engine output graph

[wangp1283]

Hi, I wonder how the torque output graph of a 4cylinder engine looks
like. For example, when they say the engine delivers 200 ft lb of
torque at 3000 rpm. Is is an average? (because the output isn't
smooth for an IC engine). If it's not smooth, can someone tell me a
general idea of how far the lowest torque deviate from the highest
torque in terms of percentage? in a cycle?

The reason I'm asking this is because I need to have an actuator
that can match the engine output force (torque times radius) in real
time. Can this be done? It might be difficult since the force isn't
constant.

Thanks.

 

[GregLocock]

That torque figure you see quoted is an average. An accurate trace of torque vs time is rarely seen, for various reasons, but it can be calculated reasonably accurately. Fora 4 cylinder I'd expect a peak torque about twice the average, but it would vary a lot.

You can do what you are proposing, active engine mounts do work.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[wangp1283]

Thanks a lot for your reply.

I just searched on some article regarding active engine mounts and it seems to be the type of technology I can use.

Are they pretty expensive? (from a vehicular perspective)

 

[wangp1283]

Do they work well in high rpm?

 

[GregLocock]

They are very expensive - I don't think anybody makes them in production.

I don't know how well they'd work at very high frequencies, I suspect that above 200 Hz or so the inertial effects would require some fairly advanced technology.

Alternatively you can buy a servo hydraulic actuator that will go to 200 Hz. It will be quite expensive.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[wangp1283]

I searched the internet and it seems a few vehicles have "active engine mounts", such as Lexus ES300

http://www.canadiandriver.com/previews/02es300.htm

and even some Honda vehicles.

Or are they an different technology from what we were talking about?

 

[GregLocock]

OH, I didn't know they were in production. That type don't provide full torque cancellation, they rely on the inertia of the engine block to damp out most of the high frequency stuff. Basically they use a hydraulic engine mount with a small loudspeaker to pump the fluid at high frequency and cancel out the vibration.

I am reminded that somebody makes a hydraulic torsional actuator, that sounds like what you are looking for.





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[ChrMeissner]

Hi!

I don't know if I understood your (first) question right, but some months ago I calculated the (theoretical) torque over the angle of the crankshaft.

It's avaible under:

http://service.gmx.net/mc/jGpwpnQScfOkGrO14WD3kEoYL1PVnA

You've to chose: "GMX Mediacenter starten" and you can download the file.

I hope, it illustrates the issue.

Christian (TU-Chemnitz, Germany)

 

[wangp1283]

So does this mean if I put a spring under the tensioned drive chain from an engine driving a vehicle. The spring will go "up and down" because of the sinuosoidal nature of the engine torque output.

In another word, the tension in the chain is always flutuating (and quite a lot too, if you say the maximum torque can be twice the average).

This makes it hard since I want to built some flexibility into the system (like a spring) to protect against some short temporary shock load. And the system you mentioned is too expensive.

It also need to feel smooth to the operator. Any ideas?

 

[MikeHalloran]

If you use a chain to drive a vehicle with a perfectly smooth engine, the spring will go up and down because of the change in instantaneous radius of the chain tension ("chordal action" in the popular press).

Take a look at inline fours with internal balance shafts, and at boxer fours, and at intentionally flexible structures.

In response to your actuator question, it's possible for hydraulic actuators to match an engine's torque, but getting a strong hydraulic system to respond above 100Hz can be difficult.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[wangp1283]

So if use some sort of spring between the engine and load, the spring will go "up and down" because the torque output isn't constant and is rather sinuosoidal, and to an almost negligible degree, the chordal effect of the chain.

The reason I need a spring or an actuator in the first place is because I need to build a SLIGHT amount of "flexiblity" in the system to smooth out EXTREMELY short period of increased (shock?) load. The amount the chain need to yield is about 0.1mm, a very tiny amount. Yet still keep the tension of the chain right (matches that of the engine/load at the time right before the shock load)

That means if a loaded chain under tension can yield around 0.1mm (due to the spring), then the problem will be solved.

So maybe I can use some sort of spring that offer a range of force in a very short distance (around 3mm), by using varible constant spring or by some type of gearing.

Then the spring stiffness will ensure that it constantly matches the engine torque, (actually, the force of the spring is a lot smaller than the chain tension because of the angle of the set up). But it can "yield" 0.1mm if needed and still keep the chain tension approx. the same. (without the risk jerking the chain or sputtering the) engine)

Just hope the "spring going up or down" won't be felt by the operator. Or affect the efficiency too much. I guess it won't since the energy of the compressed spring will be gained back (how much?) after the spring decompresses. And also the amount of travel (of the spring) is so tiny.

I think this is the simplest and the cheapest to solve my problem. Do you think so?

 

[MikeHalloran]

We don't know what your problem is.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[byrdj]

If trying to "smoothing out" the torque pulses from each cylinder's combustion, why not increase the flywheel?

 

[truck]

Several thoughts would come to mind here:

1. for smoothness, an I4 is probably the worst case engine

2. consider adding a balance shaft; an external shaft can be designed and added. It is a moderately successful solution, but very ugly.

Truck

 

[wangp1283]

Since the torque output of an IC engine is not smooth, and varies so much.

Does this mean the instantaneous acceleration of a vehicle also flutuate with the engine torque? (but we "feel" an average)

 

[GregLocock]

No, the driveline of a car is a very effective low pass filter. The main torsional resonance is at about 6 Hz, so from about 10Hz onwards you get some attenuation.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.