HYDRAULIC CYLINDER FOR A PROPULSION UNIT OF AN INBOARD OR OUTBOARD MOTOR

Abstract: A hydraulic cylinder serving as a tilting unit for a pro­ pulsion unit of an inboard or outboard motor is pivotally connected to the hull of a boat and its associated piston rod is pivotally connected to the propulsion unit. In order to act as a shock absorber when the propeller strikes an obstacle the piston (4) is formed with an oil hole (7) hav­ ing a check valve (8). The effect of possible leakage through the check valve (8) is overcome by the provision of a disc valve (13) having two concentric annular elastic sealing members and biased by a spring (14) against a cover plate (17) formed with holes (18) and constituting one face of the piston (4). The space between the sealing members is thus in communication with the end of the oil hole (7) and the disc valve (13) thus operates in series with the check valve (8) to prevent leakage of oil during operation.

Description: Hydraulic cylinder for a propulsion unit of an inboard or outboard motor In small craft such as motorboats, the propeller is. formed as part of a propulsion unit and the position of the propeller with respect to the hull may be operated by a hydraulic cylinder, which may also act as a shock absorber if the propeller strikes an obstacle when under way. The cylinder thus acts as a tilting unit for lifting the propeller when the boat is on land and for setting it at the most efficient angle, i.e. trimming it, when under way. In order to act as a shock absorber to prevent breakage when the propeller strikes an obstacle, an oil hole for generating a damping force needs to be formed in the piston of the cylinder forming the tilting unit and must be provided with a non-return or check valve. However, with the construction of cylinder described in U.S. patent no: 3,003,724 the check valve tends to leak while holding the propeller in the trimmed position while under way and therefore the set angle of the propeller will gradually vary. An object of this invention is to provide a hydraulic cylinder for the propulsion units of either inboard or outboard motors which does not suffer from this defect and which will provide a shock absorbing action with adequate damping force if the propeller strikes an obstacle. In accordance with this invention, a hydraulic cylinder for a propulsion unit of an inboard or outboard motor comprises an oil cylinder having an oil inlet and outlet port at each end and a piston fitting in the cylinder and having an oil hole fitted with a check valve and also including a disc valve having two concentric annular sealing members made of elastic material which is biased against one face of the piston so that the space between the two sealing members is in communication with the end of the oil hole whereby the disc valve may open and close the oil hole simultaneously with the check valve according to the direction of movement of the piston. The piston thus includes two valves arranged in series. The addition of the disc valve with its elastic sealing members prevents any leakage of oil during operation and the check valve controls the damping force under shock conditions. Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram showing a hydraulic cylinder according to the present invention as used in an outboard motor; Figure 2 is a longitudinal sectional view showing an embodiment of the present invention; Figure 3 is a plan view of a disc valve shown in Figure 1; Figure 4 is a sectional view on line IV - IV in Figure 2; Figure 5 is a longitduinal sectional view to an enlarged scale of an alternative form of piston; Figure 6 is a view similar to Figure 4 of still another form of piston; and Figure 7 is a schematic diagram showing a hydraulic cylinder according to the present invention as used in an inboard motor. As shown in Figures 1 and 2, a piston 4 is slidably fitted in an oil cylinder 3 having oil inlet and outlet ports 1 and 2 at respective ends, the piston rod 5 extending through one end of the oil cylinder 3. The piston 4 is fitted with an 0-ring 6 and is formed with an oil hole 7 fitted with a non-return or check valve 8 comprising a steel ball biased into contact with a seating at the end of the hole 7 by a coil spring 9. In addition, as shown in the plan view of Figure 3 and the sectional view of Figure 4, a disc valve 13 comprising concentric annular sealing members 11 and 12 made of elastic material such as rubber secured to one face of an annular base plate 10 co-operates with the lower face of the piston 4. The valve 13 is biased by means of a comparatively weak spring 14 so that the annular space between the sealing members 11 and 12 communicates with the opening at the lower side of the valve 8 in the oil hole 7. The piston 4 has an annular groove 15 in its lower surface, into which the oil hole 7 opens. The groove is closed by a cover plate 17 which is sealed by an 0-ring 16 and has a number of holes 18 communicating with the space between the sealing members 11 and 12. In use, the oil. cylinder 3 is pivotally connected to the hull H of the boat and the rod 5 is pivotally connected to a propulsion unit U -comprising the propeller and motor. When pressure oil is fed in through oil port 2 the rod 5 is extended and the propeller will be lifted above the water level to the position shown in dotted lines in Figure 1. By adjusting the piston 4 to an appropriate position and closing the oil port 1, the propeller can be set at the most efficient angle for propulsion purposes. In the alternative arrangement of Figure 7, as applied to an inboard motor, the oil cylinder 3 is again pivotally connected to the hull H of the boat and the rod 5 is connected to the propulsion unit P which includes the propeller, gearing and so forth, but not the motor, which is mounted inboard and is not shown, the drive being taken through a drive shaft S and flexible coupling C. If in the propulsion position the propeller strikes an obstacle, the rod 5 will have an upward force exerted on it so that the check valve 8 and the disc valve 13 will open and the piston 4 will move upwards. The propeller will thus be prevented from damage and the damping force will be set to an appropriate value by the force of the spring 9. Since the pressure receiving area of the ball check valve 8 is so small, a desired damping force can be obtained with a very small and weak spring 9. As the ball check valve 8 cannot completely prevent the reverse flow of oil, in the absence of the disc valve 13 the high pressure oil would gradually leak into the space above the piston 4 and the propeller setting angle would fluctuate. However, since the disc valve 13 is fitted with sealing members 11 and 12 of material such as rubber, the leakage can be completely prevented and the propeller setting angle can be prevented from fluctuating while under way. The pressure receiving area of the disc valve 13 is so large that, if an appropriate damping force were to be obtained from the valve 13, the spring 14 would have to be made very large and strong. However, in a cylinder according to the present invention, the damping force is obtained from the ball check valve 8, and the function of the valve 13 is to prevent leakage under steady conditions. Consequently the spring 14 can be made quite weak and small or can even be omitted altogether and the valve device is thus quite small and light. In the alternative construction of piston shown in Figure 5, a cavity 19 is formed in the upper face of the piston 4 in communication with several oil holes 7 and is sealed by a cover plate 21 having small holes 20. A disc valve 22 is formed by an elastic member arranged in the cavity 19 so as to close the holes 20. An 0-ring 23 is fitted to the piston rod 5. Therefore, when the piston 4 moves upwardly, the valve member 22 will bend as shown by the chain dotted lines and the holes 20 will open. Thus, exactly the same operation and effect can be obtained as in the previous example. Figure 6 shows a modification of the construction of Figure 5 in which, in order to prevent the sealing members 11 and 12 from being sucked into the holes 7 by a quick oil pressure -variation, each oil hole 7 facing the disc valve 13 is provided at its lower end with an annular projection 24. Thus, in a cylinder according to the present invention, leakage through the valve arrangement of the piston is effectively completely prevented so that variation of the propeller setting angle can be eliminated. Further, since no strong spring is required, the damping force under shock conditions can be set without difficulty at an appropriate value.

Claims: CLAIMS 1. A hydraulic cylinder for a propulsion unit of an inboard or outboard motor comprising an oil cylinder having an oil inlet and outlet port at each end and a piston fitting in the cylinder and having an oil hole fitted with a check valve and also including a disc valve having two concentric annular sealing members made of elastic material which is biased against one face of the piston so that the space between the two sealing members is in communication with the end of the oil hole whereby the disc valve may open and close the oil hole simultaneously with the check valve according to the direction of movement of the piston. 2. A hydraulic cylinder according to claim 1 including a cover plate extending over the end of the oil hole and having a hole communicating with the oil hole, the cover plate constituting the face of the piston engaged by the disc valve. 3. A hydraulic cylinder according to claim 2, in which the body of the piston has an annular groove which communicates with the oil hole and is closed by the cover plate, the cover plate having a ring of holes communicating with the space between the two sealing members of the disc valve. 4. A hydraulic cylinder according to claim 2 or claim 3 wherein the check valve comprises a ball engaging a seating within the oil hole and a spring extending between the ball and the cover plate, 5. A hydraulic cylinder according to claim 1 wherein the face of the piston remote from the disc valve is formed with a cavity which is closed by a cover plate having small holes, the check valve comprising a disc of elastic material arranged in the cavity to overlie the small holes. 6. A hydraulic cylinder according to claim 5 including an annular projection surrounding the end of the or each oil hole on the face of the piston engaged by the disc valve. 7. A hydraulic cylinder for a propulsion unit of an inboard or outboard motor constructed and arranged substantially as herein before described with reference to and as illustrated in Figures 2 to 4 or as modified by Figure 5 or Figure 6 of the accompanying drawings. 8. The combination of a propulsion unit of an inboard or outboard motor and a hydraulic cylinder according to any one of the preceding claims.

Inventors: NAKAMURA, TAMOTSU
Applicants: SHOWA MANUFACTURING COMPANY LIMITED
Application year: 1979
Main classification: B63H21
IPC codes: F16F9, F02B61, F15B15, B63H20