Solenoid valve, especially for hydraulic brake systems with slip control

A solenoid valve for use with a slip-controlled brake system has an annular piston with a switchable diaphragm in order to lower the valve noises. The annular piston moves, in response to differential pressure, between a first position at which a pressurized medium flow path parallel to the diaphragm exists and a second position at which pressurized medium flows exclusively through the diaphragm. A pressurized agent channel, arranged upstream of the valve seat, has a portion having a reduced cross section relative to the valve seat, into which a channel branch of small nominal diameter opens. With this design, the pressure energy of the pressurized medium column flowing into the solenoid valve is converted into kinetic energy, which initiates a pressure gradient in the channel branch and prevents premature switching of the annular piston into the diaphragm position during slip-free normal braking.

This application is the U.S. national-phase application of PCT 
International Application No. PCT/EP94/03622. 
FIELD OF THE INVENTION 
The present invention pertains to a solenoid valve, especially for 
hydraulic brake systems with slip control, having an opening formed in an 
annular piston in the valve and through which pressurizing medium passes 
to control brake operation. 
BACKGROUND OF THE INVENTION 
The intermittent control of pressurized medium in slip-controlled brake 
systems by digitally switchable inlet and outlet valves leads to undesired 
sound emission as a consequence of the pulsed changes in pressure. 
It was found in the brake systems described in German Patent Application 
No. P 43 19 227.0 that the solutions suggested for arranging the annular 
piston provided with a switchable diaphragm in the inlet valve do not 
always make it possible to avoid an unintended switching of the annular 
piston into the diaphragm position during manual, slip-free brake 
actuation. The annular piston having a "switchable diaphragm" moves 
between a first position and a second position (i.e., "diaphragm 
position"). At the first position, a pressurized medium flow path across a 
face of the annular piston extends unhindered from the valve seat to a 
pressure line, in parallel to the diaphragm. At the second position, this 
pressurized medium flow path is closed and pressurized medium flows from 
the valve seat to the pressure line exclusively through the diaphragm. An 
undesired premature activation of the switchable diaphragm associated with 
the inlet valve cannot be ruled out with sufficient certainty, especially 
in the case of rapid actuation of the brake (e.g., panic braking). In the 
event of such premature activation of the switchable diaphragm, the feel 
of the pedal and the vehicle-specific pressure build-up gradient will 
change. A reduction in the pressure build-up gradient brought about by the 
diaphragm action inherently leads to a reduction in braking power. 
It was therefore proposed in German Patent Application No. P 43 32 819.9 
that fixed diaphragms be additionally arranged upstream or downstream of 
the solenoid valve (inlet valve), but the result is that the switchover 
pressure or the switching pressure difference of the switchable diaphragm 
remains relatively high, which may lead to undesired fluctuations in the 
volume flow during the brake pressure control. 
SUMMARY OF THE INVENTION 
A task of the present invention is therefore to prevent a premature, 
undesired activation of the switchable diaphragm during the slip-free 
normal braking phase, while possibly maintaining unchanged the simple 
design of the brake system disclosed in German Patent Application No. P 43 
19 227.0. 
According to the present invention, a pressurized agent channel arranged 
upstream of the valve seat has a portion having a reduced cross section 
(i.e., a channel constriction). Opening into this channel is a channel 
branch of small nominal diameter, extending in the direction of a front 
surface of the annular piston. Consequently, the pressure energy of the 
pressurized medium column flowing into the solenoid valve is converted in 
the portion having a reduced cross section into kinetic energy, which 
initiates a pressure gradient in the channel branch. 
Due to the design according to the present invention, the pressure gradient 
generated directly at the narrowest flow cross section is used to hold the 
annular piston in the deactivated switching position in order to prevent 
premature switching of the annular piston into the diaphragm position 
during slip-free normal braking. 
Additional features, advantages and possible applications of the present 
invention will become apparent from the following description of a number 
of exemplary embodiments.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows a longitudinal section of an exemplary embodiment of the 
overall design of the inlet valve 1 for a slip-controlled brake system. 
The inlet valve 1 has a valve support 10, which contains the valve-closing 
member 11 and which defines the channel guide of the main pressure line 2 
coming from the brake pressure transducer 5 and from the auxiliary 
pressure pump 18. The valve support 10 is integrated in a valve-mounting 
body 9 preferably in a cartridge design (such as a screw-in cartridge, a 
wedged cartridge, or a cartridge with an expanding ring). In the selected 
representation of the valve-fastening system, the valve support 10 is 
affixed to the valve-mounting body 9 by twofold self-wedging. The sealing 
of the valve support 10 in the valve-mounting body 9 is guaranteed by 
self-wedging. 
There is a pressurized medium communication to the annular piston 8 via the 
main pressure line 2, which is connected to the brake pressure transducer 
5 and to the auxiliary pressure pump 18, through a plate filter 21 clipped 
onto the extension of the valve support 10, and via the valve-closing 
member 11, which is open in the normal position and selectively prevents 
pressurized medium flow across a valve seat 116. From the annular piston 
8, the pressurized medium flows in the direction of the ring filter 22 
arranged upstream of the connection to the wheel brake 3 via the open 
annular gap between the annular piston 8 and the solenoid core 127 and, to 
a lesser extent, also via the diaphragm 4. 
A valve sleeve, over which the valve coil, not shown explicitly in the 
figure, is drawn, projects over the solenoid core 127. The valve sleeve 
forms a unit wedged in the valve support 10 together with the solenoid 
core. A valve lifter provided with an armature extends through the 
solenoid core 127 to the valve seat 116. The valve-closing member 11 is 
formed in the end area of the valve lifter. 
The annular piston 8 assumes the switchable diaphragm function as a 
consequence of a cross hole through the wall of the annular piston. The 
annular piston 8 is guided axially moveably on an extension of the 
rotationally symmetrical central body 114 having the valve seat 116 in the 
annular space 126. Under the action of a compression spring 7, the annular 
piston 8 is supported with its outer shoulder 119, which acts as a stop, 
on the step of valve support 10 in the annular space 126. The annular 
piston 8 has essentially the shape of a sleeve, which is located opposite 
the front area of the solenoid core 127 provided with a rubber sealing 
seat 115. The annular piston 8 has a face facing the solenoid core 127 and 
exposed to annular space 126, which is in pressurized medium communication 
with main pressure line 2 leading to wheel brake 3. If desired or 
necessary, the sealing may also be designed as a metallic flat packing or 
with an O-ring inserted in the front surface area of the annular piston 8. 
A sealing ring 124, which prevents pressurized medium from flowing over 
from the brake pressure transducer 5 in the direction of the wheel brake 
3, is located in the space 117 on the side of the annular piston 8 facing 
away from the solenoid core 127. Another face of the annular piston 8 is 
exposed to the space 117, which is in pressurized medium communication 
with main pressure line 2 leading to brake pressure transducer 5 and 
auxiliary pressure pump 18. 
Via a channel branch 129, which extends between the central body 114 and 
the valve support 10, the space 117 is in pressurized medium communication 
with a portion having a reduced cross section (i.e., a channel 
constriction 130), which is provided in the lower area of the central body 
114 and is preferably formed by a diaphragm insert 131. The rotationally 
symmetrical central body 114 extending into the inner space of the valve 
is pressed or wedged into the stepped hole of the valve support 10. In the 
exemplary embodiment shown, the valve seat 116 is designed as an integral 
part of the hole of the central body 114 extending coaxially to the 
valve-closing member 11. The central body 114 is held as a stepped sleeve 
part in the valve support 10 by means of a self-wedging. 
The opening (through which pressurized medium flows) defined by channel 
constriction 130 is smaller in diameter than the opening defined by valve 
seat 116. This difference in size of the openings causes a pressure 
gradient (or decrease) in channel branch 129. The specific sizes of the 
openings of channel constriction 130 and valve seat 116 differ widely 
depending on the brake type. In one exemplary embodiment, the diameter of 
the opening defined by channel constriction 130 is about 0.3 to 0.9 mm, 
while the opening defined by valve seat 116 is approximately 1.2 mm. 
A pressurized medium path 132 extends obliquely to the central body 114 in 
the valve support 10. Disposed in path 132 is a check valve 133, which 
closes in the direction of the wheel brake 3. Check valve 133 makes 
possible a liquid-filtering pressurized medium connection between the 
wheel brake 3 and the brake pressure transducer 5 or the auxiliary 
pressure pump 18 via a ring filter located between and at spaced locations 
from the valve support 10 and the valve-mounting body 9 as well as by 
means of at least one free path shown in the figure at the plate filter 
21. 
FIG. 2 shows, unlike FIG. 1, a special design of the channel constriction 
130 by use of a diaphragm insert 131, which has essentially the contour of 
a nozzle and is designed as a thin-walled body, comparable to a venturi 
tube. The diaphragm insert 131 has a shoulder 135, which is provided with 
recesses 134 and is clamped between the plate filter 21 and the valve 
support 10. The recess 134 is designed such that it partially covers the 
check valve 133 in the pressurized medium path 132 in order to keep the 
check valve 133 in the pressurized medium path 132. The diaphragm insert 
131 is preferably designed as a pressed part made of a light-gauge sheet 
or as an injection-molded plastic part. The channel constriction 130 acts 
as a circular cross section within the diaphragm insert 131 on the 
pressurized medium flow of the brake pressure transducer 5 or of the 
auxiliary pressure pump 18. In addition, the design of the diaphragm 
insert 131 as a nozzle orifice results in a tapered annular cross section 
in the area in which the channel branch 129 opens into the main flow of 
the main pressure line 2. 
All the additional elements shown in the graphic representation in FIG. 2 
correspond essentially to the design and the function according to FIG. 1. 
FIG. 3 shows, unlike FIG. 2, a metallic sealing of the front surface at the 
annular piston 8 when the latter is moved in the direction of the solenoid 
core 127 against the action of the compression spring 7 as a consequence 
of a pressure difference at the two front surfaces of the annular piston 
8. The sealing seat 115 at the solenoid core 127 is preferably designed as 
a sealing seat that is crowned or spherical in the direction of the 
annular piston 8, so that an annular sealing surface is obtained. An 
especially simple embodiment of the diaphragm 4 in the annular piston 8 is 
obtained when the diaphragm 4 is shaped as a notch in the front surface of 
the annular piston 8, instead of as a hole. This leads to the desired 
diaphragm function at the annular piston 8 as soon as the latter comes 
into contact with the metallic sealing seat 115. Unlike in the case of the 
embodiments designed as diaphragm holes according to FIGS. 1 and 2, debris 
(possibly caused by wear) or dirt particles cannot lead to clogging of the 
notch, because it is subject to a self-cleaning function due to the 
opening and closing of the annular piston 8. All the other details shown 
in FIG. 3 can be found in the descriptions of the above exemplary 
embodiments. 
The mode of operation of the present invention is explained below: 
The inlet valve 1 is in the electromagnetically non-excited, open normal 
position during an uncontrolled, slip-free normal braking phase. When the 
brake pressure transducer 5 is actuated, an increasing pressure build-up 
gradient is initiated in the inlet valve 1, and this gradient leads to a 
considerably increasing velocity of flow, which establishes a pressure 
gradient in the direction of the space 117 in the essentially gap-like 
channel branch 129. This pressure gradient also acts on the annular piston 
8 via the sealing ring 124 at the annular piston 8. The compression spring 
7, which holds the annular piston 8 in the starting position, is 
hydrodynamically supported by the increased pressure difference between 
the two front surfaces on the annular piston 8, so that there is an 
unhindered pressurized medium communication between the sealing seat 115 
and the front surface of the annular piston 8 even during the rapid 
initial braking phase. The annular piston 8 thus remains in the starting 
position according to the figure, in contact with the step of the valve 
support 10 acting as a stop, so that pressurized medium can propagate 
unhindered to the wheel brake 3 via the annular gap between annular piston 
8 and solenoid core 127. The undesired premature activation of the 
diaphragm 4 integrated within the annular piston 8 does not occur. 
When the brake pedal is released, the brake pressure is reduced in the 
opposite direction via the open valve-closing member 11 ant via the check 
valve 133, in the direction of the brake pressure transducer 5. 
If the pressure difference between the valve inlet (main cylinder/pump 
pressure) and the outlet of the valve (wheel brake pressure) exceeds a 
value set by the compression spring 7 during a brake slip control with the 
inlet valve closed, the annular piston 8 is displaced against the spring 
force as a consequence of the resulting force of pressure at the sealing 
ring 124. This displacement causes the annular piston 8 to come into 
sealing contact with the solenoid core 127. Thus, there is a pressurized 
medium communication with the wheel brake 3 only via the diaphragm 4 of 
the annular piston 8. 
If the inlet valve 1 again opens its regular passage via the valve-closing 
member 11, the fluid supplied flows from the auxiliary pressure pump 18, 
which operates during brake slip control, exclusively via the diaphragm 4 
in the annular piston 8 to the wheel brake 3. In this way, the pressure 
shock and consequently the noise are reduced during the subsequent 
repeated closing of the inlet valve 1. When the switching pressure 
difference drops below the value necessary for actuating the annular 
piston 8, such as by an interruption in the braking process, the annular 
piston 8 returns into the starting position which increases the flow 
passage to the wheel brake 3. 
In summary, the influence of the rate of pressure build-up during manual 
brake operation is negligibly small due to the present invention, because 
the pressure gradient established at the annular piston or the pressure 
difference in the constricted flow cross section, and consequently also in 
the constricted channel branch, inevitably increases with an increasing 
rate of pressure build-up, as a result of which the switchable diaphragm 
remains ineffective during the normal braking phase and consequently with 
the valve-closing member opened. The switchover pressure, at which the 
annular piston during brake slip control is activated, can thus also be 
reduced considerably, as a result of which the variations in the volume 
flow can also be advantageously kept at a low value for the purpose of 
good control performance during brake slip control. The valve noises 
inevitably also decrease compared with the solutions suggested to date, 
and the pressure build-up gradient can be increased, if desired or 
necessary, for the manually controlled, locking-free brake operation. 
List of Reference Numbers 
1 Inlet valve 
2 Main pressure line 
3 Wheel brake 
4 Diaphragm 
5 Brake pressure transducer 
7 Compression spring 
8 Annular piston 
9 Valve-mounting body 
10 Valve support 
11 Valve-closing member 
18 Auxiliary pressure pump 
21 Plate filter 
22 Ring filter 
114 Central body 
115 Sealing seat 
116 Valve seat 
117 Space 
119 Outer shoulder 
124 Sealing ring 
126 Annular space 
127 Solenoid core 
129 Channel branch 
130 Channel constriction 
131 Diaphragm insert 
132 Pressurized medium path 
133 Check valve 
134 Recess 
135 Shoulder 
136 Fixed diaphragm