Patent Description:
Cordless power tools provide many advantages to traditional corded power tools. In particular, cordless tools provide unmatched convenience and portability. An operator can use a cordless power tool anywhere and anytime, regardless of the availability of a power supply. In addition, cordless power tools provide increased safety and reliability because there is no cumbersome cord to maneuver around while working on the job, and no risk of accidently cutting a cord in a hazardous work area. <CIT> discloses an electric power tool with a rechargable battery. <CIT> discloses a battery pack with a control unit and temperature sensor. <CIT> discloses an electrical tool with temperature sensors. <CIT> discloses a power tool according to the preamble of claim <NUM>.

However, conventional cordless power tools still have their disadvantages. Typically, cordless power tools provide far less power as compared to their corded counterparts. Today, operators desire power tools that provide the same benefits of convenience and portability, while also providing similar performance as corded power tools.

In cordless power tools operated via a battery pack, proper management of the temperature of the battery pack is important. While high battery temperature may damage the cells and presents a fire hazard, low battery temperature increases the impedance of the battery cells. Such a condition causes the voltage of the cells to sag well below their nominal voltage. What is needed is a mechanism that protect the battery pack in cold temperature conditions.

According to the invention, a power tool is provided including a housing; an electric motor disposed within the housing; a power terminal arranged to received electric power form a battery pack; a power switch circuit disposed between the power terminal and the electric motor; and a controller configured to control a switching operation of the power switch circuit to regulate power being supplied from the power terminal to the electric motor. The controller is configured to receive a temperature signal indicative of a temperature of the battery pack, determine if the temperature of the battery pack is below a lower temperature threshold, and operate the switching operation of the power switch circuit in a normal mode of operation if the temperature of the battery pack is greater than or equal to the low temperature threshold and in a cold mode of operation if the temperature of the battery pack is below the low temperature threshold.

According to the invention, the controller is configured to monitor a rotational speed of the electric motor and control the switching operation of the power switch circuit in a closed-loop speed control scheme in the normal mode of operation. In the in the closed-loop control scheme, the controller controls the switching operation of the power switch circuit based on the rotational speed of the motor. In an embodiment, the controller is configured to set a pulse-width modulation (PWM) duty cycle associated with the power switch circuit based on the rotational speed of the motor in closed-loop speed control.

According to the invention, the control is configured to control the switching operation of the power switch circuit in an open-loop speed control scheme in the cold mode of operation. In the open-loop control scheme, the controller controls the switching operation of the power switch circuit independently of the rotational speed of the motor.

According to an embodiment, at motor start-up, the controller sets a target speed for the electric motor and control the switching operation of the power switch circuit to gradually increase a rotational speed of the motor from zero to the target speed at a ramp-up rate. In an embodiment, the controller is configured to set the ramp-up rate to a first ramp-up rate in the normal mode of operation and to a second ramp-up rate that is smaller than the first ramp-up rate in the cold mode of operation.

According to an embodiment, the controller is configured to control a pulse-width modulation (PWM) duty cycle associated with the power switch circuit to control the rotational speed of the motor. The controller sets a target PWM duty cycle and increases the PWM duty cycle from zero to the target PWM duty cycle at the first ramp-up rate in the normal mode of operation and at the second-ramp-up rate in the cold mode of operation.

According to an embodiment, the controller is configured to return from the cold mode of operation to the normal mode of operation if the temperature of the battery pack is greater than or equal to a high temperature threshold that is greater than the low temperature threshold.

The drawings described herein are for illustration purposes only and are not intended to limit the scope of this disclosure in any way.

The following description illustrates the claimed invention by way of example and not by way of limitation. The description clearly enables one skilled in the art to make and use the disclosure, describes several embodiments, adaptations, variations, alternatives, and uses of the disclosure, including what is presently believed to be the best mode of carrying out the claimed invention. Additionally, it is to be understood that the disclosure is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. The disclosure is capable of other embodiments and of being practiced or being carried out in various ways.

As shown in <FIG>, according to an embodiment of the invention, a power tool <NUM> is provided including a housing <NUM> having a gear case <NUM>, a field case <NUM>, a handle portion <NUM>, and a battery receiver <NUM>. <FIG> provides a perspective view of the tool <NUM>. <FIG> provides a side view of tool <NUM> including its internal components. <FIG> and <FIG> depict two exploded views of tool <NUM>. Power tool <NUM> as shown herein is an angle grinder with the gear case <NUM> housing a gear set (not shown) that drives a spindle <NUM> arranged to be coupled to a grinding or cutting disc (not shown) via a flange (or threaded nut) <NUM> and guarded by a disc guard <NUM>. It should be understood, however, that the teachings of this disclosure may apply to any other power tool including, but not limited to, a saw, drill, sander, and the like.

In an embodiment, the field case <NUM> attaches to a rear end of the gear case <NUM> and houses a motor <NUM> operatively connected to the gear set <NUM>. The handle portion <NUM> attaches to a rear end <NUM> of the field case <NUM> and includes a trigger assembly <NUM> (also referred to as an actuator) operatively connected to a control module <NUM> disposed within the handle portion <NUM> for controlling the operation of the motor <NUM>. The battery receiver <NUM> extends from a rear end <NUM> of the handle portion <NUM> for detachable engagement with a battery pack (not shown) to provide power to the motor <NUM>. The control module <NUM> is electronically coupled to a power module <NUM> disposed substantially adjacent the motor <NUM>. The control module <NUM> controls a switching operation of the power module <NUM> to regulate a supply of power from the battery pack to the motor <NUM>. The control module <NUM> uses the input from the trigger assembly <NUM> to control the switching operation of the power module <NUM>. In an exemplary embodiment, the battery pack may be a <NUM> volt max lithium-ion type battery pack, although battery packs with other battery chemistries, shapes, voltage levels, etc. may be used in other embodiments.

In various embodiments, the battery receiver <NUM> and battery pack may be a sliding pack disclosed in <CIT>. However, any suitable battery receiver and battery back configuration, such as a tower pack or a convertible 20V/60V battery pack as disclosed in <CIT>, can be used. The present embodiment is disclosed as a cordless, battery-powered tool. However, in alternate embodiments power tool can be corded, AC-powered tools. For instance, in place of the battery receiver and battery pack, the power tool <NUM> include an AC power cord coupled to a transformer block to condition and transform the AC power for use by the components of the power tools. Power tool <NUM> may for example include a rectifier circuit adapted to generate a positive current waveform from the AC power line. An example of such a tool and circuit may be found in <CIT>.

Referring to <FIG>, the trigger assembly <NUM> is a switch electrically connected to the control module <NUM> as discussed above. The trigger assembly <NUM> in this embodiment is an ON/OFF trigger switch pivotally attached to the handle <NUM>. The trigger <NUM> is biased away from the handle <NUM> to an OFF position. The operator presses the trigger <NUM> towards the handle to an ON position to initiate operation of the power tool <NUM>. In various alternate embodiments, the trigger assembly <NUM> can be a variable speed trigger switch allowing the operator to control the speed of the motor <NUM> at no-load, similar to variable-speed switch assembly disclosed in <CIT>. However, any suitable input means can be used including, but not limited to a touch sensor, a capacitive sensor, or a speed dial.

In an embodiment, power tool <NUM> described herein is high-power power tool configured to receive a 60V max battery pack or a 60V/20V convertible battery pack configured in its 60V high-voltage-rated state. The motor <NUM> is accordingly configured for a high-power application with a stator stack length of approximately <NUM>. Additionally, as later described in detail, the power module <NUM>, including its associated heat sink, is located within the field case <NUM> in the vicinity of the motor <NUM>.

While embodiments depicted herein relate to a DC-powered power tool powered by a battery pack, it is noted that the teachings of this disclosure also apply to an AC-powered tool, or an AC/DC power tool as disclosed in <CIT>.

<FIG> depict two perspective views of motor <NUM>, according to an embodiment. <FIG> depicts an exploded view of the motor <NUM>, according to an embodiment. As shown in these figures, the motor <NUM> is a three-phase brushless DC (BLDC) motor having a can or motor housing <NUM> sized to receive a stator assembly <NUM> and a rotor assembly <NUM>. Various aspects and features of the motor <NUM> are described herein in detail. It is noted that while motor <NUM> is illustratively shown in <FIG> as a part of an angle grinder, motor <NUM> may be alternatively used in any power tool or any other device or apparatus.

In an embodiment, rotor assembly <NUM> includes a rotor shaft <NUM>, a rotor lamination stack <NUM> mounted on and rotatably attached to the rotor shaft <NUM>, a rear bearing <NUM> arranged to axially secure the rotor shaft <NUM> to the motor housing <NUM>, a sense magnet ring <NUM> attached to a distal end of the rotor shaft <NUM>, and fan <NUM> also mounted on and rotatably attached to the rotor shaft <NUM>. In various implementations, the rotor lamination stack <NUM> can include a series of flat laminations attached together via, for example, an interlock mechanical, an adhesive, an overmold, etc., that house or hold two or more permanent magnets (PMs) therein. The permanent magnets may be surface mounted on the outer surface of the lamination stack <NUM> or housed therein. The permanent magnets may be, for example, a set of four PMs that magnetically engage with the stator assembly <NUM> during operation. Adjacent PMs have opposite polarities such that the four PMs have, for example, an N-S-N-S polar arrangement. The rotor shaft <NUM> is securely fixed inside the rotor lamination stack <NUM>. Rear bearing <NUM> provide longitudinal support for the rotor <NUM> in a bearing pocket (described later) of the motor housing <NUM>.

In an embodiment, fan <NUM> of the rotor assembly <NUM> includes a back plate <NUM> having a first side <NUM> facing the field case <NUM> and a second side <NUM> facing the gear case <NUM>. A plurality of blades <NUM> extend axially outwardly from first side <NUM> of the back plate <NUM>. Blades <NUM> rotate with the rotor shaft <NUM> to generate an air flow as previously discussed. When motor <NUM> is fully assembled, fan <NUM> is located at or outside an open end of the motor housing <NUM> with a baffle <NUM> arranged between the stator assembly <NUM> and the fan <NUM>. The baffle <NUM> guides the flow of air from the blades <NUM> towards the exhaust vents <NUM>.

<FIG> depict exploded views of the power module <NUM> adjacent the motor <NUM>, according to an embodiment. As shown herein, in an embodiment, power module <NUM> includes a power board <NUM>, a thermal interface <NUM>, and a heat sink <NUM> which attach to the rear end of the motor housing <NUM> via fasteners <NUM>. Power module <NUM> may be further provided with a clamp ring <NUM> that acts to clamp and cover the power board <NUM> and act as a secondary heat sink. Power module <NUM> may be disc-shaped to match the cylindrical profile of the motor <NUM>. Additionally, power module <NUM> may define a center through-hole <NUM> that extends through the power board <NUM> to accommodate the rotor shaft <NUM> in some embodiments. In an embodiment, through-holes <NUM>, <NUM>, and <NUM> similarly extend through the clamp ring <NUM>, thermal interface <NUM>, and heat sink <NUM>, as further described later.

In an embodiment, power board <NUM> is a generally disc-shaped printed circuit board (PCB) with six power transistors <NUM>, such as MOSFETs and/or IGTBs, that power the stator windings <NUM> of the motor <NUM>, on a first surface thereof. Power board <NUM> may additionally include other circuitry such as the gate drivers, bootstrap circuit, and all other components needed to drive the MOSFETs and/or IGTBs. In addition, power board <NUM> includes a series of positional sensors (e.g., Hall sensors, not shown) on a second surface thereof opposite the first surface, as explained later in detail.

In an embodiment, power board <NUM> is electrically coupled to a power source (e.g., a battery pack) via power lines <NUM> for supplying electric power to the transistors <NUM>. Power board <NUM> is also electrically coupled to a controller (e.g., inside control unit <NUM> in <FIG>) via control terminal <NUM> to receive control signals for controlling the switching operation of the transistors <NUM>, as well as provide positional signals from the positional sensors <NUM> to the controller. The transistors <NUM> may be configured, for example, as a three-phase bridge driver circuit including three high-side and three low-side transistors connected to drive the three phases of the motor <NUM>, with the gates of the transistors <NUM> being driven by the control signals from the control terminal <NUM>. Examples of such a circuit may be found in <CIT>. In an embodiment, power board <NUM> includes slots <NUM> for receiving and electrically connecting to the input terminals <NUM>. In an embodiment, slots <NUM> may be defined and spread around an outer periphery of the power board <NUM>. The outputs of the transistors bridge driver circuit is coupled to the motor <NUM> phases via these input terminals <NUM>. Referring to <FIG>, a circuit block diagram of power tool <NUM> including a motor <NUM> and a motor control circuit <NUM> is depicted, according to an embodiment. In an embodiment, motor control circuit <NUM> includes a power unit <NUM> and a control unit <NUM>. In <FIG>, power tool <NUM> received DC power from a DC power source such as a battery pack via B+ and B- terminals.

In an embodiment, power unit <NUM> may include a power switch circuit <NUM> coupled between the power source B+/B- terminals and motor windings to drive BLDC motor <NUM>. In an embodiment, power switch circuit <NUM> may be a three-phase bridge driver circuit including six controllable semiconductor power devices (e.g. FETs, BJTs, IGBTs, etc.), such as power devices <NUM> shown in <FIG>.

In an embodiment, control unit <NUM> may include a controller <NUM>, a gate driver <NUM>, a power supply regulator <NUM>, and a power contact switch <NUM>. In an embodiment, controller <NUM> is a programmable device arranged to control a switching operation of the power devices in power switching circuit <NUM>. In an embodiment, controller <NUM> receives rotor rotational position signals from a set of position sensors <NUM> provided in close proximity to the motor <NUM> rotor. In an embodiment, position sensors <NUM> may be Hall sensors. It should be noted, however, that other types of positional sensors may be alternatively utilized. It should also be noted that controller <NUM> may be configured to calculate or detect rotational positional information relating to the motor <NUM> rotor without any positional sensors (in what is known in the art as sensorless brushless motor control). Controller <NUM> may also receive a variable-speed signal from variable-speed actuator or a speed-dial. Based on the rotor rotational position signals from the position sensors <NUM> and the variable-speed signal, controller <NUM> outputs drive signals UH, VH, WH, UL, VL, and WL through the gate driver <NUM>, which provides a voltage level needed to drive the gates of the semiconductor switches within the power switch circuit <NUM> in order to control a PWM switching operation of the power switch circuit <NUM>.

In an embodiment, power supply regulator <NUM> may include one or more voltage regulators to step down the power supply to a voltage level compatible for operating the controller <NUM> and/or the gate driver <NUM>. In an embodiment, power supply regulator <NUM> may include a buck converter and/or a linear regulator to reduce the power voltage of power supply interface <NUM>-<NUM> down to, for example, 15V for powering the gate driver <NUM>, and down to, for example, <NUM>. 2V for powering the controller <NUM>.

In an embodiment, power contact switch <NUM> may be provided between the power supply regulator <NUM> and the gate driver <NUM>. Power contact switch <NUM> may be an ON/OFF switch coupled to the ON/OFF trigger or the variable-speed actuator to allow the user to begin operating the motor <NUM>, as discussed above. Power contact switch <NUM> in this embodiment disables supply of power to the motor <NUM> by cutting power to the gate drivers <NUM>. It is noted, however, that power contact switch <NUM> may be provided at a different location. In an alternative embodiment, power contact switch <NUM> is provided within the power unit <NUM> between the battery terminal (B+ and/or B-) and the power switch circuit <NUM>. It is further noted that in an embodiment, power tool <NUM> may be provided without an ON/OFF switch <NUM>, and the controller <NUM> may be configured to activate the power devices in power switch circuit <NUM> when the ON/OFF trigger (or variable-speed actuator) is actuated by the user.

<FIG> depicts a block circuit diagram of power tool <NUM> that received powers from an AC power supply such as, for example, an AC power generator or the power grid. As the name implies, BLDC motors are designed to work with DC power. Thus, in an embodiment, power unit <NUM> is provided with a rectifier circuit <NUM> between the power supply and the power switch circuit <NUM>. In an embodiment, power from the AC power lines as designated by VAC and GND is passed through the rectifier circuit <NUM> to convert or remove the negative half-cycles of the AC power. In an embodiment, rectifier circuit <NUM> may include a full-wave bridge diode rectifier <NUM> to convert the negative half-cycles of the AC power to positive half-cycles. Alternatively, in an embodiment, rectifier circuit <NUM> may include a half-wave rectifier to eliminate the half-cycles of the AC power. In an embodiment, rectifier circuit <NUM> may further include a bus capacitor <NUM>. In another embodiment, active rectification may be employed, e.g., for active power factor correction. In an embodiment, bus capacitor <NUM> may have a relatively small value to reduce voltage high-frequency transients on the AC power supply. <FIG> depicts an exemplary power switch circuit <NUM> having a three-phase inverter bridge circuit, according to an embodiment. As shown herein, the three-phase inverter bridge circuit includes three high-side FETs and three low-side FETs. The gates of the high-side FETs driven via drive signals UH, VH, and WH, and the gates of the low-side FETs are driven via drive signals UL, VL, and WL. In an embodiment, the drains of the high-side FETs are coupled to the sources of the low-side FETs to output power signals PU, PV, and PW for driving the BLDC motor <NUM>.

<FIG> depicts an exemplary waveform diagram of a pulse-width modulation (PWM) drive sequence of the three-phase inventor bridge circuit of <FIG> within a full <NUM> degree conduction cycle. As shown in this figure, within a full <NUM>° cycle, each of the drive signals associated with the high-side and low-side power switches is activated during a <NUM>° conduction band ("CB"). In this manner, each associated phase of the BLDC <NUM> motor is energized within a <NUM>° CB by a pulse-width modulated voltage waveform that is controlled by the control unit <NUM> as a function of the desired motor <NUM> rotational speed. For each phase, the high-side switch is pulse-width modulated by the control unit <NUM> within a <NUM>° CB. During the CB of the high-side switch, the corresponding low-side switch is kept low, but one of the other low-side switches is kept high to provide a current path between the power supply and the motor windings. The control unit <NUM> controls the amount of voltage provided to the motor, and thus the speed of the motor, via PWM control of the high-side switches.

It is noted that while the waveform diagram of <FIG> depicts one exemplary PWM technique at <NUM>° CB, other PWM methods may also be utilized. One such example is PWM control with synchronous rectification, in which the high-side and low-side switch drive signals (e.g., UH and UL) of each phase are PWM-controlled with synchronous rectification within the same <NUM>° CB.

One aspect of the invention is described herein with reference to <FIG>.

<FIG> depicts control unit <NUM> of <FIG> and <FIG> according to an additional and/or alternative embodiment of the invention. As shown here, the control unit <NUM> is provided, in addition or in place of power contact switch <NUM>, with a main solid-state switch <NUM> on the path of the Vcc power line from the power supply regulator <NUM> to the gate drivers <NUM>. Main switch <NUM> in this embodiment is a MOSFET, though it must be understood that the main switch <NUM> may alternatively be an IGBT or any other solid-state switch capable of carrying sufficient current to power the gate driver circuit <NUM>. In this embodiment, main switch <NUM> is a P-type switch. It must also be understood that main switch <NUM> may be alternatively disposed at other locations within the power tool to cut off power from the power supply to the motor, e.g., between the power supply regulator <NUM> and the controller <NUM>.

In an embodiment, the gate of main switch <NUM> is controlled by the controller <NUM> via a secondary sold-state switch <NUM>. Secondary switch <NUM> is disposed between a ground signal (Gnd) and the gate of the main switch <NUM> and its gate is controlled via the controller <NUM>. The gate of the main switch <NUM> is also coupled to the Vcc signal through resistor <NUM>. Under normal operating conditions, the gate of main switch <NUM> is driven via the Gnd signal and kept ON. The resistor <NUM> allows for the Gnd signal to trump the Vcc signal and activate the main switch <NUM>. When a condition occurs that prompts the controller <NUM> to shut power to the motor, the controller <NUM> deactivates the gate of the secondary switch <NUM> via the VCC_SHUTDOWN signal, which is an active-high signal. This in turn decouples the gate of the main switch <NUM> from Gnd. The Vcc signal drives the gate of the main switch high, which turns off the main switch <NUM> and cuts off power from the power supply regulator <NUM> to the gate driver <NUM>. Such a condition may include, but is not limited to, trigger release by the user, a battery fault condition (e.g., over-current, over temperature, under-voltage), a tool fault condition (e.g., over-temperature, over-current, stall, etc.), or a motor fault condition (e.g., over-speed, or incorrect rotation of the motor). The controller <NUM> may receive a fault signal from the battery pack (not shown) and initiate shut-down accordingly when a battery fault condition occurs. Additionally and/or alternatively, the controller <NUM> may monitor various tool, motor, or battery operations and initiate shut-down on its own when it detects a fault condition, and initiates tool shutdown via the secondary switch <NUM>.

As for motor fault conditions, in an embodiment, the controller <NUM> may use the hall signals Hall U, Hall V, and Hall W signals to determine the rotational output speed and the direction of rotation of the motor. In the event the motor is rotating beyond a prescribed threshold speed (e.g., <NUM> rpm for a grinder application), or in an incorrect direction, the controller <NUM> may determine that there is a motor fault condition. Upon detection of a motor fault condition, the controller <NUM> initiates tool shut-down via the secondary switch <NUM>.

According to an embodiment, the primary controller <NUM> may fail at times for various electro-mechanical or software reasons. Such failures may include software bugs, contaminated routing and/or wiring, or a faulty micro-controller chip. It is thus important to protect users in the event of a controller <NUM> failure, particularly from motor failures that can physically harm the user. Accordingly, in an embodiment of the invention, an additional redundant controller <NUM> may be provided. Redundant controller <NUM> may be, for example, a low cost, <NUM>-bit micro-controller (such as a PIC10F200 Microchip®) that is substantially smaller in size and more inexpensive than the main controller <NUM>. In an embodiment, redundant controller <NUM> includes, in addition to power terminals Vdd+ and Vdd-, two input terminals that receive two of the hall signals (in this case Hall U and Hall V signals) and an output terminal that outputs a VCC_Shutdown_2 signal. VCC_Shutdown_2 signal is an active-high signal coupled to a gate of a third solid-state switch <NUM>, disposed in series with the secondary switch <NUM>, as shown in <FIG>. The redundant controller <NUM> determines the speed and rotational direction of the motor based on the two hall signals. If the detected speed (as determined by the time gap between the hall signals) exceeds a pre-programmed threshold, or if the sequence of the signals is opposite a pre-programmed direction indicative of an incorrect rotational direction of the motor, the redundant controller <NUM> deactivates the third switch <NUM> by disabling the VCC_Shutdown_2 signal, which in turn turns off the main switch <NUM>. This arrangement allows either the main controller <NUM> or the redundant controller <NUM> to shut off power to the motor in the event of a motor over-speed or incorrect rotation.

In this embodiment, the rotational direction of the motor is pre-programmed into the redundant controller. Such an arrangement is suitable for uni-directional tools such as a grinder. Alternatively, a redundant controller <NUM> may receive a desired rotation signal (e.g., from a forward-reverse bar in a drill or an impact driver) and compare the detected rotation to the desired rotation to determine if the motor is rotating in the correct direction.

Also, in this embodiment, the controller <NUM> and redundant controller <NUM> monitor the rotational speed and/or direction of the motor <NUM> via Hall signals Hall_U, Hall_V, and Hall_W received from positional sensors <NUM>. It must be understood, however, that the teachings of this disclosure may apply to a sensorless brushless motor system, and controller <NUM> and redundant controller <NUM> may determine the speed and/or direction of the motor <NUM> via any sensorless speed control means, e.g., by monitoring a back electro-magnetic force (back-EMF) voltage of the motor, vector-space control, etc..

Another aspect of the invention is described herein with reference to <FIG> and with continued reference to <FIG>.

Many of today's cordless power tools use lithium-ion battery packs to power the motor. An inherent characteristic of lithium-ion battery cells is that they cannot recover or be recharged for reuse once they are discharged below a minimum voltage threshold. For that reason, power tools and/or battery pack controls typically include a discharge control mechanism to ensure that the lithium-ion cells of the battery pack are not over-discharged. Such a discharge control typically monitors the state of charge (e.g., cell voltage) of the battery pack cells and shut off power supply from the battery pack in the event that the state of charge is below the minimum voltage threshold.

A problem arises when a battery pack is plugged into the power tool and the power tool is in a "stuck trigger" condition. This condition occurs when the tool trigger is inadvertently depressed (e.g., when placed against an object in a tool bag). Actuation of the trigger switch creates a path for leakage current to discharge from the battery pack even when the tool is not in use. This leakage current continues to power the controller <NUM>, and although the leakage current is relatively small, it can over-discharge the battery pack. The controller <NUM> is unable to disable the battery pack even when a battery under-voltage condition is detected. A mechanism is needed to ensure that this "stuck trigger' condition does not over-discharge the battery pack.

For example, in <FIG>, in a "stuck trigger" condition, power contact switch <NUM> continues to power the controller <NUM> through the power supply regulator <NUM>, creating a leakage path for the battery pack. As previously described, the power contact switch <NUM> may be disposed between power supply regulator <NUM> and the gate driver <NUM> and/or the controller <NUM>. Alternatively, the power contact switch <NUM> may be disposed between the battery terminal (B+ and/or B-) and the power switch circuit <NUM>. This embodiment is described, by way of example, with respect to the latter arrangement of the power contact switch <NUM>. In order to ensure that inadvertent trigger depression does not over-discharge the battery pack, in an embodiment of the invention, power supply regulator <NUM> circuit, as described with reference to <FIG>, is additionally provided with a leakage shutdown circuit <NUM>, described herein with reference to <FIG>.

In an embodiment, the power supply regulator <NUM> includes one or more voltage regulators (not shown) arranged to step down the voltage of the power supply to produce the Vcc and Vdd voltage signals, which are suitable for operating the controller <NUM> and/or the gate driver <NUM>. Resistor R-Load in this circuit represents the load asserted by the voltage regulators.

In an embodiment, the power supply regulator <NUM> includes B+ and B-terminals coupled respectively to the B+ and B- nodes of the battery pack.

Power supply regulator <NUM> also includes a solid-state load switch <NUM> provided between the B+ terminal and R-Load. When the load switch <NUM> is off, the B+ terminal is cut off from the load R-Load, thus minimizing the leakage current being discharged from the battery pack.

In an embodiment, the power supply regulator <NUM> also includes a SW_Battery terminal, which is connected to the output of power contact switch <NUM>. In other words, power contact switch <NUM> is disposed on the current path from the battery terminal B+ to both the power supply regulator <NUM> and the power switch circuit <NUM>. The power contact switch <NUM> closes when the trigger switch (e.g., trigger <NUM> in <FIG>) is actuated.

In an embodiment, an input voltage signal from the SW_Battery terminal is coupled to a gate of a control switch <NUM>, which is in turn coupled to the gate of load switch <NUM>. When the battery pack is plugged into the tool <NUM> and the tool trigger switch <NUM> is actuated, the input voltage signal through the SW_Battery terminal activates the control switch <NUM>. Activation of the control switch <NUM> grounds the gate of the load switch <NUM>, which in this embodiment is a P-type solid state switch and is turned on when its gate is grounded. This occurrence connects R-Load to the B+ terminal through diode D1, thus supplying power form the battery pack to the load R-Load.

This connection powers up the controller <NUM>. In an embodiment, the controller <NUM> is in turn configured to initiate a self-activating feedback signal Self_ON upon being powered ON. The Self_ON signal continues to keep the control switch <NUM>, and thus the load switch <NUM>, ON for as long as the controller <NUM> desires.

In an embodiment, controller <NUM> can also read the status of the trigger switch (i.e., switch <NUM> and/or signal SW_Battery) through a logic signal (herein represented by Trig_Logic). In an embodiment, the Trig_Logic signal is coupled in parallel with the C1 capacitor, across the B- terminal and the output of the power contact switch <NUM>, within power unit <NUM>. Trigger_Logic signal is coupled to a node between resistors R2 and R3 disposed in series across the B- terminal and the output of the power contact switch <NUM>. R2 and R3 resistors are sized to produce a suitable voltage logic signal on the Trig_Logic signal when power contact switch <NUM> is closed.

In an embodiment, if the Trig-Logic signal is high for an extended period of time (e.g., longer than <NUM> minutes), the controller <NUM> may determine a "stuck trigger" condition, i.e., that the trigger <NUM> has been left depressed inadvertently. Absent the leakage shutdown circuit <NUM> described in detail herein, the controller <NUM> in unable to deactivate the load switch <NUM> to cut off supply of power to R-Load, and the controller <NUM> and/or gate driver <NUM> continue to place a load on the battery pack.

To enable the controller <NUM> to shut down the load switch <NUM> while the trigger switch <NUM> is still depressed, in an embodiment, the leakage shutdown circuit <NUM> is provided on the current path from the SW_Battery terminal to gate of switch <NUM>. The leakage shutdown circuit <NUM> is activated via a self-deactivating Self_OFF signal from the controller <NUM>, and is operable to cut off the voltage signal from the SW_Battery terminal.

In an embodiment, the leakage shutdown circuit <NUM> is provided with a logic-state override switch <NUM>. In an embodiment, override switch <NUM> is disposed between the SW_Battery and B- terminals, and is coupled together with the SW_Battery terminal to the gate of the control switch <NUM>. During normal operation, the override switch <NUM> is kept OFF. When switch <NUM> is turned ON, it overrides the SW_Battery terminal signal through resister R4 and grounds the gate of control switch <NUM>, which in turn disables load switch <NUM>.

In an embodiment, when the controller <NUM> determines a "stuck trigger" condition, it initiates tool shutdown by deactivating the Self_ON signal and simultaneously activating the Self_OFF signal. The Self_OFF signal is coupled to the gate of the override switch <NUM>, and thus disables the control switch <NUM>, and subsequently load switch <NUM>, once the controller <NUM> determines a "struck trigger" condition.

Once the load switch <NUM> is turned OFF, it cuts power to the controller <NUM>. The Self_OFF signal can therefore be active for a very short period of time. In order to prevent the SW_Battery terminal from reactivating the control switch <NUM> and load switch <NUM> after the controller <NUM> loses power, the leakage shutdown circuit <NUM> is provided with a latch circuit including a first switch <NUM> and a second switch <NUM>. In an embodiment, the Self_OFF signal turns ON third switch <NUM>, which is disposed between the B- node and the gate of the second switch <NUM>. The second switch <NUM> is a P-type switch, and is therefore activated when the Self_OFF signal is high. The second switch <NUM> in turn couples the SW_Battery terminal to the gate of override switch <NUM> to keep override switch <NUM> ON. The B+ power through the SW_Battery terminal continues to keep override switch <NUM> ON even after the controller <NUM> loses power and the Self_OFF signal is disabled. The battery B+ power line is also coupled to the gate of first switch <NUM> to create a latching circuit for the gate of override switch <NUM> even after the Self_OFF signal is disabled. In an embodiment, this latching mechanism continues to keep switch <NUM> ON as long as the "stuck trigger" condition persists.

Another aspect of the invention is described herein with reference to <FIG> and <FIG>.

Use of a solenoid switch for AC power tools is well known. A solenoid switch, as shown in <FIG>, is made up on a spring-loaded power contact switch, and a solenoid. When the user presses the power tool ON/OFF switch against the force of the spring, it closes the switch. The solenoid is then energized via the electric power from the AC power source, which then asserts a magnetic force on the contact switch to keep the contact switch closed against the force of the spring.

A solenoid switch is typically used in AC power tools as a "no-volt" protection mechanism. A "no-volt" condition refers to a situation where the tool is plugged in while the power switch is in the ON position, which starts the motor immediately after the user has plugged it in. This is dangerous to the user and the work environment. By using a solenoid switch in place of a regular ON/OFF switch, the load of the spring pops the switch every time AC power is cut off from the tool. Thus, a no-volt condition is avoided the next time the tool is plugged into an AC power source.

<CIT> describes various high power cordless DC and AC/DC power tools, such as 60V or 120V power tools employing one or more 60V DC battery packs. These may include fixed-seed power tools such as cordless table saws, compressors, etc. that are conventionally corded AC tools. Instead of a trigger switch, such tools are typically provided with a current-carrying mechanical ON/OFF power switch that cuts off power from the power supply to the motor. The "no-volt" condition describes may be an issue in such tools where, for example, the battery pack (or battery packs) are inserted into the tool while the power switch is in the ON position. In addition, such tools should provide the controller the ability to shut the tool down in the event of detection of a battery pack, tool, or motor fault condition previously described.

Thus, according to an embodiment of the invention, as shown in the block diagram <NUM> of <FIG> for a high power DC cordless power tool, a switching arrangement <NUM> is provided on the DC bus line between the battery terminals B+/B- and the power switch circuit <NUM>. In an embodiment, the switching arrangement includes a solenoid switch having a spring-loaded contact ON/OFF power switch <NUM> and a solenoid <NUM>. When the user presses the ON/OFF power switch against the force of the spring, it closes the switch, which couples the power source to the tool circuitry. The solenoid <NUM>, which is arranged across the B+ and B- terminals, is then energized and asserts a magnetic force on the power switch <NUM> to keep the power switch closed against the force of the spring. By using a solenoid switch in place of a regular ON/OFF switch, the load of the spring pops the power switch <NUM> every time the battery pack is removed from the power tool, regardless of whether the user indeed turns off the power switch <NUM>. Thus, a no-volt condition is avoided the next time another battery pack is inserted into the tool battery receptacle.

Additionally, according to an embodiment, a solid-state semiconductor switch <NUM> is provided in series with the solenoid <NUM> across the B+ and B-terminals. The semiconductor switch <NUM> is controllable by the controller <NUM> via a control signal MC. The controller <NUM> may deactivate the switch <NUM> via the MC signal upon detection of a fault condition. Such conditions may include, but are not limited to, a battery fault (e.g., over-current, over temperature, under-voltage) condition, a tool fault (e.g., over-temperature, over-current, stall, etc.) condition, or a motor fault (e.g., over-speed, or incorrect rotation) condition. When switch <NUM> is deactivated by the controller <NUM>, it cuts off the solenoid <NUM> from the power supply, which in turn pops the power switch <NUM>. Thus, in addition to no-volt protection by the solenoid switch, the controller <NUM> can also de-energize the solenoid to shut off the power switch <NUM> upon detection of any fault condition.

Another aspect of the invention is described herein with reference to <FIG>.

In a DC power tool operated via a battery pack, proper management of the temperature of the battery pack is important. While high battery temperature may damage the cells and presents a fire hazard, low battery temperature increases the impedance of the battery cells. Such a condition causes the voltage of the cells to sag well below their nominal voltage by <NUM>% at full charge and by up to <NUM>% at a lower state of charge during tool start up. During normal operation of the power tool, the controller <NUM> is configured to execute various tool and motor control algorithms that optimize the performance of the power tool.

For example, in an embodiment, during normal operation, the controller <NUM> may be configured to monitor the state of charge of the battery pack and shut off power from the battery pack in the event of a cell under voltage condition (e.g., when the battery cell voltage falls to less than 2V / cell).

In an embodiment, during normal operation, the controller <NUM> may also be configured to execute a "soft-start" algorithm, where the pulse-width modulation (PWM) duty cycle of the motor drive signals is gradually increased from zero to a target PWM (e.g., at a rate of <NUM>% every <NUM>) until the motor rotational speed reaches a target speed set. This target speed may be set to a predetermined value for fixed-speed tools, or may be set in accordance to a trigger switch or a speed dial position for variable-speed tools.

In an embodiment, during normal operation, the controller <NUM> may also be configured to execute closed-loop speed control for the rotational speed of the motor. Closed-loop speed control refers to a speed control mechanism in which the rotational speed of the motor is set, not just based on trigger or speed dial position, but also based on the actual rotational speed of the motor. In an embodiment, the controller <NUM> may set a target speed based on the trigger or speed dial position, determine the actual rotational speed of the tool using the rotor positional sensors, and adjust motor speed so that the actual rotational speed of the motor matches the target speed. Thus, as load is applied to the tool, more power is supplied to the motor so as to maintain relatively constant output speed. In an embodiment, the controller <NUM> may do this by adjusting the PWM duty cycle. Additionally and/or alternatively, the controller <NUM> may adjust the conduction band and/or angle advance for each phase of the motor commutation.

When the battery pack is tool cold, the aforementioned battery management and tool control operations may require substantially more current that the battery pack can optimally handle due to the low impedance of the battery cells in cold temperatures. This adversely affects the life of the battery pack.

In order to optimize battery and motor performance while the battery pack is still cold, particularly during tool start up, according to an embodiment of the invention, the controller <NUM> is configured to perform certain battery management and tool control operations differently than during normal operation.

For example, in an embodiment, during "cold pack" mode of operation, the controller <NUM> may be configured to set a lower battery cell under-voltage threshold (e.g., <NUM>. 2V / cell rather than the normal 2V / cell). This prevents undesired battery shutdown while the battery pack is still cold.

Furthermore, in an embodiment, during cold pack operation, the controller <NUM> may be configured to set a soft-start ramp-up rate that is lower than the ramp-up rate during the normal mode of operation. For example, instead of increasing the PWM ramp-up at a rate of <NUM>% every <NUM>, the controller <NUM> may increase the PWM ramp-up at a rate of <NUM>% every <NUM>. This prevents heavy increases in current draw from the battery pack while it is still cold.

Furthermore, in an embodiment, during cold operation, the controller <NUM> may be configured to execute "open-loop" speed control, and initiate "closed-loop" control as described above during the normal mode of operation. In open-loop control, the controller sets a target PWM duty cycle in accordance with a trigger or speed dial position (for variable-speed tools), or based on a predetermined value (for fixed-speed tools), but does not use a feedback signal from the rotational speed of the motor to further adjust the motor commutation. This prevents heavy increases in current draw from the battery pack while it is still cold.

<FIG> depicts an exemplary flow diagram <NUM> for the controller <NUM> to execute "col operation" and "normal operation" as described above. In an embodiment, in this process <NUM>, which starts at A, step <NUM>, the controller <NUM> receives a battery pack temperature signal from the battery pack at step <NUM>. In an embodiment, this signal may be received directly from a thermistor within the battery pack. Then, at step <NUM>, the controller <NUM> determines whether the pack temperature is lower than a lower temperature threshold (e.g., -<NUM>). If yes, the controller <NUM> sets a cold flag at step <NUM>. Otherwise, the controller <NUM> determines whether the pack temperature is above a higher temperature threshold (e.g., -<NUM>). This hysteresis thresholding ensures that the controller <NUM> does not toggle between normal mode and cold pack mode when the battery pack temperature hovers around the threshold value. The controller <NUM> proceeds to B, at step <NUM>, and determines whether the cold flag has been set at step <NUM>. If the cold flag has been set, the controller enters the "cold operation" mode as described above, at step <NUM>. Otherwise the controller <NUM> enters the normal mode of operation at step <NUM>. The aforementioned process continues at step <NUM>.

Some of the techniques described herein may be implemented by one or more computer programs executed by one or more processors residing, for example on a power tool. The computer programs include processor-executable instructions that are stored on a non-transitory tangible computer readable medium. The computer programs may also include stored data. Non-limiting examples of the non-transitory tangible computer readable medium are nonvolatile memory, magnetic storage, and optical storage.

Claim 1:
A power tool comprising:
a housing (<NUM>);
an electric motor (<NUM>) disposed within the housing;
a power terminal arranged to received electric power from a battery pack;
a power switch circuit (<NUM>) disposed between the power terminal and the electric motor; the power tool further comprises
a controller (<NUM>) configured to control a switching operation of the power switch circuit (<NUM>) to regulate power being supplied from the power terminal to the electric motor, the controller (<NUM>) being further configured to receive a temperature signal indicative of a temperature of the battery pack, determine if the temperature of the battery pack is below a lower temperature threshold, and operate the switching operation of the power switch circuit (<NUM>) in a normal mode of operation if the temperature of the battery pack is greater than or equal to the low temperature threshold and in a cold mode of operation if the temperature of the battery pack is below the low temperature threshold wherein the controller (<NUM>) is configured to monitor a rotational speed of the electric motor (<NUM>) and control the switching operation of the power switch circuit (<NUM>) in a closed-loop speed control scheme in the normal mode of operation, wherein in the closed-loop control scheme, the controller is configured to control the switching operation of the power switch circuit based on the rotational speed of the motor charactarised in that the controller (<NUM>) is configured to control the switching operation of the power switch circuit (<NUM>) in an open-loop speed control scheme in the cold mode of operation, wherein in the open-loop control scheme, the controller is configured to control the switching operation of the power switch circuit independently of the rotational speed of the motor.