JPH0815864B2 - Control device for electric power steering - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control device for an electric power steering that controls an electric motor according to a forward / reverse rotation signal of a steering wheel and an output signal from a PWM circuit.

(Prior Art) The invention disclosed in Japanese Patent Application Laid-Open No. 60-35664 is conventionally known as a device of this type. The block diagram of FIG. 6 is a simplified illustration of this conventional device. It is a figure.

In the conventional device shown in FIG. 6, the transistors Q _{1 to} Q ₄ are operated according to the output signal from the signal processing circuit 1. For example, when a normal signal is output from the signal processing circuit 1, the transistor Q ₄ is always turned on, the transistor Q ₁ is repeatedly turned on and off according to the PWM signal, and the transistor Q ₄ is turned on and off according to the duty ratio of the PWM signal. Control the electric motor DM.

(Problems to be Solved by the Present Invention) In the conventional device as described above, the transistor Q ₄ remains on even when the transistor Q ₁ is off. Therefore, as shown by an arrow in FIG. When a motor is rotated by an external force, a current flows as shown by an arrow, and a torque is generated in the electric motor DM, which occurs regardless of the control system.

The torque of the electric motor generated irrespective of this control system has a problem that the steering wheel becomes difficult to return because it acts as a brake when the steering wheel returns due to self-aligning torque.

Therefore, it is possible to turn on / off the transistor Q ₄ according to the pulse width of the PWM control. But,
In this case, when the frequency of the PWM signal is increased, the linearity between the duty ratio of the PWM signal and the output torque of the electric motor is lost as shown in FIG. 7, and the controllability of the power steering is deteriorated. Another problem arises.

That is, as shown in FIG. 8, when the frequency of the PWM signal increases, the energy per pulse decreases. Therefore, there is a problem that the linearity between the duty ratio and the output torque of the electric motor collapses, and the controllability of the power steering deteriorates as described above.

An object of the present invention is, for example, a control in which the electric motor does not act as a brake when the steering wheel is returned by self-aligning torque and the linearity between the duty ratio of the PWM signal and the output torque of the electric motor is maintained. It is to provide a device.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a current signal processing circuit that detects a current that also flows in an electric motor, a motor current equivalent voltage output from the current signal processing circuit, and a running condition. Depending on the output signal from the comparator and the comparator that compares the command voltage output according to the conditions,
And a selection circuit for selecting whether to control the voltage applied to the electric motor or the current flowing through the electric motor. Moreover, when the command voltage is larger than the motor current equivalent voltage, the selection circuit When the control is carried out and the motor current equivalent voltage is larger than the command voltage, the current control is carried out, and when this current control is carried out, a function to correct the difference between the command voltage and the motor current equivalent voltage is provided. It is configured.

(Operation of the present invention) Since it is configured as described above, when the handle is rotated in either the forward or reverse direction, the third transistor or the fourth transistor
The transistor remains on. Therefore, a regenerative current flows through these third and fourth transistors.

The current flowing through the motor is detected by the current signal processing circuit, and the motor current equivalent voltage is output from this processing circuit.

This motor current equivalent voltage is compared with the command voltage by the comparator, and the comparison result is input to the selection circuit. In this selection circuit, when the command voltage is higher than the motor current equivalent voltage, voltage control is selected, and when the motor current equivalent voltage is higher than the command voltage, current control is selected.

Moreover, if the motor current equivalent voltage is larger than the command voltage during this current control, the motor current equivalent voltage is corrected to a lower value.

Therefore, if the regenerative current flows while the command voltage for reducing the output torque of the electric motor is output, the current control function of the selection circuit corrects the regenerative current to zero.

(Effect of the present invention) According to the control device of the present invention, for example, when the steering wheel is returned by the self-allaning torque, even if the regenerative current is flowing through the electric motor, the control function is exerted so as to make it zero Therefore, the electric motor does not act as a brake by the action of the regenerative current. Therefore, the controllability of the power steering is also improved.

Also, since the regenerative current is actively flowed,
The current flow does not become intermittent even if the PWM frequency becomes high. Therefore, the output torque of the electric motor and the PWM
Linearity with the signal duty ratio is maintained.

Further, when the steering wheel is turned off, the voltage control is executed, so that the fluctuation of the voltage is reduced. If current control is performed even when the steering wheel is turned, the command voltage constantly fluctuates in order to maintain the current at the command value. When the voltage constantly fluctuates in this way, noise may be generated from the motor. However, if the voltage control is performed when the steering wheel is turned as in the present invention, the voltage becomes equal to the command value and its fluctuation disappears, so that there is no problem of noise from the motor.

(Embodiment of the present invention) The embodiment of the present invention shown in FIGS.
The pinion 3 is connected to the tip of the input shaft 2 connected to the rack 6, and the pinion 3 is engaged with the rack 6.
Both sides of the rack 6 are connected to the wheels 1 via side rods 5 and knuckle arms 4.

Further, a speed reducer 7 is connected to the electric motor m capable of rotating in the forward and reverse directions, a pinion 9 is provided on an output shaft 8 of the speed reducer 7, and the pinion 9 is engaged with the rack 6.

Further, a vehicle speed sensor 10 for detecting the vehicle speed of the vehicle and a torque sensor 11 for detecting the steering torque acting on the input shaft 2 are provided, and these sensors 10, 11 are connected to the signal processing device 12. .

The signal processing device 12 is connected to the motor control device a, and the specific configuration of the motor control device a is as shown in the block diagram of FIG.

The motor control device a is provided with a selection circuit b to which a command voltage Vc according to the traveling condition of the vehicle is input.
This selection circuit b has a differential input type operational amplifier 13,
The command voltage V is applied to one input terminal 13a of this operational amplifier.
_C is input, and the other input terminal 13b is connected to a current signal processing circuit 14 that detects a current flowing through the electric motor m. The selection circuit b thus configured has three resistors Ra, Rs,
Rf is provided and the resistance Rf is made sufficiently larger than the resistance Rs.

Further, in the selection circuit b, the operational amplifier
A switch 15 is provided on the downstream side of 13. This switch 15
Has contacts 15a and 15b, and causes the operation amplifier 13 to function when the contact 15a is closed. Also, contact 15
When b is closed, the command voltage V _C input to the selection circuit b is made to flow directly from the bypass circuit 16 to the circuit of the control system described later, so that the operation amplifier 13 is not substantially functioned.

The switch 15 is connected to the comparator 17 and opens / closes according to the output signal of the comparator 17.

The comparator 17 includes an output signal | V _I | from the absolute value circuit 18 for converting the motor current equivalent voltage V _I of the current signal processing circuit 14 into an absolute value, and an absolute value amplification for multiplying the absolute value of the command voltage Vc by α. The output signal α | V _C | from the circuit 19 is input.

The comparator 17 is turned off when | V _I | <α | V _C | to close the contact 15b, and conversely | V _I |> α | V _C |
In case of, the comparator 17 is activated and the contact 15a
I'm trying to close.

When one of the contacts 15a is closed as described above, the command voltage V _C and the motor current equivalent voltage V _I are input to the selection circuit b, the output voltage V _{0 at} that time is V ₀ = V _{0 C} + to become _{(Rf / Rs) (V C} -V I).

Therefore, when the command voltage V _C is equal to the motor current equivalent voltage V _I , the output voltage V ₀ is equal to the command voltage V _C. If the motor current equivalent voltage V _I becomes larger than the command voltage V _C , the output voltage V ₀ is decreased, and conversely the voltage V _I
If becomes smaller, the output voltage V ₀ increases.

When the contact 15b is closed, regardless of the current flowing through the electric motor m, that is, the motor current equivalent voltage V _I ,
Outputs an output voltage V ₀ equal to the command voltage V _C.

The positive / negative determination circuit 20 and the absolute value circuit 21 are connected to the selection circuit b as described above.

The positive / negative determination circuit 20 includes first and second AND gates 22 and 23.
To the 3rd and 4th via the knot gate 24
It is also connected to AND gates 25 and 26.

An oscillation circuit 27 that outputs a predetermined pulse signal is connected to the first and third AND gates 22 and 25.
The AND gates 23 and 26 are connected to the absolute value circuit 21.
The PWM circuit 28 is connected.

Now, for example, when the positive / negative determination circuit 20 outputs the normal rotation signal A, the normal rotation signal A is output to the first and second AND gates 22,
Enter in 23. However, when a signal other than the normal rotation signal, that is, the reverse rotation signal is output from the positive / negative determination circuit 20, the knot gate 24 functions to output the reverse rotation signal, and the reverse rotation signal A is output to the third and fourth AND gates 25, Enter in 26.

Therefore, the forward rotation signal A from the positive / negative determination circuit 20 is the first
When input to the AND gate 22, the pulse signal C that is the same as the pulse signal I of the oscillation circuit 27 is output from the first AND gate 22 while the normal rotation signal A is being input. Further, when the reverse rotation signal A output from the knot gate 24 is input to the third AND gate 25, the same pulse signal D as the pulse signal I is output from the third AND gate 25 while the reverse rotation signal is input. Is output.

Further, when the normal rotation signal A is being input to the second AND gate 23, while the normal rotation signal is being input, the second
The PWM signal E is output from the AND gate 23. When the reverse signal A from the knot gate 24 is input to the fourth AND gate 26, the PWM signal F is output from the fourth AND gate 26 while the reverse signal is being input.

Further, a bridge circuit is constituted by the first to fourth field effect transistors 29 to 32 (hereinafter referred to as the first to fourth FETs) via the electric motor m. The gate sides of the first and second FETs 29 and 30 are connected to the first and second AND gates 22 and 23 via the voltage conversion circuits 33 and 34, and the gate side of the third FET 31 is directly connected to the knot gate 24, The gate side of the fourth FET 32 is directly connected to the positive / negative opposite circuit 20.

The first and second FETs 29 and 30 of the bridge circuit as described above are connected to the positive side of the battery 35, and the voltages V3 and V4 between the _third and _fourth FETs 31 and 32 are set to the ground potential. Further, the voltages V ₁ and V ₂ of the electric motor m are guided to the voltage conversion circuits 33 and 34.

The voltage conversion circuits 33 and 34 as described above are the first and second FETs.
This is for securing the gate voltages G and H of 29 and 30. That is, the source voltages V ₃ , V of the _third and fourth FETs 31, 32
_{Although 4} is always the earth potential, the source potentials V ₁ and V ₂ of the _first and _second FETs 29 and 30 change up to the voltage of the battery 35. Therefore, the voltage conversion circuits 33 and 34 are made to function so that the gate voltages G and H and the source voltages V ₁ and V _{2 of the first} and _second FETs 29 and 30 are generated.
I try to keep the relative difference with.

The voltage conversion circuit 33 and the first FET 29 are connected to the second AND gate 23 via the fifth FET 36 and the knot gate 37, and the drain side of the fifth FET 36 is set to the ground potential. Further, the voltage conversion circuit 34 and the second FET 30 are connected to the fourth AND gate 26 via the sixth FET 38 and the knot gate 39, and the drain side of the sixth FET 38 is also at the ground potential.

For example, assuming that the positive / negative determination circuit 20 outputs the normal rotation signal A, while the normal rotation signal is being output, the first AND gate 22 outputs the pulse signal C, and
This pulse signal C is input to the voltage conversion circuit 33. When the pulse signal C is input to the voltage conversion circuit 33, the voltage conversion circuit 33 outputs the gate voltage G to the first FET 29.

Further, when the normal signal A is output as described above, the normal signal A is also input to the second AND gate 23,
The output signal B from the PWM circuit 28 is the second AND gate 23.
Is output as a PWM signal E from. In this way the second
The PWM signal E output from the AND gate 23 is input to the knot gate 37. The knot signal 37 outputs a knot signal that is on when the PWM signal is off and off when the PWM signal is on. The knot signal is the 5th floor
Input to the gate side of ET36. When the knot signal input to the gate side of the fifth FET 36 is on, in other words, the PWM
When the signal E is off, a voltage is applied to the gate side of the fifth FET 36 and the fifth FET 36 turns on.

When the fifth FET 36 is turned on in this manner, the gate side of the first FET 29 is grounded, so that the gate voltage G output from the voltage conversion circuit 33 is not supplied to the gate side of the first FET 29.

On the contrary, when the knot signal is off, in other words, when the PWM signal E is on, no voltage is applied to the gate side of the fifth FET 36. Therefore, while the PWM signal E is on, the fifth FET 36 is not energized, and the voltage conversion circuit
The gate voltage G is continuously applied to the first FET 29 from 33.

Therefore, as is clear from the time chart of FIG. 3, the first FET 29 is also turned on / off according to the duty ratio of the PWM signal E.

Further, when a signal other than the normal rotation signal is input from the positive / negative determination circuit 20, the reverse rotation signal is output from the knot gate 24, and this reverse rotation signal is input to the third AND gate 25. While the reverse signal is input to the third AND gate 25, the pulse signal D is output from the third AND gate 25 and the pulse signal D is input to the voltage conversion circuit 34. When the pulse signal D is input to the voltage conversion circuit 34, the voltage conversion circuit 34 outputs the gate voltage H to the second FET 30.

At this time, the reverse signal A is also input to the fourth AND gate 26, so that the output signal B from the PWM circuit 28 is output as the PWM signal F from the fourth AND gate 26. And
This PWM signal F is input to the knot gate 39, and the knot signal output from the knot gate 39 is used to control the sixth FET 38, as in the case of the fifth FET 36.

Therefore, the second FET 30 is also on / off controlled according to the duty ratio of the PWM signal F.

As is clear from the above, the first and second FETs 29 and 30 are
Turns on / off according to the PWM signal, but the 3rd and 4th FET3
1, 32 maintain the ON state while the steering wheel H is being switched to the left or right. For example, the fourth FET 32 maintains the ON state while the normal rotation signal A is being output. Therefore, even when the PWM signal is off, the regenerative current in the direction of arrow 40 flows through the electric motor m. This electric motor m
The current I flowing through the current signal is detected by the current signal processing circuit 14. The current signal processing circuit 14 outputs a motor current equivalent voltage V _{I which} is proportional to the current I.

The motor current equivalent voltage V _I output from the current signal processing circuit 14 as described above is input to the comparator 17 via the absolute value circuit 18 and also to the operational amplifier 13.

An output signal is also input to the comparator 17 from the absolute value amplifier circuit 19 that has multiplied the command voltage V _C by α to obtain an absolute value.

Then, the comparator 17 compares the two output signals as described above, and if | V _I | <α | V _C |, closes the contact 15b of the switch 15, and conversely | V _I |> α | V _{If C} |, the contact 15a is closed. The reason why the comparator 17 is controlled as described above is to perform voltage control when the handle H is turned off and current control when the handle H is returned. This control mode will be described in more detail.

First, the motor voltage as well as proportional to the command voltage V _C, approximately in proportion with the voltage at the time of locking of the motor, eventually, will be also proportional to current at the time lock command voltage V _C and the motor. The time when the motor is locked corresponds to a so-called steering holding state in which the handle H is turned to a predetermined position and kept in that state.

Therefore, when the voltage control is performed when the handle H is turned off and the current control is performed when the handle H is returned,
The switching point between the two controls can be obtained as the voltage when the motor is locked.

Therefore, in this embodiment, the current when the motor is locked is theoretically obtained. Then, a voltage conversion value of the theoretical obtained lock current, and multiplied alpha command voltage V _C in absolute value amplifying circuit 19 alpha | V _C | to.

The voltage signal α | V _C | and the voltage signal | V _I | obtained by converting the motor current equivalent voltage V _I into an absolute value by the absolute value circuit 18 are input to the comparator 17.

Then, the result compared by this comparator 17 is | V
_{When I} | <α | V _C |, it means that the electric motor m has not reached the lock state and the handle H has been turned off. Therefore, the comparator 17 does not operate, the contact 15a of the switch 15 is opened, and the contact 15b is opened. Keep closed.

When the contact 15b is closed as described above, the command voltage V _C is directly transmitted from the absolute value circuit 21 to the PWM circuit 28.
Therefore, the motor voltage in this case is controlled according to the command voltage V _C. That is, when the handle H is turned off, the electric motor is voltage-controlled according to the command voltage V _C (see FIG. 4). As described above, when the steering wheel H is turned off, the voltage control by the command voltage V _C is performed, so that the motor voltage becomes equal to the command voltage and does not fluctuate. Therefore, the sound generated due to the voltage change is generated. Disappears.

Also, the result compared by the comparator 17 is | V _I |
When> α | V _C |, the motor has reached the locked state, so the comparator 17 operates to close the contact 15a of the switch 15 and open the contact 15b.

Therefore, in the selection circuit b, as described above, the command voltage V _C and the motor current equivalent voltage V _I are compared, and when the motor current equivalent voltage V _I is too large with respect to the command voltage V _C , for example, the command voltage Even if the value of V _C is zero, when the motor current equivalent voltage V _I is equal to or greater than zero, the output voltage V ₀ is controlled so that the current I supplied to the electric motor m becomes zero. Therefore, at this time, current control is performed to control the current I.

That is, the command voltage V _C regardless of the rotation speed of the electric motor m
Is constant, the output torque of the electric motor m is also constant regardless of the rotation speed of the electric motor m (see FIG. 4).
As is clear from this, when the handle H is returned by the self-aligning torque, the electric motor m
The return performance of the handle H is very good because it is not restricted by the number of rotations.

Further, in this embodiment, while the steering wheel H is being switched to the left or right, the third and fourth FETs 31 and 32 are always kept in the on state, and the regenerative current in the direction of arrow 40 flows, so that FIG. As shown in, there is no interruption of current flow.
Therefore, even if the frequency of the PWM signal increases, the energy is not subdivided pulse by pulse. Therefore, the linearity between the duty ratio and the output torque of the electric motor can be maintained, and the controllability of the power steering can be kept good.

Although the field effect transistor is used in the above embodiment, it is natural that a normal transistor such as the conventional device shown in FIG. 6 may be used. The point is that the type of transistor does not matter as long as the current flowing through the electric motor m can be detected and controlled according to the command voltage V _C.

[Brief description of drawings]

1 to 5 show an embodiment of the present invention.
FIG. 4 is a mechanism diagram, FIG. 2 is a block diagram of the motor control device, FIG. 3 is a time chart diagram of the motor control device, FIG. 4 is a graph showing a relationship between output torque and rotation speed of the motor, and FIG. Is a diagram showing the relationship between the pulse of the PWM signal and the regenerative current, FIG. 6 is a circuit diagram of the conventional device, and FIG. 7 is a graph showing the relationship between the duty ratio of the PWM signal and the output torque of the motor. FIG. 8 is a diagram showing the relationship between the pulse of the conventional PWM signal and the regenerative current. m: electric motor, b: selection circuit, 14: current signal processing circuit, 17: comparator, V _C: command voltage, V _I
Motor current equivalent voltage, 28 ... PWM circuit, 28-32 ... 1st
~ 4 field effect transistors.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-59-130781 (JP, A) JP-A-61-119468 (JP, A)

Claims (1)

[Claims] 1. A bridge circuit composed of four transistors and an electric motor, and a first transistor which is turned on when a PWM signal from a PWM circuit and a normal rotation signal of a steering wheel are input, and a PWM signal and a reverse rotation of the steering wheel. Control device for electric power steering including a second transistor that is turned on when a signal is input, a third transistor that is turned on when the steering wheel is normally rotated, and a fourth transistor that is turned on when the steering wheel is rotated reversely In, a current signal processing circuit for detecting a current flowing through the electric motor,
A comparator that compares the motor current equivalent voltage output from this current signal processing circuit with a command voltage output according to the running condition, and controls the voltage applied to the electric motor according to the output signal from this comparator. Or a control circuit for selecting whether to control the current flowing through the electric motor. Moreover, when the command voltage is larger than the motor current equivalent voltage, the selection circuit performs voltage control and When the motor current equivalent voltage is large,
An electric power steering control device having a function of performing current control and, at the same time as performing the current control, correcting a difference between a command voltage and a motor current equivalent voltage.