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Energy dissipation valves for hydraulic cylindersRelated Patent Categories: Pumps, Motor Driven, Electric Or Magnetic Motor, Reciprocating Rigid Pumping MemberEnergy dissipation valves for hydraulic cylinders description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060083641, Energy dissipation valves for hydraulic cylinders. Brief Patent Description - Full Patent Description - Patent Application Claims
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 angle of the drive units for proper operation of the marine craft. [0003] Such drive units have a leg which extends downwardly with a propeller located near the bottom thereof. 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. Accordingly it is conventional to permit extension of the tilt actuators and trim actuators under shock loading as occurs during collisions was underwater objects. This is conventionally achieved by providing energy dissipation valves or impact valves for tilt actuators and/or trim actuators. These valves are typically located on the piston of such an actuator and may comprise a spring-loaded valve member located on the passageway through the piston. An impact event increases pressure in the hydraulic fluid sufficiently to move the valve member against the spring and allow hydraulic fluid to flow through the passageway from one side of the piston to the other. This allows the actuator to extend as a result of an impact event. The extension of the actuator allows the drive unit to dissipate energy by tilting upwardly and minimizes damage resulting from the impact. [0004] However the configuration and specifications of such valves had to be tightly controlled in order to provide proper energy dissipation. 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. The valve must dissipate sufficient energy with respect to the impact and the inertia of the drive to not cause significant damage to the marine craft or drive. [0005] One of the critical factors with some earlier energy dissipation valves is the preload on the valve spring. The preload on the valve had to be tightly controlled in order for the valve to release at an appropriate pressure level and to dissipate the correct amount of energy during an impact event. In fact, prior art valves cope with high energy situations, for example when the motor encounters an object at high speed, by increasing the preload on the spring. 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. [0006] The invention is also applicable to other applications besides marine drives where it is desirable to dissipate energy by allowing movement of hydraulic actuators during shock or impact events. However the invention should be differentiated from standard shock absorbers, used on vehicles for example, which are active at all times and respond to hydraulic pressure fluctuations. The invention by contrast is adapted only to respond to extraordinary impact events. The valve does not responded to all impact events and resulting pressure increases below a certain threshold. SUMMARY OF THE INVENTION [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 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. [0009] According to a further aspect of the invention, there is provided a method for configuring a hydraulic actuator connecting a tiltable drive unit to a marine craft to permit the drive unit to tilt when the drive unit encounters an obstacle. The actuator includes a cylinder with a piston reciprocatingly received therewithin. The method comprises providing the piston with a passageway extending from a first side thereof to a second side thereof and providing a valve member having an open position where the passageway is open and a closed position where the passageway is closed. The valve member is biased towards the closed position with a resilient member having sufficient rigidity so that movement of the valve member towards the open position, when the encounters the obstacle, is more dependent upon the rigidity of the resilient member than upon a preload applied to the valve member. [0010] According to a still further aspect of the invention, there is provided a shock absorbing apparatus comprising a fluid actuator having a piston with a passageway therethrough and a valve controlling fluid flow from one side of the piston to another side thereof. The valve includes a closure member biased towards a valve seat by a resilient member and a stop limiting movement of the closure member away from the valve seat. The resilient member has a rigidity such that initial opening of the closure member with respect to the valve seat, due to pressure of fluid in the passageway, is determined by preload applied to the closure member by the resilient member. Movement of the closure member further away from the valve seat, until limited by said stop, is determined more by the rigidity of the resilient member than the preload. Fluid flow through the passageway is limited by an orifice between the closure member and the valve seat when the stop limits movement of the closure member away from the valve seat. [0011] According to a still further aspect of the invention, there is provided a method of absorbing shock using a fluid actuator with a piston having a passageway therethrough and a valve controlling fluid flow from one side of the piston to another side thereof, the valve including a closure member biased towards a valve seat by a resilient member. The method comprises applying a preload to the closure member with the resilient member such that initial opening of the closure member with respect to the valve seat, due to pressure of fluid in the passageway, is determined by the preload applied to the closure member by the resilient member. Rigidity for the resilient member is selected such that movement of the closure member further away from the valve seat is determined more by the rigidity of the resilient member than the preload. Movement of the closure member away from the valve seat is limited such that fluid flow through the passageway is controlled by an orifice between the closure member and the valve seat when the movement of the closure member away from the valve seat is so limited. BRIEF DESCRIPTIONS OF THE DRAWINGS [0012] FIG. 1 is a side view of a marine craft equipped with an outboard motor fitted with an actuator according to an embodiment of the invention; [0013] FIG. 2 is a simplified side view, partly in section, of the actuator; [0014] FIG. 3 is a side view, partly in section, of the piston thereof, showing an energy dissipation valve of the actuator; [0015] FIG. 4 is an enlarged, fragmentary, diagrammatic view of the energy dissipation valve; [0016] FIG. 5 is a view similar to FIG. 4, but showing a variation of the valve with a sharp edge orifice; [0017] FIG. 6 is a graph showing the responses of trim/tilt cylinders to an impact event and the force variability due to changes in spring preload; and [0018] FIG. 7 is a graph showing the responses of trim/tilt cylinders to an impact event and stroke variability due to changes in spring preload. DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS [0019] Referring to the drawings, and first FIG. 1, this shows a marine craft, in this case a boat 14 equipped with an outboard motor 12 mounted on transom 15 of the boat. The general arrangement is standard and accordingly is not described in more detail. It should also be understood that the invention is applicable for other tiltable marine drive units such as inboard/outboard drives. For example the invention is applicable to other movable member is besides marine drive units which are mounted on larger bodies other than boats. If bottom 17 of the motor contacts an object, such as rock 18, damage to the motor or boat may occur. In an extreme scenario the motor could potentially be ripped from the boat. [0020] The outboard motor or other drive unit is capable of tilting relative to the transom as indicated by arrow 16. Tilting of the motor is accomplished utilizing a tilt actuator 10 which is a generally conventional hydraulic actuator in this example. It is known in the art to provide an energy dissipation valve in the actuator to permit the motor to tilt upwardly in the event that the motor contacts an object such as the rock 18 and thereby reduce the risk of damage to the motor and boat. The invention is also applicable to actuators used for adjusting the trim of marine drives. The actuator is adjustable to a certain position, for example the tilt angle of the engine, by applying pressurized hydraulic fluid to one end of the cylinder or the other. Thereafter, subject to readjustment, the actuator is expected to remain in that position during use unless an unexpected obstacle is encountered. The actuator is not responsive to normal loading applied to the motor in a sense of a conventional shock absorber. Continue reading about Energy dissipation valves for hydraulic cylinders... Full patent description for Energy dissipation valves for hydraulic cylinders Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Energy dissipation valves for hydraulic cylinders patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Energy dissipation valves for hydraulic cylinders or other areas of interest. ### Previous Patent Application: Energy dissipation valves for hydraulic cylinders Next Patent Application: Pump Industry Class: Pumps ### FreshPatents.com Support Thank you for viewing the Energy dissipation valves for hydraulic cylinders patent info. 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