Discussion
I'm doing some brainstorming for a possible kit-car design and trying to be a bit different with the layout; so figured I would get some critique from the PH crowd (as I don't know of any other decent car forum with a technical section - is there one?).
I want to have a mid-engined AWD setup (ideally rear-mid rather than front-mid) so a thought struck me...
Take an ordinary transverse engine and box; mount it longitudinally in the rear and connect two prop-shafts to where the drive-shafts are usually. Thus making the box differential act as a centre-differential.
Connect a pair of rear differentials front and back and you have an AWD system.
I know there are a number of odd things about this setup -
- The H pattern on the box would be sideways, but some mechanical wizardry should be able to sort you our a normal shifter
- Engine tend to rotate clockwise which means that if you mount the engine behind the box you will have the shafts rotating in the wrong direction (unless you use an older Honda motor as this is anti-clockwise). However; the Nissan r180 differential housing will accept the differential unit if it is flipped so this will correct the wheel rotation issue.
If you were to use this setup with a front-mid setup then the things will spin the the correct direction anyway.
The idea is to use Torsen (or probably Quaife diffs) all round (so similar to the Audi Quattro setup really) - and yes I know there are limitations in this but I want an all mechanical AWD system without any fancy electric diffs (for now).
Now my concern is this ... having the system setup as AWD would I think put forces on the gears in the gearbox that they do not see in a normal FF situation - I'm talking about a force acting INTO the box along the drive/prop shafts ... unless you hit a wheel head on in an FF setup you are unlikely to see that sort of force.
Having said that; I also assume that gearboxes are all fairly similar to they are probably designed to withstand those types of forces anyway.
Other than the sheer "why would you do that" factor can anyone spot any other issues with the idea?
Now some more thoughts; while this would work fine and dandy with an I4 setup it would not really work with a V6 (easily) or an H4/6...
A boxer engine (Subaru) would offer much smaller packaging lengthwise really; but is too wide to run a prop-shaft down the side of (and I do not really want to mount the engine at an angle).
So I had a really stupid idea of having the boxer mounted transversely connected to a longitudional FF box; but this would mean all the engine weight is to one side of the centre-line and would really mess up having a good weight distribution.
So is my idea of using an FF I4 the only way to do it (I do not want to use exotic Porsche gearboxes; want to be able to use cheap everyday stuff) - barring any major issues someone can come up with - or is there say a transfer case used by one of the offroad vehicles that can withstand plenty of torque and that also sends the prop-shafts underneath the engine rather than down the side of the engine?
I want to have a mid-engined AWD setup (ideally rear-mid rather than front-mid) so a thought struck me...
Take an ordinary transverse engine and box; mount it longitudinally in the rear and connect two prop-shafts to where the drive-shafts are usually. Thus making the box differential act as a centre-differential.
Connect a pair of rear differentials front and back and you have an AWD system.
I know there are a number of odd things about this setup -
- The H pattern on the box would be sideways, but some mechanical wizardry should be able to sort you our a normal shifter
- Engine tend to rotate clockwise which means that if you mount the engine behind the box you will have the shafts rotating in the wrong direction (unless you use an older Honda motor as this is anti-clockwise). However; the Nissan r180 differential housing will accept the differential unit if it is flipped so this will correct the wheel rotation issue.
If you were to use this setup with a front-mid setup then the things will spin the the correct direction anyway.
The idea is to use Torsen (or probably Quaife diffs) all round (so similar to the Audi Quattro setup really) - and yes I know there are limitations in this but I want an all mechanical AWD system without any fancy electric diffs (for now).
Now my concern is this ... having the system setup as AWD would I think put forces on the gears in the gearbox that they do not see in a normal FF situation - I'm talking about a force acting INTO the box along the drive/prop shafts ... unless you hit a wheel head on in an FF setup you are unlikely to see that sort of force.
Having said that; I also assume that gearboxes are all fairly similar to they are probably designed to withstand those types of forces anyway.
Other than the sheer "why would you do that" factor can anyone spot any other issues with the idea?
Now some more thoughts; while this would work fine and dandy with an I4 setup it would not really work with a V6 (easily) or an H4/6...
A boxer engine (Subaru) would offer much smaller packaging lengthwise really; but is too wide to run a prop-shaft down the side of (and I do not really want to mount the engine at an angle).
So I had a really stupid idea of having the boxer mounted transversely connected to a longitudional FF box; but this would mean all the engine weight is to one side of the centre-line and would really mess up having a good weight distribution.
So is my idea of using an FF I4 the only way to do it (I do not want to use exotic Porsche gearboxes; want to be able to use cheap everyday stuff) - barring any major issues someone can come up with - or is there say a transfer case used by one of the offroad vehicles that can withstand plenty of torque and that also sends the prop-shafts underneath the engine rather than down the side of the engine?
rypt said:
Now my concern is this ... having the system setup as AWD would I think put forces on the gears in the gearbox that they do not see in a normal FF situation - I'm talking about a force acting INTO the box along the drive/prop shafts ... unless you hit a wheel head on in an FF setup you are unlikely to see that sort of force.
Having said that; I also assume that gearboxes are all fairly similar to they are probably designed to withstand those types of forces anyway.
It's the other way round. Propshafts are designed so that they do not transmit these forces to the gearbox - they have sliding splined sections so they can change length.Having said that; I also assume that gearboxes are all fairly similar to they are probably designed to withstand those types of forces anyway.
rypt said:
Now some more thoughts; while this would work fine and dandy with an I4 setup it would not really work with a V6 (easily) or an H4/6...
A boxer engine (Subaru) would offer much smaller packaging lengthwise really; but is too wide to run a prop-shaft down the side of (and I do not really want to mount the engine at an angle).
So I had a really stupid idea of having the boxer mounted transversely connected to a longitudional FF box; but this would mean all the engine weight is to one side of the centre-line and would really mess up having a good weight distribution.
So is my idea of using an FF I4 the only way to do it (I do not want to use exotic Porsche gearboxes; want to be able to use cheap everyday stuff) - barring any major issues someone can come up with - or is there say a transfer case used by one of the offroad vehicles that can withstand plenty of torque and that also sends the prop-shafts underneath the engine rather than down the side of the engine?
A V engine may be wider than an inline but the C of G is still vertically above the crank, so it's just packaging.A boxer engine (Subaru) would offer much smaller packaging lengthwise really; but is too wide to run a prop-shaft down the side of (and I do not really want to mount the engine at an angle).
So I had a really stupid idea of having the boxer mounted transversely connected to a longitudional FF box; but this would mean all the engine weight is to one side of the centre-line and would really mess up having a good weight distribution.
So is my idea of using an FF I4 the only way to do it (I do not want to use exotic Porsche gearboxes; want to be able to use cheap everyday stuff) - barring any major issues someone can come up with - or is there say a transfer case used by one of the offroad vehicles that can withstand plenty of torque and that also sends the prop-shafts underneath the engine rather than down the side of the engine?
Your FWD box will already be fitted to accept CV joints, which can handle running at an angle better than Hardy-Spicers; if you use CV joints on the distal ends of the driveshafts as well, then you have a degree of freedom to mount the engine more centrally with the shafts running at an angle (as long as they don't foul on the corners of the thing).
The big problem with doing this is that you have two final drives in series so you end up with a very low ratio. If you're after making a rock crawler this probably doesn't matter but for a road vehicle you'll be wanting to get a custom 1:1 final drive for the gearbox...
Pigeon said:
The big problem with doing this is that you have two final drives in series so you end up with a very low ratio. If you're after making a rock crawler this probably doesn't matter but for a road vehicle you'll be wanting to get a custom 1:1 final drive for the gearbox...
That was the main issue I saw (unless someone makes 1:1 rear differentials that is) - chances are that in order to have an ideal setup you would have to replace the final drive on each differential rather than just the one in the gearbox (I don't think you can get a 1:1 FD into a gearbox really).So perhaps using a normal longitudional FR gearbox and a transfer case from some 4x4 that has the axles run below the engine is the better solution; question is .. is there an OEM vehicle that has that (that lets you put in a decent differential in the transfer case also).
There just is no easy way to make a mid-engined (be it front or rear) AWD car :/
chuntington101 said:
this is a cleaver way of getting 4WD into a VERY small package! http://www.dpcars.net
I've seen that before and he's not far off my idea of having a shaft go forwards and backwards but using a custom made transfercase from what I can work out that then uses chain drive (I would prefer shafts to chains as well).Is it good? Well probably; but it also costs a lot and requires expensive custom made stuff (and I want to be able to use as much existing engine, gearbox and differential as possible).
Also the way his engine is mounted is fine for a single seater as the weight of engine is half balanced by weight of driver - but it is not ideal for anything above that.
Edited by rypt on Thursday 11th June 13:12
I have also spent some time thinking about a mid-engined 4WD set up. The simplest i could come up with is to use the running gear from, say, a 4WD Ford Sierra. If the front and rear differentials are flipped over, the wheels will turn backwards. Twist this arrangment 180 degrees on its Y axis, and all of a sudden the engine is at the back, and the wheels are still turning the correct way.
The only issue that stopped me from using this idea is the fact that the torque bias will be incorrect. Since the rear axle is now at the front, the most torque will be applied to the front wheels. As far as i know, it is not a simple case of swapping over a couple of gears in the transfer box to swap the torque bias around. This is assuming that transfer boxes are not usually open in a similar way to an open differential?
I have heard of adjustable torque biasing transfer boxes, however the cost, rarity and modifications required for my application would be prohibitive.
The only issue that stopped me from using this idea is the fact that the torque bias will be incorrect. Since the rear axle is now at the front, the most torque will be applied to the front wheels. As far as i know, it is not a simple case of swapping over a couple of gears in the transfer box to swap the torque bias around. This is assuming that transfer boxes are not usually open in a similar way to an open differential?
I have heard of adjustable torque biasing transfer boxes, however the cost, rarity and modifications required for my application would be prohibitive.
Have also spent a long time thinking about this, and (being somewhat of a landrover techi), came up with the use of a landrover transfer box (this is the box that spits torque to 2 axles as opposed to one)
The beatury of a landrover transfer box si that they are nigh on indestructible (about the only part that is), they are dirt cheap, have all sorts of ratios, but critically they can be driven from either the front or the rear of the transfer box- which means you can stick the negine where you want, and have any engine rotation- useful for then you turn the engine around.
The beatury of a landrover transfer box si that they are nigh on indestructible (about the only part that is), they are dirt cheap, have all sorts of ratios, but critically they can be driven from either the front or the rear of the transfer box- which means you can stick the negine where you want, and have any engine rotation- useful for then you turn the engine around.
pugwash4x4 said:
Have also spent a long time thinking about this, and (being somewhat of a landrover techi), came up with the use of a landrover transfer box (this is the box that spits torque to 2 axles as opposed to one)
The beatury of a landrover transfer box si that they are nigh on indestructible (about the only part that is), they are dirt cheap, have all sorts of ratios, but critically they can be driven from either the front or the rear of the transfer box- which means you can stick the negine where you want, and have any engine rotation- useful for then you turn the engine around.
The only issue with that is the fact that you end up with a solid 50-50 split as the box does not use an LSD I do not think (or err does it? - will look into this idea further The beatury of a landrover transfer box si that they are nigh on indestructible (about the only part that is), they are dirt cheap, have all sorts of ratios, but critically they can be driven from either the front or the rear of the transfer box- which means you can stick the negine where you want, and have any engine rotation- useful for then you turn the engine around.
)Edited by rypt on Wednesday 17th June 20:44
b
ks just typed a really really long reply and lost the damn thing
there is a landrover box called a borg warner which is a huge LSD transfer box- again driveable from both sides and will divert from 100% to 50% to either axle as needed.
http://www.milneroffroadracing.com/transmission.pd... might be of interest with some light weight custom stuff
when they say lightweight they mean it- some of the comp safair cars weigh no more than 1200kg but have 500bhp and geared to 120mph over terrain you would struggle to walk let alone run over!
ks just typed a really really long reply and lost the damn thingthere is a landrover box called a borg warner which is a huge LSD transfer box- again driveable from both sides and will divert from 100% to 50% to either axle as needed.
http://www.milneroffroadracing.com/transmission.pd... might be of interest with some light weight custom stuff
when they say lightweight they mean it- some of the comp safair cars weigh no more than 1200kg but have 500bhp and geared to 120mph over terrain you would struggle to walk let alone run over!
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