Geometrical instruments – Gauge – Cam profile or keyway
Reexamination Certificate
2000-02-11
2001-07-10
Bennett, G. Bradley (Department: 2859)
Geometrical instruments
Gauge
Cam profile or keyway
C033S501020
Reexamination Certificate
active
06256897
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a three-dimensional cam having a surface that varies continuously in the axial direction. More particularly, the present invention relates to a three-dimensional engine valve cam having a profile for controlling the opening and closing of engine valves in accordance with the operating state of the engine. The present invention also pertains to a method for measuring three-dimensional cams, measuring tools for testing profiles of three-dimensional cams, and an apparatus for measuring three-dimensional cams. The present invention also relates to an engine valve drive apparatus employing such three-dimensional cams.
FIG. 24
shows a prior art valve drive apparatus that continuously varies the opening and closing timing and lift amount of engine intake valves and engine exhaust valves. Japanese Examined Patent Publication No. 7-45803 and Japanese Unexamined Patent Publication No. 9-32519 describes such apparatus. As shown in
FIG. 24
, two valves
543
, which are either intake valves or exhaust valves, are provided for a single cylinder of an engine. Each valve
543
is connected to and driven by a three-dimensional cam
540
, which is fixed to a camshaft
542
. The cam
540
has a cam surface
540
a
used to drive the valves
543
. A cam nose, the radius of which changes continuously in the direction of the camshaft axis Y of the camshaft
542
, is defined on the cam surface
540
a
. The shifting mechanism
541
shifts the camshaft
542
to displace each cam
540
within a range denoted by D. As the cam
540
shifts, the nose radius of the cam surface
540
a
changes continuously. This varies the lift amount and opening and closing timing of the associated valve
543
. The change in the lift amount (lift control amount) occurs within a range defined between the maximum and minimum values of the cam nose radius. The shifting of the camshaft
542
along the axis Y is controlled so that the maximum lift amount of each valve
543
is small when the engine is in a low speed range and is large when the engine is in a high speed range. This improves engine performance, especially in terms of torque and stability.
As shown in
FIG. 24
, a valve lifter
549
is arranged between each valve
543
and the associated three-dimensional cam
540
. A cam follower seat
544
is defined in the top center surface of each valve lifter
549
. A cam follower
545
is pivotally received in each follower seat
544
so that the valve lifter
549
can follow the cam surface
540
a
of the associated cam
540
.
Each cam follower
545
has a flat slide surface
545
a
, which slides along the associated cam surface
540
. The shape of the cam follower
545
is shown enlarged in FIGS.
25
(
a
) and
25
(
b
). As shown in FIG.
25
(
a
), the cam follower
545
has a semicircular cross-section. FIG.
25
(
b
) is a side view of the cam follower
545
.
As shown in
FIG. 26
, the cam follower
545
has a first edge
545
b
and a second edge
545
c
that engage the cam surface
540
a
. Contact between the cam follower
545
and the cam surface
540
a
occurs between the first edge
545
b
and the second edge
545
c
. The first edge
545
b
contacts the cam surface
540
a
where the cam nose radius is smaller than that where the second edge
545
c
contacts the cam surface
540
a.
FIG. 27
is a perspective view showing the cam surface
540
a
. The uniformly dashed line represents one axial end of the cam
540
, or cam profile
547
, where the cam nose radius is smallest. The long and short dashed line represents the other axial end of the cam
540
, or cam profile
548
, where the cam nose radius is greatest. As apparent from the drawing, the profile of the cam
540
varies continuously in the axial direction. Each elemental line
546
shown in the drawing represents the same angular position on the cam surface
540
a
. In other words, the lines
546
represent intersections between the cam surface and planes that include the axis Y. Although the drawing shows a limited number of lines
546
, an infinite number of lines
546
may be defined along the cam surface
540
. Hence, the cam follower
545
comes into linear contact with the cam surface
540
a
along part of each line
540
.
As shown in
FIG. 26
, when the three-dimensional cam
540
shifts along the axis Y, the slide surface
545
a
between the first and second edges
545
a
,
545
b
of the cam follower
545
is in linear contact with and moves relative to the cam surface
540
a
. Lubricating oil is removed from the cam surface
540
a
when relative movement takes place between the cam follower
545
and the cam surface
540
a
. This occurs especially when the second edge
545
c
scrapes off the lubricating oil from the cam surface
540
a
as the cam follower
545
shifts along the cam surface
540
a
from the smaller radius side to the larger radius side. As a result, lubrication between the second edge
545
c
and the cam surface
540
a
becomes insufficient. This may lead to wear of the second edge
545
c
and the cam surface
540
a.
Generally, the small radius side of the cam
540
is used more frequently than the large radius side. Therefore, a difference in wear occurs along the cam surface
540
a
in the axial direction Y. The wear difference causes the cam surface
540
a
to become uneven. An uneven cam surface
540
a
may interfere with the movement of the second edge
545
c
and thus hinder with smooth shifting of the opening and closing timing and lift amount of the associated valve
543
.
Additionally, the cam surface
540
is machined with precision so that the surface
540
a
is straight as shown in FIG.
27
. However, tolerances permitted during machining of the cam surface
546
may result in a slight concavity in surface
540
a
, as shown in FIG.
28
. In such case, only the first and second edges
545
b
,
545
c
of the cam follower
545
contact the cam surface
540
a
. This may cause the first and second edges
545
b
,
545
c
to scratch the cam surface
540
a
during rotation of the cam
545
or cause biased wear of the cam follower
545
at the edges
545
b
,
545
c.
When scratches are formed in the cam surface
540
a
, the scratches may interfere with axial movement of the three-dimensional cam
540
. This would hinder with smooth varying of the opening and closing timing and lift amount of the associated valve
543
.
SUMMARY OF THE INVENTION
Accordingly, it is an objective of the present invention to provide a three-dimensional cam and a valve drive apparatus that enable smooth relative movement between the cam surface and the cam follower without damage or wear of the cam surface and cam follower. It is a further objective of the present invention to provide a method and apparatus for measuring the profile of such three-dimensional cam.
To achieve the above objectives, the present invention provides a cam mechanism including a cam, a cam follower, and a driven member. The cam rotates about its axis to drive the driven member with the cam follower. The cam mechanism further includes a cam surface defined on the cam to slidably engage the cam follower. The cam surface has a profile that varies continuously in the direction of the cam axis. The cam moves axially and changes the position of the cam surface with respect to the cam follower to vary the behavior of the driven member. A slide surface is defined on the cam follower to slidably engage the cam surface. At least one of the cam surface and the slide surface is convexly arched in the direction of the cam axis.
The above cam mechanism is preferably applied to a valve drive apparatus of an automobile engine.
In another aspect of the present invention, a cam for driving a driven member with a cam follower is provided. The cam is rotatable about its axis and has a cam surface to slidably engage the cam follower. The cam surface has a profile that varies continuously in the direction of the cam axis and is convexly arched in the direction of the cam axis.
In a further aspect of the present invention, a cam follower is pr
Bennett G. Bradley
Kenyon & Kenyon
Toyota Jidosha & Kabushiki Kaisha
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