Supplementary braking system? 1

[missinglink]

Hello all,
I'm Paul from Manchester England and have an interest in Automotive engineering. Although I'm not too savvy on certain subjects,for example pneumatic components.

I'm trying to devise an auxiliary braking system to my car that can suit an A-frame,or a brakeless trailer. What I have configured in my minds eye,is an pneumatic actuator fitted to the drivers footpedal,where the rod from the actuator will be already protruding,will be forced in when the brake pedal is depressed. From the actuator will be an airline going to the rear of the car,attached to another actuator which will send the rod out of the actuator to another secondary pedal,built on a frame. For the compressed air to be in the system,I supect that a fill & chuck valve would be needed.

Your opinions most welcome,and perhaps,notice any flaws in my contraption

regards
Paul

 

[GregLocock]

One has to wonder what the insurance company will say if your vehicle is involved in an accident. There are commercial braking systems available for trailers, buy one, fit it, test it, and use it.



Cheers

Greg Locock


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[patprimmer]

There are even vacuum operated ones a bit similar to your suggestion. Manifold vacuum is used to evacuate a tank. A valve actuated by the brake application applies vacuum to a line that hooks to the trailer where a diaphragm is used to apply the brakes It is now considered an obsolete system and most trailer systems use electricity to apply the brakes and do it with g sensors and wires and electro magnets.

Regards
Pat
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[MintJulep]

What you envision shows a dangerous lack of fundamental engineering knowledge.

Please just go to a local trailer shop and have one of the many commercially available trailer brake systems installed before you kill someone.

 

[LionelHutz]

The flaw is the cobbled up contraption...

Around here, you can get the electric wheel brake assemblies for about $45 each and the electric brake controller for around say $100. It's simply retarded to mess around with a cobbled together contraption to build a safety critical trailer braking system.

 

[bithkits]

Take it easy guys - many designs today came from guys like Paul who tinker in their garages.

If he had the brains to come consult the experts on eng-tips forums I am sure he also has the brains to know when to stop working on a flawed design.

Adriaan.
I am an Engineer/part time student (Mechatronics) from South Africa.
Advice from lecturer: "Be warned - when you go into industry your boss will give you a thousand things to do and he wants them done yesterday!" So far he is right...

 

[GregLocock]

Aye. Public roads are a great place to test out one's understanding of the laws and the Laws. So Adriaan how does he get around the insurance issue? Are you sure that as a South African you understand the legal implications of this on UK roads?


Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[BrianPetersen]

Setting aside the legal implications, and the fact that commercially available systems to do what the original poster wants to do very cheaply such that there is no purpose in re-inventing the wheel ...

The big problem with using air in the manner described, is that air is compressible.

Automotive braking systems use hydraulics because hydraulic fluid is (substantially, for the purpose that we are talking about here) incompressible.

Transport-truck braking systems use compressed air, but it operates differently than described. The driver's foot is not the source of pressure in the system. The driver's foot is more like an input to a servo system, in which the pressure is generated by an engine driven compressor, and the driver's foot only operates what amounts to a valve that tells how much pressure to pass into the rest of the system.

Automotive / light truck trailer braking systems are of two types, electric, or "surge". The parts for making both such systems are readily available quite cheaply. Electric brakes are easier to implement (when the vehicle's brake lamps come on, the brakes get turned on) but are "on/off" and are not proportional to how much deceleration the driver wants. Surge brakes are hydraulic, but instead of the driver's foot pushing the brake pedal which pushes the master cylinder, the mechanism that attaches to the tow vehicle's hitch ball actuates the master cylinder (on the trailer). The harder the tow vehicle brakes, the more force is transmitted, the stronger the brakes are applied. Reversing uphill with the trailer could be tricky. I don't actually know how they handle that.

And on those notes ... I'm with everyone else on this. Buy something that does what you want it to do.

 

[patprimmer]

Inertia activated electric are variable with car braking effort.

There is also an obsolete vacuum operated system that was very effective, but it was operated by a separate hand control lever.

Regards
Pat
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for site rules

 

[missinglink]

Thankyou all for your replies.
@GregLocock,you do have a point regarding insurance issues when not properly equipped to avoid an accident.
I do deem myself a responsible motorist,so safety has priority. It was mainly for A-frame application,as A-frames are illegal for long distance in the UK.
@patprimer,thanks for the options. The vacuum setup is probably similar to this

http://www.smart-tow.com/braking.htm

And I've also engine searched other varities.
@Mintjulep,thanks for being blunt,"lack of fundamental engineering knowledge" is about correct,that's why test casing a gadget is part of learning.
@LionelHutz,so it's a cobbled contraption. The electric wheel brake would suit a trailer with existing brakes,if I am not mistaken.
@Bithkits,thanks for the support. I do have a couple of brain cells to rub together *GRIN* to now realise it is a total flop.
My system was a mixture of the smart-tow and the metal cable from the surge systems.
Thanks all again.

regards
Paul

 

[LionelHutz]

So, you are talking about towing a car using a "tow bar" attached to the front frame of the car?

Posting "A-frame, or brakeless trailer" just isn't very clear. "brakeless trailer" just sounds like you have a trailer with no brakes on it.

Some transport trucks run hydraulic front axle brakes and air on the rest of the axles so I guess it could be possible to duplicate that with an actuator running the pedal in the tow vehicle...

You'd need an onboard air tank and compressor that will keep up with repeated braking though, none of this fill and chuck valve stuff will cut it.

 

[AviatorJim]

I suspect it would be easiest to use a surge brake master cylinder on the A-frame, and plumb it into the existing brake hydraulics at the master cylinder. That would also require bleeding the brakes once the tow bar is connected, and then again when it is removed.

A 12 VDC linear actuator connected via a spring could also be mounted to the brake pedal, and operated by a conventional electric brake controller it the trailer lights being used on the towed car. But as was said before, it would be an on/off system.

But cars on towbars are very hard to back up. I think if it was something I would be doing regularly, or for a long distance, a trailer would be optimal.