JP3399311B2 - Electric power steering device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention performs a light steering by detecting a steering torque applied to a steering system by a steering torque detecting means and controlling a steering assist force generated by an electric motor according to the detected value. The electric power steering device configured as described above is configured to prevent the driver from feeling uncomfortable especially when a control current abnormality occurs.

[0002]

2. Description of the Related Art As a conventional electric power steering apparatus, for example, there is one disclosed in Japanese Patent Publication No. 6-51475 (hereinafter, simply referred to as a conventional example).

In this conventional example, a steering torque detected by a steering torque detector is input to a microcomputer, and a motor current target value corresponding to the steering torque is input as a motor current detection value via a D / A conversion circuit. The output of the error amplifier is PWM-modulated and supplied to the motor drive circuit.
The motor right drive output or the left drive output of the system is supplied to the motor drive circuit configured by, for example, an H bridge circuit via the interface circuit, and the motor right of one system between the interface circuit and the motor drive circuit is supplied. An AND circuit is inserted into each of the direction drive output and the left direction drive output, and a torque signal direction determination circuit that determines the torque signal direction based on the steering torque detection value of the steering torque detector is inserted into these AND circuits. And the leftward drive signal is supplied, the motor rightward drive output or the motor leftward drive output from the microcomputer and the rightward drive signal or the leftward drive signal output from the torque signal direction determination circuit match. Sometimes the AND circuit is configured to output the right drive output or the left drive output to the motor drive circuit. Electric power steering apparatus is disclosed a.

[0004]

However, in the above conventional electric power steering apparatus, the left and right rotation direction drive signals output from the microcomputer based on the torque detection value and the motor rotation drive direction determination circuit. The AND circuit determines whether there is a match with the left-right direction drive signal output from the AND circuit, and when the two signals match, the rotation drive signal is given to the motor drive circuit. Even if the function of discriminating the direction of rotation is lost due to the influence of, for example, the motor is prevented from rotating in an unexpected direction and the safety can be remarkably improved. Is a current controllable state that is large enough to obtain a rightward drive output or a leftward drive output with the torque signal determination circuit Or microcomputer runaway, the motor current target value based on the steering torque detection value by the abnormality of the control system becomes higher outliers compared to the normal value,
As a result, a large steering assist force is generated by the steering force assist motor, and the steering torque detection value decreases, and the right rotation drive output or left drive output from the torque signal determination circuit is stopped. As a result, the drive current from the motor drive circuit to the motor is stopped, the steering assist force becomes zero, and the steering torque detection value repeatedly increases, which causes self-excited vibration. There is.

Therefore, the present invention has been made by paying attention to the unsolved problems of the above-mentioned conventional example, and it is possible to reliably prevent the occurrence of self-excited vibration due to an abnormality of the control system during steering of the steering wheel. An object is to provide a power steering device.

[0006]

In order to achieve the above object, an electric power steering apparatus according to a first aspect of the present invention is provided.
Steering torque detecting means for detecting a steering torque applied to the steering system, an electric motor for applying a steering assist force to the steering system, and control for controlling the electric current of the electric motor based on the steering torque detection value of the steering torque detecting means. In the electric power steering apparatus having means,
With respect to the current supplied to the motor based on the steering torque value detected by the steering torque detecting means, the steering torque detected
A predetermined value is added to the normal current value set based on the value
The feature is that the allowable upper limit value set to the value is set.

[0007]

Further, the electric power steering apparatus according to claim 2, in the invention according to claim 1, comprising a vehicle speed detecting means for detecting a vehicle speed, wherein, the steering
Different from the normal current value set based on the detected torque value
There are multiple allowable upper limit values that are set by adding the predetermined values.
The plurality of allowable upper limit values are set to the vehicle speed of the vehicle speed detecting means.
It is characterized in that the selection is made based on the detected value .

[0009] Furthermore, the electric power steering apparatus according to claim 3 is the invention according to claim 1 or 2,
The allowable upper limit value for the current supplied to the electric motor when the steering torque detection value of the steering torque detecting means is low is set to a current value at which the electric motor does not rotate due to mechanical friction.

[0010]

According to the first aspect of the present invention, the allowable upper limit value is set for the electric current for the electric motor that generates the steering assist force formed based on the steering torque detection value by the control means. When the target current value supplied to the electric motor that generates steering assist force due to a runaway of the microcomputer or an abnormality of the control system becomes a large abnormal value compared to the normal time, the electric current value supplied to the electric motor reaches the allowable upper limit value. Since the limitation is imposed, it is possible to suppress the generation of a large auxiliary steering force by the electric motor, the steering force becomes small, and it is possible to reliably prevent the occurrence of self-excited vibration.

[0011] Moreover, by the allowable upper limit is set to a value obtained by adding a predetermined value to the normal current value, the allowable upper limit also will be increased according to the increase of the motor current due to an increase in the detected steering torque value Therefore, it is possible to reliably suppress the generation of an excessive steering assist force over the entire steering torque control range .

[0012] According to the invention of claim 2, since be changed in accordance the tolerance upper limit vehicle speed, at a low speed area in need of steering assist force by increasing the allowable upper limit value,
In the high speed region, the effect that the occurrence of self-excited vibration can be reliably prevented by reducing the allowable upper limit value is obtained.

[0013] Furthermore, the invention according to claim 3, since the motor is set to a current value as not rotated by mechanical friction allowable upper limit supplied to the electric motor by the steering torque detection value is low The electric current can be supplied to the electric motor in advance while the steering torque detection value is small, and the responsiveness when generating the steering assist force can be improved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention, in which a steering wheel 1 is connected to an upper end portion of a steering shaft 2, and the steering shaft 2 is supported by a fixed portion and extends downward. The pinion 3 is attached to the lower end thereof.

The pinion 3 meshes with a rack 4 extending horizontally in the vehicle width direction to form a steering gear, and the rotational movement from the steering wheel 1 to the steering shaft 2 causes a linear movement (translational movement) of the rack 4. Is converted to.

Both ends of the horizontally extending rack 4 are connected to the knuckle and the steered wheels 6 via tie rods 5, respectively, and the rack 4 moves horizontally (translational movement), whereby the left and right steered wheels 6 are moved. Is steered.

A ring gear 11 constituting a speed reducer is provided above the pinion 3 of the steering shaft 2.
Is coaxially fixed, a ring gear 10 connected to a drive shaft 9 of a steering assist motor 8 is meshed with this ring gear 11, and the steering assist motor 8 is steered by a duty-controlled pulse current output from a control unit 7 described later. It is controlled to generate a steering assist force according to the torque.

Further, a torque detecting mechanism 12 is provided above the ring gear 11 on the steering shaft 2. The torque detection mechanism 12 includes a torsion bar (not shown) that connects the lower end of the steering shaft 2 and the upper end of the pinion 3, and a steering torque sensor 13 arranged on the outer periphery of the torsion bar.

As shown in FIG. 3, the steering torque sensor 13 has a predetermined neutral voltage V _N when the steering torque is "0" (T _N ).
Is turned to the right (counterclockwise with respect to the input from the pinion 3), the voltage becomes higher than the neutral voltage according to the increase of the steering torque at that time, and the steering wheel 1 is turned to the left (on the day 3 When it is turned clockwise with respect to the input from), the torque detection signal V _T having a voltage lower than the neutral voltage V _N according to the increase of the steering torque at that time is output.

Further, a current detector 14 constituting a current detecting means is attached to the steering assist motor 8, and the current detector 14 detects the actual current flowing through the steering assist motor 8 and determines the actual current. The actual current detection value i including the current signal is supplied to the current control circuit 19 described later.

As shown in FIG. 2, the control unit 7 receives the steering torque detection signal V _T output from the steering torque sensor 13, and controls the rotation direction and rotation speed of the steering assist motor 8. The microcomputer 15 that outputs the target current value i ^* , the limiting current generation circuit 16 that outputs the motor current upper limit value i _MAX based on the steering torque detection signal V _T output from the steering torque sensor 13, and the microcomputer 15 The motor target current value i ^* to be output is compared with the motor current upper limit value i _MAX output from the limited current generation circuit 16, and when the motor target current value i ^* exceeds the motor current upper limit value i _MAX , this is set. Actual motor target current i limited to motor current upper limit value i _MAX
A current limiting circuit 17 that outputs r ^* , and a duty control pulse LP that is pulse-width modulated by a deviation between the motor target current ir ^* output from the current limiting circuit 17 and the actual current detection value i from the current detector 14. And a current control circuit 19 which outputs RP, and a left rotation direction signal LT and a right rotation direction signal RT which are detected based on the steering torque detection signal V _T of the steering torque sensor 13 and have a high level according to the rotation direction. Motor rotation direction detection circuit 20, and AND gate to which the left and right cutting direction signals LD and RD output from the microcomputer 15 and the left and right rotation direction signals LT and RT of the motor rotation direction detection circuit 20 are input. 21L and 21R and these AND gates 21L and 2
The 1R output and the duty control pulses LP and DP output from the current control circuit 19 are input, and a motor drive circuit 22 that controls the rotation direction and rotation speed of the steering assist motor 8 based on these is provided. .

Here, the microcomputer 15 is
Input side interface circuit 15 having a D / D conversion function
a, an arithmetic processing unit (CPU) 15b including a microprocessor unit and the like, a storage device 15c including RAM, ROM and the like, and an output side interface circuit 15d. Then, the steering torque detection signal V _{T of the} steering torque sensor 13 is input to the input interface circuit 15a, and the motor target current value i ^*, which is an analog voltage, for driving the steering assist motor 8 is output from the output interface circuit 15d. In addition to outputting to the current limiting circuit 17, a left-turning direction signal LD and a right-turning direction signal RD indicating a steering assist force generation direction and an energization control signal CS for controlling energization of the motor drive circuit 22 are output to the motor drive circuit 22. To do.

Further, the arithmetic processing unit 15b performs the arithmetic processing of FIG. 6 described later for a predetermined sampling time ΔT (for example, 5 m).
every second sec), the steering torque detection signal V _T of the steering torque sensor 13 is converted into an actual steering torque detection value T, and based on the steering torque detection value T, the storage device 15 is preliminarily stored.
The motor target drive current i ^* is calculated with reference to the target current calculation control map stored in c, the steering direction is determined, and the left and right turning direction signals LD and RD are formed, and these are output side interface circuit 15d. Send to.

Further, the storage device 15c stores in advance a target current calculation control map, an arithmetic expression, a program, etc. necessary for the arithmetic processing of the arithmetic processing device 15b, and is necessary in the arithmetic process of the arithmetic processing device 15b. The calculation results are sequentially stored.

The target current calculation control map is shown in FIG.
As shown in, when the steering torque detection value T is an intermediate of the previously set torque value + T _R and -T _L is the target motor driving current i ^* maintains "0", the steering torque detection value If T is less than or equal to + T case where _R or and -T _L, respectively in accordance with the increase and decrease of the steering torque detection value T is the target motor driving current i ^* is set to increase.

On the other hand, the limiting current generating circuit 16 generates a function.
As shown in Fig. 5, the horizontal axis indicates steering torque detection.
Outgoing signal V_TAnd the vertical axis represents the motor current upper limit value i_MAXTake
Steering torque detection signal V_TIs the neutral voltage V_NSet to a higher value
Specified predetermined voltage V_H1When the above is reached, the steering torque detection signal
V_TMotor current upper limit value i_MAXIs increasing
Steering torque detection signal V_TIs the predetermined voltage V_H2Get bored
Steering torque detection signal V_TIs the neutral voltage V_NThan
Predetermined voltage V set to a low value_L1Steering torque
Detection signal V_TMotor current upper limit value i_MAX
Increases and the steering torque detection signal V increases._TIs the predetermined voltage V_L2Less than
Becomes saturated, and the micro value is calculated based on the steering torque detection value T.
Motor target drive calculated by computer 15 shown by broken line
Moving current i ^*Motor current upper limit value i higher by a predetermined value than
_MAXIs configured to output as an analog voltage
It

The current limiting circuit 17 is a microcomputer.
Motor target current value i output from computer 15^*And control
Motor current upper limit value i output from the current limiting circuit 16
_MAX, And the selection signal SE are input,
Motor target current value when selection signal SE is at low level
i^*When the selection signal SE is at high level,
Flow upper limit value i_MAXTo select the actual motor target current value ir
^*Analog switch 17a that outputs as
Standard current value i^*Indicates that the motor current upper limit value i
_MAXIs input to the inverting input terminal and i^*<I_MAXIs
Low level, i ^*≧ i_MAXHigh level when
Output the selection signal SE to the analog switch 17a.
And a comparator 17b.

Further, the current control circuit 19 has a current limiting circuit.
Actual motor target current value i from path 17 ^*And steering assist motor
The actual current detection from the current detector 18 which detects the drive current of 8
The output value i and is input, and the voltage signal according to these deviations is output.
The error amplifier 19a that outputs the error amplifier 19a
Pulse width modulation (PWM) of the voltage signal output from
Pulse width modulation for forming the duty control pulse signal DP
The output from the circuit 19b and this pulse width modulation circuit 19b
Pulse signal DP to be input and AND gate
The leftward signal LD output from 21L is used as a selection signal.
To the right when input and the left signal LD is low level
From the output terminal to the right direction pulse signal RP
When the left direction signal LD is at a high level,
The pulse signal DP is output from the left output terminal to the left pulse signal.
With an analog switch 19c that outputs as an LD
There is.

Furthermore, the motor rotation direction detection circuit 20
The steering torque detection signal V _T of the steering torque sensor 13 is higher than the neutral voltage V _N of the steering torque detection signal V _N at the time of non-steering at the non-inversion input terminal. The comparator 20R into which the reference voltage E _R set to a value equal to or smaller than the voltage V _H1 is input, and the steering torque detection signal V _T of the steering torque sensor 13 is input to the inverting input terminal at the non-inverting input terminal. The reference voltage E _{L, which} is lower than the neutral voltage V _N of the steering torque detection signal V _T during non-steering and is set to a value equal to or larger than the predetermined voltage V _{L1 of} the limiting current generation circuit 16 described above, is input. And a comparator 20L.

Then, the steering torque is output from the comparator 20R.
Detection signal V_TIs the reference voltage E_RSteer right when higher
The high-level right signal RT indicating that
It is output to the road 21R and the steering torque is output from the comparator 20L.
Detection signal V_TIs the reference voltage E _LLeft maneuver when lower
The high level left signal LT that indicates the rudder is AND
It is output to the circuit 21L.

Further, the motor drive circuit 22 is formed by connecting two switching elements T1 to T4 such as four MOSFETs in series to form two sets of series circuits, and the switching elements T1 and T2 of these series circuits. Between and T3 and T
The steering assist motor 8 is connected between the four terminals and the input sides of the switching elements T1 and T3 are connected to each other, and the negative side is connected to the positive side of the grounded battery 25 via the motor relay 23 and the key switch 24. The output sides of the switching elements T2 and T4 are connected to each other and are grounded via a current detector 18 which is a current detection resistor, so that a so-called H bridge circuit is formed.

The left direction signal and the right direction signal output from the AND circuits 21L and 21R are applied to the switching elements T1 and T3, respectively.
The duty control pulse signals LP and R output from the analog switch 19c of the current control circuit 19 respectively.
P is supplied to each of them, and one end of the relay coil of the motor relay 23 is connected to the NPN transistor 2 as a switching element.
While being connected to the key switch 24 via 6,
The other end is grounded, the energization control signal CS output from the output side interface circuit 15d of the microcomputer 15 is supplied to the transistor 26, and the upstream side of the current detection resistor forming the current detector 18 is connected to the current control circuit 19. Error amplifier 19a.

Next, the operation of the above embodiment will be described with reference to FIG. 6 showing the steering assist control processing procedure executed by the arithmetic processing unit 15b in the microcomputer 15. The steering assist control process of FIG. 6 is executed as a main program. First, in step S1, the energization control signal CS that turns on the motor relay 23 that starts energizing the motor drive circuit 22 is turned on, and then the process proceeds to S2. Then, after the steering torque detection signal T of the steering torque sensor 13 is read, the process proceeds to step S3.

In step S3, the non-steering state, that is, the steering torque is "0" from the read steering torque detection signal V _T.
The steering torque detection value T is calculated from the value obtained by subtracting the neutral voltage V _N , which represents the steering torque detection value T, and then proceeds to step S4 to refer to the control map of FIG. 4 based on the steering torque detection value T calculated in step S3. Then, the target drive current i ^* of the steering assist motor is calculated.

Next, in step S5, it is determined whether or not the steering torque detection value T read in step S2 is negative including zero. If T≤0, it means that the vehicle is in the left-turning state. After making a determination, the process proceeds to step S6, in which the left turning direction signal LD is turned on and the right turning direction signal RD is turned off, and the motor target current value i ^* calculated in step S4 is output. Move to S8,
When T> 0, it is determined that the vehicle is in the right-turning state, the process proceeds to step S7, the right-turning direction signal RD is turned on, and the left-turning direction signal LD is turned off.
After the motor target current value i ^* calculated in step S4 is output, the process proceeds to step S8.

In step S8, it is determined whether or not the steering assist control process is to be ended. If the steering assist control process is to be continued, the process returns to step S2. If the steering assist control process is to be ended, the step is terminated. After shifting to S9, the energization control signal CS for the motor drive circuit 22 is turned off, and the steering assist control process is ended.

Therefore, assuming that the key switch 24 is off and the vehicle is stopped, the power supply of the control unit 7 is cut off in this state.
The motor relay 23 of the motor drive circuit 22 is also turned off, and the power supply to the steering assist motor 8 is cut off.

In this stopped state, the key switch 24 is turned on to turn on the power of each part of the control unit 7, and the microcomputer 15 starts the processing. At this time, in the arithmetic processing unit 15b, as shown in FIG.
The execution of the steering assist control process is started, and the energization control signal CS in the ON state is output to the transistor 26 of the motor drive circuit 22 in step S1.

Therefore, the transistor 26 is turned on, the motor relay 23 is turned on, and the DC power from the battery 25 is started to be supplied to the H bridge circuit. At this time, when the steering wheel 1 is not steered, the steering torque detection signal V _T of the steering torque sensor 13 is substantially the neutral voltage V _N, and when the steering assist control process of FIG. 6 is executed, step S3 is performed. The steering torque detection value T calculated in step 1 is approximately "0".

Therefore, the motor target current value i ^* calculated in step S4 also becomes "0", and step S5
Then, the process proceeds to step S6 to output the high level left turning direction signal LD to the motor drive circuit 22 and the motor target current value i ^* to the current limiting circuit 17.

On the other hand, also in the limiting current generating circuit 16, since the input steering torque detection signal V _T is the neutral voltage V _N , the motor current upper limit value i _MAX becomes "0". Therefore, in the current limiting circuit 17, the motor target current value i ^* and the motor current upper limit value i input to the comparator 17b are input.
_Since both _MAX are zero, the high-level selection signal SE is output to the analog switch 17a, and the analog switch 17a selects the motor current upper limit value i _MAX , which is used as the actual motor target current value ir ^*. Is output to.

In the current control circuit 19, the error amplifier 19a
Since the actual motor target current value ir ^* and the actual current detection value i of the steering assist motor 8 which are both input to are both "0", the output is also "0" and the output of the pulse width modulation circuit 19b is also "duty ratio". 0 ", that is, the off state is maintained.

Further, in the motor rotation direction detection circuit 20,
Since the steering torque detection signal V _T input from the steering torque sensor 13 is the neutral voltage V _N , E ₁ > V _N > E ₂ and both the left rotation direction signal LT and the right rotation direction signal RT become low level, These are AND gates 21L and 2
Since it is supplied to the 1R, the output signals of the AND gates 21L and 21R are at a low level regardless of the levels of the left-turning direction signal LD and the right-turning direction signal RD from the microcomputer 15.
Since they are supplied to the switching elements T1 and T3 of No. 2, both are turned off, current does not flow in the H-type bridge circuit, and the steering assist motor 8 is maintained in the non-energized state.
The steering assist torque generated by the steering assist motor 8 is maintained at "0", and the non-steering state is continued.

In this stopped state, the steering wheel 1
When the so-called stationary steering is performed to right-turn, the steering torque detection signal V _T detected by the steering torque sensor 13 in response to this
Is increased from the neutral voltage V _N , the steering torque detection value T increases in the positive direction when the steering assist control process of FIG. 6 is executed, and the motor target current value i is increased based on the steering torque detection value T. ^* Is calculated.

Since the steering torque detection value T is positive, the process proceeds from step S5 to step S7, the right turning direction signal RD is turned on, the left turning direction signal LD is turned off, and the motor target current is set. Output the value i ^* .

On the other hand, in the motor rotation direction detection circuit 20,
When the steering torque detection signal V _T exceeds the reference voltage E _R , the right direction signal RT output from the comparator 20a becomes high level, and this is input to the AND gate 21R, so that the AND gate 21R is opened and the microcomputer 15 is opened. The left turning direction signal RD from the motor drive circuit 2
2 to the switching element T3.

Further, since the limiting current generating circuit 16 also outputs the motor current upper limit value i _MAX larger than the motor target current value i ^* based on the steering torque detection signal V _T , the comparator 17b of the current limiting circuit 17 outputs it. The output selection signal SE becomes low level and the analog switch 17a
The motor target current value i ^* is selected and is output to the current control circuit 19 as the actual motor target current value ir ^* .

Therefore, the analog switch 19c of the current control circuit 19 outputs the duty control pulse RP having the duty ratio corresponding to the actual motor target current value ir ^* , which is output to the switching element T2. Therefore,
The switching element T3 of the motor drive circuit 22 continues to be in the ON state, and in addition to this, the switching element T2 is turned on / off at the duty ratio of the duty control pulse RP, so that the steering assist motor 8 for right-turning according to the duty ratio is used. Thus, the steering assist motor 8 is rotationally driven to generate the steering assist torque for right-turn according to the steering torque detection signal V _T , so that light steering can be performed.

After that, when the stationary steering is completed, the steering torque detection value V _T returns to the initial state in which it becomes substantially the neutral voltage V _N.
From this state, when the vehicle is driven straight ahead and the steering wheel 1 is steered, the steering direction and the current i having the current value corresponding to the value of the steering torque detection signal V _T of the steering torque sensor 13 are applied to the steering assist similarly to the above. The steering assist torque is generated by being supplied to the motor 8, and light steering can be performed.

In this way, even if the steering torque detection value T increases in the positive or negative direction and either the right turn direction signal RD or the left turn direction signal LD from the microcomputer 15 becomes high level, the motor rotation direction detection is performed. The driving of the steering assist motor 8 is prohibited unless either the right direction signal RT or the left direction signal LT of the circuit 20 becomes high level, so that some abnormality occurs in the microcomputer 15 and the direction determining function is lost. In this case, it is possible to reliably prevent the steering assist motor 8 from generating a steering assist torque in a direction opposite to the steering torque.

On the other hand, program runaway occurs in the microcomputer 15 due to some abnormality, and the motor target current value i ^* calculated based on the detected steering torque value T becomes an abnormal value which is much higher than the normal value. At times, the limited current generation circuit 16 outputs a motor current upper limit value i _{MAX which} is higher than the normal value of the motor target current value i ^* calculated by the microcomputer 15 based on the steering torque detection signal V _T by a predetermined value. Current limit circuit 17
The selection signal SE output from the comparator 17b becomes high level and is supplied to the analog switch 17a, so that the motor target upper limit value i ^* is replaced with the motor target current value i ^* which is an abnormal value in the analog switch 17a. _MAX is selected, and this is input to the current control circuit 19 as the actual motor target current value ir ^* .

At this time, assuming that the right turning direction signal RD is at a high level and the left turning direction signal LD is at a low level from the microcomputer 15 and these are normal, the switching element T3 of the motor drive circuit 22 is The pulse signal RP which is controlled to be in the ON state and whose duty ratio corresponds to the motor current upper limit value i _MAX is selected by the analog switch 19c of the current control circuit 19 and is input to the switching element T2. As a result, the steering assist motor 8 is supplied with a current that is higher than the current value at the normal time but is not enough for the auxiliary steering, and the steering assist motor 8 steers the steering wheel 1 from the normal time. Generates a steering assist torque that is slightly lighter, and the steering assist torque becomes excessive to cause self-excited vibration. It is possible to reliably prevent the occurrence of.

Further, the left turning direction signal RD is at a high level,
Even when the right-turn signal is at a low level, similarly to the above, a steering assist torque larger than the normal steering assist torque is generated, and the occurrence of self-excited vibration can be reliably prevented.

As described above, according to the first embodiment, the motor current upper limit value i based on the steering torque detection signal V _T of the steering torque sensor 13 in the limited current generation circuit 16 is obtained.
_MAX is generated and the motor current upper limit value i _MAX and the motor target current value i ^* calculated by the microcomputer 15 are supplied to the current limiting circuit 17, so that the current limiting circuit 17 compares the two. , Motor target current value i ^*
There when exceeding the motor current upper limit value i _MAX, can be limited to the motor current upper limit value i _MAX, the steering assist motor 8
Therefore, it is possible to reliably prevent the generation of an excessive steering assist torque and prevent the occurrence of self-excited vibration.

Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, the motor current upper limit value i _MAX is changed according to the vehicle speed so that the optimum current limiting function according to the traveling condition of the vehicle is exhibited.

In the second embodiment, as shown in FIG. 7, two limiting current generating circuits 16A and 16B having different characteristics are connected in parallel to the steering torque sensor 13, and the limiting current generating circuits 16A and 16B are connected to each other. The output motor current upper limit values i _AMAX and i _BMAX are input to the analog switch 31 to be selected, the motor current upper limit value selected by the analog switch 31 is supplied to the current limiting circuit 17, and the vehicle speed is pulsed. A vehicle speed sensor 32 for detecting as a signal is provided, the vehicle speed detection pulse P _SP of the vehicle speed sensor 32 is supplied to a frequency-voltage conversion circuit 33 to be converted into a voltage, and this output voltage is supplied to a vehicle speed determination circuit 34 to change the vehicle speed. determine which one of a preset low vehicle speed region and high vehicle speed range, to supply the two selection signals SE _SP indicating the determination result to the analog switch 31 Except that it is configured to have the same configuration as FIG. 2 in the first embodiment.

Here, the limiting current generating circuit 16A is sufficiently larger than the normal motor target current value i ^* calculated by the microcomputer 15 for the steering torque detection signal V _T of the steering torque sensor 13. The allowable current width is set to be large so as to output the motor current upper limit value i _AMAX of the value, and the limiting current generating circuit 16B is set to the limiting current generating circuit 16A.
Motor current upper limit value i of about 1/4
_It is set to output _BMAX .

On the other hand, when the input selection signal SE _SP is at a low level, the analog switch 31 determines that it is in the low vehicle speed region and selects the limiting current generating circuit 16A, and the selection signal SE _SP is at a high level. When the vehicle is in a certain state at one time, it is determined to be in the high vehicle speed region and the limiting current generating circuit 16B is selected.

Further, in the vehicle speed discriminating circuit 34, the output voltage V _SP of the frequency-voltage converting circuit 33 is applied to the inverting input side terminal of the reference voltage V which is set to a threshold voltage corresponding to a predetermined medium vehicle speed.
Comparator 34 in which _M is input to each non-inverting input terminal
has a, low level, V _SP> a high level when a V _M selection signal SE _SP is output to the multiplexer 31 when this comparator 34a is V _SP ≦ V _M.

According to the second embodiment, when the vehicle is stopped or in a low vehicle speed range where the vehicle is traveling at a low speed,
Since the number of vehicle speed detection pulses P _SP detected by the vehicle speed sensor 31 per unit time is small, the output voltage V _SP of the frequency-voltage conversion circuit 33 is “0” or a value lower than the reference voltage V _M according to the vehicle speed. Becomes

Therefore, the selection signal SE _SP output from the comparator 34a of the vehicle speed determination circuit 34 becomes low level, which is input to the analog switch 31, and the analog switch 31 outputs the motor current output from the limited current generation circuit 16A. The upper limit value i _AMAX is selected and input to the current limiting circuit 17.

Therefore, in the low vehicle speed region requiring a large steering assist torque such as stationary steering, the limiting current generating circuit 16A having a wide allowable current width is selected and the motor current upper limit value i _AMAX is set in the current limiting circuit 17. Since a program runaway occurs for some reason in the microcomputer 15 and the motor target current value i ^* becomes an abnormal value that is a large value as compared with the normal state, the steering assist motor 8 causes a margin margin. The steering assist torque can be generated according to the large motor current upper limit value i _AMAX, and it is possible to reliably prevent the occurrence of self-excited vibration and prevent the steering assist torque from feeling insufficient.

Further, when the vehicle is traveling in the high vehicle speed range, the current limit width is within the low vehicle speed range.
Since the limiting current generating circuit 16B set to be smaller than 6A is selected, the steering assist torque becomes excessive in the high vehicle speed region where the self-aligning torque is large and the large steering assist torque is not required, and the self-excited vibration is surely generated. It is possible to reliably prevent the driver from recognizing that the excessive steering assist torque is acting.

In the second embodiment, two limiting current generating circuits 16A and 16B having different characteristics are provided, and the motor current upper limit values i _AMAX and i _BMAX from these limiting current generating circuits 16A and 16B are selected according to the vehicle speed. Although described above, it is needless to say that the present invention is not limited to this, and three or more limiting current generating circuits having different characteristics may be provided and selected according to the vehicle speed.

Further, a third embodiment of the present invention will be described with reference to FIG. The third embodiment is configured to improve the steering response by making it possible to supply current to the steering assist motor 8 within a range where the steering torque is small.

In the third embodiment, as shown in FIG. 8, the motor rotation direction detection circuit 20 and the AND gates 21L and 21 of FIG. 2 in the first embodiment described above.
R is omitted, the left-turn direction signal LD and the right-turn direction signal RD output from the microcomputer 15 are directly supplied to the switching elements T1 and T3 of the motor drive circuit 22, and the storage device 15c in the microcomputer 15 is also provided. As shown in FIG. 9, the target current calculation control map stored in FIG. 9 shows the above-mentioned characteristic line L _{1 of} FIG. 4 and the stop maintaining motor current to the extent that the steering assist motor does not rotate due to the mechanical frictional force of the steering system. The straight line L ₂ maintaining the value i _MIN, and the characteristic of the limiting current generating circuit 16 is that the steering torque detection signal V _T is within the range of the predetermined voltages V _H1 and V _L1 as shown in FIG. sometimes,
With respect to the steering assist motor 8, the above-mentioned stop maintaining motor current value i of FIG. 9 to the extent that the steering assist motor 8 does not rotate due to mechanical frictional force of the steering system including the steering assist motor 8.
Motor current upper limit value i _{MAX0 of} motor current value approximately equal to _MIN
The first described above except that it is configured to output
It has the same configuration as that of the above embodiment.

According to the third embodiment, even in the dead zone where the steering assist motor 8 is not driven in the first embodiment, the steering assist motor 8 is rotated by the mechanical friction force of the steering system. The stop maintaining motor current value i _MIN that does not start is supplied in a rotation direction according to the steering torque detection value T, and when the steering torque detection value T deviates from the dead zone, the steering system is activated. On the other hand, the steering assist torque can be increased, and the response of the steering assist control can be improved.

In each of the above embodiments, the current limiting circuits 16, 16A and 16B and the current limiting circuit 17 are provided.
However, the present invention is not limited to this, and the microcomputer 1 is not limited to this.
A microcomputer different from that of 5 may be separately applied for software processing.

In each of the above-described embodiments, the case where the steering torque sensor 13 outputs an analog voltage that increases or decreases with respect to the neutral voltage V _N has been described, but the present invention is not limited to this, and the steering torque is When it is “0”, a voltage that is “0”, for example, positive (or negative) during right steering and negative (or positive) during left steering, may be output, and in response to this, the current limiting circuit 16 The configuration of the motor rotation direction detection circuit 20 may be changed.

Further, the motor drive circuit 22 is not limited to the above configuration, and any other switching element such as a transistor or a relay can be applied to the switching element forming the H-type bridge circuit.

Furthermore, in each of the above embodiments,
The case where the control map for calculating the target current in the microcomputer 15 is fixed has been described, but the present invention is not limited to this, and a plurality of control maps having different characteristics depending on the vehicle speed are prepared, and these are set as the vehicle speed. It may be selected accordingly.

Furthermore, in each of the above embodiments,
Although the motor current upper limit value i _MAX is set to a value obtained by adding a predetermined value to the motor target current value i ^* as shown in FIG. 5, the present invention is not limited to this. The torque detection signal V _T may be changed in a parabolic manner such that the added value to the motor target current value i ^* gradually increases as the torque detection signal V _T moves away from the neutral voltage V _{N. In} this case, a large steering assist torque is applied. , The motor current upper limit value i
_{Since MAX} also becomes large, there is an advantage that a sufficient steering assist torque can be generated.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a specific example of a control unit shown in FIG.

FIG. 3 is a characteristic diagram showing a relationship between a steering torque of a steering torque sensor and a steering torque detection signal.

FIG. 4 is a control map showing a relationship between a steering torque detection value of a microcomputer in a control unit and a motor target current value.

FIG. 5 is a characteristic diagram showing a relationship between a motor torque upper limit value and a steering torque detection signal of a limited current generation circuit.

FIG. 6 is a flowchart showing an example of steering assist control processing of a microcomputer in the control unit.

FIG. 7 is a block diagram showing a specific example of a control unit similar to FIG. 2 showing a second embodiment of the present invention.

FIG. 8 is a block diagram showing a specific example of a control unit similar to FIG. 2 showing a third embodiment of the present invention.

FIG. 9 is a control map showing a relationship between a steering torque detection value of a microcomputer and a motor target current value in the third embodiment.

FIG. 10 is a characteristic diagram showing a relationship between a steering torque detection signal of a limited current generation circuit and a motor current upper limit value in the third embodiment.

[Explanation of symbols]

1 steering wheel 2 steering shaft 7 control unit 8 Steering assist motor 13 Steering torque sensor 14 Current detector 15 Microcomputer 16, 16A, 16B limiting current generation circuit 17 Current limiting circuit 19 Current control circuit 20 Motor rotation direction detection circuit 22 Motor drive circuit 31 analog switch 32 vehicle speed sensor 34 Vehicle speed discrimination circuit

Claims (3)

(57) [Claims] 1. A steering torque detecting means for detecting a steering torque applied to a steering system, an electric motor for applying a steering assist force to the steering system, and an electric motor based on a steering torque detection value of the steering torque detecting means. in the electric power steering apparatus and a control means for current control, said control means, to the current supplied to the motor based on the steering torque value detected by the steering torque detecting means, the
The normal current value set based on the steering torque detection value
A control device for an electric power steering, wherein an allowable upper limit value set to a value obtained by adding a constant value is set. 2. A has a vehicle speed detection means for detecting the vehicle speed, before
The control means is set based on the steering torque detection value.
Is set to the value obtained by adding a different predetermined value to the normal current value
Multiple allowable upper limit values are set, and the multiple allowable upper limit values are set.
To select based on the vehicle speed detection value of the vehicle speed detection means
The electric power steering device according to claim 1 , wherein the electric power steering device is configured as follows. 3. The allowable upper limit value for the current supplied to the electric motor when the steering torque detection value of the steering torque detecting means is low is set to a current value at which the electric motor does not rotate due to mechanical friction. Item 3. The electric power steering device according to Item 1 or 2 .