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, 2006
PROVISIONAL SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Variable valve timing assembly for a 4-stroke internal combustion engine INVENTORS

a) Name Nationality Address
Sheth Nitin Ramchandra
Indian National
Bajaj Auto Limited, Akurdi, Pune 411035,
Maharashtra, India
and
b) Name : Asvathanarayanan Ramesh
Nationality : Indian National
Address : Indian Institute of Technology, Madras, Adiyar, Chennai
600036, Tamil Nadu, India
APPLICANTS

Name
Nationality
Address
And
Name
Nationality
Address

Bajaj Auto Limited Indian Company Akurdi, Pune 411035, Maharashtra, India
Indian Institute of Technology, Madras an autonomous research and educational institution established in India by a special Act of the Parliament of the Republic of India under the Institutes of Technology Act 1961 Adiyar, Chennai 600036, Tamil Nadu, India

PREAMBLE TO THE DESCRIPTION
The following specification describes the invention.


FIELD OF INVENTION:
This invention relates to a variable valve timing assembly for a 4-stroke internal
combustion engine.
This invention particularly relates to a phasing type variable valve timing assembly for a 4-stroke internal combustion engine, which advances or delays the timing of opening and closing of the inlet / exhaust valves of the engine in relation to the varying position of the piston with respect to the top dead centre (TDC) in the cylinder keeping the duration of opening and closing unchanged.
This invention also relates to a 4-stroke internal combustion engine comprising the variable valve timing assembly.
It is to be understood that the 4-stroke internal combustion engine comprising the variable valve timing assembly of the invention has particular utility for use in non-stationary variable speed applications like automotive or marine engine applications. However, it is also to be understood that the invention will also have utility in other engine configurations that use cam driven valves, for instance, in those 2-stroke engines that utilize one or more cam driven valves.
BACKGROUND
The inlet and exhaust valves in a four-stroke internal combustion engine are actuated by a pair of rocker arms which are pivoted on the cylinder head. The rocker arms are actuated by the inlet cam and exhaust cam on the camshaft, which in turn is driven by the crankshaft of the engine through a chain drive. As the cams being rigidly or integrally formed on the camshaft, timing instances of valve actuation are fixed or constant and invariable in relation to the position of the piston with respect to the top dead centre. Fuel consumption of the engine at lower engine speed is lesser as compared to that at a higher engine speed. Therefore, in order to improve overall engine efficiency, that is, engine performance throughout the speed range and increase power and torque outputs
2

and reduce fuel wastage and emissions the inlet valve should ideally close early at lower rpm of the engine as compared to higher rpm of the engine.
Electronic and hydraulic variable valve timing (WT) assemblies are complicated and complex in construction and are also expensive. Besides being large in size and occupying large area they also require periodic maintenance and extra power for their operation.
Mechanical variable valve timing assemblies are simple in construction, cost effective, compact and robust, low maintenance and durable. Elrod and Nelson type variable valve timing mechanism comprises a pair of cams one of which is movable and is attached to an inner hexagonal-section shaft. An outer tubular shaft is provided on the inner shaft and is driven by a pulley or a sprocket. One of the pair of cams actuates the valve at any particular point in time. The valve control in this construction will inevitably be poor because of the sudden changes in acceleration and velocity when transferring control from one cam to the other (A Review of Variable Engine Valve Timing by C Gray, published in 1989 by Society of Automotive Engineers, Inc, p. 6636, column 2). Ford harmonic drive type variable valve mechanism comprises an eccentric coupling with a transverse slider. The slider comprises two relatively slidable components. The frictional forces and losses are high in this construction due to the relative sliding of the sliding components. Therefore, operation of the mechanism is not smooth and wear and tear to the components of the mechanism is high thereby calling for frequent maintenance (A Review of Variable Engine Valve Timing by C Gray, published in 1989 by Society of Automotive Engineers, Inc, p 6637 column 1).
OBJECTS OF INVENTION
An object of the invention is to provide a variable valve timing arrangement for a 4-stroke internal combustion engine, which varies the timing of actuation of the inlet valve in the cylinder of the engine in response to changing engine speed.
3

Another object of the invention is to provide a variable valve timing arrangement for a four-stroke internal combustion engine that improves the engine performance in terms of fuel economy, power and torque and emissions.
Another object of the invention is to provide a variable valve timing assembly for a 4-stroke internal combustion engine, which is compact and robust, simple in construction, economical, has low maintenance and is durable.
Another object of the invention is to provide a 4-stroke internal combustion engine comprising the variable valve timing assembly.
DETAILED DESCRIPTION OF INVENTION
In the internal combustion engines of prior art, engines are described as having variable camshaft timing, the opening and closing points of the valves can be varied but the actual duration of the valve opening remains fixed. A conventional camshaft that provides a fixed amount of valve opening allows an engine to achieve a maximum volumetric efficiency and hence torque at only one point in the engine's revolution range. The torque falls off on either side of this point. A cam shaft arrangement, which allows the valve opening timing to be varied so as to maximize the torque through out the engine's speed range would be very desirable. There is a constant effort to achieve mechanically continuous variable system of valve opening timing. Systems that are not continuously variable but operating on a two-stage principle has been adopted and used successfully by many. Although the main advantage of a variable valve timing camshaft is to improve the torque spread of an engine, it could also be used to provide throttle free control of the engine's induction to minimize the intake pumping losses and/or to achieve low exhaust emission. A drive means is provided in the arrangement so that positive displacements of the cam from its original position retard the timing of valve actuation whilst maintaining the same duration.
In conventional valve timing assembly, the inlet and outlet valves are actuated from a fixed camshaft lobe and the resulting valve events are a compromise between the
4

engine's valve event time requirements at various engine speeds. Now the attempt is made herein to vary the timing from the predetermined values via a fixed driven camshaft.
According to the invention there is provided a variable valve timing assembly for an internal combustion engine utilising at least one cam which cooperates with a valve actuating mechanism to operate a valve, comprising a movable cam corresponding to a valve in the cylinder head of the engine, the cam being disposed on the cam shaft adapted to translate a predetermined path on the camshaft at an angle with respect to the centre line passing through the length of the camshaft, the length of the said predetermined path and the said angle corresponding to the delay or advancement of the valve closing and opening timings in relation to the varying position of the piston of the engine with respect to the top dead centre in the cylinder, such that, in use the cam moves along the camshaft, and is rotated with respect to the crankshaft, whilst at all times being in engagement with the valve actuating mechanism.
Preferably the movement of the cam along the centerline of the camshaft, and its rotation with respect to the camshaft is a function of the engine rpm.
Preferably a drive means is mounted on the cam shaft at the drive end side of the camshaft for moving the cam forward and back on the camshaft responsive to the engine rpm.
Preferably the internal combustion engine is a 4-stroke engine and the cam is an inlet valve cam.
Preferably the predetermined path on the camshaft comprises semi-elliptical groves.
According to an embodiment of the invention, the drive means comprises a conical member comprising a central bore and a tubular projection projecting from one face of the conical member, a pair of diametrically oppositely placed guide members projecting
5

out inwardly through the tubular projection, the conical member being movably disposed on the camshaft through the central bore and tubular projection thereof with the guide members engaged in a pair of semi helical grooves provided on the camshaft diametrically opposite to each other at the said angle with respect to the centre line passing through the length of the camshaft in the vertical plane, the length of said semi helical grooves and the said angle corresponding to the delay or advancement of the inlet valve closing and opening timings in relation to the position of the engine piston with respect to the top dead centre in the cylinder and with respect to the engine speed, a plurality of spaced flyweights disposed around the camshaft and pivoted on a support member rigidly fitted on the camshaft, the distal ends of the flyweights being movably located against the conical member, the conical member being spring tensioned against the fly weights and the inlet cam being mounted on the tubular projection. Due to the centrifugal force of the flyweights, the conical member will move along the camshaft for a particular distance dependent on the helix grooved on the camshaft.
According to an embodiment of the invention each of the flyweights comprises a pair of spaced arms pivoted together on the support member and a roller located between the distal ends of the arms, the shaft of the roller being rigidly held at the distal ends of the arms and the roller bearing against the conical member adapted to roll against the conical member.
The following is detailed description of the invention with reference to the accompanying drawings, in which:
Figure 1 is side sectional view of the cylinder head and cylinder of a 4-stroke internal combustion engine including the variable valve timing assembly according to an embodiment of the invention;
Figure 2 is cross section of the cylinder head of Figure 1 along the camshaft axis;
Figure 3 is side view of the camshaft and variable valve timing assembly of Figure 1;
6

Figure 4 is isometric view of the camshaft and variable valve timing assembly of Figure
l;
Figure 5 is side view of the flyweights of the valve timing assembly of Figure 1 pivoted on the support member;
Figure 6 is a view in the direction of 'X' in Figure 5; and
Figure 7 is comparative performance data of a 4-stroke single cylinder engine when run with fixed or constant valve timing and with a typical variable valve timing assembly of the invention.
Figure 8 depicts the top view of the mechanism in two positions viz., showing the cam in its initial position corresponding to lower engine speed and then in a position where it is displaced the most along the cam shaft, corresponding to higher engine speed.
With reference to Figures 1 to 6 of the accompanying drawings, the cylinder head and cylinder of a 4-stroke internal combustion engine (not shown) are marked 1 and 2 respectively (Figures 1 and 2). The camshaft and the camshaft sprocket are marked 3 and 4 respectively. The inlet cam and exhaust cam on the camshaft are marked 5 and 6, respectively. The inlet valve and exhaust valve are marked 7 and 8, respectively (Figure 1). The rocker arms corresponding to the inlet valve and exhaust valve are marked 9 and 10 respectively (Figure 1). The rocker shafts of the rocker arms are marked 9a and 10a respectively. The rocker arms 9 and 10 are actuated by the inlet cam and outlet cam to open and close the valves 7 and 8 respectively. The inlet cam and exhaust cam on the camshaft are in turn driven by the crankshaft (not shown) connected to the camshaft sprocket through a chain drive (not shown). The other features and details of the cylinder head and cylinder of the engine have not been described herein as such are not necessary for understanding the invention.
7

A pair of semi helical grooves 11a, lib is provided on the camshaft diametrically opposite to each other at an angle with respect to the centre line passing through the length of the camshaft in the vertical plane. A conical member 12 has a central bore (not marked but can be visualized in Figures 2, 3 and 4) and a tubular projection 13 projecting from one face of the conical member. A pair of diametrically oppositely placed guide members 14a, 14b is projecting out inwardly through the tubular projection. The conical member is movably disposed on the camshaft through the central bore and tubular projection thereof with the guide members engaged in the semi helical grooves. Six flyweights 16 are disposed spaced around the camshaft. Each of the flyweights comprises a pair of spaced arms 17a, 17b pivoted together (pivot marked 18) on a support member 19 which is located on the camshaft at the drive end side thereof through a central opening 19a therein and is rigidly mounted on the drive end side of the camshaft. A roller 20 is located between the distal ends of the arms. The shaft 21 of the roller is rigidly held at the distal ends of the arms and the roller bears against and is adapted to roll against the conical member. The conical member is held spring tensioned by spring 22 disposed over the camshaft against the tubular projection of the conical member and exhaust cam 6. 23a and 23b are the camshaft bearings. The inlet cam 5 is mounted on the tubular projection. The length of each of the semi helical grooves and the said angle are selected depending on the desired delay or advancement in the closing or opening timings of the inlet valve in relation to the position of the piston of the engine with respect to the top dead centre in the cylinder and with respect to the rpm of the engine.
During working of the engine, the crankshaft (not shown) rotates due to reciprocation of the piston (not shown) in the cylinder and the camshaft rotates with the crank shaft through the chain drive. As the camshaft rotates, the conical member movably mounted on the camshaft and carrying the inlet cam and the support member fitted on the camshaft and carrying the flyweights also rotate with it. The speed of rotation of the camshaft and inlet cam and the flyweights varies with the rpm of the crankshaft. Depending upon the rpm of the camshaft, the centrifugal forces acting on the flyweights vary. Under the centrifugal forces, the flyweights fly out and the rollers thereof roll against the conical member thereby forcing the conical member carrying the inlet cam move outwardly in
8

the forward direction. During forward movement of the conical member and the inlet cam on the camshaft towards the exhaust cam against the spring force, the spring gets compressed and facilitates the forward movement.
The spring may be designed commensurate with the need to customize the response of the system to the varying engine speed, in that the spring may be of variable rate nature. Moreover, it is possible to design the spring in such a way that it would bind (that is, become fully compressed) at a predetermined position of the conical member thereby ceasing the phasing of the valve timing. These are variations of the system that are contemplated with the scope of the basic invention.
The inlet cam moves forward on the camshaft in a semi helical path guided by the guide members engaged in the semi helical grooves at the said angle with respect to the centre line passing through the length of the camshaft in the vertical plane. At lower engine rpm the speed of rotation of the camshaft and inlet cam and the flyweights will be lower. The centrifugal forces acting on the flyweights will be lower and the displacement of the inlet cam on the camshaft in the forward direction will be reduced. Due to the displacement of the inlet cam being reduced, the events or instances or timings of inlet valve closing and opening will be advanced in relation to the position of the piston with respect to TDC in the cylinder and the inlet valve will close and open early. At higher engine rpm, the speed of rotation of the camshaft and inlet cam and the flyweights will be higher. The centrifugal forces acting on the flyweights will be higher and the displacement of the inlet cam on the camshaft in the forward direction will be increased. As the displacement of the inlet cam on the camshaft increases, the events or instances or timings of inlet valve closing and opening will be delayed in relation to the position of the piston with respect to TDC in the cylinder and the inlet valve will close and open late. This enables optimum utilization of velocity of charge and optimum supply of fuel in the cylinder head at higher speeds thereby improving volumetric efficiency of the engine. When the engine is not running and the crankshaft is at rest, the spring expands and pushes the conical member and inlet cam back to their original position.
9

As illustrated and described, the drive means along with the flyweights according to the present invention is operative to discharge the fuel for a desired amount and for desired duration at a controlled rate in the entire engine operating range from low RPM to high RPM, thus achieving an optimum desired fuel injection mechanism for optimum efficient engine operation.
The performance of a typical variable valve timing assembly of the invention has been tested on 125 cc four stroke single cylinder engine (spark ignition carburetor type) vis-avis fixed valve timing. The results are graphically represented in Figure 7 of the
accompanying drawings in which the graphs denoted by correspond to fixed valve
timing and those denoted by ^ correspond to variable valve timing. All the test parameters like carburetor setting, ignition timing or compression ratio which affect the power were kept the same for both the tests. Figure 7 clearly establishes that power and torque outputs of the engine incorporating the variable valve timing assembly of the invention are high.
As the variable valve timing assembly of the invention closes and opens the inlet valve responsive to speed of rotation of the camshaft depending upon the speed of rotation of the crank shaft of the engine, the overall engine efficiency, that is the performance of the engine throughout the speed range is improved, power and torque outputs are increased and fuel waste and emissions are reduced. The variable valve timing assembly is compact and robust and occupies limited space. It is simple in construction, has low maintenance, durable and economical.
In the invention, the cam is not mounted directly on the camshaft but instead is mounted on a drive means, which drive means is movable along the camshaft, so that the cam is displaced along the camshaft in accordance with the movement of the drive means on the camshaft. The drive means is operatively connected to a flyweight means such that the radial movement of the flyweights is converted into axial movement of the cam on the camshaft. The drive means is coupled to the camshaft through a mating means, which
10

includes helical grooves on the camshaft and matching positions on the drive means, to displace the cam longitudinally and angularly along the camshaft. The length of the grooves and the angle of the grooves along with the mass of the flyweights will be so adjusted and predetermined to obtain the control characteristics desired.
The drive means for the inlet cam can be of a different construction / configuration. The flyweight construction and the number of flyweights can vary. The invention is equally applicable to and can be easily adapted to exhaust valve of the 4- stroke engine to vary the exhaust valve closing and opening timings. In a configuration where the variable valve timing assembly of the invention is used with both the inlet valve and outlet valve, the springs of the respective valve assemblies can be located against the respective conical members and a collar provided on the camshaft at an intermediate position thereof. Instead of the collar, a circlip located in a circumferential groove at an intermediate position of the camshaft can also be used to locate the springs. Such variations are to be construed and understood to be within the scope of the invention.
The main characteristic of this invention is that the inlet cam is not rigidly fixed on the camshaft. It is mounted on the movable drive means for angular and longitudinal displacement along the camshaft by a flyweight mechanism and the drive means movement longitudinally and angularly along mating grooves matching its inward protrusions towards the said grooves. Further, the movement of the drive means is directly dependent on the flyweight and the centrifugal force of the flyweight is dependent directly on the engine RPM, which means elimination of any other external means to detect the engine RPM or means to convey the engine RPM for the purpose of displacement of the inlet cam suitably. As such the invention is a simple, robust and entirely mechanical, which means the mechanism will be very reliable, cost effective as well as easy to design the predetermined control parameters of the mechanism.
Dated this 21st day of June 2006
(Jose M A)
of Khaitan & Co
Agent for the Applicants
11