Patent Description:
Temperature plays an important role in the performance of batteries. Batteries are a function of chemical reactions. In cold weather, the chemicals cannot react as fast as in warm weather. A cold battery will, thus, not have the same power as a warm one. In order to provide sufficient electrical power in all weather conditions, it is thus sometimes necessary to increase the number of batteries or use bigger batteries. However, this results in weight increase, which makes hybrid electric power plants less attractive for aircraft applications.

<CIT> discloses a prior art energy recovery and cooling system for a hybrid machine powertrain.

In one aspect according to the invention, there is provided a method of operating a hybrid electric power plant as recited in claim <NUM>.

In another aspect according to the invention, there is also provided a hybrid electric power plant as recited in claim <NUM>.

<FIG> illustrates an example of a power plant <NUM> suitable for use on a hybrid electric aircraft. The power plant <NUM> can adopt various configurations. For instance, the power plant <NUM> could be configured as a turboprop engine for driving a propeller <NUM>. According to another example, it can be configured as a turboshaft engine for driving a helicopter rotor or any other load to be driven. The hybrid electric power plant <NUM> could also be used in an auxiliary power unit (APU) installation. Other applications are contemplated as well.

According to a particular embodiment, the power plant <NUM> generally comprises a fossil-fuel powered engine <NUM> and an electric motor-generator <NUM> and a battery pack <NUM> electrically connected to the motor-generator <NUM>. The motor-generator <NUM> can consist of two distinct motor and generator machines or it can be integrated into one unit. The engine <NUM> can be drivingly connected to the electric motor-generator <NUM> via output shaft <NUM>'. The electric motor-generator <NUM> is, in turn, drivingly connected to a load (propeller <NUM> in the illustrated example) via a reductions gearbox (RGB) <NUM>. According to one possible arrangement, the fossil-fuel powered engine <NUM> and the motor-generator <NUM> could be both connected to the RGB <NUM> to drive the load. Such an arrangement is referred to as a parallel hybrid system. According to another possible arrangement, the engine <NUM> could only be used to drive the motor-generator <NUM> when used in a generator mode for charging the batteries of the battery pack <NUM>, and the load could only be driven by the electric motor <NUM> via the RGB <NUM>. This arrangement can be referred to as a series hybrid system.

The engine <NUM> may be provided in the form of a conventional internal combustion engine (e.g. a piston or rotary engine) or in the form of a compound cycle engine such as described in<CIT> or as described in<CIT>, or as described in <CIT>, or as described in <CIT>.

<FIG> illustrates an example of a compound cycle engine <NUM>' suitable for use as engine <NUM> in <FIG>. The compound cycle engine <NUM>' generally includes a supercharger compressor <NUM> for compressing the air prior to feeding an engine core <NUM> including one or more internal combustion engines <NUM>. The exhaust from the engine core <NUM> is fed to one or more turbines <NUM>, <NUM> of a compounding turbine section having an outlet fluidly connected to an exhaust duct for discharging the hot combustion gases to atmosphere. One or more of the turbines <NUM>, <NUM> is/are configured to compound power with the engine core <NUM>. In the embodiment shown, the turbine and engine shafts are coupled through a transmission provided by a gearbox <NUM>. The compressor <NUM> may be driven by the turbines <NUM>, <NUM> and/or the engine core <NUM>. In the embodiment shown, the compressor <NUM> is driven by the turbines <NUM>, <NUM>, for example by being coupled to the same shaft or being engaged to the turbine shaft through a transmission provided in the gearbox <NUM>. In another particular embodiment, the shaft of the compressor <NUM> is engaged to the output shaft of the engine core <NUM>, either directly or through a transmission.

In a particular example, the internal combustion engine(s) <NUM> of the engine core <NUM> is/are rotary intermittent internal combustion engines, for example Wankel engines; it is however understood that other types of intermittent internal combustion engines or other types of internal combustion engines may alternately be used.

As shown in <FIG>, the exemplary engine <NUM> comprises a housing <NUM> defining a rotor cavity having a profile defining two lobes, which is preferably an epitrochoid. A rotor <NUM> is received within the rotor cavity. 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 a peripheral wall <NUM> of the housing <NUM> to form and separate three working chambers <NUM> of variable volume between the rotor <NUM> and the housing <NUM>. The peripheral wall <NUM> extends between two axially spaced apart end walls <NUM> to enclose the rotor cavity.

The rotor <NUM> is engaged to an eccentric portion <NUM> of an output shaft <NUM> to perform orbital revolutions within the rotor cavity. The output 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 housing <NUM>. During each rotation of the rotor <NUM>, each chamber <NUM> varies in volume and moves around the rotor cavity to undergo the four phases of intake, compression, expansion and exhaust.

An intake port <NUM> is provided through the peripheral wall <NUM> for admitting compressed air into one of the working chambers <NUM>. An exhaust port <NUM> is also provided through the peripheral wall <NUM> for discharge of the exhaust gases from the working chambers <NUM>. Passages <NUM> for a spark plug, glow plug or other ignition mechanism, as well as for one or more fuel injectors of a fuel injection system (not shown) 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 the end or side wall <NUM> of the housing. A sub-chamber (not shown) may be provided in communication with the chambers <NUM>, for pilot or pre injection of fuel for combustion.

For efficient operation the working chambers <NUM> are sealed by spring-loaded peripheral or apex seals <NUM> extending from the rotor <NUM> to engage the inner surface of 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 inner surface of the end walls <NUM>. The rotor <NUM> also includes at least one spring-loaded oil seal ring <NUM> biased against the inner surface of the end wall <NUM> around the bearing for the rotor <NUM> on the shaft eccentric portion <NUM>.

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

As shown in <FIG>, the power plant <NUM> also comprises a lubricant system <NUM> to provide lubricant to engine <NUM> and the electric motor-generator <NUM>. The lubricant system generally comprises a tank <NUM> containing a predetermined volume of lubricant (e.g. oil), a lubricant circuit <NUM> fluidly connecting the tank <NUM> to engine <NUM> and the motor-generator <NUM>, and a pump unit <NUM>, which may comprise one or more pumps, for drawing lubricant from the tank <NUM> and moving the lubricant in a closed loop cycle through the lubricant circuit <NUM>. For instance, the pump unit <NUM> can comprise a feed pump mounted in a feed line 74a of the oil circuit <NUM> between the tank <NUM> and the engine <NUM> and the motor-generator <NUM>. The feed line 74a of the lubricant circuit <NUM> can have first and second branches 74a' and 74a" respectively fluidly connected to the engine <NUM> and the motor-generator <NUM>. The feed pump <NUM> can be disposed upstream of the first and second branches 74a' and 74a". A three-way valve <NUM> or the like may be provided in a return line 74b of the lubricant circuit <NUM> downstream of the engine <NUM> and the motor-generator <NUM> to selectively cause the lubricant coming from the engine <NUM> and the motor-generator <NUM> to flow through a heat exchanger <NUM> before being returned into the tank <NUM> or to bypass the heat exchanger <NUM> and direct the lubricant directly back into the tank <NUM>. According to the illustrated example, the heat exchanger <NUM> is an air-liquid heat exchanger. However, it is understood that other types of heat exchanger could be used. For instance, a liquid-to-liquid heat exchanger could be used to dissipate the heat picked up by the lubricant as it is circulated through the engine <NUM> and the motor-generator <NUM>. In the case of an air-liquid heat exchanger, a blower <NUM> or other air flow inducing devices may be provided to generate a flow of cooling air through the heat exchanger <NUM> to cool the lubricant. According to a particular embodiment, the blower <NUM> may be disposed to draw outside air through an air duct in fluid communication with the heat exchanger <NUM>.

An electric heater <NUM> may be provided in the tank <NUM>. The battery pack <NUM> may be electrically connected to the heater <NUM> to provide electric power to the heater <NUM> via an electric circuit. Accordingly, on cold days, before the engine <NUM> is started, the battery pack <NUM> can be used to electrically heat the lubricant in the tank <NUM> to reduce oil viscosity and, thus, facilitate starting and reduce the engine starter size. A switch <NUM> may be provided in the electric circuit to selectively electrically power the heater <NUM>.

Still referring to <FIG>, it can be appreciated that the power plant <NUM> further comprises a coolant circuit <NUM>. In a particular embodiment, the coolant circuit <NUM> can be provided in the form of a liquid coolant circuit in heat exchange relationship with the engine housing <NUM> in order to pick up waste heat from the internal combustion engine <NUM> (about <NUM>% of the output power of the engine). As shown in <FIG>, the liquid coolant circuit <NUM> may include coolant passages <NUM> extending through the walls of the engine housing <NUM>. A pumping unit <NUM>, which may include one pump or more, is strategically positioned in the coolant circuit <NUM> to move the liquid coolant in a continuous closed-loop cycle through the coolant circuit <NUM>. In a particular embodiment, the engine coolant may be for example water, or water mixed with anti-freeze liquid(s), such as ethylene glycol. The same coolant circuit or a separate/distinct cooling circuit may be used to cool down the motor-generator <NUM>.

The battery pack <NUM> can include various energy storage devices. For instance, the battery pack <NUM> may comprise any suitable combination of high power density batteries. For instance, the battery pack <NUM> may comprise one or more Lithium-ion or lead acid batteries. As mentioned hereinbefore, temperature plays an important role in the performance of electrolytic processes and, thus, on the performance of batteries. <FIG> shows typical characteristics of a Lithium-ion battery as a function of ambient temperature. In cold climates, like at -<NUM> Celsius, the battery capacity and power reduces by about <NUM>%. Therefore, on cold days, it is desirable to warm the battery pack <NUM> to improve the efficiency thereof. As the engine <NUM> comprises an internal combustion engine, it generates significant waste heat. It is herein proposed to use at least part of this waste heat to warm the batteries on cold days and, thus, preserve their power.

For instance, the waste heat picked up by the engine coolant and/or the engine lubricant while circulated through the internal combustion engine <NUM> could be used to preheat the battery pack <NUM> whenever the efficiency of the batteries is likely to be diminished by the environment temperature. For instance, as illustrated in <FIG>, the coolant circuit <NUM> could be coiled around or otherwise connected in heat exchange relationship with the battery pack <NUM>. A valve <NUM> can be provided in the coolant circuit <NUM> downstream of the internal combustion engine <NUM> to control the flow of warm coolant to the battery pack <NUM>. The valve <NUM> could, for instance, be provided in the form of a three-way valve having one of its two outlets connected to a bypass branch 90a of the coolant circuit <NUM> for the warm coolant to selectively bypass the battery pack <NUM> when the same is within an appropriate range of operating temperatures. Still referring to <FIG>, it can be appreciated that a heat exchanger <NUM> is provided in the coolant circuit <NUM> downstream of the battery pack <NUM> to further cool the coolant prior to being redirected into the internal combustion engine <NUM>. The heat exchanger <NUM> can be integrated to the lubricant heat exchanger <NUM> or separate. In the embodiment illustrated in <FIG>, the heat exchanger <NUM> is an air-liquid heat exchanger and the cooling air circulated through the heat exchanger <NUM> is drawn by the same blower <NUM> as the one used to generate a flow of air through the lubricant heat exchanger <NUM>. Accordingly, both heat exchangers <NUM>, <NUM> can be mounted in a same air conduit and fed with coolant air by a same blower <NUM> (or any other suitable air moving device).

In cold climates, the power plant <NUM> can be operated to first warm the lubricant with electric heater <NUM>. Once the lubricant has the desired viscosity, the internal combustion engine <NUM> can be started and allowed to warm up. Once the engine <NUM> is warmed up, the temperature of the liquid coolant will typically range from about <NUM> degrees Fahrenheit (<NUM>) to about <NUM> degrees Fahrenheit (<NUM>). The valve <NUM> can be operated to direct the warm engine coolant to the battery pack <NUM> to transfer waste heat picked up from the internal combustion engine <NUM> to the batteries of the battery pack <NUM>, thereby increasing the capacity and power output of the batteries for take-off in cold environments. While the batteries are being warmed up, the internal combustion engine <NUM> can be operated to drive the motor-generator <NUM> to generate electrical power for charging the batteries. Thereafter, the warmed and charged batteries can be used to provide electric power to the electric-motor generator <NUM> to drive the propeller <NUM> alone or in combination with the compound cycle engine.

As mentioned hereinbefore, the warm lubricant circuit <NUM> can also be used to warm the batteries. This can be done to supplement the heat carried to the batteries by the engine coolant or in place thereof. The person skilled in the art will appreciate that various arrangements are possible to transfer the heat absorbed by the lubricant to the battery pack <NUM>.

Conventional gas turbine engines have no coolant and very little heat available in the oil cooler, and nearly all the rejected heat is in the exhaust. Using the exhaust gas to warm the battery is more complicated as the exhaust is very hot (over <NUM> degrees Fahrenheit (<NUM>)) and ends up in a heavier system. Accordingly, while the fossil-fuel powered engine <NUM> could be provided in the form of a conventional gas turbine engine, a person skilled in the art will appreciate that the compound cycle engine embodiment shown in <FIG> offers more synergy for hybrid electric aircraft applications than conventional gas turbine engines.

Claim 1:
A method of operating a hybrid electric power plant (<NUM>), the hybrid electric power plant (<NUM>) having an internal combustion engine (<NUM>; <NUM>), an electric motor (<NUM>) and a battery pack (<NUM>), the method comprising: a) absorbing heat generated by the internal combustion engine (<NUM>; <NUM>), and b) using the heat absorbed from the internal combustion engine (<NUM>; <NUM>) to warm the battery pack (<NUM>),
wherein a) comprises circulating a coolant in heat exchange relationship with the internal combustion engine (<NUM>; <NUM>), and b) comprises circulating the coolant heated by the internal combustion engine (<NUM>; <NUM>) in heat exchange relationship with the battery pack (<NUM>),
wherein a) further comprises circulating a liquid coolant through a housing (<NUM>) of the internal combustion engine (<NUM>; <NUM>), and circulating the coolant heated by the internal combustion engine (<NUM>; <NUM>) in heat exchange relationship with the battery pack (<NUM>) comprises circulating the liquid coolant around the battery pack (<NUM>),
characterized in that
b) further comprises controlling the flow of coolant to the battery pack (<NUM>) as a function of an environmental temperature.