JP2539815B2 - 4-wheel steering system for vehicles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention steers the front wheels and the rear wheels in accordance with the operation of the steering wheel, and changes the steering ratio of the rear wheels in advance according to the vehicle speed and the like. A four-wheel steering system for a vehicle configured to change according to a set turning ratio characteristic,
In particular, the present invention relates to a four-wheel steering system for a vehicle including a constant speed traveling system that controls an engine output so as to maintain a target vehicle speed set based on a vehicle speed setting signal.

(Prior Art) A four-wheel steering system for a vehicle enhances the turning performance of the vehicle by controlling the turning ratios of the front and rear wheels in the opposite phase direction during normal low speed turning, and controls the turning ratio in the same phase direction during high speed turning. In order to improve the running stability of the vehicle, the steering angle of the rear wheels with respect to the front wheels is changed based on a predetermined turning ratio characteristic that is set in advance according to the vehicle speed or the like (for example, JP 55-91457).

In addition, a constant speed traveling device that maintains the vehicle speed of a vehicle at a desired vehicle speed set by a driver has been put into practical use. This constant-speed traveling device is, for example, as disclosed in Japanese Utility Model Laid-Open No. 58-44552, a driver performs a switch operation at the time when the vehicle speed reaches a desired speed, so that the vehicle speed becomes a target for constant speed control. The value is set as a value, and the engine output is controlled so that the actual vehicle speed is maintained at the target vehicle speed.

By the way, in a vehicle equipped with the above-described four-wheel steering device and a constant speed traveling device, the driver's concentration tends to decrease during constant speed control by the constant speed traveling device, so that the steering wheel can be easily operated rapidly. In this case, when the steering ratio of the front and rear wheels is set to the opposite phase side by the four-wheel steering device,
The oversteering tendency of the vehicle is further promoted.

(Object of the Invention) The present invention has been made based on the above technical background, and even when the driver's concentration is reduced in a constant speed control state of the vehicle by the constant speed traveling device, the vehicle oversteering is performed. A four-wheel steering system for a vehicle capable of preventing the tendency from being promoted.

(Structure of the Invention) The present invention is a four-wheel steering system that steers the front wheels and the rear wheels according to the operation of the steering wheel and changes the steering ratios of the front and rear wheels according to preset steering ratio characteristics. In a vehicle including a device and a constant speed traveling device that controls an engine output so as to maintain a target vehicle speed set based on a vehicle speed setting signal, a steering ratio of front and rear wheels is set according to the steering ratio characteristic. A turning ratio changing means for controlling, a judging means for judging that the vehicle is in a constant speed control state, and a judging signal outputted from the judging means for correcting the turning ratio characteristic to a stable running side of the vehicle. And a correction means for performing the correction.

According to the above configuration, when the vehicle is in the constant speed control state, the steering ratio characteristics of the front and rear wheels are corrected to the traveling stable side, so that the steering characteristic of the vehicle is prevented from suddenly becoming the oversteer state. To be done.

(Embodiment) FIGS. 1 and 2 show a schematic configuration of a four-wheel steering system for a vehicle, in which front wheels 1L, 1R and rear wheels 2L, 2R are supported by a front wheel steering mechanism 3 and a rear wheel steering mechanism 12, respectively. ing.

The front wheel steering mechanism 3 includes a pair of left and right knuckle arms 4
L, 4R and tie rods 5L, 5R, and these left and right tie rods 5
It consists of a relay rod 6 that connects L and 5R. A steering wheel 10 is connected to the front wheel steering mechanism 3 via a rack and pinion type steering mechanism 7. That is, the steering mechanism 7 includes a rack 8 formed on the relay rod 6, a steering shaft 11 having a steering wheel 10 connected to an upper end thereof and a pinion 9 engaging with the rack 8 attached to a lower end thereof. It is configured to steer the left and right front wheels 1L and 1R according to the operation of 10.

On the other hand, the rear wheel steering mechanism 12 is similar to the front wheel steering mechanism 3 in that the left and right knuckle arms 13L and 13R and the tie rod 1 are used.
The relay rod 15 connects the 4L and 14R to each other, and further includes a hydraulic power steering mechanism 16. The power steering mechanism 16 includes a power cylinder 17 fixed to the vehicle body and having the relay rod 15 as a piston rod. Inside the power cylinder 17, two hydraulic pressures are provided by a piston 17a integrally attached to the relay rod 15. It is divided into chambers 17b and 17c, and these hydraulic chambers 17b and 17c are connected to the control valve 20 via pipes 18 and 19, respectively. Two pipes, an oil supply pipe 22 and an oil discharge pipe 23, which reach the reserve tank 21, are connected to the control valve 20, and a hydraulic pump 24 driven by an engine (not shown) is arranged in the oil supply pipe 22. It is set up. The control valve 20 is of a known spool valve type, and is a cylindrical valve casing 20a integrally attached to the relay rod 15 via a connecting member 25.
And a spool valve (not shown) fitted in the valve casing 20a, and supplies pressure oil from the hydraulic pump 24 to one hydraulic chamber 17b (17c) of the power cylinder 17 according to the movement of the spool valve. The driving force for the relay rod 15 is assisted. In the power cylinder 17, return springs 17d, 17d for urging the relay rod 15 to a neutral position (position where the steering angle θR of the rear wheels 2L, 2R is 0) are mounted.

The relay rod 6 of the front wheel steering mechanism 3 has a rack 26 at a position different from the rack 8 constituting the steering mechanism 7.
A pinion 27 attached to the front end of a rotary shaft 28 extending in the vehicle front-rear direction is meshed with the rack 26, and the rear end of the rotary shaft 28 is connected to the rear wheel steering mechanism via a steering ratio control mechanism 29. 12 connected.

As shown in FIG. 2, the turning ratio control mechanism 29 has a control rod 30 slidably held in the vehicle width direction with respect to the vehicle body. One end of the control rod 30 is one of the control valves 20. It is connected to the spool valve. The turning ratio control mechanism 29 has a U-shaped holder at the base end.
31 includes a swing arm 33 swingably supported via a support pin 32, and the holder 31 is rotated in a casing (not shown) fixed to the vehicle body in a direction orthogonal to the movement axis of the control rod 30. It is rotatably supported via a support shaft 35 having an axis. The support pin 32 of the swing arm 33 is located at the intersection of the two axes and extends in the direction orthogonal to the rotation axis. By rotating the holder 31 about the support shaft 35, the tip of the support pin 32 is supported. The inclination angle formed by the pin 32 and the moving axis of the control rod 30, that is, the rocking locus surface of the rocking arm 33 about the support pin 32 is formed with respect to a plane orthogonal to the moving axis (hereinafter referred to as a reference plane). The tilt angle is changed.

Further, one end of a connecting rod 37 is connected to the tip end of the swing arm 33 via a ball joint 36, and the other end of the connecting rod 37 is connected to the other end of the control rod 30 via a ball joint 38. The control rod 30 is displaced in the vehicle width direction according to the displacement of the tip end of the swing arm 33 in the vehicle width direction.

The connecting rod 37 is slidably supported by the rotation imparting arm 40 via a ball joint 41 at a portion near the ball joint 36. The rotation imparting arm 40 is integrally provided with a large-diameter bevel gear 43 which is rotatably supported on the moving axis via a support shaft 42. The bevel gear 43 has a rear end at the rear end of the rotating shaft 28. Bevel gears installed 44
Are engaged with each other, and the rotation of the steering wheel 10 is transmitted to the rotation imparting arm 40. For this reason,
When the rotation imparting arm 40 and the connecting rod 37 are rotated around the moving axis by an amount according to the rotation angle of the steering wheel 10, and the swing arm 33 is swung about the support pin 32 accordingly. , When the axis of the support pin 32 coincides with the movement axis of the control rod 30, the ball joint 36 at the tip of the swing arm 33 only swings on the reference plane, and the control rod 30 is held stationary. However, if the axis line of the pin 32 is inclined with respect to the movement axis line and the swing locus surface of the swing arm 33 is displaced from the reference plane, the swing arm 33 swings around the pin 32. The ball joint 36 is displaced in the vehicle width direction, and this displacement is controlled by the connecting rod 37.
When the control rod 30 is transmitted to the control valve 30, the control rod 30 moves along the movement axis to operate the spool valve of the control valve 20. I.e. the pin
Even if the swinging angle of the swinging arm 33 around the axis of 32 is the same, the displacement of the control rod 30 in the left-right direction is a pin.
It changes in accordance with the change of the inclination angle of 32, that is, the rotation angle of the holder 31.

Then, in order to change the inclination angle of the support pin 32 with respect to the movement axis, that is, the inclination angle of the holder 31 with respect to the reference plane, a sector gear 45 as a worm wheel is attached to the support shaft 35 of the holder 31. The worm gear 47 on the rotary shaft 46 is meshed with. Also,
A bevel gear 48 is attached to the rotary shaft 46.
The bevel gear 49 mounted on the output shaft 50a of the stepping motor 50 is meshed with the holder 31 by operating the stepping motor 50 to rotate the sector gear 45.
The steering angle θR of the rear wheels 2L, 2R is controlled by changing the inclination angle with respect to the reference plane of the sector gear 45 from the neutral position where the center line of the sector gear 45 is perpendicular to the center line of the rotary shaft 46 of the worm gear 47.
When turned clockwise when viewed from above the vehicle body, the steering ratio is controlled so that the rear wheels 2L, 2R face the same direction as the front wheels 1L, 1R in the same phase.

Further, in the casing supporting the holder 31, the stopper members 51 on the opposite phase side and the same phase side, which are pins on the left and right sides of the sector gear 45 serving as the rotating member, for regulating the rotation range of the sector gear 45, 52 is attached,
When the sector gear 45 rotates to the opposite phase side and the rotation angle from the neutral position becomes, for example, −17.5 °, the sector gear 45 contacts the opposite phase side stopper member 51 and further rotation is restricted, Further, when the sector gear 45 is rotated toward the same phase, when the rotation angle from the neutral position becomes, for example, 20 °, the sector gear 45 comes into contact with the stopper member 52 on the same phase side to restrict the movement. ing. The control position of the stepping motor 50 when the sector gear 45 contacts the phase-side stopper member 51 is set to the initial position. Reference numeral 39 is a rod stopper that restricts the maximum movement range of the relay rod 15 in the rear wheel steering mechanism 12.

The stepping motor 50 functions as a turning ratio changing means, and its operation is controlled by an output from a controller 53 with a built-in microcomputer as shown in FIG. That is, the controller 53 includes a vehicle speed detecting means 55 that detects the vehicle speed according to the detection signal of the vehicle speed sensor 54, and the steering ratios of the front and rear wheels corresponding to the vehicle speed based on the steering ratio characteristics stored in advance. A turning ratio setting means 56 to be obtained, a judging means 57 for judging that the vehicle is in a constant speed control state according to a command signal output from a controller 65 of a constant speed traveling device described later, and an output of the judging means 57. Correction means 58 for outputting to the steering ratio setting means 56 a correction command signal for correcting the steering ratio characteristics by displacing the steering ratio characteristics in the in-phase direction, that is, in the direction for improving the running stability of the vehicle in accordance with the signal
And a motor control means 59 for controlling the stepping motor 50 acting as a turning ratio changing means in response to an output signal from the turning ratio setting means 56.

Further, as shown in FIG. 4, the constant speed traveling device has a controller 65 connected via a main switch 64 to a power supply circuit 63 led from a power supply 61 via an ignition switch 62. The signals from the accelerator switch 66, the coast switch 67, and the resume switch 68 as vehicle speed setting means and the signal from the vehicle speed sensor 54 are input to the controller 70, and the solenoids 70, 71, 72 of the actuator 69 are controlled by the controller 65. The signal is designed to be output.

The accelerator switch 66, the coast switch 67 and the resume switch 68 are connected between the controller 65 and the ground, and among these switches, the accelerator switch 66 is a switch that also has the function of a set switch. When the vehicle speed detected according to the signal is within the range of 40 to 100 km / h, for example, by turning on when the vehicle speed reaches the desired vehicle speed, the vehicle speed at that time is set as the target vehicle speed of the constant speed traveling device. It has a setting function and an acceleration function that keeps this ON state to increase the target value of the vehicle speed during this period, and when it is turned off, performs a constant speed running according to the increased target vehicle speed. is there. The coast switch 67 is used when decelerating in the constant speed control state, and the target value of the vehicle speed decreases during the ON operation. Furthermore, when the constant speed control is released due to a cause other than the OFF operation of the main switch 64, the resume switch 68 is turned ON to restore the target vehicle speed before the release.
And the operation of these switches 66, 67, 68 and the vehicle speed sensor
Based on a signal from 54, a control signal is output from the controller 65 to the solenoids 70, 71, 72 of the actuator 69 so as to maintain the vehicle speed, accelerate, decelerate or restore the vehicle speed.

Further, in this constant speed traveling device, a clutch switch 74 and a brake switch 75 as constant speed control releasing means for releasing the constant speed control state are arranged in parallel between the power supply circuit 63 and the controller 65. , These switches 7
Reference numerals 4 and 75 are turned on when the clutch is disengaged and the brake is actuated to input a release signal to the controller 65.
In addition, the output line 73 from the controller 65 is 4 above.
A command signal, which is connected to the controller 53 of the wheel steering system and indicates that constant speed control is being performed by the constant speed traveling device, is transmitted via the output line 73 to the controller 53 of the four wheel steering system.
It is configured to be output to.

The control operation by the controller 65 of the constant speed control device having the above-described configuration will be described with reference to the flowchart shown in FIG. When the control operation is started by turning on the ignition switch 62 and the main switch 64, first, in step S ₁ , a flag F indicating that the constant speed control operation is being executed is set to F = 0 for initialization. Next, when the accelerator switch 66 or the like in step S ₂ is turned ON to determine whether the constant speed control is started, that like the switch 66 is turned ON is confirmed, step S _In the controller of the four-wheel steering device, a command signal indicating that the vehicle is in the constant speed control state in FIG.
In addition to outputting to 53, the detection signal of the vehicle speed sensor 54 is input in step S ₄ .

After that, in step S ₅ , it is determined whether or not the constant speed control operation is started by determining whether or not the flag F is 0, and at the start time of the constant speed control operation. If it is confirmed,
In step S ₆ stores the vehicle speed V obtained in response to the detection signal of the vehicle speed sensor 54 as the target vehicle speed Vs. Also, to indicate that in step S ₇ is being executed the constant speed control operation sets the flag F to F = 1.

Then, the flag F in step S ₅ it is determined that F ≠ 0, already the process proceeds to step S ₈ when it is confirmed that the constant speed control operation is started, the current vehicle speed V and the target vehicle speed Vs Find the speed difference ε. Also, the speed difference ε is equal to or 0 in step S _9, returns to step S ₂ without performing any control when the speed difference ε is zero, maintaining the vehicle speed V To do. If it is determined in step S ₉ that the speed difference ε is not 0, it is determined in step S ₁₀ whether the speed difference ε is greater than 0, and the current vehicle speed V is the target vehicle speed. It is determined whether it is larger than Vs.

The current vehicle speed V is the target vehicle speed Vs at the step S ₁₀
If it is confirmed that it is larger than step S _11,
In step 1, a predetermined deceleration control based on a preset program is executed to reduce the engine output so that the actual vehicle speed matches the target vehicle speed Vs. Also above steps
If the current vehicle speed V in S _10, it was confirmed that less than the target vehicle speed Vs executes a predetermined speed increasing control for increasing the engine output in accordance with the speed difference ε in step S _12.

Also, the accelerator switch in Step S ₂
When the 66 or the like is judged to be OFF state, the flag F indicating that the application is running in the constant speed control operation determines whether it is set to F = 1 in step S _13, If it is confirmed that the flag F is set to F = 1, after releasing the constant speed control state to reset the flag F to F = 0 in step S _14,
Return to step S ₂ above.

Next, the control operation by the controller 53 of the four-wheel steering system will be described based on the flowchart shown in FIG. When the above control operation starts, first, step S ₁₅
In the above, it is determined whether or not a command signal indicating that the vehicle is in the constant speed control state is output from the controller 65 of the constant speed control device, and as a result of this determination, when it is determined that the vehicle does not enter the constant speed state, executes a normal steering ratio control according to the basic steering ratio characteristics stored as a data table in an unillustrated storage unit in step S _16. That is, the basic turning ratio characteristic is that the turning ratio of the front and rear wheels changes according to the vehicle speed as shown by the solid line a in FIG. 7, and when the vehicle speed is low, the turning performance of the vehicle is improved. The rear wheels are steered in the opposite direction to the front wheels, the steering ratio of the front and rear wheels becomes negative, and the steering ratio becomes 0 when the vehicle speed reaches, for example, 55 Km / h, regardless of the steering angle of the front wheels. It is configured to be in a two-wheel steering state in which the steering angle of the rear wheels is set to zero. Further, when the vehicle speed further increases, the rear wheels are steered in the same direction as the front wheels in order to improve the wheel grip force at the time of turning and improve the running stability, and the steering ratio of the front and rear wheels becomes positive. Thus, the stepping motor 50 is controlled.

Then, when the vehicle is determined that the transition to constant speed control state in step S _15, the step S ₁₇
In FIG. 7, the basic turning ratio characteristic is controlled according to the corrected turning ratio characteristic obtained by displacing the basic turning ratio characteristic in the same phase direction by a predetermined width α.

In this way, it is determined whether or not the constant speed control by the constant speed control device is being executed, and in this constant speed control state, the steering ratio characteristics after correction are obtained by displacing the steering ratio characteristics in the same phase direction. Since it is configured to control the steering ratio of the front and rear wheels accordingly,
It is possible to favorably maintain the traveling stability during the constant speed control, which tends to reduce the driver's concentration. That is,
During the constant speed control, the steering angles of the front and rear wheels are set according to the corrected steering ratio characteristic in which the steering ratio characteristic is displaced by the predetermined width α in the in-phase direction, that is, the understeer direction, as compared with the normal state. Therefore, the understeer tendency of the vehicle is strengthened, and the running stability is further improved. Moreover, in the steering ratio characteristic after the correction, the anti-phase region is restricted to the lower speed side compared to the basic steering ratio characteristic, so that the front and rear wheels are in the opposite phase during high / medium speed turning. The occurrence of the oversteering phenomenon due to the above is reliably prevented, and in this respect also, the running stability of the vehicle is improved.

In the above embodiment, during constant speed control, the turning ratio of the front and rear wheels is adjusted according to the turning ratio characteristic corrected so as to displace the preset basic turning ratio characteristic by the predetermined width α in the same phase direction. Is set to improve the running stability of the vehicle during the constant speed control, but the configuration of the present invention is not limited to the above embodiment, and various modifications can be made.

For example, as shown by the alternate long and short dash line in FIG. 7, by setting the steering ratios of the front and rear wheels according to the steering ratio characteristics corrected to eliminate the antiphase region, the running stability during constant speed control is improved. It may be configured so as to allow it. That is, as shown in the flowchart of FIG. 8, when a command signal indicating the constant speed control state in step S ₁₈ is judged to have been outputted from the controller 65 of the constant speed running device, step after read out from the basic steering ratio characteristic of the steering angle ratio β is preset between the front and rear wheels corresponding to the current vehicle speed in S _19, whether the steering angle ratio β is greater than 0 in step S ₂₀ To judge. Next, as a result of this judgment,
When it is determined that the steering ratio β is greater than 0,
In step S ₂₁ to perform a normal steering ratio control according to the basic steering ratio characteristics, as the steering ratio of the front and rear wheels becomes the same phase, sets the steering angle of the rear wheels relative to the front wheels. And if that said steering ratio β is smaller than 0 is judged controls so that the steering angle of the rear wheels becomes 0 in step S _22, becomes the rear wheel opposite phase state with respect to the front wheel By prohibiting this, running stability may be improved.

If it is confirmed that the vehicle is in the constant speed control state, the steering ratio characteristic is corrected so that the steering angle of the rear wheels is always 0 regardless of the vehicle speed. This may prevent the steering ratios of the front and rear wheels from being in the opposite phase.

Further, in the above embodiment, the vehicle speed sensitive type 4 which controls the steering ratios of the front and rear wheels based on the steering ratio characteristics corresponding to the vehicle speed.
Although the wheel steering device has been described, the configuration of the present invention is also applied to a steering angle sensitive four-wheel steering device in which the steering ratio characteristic is set so that the steering ratio changes in accordance with the steering angle of the front wheels. It is possible.

(Effects of the Invention) As described above, according to the present invention, when the vehicle is in the constant-speed control state by the constant-speed traveling device, the steering ratio characteristic serving as a reference for setting the steering ratio of the front and rear wheels is set to the traveling stable side. Since it is configured to be corrected, the oversteering tendency is prevented from being promoted in the above-mentioned constant speed control state in which the concentration of the driving vehicle is likely to decrease, and there is an advantage that the running stability of the vehicle can be improved. .

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a vehicle four-wheel steering system according to the present invention, FIG. 2 is a schematic perspective view of the steering system, and FIG. 3 is a block diagram showing functions of a controller of the steering system. , FIG. 4 is a circuit diagram showing the structure of a constant speed control device, FIG.
FIG. 6 is a flow chart showing the control operation of the constant speed control device, FIG. 6 is a flow chart showing the control operation of the four wheel steering device, FIG. 7 is a characteristic diagram of vehicle speed and turning ratio, and FIG. 7 is a flowchart showing a control operation in another embodiment of the steering device. 1L, 1R …… front wheel, 2L, 2R …… rear wheel, 10 …… steering wheel, 57 …… determination means, 58 …… correction means, 59 …… motor control means (rear wheel steering angle control means).

Claims (1)

(57) [Claims] 1. A four-wheel steering system for steering front wheels and rear wheels according to an operation of a steering wheel and changing a steering ratio of the front and rear wheels according to a preset steering ratio characteristic, and a vehicle speed. In a vehicle equipped with a constant speed traveling device that controls an engine output so as to maintain a target vehicle speed set based on a set signal, a steering that controls a steering ratio of front and rear wheels according to the steering ratio characteristic. A ratio changing means, a judging means for judging that the vehicle is in a constant speed control state, and a correcting means for receiving the judgment signal output from the judging means and correcting the turning ratio characteristic to a traveling stable side of the vehicle. A four-wheel steering system for a vehicle, comprising: