2.4. Flipover Design

The least preferable application type is what AVM terms flipover. The most identifiable trait of this type of design is that the end of the gas spring that is lowest in the closed position rotates to the highest position during the opening cycle. When using this type of system it is also preferable to mount the gas spring in a shaft pointing down orientation. This orientation insures proper lubrication of the seal system. This type of system requires special and more expensive dampening control to give a repeatable dampening characteristic. Usually if these extra measures are not taken the system will operate poorly. An example of this type of application in a hatch system is illustrated in Figure 19.

Figure 19

2.4.1 Hump

The hump characteristic is difficult to visualize due to how radically the moment arm changes during the closing cycle. This difficulty in seeing where the hump occurs causes the designer to calculate more design iterations until a suitable solution is determined. Flipover systems also tend to have the hump occur closer to the full closed position. This problem usually results in operator complaints that the liftgate needs to be pushed all the way closed.

2.4.2 Dampening

Inconsistent dampening is one of the disadvantages of a flipover system (figure 20). At the beginning of the opening cycle, the oil is pooled at the bottom of the tube. As the door opens, the oil will stay pooled until the gas spring swings through horizontal. At this point, the oil begins running down the inside of the tube wall to meet the piston moving up towards the oil.

When the piston meets the oil, the opening motion slows allowing the remaining oil to pool on top of the piston. The piston will move through the oil slowly until all the oil is on the other side of the piston. The opening cycle will then speed up and reach full open with no end of stroke dampening.

Figure 20

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