Ultrasonic motor

Details Ultrasonic motor Ultrasonic motor

1998-12-17

2001-03-13

Ramirez, Nestor (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

C310S323040

Reexamination Certificate

active

06201338

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic motor employed in vehicles. More particularly, the present invention pertains to an ultrasonic motor that lowers electromagnetic noise.
FIG. 8
illustrates a typical ultrasonic motor
50
. The motor
50
has a metal base
54
and a metal cover
58
. The base
54
and the cover
58
form a motor housing. The base
54
is secured, for example, to a vehicle body frame. The motor housing houses a stator
52
made of iron and a rotor
53
made of aluminum. The rotor
53
is pressed against the stator
52
. A rotary shaft
55
is supported by the base
54
. A ball bearing
56
is located between the shaft
55
and the base
54
to allow the shaft
55
to rotate relative to the base
54
. The rotor
53
is secured to the shaft
55
to integrally rotate with the shaft
55
.
The stator
52
includes a disk-shaped diaphragm
45
, a stationary plate
46
fixed to the inner bottom surface of the diaphragm
45
and a ring-shaped piezoelectric element
51
secured to the outer bottom surface of the diaphragm
45
. The stationary plate
46
is secured to the base
54
by screws. The diaphragm
45
has radially extending teeth
45
a
along its the circumference. The distal end
45
b
of each tooth
45
a
contacts the bottom surface of the rotor
53
.
The piezoelectric element
51
is polarized and has an A-phase region
51
a,
a B-phase region
51
b
and a vibration detecting region
51
c
as shown in FIG.
9
. Each of the regions
51
a,
51
b,
51
c
is connected to a lead wire
57
a,
57
b,
57
c
by an electrode, respectively. Further, the regions
51
a
-
51
c
are connected to a common grounding lead wire
57
d.
As illustrated in
FIG. 8
, the lead wires
57
a
-
57
d
are connected to a connector
59
located outside of the cover
58
.
As illustrated in
FIG. 9
, the connector
59
is connected to an electronic control unit (ECU)
60
by a shielded line
61
. The ECU
60
is located far from the ultrasonic motor
50
. The shielded line
61
includes an A-phase power supply wire
61
a,
a B-phase power supply wire
61
b,
a feedback signal wire
61
c
and a grounding wire
61
d.
The ECU
60
applies high-frequency voltage to the A-phase region
51
a
through the A-phase power supply wire
61
a,
the connector
59
and the lead wire
57
a.
The ECU
60
also applies high-frequency voltage to the B-phase region
51
b
through the B-phase power supply wire
61
b,
the connector
59
and the lead wire
57
b.
There is a ninety-degree phase difference between the voltage sent to the A-phase region
51
a
and the voltage sent to the B-phase region
51
b.
The high frequency voltages vibrate the A-phase region
51
a
and the B-phase region
51
b.
The vibration vibrates the distal ends
45
b
of the teeth
45
a
with respect to the stator
52
. The vibration of the distal ends
45
b
generates a progressive wave. The progressive wave rotates the rotor
53
, which is pressed against the distal ends
45
b.
The rotation of the rotor
53
is transmitted to the rotary shaft
55
.
The feedback signal wire
61
c
is connected to the vibration detecting region
51
c
by the connector
59
and the lead wire
57
c.
The region
51
c
generates voltage in accordance with vibration of the A-phase region and the B-phase region
51
b
and outputs the generated voltage to the ECU
60
. The ECU
60
feedback controls the high frequency voltage applied to the A-phase region
51
a
and the B-phase region
51
b
based on this voltage. The grounding wire
61
d
is connected to the grounding lead wire
57
b
by the connector
59
. The regions
51
a
-
51
c
of the piezoelectric element
51
are grounded to the vehicle body frame through the ECU
60
.
As illustrated in
FIG. 8
, the stationary plate
46
of the stator
52
is fastened to the base
54
. The rotor
53
is pressed against the diaphragm
45
of the stator
52
and is coupled to the rotary shaft
55
. The shaft
55
is supported by the bearing
56
. That is, the stator
52
is directly and electrically connected the base
54
and is indirectly and electrically connected to the base
54
via the rotor
53
, the rotary shaft
55
and the bearing
56
.
Therefore, the regions
51
a,
51
b,
51
c
of the piezoelectric element
51
are grounded not only through the ECU
60
but also through the base
54
. In other words, the ultrasonic motor
50
is directly grounded to the vehicle body frame. The impedance of the grounding wire
61
d
between the ultrasonic motor
50
and the ECU
60
is higher than the impedance of the body frame. Therefore, when the ECU
60
applies high frequency voltage to the motor
50
, grounded current does not flow through the grounding wire
61
d
but flows to the ECU
60
through the vehicle body frame. The motor
50
, the shielded line
61
d
and the body frame form a closed loop circuit. The closed loop circuit functions as a loop antenna, which generates electromagnetic noise. The farther from the motor
50
the ECU
60
is located, the larger the area surrounded by the closed loop circuit becomes. A larger area surrounded by the closed loop circuit increases the electromagnetic noise. The electromagnetic noise generates radio noise, which interferes with the sound of the car radio. The electromagnetic noise also adversely affects other communications devices.
SUMMARY OF THE INVENTION
Accordingly, it is an objective of the present invention to provide an ultrasonic motor that reduces electromagnetic noise.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, an ultrasonic motor is provided. The motor includes a stator, a movable body and a housing. The stator has a piezoelectric element. The movable body contacts the stator. The piezoelectric element vibrates the stator to move the movable body. The housing supports the stator. The stator is electrically insulated from the housing.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.


REFERENCES:
patent: 3693035 (1972-09-01), Ostwald
patent: 5402030 (1995-03-01), Mukohjima
patent: 6-133567 (1994-05-01), None
patent: 5-31688 (1994-12-01), None
patent: 6-88198 (1999-12-01), None

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