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Lets take a ride in a hydraulic hybrid.
Outside the car is fairly conventional, a balance of aerodynamics and practicality. No exotic materials mostly conventional body construction with attention to aero detail and low RR tires.
CD should be in the low 20s to high teens. No need for large grille openings with a smooth underside since their is no need for a power train.
The first two things that are obvious are that there is no gear shifter and only two pedals which are gimballed, meaning when you push one down the other goes up the same amount. The transmission tunnel holds the accumulator. The low pressure reservoir is the front cross member.
When you turn the ignition on there is no noise just an indicator to show you you are ready to go. The engine would only start if your accumulator pressure level was below the minimum level. The operation cycle of the engine is totally dependent on the pressure levels of the accumulator with a full throttle application creating a more aggressive engine cycle.
For reverse you will need to push a button. There is a interlock that prevents you from going backwards, because the two pedals are forward and reverse-regenerate. Without the interlock if you kept pushing on the left pedal you would stop, then start going backwards. The button prevents reverse without activation.
Pressing the right pedal control your rate of acceleration. At lower rates the hydraulic pressure is delivered from the accumulator to the wheels. At higher rates the pressure is supplied by both the engine and the accumulator. Climbing steep grades for considerable distances would deplete the accumulator pressure which would mean the power would come directly from the engine in the case where the grade exceeded the accumulator reserve.
The engine itself would be fairly large displacement. For a 2100 pound vehicle the engine would be about 2 liters displacement (if conventional). It would have no throttle control and run in the range of 1200 to 2400 RPM. If sustained grades were encountered that required more power to maintain higher speeds, a supercharger would engage to provide additional power. Engine RPM would never exceed 3500 RPM.
In normal lower speed stop and go traffic the engine would only run about 15% of the time. Duty cycle would be dependent on average power demands with 60 MPH level speeds requiring engine running about 25% of the time the vehicle is moving. Any deceleration or downhill operation would produce regeneration and additional accumulator pressure. If accumulator maximum pressure was achieved while still going downhill then restrictors in the hydraulic circuits would create drag. If you lived in mountainous areas the vehicle could use larger capacity accumulators to better recover regeneration forces.
With fully charged accumulators and supplemental engine power maximum acceleration would be only a matter of sizing the wheel motors to provide maximum torque to each wheel, up to the point where the tires would loose traction. Each wheel would have individual controls for traction control and anti lock brakes, with the typical sensors controlling the stroke position of each wheel motor to maintain traction when accelerating or braking. Normal energy losses in activation of traction control or abs systems, that use brake application or pressure interruptions to maintain traction would be accomplished by changing the stroke position of each wheel motor to provide maximum traction whether accelerating or braking (regenerating).
Each wheel motor would be an independent power application unit, requiring no interconnection of the wheels other than the sensors and control unit to determine actual vehicle speeds.
Accessory systems would be all electric, including heat and air conditioning. This is because the engine itself would be operating only a small percentage of the time the vehicle was operating. In some cases there may be enough surplus heat from engine operation to provide some heat energy to the climate control system. All accessories would be plug and play, without the complexity of belts and hoses of typical ac and heating systems.
A larger battery would permit extended operation of accessory systems when engine operation cycles were very low. Generation of electricity would only occur when the engine was running, by an integral starter generator incorporated into the engines flywheel, similar to the Honda Insight, but not used as a power supplement to the engine or hydraulic accumulator.
regards
Mech
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