JPH07291141A - Steering device provided with transmission ratio variable type steering mechanism - Google Patents

Abstract

PURPOSE:To prevent an actual steering angle of a steering wheel from becoming excessively large beyond expectations in a low car speed area so as to reduce a feeling of physical disorder that a vehicle driver feels and necessity to aggressively get used to driving. CONSTITUTION:A steering device is provided with transmission ratio variable type steering mechanisms 20, 38, 42, 46, 54. Front wheels 34, 36 are steered by the steering mechanisms, and on the basis of a car speed V detected by a car speed sensor 64, a transmission ratio of the steering mechanisms is controlled by means of an electronic controller 60 so that it becomes larger as the vehicle speed is lower. In a low vehicle speed area, the transmission ratio is controlled so as to be smaller in the case of steering in the same direction as the direction of a traffic side on a traveling road than in the case of steering in the opposite direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering device for a vehicle such as an automobile, and more particularly to a steering device having a variable transmission ratio steering mechanism configured such that the transmission ratio increases as the vehicle speed decreases. .

[0002]

2. Description of the Related Art As one of steering devices for vehicles such as automobiles, as described in, for example, Japanese Patent Laid-Open No. 4-9709, the actual turning angle of a steered wheel with respect to the steering amount of a steering input means such as a steering wheel. A steering device having a so-called vehicle speed sensitive type transmission ratio variable steering mechanism configured so that the ratio (referred to as "transmission ratio" in the present application) changes according to the vehicle speed has been conventionally known.

According to such a steering device, for example, by constructing the steering mechanism such that the transmission ratio becomes larger as the vehicle speed becomes lower, the steering ratio becomes constant regardless of the vehicle speed, as compared with the case of an ordinary general steering device. In the low vehicle speed range, the steering wheel is steered largely with a small steering input, which speeds up the turning behavior of the vehicle to secure a good steering feeling, and to put the vehicle in the garage or to move it sideways. In the high vehicle speed range, the ratio of the actual turning angle of the steered wheels to the steering input can be reduced in the high vehicle speed range to improve the steering stability during high speed running.

[0004]

However, in the steering apparatus having the conventional variable transmission ratio type steering mechanism as described above, when the steering mechanism is configured such that the transmission ratio becomes higher as the vehicle speed becomes lower, the vehicle speed range becomes lower. The actual turning angle of the steered wheels in the vehicle may become larger than expected, which causes the driver of the vehicle to feel a sense of discomfort or to become actively used to driving the vehicle. . If the degree to which the transmission ratio becomes larger as the vehicle speed becomes lower is set to reduce such a problem, the effect obtained by configuring the steering mechanism so that the transmission ratio becomes larger as the vehicle speed becomes lower becomes insufficient. The significance of incorporating the variable ratio steering mechanism is lost.

The present invention has been made in view of the above-mentioned problems in a steering apparatus having a conventional vehicle speed-sensitive type transmission ratio variable steering mechanism, and a main problem to be solved by the present invention is to solve the problems. While ensuring the effect obtained by configuring the steering mechanism so that the transmission ratio increases as the vehicle speed decreases, it prevents the actual steering angle of the steered wheels from becoming too large than expected in the low vehicle speed range. This is to reduce the discomfort felt by the driver of the vehicle and the need to actively get used to driving the vehicle.

[0006]

According to the present invention, the main problems as described above are (1) a steering system having a variable transmission ratio steering mechanism configured such that the transmission ratio increases as the vehicle speed decreases. In the above, the steering mechanism is configured to steer the front wheels, and the transmission ratio in the low vehicle speed range is set to be smaller when turning in the same direction as the traffic side of the road than when turning in the opposite direction. (2) A steering device having a variable transmission ratio steering mechanism configured such that the transmission ratio increases as the vehicle speed decreases, and the total traveling from the start of traveling of the vehicle. A means for detecting a parameter corresponding to time, and a means for controlling the steering mechanism such that the degree to which the transmission ratio increases as the vehicle speed decreases with an increase in the parameter increases. Or (3) a steering device having a variable transmission ratio steering mechanism configured such that the transmission ratio increases as the vehicle speed decreases, wherein the steering mechanism steers front wheels. In the low vehicle speed range, the steering device has a rear wheel steering means for steering the rear wheels in the opposite direction to the front wheels.

In the present specification, the "passage side of the traveling road" means that the vehicle is traveling on the left side or the right side, and "turns in the same direction as the traveling side of the traveling road". Left-hand traffic means left turn, right-hand traffic means right turn,
"Turning in the opposite direction" means a right turn for left-hand traffic and a left turn for right-hand traffic.

[0008]

In general, the turning radius of the front wheels, which are the steered wheels, is larger than the turning radius of the rear wheels, and the turning radius when turning in the same direction as the passage side of the road is greater than when turning in the opposite direction. Therefore, if the transmission ratio in the low vehicle speed range is increased, the actual steering angle of the front wheels becomes larger than expected when turning in the same direction as the traffic side of the road, and the It makes it easier for the wheel to ride on the road shoulder.

According to the above configuration (1), the transmission ratio in the low vehicle speed range is set to be smaller in the case of turning in the same direction as the traffic side of the road than in the case of turning in the opposite direction. Therefore, when turning in the same direction as the traffic side of the road, the ratio of the actual turning angle of the front wheels to the steering amount of the steering input means is smaller than when turning in the opposite direction. It is reliably prevented that the steered angle becomes too large than expected and that the rear wheel on the inside of the turn does not run on the road shoulder due to this.

Further, in a steering apparatus having a variable transmission ratio steering mechanism configured such that the transmission ratio increases as the vehicle speed decreases, when the degree of increase of the transmission ratio is more constant than at the start of operation, the vehicle travels. Since it is not always easy to understand its characteristics from the beginning of the drive, the driver may feel discomfort immediately after starting the drive or be confused about the proper steering. Get used to the characteristics.

According to the above configuration (2), the steering mechanism is controlled so that the transmission ratio becomes larger as the vehicle speed becomes lower as the parameter corresponding to the total traveling time from the start of traveling of the vehicle becomes larger. Because it is done
As the driver gets accustomed to the characteristics of the steering system, the degree to which the transmission ratio increases as the vehicle speed becomes lower gradually increases, which reliably prevents the driver from feeling uncomfortable and confused about proper steering immediately after the start of driving. To be done.

Further, when only the front wheels are steered, the turning radius of the front wheels is larger than that of the rear wheels as described above.
When the rear wheels are steered in the opposite direction to the front wheels, the difference between the turning radii of the front and rear wheels becomes smaller, and in the case of turning with the same turning radius, the rear wheels are steered in the opposite direction to the front wheels. In this case, the actual steering angle required for the front wheels is smaller than when only the front wheels are steered. Therefore, the lower the vehicle speed, the smaller the degree to which the transmission ratio increases.

According to the above configuration (3), the steering mechanism is configured to steer the front wheels, and the rear wheels are steered in the direction opposite to the front wheels in the low vehicle speed range by the rear wheel steering means. As compared with the case where only the front wheels are steered, the difference in the turning radii of the front and rear wheels becomes smaller and the transmission ratio may become smaller as the vehicle speed becomes lower. When turning at a low speed, it is possible to reliably prevent the actual turning angle of the front wheels from becoming larger than expected and the rear wheels on the inside of the turn from riding on the road shoulder due to the difference in the turning radii of the front and rear wheels.

[0014]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic configuration view showing a first embodiment of a steering apparatus having a variable transmission ratio type steering mechanism according to the present invention, and FIG. 2 is an enlarged partial perspective view showing a main part of the steering mechanism shown in FIG. It is a figure.

In these figures, reference numeral 10 denotes a steering wheel fixed to the upper end of the steering shaft 12 as steering input means. The lower end of the steering shaft 12 has a pinion 16 that meshes with the rack bar 14.
The rack bar 14 is supported by a vehicle body (not shown) so as to be capable of reciprocating in the lateral direction of the vehicle. When the steering wheel 10 is steered, the rack bar 14 is rotated in accordance with the rotation direction of the steering wheel 10. 14 is designed to reciprocate.

One end of a pivot link 20 is pivotally attached to one end of the rack bar 14 by a pivot shaft 18.
The other end of 0 is pivotally attached to a reciprocating bar 24 by a pivot 22. The ends of the reciprocating bar 24 are pivotally attached to the inner ends of tie rods 30 and 32 by ball joints 26 and 28, respectively, and the outer ends of the tie rods 30 and 32 are respectively attached to the left front wheel by ball joints not shown. 34 and the right front wheel 36 are pivotally attached to the knuckle arm.

Pivot link 20 has an elongated groove 40 extending along its length to receive pivot 18 and fulcrum roller 38. The fulcrum roller 38 is fixed to the slider 42 at one end and is rotatably supported at the other end of a shaft 44 extending perpendicularly to the plate surface of the pivot link 20. Slider 4
A screw shaft 46 extending parallel to the plate surface of the pivot link 20 is inserted through the screw shaft 2, and is screwed with the screw shaft 46. The screw shaft 46 is supported by a vehicle body (not shown) so as to be rotatable about an axis 48 and not to move along the axis 48.
0 is fixed. A worm gear 52 is meshed with the worm wheel 50, and the worm gear 52 is fixed to a shaft 56 of a motor 54 fixed to the vehicle body and is thereby rotated.

Thus, when the steering wheel 10 is steered and the rack bar 14 is driven in the lateral direction of the vehicle, the pivot link 20 is pivoted around the fulcrum roller 38, and the reciprocating bar 24 and the tie rods 30 and 32 are moved laterally of the vehicle. Driven in the direction, whereby the left and right front wheels 34 and 36 are steered. In this case, the ratio of the amount of movement of the reciprocating bar 24 to the amount of movement of the rack bar 14 is determined by the position of the fulcrum roller 38. The distance between the center of the fulcrum roller and the center of the pivot 18 is La, and the center of the fulcrum roller is If the distance between the axis and the center of the pivot 22 is Lb, then Lb / La.

The ratio Lb / La of this distance is determined by the pivot link 2
The position of the fulcrum roller 38 with respect to 0 increases as it moves upward in FIG. 1, and conversely decreases as the position of the fulcrum roller 38 moves downward as viewed in FIG. As described above, the screw shaft 46 is inserted into the slider 42 and is screwed therewith, and the worm wheel 50 has the motor 5 mounted thereon.
Since the worm gear 52 rotated by 4 meshes with the fulcrum roller 38, the position of the fulcrum roller 38 is changed by the rotation of the motor 54, whereby the transmission ratio R, that is, the left and right front wheels 34 and the steering wheel 10 with respect to the operation amount. Three
The ratio of the actual turning angles of 6 is changed.

The motor 54 is controlled by an electronic control unit 60 via a drive circuit 58. Therefore, a motor such as a stepping motor is controlled so that the rotation angle is accurately controlled according to a command signal from the electronic control unit. It is preferably a motor. The illustrated embodiment is configured as a steering device for a left-hand vehicle, and a signal indicating a steering angle θ is input to the electronic control unit 60 from a steering angle sensor 62 provided on the steering shaft 12 with the right-turn direction being positive. A signal indicating the vehicle speed V is input from the vehicle speed sensor 64, and a signal indicating whether or not the vehicle is about to turn left is input from the blinker switch 66.

As shown in FIG. 3, the electronic control unit 6
0 is a turn determination block 68 and a transmission ratio calculation block 70
And a command signal output block 72, but may actually be a microcomputer having a CPU, a RAM, a ROM, and an input / output port device. The turn determination block 68 determines whether or not the vehicle is making a left turn based on the signal from the turn signal switch 66, and outputs a signal indicating the determination result to the transmission ratio calculation block 70.

Based on the signal from the turn determination block 68, the signal indicating the steering angle θ from the steering angle sensor 62, and the signal indicating the vehicle speed V from the vehicle speed sensor 64, the transmission ratio calculation block 70 is not making a left turn of the vehicle. When the signal from the turn signal switch 66 is not the signal indicating the left turn and the signal indicating the steering angle θ from the steering angle sensor 62 is not negative, the transmission from the map corresponding to the solid line of the graph shown in FIG. The ratio R is calculated, and when the vehicle is making a left turn, the transmission ratio R is calculated from the map corresponding to the broken line in the graph shown in FIG. The command signal output block 72 outputs a command signal to the drive circuit 58 based on the transmission ratio R, thereby controlling the motor 54 so that the actual transmission ratio becomes the transmission ratio R calculated in the transmission ratio calculation block 70. .

Thus, according to the first embodiment, the steering wheel 1 when the vehicle turns left at a low speed.
By reducing the ratio of the actual turning angles of the front wheels 34 and 36 to the operation amount of 0, it is possible to reliably prevent the actual turning angles of the front wheels from becoming too large than expected. In addition, the transmission ratio when turning left without turning the turn signal is the same as when turning right, so the transmission ratio differs depending on whether left turning or right turning during stationary cutting or width adjustment. It is possible to reliably prevent the driver from feeling uncomfortable due to this.

In the illustrated embodiment, the determination of right-turning or left-turning is made based on the steering angle θ detected by the steering angle sensor 62. May be performed based on the signal from the squid switch 66. In that case, the steering angle sensor 62 may be eliminated and the configuration of the steering device may be simplified to reduce the cost.

In the illustrated embodiment, the turn determination block 68 determines whether the vehicle is making a left turn based on a signal from the turn signal switch 66. 66 and the turn determination block 68 are omitted, and the transmission ratio at the time of left turning is smaller than that at the time of right turning without making a distinction between left turning and left turning in stationary operation. It may be configured as follows. Further, when the turn signal switch 66 and the turn determination block 68 are omitted, it is possible to prevent the actual turning angle of the front wheels from becoming excessively larger than expected when turning to the left, and the transmission ratio is reduced when the vehicle is stationary. The transmission ratio R may be calculated, for example, from a map corresponding to the graph shown by the solid line in FIG.

Although the illustrated embodiment is constructed as a steering device for a left-hand side vehicle, when the vehicle is a right-hand side vehicle, the transmission ratio R is left or right cutting as compared with FIG. 4 or 5. It is calculated from the map corresponding to the reverse graph (broken line for right turn at low speed when corresponding to FIG. 4), whereby the transmission ratio R during right turn is compared with that during left turn. Configured to be smaller.

FIGS. 6 and 8 are block diagrams showing the electronic control units of the second and third embodiments of the steering system having the variable transmission ratio type steering mechanism according to the present invention, respectively.
In these figures, the parts corresponding to the parts shown in FIG. 3 are designated by the same reference numerals as those shown in FIG. Although not shown in the figure, the variable transmission ratio type steering mechanism itself in these embodiments is constructed similarly to the steering mechanism in the first embodiment shown in FIG.

In the second embodiment shown in FIG. 6, the electronic control unit 60 has a transmission ratio calculation block 70, a command signal output block 72, and a total travel distance calculation block 76. The mileage calculation block 76 calculates the total mileage L from the time when the user of the vehicle obtains the vehicle and starts traveling based on the signal from the odometer 74. The transmission ratio calculation block 70 selects the map of the graph shown in FIG. 7 based on the signal indicating the total travel distance from the total travel distance calculation block 76. In this case, the smaller the total travel distance L, the more L1
The closer the map is selected, the greater the total distance L, the more L
5 The closer map is selected. Further, the transmission ratio calculation block 70 uses the selected map and the vehicle speed V from the vehicle speed sensor 64.
The transmission ratio R is calculated based on the signal indicating. The command signal output block 72 outputs a command signal to the drive circuit 58 based on the transmission ratio R, so that the actual transmission ratio becomes the transmission ratio R calculated in the transmission ratio calculation block 70.
Control 4

Thus, according to the second embodiment, as the total traveling distance L of the vehicle increases, the degree to which the transmission ratio R increases with decreasing vehicle speed gradually increases, so that the driver of the vehicle initially operates the steering device. The driver finally feels confused about the steering characteristics in the low vehicle speed range and surely prevents the actual steering angle of the front wheels from becoming too large than expected, and the driver finally makes a decision as shown in FIG.
It is possible to unknowingly become accustomed to the steering characteristics without feeling discomfort until the transmission ratio R is controlled by the map L5.

In the illustrated embodiment, the map shown in FIG. 7 is selected based on the total traveling distance L.
For example, by totally measuring the time when the ignition switch (not shown) is on, the total traveling time Tt from the time when the user of the vehicle acquires the vehicle and starts traveling, is calculated. The smaller is L in FIG.
A map closer to 1 may be selected, and a map closer to L5 may be selected as the total traveling time Tt increases.

Further, the total traveling distance L calculated in the total traveling distance calculating block 76 or the total traveling time T corresponding thereto is calculated.
If necessary, t is reset to 0 by a reset switch (not shown) so that the total traveling distance L or the total traveling time Tt may be newly incremented when the driver changes. Mileage calculation block 76
Alternatively, the total travel time calculation block corresponding thereto may be configured to count up and store the total travel distance L or the total travel time Tt for each driver. According to these configurations, drivers of the same vehicle are Even when there are a plurality of drivers, each driver can get used to the steering characteristics without feeling a sense of discomfort.
Further, the total travel distance L or the total travel time Tt may be reset to 0 each time the ignition switch is switched from on to off.

In the third embodiment shown in FIG. 8, the rear wheel steering mechanism 82 steers the rear wheels by controlling the actuator 80 via the drive circuit 78 by the electronic control unit 60. In response to this, the electronic control unit 60 has a rear wheel steering angle calculation block 84 and a command signal output block 86 in addition to the transmission ratio calculation block 70 and the command signal output block 72. .
The detailed description of the rear wheel steering mechanism 82 is omitted because it does not form the subject of the present invention, but any rear wheel steering mechanism can be used as long as it can steer the rear wheels in relation to the steering angle θ of the front wheels. It may be structural.

As in the case of the second embodiment, the transmission ratio calculation block 70 uses the transmission ratio from the map corresponding to the graph shown by the solid line in FIG. 9 based on the signal indicating the vehicle speed V from the vehicle speed sensor 64. R is calculated, and the command signal output block 72
Outputs a command signal to the drive circuit 58 based on the transmission ratio R,
As a result, the motor 54 is controlled so that the actual transmission ratio becomes the transmission ratio R calculated in the transmission ratio calculation block 70.

On the other hand, the rear wheel steering angle calculation block 84 is based on the vehicle speed V indicated by the signal from the vehicle speed sensor 64.
The front-rear wheel steering angle ratio Rrw is calculated from the map corresponding to the graph shown in FIG. 0, and the rear-wheel steering angle ratio Rrw is calculated as the product of the front-wheel steering angle θ indicated by the signal from the steering angle sensor 62 and the front-rear wheel steering angle ratio Rrw. Calculate the steering angle θr. Command signal output block 86
Outputs a command signal to the drive circuit 78 based on the rear wheel steering angle θr calculated in the rear wheel steering angle calculation block 84,
As a result, the actuator 80 is controlled so that the actual steering angle of the rear wheels becomes θr.

According to the third embodiment, as shown in FIG. 10, the rear wheels are steered in reverse phase with respect to the front wheels in the low vehicle speed range, so that only the front wheels are steered. In comparison, the difference between the turning radii of the front and rear wheels can be reduced. Further, as shown by the solid line in FIG. 9, it is possible to reduce the degree to which the transmission ratio becomes larger as the vehicle speed becomes lower than in the case where only the front wheels are steered (one-dot chain line). Even when turning left at a low speed, the actual turning angle of the front wheels becomes too large than expected, and it is possible to reliably prevent the left rear wheel from riding on the road shoulder due to the difference in turning radius between the front and rear wheels. it can.

An electronic control unit for controlling the motor 54 for controlling the transmission ratio R of the steering mechanism for the front wheels and an electronic control unit for controlling the actuator 80 for controlling the steering angle of the rear wheels of the rear wheel steering mechanism 82. May be independent of each other, but when these control devices are common as in the illustrated embodiment, they are shown in FIGS. 9 and 10 stored in the storage device of the control device, for example. Since the map corresponding to the graph can be re-stored at the same time,
The transmission ratio characteristic and the rear wheel steering characteristic can be easily and appropriately changed and adjusted in relation to each other.

Although the present invention has been described in detail with reference to specific embodiments, the present invention is not limited to these embodiments, and various other embodiments are also possible within the scope of the present invention. It will be apparent to those skilled in the art that

For example, in the variable transmission ratio type steering mechanism in each of the illustrated embodiments, the fulcrum roller 3 is driven by the motor 54.
The transmission ratio R is controlled by moving the position of 8. However, the steering mechanism itself does not form the gist of the present invention, and the transmission ratio increases as the vehicle speed decreases. The steering mechanism may be of any construction as long as it is present.

The first to third embodiments described above may be combined as a combination of any two embodiments or a combination of all the first to third embodiments, and in each of these cases as well The effects of the example are obtained, and the effects of any of the embodiments are not diminished by the configuration of the other embodiments.

[0041]

As is apparent from the above description, according to the structure of claim 1, the transmission ratio in the low vehicle speed range is opposite in the case where the vehicle turns in the same direction as the traffic side of the road. Since it is set smaller than when turning in the same direction as the traffic side of the road, compared to when turning in the opposite direction, the actual steering of the front wheels with respect to the steering amount of the steering input means The angle ratio is so small that the actual steered angle of the front wheels becomes larger than expected when turning at the same speed as the traffic side of the road at a low speed. It is possible to reliably prevent riding on the shoulder of a road.

According to the second aspect of the present invention, the steering mechanism is controlled so that the transmission ratio becomes larger as the vehicle speed becomes lower as the parameter corresponding to the total traveling time from the start of traveling of the vehicle becomes larger. So
As the driver gets accustomed to the characteristics of the steering system, the degree to which the transmission ratio increases as the vehicle speed becomes lower gradually increases, which surely prevents the driver from feeling uncomfortable or confused about steering properly immediately after the start of driving. The driver can unknowingly become accustomed to the characteristics of the steering system.

Further, according to the third aspect of the invention, the steering mechanism is configured to steer the front wheels, and the rear wheels are steered in the direction opposite to the front wheels in the low vehicle speed range by the rear wheel steering means. Compared to the case where only the front wheels are steered, the difference between the turning radii of the front and rear wheels becomes smaller, and the lower the vehicle speed, the smaller the degree to which the transmission ratio increases. It is possible to reliably prevent the actual steered angle of the front wheels from becoming too large when turning, and to prevent the rear wheels on the inside of the turn from riding on the road shoulder due to the difference in the turning radii of the front and rear wheels. .

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of a variable transmission ratio type steering mechanism of a steering device according to the present invention.

FIG. 2 is an enlarged partial perspective view showing a main part of the steering mechanism shown in FIG.

FIG. 3 is a block diagram showing the electronic control device shown in FIG. 1.

FIG. 4 is a graph showing an example of a relationship between a vehicle speed V and a transmission ratio R.

FIG. 5 is a graph showing another example of the relationship between the vehicle speed V and the transmission ratio R.

FIG. 6 is a block diagram showing an electronic control unit of a second embodiment of the variable transmission ratio type steering mechanism of the steering system according to the present invention.

FIG. 7 shows a transmission ratio R that varies depending on the vehicle speed V and the total traveling distance L.
7 is a graph showing the relationship between and.

FIG. 8 is a block diagram showing an electronic control unit of a third embodiment of the variable transmission ratio type steering mechanism of the steering system according to the present invention.

FIG. 9 is a graph showing a relationship between a vehicle speed V and a transmission ratio R.

FIG. 10 is a graph showing a relationship between a vehicle speed V and a front / rear wheel steering angle ratio Rrw.

[Explanation of symbols]

 10 ... Steering wheel 14 ... Rack bar 20 ... Pivot link 24 ... Reciprocating bar 30, 32 ... Tie rod 38 ... Support roller 42 ... Slider 46 ... Screw shaft 54 ... Motor 60 ... Electronic control device 82 ... Rear wheel steering mechanism

Claims (3)

[Claims] 1. A steering apparatus having a variable transmission ratio steering mechanism configured such that the transmission ratio increases as the vehicle speed decreases, wherein the steering mechanism is configured to steer the front wheels, and in a low vehicle speed range. The steering device is characterized in that the transmission ratio is set to be smaller when turning in the same direction as the passage side of the traveling path than when turning in the opposite direction. 2. A steering device having a variable transmission ratio steering mechanism configured such that the transmission ratio increases as the vehicle speed decreases, and means for detecting a parameter corresponding to the total traveling time from the start of traveling of the vehicle. And a means for controlling the steering mechanism such that the degree to which the transmission ratio increases as the vehicle speed decreases as the parameter increases. 3. A steering system having a variable transmission ratio steering mechanism configured such that the transmission ratio increases as the vehicle speed decreases, the steering mechanism configured to steer the front wheels, and the steering device operates at a low vehicle speed. A steering system comprising rear wheel steering means for steering the rear wheels in the opposite direction to the front wheels in the region.