A steering Doubt

[mach11]

Hi All,

We all know how the ackerman principle works (A four Bar mechanism).


A basic representation of the Ackerman steering principle and the mechanism.

Here is my Doubt.

Let us consider that the Steering box is placed at the center with the Tie Rods meeting the hub at equal distances from the center. Therefore, the tie rods are of equal length.

Thus when the steering input is given to steer the car towards the left the inner wheel turns at an angle (Assume 43 deg.) and the outer wheel turns at an angle (Assume 28 deg.)

Why does this happen when the tie rods are of equal length???

My understanding is as follows:

The point at which the ball joints is fixed to the wheel hubs moves at an arc (A semi circular path) thus causing the variation in the angle.

Am i right??

Thanks in Advance

[747heavy]

the angle between your steering arm and your tie-rod will define your ackerman, anti-ackerman or parallel steering geometry.

maybe this helps to explain it.

http://www.muller.net/mullermachine/docs/ackerman.html

[Caito]

The ackerman arms move round in circles. What makes the car steer is basically how much you rotate them.

So the rotation is determined by the horizontal movement imposed by the steering rack.

This picture looks like an ackerman arm.The left one, lets say
http://media.photobucket.com/image/cos% ... th/sin.jpg


Our steering rack will produce an horizontal movement. Let's put a number of 1cm. You can see in the picture that to move horizontally 1 cm to the left(car steering to the right) since we are in the horizontal part of the circle, that would produce a small angle variation(hence small steering). Meanwhile, to produce 1cm to the right(car steering to the left) the ackerman needs to turn a whole deal of degrees.


You're interested in how many degrees of rotation are needed for a given horizontal displacement. If we put the arms in 90° position, we're symetrical, it's the same going to the left or to the right. But if we put them in an angle we can achieve ackerman, or anti ackerman.



If we look at the image of the cosine we can see that to have a given horizontal deflection(change cosine magnitude) we need to move a greater angle if we are near 0 degree, than if we are near 90 degree. This is because cosine changes as -sin.


This is talking ideally since the steering arm would angle as the uprighr rotates-

[johnny99]

if you look down on the arm's which the steering arm is attached to the hub, you can compare the arc, and the distance in which they move. This is also why moving the rack forward or rearward will change the ackerman angle

John

[mach11]

having calculated the steering turning angles and the turning radius and the point at which the tie rod will be mounted on the hub,

I want to perform FEA analysis on the Hub mounting points.

I have referred a few books but I am unable to find out the steering force that would be acting on the mount???

Can anyone help me out on this one....

Thanks in advance...