Abstract:
A lithium battery pack according to the present invention has inherent information stored therein, which comprises a plurality of cells, nominal voltage, maximal voltage of the cells, range of temperature etc. A charging parameter is determined by a charging controller based on an identified data of the cells and the inherent information, and is transmitted to an adapter. A controlled module in the adapter receives the charging parameter through a control terminal and adjusts an AC/DC circuit to output a current with accurate charging voltage to the battery pack.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119 of Chinese Application 200720034976.6, filed Mar. 5, 2007, which is hereby incorporated by reference. 
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     FIELD OF THE INVENTION 
     The present invention generally relates to a lithium battery pack and charging system thereof, and more particularly, to a lithium battery pack for a power tool and system for charging the same. 
     BACKGROUND OF THE INVENTION 
     Battery powered power tools are widely used in many fields because of portability. Rechargeable lithium battery packs with advantages in weight and capacity are one of the best battery choices for power tools. Lithium battery packs have special charging requirements for safety and efficiency, however. 
     A common charging system for a lithium battery pack includes a charger that outputs power having a constant current or constant voltage for charging a battery pack which has a nominal voltage. A disadvantage is that a charger is only operable to charge a corresponding battery pack. In addition, a common charger provides different charging parameters based on information of the battery cells which are stored in the battery pack. A disadvantage is that the charger needs to obtain the relative information of the battery pack before charging, and then confirm the charging parameter, which is obviously complex. 
     SUMMARY OF THE INVENTION 
     The lithium battery pack according to the present invention has a charging controller for determining the charging parameter and sending a control signal to an adapter which provides charging energy to the battery pack. A controlled module in the adapter receives the control signal and adjusts an AC/DC circuit to output an accurate voltage. 
     Furthermore, the charging controller is integrated in the battery pack. Before the process of charging, the charging controller identifies initial data of the lithium battery cells, especially the individual voltage of each cell, through sensors, such as a voltage sensor, temperature sensor, or current sensor. The battery pack also has inherent information stored therein, which comprises a plurality of cells, nominal voltage, maximal voltage of the cells, range of temperature, etc. The charging parameter is determined by the charging controller based on the identified data of the cells and the inherent information, and transmitted to the controlled module. The controlled module receives the charging parameter through a control terminal and adjusts the AC/DC circuit to provide a current with accurate charging voltage. In the whole charging process, the charging control portion is executed in the battery pack, and the adapter is only operable for providing power as required by the battery pack. Therefore the charging process will be more accurate, rapid and safe. 
     According to one aspect of the present invention, the battery pack also includes a protection module for providing charging protection and discharging protection to ensure the safety of the lithium cells. The protection module includes a charging protection module and a discharging protection module. The charging protection module has at least one function of over-current protection, overcharge protection, over-voltage protection and monitoring voltages of individual cells; the discharging protection module has at least one function of over-current protection, short preventing and over-discharge protection. 
     According to another aspect of the invention, the electrical charging system includes a first battery pack having a plurality of lithium-based battery cells, each having an individual state of charge, wherein the first battery pack has a first charging controller operable to monitor the individual state of charge of at least one battery cell and to control a charging current being supplied to the first battery pack based at least in part on the state of charge of the at least one battery cell. The system also includes a second battery pack having a plurality of lithium-based battery cells, each having an individual state of charge, wherein the second battery pack has a second charging controller operable to monitor the individual state of charge of at least one battery cell and to control a charging current being supplied to the second battery pack based at least in part on the state of charge of the at least one battery cell. The total number of lithium-based battery cells in the first battery pack is different than the total number of lithium-based battery cells in the second battery pack. Also included is an electrical device being operable to supply power to the first battery pack and the second battery pack. 
     An advantage of the present invention is that the lithium battery pack can be charged by a common adapter or charger. An additional advantage of the present invention is that lithium-based battery packs with different charging parameters can be charged by a common adapter or charger. In addition, lithium battery packs having different numbers of cells can be charged by a common adapter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a battery pack. 
         FIG. 2  is a perspective view of an adapter. 
         FIG. 3  shows the battery pack of  FIG. 1  electrically and physically connected to the adapter of  FIG. 2 . 
         FIG. 4  shows an electrical connection between a battery pack and an adapter. 
         FIG. 5  is a circuit schematic view of an adapter. 
         FIG. 6  is a circuit schematic view of a battery pack. 
         FIGS. 7   a  and  7   b  are flowcharts illustrating charging process of the battery pack embodying the present invention. 
     
    
    
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
     DETAILED DESCRIPTION OF THE INVENTION 
     A battery pack  10  as illustrated in  FIG. 1  is adapted for providing power to a power tool. The battery pack  10  includes a housing  20  which encloses a series of battery cells (not shown) and a control circuit  30  ( FIG. 4 ). Preferably, the battery cells are made of a lithium-based chemical material. The battery pack  10  has a nominal voltage, the value of which is determined by the individual voltage of each cell and the number of cells. 
     The battery pack  10  is configured to have one or more terminals  35 - 37  and is electrically connectable to an electrical device, such as an adapter  40  and/or a power tool. In some constructions, electrical connection between the terminals  35 - 37  needs support of a physical connection between the battery pack  10  and the electrical device. In other constructions, electrical connection is confirmed by signal and then electrical energy is transmitted between the battery pack  10  and the electrical device in waves. In some constructions, as illustrated in  FIG. 1 , the battery pack  10  includes a positive battery terminal  35 , a negative battery terminal  36  and a second control terminal  37 . In some constructions, the battery pack  10  can include more or fewer terminals. 
     In one embodiment, the battery pack  10  includes a controller  60  or component electrically connected to one or more battery terminals. The controller  60  analyzes the information of the battery pack  10  stored in the circuit  30  to obtain a charging parameter, and sends the charging parameter to the electrical device physically connected thereto. The charging parameter could include, for example. The number of the cells, nominal voltage, maximal voltage, temperature range, and initial state of the battery cells or any other information defining a characteristic of the cell. In some constructions, the charging controller  60  of a battery pack  10  has a Micro Control United (MCU)  61 . 
     In another embodiment, the battery pack  10  includes a voltage sampling circuit for monitoring voltage of an individual cell  15 . The voltage sampling circuit is integrated in the charging controller  60 . 
     As shown in  FIGS. 2 and 3 , the battery pack  10  is also configured to be connectable with an electrical device, such as an adapter  40 . In some constructions, the adapter  40  includes a housing  41 . The housing  41  provides a connecting portion  42  to which the battery pack  10  is connected. The connecting portion  42  includes one or more electrical terminals for electrically connecting the adapter  40  to the battery pack  10 . The terminals provided in the adapter  40  are configured to mate with the terminals of the battery pack  10  for receiving a control signal from the pack  10  and transferring power to the battery pack  10 . 
     As illustrated in  FIG. 2 , the adapter  40  includes a positive terminal  43 , a negative terminal  44 , and a first control terminal  45 . The first control terminal  45  may be configured to mate with the second control terminal  37  of the battery pack  10 . 
     The adapter  40  may also include an AC/DC section  46  and a controlled module  47 . In some constructions, the controlled module  47  includes a center controlled module  48  and a feedback module  49  ( FIG. 5 ). The center controlled module  48  could be a MCU with relevant circuit (as is known in the art), and the feedback module  49  could be an optocoupler with relevant circuit (as is also known in the art). The controlled module  47  may also include an indication circuit (as are well known in the art). 
     As shown in  FIG. 4 , inside the battery pack  10 , the charging controller  60  determines charging mode based on the state of the cells  15  and sends a control signal to the second control terminal  37 . Inside the adapter  40 , the first control terminal  45  receives the outside signal, which contains the charging parameter, and the controlled module  47  adjusts the AC/DC section  46  to convert AC supply to DC as required. 
     The adapter as shown in  FIG. 5  includes a transformer  52 , a feedback module  49 , a Pulse-Width Modulation (PWM) controller  55 , and a power metal oxide semiconductor field effect transistor (MOSFET)  56 . The AC supply flows through an Electro Magnetic Interference (EMI) suppression circuit  57  and a primary input filtering circuit to the transformer  52 , and then passes a secondary rectification circuit to output high voltage DC, which flows through the feedback module  49  and the PWM controller  55 . The MCU sends a charging control signal to the PWM controller  55 , which control the power MOSFET  56  to obtain the required output voltage or current. 
     The power supply input circuit  60  can include a protective element, e.g., a fuse, a NTC (negative temperature coefficient) or PTC (positive temperature coefficient) resistor, or a varistor (not shown), such that when a short is induced, the current flowing through the power inputting terminal  65  will not exceed a predetermined value. Thus, the impact current occurring at the beginning of the power supplying is reduced. Moreover, surge voltage in the input line is absorbed to avoid damage of the elements in the adapter  40  caused by over voltage. Rectification circuits cam also be utilized to rectify ripple voltage in the input voltage to make it smooth, and to output a relatively steady DC voltage. Meanwhile the rectification circuits filter high frequency switching noise to improve transmitting character of the circuit. 
     The charging controller  60  of the battery pack  10  includes the MCU  61  and a MOSFET  70  which controls switching on/off of the MCU  61 , as shown in  FIG. 6 . The charging controller  60  further includes a voltage sampling circuit  71 , a current sampling circuit  72 , and a temperature sampling circuit  73 , through which the MCU  61  obtains the values of the voltage, current and temperature of the battery pack  10  and sends the charging signal to the second control terminal  37  through a matching network  74 . The MCU  61  controls the output voltage of the adapter  40  in such a way that when the temperature of the cells  15  lies within a predetermined allowed range and the voltage of an individual cell is higher than a predetermined allowed charging voltage, the battery pack  10  is charged in constant current; otherwise, when the voltage of an individual cell is equal to or greater than a desired value, e.g., 4.2V, the battery pack  10  is charged in constant voltage, while the MCU  61  monitors the temperature and current, and shuts down the charging process if the current rate is smaller than a desired value, e.g., 0.1 C. 
     The charging control workflow mainly comprises two modules, which are determination module  100  as shown in  FIG. 7A  and execution module  150  as shown in  FIG. 7B . The determination module  100  judges if an adapter is coupled to the battery pack  10  at step  105 , which is confirmed if terminals of the battery pack  10  and the adapter  40  are connected. When the adapter  40  is coupled to the pack  10 , the charging controller  60  reads the information of the adapter  40 , such as the type of adapter, range of the voltage, and range of the current, through the control terminal, and determines whether the adapter  40  mates with the battery pack  10  at step  110 . If they match with each other, the process shifts to the execution module  150 . 
     In the execution module  150 , the battery pack  10  monitors state of the cells  15  to determine whether the cells should be charged in constant voltage at step  155 . If constant-voltage charging requirement is reached, the process shifts to step  165  which is the constant-voltage charging module, otherwise the process shifts to step  160  which is the constant-current charging module. After the constant-current charging process at step  160  is finished, the process shifts to the step  165 . After the constant-voltage charging process at step  165  being finished, the charging controller  60  estimates whether the cells are fully charged at step  170 . Operation returns to step  155  if the cells are not full charged, otherwise the MOSFET  70  will end the charging process. If the battery pack  10  is still coupled with the adapter  40 , it needs to determine whether a supplemental charge is required; if yes, the process returns to step  155 , otherwise it closes the power supply. The constant-current charging and constant-voltage charging are performed by either Proportional-Integral-Differential (PID) control or fuzzy control (as are well known in the art). A temperature measuring and control module is executed during the entire charging process.