Hand-held work tool with an electric drive motor

Abstract

Hand-held work device with a tool (5) driven by a drive shaft (4) in a rotating manner, wherein the drive shaft (4) is driven by an electric drive motor (2), - wherein the drive motor (2) is provided with a control unit (20), characterized in that - that the control unit (20) is assigned at least one first operating curve (I) as power (P) versus rotational speed (n) and a second operating curve (II) as power (P) versus rotational speed (n), - wherein the control unit (20) operates the electric drive motor (2) in idle mode according to the first operating curve (I) and in load mode according to the second operating curve (II), - and the first operating curve (I) covers a low power range at low speed and the second operating curve (II) covers a large power range at high speed, - wherein the drive motor (2) is powered from a battery (12), and the drive motor (2) is switched to a low power consumption operating curve (I) outside the operating range, - wherein the battery (12) is arranged in the housing of the working device, - whereby switching to the second operating curve (II) allows for higher power consumption and higher speed, - where the switching between the operating curves (I, II) exhibits a hysteresis, - wherein during operation of the drive motor (2) the power consumption (P) and the speed (n) of the drive motor (2) are monitored by the control unit (20) and the switching between the operating curves (I, II) takes place depending on its output signal, • where the operating parameters are evaluated by comparison with the data of an operating curve and the switching between the operating curves (I, II) takes place depending on a comparison of the output signal with a threshold value and - wherein if a first threshold is undershot, a switch is made to one operating curve (II) and if a second threshold is exceeded, a switch is made to the other operating curve (I).

Description

[0001] The invention relates to a hand-held work device according to the preamble of claim 1.

[0002] Brushcutters with electric drive motors according to DE 198 09 988 A1 have an on / off switch that allows the device to be switched on or off. This means that when operating without a load, the switched-on electric drive motor runs up to a maximum no-load speed that is significantly higher than the operating speed. To limit the no-load speed, a speed limiter circuit is used, which limits the electrical power consumption of the drive motor depending on the detected motor current, thus reducing the maximum speed of the electric drive motor. This limitation of the electrical speed is achieved by reducing the electrical power consumption. When the motor current increases, the electrical limit is lifted.

[0003] DE 24 07 601 C2 discloses a control device for reducing the speed of an electric motor depending on the torque M and its current speed. In switching state I, the motor runs at reduced voltage on characteristic curve I and under load on characteristic curve II.

[0004] From DE 41 00 611 A1 a control device for speed adjustment and thread tracking is known, which operates depending on the motor current.

[0005] DE 694 11 313 T2 discloses a mechanical rake with an electrically operated cutting device that is powered by the mains or a battery.

[0006] DE 295 07 982 U1 discloses an electric handheld device such as a hair clipper or a razor with an electric motor powered by a battery.

[0007] The invention is based on the objective of designing a mobile hand-held work device with an electric drive motor in such a way that an idle speed can be specified for a large working range of the work device without delaying the power consumption of the electric motor under load.

[0008] The problem is solved according to the invention according to the characterizing features of claim 1.

[0009] The drive motor is equipped with a control unit that has at least one primary and one secondary operating curve assigned to it. When the electric drive motor is idling, the power consumption is controlled according to the primary operating curve, and under load, according to the secondary operating curve. The drive motor is powered by a battery located in the housing of the implement. Outside the operating range, the drive motor switches to a lower power consumption operating curve, while switching to the secondary operating curve allows for higher power consumption and a higher speed. The operating data of the electric drive motor, such as speed, current, and voltage, are recorded by a monitoring device, and the control unit determines and sets the appropriate operating point for each curve.

[0010] The control system makes it possible to limit the electric drive motor of a handheld power tool to a predetermined no-load speed, which can be significantly lower than the maximum operating speed under load. Despite this significantly reduced no-load speed, the switching to the second operating curve under load allows for maximum power consumption by the electric drive motor, enabling it to deliver maximum power to the tool. The reduction in speed during no-load operation has no effect on power consumption or speed under load. The switching mechanism according to the invention not only enables quieter continuous operation but also saves energy, resulting in significantly longer battery runtimes.

[0011] The intended operating curves can be represented as power versus rotational speed and are expediently stored as a characteristic map. The first operating curve stored in the characteristic map corresponds to a load curve at idle, while the second operating curve corresponds to a load curve at full load. Preferably, the first operating curve covers a low power range at low rotational speed, and the second operating curve covers a large power range at high rotational speed.

[0012] The switch between operating curves can be performed according to machine-specific or operation-specific criteria. The switch exhibits a certain hysteresis, meaning that the transition from the first operating curve (idle) to the second operating curve (load) depends on various external conditions. This is intended to prevent a brief drop in load and thus an increase in rotational speed during operation of the machine from immediately triggering a switch to the idle operating curve. Ideally, the switch from the first to the second operating curve occurs essentially without time delay, while the switch from the second to the first operating curve is delayed. This can be easily achieved by using a timer, after which the switch occurs, provided the operating conditions for switching are still present at the time the timer expires.The timer is conveniently restarted each time the switching conditions are met.

[0013] The electrically powered drive motor, supplied by a battery, is operated outside the working range on a low-power operating curve, thus allowing only minimal electrical power consumption. The switching mechanism according to the invention not only enables quieter continuous operation; this operating mode also saves energy, resulting in significantly longer operating times when the device is battery-powered.

[0014] Advantageously, a sound sensor is provided whose output signal is monitored in order to switch between operating curves depending on the output signal. The sound sensor can consist of a microphone preferably located in the area of ​​the tool head or can be in the form of a structure-borne sound sensor, which can be arranged at a suitable location on the tool head, the guide rod between the drive motor and the tool head, or even on the drive motor itself.

[0015] Operating data such as speed, current, and voltage of the electric drive motor are recorded by a monitoring device, and the respective operating point is determined by the control unit. If a deviation from the first operating curve (the no-load curve) is detected, a comparison with a predefined threshold is advantageously performed. If the threshold is exceeded, the control unit switches to the second operating curve (full-load curve), particularly without time delay. Switching to the second operating curve allows for higher power consumption and a higher speed. When the electric drive motor is running on the first operating curve (no-load), the power consumption is reduced to a low value, and the speed is lowered to a predefined no-load speed, which is below the operating speed.

[0016] To switch between operating curves, a monitored output signal is compared to a threshold value. The switching process is designed so that if a first threshold value is undershot, the signal switches to one operating curve, and if a second threshold value is exceeded, the signal switches to the other operating curve. For example, the output signal of the sound sensor is evaluated such that if a first threshold value is exceeded, the signal switches to the first operating curve (idle), and only if a second threshold value is undershot, the signal switches to the second operating curve (load case).

[0017] Further features of the invention will become apparent from the further claims, the description, and the drawing, in which an embodiment of the invention, described in detail below, is illustrated. The drawing shows: Fig. 1. Schematic representation of a hand-held work tool, using a brush cutter as an example. Fig. 2 a schematic circuit diagram for the operation of the electric drive motor, Fig. 3. A graph of power versus rotational speed with individual operating curves.

[0018] The in Fig. The hand-held tool shown in Figure 1 is designed as a brush cutter 1, which includes an electric drive motor 2 as its drive unit. The electric drive motor 2 drives a tool 5, which in the illustrated embodiment is a line trimmer head 6 with a cutting line 7, via a drive shaft 4 guided and supported, for example, in a guide tube 3. A protective shield 8 is arranged at the lower end of the guide tube 3 to protect the user operating the brush cutter 1. The electric drive motor 2 can be connected to a fixed electrical supply via a connecting cable 9; alternatively, the drive motor 2 can be powered by a battery, preferably a rechargeable battery 12, which is arranged in the housing of the tool and enables cordless operation.

[0019] In the illustrated embodiment, a curved guide tube 3 is provided; straight guide tubes are also possible. The length of the drive shaft 4 is also variable; it may be advantageous to arrange the tool head 6 directly on the shaft of the drive motor 2, which then simultaneously functions as a drive shaft 4.

[0020] In the exemplary embodiment, a handle 10 for holding and guiding the brushcutter 1 is provided on the guide tube 3; a second handle 11 can advantageously be provided in the housing area of ​​the drive motor 2.

[0021] As in Fig. As shown in Figure 2, the electric drive motor 2 drives the tool head 5 via the drive shaft 4. The rotational speed of the drive shaft 4 is detected by a speed sensor 21 and transmitted to a control unit 20 via a signal line 22. In addition, current and voltage in the electrical supply line 9 are detected by a measuring arrangement 23, and the detected values ​​are transmitted to the control unit 20 via the signal line 24. Based on the transmitted data, the control unit 20 can determine the power consumption and the rotational speed of the electric motor 2 and compare them with a first operating curve I, which is stored in a characteristic map. Such an operating curve is, for example, in Fig. Figure 3 shows the power P as a function of rotational speed n.

[0022] In a first embodiment of the invention, the power consumption P and the rotational speed n are continuously monitored during operation of the electric drive motor 2 and compared with this first operating curve I. This first operating curve I advantageously corresponds to an idle curve, but can also be a different operating curve. The operating curve II corresponds to a load curve. The first operating curve I covers a low power range at low rotational speed, while the second operating curve II covers a large power range at higher rotational speed.

[0023] If, during the monitoring of the recorded operating parameters of the electric drive motor 2, it is determined that the resulting monitoring point 30 deviates from an operating point 31 of operating curve I, the magnitude of the deviation from operating curve I is determined in the control unit 20, and the switching to a different operating curve II is controlled depending on the output signal. The output signal can be easily compared with a predefined threshold value. If the threshold value representing the permissible deviation is exceeded, the system switches to the second operating curve II. Switching to the second operating curve II not only allows for a higher power output P but also a higher rotational speed n.

[0024] The switch from operating curve I (idle) to operating curve II (load) is conveniently performed without significant time delay. The switch from operating curve II (load) to operating curve I (idle), however, is conveniently delayed. The switching process itself thus exhibits hysteresis. This allows the switch to occur when the detected deviation at point 30 from operating curve I persists for an extended period, i.e., when the deviation exceeds a time threshold. This hysteresis can be easily preset by a timer 25; only after the timer 25 has elapsed does the switch to operating curve I (idle) occur, provided the switching criteria are still met at the time the timer expires. This ensures that a brief drop in power consumption during operation does not immediately switch back to the idle curve, which could impede efficient operation.

[0025] Advantageously, the on / off switch of the electrical work device can be designed such that, upon fully depressing the switch in a "kick-down" manner, it immediately switches to operating curve II. The design can be such that the switch to operating curve I (no-load curve) occurs automatically via the control unit 20, and the switch back to operating curve II (load) is effected by fully depressing the on / off switch. The on / off switch can conveniently actuate a contact (pushbutton) in the fully depressed position, which immediately triggers the switching signal to operating curve II.

[0026] The inventive method of power-adapted speed control ensures that, when the drive motor is running without load, the speed n is reduced to a low no-load speed of, for example, 6000 rpm by limiting the power input P. At the moment a load is applied, the changed operating state is detected by the deviation from the first operating curve I, in order to switch immediately to a corresponding operating point 32 of the second operating curve II, which allows for a higher power input and thus also enables higher speeds. Under load, the maximum electrical power P is drawn, and thus the higher drive power is provided by the electric drive motor.When the load is removed, the electrical power input P decreases while the rotational speed increases; this is detected by the control unit 20, which then switches back to the first operating curve I, the idle curve, with a beneficial delay. The rotational speed drops to a lower idle speed.

[0027] The switching between operating curves can alternatively or additionally be performed according to other criteria. According to a further embodiment, a sound sensor 28 is provided, which is connected to the control unit 20 via a signal line 29. The output signal of the sound sensor 28 is monitored in the control unit 20, and the switching between the operating curves is performed depending on the output signal. Advantageously, the output signal of the sound sensor 28 is compared with a threshold value. If the threshold value is exceeded, which is the case with an unloaded motor on operating curve II due to high speed at idle, a switch to operating curve I, the idle curve, occurs. The noise level decreases; the output signal of the sound sensor decreases. In order to avoid triggering an immediate switch to operating curve II, the load curve, the switch to operating curve II can be made dependent on other criteria, e.g.,of the power consumption of the drive motor 2. Another simple possibility is to specify a second threshold value, after which the system switches back to operating curve II. Thus, the second threshold value could be undershot and a switchback triggered when, while idling on operating curve I, the implement is loaded by taking on work, causing a further drop in speed and thus a decrease in the output signal.

[0028] A microphone 26 can advantageously be used as a sound receiver 28, which picks up the acoustic sound of the tool or the drive motor. The microphone is expediently arranged close to the acoustic noise source, e.g., near the tool or the tool head.

[0029] An advantageous embodiment of the sound transducer 28 can be a structure-borne sound transducer 27, which can be mounted directly on the tool head 6, the guide tube 3, or the drive motor 2 or its housing. The structure-borne sound transducer 27 is largely resistant to external acoustic interference.

Claims

[1] Hand-held work device with a tool (5) driven by a drive shaft (4) in a rotating manner, wherein the drive shaft (4) is driven by an electric drive motor (2), - wherein the drive motor (2) is equipped with a control unit (20), characterized by , - that the control unit (20) is assigned at least one first operating curve (I) as power (P) versus rotational speed (n) and a second operating curve (II) as power (P) versus rotational speed (n), - wherein the control unit (20) operates the electric drive motor (2) in idle mode according to the first operating curve (I) and in load mode according to the second operating curve (II), - and the first operating curve (I) covers a low power range at low speed and the second operating curve (II) covers a large power range at high speed, - wherein the drive motor (2) is powered from a battery (12), and the drive motor (2) is switched to a low power consumption operating curve (I) outside the operating range, - wherein the battery (12) is arranged in the housing of the working device, - whereby switching to the second operating curve (II) allows for higher power consumption and higher speed, - where the switching between the operating curves (I, II) exhibits a hysteresis, - wherein during operation of the drive motor (2) the power consumption (P) and the speed (n) of the drive motor (2) are monitored by the control unit (20) and the switching between the operating curves (I, II) takes place depending on its output signal, • where the operating parameters are evaluated by comparison with the data of an operating curve and the switching between the operating curves (I, II) takes place depending on a comparison of the output signal with a threshold value and - wherein if a first threshold is undershot, a switch is made to one operating curve (II) and if a second threshold is exceeded, a switch is made to the other operating curve (I). [2] Working tool according to claim 1, characterized by that the operating curve is stored in a characteristic map. [3] Working tool according to claim 1, characterized by , that the switch from the first operating curve (I) to the second operating curve (II) occurs essentially without time delay and the switch from the second operating curve (II) to the first operating curve (I) occurs with a time delay. [4] Working tool according to claim 1, characterized by, that a switchover occurs after the expiry of a time element (25). [5] Working device according to any one of claims 1 to 4, characterized by , that a sound sensor (28) is provided whose output signal is monitored, and that the switching between the operating curves takes place depending on the output signal. [6] Working tool according to claim 5, characterized by , that the sound sensor (28) is a structure-borne sound sensor. [7] Working tool according to claim 5, characterized by , that the sound receiver (28) is a microphone. [8] Working tool according to claim 1, characterized by , that the output signals are evaluated by comparison with the data of the first operating curve (I). [9] Working equipment according to any one of claims 1 to 8, characterized by , that the work tool is a brush cutter (1).

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