Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
2002-03-26
2003-07-08
Butler, Douglas C. (Department: 3683)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S113100, C303S117100, C303S900000, C303S068000, C303S119300, C251S129140, C251S129150, C335S220000
Reexamination Certificate
active
06588857
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to solenoid valves for brake systems of automobiles and, more particularly, to a solenoid valve used in the oil return line of an electro-hydraulic brake system.
2. Description of the Prior Art
Of a variety of brake systems recently proposed and used in automobiles, an electro-hydraulic brake system (EHB) is designed such that it senses pedal pressure, applied to the brake pedal by the driver's foot, through a pressure sensor, and controls oil pressures, which will be fed to the wheel brake cylinders, using a hydraulic modulator in response to the sensed pedal pressure.
As shown in
FIG. 1
, a conventional EHB comprises a pedal operation sensor
2
, which senses the operation of a brake pedal
1
. A master cylinder
4
is connected to the pedal
1
, and has a pressure sensor
3
used for sensing pedal pressure applied to the pedal
1
by the driver's foot. The EHB also has an oil pump
6
, which forcibly sucks oil from an oil tank
5
and outputs the oil under pressure. A accumulator
7
receives and stores the pressurized oil outputted from the pump
6
. The EHB further includes an inflow control solenoid valve
10
and an outflow control solenoid valve
20
. The inflow control solenoid valve
10
is mounted on an oil supply line extending from the accumulator
7
to a wheel brake cylinder
8
, and controls a supplying of pressurized oil from the accumulator
7
to the brake cylinder
8
. The outflow control solenoid valve
20
is mounted on an oil return line extending from the wheel brake cylinder
8
to the oil tank
5
, and controls a returning of oil from the cylinder
8
to the tank
5
. The EHB also has an emergency oil line
9
, which directly feeds pressurized oil from the master cylinder
4
to the brake cylinder
8
and brakes the wheels to provide against emergencies, such as malfunction of the brake system. A solenoid valve
9
a
is mounted on the emergency oil line
9
to control the line
9
.
The above conventional EHB is operated as follows: That is, when pedal pressure is sensed by the pressure sensor
3
of the master cylinder
4
, an electronic control unit (ECU, not shown) opens the inflow control solenoid valve
10
in response to the pedal pressure, thus allowing pressurized oil to be fed from the accumulator
7
to the brake cylinder
8
and forming braking pressure in the cylinder
8
. The accumulator
7
normally stores pressurized oil outputted from the oil pump
6
, and maintains preset oil pressure. The operation of the oil pump
6
is controlled in response to a signal outputted from a pressure sensor
7
a
provided at the outlet of the accumulator
7
. That is, the pressure sensor
7
a
senses oil pressure inside the accumulator
7
, and outputs a signal to the ECU to selectively operate the pump
6
.
At a time of removing the braking pressure from the brake cylinder
8
, the inflow control solenoid valve
10
is closed, but the outflow control solenoid valve
20
is opened under the control of the ECU. Pressurized oil is thus returned from the brake cylinder
8
to the oil tank
5
provided at the master cylinder
4
. During such an operation of the EHB, the inflow and outflow control solenoid valves
10
and
20
are alternately and repeatedly opened and dosed under the control of the ECU, thus repeatedly and intermittently applying braking pressure to the brake cylinder
8
in the same manner as a conventional anti-lock brake system (ABS). The EHB thus prevents a slippage of the wheels on the road during a braking operation. In such conventional EHBs, a normal dose-type solenoid valve (hereinbelow, referred to simply as “NC-type solenoid valve”) is typically used as each of the inflow and outflow control solenoid valves
10
and
20
. Such NC-type solenoid valves normally maintain their dosed states, and are preferably used as the solenoid valves
10
and
20
of such an EHB in consideration of desired operational characteristics and operational efficiency of the solenoid valves
10
and
20
.
FIG. 2
is a sectional view showing the construction of the inflow and outflow control solenoid valves
10
and
20
set in a modulator block of the conventional EHB. As shown in the drawing, the modulator block
30
of the EHB seats the inflow and outflow control solenoid valves
10
and
20
therein, and has a plurality of complex oil passages. When designing the modulator block
30
, it is necessary to consider such complex oil passages, in addition to work efficiency while machining the block
30
and seating the valves
10
and
20
in the block
30
, as well as the recent trend of compactness and smallness of the modulator blocks. The inflow and outflow control solenoid valves
10
and
20
are parallely installed in the modulator block
30
in consideration of such structural characteristics of the block
30
. That is, the inflow and outflow control solenoid valves
10
and
20
are parallely and vertically installed in the modulator block
30
at left- and right-hand sides of
FIG. 1
, respectively.
During the operation of the EHB, pressurized oil outputted from the accumulator
7
is introduced into the inflow control solenoid valve
10
through an inlet oil passage
31
formed in the block
30
at a position under the valve
10
. Thereafter, the inlet pressurized oil laterally flows from the inflow control solenoid valve
10
into a connecting passage
32
which communicates the two valves
10
and
20
to each other. The connecting passage
32
is also connected to another oil passage
33
, which is connected to the wheel brake cylinder
8
. Therefore, when the inflow control solenoid valve
10
is opened, pressurized oil outputted from the accumulator
7
is fed to the brake cylinder
8
, thus forming braking pressure in the cylinder
8
and braking the wheels.
At a time of removing the braking pressure from the brake cylinder
8
, the inflow control solenoid valve
10
is closed, but the outflow control solenoid valve
20
is opened under the control of the ECU. Pressurized oil is thus outputted from the brake cylinder
8
, and flows into the outflow control solenoid valve
20
through a radial oil passage
21
of the valve
20
, and is returned to the oil tank
5
of the master cylinder
4
through an outlet oil passage
34
formed in the block
30
at a position under the valve
20
.
As described above, the inflow and outflow control solenoid valves
10
and
20
are NC-type solenoid valves. The operation of the inflow control valve
10
is easily controlled, but the control of the outflow control valve
20
is difficult due to the relation between the structural characteristics of the NC-type solenoid valves and the flowing direction of oil during the operation of EHB.
In a detailed description, when the plunger
11
axially moves upward to open the orifice
12
in the inflow control solenoid valve
10
, pressurized oil from the inlet oil passage
31
passes upward through the open orifice
12
to flow into the radial oil passage
13
of the valve
10
. In such a case, a large pressure difference is formed between the inlet and outlet of the orifice
12
at the initial stage of opening the orifice
12
, and so oil pressure inside the orifice
12
acts in an upward direction wherein the plunger
11
moves to open the orifice
12
. The plunger
11
is thus biased upward by the oil pressure. After a predetermined lengthy period of time, passes, the plunger
11
sufficiently opens the orifice
12
, and so the pressure difference between the inlet and outlet of the orifice
12
is reduced to a predetermined level. In such a case, the flow rate of oil through the orifice
12
is increased, but the oil pressure inside the orifice
12
is reduced. The plunger
11
thus has a tendency to close the orifice
12
. The inflow control solenoid valve
10
thus provides a “self-equilibrating effect”. Due to such a self-equilibrating effect, it is easy to control the operation of the inflow control solenoid valve
10
, wherein the oil flows upward f
Butler Douglas C.
Ladas & Parry
Mando Corporation
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