Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to a crankshaft and piston arrangement for a combustion
engine.
In particular, the invention relates to means for balancing such an
arrangement
especially in a single cylinder or parallel twin cylinder engine.
GB 2057061 teaches the use of a balancing link pivotally connected to a
crankshaft at
a point diametrically opposed to the big end of the connecting rod to a
piston. The
balancing link is pivotally connected at its end opposite to the crankshaft to
a guide
link which is pivotally connected at a fixed point on the engine. GB 2057061
teaches
that certain relationships between the length of the connecting rod, the
separation of
the big end thereof and the centre of rotation of the crankshaft, the
separation of the
crankshaft pivot point of the balancing link and the centre of the crankshaft,
and the
separation of the pivots on the balancing link must be met. In particular,
that patent
specification states that the mutual pivot point of the balancing link and
guide link
should be positioned at the centre of percussion of the balancing link, which
pivot
point therefore has a fixed position in relation to the centre of gravity of
the balancing
link as described in the earlier patent. However, the cost of manufacture of
the engine
described in GB 2057061 is relatively expensive due to the construction of the
additional pivot link and guide link. Moreover, it is not found to provide
sufficient
reduction in engine vibration to enable high speed of revolution of the
crankshaft
and/or relatively smooth operation thereof at moderate speeds of revolution.
Accordingly, an object of the invention is to avoid or at least mitigate the
problems of
the prior art. An object is therefore to provide a well balanced engine. A
first aspect
of the invention provides a crankshaft and piston arrangement for a combustion
engine,
comprising a piston pivotally connected to a crankshaft by a connecting rod,
and
balance means comprising a connecting rod and a balance arm pivotally
connected
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thereto, the balance arm being connectable at an end remote from the
connection rod
to the engine and wherein the balance arm provides a balance mass. Preferably
this
mass is substantially provided in the region of the balance means connecting
rod thus
to produce a force substantially equal in magnitude to the force generated by
the
motion of the piston. The balance means is preferably substantially
diametrically
opposed to the piston and connecting rod in one preferred form, or provided on
the
same side of the crankshaft as the piston in another.
Beneficially, the connecting rod for the balance means can be substantially
identical
to the connecting rod for the piston.
Beneficially, the balance arm can provide a force equal in magnitude but
opposite in
direction to the force generated by the accelerations and decelerations of the
piston.
I 5 Preferably, the balance arm comprises a relatively massive end which end
is pivotally
connected to the balance means connecting rod. The massive end of the balance
arm
can be separated into two regions (or forked) such that the end of the balance
means
connecting rod is engaged between the massive forked end of the balance arm.
Further, the centre of rotation of the pivot between the balance arm and
balance means
connecting rod can be centrally disposed in the massive end of the connecting
arm.
In a preferred form, the arrangement comprises two parallel pistons each
connected by
a connecting rod and bearing to the crankshaft. Preferably, a balance arm is
provided
for each piston. More preferably, the balance arms extend in substantially
opposite
directions to one another away from their respective connecting rods.
In one form, the connecting rods of the balance means for a twin piston engine
share
a co-axial axis of rotation on the crankshaft. Also, the connecting rods can
be
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angularly displaced with respect to one another. The degree of angular
displacement
is preferably less than or equal to 10 ° and more preferably in the
order of 3 ° when the
pistons are radially outermost.
In another form a single piston arrangement is provided having two balance
means
each having a balance arm, which arms extend in substantially opposite
directions to
one another away from the crankshaft. In such an arrangement, preferably a
series of
four crankshaft webs are used to enable connection in series of a balance
means, a
piston connection rod and a second balance means to the crankshaft.
In a further preferred form, when the piston is radially outermost an angle is
presented
between the central axis of the piston and the longitudinal axis of the
balance arm
which is preferably in the order of or less than 90°. More preferably,
the angle is
greater than 45 ° and can be in the order of 50 to 75 ° . When
the piston is in a central
position of the overall stroke of the piston, preferably the balance arm or
arms are
horizontal, or present substantially a right angle between the longitudinal
axis of the
balance arm and the axis between the balance arm pivot with the connecting rod
and
the centre of rotation of the crankshaft.
The balance means and pistons can be in any order along the crankshaft.
However, in
a further preferred form of the invention, the crankshaft comprises in axially
order a
first piston, two balance means and a second piston arranged along the
crankshaft.
Preferably, each of the pistons and balance means is separated from its
neighbour by
a crank web to which each is pivotally connected by a bearing. Preferably, a
central
main bearing is disposed centrally along the axis of the crankshaft
symmetrically
between two pairs each comprising one of the pistons and one of the balance
means.
In another preferred arrangement the balance means is provided on the same
side of
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the crankshaft as the piston, this provides the benefit of a reduction in the
overall size
of the crankshaft and piston arrangement. The length of the balance means
connecting
rod is preferably shorter in this arrangement than the piston connecting rod
in order to
allow for movement of the piston. Accordingly, the connecting rod lengths and
the
stroke of the piston and balance means can be adjusted in order to maintain an
equal
L/R ratio for the balance means and piston connecting rod, or to achieve the
desired
L/R for the balance means. Where L is the length of the connecting rod and R
(the
throw) is half the stroke of the piston or balance means.
According to a second aspect of the invention there is provided a crankshaft
and piston
arrangement for combustion engines comprising two pistons each pivotally
connected
to a crankshaft by an associated connecting rod, and a pair of balance means
comprising a guided balance mass to reduce the vibrations created by movement
of the
pistons in use, the arrangement further comprising a central main bearing.
Beneficially
this inhibits crankshaft bending and so avoids out of balance forces.
Preferably the
balance means are connected on opposite sides of the central main bearing
which in
turn are connected to crankshaft webs connected to the piston connecting rods.
In this arrangement, the balance means can comprise a balance mass pivotally
connected to the crankshaft wherein the balance mass is guided by a relatively
less
massive link pivotally attachable to a fixed point in an engine in use.
Alternatively the
arrangement of the first aspect of the invention can be used each having a
central main
bearing.
According to a third aspect of the invention, there is provided an engine
having a
crankshaft and piston arrangement for combustion engines comprising a piston
pivotally connected to a crankshaft by a connecting rod and balance means
comprising
a balance mass pivotally connected to the crankshaft and a guide link
pivotally
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connected to the balance mass and connectable at an end remote from the
balance mass
to a fixed point on the engine, wherein the guide link for the balance means
is
connected to the engine on the same side of the crankshaft as the piston.
Beneficially
the balance means is therefore clear of the engine oil sump and a reduced
overall
5 engine size can be achieved. Features of the other aspects of the invention
such as use
of two pistons, two balance means for one piston, or a central main bearing
for
example can be used in combination of this aspect of the invention.
A yet further aspect of the invention provides a balance arm for a balanced
crankshaft
and piston arrangement for a combustion engine comprising a minor end
connected by
a connecting arm to a massive end adapted to engage a connecting rod for
connection
to a crankshaft arrangement. Preferably means for communicating lubricating
fluid
to the bearing between the balance arm and connecting rod is provided. Also,
an
extension to the minor end can be provided for actuating a pump or compressor
for
example. Further, the massive end can comprise a region of dense material
which
enables the centre of mass of that end to be disposed, with respect to the
minor end,
beyond the pivot axis for the connecting rod.
Embodiments of the invention will now be described, by way of example only,
with
reference to the accompanying drawings in which:
Figure 1 is a side elevation view of a first embodiment of a crankshaft and
twin
piston arrangement according to the invention;
Figures 2 and 3 are end elevation views at different points in the stroke of
the
arrangement shown in Figure l;
Figure 4 is a plan elevation view from beneath of the arrangement shown in
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Figures 1, 2 and 3.
Figures 5 and 6 are views of a balance arm according to the invention;
Figures 7 is a side elevation view of a second embodiment of a crankshaft and
piston arrangement for a single cylinder engine according to the invention.
Figure 8 is a side elevation view of a third embodiment of a crankshaft and
twin-piston arrangement according to the invention;
Figure 9 is an end elevation view of the arrangement shown in Figure 8;
Figure 10 is a side elevation view of a fourth embodiment of a crankshaft and
twin-piston arrangement according to the invention;
Figure 11 is an end elevation view of the arrangement shown in Figure 10;
Figure 12 is a side elevation view of a fifth embodiment of a crankshaft and
twin piston arrangement according to the invention;
Figures 13 and 14 are end elevation views at different points in the stroke of
the
arrangement shown in Figure 12; and
Figures 15, 16 and 17 are side, plan and sectional side elevation views of a
balance arm according to the invention.
Referring to Figure 1 there is shown a piston and crankshaft arrangement 10
according
to the invention comprising a pair of pistons 12 which are arranged parallel
to one
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another at axially displaced positions along a crankshaft 18. Each piston 12
is
connected to the crankshaft 18 by a connection rod 14 which is pivotally
mounted to
a pair of crank webs 20 at a bearing 16. A central main bearing 22 is provided
between
a pair of crank webs 20 in the centre of the arrangement as shown in Figure 1.
S Additionally, the arrangement 10 comprises a pair of balancing means 24
disposed on
each side of the main bearing 22. Each balance means 24 comprises a connecting
rod
26 pivotally attached to a pair of crank webs 20 at a bearing 28. The end of
each
connecting rod 26 remote from the crankshaft 18 is connected at a bearing 30
to a
balance arm 32.
Referring to Figures 2, 3 and 4, it can be seen that the balance arms 32a and
32b are
preferably substantially identical and preferably extend away from their
respective
connecting rod 26 in substantially opposite directions. Each balance arm 32 is
connected to the crankcase (or a fixed point) at a bearing 34 to allow pivotal
movement
thereof as can be seen by comparison of Figures 2 and 3. These figures show
schematically a section through a cylinder wall W wherein a piston 12 is shown
in an
uppermost position within its stroke, i.e. where pivot axis B at bearing 16
with
crankshaft 18 is uppermost, and an approximately mid-stroke position in which
axis
B is horizontally in line with the central longitudinal axis C of the
crankshaft 18.
In the arrangement shown in Figures 1 to 4, the position of the axis of
rotation F of
pivot 34 is preferably disposed vertically higher than the axis of rotation E
between the
balance arms 32 and connecting rods 26 when the pistons are in the positions
shown
in Figure 2. An angle G can be defined between the longitudinal axis of the
balance
arm 32 and an axis running through points A and C shown in Figure 2, in other
words
a central axis of the piston. This angle is in the order of 75 ° when
the piston is
uppermost in its stroke. Angle G' can be seen to have increased at the mid-
stroke
position shown in Figure 3 wherein G' is approximately 90 ° .
Naturally, at the
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lowermost position at the bottom of the stroke of piston 12, angle G is in the
order of
105 °. Ideally the balance arms 32 are as long as possible in order to
keep angle G as
close to 90 ° as possible throughout the stroke of the piston.
Nevertheless, the
embodiment shown in Figures 1 to 4 is found to provide excellent reduction in
vibrations and has the benefit of compactness. In the preferred form, axis F
is
positioned halfway down the stroke of the balance rod 26, thereby providing
the
arrangement shown in Figure 3.
Referring to Figure 2 it can be seen that preferably connecting rods 26a and
26b of the
balancing means share the same axis of rotation D at the crankshaft but the
connecting
rods are angularly displaced by an angle H. The angle is ideally close to zero
and
preferably in the order of 3 °in the configuration shown in Figure 2.
It can also be seen
in Figure 2, that the balance arms 32 preferably comprise recess portions 36.
Greater
detail of the preferred form of balance arms 32 is given in Figures 5 and 6.
Referring to Figures 5 and 6, the balance arm 32 comprises a minor end 38
having an
aperture 40 which connects to bearing 34. An arm 42 extends between minor end
38
and massive end 44. Arm 42 comprises a recessed region 36 in order to provide
structural rigidity for minimum weight in this region. Massive end 44 is
forked to
provide two arms 44a and 44b. Each arm comprises an aperture 46 for engaging a
bearing 30 thereby enabling connection to connecting rod 26.
Also shown in Figure 5 is an oil way for communicating lubricant to the
apertures 46
in massive end 44. The oil way comprises drillings 35 and plugs 37 which
cooperate
to guide lubricant from aperture 40 in minor end 38 through arm 42 to massive
end 44.
Referring to Figure 7, there is shown a second arrangement according the
invention
wherein the crankshaft and piston arrangement 60 shown, comprise a single
piston 62.
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The piston 62 is connected via a connecting rod 64 to a crank 70 via bearing
66. Four
crank webs 78 are disposed along crankshaft 70. A pair of balance means 74 is
also
provided such that the erid elevation view of arrangement 60 is identical to
that shown
in Figures 2 and 3 for the twin-piston arrangement. Arrangement 60 is
configured as
shown in Figure 7 where a web plate 78 is disposed on each side of a
connecting rod
76 of each of the balance means. The axially centermost pair of web plates 78
are
connected to the connecting rod 64 of piston 62. The balance means comprises a
pair
of connecting rods 76 which can be substantially identical to connecting and
64.
Further, balance means 74 comprises a pair of balancing arms 80 pivotally
connected
at their massive end 94 to one end of connecting rod 76 and to a point at the
opposite
end thereof at axis F in a minor end 88 (not shown). Preferably angle G shown
in
Figure 2 for the twin cylinder arrangement is in the order of 50°here.
As can be seen
in Figure 7 the connecting rods 76 and 64 may be substantially identical.
Beneficially, in the arrangements described above, the ratio of the length (L)
between
axes A and B (distance between centres of connecting rod 14), see Figure 2, to
the
distance (R) between the axes B and C of the piston connecting rod and
crankshaft (or
crankshaft throw) can be in the order of 3.5, and preferably is in the range
of 2.5 to 4.5
and more preferably 3 to 4. The same L/R ratio is possible for the balance
means
shown, where L is the distance between axes E and D, and R is the distance
between
the axes C and D. Because of the excellent balance characteristics of the
engine it is
possible to minimise the L/R ratios and therefore minimise the overall height
of an
engine. Additionally, it is possible to reduce the overall height of the
engine by
maintaining equal L/R ratios for the piston and balance means but use balance
means
connecting rods 26 of shorter length than the main connecting rods 14. The
connecting
rods 26 can be pivotally attached to the crankshaft at a smaller throw than
the piston.
In other words, the distance D to C shown in Figure 2 could be in the order of
0.2 to
1 times the distance C to B for the piston. Where the throws are not equal,
the mass
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of the massive end of the balance arm 32 is preferably adjusted accordingly
and for
example if the balance means throw is half that of the piston then the
rotational inertia
of the balance arm 32 should be doubled.
5 In a preferred form of the invention, the balance means 24 or 74 comprise a
connecting
rod substantially identical to that connected to the piston.
A further benefit of the arrangement shown in Figures 1 to 4 is that the
central main
bearing 22 in combination with the balance means 24 provides stability of
crankshaft
10 18 thereby to prohibit flexing of the crankshaft about the various
bearings. Any such
flexing would allow the motions of the various components to become distorted
and
produce vibration.
Beneficially a parallel twin cylinder engine according the invention provides
a size,
weight and cost benefit over known systems. Additionally. a high level of
balance is
achieved which enables very high speeds of revolution of crankshaft 18. A twin
cylinder engine according to the invention enables use of the engine instead
of a four
cylinder engine in certain applications.
Referring to Figures 8 and 9 there is shown a further embodiment of a
crankshaft and
piston arrangement 110 according to the invention. In this embodiment of a
twin
piston arrangement, balance means 124 are provided on the same side of
crankshaft
118 as pistons 112. In other respects the embodiment is similar to that shown
in
Figures I to 4 and accordingly the same two digits reference number is used
pre-fixed
with a 1 to refer to like parts.
As can be seen in Figure 9, the magnitudes of L and R for the balance means
can be
less than that for connecting rod 114. Nevertheless, in this embodiment the
L/R ratio
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of the balance means connecting rod 126 and the piston connecting rod 114 are
substantially equal.
Balance arms 130 comprise a massive end connected to balance means connecting
rod
126. Their opposite end is rotatably connected to a fixed point on the engine.
Beneficially, balance arms 130 can provide an inertia such that they produce a
force
equal and opposite to that generated by the piston.112.
In this embodiment, beneficially the balance means is kept clear of the oil
sump
reducing the possibility of oil foaming and associated drag. Also, the overall
height
of the engine may be reduced over the design shown in Figures 1 to 4.
A further embodiment of a twin-piston arrangement 210 according to the
invention is
shown in Figures 10 and 11. The arrangement uses substantially similar
components
1 S to those described in earlier embodiments and accordingly, the same two
digit
reference number pre-fixed by the numeral two is used to denote previously
described
components. In this embodiment and the further embodiment shown in Figures 12
to
14, the balance means 224 and 324 comprises a balance mass 250 and 350
pivotally
connected directly to a crankshaft web 220 and 320 respectively. The balance
mass
250 or 350 is guided by a guide link 251 or 351 of relatively minimal mass,
respectively in the two embodiments.
The balance mass 250 and 350 are separated by a main bearing 222 and 322. The
balance masses can be formed using part of a normal connecting rod design to
connect
to the crankshaft but additionally comprising a portion of increased mass
compared to
connecting rod, as can be seen in Figure 11. It has been found that without
this extra
main bearing the crankshaft flexes. This causes vibration and eventually
catastrophic
failure. Beneficially, then, the central main bearing reduces vibration and
improves
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component durability. Additionally, the design of the two links 250 and 251 is
free
from the constraints described in GB 2057061.
Figures 12,13 and 14 show a yet further embodiment of the invention which is
similar
to that shown in Figures 10 and 11 except that the balance means 324 is
positioned on
the same side of the crankshaft 318 as the pistons 312 and connecting rods
314.
Beneficially the balance means is kept clear from any oil sump thereby
reducing oil
aeration and drag. Additionally, the overall height of the engine may be
reduced. The
end of the balance mass 350 and the underside of piston 312 can be contoured
to allow
a certain length of mass 350 to be used whilst still maintaining clearance
between the
two, as can be seen in Figure 14.
Of course, whilst single cylinder and twin-cylinder arrangements have been
shown in
the preferred embodiments, the designs can be adapted for use in any number of
cylinders to provide some of the benefits discussed above. In such
embodiments, the
balance means described can be used a sole means for balancing the engine or
in
conjunction with known balance shafts.
Beneficially, dense materials such as tungsten may be used to enhance the
balance arm
to enable a relatively less massive arm overall. This is because a region of
denser
material can be positioned in the massive end to erect a large balancing force
on the
balance means connecting rod. A particular arrangement is shown in Figures 15,
16
and 17 wherein the massive end 44c of the balance arm 32c comprises a region
or plug
45 of material, eg tungsten, which is denser than the rest of the arm. This
arrangement
causes the centre of mass of the massive end to be disposed beyond the pivot
axis
through aperture 46c. The centre of mass of the whole balance arm is also
moved along the longitudinal axis AC of the arm 32c and possibly beyond the
pivot
axis at the massive end. This result can be achieved by making the massive end
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asymmetrical in shape as shown. In this embodiment of arm 32c, a cylinder or
plug
45c of dense material such as tungsten or lead for example, is inserted in an
aperture
43c which passes through massive end 44c. A tight frictional hold can be
exerted by
the aperture rim on plug 45c. Alternatively, cooperating locking means such as
a bolt
and threaded aperture can be provided to secure plug 45c in position.
Components in
common with balance arm 32 shown in Figures 5 and 6 are of course labelled
using
the same two-digit reference number with the suffix 'c'. However, in this
embodiment, in order to allow for the oscillatory movement of a connecting rod
(26c not shown) pivoted on aperture 46c, a recess or aperture is provided. In
this
embodiment, an aperture 37c extends through arm 32c and is defined by a first
rim 37d
on one side and a second rim 37e on the other side of arm 32c. First rim 37d
defines
a greater aperture than smaller rim 37e. The throughbore 37c flares outwardly
from
rim 37e to 37d. This allows for the oscillatory motion of a connecting rod
which
passes beyond rim 37d up to a crank shaft.
In another preferred form the more massive material is provided as a bridge
across the
forked, massive end of a balance arm.
In another modification the minor end can comprise an extension such as an arm
which
extends away from the pivot to the engine. The extension can be used as an
actuator
providing oscillatory motion to drive a compressor or a pump (eg for water,
oil or air
for example).
In any of the two cylinder arrangements of the invention, the pistons can be
out of
phase by 180°, in other words a 180° parallel twin. The balance
means for each piston
would of course also therefore be 180° out of phase with one another.
