Patent GB-1452829-A (GB)
Title: Power trim-tilt system
IPC: F02B61/04
Filed: 1973-12-28
Abstract: 1452829 Fluid-pressure actuators; hydraulic control circuits OUTBOARD MARINE CORP 28 Dec 1973 [4 Jan 1973] 60113/73 Headings F1D and F1P [Also in Division B7] An hydraulic system for raising and lowering an outboard motor relative to a transom on a boat comprises two hydraulic cylinder and piston assemblies 33, 35 one of which 35 is used to raise and lower the motor between operative and non- operative positions and the other of which 33 is used to trim the position of the motor when operational. To this end the assembly 33 includes two spaced and rigidly connected pistons 65, 67 allowing only limited movement within the trim range of the motor the piston-rod 59 being slidable within the sleeve 73 connecting the pistons to allow movement of the motor to its raised non-operative position by the assembly 35. The hydraulic system comprises a reservoir 43 inter-connected with a main control valve 45 and the assemblies 33, 35, pressure for the system being supplied by a reversible electric pump 41. The valve 45 includes oppositely located flow control ports 47, 49 normally closed by spring- biased valve-members 47, 49 and a central piston 121 with oppositely extending plunger portions 123 for opening the ports 47, 49. A sleeve valve 167, which is normally closed, when manually opened short-circuits the system to allow manual movement of the motor. In use with the motor in its lower most position the pump 41 is operated to pressurize line 125. This moves the piston 121 to open the port 49. The fluid-pressure opens port 47 to feed fluid to line 155 to move both piston-rods 59, 109 of the assemblies 33, 35 upwards, as shown in Fig. 3. When the piston 65 approaches the end of its movement a stem 87 slidable therein moves to open port 83 in the piston 67, thus pressurizing line 177. Check-valve 183 will not open unless the pressure increases abnormally and this will not occur until the piston 105 of assembly 35 reaches the end of its travel. Line 175 allows return of fluid from above piston 105 to the reservoir 43 via port 49. At the end of movement the ports 47, 49 are closed by valves 137, 139 hydraulically to lock the system against further movement. On downward movement line 127 is pressurized by pump 41, piston 121 opening port 47 and the piston 105 being moved by pressure from line 175. Check-valve 135 limits the pressure developed during downward movement, this being less than that required for raising the motor. If in normal use the motor strikes an underwater obstacle an abnormal pressure will be developed in line 175 causing check-valve 185 to open, and allowing the motor to clear the obstacle. After the obstacle has been passed the motor will return to its set position under gravity since the amount of fluid trapped below pistons 67, 105 has not been altered by this movement. A further embodiment is described in which the double piston arrangement in assembly 33 is not provided with port 83 and line 177 and check-valve 183 are not present. In this case a check-valve similar to the valve 135 is provided for line 125 and by-pass of the piston of assembly 35 is provided by the arrangement shown in Fig. 6 wherein the cylinder 601 is provided with an internal fixed valve stem 641 sealingly movable within a guide 627 mounted in a bore 623 in the piston-rod 609. In the position shown and on movement of the piston 605 within the trim range of the outboard motor there is no communication between one side of the piston 605 and the other, but when the stem 641 leaves the guide 627 pressure is applied from the underside of the piston 605 to a check-valve 645 which will open if excess pressures are reached allowing fluid to flow to the other side of the piston 605  by way of the annular space between the guide 627 and the bore 623 in the piston-rod and ports 661 in the piston 605.