Chainsaw and method for controlling a chainsaw

Abstract

The present disclosure relates to a chainsaw (1), comprising a guide bar (11) carrying a saw chain (9) and an electric motor (21) configured to drive the saw chain (9), the electric motor comprising windings (11) connected to an electric control arrangement (23), including an inverter (37) and a DC power supply (15) connected to a power source (13). The control arrangement is configured to switch between a driving mode, where the saw chain (9) is driven by the electric motor (21) for operation of the chainsaw (1), and a braking mode where the electric motor (21) is braked. The DC power supply (15) comprises a series switch (53) for breaking the connection between the power source (13) and the inverter (37) during the braking mode.

Description

[0001] CHAINSAW AND METHOD FOR CONTROLLING A CHAINSAW

[0002] Technical field

[0003] The present disclosure relates to a chainsaw, comprising a guide bar carrying a saw chain and an electric motor configured to drive the saw chain. The electric motor comprises windings connected to an electric control arrangement, including an inverter and a DC power supply connected to a power source, wherein the control arrangement is configured to switch between a driving mode, where the saw chain is driven by the electric motor for operation of the chainsaw, and a braking mode where the electric motor is braked.

[0004] Background

[0005] Such a chainsaw is proposed in EP-3872978-A1 where braking is initiated when a rotation movement of the chainsaw as a whole exceeds a threshold, which could indicate a hazardous situation.

[0006] One problem in chainsaws of this type is how to carry out the braking in an efficient way.

[0007] One object of the present disclosure is therefore to provide an electrically driven chainsaw having a braking function with improved efficiency and reliability.

[0008] This object is achieved by means of a chainsaw as disclosed in claim 1 . More specifically, in a chainsaw of the initially mentioned type, the DC power supply comprises a breaking switch for breaking the connection between the power source and the inverter during the braking mode. This isolates the motor from the DC power supply during braking which improves the effectiveness and safety of the braking procedure.

[0009] The chainsaw may further comprise a shunt resistor which is configured to be activated during the braking mode to dissipate energy from the inverter. This allows the chainsaw to efficiently deal with the energy released when braking the moving parts. The shunt resistor may be connected in series with a control switch controlling the amount of energy dissipated in the resistor. This control switch may be connected in parallel with a filter capacitor and in parallel with a DC input of the inverter.

[0010] The breaking switch and the control switch may be controlled by a common controller.

[0011] The controller may be supplied with power from the DC power supply on the inverter’s side of the breaking switch. In the braking mode, the voltage of the DC power supply may be controlled by pulse-width modulation of the control switch. This means that the controller can be supplied with a maintainance voltage, even when disconnected form the battery or the like.

[0012] The present disclosure also defines a method for braking a chainsaw as outlined above. This method includes activating, in the braking mode, a breaking switch in the DC power supply, breaking the connection between the power source and the inverter.

[0013] Further, a shunt resistor may be activated during the braking mode to dissipate energy from the inverter.

[0014] The controller of the chain saw may be supplied with power from the DC power supply on the inverter’s side of the breaking switch. In the braking mode, the voltage of the DC power supply may be controlled by pulse-width modulation of the control switch.

[0015] Brief description of the drawings

[0016] Figure 1 illustrates a chainsaw.

[0017] Figure 2 illustrates field-oriented control of an electric motor.

[0018] Fig 3 illustrates schematically a supply circuit layout according to the present disclosure.

[0019] Figs 4A and 4B illustrate the supply circuit in a driving mode and in a braking mode, respectively.

[0020] Detailed description

[0021] The present disclosure relates to electric chainsaws, an example of such a chainsaw 1 is illustrated in Fig 1 . The chainsaw comprises a chainsaw body 3 having a front 5 and a rear 7 handle, by means of which an operator may hold and operate the chainsaw 1. A cutting assembly comprising a saw chain 9, and an elongated guide bar 11 guiding the saw chain 9 in an elongated loop, which extends from a front end of the chainsaw body 3 along a longitudinal axis X of the chainsaw 1 , which longitudinal axis X is defined by the longitudinal axis of the guide bar 11 .

[0022] The chainsaw 1 may further comprise a removable battery 13 in a chainsaw body battery compartment, although the present disclosure would in principle also be relevant for chainsaws operated by AC power supplied by means of a cable. In any case, the saw chain 9 is driven along its elongated loop by means of an electric motor 21 via a sprocket, and the electric motor 21 is in turn driven by an electric control arrangement 23, both schematically indicated in fig 1 .

[0023] The chainsaw may have a finger-operated trigger 25 permitting the operator to selectively mobilize the saw chain 9 using the electric motor 21 , and the electric control arrangement 23 is configured to control the electric motor 21 based on input from the trigger 25. A handguard 27 in front of the front handle 5 may be operatively connected to a brake arrangement for stopping the saw chain 9 in case of a kickback.

[0024] Fig 2 illustrates the electric motor 21 and an example of the electric control arrangement 23.

[0025] The electric motor 21 comprises a stator 31 and a rotor 33, concentric with the stator. In the illustrated example, the electric motor is a brushless DC, BLDC, motor or permanent magnet synchronous motor, PMSM, having a permanent-magnet rotor. The stator may typically be a multi-phase stator, usually with three-phase windings, LIA / / W, 35. However, it would be possible in the context of the present disclosure to instead use an asynchronous- or reluctance type motor. The windings 35 are controlled by an inverter 37 using a field-oriented control, FOC, scheme. The inverter 37 receives power from a DC power supply 39, which may receive power from a chargeable battery 13, although as mentioned the power source may in principle be an AC mains voltage output in which case power is instead received from a rectifier (not shown). Generally, the DC power 39 supply is a link between the power source, and may additionally comprise passive components, typically a filter capacitor, or active components such as a buck or boost converter.

[0026] The inverter 37 feeds power to the motor windings 35 according to a pulse width modulation scheme. To employ FOC, the currents iu, iv iw applied to each winding 35 may be measured and a converter may convert those currents by means of a Clarke / Park conversion unit 41 into direct and quadrature currents, relating to the currents parallel (direct) id and perpendicular (quadrature) iq, respectively, to the instantaneous magnetic field of the rotor 33, in the latter’s coordinate system, as is well known per se. Those converted currents are fed to a controller 43, and a sensor output from an optional angular position sensor 44 estimating the orientation of the rotor 33 may be fed to the controller 43 as well. The controller 43 generally performs a control operation, such as based on a Pl-control scheme, in order to minimize the parallel current component, which does not contribute to rotor torque, and to obtain a desired perpendicular component, that does generate torque, based on an input desired torque value iq* from an input unit 45. This input unit may be partially controlled by the aforementioned finger-operated trigger 25, as will be discussed.

[0027] The controller in this way produces direct and quadrature ud, uq voltages that are converted, using an inverse Clarke and space vector modulation, SVM, modulation unit 47, into desired inverter duty cycle values du, dv, dw for control of the inverter to create corresponding winding voltages uu, uv uw. This technique is well known per se. The conversion units 41 , 47 may typically be integrated with the controller 43 which may be software-implemented.

[0028] Typically, internal combustion engine, ICE, driven chainsaws have been provided with a centrifugal clutch connecting the ICE motor to the sprocket driving the saw chain at a predetermined rotational speed. Further, a handguard has been connected to a powerful mechanical brake, quickly stopping the saw chain in case of a kickback that activates the handguard. While electrical chainsaws could be devised similarly, the use of an electric motor provides some additional freedom of design. An electric motor does not need to be idling, which means that a clutch is not strictly necessary. Further, it would be possible to use the electric motor to carry out or assist with braking by providing winding currents that generate a negative torque that brakes the electric motor.

[0029] The present disclosure is occupied with making a braking function of the electric motor more efficient and safer. This is achieved by the driving system switching between a driving or motoric mode and a braking mode as will be outlined below. Fig 3 illustrates schematically a control layout for the electric motor 21 according to the present disclosure. This controller 43 accomplishes the FOC control of the motor currents by controlling the motor 21 winding currents. This is done based on desired torque value iq* from an input unit 45, which in turn may be based on input from the finger-operated trigger 25.

[0030] In the motoric mode, the finger-operated trigger 25 (cf. fig 1 ) is used to control operation of the motor. Typically, the finger-operated trigger 25 is a lever button connected to a switch, combined with a Hall sensor and a sensor magnet or a variable resistor, or the like, providing an electric reading of the trigger 25 position. Other configurations are conceivable.

[0031] Additionally, a safety switch (not shown) may need be pushed to activate the finger- operated trigger 25 as is well known per se. While it is possible to control motor speed directly based on finger-operated trigger 25 activation, it is possible in the motoric mode to adjust the transfer between finger-operated trigger 25 position and motor speed to some extent.

[0032] The present disclosure is primarily occupied with achieving an efficient braking of the chain in a braking mode. The braking mode may be triggered in different ways. To start with, if a handguard 27 (cf. fig 1 ) is provided and is activated (pushed forward) due to a kickback of the chainsaw, the motor should be stopped as soon as possible. This may be done even if the chainsaw has a legacy-type mechanical brake also activated by the handguard 27. If this is the case, actively braking the electric motor makes the mechanical braking of the chain more efficient which improves safety of use for the chainsaw. However, the electric braking described herein may be considered so efficient that this mechanical brake is not necessary, which lowers the overall cost of the chainsaw. The handguard may still be provided and may also retain the capability of immobilizing the chain when deliberately activated, for instance when moving in difficult terrain carrying the saw.

[0033] It should be noted however that the braking function could be activated in other ways. For instance, instead of or as a complement to the handguard 27, the chainsaw may be provided with one or more accelerometers that detect changes in the instantaneous orientation of the chainsaw and activates the braking function as soon as a movement resembling a kickback is detected. Braking may also be initiated during normal operation not related to emergency braking, for instance by releasing the finger-operated trigger 25. Such normal operation braking may also be initiated on other types of electric cutting tools, such as a hedge trimmer, a brushcutter, a clearing saw or a pole saw.

[0034] When braking of the electric motor takes place, the present disclosure considers adapting the circuit supplying the inverter 37 in different ways, to facilitate the braking, which may be used individually or in combination.

[0035] Firstly, it is considered to isolate the inverter 37 from the DC supply, such as the battery or a rectifier in the case of an AC mains connected chainsaw, in order to avoid transfer of energy to the inverter 37 that could impair the braking. This is achieved with a series switch 53 as will be discussed. The series switch 53 then ensures that no energy is transferred from the DC source to the inverter 37 during braking to enhance the safety of the braking operation.

[0036] Secondly, a significant negative torque in relation to the normal direction of rotation is applied by the controller 43 and the inverter 37 to the rotor of the electric motor 21 by applying winding currents that provide a significant negative quadrature current iq. As a result, the kinetic energy stored by the moving parts, i.e. the rotor of the electric motor 21 , the sprocket and the saw chain 9, is converted to electric energy which is fed backwards in the system from the inverter 37.

[0037] The present disclosure also deals with handling of this backwards directed energy. To this end, the DC power supply 15, in addition to a filter capacitor 47, comprises a resistor 49, connected in parallel therewith which is controlled by a switch 51 , such as a MOSFET power switch.

[0038] The power supply series switch 53 may further be capable of disconnecting the inverter from the power source, such as the battery 13. This ensures also that the battery 13 for instance is not fed with a current from the motor side that could exceed a normal charging current and at circumstances, typically charging temperatures, where such a current could otherwise damage the battery. Thus, the series switch 53 may be able to block currents in both directions.

[0039] In fig 4A, the driving mode of the chainsaw in the above configuration is illustrated. In this mode, thus the saw chain 9 is driven by the electric motor 21 for operation of the chainsaw 1. Therefore, in this mode, a conventional energy transfer from the power source to the motor 21 takes place, the above power resistor 49 is inactive, and the series switch 53 connects the power source to the inverter 37.

[0040] In the braking mode of the chainsaw, illustrated in fig 4B, the series switch 53 is activated, breaking the connection to the power source such as the battery. Further, switch 51 activates resistor 49, by means of which energy transferred from the electric motor 21 may be consumed.

[0041] If MOSFET switches are used, the series switch 53 may comprise first 55 and second 57 switches for breaking currents in both directions. However, other series switch configurations would be possible. The switch 51 may in this process control the DC voltage in the power supply to a desired value. Thus, even if the power source is disconnected, the DC supply may still be capable of providing for instance a supply voltage 56 to the controller 43 during this period. It would also be possible to provide the supply voltage 56 of the controller separately from the battery. The present disclosure is not restricted to the above-described examples and may be varied and altered in different ways within the scope of the appended claims.

Claims

CLAIMS1 . A chainsaw (1 ), comprising a guide bar (11 ) carrying a saw chain (9) and an electric motor (21 ) configured to drive the saw chain (9), the electric motor comprising windings (11 ) connected to an electric control arrangement (23), including an inverter (37) and a DC power supply (15) connected to a power source (13), wherein the control arrangement is configured to switch between a driving mode, where the saw chain (9) is driven by the electric motor (21 ) for operation of the chainsaw (1 ), and a braking mode where the electric motor (21 ) is braked; characterized by, the DC power supply (15) comprising a series switch (53) for breaking the connection between the power source (13) and the inverter (37) during the braking mode.

2. Chainsaw (1 ) according to claim 1 , further comprising a shunt resistor (49) which is configured to be activated during the braking mode to dissipate energy from the inverter (37).

3. Chainsaw (1 ) according to claim 2 wherein the shunt resistor (49) is connected in series with a control switch (51 ) controlling the amount of energy dissipated in the resistor.

4. Chainsaw (1 ) according to claim 3, wherein the resistor (49) and the control switch (51 ) are connected in parallel with a filter capacitor (47) and in parallel with a DC input of the inverter (37).

5. Chainsaw (1 ) according to claim 4, wherein the series switch (53) and the control switch (49) are controlled by a common controller (43).

6. Chainsaw (1 ) according to claim 5, wherein the controller is supplied with power from the DC power supply (15) on the inverter’s (37) side of the breaking switch (53), and wherein in the braking mode, the voltage of the DC power supply is controlled by pulse-width modulation of the control switch (51 ).

7. Chainsaw (1 ) according to any of the preceding claims, wherein the series switch (53) comprises first and second switches (55, 57) connected in series and configured to break currents in both directions.

8. A method for braking a chainsaw (1 ), the chainsaw comprising a guide bar (11 ) carrying a saw chain (9) and an electric motor (21 ) configured to drive the saw chain (9), the electric motor comprising windings (11 ) connected to an electric control arrangement (23), including an inverter (37) and a DC power supply (15) connected to a power source (13), wherein the control arrangement is configured to switch between a driving mode, where the saw chain (9) is driven by the electric motor (21 ) for operation of the chainsaw (1 ), and a braking mode where the electric motor (21 ) is braked; the method characterized by, activating, in the braking mode, a series switch (53) in the DC power supply (15), breaking the connection between the power source (13) and the inverter (37).

9. Method according to claim 8, further comprising a shunt resistor (49) which is activated during the braking mode to dissipate energy from the inverter (37).

10. Method (1 ) according to claim 9, wherein the controller is supplied with power from the DC power supply (15) on the inverter’s (37) side of the breaking switch (53), and wherein in the braking mode, the voltage of the DC power supply is controlled by pulse-width modulation of the control switch (51 ).

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