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Lightning Hybrids to Introduce Hydraulic Hybrid Sports Sedan at Denver Auto Show

Rendering of the LH4. Click to enlarge.

Colorado start-up Lightning Hybrids will unveil the prototype of its hydraulic hybrid four-seat sports sedan at the Denver Auto Show 1-5 April. This will also mark the public debut for the hydraulic hybrid drivetrain.

The car, the LH4, features a 240 hp (179 kW) drivetrain consisting of a 90 hp (67 kW) proprietary 2-stroke biodiesel and 150 hp (112 kW) hydraulic system. The car will average 100 miles to the gallon and will be able to accelerate from 0 to 60 mph in less than six seconds. It has a unique clamshell door that opens upward to allow for superior aerodynamics. Cd on the car is 0.20.

The car will also be available in a three-door four-seat car, and the drivetrain technology will be made available in a fleet vehicle retrofit called a Hybrid Retrofit System (HRS) in mid-2010. Lightning Hybrids is also developing the LH3, a three-wheel commuter vehicle using the same drivetrain.

Lightning Hybrids is keeping specific design details secret, pending US and international patent filings. The company says it anticipates numerous patent filings are anticipated, the most significant attributable to the design of an integrated hydraulic axial piston engine. Claimed features of the drivetrain include:

  • Lightweight; <1 lb/hp
  • true cylinder deactivation for high part load efficiency
  • no transmission
  • no valves, flywheel or crankshaft weights
  • 100% energy braking recovery

A small carbon fiber accumulator operating between 5,000-7,000 psi will provide for braking recovery energy storage, and will provide power for a full throttle launch to 60 mph in under 5.9 seconds.

Conventional space frame design techniques fabricated from chrome molybdenum tubing will provide the major structural elements, very similar to Indy and formula cars.

Founded in 2008, Lightning Hybrids has designed two hydraulic hybrid cars. Prototype manufacturing began in January 2009. The two cars will compete in the 2010 Progressive Insurance Automotive X Prize race, with $10 million in prizes to be awarded to the teams that win a stage race for clean, production-capable vehicles that exceed 100 MPGe.



2-stroke diesel?? say what!!!


Interesting. They're the first hydraulic hybrid design I've seen that focuses on lightweight and sporty. My guess is that they don't try to store very many seconds of full thrust in their pressure tanks, and that it's mostly designed to be a cheaper-than-batteries braking energy recovery system, and perhaps a compact transmission as well. They've gone for a fairly small my guess is that top speed won't be very high, but you can get there quickly. Also, they can run their 90-hp engine at optimum RPM almost all the time, since all they're doing is charging the pressure tank with it. This should give them much better efficiency on most duty cycles. That's all the potential upside.

The potential downside are questions about noise, safety, and how quickly it wears out. Some of this technology is similar to what's used in forklifts, but people rarely put 100,000 miles on a forklift.

Do my assumptions sound right?


The hydraulic hybrids may be more efficient than electric hybrids, but you cannot charge them at home.

The high pressure hydraulic pumps are not likely to be cheap. Neither 5,000+ psi carbon fiber tank.
What about lifespan of those pumps?
Also another source of leaks.


There could be a recovery system for leaks.

Charging the accumulator would be done mostly by recovery
braking due to its low capacity.

The engine would mostly just run for continuous power beyond 0-60...

The total power train cost for this system has the potential to be very low in mass production.


Sounds like so many unusual designs - unexplored territory provides more room for optimistic claims.
Hydrostatic transmissions are usually good only if there is no handy alternative.

Re 2-stroke; All GM locomotives built prior to 1941 were the tried-and-true two-stroke 710 diesel engine.


2 stroke diesel valves free engines are not new at all, all big ships use them and they are very efficient and extremely reliable but not really clean. So they need to integrate a sytem that cleane the soot and the oil that will unavoidably makes its way in the exhaust

I thought about this type of architecture and it is a serious competitor for HEV approach, it could return better mileage for cheaper. The carbon high pressure accumulator won't be that expensive because it won't be very big in that case since it is only for breaking recovery, maybe 20 liters at best.


@MG - "The hydraulic hybrids may be more efficient than electric hybrids, but you cannot charge them at home."

Sure you can, you just use an electric motor to drive a hydraulic pump. However in this car there would be little point in doing it because it seems the capacity of the storage system is too small.


If I'm reading this right, I think this car is more about having a hydraulic transmission that allows a small, efficient motor to run at optimum RPM for fuel-to-work conversion efficiency, and uses a relatively small accumulator to provide short bursts of additional HP, to store the delta when energy needed is less than the motor produces at optimal RPM, and recapture braking energy.

It might work.

Will S



I think it's more about a small, Diesel engine for high MPG and the hydraulic accumulator for (a short) "ego" boost.
It might be just right if there are not too many (or too big) hills.

Also a "too small" accumulator means that if you charge it up for passing there will be no capacity left for breaking.



You are right that if the optimal efficiency RPM of the small diesel produces 50 hp, and the puttering along car needs only 30 hp, that the extra energy would eventually top off the accumulator, leaving no storage capacity for recapturing energy while braking.

This implies 3 things.

1) the diesel engine must turn off instantly any time it is not needed (when the car is idling, or when the accumulator has reached the max desired level)

2) the max desired level for the accumulator from engine charging should be set so that the accumulator can store the energy from an aggressive braking afterwards (probably 5-10 seconds worth of full power from the accumulator)

3) The accumulator needs to be big enough for it to be worth the inefficiency of stopping and starting the small diesel motor. This also helps on long hills.

The desire to keep the accumulator compact and low cost means a compromise size would be, what, about 30 seconds full power pressure, plus 5-10 seconds to accumulate the n+1 braking?

Henry Gibson

There is the Artemis prototype car to compare with this one and the proposed NOAX car as well. This is obviously not a plug in hybrid, but there are substantial gains in efficiency. Hydraulic Braking energy can also be wasted as electric braking energy is wasted in locomotives. It still lowers the standard brake wear. Most of the efficiency gains are not by regeneration anyway, but many small pressure tanks can be fitted into a car if wanted. ..HG..

Henry Gibson

This company could have used the NOAX free piston diesel-hydraulic engine since NOAX does not propose to use it. It could be designed to run on any fuel with compression ignition of the Homogenous Charge Compression Ignition type with very low NOX and high efficiency. ..HG..


This hydraulic-hybrid is not new, I have the orginal patent here on my desk from 1972. The first hydraulic-hybrid was adapted to a 850 Fiat in Miami, two cars followed that up to 1980. And getting over fifty miles a gallon is not new. I had my car registered in Florida and in Arizona with EPA government listing of 53 miles per gallon in 1979. (and according to those same government EPA standards, it got 40 mpg in city) But one point needs to be mentioned on electric. please drive around Pheonix in the summer with no air conditioning with the little electric car or drive around Nome, Alaska when its 40 below zero for a month straight then say how ready the electric car is. You can not cheat mother nature, if you plug in your car at night to get it charged on the grid you have already lost 50% of the power compared to where that power enetered the grid.

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