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(11) | EP 1 555 402 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Two-stroke internal combustion engine, in particular for portable tools such as power saws, bush cutters, etc... |
| (57) A two-stroke internal combustion engine, in particular for portable tools such as
power saws, bush cutters, etc., comprising a bed (2) in which for the reciprocating
piston (8) at least one chamber (44) is provided to which the mixture inlet port (20)
and the spent gas outlet port (30) are connected, characterised in that the spent
gas outlet port (30) is provided with a valve (32), the opening and closure of which
are controlled by the rotation of the piston crankshaft (16). |
[0001] This invention relates to a two-stroke internal combustion engine, in particular for portable tools such as power saws, bush cutters, etc.
[0002] Two-stroke engines are known comprising a bed on which a cylindrical seat for the reciprocating piston is applied, to which the inlet port for the mixture and the outlet port for the spent gas are connected.
[0003] However, these known engines present the drawback that during piston descent, the mixture passing through the transfer ports which connect together the two chambers separated by the piston can mix with the spent gas, with the result that on the one hand there is a decrease in efficiency and on the other hand atmospheric pollution due to the escape of unburnt mixture from the discharge port.
[0004] An object of the invention is to eliminate this drawback by providing a two-stroke internal combustion engine having high efficiency and low fuel consumption while at the same time not causing atmospheric pollution.
[0005] This and further objects which will be apparent from the ensuing description are attained according to the invention by a two-stroke internal combustion engine, in particular for portable tools such as power saws, bush cutters, etc. as described in claim 1.
[0006] The invention is further clarified hereinafter with reference to the accompanying drawings, in which:
- Figure 1
- is a longitudinal section through the engine of the invention with the piston rising towards its top dead centre,
- Figure 2
- shows it with the piston at its top dead centre,
- Figure 3
- shows it with the piston descending,
- Figure 4
- shows it with the piston at its bottom dead centre,
- Figure 5
- shows it with the piston again rising,
- Figure 6
- shows it in side view,
- Figure 7
- shows it in front view,
- Figure 8
- shows a variant thereof.
[0007] As can be seen from the figures, the internal combustion engine according to the invention comprises substantially a bed 2 provided with a cylindrical seat 6 presenting cooling fins 4 and within which there slides a piston 8 provided with a connecting rod 10 pivoted by a pin 12 to a crank 14.
[0008] The conduit 20 feeding the mixture from the carburettor and the electrodes 22 of the spark plug 26 lead into the cylindrical seat, which also presents a further aperture 28 connecting the cylindrical chamber to the conduit 30 for discharging the exhaust gas to a silencer (not shown in the drawings) via an interposed valve 32.
[0009] The valve 32 consists of a cylindrical body comprising a channel 34 of substantially rectangular cross-section with its axis perpendicular to the axis of the cylindrical body and rigid with a shaft 36, mounted on bearings 38, which engages by means of a taper fit a ring gear 40 connected by a belt 42 to a further ring gear 44 keyed onto the rotation shaft of the crank 14.
[0010] Specifically, the ring gear 40 has twice the number of teeth as the ring gear 44, so that one complete rotation of the crank 14 corresponds to one half of a rotation of the valve 32.
[0011] Moreover the two ring gears 40 and 44 are mutually coordinated such that when the piston lies in its bottom dead centre position, the channel 34 of the cylindrical body almost completely faces the discharge aperture 30.
[0012] The internal combustion engine operates in the following manner, with reference to Figures 1-5.
Figure 1: piston rising towards its top dead centre.
In this configuration the valve 32 closes the passage between the aperture 28 and
the conduit 30, the rising of the piston enabling the mixture to enter the chamber
44 through the conduit 20. During this phase the piston 8 closes the aperture of the
transfer ports 46 which connect the chamber 44 positioned below the aperture to the
chamber 48 facing the spark plug 26.
Figure 2: piston at its top dead centre.
The valve 32 again closes the passage, the conduit 20 is completely open and the mixture
completely fills the chamber 44. The spark between the electrodes 22 of the spark
plug 26 is generated to ignite the mixture contained in the chamber 48.
Figure 3: piston descending towards its bottom dead centre.
The piston 8 closes the conduit 20 and the valve 32 becomes positioned such that the
conduit 34 faces the aperture 28, to hence enable the spent gas to disperse towards
the conduit 30.
Figure 4: piston at its bottom dead centre.
The piston 8 closes the conduit 20 and the valve 32 begins to close the passage between
the aperture 28 and conduit 30. The transfer ports 46 are completely open so that
the mixture contained in the chamber 44 can pass, urged by the crank 14, into the
chamber 48.
Figure 5: piston begins to rise towards its top dead centre.
The valve 32 closes the passage between the aperture 28 and the conduit 30, the piston
8 again closes the conduit 20 and closes the transfer ports 46, and the mixture is
compressed in the chamber 48.
[0013] From the aforegoing it is apparent that the internal combustion engine according to the invention presents:
- a high efficiency due to the advance closure of the discharge, enabling the piston to more greatly compress the mixture, to hence improve combustion,
- reduced fuel consumption as the mixture passing through the transfer ports 46 is prevented from escaping from the discharge conduit entrained by the spent gas, seeing that the valve 32 closes the discharge conduit 30 before the piston 8 would have closed it, so considerably reducing environmental pollution.