Stern drive gimbal arrangement

In a stern drive for watercraft, of the type using a gimbal ring to support the external propulsion unit, the gimbal ring is provided with an upper vertical square bore, a slot across the bore, and clamping bolts to provide full engagement with the square sides of a steering swivel shaft.

BACKGROUND OF THE INVENTION 
This invention relates to a stern drive for watercraft and particularly to 
a gimbal ring steering arrangement for use with a stern drive. 
Kiekhaefer, in U.S. Pat. No. 3,136,285, describes a steering arrangement 
having a gimbal ring with a generally vertical steering swivel shaft 
rotatably disposed in a transom bracket attached to the transom of a 
watercraft. The drive unit is pivotally supported by the gimbal ring on a 
generally transverse horizontal axis to provide tilt movement. In this 
arrangement the steering swivel shaft is attached to the gimbal ring by a 
splined connection. Such an arrangement has proven highly satisfactory 
because it permits a steering arm to be attached to the steering swivel 
shaft and extend forwardly through the transom mounting opening and into 
the interior of the watercraft, thereby providing a compact arrangement 
which allows the steering control means to attach to the steering arm 
inside the boat. This prior art device fails to achieve full contact 
between the mating surfaces of the steering swivel shaft and the gimbal 
ring. 
One other prior art device utilized a square bore in the gimbal ring and a 
complementary steering swivel shaft section to replace the splined joint 
disclosed by Kiekhaefer. The swivel shaft of this device was split along 
its axis through the square section and used a screw on the shaft axis to 
spread the shaft and force it into contact with the gimbal ring. This 
device failed to achieve contact along the full vertical length of the 
mating surfaces. 
SUMMARY OF THE INVENTION 
The inventors have found that in a gimbal ring steering arrangement of the 
aforementioned type substantially full contact along the full length of 
the engaging portions of the gimbal ring and the steering swivel shaft can 
be achieved by: 
(1) using a vertical gimbal ring bore having a cross-section with four or 
less sides; 
(2) using a steering swivel shaft having a lower cross-section 
complementary to the cross-section of the vertical gimbal ring bore; and 
(3) providing the gimbal ring with a means to clamp the sides of the 
vertical gimbal ring bore against the complementary sides of the steering 
swivel shaft.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 illustrates a stern drive 15 and gimbal housing assembly 20 mounted 
to the transom 11 of a boat 12. An internally mounted engine 13 is secured 
within the boat 12 and connected through a universal joint 14 to the stern 
drive 15. The stern drive 15 generally includes a drive shaft housing 16 
having a horizontal drive shaft 17 and a vertical drive shaft 18. The 
horizontal drive shaft 17 is connected by a universal joint 14 to a shaft 
19 which in turn is connected to the crankshaft of the engine 13. 
The gimbal housing assembly 20 secures the stern drive 15 to the transom 
11. The gimbal housing assembly 20 generally includes a gimbal housing 21 
and a transom seal 22 for sealing the transom opening 23. The gimbal 
housing assembly 20 also includes openings through which the shaft 19 and 
engine exhaust tube 24 extend. The gimbal housing assembly 20 further 
includes a bell housing 25 pivotally attached by horizontal pivots 27 to 
the gimbal ring 26. The gimbal ring 26 is in turn attached to the gimbal 
housing 21 by upper and lower swivel shafts 28 and 29. The bell housing 25 
is bolted to the drive shaft housing 16. 
A steering lever 30 is attached to the upper swivel shaft 28 to provide 
steering control of the stern drive 15. The steering lever 30 is held in 
place by a retaining screw and nut 31A and nut 31. In practice, the 
internal end of the steering lever 30 may be controlled by any 
conventional boat steering system such as a steering wheel and cable 
system. 
FIGS. 2, 3, and 4 are views showing details of the preferred embodiment of 
the gimbal ring 26. The gimbal ring 26 is made of cast aluminum and has 
horizontal bores 32 to provide a pivotal attachment to the bell housing 
25. The upper gimbal ring bore 35 is square in cross-section and is formed 
by a broaching operation. The forward and aft corners 36 and 37 of the 
bore 35 are rounded to provide stress relief and the bore walls are 
provided with a substantial thickness for added strength both fore and 
aft. 
A slot 38 is provided transversely across the top of the gimbal ring 26, 
running across the side corners of the square bore 35. The slot 38 is 
formed deeper than the bore 35 so that the sides of the bore 35 will 
remain substantially parallel when clamped against the sides of the upper 
gimbal ring shaft 28 by means of the bolts 39, which run through holes 40 
in the gimbal ring 26. 
FIGS. 5 and 6 are enlarged views of the preferred embodiment of the upper 
swivel shaft 28. The shaft has a square cross-section 41 for engagement 
with the square bore 35 of the gimbal ring 26. The shaft 28 also includes 
a circular cap 42 at the lower end for correctly locating the bearing 
surfaces 43 and 46 in the gimbal housing assembly 20. In addition, male 
splines on section 44 engage with female splines on the steering lever 30, 
and the shaft 28 is axially positioned by a nut 31 engaging with the 
threaded section 45. 
The upper gimbal ring bore 35 and the square section 41 of the steering 
swivel shaft 28 are designed to have a minimal clearance for initial 
assembly, but to produce substantially full engagement of the 
corresponding flat surfaces when clamping pressure is applied by bolts 39. 
The effect of tightening bolts 39 is to produce a clamping action between 
the fore and aft sides of the bore 35. Full contact between the engaging 
sufaces is assured by placing the bolt holes 40 near the lower end of the 
bore 35, as most clearly seen in FIG. 3. This accommodates for the bending 
in the fore and aft sides of the slot 38 as the bolts 39 are tightened. 
Though the preferred embodiment of the invention has a square upper bore 35 
in the gimbal ring 26 and a corresponding square section 41 in the upper 
swivel shaft 28, it is recognized that other cross-sections, such as 
triangular or rectangular, could be used. Whatever section is used, it 
must be readily clamped by a small number of bolts to produce 
substantially full engagement between the mating surfaces, thereby 
securely retaining the upper swivel shaft in the gimbal ring.