Description:FIELD OF THE INVENTION
[001] The present invention generally relates to an internal combustion engine. More particularly, the present invention relates to an internal combustion engine for a vehicle.

BACKGROUND OF THE INVENTION
[002] Generally, in conventional vehicles, especially saddle type vehicles, one or more balancer shafts are provided to reduce or eliminate the free mass forces of a reciprocating engine to reduce operating noise and vibration. In the existing layout of crankshaft and balancer shaft assembly, the drive balancer gear is placed before the bearing. This results in an increase in the bearing span across the balancer shaft and the crankshaft. An increased bearing span causes more deflection in the respective shafts, leading to a continuous increase in backlash and higher gear noise between the balancer drive and balancer driven gear. In the existing layouts, there is a lack of minimum clearance between balancer drive and balancer driven gear due to increased bearing span. As a result, during operation, the balancer drive gear is axially shifted towards the driven gear due to width of bearing span, and noise is generated between the balancer drive and the balancer driven gear.
[003] Attempts have been made for reduction of this noise generated between the balancer drive gear and the balancer driven gear. In these systems, a noise suppressing mechanism having a primary gear, a secondary gear, and a torsional spring is provided in which the torsional spring is fit on the balancer shaft. A circular flange is formed on the primary gear and the secondary gear forms a central bore rotatably fit over the circular flange for free rotation about the circular flange with respect to the primary gear. The torsional spring is arranged between the primary and secondary gears. However, such systems require introduction of a new element in the form of torsional spring which results in an increase in the number of parts, weight and cost of the assembly.
[004] Other conventional systems for noise suppression between the balancer drive gear and the balancer driven gear provide for usage of an elastomeric vibration isolator sandwiched between the gear inner hub and gear outer ring. However, in these systems, on continuous usage, there is wear and tear in the elastomer which is made of rubber. Hence, the elastomer needs to be frequently replaced after a certain period of time.
[005] Thus, there is a need in the art for an internal combustion engine for a vehicle, which addresses at least the aforementioned problems.

SUMMARY OF THE INVENTION
[006] In one aspect, the present invention is directed towards an internal combustion engine for a vehicle. The engine has crankshaft with a first crankshaft stem and a second crankshaft stem. The first crankshaft stem and the second crankshaft stem are configured to be attached to a connecting rod connected to a piston of the engine. A rotary electric machine is attached to the first crankshaft stem. A balancer drive gear is mounted on the first crankshaft stem. A balancer shaft is provided for balancing dynamic forces within the engine. A balancer driven gear is mounted on the balancer shaft. The balancer driven gear is configured to mesh with the balancer drive gear on the first crankshaft stem, thereby allowing the balancer shaft to rotate for balancing dynamic forces within the engine.
[007] In an embodiment of the invention, the rotary electric machine has a stator and a rotor, and the rotor is attached to the first crankshaft stem.
[008] In a further embodiment of the invention, the balancer drive gear is attached to the rotor of the rotary electric machine.
[009] In a further embodiment of the invention, the balancer shaft has a first end and a second end. The balancer driven gear is mounted on the first end of the balancer shaft.
[010] In a further embodiment of the invention, the internal combustion engine has a first bearing and a second bearing for supporting the balancer shaft. The second end of the balancer shaft is supported on the second bearing. The first bearing is disposed between the balancer driven gear and the second bearing.
[011] In a further embodiment of the invention, the internal combustion engine has one or more eccentric lobes provided on the balancer shaft. The one or more eccentric lobes are disposed between the first bearing and the second bearing.
[012] In a further embodiment of the invention, the crankshaft has a first crankshaft web connected to the first crankshaft stem and a second crankshaft web connected to the second crankshaft stem, such that the connecting rod is attached to the first crankshaft web and the second crankshaft web for converting the translational motion of the piston into rotary motion of the crankshaft.
[013] In a further embodiment of the invention, the one or more eccentric lobes are configured to rotate between the first crankshaft web and the second crankshaft web.
[014] In a further embodiment of the invention, the internal combustion engine has a bearing seating portion provided on the second crankshaft stem and abutting the second crankshaft web. The bearing seating portion is configured to receive a crankshaft supporting bearing.

BRIEF DESCRIPTION OF THE DRAWINGS
[015] Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Figure 1 illustrates an internal combustion engine, in accordance with an embodiment of the present invention.
Figure 2 illustrates a crankshaft assembly of the internal combustion engine, in accordance with an embodiment of the present invention.
Figure 3 illustrates a balancer shaft of the internal combustion engine, in accordance with an embodiment of the present invention.
Figure 4 illustrates a sectional view of the internal combustion engine, in accordance with an embodiment of the present invention.
Figure 5 illustrates an exploded view of the internal combustion engine, in accordance with an embodiment of the present invention.
Figure 6 illustrates the increase in crankshaft stiffness, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION
[016] The present invention relates to an internal combustion engine for a vehicle. The internal combustion engine of the present invention is typically used for a two wheeled vehicle, or a three wheeled vehicle, or a four wheeled vehicle, or other multi-wheeled vehicles as required. However, it should be understood that the internal combustion engine as illustrated may find its application on any non-automotive application using an internal combustion engine.
[017] Figure 1 illustrates an internal combustion engine 100 for a vehicle, in accordance with an embodiment of the present invention. As further illustrated, the internal combustion engine 100 comprises a crankshaft 102. The crankshaft 102 has a first crankshaft stem 110 and a second crankshaft stem 120. The first crankshaft stem 110 and the second crankshaft stem 120 extend in a width direction of the internal combustion engine 100. In that, the first crankshaft stem 110 and the second crankshaft stem 120 are configured to be attached to a connecting rod 130, which in turn is connected to a piston (not shown) of the internal combustion engine 100. Translational motion of the piston is transmitted to the connecting rod 130, and the first crankshaft stem 110 and the second crankshaft stem 120 convert this translational motion into rotary motion required as output from the internal combustion engine 100.
[018] As further illustrated in Figure 1, the internal combustion engine 100 comprises a rotary electric machine 140 attached to the first crankshaft stem 110. In an embodiment, the rotary electric machine 140 is a magneto which is a generator of high voltage that provides ignition to the internal combustion engine 100 through spark plugs. In an embodiment, the rotary electric machine 140 has a stator (not shown) and a rotor 142 (shown in Figure 4). In that, the rotor 142 is attached to the first crankshaft stem 110. In an embodiment, the stator has a plurality of windings wound on different teeth on the stator, and the rotor 142 has a plurality of magnets. The plurality of magnets of the rotor 142, which are caused to rotate by the first crankshaft stem 110 close to the stator windings, lead to generation of a voltage which is then transmitted to spark plugs through one or more contact points.
[019] The internal combustion engine 100 further has a balancer shaft 160 for balancing dynamic forces within the internal combustion engine 100. The balancer shaft 160 is provided in a spaced apart manner from the crankshaft 102. Further, a balancer drive gear 150 is mounted on the first crankshaft stem 110. A balancer driven gear 170 is mounted on the balancer shaft 160. The balancer driven gear 170 is configured to mesh with the balancer drive gear 150 on the first crankshaft stem 110, which allows the balancer shaft 160 to rotate, which results in balancing of dynamic forces within the internal combustion engine 100. Thus, in the present invention, the balancer drive gear 150 is placed on the same side of the crankshaft 102 as the rotary electric machine 140, that is on the first crankshaft stem 110, as opposed to conventional systems wherein the balancer drive gear and the magneto are placed on opposite sides of the crankshaft.
[020] In an embodiment, as referenced in Figure 4, the balancer drive gear 150 is attached to the rotor 142 of the rotary electric machine 140. In an embodiment, the balancer driver gear 150 is riveted on to the rotor 142 of the rotary electric machine 140. As illustrated in Figures 3 and 4, the balancer shaft 160 comprises a first end 160A and a second end 160B. In that, the balancer driven gear 170 is mounted on the first end 160A of the balancer shaft 160. The internal combustion engine 100 further comprises a first bearing 162 and a second bearing 164 for supporting the balancer shaft 160. The second end 160B of the balancer shaft 160 is supported on the second bearing 164. Further, the first bearing 162 is disposed between the balancer driven gear 170 and the second bearing 164. In the present invention, the first bearing 162 is disposed between the balancer driven gear 170 and the second bearing 164, as opposed to conventional arrangements wherein the two bearing for supporting the balancer shaft are provided on two ends of the balancer shaft. Thus, arrangement of the first bearing 162 between the balancer driven gear 170 and the second bearing 164 leads to a reduced bearing span, that is reduced gap between the first bearing 162 and the second bearing 164. The reduced bearing span on the balancer shaft 160 thus reduces the gear noise that occurred due to continuous gear backlash increase encountered over usage, which in turn, occurs as a result of higher bearing span.
[021] The relationship between bearing span and noise/vibration can be understood by means of maximum beam deflection. As is known, the maximum beam deflection is directly proportional to bearing span. Thus, reduced bearing span leads to reduced value of maximum beam deflection, thus reducing noise and vibration by ensuring that backlash increase over usage is minimum.
[022] As illustrated in Figures 4 and 5, the internal combustion engine 100 comprises one or more eccentric lobes 166 provided on the balancer shaft 160. The one or more eccentric lobes 166 are disposed between the first bearing 162 and the second bearing 164. The eccentric lobes 166 are provided such that their respective centre of masses are offset with the axis of rotation of the balancer shaft 160. Thus, when the balancer shaft 160 rotates, the balancer shaft 160 and the one or more eccentric lobes 166 provided thereon rotate in the opposite directional sense to the rotation of the crankshaft 102, thus balancing out the unbalanced dynamic forces caused by the rotation of the crankshaft 102.
[023] As further illustrated in Figures 4 and 5, and referenced in Figure 2, in an embodiment, the crankshaft 102 has a first crankshaft web 112 that is connected to the first crankshaft stem 110 and a second crankshaft web 122 that is connected to the second crankshaft stem 120. The first crankshaft web 112 and the second crankshaft web 122 are provided such that the connecting rod 130 is attached to the first crankshaft web 112 and the second crankshaft web 122 for converting the translational motion of the piston into rotary motion of the crankshaft 102. In an embodiment, the one or more eccentric lobes 166 are configured to rotate between the first crankshaft web 112 and the second crankshaft web 122. This allows for usage of dead space between the first crankshaft web 112 and the second crankshaft web 122 for provision of the one or more eccentric lobes 166 which results in more compact packaging of the internal combustion engine 100.
[024] In an embodiment, the internal combustion engine 100 has a bearing seating portion 180 provided on the second crankshaft stem 120 and abutting the second crankshaft web 122. The bearing seating portion 180 is configured to receive a crankshaft supporting bearing. Conventionally, this balancer drive gear would be located between a right side crankshaft web and the bearing seating portion. In the present invention, since the balancer drive gear 150 is provided on the first crankshaft stem 110, the bearing seating portion 180 is provided abutting the second crankshaft web 122. This leads to reduction in bearing span on the crankshaft 102 in addition to the balancer shaft 160, thus further reducing noise and vibration in the internal combustion engine 100.
[025] Further, as referenced in Figure 6, due to reduced bearing span on the crankshaft 102 in the present invention, the stiffness (s1) of the crankshaft 102, and the ratio of stiffness of the crankshaft 102 to the length of the crankshaft 102, is also increased, as compared to the crankshaft stiffness (s2) in existing systems, due to reduced maximum beam deflection on the crankshaft 102.
[026] Advantageously, the present invention provides for an internal combustion engine in which bearing span is reduced at the balancer shaft and the crankshaft, thus reducing noise and vibration generated in the internal combustion engine, especially at peak combustion loads. Particularly, the noise generated by the balancer drive gear and the balancer driven gear due to incremental backlash over usage is reduced.
[027] Further, in the present invention, since the bearing span is reduced, length of the crankshaft and the balancer shaft can be reduced as per requirement, thus resulting in more efficient packaging within the internal combustion engine, and reduced weight.
[028] Furthermore, the reduced weight and the reduced vibration in the internal combustion engine also leads to an increase in mileage and fuel efficiency of the internal combustion engine.
[029] While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.

List of Reference Numerals

100: Internal Combustion Engine
102: Crankshaft
110: First crankshaft stem
112: First crankshaft web
120: Second crankshaft stem
122: Second crankshaft web
130: Connecting rod
140: Rotary Electric Machine
142: Rotor
150: Balancer drive gear
160: Balancer shaft
160A: First end of balancer shaft
160B: Second end of balancer shaft
162: First bearing
164: Second bearing
166: Eccentric lobes
170: Balancer Driven gear
180: Bearing seating portion , Claims:WE CLAIM:
1. An internal combustion engine (100) for a vehicle, comprising:
a crankshaft (102) having a first crankshaft stem (110) and a second crankshaft stem (120), the first crankshaft stem (110) and the second crankshaft stem (120) configured to be attached to a connecting rod (130) connected to a piston of the internal combustion engine (100);
a rotary electric machine (140) attached to the first crankshaft stem (110);
a balancer drive gear (150) mounted on the first crankshaft stem (110);
a balancer shaft (160) for balancing dynamic forces within the internal combustion engine (100); and
a balancer driven gear (170) mounted on the balancer shaft (160), the balancer driven gear (170) configured to mesh with the balancer drive gear (150) on the first crankshaft stem (110), thereby allowing the balancer shaft (160) to rotate for balancing dynamic forces within the internal combustion engine (100).

2. The internal combustion engine (100) as claimed in claim 1, wherein the rotary electric machine (140) comprises a stator and a rotor (142), the rotor (142) being attached to the first crankshaft stem (110).

3. The internal combustion engine (100) as claimed in claim 2, wherein the balancer drive gear (150) is attached to the rotor (142) of the rotary electric machine (140).

4. The internal combustion engine (100) as claimed in claim 1, wherein the balancer shaft (160) comprises a first end (160A) and a second end (160B), the balancer driven gear (170) being mounted on the first end (160A) of the balancer shaft (160).

5. The internal combustion engine (100) as claimed in claim 4, comprising a first bearing (162) and a second bearing (164) for supporting the balancer shaft (160), the second end (160B) of the balancer shaft (160) being supported on the second bearing (164), and the first bearing (162) being disposed between the balancer driven gear (170) and the second bearing (164).

6. The internal combustion engine (100) as claimed in claim 5, comprising one or more eccentric lobes (166) provided on the balancer shaft (160), the one or more eccentric lobes (166) being disposed between the first bearing (162) and the second bearing (164).

7. The internal combustion engine (100) as claimed in claim 1, wherein the crankshaft (102) comprises a first crankshaft web (112) connected to the first crankshaft stem (110) and a second crankshaft web (122) connected to the second crankshaft stem (120), such that the connecting rod (130) is attached to the first crankshaft web (112) and the second crankshaft web (122) for converting the translational motion of the piston into rotary motion of the crankshaft (102).

8. The internal combustion engine (100) as claimed in claim 6 and 7, wherein the one or more eccentric lobes (166) are configured to rotate between the first crankshaft web (112) and the second crankshaft web (122).

9. The internal combustion (100) as claimed in claim 7, comprising a bearing seating portion (180) provided on the second crankshaft stem (120) and abutting the second crankshaft web (122), the bearing seating portion (180) configured to receive a crankshaft supporting bearing.

Dated this 09th day of June 2022
TVS MOTOR COMPANY LIMITED
By their Agent & Attorney

(Nikhil Ranjan)
of Khaitan & Co
Reg No IN/PA-1471