Electricity: motive power systems – Constant motor current – load and/or torque control
Reexamination Certificate
1999-08-24
2001-05-29
Dang, Khanh (Department: 2837)
Electricity: motive power systems
Constant motor current, load and/or torque control
C318S254100, C318S268000
Reexamination Certificate
active
06239567
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to control devices for motors and more particularly to control devices for brushless motors which are applied to motor vehicles. More specifically, the present invention is concerned with a control device for accurately controlling the rotation speed of the brushless motor in accordance with an instruction signal applied thereto.
2. Description of the Prior Art
For driving blower fans of automotive air conditioners and cooling fans for radiators of motor vehicles, brushless motors have been widely used. For controlling the brushless motors, a control device including a microcomputer is usually employed.
In order to clarify the task of the present invention, one automotive air conditioner having a brushless motor controlled by a known control device will be described before making a detailed explanation of the present invention.
FIG. 7
is a block diagram of the known automotive air conditioner which employs a brushless motor
4
for driving a blower fan
4
a
. Denoted by numeral
2
is an air conditioning control unit for centrally controlling the air conditioner. Denoted by numeral
3
is a control panel for permitting a driver or passenger to input instructions to the control unit
2
for setting the temperature in a vehicle cabin. In the illustrated case, the control panel
3
has a power switch and a temperature control knob. Denoted by numeral
1
is a control device for controlling the motor
4
. The control device
1
comprises a processing unit
12
, a drive section
13
which includes a driver circuit and resistors, and six field effect transistors (MOSFET)
14
each two being applied to one winding of the motor
4
. Denoted by numeral
5
is a battery and
6
is a switch circuit for feeding when ON an electric power of the battery
5
to the motor
4
. The switch circuit
6
is actuated by an ignition switch (not shown). In the following, a voltage of the electric power supplied from the battery
5
through the switch circuit
6
will be referred to as “VCC voltage”.
The control panel
3
provides the air conditioning control unit
2
with an information signal representing the position of the temperature control knob, that is, a temperature desired by the passenger. In addition, information signals issued from various sensors are fed t the control unit
2
, which are signals representing the temperature in the vehicle cabin, outside temperature, quantity of solar radiation and so on. Based on the information signals received, the control unit
2
issues to the processing unit
12
a voltage signal representing a desired rotation speed of the motor
4
. Because the blower fan
4
a
is driven by the motor
4
, the rotation speed of the motor
4
controls the air amount blown from an air outlet to the vehicle cabin. By means of an analogue/digital converter (A/D converter), the voltage signal from the control unit
2
is converted to a digital data and led into the processing unit
12
for calculation of a target rotation speed value of the motor
4
. The target rotation speed value calculated by the processing unit
12
is a data representing a duty (which will be referred to as “input duty” (Din). The data is subjected to an after-described correction and finally becomes a pulse signal duty used for driving the motor
4
. Thus, controlling of the brushless motor
4
is carried out by allowing the air conditioning control unit
2
to change the target rotation speed value (viz., input duty) led into the control device
1
.
In order to allow the brushless motor
4
to run accurately at the target rotation speed, it is necessary to precisely control the rotation speed of the motor
4
in response to the input duty (Din) led into the control device
1
. For dealing with a fluctuation of the VCC voltage caused by a temperature change of the battery
5
, a so-called “proportional control” is used for controlling the motor
4
. That is, the voltage appears at both ends of each winding of the motor
4
when each field effect transistors
14
is ON, and the voltage fluctuation tends to make a fluctuation of current in the windings. In the proportional control, the input duty (Din) is corrected based on a deviation between the sensed VCC voltage and a reference voltage. This correction will be referred to as “VCC voltage correction” hereinafter.
In the processing unit
12
, the input duty (Din) is derived, and the VCC voltage is subjected to sampling to obtain VCC voltage value “Vi”. And, in a VCC correction factor calculating section
12
a
of the processing unit
12
, a VCC correction factor “Ma” is calculated by using the following equation (1).
VCC correction factor “Ma”=Vt/Vi (1)
wherein:
Vt: reference VCC voltage (=12.5V) stored in a reference voltage generating section
12
b.
The VCC correction factor “Ma” is led into a VCC correction section
12
c
of the processing unit
12
, and by using the following equation (2), a VCC voltage correction is carried out in the section
12
c
to obtain a medium duty (Dm).
medium duty =input duty (Din)×Ma (2)
After correcting the VCC voltage, a linearity correction is carried out to cause the rotation speed of the motor
4
to have a linearity to the medium duty (Dm). That is, when the medium duty (Dm) is led into a linearity correcting section
12
e
of the processing unit
12
, a linearity correction factor “Mc” corresponding to the medium duty (Dm) is looked up from a linearity correction table
12
d
, and by using the following equation (3), an output duty (Dout) of pulse signal directed to the drive section
13
is calculated.
output duty (Dout)=Dm×Mc (3)
Upon receiving the pulse signal with the output duty through the drive section
13
, the six field effect transistors
14
are turned ON in given order thereby to feed the windings of the motor
4
to drive the same. Accordingly, in the processing unit
12
, the voltage signal of the target rotation speed value for the motor
4
is processed for controlling the rotation speed of the motor
4
. With this, the rotation speed of the brushless motor
4
, that is, the amount of air blown from the air outlet is controlled to a target amount for contributing to the air conditioning in the vehicle cabin.
As is described hereinabove, in the known control device for the brushless motor employed in the automotive air conditioner, in order to drive the brushless motor
4
at a target rotation speed, both a proportional control based on the deviation of the power voltage and a correction for improving the linearity of the rotation speed of the motor
4
are practically carried out.
Recently, with increased demand for amenity in the vehicle cabin, it has become necessary to control the temperature in the vehicle cabin with a much higher accuracy and thus, the control for the brushless motor of a blower fan has needed a higher accuracy.
However, the known control device fails to provide the brushless motor
4
with finely controlled rotation due to a mechanical energy loss of the motor
4
and a ripple on the source voltage of the motor
4
. In fact, the dispersion is inevitably produced in accordance with the rotation speed of the motor
4
. For solving the drawback, various measures have been proposed. However, almost all have failed to exhibit a satisfied result.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a control device which can accurately control the rotation speed of a brushless motor throughout a widened speed range.
It is another object of the present invention to provide an improved control device for controlling a brushless motor which serves to drive a blower fan of an automotive air conditioner, a radiator cooling fan of a motor vehicle, and the like.
According to a first aspect of the present invention, there is provided a control device for a brushless motor, which comprises a first section which stores a data table provided to minimize a difference between an actual rotation sp
Araki Futoshi
Sekine Takeshi
Sunaga Hideki
Takahashi Eiji
Calsonic Kansei Corporation
Dang Khanh
Foley & Lardner
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