JP3663880B2 - Control device for electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for an electric power steering device in which a steering assist force by a motor is applied to a steering system of an automobile or a vehicle, and more particularly, offset correction of a motor current detecting means for detecting the motor current value and at the time of failure. The present invention relates to a control device for an electric power steering apparatus provided with control means for performing processing.
[0002]
[Prior art]
An electric power steering device for energizing an automobile or vehicle steering device with an auxiliary load by the rotational force of a motor is an auxiliary load applied to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer. It comes to be energized. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist torque). The feedback control adjusts the motor applied voltage so that the difference between the current control value and the motor current detection value becomes small. The adjustment of the motor applied voltage is generally performed by a PWM (pulse width modulation) control duty. This is done by adjusting the tee ratio.
[0003]
Here, the general configuration of the electric power steering apparatus will be described with reference to FIG. 6. The shaft 2 is provided with a torque sensor 10 that detects the steering torque of the steering handle 1. A motor 20 that assists the steering force of the steering handle 1 is coupled to the shaft 2 via the clutch 21 and the reduction gear 3. Has been. Electric power is supplied from the battery 14 via the ignition key 11 to the control unit 30 that controls the power steering device. The control unit 30 detects the steering torque T detected by the torque sensor 10 and the vehicle speed V detected by the vehicle speed sensor 12. Based on the above, the steering assist command value I of the assist command is calculated, and the current supplied to the motor 20 is controlled based on the calculated steering assist command value I. The clutch 21 is ON / OFF controlled by the control unit 30 and is ON (coupled) in a normal operation state. The clutch 21 is turned off (disconnected) when the control unit 30 determines that the power steering apparatus is out of order and when the power of the battery 14 is turned off by the ignition key 11.
[0004]
The control unit 30 is mainly composed of a CPU, and FIG. 5 shows general functions executed by a program inside the CPU. For example, the phase compensator 31 does not indicate a phase compensator as independent hardware, but indicates a phase compensation function executed by the CPU. The function and operation of the control unit 30 will be described. The steering torque T detected and input by the torque sensor 10 is phase-compensated by the phase compensator 31 in order to improve the stability of the steering system, and the phase-compensated steering torque. TA is input to the steering assist command value calculator 32. The vehicle speed V detected by the vehicle speed sensor 12 is also input to the steering assist command value calculator 32. The steering assist command value calculator 32 determines a steering assist command value I that is a control target value of the current supplied to the motor 20 based on the input steering torque TA and vehicle speed V, and sends the steering assist command value calculator 32 to the steering assist command value calculator 32. Is provided with a memory 33. The memory 33 stores the steering assist command value I corresponding to the steering torque with the vehicle speed V as a parameter, and is used for the calculation of the steering assist command value I by the steering assist command value calculator 32. The steering assist command value I is input to the subtractor 30A, and is also input to the feedforward differential compensator 34 for increasing the response speed. The deviation (Ii) of the subtractor 30A is input to the proportional calculator 35. The proportional output is input to the adder 30B and to the integration calculator 36 for improving the characteristics of the feedback system. The outputs of the differential compensator 34 and the integral compensator 36 are also added to the adder 30B, and the current control value E, which is the addition result of the adder 30B, is input to the motor drive circuit 37 as a motor drive signal. The motor current value i of the motor 20 is detected by the motor current detection circuit 38, and the motor current value i is input to the subtractor 30A and fed back.
[0005]
A configuration example of the motor drive circuit 37 will be described with reference to FIG. 6. The motor drive circuit 37 is a FET gate that drives the gates of the field effect transistors (FETs) FET1 to FET4 based on the current control value E from the adder 30B. A drive circuit 371, an H bridge circuit composed of FET1 to FET4, a boost power source 372 for driving the high side of FET1 and FET2, and the like. The FET1 and FET2 are turned on / off by a PWM (pulse width modulation) signal having a duty ratio D1 determined based on the current control value E, and the magnitude of the current Ir that actually flows through the motor is controlled. FET3 and FET4 are driven by a PWM signal having a duty ratio D2 defined by a predetermined linear function equation (D2 = a · D1 + b, where a and b are constants) in a region where the duty ratio D1 is small, and a region where the duty ratio D1 is large. Then, it is turned ON / OFF according to the rotation direction of the motor determined by the sign of the PWM signal. For example, when the FET 3 is in a conductive state, the current flows through the FET 1, the motor 20, the FET 3, and the resistor R 1, and a positive current flows through the motor 20. When the FET 4 is in a conductive state, the current flows through the FET 2, the motor 20, the FET 4, and the resistor R 2, and a negative current flows through the motor 20. Therefore, the current control value E from the adder 30B is also a PWM output. The motor current detection circuit 38 detects the magnitude of the positive current based on the voltage drop across the resistor R1, and detects the magnitude of the negative current based on the voltage drop across the resistor R2. The motor current value i detected by the motor current detection circuit 38 is input to the subtracter 30A and fed back.
[0006]
Here, an operational amplifier is generally used as an element for the current detection circuit. However, since the operational amplifier outputs a signal slightly offset with respect to the input signal, the offset value is also amplified when the amplification factor is large. An error that cannot be ignored occurs with respect to the detected current value. In addition, although the motor current does not actually flow, the FET drive circuit calculates the duty ratio value corresponding to the current value including the relative error of the detected offset value, resulting in undesirable vibrations. An electric current was generated, which caused the steering feeling to deteriorate.
[0007]
On the other hand, when the motor current is detected by a circuit that detects a current by inserting a common resistor downstream of two opposing arms of the H-bridge circuit and detecting a voltage drop across the resistor. Because the offset value of the operational amplifier is included in the detected current value, in this case as well, the control near the neutral position where delicate control is required cannot provide smooth steering assistance, resulting in deterioration of the steering feeling. It was.
[0008]
[Problems to be solved by the invention]
For example, Japanese Patent Laid-Open No. 9-24846 discloses an apparatus that solves the above problems. That is, FIG. 7 shows an example of the configuration of the motor control circuit 100, the motor drive circuit 110, and the motor current detection circuit 120. The motor control circuit 100 generates a PWM signal having a duty ratio D determined based on the current control value E input from the adder 30B, and rotates to determine the rotation direction of the motor based on the sign of the current control value E. A PWM circuit 101 that outputs a direction signal and a gate drive circuit 102 that drives the gates of the FETs 1 to 4 of the H bridge circuit are configured. The motor drive circuit 110 is the above-described H-bridge circuit, and its input terminal is supplied with electric power of the voltage Vb from the battery 14 via the ignition key 11 and the relay 40, and the motor 20 is connected between the output terminals. Has been. The motor current detection circuit 120 includes a current detection resistor R connected to the motor drive circuit 110, an operational amplifier OP connected to both ends thereof, and an A / D conversion connected to the output side of the operational amplifier OP. , A current correction calculator 122 that outputs the corrected motor current value i, and a memory 123 that stores the offset value and its relative error.
[0009]
Since the motor current flows through the resistor R when the motor 20 rotates in the positive direction, the difference in voltage generated across the resistor R is detected by the operational amplifier OP and A / D converted by the A / D converter 121. Thereafter, the current is input to the current correction calculator 122 and stored in the memory 123. Also, when the motor 10 rotates in the negative direction, since the motor current flows through the resistor R, the difference in voltage generated across the resistor R is detected by the operational amplifier OP, and signal processing is performed by a peak hold circuit or the like. After being A / D converted by the / D converter 121, it is input to the current correction calculator 122 and stored in the memory 123. The current correction arithmetic unit 122 cooperates with the memory 123 to calculate the motor current value from the difference between the voltages generated at both ends of the detected resistor R and to correct the relative error of the offset value of the operational amplifier OP. The corrected motor current value i is fed back to the subtractor 30A.
[0010]
Here, the operation of the current correction arithmetic unit 122 will be described. First, the motor current value is calculated. When a difference in voltage generated at both ends of the resistor R is detected by the operational amplifier OP, the input voltage is calculated. The motor current value is obtained by dividing the difference by the resistance R value. The correction calculation of the relative error of the offset value of the operational amplifier OP is performed as follows. First, when the ignition key 11 is turned from OFF to ON, all the FETs constituting the H-bridge circuit are in an OFF state, so that no motor current actually flows. Therefore, when the motor current is detected at this time, it can be recognized as an offset value from zero which is an actual current value, and thus the detected motor current value is stored in the memory 123 as an offset value. Let At this time, the output of the operational amplifier OP is input and the relative error is stored in the memory 123 as an offset value. Then, after the steering device enters the operating state, the motor current value i stored in the memory 123 is subtracted and corrected from the motor current value sampled and detected every predetermined time to obtain the motor current value i. Calculate.
[0011]
FIG. 8 is a flowchart showing an example of the operation of the part mainly related to the current correction calculation process. First, the ignition key 11 is turned on (step P1), the detected value of the motor current is read as an offset value, and the relative error is stored in the memory 123 (step P2). Next, each unit of the control device is inspected (initial check) (step P3), and it is determined whether or not the control device is normal (step P4). If the control device is normal, normal processing is performed (step P5), and it is determined whether the ignition key 11 is OFF (step P6). If it is not OFF, the process returns to step P4 and the control operation is continued. If it is OFF, the control operation is stopped. Further, if the control device is abnormal in the determination of step P4, processing at the time of abnormality is performed (step P7), and the control operation is stopped.
[0012]
FIG. 9 is a flowchart showing details of the normal processing in step P5 in the flowchart shown in FIG. That is, the steering torque T and the vehicle speed V are read by sampling processing every predetermined time (steps P11 and P12), and a current command value I which is a control target value of the current supplied to the motor 20 is calculated (step P13). The detected value of the motor current is read (step P14), the relative error of the offset value stored in the memory 123 is subtracted from the detected motor current value, and the motor current value i is corrected and calculated (step P15). Feedback control based on current command value I and motor current value i is performed, and current control value E supplied to motor 20 is calculated (step P16). Based on the current control value E, a PWM signal for driving the FET constituting the H bridge circuit with a predetermined duty ratio and a rotation direction signal for determining the rotation direction of the motor are generated (step P17), and the gate drive circuit (Step P18).
[0013]
By the way, the motor current detection means described above detects a weak voltage generated from the current detection resistor R, amplifies the detection signal by an operational amplifier OP, and performs signal processing by, for example, a peak hold circuit to perform A / D conversion. To do. At this time, an offset voltage is generated in an amplifier, a peak hold circuit, or the like, but this offset voltage may vary depending on voltage variations and temperature in the control unit. The offset voltage affects the current detection value, and a phenomenon appears that the motor 20 is recognized as if it is not flowing, but is not detected although it is flowing. Therefore, in the above-described apparatus, when the motor is not driven in an initial state such as at the start-up, the current detection value output from the current detection means is read and stored as an offset value, and then the current control is performed. The accuracy of the current detection value is improved by subtracting the offset value from the current detection value.
[0014]
However, if the motor current detection means fails and the offset value is generated as an abnormally large value, if this abnormal offset value is corrected to the current detection value as it is, it will deviate from the original purpose and may be dangerous for the driver. Situation occurs. For example, when an abnormal offset value is generated on the negative side, a larger current flows than normal when current control is performed, and there is a danger that more assist than expected by the driver is generated. Further, when an abnormal offset value occurs on the positive side, only a smaller current flows than in the normal state, and steering becomes heavy, causing the driver to feel uneasy.
[0015]
The present invention has been made under the circumstances as described above, and an object of the present invention is to appropriately perform offset correction of the motor current detection means and processing at the time of failure, and to make the driver dangerous or uneasy. It is an object of the present invention to provide a control device for an electric power steering device that does not give the above.
[0016]
[Means for Solving the Problems]
The present invention provides the motor for applying a steering assist force to a steering mechanism based on a current control value calculated from a steering assist command value calculated based on a steering torque generated in a steering shaft and a current value of the motor. The present invention relates to a control device for an electric power steering device that is controlled by driving control of a bridge circuit, and the object of the present invention is to offset correction of the motor current detecting means for detecting the motor current value and to perform processing at the time of failure. The control means comprises a storage means and an offset value abnormality detection means, and the storage means stores a first offset value at the initial time and a second offset value at the time of operation of the motor current detection means. The offset value abnormality detecting means turns off the relay connected to the drive circuit power supply at the time of startup, The second offset value output from the motor current detection means is read with all the drive elements of the drive circuit turned off, the first offset value and the second offset value are compared, and the difference is not more than a predetermined value. In this case, the second offset value is used as a correction value for the motor current value. If the difference is greater than or equal to the predetermined value, it is determined that the motor current detecting means is out of order, and the motor output and the relay off state are ignited. This is achieved by keeping the key until it is turned off.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
In order to solve the conventional problem as described above, in the present invention, as shown in FIG. 1 corresponding to FIG. 7, a storage means 124 made of RAM and an EEPROM (Electrically Erasable Programmable ROM) are provided in the motor current detection means 120. And an offset value abnormality detection means 130 for outputting a current detection means abnormality detection signal AS based on the outputs of the storage means 124 and 125.
[0018]
In such a configuration, the operation of storing the offset value at the time of shipment adjustment will be described with reference to the flowchart of FIG. The control unit is set to an adjustment mode for shipping adjustment or the like, the relay 40 is turned off, and the offset value of the motor current detection means is stored in the storage means 125 with all the FET1 to FET4 turned off, but the ignition key 11 is turned on. (Step S1), the control unit is switched to the adjustment mode (Step S2). Thereafter, the relay 40 is turned off, and all the FETs are turned off (step S3) so that no current flows through the motor 20. Then, the current detection value output from the resistance R and the motor current detection means of the operational amplifier OP is read a plurality of times via the A / D converter 121 and stored in the storage means 124 of the RAM (step S5). Reading is repeated until it becomes the same as the stored value (step S6), and when it is the same, the value is stored as an offset value in the storage means 125 of the EEPROM (step S7), and the ignition key 11 is turned OFF (step S8). And ship the control unit.
[0019]
On the other hand, when operating after being installed in the vehicle, as shown in the flowchart of FIG. 3, first, the ignition key 11 is turned on in the initial state at the time of starting (step S10), and then the relay 40 is turned off and all FETs 1 are turned on. The current detection value output from the current detection means of the motor resistance R and the operational amplifier OP is passed through the A / D converter 121 while the FET 4 remains OFF (step S11) and the motor 20 does not flow. Are read and stored in the storage means 124 (step S12). Next, the offset value stored in advance in the storage means 125 is read (step S13), and the difference from the current detection value is compared (step S14). It is determined whether or not the difference is equal to or less than a specified value (step S15). If the difference is equal to or less than the specified value, the current detection value is determined to be normal and stored as an offset value in the RAM storage means 124 that can be temporarily read and written. (Step S16). Thereafter, in the normal operation state, the stored offset value is subtracted from the detected current value detected by the motor current detecting means, and the value obtained by correcting the offset of the current detecting means is set as the detected current value i. Used for. Next, in the initial state at the time of start-up, the read current detection value is compared with the offset value. If the difference is equal to or greater than the specified value (step S15), the current detection value is read and compared with the offset value multiple times. (Step S17). If the difference between the offset value and the current detection value is greater than or equal to the predetermined value even after the predetermined number of comparisons, it is determined that the motor current detection means has failed (step S18), the subsequent sequence is stopped, and the motor output and the relay 40 are Is maintained until the ignition key 11 is turned off.
[0020]
【The invention's effect】
As described above, according to the control device for the electric power steering apparatus of the present invention, the control means for performing the offset correction of the motor current detection means for detecting the motor current value and the action at the time of failure is provided, and the magnitude of the offset value is determined. In addition, since the abnormal operation is determined a plurality of times, the offset correction of the motor current detection means and the measure at the time of failure can be reliably performed without making the driver dangerous.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an example of a partial configuration of a control unit in an electric power steering apparatus according to the present invention.
FIG. 2 is a flowchart showing an example of an offset value storing operation at the time of shipment adjustment according to the present invention.
FIG. 3 is a flowchart showing an example of an operation for storing an offset value during normal control according to the present invention.
FIG. 4 is a block diagram showing an example of an electric power steering device.
FIG. 5 is a block diagram showing a general internal configuration of a control unit.
FIG. 6 is a connection diagram illustrating an example of a motor drive circuit.
FIG. 7 is a block diagram illustrating an example of a conventional apparatus.
FIG. 8 is a flowchart showing an operation example of a conventional apparatus.
FIG. 9 is a flowchart showing an operation example of a conventional apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Steering handle 5 Pinion rack mechanism 10 Torque sensor 12 Vehicle speed sensor 20 Motor 30 Control unit 31 Phase compensator 37 Motor drive circuit 38 Motor current detection circuit 100 Motor control circuit 110 Motor drive circuit 120 Motor current detection circuits 124 and 125 Storage means 130 Offset value abnormality detection means

Claims (1)

The motor for applying a steering assist force to the steering mechanism based on a current control value calculated from a steering assist command value calculated based on a steering torque generated in the steering shaft and a motor current value of the motor is provided for the H bridge circuit. In the control device of the electric power steering apparatus that is controlled by the drive circuit, the control means for performing offset correction of the motor current detection means for detecting the motor current value and processing at the time of failure is provided. The storage means and the offset value abnormality detection means are configured to store a first offset value at the initial time and a second offset value at the time of operation of the motor current detection means, and the offset value abnormality detection means is , Turn off the relay connected between the drive circuit power supply and all the drive elements of the drive circuit The second offset value output from the motor current detecting means is read while the second offset value is read, the first offset value and the second offset value are compared, and if the difference is equal to or less than a predetermined value, the second offset value Is a correction value for the motor current value, and if the difference is greater than or equal to the predetermined value, it is determined that the motor current detecting means is out of order, and the motor output and the relay off state are maintained until the ignition key is turned off A control device for an electric power steering device.

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