Definition of a Motor

[jdogg05]

Hi everyone, just looking for some categorical clarification as I am writing a report on rotating equipment and giving brief overviews of the main types of rotating equipment. In my report I have basically categorized all rotating equipment into two classes: drivers and driven equipment.

My understanding of the hierarchical definition of a motor is that it is the most broad term. In essence, electic motors, engines (heat powered motors), hydraulics motors, pneumatic motors, etc. are all "motors". For instance I have always been of the understanding that an engine is a type of motor (a heat motor), but a motor is not necessarily an engine (e.g. an electric motor is not an engine). Does this seem to make sense?

My real question is related to turbines and motors. A turbine, like a motor, is a "driver". It converts heat and pressure energy into mechanical shaft rotation. Is a turbine a type of motor...? I mean, as per my logic above (an "engine" is a type of heat powered motor) wouldn't a typical gas turbine "engine" then be a type of motor?

I know nobody expresses things this way in a colloquial sense, but I am looking for a fundamental, hierarchical definition.

Thanks for the input!

 

[GregLocock]

In my opinion motor and engine can be used almost interchangeably. But strictly speaking you can have an engine that is merely a complex device built by an engineer, eg siege engine, analytical engine, whereas a motor always (?) seems to be a way of converting other forms of energy into force or torque.



Cheers

Greg Locock


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[ivymike]

engines (heat powered motors)

maybe fluid-powered motors ... although I can't think of any heat-powered ones which aren't fluid-powered offhand, nor vice-versa.

take that back ... hydraulic motors are not heat powered but are fluid powered. stick with heat.

 

[jdogg05]

After doing quite a bit of reading I have come to the following opinion: before the industrial revolution any complex machine/device/mechanism could be classified as an "Engine" ( as per GregLocok's comment on siege weapons). When the ICE started being used for automotive purposes the term "Motor" was invented to distinguish it from the prominent Steam Engine at the time. This is why when referring to automotive ICEs people use the word "Motor" and "Engine" interchangeably.

However, I think today in the modern day context, "Motors" are meant (or should be meant) to refer to machines that convert a certain potential energy (chemical, electric, pneumatic, hydraulic, etc.) into rotational mechanical energy. I have read a lot of opinions that a motor is something that simply converts a potential energy into a rotational OR linear force, but I don't think this makes much sense... We have a more generic term that nicely captures both: an Actuator. Actuators can be classified as both rotational and linear, with the latter encompassing everything a Motor would not. Also, when I think of a Motor I think of a rotating shaft.

Still open to any thoughts on this!

 

[berkshire]

jdogg05,
Why don't you throw this up into forum1010 and let those guys bash it around. This Motor ,Engine, Rotary actuator, Rotary expander. semantics thing varies from country to country. See what the language guys say.
B.E.

You are judged not by what you know, but by what you can do.

 

[GregLocock]

I should apologise for confusing energy and force and torque. 4am post!

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[BigClive]

GL - your original 4am statement seems valid enough to me - what do you think it should say?

 

[140Airpower]

I think the real problem here is that there never has been a widely accepted definition that distinguishes between the two terms.
But, if we accept that an electric motor and a water wheel (or water turbine) are not engines, but are motors, then... I was taught that an "engine" converts heat energy into motion. So, a steam engine consists essentially of two major components, a fire box and boiler that converts heat energy into pressure and then a motor that converts pressure into motion. So, a gas turbine consists of a burner that converts heat energy into pressure and kinetic gas flow and a turbine the converts kinetic gas flow into rotational motion. Without tapping the rotational motion of the shaft, the kinetic gas flow creates motion as a reaction to its momentum. So these are engines.
By the corresponding logic, a turbocharger could be a motor if it only converts gas momentum into rotational motion and it could be an engine if it converts exhaust heat into motion (there is a temperature drop across the turbo). So, because of adiabatic effects, the turbine of a turbocharger (and a steam motor) are not "pure" motors whereas a water wheel or water turbine would be "pure" motors.

I was not completely de-confused by what I was taught.

 

[imcjoek]

I was taught that an "engine" converts heat energy into motion

How about rocket motors?

Let us not forget that outboard motors have engines inside them.

 

[btrueblood]

Rocket engineers have their own terminology. Motors create thrust from solid propellants, while engines create thrust from liquid propellants fed from low pressure tanks (i.e. engines have integral propellant feed pumps). Thrusters take their fuel from pressurized tanks.

"I was taught that an "engine" converts heat energy into motion" - by that definition, guns and bombs are engines, and so is our atmosphere.

I really think it's like defining a screw vs. a bolt.

 

[140Airpower]

It is precisely correct that guns and bombs are heat engines by that definition and the atmosphere has commonly been called an engine (with no mechanical parts other than the working fluid itself). But, a solid rocket is an engine by that definition. The freedom of rocketeers to distinguish between these terms on the basis of the type of fuel or the complexity of auxiliary parts is an example of what happens when there is no universally accepted definition and historical use is ambivalent.

BTW a screw is not necessarily a bolt (jack screw, ships propeller), but AFAIK, a bolt has a screw as a part. Again, historical use.

 

[jdogg05]

I tend to agree with 140Airpower on his demarcation of the subject however I still feel that a motor should be the more generic term. As you stated, the pressure drop across a turbine is not adiabatic (we can't build exergetically perfect machines). Therefore, fundamentally a motor must be something that converts some type of energy (chemcial, heat, presure, kinetic, electrical, etc.) into rotational energy (or in some rare cases linear motion). In my mind, an engine is still something that converts heat energy into CONTROLLED and DELIBERATE motion for the purpose of powering something. I think the semantical classification of guns and bombs as engines could be argued, but it's really of no practicality...

Also, adressing the topic as a whole: there are always exceptions.

 

[140Airpower]

I think the definitions have been pretty loose, thus the controversy. To be more precise, if we restrict the discussion to ONLY "heat engines" we can unequivocally define anything that converts heat energy into motion (kinetic energy) as a heat engine. So, this minimally includes solid rockets, guns, bombs, the atmosphere, IC engines, external combustion engines, etc, etc, ALL of which are commonly thought of as engines. By this definition these engines include a motor function. In some cases the motor function is handled by a distinctly identifiable part of the engine. In those cases the difference between the whole engine and the motor is conceptually obvious.

Further, we might include in the definition of heat engines things that convert heat energy into forms of potential energy or stored potential energy (like the steam boiler or electrical generator, battery, etc), but then the motor function may not exist and there is no discussion about what's a motor and what's an engine.
I think the above is sufficient for the restricted discussion of heat engines.

Then we can talk about motors that convert a form of potential energy into kinetic energy in apparent isolation from any heat engine like an electric motor or a wound rubber band, but when you look closely, inevitably there will be an attached heat engine at some time somewhere be it a nuclear plant or hydro system powered by the Sun, a human or a team of mules, etc.

 

[BigClive]

It was common practice in the past refer to the whole car as a "motor" - and the "motor" had an "engine". This particular use of the word "motor" continues today in the name of a lot of second hand car lots - "Acme Motors" for example.

 

[140Airpower]

That's interesting. We never called our cars "motors" we called them "hoopties" and a hooptie might not even have a motor... or an engine either.

 

[berkshire]

140Airpower (Automotive)
Did you make them go, by yelling out " hooptie do!"

B.E.

You are judged not by what you know, but by what you can do.

 

[BigClive]

I had never heard of a "hooptie" - but I looked it up on the internet and discovered that I actually drive one.

I also discovered that a big proportion of new car makers call themselves "motor" or "motors" - such Toyota Motor Company and Nissan Motor Company etc. and even General Motors. The use of the word "motor" meaning "car" seems to have been more common than I thought.

 

[140Airpower]

I think "motor car" was a synonym for "automobile", and to make a trip by car was to motor as a verb as in "...to motor west...take the highway that's the best..." (Route 66). As for GM, they were going to use a more correctly descriptive name, "General Heat Engines", but their ad company's advice was for something shorter, thus their contribution to the confusion. BTW, "motor car" is also an aptly used name for electric commuter train cars that often are motorized.
No, we never yelled out "hooptie do". That would have been uncool. Most of what we yelled out started with "Hey baby..." and might continue with some borderline morally objectionable message. Anyway, a hooptie might not even be a running car or even a complete assembly of car parts, but the essential thing is that there was always a hope and a promise of a car.

 

[decipha]

I didn't bother to read through the discussion so excuse me if I'm way off but in simplistic terms, I always assumed motors are powered externally and engines are powered internally