Motor vehicles – Steering gear – With fluid power assist
Reexamination Certificate
2003-01-23
2004-01-27
Lerner, Avraham (Department: 3611)
Motor vehicles
Steering gear
With fluid power assist
C701S041000
Reexamination Certificate
active
06681884
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a power steering system including a flow control valve for the prevention of energy loss.
2. Description of Related Art
An example of power steering systems including a flow control valve for the prevention of energy loss is disclosed in Laid-open Japanese Patent Application No. 2001-163233 filed by the present applicant.
The flow control valve V of the power steering system of the prior art example includes, as shown in
FIG. 3
, a spool
1
having an end adjoining a pilot chamber
2
and the other end adjoining another pilot chamber
3
.
The pilot chamber
2
continuously communicates with a pump P via a pump port
4
. The pilot chamber
2
communicates via a flow path
6
, a variable orifice a and a flow path
7
with an inflow port of a steering valve
9
provided for controlling a power cylinder
8
.
The pilot chamber
3
incorporates a spring
5
and also communicates with the inflow port of the steering valve
9
via a flow path
10
and the flow path
7
. Accordingly, the variable orifice a, the flow path
7
and the flow path
10
provide the communication between the pilot chambers
2
and
3
. Pressure upstream from the variable orifice a acts on the pilot chamber
2
, and pressure downstream therefrom acts on the pilot chamber
3
. The degree of opening of the variable orifice a is controlled by a solenoid current instruction value SI for a solenoid SOL.
The spool
1
keeps a position at which the force acting on the pilot chamber
2
, the force acting on the pilot chamber
3
, and the force of the spring
5
are in balance. This balanced position determines the degree of opening of both the pump port
4
and tank port
11
.
For example, upon actuation of a pump driving source
12
such as an engine or the like, the pump P is driven to supply pressure oil into the pump port
4
to cause a flow in the variable orifice a. This flow produces a pressure difference between the two sides of the variable orifice a, and the pressure difference causes a difference in pressure between the pilot chambers
2
and
3
. The resultant pressure difference moves the spool
1
from the normal position, illustrated in
FIG. 3
, to the balanced position with opposing a force of the spring
5
.
Thus, moving the spool
1
from the normal position toward the balanced position increases the degree of opening of the tank port
11
. In accordance with the resulting degree of opening of the tank port
11
, the distribution ratio between a control flow QP introduced toward the steering valve
9
from the pump P and a return flow QT circulating back to the tank T or the pump P is determined. In other words, the control flow QP is determined in accordance with the degree of opening of the tank port
11
.
The control of the control flow QP in accordance with the degree of opening of the tank port
11
as described above results in determination of the control flow QP in accordance with the degree of opening of the variable orifice a. This is because the position to which the spool
1
is shifted, which determines the degree of opening of the tank port
11
, is determined by the differential pressure between the two pilot chambers
2
and
3
, and this differential pressure is determined by the degree of opening of the variable orifice a.
Thus, in order to control the control flow QP in accordance with the vehicle speed or the steering condition of the vehicle, the degree of opening of the variable orifice a, or the solenoid current instruction value SI for the solenoid SOL may be controlled. This is because the degree of opening of the variable orifice a is controlled in proportion to an excitation current of the solenoid SOL so that the variable orifice a holds the degree of its opening to a minimum in the non-excited state of the solenoid SOL and increases the degree of its opening as the excitation current is increased.
The steering valve
9
applied with the control flow QP controls the amount of oil supplied to the power cylinder
8
in accordance with input torque (steering torque) of the steering wheel (not shown). For example, if the steering torque is large, the amount of shifting of the steering valve
9
is increased to increase the amount of oil supplied to the power cylinder
8
, whereas if it is small, the amount of shifting of the steering valve
9
is decreased to decrease the amount of oil supplied to the power cylinder
8
. The higher the amount of supply of pressure oil, the higher the assist force the power cylinder
8
exerts. The smaller the amount of supply, the lower the assist force the power cylinder
8
exerts.
It should be noted that the steering torque and the amount of shifting of the steering valve
9
are determined by a torsion reaction of a torsion bar (not shown) or the like.
As described above, the steering valve
9
controls the flow QM supplied to the power cylinder
8
and the flow control valve V controls the control flow QP supplied to the steering valve
9
. If the flow QM required by the power cylinder
8
comes as close as possible to the control flow QP determined by the flow control valve V, it is possible to reduce the energy loss around the pump P. This is because the energy loss around the pump P is caused by a difference between the control flow QP and the flow QM required by the power cylinder
8
.
In order to make the control flow QP as close as possible to the flow QM required by the power cylinder
8
for the prevention of energy loss, the system of the prior art example controls the degree of opening of the variable orifice a. The degree of opening of the variable orifice a is determined by the solenoid current instruction value SI for the solenoid SOL as described earlier. The solenoid current instruction value SI is controlled by a controller C which will be described in detail next.
The controller C is connected to a steering angle sensor
14
and a vehicle speed sensor
15
. As illustrated in
FIG. 4
, the controller C determines a current instruction value I&thgr; on the basis of a steering angle detected by the steering angle sensor
14
, and also a current instruction value I&ohgr; on the basis of a steering angular velocity calculated by differentiating the steering angle.
The relationship between the steering angle and the current instruction value I&thgr; is determined on the basis of theoretical values giving linear characteristics to the relationship between the steering angle and the control flow QP. The relationship between the steering angular velocity and the current instruction value I&ohgr; is also determined on the basis of theoretical values giving linear characteristics to the relationship between the steering angular velocity and the control flow QP. It should be noted that the current instruction values I&thgr; and I&ohgr; outputted are zero unless both the steering angle and the steering angular velocity exceed a set value. Specifically, when the steering wheel is positioned at or around the center, the current instruction values I&thgr; and I&ohgr; are outputted at zero in order to set a dead zone around the center.
After the determination of each of the current instruction values I&thgr; and I&ohgr; as described above, the determined values I&thgr; and I&ohgr; are added together. The reasons for the addition of the current instruction values I&thgr; and I&ohgr; together are as follows.
The first reason is ensuring of response. The power cylinder
8
has a good response whenever the control rate QM supplied is higher than the flow QM required in the power cylinder
8
or the steering valve
9
. For this reason, the current instruction value I&thgr; is added to the current instruction value I&ohgr;.
The second reason is ensuring of stability in steering. Steering torque is suitable for use in estimation of the required flow QM in the steering valve
9
. However, the use of the steering torque requires an extensive change in the condition of the existing systems. Hence, the prior art system uses a steering angular velocity &ohgr; which is
Arita Tsunefumi
Shima Naoto
Shimizu Noboru
Takai Masashi
Kayaba Industry Co. Ltd.
Lerner Avraham
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