Electromagnetic reversing valve

An electromagnetic reversing valve in which a slidable armature is supported with clearance in a housing and carries a plastic seal unit for selectively closing first and second channels in the housing upon sliding movement of the armature, the sealing unit provides a separate fluid passage establishing communication between a third channel in the housing and one of the first and second channels when it is unsealed. Since the clearance space around the slidable armature is separate and independent from the fluid passage in the seal unit, it can be made substantially narrower in dimension than the fluid passage, thereby to minimize the iron-free gap between the slidable armature and the surrounding member of the magnetic circuit. The iron-free gap is formed in part by the clearance space and in part by a portion of the housing in which the magnetic circuit member is embedded. In a particular embodiment, the seal unit is formed by a central part joined to an outer part by radial, circumferentially spaced ribs defining the fluid passage.

FIELD OF THE INVENTION 
The invention relates to electromagnetic reversing valves of the type in 
which a slidable armature in a housing forms a valve sealing unit for 
selectively opening and closing two channels or passages for flow of a 
fluid. 
BACKGROUND AND PRIOR ART 
A reversing valve of the above type is disclosed in DE 34 16 336, wherein 
there are two opposed valve seats, between which is slidably disposed an 
armature provided with seals. 
The armature is slidable in a guide tube having a wall facing the armature 
provided with longitudinal recesses or grooves to provide fluid flow 
passageways between the channels. The portions of the guide tube between 
the longitudinal recesses serve for guiding the armature in its slidable 
movement. 
An electromagnetically actuated valve of a different type is disclosed in 
DE 37 16 072, in which the armature is configured with a valve sealing 
part movable in a guide borehole, through which a fluid passes. For this 
purpose, the valve sealing part comprises a cylindrical base unit having a 
smooth outer surface which forms passages for flow of the fluid. 
In electromagnetic reversing valves, there is need to minimize the 
reluctance of the magnetic circuit consisting of a yoke, a pole tube and 
the armature, i.e., minimizing the iron-free spacing between the 
structural parts. 
The arrangement in DE 34 16 366 doesn't meet this criteria, since the 
recesses extending in the longitudinal direction of the armature guide 
tube form part of the iron-free gap. The construction in DE 37 16 072 in 
which smooth surfaces are provided for the formation of fluid passages 
increases the iron-free gap between the armature and the pole tube if 
applied to the type of valve according to the invention. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide means by which the iron-free gaps 
can be substantially reduced in the magnetic circuit of a reversing valve 
of the type according to the invention. 
In accordance with the invention, the slidable armature carries a plastic 
unit which provides the seals for sealing the first and second channels in 
the housing while also providing fluid communication between a third 
channel in the housing and one of the unsealed first and second channels. 
Thereby, the fluid communication between the channels is obtained 
independently of the necessary clearance for the sliding movement of the 
armature and consequently, the clearance can be made very much smaller 
than the fluid passage. Thereby, the iron-free gap between the armature 
and the surrounding pole tube of the magnetic circuit, which extends 
across the clearance space, can be minimized. 
According to a particular embodiment of the invention, the slidable 
armature is disposed for sliding movement, under the action of the 
magnetic circuit, between longitudinally spaced first and second channels 
and the armature carries sealing means for selectively sealing said first 
and second channels upon sliding movement of said armature. The sealing 
means provides a fluid passage therein to establish communication between 
the third channel and one of the first and second channels when unsealed. 
The clearance space for sliding movement of the armature, extends around 
the armature and is separate from and independent of the fluid passage in 
the sealing means and thereby can be made substantially narrower in 
dimension than said fluid passage. The iron-free gap in the magnetic 
circuit between the slidable armature and a yoke tube of the magnetic 
circuit extends across the clearance space and thereby is formed in part 
by said clearance space. The sealing means comprises a non-magnetic unit 
fixed in a recess in the armature and having protruding ends for 
selectively sealing the first and second channels upon sliding movement of 
the armature. 
In accordance with a feature of the invention, the sealing unit comprises a 
central part joined to an outer part by radial ribs which are 
circumferentially spaced to define the fluid passage therebetween.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the drawing, there is shown an electromagnetic reversing valve 1 
comprising a plastic housing 2 containing a magnetic coil 3 and electrical 
connections 4 to energize the coil from an electrical power supply (not 
shown). The coil 3 is operatively coupled in a magnetic circuit formed by 
a yoke 5, a pole tube 6 joined to the yoke and to an armature core 7 and a 
slidable magnetic armature 9 forming an iron-free gap 8 with the pole tube 
6 in the magnetic circuit. Armature 9 is slidable in a space 10 in housing 
2 between two longitudinally aligned fluid passages or channels 11, 12 
having open ends forming respective valve seats 13, 14. Magnetic armature 
9 and space 10 are dimensioned to provide a minimum slidable clearances 
for the armature 9 in the housing and thereby provide a minimum size for 
the iron-free gap 8 which extends across the clearance. Armature 9 is 
formed as a tube and has a tubular recess 15 extending longitudinally 
therein in which a plastic unit 16 is fixed. The plastic unit 16 has a 
central part 17 with protruding elastomer ends 18, 19 forming seals for 
seating on the valve seats 13, 14 to close passages 11, 12. The central 
part 17 is integrally joined to an outer coaxial part 21 of the plastic 
unit 16 by circumferentially spaced, radial ribs 20, so that fluid flow 
passages 22 are formed by an annular space between central part 17 and 
outer part 21. 
A spring 23 is interposed between central part 17 and armature core 7 to 
urge the armature 9 against valve seat 13 of the passage 11. The passage 
12 is formed in the armature core 7 itself. The space 10 communicates with 
a third passage 24 extending transversely. Depending on whether or not 
current is supplied to coil 3, the passage 11 is connected to passage 24 
and passage 12 is closed, or passage 12 is connected to passage 24, and 
passage 11 is closed (as shown). 
Between pole tube 6 and armature 9, there is only the extremely small 
iron-free gap 8 formed by the clearance of armature 9 in space 10 and an 
intermediate wall 25 of plastic housing 2 in this region. A large magnetic 
force results due to this small iron-free gap. In this way, the range of 
movement of the reversing valve is increased, or the size or number of 
windings of coil 3 can be reduced. 
As evident from the above, by forming the passages 22 in the seal unit 
separately and independent from the clearances between the armature 9 and 
the housing 2, it is possible to make the clearances much narrower than 
the passages 22 without affecting the fluid flow through the sealing unit 
between passage 24 and passage 12 when the latter is unsealed. 
Although the invention has been described in relation to a specific 
embodiment thereof, it will become apparent to those skilled in the art 
that numerous modifications and variations can be made within the scope 
and spirit of the invention as defined in the attached claims.