JP4858006B2 - Electric power steering control device - Google Patents

Description

  The present invention relates to an electric power steering control device capable of performing offset correction of a current detection value of an electric motor that applies steering assist torque to a steering mechanism.

  As a steering assist device for an automobile, an electric power steering device that applies a steering assist torque to a steering mechanism using an electric motor is used.

  Here, a schematic configuration of the electric power steering apparatus will be described with reference to FIG. The electric power steering device includes a torque sensor 53 that detects the steering torque of the shaft 52 of the handle 51, a vehicle speed sensor 54 that detects the speed of the vehicle, and an electric motor that calculates a steering assist torque based on the detection signals of these sensors. A power steering control device (ECU) 55, an electric motor 56 that generates rotational torque based on an output signal from the ECU 55, a reduction gear 57 that transmits the generated rotational torque to the steering mechanism, and an ignition key 58 are turned on. A power source 59 for supplying current to the ECU 55, universal joints 60a and 60b for transmitting the rotational movement of the handle 51 to the wheels, a rack and pinion 61, and a tie rod 62.

  As shown in FIG. 10, the ECU 55 includes a current command value calculation unit 71 that calculates a current command value I based on signals output from the torque sensor 53 and the vehicle speed sensor 54, a current command value I, and a current detection circuit 75 described later. An adder 72 for calculating a deviation current ΔI with respect to the detected current value i detected by, a current control unit 73 for calculating a motor control signal such that the deviation current ΔI becomes zero, and a three-phase current based on the motor control signal. The driving circuit 74 is supplied to the electric motor 56, and includes a current detection circuit 75 that includes two current sensors and detects the other two current values i based on one of the three-phase currents.

  In the ECU 55 configured as described above, the assist control is realized by performing the feedback control so that the deviation current ΔI between the current command value I and the detection current i becomes zero.

  Here, if there is an offset error in the current (current detection value) detected by the two current sensors constituting the current detection circuit 75, an error also occurs in the three-phase current output from the drive circuit 74. As a result, when the electric motor 56 is a brush motor, the center feel is deteriorated due to the left / right difference in the steering assist torque or the linearity deterioration when the current is near zero. In the case of a brushless motor, torque ripple and noise are generated. Both of these adversely affect the steering feeling.

  The offset error is mainly caused by individual differences of the current sensors or temperature changes. As a method of correcting the offset error by paying attention to the temperature change, the offset error of the current detection value corresponding to each ECU temperature is measured. Some correction values are offset in the current detection values by recording and holding the required correction values in a nonvolatile memory and reading out the offset errors in the current detection values corresponding to the ECU temperature measured during operation. (For example, refer to Patent Document 1).

  In addition, there is one having a learning offset correction function that performs offset correction of the current detection value during operation based on the current detection value when the motor drive current can be regarded as substantially zero (for example, (See Patent Documents 2 and 3).

JP-A-8-163882 JP-A-8-47280 JP 2006-27294 A

  However, in Patent Document 1, it is necessary to measure all offset errors of the current detection values corresponding to each temperature for each individual at the manufacturing stage of the ECU. Further, since the relationship between the temperature and the offset correction value is recorded, there is a problem that the storage capacity is increased and the manufacturing cost is increased.

Further, in Patent Documents 2 and 3, there is no guarantee that there will be a sufficient chance that the motor drive current may be regarded as zero after activation of the assist control, so that the offset error cannot be sufficiently corrected. There is a fear. Further, there is a problem that it is not always possible to accurately cope with the correction of the offset error due to the temperature change of the ECU.
In addition, in the case of mislearning, the effect appears as it is in the offset correction value. Therefore, in order to prevent this, for example, a limiter is generally used as a safety device. As a result, the offset correction value is always limited, and even in a normal learning state, if the offset error is large, the offset correction value may be limited and correction may not be performed sufficiently. Even if there is an offset error caused by an abnormality in the current detection circuit or a function associated therewith, the current detection value is corrected only by the learning offset correction function. There is a possibility that it cannot be distinguished and judged.

  The present invention has been made in view of the above-described circumstances, and its object is to always perform offset correction with a simple configuration with high accuracy regardless of temperature changes and individual differences, as well as a current detection circuit or an accompanying circuit. An object of the present invention is to provide an electric power steering control device capable of determining an abnormality of a function to be performed.

  In order to achieve the above-described object, an electric power steering control device according to the present invention is characterized by the following (1) to (3).

(1) Current detection means for detecting a drive current of an electric motor that applies steering assist torque to the steering mechanism and outputting a current detection value; and an offset correction value for correcting an offset error included in the current detection value. In an electric power steering control device comprising an offset correction means for calculating,
Temperature detecting means for detecting the temperature of the electric power steering control device and outputting a temperature signal;
The offset correction means includes
A relationship between the temperature signal and a temperature offset correction value for correcting an offset error due to the temperature signal is recorded in the nonvolatile memory in advance, and a temperature offset correction value corresponding to the detected temperature signal is based on the relationship. Temperature offset correction means for calculating
Learning offset correction means for calculating a learning offset correction value for correcting an offset error based on the current detection value in a state where the driving current of the electric motor can be regarded as zero, and the offset correction value is
An electric power steering control device comprising the sum of the temperature offset correction value and the learning offset correction value.
(2) The temperature offset correction means includes:
At least two points, the relationship between the temperature signal and the temperature offset correction value is recorded in the nonvolatile memory in advance,
The electric power according to (1), wherein when the detected temperature signal is different from the temperature signal, a temperature offset correction value corresponding to the detected temperature is calculated by an interpolation process based on the relationship. Steering control device.
(3) The electric power steering control device includes:
further,
The electric power steering control device according to (1) or (2), further comprising abnormality determining means for determining that the current detector is abnormal when the learning offset correction value is greater than a predetermined threshold.

  According to the electric power steering control device described in (1) above, it is possible to always perform offset compensation with high accuracy with a simple configuration regardless of temperature changes and individual differences. The temperature offset correction means can cope with temperature changes and individual differences, and may be subjected to rough offset correction due to the existence of the learning offset means, so that it can have a simple configuration. In addition, even if the learning offset correction means has a small chance that the motor current can be regarded as zero, the temperature offset correction means can suppress a decrease in offset correction, and the learning offset correction value can be set to a minute value. , It is possible to suppress the influence of erroneous learning.

Further, according to the electric power steering control device described in (2) above, it is not necessary to measure all offset errors corresponding to each temperature in the manufacturing stage of the ECU, and it is avoided that the tact time is increased. can do.
Further, since it is only necessary to record offset correction values corresponding to at least two temperature signals in the nonvolatile memory, the storage cost can be reduced and the manufacturing cost can be suppressed.

  Furthermore, according to the electric power steering control device described in (3) above, since the learning offset correction value can be a minute value, when it is determined that the learning offset correction value is large, the current detection circuit Alternatively, it can be determined that an abnormality has occurred in a function associated therewith.

According to the present invention, it is possible to always perform offset correction accurately with a simple configuration regardless of temperature changes and individual differences, and it is possible to more safely offset learning by avoiding erroneous learning that leads to dangerous behavior, and The dangerous behavior can be prevented by determining the abnormality of the current detection circuit or the accompanying function.
In addition, according to the present invention, since it is not necessary to measure all offset errors corresponding to each temperature for each individual, it is possible to avoid an increase in manufacturing tact time and to further reduce the storage capacity of the memory. The manufacturing cost can be suppressed.

  Embodiments of an electric power steering control device according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic hardware configuration of an electric power steering control device (ECU) according to an embodiment of the present invention. The electric power steering apparatus according to the present embodiment is the same as the conventional structure shown in FIG. 9 except that the electric power steering apparatus includes a temperature sensor (temperature detection means) connected to the ECU. The description is omitted.

  In FIG. 1, an ECU 1 includes a bus 100, a nonvolatile memory 109, an A / D converter 110, an interface (I / F) 111, a clock generation circuit 112, a CPU 113, a ROM 114, a RAM 115, an RD converter 116, a PWM controller 117, and a motor drive. A circuit 118, a temperature sensor 119, and motor current detection circuits 120 and 121 are provided.

  The bus 100 transmits / receives data to / from the A / D converter 110, the interface 111, the clock generation circuit 112, the CPU 113, the ROM 114, the RAM 115, and the like.

  The A / D converter 110 includes a steering torque signal output from the torque sensor 4, a current detection value output from the motor current detection circuits 120 and 121, a motor rotation angle signal output from the RD converter 116, and the terminals of the motor 3. Convert voltage to digital signal.

  The interface 111 counts the vehicle speed pulse signal output from the vehicle speed sensor 2, converts it into a digital signal, and outputs it to the bus 100.

  A ROM 114 connected to the bus 100 is used as a memory for storing a control program for the motor 3, a calculation program for a PWM controller 117, which will be described later, a fail-safe program, and the like, and a RAM 115 for operating these programs. Used as work memory. The non-volatile memory 109 is constituted by, for example, an EEPROM or a flash memory, and can hold the contents stored in the memory even after the ignition key is turned off. The non-volatile memory 109 is used for recording data such as a correction table of a temperature offset correction unit described later.

  The PWM controller 117 performs pulse width modulation on the signal representing the torque of the motor 3 and converts it into duty command value pulse signals W, V, U, Wb, Vb, Ub. Here, the pulse signals W, V, and U represent positive-phase three-phase signals, and the pulse signals Wb, Vb, and Ub represent negative-phase three-phase signals.

  The motor drive circuit 118 is composed of three inverter circuits for generating currents of W, U, and V phases that drive the motor 3. Each of these inverter circuits is composed of two switching transistors cascaded between a power supply voltage and a ground potential, and positive phase duty command value pulse signals W, V, U are inputted to the gates of the upper switching transistors. The lower-stage switching transistors receive opposite-phase duty command value pulse signals Wb, Vb, Ub. As a result, the upper and lower switching transistors perform complementary operations, and alternately turn on and off to generate drive currents Iu, Iv, and Iw of the motor 3 having a desired pulse width. In order to prevent the switching transistors in the upper and lower stages from being turned on at the same time, both switching is performed before and after the on-time of W, V, U and Wb, Vb, Ub of the duty command value pulse signals of the normal phase and the reverse phase. A time (dead time) in which both transistors are turned off is provided. Thereby, it is possible to avoid a short circuit between two switching transistors connected in cascade.

  The RD converter 116 supplies an excitation current to the resolver 31 and outputs an output signal from the resolver 31 to the A / D converter 110 as a rotation angle signal.

  The motor current detection circuits 120 and 121 are configured by current-voltage conversion elements such as resistors, detect the drive currents Iu and Iw of the motor 3, and output a current detection value having a voltage corresponding to the current. The current detection value is corrected for voltage fluctuation by a power supply voltage correction circuit (not shown), amplified by the amplifier circuits 122 and 123, and then converted into a digital signal by the A / D converter 110.

  The temperature sensor 119 is constituted by, for example, a semiconductor sensor or a thermocouple sensor, and outputs a temperature signal having a voltage corresponding to the temperature of the ECU 1. The temperature sensor 119 is preferably directly attached to the amplifier circuit, but a fail-safe temperature sensor attached to a power module such as an FET may be used, for example. The detected temperature signal is converted into a digital signal by the A / D converter 110, and is used for correcting the temperature in the offset error of the current detection value.

  FIG. 2 is a block diagram showing a functional schematic configuration of the ECU 1. In the ECU 1, the control program recorded in the ROM 114 is read out, and the control program is executed by the CPU 113 to realize assist control.

  In FIG. 2, the steering torque signal output from the torque sensor 4 is A / D converted and then input to the current command value calculation unit 11. The current command value calculation unit 11 calculates a current command value based on the steering torque signal and the vehicle speed signal.

  The current command value control unit 12 controls the handle return compensation and the maximum current of the motor 3 by limiting the current command value based on the rotation speed of the motor 3. The handle return compensation performs control for restoring the handle to the neutral position. In general, in an electric power steering device, the self-aligning torque is likely to be weak due to the influence of a reduction gear or the like, and thus the handle is difficult to return to the neutral position. Therefore, the motor angular velocity is detected from the difference between the rotation angle signals of the resolver 31 or the motor angular velocity is detected from the voltage across the motor 3 and the motor drive current when the motor 3 is rotated by the action of self-aligning torque. Thus, a compensation current value for restoring the handle to the neutral position is calculated.

  The vector control unit 13 outputs a three-phase current command value I representing a current command value for each of the U, V, and W phases based on the motor angle. The current command value I is input to the adder 14, compared with a current detection value i described later, and a deviation ΔI is output to the current control unit 15.

  The motor current detection circuits 120 and 121 detect U-phase and W-phase currents supplied to the motor 3 and output a current detection value having a voltage corresponding to the current value. The current detection value is amplified by the analog amplifiers 122 and 123 in FIG. 1, converted into a digital value by the A / D converter 110, and further amplified by the digital amplifier 124.

  The current detection value amplified in this way is input to the adder 16 and the learning offset correction unit 30.

  On the other hand, the temperature signal output from the temperature sensor 119 is A / D converted and input to the temperature offset correction unit 20. The temperature offset correction unit 20 outputs a temperature offset correction value to the adder 16 with reference to a correction table provided inside based on the input temperature signal.

  Then, the learning offset correction unit 30 detects the current detection value when the operation state of the electric power steering apparatus matches a predetermined condition, for example, based on the current detection value in a state where the drive current of the electric motor 3 can be regarded as zero. Learning for correcting the current offset error is performed, and the learning offset correction value calculated by the learning is output to the adder 16 and the abnormality determination unit 40.

  The abnormality determination unit 40 determines that the motor current detection circuits 120 and 121 or functions associated therewith are abnormal when the offset correction value output from the learning offset correction unit 30 exceeds a predetermined threshold.

  The adder 16 subtracts the temperature offset correction value and the learning offset correction value from the current detection values of the U and W phases, and outputs a corrected current detection value.

  The V-phase current designating unit 17 performs correction for adjusting the gain of the V-phase current detection value output from the adder 16 to the U-phase and the W-phase, and outputs the current detection value i for each of the U, V, and W phases. To do.

  The current detection values i of the U, V, and W phases corrected in this way are compared with the three-phase current command value I in the adder 14, and the control deviation ΔI is output to the current control unit 15. The current control unit 15 performs PI control that combines proportional control and integral control based on the control deviation ΔI, calculates a pulse width-modulated three-phase duty command value, and outputs it to the drive circuit 117. The drive circuit 117 outputs a three-phase drive current to the motor 3 based on the duty command value.

  The failure determination unit 18 is for performing initial diagnosis and fail-safe processing of the electric power steering apparatus by monitoring a steering torque signal, a power supply voltage, and the like. For example, when an abnormality such as the motor 3 or the torque sensor 4 is detected in the failure determination unit 18, an instruction can be given to the current command value calculation unit 11 so as to perform a gradual reduction process of the steering assist torque.

  FIG. 3 is a block diagram showing a functional schematic configuration of the temperature offset correction unit 20. The temperature offset correction unit 20 includes a correction table 200, a correction table update unit 201, and a temperature offset calculation unit 202.

  The correction table 200 stores the relationship (combination) between the temperature signal and the temperature offset correction value. In the correction table 200, at least two combinations of the temperature signal and the temperature offset correction value may be recorded.

  The correction table update 201 unit is configured to be connectable to, for example, an operation input device (not shown), and a combination of a temperature signal and a temperature offset correction value is previously stored in the correction table 200 via the operation input device at the time of manufacture. To enter. Moreover, since the offset correction table 200 can be updated as necessary by the correction table update unit 201, the temperature offset correction value can be accurately set as appropriate regardless of a temperature change or a secular change.

  The temperature offset calculation unit 202 refers to the correction table 200 and calculates a temperature offset correction value corresponding to the input temperature signal. Here, if the input temperature signal does not match any of the temperature signals discretely recorded in the correction table 200, the combination of the temperature signal stored in advance and the temperature offset correction value, for example, the minimum Interpolation processing is performed using multiplication or the like (see FIG. 4), thereby calculating a temperature offset correction value corresponding to the input temperature signal and outputting it to the adder 16 (see FIG. 2). The interpolation processing is not limited to the least square method, and various known interpolation processing methods such as spline interpolation and Bezier curve can be employed.

  Next, the operation of the temperature offset correction unit 20 configured as described above will be described. FIG. 5 is a flowchart for explaining the operation of the temperature offset correction unit 20.

  When the temperature offset calculation unit 202 acquires the temperature signal of the ECU 1 output from the temperature sensor 119 (step S101), the temperature offset calculation unit 202 refers to the correction table 200 (step S102) and calculates a temperature offset correction value corresponding to the temperature signal. (Step S103).

  At this time, if the acquired temperature signal does not coincide with any of the temperatures discretely recorded in the correction table 200, the temperature signal acquired by the interpolation process based on the combination of the temperature signal stored in advance and the temperature offset correction value A temperature offset correction value corresponding to is calculated.

  As a result, the temperature offset correction value is output to the adder 16 (step S104).

  FIG. 6 is a block diagram showing a functional schematic configuration of the learning offset correction unit 30. The learning offset correction unit 30 includes a learning condition determination unit 301, an offset estimation unit 302, and an offset correction unit 303.

  The learning condition determination unit 301 determines whether or not to perform offset correction learning based on a plurality of learning conditions. When the learning condition determination unit 301 determines that the offset correction learning is performed, the duty ratio 50% command for fixing the current command value to the duty ratio 50% is output to the current control unit 15, and the state flag indicating learning execution Is output to the offset estimation unit 302. Note that, by fixing the duty ratio to 50%, the current to the motor 3 can be made zero, thereby making it possible to accurately detect the offset error.

  When the learning condition determination unit 301 determines that the offset correction learning is to be performed, the offset estimation unit 302 reads the current detection value when the duty ratio is 50% and estimates the offset error. The offset estimation unit 302 that has performed the estimation of the offset error in this way outputs an offset estimation value to the offset correction unit 303 together with a predetermined state flag.

  The offset correction unit 303 receives the state flag and the offset estimation value from the offset estimation unit 302, updates the previous learning offset correction value to a new learning offset estimation value, and displays the updated learning offset correction value in FIG. It outputs to the adder 16 and the abnormality determination part 40 shown. The learning offset correction value becomes a minute value due to the presence of the temperature offset correction value, and the learning offset correction unit 30 has a function of performing offset correction that cannot be corrected by the temperature offset correction unit 20.

  The abnormality determination unit 40 determines that the motor current detection circuits 120 and 121 or functions associated therewith are abnormal when the offset correction value output from the learning offset correction unit 30 exceeds a predetermined threshold. FIG. 7 is a flowchart for explaining the operation of the abnormality determination unit 40.

  First, in step S <b> 201, a learning offset correction value is input from the learning offset correction unit 30.

  Next, the input learning offset correction value is compared with a predetermined threshold value, and it is determined whether or not it is larger than the threshold value (step S202).

  If the learning offset correction value is larger than the threshold value as a result of the determination, it is determined that there is an abnormality in the current detection circuits 120 and 121 or the function associated therewith (step S203).

  Thereby, it can be determined that an abnormality has occurred in the current detection circuits 120 and 121 and the like. The threshold value is a value that can be changed from the outside, and can be flexibly changed according to the situation.

  Therefore, according to the electric power steering control device of the embodiment of the present invention, the temperature offset correction unit 20 that performs temperature correction of the offset error in the detected current value of the motor and outputs the temperature offset correction value, and learning of the offset correction And a learning offset correction unit 30 that outputs a learning offset correction value and subtracts the temperature offset correction value and the learning offset correction value from the current detection value, so that it is always accurate regardless of temperature changes and individual differences. Offset correction can be performed. Even if the correction by the temperature offset correction unit 20 is roughly performed, the fine adjustment is performed by the learning offset correction unit 30, so that the offset correction can be performed with high accuracy. Furthermore, even when the learning offset correction unit 30 has few learning opportunities for offset correction, the presence of the temperature offset correction unit 20 can suppress a decrease in offset correction.

  FIG. 8 is an example showing the effect of the electric power steering control device according to the embodiment of the present invention. FIG. 8A shows the fluctuation of the steering torque when the present invention is not applied, and FIG. Indicates a case where the present invention is applied. Thus, it can be seen that the present invention can greatly reduce the fluctuation torque during steering.

  In addition, the temperature offset correction unit 20 according to the embodiment of the present invention performs a temperature offset corresponding to the detected temperature signal by interpolation processing based on a combination of a plurality of temperature signals recorded in the nonvolatile memory and the temperature offset correction value. Since the correction value is calculated, it is not necessary to measure the characteristics of the temperature and the offset correction value many times at the manufacturing stage of the ECU, and it is possible to avoid an increase in the tact time. In addition, it is possible to reduce the storage capacity for recording the offset correction value, and to prevent an increase in cost.

  In addition, the learning offset correction unit 30 according to the embodiment of the present invention operates in a complementary manner with the temperature offset correction unit 20 so that the learning offset correction value can be set to a minute value, thereby suppressing the influence of erroneous learning. Thus, offset correction can be performed.

  Furthermore, according to the electric power steering control device of the embodiment according to the present invention, the learning offset correction value is compared with a predetermined threshold value, and when it is larger than the threshold value, the abnormal state of the current detection circuit is determined, Or abnormality of the function accompanying it can be judged.

  The description of the specific embodiments is finished above, but the aspect of the present invention is not limited to these embodiments, and modifications, improvements, and the like can be made as appropriate. For example, in the present embodiment, most of the processing is performed by software, but a part or all of the processing may be realized by hardware such as FPGA (Field Programmable Gate Array).

  The present invention can be applied to all electric power steering devices having an electric motor regardless of the type (column type, pinion type, rack type) of the electric power steering device and the type of motor (with brush, brushless, etc.). is there.

It is a block diagram which shows schematic structure of the hardware of the electric power steering control apparatus which concerns on embodiment of this invention. It is a block diagram which shows the functional schematic structure of the electric power steering control apparatus which concerns on embodiment of this invention. It is a block diagram which shows the functional schematic structure of the temperature offset correction | amendment part of the electric power steering control apparatus which concerns on embodiment of this invention. It is a figure for demonstrating the interpolation process of the temperature offset correction | amendment part in the control apparatus which concerns on embodiment of this invention. It is a flowchart for demonstrating operation | movement of the temperature offset correction | amendment part of the electric power steering control apparatus which concerns on embodiment of this invention. It is a block diagram which shows the functional schematic structure of the learning offset correction | amendment part of the electric power steering control apparatus which concerns on embodiment of this invention. It is a flowchart for demonstrating operation | movement of the abnormality determination part of the electric power steering control apparatus which concerns on embodiment of this invention. (A) is a figure which shows the fluctuation | variation of the steering torque in the conventional electric power steering control apparatus. (B) is a figure which shows the fluctuation | variation of the steering torque in the electric power steering control apparatus which concerns on embodiment of this invention. It is a figure which shows schematic structure of a general electric power steering apparatus. It is a figure which shows schematic structure of the conventional ECU.

Explanation of symbols

1 ECU
3 Electric motor 20 Temperature offset correction unit (temperature offset correction means)
30 Learning offset correction unit (learning offset correction means)
40 Abnormality determination unit 109 Non-volatile memory 119 Temperature sensor (temperature detection means)
120, 121 Current detector

Claims (3)

Current detection means for detecting a drive current of an electric motor that applies steering assist torque to the steering mechanism and outputting a current detection value, and an offset for calculating an offset correction value for correcting an offset error included in the current detection value In an electric power steering control device comprising a correction means,
Temperature detecting means for detecting the temperature of the electric power steering control device and outputting a temperature signal;
The offset correction means includes
A relationship between the temperature signal and a temperature offset correction value for correcting an offset error due to the temperature signal is recorded in the nonvolatile memory in advance, and a temperature offset correction value corresponding to the detected temperature signal is based on the relationship. Temperature offset correction means for calculating
Learning offset correction means for calculating a learning offset correction value for correcting an offset error based on the current detection value in a state where the driving current of the electric motor can be regarded as zero, and the offset correction value is
An electric power steering control device comprising the sum of the temperature offset correction value and the learning offset correction value. The temperature offset correction means includes
At least two points, the relationship between the temperature signal and the temperature offset correction value is recorded in the nonvolatile memory in advance,
The electric power according to claim 1, wherein when the detected temperature signal is different from the temperature signal, a temperature offset correction value corresponding to the detected temperature is calculated by interpolation processing based on the relationship. Steering control device. The electric power steering control device includes:
further,
3. The electric power steering control device according to claim 1, further comprising an abnormality determination unit that determines that the current detector is abnormal when the learning offset correction value is larger than a predetermined threshold value. 4.

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