JPH06103994B2 - Sensorless brushless motor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sensorless brushless motor in which a drive magnetic pole position detector is omitted.

(Prior Art) In recent years, brushless motors have been widely used. In this brushless motor, a so-called sensorless type brushless motor in which a drive magnetic pole position detector such as a Hall element is omitted is known.

FIG. 7 is a block diagram showing an example of a conventional sensorless brushless motor. FIG. 7A is an overall view and FIG.
FIG. 3 is a detailed view of the oscillation starting circuit of FIG. 3A, FIG. 2 is a waveform diagram for explaining the operation of the motor of FIGS. 1, 5, and 7 during steady rotation, and FIG. FIG. 8 is a waveform diagram illustrating an operation at the time of starting the motors of FIGS. 1, 5, and 7.

As shown in FIG. 7 (A), a four-pole drive magnetic pole 2a formed on a disk-shaped drive magnet 2 arranged on the rotor and a four-phase drive coil 3 opposed to this drive magnetic pole 2a arranged on the stator. And constitute the motor section.

In addition, a ring-shaped member arranged on the outer periphery of the drive magnet 2
A frequency generator for rotation speed detection, which includes a 32 pole FG magnetic pole 4a formed on the FG magnet 4 and an FC head 5 which is a magnetoelectric conversion element for generating a rotation speed detection signal facing the FG magnetic pole 4a arranged on this stator. (Hereinafter abbreviated as FG),
Also, a single-pole PG magnetic pole 6a formed on the PG magnet 6 arranged near the outer periphery of the rotor, and a PG head 7 which is a magnetoelectric conversion element for generating a rotational position detection signal arranged on the stator.
Pulse generator for detecting rotational position with and (hereinafter abbreviated as PG)
Are configured.

Then, with the rotation of the rotor, the PG head 7 shows the rotation angle of the PG magnetic pole 6a facing the PG head 7 once for each rotation of the rotor, as shown in FIG. 2 (A). Such a PG output a is generated, and this PG output a is supplied to the waveform shaping circuit 8a as shown in FIG. 7 (A). The waveform shaping circuit 8a waveform-shapes the PG output a into an index signal c as shown in FIG. 2C, and the index signal c is an FG frequency dividing circuit as shown in FIG. 7A.
11 and a constant speed / constant phase control circuit 12.

On the other hand, the FG head 5 produces an FG output b having a frequency proportional to the rotation speed of 16 cycles per revolution of the rotor as shown in FIG. 2 (B). It is supplied to the waveform shaping circuit 8b as shown in FIG.
In the waveform shaping circuit 8b, the FG output b is shaped into a rectangular wave as shown in FIG. 2 (D) and becomes an FG signal d. This FG signal d is confirmed to start as shown in FIG. 7 (A). Circuit 10,
It is supplied to the FG frequency dividing circuit 11 and the constant speed / constant phase control circuit 12.

When this rotor is stopped, the switch SW1 is closed and the switch SW2 is opened by the action of this start confirmation circuit 10,
The drive signal e-2 generated by the oscillation starting circuit 69 is supplied to the brushless motor drive circuit 13. Based on the drive signal e-2, the brushless motor drive circuit 13 causes the
The drive magnet 2 is rotationally driven by switching and supplying a drive current to the phase drive coil 3.

Then, based on the FG signal d, it is confirmed that the rotor has reached a predetermined number of revolutions by the action of the start confirmation circuit 10, and the switch SW1 is opened and the switch SW2 is closed, whereby the FG frequency divider circuit The output of 11 is supplied to this brushless motor drive circuit 13. In the FG frequency dividing circuit 11, the FG signal d is frequency-divided at a predetermined frequency division ratio (1/2 in this example), and is set by the index signal c to become position information in the rotation direction. Figure 2 (E)
The drive signal e-1 as shown in is generated. Based on this drive signal e-1, in the brushless motor drive circuit 13, four-phase phase current signals f-1, g- as shown in FIGS. 2 (F), (G), (H), and (I). 1, h−1, i−1 are created, and by switching and flowing the drive current through the four-phase drive coil 3, the drive magnet 2 and thus the rotor are rotationally driven.

Further, in the constant speed / constant phase control circuit 12, a constant speed / constant phase control signal which is a signal for controlling the rotor to a constant speed / constant phase is generated based on the FG signal d and the index signal c. It is supplied to the brushless motor drive circuit 13. In this brushless motor drive circuit 13,
Based on the constant speed / constant phase control signal, the drive coil 3
By adjusting the drive current flowing through the motor, a loop for negatively feeding back the speed and the phase is formed in the motor as described above, so that the rotor is controlled to the constant speed / constant phase.

The above is the description of the operation of the conventional sensorless brushless motor 41 at the time of steady rotation. Next, the operation of the motor 41 at the time of starting will be described in more detail with reference to FIGS. 7 (B) and 3. To do.

The period Td of the drive signal e-1 output from the FG frequency divider circuit 11 at the time of steady rotation has substantially the same value as shown in FIG. The period Td of the drive signal e-2 output from the oscillation starting circuit 49 gradually changes from a large value to a small value as shown in FIG.

As shown in FIG. 7B, the oscillation starting circuit 49 is composed of a time table value storage circuit 14, a time table value reading circuit 15, a time table value / time data conversion circuit 17, a drive signal generating circuit 18, and the like. ing. The timetable value storage circuit 14 stores a timetable value which is standard start-up data when the motor 41 is started. This timetable value is used when the rotor is started by the rotor start-up torque characteristic which is the difference between the start-up torque characteristic of the motor 41 alone and the start-up load torque characteristic of the load driven by the motor 41. Is the standard data of the period Td of the drive signal e-2 with respect to the time from the start of activation to the reaching of a predetermined rotation speed. This data is converted into, for example, digital data, and each is from the start of activation. ROM with addresses in time order
Remembered in.

Then, at the time of start-up, this timetable value is sequentially read by the timetable value reading circuit 15 in the order of this address and supplied to the timetable value / time data conversion circuit 17. In the timetable value / time data conversion circuit 17, the timetable value is converted into time data representing the cycle Td at the time of startup, and this time data is supplied to the drive signal generation circuit 18. The drive signal generation circuit 18 generates the drive signal e-2 whose period Td changes according to the rising data as shown in FIG. 3 (A) by the time data. Based on the drive signal e-2 having the predetermined rotor start-up period Td, the brushless motor drive circuit 13
Four-phase phase current signals f-2, g-2, h-2, i-2 as shown in FIGS. (B), (C), (D), and (E) are generated, and as described above, The rotor is activated.

(Problems to be Solved by the Invention) In the sensorless type brushless motor 41 of the conventional example having the above-described configuration, at the time of the above-mentioned start-up, the rotation speed of the rotor generally follows the drive signal e-2 at the time of the start-up. However, this start-up may fail due to variations in start-up torque characteristics of the motor 41 alone and the load driven by the motor 41.

FIG. 8 is a graph for explaining changes in the rotor start-up characteristics with respect to changes in the cycle Td of the drive signal of the motor shown in FIG. 7, where the vertical axis represents the rotor rotation speed and the horizontal axis represents time.

As shown in the figure, the drive signal e− at the time of start-up is relatively with respect to the above-described rotor start-up torque characteristic of the motor 1.
If the period Td of 2 is too small, the rotor cannot stop following the drive signal e-2 and stops.
If is too large, the overshoot becomes large and the phases are out of phase, causing the machine to stop.

The above-mentioned timetable value of this motor 41 is one standard type, but it is relatively the same as that of FIG. 8 due to variations in the starting torque characteristics of the motor 41 and the load driven by this motor 41. Since a situation may occur, there is a problem in that the startup may fail due to variations in the startup torque characteristics of the motor 41 alone and the load driven by the motor 41.

The present invention has been made in view of the above points, and an object thereof is to provide a highly reliable sensorless brushless motor that does not fail in starting.

(Means for Solving the Problems) A sensorless brushless motor according to the present invention is a motor unit including a multi-pole drive magnetic pole provided in a rotor and a multi-phase drive coil disposed opposite the drive magnetic pole provided in a stator. And a rotation speed and / or position detection means for generating a rotation speed and / or position detection signal corresponding to the rotation speed and / or position of the rotor arranged in the motor section, and the rotation speed and / or position detection Drive signal generating means for generating a drive signal of a pulse which becomes drive current switching information according to the signal, and a brushless motor for rotationally driving the rotor by switching the drive current to the multiphase drive coils based on the drive signal. At the time of starting the drive circuit and the motor, a predetermined period whose cycle changes with respect to the time from the start of starting the rotor until the predetermined rotation speed is reached, An oscillation starting circuit that outputs a driving signal having a rotor start-up period, and the driving signal from the oscillation starting circuit is supplied to the brushless motor driving circuit at the time of starting, and after the predetermined rotation speed is reached, the In a sensorless brushless motor comprising a start confirmation circuit for switching and supplying the drive signal from the drive signal generating means to the brushless motor drive circuit, the oscillation starter circuit performs the start-up trial until the start-up is successful at the start-up. For each number of times, it is determined by the rotor start-up torque characteristic based on the difference between the start-up torque generated by this motor and the load torque at the start-up of the load driven by this motor, and the rotor start-up frequency characteristic based on the rotor start-up cycle. A rotor startup characteristic switching means for sequentially switching the rotor startup characteristics at a predetermined pitch; The rotor starting time, which is the time from the start of starting the engine until it reaches a predetermined rotation speed, is detected, and the detected starting time is compared with a predetermined reference starting time corresponding to the number of start trials. In the case of a rough match, the start-up is continued, and in the case of a non-match, the start-up trial in this case is stopped and the start-up determination means for restarting the try is provided.

Further, in the sensorless brushless motor of the present invention, in the motor, the oscillation starting circuit suspends the starting and outputs an abnormal signal when the detected starting time exceeds a predetermined allowable range. The output means is provided.

Also, in the sensorless brushless motor of the present invention, in the above motor, the rotor start-up characteristic switching means is
It is configured to correct the rotor start cycle or the drive current at the time of starting.

(Embodiment) The sensorless brushless motor of the present invention is configured such that the oscillation start circuit 49 described above generates a start torque and a start torque generated by the motor for each start try count until the start is successful at the start. Rotor startup characteristics, which are determined by the rotor startup torque characteristics based on the difference between the load driven by the motor and the startup torque, and the rotor startup frequency characteristics based on the rotor startup cycle described above, are switched sequentially at a predetermined pitch. The rotor start-up characteristic switching means and the rotor start-up time, which is the time from when the rotor starts to reach a predetermined rotation speed, are detected, and the detected start-up time and a predetermined reference start-up time corresponding to the number of start trials By comparing and, the matching between this rotor startup torque characteristic and this rotor startup frequency characteristic is determined. If the constant result is fit to continue the start-up,
In the case of non-conformity, the start-up in this case is stopped and the start-up determination means for starting the retry is added to ensure the start-up.

The first embodiment, in which the rotor start-up characteristic switching means switches the rotor start-up frequency characteristic based on the rotor start-up cycle, and the start-up that is the drive current from the brushless motor drive circuit at the start-up. A second embodiment in which the current is switched will be described below.

FIG. 1 is a block diagram showing a first embodiment of a sensorless type brushless motor of the present invention. FIG. 1 (A) is an overall view and FIG. 1 (B) is a detail of the oscillation starting circuit of FIG. 1 (A). It is a figure.

As shown in the figure, the motor 1 according to the first embodiment of the present invention is
The oscillation starting circuit 9 includes a time table value multiplying circuit 16 and a starting circuit between the time table value reading circuit 15 and the time table value / time data converting circuit 17 of the oscillation starting circuit 49 of the motor 41 of the above-mentioned conventional example. Trie counter 19,
A correction coefficient generation circuit 20, a startup time detection circuit 21, a reference time generation circuit 22, and a time comparison circuit 23 are added. Therefore, the same parts as those in the conventional example are designated by the same reference numerals, and the description thereof will be omitted.

In the oscillation starting circuit 9, the number of starting tries is counted by the starting try number counter 19. The start trial number counter 19 is composed of a counter circuit and counts the number of start trials until the start of the motor 1 is successful. The start trial number signal which is an electric signal is generated by the correction coefficient generating circuit 20 and the reference time generating circuit. Supply to the circuit 22.

When the permissible range of the rotor starting time is 1 to 2 seconds when the predetermined rotation speed is, for example, 500 rpm, which represents the fluctuations of the starting torque generated by the motor 1 and the load torque at the time of starting the load to be driven. In the case where this starting torque is maximum and load torque is minimum within this permissible range, the rotor starting time is 1 second, whereas when this starting torque is minimum and load torque is maximum, the rotor starting time is 2 seconds. ,
If the fluctuation range of the rotor starting torque, which is the difference between the starting torque and the load torque, is set to, for example, 20%, in the correction coefficient generating circuit 20, when the starting try is the first time,
A correction coefficient of 0.9 for the second time, 1.0 for the third time, and 1.1 for the third time is generated, and this correction coefficient is supplied to the time table value multiplying circuit 16 each time this starting try.

In the time table value multiplication circuit 16, the correction coefficient is multiplied by the time table value from the time table value storage circuit 14 and the time table value read circuit 15, and this time table value is calculated. Correction is performed for each number of startup tries. Based on the corrected time table value, the time table value / time data conversion circuit 17 and the drive signal generation circuit 18 generate the drive signal e-2 at the start-up, as described above.

When this starting try is the first time, the rotor starts starting based on this timetable value of 0.9 times. Then, the rotor startup time, which is the time until the rotor reaches 500 rpm, is detected by the startup time detection circuit 21.

The start-up time detection circuit 21 is composed of, for example, a counter circuit provided with a counter that is reset by a start-up signal, and outputs a start-up time detection signal of an electric signal corresponding to the detected start-up time when the rotor start-up time is detected. The start-up time detection signal is supplied to the time comparison circuit 23. Further, in the reference time generation circuit 22, a start time reference signal which is an electric signal representing a reference start time of 1 second when the start trie is the first time, 1 second, the second time is 1.5 seconds, and the third time is 2 seconds is generated. The activation time reference signal is supplied to the time comparison circuit 23 each time the activation trie is performed.

In the time comparison circuit 23, the start-up time reference signal and the start-up time detection signal are compared with each other. If the two match substantially, a match signal, for example, 1 and a non-match signal, a non-match signal, for example, 0 are given. The timetable value multiplication circuit
Supplied to 16. In the time table value multiplication circuit 16, the matching signal 1 and the non-matching signal 0 are multiplied with the corrected time table value, so that when the matching signal 1 is supplied, the start-up in this case continues. Is
When the non-match signal 0 is supplied, the starting try is stopped, and after the starting confirmation circuit 10 confirms that the rotor is completely stopped by the FG signal d, the starting try is started again.

If the motor 1 has a maximum starting torque and a minimum load torque, the rotor start-up torque characteristic of the motor 1 is determined by the drive signal e-2 of the starting time.
Of the rotor start-up period Td and the frequency f which is the reciprocal of this period Td based on the time table value corrected to 0.9 times the above
The matching start signal is output from the time comparison circuit 23, and the start is continued by the match signal 1. The rotor follows the start-up frequency f to increase its rotation speed and the start-up is successful. If the rotor starting torque characteristic of the motor 1 is other than the above, the second starting trial is performed as described above.

In the second start-up trial, the timetable value multiplication circuit 16 starts the rotor based on the timetable value multiplied by 1.0 by the correction coefficient 1.0. Then, as in the case of the above-mentioned first starting trial, the matching of the detected starting time in the time comparison circuit 23 is determined by the match / non-match, so that the rotor startup torque characteristic and the rotor startup frequency characteristic in this case are matched. Is determined, and if it is a match, this activation is continued, and if it is not a match, a third activation try is performed.

In the third start-up trial, the time table value multiplication circuit 16 starts the rotor based on the time table value multiplied by 1.1 by the correction coefficient 1.1.

FIG. 4 shows the frequency f of the drive signal in the motor of FIG.
5 is a graph for explaining the correction of the startup characteristic of the number of times of starting tries, in which the vertical axis represents the frequency f of the drive signal and the horizontal axis represents time.

As shown in the figure, in the case of the first start-up trial, the rotor start-up frequency characteristic, which is the start-up characteristic of the frequency f, is tried 10% earlier, and when the detected start-up time is approximately 1 second, it remains the same. If the detected activation time is longer than the above, the second activation try is performed as described above. In the case of the second start-up trial, the rotor start-up frequency characteristic is tried with the standard characteristic. If the detected start-up time is about 1.5 seconds, the rotor is started as it is, and if it is longer than the above, the third try is performed. This start try 3
In the case of the first time, this rotor start-up frequency characteristic is tried at 10% delay and the startup is completed.

As described above, the oscillation start-up circuit 9 in the motor 1 of the first embodiment sequentially changes the rotor start-up frequency characteristic into a characteristic that changes gradually with time at a predetermined pitch for each number of start-up trials. By switching it, the rotor starting torque characteristic of the motor 1 is adapted and the rotor is started, so that reliable starting is performed.

Next, a second embodiment will be described in which the starting current, that is, the rotor starting torque characteristic is switched instead of the rotor starting frequency characteristic.

FIG. 5 is a block diagram showing a second embodiment of the sensorless type brushless motor of the present invention, in which FIG.
FIG. 2B is a detailed diagram of the oscillation starting circuit of FIG.

As shown in the figure, the motor 31 of the second embodiment of the present invention is
The oscillation starting circuit 39 is the motor 1 of the first embodiment described above.
The function of the time table value multiplying circuit 16 of the oscillation starting circuit 9 is replaced by a starting current switching circuit 36.
The same parts as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

Since the oscillation starting circuit 39 in the second embodiment switches the starting current of the motor 31 for each number of starting tries described above, the correction coefficient output from the correction coefficient generating circuit 20-2 is In this case, for example, when the starting trie is the first time, 1.1 is the second time, 1.0 is the second time, and 0.9 is the third time, which is supplied to the starting current switching circuit 36.

In this start-up current switching circuit 36, the standard rotor start-up period Td and frequency f based on the above-mentioned time table value are used.
The start-up drive signal e-2 switches the start-up current output from the brushless motor drive circuit 13 to a value according to the correction coefficient for each number of start-up trials. That is, this starting try is performed with the maximum starting current at the first starting try, the starting current smaller by about 10% the second time, and the starting current further smaller by about 10% the third time. And
As in the case of the first embodiment described above, the time comparison circuit
As described above, the matching of the detected startup time in 23 determines whether the rotor startup torque characteristic and the rotor startup frequency characteristic during this startup try match, and if they match, this startup is continued. , If they do not match, the next activation try is performed. However, in this case,
The reference activation time of the activation time reference signal output from the reference time generation circuit 22-2 is the same for the first to third activation tries.
1.5 seconds.

FIG. 6 is a graph for explaining the correction of the rotor start-up characteristic in the motor shown in FIG. 5 with respect to the number of starting tries, and the vertical axis represents the rotor rotation speed and the horizontal axis represents time.

As shown in the figure, in the case of the first start-up trial, the start-up current is tried at the maximum value, and when the rotor start-up torque is approximately medium in relation to the load torque, the rotor start-up torque in this case is The characteristics roughly match the standard rotor start-up frequency characteristics, and in this case the startup time detection circuit
Since the detection start time in 21 is approximately 1.5 seconds, the start is continued as it is by the coincidence signal 1 from the time comparison circuit 23. If the rotor start-up torque is other than the above, the non-match signal 0 causes the starting trial to be stopped and the second starting trial to be performed.

In the case of this second start-up trial, the start-up current is tried to be smaller by about 10%, and when the rotor start-up torque is approximately medium in relation to the load torque, the start-up current is started in the same manner as above. If the rotor starting torque is other than the above, the third starting trial is performed as in the above case.

As described above, the oscillation starting circuit 39 in the motor 31 of the second embodiment sequentially switches the starting current, that is, the rotor start-up torque characteristic at a predetermined pitch for each number of starting trials. Since the rotor is started in conformity with the standard rotor start-up frequency characteristic, reliable start is performed.

In the first and second embodiments of the present invention described above, the detected activation time of the activation time detection signal from the activation time detection circuit 21 exceeds the above-mentioned predetermined allowable range in the time comparison circuit 23. In this case, there is a risk that the motor and the device driven by the motor will fail if the system is in an abnormal state such as an overload, and the abnormal signal (for example, 0) output from the time comparison circuit 27 causes The abnormal signal can be output to the outside as an alarm by the abnormal signal output terminal 23a output from the time comparison circuit 23 while the start is stopped.

Further, each of the above-described embodiments has been described with reference to an example of a so-called FG count type sensorless brushless motor that obtains the switching timing of the drive current by dividing the FG signal from the FG by the FG divider circuit 11. But,
Not limited to this, omitting the above-mentioned FG, PG, FG divider circuit 11 and the like,
The present invention can also be applied to a so-called back electromotive force waveform detection type sensorless brushless motor that utilizes the back electromotive force waveform induced in the drive coil 3 by the rotation of the drive magnetic pole 2a to obtain the drive current switching timing.

(Effects of the Invention) Since the sensorless brushless motor of the present invention having the above-described configuration is reliably started without failing to start, the reliability of the motor is improved.

Further, when the detected start-up time is abnormal, the start-up is stopped and an abnormal signal is output, so that it is possible to quickly take an abnormal action.

Further, since the above function is achieved with a slight cost increase compared with the conventional motor, the function-to-cost ratio is improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a sensorless type brushless motor of the present invention, and FIG. 2 is a waveform diagram explaining the operation of the motors of FIGS. 1, 5 and 7 during steady rotation,
FIG. 3 is a waveform diagram for explaining the start-up operation of the motors of FIGS. 1, 5 and 7, and FIG. 4 is a diagram showing the start-up number of start-up characteristics of the frequency f of the drive signal in the motor of FIG. FIG. 5 is a graph illustrating the correction, FIG. 5 is a block diagram showing a second embodiment of the sensorless brushless motor of the present invention, and FIG. 6 is a description of the correction of the rotor startup characteristic of the motor of FIG. FIG. 7 is a block diagram showing an example of a conventional sensorless type brushless motor, and FIG. 8 is a graph explaining the change of the rotor start-up characteristic with respect to the change of the cycle Td of the drive signal of the motor of FIG. . 1,31,41 …… Sensorless brushless motor, 2a ……
Drive magnetic pole, 3 …… Drive coil, 4a …… FG magnetic pole, 5 …… FG
Head, 6a …… PG magnetic pole, 7 …… PG head, 9,39,49 ……
Oscillation start circuit, 10 …… Start confirmation circuit, 11 …… FG frequency divider circuit, 13 …… Brushless motor drive circuit, 16 …… Time table value multiplication circuit (rotor start-up characteristic switching means), 23
...... Time comparison circuit (startup determination means, abnormality signal output means), 23a ...... Abnormality signal output terminal (abnormality signal output means), 36 ...... Startup current switching circuit (rotor startup characteristic switching means).

Claims (4)

[Claims] 1. A motor unit comprising a multi-pole drive magnetic pole provided in a rotor and a multi-phase drive coil arranged opposite to the drive magnetic pole provided in a stator, and rotation of the rotor arranged in the motor unit. Rotational speed and / or position detection means for generating a rotational speed and / or position detection signal according to speed and / or position, and driving of pulses serving as drive current switching information according to the rotational speed and / or position detection signal Drive signal generating means for generating a signal, a brushless motor drive circuit for rotationally driving the rotor by switching drive currents to the multi-phase drive coils based on the drive signal, and a rotor of the rotor when the motor is started. An oscillation start circuit that outputs a drive signal having a predetermined rotor start-up cycle, the cycle of which has changed with respect to the time from the start of start-up to reaching a predetermined rotation speed, At the time of starting, the drive signal from the oscillation starting circuit is supplied to the brushless motor drive circuit, and after reaching the predetermined rotation speed, the drive signal from the drive signal generating means is supplied to the brushless motor drive circuit. In a sensorless type brushless motor including a start confirmation circuit that is switched and supplied, the oscillation start circuit drives the start torque generated by the motor and the start torque generated by the motor for each number of start tries until the start is successful at the start. Rotor start-up characteristics that sequentially switch the rotor start-up characteristics determined by the rotor start-up torque characteristics based on the difference between the load start-up load torque and the rotor start-up frequency characteristics based on the rotor start-up cycle at a predetermined pitch. It is the time from the start of starting the switching means and the rotor until it reaches a predetermined rotation speed. The start-up time is detected, the detected start-up time is compared with a predetermined reference start-up time corresponding to the number of start-up trials, and if the comparison result is a rough match, the start-up is continued, and if it is not matched, A sensorless brushless motor comprising: a start determination means for stopping the start try and restarting the try in this case. 2. The oscillation start-up circuit includes an abnormal signal output means for stopping the start-up and outputting an abnormal signal when the detected start-up time exceeds a predetermined allowable range. A sensorless brushless motor according to claim 1. 3. The sensorless brushless motor according to claim 1 or 2, wherein the rotor start-up characteristic switching means corrects the rotor start-up cycle. 4. The sensorless brushless motor according to claim 1, wherein the rotor startup characteristic switching means corrects the drive current at the time of starting.