[Land-speed] Non-LSR Hydraulic Hybrids

[Ed Weldon]

Pretty slick.  No question that the efficiency of recapturing and storing
energy normally lost in braking will be better than using electric
motor-generators and batteries.  The remaining question is how far can the
truck go on the energy it stores in accumulators of practical size and
pressure holding capability.  Recharging overnight wouldn't work unless an
additional electric motor and small hydraulic pump were included in the
package to repressurize the accumulators.  The other issue here is that the
efficiencies involved in the use of small diesel engines with power suitable
for light delivery trucks would largely go away if the trucks were fitted
with engines and hydraulic pump/motors of size sufficient to pull heavily
loaded trucks up long hills. And note that the size of accumulators needed
to store the energy that you try to recover from a fully loaded truck
descending from say a 1000 ft elevation would be enormous.  The numbers are
reasonably easy to calculate.
>From my experience high pressure hydraulic pumps and hydraulic motors have
efficiencies in the range of 95% or better and a practical pressure limit
around 5000 psi.  The standard power calculation for oil pumps is pressure
in psi times flow in gallons per minute divided by 1714 equals horsepower.
For the pump you divide the horsepower calculated in the formula by the
efficiency number to get the engine or accumulator input BHP you need.  For
the hydraulic motor you multiply the the horsepower by the efficiency to get
the amount that goes to the drive wheels.  So let's say you have a 50 gallon
accumulator full of oil at a pressure of 5000 psi. At 95% efficiency that
would give you 138 hp at the drive axle for one minute or 13.8 hp for 10
minutes.  Good for a light delivery truck around town with short hills.  Out
on the freeway that energy would get a 4000 lb truck a bit less than 500
feet up a 4% grade (19ft in elevation) before it would be used up not
counting the losses from aerodynamics, tire friction and drive train
friction.  Still looks reasonably good for urban light delivery use.
Overnight recharges might use about 3 kwh of electric power and likely be
able to propel the truck about 4-5 miles at 20-25mph.  These are rough
numbers with some assumptions on my part for power needed to move the truck
on flat surfaces; so don't take them to the bank
Ed Weldon

----- Original Message ----- 
From: <BWANA343 at aol.com>
To: <jolylance at earthlink.net>; <land-speed at autox.team.net>
Sent: Thursday, January 01, 2009 7:12 PM
Subject: Re: [Land-speed] Non-LSR Hydraulic Hybrids


> In a message dated 1/1/2009 9:41:46 P.M. Eastern Standard Time,
> jolylance at earthlink.net writes:
> Newer  variations on an old principle--any comments?
> The IBM story is new, the tech is not. The Ford story is three years  old
,
> witnessed by the claim in it the vehicle will be "scheduled for launch
for
> August 2008"