JPH0245273A - Four-wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To improve the steering performance at a low speed running especially by change-controlling a steering angle ratio from a reverse phase to a same phase according to the increase of vehicle speed when a front wheel steering angle is large, while controlling it to the same phase at all times irrespective of the wheel speed when the steering angle is in a range of small angle. CONSTITUTION:A four-wheel steering device is provided with a front wheel steering mechanism 1 steering front wheels FW according to the turning of a steering handle SW and a rear wheel steering mechanism 2 steering rear wheels RW. The mechanism 2 is controlled by means of a rear wheel steering control means 5 on the basis of the outputs of a vehicle speed detecting means 3 and a front wheel steering angle detecting means 4, and the rear wheel RW is steered being interlocked with the steering of the front wheels FW. In this case, a rear wheel steering control property in the means 5 is set such that a steering angle ratio is made to be reverse phase at a low speed range when a front wheel steering angle is in a large steering angle range, while made to be a same phase at a high speed range, then the steering angle ratio is made to be the same phase both at low and high speeds when the front wheel steering angle is in a small steering angle area.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention steers the front wheels in accordance with the rotation of a steering wheel, and in conjunction with the steering, moves the rear wheels in the same phase and out of phase with respect to the front wheels. The present invention relates to a four-wheel steering device for a vehicle to be steered.

[Prior Art] Conventionally, this type of device has been disclosed in, for example, Japanese Patent Application Laid-Open No. 60-67274.
As shown in the publication, by detecting the front wheel steering angle and vehicle speed, when the front wheel steering angle is large to a certain extent,
The rear wheels are steered so that the ratio of the rear wheel steering angle to the front wheel steering angle gradually changes from the opposite phase to the same phase as the vehicle speed increases, and when the front wheel steering angle is small, the steering angle is controlled in a low vehicle speed region. The rear wheels are steered so that the angle ratio is maintained at zero and the steering angle ratio gradually changes from zero to the same phase as the vehicle speed increases in a high vehicle speed region.

[Problems to be Solved by the Invention] However, in the conventional device described above, even if the front wheels are steered within a small steering angle range while the vehicle is running at low speed, the rear wheels are not steered and are kept in a neutral state. Therefore, if you make a sudden turn within the small steering angle range while driving at low speed to avoid obstacles, ruts, etc. on the road, the vehicle's behavior will become unstable, and if it sags, the vehicle's steering will be affected. There was a possibility that safety would deteriorate.

The present invention was devised in view of the above problems and the fact that the vehicle is not required to have a small turning performance within the small steering angle range of the front wheels.
The purpose is to provide a four-wheel steering system for a vehicle that solves the above-mentioned problem of steering stability when traveling at low speeds without deteriorating the turning performance of the vehicle when traveling at low speeds.

[Means for Solving the Problems] In order to solve the above problems and achieve the above objects, the structural features of the present invention are as shown in FIG. A front wheel steering mechanism 1 that steers the FW, a rear wheel steering mechanism 2 that steers the rear wheels R and W,
A vehicle speed detection means 3 for detecting vehicle speed, a front wheel steering angle detection means 4 for detecting a front wheel steering angle, and a rear wheel steering mechanism 2 which is controlled in accordance with the detected vehicle speed and the detected front wheel steering angle and linked to the steering of the front wheels FW. Rear wheel steering control means 5 for controlling the steering of the rear wheels RW by
In the four-wheel steering system for a vehicle, the rear wheel steering control characteristic in the rear wheel steering control means 5 is set to a low speed range of the detected vehicle speed when the detected front wheel steering angle is within a large steering angle range. When the steering angle ratio of the rear wheels to the front wheels is controlled to be in opposite phase at the same time as the steering angle ratio is controlled to be in the same phase in the high speed range of the detected vehicle speed, and the detected front wheel steering angle is within a small steering angle range. The steering angle ratio is set to be controlled in the same phase in the low speed and high speed ranges of the detected vehicle speed.

[Operation of the Invention] In the present invention configured as described above, if the rotation of the steering wheel SW is large to some extent and the front wheel steering angle is within the range of a large steering angle, the steering angle ratio becomes out of phase as the vehicle speed increases. The control is gradually changed from to in-phase to ensure the vehicle's tight turning performance when driving at low speeds, as well as the driving stability of the vehicle when driving at high speeds. On the other hand, the steering handle SW
If the rotation of the front wheels is small and the front wheel steering angle is within the small steering angle range, the steering angle ratio is always kept in the same phase.

[Effects of the Invention] As can be understood from the above description of the operation, according to the present invention, obstacles on the traveling path can be eliminated without affecting the vehicle's ability to turn in a small radius due to large steering angle steering of the front wheels FW during low-speed driving. Even if the vehicle is suddenly steered within a small steering angle range during low-speed driving to avoid ruts, the behavior of the vehicle is better controlled and good steering stability is maintained during low-speed driving.

[Example A, First Example Below, the first example of the present invention will be explained using the drawings.
FIG. 2 schematically shows the entire four-wheel steering system for a vehicle according to the present invention. This four-wheel steering device has left and right front wheels FWI,
Front wheel steering mechanism A that steers FW2, left and right rear wheels RWI,
A rear wheel steering mechanism B that steers RW2, and the rear wheel steering mechanism B
and an electric control device C that electrically controls the.

The front wheel steering mechanism A includes a rack par 12 that is displaced in the axial direction in response to rotation of the steering handle 11 to steer the left and right front wheels FWI, FW2. The rack par 12 is the steering handle 11
is connected to the left and right front wheels F via the binion 13 and the steering shaft 14, and is connected to the left and right front wheels F via the left and right tie rods 15a, 15b and the left and right knuckle arms 16a, 16b at both ends thereof.
W.I.

FW2 is connected so that it can be steered.

The rear wheel steering mechanism B has a steering angle ratio setting mechanism 20.

This steering angle ratio setting mechanism 20 converts the rotation of the input shaft 21 accompanying the steering of the left and right front wheels FWI and FW2 into an axial displacement of the relay rod 22, thereby adjusting the left and right rear wheels RWI.

The left and right front wheels FWI are controlled by steering the RW2 and controlling the direction and amount of displacement of the rail rod 22 with respect to the rotational direction of the input shaft 21.

It controls the setting of the steering angle ratio of the left and right rear wheels RWI and RW2 with respect to FW2. A known method disclosed in Publication No.-163064 can be used.

Further, an electric motor 23 is assembled in the steering angle ratio setting mechanism 20, and the motor 23 drives and controls a steering angle ratio changing member (not shown) in the mechanism 20.
The steering angle ratio is arranged such that the steering angle ratio is continuously changed from a predetermined out-of-phase value to a predetermined in-phase value.

The input shaft 21 is connected to the rack par 1 in the front wheel steering mechanism A via rotary shafts 24a, 24b, 24c and a pinion shaft 24d, which are connected by universal joints.
At both ends of the 9-relay rod 22 connected to the 9-relay rod 22, there are left and right tie openings/rods 25a.

25b and the left and right knuckle arms 26a, 26b, the left and right rear wheels R, W1. RW2 is connected so that it can be steered.

The electric control device C includes a front wheel steering angle sensor 31, a vehicle speed sensor 32, a steering angle ratio sensor 33, and a microcomputer 34.
The 9 front wheel steering angle sensor 31 is composed of a potentiometer assembled on the outer periphery of the steering shaft 14.
By detecting the rotation angle of the coaxial 14, the left and right front wheels FW
An analog signal representing the steering angle θf of I and FW2 is output. An A/D converter 35 is connected to the front wheel steering angle sensor 31, and the converter 35 converts the analog signal into a digital signal and outputs the digital signal. The vehicle speed sensor 32 picks up the rotation of the output shaft of a transmission (not shown) and outputs a pickup signal with a frequency proportional to the number of rotations of the output shaft, that is, the vehicle speed. A waveform shaper 36 is connected to the vehicle speed sensor 32, and the shaper 36 shapes the pickup signal into a rectangular wave and outputs the waveform.

The steering angle ratio sensor 33 is composed of a potentiometer assembled to the steering angle ratio setting mechanism 20, and the electric motor 23
By detecting the displacement of the above-mentioned steering angle ratio changing member as the mechanism 20 rotates, an analog signal representing the set steering angle ratio Ks set by the mechanism 20 is output. An A/D converter 37 is connected to the steering angle ratio sensor 33, and the converter 37 converts the analog signal into a digital signal and outputs the digital signal.

The microcomputer 34 includes a ROM 34b, a CPU 34c, and a CPU 34R connected to the bus 34a.

A M 34 d and input/output interface (hereinafter referred to as I
10) consists of 34e. The R,0M34b stores a program corresponding to flowchart 1 in FIG. 3, and also stores the target steering angle ratio KD in the form of a table. As shown in FIG. 4, this table is composed of a two-dimensional table specified by the absolute value 1θf1 of the vehicle speed V and the front wheel steering angle θf, and when the absolute value 1θf1 is large, the phase reverses as the vehicle speed V increases. (predetermined negative value)
A target steering angle ratio KD that continuously changes from 1 to a predetermined positive value in phase with each other is stored, and the absolute value 1θfI
It has the characteristic that when the vehicle speed (2) is small, the target steering angle ratio (KD) which is always in the same phase regardless of whether the vehicle speed (2) is large or small is stored.

The CPU 34c executes the program,
The RAM 34d temporarily stores data necessary for executing the program. I, 1034e inputs signals from the front wheel steering angle sensor 31, vehicle speed sensor 32, and steering angle ratio sensor 33, and outputs a control signal for controlling the rotation of the electric motor 23. This I/
A drive circuit 38 is connected to the 034 e, and the circuit 38 drives and controls the electric motor 23 in accordance with the control signal from the 034 e.

Next, the operation of the first embodiment configured as described above will be explained. Ignition switch of the vehicle (not shown)
When the CPU 34c is closed, the CPU 34c executes step ST in FIG.
Execution of the program is started at step I, and after various data in the RAM 34d are set to initial values at step ST2, the steering angle ratio setting mechanism 20 is set by a circulation process consisting of steps ST3 to S'T'7. control the steering angle ratio.

In this circulation process, the big nap signal from the vehicle speed sensor 32 is taken in via the waveform shaper 36 and the I/034e in step ST3, and the vehicle speed V is calculated based on the collected signal.
Output from the front wheel steering angle sensor 31 at T4 and A/D
Front wheel steering angle θ converted into a digital quantity by the converter 35
f is fetched via l1034e. Next, in step ST5, the absolute value 1θf1 of the front wheel steering angle θf is calculated, and the table in @ROM 34 b is referred to based on the calculated absolute value 1θf1 and the calculated vehicle speed ■, and the absolute value 1θf1 and Target steering angle ratio K corresponding to vehicle speed V
D is derived.

After deriving the target steering angle ratio, the set steering angle ratio Ks output from the steering angle ratio sensor 33 in step ST6 and converted into a digital quantity by the A/D converter 37 is l1034.
Difference data K representing the difference between the target steering angle ratio Kr and the set steering angle ratio Ks is fetched via step ST7.
o Ks is calculated, and the difference data K. −
Ks is output to the drive circuit 38 via l1034e.

The drive circuit 38 outputs a drive signal corresponding to the difference data Ko-Ks to the electric motor 23 to control the rotation of the motor 23. As a result, the electric motor 23 operates at the steering angle ratio setting I! ! 20 is controlled by the difference data KDKs, the steering angle ratio set in the aircraft 1II 20 becomes equal to the target steering angle ratio KD.

When the steering handle 11 is rotated in this state, the rack par 12 is displaced in the axial direction in response to the rotation, and the left and right front wheels FWI, FW2 are steered in response to the rotation of the steering handle 11. On the other hand, the displacement of the rack par 12 is converted into a rotational movement of the pinion shaft 24d, and the rotational movement is transmitted to the input shaft 21 of the steering angle ratio setting device 120 via the rotational shafts 24c, 24b, and 24a. rotates from the reference position by an amount proportional to the amount of steering of the left and right front wheels FWI and FW2. This rotational movement is performed by a steering angle ratio setting machine $112
0 is converted into an axial displacement of the relay rod 22, and depending on the axial displacement of the rod 22, the left and right rear wheels 1 (
Wl, R, and W2 are steered in conjunction with the aforementioned steering of the left and right front wheels FW1 and FW2.

In this case, if the steering angles of the left and right front wheels FWI, FW2 are θf, the set steering angle ratio Ks in the steering angle ratio setting mechanism 20 is set to the target steering angle ratio Kn (see FIG. 4).
The left and right rear wheels RW'l and RW2 are steered to a steering angle K D ·θf. As a result, the amount of rotation of the steering wheel 11 is large to some extent, and the absolute value 1θf of the front wheel steering angle θf is
If I is large, the target steering angle ratio KD becomes a predetermined negative value <3x'! as the vehicle speed ■ increases. ! , phase) The force changes by a predetermined positive value (in phase), so when driving at low speed, the left and right rear wheels RWI, RW2 is the left and right front wheels FW], the steering is controlled in the opposite phase with respect to FW2, and when driving at high speed. Sometimes left and right rear wheels RWI
・RW2 is steered in the same phase as the left and right front wheels FWI and FW2.7 This improves the vehicle's ability to turn around quickly when driving at low speeds, and at the same time improves the vehicle's stability when driving at high speeds. The properties become better.

On the other hand, if the amount of rotation of the steering wheel 1] is small and the absolute value 1θf1 of the front wheel steering angle θf is small, the target steering angle ratio Kn is always kept at a positive value (in phase), so the left and right rear wheels RW 1
, RW 2 is always steered in the same phase as the left and right front wheels FW], , FW2. As a result, even if the steering wheel 11 is suddenly turned within a small steering angle range while driving at low speed, the behavior of the vehicle will be changed in order to avoid obstacles, ruts, etc. on the road, rather than the slop of the vehicle's turn. This improves the stability of the vehicle, and even when driving on a slippery road such as a snowy road, the vehicle maintains good handling stability. Furthermore, when the vehicle is to be made to turn in a small amount while traveling at low speed, the left and right front wheels FWI and FW2 are always steered to a large steering angle, so that the above-mentioned ability to make a small turn in the vehicle while traveling at low speed is not affected.

b. Second Embodiment Next, the mechanical connection between the front wheel steering mechanism A and the rear wheel steering mechanism B in the first embodiment is eliminated, and the rear wheel steering mechanism B is drive-controlled by the electric control device C to rotate the left and right wheels. Rear wheel RWI, RW2
Another embodiment of the present invention in which the front left and right wheels are steered in conjunction with the left and right front wheels FWI and FW2 will be described with reference to the drawings. FIG. 5 schematically shows the entire four-wheel steering system according to this other embodiment, and the same parts as in the first embodiment are designated by the same reference numerals.

The front wheel steering mechanism A has the same structure as the first embodiment. The rear wheel steering device $11B is similar to the first embodiment described above,
The left and right rear wheels RWI, RW2 are steered via the left and right tie rods 25a, 25b and the left and right knuckle arms 26a, 26b by the relay rod 22 housed in the housing 40 so as to be displaceable in the axial direction. The relay rod 22 is driven and controlled by an electric motor 41 and a power cylinder 42. The electric motor 41 is connected to the upper end of the steering shaft 43 to rotationally drive the same shaft 43, and the lower end of the coaxial shaft 43 is connected via a pinion 44 to a rack portion 22a formed integrally with the relay rod 22. Further, a control valve 45 is installed in the middle of the steering shaft 43.
controls the supply of hydraulic oil from the hydraulic pump 47 driven by the engine 46 to the power cylinder 42 and the discharge of hydraulic oil from the power cylinder 42 to the reservoir 48 in accordance with the steering torque acting on the steering shaft 43.

The electric control device C has a configuration in which a rear wheel steering angle sensor 51 is provided in place of the steering angle ratio sensor 33 of the first embodiment, and a drive circuit 52 drives and controls the electric motor 41. Except for this point, this embodiment is the same as the first embodiment described above. The rear wheel steering angle sensor 51 is composed of a potentiometer assembled in the housing 40, and detects the displacement of the relay rod 22 in the axial direction, thereby adjusting the RWI of the left and right rear wheels.

An analog signal representing the set steering angle θrg of RW2 is output. An A/D converter 53 is connected to this rear wheel steering angle sensor 51, and the converter 53 converts the analog signal into a digital signal and outputs the digital signal. The drive circuit 52 is l1
034e and the same I/0 to the same circuit 52
34 e, the electric motor 4
1 is driven and controlled.

In addition, the ROM 34b in the microcomputer 34 stores a program corresponding to the flowchart in FIG. , negative when steering to the left) are stored in the form of a table. As shown in Fig. 7, this table is composed of a two-dimensional table specified by vehicle speed V and front wheel steering angle θf (positive when steering to the right, negative when steering to the left), and shows the absolute value of the front wheel steering angle θf. value 1θ
In a range where f1 is large, a target rear wheel steering angle θrD that continuously changes from the opposite phase to the same phase with respect to the front wheel steering angle θf as the vehicle speed V increases is stored, and the absolute value 1θ is
In a range where f1 is small, the target rear wheel steering angle θ is always in phase with the front wheel steering angle θf regardless of whether the vehicle speed V is large or small.
It has the characteristic of memorizing rD.

Next, the operation of the second embodiment configured as described above will be explained. In this case as well, when the ignition switch (not shown) of the vehicle is closed, the CPU 34c
Start execution of the program at step STI in the figure.1.
After the initial setting in step ST2, step ST3. ST4
, 5TII to 5T13.

In this circulation process, after calculating the vehicle speed V and taking in the front wheel steering angle θf in the same manner as described above in step 5T3ST4, a table in the ROM 34b is created in step 5T11 based on the calculated vehicle speed V and the counted front wheel steering angle θf. With reference to this, the target rear wheel steering angle θrD is derived.

After deriving the target rear wheel steering angle θrQ, step 5T1
In Step 2, the set rear wheel steering angle θr5 outputted from the rear wheel steering angle sensor 51 and converted into a digital quantity by the A/D converter 53 is fetched via I/034e, and in Step 5713, the set rear wheel steering angle θr5 is outputted from the rear wheel steering angle sensor 51 and converted into a digital value by the A/D converter 53. Difference data θrD-θrs representing the difference between the rear wheel steering angle θrD and the set rear wheel steering angle θrs is calculated, and the difference data θr, )-θrs is l10.
It is output to the drive circuit 52 via 34e.

The drive circuit 52 outputs a drive signal corresponding to the difference data θr, −θr to the electric motor 41 to control the rotation of the motor 41. As a result, the electric motor 41 drives and controls the steering shaft 43 by the difference data θrD −θrs, so the steering shaft 43 rotates by an amount corresponding to the difference data θro−θrs, and this rotation is caused by the pinion 44 and Rack part 2
This is converted into an axial displacement of the relay rod 22 via 2a.

Since the left and right rear wheels RWI, RW2 are steered according to the axial displacement of the relay rod 22, the same rear wheels RW1, RW2
is steered to the target rear wheel steering angle θrD. In this case, when the steering shaft 43 rotates, the control valve 45 is actuated by the torque acting on the steering shaft 43, and the supply and discharge of hydraulic oil to and from the power cylinder 42 is controlled, and the cylinder 42 controls the shaft of the relay rod 22. directional displacement is assisted.

In this way, as a result of steering control of the left and right rear wheels RWI, RW2, the same rear wheels R, W1. The RW2 is steered with the characteristics shown in FIG. 7, that is, the same characteristics as in the first embodiment, and the same effects as in the first embodiment are achieved in this second embodiment as well.

In addition, in the second embodiment, the left and right front wheels FWl, F
Target rear wheel steering angle θrD for both left and right steering of W2
is stored in the ROM 34b, but the target rear wheel steering angle θrD for the right direction of the left and right front wheels FWI, FW2
Same front wheel FW1. Since the target rear wheel steering angle θrD with respect to the left direction of FW2 has a symmetrical characteristic, the left and right front wheels FW1,
Only the target rear wheel steering angle θrD for steering FW2 in the left or right direction is stored in the ROM 34b, and the target rear wheel steering angle θrD is stored in the above for steering the front wheels FWI, FW2 in the one direction. The target rear wheel steering angle is derived in the same manner as in the second embodiment, and the sign of the derived target rear wheel steering angle θrD is reversed for the steering of the same front wheels FWl and FW2 in the other direction. Alternatively, θrD may be calculated.

[Brief explanation of the drawing]

Figure 1 is a claim correspondence diagram corresponding to the structure of the present invention, Figure 2 is a claim correspondence diagram corresponding to the structure of the present invention.
1 is an overall schematic diagram of a four-wheel steering system for a vehicle showing a first embodiment of the present invention, FIG. 3 is a flowchart of a program executed by the microcomputer shown in FIG. 2, and FIG.
FIG. 5 is an overall schematic diagram of a four-wheel steering device for a vehicle showing a second embodiment of the present invention, and FIG. 6 is a characteristic diagram of the steering angle ratio in the four-wheel steering device shown in FIG. A flowchart of the executed program and FIG. 7 are characteristic diagrams of the rear wheel steering angle in the four-wheel steering system of FIG. 5. Explanation of symbols A...Front wheel steering mechanism, B...Rear wheel steering mechanism, C...
・Electric control device, FWi, FW2..., front wheel, RWI,
RW2...Rear wheel, 11...Steering handle, 12...
・Rack bar 120... Steering angle ratio setting mechanism, 22...
Relay rod, 23゜4], ---Electric motor, 2
4a, 24b, 24. c. Rotating shaft, 31... Front wheel steering angle sensor, 32... Vehicle speed sensor, 33... Steering angle ratio sensor, 34... Microcomputer, 51...
・Rear wheel steering angle sensor. Figure 1 Applicant: Toyota Motor Corporation Agent: Patent attorney Teru Hase (1 other person) Figure 1

Claims (1)

[Claims] a front wheel steering mechanism that steers the front wheels in response to rotation of a steering wheel; a rear wheel steering mechanism that steers the rear wheels; a vehicle speed detection device that detects vehicle speed; and a front wheel steering angle detection device that detects a front wheel steering angle. A four-wheel steering system for a vehicle, comprising a rear wheel steering control means that controls the rear wheel steering mechanism according to the detected vehicle speed and the detected front wheel steering angle, and controls the steering of the rear wheels in conjunction with the steering of the front wheels. The rear wheel steering control characteristic of the rear wheel steering control means is such that when the detected front wheel steering angle is within a large steering angle range, the steering angle ratio of the rear wheels to the front wheels is controlled to have an opposite phase in a low speed range of the detected vehicle speed. and the steering angle ratio is controlled to be in phase in the high speed range of the detected vehicle speed, and when the detected front wheel steering angle is within a small steering angle range, the steering angle ratio is controlled to be in phase in the low speed and high speed range of the detected vehicle speed. A four-wheel steering device for a vehicle, characterized in that the four-wheel steering device is set to control the vehicle.