Patent Grant
7373905
The present invention relates to a multi-cylinder engine for use in light weight, high specific power applications. More particularly, the present invention is a horizontally-opposed eight cylinder diesel engine for use in aircraft.
Horizontally opposed, piston-driven engines are known in the art, and widely used in the aviation industry. However, there is a need in the industry to provide an engine that does not rely on fuel containing tetraethyl lead, a component currently contained in aviation gasoline. There is a further need for an engine offering high specific power output in a light weight package.
In the past, there was a tremendous amount of effort to increase the specific power of engines. In particular, the efforts were focused at delivering light-weight, high-power, piston engines for use in military fighter and bomber airplanes. The direction generally taken by both the Allied and Axis powers was to rely heavily on two particular strategies. The first was to develop air-cooled radial engines. These engines were designed with the shortest crankshaft available (single-throw, master-slave rod), and were arranged to make the best use of the frontal area to effectively cool the vital engine components, as shown in
Another strategy employed was to use the Vee (or “V”) configuration to reduce weight by minimizing the crankshaft length. A reduction in crankshaft length consequently reduces the engine volume and weight of the engine. Length was so important, that in extreme cases the fork-and-knife method was used to minimize engine cylinder bank offset, and further reduce weight, as shown in
In the past years Schrick (assignee of the present application) has made some monumental advances with regards to utilizing diesel engines in aero applications. One such engine was the air-cooled Hurricane engine as shown in
Accordingly, there is a need for a more production feasible solution for the General Aviation (hereinafter “GA”) community. Current GA engines have their roots in the air-cooled engines of the Second World War era. They are identical in many respects, with the exception of being horizontally-opposed engines. This engine configuration has been used in the past by Volkswagen and Porsche, as well as the dominant aero engine manufacturers Lycoming and Continental.
Although the engine configuration of
There is a further need in the industry for an engine that does not rely on tetraethyl-based lead. Lead additive is currently vital to aviation fuel for its anti-knock properties, however it is very harmful to the environment and only produced today in limited quantities.
The present invention substantially meets the aforementioned needs of the industry.
The use of a “paired-throw” configuration according to the present invention reduced the first order vibration moment by about 300%. A reduction of this magnitude allowed the use of a relatively light-weight first order moment balance shaft. This device effectively eliminates all of the first order rocking couple.
It should be mentioned here that although the example shown here is for an eight cylinder engine. The identical strategy can be used for 6, 10, and 12 cylinder engines. This technique is useful for aircraft and other engines where compactness and power density is a primary objective. It is contemplated that the present invention would also be useful in military vehicles and boats alike. In military vehicles, the engine could be placed very low in the vehicle, offering blast protection to the operators, sitting above the engine and further offering a low center of gravity for increased stability.
In a diesel engine, as in most engines, there are several circuits which must be cooled to ensure internal component reliability, such as the normal engine and oil coolers. The turbocharged diesel engine requires an additional charge-air cooler (or intercooler) to achieve maximum performance. The function of this cooler is to increase charge density and thus air mass flow through the engine.
In this particular engine design, the cooling requirements of the liquid elements of the engine are accomplished by an engine-mounted radiator. The oil is cooled by a water/oil element that ensures proper pre-warning of the oil in cold climates. Mounting on the engine is facilitated by the flat-vee configuration. It also allows the engine to be installed in traditional aircraft cowls without significant additional design work on the part of the aircraft company.
The flat-vee allows the entire width of the engine bay to be pressurized and sealed to the twin cooler matrices. This minimizes resultant aircraft drag, which has a large effect on aircraft speed and fuel economy.
By not having to remote mount the glycol and water systems, the entire engine installation remains lightweight. This is primarily due to the fact that water and oil lines are heavy, and do little to decrease the heat of the contained liquids. Also, this gives a universal cooling strategy which can be used on all air-cooled aircraft designs. Hence, the design makes it easy for the manufacturer to make a retrofit of the present engine assembly in existing aircraft.
Air-air charge air coolers share the pressure cowl with the engine cooler element. The two are in close proximity, and this feature allows for very compact packaging within constraints of the cowling. The charge air cooler installation provides for a unified engine cooling strategy.
The present invention is an engine, including two banks of cylinders in a flat, opposed cylinder arrangement and a crankshaft having a plurality of paired throws, the two throws of each respective pair of throws being disposed adjacent to each other and coplanar with respect to each other.
Any piston engine is simply a collection of pressure vessels that utilizes a crank rocker (crankshaft) mechanism to impart the expansion work of gases for the purpose of delivering useful work, as shown in
Although it is well known by engineers that modem diesel engines are more thermally efficient, the challenge has been to integrate diesels into a compact weight-efficient package. Nowhere is this more critical than in the design of aero applications. This application demands that an engine be lightweight, durable, efficient, and powerful. To achieve these characteristics simultaneously, the engineer must go through a thorough “sizing” study to determine how much engine capacity is sufficient to do the job properly.
BMEP, or “P” in the equation below, is used to compare the performance of various engine configurations. It is the average pressure over the cycle time that an engine would achieve if it were operating as a constant pressure device. The basic equation for engine power can be simplified to the following form:
Power=P×L×A×N
Where:
Power, therefore, is a function of BMEP, engine geometry, and engine speed. It should be evident then that given the same power target, the options are limited for the engine designer. It should also be evident that the only way to increase power output of a four-stroke engine is to:
Since the goal is to obtain more specific power, the task of the engine designer is to increase power without a corresponding increase in weight. The significance of this is that by definition, an increase in engine volume will result in an increase in weight. This effectively eliminates option “1” above.
To increase engine speed would certainly result in an increase in specific power. However, this is generally contradictory to engine durability. Things like bearing loading, piston speed, and dynamic vibrations are generally increased with engine speed. A gear reduction can be used to provide torque amplification when the torque capacity of an engine is insufficient. This is not without penalty, as the designer must consider the tradeoff between engine displacement, and gear reduction weight. Another consideration is the gear efficiency (sound characteristic) and torsional behavior of such a gear reduction.
An additional element to consider with regard to increasing engine speed is that the dimensional accuracy of the engine machined components must be increased to ensure proper dynamic engine behavior. This fact translates directly to increased manufacturing costs which certainly must be taken into consideration in the construction of a light-weight, high-speed engine.
The most basic choice that an engine designer faces must deal with an engine's function within the environment that it operates. The driving force behind this particular exercise was to derive a replacement for the current GA engines in widespread use. Today, virtually all of the engines are of the horizontally opposed, air-cooled, configuration. From a packaging perspective, most of the aircraft in production, and all aircraft in service are designed around this configuration. This configuration fits well within the slipstream of a two person-wide aircraft. It can be enclosed to cool the engine within the frontal area of the fuselage.
The current GA engines tend to be very long, to allow proper air cooling of the cylinder heads. By using the Vee configuration, the engine designer can effectively shorten the engine, while maintaining the same frontal profile.
This technique allows the liquid-cooled diesel engine 10 of the present invention with increased cylinder count to be packaged within the current length constraints of the GA package.
In addition to providing for an optimal installation, and package density, it was quite valuable from a design objective with engine 10 to be able to utilize “production” Vee-engine components in the prototyping phase of the engine development process of the present invention. For example, the complete cylinder head of a European passenger car could be used in the flat vee concept without modification. Other components are also useful, and this dramatically reduces the amount of development time and cost for this particular application. Components that could be “carried over” from the automotive V-8 were:
Although the engine package is important, achieving proper engine balance is probably more important to the service life of the engine, and its ancillary systems. By nature, aircraft structures tend to be very lightweight, and are greatly affected by the vibration signature of the engine.
To determine if the 180-degree engine had merit as a solution, the use of a usual “cruciform” crank as shown in
When the Vee angle is “flattened” to 180-degrees, the first order vibration moment is doubled, rendering the engine unserviceable from a vibration perspective. It was realized that although this situation could be corrected with a balance shaft turning at crank speed, the mass of the balance weights would make the engine unnecessarily heavy.
However, the use of a “paired-throw” configuration of the crankshaft 50 according to the present invention reduced the first order vibration moment by about 300%, as shown schematically in
The engine 10 of the present invention is shown generally in
Referring generally to
The crankshaft 50 (noted above) is also included in engine 10, and includes a plurality of bearing journal surfaces 52 that provide a means of securing crankshaft 50 in block 12. Crankshaft 50 further includes a plurality of connecting rod bearingjournals 54, 56, 58, and 60. As is known by one skilled in the art, the distance between the centerline of the crankshaft and the centerline of a connecting rod bearing journal is referred to as the “throw” of the crankshaft, and that term will be used alternatively herein with “connecting rod bearing journal.” Each throw operably receives two connecting rods 46, one from each cylinder bank 30a and 30b. More particularly, the connecting rod from cylinder 31 and the connecting rod from cylinder 35 are operably coupled to throw 54. Similarly, the connecting rod from cylinder 32 and the connecting rod from cylinder 36 are operably coupled to throw 56. Similarly, the connecting rod from cylinder 33 and the connecting rod from cylinder 37 are operably coupled to throw 58. Similarly, the connecting rod from cylinder 34 and the connecting rod from cylinder 38 are operably coupled to throw 60. Throws 54 and 56 are adjacent, coplanar, and generally opposed. Similarly, throws 58 and 60 are adjacent, coplanar and generally opposed. Further, the plane defined by throws 54 and 56 is orthogonally disposed to the plane defined by throws 58 and 60. See the schematic of
According to a present embodiment of the invention, the firing order of the cylinders is as follows: 31, 37, 32, 38, 36, 34, 35, 33. (1, 7, 2, 8, 6, 4, 5, 3 in
Engine 10 also includes a first cylinder head 14 and a second cylinder head 16.
Engine 10 further includes an injection system 18, as shown in
A tremendous amount of time was spent to achieve effective vibration signature within the engine design concepts. This was done for several reasons which all add up to a comprehensive engine design which is optimized for use of structural materials and weight reduction. As detailed below, the design allowed the very lightweight aluminum cooling elements to be directly mounted, as well as giving additional service life to the engine mounted components and the aircraft structure.
In the diesel 10 engine, as in most engines, there are several circuits which must be cooled to ensure internal component reliability, such as the normal engine and oil coolers. The turbocharged diesel engine 10 requires an additional charge-air cooler (or intercooler) to achieve maximum performance. The function of this cooler is to increase charge density and thus air mass flow through the engine.
In this particular engine 10, the cooling requirements of the liquid elements of the engine are accomplished by an engine-mounted radiator. The oil is cooled by a water/oil element that ensures proper pre-warning of the oil in cold climates. Mounting on the engine is facilitated by the flat-vee configuration. It also allows the engine to be installed in traditional aircraft cowls without significant additional design work on the part of the aircraft company.
The flat-vee configuration of engine 10 allows the entire width of the engine bay to be pressurized and sealed to the twin cooler matrices. This minimizes resultant aircraft drag, which has a large effect on aircraft speed and fuel economy.
By not having to remote mount the glycol and water systems, the entire engine 10 installation remains lightweight. This is primarily due to the fact that water and oil lines are heavy, and do little to decrease the heat of the contained liquids. Also, this gives us a universal cooling strategy which can be used on all air-cooled aircraft designs. Hence, we make it easy for the manufacturer to make a retrofit of the engine assembly into existing aircraft.
Air-air charge air coolers share the pressure cowl with the engine cooler element. The two are in close proximity, and this feature allows for very compact packaging within constraints of the cowling. The charge air cooler installation provides for a unified engine cooling strategy.
A cooling system 20 is also included in engine 10. Referring to
Intercooler 100 is mounted above engine 10 and adjacent to radiator 90, and is also coupled to shroud 92. Air is drawn in through air inlets 94 and 95, and passes through radiator 90 and intercooler 100 by way of shroud 92, while water pump 96 circulates engine coolant through radiator 90. Oil-to-water heat exchanger 98 provides cooling to oiling system 24 (mentioned in detail below) by circulating engine coolant next to engine oil. In an alternative embodiment, it is contemplated that engine 10 is air cooled.
Engine 10 also includes an intake system 22 and an exhaust system 23, as shown in
Referring to
While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
This application is a continuation of U.S. patent application Ser. No. 11/072,624, filed on Mar. 4, 2005, now U.S. Pat. No. 7,191,742, which claims benefits of U.S. Provisional Application No. 60/642,837, filed Jan. 11, 2005.
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| Number | Date | Country | |
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| 20070209616 A1 | Sep 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60642837 | Jan 2005 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11072624 | Mar 2005 | US |
| Child | 11687325 | US |
