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Originally Posted by Autobahnschleicher
I'd like to see a source on that, I'm genuinly curious how that is supposed to work.
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Here's a little info on UPS (United Postal Service) modifying some of their mail trucks to use a hydraulic hybrid system.
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Hydraulic hybrids are able to capture and reuse 70-80% of the otherwise wasted braking energy.
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United States Environmental Protection Agency: Hydraulic Hybrid Vehicles
The way they work is pretty simple.
- There's a hydraulic pump-motor connected to the driveline after the transmission. There are hydraulic pump-motors that are completely variable, so you can adjust the amount of regen or power.
- Connected to the hydraulic pump-motor are a reservoir and an accumulator.
- The reservoir stores hydraulic fluid at ambient pressure.
- The accumulator is basically a pressure cylinder with a gas bladder (although a piston and spring accumulator could work).
- The gas is already under pressure, so as you pump hydraulic fluid from the reservoir to the accumulator the bladder is compressed even more making it shrink in size as the rest of the accumulator fills up with hydraulic fluid, storing energy.
- Then, when the pump-motor is set into motor-mode, the bladder expands pushing high pressure hydraulic fluid through the pump-motor and into the reservoir which turns the wheels of the vehicle.
The hydraulic hybrid has the following benefits:
- Hydraulic pump motors can be as high as 99% efficient.
- Depending on the design, that efficiency can be basically the same at any RPM or torque load. Even at a dead stop since unlike an electric motor the hydraulic fluid cannot flow until the motor starts turning.
- Hydraulic pump motors allow for efficient regen braking clear down to basically 0RPM.
- Hydraulic hybrid systems can have a higher power to weight ratio than lithium ion electric systems (albeit they can't hold a lot of energy) making them ideal for stop and go traffic, such as postal or public transportation vehicles.
- They aren't hardly affected at all by cold or hot weather.
- In a series hydraulic hybrid vehicle the hydraulic system can replace the transmission much like the "power split device" on a Toyota hybrid.