Engine retarding method and apparatus

Process and apparatus for the compression release retarding of a multi-cylinder four cycle internal combustion engine are provided. The process provides a compression release event and a bleeder event or a second compression releaser event for each engine cylinder during each complete engine cycle while employing only one intake valve opening per engine cycle. In accordance with one embodiment of the invention the normal motion of the exhaust valve is disabled and replaced with an opening of the exhaust valve at about the top dead center position of the engine piston following the compression stroke; maintaining the exhaust valve in the open position during the expansion stroke; partially closing the exhaust valve during the exhaust stroke; and fully closing the exhaust valve during the intake stroke. In accordance with another embodiment of the invention, the normal intake valve opening is delayed and the normal motion of the exhaust valve is disabled and replaced with an opening of the exhaust valve at about the top dead center position of the engine piston following the compression stroke; maintaining the exhaust valve in the open position during the expansion stroke; closing the exhaust valve at the end of the expansion stroke; and opening the exhaust valve briefly at about the next top dead center position of the engine piston. The apparatus includes hydraulic and mechanical means to disable or delay the exhaust and intake valves and hydraulic, mechanical and electrical means to manipulate the exhaust and intake valves as required to perform the process.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to an improved engine retarding method and 
apparatus of the compression release type. More particularly, the 
invention relates to a compression release retarding system for a 
four-cycle internal combustion engine which provides one compression 
release event and one bleeder event or two compression release events 
during each two revolutions of the engine crankshaft while utilizing only 
one intake valve opening event and at least partially disabling the normal 
exhaust valve opening event. 
2. Prior Art 
The problem of providing adequate and reliable braking for vehicles, 
particularly large tractor trailer vehicles, is well known. When such 
vehicles are operating at normal highway speeds they possess a very large 
momentum, and this may be increased substantially when the vehicle is 
required to negotiate a long decline. While the normal drum or disc type 
wheel brakes are capable of absorbing a large amount of energy over a 
short period of time, the absorbed energy is transformed into heat which 
rapidly raises the temperature of the braking mechanism to a level which 
may render ineffective the friction surfaces and other parts of the 
mechanism. As repeated use of the wheel brakes under these conditions is 
impracticable, resort has been made to auxiliary retarding devices. 
Such auxiliary devices include hydraulic or electrodynamic retarding 
systems wherein the kinetic energy of the vehicle is transformed by fluid 
friction or magnetic eddy currents into heat which may be dissipated 
through appropriate heat exchangers. Other auxiliary systems include 
exhaust brakes which restrict the flow of air through the exhaust system 
and compression release retarder mechanisms wherein the energy required to 
compress the intake air during the compression stroke of a four cycle 
engine is dissipated by opening the exhaust valve near the end of the 
compression stroke so that the compressed air is exhausted during the 
expansion stroke of the engine. With respect to the engine compression 
release retarder, a portion of the kinetic energy of the vehicle is 
dissipated through the engine cooling system while another portion of the 
kinetic energy is dissipated through the engine exhaust system. 
A principal advantage of the engine compression release retarder and the 
exhaust brake over the hydraulic and electrodynamic retarders is that both 
of the latter retarders require dynamos or turbine equipment which may be 
bulky and expensive in comparison with the mechanism required for the 
usual exhaust brake or engine compression release retarder. A typical 
engine compression release retarder is shown in the Cummins U.S. Pat. No. 
3,220,392 while an exhaust brake is disclosed in Benson U.S. Pat. No. 
4,054,156. A form of retarder that incorporates certain of the 
characteristics of the compression release retarder with those of the 
exhaust brake is known as the bleeder brake. In this mechanism, the 
exhaust or intake valves (or both) are maintained in a partially open 
position during the braking mode so that the engine consumes energy during 
pumping of the air through the partially open valves. Bleeder brakes are 
disclosed in the Siegler U.S. Pat. No. 3,547,087 and Jonsson U.S. Pat. No. 
3,367,312. Other forms of compression release retarders are disclosed in 
Cartledge U.S. Pat. No. 3,809,033, Pelizzoni et al. U.S. Pat. No. 
3,786,792 and Dreisin U.S. Pat. No. 3,859,970. 
Since the advent of the Cummins Pat. No. 3,220,392 improvements have been 
made in various aspects of its operation while maintaining the same mode 
of operation, i.e., one compression release event for every two crankshaft 
revolutions. Such improvements include: a mechanism to prevent excess 
motion of the slave piston (Laas U.S. Pat. No. 3,405,699); a mechanism to 
prevent excess pushtube loading (Sickler U.S. Pat. No. 4,271,796); a 
mechanism to advance the opening of the exhaust valve during retarder 
operation (Custer U.S. Pat. No. 4,398,510; Price et al. U.S. Pat. No. 
4,485,780); a mechanism to open only one of the exhaust valves during 
retarding (Jakuba et al. U.S. Pat. No. 4,473,047); and a mechanism to 
close the exhaust valve promptly after the compression release event 
(Cavanagh U.S. Pat. No. 4,399,787). 
More recently, and in response to increased fuel costs and more stringent 
requirements with respect to air pollution, engine operating speeds have 
been decreased and the engine tuning specifications have been modified 
both of which adversely affect the performance of the engine retarder. In 
application Ser. No. 728,947, now U.S. Pat. No. 4,572,114 assigned to the 
assignee of the present application, a method and apparatus are disclosed 
by which two compression release events are produced during each two 
revolutions of the crankshaft for each engine cylinder. In accordance with 
this method, both the exhaust and intake valves are disabled from opening 
at the times required for the powering mode of engine operation. Means are 
provided to open the exhaust valve close to each top dead center (TDC) 
position of the piston and additional means are provided to open the 
intake valves during the ensuing expansion stroke as the piston moves 
toward the bottom dead center (BDC) position thereby providing an intake 
valve event corresponding to each compression release event. By providing 
two compression release events for each cylinder during every two 
revolutions of the crankshaft, the retarding horsepower developed by the 
engine can be increased substantially. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a method and apparatus are 
provided in a compression release retarding system to increase the 
retarding horsepower without substantially increasing the flow of air 
through the turbocharger. This is accomplished by at least partially 
disabling the exhaust valve from opening at its normal time and opening 
the exhaust valve at about the top dead center (TDC) position to produce a 
compression release event. The exhaust valve is held open until bottom 
dead center position in order to charge the cylinder with air from the 
exhaust manifold. At the ensuing bottom dead center position, the exhaust 
valve is then partially closed so as to provide a bleeder brake function 
until the intake valve partially opens in its normal fashion. 
Alternatively, the exhaust valve is fully closed near the bottom dead 
center position to permit compression of the charge of air from the 
exhaust manifold and reopened briefly near the next top dead center 
position. In either alternative, the exhaust valve will be closed shortly 
after the intake valve starts to open so as to permit a fresh charge of 
air to be drawn into the engine and compressed for use in the next 
compression release event. Where the exhaust valve is controlled by a fuel 
injector pushtube driven by a long dwell cam, a mechanism to increase the 
volume of the hydraulic system used to open the exhaust valve is provided, 
thereby allowing the exhaust valve to close partially in order to achieve 
the bleeder effect or to close fully in case of two compression release 
events. Where the exhaust valve is controlled by another exhaust valve 
pushtube or by an injector pushtube driven by a short dwell cam, a check 
valve means is included in the hydraulic circuit provided to open the 
exhaust valve in order to maintain the exhaust valve in the open position 
and a mechanism to increase the volume of the hydraulic circuit and/or a 
vent valve are provided to partially or fully close the exhaust valve. 
Where two compression release events are employed it is also necessary to 
delay the normal opening of the intake valve. A mechanism to accomplish 
this may conveniently be incorporated into the intake valve rocker arm 
adjusting screw. The mechanism for disabling the normal exhaust valve 
motion may be incorporated into the exhaust valve pushtube, the rocker arm 
adjusting screw, rocker arm, rocker arm shaft or crosshead.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is intended to be employed with an internal 
combustion engine having a normal four stroke cycle where the four strokes 
are an intake stroke, a compression stroke, a power or expansion stroke 
and an exhaust stroke. Preferably, the engine will be of the compression 
ignition type. In such engines, the valves and fuel injectors are commonly 
driven through a valve train comprising rotating cams which activate 
pushtubes or pushrods which, in turn, oscillate rocker arms. If the engine 
is equipped with dual valves, the rocker arm activates a crosshead which, 
in turn, opens the valves. The compression release retarder mechanism may 
be driven from the fuel injector pushtube for the cylinder in question or 
from an exhaust or intake valve associated with another engine cylinder. 
Reference is now made to FIG. 1 which shows the typical motion of the 
exhaust valve, intake valve and fuel injector pushtube for a compression 
ignition engine during positive power operating conditions. The schematic 
represents the valve opening schedule during one complete engine cycle of 
720 crankangle degrees or two crankshaft revolutions. As shown, the engine 
piston moves between the bottom dead center (BDC) position and the top 
dead center (TDC) position in 180 crankangle degrees. For convenience, the 
0.degree. crankangle position is designated as "TDC I" while the 
360.degree. crankangle position is designated as "TDC II." Similarly, the 
180.degree. and 540.degree. crankshaft positions are designated as "BDC I" 
and "BDC II," respectively. Curve 12 represents the motion of the fue 
injector pushtube for an engine having a long dwell fuel injector cam. As 
shown by curve 12, the fuel injector is fully seated shortly after TDC I 
and remains seated until well after TDC II. 
FIG. 1 illustrates the operation of a standard four cycle engine wherein 
the power or expansion stroke occurs between 0.degree. and 180.degree. of 
crankshaft rotation, the exhaust stroke occurs from 180.degree. to 
360.degree., the intake stroke occurs from 360.degree. to 540.degree., and 
the compression stroke occurs from 540.degree. to 720.degree.. 
Curve 14 represents the normal power motion of an exhaust valve whie curve 
16 represents the normal power motion of an intake valve. It will be noted 
that the operations of the exhaust and intake valves overlap so that 
during a brief period both valves are partially open. 
FIG. 2 illustrates a modification of the exhaust valve operation which 
occurs with various forms of the compression release retarder. Curve 16 
shows the motion of the intake valve which remains unchanged. During the 
retarding mode of operation, the motion of the fuel injector pushtube may 
be employed to partially open the exhaust valve or the dual exhaust valves 
near TDC I so as to dissipate the energy stored in the air compressed in 
the engine cylinder and produce a compression release event. Curve 18 
(solid line) shows the motion of the dual exhaust valves produced by the 
injector pushtube motion (between about 690 and 150 crankangle degrees and 
again between about 370 and 470 crankangle degrees) and the additional 
opening motion produced by the exhaust valve pushtube (between about 150 
and 370 crankangle degrees). 
When the engine compression retarder opens only one of the dual exhaust 
valves, in order to minimize the stress on the exhaust valve crosshead 
resulting from the impact of the exhaust valve rocker arm on the crosshead 
as indicated by point 20 on curve 18 of FIG. 2, reset mechanisms as 
described in Cavanagh U.S. Pat. No. 4,399,787 and Mayne et al. U.S. Pat. 
No. 4,423,712 have been developed. With such mechanisms the exhaust valve 
can be closed as shown by curve 18a prior to its normal opening by the 
exhaust valve cam. 
As noted above, the exhaust valve may be opened near TDC I to produce a 
compression release event by using the motion of a pushtube associated 
with an intake or exhaust valve for another engine cylinder when such 
motion occurs at an appropriate time. Curve 22 (FIG. 2) represents the 
motion of the exhaust valve derived from the motion of a pushtube 
associated with the exhaust valve of another cylinder of the engine. 
Reference is now made to FIG. 3A which illustrates embodiments of the 
process of the present invention as applied to an engine fitted with a 
modified compression release retarder driven from the fuel injector 
pushtube, and wherein the fuel injector is driven by a long dwell cam, or 
a retarder driven from a remote exhaust valve pushtube. Curve 16 
represents the motion of the intake valve and is identical to curve 16 on 
FIGS. 1 and 2. Curve 24 is shown in dashed lines to indicate what the 
motion of the exhaust valve would be were it not disabled during the 
retarding mode of operation in accordance with the present invention. 
Curve 26 (solid line) illustrates one motion of the exhaust valve according 
to the present invention. It will be noted that the initial portion of 
curve 26 corresponds to the motion derived from the fuel injector pushtube 
(curve 12 of FIG. 1). At point 28 a mechanism described in detail below 
causes the exhaust valve to move partway to the closed position. At point 
30 the exhaust valve begins to close further in response to the movement 
of the fuel injector pushtube. 
Curve 26' (dashed line) shows an aternative motion of the exhaust valve 
when the compression release retarder is driven from a remote exhaust 
valve pushtube instead of the fuel injection pushtube. Again, point 28 
indicates the point where a mechanism described below causes the exhaust 
valve to move partway to the closed position. At point 30', a mechanism 
described below (FIG. 4C) causes the exhaust valve to close completely. 
The effect of the valve motions outlined above is as follows: In the period 
designated as "A" on FIG. 3A which comprises the latter portion of the 
compression stroke, the exhaust valve opens to cause a compression release 
event whereby the compressed air is released to the engine exhaust 
manifold. During the period designated as "B" on FIG. 3A, the air flow 
through the exhaust valve is reversed due to the motion of the engine 
piston toward BDC I which increases the cylinder volume. The cylinder is 
thereby charged with air at low pressure from the exhaust manifold. Near 
BDC I the exhaust valve opening is substantially reduced so as to provide 
only a small orifice. As the piston moves from BDC I to TDC II during the 
period designated "C" on FIG. 3A, substantial work is done on the air 
charged into the cylinder during the previous stroke. The work in 
compressing the air and exhausting it through the slightly open exhaust 
valve represents a dissipation of energy analogous to that which occurs in 
the bleeder type retarder. During the period designated as "D" on FIG. 3A, 
a fresh charge of air is introduced into the cylinder from the engine 
turbocharger compressor while in the period designated "E" on FIG. 3A this 
fresh charge of air is being compressed. 
It will, therefore, be understood that in accordance with this form of the 
present invention two retarding events occur in each cylinder during each 
engine cycle comprising two crankshaft revolutions: the first retarding 
event is a compression release event occurring near TDC I while the second 
event is a bleeder retarding event occurring while the piston moves from 
BDC I to TDC II. 
FIG. 3B illustrates, schemetically, an alternative process in accordance 
with the present invention in which the bleeder event is replaced by a 
second compression release event. Curve 24 is identical to curve 24 of 
FIG. 3A. Curve 26a is identical to curve 26 of FIG. 3A up to the point 28 
while curve 26a' is identical to curve 26' of FIG. 3A up to the point 28. 
At point 28 the exhaust valve begins to close and is completely closed at 
point 29 at or shortly after BDC I. Curve 26b represents a brief second 
opening of the exhaust valve near TDC II. Curve 16a represents a 
modification of the intake valve motion shown by curve 16 of FIG. 3A (and 
shown in dashed lines on FIG. 3B). The modification comprises a delay in 
the opening of the intake valve so as to accommodate the second 
compression release event. 
It will be understood that the process as shown by FIG. 3B is similar to 
that shown in FIG. 3A except that the two retarding events are both 
compression release events. 
The mechanism used to perform the process illustrated in FIG. 3A will be 
described in conjunction with FIG. 4A which illustrates, diagrammatically, 
an internal combustion engine 32 having an oil sump 34 which may, if 
desired, be the engine crankcase and a retarder housing 36. As is common 
in commercial engines of the Diesel type which are equipped with 
compression release retarders, each cylinder is provided with two exhaust 
valves 38 which are seated in the head of the engine 32 so as to 
communicate between the combustion chamber and the exhaust manifold (not 
shown) of the engine. 
Each exhaust valve 38 includes a valve stem 40 and is provided with a valve 
spring 42 which biases the valve 38 to the normally closed position. A 
unitary crosshead and slave piston 258 (hereafter "crosshead") is mounted 
for reciprocating motion in a direction parallel to the axes of the valve 
stems 40. The crosshead 258 is provided with an adjusting screw 48 which 
registers with the stem 40 of one of the valves 38 to enable the crosshead 
258 to be adjusted so as to act upon both valves simultaneously. 
The unitary crosshead and slave piston 258 which functions to disable the 
exhaust valve during retarding will be described in more detail hereafter 
with reference to FIGS. 5A and 5B. If it is desired to employ separate 
crosshead and slave piston means as illustrated and described, for 
example, in Cavanagh U.S. Pat. No. 4,399,787 or Price et al. U.S. Pat. No. 
4,485,780, an exhaust valve disabling mechanism described below with 
reference to FIGS. 6A and 6B may be employed. 
The crosshead 258 is activated by an exhaust valve rocker arm 50 mounted 
for oscillatory motion on the head of the engine 32. Such oscillatory 
motion is imparted to the rooker arm 50 by an exhaust pushtube 52 through 
an adjusting screw 54 threaded into one end of the rocker arm 50 and 
locked into its adjusted position by a lock nut 56. The pushtube 52 is 
given a timed longitudinal reciprocating motion by an exhaust valve cam 58 
mounted on the engine camshaft 60 which, in turn, is driven from the 
engine crankshaft (not shown) so as to rotate at half the speed of the 
engine crankshaft. The mechanisms provided to disable the exhaust valve 
will be described in connection with FIGS. 5A and 5B, 6A and 6B. 
The compression release mechanism comprises at least one solenoid valve 62 
and, for each cylinder of the engine, a contro valve 64, a master piston 
66 and a slave piston portion of the crosshead 258 together with 
appropriate hydraulic and electrical auxiliaries as described below. 
As shown in FIG. 4A, a low pressure duct 70 communicates between the sump 
34 and the inlet port 72 of the solenoid valve 62 located in the housing 
36. A low pressure pump 74 may be located in the duct 70 to deliver oil or 
hydraulic fluid to the inlet port 72 of the solenoid valve 62. If, as 
shown in FIG. 4B, oil is to be stored within the control valve 64 as 
disclosed in Cavanagh U.S. Pat. No. 4,399,787, a check valve 71 is located 
between the pump 74 and the solenoid valve 62. The solenoid valve 62 is a 
three-way valve having, in addition to the inlet port 72, an outlet port 
76 and a return port 78 which communicates back to the sump 34 through a 
return duct 80. The solenoid valve spool 82 is normally biased by a spring 
84 so as to close the inlet port 72 and permit the flow of hydraulic fluid 
or oil from the outlet port 76 to the return port 78. The solenoid coil 
86, when energized, drives the valve spool 82 against the bias of spring 
84 so as to close the return port 78 and permit the flow of oil or 
hydraulic fluid from inlet port 72 to outlet port 76. 
The control vave 64, also positioned in the retarder housing 36, has an 
inlet port 88 which communicates with the outlet port 76 of the solenoid 
valve through a duct 90. A control valve spool 92 is mounted for 
reciprocating motion within the control valve 64 and biased toward a 
closed position by a compression spring 94. The spool 92 is provided with 
an inlet port 96, normally closed by a spring biased ball check valve 98 
and an outlet port 100 formed to include an annular groove on the outer 
surface of the spool 92. The outlet port 100 of the control valve spool 92 
communicates with a duct 102 formed in the retarder housing 36 when the 
spool 92 is in its open position as illustrated in FIG. 4A. Duct 102 
communicates between the control valve 64, slave cylinder 104, master 
cylinder 106 and volume control cylinder 108, all of which are located in 
the retarder housing 36. When oil or hydraulic fluid flows into the 
control valve 64, the spool 92 moves until the outlet port 100 registers 
with the duct 102. Thereafter, the check valve 98 opens to permit oil or 
hydraulic fluid to flow through the control valve 64 and into the slave 
cylinder 104, master cylinder 106 and volume control cylinder 108. 
The slave piston portion of the unitary slave piston and crosshead 258 is 
mounted for reciprocating motion within the slave cylinder 104 and is 
biased toward the adjustable stop 110 by a compression spring (not shown). 
A clearance of, for example, 0.018 inch may be provided between the 
crosshead 258 and the ends of the valve stems 40 when the enqine is cold 
and the crosshead 258 is seated against the adjustable stop 110. 
The master piston 66 is mounted for reciprocating movement within the 
master cylinder 106. The exterior end of the master piston 66 registers 
with one end of the adjusting screw mechanism 116 mounted on the fuel 
injector rocker arm 118. The master piston 66 is lightly biased against 
the adjusting screw mechanism 116 by a leaf spring 120. The fuel injector 
rocker arm 118 is driven through a pushtube 122 by a long dwell cam 124 
mounted on the camshaft 60. 
Mounted for reciprocating motion within the volume control cylinder 108 is 
a piston 126 which is biased toward the minimum volume position by a 
compression spring 128. A control pin 130 connects the piston 126 with the 
armature 132 of solenoid 134. The solenoid 134 provides the holding force 
to maintain the piston 126 in the minimum volume position. When the 
solenoid 134 is de-energized, the piston 126 is movable against the bias 
of spring 128 so as to increase the volume of the hydraulic circuit (which 
includes the slave cylinder 104 and the master cylinder 106) so as to 
provide a maximum volume for the hydraulic circuit. By appropriate design 
of the volume control cylinder 108, the exhaust valve 38 may be held open 
to any desired extent or closed entirely. 
The control circuit comprises, in series, the vehicle storage battery 136, 
a fuse 138, a manual switch 140, a clutch switch 142, a fuel pump switch 
144, the solenoid coil 86 and ground 146. Preferably, a diode 148 is 
provided between the switches and ground to prevent arcing of the 
switches. Switches 140, 142, and 144 are provided to permit the operator 
to shut off the retarder entirely should he desire to do so; to prevent 
fueling of the engine while the retarder is in operation; and to prevent 
operation of the retarder if the clutch should be disengaged. 
An electronic control unit 150 is powered from the vehicle battery 136 
through conduit 152 and engine retarder is activated. The control unit 
also receives a timing signal from a sensor 156 through conduit 158. 
Sensor 156 may be located adjacent the engine flywheel 160 or other 
appropriate engine or retarder component. Solenoid 134 is energized 
through the electronic control unit 150 through conduit 162 and is 
normally energized whenever the retarder is activated. However, at point 
28 (FIGS. 3A and 3B) which occurs shortly before BDC I, the electronic 
control unit 150 interrupts the power to the solenoid 134 thereby allowing 
the solenoid to open and the piston 126 to move so as to increase the 
volume of the hydraulic circuit. The solenoid 134 is reenergized at some 
point after BDC I and, preferably, after the exhaust valve closes 
completely. It will be appreciated that the solenoid 134 is required to 
close only when no substantial resisting force due to hydraulic circuit 
pressure is present. When the pressure in the hydraulic circuit is high 
during the compression release portion of the retarding cycle, the 
solenoid 134 is required only to hold the armature 132 in the closed 
position. This occurs at zero or near to zero air gap where the solenoid 
develops a maximum closing or holding force. 
The operation of the system is as follows: When the retarder is actuated by 
closing switches 140, 142 and 144, the solenoid valve 62 is energized and 
low pressure oil or hydraulic fluid flows through the solenoid valve 62 
and the control valve 64 and into the slave cylinder 104 and master 
cylinder 106. The oil flowing into the hydraulic circuit is trapped 
therein by the check valve 98. As the master piston 66 is driven upwardly 
by the motion of the fuel injector pushtube 122, the hydraulic circuit is 
pressurized and the unitary slave piston and crosshead 258 is driven 
downwardly shortly before TDC I. The downward motion of the crosshead 258 
moves the valve stems 40 thereby opening the exhaust valves 38 so as to 
produce a compression release event. 
The exhaust valves remain open until shortly before the BDC I position of 
the piston is reached (e.g., about 160.degree. crankangle position). At 
this point (point 28, FIG. 3A), the electronic control unit 150 interrupts 
the power to the solenoid 134 thereby releasing the armature 132 and 
piston 126. As the piston 126 moves within the volume control cylinder 
108, the slave piston portion of the crosshead 258 also retracts and the 
exhaust valves 38 begin to close. The diameter of the volume control 
cylinder 108 and the stroke of the piston 126 are selected to produce the 
desired bleeder opening for the exhaust valves 38. 
As noted in FIG. 3A by curve 24, the normal motion of the exhaust valves 38 
during the powering mode is disabled during the retarding mode of 
operation. Mechanisms designed to effect this result are described below 
in conjunction with FIGS. 5A, 5B, 6A and 6B. 
Beginning at about 420 crankangle degrees (e.g., point 30, FIG. 3A), the 
fuel injector pushtube 122 retracts and thereby permits the master piston 
66 to retract and depressurize the hydraulic circuit. Early in the bleeder 
portion of the cycle, solenoid 134 may be reenergized by the electronic 
control unit 150. When the hydraulic circuit is depressurized and the 
solenoid 134 is energized, the combination of solenoid force and the 
compression spring 128 bias the piston 126 to the minimum volume position 
thereby returning oil or hydraulic fluid to the hydraulic circuit. Any 
leakage of hydraulic fluid which may occur may be replenished by flow 
through the check valve 98 during the low pressure portion of the cycle 
(i.e., about 465 to about 690 crankangle degrees). 
So long as the solenoid valve 62 is energized, the control valve spool 92 
will remain in its upward position where the outlet port 100 of the spool 
is in registry with duct 102. Under these conditions, additional oil or 
hydraulic fluid may enter the slave cylinder 104 and the master cylinder 
106, but reverse flow is prevented. Thus, the high pressure hydraulic 
circuit is maintained in operating condition and the motion of the master 
piston 66 will be communicated through the high pressure hydraulic circuit 
to the crosshead 258. 
It will be understood that the cycle of events recited above will be 
repeated for every two crankshaft revolutions. For each engine cycle 
comprising two crankshaft revolutions each cylinder will therefore 
experience one compression release event and one bleeder retarding event. 
Reference is now made to curve 26' of FIG. 3A which is a diagram showing 
the process of the present invention as applied to an engine equipped with 
a compression release retarder driven by the exhaust pushtube from another 
engine cylinder or by the fuel injector pushtube where that pushtube is 
driven by a short dwell cam. In this embodiment of the invention, the 
compression release event near TDC I can be triggered by a fuel injector 
or remote exhaust valve pushtube. However, since both of these pushtubes 
return to the rest position shortly after TDC I, additional means are 
required to hold the exhaust valve open in order to charge the cylinder 
from the exhaust manifold for the bleeder retarding event later in the 
engine cycle. Curve 26' shows the exhaust valve motion required to produce 
a compression release event near TDC I and a cylinder charge and a 
subsequent bleeder retarding event between BDC I and TDC II. Curve 22 
(FIG. 2) shows the valve motion derived from the exhaust cam for another 
cylinder used to achieve the compression release event at TDC I. If, 
instead of using an exhaust valve pushtube to trigger the compression 
release event at TDC I the fuel injector pushtube were used, the initial 
portion of curve 26 in FIG. 3A would resemble the initial portion of curve 
18 of FIG. 2. 
Reference is now made to FIG. 4C which illustrates schematically the 
mechanism employed to perform the alternate process shown in FIG. 3A 
(curve 26'). Parts bearing the same designator in FIGS. 4A and 4C are 
identical and their description will not be repeated here. Modified parts 
are designated by a prime (') while alternative parts are shown by dotted 
lines. 
FIG. 4C relates principally to an exhaust driven retarder mechanism wherein 
the remote exhaust pushtube 52' is driven by a short dwell cam 58' instead 
of the long dwell cam 124 shown in FIG. 4A. It will be appreciated that 
when the remote exhaust pushtube 52' is driven by the exhaust cam 58' the 
master piston 66' will tend to retract before BDC I is reached (see FIG. 
2, curve 22). In order to prevent premature retraction of the slave piston 
portion of the unitary slave piston and crosshead 258, a check valve 168 
is located in the duct 102 between master cylinder 106 and slave cylinder 
104. 
At point 28 on curve 26' of FIG. 3A, the power to the solenoid 134 is 
interrupted by the electronic control unit 150 thereby permitting the 
piston 126 to move downwardly (as shown in FIG. 4C) in the volume control 
cylinder 108. When piston 126 moves downwardly in cylinder 108, the 
crosshead 258 retracts partially and the exhaust valves approach the 
closed position. In order to fully close the exhaust valves 38 at or 
shortly after TDC II, additional oil or hydraulic fluid must be vented 
from the hydraulic circuit. This is accomplished by means of the solenoid 
vent valve 172 which communicates between duct 102 and duct 174, which 
latter duct communicates with duct 90. Solenoid valve 172 comprises a 
solenoid 176 which is connected to the electronic controller 150 by a 
conduit 178, an armature 180, a control pin valve 182 and a spring 184 
which biases the control valve 182 in sealing relation to duct 102. At or 
shortly after TDC II (e.g., point 30', FIG. 3A), the electronic control 
unit 150 interrupts the power to the solenoid 176 permitting the control 
valve 182 to open and vent oil or hydraulic fluid from duct 102 to duct 
174. It will be understood that whenever the pressure in duct 102 between 
the master cylinder 106 and control valve 64 drops below the pressure in 
duct 90, oil or hydrauic fuid will pass through the control valve 64 so as 
to permit full retraction of the master piston and equalization of the 
pressure in ducts 90, 102 and 174. When the pressures in ducts 102 and 174 
are equalized, spring 184 will close the control valve 182. At some point 
during the intake stroke of the engine the electronic control unit 150 
reenergizes the solenoid 176 so as to maintain the control valve 182 in 
the closed position. 
As shown by dashed lines in FIG. 4C a master piston 66 is located over each 
exhaust valve rocker arm 50. The master pistons 66 will reciprocate in 
master cylinders 106 which communicate through duct 102 and check valve 
168 with the appropriate slave cylinder 104. 
It will be appreciated that the solenoid vent valve illustrated in FIG. 4C 
could also be incorporated into the apparatus shown in FIG. 4A if it were 
desired to fully close the exhaust valves 38 prior to the return motion of 
the injector pushtube 122. There would, of course, be no need to provide 
the check valve 168 in such a revision of the FIG. 4A mechanism. 
Reference is now made to FIGS. 3B and 4B which illustrate a process and 
apparatus whereby two compression release events are produced in each 
cylinder during each engine cycle which comprises two crankshaft 
revolutions. Curves or components which are common to both Figures carry 
the same designation and their description will not be repeated here. 
Modified or alternative elements will be indicated by a prime or a 
subscript. 
In FIG. 3B, curves 16 and 24 are identical to the corresponding curves in 
FIG. 3A and the portions of curves 26a and 26a' up to the point 28a are 
identical to the curves 26 and 26' up to the point 28 in FIG. 3A. Curve 
26a illustrates an apparatus wherein the compression release event at TDC 
I is derived from the molion of the injector pushtube 122 while curve 26a' 
illustrates an apparatus wherein the compression release event at TDC I is 
derived from the motion of a remote exhaust pushtube 52'. In either case, 
the second compression release event at TDC II (curve 26b) is derived from 
stored high pressure hydraulic fluid. When the compression release event 
at TDC I is derived from an injector pushtube, the storage function may be 
derived from the exhaust pushtube or from the intake pushtube. However, if 
the compression release event at TDC I is derived from a remote exhaust 
pushtube, the storage function is derived from the intake pushtube. 
In FIG. 3B, curve 16 is shown in dashed lines to indicate the motion of the 
intake valve in the normal powering mode. In accordance with the present 
invention the motion of the intake valve is delayed by a mechanism shown 
in FIGS. 7A and 7B until the compression release event at TDC II has 
occurred. The desired motion of the intake valve is indicated by curve 
16a. Curve 25 represents the motion of the exhaust valve pushtube 52 which 
could be used to trigger the motion of the exhaust valve at point 28a, if 
desired. It will be appreciated that even though the exhaust valves are 
disabled and the intake valves delayed from their normal motion, the 
pushtubes continue to operate and their motion is employed to actuate the 
master pistons 66" (or 224) which communicate with the engine retarder 
hydraulic circuit to provide for the storage function described below. 
FIG. 4B illustrates the mechanical, electrical and hydraulic circuits which 
produce the valve motions shown in FIG. 3B. Parts of FIG. 4B are similar 
to FIGS. 4A and 4C except that the retarder may be driven either by the 
fuel injector pushtube 122 (as shown in FIG. 4A) or by a remote exhaust 
pushtube 52' (as shown in FIG. 4C). As explained more fully below, where 
the mechanism as shown in FIG. 4B is driven from the fuel injector 
pushtube 122 or remote exhaust pushtube 52', it makes no difference 
whether the fuel injector cam is of the long dwell or short dwell type. A 
long dwell cam is shown by the dashed line 124; remote exhaust and short 
dwell injector cams are represented by the solid line 124'. 
As shown in FIG. 4B, a master cylinder 106" (or 226) and a master piston 
66" (or 224) are located in alignment with each exhaust pushtube 52 (or 
intake pushtube 228) so as to be actuated by the rocker arm adjusting 
screw mechanism 54 (or 310). The master piston is biased upwardly (as 
shown in FIG. 4B) by a light leaf spring 120" (or 236). The master 
cylinder 106" (or 226) communicates via duct 102' through a check valve 
186 to duct 102 and the outlet of control valve 64. The other end of duct 
102' communicates with duct 188 through a check valve 190. Duct 188 
communicates between an accumulator 192 and the inlet of a solenoid 
actuated spool trigger 194. 
The accumulator 192 comprises a cylinder 196 located in the retarder 
housing 36 containing, for example, a free piston 198 which divides the 
cylinder into a precharged gas portion 200 and a liquid portion 202. The 
spool trigger 194 comprises a cylinder 204 located in the retarder housing 
36 having an inlet port 206 and an outlet port 208. The inlet port 206 
communicates with one end of duct 188 while the outet port 208 
communicates via duct 210 with duct 102. A valve spool 212 is mounted for 
reciprocating motion within the cylinder 204 and biased away from the 
blind end of cylinder 204 by a compression spring 214. A circumferential 
groove 216 is formed on the spool 212 which is of sufficient width to 
communicate with both the inlet port 206 and the outlet port 208 of the 
cylinder 204 when the spool trigger 194 is actuated but to communicate 
with only one of the ports 206, 208 when the spool trigger 194 is not 
actuated. 
One end of a control rod 218 is affixed to the valve spool 212 while the 
other end of the control rod 218 carries the armature 220 of a solenoid 
222. The solenoid 222 is energized through the electronic control unit 150 
via conduit 224. It will be understood that when the solenoid 222 is 
energized, the valve spool 212 will be moved against the bias of spring 
214 so as to permit flow from duct 188 to duct 210. 
It has been noted above that the inlet valve motion is delayed to provide 
for the second compression release event of the exhaust valve 38. To 
accomplish this, a master piston 224 is positioned in a master cylinder 
226 located in the retarder housing 36 above each intake pushtube 228. The 
intake pushtube 228 is driven by a cam 230 mounted on the engine camshaft 
60. The pushtube 228 oscillates the intake rocker arm 232 through a 
mechanism comprising an adjusting screw 310, drive pin 324 and actuator 
pin 348 shown in detail in FIGS. 7A and 7B. The master cylinder 226 
communicates with the accumulator 192 through duct 102' and check valve 
190. If the intake pushtube 228 is not used to charge the accumulator, the 
master cylinder 226 may communicate with either the low or high pressure 
portion of the hydraulic circuit, e.g. duct 90. As shown in FIGS. 7A and 
7B, master piston 224 is biased away from the actuator pin 348 by a leaf 
spring 236. Whenever the retarder is turned on, the master piston 224 
moves downwardly (as shown in FIGS. 4B and 7B) to actuate the intake valve 
delay mechanism. 
In operation, actuation of the pushtubes 52 (or 228) will operate the 
master pistons 66" (or 226) so as to charge the liquid side 202 of the 
accumulator 192 with hydraulic fluid under pressure. Since the fuel 
inJector pushtube 122 (or remote exhaust pushtube 52') begins to move just 
before TDC I it will cause the exhaust valves 38 to open at about TDC I so 
as to produce a compression release event. Due to the check valve 168, the 
unitary crosshead 258 will not retract when the master piston 66 (or 66') 
retracts to follow the downward motion (as shown in FIG. 4B) of the 
pushtube 122 (or 52'). Due to check valve 169, motion of the master piston 
66 (or 66') will not charge the accumulator. However, motion of the 
pushtubes 52 (or 228) and master pistons 66" (or 224) will pump hydraulic 
fluid directly into the accumulator 192 through check valve 190. 
The second compression release event, which occurs nears TDC II, can be 
initiated by a signal from the electronic control unit 150 which energizes 
the solenoid 222 through conduit 224 and permits a flow of high pressure 
hydraulic fluid through ducts 210 and 102. Such high pressure fluid 
actuates the crosshead 258 to open the exhaust valves 38. 
The exhaust valves 38 may be closed after each compression release event by 
interrupting the signal in conduit 178 thereby opening the vent valve 172. 
It is desirable to store the oil or hydraulic fluid vented from the vent 
valve 172 under the spool 92 of the control valve 64 as described in the 
Cavanagh U.S. Pat. No. 4,399,787 which, in its entirety, is incorporated 
herein by reference. The oil or hydraulic fluid stored within the control 
valve 64 is returned to the hydraulic circuit through ducts 102 and 102' 
when the master pistons 66 (or 66')or 66"(or 224) retract. The stored oil 
or hydraulic fluid is maintained in the hydraulic circuit by check valve 
71. It will be understood that it is desirable to deenergize solenoid 222 
prior to opening the vent valve 172 in order to avoid a complete discharge 
of the fluid pressure in the accumulator 192. 
It has been noted above that it is necessary to disable the exhaust valves 
from opening at the time they would normally open during the positive 
power mode of engine operation. Two mechanisms designed to accomplish this 
result are disclosed in application Ser. No. 728,947 filed Apr. 30, 1985 
and assigned to the assignee of the present invention. One of these 
mechanisms involves a modification of the exhaust valve crosshead which 
temporarily prevents actuation of the crosshead by the rocker arm 50 but 
permits actuation by the slave piston. The other mechanism involves a 
modification of the rocker arm 50 wherein the portion of the rocker arm 
which contacts the crosshead is temporarily disconnected from the portion 
of the rocker arm actuated by the pushtube 52. 
A further alternative way to disable the exhaust valve is to provide an 
eccentric bushing in the rocker arm pivot point so as to raise the pivot 
or fulcrum and thereby introduce a lost motion in the valve train. Such a 
device is shown, for example in the Jonsson U.S. Pat. No. 3,367,312, 
hereby incorporated by reference in its entirety. As noted above, the lost 
motion mechanisms are also available. See, for example, Pelizzoni U.S. 
Pat. No. 3,786,792 hereby incorporated by reference in its entirety. 
A preferred mechanism for disabling the exhaust valves is shown in FIGS. 5A 
and 5B which comprises a unitary slave piston and crosshead 258. The 
unitary slave piston and crosshead 258 is mounted for reciprocating motion 
in the slave cylinder 104. The slave piston portion is generally tubular 
in shape but open at the lower end which comprises the crosshead portion. 
For convenience of lubrication, a series of annular grooves 260 may be 
formed in the circumferential surface of the slave piston portion of the 
unitary slave piston and crosshead 258. A circumferential annular channel 
262 may also be formed in the slave cylinder 104 which communicates with a 
lubricating oil duct 264 and the low pressure oil supply duct 70. A series 
of radial ports 266 is formed through the skirt of the slave piston 
portion of the unitary structure 258 near the head of the piston portion. 
When the unitary structure 258 is in its rest position against the 
adjustable stop 110, the radial ports 266 register with a circumferential 
channel 268 that communicates through duct 270 with the low pressure feed 
duct 90 for the control valve 64 (see FIGS. 4A, 4B and 4C). A 
circumferential raceway 272 is formed on the inner surface of the slave 
piston portion of the unitary slave piston and crosshead 258 adjacent the 
radial ports 266. Windows 274 are formed through the slave piston portion 
of the unitary structure to clear retainer 276 which is positioned in the 
windows and located by a retainer ring 278 seated in a groove formed in 
the slave cylinder 104. 
A slider 280, generally tubular in shape, is sized to reciprocate within 
the slave piston portion of the unitary slave piston and crosshead 258. 
Windows 282 are formed in the slider 280 to register with the windows 274. 
A rocker arm contact 284 is affixed to the lower portion of the slider 280 
by a screw 286 and locking cap 288. The rocker arm contact 284 should be 
provided with an appropriately hardened surface suitable for activation by 
the exhaust rocker arm 50. A transverse wall 290 is formed in the slider 
280 near the upper end thereof. Slave piston return springs 292 are 
positioned between the retainer 276 and the transverse wall 290 of the 
slider 280 to bias the slider 280 upwardly and, in turn, bias the slave 
piston and crosshead 258 against the adjustable stop 110. A series of 
radial ports 294 are formed in the upper end of the slider 280 above the 
transverse wall 290 so as to register with the raceway 272 when the slider 
280 is in its uppermost position. 
A piston 296 is located within the slider 2B0 above the transverse wall 
290. The piston 296 is provided with an axial shaft 298 to guide spring 
302 which biases the piston 296 away from the transverse wall 290. The 
lower circumferential portion of the piston 296 has substantially the same 
diameter as the inside of the slider 280 within which it can be 
reciprocated. The upper circumferential portion of the piston 296 is 
relieved to form a raceway 304. A plurality of balls 306, which may, for 
example, be ball bearings, is positioned in the series of radial ports 
294. The balls 306 have a diameter greater than the wall thickness of the 
slider 280 so that the balls 306 extend into the raceway 272 and lock the 
slider 280 and the unitary slave piston and crosshead 258 together. When 
the slider 280 and the slave piston and crosshead 258 are locked together, 
oscillation of the rocker arm 50 will result in reciprocation of the 
crosshead so as to activate the exhaust valves 38. 
However, when duct 270 is pressurized as a result of actuation of the 
solenoid valve 62, piston 296 is forced downwardly against the bias of 
spring 302 so that the raceway 304 comes into registry with the radial 
ports 294 and the balls 306 are cammed out of raceway 272 and toward 
raceway 304. This action unlocks the slider 280 from the unitary slave 
piston and crosshead 258 so that actuation of the slider 280 by the 
exhaust rocker arm 50 will not result in opening the exhaust valves 38. 
However, when duct 102 is pressurized by motion of the master piston 66, 
the unitary slave piston and crosshead 258 will be activated and the 
exhaust valves 38 opened. 
FIG. 5B illustrates the mechanism of FIG. 5A during the retarding mode of 
operation wherein the exhaust valves have been disabled by unlocking the 
slider 280 from the unitary slave piston and crosshead 258. It will be 
appreciated from FIG. 5B that when the exhaust valves have been disabled 
by this mechanism the exhaust valve springs 42 have, in effect, been 
removed from the remainder of exhaust valve train. If the slave piston 
return spring exerts insufficient force to avoid play in the valve train 
and maintain contact among the rocker arm, pushtube, cam follower and cam, 
a supplemental spring mechanism may be provided. Referring to FIG. 4A, a 
piston 57 may be mounted for reciprocating motion within cylinder 59 
located in the retarder housing 36 and aligned with the exhaust pushtube 
52. A compression spring 61 biases the piston 57 toward the rocker arm 
adjusting screw 54 thereby eliminating play in the exhaust valve train. It 
will, of course, be appreciated that in the mechanisms shown in FIGS. 4B 
and 4C the function of piston 57 may be performed by the master piston 66" 
(or 224), respectively. 
In the event that it is desired to employ separate crossheads and slave 
pistons in accordance with conventional practice, an alternative exhaust 
valve disabling mechanism according to the present invention may be used 
in place of the rocker arm adjusting screw 54 and locknut 56. FIG. 6A 
shows such a mechanism during the powering mode of engine operation 
wherein it performs the function of the adjusting screw 54. FIG. 6B shows 
the same mechanism during the retarding mode of engine operation wherein 
it disables the rocker arm 50 and, therefore, the exhaust valves 38. 
Point 308 represents the point about which rocker arm 50 pivots when 
actuated by the pushtube 52. The mechanism comprises a tubular adjusting 
screw 310 which replaces the solid adjusting screw 54 and which is locked 
in its adjusted position by locknut 312. The tubular adjusting screw is 
provided with three concentric bores. A large bore 314 extends a short 
distance from the pushtube end of the adjusting screw 310. An intermediate 
bore 316 extends from the large bore 316 substantially to the top of the 
adjusting screw 310. A small bore 318 extends through the top of the 
adjusting screw 310. A sloping shoulder 320 is formed between the large 
bore 314 and the intermediate bore 316 while a horizontal shoulder 322 is 
formed between the intermediate bore 316 and the small bore 318 
A drive pin 324 is positioned within the adJusting screw 310. The maximum 
diameter of the drive pin 324 is slightly less than the diameter of the 
intermediate bore 316 to permit reciprocation of the drive pin 324 
relative to the adjusting screw 310. One end of the drive pin 324 is 
adapted to mate with, and be driven by, the pushtube 52. A snap ring 326 
limits the downward (as shown in FIGS. 6A and 6B) movement of the drive 
pin 324 relative to the adjusting screw 310. The upper portion of the 
drive pin 324 has an outside diameter 328 which is slightly smaller than 
the small bore 318 of the adjusting screw 310 so as to permit relative 
reciprocation of the drive pin and adjusting screw 310. A shoulder 330 is 
defined by the diameter 328 of the upper portion of the drive pin 324 and 
the maximum diameter of the drive pin. A compression spring 332 is located 
within the adjusting screw 310 between shoulders 322 and 330 so as to bias 
the drive pin 324 downwardly (as shown in FIGS. 6A and 6B) relative to the 
adjusting screw 310. A plurality of ports 334 are disposed around the 
circumference of the drive pin 324 in the region of its largest diameter. 
The ports 334 are directed angularly downwardly (as shown in FIGS. 6A and 
6B) from the outside of the drive pin 324 toward the axis of the drive 
pin. A stepped cavity 336 is formed within the drive pin 324. The largest 
diameter 338 of the stepped cavity 336 communicates at its upper region 
with the plurality of ports 334, and with an intermediate diameter 340 
through a sloping shoulder 342. The intermediate diameter 340 terminates 
at a shoulder 344 while a smaller diameter section 346 extends from the 
shoulder 344 through the top of the drive pin 324. 
A stepped actuator pin 348 is mounted for reciprocating motion with respect 
to the drive pin 324 and includes a large diameter section 350, an 
intermediate diameter section 352 and a small diameter section 354. A 
sloping shoulder 356 joins the larger diameter section 350 and the 
intermediate diameter section 352 while a horizontal shoulder 358 is 
located between the intermediate and small diameter sections of the 
actuator pin 348. When the actuator pin 348 is in its uppermost position 
(as shown in FIG. 6A) the horizontal shoulder 358 in the actuator pin 
abuts the shoulder 344 of the drive pin 324 and the small diameter section 
354 of the actuator pin 348 extends beyond lhe upper end of the drive pin 
324. The actuator pin 348 is biased toward its uppermost position by a 
compression spring 360 located within the cavity 336. A ball 362 is 
located in each of the ports 334. The balls 362 are larger in diameter 
than the wall thickness of the drive pin 324 in the region of the ports 
334 so that when the actuator pin is in its uppermost position (as shown 
in FIG. 6A) the balls 362 extend outside the drive pin 324 and engage the 
shoulder 320 of the adjusting screw 310. However, whenever the actuator 
pin 348 is depressed as shown in FIG. 6B, the sloping shoulder 320 cams 
the balls 362 inwardly so that the balls 362 rest, at least partially, on 
the sloping shoulder 356 of the actuator pin 348. In this position (FIG. 
6B), the balls 362 clear the shoulder 320 and the drive pin 324 is free to 
reciprocate with respect to the adjusting screw 310. 
Point 364 (FIG. 6A) represents the maximum upward excursion of the drive 
pin 324 as a result of the upward movement of the exhaust valve pushtube 
52. The distance 366 (FIG. 6A) represents a clearance (which should be a 
minimum of about 0.100") between point 364 and the rest position of the 
master piston 66" (or 224) (FIG. 4B) or 66 (FIG. 4C). The master piston 
66" (or 224) is biased toward its rest position by the leaf spring 120" 
(or 236). Whenever the engine retarder is turned on, the hydraulic circuit 
will be pressurized by the low pressure pump 74 (FIG. 4A) and the master 
piston 66" will be driven downwardly (as viewed in FIGS. 6A and 6B) until 
it contacts the end of the drive pin 324 against the bias of leaf spring 
120" and compression spring 360. Under these conditions, the motion of the 
pushtube 52 will be transmitted through the drive pin 324 to the master 
piston 66" but the rocker arm 50 will remain at rest since the drive pin 
324 will be disengaged from the adjusting screw 310. However, the bias of 
compression spring 332 will maintain the rocker arm 50 in contact with the 
exhaust valve crosshead (not shown). It will be seen, therefore, that the 
exhaust valves 38 are automatically disabled by the mechanism of FIGS. 6A 
and 6B whenever the engine retarder is switched on. 
FIGS. 7A and 7B illustrate a mechanism which is very similar to the 
mechanism shown in FIGS. 6A and 6B but which is designed to delay but not 
entirely disable the motion of the intake valve. For purposes of clarity 
and brevity, parts which are common to both mechanisms carry the same 
designators. It will be understood, however, that the rocker arm 232 is an 
intake valve rocker arm, the pushtube 228 is an intake valve pushtube and 
the master piston 224 is located in alignment with the intake valve 
pushtube 228 within a master cylinder 226 located in the retarder housing 
36. 
The only significant difference in the mechanisms shown in FIGS. 7A and 7B 
over the mechanisms shown in FIGS. 6A and 6B is that an extra step is 
provided between the intermediate bore 316 and the small bore 318 so as to 
form a shoulder 364 between the intermediate bore 316 and an intervening 
bore 366. The diameter of the intervening bore 366 is smaller than the 
maximum diameter 328 of the drive pin 324. The distance 368 between 
shoulders 330 and 364 is directly proportional to the delay introduced 
into the motion of the rocker arm and valve associated therewith. It will 
be appreciated that any desired delay may be built into the mechanism. 
When the distance 368 is equal to or greater than the travel of the 
pushtube 228, the mechanism of FIGS. 7A and 7B will function exactly like 
the mechanism of FIGS. 6A and 6B. 
Although the mechanism of FIGS. 7A and 7B is intended principally to 
provide the intake valve delay required by FIG. 3B, it will be appreciated 
that this mechanism may be used whenever a delay in the intake or exhaust 
valve motion is required. Similarly, the mechanism of FIGS. 6A and 6B may 
be used whenever the intake or exhaust valves are required to be disabled. 
The terms and expressions which have been employed are used as terms of 
description and not of limitation and there is no intention in the use of 
such terms and expressions of excluding any equivalent of the features 
shown and described or portions thereof, but it is recognized that various 
modifications are possible within the scope of the invention claimed.