U.S. patent application number 09/918629 was filed with the patent office on 2002-07-11 for multi-mode control system for variable camshaft timing devices.
Invention is credited to Duffield, Mike, Gardner, Marty, Smith, Frank R., Wing, Braman C..
Application Number | 20020088413 09/918629 |
Document ID | / |
Family ID | 26947919 |
Filed Date | 2002-07-11 |
United States Patent
Application |
20020088413 |
Kind Code |
A1 |
Smith, Frank R. ; et
al. |
July 11, 2002 |
Multi-mode control system for variable camshaft timing devices
Abstract
A variable camshaft timing apparatus (10) includes a pulse
actuating circuit (24A, 50, 44, 56, 60, 24R and 24R, 52, 46, 54,
58, 24A) for oscillating the variable camshaft timing apparatus in
reaction to fluid under pulsation, and includes a pressure
actuating circuit (30, 34, 36, 40, 44, 50, 24A, 24R, 52, 46, 66,
80/180, 32 and 30, 34, 38, 42, 46, 52, 24R, 24A, 50, 44, 64,
80/180, 32) for oscillating the variable camshaft timing device in
reaction to fluid under pressure. Advance and retard valves (44,
46) are interconnected with the pulse and pressure actuating
circuits for independently and simultaneously activating the pulse
and pressure actuating circuits. Finally, an exhaust valve (80,
180, 280) is positioned in fluid communication with the pulse and
pressure actuating circuits, such that the variable camshaft timing
device may be oscillated using one or both of the pulse actuating
and pressure actuating circuits, and may be maintained in position
using one or both of the pulse actuating and pressure actuating
circuits.
Inventors: |
Smith, Frank R.; (Cortland,
NY) ; Wing, Braman C.; (Interlaken, NY) ;
Gardner, Marty; (Ithaca, NY) ; Duffield, Mike;
(Medina, NY) |
Correspondence
Address: |
BorgWarner Inc./Patent Dept.
Attn: Patent Docket Administrator
3001 W. Big Beaver Road, Suite 200
P.O. Box 5060
Troy
MI
48007-5060
US
|
Family ID: |
26947919 |
Appl. No.: |
09/918629 |
Filed: |
July 31, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60260309 |
Jan 8, 2001 |
|
|
|
Current U.S.
Class: |
123/90.15 ;
123/90.17 |
Current CPC
Class: |
F01L 2001/34426
20130101; Y10T 74/2102 20150115; F01L 1/3442 20130101; F01L 2250/06
20130101; F01L 2001/3443 20130101; F01L 2250/04 20130101; F01L
1/34409 20130101 |
Class at
Publication: |
123/90.15 ;
123/90.17 |
International
Class: |
F01L 001/34 |
Claims
The invention claimed is:
1. A variable camshaft timing apparatus comprising: pulse actuating
means for oscillating said variable camshaft timing device in
reaction to fluid under pulsation; pressure actuating means for
oscillating said variable camshaft timing device in reaction to
fluid under pressure; and switching means for independently and
simultaneously activating said pulse actuating means and said
pressure actuating means; whereby said variable camshaft timing
device may be oscillated using one or both of said pulse actuating
means and said pressure actuating means, and said variable camshaft
timing device may be maintained anywhere in position between a
fully advanced and a fully retarded condition, using one or both of
said pulse actuating means and said pressure actuating means.
2. The variable camshaft timing apparatus as claimed in claim 1,
and further comprising: an advance chamber; a retard chamber; and a
fluid pressure source positioned in fluid communication between
said advance and retard chambers.
3. The variable camshaft timing apparatus as claimed in claim 2
wherein said pulse actuating means comprises: a pulsing path having
opposite ends in fluid communication with said advance and retard
chambers, said pulsing path comprising: at least one pulse passage
having means for preventing counterflow therein that permits flow
to said advance chamber and prevents flow from said advance
chamber; valving means for activating said pulsing path and being
in fluid communication with said at least one pulse passage; and a
make-up circuit in fluid communication with said pulsing path for
supplying fluid to each of said advance and retard chambers to
make-up for fluid loss.
4. The variable camshaft timing apparatus as claimed in claim 3
wherein said valving means includes valves for permitting or
preventing fluid from flowing through said at least one pulse
passage, wherein one of said valves exhausts fluid through one of
said at least one pulse passages from one of said advance and
retard chambers through to the other of said advance and retard
chambers, while another of said valves supplies make-up fluid from
said fluid pressure source to the other of said advance and retard
chambers.
5. The variable camshaft timing apparatus as claimed in claim 4
wherein said valving means further includes a normally closed
exhaust valve positioned in fluid communication with said pulsing
path, and wherein said exhaust valve remains closed during pulse
actuated oscillation of said variable camshaft timing device.
6. The variable camshaft timing apparatus as claimed in claim 2
wherein said pressure actuating means comprises: a pressure circuit
in fluid communication with said advance and retard chambers, said
pressure circuit serving to supply fluid to said advance and retard
chambers and to return fluid under exhaust to said fluid pressure
source, said pressure circuit comprising: a supply path having one
end in fluid communication with said fluid pressure source and
having an opposite end in fluid communication with one of said
advance and retard chambers, said supply path further having a
one-way flow device therein for preventing counterflow back to said
fluid pressure source; an exhaust path having one end in fluid
communication with the other of said advance and retard chambers
and having an opposite end in fluid communication with said fluid
pressure source; and switching means for activating said pressure
circuit, said switching means being in fluid communication with
said supply and exhaust paths of said pressure circuit.
7. The variable camshaft timing apparatus as claimed in claim 6
wherein said switching means includes a normally closed exhaust
valve positioned between and in fluid communication with said
supply and exhaust paths, and wherein said exhaust valve is opened
during said pressure actuated oscillation of said variable camshaft
timing device.
8. The variable camshaft timing apparatus as claimed in claim 7
wherein said switching means includes each of said supply and
exhaust paths having a valve therein for permitting or preventing
fluid flow therethrough, wherein one of said valves is positioned
in one of said supply and exhaust paths to supply fluid from said
fluid pressure source to one of said advance and retard chambers,
while another of said valves is positioned in the other of said
supply and exhaust paths to exhaust fluid from the other of said
advance and retard chambers through said exhaust valve.
9. A control system for a variable camshaft timing apparatus
connected to a fluid pressure source (30), said control system
comprising: an advance chamber (24A); a retard chamber(24R); a
pulse actuating means for oscillating said variable camshaft timing
apparatus, said pulse actuating means interconnecting said advance
and retard chambers, wherein said pulse actuating means comprises:
a retarding pulse means (50, 44, 56) for conveying fluid under
pulsation from said advance chamber to said retard chamber, said
retarding pulse means including means (60) for preventing
counterflow from said retard chamber; and an advancing pulse means
(52, 46, 54) for conveying fluid under pulsation from said retard
chamber to said advance chamber, said advancing pulse means
including means (58) for preventing counterflow from said advance
chamber; a pressure actuating means for oscillating said variable
camshaft timing apparatus, said pressure actuating means
comprising: a retarding pressure supply means (34, 46, 52) for
supplying fluid from said fluid pressure source to said retard
chamber; a retarding pressure exhaust means (50, 44, 64, 180, 32)
for exhausting fluid from said advance chamber back to said fluid
pressure source; an advancing pressure supply means (34, 44, 50)
for supplying fluid from said fluid pressure source to said advance
chamber; an advance pressure exhaust means (52, 46, 66, 180, 32)
for exhausting fluid from said retard chamber back to said fluid
pressure source; and means (40, 42) for preventing counterflow from
said advance and retard chambers back to said fluid pressure
source.
10. The control system as claimed in claim 9, further including;
switching means for activating said pressure actuating means, said
switching means including a normally closed exhaust valve (80, 180)
in fluid communication with both of said pulse actuating means and
said pressure actuating means, wherein said exhaust valve is opened
during pressure actuated oscillation.
11. The control system as claimed in claim 10, wherein said exhaust
valve is oil pressure activated and includes a spring (86) and a
double-ended piston (182) urged closed by said spring to close said
exhaust valve, wherein fluid under a predetermined pressure acts on
one end of said piston thereby overcoming the spring force of said
spring to open said exhaust valve and permit fluid to flow
therethrough, and wherein the spring force of said spring acts on
another end of said piston to close said exhaust valve when said
fluid falls below said predetermined pressure.
12. The control system as claimed in claim 10 wherein said exhaust
valve is centrifugally activated and includes a radially disposed
spring (86) and a radially disposed piston (82) urged closed by
said spring, wherein said piston is displaced radially outwardly,
thereby overcoming the spring force of said spring under a
predetermined rotational speed of said variable camshaft timing
device.
13. The control system as claimed in claim 10 wherein said exhaust
valve is electronically activated, and said exhaust valve includes
a normally closed solenoid valve (194), wherein said solenoid valve
is opened upon receiving an electronic signal.
14. The control system as claimed in claim 10, wherein said
switching means further includes each of said pulse actuating means
and pressure actuating means sharing two valves (44, 46): wherein
one of said two valves (44 or 46) permits fluid flow from said
advance chamber to said retard chamber through said retarding pulse
means during retarding oscillation of said variable camshaft timing
device and permits fluid flow from said fluid supply source to said
advance chamber through said advancing pressure supply means during
advancing oscillation of said variable camshaft device; and wherein
the other of said two valves (44 or 46) permits fluid flow from
said retard chamber to said advance chamber through said advancing
pulse means during advancing oscillation of said variable camshaft
timing device and permits fluid flow from said fluid supply source
to said retard chamber through said retarding pressure supply means
during retarding oscillation of said variable camshaft device.
15. A variable camshaft timing apparatus attached to a camshaft
(26), said variable camshaft timing apparatus comprising: a hub
(16) attached to said camshaft and being rotatable but not
oscillatable with respect to said camshaft; a housing (12)
circumscribing said hub to define at least one fluid chamber (24)
therebetween, said housing being rotatable and oscillatable with
respect to said camshaft; said hub having at least one vane member
(22) dividing said at least one fluid chamber into at least one
advance chamber (24A) and at least one retard chamber (24R); a
fluid pressure source (30) in fluid communication with said at
least one advance and retard chambers, said fluid pressure source
having a inlet side (301) and an outlet side (300) opposite said
inlet side; a fluid supply passage (34) in fluid communication with
said outlet side of said fluid pressure source, said fluid supply
passage having at least one check valve (40, 42) for preventing
counterflow of fluid back to said fluid pressure source; an advance
valve (44) having a supply port (44S) in fluid communication with
said fluid supply passage, said advance valve further having a
control port (44C) communicable with said supply port, said advance
valve further having an exhaust port (44E) communicable with said
control port; an advance chamber passage (50) having one end in
fluid communication with said control port of said advance valve
and having an opposite end in fluid communication with said at
least one advance chamber; a retard valve (46) having a supply port
(46S) in fluid communication with said fluid supply passage, said
retard valve further having a control port (44C) communicable with
said supply port, and an exhaust port (44E) communicable with said
control port; a retard chamber passage (52) having one end in fluid
communication with said control port of said retard valve and
having an opposite end in fluid communication with said at least
one retard chamber; a retard pulse passage (56) having one end in
fluid communication with said exhaust port of said advance valve
and having an opposite end in fluid communication with said at
least one retard chamber, said retard pulse passage having a check
valve (60) therein for permitting flow from said at least one
advance chamber and for preventing flow from said at least one
retard chamber; an advancing pulse passage (54) having one end in
fluid communication with said exhaust port of said retard valve and
having an opposite end in fluid communication with said at least
one advance chamber, said advancing pulse passage having a check
valve (58) therein for permitting flow to said at least one advance
chamber and for preventing flow from said at least one advance
chamber; a retard exhaust passage (64) having one end in fluid
communication with said exhaust port of said advance valve, said
retard exhaust passage terminating in an opposite end; an advancing
exhaust passage (66) having one end in fluid communication with
said exhaust port of said retard valve, said advancing exhaust
passage terminating in an opposite end; an exhaust valve (80, 180)
in fluid communication with said opposite ends of said retard and
advancing exhaust passages for exhausting flow from said at least
one advance chamber during fluid pressure actuated retarding of
said variable camshaft timing device and for exhausting flow from
said at least one retard chamber during fluid pressure actuated
advancing of said variable camshaft timing device; and a sump (32)
in fluid communication with said exhaust valve and said inlet side
of said fluid pressure source and being interposed therebetween;
said hub being oscillatable with respect to said housing in
response to fluid pulsations from one of said at least one advance
and retard chambers to other of said at least one advance and
retard chambers; said hub being oscillatable with respect to said
housing in response to fluid pressure from said fluid pressure
source to one of said at least one advance and retard chambers; and
said hub being maintainable in position with respect to said
housing in response to fluid pressure from said fluid pressure
source to both of said at least one advance and retard
chambers.
16. A variable camshaft timing apparatus attached to a camshaft
(26), said variable camshaft timing apparatus comprising: a hub
(16) attached to said camshaft and being rotatable but not
oscillatable with respect to said camshaft; a housing (12)
circumscribing said hub to define at least one fluid chamber (24)
therebetween, said housing being rotatable and oscillatable with
respect to said camshaft; said hub having at least one vane member
(22) dividing said at least one fluid chamber (24A) into at least
one advance chamber and at least one retard chamber (24R); a fluid
pressure source (130) in fluid communication with said at least one
advance and retard chambers, said fluid pressure source having a
inlet side (130I) and an outlet side (130O) opposite said inlet
side; a fluid supply passage (134) in fluid communication with said
outlet side of said fluid pressure source, said fluid supply
passage having at least one check valve (140 or 142) for preventing
counterflow of fluid back to said fluid pressure source; a spool
valve (145) having a supply port (145S) in fluid communication with
said fluid supply passage, said spool valve further having a retard
exhaust port (145R), and an advance exhaust port (145A); an advance
chamber passage (150) having one end in fluid communication with
said advance exhaust port of said spool valve and having an
opposite end in fluid communication with said at least one advance
chamber; a retard chamber passage (152) having one end in fluid
communication with said retard exhaust port of said spool valve and
having an opposite end in fluid communication with said at least
one retard chamber; a retard pulse passage (156) having one end in
fluid communication with said supply port of said spool valve and
having an opposite end in fluid communication with said at least
one retard chamber, said retard pulse passage having a check valve
(160) therein for permitting flow from said at least one advance
chamber and for preventing flow from said at least one retard
chamber; an advance pulse passage (154) having one end in fluid
communication with said supply port of said spool valve and having
an opposite end in fluid communication with said at least one
advance chamber, said advance pulse passage having a check valve
(158) therein for permitting flow to said at least one advance
chamber and for preventing flow from said at least one advance
chamber; an exhaust valve (180) in fluid communication with said
advance and retard exhaust ports of said spool valve, said exhaust
valve for exhausting flow from said at least one advance chamber
during fluid pressure actuated retarding of said variable camshaft
timing device and for exhausting flow from said at least one retard
chamber during fluid pressure actuated advancing of said variable
camshaft timing device; and a sump (132) in fluid communication
with said exhaust valve and said inlet side of said fluid pressure
source and being interposed therebetween; said hub being
oscillatable with respect to said housing in response to fluid
pulsations from one of said at least one advance and retard
chambers to other of said at least one advance and retard chambers;
said hub being oscillatable with respect to said housing in
response to fluid pressure from said fluid pressure source to one
of said at least one advance and retard chambers; and said hub
being maintainable in position with respect to said housing in
response to fluid pressure from said fluid pressure source to both
of said at least one advance and retard chambers.
17. A variable camshaft timing apparatus according to claim 7
wherein said switching means comprises: a centrifugally operated
valve (280) for selectively permitting oil to flow from between the
advance chamber (224A) and the retard chamber (224R) without
passing through the centrifugally operated valve to an exhaust line
(232) or for permitting oil to flow from one of the advance chamber
or the retard chamber through the centrifugally operated valve to
the exhaust line.
18. Apparatus according to claim 17 and further comprising: a
double-ended axially slidable spool valve (290) having spaced apart
lands for controlling flow into or out of the advance chamber and
the retard chamber; a spring acting on an end of the spool valve to
urge the spool valve in a first direction; and an electronically
controlled, variable force solenoid acting on an opposed end of the
spool valve to urge the spool valve in an opposed direction.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based, in part, on co-pending
provisional U.S. Patent application No. 60/260,039 (attorney docket
DKT00011), which was filed on Jan. 8, 2001.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to an internal
combustion engine having a control system for controlling the
operation of a variable camshaft timing mechanism (VCT) of the type
in which the position of a camshaft is circumferentially varied
relative to the position of a crankshaft. More specifically, this
invention relates to control systems for operating VCT devices in
response to fluid under continuous pressure and fluid under
pulsation to selectively advance, retard, or maintain the position
of the camshaft.
[0004] 2. Description of the Prior Art
[0005] It is known that the performance of an internal combustion
engine can be improved by the use of dual overhead camshafts, one
to operate the intake valves of the various cylinders of the engine
and the other to operate the exhaust valves. Typically, one of such
camshafts is driven by the crankshaft of the engine, through a
sprocket and chain drive or a belt drive, and the other of such
camshafts is driven by the first, through a second sprocket and
chain drive or a second belt drive. Alternatively, both of the
camshafts can be driven by a single crankshaft-powered chain drive
or belt drive. It is also known that the performance of an internal
combustion engine having dual overhead camshafts, or but a single
camshaft, can be improved by changing the positional relationship
of a camshaft relative to the crankshaft.
[0006] It is also known that engine performance in an engine having
one or more camshafts can be improved by varying camshaft timing,
specifically in terms of idle quality, fuel economy, reduced
emissions, or increased torque. For example, the camshaft can be
"retarded" for delayed closing of intake valves at idle for
stability purposes and at high engine speed for enhanced output.
Likewise, the camshaft can be "advanced" for premature closing of
intake valves during mid-range operation to achieve higher
volumetric efficiency with correspondingly higher levels of torque.
In a dual overhead camshaft engine, retarding or advancing the
camshaft is accomplished by changing the positional relationship of
one of the camshafts, usually the camshaft that operates the intake
valves of the engine, relative to the other camshaft and the
crankshaft. Accordingly, retarding or advancing the camshaft varies
the timing of the engine in terms of the operation of the intake
valves relative to the exhaust valves, or in terms of the operation
of the valves relative to the position of the crankshaft.
[0007] There are a multitude of VCT architectures using actuating
components that include piston-cylinder devices, hub and vanes,
single lobe vanes, and opposed lobe vanes. Similarly, there are at
least three distinct styles of VCT actuation in the prior art. The
first style is referred to hereafter as an Oil Pressure Actuated
(OPA) VCT. The OPA system includes a VCT responsive to fluid under
continuous pressure generated by an engine oil pump. The second
style is referred to hereafter as a Camshaft Torque Actuated (CTA)
VCT. The CTA system includes a VCT responsive to fluid under
pulsations generated by torque pulses in the camshaft. The third
style is referred to hereafter as a multi-mode VCT. The multi-mode
system includes a VCT responsive to both fluid under pressure and
under pulsation to oscillate the camshaft.
[0008] With OPA devices, the VCT uses fluid output of an engine oil
pump where the actuation rate of the VCT is limited by the
available hydraulic power supplied by the pump. Many such VCT
systems incorporate hydraulics including a hub having multiple
circumferentially spaced vanes cooperating within an enclosed
housing having multiple circumferentially opposed walls. The vanes
and the walls cooperate to define multiple fluid chambers, and the
vanes divide the chambers into first and second sections. For
example, U. S. Pat. No. 4,858,572 (Shirai et al.) teaches use of
such a system for adjusting an angular phase difference between an
engine crankshaft and an engine camshaft using oil pressure from a
pump. Shirai et al. discloses fluid circuits having check valves, a
spool valve and springs, and electromechanical valves. Fluid is
transferred from the first section to the second section, or vice
versa, to thereby oscillate the vanes and hub with respect to the
housing in one direction or the other. Each branch of the fluid
flow path runs from one section to the other through a drainage
clearance between the hub and the camshaft, back through the oil
pump, and then through the spool valve and a check valve. The check
valve prevents fluid from flowing out of each section back to the
spool valve.
[0009] With CTA devices, the VCT uses the energy of reactive
torques in the camshaft to power the VCT hydraulically through a
check-valve fluid circuit. The camshaft is subjected cyclically to
resistant torques when the rising profiles of the cam lobes open
the valves against the action of the valve springs, and then to
driving torques when the valve springs close the valves by causing
them to follow along the descending profiles of the cam lobes. The
alternating resistant and driving torques in the camshaft translate
into slight pulsations in the vane. These pulsations result in
alternating pressure differentials across the vane that alternately
compress the fluid in the advance and retard fluid chambers. To
retard the camshaft, fluid is allowed to escape during the
pulsations from the advance chamber and flow to the retard chamber
through one branch of a one-way fluid circuit. Alternately, to
advance the camshaft, fluid is allowed to escape during the
pulsations from the retard chamber to the advance chamber through
another branch of a one-way fluid circuit. Accordingly, the VCT
changes phase by exchanging fluid from one fluid chamber to the
other using the differential in pressure of the fluid in the fluid
chambers to increase the volume of one fluid chamber at the expense
of the other.
[0010] For example, U.S. Pat. No. 5,645,017 to (Melchior) teaches
use of a torque pulse actuated VCT to change phase of a camshaft.
The '017 patent discloses a vane type VCT having a vane within a
housing that delimits opposing antagonistic chambers that are
interconnected by two unidirectional circuits having opposite flow
directions. A valve communicates with the two unidirectional
circuits so as to transfer fluid from one antagonistic chamber to
the other in response to alternating pressure differentials between
the antagonistic chambers, where the pressure differentials result
solely from torque pulsations in the camshaft and vane.
[0011] In the systems described above, VCT actuation is
accomplished in response to torque pulsation in the camshaft or in
response to engine oil pressure from an engine oil pump, but not
both. This presents a significant disadvantage.
[0012] First, there are shortcomings to using only the CTA powered
VCT. The CTA device has a significantly lower frequency response
than the OPA device, even though the potential actuation rate of
the CTA device is substantially higher than the OPA device due to
the larger amount of energy in the cam torque inputs. For example,
inline four cylinder engines typically operate at relatively high
speeds and therefore generate very high frequency torque pulses to
which CTA systems do not respond quickly enough to cause actuation
of the VCT. Thus, the relatively low frequency response of the CTA
system results in a dramatic drop in CTA performance at the higher
engine speeds of the inline four cylinder engines. Similarly,
inline six cylinder engines typically exhibit low amplitude
camshaft torque pulses that are also inadequate to actuate the
VCT.
[0013] In contrast, the OPA systems have nearly the opposite
problem. Since the actuation rate of the OPA device is strongly
dependent on engine oil pressure, the device performs well at
higher engine speeds, when the oil pump is producing an abundance
of oil pressure. At lower engine speeds, however, particularly when
the engine is running hot, the performance suffers because the oil
pump is producing relatively little oil pressure.
[0014] Because the OPA device performs well at high speed and the
CTA performs well at lower speeds, it would be advantageous to
combine both strategies and architectures into one multi-mode VCT
device and be able to selectively switch between the two
independently and/or use both simultaneously. For example, U.S.
Pat. No. 5,657,725 (Butterfield et al.), which is assigned to the
assignee hereof, teaches uses of a dual-mode VCT system to change
phase of a camshaft. The '725 patent discloses a dual-mode device
responsive to torque pulses and/or engine oil pump pressure for
actuation. In the '725 patent there is disclosed a VCT apparatus
having a vane within a housing that delimits opposing advance and
retard chambers that are interconnected by an hydraulic circuit
having two check valves and a spool valve therein. Here, fluid
flows from one chamber to the other, through one check valve and
then through the spool valve, in response to sufficiently strong
torque pulsations in the vane. When there are not sufficiently
strong pulsations present in the vane, fluid flows from the one
chamber, not through the check valve, but directly through the
spool valve to exhaust. Simultaneously, make-up fluid from the
engine oil pump flows through the spool valve both directly to the
other chamber and indirectly to the other chamber, by cycling in
parallel through the other check valve back through the spool
valve.
[0015] While the '725 patent discloses a significant improvement
upon the prior art, there are still some disadvantages. For
example, the system is two-position only and is not capable of
maintaining position between fully advanced and fully retarded
positions. Additionally, the system uses a relatively complicated
hydraulic circuit and spool valve system.
[0016] Accordingly, what is needed is a multi-mode VCT system that
is capable of advancing, retarding, and maintaining a camshaft in
intermediate positions over the entire speed range of an engine and
uses relatively inexpensive and uncomplicated and hydraulic
circuitry and components.
SUMMARY OF THE INVENTION
[0017] According to the present invention there is provided a
multi-mode VCT system that is capable of advancing, retarding, and
maintaining a camshaft in intermediate positions over the entire
speed range of an engine and uses relatively inexpensive and
uncomplicated and hydraulic circuitry and components.
[0018] The present invention includes a variable camshaft timing
device including a pulse actuating circuit for oscillating the
variable camshaft timing device in reaction to fluid under
pulsation. A pressure actuating circuit is included for oscillating
the variable camshaft timing device in reaction to fluid under
pressure. Advance and retard valves are interconnected with the
pulse and pressure actuating circuits for independently and
simultaneously activating the pulse and pressure actuating
circuits. Finally, an exhaust valve is positioned in fluid
communication with the pulse and pressure actuating circuits,
whereby the variable camshaft timing device may be oscillated using
one or both of the pulse actuating and pressure actuating circuits,
and may be maintained in position using one or both of the pulse
actuating and pressure actuating circuits.
[0019] Accordingly, it is an object of the present invention to
provide an improved variable camshaft timing device for varying
camshaft timing in an internal combustion engine.
[0020] It is another object to provide a multi-mode variable
camshaft timing device that is capable of operating in response to
fluid under pressure from a pump and fluid under pulsations from
alternating camshaft torques.
[0021] It is yet another object to provide a multi-mode variable
camshaft timing device that is capable of maintaining position
anywhere between a fully advanced and fully retarded position over
the full range of engine speed, and does not necessarily require
use of a spool valve, but may as an option.
[0022] These objects and other features, aspects, and advantages of
this invention will be more apparent after a reading of the
following detailed description, appended claims, and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is an exploded perspective view of a VCT device
according to the preferred embodiment of the present invention;
[0024] FIG. 1A is an end view of the device of FIG. 1 in its
assembled state;
[0025] FIG. 2 is a schematic view of a VCT control system according
to the preferred embodiment of the present invention, where the VCT
is maintaining position;
[0026] FIG. 3 is a schematic view of a VCT control system of the
present invention showing an alternative valve, where the VCT is
advancing under cam torque actuation;
[0027] FIG. 4 is a schematic view of the VCT control system of FIG.
3, where the VCT is retarding under cam torque actuation;
[0028] FIG. 5 is a schematic view of a VCT control system according
to the present invention showing an oil pressure actuated exhaust
valve, where the VCT is advancing under oil pressure actuation;
[0029] FIG. 6 is a schematic view of a VCT control system according
to the present invention showing an electro-hydraulic actuated
exhaust valve, where the VCT is retarding under oil pressure
actuation;
[0030] FIG. 7 is a schematic view of a VCT control system according
to an alternative and the presently preferred embodiment of the
present invention where the VCT is maintaining position;
[0031] FIG. 8 is a schematic view of another and the secondarily
preferred embodiment of a VCT control system according to the
present invention operating in a CTA mode during a phase shift to
an advance position;
[0032] FIG. 9 is a view like FIG. 8 during a phase shift to a
retard position;
[0033] FIG. 10 is a view like FIGS. 8 and 9 in which the VCT is not
operating to shift phase either to an advance position or to a
retard position;
[0034] FIG. 11 is a schematic view of the embodiment of a VCT
control system of FIGS. 8-10 operating in an OPA mode during a
phase shift to an advance position;
[0035] FIG. 12 is a view like FIG. 11 during a phase shift to a
retard position; and
[0036] FIG. 13 is a view like FIGS. 11 and 12 in which the VCT is
not operating to shift phase either to an advance position or to a
retard position.
DETAILED DESCRIPTION OF TIE PREFERRED EMBODIMENT
[0037] In general, an hydraulic timing system is provided for
varying the phase of one rotary member relative to another rotary
member. More particularly, the present invention provides a
multi-mode Variable Camshaft Timing system (VCT) that is powered
by, or is responsive to, engine oil under pressure from a pump
and/or from engine oil under pressure pulsations inherent as a
result of the tongue pulsations that occur in a rotating camshaft.
While the present invention will be described in detail with
respect to internal combustion engines, the VCT system is also well
suited to other environments using hydraulic timing devices.
Similarly, the fluid medium described herein is preferably engine
oil, but any other standard hydraulic fluid may be used.
Accordingly, the present invention is not limited to only internal
combustion engines.
[0038] Referring now in detail to the Figures, there is shown in
FIG. 1 a VCT apparatus 10 according to the preferred embodiment of
the present invention. It is contemplated that the VCT apparatus 10
operates under control of an engine control module as is commonly
known in the art. The VCT apparatus 10 includes a housing 12 having
sprocket teeth 14 circumferentially disposed around its periphery.
The housing 12 circumscribes a hub 16 to define fluid chambers 24
therebetween. The hub 16 is mechanically connected to a camshaft 26
to be rotatable therewith but not oscillatable with respect
thereto. The hub 16 is in fluid communication with the camshaft 26
via passages (not shown) as is commonly known in the art. The hub
16 includes circumferentially spaced lobes 18 extending radially
outwardly to divide each fluid chamber 24 into advance and retard
chambers 24A and 24R, as shown in FIG. 1A. Each lobe 18 includes a
slot 20 therein for housing a vane 22. The vane 22 cooperates with
the inside of the housing 12 to seal the advance and retard
chambers 24A and 24R so that they are fluid tightly separated from
one another.
[0039] Referring again to FIG. 1, the assembly that includes the
camshaft 26 with the hub 16 and housing 12 is caused to rotate by
torque applied to the housing 12 by an endless chain (not shown)
that engages the sprocket teeth 14 so that rotation is imparted to
the endless chain by a rotating crankshaft (also not shown). The
use of a cogged timing belt to drive the housing 12 is also
contemplated. Rotation, in turn, is imparted from the housing 12 to
the hub 16 through fluid in the fluid chambers 24A and 24R.
[0040] The hub 16 can be circumferentially retarded or advanced in
position with respect to the housing 12. Therefore, the housing 12
rotates with the camshaft 26 and is oscillatable with respect to
the camshaft 26 to change the phase of the camshaft 26 relative to
the crankshaft. The VCT hardware, as opposed to the VCT 10 as a
system, may be of any architecture that is well known in the art.
Accordingly, examples of well known VCT hardware architectures
include those of commonly assigned U.S. Pat. No. 5,107,804 (Becker
et al.) and the aforesaid '725 patent, which are also incorporated
by reference herein. In addition to the VCT hardware, an
oscillation control configuration is required to oscillate the VCT
apparatus 10, and is described below.
[0041] To complement the hardware example shown in FIG. 1, FIG. 2
illustrates a schematic of the VCT apparatus 10 of the present
invention. It is contemplated, and is well known in the art, that
VCT control systems include fluid circuits that are drilled or
otherwise machined or formed into the hardware components of the
VCT apparatus 10. The exact location of passages and
interconnections of such fluid circuitry is not critical to the
present invention and is therefore only schematically
illustrated.
[0042] Structurally, the control system for the VCT apparatus 10
can be described in terms of passages, valves, etc. A fluid
pressure source such as an engine oil pump 30 is located upstream
and is in fluid communication with the downstream advance and
retard chambers 24A and 24R that are separated by the lobe 18. The
engine oil pump 30 includes an inlet side 301 that communicates
with a sump 32 of the engine oil system, and includes an opposite
outlet side 300 that supplies oil to the advance and retard
chambers 24A and 24R. The sump 32 collects oil from various parts
of the control system to complete the circuits thereof An oil
supply passage 34 fluidly communicates the outlet side 300 of the
pump and branches into an advance branch passage 36 and a retard
branch passage 38. The branch passages 36 and 38 include supply
check valves 40 and 42, respectively, for permitting oil flow in a
downstream direction from the pump 30 but prevents oil flow in an
upstream direction back toward the pump 30. In other words, the
check valves 40 and 42 prevent counterflow back to the pump 30.
[0043] Downstream of each check valve, each branch passage 36 and
38 terminates in an advance or retard valve 44 or 46, respectively.
Preferably, the valves 44 and 46 are pulse width modulated (PWM)
valves, having a supply port 44S or 46S in fluid communication with
the oil supply passage 34. Each of the valves 44 and 46 also
include a control port 44C or 46C in fluid communication with one
end of an advance or retard chamber passage 50 or 52. An opposite
end of the chamber passage 50 or 52 fluidly communicates with one
of the advance or retard chambers 24A and 24R. Each valve 44 or 46
finally includes an exhaust port 44E or 46E communicable with the
control port 44C or 46C and in fluid communication with both a
pulse passage 54 or 56 and an exhaust passage 64 or 66. Each pulse
passage 54 or 56 includes one end in communication with the valve
44 or 46, and an opposite end in communication with one of the
advance or retard chambers 24A and 24R and with one of the
corresponding chamber passages 50 and 52. Each pulse passage 54 and
56 includes a pulse check valve 58 and 60, respectively, just
upstream of the connection with the chamber passage 50 or 52 to
prevent upstream oil flow through the pulse passage 54 or 56, or in
other words, to prevent counterflow from the chamber 24A or 24R
toward the valve 44 or 46. Each exhaust passage 64 and 66 includes
one end in communication with the exhaust port 44E or 46E,
respectively, of the valve 44 or 46 and with an exhaust valve 80,
such that the exhaust valve 80 terminates each of the exhaust
passages 64 and 66. Accordingly, the exhaust valve 80, as shown in
FIG. 2 includes a piston 82 that is radially disposed within a
radial valve passage 84 within the hub 16.
[0044] A spring 86 supports the valve 80 in a valve closed
position, such that a combined exhaust passage 88 is blocked by the
valve 80. The spring force may be chosen in accordance with a
calculation of the rotational speed of the engine, to establish the
desired valve opening condition, as is well known. In the valve
open position, the exhaust valve 80 and combined exhaust passage 88
communicate with the sump 32 of the engine either via passageways
or by draining down through gaps between engine components, which
is consistent with designs well known in the art. The PWM valves 44
and 46 and the exhaust valve 80 are preferably controlled by a
central source such as an engine control unit or the like, as is
well known in the art.
[0045] Systemically, the VCT control system can be described in
terms of circuits defined from the structure described above. The
VCT control system includes a pulse actuating circuit and a
pressure actuating circuit. The pulse actuating circuit is further
divided into a retard pulsing path, an advance pulsing path, and a
make-up oil circuit. The retard pulsing path includes in fluid
communication, the advance chamber 24A, the advance chamber passage
50, the advance PWM valve 44, the retard pulse passage 56, and the
retard chamber 24R. Similarly, the advance pulsing path includes in
fluid communication, the retard chamber 24R, the retard chamber
passage 52, the retard PWM valve 46, the advance pulse passage 54,
and the advance chamber 24A. Additionally, since the system is not
perfectly sealed against oil loss, the make-up oil circuit is
necessary and is defined by the oil supply passage 34, the valve 44
or 46, the chamber passage 50 or 52, and the chamber 24A or
24R.
[0046] Similarly, the pressure actuating circuit is further divided
into a pressure supply path and a pressure exhaust path. The
pressure supply path includes in fluid communication, the oil
supply passage 34, one check valve 40 or 42, one valve 44 or 46,
the chamber passage 50 or 52, and the chamber 24A or 24R. The
pressure exhaust path includes in fluid communication, the other
chamber 24A or 24R, the other chamber passage 50 or 52, the other
valve 44 or 46, the exhaust passage 64 or 66, and the exhaust valve
80.
[0047] In operation, the VCT apparatus 10 oscillates or maintains
position anywhere in and between a fully retarded position and a
fully advanced position. In the fully retarded position, the volume
of the advance chamber 24A would be approximately zero, while the
volume of the retard chamber 24R would be at a maximum. The reverse
is true for the VCT apparatus 10 in the fully advanced position. To
maintain any position intermediate the fully advanced and fully
retarded positions, the VCT apparatus 10 of the present invention
operates under closed loop control. In other words, as is well
known, the VCT system communicates with position feedback sensors
that monitor the relative position of the camshaft. The position
feedback is used by the VCT system in further controlling the phase
of the VCT apparatus 10.
[0048] In FIG. 2, the VCT apparatus 10 is shown maintaining
position halfway between the fully advanced and retarded positions.
To achieve this result, the pressure actuating circuit is activated
to supply oil to both the advance and retard chambers 24A and 24R
simultaneously. Accordingly, oil flows from the pump 30 through the
oil supply passage 34 into each oil supply branch 36 and 38. The
oil continues through each check valve 40 and 42 and into the
supply port 44S or 46S of each valve 44 or 46. Each valve 44 or 46
is positioned in an exhaust port-closed position to direct oil out
of the control port 44C and 46C and through the chamber passage 50
or 52 into the respective chamber 24A or 24R. The pulse check
valves 58 and 60 remain closed against their seats under fluid
pressure from the chamber passage 50 or 52. Thus each chamber 24A
or 24R experiences the same fluid pressure from the pump 30 through
each respective branch of the control system. Here, no fluid
pressure from the pump 30 reaches the exhaust passages 64 or 66.
Accordingly, the exhaust valve 80 may remain closed, or may be
open, because the state of the exhaust valve 80 will have no
significant effect in this control system state.
[0049] FIG. 3 illustrates the control system in an advancing state
under cam torque actuation. Cam torque actuation operates in
response to reactive camshaft torques as previously described in
the Background section above. Here, the advance valve 44 remains in
the exhaust-closed position, while the retard valve 46 is moved to
a source closed position. An exhaust valve 180 takes a closed
position. Accordingly, each torque pulsation of the VCT apparatus
10 in the advancing direction acts to momentarily compress the oil
in the retard chamber 24R. This compression causes the oil in the
retard chamber 24R to escape therefrom into the advancing pulsing
path: through the retard chamber passage 52, into the control port
46C of the advance valve 46 and out the exhaust port 46E, through
the advance pulse passage 54, past the check valve 58, and into the
advance chamber 24A. Check valve 60 prevents pulsing oil from
circumventing the advance valve 44. Make up oil flows from the pump
30, up through the advance valve 44 and into the advance chamber
24A. The supply check valve 40 prevents oil under pulsation from
discharging back to the pump 30.
[0050] The exhaust valve 180 of FIG. 3 is actuated by engine oil
pressure, and includes a spring-loaded piston 182 that is
preferably axially disposed within an axial passage 184 within the
hub 16. A spring 86 supports the valve 180 in a valve closed
position, such that a combined exhaust passage 88 is blocked by the
valve 180. As shown, the engine oil pressure is insufficient to
displace the valve 180 for OPA operation.
[0051] FIG. 4 illustrates the mirror image of FIG. 3, the control
system in a retarding state under cam torque actuation. Here, the
retard valve 46 remains in the exhaust-closed position, while the
advance chamber valve 44 is moved to a source closed position.
Accordingly, each torque pulsation of the VCT apparatus 10 in the
retarding direction acts to momentarily compress oil in each
advance chamber 24A. This compression causes the oil in the advance
chamber 24A to discharge therefrom into the retard pulsing path
through the advance chamber passage 50, into the control port 44C
of the valve 46 and out the exhaust port 44E of the valve 44,
through the retarding pulse passage 56, past the check valve 60,
and into the retard chamber 24R. The check valve 58 prevents
pulsing oil from circumventing the pulsing path. Make-up oil flows
from the pump 30, up through the retard valve 46 and into the
retard chamber 24R. The supply check valve 42 prevents oil under
pulsation from discharging back to the pump 30. The exhaust valve
180 of FIG. 4 is the same as that shown in FIG. 3.
[0052] FIG. 5 illustrates the control system in an advancing state
under oil pressure actuation. Oil pressure actuation operates in
response to available hydraulic power of the engine as previously
described in the Background section above. Here, oil flows under
pressure from the pump 30 through the pressure actuating circuit.
Specifically, oil flows through the check valve 40, into the supply
port 44S of the valve 44 and out the control port 44C thereof,
through the advance chamber passage 50, and into the advance
chamber 24A. Simultaneously, oil flows out of the retard chamber
24R, through the retard pulse passage 52, into the control port 46C
of the valve 46 and out the exhaust port 46E thereof, through the
exhaust passage 66, through the exhaust valve 180, and into the
sump 32 to be recycled through the pump 30.
[0053] The exhaust valve 180 of FIG. 5 is the same as that of FIGS.
3 and 4 and is used as a switching means to invoke oil pressure
actuation of the VCT apparatus 10. Here, the exhaust valve 180 is
opened under fluid pressure from the engine oil pump 30 at higher
engine speeds when CTA loses effectiveness. The exhaust valve 180
opens when sufficient engine oil pressure acts upon the valve 180
to overcome a predetermined spring force. An exhaust actuation
passage 190 fluidly communicates an exhaust valve chamber 192 with
the oil supply passage 34. Accordingly, oil constantly flows to the
exhaust valve 180 but only acts to open the valve 180 under a
minimum oil pressure in correlation with a predetermined engine
speed sufficient to generate the minimum oil pressure. Therefore,
the spring force is selected in accordance with a calculation of
the oil pressure of the engine as balanced against the spring force
to establish the desired valve opening condition. As shown in the
valve open position, the exhaust valve 180 and a combined exhaust
passage 188 communicate with the sump 32 of the engine either via
passageways or by draining down and over components of the engine
consistent with designs well known in the art.
[0054] FIG. 6 illustrates the mirror image of FIG. 5, the control
system in a retarding state under oil pressure actuation. Oil flows
under pressure from the pump 30 through the pressure actuating
circuit. Oil flows thorough the check valve 42, into the supply
port 46S of the retard valve 46 out the control port 46C thereof,
through the retard chamber passage 52, and into the retard chamber
24R. Simultaneously, oil flows out of the advance chamber 24A,
through the advance chamber passage 50 into the control port 44C of
the advance valve 44 and out the exhaust port 44E thereof, through
the exhaust passage 64, through the exhaust valve 180, and into the
sump 32 to be recycled.
[0055] FIG. 6 also illustrates the exhaust valve 180 alternatively
actuated by engine oil pressure controlled by a solenoid valve 194.
Here, the exhaust valve 180 is actuated similar to that the exhaust
valve 180 of FIG. 5, except the solenoid valve 194 controls
actuation. Accordingly, a much lighter spring force may be selected
such that the exhaust valve 180 will open under a relatively low
engine speed and oil pressure, but only when the solenoid valve 194
is open. This will permit a much broader range of engine speed over
which the exhaust valve 180 may open. Again, placement of hardware
such as the solenoid valve 194 is not critical to the present
invention and is engineered in accordance with techniques already
well known in the art.
[0056] FIG. 7, illustrates an alternative and the presently
preferred embodiment of the present invention that uses a purely
mechanical valving arrangement instead of the electromechanical
valve arrangement of FIGS. 2 through 6. A VCT apparatus 110 is
shown maintaining position halfway between the fully advanced and
retarded positions. To achieve this result, the pressure actuating
circuit is activated to supply oil to both advance and retard
chambers 124A and 124R simultaneously. Accordingly, oil flows from
a pump 130 through an oil supply passage 134 into an oil supply
branch 136. The oil continues through a check valve 140 and into a
supply port 145S of a spool valve 145.
[0057] The spool valve 145 is positioned in an exhaust port-closed
position to direct oil through pulse passages 154 and 156 into the
respective chambers 124A and 124R. The pulse check valves 158 and
160 open under fluid pressure from the oil supply branch 136. Thus
each chamber 124A or 124R experiences the same fluid pressure from
the pump 130 through each respective branch of the control system.
Here, no fluid pressure from the pump 130 reaches an exhaust
passage 165, because an exhaust check valve 170 blocks flow into
the exhaust passage 165, and the spool valve 145 blocks flow from
the chamber passages 150 and 152.
[0058] To advance in CTA mode, the spool valve 145 shifts to the
left to open a retard chamber passage 152 to the exhaust passage
165, which is blocked by an exhaust valve 180 near a retard exhaust
port 145R. Accordingly, oil pulsing from the retard chamber 124R
deadheads at the retarding check valve 160, flows through the
retard chamber passage 152 around the spool valve 145 on the right
side, deadheads against the spool valve 145 in the advance chamber
passage 150 on the left side, flows through the exhaust check valve
170 around the spool valve 145 into the advance pulse passage 154
past the advance check valve 158 and into the advance chamber 124A.
Here, source oil alone may or may not be sufficient to change phase
of the VCT apparatus 110, and, therefore, oil under pulsation is
used to change phase of the VCT apparatus 110. To advance in OPA
mode, the spool valve shifts to the left to open the retard chamber
passage 152 to the exhaust passage 165, which would be open to a
sump 132.
[0059] To retard in CTA mode, the spool valve 145 shifts to the
right to open an advance chamber passage 150 to the exhaust passage
165, which is blocked by the exhaust valve 180 near an advance
exhaust port 145A. Accordingly, oil pulsing from the advance
chamber 124A deadheads at the advance check valve 158, flows
through the advance chamber passage 150 around the spool valve 145
on the left side, deadheads against the spool valve 145 in the
retard chamber passage 152 on the right side, flows through the
exhaust check valve 170 around the spool valve 145 into the retard
pulse passage 156 past the retard check valve 160 and into the
retard chamber 124R. To retard in OPA mode, the spool valve shifts
to the right to open the advance chamber passage 150 to the exhaust
passage 165, which would be open to the sump 132. The shifting of
the spool valve 145 to the left or right from the position in FIG.
7 may be controllably actuated in any suitable manner, for example,
by a variable force solenoid (not shown).
[0060] FIGS. 8-13 illustrate an alternative embodiment of the
present invention in which the change from a CTA mode (FIG. 8-10)
to an OPA mode (FIGS. 11-13) is responsive to a position of a
centrifugally operated, and, therefore, radially extending control
valve 288. The valve 288 moves to and fro within a valve body 280,
which may be considered to extend radially within a rotating
camshaft 226. At low rotational speeds of the camshaft 226, the
valve 288 will be radially inwardly biased, to the left as shown in
FIGS. 8-13, by a spring 286, and in the position of the valve 288
in FIGS. 8-10, no oil will be able to flow through the valve 288 to
an exhaust line 232 that leads to an engine oil sump. In this
position of the valve 288, oil will flow either from a retard
chamber 224R of a fluid chamber 224 in a housing 212 to an advance
chamber 224A of the chamber 224 (FIG. 8) or oil will flow from the
advance chamber 224A to the retard chamber 224R (FIG. 9), or no oil
will flow between the advance chamber 224A and the retard chamber
224R (FIG. 10), depending on the position of a spool element 290
that slides to and fro within a valve body 292. In that regard, the
spool element 290 has spaced lands 290A, 290B that are adapted to
block flow into or out of chambers 224A, 224R through lines 254,
256, respectively (FIG. 10), or to permit flow out of chamber 224R
into chamber 224A (FIG. 8) through the valve body 292, or to permit
flow out of chamber 224A into chamber 224R (FIG. 9) through the
valve body 292, depending on the axial position of the spool 290
within the valve body 292. In that regard, the spool 290 is
resiliently biased to its FIG. 8 position, one of its end
positions, by a spring 294, which is positioned within the camshaft
226, the spring 294 acting on an end of the spool 290. The spool
290 is also urged to its FIGS. 9 and 10 positions by a variable
force solenoid 290, which acts on an opposed end of the spool 290,
the solenoid 296 being controlled in its operation by an electronic
engine control unit 298, in a known manner.
[0061] Control of oil flow into or out of the chambers 224A, 224R
in an OPA mode of the embodiment of FIGS. 8-13 is illustrated in
FIGS. 11, 12, the flow being out of the chamber 224R and into the
chamber 224A in FIG. 11, or there will be no flow into or out of
either chamber 224A or 224R, in FIG. 13 except for some leakage of
make-up oil across the spool 290, depending on the axial position
of the spool 290 within the valve body.
[0062] In FIG. 11, the land 2901 is positioned to allow flow out of
the chamber 224R through the line 256 and the valve body 292, but
this flow now passes into the exhaust line 232 because of the
position of the valve 280 within the valve body 280. At the same
time, engine oil with flow into the chamber 224A from a source 230
through a line 234, the valve body 292 and the line 254, the land
290A being positioned to open the line 254 to inflow. In the FIG.
12 position of the spool 290, oil will flow from the source 230
through the line 234, the valve body 292 and the line 256 into the
chamber 224R; at the same time, oil will flow out of the chamber
224A through the line 254, the valve body 292 and the valve body
280 into the exhaust line 232.
[0063] In FIG. 12, the land 290B is positioned to allow flow from
the source 230 through the valve body and the line 256 into the
chamber 224R, and the land 290A is positioned to allow flow out of
the chamber 224A through the line 254, the valve body 292 and the
valve body 288 into the exhaust line, 232, a line 266 with branches
266A, 266B extending between the valve body 288 and the valve body
292 to provide flow either from the chamber 224R to the valve body
288 through the branch line 266B and the line 266 (FIG. 11), or
from the chamber 224A to the valve body 288 through the branch
lines 266A and the line 266 (FIG. 12). In any case, the land 290A
is positioned to block oil flow through the valve body 292 into the
branch line 266A in the FIG. 11 condition of operating, and the
land 290B is position to block oil flow from the valve body 292
into the branch line 266B in the FIG. 12 condition of
operation.
[0064] The to and fro movement of the spool 290 in the valve body
292 in the OPA mode of operation of FIGS. 11-13 is the same as in
the CTA mode of operation of FIGS. 8-10, namely under a variable
force imposed on an end of the spool 290 by the variable force
solenoid 296, which is opposed by a force imposed on an opposed end
of the spool 290 by the spring 294. Likewise, the force imposed on
the spool 290 by the solenoid 296 is controlled by the engine oil
controller 298.
[0065] In the FIG. 13 condition of operation, there will be no oil
flow into or out of the chamber 224R because the land 290B of the
spool 290 is positioned to block flow through the line 256.
Likewise, in this condition of operation there will be no oil into
or out of the chamber 224A because the land 290A of the spool 290
is positioned to block flow through the line 254. In any case, it
is to be understood that the solenoid 296 can be operated with some
dither in either the FIG. 10 or the FIG. 13 conditions of the
embodiment of FIGS. 8-13 to permit some small flow of make-up oil
into the chambers 224A, 224R to replace any oil lost by leakage
thereform.
[0066] From the above, it can be appreciated that a significant
advantage of the present invention is that the camshaft may be
advanced or retarded with respect to an engine crankshaft reliably
over the entire speed range of any engine, regardless of either a
lack of sufficient oil pump capacity or an absence of sufficient
pulsations in the camshaft.
[0067] An additional advantage is that the VCT of the present
invention involves inexpensive modifications to the control systems
of already well known VCT hardware having oil passages
therethrough.
[0068] While the present invention has been described in terms of a
preferred embodiment, it is apparent that other forms could be
adopted by one skilled in the art. Accordingly, the scope of the
present invention is to be limited only by the following
claims.
* * * * *