a few engine questions.

[Brandon1023]

Ok so these questions aren't 100% related to go karts, but they have to do with energy and engines. If someone can answer a question here andthere to clear up my confusion, ill appreciate it a lot.

1. In a typical car, how does the engine continue to run when its in park? (I'm talkin about a automatic tranny.) I know in a manual, you depress the clutch which disconnects the engine. So how does "Park" work? A classmate told me that it puts the engine in neutral while it locks the driveshaft.

2. When you're driving, and you're braking with the car in "Drive", how does the engine continue to spin if you have your foot on the brake while everything is connected?

3. With a centrifugal clutch, I know how it works.. but my question is, how does the crank continue to spin despite the weight of the rider and the kart? The explosion in the piston is THAT strong? Because I've been trying to go up a hill while watching the clutch, and I can see the bolt spinning extremely fast, but the sprocket not turning. Do the shoes slip? I would think the engine would stop due to resistance.

4. Finally.. how much gas does it take for every revolution more or less? I'm wndering, because I've rode around for maybe 2 hours with my little brother on a gallon of gas. I find it interesting that it takes such little fuel to move.

I know you guys here at diygokarts are really smart and I hope these questions can be answered. Thanks in advance!

 

[Doc Sprocket]

1. In a typical car, how does the engine continue to run when its in park? (I'm talkin about a automatic tranny.) I know in a manual, you depress the clutch which disconnects the engine. So how does "Park" work? A classmate told me that it puts the engine in neutral while it locks the driveshaft.

Yup Park is "neutral" with the park pawl engaged to lock the driveline.

2. When you're driving, and you're braking with the car in "Drive", how does the engine continue to spin if you have your foot on the brake while everything is connected?

Fluid coupling- With an automatic transmission, there is not a conventional mechanical connection between the engine and drive wheels, there's slippage. More modern cars use a locking torque converter that does actually lock engine and wheels together but it is disengaged while accelerating, decelerating, shifting and standing.

3. With a centrifugal clutch, I know how it works.. but my question is, how does the crank continue to spin despite the weight of the rider and the kart? The explosion in the piston is THAT strong? Because I've been trying to go up a hill while watching the clutch, and I can see the bolt spinning extremely fast, but the sprocket not turning. Do the shoes slip? I would think the engine would stop due to resistance.

Yes, there is slippage, that pretty much the definition of a clutch...

4. Finally.. how much gas does it take for every revolution more or less? I'm wndering, because I've rode around for maybe 2 hours with my little brother on a gallon of gas. I find it interesting that it takes such little fuel to move.

Not much, but there's waaaay too many variables to quantify.

 

[Brandon1023]

Thanks! As usual great answers from Toystory.

 

[Doc Sprocket]

I will accept cash, personal or business cheques, bank drafts, Paypal, Credit cards...

LOL- Kidding...

Considering I just spent my morning diagnosing and repairing my danged truck, oh happy joy...

 

[jamilcobra]

1) The torque convertor in an automatic trans works simmilar to two fans. One is connected to the crankshaft, the other to the transmission. In easy terms, the crankshaft fan spins which blows the transmission fan until it spins. Sort of like blowing a pinwheel.
2)See above. If you would like to see how a direct drive operates search for an article on sprint car drivetrains.
3)The shoes will slip, but you should here the motor lugging some kind of bad.
4)The fuel mixture is vaporized into a mist so it would be very little, but that is a good question. Somebody out there knows, but unfortunately I'm not somebody. It would be cool just to know though.

 

[Brandon1023]

Toystory, I have 1 more question. In cars, I've seen 2 types on engines. For example, in my neighbor's lexus, he has an inline V6, and the engine is facing front to back. Now in my dad's mazda, the engine is facing at a side to side position. What's the deal with this? Like.. kind of set up do you call that? If I made this too confusing, I can upload an image if needed.

 

[Doc Sprocket]

Engine with crankshaft parallel to car is said to be mounted "longitudinally", engine with crank perpendicular to car is a "lateral" installation. It simply depends on the manufacturer's driveline intentions.

Typically, rear wheel drive cars and trucks use a longitudinally-mounted engine, and typically front-wheel-drive vehicles use a laterally mounted engine. These are GENERAL statements, and in relation to front-engined vehicles. Like anything, there are exceptions.

 

[Brandon1023]

Perfectt. I've been wondering for some time why that is. I know ikeep saying "one last question." But I really have one last question that I just thought of. If a typical engine idles around 800 rpm and you take your foot off the brake, why does the car coast? In relation to the wheels, why don't they move at 800 rpm? I'm sure some energy is lost along the way.

 

[Russ2251]

Not much, but there's waaaay too many variables to quantify

It could be measured/calculated, however.

 

[Doc Sprocket]

It could be measured/calculated, however.

True. Gotcher calculator? I ain't doin' it!

Why coast when you let off the brake? The torque converter- while slipping- is STILL pushing fluid, and between that slippage and a low starting ratio, you just crawl along.

 

[devino246]

Perfectt. I've been wondering for some time why that is. I know ikeep saying "one last question." But I really have one last question that I just thought of. If a typical engine idles around 800 rpm and you take your foot off the brake, why does the car coast? In relation to the wheels, why don't they move at 800 rpm? I'm sure some energy is lost along the way.

Better to ask questions than practice ignorance. Everyone has to learn at some point.

The driveline is geared down so that some of the engine's RPM is converted to torque. Heres a hypothetical situation:

We'll use my '79 F150. The engine idles at 550rpm. The gear ratio for first gear is 2.46:1. The differential then gears down to the tune of 1:3.55. Now say the torque converter is allowing a loss of 100rpm.

So, 450/2.46=182.9268292682927rpm Thats the speed of the driveshaft.

Now, 182.9268292682927 geared down again through the differential: 182.9268292682927/3.55=51.52868430092752rpm This is the speed that the wheels are turning.

My tires are 28.88 inches in diameter. 28.88x3.14159265=90.7291957/12= 7.560766308333333ft The circumference of my tires.

So, 51.52868430092752x7.560766308333333= 389.59634feet per minute

389.59634x60= 23375.7804feet per hour

23375.7804/5280=4.427231136363636

So my truck is moving about 4mph

BTW, this site has a built in speed calculator, but its not accurate enough for my taste it
http://www.diygokarts.com/speed-calculator.html

 

[devino246]

True. Gotcher calculator? I ain't doin' it!

Shall I break out mine?

I'll simplify everything. My truck again:

I've been getting 6.7mpg. Lets say I average 20mph (probably fairly accurate).

20x5280=105600fph

105600/60=1760fpm

1760/7.560766308333333=232.780637rpm axle

232.780637x3.55=826.371261rpm driveshaft

826.371261x1.46=1,206.50204rpm engine


So lets drive at 20mph for 20.1 minutes to burn 1 gallon of gas

1,206.50204x20.1=24130.0408round per gallon of gas

We'll measure in ounces-128 ounces in one gallon

128/24130.0408=0.00530459111 per revolution

0.00530459111 ounce: That is a tiny amount!

I do not guarantee these calculations. I probably messed up somewhere along the line. If I didn't, then thats pretty cool, eh?

 

[Doc Sprocket]

Even if you did muck it up, who's to argue? You're sick, dood.

 

[outcrydrummer]

Shall I break out mine?

I'll simplify everything. My truck again:

I've been getting 6.7mpg. Lets say I average 20mph (probably fairly accurate).

20x5280=105600fph

105600/60=1760fpm

1760/7.560766308333333=232.780637rpm axle

232.780637x3.55=826.371261rpm driveshaft

826.371261x1.46=1,206.50204rpm engine


So lets drive at 20mph for 20.1 minutes to burn 1 gallon of gas

1,206.50204x20.1=24130.0408round per gallon of gas

We'll measure in ounces-128 ounces in one gallon

128/24130.0408=0.00530459111 per revolution

0.00530459111 ounce: That is a tiny amount!

I do not guarantee these calculations. I probably messed up somewhere along the line. If I didn't, then thats pretty cool, eh?

Want to come do my taxes????

 

[devino246]

For a better grasp on the amount used, that's approximately 0.16 milliliters or a little more than 3 metric drops. Now that's in a V8 engine! So, if divided by 4 (since its a 4 stroke engine), and we're under one drop per cylinder per combustion cycle! I fee like such a nerd!!


Come to think of it, my calculations are off because I failed to account for slip in the non-locking torque converter. Not gonna make that big of difference. Aaaand, that's all the math I'll be doing in 2012

 

[devino246]

Want to come do my taxes????

Sure, but be prepared, come audit time

 

[outcrydrummer]

Sure, but be prepared, come audit time

lol ok nevermind.

 

[Doc Sprocket]

I fee like such a nerd!!

You want the bad news????

3 metric drops

.
METRIC drops? You're telling me there's metric drops?

Now that's in a V8 engine! So, if divided by 4 (since its a 4 stroke engine), and we're under one drop per cylinder per combustion cycle!

Wait a minit- Lost here- Four strokes equals one revolution- and we (Yeah. We. LOL) were trying to determine fuel consumption per revolution. Why'd we just divide by four?

 

[Brandon1023]

Wow that was some pretty impressive math. ****.. lol. Can someone send me a link to some info about gear ratios? I know a bit about them, but not nearly as much as id like to know. Ust tryin to educate myself here.

 

[Russ2251]

typically front-wheel-drive vehicles use a laterally mounted engine.

...Or more prosaically, 'transverse mounted'.
First time I saw this configuration, it was in a '62 Mini Cooper (first built was in '59) with a 4 speed manual trans.
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