Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
  • F02B33/00—Engines characterised by provision of pumps for charging or scavenging
  • F02B33/02—Engines with reciprocating-piston pumps; Engines with crankcase pumps
  • F02B33/06—Engines with reciprocating-piston pumps; Engines with crankcase pumps with reciprocating-piston pumps other than simple crankcase pumps
  • F02B33/10—Engines with reciprocating-piston pumps; Engines with crankcase pumps with reciprocating-piston pumps other than simple crankcase pumps with the pumping cylinder situated between working cylinder and crankcase, or with the pumping cylinder surrounding working cylinder

Definitions

• the invention relates to the field of two-stroke engines.
• a two-stroke combustion engine having a central cylinder and a central piston moveable in there, and an annular cylinder arranged around it with an annular piston moveable in there.
• the pressure build-up in the annular cylinder leads by less than half a stroke of the central piston.
• the annular cylinder has an air inlet and the central cylinder is provided with an injection head arranged in the cylinder head for injecting fuel, and with exit ports for discharge of combustion gases.
• the central cylinder and the annular cylinder are in fluid connection by means of passages in which spring loaded valves have been arranged in the passages which valves open when the pressure difference in the annular cylinder and the central cylinder has reached a sufficiently high value.
• Air will then flow from the annular cylinder, via the passages, to the central cylinder in order to combust the fuel injected in there.
• the passages connect more closely to the upper dead centre on the central cylinder than the exit ports do, the spring loaded valves in the passages being adjusted such that they will not open until the exit is at least almost entirely closed.
• the known two-stroke engine has the drawback that at the end of each expansion stroke of the central piston a small residue of combustion gases is left behind in the central cylinder. Said residue also remains left in the central cylinder during the next compression stroke of the central piston, which is disadvantageous for the efficiency of the engine. It is an object of the invention to improve on this.
• the invention provides a two-stroke engine comprising a central piston moveable in a central cylinder as well as an annular piston moveable in an annular cylinder, the annular cylinder comprising at least an entrance and the central cylinder comprising an exit for combustion gases, and the annular cylinder and the central cylinder being in fluid connection with each other by means of a passage, the passage, at least during a part of the stroke of the central piston, being arranged to discharge above the central piston, the top side of the exit connecting to the upper dead centre on the central cylinder more closely than the top side of the passage.
• the exit for the discharge of combustion gases will then first be released.
• means have been provided for adjusting the circumferential position of the crank pin for the annular piston with respect to the circumferential position of the crank pin for the central piston while the two-stroke engine is operational, in which the adjustment means can be operated by means of a control unit in response to the rotational speed of the crankshaft of the two-stroke engine registered by a rotational speed sensor.
• Being able to adjust the position of the crank pin for the annular piston with respect to the position of the crank pin for the central piston is related to the fact that an angle deviating from 1 80° may be required in order to achieve the correct moment for letting in gas in the central cylinder for optimally expelling combustion gases in the central cylinder.
• the system for discharging combustion gases that is connected to the exit may play a part here: when the discharge is opened for discharge of combustion gases and fresh fuel-air mixture has been allowed in the central cylinder, a small quantity of fresh fuel-air mixture may end up in the discharge system. Because gases flow into the discharge system, a "returning pressure wave" will arise in the discharge system in the direction of the exit. Said “returning pressure wave” may push back the small quantity of fuel-air mixture into the central cylinder. By suitably selecting the angle a it may be ensured that the exit closes when the small quantity of fuel-air mixture has just been entirely pushed back into the central cylinder. It is thus prevented that the fuel-air mixture escapes with the combustion gases via the discharge system.
• the adjustment means comprise a drive for moving a bush arranged around the crankshaft in axial direction of the crankshaft, the bush being coupled in rotation to the crankshaft, the bush having an engagement surface for engagement with an engagement surface of the piston rod, the engagement surface of the bush and the engagement surface of the piston rod being provided with means for shifting the piston rod in circumferential direction with respect to the bush during axial displacement of the bush.
• the means for shifting the piston rod in circumferential direction with respect to the bush during axial displacement of the bush are formed by inclined teeth arranged on the engagement surface of the bush and inclined grooves cooperating therewith arranged on the engagement surface of the piston rod.
• crank pin for the annular piston is staggered with an angle a of approximately 1 80° plus or minus
• the passage at least during a part of the stroke of the central piston during which the passage discharges above the central piston, is an unobstructed passage opening between the central cylinder and the annular cylinder. Due to the unobstructed passage opening the flow resistance of the gas through the passage opening is limited, and the gas can be guided more evenly into the central cylinder as a result of which the discharge gases can be more efficiently expelled from the central cylinder.
• the unobstructed passage opening is a passage opening in which the wall of the annular cylinder smoothly changes into the wall of the central cylinder. In this way the even, fluent inflow of the gas from the annular cylinder into the central cylinder is further stimulated.
• the unobstructed passage opening is a passage opening without valve.
• problems regarding the resonance of the two-stroke engines are counteracted.
• no problems can arise due to the valve in the passage opening breaking down which increases the operational certainty of the two-stroke engine and reduces the maintenance costs of the two-stroke engine.
• the valve may as a result of the mass inertia thereof give rise to problems regarding opening and closing correctly, at the right moment.
• the stroke volume of the annular piston is larger than the stroke volume of the central piston.
• a higher compression pressure in the central cylinder can thus be achieved, as a result of which the engine will be able to produce a greater power.
• a smaller, lighter and cheaper engine will then suffice.
• the annular piston is provided with at least one oil wiper.
• the annular piston is made of plastic, and preferably is reinforced with carbon fibre.
• the temperature in the annular cylinder does not become high because said cylinder is constantly cooled by a fresh mixture of fuel/air. As a result a plastic design is possible.
• the entrance for fuel and air of the annular cylinder is formed by an entrance opening in the wall of the annular cylinder.
• the passages which are situated closest to the exit have an orientation to guide the gas approximately horizontally into the central cylinder, in which the vertical orientation corresponds to the orientation of the centre line of the central cylinder, and the passages that are situated farthest from the exit have an orientation to guide the gas approximately at an angle ⁇ of 30° to the vertical orientation into the central cylinder.
• Said orientations are advantageous to optimally expel combustion gases from the central cylinder.
• the inner wall of the annular cylinder forms the outer wall of the central cylinder.
• the two-stroke engine comprises several central cylinders each having an accompanying annular cylinder.
• Figure 1 shows a view in cross-section in a direction parallel to the crankshaft, of an exemplary embodiment of a two-stroke engine according to the invention
• Figure 2 shows a view in cross-section in a direction perpendicular to the crankshaft, of the two-stroke engine shown in figure 1 .
• Figures 3A, 3B and 3C respectively, show a schematic top view in cross- section of the central cylinder at the location of the passages and the exit, a projected view perpendicular to the wall of the central cylinder with the passages and exit situated in there, as well as views in cross-section in tangential direction of the central cylinder wall at the location of the passages.
• Figure 4 shows a view of the mechanism for adjusting the circumferential position of the crank pin for the annular piston with respect to the circum- ferential position of the crank pin for the central piston while the two- stroke engine is operational.
• Figure 5 shows a view in perspective of some parts shown in figure 4.
• the engine 1 in figure 1 comprises a wall 18 and a central cylinder head
• the two-stroke engine 1 further comprises a central cylinder 3 having a central piston 4 moveable in there and having a side wall 4a, as well as an annular cylinder 5 having an annular piston 6 moveable in there and having a side wall 6a.
• the central cylinder 3 and the annular cylinder 5 are situated coaxially with respect to each other and comprise spaces 3a and 5a situated above the central piston 4 and above the annular piston 6, respectively.
• the central piston 4 and the annular piston 6 comprise an oil wiper 14 and an outer oil wiper 1 7, respectively.
• an inner oil wiper 1 6 has been positioned for the annular piston 6.
• the oil wipers 14, 1 6, 1 7 have the function of preventing supply of lubricating oil along the respective side walls of the pistons 4a, 6a to the respective spaces above the pistons 3a, 5a.
• the central piston 4 is connected to a crank pin 1 3 of the crankshaft 2 by means of a central piston drive rod 7.
• the annular cylinder 5 comprises an entrance opening 8 for a fuel/air mixture in which a (schematically shown) membrane inlet 9 is provided with membrane inlet valves.
• the central cylinder 3 is connected to the annular cylinder 5 by means of a number of passage openings 1 1 for the fuel/air mixture.
• the central cylinder 3 further comprises an exit opening 1 2 for combustion gases which is connected to a discharge conduit 1 5.
• Figure 2 shows a view in cross-section in a direction perpendicular to the crankshaft 2, of the two-stroke engine 1 shown in figure 1 .
• the crank pin 1 3 is accommodated in wall members 30, 31 of the crankshaft 2.
• the central piston 4 is connected to the central piston drive rod 7 by means of a traverse pin 40.
• the annular piston 6 is connected to traverse pins (big ends) 24, 25, respectively, of the crankshaft 2 by means of respective annular piston drive rods 22, 23.
• the traverse pins 24, 25, respectively, have been accommodated in wall members 32, 33, 34, 35, respectively, of the crankshaft 2.
• the annular piston 6 is connected to the respective annular piston drive rods 22, 23 by means of respective transverse pins 41 , 42.
• a lubricating system that is not further shown ensures pressurised lubricating from the engine crankcase, via bore holes in the crankshaft 2, of the crank drive rod mechanism, comparable to a four- stroke engine.
• the operation of the engine 1 is now as follows: during the downwardly oriented stroke of the annular piston 6 a mixture of fuel and air is sucked in via the entrance opening 8.
• the central piston 4 then moves upwards, the fuel/air mixture that is in the space 3a above the central piston 4 being compressed.
• the passage opening 1 1 for supply of the fuel/air mixture to the space 3a above the central cylinder 4 is closed off here by the side wall 4a of the central piston 4.
• the exit opening 1 2 for combustion gases is also closed off here.
• the two-stroke engine 1 has the advantage that mixed lubrication is not necessary because the fuel/air mixture does not come under the central piston 4 and/or under the annular piston 6. Thus, in comparison to the mixed lubrication, relatively little lubricating oil is combusted which renders the engine 1 particularly environmentally friendly.
• the two-stroke engine 1 may comprise several central cylinders 3, each having an accompanying annular cylinder 5.
• the top side of the exit opening 1 2 is situated more closely to the upper dead centre on the central cylinder 3 than the top sides of the passages 1 1 a, 1 1 b, 1 1 c and 1 1 d.
• the upper and lower dead centre on the central cylinder 3 are schematically shown in figure 3B by the dashed lines 50 and 51 , respectively.
• the orientations of the passages 1 1 a, 1 1 b, 1 1 c and 1 1 d for directing gas from the annular cylinder 5 into the central cylinder 3 are shown in figure 3C.
• the vertical orientation here corresponds to the orientation of the centre line of the central cylinder.
• the space 3a above the central piston 4 can be optimally "flushed" with the passages 1 1 a, 1 1 b, 1 1 c and 1 1 d with the accompanying orientations. At the start of each compression stroke (almost) no combustion gases will be present in the space 3a any longer.
• bushes 60, 61 arranged around the crankshaft 2, which bushes are connected in rotation with the crankshaft 2 by means of keyed connections 62, 63.
• the bushes 60, 61 can shift in axial direction with respect to the crankshaft 2 by means of drive pins 70, 71 , respectively.
• the bushes 60, 61 are provided with radially extending surfaces 64, 65, 66, 67, respectively, which form circumferential accommodation openings 68, 69 for accommodating the drive pins 70, 71 so as to be freely moveable in circumferential direction but confined in axial direction.
• the drive pins 70, 71 are arranged by means of screw connections 72, 73 on shaft 74 drivable by an engine 75. During rotation of the shaft 74 in a given direction, the drive pins 70, 71 will move towards each other or apart, depending on the rotation direction of the shaft 74, to move the bushes 60, 61 accordingly.
• the bushes 60, 61 have been provided with respective ends having internal teeth 80, 81 positioned inclined with respect to the axis of rotation, which teeth cooperate with the internal grooves 82, 83 of discs 90, 91 attached in the drive rods 22, 23, which discs perform a kind of crank pin function.
• By shifting the bushes 60, 61 in longitudinal direction the circumferential position of the discs 90, 91 with respect to the bushes 60, 61 is changed due to the cooperation of the teeth 80, 81 with the grooves 82, 83 of the discs 90, 91 .
• the circumferential position of the drive rod 7 of the central piston 4 is changed with respect to the circumferential position of the drive rods 22, 23 of the annular piston 6.
• the discs 90, 91 are accommodated in the drive rods 22, 23 by means of bearings 92, 93.
• the discs 90, 91 have been provided with openings 94, 95 eccentrically arranged therein for passage of the crankshaft 2. Due to this eccentricity the reciprocating motion of the drive rods 22, 23 is obtained.
• the engine 75 is controlled by a control unit 76.
• the rotational speed sensor 77 is provided for registering the rotational speed of the crankshaft 2, the rotational speed sensor 77 being coupled to the control unit 76.
• the control unit 76 can be programmed to control the drive 74 depending on the measured rotational speed, for changing the axial position of the bushes 60, 61 and thus the relative circumferential position of the crank pins and drive rods for the annular piston.
• Figure 5 shows the crankshaft 2, the drive rod 22, disc 90 and bush 60 in exploded view in perspective.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Lubrication Of Internal Combustion Engines (AREA)

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• 2002
  • 2002-05-28 WO PCT/NL2002/000339 patent/WO2002097246A1/en not_active Application Discontinuation
  • 2002-05-28 EP EP02736281A patent/EP1402159A1/de not_active Withdrawn

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