Can Hydraulic Systems Replace Gearboxes for High-Speed, Low-Torque Applications?

[Don Bori]

Hi! Are there any alternative mechanisms that can increase the Output Speed to 1,000rpm but with lower Input Torque as compared to the traditional gearbox system?

Target Values:

Input Speed= 0.25rpm
Output Speed = 1,000rpm
Output Torque = 1Nm

Via Gearbox:

Input Speed = 0.25rpm
Output Speed = 1,000rpm

Input Torque = 4,000Nm
Output Torque = 1Nm

Is hydraulic system (hydraulic pump - hydraulic motor) a good alternative?

Thank you!

 

[jrmichler]

Hydraulic is a good alternative. If, that is, you can find a hydraulic pump that will work at 0.25 RPM. The input torque will always be greater than 4,000 Nm because of efficiency losses. The laws of physics are not negotiable.
A 1:4000 ratio gearbox will not work. Internal friction will make the input torque much larger than 4,000 Nm.

 

[Don Bori]

Thank you for your reply jrmichler!

I thought of hydraulic motor - pump system must be the best alternative but when I do the calculation, it seems worst.

I need to drive an AC generator with the following requirements:

Output Power = 100W
Input Torque = 1Nm
Input Speed = 1,000rpm

I will drive the generator using a hydraulic motor with the following specifications:

Output Torque = 1Nm
Output Speed = 1,000rpm
Input Flow = 20lpm
Input Pressure = 17bars

Therefore I plan to use a hydraulic pump to drive the motor with these specs:

Output Flow = 20lpm
Output Pressure = 17bars
Input Torque = 240Nm
Input Speed = 20rpm

Since my main system driver that will drive the pump is fixed to 0.25rpm, then I plan to use a speed increaser gearbox between the pump and the main driver with the following calculations:

N1T1 = N2T2
T1 = (20rpm)(240Nm)/(0.25rpm)
T1 = 19,200Nm

But, if I use a directly a gearbox from the Main Driver to the Generator:

N1T1 = N2T2
T1 = (1,000rpm)(1Nm)/(0.25)
T1 = 4,000Nm

Obviously, a direct gearbox is the right choice with lower input torque as compared to a hydraulic system.

Am I missing something?

 

[jrmichler]

Yes, you are missing something.

The power delivered by the hydraulic motor is not the rated power of the motor, it is the power drawn by the generator. The flow to the hydraulic motor determines the hydraulic motor RPM, while the pressure to the hydraulic motor is whatever is needed to turn the generator.

Similarly, the torque to the hydraulic pump is whatever is needed to deliver the pressure. The hydraulic pump RPM is controlled by whatever is driving the pump. The hydraulic pump RPM determines the pump flow.

The pump and motor ratings are just that: ratings. The manufacturer tells you the maximum RPM, flow rate, and pressure for both motor and pump. It is up to you to size everything so that the system works correctly. Hydraulic motors and pumps can be run at full rated pressure and RPM, however they typically run with either flow or pressure less than the maximum.

If you do the calculations correctly, the theoretical input torque will be the same regardless of the mechanism. The actual torque will depend on the efficiency of the system components.

 

[Baluncore]

A 1:4000 ratio gearbox will not work. Internal friction will make the input torque much larger than 4,000 Nm.

Considering gears.
Gearing systems weigh and cost least when the reduction ratio of each stage is about 4.
You will need several stages to achieve that combined ratio of 4000.
To simplify the math, 4000 is close to 4096 = 2^12.
1 stage would require a ratio of 2^12 = 4096.
2 stages would require each be 2^6 = 64.
3 stages would require each be 2^4 = 16.
4 stages would require each be 2^3 = 8.
5 stages would require each be 2^(12/5) = 5.278
6 stages would require each be 2^2 = 4.

So it looks like you need a 6 stage gear reduction.
The optimum viscosity of the lubrication for each of those stages will be different. Heavy grease in the first stage to light oil in the final stage.

Maybe you could use three separate lubricated boxes, each with two stages giving each box a ratio of 16.

 

[Baluncore]

Are there any alternative mechanisms that can increase the Output Speed to 1,000rpm but with lower Input Torque as compared to the traditional gearbox system?

The product of RPM and torque is power, which is the rate of flow of energy. The best you can do is to find a higher efficiency. Gears are usually more efficient than hydraulics.

I feel we need to question the origin of the 0.25 RPM rotation with a torque of 4000 Nm = 105 watt. To me that seems to be a big water wheel, or maybe a free-energy machine. The Earth rotates one degree in the time the input shaft rotates once.

 

[Don Bori]

Yes, you are missing something.

The power delivered by the hydraulic motor is not the rated power of the motor, it is the power drawn by the generator. The flow to the hydraulic motor determines the hydraulic motor RPM, while the pressure to the hydraulic motor is whatever is needed to turn the generator.

Similarly, the torque to the hydraulic pump is whatever is needed to deliver the pressure. The hydraulic pump RPM is controlled by whatever is driving the pump. The hydraulic pump RPM determines the pump flow.

The pump and motor ratings are just that: ratings. The manufacturer tells you the maximum RPM, flow rate, and pressure for both motor and pump. It is up to you to size everything so that the system works correctly. Hydraulic motors and pumps can be run at full rated pressure and RPM, however they typically run with either flow or pressure less than the maximum.

If you do the calculations correctly, the theoretical input torque will be the same regardless of the mechanism. The actual torque will depend on the efficiency of the system components.

Thanks for this valuable input, because of these I finally came up with this plan to compensate all the efficiencies:

100W Rated Power Generator > 120W Rated Power Hydraulic Motor > 150W Rated Power Hydraulic Pump > 200W Rated Power Main Drive Unit

 

[Don Bori]

Considering gears.
Gearing systems weigh and cost least when the reduction ratio of each stage is about 4.
You will need several stages to achieve that combined ratio of 4000.
To simplify the math, 4000 is close to 4096 = 2^12.
1 stage would require a ratio of 2^12 = 4096.
2 stages would require each be 2^6 = 64.
3 stages would require each be 2^4 = 16.
4 stages would require each be 2^3 = 8.
5 stages would require each be 2^(12/5) = 5.278
6 stages would require each be 2^2 = 4.

So it looks like you need a 6 stage gear reduction.
The optimum viscosity of the lubrication for each of those stages will be different. Heavy grease in the first stage to light oil in the final stage.

Maybe you could use three separate lubricated boxes, each with two stages giving each box a ratio of 16.

Thank you Baluncore, I have additional information learned with regards to gearbox system. Actually I prefer to use gearbox because I'm quite familiar with it, but when I found out the cost of the gearbox required I thought that it is not practical for my only 100W power generation project.

I considered Cycloid gearbox as it is cheaper than gearbox, but still the cost is impractical with my project.

For now, I plan to adapt the Traction Drive System and do some modifications. In the traction drive system, I plan to replace the bearing rollers with a stationary hydraulic pump/s with its speed increaser feature (main drive diameter X hydraulic pump pinion diameter).

 

[Don Bori]

The product of RPM and torque is power, which is the rate of flow of energy. The best you can do is to find a higher efficiency. Gears are usually more efficient than hydraulics.

I feel we need to question the origin of the 0.25 RPM rotation with a torque of 4000 Nm = 105 watt. To me that seems to be a big water wheel, or maybe a free-energy machine. The Earth rotates one degree in the time the input shaft rotates once.

I just consider my project as cheaper E. and not F.E. (couldn't mention it as I may violate the rules again! LOL!).

 

[Baluncore]

Maybe you should consider a roller chain, as used on a bicycle, wrapped once around the unmentioned big slow rotating thing, driving a minimum 13 tooth sprocket. That makes the thing 4000 times the diameter of the 13 tooth sprocket. Maybe it needs a second reduction stage.

If you are talking about extracting 100 watt from an 0.25 RPM shaft then you must be in a difficult place. Buying a solar PV panel will cost you less than any gearing system.

 

[anorlunda]

I just consider my project as cheaper E. and not F.E. (couldn't mention it as I may violate the rules again! LOL!).

You didn't answer the question @Baluncore asked. What is the source of energy at 0.25 RPM?

 

[Don Bori]

Maybe you should consider a roller chain, as used on a bicycle, wrapped once around the unmentioned big slow rotating thing, driving a minimum 13 tooth sprocket. That makes the thing 4000 times the diameter of the 13 tooth sprocket. Maybe it needs a second reduction stage.

If you are talking about extracting 100 watt from an 0.25 RPM shaft then you must be in a difficult place. Buying a solar PV panel will cost you less than any gearing system.

Indeed, solar and wind turbine are cheap but it still it have disadvantages like it's only effective when the sun is shining, wind is blowing, consumes significant footprints, etc.

Just want to make it clear that my proposed project won't compete with solar and wind turbine but rather to complement them for the common goals of RE.

My RE project features zero-carbon, 24/7 operation due to unlimited buoyancy and gravity forces, battery independence, grid-connected, smaller footprint (sky is the limit), can be installed anywhere as long as there is buoyancy and gravity, in short, the Energy Miracle which Mr. Gates has been looking for.

Sounds too good to be true, just like when Wrights claimed they can fly a metallic material. That's why I'm eager to produce a prototype and make this new RE source a realization, not for monetization purpose, but as my contribution to my children's good environment.

 

[russ_watters]

Unfortunately, your idea is not workable and will do nothing but waste your time and money. And on PF we follow the laws of physics, and this clearly violates the first law of thermodynamics. Thread locked.