propshaft induced rollover.

[bill van snorkle]

Easy solution, get a proper car where they designed this out at the factory

On a G wagon the props rotate in opposite directions,

Job done.

Yet another victory for the "master race"

I asked an Australian G wagon owner a few years ago whether his rig suffered from torque roll on offcamber climbs and his answer was yes, the same as other vehicles. I do now racall however that during the latter part of World War 2 , Both Porshe and Borgward built some heavy 4wd artillary tractors that had twin contra rotating propshafts front and rear. these drove into individual 90 degree drives to each wheel. A worms eye view of the undercarriage that appeared in Wheels and Tracks magazine a few years ago suggested to me at first glance that in light of the severe metal shortages Germany was suffering,this was a lot of additional components and engineering for no possible advantage. but now I wonder if old Ferdinand Porshe did it to cancel out the effects of driveshaft torque on the vehicles ability to maintain even weight distribution on all wheels when attempting to drag heavy guns aroun offroad.

Incidently these tractors weren't very successful because due to rubber shortages they were unfortunately fitted with all metal wheels and tyres which offered very little traction.

Bill.

[ThreeSheds]

I asked an Australian G wagon owner a few years ago whether his rig suffered from torque roll on offcamber climbs and his answer was yes, the same as other vehicles. I do now racall however that during the latter part of World War 2 , Both Porsche and Borgward built some heavy 4wd artillery tractors that had twin contra rotating propshafts front and rear. these drove into individual 90 degree drives to each wheel. A worms eye view of the undercarriage that appeared in Wheels and Tracks magazine a few years ago suggested to me at first glance that this was a lot of additional components and engineering for no possible advantage. but now I wonder if old Ferdinand Porsche did it to cancel out the effects of driveshaft torque on the vehicles ability to maintain even weight distribution on all wheels when attempting to drag heavy guns aroun offroad.

Incidently these tractors weren't very successful because due to rubber shortages they were unfortunately fitted with all metal wheels and tyres which offered very little traction.

Bill.

How far apart were the propshafts? This arrangement is used in several British armoured cars and wheeled troop carriers; In this case the arrangement was used so that the props can run up the sides of the cabin and thus allow the roofline to be lowered by maybe six or eight inches (very important when people are shooting at you) It's not something similar here is it?

Another thought: Even with contra-rotating or dual propshafts there will still be some throttle-induced roll-torque from the engine - although much less than that from the propshafts trying to roll the axles.. Maybe this is what the Australian was feeling? Or perhaps the different roll-centres and suspension set up at each end of the G-Wagon means that the torque is not wholly canceled?

TS

p.s. Maybe we should be looking for a transverse engined beast with twin propshafts and viscous units between the front and back bevel drives? I have had such a vehicle (small, light, rear mounted m/cycle powerplant and indi suspension) in my mind for years!

TS

[bill van snorkle]

TS. The propshafts and 90 degree drives were side by side, close together on a common housing on a non independant arrangement, not a low silhouette effort as in armoured car application.

Engine torque reaction at a couple of hundred ft lbs is considerably less a couple of thousand ft lbs when multiplied through a truck style gearbox/transfercase unit.

Bill.

[Bush65]

Bill, the diff ratio plays a part in creating the torque roll. Torque roll is due to the reaction between the pinion and crownwheel teeth.

Because the axii of the gears in portal boxes are transverse, they do not directly contribute to torque roll. But indirectly, they may by influencing the diff ratio chosen.

As turbocharger said "torque is torque" so offset of the diff does not play a part.

Some suspension systems can be configured to balance out the torque roll. With a 3 link the single upper link would be offset to one side. Which side depends on whether the link slopes up or down toward the chassis.

The rear upper link is in tension during acceleration. If it slopes up to the chassis, offset it to left to pull that side of the chassis down. If it slopes down to the chassis, offset it to the right to pull that side up. The ideal offset is calculated from the diff ratio.

The front upper link is in compression during acceleration (tension during braking), so offset it accordingly to counter roll torque.

Torque roll can turn you over in some off camber situations.

[bill van snorkle]

Bill, the diff ratio plays a part in creating the torque roll. Torque roll is due to the reaction between the pinion and crownwheel teeth.

Because the axii of the gears in portal boxes are transverse, they do not directly contribute to torque roll. But indirectly, they may by influencing the diff ratio chosen.

As turbocharger said "torque is torque" so offset of the diff does not play a part.

Some suspension systems can be configured to balance out the torque roll. With a 3 link the single upper link would be offset to one side. Which side depends on whether the link slopes up or down toward the chassis.

The rear upper link is in tension during acceleration. If it slopes up to the chassis, offset it to left to pull that side of the chassis down. If it slopes down to the chassis, offset it to the right to pull that side up. The ideal offset is calculated from the diff ratio.

The front upper link is in compression during acceleration (tension during braking), so offset it accordingly to counter roll torque.

Torque roll can turn you over in some off camber situations.

Thankyou John. A very informative post with a clear explaination of the dynamics involved. Just one more question if I may,

Are vehicles with no suspension subject to torque roll forces ? I'm thinking of a dragster rail here. With relatively narrow overall wheel track widths and enormous accellerative forces involved, why don't they always flip over or even slew off course as torque reaction transfers more weight to the right hand rear wheel ?

Bill.

[SOA 93]

Bill,

Did you arrange your 3-link with this torque induced roll in mind?

As per Bush65's post, is your link running up or down and did you try any other configurations before getting to this one?

The offset of the link, is the LR diff offset the correct side to counter this torque, or would it be better the other side?

Andy

[bill van snorkle]

Bill,

Did you arrange your 3-link with this torque induced roll in mind?

As per Bush65's post, is your link running up or down and did you try any other configurations before getting to this one?

The offset of the link, is the LR diff offset the correct side to counter this torque, or would it be better the other side?

Andy

Well Andy, My top link angles down at a slight angle from the diff to the chassis, so in theory it is not idealy positioned to counter torque lean. Having said that I can drive along a deep trench with almost sheer banks 4ft high, and articulate over the walls at the most oblique angles without losing stability, although left side exits initially feel more unstable than right side exits. Whether it is the top link pushing the right side of the chassis down that is causing this I cant say, but the link certainly wouldn't impart a positive lifting force like it would if offset to the left, but doing that would have placed the link in conflict with what were my future engine plans.

I don't know how to calculate the downforce, or upforce for that matter of a top link with say 2000lbs of thrust pushing back against the chassis at a say 10 degree from the horizontal angle. Can anyone help?

Another couple of points to ponder.

I would guess that it would depend on the height of a vehicles roll centre whether or not a positive lifting force via the link would lower or in fact raise the vehicles COG on a sideslope.And does countering torque lean make the vehicle more stabil, or does it just mask the uneasy feeling of instability, causing one to lose the seat of pants link to the vehicle, leading one to push it beyond the limit ?

Bill.

[SOA 93]

Well Andy, My top link angles down at a slight angle from the diff to the chassis, so in theory it is not idealy positioned to counter torque lean. Having said that I can drive along a deep trench with almost sheer banks 4ft high, and articulate over the walls at the most oblique angles without losing stability, although left side exits initially feel more unstable than right side exits. Whether it is the top link pushing the right side of the chassis down that is causing this I cant say, but the link certainly wouldn't impart a positive lifting force like it would if offset to the left, but doing that would have placed the link in conflict with what were my future engine plans.

I don't know how to calculate the downforce, or upforce for that matter of a top link with say 2000lbs of thrust pushing back against the chassis at a say 10 degree from the horizontal angle. Can anyone help?

Bill.

Thanks Bill.

Just to try and clarify my earlier post, if the top centre link slopes down from the chassis to the top of diff and the diff is offset to the right ala LR will this have a negative or positive effect on roll torque?

I understand that the position of the diff has no effect on roll torque, but obviously the top of the diff is a good place to put the top link so is this offset the right or the wrong side.

My feeble brain is having a hard time visualising all the different forces going on

Andy

[bill van snorkle]

Thanks Bill.

Just to try and clarify my earlier post, if the top centre link slopes down from the chassis to the top of diff and the diff is offset to the right ala LR will this have a negative or positive effect on roll torque?

I understand that the position of the diff has no effect on roll torque, but obviously the top of the diff is a good place to put the top link so is this offset the right or the wrong side.

My feeble brain is having a hard time visualising all the different forces going on

Andy

Andy. when driving forward, the pinion is trying to rotate around the crownwheel, so the banjo housing is trying to twist backwards in the opposite direction to wheel rotation. The top link is pushing against its chassis mounting, so if the link angles up from the diff to the chassis, its thrust would impart a lifting force to the chassis. On a Landy with a higher than standard suspension the link may well angle up from diff to chassis. In this case mounting the link over the diff would be correct. If the link would angle down from the diff mounting to the chassis then offsetting the link to the left side would counter torque lean by pushing the left side of the chassis downwards. Trouble is that if any of your engine sits directly above the axle housing it is difficult to get adequate vertical separation between the lower links and the top one without remounting the engine higher up. On my own truck I could relocate the chassis mount of my top link higher up to reduce the effect of torque lean but I feel this would reduce my anti dive geometry, which I think has positive benefits both on and offroad. As someone pointed out on another thread an offroad suspension system is comprised of a wholebunch of compromises and trade offs.

Bill.

[Bush65]

Thankyou John. A very informative post with a clear explaination of the dynamics involved. Just one more question if I may,

Are vehicles with no suspension subject to torque roll forces ? I'm thinking of a dragster rail here. With relatively narrow overall wheel track widths and enormous accellerative forces involved, why don't they always flip over or even slew off course as torque reaction transfers more weight to the right hand rear wheel ?

Bill.

Vehicles with no suspension are subject to torque roll forces.

AFAIK dragster designers use suspension to obtain a largeish anti-squat (to improve traction) and to counter torque roll (again to improve traction).

[bill van snorkle]

Vehicles with no suspension are subject to torque roll forces.

AFAIK dragster designers use suspension to obtain a largeish anti-squat (to improve traction) and to counter torque roll (again to improve traction).

Thanks again John. Shows how little I know. I'd always assumed dragster rails were rigid. Never had a serious look under one though. Not my cuppa really.

bill.

[Bush65]

Well Andy, My top link angles down at a slight angle from the diff to the chassis, so in theory it is not idealy positioned to counter torque lean. Having said that I can drive along a deep trench with almost sheer banks 4ft high, and articulate over the walls at the most oblique angles without losing stability, although left side exits initially feel more unstable than right side exits. Whether it is the top link pushing the right side of the chassis down that is causing this I cant say, but the link certainly wouldn't impart a positive lifting force like it would if offset to the left, but doing that would have placed the link in conflict with what were my future engine plans.

You can't consider the front in isolation. The rear has more influence, because the forces are higher.

I don't know how to calculate the downforce, or upforce for that matter of a top link with say 2000lbs of thrust pushing back against the chassis at a say 10 degree from the horizontal angle. Can anyone help?

The forces are found from methods for solution of triangles, where the value of the link force is the hypotenuse of the triangle at the same angle as the link geometry.

Given the force (tensile or compressive) in a link, the vertical force component is: link force x sin angle of link to horizontal.

The horizontal force component is: link force x cos angle of link to horizontal.

Another couple of points to ponder.

I would guess that it would depend on the height of a vehicles roll centre whether or not a positive lifting force via the link would lower or in fact raise the vehicles COG on a sideslope.And does countering torque lean make the vehicle more stabil, or does it just mask the uneasy feeling of instability, causing one to lose the seat of pants link to the vehicle, leading one to push it beyond the limit ?

Bill.

Interesting thoughts Bill.

A high roll centre is more stable on a side slope. Suspension asymmetry to counter torque roll will help stability.

But if you try to use asymmetry to correct body lean, it will only work for either left or right sideslope, not both. As it will reduce stability on the opposite sideslope, I would not recommend doing this.

Having said all this, when determining suspension geometry there are so many constraints that determine attachment points for links, that you rarely get every aspect spot on.

It is not a common tend to employ suspension asymmetry, which counters torque roll.