JPH11245833A - Steering controller for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steering controller for vehicle which variably control the transmission ratio on the basis of the transmission ratio optimum for the traveling environment. SOLUTION: A steering controller for vehicle 2 interposing a variable gear ratio unit 14 midway of a steering transmission system which connects a steering wheel 10 and steered wheels 24, and providing with an ECU 30 which controls the transmission ratio corresponding to the condition of the vehicle, further has a navigation device 34 for detecting the traveling environment of the vehicle, and changes the transmission ratio of the variable gear ratio unit 14 through the ECU 30 on the basis of the traveling environment detected by the navigation device 34.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle steering control device for varying a transmission ratio of a steering wheel steering amount to a steered wheel.

[0002]

2. Description of the Related Art Conventionally, there is a steering device disclosed in Japanese Patent Application Laid-Open No. 63-227470 as a steering device that varies a transmission ratio of a steering wheel steering angle to a steered wheel. This steering device interposes a transmission ratio variable device that varies the transmission ratio in the middle of the steering transmission system, and increases the transmission ratio when the vehicle speed is high, and performs variable control of the transmission ratio according to the acceleration / deceleration. I have.

[0003]

By the way, in this steering device, the transmission ratio is changed based on the vehicle speed and the like. However, depending on the traveling environment, the suitable transmission ratio may differ even under the same vehicle speed and the like.

An object of the present invention is to provide a vehicle steering control device that performs variable transmission ratio control with a transmission ratio suitable for a traveling environment.

[0005]

According to a first aspect of the present invention, there is provided a steering control device for a vehicle, wherein a variable transmission ratio means for varying a transmission ratio is provided in a steering transmission system connecting a steering wheel and steered wheels. A vehicle steering control device including a control unit that controls a transmission ratio according to a state of a vehicle, comprising: a traveling environment detection unit that detects a traveling environment of the vehicle, wherein the traveling environment detected by the traveling environment detection unit includes: The transmission ratio of the transmission ratio variable unit is changed by the control unit based on the transmission ratio.

According to the first aspect of the present invention, the transmission ratio of the variable transmission ratio means is changed by the control means based on the traveling environment detected by the traveling environment detection means, so that the vehicle is adapted to the traveling environment. Thus, the transmission ratio can be obtained, and the transmission ratio can be prevented from being carelessly changed under a predetermined traveling environment.

According to a second aspect of the present invention, there is provided a vehicle steering control device according to the first aspect, wherein the traveling environment detecting means of the vehicle steering control device detects a traveling environment based on information from outside information means. Features.

According to the vehicle steering control apparatus of the second aspect, the traveling environment detecting means detects the traveling environment based on the information from the outside information means, so that the vehicle itself detects the traveling environment. Need not be provided, and the system configuration can be simplified.

According to a third aspect of the present invention, in the vehicle steering control device, the traveling environment detecting means of the vehicle steering control device detects a traveling environment based on a driver's operation state. And

According to the vehicle steering control device of the present invention, since the traveling environment detecting means detects the traveling environment based on the operation state of the driver, it is necessary to use external information to determine the traveling environment. Disappears.

Further, in the vehicle steering control device according to the present invention, when the traveling environment detecting means of the vehicle steering control device according to the first aspect detects that the vehicle is traveling on a highway, the control means controls the vehicle. The transmission ratio of the transmission ratio variable means is changed to a larger value.

According to the vehicle steering control device of the present invention, when the traveling environment detecting means detects that the vehicle is traveling on the highway, the control means changes the transmission ratio of the transmission ratio variable means to a larger value. Therefore, the responsiveness of the vehicle can be reduced, and the stability of the vehicle can be improved.

According to a fifth aspect of the present invention, in the vehicle steering control device according to the first aspect of the invention, when the poor visibility is detected by the traveling environment detecting means of the vehicle steering control device of the first aspect, the transmission is performed by the control means. The transmission ratio of the ratio variable means is changed to a larger value.

According to the fifth aspect of the present invention, when the traveling environment detecting means detects a poor visibility, the control means changes the transmission ratio of the transmission ratio variable means to a larger value. The responsiveness of the vehicle can be reduced, and the stability of the vehicle can be improved.

According to a sixth aspect of the present invention, there is provided a vehicle steering control device, wherein when a traveling on a mountain road is detected by the traveling environment detecting means of the vehicle steering control device of the first aspect, the control means controls the vehicle. The transmission ratio of the transmission ratio variable means is changed to a smaller value.

According to the vehicle steering control device of the sixth aspect, when traveling on a mountain road is detected by the traveling environment detection means, the transmission ratio of the transmission ratio variable means is changed to a smaller side by the control means. Therefore, when the vehicle is traveling on a mountainous road with many curves, the responsiveness of the vehicle is enhanced, so that the steering operability during traveling on the mountainous road can be improved.

Further, in the vehicle steering control device according to the present invention, when the traveling environment detecting means of the vehicle steering control device according to the first invention detects that the vehicle is traveling on a downhill, the control means transmits the signal to the vehicle. The transmission ratio of the ratio variable means is changed to a larger value. According to the vehicle steering control device of the present invention, when traveling downhill is detected by the traveling environment detecting means, the control means changes the transmission ratio of the transmission ratio variable means to a larger value, so In some cases, even when the front wheel load increases and the rear wheel load decreases, the vehicle responsiveness increases, the vehicle responsiveness is reduced by increasing the transmission ratio, and the vehicle stability can be improved.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a vehicle steering control device according to a first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a configuration diagram of the vehicle steering control device 2. In the drawing, a reference numeral 10 denotes a steering handle, which is connected to an upper end of an upper steering shaft 12a. The lower end of the upper steering shaft 12a is connected to the input side of the variable gear ratio unit 14, and the upper end of the lower steering shaft 12b is connected to the output side of the variable gear ratio unit 14. Here, the variable gear ratio unit 14 controls the transmission ratio, that is, the rotation speed of the input shaft / the rotation speed of the output shaft (the rotation speed of the upper steering shaft 12a / the rotation speed of the lower steering shaft) under the control of the ECU (electronic control device) 30. 12b).

A pinion (not shown) is provided at a lower end of the lower steering shaft 12b, and the pinion is meshed with a rack bar 18 in the steering gear box 16. Further, one end of a tie rod 20 is connected to each end of the rack bar 18, and a steered wheel 24 is connected to the other end of each tie rod 20 via a knuckle arm 22.

A steering angle sensor 26 for detecting a steering angle θ _H of the steering handle 10 is provided on the upper steering shaft 12a, and a steering angle (pinion angle) θ _P of the steered wheels 24 is provided on the lower steering shaft 12b. Is provided. The steering wheel 10 detected by the steering angle sensor 26
The steering angle and the pinion angle detected by the output angle sensor 28 are input to the ECU 30. In addition, navigation information from the navigation device 34 and the vehicle speed V detected by the vehicle speed sensor 32 are input to the ECU 30.

The ECU 30 includes a motor (not shown)
A control signal for controlling a motor of the variable gear ratio unit 14 having a speed reducer (not shown) using a planetary gear mechanism is output via a motor driver 36. here,
Although a speed reducer having a planetary gear mechanism is used as the speed reducer, the present invention is not limited to this, and a harmonic speed reducer, a cycloid speed reducer, or the like may be used.

In the vehicle steering control device 2, the control shown in the flowchart of FIG. 2 is performed. That is, EC
The U30 reads the vehicle speed V output from the vehicle speed sensor 32 and the steering angle θ _H of the steering wheel 10 detected by the steering angle sensor 26 (Step S10). Next, based on the navigation information output from the navigation device 34, it is determined whether or not the vehicle is currently traveling on an expressway (step S11). If it is determined that the vehicle is not traveling on the expressway, the transmission ratio G (V) based on the vehicle speed V is determined with reference to the standard map shown in FIG. 3 (step S12). That is, a standard map is selected from a standard map and a high-speed map of a vehicle speed (V) -transmission ratio (G) map stored in advance, and a transmission ratio G (V) based on the vehicle speed V is determined. set the transmission ratio G used in the case of G (V) of obtaining the target pinion angle theta _M (step S14).

On the other hand, if it is determined in step S11 that the vehicle is traveling on a highway, a high-speed map is selected from the standard map and the high-speed map shown in FIG.
A transmission ratio G (V) based on the vehicle speed V is determined, and the transmission ratio G
(V) is set to the transmission ratio G used in the case of obtaining the target pinion angle theta _M (step S14).

Next, a target pinion angle θ _M is calculated by multiplying the transmission angle G by the steering angle θ _H detected by the steering angle sensor 26 (θ _M = G × θ _H ) (step S).
15). Next, a control signal is output to the variable gear ratio unit 14 via the motor driver 36, and the pinion angle θ _P detected by the output angle sensor 28 matches the target pinion angle θ _M by driving the motor. (Step S16).

In the vehicle steering control device 2, when it is determined that the vehicle is traveling on the highway, the vehicle speed (V) -transmission ratio (G) map referred to when obtaining the transmission ratio G is changed from the standard map to the high speed. By switching to the map and changing the transmission ratio to a larger side (slow side) and reducing the rate of change of the transmission ratio to a change in vehicle speed, the vehicle response to steering wheel steering can be moderated to improve vehicle stability. It is possible to reduce driver fatigue when driving on a highway.

In the first embodiment,
Although based on the navigation information output from the navigation device 34 is performing a determination whether or not the running of the highway, as shown in FIG. 4 is not limited to this, the peak value of the steering angle theta _H, unit time Find the steering frequency per hit,
It may be determined whether or not the vehicle is traveling on a highway based on the steering frequency and the vehicle speed.

In the first embodiment,
When highway driving is detected, a high-speed map is selected and the transmission ratio is calculated based on this map. However, the present invention is not limited to this. May be multiplied to obtain the transmission ratio.

Next, a vehicle steering control device 4 according to a second embodiment of the present invention will be described with reference to FIGS. The vehicle steering control device 4 shown in FIG.
Is replaced with a navigation device 34 of the vehicle steering control device 2 according to the first embodiment, an accelerator opening detection sensor 38 for detecting the accelerator opening TH and a rotation speed sensor 40 for detecting the rotation speed NE of the engine. It is provided. The accelerator opening TH and the engine speed NE detected by the accelerator opening detection sensor 38 and the rotation speed sensor 40 are input to the ECU 30. The other configuration is the same as the configuration of the vehicle steering control device 2 according to the first embodiment.

In the vehicle steering control device 4, the control shown in the flowchart of FIG. 6 is performed. That is, EC
U30 reads the vehicle speed V output from the vehicle speed sensor 32 and the steering angle θ _H of the steering wheel 10 detected by the steering angle sensor 26 (step S20).

Next, it is determined whether or not the vehicle speed V is greater than a predetermined value A (step S21).
If it is determined to be greater than on the basis of the detected steering angle theta _H in the steering angle sensor 26, and determines whether switching to the frequency is large (step S22). In addition,
In step S21, it is determined whether the vehicle speed V is higher than the predetermined value A because whether the vehicle is traveling on a mountainous road, or entering a garage, performing parallel parking, etc. Is determined to be 20 km / h to 30 km / h. Also,
The switching frequency in step S22 is determined based on the frequency at which the steering angle θ _H passes through the neutral position.

If it is determined in step S21 that the vehicle speed V is higher than the predetermined value A, and if it is determined in step S22 that the switching frequency is high, it is determined that the vehicle is traveling on a mountainous road. Then, the mountain road map of the vehicle speed (V) -transmission ratio (G) map shown in FIG. 1 is selected, and the transmission ratio G (V) based on the vehicle speed V is obtained (step S23). That is, a mountain road map is selected from a standard map of a vehicle speed (V) -transmission ratio (G) map stored in advance, a mountain road map, and a downhill map, and the transmission ratio G (V) based on the vehicle speed V is selected.
And this correction value is set to the transmission ratio G using the transmission ratio G (V) in the case of obtaining the target pinion angle theta _M (step S2
5).

On the other hand, if it is determined in step S21 that the vehicle speed V is not higher than the predetermined value A, the process proceeds to step S21.
If it is determined in step 22 that the switching frequency is not high, it is determined that the vehicle is not traveling on a mountain road, and a standard map of the vehicle speed (V) -transmission ratio (G) map shown in FIG.
A transmission ratio G (V) based on the vehicle speed V is determined (step S2)
4). That is, a standard map of a vehicle speed (V) -transmission ratio (G) map stored in advance, a standard map from a mountain road map and a downhill map is selected, and a transmission ratio G (V) based on the vehicle speed V is obtained. It is set in the transmission ratio G using the transmission ratio G (V) in the case of obtaining the target pinion angle theta _M (step S25).

Next, the target pinion angle θ _M is calculated by multiplying the steering angle θ _H detected by the steering angle sensor 26 and the transmission ratio G (θ _M = G × θ _H ) (step S).
26). Next, a control signal is output to the variable gear ratio unit 14 via the motor driver 36, and the pinion angle θ _P detected by the output angle sensor 28 matches the target pinion angle θ _M by driving the motor. (Step S27).

In the vehicle steering control device 4, the control shown in the flowchart of FIG. 7 is performed. That is, the vehicle speed V output from the vehicle speed sensor 32, the steering angle θ _H of the steering wheel 10 detected by the steering angle sensor 26, the accelerator opening TH detected by the accelerator opening detection sensor 38, and the rotation speed sensor 40 detect The read engine speed NE is read (step S3).
0).

Next, it is determined whether or not the vehicle speed V is greater than a predetermined value A (step S31).
If it is determined to be larger than the accelerator opening TH
Is smaller than a predetermined value B (step S32). When it is determined that the accelerator opening TH is smaller than the predetermined value B, it is further determined whether or not the engine speed is larger than the predetermined value C (step S3).
3). In step S21, the vehicle speed V becomes equal to the predetermined value A.
The determination as to whether the vehicle is larger than the predetermined value A is performed to determine whether the vehicle is traveling on a downhill or entering a garage or performing stationary parking for parallel parking. Is a value of 20 km / h to 30 km / h.

In step S31, it is determined that the vehicle speed V is higher than the predetermined value A. In step S32, it is determined that the accelerator opening TH is smaller than the predetermined value B. In step S33, the engine speed is reduced to a predetermined value C. If it is determined that the vehicle speed is lower than the vehicle speed, it is determined that the vehicle is traveling on a downward slope, the vehicle speed (V) -transmission ratio (G) map shown in FIG. G (V) is obtained (step S34). That is, a downhill map is selected from a standard map of a vehicle speed (V) -transmission ratio (G) map stored in advance, a mountain road map, and a downhill map, and the transmission ratio G (V) based on the vehicle speed V is obtained. ,
The transmission ratio G (V) is set to the transmission ratio G used in the case of obtaining the target pinion angle theta _M (step S36).

On the other hand, if it is determined in step S31 that the vehicle speed V is not higher than the predetermined value A, and if it is determined in step S32 that the accelerator opening TH is not lower than the predetermined value B, the process proceeds to step S33. If it is determined that the engine speed is not higher than the predetermined value C in the above, it is determined that the vehicle is traveling on a flat road or an uphill instead of traveling on a downhill, and the vehicle speed (V) -transmission ratio shown in FIG. (G) The standard map of the map is selected, and the transmission ratio G (V) based on the vehicle speed V is obtained (step S35). That is, a standard map of a vehicle speed (V) -transmission ratio (G) map stored in advance, a standard map from a mountain road map and a downhill map is selected, and a transmission ratio G (V) based on the vehicle speed V is obtained. It is set in the transmission ratio G using the transmission ratio G (V) in the case of obtaining the target pinion angle theta _M (step S3
6).

Next, the ECU 30 calculates the target pinion angle θ _M by multiplying the steering angle θ _H detected by the steering angle sensor 26 by the transmission ratio G (θ _M = G ×
θ _H ) (Step S37). Next, the ECU 30 outputs a control signal to the variable gear ratio unit 14 via the motor driver 36, and by driving the motor, the pinion angle θ _P detected by the output angle sensor 28 becomes the target pinion angle θ Control is performed so as to match _M (step S38).

In the vehicle steering control device 4, when it is determined that the vehicle is traveling on a mountainous road, the vehicle speed (V) -the transmission ratio (G) referred to when the transmission ratio G is obtained.
Since the map is switched from the standard map to the mountain road map and the transmission ratio is changed to a smaller side (quick side), the vehicle response performance when traveling on a mountain road with many curves can be improved. When it is determined that the vehicle is traveling on a downhill, the vehicle speed (V) -transmission ratio (G) map referred to when calculating the transmission ratio G is switched from the standard map to the downhill map, and the transmission ratio is increased. Change to the side (slow side). During traveling on a downhill, the load of the vehicle moves forward, the front wheel load increases, and the rear wheel load decreases, thereby increasing the responsiveness of the vehicle (oversteer tendency). The response of the vehicle to the steering of the steering wheel at the time can be gentle, and the vehicle stability at the time of traveling downhill can be improved.

In the second embodiment,
When traveling on a mountain road or traveling downhill is detected, a mountain road map or a downward slope map is selected, and the transmission ratio is determined based on these maps. May be obtained by multiplying the standard map by a correction coefficient to obtain the transmission ratio used when traveling on a mountain road or traveling downhill.

In the second embodiment,
Mountain road travel is determined based on the vehicle speed V and the switching frequency, and downhill travel is determined based on the vehicle speed V, the accelerator opening TH, and the engine speed NE. However, the present invention is not limited to this, and is based on navigation information output from a navigation device. Alternatively, it may be determined whether the vehicle is traveling on a mountain road or traveling downhill.

Next, a vehicle steering control device according to a third embodiment of the present invention will be described with reference to FIGS. The configuration of the vehicle steering control device 6 shown in FIG. 9 is for operating the wiper instead of inputting the navigation information from the navigation device 34 of the vehicle steering control device 2 according to the first embodiment. The on signals from the wiper switch 42, the fog lamp switch 44 for turning on the fog lamp, and the head lamp switch 46 for turning on the head lamp are output from the ECU 3
0 has been entered. The other configuration is the same as the configuration of the vehicle steering control device 2 according to the first embodiment.

In the vehicle steering control device 6, the control shown in the flowchart of FIG. 10 is performed. That is, E
The CU 30 reads the vehicle speed V output from the vehicle speed sensor 32 and the steering angle θ _H of the steering handle 10 detected by the steering angle sensor 26 (Step S40).

Next, it is determined whether or not the visibility is poor (step S41). That is, when the wiper switch 42, the fog lamp switch 44, and the head lamp switch 46 are turned on, it is determined that the visibility is poor. A short-time headlamp switch 4 for so-called passing.
In order to exclude the ON of the wiper switch 6, the temporary ON of the wiper switch 42 for removing water droplets attached to the windshield, and the like, the time during which the wiper switch 42, the fog lamp switch 44 and the head lamp switch 46 are ON is considered. To determine poor visibility.

If it is determined that the visibility is poor, a poor visibility map of the vehicle speed (V) -transmission ratio (G) map shown in FIG. 11 is selected, and the transmission ratio G (V) based on the vehicle speed V is selected. Is obtained (step S42). That is, a poor visibility map is selected from a standard map of a vehicle speed (V) -transmission ratio (G) map and a poor visibility map stored in advance, and a transmission ratio G (V) based on the vehicle speed V is obtained. , This transmission ratio G (V)
The set the transmission ratio G used in the case of obtaining the target pinion angle theta _M (step S44).

On the other hand, if it is determined in step S41 that the visibility is not poor, the vehicle speed (V) shown in FIG.
-Select a standard map of the transmission ratio (G) map and set the vehicle speed V
Transmission ratio obtains the G (V) based on (step S43), and sets the transmission ratio G using the transmission ratio G (V) in the case of obtaining the target pinion angle theta _M (step S44).

Next, the target pinion angle θ _M is calculated by multiplying the steering angle θ _H detected by the steering angle sensor 26 and the transmission ratio G (θ _M = G × θ _H ) (step S).
45). Next, the ECU 30 outputs a control signal to the variable gear ratio unit 14 via the motor driver 36, and by driving the motor, the pinion angle θ _P detected by the output angle sensor 28 becomes the target pinion angle θ Control is performed so as to match _M (step S46).

In the vehicle steering control device 6, when it is determined that the visibility is poor, the vehicle speed (V) -transmission ratio (G) map referred to when the transmission ratio G is obtained is determined from the standard map when the visibility is poor. By switching to the map and changing the transmission ratio to the large side (slow side), the response of the vehicle to steering of the steering wheel when visibility is poor can be moderated, and vehicle stability can be improved.

In the third embodiment,
When poor visibility is detected, a poor visibility map is selected and the transmission ratio is determined based on this map.
When poor visibility is detected, the transmission ratio used when visibility is poor may be determined by multiplying the standard map by a correction coefficient.

[0051]

According to the first aspect of the present invention, the transmission ratio of the transmission ratio variable means is changed by the control means based on the traveling environment detected by the traveling environment detection means. Can be obtained, and it is possible to prevent the transmission ratio from being carelessly changed under a predetermined traveling environment.

According to the second aspect of the present invention, since the traveling environment detecting means detects the traveling environment based on information from the outside information means, it is necessary to provide a system for detecting the traveling environment in the vehicle itself. And the system configuration can be simplified.

According to the third aspect of the present invention, since the traveling environment detecting means detects the traveling environment based on the operation state of the driver, it is not necessary to use external information to determine the traveling environment.

According to the fourth aspect of the present invention, when the traveling environment detecting means detects the highway running, the control means changes the transmission ratio of the transmission ratio variable means to the larger side. Responsiveness can be reduced and vehicle stability can be improved.

According to the fifth aspect of the present invention, when a poor visibility is detected by the traveling environment detecting means, the control means changes the transmission ratio of the transmission ratio variable means to a larger value so that the vehicle response is improved. Operability can be reduced and vehicle stability can be improved.

According to the sixth aspect of the present invention, when traveling on a mountain road is detected by the traveling environment detecting means,
The control means changes the transmission ratio of the transmission ratio variable means to a smaller side, so that the responsiveness of the vehicle is improved when traveling on a mountain road with many curves, thereby improving the steering operability when traveling on a mountain road. Can be.

According to the seventh aspect of the present invention, when the traveling environment detecting means detects a downhill traveling,
Since the control means changes the transmission ratio of the transmission ratio variable means to a higher side, the vehicle responsiveness can be reduced and the vehicle stability can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a vehicle steering control device according to a first embodiment.

FIG. 2 is a flowchart illustrating transmission ratio variable control performed by the vehicle steering control device according to the first embodiment;

FIG. 3 is a diagram showing a map used for transmission ratio variable control by the vehicle steering control device according to the first embodiment;

FIG. 4 is a diagram showing a steering frequency used for transmission ratio variable control by the vehicle steering control device according to the first embodiment.

FIG. 5 is a configuration diagram of a vehicle steering control device according to a second embodiment.

FIG. 6 is a flowchart showing transmission ratio variable control by a vehicle steering control device according to a second embodiment.

FIG. 7 is a flowchart showing transmission ratio variable control by a vehicle steering control device according to a second embodiment.

FIG. 8 is a diagram showing a map used for transmission ratio variable control by a vehicle steering control device according to a second embodiment.

FIG. 9 is a configuration diagram of a vehicle steering control device according to a third embodiment.

FIG. 10 is a flowchart showing transmission ratio variable control by a vehicle steering control device according to a third embodiment.

FIG. 11 is a diagram showing a map used for transmission ratio variable control by a vehicle steering control device according to a third embodiment.

[Explanation of symbols]

2, 4, 6: Vehicle steering control device, 10: Steering handle, 12a: Upper steering shaft, 12b
... lower steering shaft, 14 ... variable gear ratio unit, 16 ... steering gear box, 18 ... rack bar, 20 ... tie rod, 22 ... knuckle arm, 24 ...
Steered wheels, 26: steering angle sensor, 28: output angle sensor, 30
... ECU, 32 ... Vehicle speed sensor, 34 ... Navigation device, 38 ... Accelerator opening degree sensor, 40 ... Rotation speed sensor,
42: Wiper switch, 44: Fog lamp switch, 46: Head lamp switch.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification code FI B62D 13:00 (72) Inventor Tadashi Kawamuro 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation

Claims (7)

[Claims] A transmission ratio varying means for varying a transmission ratio is provided in the middle of a steering transmission system connecting a steering wheel and steered wheels, and a control means for controlling the transmission ratio in accordance with a state of a vehicle is provided. A steering control device for a vehicle, comprising: a traveling environment detection unit that detects a traveling environment of the vehicle; and a control unit that changes a transmission ratio of the transmission ratio variable unit based on the traveling environment detected by the traveling environment detection unit. A vehicle steering control device. 2. The vehicle steering control device according to claim 1, wherein the driving environment detecting means detects the driving environment based on information from the outside information means. 3. The vehicle steering control device according to claim 1, wherein the driving environment detecting means detects a driving environment based on an operation state of a driver. 4. The transmission system according to claim 1, wherein when the traveling environment detection unit detects a highway traveling, the control unit changes the transmission ratio of the transmission ratio variable unit to a higher transmission ratio. Vehicle steering control device. 5. The vehicle according to claim 1, wherein the control unit changes the transmission ratio of the transmission ratio variable unit to a larger value when the traveling environment detection unit detects a poor visibility. Steering control device. 6. The system according to claim 1, wherein when the traveling environment detecting means detects a mountain road travel, the control means changes the transmission ratio of the transmission ratio variable means to a smaller value. Vehicle steering control device. 7. The vehicle according to claim 1, wherein when the traveling environment detecting means detects that the vehicle is traveling downhill, the control means changes the transmission ratio of the transmission ratio variable means to a larger value. Steering control device.