Note: Descriptions are shown in the official language in which they were submitted.
In the field of heat engines, the piston engine has gained wide
acceptance in the past century, primarily because of its reliability, control-
lability, and its desirable power output characteristics. Recently, interest
has increased in external combustion piston engines, such as the Stirling
cycle and Rankine cycle engines.
Typically, a piston is linked to a mechanism for transforming the
reciprocating motion of the piston to smooth rotary motion. Often, this
mechanism includes a piston rod extending from the piston to a crank on the
crankshaft. The eccentric disposition with respect to the shaft enables it
to accommodate the translational motion of the piston rod, and transform the
periodic, reciprocating force provided by the piston into smooth rotational
motion. Other mechanisms include swash plate and wobble plate devices.
It is well known in the art that the eccentric disposition of the
crank of a crankshaft and the motion of a swash plate also causes the piston
rod to undergo lateral motion as well as translational motion. This lateral
motion is generally accommodated by a wrist pin which links the piston to the
respective end of the piston rod. This mechanical system, however, does not
entirely alleviate the side thrust which is attendant with the lateral motion
of the piston rod. This side thrust, exerted on the piston through the wrist
pin, causes uneven wearing of the piston rings, or similar seal, and a deg-
radation of the seal disposed between the piston rod and the end of the
cylinder. The side thrust also contributes to the wear of the main bearings
which support the crank shaft.
Although the wear which is associated with the side thrust of the
piston rod has been minimized by superior design, balancing, and machining,
it still remains a significant factor in limiting the life span of an engine.
The end of this lifespan is often determined by the time at which the engine
must be re6uilt, including new piston rings, seals bearings, and the like.
According to the present invention 1:here is provided a drive
mechanism for linking the reciprocating pistons of an engine to a rotating
shaft, comprising a main gear disposed on saicl rotating shaft; at least one
drive gear engaging said main gear; a piston rod extending from each of said
pistons; a plurality of paired eccentric armsJ each pair of which is joined
at one end thereof to one of said piston rods; a plurality of gear wheels,
each joined to one of said drive gears in common rotation therewith; a
plurality of idler gears, each meshing with one of said gear wheels in paired
relationship; and wherein each of the other ends of said each pair of eccen-
tric arms is joined to one of a pair of said idler gears and said gear wheels.
The present invention generally comprises a drive mechanism forlinking the pistons of a heat engine to the rotary output shaft thereof, and
for converting the reciprocating motion of the pistons to the rotary power
output of the output shaft. A significant aspect of the present invention is
that it virtually eliminates the side thrust exerted on the piston rod and on
the piston, and thereby eliminates a major cause of wear and prolongs the life
of the engine. It also allows a simple slide seal on the piston rod to seal
hydrogen or helium gas below the piston, as used in Stirling cycle engines.
A preferred embodiment of the invention includes a housing having an
output shaft extending therethrough, the shaft being supported by bearings
journalled in the housing. A main bevel gear is secured to the output shaft
within the housing, and it engages a plurality of drive gears also disposed
within the housing. Each of the drive gears is secured to the proximal end
of a gear shaft, the gear shaft extending through the wall of the housing to
the exterior thereof and being supported by bearings journalled therein.
Secured to the distal end of each gear shaft is a gear wheel, which
meshes with an idler gear disposed directly adjacent thereto. Extending ec-
centrically from the gear wheel and the idler gear are a pair of eccentric
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arms, which are secured at their other ends to a connecting block.
Also secured to the connecting block is the distal end of the piston
rod, the proximal end being secured to the piston itself. As the piston re-
ciprocates the reciprocal motion is transferred through the piston rod to the
connecting block. The block drives the eccentric arms which cause the gear
wheel and idler gear to rotate. This rotational motion is transferred through
the gear shaft to the drive gear and thence to the main gear. In this way the
output shaft of the drive mechanism is driven in continuous rotational motion.
The piston rod undergoes direct translational motion along its axis,
due to the equal arm effect of the eccentric linking members. Thus there is
no side thrust exerted on the piston rod, or on the piston itself; and the
wear of the piston, the piston rod, the piston rings or seals, and the cylinder
walls is greatly reduced.
In the accompanying drawings:
Figure 1 is a plan view of a drive mechanism embodying the present
invention, shown in conjunction with a piston engine;
Figure 2 is an end view of the drive mechanism;
Figure 3 is a detailed, cross-sectional view of a portion of the
drive mechanism;
2Q Figure 4 is a detailed plan view of the dual eccentric arm feature
of the present invention, shown in a disposition commensurate with the mid-
point of the piston excursion;
Figure 5 is a detailed plan view as in Figure 4, shown in a position
commensurate with the top dead center position of the piston excursion;
Figure 6 is a detailed plan view as in Figures 4 and 5, shown in a
disposition commensurate with the midpoint of the piston excursion; and
Figure 7 is a schematic depiction of various piston positions within
its respective cylinder.
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The present invention generally comprises a drive mechanism, for
use in conjunction with a piston engine, which links the pistons of the engine
to the rotary output shaft thereof. The drive mechanism converts the recip-
rocal motion of the pistons to smooth rotary motion of the output shaft, and
it exhibits the significant advantage of imparting no side thrust to the pis-
tons or connecting rods of the engine. In describing the preferred embodiment,
reference will be made to a four-cylinder heat engine, and the preferred em-
bodiment will be described in relation thereto. However, the invention is not
limited by the number of cylinders in the engine, nor by the type of heat en-
gine with which it is used.
As shown in Figures 1 and 2, the drive mechanism embodying the
present invention includes a generally rectangular housing 11 which is secured
to one side of a base plate 12. Joined to the other side of the base plate
are a plurality of cylinders 13. Within each cylinder 13 there is disposed a
piston 14 which is driven by expanding gasses provided by external combustion
of a fuel.
As shown in Figure 3, within the housing 11 there is a cavity 16.
Disposed in this cavity and extending out of the upper end of the housing 11
is a rotary output shaft 17. The shaft 17 is supported by at least a pair of
bearings 18 and 19 to provide free rotation of the shaft 17. Supported on the
shaft 17 within the cavity 16 is a main gear 21, of the bevel type, as shown
in Figure 3.
Extending into each side 22 of the rectangular housing 11 is a gear
shaft 24, which is supported by needle bearings journalled in the side 22.
Secured to the inner end of each gear shaft 24 is a bevelled drive gear 26
which meshes with the main gear 21. The gears 21 and 26 all have an even num-
ber of teeth. Thus all of the gears 26 and the shafts 24 rotate in synchron-
ism with the gear 21 and the output shaft 17. The gears 21 and 26 may alter-
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natively comprise spur gears, worm gears, or helical gears having any de-
sired ratio of increase or decrease.
Extending outwardly from each of the sides 22 is a support arm 23.
An idler gear shaft 27 is rotatably supported by the arm 23, and an idler gear
28 secured to the outer end of the shaft 27. Secured to the outer end of each
of the shafts 24 is a gear wheel 29, which is disposed to mesh with the gear
28. The diameter and number of teeth of the gears 29 and 28 are identical.
Secured to each of the gear wheels 29 and idler gears 28 is an ec-
centric arm 31, all of the arms 31 being identical in length. Each of the
arms 31 is secured to its respective idler gear or gear wheel by means of a
stub shaft extending therefrom, and a needle bearing which provides for free
rotation of the eccentric arm about the stub shaft. For each gear wheel and
idler gear pair, there is provided one connecting block 32, to which the ec-
centric arms 31 of the respective gear pair are secured. The connecting block
32 is also provided with a pair of stub shafts and needle bearing assemblies -
so that the eccentric arms 31 may freely rotate with respect to the connecting
block.
Also secured to each connecting block 32 is a piston rod 33 which
extends from the connecting block to the piston 14 disposed in the cylinder 13
which is axially aligned with the respective connecting block. A suitably
aligned port 15 in the plate 12 is provided for each rod 33 so that it may
pass therethrough in freely rotation fashion. Each port 15 is provided with
a sleeve or gland seal 25, such as those fabricated from lubricant impregnated
plastic material.
It may be appreciated that the differential in pressure exerted on
the opposed sides of the piston 14 causes it to reciprocate in the cylinder
13, as is well known in the art. The piston drives the associated piston rod
33 in reciprocal motion, translating along the axis of the piston rod. Like-
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wise, the connecting block 32 is driven reciprocally by the piston rod 33.
It should be noted that each pair of eccentric arms 31 are secured to their
respective gear wheel and idler gear pair in exactly opposed relationship.
That is, the shafts which connect the eccentric arms to their respective
gears define a line which is always parallel to the line defined by the axes
of rotation of the gear wheel and idler gear pair. Furthermore, each piston
rod 33 extends along an axis which is midway between the rotational axes of
its associated gear wheel and idler gear pair. Due to these symmetrical re-
lationships, each connecting block 32 is maintained by its eccentric arms 31
on the axis which falls midway between its respective gear pair 29 and 28.
Thus as the connecting block 32 and the piston rod 33 translate reciprocally
and drive the gear pair 29 and 28 through the eccentric arms 31, they are
prevented from undergoing any lateral, non-axial motion due to the action of
the equally opposed eccentric arms.
As the piston 14 translates from top dead center through inter-
mediate positions to the bottom dead center, as shown in Figure 7, the gears
29 and 28 are driven by the eccentric arms 31 through commensurate rotational
angles, as shown in Figures 4, 5 and 6. That is, the block 32 drives the
eccentric arms 31 which cause the gear wheel 29 and the idler gear 28 to
rotate. This ~otational motion is transferred through the gear shaft 27 to
the drive gear 26 and thence to the main gear 21. In this way the output
shaft 17 of the drive mechanism is driven in continuous rotational motion.
In all cases, however, the connecting block 32 and the piston rod 33 are
maintained by the eccentric arms 31 on the same axis, so that the piston rods
and connecting blocks undergo axial translation only. Thus, there is no side
thrust imparted to the connecting block or piston rod, or piston rod seal 25,
and therefore no side thrust is imparted by the piston rod 33 to the piston
14 itself.
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The direction of rotation of output shaft 7 may be reversed by
exchanging the phase angle of any two opposed gear~s 26.
Thus the mechanism of the present invention not only converts the
reciprocal motion of the pistons 1~l to rotational motion of the output shaft
17, it also alleviates any side thrust which might be exerted on the pistons
and piston rod seals by the piston rods. In this way, a major cause of wear
of the pistons, cylinder walls, and intermediate seals, is eliminated. Thus,
the efficiency of the engine is increased, since compression within the
cylinder is maintained over the operating life of the engine. Furthermore,
the operating life of the engine is greatly extended, since the elimination
of side thrust on the piston greatly reduces the wear thereof.
It should also be noted that each gear assembly 29 and 28 is dyna-
mically balanced to alleviate any undue vibrational effects which might occur
when the drive mechanism is operating at speed. Furthermore, each pair of
eccentric arms 31 are also dynamically balanced, and close machine tolerances
are observed in all phases of the construction of the present invention.
A significant advantage of the present invention is that the
marked reduction in side thrust on the pistons and rods also reduces the
lubrication requirements of the engine. Thus the gears and seals of the
device may be permanently lubricated with suitable coatings or impregnations,
and the typical oil pump, splash, or spray lube system eliminated. This is a
significant advance for Stirling cycle engines in which the heat exchangers
are often clogged and contaminated by lubricating oil leaking past the seals.
It should be emphasized that the piston engine forms no part of
the present invention. Furthermore, the drive mechanism of the present
invention may be employed with any form of reciprocating piston engine,
including external combustion engines, steam engines, and the like.
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