High-speed, port-controlled, two-stroke internal combustion engine with crankcase scavenging
FIELD OF USE 
     The internal combustion engine according to the invention can be used whenever a high-speed, port-controlled, two-stroke internal combustion engine with crankcase scavenging is used as a high-performance motor, e.g. as a two-wheel drive, or as a choke motor, e.g. as a chain saw drive. 
     PRIOR ART 
     An internal combustion engine, particularly a high-speed, port-controlled, two-stroke internal combustion engine with crankcase scavenging is known from DAS No. 2,624,249. 
     Attempts have been made in connection with such an internal combustion engine to reduce the idling noise by modifying the outlet port geometry. Apart from the conventional outlet, additional auxiliary openings were provided and these and the outlet port were arranged in such a way that they satisfied given mathematical conditions. However, the known construction of the outlet port geometry for reducing noise has not proved satisfactory, because the greatest noise formation in the case of such two-stroke internal combustion engines occurs under full load and when idling, when the engine is operating at full speed, but without loading. 
     Attempts have also been made by using secondary measure to reduce the running noise of the engine. However, this led to disadvantageous effects on the performance or fuel consumption behaviour of the engines. 
     PROBLEMS, SOLUTION, ADVANTAGES 
     The present invention aims at providing a high-speed, port-controlled, two-stroke internal combustion engine in which, through a suitable construction of the inlet port geometry and/or outlet port geometry, it is ensured that the engine noise is reduced throughout its speed range, whilst maintaining the performance level and whilst simultaneously improving the specific fuel consumption. 
     Thus, to solve this problem, the invention provides a high-speed, port-controlled, two-stroke internal combustion engine with crankcase scavenging with at least one cylinder with in each case at least one suction duct with an inlet port, with in each case at least one outlet duct with an outlet port and with at least one scavenging duct with a transfer port, the inlet, outlet and transfer ports being located on the inside of the cylinder, characterized in that 
     (a) the suction duct of the cylinder 
     (a1) on the carburretor side mixed inflow side has a substantially rectangular cross-section with an upper port boundary at right angles to the cylinder longitudinal axis and a lower port boundary at right angles to the cylinder longitudinal axis, as well as lateral port boundaries approximately parallel to the cylinder longitudinal axis, the cross-section being increased over and beyond the lower port boundary in the vicinity of the vertical median plane, 
     (a2) a suction port cross-sectional profile on the inside of the cylinder and comprising a pre-inlet part and a post-inlet part upwardly following onto the latter in the cylinder longitudinal direction and having in the vicinity of the post-inlet part a substantially rectangular cross-section with a generally V-shaped channel in the vicinity of the vertical median plane and with upper port boundaries at right angles to the cylinder longitudinal axis and with lower port boundaries at right angles to the cylinder longitudinal axis, as well as lateral port boundaries running approximately parallel to the cylinder longitudinal axis and with a cross-section in the form of a geometrical shape in the vicinity of the pre-inlet part, 
     (a3) a cross-sectional profile emanating from the inflow cross-section in the flow direction and which remains constant in its horizontal extension or uniformly decreases and having a generally V-shaped channel uniformly growing in the flow direction and extending in the region of the vertical median plane, and 
     (a4) a cross-sectional profile emanating from the inflow cross-section in the flow direction and which uniformly varies in its vertical extension, and/or that 
     (b) the outlet duct of the cylinder 
     (b1) on the silencer side exhaust gas outflow side has a substantially rectangular cross-section with an upper port boundary running at right angles to the cylinder longitudinal axis and a lower port boundary running at right angles to the cylinder longitudinal axis, as well as with lateral port boundaries running approximately parallel to the cylinder longitudinal axis, the cross-section being widened over and beyond the upper port boundary roughly in the vicinity of the horizontal median plane, 
     (b2) an outlet port cross-sectional profile on the inside of the cylinder comprising a pre-inlet part and a post-inlet part following onto the bottom of the pre-outlet part in the cylinder longitudinal axis and having in the vicinity of the post-outlet part a substantially ellipsoidal cross-section with a pitch circle-shaped upper port boundary and with a pitch circle-shaped lower port boundary and with pitch circle-shaped or straight port boundaries and with a cross-section in the form of a geometrical shape in the region of the pre-outlet part, 
     (b3) a cross-sectional profile emanating from the outlet cross-sectional profile in the flow direction and which remains constant in its horizontal extension, or which uniformly decreases, 
     (b4) a cross-sectional profile emanating from the outlet cross-sectional profile in the flow direction and which varies in its vertical extension. 
     In the case of a high-speed, port-controlled, two-stroke internal combustion engine with crankcase scavenging constructed in this way, it is achieved as a result of the particular construction of the geometry of the inlet duct or outlet duct or the combination of such inlet and outlet ducts in the cylinder, that during the upward and downward movements of the piston in the cylinder as a result of a gradual opening of the particular suction and outlet ports, the noise-producing suction pipe and outlet pressure gradients and amplitudes are reduced. On the inlet side, there is an additional deflection for the propagating airborne sound directed counter to the inflow process until the actual suction pipe/carburettor connection cross-section is reached, which leads to a further noise reduction. Furthermore, and of particular importance with respect to the desired noise reduction of the working and operating noise of the internal combustion engine, on the outlet side where the propagation direction of the sound and/or pressure waves coincides with the direction of the outflowing exhaust gas, there is also an additional deflection until the actual bend/silencer connection cross-section is reached. This additional deflection of the sound and/or pressure waves on the outlet side has an even more pronounced effect than on the inlet side due to the greater excitation in the pre-outlet phase, so that the noise reduction is of a considerable nature. Thus, through the new design of the geometry of the inlet port, together with that of the suction duct connected upstream of said inlet port, as well as the new construction design of the geometry of the outlet port, together with that of the downstream-connected outlet duct and particularly the combination thereof, leads to a considerable reduction in noise in the entire speed range of the port-controlled, two-stroke internal combustion engine, so that as a result of these measures on the primary side of noise production, the use of secondary measures is rendered superfluous. 
    
    
     DEVELOPMENT OF THE INVENTION 
     Further advantageous developments of the invention can be gathered from the subclaims. 
     Embodiments are described relative to the drawings, wherein show: 
     FIG. 1 a two-stroke cylinder with the suction and outlet ducts according to the invention in a vertical sectional view. 
     FIG. 2 a two-stroke cylinder in a partial view in a vertical sectional representation turned by 90° compared with FIG. 1. 
     FIG. 3a the suction duct of the cylinder according to FIG. 1 in a side view in vertical sectional form. 
     FIG. 3b the suction duct of FIG. 3a in a view of the cylinder inside in cutaway form. 
     FIG. 3c the suction duct according to FIG. 3a in a view of the cylinder outside in cutaway form. 
     FIG. 4a the outlet duct of the cylinder according to FIG. 1 in a side view in vertical sectional representation. 
     FIG. 4b the outlet duct according to FIG. 4a in a view of the cylinder outside in cutaway form. 
     FIG. 4c the outlet duct according to FIG. 4a in a view of the cylinder outside in cutaway form. 
     FIG. 5a another embodiment of a suction duct of the cylinder in side view and vertical sectional form. 
     FIG. 5b the suction duct of FIG. 5a in a view of the cylinder inside in cutaway form. 
     FIG. 5c the suction duct of FIG. 5a in a view of the cylinder outside in cutaway form. 
     FIG. 6a a further embodiment of the outlet duct of the cylinder in side view in vertical sectional form. 
     FIG. 6b the outlet duct according to FIG. 6a in a view of the cylinder inside in cutaway form. 
     FIG. 6c the outlet duct of FIG. 6a in a view of the cylinder outside in a cutaway form. 
     FIGS. 7a to 7c a further embodiment of the cylinder outlet duct in side view in vertical sectional representation, in a view of the cylinder inside and a view of the cylinder outside in cutaway forms. 
     FIGS. 8a to 8c a further embodiment of the cylinder outlet duct in side view in vertical sectional representation, in a view of the cylinder inside and a view of the cylinder outside in cutaway forms. 
     FIGS. 9a to 9c a further embodiment of the cylinder outlet duct in side view in vertical sectional representation, in a view of the cylinder inside and a view of the cylinder outside in cutaway forms. 
     FIGS. 10a to 10c a further embodiment of the cylinder outlet duct in side view in vertical sectional representation, in a view of the cylinder inside and a view of the cylinder outside in cutaway forms. 
     FIGS. 11a to 11c a further embodiment of the cylinder outlet duct in side view in vertical sectional representation, in a view of the cylinder inside and a view of the cylinder outside in cutaway forms. 
     FIGS. 12a to 12c a further embodiment of the cylinder outlet duct in side view in vertical sectional representation, in a view of the cylinder inside and a view of the cylinder outside in cutaway forms. 
     FIGS. 13a to 13c a further embodiment of the cylinder outlet duct in side view in vertical sectional representation, in a view of the cylinder inside and a view of the cylinder outside in cutaway forms. 
     FIGS. 14a to 14c a further embodiment of the cylinder outlet duct in side view in vertical sectional representation, in a view of the cylinder inside and a view of the cylinder outside in cutaway forms. 
     FIGS. 15a to 15c a further embodiment of the cylinder outlet duct in side view in vertical sectional representation, in a view of the cylinder inside and a view of the cylinder outside in cutaway forms. 
    
    
     BEST WAY FOR REALISING THE INVENTION 
     FIGS. 1 and 2 show in longitudinal sectional form a two-stroke internal combustion engine cylinder, which is normally mounted on the top of a crankcase. The suction and outlet ports are placed in one sectional plane to make clear the associated port configuration, the suction port of suction duct 4 placed in the drawing plane only being shown in broken line form. Piston 2, shown in broken line form, works within cylinder 1 and during its upward and downward stroke passes over the suction port of suction duct 4, the outlet port of outlet duct 6 and the transfer ports of scavenging ducts 5. 3 is the combustion chamber provided in the head of cylinder 1 and 10 is the cylinder longitudinal axis. 
     Suction duct 4 of cylinder 1 is then so constructed on cylinder inside ZS that, with respect to the upward movement of piston 2 in cylinder 1, it is subdivided into a pre-inlet part VE and a post-inlet part NE, as shown in FIGS. 3a ad 3c. The post-inlet part NE with a substantially rectangular cross-section is provided on the cylinder inside ZS with a generally V-shaped channel K running in the vicinity of the vertical median plane M, which can also be referred to as a piston deflection projection and which is bounded by the upper port boundaries 34a, 34b at right angles to cylinder longitudinal axis 10, the lower port boundaries 35a, 35b at right angles to the cylinder longitudinal axis 10 and the lateral port boundaries 36, 37 approximately parallel to cylinder longitudinal axis 10. The pre-inlet part following on at the bottom in the cylinder longitudinal direction and whose cross-section together with the cross-section of the post-inlet part on the cylinder inlet side is referred to as the suction port cross-sectional profile ES, has a cross-section in the form of a geometrical shape E and which is formed by an approximately V-shaped opening VO and the longitudinal slot 39 following on at the bottom in the cylinder longitudinal direction. Longitudinal slot 39 is so constructed through its ramp-like, bottom boundary surface 139 rising from the cylinder inside ZS to the mixed inflow side GE, that the cross-sectional surface formed by it is constructed so as to decrease to zero from the cylinder inside ZS to the mixed inflow side GE. The generally V-shaped opening cross-section VO on the cylinder inside ZS bounded by the port boundaries 38a, 38b which are at an angle to one another and to the cylinder longitudinal axis 10 is constructed so as to widen and flatten from the cylinder inside ZS to the mixed inflow side GE, so that on the latter the crescent-shaped cross-sectional profile VO&#39; formed by the pitch circle-shaped boundary line 38c is constructed. The cross-sectional profile VO&#39; supplements the substantially rectangular cross-section EG to give the total cross-section, the rectangular cross-section EG being bounded by the upper port boundary 30 at right angles to cylinder longitudinal axis 10 and the lower port boundary 31a, 31b at right angles to the cylinder longitudinal axis 10, as well as the lateral port boundaries 32, 33 approximately parallel to cylinder longitudinal axis 10. 
     The outlet duct 6 of cylinder 1 shown in FIGS. 4a to 4c is constructed on the silencer side exhaust gas outflow side AA with a substantially rectangular cross-section AG, which is bounded by the upper port boundaries 40a, 40b running at right angles to the cylinder longitudinal axis 10, the lower port boundary 41 running at right angles to the cylinder longitudinal axis 10 and the lateral port boundaries 42, 43 running approximately parallel to the cylinder longitudinal axis 10, it being widened in groove-like manner over and beyond the upper port boundary 40a, 40b on the exhaust gas outflow side AA, roughly in the vicinity of the horizontal median plane M. With respect to the downward movement of the piston, the suction duct 6 of cylinder 1 is so constructed on the cylinder inside ZS, that it is subdivided into a pre-outlet part VA and a post-outlet part NA, whose cross-sectional openings together form the outlet slot cross-sectional profile AS. The post-outlet part NA is constructed with an ellipsoidal cross-section, which is bounded by the pitch circle-shaped upper port boundaries 44a, 44b and the pitch circle-shaped lower port boundary 45, as well as the pitch circle-shaped lateral port boundaries 46, 47. The cross-section constructed as a geometrical shape GA in the vicinity of the pre-outlet part VA is constructed as a V-shaped opening cross-section VO bounded by the port boundary 48a, 48b, to which the longitudinal slot 49 is connected at the top parallel to the cylinder longitudinal axis 10. The longitudinal slot cover surface 49a bounding the longitudinal slot at the top and which extends from the cylinder inside ZS to the suction outflow side AA, is constructed so as to fall away in ramp-like manner from cylinder inside ZS to the exhaust gas outflow side AA. The V-shaped opening cross-section VO formed by the port boundaries 48a, 48b and extending from the cylinder inside ZS to the exhaust gas outflow side AA is constructed in such a way from the cylinder inside ZS to the exhaust gas outflow side that its cross-section reduces. The total cross-sectional profile of outlet duct 6 of cylinder 1 is based on the outlet cross-sectional profile and widens from the cylinder inside ZS to the exhaust gas outflow side AA in diffuser-like manner to a substantially rectangular cross-section AG on the silencer side exhaust gas outflow side AA. 
     In the case of the suction duct 4 of cylinder 1 shown in FIGS. 5a to 5c, compared with the embodiment of FIGS. 3a to 3c, the cross-section constructed as a geometrical shape E in the vicinity of the pre-inlet part VE is constructed as a rectangular cross-section RE bounded by the port boundaries 138a, 138b, 138c. The bottom boundary surface 238 of the rectangular cross-section RE is constructed so as to rise from the cylinder inside ZS to the mixture inflow side GE, the area 238a positioned adjacent to the cylinder inside ZS has a more pronounced slope with respect to the cylinder longitudinal axis 10 than the area 238b positioned adjacent to the mixture inflow side GE. The total flow cross-section of suction duct 4 starting from the inflow cross-section EG in this case is made constant in its horizontal extension from the mixture inflow side GE to the cylinder inside ZS, whilst only changing to a limited extent in its horizontal extension. 
     FIGS. 6a to 6c show another embodiment of the outlet duct 6 of cylinder 1 in which, compared with the embodiment of FIGS. 4a to 4c, the V-shaped opening cross-section VO, which is bounded by port boundaries 68a, 68b, has a constant cross-section from the cylinder inside ZS to the exhaust gas outflow side AA and the longitudinal slot 69 has a longitudinal slot cover surface 69a bounding it at the top and which comprises area 69b, 69c having a different slope relative to the cylinder longitudinal axis 10. The embodiment of the outlet duct 6 of cylinder 1 shown in FIGS. 7a to 7c differs from that according to FIGS. 6a to 6c by a larger V-shaped opening cross-section VO, because the port boundaries 78a, 78b bounding the latter have a larger angle to one another and to the cylinder longitudinal axis 10. The overall flow cross-section of outlet duct 6 of cylinder 1 in the embodiments of FIGS. 6a and 7a increases from the cylinder inside ZS to the exhaust gas outflow side AA, there being only a slight increase in the horizontal extension. The V-shaped cross-sectional enlargement formed in the embodiment according to FIGS. 4a to 4c in the transition area from the pre-outlet area VA to the post-outlet area NA and which only extends in the area of outlet channel 6 adjacent to the cylinder inside ZS and which decreases with respect to the cross-sectional surface of the cross-sectional enlargement VU, is missing in the embodiments according to FIGS. 6a to 6c and 7a to 7c, as well as in the embodiments according to FIGS. 10a to 10c. 
     In the embodiment of the outlet duct 6 of cylinder 1 shown in FIG. 8, the substantially ellipsoidal cross-section is laterally bounded by the straight, lateral port boundaries 86,87 in the vicinity of the post-outlet part NA, as compared with the embodiment according to FIGS. 4a to 4c. 
     The further embodiment of the outlet duct 6 of cylinder 1 shown in FIGS. 9a to 9c is constructed in the vicinity of the longitudinal slot 99 arranged in the pre-outlet part with a further rectangular longitudinal slot 199 connected at the top in the cylinder longitudinal direction to longitudinal slot 99. The longitudinal slot cover surface bounding longitudinal slot 199 and longitudinal slot 99 at the top has a more pronounced inclination to the cylinder longitudinal axis 10 in the area 99b towards the cylinder inside ZS than in the area 99c towards the exhaust gas of FIG. 9, the substantially ellipsoidal cross-section of the post-outlet part is once again bounded by straight, lateral port boundaries 96, 97. 
     The further embodiment of outlet duct 6 of cylinder 1 shown in FIGS. 10a to 10c is similar to that of FIGS. 6a to 6c but, in the vicinity of the pre-outlet part, the embodiment of FIGS. 10a to 10c has a longitudinal slot 109, whereof the cover surface bounding the latter at the top and which extends from the cylinder inside ZS to the exhaust gas outflow side AA initially drops away in ramplike manner when starting from the cylinder inside ZS and has a constant inclination in the further area adjacent to the outflow side AA. The further embodiment of outlet duct 6 of cylinder 1 shown in FIGS. 11a to 11c, compared with that of FIGS. 4a to 4c, is provided with a generally V-shaped cross-sectional enlargement VU, which has a different angle of inclination over its course and this angle can in fact change a number of times over the same. The overall cross-section of outlet channel 6 of cylinder 1 in the embodiment of FIGS. 11a to 11c is constructed in such a way that it increases in diffuser-like manner from the cylinder inside ZS to the exhaust gas outflow side AA, whereby the cross-section AG of outlet duct 6 approximately has 3 times the cross-sectional surface in the vicinity of the exhaust gas outflow side AA compared with that of the outlet port cross-sectional profile AS. 
     In the case of the embodiment of outlet port 6 of cylinder 1 shown in FIGS. 12a to 12c in the transition area from the pre-outlet area VA to the post-outlet area NA, there is a generally V-shaped cross-sectional enlargement VU in the cylinder longitudinal direction in the vicinity of the horizontal median plane M. 
     The embodiments according to FIGS. 13a to 13c and 14a to 14c are so constructed compared with that according to FIGS. 12a to 12c that the flow cross-section of outlet channel 6 of cylinder 1 increases in diffuser-like manner from cylinder inside ZS to the exhaust gas outflow side AA in such a way that the cross-section AG of outlet channel 6 in the vicinity of the exhaust gas outflow side AA has approximately 3 times the cross-sectional surface of the outflow slot cross-sectional profile AS. The difference between these embodiments relates to the different longitudinal dimensioning of the straight, lateral port boundaries 146, 147 in FIG. 14c compared with the straight, lateral port boundaries 166,167 of FIG. 14b bounding the post-outlet part with respect to its ellipsoidal cross-section. 
     The outlet duct 6 of cylinder 1 shown in FIGS. 15a to 15c is constructed on the silencer side exhaust gas outflow side AA with a substantially rectangular cross-section AG, which is bounded by the upper port boundaries 40a, 40b at right angles to the cylinder longitudinal axis 10, the lower port boundary 41 at right angles to the cylinder longitudinal axis 10 and the lateral port boundaries 42, 43 approximately parallel to the cylinder longitudinal axis 10. With respect to the downward movement of the piston, the suction duct 6 of cylinder 1 is so constructed on the cylinder inside ZS, that it is subdivided into a pre-outlet part VA and post-outlet part NA, whose cross-sectional openings together form the outlet port cross-sectional profile AS. The post-outlet part NA is constructed with an ellipsoidal cross-section, which is bounded by the pitch circle-shaped upper port boundaries 44a, 44b, the pitch circle-shaped lower port boundary 45 and the pitch circle-shaped lateral boundaries 46, 47. The cross-section constructed as a geometrical shape GA in the vicinity of pre-outlet part VA is constructed as a V-shaped opening cross-section VO bounded by the port boundaries 48a, 48b and to which is connected at the top and parallel to cylinder longitudinal axis 10 the longitudinal slot 49. The longitudinal slot cover surface 49a, which bounds the slot at the top and which extends from the cylinder inside ZS to the exhaust gas outflow side AA, is constructed so as to fall away in ramp-like manner from cylinder inside ZS to exhaust gas outflow side AA. The V-shaped opening cross-section formed by port boundaries 48a, 48b and which extends from the cylinder inside ZS to the exhaust gas outflow side AA, is so constructed from ZS to AA that its cross-section is reduced. The overall cross-sectional profile of outlet channel 6 of cylinder 1 is based on the outlet cross-sectional profile and widens from the cylinder inside ZS to the exhaust gas outflow side AA in diffuser-like manner to the substantially rectangular cross-section AG on the silencer side exhaust gas outflow side AA. In the transition area from the pre-outlet area VA to the post-outlet area NA in the vicinity of the horizontal median plane M in the longitudinal direction of the cylinder, there is a generally V-shaped, cross-sectional enlargement VU and which is larger than in the embodiment according to FIGS. 4a to 4c.