U.S. patent number 3,633,554 [Application Number 05/059,215] was granted by the patent office on 1972-01-11 for valve timing system of automotive internal combustion engine.
This patent grant is currently assigned to Nissan Motor Company, Limited. Invention is credited to Yoshimasa Hayashi, Yasuo Nakajima, Kunihiko Sugihara.
United States Patent |
3,633,554 |
Nakajima , et al. |
January 11, 1972 |
VALVE TIMING SYSTEM OF AUTOMOTIVE INTERNAL COMBUSTION ENGINE
Abstract
A valve timing system for an internal combustion engine of a
motor vehicle, including a camshaft which is hydraulically axially
movable and which has first and second cam lobes which are
positioned and configured relative to the rocker arm for the
exhaust valve of the engine cylinder, the first and second cam
lobes being selectively aligned with the rocker arm so that the
valve is timed in different manners depending upon the driving
conditions of the motor vehicle. The hydraulic fluid for axially
moving the camshaft is controlled by a solenoid operated discharge
valve in response to an engine speed actuated switch and an intake
manifold vacuum actuated switch. The valve timing system is adapted
for the elimination of air pollution in urban areas without
impairing the performance quality of the engine. Such cam lobe
configurations may be applied to the cam lobes associated with the
intake valve so that not only the exhaust valve but the intake
valve can be timed in relation to the driving conditions of the
motor vehicle.
Inventors: |
Nakajima; Yasuo (Yokosuka,
JA), Hayashi; Yoshimasa (Yokohama, JA),
Sugihara; Kunihiko (Yokohama, JA) |
Assignee: |
Nissan Motor Company, Limited
(Yokohama City, JA)
|
Family
ID: |
26400701 |
Appl.
No.: |
05/059,215 |
Filed: |
July 29, 1970 |
Foreign Application Priority Data
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|
|
|
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Sep 1969 [JA] |
|
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44/70901 |
Jul 30, 1969 [JA] |
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44/59641 |
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Current U.S.
Class: |
123/90.18 |
Current CPC
Class: |
F01L
13/0036 (20130101); F02F 7/006 (20130101) |
Current International
Class: |
F01L
13/00 (20060101); F02F 7/00 (20060101); F01l
001/34 (); F01l 013/00 () |
Field of
Search: |
;123/90.15,90.16,90.17,90.18 ;64/25 ;74/568 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Smith; Al Lawrence
Claims
What is claimed is:
1. In an automotive internal combustion engine having engine
cylinders each including intake and exhaust valves, a valve timing
system comprising a camshaft rotatable with the crankshaft of said
engine and axially movable through a camshaft support bearing fixed
relative to the engine cylinder, said camshaft having first and
second cam lobes which are located relative to the rocker arm of
said exhaust valve, said second cam lobe being greater in size than
said first lobe, a cylinder member fixed relative to said engine
cylinder and located relative to the leading end of said camshaft,
said cylinder member being provided with a stop located for
abutting engagement with said leading end of said camshaft, a
piston securely mounted on said camshaft at a portion near said
leading end and fitted to said cylinder member to define a chamber
therebetween, a compression spring seated between said support
bearing and said piston for forcing said piston and camshaft toward
said stop, a hydraulic fluid supply passage communicating at one
end with a source of pressurized hydraulic fluid and at the other
with said chamber, a hydraulic fluid discharge passage
communicating with said chamber, valve means adapted to selectively
open and close said hydraulic fluid discharge passage, and control
means for controlling said valve means to normally close said
hydraulic fluid discharge passage and to open the discharge passage
when said engine is driven at a speed lower than a predetermined
level and when the vacuum in the intake manifold of said engine is
higher than a predetermined level, said second cam lobe being held
in an abutting engagement with said rocker arm when said valve
means is in a position to close said hydraulic fluid discharge
passage to move said piston and camshaft axially away from said
stop against said compression spring and said first cam lobe being
moved into abutting engagement with said rocker arm when said valve
means is moved to a position to open said hydraulic fluid discharge
passage to cause said piston and camshaft to axially move toward
said stop by the action of said compression spring.
2. A system according to claim 1, wherein said control means
comprises a solenoid valve including a moving core rigidly
connected to said valve means, a solenoid coil operatively
connected to a source of electric power and a spring means urging
said moving core to a position in which said valve means is
protruded to close said discharge passage, a first switch
interposed between said solenoid coil and said source of electric
power and responsive to the revolution speed of said engine, said
first switch being closed when said revolution speed is lower than
a predetermined level, a second switch connected in series with
said first switch and responsive to the vacuum in the intake
manifold of said engine, said second switch being closed when the
intake manifold vacuum is higher than a predetermined level.
3. A system according to claim 1, wherein said camshaft has another
set of first and second cam lobes which are located relative to the
rocker arm of said intake valve and of which the latter is greater
in size than the former, the second cam lobe associated with said
intake valve being held in an abutting engagement with said rocker
arm of said intake valve when said valve means is in a position to
close said hydraulic fluid discharge passage to move said piston
and camshaft axially away from said stop against said compression
spring and the first cam lobe associated with said intake valve
being moved into abutting engagement with said rocker arm of said
intake valve when said valve means is moved to a position to open
said hydraulic fluid discharges passage to cause said piston and
camshaft to axially move toward said stop by the action of said
compression spring.
4. A system according to claim 1, wherein said first cam lobe is
configured to open said exhaust valve anterior to the bottom dead
center of the piston movement in said engine cylinder and to close
the same immediately posterior to the top dead center of the engine
cylinder piston and said second cam lobe is configured to open said
exhaust valve posterior to the bottom dead center of the engine
cylinder piston and to close the same substantially at the top dead
center of the piston.
5. A system according to claim 3, wherein said first cam lobe
associated with said intake valve is configured to open the intake
valve immediately anterior to the top dead center of said engine
cylinder piston and to close the same posterior to the bottom dead
center of the engine cylinder piston and said second cam lobe
associated with said intake valve being configured to open the
intake valve substantially at the top dead center of said engine
cylinder piston and to close the same posterior to the bottom dead
center of the engine cylinder piston substantially later than the
timing at which said intake valve is caused to close by said first
cam lobe associated with said intake valve.
6. A system according to claim 4, wherein said first cam lobe is
configured to open the exhaust valve at about 50.degree. before the
bottom dead center and close the same at about 10.degree. past the
top dead center and said second cam lobe is configured to open the
exhaust valve at about 50.degree. past the bottom dead center.
7. A system according to claim 5, wherein said first cam lobe
associated with the intake valve is configured to open the intake
valve at about 10.degree. before the top dead center and to close
the same at about 50.degree. past the bottom dead center and said
second cam lobe associated with the intake valve is configured to
close the intake valve at an angle appreciably smaller than
50.degree. past the bottom dead center.
Description
This invention relates to a valve timing system for use with an
automotive internal combustion engine and, more particularly, to a
valve timing system operating in relation to the driving conditions
of the engine.
The opening and closing movements of intake and exhaust valves of
an automotive internal combustion engine cylinder is usually timed
in such a manner as to provide an optimum performance efficiency of
the engine during normal cruising of the motor vehicle. When,
however, the motor vehicle is driven at relatively low speeds as in
city-road driving, the performance quality of the engine is more or
less degraded to discharge an increased quantity of unburned or
partially burned exhaust gases containing noxious compounds such as
hydrocarbons and carbon monoxides, causing a serious pollution of
atmospheric air in urban areas. Among the various schemes proposed
to solve such air pollution problem is the practice of opening the
exhaust valve at a retarded timing so that the fired gases stay in
the engine cylinder for a prolonged period of time at a high
temperature and at a high pressure, causing the hydrocarbons and
carbon monoxides to be fully combusted. Opening the exhaust valve
at a retarded timing is, although conductive to the reduction of
unburned, toxic content of the exhaust gases especially during low
speed and/or light load operation of the motor vehicle, reflected
by a degraded performance efficiency of the engine during high
speed and/or heavy load operation. This difficulty will be
maintained insofar as the valve timing is controlled, or retarded,
without respect to the conditions in which the engine operates.
An object of the invention is, therefore, to provide a valve timing
system wherein the exhaust valve is opened at a retarded timing and
closed at a slightly advanced timing during low speed and/or heavy
load operation of the motor vehicle as in a city-road driving.
Another object is to provide a valve timing system in which not
only the exhaust valve timing is controlled as noted above but the
intake valve is controlled in such a manner as to be opened at a
retarded timing and closed at a slightly advanced timing during the
low speed and/or heavy load operation of the motor vehicle.
Still another object is to provide a valve timing system which is
controlled in relation to any of the various operating variables,
such as the engine speed and the vacuum in the intake manifold of
the engine, of the motor vehicle whereby the opening and closing
movements can be selectively timed without affecting the engine
operation.
In the drawings:
FIG. 1 is a sectional view of an embodiment of the valve timing
system according to the invention;
FIG. 2 is a view showing an essential part of the valve timing
system as seen from the plane of II--II of FIG. 1;
FIG. 3 is a schematical view showing a preferred example of a
control means for use with the valve timing system of the
invention;
FIG. 4 is a graphical representation of an example of the range in
which the system according to the invention is made operative;
FIG. 5 is a diagram illustrating the exhaust valve timing schedule
realized by the system of the invention;
FIG. 6 is a graphical representation of a relationship between the
valve lift and the crankshaft revolution angle as observed in an
engine incorporating the valve timing system of the invention;
FIG. 7 is a perspective view showing essential parts of a modified
form of the valve timing system embodying the invention;
FIG. 8 is a diagram illustrating the intake valve timing schedule
realized by the system of FIG. 7;
FIG. 9 is similar to FIG. 6 but is connected with the system shown
in FIG. 7; and
FIG. 10 contains plots indicating the relationship between the
engine speed, the intake manifold vacuum and the vehicle speed
falling within the operating range of the valve timing system of
the invention.
Referring first to FIG. 1, the valve timing system according to the
invention is combined in use with an engine cylinder including a
rocker cover 10. In the engine rocker cover 10 is provided an
exhaust valve 12 which is operatively connected to a rocker arm 14
through a retainer 16. The exhaust valve 12 is axially movable to
open and close an exhaust opening (not shown) to discharge the
exhaust gases, and is normally kept seated by the action of a
compression spring 18. The rocker arm is pivotally supported by a
pivot 20 as clearly seen in FIG. 2.
A camshaft 22 is mounted on the cylinder 10 through a camshaft gear
or sprocket 24 to which the camshaft 22 is splined. The sprocket 24
is driven from the crankshaft (not shown) so that the camshaft 22
is rotatable with the crankshaft. The camshaft 22 being splined to
the sprocket 24, the same is axially movable within the rocker
cover 10. Designated by numeral 26 is a locator by which the
sprocket 24 is properly aligned. The camshaft 22 is rotatable and
axially movably supported by a camshaft support bearing 28 which is
fixed relative to the cylinder 10. A lubricating fluid passage 28a
may be formed in the support bearing 28 so as to smooth the
rotation and axial movement of the camshaft 22.
A first cam lobe 30 and a second cam lobe 32 are formed on the
camshaft 22 and are positioned relative to the rocker arm 14 of the
exhaust valve 12. Between the leading end of the camshaft 22 and
the end wall of the rocker cover 10 is mounted a cylinder member 34
which is secured to the rocker cover. The cylinder member 34 is
positioned relative to the leading end of the camshaft 22 and has
formed on its inner wall surface a stop 36 for limiting the axial
movement of the camshaft 22. A piston 38 is securely mounted on the
camshaft 22 at a portion near the leading end of the camshaft by a
bolt 40. The piston 38 is fitted to the cylinder member 34 so as to
define a chamber 42 therebetween. A compression spring 44 is
interposed between the support bearing 28 and the piston 38 through
a thrust bearing 45 which is mounted on the piston 38, as
illustrated.
The chamber 42 communicates on one side with a hydraulic fluid
supply passage 46 and on the other side with a hydraulic fluid
discharge passage 48. The hydraulic fluid supply passage 46, in
turn, communicates through an orifice 50 with a hydraulic fluid
gallery 52 and the hydraulic fluid discharge passage 48 on the
other hand communicates with a drain chamber 54. The gallery 52
communicates with a source (not shown) of pressurized hydraulic
fluid.
The first cam lobe 30, which is intended to be operative during
high speed and/or heavy load driving of the motor vehicle, is
smaller in size than the second cam lobe 32, which is operative
during low speed and/or light load driving. The first cam lobe 30
is positioned on the camshaft 22 is such a manner that it is
normally held in an abutting engagement with the rocker arm 14 when
the piston 38 and accordingly the camshaft 22 are forced toward the
stop 36 on the cylinder member 34 by the action of the spring 44 in
the absence of a hydraulic pressure in the chamber 42. The second
cam lobe 32, on the other hand, is positioned so that it is
normally held out of alignment with the rocker arm 14 when the
first cam lobe 30 abuts thereto and is moved into abutting
engagement with the rocker arm 14 when a hydraulic pressure obtains
in the chamber 42 so as to move the piston and accordingly the
camshaft 22 is moved away from the stop 36 against the action of
the spring 44.
The hydraulic pressure to be introduced into and discharged out of
the chamber 44 is controlled by a plunger or valve means 56 which
is located relative to the hydraulic fluid discharge passage 48.
The valve means 56, in turn, is controlled by a solenoid valve
which is generally represented by numeral 58. Designated by numeral
60 is a drain passage which is intended to allow a fluid pressure
to pass therethrough when the valve means 56 is closing.
The solenoid valve 58 consists essentially of a moving core 62
which is integral with the plunger or valve means 56, a spring 64
urging the moving core 62 to be protruded so as to cause the
plunger or valve means 56 to be held in a position to close the
discharge passage 48, and a solenoid coil 66 which, when energized,
causes the moving core 62 to move into its retracted position so
that the plunger or valve means 56 is moved to open the passage
48.
The solenoid coil 66 is energized in response to predetermined
operating conditions of the motor vehicle so that the valve means
56 is in a position to open the passage 48 only when the vehicle is
driven under predetermined conditions as during highway driving.
Various operating variables of the motor vehicle may be utilized to
represent such operating conditions dictating the movement of the
valve means inasmuch as the intent of this invention is maintained.
FIG. 3 illustrates an example of an electrical arrangement which
may be used as preferable for the control of the solenoid valve
58.
Turning therefore to FIG. 3, the solenoid coil 66 is connected
through a line 66a to a first switch 68 which is responsive to
variation in the vacuum in the intake manifold (not shown) of the
engine. The switch 68 is operated by a diaphragm device 70 having a
diaphragm member 72 to which the switch 68 is rigidly connected. A
compression spring 74 is seated on the reverse side of the
diaphragm member 72, which consequently is biased to a position in
which the switch 68 is kept open. The diaphragm member 72 is
subjected to a vacuum in the intake manifold of the engine and the
compression spring 70 is selected in a manner to overcome the force
of the intake manifold vacuum lower than a predetermined level,
say, about -100 mm. of Hg for instance. When the vacuum rises
beyond such predetermined level as in the deceleration of the motor
vehicle, then the spring 74 overcomes the force of the intake
manifold vacuum so that the diaphragm member 72 is moved to a
position in which the switch 68 is closed.
In lieu of the arrangement shown in FIG. 3, the switch 68 may be
controlled from a vacuum controlled advance device of the ignition
distributor if preferred.
The switch 68 is connected operatively to a second switch 76
through a line 78. The switch 76 may be a relay switch which is
normally open and which is closed when energized with a voltage
lower than a predetermined level. More specifically, the switch 76
is operatively connected to an ignition distributor 78 through a
line 80 so as to detect the primary pulses produced therein. A
voltage is generated which is proportional to the number of the
primary pulses, which voltage is then compared with a suitable
reference voltage corresponding to a predetermined engine speed
which may be 3,200 r.p.m. for instance whereupon the switch 76 is
closed. By preference, the switch 76 may be controlled otherwise
insofar as the same is closed only when the engine is driven at a
speed lower than the predetermined level. For instance, the switch
76 may be controlled from a fluid pressure governor or governors of
a power transmission or by a tachometric device where available.
Or, the switch 76 may operate on the revolution speed detected by
an electromagnetic pickup means which is arranged to be responsive
to the rotation of a gearing mounted on the crankshaft.
The first and second switches 68 and 76, respectively, are
connected in series with a source 82 of electric power; the power
source 82 may be a series of batteries, if preferred.
When, in operation, the motor vehicle is driven on a highway or
expressway with the engine speed higher than a predetermined level
(3,200 r.p.m. for instance) and the intake manifold vacuum lower
than a predetermined value (-100 mm. of Hg, for instance), then the
switches 68 and 76 are kept open, keeping the solenoid coil 66 of
the solenoid valve 58 unexcited. The plunge or valve means 56 is
consequently kept protruded by the action of the spring 64 to close
the hydraulic fluid discharge passage 48. This results in an
increase in the fluid pressure in the chamber 42 so that the piston
38 and accordingly the camshaft 22 are moved away from the stop 36
against the action of the spring 44 until the cam lobe 32 is
brought in alignment with the rocker arm 14. The opening and
closing movements of the exhaust valve 12 is thus governed by the
rotation of the greater cam lobe 32 when the motor vehicle is
driven at a high speed.
When the motor vehicle decelerates or cruises at a low speed as in
city-road driving, the engine speed decreases and the intake
manifold vacuum increases so that the switches 68 and 76 are closed
simultaneously or differentially. With the two switches 68 and 76
concurrently kept closed, the solenoid coil 66 of the solenoid
valve 58 is excited to cause the plunger or valve means 56 to move
into its retracted position against the action of the spring 64,
opening the hydraulic fluid discharge passage 48. The fluid
pressure entrapped within the chamber 42 is now allowed into the
drain chamber 54 through the discharge passage 42. The piston 38
and accordingly the camshaft 22 are thus moved toward the stop 36
by the action of the spring 44 until the first cam lobe 30 is
brought into alignment with the rocker arm 14. The opening and
closing movements of the exhaust valve 12 are now dictated by the
rotation of the first cam lobe 30.
FIG. 4 illustrates an example of the range in which the two
cooperating switches 68 and 76 are to be closed concurrently,
wherein the first switch 68 is assumed to close when the intake
manifold vacuum is higher than -100 mm. of Hg and the second switch
76 is assumed to close when the engine speed is lower than 3,200
r.p.m., by way of example.
The first cam lobe 30, which is intended to regulate the valve
timing during high speed and/or heavy load driving of the motor
vehicle, is so configured that the exhaust valve 12 is opened
preferably at about 50.degree. anterior to the bottom dead center
(B.D.C.) of the piston movement of the engine cylinder and is
closed slightly, preferably at about 10.degree., posterior to the
top dead center (T.D.C.), as seen in FIGS. 5 and 6. The second cam
lobe 32, which is used for regulating the movements of the exhaust
valve 12 during low speed and/or light load driving of the motor
vehicle, is configured in such a manner that, as seen in FIGS. 5
and 6, the exhaust valve 12 is opened at preferably 50.degree.
anterior to the B.D.C. and is closed substantially at the T.D.C. It
will be appreciated from FIG. 6 that the valve lift is smaller when
the second cam lobe 32 is operative than when the first cam lobe 30
is operative.
Only the exhaust valve is controlled selectively depending upon the
driving conditions of the motor vehicle in the embodiment of the
valve timing system illustrated in FIGS. 1 to 3 but the intake
valve as well as the exhaust valve may be controlled on the same
principle if desired, an example being shown in FIG. 7.
Referring to FIG. 7, the intake valve is designated by numeral 86
and is associated with a rocker arm 88, retainer 90 and a
compression spring 92, similarly to the exhaust valve 12. In the
modified valve timing system shown in FIG. 7, the camshaft 22 has,
in addition to the set of lobes 30 and 32, another set of a first
lobe 94 and a second lobe 96. These cam lobes 94 and 96 are moved
and selectively aligned with the rocker arm 88 for the intake valve
86 as the lobes 30 and 32, respectively, are moved and aligned with
the rocker arm 14 for the exhaust valve 12 and, as such, discussion
of the operations of the cam lobes 94 and 96 is herein omitted.
The first cam lobe 94, which is made operative when the motor
vehicle is driven at a speed higher than a predetermined level
and/or under heavy load conditions, is configured in a manner that
the intake valve 86 is opened slightly, preferably at about
10.degree. anterior to the T.D.C. and is closed preferably at
50.degree. posterior to the B.D.C. The second cam lobe 96 which
operates during low speed and/or light load driving of the motor
vehicle, is so configured that the intake valve 86 is opened
substantially at the T.D.C. and is closed slightly anterior to the
point at which the intake valve is closed when the cam lobe 94 is
operative. This will be clearly seen in FIG. 8. FIG. 9 illustrates
that the valve lift is sizably greater when the cam lobe 94 is
operative than when the cam lobe 96 is operative.
FIG. 10 is presented to show how the engine speeds and the intake
manifold vacuums, both of which are utilized as preferred variables
to represent the driving conditions of the motor vehicle in the
system of the invention, vary markedly with the driving speeds of
the motor vehicle, from which it will be understood that the
operating range of the valve timing system can be determined
suitably so as to achieve the desired purpose of controlling the
valve timing in accordance with the driving conditions of the motor
vehicle.
It will now be apparent from the foregoing description that the
exhaust valve or both of the exhaust and intake valves can be timed
for satisfactory combustion of the air-fuel mixture in the engine
cylinder without causing a significant power loss through the
varying driving conditions of the motor vehicle.
It is, moreover, important for promoting the satisfactory
combustion of the hydrocarbons and carbon monoxides in the air-fuel
mixture that a sufficient quantity of oxygen be contained in the
fuel gases supplied to the engine cylinder. An engine operable with
a relatively lean air-fuel mixture is thus proposed and used for
this purpose and, where the engine of this type is used, it is
necessary to distribute the air-fuel mixture properly to each of
the engine cylinders, to propagate the mixture evenly throughout
the combustion chamber, and to build up a turbulent flow of the
air-fuel mixture in the combustion chamber. This will be
accomplished by throttling the intake opening of the engine
cylinder by the intake valve thereby to "squeeze" the mixture to be
passed therethrough. The modified embodiment of the valve timing
system as shown in FIG. 7 is advantageous for this purpose, because
the valve lift is significantly limited during low speed and/or
light load driving when an increased amount of unburned exhaust
gases are usually discharged.
* * * * *