Power tool having improved speed-torque profile
In a loaded condition, the controller increases at least one of the conduction band or the advance angle from a baseline value up to a maximum value within a first torque range below a torque threshold to as to maintain the output speed of the motor at a linear speed-torque profile. After the at least one of the conduction band or the advance angle reaches the maximum value, the controller maintains the at least one of the conduction band or the advance angle at the maximum value within a second torque range greater than or equal to the torque threshold so as to maintain the output speed of the motor at a naturally-curved speed-torque profile.
1. A power tool comprising:
a housing;
a brushless motor including a rotor and a stator having a plurality of stator windings corresponding to at least three phases of the motor, the rotor being rotatably moveable by the stator;
a power switch circuit comprising a plurality of high-side power switches and a plurality of low-side power switches configured as an inverter circuit for driving the phases of the motor, the power switch circuit receiving electric power from a power supply and outputting at least three phase voltage signals to the plurality of stator windings; and
a controller outputting a plurality of drive signals to the power switch circuit to control a supply of power on the at least three phase voltage signals to the motor, the controller driving the motor at an output speed of up to a maximum target speed when operating under a no-load condition, wherein each phase is associated with a conduction band within which the controller outputs the drive signal to high-side and low-side power switches associated with the respective phase to energize the corresponding stator windings,
wherein, when operating at the maximum target speed and as load is applied to the motor, the controller is configured to increase the conduction band from a baseline conduction band value up to a maximum conduction band value within a first torque range below a torque threshold, and after a detected motor torque exceeds the torque threshold or the conduction band reaches the maximum conduction band value, to maintain the conduction band at the maximum conduction band value within a second torque range greater than or equal to the torque threshold, wherein a rate at which the output speed of the motor falls with increased load is greater within the second torque range than within the first torque range.
2. The power tool of claim 1 , wherein the controller is configured to maintain a speed-torque profile that is substantially linear within the first torque range.
3. The power tool of claim 2 , wherein the controller is configured to increase the conduction band during the first torque range so as to maintain the output speed of the motor at a constant level.
4. The power tool of claim 3 , wherein the constant level is substantially equivalent to the maximum target speed.
5. The power tool of claim 2 , wherein the controller is configured to increase the conduction band during the first torque range so as to gradually reduce the output speed of the motor at a linear rate.
6. The power tool of claim 1 , wherein the motor follows a naturally-curved speed-torque profile within the second torque range.
7. The power tool of claim 1 , wherein the controller is further configured to apply an advance angle by which the conduction band is shifted for each phase of the motor, the controller increasing the advance angle from a baseline advance angle value up to a maximum advance angle value within the first torque range, and after the advance angle reaches the maximum advance angle value, maintaining the advance angle at the maximum advance angle value within the second torque range.
8. The power tool of claim 7 , wherein the controller is configured to increase the conduction band and advance angle in tandem as a function of the output speed of the motor.
9. The power tool of claim 1 , when operating at the maximum target speed and as load applied to the motor exceeds a second torque threshold defining an upper limit of the second torque range, the controller is configured to reduce the conduction band from the maximum conduction band value back to the baseline conduction band value.
10. A power tool comprising:
a housing;
a brushless motor including a rotor and a stator having a plurality of stator windings corresponding to at least three phases of the motor, the rotor being rotatably moveable by the stator;
a power switch circuit comprising a plurality of high-side power switches and a plurality of low-side power switches configured as an inverter circuit for driving the phases of the motor, the power switch circuit receiving electric power from a power supply and outputting at least three phase voltage signals to the plurality of stator windings; and
a controller outputting a plurality of drive signals to the power switch circuit to control a supply of power on the at least three phase voltage signals to the motor, the controller driving the motor at an output speed of up to a maximum target speed when operating under a no-load condition, wherein each phase is associated with a conduction band within which the controller outputs the drive signal to high-side and low-side power switches associated with the respective phase to energize the corresponding stator windings, the controller further applying an advance angle by which the conduction band is shifted for each phase of the motor,
wherein, when operating at the maximum target speed and as load is applied to the motor, the controller is configured to increase the advance angle from a baseline advance angle band value up to a maximum advance angle value within a first torque range below a torque threshold, and after a detected motor torque exceeds the torque threshold or the advance angle reaches the maximum advance angle value, to maintain the advance angle at the maximum advance angle value within a second torque range greater than or equal to the torque threshold, wherein a rate at which the output speed of the motor falls with increased load is greater within the second torque range than within the first torque range.
11. The power tool of claim 10 , wherein the controller is configured to maintain a speed-torque profile that is substantially linear within the first torque range, the controller being configured to increase the advance angle during the first torque range so as to maintain the output speed of the motor at a constant level substantially equivalent to the maximum target speed.
12. The power tool of claim 10 , wherein the controller is configured to maintain a speed-torque profile that is substantially linear within the first torque range, the controller being configured to increase the advance angle during the first torque range so as to gradually reduce the output speed of the motor from the maximum target speed at a linear rate.
13. The power tool of claim 10 , wherein the motor follows a naturally-curved speed-torque profile within the second torque range.
14. The power tool of claim 10 , wherein the controller is configured to increase the conduction band and advance angle in tandem as a function of the output speed of the motor.
15. The power tool of claim 10 , when operating at the maximum target speed and as load applied to the motor exceeds a second torque threshold defining an upper limit of the second torque range, the controller is configured to reduce the advance angle from the maximum advance angle value back to the baseline advance angle value.
16. A power tool comprising:
a housing;
a multi-phase motor including a rotor and a stator having a plurality of stator windings corresponding to at least three phases of the motor, the rotor being rotatably moveable as the stator windings are energized;
a power switch circuit comprising a plurality of high-side power switches and a plurality of low-side power switches configured as an inverter circuit for driving the phases of the motor; and
a controller outputting a plurality of drive signals to the power switch circuit to control a supply of power to the motor, the controller driving the motor at an output speed of up to a maximum rated speed when operating under a no-load condition, the controller further applying an advance angle by which the conduction band is shifted for each phase of the motor,
wherein, in a loaded condition, the controller is configured to increase at least one of the conduction band or the advance angle from a baseline value up to a maximum value within a first torque range below a torque threshold to as to maintain the output speed of the motor at a linear speed-torque profile, and after the at least one of the conduction band or the advance angle reaches the maximum value, to maintain the at least one of the conduction band or the advance angle at the maximum value within a second torque range greater than or equal to the torque threshold so as to maintain the output speed of the motor at a curved speed-torque profile.