vehicle dynamics week 2 set 1

1, What are the two types of tierod errors with respect to ride steer? And what is the effect of these errors on the toe curve?

2, If we have toe out in rebound (due to bump steer) in the rear suspension, is this an understeer effect or an oversteer effect?

3, If there were no bushings at all in the suspension (all components are hard mounted), would you still have compliance in the system? If yes, where is this coming from?

4, In a front mounted rack setup, if the suspension links are more compliant than the steering, would you have an understeer effect or an oversteer effect?

5, Why does the outer wheel almost always gain positive camber when subjected to a lateral force?

6, Can you get an oversteer effect out of aligning torque compliance steer? Why or why not? If yes, how ? (just a basic explanation)

7, Why does the rear ride frequency have to be greater than the front ride frequency?

8, Can you use the same damping force for: (why or why not) (I). Low frequency and high frequency( II). Compression and rebound

9, In a passenger vehicle, assume the front suspension has 30% anti-lift and the rear suspension has 25% anti-squat. By what percentage does the total longitudinal load transfer change?

10, Let us say, theoretically you change the brake bias so that all the braking happens only in the front I. What is the maximum possible anti-lift that you can get in the rear suspension II. Is 100% pitch compensation possible with this setup?

ANSWERS:

1.Two types of errors-

a)Tie rod length error- If the tie rod ends are not on the locus of line joining the points upper control arm pivot & lower control arm pivot OR upper ball joint & lower ball joint

Effect – Parabolic toe (out) curve in jounce & rebound( undesirable with no steering net effect, and it can lead to changing from understeer to oversteer when ride height changes)

Tie rod angle error- The tie rod is not aiming at instantaneous center.

Effect on toe curve - linear but sloped curve maybe used to add roll understeer in suspension

2-Understeer

3-Yes compliance do exist as the suspension links have their own stiffness which come into picture under loading condition

4.understeer

5-Lateral forces act at ground level on the tire. Which causes the top of the vehicle to turn away from the turn center especially when all the soft components are in the top that’s why it is always having a positive camber gain.

6-Aligning torque acts to resist turning motion which will produce understeer in the front wheel, if it happened in the rear wheel it will cause oversteer

7-If the frequencies are same, the front and rear suspension going to be in out of phase. i.e because rear part of vehicle hits the bump after the front end as there is separation due to wheelbase causing pitching motion. So to obtain flat ride frequency at rear ride frequency has to be greater than that of front to prevent pitching

8-We cannot use the same damping in case of compression or rebound During compression Spring is going to absorb the energy so damping has to be lower than that of rebound.

And in rebound as energy from the spring is released it has to take care by damper by controlling it so damping needs to be higher in rebound

And in case high speed (high frequency ) it is desirable to have low damping ratio in order to increase the passenger comfort ,while in case of low speed (low frequency) high damping ration is required to have better body control.

9- zero, as the longitudnal load transfer =w*a*h/l so it only depends on w which is the total weight ,and a is the throttle acceleration,h is the cg height and l which is the wheel base

10-i-zero,as ther is no force to cause the moment

10 ii-yes it is possible to have zero pitch angle by arranging the links to have e/d=2h/l