1. Field of the Invention
Example embodiments relate generally to diodes in a wire harness for cordless power tools.
2. Description of Related Art
Cordless products which use rechargeable batteries are prevalent throughout the workplace as well as in the home. From house wares to power tools, rechargeable batteries are used in numerous devices. Ordinarily, nickel-cadmium (NiCd), nickel metal hydride (NiMH) and/or Lithium-ion (Li-ion) battery cells are used in these devices.
Various battery technologies can be damaged when discharged in excess of the manufacturer's recommendations. Accordingly, in order to protect the battery pack, circuitry to prevent current flow is required when a battery voltage drops below a given voltage threshold, referred to as an under-voltage lockout. For example, a protection circuit may be employed in the battery pack and/or tool to sense the battery voltage, and if the voltage drops below a given voltage level, the circuit directs turning off of a discharge semiconductor device (e.g., a discharge FET). As a result, battery cells may still be susceptible to charge, but cannot discharge.
Accordingly, conventional battery packs with charge/discharge control and over-discharge protection have been designed primarily for low-voltage portable electronic devices. Such devices are characterized by using battery packs of secondary batteries cells (such as Li-ion, NiCd, NiMH) that provide a maximum output voltage of about 4.2 volts/cell, for example.
However, much higher voltages than described above are required for power electronic devices such as cordless power tools. Accordingly, modified NiCd battery packs that provide the same or greater power at lower weight, and Li-ion battery packs which may provide higher voltage outputs than current Li-ion batteries, and at a much reduced weight (as compared to NiCd or NiMH), are being developed. A characteristic of these battery packs is that both batteries may exhibit substantially lower impedance characteristics than conventional Li-ion, NiCd and NiMH batteries.
However, as these battery technologies advance, the introduction of lower impedance chemistries and construction styles to develop secondary batteries generating substantially higher output voltages (such as at least 11 V and up, for example) may possibly create compatibility issues with existing cordless power tools. Battery packs having lower impedance also means that the pack can supply substantially higher current to an attached electronic component, such as a power tool. As current through a motor of the attached tool increases, demagnetization forces (e.g., the number of armature turns of the motor times the current, ampere-turns) could substantially increase beyond a desired or design limit in the motor. Such undesirable demagnetization could thus potentially burn up the motor.
For example, a lower impedance electrical source could cause damage to a tool's motor when the tool is held at stall condition. During motor stall, the motor and battery impedances are the only mechanisms to limit the current since there is no back-EMF created by the motor. With a lower impedance pack, the currents would be higher. Higher currents through the motor might cause a stronger de-magnetization force than what the tool's permanent magnets were designed to withstand. Additionally, start-up of the tool could produce excessive starting currents and cause demagnetization of the motor.
Thermal overload could also be a result of using a low impedance electrical source in an existing power tool, as the new batteries may be designed to run longer and harder than what the original cordless tool system was designed. Accordingly, over-discharge or current limiting controls may need to be in place before these developing lower-impedance batteries may be use with existing cordless power tools, for example.
One current limiting approach has been through the use of diodes in the cordless power tools. A diode is a device that blocks current in one direction while permitting current to flow in another direction. The diodes can be used in a number of ways. For example, an electrical device that uses batteries often contains a diode that protects the device if the batteries are inadvertently inserted backward. The diode simply blocks current from leaving the battery if the polarity is reversed. This may serve as a protector for sensitive electronics in an electrical device such as a cordless tool. However, conventional diodes are generally large, and take up a substantial amount of space in the device. Moreover, conventional diodes are generally placed in a portion or location within the electrical device that may be easily acceptable to damage or malfunction.
An example embodiment is directed to a diode assembly for a wire harness which includes a printed circuit board (PCB), a diode connected to the PCB, and a plurality of diode lead wires extending from the PCB for external connections. The diode assembly includes a diode wire trap interfacing with the diode, and a heat sink in direct or indirect contact with one or more of the PCB, diode and diode wire trap for dissipating heat.
Example embodiments will become more apparent by describing, in detail, example embodiments thereof with reference to the attached drawings, wherein like procedures are represented by like reference numerals, which are given by way of illustration only and thus do not limit the present invention.
It should be noted that these figures are intended to illustrate the general characteristics of method and apparatus of example embodiments of this invention, for the purpose of the description of such example embodiments herein. These drawings are not, however, to scale and may not precisely reflect the characteristics of any given embodiment, and should not be interpreted as defining or limiting the range of values or properties of example embodiments within the scope of this invention.
As used herein, power tools may be understood as a cordless power tool with the use of light-weight portable power sources, such as Li-ion battery packs that may provide the commensurate power with its use. Example power tools may include, but are not limited to, drills, high torque impact wrenches, single-handed metal working tools, nailers, hand planers, circular saws, jig saws, variable speed belt sanders, reciprocating saws, two handed drills such as rotary and demolition hammerdrills, routers, cut-off tools, plate joiners, drill presses, table saws, planers, miter saws, metal working tools, chop saws, cut-off machines, bench grinders, etc. Some of these tools may currently be commercially available only in a corded version, but may become cordless. These classifications are not intended to be inclusive of all power tools in which example embodiments of the present invention may be applied, but are only illustrative.
It should further be appreciated by one skilled in the art that the battery pack includes a plurality of battery cells disposed within a battery pack housing. The battery pack may be embodied as at least one of a lithium ion (Li-ion), a nickel cadmium (NiCd), a nickel metal hydride (NiMH) and a lead-acid battery pack, for example, in terms of the chemistry makeup of individual cells, electrodes and electrolyte of the battery pack. The battery cells may be connected in series and/or parallel.
It should be understood to those skilled in the art that components of the power tool 10, such as the motor assembly 14, the transmission assembly 16, the chuck 20 and the trigger assembly 22 are conventional in nature and therefore will not be discussed in detail in the present application.
A battery pack (not shown) may be attached to a bottom portion of the power tool 10. The battery pack may be a rechargeable high power Li-ion battery pack comprised of a plurality of Li-ion cells having a Li-metal oxide or Li-metal phosphate cathode as the active material therein, for example. However, it should be appreciated that other battery cells make-up, such as, nickel cadmium (NiCd), nickel metal hydride (NiMH) and lead-acid battery pack, may be employed.
The bottom of the tool 10 contains grooves 27 positioned laterally at side ends (shown in
Referring to
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As best shown in
Although not shown, the PCB connector assembly 60 includes a plurality of surface mount technology (SMT) ID resistors. Use of SMT resistors allows flexibility in designing other components within the tool 10, and reduces the dimensions and size of the tool 10. The ID resistor is described in detail in co-pending U.S. patent application Ser. No. (Unassigned, Atty. Dkt. No. 0275A-001146/US), to the inventor, filed Oct. 27, 2006 and entitled “REMOTE ID RESISTOR ASSEMBLY FOR WIRE HARNESS”, which is hereby incorporated by reference in its entirety.
The wire harness assembly 14 further includes a diode assembly 35 which is described in more detail later. A single lead wire 17 is attached to a top surface of the diode assembly 35. As shown in
Referring to
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The diode 61 may be attached to the PCB 81 by a solder, for example. Due to the vertical mounting of the PCB 81, soldering of the diode lead wires 84, 85 to the PCB 81 may be easily performed. However, it should be appreciated that other attachment means may be employed to attach the diode 61 to the PCB 81. The diode wire trap 63 may be made from a plastic composite material; however the diode wire trap 63 may be fabricated from materials other than a plastic composite.
The diode 61 and diode wire trap 63 are attached to the heat sink 87 by a fastener 88 such as a riv-screw. However, it should be appreciated by one skilled in the art that other fastening means may be employed. The riv-screw 88 extends through a hole (not shown) in the diode 61 and eventually screws into a corresponding hole (not shown) in the heat sink 87. The riv-screw 88 secures the diode wire trap 63, diode 61 to the heat sink 87.
The diode wire trap 63 interfaces with the top surface topography of the diode 61 via protrusions (not shown for clarity) extending from the bottom surface of the diode wire trap 63. The riv screw 88 clamps through the diode wire trap 63 and diode 61 to the heat sink 87. The diode lead wires 84, 85, which extend from the PCB 81, are secured in the diode wire trap 63 via grooves (not shown for clarity) on an interior surface of the diode wire trap 63. The diode lead wires 84, 85 are vertically restrained within the grooves by an additional element (not shown) of the diode wire trap 63 which “wraps” overtop of the grooves and is secured by a locking element (not shown) that is integral to the diode wire trap 63.
A terminal connector 83 such as a board-in connector is formed at one end of lead wire 85 for connection to various components in the tool 10 such as terminals of the trigger switch 40 across the leads of the tool motor. The diode wire trap 63 further includes a plurality of connectors 95 disposed on a top surface of the diode wire trap 63 for receiving the lead wires 17 (as shown in
In one example, the heat sink 87 may have a general U-shape to surround the diode 61 and transfer heat generated from the diode 61. However, the shape of heat sink 87 may be other than U-shaped, such as flat, curved, etc. The heat sink 87 may also include projecting portions such as fins (not shown) to more effectively move heat towards the projecting portions of the heat sink 87. The heat sink 87 can be made from metal such as aluminum, copper, brass or any material that provides the necessary heat sinking effect for the diode 61.
It should be appreciated that the heat sink 87 may be any type of metallic sink with or without projecting portions, formed of a metallic or an electrically non-conductive material. Examples include but are not limited to potting compounds, gels and/or greases to extract the heat.
Referring to
The PCB 81 includes a tab member 89 near the bottom of the PCB 81. The tab member 89 permits a vertical mounting of the PCB 81 on the heat sink 87. The tab member 89 is inserted into a slot member 86 in the heat sink 87. The slot member 86 provides additional mechanical support for the PCB 81 (e.g., resisting damage from handling and/or reducing tool vibration).
The example embodiments of the present invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as departure from the spirit and scope of the example embodiments of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the invention.
This U.S. non-provisional patent application claims domestic priority under 35U.S.C. §119(e) to provisional application 60/731,854, filed Oct. 31, 2005, the entire contents of which are hereby incorporated by reference.