Folded guide link drive improvements

Details Folded guide link drive improvements Folded guide link drive improvements

2001-06-15

2003-07-15

Nguyen, Hoang (Department: 3748)

Power plants

Motor operated by expansion and/or contraction of a unit of...

Unit of mass is a gas which is heated or cooled in one of a...

C092S16500R

Reexamination Certificate

active

06591608

ABSTRACT:

TECHNICAL FIELD
The present invention pertains to improvements to an engine and more particularly to improvements relating to mechanical components of a Stirling cycle heat engine or refrigerator which contribute to increased engine operating efficiency and lifetime.
BACKGROUND OF THE INVENTION
Stirling cycle machines, including engines and refrigerators, have a long technological heritage, described in detail in Walker,
Stirling Engines
, Oxford University Press (1980), herein incorporated by reference. The principle underlying the Stirling cycle engine is the mechanical realization of the Stirling thermodynamic cycle: isovolumetric heating of a gas within a cylinder, isothermal expansion of the gas (during which work is performed by driving a piston), isovolumetric cooling, and isothermal compression. The Stirling cycle refrigerator is also the mechanical realization of a thermodynamic cycle which approximates the ideal Stirling thermodynamic cycle. In an ideal Stirling thermodynamic cycle, the working fluid undergoes successive cycles of isovolumetric heating, isothermal expansion, isovolumetric cooling and isothermal compression. Practical realizations of the cycle, wherein the stages are neither isovolumetric nor isothermal, are within the scope of the present invention and may be referred to within the present description in the language of the ideal case without limitation of the scope of the invention as claimed. Various aspects of the present invention apply to both Stirling cycle engines and Stirling cycle refrigerators, which are referred to collectively as Stirling cycle machines in the present description and in any appended claims.
The principle of operation of a Stirling engine is readily described with reference to
FIGS. 1
a
-
1
e
, wherein identical numerals are used to identify the same or similar parts. Many mechanical layouts of Stirling cycle machines are known in the art, and the particular Stirling engine designated generally by numeral
10
is shown merely for illustrative purposes. In
FIGS. 1
a
to
1
d
, piston
12
and a displacer
14
move in phased reciprocating motion within cylinders
16
which, in some embodiments of the Stirling engine, may be a single cylinder. Typically, a displacer
14
does not have a seal. However, a displacer
14
with a seal (commonly known as an expansion piston) may be used. Both a displacer without a seal or an expansion piston will work in a Stirling engine in an “expansion” cylinder. A working fluid contained within cylinders
16
is constrained by seals from escaping around piston
12
and displacer
14
. The working fluid is chosen for its thermodynamic properties, as discussed in the description below, and is typically helium at a pressure of several atmospheres. The position of displacer
14
governs whether the working fluid is in contact with hot interface
18
or cold interface
20
, corresponding, respectively, to the interfaces at which heat is supplied to and extracted from the working fluid. The supply and extraction of heat is discussed in further detail below. The volume of working fluid governed by the position of the piston
12
is referred to as compression space
22
.
During the first phase of the engine cycle, the starting condition of which is depicted in
FIG. 1
a
, piston
12
compresses the fluid in compression space
22
. The compression occurs at a substantially constant temperature because heat is extracted from the fluid to the ambient environment. In practice, a cooler (not shown) is provided. The condition of engine
10
after compression is depicted in
FIG. 1
b
. During the second phase of the cycle, displacer
14
moves in the direction of cold interface
20
, with the working fluid displaced from the region of cold interface
20
to the region of hot interface
18
. This phase may be referred to as the transfer phase. At the end of the transfer phase, the fluid is at a higher pressure since the working fluid has been heated at constant volume. The increased pressure is depicted symbolically in
FIG. 1
c
by the reading of pressure gauge
24
.
During the third phase (the expansion stroke) of the engine cycle, the volume of compression space
22
increases as heat is drawn in from outside engine
10
, thereby converting heat to work. In practice, heat is provided to the fluid by means of a heater (not shown). At the end of the expansion phase, compression space
22
is full of cold fluid, as depicted in
FIG. 1
d
. During the fourth phase of the engine cycle, fluid is transferred from the region of hot interface
18
to the region of cold interface
20
by motion of displacer
14
in the opposing sense. At the end of this second transfer phase, the fluid fills compression space
22
and cold interface
20
, as depicted in
FIG. 1
a
, and is ready for a repetition of the compression phase. The Stirling cycle is depicted in a P-V (pressure-volume) diagram as shown in
FIG. 1
e.
Additionally, on passing from the region of hot interface
18
to the region of cold interface
20
, the fluid may pass through a regenerator (not shown). The regenerator may be a matrix of material having a large ratio of surface area to volume which serves to absorb heat from the fluid when it enters hot from the region of hot interface
18
and to heat the fluid when it passes from the region of cold interface
20
.
The principle of operation of a Stirling cycle refrigerator can also be described with reference to
FIGS. 1
a
-
1
e
, wherein identical numerals are used to identify the same or similar parts. The differences between the engine described above and a Stirling machine employed as a refrigerator are that compression volume
22
is typically in thermal communication with ambient temperature and expansion volume
24
is connected to an external cooling load (not shown). Refrigerator operation requires net work input.
Stirling cycle engines have not generally been used in practical applications, and Stirling cycle refrigerators have been limited to the specialty field of cryogenics, due to several daunting engineering challenges to their development. These involve such practical considerations as efficiency, vibration, lifetime, and cost. The instant invention addresses these considerations.
A major problem encountered in the design of certain engines, including the compact Stirling engine, is that of the friction generated by a sliding piston resulting from misalignment of the piston in the cylinder and lateral forces exerted on the piston by the linkage of the piston to a rotating crankshaft. In a typical prior art piston-crankshaft configuration such as that depicted in
FIG. 2
, a piston
10
executes reciprocating motion along longitudinal direction
12
within cylinder
14
. Piston
10
is coupled to an end of connecting rod
16
at a pivot such as a pin
18
. The other end
20
of connecting rod
16
is coupled to a crankshaft
22
at a fixed distance
24
from the axis of rotation
26
of the crankshaft. As crankshaft
22
rotates about the axis of rotation
26
, the connecting rod end
20
connected to the crankshaft traces a circular path while the connecting rod end
28
connected to the piston
10
traces a linear path
30
. The connecting rod angle
32
, defined by the connecting rod longitudinal axis
34
and the axis
30
of the piston, will vary as the crankshaft rotates. The maximum connecting rod angle will depend on the connecting rod offset on the crankshaft and on the length of the connecting rod. The force transmitted by the connecting rod may be decomposed into a longitudinal component
38
and a lateral component
40
, each acting through pin
18
on piston
10
. Minimizing the maximum connecting rod angle
32
will decrease the lateral forces
40
on the piston and thereby reduce friction and increase the mechanical efficiency of the engine. The maximum connecting rod angle can be minimized by decreasing the connecting rod offset
24
on the crankshaft
22
or by increasing the connecting rod length. However, decreasing the connecting rod offset on the crankshaft will decreas

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