DESC:VARIABLE VALVE TIMING SYSTEM FOR ENGINES
FIELD OF INVENTION:
The present invention relates to a field of variable valve timing (VVT) system for engines and more particularly relates to a mechanism for adjusting a valve timing for engines used in automotive applications.

BACKGROUND OF INVENTION:
An engine is typically provided with intake and exhaust valves, which are operated by a camshaft. The camshaft comprises lobes on its surface. The camshaft is rotated using power from engine crankshaft, which causes the lobes to push the valves of engine against a spring force thereby operating the valves. The instant of opening or closing of the valves is an important aspect in operation of engine as it is one of the governing factor contributing to engine efficiency. Cam lob profile is one of the affecting factor on valve timing.

Generally, the engine is provided with camshaft having lobes at fixed location. The location and profile of lobes is decided based on the desired timing. These engines do not have any provision to change the location of lobes to adjust the valve timing, hence there is no flexibility to optimize the engine performance based on different operating conditions of engine or vehicle. In order to maximize the engine performance, fuel economy and reduce emission, it is advantageous to adjust the valve timing based on various engine operating conditions for example at high speed and low speed.

Therefore, there are various systems developed to adjust the valve timing. One such system is cam switching, in which two cam profiles are provided which can be engaged with the valve based on requirement, however these are costly systems. Another system has cam lobe with different profiles on its surface such that any cam profile may be selected to adjust the valve timing. This system requires precise design of cam lobes, which is very complex to manufacture. In addition, this system occupies more space.

Other systems available are having a movable cam lobe on the camshaft such that its location or phase angle may be adjusted based on the requirement. The cam lobes are moved along the camshaft using various means including hydraulics or solenoid valves. The hydraulic systems are more complex as it requires the oil pressure circuitry to be mounted along with oil pump, pipe or hoses etc. Hydraulic system has mores losses as shifting is determined by hydraulic pressure which needs to be generated through out engine operation. This consumes more space, are more costly and consumes energy from engine during its complete operation. This makes it difficult to provide these systems in a compact vehicle for example, in two-wheeled vehicle where the space available is very limited. Hence, there is a need to provide a simple and effective system for phasing the cam lobes, which consumes less space and is simple and does not require many changes in existing engine design specifically cylinder head.

Therefore, it is an object of the present invention to provide a variable valve timing system comprising cam lobe shifting mechanism, which is simple, less costly and consumes less space with retrofitting.

SUMMARY OF THE INVENTION:
With this object in view, the present invention provides a variable valve timing system comprising
an engine having at least one inlet valve and at least one exhaust valve;
a camshaft comprising at least one lobe for operating said inlet valve and at least one lobe for operating said exhaust valve using a rocker arm wherein; said the lobe for operating the inlet valve and the lobe for operating exhaust valve are adjustably mounted on the camshaft;
an actuator configured to adjust the position of said lobes on the camshaft through a slider mechanism; wherein said slider mechanism comprises
a lead screw;
a slider mounted on the lead screw and connected to the lobes;
wherein; the lead screw is rotated by said actuator to linearly move the slider along the lead screw to change the position of the lobes.

According to preferred embodiment, the actuator being an electric motor is connected to the lead screw of the sliding mechanism to provide required rotational motion to lead screw. The electric motor is connected to the lead screw through a reduction stage comprising plurality of gears connected to each other in order to transmit a controlled power from an output shaft of the motor to the lead screw. Preferably, the reduction stage comprises three gears which forms two reduction stages. However, it is possible to transmit power from motor output shaft to the lead screw through other suitable means such as chain drive or belt drive. The slider is mounted on the lead screw preferably in the form of extended arms fixed to at least one lobe of camshaft in order to transmit the linear motion of the slider to said lobe.

The lobes may be separate and connected to each other or may be formed in a single piece. According to preferred embodiment, two lobes are formed as a single piece in a form of a lobe drum which is slidably fitted on the camshaft. The lobes are provided with a specific profile designed which causes a rocker arms to move at specific timings thereby operating inlet and exhaust valves thus controlling valve timings. The camshaft is provided with a slot having plurality of steps within slot and said lobe drum is fitted on the camshaft with the help of a pin slidably mounted within said slot. According to another embodiment, the lobes may be provided as a part of two or multiple lobe drums. The lobe drums may be slidably mounted on the cam shaft using at least one pin for each drum. The sliding movement of said lobe drum may be synchronized if needed.

As, the slider mechanism is operated by the electric motor, the lobe drum shifts from one step to another which causes the lobes to move linearly as well as angularly thereby changing the timing of operating inlet and exhaust valves.

According to one of the embodiment, the camshaft phasing is done in different steps. Each step on camshaft phasing is achieved based on the required amount of angular and/ or linear shift of the lobes and based on required change in valve timing for desired engine performance. Inlet and exhaust valve timing governs the engine performance by changing the quantity of intake mixture inducted in the form of air/fuel. Therefore, each step is designed to provide a specific engine performance, thus as a step is changed from one to another, the engine performance changes. Hence, each step forms a specific mode of operation and the mode or step may be changed based on the operational requirement. For example in one of the step, timing of valves is set such that maximum fuel efficiency is achieved, in another step best torque is achieved. The provision to change the mode of vehicle may be provided to the rider such that rider may change the mode based on his requirements. Alternatively, the modes may be changed automatically based on vehicle running condition. This may be enabled by deploying a controller with a predefined strategy.

Each step provided in the slot is designed such that there is a calculated angular movement of lobe at least by few degrees. Once, the instruction to change the mode is received, the electric motor is activated which rotates the lead screw by specific degrees such that the slider is moved linearly which causes the lobe drum to slide linearly and/or angularly thereby forcing it to move from one step to another. The instruction to operate motor may be send automatically by a control unit of vehicle or manually by the rider.

The load screw has a backlash which create a clearance between the teeth of lead screw and the slider,. However, due to backlash the linear movement of the slider gets delayed and is not accurate as required. In order to compensate for this delay the slider is provided with an additional shaft as auxiliary shaft which provides a primary control axis for linear motion of the slider. The position of the primary axis of auxiliary shaft w.r.t. camshaft and leadscrew is optimized for accurate motion of slider.

The change in angular movement of lobe with respect to camshaft is defined by a slot provided in the camshaft/ cam lobe and a pin. The pin during its guidance/movement on the slot phases the camshaft by required degrees. The profile of the slot is critical for the operation of phase change. Preferably, the distance is kept constant between each center point of the step, both in vertical and horizontal direction to get constant change in angular movement of lobes as it moves from one step to another. However; it is possible to get different angular movements in each step by varying this distance in horizontal and vertical direction.

According to another embodiment of present invention, lobe drum may be provided with plurality of lobes for operating inlet valve and plurality of lobes for operating exhaust valve. Each lobe is having a different profile on its external surface and different phase angles thereby providing different valve timing. The lobe may be selectively engaged with the rocker arm for operating inlet and exhaust valve based on the timing required for different operational requirements.

The lobe drum and camshaft is provided with a position retaining mechanism to hold and retain the position of lobes in each step of the slot comprising a ball and a spring mechanism wherein, the ball is pushed by the spring into a recess to retain the position of the lobe drum in each step. According to one of embodiment, a taper locking detail (also called as undulations) for ball at the end of each step is provided with the lobe. The ball and spring gets compressed by the taper surface as the lobe drum moves further and again expands at the next taper location detail.

The ball and spring mechanism is provided with a lubrication through suitable arrangement. According to one of the embodiment, a lubrication circuit is provided around pin, lobe drum and camshaft. A slot or a groove is provided between the lobe drum and the camshaft through which pressurized oil may be supplied for required lubrication.

According to another of the aspect of the present invention, the variable valve timing system is provided with a feedback system for accurately achieving and confirming various lobe positions. A sensor is provided on the lobe slider to monitor its movement throughout the cam lobe shift. The output from the sensor is linked to a controller, which uses it for confirming the position of the lobe. Whenever there is a requirement of any change in lobe position, the current position of the lobe is checked through sensor. The pre-determined positions of the lobe are stored in the controller. Once any position is achieved it is confirmed with the help of input from sensor by the controller. The controller confirms the position of the lobe by comparing the achieved position of the lobe with predetermined position. If the predetermined position is not achieved, then controller instructs to further actuate the electric motor/ actuator until the predetermined position is achieved. The decision to shift the lobes is taken by the controller based on various parameters including sensor output, engine rpm and nature of change of rpm (increase/decrease).

The proposed variable valve timing system is having at least one component within cylinder head and at least one component outside the cylinder. The upper portion of cylinder head is provided with a space in order to accommodate at least one component of slider mechanism. Towards this, the camshaft is supported at both the ends using bearing provided within wall of the cylinder head. One end of the lead screw is also fixed within wall of cylinder head while other end is connected to the gear of reduction stage. Preferably, the lead screw is mounted above camshaft and are substantially parallel and mounted in cylinder head. The other components of slider mechanism like slider, camshaft with lobe drum etc. are designed and mounted such that they are accommodated within cylinder head. The electric motor mounted substantially parallel to the camshaft axis on the outer surface of cylinder head. A suitable mounting arrangement is provided on the outer surface of cylinder head for example a flange is provided. Preferably, the cylinder head is provided with necessary depressed portion such that the motor is accommodated within dimensions of the cylinder head. This arrangement consumes minimum space. Further, this arrangement helps in providing VVT system with minimum changes in the existing design of the cylinder head. The conventional engine may be modified to have VVT system by replacing the existing cylinder head with the cylinder head of present invention as explained above. Hence, the system of present invention is retrofitted to existing engines.

According to preferred embodiment of the invention, the engine is a single cylinder 4-stroke engine having at least one inlet and one exhaust valve. However, the present system is applicable to other types of engines as well including multi-valve engines, multi cylinder engine, single spark or multi-spark engines.

BRIEF DESCRIPTION OF THE DRAWINGS
The cam phaser system of the present invention may be more fully understood from the following description of preferred embodiments thereof, made with reference to the accompanying drawings in which

Figure 1A illustrates an isometric view of cylinder head equipped with the system according to the present invention.

Figure 1B illustrates another isometric view of cylinder head equipped with the system according to the present invention.

Figure 1C illustrates yet another isometric view of cylinder head equipped with the system according to the present invention.

Figure 2 illustrates an isometric view of variable valve timing mechanism according to the present invention.

Figure 3 illustrates another isometric view of variable valve timing mechanism according to the present invention

Figure 4 illustrates yet another isometric view of variable valve timing mechanism according to the present invention.

Figure 5 illustrates an isometric view of slider mechanism according to the present invention.

Figure 6 illustrates an isometric view of slider mechanism without lobe drum according to the present invention.

Figure 7 illustrates a sectional view of slider mechanism showing position retention mechanism according to the present invention.

Figure 8 illustrates an isometric view of camshaft slot according to the present invention.

Fig.9 illustrates section view of camshaft along with retention mechanism according to the present invention

Fig.10 illustrates a camshaft view with slot according to the present invention

Fig. 11 shows lubrication circuitry for all rotating and sliding parts on camshaft according to the present invention.

DETAIL DESCRIPTION OF DRAWINGS:
A preferred embodiment will now be described in detail with reference to the accompanying drawings. The preferred embodiment does not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.

An exemplary embodiment of variable valve timing (VVT) system of the present invention is explained herein below. The engine is a single cylinder, 4-stroke engine having single inlet and outlet valve, which are operated by a camshaft. However; the system of present invention may also be installed in any other type of engines for example engine with multivalve system. Referring now to Fig.1a to 1c, a cylinder head 101 of engine (not shown) equipped with the VVT system 100. The cylinder head 101 forms a top of engine and is bolted/ welded to the cylinder block of the engine. The VVT system 100 is accommodated within cylinder head 101 of engine. The VVT system includes a camshaft (120) provided with two lobes for operating inlet and exhaust valve (135,145) of a single cylinder internal combustion engine. The camshaft 120 is supported at both the ends using bearing provided within wall of the cylinder head. The two lobes are mounted on the camshaft such that the position of the lobes may be adjusted along the camshaft through sliding motion. Two lobes may be separately formed and connected to each other or may be provided as a single piece. According to preferred embodiment, two lobes are formed as a single piece in a form of lobe drum 250 which is fitted on the camshaft. The position of lobe drum is adjusted using a slider mechanism 150. The slider mechanism is operated using an electric motor 115 which is also mounted on cylinder head substantially parallel to an axis of camshaft on the outer surface of cylinder head. A suitable mounting arrangement is provided on the outer surface of cylinder head 101 for example a flange 101a is provided. Preferably, the cylinder head 101 is provided with a depressed portion 101b such that the motor 115 is accommodated within dimensions of the cylinder head 101. This arrangement helps in convenient packaging by consuming minimum space.

Controller power is required to operate the slider mechanism 150, therefore the motor 115 may not be directly connected to the slider mechanism. The power of motor output shaft 115a of the electric motor 115 is delivered to the slider mechanism 150 through a reduction stage 125. Two stage gear reduction mechanism is provided in the reduction stage 125. The output shaft 115a of the electric motor 115 is connected to a first gear 125a which is connected to third gear 125c through second gear 125b. The number of stages and gears may be decided best on the requirement.

Referring to the Fig. 2 to 4 the slider mechanism 150 is explained herein below. The slider mechanism 150 comprises a lead screw 220 having one end fixed on the wall of cylinder head 101 using bearing and at other end the third gear 125c of reduction stage 125 is mounted. Therefore, the lead screw 220 rotates as it receives the controller power of gear 125c. A slider 225 is mounted on the lead screw 220 and configured to slide along the lead screw 220 as it rotates. The lead screw 220 has threads provided with a specific pitch designed based on the linear movement of slider 225 required per rotation of the lead screw 220. The slider 225 moves along the auxiliary shaft 222. Therefore, as the power of electric motor 115 is received to the lead screw 220, it starts rotating thereby moving the slider 225 along a linear direction. The slider 225 comprises arms connected to the lobe drum 250 of the camshaft 120. The lobe drum 250 is configured to slide on the camshaft 120. Hence, as the slider 225 moves it causes the lobe 250 to slide on the camshaft 120.The lobe 250 has a specific profile designed which causes the rocker arms (135a, 145a) to move at specific timings thereby operating inlet and exhaust valves (135, 145) to operate.

The slider and camshaft mechanism according to one of the embodiment of present invention is further explained herein below, with the help of fig. 5 to 8. The slider 225 is provided with arms 225a which are fitted within two lobes (250a, 250b) of the lobe drum 250. The camshaft 120 is supported by bearings 124 provided on both ends provided within wall of cylinder head 101. The lobe drum 250 is fitted on the camshaft 120 with the help of a pin 527 which may slide inside a slot 601 provided on the camshaft 120. The slot 601 is provided with plurality of steps for example three steps such that the lobes are shifted at least in linear or angular direction, preferably in both directions. Each step is designed based on amount of angular shift required in each step. Also each step is designed based on required engine performance in different conditions for example power phase in which high speed is required, Initial or loading phase wherein high torque is required etc. As the slider 225 slides, the arms of the slider 225a causes the lobe to move along the camshaft 120 as the pin 527 slides within the slot 601. The lobes (250a, 250b) are shifted to next step which causes angular as well as linear movement of lobes. This movement causes the valve timing to change thereby changing the intake mixture quantity. As the timing is changed the performance of the engine is changed accordingly.

According to another of the aspect of the present invention, the variable valve timing system is provided with a feedback system for accurately achieving and confirming various lobe positions. A sensor (280) is provided on the lobe slider (225) to monitor its movement throughout the lobe shift. The output from the sensor (280) is linked to a controller (not shown) which uses it for confirming the position of the lobe (250). Whenever there is a requirement of any change in lobe position, the current position of the lobe (250) is checked. Once any position is achieved it is confirmed with the help of input from sensor (280) by the controller. The decision to shift the lobes (250) is taken by the controller based on various parameters including sensor output, engine rpm and nature of change of rpm (increase/decrease).

The lead screw 220 has a backlash which creates a clearance between the teeth of lead screw 220 and the slider 225a,. However, due to backlash the linear movement of the slider 225a gets delayed and is not accurate as required. In order to compensate for this delay the slider 225a is provided with an additional shaft 222 as auxiliary shaft which provides a primary control axis 222a for linear motion of the slider 225a. A primary control axis 22a is designed to have accurate motion of slider as shown in Fig. 7. The distances X and Y in horizontal and vertical direction are designed are optimized preferably to be lesser. Hence, the position of the primary axis of auxiliary shaft w.r.t. camshaft and leadscrew is optimized for accurate motion of the slider.

Fig. 8 illustrates the geometry of the steps provided in the slot 601. Three steps are provided in the slot 601 each having a center point (601a, 601b, 601c). The distance between these center points in vertical and horizontal direction (X1, X2, Y1, Y2) is a crucial aspect of the design as the change in angular movement of lobes with respect to camshaft (120) is defined by the slot (601) provided in the camshaft/ lobe and a pin 527. The pin (527) during its guidance/movement on the slot 601 phases the camshaft by required degrees. As shown, distance X1, X2 is a linear distance between two center points and Y1, Y2 is a vertical distance between the center points. As, these distances are changed the angular shift of the lobe changes. Preferably, the distance is kept constant between each step both in vertical and horizontal direction i.e. X1=X2 and Y1=Y2 to get constant change in angular movement of lobes as it moves from one step to another, though it is possible to get different angular movements in each step change by varying this distance in horizontal and vertical direction.

Referring to fig. 7 to 10, illustrating camshaft 120 supported at both ends with the help of bearings 124. The camshaft 120 is provided with slot 601 having three different steps wherein the pin 527 is fitted. The lobe 250 and camshaft 120 is provided with a position retaining mechanism 700 to hold and retain the position of lobe 250 in each step of the slot 601. The retaining mechanism 700 comprises a ball 720 and spring 715 mechanism and the lobe 250 is provided with a sleeve 710 having a taper locking detail (also called as undulations) for ball at the end of each step is provided with the lobe corresponding to three different steps provided in slot 601. As the lob 250 moves along the camshaft 120 the taper surface compresses the ball 720 and the spring 715 and again expands as the next taper detail comes in front of the ball 720. The ball 720 sits within the lower undulations and fixes the position of lobe in the next step.

Therefore, as a slider 225 moves linearly it forces the lobe drum 250 to move in a same direction. As explained above, the lobe drum 250 moves by the pin 527 through a slot 601 from one step to another step. Thereby the lobe drum 250 moves linearly as well as angularly. This angular movement of lobe causes phase change thereby change in valve timing. Each step provided in the slot is designed such that there is a calculated angular movement. This changes the timing and/or air/ fuel or intake mixture quantities. Due to change in timing the engine, air/ fuel/charge requirement changes which ultimately results in change in engine performance characteristics. For example, in one of the step the timing of valves is adjusted such that the maximum fuel efficiency is achieved, while in another step best torque is achieved. Therefore, a same engine/ vehicle may be operated in different modes based on rider requirement. The provision to change the mode of vehicle may be provided separately to the rider such that rider may change the mode based on his requirements. Alternatively, the modes may be changed automatically based on vehicle running condition. Once, the instruction to change the mode is received the electric motor 115 is activated and rotates the lead screw 220 by specific degrees such that the slider 225 is moved linearly which causes the lobe drum 250 to slide linearly thereby forcing it to move from one step to another. The instruction to operate motor 115 may be send automatically by a control unit (not shown) of vehicle or manually by the rider. Referring to Fig. 11 illustrating lubrication system according to one of the embodiment to provide adequate lubrication to complete assembly. Lobe 250 is fitted on the camshaft 120 through a sleeve such that a small groove or slot 801 is created between camshaft 120 and said sleeve. A pressurized oil may be supplied through this slot in order to provide lubrication to the complete mechanism.

Above specific design aspects of the variable valve transmission system is described according to one of the embodiment of present invention and it shall not limit the scope of the invention by any means as there are various alternatives possible to the above described embodiment. For example, the design features such as camshaft with three different steps may alternatively comprise plurality of steps. The angular movement provided by each step may be different based on the requirement. The lobe drum may be provided with only angular or linear movement. The retention mechanism may be replaced by any other suitable mechanism which can serve the purpose of holding or retaining the position of lob drum. The slider may be provided with any suitable arrangement to connect it to the lobe. According to another embodiment of present invention, lobe drum may be provided with plurality of lobes having a different profile on its external surface and different phase angles thereby providing different valve timing. The lobe may be selectively engaged with the rocker arm for operating inlet and exhaust valve based on the timing required.

In another aspect of present invention, the present VVT system may be applied to an to any vehicle including two-wheeled, three-wheeled or four-wheeled vehicle including hybrid vehicles comprising engine. The system is also applicable to any engine irrespective of fuel-type.
,CLAIMS:CLAIMS
We Claim:

1. A variable valve timing system for engine comprising;
an engine having at least one inlet valve and one exhaust valve;
a camshaft comprising at least one lobe for operating the inlet valve and at least one lobe for operating the exhaust valves using a rocker arm wherein;
the lobe for operating the inlet valve or lobe for operating the exhaust valve are adjustably mounted on the camshaft;
an actuator configured to adjust the position of the lobes on the camshaft through a slider mechanism; wherein the slider mechanism comprises;
a lead screw;
a slider mounted on the lead screw and connected to the lobes;
wherein;
the lead screw is rotated by the actuator to linearly move the slider along the lead screw to change the position of the lobes.
2. The variable valve timing system for engine as claimed in claim 1, wherein the lobes are formed on a lobe drum mounted on the camshaft.
3. The variable valve timing system for engine as claimed in claim 1, wherein the camshaft is mounted with multiple lobes formed as a single piece or formed as separate lobes and connected to each other.
4. The variable valve timing system for engine as claimed in claim 2, wherein the lobe drum is slidably mounted on a slot provided on the camshaft using a pin.
5. The variable valve timing system for engine as claimed in claim 4, wherein the slot on the camshaft is provided with at least one-step; wherein each step results in different position of the lobe thereby providing different valve timings and different modes of engine performance.
6. The variable valve timing system for engine as claimed in claim 5, wherein the slot on the camshaft is provided with three steps resulting in three different lobe positions each corresponding to three different modes of engine performance wherein; in first step, timing of valves is set such that maximum fuel efficiency is achieved, in second step maximum torque is achieved while in third step maximum power is achieved.
7. The variable valve timing system for engine as claimed in claim 5, wherein the mode of engine performance is changed manually or automatically based on the operational requirement.
8. The variable valve timing system for engine as claimed in claim 5, wherein the change in angular position achieved for the lobe in each step is kept same for each step or different for each step.
9. The variable valve timing system for engine as claimed in claim 2, wherein the lobe drum and camshaft is provided with a position retaining mechanism to hold and retain the position of the lobe at different positions on the camshaft wherein; the position retaining mechanism comprises a ball, a spring and a sleeve having tapered locking detail wherein, the ball is pushed by the spring into said tapered locking detail of sleeve to retain the position of the lobe drum on camshaft.
10. The variable valve timing system for engine as claimed in claim 2, wherein the lobe drum and camshaft is provided with a slot or a groove portion for supplying oil for lubrication.
11. The variable valve timing system for engine as claimed in claim 1, wherein the actuator is connected to the lead screw through at least one reduction stage comprising at least a gear pair.
12. The variable valve timing system for engine as claimed in claim 1, wherein the actuator is an electrical actuator including an electric motor.

13. The variable valve timing system for engine as claimed in claim 1, wherein the slider is provided with an auxiliary shaft having a primary control axis wherein; the position of the primary control axis is optimized to be closer to the camshaft and to the leadscrew to get accurate motion of the slider and to compensate any lag in motion created due to backlash of the lead screw.
14. The variable valve timing system for engine as claimed in claim 1, wherein the camshaft is provided with multiple lobes for operating inlet valve and exhaust valve wherein; each lobe is having a different profile on its external surface with different phase angles and each lobe is selectively used to provide different valve timings based on operational requirement.
15. The variable valve timing system for engine as claimed in claim 1, wherein the variable valve timing system is provided with a feedback system comprising;
a sensor configured to monitor the movement of lobe on the camshaft;
a controller configured to receive the position of the lobe sensed by the sensor and to instruct the actuator to adjust the position of the lobe to achieve accurate predetermined position.
16. The variable valve timing system for engine as claimed in claim 1, wherein the components of slider mechanism along with camshaft, valves, rocker arm are fitted within a cylinder head of said engine.
17. The variable valve timing system for engine as claimed in claim 16, wherein the camshaft is supported at both the ends using bearing provided within wall of the cylinder head and the lead screw is mounted substantially parallel and above the camshaft within cylinder head.
18. The variable valve timing system for engine as claimed in claim 12, wherein the electric motor is mounted substantially parallel to the camshaft axis on a mounting arrangement provided on the outer surface of cylinder head such that said electric motor is accommodated within dimensions of the cylinder head.
19. The variable valve timing system for engine as claimed in claim 1, wherein the engine is a single cylinder or multi-cylinder engine comprising single valve or multi-valves with single spark plug or multiple spark plugs.