JP7661909B2 - Electronic Control Unit - Google Patents

Description

The present invention relates to an electronic control device that controls a pump motor to control the pressure in a urea pipe.

In order to improve purification performance, urea-SCR (Selective Catalytic Reduction) systems used in vehicle exhaust gases, etc., are required to increase pipe pressure in a short time after startup so that urea water can be injected. To achieve this, it is important to start the motor for the pump that pumps the urea water at high speed for a short time, and ideally, the motor should be operated at a speed close to the rated speed immediately after startup.

However, if the characteristics of the motor or urea water change due to temperature changes, etc., the motor's rotation speed will change even if the motor is driven with the same duty ratio during PWM control. Therefore, under motor/urea water characteristics conditions that result in a high rotation speed, over-rotation during forced commutation may exceed the motor's rated rotation speed. To avoid this situation, the target rotation speed immediately after startup must be set lower than the rated rotation speed, which lengthens the time it takes to reach a high rotation speed after startup. On the other hand, under motor/urea water characteristics conditions that result in a low rotation speed, the rotation speed does not rise to the target rotation speed during forced commutation, and the time it takes to reach the target rotation speed increases.

JP 2020-48328 A JP 2008-148379 A

Both Patent Documents 1 and 2 are technologies for starting a motor in a short time. The method disclosed in Patent Document 1 can correct the duty difference of the inverter circuit, but cannot correct fluctuations due to changes in the characteristics of the motor or urea water. In addition, as disclosed in Patent Document 2, a method of increasing the current limit level during forced commutation to allow a large current to flow can be used to start the motor at a high rotation speed. However, since the motor/urea water characteristics that result in the above high rotation speed exceed the rated rotation speed, the current limit must be set to match the motor/urea water characteristics that result in a high rotation speed, and the time required to reach the target rotation speed cannot be shortened at a target rotation speed close to the rated rotation speed.

The present invention was made in consideration of the above circumstances, and its purpose is to provide an electronic control device that can start the pump motor in the shortest possible time in accordance with the characteristics of the motor and urea water.

According to the electronic control device of claim 1, the control unit PWM controls the drive of the pump motor to control the pressure in the urea pipe, and performs forced commutation processing so that the rotation speed of the pump motor reaches the target rotation speed.

The control unit compares the rotation speed detected when the pump motor is driven by the PWM signal of the test drive duty ratio during a test period before the forced commutation process is performed with a reference rotation speed corresponding to the PWM signal of the test drive duty ratio, and corrects the forced commutation duty ratio of the PWM signal to be set during the forced commutation process according to the comparison result. With this configuration, the forced commutation duty ratio can be appropriately corrected according to the detected rotation speed of the pump motor during the test period, making it possible to start the pump motor in as short a time as possible and without exceeding the rated rotation speed.

1 is a flowchart showing the contents of a start control process of a pump motor according to a first embodiment. Flowchart showing the forced commutation duty correction process Timing chart showing pump motor start control Diagram equivalent to Figure 3 when the forced commutation duty ratio is not corrected A diagram showing the configuration of an electronic control device. 11 is a flowchart showing the content of a forced commutation duty correction process according to a second embodiment. FIG. 11 is a flowchart showing the content of a forced commutation duty correction process according to a third embodiment. Timing chart showing pump motor start control 13 is a flowchart showing the content of a forced commutation duty correction process according to a fourth embodiment. FIG. 13 is a diagram showing the relationship between the rotation speed and the drive duty ratio when the motor characteristics are ideal. Figure 10 corresponds to the actual motor characteristics Diagram explaining the procedure for correcting the forced commutation duty ratio (part 1) Diagram explaining the procedure for correcting the forced commutation duty ratio (part 2) Diagram explaining the procedure for correcting the forced commutation duty ratio (part 3) FIG. 13 is a timing chart showing a start control of a pump motor according to a fifth embodiment. Flowchart showing the forced commutation duty correction process A diagram explaining the process of correcting the forced commutation duty ratio by linear interpolation.

First Embodiment
As shown in Fig. 5, the electronic control device 1 of this embodiment performs PWM (Pulse Width Modulation) control of the drive of a three-phase brushless DC motor 2. The motor 2 is a pump motor for controlling the pressure of a urea pipe in a urea SCR system applied to vehicle exhaust gas. The electronic control device 1 includes a microcomputer 3, a control IC 4, and an inverter circuit 5. The inverter circuit 5 is configured by connecting N-channel MOSFETs 6, which are switching elements, in a three-phase bridge configuration. The three FETs 6H on the power supply side are high-side switches, and the three FETs 6L on the ground side are low-side switches.

A resistor element 7 is connected between the power supply VB and the drain of FET 6H, and the power supply VB is connected to the input terminal of the microcomputer 3 via a resistor element 8. A resistor element 9 and a capacitor 10 are connected in parallel between the input terminal and ground. The microcomputer 3 detects the voltage of the power supply VB as a value obtained by dividing the voltage by the resistor elements 8 and 9. A resistor element 11 is connected between the source of FET 6L and ground, and both ends of the resistor element 11 are connected to the input terminal of the microcomputer 3 via resistor elements 12 and 13, respectively. A capacitor 14 is connected between these input terminals. The microcomputer 3 detects the current flowing through the inverter circuit 5 by detecting the terminal voltage of the resistor element 11.

The microcomputer 3, which corresponds to the control unit, inputs voltage command values for the U, V, and W phases to the control IC 4, which generates a PWM signal for each phase by comparing these voltage command values with the voltage of the carrier signal. The PWM signal is input to the gate of each FET 6.

The output terminals of each phase of the inverter circuit 5 are connected to the other end of each phase coil 15U, 15V, 15W, which is commonly connected to one end of the motor 2, via the U-, V-, and W-phase terminals of the electronic control device 1. The U-, V-, and W-phase terminals are each connected to the input terminal of the control IC 4. In addition, a series circuit of resistance elements 16 and 17 is connected in parallel to the inverter circuit 5, and their common connection point is connected to the input terminal of the control IC 4. The control IC 4 inputs a rotor position signal of the motor 2 to the microcomputer 3 by comparing each phase terminal voltage of the motor 2 with the midpoint voltage of the power supply VB divided by the resistance elements 16 and 17. The microcomputer 3 controls the motor 2 without using a position sensor based on the input rotor position signal.

The microcomputer 3 receives a sensor signal from a temperature sensor 18 that detects the temperature of a urea water tank (not shown). The microcomputer 3 controls the supply of electricity to a heater 19 that is arranged to heat the motor 2, urea piping, urea tank, etc.

Next, the operation of this embodiment will be described. As shown in FIG. 1, when the microcomputer 3 starts to determine whether to start the urea pump motor 2 (S1), if the temperature of the urea water is below 0°C (S2; Yes), it energizes the heater 19 to perform thawing control (S3), and if it is above 0°C (No), it rotates the motor 2 to perform testing to check its operation in advance (S4). During the testing period, which corresponds to the test period, a PWM signal with a test drive duty ratio set for the test is output to rotate the motor 2.

Next, the rotation speed of the motor 2 detected during testing is compared with the abnormality judgment rotation speed (S5). The abnormality judgment rotation speed is a rotation speed that is set to determine whether the motor 2 is not rotating normally due to freezing or the like. If it is less than the abnormality judgment rotation speed (No), a judgment is made on the number of times of thawing control (S6), and if it is equal to or greater than the abnormality judgment rotation speed (Yes), a judgment is made on the abnormality judgment current (S8). In step S6, if the number of times thawing control has been performed is two or less, thawing control (S3) is performed again, and if it has been performed three times, it is determined that a motor abnormality has occurred (S7) and control is terminated.

In step S8, the motor current detected during testing is compared with the abnormality determination current value. If it is greater than the abnormality determination current value (No), the process proceeds to step S7. If it is equal to or less than the abnormality determination current value (Yes), the process corrects the duty ratio during forced commutation (S9).

Then, the motor is forcibly commutated with the corrected forced commutation duty ratio and started (S10), and the system transitions to rotation speed feedback control, where the PWM duty for driving motor 2 is continuously changed to control the target rotation speed so that the pump does not step out (S11). Then, immediately after the target rotation speed is reached, motor 2 is rotated at high speed to rapidly increase the pressure, and when the pressure starts to rise, the rotation speed is reduced, and the rotation speed is adjusted to reach the target pressure, and thereafter the rotation speed is controlled so that the pressure is maintained (S12).

As shown in FIG. 2, in the forced commutation duty correction process in step S9, the rotation speed of the motor 2 detected during testing is compared with a value obtained by multiplying the reference rotation speed corresponding to the test drive duty ratio by 1.05 (S21). If the rotation speed is equal to or greater than the 1.05-fold value (Yes), the forced commutation duty ratio is corrected to a value smaller than a predetermined reference duty ratio (S22). If the rotation speed is smaller than the 1.05-fold value (No), the reference rotation speed is compared with a value obtained by multiplying the reference rotation speed by 0.95 (S23). If the rotation speed is smaller than the 0.95-fold value, the forced commutation duty ratio is corrected to a value larger than the reference duty ratio (S24). If the rotation speed is equal to or smaller than 0.95, the forced commutation duty ratio is set to the same value as the reference duty ratio (S25).

Figure 4 is a timing chart of start-up control assuming that only the operation of motor 2 is checked during testing, and forced commutation duty correction processing is not performed. Regardless of the rotation speed detected during testing, the pump motor is forcibly commutated at a preset forced commutation duty ratio, i.e., a reference duty ratio. Therefore, in the case of pump/urea water characteristics in which the rotation speed during testing is high, over-rotation beyond the rated rotation speed of the motor occurs. Also, in the case of pump/urea water characteristics in which the rotation speed during testing is low, forced commutation does not increase the motor rotation speed to the target rotation speed, and the duty transition time becomes longer, resulting in a longer time to reach the target rotation speed.

Figure 3 is a timing chart of start-up control when forced commutation duty correction processing is performed. When testing begins, motor 2 rotates, but depending on the characteristics of motor 2 and the urea water, even with the same drive duty ratio, the rotation speed may be equal to the reference rotation speed shown by the solid line, may be higher than the reference rotation speed shown by the dashed line, or may be lower than the reference rotation speed shown by the dashed line.

The rotation speed value at this time is compared with a reference rotation speed, and if it is within ±5% of the reference rotation speed, it is deemed to be equivalent. If it is higher than the reference rotation speed, the forced commutation duty ratio is corrected to the same value as the reference duty ratio, to a value smaller than the reference duty ratio, and if it is lower than the reference rotation speed, to a value larger than the reference duty ratio.

The motor is then forcibly commutated with the corrected forced commutation duty, and by correcting the duty at the testing speed, the error from the target speed can be kept small regardless of the characteristics of the motor or urea water. After forced commutation, speed feedback control is started and a duty transition process is performed that continuously changes the drive duty to reach the target speed, and after the target speed is reached, pressure boost and maintenance control is performed. By keeping the error from the target speed with forced commutation small, the time to reach the target speed is shortened.

As described above, according to this embodiment, in the electronic control device 1, the microcomputer 3 performs testing to check the rotational operation of the pump motor 2 before starting pressure control by PWM controlling the drive of the pump motor 2 for controlling the pressure in the urea pipe. After that, a forced commutation process is performed so that the rotational speed of the motor 2 reaches the target rotational speed when performing the pressure control.

During testing, the microcomputer 3 compares the rotation speed detected when the pump motor 2 is driven by the PWM signal of the test drive duty ratio with the reference rotation speed corresponding to the PWM signal of the test drive duty ratio, and corrects the forced commutation duty ratio according to the comparison result. With this configuration, the forced commutation duty ratio can be appropriately corrected according to the rotation speed of the pump motor 2 detected during testing, so that the time required for the rotation speed of the pump motor 2 to reach the target rotation speed can be shortened as much as possible, and it is possible to control the rotation speed so that it does not exceed the rated rotation speed.

Second Embodiment
In the following, the same parts as those in the first embodiment are denoted by the same reference numerals and their explanations are omitted, and only the different parts are explained. As shown in Fig. 6, in the second embodiment, when the microcomputer 3A judges "Yes" in steps S21 and S23 in the forced commutation duty correction process, the forced commutation duty ratio is set to the reference duty ratio multiplied by the ratio between the reference rotation speed and the rotation speed detected during testing (S26).

When the driving conditions according to the characteristics of the motor 2 and the urea water are the same, there is a linear correlation between the duty ratio in PWM control and the rotation speed of the motor 2. Therefore, by performing correction as in the second embodiment, it is possible to suppress fluctuations in the rotation speed during forced commutation.

Third Embodiment
7, in the third embodiment, when the microcomputer 3B judges "Yes" in steps S21 and S23 in the forced commutation duty correction process, the forced commutation duty ratio is corrected to a value obtained by multiplying the reference duty ratio by a rotation speed correction term corresponding to the difference in the rotation speeds, and by the power supply voltage detected during testing and the power supply voltage detected during forced commutation (S27). When the microcomputer 3B judges "No" in step S23, the forced commutation duty ratio is corrected to a value obtained by multiplying the reference duty ratio by the ratio between the power supply voltage detected during testing and the power supply voltage detected during forced commutation (S28).

Figure 8 shows a timing chart of start control when performing correction according to the rotation speed and power supply voltage of motor 2 in the third embodiment. Even if the rotation speed detected during testing is the same, if the power supply voltage drops during subsequent forced commutation as shown by the dashed line, and forced commutation is performed with the same forced commutation duty ratio as when the power supply voltage is constant, the rotation speed during forced commutation will decrease. Therefore, by correcting the forced commutation duty ratio to a larger value when the power supply voltage is dropping, and correcting the forced commutation duty to a smaller value when the power supply voltage is rising, it is possible to suppress fluctuations in the rotation speed during forced commutation even when the power supply voltage fluctuates.

Fourth Embodiment
As shown in FIG. 9, in the fourth embodiment, when the microcomputer 3C judges "Yes" in steps S21 and S23 in the forced commutation duty correction process, the forced commutation duty is corrected by multiplying a value obtained by subtracting a correction constant from a reference duty ratio by the ratio between a reference rotation speed and the rotation speed detected in testing, and adding the correction constant to the result (S29).

Figures 10 and 11 are examples of the relationship between the duty ratio of the PWM signal that drives a motor and the motor rotation speed. In a motor with ideal loss-free characteristics as shown in Figure 10, the relationship between the drive duty ratio and the rotation speed is proportional, but in an actual motor as shown in Figure 11, the relationship between the drive duty ratio and the rotation speed is linear but not completely proportional. Therefore, the value of the constant term of the function obtained by linearly regressing the relationship between the drive duty ratio and the rotation speed is set as a complementary constant, and the accuracy of the correction can be improved by performing a calculation that takes the correction constant into account when correcting the forced commutation duty.

For example, as shown in FIG. 12, if the relationship between the duty ratio and the motor rotation speed is a linear function, by subtracting a value equivalent to the intercept as a correction constant, the relationship between the two becomes proportional as shown in FIG. 13. In this state, the forced commutation duty ratio is corrected from the rotation speed obtained during testing. After correction, the actual forced commutation duty ratio is determined by adding the subtracted correction constant as shown in FIG. 14.

As described above, according to the fourth embodiment, when correcting the forced commutation duty ratio, if the relationship between the duty ratio and the motor rotation speed is a linear function, a value equivalent to the intercept is subtracted as a correction constant to perform the correction, and the actual forced commutation duty ratio is determined by adding the correction constant after the correction. This makes it easy to perform the correction.

Fifth Embodiment
As shown in FIG. 15, in the fifth embodiment, the microcomputer 3D changes the test drive duty ratio from small to large, for example, in testing to obtain the rotational speeds 1 and 2. The reference rotational speeds 1 and 2 are determined according to whether the test drive duty ratio is small or large. Then, in step S31 shown in FIG. 16, it is determined whether the rotational speed 1 at the testing rotational speed is 1.05 times the reference rotational speed 1 or less, and the rotational speed 2 at the testing rotational speed is 1.05 times the reference rotational speed 2 or less. If it is determined as "Yes" here, it proceeds to step S33, and it is determined whether the rotational speed 1 at the testing rotational speed is 0.95 times the reference rotational speed 1 or more, and the rotational speed 2 at the testing rotational speed is 0.95 times the reference rotational speed 2 or more. If it is determined as "Yes" here, it proceeds to step S25.

If the determination in step S31 or S33 is "No", the forced commutation duty ratio is corrected as follows (S32): Note that the "testing duty ratio" is a test drive duty ratio.
(Forced commutation duty ratio) = (target rotation speed - testing rotation speed 2)
× {(Testing duty ratio 2) - (Testing duty ratio 1)}
/ {(Testing rotation number 2) - (Testing rotation number 1)
+ (Testing duty ratio 2)}

That is, as shown in FIG. 17, by obtaining testing rotation speeds 1 and 2 corresponding to testing duty ratios 1 and 2, the forced commutation duty ratio corresponding to the target rotation speed is calculated by linear interpolation.

As described above, according to the fifth embodiment, the microcomputer 3D changes the test drive duty ratio to multiple values during testing, detects the pump motor rotation speeds corresponding to each test drive duty ratio, and determines whether or not to correct the forced commutation duty ratio according to the values of those rotation speeds. When correcting the forced commutation duty ratio, the forced commutation duty ratio is determined based on the results of linear interpolation performed on the relationship between the multiple test drive duty ratios and the corresponding rotation speeds. This makes it possible to correct the forced commutation duty ratio with high accuracy.

Other Embodiments
The processes in steps S2 and S3 may be performed as necessary.
The correction according to the ratio of the power supply voltages in the third embodiment may be applied to the fourth and fifth embodiments.
Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, and other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and concept of the present disclosure.

In the drawing, 1 indicates an electronic control device, 2 indicates a pump motor, 3 indicates a microcomputer, and 4 indicates a control IC.

Claims (6)

A pump motor (2) for controlling the pressure of the urea pipe;
A rotation speed detection unit (10, 16, 17) for detecting the rotation speed of the pump motor;
A control unit (3, 3A to 3D) that controls the drive of the pump motor by PWM (Pulse Width Modulation),
the control unit has a test period for confirming a rotation operation of the pump motor before performing a forced commutation process of the pump motor so as to make the rotation speed reach a target rotation speed ,
an electronic control device that, during the test period, compares a rotation speed of the pump motor detected when the pump motor is driven by a PWM signal of a test drive duty ratio with a reference rotation speed corresponding to the PWM signal of the test drive duty ratio, and corrects a forced commutation duty ratio of the PWM signal that is set during the forced commutation processing in accordance with a result of the comparison. The electronic control device according to claim 1, wherein the control unit (3A) corrects the forced commutation duty ratio according to the ratio between the pump motor rotation speed detected during the test period and the reference rotation speed. 2. The electronic control device according to claim 1 , wherein the control unit (3C) corrects the forced commutation duty ratio by adding a predetermined correction constant to a result obtained by subtracting a predetermined correction constant from a reference duty ratio, multiplying the result by the ratio . The electronic control device according to any one of claims 1 to 3, wherein the control unit (3B) corrects the forced commutation duty ratio in accordance with a result of comparing the power supply voltage during the test period with the power supply voltage during the forced commutation process. The electronic control device according to claim 1, wherein the control unit (3D) changes the test drive duty ratio to a plurality of values during the test period, detects the pump motor rotation speed corresponding to each test drive duty ratio, and determines whether or not to correct the forced commutation duty ratio according to the values of the rotation speed. The electronic control device according to claim 5, wherein when correcting the forced commutation duty ratio, the control unit determines the forced commutation duty ratio based on the result of linear interpolation performed on the relationship between a plurality of test drive duty ratios and the corresponding rotation speeds.

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