JPH0538962Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Field of Application) The present invention relates to an improved in-vehicle blower motor drive circuit so that a constant air flow rate can be obtained from an in-vehicle blower motor such as a car air conditioner.

(Conventional technology) Conventionally, by adjusting the drive voltage of the blower motor, the blower motor was driven at an arbitrarily set constant rotation speed, and a predetermined amount of air was blown according to the rotation speed. .

Incidentally, the amount of air taken in from outside the vehicle and supplied to the blower motor fluctuates significantly due to changes in vehicle speed, etc. For this reason, the amount of air sent out from a blower motor that is driven at a constant rotation speed is the amount of air that varies depending on the rotation speed of the blower motor plus the variation due to the intake air volume, which causes the problem that a constant amount of air cannot be obtained. The dot was hot.

Therefore, in order to improve the fluctuation in air flow due to changes in the air flow taken in from outside the vehicle, the applicant of the present invention previously proposed in Utility Model Application No. 61-49899, by adjusting the drive current of the blower motor to a constant value. We are proposing an improved in-vehicle blower motor drive circuit that can provide a blowing volume of . This proposal is based on the idea that when the intake air volume increases, the load on the blower motor increases, and since the drive current is constant, the rotation speed decreases.
The air volume is reduced according to the rotation speed so that the air flow, including the fluctuation due to the increase in intake air volume, remains constant, and conversely, when the intake air volume decreases, the rotation speed of the blower motor increases and The air volume is increased so that the air volume, including the variable part due to the decrease in the intake air volume, remains constant.

Here, a circuit diagram of the above-mentioned in-vehicle blower motor drive circuit is shown in FIG.

In FIG. 2, a blower motor 2, a detection resistor 3, and a control transistor 4 are interposed in series between a power supply terminal 1 connected to an on-vehicle battery and the ground, thereby forming a drive current path for the blower motor 2. ing. The detection resistor 3 is used for drive current detection, and both ends thereof are connected to the plus and minus input terminals of the amplification operational amplifier 5. The output terminal of this amplifying operational amplifier 5 is connected to a resistor 6 and a capacitor 7.
It is connected to the negative input terminal of the comparison operational amplifier 8 via an integrating circuit consisting of the following. The positive input terminal of this comparison operational amplifier 8 is connected to the sliding terminal of a variable resistor 9 interposed between the power supply terminal 1 and the ground to receive a reference signal, and the output terminal is connected to the base of the control transistor 4. It is connected to the.

In this configuration, the impedance of the control transistor 4 serving as the control means is adjusted, and the drive current I of the blower motor 2 flows. Then, the potential difference Vr between both ends of the detection resistor 3 is amplified by the amplification operational amplifier 5, which is an amplification means. This amplified signal
VSET is integrated and compared with a reference signal set by a variable resistor 9 by a comparison operational amplifier 8 serving as comparison means, and the impedance of the control transistor 4 is adjusted using the comparison signal. Therefore, according to the reference signal set by the variable resistor 9, the drive current I is adjusted to an appropriate constant value so that the potential difference Vr across the detection resistor 3 becomes a predetermined value.

(Problems to be Solved by the Invention) By the way, since the amplifying operational amplifier 5 is operated only by the positive power supply of the vehicle battery, an offset voltage is generated in the amplified signal VSET. This offset voltage is, for example, 0.4V as shown in Figure 3.
It is. Then, the amplification degree of the amplification operational amplifier 5 is
If it is 100, the potential difference Vr across the detection resistor 3 is
Offset voltage will be output below 4mV. Here, if the value of the detection resistor 3 is set to 2 mΩ, the amplification operational amplifier 5 outputs an offset voltage when the drive current I is 2A or less. As a result, the in-vehicle blower motor drive circuit has a problem in that it cannot be adjusted in a range where the drive current is 2A or less and the air flow is small.

Note that if the value of the detection resistor 3 is set larger than the value mentioned above, the drive current I at which the amplification operational amplifier 5 outputs the offset voltage can be made smaller than 2A, and the adjustment range on the small side can be expanded. . However, since the amplified signal output from the amplifying operational amplifier 5 increases accordingly,
The voltage set as the reference signal must also be correspondingly increased. Here, the voltage that can be set as the reference signal is limited by the power supply voltage of the vehicle battery. Therefore, a problem arises in that the adjustment range on the larger side of the drive current I is restricted.

The purpose of the present invention is to further improve the above-mentioned in-vehicle blower motor drive circuit previously proposed by the applicant of the present invention. An object of the present invention is to provide an on-vehicle blower motor drive circuit that reduces the range of drive current.

(Means to be Solved by the Invention) In order to achieve the above object, the in-vehicle blower motor drive circuit of the present invention uses an in-vehicle battery as a drive power source, and includes a detection resistor for detecting the drive current in the drive current path of the blower motor. A control means for adjusting the drive current is interposed in series, an amplification signal obtained by amplifying the potential difference across the detection resistor is amplified by the amplification means, and a reference signal are compared by the comparison means, and the control means is adjusted according to the comparison signal. In an on-vehicle blower motor drive circuit that adjusts the drive current to a constant value, the voltage dividing means that divides the amplified signal and supplies it to the comparison means is combined with the amplifying means having an offset voltage by driving one power source of the on-vehicle battery. The detecting resistor is interposed between the comparing means, and the value of the detecting resistor is set to a large value in accordance with the voltage division of the amplified signal by the voltage dividing means, and the driving voltage cannot be adjusted by the offset voltage of the amplifying means. It is configured to reduce the range of current.

(Function) Since the voltage dividing means is interposed between the comparing means and the amplifying means for amplifying the potential difference between both ends of the detection resistor for detecting the drive current which is inserted in the drive current path of the blower motor, this voltage dividing means The value of the detection resistor is increased in accordance with the partial voltage of the amplified signal by the amplification means, and the potential difference across the detection resistor applied to the amplification means is increased. By increasing the value of this detection resistor, the value of the drive current at which the output of the amplification means becomes the offset voltage can be made smaller compared to the previously proposed circuit without voltage dividing means, which is not affected by the offset voltage. The range of drive current can be reduced. Moreover, by providing a voltage dividing means, there is no need to set the reference signal large even if the amplified signal becomes large.
Accordingly, the adjustment range on the larger side of the drive current I is not restricted.

(Description of Embodiments) Hereinafter, embodiments of the present invention will be described with reference to FIG. FIG. 1 is a circuit diagram of an embodiment of an on-vehicle blower motor drive circuit of the present invention. In FIG. 1, circuit elements that are the same as those in FIG. 2 are given the same reference numerals and redundant explanations will be omitted.

The differences between Figure 1 and Figure 2 are as follows:
It is as follows.

First, a resistor 10 is connected in series between the output terminal of the amplifying operational amplifier 5 as the amplifying means and the negative input terminal of the comparative operational amplifier 8 as the comparing means. The resistors 10 and 11 form voltage dividing means for dividing the voltage of the amplified signal. and,
Corresponding to the voltage division by this voltage dividing means, the value of the detection resistor 12 for detecting the drive current, which is inserted in series with the drive current path, is set to a large value. Further, an integrating circuit consisting of a resistor 6 and a capacitor 7 is interposed between the output terminal of the comparison operational amplifier 8 and the base of the control transistor 4 serving as the control means.

Here, for example, if the resistors 10 and 11 have the same resistance value, the amplified signal VSET of the amplifying operational amplifier 5 is 1/
2, and the amplification degree of the amplification operational amplifier 5 is 100.
If they are the same, the detection resistor 12 for detecting the drive current is set to 4 mΩ, which is twice the value.

In such a configuration, the amplification operational amplifier 5 is
Since it is driven by the positive power source of the vehicle battery, an offset voltage of, for example, 0.4V is output to the amplified output terminal even if the input signal is zero.
Then, the detection resistor 1 outputs an offset voltage of 0.4V to the amplified signal VSET of the amplification operational amplifier 5.
The potential difference Vr between both ends of 2 is 4mV, and the detection resistor is
Since it is set to 4mΩ, the drive current I is 1A. Therefore, in the range where the drive current I is 1A or more, the amplification operational amplifier 5 outputs the amplification signal VSET corresponding to the drive current. In addition, the drive current I is 1A
In the following range, the amplifying operational amplifier 5 outputs an offset voltage regardless of the magnitude of the drive current I. Then, this amplified signal VSET is 1/
2 and can be applied to the comparison operational amplifier 8 as a divided voltage signal Vout. This divided voltage signal Vout is
If the driving current I is the same, the magnitude is the same as the amplified signal VSET of the previously proposed circuit shown in FIG. 2, within a range in which no offset voltage is output from the amplifying operational amplifier 5.

Therefore, the circuit of the present invention can make the range affected by the offset voltage of the amplifying operational amplifier 5 smaller than the previously proposed circuit shown in FIG.

In the above embodiment, the partial pressure by the pressure dividing means is set to 1/2, but it is needless to say that the present invention is not limited to this. Further, in the above embodiment, the reference signal for setting the rotation speed of the blower motor 2 is output from the rotation speed setting means consisting of the variable resistor 9 and the Zener diode, but the reference signal is output from a microcomputer or the like. It will be clear to those skilled in the art that the setting data value may be converted into an analog quantity by a D/A converter and applied as a reference signal to the plus input terminal of the comparison operational amplifier 8.

(Effects of the Invention) As explained above, according to the in-vehicle blower motor drive circuit of the present invention, the range of the drive current that cannot be adjusted due to the influence of the offset voltage of the amplification means driven by one power source of the in-vehicle battery. can be made smaller, and the amount of air blown can be adjusted to a smaller range. Furthermore, an excellent effect is achieved in that the adjustment range on the side where the drive current is larger is not restricted.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the in-vehicle blower motor drive circuit of the present invention, FIG. 2 is a circuit diagram of an in-vehicle blower motor drive circuit previously proposed by the applicant of the present invention, and FIG. The figure is a characteristic diagram of the drive current and amplified signal in FIG. 2. 2... Blower motor, 3, 12... Resistor for detection, 4... Transistor for control, 5... Operational amplifier for amplification, 8... Operational amplifier for comparison, 9... Variable resistor, 10, 11... Resistor.

Claims (1)

[Scope of utility model registration request] An in-vehicle battery is used as a drive power source, a detection resistor for detecting the drive current and a control means for adjusting the drive current are inserted in series in the drive current path of the blower motor, and the potential difference between both ends of the detection resistor is amplified by the amplification means. In an on-vehicle blower motor drive circuit, the amplified signal and a reference signal are compared by a comparing means, and the control means is adjusted according to the comparison signal to maintain a constant drive current. A voltage dividing means for applying the voltage is interposed between the amplifying means having an offset voltage and the comparing means by driving one power supply of the on-vehicle battery, and the voltage dividing means is provided so as to correspond to the voltage divided by the voltage dividing means of the amplified signal. A vehicle blower motor drive circuit, characterized in that the value of the detection resistor is set large to reduce the range of the drive current that cannot be adjusted by the offset voltage of the amplification means.