Brake Servo Vacuum Switch Problem

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ChopperMan
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Brake Servo Vacuum Switch Problem

Postby ChopperMan » Thu Jul 03, 2008 10:23 pm

Hi All,

We got our R2 sports car through the SVA test without the need for the servo assistance on the brakes, however I would like to get it working properly on a permanent basis. I have an electric vacuum pump which when permanently connected works great, it is also very noisy. So it needs a pressure/vacuum switch and resiovir so it's not running all the time, only when needed.

Has anybody done this before? Where do I get the parts?

Many thanks,

Ian
Electric chopper ebike with PUMA motor (1.2kW) and 36V 20Ah LiFePO4 batteries. 23 mph & 20 mile range with no peddling (Sorry, what are peddles for?).
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ChrisB
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Postby ChrisB » Fri Jul 04, 2008 10:09 pm

I'd say you need either a vac pump and s/w off say a berlingo or if you dont mind a clankier version one off an earlier BedfordCF electric.

You would need to fit a servo though.

ChrisB
I reject reality and substitute my own !!!!!!

ChopperMan
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Postby ChopperMan » Sat Jul 05, 2008 11:50 am

Hi Chris,

We have a servo and a pump, but because the pump only operated when the pedal was depressed or was on all the time the SVA guy wouldn't pass it. So we turned it off completely for the test and the brake were good enough to pass!

Now though I need a vac switch and resoviour so it operates automatically when the pressure gets low. Any ideas?

Cheers,

Ian
Electric chopper ebike with PUMA motor (1.2kW) and 36V 20Ah LiFePO4 batteries. 23 mph & 20 mile range with no peddling (Sorry, what are peddles for?).

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ChrisB
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Postby ChrisB » Sat Jul 05, 2008 2:40 pm

Now I'm confused ??

So you've got a servo , you've got a pump, how does the pump switch on then, i.e what makes the pump run when the peddle is pressed ?

It sounds to me like the SVA guy has lost the plot somewhat and doesnt understand the principle of servo brakes :roll: worrying isnt it :roll:

The servo on its own should be able to hold enough vac for a good couple of brake applications as in all vehicles , the pump will start once a preset amount of vac is lost in the servo, the pump should be able to maintain a reasonable amount of vacuum on its own to maintain good brake performance and hence may well run all the time while opperating the brakes.

The berlingo pump will run most of the time while the brakes are opperating as does the CF one , the one on my Fiesta (which was a CF one ) would run as well.

Personally I dont think he knows what hes talking about :roll:

I suspect all you may need is a vac switch on the servo, but you may already have one but as you dont say what turns the pump on and off I cant say for sure until then.

You certianly dont need a resiovir as the servo will do that bit

ChrisB
I reject reality and substitute my own !!!!!!

ChopperMan
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Postby ChopperMan » Sat Jul 05, 2008 8:52 pm

Hi Chris,

When testing we had the electric pump permanently connect to the 12V accessory battery but it was bloody loud. So we hooked it up to a normal electrical switch on the brake peddle so I could pump it a couple of times when I turned on the ignition and it worked great, topping up the servo every time you touched the brakes.

Now this is the SVA guys logic, what happens if you a travelling for 15 minutes (ie not topping up the servo by braking regularly) and then have to do an emergency stop. By this time, he believes, the servo would have lost its pressure and the switch on the peddle won't top it up in time because you would have already pressed the peddle down. Now he could have failed us at this point but he said just disconnect the pump and see if it passes the brake test unassisted, we did and it did. So I now have it SVA'd but want to improve the brakes. Belt and braces as he suggests.

You may be right, that all I need is a suitable vac switch. My problem is, I don't know which one is suitable, or where to get them from.

Cheers,

Ian
Electric chopper ebike with PUMA motor (1.2kW) and 36V 20Ah LiFePO4 batteries. 23 mph & 20 mile range with no peddling (Sorry, what are peddles for?).

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qdos
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Postby qdos » Sun Jul 06, 2008 8:18 am

I think the SVA man is rigidly sticking to the letter of the book and I can see where he is comming from but as you know you do not need to have a servo fitted. The sticky bit it seems in this case is there's no provision for a servo assisted brake where the brake system is sufficient to stop the car whithout the aid of the servo.

It could take a while to find a suitable sensor/switch but in the meatime what about fitting the pump on a rubber mounting to insulate it a bit as I suspect a significant amount of the noise is transmitted noise through the mounting which hen resonates through the structure of the car.

PS I've kind of got the same thing on my Ginetta with a non servo system which modern drivers are not used to (people now expect power assist on everything) One of the possible servos I could use is a BMW system from the 80's but I forget which BMW now. Great to hear the car is now road legal by the way :D

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EVguru
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Postby EVguru » Sun Jul 06, 2008 10:17 am

If the brakes are fine with an unpowered servo, but a little heavy, take the servo out. They have a lot of drag and the brakes will be a lot lighter without. If you make up a dummy servo, just a spacer tube and pushrod, then you can easily revert. Why have a noisy pump and an extra 12v load if you don't need to?

Performance brake setups should be quite heavy, it makes it much easier to modulate them to just under the lockup point. With practice you can comfortably out-brake ABS (which is designed to leave spare grip available for steering, NOT give you maximum stopping).
Paul

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ChopperMan
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Postby ChopperMan » Mon Jul 07, 2008 6:30 am

Kelvin, yes the SVA guy was pedantic but he could have asked us to remove the servo before he passed the car. I will try isolating the pump from the chassis and see how noisy it is...... The rest of the car is sooo quite it really does notice.

Paul, yes removing the servo probably would make the brakes better, however my legs are not very strong, Arthritis, and I prefer the security of power brakes.

Are the vacuum switches on the Berlingo and CF integral to the pumps?

Cheers,

Ian
Electric chopper ebike with PUMA motor (1.2kW) and 36V 20Ah LiFePO4 batteries. 23 mph & 20 mile range with no peddling (Sorry, what are peddles for?).

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NickJ
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Postby NickJ » Mon Jul 07, 2008 7:19 am

Ian

If you look at RS components web site or contact your local dealer for Norgren pneumatics then the following is a vacuum switch for -0.2 to -1 bar adjustable. The contacts are light so you will need a relay to operate the motor of the pump.

RS Stock No. 289-5513
Manufacturer Norgren
Manufacturers Part No. M/58024/VF
Catalogue page 3 - 4355

Hope this helps

Nick

ChopperMan
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Postby ChopperMan » Tue Jul 08, 2008 5:57 am

Hi Nick,

Thanks for your input, this looks like it could work, my one reservation is the supply voltage to activate the switch, it's showing "250Vac/dc" on the specification?

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=2895513

Thanks,

Ian
Electric chopper ebike with PUMA motor (1.2kW) and 36V 20Ah LiFePO4 batteries. 23 mph & 20 mile range with no peddling (Sorry, what are peddles for?).

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