Title of Invention	ROCKER ARM ASSEMBLY FOR AN INTERNAL COMBUSTION ENGINE
Abstract	Disclosed is a rocker arm assembly (18) for an internal combustion engine comprising: a) two rocker arm members (16) each having first and second ends (20a, 22a; 20b, 22b); and b) transmitting means (6) for actuating a rocker arm member (16) to actuate engine valves (23, 24). Each rocker arm member (16) may be disposed on opposite sides of a longitudinal axis of the transmitting means which may be camshaft (202). The first and second ends of a rocker arm member (16) are arranged to reduce friction and minimise toppling moment of each rocker arm member (16). The engine valves may be inlet and exhaust valves (23, 24). The rocker arm assembly (18) is conveniently employed in a small displacement engine (100) having a plurality of spark plugs (40, 32) enabling efficient engine operation using lean fuel/air mixtures.

Title of Invention

ROCKER ARM ASSEMBLY FOR AN INTERNAL COMBUSTION ENGINE

Abstract

Disclosed is a rocker arm assembly (18) for an internal combustion engine comprising: a) two rocker arm members (16) each having first and second ends (20a, 22a; 20b, 22b); and b) transmitting means (6) for actuating a rocker arm member (16) to actuate engine valves (23, 24). Each rocker arm member (16) may be disposed on opposite sides of a longitudinal axis of the transmitting means which may be camshaft (202). The first and second ends of a rocker arm member (16) are arranged to reduce friction and minimise toppling moment of each rocker arm member (16). The engine valves may be inlet and exhaust valves (23, 24). The rocker arm assembly (18) is conveniently employed in a small displacement engine (100) having a plurality of spark plugs (40, 32) enabling efficient engine operation using lean fuel/air mixtures.

Full Text	FORM 2 THE PATENTS ACT, 1970 (39 of 1970) As amended by the Patents (Amendment) Act, 2005 & The Patents Rules, 2003 As amended by the Patents (Amendment) Rules, 2005 COMPLETE SPECIFICATION (See section 10 and rule 13) TITLE OF THE INVENTION ROCKER ARM ASSEMBLY FOR AN INTERNAL COMBUSTION ENGINE APPLICANTS Name : Bajaj Auto Limited Nationality : Indian Company Address: Akurdi, Pune 411035, Maharashtra, India PREAMBLE TO THE DESCRIPTION The following specification particularly describes the nature of this invention and the manner in which it is to be performed: This invention relates to a rocker arm assembly for an internal combustion engine. Internal combustion engines are known in which each cylinder is provided with two valves namely inlet valve and exhaust valve. These valves open in a cavity in the cylinder head conventionally known as a combustion chamber. These valves are typically sized and arranged "in line" to optimize power output. Figure ] shows a cylinder head 1000 with inlet and exhaust valves 1001 and 1002 arranged in line for a single spark ignited engine. Figure 2 shows a cylinder head 1010 with inlet and exhaust valves 1011 and 1012 arranged for a dual spark ignited engine. The valves 1011 and 1012 are necessarily smaller than valves 1001 and 1002 so the dual spark ignited engine may potentially deliver less power for the same sized engine. This is generally considered undesirable. Inlet and exhaust valves are actuated by a rocker arm assembly having respective rocker arms actuated by a cam on a camshaft rotating in sequence with the crankshaft through a timing chain and driving and driven sprockets. Typically, in an engine in which the middle portion of rocker arms, for the inlet and exhaust valves, is rockably assembled on rocker shafts, the ends of the rocker arms are "offset" or substantially displaced opposite to each other. The centre lines of both ends of a rocker arm are not on the same plane transverse to the axis of the rocker shaft. That is, planes passing through the centre of both ends of the rocker arms are not co-planar. The "offset" of the rocker therefore adds extra mass as compared to a "straight" rocker arm. Such an arrangement is disclosed in WO 01/57368 which applies such a rocker arm construction to a multi-cylinder, multi-valve engine with two camshafts, particularly in a diesel engine. Accordingly, activation of the rocker arm assembly requires comparatively more force to overcome the inertia of the rocker arms. Due to the greater inertia, frictiona] losses occur while operating rocker arms and this is detrimental to the performance of an engine, 5 JAN 2007 particularly one having a small bore or small capacity with very different design and operational considerations than a multi-cylinder, multi-valve engine. Such performance detriment, especially in terms of fuel economy, is further compounded by the requirement for stronger and heavier rocker arms to overcome toppling forces or moment exerted on the rocker. The combination of inertial and frictional forces causes loss of fuel economy, a significant issue where fuel costs are ever increasing. It is accordingly an object of the present invention to provide a rocker arm assembly for an internal combustion engine, particularly a small bore engine, in which the rocker arm assembly is less subject to frictional losses and toppling forces. Fuel economy may thus be improved. With this object in view, the present invention provides a rocker arm assembly for an internal combustion engine comprising: a) two rocker arm members each having first and second ends; and b) transmitting means for actuating said rocker arm member to actuate engine valves, wherein the first and second ends of a or each rocker arm member are arranged to minimize toppling moment of each rocker arm member. Conveniently, each rocker arm member may be disposed on opposite sides of a longitudinal axis of said transmitting means though other arrangements are possible. The transmitting means is conveniently a camshaft of the engine, each respective rocker arm member actuating one of the intake and exhaust valves of an internal combustion engine. The first end of each rocker arm member is connected to engine valve actuating means. The second end of each rocker arm member is connected to a roller rocker. Toppling moment or force may be minimized by having centre points of the first and second ends of each rocker arm member arranged in substantially coplanar relationship with a pivot point for that rocker arm, that is, with planes passing through centre lines of both ends of each rocker arm and the pivoting axis being in the same plane transverse to the axis of the rocker shaft. In that way, the rocker arm members - being straight - and, consequently, the valve trains are subject to reduced friction. In an engine employing the rocker arm assembly of the invention, higher fuel economies may therefore be achieved. In a further embodiment of the invention, there is provided an internal combustion engine comprising: a combustion chamber; intake and exhaust valves respectively provided in said combustion chamber; a rocker arm assembly having respective rocker arm members each having first and second ends and connected to a camshaft for actuating said intake and exhaust valves wherein the first and second ends of each rocker arm member are arranged to minimize toppling moment of each rocker arm member. Conveniently, each rocker arm member is disposed on opposite sides of a longitudinal axis of said transmitting means though other arrangements are possible. The first end of each rocker arm member is connected to valve actuating means. The second end of each rocker arm member is connected to a roller element that runs of the camshaft surface. As observed above, the toppling moment of each rocker arm member is minimized by arranging the first and second ends of each rocker arm member in a substantially co-planar relationship as above defined. In that way, the rocker arm members - being 'straight1 and lacking toppling loads - and, consequently, the valve trains are subject to reduced friction. Higher fuel economies may be achieved due to such reduction in valve train friction. This may be achieved by having the valves arranged in an offset relationship, not the optimal arrangement for maximized power output. The resultant shorter and less stressed rocker arm, and smaller sized intake and exhaust valves enables the rocker arm members to be lighter than conventionally used, and it is therefore possible to reduce the size of the intake and exhaust valve train elements making them lighter, thereby reducing inertia that in turn reduces valve spring forces leading to reduced frictional forces. This is especially useful for small bore small capacity engines. Though this comes at the cost of an effective loss of power, due to the requirement for smaller sized valves, fuel economies may be appreciably increased. In addition, the layout of intake and exhaust valves, in offset relation, that may be achieved with 'straight' rocker arm members allow the convenient packaging of twin ignition means or spark plugs even in a small bore engine where twin or dual spark plugs would not normally be used. This enables further improvements in fuel economy to be achieved by combustion of lean mixtures. The rocker arm assembly could be employed with advantage in an engine having twin spark plugs, especially small bore or small capacity engines operating on the four stroke principle, the same type as disclosed in the Applicant's Indian Patent 195904 dated July 16, 2002 (corresponding international patent application WO 2005/042954 Al). However, in accordance with the invention, the arrangement and design of the rocker arms allow both spark plugs to be arranged distal, that is, away from the timing chain cavity and mechanism. For example, the combustion chamber, preferably of pent-roof construction, may be considered to be divided into quadrants. Two diagonally opposed quadrants substantially contain the inlet and exhaust valves albeit there may be some overlap of the valves with other quadrants. The remaining two diagonally opposed quadrants contain the spark plugs, allowing dual spark plug operation and combustion of lean mixtures, improving fuel economy. The rocker arm assembly may conveniently be employed in other internal combustion engines. It is particularly advantageous for use in two valve overhead cam four stroke engines particularly of the small bore single cylinder type, an engine type that raises different design and operational issues than multi-cylinder engines. The rocker arm assembly of the invention may be more fully understood from the following description of a preferred embodiment thereof made with reference to the accompanying drawings in which: Figure 3 is a top view of the cylinder head of an internal combustion engine incorporating a rocker arm assembly in accordance with prior art. Figure 4 is a bottom view of the cylinder head of an internal combustion engine suitably incorporating a rocker arm assembly in accordance with one embodiment of the invention. Figure 5 is a side sectional view of the cylinder head of Figure 4 incorporating the rocker arm assembly of one embodiment of the invention. Figure 6 is a top sectional view of the cylinder head of Figures 4 and 5 showing the camshaft for actuating engine valves. Referring to Figure 3, the inlet and exhaust valves are actuated by rockers 205 and 206. Camshaft 202 is assembled in the cylinder head 201 with bearings 212 and 213. Camshaft 202 is provided with cams 203 and 204. The rockers 205 and 206 are pivoted at central portions on rocker shafts 207 and 208. First end 205a and 206a of each of rockers 205 and 206 rest on the inlet and exhaust valves and the second end 205b and 206b is actuated by inlet and exhaust cams 203 and 204. 215 is a driven sprocket which drives the camshaft 202. It can be observed that the centerlines of ends 205a and 205b of the rocker 205 are not in one plane transverse to the camshaft axis or these are "off-set". Similarly, the centerlines of ends 206a and 206b of the rocker 206 are not in one plane transverse to the camshaft axis or these are "off-set". During actuation of the inlet and exhaust valves the design of rockers 205 and 206 with their ends not being co-planar 6 introduce toppling loads acting on the rockers and induce valve train friction in the engine, and hampering fuel economy. Referring now to Figure 4, there is shown the bottom of a cylinder head 14 of a small bore internal combustion engine 100. The cylinder head 14 includes an inlet valve 23 and an exhaust valve 24 selected to be of smaller size than conventional and to deliver less power but to the benefit of improved fuel economy. The engine 100 works on the four stroke principle. Typical characteristics of such a small bore engine include a swept cylinder volume ranging from 70 cc to 200 cc and cylinder bore diameter 45 mm to 70 mm, employed as prime movers for operation of two or three wheeled vehicles or other motorized vehicles, for example, motorcycles. The inlet and exhaust valves 23 and 24 of engine 100 are actuated by a rocker arm assembly 18 more detail of which appears in Figures 5 and 6. Each valve 23 and 24 has a respective rocker arm 16, actuated by a cam 61 on the camshaft 6 through a timing chain and driving and driven sprockets 15. Camshaft 6 is provided with camshaft bearings 7 and 8. Rocker arms 16 are arranged on the opposite sides of the longitudinal axis 6a of camshaft 6, valves 23 and 24 being similarly located on opposite sides of longitudinal axis 6a. Rocker arms 16 each have associated roller rockers 28 and fulcrum bearings 30 pivotally mounted on shafts 29 encasing roller needles 32 and are conventionally arranged in this sense. Bearings 30 are designed to prevent skidding across camshaft lobe 50 thus reducing friction. Roller rockers 28 are also designed to reduce friction. The rocker arms 16 are connected at their first ends 20a and 22a to valve elements 23a and 24a respectively. The nuts 25 and 26 connected to respective push rods 23b and 24b allow adjustment of the length of travel of the valve elements 23a and 24a. Clashes of elements 23a and 24a, during operation, are desirably avoided. Second ends 20b and 22b of rocker arms 16 are connected to the roller rockers 28. First and second ends 20a, 20b, 7 22a and 22b of each rocker arm 16 are substantially co-planar with centre lines passing through first and second ends 20a, 20b, 22a and 22b of each rocker arm 20 and 22 and a pivot point on the pivoting axis 30a passing through correspondent fulcrum bearing 30 being in alignment, thus forming 'straight' rocker arms 16. This rocker arm design, with first and second ends 20a, 20b, 22a and 22b and pivot point arranged in co-planar relation reduces or avoids toppling loads acting on the rocker arms 16 and is useful in reducing valve train friction in the engine 100, and improving fuel economy. The rocker arm assembly 18 actuates the valve elements 23a and 24a in an otherwise conventional manner, dependent on the operating requirements of engine 100. The engine 100, incorporating the rocker arm assembly 18, enables the small bore engine to be fitted with dual spark plugs 40 and 42, each of conventional manufacture, allowing the engine to operate in a lean combustion mode to improve fuel economy. As seen in Figure 4, the combustion chamber 110 may be divided into quadrants. The intake and exhaust valves 23 and 24 are offset and may be considered to reside in diagonally opposed quadrants notwithstanding some overlap of the valves 23 and 24 with other quadrants. Spark plugs 40 and 42 reside in the remaining diagonally opposed quadrants of combustion chamber 110 and do not extend through the timing chain cavity. Figure 4 also demonstrates the pent-roof construction of combustion chamber 110. The arrangement of spark plugs 40 and 42 permitted by the rocker arm assembly 18 of the invention, avoids the need for a spark plug to extend through that timing chain cavity, a lubricated location. This is another advantage of the present invention. Benefits of using an engine employing the rocker arm assembly of the present invention may be illustrated by reference to Table 1 showing a comparison for a single spark plug engine (SSP) with a prior art rocker arm assembly, subject to toppling loads as above described, and a dual spark plug engine (DSP-R) with offset valves and a rocker arm assembly as described with reference to Figures 3 and 4 above. [Table 1] Intake valve diameter (mm) 27.5 25 Intake valve weight (gm) 25.8 20.3 Exhaust valve diameter (mm) 24 21.5 Exhaust valve weight (gm) 22.8 17.6 Rocker weight (gm) 50 36.3 Valve spring Stiffness (kg/mm) 2.6/3.78 1.25/1.72 Max Power (Ps) 10.62 9.8 Max Power engine speed (rpm) 8,500 8,000 Max Torque (Nm) 9.88 10.5 Max Torque engine speed (rpm) 7,000 5,500 Fuel Economy 40 82 95 (km/litre) Fuel Economy IDC 65 72 (km/litre) IDC = Indian Driving Cycle. Table 1 It may be observed that while maximum power output of the DSP-R has marginally reduced in comparison with SSP, there is a significant improvement in the fuel economy. Modifications and variations of the rocker arm assembly of the present invention will be apparent to the skilled reader of this disclosure. Such modifications and variations are deemed within the scope of the invention. For example, the first and second ends 20a, 22a, 20b, 22b and pivot point of the rocker arm 16 need not be precisely co-planar to achieve reduced toppling loads, reduced friction, fuel economy and other benefits of the invention. We claim: 1. A rocker arm assembly for an internal combustion engine comprising: a) two rocker arm members each having first and second ends; and b) transmitting means for actuating said rocker arm member to actuate engine valves, wherein first and second ends of a or each rocker arm member are arranged to minimize toppling moment of each rocker arm member. 2. The rocker arm assembly of claim 1 wherein each rocker arm member is disposed on an opposite side of a longitudinal axis of the transmitting means. 3. The rocker arm assembly of claim 1 or 2 wherein the transmitting means is a camshaft of the engine. 4. The rocker arm assembly of any one of claims 1 to 3 wherein each respective rocker arm member actuates one of the intake and exhaust valves of an internal combustion engine. 5. The rocker arm assembly of any one of the preceding claims wherein said first and second ends and a pivot point on a pivoting axis for each rocker arm member are arranged in substantially co-planar relationship with planes passing through centre lines of both ends of each rocker arm being in the same plane transverse to the axis of the rocker shaft. 6. An spark ignited internal combustion engine comprising: a combustion chamber; intake and exhaust valves respectively provided in said combustion chamber; 5 JAN 2007 a rocker arm assembly having respective rocker arm members each having first and second ends and connected to a transmitting means for actuating said intake and exhaust valves wherein the first and second ends of a or each rocker arm member are arranged to minimize toppling moment of each rocker arm member. The engine of claim 6 wherein each rocker arm member is disposed on an opposite side of a longitudinal axis of the transmitting means. The engine of claim 6 or 7 being a single cylinder engine. The engine of claim 8 being a small bore engine, preferably having capacity of 75 cc to 225cc. The engine of any one of claims 6 to 9 wherein the inlet and exhaust valves are arranged in an offset relationship. The engine of any one of claims 6 to 10 wherein the combustion chamber has a pent roof configuration. The engine of any one of claims 6 to U wherein the combustion chamber is provided with dual spark plugs. A rocker arm assembly substantially as hereinbefore described with reference to the drawings. 14. An internal combustion engine substantially as hereinbefore described with reference to the drawings. 5 JAN 2007

Full Text

FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
ROCKER ARM ASSEMBLY FOR AN INTERNAL COMBUSTION ENGINE
APPLICANTS
Name : Bajaj Auto Limited
Nationality : Indian Company
Address: Akurdi, Pune 411035, Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

This invention relates to a rocker arm assembly for an internal combustion engine.
Internal combustion engines are known in which each cylinder is provided with two valves namely inlet valve and exhaust valve. These valves open in a cavity in the cylinder head conventionally known as a combustion chamber. These valves are typically sized and arranged "in line" to optimize power output. Figure ] shows a cylinder head 1000 with inlet and exhaust valves 1001 and 1002 arranged in line for a single spark ignited engine. Figure 2 shows a cylinder head 1010 with inlet and exhaust valves 1011 and 1012 arranged for a dual spark ignited engine. The valves 1011 and 1012 are necessarily smaller than valves 1001 and 1002 so the dual spark ignited engine may potentially deliver less power for the same sized engine. This is generally considered undesirable.
Inlet and exhaust valves are actuated by a rocker arm assembly having respective rocker arms actuated by a cam on a camshaft rotating in sequence with the crankshaft through a timing chain and driving and driven sprockets.
Typically, in an engine in which the middle portion of rocker arms, for the inlet and exhaust valves, is rockably assembled on rocker shafts, the ends of the rocker arms are "offset" or substantially displaced opposite to each other. The centre lines of both ends of a rocker arm are not on the same plane transverse to the axis of the rocker shaft. That is, planes passing through the centre of both ends of the rocker arms are not co-planar. The "offset" of the rocker therefore adds extra mass as compared to a "straight" rocker arm.
Such an arrangement is disclosed in WO 01/57368 which applies such a rocker arm construction to a multi-cylinder, multi-valve engine with two camshafts, particularly in a diesel engine.
Accordingly, activation of the rocker arm assembly requires comparatively more force to overcome the inertia of the rocker arms. Due to the greater inertia, frictiona] losses occur while operating rocker arms and this is detrimental to the performance of an engine,
5 JAN 2007

particularly one having a small bore or small capacity with very different design and operational considerations than a multi-cylinder, multi-valve engine. Such performance detriment, especially in terms of fuel economy, is further compounded by the requirement for stronger and heavier rocker arms to overcome toppling forces or moment exerted on the rocker. The combination of inertial and frictional forces causes loss of fuel economy, a significant issue where fuel costs are ever increasing.
It is accordingly an object of the present invention to provide a rocker arm assembly for an internal combustion engine, particularly a small bore engine, in which the rocker arm assembly is less subject to frictional losses and toppling forces. Fuel economy may thus be improved.
With this object in view, the present invention provides a rocker arm assembly for an internal combustion engine comprising:
a) two rocker arm members each having first and second ends; and
b) transmitting means for actuating said rocker arm member to actuate engine valves,
wherein the first and second ends of a or each rocker arm member are arranged to minimize toppling moment of each rocker arm member.
Conveniently, each rocker arm member may be disposed on opposite sides of a longitudinal axis of said transmitting means though other arrangements are possible.
The transmitting means is conveniently a camshaft of the engine, each respective rocker arm member actuating one of the intake and exhaust valves of an internal combustion engine. The first end of each rocker arm member is connected to engine valve actuating means. The second end of each rocker arm member is connected to a roller rocker.
Toppling moment or force may be minimized by having centre points of the first and second ends of each rocker arm member arranged in substantially coplanar relationship with a pivot point for that rocker arm, that is, with planes passing through centre lines of

both ends of each rocker arm and the pivoting axis being in the same plane transverse to the axis of the rocker shaft. In that way, the rocker arm members - being straight - and, consequently, the valve trains are subject to reduced friction. In an engine employing the rocker arm assembly of the invention, higher fuel economies may therefore be achieved.
In a further embodiment of the invention, there is provided an internal combustion engine
comprising:
a combustion chamber;
intake and exhaust valves respectively provided in said combustion chamber;
a rocker arm assembly having respective rocker arm members each having first and second ends and connected to a camshaft for actuating said intake and exhaust valves wherein the first and second ends of each rocker arm member are arranged to minimize toppling moment of each rocker arm member.
Conveniently, each rocker arm member is disposed on opposite sides of a longitudinal axis of said transmitting means though other arrangements are possible.
The first end of each rocker arm member is connected to valve actuating means. The second end of each rocker arm member is connected to a roller element that runs of the camshaft surface.
As observed above, the toppling moment of each rocker arm member is minimized by arranging the first and second ends of each rocker arm member in a substantially co-planar relationship as above defined. In that way, the rocker arm members - being 'straight1 and lacking toppling loads - and, consequently, the valve trains are subject to reduced friction. Higher fuel economies may be achieved due to such reduction in valve train friction. This may be achieved by having the valves arranged in an offset relationship, not the optimal arrangement for maximized power output.

The resultant shorter and less stressed rocker arm, and smaller sized intake and exhaust valves enables the rocker arm members to be lighter than conventionally used, and it is therefore possible to reduce the size of the intake and exhaust valve train elements making them lighter, thereby reducing inertia that in turn reduces valve spring forces leading to reduced frictional forces. This is especially useful for small bore small capacity engines. Though this comes at the cost of an effective loss of power, due to the requirement for smaller sized valves, fuel economies may be appreciably increased.
In addition, the layout of intake and exhaust valves, in offset relation, that may be achieved with 'straight' rocker arm members allow the convenient packaging of twin ignition means or spark plugs even in a small bore engine where twin or dual spark plugs would not normally be used. This enables further improvements in fuel economy to be achieved by combustion of lean mixtures.
The rocker arm assembly could be employed with advantage in an engine having twin spark plugs, especially small bore or small capacity engines operating on the four stroke principle, the same type as disclosed in the Applicant's Indian Patent 195904 dated July 16, 2002 (corresponding international patent application WO 2005/042954 Al).
However, in accordance with the invention, the arrangement and design of the rocker arms allow both spark plugs to be arranged distal, that is, away from the timing chain cavity and mechanism. For example, the combustion chamber, preferably of pent-roof construction, may be considered to be divided into quadrants. Two diagonally opposed quadrants substantially contain the inlet and exhaust valves albeit there may be some overlap of the valves with other quadrants. The remaining two diagonally opposed quadrants contain the spark plugs, allowing dual spark plug operation and combustion of lean mixtures, improving fuel economy.
The rocker arm assembly may conveniently be employed in other internal combustion engines. It is particularly advantageous for use in two valve overhead cam four stroke

engines particularly of the small bore single cylinder type, an engine type that raises different design and operational issues than multi-cylinder engines.
The rocker arm assembly of the invention may be more fully understood from the following description of a preferred embodiment thereof made with reference to the accompanying drawings in which:
Figure 3 is a top view of the cylinder head of an internal combustion engine incorporating a rocker arm assembly in accordance with prior art.
Figure 4 is a bottom view of the cylinder head of an internal combustion engine suitably incorporating a rocker arm assembly in accordance with one embodiment of the invention.
Figure 5 is a side sectional view of the cylinder head of Figure 4 incorporating the rocker arm assembly of one embodiment of the invention.
Figure 6 is a top sectional view of the cylinder head of Figures 4 and 5 showing the camshaft for actuating engine valves.
Referring to Figure 3, the inlet and exhaust valves are actuated by rockers 205 and 206. Camshaft 202 is assembled in the cylinder head 201 with bearings 212 and 213. Camshaft 202 is provided with cams 203 and 204. The rockers 205 and 206 are pivoted at central portions on rocker shafts 207 and 208. First end 205a and 206a of each of rockers 205 and 206 rest on the inlet and exhaust valves and the second end 205b and 206b is actuated by inlet and exhaust cams 203 and 204. 215 is a driven sprocket which drives the camshaft 202. It can be observed that the centerlines of ends 205a and 205b of the rocker 205 are not in one plane transverse to the camshaft axis or these are "off-set". Similarly, the centerlines of ends 206a and 206b of the rocker 206 are not in one plane transverse to the camshaft axis or these are "off-set". During actuation of the inlet and exhaust valves the design of rockers 205 and 206 with their ends not being co-planar
6

introduce toppling loads acting on the rockers and induce valve train friction in the engine, and hampering fuel economy.
Referring now to Figure 4, there is shown the bottom of a cylinder head 14 of a small bore internal combustion engine 100. The cylinder head 14 includes an inlet valve 23 and an exhaust valve 24 selected to be of smaller size than conventional and to deliver less power but to the benefit of improved fuel economy. The engine 100 works on the four stroke principle. Typical characteristics of such a small bore engine include a swept cylinder volume ranging from 70 cc to 200 cc and cylinder bore diameter 45 mm to 70 mm, employed as prime movers for operation of two or three wheeled vehicles or other motorized vehicles, for example, motorcycles.
The inlet and exhaust valves 23 and 24 of engine 100 are actuated by a rocker arm assembly 18 more detail of which appears in Figures 5 and 6. Each valve 23 and 24 has a respective rocker arm 16, actuated by a cam 61 on the camshaft 6 through a timing chain and driving and driven sprockets 15. Camshaft 6 is provided with camshaft bearings 7 and 8.
Rocker arms 16 are arranged on the opposite sides of the longitudinal axis 6a of camshaft 6, valves 23 and 24 being similarly located on opposite sides of longitudinal axis 6a.
Rocker arms 16 each have associated roller rockers 28 and fulcrum bearings 30 pivotally mounted on shafts 29 encasing roller needles 32 and are conventionally arranged in this sense. Bearings 30 are designed to prevent skidding across camshaft lobe 50 thus reducing friction. Roller rockers 28 are also designed to reduce friction.
The rocker arms 16 are connected at their first ends 20a and 22a to valve elements 23a and 24a respectively. The nuts 25 and 26 connected to respective push rods 23b and 24b allow adjustment of the length of travel of the valve elements 23a and 24a. Clashes of elements 23a and 24a, during operation, are desirably avoided. Second ends 20b and 22b of rocker arms 16 are connected to the roller rockers 28. First and second ends 20a, 20b,
7

22a and 22b of each rocker arm 16 are substantially co-planar with centre lines passing through first and second ends 20a, 20b, 22a and 22b of each rocker arm 20 and 22 and a pivot point on the pivoting axis 30a passing through correspondent fulcrum bearing 30 being in alignment, thus forming 'straight' rocker arms 16. This rocker arm design, with first and second ends 20a, 20b, 22a and 22b and pivot point arranged in co-planar relation reduces or avoids toppling loads acting on the rocker arms 16 and is useful in reducing valve train friction in the engine 100, and improving fuel economy.
The rocker arm assembly 18 actuates the valve elements 23a and 24a in an otherwise conventional manner, dependent on the operating requirements of engine 100.
The engine 100, incorporating the rocker arm assembly 18, enables the small bore engine to be fitted with dual spark plugs 40 and 42, each of conventional manufacture, allowing the engine to operate in a lean combustion mode to improve fuel economy. As seen in Figure 4, the combustion chamber 110 may be divided into quadrants. The intake and exhaust valves 23 and 24 are offset and may be considered to reside in diagonally opposed quadrants notwithstanding some overlap of the valves 23 and 24 with other quadrants. Spark plugs 40 and 42 reside in the remaining diagonally opposed quadrants of combustion chamber 110 and do not extend through the timing chain cavity. Figure 4 also demonstrates the pent-roof construction of combustion chamber 110.
The arrangement of spark plugs 40 and 42 permitted by the rocker arm assembly 18 of the invention, avoids the need for a spark plug to extend through that timing chain cavity, a lubricated location. This is another advantage of the present invention.
Benefits of using an engine employing the rocker arm assembly of the present invention may be illustrated by reference to Table 1 showing a comparison for a single spark plug engine (SSP) with a prior art rocker arm assembly, subject to toppling loads as above described, and a dual spark plug engine (DSP-R) with offset valves and a rocker arm assembly as described with reference to Figures 3 and 4 above.

[Table 1]

Intake valve diameter (mm) 27.5 25
Intake valve weight (gm) 25.8 20.3
Exhaust valve diameter (mm) 24 21.5
Exhaust valve weight (gm) 22.8 17.6
Rocker weight (gm) 50 36.3
Valve spring Stiffness (kg/mm) 2.6/3.78 1.25/1.72
Max Power (Ps) 10.62 9.8
Max Power engine speed (rpm) 8,500 8,000
Max Torque (Nm) 9.88 10.5
Max Torque engine speed (rpm) 7,000 5,500

Fuel Economy 40 82 95
(km/litre)
Fuel Economy IDC 65 72
(km/litre)
IDC = Indian Driving Cycle.
Table 1
It may be observed that while maximum power output of the DSP-R has marginally reduced in comparison with SSP, there is a significant improvement in the fuel economy.
Modifications and variations of the rocker arm assembly of the present invention will be apparent to the skilled reader of this disclosure. Such modifications and variations are deemed within the scope of the invention. For example, the first and second ends 20a, 22a, 20b, 22b and pivot point of the rocker arm 16 need not be precisely co-planar to achieve reduced toppling loads, reduced friction, fuel economy and other benefits of the invention.

We claim:
1. A rocker arm assembly for an internal combustion engine comprising:
a) two rocker arm members each having first and second ends; and
b) transmitting means for actuating said rocker arm member to actuate engine
valves,
wherein first and second ends of a or each rocker arm member are arranged to minimize toppling moment of each rocker arm member.
2. The rocker arm assembly of claim 1 wherein each rocker arm member is disposed on an opposite side of a longitudinal axis of the transmitting means.
3. The rocker arm assembly of claim 1 or 2 wherein the transmitting means is a camshaft of the engine.
4. The rocker arm assembly of any one of claims 1 to 3 wherein each respective rocker arm member actuates one of the intake and exhaust valves of an internal combustion engine.
5. The rocker arm assembly of any one of the preceding claims wherein said first and second ends and a pivot point on a pivoting axis for each rocker arm member are arranged in substantially co-planar relationship with planes passing through centre lines of both ends of each rocker arm being in the same plane transverse to the axis of the rocker shaft.
6. An spark ignited internal combustion engine comprising:
a combustion chamber;
intake and exhaust valves respectively provided in said combustion
chamber;
5 JAN 2007

a rocker arm assembly having respective rocker arm members each having first and second ends and connected to a transmitting means for actuating said intake and exhaust valves wherein the first and second ends of a or each rocker arm member are arranged to minimize toppling moment of each rocker arm member.
The engine of claim 6 wherein each rocker arm member is disposed on an opposite side of a longitudinal axis of the transmitting means.
The engine of claim 6 or 7 being a single cylinder engine.
The engine of claim 8 being a small bore engine, preferably having capacity of 75 cc to 225cc.
The engine of any one of claims 6 to 9 wherein the inlet and exhaust valves are arranged in an offset relationship.
The engine of any one of claims 6 to 10 wherein the combustion chamber has a pent roof configuration.
The engine of any one of claims 6 to U wherein the combustion chamber is provided with dual spark plugs.
A rocker arm assembly substantially as hereinbefore described with reference to the drawings.

14. An internal combustion engine substantially as hereinbefore described with reference to the drawings.

5 JAN 2007

ROCKER ARM ASSEMBLY FOR AN INTERNAL COMBUSTION ENGINE

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