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VARIABLE VALVE GEAR
The invention provides a variable valve gear
particularly for internal combustion engines, in which a control cam of a
camshaft acts, by way of a pair of swivellably coupled levers, to a valve to
produce an adjustment of the valve stroke. The valve stroke can vary
continuously from a maximum value to zero while the valve clearance is held
unchanged.
In the prior art several variable valve gear
mechanisms are described. The objective is always the adjustment, continuous if
possible, of valve operation, as regards valve stroke and valve timing, so that
the breathing of the engine being the best for the particular operational
conditions. Some of the most relevant patents are : US 5,899,180, US 5,373,818,
US 5,205,247, US 5,732,669, US 5,056,476, US 6,145,485, US 6,032,624,US
4,502,426, US 5,937,809, US 6,029,618, US 5,996,540, US 5,988,125, US
6,055,949, US 6,123,053, US 6,019,076, US 5,003,939 and US 5,365,895
The advantages of a continuously variable
valve gear are known to those relative to the art. Some of the side effects are
the extra cost, the lower revs limit, the involvement of strong springs, the
complication in assembly and service, the extra height, the friction loss, the
noise.
Achieving slight valve strokes allows for
elimination of the throttle valve resulting in reduced consumption, reduced
pollution and better performance, especially at partial loads, without
compromise in power output.
In the present invention the additional
components are fewer, in some realizations two additional pieces per valve,
plus a control shaft per row of valves, they can be light, especially those
ones bound to move quickly, they can be small in dimensions, so the engine’s
height can be low, they do not need special construction accuracy, the
restoring force, for secure contact of cam follower to control cam, is
generated basically by the valve spring, so additional strong restoring springs
are not a necessity, the resulting thrust force to the valve’s bucket lifter or
to the valve’s rocker arm is small, especially at high valve strokes and high
revs, the throttle in the induction system is necessary no more since the
stroke of the valve can vary from a maximum to zero, the friction is small.
The closest prior art is the US patent
5.899.180 of Fischer, where the rotation of a control shaft, which serves a row
of valves, changes the valve timing and stroke in a continuous manner. In that
patent an arm has a roller, at one end, which rolls on a control cam of a
camshaft. The arm is rotatably supported, at its other end, about an axis. As
this axis moves along a path, due to the rotation of the control shaft, the
resulting stroke/timing of the valve is changing continuously. The roller moves
along a circular arc. As this circular arc changes position relative to the
circular arc contact surface of the roller on the rocker arm, the valve stroke
and the valve timing
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changes. When the two arcs are “vertical” to
each other, the valve stroke is long. When the two arcs are “parallel” the
resulting valve stroke is small. So, by rotating the control shaft, the
stroke/timing of a row of valves is controlled.
In the present invention there is also a
control shaft. This control shaft can rotate about a, fixed to the engine,
axis. For each valve in a row there are two levers, the valve lever and the
control lever, swivellably coupled at one end. The control lever is rotatably
supported, at its other end, to the control shaft to rotate about a movable
axis, like the arm with the roller in US 5.899.180 patent. The valve lever is
swivellably coupled, at its other end, to the valve’s rocker arm or to the
valve’s bucket lifter, that is to the valve displacing device. The cam follower
is pushed by the control cam of the camshaft, forcing the swivel joint coupling
the control lever and the valve lever to oscillate along an arc whose center is
the movable axis on the control shaft. The swivel joint, coupling the valve lever
and the valve’s rocker arm or valve’s bucket lifter, can move also along a
path, circular in case of a rocker arm and linear in case of a bucket lifter.
Depending on the relative position of the two paths, that one of the swivel
joint coupling the control lever and the valve lever, and that one of the
swivel joint coupling the valve lever and the rocker arm or bucket lifter, the
stroke of the valve changes continuously from a maximum to zero. The more
“parallel” the two paths, the longer the valve stroke.
By selecting the effective lengths of control
and valve levers, and by selecting the position of the rotation axis of the
control shaft, constant valve clearance and continuously adjusted valve stroke,
from a maximum value to zero, are achievable.
To secure contact of the cam follower to the
control cam, particularly at short and very short valve strokes, an additional
spring element can be inserted to assist this contact. In case of long valve
strokes the necessary restoring force comes from the valve spring, so the
spring element mentioned can stay inactive.
The system described in this patent in
combination with some variable valve timing system provides a completely
controlled variable valve gear system.
Fig 1 shows a realization of the proposed variable
valve gear.
Fig 2 shows a disassembly of the mechanism of
Fig 1.
Fig 3 shows the assembly and interconnection
of the various constituents of Fig 1.
Fig 4 shows, from various points of view, the
main constituents of the mechanism of Fig 1.
Fig 5 shows the mechanism of Fig 1 for two
angles of the camshaft, adjusted for long valve stroke.
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Fig 6 shows the mechanism of Fig 1 for two
angles of the camshaft, adjusted for an intermediate valve stroke.
Fig 7 shows the mechanism of Fig 1 for two
angles of the camshaft, adjusted for a very short or zero valve stroke.
Fig 8 shows a temporal course of the
operation of the mechanism of Fig 1. In the upper row the mechanism is adjusted
for long valve stroke, in the intermediate row the mechanism is adjusted for
medium valve stroke and in the lower row the mechanism is adjusted for short
valve stroke. The five stages shown in each row correspond to 180 degrees total
rotation of the camshaft, of 45 degrees steps.
Fig 9 shows in sectional view what is shown
in Fig 8.
Fig 10 shows a row of 8 valves controlled by
a common control shaft. They could, for instance, be the intake or the exhaust
valves of a four in line, sixteen valve, four cycle typical engine. The control
shaft or adjusting device is shown alone at left, from three different points
of view. In the third, from right, assembly the control shaft is rotated to
give long valve stroke. In the second, from right, assembly the control shaft
or adjusting device is rotated to give a medium valve stroke. In the right
assembly the control shaft or adjusting device is rotated for zero valve
stroke.
Fig 11 shows, from another point of view,
what is shown in Fig 10.
Fig 12 shows the assembly of Fig 10 and 11
with the valves and the valve bucket lifters removed, for better understanding.
Here they are shown the valve levers, the control levers, the common control
shaft, or adjusting device, and the camshaft.
Fig 13 shows another realization. Here the
cam follower is a roller rotatably supported to valve lever either to control
lever. The rotation axis of the control lever is in a position, on the path
drawn with dashed dot line, for zero valve stroke. The mechanism is shown for
two different angles of the camshaft.
In Fig 14, 15 and 16 it is shown the
mechanism of Fig 13, for three other conditions of the adjusting device. In Fig
14 the valve stroke is very short, in Fig 15 the valve stroke is medium and in
Fig 16 the valve stroke is long. The operation of the mechanism is similar, for
the rest, to the mechanism of Fig 1.
In Fig 17 and 18 it is shown the mechanisms
of Fig 13 to 16 from other points of view.
Fig 19 shows another realization of the
present invention, for two angles of the camshaft. Here the displacing valve
mechanism is a rocker arm. The valve lever is swivellably coupled to the rocker
arm, with the swivel joint being a cylindrical surface, at the end of the valve
lever, rotating in a corresponding cylindrical journal formed on the rocker
arm. Another difference from the previous mechanisms is that the cam follower
is
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mounted on the valve lever. The shape of the
cam follower is a plane surface but it could also be any other shape, as it is
secured to the valve lever. Even so the clearance can remain constant, no
matter what is the condition of the control shaft, and the valve stroke can
change from a maximum to zero.
Fig 20 shows the mechanism of Fig 19 adjusted
to offer a shorter valve stroke.
In Fig 21 and 22 they are shown the
mechanisms of Fig 19 and 20 correspondingly, in sectional views.
In Fig 23 they are shown, from other points
of view, the mechanisms shown in Fig 19 to 22.
Fig 24 shows a realization of the present
invention with an additional spring member for providing the necessary
restoring force to assist the contact of the cam follower to the control cam,
at short valve strokes. The mechanisms shown are exactly the mechanisms shown
in Fig 5, 6 and 7 with the control shaft removed for clarity, and with the
addition of a spring member. The spring member comprises a spring inside a case
secured to the engine casing, not shown, and a stem. The spring pushes linearly
the stem. At long valve strokes the spring and the stem are idle at their
outmost position. For short valve strokes the stem comes in contact to the
control lever, offering the necessary restoring force to secure the contact of
the cam follower to the control cam. For short valve strokes the restoring
force, from the spring member, is added to the restoring force from the valve
spring. Only at zero valve stroke all the restoring force is generated by the
additional spring member. If zero valve stroke is not used at all, and if the
short valve strokes are only for low revs, an additional spring member is not
necessary.
Fig 25 shows the mechanisms of Fig 24 from
another point of view.
Referring to the mechanism shown in Figures 1
to 12, 1 is the camshaft, 2 is a control cam mounted on said camshaft 1, 3 is a
cam follower having a cylindrical shape and being mounted to the control lever
8. Said control lever 8 is rotatably supported at its end 17 to a control shaft
7, to rotate about an axis 9 of the control shaft 7. The control shaft 7 is
rotatably supported to the engine frame, not shown, to rotate about a fixed to
said engine axis 10. The control lever 8 is swivellably coupled, at
its other end 11, to the valve lever 6. The swivel joint coupling the control
lever 8
and the valve lever 6 comprises a spherical surface 12 at the end of the
valve lever 6, inserted into a corresponding spherical cavity 11 of the control
lever 8. At the other end the valve lever 6 is swivellably coupled to the
bucket lifter 5, or valve displacing device 5, of the valve 4. The swivel joint
coupling the valve lever 6 and the bucket lifter 5 is comprises a spherical
surface 13 at the end of the valve lever 6, inserted into a corresponding
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spherical cavity 18 of the bucket lifter. The
valve 4 has a corresponding valve seat 14 to rest when it is closed. The
effective length of the control lever 8, the effective length of the valve
lever 6 and the distance from the axis 10 to the axis 9 are all selected to be
substantially equal. The location of the control shaft 7, or adjusting device
7, is selected so that the axis 10 passes substantially through the center of
the swivel joint coupling control lever 8 and valve lever 6, when the valve 4
is closed. As the camshaft 1 rotates, the cam follower 3 is forced to perform a
motion. The bearing 16 on the adjusting device 7, in cooperation with the end
17 of the control lever 8, allows to the control lever 8 just an angular
displacement about the axis 9 of the adjusting device 7. Through the two swivel
joints, 11 to 12 and 13 to 18, the valve lever is pushed, at the end 12, from
the control lever 8, and is pushing, at the end 13, the bucket lifter 5 which
can move only linearly, so the rotation of the control cam 2 is translated to
angular oscillation of the control lever 8 and then , by means of the valve
lever 6, to linear oscillation of the bucket lifter 5 and valve 4. To change
the valve stroke it suffices to rotate, about the axis 10, the control shaft 7.
In case the axis 9 of the adjusting device 7 is displaced to pass through the
center of the swivel joint coupling valve lever 6 and bucket lifter 5, the
stroke of the valve 4 becomes zero. With the mechanism proposed can be achieved
both, substantially constant valve clearance and ability for valve strokes
continuously variable from a maximum to zero.
The longer the valve stroke, the heavier the
inertia loads. However at the long valve strokes is where the valve lever 6
remains almost parallel to the valve stem, Fig 8 upper row, giving slighter thrust
load to the bucket lifter 5. The restoring force, for securing the contact of
the cam follower to the control cam, can be generated by the valve spring. If
very short or even zero valve strokes are wanted, an additional spring could be
located to provide the necessary force for holding in contact the cam follower
3 and the control cam 2, as shown in Fig 24 and 25. This spring can remain, as
shown in Fig 24 and 25, completely idle at medium and long valve stroke
operation.
In Fig 3 it is shown the way for assembling
the control lever 8 to the control shaft 7, or adjusting device 7. As the
rotation angle of the control lever 8 about the axis 9 of the control shaft is
limited, there is no need for 360 degrees bearing 16 and pin 17. In the way
shown, for each valve in a row, just a control lever and a valve lever suffice.
And for the whole row of valves it is needed only one common control shaft. The
spherical swivel joints are not a necessity. They could also be cylindrical
etc.
In case the effective lengths of control
lever and valve lever, as well as the distance from 9 to 10 axis are not equal,
again the mechanism works but, depending on the selected lengths and the
location of the axis 10, the
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clearance of the valve may not be constant,
and the available valve strokes may not include very short values.
The bucket lifter 5 can obviously have some
hydraulic compensation element inside.
The operation principle, for the mechanism
shown in Fig 13 to 18, is similar. The cam follower is a roller properly
mounted to the control and valve levers. The adjusting mechanism is not shown,
but with dash dot line is shown the path of the axis 9. The swivel joints are
made with pins, one for the interconnection between the bucket lifter 5 and the
valve lever 6, and one for the interconnection between the valve lever 6 and
the control lever 8.
The mechanism shown in Fig 19 to 23 is a
similar one. Here the valve displacing device 5 is a rocker arm. The swivel
joint coupling the valve lever 6 and the rocker arm 5 comprises a cylindrical
surface at the end of the valve lever 6, cooperating with a corresponding
cavity of cylindrical form of the rocker arm. The cam follower has not a
cylindrical shape, nevertheless the valve clearance can be constant and the
valve stroke can continuously vary from a maximum to zero. The form of the cam
is not necessarily plane or cylindrical.
If it is desirable to be changed slightly the
valve clearance, depending on the valve stroke, the shape of the cam follower
could be modified or a small offset from the theoretically perfect position of
the axis 10 could be applied, or slightly different effective lengths, of
control and valve levers, could be used.
In case of bevel or conical control cams, the
previous could also be applied with some small modifications, obvious to the
relevant of the art.
In case that different adjustment for the
various valves in a row is wanted, the adjustment mechanism could be designed
to be able to displace the axis 9 of each valve independently.
Although the invention has been described and
illustrated in detail, it is to be clearly understood that the same is by way
of illustration and example, and is not to be taken by way of limitation. The
spirit and scope of the present invention are to be limited only by the terms
of the appended claims.
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CLAIMS
What is claimed is:
1. A variable valve gear, comprising:
a cam shaft (1);
a control cam (2) mounted on said cam shaft
(1);
a cam follower (3);
a valve (4);
a valve displacing device (5) for displacing
said valve (4);
a valve lever (6) between said cam follower
(3) and said valve displacing device (5), said valve lever (6) being
swivellably coupled to said valve displacing device (5);
a control lever (8) rotatable about an axis
(9) and swivallably coupled to said valve lever (6) at a swivel joint;
an adjusting device (7) for displacing said
axis (9) along a path;
whereby the stroke of said valve (4) can be
continuously variable from a maximum to a minimum, according the displacement
of said axis (9) along said path;
2. A variable valve gear, as claimed in claim
1, characterized in that:
said axis (9) is movable at a substantially
constant distance from a fixed to said engine axis (10);
thereby the stroke of said valve (4) is
controlled by the angular displacement of said axis (9) about said fixed to
said engine axis (10).
3. A variable valve gear, as claimed in claim
1, characterized in that:
said axis (9) is movable at a constant
distance from a fixed to said engine axis (10);
said constant distance being substantially
equal to the distance between said axis (9) and the center of said swivel
joint;
thereby the clearance of said valve (4) can
be constant, independent of the valve stroke of said valve (4);
4. A variable valve gear, as claimed in claim
1, wherein:
said control lever (8) has an effective
length equal to the distance from said axis (9) to the center of the swivel
joint coupling said control lever (8) and said valve lever (6);
said valve lever (6) has an effective length
equal to the distance from the center of the swivel joint coupling said control
lever (8) and said valve lever (6), to the center of the swivel joint coupling
said valve lever (6) and said valve displacing device (5);
characterized in that:
said effective length of said control lever
(8) is substantially equal to said effective length of said valve lever (6);
thereby when said axis (9) is displaced at
the center of said swivel joint
coupling said valve lever (6) and said valve
displacing device (5), the
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stroke of said valve (4) becomes zero.
5. A variable valve gear, as claimed in claim
1, wherein:
said control lever (8) has an effective
length equal to the distance between said axis (9) and the center of said
swivel joint coupling said control lever (8) and said valve lever (6);
said valve lever (6) has an effective length
equal to the distance between the center of said swivel joint, coupling said
control lever (8) and said valve lever (6), and the center of the swivel joint
coupling said valve lever (6) and said valve displacing device (5);
characterized in that:
said axis (9) moves sustaining a
substantially constant distance from a fixed to said engine axis (10);
said effective length of said control lever
(8) being substantially equal to said constant distance between said axis (9)
and said fixed to said engine axis (10);
said effective length of said valve lever (6)
being substantially equal to said constant distance between said axis (9) and
said fixed to said engine axis (10);
thereby the stroke of said valve (4) can
vary, according the angular displacement of said axis (9) about said fixed to
said engine axis (10), from a maximum value to zero, while said valve (4)
clearance is substantially constant for every stroke of said valve (4);
6. A variable valve gear, as claimed in claim
1, characterized in that:
a spring element provides force for keeping
said cam follower (3) substantially in contact with said control cam (2).
7. A variable valve gear, as claimed in claim
1, characterized in that:
a spring element provides a force for keeping
said cam follower (3) substantially in contact with said control cam (2) at
short valve strokes, while it idles at long valve strokes;
8. A variable valve gear, as claimed in claim
1, characterized in that:
said adjusting device (7) controls more than
one valves.
9. A variable valve gear, as claimed in claim
1, characterized in that:
said cam follower (3) is a roller rotatably
supported to said valve lever (6), or to said control lever (8), or both.
10. A variable valve gear, as claimed in
claim 1, characterized in that:
said cam follower (3) is made as a
cylindrical shape surface secured to said control lever (8);
the center of said swivel joint coupling said
control lever (8) and said valve lever (6) being substantially on the axis of
said cylindrical surface;
said axis (9) moves sustaining a constant
distance from a fixed to said engine axis (10);
said axis of said cylindrical surface being,
when said valve (4) is closed,
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substantially on said fixed to said engine
axis (10);
thereby the clearance of said valve (4) can
be substantially constant as the displacement of said axis (9) varies.
11. A variable valve gear, as claimed in
claim 1, characterized in that:
said cam follower (3) is mounted on said
valve lever (6).
12. A variable valve gear, as claimed in
claim 1, characterized in that:
said valve lever (6) being mere a push rod.
13. A variable valve gear as claimed in claim
1, characterized in that there is a hydraulic member for automatic clearance
compensation.
14. A variable valve gear as claimed in claim
1, characterized in that said cam shaft is driven by means of a variable valve
timing system in order to control both, the stroke and the timing of the valve.
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ABSTRACT
A variable valve gear particularly for
internal combustion engines, in which a control cam of a camshaft acts, by way
of a pair of swivellably coupled levers, to a valve to produce an adjustment of
the valve stroke. The valve stroke can vary continuously from a maximum lift to
zero lift while the valve clearance can remain unchanged.