Split four stroke engine

Details Split four stroke engine Split four stroke engine

2002-10-31

2004-04-20

Nguyen, Hoang (Department: 3748)

Power plants

Fluid motor means driven by waste heat or by exhaust energy...

C123S053100, C123S053500, C123S568110, C123S568140

Reexamination Certificate

active

06722127

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to internal combustion engines. More specifically, the present invention relates to a four-stroke cycle internal combustion engine having a pair of offset pistons in which one piston of the pair is used for the intake and compression strokes and another piston of the pair is used for the power and exhaust strokes, with each four stroke cycle being completed in one revolution of the crankshaft.
BACKGROUND OF THE INVENTION
Internal combustion engines are any of a group of devices in which the reactants of combustion, e.g., oxidizer and fuel, and the products of combustion serve as the working fluids of the engine. The basic components of an internal combustion engine are well known in the art and include the engine block, cylinder head, cylinders, pistons, valves, crankshaft and camshaft. The cylinder heads, cylinders and tops of the pistons typically form combustion chambers into which fuel and oxidizer (e.g., air) is introduced and combustion takes place. Such an engine gains its energy from the heat released during the combustion of the non-reacted working fluids, e.g., the oxidizer-fuel mixture. This process occurs within the engine and is part of the thermodynamic cycle of the device. In all internal combustion engines, useful work is generated from the hot, gaseous products of combustion acting directly on moving surfaces of the engine, such as the top or crown of a piston. Generally, reciprocating motion of the pistons is transferred to rotary motion of a crankshaft via connecting rods.
Internal combustion (IC) engines can be categorized into spark ignition (SI) and compression ignition (CI) categories. SI engines, i.e. typical gasoline engines, use a spark to ignite the air-fuel mixture, while the heat of compression ignites the air fuel mixture in CI engines, i.e., typically diesel engines.
The most common internal-combustion engine is the four-stroke cycle engine, a conception whose basic design has not changed for more than 100 years old. This is because of its outstanding performance as a prime mover in the ground transportation industry. In a four-stroke cycle engine, power is recovered from the combustion process in four separate piston movements (strokes) of a single piston. For purposes herein, a stroke is defined as a complete movement of a piston from a top dead center position to a bottom dead center position or vice versa. Accordingly, a four-stroke cycle engine is defined herein to be an engine which requires four complete strokes of one or more pistons for every power stroke, i.e. for every stroke that delivers power to a crankshaft.
Referring to
FIGS. 1-4
, an exemplary embodiment of a prior art four stroke cycle internal combustion engine is shown at
10
. For purposes of comparison, the following four
FIGS. 1-4
describe what will be termed a prior art “standard engine”
10
. As will be explained in greater detail hereinafter, this standard engine
10
is an SI engine with a 4 inch diameter piston, a 4 inch stroke and an 8 to 1 compression ratio. The compression ratio is defined herein as the maximum volume of a predetermined mass of an air-fuel mixture before a compression stroke, divided by the volume of the mass of the air-fuel mixture at the point of ignition. For the standard engine, the compression ratio is substantially the ratio of the volume in cylinder
14
when piston
16
is at bottom dead center to the volume in the cylinder
14
when the piston
16
is at top dead center.
The engine
10
includes an engine block
12
having the cylinder
14
extending therethrough. The cylinder
14
is sized to receive the reciprocating piston
16
therein. Attached to the top of the cylinder
14
is the cylinder head
18
, which includes an inlet valve
20
and an outlet valve
22
. The cylinder head
18
, cylinder
14
and top (or crown
24
) of the piston
16
form a combustion chamber
26
. On the inlet stroke (FIG.
1
), a fuel air mixture is introduced into the combustion chamber
26
through an intake passage
28
and the inlet valve
20
, wherein the mixture is ignited via spark plug
30
. The products of combustion are later exhausted through outlet valve
22
and outlet passage
32
on the exhaust stroke (FIG.
4
). A connecting rod
34
is pivotally attached at its top distal end
36
to the piston
16
. A crankshaft
38
includes a mechanical offset portion called the crankshaft throw
40
, which is pivotally attached to the bottom distal end
42
of connecting rod
34
. The mechanical linkage of the connecting rod
34
to the piston
16
and crankshaft throw
40
serves to convert the reciprocating motion (as indicated by arrow
44
) of the piston
16
to the rotary motion (as indicated by arrow
46
) of the crankshaft
38
. The crankshaft
38
is mechanically linked (not shown) to an inlet camshaft
48
and an outlet camshaft
50
, which precisely control the opening and closing of the inlet valve
20
and outlet valve
22
respectively.
The cylinder
14
has a centerline (piston-cylinder axis)
52
, which is also the centerline of reciprocation of the piston
16
. The crankshaft
38
has a center of rotation (crankshaft axis)
54
. For purposes of this specification, the direction of rotation
46
of the crankshaft
38
will be in the clockwise direction as viewed by the reader into the plane of the paper. The centerline
52
of the cylinder
14
passes directly through the center of rotation
54
of the crankshaft
38
.
Referring to
FIG. 1
, with the inlet valve
20
open, the piston
16
first descends (as indicated by the direction of arrow
44
) on the intake stroke. A predetermined mass of an explosive mixture of fuel (gasoline vapor) and air is drawn into the combustion chamber
26
by the partial vacuum thus created. The piston continues to descend until it reaches its bottom dead center (BDC), the point at which the piston is farthest from the cylinder head
18
.
Referring to
FIG. 2
, with both the inlet
20
and outlet
22
valves closed, the mixture is compressed as the piston
16
ascends (as indicated by the direction of arrow
44
) on the compression stroke. As the end of the stroke approaches top dead center (TDC), i.e., the point at which the piston
16
is closest to the cylinder head
18
, the volume of the mixture is compressed to one eighth of its initial volume (due to an 8 to 1 compression ratio). The mixture is then ignited by an electric spark from spark plug
30
.
Referring to
FIG. 3
, the power stroke follows with both valves
20
and
22
still closed. The piston
16
is driven downward (as indicated by arrow
44
) toward bottom dead center (BDC), due to the expansion of the burned gas pressing on the crown
24
of the piston
16
. Since the spark plug
30
is fired when the piston
16
is at or near TDC, i.e. at its firing position, the combustion pressure (indicated by arrow
56
) exerted by the ignited gas on the piston
16
is at its maximum at this point. This pressure
56
is transmitted through the connecting rod
34
and results in a tangential force or torque (as indicated by arrow
58
) on the crankshaft
38
.
When the piston
16
is at its firing position, there is a significant clearance distance
60
between the top of the cylinder
14
and the crown
24
of the piston
16
. Typically, the clearance distance is between 0.5 to 0.6 inches. For the standard engine
10
illustrated the clearance distance is substantially 0.571 inches. When the piston
16
is at its firing position conditions are optimal for ignition, i.e., optimal firing conditions. For purposes of comparison, the firing conditions of this engine
10
exemplary embodiment are: 1) a 4 inch diameter piston, 2) a clearance volume of 7.181 cubic inches, 3) a pressure before ignition of approximately 270 pounds per square inch absolute (psia), 4) a maximum combustion pressure after ignition of approximately 1200 psia and 5) operating at 1400 RPM.
This clearance distance
60
corresponds typically to the 8 to 1 compression ratio. Typically, SI engines operate optimally with a fixed compres

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