Solenoid valve for compression-type engine retarder

A solenoid valve for use with a solenoid as park of an engine retarder braking system includes a valve body arranged with a plurality of apertures and which receives an upper check valve pin, a lower check valve pin, and a biasing spring which acts on both check valve pins. The solenoid includes a coil and moveable armature and the braking system includes a high pressure circuit with a master piston and cylinder and a slave piston and cylinder. The two cylinders are connected by a flow passageway. The housing has a fluid inlet, a fluid outlet, and an access port. The fluid inlet receives low pressure oil which acts upon one side of the lower check valve pin. The opposite side of the lower check valve pin is acted upon by the fluid in the high pressure circuit and by the biasing spring. When the pressure difference allows the lower check valve pin to move out of its sealed position against the fluid inlet, oil is introduced into the high pressure circuit. When the upper check valve pin is sealed against the access port and the lower check valve pin is sealed against the fluid inlet, the high pressure circuit is sealed closed, allowing upward movement of the master piston to pressurize the oil in the circuit and create downward movement in the slave piston, which causes the corresponding exhaust valves to open.

BACKGROUND OF THE INVENTION 
The present invention relates in general to engine brake retarders of the 
compression release type. More particularly, the present invention 
pertains to an improved hydraulic circuit solenoid valve which combines 
solenoid and control valve functions into a single component. 
Engine brake retarders of the compression release type are believed to be 
well known in the art. These devices may be referred to as an engine brake 
or engine retarder, but regardless of the name, the theory of operation is 
basically the same. In general, such engine retarders are designed to 
control the motion of a slave piston which opens the exhaust valves of an 
internal combustion engine cylinder near the end of the compression 
stroke. As a result, the work done in compressing the intake air is not 
recovered during the expansion stroke, but rather is dissipated through 
the exhaust (and cooling) systems of the engine. 
One current style of engine retarder is represented by the Cummins Engine C 
Brake which is offered by Cummins Engine Company, Inc., of Columbus, Ind. 
The C Brake is a highly efficient engine retarder which is used for 
reducing vehicle speed. The theory of operation, which is similar in 
certain respects to other engine retarder designs, uses a hydraulic 
circuit that opens the exhaust valve(s) near the end of the compression 
stroke. When the C Brake is activated and the vehicle is moving, the 
engine produces a compression braking effect. 
The C Brake uses one solenoid valve for each pair of engine cylinders in 
combination with two control valves, one for each cylinder. These 
components are assembled into a housing which is mounted directly on top 
of the rocker housing. When the solenoid valve is energized, engine oil 
enters the C Brake system through the rocker arm pedestal. As engine oil 
flows into the C Brake, the control valve is forced in an upward 
direction. A minimum of 18 psi is required to open this control valve. 
When the cross drilling in the control valve is aligned with the high 
pressure drilling, oil flows past a check ball into the master piston and 
slave piston high pressure circuit. This entering oil added pressure 
causes the master piston and slave piston to move in a downward direction. 
As the injector push rod begins its upward travel, the injector rocker arm 
adjusting screw begins to force the master piston in an upward direction. 
This action closes the control valve check ball and as a result, oil is 
then trapped in the high pressure circuit. The continuing upward movement 
of the injector push rod increases the oil pressure and ultimately forces 
the slave piston to travel in a downward direction. With this advancing 
travel in a downward direction by the slave piston, it applies force to 
the cross head of the exhaust valves, forcing those valves to open. The 
opening of the exhaust valves allows compressed air to escape from the 
corresponding cylinder and thus a compression braking cycle has been 
completed. At the completion of this cycle, the injector push rod and 
master piston travel in a downward direction and this allows the oil 
pressure in the high pressure circuit to return to normal. Immediately, 
the slave piston moves in an upward direction, allowing the exhaust valves 
to close. Any leakage from the high pressure circuit is made up at this 
time by engine oil which enters through the solenoid valve and check valve 
within the control valve. 
When the solenoid is de-energized, oil in the C Brake is returned to the 
engine. This allows the C Brake to be returned to its de-activated 
position and the master and slave pistons are retracted by spring 
pressure. As a result, these pistons are moved out of the way of normal 
engine operation. 
One of the design realities with this type of engine retarder is the use of 
a control valve, one for each cylinder, which uses a control spring. Such 
springs have had, on occasion, reliability concerns and the elimination of 
the control valve springs would obviously avoid such concerns. Another 
design reality is the size of the control valve and its required travel 
distance. This also influences the size of the assembly housing which is 
required. If the control valve function can be combined as part of a new 
solenoid valve design, then the size of the engine retarder can be 
reduced. The present invention provides such an improved design. 
While the Cummins Engine C Brake design represents one engine retarder 
arrangement, there are other configurations which deserve consideration 
when reviewing the complexity of engine retarder systems. One example of 
another system which uses a solenoid in combination with a control valve 
is disclosed in U.S. Pat. No. 4,996,957 which issued Mar. 5, 1991, to 
Meistrick. The disclosed device of Meistrick includes a first flow network 
for the delivery of oil at low pressure to a solenoid valve and from there 
to a control valve. Oil also fills the chambers of a slave cylinder and 
master cylinder. During a retarding event, the master piston moves 
upwardly in the cylinder in response to the motion of a push tube, 
creating a high pressure force which in turn forces the slave piston to 
move in a downward direction. The corresponding movement of the slave 
piston in a downward direction opens the exhaust valves near the end of 
the compression stroke of the engine. 
As will be appreciated, the Meistrick device includes a number of 
components and controls including a specific control valve for the high 
pressure fluid circuit. There are also two flows which have to be managed 
by the controls and valves, including a low pressure oil delivery flow 
(and fill) and a high pressure, valve-opening flow. The result of this 
complexity is a significant size requirement and thus a need for a 
significant area or space in which to mount all of the required hardware 
and all in the vicinity of the cylinder exhaust valves. 
It would be an improvement to the complexity of designs such as that 
described in the Meistrick patent if a single solenoid component could be 
designed to combine both the solenoid and control valve functions into one 
item. Ideally this would permit a smaller package size for the engine 
brake. Added benefits of such an improvement would be a reduction in the 
machining required to create the now-required control valve and solenoid 
drillings. If the currently used control valve can be eliminated by a 
combined solenoid design, then the now-required control valve spring could 
also be eliminated. Since the control valve springs have historically 
presented certain problems with regard to reliability, elimination of this 
spring would represent a substantial benefit to the engine brake in terms 
of improved reliability. 
The present invention provides the aforementioned type of design 
improvement by a novel and unobvious solenoid valve which combines the 
solenoid and control valve functions into a single component. The result 
is a smaller package size and a design which handles both the low pressure 
flows as well as the high pressure flows. 
In addition to what is disclosed in the Meistrick patent, there have been 
other solenoid and control valve arrangements invented over the years. The 
following listed patent references are believed to be a representative 
sampling of such earlier solenoid and control valve designs. 
______________________________________ 
PATENT NO. PATENTEE ISSUE DATE 
______________________________________ 
2,944,565 Dahl July 12, 1960 
3,220,392 Cummins Nov. 30, 1965 
3,332,405 Haviland July 25, 1967 
3,921,666 Leiber Nov. 25, 1975 
4,251,051 Quenneville et al. 
Feb. 17, 1981 
4,460,015 Burt et al. July 17, 1984 
4,844,119 Martinic July 4, 1989 
______________________________________ 
While the handling of either low pressure flows or high pressure flows may 
be possible with one or more of the devices disclosed in the above list, 
nothing is disclosed which handles both by means of a single solenoid 
component as is provided by the present invention. For example, the 
Quenneville, et al., patent describes a solenoid which is used for 
controlling low pressure oil to an engine brake. In the Meistrick design 
the control function focuses on the high pressure circuit and not the low 
pressure supply side. 
SUMMARY OF THE INVENTION 
According to one embodiment of the present invention, a solenoid valve for 
use with a solenoid as part of an engine retarder braking system is 
disclosed. The cooperating solenoid which is used to actuate the solenoid 
valve includes a coil and a moveable armature. The braking system includes 
a high pressure circuit with a master piston disposed within a master 
cylinder, a slave piston disposed within a slave cylinder, and a flow 
passageway connecting the master cylinder with the slave cylinder. The 
solenoid valve which is combined with this system of other components 
comprises a housing arranged with the fluid inlet, a fluid outlet which is 
flow coupled to the flow passageway, and an armature access port. 
Additionally, an upper check valve pin is positioned within the housing 
and is designed to seal closed the armature access port. A lower check 
valve pin which is also positioned within the housing is disposed in axial 
alignment with the upper check valve pin and is designed to seal closed 
the fluid inlet. Both check valve pins are moveable between their sealed 
position and an open position. The solenoid valve further includes a 
biasing spring which is disposed within the housing and which is 
positioned relative to the upper and lower check valve pins so as to apply 
a separating spring force on those pins so as to bias those pins in 
opposite directions, apart from each other. When the solenoid armature is 
retracted, the upper check valve pin seals closed the access port and when 
the fluid pressure at the fluid inlet is sufficient to push the lower 
check valve pin out of sealed engagement fluid fills the high pressure 
circuit. With both check valve pins in a sealed condition, the fluid which 
is trapped in the high pressure circuit is acted on by movement of the 
master piston in order to control movement of the slave piston for opening 
of corresponding cylinder exhaust valves. 
One object of the present invention is to provide an improved solenoid 
valve as part of an engine retarder braking system. 
Related objects and advantages of the present invention will be apparent 
from the following description.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
For the purposes of promoting an understanding of the principles of the 
invention, reference will now be made to the embodiment illustrated in the 
drawings and specific language will be used to describe the same. It will 
nevertheless be understood that no limitation of the scope of the 
invention is thereby intended, such alterations and further modifications 
in the illustrated device, and such further applications of the principles 
of the invention as illustrated therein being contemplated as would 
normally occur to one skilled in the art to which the invention relates. 
Referring to FIG. 1 there is illustrated an engine retarder braking system 
10 which includes a novel solenoid valve 20 which is designed in 
accordance with the present invention. Solenoid valve 20 combines into a 
single unit the separate solenoid and control valve functions of earlier 
engine retarder designs. Illustrated as part of the FIG. 1 system are the 
masher cylinder 21 and master piston 22, properly assembled, and the slave 
cylinder 23 and slave piston 24, also properly assembled. These two 
assemblies are connected to each other (cylinder to cylinder) by oil 
passageway 25. Branch passageway 26 extends in flow communication between 
passageway 25 and solenoid valve 20. The master cylinder, slave cylinder 
and passageways 25 and 26 constitute a high pressure circuit. This circuit 
is actually able to function as a high pressure network when any oil 
escape passage or access through the solenoid valve 20 is blocked. 
Passageways 25 and 26 also provide the means for low pressure oil to fill 
cylinders 21 and 23. 
Also illustrated in FIG. 1 is a diagrammatic representation of an injector 
push rod 29 in combination with a rocker arm adjusting screw 30 which 
contacts the lower face of the master piston 22. On the opposite side of 
FIG. 1 there is illustrated, as a diagrammatic representation, exhaust 
valves 31 and 32 whose action is controlled by crosshead 33 in combination 
with springs 34 and 35. 
Solenoid 36 includes a coil 38 and an armature 39. The solenoid valve 20 
includes upper check valve pin 40, lower check valve pin 41, and check 
valve biasing spring 42. The two check valve pins 40 and 41 and biasing 
spring 42 are all positioned within the hollow interior of valve body 43 
which in turn is positioned within valve bore 44 of structural member 45. 
The valve body 43 remains stationary within valve bore 44. Overhead 
passageway 47 is the means through which oil is delivered to the solenoid 
valve and aperture 48 supplies the delivered oil to branch passageway 26. 
The actual solenoid valve mechanism includes the two check valve pins and 
the biasing spring all of which are positioned within the disclosed 
housing. The two check valve pins are in axial alignment with each other 
and the biasing spring tends to bias or push apart the two pins, in 
opposite directions. However, when the solenoid armature 39 is extended, 
the distance between the end of that armature and the inlet edge 47a of 
overhead passageway 47 is not sufficient to allow the upper and lower 
check valve pins to separate. In this particular configuration, they 
appear as a solid member and the overhead passageway 47 is sealed closed. 
The upper portion of the valve body 43 around pin 40 provides a return oil 
path for the high pressure circuit oil to drain back to the engine when 
the engine retarder braking system is not activated or energized. 
It is possible for the solenoid 36 to be thought of as part of the solenoid 
valve 20 since some type of control mechanism is required to act on the 
upper check valve pin 40. However, since such a solenoid is included as 
part of earlier engine retarder systems, and the changes provided by the 
present invention focus on the construction of valve 20, the "boundary" 
for valve 20 should be drawn to include the housing 43, the two check 
valve pins 40, 41, and the biasing spring 42. 
There is a low pressure supply of oil present at passageway 47 whenever the 
engine is operating. Whether or not oil will actually be delivered to the 
high pressure circuit via passageway 26 depends on the pressure level in 
that high pressure circuit. Whenever the low pressure level of the oil 
supply is sufficient to overcome the spring bias force of spring 42, and 
whatever opposing pressure may be present in the high pressure circuit, 
lower check valve pin 41 is lifted and the low pressure supply of oil is 
allowed to flow into and fill the high pressure circuit. Obviously as the 
high pressure circuit fills with oil, there is an exerted back pressure 
which, in combination with the biasing spring 42, will at some point 
override the entering oil pressure and return the lower check valve pin 41 
to its sealed position against the entrance 47a of passageway 47 which is 
part of the valve body or housing 43. 
The detailed specifics of the structure of solenoid valve 20 are 
illustrated in FIG. 2. In this detailed illustration, the solenoid 36 is 
included and as mentioned above, the solenoid 36 can be thought of as part 
of the solenoid valve or as a separate component, though here it is 
treated as a separate component which simply has a position and 
operational relationship to solenoid valve 20 with regard to control of 
the position of the upper check valve pin 40. In addition to what was 
illustrated in FIG. 1, solenoid 36 includes a bias spring 49 and the valve 
body 43 provides a leakage escape path defined by clearance space 50 for 
the return of oil in the high pressure circuit back to the engine. 
The stages off operation of the engine retarder braking system 10 including 
solenoid valve 20, as the engine retarder system is activated and 
de-activated, are illustrated in FIGS. 3, 4, and 5. If we start with the 
condition or assumption that the high pressure circuit is filled with oil, 
this will in turn mean that the solenoid coil has been energized and that 
pin 41 is sealed closed against inlet edge 47a (see FIG. 3). Energizing of 
solenoid coil 38 causes the solenoid armature 39 to retract or, based upon 
the orientation of FIG. 3, to move in an upward direction away from the 
upper stem portion 40a of upper check valve pin 40. The retraction of the 
armature releases the upper check valve pin 40 such that the separation or 
biasing force exerted by spring 42 is now able to actually move the upper 
check valve pin in an upward direction such that the body of the pin 
engages the inside edge 53a of armature access port 53 and thereby 
precludes the flow through or back flow of any oil to the engine. 
The assumption made with regard to the illustration of FIG. 3 is that the 
high pressure circuit was initially filled with oil. As a consequence, 
there is sufficient opposing pressure (in combination with biasing spring 
42) to prevent any upward movement of the lower check valve pin 41. The 
result is that the high pressure circuit is completely sealed closed, 
trapping in the various cylinders and passageways a volume of oil which 
has no means to escape. Sealing of the high pressure circuit is also 
accomplished at the interface between the valve body 43 and the valve bore 
44 using a precision fit. This type of precision fit also exists between 
the master cylinder 21 and master piston 22 as well as between the slave 
cylinder 23 and slave piston 24. 
With the high pressure circuit closed and sealed, upward movement of the 
injector push rod 29 in combination with the rocker arm adjusting screw 30 
pushes upwardly on the master piston 22. As the master piston moves in an 
upward direction, the pressure is increased on the oil which fills the 
high pressure circuit. The increase in oil pressure completes any sealing 
of the circuit by providing the necessary pressure difference to prevent 
the low pressure supply from lifting check valve pin 41. The movement of 
the master piston and the corresponding increase in the oil pressure acts 
against the slave piston 24 which is then moved in a downward direction. 
As the slave piston 24 is pushed down against the crosshead 33, the 
opposing spring force is overcome and exhaust valves 31 and 32 for that 
particular cylinder are opened. As previously explained, the valves are 
opened when the piston is near TDC, on the compression stroke, allowing 
the compressed air to escape from the cylinder. This effectively cancels 
the power stroke and creates the desired braking effect. 
At the end of this first compression braking cycle, the injector push rod 
and master piston travel downward, allowing the oil pressure in the oil 
circuit to return to normal. The immediate consequence is for the slave 
piston to move upward, allowing the exhaust valves 31 and 32 to close. 
When the engine retarder braking system is de-activated (see FIG. 4), the 
solenoid armature 39 is in contact with the upper check valve pin 40. 
Actually the portion which contacts the armature is the stem extension 40a 
which extends up through armature access port 53 such that the upper end 
of stem 40a actually extends out of valve body (housing) 43. The diameter 
size of extension 40a relative to the size of the access port is such that 
an annular clearance space 54 is left for flow communication between 
passageway 26 and clearance space 50. Although not believed to be the 
preferred embodiment, it would be possible to modify the shape of armature 
39 and correspondingly change the shape of upper check valve pin 40 such 
that a portion of the armature could actually extend through port 53 in 
order to act upon pin 40. 
In the FIG. 4 illustration, the oil supply which is present at overhead 
passageway 47 applies pressure on the lower check valve pin 41. However, 
pin 41 which is axially aligned with pin 40, remains closed against the 
housing entrance 47a of passageway 47 due to the force applied from the 
solenoid bias spring 49 via armature 39 and upper check valve pin 40. 
Regardless of any pressure differences between the high pressure circuit 
and the low pressure supply, lower check valve pin 40 remains closed and 
sealed against the entrance of passageway 47 when the brake is off. In 
this arrangement, oil is not allowed to enter and fill the high pressure 
circuit. Also during the solenoid valve de-activation (brake off), there 
is a leakage path created by clearance space 50 in combination with 
annular clearance space 54 and passageway 26 for oil to escape from the 
high pressure circuit and return to the engine. 
The final stage to be discussed which is actually the initializing step in 
the overall process is the step of filling the high pressure circuit with 
oil and this is illustrated in FIG. 5. The high pressure circuit is filled 
with oil during initial activation and is refilled with oil during each 
cycle. For this brake-fill stage or the stage which initializes the system 
by filling the high pressure circuit with oil, all of the internal 
components of the solenoid valve are in the same configuration as in the 
brake activated stage of FIG. 3. The only exception is that the lower 
check valve pin 40 is pushed up out of sealing engagement against the 
housing entrance 47a of passageway 47. 
In the FIG. 5 illustration, the solenoid coil 38 is energized and the 
armature 39 is pulled up and away from the upper check valve pin 40. The 
assumption made for this illustration is that the high pressure circuit is 
at a pressure level below the pressure level of the incoming oil supply. 
This is what would be expected, since the incoming oil supply will be at a 
pressure level at something above atmospheric pressure and at this point, 
the high pressure circuit or at least the unfilled portion of it, is at 
atmospheric pressure. Further, the pressure level of the incoming oil 
supply is greater or exerts a greater force than the opposing force on the 
lower check valve pin 41 exerted by spring 42. Through a simple force 
balance typical to conventional check valve design, the lower check valve 
pin 41 comes out of its sealed engagement and this allows the flow of low 
pressure oil to enter the housing. From the housing the oil is routed via 
passageway 26 to the high pressure circuit. This arrangement allows the 
high pressure circuit to fill with oil during the initial activation and 
then refill during each cycle. The repeating steps of the oil filling the 
high pressure circuit with each cycle is governed by the pressure and 
force differences and no other controls are required. 
The solenoid valve 20 of the present invention provides a unique and 
compact single component design which can be readily adapted to an engine 
retarder braking system. The engine retarder breaking system still 
includes the master piston and cylinder as well as the slave piston and 
cylinder and the connecting passageway between the two as part of the high 
pressure circuit. The system also includes a solenoid, but otherwise the 
solenoid valve and control valve functions of earlier designs are combined 
into a unique arrangement which provides greater reliability and a more 
compact size. There are, in effect, only three components to deal with in 
the sense of the solenoid valve, ignoring for now the specific size, 
shape, and configuration of the valve body or housing. The three 
components are simply the upper check valve pin, the lower check valve 
pin, and the separating or biasing spring disposed around and between 
those two members. The simplicity of this design which can handle both low 
pressure flow in a very precise and reliable manner as well as the high 
pressure circuit results in a very desireable invention which is novel and 
unobvious. 
While the invention has been illustrated and described in detail in the 
drawings and foregoing description, the same is to be considered as 
illustrative and not restrictive in character, it being understood that 
only the preferred embodiment has been shown and described and that all 
changes and modifications that come within the spirit of the invention are 
desired to be protected.