From: MV (MV@dc9.tzo.com)
Date: Wed Aug 03 2005 - 05:51:05 PDT
Bjorn,
I should have said that would be an unlikely situation for me. (;->) If
I was on a side slope sufficient to lose traction on the upside wheel,
then I would probably not want to be there in the first place. I can
see that in situations like that, being able to turn off a pinion brake
would be a very good idea. I agree the pinion brake would be most
usefull for long downhill runs where engine braking wasn't possible or
sufficient. However if I was running in conditions that were that
difficult, I would think that some type of side to side braking system
might be the most useful of all since the M35's don't have positraction.
Redundancy is almost always a good idea.
But as I said before, I think I would probably try to improve the
performance of the existing brakes before adding something else on.
Dave
Bjorn Brandstedt wrote:
> MV,
> It's not an unlikely situation at all. When you are operating your
> vehicle on a side slope and the drums lose their efficiency for some
> reason (water perhaps), the pinion brake will easily make the wheel(s)
> on the "uphill side" spin.
> As far as the deuce's hand brake being a pinion brake, that's correct,
> but you have separate control over it. It doesn't operate via the master
> cylinder. The same goes for engine braking, which is driveline braking,
> but you have separate control over it. Automatic transmissions and ABS
> makes things more complicated and yes, locking diffs would help a lot
> off-road, may be dangerous on the road, don't know, no experience here.
>
> Driving slowly and off-road probably wouldn't create the need for extra
> braking power anyway. It's the emergency situations and long downhill
> runs that needs extra braking power.
> Going downhill can almost always be accomplished without brakes with the
> right speed/gear combination so, we are down to emergency situations,
> transmission pops out of gear while driving downhill or the need for a
> sudden stop. Those would be (are) my primary concerns.
>
> The drum brakes SHOULD be able to handle the sudden stops (clean, dry
> brakes) perhaps with the aid of the emergency brake. It's that long
> downhill run with the transmission out of gear that will need the extra
> brakes for heat dissipation. Here, the pinion mounted disks will help.
> Keep in mind that the disks would have to be rather large to equal the
> heat dissipating ability of the drums on the deuce otherwise you will
> have fading here as well.
> How large I don't know, but it should be calculated by the designer and
> made known to the user.
>
> There are aslo electric driveline brakes (Telma), or "retarders" as they
> are called, but they are operated separately from the service brakes.
>
> The drums can be made more efficient at dissipating heat by drilling
> holes along the shoe/drum contact area. This will dissipate the gases
> formed when the pads get hot and also make them essentially self cleaning.
>
> To be safe if there is a mechanical failure, install a split braking
> system.
>
> Bjorn
> MVPA19212
> The Blue Ridge Mountains of Virginia
>
>
>
>
>> From: MV <MV@dc9.tzo.com>
>> Reply-To: MV@dc9.tzo.com
>> To: Bjorn Brandstedt <super_deuce@hotmail.com>
>> CC: Military Vehicles Mailing List <mil-veh@mil-veh.org>
>> Subject: Re: [MV] disc brake pressure, et al
>> Date: Wed, 03 Aug 2005 01:55:42 -0500
>>
>> Logically what you say makes sense.
>>
>> But, think about this scenario:
>>
>> An M35 with moving forward.
>> All 9x20's spinning in the same direction.
>> The brakes are applied fully and for some reason the wheel brakes
>> don't work- yet the pinion brake works and locks the drive shaft
>> (better have the clutch in fully?).
>> One wheel in the dual tandem set has tremendous traction, the other is
>> on ice.
>> The wheel on ice decellerates, stops, and reverses direction?
>>
>> I think this scenario is very unlikely realistically. There may be a
>> tendency for one wheel to slow and begin to stop since it has little
>> traction but I seriously doubt it would get anywhere close to
>> reversing direction. Besides if the road conditions are that extreme
>> perhaps the M35 should not be on the road anyway, or at least it
>> should be moving very slowly??? Even if it did reverse direction, the
>> worse thing that would happen is that the effect of the pinion brake
>> would be negated or non-effective in that situation. I can see why
>> pinion brakes are not used as main vehicle brakes, however I think it
>> is a litle ironic that the safety brake or parking brake is
>> effectively a pinion brake.
>>
>> The same type of criticism has been made against vehicles with
>> positraction. If you get in a condition where one wheel is on ice and
>> the other is on pavement and you hit the gas, the vehicle will tend to
>> turn itself due to the uneven traction. The argument against
>> positraction is that it would be better to simply have the one wheel
>> slip and the vehicle lose traction and rather than have the vehicle
>> swerve under acceleration. But from a practical standpoint
>> Positraction can keep you from getting stuck in marginal conditions.
>>
>> Dave
>>
>> Bjorn Brandstedt wrote:
>>
>>> "And as far as one wheel spinning backwards, what is there in the stock
>>> system to prevent it? Yet the issue is never raised unless pinion
>>> braking
>>> is mentioned."
>>>
>>>
>>> This is how I see it:
>>> If the driveshaft is locked then the "sum" of the two wheels spinning
>>> must equal zero. That's how a differential works.
>>> So, the two wheels can drag on the pavement, which would produce a
>>> zero "sum" or they can rotate in opposite directions and produce a
>>> "sum" equal to zero. The wheel with most traction will force the
>>> other side to turn in reverse to produce a "sum" equal to zero.
>>>
>>> When the wheels are braking at the wheels (service brakes) then the
>>> drive shaft is still spinning from the engine/transmission. If one
>>> wheel locks up, there is nothing making the other wheel reverse
>>> direction unless the transmission is placed in reverse. The drive
>>> shaft will change speed that's all.
>>>
>>> Does that make sense?
>>>
>>> Bjorn
>>>
>
>
>
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This archive was generated by hypermail 2.1.4 : Fri Oct 28 2005 - 23:25:25 PDT