Steering System

[Mostafa Habib]

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Hi everyone ,
I have a question regarding the steering system
I need to know whether this angle affects the system and how ?
And how to calculate the proper angle ?
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Mostafa Habib
Zagazig University - Egypt
ZUFS Team

[MCoach]

Yes, it looks like this:

http://en.wikipedia.org/wiki/Univers...le:UJoint2.png

Now a question back to you. What is considered proper with respect to your goals? Is proper 0% deviation for in/out angles desirable or is a non-linear gain preferential for your application?

Source:
http://en.wikipedia.org/wiki/Univers...tion_of_motion

[Claude Rouelle]

Mostafa,

1. You U joint or Constant Velocity (CV joint) catalog should give you the maximum angle you can use.

2. If you want to avoid a phase shift between your steering wheel angle and you wheel steering angle (that would send a wrong car behavior signal to the driver) you need TWO U joints. Google is your best friend for that kind of search. Here is an example

https://www.google.com/search?q=stee...ft%3B493%3B331

3. Do not fall in the trap of many FSAE / FS teams which do not design, manufacture and install at least one steering column support between the steering wheel and the steering rack.

[ritwikdas18]

How to factor in rolling resistance in steering design? Is it related to effect of front tire steering angle and slip angle on increased rolling resistance. Can someone explain it in detail?

[Claude Rouelle]

Ritwik Das,

The answer to your question is in 2 or 3 posts that were discussed on this forum in the last few weeks.

Try to make your own search before asking such kind of questions

Claude

[BillCobb]

Since this is one of my favorite subjects, excuse me while I spew on it for a while.

Nonlinear overall steering ratio characteristics can be a troublesome situation for vehicle dynamics processes. To be correct, we really mean that a 'steering ratio' is the first derivative of a function relating the average of the roadwheels angle turning to steering wheel turning. Measurements of this function are done routinely for virtually all handling test vehicles ever done. This information is needed to calculate the understeer of a vehicle given test results containing steering wheel and lateral acceleration data, (among several other important channels).

One generally thinks of the 'steer ratio' as the quotient of two simple protractor readings, but this is ridiculous now days because of the realities of the findings. First of all, the yaw dynamics of a vehicle are activated by not only steering angle but also steering angular velocity. So, it is possible to concoct an input relationship to a steering gear which has increasing steer angle but decreasing steer velocity. In cases like this, drivers, even professionals, have been known to exit a car and check for 'lash' in the steering system, because that's what it feels like. So, considerable energy and time is spent designing and building (in the vehicle assembly process) a system which avoids variation in the overall ratio.

Back to the Cardan issues: Most production vehicles have a double Cardan steering intermediate shaft between the column and the steering gear input shaft. Done mainly for safety and driver comfort issues, the double jointed shaft still can be screwed up from its (usual) constant velocity specification. That's because in order to be a true constant velocity, the input and output shaft must be co-axial (they must be parallel in all views). If not (generally because of assembly carelessness, you get a nonlinear ratio, which we call "lumpy Steering". To fix this problem, you can go to a CV type joint, either the double cross used in rear drive prop shafts, or the multi-ball joints used (for example in front wheel drive prop shafts). For example: a CV joint from a Honda or Yamaha ATV can be made into an excellent steering shaft if you address lash.

On the other hand, several vehicle manufacturers have deliberately produced a nonlinear steering ratio to change the feel of their cars. One that I worked on produced a high numeric ratio straightahead that got lower as you steered in order to make up for the loss of steering gain due to increasing limit understeer and to create a form of "Valley Feel". Another manufacturer consistently produces a low numeric ratio on-center that increased as you steered more. Keep in mind that steering effort torque effects are the opposite of the ratio, so the quick ratio getting slower produces an decreasing steering feel signal to the driver. Either method is directed to the type of driver: displacement command or effort command. (BTW: an evaluation driver that can not tell the difference between a car with these differences installed in it has no place in a vehicle development program).

Here are plots of typical overall steer ratio characteristics I've tried to describe. All three are "10:1 Boxes" as we say. A simple test can be run using steer angle and roadwheel angle transducers with the steered wheels on grease plates or air bearings. You run the test and process the data. I have a function in Matlab that describes the full effect which you see here. This is installed as a feature in a handling simulation I routinely use. Producing the road wheel angles from such a function requires angular integration of this function, chaps ! Keep in mind that there are also nonlinear steering gear boxes which give additional complexity beside that of the steering shaft effect.

Now, use of a single Cardan type joint can be used to improve your FSAE car if done properly. Now you have to analyze and decide what's best for your team.

[Tim.Wright]

There is at least one manufacturer that I know of who don't bother centering the cardan error about 0deg...

[Mostafa Habib]

Coach ,
Thank you for your response
Let me say something
This is always the problem , i mean every question faced by numbers of questions
What about if i have little or no experience and so i came to here to find an answer to what i found it difficult.
What i want to say is i cant find a specific answer for ur question so let me search about it to find the proper design for me

[Mostafa Habib]

Cloude
Thank you about ur notes
but about the 3rd one i cant understand what do you mean

[Claude Rouelle]

Mostafa,

You cannot NOT have a steering column support between the steering column and the steering rack if the steering column is in more than one part. When you will be moving the steering wheel you will see some of the steering column part moving up and down left and right. That woud produce an elasticity that would make the diver really uncomfortable and apprehensive. You need to avoid this by putting a some sort of bracket that holds a spherical joint or a rod end in which the steering column will go through.

Get it?

Be careful that this bracket does not compromise the cockpit template.