Marine propulsion – Screw propeller – With vibration dampening
Reexamination Certificate
1999-12-10
2001-11-27
Swinehart, Ed (Department: 3617)
Marine propulsion
Screw propeller
With vibration dampening
C440S083000
Reexamination Certificate
active
06322407
ABSTRACT:
PRIORITY INFORMATION
This application is based on and claims priority to Japanese Patent Application No. 10-352887, filed Dec. 11, 1998, and to Japanese Patent Application No. 11-17372, filed Jan. 26, 1999, the entire contents of which are hereby expressly incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a marine drive transmission, and more particularly to a relatively compact marine drive transmission that smoothly shifts into both the forward or reverse drive conditions.
2. Description of Related Art
A wide variety of marine propulsion units propel watercrafts. For instance, outboard motors commonly power boats and other watercraft. Stem drive units, which include an inboard motor and an outboard drive, also are often used to power boats and watercraft.
An outboard motor conventionally includes a power head at the top of the drive unit. The power head includes an internal combustion engine having an output shaft extending generally vertically. A driveshaft housing of the drive unit depends from the power head and encloses a driveshaft that extends generally vertically from the output shaft. A lower unit further depends from the driveshaft housing. A propeller shaft is provided therein and extends generally horizontally. The driveshaft and the propeller shaft are connected in the lower unit so that the propeller shaft extends normal to the driveshaft. A propulsion device such as, for example, a propeller is affixed to an outer end of the propeller shaft. A bevel gear transmission, for example, is provided between the driveshaft and the propeller shaft that includes a forward, neutral, reverse shift mechanism for switching over to one of forward, neutral and reverse positions from another position. The engine power is transmitted to the propeller through the output shaft, driveshaft, bevel gear transmission and propeller shaft. The propeller, thus, can propel the outboard motor and the associated watercraft in both forward and reverse directions, if the shift mechanism is not in the neutral position.
An outboard section of the stem drive unit has a construction similar to that of the outboard motor except that it has no engine atop thereof. The engine is placed in the hull of the associated watercraft. A propulsion device of the stem drive unit, which typically is a propeller, is powered by the engine through the driveshaft and propeller shaft combination (i.e., drive train arrangement) similar to that of the drive unit of the outboard motor.
Consumers continue to desire more powerful marine drives and prefer large propulsion units having engines which produce high horsepower. An engine, for example, which operates on a four stroke principle and having a plurality of cylinders, can provide the desired increased horsepower.
However, due to carrying such a large engine, the marine propulsion unit tends to jolt the occupants of the watercraft when the shift mechanism is operated and thereby gives the occupants an uncomfortable feeling. That is, since the large-sized engine generates a relatively large propulsion force, it gives rise an uncomfortable shock to the occupants by abrupt change of the propulsion force particularly when the shift mechanism is shifted from the neutral position to the forward drive position or to the reverse drive position.
In order to address this problem, a smoothing device for the shifting operation has been proposed in U.S. Pat. No. 4,747,796.
FIGS. 1 and 2
illustrate this type of coupling and correspond to
FIGS. 11 and 12
of U.S. Pat. No. 4,747,796.
FIGS. 1
illustrates a cross-sectional, side elevational view of a conventional coupling
20
arranged to absorb the shock, and
FIG. 2
illustrates a cross-sectional view of the same coupling
20
taken along the line
2
—
2
in FIG.
1
.
With reference to these figures, a driveshaft
22
is divided into a drive section
24
and a driven section
26
and the coupling
20
is provided therebetween to couple them. The lower end of the drive section
24
has a depending flange
28
that defines an internal cavity
30
. The upper end of the driven section
26
has a projecting portion
32
that extends into the cavity
30
. Three blocks of elastic members
34
are interposed between the internal cavity
30
and the projecting portion
32
. As seen in
FIG. 2
, the flange
28
and its internal cavity
30
have a generally triangular configuration. The projecting portion
32
is also triangular in shape with three apices
38
.
The coupling
20
provides vibration damping and force absorption under low speed and load conditions. This damping is provided by the elastic members
34
that are compressible by certain compressive force exerted thereupon. When the driving loads are increased, the elastic members
34
are extremely compressed and the apices
38
of the projecting portion
32
directly contact inner cavity
30
of the flange
28
of the drive portion
24
. The torque of the drive section
24
is transmitted to the driven section
26
by this connection.
Because the transmission shifting shock occurs under the low speed condition, the coupling
20
is quite useful for preventing the shock from occurring when the shift mechanism is shifted. However, another problem appears with this coupling
20
. The problem is that the driving force is not securely transferred from the drive section
24
to the driven section
26
when the driving loads increase. Because the driving force is conveyed by the contacts of the apices
38
with the inner cavity
30
and these contacts are not so reliable. Of course, the elastic members
34
are also involved in this force transferring mechanism. However, the elastic members
34
are slippery in the cavity
30
and do not increase reliability.
SUMMARY OF THE INVENTION
It may improve this situation to increase contact areas of the apices
38
with the cavity
30
or to employ elastic members that have large volume. Both of the improvements, however, would need a large size of housing and would thereby interfere with the arrangement of other components disposed in the housing. A need therefore exists for a marine drive transmission that can absorb a shock generated when a forward, neutral, reverse shift mechanism is shifted, with a structure as compact as possible. In addition, after the shift mechanism is shifted into the forward or reverse position, the coupling desirably securely transmits the driving force from a drive section to a driven section.
In accordance with one aspect of the present invention, a power transmission system for a marine propulsion unit comprises a first shaft arranged to be driven by a powering element. A second shaft is driven by the first shaft. The first shaft and the second shaft have a common axis. A propulsion device is arranged to be driven by the second shaft for propelling the marine propulsion unit. A first coupling mechanism and a second coupling mechanism are provided for coupling the first shaft and the second shaft. A second coupling mechanism is spaced apart from the first coupling mechanism in a direction along the common axis. The first shaft and the second shaft are coupled with each other selectively by one of the first coupling mechanism and a second coupling mechanism.
In accordance with another aspect of the present invention, a coupling for a power transmission system which includes a drive shaft and a driven shaft. The coupling comprises a first section continuously connecting the drive shaft with the driven shaft. A second section engages the drive shaft with the driven shaft when the driven shaft is driven by the drive shaft under a driving load condition that is greater than a predetermined level. The second section overrides the first section after the drive shaft is engaged with the driven shaft, i.e., the second section takes precedence over the first section as the primary mechanism for transferring torque from the drive shaft to the driven shaft. The drive shaft and the driven shaft have a common axis. The second section is spaced apart from the first sec
Knobbe Martens Olson & Bear LLP
Sanshin Kogyo Kabushiki Kaisha
Swinehart Ed
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