DESC:TECHNICAL FIELD
[0001] The present subject matter relates generally to an evaporative emission control system for an automobile. More particularly, the present subject matter relates to a carburetor for an internal combustion engine of the evaporative emission control system.
BACKGROUND
[0002] In recent times, there has been an increasing demand to control evaporative emissions from automobiles, for example from two wheeled motorcycles including scooter type motorcycles, in view of the stringent environmental norms. Therefore, in order to control evaporative emissions, an evaporative emission control device, commonly referred to as canister is being increasingly used. Use of a canister aids in controlling evaporative emissions. The canister also enables reuse of the evaporated fuel without releasing it to the atmosphere.
[0003] Activated carbon, a major constituent of the canister plays an important role in controlling evaporative emissions. Activated carbon has a tendency to adsorb and store more amount of evaporated fuel when cooled, and desorbs the evaporated fuel easily when warmed up. Thus, temperature at which the canister is maintained is important from the point of view of efficient performance of the canister. Moreover, it is important to ensure that hoses emerging from the canister are securely routed so that probability of snapping of the hoses is minimized.

BRIEF DESCRIPTION OF THE DRAWINGS
[0001] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components.
[0002] Fig. 1 illustrates a right side view of a saddle-ride type vehicle as an example, in accordance with an embodiment of the present subject matter.
[0003] Fig. 2 illustrates a detailed sectional view of an internal combustion engine, in accordance with an embodiment of the present subject matter.
[0004] Fig. 3 illustrates a schematic representation of an evaporative emission control system, in accordance with an embodiment of the present subject matter.
[0005] Fig. 4 illustrates a schematic representation of an evaporative emission control device, in accordance with an embodiment of the present subject matter.
[0006] Figs. 5 (a), 5 (b), and 5 (c) illustrates a sectional view(s) of a carburetor of the evaporative emission control system illustrated in Fig. 3, in accordance with an embodiment of the present subject matter.
[0007] Figs. 6 (a) and 6 (b)illustrate a perspective view and a sectional elevation of a piston valve of the carburetor depicted in Fig. 5, in accordance to an embodiment of the present subject matter.
[0008] Fig. 7 illustrates a characteristic graph depicting the variation of air-fuel mixture purged through the carburetor depicted in Fig. 5 at idle, low, and high engine speed, in accordance to an embodiment of the present subject matter.

DETAILED DESCRIPTION
[0009] Typically, in two-and three-wheeled vehicles, the carbon vapor canister acts as an essential part in the evaporative emission control system. For instance, the layout constraint in case of such two-wheeled vehicles. Generally, the fuel vapor generated in a fuel tank of the two-wheeled vehicle is tapped and passed to the carbon vapor canister through a discharge tube. Such vapors tend to be adsorbed in the carbon inside the canister. The adsorbed vapors are in turn sent to a throttle body or carburetor of the induction system of an IC engine of the two-wheeled vehicle, by a purging action. Typically, the carbon vapor canister is positioned in such a manner that it is protected from environmental disturbances and that its core functionality is not affected under any circumstances.
[00010] Generally, evaporative emissions collected in the canister of the evaporative emission control system have to be purged into an intake system of the internal combustion engine. For instance, direct purging into the intake system of the internal combustion engine can lead to erratic behavior and performance characteristics change in the engine. Hence, it is a general practice to introduce such emission vapors from the canister through a carburetor of the intake system. Typically, vapor emission that passes through a purge control valve of the evaporative emission control system is allowed to enter the carburetor through a purge port.
[00011] The presence of vacuum or negative pressure in carburetor enables drawing up of fuel vapor-air mixture from the canister. Vacuum is felt more in conditions such as engine idle. In the existing carburetor design, the purge port is provided on the cylindrical surface of the carburetor body. A piston valve, which is movably disposed inside the carburetor body has a slit on one side, which enables the piston valve to slide inside a hollow carburetor cavity. For instance, the slit also enable locating the piston valve and helps in avoiding the rotation of the piston valve inside the carburetor cavity. It also allows the passage of the throttle cable.
[00012] The piston valve has a recess groove on a surface that is opposite to the surface having the slit. The recess groove on the piston valve is provided for idle throttle adjustment. For instance, the recess groove on the piston valve allows an idle adjustment screw to travel horizontally.
[00013] Generally during idle condition, the vacuum inside the carburetor is high, which communicates with the purge port through the recess groove. For instance, a clearance is formed between the piston valve that is disposed in the hollow cavity on the carburetor body and an inner wall of the carburetor body. This clearance allows the vacuum, during idle condition, to communicate with the purge port through the recess groove.
[00014] Thus, purging of the fuel vapor from the canister is caused during engine idle condition, which has an adverse effect on the engine performance and engine characteristics. Therefore, there is a need to prevent purging of fuel vapor from the canister during engine idle and/or low speed conditions. For instance, purging during engine idle condition will disturb idle air-fuel ratio, which is generally rich, for example, around 13.5. Further, purging may also lead to more emissions, by leaning the air-fuel ratio. Moreover, if the air fuel ratio is affected, the engine may start to behave in an erratic manner that may lead to certain unwanted phenomenon, such as jerk.
[00015] The present subject matter provides an evaporative emission control system.The present subject matter more particularly describes a carburetor for the evaporative emission control system for an automobile.
[00016] The present subject matter provides a carburetor having a piston valve that is provided with one or more holes on a surface that is facing the cylindrical surface of the carburetor that receive the purge port. The one or more holes on the surface of the piston valve enable relieving of vacuum formed in the carburetor during engine idle/low speed conditions. In an embodiment, the vacuum formed in the carburetor, which otherwise would have communicated to the purge port through the recess groove of the piston valve and the clearance formed between the piston valve and the inner wall of the carburetor main body, is relieved by the one or more holes. Thus, the one or more holes do not allow the vacuum developed within the carburetor chamber during engine idle/low speed conditions to communicate to the purge port.
[00017] In an embodiment, the one or more holes include a primary hole, and one or more secondary holes. In an embodiment, the primary hole is vertically in line with respect to the recess groove. In one embodiment, the one or more secondary holes are not necessarily vertically in line with respect to the recess groove.
[00018] These and other advantages of the present subject matter would be described in greater detail in conjunction with the figures in the following description.
[00019] Fig. 1 illustrates a right side view of a saddle-ride type vehicle (100), in accordance with an embodiment of the present subject matter. In an embodiment, the saddle-ride type vehicle (100) of the present subject matter includes an internal combustion engine (101). The vehicle further includes a front wheel (110), a rear wheel (103), a body frame, a fuel tank (107) and seat (106). Body frame includes a head pipe (111), a main tube (112), a down tube (113), and seat rails (not shown). The head pipe (111) supports a steering shaft (not shown) with two brackets – upper bracket and lower bracket at each end. Two telescopic front suspension (114) is attached to the lower bracket on which is supported the front wheel (110). The upper portion of the front wheel (110) is covered by a front fender (115) mounted to the lower portion of a front fork at the end of the steering shaft. A handlebar assembly (108) is fixed to upper bracket and can rotate to both sides. A headlamp assembly (109) is arranged on an upper portion of the front fork. A down tube (113) is located in front of the engine (101) and stretches slantingly downward from head pipe (111). A bracket (116) is provided at the lower end of down tube (113) for supporting the internal combustion engine (101). Main tube (112) is located above the engine and stretches rearward from head pipe (111) and connects the rear of the engine. A seat supporting structure (117) is joined to the rear end of the main tube (112) and stretches rearward from the point where the main tube joins the seat rails (not shown). The seat supporting structure (117) are also called as seat rails, which are joined to the main tube (112) and stretching rearward to support a seat assembly (106) disposed above these seat rails (117). Left and right rear swing arm bracket portions (not shown) support a rear swing arm (not shown) to swing vertically, and a rear wheel (103) is connected to rear end of the rear swing arm. Generally, two rear wheel suspensions (102) are arranged between rear swing arm. A tail lamp assembly (104) is disposed on the rear cover. A grab rail (105) is also provided on the rear of the seat rails. Rear wheel (103) is arranged below seat assembly (106) and rotates by the driving force of the internal combustion engine (101) transmitted through a chain drive (118) from the engine (101).
[00020] Fig. 2 illustrates a detailed sectional view of an internal combustion engine (200), in accordance with an embodiment of the present subject matter.The engine (200) includes a crankcase (224); a cylinder block (218) coupled to the crankcase (224), and a cylinder head (202) mounted on the cylinder block (218). For example, the cylinder head (202) is coupled to an upper portion of the cylinder block (218). The cylinder block (218) has a centrally formed cylinder bore (220) allowing a reciprocating piston (216) to move slidably within the cylinder bore (220). The piston (216) is connected to a crankshaft (226) through a connecting rod (222). The crankshaft (226) is rotatably supported by the crankcase (224). Further, whenever the cylinder block (218) is vertically oriented and disposed in such a way that the long axis of the cylinder block (218) is approximately perpendicular to the longitudinal axis of the crankshaft (226). However, the concepts disclosed herein are equally applicable on a horizontal engine where the cylinder block (218) is forwardly tilted. Moreover, the cylinder head (202) includes at least two ports, namely a first port (210) and a second port (212) that communicates with a combustion chamber (214) formed by being surrounded by the cylinder bore (220), the cylinder head (202) and the piston (216). The second port (212) allows the air-fuel mixture to enter the combustion chamber (214). After the mixture is combusted, the exhaust gases are taken out of the combustion chamber (214) through the first port (210). Furthermore, in order to facilitate the entry of air-fuel mixture into the combustion chamber through the second port and the exit of exhaust gases from the combustion chamber through the first port, a valve train having a plurality of valves is provided in the cylinder head (202). A first valve (206) is provided at the combustion chamber side opening of the first port (210) whereas a second valve (208) is provided at the combustion chamber side opening of the second port (212). The valves (206), (208) in the valve train are driven by a camshaft (204) rotatably supported in the cylinder head (202). For instance, the rotational energy is transmitted from the crankshaft (226) to the camshaft (204) by a timing transmission means (not shown). In an embodiment, the timing transmission means includes a drive sprocket supported on the crankshaft (226), a driven sprocket supported on the camshaft (204) and an endless cam chain connecting the drive sprocket with the driven sprocket.
[00021] Further, in an embodiment, a spark plug (not shown) that enables ignition of the engine (200) is assembled in the cylinder head (202). The camshaft (204) enables driving of a rocker arm. In one embodiment, the valves (206), (208) enable entry and exit of air/fuel mixture and exhaust gas respectively. In an embodiment, a carburettor assembly (not shown) helps in increasing charge motion and fuel economy. For instance, an actuating mechanism is assembled in the carburettor. An intake pipe (not shown) connects the carburettor to the cylinder head (202) and allows charge to reach the cylinder head (202) through a plurality of ports (210), (212).
[00022] Fig. 3 illustrates a schematic representation of an evaporative emission control system (300), in accordance with an embodiment of the present subject matter. In an embodiment, the evaporative emission control system (300) includes a fuel tank (302) and an evaporative emission control device, for example, a canister (306) that is functionally coupled to the fuel tank (302). In an embodiment, the canister (306) receives fuel vapors from the fuel tank (302) through a tank port (308). In an embodiment, the canister (306) further includes a canister purge port (314) disposed adjoining the tank port (308). The canister purge port (314) carries the fuel vapors adsorbed by the canister (306) to an intake system of the engine (200). In an embodiment, the canister (306) further includes an atmospheric port (318), through which atmospheric air is drawn into the canister (306) is disposed at a side that is opposite to that of the canister purge port (314). In an embodiment, the canister (306) also includes a drain port (316) disposed adjoining the atmospheric port (318). Further, in an embodiment, the canister purge port (314) is routed through a purge control valve (310), which enables controlling the purging of air-fuel mixture from the canister (306). In an embodiment, a purge hose (312) connects the purge control valve (310) to a carburetor (304) of the engine (200).
[00023] Fig. 4 illustrates a schematic representation of the evaporative emission control device, for example, the canister (306), in accordance with an embodiment of the present subject matter. In an embodiment, the canister (306) has the tank port (308) through which fuel vapors (402) from the fuel tank (302) is purged into the canister (306). In an embodiment, whenever the canister (306) senses an engine vacuum at the canister purge port (314), atmospheric air (404) is drawn into the canister (306) at the atmospheric port (318) of the canister (306) and gets mixed with the fuel vapors (402) that are already drawn inside the canister (306). The air-fuel vapor mixture (406) thus formed, is then purged out of the canister purge port (314) of the canister (306) to the carburetor (not shown) of the engine (200).
[00024] Figs. 5 (a), 5 (b), and 5 (c) illustrates a sectional view(s) of the carburetor (304) of the evaporative emission control system (300) illustrated in Fig. 3, in accordance with an embodiment of the present subject matter. In an embodiment, the carburetor (304) has a carburetor main body (502) that has at least one cylindrical surface (504). In an embodiment, the at least one cylindrical outer surface (504) of the carburetor main body (502) is provided with a purge port (506) that is capable of receiving the purged air-fuel vapor mixture (406) from the canister purge port (314) of the canister (306) of the evaporative emission control system (300). In an embodiment, the purge port (506) includes at least one metered hole (508) that allows the purged air-fuel vapor mixture (406) to pass through inside the carburetor main body (502).
[00025] In one embodiment, the carburetor main body (502) has a hollow inner cavity (502a) for accommodating a piston valve (510). The piston valve (510) is movably disposed inside the hollow inner cavity (502a) of the carburetor main body (502). In an embodiment, the carburetor main body (502) is provided with a locating slot (516) at a side that is diametrically opposite to the purge port (506). In an embodiment, the locating slot (516) enables locating the piston valve (510) inside the carburetor main body (502) and helping in easy linear movement of the piston valve (510) includes a recess groove (512) disposed axially at a downward end of the piston valve (510) at a side opposite to the locating slot (516). In an embodiment, the recess groove (512) on the piston valve (510) enables an idle adjustment screw (514) to travel horizontally. In an embodiment, the idle adjustment screw (514) enables adjusting the idle condition of the engine (200). Further, in an embodiment, the piston valve (510) of the present subject matter includes a plurality of holes disposed on the surface of the piston valve (510) that is facing the purge port (506) of the carburetor main body (502). In an embodiment, the plurality of holes includes a primary hole (518), and one or more secondary hole(s) (520). In an embodiment, the primary hole (518) is vertically in line with respect to the recess groove (512). In one embodiment, the one or more secondary holes (520) are not necessarily vertically in line with respect to the recess groove (510).
[00026] In an embodiment, Fig. 5 (a) illustrates the sectional view of the carburetor (304) during an engine idle condition. For instance, the piston valve (510) of the carburetor (304) is disposed at a bottommost position when the engine (200) is in idle condition. In an embodiment, whenever the throttle of the vehicle (100) is operated, the piston valve (510) of the carburetor (304) slides up from its idle position between the cylindrical surfaces (504) of the carburetor main body (502). In an embodiment, the purged air-fuel vapor mixture (406) communicates with the carburetor (304) through the metered hole (508). Further, in an embodiment, a clearance generally exists between the sliding piston valve (510) and an inner wall of the cylindrical surface (504) of the carburetor main body (502) that enables easy sliding of the piston valve (510) along the hollow cavity of the carburetor main body (502). Generally, the engine vacuum during idle condition of the engine (200) is substantially higher. Typically, such higher engine vacuum during idle condition communicates with the purge port (506) through the recess groove (512) provided for the idle adjustment and the clearance. This is sufficient to cause purging of the air-fuel vapor mixture (406) through the clearance. For example, vacuum in carburetor (304), when communicated with the canister (306), helps the canister (306) to draw the air inside, which gets mixed with the fuel vapors and gets purged out from the canister (306). In an embodiment, the plurality of holes (518), (520) disposed on the surface of the piston valve (510) facing the purge port (506) ensures that the engine vacuum generated during engine idle condition do not communicate through the purge port (506), rather gets relieved through the plurality of holes (518), (520). Thus, purging of air-fuel vapor mixture (406) during engine idle condition, and/or engine low speed condition is substantially eliminated. In one embodiment, the presence of the primary hole (518) of the plurality of holes (518), (520) below the metered hole (508) of the purge port (506) enables effectively relieving of the vacuum and preventing communicating the engine vacuum through the purge port (506).
[00027] In an embodiment, Fig. 5 (b) illustrates the sectional view of the carburetor (304) when the engine speed increases substantially from an engine idle and/or low speed condition. For example, during the condition illustrated in Fig. 5 (b), the piston valve (510) slides upwardly from its bottommost position inside the carburetor main body (502) allowing the engine vacuum to communicate through the metered hole (508) of the purge port (506), and thereby allowing the purging of the air-fuel vapor mixture (406) through the purge port (506) into the carburetor (304). In one embodiment, the primary hole (518) of the plurality of holes (518), (520) on the piston valve (510) is disposed substantially co-axially with the metered hole (508) of the purge port (506), while the secondary hole(s) (520) of the plurality of holes (518), (520) on the piston valve (510) is disposed substantially above the metered hole (508). For instance, during such engine speed conditions, the purged air-fuel vapor mixture (406) through the metered hole (508) of the purge port (506) is allowed to pass through one or more holes of the plurality of holes (518), (520) allowing optimal purging of the air-fuel vapor mixture (406) from the canister (306).
[00028] In an embodiment, Fig. 5 (c) illustrates the sectional view of the carburetor (304) when the engine speed increases substantially higher than the engine speed condition depicted in Fig. 5 (b). For instance, in an embodiment, during such higher engine speed conditions as depicted in Fig. 5 (c), the purged air-fuel vapor mixture (406) through the purge port (506) is allowed to directly enter the carburetor main body (502) through the recess groove (512) of the piston valve (510).
[00029] Figs. 6 (a) and 6 (b) illustrate a perspective view and a sectional elevation of the piston valve (510) of the carburetor (304) depicted in Fig. 5, in accordance to an embodiment of the present subject matter. In an embodiment, Fig. 6 (a) depicts the piston valve (510) having a cylindrical body (602) with a first surface (604) that is made to face the metered hole (508) of the purge port (506) when disposed inside the hollow cavity of the carburetor main body (502). In one embodiment, the plurality of holes (518), (520) is disposed on the first surface (604) of the piston valve (510). In an embodiment, the recess groove (512) is disposed substantially below the plurality of holes (518), (520) on the first surface (604). In an embodiment, the location slot (516) of the piston valve (510) is disposed substantially opposite to the recess groove (512) along a second surface (606) of the piston valve (510).
[00030] In an embodiment, Fig. 6 (b) depicts a sectional elevation view of the piston valve (510) along the first surface (604) of the piston valve (510). In an embodiment, the recess groove (512) is centrally disposed along a longitudinal axis (608) of the piston valve (510). In one embodiment, the primary hole (518) is disposed along the longitudinal axis (608) of the piston valve (510). In one embodiment, at least one of the secondary hole(s) (520) is disposed along the longitudinal axis (608) of the piston valve (510). In an alternative embodiment, all the secondary hole(s) (520) is capable of being disposed along the longitudinal axis (608) of the piston valve (510). In another alternative embodiment, none of the secondary hole(s) (520) is disposed along the longitudinal axis (608) of the piston valve (510).
[00031] Fig. 7 illustrates a characteristic graph depicting the variation of air-fuel mixture purged through the carburetor (304) depicted in Fig. 5 at idle, low, and high engine speed, in accordance to an embodiment of the present subject matter. In an embodiment, characteristic curve (702) depicts a rate of purging depending on engine speed in case of a conventional evaporative emission system containing the carburetor without the plurality of holes (518), (520) of the present subject matter. In one embodiment, characteristic curve (704) depicts the rate of purging depending on engine speed in case of the evaporative emission control system (300) of the present subject matter including the carburetor (304) of the present subject matter having the plurality of holes (518), (520) and a purge control valve (310). In an embodiment, characteristic curve (706) depicts the rate of purging depending on engine speed in case of the evaporative emission control system (300) of the present subject matter including the carburetor (304) of the present subject matter having the plurality of holes (518), (520) but without the purge control valve (310). As can be observed from the characteristic curve (702), the purge flow rate at engine idle condition is substantially higher, which is indicative of erratic engine characteristics. On the other hand, the characteristic curve (704) and (706) of the present subject matter provides a substantially lower purge flow rate at engine idle and/or low speed conditions ensuring enhanced engine characteristics. Further, the characteristic curve (702) shows trivial or substantially no purging until the engine speed reaches substantially closer to 65 kmph. On the other hand, the characteristic curves (704), (706) shows initiation of substantially effective purging at optimally higher engine speed conditions, for instance, at about 30 to 35 kmph, which ensures optimal purging, thereby enhancing the overall performance of the evaporative emission control system (300) of the present subject matter, including better life and performance of the canister (306). For instance, as can be observed from the graph, there is not much of a difference between the characteristic curve (706) and the characteristic curve (704), which shows that the carburetor (304) provided with the plurality of holes (518), (520) of the present subject matter is still capable of achieving the optimal purging necessary for effective performance of the engine (200) and the overall enhancement of the evaporative emission control system (300) even without the purge control valve (310). Thus, the carburetor (304) of the present subject matter enables elimination of the purge control valve (310), for example, in case of engines whose engine idle vacuum is in the range of approximately =100 mbar, the evaporative emission control system (300) of the present subject matter can sustain without the purge control valve (310) and can still produce the desired optimal performance of the engine (200).
[00032] Many modifications and variations of the present subject matter are possible in the light of above disclosure. Therefore, within the scope of claims of the present subject matter, the present disclosure may be practiced other than as specifically described.
,CLAIMS:We Claim:
1. A carburetor (304) for an internal combustion (IC) engine (200) in an evaporative emission control system (300) of a vehicle (100), said carburetor (304) comprising:
a carburetor main body (502) having a cylindrical outer surface (504) and a hollow inner cavity (502a);
a purge port (506) disposed on said cylindrical outer surface (504), said purge port (506) capable of receiving purged air-fuel vapor mixture (406) from an evaporative emission control device (306) of said evaporative emission control system (300) on sensing vacuum inside said carburetor main body (502) ;
a piston valve (510) is disposed diametrically inside said hollow inner cavity (502a) of said carburetor main body (502), said piston valve (510) comprising:
a first surface (604) facing said purge port (506), and a second surface (606) opposite to said first surface (604), wherein said first surface (604) includes a recess groove (512) disposed axially at a downward end of the piston valve (510), and a plurality of holes (518, 520) substantially above said recess groove (512).
2. The carburetor (304) as claimed in claim 1, wherein said plurality of holes (518, 520) includes a primary hole (518) disposed substantially along a longitudinal axis of said piston valve (510).
3. The carburetor (304) as claimed in claim 1, wherein said plurality of holes (518, 520) includes one or more secondary hole(s) (520), wherein at least one of said one or more secondary hole(s) (520) is disposed substantially along a longitudinal axis of said piston valve (510).
4. The carburetor (304) as claimed in claim 1, wherein said piston valve (510) is capable of moving linearly inside said hollow inner cavity (502a) of said carburetor main body (502), and wherein a clearance is formed between said first surface (604) and second surface (606) of said piston valve (510) and an inner wall of said carburetor main body (502).
5. The carburetor (304) as claimed in claim 1, wherein said plurality of holes (518, 520) relieve vacuum formed inside said carburetor main body (502).
6. The carburetor (304) as claimed in claim 2 or 3, wherein said primary hole (518) is disposed substantially below said purge port (506), and said secondary hole(s) (520) is disposed substantially above said purge port (506) during an engine idle and/or low speed condition.
7. The carburetor (304) as claimed in claim 2 or 3, wherein said primary hole (518) is disposed substantially coaxial to a metered hole (508) of said purge port (506) when speed of said IC engine (200) increases substantially above an engine idle and/or low speed condition.
8. The carburetor (304) as claimed in claim 2 or 3, wherein said primary hole (518) and said secondary hole(s) (520) is disposed substantially above a metered hole (508) of said purge port (506) when speed of said engine increases substantially higher.
9. The carburetor (304) as claimed in claim 1, wherein said purged air-fuel vapor mixture (406) from said evaporative emission control device of said evaporative emission control system (300) is allowed to pass through a purge control valve (310).
10. The carburetor (304) as claimed in claim 1, wherein said purged air-fuel vapor mixture (406) from said evaporative emission control device of said evaporative emission control system (300) directly purges into said purge port (506) of said carburetor (304).