Spring devices – Vehicle – Comprising compressible fluid
Reexamination Certificate
2001-06-15
2004-03-02
Graham, Matthew C. (Department: 3683)
Spring devices
Vehicle
Comprising compressible fluid
C267S217000, C267S218000, C188S269000
Reexamination Certificate
active
06698729
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to gas springs and, particularly, to gas springs of the type that are used primarily to lift and hold open the trunk lids, tailgates, hatchback lids, and engine compartment hoods of motor vehicles.
BACKGROUND OF THE INVENTION
Gas springs are widely used to partly or totally counterbalance the engine compartment hoods, trunk lids, rear windows and tailgates of passenger cars, station wagons, and vans to facilitate opening them and to hold them open at a nearly or fully open position. It is well-known that the force outputs of gas springs vary considerably with the temperature of the gas—at low temperatures the gas spring produces a force that can be very much lower than the force produced at high temperatures. It is necessary, therefore, to design a gas spring so that it produces a sufficient force to hold open the hood, tailgate or the like (hereinafter referred to as the “load”) at a suitably selected low temperature, say, −30 degrees F. Ordinarily, gas springs are designed to provide a force of from about one to about five pounds over the load in the hold-open position of the load at the low temperature. At high temperatures, the hold-open force may increase by as much as 50 pounds, which means that the force required to move the load toward closed from the hold-open position (the “handle load”) can be more than 50 pounds.
In addition to the problem of wide variations in the handle load as a function of temperature, the counterbalancing force exerted by the gas spring on the load at all positions of the load between closed and open varies widely with temperature. In cold weather, the gas spring force exerts a considerably lower counterbalancing force on the load than at high temperatures. Depending on the geometry of the gas spring/load system, the user may have to exert a relatively large force on the load during part or all of the movement of the load from closed to fully open in cold weather. In hot weather the gas spring force may move the load from closed to open without the intervention of the user under a relatively high opening force and at a relatively high speed, which can sometimes be disconcerting to an unwary user or can damage the load if there is an obstruction that prevents the load from fully opening.
Various proposals have been made for mitigating the problem of variations due to temperature changes in the hold-open/handle load with the load open. Some examples are found in U.S. Pat. No. 5,106,065 (Staton et al., 1992) and U.S. Pat. No. 5,404,972 (Popjoy et al., 1995). Those solutions are based on having one or more bypasses between the sub-chambers of the gas chamber on opposite sides of the piston, each bypass having a spring-biased valve which is closed at low temperatures and blocks the flow of gas from the closed-end sub-chamber to the rod-end sub-chamber and opens at high temperatures to permit gas to flow through the bypass. When the bypass is closed, the relatively low force of the gas spring is supplemented by the effect of the biasing force on the valve such as to increase the hold-open force. The devices of those two patents have no effect on the force output of the gas spring when the load is moved from closed to open.
It has also been suggested that a reduction in the output force of a gas spring due to leakage of gas or low temperature can be compensated for by providing a secondary gas chamber or reservoir that contains gas at a pressure higher than that in the primary chamber and a pressure-responsive valve in a passage that connects the secondary chamber to the primary chamber and opens when the pressure in the primary chamber falls below a predetermined value. Such an arrangement is proposed in U.S. Pat. No. 5,042,782 (Mitgen, 1991). When gas is supplied from the secondary chamber to the main chamber to make up for a pressure drop in the main chamber due to a decrease in temperature, the output force is prevented from being reduced by the addition of air to the main chamber from the secondary chamber. When the force output of the gas spring rises due to an increase in temperature, gas can, if desired, be released from the main chamber through a vent (FIG. 4), thereby preventing the gas spring force from increasing to an undesirable level. The arrangement of the Mintgen patent maintains a relatively uniform force output of the gas spring over a wide range of temperatures but inherently requires releasing gas from the system, lest complete hot-cold-hot cycles of operation cause the operating force to become excessive on the next cold-hot phase of another cycle. Unless a wide difference is built into the respective valves for the replenishment of gas and release of gas, frequent venting of gas will soon deplete the gas in the secondary chamber, thus requiring recharging. The need for frequent service of the system is a disadvantage.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a gas spring that provides a controllable force output over a long useful life without the need for any service, such as replenishing a gas in a supplemental supply reservoir. Another object is to provide a gas spring that is capable of exerting forces that vary in a predetermined manner during each stroke of an operating cycle. Yet another object is to provide a gas spring that provides a force output that does not vary with temperature changes.
The objects referred to above are attained, in accordance with the present invention, by a gas spring for moving a load relative to a body that includes a cylinder member having an axis, an inner surface forming a chamber, a rod end and a closed end, a piston rod seal/guide received in the rod end of the cylinder member, and a piston rod received in the seal/guide for movement into and out of the cylinder member. A floating piston is received in the cylinder member for movement along the axis and in sealed engagement with the inner wall to define in the chamber a gas section between the floating piston and the rod end and a closed end section between the floating piston and the closed end. A mass of gas under a pressure above atmospheric pressure is contained in the gas section. A powered drive is provided for moving the floating piston axially of the cylinder member to vary the volume of the gas section of the chamber. A sensing device senses a characteristic of the gas spring that is indicative of the force applied to the rod by the gas in the gas section and produces a signal indicative thereof. The signal generated by the sensing device is used to control the drive.
A gas spring, according to the present invention, provides a predetermined force output by variation of the volume of the gas section. For example, if the temperature of the gas in the gas section drops but the volume of the gas section remains constant, the pressure of the gas and the force output of the gas spring are reduced correspondingly. The reduction in pressure is detected by the sensor. The controller responds to the change in the sensor signal by activating the power drive, which displaces the floating piston in a direction to reduce the volume of the gas section, thereby raising the pressure of the gas and the output force. The present invention makes it possible for the gas spring to provide an output force that remains substantially constant for any given stroke position, regardless of variations in temperature over a very wide range.
In a simple system the controller and drive may be activated periodically when the load is closed. The controller and drive are powered by the battery of the vehicle. Periodic activation saves battery power. A low-battery shut-off can be incorporated to prevent the battery from being drained. If the sensor detects a change in the gas pressure, the drive is activated to change the volume of the gas section and restore the pressure to the predetermined level. Therefore, when a user opens the load, the gas spring has been previously adjusted to provide the desired output force to counterbalance the load, maintain
Baker & Botts LLP
Graham Matthew C.
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