Internal-combustion engines – Two-cycle – Whirl through piston-controlled ports
Reexamination Certificate
1999-05-14
2001-04-17
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
Two-cycle
Whirl through piston-controlled ports
C123S323000
Reexamination Certificate
active
06216648
ABSTRACT:
BACKGROUND OF THE INVENTION
Internal combustion engines generally include at least one cylinder and a reciprocating piston within the cylinder connected to a crankcase. The cylinder is generally built with at least one intake (transfer) port and at least one exhaust port formed in the side walls of the cylinder.
During the engine's operation, the reciprocating piston within the cylinder alternately opens and closes the intake and exhaust ports. Initially, the intake port opens in communication with an intake passage and feeds an air/fuel mixture to the cylinder for combustion. Subsequently, the exhaust port opens to allow combusted spent gases to exit through the exhaust port in communication with an exhaust passage. This cycle is repeated.
However, since the exhaust port is fixed in size and location within the cylinder, the amount of time that this port is open for communicating the air/fuel mixture or spent gases with the cylinder bore varies according to the relative speed and position of the piston. For example, at any fixed time with respect to the engine's internal cycle, the piston may be fully blocking, fully opening or partially blocking the ports.
The engine's performance depends on the engine's cycle of opening and closing the exhaust and intake ports. In general, maintaining the exhaust passage open for a longer period improves the engine's performance at higher engine speeds. Conversely, keeping the exhaust passage open for a shorter period improves the engine's performance at lower engine speeds. Accordingly, to optimize the engine's performance, it is desirable to variably control the period during which the exhaust valve or passage is open based on the speed of the engine. Therefore, it is desirable to provide an exhaust valve having a variable valve timing that is based on the current operating conditions of the engine. For example, it is desirable to provide a variable exhaust period based on the current engine speed, load, or throttle position.
Several attempts have been made in the prior art to provide a mechanism for controlling the amount of time that the exhaust port is open. For example,
FIG. 1
illustrates an internal combustion engine
10
according to U.S. Pat. No. 4,399,788 to Bostelmann. The Bostelmann ('788) patent teaches the technique of utilizing a restricting member
12
mounted within the cylinder
14
structure for adjusting the exhaust valve position based on the gas pressure within the exhaust passage
18
. The positive pressure generated in the exhaust passage
18
is communicated via an orifice
24
in the exhaust passage
18
through a pressure tract
20
, whereby it inflates a pressure chamber
22
of the valve control mechanism
26
.
The valve control mechanism
26
comprises a flexible diaphragm
28
to which the positive exhaust gas pressure is applied. The diaphragm
28
and restricting member
12
are attached to a rigid cover
34
biased by a return spring
30
that opposes the exhaust gas pressure. Accordingly, when the positive pressure generated in the exhaust passage
18
exceeds the downward force of the return spring
30
, the rigid cover
34
lifts and retracts the restricting member
12
. The valve port restricting member
12
is thereby adapted to the exhaust passage
18
for varying the opening of the exhaust port
32
from a full flow position to a restricting flow position. The restricting member
12
effectively varies the axial extent of the exhaust port
32
along the axial length of the cylinder
14
.
Varying the axial extent of the exhaust port
32
along the axial extent of the cylinder
14
relative to a reciprocating piston (not shown), varies the period for which the exhaust port
32
is open or closed during the engine's
10
cycle. Generally, higher engine speed produces a greater pressure. Accordingly, the restricting member
12
is adjusted to effectively provide a larger exhaust port
32
opening. The valve control mechanism
26
only responds to positive pressure for moving the restricting member
12
in one direction and responds to the spring
30
force for moving the restricting member
12
in the opposite direction.
FIG. 2
illustrates an internal combustion engine, shown generally at
36
, similar to the mechanism illustrated in FIG.
1
. The engine
36
features a valve control mechanism
38
. The pressure is communicated through orifice
62
, and is directed by a one-way valve
44
, through an electronically operated valve
48
and eventually to a pressure chamber
54
. The electronically operated valve
48
is controlled by a CDI ignition unit
50
, for example. As the pressure chamber
54
pressurizes and overcomes the spring
60
force, a restricting member
46
is retracted from the exhaust passage
42
. Similarly, as the pressure decreases, the restricting member
46
is extended into the exhaust passage
42
. The valve control mechanism
38
only responds to positive pressure for moving the restricting member
46
in one direction and responds to the spring
60
force for moving the restricting member
46
in the opposite direction.
The CDI ignition unit
50
provides an RPM activated signal to the electronically operated valve
48
at a predetermined engine RPM. At such time, the valve
48
allows positive pressure to communicate with the exhaust valve control mechanism
38
through a pressure feedline
52
. The positive pressure pressurizes the pressure chamber
54
. The pressure inflates the flexible diaphragm
56
attached to a rigid cover
58
. When the CDI signal is canceled, the electronically operated valve
48
closes and disconnects the pressure feed from the one-way valve
44
to the pressure chamber
54
. The force of the return spring
60
then repositions the exhaust valve to its down position.
The electronically operated valves used in Bostelmann ('788) operate by opening only to positive pressures. For example, (
FIG. 5A
) illustrates a typical CDI valve unit
64
for activating the electronic pressure switch. The valve unit
64
comprises a CDI switch
66
and a one-way solenoid valve
68
.
Thus, prior art valve actuation systems comprise exhaust valve control mechanisms that operate only in response to positive pressure signals generated within the crankcase or the exhaust passage, and to the mechanical force of a return spring. Furthermore, the pressure cavities in these systems are flexible on all surfaces except one. Accordingly, negative pressure would have a limited effect due to limited non-moving pressure chamber surfaces. In addition, prior art systems generally must include a return spring, since no other pressure is available to force the valve assembly back into its down position.
Therefore, there is a need in the art for an exhaust valve control mechanism that responds to positive and negative pressure. For example, there is a need for an exhaust valve control mechanism that opens in response to a positive or negative pressure signal and closes in response to the opposite signal. Furthermore, there is a need in the art for an exhaust valve control system having a pressure chamber that is flexible only on one surface, thereby allowing both negative and positive pressures to be utilized. There is also a need in the art for an exhaust valve that does not utilize return springs. Finally, there also is a need in the art for an electrically switchable valve that opens on negative pressures or that closes on positive pressures or vice versa.
SUMMARY OF THE INVENTION
The invention is directed to an apparatus that comprises an exhaust valve control mechanism that is responsive to both positive and negative pressure from the crankcase, or from an independent source such as a pressure/vacuum pump. For the purposes of the present application, an independent source of pressure is one in which the pressure is not generated directly by the reciprocating motion of the piston in the cylinder, for example the separate pressure/vacuum pump mentioned above. The control of the application of positive or negative pressure can be b
Arctic Cat Inc.
Kamen Noah P.
Merchant & Gould P.C.
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