Trim-tilt device for a marine propulsion unit

In a trim-tilt device for a marine propulsion unit 20, a cylinder 41 of a cylinder device 21 is covered with a tank 28 constituting a hydraulic fluid supply/discharge device 22 and a relief valve 131 is opened when hydraulic pressure of the tank 25 becomes higher than a fixed value, so that hydraulic fluid of the tank 25 can be relieved for the second tilt chamber 32B.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a trim-tilt device for a marine propulsion
 unit such as an outboard motor or inboard/outboard motor.
 2. Description of the Related Art
 Conventionally, the trim-tilt device for a marine propulsion unit has a
 cylinder device interposed between a hull and the propulsion unit which is
 tiltably supported by the hull. By controlling supply and discharge of
 hydraulic fluid from a hydraulic fluid supply/discharge device to a
 cylinder device or vise versa, the cylinder device is expanded and
 contracted to thereby trim and tilt the marine propulsion unit.
 A prior art trim-tilt device for a marine propulsion unit is described in
 Japanese Patent Application No. 11-112856. This application suggests a
 cylinder device for a trim-tilt device for a marine propulsion unit
 comprising a housing connected to one of a hull and a marine propulsion
 unit and which forms a large-diameter trim chamber. A cylinder is
 telescopically inserted into the trim chamber of the housing which forms a
 small-diameter tilt chamber. A large-diameter trim piston is fixed to an
 end portion of the cylinder within the trim chamber of the housing which
 partitions the trim chamber into a first trim chamber of a cylinder
 accommodation side and a second trim chamber of an anti cylinder
 accommodation side. A piston rod is connected to the other of the hull and
 the marine propulsion unit and is telescopically inserted into the tilt
 chamber of the cylinder. A small-diameter tilt piston is fixed to an end
 of the piston rod within the tilt chamber of the cylinder which partitions
 the tilt chamber into a first tilt chamber of a piston rod accommodation
 side and a second tilt chamber of an anti piston rod accommodation side.
 Additionally, in the cylinder device, a portion of the cylinder or the
 cylinder device which projects outward from the housing in the trim
 operable region is covered with a tank housing constituting a hydraulic
 fluid supply/discharge device. According to this embodiment, since the
 cylinder of the cylinder device does not touch water in the outside, it is
 covered with the tank housing and it can be rustproof easily and steadily
 by hydraulic fluid within the tank housing.
 In the above mentioned trim-tilt device for a marine propulsion unit
 disclosed in Japanese Patent Application No. 11-112856, if the operation
 of the pump of the trim-tilt device stops in a trim operable region (the
 state in which the cylinder device does not finish the trim-up operation)
 during forwarding sailing and an obstacle in the water such as a floating
 log etc., collides with the propulsion unit such that a hydraulic fluid
 supply/discharge flow passage, from the hydraulic fluid supply/discharge
 device to the cylinder device, is locked, the piston rod and the cylinder
 in a body carry out a trim-stroke to the housing and the tank housing. At
 this time, in the trim-tilt device of the propulsion unit, due to the
 boosting of the hydraulic pressure at the locked state in a first tilt
 chamber, a buffer valve of a tilt piston is opened to transfer this
 hydraulic pressure to a second tilt chamber, so that an impact can be
 absorbed.
 However, when the piston rod the cylinder transfer (trim-stroke) to the
 housing and the tank housing as described above, there is a possibility
 that the tank housing which is made of resin is destroyed due to the rapid
 increase of an internal pressure of the tank, or an end plate of the pump
 motor which is made of resin is destroyed, that covers a pump chamber
 provided so as to communicate to the tank.
 SUMMARY OF THE INVENTION
 The object of the present invention is to avoid an abnormal application of
 pressure of the pump by movement of a cylinder according to the collision
 of an obstacle in the water or the like in the case that a cylinder of a
 cylinder device is covered with a tank housing of a hydraulic fluid
 supply/ discharge device in a trim-tilt device for a marine propulsion
 unit.
 According to the present invention, there is disclosed a trim-tilt device
 for a marine propulsion unit, wherein a cylinder device is mounted between
 a hull and the marine propulsion unit freely tiltably supported by the
 hull. A hydraulic fluid is supplied from a hydraulic fluid
 supply/discharge device into the cylinder device and is discharged from
 the cylinder device into the hydraulic fluid supply/discharge device to
 thereby expand and contract the cylinder device and thereby trim and tilt
 the marine propulsion unit.
 The cylinder device comprises:
 a housing connected to one of the hull and marine propulsion unit to form a
 large-diameter trim chamber;
 a cylinder telescopically inserted into the trim chamber and forming a
 small-diameter tilt chamber;
 a large-diameter trim piston fixed to an end portion of the cylinder within
 the trim chamber of the housing and serving to partition the trim chamber
 into an first trim chamber of a cylinder accommodation side and a second
 trim chamber of an anti cylinder accommodation side;
 a piston rod being connected to the other of the hull and the marine
 propulsion unit that is telescopically inserted into the tilt chamber of
 the cylinder; and
 wherein the cylinder device has a small-diameter tilt piston comprising a
 buffer valve which is fixed to an end of a piston rod within a tilt
 chamber of the cylinder, which partitions a tilt chamber into a first tilt
 chamber of a piston rod accommodation side and a second tilt chamber of an
 anti piston rod accommodation side and which is open when hydraulic
 pressure of the first tilt chamber becomes higher than a fixed value, so
 that a hydraulic fluid of the first tilt chamber can transfer to the
 second tilt chamber.
 A portion of the cylinder of said cylinder device which projects outward
 from the housing in the trim operable region is covered with a tank
 housing constituting a hydraulic fluid supply/discharge device, comprising
 relief valve which is opened when a hydraulic pressure of the tank becomes
 higher than a fixed value, so that hydraulic fluid of the tank can be
 relieved for the second trim chamber to avoid an abnormal application of
 pressure of the pump by movement of the cylinder due to addition of the
 impact in the direction that expands the cylinder device to the marine
 propulsion unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 As shown in FIG. 1, a marine propulsion unit 10 in the form of an outboard
 motor, or an inboard/outboard motor, has a damp bracket 12 fixed to a
 stern board 11A of a boat hull 11. To the clamp bracket 12 a swivel
 bracket 14 is pivoted through a tilt shaft 13 and is tiltable about the
 substantially horizontal shaft. To the swivel bracket 14 a propulsion unit
 15 is pivoted through a steerage-changing shaft that is substantially
 vertically disposed, and not illustrated, in such a way that the
 propulsion unit 15, is rockable about the steerage-changing shaft. An
 engine unit 16 is loaded at the top of the propulsion unit 15 and a
 propeller 17 is fitted to a lower part of the propulsion unit 15.
 In the marine propulsion unit 10, the propulsion unit 15 is tiltably
 supported by the damp bracket 12 fixed to the hull 11 through the tilt
 shaft 13 and swivel bracket 14. A cylinder device 21 of a trim-tilt device
 20 is interposed between the clamp bracket 12 and the swivel bracket 14.
 The cylinder device 21 is expanded and contracted by supply or discharge
 of hydraulic fluid between a hydraulic fluid supply/discharge device 22
 and the cylinder device 21. The propulsion unit 15 is thereby made
 tiltable in a trim or tilt region of FIG. 1. It is to be noted that the
 marine propulsion unit 10 may take an optimum sailing posture with respect
 to the water surface by retaining the propulsion unit 15 in a state of a
 relatively gentle slope within the trim region.
 (Cylinder Device 21)
 As illustrated in FIGS. 1 and 2, the cylinder device 21 of the trim-tilt
 device 20 has a housing 31 that is used by being connected to the damp
 bracket 12, the housing 31 having a large-diameter trim chamber 32 formed
 therein. It is to be noted that the housing 31 is casted-molded using, for
 example, an aluminum alloy, and is equipped with a mounting-pin insertion
 hold 33 for mounting the housing onto the damp bracket 12.
 Also, the cylinder device 21 has a cylinder 41 which when the trimup/down
 operation in the trim region is performed becomes telescopically inserted
 into a trim chamber 32 from a cylinder guide 34 provided in an open end of
 the housing 31, the cylinder 41 having a small-diameter tilt chamber 42
 formed therein. The cylinder guide 34 is screwed to an opening end of the
 housing 31 and is provided with a seal member 35 such as an O-ring or the
 like which closely contacts with the trim chamber 32 and a seal member 36
 such as an O-ring or the like which slides on an outer surface of the
 cylinder 41.
 Also, the cylinder device 21 has a large-diameter trim piston 51 screwed
 and fixed to an end portion of the cylinder 41 that is situated in the
 trim chamber 32 of the housing 31. The trim piston 51 is equipped with a
 seal member 52 such as an O-ring which slides on an inner surface of the
 trim chamber 32 and partitions the trim chamber 32 into a first trim
 chamber 32A on a cylinder 41 accommodation side and a second trim chamber
 32B on an anti cylinder 41 accommodation side.
 Also, the cylinder device 21 has a piston rod 61 that is provided by being
 connected to the swivel bracket 14. The piston rod 61 is inserted into the
 tilt chamber 42 for a rod guide portion 43 that is provided in an open end
 of the cylinder 41 as to be expanded and contracted when the tilt-up/down
 operation in the tilt region is performed. The rod guide portion 43 is
 equipped with a seal member 44 such as an O-ring which is in sliding
 contact with an outer surface of the piston rod 61. The piston rod 61 is
 equipped with a mounting-pin insertion hole 62A for mounting the cylinder
 device 21 onto the swivel bracket 14 to an mounting joint 62.
 Also, the cylinder device 21 has a small-diameter tilt piston 71 that is
 fixed to an end portion of the piston rod 61 situated within the tilt
 chamber 42 of the cylinder 41 by a nut 71B through a washer 71A. The tilt
 piston 71 is equipped with an seal member 72 such as an O-ring which is in
 sliding contact with the inner surface of the cylinder 41, and partitions
 the tilt chamber 42 into a first tilt chamber 42A on a piston-rod 61
 accommodation side and a second tilt chamber 42B on an anti piston-rod 61
 accommodation side.
 The tilt piston 71 has an expansion side buffer valve 73 and a check valve
 74. The expansion side buffer valve 73 is opened by a set pressure for the
 purpose of guarding a hydraulic circuit when an impact is received in the
 expansion direction at cylinder device 21, as for example, when an
 obstacle such as a floating log or the like collides with the propulsion
 unit 15, and transfers the hydraulic fluid of the first tilt chamber 42A
 to a side of a free piston 81 as later described situated within the
 second tilt chamber 42B, thereby enabling the expansion of the piston rod
 61. At this time, the free piston 81 remains at its own position and only
 the tilt piston 71 alone works. The check valve 74 is opened when after
 the valve described opening of the expansion side buffer valve 73 the tilt
 piston 71 of the piston rod 61 tends to return by the weight of the
 propulsion unit 15 to the original position to thereby return the
 hydraulic fluid between the tilt piston 71 and the free piston 81 to the
 first tilt chamber 42A
 Also, the cylinder device 21 has the free piston 81 which is usually set to
 the position of its contact with the tilt piston 71 within the second
 tiltchambers 42B and 42C of the cylinder 41. The free piston 81 is
 equipped with a seal member 83 such as an O-ring which contacts the inner
 periphery of the cylinder 41.
 Additionally, the free piston 81 has a reset one-way valve 82 (shown in
 FIG. 6, not shown in FIG. 2). When the marine propulsion unit 10 in a
 forward motion collides with an obstacle, when the brake is applied to the
 marine propulsion unit 10 in a forward motion, or when the external force
 in the expansion direction of the cylinder device 21 is applied for some
 reason upon start-up of the operation, the reset one-way valve 82 is
 opened so that it is reset to the former position, in which the tilt
 piston 71 and the free piston 81 contact each other. Further, when a
 buffer valve at the expansion side 73 is opened to extend the piston rod
 61, a hydraulic fluid which is transferred from the first tilt chamber 42A
 to the second tilt chamber 42B is inserted between the tilt piston 71 and
 the free piston 81. Here, the free piston 81 is at the lowest position and
 the free piston 81 moves forward while compressing the piston rod 61 by
 the pump action, the reset one-way valve 82 is opened so that it is reset
 to the former position, in which the tilt piston 71 and the free piston 81
 contact each other.
 In the cylinder device 21, the cylinder 41 may be formed of iron material
 by forging, and on outer pipe 41B and the above-mentioned rod guide
 portion 43 may be integrally formed by forging, so that the number of
 assembling steps is reduced and a high strength is achieved. An inner pipe
 41A is sandwiched between a recessed portion provided at an inner end face
 of the rod guide portion 43 and a recessed portion provided at an inner
 end face of the above-mentioned trim piston 51 screwed to the outer pipe
 41B, so that the cylinder 41 is structured as a tilt cylinder assembly. As
 a result of this, the cylinder 41 has a doubled-pipe structure comprising
 the inner pipe 41A and the outer pipe 41B, where a gap between the inner
 pipe 41A and the outer pipe 41B, is used as a communication passage 46 for
 communicating the first trim chamber 32A and the first tilt chamber 42A
 with each other. The first trim chamber 32A is connected directly to a
 first flow passage 91 formed in the housing 31 while on the other hand the
 first tilt chamber 42A is connected to the first flow passage 91 through a
 passage 91A formed in the inner pipe 41A of the cylinder 41, a passage 91B
 formed in the outer pipe 41B of the cylinder 41, a passage 91C formed in
 the trim piston 51, and the first trim chamber 32A As a result of this,
 the first trim chamber 32A and the first tilt chamber 42A are connected,
 (a) through the first flow passage 91, with the supply side of the
 hydraulic fluid supply/discharge device 22 during the contraction stroke
 of each of the trim and tilt operations and, (b) through the first flow
 passage 91, with the discharge side of the hydraulic fluid
 supply/discharge device 22 during the expansion stroke of each thereof.
 In the cylinder device 21, the trim piston 51 has a through-hole like
 communication passage 53 for connecting together second trim chamber 32B
 and the second tilt chamber 42C. The second trim chamber 32B is connected
 directly to a second flow passage 92 formed in the housing 31 and the
 second tilt chamber 42C is connected to the second flow passage 92 through
 the free piston 81 and the communication passage 53 of the trim piston 51
 and the second trim chamber 32B. As a result of this the second trim
 chamber 32B and the second tilt chamber 42C are communicated (a) for the
 second flow passage 92, with the supply side of the hydraulic
 supply/discharge device 22 during the expansion stroke of each of the trim
 and tilt operations and (b) through he second flow passage 92 with the
 discharge side of the hydraulic fluid supply/discharge device 22 during
 the contraction stroke of each thereof.
 (Hydraulic Fluid Supply/Discharge Device 22)
 The hydraulic fluid supply/discharge device 22 comprises a reversible motor
 23, a reversible gear pump 24, a tank 25, and a switching-valve equipped
 flow passage 26, by which the hydraulic fluid can be supplied and
 discharged, through the first flow passage 91 and the second flow passage
 92, between the hydraulic fluid supply/discharge device 22 and the first
 trim chamber 32A, second trim chamber 32B, first tilt chamber 42A and a
 second tilt chamber 42C of cylinder device 21.
 At this time, as illustrated in FIG. 5, the hydraulic fluid
 supply/discharge device 22 is arranged with a mounting base 23A for
 mounting a motor 23 installed on a motor installation surface 31A formed
 in the housing 31 of the cylinder device 21. The mounting base 23A is
 fixed thereto by bolts 27, whereby the motor 23 is laterally juxtaposed
 with the cylinder 41 of the cylinder device 21.
 The hydraulic fluid supply/discharge device 22 has a void space portion
 that forms a side of the trim chamber 32 in the housing 31 of the cylinder
 device 21 in such a way as to surround the same and uses this void space
 portion as the tank 25 in which the hydraulic fluid is stored. As opening
 25A is formed in the portion within the tank 25 of the housing 31 which
 corresponds to a lower portion of the motor 23, whereby a fitting portion
 23B that connects to the mounting base 23A of the motor 23 is
 fluid-tightly fitted into the opening 25A through a seal member 25B such
 as an O-ring. Under the motor 23 within the tank formed in the housing 31,
 the pump 24 is fixedly disposed in a state of essentially constant
 immersion in the fluid, whereby an output shaft 23C protruding from the
 fitting portion 23B of the motor 23 is connected to a driven shaft 24A of
 the pump 24.
 Additionally, in the embodiment of the present invention, a portion of the
 cylinder 41 of the cylinder device 21 which projects outward from the
 cylinder guide 34 of the housing 31 in the trim operation area is covered
 with a sub-tank housing 28 constituting the hydraulic fluid
 supply/discharge device 22. The sub-tank housing 28 is made of, for
 example, resin, a lower end opening portion of the sub-tank housing 28 is
 fitted on the cylinder guide 34, and a lower end flange portion 28A of the
 sub-tank housing 28 is fluid-tightly fastened to an opening end face of
 the housing 31 through an O-ring 29A by bolts 30. An upper end opening
 portion of the sub-tank housing 28 is provided with a seal member 28B such
 as an oil seal or the like which allows sliding of the piston rod 61
 fluid-tightly. As a result of this, the sub-tank housing 28 is provided in
 a standing manner along the longitudinal directions of the cylinder 41 and
 the piston rod 61 with a constant clearance about the cylinder 41 and the
 piston rod 61, thereby forming a sub-tank 28C. The sub-tank 28C
 communicates with the above-mentioned tank 25 of the housing 31 through a
 passage 28D formed in the cylinder guide 34 and a passage 28E formed in
 the housing 31. In FIGS. 3 and 4, reference numeral 28F denotes an oil
 syringe plug.
 The switching-valve equipped flow passage 26 of the hydraulic fluid
 supply/discharge device 22 which connects the pump 24 to the first flow
 passage 91 and second flow passage 92 is built in the housing 31, the
 switching valve equipped flow passage 26 being provided with a shuttle
 type switching valve 101, check valves 102 and 103, contraction side
 relief valve 104, expansion side relief valve 105, contraction side buffer
 valve 106A and manual switching valve 107.
 The shuttle type switching valve 101 has a shuttle piston 111 and a first
 check valve 112A and second check valve 112B that are located on both
 sides of the shuttle piston 111, and defines a first shuttle chamber 113A
 on the first check valve 112A side of the shuttle piston 111 and defines a
 second shuttle chamber 113B on the second check valve 112B side of the
 shuttle piston 111. The first check valve 112A is opened by the pressure
 of the transmission fluid applied to the first shuttle chamber 113A
 through a pipe passage 93A by the pump 24 rotating in the forward
 direction. The second check valve 112B can be opened by the pressure of
 the transmission fluid applied to the second shuttle chamber 113B through
 a pipe passage 93B by the pump 24 rotating in the reverse direction. Also,
 the shuttle piston 111 opens the second check valve 112B by the pressure
 of the transmission fluid resulting from the forward rotation of the pump
 24 and can open the first check valve 112A by the pressure of the
 transmission fluid resulting from the reverse rotation of the pump 24.
 The first check valve 112A of the shuttle type switching valve 101 is
 connected to the first flow passage 91 and the second check valve 112B is
 connected to the second flow passage 92.
 A check-valve 102 is mounted on a connection pipe passage 94A between the
 pump 24 and the tank 25. In the tilt-up stage of the marine propulsion
 unit 10, the internal volume of the cylinder 41 is insufficient in volume
 and the piston rod 61 is retracted, with the result that the circulating
 amount of the hydraulic fluid becomes deficient by that extent. Therefore,
 the check valve 102 is opened to thereby supplement from the pump 25 to
 the pump 24 the portion which corresponds to the deficiency of the
 circulating amount of fluid.
 A check valve 103 is mounted on a connection pipe passage 94B between the
 pump 24 and the tank 25. The pump 24 is still in an operative stage at the
 point in time when, at the trim-down stage of the marine propulsion unit
 10, the trim piston 51 reaches its position of maximum contraction at
 which the trim-down stage is completed. As a result the return fluid from
 the second trim chamber 32B to the pump 24 stops, and the check valve 103
 is opened whereby the hydraulic fluid can be supplied from the tank to the
 pump 24.
 The contraction side relief valve 104 is connected to the first shuttle
 chamber 113A. The contraction side relief valve 104is intended to permit
 the hydraulic circuit pressure to be relieved into the tank 25 under a set
 pressure in order to return to the tank 25 the amount of fluid
 corresponding to the volume of the rod, which is to remain at the time of
 the tilt-down and trimdown operations, and in order to guard the hydraulic
 circuit while continuing to operate the pump 24 even after the trim-down
 operation has been completed.
 The expansion side relief valve 105 is built into the shuttle piston 111.
 The valve 105 is intended to permit the hydraulic circuit pressure to be
 relieved into the tank 25 under a set pressure in order to guard the
 hydraulic circuit while continuing to operate the pump 24 even after the
 tilt-up operation time is completed, and the piston rod 61 has reached its
 position of maximum expansion.
 The contraction side buffer valve 106A is intended to relieve the hydraulic
 circuit pressure under a set pressure into the tank 25 when an impact has
 been applied to the propulsion unit 15 in the contraction direction of the
 piston rod 61, for example, when an obstacle has bumped against the
 propulsion unit 15 from behind, with the tilt piston 71 and free piston 81
 of the cylinder device 21 being located at an intermediate position of the
 tilt chamber 42.
 The manual switching valve 107 is interposed on a connecting passage 95
 between the first flow passage 91 and the second flow passage 92, and by
 connecting the first flow passage 91 and the second flow passage 92 and
 the tank 25 with each other. This permits manual expansion and contraction
 of the cylinder device 21 to thereby make the propulsion unit 15 tiltable
 in each of the trim and tilt regions.
 Further, in order to avoid that a tilt-up operation is carried out faster
 than a trim-up operation when the cylinder device 21 expands (up), even
 when an external force, such as a backward driving force during backward
 sailing or an uplifting force of a wave tending to raise the marine
 propulsion unit 15, acts in the direction for expanding the cylinder
 device 21, the marine propulsion unit 10 has a check valve 121 and a
 relief valve 122 in the hydraulic fluid supply/discharge device 22. In the
 hydraulic fluid supply/discharge device 22 the check valve 121 allows the
 hydraulic fluid to flow from the pump 24 to the first trim chamber 32A and
 the first tilt chamber 42A and the relief valve 122 which is opened if the
 hydraulic pressure of the first trim chamber 32A and the hydraulic
 pressure of the first tilt chamber 42A become higher than a fixed value
 are connect in parallel to the first flow passage 91 connecting the first
 trim chamber 32A and the first tilt chamber 42A to the pump 24. Therefore,
 even when an external force, such as a backward driving force during
 backward sailing or an uplifting force of a wave to raise a marine
 propulsion unit 15, acts in the direction for expanding the cylinder
 device 21, the cylinder device 21 is provided so as to operate
 telescopically so that it can start a tilt-up movement of the tilt piston
 71 after the cylinder device 21 finishes the trip-up movement of the trim
 piston 51.
 Additionally, FIG. 7 illustrates a relief valve 122 comprising a check
 valve 121, a valve body 123, a valve sheet 124 which is pressed into the
 valve body 123, a blind plug 125, a ball 126 of the check valve 121, a
 ball 127 of the relief valve 122, a spring sheet 128 and a relief spring
 129.
 The marine propulsion unit 10 has a relief valve 131 in the hydraulic fluid
 supply/discharge device 22, to avoid an abnormal application of pressure
 of the tanks 25 and 28C caused during forward sailing, where the operation
 of the pump 24 of the trim-tilt device 20 stops in a trim operable region,
 the state in which the cylinder device 21 does not finish the trim up and
 an obstacle in the water such as a floating log etc., collides with the
 propulsion unit 15. When the hydraulic fluid supply/discharge flow
 passages 91 and 92, from the hydraulic fluid supply/discharge device 22 to
 the cylinder device 21, are locked, a piston rod 61 and the cylinder 41
 carry out a trim-stroke in a body to the housing 31, the tank housing 28
 and the tanks 25 and 28C. The relief valve 131 is provided on a bottom in
 which a pump 24 is fixed on a lower part of a motor 23 of the tanks 25.
 The relief valve 131 is connected to a flow passage 95 (92) communicating
 with the second trim chamber 32B. The relief valve 131 is opened due to
 the boosting of the hydraulic pressure in the tanks 25 and 28C beyond a
 fixed value so that it can transfer the hydraulic fluid of the tanks 25
 and 28 into the second trim chamber 32B. Thus, an abnormal application of
 hydraulic pressure of the tanks 25 and 28C by transfer of the cylinder 41
 (trim-stroke) can be avoided when the obstacle in the water collides with
 the propulsion unit 15 and the impact is added in the expansion direction
 of the cylinder 21.
 FIG. 8 illustrates the relief valve 131, a valve body 132, a valve collar
 133 which is pressed into the valve body 132, a ball 134 and a relief
 spring 135.
 The operation of the trim-tile device 20 will hereafter be explained.
 (1) Trim-Up
 When the motor 23 and pump 24 are rotated in reverse, the hydraulic fluid
 discharged from the pump 24 flows from the pipe passage 93B to the second
 shuffle chamber 113B of the shuffle type switching valve 101, whereby the
 shuffle piston 111 moves to the right side in FIG. 6 to thereby forcibly
 open the first check valve 112A. Also, the hydraulic fluid that has flown
 into the second shuttle chamber 113B of the switching valve 101 forcibly
 opens the second check valve 112B by its own pressure and is thereby sent
 to the second trim chamber 32B through the pipe passage 92 as indicated by
 a solid-line arrow. The hydraulic fluid that has flowed into the second
 trim chamber 32B in this way tends to push up the trim piston 51. It is to
 be noted that the hydraulic fluid of the second trim chamber 32B not only
 acts on the trim piston 51 but also acts on the tilt piston 71 in close
 contact with the trim piston 51 through the through-hole connecting
 passage 53 of the trim piston 51. Since the pressure receiving area of the
 connecting passage 53 is set so that the pressure receiving area of the
 trim piston 51 may be larger than that of the tilt piston 71, the trim
 piston 51 pushes up and moves the tilt piston 71. At this time, the
 hydraulic fluid of the first trim chamber 32A flows out into the first
 flow passage 91 and further returns to the pump 24, and therefore the trim
 piston 51 is moved. Simultaneously, the cylinder 41 and piston rod 61 are
 caused to protrude outwardly from the housing 31, whereby trim-up occurs.
 When the trim piston 51 has collided with the stroke end in the trim-up
 direction within the first trim chamber 32A, the trim-up is maximized.
 (2) Tilt-Up
 After under the above item (1) the trim piston 51 has been moved up to a
 level corresponding to the maximum trim-up the hydraulic fluid within the
 second trim chamber 32B. The hydraulic fluid is further supplied to the
 second trim chamber 32B extends from the through-hole like connecting
 passage 53 formed in the trim piston 51 to an anti-piston rod 61 side of a
 tilt piston 71 end surface through the free piston 81. As a result of
 this, the hydraulic fluid supplied to the second trim chamber 32B is
 filled in to the second tilt chamber 42C formed while being gradually
 expanded between the trim piston 51 within the cylinder 41 and the free
 piston 81, and the tilt piston 71. The hydraulic fluid within the first
 tilt chamber 42A flow out into the first flow passage 91 through the
 passage 91A formed in the rod guide portion 43 of the cylinder 41,
 connecting passage 46 of the cylinder 41, passage 91B formed in the outer
 cylinder 41B of the cylinder 41, passage 91C formed in the trim piston 51
 and first trim chamber 32A Therefore, the tilt piston 71 and the free
 piston 81 are moved together. As a result of this, the piston rod 61
 protrudes outwardly from the cylinder 41, whereby tilt-up occurs. When the
 tilt piston 71 collides with the stroke end in the tilt-up direction
 within the first tilt chamber 42A, the tilt-up reaches it's maximum.
 (3) Tilt-Down
 When the motor 23 and pump 24 are rotated in a forward direction, the
 hydraulic fluid discharged from the pump 24 flows from the pipe passage
 93A into the first shuttle chamber 113A of the switching valve 101,
 whereby the shuttle piston 111 is moved to the left side in FIG. 6 to
 thereby forcibly open the second check valve 112B. The hydraulic fluid
 that has flown into the first shuttle chamber 113A of the switching valve
 101 forcibly opens the first check valve 112A by its own pressure and, as
 indicated by a broken-line arrow, is sent from the first flow passage 91
 to the first tilt chamber 42A through the first trim chamber 32A, passage
 91C, passage 91B, communication passage 46 of the cylinder 41 and passage
 91A When hydraulic fluid flows into the first tilt chamber 42A in this
 way, the hydraulic fluid pushes down the tilt piston 71, and the free
 piston 81. At this time, the hydraulic fluid of the first trim chamber 32A
 acts on the trim piston 51. However, the pressure-receiving area of the
 tilt piston 71 facing the first tilt chamber 42A is so set as to become
 larger than that of the trim piston 51 facing the first trim chamber 32A
 and therefore only the tilt piston 71 alone is depressed until the tilt
 piston 71 collides with the trim piston 51. As a result of this, the
 piston rod 61 is retracted into the cylinder 41 and is tilted down. At
 this time, the hydraulic fluid of the second tilt chamber 42C flows out
 from the through-hole connecting passage 53 of the trim piston 51 into the
 second flow passage 92 through the second trim chamber 32B and further
 into the pump 24. When the tilt piston 71 collides with the trim piston 51
 that is kept at the stroke end on the trim-up direction of the trim
 chamber 32, the tilt-down is completed.
 (4) Trim-Down
 When after the tilt-down described above (3) terminates, the hydraulic
 fluid is supplied to the first trim chamber 32A and first tilt chamber
 42A, the tilt piston 71 and the free piston 81 is depressed down to the
 second trim chamber 32B side integrally with the trim piston 51. The
 hydraulic fluid within the second trim chamber 32B flows out into the
 second passage 92, with the result that the cylinder 41 and the piston 61
 are retracted further into the housing 31 for trim-down operation. And
 when the trim piston 51 collides with the stroke end in the trim-down
 direction within the second trim chamber 32B, the trim-down is completed.
 Here, in the trim-tilt device 22, during a transition process from the
 trim-up to the tilt-up operation under the above items (1) and (2) and
 during a transition process from the tilt-down to the tri-down operation
 under the above items (3) and (4), the effective area of each of the
 pistons 51 and 71 varies between the large-diameter trim piston 51 and the
 small-diameter tilt piston 71. For this reason, the transfer speed of the
 piston rod 61 is such that transition speed in the trim region is less
 than that in the tilt region while, on the other hand the force that acts
 on the piston rod 61 is such that this force in the trim region is greater
 than in the tilt region. In the above-described embodiment, it is
 possible, (a) in the trim region, to finely adjust the trim angle while
 resisting the trust force of the propeller and also to sail in a shallow
 water area, and (b) in the tilt region, it is possible to quickly perform
 tilt up/down operations with a relatively small magnitude of force that is
 necessary for supporting the weight of the propulsion unit itself.
 Therefore, the present embodiment has the following effects.
 (A) Securing a trim-up operation when an external force for expanding the
 cylinder device 21 acts during backward sailing or the like
 (1) The check valve 121 and the relief valve 122 are connect in parallel to
 the hydraulic fluid flow passage 91 in which the first trim chamber 32A
 and the first tilt chamber 42A are connected to the pump 24. The check
 valve 121 introduces the discharging fluid of the pump 24 into the first
 trim chamber 32A and the first tilt chamber 42A (an upper chamber) upon a
 down operation of the cylinder device 21. The relief valve 122 can carry
 out an up operation only when the hydraulic pressure of the first trim
 chamber 32A and the first tilt chamber 42A increases upon an up operation
 to push open the relief valve 122. Accordingly, if the discharging
 hydraulic fluid of the pump 24 is supplied to the second trim chamber 32B
 (a lower chamber) in order to carry out an up operation of the cylinder
 device 21 when an external force, such as a backward driving force during
 backward sailing or an uplifting force of a wave to raise a marine
 propulsion unit 15, acting in the direction for expanding the cylinder
 device 21, the hydraulic pressure of the second trim chamber 32B increases
 the hydraulic pressure of the first trim chamber 32A and the first tilt
 chamber 42A (an upper chamber) through the trim piston 51 and the tilt
 piston 71. At this time, the relief valve 122 is dosed until the increased
 hydraulic pressure is increased to reach the relief pressure so that the
 hydraulic pressure flow passage from the first tilt chamber 42A to the
 pump 24 absorption side is kept unlocked. When the hydraulic pressure of
 the first trim chamber 32A and the first tilt chamber 42A increases to
 reach the relief pressure, the relief valve 122 is opened and the trim
 piston 51, which has a larger pressure-receiving area at the lower chamber
 side than that of the tilt piston 71, carries out an up operation ahead of
 the tilt piston 71.
 (2) The set pressure P of the relief valve 122 describe above in (1) is
 desirably larger that the external force Fa such as a backward driving
 force acting on the pressure receiving area S of the tilt piston 71. The
 set pressure P satisfies P&lt;Fa/S. For example, it is assumed that P is
 30 kgf/cm.sup.2. In this case, when the relief pressure P is excessively
 high, the efficiency of the pump 24 is decreased and it suffers from a
 heavy load. Therefore, for example, it is determined that P=30.+-.10
 kgf/cm.sup.2. However, because of the influence by the lost pressure in a
 pipe passage or the friction or the like, the relief pressure P may be
 smaller that the valve in P&gt;Fa/S.
 (B) Avoidance of an abnormal application of pressure of the tank 25 by
 transfer of the cylinder 41 (a trim-stroke) according to the collision
 with an obstacle in the water,
 (1) The relief valve 131, that is opened due to the increase of the inner
 pressure of the tanks 25 and 28C greater than a fixed value and transfers
 the hydraulic fluid of the tanks 25 and 28C to the second trim chamber
 32B, is provided. Accordingly, when the marine propulsion unit 15 collides
 with an obstacle in the water, the piston rod 61 and the cylinder 41 carry
 out in a body a trim-stoke in the tank housing 28. Therefore, even when
 the internal pressure in the tanks 25 and 28C suddenly increases, it is
 possible to let out the inner pressure immediately to the second trim
 chamber 32B side by the above-mentioned relief valve 131. Thus, it becomes
 possible that an abnormal application of pressure of the tanks 25 and 28C
 is avoided, the housing 28 made of resin is prevented from being
 destroyed, or an end plate which is made of resin of the pump motor 23,
 covering the pump chamber which is provided in communicating with this
 tank 28C is prevented from being destroyed.
 (2) In order to absorb an abnormal application of pressure of the tanks 25
 and 28C, it is not necessary to increase the air capacity of the tanks 25
 and 28C, so that the tanks 25 and 28C are prevented from increasing in
 size.
 (3) The value of the set pressure of the relief valve 131 described above
 may be small if the relief valve 131 is not opened by a small negative
 pressure of the tanks 25 and 28C, namely, it may be small enough to get
 the stability of an opening valve operation of the relief valve 131. For
 example, the value of the set pressure of the relief valve 131 may be
 between 1-3 kgf/cm.sup.2.
 The present embodiment has the following effect.
 (1) Since the cylinder 41 if the cylinder device 21 is covered with the
 tank 28C, it is prevented from contacting with outer water and it is
 easily and reliably made rustproof by hydraulic fluid in the tank housing
 28. As a result of this, even when the cylinder 41 serving as a member for
 transmitting a propulsion force (axial compressing force) between the hull
 11 and the marine propulsion unit 15 is made of metal material such as
 iron, such that a predetermined strength for accommodating forces can be
 secured at a small area, it is unnecessary to structure the cylinder 41
 with a high grade rustproof material or to perform a rustproof treatment
 such as coating, so that the number of machining steps for rustproof
 treatment can be reduced and cost can be decreased.
 (2) Since the outer surface of the cylinder 41 is made rustproof according
 to the above (1), rust does not occur thereon. Therefore, even when the
 cylinder 41 repeatedly slides on the seal member 35 of the cylinder guide
 34 provided on the housing 31 in the trim operation area, the outer
 surface of the cylinder 41 does not scratch the seal member 35.
 (3) The tank housing 28 of the hydraulic fluid supply/discharge device 22
 covers the entire of the cylinder 41 projecting outward from the housing
 31 along the longitudinal direction of the cylinder 41. As a result of
 this, the tank housing 28 extends along the longitudinal direction of the
 cylinder 41 and it does not budge laterally about a proximal portion of
 the cylinder 41 so that the trim-tilt device 20 can be made compact.
 Here, the housing 31 of the cylinder device 21 is formed of, for example,
 aluminum alloy by forging integrally with the tank 25 of the hydraulic
 fluid supply/discharge device 22, and it is not prevented from rusting.
 Also, the sub-tank housing 28 is made of, for example, resin to be
 rustproof.
 Incidentally, such a treatment as plating can be performed on the outer
 peripheral surface of the cylinder 41, thereby improving sliding
 performance of the housing 31 with respect to the cylinder guide 34.
 (4) Since the first trim chamber 32A and the first tilt chamber 42A have
 been interconnected with each other by the passage 46 provided in the wall
 of the cylinder 41, the exposure to the outside of the pipes of hydraulic
 fluid supplied and discharged from the supply/discharge device 22 to
 cylinder device 21 can be suppressed. As a result of this, the outer
 appearance of the cylinder device 21 is compact and there is no likelihood
 that exposed piping will be damaged and that hydraulic fluid will leak
 from the connection. At this time, since the connecting passage 46 between
 the first trim chamber 32A and the first tilt chamber 42A is provided
 within the wall of the cylinder 41, the cylinder device 21 is simple in
 construction.
 (5) The portions where the cylinder device 21 should be fluid-tightly
 sealed are only four in number and those include a portion (seal member
 35) where the cylinder 41 slides on the cylinder guide 34 provided in the
 housing 31, a portion (seal member 52) where the trim piston 51 slides on
 the inner surface of the trim chamber 32 of the housing 31, a portion
 (seal member 44) where the piston rod 61 slides with respect to the rod
 guide portion 43 provided in the cylinder 41 and a piston seal member 72
 where the tilt piston 71 slide on the inner surface of the tilt chamber 42
 of the cylinder 41. Therefore, the sealability of the cylinder device 21
 is greatly improved
 (6) The tilt piston 71 is moved up and down merely by sliding contact of
 its outer peripheral portion with the inner surface of the tilt chamber 42
 of the cylinder 41 which is made during tilt operation. Therefore, the
 assembling efficiency and slideability thereof are high and so the
 tilt-operating efficiency is improved.
 (7) By making the cylinder 41 of the cylinder device 21 into a double
 cylinder structure, the double cylinder structure is made up through the
 connection of the inner pipe 41A and the outer pipe 41B and the gap
 between both pipes 41A and 41B can be used as the connecting passage 46
 between the first trim chamber 32A and the first tilt chamber 42A As a
 result of this, construction of the cylinder device 21 is greatly
 simplified.
 (8) By building the pump 24, the tank 25 and the switching valve equipped
 flow passage 26 of the hydraulic fluid supply/discharge device 22 into the
 housing 31 of the cylinder device 21, the connecting flow passages between
 the hydraulic fluid supply/discharge device 22 and the cylinder device 21
 are not outwardly exposed, and it is possible to eliminate all use of
 exposed piping over the entire trim-tilt device 20 with (4).
 (9) The hydraulic fluid supply/discharge device 22 is integrally assembled
 to the cylinder device 21. By respectively connecting the housing 31 and
 the piston rod 61 of the cylinder device 21 to the hull 11 and marine
 propulsion unit 10, the mounting of the hydraulic fluid supply/discharge
 device 22 also is simultaneously completed.
 However, in the present invention, the connecting passage that is built
 into the wall of the cylinder and that connects the first trim chamber and
 the first tilt chamber with each other may be constructed of a hole-like
 passage formed in the wall of the cylinder. At this time the cylinder may
 be formed by using a casting and the hole-like passage may be formed by
 casting. Or, the cylinder may be formed using a pipe and the hole-like
 passage may be formed in the wall of the pipe.
 As heretofore explained, embodiments of the present invention have been
 described in detail with reference to the drawings. However, the specific
 configurations of the present invention are not limited to the embodiments
 but those having a modification of the design within the range of the
 present invention are also included in the present invention.
 As mentioned above, according to the present invention, it is an object to
 avoid an abnormal application of pressure of the pump by movement of a
 cylinder according to the collision of an obstacle in the water or the
 like in the case that a cylinder of a cylinder device is covered with a
 tank housing of hydraulic fluid supply/discharge device in a trim-tilt
 device for a marine propulsion unit.
 Although the invention has been illustrated and described with respect to
 several exemplary embodiments thereof, it should be understood by those
 skilled in the art that the foregoing and various other changes, omissions
 and additions may be made to the present invention without departing from
 the spit and scope thereof Therefore the present invention should not be
 understood as limited to the specific embodiment set out above, but should
 be understood to include all possible embodiments which can be embodied
 within a scope encompassed and equivalents thereof with respect to the
 features set out in the appended claims.