Electricity: motive power systems – Limitation of motor load – current – torque or force
Reexamination Certificate
2002-06-12
2004-04-20
Nappi, Robert (Department: 2837)
Electricity: motive power systems
Limitation of motor load, current, torque or force
C318S811000, C318S599000
Reexamination Certificate
active
06724166
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a motor for successively applying currents to respective phase windings by the ON/OFF operations of switching elements. More particularly, the invention is related to an apparatus for reducing motor driving noise, which is designed to reduce driving noise caused by the switching of a current applied to each phase winding, and also a method for generating a motor driving noise reducing signal.
2. Description of Related Art
FIG. 22
shows an example of the driving circuit of a 3 phase brushless motor
101
. In the example, each of the paired transistors Q
1
and Q
2
, Q
3
and Q
4
, and Q
5
and Q
6
as switching elements are connected in series between a power supply and a ground, wherein one end of each of the transistors Q
1
, Q
3
and Q
5
is connected to a power supply terminal, and one end of each of the transistors Q
2
, Q
4
and Q
6
is grounded through a current sense resistor
102
, and wherein one end of each of the star-connected phase windings
101
U,
101
V and
101
W of the motor
101
is connected to each of the connection points P
1
P
2
, and P
3
of each of the paired transistors Q
1
and Q
2
, Q
3
and Q
4
, and Q
5
and Q
6
.
FIG. 23
shows a circuit for generating a driving signal to be supplied/applied to each of the above-described transistors. In the drawing, a reference numeral
104
denotes an input terminal for receiving the entry of 120° current application control signals LEU, LEV and LEW (referred to as LE or LE signal, hereinafter) and 180° current application direction deciding signals INU, INV and INW (referred to as IN or IN signal, hereinafter) outputted from a pulse signal generating circuit, not shown;
105
a PWM waveform signal generator for generating a PWM waveform signal;
106
a PWM synthesizer for synthesizing the PWM waveform signal and the IN signals; and
107
an output terminal for outputting the LE signals and the IN signals outputted from the PWM synthesizer
106
, specifically outputting the LE signals and the IN signals of PWM waveform patterns shown in FIG.
24
. These six kinds of signals (current application control signals LEU, LEV and LEW, and current application direction deciding signals INU, INV and INW) have meanings as shown in FIG.
32
.
Each of
FIGS. 25A
to
25
F show a state that the motor is driven by applying the IN signals of the PWM waveform pattern to the ground side transistors Q
2
, Q
4
and Q
6
(low side), and applying the LE signals of the PWM waveform pattern to the power supply side transistors Q
1
, Q
3
and Q
5
(high side), and thereby successively supplying currents to the respective phase windings
101
U,
101
V and
101
W of the motor
101
by every 60°. In
FIGS. 24 and 26
, com
1
to com
6
show the states in which currents are supplied to the windings
101
U,
101
V and
101
W by timings in the case of 120° current application, and the timings are shown in
FIGS. 25A
to
25
F. In this case, since a square-wave current flows to each of the phase windings
101
U,
101
V and
101
W, sudden fluctuation occurs in torque, and the motor is vibrated to generate noise. This noise causes vibration by an integral multiple of the natural vibration of a casing covering the motor, and is generated in an audible band.
As explained above, the PWM driving is designed to switch a voltage applied to the motor
101
, substantially between two ways, i.e., a power supply voltage and 0V, and control the amount of current flowing to the motor to be average based on the duty thereof Consequently, the current waveform of the PWM driving becomes a square current waveform, causing the generation of noise.
Then, as shown in
FIG. 27
, a signal for increasing the current of a duty waveform pattern and a signal for reducing a current are outputted from a noise reducing waveform signal generator
108
. The signal for current increase and the signal for current reduction are selected by an INC/DEC selector
109
based on a COMOUT signal as a commutation control signal, and synthesized into the LE signals of PWM waveform patterns shown in
FIG. 28
by a signal synthesizer
110
. Then, the signals shown in
FIG. 29
are applied to the transistors Q
1
, Q
3
and Q
5
of the motor driving circuit
101
, and the currents like those shown in
FIG. 30
are supplied to the respective phase windings. Accordingly, the current change becomes continuous during commutation control, causing no sudden torque changes. Therefore, the noise generated by the motor vibration is reduced.
However, when currents are supplied to the motor windings
101
U,
101
V and
101
W by simply applying the IN and LE signals shown in
FIG. 29
respectively to the transistors Q
1
, Q
4
and A
6
, and the transistors Q
1
, Q
3
and Q
5
, phases at points A to F shown in the same drawing may be short-circuited from one another depending on PWM timings.
FIG. 31
illustrates a state where phases are short-circuited from one another. A short brake is set in when the transistors Q
1
, Q
3
and Q
5
of
FIG. 31
are simultaneously turned ON. The timing thereof is such that when the U phase turns On the power supply side transistors Q
1
, and the W phase is regenerated (transistor Q
6
is OFF, while transistor Q
5
is ON) to control a current, the current is supplied to the V phase earlier than a 120° current application timing, so that the transistor Q
3
is turned ON. At this time, the power supply side transistors Q
1
, Q
3
and Q
5
are simultaneously turned ON. However, although a current must originally be supplied to the V phase, since the ground side transistors Q
2
, Q
4
and Q
6
are all OFF, no currents flow there.
As described above, in the conventional motor driving apparatus, since a square-wave current is supplied to each phase winding of the motor, torque fluctuation caused by a sudden current change is large. Accordingly, the apparatus for reducing motor driving noise has been developed to supply a current continuously changed even at the time of phase switching to each phase winding of the motor
101
. However, although this apparatus can reduce the occurrence of vibration caused by a sudden current change, it cannot supply a current to an originally targeted phase because of the short-circuiting of the phases among one another. In other words, the problem of impossible driving has been inherent.
SUMMARY OF THE INVENTION
The present invention has been made to solve the foregoing problems, and it is an object of the invention to provide an apparatus for reducing motor driving noise, which is capable of reducing the occurrence of vibration, and preventing the short-circuiting of phases among one another. It is another object of the invention to provide a method for generating a motor driving noise reducing signal, which is executed by a digital circuit not requiring any large-capacity capacitors or the like, yet highly advantageous in cost performance and product yield.
In accordance with the invention, there is provided an apparatus for reducing motor driving noise, comprising: a plurality of switching circuits each including at least a pair of switching elements connected in series between a power supply and a ground; a motor, one end of each of its phase windings is connected to a switching element serial connection point of each of the switching circuits; a noise reducing circuit for generating a current increasing signal and a current reducing signal; a selecting circuit for selecting and outputting the current increasing signal and/or the current reducing signal based on a commutation control signal for changing a polarity at every prescribed electrical angle; a signal synthesizing circuit for synthesizing either the current increasing signal or the current reducing signal selected by the selecting circuit with a current application control signal supplied to a power supply side switching element of the pair of switching elements; a PWM waveform signal generator for outputting a PWM waveform signal based on a current control value; and a PWM synthesizer for synthe
Hoashi Masaharu
Narumi Satoshi
Tamagawa Hiroyuki
Colon Santana Eduardo
Nappi Robert
Renesas Technology Corp.
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