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Brake over-travel switch

  1. Aug 21, 2013 #1
    Hey guys

    I am working on a safety system for the brake system and I am looking for a detent switch that can be used to stop the system from working, ie the engine and fuel pumps an dother electronic controls in the car.

    The switch has to be SPST and should keep the system 'off' until the reset button is activated. I am not really sure which switch or button to use as I am finding it hard to get anything worth using. Does anyone know any company that can be of assistance in terms of finding a switch to use? Preferably in South Africa.

    Thanx in advance!
  2. jcsd
  3. Aug 23, 2013 #2


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    I am guessing that you are referring to the hydraulic brakes used on a car, and that you want to detect when the brake pedal travel is excessive due to loss of brake fluid ?

    Machine tools usually have a big red button that is pressed to stop the electric motor. The button must be rotated to re-enable the system. But I think you might need two switches, one to detect failure and another to reset the trap. A bit like a contactor on a three phase electric motor.

    I cannot help further without a better idea of how you intend it to work.
  4. Aug 26, 2013 #3
    My focus is on the control system and not really much on the actual mechanical operation of how failure occurs. I don't really want a twist release emergency stop button. I want something smaller and more compact then that.

    All I want the switch to do is be activated when failure occurs and not allow the driver to reset the system, hence the switch position has to be maintained once the button or switch is activated.
  5. Aug 26, 2013 #4


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    The problem I see is that, if it is pedal travel you must detect, then the switch will be damaged by the pedal. That suggests an intermediate component that moves sideways to press the switch, or a spring to limit switch activation.

    If there is something to remember the event, then the switch need only be momentary. In some equipment a fuse is deliberately blown by the event, that tell-tale remains as evidence after the event. A blown fuse, circuit breaker or digital flip/flop can be sensed by the control system. It cannot be easily changed by the driver.
  6. Aug 26, 2013 #5
    What is the purpose of such a system - to cause less accidents or MORE acidents.
  7. Aug 27, 2013 #6
    To decrease the possibility of an accidents occuring
  8. Aug 27, 2013 #7


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    Why so? Why must it be damaged? Why can't it just be activated but the detent is a point never reached during regular pedal travel?
  9. Aug 27, 2013 #8


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    What if you used a primary switch of the proximity or mechanical type at the pedal detent you want to trigger shutdown at and then use its output to drive a latching relay on the core power circuit of the car?

    The only way to restart will be to manually reset the latching relay and that in itself will provide evidence of what triggered the shutdown.
  10. Aug 27, 2013 #9
    The reason I asked is because in your first post you said
    That could possibly be OK if the car is stationary and the safety brake system would render the car immobile if there is insufficient brakes.

    Consider though, what would happen if the brake peddle, or a mechanical or electrical failure of the switch itself and components, activates the safety mode while the car is travelling down a highway at 60mph (100kph). With brake safety switch activating an engine cutout and electrical shutoff the driver would most likely become disoriented and wonder what the frick is going on, especially if he/she loses he feel of power steering and whatever brake assist was still available. In that situation it might be best to have a driver worry about only a reduction in braking power rather than the whole car konking out.

    As for servicing the brakes, at times it is necessary to bleed the brakes llines which requires multiple pushes of the peddle to the floor to eliminate all air from the system. You might want to consider an override of the brake safety switch for that circumstance either for the garage mechanic or the home mechanic.

    Also, would most drivers not want the engine to keep running so they could have at least heat for the interior if they have to pull over to the side of the road on a cold night to wait for a tow truck. Most people would really feel apprehensive about say their newborn baby getting frostbitten toes and fingers, as such an occurance will happen some day and they would not be too pleased.

    I just thought I would throw my 2 cents in there on some other aspects of such a brake safety system you might want to explore.
  11. Aug 27, 2013 #10
    It seems to me that this would cause more accidents what would be better is a warning light of
    some kind.

    Also a brake pedal over travel switch would not be sufficient it would only detect if there were air in the hydraulic lines. In most brake systems brakes adjust automaticly to brake pad wear I'm not sure exactly how your brakes work but often aircraft brakes have a pin that can be physically measured to check brake wear. Possibly you could make a microswitch that would activate when your brake pad wears to a certain depth.
  12. Sep 6, 2013 #11
    Is the OP still around? I'm not following the logic of the device...if your brakes fail, current systems use dual pistons in the master cylinder that act as a safety device allowing some braking to occur. The driver will definitely know that something is wrong when the pedal goes to the floor and the warning light comes on. I can't imagine anyone pushing the gas pedal to try to improve things. As previsouly posted, shutting off the engine will only make things worse. But, here's an idea for you, and even OEMs...if the brakes should fail to the point of a warning light, then have a system partially apply the emergency brake. That would actually help the situation. And with wheels sensors, could even be highly controlled to slow the car immediately. Just a thought....
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