Patent Publication Number: US-2023140885-A1

Title: Soil Compacting Device Having an Electric Drive

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a soil compacting device with an electric drive. 
     2. Description of the Related Art 
     Such a soil compacting device, in particular a so-called vibration tamper or vibrotamper, is widely known and is used for compacting soil and asphalt layers. The tampers are driven in many ways by internal combustion motors, e.g., two-stroke motors. It is also known to provide electric drive motors. 
     In an electric drive, the electric motor is usually operated at a higher speed and, via a reduction gear, drives a spring-mass system that serves as a tamping system. The electric drive motor is fed either from the electrical power supply or from rechargeable batteries that are carried along. 
     The electric drive motors have a stator and a rotor. Asynchronous machines with squirrel-cage rotors and brushless direct current motors (BLDC motors) have proven to be suitable. 
     Due to the design of the drive motors and the mode of operation of a vibration tamper, a reduction gear is required to adapt the speeds (tamping frequency) required by the tamping system. Such a gear requires installation space and additional components. In addition, it reduces the efficiency of the drive, which has a disadvantageous effect primarily due to the limited electrical capacity of the rechargeable batteries that can be used. 
       FIG.  1    shows an example of a vibration tamper known from the prior art, comprising 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 mechanism or simply spring  3 . Spring  3  supports a spring-mass system, in which a forced movement introduced via upper mass  1  causes a spring-action tamping movement of a ground contact plate  4  provided on lower mass  2 . 
     An electric motor  5  is provided on upper mass  1  and drives a crank wheel  7  in a rotating manner via a reduction gear  6 . A crank pin  8  is provided on the crank wheel  7  and is coupled to a connection rod  9 . Connection rod  9  in turn is coupled to a tamping piston  10 , the end of which interacts with the spring  3  in a manner known per se. 
     A handle  11 , for example, a handlebar, is attached to upper mass  1  via a vibration decoupling  12 , for example, rubber buffers. An operator can guide the vibration tamper with his/her hands on the handle  11 . 
     An energy storage in the form of a rechargeable battery  13  is attached to handle  11 . 
     In the embodiment of a conventional vibration tamper shown in  FIG.  1   , the rechargeable battery  13  is coupled to electric motor  5 , not only in order to route the electrical leads to electric motor  5 , but also to guide a flow of cooling air over rechargeable battery  13  and electric motor  5 . The flow of cooling air can be generated by a blower, not shown, for example by a fan provided on electric motor  5 . 
     In order to be able to accommodate the various components on the tamper, the drive motor must generally be arranged outside of the tamper axis, so that tilting moments occur as a result during operation of the tamper, decreasing the effectiveness of the tamper and downgrading the controllability. 
     SUMMARY OF THE INVENTION 
     The underlying object of the invention is to specify a soil compacting device that serves as a vibration tamper, which enables a particularly compact construction with the smallest possible number of components. 
     The object is achieved according to the invention by a soil compacting device having an upper mass and a lower mass which is coupled to the upper mass by a spring and which is movable relative to the upper mass and comprises a ground contact element for soil compaction. A a drive for generating a working movement of the ground contact element is provided on the upper mass. The drive has a tamping device and an electric motor for driving the tamping device. The tamping device has: a crank wheel that can be driven in rotating manner by the electric motor, a connection rod coupled to the crank wheel, and a tamping piston which can be moved in reciprocating fashion and is coupled to the connection rod and which interacts with the spring. The electric motor has a stator and a rotor which is rigidly or elastically coupled to the crank wheel. 
     Thus, the rotor and the crank wheel virtually form a unit. A relative rotation between the rotor and the crank wheel is not possible, apart from permissible elasticities, for example, in the case of an elastic coupling. There is also no gear interposed between the rotor and the crank wheel, in particular no reduction gear, as is required in the prior art. 
     The electric motor can be a reluctance machine, in particular a synchronous reluctance machine. A synchronous reluctance machine with a segmented stator has proven to be particularly suitable, in which the stator only extends over a specific angular range (stator block). 
     Due to the direct coupling of rotor and crank wheel, the intermediate reduction gear otherwise interposed can be dispensed with, so that a significant number of components can be eliminated. With an appropriate design of the electric motor, it is possible to operate the electric motor at a low speed, which is already suitable for the tamping process and the desired tamping frequency. Accordingly, the electric motor must provide sufficient torque at this low speed in order to be able to carry out the tamping process powerfully. A reluctance machine is particularly suitable for this purpose. 
     The omission of the reduction gear enables a particularly compact construction of the soil compacting device, which also allows a favorable weight or mass distribution of the components. With a corresponding configuration of the electric motor and the tamping device, it is possible that the center of gravity of the electric motor is arranged on the tamping axis, i.e., on the longitudinal axis of the movement of the lower mass and the tamping piston. There is then no leverage between the movement of the lower mass and the center of gravity of the electric motor. As a result, undesired tilting moments can be avoided during operation of the tamper. 
     The rotor can be formed on the circumference of the crank wheel. In this embodiment, the rotor is virtually replaced by the crank wheel, or it becomes part of the crank wheel. In this way, the rotor and crank wheel can be integrated to form one part. In this case, the rotor can be arranged radially on the outside on the circumference of the crank wheel. Crank wheel and rotor form a unit, so that the rotor can take over the function of the crank wheel, i.e., in particular driving or moving the connection rod. A classic motor shaft for connecting the rotor and crank wheel can thus be dispensed with. 
     The outer circumference of the crank wheel must be suitably configured in order to be used as a rotor. 
     The rotor can thus have a plurality of rotor poles, which can be arranged on the circumference of the crank wheel. 
     The rotor poles can be laminated, i.e., form a laminated core of stacked laminations. For electromagnetic reasons, laminated structures are to be provided for the rotor, so that the rotor poles and the pole wheel formed thereby are formed by stacked laminations. 
     The rotor poles can be laminated together with the crank wheel. That means, that the rotor poles and the crank wheel together consist of stacked laminations. A lamination can, for example, comprise the contour of the rotor poles on the circumference and of the crank wheel on the inside. By stacking and assembling the laminations, the rotor with the rotor poles and the crank wheel are formed. The laminations can be held together in a suitable manner, for example, by means of pin connections (press fits) or screw connections. 
     In one variant, the crank wheel can be embodied without laminations and can carry the laminated rotor poles, i.e., the laminated magnet wheel, on its circumference. Accordingly, the crank wheel can be embodied solid, for example, as a turned part (steel turned part or cast turned part). It serves as a carrier for the rotor with the rotor laminations and carries the stacked laminations for the rotor poles on the circumference. Accordingly, the laminated core ring is fastened to the circumference of the crank wheel. 
     The stator can enclose the rotor over an angle of less than 360°. In this variant, the motor stator can no longer be embodied as a closed rotary part or as a closed ring, but can only extend over a specific angular range. Accordingly, the stator can be embodied 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. 
     Accordingly, it is also possible to distribute several stator segments or stator blocks on the circumference of the rotor, as a result of which the performance of the motor and in particular the torque of the motor can be increased. 
     In an intended working position of the soil compacting device, the stator can be arranged above the rotor. For example, the stator can be held in the motor cover or in the cover of the drive housing or crankcase. In this case, it does not have to form a structural unit with the rotor. In particular, the stator and rotor do not have to be accommodated separately from the crank wheel in a common electromotor housing. Rather, the stator, the rotor and the crank wheel can be arranged in a common housing or separately from one another. 
     In one variant, at least two crank wheels can be provided, on the circumference of each of which a rotor is provided, with the connection rod being driven jointly by the two crank wheels. Accordingly, several rotors and stators can also be provided in this embodiment, as a result of which a particularly powerful drive of the tamping device is possible. 
     In particular, the two crank wheels and the associated rotors can be aligned coaxially in order to be able to drive the connection rod in the desired manner 
     At least part of the drive may be enclosed by a drive housing, wherein an airflow generating device may be provided for generating a flow of cooling air within the drive housing to cool the rotor and the stator. Accordingly, the drive housing can also be considered to be a crankcase or a motor housing, with the stator, the rotor, the crank wheel and at least part of the connection rod and possibly also part of the tamping piston being accommodated inside the drive housing. 
     Using the air flow generating device, it is possible to generate a flow of cooling air inside the drive housing and thus to dissipate heat from the rotor and stator, but possibly also from the tamping device. 
     The air flow generating device can have at least one of the following operating principles: An air pump effect can be generated by the movement of the tamping piston for generating the flow of cooling air, or: on the rotor at least one fan blade can be provided for generating the flow of cooling air. The tamping piston on the one hand and the rotor on the other hand thus have effective surfaces that specifically generate an air movement that can form or support the desired flow of cooling air. 
     An air inlet for the inflow of air from the environment and an air outlet for releasing air to the environment can be provided on the drive housing, wherein a check valve can be provided in the air inlet for setting an air flow direction from the environment into the drive housing, and wherein a check valve can be provided in the air outlet for setting an air flow direction from the drive housing into the environment. 
     The check valve is therefore a directional valve that allows air to flow only in one direction, namely either into the drive housing via the air inlet or out of the drive housing via the air outlet. The check valve can have, for example, a rubber flap-like element which, depending on the direction of the air flow, opens or closes a relevant opening. 
     In connection with the pumping action when the tamping piston is moving and thus a change in the air volume inside the drive housing, fresh air from the environment can be sucked into the drive housing via the air inlet, and with a compressing action of the tamping piston can be expelled via the air outlet. As a result, a constant exchange of air in the interior of the drive housing and thus a cooling effect can be achieved. 
     A motor controller be provided for controlling the electric motor in such a way that the speed of the rotor and thus the speed of the crank wheel is variable over one or more revolutions of the rotor. The motor controller is thus used for a targeted change in the speed and thus in the torque. This change is therefore based not only on a reaction of the tamping system and thus of the soil to be compacted, but on a targeted activation by the motor controller. 
     In this way, a variation of the movement of the tamping foot is possible, which, e.g., can be utilized to dynamize the tamping process, but can also be used to quiet the machine. For example, in cases where the tamping device jumps onto a hard ground, the drive power of the motor can be reduced, and the tamping device can thereby be quieted. 
     It is also possible to apply a double impact of the tamping device to the soil to be compacted by briefly increasing the speed. This can also result in the recoil forces acting on the operator operating the tamping device being able to be reduced, with high tamping energy at the same time. 
     The motor controller can also be used to scale the torque to apply impact of different intensities to the ground. 
     These and other features and advantages of the invention will become apparent to those skilled in the art from the following detailed description and the accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other advantages and features of the invention are explained in more detail below using examples with the aid of the accompanying figures. In the figures: 
         FIG.  1    shows a vibration tamper known from the prior art as a soil compacting device; 
         FIG.  2    shows a vibration tamper as a soil compacting device according to an embodiment the invention in a sectional side view and front view 
         FIG.  3    shows different variants of a vibration tamper according to an embodiment of the invention in a sectional front view; 
         FIG.  4    shows further variants of a vibration tamper according to embodiments of the invention; 
         FIG.  5    shows a variant of a vibration tamper with a rigid coupling of rotor and crank wheel; 
         FIG.  6    shows a vibration tamper with an air flow generating device; 
         FIG.  7    shows a variant of an air flow generating device; 
         FIG.  8    shows another embodiment of an air flow generating device; 
         FIG.  9    shows a vibrating tamper with a retractable handle; and 
         FIG.  10    shows a variant of a vibration tamper according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  2    shows a vibration tamper as a soil compacting device according to the invention, in a lateral sectional view in the left part of the picture and in a sectional front view in the right part of the picture. As far as components correspond functionally to the components of the vibration tamper of  FIG.  1    explained above in connection with the prior art, the same reference numerals are used. 
     Accordingly, the vibration tamper 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 mechanism, or simply, spring controller  3 . Spring controller  3  supports a spring-mass system, in which a forced movement (linear reciprocating movement of the tamping piston) initiated via upper mass  1  causes a spring-action tamping movement of a ground contact plate  4  provided on lower mass  2 . 
     A handle controller  11 , e.g., a handlebar, is attached to upper mass  1  via a vibration decoupling controller  12 , for example rubber buffers. An operator can guide the vibration tamper with his/her hands on handle controller  11 . An energy storage controller in the form of a rechargeable battery  13  is attached to handle controller  11 . 
     Inside upper mass  1 , provision is made for an electric motor  20 , comprising a stator  21  and a rotor  22 . Electric motor  20  is embodied as a synchronous reluctance machine, with stator  21  being a segmented stator, which only extends over a range of approximately 90°, as can be seen in the right-hand part of  FIG.  2   . 
     Rotor  22  is arranged on the outer circumference of a crank wheel  23 . In this way, crank wheel  23  is an integral part of electric motor  20  and is driven directly by it without a gear being interposed. 
     Rotor  22  can be designed slightly wider than the thickness of crank wheel  23 , as can be seen in the left-hand part of  FIG.  2   , where rotor  22  slightly arches over crank wheel  23 . 
     Crank wheel  23  drives a connection rod  25  via a crank pin  24 , which connection rod  25  in turn causes a tamping piston  26  to move in a linear reciprocating fashion in a manner known per se. Tamping piston  26  interacts with spring controller  3  in order to achieve a spring-action tamping movement of ground contact plate  4  from the guided reciprocating movement of tamping piston  26 . 
     Rechargeable battery  13  is also provided on upper mass  1  on handle controller  11 , which is connected to upper mass  1  via vibration decoupling device  12 . Rechargeable battery  13  serves to supply electric motor  20  with energy. 
     Rotor  22  is embodied in laminated fashion and, accordingly, has a laminated core which is fastened to or carried by crank wheel  23 , which is embodied, for example, as a rotary part or a forged part. In one variant, it is possible that rotor  22  and crank wheel  23  are formed together by stacked sheet metals, i.e., they are embodied in a laminated fashion. 
       FIG.  3    shows different variants of the tamper from  FIG.  2   , each with differently configured rotors  22  with differently configured rotor poles. In particular, it can be seen in the different variants a to f of  FIG.  3    that the rotors have different numbers of rotor poles. 
     In particular, the different variants have the following features:
         a: combination crank wheel with synchronous reluctance ring motor   b: synchronous reluctance rotor as a crank wheel   c: crank wheel with magnets arranged on the circumference   d: crank wheel with magnets arranged on the circumference and/or on the inside   e: crank wheel as an asynchronous motor rotor; also, possible as a combination   f: salient poles in asynchronous, magnetic or synchronous reluctance motors       

     In the left-hand part a,  FIG.  4    shows a variant in which two crank wheels  23  are driven by rotors  22  arranged on the circumference. Accordingly, two electric motors  20  arranged coaxially to one another are provided. Crank wheels  23  drive jointly connection rod  25 . A particularly compact and powerful drive can be implemented due to the double motor arrangement. 
     In the variant of  FIG.  4     b,  rotor  22  is arranged axially offset with respect to crank wheel  23 . This allows the weight distribution along the tamping axis to be optimally designed. 
       FIG.  5    shows another embodiment as a variant to that of  FIG.  4     b.  Here, rotor  22  and crank wheel  23  are arranged coaxially on a common shaft  27  and coupled to one another by a shaft-hub connection (here: feather key connection) in a form-fitting manner at least in the circumferential direction. 
       FIG.  6    shows a vibration tamper similar to that of  FIG.  2   . 
     In addition, it is illustrated that tamping piston  26  together with spring controller  3  forms a kind of air pump, which compresses and decompresses at intervals the air inside a drive housing  28  enclosing electric motor  20 , crank wheel  23  and parts of the tamping device. 
     The air is moved inside drive housing  28  as a result of the alternating compression and relief, as a result of which a flow of cooling air is created, which cools the components of electric motor  20 . 
       FIG.  7    shows another embodiment with an air flow generating device having fan blades  29 , which are arranged on rotor  23  and crank wheel  23 , respectively. Due to the rotation of rotor  22  and crank wheel  23 , the air inside the drive housing  28  is circulated, resulting in a cooling effect. 
       FIG.  8    shows a further variant of the air flow generating device. 
     The principle is based on the illustration in  FIG.  6   , so that the linear movement of lower mass  2  with spring controller  3  achieves a pumping effect inside drive housing  28 . Drive housing  28  has an air inlet  30  and an air outlet  31 . Air inlet  30  communicates with a first check valve  32  (inlet check valve  32 ) via an air duct  30   a.  An outlet check valve  33  is provided at air outlet  31 . 
       FIG.  8    also shows that air is guided over rechargeable battery  13  via air duct  30   a  extending between inlet check valve  32  and air inlet  30 , and thus the air initially cools rechargeable battery  13  until the air enters the interior of drive housing  28 . 
     Due to the alternating positive and negative pressures inside drive housing  28  during the tamping movement of lower mass  2 , air is alternately sucked into drive housing  28  via inlet check valve  32  and air inlet  30  and is expelled via air outlet  31  and outlet check valve  33 . A constant flow of cooling air inside drive housing  28  can thus be brought about by the pumping movement of lower mass  2 . 
       FIG.  9    shows an example of a tamping device according to an embodiment of the invention comprising a retractable handlebar  34 , with handlebar  34  depicted in the left-hand part of  FIG.  9    in a retracted position, e.g. a particularly compact transport position, while being depicted in the right-hand part of the figure in the unfolded position, namely the operating or working position. 
     Rechargeable battery  13  can be connected to the drive housing  28  via an elastic hose serving as an air duct  30   a  to enable the flow of cooling air in the manner described above and to allow the handlebar to be unfolded. 
       FIG.  10    shows a variant of vibration tamper of  FIG.  2   . In this case, stator  21  is pivoted by 90° in the direction of the axis of rotation of rotor  22 , i.e., relative to rotor  22  and thus also to crank wheel  23 . In this way the construction height of drive housing  28  and thus of the entire tamper can be reduced. 
     Air duct  30   a  extending at least between the housing of rechargeable battery  30  and drive housing  28  should have a certain elasticity in all variants shown, in particular also in the variants of  FIGS.  2 ,  4 ,  8  and  10   , to be able to compensate a relative movement of handle controller  11  carrying rechargeable battery  13  relative to the drive housing  28  of upper mass  1 .