JPH07115645B2 - Motor current detection circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detection circuit for an electric motor, and relates to operation of a steering wheel, for example, in relation to torque acting on a steering shaft when the steering wheel of an automobile is operated. The present invention proposes a motor current detection circuit suitable for detecting the current of a motor that assists force.

[Conventional technology]

The applicant of the present application has proposed a control circuit of an electric power steering apparatus for detecting the electric current of an electric motor for assisting the steering force and controlling the rotation of the electric motor, in Japanese Patent Application No. Sho 62-222828.

FIG. 3 is a schematic diagram of a main part of a control circuit of the electric power steering device. The series circuit of the transistors T1, T3 and the series circuit of the transistors T2, T4 are connected in parallel to form a bridge circuit of the transistors T1, T2, T3, T4, and the connection point of the transistors T1, T3 and the transistor T2, An electric motor M that assists the steering force is short-circuited between the connection point of T4 and the connection point. The connection point of the transistors T1 and T2 is connected to the series power source E composed of a battery. The connection point of the transistors T3 and T4 is grounded via the current detection resistor RS and is also connected to the peak hold circuit 1. The output of the peak hold circuit 1 is input to the amplifier circuit 2, and the output thereof is used for feedback control of a drive signal that PWM-controls the conduction of the transistor T1 or T2, for example.

Next, the operation of the control circuit of this electric power steering device will be described.

When the steering wheel is operated and torque acts on the steering shaft,
A torque sensor (not shown) detects the torque. Then, when the electric motor M is rotated in the arrow direction (or the direction opposite to the arrow), the drive signal PWM-controlled in relation to the detected torque is given to the transistor T1 (or T2). Further, during the period of driving the electric motor M, a DC drive signal is given to the transistor T4 (or T3) to turn it on. Then, two circuits are formed from the DC power source E through the transistor T1 (or T2), the motor M, the transistor T4 (or T3) and the current detection resistor RS, and the motor M is driven by the PWM controlled voltage in the arrow direction (or It rotates in the direction opposite to the arrow) and assists the steering force. And current detection resistor
A pulse voltage related to the current of the PWM-controlled electric motor M is generated in RS, and the pulse voltage is given to the peak hold circuit 1. The peak hold circuit 1 detects the peak value of the input pulse voltage and inputs the peak value signal to the amplifier circuit 2. The amplifier circuit 2 amplifies the peak value signal, inputs the output to a signal correction circuit (not shown), and corrects the drive signal given to the transistor T1 (or T2).

In this way, the drive signal of the transistor T1 (or T2) is PWM-controlled in order to eliminate the difference between the drive signal of the transistor T1 (or T2) and the output signal P of the amplifier circuit 2 and corresponds to the detected torque. The electric motor M outputs the electric motor torque.

[Problems to be Solved by the Invention]

In the control circuit of the electric power steering apparatus described above, the voltage applied to the electric motor M is PWM-controlled, so that the battery is supplied to the electric motor M during the period when the transistor T1 (or T2) is on. A large amount of current flows and electromagnetic energy is stored in the coil of the electric motor M. The flywheel diode connected in parallel with the transistor T4 (or T3) and the transistor T3 (or T4) by the stored electromagnetic energy while the transistor T1 (or T2) is off.
The flywheel current shown by the solid line flows through D3 (or D4). That is, the transistor T1 is connected to the current detection resistor RS.
(Or T2) current flows only when it is on, so it is necessary to correct the value with the peak hold circuit for detecting the motor current. There was an error between. In addition, since the current detection resistor RS is commonly connected to the transistors T3 and T4 that determine the rotation direction of the electric motor M, the polarities of the potentials of the terminals of the current detection resistor RS are constant, and from that polarity, the electric motor There is a problem that the current direction of the electric motor cannot be detected, and the correspondence between the operating direction of the steered wheels and the rotating direction of the electric motor M cannot be known.

In view of the above-mentioned problems, the present invention is a current detection circuit for a motor capable of operating the differential amplifier stably with a single power supply without being affected by the common-mode rejection ratio of the differential amplifier, which is given a potential related to the current of the motor. The purpose is to provide.

[Means for Solving the Problems]

The current detection circuit of the motor according to the present invention is connected to the motor to bridge the bridge circuit of the switch element, in the current detection circuit of the motor driven by the voltage PWM control the conduction of the switch element, A current detection resistor serially connected to the electric motor, and a differential amplifier to which the potential of each terminal of the current detection resistor should be input, the bridge circuit is a series circuit of switch elements whose conduction is PWM controlled,
A series circuit of switch elements that are continuously conducted selectively according to the rotation direction of the electric motor, and a connecting portion of the switch element that is continuously conducted and a terminal of the current detection resistor that is not connected to the electric motor. Is connected.

[Action]

In the present invention, the potential of the connection portion of the switch element that is selectively and continuously conducted is always stable. This stable potential is applied to one input terminal of the differential amplifier, so that the differential amplifier is not affected by the common-mode signal rejection ratio in the high frequency range, and the operation of the differential amplifier is stable.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to the drawings showing its embodiments.

FIG. 1 is a circuit diagram of a current detection circuit for an electric motor according to the present invention.

A bridge circuit is formed by connecting a series circuit of transistors T1 and T3, which are switching elements, and a series circuit of transistors T2 and T4, which are switching elements, in parallel.
The connection point of 1 and T2 is connected to a DC power source E composed of a battery. Also, the connection point of the transistors T3 and T4 is grounded. Flywheel diodes D1, D2, D3, D4 are separately connected in parallel to each of the transistors T1, T2, T3, T4. Between the connection point of the transistors T1 and T3 and the connection point of the transistors T2 and T4, a series circuit of a motor M for assisting the steering force and a current detection resistor RS for detecting the current of the motor M is interposed. There is. The connection point between the motor M and the current detection resistor RS is a resistor.
It is connected to the negative input terminal-of the differential amplifier 3 through a series circuit of R1 and R3.

The terminal of the current detection resistor RS that is not connected to the motor M is connected to the differential amplifier 3 through a series circuit of resistors R2 and R4.
Is connected to the positive input terminal + of. The connection midpoint between the resistors R1 and R3 is grounded via the capacitor C1, and the resistor R2
The intermediate connection point between R4 and R4 is grounded via a capacitor C2. The resistors R1 and R2 and the capacitors C1 and C2 form a surge absorbing filter. Further, a ripple absorbing capacitor C3 is interposed between a connection point between the resistors R1 and R3 and a connection point between the resistors R2 and R4. The reference voltage V _ref is input to the positive input terminal + of the differential amplifier 3 via the resistor R6. The output terminal 3a of the differential amplifier 3 is connected to its negative input terminal − via a resistor R5, and is also grounded via a series circuit of resistors R7 and R8 having the same resistance value.
The control power supply V _C is connected to the power supply terminal 3b of the differential amplifier 3, and the ground terminal 3c is grounded.

A noise absorbing capacitor C4 is connected in parallel to the resistor R8. The output of the differential amplifier 3 is output as the current detection signal A via the resistor R7.

Next, the operation of the electric current detection circuit of the electric motor configured as described above will be described.

When the torque sensor (not shown) detects the torque generated by the steering theory operation (not shown), the transistors T1, T2, T3, T4 are selected in relation to the torque and the direction of rotation, and the duty ratio pulse corresponding to the torque is selected. Drive signal from the transistor T1 (or T3)
A DC drive signal is applied to (or T2) during the period in which the electric motor M is driven. That is, when the electric motor M is rotated, for example, rightward (or leftward) to rotate the steering shaft in the steering direction, the transistor T1 (or T3) is supplied with the drive signal SP PWM-controlled according to the assisting torque. , A continuous drive signal SD is applied to the transistor T4 (or T2) during the driving of the electric motor M. Then, a pulse current under PWM control flows from the DC power source E through the transistor T1 (or T2), the electric motor M, the current detection resistor RS and the transistor T4 (or T3), and the electric motor M rotates to the right (or to the left). As a result, the steering shaft rotates in the steering direction to assist the steering force.

When the electric motor M is driven in this way, the current detection resistor
All current flows through RS in the same direction while driving the motor M. That is, when the transistor T1 (or T3) is off, the flywheel flowing through the flywheel diode D3 (or D1) connected in parallel to the transistor T3 (or T1) by the electromagnetic energy stored in the electric motor M. The current also flows through the current detection resistor RS in the same direction as the current flowing when the transistor T1 (or T3) is on. As a result, a voltage corresponding to the current value is generated between both ends of the current detection resistor RS, which has a polarity corresponding to the direction of the current flowing in the electric motor M. Transistor T4
(Or T2) is conducted without PWM control of its conduction. Therefore, the potential at the connection point between the transistors T2 and T4, that is, the potential of the positive input terminal + of the differential amplifier 3 is when the transistor T4 is turned on. Therefore, it is stabilized at the ground potential, and when the transistor T2 is turned on, it is stabilized at the potential of the DC power source E.

The potentials of both terminals generated in the current detection resistor RS are input to the differential amplifier 3 via the resistors R1 and R3 or the resistors R2 and R4 and differentially amplified. The output of the differential amplifier 3 is output as the current detection signal A via the resistor R7. When the electric current steering signal A is used for controlling the electric motor of the electric power steering apparatus, the electric current detection signal A is given to the PWM control circuit as a feedback signal for obtaining the electric motor current corresponding to the detected steering torque.

By the way, the output voltage V ₀ of the differential amplifier 3 is the electric potential on the electric motor M side of the current detection resistor RS is V ₁ , and the transistor T of the current detection resistor RS
If the potential on the 4 side is V ₂ , Becomes Further, the voltage V _A of the current detection signal A is changed by the voltage dividing resistors R7 and R8 having the same resistance value provided on the output side of the differential amplifier 3. Becomes

Therefore, the current voltage V _A of the detection signal A, when not driving the motor M is V _1, the reference because V ₂ is zero voltage V _ref
It becomes 1/2 of. Further, the polarities of the potentials of the terminals of the current detection resistor RS differ in relation to the direction of the current flowing through the electric motor M. As a result, the voltage V _A of the current detection signal A increases or decreases with reference to 1/2 V _ref of the voltage V _A , and the current of the electric motor M and the current direction of the electric motor M, that is, the rotation direction is accurately detected. it can. In case of applying a voltage V _A of the current detection signal A to the analog / digital conversion circuit, if the voltage to obtain a reference voltage of the converter circuit from V _ref to or the same power source, the variation of both voltage interlocked Therefore, a digital output corresponding to V _A can be obtained regardless of the fluctuation.

Further, as described above, the potential of one input terminal of the differential amplifier 3 is fixed by the rotation direction, so that the common mode rejection ratio (CM
Even if RR) deteriorates in the high frequency range, it can be used without any hindrance. In other words, a differential amplifier that requires both positive and negative power supplies generally has good CMRR even in a high frequency range, but is expensive. On the other hand, a single-supply differential amplifier has a high-frequency CM.
Inferior RR but cheap. According to the present invention, such an inexpensive differential amplifier with a single power supply can be used, and the power supply circuit can be simplified.

The surge voltage generated in the energizing circuit of the electric motor M is absorbed by the filter including the resistors R1 and R2 and the capacitors C1 and C2. Further, the capacitor C3 absorbs the ripple of the voltage generated in the current detection resistor RS. Therefore, the potential input to the input terminal of the differential amplifier 3 does not change due to surge voltage or ripple. Furthermore, since the current direction of the electric motor M can be detected, when this electric current detection circuit is used in an electric power steering device, the steering theory is operated to determine the correspondence between the rotation direction of the electric motor M and the operation direction of the steering theory. By investigating, it is possible to easily determine whether the operation is abnormal due to a failure of a transistor or a disconnection or a short circuit of a drive circuit of the transistor.

In addition, the conduction of the transistors T1 and T3 is PWM-controlled so that the motor current is detected by the current detection resistor connected in series with the motor. However, as shown in FIG.
Even in the case of PWM control of conduction of No. 2, even if a current detection resistor is connected in series to the motor and the motor current is detected by the current detection resistor, the effect of being able to detect the motor current and its direction can be obtained.

FIG. 2 is a circuit diagram of a current detection circuit of an electric motor showing another embodiment of the present invention. Connect each terminal of current detection resistor RS to resistors R3 and R
Negative and positive input terminals-, + of the differential amplifier 3 via 4 separately
Connected with. The positive input terminal + of the differential amplifier 3 is connected to the reference voltage Vref via the parallel circuit of the resistor R6 and the capacitor C5.
Connected to the power supply. Negative input terminal of differential amplifier 3 −
A parallel circuit of a resistor R5 and a capacitor C6 is interposed between the output terminal 3a and the output terminal 3a, and the output terminal 3a is grounded via a series circuit of resistors R7 and R8 having the same resistance value.
A noise absorbing capacitor C4 is connected in parallel to the resistor R8. The output of the differential amplifier 3 is output as the current detection signal A via the resistor R7. The circuit is the same as that shown in FIG. 1 except for the circuit portion configured as described above.

Also in the current detection circuit of this electric motor, the same operation is performed and the same effect is obtained.

Further, although the case where the electric current detection circuit of the electric motor is applied to the electric power steering apparatus has been described in the present embodiment, it is needless to say that the electric current steering circuit can be used for other purposes, for example, for instructing the electric current and direction of the electric motor. .

〔The invention's effect〕

As described in detail above, according to the present invention, since the potential of one input terminal of the differential amplifier to which the potential of each terminal of the current detection resistor is applied is stabilized, the differential amplifier has the same phase in the high frequency range. The differential amplifier can be stably operated without being affected by the signal rejection ratio, and can be operated by a single power source.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a current detection circuit of an electric motor according to the present invention,
FIG. 2 is a circuit diagram of a current detection circuit of an electric motor showing another embodiment of the present invention, and FIG. 3 is a schematic diagram of a control circuit of a conventional electric power steering apparatus. 3 ... Differential amplifier, T1, T2, T3, T4 ... Transistor, M
...... Motor, C1, C2 to C6 …… Capacitor, R1, R2 to R8 ……
Resistance, E ... DC power supply

Claims (1)

[Claims] 1. A motor is connected to bridge the bridge circuit of the switch element, and the conduction of the switch element is PWM.
In a current detection circuit of an electric motor driven by a controlled voltage, a current detection resistor serially connected to the electric motor, and a differential amplifier to which the potential of each terminal of the current detection resistor is to be input,
The bridge circuit is composed of a series circuit of switch elements whose conduction is PWM controlled, and a series circuit of switch elements which are continuously conducted selectively according to the rotation direction of the electric motor, and the connection of the switch elements which are conducted continuously. And a terminal of the current detecting resistor which is not connected to the electric motor, the electric current detecting circuit of the electric motor.