Most fuel efficient speed?

Cool. This is what I have learned for today.

 

me too!

 

Oh really? Then how do you explain engine braking....?

 

So an injector is only needed to spray Gas just before the intake valve is open, if it was on all the time it would flood the engine..WOW.....also all the cylinders aren't firing at the same time...I.e. firing order
Injectors typically are used for a Pulse configuration that are tuned for the long term and short term fuel strategy(s).

http://www.youtube.com/watch?v=N2y77vEKorI

 

Perhaps I should have been more specific in my statement.

Just to temporarily get off thread here, If the engine is not running, the pump is not turning. The pump is not operated by the rotation of the transmission components. Hence if an automatic transmission vehicle's engine is not running, there will be no fluid flow to the torque converter, and the input shaft of the transmission will be unable to rotate either, since if there is not fluid pressure, there is nothing to hold pressure on the clutch plates.

Engine braking in an automatic transmission can ONLY be achieved if the engine is running, and driving the fluid pump. Care to test it? Take any automatic transmission vehicle you have and run it up to 60 MPH. Now while leaving it in gear, turn off the engine. Now turn on the key. Does the engine attempt to spin up? No.




Now back on topic here, I am curious and will do more research on the DFCO system. I am more interested in how it keeps the engine from actually stalling out in an automatic transmission. Since the engine HAS to be rotating to provide pump pressure, and automatic transmissions have an overrun clutch system when in D3 and D4 which allows the transmission speed to go faster than the engine without a load, what prevents the engine RPM from dropping so low that the engine dies and then you lose pump pressure. It looks like I have a lot of reading ahead of me.

 

There were a very few old transmissions, like back in the 1960's IIRC, that had output shaft pumps. In other words, you could push start them like you can with a manual transmission.

Back to engine braking, and still slightly off the OP's original topic...

My new Tacoma sometimes feels like it has way too much engine braking in normal driving. When I let off the gas it's really slowing down and feels like I need to push in the clutch or shift to a higher gear, if I was driving a manual. Does that sound normal? It rolls smooth and easy if I put it in neutral so I think it's hurting my fuel economy a lot.

 

Yes. There are other threads, but I agree. It's a little bit much when your passenger bobs their head when it engages.

 

but if the torque converter is already full of fluid since you are coasting in gear, wouldn't that keep the engine rotating and thus keep the pump going once the injectors shut off?

Is the pump electric or manual? If it is electric then when you shut the key off while coasting, the pump will drain and it won't start the truck back up.

 

We don't buy trucks for MPG! How many times does it have to be said? If you want to drive as efficiently as possible, yet keep your sanity, there are a few things to consider:
1) Moderate your acceleration. Nothing sucks down gas lite punching it every time the light turns green. However, it's not really polite to accelerate so slow that everyone is going around you while flippin you the bird!
2) Use you brakes less. Coast up to stoplights whenever possible. If you manage to not stop completely you can save a lot of gas(less acceleration back up to speed).
3) Cruise control is your friend. I usually set it to about 65 on my speedo which equates to around 70mph with my tires. You'll do better setting it to 60mph. I just set mine where I'm comfortable. Remember, nobody likes those assholes in the slow lane doing 50mph, making the big rigs pass em and screw up traffic for the rest of us.

 

Thanks! I hadn't found those those threads and just wondered if it was common.

 

Injectors shut off to the point of preset idle. Same with a diesel.

 

Yes, I do realize that there were some autos that had twin pumps. However we are talking modern vehicles, including those with the DFCO.

On a normal automatic transmission (non-hybrid) the fluid pump is mechanical, and is driven normally by the torque converter housing where it splines into the transmission. As for fluid, it is in constant flow, not just filling up the converter. Otherwise the fluid would overheat too quickly. If engine RPM drops too low, the pump will no longer supply fluid flow sufficient to operate the turbine of the converter, or the clutches/bands.

As we have discovered through some research, the injectors ARE actually turned off COMPLETELY in certain coasting situations. I too had believed it was just to idle, but found out that was incorrect.

 

I see. And yes I know the fluid is flowing, and it being too low wouldn't be an issue if the injectors only shutoff after 2200rpm because the 2nd gen 5 spd auto stall rpm is 1800 so you would certainly still have enough fluid to keep the motor turning.

Still doesn't explain why you could shut it off and it wouldn't start back up though... (I've never tried this, just taking your word for it) unless you let it get below the stall rpm of course.

 

Fucking raping it!

 

I have always wanted to test this. I would assume 40-50 mph. I get about 21 mpg no matter what

 

Stall RPM has no bearing on this type of situation. It just won't work like you are thinking. Hard to explain without trying to give you an entire course on how the torque converter and automatic transmission works.

 

I understand the basics of it as far as power going from motor to tires. Haven't thought much about it going backwards.

And if I understand stall rpm right, it is the rpm at which the torque converter is so packed full of fluid that it essentially can't slip anymore. For example if I stand on the brake and hit the throttle in gear around 1800 rpm, I will be spinning the rear tires, or the motor will die. Since the pump is mechanical and powered off the rotation of the motor, I would think that maintaining an RPM well above 1800 would allow for the torque converter to maintain enough fluid in it to keep the motor turning via the momentum of the vehicle.

 

http://www.bankspower.com/techarticles/show/10-understanding-stall-speed

 

I'd say 55-60...I average 17.4 MPG with a 50 mile per day round trip commute that I do about 70 on. I used to average 17.1 with my 2011 DCSB TRD OR and Load Range D All Terrains. I just bought a new Jet Ski and was a little nervous towing it that fast on the highway. (First time towing jight little jet ski trailer) so I stuck to 55-60. Round trip 300 miles, pulling the trailer was about 150 miles. On the way there, I averaged 18.3 mpg (highway 75mph). On the way back, I got 21.1. Filled up before I left and after I picked up the trailer...

Personal opinion only...55-60 for best MPG. This is probabally true for just about any vehicle...I'm guessing something to do with wind resistance.

 

The motor would not die. It would simply stop increasing RPM untile either the tires began to spin, or the vehicle started to move at enough of a speed where stall was no longer needed.

The torque converter does not control how much fluid is in it. The pump supplies fluid, and the return orifice regulates bleed-off of the fluid.


The above link about stall speed describes it in great detail.Stall speed however only works in one direction. It will not work in the opposite direction because if you try to drive the turbine, fluid flow will not travel in the proper direction. Yes, you will get SOME attempted movement, but again, it would never be enough to actually drive the rotation of the engine. If wanting to discuss this more and find out more detail, start a new thread.... I think we have hijacked this one enough and got it off topic.