Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1999-07-02
2001-10-30
Schwartz, Christopher P. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S119100, C137S630140, C137S630150, C137S630170, C137S630220, C251S129190, C251S083000
Reexamination Certificate
active
06309033
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to anti-lock brake systems for automotive vehicles and more particularly, to an anti-lock brake system having a switchable orifice solenoid.
BACKGROUND OF THE INVENTION
Referring to
FIG. 1
, anti-lock brake systems typically include a normally open solenoid valve
10
that is positioned between a master cylinder brake circuit
12
and a wheel caliper circuit
14
to interrupt build-up of brake fluid pressure and restrict brake fluid flow when the brakes are actuated into an anti-lock mode. When the solenoid valve
10
is in the open position, the restriction in brake fluid flow is preferably as low as possible to prevent degradation in the braking performance during normal apply and release of the brakes. However, during the anti-lock mode, it is preferred that the flow restriction in the valve
10
be high enough such that an in-rush of brake fluid, when the valve
10
switches from closed to open, is limited. The in-rush of fluid may be quantified as the pressure gain in the wheel caliper circuit. Limiting the pressure gain when the brakes are switched to the anti-lock mode is desirable to prevent excessive overshooting of the target pressure level in the wheel caliper circuit being controlled during anti-lock mode. To accomplish high flow restriction and limit pressure gain with a one size solenoid valve, either flow restriction or a reduced pressure gain must be compromised.
To reduce the problems associated with typical anti-lock braking systems, one known brake system, as depicted in
FIG. 2
, employs a switchable orifice
100
that cooperates with a solenoid tappet
110
. The switchable orifice permits free flow of brake fluid between the master cylinder circuit
115
and the wheel caliper circuit
120
during normal braking. When the solenoid tappet
110
is energized, it closes against a valve seat
125
during the anti-lock mode. A pressure difference across a switching valve
130
overcomes a switching valve spring
135
, causing the switching valve to close and restrict the flow to the switched orifice
100
which is impressed into the switching valve. The flow path between the master cylinder circuit and the wheel caliper circuit is then restricted during anti-lock mode build cycles. The flow path remains restricted until pressure is released from the master cylinder circuit, i.e., the driver releases the brake. While systems of this type allow for high flow restriction and serve to limit pressure gain, they are undesirable due to higher part complexity, increased manufacturing costs and hysteresis of the moving portion of the valve.
This system is also undesirable as the it requires the use of a Bernoulli effect force on the back side of the switching valve to prevent unwanted switching of the valve during a fast brake apply. The Bernoulli effect is generated by use of the bernoulli orifice
140
. With this arrangement, the secondary orifice of the switching valve is limited in size such that this type of arrangement may only be useful in smaller vehicles. Further, systems of this type also require an additional elastomer seal
145
to prevent leakage of brake fluid while in the switched position.
Therefore, there exists a need for a switchable orifice solenoid valve for an anti-lock brake system that limits pressure gain during the anti-lock braking mode while simultaneously restricting in-rush of brake fluid during valve switching, where the system is cost effective to manufacture and eliminates hysteresis and the use of a Bernoulli effect force on the back side of the switching valve.
SUMMARY OF THE INVENTION
The present invention is directed to a switchable solenoid valve for an anti-lock brake system. The solenoid valve includes a valve housing having a master cylinder port and a wheel caliper port, a valve seat positioned within the valve housing between the master cylinder port and wheel caliper port, and axially movable tappet and valve plate for sealing against the valve seat. The valve seat includes a center orifice and perimeter bores formed therethrough through which pressurized fluid may flow from the master cylinder port to the wheel caliper port when the tappet and valve plate are in open positions. Fluid flow is fully interrupted when the tappet and valve plate are in closed positions. In the closed position, the tappet is sealed against the center orifice while the valve plate simultaneously seals the perimeter bores. During an anti-lock mode, a pressure difference between the master cylinder and the wheel caliper ports causes the valve plate to remained sealed against the perimeter bores, while the tappet is moved into an intermediate position. In the intermediate position, the tappet partially unseals the center orifice to permit fluid to flow restricted though the center orifice only.
In accordance with one aspect of the invention, the tappet has a shaft, a reduced diameter portion, an annular rim and a sealing portion. The valve plate is mounted on the reduced diameter portion of the tappet such that the tappet and valve plate may move axially with respect to one another. During the anti-lock mode, as the tappet is moving away from the center orifice, the valve plate serves to restrict the tappet from fully unsealing the center orifice, thereby producing restricted flow between the master cylinder and wheel caliper ports, easily and with a minimum of parts.
In accordance with another aspect of the invention, the valve plate is further provided with a plurality of radially inwardly extending notches formed on a peripheral edge. The notches allow for increased fluid flow around the valve plate when the solenoid valve is in a normally open position. The valve plate is further provided with a center bore through which the reduced diameter portion of the tappet is received. Radially outwardly extending channels may also be provided around the periphery of the center bore to further increase fluid flow and to insure that the tappet and valve plate are axially movable with respect to one another.
The present invention provides for a more simplified design than the prior art, thereby reducing manufacturing costs. Further, the present invention also eliminates the need for a second Bernoulli orifice to prevent unwanted switching operations, such that the size restrictions associated with the use of Bernoulli orifices are eliminated.
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Burch Melody M.
Continental Teves Inc.
Rader & Fishman & Grauer, PLLC
Schwartz Christopher P.
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