Electricity: electrical systems and devices – Safety and protection of systems and devices – Motor protective condition responsive circuits
Reexamination Certificate
1999-11-16
2003-09-09
Toatley, Jr., Gregory J. (Department: 2839)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Motor protective condition responsive circuits
Reexamination Certificate
active
06618228
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a current detecting apparatus which is provided in, for example, an electric power steering apparatus of an automobile and which generates a detecting signal having electric potential proportional to magnetic flux density of a magnetic field arising from a current to be detected, and an electric motor control apparatus comprising the current detecting apparatus.
BACKGROUND OF THE INVENTION
FIG. 1
is a block diagram showing one embodiment of an electric motor control apparatus comprising the conventional current detecting apparatus.
Reference numeral
10
is an electric motor control apparatus
10
which comprises an electric motor control unit
11
. The electric motor control unit
11
inputs an input signal IN which is a command of a driving signal for driving an electric motor M and compares the absolute value of the electric potential of the input signal IN with the absolute value of the electric potential of a comparing signal S
12
. Then, it generates either a driving signal S
10
for decreasing torque corresponding to the positive potential difference between the input signal IN and the comparing signal S
12
or a driving signal S
10
for increasing torque corresponding to the negative electric potential difference between the input signal IN and the comparing signal S
12
.
The electric motor M rotating by the driving signal S
10
is connected to the output of the electric motor control unit
11
. Further, the electric motor control apparatus
10
is provided with a current detecting apparatus (for example, a current detecting unit)
12
. The current detecting unit
12
is a circuit to generate the comparing signal S
12
proportional to magnetic flux density of a magnetic field B arising from the current flowing to the electric motor M driven by the driving signal S
10
. The current detecting unit
12
has the electric motor control unit
11
connected at the output thereof.
FIG. 2
is a circuit diagram showing one embodiment of the current detecting unit
12
of FIG.
1
.
The current detecting unit
12
comprises an operational amplifier (herein under called op-amp)
12
a
. A noninverting input terminal of the op-amp
12
a
is connected to a power supply electric potential VCC through a resistor
12
b
and grounded through a resister
12
c
. An inverting input terminal of the op-amp
12
a
is connected to a node Ni. A positive power supply terminal of the op-amp
12
a
is connected to a power supply electric potential VDD and a negative power supply terminal of the op-amp
12
a
is grounded. A transistor
12
d
is connected to an output terminal of the op-amp
12
a
at a base thereof and connected to a node N
2
at an emitter thereof. There is an input terminal of a hall sensor
12
e
connected between the node Ni and the node N
2
. The magnetic field B arising from the current which is a subject to be detected and which starts flowing to the electric motor M by the driving signal S
10
is applied to the hall sensor
12
e
. The hall sensor
12
e
outputs an output signal S
12
e
having the electric potential proportional to the magnetic flux density of the magnetic field B and a control current i supplied from the node N
2
. The output terminal of the hall sensor
12
e
is connected to an op-amp
12
f
for amplifying the output signal S
12
e
by the predetermined gain and supplying the comparing signal S
12
. The node Ni is grounded through a resistor
12
g.
FIG. 3
is a schematic view showing one embodiment of an electric motor power steering apparatus used in an automobile utilizing the electric motor control apparatus
10
shown in
FIG. 1
The electric motor power steering apparatus comprises a handle
21
. The handle
21
is connected with a steering shaft
22
. The steering shaft
22
is connected to a pinion
24
a
inside a steering gear box
24
with a coupler shaft
23
having free joints
23
a
,
23
b
at both ends. The handle
21
, the steering shaft
22
, the coupler shaft
23
and the steering gear box
24
constitute a hand-operated steering power generating means. The steering gear box
24
contains a rack
24
b
meshing into the pinion
24
a
. The steering power due to the handle
21
is converted into the axial direction by meshing the pinion
24
a
into the rack
24
b
to reciprocate a rack shaft
25
united with the rack
24
b
. The rack shaft
25
is connected to front wheels
27
a
,
27
b
at both ends thereof with tie rods
26
a
,
26
b.
The electric motor power steering apparatus comprises an electric motor M which is arranged in the same shaft as the rack shaft
25
and which is for applying assist torque to amplify the steering power of the hand-operated steering generation means to decrease the steering power of a driver. The electric motor M has a rotor integrated with a helical gear
28
at the driving side. The helical gear
28
meshes into a helical gear
29
b
integrated with one end of a screw shaft
29
a
of a ball screw mechanism
29
. Further, The steering gear box
24
contains a steering torque detecting means
30
for detecting hand-operated steering torque of a driver acting on the pinion
24
a
. The electric motor control apparatus
10
of
FIG. 1
is connected to the output of the steering torque detecting means
30
, and the electric motor M is connected to the electric motor control apparatus
10
.
In the electric power steering apparatus, the hand-operated steering torque generates as the driver operates the handle
21
, and the front wheels
27
a
,
27
b
are moved to change the driving direction of the automobile. At this point, the steering torque detecting means
30
detects the hand-operated steering torque and outputs a detecting signal S
30
. The detecting signal S
30
is applied to the electric motor control unit
11
of
FIG. 1
as an input signal IN. The electric motor control unit
11
outputs the driving signal S
10
corresponding to the input signal IN. The electric motor M rotates by the driving signal S
10
, and then the rotating torque is converted into the thrust through the helical gear
28
and the ball screw mechanism
29
to assist the thrust of the rack shaft
25
. The magnetic field B arising from the current which starts flowing into the electric motor M by the driving signal S
10
is applied to a hall sensor
12
e
of the current detecting unit
12
.
In the current detecting unit
12
, the electric potential of the node N
2
is controlled so that the electric potential of the node Ni is equal to the reference electric potential Vr set by the resistors
12
b
,
12
c
. Further, the control current i is supplied to the node N
2
from the power supply electric potential VDD. The value of the control current i is set by the resistor
12
g
. The control current i is applied to the hall sensor
12
e
, and the hall sensor
12
e
outputs an output signal S
12
e
having the electric potential proportional to the control current i and the magnetic flux density of the magnetic field B. The output signal S
12
e
is applied to the op-amp
12
f
and amplified, and the op-amp
12
f
outputs the comparing signal S
12
. The input signal IN is compared with the comparing signal S
12
by the electric motor control unit
11
. Then, if the comparing signal S
12
is larger than the input signal IN, the electric motor control unit
11
outputs the driving signal S
10
for decreasing torque. On the other hand, if the comparing signal S
12
is smaller than the input signal IN, the electric motor control unit
11
outputs the driving signal S
10
for increasing torque.
SUMMARY OF THE INVENTION
The conventional electric motor control apparatus
10
of
FIG. 1
has the following problems.
FIG. 4
is a graph showing the relationship between the current IM flowing to the electric motor M and the comparing signal S
12
. The vertical axis indicates the electric potential of the comparing signal S
12
and the horizontal axis indicates the current IM.
In
FIG. 4
, the assist torque is applied to the right direction with respect to the driving direction of the automobile in the p
Hironaka Shinzi
Kobayashi Akio
Kurosawa Takao
Mukai Yoshinobu
Noro Yoshiki
Honda Giken Kogyo Kabushiki Kaisha
Kitov Z
Sughrue & Mion, PLLC
Toatley , Jr. Gregory J.
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