I'm not a hydraulics guy, but I suspect they are less efficient in most ways than electric hybrids. Hydraulic equipment is heavy, so is the fluid. I'm not 100% sure about overall efficiency ignoring weight, but when you add in weight, I'd be quite surprised if hydraulics can compare to electric hybrids in efficiency.

Then consider the extra issues like leaks--both that they occur and the fluid leaked is a pollutant.

They're nearly completely ignored because they're heavy, expensive and can't store much energy.

This technology has been around for ever but isn't widely used. Either everyone else is stupid OR they know something that the author doesn't.

I've thought about this long and hard & even messed about sketching ideas on this subject, If you look at the way a hydraulic pump works I can see no reason why you couldn't design an engine with a pump as an integral part of the engine, you would control the flow by means of a throttle valve,ie,as you increase the engine revs you open a flow valve, taken to it's ultimate design you could build in braking so as to shut the valve when de accelerating & diverting some of the energy into a Ker's system so when you stop the engine stops, when you touch the throttle the car starts to move and the engine starts. to do this I would have drive motors in each wheel,so no gearbox,no differentials & no drive shafts. I can see no reason for not developing a hydraulic car.

NB,What's the difference between a JCB (or back end hoe) and a giraffe?

one's got hydraulics and the other one

doesn't.

Hydraulic hybrids are coming into the mainstream. Companies like Limo-Reid, Parker, Rex Roth, Eaton... are supplying busses, trash trucks, military vehicles... all with improved efficiency in part to the regenerative braking advantage over electric vehicles. I think it will just be a matter of time until we seeit in smaller vehicles, such as taxi cabs.

Hydraulics are significantly more efficient that batteries in terms of charge/discharge, but have a much lower energy density. According to a presentation by Charles Gray at IFPE, a 44 gallon accumulator has an energy storage potential of about .5 kw-h. A Tesla roadster has a battery with about 65 kw-h (The Tesla Roadster uses about 17.4 kW·h/100 km (0.63 MJ/km; 0.280 kW·h/mi),^[48] the EV1 used about 11 kW·h/100 km (0.40 MJ/km; 0.18 kW·h/mi^Wikipedia))

If you wanted to store as much energy as a Tesla using hydraulic accumulators, you would need the equivalent of 130 44 gallon accumulators.

Now the Tesla is an outlier with really big batteries worth about $33k. Plus with the hydraulic efficiencies, you may be able to get by with less than half that many accumulators. But your car would still look like a heavy blimp rolling down the road. It still wouldn't cost as much as a Tesla, and you wouldn't have to change the accumulators every 7 years or less.

What hydraulic accumulators are good for is large vehicles used for stop and go traffic. Like garbage and delivery trucks. Perhaps if hydraulic components are made smaller and lighter they would work on small delivery vehicles like taxi's, but currently most hydraulic components are built for large equipment.

Yo Dave and All,

I do not disagree with what you have said, but that is why it is a hybrid. You can turn the engine on and off with the hydraulic hybrid, as well as run the engine at the sweet power spot when it is operating. The engine ony needs to run when the accumulator needs charged. Most of the energy needed is to accelerate the vehicle to speed.

A lot of the energy recovered is in regenerative braking, which present hybrid electric technology cannot recover near as much as a hydraulic hybrid. (approx 40% for electric battery hybrid and approx. 80% for hydraulic hybrid). This couldd change with capacitor storage.

There is also new accumulator technology that has been recently developed that has dramatically reduced the weight and size of the accumulators. There is now bio-friendly hydraulic oil (It won't even kill the flowers) and improved connectors to eliminate leaks.

Keep watching for what is coming out new in HHV's. They are in their infancy.

Regards,

Mike

Has any body tried pneumatic(compressed air) hybrid?.Will it be better as charging could be done by a small windmill at home as well as mounted on the vehicle

Most consumers would have a hard time understanding that you can store hydraulic energy just as well as electric energy. They are use to the idea of storing electrical power in batteries, because they've been using that for years. But can you imagine a sales person trying to explain to a consumer why they should buy a hydraulic hybrid?