207~~.2~
20-DP-1703
IMPROVED CAM BECTIONB FOR A ~~V~~-TYPE DIESEL ENGINE
BACKGROUND OF T~iE INVENTION
The invention relates generally to fuel
injected diesel engines and more particularly to
direct injection type diesel engines having inverted
fuel rocker mechanisms such as "V"-type engines
suitable for use in locomotive, stationary and
marine applications.
Improved engine efficiency has been a
primary goal for diesel engine designers but has
proved to be a difficult task particularly for
older, larger and proven engine designs. With
larger engines, a small fraction of a percentage
increase in fuel efficiency can translate into a
substantial cost savings over time. One such diesel
engine is the ALCO Model 251 Series "V"-type diesel
engine previously manufactured under license by
Bombardier Inc. in Quebec, Canada and now
manufactured by G.E. Canada in Quebec, Canada.
Since purchases of large engines require a large
capital investment, it is desirable that any change
to facilitate engine efficiency improvement also
minimize retrofit costs and preferably require
little or no change to the engine block.
Known ALCO 251 diesel "V"-type diesel
engines typically include a bank of combustion
cylinders on a right side of the engine and a bank
of combustion cylinders on the left side of the
engine. Each cylinder typically has a corresponding
piston and a plurality of cams. The cams typically
include a fuel cam for moving a plunger inside a
fuel pump to supply fuel to the cylinder, a
corresponding air cam for moving air valves
typically located in the cylinder head and a
20"~~~.~
20-DP-1703
corresponding exhaust cam for moving exhaust valves
also typically located in the cylinder head. The
fuel cam contacts a roller of an inverted rocker arm
to facilitate movement of the fuel pump plunger.
The cams each have a cam profile and are rotatable
about a cam shaft axis and are fixedly positioned
with respect to each other to form a pre-determined
cam orientation.
Such diesel engines have previously been
10 designed with CQ type fuel pumps manufactured by
Lucas Bryce, Gloucester, England, and small diameter
multi-cylinder cam shafts which provided a fuel cam '
lift to fuel pump plunger lift ratio of less than
1:1. It was found that the reliability and
efficiency of such engines was limited in part by
the cam shaft configuration and the linkage from the
cam shaft to the valves or fuel pump plunger.
Improved diesel engines have been designed
to overcome some of these problems. These engines
20 typically include unit cam sections that provide a
1:1 fuel cam lift to fuel pump plunger lift ratio to
reduce loading on the cams and camshaft which
increases reliability of the engine. The unit cam
design also facilitates single cylinder cam
replacement through an existing opening on the side
of the engine instead of removing multiple cams for
multiple cylinders longitudinally through the cam
shaft bearing of the engine. Other improvements
have also been made such as increasing the thickness
30 of portions of the fuel pump support to further
increase the rigidity of the cam to valve linkages
and modifying the fuel cam profile to facilitate
higher injection pressure. Another change included
switching the fuel pump to a CV type fuel pump, also
-2-
20'~J~.2~i
20-DP-1703
manufactured by Lucas Bryce, which was believed to
have improved performance characteristics.
Although it has been found that fuel
efficiency has been increased by nearly 1.5% after
these improvements to the ALCO 251 diesel engine,
further increases in fuel efficiency would be
desirable to provide a low cost and easily
installable alternative to purchasing and installing
a new engine. Consequently there exists a need for
improving diesel engine efficiency without requiring
substantial changes to existing engine designs and
which can be readily incorporated with existing
engine blocks.
SUMMARY OF THE INVENTION
In carrying out the present invention in
a preferred form thereof, there is provided an
improved unit cam section for use in a fuel inj ected
diesel engine such as a "V"-type engine which has an
inverted fuel rocker mechanism for engaging the fuel
cam. One illustrated embodiment of the invention
disclosed herein is in the form of unit cam sections
for use in a "V"-type locomotive engine.
It is an object of the present invention
to provide a more fuel efficient diesel engine, such
as an improved ALCO 251 diesel engine which has an
inverted fuel rocker mechanism for engaging the fuel
cam.
It is another object of the invention to
provide a unit cam section which facilitates
improved engine efficiency and does not require
redesign of existing engine blocks such as engine
blocks designed for use in a diesel engines which
have an inverted fuel rocker mechanism for engaging
the fuel cam.
-3-
~or~~~~
20-DP-1703
A first unit cam section for one bank of
cylinders and a second unit cam section for another
bank of cylinders for use in a "V"-type fuel
injected diesel engine is disclosed. Each unit cam
section, having a longitudinal center axis, includes
a plurality of cams for a single cylinder and piston
wherein each of the cams has a base circle, the
center of each base circle lies along the
longitudinal center axis of the unit cam section.
The plurality of cams include a fuel cam, interposed
between an air cam and an exhaust cam, such that the
fuel cam moves a fuel pump plunger mechanism for
facilitating fuel flow to a corresponding cylinder,
the air cam moves corresponding air valves and the
exhaust cam moves corresponding exhaust valves.
Each cam has an opening flank portion and a closing
flank portion and a predetermined cam profile. Each
unit cam section is cooperative with an inverted
fuel rocker mechanism. The unit cam sections
include a base circle diameter of at least 3.75
inches for each cam. The fuel cam on each unit cam
section is adapted to provide a fuel cam lift to
fuel pump plunger lift ratio of at least 0.8:1Ø
The unit cam sections also have a predetermined cam
orientation between the fuel cam and the air cam and
the fuel cam and the exhaust cam. The first unit
cam section has a fuel cam to air cam angle of
between 56° and 63°, and a fuel cam to exhaust cam
angle of between 143 ° and 153 ° . The second unit cam
section has a fuel cam to air cam angle of between
0° and 7°, and a fuel cam to exhaust cam angle of
between 88° and 98°.
The fuel cam to air cam angle is defined
by an angle between a fuel cam reference line and an
air cam line. The fuel cam reference line is
-4-
2075 ~.2
20-DP-1703
defined by a first point and a second point wherein
the first point corresponds to a location of a
center axis of a fuel cam roller which is at a
position along the opening flank of the fuel cam
where the fuel cam engages the inverted fuel rocker
mechanism when the piston is at top dead center
during a fuel injection portion of an engine cycle.
The second point corresponds to a center axis of the
base circle of the fuel cam.
10 The air cam line is defined by a first
point corresponding to a location of a center axis
of an air cam roller which is at a position along
the opening flank of the air cam corresponding to a
location on the opening flank of the air cam where
the air cam causes the air valves to start to open.
The second point for the air cam line corresponds to
the center axis of the base circle of the air cam.
The fuel cam to exhaust cam angle is
defined by an angle between the fuel cam reference
20 line and an exhaust cam line. The exhaust cam line
is defined by a first point corresponding to a
location of a center axis of an exhaust cam roller
which is at a position along the opening flank of
the exhaust cam corresponding to a location on the
opening flank of the exhaust cam where the exhaust
cam causes the exhaust valves to start to open. The
second point corresponds to the center axis of the
base circle of the exhaust cam.
The first unit cam section has a preferred
30 fuel cam to air cam angle of between 60° and 62° and
a preferred fuel cam to exhaust cam angle of between
147 ° and 149 ° and a preferred lift ratio of 1:1.
The second unit cam section has a preferred fuel cam
to air cam angle of between 5° and 7° and a
_6_
2fl751?~
20-DP-1703
preferred fuel cam to exhaust cam angle of between
92° and 94° and a preferred lift ratio of 1:1.
An improved "V"-type direct fuel injection
diesel engine incorporating the aforedescribed first ,
and second unit cam sections is also disclosed. The
engine further includes inverted fuel rocker
mechanisms associated with each cylinder and
cooperative with the fuel cams; fuel pumps, such as
CQ type fuel pump, associated with each cylinder and
having a fuel plunger mechanism responsive to the
inverted fuel rocker means; and the fuel cams
adapted to provide a fuel cam lift to fuel pump
plunger lift ratio of at least 0.8:1.0
Other objects and advantages of the
invention will be apparent from the following
description, the accompanied drawings and the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a partial cross-sectional and
cutaway view of a fuel pump, lifter assembly and
inventive unit cam section for use in one bank of a
diesel engine;
Figure 2A is a plan view of the unit cam
section of Fig. 1 in accordance with the invention;
Figure 2B is a perspective view of the
unit cam section of Fig. 2A in accordance with the
invention;
Figure 3A is a schematic diagram of a
cross-section of a fuel cam portion of a unit cam
section depicting the cam profile in accordance with
the invention;
Figure 3B is a schematic diagram of a
cross-section of the air cam section depicting the
cam profile in accordance with the invention:
-6-
20'~51~~
20-DP-1703
Figure 3C is a schematic drawing of a
cross-section of the exhaust cam portion of the unit
cam section depicting the cam section in accordance
with the invention; and
Figure 4 is a partial plan view of a
plurality of unit cam sections for a first and
second bank of cylinders and illustrates the cam
orientation for each unit cam section in accordance
with the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
For purposes of simplicity, the following
description will be made with reference to a single
unit cam section for use with any one of a plurality
of cylinders in one bank. However, it will be
recognized that the general description also applies
to a unit cam section for use in another bank of
cylinders in a same diesel engine.
A unit cam section embodying the present
invention in one preferred form thereof is
illustrated in partial form in Figs. 1 and 2 as a
fuel cam engaging a lifter assembly pertaining to a
locomotive engine application such as an ALCO 251
engine. The lifter assembly couples to a fuel pump
12. The lifter assembly 14 includes an inverted
fuel cam rocker mechanism 16 which is coupled to
crosshead assembly 18, an air valve lifter 19 and an
exhaust valve lifter (not shown). A rotating unit
cam section 20 engages the lifter assembly 14 as
known in the art.
The fuel pump 12 is supported above the
crosshead assembly 18 by fuel pump support 22 which
is fixedly mounted to the engine block 23. The fuel
pump 12 includes a plunger 24 mounted for
reciprocating movement in a fuel pressure chamber
_7_ .
2~'~~1~3
20-DP-1703
26. The ports 28 and 30 allow fuel to enter and
exit the fuel chamber 26. The plunger 24 is
reciprocally movable to force fuel from the fuel
chamber 26 out to an injection port (not shown) to
supply the pressurized fuel to an engine cylinder as
known in the art. The engine cylinder has a chamber
for receiving a piston which compresses an air and
fuel mixture to the point of ignition as well known
in the art.
10 The fuel pump 12 is preferably a CQ type
fuel pump as known in the art which is also
available from Lucas Bryce, Gloucester, England.
Such a pump should have injection pressure
characteristics similar to those shown in Table I
corresponding to the box indicating an 18CQ pump.
_g_
20"11.23
20-DP-1703
TABLE I
CV
H
CO
Ptmp
-
226
W~pJayl
~
1100
rpm
1200
1-251
CaltS
91Ø5.16
1100 IAaxHat ,
ptdon,
Plea
cam
1SC0 ,
pump.
24.0
tlmlnp
'
'
9 1-251Ca1150.5
.376 91 10
145
noala
1000 .
PCmax-1~1 .
Du Al~xHat
platon,
Plw
eam,
18CV
pump,
24.0'
timlnp,
9'.375'145
nouis
PCmax-126
Du
700
_a
600 -
500
Zi
100
300
200
100
~'~J'
0
T'1'T'T
920.0 330.0 3eo.o
340.0 390.0
350.0 400.0
~.0 4m.o
370.0
o.e --
_ 0.6 -
Z
0.4
s o.2
0
Ø2
520.0 J30.0 3s0.0
340.0 39D.0
950.0 .100.0
9D0.0 410.0
970.0
Graph (A) compares the injection pressure of an 18CV
pump to the 18CQ pump at various cranlahaft angle
_g_
20~~~~~
20-DP-1703
positions under a constant load of approximately 225
bhp/cylinder at 1100 rpm. It was found that
although currant diesel engines of the ALCO 251
engines use a CV type pump, the CQ pump provides
higher injection pressure and a faster rate of
pressure reduction for various crankshaft angle
positions.
Graph (B) illustrates the fuel injection
needle lift over a range of crankshaft positions and
10 shows that secondary fuel injection occurs with the
CV pump between apprpximately 374° - 382° of
crankshaft angle. This secondary fuel injection
tends to reduce efficiency since fuel is being
unnecessarily injected at an improper crankshaft
angle position.
The plunger 24 moves upwardly through the
port closure distance generally indicated at 31 to
close the input ports. The port closure distance 31
may be between approximately .117 inch and .177
20 inch. A preferred distance is a nominal .155 inch
as is the case with an 18CQ pump.
The crosshead assembly 18 is a typical
assembly which includes a crosshead 32 for pushing
the plunger 24 upwardly to force fuel into the
combustion cylinder. The crosshead 32 is
reciprocally actuated through the movement of the
fuel cam on the unit cam section 20 as it engages
the rocker mechanism 16 as known in the art. The
lifter assembly 14 includes an inverted rocker arm
30 36 pivotal about a fulcrum 38. A fuel cam roller 40
is rotatably attached to the rocker arm 36 on one
side of the fulcrum 38 and an adjustment screw 42 is
attached to another end of the rocker arm 36 on
another side of the fulcrum 38 so that downward
movement of the fuel cam roller 40 causes upward
-10-
20-DP-1703
movement of the adjustment screw 42. The rocker arm
36 embodies an oil gallery 45 for supplying oil to
the sliding surface of a head 47. The adjustment
screw includes an annular groove 43 with cross
drilling and a central drilling up to the head of
the adjustment screw 47. The head 47 of the
adjustment screw 42 slidably engages a crosshead
contact block 49. Turning the adjustment screw 42
causes the port closure distance to change.
10 An air valve lifter 19 is pivotal about
another fulcrum 46. The air valve lifter 19 has an
air cam roller 48 attached at an end distal the
fulcrum 46 for engaging the air cam (not shown) of
the unit cam section 20. As known in the art, the
exhaust valve lifter (not shown) is substantially
identical in design to the air valve lifter 19.
The lifter assembly 14 also includes a
lower spring retainer 52 which is slidably
engageable with a portion of the fuel pump support
20 generally indicated at 50. Lower spring retainer 52
is coupled to the crosshead 32. The crosshead
guides the assembly through the fuel pump support 50
as it travels upwardly during actuation by the
inverted rocker arm 16. A plurality of biasing
springs 54 and 56 provide downward bias pressure
when the crosshead 32 is moved upwardly by movement
of the inverted rocker arm 16 as well known in the
art. Upper and lower spring retainers 58 and 59
serve to secure the springs 54 and 56.
30 The plunger 24 and ports 28 and 30 of the
fuel pump 12 are incorporated by a fuel pump body
70. An outer cover 72 protects the fuel pump 12 and
fuel pump support 50 from the environment. The fuel
pump 12 also has a threaded outlet 74 which connects
to a high pressure injection tube (not shown). End
-11-
2~'~~~.~
20-DP-1703
portions 80 of the outer cover 72 forcibly abut
portions of the engine block 23 by tightening a knob
78 which has a threaded bolt 79 for threadably
coupling to the fuel pump support 22.
It will be recognized that the above cam,
fuel pump and lifter assembly description applies
equally well for each set of cam, fuel pump and
lifter assembly associated with each of the
cylinders in a bank in a "V~~-type diesel engine as
known in the art.
Figs. 2A and 2B depict the unit cam
section 20 and a connect spacer 82 which houses a
dowel 84 for use in aligning one unit cam section to
another. Unit cam section 20 is an integrally
formed cam section typically machined from a piece
of metal stock. The unit cam section 20 includes
opposing ends 86 and 88 adapted with apertures 85 to
connect with spacers 82 which interconnect unit cam
sections together (best seen in Fig. 4). The unit
cam section 20 is referred to as a unit cam section
since it includes the necessary cams for a single
combustion cylinder of an engine as opposed to a cam
section which includes cams for multiple cylinders.
The unit cam section 20 includes a plurality of cams
positioned between the opposing ends 86 and 88. The
plurality of cams include an air cam 90 which causes
movement of air valves typically located in a
cylinder head (not shown), an exhaust cam 92 for
moving exhaust valves typically located in the
cylinder head, and a fuel cam 94 for moving a fuel
plunger 24 to allow fuel to be injected into the
combustion cylinder.
The air cam 90 is adjacent to the fuel cam
and the fuel cam 94 is interposed between the air
cam 90 and the exhaust cam 92. The unit cam section
-12-
20-DP-1703
20 serves as one section of an elongated cam shaft.
The cams 90, 92 and 94 are spaced apart
longitudinally along the unit cam section for
operating their respective valves. Each of the cams
has a base circle 96a-96c (best seen in Figs. 3A-3C)
which has a center axis generally indicated at 98.
The opposing ends 86 and 88 of this cam section 20
have a fillet radius portion extending from the
opposing ends.
10 Figs. 3A-3C and associated Tables II-IV
illustrate cam profiles for all unit cam sections
irrespective of the particular bank or side of the
engine in which they are employed. In particular,
Fig. 3A and Table II define a preferred cam profile
for the fuel cam 94. Table II specifies the roller
lift (in inches) at cam angles of 1° increments.
Similarly, Fig. 3B and Table III define a preferred
cam profile for the air cam 90 and Fig. 3C and Table
IV define a preferred cam profile for the exhaust
20 cam 92.
-13-
<IMG>
-14-
<IMG>
~~r~~~~J
20-DP-1703
TABLE IV
EXHAUST CAM PROFILE
9D 0.X0
91 O~
92 450
-16-
20'~~~2~
20-DP-1703
Fig, 3C also shows the positioning of an exhaust cam
roller 95 in a similar manner as the fuel and air
cam rollers shown in Figs. 3A and 3B. It will be
recognized that Tables II-IV represent nominal
lifts. As known in the art, a cam profile
corresponding to the outer contour of a lobe of a
cam may be determined by rolling a roller about the
lobe area to determine the actual cam profile.
Each cam (see Figs. 3A-3B) has an unique
cam profile and base circle 96a-96c diameter. The
base circle of each cam has a diameter of at least
3.75 inches. Each of the cams has an annular
profile extending circumferentially about a portion
of the base circle of each of the cams. Each of the
cams further includes an opening flank generally
indicated at 100, a closing flank generally
indicated at 102 and a dwell portion generally
indicated at 104. The fuel cam is adapted with a
lift section to provide a fuel cam lift to fuel pump
plunger lift ratio of at least 0.8:1Ø
As seen in Figs 3A-3C and Fig. 4, a unit
cam section 20, configured as the first (right side)
unit cam section 106, has a predetermined cam
orientation between the fuel cam and the air cam and
the fuel cam and the exhaust cam. Likewise, a unit
cam section 20, configured as a second (left side)
unit cam section has a slightly different cam
orientation due to the typical "V"-type engine
configuration.
The fuel cam to air cam angle of the first
unit cam section is between 56° and 63°. The fuel
cam to air cam angle is defined by an angle between
a fuel cam reference line 110 and an air cam line
112. The fuel cam reference line 110 is defined by
a first point and a second point wherein the first
-17-
2~'~~.~~
20-DP-1703
point 114 corresponds to a location of a center axis
of the fuel cam roller 40 which is at a position
along the opening flank 100 of the fuel cam 94 where
the fuel cam engages the inverted fuel rocker
mechanism 36 when the piston is at tap dead center
during a fuel injection portion of an engine cycle.
The second point 116 corresponds to a center axis of
the base circle 96c of the fuel cam.
The air cam line 112 is defined by a first
10 point 118 corresponding to a location of a center
axis of an air cam roller which is at a position
along the opening flank 98 of the air cam 90
corresponding to a location on the opening flank of
the air cam where the air cam 90 causes the air
valves to start to open. The second point 120 for
the air cam line 112 corresponds to the center axis
of the base circle 96a of the air cam.
The unit cam section 20 also has a fuel
cam to exhaust cam angle of between 143° and 153°.
20 The fuel cam to exhaust cam angle is defined by an
angle between the fuel cam reference line 110 and an
exhaust cam line 122. The exhaust cam line 122 is
defined by a first point 124 corresponding to a
location of a center axis of an exhaust cam roller
which is at a position along the opening flank 98 of
the exhaust cam 92 corresponding to a location on
the opening flank of the exhaust cam 92 where the
exhaust cam causes the exhaust valves to start to
open. The second point 126 corresponds to the
30 center axis of the base circle 96b of the exhaust
cam.
As similarly defined, the second unit cam
section 108 has a fuel cam to air cam angle of
between 0° and 7°, and a fuel cam to exhaust cam
angle of between 88° and 98°. The second unit cam
-I8-
~~rl~~.~J
20-DP-1703
section 108 has a preferred fuel cam to air cam
angle of between 5 ° and 7 ° and a fuel cam to exhaust
cam angle of between 92 ° and 94 ° and a lift ratio of
1:1.
Fig. 4 also illustrates the inventive cam
orientation for a plurality of interconnected unit
cam sections for each bank of cylinders. A right
bank cam shaft portion 128 and a left bank cam shaft
portion 130 each have two unit cam sections 20
10 connected by spacers 82. Although not shown, any
suitable number of unit cam spacers may be employed
depending on the number of engine cylinders. The
right camshaft portion may be used for a right bank
of cylinders and the left camshaft portion 102 may
be used for a left bank of cylinders as is typical
with an ALCO 251 diesel engine.
The cam orientation for each unit cam
section for a same side of the engine (those used
for the same bank of cylinders) is substantially
20 identical. The fuel cam is angularly displaced with
respect to both the air cam and the exhaust cam to
achieve an optimum fuel consumption level at
relatively high engine loading. Referring to Fig.
4, the preferred nominal angle displacement for the
air cam of the first unit cam section 106 is shown
at an angle of approximately 61.0° from the fuel
reference line 110. The exhaust line 114 is shown
at a nominal angle displacement of 147.8° from the
fuel cam reference line. The preferred nominal fuel
30 cam to air cam angle range is between 60° and 62°
and the preferred fuel cam to exhaust cam angle
range is between 147° and 149°. The preferred lift
ratio is 1:1.
For the second unit cam section 108, the
preferred nominal angle displacement for the air cam
-19-
20-DP-1703
is shown at an angle of approximately 6. 00 ° from the
fuel reference line 110. The exhaust line 114 is
shown at a preferred nominal angle displacement of
92.7° from the fuel cam reference line.
Table V illustrates cam timing in
crankshaft degrees from top dead center (TDC) firing
between an old ALCO 251 engine design (using a CV
type fuel pump and a unit cam section having a 1:1
fuel cam lift ration) and two new designs. It will
be recognized that the valve open numbers in Table
V were measured after valve lash (approximately .034
inch).
TABLE V
New Design New Design Prior Design
No. 2 No. 1
LEFT BANK
AIR VALVE
Open 292.9 292.9 285.5
Close 581.4 581.4 576.5
Duration 288.5 288.5 291.0
EXHAUST VALVE a
Open 119.4 119.4 117.7
Close 422.9 422.9 421.1
Duration 303.5 303.5 303.4
VALVE OVERLAP 130.0 130.0 135.6
FUEL CAM NOMINAL
LIFT AT TDC
(INCHES) 0.443 0.486 0.486
-20-
2~"l )~.~~
20-DP-1703
TABLE V (cont.)
New Design New Design Prior Design
No. 2 No. 1
RIGHT BANK
AIR VALVE
Open 293.0 293.0 287.6
Close 581.5 581.5 578.5
10 Duration 288.5 288.5 290.9
EXHAUST VALVE
Open 119.5 119.5 119.5
Close 423.0 423.0 423.0
Duration 303.5 303.5 303.5
VALVE OVERLAP 130.0 130.0 135.6
FUEL CAM NOMINAL
LIFT AT TDC
(INCHES) 0.441 0.482 0.482
New design #1 employs a CV type pump and a unit cam
20 section having a 1:1 lift ratio but with a different
cam orientation than the older design. New design
#2 employs the CQ type fuel pump and a cam section
having a 1:1 fuel lift ratio of 1:1 but with a
different cam orientation than both the old design
and the new design #1. It was found that new design
#1 increased fuel efficiency by approximately 1.5%
over the older design.
It has been found that a new design #2
ALCO 251 diesel engine using the CQ type pump
30 (having characteristics similar to those shown in
Table I) in conjunction with the cam profiles and
cam orientations, facilitate an improved fuel
efficiency of between 1 and 2.4% brake specific fuel
consumption (BSFC) over the new design #1 (it should
be noted that testing was done with one cylinder so
-21-
2~'~~~ ~ a
20-DP-1703
that BSFC numbers may vary for a multicylinder
engine due to differences in the friction power).
This dramatic increase allows current users of such
engines to improve performance of their existing
engines by changing from the CV type fuel pump to
the well known CQ type fuel pump and replacing the
existing unit cam section with the aforedescribed
unit cam section having the defined cam orientation.
As previously mentioned, the improved
10 direct fuel injection diesel engine, such as an ALCO
251 diesel engine incorporating the aforedescribed
unit cam sections in conjunction with, a CQ type fuel
pump, can offer a fuel efficiency increase of
between 1%-2.4% BSFC. Such an engine includes the
plurality of unit cam sections 106 and 108 which
have integrally formed air cams, fuel cams and
exhaust cams and a base circle portion for each cam
with a diameter of at least 3.75 inches. The engine
includes an inverted fuel rocker mechanism 16 (shown '
20 in Fig. 1) which is cooperative with the fuel cam.
The engine also has a fuel pump, such as a CQ type
fuel pump, having a fuel plunger mechanism
responsive to the rocker mechanism 16. The fuel cam
20 is adapted to provide a fuel cam lift to fuel
pump plunger lift ratio of at least 0.8:1Ø
While the method and devices herein
described constitute the preferred embodiment of the
invention, it is to be understood that the invention
is not limited to these precise methods and devices
30 and that changes may be made therein without
departing from the scope of the invention which is
defined in the appended claims. For example,
although the invention was described with reference
to direct injection diesel engine for locomotive
applications, the inventive unit cam sections may be
-22-
20-DP-1703
suitable for other diesel engine applications such
as marine applications or any other diesel engine
applications.
°23-
