Patent Description:
Double acting internal combustion engines are taught in <CIT>. This document describes a linear reciprocating piston engine having upper and lower combustion chambers either side of the piston. The lower chamber is sealed by a separation plate that is configured to accommodate the throw of the connecting rod as it moves about the crankshaft. Although such engines offer good power to weight, their reliable realisation is restricted by two major technical obstacles: The first of these is the difficulty in providing an effective seal of the lower combustion chamber; while the second is the problem of providing adequate lubrication of the piston.

<CIT> discloses a four-stroke internal combustion engine having at least one cylinder having a double acting piston dividing the cylinder into two combustion chambers, and being reciprocal within the cylinder to perform a power stroke, producing work on a crankshaft whilst moving towards or away from the crankshaft. The piston has a pivotal connection with a connecting rod which is in turn connected directly to the crankshaft. A separation plate separates the engine pump from the adjacent combustion chamber and accommodates lateral movement of the connecting rod passing sealingly therethrough.

<CIT> discloses a two-stroke cycle motor having a cylinder, a piston slidable in the cylinder, a crank case, a crank-shaft rotatable in the crank case and a connecting rod operatively connected between the crank-shaft and the piston. The connecting rod allows for reciprocating the piston upon rotation of the crank-shaft. The motor further comprises a sealing means for sealing the cylinder from the crank case, the sealing means comprising walls defining a guideway extending normal to the axis of said cylinder and disposed between the cylinder and the crank case, a slide member reciprocable in the guideway, a ball carried by and mounted for universal movement on the slide member, whereby the ball has a bore through which the connecting rod extends and is slidable, and compressible sealing means disposed between the relatively movable surface of the guideway, slide member, ball and connecting rod.

<CIT> discloses an internal combustion engine which includes at least one piston that compresses air in the lower cylinder chamber as it transitions from top dead centre to bottom dead centre during the power stroke. The air in the lower cylinder chamber is compressed between the downward-moving cylinder and a structure that substantially seals the lower chamber from the crankcase chamber so that compression takes place in a chamber smaller than the crankcase chamber.

The present invention seeks to provide an improved double acting internal combustion engine by improving the sealing of a connecting rod passing through the separation plate of a double acting engine.

According to the invention, there is provided a linear reciprocating piston engine comprising:.

The or each inner seal may be located in a respective groove in the bore of the joint.

The curved outer surface of the joint may be a spherical outer surface.

The lower end of the cylinder may be provided with a separation plate seal between the lower combustion chamber and the separation plate.

The engine may further comprise a bottom end component housing the crankshaft, the bottom end component being arranged to hold the separation plate against the lower end of the cylinder.

A seal may be disposed between the bottom end component and the separation plate.

With reference to <FIG> there is shown an internal combustion engine <NUM> according to the present invention and which is a four stroke engine operable on all conventional fuels e. g petrol, alcohol, fuel oil, hyrocarbon gases, hydrogen etc..

The engine <NUM> comprises a cylinder block <NUM> mounted on a sump <NUM>. For the sake of convenience only a single cylinder <NUM> is shown but the block <NUM> could house any number of cylinders as is desired for a particular engine configuration.

The cylinder <NUM> is divided into upper and lower combustion chambers <NUM> & <NUM> by a reciprocable piston <NUM>. Piston rings <NUM> ensure a gas tight seal between the piston <NUM> and the cylinder wall <NUM>.

The piston <NUM> is a double acting piston and is directly connected to a connecting rod <NUM> which sealingly passes through a separation plate <NUM> which separates the lower chamber <NUM> from the sump <NUM>.

The term"double acting"means that a power stroke for the engine can be performed in either direction of movement of the piston <NUM>.

The piston <NUM> is connected via a pin <NUM> to the connecting rod <NUM> which in turn is connected directly to the crank shaft <NUM> in the conventional manner. The separation plate <NUM> is configured to accommodate lateral movement of the connecting rod <NUM> as it moves around the crank shaft's axis. The term "lateral movement" means movement perpendicular to a longitudinal axis of the cylinder <NUM>, A-A. The term "vertical movement" means movement in a direction parallel to the longitudinal axis A-A of the cylinder <NUM>.

In the example of the engine <NUM> illustrated by <FIG>, the separation plate <NUM> comprises an aperture <NUM> to accommodate lateral movement of the rod <NUM>. The aperture is closed by a slide portion <NUM> with a sealed opening provided around the connecting rod. The slide portion <NUM> extends over the aperture <NUM> and slides across the separation plate <NUM> with the lateral motion of the crankshaft <NUM>. The rod <NUM> will also move vertically in the slide portion <NUM> and is sealed therein by seals <NUM> to accommodate such movement.

A different sealing arrangement is shown in <FIG> in which a pair of spring loaded seals <NUM>, <NUM> are located in the aperture <NUM> in separation plate <NUM>. The connecting rod <NUM> may bear against the seals, or may contact bearing guides <NUM> mounted against the seals <NUM> & <NUM> respectively. The seals <NUM>, <NUM> reciprocate in the aperture <NUM> to seal around the moving connecting rod.

In another example of the engine illustrated by <FIG>, the separation plate <NUM> is configured to move laterally. The separation plate <NUM> is located in a guide <NUM> disposed between the cylinder block <NUM> and the sump <NUM>, or machined into one or the other. The length of the guide <NUM> transverse to the axis A-A of the cylinder <NUM> is greater than corresponding dimension of the separation plate <NUM> so that it is free to move laterally within the guide <NUM>.

As the connecting rod <NUM> moves around the crank shaft's axis, the angle of inclination of the connecting rod <NUM> relative to the separation plate <NUM> changes. This changing angle is accommodated by a sealing joint <NUM>. The sealing joint <NUM> is provided either directly in the separation plate <NUM> or in a slide portion <NUM>, like that shown in <FIG>.

Alternatively, the separation plate <NUM> may be downwardly domed - like the separation plate of <FIG> - so that the connecting rod <NUM> remains perpendicular to a tangent of the domed separation plate throughout its movement of the crankshaft <NUM>, thus negating the need for a joint. By "downwardly domed", it is meant that the separation plate <NUM> projects away from the cylinder <NUM> and into the sump <NUM>.

The joint <NUM> is located in an opening <NUM> of the separation plate or slide portion and comprises a bore <NUM> through which the connecting rod <NUM> extends and a curved outer surface to allow rotation of the joint <NUM> within the opening <NUM>. Preferably the joint <NUM> comprises a spherical outer surface to accommodate slight rotation in other axes that might result from manufacturing tolerances. The joint <NUM> is retained by a curved inner edge of the separation plate <NUM> opening <NUM>, which is shaped to prevent the joint <NUM> moving in a vertical direction, as illustrated in <FIG>.

Referring still to <FIG>, two seals are provided: An outer seal <NUM>, disposed between the outer surface of the joint <NUM> and the separation plate, or slide portion; and an inner seal <NUM>, disposed between the connecting rod <NUM> and the bore <NUM>. Both seals <NUM>, <NUM> have to accommodate movement of underlying surfaces. The inner seal <NUM> must accommodate the connecting rod <NUM> as it moves through the bore <NUM>; while the outer seal <NUM> must accommodate rotation of the joint <NUM> and the associated relative movement of the outer surface and the separation plate <NUM> or sliding portion <NUM>. Lubrication of the joint <NUM> may be effected by natural dispersion of oil during rotation of the crankshaft <NUM> as oil is picked up from the sump <NUM> and thrown against the separation plate <NUM>, or, alternatively, oil may be sprayed from a nozzle (not shown) provided in the sump <NUM>.

The inner and outer seals <NUM>, <NUM> are split ring compression seals. In the illustrated example, the inner seal <NUM> comprises two split ring compression seals <NUM> spaced apart along the length of the bore <NUM>, each being located in a corresponding groove <NUM> in the bore wall. The split nature of the seals allows them to decrease in diameter under compression to provide a seal about their inner edge against the connecting rod <NUM>. During operation of the engine <NUM>, when combustion occurs in the lower combustion chamber <NUM>, combustion gasses expand into the bore <NUM> and grooves <NUM>, compressing each seal <NUM> against the connecting rod <NUM> and simultaneously pushing each seal <NUM> onto a seat of the corresponding groove <NUM>. This cuts off the bore <NUM> from fluid communication to prevent combustion gases from escaping into the sump <NUM>. The provision of two split ring compression seals <NUM> ensures that the split parts of each seal <NUM> can be offset to further prevent the escape of gasses during combustion. However, it shall be appreciated that it is equally feasible to use gapless compression seals, in which case only a single compression seal <NUM> is required. Gapless compression seals may comprise a sleeve which extends over the split portion of the seal or be arranged so as to have overlapping free ends.

The outer seal <NUM> also comprises split ring compression seals <NUM>, of which there are preferably two. Each seal <NUM> is located in a groove <NUM> provided about the inner edge of the opening <NUM>. During operation of the engine <NUM>, when combustion occurs in the lower combustion chamber <NUM>, combustion gasses expand into the opening <NUM> and grooves <NUM>, compressing each seal <NUM> against the outer surface of the joint <NUM> and simultaneously pushing each seal <NUM> onto a seat of the corresponding groove <NUM>. This cuts off the opening <NUM> from fluid communication to prevent combustion gases from escaping into the sump <NUM>. As with the inner seal <NUM>, it is possible to use a gapless compression seal, in which case only a single split ring compression seal <NUM> is required.

In an alternative example, the outer and inner compression seals are replaced with outer and inner labyrinth seals. An example labyrinth seal is shown in <FIG>, located in a groove <NUM> of the bore <NUM>. Each labyrinth seal comprises a castellated inner edge, the castellations being arranged in the axial direction of the seal to make a tortuous path for escaping combustion gasses. In the illustrated example, a castellated inner edge of an inner seal <NUM> is shown in abutting relation with the connecting rod <NUM>. Where a labyrinth seal is used for the outer seal <NUM>, the castellated surface will be arranged in abutting relation with the outer surface of the joint <NUM>.

In another alternative example, the outer and inner compression seals are replaced with outer and inner brush seals (not shown). Each brush seal comprises thousands of fine wires that extend from a supporting ring. The densely packed arrangement of these wires forms a barrier to escaping combustion gases whilst accommodating excursions, thermal movements of misalignments of the underlying surfaces that would otherwise reduce the efficiency of a labyrinth seal.

Compression seals, brush seals or labyrinth seals are ideally suited for dealing with the combustion forces experienced during operation of the engine. It is also possible to use split ring expansion seals where the seals are located in grooves of the other of the respective components: For example, the outer seal <NUM> is located in a groove in the outer surface of the joint and expands under the influence of combustion gases to seal against the inner edge of the opening <NUM>.

In another example of the engine, shown in <FIG>, the separation plate is upwardly curved - for example upwardly domed - by which it is meant that the separation plate <NUM> partially projects into the cylinder <NUM>. The upwardly domed shape of the plate redistributes the force to the edges of the plate and lowers the bending moment, thereby increasing longevity by decreasing the stress cycle intensity.

The separation plates <NUM> of the examples of <FIG> are supported in their guide <NUM> by a hydrostatic oil bed. Drilled oil galleries <NUM> that communicate with the guide <NUM> allow oil to well up into the space between the separation plate <NUM> and the guide walls, as shown in <FIG>. Oil pressure is maintained by an oil pump (not shown) in the conventional manner. The hydrostatic oil bed provides lubrication and protects the separation plate <NUM> and guide walls from premature wear by separating the two components by a film of pressurised oil.

A seal <NUM> is provided between the separation plate and the guide <NUM> in which it is located to prevent combustion gasses escaping around the edges of the separation plate <NUM> and into the sump <NUM>. The seal <NUM> provides the further advantage of restricting oil transfer from the guide <NUM> into the lower combustion chamber <NUM>. As illustrated, a channel <NUM> in a wall of the guide <NUM> is provided to retain the seal <NUM>. The channel <NUM> is located inward of edges of the separation plate <NUM> so that the seal <NUM> remains in contact with the separation plate <NUM> as it moves laterally with the throw of crankshaft <NUM>. The illustrated seal <NUM> is a labyrinth seal having a castellated surface in contact with the separation plate <NUM> to create a tortuous path for combustion gasses; although it shall be appreciated that any conventional sealing method may be used, including a brush seal. Preferably the seal is located on an upper surface of the separation plate <NUM>, by which it is meant that the surface facing the lower combustion chamber <NUM>. A spring <NUM> may be provided to maintain the seal <NUM> in contact with the separation plate <NUM>.

Alternatively, in another example illustrated in <FIG>, the seal <NUM> has an inclined inner edge which directs combustion gas or compressed air into the channel <NUM> to force the seal <NUM> down and onto the separation plate <NUM>, sealing the lower combustion chamber <NUM> during compression and combustion strokes. The seal <NUM> may also be configured to lift off of the separation plate <NUM> during exhaust and intake strokes to reduce friction. For example, an extension spring <NUM>, as illustrated, or a magnet (not shown) may be provided to lift the seal <NUM> off of the separation plate <NUM>, or, alternatively, the seal <NUM> may comprise an inclined outer edge (not shown) so that the seal <NUM> is lifted by the hydrodynamic effect of the film of oil. It is important the inclined outer edge is configured so that the hydrodynamic effect is easily overcome by the force of combustion gas or compressed air during compression and combustions strokes so that the combustion chamber <NUM> remains during this time. The intake, compression, combustion and exhaust strokes of the lower combustion chamber <NUM> are explained in more detail below, with reference to <FIG>.

The illustrated seal of <FIG> also comprises a lip <NUM> which extends about its outer edge and provides a seat for an additional labyrinth seal 123a, although this is merely optional.

Yet another construction of engine <NUM> according to the present invention, is shown in <FIG>. This engine is similar to the engine <NUM> excepting that the lower compression chamber <NUM> includes a portion of the sump <NUM> in which valves <NUM> & <NUM> and spark plug <NUM> are located in the wall thereof. Those components present in <FIG> will be given the same reference numbers. Each lower chamber <NUM> extends only into a portion <NUM> of the sump with the chamber <NUM> sealed by bearings/seals <NUM> around the respective portion of the crankshaft <NUM>. In a preferred condition, the total extended volume of the chamber <NUM> including the respective portion <NUM> of the sump equates with the effective working volume of chamber <NUM>.

In conventional combustion engines, the cylinder wall and piston are lubricated by the natural dispersion of oil during rotation of the crankshaft, as oil is picked up from the sump and thrown into the cylinder. In more recent engines, oil is sprayed into the cylinder from a nozzle adjacent the connecting rod. In the presently described examples of the engine <NUM>, the presence of a lower combustion chamber prevents such forms of lubrication.

Therefore, lubrication for the presently described engines <NUM> may include the use of self-lubricating fuels which may comprise added lubricants. Or, alternatively lubrication may be achieved by high pressure lubrication systems pumping lubricant along internal bores in the crankshaft <NUM> and connecting rods <NUM> and associated pins and bearings.

In one example, the lubrication system comprises an oil pump (not shown) which draws oil from the sump <NUM> and feeds it through a series of oil galleries that channel oil along the crankshaft <NUM> and up through an oil bore in the connecting rod <NUM>. The oil bore opens onto the pin <NUM>. Further oil galleries provided in the pin <NUM> transfer oil to piston galleries <NUM> (see <FIG>) from where the oil may pass out of openings <NUM> in the piston cylindrical wall to provide a film of oil on the cylinder wall.

Careful management of this film of lubricant is necessary to prevent excessive oil combustion and to ensure sufficient lubrication of the piston rings <NUM>. The proposed solution may use any combination of the oil distribution control techniques set out below:
Each of the openings <NUM> on the cylindrical wall of the piston may be provided with a valve <NUM> configured to regulate the oil film thickness on the cylinder wall. For example, the valve <NUM> may be configured so that when the hydostatic oil pressure of the film of oil between the cylindrical wall of the piston <NUM> and the cylinder <NUM> drops below the oil pressure in the piston galleries <NUM>, the valve <NUM> opens and oil passes out, replenishing the oil film. In the illustrated example each valve <NUM> comprises a ball bearing located in a countersunk mouth of the opening <NUM>.

Alternatively, valves are omitted and the oil film thickness is instead regulated simply by careful design of the diameter of each opening <NUM>.

Each piston comprises an upper and lower piston ring <NUM> with the openings of the oil galleries <NUM> located between the piston rings <NUM>. Further oil control rings <NUM> are provided to retain the oil film, as much as possible, between the piston rings <NUM>. The oil control rings <NUM> are provided outwardly of the piston rings <NUM>, that is to say nearer upper and lower surfaces of the piston <NUM>. The oil control rings <NUM> scrape excess oil from the cylinder walls to prevent excessive oil remaining in the combustion chamber during combustion.

As a further measure to control the oil film the cylindrical wall of the piston is further provided with oil scavenging ports (not shown), through which excess oil can flow back into the galleries. The oil scavenging ports comprise one way valves, such as calibrated spring loaded stem valves, to ensure oil back into the oil galleries only when the hydrostatic oil pressure exceeds a predetermined value.

The engine may use sleeved cylinders having oil porous walls and oil drainage may be provided for the removal of excess oil.

The use of oil porous metals which are pre-impregnated with oil may be possible for short life engine for example but without limitation, racing engines which are stripped between races.

The oil may also acts as a coolant for the engine.

Using the Otto cycle as an example, the operational cycle of the two chambers <NUM> and <NUM> will now be explained. In such an example, each chamber <NUM>, <NUM> is provided with respective inlet valves <NUM>, <NUM>, exhaust valves <NUM>, <NUM> and spark plugs <NUM>, <NUM>.

The engine <NUM> in this example comprises a single piston <NUM> to produce a power stroke in both directions of movement of the piston (i. e towards and away from the crankshaft), which will hereinafter be called a double stroke cycle.

One operational cycle of the two chamber <NUM> & <NUM> will be explained with reference to <FIG>:.

The cycle then begins again at step <NUM>.

In essence at any stage in the cycle, the stroke in the lower chamber <NUM> is repeated in the upper chamber <NUM> during the next consecutive stroke.

An alternative operational cycle of the two chambers will be explained with reference to <FIG>:.

The cycle then begins again at step <NUM>. In essence at any stage in the cycle the stroke in the lower chamber <NUM> is one step behind the stroke in the upper chamber.

Claim 1:
A linear reciprocating piston engine (<NUM>) comprising:
a cylinder (<NUM>);
a piston(<NUM>) located within the cylinder, the piston separating upper and lower combustion chambers (<NUM>, <NUM>) of the cylinder;
a separation plate (<NUM>) disposed across a lower end of the cylinder to seal the lower combustion chamber; and
a joint (<NUM>) disposed in the separation plate, the joint comprising a bore (<NUM>) through which a connecting rod (<NUM>) extends to connect the piston to a crankshaft (<NUM>),
wherein movement of the piston along a longitudinal axis (A-A) of the cylinder causes the connecting rod to rotate the crankshaft, said rotation of the crankshaft causing both transverse and angular movement of the connecting rod relative to the longitudinal axis of the cylinder, the angular movement of the connecting rod causing a corresponding angular movement of the joint; wherein the separation plate is configured to slide across the lower end of the cylinder to accommodate said transverse movement of the connecting rod;
characterised in that the joint comprises a curved outer surface configured to ensure contact with an outer seal (<NUM>) disposed between the separation plate and the joint during said angular movement of the joint and the connecting rod;
the joint further comprising at least two inner seals (<NUM>) disposed between the bore and the connecting rod, the at least two inner seals being spaced along the bore of the joint;
wherein the outer and inner seals are selected from any of:
a split ring compression seal;
a split ring expansion seal;
a gapless expansion seal;
a gapless compression seal;
a labyrinth seal having a castellated inner edge; and
a brush seal.