ELECTRIC-DRIVE SOIL COMPACTION DEVICE

Description

[0001] The invention relates to a soil compaction device with an electric drive.

[0002] Such soil compaction devices, in particular so-called vibratory rammers or vibratory compactors, are widely known and are used for compacting soils and asphalt layers. These rammers are often driven by internal combustion engines, e.g., two-stroke engines. It is also known to use electric drive motors.

[0003] In an electric drive, the electric motor is typically operated at a higher speed and drives a spring-mass system, which serves as a stamping system, via a reduction gear. The electric drive motor is powered either from the electrical grid or from onboard batteries.

[0004] Electric drive motors consist of a stator and a rotor. Asynchronous machines with squirrel-cage rotors and brushless DC motors (BLDC motors) have proven suitable for this purpose.

[0005] Due to the design of the drive motors and the operating principle of a vibratory rammer, a reduction gearbox is required to adapt to the rotational speeds (tamping frequency) required by the tamping system. Such a gearbox requires installation space and additional components. Furthermore, it reduces the efficiency of the drive, which has a particularly detrimental effect due to the limited electrical capacity of the batteries that can be used.

[0006] Fig. 1 Figure 1 shows an example of a vibratory rammer known from the prior art, with an upper mass 1 and a lower mass 2 movable relative to the upper mass 1, which is coupled to the upper mass 1 via a spring assembly 3. The spring assembly 3 supports a spring-mass system in which a forced movement initiated via the upper mass 1 causes a resilient rampling movement of a ground contact plate 4 provided on the lower mass 2.

[0007] An electric motor 5 is provided on the upper mass 1, which drives a crank wheel 7 via a reduction gear 6. A crank pin 8 is provided on the crank wheel 7, which is coupled to a connecting rod 9. The connecting rod 9, in turn, is coupled to a ramming piston 10, the end of which interacts with the spring assembly 3 in a manner known per se.

[0008] A handle 11, e.g. a handle bracket, is attached to the upper mass 1 via a vibration decoupling device 12, e.g. rubber buffer. An operator can guide the vibratory rammer with their hands on the handle 11.

[0009] An energy storage device in the form of a battery 13 is attached to the handle 11.

[0010] At the in Fig. 1 In the illustrated embodiment of a conventional vibratory rammer, the battery 13 is coupled to the electric motor 5, not only to conduct the electrical leads to the electric motor 5, but also to direct a cooling airflow over the battery 13 and the electric motor 5. The cooling airflow can be generated by a blower (not shown), e.g., a fan provided on the electric motor 5.

[0011] In order to accommodate the various components on the rammer, the drive motor usually has to be located outside the rammer axis, which consequently leads to tilting moments during operation of the rammer, reducing the effectiveness of the rammer and impairing its maneuverability.

[0012] In DE 10 2013 020 857 A1 a rammer with a direct drive is described in which the rotor of a drive motor directly drives a crank mechanism.

[0013] From DE 10 2010 055 632 A9 a rammer is known in which an electric motor can set a motor shaft in rotation which is connected to a crank drive via a coupling.

[0014] DE 20 2013 005 536 U1 discloses a rammer in which a drive motor is arranged on the top of an upper mass, wherein the axis of rotation of the motor is arranged parallel to the ramping direction.

[0015] The invention is based on the objective of providing a soil compaction device serving as a vibratory rammer, which enables a particularly compact design with the fewest possible components.

[0016] The object of the invention is achieved by a soil compaction device having the features of claim 1. Advantageous embodiments are specified in the dependent claims.

[0017] A soil compaction device is described, comprising an upper mass and a lower mass movable relative to the upper mass and coupled to the upper mass via a spring mechanism. The lower mass has a soil contact element for soil compaction, and a drive for generating a working movement of the soil contact element is provided on the upper mass. The drive includes a tamping device and an electric motor for driving the tamping device. The tamping device comprises a crank wheel rotatable by the electric motor, a connecting rod coupled to the crank wheel, and a reciprocating tamping piston coupled to the connecting rod, which interacts with the spring mechanism. The electric motor has a stator and a rotor, the rotor being rigidly or elastically coupled to the crank wheel.

[0018] The rotor and the crank wheel thus form a virtually single unit. Relative rotation between the rotor and the crank wheel is not possible – apart from permissible elasticities, e.g., in the case of an elastic coupling. Furthermore, no gearbox, in particular no reduction gearbox, is interposed between the rotor and the crank wheel, as is required in the prior art.

[0019] The electric motor can be a reluctance machine, in particular a synchronous reluctance machine. A synchronous reluctance machine with a segmented stator has proven particularly suitable, where the stator extends only over a specific angular range (stator block).

[0020] The direct coupling of the rotor and crank wheel eliminates the need for the otherwise required reduction gear, thus saving a significant number of components. With appropriate design of the electric motor, it is possible to operate it at a low speed, which is already suitable for the stamping process and the desired stamping frequency. Accordingly, the electric motor must provide sufficient torque at this low speed to powerfully execute the stamping process. A reluctance machine is particularly well-suited for this application.

[0021] Eliminating the reduction gear allows for a particularly compact design of the soil compaction device, which also enables a favorable weight and mass distribution of the components. With appropriate design of the electric motor and the tamping mechanism, it is possible to position the center of gravity of the electric motor on the tamping axis, i.e., on the longitudinal axis of movement of the sub-mass and the tamping piston. This eliminates any leverage effect between the movement of the sub-mass and the center of gravity of the electric motor. As a result, undesirable tilting moments during operation of the tamper can be avoided.

[0022] The rotor can be integrated into the circumference of the crankshaft. In this embodiment, the rotor is essentially replaced by the crankshaft or becomes part of it. The rotor and crankshaft can thus be integrated into a single component. The rotor can be arranged radially on the outer surface of the crankshaft's circumference. The crankshaft and rotor form a single unit, allowing the rotor to perform the function of the crankshaft, particularly driving or moving the connecting rod. This eliminates the need for a conventional engine shaft connecting the rotor and crankshaft.

[0023] The outer circumference of the crank wheel must be designed in a suitable way to serve as a rotor.

[0024] The rotor can thus have multiple rotor poles, which can be arranged around the circumference of the crank wheel.

[0025] The rotor poles can be laminated, meaning they form a laminated core from stacked sheets of metal. For electromagnetic reasons, laminated structures are required for the rotor, so the rotor poles, or the resulting pole wheel, should be formed from stacked sheets.

[0026] The rotor poles can be laminated together with the crank wheel. This means that the rotor poles and the crank wheel together consist of stacked sheets of metal. One sheet can, for example, encompass the contour of the rotor poles on the circumference as well as the inner contour of the crank wheel. By stacking and assembling the sheets, the rotor with the rotor poles and the crank wheel are formed. The sheets can be held together in a suitable manner, for example by pin connections (press fits) or screw connections.

[0027] In one variant, the crank wheel can be made without laminations and support the laminated rotor poles, i.e., the laminated pole wheel, on its circumference. The crank wheel can therefore be made of solid material, e.g., as a turned part (steel or cast). It serves as a support for the rotor with its rotor laminations and carries the layered laminations for the rotor poles on its circumference. Accordingly, the laminated core ring is attached to the circumference of the crank wheel.

[0028] According to the invention, the stator surrounds the rotor over an angle of less than 360°.

[0029] In this variant, the motor stator can no longer be designed as a closed rotating part or a closed ring, but can only extend over a specific angular range. Accordingly, the stator can be designed as a stator segment or stator block and extend over an angle of, for example, 270° or less, 180° or less, 120° or less, or 90° or less.

[0030] Accordingly, it is also possible to distribute several stator segments or stator blocks around the circumference of the rotor, which can increase the performance of the motor and, in particular, the torque of the motor.

[0031] In the intended operating position of the soil compaction device, the stator can be located above the rotor. For example, the stator can be housed in the motor cover or in the cover of the drive housing or crankcase. It does not need to be a single structural unit with the rotor. In particular, the stator and rotor do not need to be housed separately from the crankshaft in a common electric motor housing. Rather, the stator, rotor, and crankshaft can be arranged in a common housing or separately from each other.

[0032] In one variant, at least two crank wheels can be provided, each with a rotor on its circumference, with the connecting rod being driven jointly by both crank wheels. Accordingly, this embodiment can also incorporate multiple rotors and stators, enabling a particularly powerful drive for the stamping device.

[0033] In particular, the two crank wheels and the associated rotors can be aligned coaxially to each other in order to drive the connecting rod in the desired manner.

[0034] At least part of the drive can be enclosed by a drive housing, which may include an airflow generation device for generating a cooling airflow within the drive housing to cool the rotor and stator. The drive housing can accordingly also be understood as a crankcase or engine housing, wherein the stator, rotor, crank wheel, and at least part of the connecting rod, and optionally also part of the piston, are housed inside the drive housing.

[0035] With the help of the airflow generation device, it is possible to generate a cooling airflow inside the drive housing and thus remove heat from the rotor and stator, and possibly also from the stamping device.

[0036] The airflow generating device can have at least one of the following operating principles: The movement of the piston creates an air pump effect to generate the cooling airflow, or: at least one fan blade can be provided on the rotor to generate the cooling airflow. The piston on the one hand and the rotor on the other hand thus have effective surfaces that specifically generate an air movement capable of creating or supporting the desired cooling airflow.

[0037] The drive housing may be provided with an air inlet for the inflow of air from the environment and an air outlet for the release of air into the environment, wherein a check valve may be provided in the air inlet to specify an airflow direction from the environment into the drive housing, and wherein a check valve may be provided in the air outlet to specify an airflow direction from the drive housing into the environment.

[0038] The check valve is therefore a directional valve that allows airflow in only one direction: either into the actuator housing via the air inlet or out of the actuator housing via the air outlet. The check valve can, for example, have a rubber flap-like element that opens or closes a specific opening depending on the direction of airflow.

[0039] In conjunction with the pumping action during the movement of the ram piston, and thus the change in air volume inside the drive housing, fresh air from the surroundings can be drawn into the drive housing via the air inlet and expelled through the air outlet when the ram piston compresses. This allows for a continuous exchange of air inside the drive housing and thus a cooling effect.

[0040] A motor control device may be provided to control the electric motor in such a way that the rotational speed of the rotor, and thus of the crankshaft, can be varied over one or more revolutions of the rotor. The motor control device thus serves to precisely change the rotational speed and therefore the torque. This change is therefore not solely based on a reaction of the tamping system and thus of the soil to be compacted, but on precise control by the motor control device.

[0041] This allows for variation in the movement of the tamping foot, which can be used, for example, to increase the dynamism of the tamping process, but also to stabilize the machine. For example, in cases where the tamping device bounces on a hard surface, the motor's drive energy can be reduced, thereby stabilizing the tamping device.

[0042] It is also possible to deliver a double blow of the tamping device to the soil to be compacted by briefly increasing the rotational speed. This can also reduce the recoil forces acting on the operator of the tamping device, while maintaining high tamping energy.

[0043] The motor control unit can also be used to scale the torque in order to apply different levels of impact to the ground.

[0044] These and other advantages and features of the invention are explained in more detail below using examples and the accompanying figures. They show: Fig. 1 a vibratory rammer known from the prior art as a soil compaction device; Fig. 2 a vibratory rammer as a soil compaction device according to the invention in cutaway side view and front view; Fig. 3 various variants of a vibratory rammer according to the invention in cutaway front view; Fig. 4 further variants of a vibratory rammer according to the invention; Fig. 5 a variant of a vibratory rammer with a rigid coupling of rotor and crank wheel; Fig. 6 a vibratory rammer with an airflow generating device; Fig. 7 a variant of an airflow generating device; Fig. 8 another embodiment of an airflow generating device; Fig. 9 a vibratory rammer with attachable handle; and Fig. 10 a variant of a vibratory rammer according to the invention.

[0045] Fig. 2 Figure 1 shows a vibratory rammer as a soil compaction device according to the invention, in the left part of the image in a side sectional view and in the right part in a front sectional view. Insofar as components are functionally equivalent to the components of the vibratory rammer described above in connection with the prior art, the following applies: Fig. 1 If the reference symbols correspond, the same reference symbols are used.

[0046] Accordingly, the vibratory rammer has an upper mass 1 and a lower mass 2 that is movable relative to the upper mass 1 and is coupled to the upper mass 1 via a spring assembly 3. The spring assembly 3 supports a spring-mass system in which a forced movement (linear reciprocating movement of the ramming piston) initiated via the upper mass 1 causes a resilient ramming movement of a ground contact plate 4 provided on the lower mass 2.

[0047] A handle 11, e.g., a handle bracket, is attached to the upper mass 1 via a vibration decoupling device 12, e.g., a rubber buffer. An operator can guide the vibratory rammer with their hands on the handle 11. An energy storage device in the form of a battery 13 is attached to the handle 11.

[0048] Inside the upper mass 1 is an electric motor 20, comprising a stator 21 and a rotor 22. The electric motor 20 is designed as a synchronous reluctance machine, with the stator 21 being a segmented stator extending only over a range of approximately 90°, as shown in the right part of the image. Fig. 2 recognizable.

[0049] The rotor 22 is arranged on the outer circumference of a crank wheel 23. In this way, the crank wheel 23 is an integral part of the electric motor 20 and is driven directly by it, without an interposed gearbox.

[0050] The rotor 22 can be slightly wider than the thickness of the crank wheel 23, as shown in the left part of the image. Fig. 2 It is evident where the rotor 22 slightly arches over the crank wheel 23.

[0051] The crank wheel 23 drives a connecting rod 25 via a crank pin 24, which in turn sets a tamping piston 26 into a linear reciprocating motion in a manner known per se. The tamping piston 26 interacts with the spring assembly 3 to achieve a resilient tamping motion of the ground contact plate 4 from the guided reciprocating motion of the tamping piston 26.

[0052] The battery 13 is also provided on the upper mass 1 at the handle assembly 11, which is connected to the upper mass 1 via the vibration decoupling device 12. The battery 13 serves to supply energy to the electric motor 20.

[0053] The rotor 22 is made of laminated material and accordingly has a laminated core that is attached to or supported by the crank wheel 23, which is, for example, a turned or forged part. In one variant, the rotor 22 and the crank wheel 23 are formed together from layered sheets, i.e., they are laminated.

[0054] Fig. 3 shows different variants of the tamper from Fig. 2 with differently designed rotors 22 with differently designed rotor poles. In particular, the different variants a to f of Fig. 3 It is evident that the rotors have different numbers of rotor poles.

[0055] Specifically, the different variants have the following special features: a: Combination of crank wheel with synchronous reluctance ring motor b: Synchronous reluctance rotor as crank wheel c: Crank wheel with magnets arranged around the circumference d: Crank wheel with magnets arranged around the circumference and / or inside e: Crank wheel as asynchronous motor rotor; also possible as a combination f: Distinct poles in asynchronous, magnetic or synchronous reluctance motors

[0056] Fig. 4 Figure a on the left shows a variant in which two crank wheels 23 are driven by rotors 22 arranged around the circumference. Accordingly, two coaxially arranged electric motors 20 are provided. The crank wheels 23 together drive the connecting rod 25. The double motor arrangement allows for a particularly compact and powerful drive system.

[0057] In the variant of Fig. 4b The rotor 22 is arranged axially offset from the crank wheel 23. This allows for optimal weight distribution along the stamping axis.

[0058] Fig. 5 shows a different embodiment as a variant to the one by Fig. 4b . Here, the rotor 22 and the crank wheel 23 are arranged coaxially to each other on a common shaft 27 and are positively coupled to each other at least in the circumferential direction by a shaft-hub connection (here: keyway connection).

[0059] Fig. 6 shows a vibratory rammer similar to the one from Fig. 2 .

[0060] Furthermore, it is shown that the stamping piston 26 together with the spring device 3 forms a kind of air pump that intermittently compresses and decompresses the air inside a drive housing 28 enclosing the electric motor 20, the crank wheel 23 and parts of the stamping device.

[0061] The alternating compression and release of air moves the air inside the drive housing 28, creating a cooling airflow that cools the components of the electric motor 20.

[0062] Fig. 7 Figure 2 shows another embodiment with an airflow generating device comprising fan blades 29 arranged on the rotor 23 and the crank wheel 23, respectively. The rotation of the rotor 22 and the crank wheel 23 circulates the air inside the drive housing 28, thereby producing a cooling effect.

[0063] Fig. 8 shows another variant of the airflow generation device.

[0064] The principle is based on the representation of Fig. 6 , so that the linear movement of the lower mass 2 with the spring assembly 3 produces a pumping effect inside the drive housing 28. The drive housing 28 has an air inlet 30 and an air outlet 31. The air inlet 30 is connected via an air duct 30a to a first check valve 32 (inlet check valve 32). An outlet check valve 33 is provided at the air outlet 31.

[0065] In Fig. 8 It is also shown that air is guided over the battery 13 via the air duct 30a extending between the inlet check valve 32 and the air inlet 30, thus initially cooling the battery 13 until the air enters the interior of the drive housing 28.

[0066] During the pumping motion of the submass 2, alternating positive and negative pressures inside the drive housing 28 cause air to be alternately drawn into the drive housing 28 via the inlet check valve 32 and the air inlet 30, and expelled via the air outlet 31 and the outlet check valve 33. The pumping motion of the submass 2 thus creates a continuous flow of cooling air inside the drive housing 28.

[0067] Fig. 9 shows an example of a stamping device according to the invention with a foldable handle 34, wherein in the left part of the image of Fig. 9 The handle 34 is shown in the folded-down position, e.g. a particularly compact transport position, while in the right part of the image it is shown in the unfolded position, namely the operating or working position.

[0068] The battery 13 can be connected to the drive housing 28 via an elastic hose 35 serving as an air duct 30a in order to enable the cooling air flow in the manner described above and to allow the handle 34 to be folded down.

[0069] Fig. 10 shows a variant of the vibratory rammer from Fig. 2 The stator 21 is pivoted by 90° in the direction of the axis of rotation of the rotor 22, i.e., relative to the rotor 22 and thus also to the crank wheel 23. In this way, the overall height of the drive housing 28 and thus of the entire rammer can be reduced.

[0070] The air duct 30a, which extends at least between the battery housing 30 and the drive housing 28, should be present in all variants shown, especially in the variants of Fig. 2 , 4 , 8 and 10 , exhibit a certain elasticity in order to compensate for a relative movement of the handle assembly 11 carrying the battery 13 relative to the drive housing 28 of the upper mass 1.

Claims

1. Ground compaction device, comprising: - an upper mass (1); and comprising - a lower mass (2) which is movable relative to the upper mass (1), is coupled to the upper mass (1) by a spring device (3) and comprises a ground contact element (4) for ground compaction; wherein - a drive for generating a working movement of the ground contact element is provided on the upper mass (1); - the drive has a tamping device and an electric motor (20) for driving the tamping device; - the tamping device has: a crank wheel (23) which can be driven in rotating manner by the electric motor (20), a connection rod (25) which is coupled to the crank wheel (23), and a tamping piston (26) which is coupled to the connection rod (25), can be moved in a reciprocating manner and interacts with the spring device (3); - the electric motor (20) has a stator (21) and a rotor (22); and wherein - the rotor (22) is rigidly or elastically coupled to the crank wheel (23); characterised in that - the stator (21) encloses the rotor (22) over an angle of less than 360 degrees.

2. Ground compaction device as claimed in claim 1, wherein the rotor (22) is formed on the circumference of the crank wheel (23).

3. Ground compaction device as claimed in claim 1 or 2, wherein the rotor (22) has a plurality of rotor poles which are arranged on the circumference of the crank wheel (23).

4. Ground compaction device as claimed in any one of the preceding claims, wherein the rotor poles are laminated.

5. Ground compaction device as claimed in any one of the preceding claims, wherein the rotor poles are laminated together with the crank wheel (23).

6. Ground compaction device as claimed in any one of the preceding claims, wherein the crank wheel (23) is not laminated and carries the laminated rotor poles on its circumference.

7. Ground compaction device as claimed in any one of the preceding claims, wherein, in an intended working position of the ground compaction device, the stator (21) is arranged above the rotor (22).

8. Ground compaction device as claimed in any one of the preceding claims, wherein - at least two crank wheels (23) are provided, on each circumference of which a rotor (22) is provided; and wherein - the connection rod (25) is driven jointly by the two crank wheels (23).

9. Ground compaction device as claimed in any one of the preceding claims, wherein - at least a part of the drive is enclosed by a drive housing (28); and wherein - an air flow generating device is provided for generating a flow of cooling air within the drive housing (28) to cool the rotor (22) and the stator (21).

10. Ground compaction device as claimed in any one of the preceding claims, wherein the air flow generating device has at least one of the following operating principles: - by means of the movement of the tamping piston (26), an air pump effect can be generated for generating the flow of cooling air; - at least one fan blade (29) is provided on the rotor (22) for generating the flow of cooling air.

11. Ground compaction device as claimed in any one of the preceding claims, wherein - an air inlet (30) for the inflow of air from the environment and an air outlet (31) for releasing air into the environment are provided on the drive housing (28); - a check valve (32) is provided in the air inlet (30) for setting an air flow direction from the environment into the drive housing (28); and wherein - a check valve (33) is provided in the air outlet (31) for setting an air flow direction from the drive housing (28) into the environment.

12. Ground compaction device as claimed in any one of the preceding claims, wherein a motor control device is provided for activating the electric motor in such a way that the rotational speed of the rotor (22) and thus the rotational speed of the crank wheel (23) are variable over one or more revolutions of the rotor (22).