JPH107011A - Steering gear - Google Patents

Abstract

(57) Abstract: A switch circuit composed of an H-type bridge is constituted by four FETs, and the current direction is adjusted by one of the pair of FETs sandwiching the electric motor, and the F of the other pair is adjusted.
When the current value is adjusted by ET, among which the current value adjustment FET controls the current value by PWM control according to the duty ratio, an abnormality such as a triangular wave drift occurs in the PWM drive circuit, A repetition of fine overshoot with respect to a target value is detected to prevent the load on the electric motor from increasing. SOLUTION: Control signals S _RL , S _RR to current direction adjusting FET _URL , FET _URR are switched within a predetermined time n ₀ about the repetition time of the overshoot, and a high frequency band not less than a predetermined frequency at that time. When the motor current I _M is equal to or greater than a predetermined value I ₀ corresponding to the maximum current value that can normally appear and continues for a predetermined time m ₀ or more, the fail-safe control signal F / S is set to “1” and the relay is set. 51 is turned off.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering device for assisting the steering of a main steering wheel such as a front wheel by an electric motor, and a main steering wheel such as a front wheel steered by a driver's steering input. Also, the present invention relates to a four-wheel steering device that steers auxiliary steering wheels such as rear wheels with an electric motor in order to improve vehicle motion and vehicle body behavior.

[0002]

2. Description of the Related Art Among such steering devices, there is a four-wheel steering device described in, for example, JP-A-6-219300. According to this four-wheel steering system, the steering angle of the steering wheel is detected as the steering state of the front wheel, which is the main steering wheel, and the auxiliary angle is determined according to the steering angle, the vehicle speed, or the steering angular speed that is the steering speed together with the steering angle. A target steering angle of a rear wheel that is a steered wheel is set, and an actual steering angle of the rear wheel is detected together, so that a deviation between the actual steering angle and the target steering angle is “0” or near the same. A control signal is output from the control unit to an electric motor for steering the auxiliary steering wheel. That is, the actuator constituted by the electric motor operates so as to always follow the target steering angle value set by the control unit.

Incidentally, in order to rotate the electric motor by a predetermined amount in both directions such as forward and reverse in such a feedback control system, a so-called H-type bridge or the like is generally constructed using a power element such as an FET, and the electric motor is One of the power elements of the closed circuit configured to include the current element for adjusting the current direction, and the other power element is regarded as for adjusting the current value, and A drive circuit is provided, and a current direction control signal is output from the control unit to the power element for adjusting the current direction, and the drive circuit is directed to the current direction adjustment power element in response to the current direction control signal. A drive signal is output, and a current value control signal is output from the control unit to the power element for adjusting the current value. From the drive circuit in accordance with the current value control signal to the the current value adjusting power element is configured such that the driving signal is output. The current direction control signal is constituted by a so-called ON / OFF control signal, and the drive circuit to which the current direction control signal composed of the ON / OFF control signal is inputted is amplified as necessary. And output it. Further, the current value control signal is constituted by a so-called duty ratio or the like, and in a drive circuit to which the current value control signal having the duty ratio or the like is inputted, this is controlled by pulse width modulation (Pulse Widt).
h Modulation = PWM).

[0004]

As is well known, the above-described PWM waveform is obtained by comparing an analog value corresponding to a current value control signal including the duty ratio and the like with a reference wave (triangular wave). It is created. However, when an abnormality occurs in which the drift component (DC component) is superimposed on the triangular wave, the triangular wave always becomes larger than the analog value corresponding to the current value control signal, for example. The so-called full duty state where the ratio is close to 100% continues. Therefore, the auxiliary steered wheels tend to overshoot beyond the target steering angle. Of course, the actual steering angle of the auxiliary steering wheel substantially coincides with the target steering angle due to the so-called servo function based on the feedback input of the actual steering angle for a short sampling time. Is repeated, and during this time, a current signal near the maximum current value corresponding to the full duty is continuously supplied to the electric motor, so that the load on the electric motor increases and a large energy loss occurs. Of particular concern is that the device appears to be operating normally.

In order to solve these problems, it is only necessary to monitor at any time whether or not the PWM waveform corresponds to the duty ratio. In general, the PWM waveform has a very high frequency of about 20 kHz. Since the pulse is a short pulse, if the pulse is to be constantly monitored by a control unit including a microcomputer, for example, the frequency of the reading process of the microcomputer increases, and there is a possibility that the essential arithmetic processing may be hindered.

A similar problem is that the rotation direction and the rotation angle of the electric motor are controlled by using the analog switch circuit as described above so that the actual steering angle of the main steered wheels such as the front wheels coincides with the target steering angle. May be generated in the electric power steering device that steers the main steered wheels by the electric motor.

The present invention has been developed in view of these problems, and detects an abnormality of the current value adjusting power element driving circuit for performing the PWM without fail to increase the load on the electric motor and reduce energy consumption. It is an object of the present invention to provide a steering device capable of preventing loss.

[0008]

To achieve the above object, a steering apparatus according to the present invention includes an electric motor for controlling a steering angle of a steered wheel by inputting a current signal whose current direction and current value are adjusted. A current direction adjusting power element that adjusts the current direction of the current signal to the electric motor, and a switch circuit that includes a current value adjusting power element that adjusts the current value thereof; A target steering angle of the steered wheels is calculated, and a current direction control signal and a current value control signal for controlling a current direction and a current value to the electric motor according to a deviation between the target steering angle and the actual steering angle are calculated. A control means for outputting, a current direction adjusting power element driving circuit for outputting a drive signal to the current direction adjusting power element of the switch circuit in response to a current direction control signal from the control means; And a current value adjustment power element driving circuit which outputs a drive signal to the current regulating power element of the switching circuit current value control signal to a pulse width modulation,
Abnormality detection for detecting that at least the current value adjusting power element drive circuit is abnormal when the current direction control signal switches the current direction in a cycle shorter than a predetermined time, and when the current direction control signal continues for a predetermined time; Means.

In the present invention, the object to be steered may be the main steered wheel such as the front wheel or the auxiliary steered wheel such as the rear wheel. However, according to the deviation between the target steered angle and the actual steered angle of the steered wheel. It is assumed that the steering device follows the target steering angle. Therefore, if an abnormality such as a triangular wave drifts occurs in the current value adjusting power element driving circuit that performs pulse width modulation of the current value control signal, the actual steering angle of the steered wheels becomes larger than the target steering angle as described above. Thus, overshoot is repeated in a short cycle. This is because the actual steering angle of the steered wheels does not completely match the target steering angle, and the current value control signal also switches the current value to the electric motor in a short cycle, but at the same time, the current direction control signal also changes. The current direction to the electric motor is switched in a short cycle. Therefore, the abnormality detecting means monitors the current direction control signal that switches the current direction in this short cycle, and since the current direction control signal switches the current direction in a cycle shorter than a predetermined time, the abnormality detection means detects the electric current direction. It is possible to detect a repetition of a short cycle overshoot of the steering wheel steering angle by the motor, and when this continues for the predetermined time, it is possible to detect at least an abnormality in the current value adjusting power element drive circuit. Note that, for example, when the control means is constructed by arithmetic processing or the like executed by a microcomputer provided in a control unit, the current direction control signal is at least as fast as the sampling time of the arithmetic processing,
In the latter case, the switching is performed only in the time including the delay time until the electric motor operates and the steering angle of the steered wheel changes in response to the control signal output in each sampling cycle. The frequency of reading is lower than that of monitoring at any time, so that there is no hindrance to other arithmetic processing executed by the microcomputer or the like in the control unit.

[0010]

As described above, according to the steering apparatus of the present invention, when an abnormality occurs in the current value adjusting power element drive circuit for pulse width modulating the current value control signal, the target steering angle of the steered wheels is reduced. On the other hand, the overshoot of the actual steering angle is repeated in a short cycle, but at the same time, the current direction control signal for switching the current direction to the electric motor in a short cycle is monitored, and the current direction control signal is shorter than a predetermined time. When the state in which the switching of the current direction is performed in a cycle continues for the predetermined time, it can be detected that there is an abnormality in at least the current value adjusting power element driving circuit. Also, according to this, the frequency of reading the current direction control signal is low, and there is no hindrance to other arithmetic processing executed by a microcomputer or the like in the control unit, for example.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a steering device of the present invention is applied to a four-wheel steering device for steering rear wheels as auxiliary steering wheels will be described below with reference to the accompanying drawings.

First, FIG. 1 briefly shows the overall structure of a four-wheel steering system. In the figure, 10FL and 10FR are left and right front wheels serving as main steering wheels, and 10RL and 10RR are left and right rear wheels serving as auxiliary steering wheels. Of which, front wheel 1
A known rack and pinion type steering gear device 14 between 0FL and 10FR via a tie rod 13 respectively.
Connected to the rack shaft. A pinion (not shown) connected to a steering shaft 16 meshes with the rack shaft, and the front wheels 10FL and 10FR can be mechanically steered by rotating the steering wheel 15.

FIG. 2 shows a rear wheel steering device mounted on the vehicle. In the rear wheel steering device 2, the rear wheel 10R
L and 10RR are connected via a tie rod 18 via a steering shaft 20 for rear wheel steering. The actuator unit 1 moves the steering shaft 20 in the left-right direction of the vehicle to assist the rear wheels. It is. The actuator unit 1 constitutes a rear wheel steering device 2 with high efficiency and irreversible characteristics as described later using the electric motor 22 as a power source.

The actuator unit 1 will be briefly described with reference to FIG. 2. The central portion of the steering shaft 20 is housed in a tubular housing 24 so as to be movable in the left-right direction of the vehicle. Steering axis 2
The rack 26 is formed in a part of the “0”. The shaft 29 of the pinion 28 that meshes with the rack 26
The steering shaft 20 projects in the moving direction of the steering shaft 20, that is, in the direction perpendicular to the left-right direction of the vehicle, that is, in the front-rear direction of the vehicle. Further, a hypoid ring gear 30 is coaxially mounted on the pinion shaft 29, and the ring gear 30
A pinion 31 that meshes with is mounted on the rotating shaft 32 of the electric motor 22. Therefore, when the electric motor 22 is rotated, power is transmitted from the pinion 31 to the ring gear 30, the pinion 28, and the rack 26. When the electric motor 22 is rotated in both directions, the rack 26, that is, the steering shaft 20 is moved in the left-right direction of the vehicle. Therefore, the rear wheels 10RL and 10RR, which are auxiliary steering wheels, can be steered synchronously in the left-right direction.

The hypoid gear composed of the pinion 31 and the ring gear 30 used here exhibits the above-mentioned high efficiency and irreversible characteristics. That is, as shown in FIG. 3, the rotational driving force from the pinion 31 side is
Since the gear efficiency with 0 becomes a positive value (about 40%), the ring gear 30 can be rotated in a desired direction. However, even if the ring gear 30 is rotated, the rotation of the pinion 31 depends on the angle of the teeth. Since only a force is generated in the axial direction, the gear efficiency is substantially "0" or less, and neither the ring gear 30 nor the pinion 31 is rotated. Therefore, the rear wheel 10
When inputs such as cornering force and road surface irregularities acting on the RL and 10RR are made, the entirety from the pinion 31 to the rack 26 is locked, so that the rear wheels 10RL and 10RR are locked.
The direction of RR, that is, the steering angle cannot be changed.

Incidentally, reference numeral 9 in FIG.
0 and the rotation angle of the pinion 28, the rotation angle of the electric motor 22, i.e., the rear wheels 10RL, wheel steering angle sensor after consisting rotary potentiometer for detecting the actual rear wheel steering angle [delta] _R of 10RR, also reference numeral 9 ' Is a rear wheel steering angle sensor including a linear potentiometer and the like for detecting the actual rear wheel steering angle from the displacement of the steering shaft 20. Among them, in the present embodiment using a wheel steering angle sensor 9 after the former as the main, used in wheel steering angle control after which will be described below actual rear wheel steering angle [delta] _R. Note that the sub-rear wheel steering angle sensor 9 ′ initializes (initializes) the steering shaft 20 and the rear wheels 10 RL and 10 RR as comparison targets for detecting abnormality of one of the rear wheel steering angle sensors. Used for

Further, the vehicle is provided with a vehicle speed sensor 6 for detecting a longitudinal speed (vehicle speed) V _C of the vehicle, and, if necessary, a lateral acceleration (lateral acceleration) of the vehicle (not shown).
The steering shaft 16 is provided with a steering angle sensor 8 for detecting the steering angle θ of the steering wheel 15. The detection signal of the steering angle θ of the steering angle sensor 8 is a voltage signal that is positive when the steering wheel 15 is turned right and negative when the steering wheel 15 is turned left according to the magnitude of the steering angle. The detection signal of the vehicle speed V of the vehicle speed sensor 6 is
Positive when and for example the vehicle forward according to the size of the vehicle speed, becomes a voltage signal as a negative when retracted, the detection signal of the actual rear wheel steering angle [delta] _R of the rear wheel turning angle sensor 9, the rear left and right wheels 10RL,
It consists of a voltage signal according to the magnitude of the actual rear wheel steering angle from the medium position of 10RR and positive when both rear wheels 10RL and 10RR are turned right, and negative when both left wheels are turned left.

The vehicle also includes the rear wheels 10RL, 10RL.
A control unit 3 for controlling the steering angle of the RR is provided.
Have been. This control unit 3 is shown in FIG.
Input interface having at least an A / D conversion function
Base circuit 40a, central processing unit (CPU) 40b,
Storage device (ROM, RAM) 40c, with D / A conversion function
Having an output interface circuit 40d, etc.
Drive current to the computer 40 and a relay 51 described later
Signal D_{F / S}And a relay drive circuit 41 that outputs
Of the switch circuit 4 to be described,
Current signal I_RL, I_RRProvided to adjust the current direction of
FET (Field Effect Transistor)_{UR L}, FET_URL
Drive signal D to_RL, D_RRDrive circuit 42 that outputs
Of the switch circuit 4 to the electric motor 22
Current signal I_RL, I_RRProvided to adjust the current value of
FET_LRL, FET_LRRDrive signal PWM to_RL, PW
M _RRAnd a PWM drive circuit 43 that outputs the four FEs.
T_URL, FET_URR, FET_LRL, FET_LRRTo H-type
And a switch circuit 4 formed on the ridge. this
In the control unit 3, detection from each of the sensors is performed.
The signal is input and the steering wheel 15
By performing rear wheel steering in the same phase as steering, the vehicle speed in the medium speed range
Control to change steering characteristics to weak understeer direction
To improve turning performance and improve steering characteristics at high speeds.
When turning while changing control to strengthen in the understeer direction,
Improves vehicle stability during lane changes, etc.
Improve the convergence of cornering. Furthermore, mainly in the medium speed range
If a fast steering input is given,
By steering the rear wheels in antiphase, the yaw necessary for turning
-Improvement of the rate rise, response to steering,
That is, the turning performance is improved, and then the same-phase steering of the rear wheels is performed.
Improves running stability during cornering
It is also possible to do.

As described above, the switch circuit 4 is
Four FETs_URL, FET_URR, FET_LRL, FET
_LRRConstitutes an H-type bridge, one end of which is a relay 51.
Connected to battery B via the other end and grounded at the other end.
You. And the FET_URLIs an H-bridge battery
The FET is located on the left side upstream of the B side._URRIs also Batte
The FET is located on the right side of the upstream_LRLIs downstream of the ground side
Is located to the right of_LRRIs located on the left downstream of the ground side.
Of which FET_URLAnd FET_LRRElectric motor between
Connected to one terminal of the_URRAnd FE
T_LRLIs connected to the other terminal of the electric motor 22.
You. Therefore, in this switch circuit 4, the FET_URLas well as
FET_LRLTurns to the left when the electric motor 22 is turned on.
That is, the current signal I in the direction of turning the rear wheel to the left_RLFlow
And FET_URRAnd FET_LRRTurns on when
Electric power is supplied to the motor 22 in a clockwise direction, that is, in a direction in which
Flow signal I _RRFlows (actually FET_LRL, FET_LRR
Is ON / OFF controlled in a short cycle by the PWM drive signal.
Is). The current signal I_RL, I_RRIs a microcontroller
It is also taken into the pewter 40.

The relay drive circuit 41 is a drive signal D _{F / S} for closing the relay 51 when the fail-safe control signal F / S from the microcomputer 40 has a logical value “0”.
Is supplied to the solenoid of the relay 51, and when the fail-safe control signal F / S has the logical value "1", the relay 5
Open 1.

When one of the FET control signals S _RL and S _RR from the microcomputer 40 has a logical value of “1”, the FET drive circuit 42 applies a corresponding FET _URL or FET.
FET drive signals D _RL , D for _turning ON one of _URR
RR is supplied, and when the corresponding FET control signals S _RL , S _RR have a logical value “0”, the corresponding FET _URL , FET _URR are turned off.
Set to F state.

The PWM drive circuit 43 is provided with a duty ratio control signal D / T _RL , D from the microcomputer 40.
/ T _RR is converted to a corresponding analog value, and the PWM value is obtained from the comparison value between this analog value and the reference wave (triangular wave) as described above.
A voltage signal having a waveform is formed, and this is referred to as a PWM drive signal PWM.
_RL and PWM _RR are supplied to the corresponding FET _LRL and FET _LRR .

Next, the arithmetic processing executed by the microcomputer 40 of the control unit 3 will be described with reference to the flowchart of FIG. This calculation process
This is executed as a timer interrupt process for each predetermined sampling time ΔT (for example, 5 msec.). In this arithmetic processing, no step for communication is provided. However, programs and maps stored in the ROM of the storage device 40c and various data stored in the RAM are always stored in the arithmetic processing device 40b. Each calculation result transmitted to a buffer or the like and calculated by the arithmetic processing device 40b is also stored in the storage device 40c as needed.

In this calculation process, first, in step S1
It is determined whether or not the fail-safe flag F / S is in a reset state of “0”, and the fail-safe flag F / S
If / S is in the reset state of "0", then step S
Then, the process proceeds to step S3.

In step S2, the vehicle speed sensor 6
After reading the vehicle speed V _C from the steering wheel and the current value θ _(n) of the steering angle from the steering angle sensor 8, the process proceeds to step S4.
In step S4, using the present value θ _{(n) of} the steering angle read in step S2 and the previous value θ _(n-1) of the steering angle stored in the storage device 40c, according to the following equation: Step S5 after calculating and setting the steering angular velocity θ '
Move to

Θ ′ = | θ _(n) −θ _(n−1) | / ΔT (1) In step S5, the steering angle θ and the vehicle speed V _C read in step S1 and in step S4. Using the calculated steering angular velocity θ ′ and the like, the target rear wheel steering angle δ ^* _R is calculated and set based on the control map of FIG. 6 described in detail later, and then the process proceeds to step S6.

In step S6, the rear wheel steering angle control is performed.
Actual rear wheel steering angle δ which is a detection signal of the sensor 9_RDo you read
Then, the process proceeds to step S7. In the step S7,
The target rear wheel steering angle δ according to the equation (2)^* _RAnd the actual rear wheel steering angle δ _RWhen
Rear wheel steering angle deviation Δδ_RAnd then proceed to step S8.
Run. Note that this rear wheel steering angle deviation Δδ_RAfter the above
Wheel turning angle δ_RFrom the definition of, turn right when positive
Means that you need to.

Δδ _R = δ ^* _R− δ _R (2) In step S8, the rear wheel steering angle deviation Δδ _R calculated in step S7 is any value with respect to “0”. or it determines, when the rear-wheel steering angle deviation .DELTA..delta _R is "0", the process proceeds to step S9, the rear-wheel steering angle deviation .DELTA..delta
_R is migrated to step S10 if it is positive, when the rear-wheel steering angle deviation .DELTA..delta _R is a negative value step S1
Move to 1.

On the other hand, in step S3, the process proceeds from the rear wheel steering angle deviation Δδ _R "0" to the step S9. In step S9, the FET control signal S _RL ,
Both _SRRs are set to the logical value "0", and after outputting them, the process proceeds to step S12.

In step S12, the duty ratio control signals D / T _RL and D / T _RR are both set to “0”%, and after outputting them, the process proceeds to step S13.
The setting in step S10, since it is necessary to the right turn the rear wheels, the FET control signal S _RL and sets the logical value "0", the logical value "1" both FET control signal S _RR And output them, then step S
Go to 14.

In step S14, the duty
Ratio control signal D / T_RLIs set to “0”%, and
Rear wheel steering angle deviation Δδ_RConsider system responsiveness using
From the relational expression determined by the dynamic characteristics of the electric motor 22,
Duty ratio control signal D / T _RRCalculate and set them
After the output, the process proceeds to step S13.

In step S11, since it is necessary to turn the rear wheel to the left, the FET control signal S _RR
Is set to the logical value “0” and the FET control signal S _RL
Are set to the logical value "1", and after outputting them, the process proceeds to step S15.

In the step S15, the duty
Ratio control signal D / T_RRIs set to “0”%, and
Rear wheel steering angle deviation Δδ_RConsider system responsiveness using
From the relational expression determined by the dynamic characteristics of the electric motor 22,
Duty ratio control signal D / T _RLCalculate and set them
After the output, the process proceeds to step S13.

In step S13, the present value S of the FET control signal stored in the storage device 40c is set.
_{RL (n)} and S _{RR (n)} are _{respectively set} to the previous values S _{RL (n-1)} and S _{RR (n-1)}
Is updated and stored.

Next, the process proceeds to step S16, in which the FET control signals S _RL and S _RR set in steps S9 to S11 are respectively _replaced by the current value S _{RL (n)} of the FET control signal.
After updating and storing as S _{RR (n)} , the program returns to the main program.

Next, the operation of the arithmetic processing of FIG. 5 will be briefly described with the behavior of the vehicle. First, the target rear wheel steering angle δ ^* _R calculated and set in steps S2, S4, and S5 of the calculation processing in FIG. 5 is as described above, but the purpose of the setting will be briefly described. The target rear wheel steering angle δ ^* _R is basically, for example, the steering angle θ and the vehicle speed V
_The target yaw rate ψ ′ determined by _C is set to be achieved. However, as shown in FIG. 7, the vehicle characteristics in the steady state are changed from neutral steer to low understeer characteristics in a low speed range, and the understeer is strengthened in a middle and high speed range, thereby achieving both stability and maneuverability at each vehicle speed. Try to let it. In addition, in a transition period such as an initial turn, an end of turn, or a lane change, the responsiveness and followability of the vehicle to the driver's steering are improved,
Attempts to obtain characteristics with less fluctuation.

Therefore, as in the rear wheel steering angle generation mode shown in FIG. 8, in slow steering or constant steering, the rear wheels respond to the steering angle θ regardless of the vehicle speed except at extremely low speeds. Steering is performed only in the same phase (a state in which the vehicle is steered in the same direction as the front wheels) (control for increasing running stability by understeer characteristics). On the other hand, at the time of fast steering, the steering is performed in the opposite phase immediately after the start of steering according to the steering angular velocity θ ′ of the steering, thereby increasing the yaw rate to provide maneuverability such as responsiveness and followability, and then quickly. By inverting to the same phase side to make a steady steering angle,
Reduces wander and enhances stability. In addition, at the time of such a fast steering, the weighting of the opposite phase component (A) immediately after the start of the steering and the stationary in-phase component (B) is changed according to the vehicle speed V _C. More specifically, by increasing the weight coefficient of the antiphase component (A) and increasing the weight coefficient of the in-phase component (B) at higher speeds, the maneuverability in the medium speed range and the stability in the high speed range are improved. Balance with sex. Put this together,
The control map in FIG. 6 shows the target rear wheel steering angle δ ^* _R on the time axis. However, the map or table actually used in the computational processing, the steering angle theta is the main variable, the vehicle speed V _C and the steering angular velocity theta 'is used as a parameter. Although not adopted in detail in the present embodiment, the lateral acceleration can be detected or estimated as described above, and the rate of increase of the steering angle of the rear wheels can be changed according to the magnitude of the lateral acceleration. . As a result, the turning performance of the vehicle can be obtained as intended by the driver during the period from entry to exit during high-speed turning.

Then, step S7 of the calculation processing of FIG.
Then, a rear wheel steering angle deviation Δδ _R is calculated from a difference value between the target rear wheel steering angle δ ^* _R and the actual rear wheel steering angle δ _R, and in the next steps S8 to S15, the control signal to each of the FETs is calculated. Is formed and output. Among, FET control signal S _RL in step S9 when the rear wheel steering angle deviation .DELTA..delta _R is "0",
Since both _SRRs are set and output to the logical value "0", both the FET _{UR L} and the FET _URR of the switch circuit 4 are turned off, and in the next step S12, the duty ratio control signals D / T _RL and D / T _Since both _RR are set to "0"%, both the FET _LRL and the FET _LRR of the switch circuit 4 are turned off, so that neither the current signal I _RL nor I _RR is supplied to the electric motor 22, the relationship of the gear efficiency, the steering angle of the rear wheels is maintained at the actual rear wheel steering angle [delta] _R at that time.

Further, when the rear wheel steering angle deviation .DELTA..delta _R is a positive value that needs to be right clipper, FET in step S10
Since only the control signal _SRR is set and output to the logical value "1", only the FET _{URR of the} switch circuit 4 is turned on, and in the next step S14, the duty ratio control signal D
/ T _RR is set and output to a value corresponding to the magnitude of the rear wheel steering angle deviation Δδ _R from the relational expression taking into account the dynamic characteristics of the electric motor, so that the FET _{RR of the} switch circuit 4 becomes P
It is ON / OFF controlled by a PWM drive signal PWM _RR from WM driving circuit 43, so that the electric motor 22, the right turn current signal I _RR is supplied in accordance with the magnitude of the duty ratio control signal D / T _RR The rear wheel is turned right.

On the other hand, if the rear wheel steering angle deviation Δδ _R is a negative value that needs to be turned left, at step S11 the FET
Since only the control signal _SRL is set and output to the logical value "1", only the FET _{URL of the} switch circuit 4 is turned on, and in the next step S15, the duty ratio control signal D
/ T _RL is set and output to a value corresponding to the magnitude of the rear wheel steering angle deviation Δδ _R from the relational expression considering the dynamic characteristics of the electric motor, so that the FET _{RL of the} switch circuit 4 becomes P
It is ON / OFF controlled by a PWM drive signal PWM _RL from WM driving circuit 43, so that the electric motor 22, the left turn current signal I _RR in accordance with the magnitude of the duty ratio control signal D / T _RR is supplied The rear wheel is turned right.

In any case, the duty ratio control signals D / T _RL and D / T _RR are set from a relational expression corresponding to the dynamic characteristics of the electric motor in consideration of the system responsiveness. The required target rear wheel steering angle δ _R ^* is quickly achieved. Also, any chance, if the actual rear wheel steering angle [delta] _R is as had overshoots the target rear-wheel steering angle [delta] _R ^*, to the sign of the rear wheel steer angle deviation .DELTA..delta _R is reversed , The target rear wheel steering angle δ _R ^*
There is achieved as the actual rear wheel steering angle [delta] _R. Switching of the steering angle direction of the rear wheels at the time of such overshoot is performed at intervals of about 15 msec. From the system response.

Next, the operation of the microcomputer 40 of the control unit 3 for detecting an abnormality in the rear wheel steering device will be described with reference to the flowchart of FIG. This calculation process is executed as a timer interrupt process for each predetermined sampling time ΔT (for example, 5 msec.), Which is equivalent to the calculation process of FIG. Also in this arithmetic processing, the programs and maps stored in the ROM of the storage device 40c and various data stored in the RAM are always transmitted to the buffer and the like of the arithmetic processing device 40b. The calculation results calculated in are also stored in the storage device 40c at any time.

In this calculation process, first, in step S21, the switching time counter n is incremented. Next, the process proceeds to step S22, where the logical sum of the current value _{SRL (n )} and the previous value _{SRL (n-1)} of the left turn FET control signal is "1".
Is determined, and if the logical sum of the two is “1”, the process proceeds to step S23, and if not, the process proceeds to step S24.

In step S23, the right-turn F
It is determined whether or not the logical sum of the current value S _{RR (n)} and the previous value S _{RR (n−1)} of the ET control signal is “1”, and if the logical sum of both is “1”. Then, the process proceeds to step S25, and if not, the process proceeds to step S24.

In the step S25, it is determined whether or not the switching time counter n is equal to or less than a predetermined count value n ₀ corresponding to the switching time at the time of the overshoot. Value n
If it is ₀ or less, the process proceeds to step S26, and if not, the process proceeds to step S27.

In the step S26, the switching time counter n is cleared to "0", and then the process proceeds to a step S28. In the step S28, the motor current I
_After reading _RL and _IRR , the process proceeds to step S29. At this time, the motor current I _RR for turning the electric motor 22 right is a positive value, and the motor current I _RL for turning left is a negative value.

In step S29, the actual motor current I as the effective current value of the electric motor 22 is calculated according to the following three equations.
After calculating _M , the process proceeds to step S30. In step S30, a high-pass filter is applied to the actual motor current I _{M at} a predetermined cutoff frequency ω ₀ (eg, about 25 Hz) corresponding to a cycle longer than the cycle at which the current to the electric motor 22 is actually switched. (H, P, F) processing to perform high frequency band (high band in the figure) motor current I
After calculating the _MHB , the process _proceeds to step S31.

In step S31, the absolute value | I _MHB | of the high frequency band motor current is
Determines whether a preset predetermined value I ₀ or more to a maximum value of approximately normal current value flowing to 2, the absolute value of the high frequency band motor current | I _{MH B} | a predetermined value I ₀ or more If so, the process proceeds to step S32; otherwise, the process proceeds to step S33.

In step S32, the number of times of switching counter m is incremented, and then the flow shifts to step S34. On the other hand, in the step S27, the switching time counter n is cleared to "0" and then the step S3
Move to 3.

In the step S33, the number-of-times-of-switching counter m is cleared to "0", and the process proceeds to the step S24. In the step S34, the switching number counter m is equal to or a predetermined overshoot duration corresponding predetermined count value m ₀ or more, the switching number counter m is a predetermined count value m ₀ or more In this case, the process proceeds to step S35, and if not, the process proceeds to step S24.

In step S35, the fail safe control signal F / S is set to the logical value "1" and output, and then the program returns to the main program. In step S24, the fail safe control signal F / S is set to the logical value "0" and output, and then the process returns to the main program.

Next, the operation of the arithmetic processing of FIG. 9 will be described. First, the PWM drive circuit 43 converts, for example, the duty ratio control signal D / T output by the arithmetic processing of FIG. 5 into an analog voltage value corresponding to the duty ratio. When the analog voltage value corresponding to the duty ratio control signal D / T is as shown in FIG. 10A, the analog voltage value and the triangular wave voltage signal are taken into a comparator (not shown). And
In this case, when the triangular wave voltage signal is equal to or higher than the analog voltage value corresponding to the duty ratio control signal D / T, the logical value is Hi;
The driving signal PWM is output.

However, even if the analog voltage value corresponds to the equivalent duty ratio control signal D / T,
When an abnormality such as the drift component superimposed on the triangular wave voltage signal occurs in the PWM drive circuit 43 as in b, the situation in which the triangular wave voltage signal is always larger than the analog voltage value continues, and as a result, the PWM drive signal PWM has a so-called The electric motor 2 outputs a current signal I having a large current value such as full duty.
2 As a result, as described above, the current signal I having an excessively large current value with respect to the originally small current value
There is supplied to the electric motor 22, rotation angle, i.e. the actual rear wheel steering angle [delta] _R of the electric motor 22 results in overshoot.
In contrast, in the arithmetic processing of FIG. 5, since a measured value the actual rear wheel steering angle [delta] _R may exceed the target rear-wheel steering angle [delta] _R ^*, is so-called steering angle servo in subsequent processing functions the actual rear wheel steering angle [delta] _R to converge to the target rear-wheel steering angle [delta] _R ^* Te. However, even at this time, will be actually current signal I is excessively large current value to the electric motor 22 continues to be repeatedly supplied, as described above, the actual rear wheel steering angle [delta] _R, seemingly normal operation In fact, it is merely converging to the target rear wheel steering angle δ _R ^* by repeating small and short overshoots, so that the electric motor 22 is continuously supplied with excess current. Become.

Therefore, in the arithmetic processing of FIG.
In step S21, the switching time counter n is incremented.
After that, in steps S22 and S23, the electric motor
It is determined whether the current direction to the motor 22 has been switched.
That is, in the calculation processing of FIG.
When switching the flow direction, the FET control signal S_RL, S_RRof
Change the logical value from “0” to “1” or from “1”
Since it switches to "0", when switching the current direction
Is the current value S of the FET control signal._{RL (n)}, S_{RR (n)}And its
Previous value S_{RL (n-1)}, S_{RR (n-1)}Is always "1"
become. Here, left turn FET_URLOr FE for right turn
T_URRIs considered alone, the FET control signal
This time value S_{RL (n)}, S_{RR (n)}And its previous value S_{RL (n-1)},
S_{RR (n-1)}When the logical sum of is equal to "1",
For example, when left-turning continues or right-turning continues
To the electric motor 22, such as when
It may not be at the time of current direction switching, but both FEs
The current value S of the T control signal_{RL (n)}, S _{RR (n)}And its previous value S
_{RL (n-1)}, S_{RR (n-1)}And "1" at the same time
The reason is that the current direction to the electric motor 22 is switched as described above.
There is no other time than to mess around.

Then, when the current direction to the electric motor 22 is switched as described above, the flow shifts to step S25, and the switching time counter n which has been incremented up to that time is set to a short period to cope with the overshoot. When the count value is equal to or less than a predetermined count value n ₀ corresponding to a switching time of the current signal I to the electric motor switched by the above, an abnormality such as the triangular wave signal drift is caused by the PWM drive circuit 43.
Then, the process proceeds to step S26. In step S26, after clearing the switching time counter n, the next step S28, in step S29, to calculate the actual motor current I _M in which the influence of such regenerative current. Then, in the next step S30, a high frequency band motor current I _MHB is calculated by performing a high-pass filter process of the predetermined cutoff frequency ω _{0 on} the actual motor current I _M. Here, the high-pass filter processing is performed on the actual motor current I _M , as described later, because the absolute value | I _M | of the actual motor current is a predetermined value I that normally appears and corresponds to the maximum current value to the electric motor 22. ₀ or more, the repetition of the short and small overshoot, that is, the repetition of the switching of the current direction to the electric motor 22 in a short cycle is regarded as abnormal. This is because the current I _M is excluded and only the situation where the current direction to the electric motor 22 is actually repeated in the short cycle is extracted.

Next, as described above, if the absolute value | I _MHB | of the high frequency band motor current is equal to or greater than the predetermined value I ₀ , the current signal I to the electric motor 22 is switched at the short cycle. In addition, since the current value is equivalent to the maximum current value to the electric motor 22 at which the current value can normally appear, in this case, the switching counter m is incremented in the next step S32. Then, this switching counter m
Is greater than or equal to a predetermined count value m ₀ , the fail-safe control signal F / S is set to a logical value “1”, and this is output to the relay drive circuit 41. Then, the relay drive circuit 41 to which the fail-safe control signal F / S having the logical value “1” is input outputs the drive signal D _{F / S} which is an OFF signal toward the solenoid of the relay 51. Is turned off, and no power is supplied to the switch circuit 4 itself including the electric motor 22,
The rear wheel steering device 2 enters a fail-safe state.

Here, in this embodiment, the predetermined count value m ₀ for counting up of the switching number counter m is
For example, the number of times of switching due to overshoot of the current signal I to the electric motor 22 which is repeated during about 10 minutes in the actual running time is set. This assumes the following case. That is, for example, when small correction steering continues when the corners are running at high speed in a so-called winding, for example, the switching of the current signal I to the electric motor 22 also occurs frequently.
Generally, it occurs when the vehicle is turning around one corner, and does not occur at a straight line between adjacent corners. Therefore, if the predetermined count value m ₀ for counting up of the switching counter m is set to a large value,
The switching of the current signal I to the electric motor 22 which occurs even when the PWM drive circuit 43 has no abnormality is not erroneously determined to be an abnormality of the PWM drive circuit 43. In step S31, the high-frequency band motor current | I _MHB | is set to the predetermined value I ₀ corresponding to the maximum current value.
The determination as to whether or not this is the case can also detect that the actual motor current I _M normally generated by the corrective steering in such winding is not so large as to correspond to the maximum current value. Even if the counter m counts up with the predetermined count value m ₀ , the actual high frequency band motor current | I _MHB |
There is said PWM drive circuit 43 unless the maximum current value corresponding to the predetermined value I ₀ or is abnormal is not determined. Therefore, in the present embodiment, regardless of the running state, the PWM
The abnormality of the drive circuit 43 is determined by determining the switching timing of the current signal I to the electric motor 22, the motor current I _{M at} that time,
And whether or not it has continued for a predetermined time can be accurately detected, thereby preventing the load of the electric motor 22 from becoming too large, and
Energy loss can be suppressed and prevented.

As described above, the FET _URL , F shown in FIG.
ET _URR corresponds to the current direction adjusting power device of the present invention, and similarly, FET _LRL and FET _LRR shown in FIG.
Corresponds to a power element for current value adjustment, and the arithmetic processing and the microcomputer 40 in FIG. 5 correspond to control means,
The FET drive circuit 42 shown in FIG. 4 corresponds to the current direction adjusting power element drive circuit, and the PWM drive circuit 43 shown in FIG.
Corresponds to the current value adjusting power element driving circuit, and the entire arithmetic processing in FIG. 9 corresponds to the abnormality detecting means.

In the above embodiment, only the so-called four-wheel steering system or the rear wheel steering system in which the rear wheels are steered by an electric motor has been described in detail. However, the present invention is applied to the case where the front wheels are the main steering wheels. The present invention can be similarly applied to an electric motor power steering device that assists wheel steering with an electric motor. However, the switch circuit for adjusting the rotation direction and the rotation angle of the electric motor includes a power element such as an FET that is opened / closed by the rotation direction drive signal and the magnitude of the current value by the PWM drive signal as described above. F adjusted
Needless to say, a power element such as ET must be provided.

In the above-described embodiment, the case where a microcomputer is applied as the control unit 3 has been described. Alternatively, an electronic circuit such as a counter and a comparator may be combined.

[Brief description of the drawings]

FIG. 1 shows an example of a vehicle capable of four-wheel steering to which a steering device according to the present invention is applied, wherein (a) is a schematic configuration diagram of the entire vehicle, and (b) is a schematic configuration diagram of an actuator.

FIG. 2 is a detailed explanatory view of the actuator of FIG. 1;

FIG. 3 is an explanatory diagram of irreversible characteristics of the actuator of FIG. 2;

FIG. 4 is an explanatory diagram of a configuration of a control unit in FIG. 1;

FIG. 5 is a flowchart illustrating an example of a calculation process for rear wheel steering executed by the control unit in FIG. 4;

FIG. 6 is a control map for calculating and setting a target rear wheel steering angle in the calculation processing of FIG. 5;

FIG. 7 is an explanatory diagram of a steering characteristic of a vehicle according to a target rear wheel steering angle set by the control map of FIG. 6;

FIG. 8 is an explanatory diagram of a target rear wheel steering angle set by the control map of FIG. 6;

FIG. 9 is a flowchart showing an embodiment of a calculation process for detecting a drive circuit abnormality executed by the control unit of FIG. 4;

FIG. 10 is an explanatory diagram of the operation of the calculation processing in FIG. 9;

[Explanation of symbols]

 1 is an actuator unit 2 is a rear wheel steering device 3 is a control unit 4 is a switch circuit 6 is a vehicle speed sensor 8 is a steering angle sensor 9 is a rear wheel steering angle sensor 10 FL to 10 RR is a front left wheel to a rear right wheel 15 is a steering wheel 20 The steering shaft 22 is an electric motor 40 is a microcomputer

Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B62D 113: 00 137: 00

Claims (1)

[Claims] An electric motor for controlling a steering angle of a steered wheel by inputting a current signal in which a current direction and a current value are adjusted, and a current direction adjustment for adjusting the current direction in a current signal to the electric motor. A switching circuit including a power element for adjusting the current value and a power element for adjusting the current value, and calculating a target steering angle of the steered wheels at least according to a steering state. Control means for outputting a current direction control signal and a current value control signal for controlling a current direction and a current value to the electric motor in accordance with a deviation from an angle; and a current direction control signal from the control means. A current direction adjusting power element driving circuit for outputting a driving signal to the current direction adjusting power element of the switch circuit; and a current value control signal from the control means, which is pulse width modulated to control the power of the switch circuit. A current value adjusting power element drive circuit for outputting a drive signal to the current value adjusting power element; and the current direction control signal switches the current direction in a cycle shorter than a predetermined time, and the switching is performed for a predetermined time. An abnormality detecting means for detecting at least an abnormality in the current value adjusting power element drive circuit when the operation is performed.