Note: Descriptions are shown in the official language in which they were submitted.
~ 1 327493
~ RECIPROCATORY MAC~IN~S
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This invention relates broadly to reciprocatory machines
but provides, in a particular aspect, an internal combustion
engine generally having a two-stroke cycle and adaptable to
spark ignition or compression ignition.
Known internal combustion engines have proven very
difficult to tune properly. Nevertheless, variable valve
timing for conventional and other engines is well known and is
generally performed by adjusting the rotational relationship
between the crankshaft and the valve camshaft. Inbuilt
provision for timing adjustment between the crankshaft and the
valve camshaft has been proposed, for example, in British
Patent Specification 2109858 which provides separate camshafts
for the intake and exhaust valves and adjustment of the
respective camshafts in a manner which is said to produce any
desired change in the overlapping of the valve timing between
the intake and exhaust valves.
In other cases where the ports are valved ky respective
opposed pistons, it has been proposed to provide for
adjustment of the phase relationship between the pistons.
Such arrangements are suggested in German patent 616,451, in
U.S. patents 2,113,480 and 2,401,188 and in British patent
584,783. In the latter case, a turbocharger is coupled to the
intake port. In these engines, adjustment of the piston
timing, for example in response to engine load, is marginally
effective to vary the compression ratio and does inherently
alter the valve timings but is clearly incapable of providing
independent adjustment of valve timing. Moreover, altering
the phase relationship between the pistons impairs or reduces
the naturally very high level of dynamic balance within each
cylinder that occurs when the crankshafts and pistons are in
phase.
It is an object of the present invention to alleviate
the aforementioned disadvantages of reciprocatory machines.
In accordance with the invention, the present invention
has realized that difficulties experienced in achieving valve
timing adjustment in internal combustion engines stem from the
location of the intake and exhaust ports and/or associated
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valves and particularly from their close proximity in most
conventional engines, especially four-stroke engines. Thus,
in most cases both the intake and exhaust ports are located in
the cylinder head close to top dead centre where space is at a
premium and any adjustment other than minimal to the timing
relationship between the piston and the valves may cause the
piston and the valves to interfere, with consequent damage to
the engine. If adjustment is possible to the timing
relationship between the valves for the intake and outlet
ports, the adjustment is also limited by the need to avoid
interference between the valves.
The close proximity of the intake and outlet valves also
leads to the possibility of reverse or spill flows of the
inlet and exhaust gases occurring and any adjustment in the
valve timing must be sufficiently small to avoid undesired
reverse or spill flows.
i The inventor has further appreciated that adjustment
of the phase relationship between pistons also acting as
; valving means is an unsatisfactory device for achieving the
real object - adjustment of the phase relationship between the
valving means.
An aspect of the invention is as follows:
A reciprocatory machine adaptable as a 2-stroke
engine comprising means defining a working chamber, at
least one piston reciprocable within the chamber,
displaceable translating means associated with the
piston and adapted to translate reciprocating motion of
the piston into rotational movement or vice versa,
intake and exhaust ports for the working chamber and
respective intake and exhaust valve means for said ports
distinct from said at least one piston, and means for
causing said respective valve means to cyclically
operate in response to said reciprocating motion of the
s piston, wherein at least one of the valve means
comprises a sleeve valve reciprocable within said
working chamber about said at least one piston and
wherein said intake and exhaust ports are disposed at or
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adjacent to opposite ends of the working chamber
respectively and means are provided for ef-fecting
independent adjustment of the timing relationship
between the cyclic operation of each of the intake and
exhaust valve means and the displacement of the
translating means including independent adjustment of
the timing of both opening and closing of each of the
intake and exhaust valve means, and thereby to adjust
the timing relationship between the cyclic operation of
the respective valve means.
Preferably the reciprocatory machine includes
ignition means operable in the working chamber whereby
the machine comprises an engine, preferably but not
necessarily operable
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on a 2-stroke cycle. Alternatively the invention may be
adapted to, for example, a compressor.
By the present invention it is possible to provide a
substantially infinite variation of valve timing within a wide
range by virtue of the spacing of the intake and outlet ports
allowing for more precise control of the inlet and exhaust
flows and, if desired, essentially a total elimination of
reversed or spill flow of the inlet and/or exhaust gases.
Furthermore, the separation of the valve means at or adjacent
10 respective ends of the working chamber avoids the risk of
their colliding, while the risk of collision between the
piston and one of the valve means may be alleviated by
providing only small or no adjustment of that valve means with
the other valve means being fully adjustable or by using as
said one valve means a type of valve with which collision is
unlikely to occur, such as a sleeve valve. Generally however,
the invention is applicable to various combinations of types
of valve means, including sleeve valves, poppet valves and
rotary distributor type valves, and preferably the intake and
20 exhaust valve means are both adjustable for timing. Examples
of engines in which the present invention may be readily used
are the Detroit Diesel Engine having a poppet exhaust valve in
i the cylinder head and inlet ports in the cylinder wall near
s Bottom Dead Centre, and the Ricardo sleeve valve engine.
Substantially infinite variation over ~ wide range of
the valve timing may permit substantial variation of inlet
timing, exhaust timing, effective compression ratio, effective `
expansion ratio, exhaust "blow down" period and supercharging
period. This range of variation may permit a total change in
30 character of the reciprocating machine from, for example, a
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racing car engine to a low horsepower engine for a road going
~` family sedan. Advantageously the valve timing is adjustable
` during operation of the machine and by use of duplex cams,
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eccentrics and/or other suitable operating mechanisms,
. variation of timing may be effected not only continuously but
~- within each cycle.
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By the term "effective compression ratio" we mean the
volume contained in the working chamber at the first moment at
which the working chamber becomes sealed during a cycle
divided by the minimum volume contained in the working chamber
during the cycle, and by the term "effective expansion ratio"
we mean the volume contained in the working chamber at the
first moment at which the working chamber is opened to exhaust
during a cycle divided by the minimum volume contained in the
working chamber during the cycle.
One particular advantage of the invention, and in
particular of the ability to finely control valve timing, is
- to render 2-stroke engines capable of optimum conjunction with
a turbocharger. The benefits of turbocharging are well known
and have been successfully obtained for some years with
4-stroke engines. However, it has generally been found very
difficult to successfully apply turbocharging to 2-stroke
engines, due largely to the typical conflict between the
engine's general demand for inlet manifold pressure to rise as
a cube function of speed and the turbocharger's quite
different discharge pressure characteristic, and also due to a
2-stroke engine not being able to provide a positive naturally
occurring inlet stroke such as normally occurs in a 4-stroke
engine.
' These problems are met by the invention. The provision
for adjustment between the two valve means permits two notable
'j temporary timing relationships, as follows:
(i) when a warm re-start is required, early opening of
the exhaust valve will allow use of the pressure
and/or thermal and/or kinetic energy of the hot
residual gases within the cylinder to drive the
turbocharger and so facilitate the refilling cycle.
` (ii) for starts in general but especially cold starts,
the valve timing can be adjusted to raise the
compression ratio, lowering it again for subsequent
running operation.
Generally the valve means will be driven by the
translating means, which may comprise, for example, one or
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more crankshafts, and the drive means may comprise an
internally toothed belt, commonly known as a timing belt, or a
gear train, plus crank and pin or eccentric and follower
mechanisms. In a preferred embodiment, the drive means to the
or each adjustable valve includes a helical gear train and the
adjusting means comprises means for varying the phase change
across the gear train. The gear train for the or each
adustable valve may include respective helical gears on the
translating means and on a drive shaft for the valve, and
interposed helical gear means meshing with said helical gears,
with the gear means being linearly movable parallel to the
axes of the helical gears.
5' In the early years of internal combustion engines,
poppet valving experienced difficulties with excessive noise
and a tendency to induce both detonation and pre-ignition. An
alternative was sleeve valving, which was used in a number of
early commercial engines, particularly aero engines. The
history of sleeve valve engines is well summarized in the
standard text "The High-Speed Internal Combustion Engine" by
Sir Harry Ricardo (published by Blackie & Son Limited, London)
who himself built a number of successful long-life sleeve --
valve engines and carried out extensive research regarding
their performance and optimum design.
Sleeve valve engines were found to have a number of
significant advantages. Their mechanical efficiency and fuel
consumption were impressive and in part arose from the
unexpectedly low frictional losses at the interfaces between
the reciprocating sleeve, typically a nitrided steel, and the
cylinder barrel and piston. Provided the sleeve was
- 30 reciprocated both longitudinally and circumferentially, there
was excellent lubrication between the sleeve and cylinder
barrel. The Ricardo engines operated for many hours without
any significant problems in the sleeve or piston motion. The
engines were quiet and it was found that the piston
temperature in a liquid-cooled sleeve valve engine was
actually a little lower than in a poppet valve engine of
similar capacity and output, apparently because the moving oil
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film between the sleeve and cylinder wall was a very efficient
convector of heat away from the piston. Because the cylinder
head was unencumbered by ports and valves, one had complete
freedom as regards the form or capacity of the combustion
chamber.
These advantages were especially applicable to 2-stroke
engines, but there were also found to be some significant
disadvantages which mitigated against the widespread
commercial application of 2-stroke sleeve valve engines,
particularly given that the major objectionable features of
early poppet valve engines had later been resolved. Ricardo
saw two significant difficulties which he summarized at page
387 of his text (cited above):
"1. The nitrided sleeves have a life of probably 2000
to 4000 hours before wear of the top end of the sleeve
renders them unservicable. This is long enough for
military aircraft, but not nearly long enough for
ordinary commercial duties. Some means will yet have to
be found for reducing the rate of wear in this zone."
"2. Although the open-ended sleeve appears to seal
`~ perfectly under all operating conditions, it does not
provide a complete seal when starting from cold, and
some means, such as the injection of a little thick oil,
must be applied to enable the compression ignition
version to start from cold: this is rather an
objectionable feature."
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The wear of the top end of the sleeve arose from
exposure of this part of the sleeve to the full flow of
exhaust gases and/or mechanical interference with the upper
j part of the cylinder barrel or head. Secondary disadvantages
of the sleeve valve engine were the bulky and expensive
re-entrant head, known as a junk-head, which gave rise to
-- wasteful heat losses and, in air cooled applications, was
difficult to adequately cool.
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In the case of 4-stroke sleeve valve engines, the two
problems noted by Ricardo did not apply but the presence of
the junkhead was still a significant obstacle to commercial
development.
One solution to those problems not appreciated even by
Ricardo but disclosed in sritish Patent Specification 497,300
to Porkman, and in British patent 1,015,189 to Lindsay, was to
adapt the fundamentals of sleeve valving to an opposed piston
engine, that is to provide a pair of opposed pistons with
10 respective sleeves providing valves for the exhaust and intake
ports. There were a considerable number of successful and
commercial opposed piston engines, of which typical examples
-~` are Junkers Jumo,~ Rootes Diesel~ and Napier Deltic~ engines
but all relied upon piston controlled valving. So far as the
applicant is aware, an opposed piston engine of Porkman's or
Lindsay's design was never commercialized and sleeve valved
engines have remained only an historical curiosity since the
~,'J, end of World War II despite their advantages as noted by
` Ricardo. It is believed that the present invention will
:- 20 encourage those advantages to be realized, both in non-opposed
'`t and opposed piston form.
Referring now particularly to a sleeve valved engine,
the or each sleeve is preferably driven in a reciprocatory
;` motion which is both circumferential and longitudinal. The
c stroke of the circumferential motion is preferably at least
- 20% of the stroke of the longitudinal motion.
In the case of two opposed pistons in the working
-~- chamber, and sleeve valving in the form of respective sleevevalves for the spaced exhaust and intake ports, the separate
30 sleeves are advantageously reciprocable about the respective
pistons. Preferably, respective crankshafts are provided for
the two pistons, and the sleeves are reciprocable by separate
drive means from the respective crankshafts. The crankshafts
are preferably directly coupled by an internally toothed belt,
` and the drive shaft to the load is preferably parallel or
co-axially coupled to one or both of the crankshafts.
.. The intake port is advantageously coupled to a
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supercharger, and most advantageously to a turbocharger
mounted to be driven by products from the exhaust port.
Two embodiments of the invention will be further
described, by way of example only, with reference to the
accompanying drawings, in which:
FIGURE 1 is a multi axial somewhat diagr~mmatic
cross-section of a 2-stroke opposed piston sleeve valved
engine in accordance with the invention, with the pistons
shown close to top dead centre;
FIGURE 2 is an enlargement of one end of the engine of
Figure l; and
YIGURE 3 is a view similar to Figure 2 but showing the-
one end of the engine modified to operate alone.
- Referring to Figures 1 and 2, the illustrated opposed
piston 2-stroke engine 8 is substantially symmetrieal about a
transverse median plane A-A and includes a east engine bloek 9
whieh encompasses a cylindrical barrel 12, defining a working
chamber and crankcases 14, 15 with eover portions 35. The
engine further includes respeetive crankshaft assemblies 16,
17, and a pair of opposed pistons 18, 19 eoupled to the
crankshaft assemblies 16, 17 by eonneeting rods 20, 21 for
~; opposite reciproeation within the working chamber timed by an
~; internally toothed belt 24. Barrel 12 and erankease
assemblies 14, 15 are shown for eonvenienee as a single
l easting but this may be varied aeeording to circumstances.¦ Figure 1 illustrates the erankshafts in phase and the pistons
at top dead eentre, inwardly of respeetive rings of ports 26,
27 in eylinder barrel 12. The crankshafts may of course be
set out of phase as desired, for example to aehieve improved
~i 30 air seavenging in two-stroke mode. Ports 26, 27 open to
f respective annular manifolds 25, 29, which in operation
`'~ eomprise an intake manifold and an exhaust manifold, and whieh
eommunieate in turn with duets 25a, 29a. The exaet physieal
strueture of the manifolds and assoeiated duets is not
, detailed, being indieated sehematieally only in Figure 1.
Intake duet 25a is eoupled to the outlet of a turboeharger
^~ assembly 90 ineluding a blower 92 driven by a turbine 94.
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Turbine 94 is in turn powered by exhaust gases directed along
duct 29a.
The combustion chamber 13a substantially comprises a
pair of radiused cavities 28 in the heads 30, 31 of pistons
18, 19. As shown the cavities 28 are spherically radiused,
but in alternative configurations the piston heads, or
discrete crowns if desired, may be flat or convex. For spark
ignition and/or injection access to the combustion chamber,
cylinder barrel 12 is provided with peripherally spaced
ignition ports 32, and piston heads 30, 31 with registering
grooves 32a. Injection devices 1,1 for compression ignition
are illustrated in this case but it is emphasized that spark
! plugs may be substituted as desired.
The crankcase and crankshaft assemblies are
substantially identical and it is therefore proposed to
describe in detail only those at the upper end of the engine
as seen in Figure 1. This end is enlarged in Figure 2.
Crankshaft assembly 16 includes a pair of co-axial
crankshafts, a drive crankshaft 40 and a timing crankshaft
410 The two are supported in crankcase 14 and crankcase
covers 35 by spaced roller bearings 42, 44. The crankshaft
assembly is coupled to the piston in a substantially
; conventional arrangement including a tubular crankpin 46, a
gudgeon pin 50 retained in a matching or transverse bore 51 in
piston 18, and connecting rod 20 which receives crankpin 46
and gudgeon pin 50 within respective roller cages 54, 55.
The two timing crankshafts 41 are keyed through
crankshafts 40 to respective pulleys 60, 61 (Figure 1) for
timing belt 24. A tapered mounting is used as illustrated at
40a not only for the usual reason of ensuring a secure
mounting but in this case also to permit tensioning of the
timing belt in the absence of any idler pulley for such
purpose.
Cylinder barrel 12 is fitted with a pair of similar
elongate sleeve valves 10, 11 which, by virtue of spaced rings
of apertures 26a, 27a, in the sleeves, provide valving for
ports 26, 27 and are reciprocable about the respective pistons
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- 10 -
18, 19. Sleeves 10, 11 may be formed in cast iron, nitrided
; steel or other suitable materials such as ceramics or high
performance plastics~ They make a good tolerance fit within
the cylinder barrel and are each free to reciprocate both
longitudinally and circumferentially. O-ring seals are
provided where shown, for example at lOa, lla on the
- intermediate walls of the cylinder barrel and on the
cylindrical surfaces of the pistons. In operation, a thin
film of oil is supplied and maintained between the sleeves and
the barrel and it is for the purpose of maintaining proper
distribution of this film that the circumferential component
of the oscillation is primarily necessary.
Sleeves 10, 11 are reciprocable from the respective
crankshafts 40 by means of separate helical gear trains 68
which are substantially identical and which are fitted with
means for adjusting the timing relationship or phase between
, the respective pistons and the valving of the associated ports
by the sleeves, and thereby the timing relationship between
the sleeves in accordance with the present invention. Each
i 20 gear train 68 comprises respective helical gears 72, 73 on
crankshaft 41 and on a crank 74. These gears mesh with an
intermediate helical gear 71 which is both slidably and
', rotatably mounted on an interposed stud 75. As illustrated
engine is configured for 2-stroke operation, gears 72, 73 are
in 1:1 ratio.
1, Crank 74 is supported in roller bearings 74a and has a
-~ socket 76 housing a spherical bearing 78 for a spigot 80
~ projecting laterally integrally from the sleeve 10. It will
; be appreciated that this arrangement achieves the required two
component motion: the motion is optimised for lubrication
1 purposes, as described above, if the stroke of the
circumferential component of the reciprocatory motion is at
least 20% of the stroke of the longitudinal component.
Phase adjustment is achieved by way of a slidable
push-pull rod 77 which seats in an annular groove 81 of a boss
82 on intermediate gear 71. Rod 77 slidably projects through
f~ a gear case cover 79: slight movement of gear 71 along stud
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7~ will itself cause relative rotation of the gears, because
they are helical gears, and thus an alteration of the phase
between crankshaft 40 and crank 74. This in turn will vary -
the timing relationship mentioned above. This arrangement
permits infinite timing phase adjustment over a 180 range.
Instead of driving each sleeve via a crank 74, a
camshaft may be employed. This affords the additional
advantage that the timing relationship(s) may be varied, not
only by adjusting rod 77, but also, by utilising a cam of
selected shape, within each stroke of the engine.
Rod 77 may be arranged for manual control, or for
automatic control in response to, e.g., the monitoring of
intake manifold pressure, engine speed, road speed, throttle
setting and torque output.
Sleeves 10, 11 are provided with complementary scallops
32b, which register at the required times with injection ports
32 and piston grooves 32a. Apertures 26a, 27a in the sleeves
co-operate as required with barrel ports 26, 27. It is not
thought necessary to provide any specific detail regarding the
port configuration as it will depend, inter alia, on the mode
of operating the engine and on the air flow and the range of
! phasing characteristics desired. Considerations in relation
to timing adjustments under different engine load conditions
are also well known as provision of such adjustments is a
known art.
An important preferred feature of the engine disclosed
in Figures l and 2 which facilitates smooth and trouble-free
operation is the use of timing belt 24 as a direct drive
coupling between the crankshafts. Most advantageously for the
particular application this belt is preferably an advanced
belt of the HTD design marketed by the UniRoyal Company. Such
belts would also advantageously be employed to couple the
output shaft to load.
It will be appreciated that the engine illustrated in
Figures 1 and 2 may include other modifications or adaptations
in accordance with the mode in which it is operated and with
standard principles of engine design. For example, other
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forms of supercharging, e~g. Kadency and/or conventional,
positive displacement and/or mechanically driven centrifugal
superchargers may be employed. Established sleeve valve
porting principles can be applied to take advantage of the
porting in both barrel and sleeve, of the two component motion
of the sleeve, and of the lack of direct contact between the
piston rings and the barrel ports.
It will further be seen that both of the primary -
objections of 2-stroke sleeved valve engines noted by Ricardo
; 10 and quoted above are overcome: there is no longer any
relatively short-term wear of the sleeve ends due to exposure
to full flow of exhaust gases and there is no longer any
problem with lack of sealing at an open-ended sleeve when
starting from cold. The outer sleeve ends of the engine of
Figures 1 and 2 lie in the crankcases and the inner ends are
surrounded by the cylinder barrel and are thereby neither
exposed to flow of exhaust gases nor in need of sealing at
start-up. This also allows full advantage to be taken of one
of the useful features of sleeve valve engines, the self
compensating relationship between the size of the sleeve to
barrel gap and the rate of heat transferred across the gap.
,For example, when the tolerance is substantial, heat transfer
from the piston through the oil film is retarded which results
in thermal expansion of the sleeve to reduce the gap until a
balance occurs between the rate of heat dissipation across the
film and the thermally determined diameter of the sleeve.
Elimination of the junkhead means elimination of an
expensive, high heat loss component and, moreover, of a
component which was difficult to air cool because of its
substantial re-entrant bulk. In this latter respect, it is
interestin~ to note the very expensive and detailed composite
copper cooled head produced by the Bristol Aeroplane Company
to resolve the problem of air cooling the junk head.
By adapting the opposed piston configuration to sleeve
`valving in the engine of Figures 1 and 2 it has been possible
to not only overcome outstanding objections to sleeve valve
engines, but to obtain for opposed piston engines the
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significant known advantages of sleeve valving. In
particular, the mechanical efficiency and fuel consumption are
substantially improved relative to prior opposed piston
engines, and the weight to power ratio is markedly enhanced.
Thus, one of the objections to opposed piston engines in
certain key applications, their somewhat troublesome
dimensional configuration, can be overcome in that the opposed
piston engine can be reduced to a very compact size for a
given power output.
The ability to selectively vary the timing relationship
between each sleeve and the associated piston, makes it
possible to obtain infinite variation over wide ranges of
effective compression ratio, effective expansion ratio,
timing, and volume of the working space. These variations are
not merely possible from cycle to cycle but within each cycle,
allowing the control system to be promptly responsive to
changes in the engine's load requirements. This flexibility
is valuable in particular for 2-stroke operation and is to be
contrasted with the fixed compromise timing settings in most
conventional engines. The engine can work and be matched to a
variable torque load via a simple transmission: the modern
practice to achieve optimum efficiency load matching by way of
a continuously variable torque transmission may be largely
superseded by the utilisation of the engine itself. The
provision of spaced intake and exhaust valves 26 and 27 in the
engine has further advantages. For one, it renders practical
the avoidance of reverse or spill flow when varying the
effective compression ratio and/or effective expansion ratio.
This is not possible with either an opposed piston engine with
conventional valving or the modern poppet valve engine.
Variation of the valve timing in accordance with the
invention permits a most versatile turbocharged 2-stroke
engine. Conventional 2-stroke engines are not well-suited to
supercharging in general and even less so to turbocharging.
Even where turbocharging has been provided, it has not been
possible to rely on the turbocharger to adequately provide
inlet air to the engine under starting conditions or for
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significant parts of the engine's load speed curve and a
separate mechanical supercharger has been required to overcome
these deficiencies.
In cases where turbocharging of 2-stroke diesel engines
has been attempted, a separate external mechanical blower has
been required for starting purposes.
The inventive engine, in contrast, permits turbocharging
of a 2-stroke engine under the full range of operating
conditions and eliminates the need for a separate mechanical
supercharger. For example when a warm re-start is required,
early opening of the exhaust valve will allow use of the
pressure and/or thermal and/or kinetic energy of the hot
residual gases within the cylinder to drive the turbocharger
and so facilitate the refilling cycle. For starts in general
but especially cold starts, the valve timing can be adjusted
to raise the compression ratio, lowering it again for
subsequent running operation. Under all load conditions, it
is possible to vary the inlet and/or exhaust timing so as to
overcome the inherent incompatability of the engine's air
demand characteristics and the turbocharger's output
characteristics, and to generally tune or modify the engine's
characteristics to the prevailing requirements.
The ability to vary the volume of the working space, a
consequence of the invention already noted, allows the engine
to be run for more of the time at a brake mean effective
pressure which provides high thermal efficiency. In other
words, the engine output is then significantly controlled by
~s modifying its volume rather than its brake mean effective
pressure away from an efficient condition.
It will be noted that the described arrangement affords
near perfect primary and secondary balance within each
cylinder. In contrast, as previously mentioned, the known
i practice of altering the phase relationship between the
pistons in an attempt to alter compression ratio, impairs this
very high level of dynamic balance.
Figure 3 illustrates the half engine of Figure 2
,~1 modified to operate alone and since the operation of the
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1 327493
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engine 108 is substantially identical to the operation of the
half engine in Figure 2 its manner of operation will not be
described again except in relation to its differences.
The engine block 9 in Figure 3 is modified to define a
combustion head 110 with apertures 112 and 114 therein to
receive an injector or sparking plug illustrated schematically
at 116 and a poppet valve 118. The poppet valve is also
illustrated schematically in the open position but may take
any of a number of known forms which are not believed to
` 10 require detailed description. Furthermore the drive mechanism
for the poppet valve 118 is not illustrated and may be
non-adjustable in accordance with generally standard engine
practice. Alternatively, the poppet valve 118 is preferably
adjustable as to its timing and such adjustability may be
provided by for example the means illustrated in 8ritish
Patent Specification 2109858. Alternatively, the adjustment
means described herein for use with the sleeve valve 10 may be
duplicated and adapted to the drive means for the poppet
valve. Thus the crank 74 may be connected via a gear train or
belt to a camshaft having an eccentric for displacing the
` poppet valve against the bias of a spring. Adjustment of the
helical gear 71 may change the phase of the poppet valve.
`- Other modifications, alterations and advantages
applicable to the engine described with reference to Figures 1
` and 2 may be applied to the engine 108.
~, Although the invention has been described with reference
to an internal combustion engine, the principles of the
invention are also applicable to other forms of reciprocatory
machines such as pumps or compressors.
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