Background technology
Figure 12 (A) is the cutaway view that existing miniature motor is cut open from commutator.And (B) be with a pair of carbon brush of this commutator portion sliding contact in an enlarged drawing of being showed after pulling down.As shown in the figure, in miniature motor, the commutator core by resin manufacture on armature spindle is equipped with commutator, and, be installed on the end cap by brush carrier with the carbon brush of the commutator sliding contact of this rotation.End cap is embedded in the peristome of motor chassis.Illustrated commutator is made of 3 commutator segments, and groove is arranged respectively between each commutator segment.
In the past, the carbon brush that has that generally will have the above-mentioned commutator that is made of 3 commutator segments has the width (circumferential lengths) of the carbon brush of motor unshakable in one's determination, be designed to a commutator segment circumferential lengths 40~60%.For example, auto mirror minute surface drive motor uses this common motor.
Figure 13 illustrates the example of the commutator that is made of 5 commutator segments.Have a motor that surpasses 3 commutator segments for this, the width that also adopts carbon brush with respect to the circumferential lengths of a commutator segment in the design more than 30%.
In addition, as everyone knows, the width of carbon brush less (be not circumferential lengths with respect to a commutator segment, but with respect to the commutator circumferential lengths 8%~14%), can suppress the generation of motor when starting spark phenomenon and the service time of being experienced with motor irrelevant (with reference to patent documentation 1).
On the other hand, the technology of controlling according to the rotation (position) of the waveforms detection motor of motor current and to the rotation of motor is known.Figure 14 is used for pulse detection portion circuit diagram and oscillogram that the general example that carries out Position Control by the detection of motor current is described.Motor (winding) is made of inductance L and resistance R.Among the figure, constitute pulse-detecting circuit by inductance L 1, L2, capacitor C 1, C2, resistance R 1, R2.The waveform of the motor current that motor is produced when receiving DC power supply (for example 15V) is shown among the figure.When the groove of carbon brush between commutator segment passed through, the instantaneous trip of electric current can take place.Illustrated pulse detection portion is the circuit according to motor current waveform generation diagram pulse output.By this output pulse is counted, can detect the position of rotation or the revolution of motor, and the rotation of motor is controlled.
But this mode of utilizing motor current to detect motor position of rotation or revolution exists along with the motor continuity of service time, and the carbon brush wearing and tearing, the motor current waveform changes and the problem can't paired pulses counted.
Patent documentation: the spy opens clear 63-249447 communique
Description of drawings
Fig. 1 is the accompanying drawing of illustration motor general structure.
Fig. 2 shows the accompanying drawing that carries out a carbon brush among a pair of carbon brush of sliding contact with commutator.
Fig. 3 is used for to the carbon brush brought into use at first through using after a while and the accompanying drawing that the working condition when wearing and tearing describes.
Fig. 4 is the accompanying drawing that the electric current that flows in the carbon brush is described.
Fig. 5 measures it up to the carbon brush change width and the form of the durable time (durable time of actual condition) of pulsing mistake to 5 motors with above-mentioned commutator.
Fig. 6 is the curve chart that form shown in Figure 5 is depicted as curve.
Fig. 7 is the oscillogram that the situation that does not have the pulsing mistake among the present invention is fully showed.
Fig. 8 is the oscillogram that the situation of pulsing mistake in the prior art is showed.
Fig. 9 is to carry out an accompanying drawing that example is showed of the carbon brush of sliding contact after the front end narrowed width with commutator.
Figure 10 is the accompanying drawing that the carbon brush of another example of front end narrowed width by oblique straight line excision is showed.
Figure 11 is the accompanying drawing that the carbon brush of another example of front end narrowed width to excising in the mode that forms step between leading section and the root is showed.
Figure 12 be the cutaway view (A) cut open from commutator of existing miniature motor and pull down with the carbon brush that commutator carries out sliding contact after the enlarged drawing (B) showed.
Figure 13 shows the accompanying drawing that is made of the example of commutator 5 commutator segments.
Figure 14 is used for pulse detection portion circuit diagram and oscillogram that the general example that carries out Position Control by the detection of motor current is described.
Embodiment
The motor that the present invention has been specialized for example is used for the driving of reflective mirror minute surface on the arrangements for automotive doors.Not being directly to rotate the reflective mirror minute surface and when rotating with automated manner with manual mode, is the motor current waveform is detected and to determine the spinning movement of motor and mirror angle.
Fig. 1 is the figure of the general structure of this motor of illustration, (A) shows whole miniature motor with half sectional view, (B) is end cap is pulled down the figure of back when the motor internal direction is observed.Magnet is installed being by metal material on the inner peripheral surface that the casing that end hollow tube-shape forms is arranged.This shell opening portion is closed by end cap is chimeric with it.At the central part of end cap, accommodate and be used for the bearing of supporting rotating shaft.The other end of rotating shaft obtains being arranged on the support of bearing of bottom center of the casing of end hollow tube-shape.
Have laminate core on this rotating shaft, be wound on winding and commutator in this laminate core, constituted the rotor of miniature motor.In addition, a pair of carbon brush that contacts with this commutator is connected on the brush carrier.By the brush carrier that constitutes with the conductive metal sheet carbon brush is kept, carbon brush is pressed down at the elastic reaction of sheet metal touch in the enterprising line slip of commutator.For being electrically connected, it is outstanding outside that the pair of input terminals that is connected with this brush carrier is passed end cap.
The invention is characterized in the structure that is assembled in the carbon brush in this miniature motor.Carbon brush can be along with the continuity of motor service time and is worn and torn, and causes the motor current wave form varies and can't count by paired pulses.Fig. 2 illustrates with commutator and carries out among a pair of carbon brush of sliding contact one.By a plurality of commutator segments that on the surface of the commutator core of resin manufacture, are provided with and the commutator that constitutes be installed on the rotating shaft.The bearing surface of carbon brush and commutator have upwards have in the week of commutator set straight length (below be called " carbon brush width ") and rotating shaft axially on have both rectangular planar shape of measured length (carbon brush axial length).What Fig. 2 enumerated is the example that is in the carbon brush of state of wear.At this moment, with respect to the cylindrical shape commutator, carbon brush contacts with it with its whole conflict face.
Fig. 3 (A) illustrates the state that the carbon brush brought into use at first and commutator are conflicted.The bearing surface of carbon brush and commutator have upwards have in the week of commutator both measured lengths (carbon brush width) and rotating shaft axially on have both rectangular planar shape of measured length (carbon brush axial length).Therefore, between the carbon brush conflict face of the commutator of drum and flat shape, from the section of carbon brush, point (contact point) with circumferential central authorities contacts (still, see carbon brush on the whole, carbon brush has set axial length, therefore, is not with a point but contacts with a line).
Electric current for flow this moment describes in conjunction with Fig. 4.On the winding of motor, be applied with the two the voltage difference of supply voltage back electromotive force to that indicated in the drawings of certain value.That is, be applied with the voltage that is equivalent to the value of the part of blacking among the figure.Interval 1~3 among the figure is represented respectively be carbon brush and a commutator segment begin to touch leave till.
Electric current when carbon brush is brought into use at first as shown in Figure 4.When carbon brush began to contact with a commutator segment, because back electromotive force is little, thereby in fact big voltage was applied on the motor winding.But because there is inductance in the motor winding, thereby electric current will rise with set time constant.The two voltage difference of electric current after the rising and supply voltage and back electromotive force is proportional.And because as previously mentioned, carbon brush and is to contact between the commutator segment when bringing into use at first, and therefore, when this contact point arrives on the groove between commutator segment, the electric current in this interval 1 will be cut off, and, begin to contact with next commutator segment 2 interval 2.As previously mentioned, this is detected by pulse detection portion continue the electric current step that is produced when interval 2 electric currents are connected behind interval 1 the failure of current, exports and motor is controlled thereby produce pulse.
With respect to this, when along with the continuity of carbon brush service time during the carbon brush wearing and tearing, shown in Fig. 3 (B), the conflict face of carbon brush becomes the periphery shape from initial flat shape.Its result, carbon brush will be conflicted with its circumferential whole carbon brush width and commutator.This means that when still contacting with commutator segment 1 in the circumferential central authorities of carbon brush, the circumferential leading section of carbon brush has contacted (Fig. 3 (B)) with commutator segment 2.In addition, shown in Fig. 3 (C), also mean when the circumferential central authorities that are in carbon brush have contacted with commutator segment 2, the circumferential rearward end of carbon brush still with commutator segment 1 state of contact.
Electric current after the wearing and tearing of this carbon brush will become the electric current shown in the bottom of Fig. 4.That is, in fact prolong with concluding time of the electric current in the interval 1 of the circumferential guide center decision of carbon brush, on the other hand, the linking of electric current takes place in the time started of interval 2 electric current in advance.Therefore, the groove place between commutator segment, electric current is continuous sleekly, thereby can't detect with aforementioned pulse-detecting circuit.
Though " linking " in the explanation that the carbon brush width can not take place to carry out in conjunction with Fig. 3 when narrower than groove width (circumferential straight length), but reach below 19% if the carbon brush width is narrow, not enough and the problem that fractures of carbon brush mechanical strength then can appear, perhaps in the motor rotary course carbon brush can fall in the groove and increase carbon brush vibration, increase the problem of mechanicalness noise.Although it is very little but when also surpassing groove width to surpass amount at the width of carbon brush, the circumferential leading section that carbon brush can take place and rearward end be " linking " when different commutator segment contacts respectively.But in addition, as previously mentioned, even the next commutator segment of going ahead of the rest on the circumferential leading section of carbon brush and the direction of rotation contacts, initial in contact, the Yin Mada winding exists inductance also can not produce big electric current.Therefore, if the value of the electric current of the carbon brush leading section of flowing through become big before the carbon brush rearward end left commutator segment, then this moment generation is enough to by the step of the detected motor current value of pulse-detecting circuit.That is to say that the circumferential leading section of cut motor current and carbon brush had contacted with the 2nd commutator segment of going ahead of the rest on the direction of rotation and difference between current between the motor current that flows when the circumferential rearward end that this electric current step is equivalent to carbon brush was left the 1st commutator segment of rotation.In the present invention, produce enough big electric current step, thus, can produce the pulse that the rotation that is used for to motor detects like clockwork by making the carbon brush narrowed width.
Fig. 5 measures it up to the carbon brush change width and the form of the durable time (durable time of actual condition) of pulsing mistake to 5 motors with above-mentioned commutator.Fig. 6 is the curve chart that the form of Fig. 5 is depicted as curve.Long duration test is to be to carry out under rated voltage, the load of 13.5V is 5gcm, life test condition for (just changeing+reverse) * 10 seconds, the condition of not turn-offing at voltage, and 5 motors that the carbon brush width is had nothing in common with each other have carried out 55 hours.When the carbon brush width being made 0.6~0.8mm (if then be 21~28% with ratio value representation) with respect to the commutator segment circumferential lengths, even through after 55 hours, also pulsing mistake not fully.Fig. 7 is an oscillogram of showing this state.After the long duration test, still the same with A-stage, the step of current waveform does not diminish, and hence one can see that, is to produce pulse under the situation of pulsing mistake not.
When to make the carbon brush width be (if then be 38% with the ratio value representation with respect to the commutator segment circumferential lengths) more than the 1.1mm, passed through after 13 hours and produced burst errors.Fig. 8 for the oscillogram of this state of expression after long duration test, the position that exists the step of current waveform to diminish, and produced burst errors at this position as can be known.
Aforementioned prior art, the ratio of its " with respect to the carbon brush width of commutator segment circumferential lengths " has surpassed 30%, and when adopting this carbon brush, when the long duration test time reaches 7 hours, just begins to occur the motor that pulse makes mistakes.
The motor that is used for purposes such as auto mirror minute surface driving is fit to adopt carbon brush.In general, miniature motor can use the brush of the sheet of metal manufacturing, if drive purposes but be used for minute surface, then can appear under the durable condition of environment of the strictness that automobile is proposed electric contact problem of unstable takes place easily, if improve the stability of contact and adopt precious metal material, the shortcoming that causes cost to increase is then arranged.
Even in the occasion that adopts carbon brush as the present invention, if its width surpasses 30% with respect to the ratio of commutator segment circumferential lengths, long-time its phase deviation of back of using also can be excessive and can't stably detect pulse.And if below 19%, then can cause the intensity of carbon brush to reduce, fall into easily in the groove between the commutator segment and vibration increase, the mechanicalness noise of carbon brush increase.
In the present invention, be as previously mentioned with the width of carbon brush with respect to commutator segment circumferential lengths design on set ratio, and as this carbon brush width, as long as with the Front-end Design of commutator sliding contact on set ratio.Fig. 9 has enumerated the example that carries out the carbon brush of sliding contact after the front end narrowed width with commutator.When adopting this structure, can do the part that is maintained in the brush carrier of carbon brush thicker, improve confining force carbon brush.
Figure 10 and Figure 11 have enumerated other example of front end narrowed width.Be by carbon brush made the front end narrowed width with respect to the excision of one of front and rear part of direction of rotation.Figure 10 is the example of oblique straight line excision, and Figure 11 is the example that excises in the mode that forms step between leading section and the root (brush carrier installation side).Any example no matter with respect to the phase place neutral line (straight line radially of commutator circumference) of commutator, is not to make the carbon brush center line of carbon brush but the center of carbon brush front end width is aimed at it, just sliding contact well.