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Parallel bar hinge system help needed

  1. Sep 26, 2009 #1
    Hello to all,
    I am not a mechanical engineer, I am a jack of trades though.

    I am trying to solve a problem I see in a design an need your help to design a system for a lifting canopy on a car, the functions better than the current one.

    Currently, the lifting system on this car, is constructed of two pieces of U channel with two bars mounted in the same channel. These bars and U channel act as the lifting hinge for the canopy of this car. The system is powered typically by a convertible car hydraulic pump, and two hydraulic rams connected directly to one of the arms.

    See this video for an idea of the system:


    However there are a few problems with its design.

    The system is powered hydraulically. it is held up by hydraulic pressure, and held down the same way.

    The roof will wriggle loose while driving in the down position.

    The speed at which the roof opens and closes is appalling. sometimes more than 20 seconds to open it.

    The goal, is to make a simple to make, multi-link system, to gain faster opening, and closing, a hydraulic timer to add in a 6 inch creep phase at the end of the stroke up or down, to prevent slamming at the end of the stroke. Also, using the cheapest parts available is preferred. The stroke is about 8 inches at the connection point shown in the video.

    Some sort of cantilever arm link to create an over center mechanical lock to lock the top down is needed. Manufacturing these parts by hand is fine. Buying them is ok. But components bought off the shelf are very expensive for this system to make it fast. Im looking for an alternative cheaper way to make this happen more efficiently.

    Im hoping you guys/gals would like a challenge and are willing to help.
    If you need any more info I will get it to you as soon as I can.

    Everytime I try to figure out how to make this system gain more mechanical advantage, and speed ends up equalizing each other out. Im not sure what Im missing. I even broke out my kids erector set to play with various mounting points to no avail.
    Im looking at making the system internal below the body work (minus the bar hinge) so the actuator and all the links would be inside the body if possible.


    Thank you for your time.

    ydeardorff
     
    Last edited by a moderator: Sep 25, 2014
  2. jcsd
  3. Sep 26, 2009 #2

    Danger

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    Welcome to PF, Ydeardorff.
    I'm starting to get an idea or two, but I need to think on it for a while.
    Do you require the same sort of motion as is shown in the video? I ask only because I think that it would be easier to hinge the canopy at the front or back and swing it up as opposed to elevating the whole thing.
     
  4. Sep 26, 2009 #3
    yes the hinge system has to remain looking the same.
    It is the trademark part of these cars.

    But no one want to wait 20 seconds to get out of your open cockpit'ed cr when its raining out.
    Nor does anyone like the hydraulic system letting the top loose whilst driving. LOL
     
  5. Sep 26, 2009 #4

    Q_Goest

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    Hi ydeardorff. Most hydraulic systems I'm familiar with have some kind of valve or other flow restriction that limits the flow of hydraulic fluid through the circuit, and thus limits the speed that hydraulic actuators can operate at. I'd guess your system is the same. Trace the flow of hydraulic fluid from the pump/accumulator and see if you can identify where there might be a flow restriction. Many times it will be built in to the hydraulic actuator itself. It could be a valve or orifice.

    If that's what's causing the very slow movement, you may be able to change the speed simply by making an adjustment or changing the restriction. Problem may be that at the limits of the motion, your 'door' will impact much harder. If that's the case, you can add rubber stops or small, industrial shock absorbers. First, see if there's a restriction you can adjust or change.
     
  6. Sep 26, 2009 #5
    Thank you, Im working that end with a hydraulics technician as we speak.

    The other thing Im trying to do is to hide the mechanism inside the body, making some sort of over center mechanical lock to prevent the top from coming loose from relying on hydraulic pressure to keep it closed. And lastly, find a way to keep the pressure equalized side to side, so there is no binding if one side goes down quicker than the other.
     
  7. Sep 26, 2009 #6

    Q_Goest

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    Bottom line is fairly simple in my mind. The geometry of the hinges and actuator can't be changed easily. If there's no restriction in the hydraulics, then the only help is to increase the flow capacity of the hydraulic pump. The overcenter mechanism is a good idea but I think it'll be difficult to make work. If it were me, and I wanted to do the overcenter mechanism idea, I'd make a scale drawing of the hinge and design it on CAD to make sure I had the right motion before I made it in metal. I'd also look at stresses in the parts. You could also look at velocities and accelerations and even do a full dynamic analysis, but that's probably going past what you're interested in.
     
  8. Sep 26, 2009 #7

    Danger

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    To start with, I wouldn't give any thought to a hydraulic 'timer' for the last bit of travel. Think of the way that a door closer or variable-rate shock absorber works. It will take a while for me to come up with a specific design, but basically you use two hydraulic circuits in the same system. One is very low-restriction for rapid movement. When your lid is about 90% down (and maybe also up), the piston covers the main port and uncovers one leading from a high-restriction feed, which results in slow travel for the remainder of the cycle.
    Blocked flow should result in positive locking of the cylinder, so I'm not sure what's going on with that part. You can solve it by having a linkage that is tripped by the piston rod and pulls a locking lug into position.
     
  9. Sep 27, 2009 #8
    heres a picture with measurements if anyone needs it.
     

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