JP2607562B2 - Vehicle rear wheel steering system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention
A rear wheel steering device for steering the rear wheels together with the front wheels,
In particular, the present invention relates to a rear wheel steering device for a vehicle that can change and control a turning ratio of a rear wheel according to a vehicle speed.

2. Description of the Related Art Conventionally, as a four-wheel steering system having a rear wheel steering system for a vehicle, for example, as disclosed in Japanese Patent Publication No. 60-44185, the front wheel and the rear wheel are operated in accordance with the operation of a steering wheel. It is known that the wheels are steered and the steering ratio of the front and rear wheels is changed in accordance with the vehicle speed based on a predetermined steering ratio characteristic set in advance. Then, in this case, the above-described turning ratio characteristic is basically
At low vehicle speeds lower than the predetermined vehicle speed (35 km / h), the front and rear wheels are in opposite phases to enhance turning (turning) of the vehicle, and at the predetermined vehicle speed, the rear wheels are not steered so-called 2WS.
When the vehicle speed is higher than the predetermined vehicle speed, the front and rear wheels are in phase, and the running stability of the vehicle (lane change stability)
Each is set to enhance.

In such a conventional rear wheel steering device, when traveling on a curved road with a vehicle speed higher than a predetermined vehicle speed, the front and rear wheels are steered in the same phase, so that the so-called high-speed cornering characteristics are favorably maintained. Will be. Here, at the time of such high-speed cornering, for example, if an obstacle or the like is found ahead and a sudden break is stepped on, the vehicle rapidly decelerates,
As a result, the steering ratio is suddenly changed in the opposite phase direction. For this reason, originally, in order to maintain a stable posture of the vehicle during cornering and to perform stable running,
Despite the fact that the front and rear wheels must step on the same phase, the same phase decreases, and consequently the vehicle is steered to the opposite phase, acting in the direction that causes yaw rate, thereby increasing the turning performance of the vehicle become. Such a phenomenon appears as a scooping phenomenon.

In particular, when the rear wheel locks and slips due to breaking, the vehicle speed sensor used for controlling the steering ratio of the front and rear wheels determines the wheel speed even though the vehicle body is actually running at a certain speed. , Which instantaneously becomes zero. For this reason, the steering ratio is instantaneously changed to the maximum value of the opposite phase, and there is a possibility that the running state may fall into an unstable state due to the decrease in the grip force of the tire due to the locking. Yes.

Therefore, conventionally, for example, as shown in Japanese Utility Model Publication No. Sho 62-5974, when the vehicle speed-sensitive rear wheel steering device detects a sudden deceleration of the vehicle, the steering ratio of the front and rear wheels is changed. A technique is known in which the steering angle (the angle in the direction in which the slip angle increases) corresponding to the traveling condition of the vehicle is set in the range of the same phase to prevent so-called tatsukuin.

Further, as disclosed in JP-A-59-81275, in a vehicle speed-sensitive rear wheel steering system, when a sudden deceleration of a vehicle is detected, a change in a steering ratio of front and rear wheels is delayed. Thus, a technique for preventing the above-described scooping phenomenon is known.

Here, as means for detecting sudden deceleration of the vehicle, a vehicle speed sensor is used, and when the output of the vehicle speed sensor drops sharply, sudden deceleration is determined. It is known that sudden deceleration of the output of the vehicle speed sensor after the vehicle is depressed determines that rapid deceleration has occurred.

[Problems to be Solved by the Invention] However, in these related arts, after detecting a sudden deceleration of the vehicle, control of a turning ratio for preventing rake is executed. For this reason, the following problems occur.

That is, when braking is performed as described above, the vehicle speed is rapidly reduced, and the output value of the vehicle speed sensor is rapidly reduced. On the other hand, the vehicle speed sensor is configured so as to determine that a failure of the vehicle speed sensor occurs when the output value of the vehicle speed sensor suddenly decreases as one mode of failure detection because the vehicle speed sensor suddenly decreases due to its structure. I have. As a result, there is a possibility that a sudden decrease in wheel rotation due to braking is detected as a failure of the vehicle speed sensor and the fail-safe control is executed.

The present invention has been made in view of the above problems,
An object of the present invention is to maintain good traveling performance in accordance with the traveling state, such as at the time of cornering traveling,
When the output value of the vehicle speed sensor suddenly decreases due to the braking, the control for setting the steering characteristic to the stable side is surely executed so that the fail control is not executed by mistake. Another object of the present invention is to provide a rear-wheel steering device for a vehicle that can reliably execute fail control when a vehicle speed sensor fails and can ensure safety.

[Means for Solving the Problems] In order to solve the above problems and achieve the object, a rear wheel steering device for a vehicle according to the present invention has the following configuration. That is, a vehicle speed detecting means for detecting a vehicle speed and detecting a vehicle speed in a rear wheel steering device of a vehicle for steering a rear wheel with a steering characteristic according to the detected vehicle speed and the steering of a front wheel; Setting means for setting the steering characteristics of the rear wheels in accordance with the vehicle speed detected by the detecting means; abnormality determining means for determining that the detection output of the vehicle speed detecting means has decreased sharply by a predetermined value or more; And a change unit that stops the control based on the turning characteristic set by the setting unit and executes a fail-safe control when it is determined that the detection output of the vehicle speed detection unit has decreased sharply. A brake detecting means for detecting a state of the vehicle, and when the brake operating state is detected by the brake detecting means, a failsafe by the changing means is provided even if the detection output of the vehicle speed detecting means suddenly decreases. Prohibiting means for prohibiting execution of the if control.

[Operation] As described above, in the rear wheel steering device of the vehicle according to the present invention, the detection of the rapid decrease state of the wheel rotation caused by the braking is performed by:
Provided that the brake detection means detects the brake operation state, the rapid decrease in the detection output of the vehicle speed detection means in the state in which the brake operation state is detected is not a failure, but is determined to be a rapid decrease state of the wheel rotation due to braking. Is set to In this way, when the brake operation state is detected by the brake detection means, the function of prohibiting the execution of the fail-safe control by the change means is prevented even if the detection output of the vehicle speed detection means sharply decreases.

Hereinafter, an embodiment of a rear wheel steering device for a vehicle according to the present invention will be described in detail with reference to the accompanying drawings.

FIGS. 1 and 2 show a four-wheel steering mechanism 12 having a rear wheel steering device 10 according to one embodiment of the present invention.
In the figure, reference numerals FL, FR, RL, and RR indicate the four-wheel steering mechanism 12.
The left and right front wheels FL, FR are shown by the front wheel steering device 14 and the left and right rear wheels.
RL and RR are connected so as to be steered by the rear wheel steering device 10, respectively.

The above-described front wheel steering device 14 includes a pair of left and right knuckle arms 16L and 16R and tie rods 18L and 18R, and a relay rod 20 connecting the left and right tie rods 18L and 18R. A steering wheel 24 is connected to the front wheel steering device 14 via a rack and pinion type steering mechanism 22. The steering mechanism 22 includes a first rack 28 formed on the relay rod 20.
And a first pinion 30 which is connected to a steering wheel 24 at the upper end and meshes with the first rack 28 at the lower end.
And a steering shaft 32 to which is attached. In this way, the left and right front wheels FL and FR can be steered according to the operation (rotation) of the steering wheel 24.

On the other hand, the above-described rear wheel steering device 10, like the front wheel steering device 14, includes left and right knuckle arms 34L, 34R and tie rods 36L, 36R, and a relay rod 38 connecting these tie rods 36L, 36R to each other. And a hydraulic power steering mechanism 26. The power steering mechanism 26 is fixed to the vehicle body and has a relay rod.
A power cylinder 40 having a piston rod 38 is provided.

In the power cylinder 40, a piston 40a is disposed so as to be movable in the axial direction so as to slide on the inner peripheral surface thereof. The piston 40a is integrally attached to the relay rod 38. The piston 40a allows the internal space of the power cylinder 40 to have two hydraulic chambers.
It is divided into 40b and 40c. These hydraulic chambers 40b, 40c
Are connected to a control valve 46 via pipes 42 and 44, respectively. The control valve 46 has an oil supply pipe 50 and an oil discharge pipe leading to a reserve tank 48.
52 two pipes are connected. The oil discharge pipe 52 has a hydraulic pump 54 driven by an engine (not shown).
Is interposed.

Here, the above-described control valve 46 is configured by a known spool valve type. The control valve 46 includes a cylindrical valve casing 46a integrally attached to the relay rod 38 via a connecting member 56,
A spool valve (not shown) fitted in the valve casing 46a is provided. In the control valve 46 configured as described above, one of the hydraulic chambers 40b (4
0c), the compressed oil is supplied from the hydraulic pump 54, and as a result, the driving force for the relay rod 38 is assisted.

Incidentally, the respective hydraulic chambers 40b, 40
c, set the relay rod 38 in the neutral position (rear wheel R
L, return spring 40d of the steering angle theta _R of RR is biased to a position) to be respectively zero, they are respectively mounted.

A second rack 58 is formed on the relay rod 26 of the front wheel steering device 14 at a position different from the first rack 28 constituting the steering mechanism 22. The second rack 58 meshes with a second pinion 62 attached to the front end of a rear steering shaft 60 extending along the longitudinal direction of the vehicle body. This rear steering shaft 60
The rear end of the rear wheel steering device 10
Is joined to.

As shown in FIG. 2, the steering control mechanism 64 has a control rod 66 slidably held along a moving axis defined along the vehicle width direction of the vehicle body. One end of this control rod 66 is a control valve
It is connected to the spool valve in 46.

The turning ratio control mechanism 64 includes a holder 68 having a base end formed in a U-shape. Support pins 70 are rotatably supported at both ends of the U-shape of the holder 68. A swing arm 72 is fixed to the center of the support pin 70 in a state perpendicular to the center. That is, the swing arm 72 is swingably supported by the holder 68 via the support pin 70. A support shaft 74 is fixed to the center of the holder 68. The support shaft 74 is rotatably mounted on a casing (not shown) of the steering ratio control mechanism 64 fixed to the vehicle body around a rotation axis set perpendicular to the aforementioned movement axis of the control rod 66. It is freely supported.

In other words, the support pin 70 of the swing arm 72 is positioned at the intersection of the above-described two axes (that is, the movement axis of the control rod 66 and the rotation axis of the support shaft 74), and Is set so as to extend in a direction orthogonal to. By rotating the holder 68 about the rotation axis together with the support shaft 74, the inclination angle between the support pin 70 at the tip thereof and the movement axis of the control rod 66 changes. That is, the swing arm 72 around the support pin 70
Is configured such that the inclination angle formed by the swing locus plane with respect to a plane orthogonal to the movement axis (hereinafter referred to as a reference plane) changes.

One end of a connecting groove 78 is connected to the tip of the swing arm 72 via a ball joint 76. The other end of this connector groove 78 is
It is connected to the other end of the control rod 66 via a ball joint 80. In this way, the swing arm
The control rod 66 is displaced along the vehicle width direction in accordance with the swing of the tip 72.

The above-described connect grove 78 has a through hole formed in an eccentric portion of a disk-shaped rotational force applying member 82 at a portion near the ball joint int.
It slidably penetrates through 84. The rotational force applying member 82 is provided integrally with a large-diameter bevel gear 88 rotatably supported via a support shaft 86 which is coaxial with the movement axis of the control rod 66. This large bevel gear 88 has
A small-diameter bevel gear 90 attached to the rear end of the rear steering shaft 60 described above is meshed. Thus, the turning power of the steering wheel 24 is transmitted to the turning power applying member 82.

Therefore, the turning force applying member 82 rotates by an amount corresponding to the turning angle of the steering wheel 24, and as a result, the connecting rod 78 pivots around the movement axis of the control rod 66. In association with this, the swing arm 72 is
When the support pin 70 is swung about the center 70 and the axis of the support pin 70 is coincident with the movement axis of the control rod 66 (in the neutral position), the ball joint 76 at the tip of the swing arm 72 is used. Only swings in the above-described reference plane, and the control rod 66 does not move along the movement axis, and is kept stationary.

On the other hand, if the axis of the support pin 70 is inclined with respect to the movement axis and the swing trajectory plane of the swing arm 72 is displaced from the reference plane, the swing of the swing arm 72 about the support pin 70 will occur. As a result, the ball joint 76 is displaced in the vehicle width direction. During this process, the displacement is
Is transmitted to the control rod 66 via the. And
The control rod 66 moves along the movement axis, and the spool valve of the control valve 46 is operated.

That is, even if the swing angle of the swing arm 72 about the axis of the support pin 70 is the same, the displacement of the control rod 66 in the left-right direction is the inclination angle of the support pin 70, in other words, the holder 68. Will change with the change of the turning angle of.

In detail, the axis of the support pin 70 is
When the angle is formed so as to be deviated clockwise from the movement axis of the arm (when in the opposite phase position), the swing arm 72
The ball joint 76 at the tip swings obliquely so as to intersect the above-mentioned reference plane, and the steering wheel 24 is steered to the right, and the control rod 66 is deflected rightward in the drawing. Then, due to the rightward deviation of the control rod 66, the rear wheels RL and RR are steered to the left as described later. In other words, in this reverse phase state, the rear wheels are steered in a direction opposite to the steering direction of the front wheels.

On the other hand, when the axis of the support pin 70 forms an angle deviating counterclockwise from the axis of movement of the control rod 66 (when in the same phase position), the ball jog at the tip of the swing arm 72 The point 76 swings so as to obliquely intersect the above-described reference plane on the opposite side to the opposite phase, and according to the right steering of the steering wheel 24, the control rod 66
Is shifted to the left in the figure. Then, due to the rightward deviation of the control rod 66, the rear wheels RL and RR are steered to the right as described later. In other words, in this in-phase state, the rear wheels RL, RR are steered in the same direction as the steering direction of the front wheels FL, FR.

On the other hand, the inclination angle of the support pin 70 with respect to the movement axis, that is,
In order to change the angle of inclination of the holder 68 with respect to the reference plane,
A sector gear 92 as a worm wheel is integrally attached to the support shaft 74 of the holder 68. This sector gear
A worm gear 96 that rotates integrally with the rotation shaft 94 is meshed with 92. A bevel gear 98 is integrally attached to the rotating shaft 94. The bevel gear 98 meshes with a bevel gear 102 mounted coaxially with an output shaft 100a of a stepping motor 100 as a control motor.

By operating the stepping motor 100 in this manner, the sector gear 92 rotates, and the inclination angle of the holder 68 with respect to the reference plane is changed. In other words,
In accordance with the rotation drive amount of the scan Tetsu ping motor 100, the rear wheels RL, the front wheels FL steered angle theta _R of RR, same phase with respect to FR, opposite phase, so that the neutral state is changed controlled.

The sector gear 92 is centered on the worm gear.
The neutral position is defined at a position perpendicular to the center line of the rotation axis 94 of the 96. When the vehicle is turned clockwise as viewed from above the vehicle body from the neutral position, the steering ratio is changed to the rear wheel R.
L and RR are controlled to have opposite phases in the opposite directions to the front wheels FL and FR. On the other hand, when the vehicle is turned counterclockwise, the steering ratio is controlled to the same phase in which the rear wheels RL and RR face the same direction as the front wheels FL and FR.

Further, in the casing (not shown) of the steering ratio control mechanism 64 described above, in a state where it is located on the left and right sides of the sector gear 92, the opposite phase side and the same phase side formed of pins for regulating the rotation range of the sector gear 92 are provided. Stopper members 104 and 106 are attached. In this manner, when the sector gear 92 rotates in the opposite phase, when the rotation angle from the neutral position becomes, for example, -17.5 °, the sector gear 92 comes into contact with the opposite phase stop member 104, and further. The rotation is regulated.

When the sector gear 92 rotates in the same phase, if the rotation angle from the neutral position becomes, for example, 20 °, the sector gear 92 rotates.
Are in contact with the stopper member 106 on the same phase side, and further movement is restricted. Then, the sector gear 92 takes the position on the opposite phase side as the initial position,
The control position of the stepping motor 100 is regulated.

Note that rod stoppers 108 are provided on both sides of the connecting member 25 in order to regulate the maximum movement range of the relay rod 38 in the rear wheel steering device 10.

As shown in FIG. 1, an oil filter 110 is provided in the middle of the oil supply pipe 50 described above. Then, from the oil filter 110, a failsafe oil branch pipe 112 is branched separately from the oil supply pipe 50. The oil branch pipe 112 is bifurcated at the distal end, and the input ports of the fail-safe solenoid valves 114 and 116 are connected to the respective distal ends 112a and 112b. On the other hand, the output ports of these two sets of solenoid valves 114 and 116 are connected to return oil branch pipes 118a and 118b. These return oil branch pipes 118a and 118b are connected to the reserve tank 48 in a state where they are combined into one return oil pipe 118.

Here, each solenoid valve 114, 116 is energized with the turning-on operation of the ignition key of the vehicle, and the corresponding oil branch pipe is energized.
It is configured to perform closing operation of 112a and 112b and to open in a state where power is not supplied. As a result, both solenoid valves 114,
As long as 116 is closed, the hydraulic pressure from hydraulic pump 54 will act on control valve 46. On the other hand, during the rear wheel steering operation, when a later-described failure detection is performed, a later-described control unit 132 is described.
As a result, a fail-safe operation in which the energization state of both solenoid valves 114 and 116 is cut off is executed.

As a result, when one of the solenoid valves 114 and 116 is opened, the hydraulic pressure from the hydraulic pump 54 escapes to the reserve tank 48 without acting on the control valve 46. Accordingly, the hydraulic pressure no longer acts on the power cylinder 40, and the relay rod 38 is pressed from both sides by the pair of return springs 40d, and is mechanically urged to the neutral position. That is, the failsafe is activated, and the rear wheels are mechanically fixed to the neutral position, in other words, the vehicle is mechanically fixed to the two-wheel drive state (2WS).

Here, as described above, the turning ratio is defined at the turning position of the sector gear 92. Therefore, the sector gear 92 is provided with a turning ratio sensor to detect a set turning ratio by detecting a turning angle of the sector gear 92.
120 is installed. Note that this steering ratio sensor 120
Is configured to output a zero value in the neutral position, output a positive value in the same phase, and output a negative value in the opposite phase.

On the other hand, as shown in FIG. 3, in this embodiment, in order to achieve a vehicle speed-sensitive four-wheel steering system,
It has first and second two vehicle speed sensors 122 and 124. The first vehicle speed sensor 122 includes a transaxle 126
The second vehicle speed sensor 124 is mounted in the speedometer 130 and is connected to the connection of the speedometer shaft 128 to the speedometer 130. As each of the vehicle speed sensors 122 and 124, a lead switch type is adopted, and the speedometer shafts are respectively provided.
It is configured to output an output signal of 4 pulses per 128 rotations.

The above-described stepping motor 100 functions as a turning ratio changing means, and is configured such that its operation is controlled by an output from a control unit 132 having a built-in microcomputer as shown in FIG. The control unit 132 is configured to execute a fail-safe operation when a predetermined fail state occurs in the four-wheel steering state, as will be described in detail later. In this configuration, the steering ratio of the front and rear wheels is fixed to a steering ratio corresponding to the vehicle speed immediately before the detection of the lock, different from a normal characteristic set in advance.

Here, as shown in FIG. 4, a power supply voltage from a battery (indicated by + B in the figure) is supplied to the control unit 132 via a relay / timer circuit 134. On the other hand, the above-described first and second solenoid valves 114, 116
The power supply voltage from the battery is also supplied to the stepping motor 100 via the relay / timer circuit 134. Further, the voltage from the relay / timer circuit 134 is supplied to the control unit 132 via an oil level switch 136 described later.

An ignition switch (indicated by IG in the figure) is connected to the relay / timer circuit 134.
The power supply voltage from the battery is supplied to each part connected to the battery after a predetermined time elapses with the ON operation of the ignition switch. The L terminal of the alternator 138 is connected to the relay / timer circuit 134 for detecting a failure described later. When the input voltage at the L terminal is equal to or lower than a predetermined voltage, the control unit 132 disconnects the relay, stops supplying the voltage to each part, and interrupts the four-wheel steering control.

The control unit 132 detects the generated voltage value of the alternator 138, and is set so that the generated voltage value is equal to or higher than a predetermined voltage and a driving state of the engine at a predetermined rotation speed is detected.

The relay / timer circuit 134 is configured to output a fail signal to the control unit 132 when the ignition voltage input in accordance with the on operation of the ignition switch is not 9 V or more.

Here, as shown in FIG.
The 132 is connected to first and second vehicle speed sensors 122 and 124, a brake sensor 140 which is turned on when a brake pedal is depressed, and an inhibitor switch 142 attached to a select lever.

The control unit 132 is configured to execute the following two types of file detection and the following file detection from various sensors connected to the control unit 132. That is, when the first and second vehicle speed sensors 122 and 124 output the vehicle speed sudden change signal, when the output values of the first and second vehicle speed sensors 122 and 124 are different,
During running, when both output values disappear, when the calculated value of the rotation angle of the sector gear 92 due to the operation of the stepping motor 100 and the output value of the steering ratio sensor 120 are different, the output to both solenoid valves 114 and 116 is output. When the output of the steering ratio sensor 120 is out of the set range, when the output circuit of the stepping motor 100 is out of order, when the output circuit of the stepping motor 100 is broken, disconnected, or shorted, the reference output signal of the steering ratio sensor When the reading is not possible, the fail signal is set to be output to the control unit 132 when the oil level switch 136 in the tank of the hydraulic pump 54 is turned on.

The control unit 132 receives the above-mentioned fail signal and drives the stepping motor 100 to forcibly shift to the 2WS mode or cut off the power supply to both the solenoid valves 114 and 116 according to the contents of the fail signal. The hydraulic pressure does not act on the control valve 46 and the pair of springs 40
Mechanically fixed by the urging force of d, or the rear wheel steering device 10
To interrupt the control operation by shutting off the voltage supply to the
It is configured to execute three types of fail-safe operations.

Here, in this embodiment, the rotation speed is 2,200 r.
At pm or more, when the off signal from the inhibitor switch 142, that is, when the select lever is brought to a travel setting position other than the N range (neutral position) or the P range (parking position), it is determined that the vehicle is in a substantial traveling state. doing. In this state, if the vehicle speed information is not output from the first and second vehicle speed sensors 122 and 124, as described above, it is determined in the control unit 132 that the vehicle speed sensor is determined to be abnormal and the fail detection is executed. I have.

This fail detection operation itself has no mistake in the control contents. However, if the fail detection operation is always performed to cause the failsafe operation, inconvenience occurs in the following case. For this reason, in this embodiment, the setting is made such that the failure detection operation based on the abnormality of the vehicle speed sensor described above is prohibited.

That is, at the time of inspection of a vehicle at a repair shop or the like, in order to inspect whether or not the engine output is properly output, depress the accelerator pedal with the brake pedal depressed to forcibly stop the vehicle. There are tests to increase the engine speed. In this test, if the engine is normal, the engine speed will increase to the speed at which the maximum torque is exhibited. In such a test, if no restriction is placed on the fail detection, no vehicle speed information is output from both vehicle speed sensors 122 and 124 even though the traveling state is detected. Will be executed.

However, in this embodiment, when the brake pedal is depressed and the brake switch 140 is turned on, the above-described failure generation state is defined as a test, and in such a case, the failure detection is performed. Is set to be executed.

In this way, in this embodiment, the use of the break switch prohibits the useless failure detection operation during the test of the vehicle, thereby improving the workability of the test operation.

On the other hand, in the normal running state, the control unit 132 responds to the current running state, that is, the detected vehicle speed, in accordance with the normal first steering ratio characteristic shown by the solid line I in FIG. The steering ratio is set. Here, in the control unit 132, the first vehicle speed sensor 122 on the transaxle side and the second vehicle speed sensor 122 on the speedometer side
A step is performed to steer the rear wheels RL and RR based on a steering ratio determined according to the vehicle speed detected by the higher value of the two vehicle speeds detected by the vehicle speed sensor 124 of the vehicle. The driving of the ping motor 100 is controlled.

Note that this vehicle speed detection is executed by each vehicle speed sensor 122, 124 taking a moving average from the latest six vehicle speed information sampled every 131 msec.

Here, in the control unit 132, as a separate control independent of the above-described fail-safe operation, a lock control operation when a wheel is locked during running of the vehicle is set.

That is, as discussed in detail in the related art, in this embodiment, when traveling on a curved road with a vehicle speed higher than the predetermined vehicle speed of 35 km / h, the front and rear wheels are steered in phase. Therefore, the so-called high-speed cornering characteristics are favorably maintained. Here, during such high-speed cornering, if an obstacle or the like is found ahead, for example, a sudden break will be performed. When the wheels are locked due to the sudden braking, the actual speed of the vehicle does not suddenly decrease, but the vehicle speed information output from the first and second vehicle speed sensors 122 and 124 becomes zero. Therefore, the detected vehicle speed becomes lower than the predetermined vehicle speed, and the front and rear wheels are steered in opposite phases.

That is, during the cornering, the rear wheels are steered from the same phase to the opposite phase. For this reason, in order to maintain a stable posture of the vehicle during cornering and to run stably, the front and rear wheels must be stepped on in phase, but the steering is reversed to the opposite phase, and the yaw rate is reduced. Acting in the direction in which it is generated, the turning performance of the vehicle is sharply increased, and a so-called scooping phenomenon occurs,
The vehicle will spin and fall into danger.

In order to avoid such a danger, in this embodiment, when the control unit 132 detects the lock of the wheel, the danger avoidance control (hereinafter referred to as the lock control) for setting the steered ratio to the stable side. Is set to be executed.

Here, the control unit 132 executes the lock detection as follows. (1) When the brake pedal is depressed, the brake sensor 140
Is on, and (2) the detection result of the vehicle speed from the first vehicle speed sensor 122 is
And (3) the detected vehicle speed immediately before the vehicle speed is substantially determined to be zero based on the detection result of the first vehicle speed sensor 122 is 30 km / h.
Is set to determine that the wheels are locked.

Here, the first vehicle speed sensor 12 in the above (2) is used.
As described in the conventional example, the detection content of No. 2 is set to "substantially zero" because the detection accuracy is poor in the currently adopted reed switch type vehicle speed sensor and the detected vehicle speed is low. Is determined to be zero in the range of approximately 10 km / h to zero.

In the above (3), the detected vehicle speed immediately before the vehicle speed is substantially determined to be zero is the last detected vehicle speed among the six detection results used when the vehicle speed is substantially determined to be zero. 6 immediately before the sampling time of
This is defined by the average value of the detection results.

When the three conditions are satisfied, a lock determination is made. Based on the lock determination, the control unit 132 is set to execute the lock control described below.

That is, in this lock control, in order to maintain the running state on the stable side, a fixing operation of fixing the steering ratio of the front and rear wheels to the value of the steering ratio at the time when the vehicle speed immediately before the lock determination is detected is performed. Be executed. That is, the broken line in FIG.
As shown by II, in the case where the wheels are locked by suddenly stepping on the vehicle from a vehicle speed of 35 km / h or more, even if the vehicle speed detected by the first vehicle speed sensor 122 is substantially zero, the detection is performed. The subsequent steering ratio is fixed to the steering ratio on the same phase side at the point in time. By this operation of fixing the steering ratio, the steering ratio is maintained on the stable side, and the rear wheels are no longer steered. In this manner, in this embodiment, the traveling performance in a state where the wheels are locked is safely ensured.

As is clear from the above discussion, when the vehicle speed immediately before locking is 30 km / h or more and less than 35 km / h, the steering ratio on the opposite phase side is fixed. However, as described above, the turning ratio when the vehicle speed is 30 km / h or more and less than 35 km / h is almost a value of zero, and no inconvenience occurs even if the turning ratio is fixed at this value. Things.

Here, as described above, in the normal rear wheel steering control and the failure detection, the first and second vehicle speed sensors 122 and 122 are used.
Although 124 is used as the detecting means, only the first vehicle speed sensor 122 on the trunk axle side is used as the vehicle speed detecting means in the lock detecting operation, and the second vehicle speed sensor 124 on the speedometer side is used. Absent. This means that the first and second vehicle speed sensors 122 and 124 are connected to each other via a speedometer shaft 28. Here, this speedometer shaft 128 is rigid but long,
This is because a change in the rotation of the driven gear in the transaxle is not accurately and immediately transmitted to the second vehicle speed sensor 124 on the far side due to the variation in the torsional direction and the inertia during the rotation transmission.

As described above, in this embodiment, the two vehicle speed sensors 12 are used in the normal rear wheel steering control and the failure detection.
Although 2,124 are used, only one vehicle speed sensor, in particular, the first vehicle speed sensor 122 on the transaxle side is used in the lock detection operation. In this manner, the vehicle speed is detected with good responsiveness in the lock detection operation.

In this embodiment, two vehicle speed sensors 12
No comparison operation such as adopting a higher detection value after comparing 2,124 values is performed. Therefore, the operation time of the detection operation is extremely short, and the above-described good responsiveness is further ensured.

Here, in this embodiment, as the content of the above-mentioned fail control which is executed separately from the vehicle speed detecting operation in the above-described lock detecting operation, the output values of the first and second vehicle speed sensors 122 and 124 coincide with each other.・ A mismatch has been detected. And as long as both output values match,
The first vehicle speed sensor 122 is employed as vehicle speed detection means without fail detection.

However, for some reason the first vehicle speed sensor
If the output of the second vehicle speed sensor 122 suddenly changes to zero and is output only from the second vehicle speed sensor 124, the second vehicle speed sensor
Without using the detection result from 124,
Based on the mismatch between the detection outputs from the two vehicle speed sensors 122 and 124, fail detection is performed, and the above-described fail-safe operation is performed.

Specifically, the fail-safe operation in this case is the first
Also, the state of energization to the second solenoid valves 114 and 116 is cut off, and the hydraulic circuit is cut off. By cutting the hydraulic circuit, the rear wheels RL and RR are fixed to a so-called 2WS state without being steered by the biasing force of the pair of coil springs 40d, even if the front wheels FL and FR are steered. Become. Further, the fail warning lamp 144 provided in the meter panel shown in FIG. 4 blinks once. Thus, the fail-safe operation is performed.

Here, in this control unit 132,
The failure detection based on the failure of the first vehicle speed sensor 122 as described above is not performed when the brake pedal is depressed and the brake switch 140 is turned on.
It is set so as to execute the lock control described above.
The failure detection based on the sudden change of the output of the first vehicle speed sensor 122 to zero is performed by the brake switch.
It is set to run only when 140 is turned off.

That is, of the three conditions for the above-described lock determination, the state in which the detected vehicle speed from the first vehicle speed sensor 122 in (2) suddenly changes to substantially zero, and the first vehicle speed sensor 122 A state in which a failure occurs and information is not output rapidly is expressed as the same state. For this reason, in this embodiment, the control unit 132 uses the information that the output from the first vehicle speed sensor 122 when the brake switch 140 is turned on becomes zero for the lock determination, and the brake switch 140 The information that the output from the first vehicle speed sensor 122 in the off state is zero is
It is distinguished for use in file detection.

In this manner, in this embodiment, when the wheel locks due to the breaking operation during traveling, even if the output of the first vehicle speed sensor 122 becomes zero, this does not affect the wheel lock. Because it is based on
The lock detection operation is executed without detecting the file.

As a result, an inconvenience that occurs when the output of the first vehicle speed sensor 122 becomes zero based on the locking of the wheels during traveling to detect the failure and the steering state is forcibly fixed to the 2WS, that is, For example, when driving at a vehicle speed of 35 km / h or more, if the wheels are locked by stepping on a sudden break, the rear wheels must be fixed to the same phase steering ratio and a stable running state must be maintained. Nevertheless, since the operation of forcibly fixing to 2WS is performed based on the failsafe, the inconvenience of turning the rear wheels RL, RR from the position in which they are turned in phase to the neutral position is surely Will be prevented.

On the other hand, in this embodiment, during traveling, the first vehicle speed sensor 122 is turned off while the brake switch 140 is off.
Means that the first vehicle speed sensor 122 detects a stopped state in a running state in which no breaking occurs.
Therefore, for the first time in this state, the first vehicle speed sensor 122
This means that the occurrence of an abnormal state such as a failure has been found, and the above-described failure detection is executed.

In the control unit 132 described above, the following restriction conditions are imposed on lock detection. That is, in the above-described lock detection operation, when the vehicle speed detection result from the first vehicle speed sensor 122 is accompanied by a sudden increase in vehicle speed that is equal to or greater than a predetermined value, the lock detection is not performed, and
In the first steering ratio characteristic shown by the solid line I in FIG.
Is set to steer.

More specifically, the control unit 132 detects the amount of change per second of the vehicle speed detection result from the first vehicle speed sensor 122. If it is determined that the amount of change in vehicle speed per second is a sudden increase exceeding the predetermined value of 40 km / h, even if the lock detection state occurs immediately after that, in other words, For example, even if the above-described three lock determination conditions are satisfied, the shift to the lock control is prohibited without detecting the lock. Then, in such a lock control prohibited state, the rear wheels RL and RR are steered by the first steering ratio characteristic described above.

As described above, in the control unit 132, the restricting condition is imposed on the lock detection, and therefore, in this embodiment, when the traveling road surface has a low friction coefficient, in other words, it is frozen. When the vehicle is on a road, the accelerator pedal is strongly depressed at the time of starting, and when a so-called wheel spin state occurs, the traveling performance of the vehicle body can be secured safely.

That is, when wheel spin occurs at the time of starting, control of the vehicle body is lost, and the vehicle body may turn sideways. In this case, the driving vehicle operates to turn the steering wheel 24 to correct the posture of the vehicle body and to stop the vehicle body by stepping on a sudden break. In this state,
When the wheel locks, the above-described three lock determination conditions are satisfied. However, in this embodiment, as described above, lock detection immediately after the determination of a sudden increase in vehicle speed is prohibited. Therefore, by executing the lock detection, the steering ratio is fixed to the one immediately before the lock detection, and the inconvenience caused by not returning to the normal steering ratio at the time of restart is reliably prevented.

Further, in this embodiment, since the restriction condition for the lock detection is imposed as described above, chattering in the vehicle speed sensor occurs as described in the related art, and although the actual vehicle speed does not change, the detection is not performed. The output alone will surely prevent the inconvenience caused by the sudden increase in vehicle speed.

That is, if the above-mentioned restriction conditions are not imposed, 40 km
When the brake pedal is depressed lightly at / h or more and this braking occurs, and this state of zero vehicle speed is detected even for a moment, the control unit 132 detects the wheel lock and detects the steering ratio. A fixed operation will be performed. However, the occurrence of chattering necessarily accompanies a sudden increase in vehicle speed. In this embodiment,
Since the lock detection operation is prohibited by the detection of the sudden increase in the vehicle speed, the unnecessary turning ratio fixing operation based on the malfunction of the vehicle speed sensor, which is referred to as chattering, is prevented, and based on the above-described first turning ratio characteristic, Normal steering ratio control is executed, and good traveling performance is ensured.

In the above description, the lock detection operation and the lock control operation in the control unit 132, and various control operations associated therewith have been described.

However, when the lock control is executed based on the lock detection, the steering ratio is fixed to the steering ratio corresponding to the vehicle speed immediately before the lock detection as described above. Such an operation is necessary from the viewpoint of ensuring the safety of the running state, but is an unnecessary operation after the wheels are unlocked. Therefore, after the lock of the wheels is released in this way, the lock control operation is released as soon as possible, and the state in which the steering ratio is fixed is removed.
A normal steering ratio control operation must be performed. For this reason, in this embodiment, as described below, the lock control operation release operation, in other words,
A return operation from the lock control state to a normal steering ratio control operation is specified.

Hereinafter, the return operation (lock release operation) will be described.

This return operation (lock release operation) is basically performed when it is determined that it is safe to release the lock control operation after the lock detection operation. Actual vehicle speed and first vehicle speed sensor 122
The first mode in which the release operation is executed when the vehicle speed detected by the control unit substantially coincides with the vehicle speed, and the second mode in which the release operation is executed when the detected vehicle speed is lower than the actual vehicle speed, are the control unit. 132 is set.

That is, in the first embodiment, after such a lock detection operation, the case where the actual vehicle speed substantially coincides with the vehicle speed detected by the first vehicle speed sensor 122 means that the wheels are not on the road surface. Means a state in which the grip is completely gripped, and it is determined that the user has escaped the danger state without slip. Here, such a substantial match between the actual vehicle speed and the vehicle speed detected by the first vehicle speed sensor 122 is determined when any of the following three conditions is satisfied. It is.

First, the first condition is that, under any conditions (running conditions, road surface conditions), a time has elapsed in which the locked vehicle can be reliably stopped. After this time has elapsed, the vehicle speed is zero (stop state), and as described above, after the lock detection operation, the actual vehicle speed is compared with the first vehicle speed.
The vehicle speed detected by the vehicle speed sensor 122 substantially coincides, and at this timing, the lock control operation is released. Thus, the operation returns to the normal steering ratio control operation as shown by the solid line I in FIG.

Specifically, riding, three conditions described above assortment connexion lock detection performed is to lock control operation is started, release period T ₁ of the order to release the lock control operation, the vehicle is in lock just before at a speed xkm In this case, the release period T ₁ (sec) = x · C where C is a constant.

Here, in this embodiment, the constant C is 0.
142 is given. And the value of 0.142 is a vehicle running on a road with a road surface friction coefficient of 0.2 at 120 km / h, a sudden brake was applied, and the wheels were locked,
This is a value calculated from 17 seconds, which is the time during which the vehicle can stop when the vehicle continues to slide on the road. The value of the road surface friction coefficient of 0.2 occurs, for example, in a frozen state of the road surface in a severe winter season in Scandinavian countries, and is a sufficient setting condition.

In this way, as shown in Figure 6A, for example, during traveling vehicle is 50 km / h, even shall apply in the case where the wheel suddenly Bureiki is depressed has lock, release time T ₁ is, 50 × 0.142 = 7.1 (seconds), so after 7.1 seconds, it is surely stopped.

In FIG. 6A, the solid line represents the first vehicle speed sensor 122.
, And the dashed line indicates the actual vehicle speed of the vehicle. As is apparent from the dashed line in FIG. 6A, the vehicle is actually stopped 3.6 seconds after the wheel locks in this embodiment. In addition, this setting is performed according to FIGS.
The same applies to the 6D diagram.

Thus, by setting the first condition,
When the release time T ₁ as described above has passed, for example, by driving car continues down the Bureikipedaru, no matter Bureikisuitsuchi 140 is made ON, already vehicles are those stopped reliably. For this reason, after the release time T ₁ has passed,
Even if the lock control is released and the normal steering ratio control operation is set to be executed, there is no problem.

In this way, in this embodiment, when the driving vehicle notices the stopped state of the vehicle and tries to start again, the steering ratio is not fixed to the steering ratio immediately before the lock, Since the normal steering ratio control is executed, the traveling performance of the vehicle is maintained satisfactorily.

Next, a second condition for releasing the lock control operation will be described. The second condition is that the detected vehicle speed at the present time exceeds the vehicle speed immediately before the lock is detected.
By satisfying the second condition, the actual vehicle speed substantially matches the vehicle speed detected by the first vehicle speed sensor 122 at the vehicle speed immediately before the lock detection, and at this timing, The lock control operation is released.
Thus, the operation returns to the normal steering ratio control operation as shown by the solid line I in FIG.

In detail, as shown in FIG.
When the vehicle is running at / h, the wheel is locked by stepping on a sudden break, the lock is detected, and the lock control operation is started. Here, there is a case where the driver notices that the vehicle has completely stopped, releases his / her foot from the brake pedal, and depresses the accelerator pedal to accelerate the vehicle. In such a case, since the wheels are gripped, as shown by the solid line in the figure, the accelerator pedal is depressed,
The output of the vehicle speed sensor 122 will increase. And
If the detected vehicle speed at the current time is higher than the vehicle speed immediately before the lock detection, the running stability of the vehicle cannot be secured unless the steering ratio is further changed to the same phase. Therefore, from the viewpoint of driving safety, the lock control operation is naturally canceled and the rear wheels are steered at a steering ratio according to the current vehicle speed.

On the other hand, under the second condition, the driving vehicle releases the brake from the brake pedal by releasing the foot from the brake pedal at a relatively early time when the wheels are locked, in other words, while the actual vehicle speed does not decrease so much. There is a case where the operation is released and the accelerator pedal is depressed. In this case, when the wheels grip the road surface, the output of the vehicle speed sensor 122 increases in accordance with the depression of the accelerator pedal, as indicated by the solid line in the figure. Then, as described above, when the detected vehicle speed at the present time exceeds the vehicle speed immediately before the lock detection,
Unless the turning ratio is further changed to the same phase side, the running stability of the vehicle cannot be ensured. Therefore, from the viewpoint of driving safety, the lock control operation is naturally canceled and the rear wheels are steered at a steering ratio according to the current vehicle speed.

As described above, in this embodiment, when the vehicle speed is to be accelerated after the detection of the lock, the lock control operation is canceled when the current detected vehicle speed is more than the vehicle speed immediately before the lock detection. Then, by starting the normal turning ratio control operation, traveling safety is ensured.

Next, a third condition for releasing the lock control operation will be described below. The third condition is that regardless of the Bureikisuitsuchi on and off, a constant speed is continuously input for a predetermined time T _2. That is, after the lock is detected,
Vehicle speed information from the predetermined time T ₂ by the first vehicle speed sensor 122 when entered, it releases the lock control operation is performed. Thus, the operation returns to the normal steering ratio control operation as shown by the solid line I in FIG.

In detail, as shown in the left half of FIG.6C, for example, when the vehicle is traveling at 50 km / h, the wheels are locked by stepping on a sudden break, the lock is detected, and the lock control operation is started. Will be. Here, the driving vehicle may notice that the vehicle body has completely stopped, release the brake pedal, depress the accelerator pedal, and start the vehicle. In such a case, since the wheels are gripped, the output of the first vehicle speed sensor 122 increases as the accelerator pedal is depressed, as indicated by the solid line in the figure. Then, the vehicle speed information is continuously from the vehicle speed sensor 122, the output only 917msec set as the predetermined time T _2, since the wheels are grips, the steering ratio is set according to the detected vehicle speed Unless the steering ratio control is changed to the normal steering ratio control, the running stability of the vehicle cannot be ensured. Therefore, from the viewpoint of driving safety, the lock control operation is naturally canceled and the rear wheels are steered at a steering ratio according to the current vehicle speed.

On the other hand, under the third condition, as shown in the right half of FIG. 6C, when the driver is relatively fast with the wheels locked, in other words, when the actual vehicle speed does not decrease so much. Then, reduce the amount of depression of the brake pedal,
In some cases, the wheels are gripped on the road surface. in this case,
Since the foot is not released from the brake pedal, the break switch 140 is kept on. However, when the wheels grip the road surface, the output of the first vehicle speed sensor 122 returns as indicated by the solid line in the figure. Therefore, as described above, at the time point when 917 msec has elapsed from the time point at which the vehicle speed information is output from the first vehicle speed sensor 122, unless the steering ratio is changed according to the detected vehicle speed, the running stability of the vehicle is not changed. Cannot be secured.
Therefore, from the viewpoint of driving safety, the lock control operation is naturally canceled and the rear wheels are steered at a steering ratio according to the current vehicle speed.

Thus, in this embodiment, after the lock detection, only when the vehicle speed information is output a predetermined time T _2, the wheels have been grips the road surface, and the detected vehicle speed and the actual vehicle speed coincides Judge that it is. In such a state in which the wheels are gripped, whether the brake switch is on or off, the lock control is immediately released, and the normal steering ratio control operation is started, thereby improving the driving safety. Will be secured.

Next, the condition in the second mode for releasing the lock control operation, that is, the fourth condition will be described.

Under the above-described first to third conditions, as described above, when the detected vehicle speed and the actual vehicle speed match,
This means that the wheels are gripping the road surface, so there is no need to perform the lock control operation.It is set so that this lock post-birth operation is released and the normal steering ratio control operation is returned. ing.

However, the fourth condition depends on the timing at which it is determined that it is sufficiently safe even if the lock control operation is canceled substantially without waiting for the coincidence between the detected vehicle speed and the actual vehicle speed as described above. , Is set. That is, the fourth condition, after the Bureikisuitsuchi 140 is turned off operation, are set by the predetermined time T ₂ has elapsed. This fourth
Is satisfied, the wheels are moving in the direction to grip the road surface after the brake is released,
The actual vehicle speed and the vehicle speed detected by the first vehicle speed sensor 122 will eventually substantially match. Then, the lock control operation is canceled at this timing, thereby returning to the normal steering ratio control operation as shown by the solid line I in FIG.

More specifically, as shown in the right half of FIG. 6D, for example, while the vehicle is running at 50 km / h, the driver accidentally steps on a sudden break and the wheels are temporarily locked. In this locked state, when the driver notices that the wheel has locked,
When the foot is released from the brake pedal, the wheel operates in a direction to grip the road surface. In this case, when the foot is released from the brake pedal, the brake switch 140 is turned off. From the time when the brake switch 140 is turned off, a predetermined time T ₂ , in this embodiment, 786 msec
Is set so that the lock control operation is released and the normal steering ratio control operation is resumed after the time has elapsed.

That is, since 786 msec is a sampling time of 131 msec, in this fourth condition, after waiting for input of six vehicle speed information, the control content is changed from the lock control to the normal steering ratio control. It is intended to be restored. Here, as described above, the vehicle speed is set to be calculated by taking a moving average of six vehicle speed information. In this manner, the fourth condition is that the locked state of the wheels is released by releasing the brake, and the first vehicle speed sensor
It is set to be satisfied after waiting for 786 msec, which is the time for outputting the six vehicle speed information necessary for obtaining the moving average, from the time when the vehicle speed information starts to be output from 122.

Here, 786mse after the break was released like this
Since the detected vehicle speed at the time when c has elapsed is the average value of the six pieces of vehicle speed information up to that point, even if the vehicle speed at this time actually matches the actual vehicle speed, the detected vehicle speed does not match the actual vehicle speed. It does not. However, as described above, such a behavior of the vehicle is caused by an excessive depression due to an erroneous operation of the brake pedal by the driver. Therefore, unlike the above three conditions, the vehicle travels relatively stably. Is what it is. Thus, before 3
Unlike the condition, it is possible to return to the normal steering ratio control operation without causing any problem without waiting for the actual vehicle speed to match the detected vehicle speed.

In addition, under the fourth condition, in other words, at a stage before the detected vehicle speed coincides with the actual vehicle speed, the lock control is positively released and the normal steering ratio control operation is returned. ing. For this reason, the detected vehicle speed at the time of return is slower than the actual vehicle speed. Here, in order to change and control the turning ratio, the above-described stepping motor 100 is directly driven by the stepping motor 100 in accordance with an instruction from the control unit 132 so as to achieve the turning ratio according to the detected vehicle speed information. Is what is done. The operating speed of the stepping motor 100 is in the operating range, in other words,
It is set to change according to the change width of the detected vehicle speed.

Therefore, if the vehicle returns to the normal steering ratio control operation, the actual vehicle speed information is directly input to the control unit 132, and based on this, the control unit 132 attempts to drive-control the stepping motor 100. Then, since the vehicle speed information up to now has been zero, the stepping motor 100 is operated with a short operation time to make up for the difference. In this way, the rear wheels RL and RR are steered rapidly, and in the worst case, there is a possibility that the so-called decrease in rake will occur.

However, in this embodiment, when returning to the normal steering ratio control operation, the vehicle speed information based on the actual vehicle speed is not input to the control unit 132, but the six vehicle speeds including the zero information are used. A value obtained by averaging the information is employed as detected vehicle speed information. As a result, the detected vehicle speed is definitely lower than the actual vehicle speed. In this manner, at the beginning of the return, the stepping motor 100 is driven and controlled based on the detected vehicle speed lower than the actual vehicle speed, so that the rear wheels RL and RR are relatively loosely steered and the above-described problem does not occur. become.

The detected vehicle speed gradually approaches the actual vehicle speed as the sampling time of 131 msec elapses. As a result, the stepping motor 100 can also operate following the change in the vehicle speed information, so that an unreasonable operating state does not occur in the stepping motor 100 and a good operating state is achieved. Will be.

This concludes the description of the release operation of the lock control operation, in other words, the return operation from the lock control state to the normal steering ratio control operation, and will now be described with reference to the flowcharts shown in FIGS. 7A and 7B. With reference to the control unit described above
A schematic control procedure of a series of lock control operations in 132 will be described.

The control means shown in FIGS. 7A and 7B
This is executed at every sampling time of c. That is, when this control procedure is started, first, in step S1, it is determined whether or not the lock flag F is "1". Here, the lock flag F is set to 0 when the control operation is started, and is set to 1 when a lock detection operation described later is executed. In this step S1, if the lock flag F is set to 0, the lock detection operation is started, and if 1 is set, as described later, the process skips to step S13, where Matching of second vehicle speed sensors 122 and 124
It is set to execute control to detect mismatch.

Then, when it is determined NO in step S1,
In other words, when it is determined that the lock flag F is 0, in steps S2 and S3, a sudden increase in the vehicle speed is determined based on the wheel spin of the wheel, the chattering of the sensor, and the like. That is, in step S2,
The increase change amount D ₂ of the output of the second vehicle speed sensor 124 on the speedometer side, specifically, is defined by the difference in the increasing direction between the vehicle speed detection result detected at the previous sampling timing and the vehicle speed detection result detected this time. that numeric D ₂ is the predetermined value, in this embodiment, whether or not 7km / h / 131msec or more is determined. This predetermined value is set at an acceleration speed of 7 km / h per sampling time, and approximately 53 km / h per second.
Is equivalent to the amount of change.

In this step S2, if it is determined that the NO, that is, when the increasing change amount D ₂ of the output of the second vehicle speed sensor 124, is determined to be smaller than the predetermined value, in step S3, the transaxle side increasing the amount of change D ₁ of the output of the first vehicle speed sensor 122, a predetermined value, in this embodiment, whether or not 7km / h / 131msec or more is determined.

Then, in step S2 or step S3, YES
If it is determined that, i.e., increase the amount of change in the output of the first vehicle speed sensor 122 D ₁ or, when increasing the amount of change D ₂ of the output of the second vehicle speed sensor 124, it is determined to be larger than a predetermined value It is determined that the vehicle speed is rapidly increasing, and the flag A indicating the vehicle speed rapidly increasing condition is set to 1 in step S4.
Here, when the vehicle speed rapid increase flag A is 1, the vehicle speed is rapidly increasing, and the lock detection operation is prohibited. On the other hand, if the vehicle speed rapid increase flag A is 0, it indicates that the vehicle speed is not rapidly increasing, and the lock detection operation and the lock control operation are performed.

Incidentally, in the vehicle speed rapidly increasing state, as described above, since the lock detection operation is not performed, as described below,
The control procedure is set to return and return to the initial state even when the vehicle speed rapidly increasing state is due to sensor-specific chattering.

In other words, after the flag A is set to 1 in step S4, if the above-mentioned rapid vehicle speed increase state is chattering in step S5, it is determined whether or not the chattering has been completed. In this determination,
If the outputs of both vehicle speed sensors 122 and 124 are both 56 km / h or less, it is determined that chattering has been completed. If the determination in step S5 is NO, that is, if it is determined that the vehicle speed detected by the two sensors 122 and 124 is equal to or higher than 56 km / h and that the chattering has not yet been completed, the lock detection operation is not performed. Must be set as follows. Therefore, as described above, the control unit returns to the initial state.

On the other hand, if YES is determined in step S5,
That is, when the outputs of both vehicle speed sensors 122 and 124 both reach 56 km / h or less, it is determined that chattering is beginning to subside. Therefore, in this case, it is determined in step S6 whether a predetermined time, for example, 0.786 seconds has elapsed after the rapid increase determination was performed. That is, when the detected vehicle speed drops to 56 km / h or less, this 0.
After the elapse of 786 seconds, it can be determined that chattering is substantially completed, and the above-described determination is performed.

If NO is determined in this step S5, that is, if 0.786 seconds have not yet elapsed, the lock detection must still be prohibited, so the control procedure returns and returns to the initial state. . On the other hand, if YES is determined in step S5, that is, if 0.786 seconds have elapsed, the vehicle speed rapidly increases, whether it is based on wheel spin or whether it is based on chattering. In step S7, the rapid increase flag A is set to 0, and the control procedure returns.

On the other hand, if NO is determined in step S3 described above, that is, if it is determined that the vehicle speed is not in a rapidly increasing state, it is determined in step S8 whether the vehicle speed rapid increase flag A is 1. If the determination in step S8 is YES, that is, if it is determined that the vehicle speed is rapidly increasing, the vehicle speed is rapidly increased by wheel spin, but the vehicle speed is not rapidly increased by chattering. Therefore, the process returns to step S5, and waits until the chattering is completed.

If the determination in step S8 is NO, that is, if it is determined that the vehicle speed is not rapidly increasing, the lock detection operation and the lock control operation will be executed below.

That is, if the vehicle speed rapid increase flag A is 0, it is determined in step S9 whether the brake switch 140 is on. Then, in this step S9,
If the determination is YES, that is, if the break switch 140 is on, in step S10, the first sampling time of the previous sampling time, in other words, 131 msec before, is set.
It is determined whether the vehicle speed detected by the vehicle speed sensor 122 is faster than 30 km / h.

If YES is determined in this step S10, that is, if it is determined that the preceding vehicle speed detection value is faster than 30 km / h, in step S11, the first vehicle speed sensor 122 detects the current detection operation. It is determined whether the vehicle speed is substantially 0 km / h. If it is determined YES in this step S11, that is, if it is determined that the current detected vehicle speed is substantially 0 km / h, as described above, the three conditions for detecting the lock are satisfied. Since it is satisfied, lock detection will now be performed.

Based on this lock detection, the lock flag F is set to 1 in step S12. On the other hand, if NO is determined in each of the above-described steps S10 and S11, the lock detection is not established, so that the process returns to step S9 and executes step S9.

After the lock flag F is set to 1 in step S12, it is determined in step S13 whether the detection result of the first vehicle speed sensor 122 matches the detection result of the second vehicle speed sensor 124. If NO is determined in this step S13, that is, if the detection outputs of the two sensors 122 and 124 do not match, since the state is the fail state as described above, the failsafe control operation is executed in step S14. And return.

On the other hand, if YES is determined in step S13, that is, if the two detected vehicle speeds are the same, the lock detection described above is performed in a normal state, and therefore, in step S15, the lock described above is performed. Start the control operation.

Here, the reason why the determination that the lock detection is performed in the normal state is necessary is as follows. That is, as described above,
In this lock detection, only the first vehicle speed sensor 122 is used for vehicle speed detection. If the normal state is not determined in this step S13, the output of the second vehicle speed sensor 124 is different from the output of the first vehicle speed sensor 122, and this file has to be actually detected as a file. No detection will be performed. As a result, the lock may be detected based on the detection result of the first vehicle speed sensor 122 which may be incorrect.

After the lock control operation is started in step S15, it is determined in step S16 whether any of the above four lock release conditions is satisfied. If the determination in step S16 is NO, that is, if no lock release condition is satisfied, the process returns to step S15, and the lock control operation is continued.

On the other hand, if it is determined YES in step S16,
That is, if any lock release condition is satisfied, the lock control operation is released in step S17,
The operation returns to the normal steering ratio control operation. And
In step S18, the vehicle speed rapid increase flag A is set to 0, and the control operation returns to the initial state.

Here, if the determination in step S9 is NO, that is, if it is determined that the brake switch 140 is off, the lock detection operation described above is not executed. Then, in steps S19 and S20, a sudden decrease in the output of each of the vehicle speed sensors 122 and 124 is determined for fail detection.

That is, in step S19, it is determined whether the output value of the first vehicle speed sensor 122 has sharply decreased. This determination is based on the deceleration change amount E ₁ of the output of the first vehicle speed sensor 122 on the transaxle side, specifically, the deceleration direction between the vehicle speed detection result detected at the previous sampling timing and the vehicle speed detection result detected this time. numerical E ₁ defined by difference, the predetermined value, in this embodiment, whether or not 10km / h / 131msec or more is determined. This predetermined value is 10 per sampling time.
km / h deceleration, about 76km per second
/ h.

If YES is determined in this step S19, that is, if the first vehicle speed sensor 122 determines that the vehicle speed sharply decreases, a failure is detected and the above-described step is performed.
Skipping to S14, the failsafe control operation is executed.

Also, in step S19, if it is determined NO,
That is, when the first vehicle speed sensor 122 does not determine a rapid decrease in vehicle speed, in step S20, a rapid decrease in the output value of the second vehicle speed sensor 124 is determined. This judgment is
Deceleration change amount E ₂ outputs of the second vehicle speed sensor 124 of the speedometer side, a predetermined value, in this one embodiment, 10 km / h
It is determined whether it is / 131 msec or more.

If the determination in step S20 is YES, that is, if the second vehicle speed sensor 124 determines that the vehicle speed has sharply decreased, a failure is detected and the above-described step is performed.
Skipping to S14, the failsafe control operation is executed.

Also, in step S20, if the determination is NO,
That is, if the first and second vehicle speed sensors 122 and 124 do not determine a rapid decrease in vehicle speed, step S2 is executed.
In step 1, it is determined whether the detection result of the first vehicle speed sensor 122 and the detection result of the second vehicle speed sensor 124 having the same contents as in step S13 described above match. NO at this step S21
If it is determined, that is, if the detection outputs of the two sensors 122 and 124 do not match, as described above, the state is the fail state, so that step S14 is skipped and the fail-safe control operation is executed. I do.

On the other hand, if YES is determined in this step S21, that is, if the detection outputs of the two vehicle speed sensors 122 and 124 match, it is not in the fail state, so the routine returns.
It returns to the initial state of the control operation.

 As described above, a series of control operations ends.

As described in detail above, in this embodiment, the locking of the wheels is detected, and in accordance with the detection result, the danger of running is avoided by the vehicle speed-sensitive four-wheel steering device with the wheels locked. Therefore, it is not necessary to mount a so-called anti-lock brake system (ABS) for preventing the wheels from locking in order to solve the above-mentioned problems.

It is needless to say that the present invention is not limited to the configuration of the above-described embodiment, but can be variously modified without departing from the gist of the present invention.

For example, in the above-described embodiment, in the lock control operation, basically, the normal steering ratio control indicated by the solid line I in FIG. 5 is stopped to maintain the running state of the vehicle on the stable side. The steering ratio is set so as to be controlled with specific characteristics, and specifically, is set so as to be fixed to a steering ratio corresponding to the vehicle speed immediately before the lock is detected.

However, the present invention is not limited to fixing the steering ratio according to the vehicle speed immediately before the detection of the lock as the lock control on the stable side different from the normal steering ratio control. As shown in a first modified example by III, as a mode of setting the running state to the stable side in the lock control, the turning ratio is fixed to 0 and the 2WS is forcibly set.
May be set.

Although not shown, as an aspect of setting the running state to the stable side in the lock control, as a second modification, a delay control may be performed. That is, in the second modification, the lock control when the lock is detected has the same characteristics as the normal steering ratio control, but the change speed is set to be slow, in other words, stepping. The operation speed of the motor 100 is set to be low. As a result, in the lock control on the stable side in the second modified example, although the steering ratio changes according to the characteristic shown by the solid line I in FIG. The time during which the turning ratio is changed to the opposite phase according to the vehicle speed is set to be long.

Specifically, when the actual vehicle speed reaches zero due to friction while the brake pedal is continuously depressed and the wheels remain slipped, the steering ratio changes from the same phase to the opposite phase with a delay. Then, the steering ratio is set to be delayed to a value close to zero to some extent.

As described above, by setting the control content on the stable side in the lock control as in the first and second modifications, the stability control is not sufficiently stable as in the first embodiment, but is sufficiently realized. Thus, there is an effect that the return timing when the lock state is released and the control returns to the normal control is set quickly.

That is, in the above-described embodiment, the steering ratio according to the detected vehicle speed immediately before the lock is detected is fixed according to the lock detection. On the other hand, when the lock state is released, when the normal steering ratio control is resumed, the vehicle speed at the time of return, for example, if the vehicle is stopped, the vehicle speed determined to be 0 km / h. The setting is changed to the steering ratio corresponding to the steering ratio. Therefore, assuming that the steering ratio fixed according to the lock detection is on the same phase side, the stepping motor 100 must be driven to change the steering ratio to the opposite phase side. Thus, this stepping motor
Until the operation of the vehicle 100 and the setting operation to the predetermined steering ratio is completed, the normal steering ratio control operation is not substantially started.

On the other hand, in the first modification, the turning ratio is fixed to zero when the lock control operation is released, and in the second modification, the turning ratio is roughly Has reached zero. In this way, in the first and second modifications, the time required for the return operation can be shorter than in the case of the first embodiment, and the actual return timing can be set earlier. Will be achieved.

[Effects of the Invention] As described above in detail, according to the present invention, the detection of the sudden decrease in the wheel rotation caused by the braking is performed on condition that the brake detecting means detects the brake operating state. The sudden decrease of the detection output by the vehicle speed detecting means in the state where it is set is not a fail, but is set to be determined as a rapid decrease state of the wheel rotation due to braking, and when the brake detecting state is detected by the brake detecting means,
Since the execution of the fail-safe control by the changing means is prohibited even when the detection output of the vehicle speed detecting means is suddenly reduced, the wheels associated with the braking are required to maintain good running performance in accordance with the running state, such as when cornering. When the output value of the vehicle speed sensor is rapidly decreased due to braking by detecting the rapid decrease state of the rotation, the control for setting the steering characteristic to a stable side is reliably executed, and the configuration is made so that the fail control is not erroneously executed. Therefore, when the vehicle speed sensor fails, the fail control can be reliably executed to ensure safety.

[Brief description of the drawings]

FIG. 1 is a plan view schematically showing a configuration of a four-wheel steering mechanism provided with one embodiment of a rear wheel steering device of a vehicle according to the present invention; FIG. 2 is a schematic diagram showing a configuration of a rear wheel steering device. FIG. 3 is a perspective view showing a setting state of first and second vehicle speed sensors; FIG. 4 is a connection diagram of a control unit of a rear wheel steering device; FIG. 5 is various characteristics in turning ratio control. FIGS. 6A to 6D are timing charts for explaining four release conditions of the lock control, respectively; and FIGS. 7A and 7B are schematic diagrams showing the control procedure of the control unit. It is a flowchart shown. In the figure, 10: rear wheel steering device, 12: four wheel steering mechanism, 14:
… Front wheel steering device, 16L; 16R …… Nickle arm, 18L; 18R
… Tie rod, 20… relay rod, 22… steering mechanism, 24… steering wheel, 26… power steering mechanism, 28… first rack, 30… first pinion, 32… steering shaft, 34L; 34R ……
Knuckle arm, 36L; 36R ... Tie rod, 38 ... Relay rod, 40 ... Power cylinder, 40a ... Piston, 4
0b; 40c …… Hydraulic chamber, 0d …… Return spring, 42; 44
... pipe, 46 ... control valve, 46a ... valve casing, 48 ... reserve tank, 50 ... oil supply pipe, 52 ... oil discharge pipe, 54 ... hydraulic pump, 56 ... connecting member, 58 ... ... second rack, 60 ... rear steering shaft, 62 ... second pinion, 64 ... steering ratio control mechanism,
66 ... Control rod, 68 ... Holder, 70 ... Support pin, 72 ... Swing arm, 74 ... Support shaft, 76 ... Ball joint, 78 ... Connecting glove, 80 ... Ball Joint 82, a rotational force imparting member 84, a ball joint 86, a supporting shaft 88, a large bevel gear 90, a small bevel gear 92, a sector gear 94, a rotating shaft 96 … Worm gear, 98… bevel gear, 100… stepping motor, 1
00a output shaft, 102 bevel gear, 104; 106 stopper member, 108 rod stopper, 110 oil filter 112 oil branch pipe 112a; 11b tip, 114; 116
Solenoid valve, 118, return oil pipe, 118a; 118b, return oil branch pipe, 120, steering ratio sensor, 122, first vehicle speed sensor,
124: second vehicle speed sensor, 126: transaxle,
128… Speedometer shaft, 130… Speedometer, 13
2 ...... Control Units -, 134 ...... relay timer circuit, 136 ...... oil level Sui Tutsi, 138 ...... alternator, 140 ...... Bureikisensa, 142 ...... inhibitor task i Tutsi, 144 ...... Fueiru warning lamp, theta _{R ......} steering Horn, FL ...
… Left front wheel, FR …… right front wheel, RL …… left rear wheel, RR …… right rear wheel.

Claims (3)

(57) [Claims] 1. A rear wheel steering device for detecting a vehicle speed and steering a rear wheel with a steering characteristic according to the detected vehicle speed and the steering of a front wheel. Setting means for setting the steering characteristics of the rear wheels according to the vehicle speed detected by the vehicle speed detecting means; abnormality determining means for determining that the detection output of the vehicle speed detecting means has decreased sharply by a predetermined value or more; Changing means for stopping the control based on the turning characteristics set by the setting means and executing fail-safe control, when the abnormality determining means determines that the detection output of the vehicle speed detecting means has sharply decreased; A brake detecting means for detecting a brake operating state, and when the brake operating state is detected by the brake detecting means, even if the detection output of the vehicle speed detecting means suddenly decreases, the change means Rear wheel steering apparatus for a vehicle, characterized in that it comprises a prohibiting means for prohibiting the execution of Eiruseifu control. 2. The vehicle speed detecting means includes a first vehicle speed sensor on a transaxle side and a second vehicle speed sensor on a speedometer side, and the output of either the first or second vehicle speed sensor is provided. 2. The rear wheel steering device according to claim 1, wherein a sudden decrease in the detection output of the vehicle speed detecting means is detected when the vehicle speed suddenly decreases from a predetermined value. 3. The setting means uses a higher value of an output result of the first vehicle speed sensor and an output result of the second vehicle speed sensor as a detected vehicle speed, and sets a turning characteristic in accordance with the detected vehicle speed. The rear wheel steering device according to claim 2, wherein the setting is performed.