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Old 22nd May 2010, 13:25   #1
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Default Multiple Axle mechanism

Two queries that I have been searching the answer for quite some time now. Even Google has failed me on this:

1. Wanted to understand how exactly does the Multiple Axles in Heavy vehicle work? What I mean is, how does it manage to turn with two/three wheels so close and turn axis being in the center of the two axles? Have been observing turning trucks since years trying to understand. Have seen one/two of the tyres being rubbed sideways when the truck is turning. Does it not lead to heavy tyre wear? My guess is, there might be some trick that lifts that tyre when turning?

2. I have noticed lately that Truckers have started to add a third axle just behind the front cabin. It has some kind of Hydraulic steering and lift system and can be lifted when unladen. Any govt. regulation? Or a new technology?

Gurus, please enlighten lesser mortals like me with your inputs on the above two topics.

Thanks in advance!

PS: Mods, could not find this topic in a couple of the searches I did. Apologies if it already exists. If so, please merge my question to the relevant thread.

Last edited by vinayrathore : 22nd May 2010 at 13:29.
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Old 22nd May 2010, 13:42   #2
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yes , the 2nd point which you have mentioned about the third axel behind the cabin is becoming an increasing trend now . i have also noticed that several times in recent days . that axel is suspended on air bellowes , exectly 2 on each side and can be risen or lowered through a switch which in turns diverts the compressed air to the bellows and puts them down or lowers them so that the extra load can be taken over them .
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Old 22nd May 2010, 14:09   #3
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Don't know this can answer your query, sorry if found irrelevant:
Mining Truck Axle configuration ETF
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Old 22nd May 2010, 16:37   #4
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Well, the additional axle after the front wheels is to help in weight distribution, traction and to put less pressure on each individual wheel. It's only put into contact with the road with a heavy load.
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Old 22nd May 2010, 17:32   #5
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Quote:
Originally Posted by sandeepmdas View Post
Don't know this can answer your query, sorry if found irrelevant:
Mining Truck Axle configuration ETF
This seems to be a configuration specially made for the mining requirements and not the conventional Multi-Axle system we have on our Highways. But thanks Sandeep for the link. Its a great system too.

Quote:
Originally Posted by smashnerd View Post
Well, the additional axle after the front wheels is to help in weight distribution, traction and to put less pressure on each individual wheel. It's only put into contact with the road with a heavy load.
Did not get the Traction part smashnerd. This axle is not driven by the engine as I haven't seen any differential on them.
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Old 22nd May 2010, 17:56   #6
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Quote:
Originally Posted by vinayrathore View Post
Two queries that I have been searching the answer for quite some time now. Even Google has failed me on this:

1. Wanted to understand how exactly does the Multiple Axles in Heavy vehicle work? What I mean is, how does it manage to turn with two/three wheels so close and turn axis being in the center of the two axles? Have been observing turning trucks since years trying to understand. Have seen one/two of the tyres being rubbed sideways when the truck is turning. Does it not lead to heavy tyre wear? My guess is, there might be some trick that lifts that tyre when turning?
If the truck has multiple axles in the front very close to each other then usually both axles are steered.

In case of multiple rear axle the kind of rubbing you mention arise only when the trucks make tight U turn or similar turns while manouevering in parking spots to load and unload. But such a truck is at home on the highways and country roads. So whatever rubber tyre lose during such turning antics is only minimal, maybe even lesser than during hard braking.

Quote:
2. I have noticed lately that Truckers have started to add a third axle just behind the front cabin. It has some kind of Hydraulic steering and lift system and can be lifted when unladen. Any govt. regulation? Or a new technology?
You mean a second axle behind the first steered axle?
I have not seen a three front axle truck on the roads used to ferry goods. Mining yes.
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Old 22nd May 2010, 18:15   #7
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Quote:
Originally Posted by vinayrathore View Post
1. Wanted to understand how exactly does the Multiple Axles in Heavy vehicle work? What I mean is, how does it manage to turn with two/three wheels so close and turn axis being in the center of the two axles? Have been observing turning trucks since years trying to understand. Have seen one/two of the tyres being rubbed sideways when the truck is turning. Does it not lead to heavy tyre wear? My guess is, there might be some trick that lifts that tyre when turning?
You mean the rear axles?

Only one set is driven by the transmission, others just bear the load and are - I am not sure of the exact terminology - "free wheeling", like the front wheels of a rear wheel drive car, or rear wheels of a front wheel drive car.

Yes, when the turning radius is too sharp, some slippage is likely to occur. I guess the drivers have enough experience to anticipate this and will take this into account while manouvering.

Quote:
2. I have noticed lately that Truckers have started to add a third axle just behind the front cabin. It has some kind of Hydraulic steering and lift system and can be lifted when unladen. Any govt. regulation? Or a new technology?
New technology - for carrying extra load.

As a general rule, each axle cannot carry more than N tons weitht (not sure whether N is 6 of 9). Adding extra axles means the vehicle can carry extra load ons ame overall length vehicle. This is particular for carrying extra high density cargo like rolled steel.
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Old 22nd May 2010, 19:15   #8
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Guys, I mean the axles in this new Tata Prima.

Name:  Tata Worldtruck2.jpg
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Point 1. Is the rear axles that upon a tight turn the tyres on the diagonal ends slip substantially and on normal turns, the tyres slip albeit somewhat less but they do slip. My question is, how the tyre wear that takes place is minimized using some kind of mechanism we can see in the suspension? Do the diagonal tyres lift during turns? I am not able to find the pics but there is a mechanism that comprises of some levers and arms and the normal leaf springs are mounted on those arms. Wanted to understand that mechanism.

Point 2. In the same pic, we see an additional axle near the front cabin. I see many old trucks fitted with such axles on the highways these days. These have some kind of hydraulic or as mentioned by quattroa4, air suspension/lift mechanism that controls this axle. It even has a steering system aligned with the main front axle steering that allows the vehicle to turn.

Hope this helps.

Last edited by vinayrathore : 22nd May 2010 at 19:17.
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Old 22nd May 2010, 21:13   #9
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Quote:
Originally Posted by vinayrathore View Post
Guys, I mean the axles in this new Tata Prima.

Attachment 352852
Ok. This is a second front axle not the third. In this case both set of wheels in the front are steerable.

Quote:
Point 1. Is the rear axles that upon a tight turn the tyres on the diagonal ends slip substantially and on normal turns, the tyres slip albeit somewhat less but they do slip. My question is, how the tyre wear that takes place is minimized using some kind of mechanism we can see in the suspension? Do the diagonal tyres lift during turns? I am not able to find the pics but there is a mechanism that comprises of some levers and arms and the normal leaf springs are mounted on those arms. Wanted to understand that mechanism.
Those arms and levers you see connect both set of rear axles together, via leafspring perches. This setup kind of stabilises the vehicle when going over rough patches, when one axle is pushed up by the road undulation the other connected axle goes down and vice versa.

Quote:
Point 2. In the same pic, we see an additional axle near the front cabin. I see many old trucks fitted with such axles on the highways these days. These have some kind of hydraulic or as mentioned by quattroa4, air suspension/lift mechanism that controls this axle. It even has a steering system aligned with the main front axle steering that allows the vehicle to turn.
The second axle up front (and multiple axles in the rear) is for hauling heavy loads. For heavy haulage these multiple axles and wheels distribute the load more evenly which is good for the vehicle, the tyres and the road. Some trucks have the ability to raise the additional axle up and away, when the vehicle is not hauling any load. This aids in fuel efficiency and save tyre life.

Even some trailers, with three or more rear axles, have this feature which will allow axles to be tucked away.
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Old 22nd May 2010, 21:28   #10
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Quote:
Originally Posted by vinayrathore View Post
This seems to be a configuration specially made for the mining requirements and not the conventional Multi-Axle system we have on our Highways. But thanks Sandeep for the link. Its a great system too.



Did not get the Traction part smashnerd. This axle is not driven by the engine as I haven't seen any differential on them.
Well, more tires = more grip.


Quote:
Originally Posted by vinayrathore View Post

Point 1. Is the rear axles that upon a tight turn the tyres on the diagonal ends slip substantially and on normal turns, the tyres slip albeit somewhat less but they do slip. My question is, how the tyre wear that takes place is minimized using some kind of mechanism we can see in the suspension? Do the diagonal tyres lift during turns? I am not able to find the pics but there is a mechanism that comprises of some levers and arms and the normal leaf springs are mounted on those arms. Wanted to understand that mechanism.
Please clarify what you mean. Then I can help.
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Old 23rd May 2010, 00:24   #11
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Quote:
Originally Posted by vinayrathore View Post

Point 1. Is the rear axles that upon a tight turn the tyres on the diagonal ends slip substantially and on normal turns, the tyres slip albeit somewhat less but they do slip. My question is, how the tyre wear that takes place is minimized using some kind of mechanism we can see in the suspension? Do the diagonal tyres lift during turns?
If any of the tyres lift at any point of time it defeats the prupose of having them (in full load conditions). It will put a huge load on other tyres and I doubt if it will ever be designed in such way.

Quote:
Originally Posted by vinayrathore View Post


I am not able to find the pics but there is a mechanism that comprises of some levers and arms and the normal leaf springs are mounted on those arms. Wanted to understand that mechanism.
Sankar has already answered this.
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Old 25th May 2010, 21:56   #12
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Quote:
Originally Posted by vinayrathore View Post
1. Wanted to understand how exactly does the Multiple Axles in Heavy vehicle work? .....Have seen one/two of the tyres being rubbed sideways when the truck is turning. Does it not lead to heavy tyre wear? My guess is, there might be some trick that lifts that tyre when turning?
Here you have not clearly mentioned about 6x4 or 6x2 configuration.
If its a 6x4 then the slippage will be minimal as there is a differential. But in 6X2 there may be a higher slippage when the truck makes a close turn.
But technically speaking there exists no trick during turning.
Quote:
Originally Posted by vinayrathore View Post
2. I have noticed lately that Truckers have started to add a third axle just behind the front cabin. It has some kind of Hydraulic steering and lift system and can be lifted when unladen. Any govt. regulation? Or a new technology?
This is a new technology to increase the GVW of the rigid trucks to 31T as per CMVR.
There are two types in this
1.There are two front axles which are hydraulically steerable and are non liftable.AL 3116,3121, Tata Prima 3128 uses this.
2.There are three rear axles of which the first rear axle is liftable and it is non steerable. Tata 3118 uses this.
The load distribution will be
Front Axle 1 - 6T
Front axle 2(rear axle1)-6T
Rear axle1(rear axle2) - 10T
Rear axle2(rear axle3)-9T
Total - 31T

Last edited by Ashley2 : 25th May 2010 at 22:00.
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Old 12th June 2010, 13:03   #13
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i always wondered what these were, at first they seemed like spare tyres.. until i saw one in action. they have just a single tyre on both sides right?

sorry for the bad pics -
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Multiple Axle mechanism-11062010253.jpg  

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Old 12th June 2010, 13:23   #14
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That is a drop axle configuration. That axle is dropped when the truck has to haul heavier loads and weight/axle limit exceeds on the truck's main axles.
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Old 12th June 2010, 21:57   #15
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Quote:
Originally Posted by Sankar View Post
That is a drop axle configuration. That axle is dropped when the truck has to haul heavier loads and weight/axle limit exceeds on the truck's main axles.
Sankar, thanks for the information. Can you further enlighten us on its working. Earlier I thought it of as a unique way to mount the spare wheel as I had never noticed these being present on both the sides.
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