[a4anurag]

Hello Team,

I was just wondering what is the reason for the difference in the rear multi-axle arrangement when comparing the B9R and B11R.

Volvo B9R:


Volvo B11R:


Picture Source: Google Images.

In the B9R the axle consisting of two wheels is placed in front of the usual 4-wheel axle but it is opposite in the B11R (Just the Mercedes-Benz buses).

Couple of questions:

1) What is the reason for this difference;

2) What reason could it be to get this change in design?

3) Where is the power delivered in the B9R? and

4) Where is the power delivered in the B11R?

In questions 3 & 4, I meant was to which axle is the power sent - 2-wheel or the 4-wheel one?

MODS: Move it to the appropriate thread if necessary.

Anurag.

[Mr.Boss]

Originally Posted by a4anurag

3) Where is the power delivered in the B9R? and

4) Where is the power delivered in the B11R?

In questions 3 & 4, I meant was to which axle is the power sent - 2-wheel or the 4-wheel one?

In both the cases the combination tyre axle (with 4 tyres) gets the power from engine.

And regarding the axle position change, I suppose it is because of the transmission layout (sorry, I'm not an expert, it is my wild guess)
Consider the engine / GB height & Suspension stroke is same in B9R & B11R.
Incase of B9R, the propeller shaft working angle will be more than B11R (more the angel, higher the transmission loss)

And other reason I could imagine is the weight distribution.

Experts, please correct me.

[TheARUN]

Its simple, the B11R has rear axle which steers. The double tyre axle could not be made to steer and the single axle even if it steered and was placed ahead of the double tyre axle would not steer! Hence they placed the single tyre axle as the last axle and it works this way the best to steer the Bus. Also, the axle turns in the opposite direction to the front axle! much like what you have to do while reversing a tractor trailer

[a4anurag]

Originally Posted by TheARUN

Its simple, the B11R has rear axle which steers. The double tyre axle could not be made to steer and the single axle even if it steered and was placed ahead of the double tyre axle would not steer! Hence they placed the single tyre axle as the last axle and it works this way the best to steer the Bus. Also, the axle turns in the opposite direction to the front axle! much like what you have to do while reversing a tractor trailer

Thank you Arun.

I now understand and yes the length is increased over the B9R so steering that thing will be a pain hence the rear axle steering mechanism was introduced.

Anurag.

[fiat_tarun]

Does the B11R come with Volvo's I-shift AMT ?

[a4anurag]

Originally Posted by fiat_tarun

Does the B11R come with Volvo's I-shift AMT ?

Yes tee B11R is equipped with their i-shift transmission.

Anurag.

[rejoycjohn]

Originally Posted by a4anurag

Thank you Arun.

I now understand and yes the length is increased over the B9R so steering that thing will be a pain hence the rear axle steering mechanism was introduced.

Anurag.

Its also very important to note that the rear single tyre axle steers opposite to the front wheel and thats the main reason why its put behind the double trye axle. Also the angle at which the rear axle steers will not be same as the front tyre but only a %.

Maneuverability also increases when the rear tyre steers in opposite directions
compared to same direction that of front tyres

If it were to steer in the same direction as the front tyre, keeping it in front of the double tyres wouldnt have been a problem. You can see this kind of a set up on so many tractors / trailers which are ridiculously long.

[Sreedharan]

Originally Posted by rejoycjohn

Its also very important to note that the rear single tyre axle steers opposite to the front wheel and thats the main reason why its put behind the double trye axle. Also the angle at which the rear axle steers will not be same as the front tyre but only a %.

Maneuverability also increases when the rear tyre steers in opposite directions
compared to same direction that of front tyres

If it were to steer in the same direction as the front tyre, keeping it in front of the double tyres wouldnt have been a problem. You can see this kind of a set up on so many tractors / trailers which are ridiculously long.

To add to 'rejoycjohn, please find this picture of ETF concept truck. Here it has a very complicated steering geometry. You can see how each axle has a different steering angle to achieve the least possible turn circle. Notice the last 2 wheels, which turn to the opposite.

[Rahul Rao]

Originally Posted by a4anurag

I was just wondering what is the reason for the difference in the rear multi-axle arrangement when comparing the B9R and B11R.

In the B9R the axle consisting of two wheels is placed in front of the usual 4-wheel axle but it is opposite in the B11R

In multi axle set up with axles having un equal no of tyres, the one with twin tyres on each side is the driven one.

Wheel base is always between front axle and driven axle.

Unpowered axle ahead of driven axle is called a pusher axle, while one behind it is called a tag axle.

A four axle double decker design also exists with Volvo it is 20 M long with higher class of seats at lower level, and normal push back ones at higher level. Lower deck exists only between axles, and space above wheels and engine is the luggage area.

Here three axles have single tyres on each side and only one of the two rear axles has twin tyres and is the driven axle.

Rahul

[Ashley2]

Originally Posted by Rahul Rao

...
Wheel base is always between front axle and driven axle.
...

Wheelbase is always the distance between axles and not between front axle and driven axle. That will be till the centre of rear two axles.
@Anurag - One of the disadvantage of pusher axle is, the tyres are likely to have a higher wear compared to tag axles. Its because the driven axle which is just behind keeps pushing it and doesn't allow it for a free rotation as compared to the one in Tag axle.
And other info is B9R pusher axle is only 3T as compared to B11R' s tag axle' s 6T, though it has no relationship between tag and pusher axles.

[gschandra]

Originally Posted by a4anurag

Hello Team,

I was just wondering what is the reason for the difference in the rear multi-axle arrangement when comparing the B9R and B11R.

Volvo B9R:
Attachment 1246017

Volvo B11R:
Attachment 1246018

Picture Source: Google Images.

In the B9R the axle consisting of two wheels is placed in front of the usual 4-wheel axle but it is opposite in the B11R (Just the Mercedes-Benz buses).

Couple of questions:

1) What is the reason for this difference;

2) What reason could it be to get this change in design?

3) Where is the power delivered in the B9R? and

4) Where is the power delivered in the B11R?

In questions 3 & 4, I meant was to which axle is the power sent - 2-wheel or the 4-wheel one?

MODS: Move it to the appropriate thread if necessary.

Anurag.

I think the following aspects would be the reasons fro this change:

1. With B11R, Volvo introduced the steerable rear axle. For the steered rear axle layout, the vehicle dynamics and the steering dynamics require the rear most axle to be steered. Since it won't be economical to have the combination tyre axle to be steered, this is the best way to have it.

2. The difficulty in using this layout is to design and package the propeller shaft to pass over the rear axle without fouling with it during suspension travel.

You can read more details on basic steering system layouts and the geometry effects at
http://en.wikipedia.org/wiki/Steering