Final Drive Ratio

[Piyush Gupta]

Is primary Reduction ratio i.e. the reduction in the engine included in the final reduction ratio or final reduction ratio is just defined for the differential?
Also if final reduction is only for the differential then what is the total reduction ratio. Is it final reduction ratio x Gear in which car is moving or final reduction ratio x Primary reduction ratio x Gear in which car is moving???
Kindly help... http://fsae.com/groupee_common/emoticons/icon_confused.gif

[Racer-X]

On a bike and most of our cars they are three separate things.

You have the gear ratio, ie 3:1-1:1 for first through 6th, the primary reduction at the clutch basket, and finally the final reduction from the output shaft to the diff. Total is the product of all of these.

[Piyush Gupta]

Thanks for your reply
In our FSAE car we have a primary reduction ratio of 2.11 and it has a gear box with specifications
1st Gear 2.666
2nd Gear 1.937
3rd Gear 1.611
4th Gear 1.409
5th Gear 1.26
6th Gear 1.666
After this we are using chain and sprocket(with a teeth ratio of 4 i.e smaller sprocket has 11 teeth and larger have 44 teeth) which goes to the differential(QDF7ZR QUAife ATB chain driven differential).
Now what is my total reduction ratio for a given gear????
IS IT (2.11)x(2.666)x(4)x(final reduction ratio of differential) for the first gear or something else???? http://fsae.com/groupee_common/emoticons/icon_confused.gif

[Tilman]

Heyho,

usually a differential does not provide additional reduction. Therefore your total reduction ratio in first gear should be

(2.11)x(2.666)x(4)

[Racer-X]

The total reduction is the product of all the gears in the drive train.

Think of it in the order of components torque is transmitted through ie Primary => Gear => Final

You just need to multiply all the ratios.

In your case 2.11*2.666*4 would be it.

[Piyush Gupta]

Thanks everyone for your helpful replies...
I read on the web that their is a final drive ratio of the differential which is the ratio of teeth of the ring or planetary gear of the differential to the pinion gear teeth which gives it the input and it is also included in total reduction.
If not what actually is the final drive ratio???

http://www.ehow.com/info_83956...inal-gear-ratio.html (http://www.ehow.com/info_8395609_effects-tires-final-gear-ratio.html)
http://auto.howstuffworks.com/differential2.htm
http://fsae.com/groupee_common/emoticons/icon_smile.gif

[acedeuce802]

That would be true if the differential sprocket spun at a different rate than the output shafts. The 4-1 ratio of your sprocket teeth accounts for the differential sprocket size, and in most cases is the final drive ratio.

[Tilman]

Originally posted by Piyush Gupta:
I read on the web that their is a final drive ratio of the differential which is the ratio of teeth of the ring or planetary gear of the differential to the pinion gear teeth which gives it the input and it is also included in total reduction.
Heyho,

look at the picture on the howstuffworks-Website you linked. The differential case is driven by the input pinion which acts on the ring gear, and the ring gear is rigidly connected to the differential case. Since the input pinion has less teeth than the ring gear, there is a speed reduction at this point.

In the case of a chain drive, the ring gear is replaced by a sprocket and the input pinion is replaced by a sprocket, too. Your "final reduction ratio of differential" is just the reduction of the chain drive. An open differential does not have any additional reduction in rotational speed.

[Piyush Gupta]

I meant that we are using chain and sprocket which gives input to the differential input shaft i.e the input shaft of the differential on which there would be a pinion gear is driven by the sprocket.The pinion gear and the ring gear is enclosed in the differential housing from which the shaft on which pinion gear in attached is coming out which we are driving by attaching the output of chain and sprocket.So sproket is not driving the differential but driving the input shaft of the differential on which there would be a pinion gear. http://fsae.com/groupee_common/emoticons/icon_smile.gif
So basically it is the compound gear train in which the 2nd sprocket and the pinion gear would be rotating by same angular velocities.So now I think both considerations must be taken i.e the reduction through chain and sprocket and then through differential

[Tilman]

Originally posted by Piyush Gupta:
I meant that we are using chain and sprocket which gives input to the differential input shaft i.e the input shaft of the differential on which there would be a pinion gear is driven by the sprocket.The pinion gear and the ring gear is enclosed in the differential housing from which the shaft on which pinion gear in attached is coming out which we are driving by attaching the output of chain and sprocket.So sproket is not driving the differential but driving the input shaft of the differential on which there would be a pinion gear. http://fsae.com/groupee_common/emoticons/icon_smile.gif
So basically it is the compound gear train in which the 2nd sprocket and the pinion gear would be rotating by same angular velocities.So now I think both considerations must be taken i.e the reduction through chain and sprocket and then through differential
Heyho,

if you build it like you described it then you really have to take both reductions into account. But please explain to me WHY do you want to build it this way?!?!?

The QDF7ZR is a sealed differential, you do not need another case to prevent it from leaking! Moreover it is designed to be used with a chain drive, just mount a sprocket to it like it is shown in this drawing:
http://www.quaife.co.uk/sites/.../drawings/QDF7ZR.pdf (http://www.quaife.co.uk/sites/default/files/drawings/QDF7ZR.pdf)
Or do you use the pinion/ring gear at the differential to account for the lateral dispacement between the engine's sprocket and the differential?

Can you provide a CAD screenshot of your design where we can see the differential, engine, chain drive and your pinion/ring gear?

[Piyush Gupta]

Thanks for your precious replies which cleared all our doubts....
Actually that was my bad.We were trying to study the last year's car design which was made by the different team.You are right, in this differential we directly drive differential through sprocket.