From: MV (MV@dc9.tzo.com)
Date: Tue Aug 02 2005 - 23:55:42 PDT
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
>
>
>
>
> --
>
>> From: "chriscase" <chriscase@sbcglobal.net>
>> To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
>> Subject: [MV] disc brake pressure, et al
>> Date: Tue, 2 Aug 2005 19:26:23 -0700
>>
>> Disc brakes do require more overall pressure to work. That's why they
>> have
>> large or even multiple pistons, piston area may be 6 times as large,
>> giving
>> 6 times the pressure. The sole advantage of discs is that they use
>> most of
>> their circular travel to give off heat while only a small section is
>> being
>> heated by friction.
>>
>> Using a pinion brake as an add on should be trouble free, since it's
>> braking
>> will be in addition to the stock drums- the drums will prevent the one
>> wheel from spinning faster than the other, afterall, you still have
>> just as
>> much braking in the drums as ever. Adding a pinion brake will not add
>> horsepower to the spinning wheel, only add more surface area to the brake
>> system to dissipate heat.
>>
>> 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.
>>
>>
>>
>> --
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>>
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>
>
>
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