EP4115072A1

EP4115072A1 - Reciprocating assembly for an internal combustion engine

Info

Publication number: EP4115072A1
Application number: EP21714023.5A
Authority: EP
Inventors: Joseph Sumith; Jaya Jothi Johnson Vethanayagam; Ranjan Das BISWA
Original assignee: TVS Motor Co Ltd
Current assignee: TVS Motor Co Ltd
Priority date: 2020-03-02
Filing date: 2021-03-02
Publication date: 2023-01-11
Also published as: MX2022010839A; BR112022017611A2; WO2021176466A1; CN115190941A

Abstract

A vehicle's fuel efficiency can be increased by reduce overall size and weight of the engine. A longer connecting rod results in higher block height which leads to larger engine height and thereby resulting into increased engine mass. The overall weight of the engine can by reduced by reducing length of connecting rod. Thus, for improving fuel economy, a combination of crank offset and reduced L/S ratio provides better results. This is achieved by providing a L/S ratio < 1.65, where L is length of the connecting rod and S is the stroke length. According to one embodiment of the present invention, a reduced connecting rod length results into fouling of piston and crank web, which is eliminated by providing relief in the piston skirt and the crank web along the profile of interference of piston skirt and the crank web.

Description

RECIPROCATING ASSEMBLY FOR AN INTERNAL COMBUSTION

ENGINE TECHNICAL FIELD

[0001] The present subject matter generally relates to an internal combustion engine. More particularly but not exclusively, the present subject matter relates to a reciprocating assembly for the internal combustion engine. BACKGROUND

[0002] Generally, in a motor vehicle a frame assembly extends rearward from a head tube. The frame assembly acts as a skeleton for the vehicle that supports the vehicle parts. A front portion of the frame assembly connects to a front wheel through one or more front suspension(s). The frame assembly extends rearward of the vehicle, where a rear wheel is connected to a frame assembly through one or more rear suspension(s). An internal combustion (IC) engine is mounted to the frame assembly of the vehicle. The IC engine is functionally connected to the rear wheel, which provides the forward motion to the vehicle. Typically, plurality of panels are mounted to the frame assembly of the vehicle that covers various vehicle components.

[0003] The vehicle’s “fuel economy” is defined by a distance that the vehicle has travelled or the distance that it can travel using a particular amount of fuel. A vehicle’s internal combustion engine powers the vehicle to bring the laden weight of the vehicle into motion. Generally, a lower laden weight of the vehicle leads to a higher “fuel economy” compared to a vehicle with higher laden weight. Further, keeping the cost of fuel in mind, it is customer’s requirement that the “fuel economy” for a vehicle shall be as high as possible. Hence, to achieve the higher “fuel economy”, it is a constant endeavor to reduce the overall weight of the vehicle. Furthermore, friction between parts having relative motion with respect to each other such as gears and transmission components also contributes towards reduction in “fuel economy” of a vehicle. In an engine, the frictional losses arise due to friction between a piston and a side wall of the combustion chamber. If side thrust from piston to the side walls of combustion chamber is high, the piston would be pressed against sleeve wall causing higher friction. This is generally minimized by providing crank offset. Another method of increasing the fuel efficiency is to reduce overall size of the engine by reducing length of connecting rod. When connecting rod length (L) to Stroke (S) L/S ratio > = 1.65, for a fixed stroke, connecting rod length would be higher. A longer connecting rod results in higher block height which leads to higher engine height and thereby resulting into bigger engine and increased engine mass. An increased engine mass results into a vehicle with higher weight due to which fuel economy is reduced.

[0004] Further, since for meeting the vehicle engine capacity, stroke length and bore are mostly fixed values which cannot be altered much; a reduction in connecting rod length is a more viable option. A reduction in connecting rod length leads to fouling of piston with the crank web. Avoiding such fouling will mean compromise on the length making it longer or design of an engine system with small crank web which is undesirable & often not an option considering engine balancing requirements. Thus, there exists as need for a design on a compact Internal Combustion Engine (ICE) which can overcome all the above problems & other problems in known art. Hence, one of the primary objective of the present invention is to design a compact ICE which eliminates fouling of the piston with the crank web wherein the L/S ratio is kept less than 1.65.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 illustrates a cross section of an internal combustion engine.

[0006] Figure 2 illustrates a cylinder block and reciprocating assembly of the internal combustion engine with prior art problem of piston coming out of cylinder snout and piston fouling with the crank web while the piston is at BDC.

[0007] Figure 3 illustrates a modified crank web solving the problem of piston skirt fouling with the crank web while the piston is at BDC.

[0008] Figure 4 illustrates a cylinder block and reciprocating assembly of the internal combustion engine with prior art problem of. [0009] Figure 5 illustrates a perspective view of the crank web interaction with the cylinder.

DETAILED DESCRIPTION

[00010] An internal combustion engine comprises of a combustion chamber where combustion of fuel takes place. A connecting rod connects a piston and a crank web. The power generated in the combustion chamber is transmitted to the crank web through the connecting rod. One end of the connecting rod is connected to the piston using a gudgeon pin. The other end of the connecting rod is connected to the crank web through a crankshaft. In an endeavor to reduce weight of the engine, the L/S ratios of the engine is kept less than 1.65 wherein L is length of the connecting rod and S is the stroke length.

[00011] According to the present invention, the engine is also provided with an offset crankshaft. In an offset crankshaft, when the crankshaft is rotated in a clockwise direction, a distance that the piston travels from the top of the stroke (piston at maximum travel) to the bottom of the stroke (piston at the bottom of its travel) is greater than the diameter of the crankshaft rotation. The angle through which the crankshaft moves during the downstroke is greater than 180°. The engine therefore has a longer time power stroke than exhaust stroke.

[00012] Thus, for improving fuel economy and for providing sufficient torque, a combination of crank offset and reduced L/S ratio provides better results. This is achieved by providing a L/S ratio < 1.65, where L is length of the connecting rod and S is the stroke length.

[00013] Further, since for meeting the vehicle engine capacity, stroke length and bore are mostly fixed values which cannot be altered much; a reduction in connecting rod length is a more viable option. But, a reduction in connecting rod length leads to fouling of piston with the crank web. Avoiding such fouling will mean compromise on the length of the connecting rod and making it longer or design of an engine system with small crank web which is undesirable & often not an option considering engine balancing requirements. The connecting rod length reduction involves various packaging & fouling issues. Firstly, due to reduced length of connecting rod, the piston skirt comes closer to the crank web and with this reduced L/S ratio < 1.65, piston starts interfering with crank web making such a design practically unviable.

[00014] Thus, there exists as need for a design on a compact Internal Combustion Engine (ICE) which can overcome all the above problems & other problems in known art. Hence, one of the primary objectives of the present invention is to design a compact ICE which eliminates fouling of the piston with the crank web wherein the L/S ratio is kept less than 1.65.

[00015] According to one embodiment of the present invention, the fouling of the piston and the crank web is eliminated by providing relief in the piston skirt and the crank web along the profde of interference of piston skirt and the crank web. [00016]

[00017] These advantages of the present subject matter would be described in greater detail in conjunction with one or more embodiments with the corresponding figures in the following description. Figure 1 shows a typical single cylinder ICE with cross section by omitting many inside parts for clarity & brevity. A cylinder head 101, cylinder block 102, camshaft 103 is shown which is supported on said cylinder head 101. A lobe 103L on the camshaft 103 actuates a rocker arm 104. The rocker arm 104 includes a left side rocker arm 104A and a right-side rocker arm 104B. The left side rocker arm 104A and a right-side rocker arm 104B work in a similar function. The rocker arm 104 actuates an inlet tappet 105 and an exhaust tappet 106 to operate intake and exhaust valve respectively. A connecting rod 108 is connected to the piston through a connecting pin 107. The connecting rod 108 is connected to a crank web 110 through the crankshaft 109. The crank web 110 are two lobes carrying a pre determined weight to balance the engine during the reciprocating motion within the engine.

[00018] Generally, the piston along with a portion of piston skirt 111 slides in the combustion chamber within the cylinder block 102. During power stroke, the piston travels upwards and reaches a top dead center (TDC). During expansion stroke, the piston travels downwards and reaches a bottom dead center (BDC). Once length of the connecting rod 108 is shortened for an engine due to requirement of L/S ratio < 1.65, the piston skirt 111 tends to foul with the crank web 110 while the piston moves down towards bottom dead entre (BDC). [00019] Figure 2 illustrates a local cut section view of an engine assembly as per a prior art. The illustration shows a cylinder block 102, connecting rod 108, crank web 110, cylinder 201 and piston skirt 202. As clear from the illustration in Figure 2, as the piston moves down towards bottom dead entre (BDC), the piston skirt 202 is fouling with the crank web 110. [00020] Figure 3 illustrates a local cut section view of an engine assembly as per the present invention with many parts omitted for clarity. The fouling of the piston skirt 202 and the crank web 110 explained above can be avoided by creating an interface relief space (303) through recess (301, 302) which is provided on the crank web & said relief is juxtaposed at the interface of the piston skirt 202 and the crank web 110. This relief space 303created at the interface between the piston skirt 202 and the crank web 110 can be provided in multiple embodiments. As per another embodiment, an additional pair of conjugate cut-out (501, 502) is created on the piston skirt as shown in Fig 5. The at least one pair of local relief space (303) through recesses (301, 302) provided between the piston skirt 202 and the crank web 110 interface & the at least one pair of conjugate recess (501, 502) on the piston skirt allows a condition of overlapped reciprocating motion of piston skirt 202 and the crank web relative to each other while eliminating any possibility of fouling. This enables achieving a L/S ratio < 1.65 thereby enabling a design of a compact ICE.

[00021] According to one embodiment of the present invention, the crank web relief 303 at the piston skirt 202 and the crank web 110 interface is formed by providing a recess in the crank web 110 along the rotating interface profde of the piston skirt 202 and the crank web 110. The rotating interface profile is a space where the piston skirt 202 and the crank web 110 would have rubbed against each other in case the interface relief of the crank web is not provided. It is to be noted that according to one aspect of the present invention, the interface relief is provided with predetermined clearances to allow the free rotation of piston skirt 202 and the crank web 110 relative to each other. As per an aspect of the present invention, the piston skirt is provided with a cut-out of relief (501, 502) shown in Fig 5, which is juxtaposed with the corresponding at least one of the crank webs of the crankshaft assembly. Therefore, during power stroke movement, the relative rotation of the piston skirt 202 and the crank web 110 allows an overlapping of piston skirt 202 and the crank web 110 thereby enabling reduced length of connecting rod & design of a compact ICE with L/S < 1.65. Since reduced length of the connecting rod length is now achieved, the reciprocating mass of the engine is reduced. Since reciprocating mass is reduced due to the recess (301, 302) in the crank web, a lesser counter mass weight is required to balance the crank web and hence the recesses in crank web are adequate to achieve required balancing of the crank web. [00022] According to another embodiment of the present invention, the relief between the piston skirt 202 and the crank web 110 is formed by providing a plurality of recess in the piston skirt 202 along the conjugatively rotating interface profile of the piston skirt 202 and the crank web 110. The rotating interface profile is a space where the piston skirt 202 and the crank web 110 would have rubbed against each other in case the relief is not provided. It is to be noted that according to one embodiment of the present invention, the relief space is provided with the predetermined clearances to allow free rotation of piston skirt 202 and the crank web 110 relative to each other. The relative rotation of the piston skirt 202 and the crank web 110 allows an overlapping of piston skirt 202 and the crank web 110.

[00023] Figure 3 illustrates the relief space 303 provided in between the piston skirt 202 and the crank web 110. The cut-out mass at the top end of the crank web 110 to create the relief space 303 further helps in providing low inertia for the crank web 110 so as to enable easy return of the piston to top dead center after reaching the bottom dead center.

[00024] Figure 4 shows a perspective view of the relief spaces provided in between the piston skirt 202 and the crank web 110 by providing a recess in the piston skirt 202. Generally, the crank web 110 comprises of a first lobe 503 and a second lobe 504 (shown in Figure 5). The first lobe 503 and the second lobe 504 are additional weights on crank web and crankshaft which aid in providing balance to the engine and reduce vibrations during the reciprocating motion of the connecting rod and the piston. According to yet another embodiment, Figure 5 illustrates the relief recesses (501, 502) provided in between the piston skirt 202 and the crank web 110 by providing a recess on the outer periphery of the piston skirt 202. This recess in the piston skirt 202 helps in avoiding the fouling of the piston skirt 202 and the crank web 110 without adversely altering the configuration of the crank web 110. In this configuration, the relative rotation of the piston skirt 202 and the crank web 110 allows an overlapping of piston skirt 202 and the crank web 110. The relief space (303) in between the piston skirt (202) and the crank web (110) is formed by providing at least one of the recesses (501, 502) on the piston skirt (202). In yet another embodiment of the present invention, the relief space (303) in between the piston skirt (202) and the crank web (110) is formed by providing at least one of the recesses (301, 302) on the crank web (110). According to yet another embodiment, the relief space (303) in between the piston skirt (202) and the crank web (110) is formed by providing at least one of the recesses on cylinder skirt (204) of cylinder (201). The relief space (303) is formed with a conjugate shape to accommodate the first lobe (503) and the second lobe (504) when the piston is at bottom dead center. The reciprocating motion of piston skirt (202) and the crank web (110) relative to each other is overlapped at least during a portion of one stroke cycle when observed through a crankshaft axis X.

[00025] The above described relief spaces provided in one of the outer periphery of the piston skirt 202, the first lobe 503 and a second lobe 504 on the crank web 110 avoids the fouling of the piston skirt 202 and the crank web 110 when the piston skirt 202 reaches the bottom dead center. However, it is also possible that the fouling may take place at a place in between the top dead center and the bottom dead center. Hence, according to yet another embodiment of the present invention, the relief space in between the piston skirt and the crank web is formed by providing at least one of the recesses (501, 502) on the piston skirt (202) and one of the recesses (301, 302) on the crank web (110) at a location left to the bottom dead center and at a location right to the bottom dead center when observed through a crankshaft axis X. The present invention provides a compact engine with L/S ratio less than 1.65 thereby reducing the overall weight the engine and the vehicle thereby aiding in increasing fuel efficiency of the vehicle.

Claims

I/We claim:

1. A reciprocating internal combustion engine for a vehicle, the reciprocating internal combustion engine comprising: a cylinder head (101) accommodating a camshaft to actuate a rocker arm (104A, 104B) for opening and closing a plurality of intake valve (105) and exhaust valve (106); a cylinder block (102) accommodating a combustion chamber (201) where combustion of fuel takes place; a piston (203) accommodated within the combustion chamber (201), the piston (203) performing reciprocating motion, the piston (203) comprising a piston skirt (202); a connecting rod (108) connecting said piston (203) to a crankshaft (109) through a crank web (110), the crank web (110) having a first lobe (503) and a second lobe (504); and a relief space (303) is provided between the piston skirt (202) and the crank web (110) for allowing overlapped reciprocating motion of piston skirt (202) and the crank web (110) relative to each other.

2. The reciprocating internal combustion engine for a vehicle as claimed in claim 1 wherein relief space (303) in between the piston skirt (202) and the crank web (110) is formed by providing at least one of the recesses (501, 502) on the piston skirt (202).

3. The reciprocating internal combustion engine for a vehicle as claimed in claim 1 wherein relief space (303) in between the piston skirt (202) and the crank web (110) is formed by providing at least one of the recesses (301, 302) on the crank web (110).

4. The reciprocating internal combustion engine for a vehicle as claimed in claim 1 wherein relief space (303) in between the piston skirt (202) and the crank web (110) is formed by providing at least one of the recesses on cylinder skirt (204) of cylinder (201).

5. The reciprocating internal combustion engine for a vehicle as claimed in claim 1 wherein the relief space (303) includes a pre determined clearance between the piston skirt (202) and the crank web (110) for allowing fouling free relative rotation of piston skirt (202) and the crank web (110) with respect to each other.

6. The reciprocating internal combustion engine for a vehicle as claimed in claim 1 wherein the relief space (303) is formed with a conjugate shape to accommodate the first lobe (503) and the second lobe (504) when the piston is at bottom dead center.

7. The reciprocating internal combustion engine for a vehicle as claimed in claim 1 wherein the reciprocating motion of piston skirt (202) and the crank web (110) relative to each other is overlapped at least during a portion of one stroke cycle when observed through a crankshaft axis X.

8. The reciprocating internal combustion engine for a vehicle as claimed in claim 1 wherein the L/S ratio is lesser than 1.65, wherein L is the length of the connecting rod and S is stroke length of the engine.

9. The reciprocating internal combustion engine for a vehicle as claimed in claim 1 wherein the two recesses (301, 302) on the crank web (110) are continuously formed.

10. The reciprocating internal combustion engine for a vehicle as claimed in claim 1 wherein the two recesses (501, 502) on the piston skirt (202) are continuously formed.