Hydraulic Hybrids
 

Some information on a subject that has been mentioned here before:

Hydraulic Powertrains Propel These Hybrid Trucks
Not all hybrid vehicles rely on electric motors, batteries and wires. Some propel the vehicle with a combination of hydraulic pump-motors, fluid lines and accumulators -snip-

http://designnews.com/article/CA6451...rid=1922618187

That covers the power transfer, storage and recovery. Doesn't talk about power generation. The next paragraph covers that:

"In the vehicles, diesel engines drive a hydraulic pump-motor..."

You do have to read the entire article even if it is a long read. :) I can't copy the entire article into a post, I just copied the first couple lines. Nothing of interest or emphasis was meant by the first lines. Copying the first few lines is a common practice used by most news services.

I know. It's just interesting the way the article is written.

Looks like a good idea. I've some small experience with hydraulic drive systems. They work well and have many advantages.

There are some issues that have to be specifically delt with in the design. If the system is not properly designed, the drive motor can cavitate during an overdriven situation (IE compression braking when the vehicle wants to go faster than the motor is driving). If that happens, a runaway condition can be created. There are valves that will prevent this and I'm sure it's been considered. The engineering aspects of this design are interesting.

Its been a while since I worked with hydraulic power, but back then it was not very efficient at all compared to electric drives - have they improved efficiency that much in the past 5-10 years?

I think it's smaller and lighter than electrics when the system has regenerative braking.

Just curious, where are the inefficiencies or losses with a hydraulic drive system?

The inefficiencies are mainly from fluid leakage (internally) in the pumps and motors. Any clearance in the pump or motor is an internal leakage path. Then, there are the flow losses through the hoses/lines from pump to motor and back. Increasing pressure helps in some areas and hurts in others. Back in the day when I was doing hydraulic powered mowing equipment, we were often not much more than 50% efficiency for the system, as compared to 85+% for a mechanical driveline, for example. That's why I was suprised that the efficiencies had improved so much that its even a candidate, but apparently it must be the case.

Ruby-

Were you using gear motors and pumps for your equipement? Larger equipment uses much more efficient pumps and motors. In the article they are using bent-axis motors and pumps.

Here is some Parker info, follow the links in the document to the bent axis pumps.
http://www.parker.com/pumpmotor/cat/...h/1553-int.pdf

It was mostly gear motors/pumps or gerotor motors/pumps that we used. As I recall, the bent-axis piston stuff was more efficient, but much more expensive. Maybe the prices have become more in line for the 'value' equation now.

You can tell there are losses because the fluid and all the parts get hot. The reason many new cars have electric instead of hydraulic power steering is efficiency.

Jim

Electric power steering is more efficient because the PS system sits idling most of the time doing nothing. When the cars use 42V electrical systems you will see a lot more electric PS.

Gear pumps in general have terrible efficiencies. The crescent internal gear pumps do very well tho and they are much quieter.

Just as a side note: Most high performance electric motors have efficiencies above 93% and electric motor drives have efficiencies in the mid to high 90's. The big advantage of hydraulic systems, from what I understand, is that they are more power dense, not energy dense nor more efficient, than electric hybrid systems.

Whether a hydraulic system is more power dense or not is really irrelevant in case of a PS. With a hydraulic system, it always uses some power because it's constantly driven by the belt, but with an electric system, it only uses power when the steering wheel is actually moved.

That is correct. I was mainly aiming my comment at the hydraulic hybrid powertrain versus electric hybrid powertrain, not at power steering. However speaking of electric power steering, does anyone use pure electric power steering or are they all just hydraulic pumps driven by electric motors instead of belt driven?

I believe some newer cars have pure electric PS.

BTW, here's a link to a 130 mpg car: http://www.valentintechnologies.com/default.asp (still in development, so how much of that is hot air and PR BS, and how much is reality, I do not know)