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Using an inline engine as a stressed member


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#1 dav115

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Posted 08 September 2010 - 17:36

Following on from Luca Marmorini's quote here, what exactly is it about the inline layout that prevents/makes unfeasible its usage as a load bearing member?

Edited by dav115, 08 September 2010 - 21:23.


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#2 King Six

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Posted 08 September 2010 - 17:57

Is that even true, there were 4 cylinder turbo's, like someone said the BMW M12/13.

http://www.gurneyfla...bof1engine.html

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That's the BT52 (Piquet WDC 1983) Looks stressed to me, but I may be entirely horribly wrong. This era was before my time. :cat:

Edited by King Six, 08 September 2010 - 17:57.


#3 Bloggsworth

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Posted 08 September 2010 - 18:42

The front engined Diva GT used a stressed Ford 105E engine within a spaceframe chassis, but I assume you mean as a replacement for the chassis. The main problem would be vibration, it would rattle your teeth and your rivets. It's hard enough to eliminate the vibration through a road car using elastomeric mountings. Brabham may have got away with it in F1 as the drivers will put up with almost any discomfort to race competetively, and turbos have a soft powerstroke characteristic, otherwise a 1.5 litre 4 cylinder engine using a stock block would have destroyed itself PDQ.

#4 Ali_G

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Posted 08 September 2010 - 19:19

Is that even true, there were 4 cylinder turbo's, like someone said the BMW M12/13.

http://www.gurneyfla...bof1engine.html

Posted Image

That's the BT52 (Piquet WDC 1983) Looks stressed to me, but I may be entirely horribly wrong. This era was before my time. :cat:


The BT55 required a frame at the back to carry the BMW M10 engine.

#5 meb58

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Posted 08 September 2010 - 19:42

...also thought Honda had a problem a few years back suing their F1 motor as a stressed member...from memory the engine distorted enough under cornering loads to destruct itself.

#6 Greg Locock

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Posted 09 September 2010 - 00:06

" Besides this, Marmorini notes that to install an inline 4 cylinder engine would require a complete redesign of the chassis. "Like this it won't have a structural role", explains the Ferrari engineer, "It needs a reinforcement structure around it, if you are to do without a huge engine casing.""

It's not unusual to measure 30g vibration or more on a 4 cylinder, as opposed to 10 on a V8.

That's 10dB of fatigue that you really really don't want. 4IL engines are just about the horriblest practical high speed engine, although doubtless someone will come up with a 500 cc single that revs to 12000 rpm.

I don't know why an inline should be especially sensitive to torsional loading, I agree the block is less stiff in torsion than a V, but is the difference really so big?


#7 Ali_G

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Posted 09 September 2010 - 07:48

I don't know why an inline should be especially sensitive to torsional loading, I agree the block is less stiff in torsion than a V, but is the difference really so big?


Would it make much difference if the I4 engine was mounted on it's side instead of upright ?

#8 DaveW

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Posted 09 September 2010 - 08:24


Is not the engine of an F3 vehicle a) stressed & b) an in-line 4? A Dallara F3 chassis certainly has a very respectable structural integrity.



#9 gruntguru

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Posted 09 September 2010 - 09:54

Would it make much difference if the I4 engine was mounted on it's side instead of upright ?

No difference to torsional stiffness. Probably some reduction in longitudinal beaming stiffness.

#10 NeilR

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Posted 09 September 2010 - 10:22

yes and no. If you look at the 4cyl engines carefully you will see that they use specially made rocker covers and the sumps as structural members.

#11 DaveW

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Posted 09 September 2010 - 10:34

yes and no. If you look at the 4cyl engines carefully you will see that they use specially made rocker covers and the sumps as structural members.

Agreed... The same is true, I think, for current F1 engines.



#12 gruntguru

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Posted 09 September 2010 - 10:37

yes and no. If you look at the 4cyl engines carefully you will see that they use specially made rocker covers and the sumps as structural members.

(Assuming you are responding to my post) If an engine has "special" stiffer top and bottom covers, it will definitely lose beaming stiffness if you mount it on its side.

#13 Bloggsworth

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Posted 09 September 2010 - 11:11

I don't know why an inline should be especially sensitive to torsional loading, I agree the block is less stiff in torsion than a V, but is the difference really so big?


It is several orders of magnitude stiffer if it is short.

#14 Greg Locock

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Posted 09 September 2010 - 23:16

It is several orders of magnitude stiffer if it is short.


Well, it'd be an inverse function of length^1 but I was imagining the problem was torsional windup between adjacent cylinders or bearings, rather than overall.

#15 gruntguru

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Posted 09 September 2010 - 23:41

Well, it'd be an inverse function of length^1

For a given engine displacement, the volume of the block will be approximately constant and torsional stiffness will be an inverse function of length^3 (I think.)

#16 kikiturbo2

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Posted 10 September 2010 - 01:43

For a given engine displacement, the volume of the block will be approximately constant and torsional stiffness will be an inverse function of length^3 (I think.)



true, but V engine blocks will be wider, so even at equal length (however unlikely) they will be stiffer in torsion

#17 Lee Nicolle

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Posted 10 September 2010 - 01:48

I must be very conservative as to me using a high RPM lightweight alloy engine of any sort as a stressed member is a recipe for disaster. Though they have done it for 50 years!! Mounted front and rear in cradle to stiffen the chassis Yes. Like some are and the engine is then a semistressed member and not used for mounting suspension too as some are which has always scared me.But as i said I am too conservative. In all bar one [semistressed] I have always rubber mounted my engines[ cast iron production type engines] and have never viabrated my cars to bits.Or tore the side out of the block.


#18 gruntguru

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Posted 10 September 2010 - 10:19

true, but V engine blocks will be wider, so even at equal length (however unlikely) they will be stiffer in torsion

Not much. The 1/L^3 relationship already accounts for increased width and height. A V8 only has about twice the torsional stiffness of an inline 4 based on one bank of the V8.

#19 RDV

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Posted 10 September 2010 - 17:24

V8s use the cam covers and sump as shear-plates transversal(sorry about phrasing...try'normal') to the torsional load...its quite effective, and one tries not to make the block and cylinder heads work too much, think of them as spacers keeping the cam covers stable...
The sump can take care of itself...F3 4-in-lines have sumps and cam covers that quite dwarf the block...otherwise 'A' frames do the job...

Where you have the space, as in LMPs quite often you have 'A' frames even on V8s...some of the narrow angle V12 were quite bad torsionaly also...basicaly its bad to twist a block, when cylinders go oval under load, all sort of nasty things happen, plus twisting the crank loses a kot of power in friction...trust me, I've had some doozies(Tm FatBoy) :smoking:

Edit- could only unearth this on a quick google, its a 2007 Fiat F3 example...note the sump is effectively a huge flat plate, whilst the camcover is very structural...

Edited by RDV, 10 September 2010 - 17:38.


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#20 DaveW

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Posted 10 September 2010 - 22:10

Edit- could only unearth this on a quick google, its a 2007 Fiat F3 example...note the sump is effectively a huge flat plate, whilst the camcover is very structural...

Which is one of the reasons that an F3 is such a good vehicle. I'm sure Marmorini would be able to implement something similar.... BTW, I agree completely with the rest of your post. I would only add that size doesn't necessarily imply (excessive) weight, but it does mean that material is (or can be) well-placed to yield the stiff structure required both for engine reliability & for good vehicle dynamics.

Lee: I guess this will be an attempt to preach to a confirmed agnostic, but have you tried replacing your rubber engine mounts with, say, nylon look-alikes? A-frames can certainly help, but they do not constitute an efficient & stiff structure in their own right - in my opinion. I have carried out more rig tests than I care to admit to, with race vehicles covering the complete spectrum, more or less. I can recall only one having a suspended engine. That was a poor vehicle lacking contact patch load control - but it was transformed after the engine installation had been "fixed".



#21 Lee Nicolle

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Posted 11 September 2010 - 00:36

Which is one of the reasons that an F3 is such a good vehicle. I'm sure Marmorini would be able to implement something similar.... BTW, I agree completely with the rest of your post. I would only add that size doesn't necessarily imply (excessive) weight, but it does mean that material is (or can be) well-placed to yield the stiff structure required both for engine reliability & for good vehicle dynamics.

Lee: I guess this will be an attempt to preach to a confirmed agnostic, but have you tried replacing your rubber engine mounts with, say, nylon look-alikes? A-frames can certainly help, but they do not constitute an efficient & stiff structure in their own right - in my opinion. I have carried out more rig tests than I care to admit to, with race vehicles covering the complete spectrum, more or less. I can recall only one having a suspended engine. That was a poor vehicle lacking contact patch load control - but it was transformed after the engine installation had been "fixed".

Most of my cars have been production based tintops. My Sports sedan [Chev powered]may have benefited minimally from solid mounting the engine but to make engine plates and mount them to a car that was part production part spaceframe would not have achieved a great deal. And mounting the engine solidly to the side mounts on the block is an accident waiting to happen. When i backed into a tyre wall at about 100kph the rubber tore but was caught by the safety straps and apart from breaking the distributor the engine was unharmed. Do that with solid side mounts and yoou need a new block. Though when mounted on an engine plate is normally ok.
Apart from the classic supermodified [sprintcar] the rest are mounted as the manufacturer intended, partly rules and partly expediency.
I have seen a helluva lot of broken blocks primarily from crashes but some due to viabration. A solidly mounted BDG was rubber mounted again and no more cracked blocks.
Urethane engine mounts are helpful in motorsport and I would use them if i could buy them for the cars I am playing with. I have used them as all that is advailable for some older front drive road cars but they turn the car into crap with the extra noise and viabration. And the urethane comes unbonded from the metal brackets in a short time so they are not a great asset.
As an aside I have seen a lot of damage caused to road cars by using urethane suspension bushes as it does not have the elasticity of rubber [nor the noise damping either]. These incluse broken castor arms, suspension trailing arms, bottom control arms as well as the chassis pickups cracked out by using urethane. And normally a steel sleeved bush seperates so the arm is walking everywhere and in a couple of cases the buch just crumbles to bits..And sometimes rubber is actually stiffer. I have found here in Oz the best urethane bushes to be sold by Pedders. The market leading brand to me is rubbish, with so many failures.
While I use it with some trepidation on competition cars I will not fit it to road cars. If nothing else I do not need the liability claims!!

#22 DaveW

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Posted 11 September 2010 - 08:33

This is an attempt to explain my suggestion, Lee, without wishing to influence you in any way. The vehicle I referred to had a layout (very) similar to your OzV8's & was a conversion of a road car. Initially, it used standard rubber power train mounts (i.e. nothing "technical"). These were later changed for much stiffer mounts.

I should explain, perhaps, that suspension springs & dampers can develop a load only if they have something to push against. Suspension forces are reacted by the vehicle sprung mass, & mathematical modellers normally assume that to be a monolith. The assumption is never true (for any real vehicle), and that is particularly so when the power train is suspended. Hence a very useful plot to extract from a rig test is the frequency response function of the effective mass that the suspension has to work against.

This is such a plot for the front axle of the vehicle under discussion. To explain the plot a little, the function shown in red demonstrates the mass to be around (3,800/9.81) kg (per corner) at low frequencies, increasing as the frequency increases until it reaches a peak value of (14,000/9.81) kg at 8 Hz. At this frequency the power train & chassis are moving in phase, so the power train works to increase the apparent mass (it is acting as a dynamic absorber, a TMD in the current jargon). It might be concluded that a hub mode with a coincident natural frequency would be well controlled. Because the power train mode is lightly damped, however, the apparent mass reduces dramatically at frequencies greater than 8 Hz, reaching a minimum of (1,400/9.81) at 9.5 Hz., & an even lower value at 11.5 Hz. The rapid change in apparent mass demonstrates why a TMD is such a problematic device. The function shown in green shows the effect of stiffening the power train mounts. The local peak at 8 Hz is lost, but the apparent mass remains high over the 10-20 Hz frequency range - which is where the front hub modes actually occurred in this example.

It is possible to compute the energy dissipated by the suspension components during a rig test run. This plot shows the various energy dissipation functions for the standard mount case, expressed as a percentage of the input energy. Estimates are shown for the front & rear tyres, and front & rear dampers. The cyan dotted function is the sum of the four components. Significantly, the total is just 72% of the input energy at the "spot" frequency of 9.6 Hz, implying that something else (the power train mounts?) dissipated 28% of the input energy at this frequency (compared with only 12% for the front dampers). You might ask how nominally undamped mounts could achieve this, & my reply would be they could if the mount deflection was sufficiently large. You might also wonder about the effect on the standard road car. The magnitude of the problem increases as damping is increased, which is why road cars tend to be such uncontrolled jellies (but damped mounts certainly would help) or uncomfortable rattle boxes.... Anyway, here is the equivalent plot for the stiff power train mounts.

Apologies, the subject really requires a more detailed explanation, but hopefully you will be able to deduce why I think it is a good idea to stiffen power train mounts for a competition vehicle, both for vehicle dynamics reasons & for engine mount life (leaving aside the possibility of a single extreme event, perhaps).

p.s. I'm unfamiliar with urethane mounts, but I would guess they introduce damping, rather than stiffness. Which may explain why they are short-lived. Hydramounts would be a better option, I think, although they must be tuned to the vehicle.

Edited by DaveW, 11 September 2010 - 09:39.


#23 gruntguru

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Posted 11 September 2010 - 09:05

Apologies, the subject really requires a more detailed explanation, but hopefully you will be able to deduce why I think it is a good idea to stiffen power train mounts for a competition vehicle, both for vehicle dynamics reasons & for engine mount life (leaving aside the possibility of a single extreme event, perhaps).

Another great post thanks Dave - very informative. More like this please.

#24 Greg Locock

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Posted 15 September 2010 - 00:00

One reason that urethane to metal mounts tend to split is that are rather hard to design and require very careful surface prep and process control. An aftermarket parts supplier probably manages one of those three. One of the projects I was involved in used a lot of stressed urethane to metal joints as seawater proof joints for millions of dollars of electronics, hence my cynicism. (For instance, the 'radius' of the fillet where the elastomer blends into the metal requires either multiple iterations of design, or a very complex analysis, if it is not to severely compromise the fatigue life of the part).

We use a lot of pedders stuff when prototyping, they have good suppliers.







#25 McGuire

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Posted 15 September 2010 - 01:12

I just worked with Pedders USA on a project, was pleasantly surprised, impressed even.



#26 gbaker

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Posted 15 September 2010 - 01:20

...I don't know why an inline should be especially sensitive to torsional loading, I agree the block is less stiff in torsion than a V, but is the difference really so big?

I suspect "J" will be substantially higher for the V.


#27 mariner

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Posted 15 September 2010 - 04:38

Dave W's usual erudite comments above make me think about whether the longtitudinal shaking seen in top fuel dragsters is important in their tremendous launch grip. As the TF car launches the frame flexes until there is slight curve. Uncontolled this does nasty things but I wonder if the frequency is such that it helps the vital download inthe first few millseconds of "hook up".

As the things do o-100 mph in1 second it must all help.

#28 J. Edlund

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Posted 16 September 2010 - 17:56

This is how it's done with the LMP cars, which also use inline fourcylinders

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With two liters and over 500 hp, this wouldn't be much unlike a 1.6 litre 650 hp four cylinder for F1.

#29 desmo

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Posted 16 September 2010 - 20:20

Look at the strut running back from the bulkhead by the fuel filler to the gearbox case, quite reminiscent of the strut Renault added to their chassis when they went to the wide V angle on their F1 car. Is that a spherical bearing at the bulkhead end? Looks more useful for addressing bending stiffness than torsional.

#30 Tony Matthews

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Posted 16 September 2010 - 20:45

Look at the strut running back from the bulkhead by the fuel filler to the gearbox case,

I think there's one the other side, too.

#31 Greg Locock

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Posted 17 September 2010 - 00:02

I think there's one the other side, too.


Are you channelling Giugaro? He famously remarked on seeing the TR7 for the first time, Oh my god they've done it to the other side as well.



#32 desmo

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Posted 17 September 2010 - 00:27

It was certainly no TR8 in the styling department. Nosiree.

#33 gruntguru

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Posted 17 September 2010 - 03:34

It was certainly no TR8 in the styling department. Nosiree.


:rotfl:

#34 Tony Matthews

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Posted 17 September 2010 - 08:26

Are you channelling Giugaro? He famously remarked on seeing the TR7 for the first time, Oh my god they've done it to the other side as well.

:lol: Great quote! Unfortunately I was just thinking aloud, and I wish I hadn't...