Description:
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]

BREATHER STRUCTURE OF AN INTERNAL COMBUSTION ENGINE

HERO MOTOCORP LIMITED, an Indian Company at: The Grand Plaza, Plot No.2, Nelson Mandela Road, Vasant Kunj- Phase -II, New Delhi, India, 110 070

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

Field of the Invention:
[001] The present invention relates to a breather structure for reducing the lubricating oil content in a blow-by gas that leaks into the crank case through a gap between a piston and a cylinder in an internal combustion engine.

Background of the Invention:
[002] Many a times, an internal combustion engine produces a gas-liquid mixture comprising a blow-by gas and lubricating oil. This gas-liquid mixture is present in a crank chamber. It is desired to provide a breather structure to separate lubricating oil from the gas-liquid mixture. The lubricating oil thus separated can then be returned to a lubricating oil reservoir and the blow-by gas can be fed to an air-cleaner.

[003] It has been proposed to employ a standalone centrifugal separator as a breather structure to separate lubricating oil from the gas-liquid mixture. However, such proposal is not convenient to implement for various reasons known to a person skilled in the art. Additionally, it has been proposed to employ an auxiliary machinery generating centrifugal force and provided in the crank chamber of said internal combustion engine as a breather structure for centrifugally separating lubricating oil from the gas-liquid mixture.

[004] In particular, U.S. Patent No. 5,690,084 discloses a breather structure for an internal combustion engine having an alternating current generator (ACG) provided in the crank chamber of said internal combustion engine for centrifugally separating oil lubricating from the blow-by gas by rotation of a rotor portion integrated with a crank shaft. As per the document, a breather passage, for introducing the gas-liquid mixture to the rotor portion of the ACG is formed in a cover portion that covers side portions of said ACG. The breather passage comprises a substantially cylindrical wall having a center axis substantially identical to a rotational center axis of said rotor portion of said ACG formed to project from said ACG cover to said rotor portion; an outlet communicating with said breather passage formed in a base portion of said substantially cylindrical wall; and a discharge port in communication inwardly of said substantially cylindrical wall in the rotational direction of said rotor portion of said ACG for communicating from the inside to the outside of said substantially cylindrical wall, said discharge port being formed in said substantially cylindrical wall.

[005] It is however felt that forming the outlet and the discharge port in the ACG cover as per the teachings of U.S. Patent No. 5,690,084 is difficult and adversely impacts strength and size of the ACG cover.

Summary of the Invention:
[006] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[007] In one aspect of the invention, there is provided a breather structure of an internal combustion engine comprising a crank chamber defined between a right crank case and a left crank case, the crank chamber accommodating a crank shaft and an alternating current generator (ACG), the ACG being coupled to the crank shaft, the ACG comprising a stator and a rotor, the rotor is covered by either the left crank case or the right crank case, the crank case covering the rotor comprises a side wall and a peripheral wall extending from the side wall. The breather structure comprises an introduction port receiving a gas-liquid mixture of a blow-by gas and a lubricating oil from the crank chamber and introducing the same between the stator and the rotor. The breather structure further comprises a blow-by gas discharge port provided on the side wall of the crank case covering the rotor. The breather structure further comprises a lubricating oil discharge port provided in the crank chamber. In an embodiment of the invention, the blow-by gas discharge port projects obliquely from the side wall.

[008] In an embodiment of the invention, a substantially cylindrical wall is formed on the side wall of the crank case covering the rotor so as to surround the blow-by gas discharge port.

[009] In another embodiment of the invention, the substantially cylindrical wall projects inwardly and receives the stator.

[0010] In yet another embodiment of the invention, a plate is provided between the stator and the side wall.

[0011] In still another embodiment of the invention, a first end of the plate is received by the substantially cylindrical wall and a second end of the plate extends radially towards the peripheral wall portion.

[0012] In a further embodiment of the invention, a first end of the plate is received by a central yoke part of the stator and a second end of the plate extends radially towards the peripheral wall portion.

[0013] In a furthermore embodiment of the invention, the second end of the plate terminates at a location between the stator and the rotor.

[0014] In an embodiment of the invention, the blow-by gas discharge port is in communication with an air cleaner.

[0015] In another embodiment of the invention, the lubricating oil discharge port is in communication with a lubricating oil reservoir formed in the crank chamber.

[0016] In yet another embodiment of the invention, the rotor produces a turning flow of the gas-liquid mixture for permitting centrifugal separation of blow-by gas and the lubricating oil.

[0017] In still another embodiment of the invention, the lubricating oil is collected on an inner surface of the rotor.

[0018] In a further embodiment of the invention, the rotor includes a set of apertures for permitting exit of the lubricating oil collected on an inner surface towards the lubricating oil discharge port.

[0019] In a furthermore embodiment of the invention the blow-by gas discharge port is formed so as to protrude obliquely from the side wall.

[0020] In another embodiment of the invention, the blow-by gas discharge port is aligned so as to be co-axial with the axis of the crank shaft.

[0021] In still another embodiment of the invention, the blow-by gas discharge port is aligned so as to be co-axial with the substantially cylindrical wall.

[0022] In one aspect of the invention, there is provided a vehicle comprising a body frame, a pair of ground engaging members rotatably supported with respect to the body frame, an internal combustion engine supported by the body frame, the internal combustion engine generating driving power, and a transmission system transferring the driving power generated by the internal combustion engine to at least one of the ground engaging member. The internal combustion engine comprises a crank chamber defined between a right crank case and a left crank case, the crank chamber accommodating a crank shaft and an alternating current generator (ACG). The ACG is coupled to the crank shaft. The internal combustion engine produces a gas-liquid mixture comprising a blow-by gas and lubricating oil. The ACG comprises a stator and a rotor. The rotor is covered by either the left crank case or the right crank case. The crank case covering the rotor comprises a side wall and a peripheral wall extending from the side wall. The vehicle further comprises a breather structure for separating lubricating oil from the gas-liquid mixture. In an embodiment of the invention, the breather structure comprises an introduction port for receiving the gas-liquid mixture from the crank chamber and introducing the same between the stator and the rotor. In another embodiment of the invention, the breather structure comprises a blow-by gas discharge port provided on the side wall of the crank case covering the rotor. In a further embodiment of the invention, the breather structure comprises a lubricating oil discharge port provided in the crank chamber.

[0023] One advantage of the invention is that constructing a breather structure with one or more of the aforesaid feature(s) is substantially easy. Another advantage of the invention is that constructing a breather structure with one or more of the aforesaid feature(s) does not adversely affect strength of the crank case covering the rotor. Yet another advantage of the invention is that constructing breather structure with one or more of the aforesaid feature(s) does not adversely impact size of the crank case covering the rotor and in particular does not necessitate an increase in size of the crank case covering the rotor. Still another advantage of the invention is that the time required for manufacturing the breather structure with one or more of the aforesaid feature(s) is substantially less. Since the breather structure can be formed without increasing size of the crank case, cost involved in making the breather structure is substantially less. Since most of the components for making the breather structure are already present in the ACG, the cost involved in making the breather structure is substantially less. Still another advantage of the invention is that the breather structure with one or more of the aforesaid feature(s) efficiently separates lubricating oil from the blow-by gas. Yet another advantage of the invention is that the breather structure with one or more of the aforesaid feature(s) avoids the lubricating oil from being sucked into the blow-by gas discharge port.

[0024] To further clarify the advantages and features of the invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES:
[0025] In order that the invention may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying drawings, where like reference numerals refer to identical or functionally similar elements throughout the separate views. The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present invention where:

[0026] Figure 1 illustrates a side view of an exemplary two wheeled vehicle, in an embodiment of the present invention;

[0027] Figure 2 illustrates a rear view of the internal combustion engine, in an embodiment of the present invention;

[0028] Figure 3 illustrates a first side view of the internal combustion engine, in an embodiment of the present invention;

[0029] Figure 4 illustrates a sectional view of the internal combustion engine taken along section 4-4’ shown in Figure 3, in an embodiment of the present invention;

[0030] Figure 5 illustrates another side view of the internal combustion engine after removal of the ACG cover, in an embodiment of the present invention;

[0031] Figure 6 illustrates a close-up sectional view of the ACG which acts as the breather structure, in an embodiment of the present invention;

[0032] Figure 7 illustrates a close-up sectional view of the ACG which acts as the breather structure, in another embodiment of the present invention;

[0033] Figure 8 illustrates a close-up sectional view of the ACG which acts as the breather structure as shown in Figure 7, in an embodiment of the present invention; and

[0034] Figure 9 illustrates the flow of the gas-liquid mixture through the ACG which acts as the breather structure as shown in Figure 7, in an embodiment of the present invention.

[0035] It may be noted that to the extent possible, like reference numerals have been used to represent like elements in the drawings. Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have been necessarily been drawn to scale. For example, the dimensions of some of the elements in the drawings may be exaggerated relative to other elements to help to improve understanding of aspects of the present invention. Furthermore, one or more elements may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

Detailed Description of the Invention:
[0036] For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

[0037] It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the invention and are not intended to be restrictive thereof.

[0038] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.

[0039] Reference throughout this specification to “an aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase “in an embodiment”, “in another embodiment”, and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0040] The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that one or more devices or sub-systems or elements or structures or components proceeded by "comprises... a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

[0041] As used herein, and unless the context dictates otherwise, the terms "coupled to", “connected to”, “operably connected to”, and “operatively connected to” are intended to include both direct connection / coupling (in which two elements that are coupled / connected to each other contact each other) and indirect coupling / connection (in which at least one additional element is located between the two elements). Therefore, the terms "coupled to" and "coupled with" are used synonymously. Similarly, the terms “connected to” and “connected with” are used synonymously.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one ordinary skilled in the art to which this invention belongs. The device, methods, and examples provided herein are illustrative only and not intended to be limiting.

[0043] The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as being essential to the practice of the invention.

[0044] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

[0045] Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

[0046] While the present invention is illustrated in the context of a vehicle, however, cover and aspects and features thereof can be used with other types of vehicles as well. The terms “vehicle”, “two wheeled vehicle” and “motorcycle” have been interchangeably used throughout the description. The term “vehicle” comprises vehicles such as motorcycles, scooters, bicycles, mopeds, scooter type vehicles, All-Terrain Vehicles (ATV) and the like.

[0047] The terms “front / forward”, “rear / rearward / back / backward”, “up / upper / top”, “down / lower / lower ward / downward, bottom”, “left / leftward”, “right / rightward” used therein represents the directions as seen from a vehicle driver sitting astride and these directions are referred by arrows Fr, Rr, U, Lr, L, R in the Figures.

[0048] Referring to Figure 1, there is illustrated a side view of a two-wheeled vehicle (10) according to an embodiment of the present invention. The vehicle (10) comprises, inter-alia, a head pipe (12), a front fork (14), a front fender (16), a pair of ground engaging members (18 and 28), a headlight (20), a steering handle bar (22), a fuel tank (24), an internal combustion engine (26), a rear fender (30), a tail light (32), a seat (34), a tool box (36), a body frame (38), and an exhaust pipe (40). The pair of ground engaging members includes a front ground engaging member (18) and a rear ground engaging member (28). The body frame (38) rotatably supports the pair of ground engaging members (18 and 28). The body frame (38) further supports the internal combustion engine (26). The internal combustion engine (26) generates driving power which powers the vehicle (10). It may be noted that the vehicle (10) is shown to have included above stated parts, however, those skilled in the art would appreciate that the vehicle (10) includes other parts which may not be relevant for explaining the present invention and hence are not shown and described.

[0049] Referring to Figures 2 and 3, there is illustrated a rear view and a first side view, respectively of an internal combustion engine (26) according to an embodiment of the present invention. In an embodiment of the invention, the internal combustion engine (26) may be a four stroke, single-cylinder SOHC internal combustion engine. The internal combustion engine (26) comprises a cylinder block (42), a cylinder head (44), and a cylinder head cover (46) sequentially stacked on one another and fastened together as an integral body.

[0050] Referring to Figure 4, which is a sectional view of the internal combustion engine taken along section 4-4’ shown in Figure 3, there is defined a crank chamber (48) between a right crank case (50R) and a left crank case (50L). The crank chamber (48) accommodates a crank shaft (52) so as to extend horizontally in the lateral direction. The crank shaft (52) is rotatable with respect to the crank chamber (48).

[0051] A piston (54) is slidably fitted to the cylinder block (42) protruding obliquely upward from the crank chamber (48) and is connected to the crank shaft (52) via a connecting rod (56). The crank shaft (52) is rotationally driven according to movement of the piston (54). A combustion chamber (58) is formed in a lower portion of the cylinder head (44) above the piston (54).

[0052] The crank chamber (48) houses a transmission system (60) that is coupled to the at least one of the ground engaging member (18 or 28) and more particularly to the rear ground engaging member (28).

[0053] An alternating current generator (ACG) (62) is also housed in the crank chamber (48). By way of a non-limiting example, the alternating current generator (ACG) (62) may be located on a left side of the crank shaft (52) and is coupled to the crank shaft (52). By way of a non-limiting example, the alternating current generator (ACG) (62) may be located on a left side of the crank shaft (52).

[0054] Now referring particularly to Figure 5, which corresponds to another side view of the internal combustion engine (26) showing the ACG (62). The ACG (62) comprises a stator (64), and a rotor (66). The rotor (66) is covered by the left crank case (50L) or the right crank case (50R). By way of a non-limiting example, if the alternating current generator (ACG) (62) is located on the left side of the crank shaft (52), the rotor is covered by the left crank case (50L). In an embodiment of the invention, the left crank case (50L) comprises a side wall (68) and a peripheral wall (70) extending from the side wall (68).

[0055] The internal combustion engine (26) produces a gas-liquid mixture comprising a blow-by gas and lubricating oil which is present in the crank chamber (48). The internal combustion engine (26) further accommodates a breather structure (72).

[0056] Referring particularly to Figure 6, there is illustrated a close-up sectional view of the ACG which acts as the breather structure, in accordance with an embodiment of the present invention. The breather structure (72) receives the gas-liquid mixture and separates lubricating oil from the gas-liquid mixture. The lubricating oil thus separated can then be returned to a lubricating oil reservoir (not shown) and the blow-by gas can be fed to an air-cleaner (not shown). The breather structure (72) generates centrifugal force thus centrifugally separating lubricating oil from the gas-liquid mixture.

[0057] Since the ACG (62) generates centrifugal force, the ACG (62) acts as the breather structure (72). However, certain modifications have to be done to the ACG (62) in order for the same to function as the breather structure (72). For instance, an introduction port (74) is formed so as to introduce the gas-liquid mixture present in the crank chamber into the ACG (62). In particular, the gas-liquid mixture is introduced between the stator (64) and the rotor (66). Additionally, a lubricating oil discharge port (76) is provided in the crank chamber (48). Further, a blow-by gas discharge port (78) is provided in the left crank case (50L). In particular, the blow-by gas discharge port (78) is formed on the side wall (68) of the left crank case (50L). More particularly, the blow-by gas discharge port (78) is formed so as to protrude obliquely from the side wall (72).

[0058] In an embodiment of the invention, the breather structure (72) comprises a substantially cylindrical wall (82) formed on the side wall (68) of the left crank case (50L). The substantially cylindrical wall (82) projects inwardly towards the ACG (62). The substantially cylindrical wall (82) receives the stator (64). The substantially cylindrical wall (82) also surrounds the blow-by gas discharge port (78). Thus, in a preferred embodiment of the invention, the blow-by gas discharge port (78) is aligned so as to be co-axial with the axis of the crank shaft (52). The blow-by gas discharge port (78) is located to be co-axial with the substantially cylindrical wall (82).

[0059] Now referring to Figure 7 and Figure 8, there is illustrated a close-up sectional view of the ACG and a close-up view of the ACG after removal of the case cover, the ACG acting as the breather structure in accordance with an embodiment of the present invention. In an embodiment of the invention, there is provided a plate (84) between the stator (64) and the side wall (68) of the left crank case (50L). In particular, the plate (84) includes a first end (86) and a second end (88). The first end (86) of the plate (84) is received by the substantially cylindrical wall (82) while the second end (88) of the plate (84) extends radially towards the peripheral wall (70). In an alternative embodiment of the invention which has not been demonstrated, the first end (86) of the plate (84) is received by a central yoke part of the stator (64) while the second end (88) of the plate (84) extends radially towards the peripheral wall (70). The second end (88) of the plate (84) terminates at a location between the stator (64) and the rotor (66). By providing the plate (84), a place for introducing the gas-liquid mixture can be controlled. In particular, while the gas-liquid mixture is introduced between the stator (64) and the rotor (66), however, it is introduced adjacent to the rotor (66). By introducing the gas-liquid mixture adjacent to the rotor (66), an efficiency of the separation of the lubricating oil from the gas-liquid mixture is substantially improved as compared to an option wherein the plate is not provided.

[0060] Now referring to Figure 9, there is illustrated a flow path of the gas-liquid mixture through the ACG which acts as the breather structure in accordance with an embodiment of the present invention. When the gas-liquid mixture is introduced between the stator (64) and the rotor (66), the gas-liquid mixture passes through the stator (64) along the axial direction of the ACG (62). The gas-liquid mixture then experiences centrifugal force due to the rotation of the rotor (66). Due to the centrifugal force experienced by the gas-liquid mixture, the lubricating oil separates from the gas-liquid mixture. More particularly, the rotor (66) produces a turning flow of the gas-liquid mixture for permitting centrifugal separation of blow-by gas and the lubricating oil. The lubricating oil thus separated flows towards the rotor (66) as shown by first arrow (90), while the gas flows towards the stator (64) as shown by the second arrow (92). The rotor (66) is provided with apertures (80) which allow the lubricating oil to leave the rotor (66). The lubricating oil then reaches lubricating oil discharge port (76) formed in the crank chamber (48) and thereafter flows into a lubricating oil reservoir formed in the crank chamber (48). The gas flows towards the stator (64) and then comes out via the blow-by gas discharge port (78) provided on the side wall (68) of the left crank case (50L) as shown by third arrow (94).

[0061] One advantage of the invention is that constructing a breather structure (72) as mentioned above is substantially easy as compared to constructing a standalone centrifugal separator. Since the Blow-by gas discharge port (78) is formed on the side wall (68) of the left crank case (50L) and more particularly so as to protrude obliquely from the side wall (68), factors such as strength and size of the left crank cover (50L) are not adversely impacted. Still another advantage of the invention is that the time required for manufacturing the breather structure is substantially less. Since the breather structure can be formed without increasing size of the left crank case (50L), cost involved in making the breather structure is substantially less. Since most of the components of the breather structure are already present in the ACG, cost involved in making the breather structure is substantially reduced. Still another advantage of the invention is that the breather structure efficiently separates lubricating oil from the blow-by gas.

[0062] While specific language has been used to describe the disclosure, any limitations arising on account of the same are not intended. As would be apparent to a person in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein.

[0063] The figures and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples.
, Claims:WE CLAIM:

1. A breather structure (72) of an internal combustion engine (26) comprising a crank chamber (48) defined between a right crank case (50R) and a left crank case (50L), the crank chamber (48) accommodating a crank shaft (52) and an alternating current generator (ACG) (62), the ACG (62) being coupled to the crank shaft (52), the ACG (62) comprising a stator (64), and a rotor (66), the rotor (66) being covered by the right crank case (50R) or the left crank case (50L) , the right crank case (50R) or the left crank case (50L) covering the rotor (66) comprises a side wall (68) and a peripheral wall (70) extending from the side wall (68), the breather structure (72) comprising:
an introduction port (74) receiving a gas-liquid mixture of a blow-by gas and a lubricating oil from the crank chamber (48) and introducing the same between the stator (64) and the rotor (66);
a blow-by gas discharge port (78) formed on the side wall (68) of the left crank case (50L) or the right crank case (50R) covering the rotor (66); and
a lubricating oil discharge port (76) provided in the crank chamber (48).

2. The breather structure as claimed in claim 1, wherein a substantially cylindrical wall (82) is formed on the side wall (68) of the left crank case (50L) or the right crank case (50R) covering the rotor (66) so as to surround the blow-by gas discharge port (78), the substantially cylindrical wall (82) projects inwardly and receives the stator (64).

3. The breather structure as claimed in claim 1, wherein a plate (84) is provided between the stator (64) and the side wall (68).

4. The breather structure as claimed in claims 2 and 3, wherein a first end (86) of the plate (84) is received by the substantially cylindrical wall (82) and a second end (88) of the plate (84) extends radially towards the peripheral wall (70).

5. The breather structure as claimed in claims 2 and 3, wherein a first end (86) of the plate (84) is received by a central yoke part of the stator (64) and a second end (88) of the plate (84) extends radially towards the peripheral wall (70).

6. The breather structure as claimed in any of claims 4 or 5, wherein the second end (88) of the plate (84) terminates at a location between the stator (64) and the rotor (66).

7. The breather structure as claimed in claim 1, wherein:
a. the blow-by gas discharge port (78) is in communication with an air cleaner;
b. the lubricating oil discharge port (76) is in communication with a lubricating oil reservoir formed in the crank chamber (48).

8. The breather structure as claimed in claim 1, wherein the rotor (66) produces a turning flow of the gas-liquid mixture for permitting centrifugal separation of blow-by gas and the lubricating oil.

9. The breather structure as claimed in claim 1, wherein the lubricating oil is collected on an inner surface of the rotor (66) and the rotor (66) includes a set of apertures (80) for permitting exit of the lubricating oil collected on an inner surface towards the lubricating oil discharge port (76).

10. The breather structure as claimed in claim 1, wherein the blow-by gas discharge port (78) is formed so as to protrude obliquely from the side wall (68).

11. The breather structure as claimed in claim 1, wherein the blow-by gas discharge port (78) is aligned so as to be co-axial with the axis of the crank shaft (52).

12. The breather structure as claimed in claim 1, wherein the blow-by gas discharge port (78) is aligned so as to be co-axial with the substantially cylindrical wall (82).

13. A vehicle (10) comprising:
a body frame (38);
a pair of ground engaging members (18, 28) rotatably supported with respect to the body frame (38);
an internal combustion engine (26) supported by the body frame (38), the internal combustion engine (26) generating driving power, the internal combustion engine (26) additionally producing a gas-liquid mixture comprising a blow-by gas and a lubricating oil;
a transmission system (60) transferring the driving power generated by the internal combustion engine (26) to at least one of the ground engaging member (18, 28);
a breather structure (72) separating the lubricating oil from the gas-liquid mixture;
the internal combustion engine (26) comprises a crank chamber (48) defined between a right crank case (50R) and a left crank case (50L), the crank chamber (48) accommodating a crank shaft (52) and an alternating current generator (ACG) (62) coupled to the crank shaft (52);
the ACG (62) comprising a stator (64) and a rotor (66);
the rotor (66) being covered by the right crank case (50R) or the left crank case (50L);
the right crank case (50R) or the left crank case (50L) covering the rotor (66) comprises a side wall (68) and a peripheral wall (70) extending from the side wall (68); and
the breather structure (72) comprising:
an introduction port (74) receiving the gas-liquid mixture from the crank chamber (48) and introducing the same between the stator (64) and the rotor (66);
a blow-by gas discharge port (78) formed on the side wall (68) of the left crank case (50L) or the right crank case (50R) covering the rotor (66); and
a lubricating oil discharge port (76) provided in the crank chamber (48).