Abstract: The invention relates to a multi-cylinder internal combustion engine with gas flow lift valves actuated by electromagnetic actuators and controlling the intake and the exhaust of the cylinder combustion chambers. The cross-sectional area of the actuators allocated to the intake lift valves which is perpendicular to the axial direction of the lift valves is smaller than the cross-sectional area of the actuators allocated to the exhaust lift valves. If the intake lift valves and the exhaust lift valves are arranged in series one after the other in the direction of the longitudinal axis of the internal combustion engine, the width of the intake actuators measured in the plane of the actuator cross-sectional area and perpendicular to the longitudinal axis of the internal combustion engine is smaller than that of the exhaust actuators.

Abstract: A multi-valve engine comprises a plurality of intake and exhaust valves on a cylinder. Depending on use, one of the valves is made of higher heat-resistant material, and another is made of lower heat-resistant material, thereby decreasing cost and improving durability and reliability.

Abstract: A multi-valve engine comprises a plurality of intake and exhaust valves on a cylinder. Depending on use, one of the valves is made of higher heat-resistant material, and another is made of lower heat-resistant material, thereby decreasing cost and improving durability and reliability.

Abstract: In a set of heads for the cylinders of internal combustion engines with desmodromic valve operation, each head comprises an assembly of one or two inlet valves, and an assembly of one or two exhaust valves, so as to form heads with two, three and four valves. The assembly of inlet valves is positioned at an angle to the assembly of exhaust valves. The two assemblies are actuated through respective rockers by a single camshaft located substantially along the line running centrally between the two assemblies. The inlet duct and the exhaust duct are located in the same position within the head and have the same connections to the induction and exhaust systems in all the two-, three- and four-valve versions.

Abstract: The present invention seeks to provide, inter alia, further methods to generate swirl and reduce cross flow in spark ignition internal combustion engines having two inlet and two exhaust valves per cylinder head, without the use of additional moving parts.

Abstract: A poly valve system for an internal combustion engine having at least one cylinder having a bore and a cylinder center line, a piston capable of reciprocal travel within the bore, a cylinder head adjacent the bore having a hemispherical cylinder roof, intake and exhaust manifolds, and a combustion chamber defined between the cylinder head and the piston, comprising a plurality of independently operated valves. Valve seats comprise openings in the cylinder head between one of the manifolds and the combustion chamber. Poppet valves are situated in the valve seats to selectively allow communication between one of the manifolds and the combustion chamber. The valves are independently operable by a control signal, are non-parallel, and are oriented toward the cylinder center line.

Abstract: The invention relates to a method for influencing the mixture formation and charging movement in the cylinders of a piston internal combustion engine with at least one gas inlet valve and at least one gas outlet valve per cylinder, respectively. Each of these is provided with a fully variable, preferably electromagnetic valve gear and is controllable by means of an electronic control device which is designed in such a way that within predetermined speed ranges and/or in predetermined load conditions, at least some of the gas inlet valves and/or gas outlet valves can be moved in dependence on the piston stroke, respectively, with a stroke course that is variable in relation to opening and closing times and/or opening time for opening width and/or duration of opening period and/or speed of movement.

Abstract: A valve train for a small size diesel engine includes a pair of camshafts rotatively supported by and passing over a top of a cylinder head, one pair of intake and exhaust cams on each camshaft for each cylinder, two intake ports and two exhaust ports formed on the cylinder head over and around a bore center of each cylinder for communicating with the cylinder bore, two intake valves and two exhaust valves installed into the corresponding ports for selectively opening and closing the ports, rocker arms of which one end of each is connected to upper ends of the corresponding valves, and lash adjusters connected to other ends of the corresponding rocker arms for adjusting lash between the rocker arms and the cams, wherein the intake and exhaust ports are arranged in an alternative zigzag fashion.

Abstract: In an internal combustion engine with direct fuel injection including a cylinder block containing at least one cylinder with a piston, which performs an oscillating motion in the cylinder and a cylinder head including a combustion chamber for the at least one cylinder, a total of five intake and exhaust valves with respective intake and exhaust ducts are arranged in the cylinder head in a circular array and a spark plug and an injector are arranged in a center area of the combustion chamber between the intake and exhaust valves and point towards the center of the combustion chamber.

Abstract: Breathing system for four-stroke, fuel injected internal combustion engines, wherein each poppet valve of each cylinder accomplishes a dual-duty to serve both as an exhaust valve (in the final process of a given cycle) and subsequently as an inlet valve (in the first process of the following cycle). The passages (external to the cylinder) where the valve ports and stems are located are connected to both the intake and the exhaust manifolds wherein air is forced to flow under pressure by means of a fan (or a blower or a compressor) driven by the engine, in order to sweep away the combustion gases during the exhaust process and subsequently to feed a sufficient amount of fresh air during the intake process.

Abstract: An internal combustion engine with valve rest mechanisms. Exhaust secondary air is introduced at an exhaust port in a stable manner regardless of the resting, opening and closing operations of exhaust valves. Certain exhaust valves in the internal combustion engine are equipped with valve rest mechanisms. Exhaust valves that are not equipped with valve rest mechanisms located on neighboring cylinders are located on neighboring sides of their respective cylinders.

Abstract: A cylinder head for a four-valve per cylinder internal combustion engine comprises a bowl-shaped combustion chamber recess on a lower surface which cooperates with a piston in a cylinder to form a combustion chamber. The combustion chamber recess has first and second exhaust openings, and first and second intake openings. First and second exhaust ports extend from the first and second exhaust openings to an exhaust outlet through an exhaust side wall of the cylinder head. First and second intake ports, divided by a septum, extend from the first and second intake openings, along a curved flow path, to an intake passage. The intake passage delivers intake charge from an intake inlet in an intake side wall of the cylinder head to the first and second intake ports. The first and second intake ports have first and second intake valves to regulate flow of intake charge through the intake valve openings.

Abstract: A valve module that can be assembled to an internal combustion engine chamber. The valve module may have a first intake valve, a second intake valve, a third intake valve, a first exhaust valve and a second exhaust valve. The valves may be driven to an open position by hydraulically driven first pins. The exhaust valves may further have hydraulically driven second pins. The additional pins may increase the hydraulic forces which allow the exhaust valves to be opened even when there is a large pressure in the combustion chamber. The first pins of the exhaust valves may be controlled by a microprocessor controlled first control valve. The second pins may be controlled by a microprocessor controlled second control valve. The separate control valves and additional hydraulic force of the second pins may allow the microprocessor to open the exhaust valves at any point during a cycle of a combustion engine.

Abstract: The invention relates to a multicylinder four-stroke internal combustion engine having a cylinder head (1) with an intake and an outlet port arrangement for two admission valves (15, 16, 17, 18) and two exhaust valves (26, 27) per cylinder. The admission valves (15, 16, 17, 18) are fitted on opposite-lying longitudinal sides of the engine and the exhaust valves (26, 27) on respective opposite side walls in relation to the crankshaft axis. One swirl duct (11, 12) and one filling duct (13, 14) leading to the admission valves (15, 16, 17, 18) are provided per cylinder (7, 8).

Abstract: A valve module that can be assembled to an internal combustion engine chamber. The valve module may have a first intake valve, a second intake valve, a third intake valve, a first exhaust valve and a second exhaust valve. The valves may be driven to an open position by hydraulically driven first pins. The exhaust valves may further have hydraulically driven second pins. The additional pins may increase the hydraulic forces which allow the exhaust valves to be opened even when there is a large pressure in the combustion chamber. The first pins of the exhaust valves may be controlled by a microprocessor controlled first control valve. The second pins may be controlled by a microprocessor controlled second control valve. The separate control valves and additional hydraulic force of the second pins may allow the microprocessor to open the exhaust valves at any point during a cycle of a combustion engine.

Abstract: To reduce fuel consumption and exhaust emissions in an internal combustion engine a comparatively large quantity of exhaust gas is recirculated and a specific swirling flow is imposed on the exhaust gas as it is introduced into the combustion chamber. For this purpose the exhaust duct has a chamfer formed on only one side in the region of a flow cross-section. The swirling flow of exhaust gas rotating about an axis parallel to the cylinder axis, together with the supply of fresh gas, assures an increased fresh-gas concentration in the region of the spark plug.

Abstract: Several embodiments of multi-valve internal combustion engines, wherein low-speed hydrocarbon emissions are reduced by restricting the opening of at least one of the exhaust valves under this running condition. In addition, and in accordance with at least one of the embodiments, one of the intake valves is partially open during a portion of the exhaust cycle to further improve emission control.

Abstract: A valve system for an engine comprises a plurality of intake or exhaust valves, adapted to be driven by cams of which the profiles are different from each other to make maximum valve lifts of the valves different from each other, and compression springs biassing the valves toward the corresponding closing directions, the springs being identical to each other. An initial length of the spring is made shorter as the maximum valve lift of the valve becomes smaller, to make an initial load of the spring larger as the maximum valve lift of the valve becomes smaller.

Abstract: A cylinder head for a uniflow-scavenged two-stroke internal-combustion engine, particularly in motor vehicles, is provided with outlet valves which can be controlled by a camshaft. Outlet ducts connected with the outlet valves extend out of the cylinder head. A total of four outlet valves are provided for each cylinder, with the associated outlet ducts being guided to one side of the cylinder head. The camshaft is arranged laterally of the cylinder head opposite the outlet side of the outlet ducts. The outlet valves which are situated on the side facing away from the camshaft can be operated from the direction of the camshaft by way of operating members transversely penetrating the cylinder head.

Abstract: In a valve operating system designed to open and close intake valves of an internal combustion engine by an electromagnetic force, a first electromagnetic driving device for electromagnetically driving a first intake valve capable of opening and closing a first intake valve bore and a second electromagnetic driving device for electromagnetically driving a second intake valve capable of opening and closing a second intake valve bore are controlled by a control device in a manner so that when the engine is in a predetermined operational state, the first intake valve is opened and closed in a condition in which the second intake valve has been closed and stopped. Thus, it is possible to produce a swirl equivalent to that produced by changing of the lift amount, to provide a reduction in consumed electric power and to achieve a reliable engine operation, e.g., starting.

Abstract: A method of operating at least two exhaust valves in an engine cylinder using a four-way hydraulic actuator to open a first exhaust valve and after a time delay using a three-way hydraulic actuator to open a second exhaust valve to minimize the overall energy consumption in operating engine valves using hydraulic actuators.

Abstract: An engine charge control system operates by initially reducing power from full load by retarding exhaust valve closing timing to increase exhaust gas charge dilution up to the limit for efficient operation. Further load reductions are made by reducing charge mass without increased dilution via alternative steps such as throttling (in conjunction with intake check valves or using individual cylinder valves) or retarding intake valve opening timing without throttling. Partial substitution of external charge dilution is also contemplated.

Abstract: A valve mechanism for an internal combustion engine with a four-valve, double-overhead camshaft (DOHC) valve train in which the axes of valves for each cylinder diverge outwardly from and are non-parallel with respect to the axis of the cylinder, the valve mechanism having a finger follower for each camshaft lobe and valve and with a contact pad between the cam and the finger follower to permit rocking movement so that the orientation of the finger follower and the axis of the valve remains at a fixed relationship.

Abstract: A four-stroke cycle internal-combustion engine having two large- and small-diameter intake valves and two large- and small-diameter exhaust valves in one cylinder and mounted with a valve-operating mechanism on either of the intake valve side and the exhaust valve side. Each valve-operating mechanism comprises a first valve-operating cam of a narrow total valve-opening angle and a low lift, a second valve-operating cam of a wide total valve-opening angle and a high lift, a rocker arm for the small-diameter valve in direct engagement with the first valve-operating cam, a rocker arm for the large-diameter valve, and a connecting means capable of simultaneously operatively connecting the second valve-operating cam with the rocker arm for the small-diameter valve and the rocker arm for the large-diameter valve. In each cylinder at least three spark plugs are mounted. The combustion chamber is formed high on one side and low on the other side.

Abstract: This invention concerns a two-cycle internal combustion engine having a plurality of exhaust valves for each cylinder, and where during each exhaust valve control cycle, which includes a plurality of sequential combustion cycles of the engine, the exhaust valves open alternately.

Abstract: The invention relates to new and useful improvements in dual-cycle engine design and construction. The invention enhances the mechanical ability of such engines to automatically match the engine cycle with the load conditions while the system is in operation in a manner which significantly reduces the specific fuel consumption. Using the standard L-head engine configuration, the upper cylinder manifolding and the lower cylinder manifolding are combined as single flow channels reducing the number of components required to sequence flow to and from the engine. Combining the upper and lower cylinder manifold circuits standardizes the operating pressures in each system improving exhaust gas ejector efficiencies, facilitating engine control, and simplifying the application of pressure boosting in the air induction circuit. These improvements reduce the design complexity and simplify the automatic transition from 4-stroke to 2-stroke operation.

Abstract: A magnetic plate is disposed in confronting relation to the shank end of an auxiliary exhaust valve which is opened to discharge exhaust gases from a combustion chamber. The magnetic plate is attracted by an electromagnet into abutment against the shank end of the auxiliary exhaust valve, and forces the auxiliary exhaust valve in an opening direction. When the auxiliary exhaust valve is opened, the exhaust gases are discharged from the combustion chamber, and the pressure in the combustion chamber is quickly lowered. Forces required to open a main exhaust valve subsequently may thus be reduced.

Abstract: A cylinder head and valve train mechanism for an internal combustion engine having six valves per cylinder. There are provided four intake valves and two exhaust valves. In some embodiments, the size of the intake valves is varied because they are served by a common port so as to insure equal flow to the cylinder through all valves. In one embodiment, a single insert forms two of the valve seats. Also, two of the four valves are disposed at acute angles to both a plane containing the cylinder bore axis and a perpendicular plane passing through this axis in many embodiments. In these embodiments, the cam lobes that operate the angularly disposed valves have cam surfaces that are inclined relative to the axis of rotation of the camshaft. In some embodiments, all of the intake valves are operated by a single camshaft. In other embodiments, two camshafts operate different pairs of the intake valves. Various bearing arrangements for the camshafts are illustrated and described.

Abstract: A cylinder head construction for a multiple valve engine that permits the use of at least three intake valves while permitting a single piece head construction and offering ease of access of the hold down fasteners for the cylinder head. The intake tappets are all slidably supported within a projection of the cylinder head with the outer tappets being positioned closer to a plane containing the cylinder bore axis so that fastener receiving bores can be formed outwardly from this point without interference from the projection.

Abstract: An electromagnetic valve control system electromagnetically opens and closes intake and exhaust valves in an engine having a crankshaft. The electromagnetic valve control system has a valve actuator for opening an intake valve, a valve actuator for opening an exhaust valve, and a valve actuator for opening an auxiliary exhaust valve before the exhaust valve is opened.

Abstract: A number of embodiments of multiple valve internal combustion engines embodying a single camshaft for operating all of the multiple valves. The cylinder head is configured in such a way that it is reinforced across the center of the cylinder head by a bridging member and this bridging member can form a bearing surface for a center lobe of the camshaft. The camshaft is offset toward one side of the cylinder head and operates the valves through a plurality of rocker arms. In some embodiment, the rocker arms are journaled on a cam cover upon rocker arm shafts formed with reliefs aligned with openings in the cam cover for passing components such as a spark plug or a fastener for securing the cam cover to the cylinder head. Both single and multiple cylinder embodiments are disclosed.

Abstract: A valve placement arrangement for an internal combustion engine including four intake valves and two exhaust valves per cylinder wherein the exhaust valves are disposed across the combustion chamber with ports diametrically opposed externally of the intake valves, spaced as to prevent undue heating and insure minimal thermal loading. The valve placement arrangement provides a double cross flow of intake and exhaust.

Abstract: A variable valve timing and lift mechanism consists of low and high speed cams provided in phase on the camshaft of an overhead camshaft engine, the high speed cam having larger lift than the low speed cam although the base circle diameter of the two is the same. The low speed cam is coupled to port opening/closing valve(s) via a direct-driven tappet and the high speed cam is coupled to the same valve via a piston-type tappet consisting of a pair of pistons sealed in a support with an oil chamber interposed in between. The oil chamber is connected to the lubricating oil circuit of the engine by an oil passage provided with a control valve. This variable valve timing and lift device with the so-called direct attack-type dynamic valve mechanism, where the cam drives the valves directly without using any rocker arm and connecting mechanism, solves the problems created by the inability of the rocker arm, etc.

Abstract: A cylinder head and valve train mechanism for an internal combustion engine having six valves per cylinder. There are provided four intake valves and two exhaust valves. In some embodiments, the size of the intake valves is varied because they are served by a common port so as to insure equal flow to the cylinder through all valves. In one embodiment, a single insert forms two of the valve seats. Also, two of the four valves are disposed at acute angles to both a plane containing the cylinder bore axis and a perpendicular plane passing through this axis in many embodiments. In these embodiments, the cam lobes that operate the angularly disposed valves have cam surfaces that are inclined relative to the axis of rotation of the camshaft. In some embodiments, all of the intake valves are operated by a single camshaft. In other embodiments, two camshafts operate different pairs of the intake valves. Various bearing arrangements for the camshafts are illustrated and described.

Abstract: An improved head assembly for an internal combustion gasoline engine having an internal camshaft and push rod system which has a head (20) adapted to utilize four valves per cylinder using push rods (50) without modification to the engine block. The exhaust valves (36) are positioned longitudinally parallel with each cylinder and the inlet valves 38 are at a 10 to 18 degree angle from the engine cylinder centerline. The push rods (50) are so positioned as to allow contact with rocker arms (40) lifting the valves in sequence.

Abstract: A valve operating mechanism for an internal combustion engine having a plurality of exhaust valves per cylinder comprises a device for driving the exhaust valves in a same cylinder at such a valve timing that makes opening of the exhaust valves with a phase difference, i.e., at different timings relative to a crank angle. In one aspect of this invention, the exhaust valves open at the different times and close at the same time.

Abstract: An intake and exhaust valve system deployed in an internal combustion engine that improves available charge flow through the engine, provides improved charge turbulence and swirl of charge during each intake stroke for better mixture, provides for multiple independent fuel mixing at the cylinder, allows the use of concentric intake and exhaust valves also providing for balanced charge entry exit symmetry. The intake and exhaust valve system includes using a plurality of three or more concentric valve assemblies per cylinder, each intake valve being mounted within a hollow exhaust valve, the multiple intake and exhaust valves providing optimum flow area entering and exiting the cylinder. Three or more charge passage openings per cylinder strategically disposed enhances the uniform distribution of charge per unit time. Utilization of the present invention greatly increases the fuel efficiency of the engine, reduces emission pollution without sacrificing engine horsepower.

Abstract: In an internal combustion engine with two or more cylinders and two inlet valves per cylinder, in which the intake passages of two adjacent cylinders, which lead towards the inlet valves, are located side by side, symmetrically relative to the symmetry plane of the two cylinders, and in which the cylinder head is made in one piece and has one common inlet flange with an inlet channel, which is flow-connected, past a lug receiving one of the cylinder head studs, with the intake passages formed by guiding surfaces and leading towards the individual inlet valves, the intake passages leading to the inlet valves positioned at a lesser distance in the direction of flow are guided on one side of the lug and the intake passages leading to the inlet valves positioned at a greater distance are guided on the other side of the lug, and the inlet valves of the adjacent cylinders are controlled in such a way that the cylinders are fed with combustion air at different points in time.

Abstract: A two-stroke internal combustion engine comprising a cylinder head 14 having intake valves 20 and exhaust valves 22 arranged therein. A supercharger 42 is arranged in an intake pipe 44 and a tank 46 is mounted downstream of the supercharger 42. A valve 48 is arranged in an opening between the tank 46 and the pipe 44. From the pipe b 44, two intake manifolds 30 and 32 are branched, with respective branch pipes connected to the respective intake ports 24. An intake control valve 50 is arranged in one of the manifold 32, which closes at idling and under a low load of the engine. The engine further has means for generating a swirl S about an axis of the combustion chamber 18 by a portion of exhaust gas caused to flow back from the exhaust port 26 into the combustion chamber 18 after being once exhausted through the exhaust port when the exhaust valve is open.

Abstract: An exhaust gas recirculating system for a combustion engine has at least one cylinder communicating with a source of combustible air-fuel mixture through at least one intake port adapted to be selectively closed and opened for effecting the interruption and admission of the supply of the combustible mixture into the combustion chamber, the cylinder also communicating with an exhaust system through first and second exhaust ports both adapted to be selectively opened and closed.

Abstract: An internal combustion engines comprises at least one exhaust valve made of ceramics per each engine cylinder and a pluarality of intake valves made of steel. The relation in number and valve head diameter between the intake and exhaust valves is designed so as to give Pe<Pi and De>Di where Pe is the number of exhaust valves per each engine cylinder, Pi is the number of intake valve per each engine cylinder, De is the valve head diameter of the exhaust valves and Di is the valve head diameter of the intake valve.

Abstract: A cylinder head for a valve-controlled internal combustion engine having a bottom surface which faces into an associated combustion chamber and a plurality of spaced valve openings therethrough and also an injector bore for induction of fuel or ignition spark through the combustion face of said cylinder head into the cylinder, said bottom surface or combustion face of said cylinder head having a circular cut-out portion located radially spaced between said injector bore and the center lines of said valve openings, with said cut-out possibly intersecting each of said valve openings.

Abstract: An injection-type internal combustion engine with cylinders arranged in line, with two overhead camshafts, and four valves and a central pump nozzle for each cylinder, and with detachable rocker arms being provided on the cylinder head above the respective camshaft, for actuating the pump nozzles. With this arrangement, the cams for the rocker arms actuating the pump nozzles are operated from the two camshafts in turn, i.e., the first camshaft actuates the pump of one cylinder and the second camshaft actuates that of the adjacent cylinder, each rocker arm being mounted separately. This will facilitate assembly and disassembly of the pump nozzle including the corresponding actuating mechanism and valve gear.

Abstract: An internal combustion piston engine having a plurality of intake valves and a plurality of exhaust valves per cylinder employs apparatus for disabling the operation of at least one exhaust valve upon decrease in speed of the engine below a predetermined level.

Abstract: A valve apparatus for an internal combustion engine includes an intake valve plate and an exhaust valve plate mounted side-by-side for longitudinal reciprocable, slidable movement over the mouth or opening of the combustion cylinder. Each of the slidable valve plates includes a plurality of longitudinally spaced movable valve ports which are adapted to register with corresponding fixed valve ports in the valve head on the opposite side of the slidable valve plates from the engine cylinder.

Abstract: In a four-valve engine having a pair of intake ports and a pair of exhaust ports, the hole for inserting the spark plug or the fuel injection nozzle is obliquely formed between the exhaust ports so that one end of the hole opens in the lower surface of the cylinder head at the center of the combustion chamber and the other end of the hole opens between the spring seat portions for the exhaust valve springs and the opening of the exhaust ports in the side face of the cylinder head.

Abstract: An internal combustion engine, and a method of operating an internal combustion engine, of the kind in which recycled exhaust gases are reacted with a hydrocarbon fuel in a combustion space to produce a reformed fuel of enhanced calorific value by cracking molecules of the hydrocarbon fuel, the invention providing for means for the supply of air to the combustion space in the cylinder and separate means for the supply of the cracked and reformed fuel enabling an efficient engine operation to be achieved with economical use of fuel.

Abstract: An apparatus and a method for controlling the operation of intake and exhaust valves of an internal combustion engine having a plurality of intake and exhaust valves for each cylinder to provide an optimum engine output at all operating speeds. When the engine is rotating at a low speed, a part of both of the intake and exhaust valves are rendered inoperative. When the engine is rotating at a medium speed, all of the intake valves are made operative and a part of the exhaust valves are rendered inoperative. Finally, when the engine is rotating at a high speed, all of both of the intake and exhaust valves are rendered operative.

Abstract: Several embodiments of cylinder head and valve train configurations for an overhead valve internal combustion engine that permits increased valve area without interference and while maintaining simplified valve actuation. In each embodiment one pair of valves is operated by one cam shaft and lies on one side of a plane containing the axis of the cylinder. Three other valves are positioned primarily on the other side of the plane and reciprocate about axes that are not parallel with each other. These axes, however, intersect so that each of these three valves may be operated by the same cam shaft. In one embodiment of the invention the intersection of the valves axis is coincident with the axis of rotation of the respective cam shaft so as to permit direct actuation of the valves. In another embodiment the intersection lies substantially along a plane that intersects the stems of the valves when they are closed to facilitate operation of multiple valves from a single cam lobe by means of a single rocker arm.

Abstract: Herein disclosed is a valve actuating mechanism having a stopping function for use in an internal combustion engine of the type, in which at least one pair of intake or exhaust valves having an identical function and disposed adjacent to each other are arranged for one cylinder. First and second rocker arms respectively having arms abutting against the upper ends of the paired intake or exhaust valves are rockingly supported on a common support shaft which is fixed on the engine body while having an axis perpendicular to the operating directions of the valves. The first rocker arm is formed with a cylinder bore which is opened toward the second rocker arm to bear a plunger therein whereas the second rocker arm is formed with a guide bore which is opened toward the first rocker arm to fit the plunger therein.