Electricity: motive power systems – Constant motor current – load and/or torque control
Reexamination Certificate
2000-10-20
2002-12-31
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Constant motor current, load and/or torque control
C318S474000, C318S430000
Reexamination Certificate
active
06501241
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a current detector used in a control system for controlling a motor for driving a vehicle such as an electric vehicle or a hybrid vehicle, or for use in another system which requires current detection.
2. Description of the Related Art
FIG. 4
is a block diagram showing the structure of a conventional current detector used in a control system for controlling a motor for driving a vehicle. In this figure, reference numeral
1
indicates a current sensor using a Hall element. The Hall element has a function of outputting a voltage which is proportional to (i) flowing current and (ii) generated magnetic flux density.
FIG. 5
is a block diagram showing the structure of the current sensor
1
. In the figure, reference numeral
7
indicates a Hall element. Reference numeral
8
indicates a core which generates a magnetic flux when current flows through wire L. Reference numeral
9
indicates a power circuit which receives 12 V voltage, and converts it to 5 V voltage and outputs the converted voltage. Reference numeral
10
indicates an amplification circuit which is driven using the 5 V voltage output from the power circuit
9
. When voltage v
1
is input from Hall element
7
to the amplification circuit
10
, the circuit
10
amplifies voltage v
1
and also adds an offset voltage to the amplified voltage, and outputs the amplified voltage including the offset as voltage v
2
. Reference numeral
11
indicates a constant current generating circuit for supplying a constant current to the Hall element
7
. The 5 V voltage output from the power circuit
9
is supplied to the constant current generating circuit
11
as a reference voltage, and the above constant current is defined by potential-dividing the reference voltage by using a resistor.
In
FIG. 4
, reference numeral
3
indicates an A/D converter which receives voltage input via terminal C from current sensor
1
, and calculates the ratio of the input voltage to a reference voltage input from the power circuit
4
, and converts the ratio to a digital value, and outputs the digital value. Here, the power circuit
4
converts input
12
V voltage to 5 V voltage and supplies the 5 V voltage to the A/D converter
3
. Reference numeral
5
indicates a CPU (central processing unit) for receiving the above digital value from the A/D converter, and calculates and outputs the value indicating a target current flowing through wire L. Reference numeral
6
indicates a power circuit for driving CPU
5
.
Below, the operation of the current detector (used in a control system for controlling a motor for driving a vehicle) having the above-explained structure will be explained.
When a 12 V voltage is input via terminal B to current sensor
1
, the power circuit
9
converts the 12 V voltage to 5 V voltage and outputs the converted voltage to the Hall element
7
and the constant current generating circuit
11
.
On the other hand, when a target current to be measured flows through wire L, magnetic flux is generated in core
8
. When the magnetic flux is applied to Hall element
7
, the element
7
outputs voltage v
1
, proportional to the magnetic flux, to the amplification circuit
10
. The amplification circuit
10
amplifies the input voltage v
1
and adds an offset voltage to it so as to obtain voltage v
2
(0 V ≦v
2
≦5.0 V), and outputs voltage v
2
via terminal C to A/D converter
3
.
When the A/D converter
3
receives voltage v
2
via terminal C, the converter
3
calculates the ratio of v
2
to the reference voltage (i.e., 5V) input via terminal A from the power circuit
4
, and converts the calculated result to a digital value and outputs the digital value to CPU
5
.
In order to improve the accuracy of the current sensor
1
, a constant current (from the constant current generating circuit) should be stable, that is, should not be affected by the external environment. Accordingly, the voltage supplied to the constant current generating circuit should be accurate, and thus an accurately operable power circuit must be used as power circuit
9
.
In addition, the A/D converter
3
should also accurately digitize the measurement value of the current sensor
1
, and thus the power circuit
4
should also be accurate.
Therefore, conventionally, in order to accurately measure the target current, both the power circuits
4
and
9
must be accurate, thus the cost will be high.
In addition, the values of reference voltage (5 V) of the power circuits may not accurately be the same, thereby producing an error.
Furthermore, in the control of the motor for driving a vehicle, such an error of the current sensor certainly causes an error in the torque control of the motor. More specifically, the difference between the real value and the actually detected value functions as an error of the control value, so that overestimates or underestimates of the control may cause a shock to the vehicle, or excessive discharging or charging of the battery functioning as a power source.
Therefore, for example, the system must be designed in consideration of an error in the detected current; thus, the design may be limited or the system cost may be high.
SUMMARY OF THE INVENTION
In consideration of the above circumstances, an objective of the present invention is to provide a current detector used in a control system for controlling a motor for driving a vehicle, wherein accurate current measurement can be performed without using especially accurate power circuits (as explained above).
Therefore, the present invention provides a current detector used in a control system for controlling a motor for driving a vehicle comprising:
a detector (for example, a current sensor
21
in the following embodiment) for outputting a voltage corresponding to a target current, wherein the detector has a current detecting element (for example, a Hall element
27
in the following embodiment) for detecting the target current;
an amplifier (for example, an amplification circuit
30
in the following embodiment) for amplifying and outputting the output from the detector;
an analog-digital converter (for example, an A/D converter
23
in the following embodiment) for converting the output from the amplifier to a digital data; and
a power circuit (for example, a power circuit
33
in the following embodiment) for supplying an output voltage to both the detector and the analog-digital converter.
In a typical example, the detector comprises:
a Hall element (for example, a Hall element
27
in the following embodiment) functioning as the current detecting element;
a core (for example, a core
28
in the following embodiment) for applying a magnetic flux corresponding to the target current to the Hall element; and
a constant current generating circuit (for example, a constant current generating circuit
31
in the following embodiment) for supplying a constant current to the Hall element.
Preferably, the amplifier adds an offset voltage to the amplified voltage, and outputs the amplified voltage including the offset.
Also typically, the vehicle is a hybrid vehicle which uses the motor for assisting the output of an engine.
According to the present invention, the output voltage from a single power circuit is supplied to the detector for detecting the target current and to the analog-digital converter; thus, an especially accurate power circuit is not necessary, and an accurate measurement result can be obtained by using a cheap power circuit whose accuracy is relatively low.
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Ohnuki Yasumichi
Tsurumi Takafumi
Duda Rina I.
Honda Giken Kogyo Kabushiki Kaishi
Nappi Robert E.
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