The present invention relates to a hand-held machine tool with improved output efficiency and particularly to a hand-held machine tool equipped with a motor including rotor magnetic poles provided in a greater number.
Small machine tools (including pneumatic or electric driven) are compact in size, inexpensive and consume less energy, thus are well accepted in the market. They can be made in a wide variety of types, such as emery grinders, drills, pneumatic (or electric) wrenches or the like. Electric machine tool has advantages of offering precise control of driving current of the electric motor through a circuit and control of rotation rate via regulation of the current or frequency.
The primary object of the electric motor is to provide an output force to drive an output spindle which has a distal end coupled with a tool element. The horsepower and torque provided by the electric motor directly affect work performance of the machine tool. The conventional hand-held machine tool, due to considerations of size and actual operation requirements, often employs the electric motor of high rotation rate, then meets designed specifications by adjusting motor output characteristics or selectively adding a transmission gear set.
For instance, U.S. publication No. 2010/0105287 discloses a hand-held machine tool which includes a housing to hold a motor. The motor includes a casing, a stator (6) and a rotor (7). The rotor is held in the stator. The stator surrounds the rotor to form an internal-rotor motor. Due to internal space constraint of the motor the rotor has fewer magnetic poles. According to electromagnetic principle, the motor of fewer magnetic poles generates mechanical output at a high rotation rate but at a lower torque.
To remedy the drawback of the lower torque, output of the motor with the lower speed inner rotor is incorporated with a gear set so that a greater torque is generated through gear transformation via a plurality of gears. A reference of electric motor incorporating with a gear set can be found in R.O.C. publication No. 200932424 entitled “Chargeable electric driving grinding tool”. It provides an electric grinding tool with a casing to hold a chargeable lithium battery pack, a trigger switch and a driving motor. The driving motor drives an operation disk via a planetary reducing gear set which changes the horsepower and torque finally output to the operation disk. Although the horsepower and torque of the output spindle of the electric motor can be changed via the reducing gear set, the driving power transformation process incurs energy loss, and greater loss occurs when more gears are involved. As a result, electric energy utilization efficiency is lower. Moreover, adopted the gear set increases assembly and installation difficulty, production cost is higher, and more internal space of the machine tool casing is occupied. The lifespan of the gears also affects service life of the hand-held machine tool.
Hence there is still room for improvement on the hand-held machine tool, especially on the lower electric utilization efficiency.
In view of the conventional hand-held electric machine tool that adopts the principle of reducing speed via gear ratio to change the horsepower or torque between the motor and output end that results in driving power loss during gear set operation and lower electric utilization efficiency, the primary object of the present invention is to provide a hand-held machine tool with improved electric utilization efficiency.
The present invention provides a hand-held machine tool with improved output efficiency. It includes a casing, a control circuit located in the casing to connect to a power source and an electric motor. The control circuit determines amount of electric power sent to the electric motor. The electric motor includes a stator, a rotor and an output spindle. The stator has a core and a plurality of stator magnetic poles extended radially from the core. The stator magnetic poles are wound by an exciting winding connected electrically to the control circuit. The core has an axle hole. The output spindle rotatably runs through the axle hole. The rotor has a transmission portion fastened to the output spindle and an induction portion extended from the transmission portion to horizontally correspond to the stator magnetic poles. The induction portion has a plurality of rotor magnetic poles on an inner rim thereof corresponding to the stator magnetic poles. The rotor magnetic poles and stator magnetic poles are magnetically coupled to induce and generate a magnetic force to drive the output spindle to rotate against the stator in the axle hole.
More specifically, the rotor magnetic poles are provided in a number ranged from 16 to 36. The rotor magnetic poles are respectively made of a magnet. The axle hole holds at least one bearing run through by the output spindle to support steady spinning of the output spindle. The output spindle has a tool fastening end exposed outside the axle hole to fasten to a machining tool, and is coupled with a vane set at one end opposite to the tool fastening end. The induction portion of the rotor is located outside the stator to cover the stator magnetic poles. Hence the inner rim of the induction portion has greater space to hold 16 to 36 rotor magnetic poles. As the rotor has more magnetic poles and based on the principle of N=120 F/P (Rotation rate=120× Frequency/Number of magnetic poles of the motor), the rotation rate of the motor can be reduced. According to law of conversation of energy, lower rotation rate of the motor with a given output power has greater rotating torque on the rotor. Hence the invention provides the electric motor with a higher torque without the gear set. Driving power loss caused by the gear set can be reduced and occupying internal space also decreases.
The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.
The present invention aims to provide a hand-held machine tool with improved output efficiency. Please referring to
Please referring to
As shown in
While the invention has been described by means of a specific embodiment set forth above, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the invention set forth in the claims.
In summation of the above description, the present invention provides a significant improvement over the conventional techniques and complies with the patent application requirements, and is submitted for review and granting of the commensurate patent rights.