JPH08239049A - Motor-driven power steering device - Google Patents

Abstract

PURPOSE: To provide a motor-driven power steering device which can attain reduction in the number of parts used in a circuit and cost. CONSTITUTION: This power steering device is provided with a clutch driving circuit 11 controlled by a CPU 3, an electromagnetic clutch CL driven by the clutch driving circuit 11, a clutch terminal voltage monitoring circuit 12 for monitoring the terminal voltage of the electromagnetic clutch CL and giving the monitored results to the CPU 3, a means for controlling the electromagnetic clutch CL so as to obtain a prescribed time OFF condition when the electromagnetic clutch CL is kept ON, and a failure detection means for detecting some failure in the electromagnetic clutch CL based on terminal voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus which assists a steering force with a driving force of a motor.

[0002]

2. Description of the Related Art An electric power steering system in which a steering force of steering wheels of an automobile is assisted by a motor is known. The rotational force of the motor that assists this steering force is transmitted to the steering shaft via an electromagnetic clutch equipped with an electromagnetic coil. When the vehicle is traveling at low speed, the electromagnetic clutch is engaged and steering is performed. When the vehicle is traveling at high speed, the electromagnetic clutch is disengaged so that the steering force is not assisted. The electromagnetic clutch can switch the electromagnetic clutch between an on / off state by turning on / off the current of the electromagnetic coil.

FIG. 4 is a block diagram showing the structure of the essential part of a conventional electric power steering apparatus of this type. The torque detected by the torque sensor 1 that detects the torque applied to the steered wheels is input to the CPU 3 via the interface circuit 2. The vehicle speed detected by the vehicle speed sensor 4 that detects the vehicle speed of the vehicle is input to the CPU 3 via the interface circuit 5.
The relay control signal output from the CPU 3 is input to the relay drive circuit 6, and the relay drive signal output from the relay drive circuit 6 is applied to the coil 7c of the fail-safe relay 7.

The motor control signal output from the CPU 3 is input to the motor drive circuit 8 to drive the motor M. The current from the battery 9 is applied to the contact 7a of the fail safe relay 7, the motor drive circuit 8 and the motor M.
And the motor current detection resistor R _M. The terminal voltage of the motor current detection resistor R _M is input to the motor current detection circuit 10, and its detection output is input to the CPU 3. The clutch control signal output from the CPU 3 is input to the clutch drive circuit 11 to drive the electromagnetic clutch CL.

Further, the current passing from the battery 9 through the contact 7a of the fail-safe relay 7 flows through the electromagnetic clutch CL, the clutch drive circuit 11, and the clutch current detection resistor R _CL . The terminal voltage of the electromagnetic clutch CL is input to the clutch terminal voltage monitoring circuit 12, and its output is CP.
Input to U 3. The terminal voltage of the clutch current detection resistor R _CL is input to the clutch current detection circuit 13, and its detection output is input to the CPU 3.

In this electric power steering system, when the engine key switch of the automobile is turned on, a relay control signal is input from the CPU 3 to the relay drive circuit 6 to drive the relay 7, and its contact 7a is closed to close the motor. It becomes a state where M can be driven. Further, the detected vehicle speed from the vehicle speed sensor 4 is input to the CPU 3 via the interface circuit 5, and if the vehicle speed is less than or equal to a predetermined value, that is, if the vehicle speed is low, a clutch control signal is input from the CPU 3 to the clutch drive circuit 11 to cause electromagnetic interference. Drive the clutch CL, the electromagnetic clutch CL is in the ON state,
A state in which the rotational force of the motor M can be applied to a steering shaft (not shown) via the electromagnetic clutch CL is set.

In this state, when a steering operation is performed to apply a torque to the steering shaft, the torque sensor 1 detects the torque. This detected torque is input to the CPU 3 via the interface circuit 2, and the CPU 3 inputs a motor control signal corresponding to the detected torque to the motor drive circuit 8 to control the motor drive circuit 8 and drive the motor M. . As a result, the rotational force of the motor M is given to the steering shaft via the electromagnetic clutch CL to assist the steering force. When the motor M is driven in this way, a terminal voltage corresponding to the current of the motor M is generated in the motor current detection resistor R _M , whereby the motor current detection circuit 10 detects the current of the motor M, and the detection output is detected by the CPU. Input to 3. Then, the CPU 3 monitors the abnormality of the motor M.

On the other hand, when the electromagnetic clutch CL is turned on, a terminal voltage corresponding to the current flowing through the electromagnetic clutch is generated in the clutch current detection resistor R _CL , whereby the clutch current detection circuit 13 supplies the current of the electromagnetic clutch CL. Detect and input the detection output to CPU 3. Then, the CPU 3 monitors the abnormality of the electromagnetic clutch CL. The terminal voltage of the electromagnetic clutch CL is input to the clutch terminal voltage monitoring circuit 12,
The output is input to the CPU 3. Then, the CPU 3 monitors the electromagnetic clutch CL for abnormalities.

When the CPU 3 detects an abnormal operation of the motor M or the electromagnetic clutch CL, the relay control signal output from the CPU 3 is cut off to stop the drive of the fail safe relay 7 and its contact 7a. Opens. As a result, the energization of the motor M and the electromagnetic clutch CL is cut off, and the operation of assisting the steering force by the motor M is prohibited.

In this way, by detecting the terminal voltage of the electromagnetic clutch CL, the abnormal operation of the electromagnetic clutch in the disengaged state of the electromagnetic clutch is detected, and by detecting the current of the electromagnetic clutch CL, the engaged state of the electromagnetic clutch is detected. The abnormal operation of the electromagnetic clutch in is detected. When any one of the detection results is determined to be abnormal, the electromagnetic clutch is disengaged so that the motor M does not assist the steering force. The clutch drive circuit 11, the clutch terminal voltage monitoring circuit 12, and the clutch current detection circuit 13 are configured as shown in FIG.

Positive electrode V of battery 9 (see FIG. 4)_PAnd negative
Electrode V_SBetween the contact 7a, the electromagnetic clutch CL, and the
Register TR₁And resistance R₁A series circuit with is inserted. Electric
The cathode of the magnetic clutch CL is the positive electrode V_PIs on the side
The flywheel diode D is connected in parallel. Electromagnetic
Latch CL and transistor TR₁The middle point of connection with is resistance R ₂
Transistor TR with grounded emitter via₂Contact with the base of
Continued. Transistor TR₂The base is resistance R₃Through
Grounded. Transistor TR₂Is a resistor R_Four
Through the positive electrode V of the battery 9_PConnected with. Resistance R
_FourAnd transistor TR₂From the connection midpoint with the collector of
Clutch terminal voltage detection signal S_VCLWill be output
ing. Transistor TR₁The base of the resistor R_FiveTo
Via the clutch drive signal S_CLIs entered. Transis
TR₁Resistor R between the base and emitter of₆Is interposed
It Transistor TR₁Emitter and resistor R₁, R₆With
The connecting part has a resistance R₇Via the positive input terminal + of the amplifier AP
Connected, positive input terminal + is capacitor C₁Grounded through
Is done. The negative input terminal-of the amplifier AP is a resistor R₈Connect through
Grounded, resistance R₉Output terminal AP of amplifier AP via_OContact with
Continued. And output terminal AP_OFrom the electromagnetic clutch CL
Flow detection signal S_ICLIs output.

In this circuit, the clutch drive signal S _CL
Is input to the base of the transistor TR ₁ , the transistor TR ₁ is turned on, and the positive electrode V _P of the battery 9 is connected to the contact 7a.
Current flows to the electromagnetic clutch CL via the electromagnetic clutch CL
Is turned on. When the transistor TR ₁ is turned on, its collector voltage is lowered and the transistor TR ₂ is turned off, so that the clutch terminal voltage detection signal S _VCL output from the collector of the transistor TR ₂ becomes H level.

On the other hand, the current of the electromagnetic clutch CL flows through the resistor R ₁ to generate its terminal voltage, which is input to the positive input terminal + of the amplifier AP and output from the output terminal AP _O of the amplifier AP. The clutch current detection signal S _ICL goes high. On the contrary, the clutch drive signal S _CL is applied to the transistor TR ₁
When the signal is not input to the base of, the transistor TR ₁ is turned off and the electromagnetic clutch CL is turned off. As a result, the transistor TR ₂ is turned on, and the clutch terminal voltage detection signal S _{VC L} output from the collector of the transistor TR ₂ becomes L level. Further, the terminal voltage of the resistor R ₁ disappears, and the clutch current detection signal S _ICL output from the output terminal AP _O of the amplifier AP becomes L level.

When the electromagnetic clutch CL is disengaged or a ground fault occurs in the electromagnetic clutch CL, the transistor TR ₂ is turned off to detect the clutch terminal voltage detection signal S.
_VCL goes high. Further, when the electromagnetic clutch CL is disengaged or has a ground fault when the electromagnetic clutch CL is in the on state, the terminal voltage of the resistor R ₁ decreases and the clutch current detection signal S _ICL output from the amplifier AP is It becomes L level. In this way, the terminal voltage of the electromagnetic clutch CL is monitored, and the electromagnetic clutch CL in the disengaged state is monitored.
Detects electromagnetic clutch abnormality such as CL electromagnetic coil disconnection or ground fault. The current of the electromagnetic clutch CL is monitored to detect an abnormality in the electromagnetic clutch, such as a disconnection of the electromagnetic coil of the electromagnetic clutch CL or a ground fault when the electromagnetic clutch CL is in the on state.

[0015]

As described above, the conventional electric power steering apparatus needs to include both the clutch terminal voltage monitoring circuit and the clutch current detection circuit. Moreover, since the clutch current detection circuit is composed of a large number of circuit components as shown in FIG. 5, there is a problem that the cost of the electric power steering device increases. In view of such a problem, the present invention is an electric motor capable of detecting an abnormality in the electromagnetic clutch, such as disconnection of the electromagnetic clutch, ground fault, etc., regardless of whether the electromagnetic clutch is in the on state or the off state without using the clutch current detection circuit. An object is to provide a power steering device.

[0016]

An electric power steering apparatus according to a first aspect of the present invention is an electric power steering apparatus that applies a rotational force of a motor to a steering mechanism via an electromagnetic clutch that is turned on and off by an electromagnetic coil to assist the steering force. In the power steering device, a drive circuit that drives the electromagnetic clutch to be turned on and off, a detection circuit that detects the terminal voltage of the electromagnetic clutch, and when the electromagnetic clutch is on, the electromagnetic clutch is turned off for a predetermined time. And an abnormality detecting unit that detects an abnormality of the electromagnetic clutch based on the terminal voltage.

In the electric power steering apparatus according to the second aspect of the invention, the predetermined time is shorter than the time until the electromagnetic clutch is mechanically operated when the electromagnetic clutch is controlled to be in the disengaged state. It is characterized by

[0018]

In the first aspect of the present invention, when the electromagnetic clutch is in the disengaged state, the terminal voltage detection circuit detects that the terminal voltage of the electromagnetic clutch is high when the electromagnetic clutch is normal, and the electromagnetic clutch is disconnected or grounded. When it is, it detects that the terminal voltage of the electromagnetic clutch is zero. When the electromagnetic clutch is in the ON state, the electromagnetic clutch is in the mechanical ON state, and the electromagnetic clutch is in the OFF state. Then, the terminal voltage detection circuit detects that the terminal voltage of the electromagnetic clutch is high, and detects that the terminal voltage of the electromagnetic clutch is zero if the electromagnetic clutch is disconnected or has a ground fault. Thus, the abnormality of the electromagnetic clutch can be detected by the terminal voltage of the electromagnetic clutch regardless of whether the electromagnetic clutch is on or off.

In the second aspect of the invention, the control for disengaging the electromagnetic clutch is terminated before the electromagnetic clutch mechanically operates. As a result, the electromagnetic clutch can be disengaged while mechanically operating the electromagnetic clutch so that slip does not occur in the electromagnetic clutch even if the maximum torque is generated in the motor.

[0020]

The present invention will be described in detail below with reference to the drawings showing the embodiments thereof. FIG. 1 is a block diagram showing a main configuration of an electric power steering device according to the present invention. The torque detected by the torque sensor 1 that detects the torque applied to the steered wheels is input to the CPU 3 via the interface circuit 2. The vehicle speed detected by the vehicle speed sensor 4 that detects the vehicle speed of the vehicle is input to the CPU 3 via the interface circuit 5. CPU 3
The relay control signal output from the relay drive circuit 6 is input to the relay drive circuit 6, and the relay drive signal output from the relay drive circuit 6 is applied to the coil 7c of the fail-safe relay 7.

The motor control signal output from the CPU 3 is input to the motor drive circuit 8 to drive the motor M. The current from the battery 9 is applied to the contact 7a of the fail safe relay 7, the motor drive circuit 8 and the motor M.
And the motor current detection resistor R _M. The terminal voltage of the motor current detection resistor R _M is input to the motor current detection circuit 10, and its detection output is input to the CPU 3. The clutch control signal output from the CPU 3 is input to the clutch drive circuit 11 to drive the electromagnetic clutch CL.

The current passing from the battery 9 through the contact 7a of the fail-safe relay 7 flows through the electromagnetic clutch CL and the clutch drive circuit 11. The terminal voltage of the electromagnetic clutch CL is input to the clutch terminal voltage monitoring circuit 12, and its output is input to the CPU 3.

FIG. 2 is a circuit diagram of the clutch drive circuit 11 and the clutch terminal voltage monitoring circuit 12. A series circuit including a contact 7a, an electromagnetic clutch CL, and a transistor TR ₁ is provided between the positive electrode V _P and the negative electrode V _S of the battery 9 (see FIG. 1). A flywheel diode D having a cathode on the positive electrode V _P side is connected in parallel to the electromagnetic clutch CL. An intermediate connection point between the electromagnetic clutch CL and the transistor TR ₁ is connected via a resistor R ₂ to the base of the transistor TR ₂ whose emitter is grounded. The base of the transistor TR ₂ is grounded via the resistor R ₃ . The collector of the transistor TR ₂ is connected to the positive electrode V _P of the battery 9 via the resistor R ₄ . The clutch terminal voltage detection signal S _VCL is output from the connection midpoint between the resistor R ₄ and the collector of the transistor TR ₂ . Base of the transistor TR _1, the emitter resistor R ₆ is interposed. The clutch control signal S _CL is input to the base of the transistor TR ₁ via the resistor R ₅ .

Next, the electric power steer configured as described above
The operation of the ring device is shown in the flow chart of Fig. 3, which shows the control contents of the CPU.
-It will be explained together with the chart. Car engine kees
When the switch is turned on, the CPU 3 to the relay drive circuit 6
Relay control signal is input to Fail-safe relay 7
Can be driven, and its contact 7a can be closed to drive the motor M.
It becomes a state. In addition, the vehicle speed detected by the vehicle speed sensor 4 is
-The speed is input to the CPU 3 via the interface circuit 5 and the vehicle speed
If it is less than the fixed value, that is, if the speed is low, the clutch is driven from CPU 3.
To circuit 11 clutch control signal S_CLIs entered. Do so
And transistor TR₁ (See Figure 2) turns on and the battery
9 positive electrodes V _PCurrent flows from the electromagnetic clutch CL to the electromagnetic
The clutch CL is in the ON state, and the torque of the motor M is
It is in a state where it can be applied to the steering shaft (not shown) via the latch CL.
It

After the electromagnetic clutch CL is in the on state in this way, when a steering operation is performed to apply a torque to the steering shaft, the torque sensor 1 detects the torque. This detected torque is input to the CPU 3 via the interface circuit 2,
The CPU 3 inputs a motor control signal corresponding to the detected torque to the motor drive circuit 8, and the motor drive circuit 8 energizes the motor M to drive the motor M. As a result, the rotational force of the motor M is given to the steering shaft via the electromagnetic clutch CL to assist the steering force.

As described above, when the transistor TR ₁ is on, the base potential of the transistor TR ₂ is lowered,
The transistor TR ₂ is turned off, and the collector voltage of the transistor TR ₂ becomes H level. By the way, transistor TR ₁
Is turned off and the electromagnetic clutch CL is in the disengaged state,
If there is no disconnection or ground fault in the electromagnetic clutch CL,
The collector potential of the transistor TR ₁ becomes high, the transistor TR ₂ is turned on, and the clutch terminal voltage detection signal S _{VCL of the} electromagnetic clutch CL becomes L level. That is, the clutch terminal voltage monitoring circuit 12 detects that the terminal voltage of the electromagnetic clutch is high. However, when the electromagnetic clutch CL is broken or grounded, the collector potential of the transistor TR ₁ is lowered, the transistor TR ₂ is turned off, and the clutch terminal voltage detection signal S _VCL becomes H level. That is, the clutch terminal voltage monitoring circuit 12 detects that the terminal voltage of the electromagnetic clutch is zero. Therefore, the CPU 3 causes the electromagnetic clutch
When CL is off, clutch terminal voltage detection signal S
By determining whether _VCL is at the H level or not, it is possible to detect the abnormality of the electromagnetic clutch CL in the disengaged state of the electromagnetic clutch CL.

Further, the CPU 3 checks the presence / absence of a clutch control signal input to the clutch drive circuit 11 to determine whether or not the electromagnetic clutch CL is in the on state (S1). When it is determined that the electromagnetic clutch CL is not in the on state, the timekeeping value of the timekeeping operation described later is cleared (S2), the failsafe flag is subsequently reset (S3), and the control operation ends. By the way, if it is determined that the electromagnetic clutch CL is in the on state (S1), the electromagnetic clutch CL
For example, if the clutch control signal S _CL with CL in the ON state is set to 10
Repeated momentary interruption at msec cycle (S4). Then, for example
It is determined whether the instantaneous time of 100 μsec has elapsed (S
Five). This time of 100 μsec is selected to be shorter than the time until the electromagnetic clutch CL mechanically operates when the electromagnetic clutch CL is controlled to be disengaged. That is,
With the electromagnetic clutch CL kept in a mechanically operated state, the electromagnetic clutch CL is turned off, and the terminal voltage of the electromagnetic clutch CL is detected in that state.

Subsequently, whether or not the detected terminal voltage of the electromagnetic clutch CL is at H level, that is, the clutch terminal voltage detection signal S
It is determined whether or not _VCL is at L level (S6). If the detected terminal voltage is at H level, it is considered that there is no disconnection or ground fault in the electromagnetic clutch CL and no abnormality is detected in the electromagnetic clutch CL. The clock is cleared (S2) and the fail safe flag is reset (S3). However, when the detected electromagnetic clutch terminal voltage is at the L level, that is, when the clutch terminal voltage detection signal S _VCL is at the H level, it is determined that the electromagnetic clutch CL is abnormal by a timer (not shown) incorporated in the CPU 3. Start timing (S7), clutch terminal voltage detection signal S
_{The time when VCL} is at H level is accumulated. Subsequently, it is determined whether or not the measured time has reached 0.1 sec, that is, whether or not the accumulated time of the detected clutch terminal voltage being at the L level has reached 0.1 sec (S8).

If the cumulative time has reached 0.1 sec, it is determined that the electromagnetic clutch CL has a wire breakage or a ground fault, and the failsafe flag is set (S9). Then, the relay control signal output from the CPU 3 is cut off, the contact 7a of the fail-safe relay 7 is opened, and the energization of the motor M and the electromagnetic clutch CL is cut off. As a result, the motor M stops driving and the electromagnetic clutch CL is disengaged. When the rotational force of the motor M is not applied to the steering shaft and the electromagnetic clutch CL is abnormal, the steering force is not assisted by the motor M. Note that the fail-safe flag is reset (S3) and the abnormality of the electromagnetic clutch CL is not detected until 0.1 sec is reached in step (S8).

In this way, when the electromagnetic clutch CL is in the disengaged state, the abnormality of the electromagnetic clutch CL can be detected by detecting the terminal voltage of the electromagnetic clutch CL. Further, when the electromagnetic clutch CL is in the on state, the clutch control signal for controlling the electromagnetic clutch CL in the on state is momentarily interrupted, and the terminal voltage of the electromagnetic clutch CL when the electromagnetic clutch CL is interrupted is detected. An abnormality of the electromagnetic clutch in the engaged state of the electromagnetic clutch CL can be detected without detecting the current of the electromagnetic clutch CL.

Therefore, unlike the conventional electric power steering apparatus, it is not necessary to provide a clutch current detection circuit having a large number of circuit components for detecting the current of the electromagnetic clutch, and the cost can be reduced and the size can be reduced. In the present embodiment, when the electromagnetic clutch is in the on state, the control to put it in the disengaged state is performed when the vehicle is traveling at a low speed, but the power steering control is not performed when the vehicle is traveling at a high speed. At that time, if the electromagnetic clutch is controlled to be disengaged to detect an abnormality, the safety of the power steering control can be further improved. The numerical values such as 100 μsec, 10 msec, and 0.1 sec used in this embodiment are examples, and the present invention is not limited to these.

[0032]

As described in detail above, according to the present invention,
Only by detecting the terminal voltage of the electromagnetic clutch, it is possible to detect the abnormal operation of the electromagnetic clutch when the electromagnetic clutch is turned on or off. Therefore, the current detection circuit for the electromagnetic clutch, which has a large number of circuit components, is not required, and the cost and size can be reduced. Also, when the electromagnetic clutch is in the on state, the electromagnetic clutch is disengaged in a time shorter than the time until the electromagnetic clutch mechanically operates, and the terminal voltage of the electromagnetic clutch is detected in that state to detect the electromagnetic clutch Since the abnormality is detected, the electromagnetic clutch remains mechanically in the engaged state, and there is an excellent effect that there is no risk of slipping of the electromagnetic clutch.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main configuration of an electric power steering device according to the present invention.

FIG. 2 is a circuit diagram of a clutch terminal voltage monitoring circuit and a clutch drive circuit.

FIG. 3 is a flowchart showing the control contents of the CPU.

FIG. 4 is a block diagram showing a main configuration of a conventional electric power steering device.

FIG. 5 is a circuit diagram of a clutch terminal voltage monitoring circuit, a clutch drive circuit, and a clutch current detection circuit.

[Explanation of symbols]

 1 Torque sensor 3 CPU 7 Fail-safe relay 11 Clutch drive circuit 12 Clutch terminal voltage monitoring circuit M motor CL Electromagnetic clutch

Claims (2)

[Claims] 1. An electric power steering apparatus for assisting a steering force by applying a turning force of a motor to an steering mechanism via an electromagnetic clutch that turns on and off by an electromagnetic coil, wherein the electromagnetic clutch is turned on and off. Drive circuit, a detection circuit for detecting the terminal voltage of the electromagnetic clutch, a means for controlling the electromagnetic clutch to be in a disengaged state for a predetermined time when the electromagnetic clutch is in an on state, and an electromagnetic clutch based on the terminal voltage. An electric power steering device, comprising: 2. The electric power steering apparatus according to claim 1, wherein the predetermined time is shorter than a time until the electromagnetic clutch is mechanically operated when the electromagnetic clutch is controlled to be in a disengaged state. .