JPH0585382A - Power steering - Google Patents

Abstract

PURPOSE:To provide a power steering allowing stable steering feelings to be obtained with a little steering torque change caused by the ground load change of steered wheels. CONSTITUTION:The higher the vehicle speed, the more becomes the exciting current quantity of a solenoid valve to reduce assisting torque. The ground load W of front wheels, steered wheels, is computed from the oil pressure of a hydraulic cylinder forming a suspension, and the initial ground load Wo in the case of an ignition switch being turned on is subtracted to compute variation W (S1-S3). A solenoid exciting current correction factor I1 is computed on the basis of the variation W (S4), and a solenoid exciting current I2 determined according to the vehicle speed V is corrected (S7). The correction factor I1 is so set as to make assisting toque larger as the ground load W is larger than the initial ground load Wo and to make assisting torque smaller as the ground load W is smaller than the initial ground load Wo. Accordingly, even if the ground load is increased/decreased, the change of steering torque caused by this increase/decrease is reduced or nullified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering system, and more particularly to control of steering torque when a ground load on a steered wheel changes.

[0002]

2. Description of the Related Art Generally, a power steering apparatus has an assisting means for assisting a steering torque applied to a steering wheel and is configured to reduce a steering load on a driver. In such a power steering device, the assisting torque is usually determined based on the steering torque and the vehicle speed. The assist torque is increased as the steering torque increases and the vehicle speed decreases. On the other hand, in the power steering apparatus described in Japanese Patent Laid-Open No. 61-60377, it is proposed that the assisting torque is reduced and the steering is made heavier as the vehicle's carrying load increases, thereby ensuring traveling stability. There is.

[0003]

However, this causes a problem that the steering feeling is deteriorated.
For example, if the vehicle bounces or rebounds due to the unevenness of the road surface, or if load movement occurs due to acceleration or deceleration, the ground contact load will change each time, and the apparent load will decrease or increase. The steering feeling is frequently changed by increasing and decreasing the assisting torque, and the maneuverability becomes unstable. Although this problem is lightened in a normal power steering device in which the assisting torque is not increased or decreased by the load, it is not absent. It is an object of the present invention to provide a power steering device that requires less change in steering torque even when the ground load changes.

[0004]

In order to solve the above problems, the present invention provides a power steering system including the assisting means, including: (a) a ground load detecting means for detecting a ground load of a steered wheel; b) When the ground load detected by the ground load detecting means changes, the ground load changing time control means for changing the assisting torque of the assisting means in a direction to reduce the change of the steering torque due to the change is provided. That is the summary.

[0005]

In the power steering device configured as described above, the steering resistance is reduced if the ground load of the steered wheels is reduced by the load movement due to the bouncing or acceleration / deceleration of the vehicle. The assisting torque of the assisting device is reduced by the control device, the reduction of the steering torque is suppressed, and the change in the steering feeling is reduced. Further, if the ground contact load of the steering wheel increases due to vehicle rebound or load movement, the assisting torque of the assisting means is increased, the increase in steering torque due to the increase in the ground contact load is reduced, and the change in steering feeling is reduced. To be done.

[0006]

As described above, according to the present invention, even if the ground load of the steered wheels changes, the assisting torque is changed so as to reduce the change in the steering torque due to the change, so that the steering torque changes greatly. It is possible to obtain a stable steering property without performing.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. In FIG. 2, reference numeral 10 denotes a steering wheel, which is attached to one end of the steering shaft 12. The steering torque applied to the steering wheel 10 is the power cylinder 14 and the rotary valve 1.
6 and the solenoid valve 18 assisting means.

When the steering wheel 10 is rotated, the input shaft 22 constituting the steering shaft 12 is rotated, and the torsion bar is twisted by the rotation resistance of the output shaft connected to the input shaft 22 by the torsion bar. As a result, the rotary valve 16 is switched, and the power cylinder 14
One hydraulic chamber is communicated with the pump 24, and the other hydraulic chamber is communicated with the reservoir 26 to move the power piston.

The worm gear formed on the output shaft is screwed into the female screw hole formed on the inner peripheral surface of the power piston, while the sector shaft is formed on the rack formed on the outer peripheral surface of the power piston. The sector gear meshes with each other, and the movement of the power piston assists the rotation of the worm gear.
The left and right front wheels, which are steering wheels connected via a link or the like, are rotated in the rotational operation direction of the steering wheel 10.

The two hydraulic chambers of the power cylinder 14 are connected by a bypass passage 30 shown in FIG. 3, and a solenoid valve 18 is provided in the bypass passage 30. A spool 36 is axially slidably fitted in a fitting hole 34 formed in a valve body 32 of the solenoid valve 18, and is biased by a spring 40 when the solenoid 38 is demagnetized to move the forward end shown in the figure. In position.
Therefore, the pair of bypass slits 42 formed in the spool 36 and the pair of communication holes 44 formed in the valve body 32 are displaced, and the liquid passage 46 connected to one of the two hydraulic chambers of the bypass passage 30. And the communication with the liquid passage 48 connected to the other hydraulic chamber is blocked. When the solenoid 38 is excited, the spool 36 is retracted, the slit 42 and the communication hole 44 are communicated with each other, and the two hydraulic chambers are communicated with each other, and the hydraulic chamber on the high pressure side is moved to the hydraulic chamber on the low pressure side. The hydraulic fluid flows in, thereby reducing the hydraulic pressure difference between the two hydraulic chambers and reducing the assisting torque. The retracted amount of the spool 36 is proportional to the magnitude of the exciting current of the solenoid 38, and the larger the exciting current is, the larger the communicating amount between the slit 42 and the communicating hole 44 is, and the smaller the hydraulic pressure difference between the two hydraulic chambers is. As a result, the assisting torque is reduced.

The exciting current amount of the solenoid 38 is increased as the wheel speed is higher, as shown in the graph of FIG.
When the wheel speed is high, the amount of decrease in the assisting torque is increased to ensure traveling stability, and when the wheel speed is low, the amount of decrease in the assisting torque is reduced to ensure light steering. Of.

In a vehicle suspension provided with the present power steering device, actuators operated by hydraulic pressure are arranged on four wheels respectively, and the hydraulic pressure is controlled by detecting driving conditions, road surfaces and vehicle conditions by various sensors. However, it is designed to absorb unevenness of the road surface, maintain the vehicle posture horizontally, improve maneuverability and safety, and adjust the vehicle height. FIG. 4 typically shows one wheel. 50 is a hydraulic cylinder, its housing 52 is connected to the vehicle body 54, and the piston rod 56 is connected to the link 60 which supports the wheel 58. Hydraulic cylinder 5
No. 0 piston side chamber 62, rod side chamber 64 and pump 6
A servo valve 70 is provided between the control valve 6 and the reservoir 68, and the servo valve 70 is controlled by the suspension control computer 72.

The suspension control computer 72 includes a vehicle height sensor 76, a hydraulic pressure sensor 78 for detecting the hydraulic pressure in the piston side chamber 62 of the hydraulic cylinder 50, a vertical acceleration sensor 80 for detecting the vertical acceleration of the vehicle, etc. The detection values of various sensors are input, and the computer 72 controls the servo valve 70 based on the detection values. As a result, the hydraulic cylinder 50
The height of hydraulic pressure and the amount of oil in the piston side chamber 62 are adjusted to absorb unevenness of the road surface and adjust the vehicle height.

The power steering system is controlled by the control unit 90 shown in FIG. The control device 90 is C
The main component is a computer having a PU 92, a ROM 94, a RAM 96, and a bus 98 connecting them. An input interface 100 is connected to the bus 98, and a wheel speed calculation computer 102 for calculating a wheel speed (hereinafter, referred to as vehicle speed) V and the oil pressure sensor 7 are connected.
8 is connected. Computer 10 for calculating wheel speed
2 calculates the average value of the wheel speeds of the left and right rear wheels, which are the driving wheels, based on the output of the rotation sensor attached to the output shaft of the transmission.

Also on the bus 98 is the output interface 1
08 is connected, and the solenoid 38 of the solenoid valve 18 is connected via the solenoid drive circuit 110. In the ROM 94, a map defining the relationship between the vehicle speed V and the solenoid exciting current I ₂ shown in the graph of FIG. 5, the ground load change ΔW and the solenoid exciting current correction factor I ₁ shown in the graph of FIG. Various programs necessary for controlling the assisting means are stored, such as a map defining the relationship of the above, a solenoid valve control routine shown in the flowchart in FIG. Hereinafter, control of the solenoid valve 18 will be described based on the flowchart shown in FIG.

First, in step S1 (hereinafter abbreviated as S1; the same applies to the other steps), the hydraulic pressures P _L of the hydraulic cylinders 50 provided on the left and right front wheels, respectively.
After P _R is read, the ground contact load W of the front wheels at S2
Is calculated. The hydraulic cylinder 50 supports the vehicle body 54, and the value obtained by multiplying the hydraulic pressure P by the pressure receiving area S is proportional to the ground load of the wheel on which the hydraulic cylinder 50 is provided. Therefore, the ground loads W _FL , W _FR are obtained based on the oil pressures P _L , P _R of the hydraulic cylinders 50 of the left and right front wheels, and the sum thereof is set as the ground load W of the front wheels. Next, in S3, the initial ground load W ₀ is subtracted from the front wheel ground load W to obtain the ground load change amount ΔW. The initial ground load W ₀ is
The ground contact load of the left and right front wheels when the ignition switch is turned on, which is calculated in the initialization of the main routine (not shown) and stored in the RAM 96.

Subsequently, S4 is executed, and the solenoid exciting current correction factor I ₁ is obtained from the map which stores the change amount ΔW of the ground load and the solenoid exciting current correction factor I ₁ stored in the ROM 94. Then, after the vehicle speed V is read from the wheel speed calculation computer 102 in S5, the map defining the relationship between the vehicle speed V and the solenoid excitation current I ₂ which is stored in the ROM94 in S6, the solenoid excitation corresponding to the vehicle speed V The current I ₂ is required.

Next, S7 is executed, the solenoid exciting current I ₂ is multiplied by the correction factor I ₁ , and the solenoid valve 1
After the solenoid exciting current I ₃ supplied to 8 is calculated, it is output in S8. The solenoid excitation current correction factor I ₁ is set to 1 when the change amount ΔW is 0, and when the ground load W is the same as the initial ground load W ₀ , the solenoid excitation current I ₂ is not corrected and the vehicle speed V The value obtained for is directly supplied to the solenoid valve 18.

On the other hand, the ground contact load W is the initial ground contact load W.
When it is larger than _{0, the} solenoid exciting current correction factor I ₁ becomes smaller as the change amount ΔW becomes larger. Therefore, when the ground load W increases, the solenoid exciting current I ₃ is reduced, the assisting torque is increased, and the increase amount of the steering torque is decreased. Further, the ground contact load W is the initial ground contact load W _0.
When the ground load W is smaller, the solenoid exciting current correction factor I ₁ is set to be larger as the ground load W is smaller. When the ground load W is smaller, the solenoid exciting current I ₃ is larger and the assisting torque is reduced. Therefore, the reduction amount of the steering torque is reduced. Therefore, a stable steering feeling can be obtained regardless of the change in the ground load.

As is clear from the above description, in the present embodiment, the oil pressure sensor 78 and S1 and S2 of the ROM 94 are used.
And a portion of the CPU 92 for executing the steps constitute a ground load detecting means, and a portion of the ROM 94 for storing S3, S4, S7 and a portion of the CPU 92 for executing the steps serve as a ground load change control means. It is composed.

Another embodiment of the present invention is shown in FIGS. In this embodiment, the ground contact load W of the left and right front wheels is calculated based on the longitudinal acceleration and lateral acceleration of the vehicle. Therefore, the controller 90 is connected to the wheel speed calculation computer 102, the longitudinal acceleration sensor 120, and the lateral acceleration sensor 122, respectively.
The solenoid valve control routine shown in FIG. 8 is stored in M94.

In the solenoid valve control routine, first, the longitudinal acceleration and the lateral acceleration are read in S11, and then, the ground contact loads W _FL , W _FR of the left and right front wheels are calculated in accordance with the following equation in S12. _{W FL = w FL - (M} · LGG · H) / 2WB- (M · LTG · H · R F) / T R W FR = w FR - (M · LGG · H) / 2WB + (M · LTG · H · _{R F)} / T R, however, w _FL: vehicle weight according to the left front wheel in a stopped state w _FR: vehicle weight according to the right front wheel in the stop state M: mass of the vehicle LGG: longitudinal acceleration H: the height of the center of gravity of the vehicle WB : Wheel base LTG: Lateral acceleration R _F : Roll rigidity distribution of the front wheels T _R : Tread The vehicle weights w _FL and w _FR applied to the left and right front wheels in a stopped state are standard values set for the vehicle,
It is a constant value that is not related to the load, and is stored in the ROM 94.

At the time of starting, a moment (M.LGG.H) having a magnitude obtained by multiplying the longitudinal acceleration LGG by the height H of the center of gravity of the vehicle and the mass M of the vehicle is generated, and this moment is a reaction force applied to the rear wheels from the ground. Since it is balanced with the moment (F · WB) obtained by multiplying F by the wheel base WB, F =
Since (M · LGG · H) / WB is obtained, and this reaction force F is applied to the left and right rear wheels, the load on the left rear wheel increases by (M · LGG · H) / 2WB, On the contrary, the load on the left front wheel is reduced by (M ・ LGG ・ H) / 2WB. Since the longitudinal acceleration sensor 120 outputs the acceleration as a positive value and the deceleration as a negative value, the longitudinal acceleration LGG has a positive value at the time of starting and (M.LGG.
H) / 2WB will be subtracted from the vehicle weight loads w _FL and w _FR .

Further, when the vehicle turns, a load movement occurs in the left-right direction of the vehicle. When the vehicle turns, the moment (M ・ LTG ・ H) which is the magnitude of the lateral acceleration LTG multiplied by the height H of the center of gravity
Occurs, the tread T _R since the balance with the moment obtained by multiplying the reaction force F exerted from the ground to the front and rear wheels of the left (F · T _R) to F = (M · LTG · H ) / T R is obtained. This force F is shared by the front wheels and the rear wheels according to the size of the roll rigidity distribution R _F , R _R. The roll rigidity distribution is the distribution ratio of the restoring moment transmitted from the suspension device to the sprung weight to the sprung weight of the front wheel and the rear wheel when the vehicle rotates around the axis in the front-rear direction. The value obtained by multiplying T _R by the roll rigidity distribution R _F of the front wheels is the amount of change in the load on the left front wheel due to turning. If the lateral acceleration LTG at the time of turning left is represented by a positive value, in the case of the left front wheel, the load on the left wheel decreases and the load on the right wheel increases due to load movement when the vehicle turns left, and therefore the ground load of the left front wheel increases. In the formula for
_{· LTG · H · R F)} / T R is pulled, it is added in the formula for determining the vertical load of the right front wheel.

The sum of the ground contact loads W _FL and W _FR of the left and right front wheels calculated in this way is the ground contact load W of the front wheels.
13 to S18 are executed in the same manner as S3 to S8, and the solenoid valve 18 is supplied with an exciting current of a magnitude that changes the assisting torque in the direction of reducing the change in the steering torque due to the change in the ground load.

In this embodiment, the longitudinal acceleration sensor 1
20, lateral acceleration sensor 122, S11 of ROM94, S
The portion for storing 12 and the portion for executing those steps of the CPU 92 constitute the ground load detecting means.

In the embodiment shown in FIGS. 1 to 6, the initial ground load W ₀ is ₀ when the ignition switch is O.
Although it was calculated based on the pressure of the hydraulic cylinder 50 when it was set to N, the ground load is calculated when the vehicle is in the straight traveling state and the vehicle speed becomes constant immediately after the vehicle starts, and this is used as the initial ground load. Alternatively, the ground contact load may be obtained every time the vehicle speed is constant and the vehicle speed is constant, not only immediately after the vehicle starts moving, but also as the initial ground contact load.

Further, in the embodiment of FIGS. 1 to 6, a constant standard load may be set to set the initial ground load W ₀ ,
On the contrary, in the embodiment of FIGS. 7 to 8, the initial ground load W ₀ may be changed according to the loaded load.

Further, when the initial ground load W ₀ is changed according to the loading load, the larger the initial ground load W ₀ is, the larger the assisting torque before correction due to the change ΔW of the ground load becomes. The change in steering torque due to the change in load may be reduced or eliminated,
On the contrary, as in Japanese Patent Laid-Open No. 61-60377, the assisting torque can be reduced as the initial ground contact load W ₀ is increased, and the traveling stability can be increased as the loaded load is increased.

Further, a map for determining the assisting torque is set based on the speed and the ground contact load, and when the ground contact load changes, the assist torque is determined so as to reduce or eliminate the change in the steering torque due to the change. You may do so.

Further, when the present invention is applied to a power steering device of a vehicle in which the suspension is composed of springs and shock absorbers and the vehicle body moves up and down depending on the road surface condition and the like, the movement of the vehicle body with respect to the wheels is detected to detect the ground load. Can be obtained.

In addition, the present invention can be implemented in various modified and improved modes based on the knowledge of those skilled in the art without departing from the scope of the claims.

[Brief description of drawings]

FIG. 1 is an RO of a computer that is a main body of a control device that controls a power steering device according to an embodiment of the present invention.
7 is a flowchart showing a solenoid valve control routine stored in M.

FIG. 2 is a diagram schematically showing the power steering device together with the control device.

FIG. 3 is a front sectional view showing a solenoid valve of the power steering device.

FIG. 4 is a diagram schematically showing a vehicle suspension device including the power steering device.

FIG. 5 is a graph showing a relationship between a vehicle speed and a solenoid exciting current defined by a map stored in the ROM.

FIG. 6 is a graph showing a relationship between a ground load change amount defined by a map stored in the ROM and a solenoid exciting current correction rate.

FIG. 7 is a diagram showing a control device of a power steering device according to another embodiment of the present invention.

8 is an R of a computer which is the main body of the control device of FIG.
It is a flowchart which shows the solenoid valve control routine stored in OM.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Steering wheel 14 Power cylinder 16 Rotary valve 18 Solenoid valve 78 Hydraulic sensor 90 Control device 102 Wheel speed calculation computer 120 Longitudinal acceleration sensor 122 Lateral acceleration sensor

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Claims (1)

[Claims] 1. A power steering system including an assisting means for assisting a steering torque applied to a steering wheel, comprising: a ground load detecting means for detecting a ground load of a steered wheel; and a ground load detected by the ground load detecting means. A power steering apparatus comprising: a grounding load change control means for changing the assisting torque of the assisting means in a direction to reduce the change in the steering torque due to the change.