Title:
Flexible transmitter tensioner for outboard motor
Kind Code:
A1


Abstract:
An engine for an outboard motor includes an engine body, a crankshaft and one or more camshafts. A camshaft drive mechanism is arranged on a top surface of the engine body. The camshaft drive mechanism includes a timing belt to rotate the camshafts with the rotation of the crankshaft. A belt tensioner is arranged to adjust tension of the timing belt. The tensioner includes a shaft unit mounted on the engine body. A peripheral unit is swingably carried by the shaft unit and abutting on a portion of the timing belt. A swing axis of the shaft unit is offset from a center axis of the peripheral unit. The tensioner further includes a hydraulic damping mechanism to damp a vibration of the timing belt. The damping mechanism has a piston rod that urges the peripheral unit toward the timing belt. The piston rod is positioned at a location which can be generally the highest of the damping mechanism when a drive unit of the outboard motor is tilted up about a tilt axis. The shaft unit also is positioned at another location which can be higher than the center axis of the peripheral unit when the drive unit of the outboard motor is tilted up about the tilt axis.



Inventors:
Nozue, Toshihiro (Hamamatsu, JP)
Application Number:
10/072680
Publication Date:
08/29/2002
Filing Date:
02/07/2002
Assignee:
NOZUE TOSHIHIRO
Primary Class:
International Classes:
F01L1/02; F02B61/04; (IPC1-7): F01L1/02
View Patent Images:



Primary Examiner:
JOHNSON, VICKY A
Attorney, Agent or Firm:
KNOBBE MARTENS OLSON & BEAR LLP (IRVINE, CA, US)
Claims:

What is claimed is:



1. An outboard motor comprising a drive unit, a bracket assembly adapted to be mounted on an associated watercraft to support the drive unit for tilt movement about a horizontally extending tilt axis, the drive unit comprising an internal combustion engine comprising an engine body, a moveable member moveable relative to the engine body, a first rotatable member rotatable with the movement of the moveable member, an engine component comprising a second rotatable member, and a drive mechanism arranged on a top surface of the engine body, the drive mechanism comprising a flexible transmitter to rotate the second rotatable member with the rotation of the first rotatable member, a tensioner comprising a shaft unit mounted on the engine body, a peripheral unit pivotally supported by the shaft unit, the peripheral unit abutting on a portion of the flexible transmitter, said shaft unit defining a mount axis and said peripheral unit defining a center axis, said mount axis and said center axis being offset, a damping mechanism connected to the peripheral unit and comprising a damping member, the damping member being positioned at a location which is generally vertically higher than a balance of the damping mechanism when the drive unit is tilted up about the tilt axis.

2. The outboard motor as set forth in claim 1, wherein the damping mechanism additionally comprises a hydraulic cylinder, the cylinder defining an internal cavity, a piston slideably disposed within the internal cavity, the piston substantially separating a first chamber and a second chamber that are defined within the internal cavity, the first and second chambers being filled with working fluid, the piston comprising an orifice through which the first and second chambers communicate with each other, and a bias member being disposed in the second chamber to bias the piston such that the damping mechanism is extended.

3. The outboard motor as set forth in claim 2, wherein at least a portion of the cylinder is mounted on the engine body.

4. The outboard motor as set forth in claim 2, wherein at least a portion of the cylinder is mounted on a portion of the shaft unit.

5. The outboard motor as set forth in claim 1, wherein the tensioner additionally comprises an offset member coupled with the shaft unit, the offset member comprising an engage portion and the damping mechanism engaging the engage portion.

6. The outboard motor as set forth in claim 5, wherein the engage portion is placed at a second location which is capable of being generally positioned vertically higher than a shaft that is connected to the piston of the damping mechanism when the drive unit is tilted up about the tilt axis.

7. The outboard motor as set forth in claim 5, wherein the engage portion includes a pin extending outward from a balance of the offset member.

8. The outboard motor as set forth in claim 1, wherein the tensioner additionally comprises an offset member coupled with the shaft unit and the offset member generally covers the damping mechanism.

9. The outboard motor as set forth in claim 8, wherein the offset member is made of a sintered material.

10. The outboard motor as set forth in claim 9, wherein a top surface of the offset member is treated with a Parkerizing process.

11. The outboard motor as set forth in claim 1, wherein the peripheral unit has an outer surface coated with a non-electrolytic metal plating.

12. The outboard motor as set forth in claim 11, wherein the non-electrolytic metal plate includes a non-electrolytic nickel plating.

13. The outboard motor as set forth in claim 1, wherein the tensioner additionally comprises an offset member coupled with the shaft unit to connect the peripheral unit with the shaft unit, the peripheral unit includes a tension pulley and a bearing assembly mounted on the offset member to journal the tension pulley.

14. The outboard motor as set forth in claim 13, wherein the tension pulley has a height taller than a height of the bearing assembly.

15. The outboard motor as set forth in claim 1, wherein the tensioner additionally comprising a tension adjuster to adjust a tensioning force of the tensioner.

16. The outboard motor as set forth in claim 15, wherein the tension adjuster includes a biasing member that biases the peripheral unit toward the flexible transmitter relative to the engine body.

17. The outboard motor as set forth in claim 1, wherein the damping mechanism has a damping axis along which a shaft that is connected to the piston moves, the flexible transmitter is moved in one direction by the first rotatable member, and the damping axis is generally oriented toward a separating portion of the flexible transmitter where the transmitter is separating from the peripheral unit with the movement of the flexible transmitter in the one direction.

18. The outboard motor as set forth in claim 1, wherein the shaft unit is positioned at a second location which is capable to be generally higher than the center axis of the peripheral unit when the drive unit is tilted up about the tilt axis.

19. The outboard motor as set forth in claim 1, wherein the flexible transmitter includes a belt or chain.

20. An outboard motor comprising a drive unit, and a bracket assembly adapted to be mounted on an associated watercraft to support the drive unit for tilt movement about a horizontally extending tilt axis, the drive unit comprising an internal combustion engine comprising an engine body, a moveable member moveable relative to the engine body, the engine body and the moveable member together defining at least one combustion chamber, a first rotatable member rotatable with the movement of the moveable member, an air intake system arranged to introduce air to the combustion chamber, the intake system comprising at least one intake valve, an exhaust system arranged to route exhaust gases from the combustion chamber, the exhaust system comprising at least one exhaust valve, a valve actuation mechanism arranged to actuate at least one of the intake and exhaust valves between an open position and a closed position, the valve actuation mechanism comprising a second rotatable member arranged to engage the at least one of the intake and exhaust valves, and a drive mechanism arranged on a top surface of the engine body to drive the valve actuation mechanism, the drive mechanism comprising a flexible transmitter to rotate the second rotatable member with the rotation of the first rotatable member, and a tensioner arranged to adjust tension of the flexible transmitter, the tensioner comprising a shaft unit mounted on the engine body, a peripheral unit swingably carried by the shaft unit and abutting on a portion of the flexible transmitter, a swing axis of the shaft unit being offset from a center axis of the peripheral unit, and a damping mechanism to damp a vibration of the flexible transmitter, the damping mechanism having a damping member that urges the peripheral unit toward the flexible transmitter, and the damping member being positioned at a location which is capable to be generally the highest of the damping mechanism when the drive unit is tilted up about the tilt axis.

21. The outboard motor as set forth in claim 20, wherein the damping mechanism additionally includes a hydraulic cylinder defining an internal cavity, a piston slideably disposed within the internal cavity and defining first and second chambers on opposite sides thereof, the first and second chambers are filled with working fluid, the piston forms an orifice through which the first and second chambers communicate with each other, the damping member coupled with the piston and extending through the first chamber and beyond an end of the cylinder, a bias member disposed in the second chamber to bias the piston such that the damping member extends outward from the end.

22. An outboard motor comprising a drive unit, and a bracket assembly adapted to be mounted on an associated watercraft to support the drive unit for tilt movement about a horizontally extending tilt axis, the drive unit comprising an internal combustion engine comprising an engine body, a moveable member moveable relative to the engine body, a first rotatable member rotatable with the movement of the moveable member, an engine component actuation mechanism arranged to actuate at least one of engine components, the actuation mechanism comprising a second rotatable member arranged to engage the engine component, and a drive mechanism arranged on a top surface of the engine body to drive the actuation mechanism, the drive mechanism comprising a flexible transmitter to rotate the second rotatable member with the rotation of the first rotatable member, and a tensioner arranged to adjust tension of the flexible transmitter, the tensioner comprising a shaft unit mounted on the engine body, and a peripheral unit swingably carried by the shaft unit and abutting on a portion of the flexible transmitter, a swing axis of the shaft unit being offset from a center axis of the peripheral unit, and the shaft unit being positioned at a location which is capable to be generally positioned higher than the center axis of the peripheral unit when the drive unit is tilted up about the tilt axis.

23. The outboard motor as set forth in claim 22, wherein the tensioner additionally comprises an offset member coupled with the shaft unit to connect the peripheral unit with the shaft unit.

Description:

PRIORITY INFORMATION

[0001] This application is based on and claims priority to Japanese Patent Application No. 2001-030696, filed Feb. 7, 2001, the entire contents of which is hereby expressly incorporated by reference. This application further claims the benefit of U.S. Provisional Application No. 60/322,482 filed Sep. 13, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to a flexible transmitter tensioner for an outboard motor, and more particularly to an improved flexible transmitter tensioner that has a swing axis disposed offset from a center axis of the tensioner.

[0004] 2. Description of Related Art

[0005] Internal combustion engines that are used in outboard motors typically comprise a crankshaft that drives a submerged marine propulsion device through suitable shaft couplings. The crankshaft also can drive a variety of engine components, such as, for example, one or more camshafts and accessories. The accessories can include alternators or generators, high-pressure fuel pumps and various other types of devices employed for the engine operation. Normally, a flexible transmitter, such as a drive belt or chain, for example, that is disposed atop the engine, drives these devices.

[0006] Many of these flexible transmitters, however, tend to elongate during periods of long use. Moreover, distances between the various shafts may increases or decreased during engine operation due to temperature-based expansion of the engine. A tensioner, thus, is necessary to adjust tension of the flexible transmitter during operation of such engines. Without such a tensioner, the flexible transmitter may either slip or bind the driven camshafts and/or accessories. Such slipping or binding is detrimental to engine performance because the camshafts are required to rotate in a strict timed relationship with the crankshaft.

[0007] Tensioners that automatically adjust the tension on the flexible transmitter currently are provided for automobile engines. For example, Japanese Laid Open Publications No. H08-338488 and No. H10-122316 disclose some exemplary constructions of such automatic tensioners. The tensioners usually comprise a shaft unit and a peripheral unit that abuts on a flexible transmitter. The shaft unit is offset from a center axis of the peripheral unit. A tension adjuster and a damping mechanism also are provided. The tension adjuster adjusts tension of the flexible transmitter and the damping mechanism reduces vibration of the flexible transmitter. The damping mechanism normally comprises a hydraulic cylinder system that includes a piston rod extending beyond an end of a cylinder. The cylinder system urges the peripheral unit of the tensioner toward the flexible transmitter.

[0008] Outboard motors can employ the automatic tensioners. However, a problem arises with particular environmental conditions of the outboard motors and arrangements thereof. Although a protective cowling typically surrounds the engine, the outboard motor generally is used in manners that increase the likelihood of water and/or mist contacting the engine, including its accessories and accessory drive mechanisms. The water can contain salt if the outboard motor is used in the ocean. Because of such environmental conditions, water can enter the tensioner or can adhere to a surface of the tensioner.

[0009] In addition, the outboard motor typically comprises a drive unit that includes the engine and a bracket assembly that is mounted on an associated watercraft and supports the drive unit for tilt movement about a horizontally extending tilt axis. When the drive unit is tilted up, the tensioner that is disposed atop of the engine slants and the water that has entered or adhered to the tensioner tends to accumulate at a lower portion of the tensioner. The water can corrode members of the tensioner disposed at the lower portion if the drive unit is held in the tilted up position for a long period. Additionally, salt can adhere to the members. Such corrosion or salt deposition is disadvantageous because either situation can cause the tensioner to malfunction, which might leave the engine operating as though no tensioner was provided at all.

SUMMARY OF THE INVENTION

[0010] Accordingly, a need exists for an improved flexible transmitter tensioner for an outboard motor.

[0011] In accordance with one aspect of the present invention, an outboard motor comprises a drive unit. A bracket assembly is adapted to be mounted on an associated watercraft to support the drive unit for tilt movement about a horizontally extending tilt axis. The drive unit includes an internal combustion engine. The engine comprises an engine body. A moveable member is moveable relative to the engine body. A first rotatable member is rotatable with the movement of the moveable member. An engine component actuation mechanism is arranged to actuate at least one of engine components. The actuation mechanism includes a second rotatable member arranged to engage the engine component. A drive mechanism is arranged on a top surface of the engine body to drive the actuation mechanism. The drive mechanism includes a flexible transmitter to rotate the second rotatable member with the rotation of the first rotatable member. A tensioner is arranged to adjust tension of the flexible transmitter. The tensioner comprises a shaft unit mounted on the engine body. A peripheral unit is swingably carried by the shaft unit and abutting on a portion of the flexible transmitter. A mount axis of the shaft unit is offset from a center axis of the peripheral unit. A damping mechanism is provided to damp a vibration of the flexible transmitter. The damping mechanism has a damping member that urges the peripheral unit toward the flexible transmitter. The damping member is positioned at a location which is capable to be generally the highest of the damping mechanism when the drive unit is tilted up about the tilt axis.

[0012] In accordance with another aspect of the present invention, an outboard motor comprises a drive unit. A bracket assembly is adapted to be mounted on an associated watercraft to support the drive unit for tilt movement about a horizontally extending tilt axis. The drive unit includes an internal combustion engine. The engine comprises an engine body. A moveable member is moveable relative to the engine body. The engine body and the moveable member together define at least one combustion chamber. A first rotatable member is rotatable with the movement of the moveable member. An air intake system is arranged to introduce air to the combustion chamber. The intake system includes at least one intake valve. An exhaust system is arranged to route exhaust gases from the combustion chamber. The exhaust system includes at least one exhaust valve. A valve actuation mechanism is arranged to actuate at least one of the intake and exhaust valves between an open position and a closed position. The valve actuation mechanism includes a second rotatable member arranged to engage the at least one of the intake and exhaust valves. A drive mechanism is arranged on a top surface of the engine body to drive the valve actuation mechanism. The drive mechanism includes a flexible transmitter to rotate the second rotatable member with the rotation of the first rotatable member. A tensioner is arranged to adjust tension of the flexible transmitter. The tensioner comprises a shaft unit mounted on the engine body. A peripheral unit is swingably carried by the shaft unit and abutting on a portion of the flexible transmitter. A swing axis of the shaft unit is offset from a center axis of the peripheral unit. A damping mechanism is provided to damp a vibration of the flexible transmitter. The damping mechanism has a damping member that urges the peripheral unit toward the flexible transmitter. The damping member is positioned at a location which is capable to be generally the highest of the damping mechanism when the drive unit is tilted up about the tilt axis.

[0013] In accordance with a further aspect of the present invention, an outboard motor comprises a drive unit. A bracket assembly is adapted to be mounted on an associated watercraft to support the drive unit for tilt movement about a horizontally extending tilt axis. The drive unit includes an internal combustion engine. The engine comprises an engine body. A moveable member is moveable relative to the engine body. A first rotatable member is rotatable with the movement of the moveable member. An engine component actuation mechanism is arranged to actuate at least one of engine components. The actuation mechanism includes a second rotatable member arranged to engage the engine component. A drive mechanism is arranged on a top surface of the engine body to drive the actuation mechanism. The drive mechanism includes a flexible transmitter to rotate the second rotatable member with the rotation of the first rotatable member. A tensioner is arranged to adjust tension of the flexible transmitter. The tensioner comprises a shaft unit mounted on the engine body. A peripheral unit is swingably carried by the shaft unit and abutting on a portion of the flexible transmitter. A swing axis of the shaft unit is offset from a center axis of the peripheral unit. The shaft unit is positioned at a location which is capable to be generally positioned higher than the center axis of the peripheral unit when the drive unit is tilted up about the tilt axis.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other features, aspects and advantages of the present invention will now be described with reference to the drawings of a preferred embodiment, which embodiment is intended to illustrate and not to limit the present invention. The drawings comprise four figures.

[0015] FIG. 1 is a side elevational view of an outboard motor configured in accordance with certain features, aspects and advantages of the present invention. An associated watercraft is partially shown in section.

[0016] FIG. 2 is an enlarged side elevational view of an engine of the outboard motor. A protective cowling is shown in phantom line.

[0017] FIG. 3 is a top plan view of the engine of FIG. 2. An engine cover and a flywheel magneto are shown in phantom line.

[0018] FIG. 4 is a partial top plan view of the engine of FIG. 2 illustrating a timing belt tensioner that is arranged and configured in accordance with certain features, aspects and advantages of the present invention.

DETAILED DESCRIPTION OF ONE PREFERRED EMBODIMENT OF THE PRESENT INVENTION

[0019] With reference to FIGS. 1-3, an overall construction of an outboard motor 30 that features an improved timing belt tensioner 32, which is arranged and configured in accordance with certain features, aspects and advantages of the present invention, will be described.

[0020] In the illustrated arrangement, the outboard motor 30 generally comprises a drive unit 34 and a bracket assembly 36. The bracket assembly 36 supports the drive unit 34 on a transom 38 of an associated watercraft 40 and places a marine propulsion device in a submerged position with the watercraft 40 resting relative to a surface of a body of water. The bracket assembly 36 preferably comprises a swivel bracket 44, a clamping bracket 46, a steering shaft and a pivot pin 50.

[0021] The steering shaft typically extends through the swivel bracket 44 and is affixed to the drive unit 34. The steering shaft can be pivotally journaled for steering movement about a generally vertically extending steering axis defined within the swivel bracket 44. The clamping bracket 46 comprises a pair of bracket arms that preferably are laterally spaced apart from each other and that are attached to the watercraft transom 38.

[0022] The pivot pin 50 completes a hinge coupling between the swivel bracket 44 and the clamping bracket 46. The pivot pin 50 preferably extends through the bracket arms so that the clamping bracket 46 supports the swivel bracket 44 for pivotal movement about a generally horizontally extending tilt axis defined by the pivot pin 50. The drive unit 34 thus can be tilted or trimmed about the pivot pin 50.

[0023] As used through this description, the terms “forward,” “forwardly” and “front” mean at or to the side where the bracket assembly 36 is located, unless indicated otherwise or otherwise readily apparent from the context use. The terms “rear,” “reverse,” “backwardly” and “rearwardly” mean at or to the opposite side of the front side.

[0024] A hydraulic tilt and trim adjustment system preferably is provided between the swivel bracket 44 and the clamping bracket 46 for tilt movement (raising or lowering) of the swivel bracket 44 and the drive unit 34 relative to the clamping bracket 46. In some arrangements, the outboard motor 30 can have a manually operated system for tilting the drive unit 34. Typically, the term “tilt movement,” when used in a broad sense, comprises both a tilt movement and a trim adjustment movement.

[0025] The illustrated drive unit 34 comprises a power head 58 and a housing unit 60, which includes a driveshaft housing 62 and a lower unit 64. The power head 58 is disposed atop the housing unit 60 and includes an internal combustion engine 65 that is positioned within a protective cowling assembly 66, which preferably is made of plastic. In most arrangements, the protective cowling assembly 66 defines a generally closed cavity 68 in which the engine 65 is disposed. The engine, thus, is generally protected within the enclosure, which is defined by the cowling assembly 66, from environmental elements.

[0026] The protective cowling assembly 66 preferably comprises a top cowling member 70 and a bottom cowling member 72. The top cowling member 70 preferably is detachably affixed to the bottom cowling member 72 by a coupling mechanism to facilitate access to the engine and other related components.

[0027] The top cowling member 70 preferably has a rear intake opening (not shown) defined through an upper rear portion. A rear intake member with one or more air ducts can be unitarily formed with, or affixed to, the top cowling member 70. The rear intake member, together with the upper rear portion of the top cowling member 70, generally defines a rear air intake space. Ambient air is drawn into the closed cavity 68 via the rear intake opening and the air ducts of the rear intake member. Typically, the top cowling member 70 tapers in girth toward its top surface, which is in the general proximity of the air intake opening. The taper helps to reduce the lateral dimension of the outboard motor, which helps to reduce the air drag on the watercraft 40 during movement.

[0028] The bottom cowling member 72 preferably has an opening through which an upper portion of an exhaust guide member 80 extends. The exhaust guide member 80 preferably is made of aluminum alloy and is affixed atop the driveshaft housing 62. The bottom cowling member 72 and the exhaust guide member 80 together generally form a tray. The engine 65 is placed onto this tray and can be connected to the exhaust guide member 80. The exhaust guide member 80 also defines an exhaust discharge passage through which burnt charges (e.g., exhaust gases) from the engine 65 pass.

[0029] The engine 65 in the illustrated embodiment preferably operates on a four-cycle combustion principle. With reference now to FIGS. 2 and 3, the presently preferred engine 65 is a DOHC six cylinder engine and has a V-shaped cylinder block 84. The cylinder block 84 thus defines two cylinder banks which extend generally side by side with each other. In the illustrated arrangement, each cylinder bank has three cylinder bores such that the cylinder block 84 has six cylinder bores in total. The cylinder bores of each bank extend generally horizontally and are generally vertically spaced from one another. This type of engine, however, merely exemplifies one type of engine. Engines having other numbers of cylinders, having other cylinder arrangements (in-line, opposing, etc.), and operating on other combustion principles (e.g., crankcase compression two-stroke or rotary) also can be used. The illustrated engine 65 generally is symmetrical about a longitudinal center plane 88 (FIG. 3) that extends generally vertically and fore to aft of the outboard motor 30.

[0030] As used in this description, the term “horizontally” means that the subject portions, members or components extend generally in parallel to the water surface (i.e., generally normal to the direction of gravity) when the associated watercraft 40 is substantially stationary with respect to the water surface and when the drive unit 34 is not tilted (i.e., is placed in the position shown in FIG. 1). The term “vertically” in turn means that portions, members or components extend generally normal to those that extend horizontally.

[0031] A moveable member, such as a reciprocating piston, moves relative to the cylinder block 84 in a suitable manner. In the illustrated arrangement, a piston (not shown) reciprocates within each cylinder bore. Because the cylinder block 84 is split into the two cylinder banks, each cylinder bank extends outward at an angle to an independent first end in the illustrated arrangement. A pair of cylinder head members 92 are affixed to the respective first ends of the cylinder banks to close those ends of the cylinder bores. The cylinder head members 92 together with the associated pistons and cylinder bores, preferably define six combustion chambers (not shown). Of course, the number of combustion chambers can vary, as indicated above. Each of the cylinder head member 92 is covered with a cylinder head cover member 94.

[0032] A crankcase member 96 is coupled with the cylinder block 84 and a crankcase cover member 98 is further coupled with the crankcase member 96. The crankcase member 96 and the crankcase cover member 98 close the other end of the cylinder bores and, together with the cylinder block 84, define a crankcase chamber. A first rotatable member, such as a crankshaft 100, extends generally vertically through the crankcase chamber and can be journaled for rotation about a rotational axis by several bearing blocks. The rotational axis of the crankshaft 100 preferably is on the longitudinal center plane 88. Connecting rods couple the crankshaft 100 with the respective pistons in any suitable manner. Thus, the reciprocal movement of the pistons rotates the crankshaft 100.

[0033] Preferably, the crankcase cover member 98 is located at the forward-most position of the engine 65, with the crankcase member 96, the cylinder block 84, the cylinder head members 92 and the cylinder head cover members 94 being disposed rearward from the crankcase cover member 98, one after another. In the illustrated arrangement, the cylinder block 84, the cylinder head members 92, the cylinder head cover members 94, the crankcase member 96 and the crankcase cover member 98 together define an engine body 102. Preferably, at least these major engine portions 84, 92, 94, 96, 98 are made of aluminum alloy. In some arrangements, the cylinder head cover members 94 can be unitarily formed with the respective cylinder head members 92. Also, the crankcase cover member 98 can be unitarily formed with the crankcase member 96.

[0034] The engine 65 also comprises an air intake system 106. The air intake system 106 draws air from within the cavity 68 to the combustion chambers. The air intake system 106 preferably comprises six intake passages 108 and a pair of plenum chambers 110. In the illustrated arrangement, each cylinder bank communicates with three intake passages 108 and one plenum chamber 110.

[0035] The most-downstream portions of the intake passages 108 are defined within the cylinder head members 92 as inner intake passages. The inner intake passages communicate with the combustion chambers through intake ports, which are formed at inner surfaces of the cylinder head members 92. Typically, each of the combustion chambers has one or more intake ports. Intake valves are slideably disposed at each cylinder head members 92 to move between an open position and a closed position. As such, the valves act to open and close the ports to control the flow of air into the combustion chamber. Biasing members, such as springs, are used to urge the intake valves toward the respective closed positions by acting between a mounting boss formed on each cylinder head member 92 and a corresponding retainer that is affixed to each of the valves. When each intake valve is in the open position, the inner intake passage that is associated with the intake port communicates with the associated combustion chamber.

[0036] Outer portions of the intake passages 108, which are disposed outside of the cylinder head members 92, preferably are defined with intake conduits 114. In the illustrated arrangement, each intake conduit 114 is formed with two pieces. One piece is a throttle body 116 in which a throttle valve assembly 118 is positioned. The throttle valve assemblies 118 are schematically illustrated in FIG. 2. The throttle bodies 116 are connected to the inner intake passages. Another piece is an intake runner 120 disposed upstream of the throttle body 116. The respective intake conduits 114 extend forwardly along side surfaces of the engine body 102 on both the port side and the starboard side from the respective cylinder head members 92 to the front of the crankcase cover member 98. The intake conduits 114 on the same side extend generally in parallel to each other and are vertically spaced apart from one another.

[0037] Each throttle valve assembly 118 preferably includes a throttle valve. Preferably, the throttle valves are butterfly valves that have valve shafts journaled for pivotal movement about a generally vertical axis. In some arrangements, the valve shafts are linked together and are connected to a control linkage. The control linkage would be connected to an operational member, such as a throttle lever, that is provided on the watercraft or otherwise proximate the operator of the watercraft 40. The operator can control the opening degree of the throttle valves in accordance with operator demand through the control linkage. That is, the throttle valve assemblies 118 can measure or regulate amounts of air that flow through the intake passages 108 to the combustion chambers in response to the operation of the operational member by the operator. Normally, the greater the opening degree, the higher the rate of airflow and the higher the engine speed.

[0038] The respective plenum chambers 110 preferably are defined with plenum chamber units 124 which are disposed side by side in front of the crankcase cover member 98 and are affixed thereto. Preferably, the plenum chamber units 124 are arranged substantially symmetrically relative to the longitudinal center plane 88. In the illustrated arrangement, each forward end portion of the intake runners 120 is housed within each plenum chamber unit 124. As shown in FIG. 2, each plenum chamber unit 124 preferably has two air inlets 126, which extend generally rearwardly between the respective intake runners 120. The respective air inlets 126 define inlet openings 128 through which air is drawn into the plenum chambers 110. The intake runners 120 and the air inlets 126 can be unitarily formed with the associated plenum chamber unit 124 and those three components 120, 124, 126 can be made of plastic. The respective plenum chamber units 124 are connected with each other through one or more connecting pipes 130 (FIG. 3) to substantially equalize the internal pressures within each chamber unit 124. The plenum chambers 110 coordinate or smooth air delivered to each intake passage 108 and also act as silencers to reduce intake noise.

[0039] The air within the closed cavity 68 is drawn into the plenum chambers 110 through the inlet openings 128 of the air inlets 126. The air expands within the plenum chambers 110 to reduce pulsations and then enters the outer intake passages 108. The air passes through the outer intake passages 108 and flows into the inner intake passages. The level of airflow is measured by the throttle valve assemblies 118 before the air enters the inner intake passages.

[0040] The engine 65 further comprises an exhaust system that routes burnt charges, i.e., exhaust gases, to a location outside of the outboard motor 30. Each cylinder head member 92 defines a set of inner exhaust passages that communicate with the combustion chambers through one or more exhaust ports, which may be defined at the inner surfaces of the respective cylinder head members 92. The exhaust ports can be selectively opened and closed by exhaust valves. The construction of each exhaust valve and the arrangement of the exhaust valves are substantially the same as the intake valve and the arrangement thereof, respectively. Thus, further description of these components is deemed unnecessary.

[0041] Exhaust manifolds preferably are defined generally vertically within the cylinder block 84 between the cylinder bores of both the cylinder banks. The exhaust manifolds communicate with the combustion chambers through the inner exhaust passages and the exhaust ports to collect exhaust gases therefrom. The exhaust manifolds are coupled with the exhaust discharge passage of the exhaust guide member 80. When the exhaust ports are opened, the combustion chambers communicate with the exhaust discharge passage through the exhaust manifolds.

[0042] A valve cam mechanism preferably is provided for actuating the intake and exhaust valves in each cylinder bank. Preferably, the valve cam mechanism includes second rotatable members such as a pair of camshafts 132 per cylinder bank, although one of them is not seen in the illustrated arrangement. The camshafts 132 preferably comprise intake and exhaust camshafts. The camshafts 132 preferably extend generally vertically and are journaled for rotation between the cylinder head members 92 and the cylinder head cover members 94. The camshafts 132 have cam lobes to push valve lifters that are affixed to the respective ends of the intake and exhaust valves in any suitable manner. The cam lobes repeatedly push the valve lifters in a timed manner, which is in proportion to the engine speed. The movement of the lifters generally is timed by rotation of the camshafts 132 to appropriately actuate the intake and exhaust valves.

[0043] A camshaft drive mechanism 134 preferably is provided for driving the valve cam mechanism. The camshaft drive mechanism 134 in the illustrated arrangement is formed above a top surface 135 (see FIG. 2) of the engine body 102 and comprises driven sprockets 136 positioned atop at least one of each pair of camshafts 132, a drive sprocket 138 positioned atop the crankshaft 100 and a flexible transmitter, such as a timing belt or chain 140, for instance, wound around the driven sprockets 136 and the drive sprocket 138. The crankshaft 100 thus drives the respective camshafts 132 through the timing belt 140 in the timed relationship.

[0044] The illustrated timing belt 140 moves in a direction indicated by the arrows 141 shown in FIG. 3. The belt tensioner 32 advantageously maintains the timing belt 140 under a desired degree of tension. The belt tensioner 32 preferably is mounted on the cylinder block 84 so that a peripheral unit 142 of the belt tensioner 32 abuts on a portion of the timing belt 140. In the illustrated arrangement, the other camshaft (not shown) on each bank is driven by the first camshaft via another timing belt or chain (not shown). Because the camshafts 132 must rotate at half of the speed of the rotation of the crankshaft 100 in a four-cycle engine, a diameter of the illustrated driven sprockets 136 is twice as large as a diameter of the illustrated drive sprocket 138. The camshaft drive mechanism 134, including the belt tensioner 142, will be described in greater detail later.

[0045] Most of the engine components described above are well known to those skilled in the art and are disclosed, for example, in U.S. Pat Nos. 5,704,819, 5,865,655, 5,941,205 and 6,044,817, the disclosures of which are hereby incorporated by reference in their entirety.

[0046] The illustrated engine 65 further comprises indirect, port or intake passage fuel injection. In one arrangement, the engine 65 comprises direct fuel injection and, in another arrangement, the engine 65 is carbureted. The illustrated fuel injection system preferably comprises six fuel injectors 144 with one fuel injector allotted to each one of the respective combustion chambers. The fuel injectors 144 preferably are mounted on the throttle bodies 116 of the respective banks with a pair of fuel rails 146. In the illustrated arrangement, the fuel rails 146 connect the fuel injectors 144 on the same banks with each other and also define portions of fuel conduits to deliver fuel to the injectors 144.

[0047] Each fuel injector 144 preferably has an injection nozzle directed downstream within the associated intake passage 108. The injection nozzle preferably is disposed downstream of the throttle valve assembly 118. The fuel injectors 144 spray fuel into the intake passages 108 under control of an electronic control unit (ECU) (not shown). The ECU controls both the initiation timing and the duration of the fuel injection cycle of the fuel injectors 144 so that the nozzles spray a desired amount of fuel each combustion cycle.

[0048] A fuel supply tank preferably is disposed on a hull of the associated watercraft 40. The fuel supply tank contains a supply of fuel. From the tank, the fuel is delivered to the fuel rails 146 through suitable fuel conduits.

[0049] A vapor separator 148 preferably is in fluid communication with the tank and the fuel rails, and can be disposed along the conduits in one arrangement. The vapor separator 148 separates vapor from the fuel and can be mounted on the engine body 102 at the side surface on the port side.

[0050] The fuel injection system preferably employs at least two fuel pumps to deliver the fuel to the vapor separator 148 and to send out the fuel therefrom. More specifically, in the illustrated arrangement, a lower pressure pump 150, which is affixed to the vapor separator 148, pressurizes the fuel toward the vapor separator 148 and a high pressure pump (not shown), which is disposed within the vapor separator 148, pressurizes the fuel passing out of the vapor separator 148.

[0051] A vapor delivery conduit 152 couples the vapor separator 148 with at least one of the plenum chambers 110. The vapor removed from the fuel supply by the vapor separator 148 thus can be delivered to the plenum chamber 110 for delivery to the combustion chambers with the combustion air. In other applications, the engine 65 can be provided with a ventilation system arranged to send lubricant vapor to the plenum chamber(s). In such applications, the fuel vapor also can be sent to the plenum chambers via the ventilation system.

[0052] The engine 65 further comprises an ignition system. Each combustion chamber is provided with a spark plug which preferably is disposed between the intake and exhaust valves. Each spark plug has electrodes that are exposed in the associated combustion chamber. The electrodes are spaced apart from each other by a small gap. The spark plugs are connected to the ECU through ignition coils. The spark plugs generate a spark between the electrodes to ignite an air/fuel charge in the combustion chamber according to desired ignition timing maps or other forms of controls.

[0053] Generally, during an intake stroke, air is drawn into the combustion chambers through the air intake passages 108 and fuel is mixed with the air by the fuel injectors 144. The mixed air/fuel charge is introduced to the combustion chambers. The mixture is then compressed during a compression stroke. Just prior to a power stroke, the respective spark plugs ignite the compressed air/fuel charge in the respective combustion chambers. The air/fuel charge thus rapidly bums during the power stroke to move the pistons. The burnt charge, i.e., exhaust gases, then is discharged from the combustion chambers during an exhaust stroke.

[0054] A flywheel assembly 156, which is schematically illustrated with phantom line in FIG. 3, preferably is positioned atop the crankshaft 100 and is mounted for rotation with the crankshaft 100. The flywheel assembly 156 comprises a flywheel magneto or AC generator that supplies electric power directly or indirectly via a battery to various electrical components such as the fuel injection system, the ignition system and the ECU. An engine cover 158 preferably extends over almost all of the engine 65, including the flywheel assembly 156.

[0055] The engine 65 may comprise any other systems, mechanisms, devices, accessories and components other than those described above such as, for example, a cooling system and a lubrication mechanism. Those systems, mechanisms, devices, accessories and components can be directly or indirectly driven by the crankshaft 100 through a flexible transmitter, such as the timing belt 140. In some arrangements, flexible transmitter tension can be adjusted by two or more tensioners that are arranged and configured in accordance with certain features, aspects and advantages of the present invention.

[0056] With reference again to FIG. 1, the driveshaft housing 62 depends from the power head 58 and supports a driveshaft, which is coupled with the crankshaft 100 and which extends generally vertically through the driveshaft housing 62. The driveshaft is journaled for rotation and is driven by the crankshaft 100.

[0057] The driveshaft housing 62 preferably defines an internal section of the exhaust system that leads the majority of exhaust gases to the lower unit 64. The internal section includes an idle discharge portion that extends from a main portion of the internal section to discharge idle exhaust gases directly to the atmosphere through a discharge port that is formed on a rear surface of the driveshaft housing 62 engine idle.

[0058] The lower unit 64 depends from the driveshaft housing 62 and supports a propulsion shaft that is driven by the driveshaft. The propulsion shaft extends generally horizontally through the lower unit 64 and is journaled for rotation. A propulsion device is attached to the propulsion shaft. In the illustrated arrangement, the propulsion device is a propeller 160 that is affixed to an outer end of the propulsion shaft. The propulsion device, however, can take the form of a dual counter-rotating system, a hydrodynamic jet, or any of a number of other suitable propulsion devices.

[0059] A transmission preferably is provided between the driveshaft and the propulsion shaft, which lie generally normal to each other (i.e., at a 90° shaft angle) to couple together the two shafts by bevel gears. The outboard motor 30 has a clutch mechanism that allows the transmission to change the rotational direction of the propeller 160 among forward, neutral or reverse.

[0060] The lower unit 64 also defines an internal section of the exhaust system that is connected with the internal exhaust section of the driveshaft housing 62. At engine speeds above idle, the exhaust gases generally are discharged to the body of water surrounding the outboard motor 30 through the internal sections and then a discharge section defined within the hub of the propeller 160.

[0061] With reference still to FIG. 3 and with additional reference to FIG. 4, the illustrated camshaft drive mechanism 134 and the illustrated timing belt tensioner 32 will now be described in great detail. The timing belt tensioner 32 preferably comprises the peripheral unit 142, a shaft unit 170, an offset member 174, a tension adjuster 176 and a damping mechanism 178.

[0062] The shaft unit 170 comprises a shaft affixed to the top surface 135 of the engine body 102 and, more specifically, to the cylinder block 84 in the illustrated arrangement. In the illustrated arrangement, a hexagonal socket-head bolt 180 is the shaft and also functions to secure the shaft unit 170 to the cylinder block 84. The bolt 180 has a head portion 182 which has an outer diameter that is greater than an outer diameter of a shaft portion. A hexagon recess 184 is formed at the head portion 182 to fasten or loosen the bolt 180 with a hexagon head tool (e.g., an Allen wrench) that has a proper outer diameter fitting with an inner diameter of the hexagon recess 184. The shaft unit 170 preferably includes a collar 186 surrounding the shaft portion. The balance of the illustrated tensioner 32, which includes the peripheral unit 142 and the offset member 174, is pivotally supported by the shaft 180 via the collar 186.

[0063] The illustrated peripheral unit 142 comprises a tension pulley 190 and a bearing assembly 192 that journals the tension pulley 190. The tension pulley 190 abuts a portion of the timing belt 140. The illustrated tension pulley 190 abuts on the belt 140 in a range 194 as shown in FIG. 4. More than one tension pulley 190 can be used and the location of the tension pulley 190 can be varied to accommodate various engine components.

[0064] The bearing assembly 192 includes an inner ring 196, a plurality of rollers or balls and retainers. A combination of the rollers (or balls) and the retainers are schematically indicated by a reference numeral 198. Generally speaking, the peripheral unit 142 defines a roller bearing or a ball bearing. In other words, the tension pulley 190 and the inner ring 196 define an outer race and an inner race of the bearing, respectively, with the rollers (or balls) being positioned between the two components. Thus, the tension pulley 190 is rotatable relative to the inner ring 196. Alternatively, the peripheral unit 172 can be further provided with an outer ring or race that is independent of the pulley 190.

[0065] The illustrated tension pulley 190 has a height taller than a height of the bearing assembly 192. Both the tension pulley 190 and the bearing assembly 192 preferably are generally made of metal material. An outer surface of the tension pulley 190 that contacts the timing belt 140 preferably is coated with a non-electrolytic nickel plating. Because of this plating, a relatively deep and hard plating layer is formed and the outer surface of the tension pulley 190 is well protected from water corrosion even if salt is contained in the water.

[0066] The offset member 174 couples the peripheral unit 142 with the shaft unit 170 such that respective rotational axes of each is offset from the other. More specifically, a swing axis 200 of the shaft unit 170 is offset from a center axis 202 of the peripheral unit 142 as shown in FIG. 4.

[0067] The illustrated offset member 174 substantially occupies a space surrounded by the peripheral unit 142 except the shaft unit 170. The offset member 174 is positioned above the damping mechanism 178. Desirably, the shaft unit 170 is positioned at a location which is positioned generally higher than the center axis 202 when the drive unit 34 is tilted up about the tilt axis defined the pivot pin 50.

[0068] An engagement portion, such as a pin 204, preferably extends downwardly from a bottom surface of the offset member 174. In other words, an axis 206 of the engage portion, i.e., the pin 204 extends generally vertically. The pin 204 preferably is positioned next to the shaft unit 170. In one arrangement, the pin 204 is a discrete member mounted to the offset member 174 and, in another arrangement, the pin 204 is a projection integrally formed on the offset member 174.

[0069] The offset member 174 preferably is made of metal alloy manufactured by a sintering process. A top surface of the offset member 174 preferably is treated with a Parkerizing process that gives an anti-corrosion property to the top surface.

[0070] The offset member 174 comprises an elongated recess 208 that has a longitudinal axis 210 that extends generally horizontally. The axis 210 preferably extends toward a contact position 211 where the belt 194 contacts the tension pulley 190.

[0071] The recess 208 receives the tension adjuster 176, which comprises a bias member, such as a spring 212, a spring retainer 214 and a pin 216. The pin 216 extends upwardly from the damping mechanism 178. In the illustrated arrangement, an axis 218 of the pin 216 extends generally vertically.

[0072] The bias spring 212 preferably is a coil spring and is confined within the recess 208 along the axis 210 under a compressed condition between one end 219 of the recess 208 and a spring retainer 214, which is secured in position between the spring 212 and the pin 216. The spring 212 thus pushes the offset member 174 against the pin 216, which sets up forces that bias the peripheral unit 142 toward the timing belt 140. The biasing force of the spring 212 swings the tensioner 32 around the swing axis 200 of the shaft unit 170. The tensioner 32 swings until a tension force of the timing belt 140 and the biasing force of the spring 212 balance. Accordingly, the tension of the timing belt 140 is well adjusted.

[0073] The damping mechanism 178 reduces vibration of the timing belt 140. In the illustrated arrangement, the mechanism 178 is placed generally below the offset member 174 and the peripheral unit 142, and comprises a hydraulic cylinder member 220 that defines a cavity 222. The cavity 222 comprises a longitudinally extending damping axis 224 that extends generally horizontally. The axis 224 preferably is oriented toward a portion 226 of the pulley 190 where the belt 194 is separating from the tension pulley 190. The axis 206 of the pin 204 preferably intersects with this axis 224 and the axis 206 of the pin 204 preferably lies generally normal to the axis 224.

[0074] An end portion 225 of the cylinder member 220 extends out of the peripheral unit 142 and is affixed to the cylinder block 84 by a fastener, such as a bolt 226, for instance, which comprises a vertical axis 227. The cylinder member 220 comprises a projecting portion that extends toward the shaft unit 170. This projecting portion also can be affixed to the cylinder block 84, together with the shaft unit 170, by the hex socket head bolt 180, for instance. The pin 216 extends upwardly from the projecting portion of the cylinder member 220. In one arrangement, the pin 216 is a discrete member mounted to the cylinder member 220 and, in another arrangement, the pin 216 is a projection formed on the cylinder member 220.

[0075] In the illustrated arrangement, a hydraulic piston 228 is slideably disposed within the cavity 222 along the axis 224 and defines first and second chambers 230, 232 on opposite sides thereof. An orifice 236 formed through the piston 228 generally in parallel to the axis 224 connects both the first and second chambers 230, 232. A damping member, such as a piston rod 238, for instance, that is coupled with the piston 228 extends through the first chamber 230 and beyond the end of the cylinder member 220 that is located next to the pin 204. The term “coupled with” means either that the piston rod 238 is a separate member from the piston 228 and then is affixed to the piston 228 or that the piston rod 238 is unitarily formed with the piston 228. Desirably, the piston rod 238 is positioned at a location that is generally the highest portion of the damping mechanism 178 when the drive unit 34 is tilted up about the tilt axis defined by the pivot pin 50. Nevertheless, the pin 204 preferably is positioned higher than the piston rod 238 under the tilt up condition.

[0076] The first and second chambers 230, 232 preferably are filled with a working fluid such as, for example, oil. The working fluid can move between the first and second chambers 230, 232 through the orifice 236 when the piston 228 translates within the cavity 222. Preferably, the orifice 236 is narrow enough to generate some flow resistance when the fluid moves between the chambers 230, 232. Thus, movement of the piston 228 is advantageously quite slow. Because a certain volume of the piston rod 238 goes in and out of the cavity 222 with movement of the piston 228, a fluid reservoir (not shown) can be provided in the damping mechanism 178 to compensate for the volume of the piston rod 238.

[0077] In the illustrated arrangement, a bias spring 242 also is disposed within the second chamber 232 to bias the piston 228 toward the pin 204. The bias spring 242 preferably is a compressed coil spring and, in one arrangement, is confined in the second chamber 232 (i.e., along the axis 224). Thus, the bias spring 242 normally pushes the piston rod 238 toward the pin 204. Because the offset member 174, which comprises the pin 204, is coupled with the peripheral unit 142, the biasing force of the spring 242 also biases the peripheral unit 142 toward the timing belt 140.

[0078] Vibration of the belt 140 causes slight swings of the tensioner 32 about the swing axis 200. With this slight swing, the pin 204 pushes the piston rod 238 toward the bolt 227 or moves toward the timing belt 140. However, the working fluid in the chambers 230, 232 inhibits the piston 228 from moving quickly due to the narrow orifice 236. Accordingly, the pin 204 remains substantially at an initial position and vibration is effectively damped.

[0079] As will be appreciated, the tensioner 32 for the outboard motor 30 moves up and down with tilting movement of the drive unit 34. At any position between a fully tilted up position and a fully tilted down position, the tensioner moves in accordance with the movement of the engine body 102. Accordingly, the tensioner 32 may be angled relative to gravity and water adhering on the tensioner 32 can accumulate at a lower portion of the tensioner 32 when the drive unit 34 is held in the tilted up position for long time. To reduce the likelihood of such a situation, both the shaft unit 170 and the piston rod 238 are positioned above the portion of the outboard motor in which water typically accumulates.

[0080] Additionally, because the tension pulley 190 is moved with a relatively great force by the timing belt 140, insignificant corrosion or salt adhesion on the peripheral unit 142 itself does not matter seriously. In fact, the amount of force required to move the tension pulley in the illustrated arrangement is several times greater than that required to move prior tensioner arrangements. Moreover, because the piston rod 238 is directed toward the separating portion 226 rather than the contact portion 211, water splash or water mist deflected by the timing belt 140, if any, is unlikely to affect the piston rod 238.

[0081] Of course, the foregoing description is that of a preferred construction having certain features, aspects and advantages in accordance with the present invention. Various changes and modifications may be made to the above-described arrangements without departing from the spirit and scope of the invention, as defined by the appended claims. For instance, the second rotatable member can be any one of a number of engine components or accessories, other than the camshafts such as, for example, a fuel pump or an alternator inasmuch as those components are driven by a drive mechanism arranged on a top surface of the engine body. Accordingly, the scope of the present invention should not be limited to the illustrated configurations, but should only be limited to a fair construction of the claims that follow and any equivalents of the claims.