JPH0457543B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an electric power steering device that generates auxiliary torque by a steering force booster using an electric motor, and particularly relates to an electric power steering device that generates auxiliary torque by a steering force booster using an electric motor. Related to improving the return characteristics of a steering system.

(Prior Art) Generally, as an electric power steering device, a control system is configured by a steering force booster using an electric motor as an auxiliary torque generation source and an arithmetic control device such as a microcomputer. That is,
The steering torque and steering rotation speed applied to the steering system are detected, and a drive control signal for the electric motor is determined and outputted by an arithmetic and control unit based on these detection signals.This improves the response performance of the electric motor and improves the steering feel. We are trying to improve the quality of our products. This type of prior art is known, for example, from a patent application filed by the present applicant.
60-9545 (see Japanese Patent Application Laid-Open No. 61-169367) and Japanese Patent Application No. 60-9546 (see Japanese Patent Application Laid-open No. 61-169368).

Conventionally, drive control of such an electric motor has been performed by constant frequency PWM control (Pulse Width Modulation), and has been based on a drive circuit as shown in FIG.

In the figure, 1 is a bridge circuit that constitutes a motor drive circuit, 2, 3, 4, and 5 are NPN switching transistors that constitute each arm of bridge 1, and 6, 7, 8, and 9 are transistors 2, 3, and 3, respectively. , 5, 4 connected in antiparallel,
10 is a motor to be controlled connected to the output terminal of the bridge circuit 1; 11 is a battery power supply connected to the input terminal of the bridge circuit 1; 12 is an arithmetic control signal 13 from a microcomputer, etc., connected to each transistor through its output port; This is a drive unit that is distributed between 2 and 5. When the motor is rotated in the forward direction, the arithmetic control signal 13 is applied to the transistors 2 and 5.
The drive unit 12 is operated to drive one set of transistors 3 and 4, and when the motor is to be reversed, the drive unit 12 is operated to drive one set of transistors 3 and 4. In accordance with the arithmetic control signal 13, the drive unit 12 turns on the transistor 2 during normal rotation drive, for example, in terms of a pair of transistors 2 and 5, and the other transistor 5 controls the steering torque and the steering control, which are control parameters. PWM control is performed with a duty ratio corresponding to the rotation speed. As you can see, bridge circuit 1
has a function of controlling the rotation direction of the electric motor 10 and its driving power.

A motor drive circuit having such a bridge circuit 1 operates as shown in FIG. 16. Electric motor 1
Consider the case where transistors 2 and 5 are driven in order to rotate 0 in the normal direction. When transistor 2 is kept on and PWM control is performed using transistor 5, the moment when transistor 5 is on is the first
As shown in FIG. 6a, a driving current i is supplied to the motor through a closed circuit including a power supply 11, a transistor 2, a motor 10, and a transistor 5. At the moment when the transistor 5 is off, as shown in FIG. 16b, a blocking current i flows through the closed circuit consisting of the transistor 2, the motor 10, and the diode 9 in an attempt to prevent the current from stopping due to the inductance of the motor. As will be described later, such a blocking current i impairs the steering characteristics and is harmful.

(Problem to be solved by the invention) In this case, when turning the steering wheel against the reaction force from the steering wheels (tires) (so-called forward operation state of the steering system), the load torque applied to the electric motor 10 causes the steering wheel to turn off. The blocking current i can be reduced by reducing the duty ratio of the transistor 5. However, when the steering wheel is returned by the reaction force from the steering wheel (so-called return operation state of the steering system),
It is not possible to reduce the blocking current i. This is because the load torque acting on the electric motor 10 decreases and the direction of steering rotation becomes opposite to the rotation direction of the electric motor, so that the armature current increases due to the back electromotive force of the electric motor in the closed circuit shown in FIG. 16b. increase,
It acts in the direction of reducing the rotation of the electric motor 10.
Therefore, even if the duty ratio of the transistor 5 is controlled in the motor 10, the off-state current cannot be controlled. This will be further explained with reference to FIG.

FIG. 17 shows the relationship between the armature current i of the motor 10 and the duty ratio. From the armature current i and the motor rotation speed n to obtain the required torque, the drive circuit shown in FIG. This is to obtain the duty ratio D to be formed. In the figure,
The horizontal axis is the duty ratio D, and the vertical axis is the armature current i. In addition, the rotation speed n of the electric motor 10 is a parameter; when the rotation speed n is positive, it indicates that the rotation direction of the electric motor and the direction of torque action match, and when it is negative, the rotation direction of the electric motor and the torque This indicates that the direction of action does not match (return operation state). Here, for example, the duty ratio when the armature current i corresponding to the motor torque is _i1 is determined from the diagram. First, it can be seen that when the motor rotation speed is zero (n=0), the motor should be driven at the duty ratio D1. Second, when the rotational direction of the motor and the direction of torque action match, the rotational speed n is positive, and the back electromotive force of the motor is proportional to the motor rotational speed n, and the armature current i decrease. Therefore, it is sufficient to drive the transistor 5 with a duty ratio D2 obtained by adding the decreased amount D2-D1. However, thirdly, if the rotational direction of the electric motor and the direction of torque action do not match, the rotational speed n is negative, and the back electromotive force of the motor is proportional to the motor rotational speed n. Increase current i.
In this case, it is sufficient to drive the transistor 5 with the duty ratio D0 obtained by subtracting the increased amount D1 - D0, but in reality, as the negative rotation speed increases, the load torque decreases, so the motor torque Therefore, the armature current i must be reduced.
However, since the duty ratio D cannot be made negative, there is a limit to how much the armature current i can be reduced in this case. Therefore, when the steering wheel is in a return operation state, an uncontrollable state occurs in which the armature current i cannot be reduced below a certain value.

When this uncontrollable state occurs, the operation of the electric motor is no longer able to follow the steering operation, causing a defective return operation or return hunting, and deteriorating the steering feel.

Therefore, the present invention has been made in an attempt to eliminate the above-mentioned drawbacks of the prior art, and provides a steering system with good return operation characteristics regardless of the characteristics of the motor drive circuit, without impairing the steering feeling. The purpose of the present invention is to provide an electric power steering device.

(Means and effects for solving the problem) An electric motor 49 that generates auxiliary torque in response to the operation of the steering system, a steering torque detection means 72 that detects the steering torque of the steering system, and a steering rotation of the steering system. steering rotation detection means 76 for detecting the number of steering rotations, and these steering torque detection means 7
2 and the steering rotation detection means 76, a motor control signal generation means for forming a motor control signal to cause the electric motor 49 to generate a predetermined auxiliary torque using the steering torque and the steering rotation speed as control parameters. 70, which is operated by the motor control signal of the motor control signal generating means 70, supplies an on-off voltage with a predetermined duty ratio to the motor 49, performs PWM control, and generates a blocking current due to the inductance of the motor 49 when the on-off voltage is turned off. In an electric power steering device equipped with an electric motor drive circuit 82 having a closed circuit through which the steering torque flows, when the direction of rotation of the steering system and the direction of the steering torque match (forward operation state), and the direction of rotation of the steering system and the direction of the steering torque do not match (return operation state)
In addition, during this return operation state, the blocking current generated in the closed circuit is passed through a separate circuit to prevent the blocking current from increasing, allowing the steering to return smoothly and improving the steering feel.

(Embodiments of the invention) Examples of the invention will be described below with reference to the accompanying drawings. Note that the same reference numerals in each figure indicate similar objects.

FIG. 1 and FIG. 2 show an electric power steering device according to an embodiment of the present invention, and mainly show the mechanical configuration. The electrical system will be explained later with reference to FIGS. 3 and 4.

According to the embodiment shown in FIG. 1, the electromagnetic booster 20 constituting the power steering is divided into detection means 35, 40 on the rack 21 side, a pinion 22, and an electric motor 49. That is, the electromagnetic booster is assembled into a rack-and-pinion mechanism constituted by a rack 21 and a pinion gear 22 that meshes with the rack 21 on the rear right side of the rack 21 in the figure.

The pinion gear 22 has both ends
It is rotatably supported by contact bearings 23 and 24, and is pressed in the direction of the input shaft 26 by a disc spring 25 mounted around the lower part of the bearing 24. The input shaft 26 is connected to a pinion shaft 22a at one end of the pinion gear 22 via a torsion bar 27. A bearing 28 is disposed between one end of the input shaft 26 and the pinion shaft 22a, and a bearing 34 and a flange 41 having a substantially U-shaped cross section are disposed at the other end of the input shaft 26. It is supported by the rotating shaft. Inside the pinion shaft 22a,
Two protrusions 22b each having a substantially fan-shaped cross section are integrally formed at positions approximately 180 degrees apart on the inner circumferential surface. A groove 26a having a fan-shaped cross-sectional shape complementary to the cross-sectional shape of the protrusion 22b is bored in the input shaft 26 at a position corresponding to the protrusion 22b. Therefore, the input shaft 26 and the pinion shaft 22a can rotate relative to each other to a certain extent, but beyond that they rotate integrally.

A steering torque detection sensor 35 is provided on the outer periphery of the pinion shaft 22a near where the protrusion b is formed. The steering torque detection sensor 35 electrically detects the displacement of the slider 29 that moves in the axial direction as the input shaft 26 and pinion shaft 22a rotate relative to each other. The slider 29 is generally cylindrical and has axially parallel slots 29a-29a bored in its side surfaces at symmetrical positions 180 degrees apart. Further, diagonal slots 29b-29b having a constant angle with respect to the axial direction are bored on the side surfaces of the slider rotated 90 degrees from the slots 29a-29a, respectively. This slider 29 is fitted onto the input shaft 26 and pinion shaft 22a. At this time, the parallel slots 29a-29a are connected to the protrusion 22 of the pinion shaft 22a.
The diagonal slot 29b-29b engages with the pin 22c provided in the input shaft 26, and the diagonal slot 29b-29b engages with the pin 22c provided in the
The pin 30- provided on the protruding portion 26b-26b of a
30. According to such a configuration, the torsion bar 27 relatively rotates the input shaft 26 and the pinion shaft 22a in proportion to the steering torque, and the slider 29 converts the relative rotation in proportion to the steering torque into an axial displacement. do.

This displacement of the slider 29 is determined by the slider 2
A differential transformer 31 provided on the outer periphery of the steering wheel 9 with an appropriate gap therebetween converts the signal into an electric signal to obtain a steering torque detection signal. The differential transformer 31 includes a primary winding 31a,
It consists of secondary windings 31b and 31c, both of which are fixed to a pinion case 33. Primary winding 3
An AC pulse signal is applied to 1a from the main controller 32, and analog pulse electric signals are differentially taken out from the secondary coils 31b and 31c. That is, when there is no relative rotation as described above, the slider 29 is at the initial position and the output signals of the secondary coils 31b, 31c are zero. The output signal was starting to change. Therefore, the output signal of the differential transformer 31 is proportional to the relative rotation of the input shaft 26 and the pinion shaft 22a, that is, the steering torque.

A steering rotation detection sensor 40 is provided near the bearing 34 that supports the input shaft 26. As shown in FIG. 2, the steering rotation detection sensor 40 includes a toothed pulley 36 coaxially mounted on the input shaft steering rotation detection sensor 26, a DC generator 37, and a DC generator 37.
A small-diameter toothed pulley 38 fixed to a rotating shaft of the motor is provided, and a timing belt 39 for transmitting the rotation of the toothed pulley 36 to a DC generator 37 via the small-diameter toothed pulley 38. Therefore, the rotational direction and rotational speed of the input shaft 26 can be detected from the output signal of the DC generator 37.

Incidentally, the case 33 and the flange 41 are designed to remove each component of the pinion shaft as described above with flying stones,
This is to protect from dust, water, etc.

The electric motor 49 for generating the auxiliary torque is arranged on the left side of the rack 21 in the drawing. The electric motor 49 is
Consisting of a stator 58, a permanent magnet 59, an armature core 6, an armature winding 61, a commutator 62, and a flange 63, the control device 32 determines the necessary auxiliary torque and rotation based on the detection signals of each detection means 35 and 40. It is controlled by a drive signal that determines the number and sends it out. A rotor rotating shaft 50 of the electric motor 49 is rotatably supported by bearings 55 and 56, and the bearing 56 is further pressed toward the output end by a disc spring 57 from behind. The rotational torque of the electric motor 49 is
A toothed pulley 53 similar to that shown in FIG. is transmitted to the ball screw mechanism. Ball screw mechanism is easy 2
A ball screw 42 integrally formed on the left end of 1;
It consists of two ball nuts 43, 44 separated in the axial direction that mesh with this screw 42, and a ball 45 interposed between the ball screw 42 and the ball nuts 43, 44. An oil seal 43a is provided at one end of the ball nut 43, and a flange 4 is provided at the other end.
An elastic member 43c is provided integrally with the elastic member 3d, and a toothed pulley 43b similar to the pulley 53 is integrally formed on the outer periphery of the elastic member 43c. The diameter of the toothed pulley 43b integrally formed with the ball nut 43 is larger than the diameter of the pulley 53, and the rotation of the electric motor 49 is transmitted to the output end at a reduced speed. Further, the ball nut 43 is rotatably supported within the case 33 by angular contact bearings 46 and 47, and is pressed toward the shaft end by a disc spring 48, reducing the gap between the bearings to almost zero. I have to. At one end of the ball nut 44,
An oil seal 44a is provided, and the other end is crowned with a flange 43d having a bent portion 43e. The ball nut 43 and the ball nut 44 bent and fixed to the flange 43d are connected to each other by compressing an elastic member 43c such as rubber. A ball nut 44 is attached to this elastic member 43c.
rotates in a direction that presses the flange 43d,
After applying an initial load, the flange 43d is bent and the bent portion 43e is fixed to the ball nut 44. That is, the ball nut 44 is used to apply an initial load to zero the gap between the ball nut 43, the ball 45, and the ball screw 42.

A control device 32 that controls such a power steering mechanism is configured as shown in FIG. 3, for example.

In the figure, 70 is a microcomputer unit, and each detection signal S1 to S4 output by the steering torque detection means 72 and the steering rotation detection means 76
is input via the A/D converter 71 at a timing determined by the microcomputer unit itself. Microcomputer unit 70
calculates these detection signals S1 to S4 and drives the electric motor 49 via the drive unit 81 and motor drive circuit 82 to generate an appropriate auxiliary torque. In the figure, 90 is a battery power supply, 91 is an ignition switch, 92 is a fuse, 93 is a relay circuit, and 94 is a constant voltage circuit.

The steering torque detection means 72 includes the above-mentioned steering torque detection sensor 35 and the primary coil 31a of the sensor 35.
The drive unit 73 connected to
4A and 74B, respectively, are provided with low pass filters 75A and 75B. The drive unit 73 appropriately divides the internal clock _T1 of the microcomputer 70 to obtain a rectangular wave or a sine wave.
This current is amplified and supplied to the primary coil 31a. The electric signals obtained by the secondary coils 31b and 31c change depending on the displacement of the slider 29, and each electric signal is rectified by a rectifier circuit,
In order to obtain a more stable DC voltage, high frequency components are removed by low-pass filters 75A and 75B.

The steering rotation detection means 76 includes the DC generator 37 of the above-mentioned steering rotation detection sensor 40 and this generator 3.
7, and includes two subtraction circuits 77A and 77B that detect the direction and magnitude of steering rotation.

Output signals S1~ of these detection means 72, 76
S4 are as shown in FIGS. 4 and 5, respectively, and the microcomputer unit 70 generates the respective difference signals T(=S1-S2) and N( at predetermined timings based on these signals S1 to S4. =
S3-S4) are calculated. These detection signals S1
.about.S4 and the calculation signals T and N are sequentially stored in the memory (not shown) of the microcomputer unit 70. The configuration of the main parts of the microcomputer unit 70 related to the embodiment of the present invention is as follows.
As shown in the figure.

The microcomputer unit 70 includes a return detection means 70B, correction tables 70C, 70D, 70E, and 70F for providing various correction signals, a selection means 70G, and an arithmetic means 70H.

The return detection means 70B is the steering torque detection means 7
2 and the detection signal of the steering rotation detection means 76,
It is detected whether the steering operation is a return operation, that is, whether the direction of the steering torque and the direction of the electric motor torque match. The table 70C determines the duty ratio of the drive voltage of the motor corresponding to the armature current of the motor consumed according to the friction of each gear, etc., based on the steering torque detection signal T=S1-S2. Conversion characteristics as shown in Figure 7
I remember DF. The table 70D determines the duty ratio of the motor drive voltage corresponding to the motor armature current consumed according to the load torque, based on the steering torque detection signal T=S1-S2, and is shown in FIG. The conversion characteristic DT as shown in
I remember. The table 70E determines the duty ratio of the drive voltage of the motor that corrects the armature current of the motor consumed according to the torque during the return operation of the steering system, based on the steering torque detection signal T=S1-S2. , and stores the conversion characteristic DR as shown in FIG. The table 70F determines the duty ratio of the drive voltage of the motor corresponding to the induced electromotive voltage of the motor required according to the rotation speed of the steering system, based on the steering rotation detection signal N=S3-S4, 1st
The conversion characteristic DN as shown in Figure 0 is stored.

The selection means 70G selects tables 70C and 7 depending on whether the steering operation is "go" or "return".
This determines whether to select either 0D or 70E, and in the case of "bound", table 70C,
70D is selected, and in the case of "return", all tables 70C, 70D, and 70E are selected. As a result, the output of the arithmetic means 30H, that is, the signal that the microcomputer unit 70 supplies to the motor drive circuit 82, relates to the steering torque as shown in FIG.

The motor drive circuit 82 is similar to that described in FIG. 15, and includes at least two motors connected in series.
A bridge circuit 1 has four arms in which two series circuits each including switching elements 2, 3 and 4, 5 are connected in parallel, and a power supply voltage of a specific polarity is supplied to a node connecting the two series circuits. Further, the nodes connecting at least two switching elements of each series circuit to each other are connected to the motor 49 as output terminals, and the switching elements 2 and 5 of the bridge circuit 1 are arranged in opposite positions with respect to the series circuit of the bridge circuit 1. Alternatively, 3 and 4 are controlled on and off as a set. In this case, according to the embodiment of the present invention, when the direction of rotation of the steering system caused by the steering operation and the direction of the steering torque match (the forward operation state), one of the switching elements of the set of the electric motor drive circuit 82 2 is turned on, and the other switching element 5 is driven at a duty ratio (DF+DT+DN) determined based on both of the control parameters, and the direction of rotation of the steering system by the steering operation and the direction of the steering torque match. If not (return steering state), one set 2 of the switching elements of the motor drive circuit 82 is driven at a duty ratio (1-Dn) corresponding to the steering rotation speed, and the other switching element 5 is driven at the duty ratio (1-Dn) corresponding to the steering rotation speed. The microcomputer 70 is operated to drive at a duty ratio (DF+DT-DR) corresponding to the operating torque. The operation in this “return operation state” is as follows.
Shown in Figure 2. In figure a, both elements 2 and 5 are PWM.
When the control is on, Figure b shows a case where one 2 is on and the other 5 is off, and Figure c shows a case where both are on.

With this configuration, in the return operation state, as can be seen from FIG. 12c, the electric motor 4
9, the diode 9, the power supply 90, and the diode 7 form a double closed circuit, and the armature current i of the motor 49 can be reduced according to the motor rotation speed n. This phenomenon is shown graphically in FIG. 13. In Figure 13, the horizontal axis is the negative motor rotation speed -
n, the vertical axis and the duty ratio of transistor 2
Du, and the duty ratio Do of transistor 5 is
is used as a parameter.

Here, the curve 130 shows the armature current i flowing through the motor when an arbitrary duty ratio is given to the transistor 5 when the motor rotation speed n is zero, and when the motor rotation speed is a certain negative value. This shows the duty ratio of transistor 2 when the armature current flowing in and the armature current match.

From this curve 130, regardless of the duty ratio of transistor 5, by decreasing the duty ratio of transistor 2 in response to the negative rotational speed of the motor, the armature current of the motor is reduced by transistor 5.
It can be seen that it is given by the duty ratio of

Next, the operation of the above embodiment will be explained with reference to the flowchart of FIG. 14. In the following description, the symbols P ₀ to _{P 37} correspond to the numbers of each step in the flowchart. Also (P ₅ −Y) or (P ₅
-N) indicate cases where the judgment _P5 is positive and negative, respectively.

When the key switch 91 of the ignition key is turned on, power is supplied to the microcomputer unit 70 and other circuits, and control is started P ₀ . First, microcomputer unit 7
At P ₀ , the data in each register and RAM is cleared and becomes the initial state.

Next, read the steering torque detection signals S ₁ and S ₂ sequentially.
_P2 . Here, since the steering torque sensor 35 is constituted by a differential transformer, the relationship with the steering torque detection signals S ₁ and S ₂ is as shown in FIG. 4 described above. After this, the read steering torque detection signal S ₁ ,
Diagnose whether _S2 is normal or not (P3 ₎ , and if normal, proceed to step _P4 . In step _P4 , S ₁ -S ₂ is calculated, and this is set as the steering torque T. Note that the steering torque T is as shown in FIG.

Based on this steering torque T, the rotation direction of the steering system is determined P ₅ . If the steering torque T is negative, the absolute value _of this torque is converted to P ₅ -Y, and the register flag is set to F = 1, which indicates clockwise rotation.
and P ₈ . Also, if the torque T is not negative, P( ₅ −
N), set the register flag to F = 0, which indicates left rotation.
and P ₆ . After setting the flags P ₆ and P ₈ , the process moves to steps P ₉ and P ₁₀ . In step _P9 , the table 1 explained in FIG. 7 is accessed using the absolute value T of the steering torque as an address, and the motor torque control signal representing the duty ratio DF corresponding to the friction torque is called. In step _P10 , the table 2 described in FIG. 8 is accessed using the absolute value T of the steering torque as an address, and the motor torque control signal representing the duty ratio DT corresponding to the load torque is called out.

Next, the amount of change in steering torque A=T-T ₀ is calculated (P _{11 )} , and the current torque value is replaced with the next reference value T ₀ (P _{12 )} . Subsequently, it is determined whether the change amount A is positive or negative (P _{13 )} , and it is determined whether the steering torque is in a decreasing state. When the change amount A is positive (P ₁₃ −N)
In this case, it is determined that there is no return operation state and the duty ratio DR is set to zero P ₁₅ . If the change amount A is negative (P ₁₃ -Y), it is determined that the return operation is in progress,
The table 3 explained in FIG. 9 is accessed as the address of the absolute value T of the steering torque, and the motor torque control signal representing the duty ratio DR for correcting the return torque is called P ₁₄ . After this, the calculation means 70H of the microcomputer unit 70 calculates DF+
DT-DR (=D1) is calculated _P16 .

Next, the steering rotation speed detection signals S ₃ and S ₄ from the steering rotation detection means 76 are sequentially read in P ₁₇ . here,
The detection signals S ₃ and S ₄ from the steering rotation detection means 76 are as follows:
It is as shown in FIG. 5 above. This is set as the steering rotational speed N at step _P18 , and the process moves to step _P19 to determine the direction of the steering rotational speed N. If the rotation N is positive at step P ₁₉ (P ₁₉ =N), the steering rotation direction register graph G is set to 0 to indicate that the steering rotation direction is to the left. If the steering rotation N is negative ( _P19 -Y), absolute value conversion is performed with N=-N in step _P21 ,
P ₂₂ where the register flag is set to G=1 to indicate that the steering rotation direction is to the right. Thereafter, the contents of table 4 whose address is the absolute value N of the steering rotation speed are called up. Table 4 shows the product of the induced electromotive constant k and the rotational speed N _M of the motor 49 in order to determine the rotational speed N _M of the electric motor 49 corresponding to the absolute value N of the steering rotational speed as explained in FIG. That is, a duty conversion value Dn serving as a motor rotation control signal is stored. Therefore, the memory contents corresponding to the address based on the absolute value N of the steering rotation speed, ie, the motor rotation control signal Dn, are called, and the process advances to step _P24 .

In step _P24 , a determination is made between the sign F representing the direction of steering rotation and the sign G representing the direction in which the steering torque is applied. If F=G, then P ₂₄ , since both F and G are in the same direction, it is determined that the steering wheel is being turned in the forward operation state, that is, the steering wheel is being turned against the reaction force from the steering wheel, and step P is executed. ₂₇ , proceed to page ₂₈ . On the other hand, if F≠G, the directions of P ₂₄ , F and G do not match, so there is a return operation state, that is,
It is determined that the steering wheel is being returned due to the reaction force from the steering wheel, and the step
Proceed to P ₂₅ and P ₂₆ .

Here, steps P ₂₅ and P ₂₇ are both the duty ratio of the switching element 5 of the motor drive circuit 82.
Determine the contents of DD, and step P ₂₆ and P ₂₈ .
Both determine the duty ratio DU of the switching element 2 of the motor drive circuit 82.
Specifically, in the return operation state, the duty ratio DD of the switching element 5 is set to D1, and the duty ratio DU of the switching element 2 is set to (1-DN).
shall be. In addition, in the forward operation state, the duty ratio DD of switching element 2 is set to D1+DN,
The duty ratio DU of the switching element 5 is set to 1 (that is, it remains on).

After the above duty ratio determination process,
It sequentially checks P ₂₉ whether the duty ratio DD is zero, and P ₃₀ whether the aforementioned flag F is 1, and determines whether the steering direction is right R or left L.
_P31 , _P32 , _P33 . The direction in which either flag R or L is 1 is the steering direction. After determining the steering direction, the contents of register flags R and L are output according to the determination, and the duty ratios _DD and DU described above are output.
P ₃₅ , which outputs a motor torque control signal corresponding to P 35 .
The result of this control is inputted to the microcomputer 70 as a feedback signal _S5 from the drive circuit 82 ( _P36 ), and is used to diagnose whether or not the electric motor 49 is operating normally ( _P37) . If the diagnosis result is normal,
The control process returns to the beginning.

In the above explanation, an NPN type bipolar transistor was used, but the same applies to a PNP type bipolar transistor, and if an N-channel enhancement type MOS field effect transistor is used, there is an internal reverse diode, so the diode can be reversed. Those skilled in the art can easily infer that there is no need to connect them in parallel.
Furthermore, this invention is not limited to the above-described embodiments and modifications, and various other embodiments and modifications are possible within the technical scope of this invention, and conversions of equivalent components are possible. It is clear to those skilled in the art that this is possible.

(Effects of the Invention) According to the present invention, when the steering operation is in the return operation state as described above, the return characteristic of the steering system is improved by flowing the blocking current generated in the closed circuit to a separate circuit. Therefore, it is possible to obtain an electric power steering device that does not impair steering feeling.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of an electric power steering device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the - arrow in FIG. 1 showing a DC generator, and FIG. 3 is an embodiment of the present invention. FIG. 4 and FIG. 5 are characteristic diagrams of the output signal of the detection means according to the embodiment of the present invention, and FIG. 6 is a block diagram of the electric power steering device according to the embodiment of the present invention. 7 to 11 are characteristic diagrams for explaining the configuration and operation of the microcomputer unit shown in FIG. 6, and FIG. 12 is an electric type according to an embodiment of the present invention. A circuit diagram for explaining the operation of the power steering device, FIG. 13 is a characteristic diagram for explaining the operation of the electric power steering device according to the embodiment of the present invention, and FIG. 14 is a circuit diagram for explaining the operation of the electric power steering device according to the embodiment of the present invention. Flowcharts for explaining the operation of the electric power steering device, FIGS. 15 to 17 are explanatory diagrams of a conventional example. In the drawing, 1 is a bridge circuit, 2, 3, 4, and 5 are switching means, 49 is an electric motor, 70 is an electric motor control signal generation means, 72 is a steering torque detection means,
76 is a steering rotation detection means, and 82 is a motor drive circuit.

Claims (1)

[Claims] 1. An electric motor that generates an auxiliary torque in response to the operation of the steering system, a steering torque detection means that detects the steering torque of the steering system, a steering rotation detection means that detects the steering rotation speed of the steering system, and these steering torques. motor control signal generating means for generating a motor control signal to cause the motor to generate a predetermined auxiliary torque using the steering torque and the steering rotation speed as control parameters based on detection signals from the detection means and the steering rotation detection means; , a closed circuit is operated by the motor control signal of the motor control signal generating means, supplies an on-off voltage of a predetermined duty ratio to the motor, performs PWM control, and a blocking current flows due to the inductance of the motor when the on-off voltage is turned off. In an electric power steering device equipped with an electric motor drive circuit having a motor drive circuit, when the direction of rotation of the steering system and the direction of the steering torque match (a forward operation state), and the direction of rotation of the steering system and the direction of the steering torque match. An electric power steering device characterized in that the blocking current generated in the closed circuit is caused to flow in a separate circuit in the return operation state.