U.S. patent application number 11/927138 was filed with the patent office on 2009-04-30 for dual crankshaft engine with counter rotating inertial masses.
This patent application is currently assigned to FORD GLOBAL TECHNOLOGIES, LLC. Invention is credited to Al Henry Berger, James R. Clarke.
Application Number | 20090107426 11/927138 |
Document ID | / |
Family ID | 40581223 |
Filed Date | 2009-04-30 |
United States Patent
Application |
20090107426 |
Kind Code |
A1 |
Berger; Al Henry ; et
al. |
April 30, 2009 |
DUAL CRANKSHAFT ENGINE WITH COUNTER ROTATING INERTIAL MASSES
Abstract
A dual crankshaft internal combustion engine is symmetrically
constructed to form a perfectly balanced engine assembly. A first
crankshaft, having a first end, a second end, and being formed of a
shape and with a torsional flexibility, is housed within a cylinder
block and connected to a first series of cooperating pistons and
cylinders. A second crankshaft, having a first end and a second
end, is formed of substantially the same shape as the first
crankshaft and has substantially the same torsional flexibility as
the first crankshaft. The second crankshaft is also housed within
the cylinder block and connected to a second series of cooperating
pistons and cylinders, while being positioned parallel to the first
crankshaft, with the first end of the first crankshaft being
positioned adjacent to the second end of the second crankshaft.
Inventors: |
Berger; Al Henry;
(Brownstown, MI) ; Clarke; James R.; (Levering,
MI) |
Correspondence
Address: |
DIEDERIKS & WHITELAW, PLC;Everett G. Diederiks, Jr.
12471 Dillingham Sq., #301
Woodbridge
VA
22192
US
|
Assignee: |
FORD GLOBAL TECHNOLOGIES,
LLC
Dearborn
MI
|
Family ID: |
40581223 |
Appl. No.: |
11/927138 |
Filed: |
October 29, 2007 |
Current U.S.
Class: |
123/52.4 ;
123/192.2; 123/197.4; 180/65.6; 903/902 |
Current CPC
Class: |
B60K 6/24 20130101; Y02T
10/62 20130101; Y02T 10/6226 20130101; B60K 5/08 20130101; F02B
75/225 20130101; Y02T 10/6295 20130101; B60K 6/26 20130101; B60K
6/485 20130101 |
Class at
Publication: |
123/52.4 ;
123/192.2; 123/197.4; 180/65.6; 903/902 |
International
Class: |
B60K 6/22 20071001
B60K006/22; B60K 6/30 20071001 B60K006/30; F02B 75/06 20060101
F02B075/06; F02B 75/18 20060101 F02B075/18 |
Claims
1. A dual crankshaft internal combustion engine for a vehicle
comprising: a cylinder block; a first series of cooperating pistons
and cylinders mounted in the cylinder block; a second series of
cooperating pistons and cylinders mounted in the cylinder block; a
first crankshaft having a first end, a second end, a torsional
flexibility and a shape, the first crankshaft being housed within
the cylinder block and connected to the first series of cooperating
pistons and cylinders, such that movement of the pistons of the
first series within the cylinders of the first series causes the
first crankshaft to rotate; a second crankshaft having a first end,
a second end, a torsional flexibility and a shape substantially
identical to the shape of the first crankshaft, the second
crankshaft being housed within the cylinder block, connected to the
second series of cooperating pistons and cylinders and positioned
parallel to the first crankshaft, with the first end of the first
crankshaft being positioned adjacent to the second end of the
second crankshaft; a first gearset mounted in the internal
combustion engine and connecting the first end of the first
crankshaft to the second end of the second crankshaft; a second
gearset mounted in the internal combustion engine and connecting
the second end of the first crankshaft to the first end of the
second crankshaft; a first mass having an inertia connected to the
first end of the first crankshaft; a second mass having
substantially the same inertia as the first mass connected to the
first end of the second crankshaft; whereby the first and second
crankshafts counter rotate and various forces and moments produced
by the pistons and rotating crankshafts are balanced.
2. The engine of claim 1 wherein the gears on the first crankshaft
has a handed helix and the gears on the second crankshaft have an
oppositely handed helix as compared to the handed helix of the
gears on the first crankshaft.
3. The engine of claim 1 wherein the second mass is a flywheel.
4. The engine of claim 1 wherein the second mass is a torque
converter.
5. The engine of claim 1 wherein the first mass is a
motor/generator.
6. The engine of claim 1 wherein the first gearset includes a
scissors gear.
7. The engine of claim 1 wherein the first and second crankshafts
are preloaded with a rotational tension stored in the torsional
flexibility of each shaft.
8. A vehicle comprising: a body; a plurality of wheels; a dual
crankshaft internal combustion engine including: a cylinder block;
a first series of cooperating pistons and cylinders mounted in the
cylinder block; a second series of cooperating pistons and
cylinders mounted in the cylinder block; a first crankshaft having
a first end, a second end, a torsional flexibility and a shape, the
first crankshaft being housed within the cylinder block and
connected to the first series of cooperating pistons and cylinders
such that movement of the pistons of the first series within the
cylinders of the first series causes the first crankshaft to
rotate; a second crankshaft having a first end, a second end, a
torsional flexibility and a shape substantially identical to the
shape of the first crankshaft, the second crankshaft being housed
within the cylinder block, connected to the second series of
cooperating pistons and cylinders and positioned parallel to the
first crankshaft, with the first end of the first crankshaft being
positioned adjacent the second end of the second crankshaft; a
first gearset mounted in the internal combustion engine and
connecting the first end of the first crankshaft to the second end
of the second crankshaft; a second gearset mounted in the internal
combustion engine and connecting the second end of the first
crankshaft to the first end of the second crankshaft; a first mass
having an inertia connected to the first end of the first
crankshaft; and a second mass having substantially the same inertia
as the first mass connected to the first end of the second
crankshaft; whereby the first and second crankshafts counter rotate
and various forces and moments produced by the pistons and rotating
crankshafts are balanced; and a powertrain interconnecting the
internal combustion engine to at least one of the plurality of
wheels.
9. The vehicle of claim 8 wherein on the first crankshaft gears
have a handed helix and the second crankshaft gears have an
oppositely handed helix as compared to the handed helix of the
gears on the first crankshaft.
10. The vehicle of claim 8 wherein the second mass is a
flywheel.
11. The vehicle of claim 8 wherein the second mass is a torque
converter.
12. The vehicle of claim 8 wherein the first mass is a
motor/generator, and the vehicle is a hybrid vehicle.
13. The vehicle of claim 8 wherein the first gearset includes a
scissors gear.
14. The vehicle of claim 8 wherein the first and second crankshafts
are preloaded with a rotational tension stored in the torsional
flexibility of each of the first and second crankshafts.
15. A method for balancing a dual crankshaft internal combustion
engine in a vehicle comprising: mounting first and second series of
cooperating pistons and cylinders in a cylinder block; positioning
a first crankshaft parallel to a second crankshaft in the cylinder
block, with a first end of the first crankshaft being positioned
adjacent a second end of the second crankshaft; connecting the
first end of the first crankshaft to a first mass and connecting
the first end of the second crankshaft to a second mass having the
same amount of inertia as the first mass; counter-rotating the
first and second crankshafts to balance various forces and moments
produced by the pistons and rotating crankshafts.
16. The method of claim 15 further comprising eliminating gear
rattle by placing a scissors gear in the gearset.
17. The method of claim 15 further comprising eliminating gear
rattle by preloading the first and second crankshafts with a
rotational tension stored in torsional flexibility of each of the
first and second crankshafts.
18. The method of claim 15 further comprising operating the
internal combustion engine with a firing order wherein no two
cylinders of the first series of cooperating pistons and cylinders,
which is on the first crankshaft, fire simultaneously.
19. The method of claim 15 further comprising selectively disabling
or re-enabling the firing of cylinders from the first and second
series of cooperating pistons and cylinders, in accordance with
power requirements of the vehicle.
20. The method of claim 15 further comprising operating with the
internal combustion engine with a homogeneous charge compression
ignition combustion process.
Description
FIELD OF INVENTION
[0001] The present invention pertains to the art of internal
combustion engines used in vehicles and, more specifically, to a
balance and noise reduction system for a dual crankshaft
engine.
BACKGROUND OF THE INVENTION
[0002] Conventional internal combustion engines employ piston and
cylinder arrangements that tend to vibrate during operation. The
vibration often creates a disturbance in a vehicle passenger
compartment and is considered undesirable.
[0003] Most internal combustion engines develop power in impulses
generated by the explosion of a combination of air and fuel in the
engine's cylinders. The power is transferred to pistons that are
located in the cylinders and are coupled to a rotating crankshaft
with connecting rods. The power then flows to a flywheel that is
connected to other downstream components of a powertrain. All
conventional, single crankshaft, piston engines have a firing
frequency vibration caused by uneven torque delivery to the
flywheel. On a combustion or expansion event, the flywheel's
rotational speed increases and, on a compression event, the
rotational speed of the flywheel decreases. The torque that causes
vibrational speed variations of the flywheel reacts against the
cylinder block and causes torsional vibration of the cylinder
block.
[0004] This fluctuating torque causes one source of vibration.
Other disturbing engine vibrations are caused by unbalanced
accelerations of internal engine components, especially linear
accelerations of the piston masses within the cylinder bores. To
address these problems, rubber engine mounts have been used to
isolate the vehicle chassis from much of the cylinder block
vibration. Still, some vibration is transmitted through the mounts
and is sensed in the passenger compartment.
[0005] A partial solution is to have multi-cylinder engines
generally configured so that the linear acceleration forces of the
various pistons partially or completely cancel each other. Inline
and opposed 6-cylinder engines, as well as inline and 90 degree V8
engines, usually have theoretically perfect balance of piston
acceleration forces, but most other engines have residual
unbalanced forces or moments. For example, all single crankshaft V6
engines with less than 180 degrees of bank angle have inherent
unbalanced couples due to piston acceleration forces. Furthermore,
all conventional single crankshaft engines have unbalanced
torsional accelerations imposed upon the block structure due to
flywheel rotational accelerations.
[0006] As an example, the Volkswagen 15 degree bank angle V6 engine
is narrower than other 60 or 90 degree V6 engines and has a
one-piece cylinder head that spans between two cylinder banks.
However, there are numerous undesirable qualities with such a
design. The intake manifold is on one side of the cylinder head and
the exhaust manifold is on the other, causing three cylinders to
have long intake and short exhaust passages while the other three
cylinders have short intake and long exhaust passages. An asymmetry
exists between the cylinder banks with regard to the location of
the intake and exhaust valves. Further, one bank has mostly
vertical intake valves and highly inclined exhaust valves, while
the other bank has highly inclined intake valves and mostly
vertical exhaust valves. Finally, the center planes of the cylinder
bores intersect some distance below the crankshaft rotational axis,
so that the cylinder bores on each bank are offset from the
crankshaft axis in opposite directions. This arrangement causes the
piston velocities in each of the two banks to be different. On one
bank, the pistons are slower during upward motion than they are
during downward motion. On the other bank, the pistons are faster
during upward motion than they are during downward motion.
[0007] The use of two crankshafts in one cylinder block is not
unprecedented. One example can be found in the Ariel motorcycle.
The Ariel motorcycle was manufactured for many years with a dual
crankshaft engine. This Ariel "Square Four" engine included two
inline, two-cylinder crankshafts operating in a common cylinder
block structure, with the resulting four cylinder bores being
oriented in a square fashion. Each of the two crankshafts operates
two pistons, with a 180-degree phase angle between the crankpins on
each crankshaft. One pair of straight cut spur gears is arranged to
couple the crankshafts to each other to make the crankshafts rotate
in opposite directions. This arrangement has some apparent
drawbacks. First, the arrangement is very noisy in operation
because the single gearset has backlash and rattles each time the
direction of torque transfer reverses. Also, because each cylinder
bank contains only two cylinders, each bank of cylinders has a
second order vertical shaking force that is in phase with the
vertical shake of the other bank. Thus, the whole engine assembly
has a second order vertical shake equivalent to that of an inline
four cylinder engine. Furthermore, the two counter-rotating
crankshafts do not carry equal amounts of rotating inertia so the
firing pulse accelerations of the crankshafts produce a reaction on
the engine's cylinder block.
[0008] Based on the above, there is a need in the art for a dual
crankshaft engine that is well balanced and produces much less
vibration than conventional engines, while avoiding the
disadvantages set forth above.
SUMMARY OF THE INVENTION
[0009] The present invention is directed to a dual crankshaft
internal combustion engine that is symmetrically constructed to
form a balanced engine assembly. The dual crankshaft internal
combustion engine comprises first and second series of cooperating
pistons and cylinders mounted in a cylinder block. A first
crankshaft, formed of a distinct shape and with a certain torsional
flexibility, is positioned within the cylinder block and connected
to the first series of cooperating pistons and cylinders. A second
crankshaft is formed of substantially the same distinct shape as
the first crankshaft and has substantially the same torsional
flexibility as the first crankshaft. The second crankshaft is also
positioned within the cylinder block, while being connected to the
second series of cooperating pistons and cylinders and positioned
parallel to the first crankshaft, with a first end of the first
crankshaft being positioned adjacent to a second end of the second
crankshaft.
[0010] A first gearset is mounted in the internal combustion engine
connecting the first end of the first crankshaft to the second end
of the second crankshaft, while a second gearset is mounted in the
internal combustion engine connecting the second end of the first
crankshaft to the first end of the second crankshaft. With this
interconnection, the first and second crankshafts are configured to
rotate in opposite directions. A first mass, having an associated
inertia, is connected to the first end of the first crankshaft and
a second mass, having substantially the same rotational inertia as
the first mass, is connected to the first end of the second
crankshaft. Preferably, the first mass is a motor/generator or a
starter, and the second mass constitutes a flywheel or a torque
converter. The first and second crankshafts are preloaded with a
rotational tension stored in the torsional flexibility of each
shaft to eliminate gear rattle. An alternative embodiment is to
have a single gearset between the two crankshafts with one of the
gears including a spring loaded scissors gear.
[0011] In operation, the cylinders preferably have a firing order
where the piston motion is diametrically symmetrical. That is to
say that the rear piston of the left cylinder bank has a motion
that is substantially identical to and in phase with the motion of
the front piston of the right cylinder bank. Likewise, the second
piston from the rear of the left bank is in phase with the second
piston from the front of the right bank, etc. Also, the total
rotational inertia of the left bank crankshaft, including flywheel,
torque converter, and other rigidly attached rotating parts is
substantially equal to that of the right bank crankshaft with its
rigidly attached rotating parts. In any case, with this
construction, the engine assembly will have substantially perfect
internal balance of piston forces, while also providing
substantially perfect internal balance of crankshaft rotational
moments.
[0012] Additional objects, features and advantages of the present
invention will become more readily apparent from the following
detailed description of a preferred embodiment when taken in
conjunction with the drawings, wherein like reference numerals
refer to corresponding parts in the several views.
BRIEF DESCRIPTION OF DRAWINGS
[0013] FIG. 1 is a schematic view of a vehicle incorporating a dual
crankshaft engine embodying the invention;
[0014] FIG. 2 is a simplified isometric view of the dual crankshaft
engine of FIG. 1 shown in a simplified form with various parts of
the engine, such as the valves and cylinders, being omitted so the
moving parts of the engine attached to the crankshafts may be seen
more easily;
[0015] FIG. 3 is an end view of the engine of FIG. 2 showing one of
the two gearsets that connect the crankshafts;
[0016] FIG. 4 is a downward looking cross-sectional view of the
engine of FIG. 3 taken along line 4-4 showing more details of the
crankshafts, along with added inertial masses including a torque
converter and a starter/generator;
[0017] FIG. 5 is a top view of the engine of FIG. 3 showing the
engine with six cylinders, along with associated intake ports and
passages leading from an intake manifold;
[0018] FIG. 6 is a cross-sectional view of the engine of FIG. 3
taken along line 6-6, showing details of a gear that is
incorporated into one of the counterweights on the crankshaft;
and
[0019] FIG. 7 shows an embodiment where the gear of FIG. 6 is a
scissors gear.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0020] With initial reference to FIG. 1, there is shown an
automotive vehicle 10 having a body 11 and a dual crankshaft engine
12. The engine 12 is preferably attached to a first mass 14, having
an associated inertia such as motor/generator or a starter motor.
The engine 12 is also attached to a second mass 16, having an
associated inertia, such as torque converter or a flywheel. The
rotational inertia of the first mass 14 is preferably the same as
the rotational inertia of the second mass 16. Power from the engine
12 is transmitted through the flywheel or torque converter to a
transmission 18, then to the other portions of a powertrain 20 and
eventually drives wheels 22.
[0021] In FIG. 1, the vehicle 10 is shown as a rear wheel drive
vehicle but, as will become readily apparent from the discussion
below, any type of powertrain arrangement, including a front wheel
or all wheel drive, could be used. At this point, it should be
readily recognized that a flywheel would be commonly used as second
inertia mass 16 with a manual type countershaft transmission, while
a torque converter would be used when an automatic type
transmission is employed. Similarly, the first mass 14 is
preferably a motor/generator in the case of a hybrid vehicle,
otherwise the first mass 14 is a starter. As more fully discussed
below, the first mass 14 may also include a combination of other
accessories that, when taken together, have the same inertia as the
second mass 16. For simplicity in connection with describing the
invention herein, the first mass 14 will generally be referred to
as a motor/generator 24 and the second mass 16 will be generally be
referred to as a flywheel 26 as shown in FIG. 4.
[0022] Referring now to FIGS. 2-5, the engine 12 is shown with a
cylinder block 28 containing first and second counter-rotating
crankshafts 30 and 32. A first series 34 of cooperating pistons and
cylinders are mounted in the cylinder block 28 and connected to
first crankshaft 30, while a second series 36 of cooperating
pistons and cylinders are mounted in the cylinder block 28 and
connected to second crank shaft 32. More specifically, cylinders
41-46 slidably receive respective pistons 51-56 thus defining
multiple combustion chambers, two of which are shown at 72 and 75
in FIG. 3. The pistons 51-53 connected to the first crankshaft 30,
along with their associated cylinders 41-43 as best seen in FIG. 5,
collectively constitute the first series 34 of cooperating pistons
and cylinders, while the pistons 54-56 connected to the second
crankshaft 32, along with their associated cylinders 44-46 as also
best seen in FIG. 5, collectively constitute the second series 36
of cooperating pistons and cylinders.
[0023] Each of the first and second crankshafts 30 and 32 is
rotatably mounted on respective main journals 81-84 and 85-88. As
one skilled in the art would understand, each main journal 81-88 is
rotatably coupled to a main bearing of the engine 12, thereby
rotatably coupling the respective crankshafts 30 and 32 to the
engine 12. Each of the crankshafts 30, 32 also has a respective
plurality of rod journals 90, 92 integrally formed therein. Each
connecting rod 101-106 is mated to an associated journal 111-116 on
one of the two crankshafts 30, 32. Each connecting rod 101-106 is
also connected to an associated reciprocating piston 51-56, thus
allowing the pistons 51-56 to drive the crankshafts 30, 32 when the
engine 12 is in operation. As best seen in FIG. 3, the first
plurality of rod journals 90 includes first, second and third
connecting rod journals 111-113 that are evenly spaced around a
rotational axis 120 of the first crank shaft 30 such that the
journals 111-113 are spaced approximately 120 degrees apart.
Similarly, the second plurality of journals, which includes the
fourth, fifth and sixth journals 114-116 on the second crankshaft
32, are set 120 degrees apart around a rotational axis 121.
[0024] As can be seen from the above discussion, the two
crankshafts 30 and 32 are fabricated to be essentially identical to
each other and formed of the same distinct shape, but they are
installed "end-for-end" so that crankshaft 30, as viewed from the
front of the engine 12, has the same direction of rotation and rod
journal positions as crankshaft 32, as viewed from the rear of the
engine 12. This creates an arrangement that is symmetrical about a
central axis 125 as shown in FIG. 4. In this manner, any pitching
couples generated by piston linear acceleration forces of the first
series 34 cooperating pistons and cylinders are equal in magnitude
and phase angle, but opposite in sign to the couples generated by
the second series 36 of cooperating pistons and cylinders. Note,
for example, the sixth piston 56 closest to the flywheel 26 moves
up and down in synchronism with the first piston 51 closest to the
motor/generator 24, as can best be seen in FIG. 2 with respect to
reference plane 126.
[0025] Each crankshaft 30, 32 has a first end 131, 132 and a second
end 133, 134 respectively. As best shown in FIG. 4, a first gearset
135 connects the first end 131 of the first crankshaft 30 to the
second end 134 of the second crankshaft 32, while a second gearset
136 connects the second end 133 of the first crankshaft 30 to the
first end 132 of the second crankshaft 32. With this construction,
the two crankshafts 30 and 32 are forced to counter-rotate. In the
case of the first crankshaft 30, the first end 131 has a flange 140
integrally formed therein. As shown, the flange 140 is connected to
the motor/generator 24. In a single crankshaft engine, the second
end of the crankshaft would normally be connected to a flywheel.
However, the first crankshaft 30 as shown simply ends at the main
journal 84 with or without a thrust surface 141. In the case of the
second crankshaft 32, the first end 132 also has a flange 145
integrally formed therein but, in this case, the flange 145
connects to the flywheel 26.
[0026] Firing frequency rotational accelerations of the flywheel 26
result in equal and opposite inertial vibration torque imposed upon
cylinder block 28. To cancel this torsional excitation of the
cylinder block 26, the motor/generator 24 and the flywheel 26
preferably have an equivalent amount of rotational inertia. Since
the magnitude of both the clockwise and the counterclockwise
rotating inertias are equal to each other and their rotational
accelerations are equal but opposite, the reactions that they
impose upon the cylinder block 28 mutually cancel, and the block 28
does not vibrate from internal inertial forces. This cancellation
of the crankshaft's torsional reaction against the cylinder block
structure 28 presents an opportunity. Since the cylinder block
structure 28 has less vibration in response to crankshaft torsional
vibrations than a conventional engine, the engine 12 may be
operated in more fuel efficient modes where the crankshaft
vibration increases. One example of a more fuel efficient mode of
operation that increases crankshaft torsional vibration is cylinder
deactivation, sometimes referred to as "variable displacement
internal combustion" engine (VDIC). The present invention allows
selective disabling or re-enabling of cylinders 41-46 from the
first 34 and second 36 series of cooperating pistons and cylinders
in accordance with power requirements of the vehicle 10. Current
production VDIC equipped vehicles are calibrated to avoid cylinder
deactivation under many conditions where the engine 12 with
deactivated cylinders could produce adequate power, but the
resulting vehicle NVH (noise vibration and harshness) would be
unacceptable. Furthermore, the increase of cylinder block width, to
enclose two crankshafts 30, 32 and two banks of cylinders 41-43 and
44-46 in one integral structure, functions to stiffen the cylinder
block 28 and reduce vibrations and radiated sound from the engine
12. The motor/generator 24 serves to capture vehicle kinetic energy
during deceleration as well as to add torque to enhance vehicle
acceleration.
[0027] The motor generator 24 can also be used as an "active
flywheel". A control strategy for using a starter as an "active
flywheel" is disclosed in U.S. Pat. No. 6,256,473, which is
incorporated herein by reference. The additional rotating inertia
of the motor/generator 24, along with the ability of the
motor/generator 24 to create or absorb torque, also allows the
engine 12 to operate with a more efficient combustion process, such
as HCCI (Homogeneous Charge Compression Ignition). The
motor/generator 24, with dynamic torque control, can remove torque
from strong combustion events and add torque to weak combustion
events. This torque compensation, along with the cancellation of
the crankshaft internal inertial reaction torque on the cylinder
block 28 allows reliable and smooth engine operation with a
combustion process that may have reduced robustness in favor of
more efficiency.
[0028] As shown in FIG. 1, the flange 140 may also provide a
mounting place for various ancillary equipment, generally indicated
at 148 in FIG. 1, such as a camshaft drive mechanism, an engine
driven coolant pump, a power steering pump, climate control system,
fan belt pulleys, or the like. Power from the engine 12 could be
taken from either end of either crankshaft 30, 32 in either hand of
rotation as long as the two crankshafts 30, 32 have essentially
symmetrical construction with equivalent rotating inertias and
opposite directions of rotation. Preferably, the total inertia of
the ancillary equipment 148 that is tightly coupled to the
crankshaft 30 and the motor/generator 24 is the same as the inertia
of the flywheel 26. The motor/generator 24, with inertia mass
equivalent to the flywheel 26 or torque converter, has very large
current generating capacity, even at engine idle, and could enable
electrical powering of various ancillary equipment 148 that are
normally driven mechanically by a belt from a crankshaft.
Conventionally, an engine driven coolant pump and a power steering
pump are sized for their most severe operating conditions, and
during other engine operating conditions they are over-driven and
waste much energy. Even with the conversion inefficiencies between
electrical and mechanical energy, these machines would be more
efficient if they were electrically driven at speeds in accordance
with need. Technically, the vehicle 10 is not a full hybrid because
the engine 12 will always be running when vehicle propulsion is
needed. Regardless, the large electric motor/generator 24 could
crank the engine 12 and bring it up to speed very quickly and
quietly, so that if the vehicle 10 is equipped with an electrically
powered climate control system or other ancillary equipment 148
powered from a rechargeable battery, the engine 12 may shut off
whenever it is not needed for vehicle propulsion and restarted
again, as needed, without adversely affecting the comfort of
passengers or the drivability of the vehicle 10.
[0029] Furthermore, each crankshaft 30, 32 includes two types of
integral counterweights as shown in FIG. 4. Counterweights 152a,
152b, 155a and 155b for the second and fifth pistons 52, 55 are
formed as two parallel lobed weights. The counterweights for the
first, third, fourth and sixth pistons 51, 53, 54, 56 include a
respective one lobed weight 151, 153, 154, 156 and a respective
weight 161, 163, 164, 166 that is incorporated into respective
gears 171, 173, 174, 176. As can best be seen in FIG. 6, the
crankshaft cheek 191 is provided with at least two annularly placed
holes 181 and 182. The gear 171 is also provided with holes 183 and
184 that align with the holes 181 and 182 in the cheek 191.
Threaded fasteners 185 and 186 pass through respective aligned ones
of the holes 181, 182, 183, 184 to secure the gear 171 to the cheek
191 and thus to the crankshaft 30. The counterweights 152a, 152b,
155a, 155b, 151, 153, 154, 156, 161, 163, 164, 166 have the
appropriate masses and are located to generate forces on the
crankshafts 30, 32 that cancel the lateral first order forces
imposed on the crankshafts 30, 32 by the acceleration forces of the
connecting rods 101-106. First order unbalance refers to the forces
and couples that vary as a sinusoidal function with one cycle of
force occurring with each rotation of the crankshaft. Second order
unbalance is caused by the changing vertical force components based
on the varying vertical component of the connecting rod lengths
caused by the cyclical inclinations of the rods 101-106 due to
lateral movement of the associated journals 111-116.
[0030] Preferably, pistons 51-56 and their associated connecting
parts have the same reciprocating mass and stroke, and each
crankshaft 30, 32 has equal angular and axial spacing between rod
journals 111-116 so that the reciprocating pistons 51-56 and
connecting rods 101-106 coupled to each crankshaft 30, 32 generate
no unbalanced shaking forces or moments. Symmetry of construction
achieves substantially perfect balance of the engine 12. The
crankshafts 30, 32 are far enough apart to prevent interference
between the connecting rods 102, 105, as illustrated in phantom
lines in FIG. 4. The first series 34 of cooperating pistons and
cylinders and the second series 36 of cooperating pistons and
cylinders are preferably equidistant fore and aft, as illustrated,
so that the engine 12 will have minimum length, and the block 28
will have maximum strength and stiffness. This overall arrangement
will function to cancel those first order vibrations not cancelled
by the counterweights 152a, 152b, 155a, 155b, 151, 153, 154, 156,
161, 163, 164, 166, while also canceling any second order
vibrations due to the symmetry of the engine 12 about axis 125.
[0031] FIGS. 3 and 5 illustrate how an intake manifold 200 is
preferably oriented above the engine 10 in a fashion that
advantageously provides the same length passages 205 between the
manifold plenum 207 and the intake valves 210 of every cylinder
41-46.
[0032] Since gear sets 135 and 136 are driven directly from the
crankshafts 30 and 32, the gear sets 135, 136 have the potential to
be very noisy due to the crankshafts' torsional vibrations causing
rattle between the gears 171, 173, 174, 176. A properly designed
scissors gear set 270, shown in FIG. 7, is therefore provided to
eliminate rattle between the gears 171, 173, 174, 176. The scissors
gear set 270 includes a one-piece gear 174 on the crankshaft 32
meshing with a split gear 271 on the crankshaft 30. The split gear
271 has a first rigid portion 273 that is attached to the
crankshaft 30, while a second spring-loaded portion 274 is
rotationally biased relative to the first portion 273 by a spring
275. In operation, the first rigid portion 273 transfers torque to
the gear 174 in one direction of torque, while the second
spring-loaded portion 274, through the spring 275, transfers torque
to the mating gear 174 in the opposite direction of torque. If the
spring pre-load is greater than the maximum reverse torque that the
second spring-loaded portion 274 of the gear set 270 must carry,
the gear set 270 will not rattle. Since the crankshaft 32 receives
very large input torques in both the forward and backward
directions, the scissors gear set 270 is designed so that the
spring 275 is very strong.
[0033] In another preferred embodiment of the invention, the
torsional flexibility of the crankshafts 30, 32 is used to reduce
vibration instead of using the scissors gear set 270. This is done
when mounting the gear sets 135, 136 between the crankshafts 30, 32
at both ends of the engine 12. More specifically, the first three
gears 171, 173, 174 are clamped to the crankshafts 30, 32 as they
are installed into the engine 12. Then the fourth gear 176 is
placed, but not clamped, so that it is free to rotate slightly
relative to crankshaft 32. The ends 132, 133 of the crankshafts 30,
32 near the unclamped gear 176 can be twisted relative to each
other and held in the twisted position while the last gear 176 is
clamped in place to provide a torsional preload. The twisted
crankshafts 30, 32 serve as preload springs for the gear sets 135,
136, thereby eliminating gear rattle by preloading the first and
second crankshafts 30, 32 with a rotational tension stored in the
torsional flexibility of each shaft 30, 32. Preferably, one
crankshaft 30 carries two gears 171, 173 with a handed helix, while
the other crankshaft 32 carries two gears 174, 176 with an opposite
handed helix. In this manner, the thrust loads generated by the
torsional preload will create both fore and aft thrust on each
crankshaft 30, 32, allowing the thrusts from the preload to cancel
within each crankshaft 30, 32 without imposing extra loads on the
crankshaft support bearings.
[0034] The engine configuration described in this invention
disclosure provides near perfect internal balance of piston
acceleration forces, unlike conventional single crankshaft V6
engines, and it will provide near perfect internal balance of
rotational accelerations of the flywheel, unlike all conventional
single crankshaft engines. Furthermore, the upper portion of this
dual crankshaft engine is narrower than that of conventional V6 and
V8 engines. Although described with reference to a preferred
embodiment of the invention, it should be readily understood that
various changes and/or modifications could be made to the invention
without departing from the spirit thereof. For instance, both
crankshafts could be offset from the plane of their corresponding
cylinders to reduce piston side loading during the power stroke, as
long as symmetry is maintained with both crankshafts having the
same magnitude of offset. The shown engine has three cylinders in
each bank, however each crankshaft may have more cylinders so long
as the rows of cylinders each have the same number of cylinders. If
the engine assembly has fewer than six cylinders, such as was done
in the construction of the Ariel Square Four motorcycle engine,
balance shafts or another balancing mechanism would be required to
achieve the desired engine balance. In general, the invention is
only intended to be limited by the scope of the following
claims.
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