JPS6185280A - Four wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To detect real abnormality by obtaining a variation between two continuous sampling values of A/D convertor and deciding to be abnormality if abnormal variation higher than predetermined level has occurred more than predetermined times within predetermined time thereby removing independent disturbance. CONSTITUTION:Analog output current from steering ratio sensor 57 is converted through A/D converter 60 into digital signal which is fed to control means F. The control means F will set the maximum allowable variation of sampling value on the basis of the maximum variation of sampling value during two continuous samplings through A/D converter 60 under normal state while consid ering the influence of noise. Furthermore, it is decided whether abnormal varia tion exceeding over said maximum allowable value has occurred more than predetermined times within predetermined continuous samplings and if the answer is YES, it is decided to be abnormality of steering ratio sensor 57 by means of abnormality detecting circuit 61.

Description

[Detailed description of the invention] [Industrial application fields] The present invention relates to a four-wheel steering system for a vehicle.

[Prior Art] In vehicles such as automobiles, four-wheel steering devices are well known in which both front wheels and rear wheels are steered when a steering wheel is turned. By the way, in such a four-wheel steering system, the required characteristic of the rear wheel steering ratio, that is, the ratio of the rear wheel steering angle to the steering angle of the steering wheel, differs depending on the vehicle speed, etc. A vehicle equipped with a steering ratio changing device that can change the steering ratio of the rear wheels accordingly has been proposed (see Japanese Patent Laid-Open No. 59-92263).

That is, as shown in FIG. 7, this four-wheel steering system sets the maximum negative steering ratio corresponding to zero vehicle speed, and gradually changes the steering ratio toward the maximum positive value as the vehicle speed increases. In low speed ranges, the rear wheels are steered in the opposite direction (in opposite phase) to the steering direction of the steering wheel, while in high speed ranges, the rear wheels are steered in the same direction (in phase) as the steering direction of the steering wheel. This is how it was done.

By the way, in the above-mentioned four-wheel steering system, when a steering ratio sensor that transmits an analog signal, such as a button wheel meter, is used to detect the steering ratio of the rear wheels, the analog signal is transmitted to an A/D converter. The signal is input to the control means for controlling the operation of the steering ratio changing device. Incidentally, such analog signals often contain noise.

In particular, automobiles tend to generate noise due to the ignition system, etc., and if abnormal signals caused by such noise are dealt with every time, it is difficult to ensure smooth operation of the steering ratio changing device.

On the other hand, if the steering ratio sensor itself is abnormal or the steering ratio sensor and A/D
It is important to remove the coupler that connects the converter.If an error actually occurs in the equal steering ratio sensor, the steering ratio change control will not be performed effectively, which will worsen the steering feel of the steering wheel, and in severe cases. There is a problem in that it can lead to accidents.

[Object of the Invention] The present invention has been made in view of the above-mentioned problem, and since there is an upper limit to the speed at which the steering ratio is changed in the steering ratio changing device, it is difficult for the analog two steering ratio sensors to operate normally. The rate at which the analog output signal of the steering ratio sensor changes is relatively small when the steering ratio sensor is
The amount of change between When an abnormality such as a dropout occurs, the amount of change in the sampling value in the A/D converter becomes large and large, and we focused on the fact that such abnormal changes are observed continuously during multiple samplings. The purpose of this invention is to quickly detect a true abnormality in the steering ratio sensor after excluding any external disturbances.

[Structure of the Invention J] Therefore, the present invention calculates the amount of change between the sampling values during two consecutive samplings in the A/D conversion means (A/D converter), and determines the amount of change between the sampling values at the time of two consecutive samplings in the A/D conversion means (A/D converter). An abnormality determining means is provided for determining an abnormality when an abnormal change occurs a predetermined number of times or more.

[Effects of the Invention] According to the present invention, when an abnormality such as disconnection of a coupler occurs in the steering ratio detection means (steering ratio sensor), it can be quickly detected by the abnormality determination means.
The safety of this type of four-wheel steering device can be improved.

Further, since the abnormality determining means determines that the steering ratio detecting means is abnormal only when an abnormal change of a predetermined level occurs a predetermined number of times or more within a predetermined time, it is determined that the steering ratio detecting means is abnormal. Even if a one-off abnormal change occurs, it is not immediately assumed to be an abnormality in the steering ratio detection means, but it is possible to accurately determine an abnormality in the steering ratio detection means.

[Example] Hereinafter, the present invention will be described in detail based on the accompanying drawings.

As shown in FIG. 2, a steering mechanism A having a handle 1 is linked to a front wheel steering mechanism B that steers front wheels 2R and 2L, and the front wheel steering mechanism B includes a long intermediate rod 3, a rear wheel 4,
Steering ratio θd of R94L 1 to 4 = Ratio of steering ratio θd of rear wheels 4R, 4L to steering angle θH of rehandling 1 = θ / Steering ratio changing device C that changes θH and bent control rod 5 It is linked to a rear wheel steering mechanism E having a hydraulic power steering mechanism. Then, by steering the handle l, the front wheel 2
R and 2L are always steered at a constant steering ratio with respect to the steering angle OH of the steering wheel l, and the rear wheels 4R and 4L are controlled by the vehicle speed sensor 6.
The vehicle is steered at a steering ratio θd corresponding to the vehicle speed calculated by a control means (for example, a microcomputer) F based on a vehicle speed signal from the vehicle.

The front wheel steering mechanism B has a rack 10 that meshes with a pinion 8 provided at the lower end of the steering shaft 7 of the steering mechanism A, a relay rod 11 that is moved laterally by rotation of the handle 1, a front wheel 2R, Knuckle arm 12R1+2L supporting 2L, and the knuckle arm 1
2R, +2L and both ends of the relay rod II are rotatably connected, and as the relay rod 11 is displaced, the front wheels 2R, 2
It is composed of tie rods +3R and +3L that steer L.

A pinion 14 is fixed to the front end of the intermediate rod 3,
The pinion 14 is connected to a rack 15 provided on the relay rod 11.
The intermediate rod 3 is rotated in the same direction as the handle 1 by engaging with the intermediate rod 3, and the rear end of the intermediate rod 3 is connected to a steering ratio changing device C.

The rear wheel steering mechanism E is connected to the control rod 5, and includes a steering rod 16 that is laterally displaced integrally with the control rod 5, knuckle arms 17R, 17L that support the rear wheels 4R74L, and knuckle arms 17R, 17L that support the rear wheels 4R74L.
It is comprised of tie rods 18R and 18L which rotatably connect the relay rod 7L to both ends of the relay rod 16.

In addition, the power steering mechanism is connected to the relay rod 16.
a power cylinder 20 that fits into the power cylinder 20;
is fixed to the relay rod 16 within the power cylinder 20
A piston 21 that divides the inside into two hydraulic chambers 22 and 23, a control valve 24 that is switched by displacement of the hydraulic rod 5, and a supply pipe 26, a control valve 24, and a piping 2 for supplying oil in a reservoir tank 25.
It consists of an oil pump 29 that supplies oil to any of the hydraulic chambers 22, 23 in the power cylinder 20 through 7° 28,
In addition, a drain pipe 3o is provided that communicates the control valve 24 and the reservoir tank 25.

When the control rod 5 is displaced to the right, the control valve 24 is connected to the supply pipe 26, the pipe 28, and the drain pipe 3.
1 and piping 27, respectively, and when the control rod 5 is displaced to the left, the supply pipe 26 and piping 27, and the drain pipe 30 and piping 28 are brought into communication, respectively, and the oil pump 29
The piston 21 is driven by the hydraulic pressure in the same direction as the control rod 5 to assist in steering the rear wheels 4R and /IL. 31, 3] is a spring that urges the piston 21 to the neutral position, 32 is a power source (battery), and 33
is the ignition switch.

As shown in FIG. 3, the steering ratio changing device C transmits the steering angle θH of the steering wheel l to a connecting rod 35 whose one end is connected to the control rod 5 via a ball joint 34. It has a steering angle transmission unit CI that rotates the control rod 5 by a predetermined angle corresponding to the steering angle θH around the central axis g1 of the control rod 5 using the ball joint 34 as a fulcrum, and a stepping motor 36 for driving,
The connecting rod 35 via the ball joint 37
The steering ratio change lever 38 connected to the other end of the control rod 5 is rotated according to the vehicle speed. 1 and a steering ratio changing section C2 that rotates around an axis 07 orthogonal to the steering wheel 1 and changes the steering ratio of the rear wheels 4R and 4L. The rotation angle of the connecting rod 35, that is, the ball joint 37, around axis B corresponding to the steering wheel steering angle θH, and the rotation angle of the steering ratio change lever 38 around axis 07, which is controlled in accordance with the vehicle speed. In response, the control rod 5 is laterally displaced by a predetermined stroke.

The steering angle transmitting section CI is supported by the vehicle body G coaxially with the central axis Q of the control rod 5, and the bevel gear 42 at the tip engages the bevel gear 43 at the rear end of the intermediate rod 3. and a vertical boss portion 45 of the rod 44.
The steering angle transmission shaft 46 is rotatably and slidably connected to the connecting rod 35 via a spherical joint 47.

On the other hand, the steering ratio changing section C2 includes a drive gear 49 fixed to the output shaft 48 of the stepping motor 36 for driving, and an arm 51 provided with a sector gear 50 meshed with the drive gear 49. 51 is supported by the vehicle body G, and as shown in FIG. 4, a spring 53 53 is stretched between the arm 51 and the vehicle body 0 to bias the arm 51 to the neutral position. . Further, stopper surfaces 54 and 54 for regulating the swing angle of the arm 51 are formed on the vehicle body G.

Returning to FIG. 3, the rotation shaft 52 has a U-shaped holder 5.
5 is fixed, and the steering ratio change lever 38 is fixed to the holder 55.
A bin 56 integrated with the rotary shaft 5 is pivotally connected to the
On the small diameter portion of No. 2, there is a steering ratio sensor (rotary button yometer) that detects the rotation angle of the steering ratio change lever 3B and the steering ratio Od of the rear wheels 4R and 4L by changing the resistance value. 57 are arranged. 58 is a length adjustment portion of the connecting rod 35; 59
is a drive circuit for the stepping motor 36.

In this steering ratio changing device C, the steering ratio changing lever 38
is facing the reference direction, that is, as shown by the solid line O in FIG. Since the rotation orbital plane I7 of the ball joint 37 around the axis ρ8 coincides with the vertical plane, the control rod 5 is not displaced laterally even when the handle 1 is steered, and therefore the steering ratio θd becomes zero.

In response, the steering ratio changing lever 38 is rotated in either direction, and the ball joint 37 is rotated as shown by the imaginary line in FIG.
When the rotational track plane L' of the rotary track plane L' is inclined with respect to the vertical plane, the control rod 5 will be displaced laterally as the handle l is steered. The lateral stroke S of the control rod 5 is defined as α, the angle of inclination of the rotational track surface L' with respect to the vertical plane, β, the rotation angle of the ball joint 37 with respect to the horizontal plane in FIG. 8, and the length of the steering ratio changing lever 38 with r. Then, S = rt
anαsinβ. When the rotating orbital surface L' is inclined counterclockwise in FIG. 9 with respect to the vertical plane, a negative steering ratio is obtained.
A positive steering ratio is set when tilting clockwise.

The first diagram is a block diagram of the steering ratio control system for rear wheels 4R and 4L.
In the figure, the control means F stores in advance the steering ratio characteristic of the rear wheels/I11.4L that changes depending on the vehicle speed as shown in FIG. 7, as shown in FIG. A steering ratio θd corresponding to the vehicle speed transmitted from the vehicle speed sensor 6 is calculated based on the steering ratio characteristic. Then, if necessary, a drive pulse and a rotation direction signal are sent to the drive circuit 59 to drive the stepping motor 36, thereby changing the steering ratio Od, or the angular position of the steering ratio changing lever 38. . The angular position of the steering ratio changing lever 38 is fed back from the steering ratio sensor 57 to the control means F via the A/D converter 60. Note that at the time of starting 11, an A/D conversion start signal is sent from the control means F to the A/D converter 60, and when the vehicle is stopped or a failure of the steering ratio sensor 57 is detected, an A/D conversion end signal is sent.

The rated voltage of the power supply 32 is applied to the steering ratio sensor 57, and when the steering ratio change lever 38 rotates and the resistance value of the steering ratio sensor 57 changes, the steering ratio sensor 57 is analog The output current changes and this analog output current becomes A/
In the D converter 60, the signal is converted into an 8-bit 256-level digital signal at a sampling interval of, for example, 1OO μsec, and the digital signal is transmitted to the control means F. The control means F includes an abnormality determination circuit 61 that calculates the amount of change in the digital signal, that is, the sampling value in the A/D converter 60, and detects an abnormality in the steering ratio sensor 57 based on the magnitude of the amount of change. Built-in.

That is, the rotational speed of the steering ratio change lever 38 is determined by the maximum rotational speed of the stepping motor 36 (for example, 10°/s).
There is an upper limit value determined by ec), and accordingly, there is also an upper limit value for the rate of change of the analog output current of the steering ratio sensor 57. Thereby, consecutive two
Sampling value when sampling times (digital output)
Calculated, the amount of change in is at most a rubel.

On the other hand, if, for example, the cover 62 connecting the steering ratio sensor 57 and the A/D converter 60 is disconnected from the steering ratio sensor 57, the input of the A/D converter 60 becomes high impedance and becomes large. Noise is generated, and the amount of change in the sampling value in the A/D converter 60 becomes large, but such abnormal changes occur continuously during multiple samplings.

Therefore, in this embodiment, the influence of noise in the steering ratio sensor 57 is added to the maximum value (level) of the amount of change in the sampling value during two consecutive samplings in the A/D converter 60 during normal operation. A permissible maximum value (for example, 2 levels) X of the amount of change in the sampling value is set, and an abnormal change exceeding the permissible maximum value X occurs a predetermined number L (L<M ), the abnormality detection circuit 61 determines that the steering ratio sensor 57 is abnormal. In this way, for example, when an abnormal change that exceeds the -time tolerance value X occurs, as shown in ΔS6 in FIG. On the other hand, when abnormal changes exceeding the allowable value X occur continuously, as in ΔS12 to ΔS18, it can be determined that the steering ratio sensor 57 is abnormal. Thereby, noise in the steering ratio sensor 57 can be distinguished from actual abnormality, and abnormality in the steering ratio sensor 57 can be accurately detected.

Here, the calculation procedure of the abnormality determination circuit 61 at each sampling time will be explained according to the flowchart of FIG.

(i) In step S1, the number of samplings is counted.

(ii) In S2, the sampling value SN of that time is read.

(iii) At S3, the amount of change ΔS1. from the previous sampling value 58-3. I is required.

(iv) In S4, it is determined whether ΔS8 exceeds the allowable value X or not. If ΔS− is less than or equal to the allowable value X, the operator αH is set to “
If "0" exceeds the allowable value X, "B" is set to the operator α8.

(v) Number of abnormal value detections UN during M consecutive samplings from the (N-M+I)th time to the Nth time in S5
is calculated. In other words, before the Nth sampling,
Since the abnormality detection circuit 61 stores the number of abnormal value detections UN-+ during M samplings between the (N-M)th and (N-1)th times, a new value is added to UN-+ in S5. The value of operator α8, which indicates the presence or absence of an abnormal change at the time of the Nth sampling, which is the target of determination, is added, and an operation that indicates the presence or absence of an abnormal change, at the time of the (N - M)th sampling, which is not the target of determination. Child αN-M
The value of is subtracted.

(vi) Limit value L (L<
It is determined whether or not M) is exceeded. If Ul is 17 or less, the process returns to Sl and the next sampling is performed. U
If N exceeds L, it is determined that the steering ratio sensor 57 is abnormal.

If an abnormality in the steering ratio sensor 57 is detected in the above procedure, the following measures can be taken.

(a) An abnormality in the steering ratio sensor 57 is notified to the driver using a lamp, a buzzer, etc. provided on the instrument panel.

(b) Stop controlling the steering ratio θd, and fix the steering ratio θd to the value at the time of abnormality detection.

(c) In the control system of FIG. 1, the steering ratio θd is set to zero in an open loop, and the steering is switched to two-wheel steering. That is, since the rotation angle of the stepping motor 36 can be controlled by the number of drive pulses, the steering ratio change lever 38 is once set to the maximum rotation angle position on one side (when the sector gear 50 in FIG. 4 collides with one of the stopper surfaces 54). position), then
The steering ratio changing lever 38 can be rotated in the opposite direction and fixed at an angular position corresponding to the steering ratio θd-0.

In addition, the above (a) and (b) or (a) and (C
) is preferable in combination.

As explained above, in the on-ice embodiment, the rear wheels 4R, 4L
If an abnormality occurs in the steering ratio sensor 57 that detects the steering ratio θd, it can be quickly detected by the abnormality determination circuit 61, and as a result, the steering ratio θd can be fixed at the value at the time the abnormality was detected. , can be set to zero, steering ratio sensor 5
It is possible to minimize the deterioration of the steering feeling due to the abnormality in item 7 and improve the safety of a vehicle equipped with this type of steering ratio changing device C.

In the above embodiment, the stepping motor 36 is used as a driving means for the steering ratio changing device C, but a DC motor may be used instead. At that time, if an abnormality in the steering ratio sensor 57 is detected, the steering ratio O
It is sufficient to fix the value to the value at the time of abnormality detection.

Further, in the above embodiment, the steering ratio θd is controlled in response to vehicle speed, but the steering ratio θd may also be controlled in response to lateral acceleration, front wheel steering angle, etc. The switching may be performed in multiple stages using a switching switch provided on the panel. Furthermore, in the abnormality detection circuit 61, the front wheel steering mechanism B and the rear wheel steering mechanism E are not mechanically connected, and the rear wheels 4R and 4L are electronically controlled independently of the front wheels 2R and 2L. The present invention can be similarly adopted in a four-wheel steering system configured as described above.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a rear wheel steering ratio control system in a vehicle equipped with a four-wheel steering device according to the present invention, FIG. 2 is an overall explanatory diagram of the four-wheel steering device, and FIG. 3 is a steering ratio control system. An enlarged explanatory view of the changing device, FIG.
The figure shows the relationship between the number of samplings and the amount of change in the sampling value in the A/D converter, Figure 6 is a flowchart showing the calculation procedure of the abnormality detection circuit at each sampling time, and Figure 7 shows the vehicle speed and rear wheel steering. The diagrams illustrating the relationship with the steering ratio, FIGS. 8 and 9, are explanatory views of the operation of the steering ratio changing device. C... Steering ratio changing device, F... Control means, 4R,
/IL/rear wheel, 57... Steering ratio sensor (steering ratio detection means), 60 A/D converter (A/D conversion means),
61・Abnormality determination circuit (abnormality determination means).

Claims (1)

[Claims] (1) A four-wheel steering system for a vehicle equipped with a steering ratio changing device that changes the steering ratio of the rear wheels with respect to the steering angle, comprising a control means for controlling the operation of the steering ratio changing device, and a control means for controlling the operation of the steering ratio changing device; analog steering ratio detection means for detecting the steering ratio of the wheels;
A/D converting means for A/D converting the analog signal of the steering ratio detecting means at predetermined sampling intervals and transmitting the A/D converting means to the control means; and sampling during two consecutive samplings in the A/D converting means. A four-wheel steering system for a vehicle, characterized in that it is provided with an abnormality determining means that calculates the amount of change between the values and determines that the abnormality is abnormal when an abnormal change of a predetermined level or higher occurs a predetermined number of times or more within a predetermined time. .