A motor device with an automatically adjustable output torque, comprising:
- a hollow frame body including an inner surrounding wall surface that surrounds an axis and that confines an accommodating space extending in an axial direction parallel to the axis;
- at least two magnetic pole pieces of opposite polarity disposed on said inner surrounding wall surface to extend in the axial direction and to be spaced diametrically apart from each other in a first transverse direction radial to the axial direction so as to produce a first magnetic field having a first magnetic flux therebetween;
- an armature disposed to be rotatable between said two magnetic pole pieces, including:
- an armature core including front and rear ends opposite to each other in the axial direction and having two first core segments diametrically opposite to each other in a second transverse direction radial to the axis such that said two first core segments are alternately brought to radially and spacedly face said two magnetic pole pieces, respectively, when said armature is rotated about the axis;
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- an armature winding with first and second ends, said armature winding being disposed on said armature core to produce a second magnetic field having a second magnetic flux in the second transverse direction when electric current flows therethrough via one of said first and second ends;
- an output shaft disposed to extend from said front end of said armature core along said axis so as to be adapted to drive a wheel of a motorcycle;
- a mounting shaft disposed to extend from said rear end of said armature core and coaxial to said output shaft;
- a commutator disposed to be rotated with said mounting shaft about said axis, said commutator including two first conductive segments insulated from each other and respectively and electrically connected to said first and second ends of said armature winding;
- two first brush members adapted to be respectively connected to first positive and negative electrodes of a first DC power supply, and disposed to respectively and slidably contact said two first conductive segments to provide a direct current to said armature winding via one of said two first conductive segments through one of said first and second ends of said armature winding, respectively, so as to initiate rotation of said armature as well as said commutator about the axis, while inducing a counter electromotive force in said armature, and to subsequently maintain the rotation by alternately providing the direct current to said first and second ends of said armature winding via alternate and sliding contact of said two first brush members with said two first conductive segments, respectively;
- a regulating winding with third and fourth ends adapted to be respectively connected to second positive and negative electrodes of a second DC power supply, said regulating winding being disposed on one of said armature core and said magnetic pole pieces to produce a third magnetic field having a third magnetic flux in one of the first and second transverse directions when electric current flows therethrough via one of said third and fourth ends;
- a controlling member adapted to be disposed between said regulating winding and the second DC power supply and to be actuated to permit the flow of direct current from the second DC power supply through said third end to increase the flux amount of said first magnetic flux by adding that of said third magnetic flux so as to induce an increased counter electromotive force in said armature to thereby decrease the speed thereof when a greater torque is needed, or through said fourth end to diminish the flux amount of said first magnetic flux by counteraction of said third magnetic flux which is oriented in the opposite direction relative to that of said first magnetic flux so as to result in a decreased counter electromotive force in said armature to thereby increase the speed thereof when a lower torque is required;
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- a sensor member disposed to actuate said controlling member in response to change of the speed of the wheel of the motorcycle.