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Title:
INVERTED I.C. ENGINE CONFIGURATION
Document Type and Number:
WIPO Patent Application WO/2000/063537
Kind Code:
A1
Abstract:
An inverted aircraft i.c. piston engine (10), such as a two-stroke, compression-ignition (diesel), incorporates: a wet sump lubrication system, with a combined under-slung camshaft or valve gear cover and sump housing (30); a turbo-charger (24), located above the wet sump operational oil level (33) and lubricated from the wet sump system, with gravity return to the sump.

Inventors:
Wilksch, Mark Conrad (8 Partridge Close Buckingham Bucks MK18 7HH, GB)
Application Number:
PCT/GB2000/001528
Publication Date:
October 26, 2000
Filing Date:
April 19, 2000
Export Citation:
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Assignee:
SENECA TECHNOLOGY LIMITED (P.O. Box 107 Oceanic House Grand Turk, TC)
Wilksch, Mark Conrad (8 Partridge Close Buckingham Bucks MK18 7HH, GB)
International Classes:
F01M11/06; F01P3/18; F02B39/14; F02B67/10; F01M1/12; F02B3/06; F02B75/02; (IPC1-7): F01M1/02
Attorney, Agent or Firm:
Wilksch, Mark Conrad (8 Partridge Close Buckingham Bucks MK18 7HH, GB)
Wilksch, Mark Conrad (8 Partridge Close Buckingham Bucks MK18 7HH, GB)
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Claims:
CLAIMS
1. An inverted piston engine (10), with a wet sump lubrication system, including a combined sump casing and, cylinder head, camshaft or valve gear, cover (30).
2. An inverted engine and wet sump, according to Claim 1, with an inhead camshaft, and/or valve gear, at least partially immersed in, or splashed by, lubricant, such as oil, entrained within the sump.
3. An inverted engine and wet sump, according to either of the preceding claims, of a caminhead configuration, with a rotary lubricant pump, driven directly from the camshaft, or indirectly through a camshaft drive train.
4. An inverted engine and wet sump, according to any of the preceding claims, configured with multiple rows of cylinders, with [cooperatively interconnected,] (respective) individual sumps, or a common sump.
5. An inverted engine and wet sump, according to any of the preceding claims, incorporating one or more turbocharger (s) (24), in an exhaust manifold path (22), adjacent a cylinder head (16), the turbocharger mounted generally above the wet sump (30).
6. An inverted engine and wet sump, according to Claim 5, with turbocharger lubricant (oil) feed from an engine oil pump, and gravity return of turbocharger lubricant (oil), to the wet sump.
7. An inverted engine and wet sump, according to either Claim 5 or 6, wherein the turbocharger (s) is (are) mounted, via an exhaust manifold (s), to a cylinder head.
8. An inverted engine and wet sump, according to any of Claims 5 through 7, wherein the turbocharger (s) is (are) mounted to one (or both) side (s) of the engine.
9. An inverted engine and wet sump, according to any of Claims 5 through 7, wherein the turbocharger (s) is (are) mounted at one (or both) (front or rear) end of the engine.
10. An inverted engine and wet sump, according to any of Claims 5 through 9, wherein the turbocharger (s) is (are) at least partially supported upon an exhaust manifold.
11. An inverted engine and wet sump, according to any of Claims 5 through 10, where the turbocharger (s) is (are) at least partially supported, by a bracket (s), independently of the exhaust manifold.
12. An inverted engine and wet sump, according to any of Claims 5 through 11, with a multiple branch exhaust manifold, whose individual branch length, is less than twice cylinder spacing.
13. An inverted engine and wet sump, according to any of the preceding claims, configured for exclusive or partial liquid cooling.
14. An inverted engine and wet sump, according to any of the preceding claims, configured for at least partial air cooling.
15. An inverted engine and wet sump, according to any of the preceding claims, configured for twostroke combustion cycle.
16. An inverted engine and wet sump, according to any of claims 1 through 14, configured for fourstroke combustion cycle.
17. An inverted engine and wet sump, according to any of the preceding claims, configured for compression ignition.
18. An inverted engine and wet sump, according to any of the preceding claims, with an inline configuration.
19. An inverted engine and wet sump, according to any of the preceding claims, with a mutuallyinclined cylinder bank configuration, such as a'V'or'W', allowing for multiple in line cylinders in a bank.
20. An inverted engine and wet sump, according to any of the preceding claims, configured for aircraft propulsion.
21. An inverted engine and wet sump, substantially as hereinbefore described, with reference to, and as shown in, the accompanying drawings.
22. An inverted engine and wet sump, incorporating a turbocharger (s) (24), in an exhaust manifold path (s) (22), adjacent a cylinder head (s) (16), mounted generally above a wet sump (30), and/or a wet sump lubricant level (33).
23. An inverted aircraft engine, of either the spark or compression ignition type, with a turbocharger (s) mounted on one side or both sides of the engine.
Description:
INVERTED I. C. ENGINE CONFIGURATION This invention relates to various aspects of internal combustion (i. c.) engine orientation, the disposition of engine ancillaries and their constructive combination, including: * a so-called'wet sump'engine lubrication system; 'turbo-charger location, installation and lubrication; for an inverted engine, in particular one configured for aircraft propulsion.

Within this patent the terminology used is defined as follows:- A primary feature of the invention concerns the lubricant (oil) storage provision. In that context, both for clarity of definition and to differentiate from the prior art, it is appropriate and helpful to use the various terms,'sump','wet sump'and'dry sump' which have special meanings attributed to them in the context of i. c. engines.

Broadly, the term'sump'could, in principle, embrace any form of reservoir-whether configured as an open or closed chamber, or container-at whatever (dis) position, orientation or level.

However, in established i. c. engine parlance, the term sump generally characterises an on-board, (ie engine-mounted) or (engine) integrated chamber, for the collection of lubricant (oil), by a gravity return flow, typically after circulation under pressure by an oil pump.

In a conventional'upright'i. c. engine orientation, with a crankshaft at the bottom, the sump is at the bottom of the engine, and forms part of the crankshaft housing.

In that situation, lubricant (oil) can drain (passively) under gravity in a return flow to the underlying sump-from where it can be collected for (re-) circulation by an engine oil pump.

Again, in accepted i. c. engine parlance, the term, or expression, 'wet sump'signifies that the sump not only collects returned oil, but serves as a primary reservoir or store for engine oil.

Thus, in practice, a substantial (and generally majority) proportion of a total overall engine oil system capacity is stored in the'wet sump'-hence the qualifying designation'wet'.

Typically, a wet sump is integrated with the engine housing.

With an inverted engine, the crankcase is at the top of the engine and a sump located in the conventional position adjacent the crankshaft is not in a position to receive a gravity return flow of oil from all parts of the engine.

Thus a'conventional'inverted engine oil system would employ a so- called'dry sump', as now described.

In contrast to a wet sump, and again in accepted i. c. engine parlance, the term, or expression,'dry sump'reflects an (albeit temporary intermediate) collection role of the sump, in a gravity return flow of oil-but the sump fulfils no (longer term) substantial storage or reservoir role.

Rather a discrete oil'tank'-generally apart from the engine (and its engine-mounted dry sump) and connected thereto by umbilical plumbing pipe-work-is used to store (long term) a substantial (again generally the majority) proportion of the total overall oil system capacity.

That is, the separate oil tank, not the (engine mounted) sump, fulfills the role of primary, (long term or permanent) engine oil reservoir.

Hence the sump itself is appropriately qualified by the designation 'dry'-which is nevertheless a strictly relative term, since some oil is present in the sump, albeit a modest amount compared with a conventional wet sump.

The role of an engine oil pump, when provided, is to draw oil from the main oil reservoir and supply it to the necessary engine parts.

Additionally, an oil pump may be provided to transfer, or 'scavenge', oil from a'dry'sump and return it to an oil tank.

Notwithstanding the foregoing usage, engines are known whose oil systems exhibit characteristics of wet and dry sump systems-and these may be regarded as hybrid or combined systems.

The term'turbo-charger'is used herein to embrace any form of indirectly, for example exhaust flow turbine, driven flow promoter, with or without pressure gain, for engine combustion intake.

A turbo-charger represents a particular category, or variant of super-charger, a term which is commonly used to designate a mechanically-driven intake flow promoter, or compressor.

As such, the term turbo-charger can be regarded as an abbreviation, or equivalent of, turbo-supercharger.

There now follow descriptions of various existing engine configurations which can be regarded as background information.

The diversity of (multi-) cylinder configurations, for (aircraft) piston engines-typically with a single, common crankshaft toward the bottom of the engine-include, for example: * a single-file row (ie an'in-line'configuration) ; multiple, discrete,'angularly-splayed', or angularly offset,'rows' (albeit there may be only one cylinder in each'row')-such as a'V'or'W'configuration; * in rows opposed, either horizontally, vertically, or at some other angle (eg. a flat'configuration); individually, around a common crankshaft axis, generally equi-angularly spaced, in one or more planes (eg a 'radial'configuration).

There have been some engines with multiple crankshafts-for example, with cylinders arranged in an'H' (in effect, two flat' engines, sharing a single common crankcase), or with two pistons per cylinder, working in opposition, in various'opposed-piston' arrangements.

It is known to invert'an in-line, or'V', configuration-so that the cylinders are below the crankshaft, which is thus toward the top of the engine.

A prime advantage of such engine inversion, for aircraft propeller propulsion, is that the crankshaft sits high (er) on the engine- and so a propeller mounted directly upon it will be farther from the ground.

At critical flight phases of take-off and landing, it is important to maintain adequate clearance between propeller and ground.

The object is to reduce the chance of accidental damage, allowing for undercarriage travel and fuselage forward tipping moment about the undercarriage.

Other ways to improve ground clearance include: * lengthening the undercarriage, in order to raise the whole aircraft further from the ground; * reducing the diameter of the propeller; and * raising the engine installation in the aircraft -but all have their drawbacks.

It is thus well-established for smaller aircraft, that use 'directly-driven'propellers (ie mounted directly upon a crankshaft end), to use an inverted engine arrangement.

Engines that are not inverted-that is which have the crankshaft generally at the bottom of the crankcase, and the cylinders generally upright or vertical, with the cylinder heads uppermost (in the case of in-line engines)-commonly have a so-called'wet sump'lubrication system, reliant upon a gravity return of a (re-) circulatory lubricant (oil).

More specifically, a lower part of the crankcase is typically extended, to provide a reservoir (ie the sump) of lubricant (oil).

Thus, in practice, a sump body, or casing, is commonly secured directly to part of the engine body, housing, or casing.

Alternatively, engines may have a so-called'dry sump'lubrication system, reliant upon a pumped (re-) circulatory flow return of lubricant (oil) to a discrete reservoir.

Thus, in practice, lubricant (oil) is typically drained away, partly (passively) under gravity, to one or more internal engine collection point (s).

Collected (oil) is then (actively) pumped (scavenged), or returned by some other positive displacement or pressure-differential means, to a'separate' (oil) tank that serves as an (external) engine lubricant (oil) reservoir (ie outside an internal engine lubricant path).

One dry sump arrangement (eg. ROTAXTM) uses ambient crankcase pressure to return used oil to an oil tank.

Alternatively, the oil may drain naturally from the dry sump to a (separate) oil tank at a lower level.

Also, radial engines are known in which'used'oil, from each cylinder head, as well as the crankcase, is returned to a separate oil tank.

Hitherto, inverted aircraft engines have used a dry sump arrangement-that is with'used'oil being returned to a (discrete, dedicated) tank, disposed externally of the engine, by draining (passively) under gravity, and/or being (actively) drawn away by an oil (scavenge) pump.

According to one aspect of the invention, an inverted engine has a 'wet sump'lubrication system, with a combined sump casing and cylinder head, camshaft or valve gear, cover.

Elimination of a'separate'oil tank, and its associated feed supply and (re-) circulatory return pipe-work or plumbing, provides the advantages of an integral oil system, such as an on-board or integral sump.

The'wet'sump approach removes the inherent disadvantages of the 'dry'sump approach.

Thus, it is simpler-with far fewer parts, pipes, joints, etc., that may fail or leak, and the integration of oil system and engine creates a single,'stand-alone'package.

Installation issues are significant for the light aeroplane market, which is sensitive to first cost and ongoing running and maintenance costs and may also use installers with limited skills such as builders of kit aircraft.

By combining a'cam (shaft)-in-head', inverted engine configuration and wet sump lubrication, according to the invention, lubricant (oil) in the sump can provide'constant'lubrication, by indirect splash and/or direct immersion, to the camshaft lobes.

This is particularly important at engine start-up.

During normal operation, there will be oil mist/splash lubrication present-and so force-feed lubrication of the camshaft and valve train may not be necessary, thus simplifying the design.

Another potential problem of non-inverted engines-where a camshaft is generally mounted high in the engine-is that the cam lobes and followers can become dry, during periods of engine non- use.

Critical wear surfaces can thus be scored, scuffed and otherwise damaged, due to lack of lubricant, at engine start-up.

In a wet sump, inverted engine, according to the invention, the cam can remain'flooded'with oil-even during long periods of non-use -so ameliorating, or even eliminating altogether, the possibility of dry cam lobes.

Aside from cam-in-head configurations, a similar'constant lubrication'benefit could be provided for rocker arms and other valve gear components commonly used with push-rod type valve actuation.

Advantageously, with a cam-in-head configuration, a rotary oil pump and fittings could be mounted close to the oil sump, and integrated with, or coupled to, a camshaft drive.

Indeed, the pump could be mounted upon the camshaft itself.

A wet sump lubrication system in an inverted engine, according to the invention, can be applied to'in-line'or'V'configurations.

An engine may be of otherwise conventional design.

This aspect of the invention, along with the various other aspects, described elsewhere, taken both individually and collectively, are generally compatible with: two, or four-stroke combustion cycles; * high, or low-mounted camshafts; * multiple cylinders; * compression-ignition ('diesel') combustion; * spark-ignition combustion; * liquid fuel (eg gasoline, kerosene, fuel oil or liquefied petroleum gas); or * gaseous fuel.

The engine may be equipped with a turbo-super-charger or multiple turbo-super-chargers which may be connected in series or parallel.

A downstream turbine may be fitted, and geared to provide extra power to the crankshaft (usually known as'turbo-compounding').

A mechanically-driven super-charger, or multiple super-chargers, may be used in the pressure charging system.

There now follows a description of some particular embodiments of this particular aspect of the invention, by way of example only, with reference to the accompanying diagrammatic and schematic drawing (s), in which: Figure 1 shows a schematic (front or rear) end view of an engine and turbo-charger; Figure 2 shows an end elevation of an inverted, in-line, i. c. piston engine, with a wet sump lubrication system; and Figure 3 shows a side elevation of the engine of Figure 2.

The particular engine depicted in this case is a two-stroke, compression-ignition (or diesel) combustion cycle with integral cooling heat exchanger or radiator The primary outward distinguishing feature of this aspect of the invention is a'integrated'sump casing 30, at the bottom of the engine 10.

The sump 30 serves as a permanent,'on-board', engine lubricant (oil) reservoir.

More specifically, the casing or housing of the sump 30 is secured to a cylinder head 16, at the bottom of the engine, configured and disposed to enshroud the (overhead') cam-shaft or other valve drive gear (not shown).

A normal operational oil level in the sump 30 is indicated by broken line 33, and although subject to fluctuation with manoeuvring accelerative loads, is generally sufficient to ensure permanent lubrication of the camshaft or other valve gear.

A positive pressure, or displacement, pump lubrication system collects oil from the sump at one or more internal engine collection points, and delivers it (actively) to certain key internal engine oil-ways, or galleries, in an internal lubricant oil pathway.

This oil pathway feeds more remote engine componentry-from which oil progressively returns, (passively) under gravity to the sump; the (re-) circulatory cycle being arranged to maintain a consistent level.

Other aspects of the engine are shown in Figures 1,2 and 3.

For convenience, the same reference numerals are used for corresponding or equivalent components throughout the drawings.

Turning now to another aspect of the invention: Many positive displacement (in particular, piston-in-cylinder) i. c. engines use turbo-super-chargers (henceforward referred to as turbo-chargers), for various benefits. An over-riding benefit is an increase in engine airflow.

This allows an engine to produce a much greater power, than if it were'naturally' (ie un-forced) aspirated.

Adoption of single, or multiple, turbo-chargers is common on many engine types, for diverse uses, including automotive, agricultural, commercial, industrial, marine and aviation (viz. aircraft).

Whilst turbo- (super-) charging increases engine system complexity- the increase in engine power output, and the other benefits, generally outweigh this otherwise significant disadvantage.

In addition to connections to the exhaust and air intake systems, nearly all turbochargers also require to be supplied with a lubricating fluid, in particular oil.

This is usually taken from the engine's own oil system, via small (bore) pipe-work-as the quantity required is not great. The oil return to the engine sump is more problematic.

Thus, there is almost always some flow of air and exhaust gas past the turbo-charger shaft seals, so a drain tube has to cope with this flow of gas, as well as the, by now aerated, returning oil.

If the drain tube is not of sufficient diameter, the turbo-charger shaft and seals may become bathed in oil.

The pressure in the turbo-charger housing will rise, and there can be considerable problems with oil leakage, oil carbonisation etc.

For the majority of i. c. (piston) engines, it is relatively easy to provide oil gravity drainage.

This is because most engines are orientated'upright'-that is with crankshaft lowermost, and cylinder head and exhaust ports uppermost.

The turbo-charger is attached to an exhaust manifold, itself attached to a cylinder head. The turbo-charger is thus usually mounted relatively high on the engine.

A simple (although relatively large diameter) drain tube can carry 'used'oil back to an integral engine sump at the bottom of the engine.

Sometimes difficulties arise in fitting the drain tube, because of its large size, but these are rarely insurmountable.

For piston engines with nearly horizontal cylinders, such as are often used on buses and coaches, (where they are typically mounted under the floor), or on aircraft (where flat'4 and 6 cylinder engines are common), turbo-charger oil return poses a much greater problem.

It may not be possible for a simple drain tube to have sufficient angle of inclination (or'fall'), to prevent returning oil partially obstructing the flow of frothed oil and blow-by gas.

This may cause raised pressure in the turbo-charger housing, flooding of the housing, and leakage, carbonisation, etc., problems.

The level of oil in the engine's sump may be only slightly lower than the oil drain port on the turbo-charger housing-which may be some way from the sump itself inhibiting (passive) gravity return.

In considering relative heights or levels, for simplicity, engine orientation is referred to as if the aircraft were on its ground landing gear.

A'gravity'drain will not always work under gravity alone, but will also function under accelerated manoeuvring loads-but nonetheless provides a simple oil return, without pumping, or other special provision.

Most aircraft are operated, for most of the time, in an attitude where the acceleration due to gravity and any acceleration due to manoeuvring lie in approximately the same direction-although the accelerations due to manoeuvring may add to or subtract from the gravitational acceleration.

An aircraft engine that is to be fitted to an aeroplane that is to fly inverted for a considerable period of time must have special systems and features to cope with this requirement.

That said, the present invention is not specifically concerned with such special adaptation for prolonged aerobatic flight modes.

The horizontal (flat') configuration, often with the exhaust ports underneath the engine, commonly adopted for piston aircraft engines poses particular problems in turbo-charger location and mounting.

This makes it difficult to mount an exhaust-driven turbo-charger in a relatively high position, and still provide turbo-charger'used' oil gravity drainage.

For such an aircraft engine installation, the turbo-charger is often mounted, either below, or behind the engine.

A supplementary oil pump is then used to'scavenge', or suck, the oil, from the turbocharger outlet, and return it back to the engine sump, or oil tank.

Extra complexity brings further failure modes and greater risk- which in an aircraft engine is especially undesirable.

A long exhaust manifold also needs special measures (expansion joints, vibration isolation etc), to ensure durability.

Moreover, its large internal volume adversely affects turbocharger performance.

Supplementary Statement of Invention According to another aspect of the invention, a turbo-charger installation, for an'inverted'i. c. engine configuration, with a wet sump, according to one aspect of the invention, is mounted fat a level somewhat} above an operational lubricant (oil) level in the wet sump.

In practice, the turbo-charger location may be to one side and/or at one (front or rear) end of the engine.

A variety of turbo-charger locations may be employed-provided generally above the wet sump operational oil level, in order to allow a gravity oil return to the sump, after turbo-charger lubrication.

The inverted'engine may be of in-line'or'V'etc configuration, where the crankshaft is toward the top of the engine and the cylinder head (s) and valve gear are below it, near the bottom.

A turbo-charger lubricant (oil) feed is taken from a positive displacement and/or pressure lubricant (oil) pump, in an overall engine lubricant (re-) circulatory lubrication system-with a (passive) gravity drain return to the wet sump, which is itself conveniently integrated with a lower engine casing or housing for a cam-shaft or valve gear, according to one aspect of the invention.

The turbo-charger can conveniently be mounted directly upon an exhaust manifold.

The manifold itself can be of compact construction.

Individual manifold branches are made as short as possible-and are desirably shorter than twice the cylinder spacing.

The combination of inverted'engine, wet sump and close-mounted turbocharger layout, according to an aspect of the invention, affords a considerable safety improvement for a turbo-super-charged aircraft engine-primarily because of the reduction in overall complexity, whilst preserving their respective individual benefits.

Indeed, overall, the inverted'engine layout makes the mounting of a turbo-charger, with gravity drain, to an under-slung wet sump, little more difficult than with a conventional (non-inverted) layout-as typically used for automotive (truck and car) engines.

Other benefits include: * reduced component and installation cost and complexity; * integration of components into an engine package, that can be assembled and tested as a stand-alone unit, ready for installation in an airframe; * ready and rapid engine removal, for servicing etc., with a minimum of disturbance to the rest of the aeroplane; * improved engine performance attendant a small volume exhaust manifold.

In some cases, the general aircraft requirement of light weight may best be satisfied by using a very low weight exhaust manifold, incapable of supporting the mass of the turbo-charger.

In this situation, rather than risk structural failure of the manifold, or increase engine weight by strengthening the manifold, it may be advantageous to support the turbocharger upon a separate bracket.

Slip-joints, flexible pipes, or some other means of providing flexibility, could then be used, in order to ensure that the bracket only carries the structural loads and does not suffer from additional loading due to thermal growth.

In this way, thin-wall tubing may be used for a light-weight manifold, with reduced risk of cracking.

An inverted i. c. piston engine 10, comprises a crankcase 11, surrounding a crankshaft (not shown), cylinder block 14, cylinder head 16, etc.

An exhaust manifold 22, is mounted upon the cylinder head 16. A turbo-charger 24, is mounted upon the exhaust manifold 22.

The turbo-charger 24 is supplied with lubricant (oil), through a feed line 26, from the delivery or output side of a dedicated (conveniently directly engine-driven) lubricant pump (not shown), in a (re-) circulatory lubricant (oil) path, including an integral, underslung, permanent oil supply reservoir, or (wet) sump 30.

The turbo-charger 24 is positioned, in accordance with the second aspect of the invention, at a level above the operational lubricant (oil) level, indicated by broken line 33, in the sump 30, to allow such (passive) gravity lubricant (oil) return.

The sump 30 casing serves as a combined cylinder-head (camshaft or rocker gear) cover and in that sense is effectively integrated with part of the engine housing or casing.

In the (re-) circulatory return flow, lubricant (oil) drains, under gravity (and/or manoeuvring accelerations), through a drain line 28 -of somewhat larger bore diameter than the feed line 26-to the sump 30.

Also shown is an'after-cooler' (sometimes called an'inter- cooler') 42, connected between a turbo-charger flow enhancement or compressor stage 24 and an engine inlet manifold 40.

The (dis) position, height or level, and orientation of the after- cooler 42 can be varied somewhat in relation to the engine 10.

Similarly, additional turbo-chargers, inter-coolers, etc., may be included, as required.

COMPONENT LIST 10 i. c. engine 11 crankcase 12 forward crankcase extension 13 crankshaft extension 14 cylinder block 16 cylinder head 17 propeller mount 22 exhaust manifold 24 turbo-charger 26 lubricant (oil) feed line 28 lubricant (oil) drain line 29 fastener 30 wet sump 33 operational sump lubricant (oil) level 34 radiator (to engine) mounting 35 radiator (to engine) mounting 40 inlet manifold 42 after (inter)-cooler