Drive unit for a mobile machine tool, and mobile machine tool

Abstract

The invention relates to a drive unit for a mobile machine tool, comprising a battery unit for providing an output-side DC voltage, an electric motor, and a switching device which is connected between the battery unit and the electric motor and by means of which the output-side DC voltage can be switched in order to control the electric motor, wherein the switching device has at least two switches, each of which is switched at a switching frequency which is greater than or equal to 50 kHz, preferably greater than or equal to 100 kHz.

Description

[0001] 2024ID00120

[0002] Hilti Aktiengesellschaft in Schaan

[0003] Principality of Liechtenstein

[0004] Drive unit for a mobile machine tool and mobile machine tool

[0005] AREA OF INVENTION

[0006] The present invention relates to a drive unit for a mobile machine tool and a mobile machine tool with such a drive unit.

[0007] A switching device for operating an electric motor in a mobile machine tool is supplied with a direct current voltage, which is often provided by a high-performance battery.

[0008] Modern mobile power tools increasingly utilize more powerful batteries. The performance of these batteries is still largely limited by their internal resistance. The lower the internal resistance, the less heat and thus less power loss occurs within the battery, allowing for higher power outputs or electrical currents. However, decreasing internal resistance introduces new challenges.

[0009] The battery of a standard drive train in a mobile machine tool exhibits parasitic properties under high-frequency excitation, which can no longer be ignored as the battery's internal resistance decreases. Among other things, such a battery displays parasitic inductive properties. This parasitic inductance, together with a commonly used DC link capacitor in the drive train, forms a so-called LC resonant circuit.

[0010] The resonant frequency of this LC resonant circuit can be calculated as follows:

[0011]

[0012] The batteries of today's mobile machine tools (including the electrical cables and connections) have an inductance of approximately 200 nH. Typical intermediate circuit capacitances are around 200 pF. Based on these values, a resonant frequency is calculated - 2 - 20234ID00120

[0013] of 25 kHz. However, this resonant frequency lies precisely within the range of a typical pulse-width modulation (PWM) frequency used in a motor inverter bridge. This PWM frequency thus acts as a resonant excitation for the LC resonant circuit. The resulting oscillations can damage the battery's electronics (including battery management) or at least negatively affect analog measurements during motor control.

[0014] Furthermore, these vibrations cause additional losses in the battery, as the otherwise rectilinear battery current is superimposed with an alternating current component that only generates losses in the battery without providing any additional power in the drive train.

[0015] In principle, the internal resistance of a battery dampens the LC resonant circuit. The higher the battery's internal resistance, the lower the amplitude at resonance. This positive effect, resulting from the otherwise undesirable internal resistance of the battery, is, however, counteracted by the ever-decreasing internal resistance in modern batteries. Therefore, a different approach is being taken to counteract resonance.

[0016] Against this background, the object of the present invention is to create an improved drive unit for a mobile machine tool and / or an improved mobile machine tool.

[0017] REVELATION OF THE INVENTION

[0018] According to a first aspect, a drive unit for a mobile machine tool is proposed. The drive unit comprises a battery unit for providing an output DC voltage, an electric motor for driving a tool of the mobile machine tool, and a switching device. The switching device is connected between the battery unit and the electric motor. The switching device controls the output DC voltage for controlling the electric motor. The switching device has at least two switches, each of which can be switched at a switching frequency of 50 kHz or higher, preferably 100 kHz or higher.

[0019] The battery unit is preferably designed to supply a direct current (DC) voltage. The battery unit preferably forms an integral part of the drive unit and is - 3 - 20234ID00120

[0020] The battery unit is used to supply energy to the electric motor. It preferably has at least two or more contacts or contact points. These contacts are preferably connection points through which electrical energy is transferred from the battery unit to the drive unit. The battery unit is preferably a rechargeable energy storage device or a rechargeable battery that can store electrical energy and release it as needed.

[0021] The proposed drive unit increases the excitation frequency (PWM frequency) of the switching device to such an extent that parasitic excitation of the battery unit no longer occurs. The switches are designed to exhibit low switching losses, which are directly proportional to the switching frequency. To avoid problems with heat generation from the switches, particularly fast-switching switches are used, representing a fundamental innovation compared to existing drive units for mobile machine tools, which have previously used silicon-based transistors as switches. The fast-switching switches allow for a higher PWM frequency, thus moving beyond the critical resonance range of the battery DC link resonant circuit. Increasing the PWM frequency reduces motor current ripple and improves efficiency.

[0022] According to a second aspect, a mobile machine tool with such a drive unit is proposed.

[0023] The mobile machine tool can be a handheld power tool or a mobile machine tool, such as a drill, screwdriver, chisel, grinder, saw, or the like. It is also conceivable that the mobile machine tool is a construction robot or includes a construction robot. The mobile machine tool can have a manipulator, in particular a multi-axis manipulator. The mobile machine tool can have a drive device for driving a tool, such as a drill, chisel, vacuum cleaner, or the like.

[0024] The mobile machine tool can be set up, for example, for processing stone, such as concrete, and / or metal and / or wood. It can be designed, for example, for drilling, chiseling, sawing and / or grinding. - 4 - 20234ID00120

[0025] Generally, the mobile machine tool can be set up for carrying out work in building construction and / or civil engineering. It is conceivable that it is not set up for use in mining.

[0026] The mobile machine tool can be portable; for example, it can weigh less than 50 kg, and in particular less than 25 kg.

[0027] The specifications for the drive unit apply accordingly to the mobile machine tool and vice versa.

[0028] In one embodiment, it is proposed that the switching device forms a motor inverter bridge, in particular a voltage source inverter, which converts the DC voltage provided by the battery unit into an AC voltage, for example by means of pulse-width modulation, by which the electric motor can be driven.

[0029] The switching device preferably forms a motor inverter bridge, functioning as a gate-source inverter (GSI). The DC voltage supplied by the battery unit is preferably converted into AC voltage using pulse-width modulation. This pulsed AC voltage enables the electric motor to be driven. The pulse-width modulation ensures precise control of the output voltage and frequency, thereby allowing efficient regulation of the electric motor's power output.

[0030] In one embodiment, it is proposed that an intermediate circuit capacitor is connected between the battery unit and the switching device, in particular in parallel.

[0031] The DC link capacitor is also commonly referred to as the DC link. Due to the fast-switching switches used in the switching device, the DC link is no longer subjected to oscillation. The DC link capacitor is used in a powertrain with a battery unit and switching device connected in parallel to smooth voltage fluctuations and ensure stable operating conditions. For example, the battery unit cannot always compensate directly and quickly for sudden load changes; therefore, the DC link capacitor buffers energy and supplies the switching device (e.g., the inverter) with additional energy when needed. This reduces voltage spikes and protects the components from damage caused by high currents. At the same time, the DC link capacitor supports pulse-width modulation by dampening rapid current fluctuations, which improves the efficiency and lifespan of the entire system.

[0032] The system's capacitance is increased. Depending on the circuit, however, the DC link capacitance may be omitted, which is why it should be considered optional. A high DC link capacitance, however, has the disadvantage of being associated with high (material) costs, increased installation space, and reduced robustness.

[0033] In one embodiment, it is proposed that the DC link capacitance has a nominal capacitance of less than 500 pF, preferably less than 450 pF.

[0034] The nominal capacitance of the DC link or an DC link capacitor preferably denotes the amount of electrical energy that the capacitor can store and is preferably specified in farads (F). This nominal capacitance determines how much energy can be buffered in the DC link and how effectively voltage fluctuations are smoothed. A higher capacitance preferably allows for better damping of voltage spikes and current fluctuations caused by load changes in the switching device or electric motor. The nominal capacitance is preferably designed such that the DC link can supply or absorb sufficient energy during rapid load changes to ensure stable voltage conditions.

[0035] In one embodiment, it is proposed that the intermediate circuit capacitance comprises a ceramic capacitor, MLCC.

[0036] Preferably, the majority of the DC link's capacitance is provided by a ceramic capacitor. Particularly preferred is, for example, at least 60%, preferably 75%, of the total DC link capacitance covered by a ceramic capacitor. Furthermore, tantalum and / or electrolytic capacitors can also be used.

[0037] A ceramic capacitor is a type of electrical capacitor that uses ceramic as the dielectric material. These capacitors preferably consist of thin ceramic layers alternately stacked with metal foils as electrodes. Ceramic capacitors are used in a compact format due to their high stability, temperature resistance, and capacitance. MLCC stands for Multilayer Ceramic Capacitor. MLCCs are a special type of ceramic capacitor consisting of multiple layers of ceramic material and metal, stacked alternately and then compressed into a small, compact package. This design allows for high capacitance values ​​in a small space. - 6 - 20234ID00120

[0038] In one embodiment, it is proposed that the at least two switches are each designed as semiconductor material-based transistors with a band gap of the semiconductor material greater than 3 eV.

[0039] At least one of the at least two switches can be configured as a gate-terminal transistor, in particular as a metal-oxide-semiconductor field-effect transistor, and / or as a 3-terminal transistor, in particular as a high-electron-mobility transistor. Other semiconductor-based transistor types, such as gate-insulated bipolar transistors (IG-BTs), can also be used.

[0040] The band gap (also known as band gap) is preferably the energy required to promote an electron from the valence band to the conduction band of a semiconductor material. Examples of semiconductor materials used include beta-gallium oxide (β-Ga₂O₃) and gallium nitride (GaN). Beta-gallium oxide (β-Ga₂O₃) has a band gap of approximately 4.8 to 4.9 eV. Beta-gallium oxide is an ultra-wideband semiconductor. Gallium nitride (GaN) has a band gap of approximately 3.4 eV.

[0041] In one embodiment, it is proposed that the at least two switches are each designed as gallium nitrite transistors.

[0042] The ability of gallium-based switches to switch quickly (i.e., in 20 nanoseconds or less) while generating lower switching losses makes them particularly attractive for applications where high switching efficiency and performance are critical, such as the drive unit in question. Gallium-based switches enable significantly faster switching compared to silicon-based switches.

[0043] In one embodiment, it is proposed that the battery unit comprises a cell arrangement of several cells, in particular several battery cells, wherein the cells each have an internal resistance based on the nominal voltage of the battery unit of less than 1.4 mOhm / V, preferably less than 1.3 mOhm / V, and particularly preferably less than 1.2 mOhm / V.

[0044] The nominal voltage of a battery unit is preferably the voltage that the battery unit typically delivers under normal operating conditions. It is preferably an average voltage value derived from the chemical composition of the battery. - 7 - 20234ID00120

[0045] This results from the cells and their series connection. For battery units consisting of several cells in series, the cell voltages add up to the total voltage of the unit. Thus, a battery unit with ten cells connected in series has a nominal voltage equivalent to 10 individual cells.

[0046] If, for example, the cells have an internal resistance of less than 1.2 mΩ / V relative to the nominal voltage of the battery unit, it is preferable for the switches to operate at a frequency of at least 50 kHz. If necessary, the capacitance of the intermediate circuit can also be increased and / or a specific capacitor material selected, which entails additional costs, components, and space requirements, since oscillation or excitation of the LC resonant circuit occurs primarily with a small intermediate circuit capacitance and a low parasitic series resistance of the intermediate circuit capacitor. This is particularly typical for ceramic capacitors. Some capacitor materials can also increase the risk of fire or contain electrolytes that are subject to rapid aging.

[0047] In one embodiment, it is proposed that the cells are designed as pouch cells or as solid-state battery cells.

[0048] Pouch cells are preferably flat battery cells with a flexible casing made of aluminum or an aluminum-plastic composite material. This shape allows for high energy density and good heat dissipation and is particularly space-saving.

[0049] Solid-state battery cells use a solid electrolyte instead of a liquid one, which increases safety and reduces the risk of fires and short circuits. They offer high energy density and promise a longer lifespan as well as lower self-discharge.

[0050] Pouch cells and / or solid-state battery cells each exhibit a high energy density. Furthermore, pouch cells and / or solid-state battery cells have a low internal resistance.

[0051] In the present context, "resistance" refers to an ohmic resistance. Further possible implementations of the invention also include combinations of features or embodiments described previously or subsequently with regard to the exemplary embodiments, even if not explicitly mentioned. In such cases, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention. 20234ID00120

[0052] Further advantageous embodiments and aspects of the invention are the subject of the dependent claims and the exemplary embodiments of the invention described below. The invention is further explained below with reference to preferred embodiments and the accompanying figures. - 9 - 20234ID00120

[0053] BRIEF DESCRIPTION OF THE FIGURES

[0054] The following description explains the invention with reference to exemplary embodiments and figures. The figures show:

[0055] Fig. 1 shows a schematic view of a battery-powered mobile machine tool;

[0056] Fig. 2 shows a schematic view of a drive unit; and

[0057] Fig. 3 shows a schematic view of a drive unit.

[0058] Identical or functionally equivalent elements are indicated by the same reference symbols in the figures, unless otherwise specified. - 10 - 20234ID00120

[0059] FORMS OF EXECUTION OF THE INVENTION

[0060] Fig. 1 shows a schematic view of a battery-powered mobile machine tool 100, which here is configured as an impact drill. The mobile machine tool 100 has a mounting bay 104, which in this example has two contacts K1, K4. The mounting bay 104 is designed to receive a battery unit 130. In each case, the two contacts K1, K4 of the mounting bay 104 are brought into contact with two corresponding contacts KT, K4' of the battery unit 130.

[0061] A consumer of the mobile machine tool 101, in particular an electric motor 108, is connected between contacts K1 and K4 of the receiving bay 104. In the illustrated example, contacts K1 and K4 are connected to a switching device 102, which switches the drive current for the electric motor 108. The switching device 102 and the electric motor form part of an electric drive unit 101, which is shown in more detail in Figures 2 and 3 according to various embodiments.

[0062] The dashed box in Fig. 1 illustrates, purely by way of example, a system 1000 comprising a battery-powered mobile machine tool 100 and a battery unit 130 with several cell arrangements 131, 132, each comprising cells 133. The cells 133 each have an internal resistance R (see schematic in Fig. 3) relative to the nominal voltage of the battery unit 130 of less than 1.4 mΩ / V, preferably less than 1.3 mΩ / V, and particularly preferably less than 1.2 mΩ / V. The battery unit 130 can be represented in a simplified equivalent circuit as a series connection of an inductor L and the (internal) resistance R. The cells 133 are preferably designed as pouch cells or as solid-state cells.

[0063] The mobile machine tool 100 has a main switch 105, via which the drive unit 101 can be switched on and off, and preferably the power extraction from the battery unit 130 and thus the drive power of the electric motor can be controlled.

[0064] The mobile machine tool 100 also has a tool holder 106 for receiving a drilling tool 107. The mobile machine tool 100 can be held by means of a handle 109, to which, for example, the main switch 105 is attached. The drive unit 101 sets the drilling tool 107 into rotation about a drive axis 110. - 11 - 20234ID00120

[0065] As shown in Fig. 2, switching device 102 has at least two switches 200 (six switches 200 in this case), each of which can be switched at a switching frequency of 50 kHz or greater, preferably 100 kHz or greater. To provide these high switching frequencies, the at least two switches 200 are each designed as semiconductor-based transistors with a bandgap of the semiconductor material of greater than 3 eV. The at least two switches 200 are, for example, each designed as galvanic nitride transistors.

[0066] The switching device 102 forms a motor inverter bridge 202, in particular a voltage source inverter, which converts the DC voltage provided by the battery unit 130 into an AC voltage, by which the electric motor 108 can be driven.

[0067] A DC link capacitor 204 with at least one DC link capacitor 206 is connected in parallel between the battery unit 130 and the switching device 102. The DC link capacitor 206 has a nominal capacitance C of less than 500 pF. The DC link capacitor 204, or rather the at least one DC link capacitor 206, comprises a ceramic capacitor, MLCC. Depending on the excitation frequency f, the capacitance C of the DC link capacitor 206 and the battery unit 130, or rather its internal inductance L, can lead to the formation of an LC resonant circuit, which causes losses. The internal resistance R of the battery unit 130 has a damping effect on the LC resonant circuit. In this case, such excitation can be prevented because the switching frequencies f of the switches 200 are each selected to be greater than or equal to 50 kHz, which is outside the resonant frequency for the LC resonant circuit. - 12 - 20234ID00120

[0068] REFERENCE MARK LIST

[0069] 100 mobile machine tool 101 drive unit

[0070] 102 Switching device

[0071] 104 Arrival bay

[0072] 105 Main switch

[0073] 106 Tool holder

[0074] 107 Drilling tool

[0075] 108 Electric motor

[0076] 109 Handle

[0077] 110 working axis

[0078] 130 battery unit

[0079] 131 cell arrangement

[0080] 132 cell arrangement

[0081] 133 Cell

[0082] 200 switches

[0083] 202 Motor inverter bridge

[0084] 204 DC link capacity 206 DC link capacitor 1000 system

[0085] f frequency

[0086] K1 Contact

[0087] K1 ' Contact

[0088] K4 Contact

[0089] K4' Contact

[0090] R ohmic resistance

[0091] C capacity

[0092] L Inductance

Claims

- 13 - 20234ID00120 PATENT CLAIMS 1. Drive unit (101) for a mobile machine tool (100), comprising: a battery unit (130) for providing an output DC voltage; an electric motor (108); and a switching device (102) which is connected between the battery unit (130) and the electric motor (108), and through which the output DC voltage can be switched to control the electric motor (108), wherein the switching device (102) has at least two switches (200) which can each be switched at a switching frequency of greater than or equal to 50 kHz, preferably greater than or equal to 100 kHz.

2. Drive unit (101) according to claim 1, wherein the switching device (102) forms a motor inverter bridge (202), in particular a voltage source inverter, which pulses the DC voltage provided by the battery unit (130), by which the electric motor (108) can be driven.

3. Drive unit (101) according to claim 1 or 2, wherein an intermediate circuit capacity (204) is connected between the battery unit (130) and the switching device (102).

4. Drive unit (101) according to claim 3, wherein the intermediate circuit capacity (204) has a nominal capacity (C) of less than 500 pF.

5. Drive unit (101) according to claim 3 or 4, wherein the intermediate circuit capacitance (204) comprises a ceramic capacitor, MLCC.

6. Drive unit (101) according to one of claims 1 to 5, wherein the at least two switches (200) are each designed as semiconductor material-based transistors with a band gap of the semiconductor material greater than 3 eV.

7. Drive unit (101) according to one of claims 1 to 6, wherein the at least two switches (200) are each designed as gallium nitrite transistors.

8. Drive unit (101) according to one of claims 1 to 7, wherein the battery unit (130) has a cell arrangement (131, 132) of several cells (133), wherein the cells (133) each have an internal resistance (R) based on the nominal voltage of the - 14 - 20234ID00120 Battery unit (130) having an impedance of less than 1.4 mOhm / V, preferably less than 1.3 mOhm / V, particularly preferably less than 1.2 mOhm / V.

9. Drive unit (101) according to claim 8, wherein the cells (133) are designed as pouch cells or as solid-state battery cells.

10. Mobile machine tool (100) with a drive unit (101) according to one of claims 1 to 9.

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