JPH0224270A - Steering device for vehicle - Google Patents

Abstract

PURPOSE:To improve stability at the time of a two-wheel-steering operation by providing a rigidity variable means for varying the steering rigidity of front wheels to a soft side and varying the steering rigidity of the front wheels to the soft side at the time of detecting the stoppage of function of a rear-wheel steering means. CONSTITUTION:A four-wheel-steering device for shifting from a two-wheel- steering (2WS) condition to a four-wheel-steering (4WS) condition and vice versa has a steering system (b) for steering front wheels and a rear-wheel- steering means (a) for steering rear wheels in accordance with at least the steering physical quantity of the front wheels. In this case, a rigidity variable means (c) for varying the steering rigidity of front wheels is provided on the steering system (b) of the front wheels. Also, by providing a detecting means (d) for detecting the stoppage of function of the rear-wheel-steering means (a), when this detecting means (d) detects the stoppage of function of the rear- wheel-steering means (a), the rigidity variable means (c) is controlled via a signal output means (e) to vary the rigidity of the steering system (b) to a soft side.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a steering device for a vehicle, and particularly to a steering device for a vehicle equipped with a four-wheel steering system.

(Prior Art) A mechanism for causing a turning behavior in a vehicle is explained as follows.

In other words, (1) When the steering wheel is operated, (n) The movement of the steering wheel is transmitted to the tires via the steering mechanism, (III) The orientation of the tires changes and a slip angle of 5AGL is applied to the tires, (IV) This causes , a cornering force CF is generated on the tire as shown by the following formula. (Vl) As a result, the vehicle begins a turning motion around the Z axis.

By the way, if there is a time delay between (1) and (II), that is, if the stiffness of the steering mechanism is low, the movement of the steering wheel will be mildly transmitted to the tires, and the turning characteristics will tend to understeer. This is preferable because it improves turning stability, but excessively mildness also deteriorates high-speed straight running performance. On the other hand, increasing the steering stiffness improves high-speed straight-line performance, but at the same time, the turning characteristics become more neutral (oversteer in some cases) and sharp turning response can be obtained. It becomes difficult.

The above turning mechanism has been described focusing only on the front wheel side, but the actual turning mechanism is also deeply involved in the rear wheel side. The turning stability of the vehicle, including the front and rear wheels, is expressed by a stability factor Ks expressed by the following formula (2), and if this Ks is small, there is a risk of spinning in some cases.

However, M: Vehicle mass 2: Wheelbase a: Center of gravity - front wheel contact point distance b: Center of gravity - rear wheel contact point distance C□: Front wheel equivalent cornering power C□: Rear wheel equivalent cornering power Also, CPF and CPR is calculated by the following formulas, ■ and ■, respectively.
It is expressed according to

・・・・・・■ However, DF: Front wheel compliance steer due to lateral force DR: Rear wheel compliance steer due to lateral force C□′: Cornering power of the front tire alone C□′: Cornering of the rear tire alone Power Lc: Front wheel caster trail TP: Front wheel pneumatic trail Ks Steering rigidity For example, a normal two-wheel steering system that steers only the front wheels (
2WS), when a slip angle of 5AGL is applied to the tire by operating the steering wheel, this SAG
The cornering force on the front wheels, which is the product of L and CPF, will increase when the vehicle enters a turn, but since this kind of turning operation mainly operates on the CFF side, increasing CPF unnecessarily will result in a decrease in Ks. This is not preferable in terms of stability. Furthermore, the index of maneuverability (ease of maneuverability) is expressed by the steering capacity Cs shown by the following formula 〇, but with 2WS, which mainly increases the CFF side, there is a limit to the improvement of maneuverability.

M Therefore, when driving at high speed, the rear wheels will be activated depending on the steering wheel operation.
By giving a steering angle in the same phase as the front wheel steering angle, CPI (
A four-wheel steering system (hereinafter referred to as 4W5) that apparently increases rear wheel equivalent cornering power (rear wheel equivalent cornering power) than a normal 2WS has been put into practical use.

As a conventional 4WS of this type, for example, JP-A-61-
There is a system described in Japanese Patent No. 220974, and this system calculates the steering angle control value for the rear wheels based on the ratio of the front wheel steering angle and the rear wheel steering angle at the time of turning derived from the vehicle characteristics. The rear wheels are steered by driving the steering angle actuator according to the control value.

By the way, this type of 4WS increases Cs and improves steering performance, and the stability of the vehicle seems to be at an appropriate value K.
In order to set s, it is desirable to set the value of cpv to be larger than the normal 2WS.

(Issues to be solved by the invention) However, in such conventional 4WS, when turning, the equivalent cornering power (CPF) of both the front and rear wheels is
, C□) according to the cornering force (C□, CF
II), which applies yawing torque to the vehicle and causes it to turn, so if, for example, the front wheel steering angle input signal fails and becomes zero, the vehicle will temporarily 2WS, but in this case, sufficient CFR cannot be obtained, so C7. (equivalent cornering power on the front wheel side) increases relatively compared to when running in 4WS, and as a result, Ks decreases and stability is lost. Specifically, as mentioned above, CPF is set to 2
Since it is set to a larger value than that of a WS vehicle, it causes problems such as the turning characteristics of the vehicle changing toward neutral steer or oversteer.

On the other hand, if we set the CPF to a small value similar to that of a normal 2WS vehicle in anticipation of the above-mentioned problems when switching from 4WS to 2WS, in the end the K when operating at 4WS
There was a problem that s (stability) and Cs (manoeuvrability) could not be made sufficient.

(Objective of the Invention) Therefore, the present invention aims to increase the steering rigidity while operating in 4WS, and when shifting from 4WS to 2WS.
By lowering the steering stiffness, the CFF required for 4WS and the CtaF required for 2WS can be set to be appropriate for each, thereby improving stability during 2WS operation.
The aim is to achieve both stability and improved maneuverability during 4WS operation.

(Means for Solving the Problems) In order to achieve the above object, the vehicle steering device according to the present invention includes a rear wheel steering means a that applies a steering angle also to the rear wheels according to at least the steering physical quantity of the front wheels, and a predetermined control signal. a stiffness variable means C for changing the stiffness of the front wheel steering system to a softer side when input is input, and a detecting means d for detecting a functional stoppage of the rear wheel steering means a; When a malfunction is detected, the stiffness of the steering system is changed to a soft side (signal output means e for outputting a predetermined control signal) is provided.

(Function) According to the present invention, the function of the rear wheel steering means is stopped and the 2W
When shifting to S, the stiffness of the front wheel steering system is changed to the soft side (that is, the stiffness is reduced).

Therefore, in the previous equation ■, the value of A becomes smaller and CP
F decreases, and Ks during 2WS operation increases (previous formula ■
reference). As a result, the turning characteristics of the vehicle are maintained on the understeer side, and stability during 2WS operation is improved.

Also, if the function of the rear wheel steering means has not stopped (4W
During S operation), the steering stiffness is in a high state, and in this case, sufficient C□ required for 4WS is obtained, the values of Ks and Cs become large, and stability and maneuverability are improved. It will be planned.

(Example) Hereinafter, the present invention will be explained based on the drawings.

2 to 4 are diagrams showing an embodiment of the vehicle steering device according to the present invention, and are examples in which the present invention is applied to a vehicle equipped with a four-wheel steering system of the steering angle steering angle type.

First, the configuration will be explained. In FIG. 2, IL, 1 is the left and right front wheels, 2L, 2 is the left and right rear wheels, respectively, and left and right front wheels IL, 11, is the steering wheel from the steering wheel 4 via the steering gear mechanism (steering system) 3. It is steered by receiving input.

A steering angle θ (physical steering quantity) of the steering wheel 4 is detected by a steering angle sensor 5. Left and right rear wheels 2L, 2
．． is suspended on a rear suspension member 9 by a rear suspension device 8 including transverse links 6L, 61 and upper links 7L, 7R, and is rotated by a side rod 11L2111 and an actuator 12 that connect the rear wheel knuckle arm IOL, 10m. It is possible to steer. The actuator 12 is
For example, a spring center type double acting hydraulic cylinder is used, and its two chambers 12L and 12m are connected to pipes t3t and 1, respectively.
3R is connected to the electromagnetic proportional pressure valve 14. The electromagnetic proportional pressure valve 14 further includes a hydraulic line 17 from a hydraulic source including a hydraulic pump 15 and a reservoir tank 16 .
18 are connected to each other. The electromagnetic proportional pressure valve 14 is, for example, a spring center type electromagnetically controlled three-position valve, and when both solenoids 14L and 14R are de-energized, the pipes 13L and 13R are in a pressure-free state, and when the solenoid L4t is energized, the amount of energized current is changed. Proportional oil pressure is applied to line 13. When the solenoid 14i is energized, a hydraulic pressure proportional to the amount of energized current is supplied to the conduit 13R. Both solenoids 14t
, 14* are electronically controlled by a controller CT.

The controller CT is constituted by, for example, a microcomputer, and signals from a vehicle speed sensor 29 that detects the steering angle θ from the aforementioned steering angle sensor 5 and the vehicle speed V are added to the controller CT. Controller C
T executes a program process for calculating a rear wheel steering control value according to these signals θ and ■. Examples of such processing include the following. In other words, by referring to the steering angle ratio (δr/δr) map between the front wheel steering angle δf and the rear wheel steering angle δr derived from preset vehicle characteristics, the optimum value corresponding to the current θ and ■ is determined. The rear wheel steering control value X is determined, and the actual operation amount X' is determined by taking into account the transfer function 1/G(S) that compensates for the response delay of the actuator 12, and this is applied to the electromagnetic proportional pressure valve 14. Add. Note that the above-mentioned steering angle ratio (δr/δf) map is such that the front and rear wheels are steered in opposite phases in a low speed range, and are steered in the same phase in a medium/high speed range. As a result of such processing, in the low speed range, the rear wheel steering angle operation amount is output in the opposite phase direction according to the magnitude of θ and ■ at that time, and in the middle and
In the high speed range, the rear wheel steering angle operation amount is output in the same phase direction according to the magnitudes of θ and ■ at that time. That is, the controller CT, together with the actuator 12 and the electromagnetic proportional pressure valve 14, has a function as rear wheel steering means.

The controller CT performs the above processing and also performs fail mode determination processing described below. That is, in addition to the above-mentioned θ and ■, the controller CT receives a signal from the fund brake switch 30 that generates the foot brake depression signal FLLK when the foot brake is depressed, and a parking brake operation signal pa when the parking brake is operated.
A signal from the parking brake switch 31 that generates x and a signal from the gear position switch 32 that generates gear neutral signals G and 4 when the gear position of the transmission is in the neutral position are input, and the controller CT are each of these signals, F BK% P mKs G
In accordance with N and ■, execute the fail mode processing program described later, fail mode I indicates that the rear wheel steering function has stopped, fail mode ■ indicates that some functions have stopped, and confirm that there is no function stop. Then, when fail mode I is determined, a stiffness operation signal Sc is output to the solenoid actuator 33. Solenoid actuator 3
3 operates according to this SC, and the steering gear mechanism 3
The rigidity of the rack mount insulator 3b that elastically supports the gear housing 3a on the vehicle body side is adjusted to the soft side. Therefore, the controller CT has a function as a detection means and a signal output means, and the solenoid actuator 33 and the rack mount insulator 3b have a function as a rigidity variable means.

FIG. 3 is a configuration diagram of main parts including the solenoid actuator 33, gear housing 3a, and rank mount insulator 3b. In Fig. 3, 34 is the vehicle body;
5 is a rigid bracket attached to the vehicle body 34, and the rank mount insulator 3b is attached to the rigid bracket 35.
The gear housing 3a is elastically coupled to the gear housing 3a, and has a fluid chamber A filled with fluid (for example, hydraulic oil). The fluid chamber A is operated so that the internal pressure thereof is lowered in accordance with the operation of the solenoid actuator 33.

That is, when the solenoid actuator 33 is activated, the rigidity of the rack mount insulator 3b is changed to the soft side. Note that 3c in FIG. 3 is a rank axis.

Next, the effect will be explained.

FIG. 4 is a flowchart of a fail mode determination processing program executed in the controller CT. Note that this program is executed once at a predetermined time by an interrupt or the like. First, an abnormality in θ is determined using Pl. This can be determined if, for example, a change in θ is not observed for a predetermined period of time even though the driver is driving (judging by no V), or if the θ does not occur during normal steering operation.
It is sufficient to determine that there is an abnormality when a change trend is observed. If there is an abnormality in θ, it is no longer possible to perform normal rear wheel steering, so proceed to P2 and set fail mode I.
, and the vehicle is operated as 2WS. Then,
A stiffness operation signal S is sent to the solenoid actuator 33 at P.
c is output to perform control to reduce the stiffness (KI?) of the front wheel steering system.

As a result, the equivalent cornering power OFF of the front wheels decreases (see Part 2), and KS increases, thereby improving stability during 2WS operation.

On the other hand, if θ is normal, the abnormality of ■ is determined in P4. As a method for this determination, for example, it may be determined that an abnormality occurs when the width of change in ■ exceeds the acceleration/deceleration capability of the vehicle, or when ■ is not zero even though the vehicle is stopped. Note that the determination as to whether the vehicle is stopped may be made according to F□ and PIIK%GN. In other words, in the case of a vehicle with an automatic transmission, when the vehicle is stopped, the foot brake should be depressed in preparation for the creep phenomenon, or the parking brake should be operated, or if both brakes are not operated. The gear position should be in neutral. Therefore, it is possible to determine whether the vehicle is stopped from these brakes or the neutral position. Furthermore, in the case of a vehicle with a manual transmission, depression of the clutch pedal may be added as a criterion.

If the abnormality in ■ is determined, θ is normal, so
At P, determine the amount of steering angle of the rear wheels according to θ so that the steering angle ratio of the front and rear wheels is maximum and in phase (fail mode ■)
. Although this reduces turning performance at low speeds,
The turning characteristics at high speeds are controlled to be on the safe side. Then, at P, the output of the stiffness operation signal Sc is stopped, and control is performed to increase the stiffness of the front wheel steering system. As a result, 4
CPF increases during WS operation, and in combination with CPII, Ks and Cs change to the increasing side, improving stability and maneuverability. Note that if the abnormality (■) is not determined in P4, the process proceeds to P7, and normal 4WS control is executed based on normal θ and V. In this case, the rigidity of the front wheel steering system is set to be high.

As described above, in this embodiment, when the 4WS function is lost due to an abnormality in θ and the 4WS operates as a 2WS, the internal pressure of the fluid chamber A in the rack mount insulator 3b is lowered to lower the rigidity of the front wheel steering system. . Therefore, the CPF during 2WS operation can be reduced, and Ks can be increased to improve stability.

Further, during the 4WS operation, the indoor pressure of the fluid chamber A in the rack mount insulator 3b is increased, and the rigidity of the front wheel steering system is increased to increase the CFF. Therefore, in combination with CPII during 4WS operation, Ks and Cs
(Can be made thicker, which can improve stability and maneuverability.)

In other words, it is possible to obtain CPF suitable for each of 4WS and 2WS, and KS (stability) when operating in 4WS.
and Cs (manoeuvrability) can be made sufficient.

In the above embodiment, the fluid sealed in the fluid chamber A of the rank mount insulator 3b is, for example, hydraulic oil, but ER fluid may also be used as the fluid. In other words, the viscosity of an ERR body can change from fluid to almost solid depending on the magnitude of the applied electric field, so the ER
While the stiffness of the steering can be increased while the viscosity of the fluid is substantially solid, the stiffness of the steering can be lowered by making the viscosity of the fluid a fluid. However, when ER fluid is used, it goes without saying that an electric field generator is required in place of the solenoid actuator 33.

Further, in the above embodiment, the gear housing 3a is connected to the vehicle body 34.
Although an example in which the rigidity of the rack mount insulator 3b supported by the rack mount insulator 3b is changed is shown, the present invention is not limited to this. In short,
The rigidity of the front wheel steering system should be lower during 2WS operation,
For example, as is known from Utility Model Application No. 60-175773, the steering shaft is divided into two parts, and the divided parts are connected by an elastic body (or a member such as a torsion bar that can be slightly torsionally deformed). A clutch (for example, a dog clutch) is interposed between the two divided steering shafts, and the clutch is in contact during 4WS operation.
The clutch may be disconnected during the 2WS operation. Even in this case, the stiffness of the steering system during 2WS can be reduced.

Furthermore, in the above embodiment, an example was shown in which the steering angle θ was specifically used as the steering physical quantity of the front wheels, but a value obtained by adding the steering angular velocity θ to this is expressed as θ to tθ (K and L are constants). Alternatively, the steering torque T or the like may be used.

(Effects of the Invention) According to the present invention, the steering rigidity of the front wheels is made high during 4WS operation, and when shifting from 4WS to 2WS,
The steering rigidity of the front wheels can be lowered. Therefore, the CP required for each of 4WS and 2WS is 4W
It can be made sufficient for both S and 2WS, and as a result, it is possible to achieve both improved stability during 2WS operation and improved stability and maneuverability during 4WS operation.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram of the present invention, Figs. 2 to 4 are diagrams showing an embodiment of a vehicle steering system according to the present invention, Fig. 2 is an overall configuration diagram thereof, and Fig. 3 is a schematic diagram thereof. FIG. 4 is a flowchart of the fail mode determination processing program. 3... Steering gear mechanism (steering system), 3b... Rack mount insulator (rigidity variable means), 12... Actuator (rear wheel steering means), 1
4... Electromagnetic proportional pressure valve (rear wheel steering means), 33
... Solenoid actuator (rigidity variable means), CT ... Controller (rear wheel steering means, detection means, signal output means).

Claims (1)

[Scope of Claims] Rear wheel steering means (a) that applies a steering angle to the rear wheels according to at least the steering physical quantity of the front wheels; and (b) that controls the stiffness of the front wheel steering system when a predetermined control signal is input. a rigidity variable means (c) for changing the stiffness to the soft side; a detection means (d) for detecting a functional stoppage of the rear wheel steering means (a); and signal output means (e) for outputting a predetermined control signal to change the stiffness of the steering system (b) to the soft side.