Energy dissipation valves for hydraulic cylinders

Abstract

A hydraulic actuator comprises a cylinder, a piston reciprocatingly received within the cylinder, a piston rod connected to the piston and a pressure release mechanism which allows hydraulic fluid to pass from a first side of the piston to a second side of the piston when the actuator encounters shock loading. This permits the piston to move. The pressure relief mechanism includes a passageway extending from the first side of the piston to the second side of the piston and a valve member adjacent to the passageway which releasably engages the piston. The valve member has a closed position where the valve member closes the passageway and engages the piston. A resilient member biases the valve member towards the closed position. A valve member limiter limits movement of the valve member away from the closed position. The resilient member has a rigidity sufficiently great so that movement of the valve member away from the closed position is more dependent upon the rigidity of the resilient member than upon a preload applied to the valve member.

Description

BACKGROUND OF THE INVENTION [0001] This invention relates to actuators and to energy dissipation devices therefor and, in particular to energy dissipation valves for hydraulic actuators used for tiltable marine drive units. [0002] Linear hydraulic actuators typically include a piston reciprocatingly received within a cylinder. A piston rod is connected to the piston and extends through one end of the cylinder at least. The piston is moved by supplying pressurized hydraulic fluid to the cylinder on one side of the piston, causing the piston to move in the opposite direction. These actuators may be used for many purposes including tilt actuators and / or trim actuators for tiltable marine drive units. Tilt actuators are used to tilt outboard motors or inboard / outboard drives located at the stern of the marine craft. Tilt actuators tilt the drive units downwardly to render the drive units operational and tilt the drive units upwardly when not in use. Trim cylinders are used to adjust the...

AI Technical Summary

Benefits of technology

[0007] According to one aspect of the invention there is provided a hydraulic actuator comprises a cylinder, a piston reciprocatingly received within the cylinder, a piston rod connected to the piston and a pressure release mechanism which allows hydraulic fluid to pass from a first side of the piston to a second side of the piston when the actuator encounters shock loading. This permits the piston to move. The pressure relief mechanism includes a passageway extending from the first side of the piston to the second side of the piston and a valve member releasably engaging the piston adjacent to the passageway. The valve member has a closed position where the valve member closes the passageway and engages the piston. A resilient member biases the valve member towards the closed position. A valve member limiter limits movement of the valve member away from the closed position. The resilient member has a rigidity sufficiently great so that movement of the valve member away from the closed position is more dependent upon the rigidity of the resilient member than upon a preload applied to the valve member.

[0008] According to another aspect of the invention, there is provided a marine craft with a stern and a tiltable drive unit at the stern, the drive unit having a hydraulic actuator connected to the craft. The hydraulic actuator comprises a cylinder, a piston reciprocatingly received within the cylinder, a piston rod connected to the piston and a pressure release mechanism which allows hydraulic fluid to pass from a first side of the piston to a second side of the piston when the drive unit encounters an obstacle. This permits the unit to tilt. The pressure relief mechanism includes a passageway extending from the first side of the piston to the second side of the piston and a valve member releasably engaging the piston adjacent to the passageway. The valve member has a closed position where the valve member closes the passageway and engages the piston. A resilient member biases the valve member towards the closed position. A valve member limiter limits movement of the valve member away from the closed position. The r

Problems solved by technology

The leg and propeller are located below the bottom of the marine craft and are susceptible to hitting underwater objects.

Damage to the drive unit, the marine craft itself or both the drive unit and the marine craft may occur as a result of such collisions.

Simply put, if the valves only release once the pressure is at too high a level, then the drive unit would encounter too much resistance to tilting in the event that the motor contacts an object, potentially resulting in damage to the motor or boat.

On the other hand, if the valve releases at too low a pressure, the motor may swing upwardly too fast, again potentially damaging the motor or boat.

However the effect of increasing preload is to lose low energy capability.

In other words, the valve does not sufficiently open to dissipate energy during low speed collisions.

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