Offset crankshaft engine

The cylinders (12; 48, 50) are disposed such that each piston-cylinder axis (16; 56, 58) does not intersect the crankshaft axis (20; 47). Timing of combustion within each cylinder is controlled to cause maximum combustion pressure to occur when an imaginary plane that contains both a respective connection axis (28; 66, 70) of a respective connecting rod (24; 62, 64) to the respective piston (14; 52, 54) and a respective connection axis (30; 68, 72) of the connecting rod to a respective throw of the crankshaft is substantially coincident with the respective cylinder axis along which the piston reciprocates. In a V-type engine the axes of those cylinders in a respective bank are disposed in a respective imaginary plane (76; 78) forming a respective side of a V. The respective imaginary planes intersect along an imaginary line (74) that is parallel to the crankshaft axis and spaced from the crankshaft axis by a distance (A) substantially equal to the distance (A) by which the connection axis of each connecting rod to the respective throw is spaced from the crankshaft axis when the imaginary plane that contains both the respective connection axis to the respective piston and the respective connection axis to the respective throw is substantially coincident with the respective cylinder axis.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to reciprocating piston type internal 
combustion (I.C.) engines. More specifically it relates to such an I.C. 
engine in which the axes of the pistons do not intersect, i.e. are 
geometrically offset from, the crankshaft axis. 
2. Background Information 
Certain technology relating to reciprocating piston I.C. engines in which 
the crankshaft axis is offset from the piston-cylinder axes is described 
in U.S. Pat. Nos. 810,347; 2,957,455; 2,974,541; 4,628,876; and 4,945,866; 
in Japan patent document 60-256,642; in Soviet Union patent document 
1551-880-A; and in JSAE Conference proceedings 966, 1996-10. According to 
descriptions contained in those publications, the various engine 
geometries are motivated by various considerations, including power and 
torque improvements and friction and vibration reductions. 
A production V-type engine in which the crankshaft axis is offset from the 
piston-cylinder axes is the Volkswagen narrow V engine, which has six 
cylinders and a 15.degree. V, and is known as the VR6 engine. Because a 
15.degree. V is quite narrow for a V-type engine, it is believed that a 
reason for offsetting the crankshaft axis is to control the height of the 
engine. 
In-line, or straight, engines in which the crankshaft axis is offset from 
the piston axes were used in early twentieth century racing engines. 
SUMMARY OF THE INVENTION 
The present invention relates to further improvements in reciprocating 
piston I.C. engines in which the crankshaft axis is offset from the piston 
axes. 
One general aspect of the invention relates to a multiple cylinder internal 
combustion engine comprising: a crankshaft, comprising multiple throws, 
journaled for rotation about a main axis of the engine; multiple cylinders 
within each of which a respective piston reciprocates along a respective 
piston-cylinder axis as the respective piston executes a repeating 
operating cycle that comprises a power stroke during which combustion 
pressure is applied to the respective piston; the cylinders being disposed 
such that each piston-cylinder axis does not intersect the main axis; 
multiple connecting rods each of which connects a respective piston with a 
respective throw to relate reciprocal motion of the respective piston to 
rotation of the crankshaft; each connecting rod being attached to a 
respective piston and to a respective throw such that as the respective 
piston reciprocates within the respective cylinder, the respective 
connecting rod oscillates relative to the respective piston over an acute 
angular span about a respective piston connection axis parallel to the 
main axis and revolves on the respective throw about a respective throw 
connection axis that is parallel to and spaced from the main axis; and a 
control for controlling timing of combustion within each respective 
cylinder to cause maximum combustion pressure within a respective cylinder 
during a power stroke to occur when an imaginary plane that contains both 
the respective piston connection axis and the respective throw connection 
axis is substantially coincident with the respective piston-cylinder axis. 
Another general aspect relates to a method of operating a multiple cylinder 
internal combustion engine, ne engine comprising: a crankshaft, comprising 
multiple throws, journaled for rotation about a main axis of the engine; 
multiple cylinders within each of which a respective piston reciprocates 
along a respective piston-cylinder axis as the respective piston executes 
a repeating operating cycle that comprises a power stroke during which 
combustion pressure is applied to the respective piston; the cylinders 
being disposed such that each piston-cylinder axis does not intersect the 
main axis; multiple connecting rods each of which connects a respective 
piston with a respective throw to relate reciprocal motion of the 
respective piston to rotation of the crankshaft; each connecting rod being 
attached to a respective piston and to a respective throw such that as the 
respective piston reciprocates within the respective cylinder, the 
respective connecting rod oscillates relative to the respective piston 
over an acute angular span about a respective piston connection axis 
parallel to the main axis and revolves on the respective throw about a 
respective throw connection axis that is parallel to and spaced from the 
main axis; the method comprising controlling timing of combustion within 
each respective cylinder to cause maximum combustion pressure within a 
respective cylinder during a power stroke to occur when an imaginary plane 
that contains both the respective piston connection axis and the 
respective throw connection axis is substantially coincident with the 
respective piston-cylinder axis. 
Still another general aspect relates to a multiple cylinder internal 
combustion engine comprising: a crankshaft, comprising multiple throws, 
journaled for rotation about a main axis of the engine; multiple cylinders 
within each of which a respective piston reciprocates along a respective 
piston-cylinder axis as the engine operates; some of the cylinders being 
arranged to form a first cylinder bank in which the corresponding 
piston-cylinder axes occupy a common first imaginary cylinder plane that 
is spaced from, and parallel to, the main axis; others of the cylinders 
being arranged to form a second cylinder bank in which the corresponding 
piston-cylinder axes occupy a common second imaginary cylinder plane that 
is spaced from, and parallel to, the main axis; multiple connecting rods 
each of which connects a respective piston with a respective throw to 
relate reciprocal motion of the respective piston to rotation of the 
crankshaft; each connecting rod being attached to a respective piston and 
go a respective throw such that as the respective piston reciprocates 
within the respective cylinder, the respective connecting rod oscillates 
relative to the respective piston over an acute angular span about a 
respective piston connection axis parallel to the main axis and revolves 
on the respective throw about a respective throw connection axis that is 
parallel to and spaced from the main axis; and the first and second 
imaginary cylinder planes intersecting along an imaginary line that is 
parallel to the main axis and that is spaced substantially equidistant 
from two imaginary reference planes, a first of which contains the main 
axis and is parallel to the first imaginary cylinder plane, and a second 
of which contains the main axis and is parallel to the second imaginary 
cylinder plane. 
Other general and more specific aspects will be set forth in the ensuing 
description and claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
FIG. 1 shows a portion of a representative internal combustion engine 10 
incorporating principles of the present invention. The Figure shows an 
engine combustion cylinder 12 within which a piston 14 reciprocates along 
a piston-cylinder axis 16. A crankshaft 18, comprising a throw 20, is 
journaled for rotation about a main axis 22. The direction of rotation is 
represented by the curved arrow. A connecting rod 24 connects piston 14 
with throw 20 to relate reciprocal motion of piston 14 and rotation of 
crankshaft 18. 
Connecting rod 24 is attached to piston 14 and to throw 20 such that as 
piston 14 reciprocates within cylinder 12, connecting rod 24 oscillates 
relative to the piston over an acute angular span 26 about a piston 
connection axis 28 parallel to main axis 22 and revolves on the crankshaft 
throw about a respective throw connection axis 30 that is parallel to and 
spaced from main axis 22. 
It is to be understood that the Figure is presented for clarity in 
illustration of the inventive principles, and therefore, certain details 
such as piston rings, crankshaft bearings, etc. are not specifically 
portrayed although they may be present in an actual engine. 
A control 32 controls timing of combustion within cylinder 12 to cause 
maximum combustion pressure within the cylinder during a power stroke to 
occur when an imaginary, plane that contains both axis 28 and axis 30 is 
substantially coincident with axis 16. that Position is the position shown 
by FIG. 1. Such a control may be a spark timing control in the case of a 
spark ignited internal combustion engine. 
FIG. 3 displays a representative graph plot 34 of cylinder combustion 
pressure as a function of crankshaft angle of rotation immediately 
preceding and during combustion. Although the graph plot is 
non-dimensional, the location of piston top dead center (TDC) position is 
marked for the purpose of showing that maximum combustion pressure MCP 
occurs during a power stroke after the piston has passed TDC. 
Important benefits are believed to result by timing the combustion process 
such that the maximum combustion pressure within cylinder 12 occurs when 
the imaginary plane that contains both axis 28 and axis 30 is 
substantially coincident with axis 16, meaning coincident within one or 
two degrees of crankshaft rotation. 
Because of the offset of the crankshaft axis, the piston will be past TDC 
as the combustion pressure builds no toward its peak pressure MCP. It 
therefore becomes possible for the axis of the connecting rod to be 
substantially coincident with the co-axis of the piston and cylinder when 
that peak is reached. As a result, there is at that instant, at least 
theoretically, no side force acting on the piston. Friction between the 
piston and the cylinder wall is significantly reduced, essentially to that 
caused by the piston rings bearing against the cylinder wall. While it is 
true that the piston may encounter side force at and immediately after 
leaving TDC, such force would be encountered at times when the piston 
would be moving more slowly than it would when the connecting rod axis is 
coincident with the piston-cylinder co-axis, and moreover, the combustion 
pressure is, at that time, still well below its peak. It is believed that 
a meaningful improvement in efficiency of transmitting piston stroking to 
cranking motion results because a lesser amount of energy is dissipated by 
friction over the full duration of a cylinder's operating cycle that 
comprises intake, compression, power, and exhaust strokes spanning 
720.degree. of crankshaft rotation in a four-stroke I.C. engine. 
It is also believed that some reduction in loads imposed on the crankshaft 
main bearings may be obtained because the connecting rod axis is 
coincident with the piston-cylinder co-axis at the time that maximum force 
must be reacted by the adjacent bearings. 
FIG. 2 shows principles of the invention applied to a multiple cylinder, 
V-type engine 40. A crankshaft 42 having multiple throws, such as 44, 46, 
is journaled for rotation about a main axis 47 of engine 40. Each of 
multiple cylinders, such as 48, 50, contains a respective piston, such as 
52, 54, which reciprocates along a respective piston-cylinder axis, such 
as 56, 58, as engine 40 operates. Cylinder 48 is representative of one of 
multiple cylinders arranged to form a first cylinder bank in which 
corresponding piston-cylinder axes 56 occupy a common first imaginary 
cylinder plane that is spaced from, and parallel to, main axis 47. 
Cylinder 50 is representative of one of multiple other cylinders arranged 
to form a second cylinder bank in which the corresponding piston-cylinder 
axes 58 occupy a common second imaginary cylinder plane that is spaced 
from, and parallel to, main axis 47. In each cylinder bank the respective 
pistons execute respective operating cycles in properly phased relation so 
that torque is applied to the crankshaft at fairly regular intervals of 
crankshaft rotation. 
A respective connecting rod 62 connects a respective piston 52 with a 
respective throw 44 to relate reciprocal motion of the respective piston 
to rotation of crankshaft 42. A respective connecting rod 64 connects a 
respective piston 54 with a respective throw 46 to relate reciprocal 
motion of the respective piston to rotation of crankshaft 42. 
Each connecting rod 62 is attached to a respective piston 52 and to a 
respective throw 44 such that as the respective piston 52 reciprocates 
within the respective cylinder 48, the respective connecting rod 62 
oscillates relative to the respective piston 52 over an acute angular span 
about a respective piston connection axis 66 parallel to main axis 47 and 
revolves on the respective throw 44 about a respective throw connection 
axis 68 that is parallel to and spaced from main axis 47. 
Each connecting rod 64 is attached to a respective piston 54 and to a 
respective throw 46 such that as the respective piston 54 reciprocates 
within the respective cylinder 50, the respective connecting rod 64 
oscillates relative to the respective piston 54 over an acute angular span 
about a respective piston connection axis 70 parallel to main axis 47 and 
revolves on the respective throw 46 about a respective throw connection 
axis 72 that is parallel to and spaced from main axis 47. All connecting 
rods 62, 64 are identical in that the distance between axis 66 and axis 68 
in all connecting rods 62 and between axis 70 and axis 72 in all 
connecting rods 64 is the same. 
The first and second imaginary cylinder planes intersect along an imaginary 
line 74 that is parallel to main axis 47 and that is spaced substantially 
equidistant (dimensions A in FIG. 3) from two imaginary reference planes, 
a first 76 of Which contains main axis 47 and is parallel to the first 
imaginary cylinder plane, and a second 78 of which contains main axis 47 
and is parallel to the second imaginary cylinder plane. 
The positions of the two pistons illustrated in FIG. 2 denote at least an 
approximate relative phasing between them within their respective 
cylinders with piston 52 being shown substantially at its TDC position. It 
can be appreciated that at TDC each axis 68, 72 has just passed through 
the respective plane 76, 78. 
FIG. 4 shows a three-cylinder radial engine 84 in which each cylinder has a 
configuration like that shown in FIG. 1, and the same reference numerals 
that were used in FIG. 1 designate like parts in FIG. 4. The respective 
pistons of engine 84 are suitably phased in their cylinders. Maximum 
combustion pressure in each cylinder occurs when the connecting rod axis 
is coincident with the respective piston-cylinder axis. The inventive 
principles may be applied to various other radial engines. 
FIG. 5 shows a boxer-type engine in which each cylinder has a configuration 
like that shown in FIG. 1, and the same reference numerals that were used 
in FIG. 1 designate like parts in FIG. 5. The respective pistons are 
phased in opposition in their cylinders. Maximum combustion pressure in 
each cylinder occurs when the connecting rod axis is coincident with the 
respective piston-cylinder axis. 
FIG. 6 shows a W-type engine 88 in which each cylinder has a configuration 
like that shown in FIG. 1, and the respective pistons are suitably phased 
in their cylinders. This engine is like a V-engine but with a third 
cylinder bank 90. The same reference numerals from FIG. 2 are used in FIG. 
6 to designate like parts of the two outer cylinder banks. The third 
cylinder bank 90 is nested within the V formed by the first two cylinder 
banks. It is to be observed that an imaginary plane 92 containing the 
piston-cylinder axes of the third cylinder bank also contains imaginary 
line 76. Combustion is controlled such that maximum combustion pressure in 
each cylinder occurs when the connecting rod axis is coincident with the 
respective piston-cylinder axis. 
While a presently preferred embodiment has been illustrated and described, 
it is to be appreciated that the invention may be practiced in various 
forms within the scope of the following claims.