JP2000089805A - Filter device and feedback controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter device for reducing a noise existing inside a detection value corresponding to the behavior of a detection object. SOLUTION: The detection value of steering torque outputted from a steering torque sensor to an ECU is made to pass through an LPF, then A/D-converted in an A/D converter inside a microcomputer and fetched to a CPU. In the CPU, the detection value is stored up to the one of two times before (S50), and when the absolute value of a difference between the value Ti of this time and the value Ti-2 of the two times before is equal to or less than a threshold Tt, the steering torque Ti fetched this time is made as the steering torque Tx for control (S30). On the other hand, at the time of exceeding the threshold Tt, the value Ti-1 of a previous time is made as the steering torque Tt for control (S40). Thus, a noise generated as a pulse caused singly is surely eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter device for performing a predetermined filtering process on a detection value according to the behavior of a control target, and a feedback control device including the filter device.

[0002]

2. Description of the Related Art As an example of a feedback control device, there is a device for controlling an electric power steering. In this electric power steering control device, the driver's steering load is reduced by controlling the electric current of the electric motor in accordance with the steering torque signal. In general, motor control is performed by adding not only a current command proportional to the steering torque signal, but also a signal obtained by differentiating the steering torque signal or a signal whose phase is advanced from the steering torque signal to the current command value, thereby obtaining a response of the motor. And hunting of the motor is prevented (Japanese Patent Application Laid-Open Nos. 62-34856 and 61-115770).
Reference).

Also, a microcomputer (microcomputer)
By performing the control calculation, the steering feeling can be further improved. For this purpose, the steering torque signal is first taken in as a digital value by the A / D converter. A derivative signal or a transfer function is used to generate a signal whose phase is advanced from the taken steering torque signal, and a signal proportional to the steering torque signal is added to obtain a current command value of the motor. By performing current control according to the current command value, steering assist is realized. In order to achieve simplification and cost reduction of the control device including this microcomputer, the processing is performed at a calculation cycle of several hundred μs to several ms using a lower function microcomputer, and various fail-safe calculations are also performed by the microcomputer. Will be done. The longer the operation cycle, the more various operations can be performed.

However, as the digitization of a circuit using a microcomputer progresses, noise around the substrate increases, and noise is likely to be superimposed on a sensor signal through a power supply system. If a strain gauge or a potentiometer is used for the sensor, vibration and sliding noise appear. These noises are often perceived as a single pulse when the sensor signal is sampled. When a command value is given to the control target in proportion to the signal or when a differential element of the signal is added to the command value, high-frequency vibration is generated in the control target. In particular, the differential of the signal on which the pulse is superimposed has an abnormally amplified amplitude only for the pulse, so that the vibration of the control target also increases. For example,
In the electric power steering, there is a disadvantage that high-frequency vibration appears as vibration of a steering wheel operated by a driver or vibration noise of a power transmission system. The vibration is particularly noticeable when the steering wheel is held.

In order to prevent such unnecessary vibration noise from being superimposed on the sensor and driving the electric motor, for example, a process of passing a steering torque signal through hysteresis has been proposed (Japanese Patent Application Laid-Open No. 63-306969). reference). Also,
In an electric system, a general method such as devising a method of obtaining a GND line, using a shield line, or interposing an EMI filter in a signal line is employed.

[0006] The electric power steering control device generates an assist torque by flowing a current to the electric motor, changes a steering torque signal after the steering mechanism operates, and detects the steering torque signal to generate a current command value. It forms a feedback control system of giving. This feedback control system
The transmission characteristic from the current to the steering torque has a resonance point and a large phase lag. Therefore, phase compensation is realized by using a differential element of the steering torque. If the control is performed using a microcomputer or the like while keeping the operation cycle long, the phase delay described above is further reduced due to the relationship between the preamplifier before sampling (for example, a low-pass filter that prevents aliasing noise during A / D conversion) and the sampling time. Increase.

That is, unless the amount of phase lead provided in the phase compensation is further increased, the system becomes unstable, and resonance vibration of the steering device itself occurs. Hysteresis has the characteristic that the phase lag increases as the amplitude decreases, so in the case of digital computation control, which wants to secure a large amount of phase advance, the noise of the pulse is reduced but the resonance oscillation is caused. Occurs. In particular, when the steering wheel is steered, the vibration appears remarkably.

[0008] As a general countermeasure against noises performed in an electric system, some elements need to be added, and in a device provided with a circuit for driving a motor by switching a large current, a large number of steps are required for the treatment. Although a measure of passing through a low-pass filter by software of a microcomputer is also conceivable, it is not advisable to reduce the amount of phase lead for reducing resonance vibration.

It is to be noted that such noise countermeasures are taken into consideration not only in the above-described feedback control device, but also in noise superimposed on the detection signal when, for example, the behavior of a throttle operated by a driver is detected. There is a need to. Therefore, an object of the present invention is to solve the above problem and provide a filter device for reducing noise included in a detection value according to the behavior of a detection target, and a feedback control device including the filter device. And

[0010]

According to a first aspect of the present invention, there is provided a filter device, comprising: a detecting unit that electrically outputs a detected value according to a behavior of a control target; The detected value is stored up to twice before. Then, the current value and the value two times before are compared, and filter processing for selecting the current value or the previous value based on the comparison result is performed. This selection is performed, for example, when the absolute value of the difference between the current value and the value two times before is equal to or smaller than a predetermined threshold, and the current value is selected. May select the previous value.

By executing such a filtering process, the following noise can be reliably removed. As shown in FIG. 8, it is assumed that noise is generated as a single pulse when sampling a detection value.
In this case, the current value, the previous value, and the value two times before are represented by Ti, Ti-1, and Ti-2, respectively. Here, a case where the filter processing according to claim 2 is applied will be considered.

First, consider the case where the current value (Ti) contains noise as shown in FIG. 8 (a).
Since the difference between the current value and the value two times before (the absolute value of (Ti−Ti−2) is larger than a predetermined threshold value (expressed as Tt), the previous value T
Select i-1. Assume that the previous value (Ti-1) contains noise as shown in FIG. 8B. In this case, the difference between the current value and the value two times before ((Ti−
Since the absolute value of Ti-2) is equal to or smaller than the threshold value Tt, the current value Ti is selected. Assume that the value (Ti-2) two times before contains noise as shown in FIG. 8C. In this case, the difference between the current value and the value two times before ((Ti−
Since the absolute value of Ti-2) is larger than the threshold value Tt, the previous value Ti
Select -1. By such a filtering process, a detection value including noise is not selected.

In this case, as an example, the case where the determination is made based on the difference between the current value and the value two times before is taken as an example, but the determination may be made based on, for example, a ratio. . The point is that it is only necessary to be able to judge whether the degree of change between the two values is sudden or not, and any comparison method may be used.

That is, as shown in FIG. 8B, when the change of the current value is small compared to the value two times before, the current value is adopted as it is, so that the influence on the input signal is affected. , And the original signal with little noise is adopted as it is. On the other hand, as shown in FIG. 8A, when a single pulse noise whose change is larger than the threshold is received, the previous value, that is, the value at the time when the single pulse noise is not received, is used. , The pulse noise is removed.
As shown in FIG. 8 (c), the value that has received the pulse noise is also used as the “value two times before” for comparison, in which case the previous value is adopted. There is no problem because the value does not receive noise.

Of course, only one-shot noise is not always generated as described above. However, depending on the system to be applied, only one-shot noise is generated, and some noise is almost one-shot noise. It is very effective when applied to such a system. In particular, this is a filtering process using the present value, the previous value, and the value two times before, and has a very simple configuration of storing three values, comparing between the two values, and selecting one of the two values. ,
Since the realization by hardware and the realization by software can be very simplified, it greatly contributes to the cost reduction of the filter device.

The detection value to be subjected to the filtering process is, for example, a detection value output by the detection means in an analog form, and is a value obtained by converting the analog detection value output therefrom into a digital value. It is possible.
However, the present invention is not limited to this. For example, a filter may be applied to the analog detection value itself, or the detection means may output a digital detection value.

Such a filter device can be applied to the following devices. That is, as set forth in claim 4, a detecting means for electrically outputting a detected value corresponding to the behavior of the control target, the filter device according to any one of claims 1 to 3, and a filter processing by the filter device. And a control means for calculating a control amount for controlling the control target based on the obtained value and controlling the drive of the control target based on the control amount.

In such a feedback control device, for example, the object to be detected by the detecting means is a steering torque of the vehicle, and the object to be controlled is an electric motor for assisting the front wheel or the rear wheel of the vehicle. It is conceivable to configure an electric power steering control device which is an electric motor in a steering mechanism to be steered.

Further, in the feedback control device including such an electric power steering control device, as set forth in claim 6, the control means controls based on a differential value of the value selected by the sample selection means. It is conceivable to calculate the amount.

If the present invention is applied to an electric power steering, it is possible to remove pulse noise without causing a phase delay of the steering torque, so that it is possible to suppress the generation of a pulse having a large amplitude as a result of performing the advance processing or the differential processing. Therefore, high frequency vibration is not caused in the electric motor and the steering mechanism. This represents a margin that the amount of phase advance can be further increased, and leads to the fact that phase compensation necessary and sufficient to prevent resonance vibration can be performed. And unpleasant vibration when the driver steers or holds the steering wheel is prevented. In addition, the use of an inexpensive microcomputer, a reduction in the number of design steps, and a reduction in the number of components are required for realizing the device.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. It is needless to say that the embodiments of the present invention are not limited to the following examples, and can take various forms as long as they belong to the technical scope of the present invention.

FIG. 1 is a vehicle configuration diagram mainly showing an electric power steering control device according to an embodiment to which the above-described invention is applied. A steering wheel (steering wheel) 11 steered by a vehicle driver is connected to a shaft (steering shaft) 12.
Is connected to the rack 13 and the pinion gear 14. When the shaft 12 rotates in response to the steering of the handle 11, the rotation angle of the shaft 12 becomes the moving amount of the rack 13. Tie rods 15 are provided at both ends of the rack 13, and the tie rods 15 steer the evening ear 16 left and right.

The shaft 12 is provided with a steering torque sensor 21 as "detecting means", and outputs a signal (steering torque signal) corresponding to the torque generated when the vehicle driver steers the steering wheel. An electric motor 23 is mounted between the steering torque sensor 21 and the rack 13 and the pinion gear 14 via a speed reducer 22. The speed reducer 22 is a well-known speed reducer including a worm and a worm wheel. If the motor 23 is energized and driven,
The force when rotating the handle 11 is reduced.

The ECU 30, which controls the energization of the electric motor 23, controls the electric motor 23 based on the steering torque signal from the steering torque sensor 21 and the vehicle speed signal from the vehicle speed sensor 50 for detecting the speed of the vehicle. To control the current flowing through the. Next, the internal configuration of the ECU 30 will be described with reference to the processing block diagram of FIG.

In order to digitally calculate the motor control based on the signal output from the steering torque sensor 21, E
Inside the CU 30, first, the LPF 31
After passing the detection signal through the microcomputer 3
After A / D conversion by the A / D converter 33 provided in the CPU 2, the data is taken into the CPU 35. Here, LPF31
Is the Nyquist frequency (1/2 of the sampling frequency) to remove aliasing noise during A / D conversion
It is configured as a filter with the following cutoff frequency:

The CPU 35 takes in a signal corresponding to the steering torque from the A / D converter 33 as a detection value in one calculation cycle (one processing cycle). Then, a predetermined filter process is performed on the detected value, and a current command value for steering torque control is calculated and output to the drive circuit 36. The processing operation executed by the CPU 35 will be described with reference to a flowchart shown in FIG. 3 and a control block diagram shown in FIG.

First, the steering torque detection value Ti converted into digital data by the A / D converter 33 is fetched (S
10). The absolute value of the difference between the detected steering torque detection value (current value) Ti and the detection value of the steering torque captured two times before (the value two times before) Ti-2 is calculated as a threshold value Tt.
And (S20). That is, it is determined whether the change from the value two times before is equal to or smaller than the threshold value Tt.

If the value is equal to or smaller than the threshold value Tt, the steering torque Ti taken in this time is used as a control steering torque Tx (S
30). If the threshold value Tt is exceeded, the steering torque detection value (previous value) Ti-1 taken immediately before is used as the control steering torque Tt (S40). After the processing in S30 or S40, the previous value Ti-1 is updated and stored in the storage location of the previous value Ti-2 twice, and the current value Ti is stored in the storage location of the previous value Ti-1 in preparation for the next calculation. Update and store.

The signal of the vehicle speed sensor 50 (see FIG. 2) is a signal whose pulse frequency generally changes according to the vehicle speed. This signal is subjected to waveform shaping by a waveform shaping section 38 in the ECU 30 and input to a port of the CPU 35. CP
U35 calculates the vehicle speed V by measuring the cycle of the vehicle speed pulse (S60 in FIG. 3).

Then, the CPU 35 processes the control steering torque Tx by a transfer function G (s) shown by the following equation to obtain a torque advance signal Tp advanced in phase with respect to the steering torque Tx (FIG. 3). S70). G (s) = (Ts + 1) / (ATs + 1) (where T and A are constants (where A <1) and s is a Laplace operator.) Further, the steering torque signal is expressed by a differential equation such as the following equation. Is used to obtain a torque differential signal Td (S80 in FIG. 3).

Yi = (1/6 ts) × (Xi + 3Xi−
(1-3Xi-2-Xi-3) (where ts represents a calculation cycle, and in represents an n-th previous value.) Then, the vehicle speed V is added to the torque advance signal Tp obtained in S70.
A gain map that changes in accordance with the above is made to be a current command value, and a value obtained by multiplying the torque differential signal Td obtained in S80 by a gain K is added to obtain a final current command value I of the electric motor 23 (S90 ). The following is a mathematical expression.

I = map (Tp, V) + K · Td Current control is performed based on the current command value I. That is, a command value is output to the drive circuit 36 (S100).
Drive circuit 36 to which a current command value from CPU 35 has been input
Then, the switching of the power transistor 37 is performed so that the actual current of the electric motor 23 follows (see FIG. 2).

As can be seen from the above description,
In the present embodiment, the microcomputer 32 in the ECU 30 corresponds to a “filter device”, and corresponds to S10 shown in FIG.
Steps S50 to S50 correspond to execution as “filter processing”.
That is, the filter device is realized by software.

According to the electric power steering control apparatus of the present embodiment having the above-described structure and operation, the detected value of the steering torque output from the steering torque sensor 21 to the ECU 30 passes through the LPF 31 and then changes to the microcomputer 3.
A / D conversion is performed by the A / D converter 33 in the
5. In this CPU 35, the detected value can be stored up to two times before (S50). If the absolute value of the difference between the current value Ti and the value Ti-2 two times before is equal to or smaller than the threshold value Tt, the detected value is stored. The taken steering torque Ti is set as the control steering torque Tx (S30), while if the threshold Tt is exceeded, the previous value Ti-1 is set as the control steering torque Tt (S40).

By executing such a filtering process, as shown in FIG. 8, when a detected value is sampled, noise generated as a single pulse can be reliably removed. That is, as shown in FIG. 8A, when the current value Ti includes noise, the absolute value of the difference (Ti−Ti−2) between the current value and the value two times before is set to the threshold value. Since it is larger than Tt, the previous value Ti-1 is selected (S40 in FIG. 3).
reference). Also, as shown in FIG. 8B, the previous value Ti-1
Contains noise, the current value Ti is selected because the absolute value of the difference ((Ti−Ti−2)) between the current value and the value two times before is equal to or smaller than the threshold value Tt (FIG. 3). S30).
Then, as shown in FIG. 8C, the value (Ti-2) two times before
Contains a noise, since the absolute value of the difference ((Ti−Ti−2)) between the current value and the value two times before is larger than the threshold value Tt, the previous value Ti−1 is selected. (See S40 in FIG. 3).

As shown in FIG. 8B, when there is little change in the current value with respect to the value two times before, the current value is adopted as it is, so that the input signal is not affected. And the original signal with little noise is used as it is (FIG. 5).
A part inside). On the other hand, as shown in FIG. 8A, when a single pulse noise whose change is larger than the threshold is received, the previous value, that is, the value at the time when the single pulse noise is not received, is used. , The pulse noise is removed (see B portion in FIG. 5). FIG.
As shown in (c), the value that has received the pulse noise is also used as the “two-time previous value” for comparison, in which case the previous value is adopted. In this case, the previous value has received the pulse noise. There is no problem because there is no value.

Of course, such a single noise does not always occur, but if, for example, a state in which the change of the current value with respect to the value two times before is larger than the threshold value continues, the previous value becomes continuous. However, the delay of the signal due to this is limited to the order of the sampling period (see the portion C in FIG. 5). Furthermore, in the electric power steering control device to which the present embodiment is applied, since it can be assumed that most of the generated noise is sporadic, such filter processing is very effective as a whole. is there.

In particular, the current value Ti and the previous value Ti-1
This is a filtering process using the value Ti-2 two times before, and 3
Storage of values (Ti, Ti-1, Ti-2) and binary values (Ti, Ti-
2) Comparison between the two, and a very simple configuration of selecting either one of the two values (Ti, Ti-1), so that the software for realizing it can be greatly simplified, and the cost can be reduced. It is valid.

Although the present embodiment is applied to the electric power steering, the pulse noise can be removed without causing the phase delay of the steering torque. As a result of the processing (see FIG. 7), generation of a pulse having a large amplitude can be suppressed. Therefore, high frequency vibration is not caused in the electric motor 23 and the steering mechanism. This represents a margin that the amount of phase advance can be further increased, and leads to the fact that phase compensation necessary and sufficient to prevent resonance vibration can be performed. Unpleasant vibrations when the driver steers or holds the steering wheel 11 are prevented. In addition, the use of an inexpensive microcomputer, a reduction in the number of design steps, and a reduction in the number of components in realizing the apparatus lead to an advantage that the entire apparatus can be manufactured at a low cost.

As described above, the present invention is not limited to such embodiments at all, and can be implemented in various forms without departing from the gist of the present invention. For example, in the above-described embodiment, the case where the determination is made based on the difference between the current value and the value two times before is taken as an example, but the determination may be made based on, for example, a ratio. The point is that it is only necessary to be able to judge whether the degree of change between the two values is sudden or not, and any comparison method may be used.

In the above-described embodiment, the detection value to be filtered is an analog detection value output from the steering torque sensor 21.
Although the digital value is converted by the / D converter 33, the present invention is not limited to this. For example, a filter value may be applied to the analog detection value itself. Further, the detection means itself may output a digital detection value.

In the above-described embodiment, the CPU 35 executes the filtering process. That is, the example in which the filter processing is executed by software has been described, but the filter processing may be realized by hardware. Even in such a case, as described above, a very simple configuration in which the current value, the previous value, and the value two times before are used, and three values are stored, a comparison between the two values, and one of the two values is selected. Therefore, even if it is realized by hardware, the simplification can be greatly simplified, and the point that greatly contributes to the cost reduction of the filter device remains unchanged.

Although the above embodiment has been described in connection with the case where the present invention is applied to an electric power steering control device, the application is not limited to this. For example, feedback control for an ABS system or a linkless throttle device mounted on a vehicle is performed. It is also applicable when performing. The present invention is not limited to such an in-vehicle device, and can be applied to an automatic control device that detects the behavior of a control target such as an automatic machine tool and controls the drive of the control target in accordance with the detection result.

Furthermore, the filter device of the present invention can be applied without assuming feedback control. For example, it can be used in processing of a detection value when detecting an operation amount of a link throttle mechanically connected to an accelerator pedal, and the like. That is, the present filter device is effective when used for the purpose of removing the influence of noise included in the detection value.

[Brief description of the drawings]

FIG. 1 is a vehicle configuration diagram mainly showing an electric power steering control device according to an embodiment to which the present invention is applied.

FIG. 2 is a processing block diagram illustrating an internal configuration of an ECU according to the embodiment.

FIG. 3 is a flowchart illustrating a process executed by a CPU in an ECU according to the embodiment.

FIG. 4 is a control block diagram of a CPU in an ECU according to the embodiment.

FIG. 5 is a graph showing that a value after filtering is noise-removed from an A / D converted value.

FIG. 6 is a graph showing that, when advance compensation is performed, a filtered value is noise-removed from an A / D converted value.

FIG. 7 is a graph showing that, when a differentiation process is performed, a value subjected to a filter process is noise-removed from an A / D conversion value.

FIG. 8 is an explanatory diagram of a filter function for removing a single pulse noise.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 ... Handle 12 ... Shaft 13 ... Rack 14 ... Pinion gear 15 ... Tie rod 16 ... Evening ear 21 ... Steering torque sensor 22 ... Reduction gear 23 ... Electric motor 30 ... CPU 31 ... LPF 32 ... Microcomputer 33 ... A / D converter 35 ... CPU 36 Drive circuit 37 Power transistor 38 Waveform shaping unit 50 Vehicle speed sensor

Continued on the front page F term (reference) 3D032 CC09 CC48 DA15 DA23 DC03 DC08 DC10 DC11 DC21 DC33 DC34 DD06 DD17 EA01 EA02 EB11 EC23 GG01 3D033 CA03 CA13 CA16 CA21 CA32 5H004 GA07 GA08 GB12 HA07 HA10 HA16 HB08 HB10 JB03 KA45 KB44 KB06 KB22 KB24 KB26 KB28 KC32 KC54 MA12 MA21

Claims (6)

[Claims] The detection value output from a detection means for electrically outputting a detection value according to the behavior of a control target is stored up to two times before, and a current value and a value two times before are stored. Performing a filter process of comparing the current value or the previous value based on the comparison result. 2. The filter device according to claim 1, wherein the present value is selected when the absolute value of the difference between the present value and the value two times before is equal to or less than a predetermined threshold value, and when the absolute value exceeds the threshold value. In the filter device, the previous value is selected. 3. The filter device according to claim 1, wherein the storage of the detected value is such that an analog detected value output from the detecting means is converted into a digital value and then stored. Characteristic filter device. 4. A detecting means for electrically outputting a detected value according to a behavior of a controlled object, a filter device according to any one of claims 1 to 3, and based on a value filtered by the filter device. A control unit for calculating a control amount for controlling the control target, and controlling the drive of the control target based on the control amount. 5. The feedback control device according to claim 3, wherein the detection target of the detection means is a steering torque of the vehicle, and the control target is a steering mechanism that assists a front wheel or a rear wheel of the vehicle with an electric motor. A feedback control device, which is configured as an electric power steering control device that is the electric motor. 6. The feedback control device according to claim 4, wherein the control means calculates the control amount based on a differential value of a value selected by the sample selection means. Control device.