Patent Description:
In certain rotary engines, liquid cooling is provided in the side or end casings, and when multiple rotors are present, in the intermediate casing(s). In these engine casings, fluid cavities are provided to cool the rotor housings. However, the manufacturing of such engine casings can be complex and limited to specific manufacturing methods, such as casting. Moreover, since the casings have surfaces in sliding contact with the rotating rotors, wear and damage is inevitable. Yet, because of the cooling passages these can be expensive components to replace.

<CIT> discloses a prior art rotary engine casing having the features of the preamble of claim <NUM>. <CIT>, <CIT>, <CIT> and <CIT> may also be useful for understanding the invention.

In one aspect of the present invention, there is provided a rotary engine casing in accordance with claim <NUM>.

In a further aspect of the present invention, there is provided a method of manufacturing a rotary engine casing in accordance with claim <NUM>.

Referring to <FIG>, a rotary engine <NUM> according to a particular embodiment is shown. The rotary engine is a Wankel engine and comprises a casing <NUM> having at least one internal cavity <NUM> (only one being visible in <FIG>), each internal cavity <NUM> being defined by two axially spaced apart end walls <NUM> interconnected by a peripheral wall <NUM>. Each internal cavity <NUM> has a profile defining two lobes, which is preferably an epitrochoid. A rotor <NUM> is received within each internal cavity <NUM>. The rotor defines three circumferentially-spaced apex portions <NUM>, and a generally triangular profile with outwardly arched sides. The apex portions <NUM> are in sealing engagement with the inner surface of the peripheral wall <NUM> of the casing <NUM> to form three working chambers <NUM> between the rotor <NUM> and the casing <NUM>.

The rotor <NUM> is engaged to an eccentric portion <NUM> of a shaft <NUM> to perform orbital revolutions within the internal cavity <NUM>. The shaft <NUM> performs three rotations for each orbital revolution of the rotor <NUM>. The geometrical axis <NUM> of the rotor <NUM> is offset from and parallel to the axis <NUM> of the casing <NUM>. During each orbital revolution, each chamber <NUM> varies in volume and moves around the internal cavity <NUM> to undergo the four phases of intake, compression, expansion and exhaust.

An intake port <NUM> is provided through the peripheral wall <NUM> for successively admitting compressed air into each working chamber <NUM>. An exhaust port <NUM> is also provided through the peripheral wall <NUM> for successively discharging the exhaust gases from each working chamber <NUM>. Passages <NUM> for a glow plug, spark plug or other ignition element, as well the fuel injectors are also provided through the peripheral wall <NUM>. Alternately, the intake port <NUM>, the exhaust port <NUM> and/or the passages <NUM> may be provided through one of the end walls <NUM> of the casing <NUM>; and/or, the ignition element and a pilot fuel injector may communicate with a pilot subchamber (not shown) defined in the rotor casing <NUM> and communicating with the internal cavity <NUM> for providing a pilot injection. The pilot subchamber may be for example defined in an insert (not shown) received in the peripheral wall <NUM>.

In a particular embodiment, the fuel injectors are common rail fuel injectors, and communicate with a source of heavy fuel (e.g. diesel, kerosene (jet fuel), equivalent biofuel), and deliver the heavy fuel into the engine(s) such that the combustion chamber is stratified with a rich fuel-air mixture near the ignition source and a leaner mixture elsewhere.

For efficient operation the working chambers <NUM> are sealed, for example by spring-loaded apex seals <NUM> extending from the rotor <NUM> to engage the peripheral wall <NUM>, and spring-loaded face or gas seals <NUM> and end or corner seals <NUM> extending from the rotor <NUM> to engage the end walls <NUM>. The rotor <NUM> also includes at least one spring-loaded oil seal ring <NUM> biased against the end wall <NUM> around the bearing for the rotor <NUM> on the shaft eccentric portion <NUM>. Alternately, the oil seal ring(s) may be provided in the end walls <NUM> to engage the rotor <NUM>.

In a particular embodiment which may be particularly but not exclusively suitable for low altitude, each Wankel engine has a volumetric expansion ratio of from <NUM> to <NUM>, and operates following the Miller cycle, with a volumetric compression ratio lower than the volumetric expansion ratio, for example by having the intake port located closer to the top dead center (TDC) than an engine where the volumetric compression and expansion ratios are equal or similar. Alternately, each Wankel engine may operate with similar or equal volumetric compression and expansion ratios.

It is understood that other configurations are possible for the engine <NUM>. The configuration of the engine <NUM>, e.g. placement of ports, number and placement of seals, number of fuel injectors, etc., may vary from that of the embodiment shown.

Referring to <FIG>, in a particular embodiment the rotary engine casing <NUM> defines two axially spaced internal cavities each receiving one of two rotors engaged to a common shaft. The engine casing <NUM> includes multiple assembled casing sections which cooperate to define the internal cavities and contain the rotors and shaft, and include bearing-support features, and cooling and lubrication passages, as detailed further below.

In the particular embodiment shown in <FIG>, the engine casing <NUM> includes two end-casing sections <NUM>, located at opposite ends of the engine casing <NUM>, and each defining an end wall <NUM> of a respective one of the internal cavities <NUM>, and a central-casing section <NUM> mounted between the two end-casing sections <NUM>. The central-casing section <NUM> includes two rotor housings <NUM> each defining the peripheral wall <NUM> of a respective internal cavity <NUM>, and an intermediate section <NUM> defining the end wall <NUM> extending between both internal cavities <NUM> to separates and seal the internal cavities <NUM>. Each end-casing section <NUM> is split to allow separation of the end-casing section <NUM> into two sub-parts <NUM>, <NUM> and the intermediate section <NUM> is split into three sub-parts <NUM>, <NUM>. Advantageously, the sub-parts can be machined, dowelled and/or bolted together and kept as a semi-permanent sub-assembly to ease in the process of engine assembly. Although the casing <NUM> is described herein with the two end-casing sections <NUM> and the intermediate section <NUM> (i.e. all end walls <NUM>) having a split configuration, it is understood that in an alternate embodiment, only one or two of the end-casing sections <NUM> and intermediate section <NUM> may have a split configuration.

The central-casing section <NUM> shown in <FIG> has two rotor housings <NUM> separated by one intermediate section <NUM>, to receive two rotors. In an alternate embodiment, the engine <NUM> can have any other adequate number of rotors and accordingly the central-casing section <NUM> can have a corresponding number of rotor housings <NUM>. If only one rotor housing <NUM> is provided, the intermediate section <NUM> is omitted and, if multiple rotor housings <NUM> are provided, each pair of rotor housings <NUM> is separated by an intermediate section <NUM>.

Referring to <FIG>, each end-casing section <NUM> includes an end-casing member <NUM> having a mating surface <NUM>. The end-casing member <NUM> is an end portion delimiting the axial boundary of the engine casing <NUM>.

Each end-casing section <NUM> also includes a seal-engaging plate <NUM> connected to the end-casing member <NUM>. The seal-engaging plate <NUM> has a mating surface <NUM> abutted to the mating surface <NUM> of the end-casing member <NUM>, and a sliding surface <NUM>, which in a particular embodiment is a hardened surface, facing away from the end-casing member <NUM> and defining a surface of the respective internal cavity <NUM>. The seal-engaging plate <NUM> sealingly engages the peripheral wall <NUM> defined by the adjacent rotor housing <NUM> to partially seal the corresponding internal cavity. In use, the face seals <NUM> of the rotor <NUM> (see <FIG>) thus engage the sliding surfaces <NUM>. The sliding surfaces <NUM> can have any surface finish suitable for sealing engagement with the face seals <NUM>.

Each end-casing member <NUM> has an aperture <NUM> defined therethrough to receive a bearing housing (not shown) supporting the engine shaft <NUM> (<FIG>). Similarly, each seal-engaging plate <NUM> has an aperture <NUM> defined therethrough concentrically with the aperture of the associated end-casing member <NUM>, sized to receive the engine shaft <NUM> therethrough.

As can be best seen in <FIG>, the end-casing member <NUM> also include oil scavenge cavities <NUM> defined in the mating surface <NUM> around the aperture, and oil circulation passages <NUM> in fluid communication with the scavenge cavities and with an oil reservoir <NUM> forming part of an oil path providing oil or other lubricating fluid circulation through the engine <NUM>, including the central-section <NUM>.

Still referring to <FIG>, each end-casing section <NUM> also includes at least one fluid cavity <NUM> in fluid communication with a source of liquid coolant (e.g. water) through a cooling fluid path of the engine casing <NUM>, for cooling the end-casing section <NUM>. The cooling fluid path includes an inlet and an outlet which may be defined in one of the end-casing sections <NUM>, and is in fluid communication with an appropriate cooler (not shown).

Each end-casing fluid cavity <NUM> is located between the mating surfaces <NUM>, <NUM> and is defined by surface depression(s) <NUM> formed on one or both of the mating surfaces <NUM>, <NUM>. In the particular embodiment shown in <FIG>, the end-casing fluid cavity <NUM> includes multiple cooperating surface depressions <NUM> formed on the mating surfaces <NUM>, <NUM>. The surface depressions <NUM> are sized and positioned to allow adequate cooling of the engine casing <NUM>. As can be best seen in <FIG>, complementary surface depressions <NUM> are defined in each of the mating surfaces <NUM>, <NUM> and cooperate to form the end-casing fluid cavities <NUM>. The end-casing fluid cavity <NUM> can have any configuration suitable for circulating a cooling fluid therein. In the particular embodiment shown, the fluid path includes a plurality of apertures <NUM> defined across the engine casing <NUM>, including the seal-engaging plate <NUM> and central-casing section <NUM>, in fluid communication with the fluid cavities <NUM>, such that the cooling fluid can circulate within the cavities <NUM> and through the various sections of the engine casing <NUM>. In the embodiment shown, the apertures <NUM> extend axially across seal-engaging plate <NUM> and central-casing section <NUM>, from the fluid cavities <NUM> of one of the end-casing sections <NUM> to the fluid cavities <NUM> of the other of the end-casing sections <NUM>. It is understood that any other adequate type of fluid communication may alternately be used.

In an alternate embodiment which is not shown, the surface depression(s) <NUM> of the end-casing fluid cavity <NUM> is/are located only on the mating surface <NUM> of the end-casing member <NUM>. In that case, the mating surface <NUM> of the seal-engaging plate <NUM> does not include surface depressions. In another alternate embodiment which is not shown, the surface depression(s) <NUM> of the end-casing fluid cavity <NUM> is/are located on the mating surface <NUM> of the seal-engaging plate <NUM>. In that case, the mating surface <NUM> does not include surface depressions. It is also understood that any combination of fluid cavities defined by depressions in only one of the mating surfaces <NUM>, <NUM> and defined by depression in both of the mating surfaces <NUM>, <NUM> can be used.

In the embodiment shown, and as can be seen more clearly in <FIG>, the two end-casing sections <NUM> have different configurations and each end-casing sections <NUM> has a different number of end-casing fluid cavities <NUM>. Alternately, the two end-casing sections <NUM> may have similar fluid cavities <NUM>.

The end-casing member <NUM> has a thickness greater than a thickness of the seal-engaging plate <NUM>. In a particular embodiment, the seal-engaging plate <NUM> has a thickness of <NUM> times that of the end-casing member <NUM>; other relative dimensions may alternately be used.

Referring back to <FIG>, the central-casing section <NUM> of the particular embodiment shown includes two rotor housing <NUM> each defining a respective internal cavity <NUM> for receiving a respective rotor <NUM> (shown in <FIG>). Each adjacent ones of the rotor housings <NUM> are separated by an intermediate section <NUM>. The intermediate section <NUM> has similar functionalities as the end-casing section <NUM> described above and separates adjacent rotor housings <NUM> in multi-rotor engines.

The intermediate section <NUM> includes an intermediate member <NUM> which has opposite, parallel mating surfaces <NUM>. The intermediate section <NUM> also includes a pair of intermediate seal-engaging plates <NUM> connected to the intermediate member <NUM>. Each intermediate seal-engaging plate <NUM> has a mating surface <NUM> abutted to a respective one of the mating surfaces <NUM> of the intermediate member <NUM> and, a sliding surface <NUM>, which in a particular embodiment is a hardened sliding surface, facing away from the intermediate member <NUM> and defining a surface of the respective internal cavity <NUM>. The seal-engaging plates <NUM> each sealingly engage the peripheral wall <NUM> defined by the adjacent rotor housing <NUM> to partially seal the corresponding internal cavity.

As can also be seen in <FIG>, the intermediate member <NUM> has an aperture <NUM> defined therethrough concentrically with the apertures <NUM>, <NUM> of the end-casing sections <NUM> to the engine shaft <NUM> therethrough; although not shown, the aperture <NUM> could also be sized to receive a bearing housing, particularly but not exclusively for engines including more than two rotors. Similarly, each seal-engaging plate <NUM> has an aperture <NUM> defined therethrough concentrically with the aperture of the intermediate member <NUM>, sized to also receive the engine shaft <NUM> therethrough. The intermediate member <NUM> includes an oil scavenge passage <NUM> communicating with the aperture <NUM> and with the oil reservoir <NUM>.

The intermediate section <NUM> also includes at least one intermediate fluid cavity <NUM> in fluid communication with the fluid path of the engine casing <NUM>, for cooling the rotor housing <NUM>. Each intermediate fluid cavity <NUM> is located between the intermediate member <NUM> and the intermediate seal-engaging plates <NUM>. Each intermediate fluid cavity <NUM> is defined by a surface depression <NUM> formed on the mating surface <NUM> of the respective seal-engaging plate <NUM>, while the mating surfaces <NUM> of the intermediate member <NUM> are free of depressions.

In an alternate embodiment which is not shown, one or more of the intermediate fluid cavities <NUM> may be defined by depressions in the mating surface <NUM> of the intermediate member <NUM>, alone or in combination with a complementary depression in the mating surface <NUM> of the corresponding seal-engaging plate <NUM>. It is also understood that any combination of fluid cavities defined by depressions in only one of the abutting mating surfaces <NUM>, <NUM> and defined by depression in both of the abutting mating surfaces <NUM>, <NUM> can be used.

The intermediate fluid cavity <NUM> can have any configuration suitable for circulating a cooling fluid therein. In the particular embodiment shown, the apertures <NUM> of the fluid path defined across the engine casing <NUM> extend through the seal-engaging plates <NUM> and the intermediate member <NUM>, in fluid communication with the intermediate fluid cavities <NUM> to connect the fluid cavities <NUM> to the fluid path. It is understood that any other adequate type of fluid communication may alternately be used.

In the illustrated embodiment, the intermediate fluid cavities <NUM> are shaped differently from the end-casing fluid cavities <NUM>, and are positioned along different circumferential portions of the engine <NUM>. The shape and position of the fluid cavities can be optimized based on engine operating conditions and/or configuration. In the embodiment shown, the intermediate fluid cavities <NUM> are concentrated along the circumferential portion of the rotor housing <NUM> where combustion occurs.

In the embodiment shown, and as can be seen more clearly in <FIG>, the two seal-engaging plates <NUM> have different configurations and different intermediate fluid cavities <NUM> are defined on each side of the intermediate member <NUM>. Alternately, the two sides of the intermediate member <NUM> may have similar fluid cavities <NUM>.

The intermediate member <NUM> has a thickness greater than a thickness of the seal-engaging plates <NUM>. In a particular embodiment, the seal-engaging plates <NUM> each have a thickness of <NUM> times that of the intermediate member <NUM>; other relative dimensions may alternately be used.

In a particular embodiment, the engine casing <NUM> allows for replacement of the seal-engaging plates <NUM>, <NUM> without replacing the entire end-casing section <NUM> or the entire central-casing section <NUM>, for example in case of damage to the sliding surfaces <NUM>, <NUM>.

As shown in <FIG>, fasteners such as circumferentially spaced bolts <NUM> (only one of which is shown) interconnect the sections to form the engine casing <NUM>.

In a particular embodiment, the fluid cavities <NUM>, <NUM> of the engine casing <NUM> are created by forming the fluid cavities on the mating surfaces of the engine casing sections. Advantageously, more economical techniques may become available, such as machining.

In a particular embodiment, manufacturing of the rotary engine casing <NUM> includes manufacturing a member having a first mating surface such as end-casing member <NUM> and/or intermediate member <NUM>, and a seal-engaging plate having a second mating surface such as seal-engaging plate <NUM> and/or intermediate seal-engaging plate <NUM>. The surface depression(s) can then be machined on at least one of the mating surfaces to form the fluid cavity. In a particular embodiment, the method includes forming corresponding depressions on both mating surfaces to form the fluid cavity. Once the depressions are formed the member is assembled with the seal-engaging plate such that the surface depression defines a fluid cavity in communication with the fluid path for circulating a cooling fluid therein. The member and the seal-engaging plate are connected through abutment of the first and second mating surfaces. In a particular embodiment, this includes dowelling and/or bolting the member with the seal-engaging plate in a semi-permanent sub-assembly.

In a particular embodiment, the end-casing members <NUM>, seal-engaging plates <NUM>, rotor housings <NUM>, seal-engaging plates <NUM> and <NUM> intermediate member(s) <NUM> are made of a same material; alternately, different materials may be used.

In a particular embodiment, the split casing sections allow to ease the engine casing <NUM> assembly process. In such an embodiment, it is simpler and more economical to form the fluid cavities as compared to other manufacturing techniques, such as casting.

Claim 1:
A rotary engine casing (<NUM>) for a rotary engine (<NUM>) having a bearing housing, an engine shaft (<NUM>) and a rotor (<NUM>), the rotary engine casing (<NUM>) comprising first and second axially spaced apart end walls (<NUM>) interconnected by a peripheral wall (<NUM>), the first end wall (<NUM>), second end wall (<NUM>) and peripheral wall (<NUM>) together enclosing an internal cavity (<NUM>) configured to sealingly engage a rotor (<NUM>) rotatable therein, at least the first end wall (<NUM>) having a split configuration including a seal-engaging plate (<NUM>, <NUM>) sealingly engaging the peripheral wall (<NUM>) to partially seal the internal cavity (<NUM>) and a member (<NUM>, <NUM>) mounted adjacent the seal-engaging plate (<NUM>, <NUM>) outside of the internal cavity (<NUM>), the member (<NUM>, <NUM>) having a first aperture (<NUM>, <NUM>) defined therethrough, the seal-engaging plate (<NUM>, <NUM>) having a second aperture (<NUM>, <NUM>) defined therethrough concentrically with the first aperture (<NUM>, <NUM>), the second aperture (<NUM>, <NUM>) sized to receive the engine shaft (<NUM>) therethrough, the seal-engaging plate (<NUM>, <NUM>) having a sliding surface (<NUM>, <NUM>) facing away from the member (<NUM>, <NUM>) and defining a surface of the internal cavity (<NUM>), and a mating surface (<NUM>, <NUM>) abutted to a mating surface (<NUM>, <NUM>) of the member (<NUM>, <NUM>), at least one fluid cavity (<NUM>, <NUM>) being located between the mating surfaces (<NUM>, <NUM>, <NUM>, <NUM>) of the member (<NUM>, <NUM>) and of the seal-engaging plate (<NUM>, <NUM>), the at least one fluid cavity (<NUM>, <NUM>) communicating with a source of liquid coolant, the at least one fluid cavity (<NUM>, <NUM>) configured to in use cool the rotor (<NUM>),
characterised in that:
the first aperture (<NUM>, <NUM>) is defined to receive a bearing housing supporting the engine shaft (<NUM>).