JPH07225623A - Method and device for load control - Google Patents

Abstract

PURPOSE:To hold a load current at a desired value with high precision. CONSTITUTION:The load control unit 1 which controls a load current by turning ON and OFF a transistor(TR) 4 with a control signal outputted by a control circuit 6 in response to the detection result of a load current obtained by a current detecting circuit 2 delays the detection result by a predetermined time through a delay part 7 and outputs it as a trigger signal to a store part 8 once the control part 6 detects a break of power supply to a load 5, and the store part 8 stores the current detection result of the load current as an offset value. At next load control time, the control part 6 outputs a control signal in response to the value obtained by correcting the detection result of the load current at the circuit 2 with the offset value. Therefore, a detection error of the load current due to an increase in the resistance value of a current detection resistance, etc., accompanying the power supply to the current detecting circuit 2 is eliminated to hold the load current at the desired value with high precision.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load control method and apparatus for controlling a constant current type load such as a stepper motor for driving a fuel pump or a throttle valve of an automobile.

[0002]

2. Description of the Related Art Conventionally, a so-called constant current type load that generates a desired torque when a certain rated current is applied has a current detection function for detecting a load current in relation to the load. A circuit is provided. In response to the detection result of the current detection circuit, the control circuit controls the energization timing of a drive element realized by a power transistor or the like so that the load current has a desired value, thereby controlling the load. Performs constant current control. A typical load control device for controlling the load current of such a constant current type load is disclosed in JP-A-5-49252.

FIG. 10 shows a load control device 3 of the prior art.
2 is a circuit diagram of FIG. The load control device 31 generally includes a transformer T, a field effect transistor (hereinafter abbreviated as “FET”) Q, a detection resistor R, and a central processing circuit (hereinafter “C”).
PU) 32, pulse width modulator (hereinafter "PW")
(Abbreviated as “M”) 33 and the like.

The transformer T comprises a primary coil α and a secondary coil β, and the primary coil α has the F
The ETQ is interposed in series with the primary coil α. A direct current voltage is applied to the series circuit of the primary coil α and the FET Q, and the FET Q is turned on / off in response to the control signal given from the PWM 33, so that the secondary coil β receives the control signal of the control signal. An alternating voltage corresponding to the duty is induced.

After the AC voltage induced in the secondary coil β is rectified and smoothed by the diode D and the capacitor C in this way, the obtained current is supplied to the load.

The detection resistor R is a resistor for detecting a load current, and converts the load current into a voltage across its terminals. The voltage between the terminals is amplified by an amplifier 34, and then an analog / digital (hereinafter abbreviated as “A / D”) converter 35.
And output to the comparator 36. The A / D converter 35
The output from is compared with a preset set value in the CPU 32 realized by a microcomputer or the like.
Based on the comparison result, the CPU 32 sets the duty of the control signal so that the load current becomes the set value. In this way, the constant current control of the load is performed.

Further, the comparator 36 compares the output of the amplifier 34 with a preset set value, and outputs the result as comparison data to the PWM 33. The PWM 33 sets a correction value in response to the comparison data, corrects the control signal from the CPU 32 based on the correction value, and outputs the newly generated control signal to the FETQ. In this way, the detection error is corrected.

[0008]

The load control device 3 described above.
In No. 1, the detection result of the load current value is used as it is for the correction. Therefore, it is necessary to cope with the characteristic change of the load element due to the temperature rise of the constituent elements of the load control device 31 or the fluctuation of the power supply voltage. I can't.

An object of the present invention is to provide a load control method and device capable of maintaining a load current to a constant current type load at a desired value with high accuracy.

[0010]

SUMMARY OF THE INVENTION The present invention is a method for detecting a load current and controlling the load current to reach a desired value in response to the detection result. The detection result is stored as an offset value after a lapse of a predetermined time after shutting off, and the load current is controlled in response to the value obtained by correcting the detection result of the load current with the offset value at the next load control. This is a load control method characterized by:

Further, the present invention is characterized in that the predetermined time is determined based on a detection result of the load current immediately before the power supply to the load is cut off.

Furthermore, the present invention is characterized in that the predetermined time is a time until the rate of change in the detection result of the load current becomes a predetermined value or less after the energization of the load is cut off. To do.

According to the present invention, the detecting means interposed in the current path to the load, the control means outputting a control signal in response to the detection result of the detecting means, and the detecting means interposed in series in the current path, In a load control device including a control element that controls the load current in response to a control signal, an energization detection unit that detects that the control signal is input and the energization of the load is cut off, and the energization detection unit The detection result is delayed by a predetermined time and output, and a storage unit that stores the detection result of the detection unit as an offset value in response to the output of the delay unit. The load control device outputs the control signal in response to a value obtained by correcting the detection result of the means with the offset value.

[0014]

According to the present invention, in response to the detection result of the detection means interposed in the current path to the load, the control signal output from the control means causes the control element realized by, for example, a transistor to be turned on / off. In the load control device that controls the load current to a desired value by driving, an energization detection unit, a delay unit, and a storage unit are provided.

When the energization detecting means to which the control signal is input detects the interruption of the energization to the load, the delay means delays the detection result of the energization detecting means by a predetermined time and outputs it to the store means. The storing means stores the detection result as an offset value in response to the output of the delaying means. Then, at the next load control, the control means outputs the control signal in response to the value obtained by correcting the detection result of the load current by the detection means with the offset value.

As a result, for example, a change in the characteristics of the current detection circuit due to a temperature rise due to energization, a variation in the resistance value between the base and the emitter when the control element is realized by a transistor, a variation in the power supply voltage, etc. Since the current detection error is eliminated, the load current can be held at a desired value with high accuracy.

Preferably, the predetermined time is
It is determined based on the detection result of the load current immediately before the power supply to the load is cut off, or after the power supply to the load is cut off,
It is the time until the rate of change of the detection result of the load current becomes less than or equal to a predetermined value.

Therefore, it is not necessary to unnecessarily set a long time from the interruption of the energization of the load to the detection of the load current.

[0019]

1 is a functional block diagram of a load controller 1 according to a first embodiment of the present invention. The load control device 1 generally includes a current detection circuit 2, a control circuit 3 realized by a microcomputer or the like, and a transistor 4 which is a control element.
And is a device for controlling a load current for driving the load 5. The load control device 1 is used as a vehicle-mounted type, and the load 5 is a so-called constant current type load such as a fuel pump or a stepper motor for driving a sub-throttle in a traction control system, that is, when a certain rated current is supplied. , A load that generates a predetermined torque.

The current detection circuit 2 is realized by, for example, a current mirror circuit, detects the load current value supplied to the load 5, and derives an output voltage corresponding to the detection result to the control unit 6. In response to the output voltage, the control unit 6 pulls in the base current of the transistor 4 to drive the transistor 4 to conduct or cut off, thereby performing duty control so that the load current has a desired value. To do. When the transistor 4 is conducting, the load 5 is driven with a constant torque.

The control circuit 3 is composed of a control section 6 having an energization detecting function, a delay section 7 and a store section 8. When the transistor 4 is switched from the conductive state to the cutoff state, the control unit 6 outputs a trigger signal indicating a voltage cutoff to the delay unit 7. The delay unit 7 delays the trigger signal by a predetermined time W1, for example, 200 μs, and then,
Output to the store unit 8. In response to this, the store unit 8
The output voltage of the current detection circuit 2 is read and the output voltage is stored as an offset value. This offset value is given to the control unit 6 and is used to correct the detection result of the load current at the next load control.

FIG. 2 is a circuit diagram showing a specific configuration of the current detection circuit 2. The current detection circuit 2 is a so-called current mirror circuit and includes a pair of transistors Q1 and Q2.
, Amplification resistors R1 and R2, and a constant current source 11. One transistor Q1 pulls in a current from the terminal P1 on one end side of the detection resistor R3 via the constant current source 11, and the other transistor Q2 has the amplification resistor R3.
An electric current is drawn in from the terminal P2 on the other side of the detection resistor R3 via R1 and R2. Since the pair of transistors Q1 and Q2 form a current mirror circuit, the current values supplied to the transistor Q1 and the transistor Q2 are equal to each other.

When a load current is supplied to the current detection circuit 2 thus constructed, both terminals P1 and P2 of the detection resistor R3 are supplied.
The voltage V0 between them is amplified by R2 / R1 times and is derived from the output terminal P3 as the output voltage VOUT. This output voltage VOUT is expressed by the following equation.

V0 × R2 / R1 = VOUT (1) The control circuit 3 digitally outputs the output voltage VOUT input from the output terminal P3 by an analog / digital converter (not shown) built in the control circuit 3. After converting to
The duty of the control signal to the transistor 4 is determined to control the constant current of the load.

In the load control device 1 configured as described above, the characteristic change of the current detection circuit 2 including the detection resistor R3 and the change of the resistance value between the base and the emitter of the transistor 4 due to the temperature rise due to energization. As a result, a detection error occurs in the load current. The temperature characteristic of such a current detection circuit 2 is shown in FIG. The load current I is plotted on the abscissa and the output voltage V is plotted on the ordinate. The values of the output voltage V when the load current I is changed when the environmental temperature is 25 ° C. and 80 ° C. are shown in line L1 and line L2, respectively. Shown in.

For example, when the load current I1 is supplied to the load 5, the current detection circuit 2 derives the output voltage V1 when the environmental temperature is 25 ° C. and outputs it when the environmental temperature is 80 ° C. The voltage V2 is derived. That is, even if the same amount of load current is supplied to the load 5, the output voltage is
When the environmental temperature is 80 ° C, Δ is more than when it is 25 ° C.
Since the output is increased by V = V2-V1, the control circuit 3
Is the load current value I when the same output voltage V2 is derived.
The difference ΔI between 2 and I1 is stored in the storage unit 8 as the offset value.

FIG. 4 is a graph showing how the load current converges to zero. The horizontal axis indicates time t, and the vertical axis indicates load current I.
Take When the load current Imax is supplied to the load 5 and the energization is cut off at time t1, the load current gradually converges to 0 due to the influence of the parasitic capacitance of the load 5, the inductance component of the load 5, and the like. The current value becomes 0 at time t2. Therefore, the store timing of the difference ΔI is the convergence time after power interruption, that is, t2-t1.
Time W1 in the delay unit 7 so as to be longer than
Is chosen.

FIG. 5 is a flow chart showing a load control operation by the control circuit 3 for setting the load current value to a desired value. In step s1, the control unit 6 determines the target duty of the control signal, and in step s2, supplies the control signal to the transistor 4 to make the transistor 4 conductive and start energizing the load 5. In step s3,
The detection result of the current detection circuit 2 in the energized state of the load 5 is read, and in step s4, the control unit 6 determines the load current value actually supplied to the load 5 as (read value)-(correction value). ) Calculate based on the formula. The correction value is the offset value stored at the time of the previous load control.

In step s5, the load current value and the target value are compared with each other. If the result is that the load current value is less than the target value, the process returns to step s2 to continue the on-duty period of the control signal. The load current is controlled to approach the target value. On the other hand, when the load current value is equal to or larger than the target value, the process proceeds to step s6, and the energization from the control unit 6 to the transistor 4 is stopped.

In step s7, the load current value of the current detection circuit 2 immediately after the supply of the control signal is stopped is read, and step s7
Go to 8 and set the load current value to (read value)-(correction value)
Calculate based on the formula.

In step s9, the control section 6 compares the load current value with the target value, and if the result is that the load current value is less than the target value, the process returns to step s2 to energize. The control is restarted to bring the load current value close to the target value. On the other hand, if the load current value is equal to or larger than the target value in step s9, the process proceeds to step s10, and it is determined whether or not the energization control to the load 5 is ended.

If the energization is continued in step s10, the process returns to step s6 and the energization is kept stopped.
On the other hand, when the energization control to the load 5 is ended in step s10, the process proceeds to step s11, and the delay unit 7
The trigger signal given from the control unit 6 is delayed by the time W1 and output to the store unit 8. In step s12, the store unit 8 reads the detection result of the current detection circuit 2 at that time, and then proceeds to step s13 to store the detection result as an offset value.

As described above, in this embodiment, the detection result of the load current in the current detection circuit 2 after the elapse of the predetermined time W1 from the interruption of the energization of the load 5 is stored in the storage unit 8 as the offset value. Incidentally, at the time of the next load control, the load current is controlled based on the value obtained by correcting the detection result with the offset value.Therefore, the highly accurate constant current control in which the detection error caused by the above-mentioned reason is eliminated. It can be performed.

In the second embodiment of the present invention, in addition to the structure of the first embodiment described above, for example, the load 5 is a four-phase motor, the ratio of the load current supplied to each phase is changed, and the rotor is changed. It is assumed that the throttle valve opening degree is controlled by holding the position of, for example, in 16 stages.

FIG. 6 shows the rated load currents I1, I2, I3 (I1 <I2 <required to change the position of the rotor.
I3) and how the load current is converged to 0 after the supply thereof is stopped. The time T is plotted on the horizontal axis and the load current I is plotted on the vertical axis. When the load current is cut off at a certain time T0,
The current I1 converges to 0 at time T1, the current I2 at time T2, and the current I3 at time T3. In addition, T
Since 1 <T2 <T3, it is understood that the larger the load current value, the longer the convergence time.

FIG. 7 is a flow chart showing the load control operation of the above-mentioned second embodiment. This flow chart is
Similar to the embodiment shown in FIG. 5, the same reference numerals are used for the same steps. In the present embodiment, when the end of energization to the load 5 is detected in the step s10, the load current value immediately before the interruption of the energization is read in the next step s10a, and the process proceeds to step s10b, where the load current value is From the above, the delay time W1 is determined based on the graph shown in FIG.

As described above, in this embodiment, the delay time W1 from the interruption of the energization of the load 5 to the detection of the offset value is set corresponding to the load current value immediately before the interruption of the energization. It is not necessary to set the delay time W1 too long.

In the third embodiment of the present invention, the delay time W1 is set.
Is a time until the change rate of the detection result of the load current becomes less than a predetermined value after the energization of the load 5 is cut off. The time T is plotted on the abscissa and the output voltage V of the current detection circuit 2 is plotted on the ordinate, and FIG. 8 shows how the output voltage V changes after the end of energization of the load 5.

The output voltage V shown on line L7 is
When the energization of the load 5 is completed, the load 5 gradually converges to zero.
It is assumed that the output voltage at time T7 is V3, and the output voltage at time T8 after the calculation cycle ΔT of the control circuit 3 from time T7 is T4. At this time, when the change amount ΔV = V3−V4 of the output voltage during the calculation cycle ΔT becomes less than a predetermined threshold Vth, for example, 50 mV, the store unit 8 sets the detection result of the load current as an offset value. Store.

FIG. 9 is a flow chart showing the load control operation of the above-mentioned third embodiment. This flow chart is
Similar to the embodiment shown in FIG. 5, the same reference numerals are used for the same steps. Step s10
Then, when the energization of the load 5 is completed, the process proceeds to step s12, the control unit 6 reads the output voltage value corresponding to the detection result of the current detection circuit 2, and in step s12a, the previous output voltage value Vo and the current output voltage value Vo Change amount Δ from output voltage value Vi
It is determined whether V is less than the threshold value Vth.

If the amount of change ΔV is equal to or more than the threshold value Vth, the process proceeds to step s12b, the voltage value Vo is updated to Vi, and then the process returns to step s12, thus ΔV <Vth.
The control unit 6 reads the output voltage value Vi until
On the other hand, if ΔV becomes less than the threshold value Vth in step s12a, it is determined that the output voltage has converged, the process proceeds to step s14, and the detection result of this time is stored in the storing unit 8 as an offset value.

Therefore, also in this embodiment, the delay time W1 need not be set unnecessarily long.

[0043]

As described above, according to the present invention, the detection result of the load current after the lapse of a predetermined time from the interruption of the energization to the load is stored as an offset value, and the load current is controlled at the next load control. Since the detection result of is corrected by the offset value, for example, an increase in the resistance value of the detection means caused by energization, a variation in the resistance value between the base and the emitter when the control element is a transistor, and a load forming a load The detection error caused by the fluctuation of the resistance value of the element and the fluctuation of the power supply voltage is eliminated, and the load current can be controlled to a desired value with higher accuracy.

Further preferably, the predetermined time is
It is determined based on the detection result of the load current immediately before the power supply to the load is cut off, or after the power supply to the load is cut off,
Since it is selected as the time until the rate of change of the detection result becomes less than or equal to a predetermined value, the time from the interruption of power to the load to the detection of the load current value is predicted and set appropriately. This makes it unnecessary to set the predetermined time unnecessarily long.

[Brief description of drawings]

FIG. 1 is a functional block diagram of a load control device 1 according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a specific configuration of a current detection circuit 2.

FIG. 3 is a graph showing a temperature characteristic of the current detection circuit 2.

FIG. 4 is a graph showing how the load current converges to zero.

FIG. 5 is a flowchart showing a load control operation by the control circuit 3 for setting a load current value to a desired value.

FIG. 6 shows a rated load current in the second embodiment of the present invention,
It is a graph which shows the state of the convergence.

FIG. 7 is a flowchart showing a load control operation of the second embodiment of the present invention.

FIG. 8 is a graph for explaining the concept of the third embodiment of the present invention.

FIG. 9 is a flowchart showing a load control operation of the third embodiment of the present invention.

FIG. 10 is a circuit diagram of a typical prior art load control device 31.

[Explanation of symbols]

 1 load control device 2 current detection circuit 3 control circuit 4 transistor 5 load 6 control unit 7 delay unit 8 store unit 11 constant current source

Claims (4)

[Claims] 1. A method for detecting a load current and controlling the load current so as to reach a desired value in response to the detection result, wherein a predetermined time is set after the power supply to the load is cut off. The load detection is characterized in that the detection result after the passage is stored as an offset value, and the load current is controlled in response to a value obtained by correcting the detection result of the load current with the offset value at the next load control. Method. 2. The load control method according to claim 1, wherein the predetermined time is determined based on a detection result of the load current immediately before the power supply to the load is cut off. 3. The predetermined time is set to be a time after the power supply to the load is cut off until the rate of change of the detection result of the load current becomes equal to or less than a predetermined value. The load control method described. 4. A detection means interposed in a current path to a load, a control means outputting a control signal in response to a detection result of the detection means, and a detection means interposed in series in the current path to generate the control signal. In a load control device including a control element that controls the load current in response, the control signal is input, an energization detection unit that detects that energization to the load is cut off, and a detection result of the energization detection unit Including a delay means for delaying and outputting by a predetermined time, and a store means for storing the detection result of the detecting means as an offset value in response to the output of the delay means, wherein the control means detects the detection by the detecting means. A load control device which outputs the control signal in response to a value obtained by correcting the result with the offset value.