Steering rack and feel (Pressure angle, number of teeth)?

[Nihal]

I am trying to design a steering rack and had some questions about the design and steering feel of the rack it self.

1. Does the pressure angle between the pinion gear and rack gear make a difference in how smooth the steering feels and how much feedback it relayed to the driver?

2. Do the number of teeth meshed or the surface area of the teeth meshed make a difference in the feel?

3. I am planning on using a bearing for the pinion shaft and bushings for the rack to slide in and out of the mount. What material do you suggest for the bushings on the outside mounts. I was thinking delrin or brass. Which one would provide less friction, is there some sort of material constant that governs the mu between two different materials (in this case, either brass on Al or delrin on Al)?
Thanks

[Nihal]

I am trying to design a steering rack and had some questions about the design and steering feel of the rack it self.

1. Does the pressure angle between the pinion gear and rack gear make a difference in how smooth the steering feels and how much feedback it relayed to the driver?

2. Do the number of teeth meshed or the surface area of the teeth meshed make a difference in the feel?

3. I am planning on using a bearing for the pinion shaft and bushings for the rack to slide in and out of the mount. What material do you suggest for the bushings on the outside mounts. I was thinking delrin or brass. Which one would provide less friction, is there some sort of material constant that governs the mu between two different materials (in this case, either brass on Al or delrin on Al)?
Thanks

[Buckingham]

Of your three questions, your third question will probably have the most imact on feel.

[Cement Legs]

I would think that steering box gear ratio, moment arm from kingpin axis to to tie rod location and caster angle will be 3 of the largest factors contributing to feel or feedback at the steering wheel. Regardless of any combination you use (within reason of course) you will get feedback to the wheel simply because that is characteristic of rack and pinion. I cant see how the number of teeth meshed would affect anything going from say 1.4 to 2.2, but pressure angle hmmmmmm....

[nathan s]

It is my understanding that most of your feedback comes from your scrub radius rather than the actual pressure angles and friction between materials. Higher tooth numbers will make the gear meshing smoother, but the steering travel is governed by the steering arm length. That is why we went with a 10 pitch rather than an 8 pitch.

I guess I am seconding Cement Legs on this.

[Nihal]

I know about the geometrey stuff, but that is set. I am just trying to optomize the steering rack it self. I understand the number of teeth thing making it smoother, but I'm still wondering about the material choice and pressure angle thing.

[NovaCat2005]

Powergear (http://www.gear-doc.com/powergear.html)

I've used this program to design helical gears for a class assignment, and it saved me a lot of time. It follows AGMA standards. I haven't used it to design a rack and pinion, but you can give it a try.

The involute form of the teeth ensure that you have a linear transfer of power, however like cement legs said you want to have 1.4-2.2 teeth meshed. This way there is always 2 points of contact so there will be no compliance.

A higher pressure angle will make higher radial thrusts, but you can get away with using smaller gears. That is the main relationship I noticed from changing pressure angles. I would guess that higher radial thrusts from a higher pressure angle may increase the friction force. As for material selection, just choose something that isn't going to break.

The manufacturing process you use will obviously affect the quality of your rack and pinion. Having the proper amount of backlash is critically important. Consult with someone that has experience designing and manufacturing gears.