JP2887613B2 - Vehicle front wheel steering system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a front wheel steering device for steering a front wheel of a vehicle.

2. Description of the Related Art Generally, a front wheel steering device for a vehicle includes a front wheel steering rod that steers a front wheel by a displacement in a vehicle width direction, a steering wheel attached to one end, and a front wheel steering rod engaged and connected to the other end. The steering shaft converts rotational displacement of the steering wheel into displacement of the front wheel steering rod in the vehicle width direction. On the other hand, in recent years, as disclosed in, for example, JP-A-64-1663, the steering shaft is not engaged and connected to the front wheel steering rod,
A so-called steer-by-wire system in which a rotational displacement of a steering wheel is detected at a portion corresponding to a steering shaft, an actuator is operated according to the detection signal, and the front wheel steering rod is displaced in a vehicle width direction by the actuator. Has been proposed.

(Problems to be Solved by the Invention) By adopting such a steer-by-wire type front wheel steering device, front wheel steering excellent in steering stability according to a vehicle running state as well as by a driver's steering operation is possible. On the other hand, in such a device, the steering wheel and the front wheel steering rod are not mechanically connected to each other. Therefore, if an abnormality occurs in the control system, it becomes difficult to perform front wheel steering according to the driver's intention.

The present invention has been made in view of such circumstances, and it is possible to perform front wheel steering with excellent steering stability peculiar to a steer-by-wire system, and an abnormality has occurred in a control system of the system. It is an object of the present invention to provide a front wheel steering device for a vehicle that does not cause a problem in front wheel steering even in such a case.

(Means for Solving the Problems) A front wheel steering device for a vehicle according to the present invention includes an actuator of a steer-by-wire device and a steering shaft engaged and connected to a front wheel steering rod, and an intermediate portion of the steering shaft. By providing a predetermined dead zone, the front wheel steering by the actuator can be performed within the dead zone region, and the front wheel steering by the steering shaft can be performed outside the dead zone region, thereby achieving the above object. It is like that.

That is, a front wheel steering rod that steers the front wheels by displacement in the vehicle width direction, a steering wheel is attached to one end, and the front wheel steering rod is engaged and connected to the other end, and the rotational displacement of the steering wheel is controlled by the front wheel. A front shaft steering device for a vehicle, comprising: a steering shaft for converting a steering rod into a displacement in a vehicle width direction; an upstream side located at an intermediate portion of the steering shaft, the steering shaft being located at the one end side. Part and a downstream part located on the other end side, and these two parts are relatively rotatable in a range of a predetermined angle around the axis of the steering shaft without transmission of rotational power. A dead zone joint connected in a state where a dead zone is provided, and a rotational change of the upstream portion and the downstream portion. An upstream-side steering angle sensor and a downstream-side steering angle sensor that respectively detect the steering wheel; an actuator that displaces the front-wheel steering rod in the vehicle width direction separately from the steering shaft; And control means for controlling the actuator so that the detection signals from the steering angle sensor coincide with each other.

(Operation and Effect of the Invention) As shown in the above configuration, the rotational displacements of the upstream portion and the downstream portion of the steering shaft provided with the dead zone joint are respectively detected by the steering angle sensor, and controlled in accordance with these detection signals. Means actuate the actuator,
Since the front wheel steering rod is displaced in the vehicle width direction by this actuator, in the dead zone area of the dead zone joint, not only the steering operation by the driver but also the vehicle behavior (transverse acceleration of the vehicle, yaw rate, etc.) Front steering can be performed in accordance with the vehicle running state such as the steering operation speed (detected as the rate of change in the rotational displacement of the steering wheel). On the other hand, outside the dead zone, the upstream portion and the downstream portion of the steering shaft are mechanically connected, so that the front wheel steering rod can be directly displaced in the vehicle width direction by the steering shaft.

Therefore, according to the present invention, it is possible to perform front wheel steering excellent in steering stability peculiar to the steer-by-wire system, and even if an abnormality such as a failure occurs in the control system of the system, the front wheel steering is not hindered. There is no possibility of occurrence and safety can be improved.

When the abnormality of the control system occurs during high-speed running, it is preferable that the mechanical connection of the steering shaft can be quickly performed. Therefore, the dead zone width of the dead zone joint is increased with increasing vehicle speed. It is effective to provide a dead zone width changing means for reducing the width.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the accompanying drawings.

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

This front wheel steering device 10 includes a front wheel steering rod 12 that steers a front wheel (not shown) by displacement in a vehicle width direction, and a steering wheel 14 attached to one end and a front wheel steering rod 12 attached to the other end.
A steering shaft 18 is engaged and connected at 16 and converts the rotational displacement of the steering wheel 14 into the displacement of the front wheel steering rod 12 in the vehicle width direction.

In the middle part of the steering shaft 18, the steering shaft 18 is divided into an upstream portion 18A located at the one end and a downstream portion 18B located at the other end. A dead zone joint 20 is provided to connect the steering shaft 18 and the steering shaft 18 in a state where a dead zone that can be relatively rotated by a predetermined angle is provided around the axis of the steering shaft 18.
In the vicinity of each of the upstream portion 18A and the downstream portion 18B of the steering shaft 18, an upstream steering angle sensor 22A and a downstream steering angle sensor 22B for detecting the rotational displacement are provided.

Further, the front wheel steering device 10 responds to detection signals from a hydraulic actuator 24 that displaces the front wheel steering rod 12 in the vehicle width direction separately from the steering shaft 18 and detection signals from an upstream steering angle sensor 22A and a downstream steering angle sensor 22B. And a controller 26 as control means for controlling the hydraulic actuator 24. The hydraulic actuator 24 includes a piston 28 fixed to the front wheel steering rod 12 and a cylinder 30 fixed to the vehicle body. A hydraulic control valve 32 operates according to a control signal from a controller 26, and an oil pump 34 The supply and discharge of the hydraulic pressure to and from the hydraulic actuator 24 and the direction control are performed.

As shown in FIG. 2, the dead zone joint 20 includes a small-diameter cylindrical body 20A fixed to the end of the upstream portion 18A of the steering shaft 18 and a large-diameter cylindrical body attached to the end of the downstream portion 18B. 20B is fitted so as to be relatively slidable in the axial direction of the steering shaft 18 and relatively rotatable in the circumferential direction thereof, and the large-diameter cylindrical body 20B is provided with a pin 20B extending on one diameter thereof.
While a is fixed, a pair of insertion holes 20Aa through which the pins are inserted are formed in the small-diameter cylindrical body 20A at positions facing each other. Each insertion hole 20A is formed as an isosceles triangle having an apex on the upstream side, and each corner thereof is
It is formed with a corner R having substantially the same curvature as that of FIG.

The small-diameter cylindrical body 20A of the dead zone joint 20 is connected to the steering shaft case via a bearing 36 together with the upstream portion 18A.
38 is rotatably supported. On the other hand, large-diameter cylindrical body 20B
Is spline-engaged with the downstream portion 18A and is slidable in the axial direction of the steering shaft 18, but is urged upstream by a return spring 40 interposed therebetween. The connection position between the large-diameter cylindrical body 20B and the downstream portion 18B is determined by the position of the vehicle body-side plate 44 supporting the downstream portion 18B via the bearing 42 and the hydraulic actuator 46 attached to the vehicle body-side plate 44. The large-diameter cylindrical body 20B is fixed to the tip of the output rod
, And is set by the distance between the stopper plate 52 and the stopper plate 52 that is supported by the stopper. The hydraulic actuator 46 operates via a hydraulic control valve 54 that supplies and adjusts hydraulic pressure according to a control signal from the controller 26. When the hydraulic pressure is not supplied to the hydraulic actuator 46, as shown in the figure, the elastic force of the return spring 40 causes the pin 20Ba of the large-diameter cylindrical body 20B to move to the upstream end face of the insertion hole 20Aa of the small-diameter cylindrical body 20A. When the hydraulic pressure is supplied to the hydraulic actuator 46 by taking the contact position, the large-diameter cylinder 20B
Moves rightward in the figure against the elastic force of the return spring 40, and as shown by the two-dot chain line in FIG.
The large-diameter cylindrical body 20B can move to a position where it contacts the downstream end face of Aa. The position of the large-diameter cylindrical body 20B is detected by detecting the position of the stopper plate 46 by a stroke sensor 56 attached to the vehicle body-side plate 44, and this detection signal is input to the controller 26. .

When the pin 20Ba of the large-diameter cylinder 20B is in contact with the upstream end surface of the insertion hole 20Aa of the small-diameter cylinder 20A as shown in FIG. 2, there is no circumferential play between the two cylinders. Therefore,
When the steering wheel 14 is operated (rotated) in this state, the steering shaft 18 is integrated with the upstream portion 18A and the downstream portion 18B (that is, the dead zone 0).
). On the other hand, pin 20
When Ba moves to the right, a gap is formed above and below the end face of the insertion hole 20Aa, and play in the circumferential direction occurs. Therefore, in this state, even if the upstream portion 18A rotates, the downstream portion 1
8B does not rotate within the range of the above-mentioned play, and only after that, does it rotate with the upstream portion 18A. That is, a dead zone is formed between the upstream portion 18A and the downstream portion 18B so as to be relatively rotatable by a predetermined angle.

The width of the dead zone is widest when the pin 20Ba is at the position shown by the two-dot chain line in FIG.
As shown in FIG. 3, which is a cross section taken along the line I-III, the angle α
In this case, the maximum value is obtained when α = α ₀ . In addition,
The angle α indicates one side width of the dead zone. This dead band width is
The operating pressure changes depending on the axial position of the steering shaft 18 of 20Ba, that is, the operating oil pressure of the hydraulic actuator 46. The operating oil pressure is controlled by the controller 26. In this control, as shown in FIG. 4, a dead zone width is set in advance in accordance with the vehicle speed V, a dead zone width is searched on a map based on a detection signal from a vehicle speed sensor (not shown), and a control signal corresponding to the dead zone width is obtained. The output is output to the control valve 54. Thus, the controller 26, the hydraulic control valve 54, the hydraulic actuator 46, and the dead zone joint 20 constitute a dead zone width changing unit.

On the other hand, the control of the controller 26 for the hydraulic actuator 24 shown in FIG. 1 is performed according to the main flow shown in FIG.

That is, first, in step S1, the upstream rudder angle sensor 22A
The upstream steering angle theta _H1 detected input by, the theta _H1 is (what is corrected by later-described correction amount addition added) the detected downstream steering angle theta _H2 by the downstream side steering angle sensor 22B in S2 It is determined whether or not the operation is coincident with the operation.If they are coincident with each other, the drive of the hydraulic actuator 24 is unnecessary, so that the operation is not performed, and the process returns to S1. The hydraulic actuator 24 is driven by the signal output. Then, it is determined again whether or not θ _H1 matches θ _H2 in S4. If they match, the hydraulic actuator is determined in S5.
The drive in step 24 is stopped. On the other hand, if they do not match, it is determined in S6 whether a predetermined set time has elapsed. If this has elapsed, it is determined that an abnormality has occurred in the control system due to a failure in the hydraulic circuit, the electric circuit, or the like, the control is stopped in S7, and the hydraulic pressure to the hydraulic actuator 24 is drained via the hydraulic control valve 32. On the other hand, if the set time has not elapsed, θ _H1 and θ _H
Whether the absolute value of the difference between _H2 is now alpha ₀ (see FIG. 3) (i.e., whether pin 20Ba comes into contact with the end face of the insertion hole 20Aa) are determined, sufficient that alpha ₀ For example, if an abnormality has occurred in the control system, the control is stopped in S7. On the other hand, the process proceeds to S3 if not become α _0.

It should be noted that, along with the stop of the control in S7, the control of the dead zone width by the controller 26 is also stopped. That is, the hydraulic pressure to the hydraulic actuator 46 is
To make the dead zone width of the dead zone joint 20 zero. As a result, the front wheels can be steered by a normal steering shaft, and safety can be improved.

FIGS. 6A, 7A, 8A and 9A show S in the main flow of FIG.
2 is a sub-flow for correcting θ _H2 shown in S4.

FIG. 6A is a flowchart for obtaining a correction amount A for the lateral G (lateral acceleration of the vehicle). That is, in S11, the lateral G from the lateral G sensor, which is a vehicle behavior detecting means (not shown), is input, and in S12, the correction amount A is obtained from the map shown in FIG.
Adds the A into theta _H2 at 13 corrects the theta _H2 and. In addition,
The correction is performed by the controller 26 as a correction amount control unit. The same applies to other examples below. The correction amount A is set so as to increase as the lateral G increases. However, this is because when the lateral G increases, the vehicle tends to understeer. (Increasing steering) is automatically performed.

FIG. 7A is a flowchart for obtaining a correction amount B for a low μ road (a road surface having a small friction coefficient μ between the vehicle and a wheel). That, is input mode from the vehicle behavior detecting means serving wiper switch (not shown) in S21, obtains a correction amount B from the map shown in Figure 7B in S22, the correction of _H2 theta by subtracting the B from theta _H2 in S23 I do. The correction amount B is set so as to gradually increase as the mode of the wiper switch becomes Lo and Hi. This means that frequent use of the wiper means that the amount of rainfall is large. , This can be considered indirectly detecting the μ state of the road surface,
When the rainfall increases and μ decreases, the vehicle operation becomes slower by correcting the driver's operation amount to decrease, and the running stability is improved.

FIG. 8A shows the steering operation speed, that is, the rate of change in the rotational displacement of the upstream portion 18A of the steering shaft 18.
_{9 is} a flowchart for _obtaining a correction amount C for _H1 . That is,
In step S31, _H1 is calculated as a differential value of θ _{H1 by} the controller 26 as the rotational displacement change rate detecting means. In step S32, it is determined whether a brake switch (not shown) is on or off. If the brake switch is on, a map shown in FIG. C ₁₎ obtains a correction amount C ₁ from by adding the C ₁ to theta _H2 in S34 performs theta _H2 correction. On the other hand, if the brake switch is off, the sixth
Obtain a correction amount C ₂ from the map (C ₂₎ shown in B Figure, this in S36
The correction of θ _H2 is performed by adding C ₂ to θ _H. These correction amounts
C ₁ and C ₂ are set to be larger as | _H1 | is larger. This means that | _H1 is larger.
It is considered that this indicates the driver's intention to turn, so this is automatically performed.
Incidentally, the C ₁ than C ₂ is large, the the brake is taking it decreases cornering force, in order to correct this.

FIG. 9A is a flow chart for obtaining a correction amount D for the yaw rate (angular velocity about the vertical axis of the vehicle). That is, in S41, it is determined whether or not the steering wheel 14 is in a substantially neutral position (whether or not θ _H1 ≒ 0). If the steering wheel 14 is in a substantially neutral position, the yaw rate from a yaw rate sensor, which is a vehicle behavior detecting means (not shown) is determined in S42. are input, obtains a correction amount D from the map shown in FIG. 9B in S43, it corrects the theta _H2 by subtracting the D from theta _H2 at S44. On the other hand, if the steering wheel 14 is not substantially at the neutral position, the above correction is not performed. In other words, this sub-flow is a correction flow for countermeasures against crosswinds during high-speed running. The sleeve positive amount D is set so as to become larger as it becomes larger. However, as this becomes larger, corrective steering (turnback steering) for canceling this is required, but this is automatically performed. It is like that.

As described above in detail, according to the present embodiment, the dead zone joint 20
18A on the upstream side of the steering shaft 18 with the
And the rotational displacement of the downstream portion 18B are controlled by the steering angle sensor 2 respectively.
2A and 22B, the control unit 26 activates a hydraulic actuator 24 in response to these detection signals, and the hydraulic actuator 24 controls the front wheel steering rod.
12 is displaced in the vehicle width direction, so in the dead zone area of the dead zone joint 20, not only the driver's steering operation but also the vehicle behavior (detected as the lateral G of the vehicle, yaw rate, etc.) The front wheels can be steered according to the vehicle running state such as the steering operation speed (detected as the rotational displacement change rate _H of the steering wheel). On the other hand, outside the dead zone region, the upstream portion 18A and the downstream portion 18B of the steering shaft 18 are mechanically directly connected, so that the front shaft steering rod 12 is directly displaced in the vehicle width direction by the steering shaft 18. Can be done.

Therefore, according to the present embodiment, it is possible to perform front wheel steering with excellent steering stability peculiar to the steer-by-wire system, and even if an abnormality such as a failure occurs in the control system of the system, the front wheel steering is not hindered. Is not generated, and safety can be improved.

Furthermore, according to the present embodiment, the dead zone width α of the dead zone joint 20 is configured to be narrowed with an increase in the vehicle speed V. Therefore, even when an abnormality in the control system occurs during high-speed traveling. Thus, the mechanical connection of the steering shaft 18 can be quickly performed.

In this embodiment, the hydraulic actuator 46 is used as a means for obtaining the dead zone width α according to the vehicle speed V.
Needless to say, a motor or the like may be used.

The dead zone width α according to the vehicle speed V is obtained in a stepless manner by the map shown in FIG. 4, but as shown in FIG. 10, the vehicle speed V is changed to V ₀ , V ₁ , V ₂ (V ₀ <V ₁ <V ₂ ) and the corresponding dead zone width α ₀ ,
By setting α ₁ , α ₂ , α ₃ (α ₀ > α ₁ > α ₂ > α ₃ ), the dead zone width may be changed stepwise. In this case, V ₀ , V ₁ , and V ₂ are, for example, 30 km / h, 60 km / h, 80 km,
Km / h can be set respectively.

Furthermore, as shown in FIG. 11, when the brake switch is and greater deceleration on, i.e. when the sudden braking was applied, the dead zone width alpha may perform correction to the maximum width alpha _0. By doing this,
It is possible to automatically perform the vehicle attitude control in the sudden braking state.

[Brief description of the drawings]

1 is an overall configuration diagram showing an embodiment of a front wheel steering device for a vehicle according to the present invention, FIG. 2 is a cross-sectional view of a main part of the above embodiment, and FIG. 3 is III-III in FIG. FIG. 4 is a graph showing the characteristics of the dead zone width with respect to the vehicle speed in the above embodiment, FIG. 5 is a main flowchart showing the operation of the above embodiment, and FIGS. 6A, 7A, 8A and 9A are FIGS. 6B, 7B, 8B and 9B are graphs showing the correction amounts in the above sub-flowcharts, and FIGS. 10 and 11 are sub-flowcharts showing other embodiments. 10 front wheel steering device, 12 front wheel steering rod 14 steering wheel 18 steering shaft 18A upstream section, 18B downstream section 20 dead zone joint (dead zone width changing means) 20A small diameter Cylindrical body, 20Aa… Insertion hole 20B… Large-diameter cylindrical body, 20Ba… Pin 22A… Upstream rudder angle sensor 22B… Downstream rudder angle sensor 24… Hydraulic actuator (actuator) 26… Controller (control) Means, control amount correction means, dead zone width changing means) 46 ... Hydraulic actuator (dead zone width changing means)

Claims (4)

(57) [Claims] 1. A front wheel steering rod for steering a front wheel by displacement in a vehicle width direction, a steering wheel attached to one end, and the front wheel steering rod engaged and connected to the other end, and a rotational displacement of the steering wheel. And a steering shaft that converts the front-wheel steering rod into a displacement in the vehicle width direction. A front-wheel steering device for a vehicle, comprising: a steering shaft disposed at an intermediate portion of the steering shaft; The steering shaft is divided into an upstream part and a downstream part located on the other end side, and these parts are relatively rotated within a range of a predetermined angle around the axis of the steering shaft in a state where rotational power is not transmitted. A dead zone joint connected with a movable dead zone provided, and rotation of the upstream portion and the downstream portion An upstream rudder angle sensor and a downstream rudder angle sensor for respectively detecting the position; an actuator for displacing the front wheel steering rod in a vehicle width direction separately from the steering shaft; Control means for controlling the actuator so that detection signals from the side rudder angle sensors coincide with each other. 2. A front wheel steering apparatus for a vehicle according to claim 1, further comprising a dead zone width changing means for narrowing a dead zone width of said dead zone joint with an increase in vehicle speed. . 3. A front wheel steering apparatus for a vehicle according to claim 1, wherein said vehicle behavior detecting means detects a lateral acceleration or a yaw rate acting on the vehicle; A front wheel steering device for a vehicle, comprising: a control amount correction unit that corrects a control amount of the control unit with respect to the actuator within a dead zone region of the dead zone joint. 4. A front wheel steering apparatus for a vehicle according to claim 1, 2 or 3, wherein a rotational displacement change rate detecting means for detecting a rotational displacement change rate of said upstream portion of said steering shaft, and said rotational displacement change rate. A front-wheel steering device for a vehicle, comprising: a control amount correction unit that corrects a control amount of the control unit with respect to the actuator in a dead zone of the dead zone joint in response to a detection signal from the detection unit. .