Impact and / or tamping device with improved electric drive

Abstract

A percussion or tamping device is specified, comprising a working device for generating a percussion or tamping movement; an electric motor (1) for driving the working device; and a drive train (4) for transmitting a rotary movement generated by the electric motor (1) to the working device; wherein an energy store (8) is provided in the drive train (4); and wherein the energy store (8) is designed such that it alternately stores and releases energy during a percussion or tamping cycle in order to even out the energy consumption of the electric motor (1).

Description

[0001] The invention relates to a striking or stamping device with an improved electric drive.

[0002] Impact devices are known. These can be, for example, demolition hammers or rotary hammers, in which impacts are exerted on a tool, e.g., a chisel, during operation.

[0003] Tamping devices are also known, especially tampers for soil compaction.

[0004] Such machines are increasingly being equipped with an electric drive, whereby the electrical energy required for the electric drive is provided by a battery that serves as a storage device and is located on the machine itself.

[0005] Such devices or machines for striking and / or stamping have an uneven power requirement due to their design and operating principle. In particular, the power requirement can vary considerably during a work cycle, i.e., a striking or stamping process.

[0006] For example, when the ground contact plate (tamping foot) of a rammer strikes the ground, a high power demand arises within a very short time interval, namely during the tamping action, to keep the electric motor at a constant speed against the recoil from the tamping mechanism. The impact on the ground and the resulting recoil exert a strong braking effect on the motor, which it attempts to counteract with increased current draw.

[0007] This results in very high peak currents throughout the entire system, which can be detrimental to the battery. In particular, the efficiency, lifespan, and operating time of the battery can be significantly reduced due to the highly variable currents, but especially because of the very high peak currents.

[0008] In addition, the battery management system (BMS) and, if necessary, the motor electronics must be designed to withstand these high peak currents.

[0009] The same problem arises with jackhammers. There, too, the temporarily occurring high peak currents can put a heavy strain on the battery.

[0010] The high motor currents, in addition to reducing battery life and running time, also lead to a higher cooling requirement for the battery cells and an overall lower efficiency.

[0011] The invention is therefore based on the objective of providing a striking or stamping device with an improved electric drive in which the previously occurring high peak currents can be reduced.

[0012] The problem is solved according to the invention by a striking or stamping device with the features of claim 1. Advantageous embodiments are specified in the dependent claims.

[0013] A striking or stamping device is described, comprising a working device for generating a striking or stamping motion; an electric motor for driving the working device; and a drive train for transmitting a rotary motion generated by the electric motor to the working device; wherein an energy storage device is provided in the drive train; and wherein the energy storage device is designed to alternately store and release energy during a striking or stamping cycle in order to even out the energy input of the electric motor.

[0014] The impact or stamping device can be designed, for example, as a tamper for concrete compaction or as a demolition hammer.

[0015] Depending on its design, the working device can be a striking device, a percussion mechanism, or a stamping device. The construction of such devices is well-known and therefore does not need to be explained in detail here.

[0016] The electric motor can typically have a power output in the range of 1.5 kW to 3 kW and is therefore suitable for driving a hand-held striking or stamping device.

[0017] The energy storage system allows energy to be stored during a hammering or stamping cycle and subsequently released, thus smoothing the energy consumption of the electric motor. In particular, the energy storage system prevents the significant recoil energy, which can occur, for example, when a stamping foot strikes already compacted soil, from being fed back directly and completely to the electric motor, which would result in the high peak currents described above. Instead, the energy storage system is able to either absorb the recoil energy or assist the motor's ability to counteract it. The motor itself can then run more smoothly, thus also smoothing its current consumption. Very high peak currents can therefore be avoided.

[0018] For example, the energy storage device can be designed to have additional inertia, which allows energy to be stored within the system. This inertial energy can be stored, in particular, in the powertrain using the energy storage device.

[0019] For example, the energy storage device can have an additional rotating mass to increase the moment of inertia of the drivetrain. The drivetrain can be broadly defined here and encompass the entire drive system from the electric motor to the working motion, i.e., the impact or stamping motion.

[0020] The energy storage device must be located in a suitable position. In particular, the energy storage device should be positioned in the force or torque flow between the electric motor and the point of action (tamping foot in a rammer, chisel in a demolition hammer) or positioned in such a way that it can influence the force or torque flow.

[0021] The drivetrain can include a motor shaft for the electric motor, with the energy storage device potentially comprising a flywheel mounted on the motor shaft as an additional rotating mass. This rotating mass, or flywheel, should be rigidly coupled to the motor shaft. For example, the rotating mass or flywheel can be rigidly connected to the motor shaft, e.g., by positive or frictional engagement, so that it is directly coupled to the rotation of the motor shaft. The additional inertia provided by the rotating mass of the flywheel can store energy, thereby increasing the inertia of the drivetrain system.

[0022] A fan wheel can be mounted on the motor shaft to generate a cooling airflow during operation of the electric motor, with the flywheel being attached to the fan wheel. In this case, it may be advantageous to utilize the available installation space for the flywheel as well.

[0023] In one variant, the flywheel and the fan wheel can be integrated into a single, in particular a one-piece, component.

[0024] In another variant, the flywheel and the fan wheel can be provided as separate components that are arranged or attached together on the motor shaft.

[0025] In both the integrated solution and the split solution with separate components, it is possible to reduce the height of the fan wheel (axial extent). This frees up installation space that can be used by the flywheel. Reducing the height of the fan wheel, and thus its effectiveness, is possible because the drive components require less cooling. Due to the flywheel's effect, as explained above, peak flow rates are reduced, thereby decreasing the need for component cooling. Accordingly, it is sufficient to design the fan or fan wheel with a lower cooling capacity. Even a small airflow can be enough to provide adequate cooling.

[0026] In the split solution described above, with individual, separate components (flywheel, fan wheel), the two components can also be pre-assembled together before being mounted as a unit on the motor shaft.

[0027] The electric motor can have a rotor mounted on the motor shaft, where the moment of inertia of the additional rotating mass can be greater than or equal to the combined moment of inertia of the motor shaft and rotor. Accordingly, it is important that the additional rotating mass has a significant moment of inertia relative to the motor shaft and rotor in order to achieve the desired smoothness of the current draw.

[0028] For example, the combined moment of inertia of the flywheel and fan wheel can be greater than or equal to the combined moment of inertia of the motor shaft and rotor of the electric motor.

[0029] The electric motor can, in the usual way, have a rotor and a stator. The rotor can be mounted as a separate component on the motor shaft. Alternatively, it can also be integrated with the motor shaft to form a single component.

[0030] The combined moment of inertia can be calculated as the sum of the individual moments of inertia of the flywheel and fan wheel on the one hand, and of the motor shaft and rotor on the other. However, in a direct comparison, the combined moment of inertia of the flywheel and fan wheel should be greater than that of the motor shaft and rotor. Therefore, the moment of inertia of the motor shaft and rotor can be at least doubled by the flywheel and fan wheel.

[0031] The combined moment of inertia of the flywheel and fan wheel can be at least 10%, in particular at least 25%, in particular at least 50% greater than the combined moment of inertia of the motor shaft and rotor of the electric motor.

[0032] In this context, it should be noted that in the construction of a known electric drive, the fan wheel is usually made of a very light material, e.g., plastic or aluminum. Accordingly, the moment of inertia of the fan wheel (without a flywheel) is considerably lower than the combined moment of inertia of the motor shaft and rotor, which are often made of other materials, e.g., steel or cast iron. In contrast, the invention achieves a much higher moment of inertia due to the additional rotating mass.

[0033] In a specific embodiment, the combined moment of inertia of the motor shaft and rotor can be in a range of 1,300 to 1,700 kg mm. 2 In particular, the moment of inertia can be 1,500 kg mm. 2 This value is typical for an electric motor with a power output in the range of 1.5 kW to 3 kW.

[0034] The combined moment of inertia of the flywheel and fan wheel can range from 1,800 to 2,200 kg mm. 2 lie, especially at 2,000 kg mm 2 .

[0035] These values ​​have proven effective in practice and have led to significant reductions in peak currents.

[0036] The invention makes it possible to implement a modular system. In particular, a space can be provided on the electric drive that is optionally used entirely by the fan wheel or alternatively by a combination of fan wheel and flywheel. In this way, a conventional electric drive known from the prior art can also be easily retrofitted and equipped with a flywheel to smooth the current flow.

[0037] Depending on the requirements and application, the motor shaft can then be determined with the fan wheel alone or with a combination of fan wheel and flywheel, without having to change other components of the electric drive.

[0038] The invention is explained in more detail below using examples and the accompanying figures. These show: Fig. 1 a cross-section through an electric drive with conventional design; Fig. 2 a section through an electric drive according to the invention; Fig. 3. the current flow over time in a conventional electric drive; and Fig. 4 the current profile over time in an electric drive according to the invention.

[0039] Fig. Figure 1 shows a schematic section through a state-of-the-art electric drive that can be integrated into a striking or tamping device. The electric drive can, for example, be used to power a rammer for soil compaction. For this purpose, the electric drive can be attached to a tamping housing and connected accordingly.

[0040] The electric drive comprises an electric motor 1 with a stator 2 and a rotor 3, which is mounted on a motor shaft 4. One shaft end 5 can be connected to a working device (not shown). In the case of a rammer for soil compaction, the working device is a suitably designed and known rammer. Alternatively, the electric drive can also be attached to an impact device, e.g., a breaker hammer. In this case, the shaft end 5 is connected to a suitably designed impact device, e.g., an air-spring impact mechanism.

[0041] Opposite the shaft end 5, a shaft shoulder 6 is provided on the motor shaft 4, on which a fan wheel 7 is arranged.

[0042] When the electric motor 1 is operated, the rotor 3 drives the motor shaft 4 by rotating it. This also causes the fan wheel 7 to rotate, generating a cooling airflow for the electric motor 1, which can be directed in particular past the rotor 3 and stator 2.

[0043] Fig. Figure 2 shows an electric drive according to the invention, which is largely analogous to the electric drive of Fig. It is structured as follows: 1. Accordingly, the same reference symbols are used.

[0044] In the variant of Fig. 2 However, the height of the fan wheel 7, i.e. the axial extent of the fan wheel 7, is different compared to the prior art variant according to Fig. 1 reduced. The fan wheel 7 is therefore smaller and results in a lower cooling airflow, which is unproblematic due to the even power consumption, as will be explained later.

[0045] The space freed up by reducing the size of the fan wheel 7 is filled by a flywheel 8, which serves as an additional rotating mass and is also mounted on the shaft shoulder 6. The flywheel 8 is made of a suitable material to provide an appropriate rotating mass. For example, metallic materials such as cast metal, steel, or aluminum are conceivable.

[0046] The flywheel significantly increases the inertia of the overall system without requiring any modifications to the electric motor 1, in particular the motor shaft 4 and the rotor 3. This makes it possible to continue using standard electric drives without having to change any other components.

[0047] Fig. Figure 3 shows an example of a comparative measurement on a prior art electric drive, depicting the current drawn from a battery over the measurement period. It can be seen that the current reaches a level of up to 100 A in each cycle. A total of six cycles are shown in the diagram.

[0048] The effective value of the current (RMS current value) is 48.5 A in the example shown.

[0049] In comparison, in Fig. 4. The battery current drawn by the electric motor was measured over time in an electric drive equipped with a flywheel 8 according to the invention. It can be seen that the peak currents are now only about 75 A, thus reducing them by approximately 25%. The RMS current was reduced from 48.5 to 44.4 A, a decrease of 9%.

[0050] By comparing the measurement curves of Fig. 3 and Fig.Figure 4 clearly shows how the additional inertia due to the rotating mass in the form of the flywheel 8 can achieve a smoother current flow. This results in a lower load on the battery powering the electric motor 1.

[0051] The invention allows for the provision of an additional rotating mass in or on the motor to increase its inertia. The electric motor 1 itself, i.e., the motor shaft 4 and the rotor 3, do not need to be modified.

[0052] Due to thermal losses in the electric motor 1, it must be cooled by means of the fan wheel 7. The fan wheel 7, or rather the shaft end there (shaft shoulder 6), can be used for the additional inertial mass in the form of the flywheel 8.

[0053] The improved efficiency also allows for a reduction in motor cooling. Therefore, the reduced height of the fan wheel 7 may be sufficient.

[0054] The fan wheel 7 and the flywheel 8 can be manufactured as a single piece. Alternatively, the two components can be attached separately to the motor shaft 4 as a two-piece assembly.

Claims

[1] Striking or stamping device, with - a working device for generating a striking or stamping motion; - an electric motor (1) for driving the working device; and with - a drive train (4) for transmitting a rotary motion generated by the electric motor (1) to the working device; wherein - an energy storage device (8) is provided in the powertrain (4); and wherein - the energy storage device (8) is designed in such a way that it alternately stores and releases energy during a striking or stamping cycle in order to even out the energy input of the electric motor (1). [2] Impact or stamping device according to claim 1, wherein the energy storage device has an additional rotating mass (8) to increase the moment of inertia of the drive train (4). [3] Striking or stamping device according to any of the preceding claims, wherein - the drive train includes a motor shaft (4) of the electric motor (1); and wherein - the energy storage device has a flywheel (8) as an additional rotating mass, which is arranged on the motor shaft (4). [4] Striking or stamping device according to claim 3, wherein - a fan wheel (7) is arranged on the motor shaft (4) to generate a cooling airflow during operation of the electric motor (1); and wherein - the flywheel (8) is arranged on the fan wheel (7). [5] Impact or stamping device according to claim 4, wherein the flywheel (8) and the fan wheel (7) are integrated into one component. [6] Impact or stamping device according to claim 4, wherein the flywheel (8) and the fan wheel (7) are separate components that are arranged together on the motor shaft (4). [7] Striking or stamping device according to any of the preceding claims, wherein - the electric motor (1) has a rotor (3) which is arranged on the motor shaft (4); and wherein - the moment of inertia of the additional rotating mass (8) is greater than or equal to the common moment of inertia of the motor shaft (4) and rotor (3) of the electric motor (1). [8] Striking or stamping device according to any of the preceding claims, wherein - the electric motor (1) has a rotor (3) which is arranged on the motor shaft (4); and wherein - the combined moment of inertia of flywheel (8) and fan wheel (7) is greater than or equal to the combined moment of inertia of motor shaft (4) and rotor (3) of the electric motor (1). [9] Impact or stamping device according to one of the preceding claims, wherein the common moment of inertia of flywheel (8) and fan wheel (7) is greater by at least 10%, in particular by at least 25%, in particular by at least 50% than the common moment of inertia of motor shaft (4) and rotor (3) of electric motor (1). [10] Impact or stamping device according to one of the preceding claims, wherein the common moment of inertia of motor shaft (4) and rotor (3) is in a range of 1,300 to 1,700 kg*mm 2 lies. [11] Impact or stamping device according to one of the preceding claims, wherein the common moment of inertia of flywheel (8) and fan wheel (7) is in a range of 1,800 to 2,200 kg*mm 2 lies.

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