JPH01229773A - Device for steering rear wheel of vehicle - Google Patents

Abstract

PURPOSE:To carry out safer rear wheel steering control by providing two systems of front wheel steering angle detecting means and carrying out rear wheel steering control based on the smaller front wheel steering angle out of detected two front wheel steering angles. CONSTITUTION:In the captioned device in which a rear wheel steering mechanism A is displaced by a driving means B, first and second front wheel steering angle detecting means C1, C2 detects the steering angle of front wheels. Out of two front wheel steering angles detected by these two front wheel steering angle detecting means C1, C2, the smaller front wheel steering angle is selected by a front wheel steering angle selecting means D. A target rear wheel steering angle is determined by a target rear wheel steering angle determining means E based on the selected front wheel steering angle, and the driving means B is controlled by a drive control means F so as to make the determined rear wheel steering angle the target rear wheel steering angle. The detecting means C1, C2 are provided so as to detect each mechanical displacement of, e.g., a front wheel steering mechanism and a steering mechanism.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rear wheel steering device for a vehicle that steers the rear wheels.

(Prior Art) Some vehicles have so-called four-wheel steering (4WS) in which both the front wheels and the rear wheels are steered.

In this four-wheel steering, the steering mechanism for the rear wheels is
A mechanical type in which a front wheel steering mechanism and a rear wheel steering mechanism are mechanically connected, and a mechanical type in which a front wheel steering mechanism and a rear wheel steering mechanism are mechanically connected, and a mechanical type in which a rear wheel steering mechanism is provided with an electromagnetic drive means such as an electric motor, as seen in Japanese Utility Model Application Publication No. 62-25275. It is roughly divided into an electric type in which the rear wheels are steered by the driving force of this driving means in conjunction with each other. In this electric type, it has also been proposed to interpose a speed reduction mechanism between the drive means and the rear wheel steering mechanism in order to minimize the capacity of the drive means (1986- 252
(See Publication No. 77).

In the case of the type thermoelectric type, the operation of the electric motor as the driving means is controlled every time so as to achieve a predetermined steering characteristic indicating the relationship between the front wheel steering angle and the rear wheel steering angle. As the above-mentioned predetermined steering characteristics, a heavy speed responsive type and a steering angle responsive type are generally well known.

By the way, in the case of electric type, rear wheel steering is exclusively used.
Since it is electrically controlled, sufficient consideration must be given to fail-safe measures such as failure of the control system. From this point of view, as seen in Japanese Unexamined Patent Publication No. 61-202977, it has been proposed to attach a middle retaining means to the rear wheel steering mechanism to constantly bias the rear wheel steering mechanism in the neutral direction. . This proposal is based on the idea that if any failure occurs in the control system, the rear wheel steering control will be stopped and the rear wheels will be forcibly returned to the neutral position using the intermediate holding stage (F). It is.

(Problems to be Solved by the Invention) By the way, when electrically controlling the rear wheels, it is necessary to detect the steering angle of the front wheels as a premise. The front wheel steering angle is generally detected by detecting the steering wheel angle.

However, if an abnormality occurs in the detection of this front wheel steering angle, an abnormality will occur in the control of the rear wheels, which will be undesirable.
Some kind of countermeasure is desired at the iron point. In other words, considering the case where the steering ratio characteristic is vehicle speed sensitive, the steering angle of the rear wheels increases as the front wheel steering angle increases, and therefore the front wheel steering angle detection means If the value is detected as being considerably larger than the actual turning angle of the front wheels, the rear wheels will be turned more than necessary, which is undesirable. Also, consider a case where the steering ratio characteristic is responsive to the steering angle of the steering wheel. In this case, the larger the steering angle, the more the rear wheels are steered toward the opposite phase side, that is, the rear wheels are steered in a direction that makes the vehicle unstable. Therefore, if the front wheel steering angle is submitted as a much larger value than the actual front wheel steering angle, the rear wheels may be steered more than necessary in a direction that makes the vehicle unstable. Become.

Therefore, an object of the present invention is to prevent undesirable steering of the rear wheels based on a detection error of the front wheel steering angle, assuming that rear wheel steering is electrically controlled. An object of the present invention is to provide a rear wheel steering device for a vehicle.

(Means and operations for solving the problems) In order to achieve the above-mentioned object, the present invention has the following configuration. That is, a rear wheel steering mechanism for steering the rear wheels, a drive means linked to the rear wheel steering mechanism and serving as a drive source for displacing the rear wheel steering mechanism, and a drive means for detecting the steering angle of the front wheels, respectively. 1. The smaller of the two front wheel turning angles detected by the second two front wheel turning angle detection means and the first and second two front wheel turning angle detection means. Front wheel steering angle selection means for selecting.

a target rear wheel turning angle determining means for determining a target rear wheel turning angle based on the front wheel turning angle selected by the front wheel turning angle selecting means; and a drive control means for controlling the means.

In this way, the present invention detects the front wheel turning angle in two ways.
Based on the smaller of the two front wheel steering angles detected, the rear wheel steering, that is, the steering of the rear wheels is controlled in a direction preferable for ensuring safety.

It is preferable that the above-mentioned first and second front wheel turning angle detection stages f detect the mechanical displacement of the front wheel steering angle as much as possible. In particular, for front wheel steering, there is a front wheel steering mechanism including a tie rod, etc., and a steering mechanism linked to this front wheel steering mechanism and equipped with a handle.One of the front wheel steering angle detecting means is It is preferable that the other front wheel steering angle detecting means detects the mechanical displacement of the steering mechanism. To explain this point in detail, between the front wheel steering mechanism and the steering mechanism, a steering force direction changing mechanism such as a rack-and-binion type or Paulnaude type is interposed between the front wheel steering mechanism and the steering mechanism, or a power steering mechanism is interposed. Due to the relationship between the two parts, the mechanical displacement will be different depending on the play, and failures in these parts are more likely to occur than failures in other parts. Therefore, it is preferable to detect the mechanical displacement of both the front wheel steering mechanism and the steering mechanism, for example, by detecting the mechanical displacement of both the front wheel steering mechanism and the steering mechanism. This is more advantageous than the case where two second front wheel turning angle detection means are provided.

Generally, the front wheel steering angle detected by the front wheel steering mechanism appears smaller than the front wheel steering angle detected by the steering mechanism.

Therefore, in the case of the configuration as described in claim (2), since the front wheel steering mechanism side becomes smaller, this side is used for control. Therefore, the steering control of the rear wheels can be performed simultaneously with the steering of the front wheels. That is, when the steering is controlled, a control signal is sent to the rear wheels even though the front wheels are not steered due to play, so there is a possibility that the rear wheels will be steered before the front wheels. This kind of undesirable form can be prevented at the same time.

(The following is a blank space) (Example) An example of the present invention will now be described based on the attached drawings.

In Figure 1, IR is the right front wheel, IL is the left front wheel, 2R is the right rear wheel, 2L is the left rear wheel, and the left and right front wheels IR,1,L
are linked by the front wheel steering mechanism A, and the left and right rear wheels 2R
, 2L are linked by a rear wheel steering device aB.

In the embodiment, the front wheel steering mechanism A includes a pair of left and right knuckle arms 3R13L and a tie rod 4R14L, and a relay rod 5 that connects the pair of left and right tie rods 4R14L. A steering mechanism C is linked to this front wheel steering mechanism A, and the steering mechanism C is of a rack-and-binion type in this embodiment, and the pinion 6, which is a 4W component, is connected to the shaft 7.
It is connected to the handle 8 via. As a result, when the handle 8 is operated to the right, the relay rod 5 is displaced to the left in FIG. 1, and the knuckle arm 3R1
3L is steered clockwise in the figure by an amount corresponding to the operational displacement of the handle 8, that is, the steering angle, about the center of rotation 3R' and 3L'. Similarly, handle 8
When an operation is performed to turn the vehicle to the left, the left and right front wheels IR and 1L are steered to the left in accordance with this operation displacement layer.

The rear wheel steering mechanism B is similar to the front wheel steering mechanism A.

A pair of left and right knuckle arms l0R110L and tie rods IIR and IIL, respectively, and the tie rod 11R.
, and a relay rod 12 that connects the comrades.
A neutral holding means 13 is attached to this relay rod 12. As shown in FIG. 3, the neutral holding means 13 has a casing 15 fixed to the vehicle body 14, and a pair of spring receivers 16a and 16b are loosely fitted into the casing 15. Compression spring 1 between 16a and 16b
7 are arranged. A relay rod 12 denoted by L extends through the casing 15, and a pair of flanges 12a and 12b are formed at intervals on this relay rod 12, and the spring receivers 16a and 16b are received by the flanges 12a and 12b. The relay rod 12 is configured to have a compression spring 17
is always biased in the neutral direction. Of course, the compression spring 17 is provided with a spring force sufficient to overcome the side force during cornering.

The rear wheel steering mechanism B shown in L is linked to a servo motor 20 as a drive source for steering the rear wheels 2R and 2L. More specifically, during the linkage mechanism between the relay rod 12 and the thermostat 20, the gear train 2 is sequentially connected from the relay rod 12 side.
A reduction mechanism 21 including a bolt 1a and a bolt screw 21b, a clutch 22, and a brake mechanism 23 are interposed. As a result, the clutch 22 is configured to mechanically disconnect the servo motor 20 and the rear wheel steering mechanism B as appropriate, and the brake mechanism 23 is configured to mechanically disconnect the servo motor 20 from the rear wheel steering mechanism B.
The rotation of the output shaft can be locked by gripping the output shaft.

With the configuration described below, when the clutch 22 is in the connected state, the relay rod 12 is displaced to the left or right in FIG. 1 by the forward or reverse rotation of the servo motor 20, and the knuckle arms 10R and IOL are Its rotation center 1
The steering wheel is steered clockwise or counterclockwise in the figure by an amount corresponding to the amount of rotation of the servo motor 20 with 0R' and IOL' as the center. On the other hand, when the clutch 22 is in a disengaged state, the rear wheels 2R12L are forcibly returned to the neutral position by the neutral holding means 13,
It will be held at this neutral position. In other words, when the clutch 22 is disengaged, only the front wheels IR1IL are steered, resulting in a so-called 2WS vehicle.

The control of the rear wheel steering is herein assumed to be responsive to the vehicle speed, and an example of changing the steering ratio in response to the vehicle speed is as shown in FIG. 3. When the control characteristics shown in FIG. 3 are applied, the rear wheel steering angle relative to the steering wheel steering angle changes in the same phase direction as the vehicle speed increases. This situation is shown in FIG. In order to perform such control, the control unit U basically includes a steering wheel angle sensor 30. Signals from the vehicle speed sensor 31 and the encoder 32 that detects the rotational position of the servo motor 20 are input, and the control unit U calculates a target rear wheel steering angle based on the steering wheel steering angle and the vehicle speed. A control signal corresponding to the amount of rear wheel steering is sent to the servo motor 20.
is output to. The encoder 32 constantly monitors whether or not the servo motor 20 is operating properly.
12L steering is performed.

The basic control system described above has a dual configuration for fail-safe purposes. That is, a front wheel steering angle sensor 34 is added to the above-mentioned steering wheel steering angle sensor 30, a second vehicle speed sensor 35 is added to the vehicle speed sensor 31, and a second vehicle speed sensor 35 is added to the encoder 32, which is located closer to the relay rod 12 than the clutch 22. A rear wheel steering angle sensor 36 is added to detect the mechanical displacement of the member, and the rear wheels are steered only when both corresponding sensors among these sensors 30 to 36 detect the same value. There is.

That is, in the L sensors 30 to 36, for example, when the vehicle speed detected by the l-th vehicle speed sensor 31 and the vehicle speed detected by the second vehicle speed sensor 35 are different, a failure has occurred, which will be described later. The rear wheels 2R12L are maintained in a neutral state through control during mode.

Further, in order to detect various failures, on/off signals from switches 37 to 40 are inputted to the control unit U, and a signal indicating the presence or absence of power generation is inputted from the L terminal 41 of the alternator. Ru. Here, the switch 37 is a neutral clutch switch, the switch 38 is an inhibitor switch, the switch 39 is a brake switch, and the switch 40 is an engine switch. here,
In a vehicle equipped with a manual transmission, the neutral switch 37 outputs an off signal when the shift position of the manual transmission is neutral or when the clutch pedal is depressed, and otherwise outputs a Φon signal. Inhibitor switch 38 is used when the range is neutral (N) in a vehicle equipped with an automatic transmission.
Alternatively, an on signal is output when the vehicle is in parking (P), and an off signal is output when the vehicle is in the driving range. The brake switch 39 outputs an on signal when the brake pedal is depressed, and the engine switch 40 outputs an on signal when the engine switch is in the M rotation state.

A block diagram of the above control system is shown in FIG. 5. That is, the microprocessor 50 has two
The microprocessor 50 has a heavy structure, and signals from the heavy speed sensors 31, 35, switches 37 to 40, and the L terminal 41 of the alternator are inputted to the microprocessor 50 via a buffer 51.・The signal from 6 is input via the A/D converter 52, and the signal from the encoder 32 is inputted via the A/D converter 52.
A signal is input via the interface 53.

On the other hand, the signal generated in the microprocessor 50 is sent to the servo motor 29 via the drive circuit 54,
In addition, the motor brake 23
or to the clutch 22 via the clutch drive circuit 56. This rear wheel steering control is performed when the signal from the L terminal 41 of the alternator is high (H,,i).
It is designed to be started on the condition that the following happens.

In addition, in the figure, reference numeral 57 is a battery, 58 is an ignition key switch, and 59 is a relay, and if any failure occurs in the four-wheel steering control system, the relay drive circuit 60
As a result of this operation, the current supply to the coil 61 is stopped, and as a result, the B contact of the relay 59 is closed and the warning lamp 62 is turned on. -Next, we will explain failures and their treatments.Here, we will take measures that correspond to the location where the failure has occurred, and there are the following two modes of treatment.

Treatment mode A (first fail mode control t!1) Rear wheel 2
This is a case where control of R12L and determination of its position are still possible. That is, when it is possible to return the vehicle to neutrality using the motor 20, the motor 20 is used to return the vehicle to neutrality. Specifically, the contents of this procedure are as follows: (1) After the q blue lamp 62 lights up, (4) the rear wheels 2R12L are returned to the neutral position by the drive of the servo motor 20 ( ≦) After that, the motor brake 23 is engaged.

・Treatment mode B (control during second fail mode) Rear wheel 2R1
This is a situation when control of 2L and determination of its position become impossible. The details of this procedure are as follows.

■After the warning lamp 62 lights up, ■The clutch 22 is turned off, and the linkage between the motor 20 and the rear wheel steering mechanism B is disconnected.

(3) Due to the spring force of the neutral holding means 13, the rear wheel 2R12
After waiting for L to return to the neutral position.

(4) The clutch 22 is connected.

Preferably, the motor brake 23 is engaged after the clutch 22 is disengaged. As a result, the rear wheel 2R5 due to the runaway of the motor 20
The steering of the 2L is physically prohibited. After that, the supply of power to the motor 20 is cut off.

Next, a control example of the present invention will be explained with reference to FIG. Note that in the following explanation, Q indicates a step.

After the system is initialized in step Ql, signals from each sensor or switch are inputted in step Q2. At this time, the steering shaft 7
The output of the sensor 30 (front wheel steering angle) attached to the relay rod 5 is read as OH, and the output c (front wheel steering angle) from the sensor 34 attached to the relay rod 5 is read as OA.

After Q2, in Q3, it is determined whether the difference between 1.OH and OA is smaller than a set value α that is an allowable range. If the determination in Q7 is YES, in Q4, O
It is determined whether A is less than or equal to OH. When the determination in Q4 is YES, that is, when the OA is below OH, this OA is set as the front wheel steering angle OF for rear wheel control in Q5.
On the other hand, if the determination in Q4 is NO,
In Q6, OH is set as the front wheel steering angle θF for rear wheel control.

After Q5 or Q6, in Q7,
A target rear wheel steering angle θr corresponding to the front wheel steering angle θF is determined based on the steering ratio characteristics shown in FIG. After this, Q8
At this time, the motor 20 is feedback-controlled so that the rear wheels 2R2I reach the target rear wheel turning angle θr.

When the determination in Q3 is No, the process moves to Q9, and 2WS is performed while keeping the rear wheels 2R12L in the neutral position (rear wheel steering is prohibited, for example, the clutch 20 is disengaged). Note that the process in Q9 is , may be performed when both OH and OA indicate an output of a magnitude exceeding a predetermined setting range (): limit value or lower limit value.
When only one of the two outputs exceeds the above setting range, the output of the other one may be used to steer the rear wheels, or in this case, the steering of the rear wheels may also be prohibited.

Although the embodiments have been described above, the drive means as the drive source of the rear wheel steering mechanism B may be an electromagnetic hydraulic actuator or other appropriate drive means. In this case, as a braking means, a switching valve that supplies and discharges hydraulic pressure to and from a hydraulic actuator may be used. In other words, the switching valve must be maintained in a state in which no pressure oil is supplied or discharged from the hydraulic actuator. This locks the hydraulic actuator.

(Effects of the Invention) As is clear from the above description, according to the present invention, the rear wheel steering angle is set in a direction with higher safety in accordance with the front wheel steering angle, which is preferable from the viewpoint of safety measures. becomes.

In addition, when configured as described in claim (2), play in the front wheel steering system is absorbed and a situation in which the rear wheels are steered even though the front wheels are not steered can be reliably prevented. Can be prevented.

[Brief explanation of the drawing]

FIG. 1 is an overall system diagram showing one embodiment of the present invention. Figure 2 is a configuration diagram of the rear wheel steering mechanism. FIG. 3 is an enlarged sectional view of the neutral holding means. FIG. 4 is a control characteristic diagram of a heavy speed sensitive type, which is an example of rear wheel steering. FIG. 5 is a characteristic diagram showing changes in rear wheel steering angle according to vehicle speed. FIG. 6 is a block diagram of a control system according to the embodiment. FIG. 7 is a flowchart showing a control example of the present invention. FIG. 8 is a block diagram showing the configuration of the present invention. l: Front wheel 2: Rear wheel 20: Servo motor (drive means) 30: Sensor (for front wheel steering angle detection) 34: Sensor (for front wheel steering angle detection) U: Control unit B: Rear wheel steering mechanism Fig. 2 Figure 3 Figure 5

Claims (2)

[Claims] (1) A rear wheel steering mechanism for steering the rear wheels, a drive unit linked to the rear wheel steering mechanism and serving as a drive source for displacing the rear wheel steering mechanism, and each detecting the steering angle of the front wheels. First and second two front wheel turning angle detection means, and front wheel turning of the smaller of the two front wheel turning angles detected by the first and second two front wheel turning angle detection means. a front wheel steering angle selection means for selecting a front wheel steering angle; a target rear wheel steering angle determining means for determining a target rear wheel steering angle based on the front wheel steering angle selected by the front wheel steering angle selection means; A rear wheel steering device for a vehicle, comprising: drive control means for controlling the drive means so as to achieve a target rear wheel turning angle. (2) a front wheel steering mechanism for steering the front wheels; a steering mechanism linked to the front wheel steering mechanism and provided with a handle; a rear wheel steering mechanism for steering the rear wheels; and the rear wheel steering mechanism. a drive means as a drive system that is linked to a steering mechanism and displaces the rear wheel steering mechanism; a first front wheel steering angle detection means that detects a mechanical displacement of the front wheel steering mechanism; a second front wheel turning angle detection means for detecting displacement; and a smaller front wheel turning angle of the two front wheel turning angles detected by the first and second front wheel turning angle detection means. a front wheel turning angle selecting means to select; a target rear wheel turning angle determining means determining a target rear wheel turning angle based on the front wheel turning angle selected by the front wheel turning angle selecting means; A rear wheel steering system for a vehicle, comprising: a drive control means for controlling the drive means so that the rear wheel steering angle is adjusted to a rear wheel steering angle.