Motor vehicles – Steering gear – With fluid power assist
Reexamination Certificate
1999-07-20
2001-02-27
Dickson, Paul N. (Department: 3618)
Motor vehicles
Steering gear
With fluid power assist
C180S422000, C137S599110
Reexamination Certificate
active
06193009
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electromagnetic valve used for correcting the difference between the angle of a steering wheel and that of a steered wheel in the hydraulic circuit of a vehicle hydraulic power steering device and to a hydraulic power steering device using such a valve.
Recently, many types of industrial vehicles, including forklifts, have been equipped with power steering devices, some of which include hydraulic power steering devices. However, the hydraulic power steering devices have drawbacks. In a steering valve, which forms part of the hydraulic power steering device and is driven by the manipulation of a steering wheel, the relationship (discharge efficiency=actual discharge amount/theoretical discharge amount) between the movement of the steering wheel and the amount of oil discharged from the steering valve changes slightly depending on the angular velocity of the steering wheel. Also, oil can not be prevented from leaking slightly from the oil hydraulic circuit. For this reason, a difference in position between the steering wheel and the steered wheel occurs.
In order to solve this problem, Japanese Patent Publication No. 3-30544, Japanese Patent Publication No. 4-24270 and Japanese Utility Model Publication No. 7-5364 disclose devices for correcting the difference in position between the steering wheel and the steered wheel.
FIG. 5
shows such a device for correcting the angle of a steering wheel.
An entire-hydraulic power steering device
71
includes a steering valve
73
driven by manipulation of a steering wheel
72
and a steering cylinder
75
for steering the tires, or steered wheels
74
. The steering valve
73
and the steering cylinder
75
are connected by two hydraulic pipes
76
,
77
. An electromagnetic valve (a correcting valve)
78
is located in the pipes
76
,
77
at an intermediate location of the pipes
76
,
77
. When the steering wheel
72
is manipulated, the steering valve
73
discharges hydraulic oil flowing in from a hydraulic pump
79
to the pipes
76
,
77
corresponding to the manipulation direction of the steering wheel and exhausts return oil (returning from the steering cylinder
75
) from the other of the pipes
76
,
77
to an oil tank
80
.
A controller
81
is connected to a first sensor
82
for detecting the angular position of the steering wheel and a second sensor
83
for detecting the steered angle of one of the steered wheels
74
. The controller
81
calculates a target angle of the steered wheel
74
based on a value detected by the first sensor and compares the actual angle of the steered wheel
74
detected by the second sensor with the target angle to determine the difference between the target angle and the actual angle. When the difference exceeds a tolerance limit, the controller
81
causes the electromagnetic valve
78
to open. When the steering wheel
72
is manipulated while the valve
78
is open, some of the hydraulic oil is returned to the oil tank
80
through the valve
78
, which decreases the amount of hydraulic oil sent to the steering cylinder
75
. Accordingly, the steering wheel
72
races. When the angle of the steering wheel coincides with the angle of the wheel
74
, the valve
78
is closed. This procedure corrects the relationship between the wheel
74
and the steering wheel
72
.
The electromagnetic valve
78
in the prior art has a structure shown in FIG.
6
. The valve
78
includes a driving control unit
85
and a manifold
86
. The driving control unit
85
includes a solenoid
87
and a plunger (valve body)
88
. The plunger
88
is urged downwardly and away from a plug
90
by a spring
89
and is driven upwardly in a direction approaching the plug
90
by the solenoid
87
, thus the plunger
88
is displaced axially. The plunger
88
has a ball
92
fitted on the tip portion thereof. A spool
91
is located below the plunger
88
. Oil paths
91
a
,
91
b
are formed in the spool
91
to return the hydraulic oil. Also, an oil path
91
c
is formed by a recess in the outer peripheral surface of the spool
91
. When the hydraulic oil is not returned, the hydraulic oil passes through the oil path
91
c
. By vertically displacing the plunger
88
, the ball
92
is separated from and abutted against the upper end surface of the spool
91
, which opens and closes the return oil paths
91
a
,
91
b
. Four straight-type fittings
93
a
,
93
b
,
94
a
,
94
b
are attached to the manifold
86
. The left fittings
93
a
and
93
b
are respectively connected to the two pipes extending from the steering valve
73
and the right fittings
94
a
and
94
b
are respectively connected to the two pipes extending from the steering cylinder
75
. A passage
95
connects the fittings
93
a
and
94
a
at the upper side of the manifold
86
, and a passage
96
connects the fittings
93
b
and
94
b
at the lower side of the manifold
86
. The terms “upper” and “lower” refer to the orientation of FIG.
6
.
When the valve
78
is closed (in the state shown in FIG.
6
), the feed oil and the return oil pass through the passages
95
and
96
. In
FIG. 6
, the passage
95
at the upper side of the manifold
86
includes the oil path
91
c
. Since the oil path
91
c
is formed in the outer peripheral surface of the spool
91
, it is difficult to make the oil path
91
c
with a large inside diameter. Therefore, the oil path
91
c
has a relatively small inside diameter.
Thus, even if the valve
78
is closed, either the feed oil or the return oil must pass through the narrow oil path
91
c
around the spool
91
. Since the oil path
91
c
is not only narrow, but it bends, the hydraulic oil passing through this path is subject to a pressure loss. Accordingly, since the pressure of the hydraulic oil sent to the steering cylinder
75
is relatively weak, this adversely affects the response to manipulation of the steering wheel
72
. The consequences are, for example, that the response of the steered wheel
74
to the manipulation of the steering wheel
72
is delayed, and the steered wheel
74
cannot be turned if the steering wheel
72
is only slightly manipulated. Therefore, drivers feel that the steered wheel
74
has a poor response to the manipulation of the steering wheel
72
.
Also, when hydraulic oil passes through the narrow oil path
91
c
, friction heat is likely to occur, which will raise the temperature of the oil. Warmer oil causes heat damage to packing materials and leads to oil leakage. Further, warmer oil imposes a heat burden on parts of the electric system, such as the solenoid
87
, which shortens the life of the electric system.
SUMMARY OF THE INVENTION
In order to solve these problems, it is a first object of the present invention to provide an electromagnetic valve for a vehicle that returns at least some of the hydraulic oil sent to a hydraulic actuator such that the pressure loss of the hydraulic oil passing through the valve when the valve is closed is not significant.
Further, it is a second object of the present invention to provide a hydraulic power steering device equipped with a function for correcting the difference in position between the steering wheel and the steered wheel, such that the steered wheel is very responsive to the manipulation of the steering wheel when the correction of the difference in position is not being performed.
In order to achieve these object, in accordance with a first aspect of the present invention, there is provided an electromagnetic valve used in a vehicle having an oil supplying device for supplying hydraulic oil, a hydraulic actuator driven by the hydraulic oil supplied from the oil supplying device, and two pipes connecting the oil supplying device and the hydraulic actuator. The two pipes are such that, when one of the pipes supplies hydraulic oil from the oil supplying device to the hydraulic actuator, the other returns hydraulic oil from the hydraulic actuator to the oil supplying device and vice versa. The electromagnetic valve comprises: a body; two passages located at intermediate po
Chino Kenji
Katae Kenichi
Dickson Paul N.
Kabushiki Kaisha Toyoda Jidoshokki Seisakusho
Lerner Avraham H.
Morgan & Finnegan L.L.P.
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