problem with portal axle gear box in off road vehicle.

vikram singh tI'm making an off road vehicle with Engine of Cummins 4BT, 1800 rpm, torque 269 pound-feet with portal axle gear box. Meanwhile i have increased the rpm to 3000 and also ratio maintained in portal gear is 1:2.

While driving off road the output shaft of gearbox is shearing for all four wheels
can anyone help me with this..//

can you also specify the dimensions of the shaft which you are using and get sheared and also the coupling after output shaft.

Anku2993can you also specify the dimensions of the shaft which you are using and get sheared and also the coupling after output shaft.

The input shaft dia 32 after reduction( ration of 2:1)the output shaft dia is also maintained same.Consider the ratio as 2:1 instead of 1:2 as mentioned earlier.there is no coupling .Shaft will rotate hub to which wheel rim is fitted.

vikram singh tThe input shaft dia 32 after reduction( ration of 2:1)the output shaft dia is also maintained same.Consider the ratio as 2:1 instead of 1:2 as mentioned earlier.there is no coupling .Shaft will rotate hub to which wheel rim is fitted.

Dear, still i have doubt.
Your input rpm is 1800 and then you reduce it to 900(2:1) at output. And then you increase the input to 3000 rpm and your output is 1500 rpm. Am i right?
And also can you specify the material of the shaft? and also the weight of the laden vehicle(weight of vehicle along with passengers and whatever it has to carry)?

it is off road vehicle, the total weight of the vehicle is 2.5 ton & shaft material is EN353,
As you said 1500 RPM will be required when we are driving against the steep roads(uneven terrain ).

vikram singh tit is off road vehicle, the total weight of the vehicle is 2.5 ton & shaft material is EN353,
As you said 1500 RPM will be required when we are driving against the steep roads(uneven terrain ).

Ok dear, i got your situation. One more thing i want to know in order to check the shaft whether it is correct or not.
Can you specify the torque or power at input side at 3000 RPM? You already specified the torque at 1800 Rpm, But in order to do the calculations we must know the power at 3000 RPM at input side because you want 1500 RPM not 900 RPM at outside in order to run the vehicle.
And can you also attach the photograph of sheared shaft? And also what is the size of Tyres you are using?
And what is the yield strength of EN353? I tried but can't able to find!

rpm 1800 to 3000 rpm was raised by adjusting and introducing some valves in fuel injection system.Torque is still constant

The RPM of the engine is increased from 1800 to 3000 with the help of extra auxiliaries like custom fuel injection system..etc, while making sure that torque is maintained same, & yield strength of the En353 material is around 620 N/mm^2, i'm unable to upload the pics as of now due to few reasons, i will be uploading them in near future, (Thanks a lot Anku2293 for your never ending support, i really appreciate it (^.^)..//)

here's the pic of tire i'm not sure about exact size of the tire but i guess we can approximate the size of the tire from the pic roughly

i know Anku2993 that i am not being specific with the all the information that im sharing, please bear with me..//

vikram singh tyield strength of the En353 material is around 620 N/mm^2

Dear, From where did you get this yield strength? Because when i searched it on google, i found it as 241 MPA. here is the link-
<a href="https://www.ssroundbar.com/roundbar-rodbar/alloysteel-roundbar-alloysteel-rodbar/rodbar-type-en353-alloy-roundbar/" target="_blank" rel="nofollow noopener noreferrer">EN 353 Alloy Steel Round Bar |EN 352 Round Bar | ssroundbar</a>
But it is mentioned in annealed condition, But the EN shafts are hardened. So, I was not sure about this yield strength, that's why i asked you in my previous reply.
1. Are you sure that the yield strength is 620 MPA? Because it's too high. Do you have any data or link regarding this? Kindly share.
2. Also, are you sure that 1500 rpm is enough for 2.5 ton and off-roads(including starting inertia and frictions)? have you done calculations for this and get 1500 rpm required?
If yes, Then i will use 1500 rpm for calculations. So, please be sure and if possible kindly share calculations for same.
3. How much F.O.S have you considered for shaft calculations? Because in industry, 3 to 3.5 F.O.S is considered for off-road vehicles.
4. How can you able to get same torque even at 3000 Rpm? Because in order to increase RPM it's obvious that you increased the fuel input and hence more power. So, are you sure that all the increased power is compensated in increased Rpm and hence constant torque?

Hi There Ankush, i got the yield strength of En353 from solidworks material database, yes 1500 RPM is enough for 2.5 ton weighing vehicle as Cummins 4BT was also used in some of the buses and tow trucks.

the basic Cummins 4 Bt generates 105 Hp @ 2400 RPM so this gets to 230 lb Ft torque,
basically what im trying to do is to increase and maintain torque in a specific rage so that vehicle can climb the steep heights, so for increasing the torque i have reduced the rpm of the vehicle by adding portal gear box which gives me two plus ++ points 1) the height of the vehicle is increased and 2) im able to draw more torque out of the engine at reduced rpm, so as i have mentioned earlier engine was generating 269 lb-ft torque at 1800 rpm( at engine output shaft & before portal gear box) which gives 92 Hp approx..so after adding portal gear box(i.e., obviously torque will increase because we have reduced RPM) so when driving vehicle in terrain region the output shaft(i.e., output shaft of portal gear box) is shearing, im not sure what is the amount of torque increased after adding portal gear box but i do know the rpm which is 900 (Because of gear reduction of 2:1 Ratio)..

I haven't done any kind of calculation the shaft dia was selected solely based on previous working experience