JP2583369B2 - Vehicle front and rear wheel steering system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a front and rear wheel steering device for a vehicle, and more particularly to a front and rear wheel steering device for turning a rear wheel biased to a neutral position by a spring or the like by an electric motor. TECHNICAL FIELD The present invention relates to a front and rear wheel steering device capable of inspecting a mechanical element of a mechanism for fatigue over time.

[0002]

2. Description of the Related Art As is well known, in a front and rear wheel steering device for steering a rear wheel together with a front wheel, a target steering angle of a rear wheel is determined based on steering of a steering wheel, vehicle speed, and the like. The mechanism turns the rear wheels to the target steering angle. Conventionally, an actuator such as an electric motor is assembled as such a rear-wheel steering mechanism. However, the rear-wheel steering mechanism is provided with a neutral biasing spring that biases the rear wheel to a neutral position to provide a fail-safe mechanism. Is being planned. The neutral position biasing spring includes an elastic body for reducing contact noise between the gear housing and the like, and also applies the rear wheel only in a range excluding a dead band area having a predetermined width centered on the neutral position. It is configured to be energized.

In the above-described front and rear wheel steering devices, deterioration of the neutral position biasing spring or the mechanism of the rear wheel steering mechanism with time (increased friction) is inevitable. Is known to affect the size of the dead zone, the responsiveness of the rear wheel steering mechanism, and the like. For this reason, in the above-described steering device, it is desired to confirm fatigue of a mechanical element such as a spring or deterioration of an elastic body over time at the time of periodic inspection or the like.

[0004]

However, in the conventional front and rear wheel steering apparatus as described above, the rear wheel steering mechanism is disassembled in order to check the state of deterioration of the rear wheel steering mechanism or the neutral biasing spring. Inspection must be carried out visually or with an inspection jig or the like, which is difficult. The present invention has been made in view of the above circumstances, and has as its object to provide a front and rear wheel steering device for a vehicle that can easily inspect a rear wheel steering mechanism for deterioration with time, fatigue status, and the like.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a front wheel turning mechanism for turning a front wheel in response to steering of a steering wheel, and a rear wheel turning by an output of an electric motor. A rear wheel steering mechanism, a neutral position urging spring for urging the rear wheel to a neutral position, an elastic body interposed between the spring and the gear housing, and a steering wheel for energizing the electric motor. In the front and rear wheel steering device for a vehicle having control means for controlling according to the condition, the mode shifts to an inspection mode under a predetermined condition, and in this inspection mode, the length of the neutral position urging spring is adjusted by applying a current value to the electric motor to the electric motor. Set to the current value that is the largest and the deformation of the elastic body is the largest,
The steering angle of the rear wheel in this state is configured to be compared with a predetermined reference value.

According to the present invention, when the steering wheel is steered from the neutral position, the vehicle speed is 0 or substantially zero, and the steering mode is shifted to the inspection mode for a predetermined time without steering the steering wheel. It can be configured to be performed on the condition that the elapsed time.

[0007]

In the vehicle front and rear wheel steering apparatus according to the present invention, the current supplied to the electric motor in the inspection mode is set to a value that can specify the mechanical dimensions. The degree of fatigue and the like can be easily determined by comparing with the standard dimensions and the like, and the inspection can be performed very easily without being disassembled.

According to the present invention, the mode of transition to the inspection mode is determined based on the vehicle speed and whether or not the steering wheel is steered, so that the mode is automatically switched to the inspection mode using a sensor mounted on the vehicle. The inspection can be automated easily.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 6 show a front and rear wheel steering device for a vehicle according to an embodiment of the present invention. FIG. 1 is an overall schematic configuration diagram, FIG. 2 is an enlarged sectional view of a partial mechanism, and FIG. 3 is a block diagram of a control system. 4 is a flowchart showing control processing in the normal mode, FIG. 5 is a flowchart showing control processing in the inspection mode, and FIGS. 6A and 6B are graphs for explaining the operation.

As shown in FIG. 1, in this embodiment, a front wheel 13 is steered by a front wheel steering device 12 connected to a steering wheel 11, and a rear wheel 15 is steered by a rear wheel steering device 14. The front wheel steering device 12 has a well-known rack and pinion type steering gear mechanism, and includes a steering wheel 11 and a front wheel 13.
Are connected mechanically.

The steering wheel 11 has a main front wheel steering angle sensor 16 for detecting the steering angle, that is, the steering angle of the front wheel 13, and the front wheel steering device 12 has a sub front wheel steering angle sensor for detecting the steering angle of the front wheel 12. 17 is attached. The main front wheel steering angle sensor 16 is constituted by a digital sensor such as an encoder, and the sub front wheel steering angle sensor 17 is constituted by an analog sensor such as a differential transformer. These sensors 16 and 17 are connected to a controller 18. 19a and 19b are vehicle speed sensors. The vehicle speed sensor 19a detects the rotational speed of the front and rear wheels 13 and 15, and the vehicle speed sensor 19b detects the rotational speed of an output shaft of a transmission (not shown).

The rear wheel steering device 14 has an electric motor 20 as a rear wheel steering actuator and a ball screw mechanism 80, and the electric motor 20 and the ball screw mechanism 80 are housed in a gear housing 83. . FIG.
As shown in detail, the electric motor 20 has a cylindrical rotating shaft 85 extending in the vehicle width direction, and a stator 84 having a coil 84a on an inner wall of a gear housing 83 radially outward of the rotating shaft 85. It is fixed. This electric motor 20
The coil 84 a of the stator 84 is connected to the controller 18, and the connecting rod 81 is loosely inserted into the rotating shaft 85.

Although not explicitly shown in the figure, a main rear wheel steering angle sensor 22 and a sub rear wheel steering angle sensor 23 for detecting the turning angle of the rear wheel 15 are provided in the gear housing 83 (see FIG. 3). . As with the sensors 16 and 17 of the front wheel 13 described above,
The main rear wheel steering angle sensor 22 is a digital rotary pulse encoder, and the sub rear wheel steering angle sensor 23 is an analog differential transformer. These sensors are connected to the controller 18.

The connecting rod 81 slidably penetrates the left and right ends of the gear housing 83, and the left and right ends protrude to the outside and are connected to the left and right rear wheels 15 via tie rods or the like. A screw portion 81 a is formed on the connecting rod 81 on the left side of the electric motor 20 in FIG. 2, and a ball nut 90 is screwed to the screw portion 81 a via a number of balls 91 so as to be relatively rotatable. The ball nut 90 is rotatably connected to the rotating shaft 85 of the electric motor 20, and the ball nut 90 and the connecting rod 81 relatively rotate while rolling the ball 91. The ball nut 90, the screw portion 81a and the ball 91 constitute a well-known ball screw mechanism 80.

The connecting rod 81 includes an electric motor 20.
2, a spring holder 88 is fixedly mounted on the right side in FIG. 2, and a neutral position biasing spring 89 is provided between the spring holder 88 and the gear housing 83 at both ends thereof with retainers 93L and 93R (hereinafter, suffixed as necessary). (Represented by a number). The spring holder 88
A belt-like groove 88a for accommodating the above-mentioned spring 89 is formed by assembling the two members, and an arm portion 88b that engages with the housing 83 to restrict the rotation of the connecting rod 81.
Is formed.

The retainers 93L and 93R have a spring 89 interposed between opposing surfaces, and a sheet member 9 made of an elastic material such as urethane rubber is provided on the surface opposite to the spring 89.
4L, 94R (hereinafter, represented by a number without a subscript if necessary) is attached. Each of the retainers 93 has an inner peripheral end engaged with an end of the band-shaped groove 88 a of the spring holder 88 via a sheet member 94, and similarly, an outer peripheral end of the retainer 93 is engaged with a step portion on the inner wall surface of the gear housing 83. 9
4 to engage. The spring 89 is connected to the connecting rod 81.
One of the retainers 93 is moved to expand and contract by the axial movement, and the connecting rod 81 is urged to a position corresponding to the neutral position of the rear wheel 15.

As shown in FIG. 3, the controller 18
It has a control unit 24 and a drive unit 25, and the above-described sensors are connected to the control unit 24, and the electric motor 20 is connected to the drive unit 25. The control unit 24 is configured by connecting an ECU such as a microcomputer and the input interfaces 27 to 32 via a bus, and performs an arithmetic process on a detection signal output from each sensor.
The control unit 24 controls the rear wheels 15 based on the detection signals of the respective sensors.
Is determined, and a control signal indicating a duty factor corresponding to the target steering angle is output to the drive unit 25.

The drive section 25 has a gate drive circuit 36, a drive circuit 37 and the like, and the electric motor 20 is connected to the drive circuit 37. The drive circuit 37 includes four FETs Q1 to Q1.
Q4 (subscripts are omitted as appropriate) are connected in a bridge shape, and the gates of these FETs Q
The electric motor 20 is connected to the source / drain connection of the FET Q. This drive circuit 37
A current having a duty factor according to a control signal input from the control unit 24 is supplied to the electric motor 20.

In FIG. 3, reference numeral 34 denotes a current sensor for detecting a current supplied to the electric motor, and the current sensor 34 is connected to the control unit 24. Reference numeral 38 denotes a power-off relay, 39 denotes a drive circuit of the relay 38,
Reference numerals 41 and 42 denote relays for braking the electric motor 20 in the event of a failure or the like. Reference numerals 43 and 44 denote drive circuits for the relays 41 and 42, respectively, and reference numeral 35 denotes a voltage sensor for relay failure diagnosis.

In the front and rear wheel steering device of this embodiment,
In the normal control, the steering angle of the rear wheel 15 is controlled by repeatedly executing the processing shown in the flowchart of FIG. As shown in the figure, in step 1, the front wheel steering angle θf, the rear wheel steering angle θr, the vehicle speed V, and the like are read from the detection signals of the sensors, and a failure diagnosis is performed.

Next, in step 2, the steering angle ratio k is determined by a map search based on the vehicle speed V, and in the next step 3, the front wheel steering angle θf is multiplied by the steering angle ratio k to calculate the rear wheel target steering angle θt. I do. Then, in step 4, a deviation Δθ between the target rear wheel steering angle θt and the rear wheel actual steering angle θr is calculated, and the next step 5
, The duty factor D of the current supplied to the electric motor 20 is determined using the deviation Δθ as an address.

In the following step 6, it is determined whether or not a failure has occurred. If it is not a failure, output processing is performed in step 7, and if it is determined that a failure has occurred, the processing in and after step 8 is performed.
In step 7, the electric current having the duty factor is supplied to the electric motor 20, and the rear wheel 15 is steered to the rear wheel target steering angle. This output processing is described in detail in various patent applications and the like previously submitted by the present applicant, and therefore, the description thereof is omitted.

In step 8, the relay 38
The contactor is opened to disconnect from the battery and the relay 4
The contactors 1 and 42 are closed to short-circuit the coil 81a. Then, in step 9, it is determined whether or not the drive unit 25 has failed. If the drive unit 25 has failed, all the FETs are turned off.
If the drive unit 25 does not fail, the FETs Q1 and Q3 are turned off,
The FETs Q2 and Q4 are turned on.

On the other hand, when the vehicle has entered a repair shop or the like, as shown in the flowchart of FIG. 5, when a certain condition is satisfied, the mode shifts to the inspection mode, the inspection is performed, and the rear wheel steering is performed. The deterioration or fatigue state of the ball screw mechanism 80, the neutral position urging spring 89, the seat member 94, and the like of the device 14 is determined.

As shown in FIG. 5, in step 1, the vehicle speed V
Is determined to be less than or equal to a predetermined vehicle speed, and in step 2 it is determined whether the steering wheel 11 is steered. When the vehicle speed V exceeds a predetermined value, the steering wheel 11
In step 3, the timer T is reset to 0 in step 3, the flag F is set to 0 in step 4, and the normal mode is controlled by returning to the normal mode in step 5 as described above. Do.

On the other hand, if it is determined in steps 1 and 2 that the vehicle speed V is equal to or lower than the predetermined vehicle speed and that the steering wheel 11 is not steered, a timer T is integrated in step 6 to count the number of executions T of the routine. That is, the time T in which the state in which the steering wheel 11 is not steered while the vehicle speed V is equal to or lower than the predetermined vehicle speed is measured.

Next, in step 7, it is determined whether or not the number of executions of the routine, that is, the counted time T has exceeded a predetermined time φ, and if not, the processing of step 8 is executed. In step 9, 1 is set to the flag F. In step 8, the value of the flag F is determined. If the flag F is 0, the normal control is performed in step 5 described above. If the flag F is 1, the process in step 9 is performed.

In the following step 10, the magnitude of the rear wheel target steering angle θt is determined. And this step 10
Then, if the rear wheel target steering angle θt is larger than the predetermined value K, a predetermined value δ is subtracted from the rear wheel target steering angle θt in step 11, and if the rear wheel target steering angle θt is equal to or smaller than the predetermined value K, the rearward in step 12 The wheel target steering angle θt is held. The predetermined value K in step 10 corresponds to the value of the energizing current to the electric motor 20, and determines the output of the electric motor 20 to a value that maximizes the length of the spring 89 and maximizes the deformation of the seat member 94. Is done.

Thereafter, an output process is performed in step 13,
In the next step 14, the target steering angle θt obtained in steps 11 and 12 is stored as data θtz in preparation for the execution of the next routine. Thereafter, the processing from step 1 is repeated.

Here, by repeatedly executing the above-described routine, the duty factor D of the current supplied to the electric motor 20 gradually decreases in an arithmetic progression, that is, the current value gradually decreases with a preset characteristic. With the decrease, the output of the electric motor 20 also decreases. Therefore, as the output of the electric motor 20 decreases, the rear wheel 15 is urged toward the neutral position by the neutral position urging spring 89, and the steering angle decreases.

At this time, a change in the steering angle of the rear wheel 15 is detected by a turntable having a radius gauge or the like.
It is determined whether or not the change in the steering angle of the vehicle coincides with the characteristic determined in advance corresponding to the characteristic in which the current value gradually decreases. That is, when the current value is gradually decreased in a predetermined characteristic in a normal state, as shown in FIG. 6, the steering angle of the rear wheel 15 changes at a time change rate (ideal characteristic) corresponding to the characteristic in which the current gradually decreases ( The solid line in FIG. 6a), the time rate of change can be known in advance through experiments and the like.

When the friction of the ball screw mechanism 80 increases, or when the elastic force changes due to the fatigue of the spring 89, the time change rate of the steering angle of the rear wheel 15 differs from the ideal characteristic described above. Fatigue or deterioration can be determined based on the magnitude of this difference. Therefore, when a region that can be determined to be normal is defined as shown by the hitting region in FIG. 6B, it is determined whether the actual steering angle change (solid line) of the rear wheel 15 is within a predetermined allowable value. If the change in the steering angle of the wheel 15 is within the allowable range, it is determined that the steering is normal.

When the current value is reduced to a predetermined value, that is, when the output of the electric motor 20 reduces the length of the spring 89 to the maximum and the deformation of the seat member 94 to the maximum,
As in the case described above, if the spring 89 or the like is normal, the steering angle of the rear wheel 15 matches the steering angle corresponding to the design value (referred to as an ideal steering angle for convenience and corresponding to K in FIG. 6). When the seat member 94 or the like is deteriorated, the steering angle is different from the ideal steering angle. Therefore, when the value of the current supplied to the electric motor 20 is set to the above-described predetermined value, it is determined whether or not the actual steering angle is within the range indicated by the dots in FIG. Deterioration or fatigue can be determined, and the occurrence of problems due to fatigue or the like can be prevented. In particular, since the above-mentioned ideal steering angle can be easily known from design standards or the like, its determination is also easy.

As described above, the front and rear wheel steering apparatus for a vehicle according to this embodiment enters the inspection mode when a predetermined condition, that is, when the vehicle speed is substantially 0 and the steering wheel 11 is not steered for a predetermined time. Then, the current supplied to the electric motor 20 is gradually reduced, and it is determined from the change (change state) of the steering angle of the rear wheel 15 at this time whether the mechanical element is fatigued or deteriorated. Therefore, the rear wheel steering device 14 can be inspected without disassembly, the inspection can be easily performed, and the shift to the inspection mode can be automatically performed, so that the inspection work is easy.

FIG. 7 shows a front and rear wheel steering device for a vehicle according to another embodiment of the present invention. This embodiment has the same mechanical configuration and the like as the above-described embodiment, and the same portions are denoted by the same reference numerals and description and illustration thereof will be omitted. This example is
The configuration is such that a driver or the like can perform a self-diagnosis using a sensor mounted on a vehicle, and repeatedly executes a process shown in a flowchart of FIG. 7 in an inspection mode. In the flowchart of FIG. 7, the processing from step 1 to step 13 is the same as the processing from step 1 to step 13 in FIG. 5, and step 17 is step 14 in FIG.
The description is omitted.

As shown in FIG. 7, after step 13, it is determined in step 14 whether the time measured by the timer T has reached a predetermined time φ '. The predetermined time φ ′ is
As shown in FIG. 6, it is defined as the time when the length of the spring 89 is maximum and the deformation of the seat member 94 is maximum in the normal state. The time measured by the timer T is a predetermined time φ.
If not, the processing from step 1 is performed again after performing the processing in step 17, and if the time measured by the timer T has reached the predetermined time φ ', the processing in step 15 is performed.

In step 15, it is determined whether or not the rear wheel steering angle θr read from the output signals of the rear wheel steering angle sensors 22 and 23 is within a predetermined range (K−A <θr <K + A). . The values K and A defining this range are, as shown in FIG. 6B, the maximum length of the spring 89 and the seat member 9.
In a state where the steering wheel 4 is deformed to the maximum, a range allowable as the steering angle of the rear wheel 15 is defined.

In step 15 described above, if it is determined that the rear wheel steering angle θr is within a predetermined range, it is determined that the rear wheel steering angle θr is normal, and the processing from step 1 is performed after the processing in step 17. If it is determined that θr is out of the predetermined range, a warning is issued by performing processing such as turning on a warning lamp in step 16.

As described above, in this embodiment, since the rear wheel steering angle is detected by using the rear wheel steering angle sensors 22 and 23 mounted on the vehicle, the driver himself / herself can be used without entering a repair shop or the like. Can be done easily. Therefore, it can be performed as a daily check.

[0040]

As described above, according to the vehicle front / rear wheel steering system according to the present invention, when the inspection mode is entered, the neutral position urging spring has the maximum length, and the elastic body generates the maximum deformation current. Since the electric motor is energized and the fatigue state or the like is determined based on the rear wheel steering angle at this time, the inspection can be performed without disassembling or the like, and the inspection is easy.

In particular, the present invention automatically switches to the inspection mode because the vehicle shifts to the inspection mode on condition that the vehicle speed is almost zero and a predetermined time has elapsed while the steering wheel is steered from the neutral position. The transition can also be made, and the inspection can be automated.

[Brief description of the drawings]

FIG. 1 is an overall schematic configuration diagram of a front and rear wheel steering device for a vehicle according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a mechanism part of the front and rear wheel steering device.

FIG. 3 is a block diagram of a control system of the front and rear wheel steering device.

FIG. 4 is a flowchart showing control processing during normal control of the front and rear wheel steering devices.

FIG. 5 is a flowchart showing a control process of the front and rear wheel steering device in an inspection mode.

FIG. 6 is a diagram for explaining the operation of the front and rear wheel steering device.

FIG. 7 is a flowchart showing the same control processing as in FIG. 5 for the front and rear wheel steering device for a vehicle according to another embodiment of the present invention;

[Explanation of symbols]

11 ... steering wheel, 12 ... front wheel steering device, 13 ...
Front wheel, 14: Rear wheel steering device, 15: Rear wheel, 16, 17
... front wheel steering angle sensor, 18 ... controller, 19 ... vehicle speed sensor, 20 ... electric motor, 22, 23 ... rear wheel steering angle sensor, 24 ... control unit, 25 ... .Drive unit, 26 EC
U, 80: ball screw mechanism, 81: connecting rod,
81a: screw portion, 89: spring for biasing neutral position, 9
0: ball nut, 94: seat member.

Claims (2)

(57) [Claims] 1. A front wheel steering mechanism that steers front wheels in response to steering of a steering wheel, a rear wheel steering mechanism that steers rear wheels by an output of an electric motor, and biases a rear wheel to a neutral position. A front and rear wheel steering device for a vehicle, including a neutral position urging spring, an elastic body interposed between the spring and the gear housing, and control means for controlling energization of the electric motor in accordance with steering of a steering wheel. At this time, the mode shifts to the inspection mode under a predetermined condition, and in this inspection mode, the current supplied to the electric motor is changed to a current value at which the length of the neutral position biasing spring is maximum and the deformation of the elastic body is maximum. A front and rear wheel steering device for a vehicle, wherein the steering angle is set and a rear wheel steering angle in this state is compared with a predetermined reference value. 2. The front and rear wheel steering system for a vehicle according to claim 1, wherein the shift to the inspection mode is performed when the vehicle speed is zero or substantially zero while the steering wheel is steered from a neutral position. A front and rear wheel steering device for a vehicle, which is performed on condition that a predetermined time has elapsed without steering of a direction steering wheel.