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Neil, the linked INNAS vehicle uses fixed displacement in wheel drives and their "transformer" to proivde the pressure to the drives. Mine uses a variable stroke position from 0 stroke to the maximum of probably 3-4 inches depending on the wheels daimeter, larger daimeter=greater stroke. The "gear ratios" are the stroke position which can be adjusted at each wheel individually. Moving the journal distance A provides 2A stroke position change. The amount of fluid consumed is directly proportional to the stoke position. At 0 stroke there is no fluid movement which is the equivalent of neutral. When the stroke position is moved from 0 the fluid volume increases as the wheel provides power to the vehicle. To provide the same level of power as the accumulator pressure reserve is depleted the stoke position would be increased.
When the engine comes on to replenish the accumulator pressure, as the pressure rises the stroke position decreases to provide the exact same amount of power to the wheel.
Your point about fixed displacement drives using the same volume of fluid regardless of the load is valid, but if that was the case you would have no control of the power applied to the wheel and no way to regulate that power as accumulator pressure depleted.
Accumulators are never completely depleted, pressure wise, they will have around 1000 to 1500 PSI precharges and max pressures from 3-12K PSI. The EPA used 5k PSI accumulators in their calculations 7 years ago.
A bladder contained in a high pressure vessel is collapsed by hydraulic fluid, which can be biodegradable and non toxic. As the fluid volume increases the bladder collapses and compresses an inert gas. Life expectancy is considerable, usually measured in hundreds of thousands of cycles, and bladder replacement is all that is necessary to restore the accumulator to new condition as long as the containment vessel is not damaged.
The accumulator can dump its total charge in a matter of seconds at extremely high power levels, but when yo uare trying to move a vehicle that will not happen unless you are trying to smoke all 4 wheels (assuming one drive per wheel or one drive per 2 wheels).
Each drive operates independently of the other drives and in a 4 wheel drive configuration you just place two drives in the ) stroke position and they are basically freewheeling axles with no fluid consumed.
Braking means you use the "reverse" stroke position which also works as a reverse "gear".
Regeneration occurs when the stoke position is reversed in relation to the vehicles motion.
regards
Mech
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