U.S. patent application number 12/137207 was filed with the patent office on 2009-12-17 for cam-driven hydraulic lost-motion mechanisms for overhead cam and overhead valve valvetrains.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS, INC.. Invention is credited to Burak A. Gecim, John I. Manole.
Application Number | 20090308340 12/137207 |
Document ID | / |
Family ID | 41413605 |
Filed Date | 2009-12-17 |
United States Patent
Application |
20090308340 |
Kind Code |
A1 |
Gecim; Burak A. ; et
al. |
December 17, 2009 |
Cam-Driven Hydraulic Lost-Motion Mechanisms for Overhead Cam and
Overhead Valve Valvetrains
Abstract
A valve operating system includes a cam and a roller follower.
An input piston is spring-biased to follow motion of the roller
follower. A hydraulic chamber filled with fluid selectively
transfers motion from the input piston to an output piston
operatively engaged with a poppet valve. A variable-bleed valve is
in fluid communication with the hydraulic chamber and an outlet
channel and configured to selectively vary a bleed rate between the
hydraulic chamber and outlet channel. Displacement of the input
piston into the hydraulic chamber causes movement of the output
piston, depending on the bleed rate. A pushrod may transfer motion
from the roller follower to the input piston. A hydraulic damping
shoulder may restrict the closing velocity of the output piston.
The system may be further characterized by an absence of a rocker
arm. An auxiliary piston may replace the variable-bleed orifice in
the lost-motion hydraulic linkage.
Inventors: |
Gecim; Burak A.; (Rochester
Hills, MI) ; Manole; John I.; (Chesterfield,
MI) |
Correspondence
Address: |
Quinn Law Group, PLLC
39555 Orchard Hill Place, Suite 520
Novi
MI
48375
US
|
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS,
INC.
Detroit
MI
|
Family ID: |
41413605 |
Appl. No.: |
12/137207 |
Filed: |
June 11, 2008 |
Current U.S.
Class: |
123/90.57 |
Current CPC
Class: |
F01L 13/0005 20130101;
F01L 1/185 20130101; F01L 13/0031 20130101; F01L 9/11 20210101;
F01L 1/14 20130101; F01L 9/14 20210101; F01L 1/146 20130101; F01L
2001/34446 20130101; F01L 9/12 20210101; F01L 2305/00 20200501 |
Class at
Publication: |
123/90.57 |
International
Class: |
F01L 1/245 20060101
F01L001/245 |
Claims
1. A valve operating system for an internal combustion engine
comprising: a cam; a roller follower configured to follow motion of
said cam san input piston spring-biased to follow motion of said
roller follower; an output piston operatively engaged with a poppet
valve for opening said poppet valve; a hydraulic chamber filled
with a fluid; and a variable-bleed valve in fluid communication
with said hydraulic chamber and an outlet channel, wherein said
variable-bleed valve is configured to selectively vary a bleed rate
between said hydraulic chamber and said outlet channel; wherein
said input piston, output piston and variable-bleed valve are in
fluid communication with said fluid in said hydraulic chamber, such
that displacement of said input piston into said hydraulic chamber
causes a proportional displacement of said output piston, and said
proportional displacement of said output piston is dependent on
said bleed rate.
2. The valve operating system of claim 1, further comprising an
end-pivoted finger carrying said roller follower, wherein said
end-pivoted finger has a first end configured to transfer motion of
said end-pivoted finger to said input piston; and a lash adjuster
pivotably attached to a second end of said end-pivoted finger;
wherein said roller follower is disposed between said first end and
second end, such that the motion of said cam is proportionally
transferred to said input piston.
3. The valve operating system of claim 2, wherein said lash
adjuster is a mechanical lash adjuster.
4. The valve operating system of claim 2, wherein said cam is an
overhead cam.
5. The valve operating system of claim 1, further comprising: a
center-pivoted finger carrying said roller follower, wherein said
center-pivoted finger has a first end configured to transfer motion
of said center-pivoted finger to said input piston and said roller
follower is disposed on a second end; and a pivot member disposed
between said first end and said second end, such that the direction
of motion of said cam is changed as motion is transferred through
said center-pivoted finger to said input piston.
6. The valve operating system of claim 5, wherein said cam is an
overhead cam.
7. The valve operating system of claim 1, further comprising a
pushrod interposed between said roller follower and said input
piston, such that motion of said cam is transferred through said
pushrod to said input piston.
8. The valve operating system of claim 7, further comprising: a
valve spring biasing said output piston toward a closed position;
and a hydraulic damping shoulder interposed between said output
piston and said hydraulic chamber, wherein said hydraulic damping
shoulder is configured to restrict the velocity of said output
piston in proximity to said closed position.
9. The valve operating system of claim 8, further comprising a
pressure accumulator in fluid communication with said outlet
channel.
10. The valve operating system of claim 7, further characterized by
an absence of a rocker arm.
11. An internal combustion engine valve operating system
comprising: a cam; a roller follower configured to follow motion of
said cam; an input piston spring-biased to follow motion of said
roller follower; an output piston operatively engaged with a poppet
valve for opening said poppet valve; a hydraulic chamber filled
with a fluid; and an auxiliary piston in fluid communication with
said hydraulic chamber and movable with respect to an adjustable
stop member; wherein said input piston, output piston and auxiliary
piston are in fluid communication with said fluid in said hydraulic
chamber, such that displacement of said input piston into said
hydraulic chamber causes movement of said output piston and/or said
auxiliary piston, depending on the adjusted position of said
adjustable stop member, while the volume of fluid in said control
chamber remains substantially constant.
12. The valve operating system of claim 11, further comprising a
pushrod interposed between said roller follower and said input
piston, such that motion of said cam is transferred through said
pushrod to said input piston.
13. The valve operating system of claim 12, further characterized
by an absence of a rocker arm.
14. The valve operating system of claim 13, further comprising: a
valve spring biasing said output piston toward a closed position;
and a hydraulic damping shoulder interposed between said output
piston and said hydraulic chamber, wherein said hydraulic damping
shoulder is configured to restrict the velocity of said output
piston in proximity to said closed position.
15. The valve operating system of claim 14, further comprising a
pressure accumulator in fluid communication with said outlet
channel.
Description
TECHNICAL FIELD
[0001] This disclosure relates to cam-driven, variable valve
timing, valvetrains for internal combustion engines.
BACKGROUND OF THE INVENTION
[0002] Variable valve actuation timing seeks to adjustably control
valve lift and timing during cam rotation in an internal combustion
engine. At low engine speeds, it may be desirable to reduce cam
lift and/or delay valve-open timing to minimize the amount of air
drawn into the cylinder to increase efficiency and improve
torque.
SUMMARY
[0003] A valve operating system for an internal combustion engine
is provided, including a cam and a roller follower configured to
follow the oscillatory motion of the cam. An input piston is
spring-biased to follow motion of the roller follower. A hydraulic
chamber filled with fluid selectively transfers motion from the
input piston to an output piston operatively engaged with a poppet
valve for opening the poppet valve. A variable-bleed valve is in
fluid communication with the hydraulic chamber and an outlet
channel. The variable-bleed valve is configured to selectively vary
a bleed rate between the hydraulic chamber and outlet channel,
which allows volumetric and pressure control over the fluid in the
hydraulic chamber. The input piston, output piston and bleed valve
are all in fluid communication with the hydraulic chamber, such
that displacement of the input piston into the hydraulic chamber
causes movement of the output piston, depending on selection of the
bleed rate.
[0004] A pushrod may be interposed between the roller follower and
the input piston, such that motion of the cam is transferred
through the pushrod to the input piston. A valve spring may bias
the output piston toward a closed position, and a hydraulic damping
shoulder may be interposed between the output piston and hydraulic
chamber and configured to restrict the closing velocity of the
output piston. Additionally, the valve operating system may include
a pressure accumulator in fluid communication with the outlet
channel, and may be further characterized by an absence of a rocker
arm.
[0005] In another embodiment, an auxiliary piston is in fluid
communication with the hydraulic chamber and movable with respect
to an adjustable stop member. The auxiliary piston replaces the
variable-bleed orifice in the lost-motion hydraulic linkage. The
input piston, output piston and auxiliary piston are in fluid
communication with the fluid in the hydraulic chamber, such that
displacement of the input piston into the hydraulic chamber causes
movement of the output piston and/or auxiliary piston, depending on
the adjust position of the adjustable stop member, while the volume
of fluid in the control chamber remains substantially constant.
[0006] The above features and advantages and other features and
advantages of the present invention are readily apparent from the
following detailed description of the best modes and other
embodiments for carrying out the invention when taken in connection
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a cross-sectional view of an embodiment of a
cam-driven hydraulic lost-motion valvetrain having an overhead
camshaft valvetrain configuration with an end-pivoted roller finger
follower and a mechanical lash adjuster;
[0008] FIG. 2 is a cross-sectional view of another embodiment of a
cam-driven hydraulic lost-motion valvetrain having an overhead
camshaft valvetrain configuration with a center-pivoted roller
finger follower and no lash adjuster;
[0009] FIG. 3 is a cross-sectional view of another embodiment of a
cam-driven hydraulic lost-motion valvetrain having a pushrod,
overhead valve configuration with a roller lifter follower; and
[0010] FIG. 4 is a cross-sectional view of another embodiment of a
cam-driven hydraulic lost-motion valvetrain having an overhead
camshaft valvetrain configuration with an end-pivoted roller finger
follower and a mechanical lash adjuster, and having an auxiliary
piston mechanism for storing lost motion.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0011] Referring to the drawings, wherein like reference numbers
correspond to like or similar components throughout the several
figures, there is shown in FIG. 1 an embodiment of a cam-driven
hydraulic lost-motion valvetrain 10 (for simplicity, referred to
hereinafter as "valvetrain 10"). In this embodiment, valvetrain 10
is an overhead camshaft configuration.
[0012] A cam 12 drives a follower 14 creating an oscillatory
motion. The follower 14 is an end-pivoted roller finger follower. A
pivot end 16 (on the right, as viewed in FIG. 1) of the follower
14, having the form of a hemi-spherical socket, is pivoted on a
mechanical lash adjuster 18.
[0013] Lash compensation closes any gaps in fixed
cam-follower-to-valve connections. These gaps are designed
expansion joints and are normally closed by thermal expansion as
the engine heats up. Without some form of lash compensation, there
may be gaps between the moving elements of the valvetrain,
especially while the engine is cold, which may result in increased
noise or wear. Furthermore, valvetrain component wear may cause
gaps over time. A hydraulic lash adjuster is a mechanism which
closes gaps during both cold and hot operating conditions by using
pressurized fluid to move the lash compensator into contact with
the follower element, regardless of engine and valvetrain
temperature.
[0014] The mechanical lash adjuster 18 is a support element that
provides mechanical lash compensation. An initial adjustment,
usually at the time of assembly of the valvetrain 10, is made to
contact the mechanical lash adjuster 18 to the pivot end 16. Due to
the hydraulic characteristics (described in detail below) of the
valvetrain 10, it does not require a separate hydraulic
lash-compensating support element.
[0015] At the center of the follower 14 is a roller 20, through
which the oscillatory motion of cam 12 is transferred to follower
14. An alternative embodiment (not shown) the cam 14 would act
directly on a flat surface on top of (as viewed in FIG. 1) follower
14, which means that the contact surfaces between the cam 12 and
follower 14 are moving relative to each other.
[0016] Roller 20 maintains contact with cam 12 without relative
motion between the contact surfaces. In the valvetrain 10 shown,
therefore, the use of the roller 20 on the finger follower 14
yields lower valvetrain friction losses due to the elimination of
cam-to-follower contact friction. In other embodiments of a
cam-driven hydraulic lost-motion valvetrain, the cam 12 acts
directly on a flat surface that is integral with the input piston
24, such that there is no follower 14.
[0017] An input end 22 is on the opposing end of the follower 14
from the pivot end 16. The input end 22 has a defined radius of
curvature and contacts the tip of an input piston 24. As cam 12
rotates, the input piston 24 is driven in a reciprocating linear
motion by the follower 14 against a biasing spring 26, which
maintains contact between the input piston 24 and input end 22
(and, indirectly, the cam 12). With each rotation or event of the
cam 12, the roller 20 moves from riding on the base circle portion,
during which no axial displacement is transferred to the input
piston 24, to riding on the lift profile portion, during which the
follower 14 causes the input piston 24 to rise and fall.
[0018] The input piston 24 acts through a hydraulic linkage 28
(described in detail below) on an output piston 30. Depending upon
the settings of the hydraulic linkage 28, the output piston 30 is
driven in a reciprocating linear motion by the hydraulic linkage
28.
[0019] As shown in FIG. 1, the output piston 30 acts on a cylinder
valve 32, including a valve guide 34, a valve biasing spring 36, a
spring cap 38 and retainers 40. Cylinder valve 32 is a poppet valve
in the embodiment shown and may be an intake or exhaust valve for a
piston cylinder (not shown). Cylinder valve 32 and valve guide 34
are carried in a block 35. The output piston 30 is positioned
co-axially with the cylinder valve 32, and imparts its linear
motion to the cylinder valve 32. Those having ordinary skill in the
art will recognize that, while only one cylinder valve 32 is shown
in FIG. 1, the output piston 30 could act on multiple cylinder
valves 32, or that multiple output pistons 30 could each act on a
separate cylinder valve 32.
[0020] Although the cylinder valve 32 in this embodiment is shown
to be substantially aligned with the input piston 24, the two do
not have to be aligned. For example, the axis of cylinder valve 32
could be perpendicular to the axis of the input piston 24.
Furthermore, the centerlines of input piston 24 and cylinder valve
32 do not have to be on the same plane. One input piston 24 could,
for example, actuate two cylinder valves 32 of the same cylinder,
simultaneously. Those having ordinary skill in the art will
recognize that the tip geometry of the input piston 24 may be
comparable to the tip of a cylinder valve used in conventional
engines not having a hydraulic linkage.
[0021] The input and output pistons 24 and 30 hydraulically
communicate with each other through the hydraulic linkage 28. A
hydraulic fluid 42 having low compressibility, such as engine oil,
fills a high-pressure chamber 44, which is in fluid communication
with both the input piston 24 and output piston 30. The chamber 44
is located within a housing 45. Per rotation of cam 12, a fixed
volume of fluid 42 is displaced, every cycle, by the input piston
24.
[0022] Displacement by input piston 24 results in hydraulic
pressure generation in the chamber 44. If the chamber 44 is
otherwise closed--such that the volume of fluid 42 within the
chamber 44 remains essentially constant without substantial
leakage--and the hydraulic fluid 42 is substantially
incompressible, the output piston 30 will be displaced by an equal
volume. If the input and output pistons 24 and 30 have
substantially equal diameter (a hydraulic diameter ratio of 1:1)
the axial displacement of the input piston 24 results in a
substantially equal axial displacement of the output piston 30,
thereby displacing the cylinder valve 32 by the same distance.
[0023] A checked supply line 46 connects the chamber 44 to a
hydraulic pressure source, such as the oil pump (not shown), and
permits flow into the hydraulic linkage 28 when the pressure inside
the hydraulic linkage 28 falls below the supply pressure. A check
valve 48 located on the supply line 46 prevents backflow towards
the pressure source when the pressure inside of hydraulic linkage
28 is above the supply pressure.
[0024] Also shown in FIG. 1 is a variable-bleed orifice 50
configured to selectively vary the bleed rate of fluid 42 from the
chamber 44. In the embodiment shown in FIG. 1, the variable-bleed
orifice includes a flow control valve 52 configured to selectively
vary the size of a drain port 54 in fluid communication with the
chamber 44. Variable-bleed orifice 50 connects the fluid 42 to a
drain 56, which may connect to an oil sump (not shown) or a
pressure accumulator (not shown).
[0025] The flow control valve 52 shown in FIG. 1 is shown for
exemplary purposes only. Those having ordinary skill in the art
will recognize numerous types of valves, or combinations of valves,
that may be used within variable-bleed orifice 50 to selectively
control the bleed rate of fluid 42 from chamber 44.
[0026] Those having ordinary skill in the art will recognize that
neither the variable-bleed orifice 50 nor the drain 56 have to be
located in the either the block 35 or housing 45. The
variable-bleed orifice 50 need only be in fluid communication with
chamber 44 and the drain 56. Furthermore, the drain 56 may feed the
pressurized fluid 42 escaping chamber 44 into an accumulator which
supplies downstream components with pressurized fluid instead of
repressurizing fluid for those components directly with a pump.
Furthermore, the accumulator could also return the bled volume of
fluid 42 back to the hydraulic chamber 44 during the base-circle
event (during which the chamber 44 is repressurized).
[0027] The proportion of the displaced volume of fluid 42 converted
into motion of the output piston 30 is dependent on the bleed rate
through the variable-bleed orifice 50 to the drain port. The
principle of volume continuity requires that the sum of the bled
volume and the volume swept by the output piston 30 equals the
volume displaced by the input piston 24--neglecting any leakage and
fluid compressibility effects.
[0028] In one extreme, where the flow control valve 52 is set to
provide the largest variable-bleed orifice 50 opening, the
displaced input volume could equal the bled volume. At this
operating condition, all motion of the input piston 24 is lost in
the hydraulic linkage 28, and the output piston 30 and the cylinder
valve 32 remain stationary. This total lost-motion condition may be
used to completely deactivate the cylinder, or may be used to limit
intake or exhaust flow by deactivating one of multiple intake or
exhaust valves.
[0029] In the other extreme, the variable-bleed orifice 50 could
completely seal the drain port 54, enabling the transfer of the
entire input motion through the hydraulic linkage 28 to the output
piston 30 and the cylinder valve 32. This zero lost-motion
condition directly transfers lift of the cam 12 to the cylinder
valve 32 as if the hydraulic linkage 28 were a mechanical linkage.
For any intermediate setting of the variable-bleed orifice 50 by
the flow control valve 52, displacement is proportionally
transferred from the input piston 28 to the output piston 30, and
different cylinder valve 32 lift profiles are achieved, from no
lift (valve deactivation due to total lost-motion) to full lift
(relative to the lift profile of the cam 12).
[0030] Those having ordinary skill in the art will recognize that
even where the variable-bleed orifice 50 has completely closed the
drain port 54 for the zero lost-motion condition, the linear
displacement of the input and output pistons 24 and 30 may not be
exactly equal. Leakage of fluid 42 from the chamber 44 will reduce
the displaced volume transferred to outlet piston 30, and
compression of the (non-ideal) fluid 42 may also reduce the
displacement of outlet piston 30.
[0031] Those having ordinary skill in the art will recognize
that--even in a perfectly sealed chamber 44 filled with an
incompressible fluid 42--displacement of the output piston 30 is
dependent upon the hydraulic diameter ratio of the input and output
pistons 24 and 30. Matching linear displacement of the valve 32
(through the output piston 30) to the axial displacement of the cam
12 (through linear displacement of the input piston 24), dictates a
1:1 ratio of hydraulic diameters. The linear displacement ratio of
the input piston 24 over the output piston 30 is equal to the ratio
of the area of output piston 30 over the area of input piston 24
(if there is no lost motion).
[0032] Where the input and output pistons 24 and 30 are not equal
in diameter, the linear displacement ratio is inversely related to
the hydraulic diameter ratio. For example, where the hydraulic
diameter ratio (input:output diameter) is 2:1, the output piston 30
will have four times the linear displacement of the input piston 24
(the input:output linear displacement ratio will be 1:4). A
configuration having a smaller output piston 30 allows a relatively
smaller cam 12, because displacement of the input piston 24 is
multiplied through the hydraulic linkage 28 to result in larger
displacement of the cylinder valve 32.
[0033] In operation, the volume displaced by the input piston 24
equates approximately to the summation of the volumes displaced by
the output piston 30 and the volume lost through the variable-bleed
orifice 50. A small amount of volumetric loss results from fluid
compressibility and leakage through piston-to-wall clearances and
other sealing surfaces. The input motion from the cam 12 has a
fixed displacement-time characteristic determined from the cam
profile. However, the output motion of the cylinder valve 32 can be
varied by controlling the variable-bleed orifice 50.
[0034] Coming off of the base circle of the cam 12, at the start of
the down stroke (into the chamber 44) of the input piston 24, the
fluid 42 in chamber 44 is pressurized, and the check valve 48 is
sealed. The rate of pressure increase depends on the bleed rate
through variable-bleed orifice to the drain 56 because it takes
time for the fluid 42 to flow out of the chamber 44.
[0035] The pressure gradually rises to a level just enough to
overcome the preload of the valve biasing spring 36, and the
cylinder valve 32 lifts off. Subsequently, pressure in chamber 44
continues to increase while input piston 24 continues to be forced
into chamber 44, further compressing the spring 36 and lifting the
cylinder valve 32. Simultaneous with the valve motion, the bleed
off of fluid 42 to the drain 56 continues.
[0036] As long as the pressure in chamber 44 applies a force to
output piston 30 greater than the spring force of valve biasing
spring 36, the cylinder valve 32 will continue to lift. Those
having ordinary skill in the art will recognize that the spring
force of valve biasing spring 36 increases with displacement of
spring, and that the force on output piston 30 is equal to the
pressure in chamber 44 divided by the area of output piston 30.
When the force applied to output piston 30 is less than the spring
force of valve biasing spring 36, the cylinder valve 32 begins to
close under the force of valve biasing spring 36.
[0037] Partial lifts of cylinder valve 32 correspond to rotations
of the cam 12 in which the cylinder valve 32 is displaced a shorter
distance than, or stays open for less time then, the lift profile
of the cam 12 would directly provide. The partial lifts occur
whenever the variable-bleed orifice 50 allows fluid 42 to bleed off
of the hydraulic linkage 28 during the lift profile of cam 12.
[0038] Maximum lift of cylinder valve 32 is achieved when the force
on output piston 30 reaches a level corresponding to the spring
force of valve biasing spring 36 at that displacement. The maximum
pressure in chamber 44 is determined by the variable-bleed orifice
50 setting and the rate of input piston (24) motion. Maximum lift
of cylinder valve 32 always occurs at or before the time of maximum
lift of the cam 12. Also, the time of cylinder valve 32 liftoff is
always at or before maximum velocity of the profile of cam 12.
[0039] The cylinder valve 32 will not continue to open if the input
piston 24 is already into its return motion (upward in FIG. 1).
Given a fixed bleed rate (corresponding to a fixed position of
variable-bleed orifice 50), if the pumping rate of the input piston
24 isn't sufficient to create enough pressure to overcome the
preload of valve biasing spring 36 at input piston's (24)
highest-speed point, then the cylinder valve 32 will not liftoff
during the remainder of the cam 12 rotation event.
[0040] The closing motion (upward in FIG. 1) of the cylinder valve
32 is primarily governed by the balance of the spring force of
valve biasing spring 36 and the pressure in the chamber 44. With
smaller bleed rates, the cylinder valve 32 starts to close while
the input piston 24 is in down stroke, but continues with the
closing motion while the input piston 24 is also returning. In this
case, the bled volume is smaller and accounts for the difference in
rates of return of the output and the input pistons 30 and 24.
[0041] With larger bleed rates to drain 56, the cylinder valve 32
could close completely while the input piston 24 is still in the
down-stroke motion. In this case, the bled volume to drain 56
accounts for the sum of the volumes swept by the input piston 24 in
down stroke and the output piston 30 in return.
[0042] At the end of each event (rotation through the lift profile
portion of cam 12), when the cam 12 is on the base circle and the
cylinder valve 32 seated, the check valve 48 opens and permits flow
into the chamber 44 to replenish the bled volume of fluid 42.
[0043] At very high camshaft rotation speeds, if there are large
drag forces acting on the piston-bore clearances, the high-pressure
chamber could cavitate, causing the check valve 48 to open and
allow supply oil from supply line 46 to come in while the cylinder
valve 32 is still open. This accelerates valve closing as the
pressure is now lower than the spring force of valve biasing spring
36, and violates the volume continuity causing a temporary
"pump-up" of the system. Subsequently, on the cam 12 base circle,
there should be enough time to bleed off the excess volume of fluid
42 to properly seat the cylinder valve 32 for the next cam
event.
[0044] During partial lifts of cylinder valve 32, at the time of
valve closing the valve seating isn't controlled by the closing
ramps of cam 12. Hence, a damper mechanism 58 may be incorporated
into the output piston 30 or adjacent portions of chamber 44 to
trap fluid 42 in a damper chamber formed between the output piston
30 and the housing 45.
[0045] During valve closing, at a pre-designed distance from the
valve seat, the cylinder valve 32 is slowed down by gradual
engagement of the output piston 30 into the housing 45. The trapped
fluid 42 between the output piston 30 and the adjacent walls of the
housing 45 bleeds back into the chamber 44 through a constricted
passage 59 in the output piston 30. Fluid viscosity restricts the
ability of fluid to quickly flow through the passage 59 and creates
a force on the output piston 30 opposing the valve biasing spring
36. Those having ordinary skill in the art will recognize several
applicable damper designs. Designing the distance between the
output valve 30 and seat at the start of the damping, and the
damping rate, may require application-specific attention, because
the valvetrain 10 will operate at different temperatures (fluid
viscosity) and speeds.
[0046] The mode of operation of valvetrain 10 described above can
be called a semi-active mode of control as different bleed rates
can be set for different engine conditions, but the rates are not
modulated per cam event. In this mode of operation, initial
duration of pressure build up during the input piston 24 down
stroke enables late intake valve opening (LIVO) strategy. The
cylinder valve 32, due to lost motion, always closes at or before
the closing point of the cam 12, enabling the early intake valve
closing strategy (EIVC). The two attributes combined allow control
over the duration of opening cylinder valve 32, which enables
non-throttled engine load control.
[0047] Charge control at the cylinder valve 32 also helps to
eliminate partial load engine-pumping losses. The lower valve lifts
associated with shorter valve-open durations, a capability of
valvetrain 10, assist in achieving acceptable high speed dynamics
of valvetrain 10. In the semi-active mode of operation, with a
given design, the variable-bleed orifice 50 setting is the only
control parameter at a given engine speed. Maximum valve lift,
opening and closing points, and hence the valve-open duration, are
not independently controllable.
[0048] In an active mode of control, the bleed rate can be
modulated per event. Changing the bleed rate from a higher to a
lower value in the early down stroke of the input piston 24 could
yield later opening without affecting maximum lift and valve-open
duration. Conversely, keeping the bleed orifice sealed (or allowing
only very small bleed rates) early in the input down stroke
followed by a rapid increase in bleed rate would yield early
opening of intake valve (for intake/exhaust overlap control)
combined with early closing and shorter duration.
[0049] FIG. 2 shows a second embodiment of a cam-driven hydraulic
lost-motion valvetrain 210. In this embodiment, valvetrain 210 is a
center-pivoted roller finger follower valvetrain configuration.
Many of the operating principles of this embodiment are the same as
those described in detail above for the valvetrain 10 with the
end-pivoted configuration.
[0050] A roller 220 is located on one end of a follower 214 and
follows motion of a cam 212. The follower 214 pivots about a center
pivot 216 and transfers oscillatory motion of the cam 212 to an
input piston 224 via an input end 222. As in valvetrain 10, the
valvetrain 210 does not require a separate hydraulic lash
adjustment element. Lash compensation occurs via pressure in a
high-pressure chamber 244 and the spring force of a biasing spring
226.
[0051] The input piston transfers its linear movement through a
hydraulic linkage 228 to an output piston 230 which is attached to
a cylinder valve 232 operating against the force of a valve biasing
spring 236. A variable-bleed orifice 250 alters the displacement of
output piston 230 by selectively allowing a fluid 242 to be bled
from the chamber 244 into a drain 256 in a block 235. Valvetrain
210 may also include a hydraulic damping shoulder 258 and a fluid
passage 259 to restrict closing and seating velocity of the
cylinder valve 232 following partial lift events.
[0052] Referring now to FIG. 3, there is shown a third embodiment
of a cam-driven hydraulic lost-motion valvetrain 310. In this
embodiment, valvetrain 310 is a push-rod, overhead valve
configuration. Many of the operating principles of this embodiment
are similar to those described in detail above for the valvetrains
10 and 210.
[0053] In the valvetrain 310, the conventional rocker arm normally
used in overhead valve configurations is replaced by a hydraulic
linkage 328, effectively yielding a variable rocker ratio
mechanism. For the same motion of an input piston 324, a
continuously-variable displacement of an output piston 330
achievable.
[0054] The finger-type follower (14 and 214) used in valvetrains 10
and 210 is replaced with a lifter 313 and a pushrod 315 (shown in
FIG. 3 with interrupted lines, as the length of pushrod 315 may be
much longer than shown) which drives the input piston 324. A cam
312 transfers oscillatory motion to a roller 320 attached to the
lifter 313. Lash compensation is provided--without a separate
mechanical or hydraulic lash adjuster element--by fluid 342 in
chamber 344 and a biasing spring 326.
[0055] A variable-bleed orifice 350 selectively alters motion
transfer through the hydraulic linkage 328 by bleeding fluid 342 to
a drain 356. In the embodiment shown in FIG. 3, the drain 356 and
chamber 344 are in a housing 345 located above the lifter 313 and
cam 312. A checked oil supply 346 located in an engine block 335
repressurizes fluid 342 when a check valve 348 opens. Valvetrain
310 may also include a hydraulic damping shoulder 358 and a fluid
passage 359 to restrict closing and seating velocity of the
cylinder valve 332 following partial lift events.
[0056] Valvetrain 310 may be adapted to existing pushrod, overhead
valve engines. Removal of the rocker mechanism may allow the
hydraulic linkage 328 to be packaged into the space already
available on the engine head. Adding valvetrain 310 to an existing
overhead valve configuration may require minimal changes to the
rest of the valvetrain.
[0057] Referring now to FIG. 4, there is shown a fourth embodiment
of a cam-driven hydraulic lost-motion valvetrain 410. In this
embodiment, valvetrain 410 is an overhead camshaft configuration
having an end-pivoted roller finger follower, similar to the
valvetrain 10 of FIG. 1. A cam 412 acts on a roller 420 attached to
an end-pivoted follower 414 with a mechanical lash adjuster 418.
Oscillatory motion of the cam 412 is transferred by an input piston
424 to an output piston 430 and cylinder valve 432 through a
hydraulic linkage 428.
[0058] A high-pressure chamber 444 contains a hydraulic fluid 442.
Valvetrain 410, however, does not contain a variable-bleed orifice
to drain fluid 442 from the chamber 444. Instead of bleeding fluid
442 in order to decrease volume displacing the output piston 430
(and thereby causing motion loss), the valvetrain 410 contains an
auxiliary piston 460 in fluid communication with chamber 444. The
auxiliary piston is biased toward the chamber 444 by an auxiliary
piston spring 462. A variable stop 464 extends into the auxiliary
piston 460 and is configured to selectively restrict the allowable
displacement (right to left, as viewed in FIG. 4) of the auxiliary
piston 460. Those having ordinary skill in the art will recognize
that other embodiments--such as, for example, those having
center-pivoted or pushrod configurations--may also utilize an
auxiliary piston instead of a variable-bleed orifice.
[0059] Accordingly, the input piston 424, output piston 430, and
auxiliary piston 460 are all in continuous contact with the fluid
442 in the chamber 444 such that these pistons 424, 430, 460 are in
fluid communication with each other. The trapped volume of fluid
442 inside the control chamber 444 may be replenished through a
check valve 448 to compensate for leakage. By replacing the
variable-bleed orifice with the auxiliary piston 460, the
valvetrain 410 is able to store the lost-motion energy and
repressurize the chamber 444 following the cam event.
[0060] In operation, the volume displaced by the input piston 424
equates approximately to the summation of the volumes displaced by
the auxiliary piston 460 and output piston 430. A small amount of
volumetric loss may result from fluid compressibility and leakage
through piston-to-wall clearances. As is known in the relevant art,
the input motion from the cam 412 has a fixed displacement-time
characteristic determined from the cam profile. However, the output
motion of the cylinder valve 432 can be varied by controlling the
motion of auxiliary piston 460.
[0061] One of the two operating parameters that control the
displacement of auxiliary piston 460 is the relative specific force
(i.e., force per unit piston area) of the valve biasing spring 436
and auxiliary piston spring 462. Where auxiliary piston spring 462
has lower relative specific force, it will be displaced further by
less pressure in the chamber 444.
[0062] The other controlled parameter is the displacement of the
variable stop 464, which serves as a dead stop that limits the
displacement of the auxiliary piston 460. Therefore, if the
variable stop 464 is set to allow no movement of auxiliary piston
460, all volume displaced by the input piston 424 will displace
only the output piston 430, and the hydraulic linkage 428
essentially mimics a mechanical linkage.
[0063] Specifying the diameters of each one of the input piston
424, auxiliary piston 460, and output piston 430 determines their
individual linear displacements per fixed cam 412 displacement.
Once the piston dimensions are fixed, the cylinder valve 432 timing
(e.g., valve opening point) can be determined by selection of the
relative values for the valve and auxiliary biasing springs 436 and
462. For a late intake valve opening (LIVO) strategy, the auxiliary
piston's (460) specific preload, has to be smaller than that of the
valve biasing spring 436. This will cause a delay in the opening
point of the cylinder valve 432 where displaced volume of the input
piston 424 approximately equals the displaced volume of the
auxiliary piston 460 until the auxiliary piston 460 contacts
variable stop 464.
[0064] The exact timing of the cylinder valve 432 liftoff is
controlled by the dead stop function of the variable stop 464. As
motion of the auxiliary piston 460 is stopped or slowed, more (or
all) of the volume displaced by input piston 424 must be displaced
by output piston 430. By selectively adjusting variable stop 464 to
allow more displacement of the auxiliary piston 460, more motion is
lost into the auxiliary piston 460 and is not available to displace
the output piston 430 and cylinder valve 432.
[0065] A fifth embodiment (not shown) of a cam-driven hydraulic
lost-motion valvetrain could include a hydraulic network linking
the high-pressure chambers of adjacent cylinders in the engine.
Selectively allowing fluid passage between the chambers may allow
further variability in the lost-motion hydraulic linkages. Those
having ordinary skill in the art will recognize benefits of
hydraulic networks linking the high-pressure chambers of multiple
cylinders, such as, without limitation: bleeding pressure to an
adjacent chamber instead of the drain; repressurizing the chamber
during a cam event without altering the variable-bleed orifice; or
by quickly restoring pressure to the high-pressure chamber.
[0066] While the best modes and other embodiments for carrying out
the claimed invention have been described in detail, those familiar
with the art to which this invention relates will recognize various
alternative designs and embodiments for practicing the invention
within the scope of the appended claims.
* * * * *