Drivetorque Reaction: Hi Pfians & Friends

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Discussion Overview

The discussion centers around the mechanics of drive torque in vehicles, specifically how the rotation of the propeller shaft affects the rear axle and chassis dynamics. Participants explore concepts related to torque, moments of inertia, and the implications of traction on vehicle behavior, with a focus on both theoretical and practical aspects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that the rotation of the propeller shaft causes the engine and transmission to rotate in the opposite direction, leading to lateral load transfer, but questions whether this also causes the rear axle to rotate.
  • Another participant relates the Principal Axis Theorem for moments of inertia to torque and questions the effects of differential placement on wheel behavior under torque.
  • Some participants argue that the axle would not rotate, drawing analogies to drill machines and emphasizing that the chassis would roll instead.
  • A later reply describes a scenario where a vehicle on slippery ice engages the clutch, illustrating that while the axle rotates, no movement occurs due to lack of traction, contrasting this with a scenario on dry pavement where movement does occur.
  • One participant clarifies that they are specifically discussing axle rotation about its longitudinal axis and its effect on lateral load transfer.
  • Another participant discusses the effects of traction on chassis dynamics, noting that under high traction, torque can lead to significant chassis movement and even wheel stands.
  • A participant shares a photo illustrating torque reaction in a vehicle under acceleration, indicating a desire for clarification on the original question.

Areas of Agreement / Disagreement

Participants express differing views on whether the rear axle rotates in response to drive torque, with some asserting it does and others arguing against it. The discussion remains unresolved, with multiple competing perspectives presented.

Contextual Notes

Participants reference analogies and examples from mechanical systems, but there are limitations in the assumptions made regarding traction, axle dynamics, and the specific conditions under which these phenomena occur.

R Power
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Hi Pfians and friends

When propeller shaft rotates , due to action reaction transmission and also engine rotate in opposition direction to that of propeller shaft and so the whole chassis will and this would cause lateral load transfer. Correct me if I am wrong upto here.
My question is: Will the reaction of drive torque rotate the rear axle also?If yes ,why?
Well, I thought it won't rotate because since engine or transmission block is unsprung mass , then only the unsprung mass would rotate with it in a direction opposite to driveshaft rotation, which doesn't include rear axle.
But on searching net i found axle will also rotate! Can you expalin why?
Thanx
 
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Can you relate the Principal Axis Theorem for moments of inertia to torque? What would happen if the differential (on a solid axle) were at one of the two drive wheels rather than at the center? Do you believe that if the propeller shaft torque were high enough, one of the two drive wheels could rise off the ground?
Bob S
 
I don't believe that either of the wheels would rise off the ground, whether the differential is at center or at end.
Only the suspended chassis would roll side ways compressing and extending springs.
Because everywhere this phenomenon is explained as a drill machine. Rotor rotates in one direction and then the casing tend to rotate in opposite direction that's why proper hold links are made.
In case of a car engine or transmission is like the drill machine, so propeller shaft rotates in one direction and the casing along with the chassis rotates the other way.
Why would axle rotate?
 
see post on mech forum -Weight transfer due to drive torque! Nov10-09, 09:08 PM
 
that thread was started by me in fact!
I am sorry for starting a similar new thread ,

but in that everyone gave me same answer of action and reaction, screw driver, drill machine, helicopter and i understand action and reaction but it should be betweem engine(or transmission) and it's casing and chassis. Engine crankshaft is like electric screw drivers motor and propeller shaft like the driver shaft. So shaft spins one way and screw driver's casing spins the other way. Similarly the engine crankshaft and prop shaft spins one way and the casing along with chassis spins other way , then why will axle rotate??/
Please help me!:confused:
 
imagine a rear wheel drive automobile that is on ice. totally slippery condition. if you engage the clutch, the drive shat rotates as doe the axle and wheel. but we have no movement because the tires lack traction. we have no chassis movement. now if we move the automobile to dry pavement and again engage the clutch , we have movement. the engine rotates the drive shaft and axle. the wheel and tire rotate and because we now have friction we have force transferred from the rotating tire to the pavement. since there is no tire spin force is applied to the pavement in varying amounts as controlled by the accelerator pedal. the more we press the pedal the more fuel air mixture is admitted and the engine makes more power. the more power applied to the pavement will cause more movement in the form of vehicle speed or wheel spin ( because more torque is a applied than the tire tread can transmit to the pavement) and the more chassis roll as a reaction to the tire adhesion to the pavement. In all cases the axle will rotate. it is a matter of how fast the axle will rotate but it will always rotate. are you following this?
 
I am talking about axle rotating about the logitudnal axis of vehicle i.e about the axis prependicular to the axle and thus tranfering load laterally.
 
when we have a lot of traction ( tire plants torque on the pavement without breaking traction..spinning) the reaction to this torque is to compress the right rear spring AND try to lift the entire chassis. in extreme cases this is the classic wheel stand. both the lateral and longitudinal twisting forces are the direct reaction of torque meeting pavement. in most cases we have wheel spin and the above two twisting forces displayed.
 
This photo shows the torque reaction in the attitude of a car under heavy acceleration:

http://www.buyagift.co.uk/Images/product/large/2095_drag.jpg

but I'm not sure I understand the basic question so if it helps to clarify anything let me know.
 
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