Vacuum Pump Circuit and its Usage in automotive

[Rhyder88]

I have an vague idea that vacuum is used for effective braking system . Is there any online source available to understand about the circuit of automotive engine vacuum pump circuit and its uses .
Else could you elaborate about this circuit?

 

[patprimmer]

An Otto cycle engine at speed against a closed throttle is inherently a vacuum pump.

Regards
Pat
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[Rhyder88]

thanks patprimmer. what will happen if there is no vacuum pump in the engine

 

[patprimmer]

Do you know what the Otto cycle is?

Do you imagine a situation where you would not close the throttle as well as applying the brakes?

Are you a high school student?

Are you ant sort of engineer?

Regards
Pat
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[benta]

Hmmmm. This question makes me wonder how BMW solved the vacuum issue in the ValveTronic engines (no throttle, variable intake valve lift instead).

Benta.

 

[SomptingGuy]

Or pretty much all the diesel cars running around Europe. I think mine has a vacuum pump on it, but I've not looked and probably wouldn't recognise it anyway.

- Steve

 

[crerus75]

I know that some US market diesels currently use vacuum pumps of one type or another (I see a listing for replacement vacuum pumps for some Ford trucks up to the 2011-2012 model years on rockauto.com). GM seems to be using some flavor of the Hydroboost system, where braking assist is provided by power steering pump pressure, not vacuum. Two other diesels I glanced at (2006 Jeep Liberty and late 2000s Mercedes E-series) seem to use conventional brake boosters, implying a throttle of some sort. I don't know if there are currently any other systems out there.

 

[Tmoose]

My 1975 gasoline burning Volvo 245 had an auxiliary engine driven vacuum pump. When it failed I still had enuff vacuum to run the brakes OK, so I did not replace or fix it. (The repair kit is probably in a box out in the garage). My Later Volvo 240s don't have an aux pump. They all have plastic vacuum reservoirs hidden under the dash.

http://i.ebayimg.com/t/G4-87-VOLVO-...QCGk~$(KGrHqJ,!h!Ew5I(pyeSBMQbfmIQLw~~_35.JPG

 

[patprimmer]

Yes. Unthrottled engines need a vacuum pump.

The BMW ValveTronic uses the inlet valves as throttles. Closed inlet valves on the inlet stroke do the same thing as a closed throttle plate.

Regards
Pat
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[140Airpower]

Rhyder88,
"...what will happen if there is no vacuum pump in the engine..." ?
The answer to this is No Brakes. If the engine quits or the THROTTLE STICKS OPEN, brake vacuum is lost and the driver will have a hell of a time trying to stop the car. Engine quitting happened to me on a mountain road (hole in gas tank) and I almost flew over a cliff "to heaven". A runaway throttle is similar. Poor braking against a pulling engine may cause the driver to pump the brakes, dumping the stored vacuum and having no ability whatsoever to brake the car.
Usually, the engine-as-vacuum-pump is a reliable built-in source for vacuum-powered brakes. Normally, under braking the engine is idling or motoring at closed throttle, pulling a high vacuum and continuously replenishing the vacuum canister. Fine system. I would prefer an auxiliary vacuum pump (wouldn't have solved my mountain road problem) or electric power brakes (not available).

 

[patprimmer]

Brakes actually work with no vacuum. You just have to push the pedal harder. With both feet if necessary in an emergency with an automatic transmission. With a stick shift, vacuum still works so long as it is in gear and the throttle is closed.

Up until about 50 years ago, very few cars had power assistance to the brakes and they still stopped.

Regards
Pat
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[IRstuff]

I concur, losing vacuum is no fun when it comes to braking, but it can be done, assuming your legs haven't completely atrophied, and you recognize what the problem is.

TTFN
faq731-376

 

[Tmoose]

drum brakes typically have some degree of self energization.
Disk brakes don;t.
When I was younger and stronger I had a non power brake Ford F150 pickup, with front disks (and a factory 8 track player). I often used both feet for normal stopping.

 

[NormPeterson]

The first new car I bought had an unassisted disc/drum system that was easy enough for most anybody to be able to use.

Of course, that car weighed half a ton less than most of today's cars and a ton less than some.


Norm

 

[dgallup]

I had a beater Dodge pickup with a leaky vacuum booster (ruptured diaphragm). The booster and master cylinder were integral so the replacement cost was roughly what the truck was worth. I just disconnected the vacuum line so the engine (440 wedge) would run properly. It took a firm push but you could stop it. Emergency stops with a load in the bed required standing on the pedal and pulling up on the steering wheel for all you were worth.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[HowDidYouBreakThat]

The '88 Ford Ranger I drive to the office every day has manual everything, including brakes. You don't even notice it until you get into a car with power brakes and give your passenger whiplash at the first stop sign.

Terry
KI6FCI

 

[140Airpower]

Hmmm, you guys are biased. I too have driven all varieties of crippled DIY "cars": ones with sticking throttles -quick shift to neutral and cut ignition off; ones that wouldn't idle -learn heel-and-toe on the fly; no hydraulic brakes -have to modulate the parking brake; no clutch -learn clutchless shifting on the fly; no seat -sitting on a milk crate; etc.
I don't call that driving.
In the scenario I described I didn't mention that I also lost power steering on a Camaro w 2.7 turns lock-to-lock. It was downhill. It took ALL my strength to slow the car enough and to turn the wheel enough to stay alive. That was many years ago. Today I wouldn't make it, nor would any woman, nor an elderly person.
In general, sudden loss of brake boost is potentially fatal. Same for a runaway throttle, especially for a person with no expectation and experience. The fail-safe condition for safety systems is that they should work under loss of power. The power brakes on that Camaro did not work if I, a strong man, was standing on the pedal and could not lock the wheels.

HowDidYouBreakThat, I'm curious about your Ford truck. I was not aware of any disk brake system on a heavy vehicle that did not have boost. As mentioned, drum brakes have self-servoing action, but disks do not. Did the pedal have more travel than normal?

 

[HowDidYouBreakThat]

It's just a Ranger, I wouldn't consider it a 'heavy' vehicle. I never thought about it, but it does have a few inches of travel, where a car with power brakes might have one. I guess I'm just used to it.

How about this for fun: I was driving a Freightliner w/53' trailer across Montana when my transmission exploded. The input shaft was locked, but the truck would roll. Tow truck pulled me about two miles with chains to the top of the hill so I could drop the trailer. One foot on the clutch, one foot on the brake with the engine idling. My left leg almost didn't make it to the top.

Terry
KI6FCI

 

[140Airpower]

When I say "heavy" I mean not light. Anything with much more than 1000 lb on the front wheels should have power disks, IMHO. But, it just takes more master cylinder stroke to get the mechanical advantage to make enough pressure.

 

[patprimmer]

For the same braking effect, the pedal travel is the same boosted or non boosted. It is the amount of fluid displaced by the M/C. Only difference is the amount of force required on the pedal to get that displacement.

Regards
Pat
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