JP3214061B2 - Motor drive device for electric power steering device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor driving device for an electric power steering device, and more particularly to a motor driving device for a power steering device for assisting a steering force by a rotation output of a motor.

[0002]

2. Description of the Related Art In recent years, electric power steering devices using motors have been used in place of hydraulic power steering devices, and motors are increasing in the future because of their advantages such as small size and light weight as actuators.

FIG. 17 is a structural view showing an example of a mechanical system of a conventional electric power steering apparatus. In this figure, the turning force of a steering wheel 1 is transmitted to a steering gear 2 including a pinion gear via a handle shaft. At the same time, the power is transmitted to the rack shaft 3 by the pinion gear, and the wheels 4 are turned through a knuckle arm or the like. The torque of a steering assist (auxiliary) motor (DC motor) 6 controlled and driven by the control device 5 is transmitted to the rack shaft 3 by meshing the steering gear 7 including a pinion gear with the rack shaft 3, and the steering wheel 1 This will assist steering.

[0004] The rotating shaft of the handle 1 and the motor 6 is the gear 2,
7 and the rack shaft 3. Steering torque (return torque) by the steering torque sensor 11
Is detected, and the vehicle speed is detected by the vehicle speed sensor 12.
Then, the control device 5 controls the motor 6 based on the detected torque, vehicle speed, and the like. The operating power is supplied to the control device 5 and the motor 6 from a battery 8 mounted on the vehicle.

As shown in FIG. 18, a control device 5 includes a motor current detection circuit 21, a motor drive circuit 22 for driving the motor 6, and a CPU for controlling the overall control of the motor 6.
23 (for example, a microprocessor), a memory 24, and an interface circuit (not shown) between the computer and the input / output device.

In FIG. 18, a steering torque detected by a steering torque sensor 11 is converted into a digital signal by an A / D conversion circuit 25 and then taken into a CPU 23. The vehicle speed detected by the vehicle speed sensor 12 is counted by the counter 26, and a count value representing the vehicle speed is taken into the CPU 23. The CPU 23 generates an assist command based on the input steering torque and vehicle speed, outputs a control signal based on the assist command to the motor drive circuit 22, and the motor 6 is driven by the motor drive circuit 22. As a result, the assist torque value output from the motor driving circuit 22 (or the electric current value), as shown in FIG. 19, a value determined by the detected torque V _T and the detected vehicle speed V _S.

[0007] Figure 19, in accordance with the steering torque V _T, which substantially proportional to the motor current (assist torque is generated) flows against the steering torque V _T of a range, when it exceeds the above range, as constant motor current flows (the assist torque is generated), also according to the vehicle speed V _S, the motor current (assist when when the vehicle speed V _S is high to reduce the motor current (assist torque), the vehicle speed V _S is low This indicates that an assist command for controlling the motor 6 is generated so as to increase the torque).

Returning to FIG. 18, the motor current is detected by the motor current detection circuit 21 and is converted into a digital signal by the A / D conversion circuit 27 before being taken into the CPU 23. The memory 24 stores programs and data necessary for the processing of the CPU 23.

By the way, in a motor drive device of an electric power steering device, a motor line ground fault is detected.
If there is no means to power off the motor drive current,
When a ground fault of the motor wire occurs, it will lead to element destruction and motor failure. Therefore, conventionally, as shown in FIG. 20, a shunt resistor for detecting a motor current is provided on the upper side of a motor drive circuit composed of an H-bridge, that is, on a power supply side, to detect a motor line ground fault.

[0010]

By the way, in the above-mentioned motor drive device of the conventional electric power steering device, a shunt resistor is provided on the upper side of the motor drive circuit, that is, on the power supply side to detect the ground fault of the motor line. Although such a method has the advantage that the motor line ground fault can be detected even in an overcurrent failure mode such as a load short circuit, a differential amplifier is required in the motor current detection circuit. However, there is a problem that the cost becomes high because the offset adjustment with high accuracy is required. By providing the shunt resistor on the lower side of the motor drive circuit, that is, on the ground side, the price of the motor current detection circuit can be kept low.However, detection of the motor line ground fault becomes impossible in overcurrent failure mode such as load short circuit. Therefore, in the worst case, a situation may occur in which the power MOSFET that controls the motor current is destroyed.

Further, in the motor drive device of the conventional electric power steering device, no measure is taken against an initial ground fault at the time of engine start. There is a possibility that the power MOSFET that controls the current may be destroyed.

Further, in the conventional motor drive device of the electric power steering device, when an erroneous detection of a motor line ground fault due to a pulse-like power supply voltage fluctuation (decrease) at the time of engine start or the like is performed. There was also a problem that there was a possibility of going down.

Therefore, the present invention provides a low-cost, high-precision detection of an initial ground fault at the start of the engine, a motor line ground fault even in an overcurrent failure mode such as a load short circuit, and a pulse-like power supply voltage. An object of the present invention is to provide a motor drive device of an electric power steering device that can prevent a system down by eliminating erroneous detection of a motor line ground fault due to fluctuation.

[0014]

According to a first aspect of the present invention, there is provided a motor driving apparatus for an electric power steering apparatus, comprising: A current command value for assisting the motor is created, four switching elements connected to the motor in an H-bridge type, a deviation between the assist current command value and the detected motor current, and an assist current command value. A motor driving device for an electric power steering device including a current driving unit that controls the switching element by a pulse width modulation method according to the polarity of a motor terminal voltage detection unit that detects a voltage across the motor; Comparing the sum of the voltages across the motor and a predetermined value, and when the sum of the voltages across the motor is below the predetermined value, Provided a ground fault tolerance means for allowing the detection of fault, the current driving means, when the detection of the motor of the ground fault in the control of the switching element is allowed,
It is characterized in that all of the switching elements are turned off.

According to a second aspect of the present invention, there is provided a motor driving device for an electric power steering device, which generates a current command value for assisting a motor of the electric power steering device based on a detected steering torque, a detected vehicle speed, and the like. , Connected to the motor in an H-bridge type
An electric motor comprising: a plurality of switching elements; and a current driving means for controlling the switching elements by a pulse width modulation method in accordance with a deviation between the assist current command value and the detected motor current and a polarity of the assist current command value. In a motor drive device of a power steering apparatus, a cold terminal voltage detecting means for detecting a cold terminal voltage of the motor, a duty ratio of a pulse for turning on / off the switching element, the motor current and the cold terminal voltage Ground fault permitting means for permitting detection of a ground fault when at least is within a predetermined detection range, wherein the current driving means is configured to permit detection of a ground fault of the motor during control of the switching element. , Wherein all of the switching elements are turned off.

According to a third aspect of the present invention, there is provided a motor driving device for an electric power steering device, which generates a current command value for assisting a motor of the electric power steering device based on a detected steering torque, a detected vehicle speed, and the like. , Connected to the motor in an H-bridge type
An electric motor comprising: a plurality of switching elements; and a current driving means for controlling the switching elements by a pulse width modulation method in accordance with a deviation between the assist current command value and the detected motor current and a polarity of the assist current command value. In the motor driving device of the type power steering device, an initial ground fault detecting means for detecting a ground fault of the motor after turning off all of the switching elements is provided, and the current driving means includes a switching element after detecting the initial ground fault. Are controlled by a pulse width modulation method.

According to a fourth aspect of the present invention, there is provided a motor driving device for an electric power steering device, which generates a current command value for assisting a motor of the electric power steering device based on a detected steering torque, a detected vehicle speed, and the like. , Connected to the motor in an H-bridge type
An electric motor comprising: a plurality of switching elements; and a current driving means for controlling the switching elements by a pulse width modulation method in accordance with a deviation between the assist current command value and the detected motor current and a polarity of the assist current command value. An initial ground fault detecting means for detecting a ground fault of the motor after turning off all of the switching elements, and controlling the motor during control of the switching elements after detecting the initial ground fault. When a ground fault is detected, after all of the switching elements are turned off, ground fault determining means for determining whether or not a ground fault of the motor has been erroneously determined is provided. The switching element is controlled by a pulse modulation method after detecting a ground fault and after erroneously determining a ground fault of the motor.

[0018]

According to the first aspect of the invention, when the sum of the voltages at both ends of the steering assist motor becomes equal to or less than a predetermined value, detection of a ground fault in the motor line is permitted. Thereby, all of the switching elements are turned off. Therefore, even if the shunt resistor for detecting the motor current is provided below the drive circuit constituted by the H bridge, that is, on the ground side, a motor line ground fault in an overcurrent fail mode such as a load short circuit is detected, and Destruction is prevented. Further, since the shunt resistor is provided below the drive circuit composed of the H bridge, the motor current detection circuit can be made inexpensive, and the overall price can be kept low.

According to the second aspect of the present invention, when the duty ratio of the pulse for turning on / off the switching element, the motor current, and the cold-side terminal voltage are at least within a predetermined detection range, the motor line cold-side ground fault may occur. Detection is allowed. Thereby, all of the switching elements are turned off. Therefore, the ground fault on the cold side of the motor wire is reliably detected, and the destruction of the power element is prevented.

According to the third aspect of the present invention, after all of the switching elements are once turned off, an initial ground fault of the steering assist motor is detected, and after the detection of the initial ground fault, the switching elements are controlled by a pulse modulation method. The motor assist is started. Therefore, the initial ground fault at the time of starting the engine is accurately detected, and the switching element is prevented from being destroyed.

Further, according to the present invention, when a ground fault of the steering assist motor is detected during the control of the switching element after the detection of the initial ground fault, all of the switching elements are once turned off, and then the motor is turned off. It is determined whether or not a ground fault has been erroneously determined. Therefore, erroneous detection of a motor line ground fault due to a pulse-like power supply voltage fluctuation is eliminated, and system down is effectively prevented.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIGS. 1 to 6 are views showing a first embodiment of a motor drive device of an electric power steering device according to the present invention. In the description of the present embodiment, the same components as those of the conventional example are denoted by the same reference numerals, and redundant description will be omitted. FIG. 1 is a block diagram showing a hardware configuration of the present apparatus.

In this figure, reference numeral 30 denotes a CPU in the control device. The CPU 30 receives signals from the steering torque sensor 11, the vehicle speed sensor 12 and the like and controls the overall control of the motor 6 as in the prior art. Specifically, a current command value for assisting the motor 6 is created based on the detected steering torque, the detected vehicle speed, and the like. The current command value is input to the drive control circuit 31. The drive control circuit 31 determines four values according to the deviation between the assist current command value and the motor current detected by the motor current detection circuit 32 and the polarity of the assist current command value. Switching elements SW1 to SW4
Is calculated by a pulse width modulation method (PWM method), and the control value is output to the gate drive circuit 33.

The CPU 30 has a read-only memory (for example, a ROM) in which a command program for performing the above operation is written.
And a work memory (eg, RAM) used in the operation, and A for converting an analog signal to a digital signal.
A / D converter and the like are built in. The gate drive circuit 3
3 receives the battery voltage boosted by the boost power supply circuit 34 based on the control value from the drive control circuit 31,
The gates of the four switching elements SW1 to SW4 are driven by the M method.

The H-bridge circuit 35 supplies the motor 6 with H
Four switching elements SW1 connected in a bridge type
SW4 and four diodes D1 to D4, and controls the switching of the current of the motor 6. The H-bridge circuit 35 is connected to the battery 8 via a power relay 36.

The H-bridge circuit 35 is driven by pulse width modulation as described above. For example, in FIG. 2, in the case of normal rotation, the switching elements SW1 and SW4 are driven by pulse width modulation, and the current when the PWM is on is changed from the battery 8 → the switching element SW1 → the motor 6 → the switching element SW4 →
The shunt resistor flows through the path of Rs → GND, and the current when the PWM is off is the motor 6 → the diode D3 → the battery 8
The current flows through the path of GND, shunt resistor Rs, diode D2, and motor 6. In this case, the terminal voltage M1 is on the hot side, and the terminal voltage M2 is on the cold side.

The drive characteristics of the H-bridge circuit 35 are as shown in FIG. 3. In the case of normal rotation, the load current sharply increases when the PWM duty ratio exceeds 50%, and in the case of reverse rotation, the PWM current increases. When the duty ratio exceeds 50%, the load current sharply decreases. In this case, when the PWM duty ratio is 0%, the entire gate-off mode is set, and when the PWM duty ratio is 50% or less, the load current intermittent mode (in this mode, the load current is set to “0” once within the PWM carrier cycle). ). When the PWM duty ratio is 5
When it is 0% or more, the load current continuous mode is set.

In this case, the waveforms of the terminal voltages M1 and M2 in the all-gate off mode are as shown in FIG.
The waveform of No. 2 is as shown in FIG. The waveforms of the terminal voltages M1 and M2 in the load current intermittent mode are shown in FIG.
The result is as shown in FIG.

Returning to FIG. 1, the motor current detection circuit 32 detects the motor current from the voltage across the shunt resistor RS.
This detection result is input to the overcurrent detection circuit 37, which detects the motor overcurrent
Input to U30. Further, the ground fault of the motor 6 is detected by the motor line ground fault detection circuit 38, and the detection result of the ground fault is similarly input to the CPU 30. Overcurrent detection circuit 3
7 and the output of the motor line ground fault detection circuit 38 are OR gate 39
When the overcurrent of the motor or the ground fault of the motor 6 is detected, the driving of the motor 6 is prohibited.

FIG. 5 is a diagram showing an example of the motor line ground fault detection circuit 38. In this figure, the terminal voltage M of the motor 6
1 and M2 are expressed by dividing the battery voltage BAT into に よ っ て by two resistors R0 equivalently equivalent to the four switching elements SW1 to SW4 of the H-bridge circuit 35, and this divided voltage is further divided. The voltage is divided into R1 / (R1 + R2) by the resistors R1 and R2, and is applied as a detection voltage A to one terminal of the comparator 50 through the resistor R3. This detection voltage A is independent of the mode of the load current,
Also, it is not affected by the induced voltage generated by the rotation of the motor 6, and is always (battery voltage BAT) × [R1 /
(R1 + R2)], which is a constant value. Note that the resistors R1 and R2 form a voltage dividing circuit 51, and the resistor R3
The capacitor C1 forms an addition circuit 52.

On the other hand, a reference voltage B is applied to the + terminal of the comparator 50, and the reference voltage B is connected to the resistors R4 to R8.
And a voltage of 5 V divided by a capacitor C2. These resistors R4 to R8, capacitor C2 and comparator 50 constitute a comparator circuit 53 with hysteresis.

During normal operation, the detection voltage A is sufficiently higher than the reference voltage B. However, when a motor line ground fault occurs, the detection voltage A becomes smaller than the reference voltage B, and the output of the comparator 50 is inverted. The output is the CPU via the inverter 54
A 30 interrupt port INT1 is supplied as a negative logic interrupt signal indicating a motor line ground fault. As a result, the power relay 36 is immediately turned off to stop the motor drive output. In this case, by taking the sum of the voltages across the motor 6, even if the shunt resistor Rs is provided on the ground side of the H-bridge circuit 35, a motor line ground fault in an overcurrent fail mode such as a load short circuit can be detected.

The CPU 30, the drive control circuit 31, the motor current detection circuit 32, the gate drive circuit 33, the boost power supply circuit 34 and the overcurrent detection circuit 37 constitute a current drive means 60 as a whole. In addition, the motor line ground fault detection circuit 38
Has a function as a motor terminal voltage detecting means and a ground fault permitting means.

Next, the operation of the power steering control of the first embodiment will be described. FIG. 6 is a main program showing the processing of the power steering control. In this figure, when the engine is started, it is first determined in step S1 whether or not the ignition voltage is ON (specified value). If NO, the process waits in this step, and YES
Then, in step S2, it is determined whether or not there is welding to the power relay 36 that has turned the motor 6 on / off. When the fail safe is NG (when the power relay 36 is welded), the process proceeds to step S6, where the power relay 36 is turned off, and the routine ends. As a result, when the power relay 36 is welded, the power supply is immediately turned off, and the steering system is not assisted, so that the element destruction of the motor driving device and the motor failure are avoided.

On the other hand, in step S2, fail safe
If K (the power relay 36 is not welded), the process proceeds to step S3 to turn on the power relay 36, and enters the assist state in step S4. Next, in step S5, it is determined whether there is a motor line ground fault. This determination is performed, for example, by interrupting the CPU 23. Specifically, the CPU 23 compares the sum of the voltages across the motor 6 (detected voltage A) with a predetermined value (reference voltage B). When the detected voltage A is equal to or lower than the reference voltage B, the CPU 23 detects the falling edge of the comparator output. Interrupt When there is no interrupt, there is no ground fault in the motor line. Step S
If there is a motor line ground fault from the determination result of step 7, the process proceeds to step S6.
To stop the assist process, and if not, go to step S4.
And the assist process is continued. Therefore, when a motor line ground fault occurs, the CPU 23 is interrupted at the falling edge of the comparator output, and the power relay 36 is immediately turned off.

As described above, in the algorithm of the motor line ground fault detection processing in the present embodiment, the sum of the voltages across the motor 6 (detection voltage A) and the predetermined value (reference voltage B) are compared, and the detection voltage A is If the voltage is below the reference voltage B, it is determined that a motor line ground fault has occurred. As a result, the power relay 36 is immediately turned off, the motor drive output is stopped, and all the gates of the four switching elements SW1 to SW4 are turned off.

Next, FIGS. 7 to 13 show a second embodiment of the motor driving device of the electric power steering device according to the present invention. The hardware configuration of this embodiment is the same as that of the first embodiment except for the motor line ground fault detection circuit 70, and a description thereof will be omitted. The CPU 30 and the motor line ground fault detecting circuit 70 constitute a cold side terminal voltage detecting means 80. Also, the CPU 30
Has a function as a ground fault permitting means. In the present embodiment, the detection of the ground fault on the cold side of the motor wire is enabled.

FIG. 7 is a diagram showing an example of the motor line ground fault detection circuit 70. As shown in this figure, the motor line ground fault detecting circuit 70 is composed of the adding circuit 52 of the motor line ground fault detecting circuit 38 and the comparator circuit 53 with hysteresis.
And the motor terminal voltages M1 and M2 are
The A / D 2 and 3 ports 30 are configured to be input.

The CPU 30 detects the motor line cold side ground fault by inputting the motor terminal voltages M1 and M2 output from the motor line ground fault detection circuit 70. FIG. 8 is a waveform diagram showing the basics of cold-side ground fault detection. As shown in FIG. 8, when the cold-side terminal voltage falls below a predetermined detection threshold, a ground fault is detected. The detection threshold is specifically set to a value of about 3% of the battery voltage BAT. For example, if the battery voltage BAT is 12V, the voltage is set to about 0.4V.

If a ground fault is detected when the motor line cold-side terminal voltage falls below the detection threshold, the ground fault is detected, for example, even for a pulse-like power supply voltage fluctuation. Therefore, the following two conditions are added to prevent such erroneous detection.
Only when these conditions are satisfied at the same time, the ground fault detection on the cold side of the motor line is performed.

The PWM duty ratio is equal to or less than a predetermined value. The reason is that as the PWM duty ratio increases, the cold-side terminal voltage decreases. For example, if the predetermined value is set to about 94% and the check range is limited to this value or less, it is possible to prevent the cold-side terminal voltage from dropping to the detection threshold. That is, when the predetermined value is set to 94%, as shown in FIG.
When it is lowered to 8V × (1−0.94) = 0.48
V, which does not drop to the detection threshold (0.4 V). In the case where the detection threshold can be varied according to the battery voltage BAT, the limit value may be varied.

The motor current is equal to or higher than a predetermined value. The reason for this is that when the motor current is small, the current intermittent mode is set as described above, so that the generation of the induced voltage may lower the cold-side terminal voltage. For example, by setting the motor current to about 10% of the rated current and limiting the check range to this value or more, it is possible to prevent the cold-side terminal voltage from dropping to the detection threshold. When the rated current is 30 A, the predetermined value is 3 A.

Here, for reference, FIG. 10 shows a cold-side terminal voltage waveform and a motor current waveform in the current intermittent mode. FIG. 11 shows a cold-side terminal voltage waveform and a motor current waveform in the current continuous mode. Note that the missing portion in the cold-side terminal voltage waveform in the current interrupt mode changes depending on the value of the resistor R0.

Next, the motor line cold side ground fault detection processing according to the above configuration will be described with reference to the program shown in FIG. This program is executed at predetermined time intervals by interruption. Further, as shown in FIG. 13, various storage areas are secured in the work memory built in the CPU 30, and the label MTCURR among them is provided.
In the area indicated by, the motor current detection value is indicated by the label MTV.
A motor terminal voltage detection value is written in each area indicated by OLTR and MTVOLTL, and a check counter value is written in an area indicated by label CFLSHO.

In FIG. 12, after performing initial processing such as clearing of the contents of the work memory in step S10, the flow advances to step S11 to determine whether or not the PWM duty ratio is "0". Proceeds to step S12.
In step S12, it is determined whether or not the PWM duty ratio is equal to or less than 94%. If not, the value of the check counter is set to "0" in step S13, and the process returns to step S11.

On the other hand, if it is determined in step S12 that the PWM duty ratio is equal to or less than 94%, the flow advances to step S14 to determine whether the motor current is equal to or more than 3A.
If it is 3A or less, the process proceeds to step S13. If it is 3 A or more, the process proceeds to step S15, and the cold-side terminal voltage of the motor 6 is selected from the bridge polarity of the H-bridge circuit 35. In this case, the bridge polarity of the H bridge circuit 35 is
It is determined when the CPU 30 generates the assist current command value to be supplied to the drive control circuit 31, and selects the cold-side terminal voltage based on the determined value. For example, in the case shown in FIG. 2, the terminal voltage M2 is the cold-side terminal voltage.
Then, the terminal voltage M2 is read from the area of the label MTVOLTR.

After reading the cold-side terminal voltage, it is determined in step S16 whether the voltage is 0.4 V or less. If not less than 0.4 V, the process proceeds to step S13,
If it is 0.4 V or less, the process proceeds to step S17. In step S17, the value of the check counter is incremented (1 is added), and thereafter, it is determined in step S18 whether or not the value of the check counter is "2". In this case, if "2", the fail process is performed in step S19, and if "2", the process returns to step S11.

In step S19, the power relay 36 is immediately turned off to stop the motor drive output as a fail process. As a result, the power supply to the motor 6 is turned off, the steering system is not assisted, and the element destruction of the motor drive device and the motor failure due to the cold-side terminal ground fault are avoided.

As described above, according to the algorithm for detecting the ground fault on the cold side of the motor line in the present embodiment, when the PWM duty ratio is 94% or less, and the motor current is 3 A or more,
When the condition that the cold-side terminal voltage is 0.4 V or less is met, it is determined that the motor line cold-side ground fault has occurred. As a result, the power relay 36 is immediately turned off, the motor drive output is stopped, and the four switching elements S
All the gates of W1 to SW4 are turned off.

Next, FIG. 14 is a main program showing a power steering control process of a third embodiment of the motor drive device of the electric power steering device according to the present invention. The hardware configuration of this embodiment is the same as that of the first embodiment, and a description thereof will be omitted. In the present embodiment, the detection of the initial ground fault of the motor wire is enabled, and the CPU 30 has a function as an initial ground fault detecting means. In the description of this program, steps that perform the same processing as the program of FIG. 20 shown as a conventional example are assigned the same step numbers, and duplicate explanations are omitted.

In FIG. 14, when the engine starts,
After performing the same processing as in the related art in steps S1 to S3, in step S30, all the gates of the four switching elements SW1 to SW4 of the H-bridge circuit 35 are turned off. Thereby, the four switching elements SW1 to S
No current flows through W4. Then, step S
At 31, the level of the ground fault detection interrupt signal is read (read), and when it is at the "H" level, it is determined that a ground fault has not occurred, and assistance is started at step S13.

On the other hand, at the time of "L" level, that is, CP
When a negative logic interrupt signal indicating an initial ground fault of the motor line is supplied to the interrupt port INT1 of U30, the process proceeds to step S6 to immediately turn off the power relay 36 and stop the motor drive output. As a result, the power supply to the motor 6 is turned off, the steering system is not assisted, and the element destruction of the motor drive device and the motor failure due to the initial ground fault are avoided.

As described above, in this embodiment, the ignition switch is turned on, the battery voltage is supplied, and the power relay 36 is turned on by the algorithm of the initial ground fault detection processing of the motor line.
Immediately after turning on, four switching elements SW1
All the gates of SW4 are turned off, and the ground fault of the motor line is detected in a state where no current flows through the four switching elements SW1 to SW4. Therefore, even if an initial ground fault in which the motor wire is grounded from the beginning of power-on, the initial ground fault of the motor wire can be accurately detected regardless of the switching elements SW1 to SW4. As a result, switching elements SW1 to S
W4 (power MOSFET) can be prevented from being destroyed.

Next, FIGS. 15 and 16 show a fourth embodiment of the motor drive device of the electric power steering device according to the present invention. The hardware configuration of this embodiment is the same as that of the first embodiment, and a description thereof will be omitted. The CPU 30 has a function as a ground fault determining unit.

FIG. 15 is a waveform diagram of a pulse-like power supply voltage fluctuation (decrease) at the time of starting the engine or the like. As shown in FIG. 15, the battery voltage BAT = 12 V instantaneously (for example, t = 1 ms, or When the voltage drops to V _B = 0 V (for 10 ms), it may be erroneously determined that a ground fault has occurred in the motor wire. At this time, if the CPU 30 is reset, the program is started again, so that it is not at least determined that the motor line is grounded.

Incidentally, it is preferable that the ground fault detection processing is essentially ignored for the pulse-like power supply voltage fluctuation as described above. Therefore, in this embodiment, this problem is avoided by the program shown in FIG.

That is, in FIG.
1. After step S2, it is determined in step S21 whether an initial ground fault has occurred. If it has occurred, the process proceeds to step S6 to turn off the power supply. On the other hand, when the initial ground fault has not occurred, the process proceeds to step S4 to start the assist process, and then performs a normal ground fault detection in step S5. If no ground fault is detected in step S5, the process returns to step S4. If a ground fault is detected, the process proceeds to step S4.
Proceeding to 40, a determination is made as to whether or not an erroneous determination has been made.

That is, when the processing shifts to steps S40 and S41, which are the characteristic portions of the present embodiment, first, in step S40, all the gates of the four switching elements SW1 to SW4 of the H-bridge circuit 35 are turned off. Thus, no current flows through the four switching elements SW1 to SW4. Next, in step S41, the level of the ground fault detection interrupt signal is read (read).
When it is at the "H" level, it is determined that no ground fault has occurred, and the process returns to step S4 to continue assisting.

On the other hand, at the time of "L" level, that is, CP
When a negative logic interrupt signal indicating a ground fault of the motor line is supplied to the interrupt port INT1 of U30, step S6 is executed.
Then, the power relay 36 is turned off immediately to stop the motor drive output. As a result, the power supply to the motor 6 is turned off, the steering system is not assisted, and the element destruction of the motor drive device and the motor failure due to ground fault are avoided.

As described above, in the algorithm of the ground fault detection processing of the motor line in the present embodiment, the initial ground fault is determined, the normal ground fault detection is performed after the assist processing is started, and the ground fault detection is performed. , Once all gates of the four switching elements SW1 to SW4 are turned off,
The level of the ground fault detection interrupt signal of the motor line is determined in a state where no current flows through the switching elements SW1 to SW4.

Therefore, even if there is a pulse-like power supply voltage fluctuation (decrease) at the time of starting the engine shown in FIG. 15, the ground of the motor line is kept in a state where no current flows through the four switching elements SW1 to SW4. Since the level of the ground detection interrupt signal is determined, the sensitivity is higher than when the CPU 30 is reset, rather than detecting the edge of the signal, and the possibility of erroneously determining that a ground fault in the motor wire has occurred is avoided. be able to. As a result, it is possible to prevent the system from going down due to erroneous determination.

It is needless to say that the above-described first to fourth embodiments may be used alone or in combination.

[0063]

According to the first aspect of the present invention, when the sum of the voltages across the motor of the electric power steering apparatus becomes equal to or less than a predetermined value, detection of the motor line ground fault is permitted and all the switching elements are turned off. Therefore, even if the shunt resistor for detecting the motor current is provided below the drive circuit composed of the H-bridge, that is, on the ground side, the motor line ground fault in the overcurrent failure mode such as a load short circuit occurs. The power element can be detected and the destruction of the power element can be prevented. Further, since the shunt resistor is provided below the drive circuit composed of the H bridge, the motor current detection circuit can be made inexpensive, and the overall price can be kept low.

According to the second aspect of the present invention, when the duty ratio of the pulse for turning on / off the switching element, the motor current and the cold-side terminal voltage are at least within a predetermined detection range, the detection of the motor line ground fault is performed. Since it is allowed and all of the switching elements are turned off,
The ground fault on the cold side of the motor wire can be reliably detected, and the destruction of the power element can be prevented.

According to the third aspect of the invention, after all of the switching elements are once turned off, an initial ground fault of the motor is detected, and after the detection of the initial ground fault, the switching elements are controlled by a pulse modulation method to assist the motor. Is started, the initial ground fault at the time of starting the engine can be accurately detected, and the destruction of the power element can be prevented.

According to the invention, when a ground fault of the motor is detected during the control of the switching element after the detection of the initial ground fault, all of the switching elements are once turned off, and then the ground of the motor is turned off. Since it is determined whether or not a fault has been erroneously determined, in addition to the above-described effects, erroneous detection of a motor line ground fault due to a pulse-like power supply voltage fluctuation can be eliminated, thereby effectively preventing a system down. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a hardware configuration of a first embodiment of a motor drive device of an electric power steering device according to the present invention.

FIG. 2 is a diagram for explaining an example of motor driving of the embodiment.

FIG. 3 is a diagram for explaining an example of motor driving of the embodiment.

FIG. 4 is a waveform chart for explaining an example of motor driving of the embodiment.

FIG. 5 is a circuit diagram showing an example of a motor line ground fault detection circuit of the embodiment.

FIG. 6 is a flowchart of a main program for power steering control according to the embodiment.

FIG. 7 is a circuit diagram showing an example of a motor line ground fault detection circuit of a second embodiment of the motor drive device of the electric power steering device according to the present invention.

FIG. 8 is a waveform diagram for explaining detection of a ground fault on a motor line cold side according to the embodiment.

FIG. 9 is a waveform chart for explaining detection of a ground fault on a motor line cold side in the embodiment.

FIG. 10 is a waveform chart for describing detection of a ground fault on a motor line cold side according to the embodiment.

FIG. 11 is a waveform diagram for describing detection of a ground fault on a motor line cold side in the embodiment.

FIG. 12 is a flowchart of a program for a motor line cold side ground fault detection process of the embodiment.

FIG. 13 is a diagram for explaining a motor line cold side ground fault detection process of the embodiment.

FIG. 14 is a flowchart of a main program for power steering control of a third embodiment of the motor drive device of the electric power steering device according to the present invention.

FIG. 15 is a waveform diagram for explaining voltage fluctuations in a fourth embodiment of the motor drive device of the electric power steering device according to the present invention.

FIG. 16 is a flowchart of a main program of power steering control of the embodiment.

FIG. 17 is a configuration diagram illustrating an example of a mechanical system of a conventional power steering device.

FIG. 18 is a detailed block diagram of a control device of a conventional power steering device.

FIG. 19 is a diagram showing characteristics of assist torque of a conventional power steering device.

FIG. 20 is a block diagram for explaining a problem of the conventional power steering device.

[Explanation of symbols]

Reference Signs List 1 steering wheel 6 motor 11 steering torque sensor 12 vehicle speed sensor 30 CPU (ground fault permitting means, initial ground fault detecting means, ground fault determining means) 31 drive control circuit 32 motor current detection circuit 33 gate drive circuit 34 step-up power supply circuit 35H Bridge circuit 37 Overcurrent detection circuit 38 Motor line ground fault detection circuit (motor terminal voltage detection circuit, ground fault tolerance means) 60 Current drive means 70 Motor line ground fault detection circuit 80 Cold side terminal voltage detection means

Continuation of the front page (56) References JP-A 1-278878 (JP, A) JP-A 2-81769 (JP, A) JP-A 3-96476 (JP, A) JP-A 3-182875 (JP , A) Japanese Utility Model 62-115731 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) B62D 5/04

Claims (4)

(57) [Claims] 1. A current command value for assisting a motor of an electric power steering device is generated based on a detected steering torque, a detected vehicle speed, and the like, and four switching elements connected to the motor in an H-bridge type. An electric power steering apparatus comprising: a current driving unit that controls the switching element by a pulse width modulation method according to a deviation between the assist current command value and the detected motor current and a polarity of the assist current command value. A motor terminal voltage detecting means for detecting a voltage across the motor; comparing a sum of the voltages across the motor with a predetermined value; Ground fault permitting means for permitting detection of a ground fault, wherein the current driving means includes a ground fault of the motor during control of the switching element. When detection is permitted, the motor driving device of the electric power steering apparatus characterized by turning off all of the switching elements. 2. A current command value for assisting a motor of an electric power steering apparatus is generated based on a detected steering torque, a detected vehicle speed, and the like, and four switching elements connected to the motor in an H-bridge type. An electric power steering apparatus comprising: a current driving unit that controls the switching element by a pulse width modulation method according to a deviation between the assist current command value and the detected motor current and a polarity of the assist current command value. A cold-side terminal voltage detecting means for detecting a cold-side terminal voltage of the motor; and a duty ratio of a pulse for turning on / off the switching element, the motor current and the cold-side terminal voltage being at least a predetermined value. Ground fault permitting means is provided to allow detection of ground fault when it is within the detection range. Said current drive means, said the detection of the motor of the ground fault in the control of the switching element is allowed, the motor driving device of the electric power steering apparatus characterized by turning off all of the switching elements. 3. A current command value for assisting a motor of an electric power steering device based on a detected steering torque, a detected vehicle speed, and the like, and four switching elements connected to the motor in an H-bridge type. An electric power steering apparatus comprising: a current driving unit that controls the switching element by a pulse width modulation method according to a deviation between the assist current command value and the detected motor current and a polarity of the assist current command value. In the motor drive device, after all of the switching elements are turned off, an initial ground fault detecting means for detecting a ground fault of the motor is provided, and the current driving means performs pulse width modulation on the switching elements after detecting the initial ground fault. A motor drive device for an electric power steering device, wherein the motor drive device is controlled by a system. 4. A current command value for assisting a motor of an electric power steering apparatus based on a detected steering torque, a detected vehicle speed, and the like, and four switching elements connected to the motor in an H-bridge type. An electric power steering apparatus comprising: a current driving unit that controls the switching element by a pulse width modulation method according to a deviation between the assist current command value and the detected motor current and a polarity of the assist current command value. In the motor drive device, after all of the switching elements are turned off, an initial ground fault detecting means for detecting a ground fault of the motor; When detected, after turning off all of the switching elements, it is determined whether or not the ground fault of the motor is erroneously determined. Ground current determining means, wherein the current drive means controls the switching element by a pulse modulation method after detecting an initial ground fault and after erroneously determining a ground fault of the motor. Motor drive for electric power steering.