Transmissions and final drives

[roguetechie]

49 minutes ago, Xoon said:

few quick questions:

1. For how long can the accumulator keep the stored energy?

2. How much of the energy can the hydraulic regenerative breaks recover?

3. What makes a hydraulic system more suited for heavy vehicles?

4. The ultra caps can only store the energy for a short period of time right? So when traveling downhill for long amounts of time, the energy is lost?

5. Do you know how efficient the system would be?

6. Could you draw a hydraulic circuit to show how you can vary the speed of the motors and mix power?

Xoon, 

1. Depends entirely upon the system design, an early hydraulic hybrid car retrofit I know of could sit for at least a week without full pressure loss

2. Again that's going to be wildly dependent upon the system, but if you believe Ford in the early 2000's they they basically quadrupled the mileage of an F150 compared to their V8 offering with a pretty mild hydraulic hybrid combination that was supposed to cost Ford less than $1000 extra to install at the factory in full scale serial production.

3. Going out on a limb here, my guess is that it's similar to why you don't see bobcats much less D9's with all electronic actuators. Also UPS and a few other companies have come out to say that their studies show this as well. From what I understand their logic behind this is relatively sophisticated involving initial capital outlays, availability and affordability of qualified technicians, and matching the hybrid components to expected vehicle service lives and etc. With the final consideration being that a hydraulic hybrid system including energy storage components will have less cubic volume on average.

4. Considering that at least a couple projects are working towards ultracap based energy storage for red dots and holo sights, I'd say no this wouldn't even be a potential concern on a time scale 100x longer than even a LONG descent from a mountain pass.

5. I'm not 100% clear on overall thermodynamic efficiency other than to say that they CAN be very competitive with battery electric hybrids if done right. That's really a fantastically complicated question of the type that I'm just educated enough to know that I'm nowhere near qualified to answer! 

6. I've got diagrams of various systems saved various places, but TBH no I don't know exactly how you'd do it. My primary research push lately has been in the brushless DC electric motor area, specifically WRT closed loop machine control and using them as dampers and suspension components etc.

 

All apologies for the lack of concrete answers, I was just really excited to be able to contribute to the conversation here.

[Xlucine]

1 hour ago, Collimatrix said:

The torque converters usually compromise the tank's ability to engine brake.

I don't buy this, I've driven a ferret AC and it definitely had engine braking. Many automatic cars have a 'hill mode' that keeps it in lower gear to help maximise engine braking (since you'd choose a lower gear automatically for downhill bits in a manual)

[Collimatrix]

8 hours ago, Xlucine said:

I don't buy this, I've driven a ferret AC and it definitely had engine braking. Many automatic cars have a 'hill mode' that keeps it in lower gear to help maximise engine braking (since you'd choose a lower gear automatically for downhill bits in a manual)

 

I may have to look into this more.  I recall that ToT said something to the effect that torque converters generally screw up engine braking though.  Maybe it's not so bad if it's a fancy torque converter that can lock?

Also, engine braking is going to work generally better in a car than a tank.

[Jeeps_Guns_Tanks]

Are images like this of interest over here? I don't think big scans of these drawings are out on the net. These are all from the final Sherman powertrain. 

 

 

 

 

[Xlucine]

3 hours ago, Collimatrix said:

 

I may have to look into this more.  I recall that ToT said something to the effect that torque converters generally screw up engine braking though.  Maybe it's not so bad if it's a fancy torque converter that can lock?

Also, engine braking is going to work generally better in a car than a tank.

I don't doubt that with the higher ratio of mass to engine in a tank engine braking will be less effective, resulting in the need for the hydraulic brakes, but in my experience torque converters definitely run both ways. The ferret transmission is not locking, the manual (page 70 of this pdf) mentions non-zero slip even at high engine speed

[Xoon]

17 hours ago, roguetechie said:

1. Depends entirely upon the system design, an early hydraulic hybrid car retrofit I know of could sit for at least a week without full pressure loss

But does this mean that after a week, all the pressure would be gone?

 

17 hours ago, roguetechie said:

3. Going out on a limb here, my guess is that it's similar to why you don't see bobcats much less D9's with all electronic actuators. Also UPS and a few other companies have come out to say that their studies show this as well. From what I understand their logic behind this is relatively sophisticated involving initial capital outlays, availability and affordability of qualified technicians, and matching the hybrid components to expected vehicle service lives and etc. With the final consideration being that a hydraulic hybrid system including energy storage components will have less cubic volume on average.

You should be careful when comparing bulldozers and bobcats to tanks. First of all, those vehicles use actuators. Since hydraulic actuators are much cheaper than electric actuators, also electric actuators require cooling in some cases, the hydraulic actuator reigns supreme. Now, this means you need a pump to power the hydraulic circuit, so why not make the motors hydraulic too? This saves complexity, time and money. 

Now, in modern tanks we do have some hydraulic systems like the turret traverse and elevation, but these are required to run even when the engine is off, aka silent overwatch. So you can't combine the transmission circuit with the rest.  Also, tanks are slowly switching over to electric traverse and elevation mechanisms for safety reasons. 

 

17 hours ago, roguetechie said:

5. I'm not 100% clear on overall thermodynamic efficiency other than to say that they CAN be very competitive with battery electric hybrids if done right. That's really a fantastically complicated question of the type that I'm just educated enough to know that I'm nowhere near qualified to answer! 

I was mainly wondering if you had some rough numbers on the power factor of the hydraulic transmission parts.

 

17 hours ago, roguetechie said:

6. I've got diagrams of various systems saved various places, but TBH no I don't know exactly how you'd do it. My primary research push lately has been in the brushless DC electric motor area, specifically WRT closed loop machine control and using them as dampers and suspension components etc.

Something like this:

 

 

 

17 hours ago, roguetechie said:

All apologies for the lack of concrete answers, I was just really excited to be able to contribute to the conversation here.

No problem, all contribution are welcome.

[roguetechie]

Xoon, 

Even before I showed up here I was acutely aware of the limits of my knowledge where it comes to all things armored warfare. To say the least coming here has been...humbling

I try to be cagey and apply lots of disclaimers to what I say in the armored warfare forum because I know I'm almost guaranteed to be wrong on some of it.

If I make mistakes please let me know, I'm here to learn not to teach.

On that note, this is why I brought up heavy equipment and UPS trucks.

[Meplat]

18 hours ago, Jeeps_Guns_Tanks said:

Are images like this of interest over here? I don't think big scans of these drawings are out on the net. These are all from the final Sherman powertrain. 

 

 

 

 

Bevel cut final drives..FILTH, PURE FILTH.  *Furiosly wanking*   YOU SHOULD BE ASHAMED! THIS IS ALL YOU FAULT!

[Meplat]

14 hours ago, Xlucine said:

I don't doubt that with the higher ratio of mass to engine in a tank engine braking will be less effective, resulting in the need for the hydraulic brakes, but in my experience torque converters definitely run both ways. The ferret transmission is not locking, the manual (page 70 of this pdf) mentions non-zero slip even at high engine speed

Wait, what?

 

Yeah. fluid clutches are for the most part "symmetrical" in that they work both ways. And the Ferret preselective trans is only "slipped" by the fluid clutch. Which is minimal, if at all.

[Ramlaen]

Quote

Transmission should be in the front because using available transmissions in the rear mounted configuration with lever linkages would take considerable effort to use, fatiguing the driver

Does this sound like a valid argument for front mounted transmissions?

[Meplat]

1 minute ago, Ramlaen said:

Does this sound like a valid argument for front mounted transmissions?

Mos of the argument for a front drive sprocket was based on reduced wear to the sprocket and track. Not because of linkage issues. Look at a Czech '35 or Hetzer, for example.  Looks wacky as hell.

[Collimatrix]

1 hour ago, Ramlaen said:

Does this sound like a valid argument for front mounted transmissions?

No more valid than arguing that ailerons and rudders on airplanes should be mounted right next to the cockpit so that the pilot doesn't fatigue from pulling the long linkage cables.

[DogDodger]

23 hours ago, Ramlaen said:

Does this sound like a valid argument for front mounted transmissions?

It's not valid as far as steering is concerned, but it nevertheless seems to a pretty widely held thought. In his book on the Pz.Kpfw.III, Spielberger cites as a disadvantage of the rear-drive setup that "Long transmission lines were necessary for the steering system." This doesn't necessarily imply fatigue, of course: longer, more complex linkages may have been thought to be a pain in themselves. Also, beginning at ~0:50 in his video on the Grant, Fletcher asserts that the front-mounted transmission made driving easier, but doesn't elaborate on how. The most consistent arguments for a front sprocket seem to be the cleaning action of the top run of the track, and weight distribution has been cited in the case of the GMC M18.

 

[Xoon]

Felt like sharing this gem:
http://www.ffi.no/no/Rapporter/08-01220.pdf

 

A report on hybrid electric vehicles. 

 

A neat idea here is to use the hybrid electric system to power a ETC gun. This could solve the power issue, at the cost of no or reduced mobility during firing. 

[Meplat]

On 3/22/2017 at 9:16 PM, DogDodger said:

It's not valid as far as steering is concerned, but it nevertheless seems to a pretty widely held thought. In his book on the Pz.Kpfw.III, Spielberger cites as a disadvantage of the rear-drive setup that "Long transmission lines were necessary for the steering system." This doesn't necessarily imply fatigue, of course: longer, more complex linkages may have been thought to be a pain in themselves. Also, beginning at ~0:50 in his video on the Grant, Fletcher asserts that the front-mounted transmission made driving easier, but doesn't elaborate on how. The most consistent arguments for a front sprocket seem to be the cleaning action of the top run of the track, and weight distribution has been cited in the case of the GMC M18.

 

All I can offer is that "the M-18 is "easy" to drive for ww2 era armor".  (And I've driven "a few" examples of armor of the era.)

It's still terrifying at at speed. As in "Bring a change of skivvies,and/or another pair of trousers".

[Walter_Sobchak]

Promotional newsletter from 1952 from Allison Transmission.

 

 

Spoiler

 

 

 

 

 

 

 

[Walter_Sobchak]

Speaking of Allison Transmission, they must have had some sort of corporate policy to try to keep their engineers from ever getting laid.  I mean, how else do you explain this promotional item from Allison that recently came into my possession?

 

Imagine some poor Allison engineer sitting in a bar.  A woman comes up to him and asks for a light.  He reaches into his pocket to fish out what looks like a normal pack of matches.

 

 

He then proceeds to open the match book, only to reveal that it is not matches at all, but actually a tiny pocket calculator.

 

 

At this point the woman rolls her eyes and walks away while the poor engineer rather hopelessly tells her he can calculate some sums for her.

 

[Jeeps_Guns_Tanks]

So the matches, don't work?

[Walter_Sobchak]

5 minutes ago, Jeeps_Guns_Tanks said:

So the matches, don't work?

nope, they are plastic.  Unfortunately, the battery powering the calculator went dead long ago. I suppose I could go get a new one, it's a 389A battery. 

[Collimatrix]

9 hours ago, Walter_Sobchak said:

Speaking of Allison Transmission, they must have had some sort of corporate policy to try to keep their engineers from ever getting laid.  

 

 

 

What is even weirder is that they thought that was something they actively needed to stop.  Have they met engineers?

[Xoon]

It just struck me, but, does AFVs use ABS?

[Collimatrix]

On 6/23/2017 at 4:07 PM, Xoon said:

It just struck me, but, does AFVs use ABS?

 

I have no idea.  There would be some interesting problems in implementing ABS in a tracked vehicle though, such as the fact that the tracks have to be allowed to skid laterally for the vehicle to turn.  How would the ABS accelerometer tell an intentional amount of skid from an uncontrolled, unintentional amount?

[Xlucine]

ABS is just a counter that tracks how fast the wheels are turning, normally*. It can't detect lateral slip, or indeed directly measure any slip - it only spots when one wheel significantly decelerates relative to the other wheels. It'd be trivially simple to have something in the transmission that looks at the relative speeds of the output shafts to do the ABS thing, and turning wouldn't be an insurmountable issue. You could have sensors (like the one on a brake pedal that turns on the brake lights, or the one that turns on reversing lights) so the system only activates when the main brakes are being used. ABS reduces the brake force on the wheel in question, and for a modern tank gearbox in a wide turn they don't use brakes, only the magic in the gearbox AIUI - so it won't matter if the ABS gets upset, as it won't be able to do anything because there's no brake force to reduce. In a pivot or neutral turn a sensor can inform the ABS that it isn't needed as well.

 

Looking at the magnitude of the difference in wheel/track speeds to differentiate between corners and locked wheels isn't too hard either - after all, in a car there's a slight difference in rotational speed when cornering. If an ABS system can manage that, then it should be completely possible to have a functional ABS system in a tracked AFV.

 

*Also used for 'low tyre' warning systems, as an underinflated tyre will have slightly smaller effective radius

[Walter_Sobchak]

It seems that the issue of front vs rear drive sprocket has been a hot topic lately.  Here is the oldest document I know of that addressed the issue.  From "The Fighting Tanks" from 1933 by Icks, Rarey and Jones.

 

Basically, they seem to think that rear mounted engine and final drives are ideal, although they note that transmission in the front with engine in the rear makes for better weight balance and that the rear idler will kick most of the mud off the track before it reaches the sprocket, which may be "a slight advantage."

 

 

 

[EnsignExpendable]

Huh, interesting, Soviet tank design favoured the rear final drives, except in cases of light tanks, and then it could be either or (but rear was still preferred in the late war).