Note: Descriptions are shown in the official language in which they were submitted.
9~ 9~
ENGINE BRAKING SYSTEM
TECHNICAL FIELD
This invention generally relates to an engine
braking system of a gas compression relief type The
invention relates more particularly to engine brakes
wherein the exhsust valves of the engine are opened
near the top of the compression stroke of the engine
so that the ene~gy absorbed by the engine during the
compression stroke is not returned to the engine during
the expansion stroke. The present invention relates
specifically to a timing mechanism for an engine brake
of the above type.
~ACKGRO~ND ART
For many years it has been recognized that the
ordinary wheel brakin~ mechanisms, commonly of the disc
or drum type fitted to commercial vehicles, while
capable of absorbing a large amount of energy during
a short period, are incapable of absorbing the lesser
amounts of energy over an extended period of tLme which
may be required, for example, during descent of a long
decline. In such circumstances, the friction ma~erial
used in the brake mechanism will become overheated
(~causing "brake fading") and may be destroyed while
the metallic parts may warp or buckle. In general~
the problem has been resolved either by using a lower
gear ratio so that the engine can function more
effectively as a brake due to its inherent friction
~or by employing some form of auxiliary braking system.
A number of such auxiliary braking systems, generally
known as engine retarders, have been developed by the
art, including hydrokinetic retarders, exhaust brakes,
~k
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electric brakes, and engine brakes. In each of these
systems, a portion of the kinetic energy o~ the vehicle
is transformed into heat as a result of gas compression,
fluid friction, or electrical resistance and, there-
after dissipated to the atmosphere directly or throughthe exhaust or cooling system. T~e common characteristic
of such auxiliary braking systems is the abîlity to
absorb and dissipate a certain amount of power con
tinuously or at least for an indefinite period of time,
Each of the types of engine retarder referred to above
is described in detail in the publication "Retarders
for Commercial Vehicles" published in 1975 by Mechanical
Engineering Publications Limited, London, England
The hydrokinetic and electric retarders are
generally quite heavy and bulky since they require
turbine or dynamo mechanism and thus may ~e undersirable
from the viewpoint of initial cost as well as operating
cost. The exhaust brake, while generally simple and
compact, necessarily increases the exhaust manifold
pressure and may occasion "floating" of the exnaust
valves of the engine, a generally undesirable condition
It has long been recognized that in the
ordinary operation of an internal combustion engine
employing the Otto or the Diesel cycle, for example, a
considerable amount o~ work is done during the
compression stroke upon the air or air/fuel mixture
introduced into the cylinders. During the expansîon
or power stroke of the engine the work of compression
is recovered so that, neglecting friction losses, the
net work due to compression and expansion is zero and
the net power output is that resulting from the
combustion of the fuel/air mixture. ~hen the throttle
is closed, or the fuel supply interrupted, the engine
will, of course, function as a brake to the extent of
the friction inherent-in the engine mechanism.
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Many attempts have been made to increase the
braking power of an engine by converting the engine to
an air compressor and dumping the compressed air
through the exhaust system. A simple and practical
method of accomplishing this end is disclosed in U.S.
Patent 3,220,392. In that patent an auxiliary exhaust
valve actuating means synchronized with the engine
crankshaft is provided which opens the exhaust valve
near the end of the compression stroke, without
interfering with the normal actuating cam means for
the exhaust valve, together with appropriate control
means for the auxiliary exhaust valve actuating means.
While the engine brake means set forth in detail in
U.S. Patent 3,220,3~2 is capable of producing a
retarding power approaching the driving power of the
engine under normal operating conditions, experience
with this mechanism has reYealed that the retarding
power may be affected significantly by-the timing of
the opening of the engine exhaust valve.
If the exhaust val~e is opened too late a
significant portion of-the retarding power may be lost
due to the expansion of the compressed air during the
initial part of the expansion stroke. On the other
hand, if the exhaust valve is opened too early there
may be insufficient compression during the compression
stroke which, similarly, will reduce the amount of
retarding power that can be developed.
The timing of the exhaust valve opening is
affected to a significant degree by the temperature
conditions in the engine which vary as a result
of changes in ambient conditions as well as changes
in operating conditions. It will be appreciated, for
example, that the length of the engine exhaust YalYe
will increase with increases in temperature, thereby
reducing the clearances in the valve actuating
mechanism. ~hile it is known to provide ad~usta~le
~6 3g~
elements in the valve actuating mechanism by means of
which the clearance may be set (see, for example, U.S.
Patent 3,220,392, Fig. 2, element 301), the clearance
as determined by the rocker arm adjusting screw (or
equivalent element) must be at least large enough when
the engine is cold ~o that some clearance will remain
when the engine is hot. If there is inadequate clear-
ance when the engine is hot, the exhaust valve may be
held in a partially open condition. In this circumstance,
the operation of the engine may be affected adversely
and the exhaust valves are apt to be burned. To avoid
such effects, it is c~mmon to provide a clearance in
the actuating mechanisms for the exhaust (and intake)
valves of an internal combustion engine on the order
of Q.018 inch so as to compensate for dimensional changes
in the mechanism resulting from temperature variations.
When using the exhaust valve actuating mechanism as part
of an engine brake mechanism, it is highly advantageous
to minimize the clearance or backlash in the valve
actuating mechanism to provide a precise control of the
valve timing where~y the retarding power of the engine
is maximized.
DrSCLOSURE OF INVENTION
With the foregoing in mind, we provide in
accordance with the invention an engine braking system
of a gas compression relief type and comprising a
combustion engine having exhaust valve means and an
adjustable body engageable with a first piston
for positioning said first piston to open said exhaust
valve means at a selected predetermined time after
hydraulic pressure fluid is applied to said first piston,
characterized by a second piston mounted for reciprocating
m~nt within the body,which is hollow,between a retracted and
an extended position, said second piston being urged
into its retracted posîtion against the counter force
of a spring by the first piston in the absence of said
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hydraulic fluid pressure thereto,`and check valve means
operatively related to the second piston to maintain
said second piston in its extended position to prevent
return of said first piston for engagement with said
hollow body while said hydraulic fluid pressure is
applied to said first piston.
By virtue o our braking system the clearance
between the first piston and the valve stem is reduced
to a value maximi~ing the performance whenever the
en~ine brake is activated. B~ so reducing the clearance
the exhaust valve is opened sooner and the timing o~
the valve opening coincides more nearly with the
activation of the engine brake master piston so as to
maximize the retarding pawer developed by the engine.
An additional advantage resulting fxom the
present invention is that the maximum pushrod load
may be decreased. The pushrod load is caused by the
force required to open the exhaust valve against the
pressure of the air compressed during the compression
cycle and the force required to actuate t~e fuel
injector. By effectively decreasing the clearance as
aforenoted, the timing of the exhaust valve opening is
advanced so as to increase the time interval between
brake actuation load and the inJector actuation load,
and thereby minimize the combined effect of the two
events. Moreover, by advancing the timing of the
exhaust valve opening, the peak engine cylinder pressure
may be reduced which also serves to reduce pushrod
load.
In certain engines, the design of the intaXe
or exhaust valve pushrods or injector pushrods may be such
that the maximum pushrod load induced when the engine brake
is in operation may not sa~ely be tolerated. To accommodate
such a contingency, it may be desired to provide a negative
clearance in the exhaust valve operating mechanism during
the engine braking mode of operation so that the exhaust
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valves will not close fully, thereby limiting the
load imposed on the pushrods. Of course, during
the fueling mode of engine operation, a positive
clearance is required to avoid damage, such as burning,
to the valves.
Description of the Drawin~s
Further objects and advantages o the
invention will become apparent from the following detailèd
description of the invention and the accompanying drawings
in which: :
Figure is a schematic view of an engine brake
incorporating the timing advance mechanism according to
,
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the present invention,
Figure 2 is an enlarged fragmentary cross-
section of a portion of the engine brake mechanism shown
in Figure 1 showing the timing mechanism of the present
invention in more detail;
Figure 3 is a bottom plan view taken along line
3-3 of Figure 2; and
Figure 4 is a graph showing a compari~on of the
retarding power developed by two engines incorporating
the timing advance mechanism of the present invention
and the same tw~ engines without the inventive device.
DETAILED DESCRIPTION OF THE INVENTION
_ .
Referring to Figure 1, the numeral 10 descri~es
various fragmentar~ portions of the engine brake housing
while 12 is a schematic view of the engine sump contain-
ing oil 14. Oil 14 may ~e withdrawn from the sump 12
through a duct 16 ~y an oil p~mp 18 and then directed
into a solenoid valYe 20 via duct 22. The solenoid valYe
20 comprises a valve body 24 secured to the englne brake
housing 10, having an inlet port 26, an outlet port 28
and a dump port 3Q, The lnlet port 26 and d~mp port 30
communicate wlth the Yalve cavity 32 respectively at
the upper and lower ends thereof while the outlet port
28 communicates with an enlarged central portion of the
valve cavity 32. A valve stem 34 is journalled for
reciprocating movement within the valve body 24 and
carries a cylindrical valve seat 36 adapted to seat
against the shoulders formed ~y the enlarged central
portion of the valve cavlty 32. A spring 38 normally
~iases the valve stem 34 so as to prevent the flow of
oil from the inlet port 26 to the outlet port 28 of the
solenoid valve.
A solenold coil 40 surrounding the upper end
of the Yalve stem 34 is deslgned to open the solenoid
valve 20 agalnst the ~ias of the spring 38 wheneyer
electrical current flows through the coil, The solenoid
~11 6(~9;20
coil circuit includes, in series, a fuel pump switch 42,
a clutch switch 44, a dash switch 46, a fuse 48 and the
vehicle battery 50 The purpose of each of the logic
switches 42, 44 and 46 will be set forth in connection
with an explanation of the operation of the engine
brake.
The dump port 30 communicates through a duct
52 with the engine sump 12 while the outlet port 28
communicates with a control valve 54 through a duct
56. The control valve 54 is generally in the form of
a piston mounted for reciprocating motion wîthin a
control valve cylinder 58 formed in the engine brake
housing 10. The control valYe contains an inlet port 60
which communicates with an outlet port 62. The control
valve inlet port 6Q is normally closed by a ball check
valve 64 biased by a valYe spring 66.
~ hen the solenoid valve 20 is in the open
position as shown in Figure 1, oil 14 from the sump 12
flows through the solenoid YalYe 20 and outlet duct 56
to the inlet port 60 of the control valve 54, The oil
then lifts the control Yalve 54 against the bias of a
control valve spring 68 until the annular outlet port
62 registers with the control Yalve cylinder outlet
port 70. Thereafter the pressure of the oil opens the
check valve 64 permitting oil to pass through the
control valve 54 and înto the duct 72 which c~mmunicates
between the outlet port 7Q of the control valve and the
inlet port 74 to the slave cylinder 76.
The slaYe c~linder 76 is formed in the
engine brake housing lQ so as to be aligned with an
exhaust valve 78 which is biased to a closed position by
:~ an exhaust valve spring 80. A slave piston 82 is
positioned for reciprocating movement within the cylinder
76. One end of the slaYe piston 82 is adapted to contact
the eXhaust Yalve stem cap 84 while the opposite end of
the slaYe piston contacts an adjustable timing mechanism
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86 which îs threaded into the engine brake housing 1
in alignment with the slave piston 82 and locked in
position by locknut 88. A slave piston return spring
77 is located within the slave piston 82 so that one
end of the spring biases the slaYe piston upwardly
against the timing mechanism ~6, The opposite end of
the spring 77 is carried ~y a retainer 79 seated in the
engine brake housing. The slave cylinder 76 contains
an outlet port 90 which communicates with the inlet port
92 of a master cylinder 94 formed in the engine ~rake
housing 10 through a duct 46, A master piston 9.8 is
mounted for reciprocating motion in the master cylinder
94 and its outer end is adapted to contact the rocker
arm adjusting screw 100 of the appropriate fuel injector
or intake valve rocker arm 102 which, in turn, is
actuated by the pushrod 104. The master piston 98 is
held in the housing hore ~y a light leaf spring 106.
It will be understood that, ordinarily7 there
will be a slave piston ~2 associated with each exhaust
valve so that a six cylinder engine will have six slave
pistons while a four cylinder engine will ha~e four
slave pistons. In addition, each slave piston is inter-
connected wi~h a master piston as.sociatedwith an intake
or fuel lnjector rocker arm and pushrod. ~f course, the
master and its related slaYe piston may be associated
with different engine cylinders. An exemplar~ relation-
ship for this alternative is shown in Table l below for
a six cylinder engine:
TABLE 1
30 Location of Master Pi'ston L'ocation of'Slave Piston
... . .. .
No. 1 Pushrod No. 3 Exhaust Valve
No. 5 Pushrod No. 6 Exhaust Valve
No. 3 Pushrod No. 2 Exhaust Valve
No. 6 Pushrod No. 4 Exhaust Valve
No. 2 Pushrod No, 1 Exhaust Yalve
No. 4 Pushrod No, 5 Exhaust Valve
\ 9 ~9~o
It will be understood that when the solenoidvalve 20 is opened, oil 14 flows through the solenoid
valve and control valve 54 and fills the ducts 72 and 96
as well as the slave cylinder 76 and master cylinder 94.
Check valve 64 prevents a reverse flow of oil 14 from
the slave and master cylinders. Thereafter, activation
of the pushrod 104 will move the master piston ~8
upwardly in the master cylinder 94 causing a rapid rise
in the pressure of the oil. The hydraulic pressure in
the slave cylinder 76 w;ll force the slave piston 82
downwardly so as to open the exhaust valYe 78
It will be appreciated that if the slave piston
82 is not seated against the exhaust valve stem cap 84
when the master piston ~8 begins to move, the opening
of the exhaust valve 78 will be delayed by the time
required to take up the clearance in the system However,
it is necessary to acc~mmodate dimensional changes in
the mechanism, such as the exhaust valve stem, due to
temperature changes In the prior art deYice J the
clearance was controlled ~y an adjusting screw located
in the position of the timing mechanism 86 and set to a
clearance of, for example, 0.018 inch when the engine
was cold. In accordance with the present invention, a
timing mechanism 86 is provided which effectively
maintains a zero clearance in the exhaust valYe actuating
mechanism so that movement of the exhaust valYe will
begin as soon as master piston begins to move whenever
the brake mechanism is operated.
Referrîng now to Figures 2 and 3, the timing
mechanism 86 comprises an adjustable body 108 having
threads formed on its external cylindrical surface which
is threadably engaged with the engîne brake housing 10
in alignment with the slave cylinder 76. The body lQ8
may be provided with a slot llO or other appropriate
recess for convenience of ad~ustment and ~ay be locked
in the desired position by a locknut 88. While the
.`10~ 0
timing mechanism 86 may be located elsewhere, for example t
between the slave piston 82 and exhaust valve stem cap 84,
or within the slave pîston, it is prefera~le for purposes
of convenient ad~ustability to position one end of the
mechanism exteriorly o the exhaust valve mechanism.
A series of three coaxial bores 112, 114 and
116 are formed in the body 108 extending partially
through the body 108 from the end opposite that contain-
ing the adjusting slot 110, The first, and largest,
bore 112 extends approximately halfway through the
body 108 and is adapted to receive a timing piston 118.
The intermediate bore 114 extends approximately halfway
through the remaining length of the body 108 and contains
therein a compression spring 120, The third and smallest
bore 116 extends slightly deeper than the intermediate
bore 114 to provide a seat for check valve spring 122.
It will be understood, of course, that a single bore
having the diameter of bore 112 and the depth of bore
116 may be used in place of the three bores shown and
described above.
The timing piston 118 is formed with an axial
bore 124 extending entirely through the piston 118 At
the inner or upper end of the piston an enlarged bore
126 is formed to provide a seat 128 for a ball check
25 valve 130. The ball check Yalve 130 is normally urged
against the seat 128 by the compression spring 122 A
transverse bore or slot 132 is formed across a diameter
of the piston 118. The body lQ8 contains a transverse
bore 134 within which is pressed a pin 136, The bore or
30 slot 132 is substantially wider than the pin 136 so as
to permit the piston 118 to move axially relative to
; the body 108 within a limited range, In the present
embodiment, the range of movement of the piston 118 i8
: from a first position slightly within the body 108 to
a second position wherein the piston 118 extends
sIightly beyond the end of the body 108, for example,
0.018-0.028 inches.
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It will be appreciated that the compression
spring 120 normally urges the piston 118 to its extended
position while the lighter, i.e lower rate, compression
spring 122 urges the ball check valve to a closed
position.
While it is convenient to use a ball check
valve 13Q and compression spring 122, it will be
understood that other check valve means may be employed.
For example, a leaf valve or other form of check valve
may be located either on the timing piston 118 or in a
separate duct communicating between the slave cylinder
76 and the region of the bores 112, 114, 116 a~ove the
timing mechanism pîston 118. Similarly, means other
than the pin 136 and slot 132 may be employed to provide
limited axial movement of the piston 118 within the
adjustable body 108, Such alternate means may include
a reduced diameter at the lower end of the piston 118
and a mating inwardly directed flange or lip on the
lower end of the ad~ustable body 108.
The operation of the mechanism will now be
described. First, the ad~ustable body 108 may be set,
as with the aforementioned prior art device, to provide
any desired clearance, for example, 0.018 inch between
the slave piston 82 and the exhaust valve stem cap 84
to insure that, under all operating conditions, there
will be sufficient clearance to prevent unintentional
partial opening or lifting of the exhaust valve 78.
Under these conditions, the timing mechanism piston 118
of the invention will not extend from the body 108 and
the body 108 will be in direct contact with the top of
the slave piston 82.
When it is desired to operate the engine
brake, the solenoid valve 20 and the control valve 54
are actuated. This results in a flow of oil 14 through
35 the ducts 72 and 96 and into the slave cylinder 76 and
master cylinder 94. When the master piston 98 begins to
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move, pressure is immediately built up in the hydraulic
circuit as that circuit has ~een fully filled with oil
14. Thus, the movement of the master piston 98 will
immediately result in movement of the slave piston 82
and, as with the prior art device, after clearance
in the mechanism has béen taken up, opening of the
exhaust valve with which the slave piston is associated.
In accordance with the invention, as the slave
piston 82 moves away from the timing mechanism body 108,
the timing mechanism piston 118 extends a predetermined
distance, governed by pin 136, from the timing mechanism
body due to force from compression spring 120. This
creates a pressure differential sufficient to cause the
ball check valve 130 to unseat and admit oil to the region
lS of the bores 112, 114 and 116. Upon return o~ the slave
piston 82, undér action of spring 77, toward its initial
position it encounters the timing mechanism piston 118.
The oil which entered the timing mechanism through the
chéck valve 130 being trapped, and being relatively
incompressible, opposes the force applied to the slave
piston 82 by the slave return spring 77 Thus the
slave piston 82 assumes a new initial position for all
subsequent operating cycles, controlled by the predeter-
mined stroke of the timing mechanism piston 118 and vary-
ing only by the timing mechanism piston 118 movementdue to leakage through such piston and bore clearance
~etween cycles. This leakage loss is replaced through
the ball check valve 130 during each cycle.
When the engine ~rake solenoid valve 20 and
control valve 54 are deactivated, the hydraulic circuît
is vented to drain. As the cyclic motion of the slave
piston 82 ceases and it comes to rest on the timing
mechanism piston 118, leakage past the timing mechanism
piston, due to ~ore clearance, will permit full
retraction of the timing mechanism piston and reloca-
tion of the slave piston to its original position against
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adjusting screw body 108,
The result of effectively eliminating clearance
or backlash in the valve actuating mechanism is demon-
strated in Figure 4. Figure 4 is a graph showing the
relationship between engine speed and absorbed or
braking power for a sîx cylinder and a four cylinder
engine with and without the timing mechanism of the
present invention. Curve 138 is a plot of the braking
horsepower obtained from a six cylinder diesel engine
fitted with a Jacobs engine brake and having the
clearance adjustment set at 0,018 inch in accordance
with the prior art. Curve 140 is a plot of the braking
horsepower obtained fr~m the same engine wherein the
clearance adjusting screw was replaced with a timing
advance mechanism in accordance with ~he present
invention. In a similar manner curve 142 is a plot
of the braking horsepower developed by a four cylinder
diesel engine equipped with a standard Jacobs engine
brake*while curve 144 shows the effect of su~stituting
the timing advance mechanîsm of the present invention
for a standard adjusting screw set for a cleaxance of
0.018 inch. It will be o~served that at normal engine
operating speeds in the range of 20Q0 r.p,~,, a very
substantial increase in retarding horsepower is
attained by the practice of the present invention,
As indicated schematically in Figure 1~ the
engine brake of the present invention is operated by a
solenoid valve which is wired in series with three
switches, a fuel pump switch 42, a clutch switch 44
and a dash switch 46. It will be appreciated that if
any one or more of these switches is in the open posi-
tion, the brake cannot be operated. The fuel pump
switch 42 disables the brake system whenever the engine
is being fueled, i.e. whenever the throttle is opened.
The clutch switch 44 opens whenever the clutch is dis-
engaged in order to prevent stalling o~ ~e engine. Theda&h switch 46 is a manual control to enable th~ operator
*see for example U.S. Patent 3,220,392
t . ~ ~
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to disengage the brake system if he should wish to do
so. The dash swit~h 46 may also be of the multi-position
type which deactivates a portion of the system so that
the operator can select partial or full braking power
S as may be desired under particular operating conditions.
In addition to th~ primary advantage of
substantially increasing the braking horsepower of the
engine as shown by Figure 4, the timing advance mechanis~
o the present invention can be retrofitted on engines
having engine brakes of the type herein disclosed
without requiring any modification of the engine. A
secondary advantage of the timing advance mechanism
here disclosed is a decrease in the pushrod loading when
the device is employed in an engine having mechanical
fuel injectors operated from pushrods. This advantage
results from the increase in the time interval between
the opening of the exhaust valve and the actuation o
the fuel injector~ Applicant has found that for each
0.001 inch decrease in clearance the pushrod load is
decreased by about 50 pounds in engines of the character
tested for Figure 4.
Up to this point, the present invention
has been described with respect to an embodiment wherein
the normal exhaust ~alve operating mechanism clearance
is effectively reduced to zero during the braking mode
of operation. In such an embodiment, if the normal cold
clearance is 0.018 inch, the timing mechanism is designed
50 that the piston 118 extends outwardly, during operation,
a distance of 0.018 inch from the end of the body 108.
This may be accomplished by controlling the width of
the slot 132 to permit the desired extension of 0.018
inch.
1~ '.
-14a~ g 20
It will be appreciated that by an
appropriate change in the width of the slot 132, the
motion of the piston 118 may be increased or decreased.
Thus, if it were desired to provide a small positive
clearance of, ~or example, 0.005 inch during braking
in an engine having a clearance when cold of 0.018
inch in the fueling mode, the extension of the piston
118 would be designed to be 0.013 inch. Similarly, if
it were desired to provide a small negative clearance
of, for example, 0.005 inch during braking in an engine
having a clearance when cold of 0.018 inch in the
fueling mode, the extension of the piston 118 would be
designed to be 0.023 inch.
The foregoing examples are, of course, merely
illustrative of the principle involved because, in each
case, consideration must be given to the actual~exhaust
valve clearance during normal engine operation, which
clearance depends upon the design of ~he particular
en~ine involved and the conditions under which it is
operated. Once these factors are established or
specified, the timing mechanism according to the present
invention can be designed to give the desired braking
clearance which may be positive, negative, or essentially
zero. It will be understood that a number of timing
-mechanisms may be supplied to provide a number of standard
extensions so that the engine owner may select the
appropriate timing device to optimize the braking operation
of his particular engine.
