Crank loop motor

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Four-cylinder crank loop motor according to Russell L. Bourke
Figure 2 from patent US 2172670 A
Figure 1 from patent US 2172670 A
Animation of a four-cylinder crank loop motor

A crank loop motor is an internal combustion engine based on the principle of the Scotch-Yoke crank drive .

General

As far as we know today, the first engine based on this principle was registered for a patent by Russell Lyle Bourke in 1932 , from which the name Bourke engine (English: Bourke engine ) later developed. Bourke's efforts were originally aimed at improving the gasoline engine cycle .

Other common names for this type of engine are:

  • Scotch-yoke motor based on the scotch-yoke principle
  • Slider Engine Slider Engine Technologies, a 90 ° -Doppelkurbelschlaufenmotor (patents from 2000 and 2002)

Bourke engine

In 1938 Russell Lyle Bourke not only applied for a patent for the engine in the USA, but developed it further and applied for another patent in Great Britain to improve the Bourke engine. In 1939 the engine was then registered for a patent in France .

Despite his success in translating his design into various running engines, Bourke still had little luck. The outbreak of World War II , his poor health and the "know-it-all" attitude all resulted in his engine never appearing on the market, despite the alleged advantages.

The engine was in pre-production at Hudson Motor Car Co. (now American Motors ) but was not produced as World War II began. To this day, into the 21st century, there are various small groups who praise the merits of this engine design.

Design features

A Bourke engine has two cylinders facing each other, the pistons of which are linked by a scotch yoke mechanism. Because the pistons move in a perfect sine wave versus time versus stroke , the fuel burns in a smaller volume at a higher temperature. The use of a scotch-yoke crank mechanism reduces the vibrations when the piston rod moves. The injection valves are replaced by connections, and the reduction in the number of components increases the volume-related efficiency of the machine.

It is believed that the features that increase engine economy, particularly the way the fuel burns, can cause emissions problems. The higher temperature during the combustion in combination with the longer cycle time at the top dead center can lead to increased nitric oxide - emissions result. To date, there are no verified measurements of nitrogen oxide emissions from running engines that would confirm or refute these emission problems.

Bourke engines differ from gasoline engines, diesel engines, or Wankel engines .

  • Scotch-Yoke crank drive instead of piston rods ( connecting rods ) to convert the translational movement into a rotational movement :
  • In the two-cylinder only three moving parts
  • Quieter running thanks to the purely sinusoidal path / crank angle function (the slider-crank mechanism usually used in internal combustion engines delivers comparatively lower piston accelerations at bottom dead center and higher at top dead center with a finite connecting rod length.)
  • Two working cycles per revolution , i.e. H. Two-stroke of the opposing pistons instead of one working stroke for every second revolution as in a single - cylinder four- stroke engine, resulting in almost double the force at a given speed .
  • A partition wall seals the underside of the piston against the crankcase, so there is no need to add oil to the fuel, as is usual with other two-stroke engines, and blow-by is prevented so that the oil in the crankcase does not get dirty and its service life is extended.

Simplified functional principle

A Bourke engine is basically a two-stroke engine with a slightly different piston movement.

In the first stroke, the piston moving in the direction of the cylinder head compresses the mixture, which is heated under the pressure ; but since the piston head and cylinder walls are cold, this is not heated sufficiently to ignite itself, although the self-ignition is close because of the high compression ratio (more than 10: 1). Just before top dead center, the spark plug sparks and ignites the mixture. The fuel burns almost completely in the oxygen in the heated air.

In the second stroke, the piston moves downwards in the cylinder, the gas following the piston expands and cools down in the process. In the vicinity of the bottom dead center, the piston releases the scavenging slots in the cylinder and thus time for the exhaust gases to flow out and for the fresh gas-air mixture to be injected.

Fuel choice

The mixture must be lean enough so that the heat of compression of the mixture does not lead to self-ignition before reaching top dead center. If this is not the case, the engine does not run at all or only runs very rough. The fuel-air mixture must be in the "explosive" zone, i. This means that the engine must have the correct mixing ratio so that it runs properly. Any fuel mixed in the correct ratio can be used with this engine; That is, the engine is capable of burning a wide variety of fuels.

Torque and Effectiveness

As in conventional engines, the maximum pressure on the piston occurs shortly after top dead center has been reached. Complete combustion of the fuel is important for the efficiency and low emissions of an engine.

cycle

The cooling behind the piston head caused by the expanding gases, the scarce combustion of fuel during the piston movement and the evaporation of fuel during the injection are decisive for the low exhaust gas temperature. The cooling of the piston head also prevents knocking or nailing during the next compression cycle.

The fuel-air mixture is sucked in behind the piston during the piston return stroke and compressed like in a compressor during the working stroke . It then flows into the combustion chamber in front of the piston. Injection takes place at the same time as the exhaust gas is discharged, but on the other side of the cylinder. Due to the shape of the piston, the injected mixture reaches the beveled piston head, which leads to an evaporation of the fuel droplets, which further cools the piston head and causes a vortex flow that leads to a complete mixing of the fuel-air mixture. This mixture contributes to complete combustion. The beveled piston head effectively separates the incoming mixture from the exhaust gases to be expelled.

Scotch yoke

The piston is connected to the "Scottish connecting rod" by means of a "triple sliding guide" (a type of hydrodynamic swivel block guide ). This guide absorbs and smooths the force of the combustion and thus prevents deformation or destruction of engine parts. The guide also absorbs all lateral forces, which prevents vibrations .

Compression ratio

The compression ratio must be adapted to the fuel to be burned. If the compression ratio is set too high, the speed will become irregular and difficult to control due to knocking. By adjusting the compression ratio, both low and high octane fuels can be burned.

The piston shape with a larger volume at the tip also supports complete combustion.

Crank loop motor patents

A large number of patents exist around the world for crank loop motors . With the search term "Scotch Yoke Engine" alone, at least 45 different patents, scattered around the world, can be found that deal with Scotch Yoke engine technology. "Scotch Yoke Motor" delivers more hits.

A comparatively small selection of patents on the subject of loop crank motors can be found on the website of Slider Engine Technologies, an Australian company that specializes in loop crank motors and holds several patents on this topic, as well as many animations of the various motor types.

The following list of patents is arranged alphabetically by company name.

In the past 20 to 25 years, work has been intensified again on the further development of these engines, which can be seen in particular from the large number of patents that have been registered since then.

Advantages and disadvantages

The growing interest of the automotive industry in these engines is not only due to environmental reasons but also to the advantages of the scotch-yoke principle over crankshafts and connecting rods. These are u. a .:

  • Fewer moving parts
  • Ease of movement
  • In engine applications, there are no additional connection points due to the piston pin
  • large torque with small cylinder size
  • Less time at top dead center improves the efficiency of the engine
  • A higher proportion of time at bottom dead center improves the emission of exhaust gases

Disadvantages of the crank loop are:

  • Rapid wear of the pin bearing
  • A single crank loop cannot produce any rotation by itself; at least two axially offset loops are required.
  • A break in the lubricating film on the bearing of the connecting rod crankshaft due to the oscillating kinematics can cause the engine to self-destruct

See also

swell

Web links

Commons : Bourke engine  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c https://www.google.co.in/patents/US2172670
  2. ↑ Patent US2122677 . ‌
  3. ↑ patent GB514842 . ‌
  4. ↑ Patent FR838777 . ‌
  5. ^ "Scotch Yoke Engine"
  6. ↑ "Scotch Yoke Motor"
  7. ↑ Patent US5943987 . ‌
  8. ↑ Patent US6012423 . ‌
  9. ↑ Patent WO9006426 . ‌
  10. ↑ patent DE3624753 . ‌
  11. ↑ patent WO0106092 . ‌
  12. ↑ Patent EP0187930 . ‌
  13. ↑ Patent US4776310 . ‌
  14. ↑ Patent WO93123664 . ‌
  15. ↑ Patent WO0060216 . ‌
  16. ↑ Patent WO02088530 . ‌
  17. ↑ Patent WO0227163 . ‌
  18. ↑ Patent JP8014061 . ‌
  19. ↑ patent DE19725227 . ‌
  20. ↑ patent US4013048 . ‌
  21. ↑ Patent US5315967 . ‌
  22. ↑ Schoell Marine Inc. Innovations