JPH03273972A - Rear wheel steering device of vehicle - Google Patents

Abstract

PURPOSE:To improve steering feeling in a vehicle where a change rate ratio vS/vL is corrected in such a manner that the larger the front wheel steering speed, the larger the change rate ratio vS/vL, and the change rate ratio of rear wheel steering angle to front wheel steering angle in front wheel steering area is variable. CONSTITUTION:To control the operation of a stepping motor 50 for controlling rear wheel steering angle by a control unit 100, the rear wheel steering angle is first calculated by a rear wheel operating angle calculating part 103 on the basis of the output signals of a vehicle speed sensor 101 and a front wheel steering angle sensor 102, and outputted to a driving means 104. The front wheel steering angle is differentiated from a front wheel steering angle detection signal SA by a steering angel correction means 105 to calculate the change rate of the front wheel steering angle, and a correction signal according to the steering speed is outputted. The control is such that the larger the front wheel steering speed, the larger the change rate ratio vS/vL of the change rate vL of the rear wheel steering angle to the front wheel steering angle in the area having a large front wheel steering angle to the change rate vS in the area having a small front wheel steering angle.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a rear wheel steering system for a vehicle, and more particularly, to a system for controlling the steering angle of the front wheels in a region where the steering angle of the front wheels is large at a predetermined vehicle speed or higher. The change rate ratio vs/vL of the change rate V of the rear wheel steering angle and the front wheel steering angle in a region where the front wheel steering angle is small: the corresponding change rate vS of the rear wheel steering angle is large, and The higher the vehicle speed,
A rear wheel steering device for a vehicle equipped with a rear wheel steering means for steering the rear wheels so that the rear wheels of the vehicle are larger, the rear wheels of the vehicle having steering characteristics more faithful to the driver's intention and improved steering feeling. This invention relates to a steering device.

BACKGROUND ART In a vehicle having four wheels, a rear wheel steering device is known that, when the front wheels, which are steered wheels, are steered, the rear wheels are also steered in a predetermined relationship.

For example, as shown in Japanese Patent Publication No. 63-65546, when the front wheels are steered in a low vehicle speed region, or when the front wheels are largely steered, the driver can: On the other hand, when the front wheels are steered or the steering angle of the front wheels is small at medium to high vehicle speeds, there is often a desire to change the direction of the vehicle, and on the other hand, when the front wheels are steered or the steering angle of the front wheels is small, there is a desire to move the vehicle slightly sideways, such as when changing lanes. Based on the empirical rule that, in low vehicle speed regions, the rear wheels are steered in the opposite direction to the front wheel steering direction, that is, in the opposite phase, and on the other hand, in medium and high vehicle speed regions, the front wheels are With respect to the direction, the rear wheels are steered in the same direction, that is, in the same phase, and the change rate vL of the rear wheel steering angle with respect to the front wheel steering angle in a region where the front wheel steering angle is large, and the front wheel steering angle are The rear wheels are steered so that the ratio Vs/VL of the change rate of the rear wheel steering angle to the front wheel steering angle in a small region is large and becomes larger as the vehicle speed increases. something is known.

Problems to be Solved by the Invention However, when the rear wheels are steered based only on the vehicle speed and the size of the steering angle of the front wheels, the rear wheels are not necessarily steered faithfully to the driver's intention. There were cases where there was none.

In other words, even when the steering angle of the front wheels is small, when the steering speed is high, the driver often wants to change the direction of the vehicle largely and rapidly.
Therefore, if the rear wheels are simply steered based only on the vehicle speed and the magnitude of the steering angle of the front wheels, there is a problem in that the steering feeling deteriorates in such cases.

Purpose of the Invention The present invention provides, at a predetermined vehicle speed or higher, the rate of change vL of the rear wheel steering angle with respect to the front wheel steering angle in a region where the front wheel steering angle is large, and the change rate vL of the rear wheel steering angle with respect to the front wheel steering angle in a region where the front wheel steering angle is small. The rear wheel of a vehicle equipped with a rear wheel steering means for steering the rear wheels is set so that the change rate ratio V s / V L of the wheel steering angle change*vs becomes larger and becomes larger as the vehicle speed increases. An object of the present invention is to provide a rear wheel steering device for a vehicle that has steering characteristics that are more faithful to the driver's intention and has improved steering feel.

Structure of the Invention An object of the present invention is that the higher the steering speed of the front wheels, the more the steering speed of the front wheels increases.
This is achieved by providing a correction means that corrects the rate of change ratio 1/5/VL to become larger.

Effects of the Invention According to the present invention, the control means controls the rate of change vL of the rear wheel steering angle with respect to the front wheel steering angle in a region where the front wheel steering angle is large as the front wheel steering speed increases, and the front wheel steering angle. Since the change rate ratio Vs/VL of the change rate vS of the rear wheel steering angle to the front wheel steering angle in a small region is controlled to be large, it is possible for the driver to steer the front wheels at a large steering speed. In this case, the steering angle of the rear wheels becomes smaller with respect to the same steering angle of the front wheels, and therefore the direction of the vehicle can be changed greatly and rapidly.
This allows the rear wheels to be steered more faithfully to the driver's intentions, improving steering feel.

EXAMPLES Hereinafter, examples of the present invention will be described in detail based on the accompanying drawings.

FIG. 1 is a schematic configuration diagram of a rear wheel steering device for a vehicle according to an embodiment of the present invention, and FIG. 2 is a schematic perspective view thereof.

In FIGS. 1 and 2, the front wheels IL, IR and the rear wheels 2L, 2R are supported by a front wheel steering mechanism 3 and a rear wheel steering mechanism 12, respectively, and the front wheel steering mechanism 3 is supported by a pair of left and right knuckle arms. 4L, 4R and tie rod 5L
, 5R, and a relay rod that connects these left and right tie rods 5L and 5R. This front wheel steering mechanism 3 is connected to the front wheel steering mechanism 3 via a rack and pinion type steering mechanism 7.
A steering wheel 10 is connected. The steering mechanism 7 includes a rack 8 formed on the relay rod 6, a steering shaft 11 to which a steering wheel 10 is connected at the upper end and a pinion 9 which meshes with the rack 8 at the lower end. However, when the steering wheel 10 is operated, the left and right front wheels IL and IR are steered according to the amount of operation.

On the other hand, the rear wheel steering mechanism 4, like the front wheel steering mechanism 3, includes a pair of left and right knuckle arms 13L, 1.3R and tie rods 14L, 14R, and these left and right tie rods 14L.
, 14R, and further includes:
A hydraulic power steering mechanism 16 is provided. The power steering 16 includes a power cylinder 1 fixed to the vehicle body and having the relay rod 15 as a piston rod.
7, the inside of the power cylinder 17 is divided into two hydraulic chambers 17b and 17c by a piston 17a attached to the relay rod 15, and these hydraulic chambers 17
b, 17c are connected to the control valve 20 via piping 18, 19, respectively. An oil supply pipe 22 and an oil discharge pipe 23 that communicate with a reserve tank 21 are connected to the control valve 20, and a hydraulic pump 2 driven by an engine (not shown) is connected to the oil supply pipe 22.
4 are arranged.

The control valve 20 is constituted by a known spool valve type valve, and is connected via a connecting member 25.
It includes a cylindrical valve casing 20a integrally attached to the relay rod 15 and a spool valve (not shown) fitted in the valve casing 2Oa. Pressure oil is supplied from the hydraulic pump 24 to the hydraulic chambers 17b and 17c to assist the driving force for the relay rod 15. Also, inside the power cylinder 17, there is a relay rod 1.
5 is the rear wheel 2L, 2R (7) P4 steering angle θ.

Return springs 17d and 17d are attached to bias the lid at a position where the value is 0, that is, at a neutral position.

A rack 26 is formed on the relay rod 6 of the front wheel steering mechanism 3 at a different position from the steering mechanism 70 rack 8, and a binion 27 attached to the front end of a rotating shaft 28 extending in the longitudinal direction of the vehicle body meshes with the rack 26. The rear end of the rotating shaft 28 is connected to the rear wheel steering mechanism 1 via a steering ratio control mechanism 29.
It is connected to 2.

As shown in FIG. 2, the steering ratio control mechanism 29 includes a control rod 30 that is slidably held in the vehicle width direction with respect to the vehicle body.
(7)-H! , connected to the spool valve of the control valve 20. Further, the steering ratio control mechanism 29 includes a swing arm 33 whose one end is swingably supported by a U-shaped holder 31 via a support pin 32.
1 is rotatably supported by a casing (not shown) fixed to the vehicle body via a support shaft 35 having a rotation axis perpendicular to the movement axis of the control rod 30.

The support pin 32 of the swing arm 33 is located at the intersection of the movement axis of the control rod 30 and the rotation axis of the support shaft 350, and extends in a direction perpendicular to the rotation axis. 35, the angle of inclination between the support pin 32 and the axis of movement of the control rod 30, that is, the swing locus plane of the swing arm 33 centered on the support pin 32, changes the movement of the control rod 30. The angle of inclination made with respect to a plane perpendicular to the axis (hereinafter referred to as "reference plane") is changed.

Further, one end of a connecting rod 37 is connected to the tip of the swing arm 33 via a ball joint 36, and the other end of the connecting rod 37 is connected to the control rod 30 via a ball joint 38.
The control rod 30 is connected to an end that is not connected to the spool valve, and is adapted to displace the control rod 30 in the vehicle width direction in response to displacement of the tip of the swing arm 33 in the vehicle width direction.

The connecting rod 37 is slidably supported by a large-diameter bevel gear 40 via a ball joint 41 at a portion near the ball joint 36 . The large diameter bevel gear 40 is rotatably supported on the movement axis of the control rod 30 via a support shaft 42, and the bevel gear 40 has a rotating shaft 28 as shown in FIG. A bevel gear 44 attached to the rear end is meshed so as to transmit rotation of the steering wheel 100 to the bevel gear 40, which in turn transmits the rotation to the connecting rod 37. It is configured. Therefore, the bevel gear 40 and the connecting rod 37 rotate around the movement axis of the control rod 30 by an amount corresponding to the rotation angle of the steering wheel 10, and accordingly, the swing arm 33 moves toward the support pin 32. When the axis of the support pin 32 coincides with the axis of movement of the control rod 30, the ball joint 36 at the tip of the swing arm 33 will be
Although the control rod 30 is held stationary by only swinging on the reference plane, the axis of the support pin 32 is inclined with respect to the movement axis of the control rod 30, and the swing trajectory of the swing arm 33 is changed. When the plane deviates from the reference plane, the ball joint 36 is displaced in the vehicle width direction as the swing arm 33 swings about the support pin 32, and this displacement is caused by the connecting rod 37. hand,
The control rod 30 is configured to move along its axis of movement and actuate the spool valve of the control valve 20. That is, even if the swing angle of the swing arm 33 about the axis of the support pin 32 is the same, the displacement of the control rod 30 in the left-right direction is the inclination angle of the support pin 32, that is, the rotation angle of the holder 310. It is expected to change with changes in

Further, in order to change the inclination angle of the support pin 32 with respect to the movement axis of the control rod 30, that is, the inclination angle with respect to the reference plane of the holder 31, the support shaft 35 of the holder 31 is
A sector gear 45 as a worm wheel is attached to the worm wheel, and a worm gear 47 that rotates together with a rotating shaft 46 meshes with the sector gear 45 . Further, a bevel gear 48 is attached to the rotating shaft 46, and a bevel gear 49 attached to the output shaft 50a of the stepping motor 50 is meshed with the bevel gear 48, and the stepping motor 50 is operated. By rotating the sector gear 45, the angle of inclination of the holder 31 with respect to the reference plane is changed to control the steering angle θk of the rear wheels 2L, 2R.
The steering angle of the rear wheels 2L and 2H is controlled to be in the same phase as the steering angle of the front wheels IL and IR when the rear wheels 2L and 2H are rotated clockwise when viewed from above the vehicle body from the middle 2 position perpendicular to the rear wheels. It is configured to

In addition, the casing that supports the holder 31 is provided with a first stopper pin 51 on the left and right sides of the sector gear 45 to restrict the rotation of the sector gear 45 on the opposite phase side, and a second stopper pin 52 that restricts the rotation on the same phase side. The sector gear 45 is rotated at a predetermined angle to the opposite phase side, for example, -1.
When the sector gear 45 rotates by 7.5 degrees, the sector gear 45 comes into contact with the first stopper pin 51, and further rotation is restricted.
On the other hand, when the sector gear 45 rotates to the same phase side by a predetermined angle, for example, 20 degrees, the sector gear 45 comes into contact with the second stopper pin 52, and further rotation is restricted. In FIG. 2, 39 is a rod stopper that restricts the maximum movement range of the relay rod 15 of the rear wheel steering mechanism 12.

The operation of the stepping motor 50 is configured to be controlled by a control unit 100, and the control unit 100i: +-! , a vehicle speed detection signal Sv from a vehicle speed sensor 101 that detects the vehicle speed V is also attached to the steering shaft 11, and is connected to the front wheels IL, I.
A front wheel steering angle detection signal from a front wheel steering angle sensor 102 that detects the steering angle θ of the vehicle R is input.

FIG. 3 shows a block diagram of the control unit 100, and the control unit 100 receives the vehicle speed detection signal Sv from the vehicle speed sensor 101 and the front wheel steering angle detection signal SA from the front wheel steering angle sensor 102, and uses these human inputs. A rear wheel steering angle calculation unit 103 calculates the steering angle θ□ of the rear wheels 2L and 2R and the corresponding number of steps based on the signal and outputs the calculated result to the drive means 104 according to a map stored in advance. , receives the front wheel steering angle detection signal SA from the front wheel steering angle sensor 102, differentiates the steering angle θF of the front wheels LL and IR, and calculates the front wheel IL,
The rate of change of the steering angle θ of the IR, that is, the steering speed of the steering wheel 10 is calculated, and a correction signal corresponding to the calculated steering speed is sent to the rear wheel steering angle calculating section according to a map stored in advance. 103 is provided.

FIG. 4 shows the first basic map stored in the rear wheel steering angle calculating section 103, and shows the first basic map for the rear wheel 2L.

The steering angle θ of 2R and the steering angle θ of front wheels IL and IR.

This shows the relationship between the steering ratio θR/θ, which is the ratio of θR/θ, and the vehicle speed V. As shown in FIG. 4, the steering ratio R is set to a negative value in a low vehicle speed region where the vehicle speed V is small, and the rear wheels 2L and 2R are set in opposite phases to the front wheels IL and IR. By steering, the direction of the vehicle can be changed significantly. The steering ratio R is set to gradually increase as the vehicle speed V increases, that is, as the vehicle speed shifts from a low vehicle speed region to a medium vehicle speed region, and further from a medium vehicle speed region to a high vehicle speed region. This is intended to prevent unstable driving conditions due to large changes in the direction of the vehicle in medium to high vehicle speed ranges.

FIG. 5 shows the second basic map stored in the rear wheel steering angle calculating section 103, and shows the steering angle θ of the rear wheels 2L and 2R.
1. Steering angle θ of front wheels IL and IR.

and vehicle speed.

As shown in FIG. 5, in a low vehicle speed region where the vehicle speed is low, the steering angle θ of the front wheels IL and IR.

On the other hand, the steering angle θ of the rear wheels 2L and 2R is set to a negative value, and when the vehicle speed exceeds a predetermined value V, the steering angle θ of the front wheels IL and IR becomes a positive value, at least in the region where the steering angle θF of the front wheels IL and IR is small. Along with the setting, front wheel IL.

Front wheel IL in a region where the IR steering angle θ is large.

The rate of change V in the steering angle θ of the rear wheels 2L, 2R with respect to the steering angle θF of the IR, and the steering angle θ of the front wheels IL, IR in a region where the steering angle θ of the front wheels IL, IR is small, the rear wheel 2L, The change rate ratio V of the steering angle θ of 2R with the change rate vS
5/The larger VL and the faster the vehicle speed,
θ and −θ at each vehicle speed V are set so that they become larger.

The characteristic curve is set to have an inflection point.

Therefore, in the low vehicle speed region, the rear wheels 2L and 2R are steered in the opposite phase to the front wheels LL and IR, satisfying the requirement that the direction of the vehicle can be changed significantly, and at medium and high vehicle speeds. In the area, rear wheel 2L,
2R is steered at a predetermined angle in the same phase to satisfy requests for lateral movement such as changing lanes, and in the medium vehicle speed region, the front wheels IL and IR are steered according to the vehicle speed V and the steering angle θ of the front wheels IL and IR. When the steering angle θ is large, it is possible to satisfy the requirement to change the direction of the vehicle.

FIG. 6 shows a correction map stored in the steering angle correction means 105, and shows the correction map for the front wheel IL.

Depending on the steering speed of the IR, the steering angle θ of the rear wheels 2L and 2H!
It shows how to correct. That is, front wheel LL
When the IR steering speed is high, it is thought that the driver often has an intention to change the direction of the vehicle for some reason, even if the vehicle speed V is in the medium-to-high vehicle speed range above a predetermined value. , Therefore, the front wheels IL, I
By correcting the change rate V of the steering angle θ of the rear wheels 2L, 2R with respect to the steering angle θ of the rear wheel R as quickly as possible, the rear wheels 2L, 2RLy) can be steered in accordance with the driver's intention. It is necessary to do this. Therefore, in Fig. 5, the front wheel IL is
, θ, −θ at each vehicle speed V according to the steering speed of IR.
This requirement is met by shifting the inflection point of the characteristic curve to a value where the steering angle θP of the front wheels IL and IR is small. Figure 6 shows θ and -θ at each vehicle speed V.
, the steering angles θFr of the front wheels IL and IR at the inflection points of the characteristic curves are expressed as follows: The amount of transition of the white point indicating how much the transition is to be made is 100% when the amount of transition of the inflection point is (θF knee θ, .), and the front wheel 1. - It is shown in relation to the steering speed Vθ of L and IR.

As shown in FIG. 6, the steering speed V of the front wheels IL and IR is
When θ is less than a predetermined value VθF1, the inflection point shift amount is 0%, the inflection point I is not shifted, and the steering angle θ of the rear wheels 2L and 2R is controlled according to the second basic map. Ru. On the other hand, when the steering speed Vθ, exceeds the predetermined value VθF1, the inflection point I of the θF-θ mouse characteristic curve at each vehicle speed V is set so that the amount of inflection point shift increases linearly until the predetermined value Vθ,2. The steering angles θ, 1 of the front wheels IL, IR are the front wheels LL, I.
The steering angle of R is shifted toward the steering angle θFC, and the predetermined value V5F□
When reaching , the steering angle θ of the front wheels IL and IR at the inflection point I becomes the steering angle θ. The steering angle is corrected to be equal to .

FIG. 7 shows an example of θ, -θ, and a characteristic curve corrected according to the steering speed Vθ2 of the front wheels IL and IR based on FIG. 1 is the corrected θ, -〇8 characteristic curve when the inflection point shift amount is 50%, and curve 12 is the corrected θ, -〇 characteristic curve when the inflection point shift amount is 100%. The curves are shown respectively.

In this way, the steering angle correction means 105 calculates a correction value based on the steering speed VeF according to FIG.
, 1 as θ. A correction signal S indicating that it should be replaced with. is output to the rear wheel steering angle calculation section 103.

Based on the correction signal Sc, the rear wheel steering angle calculation unit 103
Based on the vehicle speed detection signal Sv from the vehicle speed sensor 101 and the front wheel steering angle detection signal from the front wheel steering angle sensor 102, according to the first basic map and the second basic map shown in FIGS. 4 and 5, Calculated rear wheel 2L,
The steering angle θ of 2R and the number of steps corresponding thereto are output to the driving means 104. The driving means 104 drives the stepping motor 50 according to the step number signal inputted from the rear wheel steering angle calculating section 103, and drives the sector gear 4.
5 to control the steering angle θ of the rear wheels 2L and 2R as desired.

According to the present embodiment, the θ, -θ and characteristic curves of the second basic map shown in FIG. 5 set based on the vehicle speed V and the steering angle θP of the front wheels IL and IR are converted into Accordingly, the steering speed Vθ of the front wheels IL and IR is set to a predetermined value V.
When θ exceeds 1, the inflection point is corrected so that it occurs at a smaller steering angle θ, so the direction of the vehicle can be changed without impairing the running stability of the vehicle in the medium and high speed range. Since the rear wheel steering can be controlled in accordance with the driver's wishes, it is possible to improve the steering feeling.

The present invention is not limited to the above-mentioned examples, but various modifications can be made within the scope of the invention described in the claims, and these are also included within the scope of the present invention. Needless to say.

For example, in the embodiment described above, the inflection point I is only corrected according to the steering speed VθF of the front wheels IL and IR so that it occurs at a smaller steering angle θF, but in addition to this, From the inflection point ■, the steering angle θF of the front wheels IL and IR
In the region where θ, -〇, the slope of the characteristic curve is small, that is, the steering angle θ of the front wheels IL and IR is
The rate of change v of the steering angle θ of the rear wheels 2L and 2R with respect to , is
The steering angle correction means 105 may correct the angle so that it becomes smaller.

Effects of the Invention According to the present invention, at a predetermined vehicle speed or higher, the change rate vL of the rear wheel steering angle with respect to the front wheel steering angle in a region where the front wheel steering angle is large, and the front wheel steering angle in a region where the front wheel steering angle is small. The vehicle is equipped with a rear wheel steering means for steering the rear wheels such that the change rate ratio V, /vL of the rear wheel steering angle to It is possible to provide a rear wheel steering device for a vehicle, which has steering characteristics that are more faithful to the driver's intention and has improved steering feel.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a rear wheel steering device for a vehicle according to an embodiment of the present invention, and FIG. 2 is a schematic perspective view thereof. Third
The figure is a block diagram of the control unit. FIGS. 4 and 5 are graphs respectively showing the first basic map and the second basic map stored in the rear wheel steering angle calculating section. FIG. 6 is a graph showing a correction map for rear wheel steering angle correction stored in the steering angle correction means. FIG. 7 is a graph showing an example of θF-0 and characteristic curves corrected using the correction map shown in FIG. IL, IR...Front wheels 2L, 2R...Rear wheels 3...Front wheel steering mechanism, 10...Steering wheel, 12...Rear wheel steering mechanism, 20...Control rod, 29... Steering ratio control mechanism, 30... Control rod, 45... Sector gear, 50... Stepping motor, 100... Control unit, 101... Vehicle speed sensor, 2... Front wheel steering angle sensor, 3. ... Rear wheel steering angle calculating section, 4... Drive means, 5... Steering angle correction means. Figure 4 Figure 4 Figure 4

Claims (1)

[Claims] At a predetermined vehicle speed or higher, the rate of change of the rear wheel steering angle with respect to the front wheel steering angle in a region where the front wheel steering angle is large
L and the rate of change v_S of the steering angle of the rear wheels relative to the steering angle of the front wheels in a region where the steering angle of the front wheels is small;
In a rear wheel steering device of a vehicle equipped with a rear wheel steering means that steers the rear wheels such that S/v_L becomes larger and becomes larger as the vehicle speed becomes larger, the larger the steering speed of the front wheels is, the larger the change becomes. A rear wheel steering device for a vehicle, comprising a correction means for correcting the ratio v_S/v_L to become larger.