Valve operating system in internal combustion engine

Abstract: An actuator (51 1 ) is connected to one of components forming a power transmitting device capable of transmitting a power provided by a valve operating cam (29I) provided on a cam shaft (28), so that the actuator can drive an engine valve (VI) in a lift amount which is obtained by addition of a lift amount of the engine valve (VI) based on a cam profile of the valve operating cam (29I) and a lift amount of the engine valve (VI) based on the operation of the actuator (51 1 ). Thus, a portion of the lift amount of the engine valve (VI) is borne by the valve operating cam (29I), whereby a valve-opening power borne by the actuator (51 1 ) can be reduced, as compared with a system designed so that the engine valve (VI) is driven by the actuator (51 1 ) only. The amount of electric power consumed by the actuator (51 1 ) can be smaller.

Description: Background of the Invention 1. Field of the Invention The present invention relates to a valve operating system in an internal combustion engine, and particularly, to a valve operating system in an internal combustion engine including an electric actuator which enables a force to be applied in a valve-opening direction to an engine valve that is biased in a valve-closing direction by a spring. 2. Description of the Related Art Such a valve operating system is conventionally already known, for example, from Japanese Patent Application Laid-open No. 3-92520. In the above known system, however, the engine valve is opened and closed only by the electric actuator. For this reason, the operational characteristic of the engine valve can be changed depending on the operational state of the engine. But the actuator must exhibit a driving force corresponding to a maximum lift amount of the engine valve, resulting in an increased amount of electric power consumed in the actuator. Japanese Patent Application Laid-open No 60-164 613 discloses another known valve operating system including an electric actuator. EP-A-826 866, as prior art relevant to Article 54(3) and (4) EPC, shows: a valve operating system in an internal combustion engine, comprising an electric actuator which enables a power to be applied in a valve-opening direction to an engine valve that is biased in a valve-closing direction by a spring, wherein said actuator is connected to one of components of a power transmitting means capable of transmitting a power provided by a valve operating cam provided on a cam shaft to the engine valve, so that said engine valve can be driven in a lift amount obtained by addition of a lift amount of said engine valve based on a cam profile of said valve operating cam and a lift amount of said engine valve based on the operation of said actuator. There, the power of the electric actuator is not independent of the power of the valve operating cam in the valve opening direction. Summary of the Invention It is an object of the present invention to provide a valve operating system in an internal combustion engine, wherein the control of the operation of the actuator can be reduced. To achieve the above object, according to a first aspect and feature of the present invention, there is provided a valve operating system according to claim 1. Therefore, immediately before the closing and seating of the intake valves, the intake valves are gently seated according to the cam profile of the intake-side valve operating cam, whereby the occurence of the bouncing of the intake valves can be prevented. Thus, it is unnecessary to finely control the operation of the actuator by the control means in order to provide the gentle operation of the intake valves whereby the control of the operation of the actuator can be simplified. The engine valve can be driven in a lift amount obtained by adding a lift amount of the engine valve based on a cam profile of the valve operating cam and a lift amount of the engine valve based on the operation of the actuator. With such arrangement, a portion of the lift amount of the engine valve is borne by the valve operating cam. Therefore, the valve-opening force borne by the actuator can be small when compared with a system in which the engine valve is driven only by the actuator. Hence, the amount of electric power consumed in the actuator can be also small. According to a second aspect and feature of the present invention, in addition to the first feature, the force transmitting means comprises many components. An inner ring is turnable about an axis parallel to the cam shaft. An outer ring is turnable about the same axis as the inner ring and surrounds the inner ring. A carrier on which planetary rotors disposed between the inner and outer rings are carried for rotation about axes parallel to the axis of the inner and outer rings. The carrier is turned in operative association with a revolving movement of the planetary rotors around the inner ring. A first one of the components is connected to the engine valve, while a second one of the components is operatively connected to the valve operating cam, and the actuator is connected to a third one of the components. With the arrangement of the second feature, the force transmitting means is formed into a planetary gear type or a planetary friction type from the inner and outer rings and the carrier as the components. The three components are connected to the engine valve, the valve operating cam, and the actuator, respectively. Therefore, when the independent forces from the valve operating cam side and the actuator side are simultaneously applied to the force transmitting means, they can be synergetically transmitted to the engine valve, while avoiding the creation of a collision point, thereby providing a reduction in size of the force transmitting means. According to a third aspect and feature of the present invention, in addition to the first feature, the valve operating cam has a cam profile. The cam profile provides a lift characteristic describing a buffer curve immediately before closing and seating of the engine valve. With the arrangement of such third feature, at least at a moment immediately before closing and seating of the engine valve, the engine valve is gently seated according to the buffer curve of the cam profile of the valve operating cam. Thus, the bouncing of the engine valve can be prevented from occurring. Also it is unnecessary to finely control the operation of the actuator in order to provide the gentle operation of the engine valve. Thus, the control of the operation of the actuator is simplified. According to a fourth aspect and feature of the present invention, in addition to the arrangement of the second feature, the inner ring is connected to the engine valve. One of the carrier and the outer ring is operatively connected to the valve operating cam on the cam shaft for turning movement in response to the rotation of the cam shaft, and the actuator is connected to the other of the carrier and the outer ring. With such an arrangement, the amount of turning movement of the carrier or the inner ring operatively connected to the cam shaft is smaller than the amount of turning movement of the inner ring operatively connected to the engine valve. Therefore, the size of the valve operating cam can be set at a remarkably small value relative to the lift amount required for the engine valve, i.e., the amount of turning movement of the inner ring. Whereby, the load received from the valve operating cam by the carrier or the outer ring can be remarkably reduced to contribute to the alleviation of the valve operating load. Further, a space required for the rotation of the valve operation cam, as well as a space required for the operation of the portion of the carrier operatively connected with the valve operating cam, can be relatively reduced because the size of the valve operating cam is relatively reduced. Hence, a valve operating chamber in which the valve operating system disposed can be made compact. The force transmitting means can be arranged to be compact, thereby providing a reduction in size of the valve operating system. According to a fifth aspect and feature of the present invention, in addition to the arrangement of the fourth feature. the carrier is operatively connected to the valve operating cam, and the actuator is connected to the outer ring. With such an arrangement, the amount of turning movement of the carrier operatively connected to the valve operating cam relative to the amount of turning movement of the inner ring connected to the engine valve is smaller than the amount of turning movement of the outer ring in a case where the outer ring is operatively connected to the valve operating cam. Therefore, the size of the valve operating cam can be set at a smallest value relative to the lift amount required for the engine valve, i.e., the amount of turning movement of the inner ring, as compared with a case where the outer or the inner ring of the force transmitting means is operatively connected to the valve operating cam. Thus, the load received from the valve operating cam by the carrier is minimized to further alleviate the valve operating load. Moreover, because the valve operating cam is smaller in size, a space required for the rotation of the valve operating cam, as well as a space required for the operation of the portion of the carrier operatively connected with the valve operating cam, is relatively small. Hence, the valve operating chamber in which the valve operating system disposed can be made further compact. Further, the amount of turning movement of the outer ring caused by the actuator is also relatively small. Hence, the actuator can be of a relatively reduced size, thereby leading to a simplified structure of connection between the outer ring and the actuator and also to an increased freedom degree in the disposition of the connected portions of the outer ring and the actuator. According to a sixth aspect and feature of the present invention, in addition to the arrangement of the second feature, the force transmitting means is formed into a planetary gear type system having a sun gear which is the inner ring, a ring gear which is the outer ring, and the carrier on which planetary gears rotors are rotatably carried as the planetary. With such an arrangement, the operational characteristic of the engine valve can be accurately controlled by meshed connections of the components forming the force transmitting means with one another. According to a seventh aspect and feature of the present invention, in addition to the arrangement of the second feature, a support shaft supports the inner ring for turning movement. The support shaft has an axis disposed in parallel to, but offset from, the axis of the cam shaft. With such an arrangement, the cam shaft can be formed in a simple structure in which the valve operating cam is only provided thereon. According to an eighth aspect and feature of the present invention, in addition to the arrangement of the fifth feature, the carrier is integrally provided with a roller retaining arm extending on the side of the valve operating cam. A roller is pivoted at a tip end of the roller retaining arm to come into rolling contact with the valve operating cam. With such an arrangement, by forming the roller retaining arm to be integral with the carrier, the rigidity of the carrier itself can be enhanced, and the operations of the inner and the outer rings and the planetary rotors are stably carried out. Thus, the accuracy of the operational characteristic of the engine is enhanced. In addition, the valve operating cam and the carrier are operatively connected to each other by the rolling contact of the roller pivoted at the tip end of the roller retaining arm with the valve operating cam and therefore, the resistance friction between the valve operating cam and the carrier can be reduced. According to a ninth aspect and feature of the present invention, in addition to the arrangement of the eighth feature, the carrier comprises a pair of support plates disposed on opposite sides of the planetary rotors. Shafts extend between the support plates on which the planetary rotors are rotatably carried. The roller is formed larger than an entire axial length of the planetary rotor and is supported rotatably by a roller shaft. The roller shaft is fixed at opposite ends thereof to a pair of the roller retaining arms integrally provided on the support plates, with steps for supporting the outer ring being formed between inner surfaces . of the roller retaining arms and inner surfaces of the support plates. With such an arrangement, notwithstanding that the roller retaining arms are integrally provided on the carrier, the structure of supporting the outer ring for rotation by an outer periphery of the carrier can be simplified. In addition, by setting the axial length of the roller at a relatively large value, the area of contact between the roller and the valve operating cam can be increased to a relatively large value, thereby further reducing the resistance of friction between the valve operating cam and the carrier. According to a tenth aspect and feature of the present invention, in addition to the second feature, the second one of the components of the force transmitting means is operatively connected to a first valve operating cam provided on the cam shaft. The valve operating system further includes a connection switch-over means provided between one of the first and second components. A rocker arm rotatable about the same axis as of the inner ring in a manner to follow a second valve operating cam is provided on the cam shaft. The connection switch-over means is capable of being switched over between a connecting state in which the one of the first and second components is connected to the rocker arm, and a disconnecting state in which the connection between the one of the first and second components and the rocker arm is released. A control means for controlling the operations of the actuator and the connection switch-over means is arranged to change over a control mode thereof, depending on the operational state of the engine, between a first control mode in which the actuator is in an operative state and the connection switch-over means is brought into the disconnecting state, and a second control mode in which the actuator is brought into an inoperative state and the connection switch-over means is brought into the connecting state. With such an arrangement of the tenth feature, when the control means selects the first control mode, the first and second components of the three components forming the force transmitting means are operatively connected to the first valve operating cam and the engine valve, respectively. The third component is rotated by the actuator so that the turning movement of the second component attendant on the turning movement of the first component caused by the rotation of the cam shaft, i.e., the operational characteristic of the engine valve, is controlled thereby. Thus, the operational characteristic of the engine valve can be finely controlled by finely controlling the turning movement of the third component by the actuator. When the control means selects the second control mode, the turning movement of the third component by the actuator is canceled. Hence, the valve operating force is not transmitted from the first valve operating cam through the force transmitting means. However, the rocker arm driven by the second valve operating cam is connected to either of the first and second components. Hence, the engine valve can be opened and closed by the second valve operating cam. Therefore, in an operational range in which a problem arises due to the operation of the actuator, the engine valve is driven by the second valve operating cam by selecting the second control mode, thereby making it possible to avoid the problem due to the operation of the actuator. According to an eleventh aspect and feature of the present invention, in addition to the tenth feature, the connection switch-over means is arranged so that the connecting state and the disconnecting state are switched over from one to the other in accordance with a hydraulic pressure. The control means is formed to output a signal indicative of a command to bring the electric actuator into the inoperative state after completion of the connecting operation of the connection switch-over means, when the control mode is switched over from the first control mode to the second control mode, and to output a signal indicative of a command to bring the connection switch-over means into the disconnecting state after outputting of a signal indicative of a command to bring the actuator into the operative state, when the control mode is switched over from the second control mode to the first control mode. With such an arrangement of the eleventh feature, when the control mode is switched over from the first control mode to the second control mode, the actuator is brought into the inoperative state after completion of the connecting operation of the hydraulic connection switch-over means, whose connecting operation is liable to be late, as compared with the operation of the electric actuator. Therefore, it is possible to prevent the operation of the engine valve from being disturbed because the actuator is brought into the inoperative state before the driving of the engine valve by the second valve operating cam is started. When the control mode is switched over from the second control mode to the first control mode, the actuator is brought into the operative state, before the connection switch-over means is brought into the disconnecting state. Therefore, it is possible to prevent the operation of the engine valve from being disturbed because the connection switch-over means is brought into the disconnecting state before the driving of the engine valve by the force transmitting means and the actuator is started. According to a twelfth aspect and feature of the present invention, in addition to the eleventh feature, the control means is arranged to select the second control mode in a lower-speed operational range of the engine and to select the first control mode in a higher-speed operational range of the engine. With the arrangement of the twelfth feature, it is possible to avoid the consumption of the electric power of a battery by the actuator in the lower-speed operational range of the engine in which the charged amount of the battery is relatively small, thereby preventing the operation of the actuator from exerting an adverse influence on the battery. According to a thirteenth aspect and feature of the present invention, in addition to the tenth feature, the control means is arranged to select the first control mode in a lower-speed operational range of the engine and to select the second control mode in a higher-speed operational range of the engine. With the arrangement of the thirteenth feature, it is possible to ensure that the responsiveness required for the actuator corresponds to the lower-speed operational range of the engine. Therefore, it is unnecessary to increase the speed of the operation of the actuator and to reduce the size of the actuator, which can contribute to a reduction in consumption of electric power, when the actuator is of an electric type. The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figs.1 to 9 show a first embodiment of the present invention, wherein Fig.1 is a vertical sectional view of an essential portion of an internal combustion engine; Fig.2 is an enlarged sectional view taken along a line 2-2 in Fig.1; Fig.3 is an enlarged sectional view taken along a line 3-3 in Fig.1; Fig.4 is a schematic sectional view showing an arrangement of an actuator; Fig.5 is a diagram of a valve-opening lift characteristic for an intake valve; Fig.6 is a sectional view showing a situation of an operation of the actuator at the start of the opening of the intake valve; Fig.7 is a sectional view showing a situation of the operation of the actuator when the intake valve is maintained in an opened state; Fig.8 is a sectional view showing a situation of the operation of the actuator when the intake valve is closed; Fig.9 is a sectional view showing a situation of the operation of the actuator when the intake valve is maintained in a closed state; Fig.10 is a schematic vertical sectional view of an intake-side valve operating device in a closed state of an intake valve according to a second embodiment of the present invention; Figs.11 to 19 show a third embodiment of the present invention, wherein Fig.11 is a vertical sectional view of an essential portion of a multi-cylinder internal combustion engine; Fig.12 is a sectional view taken along a line 12-12 in Fig.11; Fig.13 is an enlarged sectional view taken along a line 13-13 in Fig.12; Fig.14 is a sectional view taken along a line 14-14 in Fig.12; Fig.15 is a sectional view taken along a line 15-15 in Fig.12; Fig.16 is a plan view taken along a line 16-16 in Fig.11, with a head cover being omitted; Fig.17 is a block diagram showing an arrangement of a control system; Fig.18 is a flow chart showing a control procedure, when the control mode is switched over from a first control mode to a second control mode; Fig.19 is a flow chart showing a control procedure, when the control mode is switched over from the second control mode to the first control mode; and Fig.20 is a sectional view similar to Fig.14, but according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will now be described with reference to Figs.1 to 9. Referring first to Fig.1, a combustion chamber 15 is defined between an upper surface of a piston slidably received in a cylinder block (not shown) and a cylinder head 14. A pair of intake valve bores 16 and a pair of exhaust valve bores 17 are provided in the cylinder head 14 so that they open into a ceiling surface of the combustion chamber 15. The intake valve bores 16 communicate with an intake port 18 and the exhaust valve bores 17 communicate with an exhaust port 19. Stems 20 of intake valves VI as a pair of engine valves capable of opening and closing the intake valve bores 16 are slidably received in guide tubes 21 mounted in the cylinder head 14, respectively. Coiled valve springs 23 are mounted between the cylinder head 14 and retainers 22 mounted at upper ends of the stems 20 projecting upwards from the guide tubes 21 to surround the stems 20, so that the intake valves VI are biased by the valve springs 23 in a direction to close the intake valve bores 16. Stems 24 of a pair of exhaust valves VE capable of opening and closing the exhaust valve bores 17 are slidably received in guide tubes 25 mounted in the cylinder head 14, respectively. Coiled valve springs 27 are mounted between the cylinder head 14 and retainers 26 mounted at upper ends of the stems 24 projecting upwards from the guide tubes 25 to surround the stems 24, so that the exhaust valves VE are biased by the valve springs 27 in a direction to close the exhaust valve bores 17. A cam shaft 28 parallel to an axis of a crankshaft (not shown) is rotatably disposed between the intake valves VI and the exhaust valves VE so that they are located lower than upper ends of the intake valves VI and upper ends of the exhaust valves VE. The cam shaft 28 is operatively connected to the crankshaft in such a manner that it is rotated in a counterclockwise direction as viewed in Fig.1 with a reduction ratio of 1/2. Moreover, an oil bath 30 is defined in an upper surface of the cylinder head 14 and the cam shaft 28 is disposed at a location at which an intake-side valve operating cam 29I and an exhaust-side valve operating cam 29E can be submerged in an oil in the oil bath 30. An intake-side valve operating device 31I 1 is provided between the intake valves VI and the intake-side valve operating cam 29I of the cam shaft 28 and is capable of converting the rotating movement of the cam shaft 28 into the opening and closing movement of the intake valves VI. An exhaust-side valve operating device 31E 1 is provided between the exhaust valves VE and the exhaust-side valve operating cam 29E of the cam shaft 28 and is capable of converting the rotating movement of the cam shaft 28 into the opening and closing movement of the exhaust valves VE. The exhaust-side valve operating device 31E 1 includes a rocker arm shaft 32 fixedly disposed and having an axis parallel to the cam shaft 28, and a rocker arm 33 provided between the exhaust valves VE and the exhaust-side valve operating cam 29E and rotatably carried on the rocker arm shaft 32. A cam slipper 34 is provided at one end of the rocker arm 33 to come into contact with the exhaust-side valve operating cam 29E. A pair of tappet screws 35 are threadedly inserted into the other end of the rocker arm 33 to come into contact with the upper ends of the exhaust valves VE, so that the advanced and retreated positions thereof can be regulated. The intake-side valve operating device 31I 1 includes a force transmitting means 36, and an electric actuator 51 1 fixed to a head cover 52. Referring to Figs.2 and 3, the force transmitting means 36 is formed into a planetary gear type system and comprises a sun gear 37 as an inner ring supported on a support shaft 41 supported in the cylinder head 14 for rotation about an axis of the support shaft 41. A ring gear 38 is an outer ring provided for rotation about the same axis as the sun gear 37 to surround the sun gear 37. A carrier 39 on which planetary gears 40 are planetary rotors are carried for rotation about an axis parallel to the axes of the sun gear 37 and the ring gear 38 and which is turned in operative association with the revolution of the planetary gears 40 around the sun gear 37. The support shaft 41 has an axis parallel to the axis of the cam shaft 28 and is fixedly disposed between the cam shaft 28 and the intake valves VI at a location different from the axis of the cam shaft 28. By disposing the support shaft 41 in the above manner, the intake-side valve operating device 31I 1 can be easily disposed in a common valve operating system which is conventionally employed, while avoiding that the structure between the cam shaft 28 and the intake valves VI is complicated. A pair of connecting arms 42 extend toward the intake valves VI at locations spaced apart from each other in a tangential direction of the support shaft 41, and have base portions 42a which are fitted and secured to opposite sides of the sun gear 37 as first one of the three components: the sun gear 37, the ring gear 38 and the carrier 39 constituting the force transmitting means 36. Tappet screws 43 are threadedly inserted into tip ends of the connecting arms 42 to come into contact with upper ends of the stems 20 in the intake valves VI so that the advanced and retreated positions thereof can be regulated. Thus, the sun gear 37 is operatively connected to the intake valves VI so that the intake valve VI is opened and closed in response to the turning movement of the sun gear 37. The carrier 39 is a second one of the components making up the force transmitting means 36 and includes a pair of ring-shaped support plates 39a rotatably carried on the base portions 42a of the connecting arms 42, a plurality of, e.g., six, shafts 39b having an axis parallel to the axis of the support shaft 41 and supported at their opposite ends on the support plates 39a. The planetary gears 40 meshed with the outer periphery of the sun gear 37 and the inner periphery of the ring gear 38 are rotatably carried by the shafts 39b disposed at locations spaced at equal distances apart from one another in the peripheral direction of the support shaft 41. The support plates 39a included in the carrier 39 are integrally provided with roller retaining arms 45 extending on. the side of the intake-side valve operating cam 29I. A roller 44 longer than the entire axial length of the planetary gears 40 is carried on tip ends of the roller retaining arms 45. The roller retaining arms 45 are extended on the side of the cam shaft 28 so as to form steps 46 between inner surfaces of the roller retaining arms 45 and inner surfaces of the support plates 39a. A roller shaft 47 having an axis parallel to the axis of the support shaft 41 is fixed at its opposite ends at tip ends of the roller retaining arms 45. A needle bearing 48 is interposed between the roller shaft 47 and the roller 44 which is in rolling contact with the intake-side valve operating cam 29I having a width along the axis of the cam shaft 28 larger than the entire axial length of the roller 44. Thus, the carrier 39 is operatively connected to the intake-side valve operating cam 29I of the cam shaft 28 so that the carrier 39 is driven in turning movement by the intake-side valve operating cam 29I in response to the rotation of the cam shaft 28. The ring gear 38, which is a third one of the three components making up the force transmitting means 36, is rotatably carried on the carrier 39. Namely, the ring gear 38 formed into a cylindrical shape is rotatably supported at its opposite ends on outer peripheral edges of inner surfaces of the support plates 39a. The ring gear 38 is rotatably supported at its opposite ends on the steps 46 formed between the support plates 39a and the roller retaining arms 45 in locations corresponding to the roller retaining arms 45 connected to the support plates 39a. The ring gear 38 is integrally provided with a control arm 49 extending in a direction perpendicular to the axis of the support shaft 41. An actuator 51 1 is fixed to the head cover 52 and has a rod 57 that is in contact with the control arm 49 in a substantially perpendicular direction. Referring to Fig.4, the actuator 51 1 includes a housing 53 formed into a cylindrical shape, an electromagnet 54 fixedly disposed in one end of the housing 53, a plunger 56 disposed in an opposed relation to the electromagnet 54 within the housing 53, a rod 57 axially movably disposed to extent through a central portion of the electromagnet 54 and the housing 53 and connected at its base end to the plunger 56, and a return spring 58 mounted between the housing 53 and a spring receiving portion 57a fixed to a tip end of the rod 57 outside the housing 53. The actuator 51 1 is fixed to the head cover 52 so that the tip end of the rod 57 can be put into abutment against the control arm 49 of the ring gear 39. Moreover, the spring load of the return spring 58 is set at an extremely small value, as compared with the spring load of the valve spring 23. With such an actuator 51 1 , the rod 57 is moved axially between a position in which the plunger 56 is attracted to the electromagnet 54 and a position in which the plunger 56 is received by the other closed end of the housing 53. The tip end of the rod 57 is normally in contact with the control arm 49 under such an action of the return spring 58. The operation of the actuator 51 1 is controlled by a control means 60 1 . During operation of the intake valves VI in the closing direction within a period when the intake valves VI are open, the control means 60 1 stops supplying electric power to the electromagnet 54 to stop delivery of a driving force from the actuator 51 1 to the control arm 49 of the force transmitting means 36. The lift characteristic of the intake valve VI, as shown in Fig.5, depends on the force inputted from the actuator 51 1 to the force transmitting means 36 and the force inputted from the intake-side valve operating cam 29I to the force transmitting means 36. In Fig.5, the intake-side valve operating cam 28I has a cam profile, which provides a lift characteristic, as shown by a dashed line, when the intake valves VI are opened and closed only by the intake-side valve operating cam 29I. This cam profile provides a lift characteristic in which a gentle buffer curve C 1 is described at the start of the operation of the intake valves VI, and a gentle buffer curve C 2 is described immediately before closing and seating of the intake valves VI. The actuator 51 1 can start the opening of the intake valves VI at a time point t 1 , which is when the intake valves VI are opened, regardless of the valve-opening starting time point determined by the intake-side valve operating cam 29I. As shown in Fig.6, the electromagnet 54 is then excited to attract the plunger 56. Thus, the sun gear 37 is turned by pushing the control arm 49 of the ring gear 38 using the rod 57, thereby operating the intake valves VI in an opening direction. In this case, when the roller retaining arms 45 are pushed by the intake-side valve operating cam 29I through the roller 44, the force from the actuator 51 1 and the force from the intake-side valve operating cam 29I are synergetically applied to the sun gear 37, whereby the intake valves VI are lifted a total lift amount measured by adding a lift amount attendant on an amount of operation of the actuator 51 1 and a lift amount provided by the intake-side valve operating cam 29I. Thus, when the maximum lift amount of the intake valve VI is, for example, 8 mm, the actuator 51 1 can bear, for example, 7 mm, and the intake-side valve operating cam 29I can bear, for example, 1 mm. After a time point t 2 when the lift amount of the intake valves VI becomes maximum, the plunger 56 is left attracted to the electromagnet 54, as shown in Fig.7. When the exciting of the electromagnet 54 is stopped at a time point t 3 , the intake valves VI start to be closed by the spring force of the valve spring 23, and the actuator 51 1 causes the rod 57 to be pushed by the control arm 49, as shown in Fig.8, whereby the plunger 56 is brought into a state in which it is in abutment against the other closed end of the housing 53. Thus, after a time point t 4 immediately before closing and seating of the intake valves VI, the intake valves VI show a lift characteristic determined by the cam profile of the intake-side valve operating cam 29I, and are slowly closed and seated according to the buffer curve C 2 . After closing and seating of the intake valves VI, the rod 57 of the actuator 51 1 remains in abutment against the control arm 49 under the action of the spring force of the return spring 58. However, the return spring 58 cannot disturb the operation of the intake valves VI because the spring load of the return spring 58 is set at a enough small value to avoid any problems, as compared with the spring load of the valve spring 23. The operation of the first embodiment will be described below. Since the intake-side valve operating cam 29I bears a portion of the lift amount of the intake valve VI, the valve opening force borne by the actuator 51 1 may be small, as compared with a system designed so that the intake valves VI are opened and closed only by the actuator 51 1 . Therefore, the amount of electric power consumed by the actuator 51 1 is also small and hence, the size of the actuator 51 1 can be reduced. Moreover, the operational characteristic can be changed by controlling the timing of operation of the actuator 51 1 . When the actuator 51 1 is broken down, the intake valves VI can be driven only by the intake-side valve operating cam 29I. When the break-down of the actuator 51 1 is taken into consideration, a cam profile of the intake-side valve operating cam 29I may be established so that a lift characteristic shown by the two-dot dashed line in Fig.5 forms a higher mountain-shaped curve. If such a profile is established, the driving of the intake valves VI can be ensured despite the break-down of the actuator 51 1 . The force transmitting means 36 is provided between the intake-side valve operating cam 29I and the intake valves VI, and the actuator 51 1 is connected to one of the components of the force transmitting means 36, e.g., the ring gear 38. The force transmitting means 36 is of the planetary gear type and hence, when the forces from the intake-side valve operating cam 29I and the actuator 51 1 , which are independent from each other, are simultaneously applied to the force transmitting means 36, both the forces can be synergetically transmitted to the intake valves VI while avoiding the creation of a collision point. Moreover, since the force transmitting means 36 is of the planetary type comprising the sun gear 37, the ring gear 38 and the carrier 39, which are each disposed for rotation about the same axis, the force transmitting means 36 can be made compact and thus, the size of the intake-side valve operating device 31I 1 can be reduced. Further, the operational characteristic of the intake valves VI can be accurately controlled by the meshed connection of the components 37, 38 and 39 making up the force transmitting means 36 with one another. Moreover, since the ring gear 38, the planetary gears 40 and the carrier 39 are disposed between the pair of connecting arms 45 connected respectively to the intake valves VI, the force transmitting means 36 can be made further compact. In such force transmitting means 36, the rotational amount of the carrier 29I is remarkably smaller than the rotational amount of the sun gear 37. The carrier 39 is operatively connected to the intake-side valve operating cam 29I of the cam shaft 28. The sun gear 37 is operatively connected to the intake valves VI. Therefore, the size of the intake-side valve operating cam 29I relative to the lift amount required for the intake valves VI, i.e., the rotational amount of the sun gear 37 can be remarkably reduced. Thus, the load received by the carrier 39 from the intake-side valve operating cam 29I can be relatively decreased to contribute to the alleviation of valve operating load. In addition, since the roller 44 supported on the roller retaining arms 45 of the carrier 39 is in rolling contact with the intake-side valve operating cam 29I, the valve operating load can be further alleviated. Further, because the intake-side valve operating cam 29I is relatively small, a space required for the rotation of the valve operating cam 29I and a space required for the operation of the pair of roller retaining arms 45 integral with the carrier 39 are relatively small. Therefore, a valve operating chamber in which the intake-side valve operating device 31I 1 is disposed can be made compact. Since the intake-side and exhaust-side valve operating cams 29I and 29E are submerged in the oil within the oil bath 30 defined in the upper surface of the cylinder head 14, the force transmitting means 36 can be sufficiently lubricated by raking up the oil by the intake-side and exhaust-side valve operating cams 29I and 29E. In this case, the oil raked up by the intake-side and exhaust-side valve operating cams 29I and 29E can be effectively scattered toward the force transmitting means 36 to effectively lubricate the force transmitting means 36. Further, the support shaft 41 supporting the force transmitting means 36 is disposed in parallel to the cam shaft 28 at a location offset from the axis of the cam shaft 28. The cam shaft 28 can formed into a simple structure in which the valve operating cams 29I and 29E are only provided thereon, as in the prior art valve operating system. Additionally, since the pair of roller retaining arms 45 extending on the side of the intake-side valve operating cam 29I are integrally provided on the carrier 39, the rigidity of the carrier 39 itself can be enhanced, and the stable operation of the ring gear 38 and the planetary gear 40 can be carried out to enhance the accuracy of the operational characteristic of the intake valves VI. In addition, since the roller 44 is supported on the roller retaining arms 45 to come into rolling contact with the intake-side valve operating cam 29I, the resistance friction between the intake-side valve operating cam 29I and the carrier 39 can be reduced. Moreover, the carrier 39 is comprised of the pair of support plates 39a disposed on the opposite sides of the planetary gears 40, and the shafts 39b which are provided to extend between the support plates 39a and on which the planetary gears 40 are rotatably carried. The opposite ends of the roller shaft 47 on which the roller 44 longer than the entire axial length of the planetary gears 40 is rotatably supported, are fixed to the roller retaining arms 45, and the steps 46 supporting the ring gear 38 are formed between the inner surfaces of the roller retaining arms 45 and the inner surfaces of the support plates 39a. Therefore, the structure in which the ring gear 38 is rotatably carried on the outer periphery of the carrier 39 can be simply constructed, but also because the axial length of the roller is relatively large, the area of contact between the roller 44 and the intake-side valve operating cam 29I can be relatively large, whereby the resistance of friction between the intake-side valve operating cam 29I and the carrier 39 can be further reduced. Further, the intake-side valve operating cam 29I has the cam profile which provides the lift characteristic in which the gentle buffer curves C 1 and C 2 are described at the start of the opening of the intake valves VI and immediately before the closing and seating of the intake valves VI, when the intake valves VI are opened and closed. The control means 60 1 controls the actuator 51 1 so that the delivery of the driving force to the force transmitting means 36 is stopped at least immediately before the closing and seating of the intake valve VI during operation of the intake valves VI in the closing direction within the period while the intake valves VI are open. Therefore, immediately before the closing and seating of the intake valves VI, the intake valves VI are gently seated according to the cam profile of the intake-side valve operating cam 29I, whereby the occurrence of the bouncing of the intake valves VI can be prevented. Thus, it is unnecessary to finely control the operation of the actuator 51 1 by the control means 60 1 in order to provide the gentle operation of the intake valves VI, whereby the control of the operation of the actuator 51 1 can be simplified. Fig.10 is a simplified vertical sectional view of an intake-side valve operating device in a valve-closed state according to a second embodiment of the present invention, wherein portions or components corresponding to those in the first embodiment are designated by like reference characters. The intake-side valve operating device includes a force transmitting means 36 provided between an intake-side valve operating cam 29I on a cam shaft 28 and an intake valve VI, and an electric actuator 51 2 connected to a control arm 49 provided on a ring gear 38 of the force transmitting means 36. The actuator 51 2 includes a housing 53 formed into a cylindrical shape. A first electromagnet 54 is fixedly disposed in one end of the housing, while a second electromagnet 55 is fixedly disposed in the other end of the housing 53. A plunger 56 is accommodated in the housing 54 between both the electromagnets 54 and 55. A rod 57 that is axially movable is provided to extend through a central portion of the first electromagnet 54 and the housing 53 and is connected at its base end to the plunger 56. A return spring 58 is mounted between the housing 53 and a spring receiving portion 57a fixed to a tip end of the rod 57 outside the housing 53. In this actuator 51 2 , the plunger 56 and thus, the rod 57 are reciprocally moved by switching-over the excitation and deexcitation of the first and second electromagnets 54 and 55. The control means 60 1 (see Fig.1) excites the first electromagnet 54 and deexcites the second electromagnet 55, when the intake valve VI is operated in an opening direction and excites the second electromagnet 55 and deexcites the first electromagnet 54, when the intake valve VI is operated in a closing direction. When the intake valve VI is in a closed state, the plunger 56 remains attracted to the second electromagnet 55, as shown in Fig.10, and a gap is produced between the tip end of the rod 57 and the control arm 49, whereby the spring force of the return spring 58 cannot act on the power transmitting means 36. In the second embodiment, the second electromagnet 55 remains excited in the closed state of the intake valve VI. Hence, the amount of electric power consumed is slightly larger than that in the first embodiment, but the actuator 51 2 and the intake-side valve operating cam 29I cooperate with each other to open the intake valve VI. Therefore, the amount of electric power consumed in the actuator 51 2 can be decreased to provide a reduction in size of the actuator 51 2 , as compared with a system designed so that the intake valves VI are opened and closed by only the actuator 51 2 . A third embodiment of the present invention will, now be described with reference to Figs.11 to 19. Referring first to Figs.11 and 12, support portions 14a are provided on a cylinder head 14 on opposite sides of a combustion chamber 15 in each cylinder and the cam shaft 28 is rotatably carried between the support portions 14a and shaft holders 66 fastened to the support portions 14a. The rocker arm shaft 32 is fixedly supported by the shaft holders 66. An exhaust-side valve operating device 31E 2 includes a pair of a rocker arms 33 carried on the rocker arm shaft 32 in correspondence to exhaust valves VE. Mounted on the rocker arm shaft 32 are a cylindrical spacer 67 for maintaining the spacing between both the exhaust-side rocker arms 33, and a cylindrical spacers 68 for maintaining the spacing between the exhaust-side rocker arms 33 and the shaft holders 66. Referring to Figs.13 and 14, an intake-side valve operating device 31I 2 includes a planetary gear-type force transmitting means 36 for each of the cylinders. The force transmitting means 36 has a sun gear 37 rotatably supported on a support shaft 41, which is fixedly disposed between the cam shaft 28 and the intake valves VI and has an axis parallel to the cam shaft 28. The support shaft 41 is fixedly supported by the shaft holders 66, which support the rocker arm shaft 32. The sun gear 37, which is one of the three components constituting the force transmitting means 36, i.e., the sun gear 37, the ring gear 38 and the carrier 39, is integrally provided with cylindrical portions 69 and 70, which extend on opposite sides of the sun gear 37 to surround the support shaft 41. Cylindrical spacers 71 and 72 are mounted on the support shaft 41 between outer ends of the cylindrical portions 69 and 70 and the shaft holders 66. Base portions 73a of a pair of connecting arms 73 extending toward the intake valves VI are fitted and secured to the outer ends of the cylindrical portions 69 and 70 integral with the sun gear 37. Tappet screws 35 are threadedly inserted into tip ends of the connecting arms 73 to come into contact with upper ends of the stems 20 in the intake valves VI, so that the advanced and retracted positions thereof can be regulated. Thus, the sun gear 37 is operatively connected to the intake valves VI so that the intake valves VI are opened and closed in response to the rotation of the sun gear 37. The carrier 39, which is one of the components constituting the force transmitting means 36, includes a pair of ring-shaped support plates 39a rotatably carried on the cylindrical portions 69 and 70 of the sun gear 37, and a plurality of, e.g., six, shafts 39b each supported at opposite ends on the support plates 39a. Planetary gears 40 meshed with an outer periphery of the sun gear 37 and an inner periphery of the ring gear 38 are rotatably carried on the shafts 39b disposed at locations spaced apart from one another at equal distances in a circumferential direction of the support shaft 41. A roller 44 is carried at tip ends of roller retaining arms 45 that are integrally provided on the support plates 39a included in the carrier 39. The roller 44 is in rolling contact with the first intake-side valve operating cam 29I 1 provided on the cam shaft 28. Thus, the carrier 39 is operatively connected to the first intake-side valve operating cam 29I 1 of the cam shaft 28 so that the carrier 39 is driven in turning movement by the first intake-side valve operating cam 29I 1 in response to the rotation of the cam shaft 28. The ring gear 38, which is the remaining one of the three components constituting the force transmitting means 36, is rotatably carried by the carrier 39. Referring also to Fig.15, a cam slipper 75 integrally provided on the intake-side rocker arm 74 is in sliding contact with a second intake-side valve operating cam 29I 2 provided on the cam shaft 28. The intake-side rocker arm 74 is turnably carried on the cylindrical portion 70 of the sun gear 37 in such a manner that it is clamped between one of the pair of support plates 39a included in the carrier 39 and the base portion 73a of one of the connecting arms 73. The intake-side valve operating cam 29I 1 has a cam profile corresponding to a lower-speed operational range of the engine, while the second intake-side valve operating cam 29I 2 has a cam profile corresponding to a higher-speed operational range of the engine. A hydraulic connection switch-over means 76 is provided between the intake-side rocker arm 74 and the base portion 73a of the one connecting arm 73 and is capable of switching-over the connection and disconnection between the rocker arm 74 and the one connecting arm 73, i. e., the sun gear 37. The connection switch-over means 76 includes a connecting piston 77 which is slidably received in the base portion 73a of the one connecting arm 73 so that it can be fitted into the intake-side rocker arm 74. A bottomed cylindrical interlocking member 78 is slidably received in the intake-side rocker arm 74 for movement with the connecting piston 77. A return spring 79 mounted between the interlocking member 78 and the intake-side rocker arm 74 exhibits a spring force to bias the interlocking member 78 toward the connecting piston 77. A first bottomed slide bore 80 is provided in the base portion 73a of the one connecting arm 73 with its axis parallel to the axis of the support shaft 41, and opens toward the intake-side rocker arm 74. The connecting piston 77 is slidably received in the first slide bore 80 to form a hydraulic pressure chamber 81 between the piston 77 and a closed end of the first slide bore 80. A second slide bore 82 having the same diameter as the first slide bore 80 and a smaller-diameter open bore 83 are provided in the intake-side rocker arm 74 to extend between opposite ends of the intake-side rocker arm 74 and to have axes parallel to the axis of the support shaft 41. The open bore 83 is coaxially connected to the second slide bore 82 with an annular step formed therebetween. The interlocking member 78, with its closed end in sliding contact with the connecting piston 77, is slidably received in the second slide bore 82. Further, the return spring 79 is mounted under compression between the interlocking member 78 and the step between the second slide bore 82 and the open bore 83. An oil passage 84 is coaxially provided in the support shaft 41. A communication passage 85 is provided in the cylindrical portion 70 of the sun gear 37 and the base portion 73a of the connecting arm 73 for permitting the communication between the oil passage 84 and the hydraulic pressure chamber 81 despite the turning movement of the sun gear 37. A hydraulic pressure source is connected to the oil passage 84 through a control valve means 86. A working oil, whose hydraulic pressure can be changed to higher and lower levels by the control valve means, is supplied to the oil passage 84 and to the hydraulic pressure chamber 81. A pressure sensor 88 for detecting the hydraulic pressure being risen to a preset pressure is added to the oil passage 84 downstream from the control valve means 86. In such connection, switch-over means 76, when the hydraulic pressure in the hydraulic pressure chamber 81 is lower, sliding faces of the connecting piston 77 and the interlocking member 78 lie between the base portion 73a of the connecting arm 73 and the intake-side rocker arm 74, thereby enabling the relative rotation of the connecting arm 73, i. e., the sun gear 37 and the intake-side rocker arm 74. However, when the hydraulic pressure in the hydraulic pressure chamber 81 is increased to a higher level, a portion of the connecting piston 77 is fitted into the second slide bore 82 while pushing the interlocking member 78 against the spring force of the return spring 79. Thus, the base portion 73a of the connecting arm 73 and the intake-side rocker arm 74 are connected to each other through the connecting piston 77 and thus rotated in unison with each other. The pressure sensor 88 detects that the connecting operation of the connection switch-over means 76 has been completed, since the hydraulic pressure in the hydraulic pressure chamber 81 has been increased to the higher level. A control arm 49 is integrally provided in the ring gear 38 of the force transmitting means 36 to extend outwards from the ring gear 38, and an electric actuator 51 1 or 51 2 is connected to the control arm 49. An actuator holder 90 is secured to a housing 53 of the actuator 51 1 . The actuator holder 90 is mounted to a pair of shaft holders 66, which are fastened to the support portion 14a of the cylinder head 14 on opposite sides of the combustion chamber 15 in each of the cylinders for fixedly supporting the rocker arm shaft 32 and the support shaft 41 and for supporting the cam shaft 28 for rotation between the support portions 14a. A tip end of the rod 57 of the actuator 51 1 is in contact with the control arm 49. Referring also to Fig.16, the actuator holder 90 is mounted to extend between the pair of shaft holders 66 disposed on the opposite sides of the combustion chamber 15. The actuator holder 90 is fastened at one end to the cylinder head 14 by a bolt 91 along with the end (on the side of the intake valves VI) of the shaft holder 66 disposed in one side in a direction of arrangement of the cylinders. The actuator holder 90 is also a fastened at the other end to the cylinder head 14 by a bolt 92 along with the end (on the side of the exhaust valves VE) of the shaft holder 66 disposed on the other side in the direction of arrangement of the cylinders. Thus, the actuator holder 90 is fixed on both the shaft holders 66 to form an acute angle with the direction of arrangement of the cylinders. On the other hand, a laterally and upward extending insertion tube 93 is secured at its lower end to the cylinder head 14 between both the exhaust-side rocker arms 33 in the exhaust-side valve operating device 31E 2 , so that a spark plug 94 screwed into the cylinder head 14 to face a central portion of the combustion chamber 15 can be inserted into the insertion tube 93. An arcuate notch 90a is provided in the actuator holder 90 so as to prevent the hindrance to the operation for inserting and removing the spark plug into and from the insertion tube 93. A cylindrical cover portion 95 is integrally provided at an upper portion of a head cover 52' fastened to the cylinder head 14, and an upper portion of the housing 53 of the actuator 51 1 with the opposite ends of the actuator holder 90 fastened to the shaft holders 66 is inserted into the cover portion 95. Referring to Fig.15, a resiliently biasing means 96 is mounted on a lower surface of the actuator holder 90 at a location above the intake-side rocker arm 74 to exhibit a biasing force for permitting the cam slipper 75 of the intake-side rocker arm 74 to be normally in contact with the second intake-side valve operating cam 29I 2 . The resiliently biasing means 96 includes a cylindrical guide tube 97 that is secured at its upper end to the lower surface of the actuator holder 90 and extends vertically, a piston 98 that is slidably received in the guide tube 97, and a spring 99 that is accommodated in the guide tube 97 to exhibit a spring force for biasing the piston 98 downwards. A lower end of a rod 98a extending downwards from the piston 98 is in contact with the upper surface of the intake-side rocker arm 74. Referring to Fig.17, a control means 60 2 controls the operations of the actuator 51 1 and the connection switch-over means 76, i.e., the operation of the control valve means 86 capable of changing the hydraulic pressure in the hydraulic pressure chamber 81 from one of the higher and lower levels to the other. Inputted to the control means 60 2 are (1) a detection value provided by a rotational speed sensor 100 for detecting a rotational speed of the engine, and (2) a detection value provided by the pressure sensor 88 for detecting the completion of the connecting operation of the connection switch-over means 76. Thus, the control means 602 controls the operation of the actuator 51 1 and the control valve means 86 based on the detecting valves of the pressure sensor 88 and the rotational speed sensor 100. The control means 60 2 controls the actuator 51 1 and the connection switch-over means 76 in a state in which it has been switched over between a first control mode in which the connection switch-over means 76 is brought into a disconnecting state, in a lower-speed operational range of the engine, and a second control mode in which the actuator 51 1 is brought into an inoperative state and at the same time, the connection switch-over means 76 is brought into a connecting state, in a higher-speed operational range of the engine. When the mode of the control means 60 2 has been switched over from the first control mode to the second control mode, the control means 60 2 controls the actuator 51 1 and the connection switch-over means 76 according to a procedure shown in Fig.18. At Step S1 in Fig.18, it is determined whether the rotational speed NE of the engine detected by the rotational speed sensor 100 exceeds a preset first rotational speed N1, e.g., 3,100 rpm. When ME > N1, the following signal is outputted at Step S2: a signal indicative of a command to provide the connecting operation of the connection switch-over means 76, i.e., a signal indicative of a command to operate the control valve means 86 to control the hydraulic pressure in the oil passage 84. At Step S3, it is determined whether the pressure sensor 88 has detected the higher hydraulic pressure, i.e., whether the connecting operation of the connection switch-over means 76 has been substantially completed. When it is determined that the connecting operation has been completed, the operation of the actuator 51 1 is stopped at Step S4. Namely, the control means 60 2 stops the operation of the actuator 51 1 after completion of the connecting operation of the hydraulic connection switch-over means 76, whose switching-over operation is liable to be late, as compared with the operation of the electric actuator 51 1 . When the second control mode is changed to the first control mode, the control means 60 2 controls the actuator 51 1 and the connection switch-over means 76 according to a procedure shown in Fig.19. At Step S11, it is determined whether the rotational speed NE of the engine detected by the rotational spewed sensor 100 is smaller than the first preset rotational speed N1. When NE < N1, the actuator 51 1 is operated at Step S12 and then, it is determined at Step S13 whether the rotational speed NE of the engine is smaller than the second preset rotational speed N2 previously determined as a value smaller than the first preset rotational speed N1, e.g., 2,900 rpm. When NE < N2, the processing is advanced to Step S14, at which point a signal indicative of a command to bring the connection switch-over means 76 into the disconnecting state is outputted. Therefore, when the second control mode is changed to the first control mode, the operation of the actuator 51 1 is first started and thereafter, the operation of connection switch-over means 76 to the disconnecting state is started. Moreover, the second preset rotational speed N2, which is a criterion for determining the changing of the second control mode to the first control mode, is set smaller than the first preset rotational speed N1, which is a criterion for determining the changing of the first control mode to the second control mode, thereby providing a hysteresis. Thus, it is possible to prevent a hunting from being produced in the control of the changing-over of the first and second control modes from one to the other. With the third embodiment, in the intake-side valve operating device 31I 2 , the connection switch-over means 76 is brought into the disconnecting state and the actuator 51 1 is operated by selecting the first control mode by the control means 60 2 in the lower-speed operating range of the engine, and the ring gear 38 in the force transmitting means 36 is driven by the actuator 51 1 , whereby the operational characteristic of the intake valves VI can be finely controlled. In the higher-speed operational range of the engine, the connection switch-over means 76 is brought into the connecting state and the operation of the actuator 51 1 is stopped by selecting the second control mode by the control means 60 2 . This causes the sun gear 37 to be swung along with the intake-side rocker arm 74 driven in swinging movement by the second intake-side valve operating cam 29I 2 , thereby opening and closing the intake valves VI with the operational characteristic corresponding to the cam profile of the second intake-side valve operating cam 29I 2 . In this way, in the lower-speed operational range of the engine, the operational characteristic of the intake valves VI can be changed by use of the force transmitting means 36 and the actuator 51 1 , and in the higher-speed operational range of the engine, the intake valves VI are driven with the operational characteristic determined by the second intake-side valve operating cam 29I 2 . Thus, the responsiveness required for the actuator 51 1 may be one corresponding to the lower-speed operational range of the engine, whereby a reduction in size of the actuator 51 1 can be provided, and a reduction in amount of electric power consumed can be provided. Namely, in the higher-speed operational range of the engine in which the responsiveness of the actuator 51 1 is of a consideration, the intake valves VI are driven by the second intake-side valve operating cam 29I 2 by selecting the second control mode and in this manner, it is possible to avoid a problem from arising due to the operation of the actuator 51 1 . Moreover, when the first control mode is changed to the second control mode, the electric actuator 51 1 is brought into the inoperative state after it has been detected by the pressure sensor 88 that the connecting operation of the connection switch-over means 76 has been completed. Therefore, after completion of the connecting operation of the hydraulic connection switch-over means 76, whose switching operation is liable to be late as compared with the operation of the actuator 51 1 , the actuator 51 1 is brought into the inoperative state. In this manner, it is possible to prevent the operation of the intake valves VI from being disturbed because the actuator 51 1 is brought into the inoperative state before starting of the driving of the intake valves VI by the second intake-side valve operating cam 29I 2 . On the other hand, when the second control mode is changed to the first control mode, the connection switch-over means 76 is brought into the disconnecting state after outputting of the signal indicative of the command to bring the actuator 51 1 into the operative state. Therefore, the actuator 51 1 is brought into the operative state before the connection switch-over means 76 is brought into the disconnecting state, and in this manner, it is possible to prevent the operation of the intake valves VI from being disturbed because the connection switch-over means 76 is brought into the disconnecting state before starting of the driving of the intake valves VI by the first intake-side valve operating cam 29I 1 , the force transmitting means 36 and the actuator 51 1 . In addition, since the actuator 51 1 is mounted to the shaft holders 66, which is fastened to the cylinder head 14 with the rocker arm shaft 32 and the support shaft 41 fixedly supported thereon, the rigidity of mounting of the actuator 51 1 can be enhanced, as compared with a case where the actuator is mounted to the head cover, and the position of the actuator 51 1 relative to the force transmitting means 36 cannot be offset, when the head cover 52' is mounted or removed. Thus, it is easy to mount and remove the head cover 52'. The actuator holder 90 is fixedly mounted to extend between the shaft holders 66 disposed on the opposite sides of the combustion chamber 15, and the actuator holder 90 and the shaft holders 66 are fastened to the cylinder head 14 by the common bolts 91 and 92. Therefore, the rigidity of the shaft holders 66 can be increased, and the actuator 51 1 can be mounted to the shaft holders 66 in a compact structure with a reduced number of parts. Further, the actuator holder 90 is fastened at one end to the cylinder head 14 by the bolt 91 along with the end (on the side of the intake valves VI) of the shaft holder 66 disposed in one side of each of the cylinders, and at the other end to the cylinder head 14 by the bolt 92 along with the end (on the sides of the exhaust valves VE) of the shaft holder 66 disposed on the other side of each cylinder. Therefore, the actuator holder 90 is mounted to the shaft holders 66 by the minimum number of, i.e., two bolts 91 and 92, and the actuator 51 1 can be mounted to the shaft holders 66 in a compact structure in which the mounting and removing operation is easy. Fig.20 shows a fourth embodiment of the present invention, wherein portions or components corresponding to those in the first embodiment are designated by like reference characters. Intake valves VI (see the third embodiment) are connected to a sun gear 37 of a power transmitting means 36', and an actuator 51 1 (see the third embodiment) is operatively connected to a ring gear 38. A first intake-side valve operating cam 29I 1 (see the third embodiment) is operatively connected to a carrier 39'. The carrier 39' includes a pair of ring-shaped support plates 101 and 102, and a plurality of shafts 39b supported at opposite ends on the support plates. Planetary gears 40 are rotatably carried on the shafts 39b. Moreover, a connection switch-over means 76' is provided between an intake-side rocker arm 74' moved following a second intake-side valve operating cam 29I 2 (see the third embodiment) and a support plate 102 for the carrier 39'. The connection switch-over means 76' includes a connecting piston 77 which is slidably received in the intake-side rocker arm 74', so that it can be fitted into the support plate 102, a bottomed cylindrical interlocking member 78 that is slidably received in the support plate 102 for movement along with the connecting piston 77, and a return spring 79 mounted between the interlocking member 78 and the support plate 102 to exhibit a spring force for biasing the interlocking member 78 toward the connecting piston 77. A first bottomed slide bore 103 is provided in the intake-side rocker arm 74' with its axis parallel to the axis of the support shaft 41, and opens toward the support plate 102. The connecting piston 77 is slidably received in the first slide bore 103 to define a hydraulic pressure chamber 104 between the connecting piston 77 and a closed end of the first slide bore 103. The support plate 102 is also provided with a second bottomed slide bore 105 having the same diameter as the first slide bore 103, and an open bore 106 leading to a closed end of the second slide bore 105. The interlocking member 78, with its closed end in sliding contact with the connecting piston 77, is slidably received in the second slide bore 105. Further, the return spring 79 is mounted under compression between the closed end of the second slide bore 105 and the interlocking member 78. A communication passage 106 is provided in the intake-side rocker arm 74', a cylindrical portion 70 of the sun gear 37 and the support shaft 41 to permit the oil passage 84 in the support shaft 41 to communicate with the hydraulic pressure chamber 104 despite the turning movement of the intake-side rocker arm 74'. Even in the fourth embodiment, in a lower-speed operational range of the engine, the connection switch-over means 76' is brought into its disconnecting state, and in a higher-speed operational range of the engine, the connection switch-over means 76' is brought into its connecting state. When the connection switch-over means 76' is in the connecting state, the carrier 39' is swung along with the intake-side rocker arm 74' driven in swinging movement by the second intake-side valve operating cam 29I 2 . In this case, the ring gear 38 is driven in turning movement by the actuator 51 1 which is in the inoperative state(see the third embodiment). Therefore, the sun gear 37 is turned by the carrier 39' swung along with the intake-side rocker arm 74', and the intake valves VI are opened and closed with an operational characteristic corresponding to the cam profile of the second intake-side valve operating cam 29I 2 . In an alternative embodiment of the present invention, the second control mode in which the actuator 51 1 or 51 2 is brought into the inoperative state and the connection switch-over means 76 or 76' is brought into the connecting state, may be selected in the lower-speed operational range of the engine. The second control mode in which the actuator 51 1 or 51 2 is operated and the connection switch-over means 76 or 76' is brought into the disconnecting state, may be selected in the higher-speed operational range of the engine. If the control mode is selected in the above manner, it is possible to avoid that the electric power of a battery is consumed by the actuator 51 1 or 51 2 in the lower-speed operational range of the engine in which the charged amount of the battery is reduced, and it is possible to prevent an adverse influence from being exerted to the battery due to the operation of the actuator 51 1 or 51 2 . In the above-described embodiments, it has been determined based on the detection value provided by the pressure sensor 88 for detecting the hydraulic pressure that the connecting operation of the hydraulic connection switch-over means 76 or 76' has been completed. However, the completion of the connecting operation of the connection switch-over means 76 or 76' may be determined based on the lapse of a preset time after outputting of the signal indicative of the command to provide the connecting operation of the connection switch-over means 76 or 76'. Alternatively, the completion of the connecting operation of the connection switch-over means 76 or 76' may be determined by directly detecting the operation of the connecting piston 77 or the interlocking member 78 in the connection switch-over means 76 or 76'. In a further alternate embodiment of the present invention, a planetary friction-type force transmitting means (a traction drive) as disclosed in Japanese Patent Application Nos.5-33840, 5-79450, 5-157149, 6-34005 and 6-66360, may be used as a force transmitting means. The present invention is applicable to an exhaust valve as an engine valve.

Claims: A valve operating system in an internal combustion engine, comprising an electric actuator (51 1 , 51 2 ) which enables a power to be applied in a valve-opening direction to an engine valve (VI) that is biased in a valve-closing direction by a spring (23), wherein said actuator is connected to one of components of a power transmitting means (36) capable of transmitting a power provided by a valve operating cam (29I) provided on a cam shaft (28) to the engine valve, so that said engine valve can be driven in a lift amount obtained by addition of a lift amount of said engine valve based on a cam profile of said valve operating cam (29I) and a lift amount of said engine valve based on the operation of said actuator (51 1 , 51 2 ), and said system further includes a control means (60 1 , 60 2 ) for controlling said actuator, characterized in that said control means being arranged to stop the delivery of a driving force from said acutator (51 1 , 51 2 ) to said power transmitting means (36) at least at a moment immediately before closing and seating of said engine valve within a period while said engine valve is open. A valve operating system in an internal combustion engine according to claim 1, wherein said components of said power transmitting means (36) are: an inner ring (37) which is turnable about an axis parallel to said cam shaft; an outer ring (38) which is turnable about the same axis as of said inner ring and surrounds said inner ring; and a carrier (39) on which planetary rotors (40) disposed between said inner and outer rings are carried for rotation about axes parallel to the axis of said inner and outer rings, said carrier (39) being turned in operative association with a revolving movement of said planetary rotors (40) around said inner ring (37), a first one of said components being connected to said engine valve, a second one of said components being operatively connected to said valve operating cam (29I), and said actuator (51 1 , 51 2 ) being connected to a third one of said components. A valve operating system in an internal combustion engine according to claim 1, wherein said valve operating cam (29I) has a cam profile which provides a lift characteristic describing a buffer curve (C2) immediately before closing and seating of said engine valve. A valve operating system in an internal combustion engine according to claim 2, wherein said inner ring (37) is connected to said engine valve (VI); one of said carrier (39) and said outer ring (38) is operatively connected to said valve operating cam (29I) on said cam shaft (28) for turning movement in response to the rotation of said cam shaft, and said actuator (51 1 ,51 2 ) is connected to the other of said carrier and said outer ring (38). A valve operating system in an internal combustion engine according to claim 4, wherein said carrier (39) is operatively connected to said valve operating cam (29I), and said actuator (51 1 ) is connected to said outer ring (38). A valve operating system in an internal combustion engine according to claim 2, wherein said power transmitting means (36) is formed into a planetary gear type having a sun gear (37) which is said inner ring, a ring gear (38) which is said outer ring, and said carrier (39) on which planetary gears (40) as said planetary rotors are rotatably carried. A valve operating system in an internal combustion engine according to claim 2, further including a support shaft (41) for supporting said inner ring (37) for turning movement, said support shaft (41) having an axis disposed in parallel to but offset from the axis of said cam shaft (28). A valve operating system in an internal combustion engine according to claim 5, wherein said carrier (39) is integrally provided with a roller retaining arm (45) extending on the side of said valve operating cam, with a roller (44) being pivoted at a tip end of said roller retaining arm (45) to come into rolling contact with said valve operating cam (29I). A valve operating system in an internal combustion engine according to claim 8, wherein said carrier (39) comprises a pair of support plates (39a,39a) disposed on opposite sides of said planetary rotors (40), and shafts (39b,39b) which are provided to extend between said support plates and on which said planetary rotors are rotatably carried, and said roller (44) is formed longer than an entire axial length of the planetary rotor (40) and is supported rotatably by a roller shaft (47), said roller shaft being fixed at opposite ends thereof to a pair of said roller retaining arms (45,45) integrally provided on said support plates (39a,39a), with steps (46) for supporting said outer ring (38) being formed between inner surfaces of said roller retaining arms and inner surfaces of said support plates. A valve operating system in an internal combustion engine according to claim 2, wherein said second one (39) of the components of said power transmitting means is operatively connected to a first valve operating cam (29I 1 ) provided on said cam shaft, and said valve operating system further includes a connection switch-over means (76) which is provided between one of said first and second components (37) and a rocker arm (74) rotatable about the same axis as of said inner ring in a manner to follow a second valve operating cam (29I 2 ) provided on said cam shaft, said connection switch-over means being capable of being switched over between a connecting state in which said one of said first and second components (37) is connected to said rocker arm (74), and a disconnecting state in which the connection between said one of said first and second components and said rocker arm (74) is released, and a control means (60 2 ) for controlling the operations of said actuator (51 1 ) and said connection switch-over means (76), said control means (60 2 ) being arranged to change over a control mode thereof, depending on the operational state of the engine, between a first control mode in which said actuator (51 1 ) is in an operative state and said connection switch-over means (76) is brought into said disconnecting state, and a second control mode in which said actuator (51 1 ) is brought into an inoperative state and said connection switch-over means (76) is brought into said connecting state. A valve operating system in an internal combustion engine according to claim 10, wherein said connection switch-over means (76) is arranged so that the connecting state and the disconnecting state are switched over from one to the other in accordance with a hydraulic pressure, and said control means (60 2 ) is formed to output a signal indicative of a command to bring said electric actuator (51 1 ) into said inoperative state after completion of the connecting operation of said connection switch-over means (76), when the control mode is switched over from the first control mode to the second control mode, and to output a signal indicative of a command to bring said connection switch-over means (76) into said disconnecting state after outputting of a signal indicative of a command to bring said actuator (51 1 ) into said operative state, when the control mode is switched over from the second control mode to the first control mode. A valve operating system in an internal combustion engine according to claim 11, wherein said control means (60 2 ) is arranged to select the second control mode in a low-speed operational range of the engine and to select the first control mode in a high-speed operational range of the engine. A valve operating system in an internal combustion engine according to claim 10, wherein said control means (60 2 ) is arranged to select the first control mode in a low-speed operational range of the engine and to select the second control mode in a high-speed operational range of the engine.

Inventors: GOMI TAKESHI, ISHIGURO TETSUYA, NEMOTO HIROTOMI, OHISHI HIDETOSHI, SHIMASAKI YUICHI, TANAKA SHIGEKAZU, GOMI, TAKESHI, ISHIGURO, TETSUYA, NEMOTO, HIROTOMI, OHISHI, HIDETOSHI, SHIMASAKI, YUICHI, TANAKA, SHIGEKAZU
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1998
Main classification: F01L13
IPC codes: F01L13, F01L1, F01L9