Any gearbox experts here? Just puzzling over why really big gearboxes are commonly avoided. Locomotives mostly use electric transmission and the reliability of gearboxes in things like wind turbines isn't great.

Is there some reason to do with scaling the geometry, like if you double the size of every dimension, the shaft can transmit more torque than the teeth? At a quick glance, it doesn't seem that simple. Or is there more slip between the teeth and more wear? I can't figure out a concrete reason and it's bugging me :-).

Chris

On Tue, 15 Aug 2017 23:47:37 -0700 (PDT), Christopher Tidy
wrote:

Any gearbox experts here? Just puzzling over why really big gearboxes are commonly avoided. Locomotives mostly use electric transmission and the reliability of gearboxes in things like wind turbines isn't great.

Is there some reason to do with scaling the geometry, like if you double the size of every dimension, the shaft can transmit more torque than the teeth? At a quick glance, it doesn't seem that simple. Or is there more slip between the teeth and more wear? I can't figure out a concrete reason and it's bugging me :-).

Chris


These are pretty big: https://goo.gl/7dcoqC


Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca

void _-void-_ in the obvious place



---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

On 16/08/17 07:47, Christopher Tidy wrote:
Any gearbox experts here? Just puzzling over why really big gearboxes are commonly avoided. Locomotives mostly use electric transmission and the reliability of gearboxes in things like wind turbines isn't great.

Is there some reason to do with scaling the geometry, like if you double the size of every dimension, the shaft can transmit more torque than the teeth? At a quick glance, it doesn't seem that simple. Or is there more slip between the teeth and more wear? I can't figure out a concrete reason and it's bugging me :-).

Chris

I don't think the guy I know that used to work for David Brown would
agree. While he is no longer full time he does get call upon to work on
North Sea oil rig gearboxes from time to time and has worked on large
ship gearbox installations in the past from what he has said.

Am Mittwoch, 16. August 2017 13:32:32 UTC+2 schrieb David Billington:

I don't think the guy I know that used to work for David Brown would
agree. While he is no longer full time he does get call upon to work on
North Sea oil rig gearboxes from time to time and has worked on large
ship gearbox installations in the past from what he has said.

It might just be that big gearboxes cost dramatically more than smaller ones, and so other solutions become economic. Could be that simple. I'm just interested to know if there are technical reasons about gearbox scaling which affect the choice as well.

Chris

On Wed, 16 Aug 2017 04:43:06 -0700 (PDT), Christopher Tidy
wrote:

Am Mittwoch, 16. August 2017 13:32:32 UTC+2 schrieb David Billington:

I don't think the guy I know that used to work for David Brown would
agree. While he is no longer full time he does get call upon to work on
North Sea oil rig gearboxes from time to time and has worked on large
ship gearbox installations in the past from what he has said.

It might just be that big gearboxes cost dramatically more than smaller ones, and so other solutions become economic. Could be that simple. I'm just interested to know if there are technical reasons about gearbox scaling which affect the choice as well.

Chris
It might be just that. Since the volume of metal increases by the
square of the diameter of the gear they must reach a point where
moving that volume of metal takes too much energy compared to the
amount of energy transmitted. So the cost of the gearbox plus the cost
of transmitting the energy just gets too expensive.
Eric

On Wed, 16 Aug 2017 08:24:01 -0700, wrote:

On Wed, 16 Aug 2017 04:43:06 -0700 (PDT), Christopher Tidy
wrote:

Am Mittwoch, 16. August 2017 13:32:32 UTC+2 schrieb David Billington:

I don't think the guy I know that used to work for David Brown would
agree. While he is no longer full time he does get call upon to work on
North Sea oil rig gearboxes from time to time and has worked on large
ship gearbox installations in the past from what he has said.

It might just be that big gearboxes cost dramatically more than smaller ones, and so other solutions become economic. Could be that simple. I'm just interested to know if there are technical reasons about gearbox scaling which affect the choice as well.

Chris
It might be just that. Since the volume of metal increases by the
square of the diameter of the gear they must reach a point where
moving that volume of metal takes too much energy compared to the
amount of energy transmitted. So the cost of the gearbox plus the cost
of transmitting the energy just gets too expensive.
Eric

This may or may not be an issue, but when gears get really large, they
can become more expensive than the simple size proportion would
indicate.

It has to do with heat treatment and the relative risk (and cost) of
failure. Big ones are often case-hardened, teeth only. As you go
smaller, the tendency is toward flame hardening of teeth, and then
through-hardening for the still smaller ones. We're talking about
heavy-duty industrial gears here.

I've watched this being done on 36-inch Curvics or spiral-bevels (I
forget which) at Gleason Works, 30 years ago, and the really big ones
go through a lot of steps. They're spotted with rouge and lapped after
hardening in the biggest sizes. Lapping each gear can take a whole
day.

--
Ed Huntress

"Ed Huntress" wrote in message
...
On Wed, 16 Aug 2017 08:24:01 -0700, wrote:

On Wed, 16 Aug 2017 04:43:06 -0700 (PDT), Christopher Tidy
wrote:

Am Mittwoch, 16. August 2017 13:32:32 UTC+2 schrieb David
Billington:

I don't think the guy I know that used to work for David Brown
would
agree. While he is no longer full time he does get call upon to
work on
North Sea oil rig gearboxes from time to time and has worked on
large
ship gearbox installations in the past from what he has said.

It might just be that big gearboxes cost dramatically more than
smaller ones, and so other solutions become economic. Could be that
simple. I'm just interested to know if there are technical reasons
about gearbox scaling which affect the choice as well.

Chris
It might be just that. Since the volume of metal increases by the
square of the diameter of the gear they must reach a point where
moving that volume of metal takes too much energy compared to the
amount of energy transmitted. So the cost of the gearbox plus the
cost
of transmitting the energy just gets too expensive.
Eric

This may or may not be an issue, but when gears get really large,
they
can become more expensive than the simple size proportion would
indicate.

It has to do with heat treatment and the relative risk (and cost) of
failure. Big ones are often case-hardened, teeth only. As you go
smaller, the tendency is toward flame hardening of teeth, and then
through-hardening for the still smaller ones. We're talking about
heavy-duty industrial gears here.

I've watched this being done on 36-inch Curvics or spiral-bevels (I
forget which) at Gleason Works, 30 years ago, and the really big
ones
go through a lot of steps. They're spotted with rouge and lapped
after
hardening in the biggest sizes. Lapping each gear can take a whole
day.

--
Ed Huntress

https://www.geartechnology.com/issue...nstruction.pdf

"Christopher Tidy" wrote in message
...
Any gearbox experts here? Just puzzling over why really big gearboxes
are commonly avoided. Locomotives mostly use electric transmission and
the reliability of gearboxes in things like wind turbines isn't great.

Is there some reason to do with scaling the geometry, like if you
double the size of every dimension, the shaft can transmit more torque
than the teeth? At a quick glance, it doesn't seem that simple. Or is
there more slip between the teeth and more wear? I can't figure out a
concrete reason and it's bugging me :-).

Chris
============================
From what I've read it seems the reasons are mismatches between the
engine and load torque/speed requirements and problems keeping the
shafts aligned in large, somewhat flexible structures like ships.
http://www.navweaps.com/index_tech/tech-038.htm

https://www.wartsila.com/docs/defaul...la-o-gears.pdf

Gears worked better when the speed was relatively constant or the load
demand could be controlled by varying propellor blade pitch as on
large WW2 aircraft engines.
http://www.newcomen.com/wp-content/u...r-13-White.pdf

http://www.machinedesign.com/news/co...tary-gearboxes

Usually lowest overall cost drives the choice.
-jsw

The reason locomotives are diesel-electric is that the electric motors can deliver torque at 0 RPM - no need to slip a clutch until the huge mass got rolling.

Am Mittwoch, 16. August 2017 22:52:01 UTC+2 schrieb :
The reason locomotives are diesel-electric is that the electric motors can deliver torque at 0 RPM - no need to slip a clutch until the huge mass got rolling.

Interesting comment. I can see this being a key problem. Just thinking about it, how do diesel engines scale? I mean, the bell housing on a small car engine has a diameter of what? 30 cm? And on a locomotive engine maybe 100 cm? So you can have something like a 25 cm diameter clutch in a car and a 85 cm diameter clutch in a locomotive? Let's assume it's a single plate clutch for now.

Taking this a bit further, if you have maximum engine torque and 0 rpm at the wheels, how much power are you briefly sinking into the clutch? Maybe 50 kW in the car and 1500 kW in the locomotive? Which means you have 11 times the clutch area and 30 times the power. Following this logic, I can see how clutch scaling is going to max out at about the size of a large truck, and on top of that, trains accelerate quite slowly. The heating might not be so brief.

Nice thought, Randall.

Chris

"Christopher Tidy" wrote in message
...
Am Mittwoch, 16. August 2017 22:52:01 UTC+2 schrieb
:
The reason locomotives are diesel-electric is that the electric
motors can deliver torque at 0 RPM - no need to slip a clutch until
the huge mass got rolling.

Interesting comment. I can see this being a key problem. Just thinking
about it, how do diesel engines scale? I mean, the bell housing on a
small car engine has a diameter of what? 30 cm? And on a locomotive
engine maybe 100 cm? So you can have something like a 25 cm diameter
clutch in a car and a 85 cm diameter clutch in a locomotive? Let's
assume it's a single plate clutch for now.

Taking this a bit further, if you have maximum engine torque and 0 rpm
at the wheels, how much power are you briefly sinking into the clutch?
Maybe 50 kW in the car and 1500 kW in the locomotive? Which means you
have 11 times the clutch area and 30 times the power. Following this
logic, I can see how clutch scaling is going to max out at about the
size of a large truck, and on top of that, trains accelerate quite
slowly. The heating might not be so brief.

Nice thought, Randall.

Chris

===========

http://www.railway-technical.com/tra...l-locomotives/

On Thu, 17 Aug 2017 19:52:19 -0700 (PDT), Christopher Tidy
wrote:

Am Mittwoch, 16. August 2017 22:52:01 UTC+2 schrieb :
The reason locomotives are diesel-electric is that the electric motors can deliver torque at 0 RPM - no need to slip a clutch until the huge mass got rolling.

Interesting comment. I can see this being a key problem. Just thinking about it, how do diesel engines scale? I mean, the bell housing on a small car engine has a diameter of what? 30 cm? And on a locomotive engine maybe 100 cm? So you can have something like a 25 cm diameter clutch in a car and a 85 cm diameter clutch in a locomotive? Let's assume it's a single plate clutch for now.

Taking this a bit further, if you have maximum engine torque and 0 rpm at the wheels, how much power are you briefly sinking into the clutch? Maybe 50 kW in the car and 1500 kW in the locomotive? Which means you have 11 times the clutch area and 30 times the power. Following this logic, I can see how clutch scaling is going to max out at about the size of a large truck, and on top of that, trains accelerate quite slowly. The heating might not be so brief.

Nice thought, Randall.

Chris
A Loco doesn't use a clutch. The generator is directly coupled to the
diesel. The traction motor is directly geared to the wheels. No
clutch, just feild controls on the generator and motor to control
voltage and current, and switching gear for reversing and braking.

Am Freitag, 18. August 2017 05:43:55 UTC+2 schrieb Cla

A Loco doesn't use a clutch.

I know. It was hypothetical. I was trying to work out why not.

"Christopher Tidy" wrote in message
...
Am Freitag, 18. August 2017 05:43:55 UTC+2 schrieb Cla

A Loco doesn't use a clutch.

I know. It was hypothetical. I was trying to work out why not.

The history of locomotive engineering is interesting in that the
demands of being such a heavy and powerful moving vehicle made the
simplest-seeming things like following a curve or wheel balance very
difficult.
https://en.wikipedia.org/wiki/Hammer_blow

One consequence was the gradual weakening of cast-iron bridge
components:
https://en.wikipedia.org/wiki/Tay_Bridge_disaster
"A joiner who had worked on the bridge from May to October 1879 also
spoke of a lateral shaking, which was more alarming than the
up-and-down motion, and greatest at the southern junction between the
high girders and the low girders. He was unwilling to quantify the
amplitude of motion, but when pressed he offered 2 to 3 inches (50 to
75 mm). When pressed further he would only say that it was distinct,
large, and visible."

In addition to hammer blow the necessary 90 degree piston offset
between the two sides to avoid being stuck on top-dead-center makes
the loco wiggle (yaw) sideways.
-jsw

Not "clutch".
There were "diesel-hydraulic" locos in Britain.
"Hymek" and "Warship Class" (???).
Were they British "licences" of German designs?
Seems a very German example of precision engineering - not easily
replicated elsewhere.
Advantage is said to be that hydraulic-mechanical transmission weighed
less than electric transmission, so could pack more punch if the loco
had to be small and light due to track / axle-load, etc.
Check the real facts if interested.

On Fri, 18 Aug 2017 08:05:27 +0100, Richard Smith
wrote:

Not "clutch".
There were "diesel-hydraulic" locos in Britain.
"Hymek" and "Warship Class" (???).
Were they British "licences" of German designs?
Seems a very German example of precision engineering - not easily
replicated elsewhere.
Advantage is said to be that hydraulic-mechanical transmission weighed
less than electric transmission, so could pack more punch if the loco
had to be small and light due to track / axle-load, etc.
Check the real facts if interested.
Used primarily on narrow guage??

writes:

On Fri, 18 Aug 2017 08:05:27 +0100, Richard Smith
wrote:

Not "clutch".
There were "diesel-hydraulic" locos in Britain.
"Hymek" and "Warship Class" (???).
Were they British "licences" of German designs?
Seems a very German example of precision engineering - not easily
replicated elsewhere.
Advantage is said to be that hydraulic-mechanical transmission weighed
less than electric transmission, so could pack more punch if the loco
had to be small and light due to track / axle-load, etc.
Check the real facts if interested.
Used primarily on narrow guage??

Mainline - Standard gauge - Western region of UK. Hilly routes.
https://en.wikipedia.org/wiki/British_Rail_Class_35
https://en.wikipedia.org/wiki/British_Rail_Class_42

On Thu, 17 Aug 2017 19:52:19 -0700 (PDT), Christopher Tidy
wrote:

Am Mittwoch, 16. August 2017 22:52:01 UTC+2 schrieb :
The reason locomotives are diesel-electric is that the electric motors can deliver torque at 0 RPM - no need to slip a clutch until the huge mass got rolling.

Interesting comment. I can see this being a key problem. Just thinking about it, how do diesel engines scale? I mean, the bell housing on a small car engine has a diameter of what? 30 cm? And on a locomotive engine maybe 100 cm? So you can have something like a 25 cm diameter clutch in a car and a 85 cm diameter clutch in a locomotive? Let's assume it's a single plate clutch for now.


There is no clutch on the usual a diesel-electric drive. Just an
rheostat to control the electricity going to the motor(s). A
diesel-electric vehicle often has a number of motors.

Taking this a bit further, if you have maximum engine torque and 0 rpm at the wheels, how much power are you briefly sinking into the clutch? Maybe 50 kW in the car and 1500 kW in the locomotive? Which means you have 11 times the clutch area and 30 times the power. Following this logic, I can see how clutch scaling is going to max out at about the size of a large truck, and on top of that, trains accelerate quite slowly. The heating might not be so brief.


The motor torque is normally applied directly to the driven wheel.

Nice thought, Randall.

Chris

On Wednesday, August 16, 2017 at 4:52:01 PM UTC-4, wrote:
The reason locomotives are diesel-electric is that the electric motors can deliver
torque at 0 RPM - no need to slip a clutch until the huge mass got rolling.

The engine block always need antifreeze.

Christopher Tidy wrote:
Any gearbox experts here? Just puzzling over why really big
gearboxes are commonly avoided. Locomotives mostly use electric
transmission and the reliability of gearboxes in things like
wind turbines isn't great.

On locomotives you need some means to connect an engine doing
and requiring a couple of hundreds revs/min to wheels doing
zero revs/min with some hundreds of kilonewtons drawbar power
when taking off.

--

"I'm a doctor, not a mechanic." Dr Leonard McCoy
"I'm a mechanic, not a doctor." Volker Borchert

Ships of all sizes use them, Oil services use them some gears are so
large that they have to be on 80' heavy duty trailers mounted on an
angle so the width would fit in 1 or 2 lanes and still under mandatory
overpasses. Lufkin Industries here in town before being bought out
by GE used to move some rather large gears to be used world wide.

They had a gear box group that still works here - 'black magic' you
don't mess with in the works. Large industrial air handlers and
mills.... the gear boxes have to be designed right considering
many parameters that are often ignored until the box blows up.

Martin

On 8/16/2017 1:47 AM, Christopher Tidy wrote:
Any gearbox experts here? Just puzzling over why really big gearboxes are commonly avoided. Locomotives mostly use electric transmission and the reliability of gearboxes in things like wind turbines isn't great.

Is there some reason to do with scaling the geometry, like if you double the size of every dimension, the shaft can transmit more torque than the teeth? At a quick glance, it doesn't seem that simple. Or is there more slip between the teeth and more wear? I can't figure out a concrete reason and it's bugging me :-).

Chris