Internal-combustion engines – Combustion chamber means having fuel injection only – Injected fuel spraying into whirling fluid
Reexamination Certificate
2000-05-25
2002-03-26
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Injected fuel spraying into whirling fluid
C123S298000, C123S188140
Reexamination Certificate
active
06360715
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a combustion system for engines having at least one cylinder.
BACKGROUND OF THE INVENTION
In today's combustion engines it is generally desirable to increase the output power of the engine. In order to achieve this, there are many different solutions. One method is to decrease the flow resistance in the intake duct resulting in an increased volumetric filling efficiency. This may, however, entail a deterioration of the combustion quality. This deterioration may also be caused by a difficulty in creating enough micro-turbulence during the combustion phase at low loads and rotational speeds. At too low turbulence levels, an unacceptably low combustion velocity is obtained, as well as excessive cycle-to-cycle variations of the output performance. One method of increasing the combustion quality is to raise the level of the so-called “tumble effect”, an aspect that is generated in the combustion chamber during the intake or suction stroke. The tumble effect is defined as a rotating motion of the air volume moving transversely in relation to the cylinder between the top of a piston and the upper part of the cylinder chamber. In order to increase the tumble effect, the intake duct is normally designed in a special manner that will be described in more detail below, but which normally entails an increased flow resistance. This compromise is well known.
Referring to
FIG. 1
that is included herewith, an illustration is provided depicting an intake duct
20
a
for a high flow (marked and denoted by dashed lines) and another one for high tumble that is superimposed thereupon (also marked, but denoted by full lines), each of which denote known systems and the differences of which will be explained below. Each one of these systems could be described generally as a combustion system for engines having at least one cylinder
10
. The combustion system of the respective systems comprises at least one exhaust duct
20
b
, one intake duct
20
a
provided with a generally cylindrical wall
22
,
22
a
(respectively for the high flow intake duct and high tumble intake duct) and a cylinder chamber
30
(also called a combustion chamber) delimited by a top
100
, (also called a cylinder head). A centerline
21
a
,
21
b
(respectively for the high flow intake duct and high tumble intake duct) extends mainly along the center of the intake duct
20
a
. Further, the cylinder is provided with a cylinder head (not shown) having fuel injectors functioning to inject fuel into the intake duct
20
a
or directly into the cylinder chamber
30
. A piston
40
, provided with a head
60
, also called a crown, performs a reciprocating motion inside the cylinder
10
. Each cylinder is provided with at least one valve
70
a
for intake and one valve for exhaust
70
b
. The exhaust valve
70
b
will not be referred to in the remainder of this portion of the specification; therefore, any future references to a “valve” shall be read to refer to intake valve
70
a
. The valve
70
a
is arranged in a guide
72
, guiding the valve
70
a
, where the guide has a longitudinal axis
110
which is angled relative to the top
100
of the cylinder chamber
30
. This longitudinal axis touches the centerline
21
a
,
21
b
of the intake duct
20
a
and defines a radius
23
a
,
23
b
(respectively for the high flow intake duct and high tumble intake duct) therebetween, i.e. the radius is tangent to both the longitudinal axis and the centerline. The intake duct
20
a
is connected to the cylinder chamber
30
by means of a mouth
80
and the valve
70
a
is arranged to open and close the connection between the intake duct
20
a
and the cylinder chamber
30
. The upper portion of the centerline
21
a
,
21
b
, i.e. the portion of the centerline
21
a
,
21
b
located upstream of the longitudinal axis
110
and the radius
23
a
,
23
b
, and the longitudinal axis
110
, together define a bending angle
25
a
,
25
b
. The centerline
21
a
,
21
b
will touch the radius
23
a
,
23
b
, provided that the starting point for the radius
23
a
,
23
b
is the same at the end towards the mouth
80
.
In the intake duct
20
a
(dashed contour in
FIG. 1
) for high flow, the centerline
21
a
, starting from the mouth
80
of the duct in the cylinder chamber
30
, has a preferably maximized radius
23
a
that touches the longitudinal axis
110
of the valve guide
72
. This radius
23
a
is principally the same as the corresponding curve
24
of the wall
22
of the intake duct, starting from the mouth
80
. In order to obtain a maximized radius
23
a
, the bending angle
25
a
will be minimized with regard to available upwards space in a manner allowing the duct to run free of the existing engine components. Existing components are defined as e.g. valve guides, valves, camshaft and seals. The curve of this type of intake duct will be intermittent. By using this type of intermittently curved intake duct, the flow capacity will increase, partly because the duct can adopt a lower angle of attack
27
a
,
27
between the intake duct and the cylinder centerline
130
. Another advantage, also contributing to increased flow, is that the air flow can be evenly distributed along the circumference of the valve. In a tumbling duct, the main part of the air flow is directed towards the upper part of the valve circumference. In a so called “filling duct”, i.e. a duct for a high flow, the air flow is distributed as evenly as possible and will use the flow area maximally. The tumbling effect, however, will be reduced when this type of duct is used. Furthermore, it may be unfavorable to use a small valve angle, normally about 15°-20°, as this can lead to a relatively limited valve size and a high cylinder head which would require substantial modifications of existing production lines.
In the other case, where the intake duct
20
a
is configured for high tumbling effect, the centerline
21
b
, starting from the mouth
80
of the duct in the cylinder chamber
30
, has a preferably minimized radius
23
b
that touches the longitudinal axis
110
of the valve guide
72
. This radius
23
b
creates a curve
24
a
of the intake duct wall
22
a
, starting from the mouth
80
, that then bends sharply at
24
b
towards the valve guide
72
. In order to obtain a maximal guidance of the flow towards the top side of the valve, the bending angle
25
b
will be maximized with regard to available downwards space. By using this type of intermittently curved intake duct, the tumbling effect will increase, due to the shape of the duct. The flow capacity, however, will be decreased when using such a duct.
FIG. 2
displays a schematic diagram showing that the relationship between flow and tumbling level is inversely proportional, i.e. linear. The tumbling level may, e.g. be defined as the kinetic energy of the tumbling air mass. The flow in the diagram is the flow rate of air. If a comparison is made between the two designs shown in
FIG. 1
, one will find that if the radius is maximized according to
23
a
and the angle
25
a
is minimized, this will result in a duct having a lower tumbling level and a higher flow capacity. This comparison corresponds to point
10
in FIG.
2
. If it were desirable to increase the flow and decrease the tumbling level, this design would be preferable. If another comparison is made between the two designs shown in
FIG. 1
, where the radius is minimized according to
23
b
and the angle
25
b
is maximized, this will result in a duct having a higher tumbling level and a lower flow capacity. This comparison corresponds to point
20
in FIG.
2
.
Further, the crown
60
of the piston
40
may vary somewhat, depending on the application. The simplest form of the crown
60
of a piston
40
is of course a completely flat surface. In order to increase the tumbling effect, the crown
60
of the piston
40
may for example be provided with a bowl-shaped cavity (not shown). This cavity may, for example, be provided in the direction of the tumbling motion to support the creation of the tumbling motion. Furth
Gustavsson Magnus
Nisbet Jonny
Strömberg Stefan
Kilpatrick & Stockton LLP
Vo Hieu T.
Volvo Car Corporation
Yuen Henry C.
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