Power unit with variable valve timing system

Abstract

The present subject matter relates to a power unit having a variable valve timing system. The power unit (100) includes a cylinder head assembly (102). The variable valve timing system provided on the cylinder head assembly (102) includes a first cam (142) for actuating one or more first valves (132) through a first rocker arm (144) capable of pivoting about a first axis (S-S'). A second cam (152) is for selectively actuating one or more first valves (132) through a second rocker arm (154) capable of pivoting about the first axis (S-S'). An engagement unit (145, 160, 162) is provided about the first axis (S-S') and is configured to selectively engage the second rocker arm (154) with the first rocker arm (144). The present invention provides a system having a lower inertia due to mass accumulation close to the first axis (S-S'), thereby making the power unit easy to operate and operate at a higher speed.

Description

Technical Field

[0001] The present subject matter generally relates to a power unit, and more particularly to a variable valve timing system for a power unit. Background Art

[0002] Generally, a power unit such as an internal combustion (IC) engine converts chemical energy into mechanical energy by burning an air-fuel mixture in a combustion chamber of the internal combustion engine. Among other components, the internal combustion engine has a cylinder head assembly at the top of the cylinder block. The cylinder block defines a combustion chamber that houses a reciprocating piston. Combustion of the air-fuel mixture subjects the piston to reciprocating motion, thereby transferring the energy generated during combustion to the crankshaft via a connecting rod, thereby driving the crankshaft in a rotational manner.

[0003] Combustion of the air-fuel mixture generates exhaust gases that need to be discharged from the combustion chamber through an exhaust system. Accordingly, the cylinder head assembly disposed at the top of the cylinder block is provided with a plurality of valves that open and close at regular intervals for allowing the air-fuel mixture to enter the combustion chamber and for discharging the exhaust gases from the combustion chamber. Brief Description of the Drawings

[0004] The detailed description is made with reference to the accompanying drawings. In the drawings, like numerals are used throughout to denote like features and components.

[0005] Figure 1 A front perspective view of a power unit according to an embodiment of the present subject matter is shown.

[0006] Figure 2 A top view of a cylinder head assembly according to an embodiment of the present subject matter is depicted.

[0007] Figure 3 A side view of a cylinder head assembly according to an embodiment of the present subject matter is depicted.

[0008] Figure 4 A detailed schematic view of a variable valve timing system according to an embodiment of the present subject matter is depicted.

[0009] Figure 5 An exploded view of selected components of a variable valve timing system according to an embodiment of the present subject matter is depicted.

[0010] Figure 6 A detailed schematic view of a part of a variable valve timing system according to an embodiment of the present subject matter is depicted.

[0011] Figure 7 A schematic view of a variable valve timing system according to an embodiment of the present subject matter is depicted.

[0012] Figure 8 Depicted according to an embodiment of the present subject matter along as Figure 6Cross-sectional view of a portion of a variable valve timing system taken along the axis X-X' shown.

[0013] FIG. 9(a) depicts an exemplary graph showing the operation of a decompression system according to an embodiment of the present subject matter.

[0014] FIG. 9(b) depicts an exemplary graph of valve lift in the engaged and disengaged states according to an embodiment of the present subject matter.

[0015] Figure 10 Schematic diagram depicting a variable valve timing system in an actuated state according to an embodiment of the present subject matter. Detailed Description

[0016] Generally, a power unit is provided with a plurality of valves. The plurality of valves correspond to the intake and exhaust of the power unit. For example, the basic configuration of the valves may have a single intake valve and a single exhaust valve, which are respectively used to allow the air-fuel mixture to enter and the exhaust gas to exit. Depending on the intake and exhaust requirements, more than one valve is typically provided for intake and more than one valve is provided for exhaust. Generally, the plurality of valves are in a normally closed state, and a valve timing mechanism is used to open each valve at a defined time interval. The valve timing mechanism includes a camshaft for opening and closing the valves, wherein the camshaft can be driven by a chain.

[0017] Generally, fixed valve timing is provided in smaller commuter vehicles (such as two-wheelers, three-wheelers) or small cars incorporating a power unit of 1000 cc or less. The term "valve timing" generally refers to the opening time and closing time of the valves. Fixed valve timing has fixed valve opening and closing times. Since valve timing depends on the rotation of the crankshaft and the camshaft, the duration for which the valve remains open decreases as the engine speed increases (due to an increase in revolutions per minute). The fixed valve timing of the intake and exhaust systems significantly affects the volumetric efficiency of the power unit. For example, during high-speed operation of an internal combustion engine, the breathing of the power unit may be affected due to valve timing adjusted for lower engine speeds. Similar problems may occur due to insufficient combustion time or insufficient exhaust time. Therefore, traditional internal combustion engines can only operate efficiently within a certain engine speed range, and their performance is affected at low or high speeds.

[0018] Various attempts have been made in the past to address the above problems associated with the fixed valve timing of a power unit by providing a variable valve timing system. However, such variable timing systems are implemented in racing applications or provided as an advanced feature in vehicles due to their cost and complexity. One attempt has been to achieve variable valve timing through cam profile switching. The disadvantage of such known systems is that they make the entire engine assembly bulkier. Therefore, it has been a challenge to design variable valve timing in a compact power unit, such as a single-cylinder internal combustion engine, because of the limited available space in the cylinder head assembly area of such engines. The cylinder head usually also requires sufficient working space in its vicinity to provide an operating space for servicing the system and its peripheral parts. In addition, it is often necessary to install power train peripheral systems, such as a cooling system, sensors, etc., near the cylinder head, which makes the design more complex.

[0019] Furthermore, a hydraulic / pressure-based system that requires an axial path to be provided inside the parts makes the parts larger in volume, and due to the use of a hydraulic or pressure system, the system requires regular maintenance. Other setups, such as a mechanical engagement unit between shafts for cam switching, are also known in the art. However, the mechanical engagement unit has a high inertial weight and thus has limitations in operating at higher engine speeds. Such an engine with higher inertia requires a larger actuation system, which is challenging to accommodate in a compact power unit. In addition, such known systems are bulkier because the camshaft either extends axially to incorporate the switching system or radially to incorporate a hydraulic or mechanical actuation system, making the camshaft and valve timing assembly bulkier.

[0020] Therefore, there is a need to provide a compact power unit having a variable valve timing system that includes a compact camshaft and a compact valve timing assembly so that it can be encapsulated even in a small and compact power unit layout with a crowded cylinder head assembly section. In addition, the components for the variable valve timing system should have a low inertia so that a smaller actuation system can be used, which can be accommodated even in a small engine, and the low inertia enables easy and reliable operation at higher speeds.

[0021] The present subject matter provides a power unit having a cylinder head assembly. The cylinder head assembly relates to a variable valve timing system having a camshaft, the camshaft including a first cam and a second cam for actuating one or more first valves. A first rocker arm corresponding to the first cam actuates the one or more first valves. A second rocker arm corresponding to the second cam is configured to selectively actuate the one or more first valves. During a first predetermined speed range of the power unit, the one or more first valves are actuated by the first rocker arm, and during a second predetermined speed range of the power unit, the one or more first valves are actuated by the second rocker arm. Thus, the term "selectively" defines the operation of the second rocker arm and the corresponding second camshaft within a predetermined speed range of the power unit. The first rocker arm and the second rocker arm are configured to swing about a first axis due to rotation of the camshaft. An engagement unit is also provided about the first axis and configured to selectively (in accordance with one embodiment, "selectively" refers to a predetermined speed range of the power unit) engage the second rocker arm with the first rocker arm.

[0022] On the one hand, the engagement unit is configured to be adjacent to the first axis which is the swing axis of the first rocker arm and the second rocker arm. In one embodiment, the engagement unit operates about an operating axis and the operating axis overlaps with the first axis. Thus, the inertia of the system is lower, especially the inertia of the rocker arm, since the weight is mainly concentrated around the first axis. Less work or force is required to actuate the rocker arm. Further, the rocker arm can be easily operated even at higher engine operating speeds.

[0023] Characterized in that an engagement unit capable of selectively engaging the first rocker arm with the second rocker arm is provided between the first rocker arm and the second rocker arm, and the first rocker arm, the second rocker arm and the engagement unit include a common axis, i.e., the first axis. One axial side of the engagement unit engages with one of the first rocker arm and the second rocker arm, and the other axial side of the engagement unit selectively engages with the other of the first rocker arm and the second rocker arm, wherein the engagement unit is configured to move about the first axis. Thus, the engagement unit is compactly accommodated between the first rocker arm and the second rocker arm, thereby providing an improved weight distribution. If the design is to dispose the engagement unit towards an axial end of the first rocker shaft, an undesired stress will be applied to the rocker shaft, resulting in premature failure of the shaft due to stress concentration in a single area, or may cause the rocker shaft to bend, thereby affecting the clearance between the rocker arm and the camshaft.

[0024] When the engagement unit is in the actuated state, the first rocker arm and the second rocker arm are selectively engaged, whereby the engagement unit couples the first rocker arm and the second rocker arm to simultaneously swing the first and second rocker arms about a first axis. The coupling / engagement is not limited to a mechanical manner and includes other coupling means, such as magnetic coupling, etc. Further, the corresponding cam and rocker arm with a higher lift (e.g., the second rocker arm) are actuated first, and due to the engagement or coupling between the rocker arms, the other rocker arm (the first rocker arm) is also actuated due to the engagement or coupling, thereby achieving a longer lift. The engagement is performed for a predetermined speed range of the power unit / engine speed. Thus, the rocker arms are selectively engaged.

[0025] One or more of the foregoing first valves correspond to at least one of an intake system or an exhaust system. For example, the first valve may be an intake valve, which requires a variable valve timing system according to the engine operating state. The power unit includes a third cam and a corresponding third rocker arm for driving at least one second valve, and the second valve may be an exhaust valve. In one embodiment, the third cam is disposed between the first cam and the second cam, and correspondingly, the third rocker arm disposed in the opposite direction has at least a portion received between the first rocker arm and the second rocker arm, wherein the second rocker arm is an auxiliary arm.

[0026] On the one hand, the third cam and the third rocker arm (corresponding to the exhaust system) are respectively disposed between the first cam and the second cam and between the first rocker arm and the second rocker arm. This makes the assembly compact and enables it to be accommodated in the cylinder head assembly.

[0027] Characterized in that the engagement unit is substantially received between the first rocker arm and the second rocker arm, and when viewed in the radial direction, at least a portion of the engagement unit overlaps at least a portion of the third cam of the camshaft. The current feature embodies the compact characteristic of the variable valve timing system, because the space (considering the radial direction) allocated to the third cam and the third rocker arm is also used for encapsulating the engagement unit, thereby providing a compact encapsulation.

[0028] Characterized in that the engagement unit is mounted to the first rocker arm shaft, and the first rocker arm shaft is rotatably supported on the cylinder head assembly by one or more rotary support members. In an embodiment, the rotary support members enable the first rocker arm shaft to rotate, thereby avoiding stress concentration on a specific portion of the first rocker arm shaft, thereby making it a durable and reliable structure.

[0029] Further, the first rocker arm shaft supports the first rocker arm and the second rocker arm such that they can swing about the first axis. The present invention uses the same axis, i.e., the first axis, for the swing of the rocker arms and the operation of the engagement unit, thereby concentrating the weight near the first axis. Thus, the amount of mass to be moved is smaller, and thus the inertia remains low.

[0030] According to one embodiment, the engagement unit includes a spline shaft, an interlocking member, and a locking portion. The first rocker arm shaft includes at least a length with a smaller diameter to accommodate the spline shaft, and the second rocker arm is mounted to the spline shaft. However, the first rocker arm is directly mounted to the first rocker arm shaft at a portion having a greater width. One aspect of the present subject matter is that the spline shaft, which is part of the engagement unit, is compactly accommodated on the first rocker arm shaft without affecting the radial thickness of the first rocker arm shaft and the rocker arm. In one embodiment, the spline shaft can rotate independently around the first rocker arm shaft.

[0031] Characterized in that the interlocking member engages with the spline shaft, and the interlocking member is capable of sliding axially (along the first axis) around the spline shaft. The interlocking member can selectively engage with the first rocker arm upon actuation. Before actuation, the second rocker arm swings independently of the first rocker arm.

[0032] Characterized in that the first rocker arm includes a locking portion configured to engage with the interlocking member; preferably, the locking portion is integrally formed with the first rocker arm to increase stiffness and reduce the number of parts for assembly. On the one hand, the locking portion, which is part of the engagement unit, is integrated with the first rocker arm to reduce the number of parts. On the one hand, the engagement is completed under the base circle condition. The base circle is the smallest circle drawn around the outer periphery of the cam, and the radius of the circle intercepted from the cam center is the smallest. Therefore, the aforementioned engagement unit operates during the state where the rocker arm contacts the corresponding cam around the base circle portion of the cam, and thus the engagement is performed under the base circle condition of the cam.

[0033] Characterized in that the first cam provides a first lift with a first timing for actuating one or more first valves, and the second cam provides a second lift with a second timing for actuating one or more first valves. The duration of the first timing is shorter than that of the second timing. The first cam is activated during lower engine speeds, while the second cam operates during higher speeds, where the intake and exhaust of the power unit are crucial for transmitting the necessary power / torque.

[0034] Characterized in that the present invention having the first cam with a smaller lift is capable of providing a decompression system coupled to the first cam and disposed adjacent to the first cam. Thus, the decompression system is not sandwiched between the cams, which would affect the compact layout of the rocker arms because additional space would be provided between the cams to encapsulate the decompression system. Encapsulating the decompression system between the cams would also cause the rocker arms to move away from each other (since the rocker arms work with the cams), thus requiring a longer rocker arm shaft, which would increase weight, occupy more space, and increase cost.

[0035] Characterized in that the power unit includes an actuator, and the actuator is functionally connected to the interlocking member through a pivot arm. The pivot arm pivots around a pivot point, and the actuator is configured to actuate the pivot arm, which causes the pivot arm to pivot, thereby causing the movement of the engagement unit (especially the interlocking member).

[0036] Characterized in that the actuator includes a solenoid or a motor, etc. On the one hand, a solenoid that requires power to only change the state from the actuated state to the non-actuated state (or from the non-actuated state to the actuated state) can be used, which consumes less power. Since the required workload is less due to lower inertia, a smaller-sized actuator can be used. In addition, the actuator can be installed on the cylinder head assembly or the cylinder head cover.

[0037] According to another aspect, the subject matter can be incorporated in a three-valve or four-valve engine. The power unit with a variable valve timing system as described above can be installed on the intake side and the exhaust side, whether it is a single overhead cam system (SOHC) or a double overhead cam system (DOHC).

[0038] Therefore, the present invention provides improved driving characteristics because the power unit can be implemented on two-wheelers, three-wheelers or multi-wheelers, which aims to provide the best low-speed driving performance through a low-speed cam - for urban road conditions; provide the best high-speed driving performance through a high-speed cam lobe - for racing road conditions; and provide the best low-speed and high-speed conditions - a combination of urban and highway road conditions.

[0039] Characterized in that the system operates or performs switching in a higher gear, wherein the power unit operates at a higher engine speed, thereby providing improved acceleration.

[0040] In an embodiment, when the variable valve timing system is actuated using an actuator, the cut-off speed can vary for different applications, and actuation can be accomplished using a controller / ECU or a manually operated switch.

[0041] In one embodiment, when an electronic actuator is used for the variable valve timing system, the electronic throttle can be synchronously closed to reduce the speed of synchronization and engagement between the cams.

[0042] These and other advantages of the subject matter will be described in more detail in connection with embodiments of the power unit and the accompanying drawings in the following description. Various other features and embodiments of the subject matter will be apparent from the following further description set forth below.

[0043] The present invention is explained in detail with the aid of a single-cylinder internal combustion engine, but the concepts introduced herein are applicable to multi-cylinder engines with a single overhead cam (SOHC) or a double overhead cam (DOHC).

[0044] Figure 1A front perspective view of a power unit according to an embodiment of the present subject matter is shown. The power unit 100 is an internal combustion engine with or without an electric assist motor. Hereinafter, the terms "power unit" and "internal combustion (IC) engine" may be used interchangeably. According to the depicted embodiment, the power unit 100 includes crankcase assemblies 104, 105, a cylinder block 103 coupled to the crankcase assemblies 104, 105, and a cylinder head assembly 102 coupled to the upper portion of the cylinder block 103. A cylinder head cover 101 is mounted to the cylinder head assembly 102 for covering the valve train system and other components mounted thereon. In the present embodiment, the cylinder block 103 defines a cylinder portion (not shown), and the cylinder portion has a forwardly inclined cylinder axis to minimize the overall size of the power unit. A reciprocating piston (not shown) is slidably fitted in the cylinder block 103, and the reciprocating piston is connected to a crankshaft (not shown) via a connecting rod (not shown). The crankshaft (not shown) is rotatably supported by the crankcase assemblies 104, 105. The crankcase assemblies 104, 105 are provided with one or more covers 125 for covering the components supported by the crankcase assemblies 104, 105 from the lateral direction RH-LH.

[0045] The cylinder head assembly 102 includes an intake port 114 formed thereon (as Figure 3 shown) and an exhaust port (not shown). The intake port 114 allows an air-fuel mixture to enter the combustion chamber, and after the air-fuel mixture burns, the exhaust gas is discharged from the combustion chamber through the exhaust port 115. A plurality of valves are provided in the cylinder head assembly 102, and the plurality of valves are closed and opened at each determined timing to facilitate the intake and exhaust processes. In the depicted embodiment, the power unit 100 includes two valves, namely a first valve 132 and a second valve 134 (as Figure 2 shown).

[0046] Figure 2 A top view of a cylinder head assembly according to an embodiment of the present subject matter is depicted. Figure 3 A side view of a cylinder head assembly according to an embodiment of the present subject matter is depicted. The first valve 132 is supported on the intake side, while the second valve 134 is supported on the exhaust side. The valves 132, 134 are driven by a camshaft 120 rotatably supported in the cylinder head assembly 102 to open and close the valves. The rotational power is transmitted from a crankshaft (not shown) to the camshaft 120 through a timing drive mechanism (not shown). In an embodiment, the timing drive mechanism includes a driving sprocket supported on the crankshaft, a driven sprocket supported on the camshaft, and an endless cam chain connecting the driving sprocket and the driven sprocket.

[0047] The cylinder head assembly 102 defines a peripheral wall portion 110, on the periphery of which a plurality of fins 111 are defined. The camshaft 120 is rotatably supported on the cylinder head assembly 102. The camshaft 120 includes one or more bearings 121A, 121B for rotatably supporting the camshaft on the cylinder head assembly 102. The camshaft 120 includes a sprocket 123 for being driven by a crankshaft or any actuator. The camshaft 120 includes a plurality of cams having cam lobes for driving a first valve 132 and a second valve 134 through a rocker arm. One or more spark plugs 135 are provided on the cylinder head assembly to effect combustion of an air-fuel mixture. In addition, Figure 3 depicts a mounting architecture 205 for supporting an actuator 112. The mounting architecture 205 is a raised portion, the profile of which is set to complement the profile of the actuator 112.

[0048] In the present embodiment, the camshaft 120 includes a third cam 124 having a third cam lobe for driving the second valve 134. The third cam 124 enables a third rocker arm (not shown) to swing, thereby causing the opening / closing of the second valve 134. In addition, the present invention provides a power unit having a variable valve timing system for changing the opening / closing timing of the first valve 132. The variable valve timing system 200 (hereinafter the "variable valve timing system" is abbreviated as the "system") includes an actuator 112 capable of changing the valve timing.

[0049] Figure 4 depicts a detailed schematic perspective view of a variable valve timing system according to an embodiment of the present subject matter. The camshaft 120 includes a first cam 142 that drives a first valve 132 (also shown in Figure 3 ) through a first rocker arm 144. The first rocker arm 144 swings about a first rocker arm shaft 146 that is placed substantially parallel to the cam axis C-C' of the camshaft 120. The first rocker arm shaft 146 has a first axis S-S'. The valve end of the first rocker arm 144 is arranged to contact the first valve 132. Thus, when the first cam lobe of the first cam 142 rotates, the cam follower of the first rocker arm 144 is lifted, causing the first rocker arm 144 to pivot about the axis S-S' of the shaft 146, causing the first valve 132 to move downward, thereby opening the port.

[0050] The camshaft 120 includes a second cam 152 having a second cam lobe. The system 200 includes a second rocker arm 154 corresponding to the second cam 152, wherein the second cam 152 is capable of driving / operating the second rocker arm 154. In one embodiment, the second rocker arm 154 is also supported about a first rocker shaft 146 and pivots about a first axis S-S'. The second cam 152 is axially spaced from the first cam 142 on the camshaft 120, and the second cam 152 drives a cam follower mounted to the cam end of the second rocker arm 154.

[0051] In addition, an engagement unit is disposed between the first rocker arm 144 and the second rocker arm 154 and is preferably supported on the first rocker shaft 146. The engagement unit is disposed about the first axis S-S' and is configured to selectively engage the second rocker arm 154 with the first rocker arm 144. The engagement unit is connected to a fork member 165, and the fork member 165 is functionally connected to a pivot arm 172. The pivot arm 172 pivots about a pivot point 174, with one end of the pivot arm 172 connected to the fork member 165 and the other end connected to the actuator 112. In one embodiment, a third cam 124 corresponding to the second valve 134 (e.g., an exhaust valve) is disposed between the first cam 142 and the second cam 152, thereby achieving a compact packaging of the valve timing assembly. In one embodiment, the second rocker arm 154 is shorter in length compared to the first rocker arm 144, making the system 200 more compact.

[0052] The actuator 112 can be a small solenoid ( Figure 4 The actuator 112 in is shown in an enlarged view and the relative dimensions to other components are not considered). The actuator 112 can be mounted and configured within the cylinder head assembly 102 or the cylinder head cover. In addition, the actuator can be a solenoid or the like, which requires power to change from only one state / condition to another state / condition and thus requires low power.

[0053] Figure 5 A exploded view depicting selected components of a system according to an embodiment of the present subject matter. The first rocker shaft 146 supports the first rocker arm 144 and the second rocker arm 154. According to this embodiment, at least a portion of the length of the first rocker shaft 146 is configured with a first diameter D1, and the remaining length is configured with a second diameter D2, wherein, according to the embodiment, the second diameter D2 is also smaller than the first diameter D1.

[0054] System 200 includes a splined shaft 162 that is mounted to a first rocker arm shaft 146 about a portion including a second diameter D2. In one embodiment, the splined shaft 162 is rotatable freely about the first rocker arm. A second rocker arm 154 is mounted to the splined shaft 162. The splined shaft 162 includes a plurality of splines 162S and an interlocking member 160 including a plurality of grooves 160G, and it is slidably mounted to the splined shaft 162. The interlocking member 160 is provided with one or more engagement pins 160P extending in the axial direction along the axis of the rocker arm shaft. In addition, the interlocking member 160 includes one or more grooves 160S disposed at least partially on the annular perimeter of the interlocking member 160. The first rocker arm 144 includes a locking portion 145 disposed on one axial side, wherein the locking portion 145 includes one or more slots corresponding to the one or more engagement pins 160P of the interlocking member 160. When engaged, the splined shaft 162, the first rocker arm 144, and the second rocker arm 152 act as a single component and swing together.

[0055] In one embodiment, the first rocker arm 144, which is longer and / or larger than the second rocker arm 154, is additionally provided with grooves 144I on the outer periphery (both sides) to reduce weight and obtain lower inertia. The grooves 144I provided on at least one of the two sides will produce an I-shaped cross-section of the rocker arm 144, which is lightweight and has high structural stiffness.

[0056] Figure 6 A detailed schematic diagram depicting a part of the system according to an embodiment of the present subject matter. According to the current embodiment, in the assembled state as shown Figure 6 shown, the interlocking member 160 is connected to the fork member 165. In addition, the fork member 165 is connected to the connecting shaft 176. The system 200 further includes a pivot arm 172 that pivots about a pivot point 174. One end of the pivot arm 172 is connected to the connecting shaft 176, while the other end of the pivot arm 172 is connected to the actuator 112. The actuator 112 in this embodiment is schematically shown in a larger size. However, a compact actuator, such as a solenoid or a compact electric switch / motor, can be used, which will be compact for mounting to the cylinder head assembly 102. Actuation of the actuator 112 causes the pivot arm 172 to pivot about the pivot point 174 (the direction of movement is depicted using an arrow), thereby causing the connecting shaft 176 to move. The connecting shaft 176 moves the interlocking member 160, thereby causing the engagement unit to engage with the first rocker arm 144, thereby establishing a connection between the second rocker arm 154 and the first rocker arm 144. For example, the engagement pins 160P of the interlocking member 160 will engage with the locking portion 145 of the first rocker arm 144, thereby establishing a connection. Figure 6 Shows the engagement unit in a non-actuated state, whereby the first rocker arm 144 swings independently of the second rocker arm 154.

[0057] Figure 7Schematic diagram depicting a system according to an embodiment of the present subject matter. Figure 8 Depicting a cross-sectional view of a portion of the system taken along axis X-X' as shown according to an embodiment of the present subject matter. Refer to Figure 6 and Figure 7 and Figure 8 , according to an embodiment, during the non-actuated state, the first rocker arm 144 is driven by the first cam 142, and the first cam 142 includes a lower lift. The first valve 132 is opened / closed based on the swing of the first rocker arm 142. When the power unit 100 operates at a lower engine speed, the actuator 112 is in the non-actuated state. As Figure 7 shown, the engagement pin 160P of the interlock member 160 is in a non-engaged state with the locking portion 145 of the first rocker arm 144. Thus, the second rocker arm 154 swings around the first rocker arm 146 without affecting the opening / closing of the first valve 132. The second rocker arm 154 is driven by the second cam 152. Compared with the lift provided by the first cam 142, the second cam 152 is configured to provide a higher lift. Converting to valve opening time, compared with the valve opening time provided by the first cam 142, the second cam 152 provides a higher opening time. However, in the non-actuated state, the timing or lift provided by the second cam 152 is not transferred to the first valve 132.

[0058] According to another embodiment, the first rocker arm shaft 146 is additionally supported by one or more rotary support members 147, and the rotary support members 147 enable the first rocker arm shaft 146 to rotate around the first axis S-S', whereby the entire circumference of the shaft receives force instead of a single point receiving force, which would cause the first rocker arm shaft to bend, thus affecting the lift / timing.

[0059] Furthermore, as Figure 7 shown, the present subject matter provides a compact layout of the variable valve timing system 200. The third cam 124 corresponding to the second valve 134 is disposed between the first cam 142 and the second cam 152, and the third rocker arm (not shown) corresponding to the second valve 134 is compactly arranged between the first rocker arm 144 and the second rocker arm 154. In addition, the engagement unit composed of the spline shaft 162, the interlock member 160, and the locking portion 145 is generally accommodated between the first rocker arm 144 and the second rocker arm 154. In addition, when viewed in the radial direction of the first rocker arm shaft 146, the engagement unit 160 overlaps at least a portion of the third cam 124 corresponding to at least one second valve 134 (shown in dashed lines as OL) when viewed in the radial direction.

[0060] In addition, the engagement unit is disposed between the first rocker arm 144 and the second rocker arm 154, and the engagement unit operates around the first axis SS' by performing an engagement operation by moving around the first axis SS'. The engagement unit can move around the first axis to selectively engage the second rocker arm 154 with the first rocker arm 144 to change the lift / timing. The engagement unit is composed of at least one of the spline shaft 162, the interlocking member 160 and the locking portion 145, and is disposed around the first axis SS' to reduce inertia. Since the weight is accumulated adjacent to the first axis SS', the amount of work or force required to perform the shift is less. In addition, due to the lower inertia, the system 200 can operate at a higher engine speed.

[0061] In addition, in one embodiment, the decompression system 180 is disposed on the intake side, i.e., adjacent to the first cam 142 having a smaller lift. FIG. 9( a) depicts an exemplary graph of the operation of the decompression system according to an embodiment of the present subject matter. The decompression system 180 is provided to facilitate reverse, braking, starting, changing the compression ratio, or other specific operations. Preferably, during the start of the power unit, the decompression system 180 is capable of reducing the compression pressure, thereby reducing the amount of work required to manually or electrically start the power unit 100. The decompression system 180 is disposed adjacent to the first cam 142 and the decompression system 180 includes a pin, which includes a raised side and a flat side acting on the first cam 142. Therefore, during lower speeds, the raised side engages with the rocker arm to perform decompression, and at higher speeds, at speeds greater than idle, the flat side can operate without causing any valve lift. Therefore, as shown in the graph, curve E represents the lift of the exhaust valve / second valve, curve I represents the lift of the intake valve / first valve, and curve D represents the decompression that occurs during intake due to the decompression system 180.

[0062] FIG. 9( b) depicts an exemplary graph of valve lift in an engaged and disengaged state according to an embodiment of the present subject matter. In the present embodiment, the variable valve timing system is configured on the intake valve. Curve E represents the lift of the exhaust valve / second valve. Curves EC and DC represent the valve lift of the intake valve / first valve according to the engaged or disengaged (actuated or unactuated) state of the variable valve timing system 200. In the unactuated state, the first valve has a smaller valve lift due to the first cam and the corresponding first rocker arm actuating the valve, as represented by curve DC. In the actuated state, the first valve has a larger lift due to the second cam and the corresponding second rocker arm actuating the first valve, as represented by curve EC. In addition, in the actuated state, the second rocker arm is in an engaged state with the first rocker arm and the second cam drives the second rocker arm. The present invention enables variable valve timing even at higher speeds without stabilizing to a fixed valve lift that will be between curves DC and EC.

[0063] Figure 10Schematic diagram depicting the system in an actuated state according to an embodiment of the present subject matter. The system may include an electronic control unit (ECU) (not shown), or an integrated controller, or a manual switch to effectuate actuation of the system 200. In the actuated state of the actuator 112, the connecting shaft 176 is pushed by the pivot arm 172. The fork member 165 connected to the connecting shaft 176 is in turn pushed. The interlock member 160 connected to the fork member 165 slides around the spline shaft 160. The engagement pin 160P of the interlock member 160 engages with the slot in the locking portion 145 of the first rocker arm 144, thereby forming a rigid connection therebetween.

[0064] Accordingly, when the system 200 is actuated, the actuator 112 slides the engagement unit axially towards the locking portion 145 when at least one slot of the locking portion 145 of the first rocker arm 144 receives at least one engagement pin. Actuation is performed during the base circle condition. The second rocker arm 154 is operably engaged with the first rocker arm 144 through the engagement unit, and there is no free rotation between the two shafts during the actuated state. In the actuated state, the second cam 152 having a cam lobe with a greater lift first engages and the lift is transmitted to the first rocker arm 144 causing the lift of the first valve. The second cam 152 drives the first valve 132. Since the second cam 152 has caused the lift, the influence of the first cam 142 on the first rocker arm 144 is zero or negligible.

[0065] It should be understood that aspects of the embodiments are not necessarily limited to the features described herein. Many modifications and variations of the present subject matter are possible in view of the above disclosure. Accordingly, within the scope of the claims of the present subject matter, the present disclosure may be practiced in a manner different from that specifically described.

[0066] List of Reference Signs

[0067] 100 Power unit 146 First rocker shaft

[0068] 101 Cylinder head cover 147 Support member

[0069] 102 Cylinder head assembly 152 Second cam

[0070] 103 Cylinder block 154 Second rocker

[0071] 104, 105 Crankcase assembly 160 Interlock member

[0072] 110 Peripheral wall portion 160G Groove

[0073] 111 Flap 160P Engagement pin

[0074] 112 Actuator 160S Fork slot

[0075] 114 Intake port 162 Splined shaft

[0076] 115 Exhaust port 162S Spline

[0077] 120 Camshaft 165 Fork member

[0078] 121A, 121B Bearings 172 Pivot arm

[0079] 123 Sprocket 174 Pivot point

[0080] 124 Third cam 176 Connecting shaft

[0081] 125 Cover 180 Decompression system

[0082] 132 First valve 200 Variable valve timing system

[0083] 134 Second valve 205 Mounting structure

[0084] 135 Spark plug C - C' Cam axis

[0085] 142 First cam D1 First diameter

[0086] 144 First rocker arm D2 Second diameter

[0087] 144I Groove S - S' First axis

[0088] 145 Locking part

Claims

1. A power unit (100), comprising: a variable valve timing system (200), comprising: a first cam (142) for actuating one or more first valves (132) via a first rocker arm (144), the first rocker arm (144) being pivotable about a first axis (S - S'), the first rocker arm (144) having a locking portion (145) on one axial side; a second cam (152) for selectively actuating the one or more first valves (132) via a second rocker arm (154), the second rocker arm (154) being pivotable about the first axis (S - S'); and an engaging unit (145, 160, 162) disposed about the first axis (S - S'), the engaging unit (145, 160, 162) comprising a spline shaft (162), an interlocking member (160) and the locking portion (145), and the engaging unit (145, 160, 162) being configured to selectively engage the second rocker arm (154) with the first rocker arm (144); wherein the interlocking member (160) engages with the spline shaft (162), and the interlocking member (160) is slidable about the spline shaft (162) along the first axis (S - S'), and wherein the interlocking member (160) can selectively engage with the locking portion (145) on the first rocker arm (144) when actuated; wherein the power unit (100) includes an actuator (112), and the actuator (112) is functionally connected to the interlocking member (160) via a pivot arm (172), the pivot arm (172) pivoting about a pivot point (174) and the actuator being configured to actuate the pivot arm (172).

2. The power unit (100) according to claim 1, wherein, one axial side of the engaging unit (145, 160, 162) engages with one of the first rocker arm (144) and the second rocker arm (154), and the other axial side of the engaging unit (145, 160, 162) selectively engages with the other of the first rocker arm (144) and the second rocker arm (154), wherein the engaging unit (145, 160, 162) is configured to move about the first axis (S - S').

3. The power unit (100) according to claim 1, wherein, the variable valve timing system (200) is mounted to a cylinder head assembly (102), the cylinder head assembly (102) including a third cam (124) for driving at least one second valve (134) and a corresponding third rocker arm, wherein the third cam (124) is disposed between the first cam (142) and the second cam (152).

4. The power unit (100) according to claim 1, wherein, The engaging units (145, 160, 162) are received between the first rocker arm (144) and the second rocker arm (154), and at least a part of the engaging units (145, 160, 162) overlaps (OL) at least a part of a third cam (124) of the camshaft (120) when viewed in its radial direction.

5. The power unit (100) according to claim 1, wherein, the engaging units (145, 160, 162) are mounted to a first rocker arm shaft (146), and the first rocker arm shaft (146) is rotatably supported on the cylinder head assembly (102) by one or more rotary support members (147), wherein the first rocker arm shaft (146) supports the first rocker arm (144) and the second rocker arm (154) so as to achieve swinging about the first axis (S-S').

6. The power unit (100) according to claim 5, wherein, the first rocker arm shaft (146) includes at least one length having a second diameter (D2) that is smaller than a first diameter (D1) of the remaining length of the first rocker arm shaft (146), and the spline shaft (162) is disposed around the second diameter (D2), and the second rocker arm (154) is mounted to the spline shaft (162).

7. The power unit (100) according to claim 6, wherein, the first rocker arm (144) includes a locking portion (145) configured to engage with the interlocking member (160), and the locking portion (145) is integrally formed with the first rocker arm (144).

8. A power unit (100), comprising: a variable valve timing system (200), including: a first cam (142) for actuating one or more first valves (132) through a first rocker arm (144) that is pivotable about a first axis (S-S'); a second cam (152) for selectively actuating the one or more first valves (132) through a second rocker arm (154) that is pivotable about the first axis (S-S'); and Engaging units (145, 160, 162) that are arranged around the first axis (S-S'), and are configured to selectively engage the second rocker arm (154) with the first rocker arm (144), wherein the first cam (142) provides a first lift with a first timing for actuating the one or more first valves (132), and the second cam (152) provides a second lift with a second timing for actuating the one or more first valves (132), wherein the first timing is shorter than the second timing, and wherein a decompression system (180) is coupled to and arranged adjacent to the first cam (142); wherein the engaging units (145, 160, 162) include a splined shaft (162), an interlocking member (160), and a locking portion (145), the interlocking member (160) engages with the splined shaft (162), and the interlocking member (160) is capable of sliding around the splined shaft (162) along the first axis (S-S'), and wherein the interlocking member (160) is capable of selectively engaging with the locking portion (145) on the first rocker arm (144) upon actuation; wherein the power unit (100) includes an actuator (112), and the actuator (112) is functionally connected to the interlocking member (160) by a pivot arm (172), the pivot arm (172) pivots around a pivot point (174) and the actuator is configured to actuate the pivot arm (172).

9. A variable valve timing system (200) for a power unit, the variable valve timing system (200) comprising: a first rocker arm (144) that is pivotable about a first axis (S-S'), and has a locking portion (145) on one axial side; a second rocker arm (154) that is pivotable about the first axis (S-S'); a first cam (142) for actuating one or more first valves (132) through the first rocker arm (144); a second cam (152) for selectively actuating the one or more first valves (132) through the second rocker arm (154); and engaging units (145, 160, 162) that are arranged around the first axis (S-S'), the engaging units (145, 160, 162) include a splined shaft (162), an interlocking member (160), and the locking portion (145), and the engaging units (145, 160, 162) are configured to selectively engage the second rocker arm (154) with the first rocker arm (144); Wherein, the interlocking member (160) is engaged with the spline shaft (162), and the interlocking member (160) is capable of sliding around the spline shaft (162) along the first axis (S-S'), and wherein the interlocking member (160) is capable of selectively engaging with the locking portion (145) on the first rocker arm (144) upon actuation; Wherein, the power unit (100) includes an actuator (112), and the actuator (112) is functionally connected to the interlocking member (160) through a pivot arm (172), the pivot arm (172) pivots around a pivot point (174) and the actuator is configured to actuate the pivot arm (172).

Images