Governers in Automobile Engines

In modern petrol engines, there is no governor as such. However, rev limiting (limiting maximum RPM) is accomplished by the engines ECU (electronic control unit).

Sorry to say but...not a well-conceived, well-defined, unambiguous, or well-thought-out question...or one lending itself to any single definitive answer (or even a score of answers). A better question (albeit also overly broad) would ask: what are the most obvious and feasible mechanisms for top-limit speed governing of reciprocating, internal combustion engines used in motor vehicles. You would do well to reformulate and repost your question with, for example, these things also in mind.

What do you mean by "governor"? Maximum speed? Not operator controllable or intervenable?

What do you mean by "modern"? In the present post-modern period, most of the history of automobiles (and of IC engines) could be held to have passed with the modern era--at least, arguably, since the great war or 1920's.

What do you mean by "mechanism"? Mechanical only? Hydraulic or pneumatic? Electronic? Firmware?...Or what might you have intended to exclude...to prevent your being overwhelmed with different answers as to approaches which have been used or which could be used.

What manner of fuel pump (or fuel delivery system) have you in mind? A fuel pump "system" (fuel pumping system) can mean many things and encompass subsystems not typically thought of as part of "pumping" per se. For example, of all the "automobiles" produced to date, most are normally aspirated--with carburetion.

To give a starting point for thinking through...here are some ideas (but by no means all) about how engine governing has been and could be accomplished.

Manual or fixed mechanical adjustment of ignition advance--as in the Model T.

Cruise controls with inputs from varying sources, such as: drive shaft, RPM sensors...

Throttling of the engine

Restriction of air intake or fuel delivery by various means

Centrifigal weights or air vane feedback mechanisms

Restriction of exhaust

ECU calibration

...the list could go on...

So, if you have in mind some methods of engine governing and want to learn of others, you might want to state which you are already familiar with.

If you have a particular, specific, project application in mind (or a tentative concept for same) you might wish to describe the direction(s) you have in mind...so that others can help fill in the blanks, so to speak, and not need to post in an encyclopedic manner.

Hope this is found to be helpful....

You didn't mean to help. But you were ambiguous. A simple question to satisfy ignorance only needs a simple answer. Now we all know which bulb is brighter!

I take it from the complex reply you chose to make to a sensible, if brief opening question, that you are not an engineer? I would guess that your interests lie in politics - or perhaps you are a teacher, perhaps of history.

The question as posed was fair.

"Modern automobiles" can easily be translated into: automobiles in current production.

The term governor is also fair as it is usually taken to mean maximum speed governor.

As Blink replies, most engines - both petrol and diesel - are now governed by the software in the EMM or ECU. Thus the engine tuners and racing enthusiasts can re load new software maps to make the engines rev more - at the expense of fuel economy, emissions and engine life - in order to boost performance.

The subscriber is trying to impress the questioner by his "knoledge" of IC engines partcularly automotive so he could AWE him or her. This does not suit our purpose in conducting rational dialogs

Then the subscriber must suppose that you all are trying to impress the questioner not only with your with limitations of experience with automobiles and governors, but also with your reading comprehension and literacy as well--not to mention your clairvoyance as to what an unseen person's intentions are. But you left out one thing--two actually. First, you did not offer one iota of responsive information to the questioner's question--even though you purport to know exactly what information he was seeking, and in what exact context. Second, a well reasoning reader--engineer even--would have been willing to wait and see how the questioner responded--to let him be the judge of whether or not he benefitted from the suggestions, as hoped; or was insulted by the attempt to help...as somehow you have been. Try having more open minds, and less fragile egos, and you might find there are almost always different ways to look at things, and sometimes something new to learn.

In other words, you have gained nothing by responding with personal attacks. Let's hope the original questioner is less prone to personal volatility and insecurity.

You are defo not an engineer. An engineer makes life simple. There is nothing wrong with that question. A fuel pump is a fuel pump. If he said fuel system or fuel pumping system then there may be some confusion.

most are normally aspirated--with carburetion

Most recent -- with in the last 5 yrs or so --- autos are "Fuel Injected" a very different method than carburetion. Carb can only deliver to a limited point so limiting the revs is due to lack of fuel when the carb cant keep up. Fuel injectors will meet the demand required by the engine at all revs so limitation is required. I am not really sure but i think fuel flow is interupted electronically by the control unit when the safe rev zone is exceeded.

Guest 2 -- The question is an appropriate question and easily understood. Your complex answer was far to difficult to decipher. If you are going to criticize or nit pick at least get a screen name so we can all tell who you are.

Guest 1 also get a screen name.

You sound like me, when it comes to dates -- you must be getting old too!

It has actually been 20 years or so since the majority of cars became fuel injected. I still have a 1990 Daihatsu, a simple, run-of-the-mill car, and it is fuel injected, as were all its contemporaries.

You are right re fuel flow limitation, although most systems first retard ignition timing and then cut off (entirely) fuel flow to alternate, and then all cylinders. (The cutoff must be entire or the cylinders would run lean, which can cause engine damage.) Most modern systems act pretty smoothly, and can go through several (increasingly severe) steps in milliseconds.

Actually, it is very easy to over-rev many carburated engines, as well. Conservatively tuned ones would encounter valve float at a little over redline, and in many engines, this was self-limiting: it worked like an unintended rev limiter. When the valves can no longer follow the cam profile (due to inertia overcoming the valve springs) the engine runs poorly.

On the other hand, in highly tuned engines, the clearance between valve and piston can be small and overreving could cause damage. It was not uncommon (in racing) that one missed shift would scatter an engine from overreving. Porsche was one of the earliest manufacturers to fit a rev-limiter to a production car -- the first limited ignition only, and was implemented when the Porsche 911 still used fully mechanical fuel injection.

Without a governor, an unloaded diesel engine given a full power demand will accelerate without limit, as the fuel is injected in at a rate proportional to the engine speed. Such an uncontrolled situation can cause the engine to disassemble itself spectacularly and potentially tragically. The purpose of the governor is to trim the supply of fuel as the speed rises, thereby reducing the risk of self-disassembly.

Carburettor engines do not suffer this difficulty, as the engine is limited by its ability to aspirate, which becomes more difficult as engine speed rises.

Governors appeared at first on fixed reciprocating steam engines as a method of maintaining a constant speed as the load and steam pressure fluctuated. Examples may be found for inspection at technical museums world-wide.

PWSlack,

What a wonderful phrase " self disassembly"

It reminds me of the consequences of a too complex gearbox design which GM specified for a truck we were building. This involved a range change and a splitter shift. Thus it was far to easy to change from 8th to 1st at full throttle instead of 8th to 9th on a 16 speed box.

The effect was to encourage the twin countershafts to move apart rather rapidly, the truck stops dead, and the parts of the gearbox fall onto the road in front of the truck, having passed clear over the cab.

PWSLack wrote:

"Without a governor, an unloaded diesel engine given a full power demand will accelerate without limit, as the fuel is injected in at a rate proportional to the engine speed. Such an uncontrolled situation can cause the engine to disassemble itself spectacularly and potentially tragically. The purpose of the governor is to trim the supply of fuel as the speed rises, thereby reducing the risk of self-disassembly."

PW, thank you for your very comprehending and adroit message...as it helps to clarify my suggestions to original questioner (OQ) as to ways the question might have been narrowed--and the ensuing storm calmed in advance, so to speak.

The operative word in your message, I believe, is: trim--as in trim the injection/intake rate at the chamber(s). I would offer--and, yes, this is another way of stating what you have stated--that governing is a way of matching fuel delivery to the load (or permissible speed limit) imposed on (or within) the engine; whether it be to slow or (in some applications) to speed the engine cycling speed; whether it be implemented systemwise or by a discrete governor device (or loop) as OQ's choice of thread title seemed to suggest.

However, I am not yet aware (until other discussion participants advise...) that any car engine governing "mechanism" involves discrete inputs (presumably, to control flow rate), as could be inferred from OQ's post, to the fuel pump itself; whether it be in current production engines using electric pumps--either fuel injected engines with recirculating fuel delivery or carburetor-fitted engines--or even engines employing mechanical pumps. The trim word also seems to comprehend this--and that engine governing even (as said by Blink) if implemented in part at the ECU, does not involve the pump as an engine speed governing component. (Again, I stand willing to be corrected or referred to more current information.)

To others who perceived that I was jumping on OQ's, or Blink's, post I now retract my retort to you and replace it with an apology to anyone taking umbrage. I also ask your future forbearance, in understanding the inherent risk of being an early responder to most any new (especially, ambiguous new) question. Any self-serving appearance on my part was not intended; and sometimes a little misunderstanding and controversy is unavoidable... just to get a civil, and productive, conversation going. And, I can't always be the one to step back, waiting, for others to hazard the first step...

Might I suggest that the most constructive step towards obtaining forbearance would be to register yourself. It's very easy to take umbrage to long and possibly excessively pedantic responses from "guest".

As you become more accustomed to this forum, you will find that we may engage in spirited debate on the technicalities of an issue. However, you will also find that most of us will not berate a poster for being imprecise in a question. I am certain that there are many posters here who speak and write their first, second, and third languages as clearly as I do my first, but may have a harder time with their fourth. So, if a post is a little muddy, most of us will give the poster the benefit of the doubt before criticising the question. After all, what possible beneficial purpose could be served by the criticism?

Most responders here found it very easy to understand what the original poster was asking -- most of us are familiar with the historic use of governors. The fact that you can't find a mechanical or electronic device on a modern (current production) car (diesel or petrol) actually called a governor is of no concern: we all knew just what he meant.

And the answer is very simple: now, rpm limiting and vehicle speed limiting is handled by the ECU (or brand name equivalent). The concept is phenomenally simple. No, the control of fuel flow is not literally done at the "fuel pump," but the original poster might have used the term (as diesel mechanics often do) to mean the injection pump, in which or on which the classic mechanical governor used to reside.

That you were unable to intuit the meaning of a simple question is no reason to berate the questioner. Better to look inside. If you want to avoid the inherent risk of being an early responder to most any new (especially, ambiguous new) question, then I'd suggest you take a moment to think first, before responding. That you still seem to be trying to imply that it was the question that was lacking, and not your response, reinforces for me the notion that you might spend a little more time looking inside, to see what you gain by criticising the original question. You're clearly a fairly smart guy, but apparently have a lot to learn... as we all do.

What I regret most is that some responders did not observe the pains I took to avoid the very things you say others perceived (but, rather, took my efforts as if they were addressed to themselves.) Else, why would I have opened with an apology--a self effacement--in order to impart to the questioner that my intention was not to berate. Should I have said to the questioner something like, "Why, the engine is governed practically all over, except at the pump?--and, thereby, suffered the questioner to perhaps be thought he was being called a fool, implicitly? Why also would I have then proceeded to sit at my keyboard thinking of points, not for my own aggrandizement but, points which might be taken (by the guest questioner, that is) as ways in which the original question might be misunderstood without a bit of clarification? Yes, you can say--and perhaps everyone will agree--that "everyone" except me knew precisely the questioner's intent and the full scope of his question; but what I perceive--and I say this in most humble terms--is that:

(first) No one responded (except you) prior to my post--prior to having some cues as to what might be the consensus opinion as to what the question's actual intent and scope was;

(second) A shared trait among some (but not all) was to assume what should be read into a question (even when the question seems, at least in part (and no one seems to refute this so far) to belie those assumptions)--not only assume respecting the question and the questioner (and that it was from a like-minded engineer of equal experience), but also assume my motivations as a respondent for not making assumptions but, rather, positing examples as to ways the question might elicit unintended (i.e, misapprehended or superfluous) responses, and examples by way of ideas (which, it was hoped the questioner would ponder) which might stimulate or persuade the questioner to narrow his question to his fully intended purpose;

(third) Some, evidently not observing that the points in my post were confined to the question and the subject matter, and were in no instance directed...(as pertaining) personally to/at the questioner; and also not observing--not even assuming what might have readily been read between the lines--efforts to avoid accidental affront (to the questioner)...those same some saw fit to assist the questioner by joining to direct ad hominens, belittlements, and public ridicule--things pertaining to anything but the questioner's subject--to me; doing so apparently so as to demonstrate their own social (and technical?) acumen as compared with mine.

You have suggested that answering a question (so long as it is most of us with the answer?) with certainty for which the question was muddy demonstrates giving the benefit of doubt (presumably with or without feedback from the questioner to see such doubt vanquished), and I have no reason to dispute that this truly reflects the spirit of your intentions; or that such is not a valid approach. By the same token, however, how, and why, should it be said (other than as a group imperative) that (even merely) an attempt to unmuddy the water--to diminish doubt before venturing an answer--is not also extending benefit of doubt; extending it merely in different form: extending it so as to elicit participation of the doubted in removing doubt(?). It seems here that to disregard that possibility can only (in this instance) have found justification in a predisposition to see my efforts as bent not on engaging the questioner, not even on mild admonishment, but only on mindless, calculated, or otherwise destructive criticism. I must respectully (still) reject that assertion.

You have offered a perception that I am lacking in introspection and circumspection, but I would offer all of the above, and my answer to the original question--albeit that it is admittedly not without fault--as evidence to the contrary...if one is willing to see. It might interest you also that in the course of any one year, for as many years as I care to remember, I typically devote hundreds if not thousands of hours engaged in helping others--some in work setting some not--some unimpaired some who are profoundly troubled or incapacitated--some with mundane problems some whose problems and abilities to cope with same are as intractable as any matter that might appear on this board or elsewhere. It has been my experience that most persons have not judged my efforts or interactions with them (and others) as lacking, inappropriate, detrimental, inhospitable, or (in most instances) unsuccessful.

That said, rest assured I will give your admonishments and the tone in which they were offered all their due consideration. I seek not to be smart (although I thank you for the compliment) because I know of the troubles which that nebulous affirmation can bring--and of the general misunderstanding and pointlessness of that word. My intent only has been that the questioner's difficulty would be resolved--in that there is satisfaction--irrespective of whose, or who all's, response(s) were the key. Believe it...or not. With that in mind I think best to withdraw from this forum until such time as the original questioner chooses (we should all anticipate) to advise that his question has, or has not, been adequately answered. I would like to add that I greatly enjoy posts and interactions--including yours--which I have seen and sometimes interacted in--including yours--on this board. There are lots of really bright and knowledgable people here...and plenty whose contributions remind me how much I have to learn--or will never have time to learn.

OK fellows, don´t make a storm in a water glass; all of you are right, because engineers got to be PRACTICAL but also PRECISE, that is why, in any design, you have two different phases: CONCEPTUAL and DETAILED; that is, you begin with a very general simple idea to solve a practical need, then you refine and specify it

On behalf of those who post questions at this forum, let´s try to be both: concise and informative, in order to give them some real assistance

Traditional governers were designed to regulate engine speed, reducing the fuel supply as the engine speed increased until a balance point was reached.

Now, a lot of the purpose has changed - as the construction of engines has improved, the need to restrict accelleration rates is less (faster accelleration is usually encouraged) so the software approach allows great changes in speed in low/mid range, and less as the maximum engine speed is reached.

In trucks - and some sports cars - there are also maximum speed regulations, so there have been various ways employed to restrict the maximum vehicle speed.

Some involve capping engine speed at that which would give maximum road speed in top gear. These methods do not allow quick accelleration in lower gears, and result in the vehicle struggling needlessly on uphill sections.

Mercedes "experimented" with a unit which pushed the accellerator pedal up when maximum road speed was reached, but some of these were too strong and the driver's foot was thrown from the pedal.

Now input is also taken from the speedometer, so that this can be used to limit the top speed gradually rather than suddenly. The result is effectively an automatic cruise control, as the vehicle can be driven at the maximum set speed with the pedal floored, and the fuel injected being optimised for the load.