U.S. patent number 3,786,792 [Application Number 05/147,833] was granted by the patent office on 1974-01-22 for variable valve timing system.
This patent grant is currently assigned to Mack Trucks, Inc.. Invention is credited to Richard B. Gibson, Jack F. Greathouse, Frank J. Pekar, Jr., Winton J. Pelizzoni.
United States Patent |
3,786,792 |
Pelizzoni , et al. |
January 22, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
VARIABLE VALVE TIMING SYSTEM
Abstract
A system for varying the valve timing of an internal combustion
engine to increase the retarding effect of the engine for braking
purposes, to increase the compression ratio of a relatively low
compression ratio engine to enhance starting, and to optimize
breathing to improve the engine performance over the useful
operating speed range. The valve timing is varied by changing the
total valve train length so as to shift the points on the cam
profile at which the valve opening and closing events are
determined.
Inventors: |
Pelizzoni; Winton J.
(Hagerstown, MD), Greathouse; Jack F. (Hagerstown, MD),
Pekar, Jr.; Frank J. (Hagerstown, MD), Gibson; Richard
B. (Hagerstown, MD) |
Assignee: |
Mack Trucks, Inc. (Allentown,
PA)
|
Family
ID: |
22523087 |
Appl.
No.: |
05/147,833 |
Filed: |
May 28, 1971 |
Current U.S.
Class: |
123/321;
123/90.17; 123/90.16 |
Current CPC
Class: |
F01L
13/0031 (20130101); F01L 1/2422 (20130101); F01L
13/04 (20130101); F01L 13/06 (20130101); F01L
1/245 (20130101); F01L 13/08 (20130101); F01L
1/08 (20130101) |
Current International
Class: |
F01L
13/08 (20060101); F01L 1/20 (20060101); F01L
13/06 (20060101); F01L 1/24 (20060101); F01L
13/00 (20060101); F01L 1/245 (20060101); F01L
13/04 (20060101); F02d 013/04 () |
Field of
Search: |
;123/90.16,90.15,97B |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Fuel Injection and Controls for Internal Combustion Engines", by
Burman & DeLuca, 1962, pages 176-177.
|
Primary Examiner: Goodridge; Laurence M.
Assistant Examiner: Cox; Ronald B.
Attorney, Agent or Firm: Brumbaugh, Graves, Donohue &
Raymond
Claims
We claim:
1. A variable valve timing system for an internal combustion engine
having a crankshaft and at least one cylinder, a piston
reciprocable in each cylinder and connected to the crankshaft for
rotation thereof, and at least one valve for each cylinder,
comprising at least one cam means driven by the crankshaft, the cam
means including a first profile for actuating a corresponding valve
in a first timed relation to the rotation of the crankshaft and a
second profile for actuating at least one of the valves in a second
timed relation to the rotation of the crankshaft, the cam means for
actuating any valve in two timed relations to the rotation of the
crankshaft including a cam having the first and second profiles
formed thereon circumferentially spaced from each other, a valve
gear train coupling each valve to a corresponding one of the cam
means, means for expanding at least one of the valve gear trains
from a collapsed condition in which the first profile is effective
for actuating the corresponding valve in the first timed relation
to the rotation of the crankshaft to an expanded condition in which
the second profile is effective for actuating the corresponding
valve in the second timed relation to the rotation of the
crankshaft, each valve capable of being actuated in the two timed
relations to the rotation of the crankshaft being coupled to the
first and second profiles of the corresponding cam by a single
valve gear train, and means for locking each expanded valve gear
train in the expanded condition, whereby each valve actuated by an
expandable valve gear train is actuated in one of two predetermined
timed relations to the rotations of the crankshaft corresponding to
the collapsed and the locked expanded conditions of the
corresponding valve gear train, each expanding means including
means forming a hydraulic chamber having an inlet port, a piston
reciprocally disposed in the chamber, and means for supplying
pressurized hydraulic fluid through the inlet port into the
chamber, and the locking means including check valve means for
trapping the pressurized hydraulic fluid in the chamber and
preventing the trapped fluid from exiting the chamber, and means
for biasing the check valve means to seal the chamber to prevent
hydraulic fluid in the chamber from exiting therefrom.
2. A variable valve timing system for an internal combustion engine
having a crankshaft and at least one cylinder, a piston
reciprocable in each cylinder and connected to the crankshaft for
rotation thereof, and at least one valve for each cylinder,
comprising at least one cam means driven by the crankshaft, the cam
means including a first profile for actuating a corresponding valve
in a first timed relation to the rotation of the crankshaft and a
second profile for actuating at least one of the valves in a second
timed relation to the rotation of the crankshaft, the cam means for
actuating any valve in two timed relations to the rotation of the
crankshaft including a cam having the first and second profiles
formed thereon circumferentially spaced from each other, a valve
gear train coupling each valve to a corresponding one of the cam
means, means for expanding at least one of the valve gear from a
collapsed condition in which the first profile is effective for
actuating the corresponding valve in the first timed relation to
the rotation of the crankshaft to an expanded condition in which
the second profile is effective for actuating the corresponding
valve in the second timed relation to the rotation of the
crankshaft, each valve capable of being actuated in the two timed
relations to the rotation of the crankshaft being coupled to the
first and second profiles of the corresponding cam by a single
valve gear train, each expanding means including means forming a
hydraulic chamber having an inlet port, a piston reciprocally
disposed in the chamber, and means for supplying pressurized
hydraulic fluid through the inlet port into the chamber, means for
locking each expanded valve gear train in the expanded condition,
whereby each valve actuated by an expandable valve gear train is
actuated in one of two predetermined timed relations to the
rotation of the crankshaft corresponding to the collapsed and the
locked expanded conditions of the corresponding valve gear train,
the locking means including check valve means for trapping the
pressurized hydraulic fluid in the chamber and preventing the
trapped fluid from exiting the chamber through the inlet port, and
means for biasing the check valve means to seal the inlet port to
prevent the hydraulic fluid from exiting therethrough, and also
including means for biasing the piston in the direction to expand
the associated valve gear train, and control means for selectively
disabling the check valve means and preventing the hydraulic fluid
from being trapped in the chamber, whereby when the check valve
means is disabled, the piston is able to reciprocate in the
chamber, the corresponding second profile is rendered ineffective,
and the corresponding valve is actuated in the first timed relation
to the rotation of the crankshaft.
3. A variable valve timing system for an internal combustion engine
having a crankshaft and at least one cylinder, a piston
reciprocable in each cylinder and connected to the crankshaft for
rotation thereof, and at least one valve for each cylinder,
comprising at least one cam means driven by the crankshaft, the cam
means including a first profile for actuating a corresponding valve
in a first timed relation to the rotation of the crankshaft and a
second profile for actuating at least one of the valves in a second
timed relation to the rotation of the crankshaft, a valve gear
train coupling each valve to a corresponding one of the cam means,
means for expanding at least one of the valve gear trains to render
the second profile effective for actuating the corresponding valve
in the second timed relation to the rotation of the crankshaft,
each expanding means including means forming a hydraulic chamber
having an inlet port, a piston reciprocally disposed in the
chamber, and means for supplying pressurized hydraulic fluid
through the inlet port into the chamber, means for locking each
expanded valve gear train in an expanded condition, the locking
means including check valve means for trapping the pressurized
hydraulic fluid in the chamber and preventing the trapped fluid
from exiting the chamber through the inlet port, means for biasing
the piston in the direction to expand the associated valve gear
train, means for biasing the check valve means to seal the inlet
port to prevent the hydraulic fluid from exiting therethrough, and
control means for selectively disabling the check valve means and
preventing the hydraulic fluid from being trapped in the chamber,
whereby when the check valve means is disabled, the piston is able
to reciprocate in the chamber, the corresponding second profile is
rendered ineffective, and the corresponding valve is actuated in
the first timed relation to the rotation of the crankshaft, the
control means including means forming a control chamber, a control
piston reciprocally disposed in the control chamber, the control
piston including a finger adapted to displace the check valve means
into spaced non-sealing relation to the inlet port to permit
hydraulic fluid to exit therethrough, means for biasing the control
piston to displace the check valve means, and means for supplying
pressurized hydraulic fluid to the portion of the control chamber
intermediate the control piston and the check valve means to
develop a force which urges the control piston away from the check
valve means.
4. The system according to claim 3, wherein the cam means for
actuating any valve in two timed relations to the rotation of the
crankshaft includes a cam having the first and second profiles
formed thereon circumferentially spaced from each other.
5. The system according to claim 3, wherein the control means also
includes means for supplying hydraulic fluid to the portion of the
control chamber on the side of the control piston remote from the
check valve means, and means for selectively shifting the pressure
of the hydraulic fluid in the remote control chamber portion
between substantially atmospheric pressure and substantially the
same pressure as that of the pressurized hydraulic fluid in the
control chamber portion between the control piston and check valve
means.
6. The system according to claim 1, wherein each hydraulic chamber
forming means and each corresponding piston comprise a portion of
the corresponding valve gear train coupling the corresponding valve
with the second cam profiles.
7. The system according to claim 6, wherein each hydraulic chamber
forming means and each corresponding piston are mounted for
reciprocation in the block of the internal combustion engine.
8. The system according to claim 6, wherein the valve gear trains
include rocker arms coupling the valves to at least some of the cam
means, and each hydraulic chamber forming means and each
corresponding piston are mounted in the rocker arm which actuates
the corresponding valve in the first and second timed relations to
the rotation of the crankshaft.
9. The system according to claim 8, including at least one rocker
arm shaft for mounting the rocker arms for rocking motion, each
rocker arm shaft mounting a rocker arm coupled to a valve whose
timing may be varied being formed with two passageways, the first
passageway being adapted to be communicated with a source of
pressurized hydraulic fluid for supplying pressurized hydraulic
fluid for lubricating each rocker arm carried by the rocker arm
shaft, and the second passageway being adapted to be communicated
with the expanding means, control valve means mounted in each
rocker arm shaft formed with the two passageways for selectively
communicating the second passageway with the first passageway, and
for selectively sealing the second passageway from the first
passageway and exposing the hydraulic fluid in the second
passageway to atmospheric pressure, and means for actuating the
control valve means to expand the valve gear trains of the valves
whose timing is to be varied.
10. A variable valve timing system for an internal combustion
engine having a crankshaft and at least one cylinder, a piston
reciprocable in each cylinder and connected to the crankshaft for
rotation thereof, and at least one valve for each cylinder,
comprising at least one cam means driven by the crankshaft, the cam
means including a first profile for actuating a corresponding valve
in a first timed relation to the rotation of the crankshaft and a
second profile for actuating at least one of the valves in a second
timed relation to the rotation of the crankshaft, a valve gear
train coupling each valve to a corresponding one of the cam means,
each valve gear train including a rocker arm coupling the valve to
a corresponding cam means, means for expanding at least one of the
valve gear trains to render the second profile effective for
actuating the corresponding valve in the second timed relation to
the rotation of the crankshaft, each expanding means including
means forming a hydraulic chamber having an inlet port, a piston
reciprocally disposed in the chamber, and means for supplying
pressurized hydraulic fluid through the inlet port into the
chamber, means for locking each expanded valve gear train in an
expanded condition, the locking means including check valve means
for trapping the pressurized hydraulic fluid in the chamber and
preventing the trapped fluid from exiting the chamber through the
inlet port, each hydraulic chamber forming means and each
corresponding piston comprising a portion of the corresponding
valve gear train coupling the corresponding valve with the second
cam profile and being mounted in the rocker arm which actuates the
corresponding valve in the first and second timed relations to the
rotation of the crankshaft, at least one rocker arm shaft for
mounting the rocker arm for rocking motion, each rocker arm shaft
mounting a rocker arm coupled to a valve whose timing may be varied
being formed with two passageways, the first passageway being
adapted to be communicated with a source of pressurized hydraulic
fluid for supplying pressurized hydraulic fluid for lubricating
each rocker arm carried by the rocker arm shaft, and the second
passageway being adapted to be communicated with the expanding
means, control valve means mounted in each rocker arm shaft formed
with the two passageways for selectively communicating the second
passageway with the first passageway, and for selectively sealing
the second passageway from the first passageway and exposing the
hydraulic fluid in the second passageway to atmospheric pressure,
means for actuating the control valve means to expand the valve
gear train of each valve whose timing is to be varied, means
forming a control chamber mounted in each rocker arm coupled to a
valve whose timing is to be varied, a control piston reciprocally
disposed in the control chamber, the control piston including a
finger adapted to displace the check valve means into spaced
non-sealing relation to the inlet port to permit hydraulic fluid to
exit therethrough, means for biasing the control piston to displace
the check valve means, a first conduit communicating the portion of
the control chamber intermediate the control piston and the check
valve means with the first passageway in the rocker arm shaft, and
a second conduit communicating the portion of the control chamber
on the side of the control piston remote from the check valve means
with the second passageway in the rocker arm shaft.
11. The system according to claim 10, including means for biasing
the piston in the hydraulic chamber to expand the associated valve
gear train, and means for biasing the check valve means to seal the
inlet port of the hydraulic chamber.
12. A variable valve timing system for an internal combustion
engine having a crankshaft and at least one cylinder, a piston
reciprocable in each cylinder and connected to the crankshaft for
rotation thereof, and at least one inlet valve and at least one
exhaust valve for each cylinder, comprising a plurality of cam
means driven by the crankshaft, the cam means including first
profiles for actuating the valves in a first timed relation to the
rotation of the crankshaft and second profiles for actuating at
least one of the valves in a second timed relation to the rotation
of the crankshaft, a plurality of valve gear trains coupling the
inlet and exhaust valves to corresponding ones of the cam means,
means for expanding at least one of the valve gear trains from a
collapsed condition in which the first profiles are effective for
actuating the corresponding valves in the first timed relation to
the rotation of the crankshaft to an expanded condition in which
the second profiles are effective for actuating the corresponding
valves in the second timed relation to the rotation of the
crankshaft, and means for locking the expanded valve gear trains in
the expanded condition, whereby the valves actuated by the
expandable valve gear trains are actuated in one of two
predetermined timed relations to the rotation of the crankshaft
corresponding to the collapsed and the locked expanded conditions
of the corresponding valve gear trains, each expanding means
including means forming a hydraulic chamber having an inlet port, a
piston reciprocally disposed in the chamber, and means for
supplying pressurized hydraulic fluid through the inlet port into
the chamber, and wherein the locking means includes check valve
means for trapping the pressurized hydraulic fluid in the chamber
and preventing the trapped fluid from exiting the chamber through
the inlet port, each hydraulic chamber forming means and each
corresponding piston comprising a portion of the corresponding
valve gear train coupling the corresponding valve with the second
cam profiles, the valve gear trains including rocker arms coupling
the valves to at least some of the cam means, and each hydraulic
chamber forming means and each corresponding piston being mounted
in the rocker arm which actuates the corresponding valve in the
first and second timed relations to the rotation of the crankshaft,
including at least one rocker arm shaft for mounting the rocker
arms for rocking motion, each rocker arm shaft mounting a rocker
arm coupled to a valve whose timing may be varied being formed with
two passageways, the first passageway being adapted to be
communicated with a source of pressurized hydraulic fluid for
supplying pressurized hydraulic fluid for lubricating each rocker
arm carried by the rocker arm shaft, and the second passageway
being adapted to be communicated with the expanding means, control
valve means mounted in each rocker arm shaft formed with the two
passageways for selectively communicating the second passageway
with the first passageway, and for selectively sealing the second
passageway from the first passageway and exposing the hydraulic
fluid in the second passageway to atmospheric pressure, and means
for actuating the control valve means to expand the valve gear
trains of the valves whose timing is to be varied, each rocker arm
shaft mounting a plurality of rocker arms coupled to valves whose
timing may be varied being formed with a third passageway adapted
to be communicated with some of the expanding means, the second
passageway being adapted to be communicated with the other
expanding means, and including additional control valve means for
selectively communicating the third passageway with the first
passageway, and for selectively sealing the third passageway from
the first passageway and exposing the hydraulic fluid in the third
passageway to atmospheric pressure, and means for actuating the
additional control valve means to expand the corresponding valve
gear trains independently of the expansion of the valve gear trains
associated with the second passageway, whereby the timing of some
of the valves may be shifted to one timed relation to the rotation
of the crankshaft upon expansion of the associated valve gear
trains, and the timing of other valves may be shifted to a
different timed relation upon expansion of the associated valve
gear trains.
13. The system according to claim 1, wherein each first cam profile
is disposed with respect to the position of the crankshaft such
that the corresponding valve is opened and closed at optimum times
for enhancing engine performance in the lower engine operating
speed range, and each second cam profile is disposed with respect
to the position of the crankshaft such that the corresponding valve
is opened and closed at optimum times for enhancing engine
performance in the upper engine operating speed range, and
including engine speed responsive means for controlling the means
for expanding the valve gear train to render each second cam
profile effective.
14. The system according to claim 1, wherein there is at least one
inlet valve for each cylinder and at least one inlet valve may be
actuated in response to the first and second cam profiles, each
second cam profile being disposed with respect to the position of
the crankshaft such that the corresponding inlet valve is closed in
response thereto during the initial portion of the compression
stroke, and each first cam profile being disposed with respect to
the position of the crankshaft such that the corresponding inlet
valve is closed in response thereto when the corresponding piston
is closer to the bottom dead center position, so that the effective
compression ratio is higher when the timing of the corresponding
inlet valve is determined by the first cam profile than when the
timing is determined by the second cam profile, and including means
for actuating the means for expanding the valve gear train to
render each second cam profile effective and for collapsing the
valve grear train to render the first cam profile effective.
15. The system according to claim 14, including means for limiting
the maximum engine speed when the valve gear train is collapsed to
render the first cam profile effective, the engine speed limiting
means being coupled to the means for actuating the valve gear train
expanding means so that the maximum engine speed limiting means is
automatically activated when the valve gear train is collapsed.
16. The system according to claim 15, wherein the internal
combustion engine is supplied with fuel by a fuel injection system
including an engine speed governor and a control element which may
be positioned for a desired governed engine speed, and wherein the
maximum engine speed limiting means includes a displaceable stop
member for limiting the travel of the control element.
17. The system according to claim 1, wherein there is at least one
exhaust valve for each cylinder and at least one exhaust valve may
be actuated in response to the first and second cam profiles, each
second cam profile being disposed with respect to the position of
the crankshaft such that the corresponding exhaust valve is opened
in response thereto at or near the end of the compression stroke to
dump the compressed air in the corresponding cylinder so as to
increase the retarding effect of the engine, and including means
for actuating the means for expanding the valve gear train to
render each second cam profile effective and for collapsing the
valve gear train to render the first cam profile effective.
18. A variable valve timing system for an internal combustion
engine having a crankshaft and at least one cylinder, a piston
reciprocable in each cylinder and connected to the crankshaft for
rotation thereof, and at least one valve for each cylinder,
comprising at least one cam means driven by the crankshaft, the cam
means including a first profile for actuating a corresponding valve
in a first relation to the rotation of the crankshaft and a second
profile for actuating at least one of the valves in a second timed
relation to the rotation of the crankshaft, the cam means for
actuating any valve in two timed relations to the rotation of the
crankshaft including a cam having the first and second profiles
formed thereon circumferentially spaced from each other, a valve
gear train coupling each valve to a corresponding one of the cam
means, means for expanding at least one of the valve gear trains
from a collapsed condition in which the first profile is effective
for actuating the corresponding valve in the first timed relation
to the rotation of the crankshaft to an expanded condition in which
the second profile is effective for actuating the corresponding
valve in the second timed relation to the rotation of the
crankshaft, each valve capable of being actuated in the two timed
relations to the rotation of the crankshaft being coupled to the
first and second profiles of the corresponding cam by a single
valve gear train, and means for locking each expanded valve gear
train in the expanded condition, whereby each valve actuated by an
expandable valve gear train is actuated in one of two predetermined
timed relations to the rotation of the crankshaft corresponding to
the collapsed and the locked expanded conditions of the
corresponding valve gear train, at least one exhaust valve capable
of being actuated in response to the first and second cam profiles,
each second cam profile being disposed with respect to the position
of the crankshaft such that the corresponding exhaust valve is
opened in response thereto at or near the end of the compression
stroke to dump the compressed air in the corresponding cylinder so
as to increase the retarding effective of the engine, and including
means for actuating the means for expanding the valve gear train to
render each second cam profile effective and for collapsing the
valve gear train to render the first cam profile effective, the
internal combustion engine including fuel supply means for
delivering fuel to the cylinders, and including means for sensing
the fuel delivery to the cylinders, and means responsive to the
fuel delivery sensing means for disabling the means for actuating
the valve gear train expanding means while fuel is delivered to the
cylinders.
19. The system according to claim 18, wherein the fuel supply means
includes a movable member for controlling the fuel delivery to the
cylinders, and the means for actuating the valve gear train
expanding means is responsive to motive force, and including a
source of motive force, means for communicating the actuating means
with the source of motive force, and wherein the fuel delivery
sensing means and the disabling means include switch means in the
communicating means operable to selectively effect and terminate
communication between the source of motive force and the actuating
means, and means coupling the switch means with the movable
member.
20. The system according to claim 19, wherein the fuel supply means
includes a fuel injection pump having a control rack, and wherein
the switch means is mounted in operative relation to the control
rack, whereby the switch means is actuated by the control rack to
collapse the valve gear trains to render the first cam profiles
effective before fuel is delivered to the cylinders.
21. The system according to claim 20, wherein the fuel supply means
includes an engine speed responsive governor coupled to the control
rack, whereby the governor prevents stalling of the engine by
positioning the control rack to actuate the switch means and
disable the actuating means and to deliver fuel to the
cylinders.
22. The system according to claim 19, wherein the internal
combustion engine is mounted in a vehicle having braking means, and
a brake pedal for activating the brake means, and including switch
means mounted in operative relation to the brake pedal and
connected in the communicating means in series with the source of
motive force, the disabling switch means and the actuating means,
whereby the valve gear trains may be expanded when the brake pedal
is depressed to activate the brake pedal switch means and there is
no fuel delivery to the cylinders.
23. A variable valve timing system for an internal combustion
engine having a crankshaft and at least one cylinder, a piston
reciprocable in each cylinder and connected to the crankshaft for
rotation thereof, at least one exhaust valve for each cylinder, and
means for supplying fuel to each cylinder, comprising means forming
a first cam profile for actuating each exhaust valve in a first
timed relation to the rotation of the crankshaft for normal
operation of the engine, means forming a second cam profile for
opening at least one exhaust valve at or near the end of the
compression stroke to dump the compressed air from each
corresponding cylinder so as to increase the retarding effect of
the engine, means for selectively coupling the second cam profile
means with each corresponding exhaust valve, means for sensing the
fuel delivery to the cylinders, and means responsive to the fuel
delivery sensing means for disabling the coupling means and thereby
rendering the second cam profile means ineffective while fuel is
delivered to the cylinders.
24. Apparatus for varying the timing of at least one of the valves
of an internal combustion engine having a crankshaft and at least
one cylinder associated with the valves, a piston reciprocable in
each cylinder and connected to the crankshaft for rotation thereof,
first cam means for actuating the valves in a first timed relation
to the rotation of the crankshaft, second cam means for actuating
at least some of the valves in a second timed relation to the
rotation of the crankshaft, and a plurality of valve gear trains
coupling the valves to the corresponding first and second cam
means, comprising means forming a hydraulic chamber having an inlet
port and adapted to receive pressurized fluid through the inlet
port, a piston reciprocally disposed in the chamber, the hydraulic
chamber forming means and the piston being a portion of each valve
gear train coupling a valve with the corresponding second cam
means, check valve means for trapping the pressurized hydraulic
fluid in the chamber and preventing the trapped fluid from exiting
the chamber, and means for biasing the check valve means to seal
the chamber to prevent hydraulic fluid in the chamber from exiting
therefrom.
25. Apparatus for varying the timing of at least one of the valves
of an internal combustion engine having a crankshaft and at least
one cylinder associated with the valves, a piston reciprocable in
each cylinder and connected to the crankshaft for rotation thereof,
first cam means for actuating the valves in a first timed relation
to the rotation of the crankshaft, second cam means for actuating
at least some of the valves in a second timed relation to the
rotation of the crankshaft, and a plurality of valve gear trains
coupling the valves to the corresponding first and second cam
means, comprising means forming a hydraulic chamber having an inlet
port and adapted to receive pressurized fluid through the inlet
port, a piston reciprocally disposed in the chamber, the hydraulic
chamber forming means and the piston being a portion of each valve
gear train coupling a valve with the corresponding second cam
means, check valve means for trapping the pressurized hydraulic
fluid in the chamber and preventing the trapped fluid from exiting
the chamber through the inlet port, means for biasing the piston in
the direction to expand the volume of the hydraulic chamber, means
for biasing the check valve means to seal the inlet port to prevent
hydraulic fluid in the chamber from exiting therethrough, and
control means for selectively disabling the check valve means and
preventing hydraulic fluid in the chamber from being trapped
therein, whereby when the check valve means is disabled, the piston
is able to reciprocate in the chamber, the corresponding second cam
means are rendered ineffective, and the corresponding valve is
actuated in the first timed relation to the rotation of the
crankshaft.
26. Apparatus for varying the timing of at least one of the valves
of an internal combustion engine having a crankshaft and at least
one cylinder associated with the valves, a piston reciprocable in
each cylinder and connected to the crankshaft for rotation thereof,
first cam means for actuating the valves in a first timed relation
to the rotation of the crankshaft, second cam means for actuating
at least one of the valves in a second timed relation to the
rotation of the crankshaft, and a plurality of valve gear trains
coupling the valves to the corresponding first and second cam
means, comprising means forming a hydraulic chamber having an inlet
port and adapted to receive pressurized fluid through the inlet
port, a piston reciprocally disposed in the chamber, the hydraulic
chamber forming means and the piston being a portion of each valve
gear train coupling a valve with the corresponding second cam
means, check valve means for trapping the pressurized hydraulic
fluid in the chamber and preventing the trapped fluid from exiting
the chamber through the inlet port, means for biasing the piston in
the direction to expand the volume of the hydraulic chamber, means
for biasing the check valve means to seal the inlet port to prevent
hydraulic fluid in the chamber from exiting therethrough, and
control means for selectively disabling the check valve means and
preventing hydraulic fluid in the chamber from being trapped
therein, whereby when the check valve means is disabled, the piston
is able to reciprocate in the chamber, the corresponding second cam
means are rendered ineffective, and the corresponding valve is
actuated in the first timed relation to the rotation of the
crankshaft, the control means including means forming a control
chamber, a control piston reciprocally disposed in the control
chamber, the control piston including a finger adapted to displace
the check valve means into spaced non-sealing relation to the inlet
port to permit hydraulic fluid to exit therethrough, and means for
biasing the control piston to displace the check valve means.
27. Apparatus according to claim 26, including means forming a
first port communicating with the portion of the control chamber
intermediate the control piston and the check valve means adapted
to admit pressurized hydraulic fluid thereto, and means forming a
second port communicating with the portion of the control chamber
on the side of the control piston remote from the check valve means
adapted to admit pressurized hydraulic fluid thereto.
28. The system according to claim 3, wherein the hydraulic chamber
forming means and the corresponding piston of each expanding means
are mounted for reciprocation in the block of the internal
combustion engine.
29. The system according to claim 3, wherein the valve gear trains
include rocker arms coupling the valves to at least some of the cam
means, and the hydraulic chamber forming means and the
corresponding piston of each expanding means are mounted externally
of the rocker arm which actuates the corresponding valve in the
first and second timed relations to the rotation of the
crankshaft.
30. The system according to claim 3, wherein the valve gear train
includes rocker arms coupling the valves to at least some of the
cam means, and the hydraulic chamber forming means and the
corresponding piston of each expanding means are mounted in the
rocker arm which actuates the corresponding valve in the first and
second timed relations to the rotation of the crankshaft.
31. The system according to claim 10, wherein the cam means for
actuating any valve in two timed relations to the rotation of the
crankshaft includes a cam having the first and second profiles
formed thereon circumferentially spaced from each other.
32. The apparatus according to claim 26, wherein the hydraulic
chamber forming means and the corresponding piston of each valve
gear train coupling a valve with the corresponding second cam means
are mounted for reciprocation in the block of the internal
combustion engine.
33. The apparatus according to claim 26, wherein the valve gear
trains include rocker arms coupling the valves to at least some of
the cam means, and the hydraulic chamber forming means and the
corresponding piston of each valve gear train coupling a valve with
the corresponding second cam means are mounted externally of the
rocker arm which actuates the corresponding valve in the first and
second timed relations to the rotation of the crankshaft.
34. The apparatus according to claim 26, wherein the valve gear
trains include rocker arms coupling the valves to at least some of
the cam means, and the hydraulic chamber forming means and the
corresponding piston of each valve gear train coupling a valve with
the corresponding second cam means are mounted in the rocker arm
which actuates the corresponding valve in the first and second
timed relations to the rotation of the crankshaft.
35. The apparatus according to claim 26, wherein the first and
second cam means for each valve capable of being actuated in two
timed relations to the rotation of the crankshaft include a first
profile and a second profile formed on a single cam, the first and
second profiles being circumferentially spaced from each other.
36. Apparatus for varying the timing of at least one of the valves
of an internal combustion engine having a crankshaft and at least
one cylinder associated with the valves, a piston reciprocable in
each cylinder and connected to the crankshaft for rotation thereof,
first cam means for actuating the valves in a first timed relation
to the rotation of the crankshaft, second cam means for actuating
at least one of the valves in a second timed relation to the
rotation of the crankshaft, and a plurality of valve gear trains
coupling the valves to the corresponding first and second cam
means, comprising means forming a hydraulic chamber having an inlet
port and adapted to receive pressurized fluid through the inlet
port, a piston reciprocally disposed in the chamber, the hydraulic
chamber forming means and the piston being a portion of each valve
gear train coupling a valve with the corresponding second cam
means, check valve means for trapping the pressurized hydraulic
fluid in the chamber and preventing the trapped fluid from exiting
the chamber through the inlet port, means for biasing the check
valve means to seal the inlet port to prevent hydraulic fluid in
the chamber from exiting therethrough, and control means for
selectively disabling the check valve means and preventing
hydraulic fluid in the chamber from being trapped therein, whereby
when the check valve means is disabled, the piston is able to
reciprocate in the chamber, the corresponding second cam means are
rendered ineffective, and the corresponding valve is actuated in
the first timed relation to the rotation of the crankshaft.
Description
BACKGROUND OF THE INVENTION
This invention relates to variable valve timing systems and, more
particularly, to systems for varying the valve timing of vehicle
internal combustion engines to convert the engine into an air
compressor to exert a braking effect on the drive train, to
increase the effective compression ratio of a relatively low
compression ratio engine to enhance starting, or to adjust the
valve timing of a high speed engine to improve the performance
throughout the operating speed range.
Various systems for varying valve timing have been proposed for
some of the above and other purposes. Thus, the Lewis U. S. Pat.
No. 754,466 shows an arrangement for relieving compression to
enhance starting by manually extending an element mounted on the
rocker arm to engage the exhaust cam and open the exhaust valve
during a portion of the compression stroke.
Other devices for relieving compression to enhance starting are
disclosed in the Jackson U. S. Pat. No. 1,172,362 and the Rounds
U.S. Pat. No. 1,175,820. Here the exhaust cams are provided with an
auxiliary relief or lobe which is circumferentialy spaced from the
main lobe which opens the exhaust valve during the exhaust stroke.
During normal operation the exhaust valve is not raised by the
auxiliary lobe, but during starting the exhaust valve gear train is
manually expanded so that the auxiliary lobe raises the exhaust
valve during a portion of the compression stroke. In addition, the
Rounds patent shows apparatus for manually adjusting the timing of
the inlet and exhaust valves.
The Saurer U. S. Pat. No. 934,762 discloses an engine brake in
which the exhaust cam is shifted circumferentially from its normal
position to open during the "expansion" stroke, ignition being
discontinued, so that air is compressed during the compression and
"exhaust" strokes, and necessarily dumped at the beginning of the
inlet and "expansion" strokes, so that the energy of the compressed
air is not returned to the drive train during the expansion
stroke.
The Kirchensteiner U.S. Pat. No. 1,637,118 and the Loeffler U.S.
Pat. No. 1,947,996 disclose engine brakes in which the cam shaft is
axially shifted for braking to de-activate the inlet valve and to
drive the exhaust valve by a special double lobe cam, one lobe
opening the exhaust valve during the intake stroke, while the other
lobe dumps the compressed air near the end of the compression
stroke. A graduated degree of braking is available in the
Kirchensteiner engine brake by selectively inserting wedge elements
beneath predetermined ones of the exhaust rocker arms to prevent
the corresponding exhaust valves from closing, thereby eliminating
the braking effect in the corresponding cylinders.
The engine brake according to the Ucko U.S. Pat. No. 2,002,196
obtains the results of the Loeffler brake without axially shifting
the cam shaft. Rather, the rocker arm shaft is shifted
eccentrically to render the push rods (and the inlet and exhaust
cams) ineffective. An auxiliary double lobe exhaust cam is
hydraulically coupled to the exhaust valve through a master piston,
which is driven by the double lobe cam, and a slave piston which
drives the exhaust valve rocker arm to open the exhaust valve
during the intake and expansion strokes. A graduated braking effect
is obtained by sequentially converting groups of one or more
cylinders to air compressors.
The Cummins U.S. Pat. No. 3,220,392 discloses another engine
braking system employing hydraulically coupled master and slave
pistons, the slave piston driving the exhaust valve rocker arm, and
the master piston being driven by an auxiliary exhaust cam, the
injector rocker arm of the corresponding cylinder, or by the inlet
or exhaust rocker arm of another cylinder, so as to dump compressed
air at or near the end of the compression stroke. Unlike Ucko,
however, the Cummins mechanism for opening an exhaust valve at or
near top dead center does not interfere with the actuation of the
exhaust valve by the normal exhaust valve actuating mechanism.
Nevertheless, the independent mechanism for actuating the exhaust
valve for braking requires considerable additional structure, thus
increasing the complexity and cost of that engine brake.
Furthermore, hydraulic coupling between the exhaust rocker arm of
one cylinder and the inlet or exhaust rocker arm of the appropriate
other cylinder would be difficult to arrange with a V-8 engine.
In the engine brake according to the Jones et al. U.S. Pat. No.
3,439,662 a single auxiliary cam sequentially drives the master
pistons, which in turn actuate the corresponding slave pistons to
open the exhaust valves at the end of the compression stroke.
Apparatus is included to change the timing of the opening of the
exhaust valves in accordance with the engine speed in order to
increase the braking effect with increasing engine speed.
The Siegler U.S. Pat. No. 3,547,087 discloses another engine brake
employing a mechanism external to the intake and exhaust valve gear
train, but in this system a solenoid operated hydraulic valve
remote from the engine brake mechanism is actuated to pump up a
piston so as to block the return movement of the rocker arm,
thereby holding the intake or exhaust valve partially open
throughout the braking period.
The Haviland U.S. Pat. No. 3,332,405 shows an engine brake in which
the exhaust valve is opened at the end of the compression stroke by
a separate engine braking cam when a plunger mounted in the rocker
arm is hydraulically pumped up to engage the braking cam in
response to a remote solenoid valve. In an effort to improve the
response time of the system, a separate low pressure oil supply is
required to keep the lines filled with oil.
The Jonsson U.S. Pat. No. 3,367,312 discloses an engine braking
system in which the normal base circle of the exhaust cam is
relieved to form an auxiliary base circle, the transition between
the two base circles constituting an auxiliary ramp displaced
circumferentially from the normal opening ramp, so that when the
lash is removed from the exhaust valve train, the exhaust valve is
opened by the auxiliary ramp at the end of the compression stroke.
The lash is removed by a plunger mounted in the rocker arm which
may be hydraulically extended when a remote valve is manually
actuated to communicate the plunger with the lubrication pump.
Inasmuch as there is no mechanism for hydraulically locking the
plunger in the extended position, the rotating exhaust cam will
reciprocate the plunger in its cylinder despite the hydraulic force
supplied by the lubrication pump, thereby substantially impairing
the performance of the engine brake. Furthermore, a very large
force is applied to the exhaust valve and the plunger when the
piston travels through its compression stroke, such force being a
function of speed, exhaust valve opening, exhaust valve diameter
and compression ratio. In a diesel engine such force would greatly
exceed the opposite force on the plunger developed by the engine
lubricating pump, so that the plunger would be collapsed and the
desired braking effect minimized.
The Muir U.S. Pat. No. 3,525,317 discloses an engine brake
providing a graduated braking effect by arranging a
multiple-position switch for operation as the throttle pedal is
retracted beyond the idling position. At the first position the
fuel is cut off to create "motoring" friction, at the second
position the exhaust valves are held continuously in a partially
open position, and at the third position a butterfly valve in the
exhaust mainfold is actuated to provide back pressure therein.
The Sweat U.S. Pat. No. 2,806,459 discloses an intricate device for
changing the timing of motor valves in accordance with the speed of
the motor by adjusting the position of the rocker arm fulcrum and
thereby adjusting the clearance in the valve train and the amount
of valve opening. The rocker arm fulcrum is driven by a motor, the
electrical contacts for which are operated by a piston displaced by
air pressure generated by a fan driven by the motor. The cam shaft
is arranged to provide advanced timing when the clearance in the
valve train is small, at high speeds, while at lower speeds the
clearance is larger and the valve timing is thus retarded.
The Lieberherr U.S. Pat. No. 2,936,575 discloses apparatus for
varying the valve timing of a supercharged gas engine in accordance
with the pressure of the intake manifold or the governor fuel
control shaft in an effort to obtain an approximately constant
air-fuel ratio at all loads. The timing is varied by lateral
displacement of the cam follower in response to the intake manifold
pressure or the fuel control shaft.
The Ostborg U.S. Pat. No. 3,224,423 shows a valve timing system in
which the timing of the inlet and exhaust valves is varied in
accordance with the intake manifold pressure, the phase of the
inlet and exhaust camshafts being shifted in opposite directions
with respect to that of the crankshaft by means of planetary gear
systems.
The above conventional variable valve timing devices are relatively
complex in construction, expensive to manufacture and install,
susceptible to malfunction, and require relatively frequent
servicing. In the prior art engine brakes using hydraulic
circuitry, the control valve is remote from the operating pistons,
providing an inherently slow reaction time. This can be disastrous
to the system, because if the engine is allowed to fire while the
engine brake is on, the cylinder pressure will destroy the valve
train. The time required to deactivate the engine brake is
therefore extremely important.
Another difficulty with conventional engine brakes results from the
fact that the fuel condition is not sensed before the brake is
activated. Rather, the fuel is shut off and the engine brake
activated through separate control circuitry, so that the valve
train will be destroyed if the fuel shut-off circuitry
malfunctions.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the
above-mentioned difficulties and shortcomings of conventional
systems for varying the valve timing of an internal combustion
engine. Another object of the invention is to provide novel methods
and apparatus for selectively controlling the timing events of one
or more valves of an internal combustion engine. A further object
of the invention is to provide a reliable, but relatively simple,
system for converting an internal combustion engine into an air
compressor to enhance engine retardation for braking purposes. A
still further object of the invention is to provide a vehicle
engine braking system which has a rapid response time and which may
be readily incorporated in any internal combustion engine with
minimum modification thereof. Yet another object of the invention
is to provide an engine braking control system which ensures that
the engine brake is deactivated while fuel is being delivered to
the engine. Still another object of the invention is to provide a
variable valve timing mechanism to provide additional breathing at
the higher engine speeds so as to improve the performance
throughout the operating speed range. Still a further object of the
invention is to provide a variable valve timing system which
enhances starting of internal combustion engines of relatively low
compression ratio by increasing the effective compression
ratio.
These and other objects of the invention are attained by
selectively changing the total valve train length so as to shift
the points on the cam profile at which the valve opening and
closing events are determined. The change in total valve train
length is effected by a novel hydraulic lash adjuster which forms a
portion of the valve train. The hydraulic lash adjuster is made to
expand and lock hydraulically, or collapse, upon command, thereby
regulating the lash in the valve train.
The lash adjuster includes a piston which is spring biased in a
direction to expand the lash adjuster and thereby lengthen the
valve train, the piston being hydraulically locked in the expanded
position when a ball check valve is permitted to seat and seal a
high pressure chamber to which oil under pressure is admitted past
the check valve. The oil under pressure is also constantly applied
to one side of a control piston, on the opposite side of which is
exerted a biasing force and a variable hydraulic pressure which may
be selectively varied between atmospheric pressure and the same
pressure as applied to the first side of the control piston. When
the variable hydraulic pressure is at atmospheric pressure, the
force on the first side of the control piston overcomes the biasing
force and displaces the control piston away from the ball check
valve, which may then seat to lock the lash adjuster in its
expanded state.
On the other hand, when the variable hydraulic pressure is raised
so that the pressures on both sides of the control piston are
equal, the biasing force displaces the control piston to unseat the
ball check valve, thereby collapsing the hydraulic lash
adjuster.
The hydraulic lash adjuster is preferably mounted in the rocker arm
coupled to the valve whose timing is to be varied. The rocker arm
shaft is provided with two longitudinal passageways, one of which
is communicated with a source of oil under pressure. This
passageway supplies oil under pressure past the ball check valve
into the high pressure chamber of each of the various hydraulic
lash adjusters, and also supplies oil under pressure to one side of
the control piston thereof. A solenoid operated valve selectively
communicates the first passageway in the rocker arm shaft with the
second passageway therein, which in turn pressurizes the oil on the
opposite side of the control piston in each lash adjuster when
permitted to do so by the solenoid actuated valve. A very rapid
reaction time is attained for the hydraulic lash adjusters by
mounting the control valve in the rocker arm shaft.
When the variable valve timing system is sued for engine braking,
the hydraulic lash adjusters are mounted in the rocker arms for the
exhaust valves, and the normal base circle of each exhaust cam is
relieved to provide a secondary cam base circle, thereby forming
secondary opening and closing profiles between the normal and
secondary base circles. The secondary opening profile is
circumferentially located so as to open the exhaust valve at or
near the end of the compression stroke when the hydraulic lash
adjuster is expanded to substantially eliminate the valve lash.
It is absolutely necessary that the engine brake not be operated
while fuel is being delivered to the engine, since ignition could
occur in a compression-ignition engine. This requirement is
satisfied by including in the electrical control circuitry which
energizes the solenoid operated valve mounted on the rocker arm
shaft a switch which is closed when the injection pump rack is in
its dead rack or no fuel position. Thus, the engine brake can only
be energized when the vehicle overruns the particular setting of
the throttle, in which condition the governor moves the injection
pump rack to the dead rack position. As the engine decreases to
idle condition, the governor then moves the rack to turn on idle
fuel, but before the fuel is turned on, the rack opens the switch
to deactivate the engine brake. Accordingly, the engine can never
stall, because the engine brake will not function below idle
speed.
The variable valve timing system is employed to enhance the
starting of a relatively low compression ratio engine, by mounting
the hydraulic lash adjusters in the rocker arms which actuate the
inlet valves, so that the total length of the inlet valve train may
be selectively extended or contracted. This displaces the locations
along the profile of each inlet cam at which the opening and
closing events of the corresponding inlet valve are determined.
With the last adjusters extended so as to lengthen the total inlet
valve trains, the inlet valves close in the normal manner somewhat
after bottom dead center, at which time the compression actually
begins. Thus, the effective compression ratio is somewhat lower
than the theoretical compression ratio which would be attained if
the inlet valve closed at bottom dead center. To enhance the
starting of the relatively low compression ratio engine, each
hydraulic lash adjusterm is collapsed to provide an excess inlet
valve clearance sufficient to displace the closing point of the
inlet valve to bottom dead center, so that the actual compression
ratio under such starting conditions equals the theoretical
compression ratio.
In order to prevent any possible damage to the inlet valve gear
components when the engine operates with excess inlet valve
clearances, a throttle limiting member is automatically extended to
limit the maximum engine speed when the hydraulic lash adjusters
are collapsed. After the engine has started and warmed up, the
hydraulic lash adjusters are expanded to provide normal inlet valve
clearance, and simulataneously the throttle limiting member is
retracted to permit normal full throttle operation.
The variable valve timing system can also be employed to increase
the performance of internal combustion engines throughout the
operating speed range by increasing the valve lift of the inlet
and/or exhaust valves, as well as the time period during which they
are open, at high engine speeds to provide additional breathing. In
this application, the normal cam base circles of the corresponding
valves are relieved to provide auxiliary opening and closing
profiles which are mutually spaced apart to a greater extent than
the opening and closing profiles which are effective in the lower
speed range. Thus, when the hydraulic lash adjusters are expanded
for the higher engine speeds, the opening and closing of the
corresponding valves is determined by the auxiliary opening and
closing profiles, thereby increasing the valve lift and the period
during which such valves are open.
BRIEF DESCRIPTION OF THE DRAWINGS
All of the above is more fully explained in the detailed
description of the preferred forms of the invention which follows,
this description being illustrated by the accompanying figures of
the drawings, in which:
FIG. 1 is a chart illustrating the pressure-volume relationship for
a four cycle internal combustion engine during "motoring," when
ignition does not occur;
FIG. 2 is a chart illustrating the change in the pressure-volume
relationship when the cylinders are converted to compressors to
effect engine braking;
FIG. 3 is a chart illustrating cylinder pressure and inlet and
exhaust valve lift vs. crank angle under normal operation, when
ignition is prevented to provide motoring friction, and during
engine braking;
FIGS. 4A, 4B, and 4C illustrate the cam profiles of the inlet and
exhaust cams in the variable valve timing mechanism according to
the present invention for engine braking;
FIG. 5 is a schematic illustration, partially in vertical section,
of the variable valve timing system employing cams formed in
accordance with FIGS. 4A, 4B, and 4C;
FIG. 6 is a chart illustrating the brake horsepower and torque
developed under normal operation, as well as the negative
horsepower obtained from motoring friction and from the engine
braking system of FIG. 5;
FIG. 7 is a view taken along the line 7--7 of FIG. 5 and looking in
the direction of the arrows;
FIG. 8 is a partial side elevational view, partly in section, of
the rocker arm shaft of FIG. 7;
FIGS. 9A and 9B are views taken along the line 9--9 of FIG. 7 and
looking in the direction of the arrows, showing the hydraulic lash
adjuster in contracted and expanded states, respectively;
FIG. 10 is an enlarged sectional view of the hydraulic lash
adjuster of FIG. 9;
FIGS. 11A, 11B, 11C and 11D are schematic illustrations of
alternative electrical control circuitry suitable for employment
with the engine braking system of FIGS. 4-10;
FIG. 12 is a schematic illustration, partially in vertical section,
of another embodiment of the variable valve timing system for
engine braking;
FIG. 12A is an enlarged view, in vertical section, of the hydraulic
lash adjuster shown in FIG. 12;
FIG. 13 is a schematic diagram illustrating the opening durations
of the inlet and exhaust valves during the normal operation of an
internal combustion engine;
FIG. 14 is a chart illustrating the inlet valve timing when excess
clearance is provided by the variable valve timing system according
to another embodiment of the invention;
FIG. 15 is a schematic diagram illustrating the inlet valve opening
duration with the excess clearance shown in FIG. 14;
FIG. 16 is a chart illustrating the pressure characteristics in the
cylinders during the compression and expansion strokes with normal
and excess inlet valve clearances;
FIG. 17 is a schematic illustration of the relative position of the
piston in the bore when the inlet valve closes under normal
conditions;
FIG. 18 is a schematic illustration of the relative position of the
piston in the bore at the time that the inlet valve closes when
excess clearance is provided;
FIG. 19 is a schematic illustration, partially in vertical section,
of the variable valve timing system for producing the effects
illustrated in FIGS. 14, 15, 16 and 18, thereby increasing the
compression ratio in order to enhance the starting of a relatively
low compression ratio engine;
FIG. 19A is a partial side elevational view, partly in section, of
the rocker arm shaft of FIG. 19;
FIG. 20 is a schematic illustration of a variable valve timing
system for engine braking and for enhancing the starting of a
relatively low compression ratio engine;
FIG. 21 is another system employing the variable valve timing
mechanism for engine braking and for enhancing the starting of a
relatively low compression ratio engine;
FIGS. 22A, 22B and 22C illustrate the cam profiles of the inlet and
exhaust cams employed in another embodiment of the variable valve
timing system for improving the performance of internal combustion
engines throughout the operating speed range;
FIG. 23 is a schematic illustration, partially in vertical section,
of the variable valve timing system employing cams formed in
accordance with FIGS. 22A, 22B and 22C;
FIG. 23A is a partial side elevational view, partly in section, of
the rocker arm shaft of FIG. 23;
FIG. 24 is a chart illustrating the volumetric efficiency attained
with the system of FIG. 23; and
FIG. 25 is a schematic illustration of a variable valve timing
system for engine braking and for increasing the performance of an
internal combustion engine throughout the operating speed
range.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As the gross weights and road speeds of vehicles increase, greater
demands are placed upon the braking systems. It is advantageous to
use the friction of the drive train and the engine for its
retardation effect to aid in vehicle control, espcially under
downhill or coasting conditions, in order to reduce dependence on
the conventional service brakes, prolong the useful life of the
brake components, and promote safety.
A light braking effect is obtained from an internal combustion
engine by preventing ignition, either by deactivating the ignition
circuit in a spark-ignition engine, or by stopping the injection of
fuel in a compression-igniton engine. During such "motoring," the
vehicle drives the engine, and retardation occurs because of the
friction of the moving parts and because of the pneumatic forces on
each piston as it moves in its cylinder.
In FIG. 1, the curve 31 represents the pressure-volume relationship
during motoring, and it is apparent that the compression and
expansion portions of the curve are very similar. Accordingly, the
negative work, or power absorbed by the gases, during compression
only slightly exceeds the positive work exerted by the gases on the
pistons during expansion. Thus, most of the negative work occurs
during the intake and exhaust strokes when air is drawn in, or
forced out, through the constrictions surrounding the open inlet
and exhaust valves, respectively.
The positive work developed during the expansion stroke may be
minimized to enhance engine retardation by converting the engine
into an air compressor by opening the exhaust valve at or near the
completion of the compression stroke to dissipate the energy of the
compressed air to atmosphere. Such compression release type of
engine braking provides the pressure-volume characteristic shown by
curve 32 in FIG. 2. Here it may be seen that negative work still
occurs during the compression stroke until the exhaust valve is
opened to allow the gases to expand into the exhaust manifold. The
pressure then drops rapidly, so that the gases no longer do
positive work on the piston during the expansion stroke. If the
engine is equipped with a turbocharger, the "dumped" gases drive
the turbocharger and thus increase the charging pressure, so that
the pressure during the intake stroke is somewhat higher during
engine braking than it is during motoring. The resulting increased
air flow through the engine, drawn in during the intake stroke and
exhausted during the exhaust stroke, results in additional negative
work or power absorbed.
The upper portion of the chart shown in FIG. 3 shows cylinder
pressure characteristics as a function of the position of the
crankshaft, curve 34 being the pressure characteristic during
ignition, curve 35 the pressure characteristic during "motoring,"
when there is no ignition, and curve 36 showing the pressure
characteristic when the exhaust valve is opened near the end of the
compression stroke to dump the compressed air and effect engine
braking.
The lower portion of the chart of FIG. 3 shows the valve lift of
the inlet and exhaust valves of an internal combustion engine
provided with the variable valve timing system according to the
present invention for opening the exhaust valve near the end of the
compression stroke to effect engine braking. Curve 37 shows that
the inlet valve timing under all conditions remains the same as
that found in any four stroke cycle engine. There are two different
timings for the exhaust valves, however, depending on whether or
not the engine brake is activated. Thus, curve 38 shows the exhaust
valve lift when the engine brake is off, while curve 39 shows that
when the engine brake is on, the exhaust valve opens near the end
of the compression stroke shortly before top dead center.
The valve lifts illustrated in FIG. 3 are obtained from the cam
profiles shown in FIGS. 4A, 4B and 4C. The conventional inlet valve
lift 37 is obtained from the conventional inlet cam 40 (see FIG.
4B), while the profile of the exhaust cam 42 (see FIG. 4C) is
relieved at 43 to provide a secondary base circle. Accordingly,
there is provided between the secondary base circle 43 and the
conventional base circle 44 an auxiliary opening profile 46 and an
auxiliary closing profile 47.
When the exhuast exhaust gear train is expanded so as to provide
only the lash 48 to accommodate changes in valve train length due
to temperature variations, the exhaust valve will open slightly
before top dead center where indicated on the auxiliary opening
profile 46, and will close where indicated on auxiliary closing
profile 47, to provide the valve motion shown by curve 39. In
addition to extending the time during which the exhaust valve is
open during the engine braking mode, the reduction in lash
clearance resulting from the extension of the exhaust valve train
causes the additional exhaust valve lift indicated at 50.
When additional valve lash is introduced into the exhaust valve
gear train, so as to provide the total lash indicated at 52, the
auxiliary opening and closing profiles 46 and 47 are rendered
ineffective. The normal exhaust valve timing is then obtained,
providing the valve lift shown by the curve 38 in FIG. 3.
The variable valve timing system employing the exhaust cam 42 for
engine braking is shown in FIG. 5. The cam 42 is formed on a
camshaft 55 which is conventionally driven by a crankshaft 56,
which in turn is driven by eight pistons 58 through corresponding
connecting rods 59 in a V-8 engine in the illustrated embodiment,
only one piston and associated elements being shown for simplicity.
Each piston 58 reciprocates in a conventional sleeve 60, which is
mounted in the engine block 61, to which are secured four cylinder
heads 63, 64, 65, and 66, which mount rocker arm shafts 67, 68, 69,
and 70, respectively. Each rocker arm shaft carries the inlet and
exhaust rocker arms for two cylinders.
Mounted for reciprocation in the cylinder head 63 is an exhaust
valve 72, which is driven by one end of an exhaust rocker arm 74,
which is mounted for rotation on the rocker arm shaft 67. A valve
seat insert 73 is suitably recessed so that the exhaust valve will
not engage the piston when the valve train is expanded for engine
braking, during which time the exhaust valve is provided with
additional lift as shown by curve 39 of FIG. 3.
The opposite end of the rocker arm 74 mounts a hydraulic lash
adjuster 76, which will be described in detail hereinafter. The
lash adjuster 76 receives the upper end of a pushrod 78, the lower
end of which is received in a cam follower 80, which engages the
exhaust cam 42. The pushrod is preferably of somewhat heavier
construction than those used to rock the inlet rocker arms, because
of the forces exerted on the exhaust valve train when the exhaust
valve is opened near the end of the compression stroke.
The hydraulic lash adjuster 76 is threadedly received in the rocker
arm 74, so that the lash adjuster may be positioned in the rocker
arm when the exhaust valve train components are cold so as to
provide sufficient lash to accommodate the thermal expansion of the
valve gear train elements. The last adjuster is locked in the
desired position by a lock nut 82.
A conventional solenoid 85 mounted on the rocker arm shaft 67 may
be energized to expand the hydraulic lash adjusters 76 mounted in
the exhaust rocker arms 74 and 74a, as will be explained in detail
hereinafter, so that the exhaust valves 72 of the two cylinders
associated with the cylinder head 63 are opened by the auxiliary
profiles 46 of the exhaust cams 42 to dump the compressed air in
these cylinders near the end of the compression stroke. When the
solenoid 85 is de-energized, the associated hydraulic lash
adjusters 76 are collapsed, and the corresponding exhaust valves
open near the end of the expansion stroke, thereby discontinuing
the engine braking. Similarly, solenoids 86, 87 and 88, identical
in construction and operation to the solenoid 85, are mounted on
the rocker arm shafts 68, 69 and 70, respectively, and may be
selectively energized or de-energized to expand or collapse,
respectively, the hydraulic lash adjusters 76 mounted on the
corresponding rocker arms 74 and 74a to shift the timing of the
exhaust valves of the corresponding cylinders.
The solenoids 85, 86, 87 and 88 may be selectively energized by the
switches 93, 94, 95 and 96, respectively, which are mounted so as
to be sequentially actuated by the brake pedal 98, provided that a
manual cab switch 100 and a limit switch 102 are closed. The cab
switch 100 and the limit switch 102 are series connected between
each of the switches 93-96 and a suitable source 104 of electric
power, such as the conventional vehicle battery. The cap switch 100
enables the operator to override or de-activate the automatic
operation of the engine brake.
The limit switch 102 is mounted in operative relation to the
control rack 106 of a conventional fuel injection pump manufactured
by American Bosch Arma Corporation, which is provided with a fuel
limiting governor identified as the GVB/C governor, manufactured by
American Bosch Arma Corporation and conventionally supplied with
the pump. Briefly, the governor includes a plurality of flyweights
110 driven by the crankshaft 56, and as the weights revolve,
centrifugal force tends to move them outwardly, this movement being
opposed by a governor spring 112 acting through a sliding sleeve
assembly 114. The sliding sleeve assembly provides the pivot for a
fulcrum lever 115, one end of which is positioned by a control or
throttle lever (not shown), and the other end of which positions
the control rack 106. Displacement of the control rack rotates the
fuel injection plungers (not shown), the rotational disposition of
which determines the quantity of fuel delivered with each stroke of
the pumping mechanism through a plurality of high pressure fuel
lines 117 to a plurality of injector nozzles 118, one of which is
provided for each combustion chamber of the engine, as is well
known to those skilled in the art.
The limit switch 102 is located so that it is only closed when the
control rack 106 is in its dead rack or zero fuel delivery
position. Accordingly, the engine brake control system senses the
delivery of fuel to the combustion chambers, and ensures that the
engine brake cannot be activated when fuel is being delivered to
the combustion chambers. This not only prevents wasted fuel during
engine braking, but more importantly prevents the damage to the
valve train which would result if combustion occurred while the
exhaust valve is open, such combustion being possible in a
compression-ignition engine even though the exhaust valve is
open.
The switches 93-96 are so disposed with respect to the brake pedal
98 that they are sequentially closed before the vehicle service air
brake is activated. The chart shown in FIG. 6 illustrates the
graduated or modulated braking effect available with the system
shown in FIG. 5. Thus, the curves 120 and 121 show the brake
horespower and torque, respectively, developed by a representative
V-8 diesel engine under normal operation.
If the operator wishes to retard the vehicle, either during
downhill operation or when approaching a traffic light or
intersection on level terrain, for example, he lifts his foot from
the throttle pedal (not shown) and the governor will drive the
control rack 106 to the dead rack or no fuel position. This
terminates combustion and effects engine or motoring friction,
during which condition the negative or absorbed horespower is
proportional to the engine RPM, as illustrated by the curve 122.
When the rack is in the no fuel position, the limit switch 102 is
closed, permitting activation of the engine brake providing that
the manual override switch 100 is closed.
Should the operator desire additional braking, he depresses the
brake pedal 98 to close the switch 93 thereby converting the two
cylinders associated with the cylinder head 63 to air compressors
and thus obtaining the retarding effect shown by the curve 123. If
the brake pedal 98 is further depressed to close the switch 94
(while maintaining the switch 93 in its closed position), the
solenoid 86 is energized to convert the two cylinders associated
with the cylinder head 64 to air compressors, thus obtaining the
retarding effect shown by the curve 124. Similarly, when the brake
pedal is further depressed to close the switches 95 and 96 (the
switches 93 and 94 remaining closed), the solenoids 87 and 88 are
energized and an engine braking effect is obtained from the
cylinders associated with the cylinder heads 65 and 66,
respectively, thus obtaining the braking effects illustrated by the
curves 125 and 126, respectively.
Should still additional braking be desired, the brake pedal 98 is
further depressed to actuate an air valve 128 and thus activate the
conventional service brake (not shown). Thus, the present engine
braking system provides the operator with great flexibility to
obtain the desired degree of braking in accordance with the
particular downhill or other condition.
The rocker arm shaft assembly for the rocker arm shaft 67 is shown
in FIGS. 7 and 8, it being understood that the corresponding
assemblies for the other rocker arm shafts are identical. The
rocker arm shaft 67 is supported on the cylinder head 63 by a pair
of spaced brackets 130 and 131. A pair of inlet rocker arms 133 and
133a are mounted for rocking motion on the rocker arm shaft 67 and
are urged against the brackets 130 and 131 by a pair of spring
elements 135, anchoring portions of which are received in a pair of
grooves 137 and 138, respectively, formed in the rocker arm shaft
67.
Similarly, the exhaust rocker arms 74 and 74a are urged against the
brackets 130 and 131 by a pair of springs 140, the remote ends of
which bear against a pair of washers 141 which are retained by a
pair of snap rings 142, the snap rings being received in a pair of
grooves 143 and 144, respectively, formed in the rocker arm shaft
67.
Each of the inlet rocker arms 133 and 133a is driven by a pushrod
146 (shown in phantom), the upper end of which is received in an
adjusting screw 148 which is threadedly received in the inlet
rocker arm. The position of the adjusting screw 148 is set when the
inlet valve train components are cold so as to provide sufficient
lash to accommodate the expansion of the valve train elements when
their temperature rises. The adjusting screws are locked in the
desired position by a locking nut 150. The lower end of each
pushrod 146 is received in a cam follower (not shown) which rides
upon a corresponding inlet cam (not shown) formed on the camshaft
55.
The rocker arm shaft 67 is formed with two longitudinal passageways
154 and 155, which are plugged at each end by a plug 156 and 157,
respectively. Oil under pressure is supplied through a conduit 158
to the passageway 155 from a conventional oil pump 160 (see FIG.
5), which draws oil from the engine sump 161 through a conduit 162,
the conduit 158 communicating with the passageway 155 through a
bore 164 in the bracket 131. The oil pump 160 may also supply oil
to bearings and other engine components (not shown) for purposes of
lubrication and/or cooling. The bore 164 includes a threaded
reduced diameter portion 165 threadedly receives a plug 166, which
extends into and is snugly received in a lateral bore 168 formed in
the rocker arm shaft 167 and communicating with the passageway 155.
The plug 166 locks the rocker arm shaft 67 against rotational or
axial displacement with respect to the brackets 130 and 131, and a
bore 170 extending through the plug 166 communicates the conduit
158 with the oil gallery 155.
Oil under pressure flows from the oil gallery 155 through a pair of
lateral bores 173 and 174 to lubricate the rocking motion of the
inlet rocker arms 133 and 133a on the rocker arm at 67, and also
shows through a pair of lateral bores 175 and 176 to lubricate the
rocking motion of the exhaust rocker arms 74 and 74a and to supply
oil under relatively constant pressure through a lower bore 178 in
the exhaust rocker arms to the hydraulic lash adjusters 76 (see
FIG. 9).
The exhaust rocker arms 74 and 74a are grooved (see groove 180 in
the exhaust rocker arm 74a as viewed in FIG. 9) so as to permit
sufficient oil to pass through a pair of bores 181 and 182,
respectively, to drip over the noses of the exhaust rocker arms and
thus lubricate the slipper faces 183 and 184 thereof. Similarly,
the intake rocker arms 133 and 133a are grooved to supply oil
through a pair of bores 185 and 186, respectively, therein so as to
lubricate the slipper faces thereof.
The rocker arm shaft 67 is formed with a lateral bore 189 to
threadedly receive a control valve 190 by means of which oil under
pressure may be selectively communicated from the oil gallery 155
to the "on-off" oil gallery 154. The control valve 190 includes a
valve body 191 upon which is mounted the solenoid 85, the valve
body being formed with a central bore 192 into the which the
solenoid armature 193 extends. Mounted in the upper portion of the
bore 192 is an upper valve seat 194 having a central bore 195 so
formed that an annular space exists between the bore 195 and the
armature 193 for all positions of the armature. A lower valve seat
197 is mounted in the lower portion of the bore 192, and a ball
valve element 198 is disposed between the upper valve seat 194 and
the lower valve seat 197.
A plurality of lateral bores 200 in the valve body communicate the
portion of the bore 192 between the upper and the lower valve seats
with the "on-off" oil gallery 154. The lower portion of the bore
192 communicates with the "constant" oil supply gallery 155, a seal
202 ensuring that oil may only flow between the two galleries 154
and 155 through the central bore 192 and the lateral bore 200.
Thus, when the ball valve 198 is displaced from the lower valve
seat 197, communication is established between the oil galleries
154 and 155. A plurality of upper lateral bores 204 in the valve
body 191 communicate the upper portion of the bore 192 above the
upper valve seat 194 with atmosphere, so that when the ball valve
198 is displaced from the upper valve seat 194, the "on-off" oil
gallery 154 is exposed to atmospheric pressure.
When the solenoid 85 is de-energized, the pressurized oil in the
gallery 155 (at the "constant" pressure established by the oil pump
160) drives the ball 198 upwardly against the upper valve seat 194,
simultaneously displacing the armature 193 upwardly.
(Alternatively, the upper valve seat 194 could support a light
spring for biasing the armature 193 upwardly.) Pressurized oil then
flows through the bore 192 and the lateral bores 200 to the
"on-off" gallery 154, and through a pair of lateral bores 206 and
208 in the rocker arm shaft 67 to a pair of upper bores in the
rocker arms 74 and 74a, FIG. 9 showing the upper bore 210 in the
rocker arm 74a.
The upper bore 210 communicates with the hydraulic lash adjuster
76, and when the pressure of the oil in the bore 210 is raised to
that of the pressurized oil in the constant supply gallery 155 by
communicating with the bore 210 with the gallery 155 (see FIG. 9A),
the hydraulic lash adjuster 76 is in its collapsed state, as will
be explained hereinafter.
When the solenoid 85 is energized, the armature 193 drives the ball
198 against the lower valve seat 197, sealing the "on-off" gallery
154 from the constant oil supply gallery 155. At the same time, the
oil in the gallery 154 is exposed to atmospheric pressure through
the lateral bores 200, the bore 195 and the lateral bores 204 (see
FIG. 9B). When the upper bores 210 are vented to atmospheric
pressure, the hydraulic lash adjusters 76 expand, as will be
explained hereinafter.
Referring now to FIGS. 9 and 10, the hydraulic lash adjuster 76
includes a body 215, the outer lateral surface of which is threaded
so as to permit vertical adjustment in a complementary bore 216
formed in the exhaust rocker arms 74 and 74a, in order to obtain
the desired lash to accommodate for the thermal expansion of the
valve gear train components, as mentioned above. The lateral
surface of the body 215 is also formed with a pair of spaced
annular grooves 217 and 218, which communicate with the bores 178
and 210, respectively, in the exhaust rocker arms. A pair of
lateral bores 219 and 220 in the body 215 communicate the annular
groove 217 with a central chamber 222, and a lateral bore 224
communicates the groove 218 with an upper chamber 226, a control
piston 228 being disposed between the central chamber 222 and the
upper chamber 226.
Oil is prevented from escaping from the upper chamber 226 by a plug
229 which is retained by a snap ring 230, the snap ring being
seated in a complementary groove formed in the body 215. A seal
ring 231 provides a liquid-tight seal between the plug 229 and the
body 215. A compression spring 223 acts between the plug 229 and
the control piston 228 to bias the latter downwardly, the control
piston being bored at 235 to receive the compression spring. The
control piston 228 is reciprocable between the plug 229 and stop
237 formed in the interior of the body 215.
A finger 238, depending upon the control piston 228, extends into a
port 239 communicating the central chamber 222 with a high pressure
chamber 240. A perforated ring carrier 242 disposed in the high
pressure chamber supports a light compression spring 243 which
biases a ball check valve 245 upwardly to seal the port 239.
The high pressure chamber 240 is closed by a socket piston 247,
which is slidably received in a cylinder 248 formed in the lower
portion of the body 215. The socket piston 247 is formed with a
socket 249 in the lower portion thereof adapted to receive the
upper end of the pushrod 78, and the socket piston is biased
downwardly (as viewed in FIGS. 9 and 10) by a compression spring
250. The compression spring 250 is received in a pocket 251 formed
in the upper portion of the socket piston, the upper end of the
compression spring 250 being received in an outwardly extending
flange 252 of the spring carrier 242. The compression spring 250 is
relatively stiff compared with the ball valve biasing spring 243,
and so retains the spring carrier 242 against the lower face 254 of
the inwardly extending portion of the body 215 which forms the port
239.
The socket piston 247 may reciprocate between a snap ring 256,
which is seated in a complementary groove formed in the lower
interior portion of the body 215, and a stop 258 formed in the body
215 at the upper end of the cylinder 248. The outer lateral surface
of the socket piston 247 includes a plurality of spaced annular
grooves 259, which retain oil therein to lubricate the movement of
the socket piston and thus extend its life. The bleed down rate of
the oil in the high pressure chamber 240 past the socket piston
when it is hydraulically locked is sufficiently low so that
movement of the socket piston is negligible during the valve event.
Furthermore, as soon as the cam follower 80 engags the secondary
base circle 43, the socket piston is restored to its fully expanded
position.
The hydraulic lash adjuster 76 is made to expand and collapse as
follows. when the solenoid 84 is de-energized, pressurized oil from
the constant oil supply gallery 155 in the rocker arm shaft 67
flows through the bore 192 and the lateral bores 200 (see FIG. 8),
through the "on-off" gallery 154, the lateral bore 208 and the
rocker arm bore 210 to the annular groove 218 in the lash adjuster
76 in the exhaust rocker arm 74a simultaneously through the lateral
bore 206 to the lash adjuster 76 in the exhaust rocker arm 74). The
pressurized oil flows through the bore 224 in the lash adjuster to
the upper chamber 235, thereby developing a hydraulic force which
urges the control piston 228 downwardly.
This hydraulic force is opposed by an equal and opposite hydraulic
force developed by the pressurized oil in the central chamber 222,
which communicates with the constant oil supply gallery 155 through
the bores 176 and 178, the annular groove 217, and the lateral
bores 219 and 220. Accordingly, the control piston 228 is driven
downwardly by the compression spring 233, and the control piston
finger 238 displaces the ball check valve 245 away from its valve
seat in the inner edge of the surface 254 adjacent the lower
entrance to the port 239, thereby overcoming the light biasing
force of the spring 243.
The compression spring 250 can drive the socket piston 247 against
the snap ring 256 which the cam follower 80 rides upon the
secondary exhaust cam base circle 43, and the pressurized oil can
flow from the central chamber 222 through the port 239 and fill the
expanded chamber 240, but the socket piston 247 is not
hydraulically locked in its expanded position because the ball
check valve 245 is held off its seat. Thus, when the cam follower
80 rides up the auxiliary opening profile 46, the pushrod 78 drives
the socket piston 247 upwardly against the stop 258, thus
collapsing the high pressure chamber 240 (and thereby collapsing
the lash adjuster 76). The excess oil expelled from the chamber 240
flows through the central chamber 222 and out the lateral bores 219
and 220.
In summary, when the hydraulic lash adjuster is in its "collapsed"
state, the socket piston 247 is reciprocated by the compression
spring 250 and the pushrod 78, and the pressurized oil flows back
and forth through the bores 219, 220, 176 and 178 (see FIG. 9A).
Accordingly, the hydraulic lash adjuster 76 has no effect on the
timing of the corresponding exhaust valve, which opens and closes
at the normal times.
In order to obtain an engine braking effect from the two cylinders
associated with the cylinder head 63, when the manual cab switch
100 is closed and the control rack 106 is in its no fuel position
to close the limit switch 102, the operator depresses the brake
pedal 98 to close the switch 93 and thus energize the solenoid 85.
The ball valve 198 is driven against the lower seat 197 to
interrupt the communication between the constant oil supply gallery
155 and the "on-off" oil gallery 154, whereupon the pressure of the
oil in the upper chamber 226 drops to atmospheric pressure,
inasmuch as the upper chamber is communicated to atmosphere through
the bores 224, 210, 208, 154, 200, 195 and 204. The upward force
developed by the pressurized oil in the center chamber 222 then
overcomes the downward biasing force of the spring 233, so that the
control piston 228 is driven upwardly against the plug 229. This
expells an amount of oil through the lateral bores 204 in the valve
body 191 equal to the reduction in volume of the upper chamber
226.
Withdrawal of the control piston finger 238 permits the ball check
valve 245 to seat Thus, when the cam follower 80 rides on the
secondary cam base circle 43, permitting the spring 250 to drive
the socket piston 247 against the snap ring 256, pressurized oil
from the central chamber 222 is drawn into the high pressure
chamber 240 through the port 239, overcoming the biasing force of
the spring 243, but the oil is trapped and locked in the high
pressure chamber 240 by the check vlave 245 (see FOG, 9B).
Accordingly, the socket piston 247 (and thus the lash adjuster 76)
is hydraulically locked in its expanded position, so that the two
exhaust valves are opened as the cam followers 80 ride up on the
secondary opening profiles 46 near the end of the compression
stroke, thus dumping the compressed air so that the energy thereof
is dissipated to atmosphere and does not return to the engine
during the expansion stroke.
Should the operator desire a greater engine braking effect, he
further depresses the brake pedal 98 to close the switches 94, 95
and 96 and obtain the additional braking effect of the pairs of
cylinders associated with the cylinder heads 64, 65 and 66,
rspectively, as discussed above. Thereafter, additional braking may
be obtained by further depressing the brake pedal to activate the
conventional service brakes.
FIGS. 11A-D show alternative electrical control circuitry which may
be used with the engine braking system of FIGS. 4-10. If a
graduated degree of engine braking is not necessary for a
particular application, then the electrical control circuitry shown
in FIG. 11A may be employed, in which a single switch 260 is
mounted so as to be closed when the brake pedal 98 is partially
depressed, but before the conventional service brake is actuated.
When the manual cab switch 100 is closed and the control rack 106
is in the no-fuel position so as to close the limit swich 102, the
closing of the switch 260 simultaneously energizes the solenoids
85-88, thereby to convert all eight cylinders of the V-8 engine to
air compressors and thus obtain the maximum engine braking
effect.
If all brake pedal actuated switches are omitted, as illustrated in
FIG. 11B, then the solenoids 85-88 will be simultaneously energized
to obtain the maximum engine braking effect whenever the vehicle
overruns the particular setting of the throttle (provided the cab
switch 100 is closed), which occurs, for example, when the throttle
pedal is released, whereupon the governor drives the control rack
106 to the no-fuel position and closes the limit switch 102. (As
discussed above, when idling speed is reached, the governor will
automatically move the rack to the idle fuel position, after
deactivating the engine braking, thereby preventing stalling of the
engine.) With this control system, it will be noted that the
lighter degree of "motoring" friction is unavailable, since the
engine brake is automatically activated whenever the injection of
fuel is stopped (assuming the cab switch is closed).
This system has the advantage of acting as a clutch brake during
upshifting of slowing down the countershaft(s) and thus bringing
the gear set to be engaged more rapidly into synchronism. On the
other hand, difficulty might be encountered in double clutching for
downshifting, inasmuch as the counter-shaft(s) will be slowed down
by the engine brake before it is deactivated when the throttle is
opened to speed up the counter-shaft(s), so that it will take
longer to get the countershaft(s) up to synchronized speed. The
operator can overcome this difficulty by insuring that the throttle
pedal is sufficiently depressed during downshifting, so that the
limit switch 102 does not close and the engine brake is not
activated.
The control circuitry of FIG. 11C overcomes the down-shifting
difficulty of the previous control circuitry by including a series
connected manual switch 262 mounted on the shift lever, thereby
permitting the operator to deactivate the engine brake during
downshifting without having to manipulate the throttle, while
retaining the clutch brake effect during up-shifting. Thus, during
upshifting the switch 262 is left in its normally closed position,
so that the engine brake is automatically activated during
upshifting (assuming the cab switch 100 is closed) to slow down the
countershaft(s) when the throttle is released to idle position.
During downshifting, however, the operator opens the switch 262 to
prevent any undesirable engine (clutch) braking during this
operation.
In the control system according to FIG. 11D, a normally closed
pedal switch 264 is included, thereby eliminating the engine brake
during downshifting. When the clutch is disengaged, the switch 264
is opened to deactivate the engine brake, and when the transmission
is in neutral and the clutch engaged during double clutching, the
throttle will be opened to speed up the countershaft(s) and
simultaneously open the limit switch 102 to deactivate the engine
brake. On the other hand, during upshifting, when the transmission
is in neutral and the clutch engaged during double shifting, the
engine brake will be automatically activated to act as a clutch
brake and facilitate the shift by slowing down the
countershaft(s).
FIG. 12 shows another embodiment of the engine braking system of
FIGS. 4-10. In this embodiment, a hydraulic lash adjuster 270,
similar in construction and identical in operation with the
hydraulic lash adjuster 76 of the previous embodiment, is mounted
in the engine block 61 rather than in the exhaust rocker arm.
Accordingly, each exhaust valve 72 is reciprocated by a
conventional exhaust rocker arm 272, which is identical to the
corresponding one of the inlet rocker arms 133 and 133a of the
previous embodiment. Each pair of exhaust rocker arms 272
associated with one of the four cylinder heads of the V-8 engine is
carried by a rocker arm shaft 274 having a single longitudinal bore
275 therein, the bore 275 being supplied with pressurized oil from
the lubrication pump 160. Each rocker arm shaft 274 contains four
lateral bores (not shown) which communicate lubricating oil from
the longitudinal bore 275 to the two exhaust rocker arms and the
two inlet rocker arms carried thereby.
Each exhaust pushrod 78 is received at its upper end in the
adjusting screw 148, which is threadedly received in the exhaust
rocker arm 272 so as to enable adjustment to provide sufficient
lash to accomodate the thermal expansion of the valve train
elements, the adjusting screw being locked in the desired position
by the locking nut 150. The lower end of the pushrod 78 is received
in one end of the lash adjuster 270, the other end of which rides
upon the exhaust cam 42.
As before, a graduated degree of engine braking may be obtained by
depressing the brake pedal 98 to sequentially close the switches
93, 94, 95 and 96, assuming that the cab switch 100 and the control
rack limit switch 102 are closed. The switches 93, 94, 95 and 96
are connected to the solenoids 278, 279, 280 and 281, respectively,
which, when energized, activate the valves 283, 284, 285 and 286,
respectively, by which the pressurized oil from the pump 160 may be
selectively communicated with one portion of the lash adjusters
270, pressurized oil being constantly supplied to the other portion
thereof.
Referring now to the enlarged view of one of the pair of lash
adjusters 270 associated with the solenoid 278 shown in FIG. 12A,
oil under pressure is supplied by the pump 160 through a conduit
290 to a constant oil supply gallery 291, which has branch conduits
291a and 291b communicating with the central chambers 222' of the
two-lash adjusters 270 whose operation is controlled by the valve
283. Each lash adjuster 270 reciprocates in a sleeve 293 mounted in
the engine block 61. The lash adjuster 270 includes a body 295
having a first annular groove 297 formed in the outer lateral
surface thereof, a pair of lateral bores 298 and 299 communicating
the groove 297 with the central chamber 222'. The axial length of
the groove 297 is such that during the reciprocation of the lash
adjuster 270 in the sleeve 293, the chamber 222' is always in
communication with the constant oil supply gallery 291 through a
bore 300 in the sleeve.
When the solenoid 278 is de-energized, as shown in FIG. 12A, the
valve 283 communicates with the oil under pressure in the conduit
290, and a conduit 302 connected thereto, with an "on-off" oil
gallery 304, which in turn supplies oil under pressure through the
branch conduits 304a and 304b to the chambers 226' of the two
hydraulic lash adjusters 270 controlled by the valve 283. In
particular, the gallery 304 communicates with each chamber 226'
through a bore 306 in the sleeve 293, a groove 307 formed in the
outer lateral surface of the body 295, and a lateral bore 308 in
the body 295. The axial length of the groove 307 is such that it is
always in communication with the "on-off" oil gallery 304.
The compression spring 233' is received in the bore 235' in the
control piston 228', and bears against a plug 310 which seals the
chamber 226', a seal ring 312 providing a liquid-tight seal between
the plug 310 and the body 295. The lower surface of the plug 310
rides on the exhaust cam 42. The socket piston 247' receives in its
socket 249' the lower end of the pushrod 78, and the socket piston
may reciprocate between the stop 258' and the snap ring 256'.
With pressurized oil in both chambers 222' and 226', the spring
233' drives the control piston 228' upwardly againt the stop 237',
so that its finger 238' engages the ball check valve 245' and lifts
it from it seat, overcoming the biasing force of the light spring
243'. When the lash adjuster 270 is riding on the secondary exhaust
cam base circle 43, the compression spring 250' drives the socket
piston 247' against the snap ring 256', but as the lash adjuster
rides up the auxiliary opening profile 46, the pushrod 78 collapses
the socket piston 247' (and thus the lash adjuster 270), driving
the excess oil out of the chamber 240', inasmuch as the ball check
valve 245' is held off its seat by the control piston 228'.
When the injection pump switch 102 closes, sensing and verifying a
zero fuel condition, and the switch 93 is closed by the brake pedal
98 to energize the solenoid 278 (assuming the cab switch 100 is
closed), the valve 283 is actuated to de-couple the "on-off"
gallery 304 from the pressurized oil in the conduit 290, and the
pressure of the oil in the chamber 226' and in the gallery 304
drops to atmospheric pressure, due to the communication of the
gallery 304 with atmosphere through the valve 283 and a vent
conduit 314. The pressure of the oil in the chamber 222' then
overcomes the force of the spring 233', and so the control piston
228' is driven downwardly against the plug 310, thus disengaging
the finger 238' from the ball check valve 245'. The oil driven from
the chamber 226' is relieved through the conduits 304 and 314.
Accordingly, when the plug 310 next rides on the secondary exhaust
cam base circle 43, the spring 250' drives the socket piston 247'
against the snap ring 256', drawing additional pressurized oil into
the high pressure chamber 240'. This oil is locked in the chamber
240' by the ball check valve 245', which is urged against its seat
by the biasing spring 243', and so the socket piston 247' (as well
as the lash adjuster 270) is locked in its expanded position.
The lash being removed from the exhaust valve mechanism (except for
the lash 48 shown in FIG. 4A), the exhaust valves 72 associated
with the solenoid 278 are opened by the auxiliary opening profile
46 near the end of the compression stroke to provide ening braking.
Should a greater engine braking effect be desired, the brake pedal
is further depressed to energize the desired ones of the solenoids
284-286, as discussed above.
In the above-described operation of the engine braking system, it
will be recalled that each lash adjuster 76 is positioned in its
rocker arm 74 (see FIG. 5), and each adjusting screw 148 is
positioned in its rocker arm 272 (see FIG. 12), when the valve
train elements are cold to accommodate the thermal expansion
thereof. Accordingly, the time at which the exhaust valve opens to
dump the compressed air for engine braking varies in accordance
with the point along the auxiliary opening profile 46 at which the
prevailing lash 48 is taien up, and this is determined by the
degree of thermal expansion of the valve train elements, upon which
the amount of the lash 48 depends.
The time at which each exhaust valve is opened to dump the
compressed air may be maintained at a desired point by removing all
lash during the engine braking. With zero lash, each exhaust valve
opens as soon as the associated cam followr is raised by the
initial portion of the auxiliary opening profile 46, regardless of
any variation in the exhaust valve train length due to thermal
effects.
The zero lash is obtained by positioning each lash adjuster 76, or
adjusting screw 148, in its rocker arm 74, or 272, when the valve
train elements are cold, so that the corresponding cam follower
engages the secondary exhaust cam base circle 43 when the
associated hydraulic lash adjuster is expanded. Any extension of
the corresponding valve train length due to thermal expansion or
other loading effects is accommodated by a corresponding small
leakage of oil from the high pressure chamber 240 or 240' past the
socket piston 247 or 247'. Such leakage is so slow that movement of
the socket piston is negligible during the valve event.
If the valve train length should contract from thermal or other
effects, the zero lash condition will be maintained (during engine
braking) during the unloading or valve closing portion of the lift
cycle when the spring 250 or 250' drives the socket piston 247 or
247' against the secondary base circle 43, drawing pressurized oil
from the chamber 222 or 222' into the high pressure chamber 240 or
240', where the oil is trapped and locked by the ball check valve
245 or 245'.
Accordingly, when the engine braking apparatus is operated with all
lash removed, the socket piston 247 and 247' (and thus the
hydraulic lash adjuster 76 or 270, respectively) is hydraulically
locked in an expanded condition in which the associated cam
follower engages the secondary base circle 43, even though the
socket piston may not engage the snap ring 256 or 256'.
FIGS. 13-21 relate to another embodiment of the variable valve
timing system in which the starting of a relatively low compression
ratio internal combustion engine is enhanced by increasing the
effective compresson ratio during starting. As shown in FIG. 13,
the inlet valve opening sector 320 indicats that in a typical
compression-ignition engine the inlet valve opens approximately
20.degree. before the top dead center postion of the engine crank
during the latter part of the exhaust stroke and before the exhaust
valve closes (see the opening sector 321) to promote scavening, and
the inlet valve closes approximately 40.degree. after bottom dead
center during the initial portion of the compression stroke, with
the normal valve tappet clearance or lash to accommodate the
thermal expansion of the valve train components. The actual
beginning of compression occurs when the inlet valve closes, and so
under normal operation, the effective compression ratio is somewhat
lower than the numerical or theoretical compression ratio, which
could only be obtained if the inlet valve closed at bottom dead
center.
The inlet valve timing is shown in FIG. 14. during normal operation
with a standard lash indicated at 322, the normal timng corresponds
to the inlet valve opening duration shown at 320 in FIG. 13. If
excess clearance or lash is provided in the inlet gear train as
indicated at 324, the inlet valve opening function is reduced,
retarding the opening point to somewhat after top dead center and
advancing the closing point to bottom dead center. This reduced
inlet valve opening duration caused by excess clearance is
illustrated by the opening sector 326 in FIG. 15.
FIG. 16 shows the cylinder pressure characteristics during the
compression and expansion strokes when the inlet valve normally
closes somewhat after bottom center (see curve 328) and also when
the inlet valve closes (and thus the actual beginning of
compression starts) at bottom center, as seen in the curve 330. It
is apparent that the peak compression is higher when the inlet
valve closes at bottom dead center as compared with the peak
pressure attained when the inlet valve normally closes after bottom
dead center.
FIG. 17 shows the positions of a control connecting rod 336 and
piston 337 in a cylinder 338 when the inlet valve closes normally
somewhat after bottom dead center during the initial portion of the
compression stroke. During such normal operation, the actual
compression ratio depends upon the volume swept by the piston
during the compression stroke after the inlet valve closes,
indicated at 339, and the clearance volume which exists between the
piston 337 and the cylinder head when the piston is at top center,
such clearance volume being indicated at 340.
FIG. 18 shows the position of the crank, connecting rod and piston
when the inlet valve closes at bottom center. Hence it will be
noted that the effective compression volume, indicated at 341, is
greater than the effective compression volume indicated at 339
under normal conditions, although the clearance volume 340 in the
two cases is identical, thereby providing a higher peak compression
pressure and a higher actual or effective compression ratio when
the closing of the inlet valve is advanced to bottom dead
center.
As is well known, reducing the compression ratio of an internal
combustion engine reduces the peak cylinder firing pressures and
thus permits a higher engine output to be obtained at the same peak
firing pressures as are developed in a higher compression ratio
engine of lower output. A conventional internal combustion engine
having a rated or theoretical compression ratio of 15:1, for
example, actually has an effective compression ratio of
approxiately 14:1 due to the fact that the inlet valve closes
somewhat after bottom center during the initial portion of the
compression stroke, as discussed above. If excess clearance or lash
is introduced into the inlet valve gear train in order to advance
the closing of the inlet valve to bottom center during starting,
the effective compression ratio of the "15:1" compression ratio
engine will be increased to approximately 15:1, for example,
thereby enhancing the starting of the compression-ignition
engine.
Alternatively, the performance of the engine could be further
increased by redesigning it to provide a still lower effective
compression ratio of 13:1, for example, during normal operation
when the inlet valve closes somewhat after bottom center, and then
by introducing excess clearance or lash in the inlet valve gear
train during starting, the actual compression ratio would be
approximately 14:1. Accordingly, the startng of the modified low
compression ratio engine would equal that of a conventional enging
having a rated compression ratio of 15:1, but an actual effective
ratio of only 14:1.
The variable valve timing system for selectively introducing excess
clearance into the inelt valve gear train in order to increase the
effective compression ratio of a relatively low compression ratio
engine during starting is shown in FIG. 19, as applied to the same
basic V-8 engine used to illustrate the engine braking system
described above. Accordingly, identical components of the engine in
these two embodiments bear the same reference numerals and need not
be described again in detail.
Each inlet valve 345 is driven by a corresponding one of the pair
of inlet rocker arms 346 and 346a associated with each of the
cylinder heads 63-66. The inlet rocker arms 346 and 346a are
identical to the exhaust rocker arms 74 and 74a described above in
connection with the engine braking system and illustrated in FIGS.
7-9.
The opposite end of each inlet rocker arm mounts the hydraulic lash
adjuster 76, which has been described in detail above and is
illustrated in FIGS. 9 and 10. Each lash adjuster 76 receives the
upper end of a pushrod 348, the lower end of which is received in a
cam follower 350, which engages a conventional inlet cam 352 formed
on the camshaft 55, which in turn is conventionally driven by the
crankshaft 56.
The hydraulic lash adjusters 76 are threadedly received in the
rocker arms 346 and 346a so that the lash adjuster may be
positioned in the rocker arm when the inlet valve train components
are cold so as to provide a standard lash indicated at 322 in FIG.
14 to accomodate the thermal expansion of the valve gear train
elements. Each lash adjuster is locked in the desired position by a
lock nut 82.
Each of the cylinder heads 63-66 mounts a rocker arm shaft 355,
upon which are mounted for rocking motion the inlet rocker arms 346
an 346a, as well as a pair of exhaust rocker arms 357 and 357a,
which are identical to the inlet rocker arms 133 and 133a described
above in connection with the engine braking system and illustrated
in FIGS. 5, 7 and 8.
Each rocker arm shaft 355 includes a constant oil supply gallery
360, closed at each end by a plug 361, and an "on-off" gallery 363,
plugged at each end by a plug 364 (see FIG. 19A). As before, oil
under pressure is supplied through the conduit 158 to the constant
oil supply gallery 360 from the oil pump 160, which draws oil from
the engine sump 161 through the conduit 162, the condut 158
communicating with the passageway 360 through the bore 164 in the
rocker arm shaft supporting bracket 131. The bore 164 includes a
threaded connection diameter portion 165 which threadedly receives
a plug 166, which extends into and is snugly received in a lateral
bore 366 formed in the rocker arm shaft 355 and communicating with
the passageway 360. The plug 166 locks the rocker arm shaft against
rotational or axial displacement with respect to the rocker arm
shaft supporting brackets, and a bore 170 extending through the
plug communicates the conduit 158 with a constant oil supply
gallery 360.
Oil under pressure flows from the oil gallery 360 through a pair of
lateral bores 368 and 369 to lubricate the rocking motion of the
exhaust rocker arms 357 and 357a, and also flows through a pair of
lateral bores 370 and 371 to lubricate the rocking motion of the
inlet rocker arms 346 and 346a and to supply oil under relatively
constant pressure through a lower bore 373 in the inlet rocker arms
to the hydraulic lash adjusters 76.
As in the previous embodiment, the inlet and exhaust rocker arms
346, 346a, 357 and 357a, are grooved and bored (see the bore 375 in
FIG. 19) so that sufficient oil from the constnat supply gallery
360 drips over the noses of the rocker arms and thus lubricates the
slipper faces thereof.
Each rocker arms shaft 355 is formed with a lateral bore 377 to
threadedly receive the conrol valve 190 by means of which oil under
pressure may be communicated from the oil gallery 360 to the
"on-off" oil gallery 363, or in the oil in the "on-off" gallery may
be exposed to atmospheric pressure, as discussed above, The
solenoid 85 is mounted on the body of the control valve 190 and
includes the armature 193 for displacing the ball valve element 198
of the valve 190. When the solenoid 85 is de-energized, pressurized
oil from the gallery 360 is communicated through the "on-off"
gallery 363, through a pair of lateral bores 380 and 381 in the
rocker arm shaft 355, and through an upper bore 383 in each of the
inlet rocker arms to the hydraulic lash adjuster 76 mounted
therein.
The lower bore 373 and the upper bore 383 in each inlet rocker arm
communicate with the central chamber 222 and the upper chamber 226,
respectively, in the lash adjuster 76, (see FIG. 10), and when the
solenoid 85 is de-energized, pressurized oil is supplied above and
below the control piston 228, which is then driven downwardly by
the compression spring 223 to displace the ball check valve 245
from its seat, thereby collapsing the hydraulic lash adjuster 76,
as explained above.
When the solenoid 85 is energized, the control valve 190 is
actuated to seal the on-off gallery 363 from the constant oil
supply gallery 360, and at the same time expose the oil in the
gallery 363 and in the upper chamber 226 of the lash adjuster to
atmospheric pressure, whereupon the force developed by the
pressurized oil in the central chamber 222 overcomes the force of
the compression spring 233 and the control piston 228 is driven
upwardly, thereby permitting the ball check valve 245 to seat and
hydraulically lock the socket piston 247 (and thus the lash
adjuster 76) in its expanded position.
When the operator wishes to start the relatively low compression
ratio V-8 engine illustrated in FIG. 19, he opens a manual switch
385 located in the cab to de-energize the four solenoids 85
associated with the cylinder heads 63-66, thereby collapsing the
hydraulic lash adjusters 76 mounted in all of the inlet rocker arms
346 and 346a. This contracts all of the inlet valve gear trains,
providing therein the excess clearance indicated at 324 in FIG. 14,
so that the closing time of each inlet valve is advanced to bottom
dead center to increase the effective compression ratio to the
maximum or theoretical value. This maximizes the peak compression
pressures attained during the compression stroke and thereby
enhances the starting of the compression-ignition engine.
After the engine has warmed up, the operator closes the cab switch
385, thereby simultaneously energizing the four solenoids 85 so as
to expand and hydraulically lock each hydraulic lash adjuster 76 in
its expanded condition, in which the socket piston 247 engages the
snap ring 246. This expands each inlet valve train to eliminate the
excess clearance 324 and provide merely the standard lash indicated
at 322 necessary to accommodate the thermal expansion of the inlet
valve train elements. Accordingly, the opening time of each inlet
valve is retarded to the normal time during the initial portion of
the compression stroke, thereby reducing the compression ratio to
the nominal value and thus increasing the performance of the
engine.
Operating the engine with excess inlet valve clearances for a
prolonged period of time or in the upper engine speed range might
damage the inlet valve gear components. Accordingly, provision is
made to automatically limit the engine speed to a safe range. As
discussed above, the control rack 106 of the fuel injection system
108 is displaced to adjust the fuel delivery by one end of the
fulcrum lever 115, which is pivoted on the sliding sleeve assembly
114, the position of which is determined by the opposing forces
thereon developed by the governor spring 112 and the flyweights
110. The opposite end of the fulcrum lever 115 is positioned by a
control lever 388, which in turn is positioned through a linkage
389 by the throttle pedal 390.
A throttle limiting solenoid 392 is mounted in operative relation
to the control lever 388, so that a stop member 394 mounted on the
solenoid armature normally extends into the path of travel of the
control lever 388, the stop member 394 being biased in its extended
position by a spring (not shown). The stop member 394 is mounted so
that when extended the control lever 388 is engaged at a position
at which the governor limits the engine speed to approximately
1,000 RPM for an engine having an operating speed range of 1,200 to
2,100 RPM, for example. Thus, when the manual switch 385 is opened
to collapse the hydraulic lash adjusters 76 and provide the excess
clearance 324 to increase the effective compression ratio during
starting, the extended stop member 394 limits the travel of the
contrl lever 388 to prevent the engine speed from exceeding
approximately 1,000 RPM, thus preventing any possible damage to the
inlet valve gear components.
After the engine has warmed up, the operator closes the manual
switch 385 to energize the solenoids 85 and thus expand the lash
adjusters 76 (and thereby the inlet valve trains), thereby removing
the excess clearance 324, whereupon the inlet valves close during
the initial portion of the compression stroke and thereby reduce
the effective compression ratio. At the same time, the throttle
limiting solenoid 392 is energized to retract the stop member 394
from the path of travel of the control lever 388, overcoming the
armature biasing force. Thus, when the standard lash 322 exists in
the inlet valve train (providing the lower effective compression
ratio), the full throttle operation of the engine is available.
It is to be understood that the engine braking system illustrated
in FIGS. 12 and 12A could be included in the variable effective
compression ratio engine described above in connection with FIG.
19. Alternatively, the engine braking system illustrated in FIG. 5
could be used in a low compression ratio engine, the effective
compression ratio of which is increased for starting by introducing
excess clearance into the inlet valve trains with hydraulic lash
adjusters mounted in the block and constructed as the lash adjuster
270 in FIG. 12A. Such lash adjusters would engage the inlet cams
352, and the control valve actuating solenoids 278 would be
energized by the electrical control circuitry shown in FIG. 19.
FIG. 20 illustrates an arrangement in which the present variable
valve timing system is employed in a V-8 low compression ratio
compression-ignition engine to provide a modulated engine braking
effect available from four of the cylinders and to enhance starting
by increasing the effective compression ratio of the other four
cylinders, all of the hydraulic lash adjusters being mounted in the
rocker arms.
The cylinder heads 63 and 64 mount the identical rocker arm shafts
67 and 68, respectively, described above and illustrated in FIGS. 7
and 8. These rocker arm shafts mount the conventional inlet rocker
arms 133 and 133a, and the exhaust rocker arms 74 and 74a described
above and illustrated in FIGS. 7 and 9. Each of the exhaust rocker
arms mounts the hydraulic lash adjuster 76, which may be expanded
to render effective the auxiliary opening profile 46 of the exhaust
cam 42 to open the exhaust valve and effect engine braking, when
the corresponding one of the identical solenoids 85 and 86 are
energized by depressing the brake pedal to close the switches 93
and 94, respectively, assuming that the switches 100 and 102 are
closed, as described above in detail. This permits the operator to
obtain the degrees of engine braking represented by the curves 123
and 124 in FIG. 6, before activating the service brakes, if
necessary.
The cylinder heads 65 and 66 mount the rocker arm shafts 355,
described above and illustrated in FIG. 19A. These rocker arm
shafts mount the conventional exhaust rocker arms 357 and 357a, and
the inlet rocker arms 346 and 346a described above and illustrated
in FIGS. 19 and 19A. Each inlet rocker arm mounts the hydraulic
lash adjuster 76, all four of which associated with the cylinder
heads 65 and 66 may be simultaneously contracted when the
corresponding solenoids 85 are de-energized by opening the manual
cab switch 385. This shifts the points on the profiles of the inlet
cams 352 at which the corresponding inlet valves 345 open and
close, because of the excess clearance 324 introduced in the inlet
valve train, as described above in detail. In particular, the inlet
valve closing points are advanced to bottom dead center, thereby
maximizing the effective compression ratio to facilitate
starting.
Opening the cab switch 385 also de-energizes the throttle limiting
solenoid 392, whereupon the spring-biased stop member 394 (see FIG.
19) extends into the path of travel of the control lever 388,
thereby limiting the engine speed while the excess clearance 324 is
in the inlet valve train and preventing any possible damage to the
inlet valve train components. After the engine has warmed up, the
cab switch 385 is closed to establish the normal lash 322, and thus
the lower compression ratio in the cylinders associated with the
cylinder heads 65 and 66, and to retract the stop member 394 to
permit full throttle operation.
FIG. 21 illustrates another arrangement in which the variable valve
timing system incorporates a modulated engine braking effect and a
variable effective compression ratio for enhanced starting in a low
compression ratio compression-ignition engine, with all of the
hydraulic lash adjusters being mounted in the rocker arms. In this
arrangement, however, the engine braking and variable effective
compression ratio effects may be obtained from all eight cylinders
of a V-8 engine.
Each of the cylinder heads 63-66 mounts a rocker arm shaft 400,
upon which are mounted for rocking motion the pair of exhaust
rocker arms 74 and 74a and the pair of inlet rocker arms 346 and
346a, each rocker arm mounting a hydraulic lash adjuster 76. Each
rocker arm shaft 400 contains a constant oil supply gallery 402 and
a pair of "on-off" galleries 403 and 404. The galleries 402, 403
and 404 are plugged at each end by a plug 405, 406 and 407,
respectively.
The "on-off" gallery 403 communicates through a pair of lateral
bores 410 in the rocker arm shaft with the corresponding upper
bores 210 in the exhaust rocker arms 74 and 74a (see FIG. 9), and
thus with the upper chambers 226 of the hydraulic lash adjusters 76
mounted therein. A passageway 412 between the oil galleries 402 and
403 receives a control valve 190, by means of which the pressure of
the "on-off" gallery 403 (and thus the lash adjuster chambers 226)
is selectively varied between atmospheric pressure and the pressure
established in the constant oil supply gallery 402 by the oil pump
160 through the conduit 158, the bore 164 in the bracket 131 and a
lateral bore 414 in the rocker arm shaft 400, as described in
detail in connection with FIG. 8.
A pair of lateral bores 416 in the shaft 400 communicate the
constant supply gallery 402 with the lower bores 178 in the
corresponding exhaust rocker arms 74 and 74a (see FIG. 9), and thus
with the central chambers 222 of the associated lash adjusters
76.
The control valves 190 in the four rocker arm shaft passageways 412
may be actuated to seal the corresponding galleries 403 from the
galleries 402 and expose the corresponding lash adjuster upper
chambers 226 to atmospheric pressure and expand these exhaust
rocker arm lash adjusters to convert the corresponding cylinders to
compressors, as the corresponding solenoids 85-88 are energized by
the brake pedal switches 93-96, assuming that the switches 100 and
102 are closed. This will provide the graduated engine braking
effect illustrated by the curves 123-126 in FIG. 6.
The "on-off" gallery 404 communicates through a pair of lateral
bores 420 in the rocker arm shaft with the corresponding upper
bores 383 in the inlet rocker arms 346 and 346a (see FIG. 19), and
thus with the upper chambers 226 of the hydraulic lash adjusters 76
mounted therein. A passageway 422 between the galleries 402 and 404
receives a control valve 190, by means of which the pressure of the
"on-off" gallery 404 (and thus the corresponding lash adjuster
chambers 226) is selectively varied between atmospheric pressure
and the pressure of the constant supply gallery 402.
A pair of lateral bores 424 in the shaft 400 communicate the
gallery 402 with the lower bores 373 in the corresponding inlet
rocker arms 346 and 346a, and thus with the central chambers 222 of
the associated lash adjusters 76.
The control valves 190 in the four rocker arm shaft passageways 422
may be simultaneously actuated to collapse the lash adjusters 76 in
all the inlet rocker arms 346 and 346a when the cab switch 385 is
opened to de-energize the four solenoids 85a mounted on the rocker
arm shafts 400, to introduce excess clearance in the inlet valve
trains and increase the effective compression ratio to enhance
starting, as explained above in detail in connection with FIG. 19.
Opening the switch 385 also de-energizes the throttle limiting
solenoid 392 to limit the maximum engine speed while there is
excess clearance in the inlet valve trains, thus preventing
possible damage to the inlet valve gear components.
FIGS. 22-24 relate to another embodiment of the variable valve
timing system for improving the performance of an internal
combustion engine throughout the operating speed range by
optimizing the breathing in the lower and higher portions of the
operating speed range.
Each inlet cam 430 includes adjacent the cam base circle 431 a pair
of contours 432 and 433 (see FIG. 22B) which comprise auxiliary
opening and closing profiles, respectively, which are effective
during the high speed portion of the engine operating speed range,
as will be explained below. The high speed opening and closing
profiles 432 and 433 are between the cam base circle 431 and the
opening and closing profiles 434 and 435, respectively, which are
effective during the low speed portion of the operating speed
range.
Similarly, each exhaust cam 438 includes adjacent the cam base
circle 439 a pair of auxiliary opening and closing profiles 440 and
441 (see FIG. 22C), which are effective during the high speed
portion of the operating speed range, and which are between the cam
base circle 439 and the opening and closing profiles 442 and 443,
respectively, which are effective during the low speed portion of
the operating speed range.
FIG. 22A shows the cam profiles, as well as the lash and valve lift
obtained at low and high speeds. When the inlet and exhaust valve
gear trains are expanded during high speed operation so as to
provide only the lash indicated at 445 to accomodate changes in
valve train length due to temperature variations, the high speed
opening and closing profiles are effective to advance the opening
of the inlet and exhaust valves and to retard the closing thereof.
This increases the valve opening duration and causes the additional
valve lift indicated at 447 for the inlet and exhaust valves,
thereby providing additional breathing during the high speed
portion of the operating speed range.
When additional valve lash is introduced by collapsing the inlet
and exhaust valve gear trains so as to provide the total lash
indicated at 449, the high speed opening and closing profiles are
rendered ineffective, and the valve timing is determined by the low
speed opening profiles 434 and 442 and closing profiles 435 and
443. This reduces the valve opening duration and the valve lift to
provide the appropriate breathing for the low speed portion of the
operating speed range.
The variable valve timing system employing the inlet and exhaust
cams 430 and 438, respectively, to optimize breathing and improve
the engine performance throughout the useful operating speed range
is shown in FIG. 23. In the illustrative embodiment, the valve
timing system is employed with the same basic V-8 engine described
in the previous embodiments, and so identical parts bear the same
reference numerals.
Each of the cylinder heads 63-66 mounts a rocker arm shaft 450 (see
also FIG. 23A), which in turn mounts for rocking motion two exhaust
rocker arms 74 and 74a and two inlet rocker arms 346 and 346a. A
hydraulic lash adjuster 76 is mounted in each of the rocker arms,
and a control valve operating solenoid 85 is mounted on each rocker
arm shaft 450. The construction and operation of the lash adjuster,
the solenoid and these rocker arms have been described in detail in
connection with the previous embodiments.
Each rocker arm shaft 450 has a constant oil supply gallery 452,
plugged at each end by a plug 453, and an "on-off" gallery 455,
plugged at each end by a plug 456. Pressurized oil is supplied to
the gallery 452 from the oil pump 160 through the conduit 158, the
bore 164 in the bracket 131, and a lateral bore 458 in the rocker
arm shaft 450. Four lateral bores 460-463 constantly supply
pressurized oil from the constant supply gallery 452 through the
lower bores 373 and 178 in the inlet and exhaust rocker arms,
respectively, to the central chambers 222 in the hydraulic lash
adjusters 76 mounted therein.
A threaded bore 465 in the shaft 450 receives the control valve
190, which may be actuated by the solenoid 85 to control the
communication between the galleries 452 and 455 and to selectively
expose the "on-off" gallery 455 to atmospheric pressure, as
explained above in connection with the previous embodiments. Four
lateral bores 467-470 in the shaft 450 communicate the "on-off"
gallery 455 through the upper bores 383 and 210 in the inlet and
exhaust rocker arms, respectively, with the upper chambers 226 in
the lash adjusters 76 mounted therein.
The four solenoids 85 are simultaneously energized from the vehicle
battery 104 when an engine speed responsive switch 472 is closed.
The switch 472 is actuated by a conventional speed responsive
device 474 including a switch engaging plunger 475 having a collar
476. A spring 477 bears against one side of the collar and biases
the plunger 475 in the direction for opening the switch 472. A
plurality of flyweights 478 are driven by the engine through
conventional means (not shown), and as the weights revolve,
centrifugal force tends to move them outwardly about their pivots
480. The flyweight noses 482 bear against the side of the collar
476 remote from the spring 477, and outward movement of the
flyweights 478 drives the plunger 475 in the direction to close the
switch 472.
During the low speed portion of the engine operating speed range
the centrifugal force on the flyweights 478 is not sufficient to
close the switch 472, the solenoids 85 are de-energized, and the
hydraulic lash adjusters 76 are collapsed. Accordingly, the
relatively large amount of lash indicated at 449 (see FIG. 22A)
exists in the inlet and exhaust valve trains, and the shorter valve
opening duration and smaller valve lift obtain which are
appropriate for low speed operation.
When the engine reaches a predetermined speed at which the valve
lift and opening duration are to be increased to provide additional
breathing in the high speed range, the force of the flyweights 478
overcomes that of the spring 477, and the switch 472 is closed to
energize the four solenoids 85. The lash adjusters 76 are expanded
and locked, thereby extending the inlet and exhaust valve gear
trains and reducing the lash to that indicated at 445. The high
speed opening and closing profiles 432, 440, 433 and 441 are
rendered effective, thereby increasing the opening duration and
lift of the inlet and exhaust valves, and thus increasing the
breathing, volumetric efficiency and performance of the engine in
the upper operating speed range.
FIG. 24 illustrates the manner in which the performance of the
engine is improved, by showing the volumetric efficiency
characteristic. Thus, the curve 485 shows the volumetric efficiency
characteristic obtaining when the hydraulic lash adjusters 76 are
collapsed and the relatively large amount of lash indicated at 449
exists in the inlet and exhaust valve trains. Under these
conditions the valve opening and closing times are determined by
the low speed opening and closing profiles 434, 442, 435 and 443.
This valve timing maximizes the volumetric efficiency during the
low speed portion of the operating speed range.
When the predetermined engine speed indicated at 486 is reached,
the speed responsive switch 472 is closed, energizing the solenoids
85 to expand the hydraulic lash adjusters, and thus the inlet and
exhaust valve trains, thus reducing the lash to that shown at 445.
This renders the high speed opening and closing profiles 432, 440,
433, and 441 effective, thereby increasing the valve opening
duration and valve lift to provide the volumetric efficiency
characteristic shown by the curve 487, in which the volumetric
efficiency is maximized during the high speed portion of the
operating speed range.
The speed at which the valve timing is shifted depends upon the
characteristics of the particular engine and locations at which the
low speed and high speed opening and closing profiles are formed in
the cams. For an engine having a useful operating speed range of
1,200-2,400 RPM, for example, the valve timing shift speed might be
approximately 1,900 RPM.
FIG. 25 illustrates an arrangement in which the variable valve
timing system incorporates a modulated engine braking effect with a
system for varying the valve timing in accordance with engine speed
in order to improve the engine performance throughout the operating
speed range. This system is incorporated in the same basic V-8
engine used to illustrate the previous embodiments.
Each of the cylinder heads 63-66 mounts the rocker arm shaft 400,
upon which are mounted the exhaust rocker arms 74 and 74a and the
inlet rocker arms 346 and 346a, as in the embodiment described
above in connection with FIG. 21. As before, the exhaust cams 42
drive the exhaust rocker arms, the hydraulic lash adjusters of
which are controlled by the "on-off" gallery 403 from the
corresponding one of the brake pedal switches 93-96 to provide the
graduated engine braking effect illustrated by the curves 123-126
of FIG. 6.
The lash adjusters 76 mounted in the inlet rocker arms 346 and 346a
are simultaneously controlled by the "on-off" gallery 404 from the
four solenoids 85a, as in the FIG. 21 embodiment, but the inlet
rocker arms are driven by the inlet cams 430 and the solenoids 85a
are energized by the speed responsive switch 472, as in the FIG. 23
embodiment. Accordingly, the timing of the inlet valves is
automatically adjusted in accordance with the engine speed to
improve the engine performance throughout the useful operating
speed range.
It is to be understood that the above-described embodiments are
susceptible to modifications, substitutions and changes by those
skilled in the art without departing from the spirit and scope of
the invention. For example, pneumatic or hydraulic control
circuitry could be substituted for part or all of the electrical
control circuitry, and fluidic control devices could be substituted
for the illustrated switching and valving. Also, the contol valving
for the hydraulic lash adjusters could be mounted in other rocker
arm support structures, such as the rocker arm shaft supporting
brackets, or the individual ball pivots supporting the rocker arms
where there is no rocker arm shaft, for example.
Similarly, the lash adjuster control valving could be mounted
independently of, but adjacent to, the rocker arm support
structure, external conduits coupling the control valving with the
lash adjusters through the rocker arm shaft, or directly through
the rocker arms, a flexible hose or a slip joint being provided
between each rocker arm and the external conduit. Also, such
external control valving and conduits could be employed to control
the lash adjusters in the inlet rocker arms to vary the timing of
the inlet valves to enhance starting or to increase engine
performance, while the lash adjusters in the exhaust rocker arms
are controlled by control valving and conduits in the rocker arm
shaft, for example.
Furthermore, equivalent valve elements could be substituted for the
ball valve element in the control valves and the ball check valve
in the hydraulic lash adjusters. Also, other conventional
adjustable, normally open centrifugal switches could be substituted
for the speed responsive switch 472, such as an off-center weighted
spring leaf carrying the necessary contact points or activating a
microswitch, for example. In addition, the face of each piston
could be suitably recessed to accommodate the additional valve lift
when the valve gear trains are expanded, thereby preventing
engagement between the valve head and the piston, rather than
recessing the valve seat inserts 73.
It is also to be understood that the hydraulic lash adjusters could
be independent of the gear train by which the valves are
reciprocated during normal operation, the lash adjusters being
mounted in operative relation to auxiliary opening and closing
profiles which are formed on auxiliary cams remote from the cams
which determine the normal valve timing. In such modification, the
lash adjusters would be expanded to render the auxiliary opening
and closing profiles effective for engine braking, to enhance the
starting of a relatively low compression ratio engine, or to adjust
the valve timing in accordance with engine speed to improve engine
performance. Accordingly, all such substitutions and modifications
are to be included in the scope of the invention as defined by the
following claims.
* * * * *