Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE
HYDRAULICALLY POWERED MARINE PROPULSION
TILTING AND TRIMMING SYSTEM WITH MEMORY
INVENTORS
CHARLES B. HALL
ROBERT F. YOUNG
RELATED APPLICATION
This application is related to co-pending Canadian
application Serial No. 245,922, filed February 17, 1976.
BACKGROUND OF THE INVENTION
The invention relaLes generally to marine propulsion
devices such as outboard motors and stern drive units.
The invention also relates to arrangements for tilt-
ing and trimming the propulsion assemblies of such marine pro-
pulsion devices.
The invention further relates to hydraulically operated
trimming and tilting arrangements for the propulsion assemblies
of such marine propulsion devices.
Attention is directed to the following prior United
States Patents:
Mercier 3,508,400 issued April 28, 1970
Carpenter 3,722,455 issued March 27, 1973
Kurling 3,799,104 issued March 26, 1974
Shimanckas 3,847,198 issued November 12, 1974
Borst 3,863,592 issued February 4, 1975
Borst 3,885,517 issued May 27, 1975
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SUMMARY OF THE INVENTION
The invention provides a marine propulsion
device including a member adapted to be attached to
a boat hull, a propulsion assembly pivotally connected
: 5 to the member for vertical swinging movement when the
member is attached to the boat hull, a tilt hydraulic
cylinder-piston assembly connected between the member
and the propulsion assembly and including a tilt
cylinder having opposed first and second ends, a trim
hydraulic cylinder-piston assembly including a trim
cylinder fixed relative to one of the member and the
propulsion assembly, having opposed first and second
ends, and having therein a reciprocably movable trim
' piston having a piston rod extending through one of
said ends of the trim cylinder and adapted for releasable
engagement with the other of the member and the
propulsion assembly, a reversible pump including first
. and second ports, which pump is operative, when the pump
is operaitng in a first mode, to supply hydraulic fluid
under pressure at the first port and to provide suction
~. at the second port and is operative, when the pump is ~- -
i operating in a second mode, to supply hydraulic fluid
under pressure at the second port and to provide suction
.. at the first port, first conduit means communicating --
between the first end of the tilt cylinder and the first -.
' pump port and including a first valve biased so as to
releasably prevent flow from the first end of the tilt -
cylinder to the first pump port and so as to permit fluid - :-
flow from the first pump port to the first end of the
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tilt cylinder in response to the presence of hydraulic fluid
under pressure at the first pump port, second conduit
means communicating between the first end of the trim
cylinder and the first pump port, third conduit means
communicating between the second pump port and the
second ends of the trim cylinder and the tilt cylinder,
and means communicating with the second pump port for
actuating the first valve against the bias thereof and
in response to the presence of hydraulic fluid under
pressure at the second pump port so as to permit
hydraulic fluid flow from the first end of the tilt
cylinder to the first pump port.
In accordance with one embodiment of the
invention, the first valve includes a valve seat, a
valve member movable relative to the valve seat between
an open position permitting fluid flow through the
- first valve and a closed position preventing fluid
flow through the first valve, and a spring biasing the
valve member toward the closed position.
In accordance with an embodiment of the
invention, the means for actuating the first valve
comprises a housing having therein a cylinder with a
first end communicating with the second pump port, a
second end communicating with the first conduit means
intermediate the first valve and the first pump port,
and a piston located in the cylinder intermediate the
ends thereof and movable in the cylinder relative to
a position engaging the valve member to displace the
valve member to the open position in response to the
presence of hydraulic fluid under pressure at the
first cylinder end.
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In accordance with an embodiment of the
invention, the housing includes a portion of the first
conduit means including the valve seat and the valve
member and the spring are located in th e housing.
In accordance with an embodiment of the
invention, the first and second conduit means communicate
with the first pump port independently of each other.
In accordance with an embodiment of the
invention, the marine propulsion device also includes
a shuttle valve housing having a first end communicating
between the first pump port and the first and second
conduit means, and a second end communicating between
the second pump port and the third conduit means. In
addition, there is provided a second valve which is
normally closed and which communicates between the
first end of the shuttle valve housing and the second
conduit means and is arranged to releasably prevent - -
fluid flow therethrough to and from the first end of
the shuttle valve housing, and a third valve which is
normally closed and which communicates between the
second end of the shuttle valve housing and the third
conduit means and which is arranged to releasably
prevent flow therethrough to and from the second end `-
of the shuttle valve housing. Still further in addition,
the first conduit means communicates through the first
end of the shuttle valve housing with the first pump ~ `
port.
Located in thP shuttle valve housing is a
shuttle piston movable relative to a centered position
located midway between the first and second ends of the
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:
shuttle valve housing, a first end position located
adjacent to the first end of the shuttle valve housing,
and a second end position located adjacent to the
second end of the shuttle valve housing, together with
means on the piston opening the second valve when
the piston is in the first end position, and means on
~` the piston opening the third valve when the piston is
in the second end position.
In accordance with one embodiment of the
invention, the marine propulsion device further includes
additional conduit means communicating between the
first and second ends of the tilt cylinder and
including means operative for temporarily affording
" hydraulic fluid flow from the first end of the tilt
, 15 cylinder to the second end of the tilt cylinder in
., .
response to the generation of relatively high pressure
adjacent the second end of the tilt cylinder occurring
incident to the striking of an underwater obstacle. -
~, One of the principal features of the invention
is the provision of an improved selectively operable
hydraulic system for power raising and lowering a
propulsion assembly of a marine propulsion device.
~ One of the principal features of the invention
; is the provision of a marine propulsion device which
includes a hydraulic system for raising and lowering a
propulsion assembly, which hydraulic system includes -
provision for insuring return of the propulsion assembly to - ~ -
., ~.
a previously set trim position after the striking of an
'` underwater obstacle. -
, 30 Another of the principal features of the
invention is the provision of a power operated hydraulic
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system for trimming and tilting the propulsion assembly
of a marine propulsion device, which system includes
means for affording automatic let-down of the propulsion
assembly after the striking of an underwater obstacle to
a previously set trim position.
Other features and advantages of the embodiments
of the invention will become apparent from the following
general description, claims and appended drawings.
THE DRAWINGS -
Figure 1 is a partially schematic side-
elevation view, partially in section, of a marine
propulsion device incorporating various of the features
of the invention.
Figure 2 is a schematic diagram of the
hydraulic system incorporated in the marine propulsion
device shown in Figure 1.
Before explaining the embodiments of the
invention in detail, it is to be understood that the
invention is not limited in its application to the
details of construction and the arrangement of the
components set forth in the following description or
illustrated in the drawings. The invention is capable
of other embodiments and of being practiced and carried
out in various ways. Also it is to be understood that
the phraseology and terminology employed herein is for
purpose of description and should not be regarded as -
limiting.
GENERAL DESCRIPTION
Shown in the drawings is a marine propulsion
device which is shown schematically in the form of an
outboard motor 11 including a member 13 adapted to be
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suitably attached to a boat hull 15, and a propulsion
assembly 17 connected to the member 13 for vertical
swinging movement between a fully lowered position
and a fully raised position when the member 13 is
connected to the boat hull 15. Any suitable form
of propulsion assembly can be employed, including,
for instance, a swivel bracket 19 connected to the
member 13 about a horizontal tilt pin 21 and a -
propulsion unit 23 connected to the swivel bracket
13 for steering movement relative thereto. The
invention is equally applicable to stern drive units
and to outboard motors. - -
Connected between the member 13 and the
propulsion assembly 17 is (See Fig. 2) a hydraulic
system 25 for tilting and trimming the propulsion
assembly 17 relative to the boat mounted member 13.
As used herein, "trimming" refers to angular adjustment
or movement within a trim range extending up and
from the fully lowered position of the propulsion assembly
17 and "tilting" refers to angular adjustment or
movement within a tilt range extending upwardly from
the top of the trim range to the fully elevated or
raised position of the propulsion assembly 17. -
The hydraulic system 25 includes one or more
trim and tilt hydraulic cylinder-piston assemblies 31 -
- and 33, respectively, which are connected between the
member and the propulsion assembly. More particularly,
the tilt cylinder-piston assembly 33 comprises a tilt
cylinder 35 which has opposed first and second ends 37
and 39, respectively, which, at its first end 37, is
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pivotally connected to one of the member 13 and the
propulsion assembly 17, and which contains a tilt
piston 41 connected to a piston rod 43 which extends
through the second tilt cylinder end 39 and is
pivotally connected to the other of the member 13 and
the propulsion assembly 17. Preferably, the tilt
cylinder-piston assembly is connected between the
member 13 and the swivel bracket 19 and the first end ~-
37 of the tilt cylinder 35 is pivotally connected to
the member 13 and the piston rod 43 is pivotally
connected to the swivel bracket 19. --
The trim cylinder-piston assembly 33 comprises
a trim cylinder 45 which has opposed first and second ~ ;:
ends 47 and 49, respectively, which is fixed to one
of the member 13 and the propulsion assembly 17 and
which includes a trim piston 51 connected to a piston
rod 53 which extends through the second end 49 of the
trim cylinder 45, and which is releasably engagable
with the other of the member 13 and the propulsion :
assembly 17. Preferably, the trim cylinder 45 is fixed
to the member 13 and the piston rod 53 is releasably
engagable with the swivel bracket 19. -
Located in the tilt piston 41 is a one way valve
61 which is in the form of a spring biased ball check
valve and which prevents flow from the first end 37
of the tilt cylinder 35 to the second end 39, but which
permits flow from the second end 39 of the tilt cylinder
35 to the first end 37 of the tilt cylinder 35 so that,
in the event the propulsion assembly 17 impacts an
underwater obstacle and the tilt cylinder 35 accordingly
extends rapidly, the valve 61 will accommodate flow from
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thesecondend 39 of the tilt cylinder 35 through the
tilt piston 41 to the first end 37 of the tilt
cylinder 35. The bias on the valve 61 is relatively
high, for instance, about 2500 lhs./sq/in.
The hydraulic system 25 also includes
hydraulic fluid supply and control means for selectively
supplying the trim and tilt cylinder-piston assemblies -
31 and 33 with hydraulic fluid. While various means
can be employed, in the illustrated construction, such
means comprises a reservois or sump 71, a pump 73
operably connected to the sump 71, a shuttle valve 75
connected to the pump 73, and valved fluid conduits
communicating between the shuttle valve 73 and the tilt
and trim cylinders 35 and 45.
More specifically, the pump 73 is in the form
of a reversible pump which includes first and second -.
fluid connections or ducts or ports 77 and 79, respectively, ~ ~
which are arranged so that, when the pump 73 is rotating . - -
in one direction, the first duct or port 77 is supplied ~:
fluid under pressure and the second duct or port 79 is
subject to a suction condition and so that, when the pump
73 is running in the opposite direction, the duct or port
79 is supplied hydraulic fluid under pressure and the
first duct or port 77 is subject to a suction condition.
In addition, the ducts or ports 77 and 79 are respectively
connected through conduits 81 and 83 with the reservoir
71. In turn, the conduits 81 and 83 include respective
one-way valves 87 and 89 permitting flow to the pump 73
and preventing flow to the reservoir 71. Preferably, the
conduits 81 and 83 communicate with the sump or reservoir
71 through a common filter 91.
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The shuttle valve 75 comprises a housing 93
which has opposing first and second ends 95 and 97
communicating respectively with the ducts or ports 77
and 79 so that the first end 95 of the housing 93 is
pressurized when the pump 73 is rotating in one direction
and so that the second end 97 of the housing 93 is
pressurized when the pump 73 is rotating in the other
direction. The shuttle valve 75 includes therein a
piston 99 movable from a centered position to each of
first and second end positions respectively adjacent
to the first and second ends 95 and 97 of the housing 93.
Communicating with the second end 97 of the
valve housing 93 is a spring biased, normally closed
: valve 111 which also communicates through respective
conduits 113 and 115 with the second end 49 of the
trim cylinder 45 and with the second end 39 of the tilt
cylinder 35. Communicating with the first end 95 of
, the control valve housing 93 is another spring biased, -
normally closed valve 121 which communicates directly
with the first end 47 of the trim cylinder 45 through
a conduit 131.
- Means are provided on the shuttle valve piston
99 in the form of oppositely extending projections 123
and 125 for respectively opening the valves 121 and 111
when the shuttle valve piston 99 is located in the first
and second end positions. More specifically, when the
first end 95 of the shuttle valve housing 93 is pressurized,
the projection 125 opens the valve 111 to permit fluid
~, flow into the housing 93 from the second end 39 of the
tilt cylinder 35 and from the second end 49 of the trim
cylinder.
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When the second end 97 of the control valve
housing 93 is pressurized, the projection 123 opens
the valve 121 to permit inflow of hydraulic fluid from
the first end 47 of the trim cylinder 45.
When the pump 73 is not operating, the piston
99 is located in its centered position and both valves
111 and 121 are closed by their respective springs. : -
Communicating with the first end 37 of the
tilt cylinder 35 is a conduit 137 which includes a
normally closed valve 139 and which extends to the
first end 95 of the shuttle valve housing 93 and
therefore, in effect, communicates directly with the ~
first pump port 77. The valve 139 is biased so as to .
releasably prevent flow from the first end 37 of the :
tilt cylinder 35 and so as to permit flow from the first
pump port 77 to the first end 37 of the tilt cylinder
35 in response to the presence of hydraulic fluid
under pressure at the first pump port 77.
Means are also provided for actuating the
valve 139 against the bias thereof so as to permit `
hydraulic fluid flow from the first end 37 of the tilt
cylinder 35 to the first pump port 77 in response to
the presence of hydraulic fluid under pressure at the
second pump port 79. While other constructions could
be e~ployed, in the illustrated constrution, the conduit
137 includes a portion 201 communicating through the
first end 95 of the shuttle valve housing 93 with
the first pump port 77, another portion 203 communicating
: with the first end 37 of the tilt cylinder 35, and an
intermediate portion 205.
While other constructions could be employed,
- in the illustrated construction, the valve 139 includes a
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. -
valve seat 211 included in the intermediate
portion 205 of the conduit 137, together with a valve
member 213 which is in the form of a ball and which is
movable relative to the valve seat 211 between an open
position permitting hydraulic fluid flow through the
valve 139 and a closed position preventing hydraulic
fluid flow through the valve 139, and a spring 215
biasing the valve member 213 towards the closed position.
While other constructions could be employed,
in the illustrated construction, the intermediate conduit
portion 205, the valve 139, and the valve actuating means
are incorporated in a housing 231 which includes a
cylinder 233 having a first end 235 communicating through
a conduit 239 with the second pump port 79, together with
a second end 239 communicating with the intermediate conduit
portion 205. In the specifically illustrated construction,
the conduit 237 communicates with the second pump port 79
through ~he valve 111 and through the second end 97 of - --
the shuttle valve housing 93. In addition, the cylinder 233
includes a piston 241 located intermediate the ends 233
and 239 of the cylinder 233 and having a projection 243
extending towards the valve member 213. The piston is
movable, in response to the pressure of hydraulic fluid -
j under pump pressure at the first end 235 of the cylinder
- 25 233, to a position with the projection 243 engaging the
valve member 213 so as to displace the valve member 213 ~ -
to the open position. In addition, the piston 241 is
movable away from the position opening the valve member
213 in response to the presence at the second end 239
of the cylinder 233, i.e., in the intermediate conduit
portion 205, of hydraulic fluid under pump pressure.
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The hydraulic system 25 also includes let-
down means providing automatic transfer of hydraulic fluid
from the first end 37 of the tilt cylinder 35 to the
second end 39 of the tilt cylinder 35 in order to
accommodate let-down of the propulsion assembly 17 after
the striking of an underwater obstacle. More particularly,
there is hydraulically connected between the ends 37 and
39 of the tilt cylinder 35 an automatic let-down assembly
151 which includes an actuating valve 153 which is in the
form of a normally closed spring biased check valve, and
which communicates through a conduit 154 with the second
end 39 of the tilt cylinder 35 and which is arranged
to prevent flow to the second end 39 of the tilt cylinder
35 and to releasably prevent or permit flow from the
second end 39 of the tilt cylinder 35 therethrough. The
bias on the valve 153 is relatively high, for instance,
about 2500 lbs.lsq.in.
Also included in the let-down valve assem~ly
151 is a letdown valve 155 including a housing 157 having
a first end 159 communicating with the valve 153 and a
second end 161 communicating with a by-pass valve 163
j;,,(
which is in the form of a normally closed spring biased
~, check valve and which, in turn, communicates through
: a conduit 165 with the portion 203 of the conduit 137
which, in turn, communicates with the first end 37 of
the tilt cylinder 35. The bias on the valve 163 is
. relatively low, for instance, about 25 lbs./sq.in.
-` Located within the let-down valve housing 159
: is a let-down piston 171 which is movable between a
first position adjacent to the first end 159 of the
; let-down valve housing 157 and a second position spaced
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:
from the first position in the direction toward the
second end 161 of the let-down valve housing 157.
The let-down piston 171 includes a restricted orifice
or slot 172 which communicates between the first and
second ends of the let-down valve housing 157. In
addition, the let down piston 171 also includes a
projection 173 which is operable, upon movement of
the piston 171 to the second position, to open the
valve 163 so as to permit fluid flow from the first
end 37 of the tilt cylinder 35 into the let-down valve
housing 157.
Communicating between the second end of the
let-down valve housing 157 and the second end 39 of
the tilt cylinder 35 is conduit means including a -.-
conduit 175 extending from adjacent the second end 161
of the let-down valve housing 157 to the sump 71, and
a conduit 177 extending from the sump 71 to the second .
end 39 of the tilt cylinder 35 and including a one-way
valve 179 preventing flow to the sump 71 and permitting
flow from the sump 71. Included in the conduit 177 is
the fil~er 91.
The hydraulic system 25 also includes a
normally closed overload or relief valve 191 which
communicates with the conduits 137 and 165 and with the
conduit 175 and which is in the form of a normally closed
spring biased check valve arranged so as to permit flow
from the conduits 137 and 165 to the conduit 175 and
to prevent flow from the conduit 175 to the conduits 137
and 165 and hence to p-ermit hydraulic fluid flow from
the first end 37 of the tilt cylinder 35 to the sump 71
in the event excess thrust is developed during operation
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of the propulsion assembly 17. In addition, when the -
shuttle valve piston 99 is in the position providing
power operated upward movement of the propulsion assembly
17, the overload valve 191 prevents overloading of the
pump 73 by permitting bypassing of the pressure fluid
to the sump 71 whenever movement of the trim piston
51 or tilt piston 41 is blocked, or when the propulsion
assembly 17 is in the fully raised position. It is
noted that the spring bias on the valve 191 is greater
than the spring bias on the valve 139.
The hydraulic system 25 also includes a
pressure relief valve 193 which communicates with the
sump 71 through a conduit 195 which communicates with
the second end 97 of the shuttle valve housing 93, and
which is operative to permit flow from the second end
97 of the shuttle valve housing 93 to the sump 71 in -
the event of excess pressure when the shuttle piston
99 is in the position providing power operated lowering
of the propulsion assembly. In addition, the relief
valve 193 also operates, when the shuttle valve piston
99 is in the position affording power operated raising
of the propulsion assembly 17, to prevent the relatively
high pressures resulting from impact or shock absorption
from adversely affecting the pump 73. The pressure relief
valve 193 is preferably in the form of a normally closed,
- spring biased check valve and has a spring bias which is
- greater than the valve 111.
The hydraulic system 25 also includes a conduit
197 which connects the opposed ends 37 and 39 of the tilt
cylinder 35 and which includes a manually operable valve
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:` 199 permitting bypass of fluid around the tilt piston 41
to accommodate manual raising and lowering of the
propulsion assembly 17.
In operation and when it is desired to raise
the propulsion assembly 17 by power operation, the pump
73 is operated in the proper direction to pressurize
the first end 95 of the shuttle valve housing 93 so as to
displace the piston 99 toward the end 97 of the shuttle
valve housing 93, thereby opening the adjacent valve 111.
At the same time, the pump pressure opens the other valve
121 against its spring to supply pressure fluid through
the conduit 131 to the first end 47 trim cylinder 45.
In addition, pressurized hydraulic fluid flows through :
~ the conduit 137 and through the valve 139 to the first
`~ 15 end 37 tilt cylinder 35.
At the same time, hydraulic fluid adjacent
to the second end 39 of the tilt cylinder 35 and hydraulic
fluid adjacent to the second end 49 of the trim cylinder ~-
45 flows through the conduits 113 and 115 past the open ~ -
valve 111 through the second end 97 of the valve housing
93 and through the second duct or port 79 to the intake
of the pump 73. Make-up fluid is drawn from the sump 71
through the conduit 83 and through the check valve 89. ~ -
, In the event there is an obstruction to upward
; 25 travel of the propulsion assembly 17 or at the end of
such travel, the hydraulic fluid supplied by the pump 73
flows back to the sump 71 through the conduit 137 including : :
the valve 139, through the conduit 165, and through the -- -
overload valve 191 which operates as a pressure relief
valve, and through the conduit 175 to the sump 71.
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During power operated lowering of the
propulsion assembly 17, the pump 73 is operated in the
opposite direction, and serves to deliver hydraulic
fluid through the second duct or port 79 to the second
end 97 of the shuttle valve housing 93, thereby opening
the adjacent valve 111 and displacing the shuttle valve
piston 99 to the position adjacent the first end 95 of
the shuttle valve housing 93 so as to also open the valve
121. Hydraulic fluid flows through the valve 111 and
through the conduit 113 to the second end 49 of the trim
cylinder 45 so as to retract the piston rod 51 and through
the conduit 115 to the second end 39 of the tilt cylinder
35 to contract the trim cylinder-piston assembly 31.
At the same time, hydraulic fluid flows through
the conduit 237 and acts against the piston 241 to
displace the piston 241 so as to open the valve 139 against
the action of the spring 215 and thereby to permit flow
of hydraulic fluid from the first end 37 of the tilt
cylinder 35 back to the first pump port 77 for return
to the pump 73.
Also during power operated lowering of the
propulsion assembly 17, hydraulic fluid from the first
end 47 of the trim cylinder 45 flows through the conduit
131 and valve 121 to the first pump port 37 for return
to the pump 73.
If there is an obstruction to movement of
the propulsion assembly 17, or at the end of such
movement when the propulsion assembly 17 is in the
fully lowered position, pressure fluid produced by the
pump 73 is returned to the sump 71 via the pressure ?
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: relief valve 193 through the conduit 195. Fluid is
` supplied to the pump 73 from the sump 71 for priming
purposes through the conduit 81 and check valve 87.
In the event the propulsion assembly 77 strikes
an underwater obstacle, sudden upward movement of the
propulsion assembly 17 will cause extension of the tilt
cylinder 35 and consequent immediate relatively high
pressurization of the hydraulic fluid adjacent to the
,' second end 39 of the tilt cylinder 35. Under such
circumstances, the hydraulic fluid flows past the tilt
piston 41 through the valve 61 from the second end 39
to the first end 37 of the tilt cylinder 35 so as to
permit such extension. As the pump 73 is not running,
the shuttle valve piston 99 is centered and both -
valves 111 and 121 are closed. During the period when
the second end 39 of the tilt cylinder 35 is highly
pressurized, such pressurization will be imparted
through the conduit 154 to open the valve 153 so as
to permit passage of a relatively small amount of highly
pressurized hydraulic fluid therethrough to the first
end 159 of the let-down valve housing 157, which fluid
is effective to displace the let-down piston 171 from
the first position to the second position.
Upon full extension of the tilt cylinder 35,
the pressure condition at the second end 39 thereof will
be relieved and the valve 153 will again close preventing
return of the hydraulic fluid at the first end 159 of
the let-down valve housing 157 through the valve 153
, to the second end 39 of the tilt cylinder 35, thereby
temporarily retaining the let-down valve piston 171 in
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the second position so as thereby to retain the valve
163 open.
Upon reaching the fully raised position, the
propulsion assembly 17 will tend to return downwardly
either because of impacting at the fully raised position
or simply because of the weight of the motor. Temporary
maintenance of the open condition of the valve 163 by
the let-down valve piston 171 permits contraction of
the tilt cylinder 35 accompanying lowering of the
propulsion assembly 17. In this regard, contraction
of the tilt cylinder 35 causes outflow of hydraulic
fluid from the first end 37 thereof, which outflow
travels through the conduit 165, through the valve 163
into the second end 161 of the let-down valve housing 157
and through the conduit 175 back to the sump 71. At the
same time, the expanding space at the second end 39 of
the tilt cylinder 35 draws hydraulic fluid from the
sump 71 through the filter 91, and through the conduit
177 including the one-way valve 179 to the second end
39 of the tilt cylinder 35 to maintain the second end 39
of the tilt cylinder 35 fully occupied with hydraulic
fluid.
Referring to the hydraulic fluid trapped at the
first end 159 of the let-down valve housing 157, such
fluid gradually flows through the restricted orifice or
slot 172 to the second end 161 of the let-down valve
housing 157 and then through the conduit 175 to the sump
71. Such travel of the trapped fluid past the let-down
piston 171 causes return movement of the let-down piston
171 toward the first end 159 of the let-down valve housing
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157 under the influence of the spring biasing the valve
163 to the closed position, thereby eventually again
permitting closing the valve 163 after completion of
fluid flow from the first end 37 of the tilt cylinder
35 to the sump 71, Thus, the hydraulic system 25 is
again conditioned for power operation, up or down, or
for another impact.
Pressurization of the hydraulic fluid at the
second end 39 of the tilt cylinder 35 also serves to
pressurize the hydraulic fluid at the first end 235
of the valve housing 231. Such pressurization causes
movement of the piston 241 so as to displace the valve
member 213 to the open position. However, as hydraulic
fluid at the first end 37 of the tilt cylinder 35 is
not under pressure during upward swinging of the
propulsion assembly 171, there is no flow through the
valve 139. When the propulsion assembly 17 starts its - :
downward movement, the pressure of the hydraulic fluid ~ . -
at the first end 235 of the housing 231 is relieved and
the spring 215 serves to displace the valve member 213
to the closed position and to return the piston 241 ---
toward the first end 235 of the housing 231. Thus,
although the valve 139 is opened in response to the
striking of an underwater obstacle, such opening does
not resul~ in any material flow of hydraulic fluid
through the valve 139.
It is particularly noted that the first end : -
37 of the tilt cylinder 35 is hydraulically isolated
from the first end 47 of the trim cylinder 45 as the
trim cylinder 45 is connected to the first pump port 77
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through the conduit 131 and valve 121 independently of
: connection of the tilt cylinder 35 to the first pump
port 77 through the conduit 137 and valve 139. Thus,
hydraulic flow relative to the tilt cylinder 35 occurring
consequent to the striking of an underwater obstacle does not
affect the position of the trim piston 51. Thus, the
trim piston 51 does not move during impact tilting or
letdown return, and thus the propulsion assembly 17 will
always return after an impact to the previously set
trim position. It is also noted that the pump 73 is
isolated from the relatively high pressures generated
in the second end 93 of the tilt cylinder 35 by sudden
impact of the propulsion assembly 17 with an underwater
obstacle by reason of the centered position of the valve
15 piston 99 and the closed condition of the valve 111.
Various of the features of the invention are
set forth in the following claims.
-21-
;
.
