Camshaft drive assembly

Abstract: A camshaft drive assembly comprises a crankshaft 14 mounted on a cylinder block 2, a camshaft 5 mounted on a cylinder head 3, and a first and second intermediate shaft 8,11 for transmitting rotation of said crankshaft to the camshaft 5. Both, the first intermediate shaft 8 and the second intermediate shaft 11 are mounted on the cylinder block. Accordingly, the camshaft assembly will not restrict the placement of the air intake ports, etc., in the cylinder head, thereby improving engine performance. Further assembly operations can be facilitated and a highly reliable structure can be provided.

Description: The present invention relates to a camshaft drive assembly for an internal combustion engine. More specifically, the invention relates to a camshaft drive assembly comprising the features of the preamble portion of claim 1. Such a camshaft drive assembly is known from EP-A-335246. In order to open and close the air intake valves and the exhaust valves of four-cycle engines at the required timing, cams located on a camshaft rotated synchronously with the crankshaft by means of a dynamic valve cam mechanism push upon the air intake valves and exhaust valves to cause them to open and close. This type of cam mechanism transmits the rotation of the crankshaft mounted on the cylinder block of the engine by drive transmission means comprising belts or chains to the overhead camshaft for the cylinder head air intake valves and exhaust valves. For reasons involving engine layout, an intermediate shaft located between the crankshaft and camshaft is used as a means to transmit rotational motion to the camshaft. Figure 4 shows a conventional cam drive mechanism using this type of intermediate shaft. Figure 4 shows the structure of the engine in a side view. The engine 1 is a four-cycle, five-cylinder engine which has a cylinder head 3 is affixed to its cylinder block 2. There are five air intake ports 4 arrayed in a line in the cylinder head that connect with each cylinder (the exhaust ports are not shown). Mounted atop the cylinder head 3 is an SOHC type of cam mechanism that includes camshaft 5. A crankshaft (not shown) is mounted inside the cylinder block 2 and a first intermediate drive shaft 3 mounted at inside the flange mating surface 6 is connected by gear 7 to the crankshaft, which is covered by a cover (not shown). This first intermediate shaft is rotatably supported to the cylinder block by a plurality of journals (bearings). The first intermediate shaft 8 is connected by a first chain 10 to the second intermediate shaft that is mounted inside the cylinder head 3. In this case, the sprocket 13 which engages the first chain 10 is affixed to the end of the second intermediate shaft and is located below and between two of the air intake ports so as not to interfere with the air intake ports. The second intermediate shaft 11 is connected to the camshaft 5 by means of a second chain 12. With this type of mechanism, the rotation of the crankshaft is transmitted by gears 7 to the first intermediate shaft 10, and from there to the second intermediate shaft 11 by means of the first chain 12, and then by the second chain 12 to the camshaft 5. This configuration causes the shaped cams 5a attached to the camshaft 5 to open and close the air intake valves and exhaust valves (not shown) synchronously with the rotation of the camshaft at the required timing. Here, since the rotational drive is transmitted from the crankshaft by the second intermediate shaft 11 mounted on the cylinder head to the camshaft which is mounted on the cylinder head, it is necessary to mount the cam drive transmission system so that it protrudes from the cylinder block. However, with regard to the above described conventional camshaft drive structure, the second intermediate shaft 11, being located beneath the air intake ports in the cylinder head as a means to avoid interference between the chain and sprocket with the air intake ports, the layout of the ports, chain and the first intermediate shaft is a restrictive one that does not allow much freedom of design. Further, since the chain is engaged in the area between two air intake ports, said intake ports pose obstacles to the installation or removal of the chain. Further, because this chain is engaged in the area between two air intake ports, it is inside the journal supporting the first intermediate shaft's end. Accordingly, during assembly, the chain must be first installed prior to attaching the journal and mounting the first intermediate shaft therein. This makes the assembly process cumbersome. In addition, because the first chain spans the first intermediate shaft on the cylinder block and the second intermediate shaft on the cylinder head, the chain cover for this first chain must span the cylinder block and the cylinder head. This design diminishes the reliability of the cover seal. The objective of the present invention is to resolve the foregoing problems by providing a compact camshaft drive assembly which offers large freedom of design regarding the intake and exhaust ports of an internal combustion engine wherein the assembly/disassembly and serviceability of the second rotational drive transmission means as well as the reliability of a cover seal should be improved. Said objective is achieved according to the invention by a camshaft drive assembly according to claim 1. Since the first and second intermediate shafts between the crankshaft and the camshaft are mounted on the cylinder block side, no restrictions are imposed upon the air intake ports in the cylinder head. Accordingly, this configuration makes it possible to use an optimal air intake port layout in terms of engine performance, exhaust emissions, etc. In addition, since the position of the first and second intermediate shafts that comprise rotational drive transmission means is unrestricted by the air intake ports, these rotational drive transmission means can be positioned in the optimal position on the cylinder block for ease of assembly and reliability, thereby improving assembly and maintenance operations. Further, since the first and second intermediate shaft rotational drive transmission means do not span both the cylinder head and the cylinder block, a more reliable seal can be obtained when these rotational drive transmission means are covered. According to the invention, a cover is mounted only on the cylinder block, said cover covering said second rotational drive transmission means. Preferably, the first intermediate shaft comprising an end portion extending beyond an end journal of said journals, said end portion of said first intermediate shaft being coupled with said second rotational drive transmission means. Accordingly, assembly and disassembly of the second rotational drive transmission means can be facilitated. Moreover, serviceability of the camshaft drive assembly will be improved. In a preferable embodiment, a balancer and auxiliary equipment drive pulley are attached to the foregoing first intermediate shaft. Further,the first intermediate shaft is rotatably supported at the center of the block and on the end by journals. Thus, with this structure, the first intermediate shaft serves double duty as a balancer and as an auxiliary engine equipment drive, with only a very compact structure. Since the chain is attached in an area toward the outside from the journal supporting the first intermediate shaft, the chain can be attached after supporting the intermediate shaft in the journal during assembly, and be easily removed/attached for maintenance, thereby improving the reliability and ease of assembly. In a further preferred embodiment, the foregoing first drive transmission means is composed of a pair of engaging gears attached to the ends of the foregoing crankshaft, and the first intermediate shaft. Preferably, the second drive transmission means and also the third drive transmission means is composed of a chain. With such a structure, the rotation of the crankshaft is transmitted by gears to the first intermediate shaft, from there by means of a first chain to the second intermediate shaft, and further and from there by means of second chain to rotate the camshaft. In addition to this configuration being a highly reliable drive transmission structure, the drive transmission structure allows more design latitude and improved ease of assembly. Further embodiments are laid down in the subclaims. An example of the invention will be described hereinafter with reference to the appended drawings, wherein: Figure 1 is a front view of the principal components of an engine embodiment of this invention. Figure 2 is a side view of the principal components of the engine of Figure 1. Figure 3 is a top view of the principal components of the engine of Figure 1. Figure 4 is a front view of the principal components of a conventional engine. Figures 1, 2 and 3 show respective front, side and top views of an engine embodiment equipped with the cam drive mechanism of this invention. This engine, as was previously explained for the example shown in Figure 4, is a four-cycle, five-cylinder engine composed of a cylinder head 3 attached to the top of a cylinder block 2. There are five air intake ports 4 arrayed linearly in the cylinder head 3 that are connected to respective cylinders (the exhaust ports are not shown). A SOHC type of cam mechanism composed of camshaft 5 is mounted atop the cylinder head 3, and one set of cams are formed upon it for each cylinder. The crankshaft 14 (Figs. 2 & 3) is mounted in the cylinder block, and crank pins 15a (Fig. 3, dotted lines) and crank webs connect the crankshaft 14 by connecting rods (not shown) to the pistons (not shown). A gear 7a is mounted on the crankshaft in a position corresponding to the crank web, and this gear 7a engages a gear 7b that is attached to the first intermediate shaft 8. This pair of gears, 7a, 7b transmit the rotation of the crankshaft 14 to the first intermediate shaft 8. A plurality of balancers 19 are attached to the first intermediate shaft 8, and a pulley 20 is mounted on the end used to drive the oil pump, alternator and other auxiliary engine equipment. There are a plurality of journals (bearings) 9 which support the first intermediate shaft rotatably in the cylinder block 2. The foregoing journals are mounted inside the end journal 9 for the first intermediate shaft 8, and a sprocket 15 is attached to that shaft outside the end journal 9. A first chain 10 is wound around this sprocket 15 and the sprocket 13a mounted on the second intermediate shaft 11. The second intermediate shaft 11 is mounted inside the cylinder block. Accordingly, there is no restriction upon the position of the air intake ports as there was in the prior art example (Fig. 4), thereby making it possible to place the chain 10 outside the journal 9 at the end of the first intermediate shaft 8. Thus, by placing the chain 10 outside the journal 9, the chain 10 can be installed after affixing the journals 9 for the first intermediate shaft to the cylinder block. Not only does this feature ease the attachment operation for the first intermediate shaft 8, but it also facilitates the installation of the chain. A cover 17 having a gear cover area 17a is attached (Fig. 2) at the cylinder block mating surface 6 to cover the exposed gear 7b on the first intermediate shaft 8. Further, the chain 10 that spans the first and second intermediate shafts 8, 11 is also covered by the chain cover area 17b of the cover 17. This cover 17 is mounted only upon the cylinder block and does not reach the cylinder head. This design improves the reliability of the seal at the mating surface 5. A sprocket 13b is attached to the end of the second intermediate shaft 11 that potrudes from the cylinder block 3. A second chain 12 is wound around this sprocket 13b. This second chain 12 also engages the sprocket 16 which is mounted on the end of the camshaft 5 that protrudes from the cylinder head 3. Thus, the second chain 12 is covered by a common cover 22 mounted on the side of the engine 1. With this structure, the rotation of the crankshaft 14 is transmitted by gears 7a, 7b to the first intermediate shaft 8, and from there by the first chain 10 to the second intermediate shaft 11, and then further by the second chain 12 to the camshaft 5. This configuration makes it possible for the cams 5a on the camshaft 5 to open and close the various air intake valves and exhaust valves (not shown) in synch with the rotation of the crankshaft at the required timing. As has been described above, because the first and second intermediate drive-transmitting shafts between the crankshaft and the camshaft are both installed on the cylinder block, they pose no restriction upon the placement of the air intake ports in the cylinder head. This design makes possible a port layout that is optimized for engine performance, exhaust emissions, etc., to thereby improve engine performance and exhaust emissions. Further, because the chain, for example, between the first and second intermediate shafts does not interfere with the position of the air intake ports, it is possible locate the rotational drive transmission means (chain) at the side of the cylinder block in a position optimal for reliability and easy installation of the chain, thereby easing assembly and installation/removal maintenance operations. Further, since the rotational drive transmission means (eg. chain) that spans the first and second intermediate shafts is mounted entirely on the cylinder block side without involving the cylinder head, it is possible to improve the reliability of the seal of the cover that covers this rotational drive transmission means (chain).

Claims: Camshaft drive assembly for an internal combustion engine (1) comprising: a crankshaft (14) mounted on a cylinder block (2), a camshaft (5) mounted on a cylinder head (3), a first intermediate shaft (8) linked by a first rotational drive transmission means (7a,7b) to the crankshaft (14), a second intermediate shaft (11) linked by a second rotational drive transmission means (10) to said first intermediate shaft (8), and a third rotational drive transmission means (12) linked to the second intermediate shaft (11) and the camshaft (5), wherein both the first intermediate shaft (8) and the second intermediate shaft (11) are mounted on the cylinder block (2), characterized in that the first intermediate shaft (8) is rotatably supported on the cylinder block by journals (9), said first intermediate shaft (8) comprising an end portion extending beyond an end journal (9') of said journals (9) and said end portion of said first intermediate shaft (8) being coupled with said second rotational drive transmission means (10). Camshaft drive assembly according to claim 1, characterized in that the second rotational drive transmission means (10) is arranged on the outside of the said end journal (9') with respect to a main portion of said first intermediate shaft (8) which is arranged inside said end journal (9'). Camshaft drive assembly according to one of claim 1 or 2, characterized in that a cover (17) is mounted only on the cylinder block (2), said cover (17) covering said second rotational drive transmission means (10). Camshaft drive assembly according to claim 3, characterized in that said cover (17) also covers said first rotational drive transmission means (7a,7b). Camshaft drive assembly according to one of claims 1 to 4, characterized in that a balancer (19) and auxiliary equipment drive pulley (20) are attached to the first intermediate shaft (8). Camshaft drive assembly according to one of claims 1 to 5, characterized in that the first rotational drive transmission means (7a,7b) is composed of a pair of intermeshed gears attached to the crankshaft (14) and the first intermediate shaft (8). Camshaft drive assembly according to one of claims 1 to 6, characterized in that the second rotational drive transmission means (10) is a chain. Camshaft drive assembly according to one of claims 1 to 7, characterized in that the third rotational drive transmission means (12) is another chain.

Inventors: ASANO YUICHI, UEMA HITOSHI, ASANO, YUICHI, UEMA, HITOSHI
Applicants: YAMAHA MOTOR CO LTD, YAMAHA HATSUDOKI KABUSHIKI KAISHA
Application year: 1998
Main classification: F01L1
IPC codes: F02B75, F01L1