JPH02124372A - Rear wheel steering device of vehicle - Google Patents

Abstract

PURPOSE:To enhance the reliability of a rear-wheel steering actuator by furnishing a means to alter the judgement reference car speed for starting the steering control to a smaller judgement reference car speed when the car is decelerated, and thereby suppressing the operating frequency of the actuator. CONSTITUTION:A rear-wheel steering device, which steers the left and right rear wheels at least in the toe-in direction through the action of an actuator, is equipped with a car speed sensing means MA and a deceleration sensing means MB to sense deceleration of the car. The output signal of this car speed sensing means MA is fed to a steering start control means MC, and when the sensed car speed has attained the specified car speed value (judgement reference car speed), a signal is emitted for starting the rear-wheel steering If at this time deceleration of the car is sensed by the deceleration sensing means MB, the judgement reference car speed is altered by a judgement reference value altering means MD into a smaller judgement reference car speed. This turns areas around the judgement reference car speed into one sort of non-sensitive zone, which prevents hunting associate with variation in the car speed.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a rear wheel steering device for a vehicle.

(Prior art) Some four-wheel steering vehicles in which the rear wheels are also steered along with the 1i steering wheel, as shown in Japanese Patent Application Laid-Open No. 60-193780, have a system in which the left and right rear wheels are simultaneously steered in the toe-in direction. There is one that allows you to steer the ship.

In other words, cylinder devices are installed between the left and right suspension shore arms that support the rear wheels and the vehicle body, and these left and right cylinder devices are used to improve compliance, for example.
Within the range of elastic deformation of elastic bushings in a suspension, a system has been proposed in which both the left and right rear wheels are controlled in the toe-in direction when the front wheels are steered.

In this way, in a vehicle in which both the left and right rear wheels are toe-in, the inner rear wheel when turning can be set toe-in in advance in preparation for the primary turning in the opposite direction. As a result, toe-in of the rear wheels, which are the outer wheels during a turn, can be obtained in a responsive manner even on a running road where there are continuous left and right curves, which is preferable in terms of ensuring the stability of the vehicle.

(Problem to be solved by the invention) However, in order to toe-in the left and right rear wheels at the same time,
As stated in the above publication, it is not possible to react to the vehicle speed and automatically start restraining the rear wheels when the vehicle speed reaches a predetermined speed.
When the vehicle is traveling close to this discrimination reference heavy speed, an excessive C load is forced on the rear wheel steering control system.

In other words, when toe-in is performed to ensure the running stability of a vehicle, for example, assuming that a dead running speed of 60 km/l-1 is set as the discrimination standard 11i speed, the actual vehicle speed is 60 km/H. When it exceeds
Control in the toe-in direction is started, and when the vehicle reaches exactly 60 km/II, toe control is stopped. This means that the actuator that steers the rear wheels operates each time the control is started or +1 is positive. For this reason, for example, when driving on a road with undulations, it is normal for the vehicle speed to fluctuate by ±a within 60 km/h, which causes the problem that the actuator has to be operated more frequently. be.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a rear wheel steering device for a vehicle that reduces the frequency of actuation of an actuator that steers the rear wheels to improve its reliability.
゜(F-stage, operation to solve the problem) In order to achieve the technical problem 11, in the present invention, as shown in FIG. , a vehicle speed detection means for detecting vehicle speed by setting a rear wheel steering device of a vehicle steered in at least a toe-in direction as +Ti; and a deceleration detection means for detecting deceleration of a small mountain.

Steering start control means that starts steering the rear wheels when a predetermined 11th speed is reached according to the vehicle speed, and a determination reference vehicle speed that determines the start of steering of the rear wheels according to 1111, when the vehicle is decelerating.
This configuration includes a determination reference value changing means for changing to another smaller determination reference vehicle speed.

In other words, if the actual vehicle speed is less than the reference vehicle speed for starting control, it means that the vehicle is decelerating.
When the vehicle is in this deceleration state, the determination reference vehicle speed is changed to a small value.

With this configuration, the vicinity of the judgment reference speed II becomes a kind of dead zone, and even if the vehicle speed fluctuates slightly, this prevents the occurrence of the °1 failure in which the control is repeatedly started or stopped. IF, it will be done.

(Example) Hereinafter, an example of the present invention will be described based on the attached drawings.

At No. φ1, 1 [( is the right 1F 1 wheel, IL is the left front wheel, 2R is the right rear wheel, 2L is the left rear wheel, and the left and right front wheels I
n and IL are linked by a +iif wheel steering mechanism A, and the left and right rear wheels 2R12L are linked by a rear wheel steering mechanism B.

In the embodiment, the front wheel steering mechanism A includes a pair of left and right knuckle arms 3R13L and a tie rod 41, respectively.
and a relay rod 5 that connects the pair of left and right tie rods 41.degree. 4L. Steering mechanism 0 is linked to this +iii transverse steering mechanism △,
In this embodiment, the steering mechanism C is of a rack-and-pinion type, and when the steering wheel 6 is turned to the right, the relay rod 5 is displaced to the Hy+ left side, and the steering wheel 6 is moved to the left. Operational displacement: f, that is, the left and right front wheels IR,+1 are steered to the right by an amount corresponding to the steering angle of the steering wheel. Similarly, when the steering wheel 6 is turned to the left, the left and right movement is 1111 degrees depending on this operation displacement: ■.
R11F is steered to the left.

Similarly to the front wheel steering mechanism △, the rear wheel steering mechanism B also has a pair of left and right knuckle arms lOR41°L and a tie rod 11]<, l l L, as well as a coupling mechanism that connects the tie rods llR and IIL. 1].

The above connection mechanism will be described in detail with reference to FIG. 23.

The connection mechanism is connected between the left and right rear wheels 2R12L.
It has a pair of rocking pieces 201 (, 2OL) attached to the i-body so as to be able to swing freely in the left and right directions.The rocking center of the R12OL is shown. The piece 2011 is connected to the inner end in the vehicle width direction of the right relay rod 21R, and the outer end of the right relay rod 2]R is connected to the +i
i 3E Connected to right tie rod IIR. Similarly, the left swing piece 20L is connected to the inner end in the vehicle width direction of the left relay rod 21L, and the outer end of the left relay rod 21L is connected to the left tie rod l1l-. and,
The above-mentioned pair of rocking pieces 2OR12OL are also.

5 are connected to the left and right pair of connecting rods 221 (, 22L), and the left and right pair of connecting rods 22R122 [,
Its inner end is connected to a pole nut 23.

The ball nut 23 is supported so as to be able to be displaced in the axial direction with respect to the vehicle body, and is attached with its axis facing toward the rear of the vehicle body 1i. Inside the pole nut 23 is a threaded rod 2.
4 is inserted, and the outer peripheral surface of this threaded rod 24 and the Polnut 2
A large number of balls 25 are movably disposed between the inner circumferential surface of the ball 3 and the inner circumferential surface of the ball 3. Incidentally, a threaded groove in which the ball 25 rolls is formed on the inner circumferential surface of the pole nut 23 and on the outer circumferential surface of the threaded rod 24, but since such a structure is already known, it is not shown in the drawing in a simplified manner. be. As a result, the pole nut 23 is displaced toward the rear of the vehicle body 1i in response to the iE reverse rotation of the threaded rod 24, and the left and right relay rods 21R and 211 are gradually approached or separated in the vehicle width direction. Now, when the Polnut 23 is displaced in a predetermined constant direction, the right relay rod 2+11 is displaced to the right in FIG. 21L is displaced to the left in Fig. 3, and the left rear wheel 2
L is also towed in.

The first stage for driving the rear wheel steering mechanism B, that is, the drive means 13 for steering the left and right rear wheels 2R1214 will be described. This drive means E is composed of a step motor 30, which is fixed to a small body and whose output shaft 30a is connected to the threaded rod 24. Therefore, in accordance with the forward and reverse rotation of the step dryer 30, the bolt nut 23 is displaced in the longitudinal direction of the heavy body, and the displacement of the bolt nut 23 causes the left and right rear wheels 2R12L to be simultaneously steered in the toe-in or toe-out direction.

The reference numeral 40 in FIGS. 2 and 3 is a control unit configured by a microcomputer, and is basically a control unit configured by a microcomputer.
l, ROM, RAM, and a step motor 30
It has a built-in control means 41 for changing the rotation speed of the motor. Signals from sensors S1 to S6 are input to this control unit 40.

The sensor Sl detects the iIi speed. sensor S
2 detects the throttle position. The sensor S23 detects depression of the brake pedal (brake switch). Sensor S4 detects the steering angle of the steering wheel. Sensor S5 is a wiper switch, and sensor S6 is an encoder that detects rotational displacement of step motor 20.

Next, the content of control for rear wheel steering will be explained. First, the toe angle of the rear wheels is controlled in the toe-in direction or the toe-out direction, based on a predetermined reference toe angle To (initial toe angle), depending on the driving condition. Here, this rear wheel steering control is performed according to the vehicle speed, the brake switch being turned on (depressing the brake pedal), the steering wheel steering angle, and the road surface μ. When a predetermined value is set, for example, a control target value based on vehicle speed and a control target value based on braking, these control target values are added up to obtain the final control target value. It is now set as . In other words, 11 (speed-based control target) is as shown in Fig. 4. When the Ilj vehicle is in an accelerating state, the vehicle speed of 90 km/If is set as the base vehicle speed for determining the start of control in the toe-in direction. When the vehicle speed exceeds 90 km/h, a control target value of +6 mm is set to 11.-rate.

Here, +6 mm means, as explained with reference to FIG. 9, that the initial toe angle is further shifted by -B=6 mm in the toe-in direction. Note that in FIG. 4, the solid line is for acceleration, and the broken line is for deceleration. Here, when accelerating, 90 km
/H, it is controlled in the toe-in direction and 20
From km/II to 70 km/Ll, it is controlled in the toe-out direction; conversely, when decelerating, it is 80 km/Ll.
Toe-in control is stopped when the speed drops below I-1, and control is performed in the toe-out direction when the speed falls below 60 km/■. In this way, since toe angle control is performed using different discrimination base vehicle speeds during acceleration and deceleration, for example, when traveling at 90 km/h, toe-in control can be started with a slight acceleration or deceleration. Alternatively, it is possible to prevent repetition of middle l. Furthermore, between the control in the toe-out direction and the control in the toe-in direction, there is a region where no control is performed (2WS region), that is, during acceleration, for example, 70 km/! Since the range from 1 to 90 km/H is provided, the control in the toe-out direction immediately switches to the control in the toe-in direction (no 2WS range), so it is more suitable for control during acceleration or deceleration. It has the advantage of being able to be made smaller.

In other words, assuming a case where the driving state changes from deceleration to acceleration, the deceleration results in a reduction of 60 km/l-1.
Suppose that the vehicle enters the 80km/II range. At this time, the rear wheels are in an initial toe state (2WS state). If the vehicle is accelerated from this state to a medium speed exceeding 90 km/II, the rear wheels 2R12[, , will be steered in the toe-in direction. In other words, the rear wheels 2R and 2L are steered from initial toe to toe-in as the vehicle shifts from deceleration to acceleration. On the other hand, as mentioned above, in the case where there is no 2WS area, the rear wheel
](,21, is steered to -salt toe-out, and then steered from this toe-out to toe-in with acceleration, and large controls i and l are required.Especially, in this implementation In the example, as will be described later, the control is based on the 11th speed to slowly rotate the step motor 30, so the steering of the rear wheels 21?, 2L is as follows:
As shown in FIG. 8, this is done slowly. Therefore, when considering the above example, it is sufficient to shift the steering from the toe-in state to the final toe-in as shown by the arrow in the figure, which has the advantage that the load on the step motor 30 can be further reduced.

FIG. 5 shows the setting of the control target value in the toe-in direction during braking. This control is performed on the condition that the vehicle speed exceeds 50 km/ll.

FIG. 6 shows setting of a control target value in the toe-in direction based on the steering angle of the steering wheel. In this case, even if the steering angle is the same, a larger value is set as the vehicle speed increases. Further, the control based on the steering wheel angle is such that the rotational speed of the step motor 30 is decreased by [t] as the operating speed of the steering wheel increases. In other words, the faster the steering wheel is turned, the faster the rear wheels 2+1.2L are steered. This improves driving stability during cornering.

FIG. 7 shows the setting of the control target value in the toe-in direction based on the road surface μ. The road surface μ is determined to be a low μ road on the condition that the wiper switch S5 is turned on. That is, when the wiper switch s5 is turned on, it is assumed that the vehicle is on a low μ road, and control is performed in the toe-in direction to ensure the stability of running on the low μ road.

On the premise of the above, a more detailed explanation will be given based on the flowcharts shown after FIG. 1O.

Note that the rotational displacement of the step motor 30 is fed back by the encoder S6.

FIG. 1O shows control 1] target value setting based on li speed.

First, in step Pl (hereinafter, step numbers are indicated by P), the vehicle speed is manually determined, and in the next steps 1 and 2, the acceleration/deceleration state of light rain is determined. When it is determined that the vehicle is in an acceleration or steady running state, the range is determined in Pco3 to P5, and when the 111th speed is smaller than 20km/If, initial toe ('1゛0) is set (P6
), the state is 2WS. Vehicle speed: 20km/
In the range from H to 70 km/I-1, a target value for steering in the out direction is set (I) 7) from the initial toe 4 mm). 7゜km/H
Initial toe T in the range from 90 km/H
o is set (P8), and the state is set to 2WS. 90
In the area above km/I-1, initial-T
A target value is set for steering the vehicle in the toe-in direction by 6 mm from o to ensure high-speed running stability.

In square P2, when it is determined that the vehicle is in a decelerated running state, the process moves to the steps after PIO. The standard vehicle speed for this deceleration driving is 80 km/It, 60 km
/l-1, etc., the vehicle speed is changed to a smaller value than that at the time of acceleration, and a target value corresponding to each region is set (P13 to PI5) (see FIG. 4). Note that T1 shown in FIG. 9 indicates a control target value based on vehicle speed,
In the control based on this di speed, the step motor 30 is rotated relatively slowly at a speed of 1 sec.

FIG. 11 shows control during braking.

First, in step 1) 20, it is determined whether the flag F=1. Flag F=1 means that toe-in control based on braking is being performed. Now I='
If = 0, proceed to P2+ and the vehicle speed will be 50 km/It.
1] When the brake switch S5 is turned on, that is, when the brake pedal is depressed, 6 mm is added in the toe-in direction to the control target value T1 based on the vehicle speed. A target price is set (1) 23>. The toe-in control speed during this braking, that is, the rotation of the step dryer 30 is 50 m5
It rotates quickly at the OC speed 1, which quickly ensures running stability during control. In this toe-in control, the flag F is set to 1 (P24) and this toe-in state is continued (from P2O to P22) until the braking is released. Note that the flag 17 is reset when the braking is released at a vehicle speed of 50 km/If or less.

Control based on this braking is not performed unless the brake pedal is depressed, and the target value T1 based on the tonne speed recorded in 1iif is set as is (1) 25, l)
26). Note that the control in the door/outward direction (P26) upon release of the brake is performed when the rotational speed of the step motor 30 is 1.
sec, and is performed relatively slowly to ensure running stability. In this figure, T2 indicates a control target value that takes into account braking.

FIG. 12 shows control based on the steering wheel angle.

The vehicle speed is manually adjusted at P30, and the steering wheel angle is manually adjusted at P31. Using these vehicle speed and steering angle as parameters, a toe-in control target value F(V,
θII ) is set (see P32, Figure 6), and P33
A control target value T3 is set in consideration of this steering angle. As mentioned above, the toe-in control based on the steering wheel angle is performed at a speed that corresponds to the steering speed of the steering wheel, and the rotational speed of the step motor 30 is set at a speed that matches the steering speed of the steering wheel. It is supposed to be done.

FIG. 13 shows control based on road surface μ. Toe-in control based on this road surface μ is performed by turning on the wiper switch S5,
OF +", when the wiper switch S5 is turned on, a 1 mm toe-in []1 mark T is set (P41).

This control based on the road surface μ is performed relatively slowly, with the rotational speed of the step motor 30 being set to lsc=c.

(Effects of the Invention) As is clear from the explanation in 11 below, according to the present invention, the frequency of operation of the actuator for steering the rear wheels can be reduced, and the reliability of the actuator can be improved.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of the present invention, FIG. 2 is a system diagram of a control system according to an embodiment, and FIG. 3 is a detailed diagram of main parts. FIG. 4 is a diagram showing control target values based on vehicle speed, FIG. 5 is a diagram showing control target values based on braking, and FIG. 6 is a diagram showing control target values based on steering angle. Fig. 7 is a diagram showing the control target value based on road surface μ; Fig. 8 is an explanatory diagram showing the state of rear wheel steering based on vehicle speed; Fig. 9 is an explanatory diagram of toe-in control target value setting; FIG. 13 is a flowchart showing an example of control. 2 R12 [, ■] I: Left and right rear wheels: Rear wheel steering mechanism Two connection mechanisms: Rear wheel drive mechanism Two ball nuts: Step motor (actuator): Control unit: Step rotation speed control means Two vehicle speed sensors: Throttle position sensor: Brake switch: Handle steering angle sensor Wiper switch: Encoder

Claims (1)

[Claims] (1) In a rear wheel steering system of a vehicle in which the left and right rear wheels are respectively steered in at least the toe-in direction by the operation of an actuator, the vehicle speed detection means detects the vehicle speed; the deceleration detection means detects the deceleration of the vehicle; A steering start control means that starts steering the rear wheels when the vehicle speed reaches a predetermined speed according to the vehicle speed; A rear wheel steering device for a vehicle, comprising: determination reference value changing means for changing the vehicle speed to a reference vehicle speed.