Longitudinal motorcycle engine - torque effects 1

[amorrison]

Lateral engine torque reactions are produced at the wheels.
Where are the reactions for a longitudinal engine ?
Rider sidewise lean?

 

[thruthefence]

"I race a 150hp Mini...You have no idea what 'torque steer' is until you put your foot down hard in a tight turn with limited slip diff."

Man, I wish I still had the thing, a victim of a divorce. Rod, have you seen the Honda Conversions for the "classic minis"? I bet that would be a hoot!

 

[evelrod]

A friend and fellow Mini racer does these conversions. Some are quite nice, some are a bit over the top. I saw a Clubman conversion with a 1600 VTEC that was quite nice. Street ready at <1500 lbs with 150+ hp. Tractable, good fuel mileage and not a handfull to drive. My race car is the antithesis of this...

Rod

 

[SomptingGuy]

Rod,

Please post more videos.

- Steve

 

[evelrod]

I post them all on YouTube (eventually) under "evelrod's videos"

http://www.youtube.com/my_videos

I'm not too good at editing...wow, that's an understatement...If I can get my son to edit the raw footage from Chuckwalla I'll add it.

This is one from a BMW 2002 that shows my very wounded white #130 Mini being lapped. It was posted to add to my campaign to have the dangerous pit wall changed before someone gets killed.

http://www.youtube.com/watch?v=NgVvi5LgqVA

Sorry for the hijack, amorrison. This really should be in the Pub, Steve.

Rod

 

[TheBlacksmith]

I believe both Ford and GM have come out with a new front end design that moves the upper pivot point to the top of the spindle (from the top of the McPherson strut), reducing the scrub radius and resultant torque steer.

 

[HRHtex]

BrianPetersen - you wrote above "A universal joint that is not straight, exerts force on its mountings"
Is this another way of saying that a CV joint operating under load at an angle will attempt to straighten itself out?

When a car is accelerating in a straight line (when most people notice torque steer) the difference in CV operating angles from each side of the car must be very small - a few degrees at most - surely not enough to cause torque steering effects?

 

[evelrod]

I really don't think the tq-steer problem has much to do with u joints, cv joints or, even unequal length axles, all being in top condition. From my observation, it is much more prevalent under traction conditions that are not equal, side to side. Under acceleration should one tire get more traction than the other (FWD) the car is likely to pull to that side. This phenom is observable under braking as well. A limited slip diff could possibly mitigate this but, limited slips on FWD's are not viable without some power assist on street cars. Electronic traction control has made great strides but, again in my experience, has not completely cured the so called tq-steer of FWD under limited traction conditions.

Also, pertaining to broken axle in a RWD race car...obviously I would not drive a street car with a broken axle...tq-steer is very evident. I did not break an axle to find out, it sorta found me.

Rod

 

[BrianPetersen]

Certainly unequal grip will give torque steer, but I've driven a few very old-design front-drive cars that torque steered during acceleration at well below the traction limit on dry pavement while driving straight ahead on level ground. I've owned a front-drive car with unequal half-shafts (first-generation Honda Civic) in which the steering wheel moved visibly (if you didn't manually stop it from happening) on every gear change! It's not a grip issue. I test-drove a Suzuki Swift once upon a time which did this even worse than my Civic did.

Back then, you just got used to the way the car drove, and dealt with it.

It's very true that the angle of the half-shafts is small, and there is a big mechanical disadvantage of that torque reaction back to the steering wheel - but the drive force at the wheels is vastly higher than the torque the driver applies to the steering wheel (these cars were all manual steering - no power steering mechanism to cover it up).

 

[Warpspeed]

It is not normally very easy to do a back to back test on the same car with similar versus different front driveshaft lengths !
But I have had the opportunity to do exactly that.

In Australia the Mazda 323/ Ford Laser comes normally aspirated with unequal driveshafts, turbo with a different gearbox and equal front driveshafts, and 4WD turbo, also with equal length driveshafts.

The normally aspirated (with only 55Kw stock) did not torque steer, but it sure did when a turbo was fitted.
Upgrading to the turbo transmission with equal length driveshafts, and the same identical car and turbo engine, it still torque steered just as badly.

Upgrading again to 4WD, with the same car and engine, there was no evidence of any torque steer whatsoever. It just went where it was pointed.

I might suggest that very high front tractive effort, along with less than ideal suspension geometry is what causes torque steer.
Feeding less power through the front makes it pretty benign, no matter what it is.
But the problems of directional stability multiply rapidly as front tractive effort is increased.

 

[SomptingGuy]

I created a full model of a Fiat Tipo powertrain many years ago (in ADAMS). It had unequal length half-shafts. It was driven through an engine model, with throttle angle being the only dynamic input. I was very amused/impressed when it exhibited torque steer.

- Steve

 

[GregLocock]

The issue with torque steer is that you are dealing with controlling torques of the order of 300 Nm via a sensing system that can resolve 0.3 Nm, regards 25 Nm as a maximum, AND has a 17:1 mechanical advantage. Almost any errors in cancellation will be sensed.


Cheers

Greg Locock


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

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

 

[PEW]

In 1977 I was loaned one of the first BMW R100RS Boxer twins in the UK for the afternoon.

I got a bit carried away trying to see how fast it was (about 125mph) and it got airborne over a bump on the A19 near Thirsk in Yorkshire. I snapped the throttle shut and it rolled to one side in mid air. Very frightening at the time because it landed back on its wheels leaning the wrong way for the next bend which I was rapidly approaching....

Didn't do that again.

 

[HRHtex]

Warpspeed - I was interested to see your comments on the non-turbo and turbo Mazda 323.
I wonder if some torque steer in a powerful FWD car can be just due to the various rubber bushes in the suspension deforming/deflecting under the increased load and allowing the wheels to move about and do a bit of unasked-for steering.

 

[Warpspeed]

As you know the 323/Laser uses a typical strut type front suspension.

While high lateral cornering forces will certainly create some definite compliance steer, pure tractive effort should not.
The front wheels may move forwards slightly due to rubber compliance, but there is nothing there to cause the front wheels to steer.

Put another way, the steering arms, and lower control arms remain unloaded from tractive effort, and it is the relationship between these two that provides the normal steering input to the front wheels.

Torque steer either has to come from the drive shafts or the contact patches.

My money is on the contact patches not being directly centered on the steering axis. But others here seem to feel very strongly that unequal drive shaft length can steer the wheels.

Question.
If you have a long drive shaft, and a short drive shaft, which way will the vehicle torque steer. Will it ALWAYS pull the same way ? It absolutely must if that is the root cause.

So why does the vehicle weave instead of just pulling strongly one way if drive shaft length difference is the true cause of torque steer.

Not trying to be difficult, just trying to get my head around the unequal drive shaft length causing torque steer theory.

 

[pontiacjack]

PEW- thanks for sharing that episode with the BMW boxer. That's something I never experienced (and don't want to). I'm curious whether you also detected a pitching moment while airborne? If so, was it an up- or down-pitch (I have trouble remembering/applying the rule of gyroscopic torques!)?

So... was that air-time on the Beemer the impetus to start you on an aeronautical career?

 

[HRHtex]

Warpy - if the lower arms remain unloaded from tractive effort - what does transfer the tractive effort from the wheels to the chassis?

I am inclined to agree about the contact patches not being centered being likely culprits.

One reason that I think the unequal shafts may be the cause (although, like you, I still can't see why) is that a lot of car companies have spent a lot of money to arrange equal length drive shafts - surely their testing showed them that it reduced (at least) torque steer.

 

[evelrod]

HEHtex---

One reason that I think the unequal shafts may be the cause (although, like you, I still can't see why) is that a lot of car companies have spent a lot of money to arrange equal length drive shafts - surely their testing showed them that it reduced (at least) torque steer.

Hmmmmm. Seems I heard that particular line of reasoning once or twice...

pontiacjac---

Jumping on a dirt bike, I revved the engine to pull the front up, chopped the throttle to drop the front wheel. When I was younger, had a lot of practice at that. Kinda miss it, too.

Warpspeed---

I agree with the others here that some anomaly in the suspension certainly can cause tq steer but I maintain that it is caused primarily by traction issues. My little car has lots of power, unequal length axles and soft, fat tires. It tends to steer if one wheel has a bit less traction, never the same way each and every time, more prevalent at low speeds and, very difficult to control with any steering input at low speeds. I've posted several videos where you can see all this in action. A racing Mini Cooper is just not a car you can, as my dad put it, "loose heard" down the road.

Also, as I said before...I've only driven a few FWD cars and I never felt any difference from any other cars I've owned. Of course, most all my driving is in sunny, dry SoCal. Also I'm not the greatest driver on the street so I don't push the issue. My few times racing in the rain, I'll take a FWD over a RWD, any day! )

Rod

 

[Warpspeed]

Tex, the lower lateral link is not as heavily loaded during braking and acceleration as it is in cornering.
It is the radius link that suffers most of the pushing and pulling, during braking and acceleration.
I know it is not really all that clear cut and simple, but you can probably see what I am trying to get at.
Side to side compliance movement of the lower ball joint will steer the wheel. Fore and aft compliance movement of the lower ball joint should not.

My little car has lots of power, unequal length axles and soft, fat tires. It tends to steer if one wheel has a bit less traction, never the same way each and every time, more prevalent at low speeds and, very difficult to control with any steering input at low speeds.

That is precisely what I am seeing too Rod.
The key words being never the same way each time.
But the short drive shaft is always on the same side ?
If drive shaft length was the the true fundamental cause, it surely must show a preference to always pull one way ?

 

[GregLocock]

Some cars definitely torque steer predictably. Some cars 'squirm' or dart under acceleration. I'm not convinced they are exactly the same thing. I can easily believe that darting is caused by a positive feedback mechanism at the contact patch.

Incidentally a CV joint at an angle behaves as a force amplifier, generating various reaction forces proportional to the torque it is transmitting.

The Rev O Knuckle and the like are a good shot at removing most of the geometry errors and so on (I had to say that the guy at the next desk is one of the patentees), yet if you stick enough torque through them even with equal length driveshafts you get some sort of torque steer again.

It seems to me that if you have equal length driveshafts and no silly errors, you don't get too much torque steer up to about 200 hp.

Cheers

Greg Locock


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

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

 

[Warpspeed]

Thanks Greg.
There are probably several potential causes of torque steer, and as you say, more torque and tractive effort multiplies whatever is going on.