JP3574908B2 - Electric power steering device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an electric power steering device in which a steering force is assisted by a motor.
[0002]
[Prior art]
FIG. 7 is a schematic circuit diagram showing an electric circuit configuration of a conventional electric power steering device. Based on a detection signal of a torque sensor that detects a torque applied to a steering shaft (not shown), a PWM signal corresponding to the torque is generated, and power transistors T ₁ , T ₂ , T ₃ , and T ₄ connected in a bridge are connected to power transistors. When a pair of T ₁ , T ₄ or T ₂ , T ₃ is switched by the PWM signal, a current flows from the battery 1 to the motor 3 through the fail-safe relay 2, and the motor 3 is rotated in a required direction. Drive at the required duty.
[0003]
Current of the motor 3 is adapted to flow through the current detection resistor R _M, the terminal voltage of the current detection resistor R _M changes according to the current of the motor 3. When ground fault E is generated in the terminal of the motor 3, no longer current flows almost to the current detection resistor R _M, when its terminal voltage falls below a predetermined value, actuates the fail-safe relay 2, the power supply to the motor 3 In short, power steering control is prohibited.
[0004]
Incidentally, the ground fault E is generated in the motor terminals when the current detected by the current detection resistor R _M is small relative to the target current of the motor 3, the power transistors T ₁ so as to increase the current of the _motor, T ₂ , T ₃ , T ₄ may be controlled so as to increase the duty of the PWM signal, and the ground fault E may not be detected immediately. Moreover, fast steering when the operation was performed, the counter electromotive force current of the current detection resistor R _M decreases occurred in the motor 3 by the operation, actuating the fail safe relay 2 the terminal voltage drops Become.
[0005]
However, the case of the back electromotive force of the motor 3 is temporary, and in this case, it is necessary to prevent the fail-safe relay 2 from operating. Therefore the time the terminal voltage of the current detection resistor R _M is reduced, when it is detected that continues example 500msec or 1sec or more, and actuates the fail-safe relay 2. Therefore, when the ground fault E occurs, there is a problem that it cannot be detected immediately.
[0006]
Therefore, an electric circuit of the electric power steering device shown in FIG. 8 has been considered as a countermeasure for this.
In this electric power steering device, a PWM signal corresponding to the torque is generated based on a detection signal of a torque sensor that detects a torque applied to a steering shaft (not shown), and the power transistors T ₁ , T ₂ , and T ₃ connected in a bridge. , T ₄ and the pair of power transistors T ₁ , T ₄ or T ₂ , T ₃ are switched by this PWM signal, a current flows from the battery 1 to the motor 3 through the fail-safe relay 2 and the motor 3 3 is rotated in a required rotation direction at a required duty. Current of the motor 3 is allowed to flow to the current detection resistor R _M, since the terminal voltage of the current detection resistor R _M changes according to the current of the motor 3, the differential terminal voltage of the current detection resistor R _M The signal is amplified by the amplifier 4 and a motor current detection signal _SIM corresponding to the motor current is obtained from the amplifier 4.
[0007]
Also, the voltage of the electric circuit A connected to the battery 1 via the key switch 5 and the voltage of the electric circuit B connected to the battery 1 via the fail-safe relay 2 are input to the comparator 6. Has become. When a ground fault E occurs at the terminal of the motor 3 and a large current flows through the electric circuit B, the voltage of the electric circuit B is greatly reduced. However, since the current of the motor 3 does not flow through the electric circuit A, the voltage does not change. As a result, the voltage difference between the electric circuits A and B increases, and the voltage difference signal S _AB is obtained from the comparator 6. Then, the fail safe relay 2 is operated by the obtained voltage difference signal SA _-B , so that the power supply to the motor 3 is cut off. Accordingly, when a ground fault occurs, the ground fault can be detected without a time delay.
[0008]
[Problems to be solved by the invention]
As described above, the electric power steering apparatus shown in FIG. 8 can immediately detect a ground fault at the terminal of the motor. However, even when the motor 3 is operating normally, the electric current of the electric circuit B can be detected by the motor current. Voltage drops. Then, a voltage difference occurs between the voltage of the electric circuit A and the voltage of the electric circuit B, and the voltage difference signal SA _-B is output. Therefore, the operation threshold voltage of the comparator 6 is set higher in consideration of the voltage drop of the electric circuit B due to driving the motor 3 when no ground fault occurs at the terminal of the motor 3. It is necessary to keep.
[0009]
However, when the operation threshold voltage of the comparator 6 is increased in this way, the power transistors T ₁ , T ₂ , T ₃ , T ₄ and the fail-safe relay 2 are kept until the voltage difference reaches the operation threshold voltage. However, there is a problem that the current load is large. In addition, when the operation threshold voltage is high, in the case of a ground fault with a small current, it cannot be detected, and the detection of the ground fault becomes uncertain. Further, there is a problem that an excessive auxiliary steering force generated due to an increase in a current flowing through the motor due to a ground fault of the motor cannot be detected.
[0010]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an electric power steering device that can immediately detect a ground fault of a motor that assists a steering force and that has a small current load on circuit components during a ground fault.
[0011]
[Means for Solving the Problems]
An electric power steering apparatus according to a first aspect of the present invention is an electric power steering apparatus in which a motor for assisting a steering force is driven by a power supply, wherein a voltage of an electric path through which a current of the motor flows and an electric path through which a current of the motor does not flow. A voltage difference detection unit that detects a voltage difference between voltages, a current detection unit that detects a current of the motor, a predetermined value that decreases in accordance with a decrease in a current value detected by the current detection unit, and the voltage A comparison unit for comparing the difference, wherein a ground fault of the motor is detected based on a comparison result of the comparison unit .
[0013]
[Action]
In the first invention, when a ground fault occurs on the motor side, the detection current of the current detection unit decreases, and the voltage of the electric circuit through which the current of the motor flows greatly decreases. On the other hand, the voltage of the electric circuit through which the motor current does not flow does not change even if a ground fault occurs. When the voltage difference between the voltage of the electric circuit in which the current of the motor flows and the voltage of the electric circuit in which the current of the motor does not flow is greater than a predetermined value that decreases in accordance with the decrease in the current detected by the current detection unit. The occurrence of the ground fault of the motor can be detected from the comparison result of the comparing unit .
[0015]
【Example】
Hereinafter, the present invention will be described in detail with reference to the drawings showing examples. FIG. 1 is a block diagram showing a main configuration of another electric power steering apparatus for explaining the electric power steering apparatus according to the present invention.
The detected torque of the torque sensor 10 that detects the torque applied to the steering shaft (not shown) is input via the interface circuit 11 to the CPU 12 including the timer TM. The detection output of the vehicle speed sensor 13 for detecting the vehicle speed of the automobile is input to the CPU 12 via the interface circuit 14. The relay control signal output from the CPU 12 is input to the relay drive circuit 15, and the relay drive signal output from the relay drive circuit 15 is applied to the relay coil 2c of the fail-safe relay 2. The motor control signal output from the CPU 12 is input to the motor drive circuit 16 so that the motor 3 is driven. The current from the battery 1 and the contact point 2a of the fail safe relay 2, a motor driving circuit 16, a motor 3, so that the flow through the current detection resistor R _M which detects the current of the motor.
[0016]
The terminal voltage of the current detection resistor R _M is inputted into the motor current detection circuit 17, the detection output is input to CPU 12. A clutch control signal output from the CPU 12 is input to a clutch drive circuit 18, and the output drives an electromagnetic clutch 19. The current flowing from the battery 1 through the contact 2 a flows through the electromagnetic clutch 19 and the clutch drive circuit 18. The voltage of the battery 1 is supplied to the power supply circuit 20 via the key switch 5. The voltage V _s of the path A which is connected to the battery 1 via the key switch 5, the voltage V _m of the path B to be connected to the battery 1 through the voltage of the motor drive circuit 16, i.e., the contact 2a of the fail safe relay 2 Is input to the motor terminal ground detection circuit 21, and the detection signal is input to the CPU 12. Note that the motor drive circuit 16 is configured by bridge-connecting four power transistors, as described above.
[0017]
Next, the operation of the electric power steering apparatus thus configured will be described with reference to the flowchart of FIG. 2 showing the control contents of the CPU 12 and the motor terminal ground fault detection circuit 21.
When the key switch 5 is turned on, a relay drive signal is input from the CPU 12 to the relay drive circuit 15, the fail-safe relay 2 is driven, the contact 2a thereof is closed, and the motor 3 can be driven. Further, a detection output of a vehicle speed sensor 13 that detects the vehicle speed of the automobile is input to the CPU 12, and if the vehicle speed is equal to or lower than a predetermined value, a clutch control signal is input from the CPU 12 to the clutch driving circuit 18 to drive the electromagnetic clutch 19. Then, the electromagnetic clutch 19 is brought into the engaged state, and a state in which the rotational force of the motor 3 can be applied to a steering shaft (not shown) via the electromagnetic clutch 19 is established.
[0018]
In this state, when a steering operation is performed to apply a torque to the steering shaft, the torque is detected by the torque sensor 10, and the detection output is input to the CPU 12 via the interface circuit 11. Accordingly, the CPU 12 inputs a motor control signal according to the detected torque to the motor drive circuit 16 to drive the motor 3. As a result, the rotational force of the motor 3 is given to the steering shaft via the electromagnetic clutch 19 to assist the steering force. Thus occurs the terminal voltage according to the current of the motor 3 is a motor 3 to the current detection resistor R _M is driven, by detecting the current of the motor 3, and inputs the detected output to the CPU 12. The voltage V _s of the path A, the motor terminal ground fault detector circuit 21 detects a ground fault the voltage difference between the voltage V _m of the path B, it will enter the detection signal to the CPU 12.
[0019]
Now, in the driving state of the motor 3, the CPU 12 checks the voltage difference between the electric circuits A and B and the detected current of the motor at a period of, for example, 4 msec. Now, the terminal of the motor 3 is a current of the current detection resistor R _M when ground fault is decreased, the detection current motor current detection circuit 17 detects decreases. The voltage V _m of the path B is reduced by greater current to ground fault flows. On the other hand, the voltage V _s of the path A current of the motor 3 does not flow will not change. The CPU 12 determines whether the current detected by the motor current detection circuit 17 is less than 10 A, for example (S1). If it is determined that it is less than 10A, subsequently it is determined whether or not the _{V m (V) <V s} (V) -1 (V) (S2). That is, the voltage V _m of the path B by the occurrence of a ground fault of the motor 3, it determines whether the reduced range V _s of the voltage by the motor current _(V) -1 _(V) when a ground fault has not occurred I do. If it is determined that where a _{V m (V) <V s} (V) -1 (V), small detection current of the motor 3, moreover by the voltage drop of the path B is large, the motor 3 of the terminal The occurrence of a ground fault will be detected. The signal that detected the ground fault is input to the CPU 12.
[0020]
Subsequently, time measurement is started by a timer TM built in the CPU 12 (S3). After the start of the time measurement, it is determined whether or not 30 msec has been measured (S4). If it is determined that 30 msec has been measured, the fail safe flag is set (S5). As a result, the relay control signal is cut off by the CPU 12, the contact 2a of the fail-safe relay 2 is opened, the power supply to the motor 3 is cut off, and abnormal power steering control is prohibited. Incidentally, when the detection current of the motor current detecting circuit 17 is determined to be not less than 10A (S1), a normal current is flowing to the motor 3, and _{V m (V) ≧ V s} (V) - If it is determined that the voltage is 1 (V) (S2), it is determined that there is no voltage drop of the electric circuit B due to the ground fault, no ground fault is detected. To end. Thus, when a ground fault occurs at the terminal of the motor 3, it can be detected immediately. In addition, an excessive assisting operation of the steering force can be detected.
[0021]
Figure 3 is a block diagram showing the configuration of a real施例of an electric power steering apparatus according to the present invention.
The detected torque of the torque sensor 10 that detects the torque applied to the steering shaft (not shown) is input to the CPU 12 via the interface circuit 11. The detection output of the vehicle speed sensor 13 for detecting the vehicle speed of the automobile is input to the CPU 12 via the interface circuit 14. The relay control signal output from the CPU 12 is input to the relay drive circuit 15, and the relay drive signal output from the relay drive circuit 15 is applied to the relay coil 2c of the fail-safe relay 2. The motor control signal output from the CPU 12 is input to the motor drive circuit 16 so that the motor 3 is driven. The current from the battery 1 and the contact point 2a of the fail safe relay 2, a motor driving circuit 16, a motor 3, so that the flow through the current detection resistor R _M which detects the current of the motor 3.
[0022]
The terminal voltage of the current detection resistor R _M is inputted into the motor current detection circuit 17, the detection output is input to CPU 12. A clutch control signal output from the CPU 12 is input to a clutch drive circuit 18, and the output drives an electromagnetic clutch 19. The current flowing from the battery 1 through the contact 2 a flows through the electromagnetic clutch 19 and the clutch drive circuit 18. The voltage of the battery 1 is supplied to the power supply circuit 20 via the key switch 5. The voltage V _s of the path A which is connected to the battery 1 via the key switch 5, the voltage V _m of the path B to be connected to the battery 1 through the voltage of the motor drive circuit 16, i.e., the contact 2a of the fail safe relay 2 Is input to the voltage difference detection circuit 22, and the detection signal is input to the CPU 12.
[0023]
The CPU 12 incorporates a timer TM and a memory M. The memory M, the data of the threshold voltage corresponding to the detected current of the motor current detection circuit as shown in FIG. 4, i.e., with respect to the voltage V _m of the path B to be reduced in accordance with the current of the motor 3 the earth Threshold voltage data serving as a reference for detecting a fault is stored in advance. In FIG. 4, the horizontal axis represents the detected current of the motor, and the vertical axis represents the threshold voltage.
[0024]
FIG. 5 is a block diagram showing a configuration of the voltage difference detection circuit 22, the motor drive circuit 16, and the motor current detection circuit 17.
The positive electrode of the battery 1 that is grounded anode is connected via a series circuit with the positive input terminal + of the differential amplifier 22a of the key switch 5 and the resistor R _1, to the positive input terminal + via the resistor R ₂ the voltage _{V s} is given. The positive electrode of the battery 1 and the fail safe relay 2 negative input terminal of the differential amplifier 22a via a series circuit of a resistor R ₃ - is connected to the negative input terminal - of through the resistor R ₄ differential amplifiers 22a Connected to output terminal 22o. Output terminal 22o is connected to one terminal of the resistor R _5, the other terminal of the resistor R ₅ is grounded through a resistor R _6. A voltage difference signal _{S A-B} is output from the connection of the resistor _{R 5} and _{R 6.} Connection point between the resistor _{R 3} and the fail safe relay 2 is connected to the transistors _{T 1,} T _2, T 3, _{T 4} the connection of the transistors _{T 1} and _{T 2} which is bridge-connected, the transistors _{T 3} and T connections and ₄ are connected to the negative electrode of the battery 1 through the current detection resistor R _M. A common connection of the transistors T ₁ and T _3, between the common connection of the transistors T ₂ and T _4, the motor 3 to assist the steering force is interposed. One terminal of the current detection resistor _{R M} (other terminal) the positive input terminal of the differential amplifier 17a via a resistor _R 7 _{(R 8)} + (negative input terminal -) is connected to. The negative input terminal of the differential amplifier 17a - between the output terminal 17o, resistor _{R 9} is interposed, the motor current detection signal _{S IM} from the output terminal 17o is output.
[0025]
Next, the operation of the electric power steering apparatus thus configured will be described with reference to the flowchart of FIG. 6 showing the control contents of the CPU 12 and the voltage difference detection circuit 22.
The operation from turning on the key switch 5 to driving the motor 3 according to the detection output of the torque sensor 10 to assist the steering force is the same as the control operation of the electric power steering apparatus in FIG. Is omitted.
[0026]
In the driving state of the motor 3, the voltage difference between the electric circuits A and B and the detected current of the motor are checked by the CPU 12 at a cycle of, for example, 4 msec. Now, ground fault E is generated in the terminals of the motor 3 (see FIG. 5), decreases the current of the current detection resistor R _M is, the detection current motor current detection circuit 17 detects decreases. The voltage V _m of the path B by a large current due to a ground fault E flows in the path B is significantly reduced. On the other hand, the voltage V _s of the path A current of the motor 3 does not flow does not change. Now, the detection current of the motor current detection circuit 17 is taken in by the CPU 12 (S11). Subsequently, an operation threshold voltage corresponding to the detected current value stored in the memory M is read based on the detected current value taken in by the CPU 12 (S12). Then the voltage difference _V s -V _m is, determines greater or not than the read threshold voltage (S13). If it is determined that the voltage V _s -V _m greater than the threshold voltage read out, thereby detecting the ground fault of the motor 3 terminal (S14).
[0027]
Subsequently, time measurement is started by the timer TM built in the CPU 12 (S15). After the start of the timing, it is determined whether or not 30 msec has been measured, for example (S16). If it is determined that 30 msec has been measured, the fail-safe flag is set (S17). As a result, the relay control signal is cut off by the CPU 12, the contact 2a of the fail-safe relay 2 is opened, the power supply to the motor 3 is cut off, and abnormal power steering control is prohibited. Incidentally, the voltage difference V _s -V _m, if it is determined to be less than or equal to the read operation threshold voltage (S13), not detect ground faults as voltage drop path B is small, counting of the timer TM The value is cleared (S18), and the control operation ends. The fail-safe flag is not set until 30 msec is counted.
[0028]
Thus path A, the voltage V _s of B, and the threshold voltage for detecting the voltage difference between V _m, by changing in response to the detection current of the motor, a ground fault generated in the motor terminal It can be detected immediately and a ground fault can be reliably detected. Further, an excessive assisting force for assisting the steering force is detected.
Note that the values of 4 msec, 30 msec, and the value of 10 A used in the present embodiment are examples, and the present invention is not limited to these values.
[0029]
【The invention's effect】
As described in detail above, according to the present invention, the threshold voltage to be compared with the voltage difference is changed according to the detected current of the motor, and when it is determined that the voltage difference is equal to or higher than the changed threshold voltage, The occurrence of a motor ground fault can be detected immediately. Therefore, there is an excellent effect that the detection of the ground fault is not delayed as in the related art, and the current burden on the circuit components can be reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of another electric power steering device for explaining an electric power steering device according to the present invention.
FIG. 2 is a flowchart showing control contents of a CPU and a motor terminal ground fault detection circuit.
3 is a block diagram showing the configuration of a real施例of an electric power steering apparatus according to the present invention.
FIG. 4 is a diagram showing a relationship between a threshold voltage and a detection current of a motor.
FIG. 5 is a circuit diagram of a voltage difference detection circuit, a motor drive circuit, and a motor current detection circuit.
FIG. 6 is a flowchart showing control contents of a CPU and a voltage difference detection circuit.
FIG. 7 is a circuit diagram showing a main configuration of a conventional electric power steering device.
FIG. 8 is a circuit diagram of an electric circuit showing a main part configuration of a conventional electric power steering device.
[Explanation of symbols]
1 Battery 3 Motor 12 CPU
Reference Signs List 16 Motor drive circuit 17 Motor current detection circuit 21 Motor terminal ground fault detection circuit 22 Voltage difference detection circuits 17a, 22a Differential amplifiers A, B

Claims (1)

In an electric power steering device configured to drive a motor that assists a steering force with a power supply,
A voltage difference detection unit that detects a voltage difference between a voltage of an electric circuit through which the current of the motor flows and a voltage of an electric circuit through which the current of the motor does not flow; a current detection unit that detects a current of the motor; and a current that the current detection unit detects. A comparison unit that compares the voltage difference with a predetermined value that decreases in accordance with a decrease in the value, wherein a ground fault of the motor is detected based on a comparison result of the comparison unit. Electric power steering device.

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