U.S. patent application number 14/075926 was filed with the patent office on 2015-05-14 for lubricating configuration for maintaining wristpin oil pressure in a two-stroke cycle, opposed-piston engine.
This patent application is currently assigned to Achates Power, Inc.. The applicant listed for this patent is Achates Power, Inc.. Invention is credited to John M. Kessler, Clark A. Klyza.
Application Number | 20150128920 14/075926 |
Document ID | / |
Family ID | 51795004 |
Filed Date | 2015-05-14 |
United States Patent
Application |
20150128920 |
Kind Code |
A1 |
Kessler; John M. ; et
al. |
May 14, 2015 |
Lubricating Configuration for Maintaining Wristpin Oil Pressure in
a Two-Stroke Cycle, Opposed-Piston Engine
Abstract
A lubricating configuration in a two-stroke cycle,
opposed-piston engine for a piston wristpin minimizes losses in oil
pressure at the wristpin as the piston approaches bottom center and
reduces the required oil supply pressure to the engine. The
wristpin is constructed to absorb and store oil pressure energy
when oil pressure at the wristpin is high, and to release that
stored energy to pressurize the oil at the wristpin when connecting
rod oil pressure is low.
Inventors: |
Kessler; John M.;
(Oceanside, CA) ; Klyza; Clark A.; (San Diego,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Achates Power, Inc. |
San Diego |
CA |
US |
|
|
Assignee: |
Achates Power, Inc.
San Diego
CA
|
Family ID: |
51795004 |
Appl. No.: |
14/075926 |
Filed: |
November 8, 2013 |
Current U.S.
Class: |
123/61R ;
123/65R |
Current CPC
Class: |
F01M 1/06 20130101; F01M
2011/0095 20130101; F01M 1/00 20130101; F01M 2011/021 20130101;
F02B 75/28 20130101; F01M 2001/066 20130101; F16J 1/16
20130101 |
Class at
Publication: |
123/61.R ;
123/65.R |
International
Class: |
F02B 75/28 20060101
F02B075/28 |
Claims
1. A lubricating configuration in a two-stroke cycle engine in
which a piston includes a bearing support structure with a bearing
surface, and a wristpin fixed to the small end of a connecting rod,
and the bearing support structure retains the wristpin for
oscillation in the bearing surface, the lubricating configuration
comprising: an internal oil reservoir in the wristpin in
communication with one or more wristpin oil outlet passages
operative to pass oil through the wristpin into an interface
between the wristpin and the bearing surface; at least one oil
pressure absorber disposed in the oil reservoir; a wristpin oil
inlet passage in communication with the oil reservoir; an oil
delivery passage in the connecting rod; and, a pressure-responsive
control device coupling the oil delivery passage with the wristpin
oil inlet passage; in which the pressure-responsive control device
is oriented so as to open for passage of oil into the reservoir
when oil pressure in the oil delivery passage exceeds the oil
pressure in the oil reservoir and to close otherwise.
2. The lubricating configuration of claim 1, in which the bearing
is one of a rocking wristpin bearing, a ladder bearing, a pressed
pin bearing, and a full floating wrist pin bearing.
3. The lubricating configuration of claim 1, in which the reservoir
is a generally cylindrical recess in the wristpin, closed at
opposite ends, and the oil pressure absorber is seated proximate
one end of the cylindrical recess.
4. The lubricating configuration of claim 3, in which the
cylindrical recess has an axis and a ledge with an annular surface
opposing the one end in a plane perpendicular to the axis, and the
oil pressure absorber includes: a piston disposed between the
annular surface and the one end for being moved therebetween, along
the axis, in response to a change in oil pressure in the reservoir;
and a spring compressed between the piston and the one end that
urges the piston toward the annular surface.
5. The lubricating configuration of claim 4, in which the
pressure-responsive control device is a check valve mounted to the
connecting rod, near the small end.
6. The lubricating configuration of claim 1, in which the reservoir
is a generally cylindrical recess in the wristpin, closed at
opposite ends, a first oil pressure absorber is seated proximate a
first end of the cylindrical recess, and a second oil pressure
absorber is seated proximate a second end of the cylindrical
recess.
7. The lubricating configuration of claim 6, in which the
cylindrical recess has an axis, a first ledge with an annular
surface opposing the first end in a plane perpendicular to the
axis, a second ledge with an annular surface opposing the second
end in a plane perpendicular to the axis, and each oil pressure
absorber includes: a piston disposed between a respective annular
surface a respective end for being moved therebetween, along the
axis, in response to a change in oil pressure in the reservoir; and
a spring compressed between the piston and the respective end that
urges the piston toward the respective annular surface.
8. The lubricating configuration of claim 7, in which the
pressure-responsive control device is a check valve mounted to the
connecting rod, near the small end.
9. The lubricating configuration of claim 1, in which the
pressure-responsive control device is one of a check valve, a
diaphragm valve, a swing or tilting disc valve, a lift or an
in-line valve, and a reed valve.
10. An opposed-piston engine comprising at least one cylinder with
longitudinally-separated exhaust and intake ports, a pair of
pistons disposed in opposition to one another in a bore of the
cylinder, and a pair of connecting rods, each piston being
connected to a small end of a respective connecting rod by a
wristpin, in which a lubricating configuration for each wristpin
comprises: an internal oil reservoir in the wristpin that
communicates with one or more wristpin oil outlet passages
operative to pass oil through the wristpin into an interface
between the wristpin and a bearing surface; an oil pressure
absorber disposed in the oil reservoir; a wristpin oil inlet
passage in communication with the oil reservoir; an oil delivery
passage in the connecting rod; and, a pressure-responsive control
device coupling the oil delivery passage with the wristpin oil
inlet passage; in which the pressure-responsive control device is
oriented so as to open for passage of oil into the reservoir when
oil pressure in the oil delivery passage exceeds the oil pressure
in the oil reservoir and to close otherwise.
11. The opposed-piston engine of claim 10, in which the bearing is
one of a rocking wristpin bearing, a ladder bearing, a pressed pin
bearing, and a full floating wrist pin bearing.
12. The opposed-piston engine of claim 10, in which the reservoir
is a generally cylindrical recess in the wristpin, closed at
opposite ends, and the oil pressure absorber is seated proximate
one end of the cylindrical recess.
13. The opposed-piston engine of claim 12, in which the cylindrical
recess has an axis and a ledge with an annular surface opposing the
one end in a plane perpendicular to the axis, and the oil pressure
absorber includes: a piston disposed between the annular surface
and the one end for being moved therebetween, along the axis, in
response to a change in oil pressure in the reservoir; and a spring
compressed between the piston and the one end that urges the piston
toward the annular surface.
14. The opposed-piston engine of claim 13, in which the
pressure-responsive control device is a check valve mounted to the
connecting rod, near the small end.
15. The opposed-piston engine of claim 10, in which the reservoir
is a generally cylindrical recess in the wristpin, closed at
opposite ends, a first oil pressure absorber is seated proximate a
first end of the cylindrical recess, and a second oil pressure
absorber is seated proximate a second end of the cylindrical
recess.
16. The opposed-piston engine of claim 15, in which the cylindrical
recess has an axis, a first ledge with an annular surface opposing
the first end in a plane perpendicular to the axis, a second ledge
with an annular surface opposing the second end in a plane
perpendicular to the axis, and each oil pressure absorber includes:
a piston disposed between a respective annular surface a respective
end for being moved therebetween, along the axis, in response to a
change in oil pressure in the reservoir; and a spring compressed
between the piston and the respective end that urges the piston
toward the respective annular surface.
17. The opposed-piston engine of claim 16, in which the
pressure-responsive control device is a check valve mounted to the
connecting rod, near the small end.
18. The opposed-piston engine of claim 10, in which the
pressure-responsive control device is one of a check valve, a
diaphragm valve, a swing or tilting disc valve, a lift or an
in-line valve, and a reed valve.
19. A method for lubricating a wristpin bearing of an
opposed-piston engine; in which the wristpin bearing couples a
piston to a connecting rod: transporting oil through an oil
passageway in the connecting rod to an internal oil reservoir in
the wristpin while the oil pressure in the connecting rod exceeds
the oil pressure in the internal oil reservoir; accumulating energy
in an oil pressure absorber disposed in the oil reservoir while oil
is transported into the internal oil reservoir; conducting oil from
the internal oil reservoir through one or more wristpin oil outlet
passages into an interface between the wristpin and a bearing
surface in response to transport of oil into the internal oil
reservoir; preventing the transport of oil from the internal oil
reservoir to the oil passageway while the oil pressure in the
connecting rod is equal to or less than the oil pressure in the
internal oil reservoir releasing energy from the oil pressure
absorber disposed in the oil reservoir while oil is prevented from
being transported to the oil passage; and, conducting oil from the
internal oil reservoir through the one or more wristpin oil outlet
passages into the interface between the wristpin and the bearing
surface in response to release of energy from the oil pressure
absorber.
20. A method for lubricating a wristpin bearing of an
opposed-piston engine; in which the wristpin bearing couples a
piston to a connecting rod: transporting oil through an oil
passageway in the connecting rod to an internal oil reservoir in
the wristpin during movement of the piston from a bottom center
(BC) location to a top center (TC) location; accumulating energy in
an oil pressure absorber disposed in the oil reservoir while oil is
transported into the internal oil reservoir; conducting oil from
the internal oil reservoir through one or more wristpin oil outlet
passages into an interface between the wristpin and a bearing
surface in response to transport of oil into the internal oil
reservoir; preventing the transport of oil from the internal oil
reservoir to the oil passageway during movement of the piston from
the TC location to the BC location releasing energy from the oil
pressure absorber disposed in the oil reservoir while oil is
prevented from being transported to the oil passage; and,
conducting oil from the internal oil reservoir through the one or
more wristpin oil outlet passages into the interface between the
wristpin and the bearing surface in response to release of energy
from the oil pressure absorber.
Description
RELATED APPLICATIONS
[0001] This application contains subject matter related to the
subject matter of U.S. patent application Ser. No. 13/136,955,
filed Aug. 15, 2011 for "Piston Constructions for Opposed-Piston
Engines," published as US 2012/0073526 on Mar. 29, 2012, and U.S.
patent application ser. No. 13/776,656, filed Feb. 25, 2013 for
"Rocking Journal Bearings for Two-Stroke Cycle Engines".
BACKGROUND
[0002] The field is lubrication management for two-stroke cycle
engines. More specifically the application relates to
implementation of a wristpin oil pressure recovery device for
pistons of a two-stroke cycle, opposed-piston engine.
[0003] Wristpins in reciprocating engines must be lubricated to
mitigate the risk of highly loaded asperity contact in the joint.
If asperity contact in the joint is sustained at high loads,
excessive friction, wear and even catastrophic failure is possible.
The applied load that causes this asperity contact is constantly
changing as engine speed and load change.
[0004] In some aspects of two-stroke cycle opposed-piston engine
operation, the nature of the cycle presents two distinct threats to
wristpin durability: continuous compression loading and oil
pressure variation.
[0005] Continuous compression loading results because load reversal
on the wristpin bearings of a two-stroke engine may never occur
during the normal speed and load range operation of the engine.
During operation of a two-cycle engine, a combustion event occurs
every cycle and there is nearly always a gas pressure loading the
crown of a piston near top center (TC), which, even at high piston
speeds, is still greater than the inertial force of the piston
assembly on a wristpin bearing. At the other end of the cycle, at
bottom center (BC), the inertial force of the piston assembly keeps
the bearing loaded as well. As a result, the bearing is nearly
always under positive load throughout the cycle, and it is
difficult to replenish it with oil. Furthermore, given limited
angular oscillation of the bearing, oil introduced between the
bearing surfaces does not completely fill the bearing. Eventually
the bearing begins to operate in a boundary layer lubrication mode
which leads to excess friction, wear, and then bearing failure.
[0006] Solutions to the first problem include bearing constructions
that cause separation of bearing parts in response to bearing
rotation. One such solution is disclosed in related U.S.
application Ser. No. 13/776,656: wristpins coupling the pistons of
an opposed-piston engine are constructed with rocking journal
bearings that provide biaxial rotation of bearing parts, which
separates the parts to allow introduction of oil between the
bearing surfaces. This bearing construction includes a reservoir in
the rocking journal that acts as an accumulator to receive and
maintain a volume of pressurized oil that is delivered to the
bearing parts via outlet passages through the journal. An inlet
passage in the journal for delivering oil to the accumulator is fed
from a high-pressure oil passage in the associated connecting rod.
Pressurized oil is transported to the oil passages of the
connecting rods from a main oil gallery in an engine block. Here,
the second problem becomes apparent.
[0007] As a pair of pistons move in opposition in a cylinder bore,
the pressurized oil fed to their respective wristpins undergoes
inertial loading that is most pronounced when the pistons change
direction in the reversal zones at their top center (TC) and bottom
center (BC) locations. Given the direction of motion from TC to BC
during a power stroke, the inertial load can cause the oil pressure
in the connecting rod oil passages to drop below a minimum level
for effective wristpin lubrication as the pistons reverse direction
at BC. Providing adequate oil pressure to lubricate the wristpins
throughout the operating cycle of an opposed-piston engine,
especially in the face of non-reversing loads, may require that the
supply pressure to the main oil gallery increase with engine speed
to overcome inertial forces on the oil column in the connecting
rod. Typically, the main oil gallery is fed from a positive
pressure pump, and it is possible to control the pump so as to vary
the supply pressure with the speed of the engine. However,
increasing engine-wide oil pressure solely for wristpin
lubrication, as the speed of the engine increases, may result in
oil pressure in excess of that required for the rest of the engine
lubrication system. This will result in higher parasitic loads for
the lubrication system and a higher
friction-mean-effective-pressure (FMEP) for the engine.
[0008] Accordingly, there is a need for maintaining oil pressure in
the oil reservoir of the wristpin of a two-stroke cycle,
opposed-piston engine during engine operation. It is particularly
desirable that the oil pressure be maintained at levels that
guarantee effective lubrication throughout the operating cycle, at
all engine speeds, without imposing excessive pumping losses on
engine performance.
SUMMARY
[0009] In order to minimize losses in oil pressure at the wristpin
as the piston approaches BC and reduce the required oil supply
pressure, a wristpin is constructed to absorb and store oil
pressure energy when oil pressure at the wristpin is high, and to
release that stored energy to pressurize the oil at the wristpin
when connecting rod oil pressure is low.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 schematic drawing of a prior art opposed-piston
engine with a pump-supplied oil gallery, and is appropriately
labeled "Prior Art"
[0011] FIG. 2 is a graph showing wristpin oil supply pressures
through one revolution from TC-to-BC-to-TC of a
compression-ignition, two-stroke cycle, opposed-piston engine for
various gallery oil pressures.
[0012] FIG. 3 is a side view, in perspective, of a
piston/connecting rod assembly for a two-stroke cycle,
opposed-piston engine according to the detailed description.
[0013] FIG. 4A is an axial sectional view taken along line A-A of
the piston and connecting rod of FIG. 3 showing a wristpin
lubricating configuration. FIG. 4B is a sectional view taken along
line B-B of FIG. 3.
[0014] FIG. 5 is an exploded view of the piston and connecting rod
showing elements of the wristpin lubricating configuration.
[0015] FIG. 6 is an enlarged sectional view, in perspective,
showing the wristpin partially disassembled.
[0016] FIG. 7 is an exploded view of the piston and connecting rod
showing elements of a pressure-responsive control device configured
to couple an oil delivery passage in the connecting rod with an oil
inlet passage in the wristpin
DETAILED DESCRIPTION
[0017] A two-stroke cycle engine is an internal combustion engine
that completes a power cycle with a single complete rotation of a
crankshaft and two strokes of a piston connected to the crankshaft.
One example of a two-stroke cycle engine is an opposed-piston
engine in which a pair of pistons is disposed in opposition in the
bore of a cylinder.
[0018] As seen in FIG. 1, an opposed-piston engine 49 has at least
one ported cylinder 50. For example, the engine may have one ported
cylinder, two ported cylinders, three ported cylinders, or four or
more ported cylinders. For purposes of illustration, the engine 49
is presumed to have a plurality of ported cylinders. Each cylinder
50 has a bore 52: exhaust and intake ports 54 and 56 are formed in
respective ends thereof. The exhaust and intake ports 54 and 56
each include one or more circumferential arrays of openings.
Exhaust and intake pistons 60 and 62 are slidably disposed in the
bore 52 with their end surfaces 61 and 63 opposing one another. The
exhaust pistons 60 are coupled to a crankshaft 71, and the intake
pistons are coupled to a crankshaft 72. Each of the pistons is
coupled to its associated crankshaft by a wrist pin 74 and a
connecting rod 76. When the pistons 60 and 62 of a cylinder 50 are
at or near respective TC locations, a combustion chamber is defined
in the bore 52 between the end surfaces 61 and 63 of the pistons.
Fuel is injected directly into the combustion chamber through at
least one fuel injector nozzle 100 positioned in an opening through
the cylinder's sidewall.
[0019] A lubrication system that supplies oil to lubricate the
moving parts of the engine 49 includes an oil reservoir 80 from
which pressurized oil is pumped by a pump 82 to a main gallery 84.
The main gallery supplies pressurized oil to the crankshafts 71 and
72, typically through drillings to the main bearings (not seen).
From grooves in the main bearings, pressurized oil is provided to
grooves in the big end bearings of the connecting rods 76. From
there, pressurized oil flows through drillings 77 in the connecting
rods to the wristpins 74.
[0020] The engine 49 is equipped with an air management system 51
that includes a supercharger 110 and a turbocharger 120. The
turbocharger has a turbine 121 and a compressor 122 rotating on a
common shaft 123. The turbine 121 is coupled to the exhaust
subsystem and the compressor 122 is coupled to the charge air
subsystem. Exhaust gas emptied into the conduit 125 from the
exhaust port 54 rotate the turbine 121. This rotates the compressor
122, causing it to generate charge air by compressing intake air.
The charge air output by the compressor 122 flows through a conduit
126, whence it is pumped by the supercharger 110 to the openings of
the intake port 56.
[0021] The operational cycle of an opposed-piston engine is well
understood. In response to combustion occurring between their end
surfaces 61, 63 the opposed pistons 60, 62 move away from their TC
locations in the cylinder. While moving from TC, the pistons keep
their associated ports closed until they approach respective BC
positions. The pistons may move in phase so that the exhaust and
intake ports 54, 56 open and close in unison; alternatively, one
piston may lead the other in phase, in which case the intake and
exhaust ports have different opening and closing times. As the
pistons move through their BC locations exhaust products flowing
out of the exhaust port 54 are replaced by charge air flowing into
the cylinder through the intake port 56. After reaching BC, the
pistons reverse direction and the ports are again closed by the
pistons. While the pistons continue moving toward TC, the charge
air in the cylinder 50 is compressed between the end surfaces 61
and 63. As the pistons advance to their respective TC locations in
the cylinder bore, fuel is injected through the nozzles 100 into
the charge air, and the mixture of charge air and fuel is
compressed between the pistons 60 and 62. When the mixture reaches
an ignition temperature, the fuel ignites. Combustion results,
driving the pistons apart, toward their respective BC
locations.
[0022] FIG. 2 is a graph that shows the oil pressures at the
wristpins of a representative opposed-piton engine during a full
cycle of the engine from a crank angle (CA) of 0.degree. at TC to
BC (180.degree. CA) and back to TC (360.degree. CA) for several
main gallery oil pressures. As can be seen in FIG. 2, for a given
gallery pressure, the oil pressure at the wristpins is at its
highest at TC and at its lowest at BC. If main gallery pressure is
below an engine-specific threshold, the pressure of the column of
oil in the connecting rod drilling supplying the wristpin will go
negative and the wristpin will not have pressurized oil available
until such time in the cycle that the column pressure is positive
again. As per FIG. 2, for a given engine geometry and crankshaft
speed a main gallery pressure below five bar results in the oil
pressure at the wristpin being negative at 180.degree. CA (BC). At
a main gallery oil pressure of five bar, the wristpin oil pressure
is slightly positive and at six bar the wristpin oil pressure is at
slightly above one bar which is the desired minimum pressure. A
three bar main gallery oil pressure may be sufficient for all other
lubrication systems in the engine, but a gallery oil pressure twice
that amount is required to adequately lubricate the wristpin
assembly during an entire engine cycle. With reference to FIG. 2,
it is desirable that the lubrication system of an opposed-piston
engine be configured to deliver lubricating oil in an amount
sufficient to guarantee oil availability to the wristpins during
the entire two-stroke engine cycle.
[0023] FIG. 3 is a perspective view of a piston assembly used in an
opposed-piston engine that shows the piston 200 and its associated
connecting rod 210. The piston 200 has a crown 206 attached to a
skirt 207. An end surface 208 of the crown is configured to form a
combustion chamber in cooperation with the end surface of an
opposing piston, when both pistons are at or near TC. See, for
example, the piston configurations described and illustrated in US
publication 2011/0271932 and WO publication 2012/158756, and the
piston configurations described and illustrated in U.S. application
Ser. No. 13/843,686 and U.S. application Ser. No. 14/026,931. The
connecting rod 210 has a large end 212 for coupling to a crank
throw of a crankshaft (not seen). An oil groove 214 in the large
end transports oil to a drilling in the shaft of the connecting
rod. As per FIGS. 4A, 4B, and 5, the piston 200 further includes a
bearing support structure 219 fixed to the lower surface of the
crown 206 and disposed in the recess formed by the skirt 207. The
bearing support structure 219 includes a generally cylindrical
bearing surface 220 that receives a wristpin 221 (also called a
"journal") mounted to the small end 215 of the connecting rod 210.
The wristpin 221 includes an internal oil reservoir 222 in
communication with one or more oil outlet passages 225 drilled
through the wristpin 221 and operative to pass oil from the
reservoir, through the wristpin and into an interface between the
wristpin and the bearing surface. In some aspects, best seen in
FIG. 4A, the oil reservoir 222 can be configured as a cylindrical
recess with opposing ends and an axis that corresponds to the axis
on which the wristpin 221 oscillates. Pressurized oil is
transported from the groove 214 for delivery to the oil reservoir
222 through an oil delivery passage 216 in the connecting rod
210.
Lubricating Configuration for Maintaining Wristpin Oil Pressure
[0024] A lubricating configuration for maintaining wristpin oil
pressure at a level sufficient to guarantee oil availability to the
wristpins of an opposed-piston engine during the entire two-stroke
engine cycle is illustrated by an embodiment shown in FIGS. 4A, 4B,
5, and 6. However, it should be understood that no aspect of the
embodiment is meant to be specifically limiting.
[0025] In this example, a lubrication configuration includes at
least one oil pressure absorber 250 disposed in the oil reservoir
222, a wristpin oil inlet passage 223 in communication with the oil
reservoir 222, the oil delivery passage 216 in the connecting rod
210, and a pressure-responsive control device 260. The
pressure-responsive control device 260 can be configured to couple
the oil delivery passage 216 with the wristpin oil inlet passage
223 for transport of oil into the reservoir 222 while oil pressure
in the oil delivery passage 216 slightly exceeds the oil pressure
in the oil reservoir 222, and to decouple the oil delivery passage
216 from the wristpin oil inlet passage 223 so as to block the
transport of oil from the reservoir 222 to the oil delivery passage
when oil pressure in the oil delivery passage 216 decreases with
respect to the oil pressure in the oil reservoir 222. Thus, while
the piston 200 moves from BC to TC and inertial forces cause the
oil pressure in the oil delivery passage 216 to rise and peak, the
oil delivery passage 216 is coupled with the wristpin oil inlet
passage 223 and the energy in the incoming surge in oil pressure is
absorbed by the oil pressure absorber 250. In response to the
surge, the oil pressure absorber 250 absorbs energy in such a
manner as to create additional space in the oil reservoir 222 for
more pressurized oil. While the piston 200 returns from TC to BC,
the inertial forces on the oil column in the oil delivery
passageway 216 reverse, whereby the oil pressure in the oil
delivery passageway 216 drops. When the oil pressure in the oil
delivery passage 216 begins to fall with respect to the oil
pressure in the reservoir, the oil delivery passage 216 is
decoupled from the wristpin oil inlet passage 223 so as to block
transport of oil from the reservoir to the oil delivery passage
216. The energy stored in the oil pressure absorber 250 is
released, causing the absorber to act on the oil stored in the oil
reservoir 222 by reducing the additional space, which maintains oil
pressure in the reservoir at a level sufficient to continue
separating and lubricating the wristpin/bearing surface interface
until the piston 200 reverses direction and the oil delivery
passage 216 is again coupled with the wristpin oil inlet
passage.
[0026] In a preferred embodiment, the oil pressure absorber 250 is
constructed to absorb energy by compressing, and to release stored
energy by expanding. In some aspects, seen in FIGS. 4A, 5, and 6,
an oil pressure absorber 250 is configured as a piston 251 with a
closed end 253 and a spring 256 disposed in the axial space of the
piston 251. The cylindrical recess forming the reservoir 222
includes a ledge 272 with an annular surface 273 opposing an end
274 of the wristpin 221 that is closed by a press-fit plug 276. The
annular surface 273 lies in a plane perpendicular to the axis 270,
which is shared by the wristpin and the cylindrical recess. The
piston 251 is disposed between the annular surface 273 and the end
274 for being moved therebetween, along the axis 270, in response
to a change in oil pressure in the reservoir 222. Movement of the
piston 251 is controlled by the spring 256, which acts between the
closed end 253 and the plug 276. When the parts 221, 251, 256, and
276 are assembled, the spring 256 is compressed enough to urge the
piston toward, if not against, the annular surface 273. As oil
pressure in the reservoir increases and exceeds the pressure of the
spring 256, the piston 251 is urged by the oil pressure away from
the surface 273, toward the plug 276, further compressing the
spring 256; as the oil pressure drops, the spring compressed 256
pushes the piston 251 once again back toward the surface 273.
[0027] Two oil pressure absorbers are shown in FIGS. 4A, 5, and 6,
one at each end of the wristpin 221. However, it should be
understood that this number is not meant to be specifically
limiting; instead, one absorber 250 can be provided at either end
of the wristpin. Further, the oil pressure absorber is configured
as a piston/spring combination. However, it should be understood
that this configuration is not meant to be specifically limiting.
Instead, the absorber can be configured as a bladder, a bellows, or
another equivalent structure capable of absorbing, storing, and
releasing energy in response to changes in oil pressure.
[0028] With reference to FIGS. 4B and 7, the pressure-responsive
control device 260 can be configured to couple the oil delivery
passage 216 with the wristpin oil inlet passage 223 in response to
a difference in oil pressures in the passages. For example, the
device can be configured as a check valve 282 seated in a recess
284 in the connecting rod 210 by a threaded or press-fit plug 286
which may be separate from or integral with the check valve. The
check valve 282 is positioned between the oil delivery passage 216
and an auxiliary oil passage 288 formed in the connecting rod 210
in alignment with the oil inlet passage 223. The check valve 282 is
a passive valve that reacts to the pressure of the oil in the oil
delivery passage 216. When the oil pressure in the passage 216 is
high, as when the piston 200 approaches TC, the valve ball
depresses the spring, which opens the check valve 282 to allow
pressurized oil into the wristpin oil reservoir 222. As the piston
200 reverses and accelerates during the combustion cycle, oil in
the wristpin reservoir 222 will start migrating down the oil
delivery passage 216 which results in a pressure differential
across the check valve 282. This pressure differential causes the
check valve 282 to close thereby closing the auxiliary oil passage
288. Therefore, the pressurized oil in the reservoir 222 stays at
its high pressure level for lubricating the wristpin
interfaces.
[0029] The pressure-responsive control device 260 is configured as
a ball check valve. However, it should be understood that this
configuration is not meant to be specifically limiting. Instead,
the pressure-responsive control device 260 can be configured as a
diaphragm valve, a swing or tilting disc valve, a lift or an
in-line valve, a reed valve, or another one-way device that that
normally allows oil or lubricant to flow through it in only one
direction.
[0030] During any engine cycle at TC there is an abundance of
galley oil pressure available at the wristpin assembly. By
capturing this high oil pressure at the wristpin when it is
available and storing it until it is needed during the engine cycle
when the available galley oil pressure is at a minimum, a more
constant oil pressure can be maintained for the wristpin during an
entire engine cycle.
[0031] The lubricating configuration embodiments that are described
herein, and the devices and procedures with which they are
implemented, are illustrative and are not intended to be
limiting.
* * * * *