VALVE DRIVING SYSTEM FOR INTERNAL COMBUSTION ENGINE

Abstract: A valve driving system for an internal combustion engine having two intake valves 2a,2b and/or two exhaust valves 3 for each cylinder, includes a cam shaft 4 formed with a pair of low speed cams 5a,5b and a high speed cam 6 located between the low speed cams. A pair of first rocker arms 10a,10b are driven by the low speed cams, and each has a portion engaged with one of the valves. A second rocker arm 13 is driven by the high speed cam and is located between the first rocker arms. Two oil pressure chambers 17c are formed in the second rocker arm facing respective first rocker arms, and each contains a plunger 17b. Bores 21 are formed for engagement by the plungers in the first rocker arms, and oil passage 17c is formed in the second rocker arm to communicate with the oil pressure chambers and a control valve 20 for controlling the oil pressure fed to the oil passage in accordance with the engine operating condition.

Description: The present invention relates to a valve driving system for an internal combustion engine, and more particularly to such a valve driving system capable of selecting one of a plurality of cams for driving intake valves and/or exhaust valves in accordance with engine rpm. There is known an internal combustion engine which has two intake valves and/or two exhaust valves to take in greater amount of intake air and/or discharge greater amount of exhaust gas and which is suitable for operation at high engine rpm or high engine output. However, since the cross-sectional area of the intake passage and/or the exhaust passage is large in this engine, intake air often passes through directly from the intake passage to the exhaust passage and the charging efficiency is inevitably decreased at low engine rpm, whereby the engine output is degraded. In order to solve this problem, Unexamined Japanese Utility Model Publication No. 58605/1986 discloses a valve driving system for an internal combustion engine having two intake valves and two exhaust valves for each cylinder thereof. In this prior art system, there are provided a first rocker arm pivotally mounted on a rocker shaft and engaged with the respective intake valves for driving them under low speed engine operating condition in accordance with the movement of a low speed cam having a cam lobe suitable for low speed engine operation and, on the side of the first rocker arm, a second rocker arm pivotally mounted on the rocker shaft for driving the respective intake valves by engagement with the first rocker arm under high speed engine operating condition in accordance with the movement of a high speed cam having a cam lobe suitable for high speed engine operation and an engaging means for engaging the second rocker arm with the first rocker arm under high engine rpm and releasing the engagement between the second rocker arm and the first rocker arm under low engine rpm. For the respective exhaust valves, an identical valve driving mechanism is employed. According to this prior art system, since the second rocker arm is not engaged with the first rocker arm at low engine rpm and it is engaged with the first rocker arm at high engine rpm, it is possible to drive the intake valves and exhaust valves in accordance with movement of the low speed cam under low engine rpm operating condition and drive the intake valves and exhaust valves in accordance with the high speed cam under high engine rpm operating condition, whereby the intake valves and exhaust valves can be opened and closed at timings determined in accordance with engine rpm. However, in this prior art system, since the second rocker arm is arranged on the side of the first rocker arm and the high speed cam is not positioned at a center portion of both intake valves, an undesired force which produces a moment of force in a plane other than the plane perpendicular to the axis of the rocker shaft acting on the rocker shaft, whereby the frictional resistance between the rocker shaft and the second rocker arm is increased and the durability of the valve driving system is lowered since the second rocker arm and the rocker shaft are often worn non-uniformly. From EP-A-0213758 and EP-A-0259106, both of which are intermediate documents, it is known to provide a valve driving system for an internal combustion engine in which two intake valves are provided in each cylinder, said valve driving system comprising cam shaft formed with cams or different shapes, including a pair of low speed cams located at the end portion of the cam shaft and a high speed cam located substantially centrally of the cam shaft, a pair of first rocker arm means driven by the low speed cams, each having a portion engaged with one of the valves, second rocker arm means driven by the high speed cam and located between the first rocker arm means, a pair of oil pressure chambers formed in the second rocker arm means, a pair of plungers each being provided in one of the oil pressure chambers, a pair of bores each being formed engageably with one of the plungers in one of the first rocker arm means, oil passage means formed in the second rocker arm means and communicated with the oil pressure chambers, and control means for controlling oil pressure fed to the oil passage means in accordance with engine operating conditions. An object of the invention is to provide a valve driving system for an internal combustion engine having two intake valves and a single exhaust valve for each cylinder thereof which has high durability and simple structure. According to the invention there is provided a valve driving system for an internal combustion engine having a pair of intake valves and an exhaust valve for each cylinder, the valve driving system comprising a pair of low speed cams; a pair of first rocker arm means driven by the respective low speed cams and each having a portion engageable with a respective intake valve; a high speed cam located between the low speed cams; second rocker arm means located between the two first rocker arm means and driven by the high speed cam; an exhaust valve cam; the low speed cams, the high speed cam and the exhaust valve cam being located on a common camshaft disposed over the cylinder head; third rocker arm means driven by the exhaust valve cam; a pair of oil pressure chamber means formed in the second rocker arm means; plunger means provided in each oil pressure chamber means and movable toward the first rocker arm means; bore means formed in the first rocker arm means and arranged to receive the plunger means, whereby the intake valves can be driven by either the low speed cam or the high speed cam by selectively connecting the second rocker arm means to the first rocker arm means by means of the plunger means, by controlling the oil pressure in the pair of oil pressure chamber means; and, oil passage means in the second rocker arm means, for feeding oil to the oil pressure chamber means, the oil passage means being arranged to feed the same oil pressure to each of the oil pressure chamber means, so that the plunger means are moved simultaneously in opposite directions. In the drawings:- Figure 1 shows a plan view of a valve driving system for an engine according to the invention. Figure 2 is a schematic drawing showing a side view of the valve driving system of figure 1; Figure 3A is a schematic drawing showing a plan view of a rocker arm engaged with an intake valve, and which is used in the valve driving system; Figure 3B is a schematic drawing showing a side view of the rocker arm; Figure 4A is a schematic drawing showing a plan view of a rocker arm driven by a high speed cam, and which can be used for the present invention; Figure 4B is a schematic drawing showing a side view of a rocker arm driven by a high speed cam, which can be used for the present invention. Figure 4C is a schematic drawing showing a partial cross sectional view of a rocker arm driven by a high speed cam, which can be used for the present invention. Referring to Figures 1 and 2, there is shown one cylinder of an internal combustion engine having a plurality of cylinders formed below a cylinder head 1 and each cylinder has two intake valves 2a and 2b for opening and shutting respective intake ports and one exhaust valve 3 for discharging exhaust gas from the cylinder. Over the cylinder head 1, a camshaft 4 is provided between the intake valves 2a and 2b and the exhaust valve 3, and is formed with a pair of low speed cams 5a and 5b and a high speed cam 6. The high speed cam 6 is located at substantially the center portion between the low speed cams 5a and 5b. The high speed cam 6 has a cam lobe which is larger than the cam lobes in the low speed cams 5a and 5b so that the high speed cam 6 can provide greater cam lift and cam open period than the low speed cams 5a and 5b. A cam 7 for driving the exhaust valve 3 is provided between one of the low speed cams 5b and the high speed cam 6. Further, there are arranged a first rocker shaft 8 on the side of the intake valves 2a and 2b with respect to the camshaft 4 and a second rocker shaft 9 on the side of the exhaust valve 3b with respect to the camshaft 4. There are pivotally mounted on the first rocker shaft 8 first rocker arms 10a and 10b for driving the intake valves 2a and 2b respectively. The respective first rocker arms 10a and 10b are arranged so that they are engaged with the stem of the intake valves 2a, 2b at one end thereof and that they are engaged with the low speed cams 5a and 5b at the other end. At one end of each of the first rocker arms 10a and 10b, a hydraulic lash adjustor 11 is provided so that the end of each of the first rocker arms 10a and 10b is engaged with the stem of one of the intake valves 2a and 2b without any lash between them and at the other end of each of the first rocker arms 10a and 10b, there is provided roller cam followers 12 for reducing sliding friction between the end of each of the first rocker arms 10a, 10b and one of the low speed cams 5a, 5b. An oil passage 18 is formed in the first rocker shaft 8 for feeding oil to the hydraulic lash adjustor 11 and an engaging device (explained later). The reference numeral 25 designates an oil passage communicated with the oil passage 18 for feeding oil to the hydraulic lash adjustors 11. A second rocker arm 13 for transmitting the movement of the high speed cam 6 to the respective first rocker arms 10a and 10b is pivotally mounted on the first rocker shaft 8 at substantially the center portion between the first rocker arms 10a and 10b and it is engaged with the high speed cam 6 at one end thereof. There is provided a spring 26 for pressing the end of the second rocker arm 13 against the high speed cam 6 and preventing the second rocker arm 13 from rattling against the high speed of cam 6 at low engine rpm. At the end of the second rocker arm 13, there is provided a roller cam follower 14 for reducing sliding friction between the end of the second rocker arm 13 and the high speed cam 6. The axial length of the roller cam follower 14 is determined larger than that of the roller cam follower 12. Moreover, a third rocker arm 15 for transmitting the movement of the cam 7 for driving the exhaust valve 3 to the exhaust valve 3 is pivotally mounted on the second rocker shaft 9 and at one end thereof, a roller cam follower 16 is provided for reducing sliding friction between the the end of the third rocker arm 15 and the cam 7. In order to releasably connect the first rocker arms 10a and 10b and the second rocker arm 13, there are provided a pair of engaging devices 17. Each of the engaging devices 17 comprises a cylinder bore 17a formed in the second rocker arm 13, a plunger 17b slidably received in the cylinder bore 17a and a oil pressure chamber 17c formed by the cylinder bore 17a and the plunger 17b. There is provided a wall 17d for separating the oil pressure chamber of one engaging device 17 from that of the other between the oil pressure chambers 17c of the respective engaging devices 17. An oil passage 17e for feeding oil to the respective oil pressure chambers 17c opens to the respective oil pressure chambers 17c at the wall 17d. The oil passage 17e is communicated with the oil passage 18 formed in the first rocker shaft 8. It is preferable that the oil passage 17e be formed by a drill so as to be oblique toward the upstream direction of the oil passage 18 , so that oil can be easily introduced into the oil pressure chamber 17c. Each of the oil pressure chamber 17c is communicated with an oil pump 19 through an oil passage 17e formed in the second rocker arm 13, an oil passage formed in the rocker shaft 8 and an oil passage 18. There is provided within the oil passage 18 a valve 20 for opening and closing the oil passage 18 in accordance with engine rpm. Bores 21 for receiving the plunger 17b are formed in the respective first rocker arm 10a and 10b and plunger receivers 22 are provided in the respective bores 21 so that the respective plungers are maintained in abutting engagement with it. In each of the bores 21, there is a spring 23 which biases the plunger 17b outwards through the plunger receiver 22. At low engine rpm, the opening of the valve 20 is reduced to reduce the amount of oil fed to the oil pressure chamber 17c and the oil pressure in the oil pressure chamber 17c becomes low, whereby the plunger 17b is forced to be moved outside of the bore 21 by the spring 23 and to be received by the wall 17d in the cylinder bore 17a and the second rocker arm 13 gets unengaged with the first rocker arms 10a and 10b. On the other hand, at high engine rpm, the valve opens the oil passage 18 and the oil pressure in the respective oil pressure chambers 17c is increased to become larger than pressure by the spring 23, whereby the respective plungers 17b get received in the bores 21 of the first rocker arms 10a and 10b and the second rocker arm 13 get engaged with the respective first rocker arms 10a and 10b. According to the above described embodiment, since the second rocker arm 13 is not engaged with the first rocker arms 10a and 10b at low engine rpm, the movement of the low speed cams 5a and 5b is transmitted to the intake valves 2a and 2b by the first rocker arms 10a and 10b and the intake valves 2a and 2b are driven by the low speed cams 5a and 5b, and, on the other hand, at high engine rpm, since the second rocker arm 13 is engaged with the first rocker arms 10a and 10b the movement of the high speed cam 6 is transmitted to the intake valves 2a and 2b through the second rocker arm 13 and the first rocker arms 10a and 10b and the intake valves 2a and 2b are driven by the high speed cam 6. Referring to Figures 3A and 3B, there are shown details of the first rocker arms 10a, 10b used in this embodiment. In Figures 3A and 3B, the reference numeral 30 designates a fork portion for supporting the roller cam follower 12 and there is provided at the fork portion a bore 30a for engaging a shaft for supporting the roller cam follower 12. Further, there are provided a bore 31 in which the first rocker shaft 8 extends and a housing 32 for the hydraulic lash adjustor 11. A portion in the vicinity of the bore 31 and the housing 32 are connected by a reinforcing rib 33, extending substantially straight, in which the oil passage 25 for feeding oil to the hydraulic lash adjustor 11 is formed. The oil passage 25 consist of a bore 25a having large diameter and a bore 25b having small diameter and is formed by a drill so that the bore 25a is drilled from the side of the rocker shaft bore 31 and that the bore 25b is drilled from the side of the housing 32 through a reservoir chamber 32a, since it is difficult to form the oil passage 25 over the whole length by a drill having small diameter although it is preferable for effectively removing air from the reservoir chamber 32a that the diameter of the bore be small. Figures 4A to 4C show details of a second rocker arm 13 which is somewhat different from that used in the above described embodiment in the structure of the engaged portion with the high speed cam 6, although the basic structure is the same as that in the above described embodiment so that corresponding parts are designated by the same numerals as in the previous embodiment. In Figures 4A to 4C, the end of the second rocker arm is formed with a slipper 33 and is directly and slidably engaged with the high speed cam 6 in place of interposing the roller cam follower 14 between them in order to prevent the weight of the system from increasing, since the end portion of the second rocker arm 13 is engaged with the high speed cam 6 only at high rpm, while the end of each of the first rocker arms 10a and 10b is engaged under normal engine operating condition. The main body of the second rocker arm 13 is usually made of aluminum alloy but it is preferable to make the slipper 33 of special cast iron or ceramic for improving wear resistance. As shown in Figure 4C, the oil passage 17e communicates with a bore 13a formed in the second rocker arm 13 for extending the passage 18 in the rocker shaft 8 therein to the wall 17d for separating the respective oil pressure chambers 17c, and is formed by a drill so as to extend obliquely and upwardly toward the downstream direction of oil in order to make it easier to feed oil to the respective oil pressure chambers 17c and increase the oil pressure in the oil pressure chambers 17c to a predetermined pressure as soon as the valve 20 is opened. Further, there is provided a hole 34 for removing air from the respective oil pressure chambers 17c. The reference numeral 35 designates a supporting portion for securing the spring 26 for pressing the second rocker arm 13 against the high speed cam 6. According to the present invention, since forces produced by the high speed cam are transmitted from the high speed cam to the respective intake valves through substantially symmetrical paths with respect to the high speed cam, no moment of a force acts on the rocker shaft in a plane other than the plane perpendicular to the axis of the rocker shaft and the second rocker arm and the rocker shaft can be prevented from being non-uniformly worn, whereby the durability of the valve driving system can be remarkably improved. Further, since the engaging devices for engaging the second rocker arm with the respective first rocker arms are located within the second rocker arm, oil can be fed to the respective engaging devices by a single oil passage, whereby the structure of the valve driving system can be made simple. The present invention has thus been shown and described with the reference to the specific embodiments. However, it should be noted that the present invention is in no way limited to the details of the described arrangements but changes and modifications may be made without departing from the scope of the appended claims. For example, although the internal combustion engine is provided with two intake valves and one exhaust valve in the above described embodiments, the present invention can be applied to an engine having two intake valves and two exhaust valves. Further, although the intake valves are driven by the low speed cams or the high speed cam selectively in accordance with engine rpm in the above described embodiments, two exhaust valves can be driven in accordance with the present invention. Furthermore, although the oil passages 17e and 25 are communicated with the oil passage 8a in the above described embodiment, they can be independent passages for controlling the oil pressure in them independently. In such case, it is very advantageous to provide the oil passage 25 for feeding oil to the lash adjustor 11 in each of the first rocker arms 10a and 10b as shown in the above described embodiment.

Claims: A valve driving system for an internal combustion engine having a pair of intake valves (2a,2b) and an exhaust valve (3) for each cylinder, the valve driving system comprising a pair of low speed cams (5a,5b); a pair of first rocker arm means (10a, 10b) driven by the respective low speed cams and each having a portion engageable with a respective intake valve (2a,2b); a high speed cam (6) located between the low speed cams (5a,5b); second rocker arm means (13) located between the two first rocker arm means (10a,10b) and driven by the high speed cam (6); an exhaust valve cam (7); the low speed cams, the high speed cam and the exhaust valve cam being located on a common camshaft disposed over the cylinder head (1); third rocker arm means (15) driven by the exhaust valve cam (7); a pair of oil pressure chamber means (17c) formed in the second rocker arm means (13); plunger means (17b) provided in each oil pressure chamber means and movable toward the first rocker arm means (10a, 10b); bore means (21) formed in the first rocker arm means and arranged to receive the plunger means (17b), whereby the intake valves (2a, 2b) can be driven by either the low speed cam or the high speed cam by selectively connecting the second rocker arm means (13) to the first rocker arm means (10a,10b) by means of the plunger means (17b), by controlling the oil pressure in the pair of oil pressure chamber means (17c); and oil passage means (17e) in the second rocker arm means (13), for feeding oil to the oil pressure chamber means (17c), the oil passage means (17e) being arranged to feed the same oil pressure to each of the oil pressure chamber means (17c), so that the plunger means (17b) are moved simultaneously in opposite directions. A system in accordance with claim 1, which further includes rocker shaft means (8) for pivotally mounting the first (10a,10b) and second (13) rocker arm means; each of the oil pressure chamber means (17c) having a cylindrical bore (17a) in which the plunger means (17b) can be moved Slidably and in which a bore (21) is formed in the second rocker arm means (13), through which the rocker shaft means (8) extends, which further includes wall means (17d), for separating the oil pressure chamber means and receiving the plunger means (17c), and in which said oil passage means (17e) formed in the second rocker arm means communicates with the respective cylindrical bores (17a) and the bore (13a) formed in the second rocker arm means and opening at the wall means. A system in accordance with claim 1 or claim 2, which further includes lash adjusting means (11) for adjusting lash between the end of the first rocker arm means (10,10b) and the intake valve means (2a,2b) for the end portion of each of the first rocker arm means and oil passage means (25) formed in the first rocker arm means for feeding oil to the lash adjusting means. A system in accordance with claim 3, which further includes a bore (31) formed in the first rocker arm means mounting on the rocker shaft means (8), a housing (32) for the lash adjusting means (11) and a substantially straight rib means (33) for connecting the housing and a portion in the vicinity of the bore and in which the oil passage means (25) is formed. A system in accordance with any of claims 1 to 4, which further includes roller cam follower means (12) located between the first rocker arm means (10a,10b) and the low speed cam (5a,5b). A system in accordance with claim 1, in which wall means (17d) is provided for separating the respective oil pressure chamber means (17c) and receiving the plunger means (17b), the oil passage means (17e) communicating with the oil pressure chamber means via the wall means.

Inventors: MASUDA, SHUNJI, NAKAI, EIJI
Applicants: MAZDA MOTOR CORPORATION
Application year: 1987
Main classification: F01L31
IPC codes: F02F1, F01L1, F01L13