DC MOTOR STRUCTURE WITH HOLLOW ROTOR AND INNER AND OUTER STATORS

The present invention provides a DC motor structure with a hollow rotor and inner and outer stators includes a housing, a commutator, and an output element, in addition to the hollow rotor and the stators. The commutator and the output element are received at the front and rear ends of the housing respectively. The outer stator, the hollow rotor, and the inner stator are sequentially arranged in the housing in a direction toward the central axis of the housing. The hollow rotor between the stators is wound with plural windings and has a front end and a rear end respectively connected to the commutator and the output element. When each winding receives a current from the commutator, the hollow rotor generates a corresponding electromagnetic field such that the commutator and the output element rotate simultaneously with the hollow rotor to output directly through the output element the rotating force generated by the hollow rotor.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to direct-current motors and more particularly to a direct-current motor structure having a hollow rotor and a stator inside as well as outside the hollow rotor.

2. Description of Related Art

An electric motor, or generally referred to as a motor, serves mainly to convert the electricity received into mechanical energy and produce kinetic energy from the mechanical energy in order to drive another device. Hence, motors have been extensively used in a variety of products such as electric vehicles, lathes, electric fans, and water pumps. Direct-current (DC) motors are the first devices capable of converting electricity into mechanical energy, followed by induction motors and synchronous motors, both of which emerged due to the prevalence of alternating-current (AC) electric power and have since lowered the importance and reduced the applications of DC motors. However, with the advent of silicon controlled rectifiers (SCRs) and the improvement of magnetic materials, carbon brushes, and insulating materials, plus the increasing demand for variable-speed control, DC motors have once again become a crucial technology in industrial automation. This is mainly because both the “rotation speed vs. torque” and “current vs. torque” characteristic curves of DC motors are linear, which renders DC motors simple and easy to control. DC motors, therefore, remain the most common motors for variable-speed control.

Referring toFIG. 1A, the structure of a conventional DC motor1essentially includes a housing10, a pivot shaft11, a rotor12, a stator13, and a commutator14. The housing10is provided therein with a receiving space101. The pivot shaft11is pivotally provided in the housing10and has one end formed as an output shaft111. The output shaft11juts out of the housing10. The rotor12is assembled from a plurality of silicon steel plates, is fixedly mounted around the pivot shaft11, and is wound with a plurality of windings. The stator13is composed of permanent magnets, is fixedly provided on the inner wall of the housing10, corresponds to the outer periphery of the rotor12, and is spaced from the rotor12. The commutator14is provided in the receiving space101, is configured to receive external electricity, and is electrically connected to the windings in order to supply electricity to the windings. The commutator14can also change the direction of the current supplied to the windings. According to Fleming's left-hand rule or right-hand palm rule, a conductive wire placed in a magnetic field and supplied with a current generates a magnetic field which cuts through the existing magnetic field lines such that the conductive wire is moved. When the windings on the rotor12are supplied with electricity, therefore, the magnetic fields generated by the windings cut through the lines of magnetic force generated by the stator13, producing a torque that rotates the rotor12and thereby converts electrical energy into kinetic energy. For example, referring toFIG. 1B, where the lines of magnetic force of the stator13are from left to right, a current flowing into the windings of the rotor12from the right and exiting to the left causes the rotor12to generate a torque that forces the rotor12into clockwise rotation.

Generally, referring back toFIG. 1A, the kinetic energy generated by the rotor12is output through the output shaft111at one end of the pivot shaft11, so it is typically required that a transmission mechanism (e.g., a gear) be mounted to the output shaft111at one end of the pivot shaft11. This transmission mechanism, however, leads to a complicated structure when the DC motor1is put to use. Moreover, the output shaft111, which juts out of the housing10as a free end, often has a small length to prevent the axis of the output shaft111from shifting, but given the typical high rotation speed of the pivot shaft11needed to generate a rotating force large enough to drive the transmission mechanism, the components of the transmission mechanism are subject to wear and tear caused by long-term excessive loading and may hence render uneven the force acting on the output shaft111, thus shifting the axis of the output shaft111anyway.

According to the above, the overall structure of the existing DC motors still leaves room for improvement in practical use. It is therefore an important issue for DC motor manufacturers and designers to develop a novel DC motor structure which can overcome the foregoing problems and generate a rotating force featuring a low rotation speed and a large torque to win users' favor.

BRIEF SUMMARY OF THE INVENTION

In view of the imperfection of the conventional DC motor structure described above, the inventor of the present invention incorporated years of practical experience into extensive research and experiment and finally succeeded in developing a DC motor structure with a hollow rotor and inner and outer stators as disclosed herein. The present invention is intended to provide a DC motor which performs better than its prior art counterparts.

It is an objective of the present invention to provide a DC motor structure having a hollow rotor and inner and outer stators. The DC motor structure includes a housing, an outer stator, a commutator, an output element, a hollow rotor, and an inner stator. The housing is cylindrical and is provided therein with a receiving space. The rear end of the housing is formed with at least one output hole in communication with the receiving space. The commutator and the output element are received at the front and rear ends of the housing respectively. The outer stator, the hollow rotor, and the inner stator are sequentially arranged in the housing in a direction toward the central axis of the housing. The hollow rotor is wound with a plurality of windings. The front and rear ends of the hollow rotor are connected with the commutator and the output element respectively. The two ends of each winding are respectively and electrically connected to two adjacent commutator plates on the commutator in order to receive the current supplied by the commutator. Each two adjacent commutator plates on the commutator are configured to reverse the current direction in the corresponding winding at a preset frequency so that the electromagnetic field generated by the corresponding winding is simultaneously reversed too. The reversal of current direction is repeated again and again at the preset frequency in order for the hollow rotor to generate the corresponding electromagnetic fields. The outer stator includes a plurality of outer magnets which are fixed to the inner wall of the housing along the circumferential direction of the housing. Each two adjacent outer magnets are spaced apart and are opposite in polarity. The inner stator includes a plurality of inner magnets which are fixed to the outer periphery of the inner stator along the circumferential direction of the housing. Each two adjacent inner magnets are spaced apart and are opposite in polarity. Moreover, the inner magnets correspond to the outer magnets respectively. When the windings receive the currents supplied by the commutator and generate the corresponding electromagnetic fields, both the inner magnets of the inner stator and the outer magnets of the outer stator are repelled by the electromagnetic fields such that the hollow rotor is rotated and drives the output element simultaneously. Thus, by way of a transmission element (e.g., a chain or belt), the rotating force generated by the hollow rotor is output by the output element to a load (e.g., a gearbox) through the output hole, wherein the rotating force features a low rotation speed and a large torque. The power efficiency and service life of the DC motor structure are therefore improved in comparison with those of the conventional DC motors.

DETAILED DESCRIPTION OF THE INVENTION

As stated above, the conventional DC motors output power via an output shaft, which, like the output shaft111inFIG. 1A, is part of a pivot shaft. Therefore, when the load of a conventional DC motor (e.g., the gearbox of an electric vehicle, or other large equipment) has to be driven by a great rotating force, the conventional DC motor must rotate at high speed to generate the required rotating force. And because of that, the conventional DC motor is subject to structural damage and consumes considerable electricity. In light of this, the inventor of the present invention specifically designed a novel DC motor structure which dispenses with the output shaft111inFIG. 1Aand is capable of driving a transmission mechanism by generating a large torque at a low rotation speed. It should be pointed out that the DC motor structure with a hollow rotor and inner and outer stators of the present invention is not limited to that which is depicted in the accompanying drawings. A person skilled in the art who has fully grasped the technical features of the invention should be able to adjust the shapes and number of the components in the embodiments disclosed herein.

The present invention provides a DC motor structure having a hollow rotor and inner and outer stators. In a preferred embodiment of the invention, referring toFIG. 2andFIG. 3(with the leftward direction inFIG. 2defined as the front direction of each component, and the rightward direction, the rear direction of each component), the DC motor structure2includes a housing20, an outer stator21, a commutator22, an output element23, a hollow rotor24, and an inner stator25. The housing20is cylindrical and is provided therein with a receiving space200. The rear end of the housing20is formed with three output holes201in communication with the receiving space200. In other embodiments of the present invention, however, there may be only one output hole201, and the configuration of the at least one output hole201may vary according to practical needs. In the present invention, the term “output hole201” refers to a space through which the output element23can connect with an external transmission mechanism, and all arrangements allowing the output element23to connect with an external transmission mechanism should be viewed as equivalent configurations. The present invention imposes no limitations on the configuration of the at least one output hole201.

In this embodiment, the housing20is assembled from a front cover20A, a rear cover20B, and a housing body20C. The front cover20A is peripherally provided with a plurality of front connecting portions202A (e.g., locking holes). A plurality of carbon brushes204are mounted in the front cover20A and are configured to receive an external current. The rear cover20B is provided with the output holes201and is peripherally provided with a plurality of rear connecting portions202B (e.g., locking holes). The housing body20C is tubular and is engaged between the front cover20A and the rear cover20B. Each corresponding pair of front connecting portion202A and rear connecting portion202B can be respectively and fixedly connected with the two ends of a connecting rod203to connect the front cover20A, the rear cover20B, and the housing body20C together, thereby forming the housing20of the present invention. To prevent the housing body20C from rotation, the front cover20A and the rear cover20B are each provided with a plurality of engaging portions205(e.g., protruding plates) for engaging with one of the two ends of the housing body20C. In other embodiments of the present invention, however, the housing20may be designed as a single component or as a combination of at least two components (e.g., the front cover20A and the rear cover20B alone, or with more than one housing body20C). The housing20is by no means limited to the assembly of the three components disclosed herein, i.e., the front cover20A, the rear cover20B, and the housing body20C.

As shown inFIG. 2, the outer stator21is mounted in the receiving space200and includes a plurality of outer magnets211. In this embodiment, the outer magnets211are located in the housing body20C and are fixed to the inner wall of the housing body20C along the circumferential direction of the housing body20C (i.e., of the housing20). Each two adjacent outer magnets211are spaced apart and are opposite in polarity. Each outer magnet211can be a single magnetic component or composed of a plurality of magnetic components of the same polar direction; the present invention has no limitations in this regard. In other embodiments of the present invention, the outer stator21may further include an outer stator body which is tubular and is fixed to the inner wall of the housing20, with the outer magnets211fixed in the outer stator body. This allows the outer stator21to be manufactured independently or custom-made, adding to the convenience of production. It is worth mentioning that the outer stator body, if provided, resembles the housing body20C in configuration, and that the outer stator body not only can be omitted as in this embodiment, but also can be integrated with the housing20, in order to reduce the number of components of the DC motor structure2.

Referring toFIG. 2andFIG. 3, the commutator22is mounted in the receiving space200and is pivotally connected to the inner wall of the front end of the housing20along the axial direction of the housing20. In this embodiment, the commutator22is located in the front cover20A and is electrically connected to the carbon brushes204in the front cover20A in order to receive an external current through the carbon brushes204. The commutator22includes a disk220and a plurality of commutator plates221. The commutator plates221are mounted on the front side of the disk220, with a space between each two adjacent commutator plates221. It should be pointed out that the electrical connection between the carbon brushes204and the commutator22of the present invention is well known in the art and therefore will not be detailed herein. The carbon brushes204and the commutator22can be connected in many different ways provided that they can deliver an electric current to each other. The output element23is mounted in the receiving space200, is pivotally connected to the inner wall of the rear end of the housing20along the axial direction of the housing20, and corresponds in position to the output holes201. In this embodiment, the output element23is gear-shaped, is located in the rear cover20B, and corresponds in position to the output holes201. A transmission element (e.g., a chain) can be passed through the output holes201and connected with the output element23, allowing the kinetic energy generated by the DC motor structure2during operation to be output to a load (e.g., a gearbox) sequentially through the output element23and the transmission element, in order for the kinetic energy to drive the load into operation. In other embodiments of the present invention, however, the output element23may be a hub or other components, and the transmission element may be a closed-loop belt or other components. That is to say, the output element23may vary in configuration, depending on the load and the form of the transmission element, so that the DC motor structure2of the present invention can be applied to a greater variety of equipment or devices.

With continued reference toFIG. 2andFIG. 3, the hollow rotor24is mounted in the outer stator21along the axial direction of the housing20and is spaced from the outer stator21by a first spacing24A to enable free rotation of the hollow rotor24within the outer stator21. The hollow rotor24is assembled from a plurality of iron cores. An axial hole240is formed in the hollow rotor24and extends along the axial direction of the hollow rotor24. The front end of the hollow rotor24is connected with the commutator22while the rear end of the hollow rotor24is connected with the output element23. The hollow rotor24is wound with a plurality of windings27. Each winding27has two ends respectively and electrically connected to two adjacent commutator plates221on the commutator22in order to receive a current from the commutator22and thereby cause the hollow rotor24to generate a corresponding electromagnetic field. Each two adjacent commutator plates221on the commutator22can reverse the current direction in the corresponding winding27at a preset frequency so that the electromagnetic field generated by the corresponding winding27is reversed at the same time. The reversal of current direction is repeated again and again at the preset frequency. When rotated under the action of magnetic fields, the hollow rotor24rotates the commutator22and the output element23simultaneously.

Reference is now made toFIG. 2andFIG. 4for a detailed description of the structure of the hollow rotor24. The hollow rotor24includes an outer iron core241and an inner iron core242. Each of the outer iron core241and the inner iron core242is assembled from a plurality of silicon steel plates. The outer surface of the outer iron core241is provided with a plurality of outer winding grooves243which extend along the axial direction of the outer iron core241. The inner surface of the outer iron core241is provided with a plurality of first recesses244A which also extend along the axial direction of the outer iron core241. The inner surface of the inner iron core242is provided with a plurality of inner winding grooves245which extend along the axial direction of the inner iron core242, and the outer surface of the inner iron core242is provided with a plurality of second recesses244B which also extend along the axial direction of the inner iron core242. The outer winding grooves243and the inner winding grooves245are configured to be wound with the windings27. When the outer iron core241and the inner iron core242are put together, the inner surface of the outer iron core241lies against the outer surface of the inner iron core242, with each first recess244A corresponding to one second recess244B to form a fixing hole244. The fixing holes244, therefore, are arranged along the circumferential direction of the hollow rotor24. A plurality of fixing rods246are inserted into the fixing holes244respectively to connect with the hollow rotor24. The front end of each fixing rod246is exposed from the hollow rotor24and is fixed to the rear side of the disk220of the commutator22. The rear end of each fixing rod246is also exposed from the hollow rotor24and is fixed to the output element23. As a result, the hollow rotor24, the commutator22, and the output element23are assembled together as a single unit for simultaneous rotation.

Referring again toFIG. 2andFIG. 4, in order to prevent the commutator22and the output element23from contact with the windings27on the hollow rotor24, the front and rear ends of each fixing rod246are each mounted with a position-limiting tube247whose outer diameter is greater than the diameter of the fixing holes244and which therefore cannot extend into any fixing hole244and is located either between the commutator22and the hollow rotor24or between the output element23and the hollow rotor24to keep the commutator22or the output element23from contact with the windings27on the hollow rotor24. It should be pointed out that, in other embodiments of the present invention, the hollow rotor24, the commutator22, and the output element23may be connected in other ways, provided that the hollow rotor24is able to drive the commutator22and the output element23simultaneously and is spaced from each of the commutator22and the output element23by a predetermined spacing.

As shown inFIG. 2andFIG. 4, the outer iron core241and the inner iron core242are fixedly connected together by the windings27, which prevent the outer iron core241and the inner iron core242from separation from each other and thereby fix the fixing rods246in the fixing holes244respectively. The windings27of the present invention are wound in the following manner, although in other embodiments of the invention the windings27may be wound onto the hollow rotor24by different methods. Referring toFIG. 5, which shows only a portion of the hollow rotor24and two windings27for the sake of simplicity, the outer surface of the outer iron core241is formed with two adjacent outer winding grooves243A and243B, and the inner surface of the inner iron core242is formed with two adjacent inner winding grooves245A and245B. The outer winding groove243A corresponds to the inner winding groove245A while the outer winding groove243B corresponds to the inner winding groove245B. One end (hereinafter the first end) of the winding27A is electrically connected to a commutator plate221. The other end (hereinafter the second end) of the winding27A is inserted into the front end of the outer winding groove243A; passes through the outer winding groove243A; extends out of the rear end of the outer winding groove243A; is then inserted into the rear end of the inner winding groove245A; passes through the inner winding groove245A; extends out of the front end of the inner winding groove245A; runs diagonally to and is inserted into the outer winding groove243B; then runs sequentially through the outer winding groove243B, the rear end of the outer winding groove243B, the rear end of the inner winding groove245B, and the inner winding groove245B; extends out of the front end of the inner winding groove245B; and is electrically connected to another commutator plate (hereinafter the second commutator plate)221. The winding27A wound in the foregoing manner is referred to as one turn of winding27A. When it is desired to wind another turn or more turns of winding27onto the hollow rotor24, all that needs to be done is to pass diagonally the winding27A jutting out of the front end of the inner winding groove245B into the front end of the outer winding groove243A and then repeat the winding steps described above. The winding27B is adjacent to the winding27A and has its second end (equivalent to the second end of the winding27A) jutting out of the front end of the inner winding groove245A. Thus, both the first end of the winding27A and the second end of the winding27B are electrically connected to the same commutator plate221. While supplying a current to the first end of the winding27A, this commutator plate221receives the current delivered through the second end of the winding27B. When the commutator plate221subsequently performs reversal of current direction, the aforesaid current directions are reversed, in order for each of the windings27A and27B to generate an electromagnetic field corresponding to the existing current direction.

Referring back toFIG. 2andFIG. 3, the inner stator25is mounted in the axial hole240of the hollow rotor24, and the front and rear ends of the inner stator25are fixed to the front and rear ends of the housing20respectively. The inner stator25is spaced from the hollow rotor24by a second spacing24B to enable free rotation of the hollow rotor24outside the inner stator25. In this embodiment, the inner stator25includes an inner stator body250and a plurality of inner magnets251. The inner magnets251are fixed to the outer wall of the inner stator body250along the circumferential direction of the housing20. Each two adjacent inner magnets251are spaced apart and are opposite in polarity. Each inner magnet251can be a single magnetic component or composed of a plurality of magnetic components of the same polar direction; the present invention has no limitations in this regard. Two positioning rods252are respectively and protrudingly provided at the front and rear ends of the inner stator body250and are fixed to the front and rear ends of the housing20via bearings26A and26B respectively, wherein the bearings26A and26B are respectively and pivotally connected to the commutator22and the output element23. Thus, when the hollow rotor24, the commutator22, and the output element23are rotated, the inner stator25will not be driven, and stability of the inner stator25is maintained. In this embodiment, the positioning rods252are fixed to the front cover20A and the rear cover20B respectively. In other embodiments of the present invention, however, the fixing positions and methods of the positioning rods252may vary as appropriate. That is to say, the connection between the inner stator25and the housing20may vary, provided that the inner stator25is fixed in the housing20and is kept from rotation. In addition, the inner stator body250can be adjusted in configuration or even omitted, provided that the inner stator25is mounted in the axial hole240of the hollow rotor24, that the front and rear ends of the inner stator25are fixed to the front and rear ends of the housing20respectively, and that the inner magnets251are fixed to the outer periphery of the inner stator25along the circumferential direction of the housing20.

Referring toFIG. 2, once the outer stator21, the hollow rotor24, and the inner stator25are put together, the inner magnets251correspond to the outer magnets211respectively. In a preferred embodiment, each pair of corresponding inner magnet251and outer magnet211have the same polarity. In practice, however, the winding schemes may be modified in such a way that each pair of corresponding inner magnet251and outer magnet211have opposite polarities to suit the current directions in different sections of the windings27. As shown inFIG. 2, when the windings27receive the currents supplied by the commutator22and generate the corresponding electromagnetic fields, the electromagnetic fields repel the magnetic fields generated by the inner stator25and the outer stator21; in consequence, the hollow rotor24is rotated and drives the output element23simultaneously. The output element23drives the transmission element and the load in turn through the output holes201such that the rotating force generated by the hollow rotor24and featuring both a low rotation speed and a large torque is output to the load. It can be known from the above that the DC motor structure2of the present invention is totally different from the conventional DC motors: a conventional DC motor drives a load through the output shaft, which, exemplified by the output shaft111inFIG. 1A, is a portion of the motor shaft, whereas the present invention drives a load through the output element23, which is fixed to the rear end of the hollow rotor24by plural fixing rods246and has a greater volume than the conventional output shaft to prevent the axis shift problem typical of the conventional DC motors. Furthermore, compared with the conventional DC motors, the DC motor structure2of the present invention can generate a greater rotating force at a low rotation speed, so the components of the DC motor structure2are subject to less wear and tear; that is to say, the DC motor structure2is expected to have a longer service life.