Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1999-11-15
2001-08-21
Butler, Douglas C. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S117100, C303S113100, C303S900000, C303S901000
Reexamination Certificate
active
06276764
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an anti-lock brake system, and more particularly, to a solenoid valve for an anti-lock brake system that can enhance a braking performance by variably controlling an amount of hydraulic oil to be supplied during a slip control.
2. Description of Related Art
Generally, a brake system comprises a wheel cylinder mounted on an automotive wheel to generate braking force using hydraulic pressure, a booster/master cylinder assembly for generating hydraulic pressure and applying the same to the wheel cylinder, and a modulator for controlling the hydraulic pressure to be supplied according to a running condition of a vehicle in accordance with signals transmitted from an electronic control unit.
The modulator is equipped with normal-open and normal-close solenoid valves for controlling the supply of braking pressure. The normal-open solenoid valve is designed to, in a normal brake mode, maintain an opened state to supply hydraulic pressure to the master cylinder without pressure reduction, and in a slip control mode, control an amount of the hydraulic oil to control the braking pressure.
The normal-open solenoid valve controls an amount of the hydraulic oil by a simple On/Off operation of a plunger. Accordingly, the flow rate of the hydraulic oil which can pass through the valve at the slip control mode is the same as at the normal brake mode.
Therefore, in such a conventional normal-open solenoid valve, an amount of the hydraulic pressure to be supplied cannot be precisely controlled, making it difficult to accurately perform a slip control. Furthermore, a water hammering phenomenon occurs by pulsations of fluid due to the plunger's movement to open and close positions, thereby generating noises and deteriorating the durability of parts.
To solve the above described problems, a normal-open solenoid valve which is designed to reduce an amount of the hydraulic oil to be supplied to the wheel cylinder in proportion to a slip rate, while alleviating pulsations of the fluid during a slip control, has been developed.
As shown in
FIG. 1
, an example of such a normal-open solenoid valve is disclosed in the U.S. Pat. No. 5,647,644, which comprises a valve seat
23
, a magnetic core
21
, a plunger
22
, and a piston
24
, all of which are installed in a valve housing
20
. The valve seat
23
is forcedly fitted in a lower portion of the valve housing
20
and provided with a longitudinal through hole. The plunger
22
is mounted passing through the magnetic core
21
such that a lower end thereof is disposed in the vicinity of the top of the valve seat
23
. The piston
24
is disposed around the valve seat
23
and biased against the magnetic core
21
by a spring
25
.
The normal-open solenoid valve is provided with two orifices, one of which is an invariable orifice formed on an upper end of the valve seat
23
and the other of which is a variable orifice
40
that is defined by a slot
26
formed on the top of the piston
24
when the piston
24
contacts the magnetic core
21
during a slip control.
In addition, a hydraulic channel branch
31
is defined between one side wall of the valve seat
23
and the valve housing
20
so that hydraulic pressure supplied through an inlet
27
can be applied to the piston
24
through the hydraulic channel branch
31
, thereby displacing the piston
24
upward while overcoming the biasing force of the spring
25
. A stepped portion
23
a
is formed on another lower side of the valve seat
23
so as to forcedly fit the valve seat
23
into the valve housing
20
.
In the normal brake mode, the plunger
22
is urged upward while the piston
24
is biased downward by the spring
25
. Therefore, hydraulic oil is supplied through the inlet
27
, then directed to an outlet
28
through the invariable orifice
30
.
In the slip control mode, the plunger
22
is displaced downward to close the invariable orifice
30
. As a result, the hydraulic oil supplied through the inlet
27
is applied to the piston
24
through the hydraulic channel branch
31
so that the top of the piston
24
contacts the magnetic core
21
by being moved upward while overcoming the elastic force of the spring
25
. After this, when the plunger
22
is moved upward, the hydraulic pressure generated by the master cylinder is directed to the wheel cylinder through the variable orifice
40
formed by the slot
26
of the piston
24
contacting the magnetic core
21
.
When the braking force is released, the hydraulic oil within the wheel cylinder is returned to the master cylinder through the return passage
29
formed passing through the valve housing
20
to communicate the inlet
27
with the outlet
28
. After this, the plunger
22
is moved upward so that the solenoid valve is returned to its open state.
However, in the above-described normal-open solenoid valve, since the lower portion of the valve seat is designed to have the stepped portion and the channel branch defining portion, and the channel branch defining portion should be precisely formed, it is difficult to manufacture the valve seat.
In addition, since the special valve housing for receiving the magnetic core, the valve seat, the piston and the fluid passages is required, the entire size of the solenoid valve is increased.
SUMMARY OF THE INVENTION
Therefore, this invention has been made in an effort to solve the above described problems.
It is an object of this invention to provide a solenoid valve for an anti-lock brake system, which can vary an amount of hydraulic oil to be supplied during a slip control.
It is another object of this invention to provide a solenoid valve, which is simple in the structure and easy to be manufactured by forming oil passages and two orifices using a valve seat and a piston.
To achieve the above objects, this invention provides a solenoid valve which comprises a magnetic core, a plunger, a piston and a valve seat, and is mounted on the modulator of an anti-lock brake system.
The magnetic core is mounted in a bore formed on the modulator, and has a plunger hole formed vertically passing through its interior.
The valve seat is disposed below the magnetic core in the bore, and has an invariable orifice formed at its inner middle, an inlet passage formed below the invariable orifice, and an outlet passage formed above the invariable orifice.
The plunger is movably mounted in the plunger hole and has a ball formed at its lower end for opening and closing the upper end of the invariable orifice.
The piston is movably mounted at the periphery of the valve seat, and has a variable orifice formed passing through one side of its upper portion, a first projection formed at a middle portion of its periphery, and a second projection formed at its lower end. The front end of the first projection is disposed adjacent to the inner periphery of the bore, and the second projection which has a length shorter than the first projection, is disposed near the bottom surface of the bore.
A spring is provided between the first projection and the magnetic core for urging the piston toward the direction to open the outlet passage.
A lip seal is provided between the first and second projections for preventing oil from flowing to the outlet passage through the piston.
As a first embodiment of this invention, the lower end of the valve seat is fixed to the bottom surface of the bore, and in this state the upper end of the valve seat is spaced a given distance away from the lower end of the magnetic core to form an oil outlet therebetween. In this first embodiment, a ring-shaped support member is mounted between the second projection of the piston and the bottom surface of the bore. Further, a side hole is formed at a lower portion of the valve seat and a slot is formed on the support member aligning with the side hole so that the inlet passage and the lip seal fitted to the outer periphery of the piston are communicated with each other.
As a second embodiment of this invention, the upper end of the valve seat is fixed to the lower en
Butler Douglas C.
Ladas & Parry
Mando Machinery Corporation
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