Mechanical Variable Speed Gears - Alternatives 1

[JamesDUK]

Hello,

I've just been working on a project using a Voith Vorecon variable speed gearbox. An interesting piece of kit but with some problems, cost being one!
Does anyone know of available alternatives to this technology, for high speed (12,000 rpm output) and high power (2MW+).
Thanks

 

[Windward]

I guess that your driver is a gas or steam turbine. What ratio range do you need?

 

[JamesDUK]

No it's a fixed speed electric motor, 1500 rpm.

The output range we need is about 10,000 to 15,000 rpm.

 

[tbuelna]

JamesDUK,

Due to the high power requirement (2MW+), your only other practical option would be a variable frequency AC drive and a speed increasing gearbox. Probably not much cheaper than the Voith Vorecon though.

Just as a matter of curiosity, what are the issues you noted with the Vorecon? Does it have reliability issues? Is the efficiency poor? As for the unit price, it is possible for you to provide a ballpark cost of the 2MW drive?

Best regards,
Terry

 

[JamesDUK]

Ok, thanks for the reply, a workmate thought a US company did a similar gearbox. VFD wasn't an option due to space constraints.


Problems on the vorecon with a bit of vibration on the output shaft.

Cost is well into 7 figures (euros).

 

[Windward]

I wonder whether the vibration is inherent in the Voith variable speed devices. All of them use the same method of varying the speed - a hydraulic torque converter. Usually a hydraulic coupling dampens vibration, but I don't know enough about their system to comment further.

The Voith website says that the efficiency of their variable speed devices is at least 95%. If so, the hydraulic element must be close to 100% efficient, since there are also one or more gear meshes in the unit. This is a puzzle.

Maybe the US company your workmate was thinking of is Universal Transmission,

http://www.moongears.com/

US Pat. 7,892,129

This a a complicated device. It varies the speed by orbital motions of several ring gears. The company claims to have a unit large enough for wind turbines. If so, the power and speed ratios should be great enough for your application.

I have no opinion of this device that I can disclose to the public at this time.

 

[tbuelna]

JamesDUK,

The Voith Vorecon is probably the highest quality mechanical variable speed drive in the multi-megawatt size, thus the high price. The basic Vorecon consists of a hydrodynamic torque converter (pump/turbine/stator) and planetary combining gearset. Other versions can also include fluid couplings, additional gear reduction stages, and brakes.

There are other manufacturers besides Voith that market more basic variable speed hydrodynamic drives:

http://www.transfluid.eu/ProdInquiry.aspx?PRID=32&Lang=en

I'd sure like to know more details about your 2MW Vorecon if you're at liberty to discuss it. Was that price of >10 million Euro correct? Does the Vorecon itself include the speed increasing gear stage, or is that a separate device? Does the Vorecon include other devices such as fluid coupling or brakes?

Regards,
Terry

 

[JamesDUK]

Hi
Thanks for the replies, hadn't heard of transfluid or moongear before. That moongear sounds very interesting, not an applications I'd use but it's interesting to an engineer.

I can't really take in depth about the project I am working on. Just to point out cost is 1millon+ not 10million. The vorecon is the speed increasing gearbox, it is as described the torque convertor and planetary combined gearbox. It is a high quality and original product.

As I understand the other difference with the Vorecon (the RWE model), is the torque convertor is "offline", i.e. not the main drive.

 

[Windward]

James, can you give us some detail on why you would not consider the Universal Transmission for your application?

I didn't know about Transfluid either. The hydraulic torque converter looks to be the same kind as the one Voith uses. Maybe someone can explain why this device is better than a hydraulic pump/motor for varying the speed.

An Israeli company, IQ Wind,

http://www.iqwind.com/

claims to have a variable pitch gear. They are applying it to wind turbines first. They compare a mechanical variable speed device to the hydraulic type like the Vorecon:

"Hydraulic systems are therefore less efficient relative to fully-mechanical variable solutions. This limitation is especially pronounced at low loads that account for most of the turbines’ working hours. In addition, a hydraulic torque converter does not obviate the need for a mechanical speed-up gear stage and thus, in practice, represents an additional gear stage leading to extra cost and complexity. Finally, hydraulic solutions introduce significant temperature management and environmental issues that do not exist in fully mechanical drive trains."

I know of a UK group that claims to have a method of converting the variable speed of a wind turbine rotor to constant speed for the generator. I asked them how they are doing it, not expecting to get any information. I didn't even get a reply. I can look up the location of this outfit if anyone wants to know. It is at one of the UK universities.

A German company claims that they can achieve variable to constant speed operation in a wind turbine by rotating the gearcase of an inline shaft gearbox at a speed required to provide constant output speed given the varying input speed. This is an old idea. Henry Ford used it in the Model T. It is the principle of all modern automatic transmissions.

But in the German arrangement, to avoid a high rotational speed of the gearcase at one end of the speed range, they allow the cage to rotate one direction at varying speeds for part of the range and in the reverse direction for the other part. In other words, they put power into the gearcase for one part of the range and take it out for the other part. This reversal of direction may be acceptable but it is not ideal. They must use a motor/generator for this operation, and have some means of absorbing the generated power.

For your case, James, using the German arrangement, if you have a gearbox of about 6.66 ratio and input a constant speed of 1500 rpm from the motor, you would get 10,000 rpm out with an almost stationary gearcase. To increase the output speed to 15000 rpm with 1500 rpm input, you must rotate the cage about 880 rpm in the direction opposite to the motor rotation. This is theoretically possible, but a large gearcase rotating at 880 rpm may not be practical.

 

[tbuelna]

As I understand the other difference with the Vorecon (the RWE model), is the torque convertor is "offline", i.e. not the main drive

JamesDUK,

In the Vorecon, the torque converter is indeed in the main power path. The Vorecon uses a "torque split" architecture, where the incoming drive is split into two separate drive paths. One drive path passes through the torque converter, which varies the speed. The other drive path speed remain unchanged. The two input drives are then recombined into a single output drive using a planetary gear differential. The differential output speed becomes a function of the two differential input speeds delta.

The Vorecon uses a torque split arrangement (as opposed to passing 100% of the input torque through the torque converter) for reasons of efficiency. The efficiency of the hydrodynamic torque converter is relatively poor over much of its operating range. So passing only a portion of the power through the TC helps minimize losses.

As I noted, some versions of the Vorecon also have a fluid coupling at the input. This allows the prime mover to start up without load. During normal operation, the fluid coupling is locked up.

Thanks again for the information you provided.
Terry

 

[Windward]

I believe the UK University group I mentioned above has developed into a company:

http://www.magnomatics.com/about-us/Default.aspx

There is a lot of information on this website. They say that their claims are being verified, and that the device is exceeding expectations. This could be a significant technology.