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Old 05-25-2021, 12:06 PM   #11 (permalink)
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I don't think it's all doom and gloom. Hydraulic hybrids normally compress a gas by pumping hydraulic fluid into an enclosed "accumulator" with a gas filled bladder. And those can reach some surprisingly high levels of efficiency: 80% IIRC.

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Old 05-25-2021, 02:28 PM   #12 (permalink)
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Quote:
Originally Posted by Isaac Zachary View Post
surprisingly high levels of efficiency: 80% IIRC.
I'd like to see a source on that, I'm genuinly curious how that is supposed to work.
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Old 05-25-2021, 05:36 PM   #13 (permalink)
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Originally Posted by freebeard View Post
Maybe it's worth mentioning that I keep pointing to the Scuderi Split-Cycle engine
Considering its claimed suitability to operate on a pneumatic hybrid setup.


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one could generate compressed air on regenerative braking
IIRC the current-generation Volvo D5 engine is coupled to a 48-volt electrical system which provides mild-hybrid capability, so maybe the electric compressor which provides air for the PowerPulse system could be considered analogue to a regenerative braking
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Old 05-25-2021, 06:05 PM   #14 (permalink)
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Originally Posted by Autobahnschleicher View Post
I'd like to see a source on that, I'm genuinly curious how that is supposed to work.
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.
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.

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Old 05-25-2021, 06:14 PM   #15 (permalink)
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IIRC the first prototype to feature Ford's 6.0 PowerStroke was also fitted with a hydraulic hybrid setup.
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Old 05-25-2021, 09:03 PM   #16 (permalink)
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Quote:
Originally Posted by Isaac Zachary View Post
Here's a little info on UPS (United Postal Service) modifying some of their mail trucks to use a hydraulic hybrid system.

The hydraulic hybrid has the following benefits:[list][*]Hydraulic pump motors can be as high as 99% efficient.
That’s incredible. Thanks for sharing, I hadn’t heard about this. Glad to see it implemented in humongous vehicles.

Brilliant solution to braking energy recapture. I hope it’s reliable and safe. Do you know how long UPS has been doing this? I might have missed that part, thanks.

Hope to see cars with a solution that is as efficient also. I’ve seen flywheels, but not sure it’s gained any traction.

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Old 05-25-2021, 09:42 PM   #17 (permalink)
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Originally Posted by Autobahnschleicher View Post
Only advantage of storing energy in compressed air is that pneumatic cylinders can be used for suspension and active aero
I remember an article on a compressed air car targeted at India. They made a big deal that air conditioning was "free" in the car... so I guess nice for hot climes.

Edit: it was Tata
https://trak.in/tags/business/2008/0...r-minicat/amp/
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Old 05-25-2021, 10:18 PM   #18 (permalink)
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Originally Posted by Galvatron1 View Post
Thatís incredible. Thanks for sharing, I hadnít heard about this. Glad to see it implemented in humongous vehicles.

Brilliant solution to braking energy recapture. I hope itís reliable and safe. Do you know how long UPS has been doing this? I might have missed that part, thanks.

Hope to see cars with a solution that is as efficient also. Iíve seen flywheels, but not sure itís gained any traction.
It seems like there was a bit of attention drawn to hydraulic hybrids when UPS deployed their first HHV truck. After that there seemed to be a small amount of news about them until EV's started rolling out. Then the idea seems to have kind of been lost.
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Old 05-26-2021, 03:17 AM   #19 (permalink)
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They made a big deal that air conditioning was "free" in the car... so I guess nice for hot climes.
Something along the lines of the air-cycling machine featured on pressurized aircraft would be viable on a car too, but I'd take with a grain of salt any claim of "free" air conditioning. Unless the wasted heat gets recovered through a Sterling motor.
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Old 05-26-2021, 09:00 PM   #20 (permalink)
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The expanding air has to absorb a lot of heat... it requires an exchanger for this purpose.

The air conditioning is "free" the same way heat is free in an IC car.

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