Adjustable shock absorber, particularly for motor vehicles, which includes a cylinder containing damping fluid, an axially-movable piston rod which projects in a sealed manner into the cylinder, and a piston fastened to the rod and dividing the cylinder chamber into two working chambers interconnected by at least one passage which produces a damping force, the effective cross section of which can be adjusted by means of a throttle valve. The bypass includes a flexible membrane enclosed in a chamber such that on the one side of the membrane, there is at least one inflow passageway and at least one outflow passageway of the passage which can be sealed off from one another by the membrane, a control edge (or valve seat) which interacts with the membrane, and on the other side of the membrane, a control chamber carrying a control bypass flow and sealed off from the passage.

An improved hydraulic cylinder arrangement for a marine propulsion unit permits primarily effective tilt and trim movement through a compound tilt and trim cylinder. At least one first shock absorber valve is provided on a tilt piston and at least one second shock absorber valve is provided on a tilt cylinder that acts as a trim piston in a trim adjusted range operation. In another feature of the invention, a filter is disposed upstream of the second shock absorber valve.

A tilt cylinder unit for use with an outboard engine on a boat hull has a cylinder, a piston slidably disposed in the cylinder, and a rod having an end coupled to the piston. The cylinder may be coupled to the outboard engine or the boat hull, and the rod may be coupled to the boat hull or the outboard engine. The cylinder has a first chamber which is expanded when the tilt cylinder unit is extended and a second chamber which is compressed when the tilt cylinder unit is contracted, the first and second chambers being defined in the cylinder by the piston. A third chamber, which may be defined in the cylinder or an auxiliary tank separate from the cylinder has a portion filled with a gas. The second and third chambers are interconnected by an orifice, and the first, second, and third chambers are interconnected by a plurality of communication passages. A manually operable valve is coupled between the communication passages for selectively opening and closing the communication passages simultaneously.

An improved hydraulic circuit for a tilt and trim adjustment system allows an associated marine drive to be trimmed up into a tilt range for running in shallow water. The circuit includes a tilt relief valve. The valve differentiates between the hydraulic pressures within the system caused by various running conditions, and opens the valve only when two conditions are met: (i) the associated pump is activated and (ii) high pressure exists at the valve's inlet side, which usually occurs when running at high speeds. The valve, however, remains closed at slower speeds. The marine drive thus can be raised up and operated within the tilt range, provided that the speed is slow enough.

A tilt and trim unit for a marine drive eases manual trim or tilt up of the drive, while presenting a compact construction. The unit includes a cylinder having upper and lower fluid chambers. A bypass arrangement selectively bypasses a shock absorbing mechanism of the tilt and trim unit. The bypass arrangement is formed by a sub-chamber and a valve positioned in series on one side of the fluid chambers. This arrangement produces a compact construction. The valve also desirably establishes three operating states for the tilt and trim unit. In one state, the valve is open and the tilt and trim unit is easily moved. In another state, the valve is closed to prevent movement of the tilt and trim unit. In a third state, the valve operates as a one-way valve permitting extension of the tilt and trim unit to raise the marine drive, but inhibiting retraction of the tilt and trim unit. This latter operating state allows a person to raise the outboard motor and then close the valve without having to continuously hold the outboard motor when closing the valve.