Manifold and water trap system for marine engine

A personal watercraft having a compact engine arrangement for driving a propulsion device such as a jet pump positioned to the rear of and on the underside of the watercraft. The engine is disposed so that its cylinder block is at an angle to a vertical plane, with the exhaust manifold being positioned on the underside of the cylinder bank. An expansion chamber device is provided at the rear end of the engine and at a height that is higher than the exhaust ports of the engine and the discharge of the exhaust system so as to provide a trap for precluding flow of water to the engine through the exhaust system. This positioning of the engine places its crankshaft in offset relationship to the drive shaft of the propulsion device, and a two-stage step-down transmission drives the drive shaft from the crankshaft.

BACKGROUND OF THE INVENTION 
This invention relates to a marine propulsion unit and more particularly to 
a manifold and water trap and output shaft arrangement for such an engine. 
There is a very popular and rapidly growing segment of the watercraft 
market for a type of water vehicle called a "personal watercraft." This 
type of watercraft is designed primarily to be operated by a rider and 
accommodate a relatively small number of passengers. Frequently, the 
rider's area is generally open and the watercraft and rider's area is 
designed so as to be boarded from the body of water in which the 
watercraft is operating. Obviously, these vehicles are quite compact in 
nature. 
The propulsion systems for these personal watercraft normally include an 
inboard mounted engine and frequently a jet propulsion unit in the form of 
a jet pump that is positioned on the underside at the rear of the hull. 
Oftentimes the engine is positioned at least in part beneath the rider's 
area and frequently beneath a raised straddle-type seat that runs 
longitudinally through the center of the rider's area. 
This compact construction for the watercraft presents a number of unique 
design problems. Not the least of these is the layout of the exhaust 
system for the engine. The problem is rendered particularly acute since, 
as is typical with marine propulsion systems, the engine exhaust gases are 
discharged to the atmosphere either at, below or close to the water level 
at which the watercraft is operating. Thus, care must be taken to ensure 
that water cannot enter the engine through the exhaust system. This 
problem is particularly acute since this type of watercraft is very 
sporting in nature, and the rider and occupants expect the watercraft to 
capsize at times. When capsized and subsequently righted, there is a 
problem that water may flow through the exhaust system into the engine 
with obviously undesirable results. 
Although these types of watercraft are often powered by two-cycle crankcase 
compression internal combustion engines, for a wide variety of reasons, 
there may be advantages in employing four-cycle engines. However, when 
four-cycle engines are employed, the engine configuration is generally 
more bulky than that of a two-cycle engine for obvious reasons. A large 
percentage of this bulk is created by the fact that unlike two-cycle 
engines, the induction system and the exhaust system for the engine is 
normally mounted on the cylinder head. This gives rise to an increased 
bulk at the top of the engine and makes engine placement, particularly 
under a rider's seat, difficult, if not impossible. 
It is, therefore, a principal object of this invention to provide an 
improved propulsion unit and layout for a small personal-type watercraft. 
It is a further object of this invention to provide an improved engine 
arrangement for such a watercraft wherein the engine's center of gravity 
may be kept low and the bulk of the engine reduced. 
One way in maintaining a low center of gravity and moving the large bulk of 
the engine to a lower level where it will permit positioning of a rider's 
area over it is to cant the engine to one side. If this type of canting 
arrangement is employed, there are some certain advantages in maintaining 
the induction system on the high side of the engine. Not the least reason 
for this is the fact that the induction system generally requires 
servicing more frequently than the exhaust system. However, if the exhaust 
system is placed on the low side of the engine, then the water entry 
problems aforenoted may be increased. 
It is, therefore, a still further object of this invention to provide an 
improved engine arrangement for a marine watercraft wherein the engine may 
be canted so that the exhaust side is low but wherein protection against 
water intrusion into the engine through the exhaust system is optimized. 
It is a further object of this invention to provide an improved engine and 
exhaust system arrangement for a watercraft. 
As has been previously noted, the typical propulsion system for this type 
of watercraft employs a jet pump that is disposed on the underside of the 
hull and toward the rear of the hull. Generally, it is the practice to 
position the engine so that its output shaft is generally aligned with the 
impeller shaft of the jet pump so as to facilitate coupling therebetween. 
However, this has several disadvantages. 
First, if it is desired to cant the engine over to one side or the other 
from the vertical, then it is difficult to maintain the in-line 
relationship between the engine output shaft and the watercraft drive 
shaft unless the entire engine is disposed substantially on one side of 
the longitudinal plane. This one-side positioning of the engine is not 
desirable because it can adversely affect the balance of the watercraft. 
If, however, the watercraft engine is canted and its output shaft axis is 
offset from the drive shaft axis, then some form of transmission must be 
employed for transferring the drive. In some instances this is not a 
particular disadvantage because it may be desirable to provide a step-down 
transmission between the engine output shaft and the impeller shaft. 
One reason for this is that high-performance engines normally run at a high 
engine speed so as to achieve a high output for a given displacement. 
However, marine propulsion systems such as propellers or impellers for jet 
pumps can be subject to cavitation if driven at high rates of speed. 
Therefore, there are advantages in providing a step-down transmission 
between the engine output shaft and the drive shaft of the watercraft. 
However, to provide large speed reductions requires a relatively large 
transmission, since the ratio between the driving element and the driven 
element should be relatively large. Although offsetting of the engine 
output shaft relative to the drive shaft can facilitate this, the normal 
degree of offsetting does not provide adequate space for a suitable 
step-down transmission. 
It is, therefore, a still further object of this invention to provide an 
improved engine propulsion unit layout for a watercraft and a step-down 
transmission therebetween. 
SUMMARY OF THE INVENTION 
A first feature of this invention is adapted to be embodied in an internal 
combustion engine for propelling a watercraft. The engine is comprised of 
a crankcase containing a crankshaft rotatable about an axis for 
longitudinal disposition in the watercraft. A cylinder bank extends 
upwardly from the crankcase and is inclined to a vertical plane containing 
the crankshaft axis. At least one exhaust port is formed in the cylinder 
bank and faces in a generally downward direction. An exhaust manifold 
collects exhaust gases from the exhaust port and delivers them in a 
downward direction and then toward one end of the engine. An expansion 
chamber device extends transversely across the one end of the engine and 
receives exhaust gases from the exhaust port. An exhaust pipe discharges 
the exhaust gases from the expansion chamber to the atmosphere at a point 
contiguous to the water level at which the watercraft is operating. In 
accordance with this feature of the invention, the expansion chamber is 
disposed so that it lies at least in part above the exhaust port so as to 
form a trap section between the exhaust pipe outlet and the exhaust port 
that will reduce the likelihood of water entering the engine through the 
exhaust system. 
Another feature of the invention is adapted to be embodied in the 
propulsion system for a watercraft having a hull. A propulsion device is 
provided on the underside of the hull and is driven by a drive shaft that 
extends generally longitudinally within the hull and substantially on its 
centerline. An internal combustion engine is supported within the hull 
forwardly of the propulsion device and with an output shaft that rotates 
about a generally longitudinally disposed axis. The engine is mounted in 
the hull so that a cylinder bank thereof is inclined to a vertically 
extending plane containing the axis of rotation of the engine output 
shaft. This axis is offset to one side of the drive shaft axis. A first 
transmission transmits drive from the engine output shaft to an 
intermediate shaft, and a second transmission drives the drive shaft from 
the intermediate shaft. The intermediate shaft is positioned vertically 
above the drive shaft and the engine output shaft, and the transmissions 
effect a step-down in the speed of the drive shaft from that of the engine 
output shaft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
Referring now in detail to the drawings, a personal watercraft constructed 
in accordance with an embodiment of the invention is identified generally 
by the reference numeral 11. Although a specific configuration for the 
watercraft 11 will be described, it should be readily apparent to those 
skilled in the art that many facets of the invention are adaptable for use 
with watercraft types considerably different than that disclosed. In 
addition, many features of the invention are not limited to, but may have 
primary utility in, personal-type watercraft. That is, a number of the 
features which are disclosed have ready applicability to more conventional 
larger-type watercraft. 
The watercraft 11 is comprised of a hull, indicated generally by the 
reference numeral 12, and which is comprised of a lower hull part 13 and 
an upper deck part 14. These hull parts 13 and 14 may be formed from any 
suitable material such as a molded fiberglass resin or the like. 
The rearward portion of the deck part 14 forms a rider's area through which 
a longitudinally extending raised straddle-type seat 15 is positioned. The 
seat 15 is comprised of a lower base 16 which may be formed from the same 
material as the deck 14 itself. Disposed over this is the seat 15 which 
may be formed from a cushioning material and which has sufficient length 
so as to accommodate one or more riders. If plural riders are 
accommodated, they are seated in straddle-tandem fashion. 
The rider's area is completed by a pair of foot areas 17 (FIG. 5) that are 
disposed on opposite sides of the raised portion 16 and upon which the 
riders seated on the seat 15 may place their feet. A pair of raised 
gunnels 18 forms the outer peripheral edge of the rider's area. To the 
rear of the foot areas 17 and of the raised seat base 16 there is provided 
a deck area which opens through the transom of the watercraft to define a 
rear deck 19 via which riders may board the watercraft 11 from the body of 
water in which the watercraft 11 is operating. 
A control mast 20 is disposed forwardly of the seat 15, and it should be 
noted that the seat cushion 15 has a pair of forwardly extending parts 
that extend in part beneath this mast and around which the rider/operator 
may place his knees. A handlebar assembly 21 is mounted at the upper end 
of the mast 20 for control of certain functions of the watercraft, such as 
its steering or the like. 
The area between the hull portion 13 and deck portion 14 and enclosed 
thereby forms a closed compartment, the forward part of which comprises an 
engine compartment. This engine compartment extends at least in part 
beneath the seat 15 and terminates in a transversely extending bulkhead 
22. An internal combustion engine 23, of the type which will be described 
later, is mounted in this engine compartment and has an output shaft which 
is connected through a transmission, as will be described, to a drive or 
impeller shaft 24 that extends rearwardly through the bulkhead 22. The 
drive shaft 24 drives a jet propulsion unit, indicated generally by the 
reference numeral 25, which is positioned in a tunnel formed on the 
underside of the hull portion 13 to the rear of the bulkhead 22. 
The jet propulsion unit 25 may be of any known type and for that reason is 
not illustrated in any detail. However, it basically includes a downwardly 
facing water inlet portion through which water is drawn from an opening in 
the underside of the hull portion 13. This water is drawn by an impeller 
that is affixed to the impeller shaft 24 and is discharged rearwardly 
through a discharge nozzle to a steering nozzle 26. The steering nozzle 26 
is supported for pivotal movement about a vertically extending axis so as 
to change the direction in which the water is discharged, and thus steer 
the watercraft, as is well known in this art. The handlebar assembly 21 is 
coupled suitably to this steering nozzle 26 for effecting this steering 
operation. 
The engine 23 will now be described, and it appears in most detail in FIGS. 
3-5, although certain components of it appear in other figures. The engine 
23 is, in the illustrated embodiment, of the two-cylinder in-line type and 
operates on a four-stroke principle. In addition, the engine 23 is of the 
double-overhead-cam type. As previously noted however, a number of facets 
of the invention may be employed in conjunction with engines of other 
types. 
The engine 23 is comprised of a crankcase 27 in which a crankshaft 28 is 
supported for rotation about a longitudinally extending axis. As may be 
seen in FIG. 5, this axis is offset slightly to one side of a vertically 
extending longitudinal plane 29 which defines a center plane of the 
watercraft hull 12. The impeller shaft 24 rotates about an axis that lies 
in this center plane. 
A cylinder block 31 forms a cylinder bank that extends vertically upwardly 
from the crankcase 27 and defines a pair of aligned cylinder bores that 
have their axes lying on a plane 32 that is disposed at an acute angle to 
the center plane 29 and which contains the axis of rotation of the 
crankshaft 28. 
A cylinder head assembly 33 is affixed to the cylinder block 31 in a known 
manner and closes the cylinder bores formed therein. The cylinder head 33 
journals a pair of overhead camshafts and is closed by a cam cover 34. 
Except for the location of the crankshaft 28 and the orientation of the 
cylinder block 31, cylinder head 33, and certain external auxiliaries, the 
internal construction of the engine 23 forms no part of the invention. A 
further description of it is not required to permit those skilled in the 
art to practice the invention. Where any details of the construction of 
the engine 23 are omitted, they may be considered to be conventional. 
An important feature of the invention, however, is the canting of the 
cylinder bore axis containing plane 32 from the vertical. As seen in FIG. 
5, this permits the engine 23 to be positioned beneath the raised seat 
base portion 16 and still maintain a low center of gravity and a 
relatively narrow width. This narrow width is important due to the fact 
that the riders sit on the seat 15 in straddle fashion, as aforenoted. 
An induction system, indicated generally by the reference numeral 35, is 
provided in the area of the engine compartment above the cylinder head 33 
and directly beneath the seat portion 23 and the mast 20. This induction 
system 35 includes an air inlet device 36 which draws atmospheric air from 
within the engine compartment. This air is, in turn, transferred to a 
plenum chamber 37 which, in turn, supplies air to charge formers 38 such 
as carburetors which feed the intake ports of the engine either directly 
or through an interposed manifold system. It should be noted that the 
induction system 35 defines a pair of flow axes 39 which lie in a plane 
that is disposed at an angle to the cylinder bore containing plane 32 and 
which is offset to the other side of a vertical plane. However, this axis 
also lies generally on the same side as the longitudinal center plane 29 
of the watercraft. Said another way, the induction system is disposed 
primarily on the same side of the plane 29 as the cylinder block 31 and 
cylinder head 33. 
Fuel is supplied to the charge formers 38 or other charge-forming system of 
the engine from a forwardly positioned fuel tank 41. This fuel tank 41 is 
disposed generally centrally within the hull 12 at a forward location so 
as to maintain the desired fore and aft balance for the watercraft 11. The 
fuel tank 41 has a forwardly disposed fill neck 42 that is accessible from 
externally of the watercraft 11 for refueling. 
Also, a storage locker or storage compartment 43 is formed at the front of 
the deck portion 14 beneath the mast 20 and is accessible through a 
suitable hatch cover. This storage compartment 43 is disposed generally 
forwardly of the engine induction system 35. 
A pair of spark plugs (not shown) are mounted in the cylinder head 33 for 
firing the charge inducted into the engine cylinders through the induction 
system 35. These spark plugs are fired by an ignition circuit that 
includes a magneto generator 44 that is driven off the front of the 
crankshaft 28 and which is disposed at the front of the engine and beneath 
the storage compartment 43. The storage compartment 43 may be provided 
with a false bottom through which the magneto generator 44 may be accessed 
for service purposes. 
As should be apparent from the foregoing description, the induction system 
35 delivers the fuel-air mixture to intake ports formed in the cylinder 
head 33 on the upper side thereof. This charge is delivered to the 
combustion chambers through intake passages formed in the cylinder head 
33. 
The burnt charge is delivered through exhaust ports formed on the lower 
side of the cylinder head 33 and which face generally downwardly to an 
exhaust manifold, indicated generally by the reference numeral 45. This 
exhaust manifold 45 is comprised of a pair of runner sections 46 and 47, 
each of which collects the exhaust gases from a respective exhaust port 
and delivers it to an expansion chamber type of device, indicated by the 
reference numeral 48, and which may be considered to form a collector 
section of the exhaust manifold 45. This collector section 48 is of a 
double-wall construction, and thus forms a water jacket that surrounds the 
exhaust manifold pipes 46 and 47. It should be noted that the pipes 46 and 
47 extend downwardly and then turn rearwardly and terminate behind a rear 
face of the engine 23. 
The engine 23 is water cooled, and water for its cooling purposes is drawn 
from the body of water in which the watercraft is operated, in any 
well-known manner. In order to assist in silencing and to provide some 
cooling for the exhaust manifold 45, water is delivered to the water 
jacket formed around the expansion chamber device through a supply conduit 
49. Either all or a substantial portion of the cooling water from the 
engine is delivered to this jacket through the conduit 49. It should be 
noted that this water is not, at this point, mixed with the exhaust gases. 
It should be obvious from the foregoing description that the described 
configuration means that the exhaust manifold 45 actually lies below the 
exhaust ports. Thus, this raises a risk that water might enter the engine 
through the exhaust system. However, in order to preclude this 
possibility, there is provided a transversely extending trap system 
indicated generally by the reference numeral 50 which includes an 
expansion chamber 51 which has a generally cylindrical configuration and 
which extends transversely across the rear of the engine but at a level 
that is at least as high or higher than the exhaust ports which the 
exhaust manifold runners 46 and 47 serve. The exhaust gases are delivered 
to this expansion chamber 51 through a generally L-shaped pipe section 52 
which extends upwardly from the discharge end of the exhaust manifold 45 
and may, in fact, form an integral portion of it. These exhaust gases can 
expand in the expansion chamber 51 for further silencing and then are 
discharged at the opposite end thereof through a discharge pipe 53. 
The expansion chamber device 51 is also formed with a double-wall 
construction, and this double-wall construction forms a further water 
jacket. Cooling water is delivered to this water jacket from the exhaust 
manifold cooling jacket formed around the expansion chamber 48 by a 
flexible conduit 54. This water enters one end of the expansion chamber 51 
and flows transversely across it for discharge through a discharge conduit 
55. This discharge conduit 55, in turn, discharges to an inlet conduit 56 
of a cooling jacket section 57 which encircles the exhaust pipe 53. This 
cooling jacket 57 discharges the spent cooling water into the exhaust 
system at this point through a plurality of nozzle-like spray openings. 
The water is thereafter mixed with the exhaust gases. However, since this 
introduction takes place on the low side of the expansion chamber 51, 
there is not any likelihood that the water can flow back into the engine 
through the exhaust system. Also, note that the pipe 52 that delivers the 
exhaust gases to the chamber 51 extends to its upper end, and this further 
assists in the trap-like operation of the exhaust system trap 50. 
The exhaust pipe 53 extends rearwardly along the side of the engine 
opposite the exhaust manifold 45, through the bulkhead 22, and enters into 
a water trap device 58 that is formed on one side of the tunnel that 
contains the jet propulsion unit 25. This water trap device 58 is of any 
known type and may include internal baffles that will permit the exhaust 
gases to flow freely. However it forms a sufficient volume area to permit 
water to collect before it can flow upwardly to the engine through the 
exhaust system, even though the watercraft may have been inverted and 
subsequently righted. 
A tailpipe 59 extends out of the water trap device 58 across the top of the 
jet propulsion unit 25 and the tunnel which contains it and discharges 
through a side wall 61 of the tunnel at a level that is at or near the 
water level. Although this type of discharge is incorporated, the 
trap-like arrangement of the exhaust system will ensure that any water 
which may enter the exhaust pipe 59 cannot flow back to the engine. The 
exhaust pipe 58 itself forms a trap section, and the pipe 58 operates as a 
further water trap. Also, as has been noted, the water trap 50 including 
the expansion chamber 51 also functions as a water trap because of the 
fact that it is higher than the discharge end of the exhaust pipe 59 and 
also higher than the exhaust ports with which the manifold runners 46 and 
47 cooperate. 
It has been noted that the engine crankshaft axis 28 is offset from the 
impeller shaft 24 and its axis which lies on the plane 29 (FIG. 5). In 
order to transmit the drive therebetween and to provide a step-down 
transmission, there is provided a two-stage transmission comprised of a 
first step-down gear transmission, indicated generally by the reference 
numeral 62, and a second step-up chain or belt transmission 63. These 
transmissions 62 and 63 are contained within a transfer case 64 that may 
be either formed separately from or as a part of the engine assembly. 
Preferably, a separate cover piece affixed to the cylinder block 31 and 
crankcase 27 forms this transmission closure. 
The gear transmission 62 includes a driving gear 65 that is affixed to the 
crankshaft 68 and which drives a driven gear 66 that is rotatably 
journaled on an idler or intermediate shaft. The axis of this intermediate 
shaft lies on the same side of the plane 29 as the crankshaft axis, but at 
a substantially higher level than it. The actual ratio between the gears 
65 and 66 will depend upon the total step-down that is required. 
Affixed for rotation with the driven gear 66 and journaled on the 
aforenoted intermediate shaft is a driving sprocket 67. This sprocket 
drives a drive chain or belt 68 which forms a portion of the second 
transmission 63. This drive belt or chain 68 encircles a driven pulley or 
sprocket 69 that is affixed to a stub shaft 71 that is aligned with and 
spaced forwardly of the drive shaft 24. These shafts 71 and 24 are 
connected to each other by a suitable elastic coupling 72. 
The impeller shaft 24 extends rearwardly through the bulkhead 22 as 
aforenoted and is journaled by a bearing 73 mounted on the forward side of 
the bulkhead 22. The ratio of the transmission 62 and 63 is such that the 
stub shaft 71 and impeller shaft 24 are rotated at a substantially slower 
rate of speed than the crankshaft 28 for the reasons aforenoted. 
Finally, the crankshaft 28 may also contain a gear or sprocket (not shown) 
that drives the aforenoted camshafts for the engine. 
From the foregoing description it should be readily apparent that the 
described construction provides a very compact power unit for a watercraft 
such as a personal watercraft. The power unit can be easily serviced and 
is positioned at least in part beneath the rider's seat. This which will 
ensure that the impeller shaft is driven at the appropriate speed while 
the engine can be operated at a high speed to obtain high efficiency. In 
addition, the exhaust system will ensure that water cannot enter the 
engine through the exhaust system. All of this is achieved with a compact 
construction, as should be readily apparent. 
Of course, the foregoing description is that of a preferred embodiment of 
the invention, and various changes and modifications may be made without 
departing from the spirit and scope of the invention, as defined by the 
appended claims.