JPS61207274A - Power steering device for 4-wheel-drive-vehicle - Google Patents

Abstract

PURPOSE:To prevent missing of steering feeling upon changeover by differentiating the ratio of the assist steering force to be produced under 2-wheel-drive traveling against the steering force from the ratio to be produced under 4-wheel- drive traveling thereby preventing variation of steering characteristic upon changeover. CONSTITUTION:A transfer 23 will changeover between 2-wheel-drive and 4-wheel- drive while a switch 24 for detecting the operating position of an operating lever 23a is provided on said lever 23a. Said switch 24 is connected to a control circuit 21 to provide a signal for indicating whether said lever 23a is at 2-wheel- drive position or at 4-wheel-drive position to the control circuit 21. The control circuit 21 will control power supply to the solenoid 20a of a flow control valve 20 on the basis of the output signal from the switch 24 such that power is fed to said solenoid 20a only when said lever 23a is at 2-wheel-drive operating position.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention is applicable to □ two-wheel drive driving in which only one of the front wheels or rear wheels is driven, and four-wheel drive driving in which driving is performed by driving both the front wheels and the rear wheels. This invention relates to a power steering system for a four-wheel drive vehicle that is capable of switching between two-wheel drive and four-wheel drive; It relates to a power steering device.

(Prior Art) Even in a four-wheel drive vehicle that can switch between two-wheel drive and four-wheel drive, the front wheels are generally set as steering wheels, and the Or JP-A-5
A hydraulic power steering device as described in Japanese Patent No. 5-79754 and the like is provided.

(Problem to be solved by this invention) However,
The above-mentioned Japanese Patent Application Laid-open No. 56-99859 or Japanese Patent Application Laid-Open No. 1983
Conventional power steering devices such as those described in Publication No. 5-79754 merely control the steering assist force generated depending on driving conditions such as vehicle speed. It was difficult to obtain a satisfactory steering feel in both cases when driving. In other words, in a four-wheel drive vehicle, the steering resistance differs between two-wheel drive and four-wheel drive. In a 4-wheel drive vehicle that is constantly driven, the driving force is also distributed to the front wheels, so the self-lining torque during steering increases, and as shown in Figure 3, the steering resistance is greater than when driving with 2-wheel drive (dashed line). is larger when driving in four-wheel drive (solid line); conversely, in four-wheel drive vehicles that constantly drive the front wheels, such as those based on front engine front-wheel drive vehicles (FF vehicles), the distribution of driving force to the front wheels decreases. Therefore, the self-lining torque during steering decreases, and the steering resistance increases during two-wheel drive driving. Therefore, a four-wheel drive vehicle equipped with the conventional power steering system as described above has a problem in that the steering feel suddenly changes when switching between two-wheel drive and four-wheel drive. In particular, in 4-wheel drive vehicles based on FR vehicles, when switching from 2-wheel drive to 4-wheel drive, the driving force applied to the front wheels, which are the steering wheels, is transmitted to the steering wheel, so the steering feel The changes were also significant.

For reference, in a four-wheel drive vehicle based on an FF vehicle, driving force is constantly transmitted to the front wheels, which are steering wheels, so the change in steering feel is slight.

(Means for Solving the Problems) The present invention has been made with the aim of solving the above problems. Attached to a four-wheel drive vehicle that can switch between four-wheel drive and four-wheel drive driving, which drives both wheels, it adds steering assist force generated by an actuator according to the steering force to the manual steering force applied to the steering wheel. In a power steering system for a four-wheel drive vehicle that transmits power to a steering wheel set on at least one of a front wheel or a rear wheel, a driving wheel discriminating means for determining whether the vehicle is traveling in two-wheel drive or four-wheel drive;
A steering assist force changing means capable of changing the ratio of the steering assist force generated by the actuator to the steering force, and the steering assist force changing means are driven based on the output signal of the drive wheel discriminating means, and the steering assist force changing means is driven based on the output signal of the drive wheel discriminating means, and the steering assist force changing means is driven based on the output signal of the drive wheel discriminating means. Adjustment means is provided for changing the ratio of the steering assist force to the steering force depending on whether the vehicle is running in wheel drive.

(Function) According to this power steering system for a four-wheel drive vehicle, the ratio of the steering assist force to the steering force changes depending on whether the vehicle is traveling in four-wheel drive or two-wheel drive. There is also no change in steering feel when switching between driving and driving. That is,
For example, in a 4-wheel drive vehicle based on an FR vehicle in which the front wheels are set as steering wheels, the above ratio is increased during 4-wheel drive driving when steering resistance increases, so the driver has to adjust the steering feel. This eliminates the feeling and improves steering performance.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a diagram showing an embodiment of the power steering system for a four-wheel drive vehicle according to the present invention, which is commonly applied to a four-wheel drive vehicle based on an FR vehicle.

First, to explain the configuration, in the figure, 11 is a steering handle, and the steering handle 11 is connected via a steering shaft 12 to a rack-and-pinion type steering gear mechanism housed in a gear box 13. . Also inside the gearbox 13 is a steering handle 11.
A known control valve for controlling pressure fluid (pressurized oil) according to the steering direction and steering force is housed, and further,
A hydraulic actuator 14 is provided in the rack 15 and is supplied with pressure oil from this control valve to generate a steering assist force.

A supply conduit 17 is connected between the control valve in the gear box 13 and the discharge port of the pump 16.
Also, a return conduit 18 is provided between the suction boat of the pump 16 and the suction boat of the pump 16.
is piped. The pump 16 has a built-in reservoir tank, pressurizes the oil flowing back from the return conduit 18, and discharges it to the control valve via the supply conduit 17. The supply side conduit 17 and the return side conduit 18 are short-circuited by a bypass pipe 19 in which an electromagnetic flow control valve 20 is interposed. The flow rate control valve 20 has a solenoid 20a connected to a control circuit (corresponding to an adjusting means) 21, and as shown in FIG. is maintained at the flow rate Q8, and
When the solenoid 20a is de-energized (OFF), the pressure oil flowing through the bypass pipe 19 is set to a flow rate Q, (Q2) smaller than the flow rate Q1.
Q8). Note that the bypass pipe 19 and the flow control valve 20 constitute a steering assist force changing means 22.

The yoke is a transfer for switching between two-wheel drive and four-wheel drive, and the operation lever yaw a of the transfer yoke is provided with a switch (driving wheel discriminating means) 24 for detecting the operating position of the operation lever 23a. This switch U is connected to the control circuit 21 and outputs to the control circuit 21 a signal indicating whether the operating lever 23a is in the operating position of two-wheel drive or four-wheel drive. The control circuit 21 controls the energization of the solenoid 20a of the flow control valve 20 based on the output signal of the switch 24, and turns on the solenoid 20a of the flow control valve 20 only when the control lever 23a is in the two-wheel drive operating position. Turn on electricity.

Next, the effect will be explained.

If the operating lever 233 of the transfer 23 is now operated to the two-wheel drive operating position and the vehicle is running in two-wheel drive driving only the rear wheels, the switch 24 outputs an output that detects the operating position of the operating lever 23a. Control circuit 2 based on the signal
1 energizes the solenoid 20a of the flow control valve 20.

Therefore, a part of the flow rate Q1 of the pressure oil discharged by the pump 16 (for convenience, let Qo be the flow rate) is recirculated through the bypass pipe 19 without being supplied to the control valve.
The hydraulic actuator 14 generates a steering assist force corresponding to the pressure oil flow Ji (Qo-Q□) supplied to the control valve.

Next, when the operation lever 23a of the transfer n is operated to the four-wheel drive operation position and the vehicle shifts to a four-wheel drive state in which the front and rear wheels are driven, the control circuit similarly operates based on the output signal of the switch 24. 21 stops energizing the solenoid 20a of the flow control valve 20.

Therefore, of the total flow rate Qo of pressure oil discharged by the pump 16, a part of the flow rate Q2 is returned via the bypass pipe 19, and the control valve is supplied with the flow rate (Qo
-QI), the hydraulic actuator 14 is supplied with pressure oil with a larger flow rate (Qo -Q2) than the pressure oil flow rate (Qo - Q2).
A larger steering assist force is generated than during the above-mentioned two-wheel drive driving corresponding to 2).

In this way, according to the power running device of this four-wheel drive vehicle,
During four-wheel drive driving, where steering resistance increases, the steering assist force generated by the hydraulic actuator 14 also increases in response to the increase in steering resistance. When switching to two-wheel drive driving, the steering characteristics do not suddenly change, and the driver does not feel any discomfort.

In the above-described embodiments, the hydraulic actuator generates the steering assist force, but it goes without saying that the present invention can be achieved even in an actuator such as an electric motor that generates the steering assist force. None. In addition, in order to apply the present invention to a power steering system for a four-wheel drive vehicle based on a front-wheel drive vehicle, the steering assist force generated during two-wheel drive driving must be increased, contrary to the above embodiment. This is as mentioned above.

Furthermore, it goes without saying that the present invention is applicable to vehicles in which both the rear wheels and the front wheels can be steered, such as part-time four-wheel drive vehicles based on front engine front wheel drive vehicles (FF vehicles). Then, the ratio of the rear wheel steering assist force to the steering force is set to be larger during four-wheel drive than during two-wheel drive.

(Effects of the Invention) As explained above, according to the power steering system for a four-wheel drive vehicle according to the present invention, the ratio of the steering assist force to the steering force generated during two-wheel drive driving and the Since the ratio of the generated steering assist force to the steering force is made different so that the steering characteristic does not change at the time of switching, the steering feeling is not impaired at the time of switching, and the steering performance can be improved.

[Brief explanation of drawings]

1 to 3 are diagrams showing one embodiment of a power steering system for a four-wheel drive vehicle according to the present invention, in which FIG. 1 is a schematic overall view, and FIG. 2 is a flow control valve. Diagram showing flow characteristics,
FIG. 3 is a graph showing a comparison of steering resistance with respect to steering angle in a four-wheel drive vehicle based on an FR vehicle when traveling in two-wheel drive and when traveling in four-wheel drive.

Claims (1)

[Claims] It is installed on a four-wheel drive vehicle that can switch between two-wheel drive, in which only one of the front wheels or rear wheels is driven, and four-wheel drive, in which both front and rear wheels are driven. In a power steering system for a four-wheel drive vehicle, the steering assist force generated by an actuator is added to a manual steering force applied to a steering wheel and transmitted to a steering wheel set at at least one of a front wheel or a rear wheel. , a drive wheel discriminating means for discriminating whether running in two-wheel drive or four-wheel drive; a steering assist force changing means capable of changing the ratio of the steering assist force generated by the actuator to the steering force; and the drive wheel discriminating means. The vehicle is characterized by further comprising an adjusting means for driving the steering assist force changing means based on an output signal and changing the ratio of the steering assist force to the steering force depending on whether the vehicle is traveling in two-wheel drive or four-wheel drive. Power steering device for four-wheel drive vehicles.