Method for braking power tool comprising at least two power supplies, and power tool

Abstract

The invention relates to a method for braking a power tool, which is a battery-operated power tool and can be connected to at least one first power supply and a second power supply so as to be supplied with electrical energy. The electric energy released when the power tool is braked is fed back to the first power supply device and / or the second power supply device of the power tool. The power supplies are connected in series, and the method may include actively controlling the DC link voltage, where a limit value UZwitchenkreis, Limit of the DC link voltage is less than the sum of limit values UAkkuppack, Limit of the voltages of the power supplies. In a second aspect, the invention relates to a power tool for performing the braking method.

Description

Technical Field

[0001] This invention relates to a method for braking a power tool, the power tool being a battery-operated power tool and capable of being connected to at least one first power supply device and a second power supply device to be supplied with electrical energy. The electrical energy released when the power tool is braked is fed back to the first power supply device and / or the second power supply device of the power tool. These power supply devices are connected in series, and the method may include active control of the DC link voltage, wherein the limit value of the DC link voltage, U_Zwischenkreis, Limit, is less than the sum of the limit values ​​of the voltages of these power supply devices, U_Akkupack, Limit. In a second aspect, the invention relates to a power tool for performing this braking method. Background Technology

[0002] In the prior art, power tools are known to be able to be connected to more than one power supply device to be supplied with electrical power. These power supply devices are typically connected in series to increase the system voltage or to handle applications with higher power requirements. Additionally, using more than one power supply device can increase the battery life or operating time of the power supply device. Power tools should be brought to a standstill quickly. This prevents the power tool or its components from remaining stationary for extended periods, during which accidents or injuries to the user of the power tool are particularly likely to occur.

[0003] The electrical energy released when a power tool is braked can be fed back to the power tool's power supply unit ("energy recovery"). When energy is fed back, it is necessary to ensure that the power supply unit is not damaged by overload, etc. This can be particularly challenging when the power tool includes more than one power supply unit, because, for example, the voltage and / or current may be unevenly distributed across the existing power supply units. Such an asymmetrical distribution can lead to a situation where the individual power supply units are subjected to unequal loads, thus adversely affecting the power tool's energy recovery or other characteristics. For example, if one of the multiple power supply units exceeds its current and / or voltage limits, but another power supply unit still operates well below these limits, either one of the power supply units may be overloaded and thus at risk of damage, while the other power supply unit may remain below its capacity, and therefore, for example, less electrical energy is fed back to the power supply unit than technically possible.

[0004] The purpose of this invention is to overcome the defects and disadvantages of the prior art described above, and to provide a method for braking a power tool comprising two power supply devices, and to provide such a power tool, the provided method and power tool firstly allowing for the most effective protection of the user of the power tool, and secondly allowing for power tools with particularly long operating time or battery life, i.e., the power energy is fed back to the power supply devices of the power tool as efficiently as possible, especially when the power tool has two power supply devices.

[0005] This objective is achieved through the subject matter of the independent claim. Advantageous embodiments of the subject matter of the independent claim can be found in the dependent claims. Summary of the Invention

[0006] According to the present invention, a method for braking a power tool is provided. The power tool is a battery-operated power tool and is connectable to at least one first power supply device and a second power supply device to be supplied with electrical energy. The electrical energy released when the power tool is braked is fed back to the first and / or second power supply devices of the power tool. These power supply devices are connected in series, and the limit value of the DC link voltage, U_Zwischenkreis,Limit, is less than the sum of the limit values ​​of the voltages of these power supply devices, U_Akkupack,Limit. Preferably, according to the present invention, the proposed braking method can be used to brake the power tool itself, its motor, or the tool itself.

[0007] This method advantageously allows the released braking energy to be fed back to the power supply device particularly efficiently. In the context of this invention, it is preferred that the power tool be connected to at least two power supply devices to supply electrical energy to it. The method may be described with respect to a first power supply device and a second power supply device, but it is equally applicable to power tools comprising three, four, five, six, seven, or more power supply devices. These other power supply devices may be referred to as the "nth power supply device" (see the accompanying drawings for details). For example, the power tool may have a receiving area or an option for connecting two or more power supply devices. According to the invention, it is preferred that the terms "rechargeable battery," "battery," "battery pack," and "power supply device" be used synonymously. According to the invention, it is also preferred that the terms "limit" and "limit" be used synonymously. According to the invention, it is preferred that the control of the energy recovery or braking process be referred to as method step S1.

[0008] Preferably, the DC link voltage limit can be determined such that even in cases of significant voltage asymmetry across the power supply devices, the voltage limit of each power supply device in the power tool will not be exceeded. This advantageously achieves the effect that the DC link voltage does not exceed the DC link voltage limit U_Zwischenkreis, Limit during energy recovery. This also advantageously allows adherence to the voltage limits of each power supply device. The invention advantageously ensures adherence to permissible current and voltage limits even in power tool systems comprising multiple power supply devices connected in series. For this purpose, the power tool may include electronic or motor electronics that appropriately control energy recovery to each power supply device. According to the invention, it is particularly preferred that the maximum energy recovery current and the maximum battery pack voltage are not exceeded.

[0009] According to the invention, it is preferred to monitor the voltage of the system comprising the power tool and the power supply device. This monitoring can be ensured, for example, by the electronics of the power tool or the motor electronics. According to the invention, this voltage of the system comprising the power tool and the power supply device can preferably be referred to as the "system voltage". Furthermore, according to the invention, it is preferred to monitor the DC link voltage during energy recovery so as not to exceed the maximum permissible voltage of the power supply device. This can be advantageously ensured by the invention because the limit value of the DC link voltage, U_Zwischenkreis, Limit, is less than the sum of the limit values ​​of the voltages of these power supply devices, U_Akkupack, Limit. This particularly prevents one power supply device from exceeding the voltage limit for energy recovery while the voltage of another power supply device remains significantly below the limit value. Tests have shown that the invention exhibits particularly good results in cases where the power supply devices have different states of charge, different temperatures, and therefore different internal resistances, such that the DC link voltage is particularly asymmetrically segmented across the voltages of the power supply devices. In these cases, the invention allows for particularly efficient energy recovery of electrical energy.

[0010] According to the invention, it is particularly preferred that the energy recovery current be limited to a low value so that the voltage increase during energy recovery remains sufficiently low, such that the voltage of the power supply device does not exceed the applicable current and voltage limits under all operating conditions of the power tool. This can be advantageously achieved because the limit value of the DC link voltage, U_Zwischenkreis,Limit, is less than the sum of the limit values ​​of the voltages of these power supply devices, U_Akkupack,Limit. It has been shown that this allows for the maximum possible energy recovery in a system comprising a power tool and multiple power supply devices connected in series. In particular, the invention allows for active control of the DC link voltage, preferably achieved by adjusting the braking process of the power tool. This can advantageously achieve the effect that the power supply devices do operate within their power limits, but do not exceed the current and / or voltage limits.

[0011] This invention specifically provides a method for energy recovery in a series connection comprising multiple power supply devices, the method preventing the maximum permissible voltage of the series-connected power supply devices from being exceeded. This invention advantageously allows for optimal energy recovery in a series connection comprising multiple power supply devices. A particular advantage of this invention is that optimized energy recovery also minimizes the braking time of the power tool or the tool itself to a stationary state, and therefore makes the use of the power tool particularly safe for the user.

[0012] In power tools with series connections including power supply units, the power supply units may acquire or have different characteristics during operation of the power tool or while electrical energy is being fed back to the power supply units. Power supply units may differ, for example, in their state of charge, temperature, and / or internal resistance. This invention allows for maximizing the feedback of electrical energy to the power supply units, which advantageously minimizes the braking time of the power tool. This is because a particularly short braking time provides exceptional protection for the user of the power tool against injury. An advantage of this invention is that the limits of the series-connected power supply units can be optimally utilized without exceeding the current and voltage limits of any single power supply unit within the series connection. This invention allows for active control of the DC link voltage by adjusting the braking process, ensuring that the limits of the power supply units are indeed (almost) reached but not exceeded. The limits of the power supply units are preferably the voltage and current limits.

[0013] According to a preferred embodiment of the present invention, the limit value U_Zwischenkreis, Limit of the DC link voltage is obtained by multiplying the voltage limit value U_Akkupack, Limit by the number of power supply devices n and the factor k_Unbalance. The inventors have recognized that by introducing the so-called unbalance factor k_Unbalance (which can be multiplied by the series connection of the voltage limit value U_Akkupack, Limit of the power supply devices), asymmetric voltage distribution across different power supply devices can be offset. Furthermore, the voltage limit value U_Akkupack, Limit of the power supply devices is multiplied by the number of power supply devices n to obtain the DC link voltage limit value U_Zwischenkreis, Limit. According to a preferred embodiment of the present invention, the calculation of the unbalance factor is referred to as method step S2.

[0014] When calculating the DC link voltage limit U_Zwischenkreis, Limit as the product of the voltage limit U_Akkupack, Limit, the number of power supply devices n, and the factor k_Unbalance, it is assumed that the voltage limits of the power supply devices used in the power tool have the same or substantially the same amplitude. Therefore, the constant or substantially constant voltage limit U_Akkupack, Limit can be multiplied by the number of power supply devices n to obtain the sum of the voltage limits of the power supply devices. If the voltage limits of the power supply devices are not the same for all power supply devices of the power tool, then the product of the number of power supply devices n and the voltage limit U_Akkupack, Limit can be summed. replace.

[0015] To obtain the limit value U_Zwischenkreis, Limit of the DC link voltage, this sum can be multiplied by the unbalance factor k_Unbalance.

[0016] According to the present invention, the factor k_Unbalance is preferably between 0 and 1. The factor k_Unbalance can also take extreme values ​​of 0 and 1, with a factor k_Unbalance of 1 preferably indicating that, according to the present invention, there is no imbalance between the power supply devices, i.e., no “imbalance”. In this case, the power supply devices of the power tool all behave in the same or substantially the same way. Preferably, a high imbalance factor k_Unbalance in the range of 1 indicates power supply devices that behave very similarly, while a low imbalance factor k_Unbalance close to 0 indicates that there are significant differences in the performance of the individual power supply devices of the power tool.

[0017] According to a preferred embodiment of the invention, the proposed method involves not exceeding a limit value I_Rekuperation, Limit for the energy recovery current. In this configuration of the invention, active control of the energy recovery current can be allowed by adjusting the braking process, ensuring that the limit value of the power supply device is indeed (almost) reached but not exceeded. According to a preferred embodiment of the invention, in a series connection, the current throughout all power supply devices is the same or substantially the same, and therefore it is particularly easy to ensure the limit value of the energy recovery current for all power supply devices. Advantageously, this configuration of the invention not only ensures that the voltage limits of the power supply devices are followed, but also that the maximum permissible energy recovery current of the series-connected power supply devices is followed. Preferably, in a series connection, the current throughout the power supply devices is the same or substantially the same, and therefore the power tool or its electronics can particularly easily monitor this constant or substantially constant current for the maximum permissible energy recovery current.

[0018] According to the present invention, preferably, the limit value of the energy recovery current, I_Rekuperation, Limit, corresponds to the minimum value among the limit values ​​of the energy recovery current of the power supply device. According to the present invention, this preferably means that the limit value of the energy recovery current, I_Rekuperation, Limit, can be determined based on the minimum value among the limit values ​​of the energy recovery current of the series-connected power supply devices.

[0019] The following exemplary application of the invention explains the possible calculation of the factor k_Unbalance, which involves a series connection of two battery packs. The designations U_Akku, 1 and U_Akku, 2 preferably represent the voltages of the first and second power supply devices measured during energy recovery. If the voltage U_Akku, 1 measured at the first power supply device is greater than the voltage U_Akku, 2 measured at the second power supply device, the factor k_Unbalance can be calculated as follows: In other cases, the factor k_Unbalance can be calculated as follows: Since the calculation of the factor k_Unbalance varies depending on how the voltages of the power supply devices of the power tool are related to each other, it is advantageous to calculate the factor k_Unbalance for all possible states of the system including the power tool and the power supply devices. For power tools that are supplied with electrical energy by more than two power supply devices, those skilled in the art can appropriately adjust the above distinctions and formulas.

[0020] According to a preferred embodiment of the invention, the voltage measurement and / or the calculation of the factor k_Unbalance are updated at a period duration significantly shorter than the rise time of the energy recovery current. This allows for ensuring that any asymmetrical voltage splits between power supply devices are monitored sufficiently closely during the rise of the energy recovery current. This can be achieved, in particular, by determining the electrical parameters of the power tool or power supply device through periodic measurements, enabling the factor k_Unbalance to be calculated at regular intervals and adjusted as necessary. In particular, this allows for a particularly rapid and flexible response to changes in the operating parameters of the power supply device (e.g., state of charge, temperature, and / or internal resistance) to ensure that as much electrical energy as possible is fed back to the power supply device.

[0021] In a second aspect, the present invention relates to a power tool for performing the proposed method. The terminology, definitions, and technical advantages introduced for the braking method are preferably applied to the power tool with necessary modifications. The power tool is preferably configured to decelerate itself, its motor, or the tool itself. According to the invention, it is particularly preferred that the proposed braking method brings the tool to a standstill or substantially to a standstill. According to the invention, the statement "substantially to a standstill" preferably means that a large portion of the rotational kinetic energy is stripped from the tool, motor, and / or power tool, resulting in deceleration of the power tool.

[0022] The motor of the power tool is preferably a brushless motor, which can preferably deliver a power greater than 1.8 kilowatts (kW). Preferably, the power tool can be a brushless control electrical unit with braking function. For example, the power tool can be in the form of an electrically operated cutting grinder. According to the invention, it is particularly preferred that the power tool is a battery-operated cutting grinder having a cutting disc as a tool. The power tool can be connected to at least two power supply devices so that electrical energy can be supplied by these power supply devices. For example, the power supply devices of the power tool can deliver a voltage greater than 20 volts (V). A rated voltage between 21 V and 22 V is particularly preferred. The power tool can also have three or more power supply devices. Those skilled in the art will recognize that this voltage can vary depending on the state of charge of the power supply devices.

[0023] The cutting disc is a disc-shaped tool of a cutting-type grinding machine, which can be decelerated and brought to a standstill using the proposed braking method. The cutting disc can have a diameter greater than, for example, 230 mm. For example, the cutting disc can have a diameter of 300 mm, 250 mm, or 400 mm, but is not limited to these. For example, the weight of the cutting disc can be in the range of 200 grams to 2500 grams, i.e., between 0.2 kg and 2.5 kg. For example, the weight of the cutting disc can be values ​​of 210 grams, 530 grams, 550 grams, 930 grams, 1270 grams, 1280 grams, 1720 grams, or 2450 grams, but is not limited to these. For example, the cutting disc can be a diamond cutting disc or an abrasive cutting disc with bonded abrasive particles. A diamond cutting disc is preferably characterized by having a steel core with a diamond segment. Of course, the present invention is not limited to use in cutting and grinding machines, and the proposed method can be used in many other power tools or electrical equipment used on construction sites.

[0024] Further advantages will become apparent from the following description of the drawings. The drawings, description, and claims contain many combinations of features. Those skilled in the art will also be able to consider these features individually and combine them to produce other useful combinations. Attached Figure Description

[0025] In the accompanying drawings, identical and similar parts are indicated by the same reference numerals.

[0026] In the attached diagram: Figure 1 A possible block diagram is shown for calculating the energy recovery limit for a series connection containing multiple power supply devices.

[0027] Figure 2 A schematic representation of a power tool including two power supply devices is shown. Detailed Implementation

[0028] Figure 1 A possible block diagram is shown for calculating the energy recovery limit for a series connection of multiple power supply devices 14, 16 included in the power tool 10. Figure 2 The power tool 10 is schematically shown in the diagram. Figure 1 The block diagram shown specifically illustrates method steps S1: controlling the energy recovery or braking process, and S2: calculating the imbalance factor k_Unbalance.

[0029] according to Figure 1 The block diagram depicted uses the voltages measured during energy recovery for each power supply device 14, 16 in the power tool 10 to calculate the factor k_Unbalance. Specifically, Figure 1The diagram illustrates the voltages of the first power supply device 14, the second power supply device 16, and the nth power supply device (without reference numerals) involved in calculating the factor k_Unbalance. Next, the factor k_Unbalance can be multiplied by the limit value U_Akkupack, Limit of the power supply devices 14 and 16, and the number n of the power supply devices 14 and 16, which is indicated by "x" in the block diagram. In this way, the limit value U_Zwischenkreis, Limit of the DC link voltage is obtained. This limit value U_Zwischenkreis, Limit of the DC link voltage is then used in method step S1: controlling the energy recovery or braking process. Controlling the energy recovery or braking process may also involve, in particular, the maximum permissible energy recovery current I_Rekuperation, Limit. The maximum permissible energy recovery current I_Rekuperation, Limit is preferably the limit value of the energy recovery current I_Rekuperation. The limit value of the energy recovery current, I_Rekuperation, Limit, is preferably calculated based on the minimum value among the energy recovery current limits of the various power supply devices 14, 16 connected in series in the proposed power tool 10. Figure 1 In the block diagram shown, the minimum value is indicated by the label "min". The energy recovery current limit of the first power supply device 14 is... Figure 1 The preferred value is referred to as I_Rekuperationlimit, Akku, 1, while the limit value of the energy recovery current of the second power supply device 16 is... Figure 1 The preferred value is referred to as I_Rekuperationlimit, Akku, 2. The limit value of the energy recovery current of the nth power supply device is... Figure 1 The preferred option is referred to as I_Rekuperationlimit, Akku, n.

[0030] Figure 2 A schematic representation of a power tool 10 including two power supply units 14, 16 is shown. The power tool 10 may also have a motor 12, preferably in the form of a brushless motor. Of course, the power tool 10 may also have many other components, such as electronics, a tool 18, a tool chuck, and / or receiving devices for the power supply units 14, 16, but is not limited thereto. The tool 18 of the power tool 10 may be surrounded by a blade guard (not shown in the figures) to protect the user of the power tool 10 from flying sparks or debris. The power tool 10 may also have a handle (not shown in the figures), which the user can use to transport the power tool or guide it during work.

[0031] List of reference numerals 10 Power Tools 12 motors 14 First power supply device 16 Second power supply device 18 tools S1 controls the energy recovery or braking process. S2 calculates the imbalance factor.

Claims

1. A method for braking a power tool (10), the power tool (10) being a battery-operated power tool and capable of being connected to at least one first power supply device (14) and a second power supply device (16) to be supplied with electrical energy, wherein the electrical energy released when the power tool (10) is braked is fed back to the first power supply device (14) and / or the second power supply device (16) of the power tool (10), the power supply devices (14, 16) being connected in series. Its features are, The limit value of the DC link voltage, U_Zwischenkreis, Limit, is less than the sum of the limit values ​​of the voltages of these power supply devices (14, 16), U_Akkupack, Limit.

2. The method as described in claim 1, Its features are, The limit value of the DC link voltage, U_Zwischenkreis, Limit, is obtained by multiplying the limit value of these voltages, U_Akkupack, Limit, by the number n of the power supply devices (14, 16) and the factor k_Unbalance.

3. The method as described in claim 2, Its features are, The factor k_Unbalance is between 0 and 1.

4. The method as described in any one of the preceding claims, Its features are, The current shall not exceed the limit value of the energy recovery current, I_Rekuperation, Limit.

5. The method as described in claim 4, Its features are, The limit value of the energy recovery current, I_Rekuperation, Limit, corresponds to the minimum of the limit values ​​of the energy recovery current for these power supply devices (14, 16).

6. A power tool (10) for performing the method as described in any one of the preceding claims.

7. The power tool (10) as described in claim 6. Its features are, The motor (12) of the power tool (10) is a brushless motor.

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