JPS6357373A - Four-wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To suppress an increase of an understeering tendency by correcting the steering ratio so that the steering state of front wheels and the steering state of rear wheels are in the opposite phase relationship and making the correction quantity manually variable when a lateral force is a predetermined value or more. CONSTITUTION:A rear wheel steering mechanism interlocked with the steering of front wheels has a pulse motor 30 moving a rear wheel steering rod and a pump drive motor 44 applying a hydraulic assist force and is controlled by a control unit 50. In this case, the control unit 50 is constituted of a steering ratio characteristic selecting unit 59 selecting one of multiple steering ratio characteristics stored in a memory unit 58 based on the detected value of a lateral force and a rear wheel steering angle arithmetic unit 60 calculating the rear wheel steering angle based on the steering ratio characteristic and the detected values of the steering angle and vehicle speed. This steering ratio is selected so that the steering state of front wheels and the steering state of rear wheels are in the opposite phase relationship when the lateral force is a predetermined value or more, and this selection is made variable in response to a signal from a travel mode selecting switch 57.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a four-wheel drive system of a vehicle in which when the front wheels are steered by a steering operation via a steering wheel, the rear wheels are also steered at the same time. This invention relates to a wheel steering device.

(Prior art) When the front wheels are steered by a steering operation performed through the steering wheel, the rear wheels are also steered as the front wheels are steered, thereby preventing side slip of the rear wheels. A four-wheel steering device is known that improves the drivability of the vehicle by steering the vehicle in a reduced state.

As such a four-wheel steering device, for example,
As described in Japanese Patent No. 91457, a vehicle speed-sensitive steering ratio characteristic in which the ratio of the steering angle of the rear wheels to the steering angle of the front wheels, that is, the steering ratio, is changed according to the vehicle speed. has been proposed. In a four-wheel steering system having such a vehicle speed-sensitive steering ratio characteristic, when the vehicle is traveling at a relatively low speed, the front wheel steering state and the rear wheel steering state usually have an opposite phase relationship. When the vehicle is running at a relatively high speed, the front wheel steering state and the rear wheel steering state are assumed to have the same phase relationship. The steering ratio is set. When the steering ratio is set so that the front wheel steering state and the rear wheel steering state are in an opposite phase relationship, the vehicle tends to oversteer, and the turning performance is improved. When the steering ratio is set so that the front wheel steering state and the rear wheel steering state have the same phase relationship, the vehicle tends to understeer, and driving stability is improved. It will be done.

(Problems to be Solved by the Invention) However, in a four-wheel steering system having a vehicle speed-sensitive steering ratio characteristic as described above, the phase difference between the front wheel steering state and the rear wheel steering state is generally The relationship and steering ratio are
Regardless of the friction characteristics of the road surface, it is uniquely set according to the vehicle speed, so for example, the coefficient of friction of the road surface is relatively small during rain or snow, and when the road surface is sunny, etc. There is a problem in that the driving behavior of the vehicle becomes significantly different depending on the state in which the coefficient of friction is relatively large.

Additionally, as the vehicle transitions from a low-speed driving state to a high-speed driving state while turning, the front wheel steering state and the rear wheel steering state change from an opposite phase relationship to an in-phase relationship. As a result, the tendency of the vehicle to understeering becomes even stronger, which causes an inconvenience to the driver.

Therefore, if the friction coefficient of the road surface is relatively small,
By changing the steering ratio to the same phase side where the front wheel steering state and the rear wheel steering state are in the same phase relationship, the running stability of the vehicle is improved. ,
If the friction coefficient of the road surface is relatively large, the steering ratio should be
It is conceivable to improve the turning performance of the vehicle by changing the steering state of the front wheels and the steering state of the rear wheels to the opposite phase side, where they have an opposite phase relationship.
When the steering ratio is automatically changed according to the coefficient of friction of the road surface, the driving mode desired by the driver and the actual driving mode do not necessarily match, and the vehicle does not behave as the driver desires. There is a possibility that the running condition cannot be obtained.

In view of the above, the present invention is designed to allow the rear wheels to be steered when the front wheels are steered, and to change the steering ratio in accordance with the vehicle speed. The steering ratio should be controlled in accordance with the frictional characteristics of the road surface, so that the driving condition desired by the user can be obtained. To provide a four-wheel steering device for a vehicle, which is capable of suppressing an increase in the tendency of understeering of a vehicle even when a vehicle that performs cornering transitions from a low-speed driving state to a high-speed driving state. purpose.

(Means for Solving the Problems) In order to achieve the above-mentioned object, a four-wheel steering device for a vehicle according to the present invention includes a front wheel steering mechanism that steers the front wheels in response to a steering operation, and a front wheel steering mechanism that steers the front wheels in response to a steering operation. a rear wheel steering mechanism that steers the rear wheels according to the vehicle speed, a steering ratio control means that changes the steering ratio according to the vehicle speed, a lateral force detection means that detects a force acting on the vehicle in the vehicle width direction; The steering ratio correction means comprises a steering ratio correction means for correcting and controlling the steering ratio in accordance with the force in the vehicle width direction acting on the vehicle detected by the force detection means, and a correction amount variable means. , when the force acting on the vehicle in the vehicle width direction is equal to or greater than a predetermined value, the steering ratio controlled by the steering ratio control means is adjusted so that the steering state of the front wheels and the steering state of the rear wheels are in an opposite phase relationship. The correction amount variable means can manually change the amount of correction of the steering ratio by the steering ratio correction means.

(Function) In the four-wheel steering system for a vehicle according to the present invention configured as described above, when the front wheels are steered by the front wheel steering mechanism, the rear wheel steering mechanism turns the rear wheels along with the steering of the front wheels. The wheels are steered, and at this time, the steering ratio is changed in accordance with the vehicle speed by the steering ratio control means. When the lateral force detection means detects that the force in the vehicle width direction acting on the vehicle is equal to or greater than a predetermined value, the steering ratio correction means causes the steering ratio to be controlled by the steering ratio control means. ratio of
The front wheel steering state and the rear wheel steering state are corrected to the opposite phase side so that they have an opposite phase relationship, and at this time, the correction amount of the steering ratio is manually adjusted through the correction amount variable means. controlled.

In general, when a vehicle is running, if the friction coefficient of the road surface is relatively small, steering is performed more carefully than if it is relatively large. If the coefficient of friction of the road surface is relatively small, the force in the vehicle width direction (lateral force) acting on the vehicle will be relatively small, and if the coefficient of friction of the road surface is relatively large, the lateral force acting on the vehicle will be relatively small. It is thought that it will be relatively large. Therefore, in the four-wheel steering system for a vehicle according to the present invention described above, the difference in the coefficient of friction of the road surface is equivalently detected by the lateral force detection means.
The steering ratio that is changed according to the vehicle speed by the steering ratio control means is appropriately corrected according to the coefficient of friction of the road surface, and furthermore, the correction amount of the steering ratio at this time is changed by manual operation through the correction amount variable means. As a result, after driving in the manner desired by the driver, appropriate driving characteristics are obtained in accordance with the coefficient of friction of the road surface. Furthermore, when the vehicle performs turning acceleration, based on the fact that the lateral force acting on the vehicle exceeds a predetermined value, the steering ratio is such that the front wheel steering state and the rear wheel steering state are in opposite phases. Correction control is performed to the opposite phase side, which is considered to be the relationship, and the tendency of the vehicle to understeering is suppressed from becoming excessively strong.

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

FIG. 1 schematically shows an example of a four-wheel steering system for a vehicle according to the present invention. In Figure 1, left and right front wheels 2L and 2
A front wheel steering mechanism 5 is provided to steer the wheel R in response to steering via the steering wheel 3. A pair of knuckle members 6 supported by the vehicle body (not shown) via. A rack having a pair of tie rods 8 each having one end connected to the knuckle arms 6a of these knuckle members 6, and a rack shaft 9 having the other ends of each of the pair of tie rods 8 connected to both ends thereof. It is comprised of a steering gear mechanism 10 that is of an and-pinion type.

In such a front wheel steering mechanism 5, the steering force from the steering wheel 3 is transmitted to the tie rod 8 by the steering gear mechanism 10, and the tie loft 8 reciprocates in the vehicle width direction. As a result, the knuckle member 6 is rotated around the joint portion 4, and the front wheels 2L and 2R are steered.

Also, replace the left and right rear wheels 12L and 12R with the front wheels 2L and 2
A rear wheel steering mechanism 11 is provided which steers the rear wheels 12L as each wheel R is turned.
A pair of knuckle members 16 which rotatably support and 12R and are supported by a vehicle body (not shown) via a joint portion 14, and a pair of tie rods 1 each having one end connected to a knuckle arm 16a of the knuckle member 16.
8, and a rear wheel steering rod 20, the other end of each of which is connected to both ends of the pair of tie rods 18. A rack 22 is formed on the rear wheel steering rod 20,
The rack 22 is meshed with a pinion 26 fixed to one end of a pinion shaft 24. A bevel gear 28 is fixed to the other end of the pinion shaft 24, and the bevel gear 28 is a bevel gear 3 fixed to the output shaft of the pulse motor 30.
2 is engaged. In such a rear wheel steering mechanism 11, the driving force of the pulse motor 30 is transmitted to the pinion shaft 24 via the bevel gears 32 and 28.
The rear wheel steering rod 20 is moved along the vehicle width direction in accordance with the rotation direction and rotation time of the pulse motor 30.

Furthermore, a power cylinder 34 is arranged in relation to the rear wheel steering rod 20. The power cylinder 34 has a piston 34a fixed to the rear wheel steering rod 20 and hydraulic chambers 34b and 34c partitioned by the piston 34a. The hydraulic chambers 34b and 34C communicate with a control valve 38 through hydraulic passages 36 and 37, respectively.

The control valve 38 is communicated with a hydraulic pump 42 via an oil supply passage 40 and an oil return passage 41, and the hydraulic pump 42 is rotationally driven by a pump driving motor 44.

The control valve 38 controls the hydraulic chambers 34b and 34 of the power cylinder 34 depending on the rotational direction of the pinion shaft 24.
For example, when the rear wheels 12L and 12R are steered clockwise in FIG. Pressure oil from the pump 42 is supplied into the hydraulic chamber 34b, and the oil return passage 41 and the hydraulic passage 37 are brought into communication, so that the pressure oil in the hydraulic chamber 34C is returned to the hydraulic pump 42. Further, when the rear wheels 12L and 12R are steered counterclockwise in FIG. 1, the oil supply passage 40 and the hydraulic passage 37 are brought into communication, and pressure oil from the hydraulic pump 42 is supplied into the hydraulic chamber 34c. Then, the oil return passage 41 and the hydraulic passage 36 are brought into communication, and the pressure oil in the hydraulic chamber 34b is transferred to the hydraulic pump 42.
will be returned to. In this way, the driving force of the pulse motor 30 is transmitted to the pinion shaft 24 via the bevel gear 32 and the pinion shaft 24, so that when the rear wheel steering rod 20 is moved in the vehicle width direction, the power cylinder 34 Hydraulic chamber 3
Pressure oil is supplied to and discharged from the rear wheels 4b and 34C, thereby assisting the movement of the rear wheel steering rod 20 in the vehicle width direction, and steering the rear wheels 12L and 12R.

The pulse motor 30 and the pump drive motor 44 receive drive signals Sa and s sent from the control unit 50, respectively.
The drive is controlled by b. The control unit 50 receives a detection signal Ss from a steering angle sensor 52 that detects the steering angles of the front wheels 2L and 2R in relation to the front wheel steering mechanism 5, and a vehicle speed based on the rotation speed of the wheel (in this example, the left front wheel 2L). a detection signal SV from the vehicle speed sensor 54 that detects the vehicle speed sensor 54, a detection signal Sg from the lateral force sensor 56 that detects the force in the vehicle width direction that acts on the vehicle body when the vehicle is turning, that is, the lateral force, and A driving mode selection switch 57 that is manually operated by a driver or the like to select a normal driving mode or a sports driving mode of the vehicle is supplied with a signal Sm indicative of a normal driving mode or a sports driving mode.

The control unit 50 has, for example, a specific configuration as shown in FIG. 2, and includes a steering ratio characteristic storage section 58 that stores a plurality of steering ratio characteristics, and a lateral force sensor
In response to the detection signal Sg from the drive mode selection switch 57 and the signal Sm from the driving mode selection switch 57, a detection signal Sg is generated from among a plurality of steering ratio characteristics stored in the steering ratio characteristic storage section 58. A steering ratio characteristic selection unit 59 that selects an appropriate steering ratio characteristic according to the driving mode of the vehicle and sends out a signal Sk corresponding to the selected steering ratio characteristic, and detection from the steering angle sensor 52. Upon receiving the signal Ss and the detection signal Sv from the vehicle speed sensor 54, the steering ratio characteristic selection section 59
A signal Sk indicating the steering ratio characteristics is received from the signal Sk, and based on the signal Sk, a calculation is performed to calculate a front wheel steering angle and a rear wheel steering angle according to the vehicle speed, and a signal corresponding to the calculated rear wheel steering angle is generated. Sr.
a rear wheel steering angle calculation unit 60 that sends out the rear wheel steering angle calculation unit 60;
A pulse signal forming unit 61 that forms a pulse signal Sp based on a signal Sr from the pulse signal forming unit 61 generates drive signals Sa and sb for the pulse motor 30 and the pump drive motor 44 based on the pulse signal Sp obtained from the pulse signal forming unit 61. The drive unit 62 is configured to include a drive unit 62 that sends out the . here,
Rear wheel steering angle calculation section 60 in the control unit 50. Pulse signal forming section 61, driving section 62, and pulse motor 3
0 etc., the rear wheel 12 relative to the steering angle of the front wheels 2L and 2R
A steering ratio control means is configured to control the steering ratio obtained by the ratio of the steering angles L and 12R. When the lateral force is greater than a predetermined value, the steering ratio changed by the steering ratio control means is such that the steering state of the front wheels 2L and 2R and the steering state of the rear wheels 12L and 12R are in an opposite phase relationship. In addition, a steering ratio correction means is formed to perform correction control to the opposite phase side, and a driving mode selection switch 57 is also provided.
The signal Sm from the above-mentioned vehicle is used to form correction amount variable means for changing the correction amount of the steering ratio according to the driving mode of the vehicle in which the vehicle is in trouble.

The steering ratio characteristics stored in the steering ratio characteristics storage section 58 are as follows:
For example, as shown in the graph of FIG. 3, where the vertical axis represents the steering ratio K and the horizontal axis represents the vehicle speed V, the steering angle is determined when the friction coefficient of the road surface is relatively small. Steering ratio characteristic kl
+ Steering ratio characteristic taken when the coefficient of friction of the road surface is relatively large, and steering taken when the coefficient of friction of the road surface is larger than the case where 2 is taken for the steering ratio characteristic. It is roughly divided into ratio characteristics. These steering ratio characteristics are those in which the steering ratio K takes a negative value when the vehicle speed is less than 78, which is greater than Vt, V2, and V2, respectively. , the steering status of the front wheels 2L and 2R and the rear wheel 12
The steering state of the front wheels 2L and 12R is in an opposite phase relationship, and the steering ratio K takes a positive value when the vehicle speed is Vl, v2 and 73 or more, that is, the steering of the front wheels 2L and 2R. The steering condition and the steering condition of the rear wheels 12L and 12R are made to have the same phase relationship. Furthermore, the steering ratio characteristics, , 2, and 2, respectively, increase as the vehicle speed increases, and take a common negative value at low vehicle speeds. It is designed to take a common positive value even at high vehicle speeds. 2 in the steering ratio characteristic is the steering ratio characteristic k.

Compared to , the steering ratio K has shifted to the opposite phase side where the steering state of the front wheels 2L and 2R and the steering state of the rear wheels 12L and 12R are in an opposite phase relationship. The ratio characteristic is 2, and the steering ratio K further makes the steering state of the front wheels 2L and 2R and the steering state of the rear wheels 12L and 12R have an opposite phase relationship. The relationship is such that the phase has shifted to the opposite phase side.

Based on the above-described configuration, when the vehicle is running, the detection signal Sg from the lateral force sensor 56 is supplied to the steering ratio characteristic selection section 59 of the control unit 50.
At step 9, it is determined whether the lateral force caused by the detection signal Sg is greater than or equal to a predetermined value.

That is, in the steering ratio characteristic selection section 59, the lateral force sensor 56
It is detected whether the lateral force acting on the vehicle detected by the lateral force is greater than or equal to a predetermined value. Further, the signal Sm from the driving mode selection switch 57 is also supplied to the steering ratio characteristic selection section 59, and the steering ratio characteristic selection section 59 determines whether the signal Sm is the normal driving mode or the sport driving mode of the vehicle. is determined.

When the steering ratio characteristic selection unit 59 detects that the lateral force generated by the detection signal Sg is less than a predetermined value, and therefore the coefficient of friction of the road surface is considered to be relatively small, For example, 1 is selected as the steering ratio characteristic shown in FIG. 3 from among the steering ratio characteristics stored in the steering ratio characteristic storage section 58 by the steering ratio characteristic selection section 59, and the steering ratio A signal Sk corresponding to the characteristic 1 is supplied to the rear wheel steering angle calculation section 60. As a result, in the rear wheel steering angle calculating section 60, the detection signal Sv from the vehicle speed sensor 54 is determined as the vehicle speed, the signal Sk is determined as the steering ratio characteristic, and the steering ratio K obtained from
, and from the front wheel steering angle at which the detection signal Ss from the steering angle sensor 52 is generated, a rear wheel steering angle corresponding to the vehicle speed at which the detection signal SV is generated is calculated, and a signal Sr corresponding to the obtained rear wheel steering angle is calculated.
is supplied to the pulse signal forming section 61. Then, in the pulse signal forming section 61, a pulse signal Sp corresponding to the rear wheel steering angle indicated by the signal Sr is formed and supplied to the drive section 62, and the drive section 62 forms drive signals Sa and sb based on the pulse signal Sp. and they are pulse motor 3
0 and the pump drive motor 44, respectively. As a result, the pulse motor 30 and the pump drive motor 44 are driven according to the rear wheel steering angle calculated by the rear wheel steering angle calculating section 60.

In this way, by controlling the drive of the pulse motor 30 and the pump drive motor 44, the rear wheels 12L and 12R are steered according to the steering ratio characteristic of 1, and when the vehicle runs at a speed less than 71, the rear wheels 12L and 12R are steered according to the steering ratio characteristic of 1. , front wheels 2L and 2
The steering state of R and the steering state of rear wheels 12L and 12R are in an opposite phase relationship, and good turning performance is obtained.
When the vehicle runs at a vehicle speed of 71 or more, the steered states of the front wheels 2L and 2R and the steered states of the rear wheels 12L and 12R are in the same phase relationship, resulting in a stable running state.

On the other hand, the steering ratio characteristic selection unit 59 detects that the lateral force caused by the detection signal Sg is greater than or equal to the predetermined value, and therefore it is determined that the coefficient of friction of the road surface is relatively large. , signal S from the running mode selection switch 57
If it is detected that the driving mode of the vehicle in which m is in a hailstorm is the normal driving mode, the steering ratio characteristic selection unit 59 selects one of the steering ratio characteristics stored in the steering ratio characteristic storage unit 5B. For example, 2 is selected as the steering ratio characteristic shown in FIG. 3, and a signal Sk corresponding to the steering ratio characteristic kt is supplied to the rear wheel steering angle calculation section 60. As a result, in the rear wheel steering angle calculating section 60, the steering ratio K and the steering angle obtained from the detection signal Sv from the vehicle speed sensor 54 and the steering ratio characteristics obtained from the actual vehicle speed and the signal Sk, respectively. A rear wheel steering angle corresponding to the vehicle speed at which the detection signal Sv is generated is calculated from the front wheel steering angle at which the detection signal Ss from the sensor 52 is generated, and a signal Sr corresponding to the obtained rear wheel steering angle is sent to the pulse signal forming section. 61. Also in this case, the pulse signal forming section 61 supplies the pulse signal Sp corresponding to the rear wheel steering angle indicated by the signal Sr to the drive section 62, and the drive section 62 supplies the pulse signal Sp corresponding to the rear wheel steering angle indicated by the signal Sr.
The drive signals Sa and sb based on p are supplied to the pulse motor 30 and the pump drive motor 44, respectively, and the rear wheel steering angle calculated by the rear wheel steering angle calculating section 60 of the pulse motor 30 and the pump drive motor 44 is calculated. The drive is performed accordingly.

In this way, by driving and controlling the pulse motor 30 and the pump drive motor 44, the rear wheels 12L and 12R are steered according to the steering ratio characteristic of 2, and when the vehicle runs at a speed less than 72 , front wheels 2L and 2
The steering state of R and the steering state of rear wheels 12L and 12R are in an opposite phase relationship, and good turning performance is obtained.
When the vehicle runs at a vehicle speed of 72 or more, the steered state of the front wheels 2L and 2R and the steered state of the rear wheels 12L and 12R are in the same phase relationship, resulting in a stable running state.

In this case, the steering ratio characteristic of 2 is different from the steering ratio characteristic of 1 in that the steering ratio K is different from the steering state of the front wheels 2L and 2R and the rear wheel 12.
It is assumed that the steering state of the front wheels 2L and 2R has shifted to the opposite phase side, which makes the steering state of the front wheels 2L and 12R in an opposite phase relationship, and the steering state of the front wheels 2L and 2R and the rear The state in which the steered states of wheels 12L and 12R are in an opposite phase relationship is maintained. Therefore, when the coefficient of friction of the road surface is relatively large, good turning performance can be obtained not only when the vehicle is running at a relatively low speed but also when the vehicle is running at a relatively high speed.

In addition, in the steering ratio characteristic selection unit 59, when the detection signal Sg indicates that the lateral force to be caused is detected to be equal to or greater than a predetermined value, and the signal Sm from the driving mode selection switch 57 indicates that the driving mode of the vehicle is set to sport. When the driving mode is detected, the steering ratio characteristic selection section 59 selects, for example, the steering ratio characteristics shown in FIG. 3 from among the steering ratio characteristics stored in the steering ratio characteristic storage section 58. 3 is selected as the steering ratio characteristic, and a signal Sk corresponding to the steering ratio characteristic is supplied to the rear wheel steering angle calculation section 60. As a result, rear wheels 12L and 12
R is steered according to the steering ratio characteristic 3.

On the other hand, when the vehicle transitions from a low-speed running state to a high-speed running state during cornering, the lateral force acting on the vehicle detected by the lateral force sensor 56 increases. In such a case, the steering ratio characteristic selection unit 59 selects the steering ratio characteristic according to the lateral force generated by the detection signal Sg and the driving mode of the vehicle generated by the signal Sm as described above.
For example, when the vehicle speed is Va as shown in FIG.
If the sport driving mode is selected by , and the steering ratio characteristic shown in FIG. 3 is switched from + to the steering ratio characteristic, while the vehicle speed increases from Va to vb, The steering ratio varies only in Δ from a negative value Ka having a relatively large absolute value to a positive value Kb having a relatively small absolute value. On the other hand, if the steering ratio characteristic is not selected according to the lateral force caused by the detection signal Sg, and the vehicle speed is Va.
Rear wheels 12L and 1 follow the steering ratio characteristic even if the above is the case.
Assuming that 2R steering is performed, as shown in FIG. 3, while the vehicle speed increases from Va to vb, the steering ratio has a negative value K al with a relatively small absolute value. to a relatively large positive value Kb'.

Comparing these changes in the steering ratio, Δ and Δ, Δ is more sensitive to the steering conditions of the front wheels 2L and 2R and the rear wheels 12L and 12R than to Δ. is on the opposite phase side, which makes the change in the steering ratio Δ, compared to the case where the change in steering ratio becomes Δ,
While the vehicle speed increases from Va to vb, the state in which the steered state of the front wheels 2L and 2R and the steered state of the rear wheels 12L and 12R are in an opposite phase relationship is prolonged.

Therefore, when the vehicle transitions from a low-speed driving state to a high-speed driving state during turning, and the lateral force acting on the vehicle detected by the lateral force sensor 56 increases accordingly, as described above, By selecting the steering ratio characteristic in accordance with the lateral force generated by the detection signal Sg in the steering ratio characteristic selection section 59, an increase in the tendency of understeering due to turning of the vehicle is effectively suppressed. Excessive understeering tendency is avoided.

FIG. 4 shows another specific example of the configuration of the control unit 50 used in the embodiment shown in FIG.

The specific configuration example shown in FIG. 4 includes, for example, a steering ratio characteristic storage section 58' that stores only 1 in the steering ratio characteristic shown in FIG. The detection signal Sv from the vehicle speed sensor 54 is supplied, and the rear wheel steering angle is calculated based on the detected front wheel steering angle and vehicle speed, and the steering ratio characteristic stored in the steering ratio characteristic storage section 58''. A signal Sr corresponding to the calculated rear wheel steering angle is calculated.
The detection signal Sg from the lateral force sensor 56 and the signal Sm from the driving mode selection switch 57 are supplied to the rear wheel steering angle calculating section 60 which sends out the lateral force and the signal Sm indicates the lateral force to be detected and the signal Sm to the vehicle. a correction unit 65 that corrects the rear wheel steering angle calculated by the rear wheel steering angle calculation unit 60 according to the driving mode of the rear wheel steering angle, and sends out a signal Sr'' corresponding to the rear wheel steering angle that has undergone the necessary correction; Based on the pulse signal forming section 61 which forms the pulse signal Sp according to the signal Sr' from the section 65 and the pulse signal Sp obtained by the pulse signal forming section 61,
It includes a drive section 62 that sends drive signals Sa and sb to the pulse motor 30 and the pump drive motor 44.

Based on this configuration, when the vehicle is running, the rear wheel steering angle calculating section 60 calculates the detected signal Sv from the vehicle speed sensor 54 to determine the actual vehicle speed and steering stored in the steering ratio characteristic storage section 58'. From the steering ratio K obtained from the ratio characteristic of 1 and the front wheel steering angle at which the detection signal Ss from the steering angle sensor 52 is generated, the rear wheel steering angle according to the vehicle speed at which the detection signal Sv is generated is calculated,
A signal Sr corresponding to the obtained rear wheel steering angle is supplied to the correction section 65.

Further, the detection signal Sg from the lateral force sensor 56 and the signal Sm from the driving mode selection switch 57 are supplied to the correction section 65, and the correction section 65 determines whether or not the lateral force caused by the detection signal Sg is greater than or equal to a predetermined value. It is also determined whether the driving mode of the vehicle in which the signal Sm is generated is the normal driving mode or the sport driving mode. If the detection signal Sg in the correction unit 65 indicates that the lateral force is less than a predetermined value and therefore the friction coefficient of the road surface is considered to be relatively small, the rear wheel steering angle calculation unit in the correction unit 65 No correction is made to the rear wheel steering angle that is affected by the signal Sr from 60.

Therefore, the signal Sr from the rear wheel steering angle calculation section 60 is directly obtained from the correction section 65 as a signal Sr', and is supplied to the pulse signal formation section 61. Then, in the pulse signal forming section 61, a pulse signal Sp corresponding to the rear wheel steering angle indicated by the signal srl is formed and supplied to the drive section 62, and the drive section 62 generates drive signals Sa and sb based on the pulse signal Sp. The pulse motor 30
and the pump drive motor 44, respectively. As a result, the pulse motor 30 and the pump drive motor 44,
Drive is performed according to the rear wheel steering angle calculated by the rear wheel steering angle calculating section 60.

In this way, by driving and controlling the pulse motor 30 and the pump drive motor 44, the rear wheels 12L and 12R are steered according to the steering ratio characteristic of 1, as shown in FIG. The same running state of the vehicle as in the case of the configuration example can be obtained.

On the other hand, the correction unit 65 detects that the lateral force caused by the detection signal Sg is greater than or equal to the predetermined value, and therefore,
When it is determined that the coefficient of friction of the road surface is relatively large, the correction section 65 corrects the rear wheel steering angle based on the signal Sr from the rear wheel steering angle calculation section 60, and adjusts the steering ratio accordingly. Corrected.

At this time, the amount of correction of the steering ratio differs depending on the driving mode of the vehicle detected by the correction unit 65 based on the signal Sm. For example, when the normal driving mode is used, the rear wheel steering angle calculation unit 60 determines the steering ratio characteristic.
If the calculation using 2 for the steering ratio characteristic shown in FIG. 3 is performed instead, a corrected rear wheel steering angle corresponding to the rear wheel steering angle calculated at that time is obtained. Also,
When the sport driving mode is selected, the steering ratio characteristic is set to 1 in the rear wheel steering angle calculation unit 60, and the steering ratio characteristic is set to 1.
, a corrected rear wheel steering angle is obtained which corresponds to the rear wheel steering angle calculated at that time. Then, the correction section 65 supplies a signal Sr' corresponding to the corrected rear wheel steering angle to the pulse signal formation section 61. Also in this case, from the pulse signal forming section 61,
Pulse signal S corresponding to the corrected rear wheel steering angle indicated by the signal Sr”
p is supplied to the drive section 62, and from the drive section 62, drive signals Sa and sb based on the pulse signal sp are sent to the pulse motor 3.
0 and the pump drive motor 44, and the pulse motor 30 and the pump drive motor 44 are driven according to the rear wheel steering angle calculated by the rear wheel steering angle calculating section 60. .

In this way, by driving and controlling the pulse motor 30 and the pump drive motor 44, the rear wheels 12L and 12R are steered according to the steering ratio characteristic of 2 or 3, as shown in FIG. The same running state of the vehicle as in the specific configuration example shown will be obtained.

In the above-described embodiment, the lateral force sensor 56 is used as a means for detecting the lateral force acting on the vehicle, but instead of using the lateral force sensor 56, for example, the front wheel steering angle is plotted on the vertical axis. A plurality of lateral force curves G, as shown in the graph of FIG. 5, where θ is plotted and vehicle speed ■ is plotted on the horizontal axis.
A front wheel steering angle and vehicle speed sensor 54 receives a detection signal Ss from the steering angle sensor 52 according to cz, G, G4, etc.
The lateral force acting on the vehicle may be detected by determining the lateral force value corresponding to the vehicle speed detected by the detection signal Sv from the vehicle.

FIG. 6 shows another example of the four-wheel steering system for a vehicle according to the present invention. In FIG. 6, each part corresponding to the example shown in FIG. 1 is shown with the same reference numerals as in FIG. 1, and repeated explanation thereof will be omitted.

In the example shown in FIG. 6, a rack 70 is formed on the rank shaft 9 of the steering gear mechanism 10 that constitutes the front wheel steering mechanism 5''. A pinion 74 fixed to one end of a transmission rod 72 extending in the longitudinal direction of the vehicle is meshed with the rack 70.
The other end of 2 is connected to a steering ratio changing mechanism 76. The steering ratio changing mechanism 76 includes a slide member 78 supported movably in the vehicle width direction. A rack 80 is formed on the slide member 78, and a pinion 82 fixed to one end of the pinion shaft 24 is meshed with the rack 80. A pinion 26 is attached to the other end of the pinion shaft 24.
is fixed, and this pinion 26 is meshed with a rack 22 formed on the rear wheel steering rod 20.

For example, as shown in FIG. 7, the steering ratio changing mechanism 76 has a shaft 83 rotatably supported around a central axis O3 extending in the height direction of the vehicle, and one end of the shaft 83 A holder 84 having a bifurcated shape is attached to the portion. One end of the rotating arm 8 is connected to the holder 84 via a pin 86, and the center of the pin 86 is aligned with the central axis 02 which is orthogonal to the central axis 01 and along the vehicle width direction.
It is assumed that Therefore, the angle of the rotation locus of the rotation arm 88 about the bin 86 with respect to the central axis 0□ is 0. It changes as the holder 84 rotates around .

The other end of the rotating arm 88 is connected to the slide member 78 via a link member 92 whose intermediate portion is connected by a ball joint 90.

The other end of the rotating arm 88 and one end of the link member 92, and the other end of the link member 92 and the slide member 78, respectively, are connected to the center axis 0. and ot via ball joints 94 and 95. Link member 92
The intermediate portions of the ball joints 90 and 94 are supported by a cylindrical member 96 so as to be slidable in the vehicle width direction. The cylindrical member 96 is fixed to the other end of a rotating arm 100, which has one end fixed to a rotating shaft 98 that is rotatably supported around the central axis OR. A bevel gear 102 is fixed to one end of the rotating shaft 98.
is meshed with a bevel gear 104 fixed to the other end of the transmission rod 72.

Therefore, the cylindrical member 96 is rotated about the rotating shaft 98 by the rotation of the transmission rod 72 accompanying the operation of the front wheel steering mechanism 5'. In such a state, the rotation locus of the rotation arm 88 is the central axis O! If the link member 92 is tilted relative to the arrow F in FIG.
This causes the slide member 78 to be displaced in the vehicle width direction.

The amount of displacement of the slide member 78 is determined by the angle between the rotation locus of the rotation arm 88 about the pin 86 and the center axis 0□, that is, the rotation angle of the holder 84 about the center axis vA01. Ru. Therefore, the sector gear 106 is attached to the other end of the shaft 83 to which the holder 84 is fixed.
is fixed, and a pinion 110 fixed to the output shaft of a motor 1.8 whose drive is controlled by a drive signal Sa from a control unit 50 is meshed with the sector gear 106. In this example, the rear wheel steering angle calculating section 60 in the control unit 50. The pulse signal forming section 61, the driving section 62, the steering ratio changing mechanism 76, and the like constitute a steering ratio control means.

When a vehicle equipped with the four-wheel steering device configured as described above is running, the steering force from the steering wheel 3 is transmitted to the steering ratio changing mechanism 76 via the front wheel steering mechanism 5° and the transmission rod 72. When the steering angle sensor 52, vehicle speed sensor 54 . Detection signal S from lateral force sensor 56 and driving mode selection switch 57
The steering ratio is set based on s, SV, Sg, and signal Sm. Then, a drive signal S according to the set steering ratio
a is supplied from the control unit 50 to the steering ratio changing mechanism 76, thereby displacing the slide member 78 by a predetermined amount. The displacement of the slide member 78 is transmitted to the rear wheel steering rod 20 via the binion shaft 24, and the knuckle member 16 is rotated around the joint portion 14, thereby causing the rear wheels 12R and 12L to move to a predetermined position. It is steered based on the steering ratio.

Other configurations and operations in the embodiment shown in FIG. 6 are similar to those in the embodiment shown in FIG.

(Effects of the Invention) As is clear from the above description, according to the four-wheel steering device for a vehicle according to the present invention, when the front wheels are steered, the rear wheels are accordingly steered, and the steering ratio is That is, the ratio of the steering angle of the rear wheels to the steering angle of the front wheels is changed according to the vehicle speed, and the steering ratio is appropriately corrected according to the coefficient of friction of the road surface on which the vehicle travels. Since the correction amount of this steering ratio can be changed manually, the running stability of the vehicle can be improved when the friction coefficient of the road surface is relatively small; To obtain an appropriate vehicle running condition in accordance with the difference in the coefficient of friction of the road surface and in accordance with the driving mode desired by the driver, such as improving the turning performance of the vehicle under conditions where the vehicle is large. Can be done. In addition, when the vehicle transitions from a low-speed driving state to a high-speed driving state during turning, the steering ratio changes to the front wheel steering state based on the fact that the lateral force acting on the vehicle exceeds a predetermined value. Since the correction control is performed to the opposite phase side, which means that the steering state of the rear wheels is in an opposite phase relationship, it is possible to effectively suppress the tendency for understeering to become excessively strong as the vehicle turns. Become.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram schematically showing an example of a four-wheel steering system for a vehicle according to the present invention, and FIG. 2 is a block diagram showing a specific configuration example of a control unit used in the example shown in FIG.
FIG. 3 is a diagram showing steering ratio characteristics used to explain the operation of the specific configuration example of the control unit shown in FIG. 2, and FIG.
FIG. 5 is a block diagram showing another specific example of the configuration of the control unit used in the example shown in FIG. 1, and FIG. 7 is a general configuration diagram showing another example of a four-wheel steering device for a vehicle according to the present invention, and FIG. 7 is a schematic configuration diagram showing a specific configuration example of a steering ratio changing mechanism used in the example shown in FIG. 6. be. In the figure, 2L and 2R are front wheels, 5 and 5' are front wheel steering mechanisms, 11 is a rear wheel steering mechanism, 12L and 12R are rear wheels, 30
50 is a pulse motor, 50 is a control unit, 56 is a lateral force sensor, 57 is a driving mode selection switch, 58 and 58° are a steering ratio characteristic storage section, 59 is a steering ratio characteristic selection section, 60 is a rear wheel steering angle calculation 61 is a pulse signal forming section, 62 is a drive section, 65 is a correction section, and 76 is a steering ratio changing mechanism. Patent applicant Mazda Motor Corporation Figure 6 Hathorn Song Figure 7

Claims (1)

[Claims] A front wheel steering mechanism that steers a front wheel in response to a steering operation in a vehicle, a rear wheel steering mechanism that steers a rear wheel in response to the steering of the front wheel, and a steering angle of the rear wheel relative to a steering angle of the front wheel. steering ratio control means for changing the ratio according to vehicle speed; lateral force detection means for detecting a force in the vehicle width direction acting on the vehicle; and a force in the vehicle width direction acting on the vehicle by the lateral force detection means. is greater than a predetermined value, the ratio of the steering angle of the rear wheels to the steering angle of the front wheels controlled by the steering ratio control means is calculated based on the steering state of the front wheels and the steering angle of the rear wheels. A steering ratio correction means for correcting the steering ratio to the opposite phase side so that the steering state has an opposite phase relationship, and correction of the ratio of the steering angle of the rear wheels to the steering angle of the front wheels by the steering ratio correction means. A four-wheel steering device for a vehicle, comprising: correction amount variable means that allows the amount to be changed by manual operation.