>. In this case, the power charged to the module <b>5</b>-<i>n </i>can be distributed to another module <b>5</b> by performing the cell balance. Furthermore, the switch <b>9</b> can be turned off, the switch <b>8</b>-<i>n </i>and the switch <b>10</b> can be turned on, and the switch <b>11</b> can be turned on and off, thereby charging the module <b>5</b>-<i>n. </i>

0042In the embodiment above, the switch <b>8</b> is provided between the negative terminal of the module <b>5</b> and the second coils <b>14</b> and <b>16</b>, but the can also be provided between the positive terminal of the module <b>5</b> and the second coils <b>14</b> and <b>16</b>.

0043According to the present invention, with the auxiliary battery charging apparatus for charging an auxiliary battery in addition to the main battery, the variations between the output voltages of each rechargeable battery cell of the main battery can be suppressed with the increase of the size of the apparatus reduced.