Electromagnetically operated control valve

The electromagnetically operated sliding spool control valve particularly for use in connection with an automatic transmission system of a motor vehicle, comprises an armature of the electromagnet which is supported at one end of a plunger the other end of which is formed into a sliding spool. The spool is guided in a valve sleeve integrally connected to a fixed core of the electromagnetic coil. A return spring is arranged around a plunger portion between the core and the armature. The valve sleeve is seated in a central boring of a valve channel plate provided with a plurality of annular grooves communicating via transverse borings with the central passage of the sleeve. The sleeve opens into a pressure space which communicates via a flow return channel with a port for the main pressure so that the main pressure acts against the free end of the spool.

BACKGROUND OF THE INVENTION 
This invention relates in general to directional control valves and more 
specifically it relates to a sliding spool control valve controlled by an 
electromagnet and designed particularly for use in shift control systems 
of a motor vehicle. Conventional control valves of this type have a 
separate sliding spool which at one face is coupled to the armature 
whereas the other face of the spool cooperates with a differential piston. 
The disadvantage of this known construction is the separation of the 
electromagnet and of the valve proper into two separate structural units 
so that the resulting electromagnetically controlled valve is oversized 
and expensive to manufacture. In addition, conventional sliding spool 
valves are exposed to the danger of magnetic clamping of the sliding spool 
when a portion of the magnetic flux affects the sliding spool (German 
"Gebrauchsmuster" DE-GBM No. 72 02 049). 
SUMMARY OF THE INVENTION 
It is therefore a general object of the present invention to overcome the 
aforementioned disadvantages. 
More particularly, it is an object of the invention to provide an improved 
electromagnetically operated sliding spool control valve which is simple 
in operation and compact in structure, which has a short response time and 
large cross-section of its ports. 
In keeping with these objects and others which will become apparent 
hereafter, one feature of the invention resides, in an electromagnetically 
operated sliding spool control valve in a combination which comprises an 
electromagnet having a fixed magnetizable core defining a central passage, 
an armature movably arranged opposite face of the magnetizable core, a 
plunger coaxially attached to the armature and projecting into the passage 
of the core, a portion of the core forming a valve housing defining at 
least a load port and fluid return port, and the sliding spool being 
movable in this valve housing and being integrally connected to the ends 
of the plunger. Return spring normally holds the armature apart from the 
core thus keeping the spool in a starting position relative to the valve 
housing. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The electromagnetically operated slide spool control valve assembly 10 
includes an electromagnet 11 and a valve unit 12. The valve 12 is disposed 
in a cylinder plate 13 which is attached to housing 14 of the whole valve 
assembly 10. Housing 14 encloses a tubular electromagnetic coil 16 an end 
plate 17 of a magnetically conductive material and a cover 18 closing one 
end of the housing 14. 
A movable armature 20 is coaxially supported on a plunger 21 and movable in 
both axial directions in the cylindrical passage 10 in coil 16. The 
plunger 21 is supported for the axial movement in bearing 22 disposed in 
the cover 18 and in another bearing 23 which is formed in the tubular core 
24 of a magnetizable material. The central boring 26 of the core 24 
exceeds in diameter the clearance of the bearing 23 and the resulting 
annular interspace 26 serves for accommodating a pressure spring 27 which 
rests at one end of a shoulder 28 of the bearing 26 and at the other end 
abuts against the armature 20. Bearing 23 which is a part of the fixed 
core 24 is extended outwardly to form a valve sleeve 32 and the end 
portion of plunger 21 which projects into the valve sleeve forms the 
sliding spool 21' of the valve unit. Two diametrically opposed axial 
grooves 29 and 30 are formed between piston areas of the spool which are 
tightly guided in boring 31 of the sleeve 32. 
Pistons and the axial grooves 29 and 30 cooperate with three transverse 
borings 33, 34 and 35 formed in valve sleeve 32 to connect boring 31 with 
corresponding annular grooves 39, 40 and 41 formed in plate 13. The 
annular grooves are concentrically arranged about boring 38 in the valve 
plate 13 in which the valve sleeve 32 is seated. A fluid return channel 42 
connects the annular groove 40 to a pressure space 43 formed at the end of 
boring 38 and communicating with the central boring 31 of the valve sleeve 
32. The end space 43 is connected to port 44. The annular groove 35 is 
connected via an inclined boring 46 in the tubular core 24 to the 
intermediate space 26 in the core. The annular grooves 39, 40 and 41 
communicate respectively with ports 47, 48 and 49 in the outer wall of the 
valve plate 13. 
When the control valve of this invention is employed for the shift control 
of an automatic transmission of a motor vehicle, the port 47 is connected 
to the main pressure fluid of the shift control system, whereas the ports 
44 and 48 lead to conduits supplying a regulated pressure fluid to the 
coupling members of the transmission. Port 49 opens in a pressure free 
space. 
The operation of the electromagnetically controlled guide spool valve of 
this invention is relatively simple. According to the energization of the 
electromagnet 11, the plunger 21 moves axially to the right or to the 
left. In the left end position of the plunger borings 34 and 33 are 
interconnected by the axial grooves 29 and 30 so that the main pressure is 
applied to the coupling of the transmission. At the same time, this main 
pressure is admitted via the return flow channel 42 also against the left 
face of the plunger 21 communicating with the end space 44. As a 
consequence the shifting pressure is quickly adjusted to its correct 
volume. If the sliding spool 21' is moved to its right-hand end position, 
the coupling is connected via port 48, the transverse boring 34, the 
groove 30, and transverse boring 35 to the port 49 leading to a pressure 
free space so that the coupling becomes unloaded. 
The pressure spring 27 assist the control moment of the sliding spool even 
when small pressures are applied. For the operation of the valve it is 
important that after the response of the valve the pressure be relieved as 
soon as possible. A fast pressure relief in the valve of this invention is 
enabled by relatively large cross-sections of the flow passages defined by 
the annular grooves 39 through 41. It is also of advantage when the return 
flow channel 42 is an integral part of the valve plate 13. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
constructions differing from the type described above. 
While the invention has been illustrated and described as embodied in a 
specific example of the electromagnetically operated slide spool valve, it 
is not intended to be limited to the details shown, since various 
modifications and structural changes may be made without departing in any 
way from the spirit of the present invention.