JPH0468187B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a four-wheel steering system for a vehicle that also steers the rear wheels in accordance with the steering of the rear wheels, and particularly in response to lateral acceleration during turning. The present invention relates to a vehicle and a four-wheel steering device in which the steering angle of the rear wheels is controlled by the steering angle of the rear wheels.

(Prior art) When a vehicle turns at high speed, the sideslip angle of the driving tires becomes larger than the sideslip angle of the non-driving tires, as shown in Fig. 4, and as shown by the solid line a in Fig. Understeering characteristics occur, and oversteering characteristics occur in rear-wheel drive vehicles, as shown by the solid line b in the figure. It is generally well known that this understeering tendency and oversteering tendency rapidly increase as the lateral acceleration applied to the vehicle increases, and that it becomes impossible to control the vehicle above a certain lateral acceleration.

BACKGROUND ART Today, four-wheel steering devices are being developed that steer the rear wheels of a vehicle following the steering of the front wheels. (For example, see Japanese Patent Application Laid-open No. 57-70774.) In this four-wheel steering system, the rear wheels are normally steered in the same phase direction as the front wheels in a high vehicle speed range, for example when changing lanes on a highway. It is stable and can be performed extremely smoothly. In addition, the rear wheels are steered in the opposite phase to the front wheels in a low vehicle speed range, making it possible to reduce the turning radius, and this four-wheel steering system is attracting attention as an excellent steering system.

However, in conventionally known four-wheel steering devices, the rear wheel steering angle is determined relative to the front wheel steering angle depending on the vehicle speed or the corresponding front wheel steering angle. When the rear wheels are steered in the same phase and receive lateral acceleration, the sideslip angle of the driving tires becomes larger than the sideslip angle of the non-driving tires, and the vehicle is controlled in the same way as a conventional two-wheel steering vehicle. I had a problem that I couldn't do it.

In order to solve this problem, the present inventor changed the ratio of the steering angle of the rear wheels to the steering angle of the front wheels according to the lateral acceleration that the vehicle body receives, thereby reducing understeering that occurs during high-speed turns. We have proposed a four-wheel steering system for vehicles that improves the limit characteristics during cornering by eliminating oversteering characteristics. However, the acceleration detectors known today that detect lateral acceleration have poor responsiveness, and the steering angle of the rear wheels is not directly corrected during high-speed turns, resulting in a problem in that the vehicle cannot be adequately controlled. .

(Objective of the Invention) Therefore, the object of the present invention is to provide a ratio of the steering angle of the rear wheels to the steering angle of the front wheels (hereinafter referred to as steering ratio) in accordance with the lateral acceleration to which the vehicle is subjected in an extremely responsive manner.
An object of the present invention is to provide a four-wheel steering system for a vehicle that has high limit characteristics during cornering and good handling characteristics.

(Structure of the Invention) A four-wheel steering device for a vehicle according to the present invention includes a steering device that steers front wheels, and a steering device that steers front wheels in the same phase direction according to a predetermined steering ratio according to a front steering angle steered by the steering device. A rear wheel steering device that steers the rear wheels to
A vehicle speed sensor that detects a vehicle speed, a front wheel steering angle sensor that detects a steering angle of the front wheels, a vehicle speed detected by the vehicle speed sensor, and a front wheel steering angle and a front wheel steering angle that are detected by the front wheel steering angle sensor. and a front wheel steering angular velocity obtained by detecting a temporal change in the steering ratio. Based on the front wheel turning angle detected by the steering angle sensor and the front wheel turning angular velocity obtained by detecting the temporal change in the front wheel turning angle, it is substantially determined that the lateral acceleration that the vehicle body receives is greater than or equal to the set lateral acceleration. If it is determined, the steering angle of the rear wheels, that is, the steering ratio, which is determined according to the vehicle speed or the steering angle of the front wheels corresponding to the vehicle speed, is changed.
Since the steering ratio can be changed at the same time as lateral acceleration occurs without the response delay that occurs when an acceleration sensor is used, high limit characteristics and good handling characteristics can be obtained during cornering.

When the vehicle speed, front wheel steering angle, temporal change in front wheel steering angle, and lateral acceleration are respectively V, θ _H , θ〓 _H and G, the lateral acceleration is G can be expressed as G=αV ² θ _H +βθ〓 _H. Therefore, the detected steering angle θ _H
The lateral acceleration may be calculated from the vehicle speed V according to the above equation, and it may be determined whether the calculated lateral acceleration is greater than or equal to the set lateral acceleration. Also, when determining the magnitude of lateral acceleration using the above formula, instead of actually calculating the lateral acceleration, each detected value, that is, vehicle speed V, front wheel steering angle θ _H , and temporal change θ of front wheel steering angle It is also possible to determine whether the lateral acceleration is greater than or equal to the set acceleration by comparing the value of _H with each set value to determine the magnitude relationship.

If it is detected by such a determination that the estimated lateral acceleration is equal to or higher than the set increase speed, the ratio of the rear wheel steering angle to the front wheel steering angle, that is, the steering ratio is changed. Usually, in a front-wheel drive vehicle or a four-wheel drive vehicle in which the driving force is distributed to the front wheels, the steering ratio is changed in a direction that reduces the steering ratio so as to eliminate the understeering characteristic.

In a rear-wheel drive vehicle or a four-wheel drive vehicle in which driving force is distributed to the rear wheels, the steering ratio is changed in the direction of increasing it so that the oversteering tendency can be eliminated.

However, it is possible to change a vehicle with understeering characteristics to one with oversteering characteristics to give it a sporty feel, or conversely, change a vehicle with oversteering characteristics to one with understeering characteristics to improve stable operability. It is also possible to have a vehicle with

(Example) Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 1 is a schematic diagram of a first embodiment of the present invention. The steering device 2 that steers the front wheels 1L and 1R includes a steering wheel 3 to be steered, and a pinion 4a and a rack 4b that convert the steering force of the steering wheel 3 into reciprocating motion in the vehicle width direction (left-right direction) and transmit the same. , left and right tie rods 5 whose base ends are connected to each end of this rack 4b,
5', and knuckle arms 6, 6' whose one end is connected to the tip of each tie rod 5, 5' and the other end is connected to the left and right front wheels 1L, 1R, respectively. 5 and 5' are reciprocated in the vehicle width direction to steer the left and right front wheels 1L and 1R left and right.

A front cylinder 7 is installed approximately in the center of the rack 4b of the steering device 2. The front cylinder 7 is provided integrally with a cylinder case 7a fixed to the vehicle body and the rack 4b, and is divided into sections by a piston 7b slidably fitted into the cylinder case 7a, and a piston 7b that is slidably fitted into the cylinder case 7a. The volume of the left chamber 7c and right chamber 7d changes as the piston 7b moves in the vehicle width direction (horizontal direction) in conjunction with the rack 4b of the steering device 2. It is configured as follows.

On the other hand, reference numerals 8 and 8' denote wheel support members that rotatably support the left and right rear wheels 9L and 9R. , Lateral link 1 as two front and rear link members for steering 9R
0, 10', 11, and 11' are connected, respectively. The left and right front lateral links 10, 10' are connected between their inner ends by a link-shaped first connecting member 12, and the left and right rear lateral links 11, 11' are also connected between their inner ends. The left and right high ends 9L and 9R are connected via the wheel support member 8 as the front and rear lateral links 10 and 11 move in the vehicle width direction (left and right direction). It supports steering with the wheel center as the steering center.

Furthermore, the first and second connecting members 12, 1
3 is provided with a pair of first and second rear cylinders 14 and 15 that reciprocate the first connecting member 12 and the second connecting member 13 in opposite directions. These rear cylinders 14 and 15 are
Cylinder cases 14 each fixed to the vehicle body
a, 15a, and pistons 14b, 15b that are integrally provided with the connecting members 12, 13 and are slidably fitted into the cylinder cases 14a, 15a.
and left chambers 14c, 15c and right chambers 14d, 1 divided by these pistons 14b, 15b.
5d, and these left and right chambers 14.
Return springs 14e and 15e are symmetrically installed in the springs c, 14d, 15c, and 15d, respectively. Each of these return springs 14e, 14
One end of e', 15e, 15e' is the cylinder case 14
a, 15a, and the other end is a pressing plate 14f, which is provided on the connecting members 12, 13, respectively.
14f', 15f, and 15f'. These pressing plates 14f, 15f are annular engagement pieces 14g, 14g' provided integrally with the connecting members 12, 13,
15g, 15g' and is regulated by stopper pieces 14h, 14h', 15h, 15h' which are integrally provided on the cylinder cases 14a, 15a. In other words, while the pistons 14b, 15b are pressed and held in the neutral position with a set load by the return springs 14e, 14e', 15e, 15e', the connecting members 12, 13 are moved in the left-right direction as the pistons 14b, 15b move in the left-right direction. The front and rear lateral links 10, 10', 11,
It is configured to steer the left and right rear wheels 9L and 9R via the steering wheel 11'.

Oil passages 17, 17' communicating with the left and right chambers 7c, 7d of the front cylinder 7 communicate with cylinders 16a, 16a' of the same-phase/opposite-phase switching devices 16, 16'. The oil passage 1 is provided in the cylinders 16a, 16a' of the switching devices 16, 16'.
Pistons 16b, 16b' are fitted so as to be movable across the apertures 7, 17'. These pistons 16b, 16b' cause the cylinder 16
a, 16a' are inner chambers 16c, 16c', outer chamber 16d,
It is separated by 16d'. The inner chambers 16c, 16c' are the first rear cylinder left and right chambers 14c, 14, respectively.
d through oil passages 18, 18'. The outer chambers 16d and 16d' are connected to the oil passage 1 in the left and right chambers 15c and 15d of the second rear cylinder, respectively.
9 and 19'. switching device 16,
Pistons 16b and 16b' of 16' are connected to oil passages 17 and 17' by actuators 16e and 16e'.
The oil passages 17 and 17' are moved in the width direction of the vehicle body across the oil passage 1.
8, 18' or 19, 19'. Furthermore, steering angle adjusting devices 20, 20' are interposed in the oil passages 17, 17'.
These steering angle adjusting devices 20, 20' include an oil chamber 20a,
20a', and pistons 20b and 20b' are movably fitted into the oil chambers 20a and 20a'. The pistons 20b, 20b' are urged inward by springs 20c, 20c'. The urging force of the springs 20c, 20c' is variably controlled by actuators 20d, 20d' depending on the vehicle speed. In addition, the in-phase and anti-phase switching device 1
6, 16' actuators 16e, 16e' and steering angle adjustment devices 20, 20' and actuator 2
0d and 20d' are vehicle speed sensor 21 and steering angle sensor 2
The controller 23 receives the vehicle speed signal V and the steering angle signal θ detected by the controller 23. In this controller 23, a temporal change θ in front wheel steering is calculated from the steering angle signal θ.

The four-wheel steering system for a vehicle constructed in this manner operates as follows.

When the vehicle is running at extremely low speed, the steering angle adjustment device 20,
The biasing force of the springs 20c, 20c' disposed in the spring 20' is set larger than the biasing force of the return spring 14e by the operation of the actuators 20d, 20d'. Therefore, the oil chambers 20a, 2
Even if oil pressure is applied to 0a', the pistons 20b and 20
b' becomes difficult to move outward, and therefore, the oil discharged from the front cylinder 7 as the steering device 2 is operated is sent to the rear cylinder via the in-phase and anti-phase switching devices 16 and 16'. Since the vehicle speed sensor 21 has detected an extremely low speed running state, the actuators 16e and 16e' of the in-phase and anti-phase switching devices 16 and 16' are controlled by the controller 23 and each piston is moving inward, and the front cylinder The left chamber 7c and right chamber 7b of 7 are the left chamber 15c of the second rear cylinder 15, respectively.
and the right ventricle 15d. When the volume of the left chamber 7c of the front cylinder 7 decreases due to the operation of the steering device 2, oil is discharged by this amount, and this discharged oil is transferred to the second chamber 7c.
is inserted into the left chamber 15c of the rear cylinder 15, but the rear cylinder 15 by the front cylinder 7
Since the rate of change in volume of the rear tire 9 is increasing,
The ratio of the steering angles of L and 9R to the steering angles of front tires 1L and 1R is large, and the tires are steered in the opposite phase direction.
The turning radius has been reduced, making it easier to turn around.

As the vehicle speed increases, the steering angle adjustment device 2
Spring 20c, 20 arranged in 0, 20'
Since the actuators 20d and 20d' are controlled by the controller 23, the biasing force of c' is reduced, so that the rear cylinder 15 is exerted by the front cylinder 7.
The volume change rate decreases, and the ratio of the front wheel steering angle to the rear wheel steering angle decreases. During medium/high speed driving, the in-phase and anti-phase switching device 16, 1 is activated by the output of the vehicle speed sensor.
The pistons 16b and 16b' of the front cylinder 7 are moved outward by the actuators 16e and 16e' being controlled by the controller 23, respectively, and the left chamber 7c and the right chamber 7d of the front cylinder 7 are
It is connected to the left chamber 14c and right chamber 14d of the rear cylinder. In this state, when the steering device 2 is operated and the volume of the left chamber 7c of the front cylinder 7 decreases, oil is discharged by this amount. This oil is in the left chamber 14c of the first rear cylinder 14.
The rear tires 9L, 9R are steered in the same phase direction with respect to the steering of the front tires 1L, 1R. At this time, the biasing force of the springs 20c, 20c' disposed in the steering angle adjustment devices 20, 20' and the spring 1 disposed in the first rear cylinder 14
By controlling the relationship between the biasing forces of 4e and 14e', the rear cylinder 14 by the front cylinder 7 is
By changing the rate of change in volume, the ratio between the front wheel steering angle and the rear wheel steering angle can be changed in accordance with the vehicle speed.

During medium and high-speed driving, by increasing the biasing force of the springs 20c and 20c' as the vehicle speed increases, the rear cylinder 14 is activated by the front cylinder.
The rate of change in volume is increased.

The controller 2 determines that the lateral acceleration applied to the vehicle is greater than or equal to the set acceleration based on the vehicle speed V detected by the vehicle speed sensor 21, the front wheel steering angle θ detected by the steering angle sensor 22, and the temporal change in the front wheel steering angle θ.
3, in the case of a front-wheel drive vehicle or a four-wheel drive vehicle in which the driving force is applied by the front wheels, each piston 16b,
16b' are actuators 16e and 16, respectively.
e', and the left chamber 7c and right side 7d of the front cylinder 7 are connected to the left chamber 15c and right chamber 15d of the second rear cylinder 15, respectively. In this state, when the steering device 3 is further steered and the volume of the left chamber 7c of the front cylinder 7 is reduced, the oil discharged at this time flows into the left chamber 15c of the second rear cylinder 15, and the oil discharged at this time flows into the left chamber 15c of the second rear cylinder 15. The piston 15b installed inside is moved to the right in the figure. Therefore, as shown in Figure 6, as the steering angle increases, the rear wheel turning angle decreases, the understeering characteristic that occurs in front-wheel drive vehicles is canceled out, the limit characteristics during cornering are improved, and driving stability is improved. Can turn well. In the case of a rear-wheel drive vehicle or a four-wheel drive vehicle in which driving force is applied by the rear wheels, when the controller 23 determines that the estimated lateral acceleration applied to the vehicle is equal to or higher than the set acceleration, the steering angle adjustment devices 20, 20 The pistons 20b, 20b' are moved inward by actuators 20d, 20d', respectively, and operate to further increase the biasing force of the springs 20c, 20c'. In this state, when the steering device 2 is further operated and the volume of the left chamber 7c of the front cylinder 7 decreases,
At this time, the discharged oil flows into the left chamber 14c of the first rear cylinder 14 without being absorbed by the steering angle adjustment device 20, and moves the piston 14b installed in the first rear cylinder 14 to the right in the figure. Moving. Therefore, as shown in Fig. 7, as the steering angle increases, the rear wheel turning angle increases with a larger steering ratio, and the oversteering characteristics that occur in rear-wheel drive vehicles are canceled, and the limit characteristics during cornering are reduced. This improves driving stability and makes it possible to turn with better driving stability.

Next, a second embodiment of the present invention will be described. FIG. 2 is a schematic explanatory diagram illustrating a second embodiment. Steering device 2 that steers the left and right front wheels 1L and 1R
is the steering wheel 3 as in the first embodiment.
and a rack 4a and pinion 4b that convert the rotational motion of the steering wheel 3 into linear reciprocating motion.
, left and right tie rods 5, 5' whose base ends are connected to each end of this rack 4a, one end to the tip of each tie rod 5, 5', and the other end to the left and right front wheels 1L, 1R.
The steering wheel is composed of knuckle arms 6, 6' connected to the steering wheel 3, respectively, and is configured to reciprocate the left and right tie rods 5, 5' in the vehicle width direction in response to the steering operation of the steering wheel 3, thereby steering the left and right front wheels 1L, 1R left and right. has been done.

On the other hand, the rear wheel steering device 28 that steers the left and right rear wheels 9R, 9L includes a rear wheel operating rod 27 held on the vehicle body so as to be slidable in the left and right direction, and tie rods 30 at both left and right ends of the rod 27, respectively. It has left and right knuckle arms 31, 31' connected via a shaft 30', and by moving the operating rod 27 in the axial direction, the rear wheels 9L, 9R' are steered. Operation rod 2
A rack 32 is formed in a part of the motor 7, and a pinion 33 meshing with this rack 32 is connected to a pulse motor 34.
A pair of bevel gears 35, 36 and pinion shaft 3
7, the rear wheel 9 is rotated in accordance with the direction and amount of rotation of the pulse motor 34.
Turn L and 9R.

Further, the rear wheel operating rod 27 passes through the power cylinder 38, and a piston 39 that partitions the inside of the cylinder 38 into left and right hydraulic chambers 38a, 38b is fixed to the operating rod 27, and is connected to the hydraulic chambers 38a, 38b. Hydraulic passages 41a and 41b led from a control valve 40 provided around the pinion shaft 37 are connected, respectively, and a pump 43 driven by a motor 42 is connected between the control valve 40 and the pump 43. Hydraulic supply passage 4
4 and a return passage 45 are provided. Here, the control valve 40 operates according to the rotational force applied to the pinion shaft 37 when the pulse motor 34 rotates, and the control valve 40 operates from the pump 43 to the hydraulic pressure supply passage 4.
4 is introduced into either one of the hydraulic chambers 38a or 38b of the power cylinder 38 depending on the direction of the rotational force, and the hydraulic pressure supplied through the
Alternatively, it functions to return the hydraulic oil in 38a to the pump 43 via the return passage 45. Therefore, the pulse motor 34 operates the bevel gears 35,
When the operating rod 27 is moved in the axial direction via the pinion shaft 37, the pinion 33, and the rack 32, the hydraulic pressure introduced into the power cylinder 38 assists the movement of the operating rod 27 via the piston 39.

A vehicle speed signal A output from a vehicle speed sensor 47 and a front wheel turning angle B from a front wheel turning angle sensor 48 that detects the front wheel turning angle are input to the controller 46 . The controller 46 outputs signals C and D based on these input signal values, and these signals C and D drive the pulse motor 34 and the pump drive motor 42, respectively.

Next, the configuration of the controller 46 will be explained using FIG. 3. A vehicle speed signal A from the vehicle speed sensor 47,
The front wheel turning angle signal B from the front wheel turning angle sensor 48 is input to the rear wheel turning angle calculating section 51. This calculation unit 51 first detects the vehicle speed detected by the vehicle speed sensor 47, the front wheel steering angle detected by the front wheel steering angle sensor 48, and the temporal change in the front wheel steering angle. Based on the calculated front wheel turning angular velocity, it is determined whether the estimated lateral acceleration that the vehicle body receives is equal to or higher than the specified acceleration based on the above-mentioned formula, and if it is equal to or lower than the set acceleration,
Based on the vehicle speed and the front wheel steering angle, the calculation unit 51 increases the rear wheel steering angle in an opposite phase as the front wheel steering angle increases at low speeds, and increases the rear wheel steering angle at high speeds based on the vehicle speed and the front wheel steering angle. Calculation is made so that the increase is in the same phase as the increase. Therefore, it is possible to reduce the turning radius at low speeds, and to change lanes smoothly and with good maneuverability at high speeds.

The target signal E carrying the target rear wheel turning angle calculated by the rear wheel turning angle calculating section 51 in this manner is input to the driver 52 of the pulse motor 34 . Upon receiving this signal E, the driver 52 turns the rear wheels 9L, 9
A pulse signal A is output to rotate the pulse motor 34 so that L' is set to the target rear wheel turning angle. When this pulse signal A is input to the pulse motor 34, the pulse motor 34 rotates by the number of times corresponding to the target rear wheel turning angle, and the The rear wheel operating rod 27 is moved in the axial direction. As a result, the rear wheels are steered to the target rear wheel turning angle.
At this time, the power cylinder 38 is activated to assist the movement of the operating rod 27.

During high-speed driving, that is, when the front wheels and rear wheels are being steered in the same phase, when the calculation unit 51 determines that the estimated lateral acceleration to which the vehicle is subjected is greater than or equal to the set lateral acceleration, the rear wheels are steered. In the case of a front-wheel drive vehicle or a four-wheel drive vehicle in which the driving force is applied by the front wheels, the target rear wheel turning angle calculated by the angle calculation unit 51 is calculated when the estimated lateral acceleration to which the vehicle is subjected is less than the set lateral acceleration. The steering ratio is set to be smaller than the steering ratio. For rear-wheel drive vehicles or four-wheel drive vehicles in which driving force is applied by the rear wheels, the steering ratio is set to be larger than the steering ratio when the lateral acceleration received by the vehicle is less than the set lateral acceleration. .

Furthermore, in each of the above embodiments, instead of simply converting a vehicle with oversteering characteristics or understeering characteristics into a vehicle with neutral steering characteristics, as described above, a vehicle with understeering characteristics is changed to a vehicle with oversteering characteristics. It is possible to change the vehicle to have sportiness, or to change the vehicle to have oversteering characteristics, and to have stable maneuverability.

(Effects of the Invention) The present invention provides the following advantages:
Based on the vehicle speed detected by the vehicle speed sensor and the front wheel turning angle and front wheel turning angular velocity detected by the front wheel turning angle sensor, it is substantially determined that the estimated lateral acceleration to which the vehicle body is subjected is greater than or equal to the set lateral acceleration. and,
Since the steering angle of the rear wheels, that is, the steering ratio, which is determined according to the vehicle speed or the steering angle of the front wheels corresponding to the vehicle speed, is changed, there is no response delay that would occur when using an acceleration sensor. Since the steering ratio is changed and understeering characteristics or oversteering characteristics are eliminated, high limit characteristics and good handling characteristics can be obtained during cornering.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are schematic diagrams showing first and second embodiments of the four-wheel steering device of the present invention, respectively;
FIG. 3 is an internal configuration diagram of the controller in FIG. 2, FIG. 4 is a graph showing the relationship between lateral acceleration and sideslip angle of non-driving tires and driving tires, and FIG.
The figure is a graph showing the steering characteristics of a front wheel drive vehicle and a rear wheel drive vehicle, and FIGS. 6 and 7 are graphs showing the steering angle and rear wheel turning angle characteristics of the front wheel drive vehicle and the rear wheel drive vehicle according to the present invention, respectively. This is a graph showing. 1L, 1R...front wheel, 2...steering device, 7...front cylinder, 9L, 9R...rear wheel, 14...first rear cylinder, 15...second
Rear cylinder, 16, 16'... In-phase and negative phase switching device, 20, 20'... Rudder angle adjustment device, 21, 4
7... Vehicle speed sensor, 22, 48... Rudder angle sensor,
23, 46...Controller, 27...Operation rod, 38...Power cylinder, 42...Motor,
43...Pump.

Claims (1)

[Claims] 1 A steering device that steers the front wheels, a rear wheel steering device that steers the rear wheels in the same phase direction using a predetermined steering ratio according to the front steering angle steered by the steering device, and detects vehicle speed. a front wheel steering angle sensor that detects the steering angle of the front wheels; a temporal relationship between the vehicle speed detected by the vehicle speed sensor, the front wheel steering angle and the front wheel steering angle detected by the front wheel steering angle sensor; A four-wheel steering system for a vehicle, comprising a correction means for changing the steering ratio when an estimated lateral acceleration obtained from a front wheel turning angular velocity obtained by detecting a change is greater than or equal to a set lateral acceleration.