Internal-combustion engines – Igniters – Sparkers
Reexamination Certificate
2000-09-29
2001-05-29
Argenbright, Tony M. (Department: 3747)
Internal-combustion engines
Igniters
Sparkers
C123S182100, C123S1980DC
Reexamination Certificate
active
06237555
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to internal combustion engines, and more particularly to suppressing an electrical spark during the exhaust stroke of a four-stroke small internal combustion engine, for use in generators, lawnmowers and other lawn and garden equipment and the like.
A four-stroke reciprocating engine has four strokes of the piston and two revolutions of the crankshaft for each engine cycle. The first stroke, or the intake cycle, occurs as the piston moves downward, creating a partial vacuum in the cylinder. In the intake stroke, the intake valve opens, allowing an air and fuel mixture to enter the cylinder. The second stroke, or the compression stroke, compresses the air and fuel mixture as the piston moves upward. At the end of the compression stroke, the spark plug is fired to ignite the air and fuel mixture typically just before the piston reaches top dead center. The third stroke is the power stroke or expansion stroke. In the power stroke, the air and fuel mixture burns and expands, forcing the piston downward. The fourth stroke, or the exhaust stroke, forces burned gases out of the cylinder through the open exhaust valve as the piston moves upward.
Small 4-stroke, spark ignition internal combustion engines often use either an inductive-magneto or capacitor-discharge ignition system that generates a spark plug arc during each engine flywheel revolution. The spark plug arc generated near the end of an engine's compression stroke is used to generate engine power, while the spark plug arc generated near the end of the engine's exhaust stroke does not have any practical value.
When an engine has been running and then coasts to a stop while the engine's ignition switch is in the off position, fuel and fuel vapors may accumulate in the engine's exhaust system. When attempting to restart an engine with fuel and/or fuel vapors accumulated in the engine's exhaust system, the mixture of fuel and fuel vapors may be ignited by the spark plug arc that is generated during the engine's exhaust stroke. When this occurs, a loud popping sound may be generated within the engine's exhaust system.
FIGS. 1 and 2
illustrate a typical prior art small 4-stroke internal combustion engine with overhead valve (OHV) configuration. A pull rope
4
is used to rotate a manual starter
8
, causing rotation of a crankshaft
12
. An intake valve
16
controls the flow of fuel between a port
17
and a combustion chamber
20
. Valve
16
is of the usual poppet type having a head
24
that is alternately seated and unseated on a seat
28
. The valve
16
is operated by a valve operating mechanism
32
that moves the valve
16
between its closed position and its open position. Mechanism
32
includes a valve stem
36
connected to the valve head
24
. Valve stem
36
is confined to axial movement in a valve guide
40
typically pressed into an engine cylinder head
42
on an OHV engine or in the engine housing on side valve engines. The exhaust valve (not shown) is operated by a valve mechanism that is similar to mechanism
32
.
Valve operating mechanism
32
also includes a return spring
48
, a cam follower
56
and a cam
60
. Cam follower
56
may alternately engage and disengage both the cam
60
disposed on a cam shaft
64
and a compression release assembly (not shown). The cam
60
includes a lobe portion
68
. U.S. Pat. No. 5,150,674 issued to Gracyalny and assigned to Briggs & Stratton Corporation, the assignee of the present invention, discloses such a compression release assembly. U.S. Pat. No. 5,150,674 is incorporated by reference herein. A push rod
84
is moved by the cam follower
56
axially toward a rocker arm
76
, the rocker arm
76
having a first portion
77
and a second portion
78
. As the push rod
84
moves the first portion
77
, the rocker arm
76
pivots about a rocker fulcrum
80
, allowing the second portion
78
to in turn move the valve stem
36
.
Spring
48
extends axially about valve stem
36
and is retained in place by a spring retainer
49
. The spring force of spring
48
biases valve
16
to its seated or closed position. The spring force of spring
48
is opposed by the axial movement of the cam follower
56
that moves the valve
16
to its unseated or open position.
A variety of means have been considered in attempting to prevent spark plug arcing from occurring during a small engine's exhaust stroke. Typically, such methodologies require sophisticated and expensive electronic circuitry to determine the current stroke of the engine in order to blank the appropriate spark plug arc. Due to the relative degree of sophistication and associated high costs, previous methodologies are not cost effective for use on a low-cost internal combustion engine.
SUMMARY OF THE INVENTION
The present invention comprises a four-stroke cycle, spark ignition (SI), internal combustion engine that suppresses an electrical spark in the exhaust stroke of a small internal combustion engine. In an internal combustion engine having a compression stroke, an exhaust stroke and an ignition primary winding, the internal combustion engine comprises valve operating assemblies that operate an intake and an exhaust valve. Each valve operating assembly may include a cam, a cam shaft, a cam follower, a rocker arm, a rocker fulcrum, a return spring, and a push rod, depending on the valve layout. An automatic compression release assembly may also be provided for the exhaust valve.
A switch is electrically interconnected with the primary winding, mechanically interconnected with the cam shaft and actuated in timed relation to cam shaft rotation such that during the exhaust stroke, the primary winding may be electrically connected to ground. In the alternative, the switch may also be positioned to electrically connect the primary winding to an energy storage device during the exhaust stroke or to electrically connect the primary winding to a load. The switch may comprise two electrically conductive contacts, which may be positioned to be in electrical contact with each other when the unnecessary spark is suppressed. The energy storage device may be a capacitor or a battery, and may be used to drive a variety of loads such as a light emitting diode, a light, or a controller. Alternatively, the primary winding could be electronically connected such that it directly drives a load during the exhaust cycle. A second switch may be positioned to be actuated by the first switch to either electrically connect the primary winding to ground or to transfer the energy from the primary winding to the energy storage device.
Accordingly, a principal feature and advantage of the invention is to provide an apparatus for blanking an unnecessary spark during the exhaust stroke of an internal combustion engine.
It is another feature and advantage of the invention to substantially eliminate the prefire condition of an internal combustion engine caused by the unnecessary spark.
It is another feature and advantage of the invention to utilize the energy provided by the unnecessary spark for other functions of the internal combustion engine or the device powered by the engine.
Other features and advantages of the invention are set forth in the following drawings, detailed description and claims.
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patent: 934978 (1909-09-01), Mark
Dykstra Richard A.
Gracyalny Gary J.
Mitchell Robert K.
Argenbright Tony M.
Briggs & Stratton Corporation
Michael & Best & Friedrich LLP
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