Auxiliary carburation device in direct fuel injection engines

Abstract: An auxiliary carburation device in direct fuel injection engines, to be positioned in correspondence with a main duct (12) feeding air to the engine crankcase (10), a throttling member (38) being located in the main duct (12), comprising a block (13) containing at least one selective regulating element (15, 25) positioned in a connection duct (19, 20; 30) which is connected at one end to a vessel (14; 45, 51) containing a constant predeterminable amount of fuel and to a mixing air duct (23, 32), and at the other end to the main duct (12) feeding the crankcase (10).

Description: This invention relates to an auxiliary carburation device for direct fuel injection engines, as disclosed in EP-A-410355. In two-stroke engines, various arrangements or relative devices are known in which the fuel is fed directly into the cylinder, whereas only air is drawn into the main crankcase. In these known devices, on starting the engine under cold conditions at low rotational speed, ie below the engine self-sustaining speed, a considerable fuel quantity is required. The injection system encounters difficulty in supplying this considerable fuel quantity. The difficulties generally arise for the following reasons: when the engine is cold, considerable condensation takes place on the inner walls of the cylinder; the low rotational speed results in low turbulence and more difficult mixing; the formation of intermediate combustion products is hindered because of the low available time and low temperature, leading to direct injection difficulties. GB-A-607692 relates to a device comprising a selective regulating element which is located in a connection path and which controls the air-fuel mixture. The object of the present invention is to obviate the aforesaid drawbacks, particularly in two-stroke engines. This object is attained according to the present invention by an auxiliary carburation device for direct fuel injection engines according to claim 1. The characteristics and advantages of an auxiliary carburation device according to the present invention will be more apparent from the following detailed description given by way of example with reference to the accompanying schematic drawings, in which: Figure 1 is a cross-section through the device of the present invention; Figure 2 is a detail of a further embodiment of the device of Figure 1; and Figure 3 is a detail of yet a further embodiment of the device of Figure 1. Figure 1 shows an auxiliary carburation device 11 according to the invention for installation in direct fuel injection engines, to be fitted either to the engine cylinder head (not shown) or to a main duct 12 feeding air to the engine crankcase, partly shown at 10. The device comprises a block 13 containing regulating elements, and a fuel vessel 14, which can either be connected to the block 13 or form an integral part of it. In the illustrated embodiment the block 13 comprises a first regulating element 15, consisting for example of a piston 16 positioned in a relative seat 17 and operable by a rod 18. The rod 18 can either be connected to an electrical, pneumatic or thermal drive, or be manually operated from the outside, depending on the particular requirements. The piston 16 selectively interrupts or connects together two successive portions 19 and 20 of a connection duct which open on opposite sides of the seat 17. The portion 19 is connected to a fuel pipe 21 extending from the vessel 14, and the portion 20 is connected to the main duct 12 feeding the crankcase 10. Interposed between the pipe 21 and the duct portion 19 there is a mixing unit 22 connected to an air intake duct 23. The duct 23 feeds a predetermined mixing air volume to said mixing unit 22 via a sized nozzle 24. In the illustrated embodiment there is also a second regulating element 25, consisting for example of a piston 26 arranged in a relative seat 27 and operable by a rod 28. Again, the rod 28 can either be connected to an electrical, pneumatic or thermal drive, or be manually operated from the outside, depending on the particular requirements. The piston 26 contained in the seat 27 selectively interrupts or connects together a fuel pipe 29 and a connection duct 30 which open into opposite sides of the seat 27. The fuel pipe 29 is connected to the vessel 14 via a conical seal 31 and the connection duct 30 is connected to the main duct 12 feeding the engine crankcase 10. Into the seat 27 close to where the pipe 29 is connected, there opens an air intake duct 32 having at its other end a sized nozzle 33. The fuel pipes 21 and 29 are inserted into the vessel 14 and carry at their ends sized nozzles 34 through which the fuel flows at a regulated rate. The fuel is fed into the vessel 14, of the constant level type, via a pipe 35, at the end of which there is a valving element 36, for example in the form of a needle valve, controlled by a float 37 which adjusts the fuel flow to maintain a constant level within the vessel 14. Within the main feed duct 12 there is provided for example a throttle or regulating member 38 such as a butterfly valve, to selectively open the duct 12 to an extent depending on the output power to be generated. At that end of the main duct 12 facing the engine crankcase 10 there is provided a flap valve indicated schematically at 39, which opens in accordance with the vacuum generated in said crankcase 10, and in combination with the positioning of the throttle member enables a variable air quantity to be drawn into and compressed within the crankcase. The inclusion of at least one of said regulating elements 15 and/or 25 in the auxiliary carburation device of the present invention hence enables the feed to be effected for a determined time sufficient to overcome the initially stated problems of controlled-ignition two-stroke engines with direct fuel injection. Figure 2 shows an alternative embodiment of the auxiliary carburation device of the present invention, in which equal elements carry the same reference numerals. In this embodiment, instead of intercepting the connection duct towards the main duct by means of the piston, the regulating element is used to connect that connection duct portion 20 connected to the main duct 12 directly to atmosphere so that fuel is no longer drawn in. In this respect, into that portion 20 of the connection duct provided between the fuel pipe 21 and the main duct 12 there opens a further duct 40 connected to a cylinder 41 acting as a seat for a piston 42. The piston 42, operable by means of a rod 43, enables the further duct 40 to be connected to an exit duct 44, ie directly to atmosphere to interrupt the flow of fuel mixture to the main duct 12 because of the fall in pressure. This is because on connecting the main duct 12 to atmosphere downstream of the mixing unit 22, the pressure falls so preventing fuel intake. Figure 3 shows in detail a modified embodiment of the vessel to be associated with an auxiliary carburation device of the present invention. In this embodiment, instead of the vessel 14 of traditional constant level type, analogous devices provided for example with a membrane are used. Specifically, the fuel feed pipe 35 is connected to a first chamber 45, one wall 46 of which consists of a membrane on which atmospheric pressure acts. At the end of the first chamber 45 there are valves 47 and 48, for example of the one-way single direction type, which selectively connect the pipe 35 to a downstream pipe 49. The other end of the pipe 49 is closed by a valving element 50 which is contained in a second chamber 51, one wall 52 of which also consists of a membrane on which atmospheric pressure acts. In the example, the valving element 50 consists of a needle valve maintained in position within the end of the pipe 49 by the combined action of the second wall or membrane 52 and a spring 53 which opposes atmospheric pressure. A further pipe piece 54 connects the chamber 51 to the fuel feed pipe, for example 21, by way of a sized nozzle 55.

Claims: An auxiliary carburation device for direct fuel injection two-stroke engines, to be positioned in correspondence with a main duct (12), feeding air to the engine crankcase (10), wherein a throttling member (38) is located in said main duct (12), comprising a block (13) with a connection duct (19, 20; 30) which is connected at one end to a fuel vessel (14; 45, 51) containing a constant predeterminable amount of fuel and to a mixing air duct (23, 32), and at the other end to said main duct (12) feeding the crankcase (10) of the engine characterised in that at least one selective regulating element (15, 25) is positioned in said connection duct (19, 20; 30) and consists of a seat (17, 27) intercepting said connection duct (19, 20; 30) and housing a piston (16, 26) operable from the outside (18, 28), and in that upstream of at least one of said regulating element (15) there is provided a mixing unit (22) connected to said air duct (23) and to an exit pipe (21) from said fuel-containing vessel (14; 45, 51). A device as claimed in claim 1, characterised in that a sized nozzle (24, 33) is provided in said air duct (23, 32). A device as claimed in claim 1, characterised in that said air duct (32) and an exit pipe (29) from said fuel-containing vessel (14; 45, 51) are connected to one end of said seat (27). A device as claimed in claim 1, characterised in that at least one of said regulating element (15) consists of a seat (41) housing a piston (42) operable from the outside (43) to intercept a further duct (40, 44) connected at one end to said connection duct (20) and at its other end to atmosphere. A device as claimed in claim 1, characterised in that said vessel is of the type comprising a float (37) controlling a valving element (36) for a pipe (35) feeding fuel into the vessel. A device as claimed in claim 1, characterised in that said vessel is of the type comprising at least one membrane (46, 52) controlling a valving element (50) for a pipe feeding fuel into the vessel.

Inventors: NUTI MARCO, NUTI, MARCO
Applicants: PIAGGIO VEICOLI EUROP, PIAGGIO VEICOLI EUROPEI S.P.A.
Application year: 1993
Main classification: F02M1
IPC codes: F02M17, F02M1, F02M71